JP6149801B2 - Engine control device - Google Patents

Description

  The present invention relates to an apparatus for controlling an engine that can be switched between all-cylinder operation in which fuel is supplied to all cylinders for combustion and reduced-cylinder operation in which fuel supply to some cylinders is stopped.

  2. Description of the Related Art Conventionally, in the field of multi-cylinder engines having a plurality of cylinders, there has been known a technique for reducing cylinder operation in which fuel supply to some cylinders is stopped and put into a resting state. The engine described in is known.

  Specifically, the following Patent Document 1 describes a 6-cylinder engine in which a maximum of 3 cylinders can be stopped, that is, a 6-cylinder operation mode in which all 6 cylinders are operated, and a specific 2 cylinders in a stopped state and the remaining 4 cylinders. An engine that can be switched between a four-cylinder operation mode to be operated and a three-cylinder operation mode in which specific three cylinders are deactivated and the remaining three cylinders are operated is disclosed. The engine includes a mechanism (cylinder deactivation mechanism) for stopping the opening and closing operations of the intake valve and the exhaust valve in the deactivated cylinder, and is deactivated when operated in the 4-cylinder operation mode or the 3-cylinder operation mode. The intake valves and exhaust valves for three or three cylinders are stopped.

  In addition, the engine of Patent Document 1 includes a device that determines a cylinder rest state by performing spectral analysis on the waveform of the intake air flow rate. That is, the waveform of the intake flow rate, which is the flow rate of air flowing through the intake passage of the engine, varies depending on the number of deactivated cylinders in which the intake valve and the exhaust valve are stopped. Therefore, in Patent Document 1, the intake flow rate of the engine is detected by an air flow meter, and the resting state of each cylinder is determined based on the spectrum value obtained by Fourier transforming the detected intake flow rate value. Specifically, by calculating a spectrum value of frequency components having a cycle of 240 ° crank angle, 360 ° crank angle, and 720 ° crank angle by Fourier transform, and comparing the spectrum value of each frequency component with a predetermined threshold value Then, the resting state of each cylinder is determined.

  According to the engine of Patent Document 1 including the determination device as described above, for example, the target cylinder is deactivated in the 4-cylinder operation mode or the 3-cylinder operation mode, or the 6-cylinder operation mode is selected. It is possible to determine whether everything is operating normally. On the other hand, if it is confirmed that the cylinders other than the target cylinder are in a dormant state, the cylinder is malfunctioning, that is, the intake valve and the exhaust valve of the cylinder are broken. Can be determined.

Japanese Patent No. 4767312

  Here, the engine disclosed in Patent Document 1 determines whether or not each cylinder is inactive based on the intake air flow rate detected by an air flow meter having relatively low responsiveness, and thus whether or not the intake / exhaust valve has failed. However, there is a possibility that high determination accuracy cannot be obtained. Therefore, it is proposed to determine whether or not the intake / exhaust valve has failed based on the intake pressure having higher responsiveness than the intake flow rate (which changes relatively remarkably as the intake air changes).

  However, even if there is a failure, there are various patterns in the failure. For example, when only the exhaust valve is broken and the intake valve is normal, when only the intake valve is broken and the exhaust valve is normal, both the intake valve and the exhaust valve may be broken. According to the inventor's research, it has been found that it is difficult to recognize all of the above failure patterns only by spectral analysis of highly responsive intake pressure.

  More specifically, there may be a case where it is not possible to clearly distinguish between a state where only the exhaust valve is malfunctioning (a state where only the intake valve is normal) and a state where both the intake valve and the exhaust valve are normal. found. This means that, for example, there is a possibility that it may be erroneously determined that the exhaust valve is operating normally even though the exhaust valve of a certain cylinder is stopped (fixed) in a closed state. To do. When such a misjudgment occurs, combustion in the cylinder is permitted, resulting in a so-called backfire in which high-temperature exhaust gas flows backward through the intake passage without being discharged into the exhaust passage. May have a serious impact on the engine.

  The present invention has been made in view of the circumstances as described above. By accurately determining the states of both the intake valve and the exhaust valve, switching from reduced-cylinder operation to all-cylinder operation can be performed safely and appropriately. An object of the present invention is to provide an engine control device that can be used.

In order to solve the above problems, the present invention includes a plurality of cylinders, a plurality of intake valves provided at a rate of one or more per cylinder to control introduction of intake air into each cylinder, A plurality of exhaust valves provided at a ratio of one or more for each cylinder to control gas discharge from the cylinders, and a plurality of injectors for supplying fuel to the respective cylinders. Fuel is supplied from the injectors to all the cylinders. Is an apparatus that controls an engine that can be switched between all-cylinder operation in which fuel is supplied and burned and reduced-cylinder operation in which the supply of fuel to the deactivated cylinder is stopped in order to make some cylinders deactivated. Te, a valve stop mechanism that maintain the closed state stops the opening and closing operation of the intake and exhaust valves in the stopped cylinders during the reduced-cylinder operation, there is a switching request to the all-cylinder operation from the reduced-cylinder operation When the above valve stops A valve control unit that outputs a return command to the mechanism to resume the opening and closing operation of the intake valve and the exhaust valve, and a spectrum analysis of the intake pressure detected over a predetermined period including the intake stroke of the idle cylinder after the return command On the basis of the result, an intake valve return determination unit that determines whether or not the intake valve of the idle cylinder has returned to a normal state, and after the return command, the intake valve of the idle cylinder opens. Based on the pressure fluctuation of the intake air before and after the start time, the exhaust valve return determination unit for determining whether or not the exhaust valve of the deactivated cylinder has returned to a normally openable state and the intake valve return determination unit When the normal return of the valve is confirmed and the normal return of the exhaust valve is confirmed by the exhaust valve return determination unit, the injector is supplied with fuel to the idle cylinder in order to resume combustion in the idle cylinder. And a combustion control unit for opening, is characterized in that (claim 1).

  According to the present invention, the success or failure of the return of the exhaust valve is determined based on the pressure fluctuation of the intake air before and after the timing when the intake valve of the deactivated cylinder starts to open. In this case, the exhaust valve is compressed by utilizing the fact that the gas in the idle cylinder is compressed during the exhaust stroke and then blown back to the intake passage as the intake valve opens (thereby, the intake pressure fluctuates). Can reliably recognize that the return has failed. In addition, since it is determined whether or not the return of the intake valve is successful by performing a spectrum analysis of the intake pressure over a predetermined period including the intake stroke of the idle cylinder, if the intake valve of the idle cylinder fails to return, the intake valve It is possible to reliably recognize that the intake valve has failed to return by utilizing the fact that periodicity different from that in the normal state appears in the waveform of the intake pressure.

  Only when it is confirmed by the highly accurate determination as described above that both the intake valve and the exhaust valve have returned to normal, the fuel supply to the idle cylinder is resumed. Switching to cylinder operation can be performed safely and appropriately. For example, when the supply of fuel to the deactivated cylinder is resumed even though the exhaust valve fails to return, a so-called backfire in which high-temperature exhaust gas generated by combustion in the deactivated cylinder flows backward in the intake passage It is assumed that it will happen and have a significant impact on the engine. In addition, when the fuel supply to the deactivated cylinder is resumed even though the intake valve has failed to return, misfire due to insufficient intake air in the deactivated cylinder occurs, and the supplied fuel is wasted. is assumed. In contrast, according to the present invention, the fuel supply is not resumed unless both the intake valve and the exhaust valve have returned to normal, so that the entire operation from the reduced cylinder operation can be safely and appropriately performed without causing backfire or misfire. Switch to tube operation.

  In the present invention, it is preferable that the exhaust valve return determination unit determines that the exhaust valve of the idle cylinder has returned to normal when the pressure fluctuation of the intake air is smaller than a predetermined threshold.

  According to this configuration, the success or failure of the return of the exhaust valve can be determined by a simple procedure that simply compares the pressure fluctuation of the intake air with the threshold value.

  Here, when the opening / closing operation is resumed in the order of the exhaust valve and the intake valve by the return command from the valve control unit, the exhaust valve return determination unit determines when the intake valve starts to open for the first time after the return command. Even if the pressure fluctuation of the intake air before and after is specified and the pressure fluctuation is smaller than the above threshold, it is not determined that the exhaust valve has returned to normal at that time, and the intake valve opens for the second time after the return command It is preferable that the pressure fluctuation of the intake air before and after the start of the engine is specified and it is determined that the exhaust valve has returned to normal if the pressure fluctuation is smaller than the threshold value.

  If the exhaust valve return determination is made only based on the intake pressure fluctuation at the time of the first intake valve opening, the gas in the idle cylinder leaks to the outside during the reduced cylinder operation, and the idle cylinder Due to the gradual decrease in internal pressure, the accuracy of exhaust valve return determination is expected to decrease. On the other hand, according to the above configuration, even if the pressure variation of the intake air accompanying the first opening of the intake valve is smaller than the threshold value, it is not determined that the exhaust valve has returned to normal at that time, and 2 Since the pressure fluctuation of the intake air accompanying the opening of the intake valve for the second time is compared with the threshold value and the exhaust valve return determination is performed, it is possible to prevent the deterioration of the determination accuracy as described above, and exhaust with sufficiently high accuracy. It is possible to determine whether the valve has returned successfully.

  On the other hand, when the opening / closing operation is resumed in the order of the intake valve and the exhaust valve by the return command from the valve control unit, the exhaust valve return determination unit determines whether the intake valve starts to open for the second time after the return command. It is preferable that the pressure fluctuation of the intake air before and after is specified and it is determined that the exhaust valve has returned to normal if the pressure fluctuation is smaller than the threshold value.

  According to this configuration, it is possible to avoid erroneously determining that the exhaust valve has failed to return due to fluctuations in the intake pressure caused by the intake valve restarting the opening / closing operation prior to the exhaust valve. The accuracy of the exhaust valve return determination can be ensured satisfactorily.

  In the present invention, it is preferable that the intake valve return determination unit is configured to analyze a primary intensity which is an intensity of a primary frequency component having a predetermined crank angle as a period and a period longer than the predetermined crank angle by spectral analysis of the intake pressure. The high-order intensity, which is the intensity of the short high-order frequency component, and when the high-order intensity is greater than the intake valve determination threshold defined by the linear function of the primary intensity, Is determined to have returned to normal (claim 5).

  According to this configuration, the success or failure of the return of the intake valve can be accurately determined by using the fact that the cycle of the change in intake pressure that appears when the intake valve returns to normal is shorter than the cycle of change when the return fails. Can be determined. In addition, each value of the intensity of the primary frequency component (primary intensity) and the intensity of the higher frequency component (higher order intensity) is not compared with a specific threshold value, but is defined by a linear function of the primary intensity. The threshold value (intake valve determination threshold value) is compared with the high-order strength (that is, the correlation between the primary strength and the high-order strength is examined). The accuracy of the return determination can be ensured satisfactorily.

  As described above, according to the engine control apparatus of the present invention, the states of both the intake valve and the exhaust valve can be accurately determined, and switching from the reduced cylinder operation to the all cylinder operation can be performed safely and appropriately. It can be carried out.

1 is a schematic plan view showing an overall configuration of an engine according to an embodiment of the present invention. It is sectional drawing of an engine main body. It is sectional drawing which shows the structure of the hydraulic lash adjuster which incorporated the valve stop mechanism. It is a block diagram which shows the control system of the said engine. It is the time chart which showed the state change of the idle cylinder at the time of switching from reduced cylinder operation to all cylinder operation. It is a time chart which shows the state change of the idle cylinder by the pattern different from FIG. It is a figure for demonstrating the pressure fluctuation of the intake air which arises when the exhaust valve of a dormant cylinder fails to return. It is a figure which expands and shows the pressure fluctuation of the intake shown in FIG. It is the figure which showed what kind of probability the case where the exhaust valve returned to normal and the case where the return failed failed appeared with the pressure fluctuation of intake as a parameter. It is a figure which shows the waveform of the intake pressure which changes according to a crank angle, (a) shows the waveform at the time of all cylinder operation, (b) has shown the waveform at the time of reduced cylinder operation. It is a figure which shows the result of having analyzed the waveform of Fig.10 (a) (b). It is the graph which processed the data obtained by carrying out the spectrum analysis of the intake pressure on various driving | running conditions so that the correlation of a primary spectral intensity and a secondary spectral intensity might be represented. It is a flowchart which shows the procedure of the control performed at the time of the switch from reduced cylinder operation to all cylinder operation. 14 is a subroutine showing a specific procedure of first determination processing in FIG. 13. 14 is a subroutine showing a specific procedure of second determination processing in FIG. 13. FIG. 13 is a view corresponding to FIG. 12 for describing a modification of the embodiment.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing an embodiment of an engine to which a control device of the present invention is applied. The engine shown in the figure is a 4-cycle multi-cylinder gasoline engine mounted on a vehicle as a power source for traveling. Specifically, this engine is generated by an in-line four-cylinder engine main body 1 having four cylinders 2A to 2D arranged in a straight line, an intake passage 30 for introducing air into the engine main body 1, and the engine main body 1. And an exhaust passage 35 for discharging the exhaust gas.

  FIG. 2 is a cross-sectional view of the engine body 1. As shown in the figure, an engine body 1 includes a cylinder block 3 in which the four cylinders 2A to 2D are formed, a cylinder head 4 provided on the upper side of the cylinder block 3, and an upper side of the cylinder head 4. It has a cam cap 5 provided and a piston 11 inserted into each of the cylinders 2A to 2D so as to be slidable back and forth.

  A combustion chamber 10 is formed above the piston 11, and fuel mainly composed of gasoline injected from an injector 12 (FIG. 1) described later is supplied to the combustion chamber 10. The supplied fuel burns in the combustion chamber 10, and the piston 11 pushed down by the expansion force due to the combustion reciprocates in the vertical direction.

  The piston 11 is connected to a crankshaft 15 that is an output shaft of the engine body 1 via a connecting rod 14, and the crankshaft 15 rotates about the central axis in accordance with the reciprocating motion of the piston 11. Yes.

  As shown in FIG. 1, the cylinder head 4 includes an injector 12 that injects fuel (gasoline) toward the combustion chamber 10 of each of the cylinders 2 </ b> A to 2 </ b> D, and a mixture of fuel and air injected from the injector 12. A spark plug 13 for supplying ignition energy by spark discharge is provided. In the present embodiment, a total of four injectors 12 are provided at a rate of one for each cylinder, and a total of four spark plugs 13 are also provided at a rate of one for each cylinder.

  In the four-cycle four-cylinder gasoline engine as in this embodiment, the pistons 11 provided in the cylinders 2A to 2D move up and down with a phase difference of 180 ° (180 ° CA) in crank angle. Correspondingly, the ignition timing in each of the cylinders 2A to 2D is also set to a timing shifted in phase by 180 ° CA. Specifically, in order from the left side of FIG. 1, assuming that the cylinder 2A is the first cylinder, the cylinder 2B is the second cylinder, the cylinder 2C is the third cylinder, and the cylinder 2D is the fourth cylinder, the first cylinder 2A → the third cylinder Ignition is performed in the order of 2C → fourth cylinder 2D → second cylinder 2B.

  Although the details will be described later, the engine of the present embodiment is a variable cylinder engine capable of performing an operation in which two of the four cylinders 2A to 2D are deactivated and the remaining two cylinders are operated, that is, a reduced-cylinder operation. It is. For this reason, the ignition sequence as described above is for normal operation that is not reduced-cylinder operation (during all-cylinder operation in which all four cylinders 2A to 2D are operated). On the other hand, during the reduced-cylinder operation, the ignition operation of the spark plug 13 is prohibited in two cylinders (the first cylinder 2A and the fourth cylinder 2D in this embodiment) whose ignition order is not continuous, and ignition is performed by skipping one. become.

  As shown in FIGS. 1 and 2, the cylinder head 4 has an intake port 6 for introducing air (intake air) supplied from the intake passage 30 into the combustion chamber 10 of each cylinder 2A to 2D, and each cylinder 2A. An exhaust port 7 for leading the exhaust gas generated in the 2D combustion chamber 10 to the exhaust passage 35 and an opening on the combustion chamber 10 side of the intake port 6 for controlling the introduction of intake air through the intake port 6 An intake valve 8 that opens and closes and an exhaust valve 9 that opens and closes an opening of the exhaust port 7 on the combustion chamber 10 side in order to control gas discharge from the exhaust port 7 are provided. In the present embodiment, a total of eight intake valves 8 are provided at a rate of two per cylinder, and a total of eight exhaust valves 9 are also provided at a rate of two per cylinder.

  As shown in FIG. 1, the intake passage 30 includes four independent intake passages 31 communicating with the intake ports 6 of the cylinders 2 </ b> A to 2 </ b> D, and upstream ends of the individual intake passages 31 (on the upstream side in the intake flow direction). A surge tank 32 commonly connected to the end) and a single intake pipe 33 extending upstream from the surge tank 32. An openable / closable throttle valve 34 for adjusting the flow rate of intake air introduced into the engine body 1 is provided in the middle of the intake pipe 33.

  The exhaust passage 35 has four independent exhaust passages 36 communicating with the exhaust ports 7 of the cylinders 2A to 2D, and one downstream end portion (end portion on the downstream side in the exhaust gas flow direction) of each independent exhaust passage 36. And a single exhaust pipe 38 extending downstream from the collective portion 37.

(2) Valve Mechanism Next, a mechanism for opening and closing the intake valve 8 and the exhaust valve 9 will be described in detail with reference to FIGS. The intake valve 8 and the exhaust valve 9 are driven to open and close in conjunction with the rotation of the crankshaft 15 by a pair of valve mechanisms 28 and 29 (FIG. 2) disposed in the cylinder head 4.

  The valve operating mechanism 28 for the intake valve 8 includes a return spring 16 that urges the intake valve 8 in the closing direction (upward in FIG. 2), a cam shaft 18 that rotates in conjunction with the rotation of the crankshaft 15, and a cam shaft. 18, a cam portion 18 a provided so as to rotate integrally with the shaft 18, a swing arm 20 that is periodically pressed by the cam portion 18 a, and a pivot portion 22 that serves as a swing fulcrum of the swing arm 20.

  Similarly, the valve operating mechanism 29 for the exhaust valve 9 includes a return spring 17 that urges the exhaust valve 9 in the closing direction (upward in FIG. 2), and a cam shaft 19 that rotates in conjunction with the rotation of the crankshaft 15. A cam portion 19a provided to rotate integrally with the cam shaft 19, a swing arm 21 periodically pressed by the cam portion 19a, and a pivot portion 22 serving as a swing fulcrum of the swing arm 20. ing.

  By the valve mechanisms 28 and 29 as described above, the intake valve 8 and the exhaust valve 9 are driven to open and close as follows. That is, when the camshafts 18 and 19 are rotated with the rotation of the crankshaft 15, the cam followers 20a and 21a that are rotatably provided at the substantially central portions of the swing arms 20 and 21 are periodically lowered by the cam portions 18a and 19a. While being pressed, the swing arms 20 and 21 swing and displace with the pivot portion 22 supporting one end thereof as a fulcrum. Accordingly, the other ends of the swing arms 20 and 21 press the intake and exhaust valves 8 and 9 downward against the urging force of the return springs 16 and 17, thereby opening the intake and exhaust valves 8 and 9. To do. The intake / exhaust valves 8 and 9 once opened are returned to the closed position again by the urging force of the return springs 16 and 17.

  The pivot portion 22 is supported by known hydraulic lash adjusters 24 and 25 (hereinafter abbreviated as “HLA”, which is an acronym for “Hydraulic Lash Adjuster”) that automatically adjusts the valve clearance to zero. Among them, the HLA 24 automatically adjusts the valve clearances of the second cylinder 2B and the third cylinder 2C on the center side in the cylinder row direction, and the HLA 25 is the first cylinder 2A and the first cylinders at both ends in the cylinder row direction. The valve clearance of the 4-cylinder 2D is automatically adjusted.

  The HLA 25 for the first cylinder 2A and the fourth cylinder 2D has a function of switching whether the intake / exhaust valves 8 and 9 are opened / closed or stopped depending on whether the engine is in a reduced cylinder operation or an all cylinder operation. That is, the HLA 25 opens and closes the intake / exhaust valves 8 and 9 of the first and fourth cylinders 2A and 2D during all cylinder operation of the engine, while the intake and exhaust valves of the first and fourth cylinders 2A and 2D operate during reduced cylinder operation of the engine. The exhaust valves 8 and 9 are stopped while being closed. For this reason, the HLA 25 has a valve stop mechanism 25a shown in FIG. 3 as a mechanism for stopping the opening / closing operation of the intake and exhaust valves 8, 9. On the other hand, the HLA 24 for the second cylinder 2B and the third cylinder 2C does not include the valve stop mechanism 25a and does not have a function of stopping the opening / closing operation of the intake and exhaust valves 8 and 9. Below, in order to distinguish these HLA24 and 25, the HLA25 provided with the valve stop mechanism 25a is called S-HLA25 (abbreviation of Switchable-Hydraulic Lash Adjuster) especially.

  The valve stop mechanism 25a of the S-HLA 25 includes a bottomed outer cylinder 251 that accommodates the pivot portion 22 so as to be slidable in the axial direction, and two through-holes provided on the peripheral surface of the outer cylinder 251 so as to face each other. A pair of lock pins 252 capable of entering and exiting 251a and capable of switching the pivot portion 22 between a locked state and an unlocked state; a lock spring 253 that urges the lock pins 252 radially outward; and an inner bottom portion of the outer cylinder 251 And a lost motion spring 254 that presses and urges the pivot portion 22 above the outer cylinder 251.

  As shown in FIG. 3A, when the lock pin 252 is fitted in the through hole 251a of the outer cylinder 251, the pivot portion 22 is in a locked state in which it is fixed while protruding upward. In this locked state, as shown in FIG. 2, the top portion of the pivot portion 22 serves as the swing fulcrum of the swing arms 20 and 21, so that the cam portions 18a and 19a rotate the cam followers 20a and 21a as the cam shafts 18 and 19 rotate. When pressed downward, the intake / exhaust valves 8, 9 are displaced downward against the urging force of the return springs 16, 17, and the intake / exhaust valves 8, 9 are opened.

  During all-cylinder operation in which all the four cylinders 2A to 2D are operated, the valve stop mechanism 25a is locked, so that the intake and exhaust valves 8 and 9 of the first and fourth cylinders 2A and 2D are driven to open and close. That is, during all-cylinder operation, the intake and exhaust valves 8 and 9 are driven to open and close in all the cylinders 2A to 2D including the first and fourth cylinders.

  In order to release the locked state of the valve stop mechanism 25a as described above, the pair of lock pins 252 are pressed radially inward by the hydraulic pressure. Then, as shown in FIG. 3B, the pair of lock pins 252 move in a direction approaching each other (in the radial direction of the outer cylinder 251) against the tensile force of the lock spring 253. Thereby, the fitting between the lock pin 252 and the through hole 251a of the outer cylinder 251 is released, and the pivot portion 22 is in an unlocked state in which it can move in the axial direction.

  With the change to the unlocked state, the pivot portion 22 is pressed downward against the urging force of the lost motion spring 254, thereby realizing the valve stop state as shown in FIG. That is, the return springs 16 and 17 that urge the intake and exhaust valves 8 and 9 upward have a stronger urging force than the lost motion spring 254 that urges the pivot portion 22 upward. In the released state, when the cam portions 18a and 19a press the cam followers 20a and 21a downward as the cam shafts 18 and 19 rotate, the top portions of the intake and exhaust valves 8 and 9 become the swing fulcrum of the swing arms 20 and 21. The pivot portion 22 is displaced downward against the urging force of the lost motion spring 254. That is, the intake / exhaust valves 8 and 9 are maintained in a closed state.

  During the reduced-cylinder operation in which the first and fourth cylinders 2A and 2D are deactivated, the valve stop mechanism 25a is unlocked to open and close the intake and exhaust valves 8 and 9 of the first and fourth cylinders 2A and 2D. Is stopped. That is, during the cylinder reduction operation, only the intake and exhaust valves 8 and 9 of the second and third cylinders 2B and 2C are driven to open and close, and the intake and exhaust valves 8 and 9 of the first and fourth cylinders 2A and 2D are closed. Maintained.

(3) Control system Next, an engine control system will be described. Each part of the engine of this embodiment is centrally controlled by an ECU (engine control unit) 50 shown in FIG. As is well known, the ECU 50 is a microprocessor including a CPU, a ROM, a RAM, and the like.

  The engine and the vehicle are provided with a plurality of sensors for detecting the state quantities of the respective parts, and information from each sensor is input to the ECU 50.

  For example, the cylinder block 3 is provided with a crank angle sensor SN1 that detects a rotation angle (crank angle) and a rotation speed of the crankshaft 15. The crank angle sensor SN1 outputs a pulse signal in accordance with the rotation of a crank plate (not shown) that rotates integrally with the crankshaft 15. Based on the pulse signal, the rotation angle and the rotation speed of the crankshaft 15 are output. Are to be identified. In the following, the rotational speed of the crankshaft 15 is referred to as “engine rotational speed” or simply “rotational speed”.

  The cylinder head 4 is provided with a cam angle sensor SN2. The cam angle sensor SN2 outputs a pulse signal according to the passage of the teeth of the signal plate that rotates integrally with the camshaft (18 or 19), and this signal and the pulse signal from the crank angle sensor SN1 Based on this, cylinder discrimination information indicating which cylinder is in what stroke is generated.

  The surge tank 32 of the intake passage 30 is provided with an intake pressure sensor SN3 that detects the pressure of intake air introduced into the cylinders 2A to 2D of the engine body 1.

  The vehicle is provided with an accelerator opening sensor SN4 that detects the opening degree of an accelerator pedal (accelerator opening degree) that is operated by the driver and that is not shown.

  The ECU 50 is electrically connected to these sensors SN1 to SN4, and based on signals input from the sensors, the above-described various information (crank angle, engine speed, cylinder discrimination information, intake pressure, accelerator) Get the opening).

  Further, the ECU 50 controls each part of the engine while executing various determinations and calculations based on the input signals from the sensors SN1 to SN4. That is, the ECU 50 is electrically connected to the injector 12, the spark plug 13, the throttle valve 34, and the valve stop mechanism 25a, and outputs drive control signals to these devices based on the results of the above calculations and the like. To do. In the present embodiment, there are a total of four sets of injectors 12 and spark plugs 13 at a rate of one set per cylinder, but in FIG. 4, each of the injectors 12 and the spark plugs 13 is represented by one block. . Further, the valve stop mechanism 25a is connected to each intake-side and exhaust-side S-HLA 25 provided for the first cylinder 2A and each intake-side and exhaust-side S-HLA 25 provided for the fourth cylinder 2D. There is one each, and there are a total of four valve stop mechanisms 25a, which are represented by one block in FIG.

  More specific functions of the ECU 50 will be described. The ECU 50 includes an operation request determination unit 51, a valve control unit 52, an intake valve return determination unit 53, an exhaust valve as specific functional elements related to so-called cylinder number control (switching control for all cylinder operation or reduced cylinder operation). A return determination unit 54 and a combustion control unit 55 are provided.

  The driving request determination unit 51 determines whether the engine has reduced cylinder operation or all cylinder operation based on the engine operating conditions (load, rotational speed, etc.) specified from the detected values of the accelerator opening sensor SN4 and the crank angle sensor SN1. Is to be selected. For example, the operation request determination unit 51 deactivates the first and fourth cylinders 2A and 2D when the engine load and the rotational speed are in a specific operation condition that is relatively low (second and third cylinders 2B and 2C). It is determined that there is a request for reduced-cylinder operation. Conversely, when the remaining operating conditions except for the specific operating conditions are present, it is determined that there is a request for all-cylinder operation for operating all of the first to fourth cylinders 2A to 2D.

  When the operation request determination unit 51 confirms that there is a request for switching from all-cylinder operation to reduced-cylinder operation or a request for switching from reduced-cylinder operation to all-cylinder operation, the valve control unit 52 The operation states of the intake and exhaust valves 8 and 9 of the four cylinders 2A and 2D are switched. For example, when there is a request for switching from all-cylinder operation to reduced-cylinder operation, the valve control unit 52 operates the hydraulic pressure so that the valve stop mechanism 25a of the S-HLA 25 is in the unlocked state (see FIG. 3C). Is controlled to stop the opening and closing operations of the intake and exhaust valves 8 and 9 of the first and fourth cylinders 2A and 2D. On the other hand, when there is a request for switching from reduced-cylinder operation to full-cylinder operation, the valve control unit 52 controls the hydraulic pressure so that the valve stop mechanism 25a is in a locked state (see FIG. 3A). Then, the intake and exhaust valves 8, 9 of the first and fourth cylinders 2A, 2D are returned to a state in which they can be opened and closed.

  The intake valve return determination unit 53 determines whether or not the intake valves 8 of the first and fourth cylinders 2A and 2D have normally returned to the openable / closable state when switching from reduced-cylinder operation to full-cylinder operation, It is determined whether or not the opening / closing operation of the intake valve 8 has actually been resumed.

  The exhaust valve return determination unit 54 determines whether or not the exhaust valves 9 of the first and fourth cylinders 2A and 2D have normally returned to a state in which the exhaust valves 9 can be opened and closed, that is, whether or not the opening / closing operation of the exhaust valves 9 has actually been resumed. This is a judgment.

  Although details will be described later, the return determination of the intake / exhaust valves 8 and 9 by the determination units 53 and 54 is performed based on the intake pressure detected by the intake pressure sensor SN3.

  The combustion control unit 55 switches the control of the injectors 12 and the spark plugs 13 of the first and fourth cylinders 2A and 2D depending on whether the cylinder reduction operation or all cylinder operation is performed. That is, when the engine is operating in all cylinders, the combustion control unit 55 drives the injectors 12 and spark plugs 13 of all cylinders 2A to 2D to execute fuel injection and ignition, and in all cylinders 2A to 2D. Burn the mixture. On the other hand, when the engine is in a reduced cylinder operation, the combustion control unit 55 is configured to stop the combustion in the first and fourth cylinders 2A and 2D, which are idle cylinders, of the injector 12 and the spark plug 13 of the cylinder. Prohibit driving. In particular, when switching from reduced-cylinder operation to all-cylinder operation, the combustion control unit 55 uses the intake valve and exhaust valve return determination units 53 and 54 to normalize the intake and exhaust valves 8 and 9 of the first and fourth cylinders 2A and 2D. After the return is confirmed, fuel injection and ignition to the cylinders 2A and 2D are resumed.

(4) Valve Return Determination Logic Next, when switching from the reduced cylinder operation to the all cylinder operation, the normal return of the intake and exhaust valves 8 and 9 of the first and fourth cylinders 2A and 2D is the above-described determination units 53 and 54. Will be described in detail. Hereinafter, the first cylinder 2A or the fourth cylinder 2D that is in a deactivated state during the reduced-cylinder operation may be simply referred to as a “deactivated cylinder”.

  FIG. 5 is a time chart showing the state change of a specific deactivation cylinder (first cylinder 2A or fourth cylinder 2D) at the time of switching from the reduced cylinder operation to the all cylinder operation in time series. In the example of FIG. 5, it is assumed that there is a request for switching from reduced-cylinder operation to all-cylinder operation at time ts. Prior to time ts, the valve stop mechanism 25a is in the unlocked state shown in FIG. 3C, and both the intake valve 8 and the exhaust valve 9 of the deactivated cylinder are stopped while being closed (FIG. 3). 5, the intake valve 8 is expressed as “IN” and the exhaust valve 9 is expressed as “EX”). On the other hand, when there is a request to switch to all-cylinder operation at time ts, the hydraulic pressure is controlled so that the valve stop mechanism 25a is displaced to the locked state shown in FIG. A control signal (hereinafter referred to as a return command) is output. Thus, in the idle cylinder, for example, the opening / closing operation of the exhaust valve 9 is restarted from the first exhaust stroke after time ts, and the opening operation of the intake valve 8 is restarted from the subsequent intake stroke.

  Here, a certain amount of time (operation delay time) is required until the valve stop mechanism 25a is actually displaced to the locked state. For this reason, for example, when a request to switch to all-cylinder operation occurs immediately before the exhaust stroke, even if a return command is output at that time, the exhaust valve 9 is opened and closed from the first exhaust stroke after that command. I can't let you. Therefore, in such a case, as shown in FIG. 6, the opening / closing operation is resumed from the intake valve 8 instead of the exhaust valve 9.

  That is, in the example of FIG. 6, since the time ts of the request for switching to the all-cylinder operation is immediately before the exhaust stroke, even if a return command is output to the valve stop mechanism 25a at the time ts, the exhaust valve 9 immediately after that is output. At the valve opening start time, the valve stop mechanism 25a has not yet been displaced into the locked state. For this reason, in the first exhaust stroke after the switching request, the driving force is not transmitted to the exhaust valve 9, and the exhaust valve 9 remains closed. On the other hand, if the displacement to the locked state is completed in the middle of the exhaust stroke, the driving force is transmitted to the intake valve 8, and the intake valve 8 resumes the opening / closing operation from the first intake stroke after the switching request. Thereafter, the exhaust valve 9 resumes the opening / closing operation for the first time when the exhaust stroke of the next cycle is reached. In this way, depending on the timing at which a request for switching to the all-cylinder operation is issued, the opening / closing operation may be resumed first from the intake valve 8.

  As described above, when switching from reduced-cylinder operation to all-cylinder operation, a return command is output to the valve stop mechanism 25a at the time ts when the change request is made, and the exhaust valve 9 and the intake valve 8 are sequentially switched or the intake air is taken. The opening / closing operation is restarted in the order of the valve 8 → the exhaust valve 9.

  However, the opening / closing operation of the intake and exhaust valves 8 and 9 may not be resumed (failed to return) for some reason, such as a failure of the valve stop mechanism 25a. Therefore, the intake / exhaust valve return determination units 53 and 54 determine whether or not the intake / exhaust valves 8 and 9 have returned to normal after a return command output time ts using predetermined determination logic. Hereinafter, each determination logic for the intake / exhaust valves 8 and 9 will be described in detail.

(I) Exhaust Valve Return Determination Logic First, what kind of determination logic is used to determine whether or not the exhaust valve 9 has returned to normal will be described. In this embodiment, the exhaust valve return determination unit 54 determines whether or not the exhaust valve 9 of the deactivated cylinder has returned to normal based on the pressure fluctuation of the intake air before and after the timing when the intake valve 8 of the deactivated cylinder starts to open. Determine.

  For example, if the exhaust valve 9 of the deactivated cylinder is stopped in a closed state due to a failure of the valve stop mechanism 25a or the like, the piston 11 of the deactivated cylinder rises to the exhaust top dead center in the process of raising the piston 11 Compresses the gas (air or exhaust gas or mixture thereof) in the combustion chamber 10. Therefore, as shown in FIG. 7, when the intake valve 8 starts to open near the exhaust top dead center (this time is expressed as IVO in FIG. 7), the compressed gas in the combustion chamber 10 is taken into the intake air. Blowback that flows back to the intake passage 30 through the port 6 occurs, and the intake pressure temporarily rises. On the other hand, if the exhaust valve 9 of the idle cylinder has returned to normal, the above-described gas compression does not occur during the exhaust stroke, so that the intake pressure does not increase so much even if the intake valve 8 is opened.

  If the phenomenon as described above is utilized, it can be determined that the exhaust valve 9 has returned to normal when the intake pressure fluctuation at the opening start time of the intake valve 8 is small, and the exhaust valve 9 is restored when the pressure fluctuation is large. Can be determined to have failed. Therefore, in the present embodiment, the exhaust valve return determination unit 54 examines the intake pressure detected by the intake pressure sensor SN3 over a predetermined period sandwiching the opening start timing of the intake valve 8 of the idle cylinder, and is identified therefrom. Based on the intake pressure fluctuation, it is determined whether or not the exhaust valve 9 has returned to normal.

  The intake pressure fluctuation in this case may be any value that indicates how much the intake pressure has increased as the intake valve 8 is opened, and various state quantities as shown in FIG. 8 should be adopted. Can do. For example, the difference between the maximum value of the intake pressure detected within the predetermined period and the pressure value of the valley portion of the pressure waveform appearing immediately before it is taken ((x) in FIG. 8), and this is adopted as the pressure fluctuation. It is possible. Further, the difference between the maximum value and the minimum value of the intake pressure detected within the predetermined period may be taken ((z) in FIG. 8), and this may be adopted as the pressure fluctuation. Alternatively, the rate of increase (inclination) when the intake pressure increases toward the maximum value may be taken ((y) in FIG. 8), and this may be adopted as the pressure fluctuation.

  FIG. 9 is a diagram showing the probability of occurrence of a case where the exhaust valve 9 of the deactivated cylinder returns to normal and a case where the return fails due to the pressure fluctuation of the intake air (pressure fluctuation in the increasing direction) as a parameter. It is. According to this figure, when the pressure fluctuation of the intake air is smaller than β, the exhaust valve 9 always returns to the normal state, and there is no possibility that the return has failed (stopped in the closed state). It is done. On the other hand, when the pressure fluctuation of the intake air is larger than β, the exhaust valve 9 always fails to return, and it is considered that there is no possibility of returning to normal. Therefore, in determining whether the exhaust valve 9 has returned to normal, β in FIG. 9 is used as a threshold value. That is, the exhaust valve return determination unit 54 determines that the exhaust valve 9 has returned to normal when the intake pressure fluctuation is smaller than the threshold value β, and when the intake pressure fluctuation is greater than or equal to the threshold value β, It is determined that the valve 9 has failed to return.

(Ii) Intake Valve Return Determination Logic Next, what kind of determination logic is used to determine whether or not the intake valve 8 has returned to normal will be described. In the present embodiment, the intake valve return determination unit 53 determines whether or not the intake valve 8 of the deactivated cylinder has returned to normal based on the result of spectral analysis of the intake pressure over a predetermined period including the intake stroke of the deactivated cylinder. .

  FIGS. 10A and 10B show the waveform of the intake pressure that changes according to the crank angle. Specifically, FIG. 10A shows the waveform of the intake pressure during all cylinder operation in which the intake valves 8 and the exhaust valves 9 of all the cylinders are opened and closed, and FIG. 10B shows the intake valve of the deactivated cylinder. 8 shows the waveform of the intake pressure during the reduced-cylinder operation in which 8 and the exhaust valve 9 are stopped in the closed state. As understood from these figures, the waveform of the intake pressure during all cylinder operation (FIG. 10A) in which the intake and exhaust valves 8 and 9 of all cylinders are driven to open and close has a periodicity of approximately 180 ° CA. Have. On the other hand, the waveform of the intake pressure during the reduced-cylinder operation in which the intake and exhaust valves 8 and 9 of the idle cylinder are stopped (FIG. 10B) has a periodicity of approximately 360 ° CA. This is because combustion in each of the cylinders 2A to 2D is performed by shifting the phase by 180 ° CA during all-cylinder operation, whereas during the reduced-cylinder operation in which the first cylinder 2A and the fourth cylinder 2D are deactivated, the combustion interval This is because it becomes 360 ° CA which is doubled.

  FIGS. 11 (a) and 11 (b) show the results of spectral analysis of the intake pressure during all-cylinder operation and reduced-cylinder operation as described above, with a frequency having 360 ° CA as one cycle as a fundamental frequency. Yes. In each figure, the horizontal axis indicates the order (primary, secondary, tertiary, etc.) with respect to the fundamental frequency, and the vertical axis indicates the spectrum intensity. Since the intake pressure during all-cylinder operation has a periodicity of 180 ° CA, if this is subjected to spectrum analysis, the spectrum intensity becomes a secondary one (FIG. 11A). On the other hand, since the intake pressure during the reduced-cylinder operation has a periodicity of 360 ° CA, if this is subjected to spectrum analysis, the spectrum intensity becomes higher in the first order (FIG. 11 (b)).

  FIG. 12 shows the correlation between the primary spectral intensity (primary intensity) SP1 and the secondary spectral intensity (secondary intensity) SP2 obtained from spectral analysis of the intake pressure under various operating conditions. It is the graph processed so that it might represent. A region A shown in this graph is a plot region of data obtained when the intake valves 8 and the exhaust valves 9 of all the cylinders are driven to open and close, and a region B is the first and fourth cylinders 2A and 2D. This is a plot region of data obtained when only the intake valve 8 is driven to open and close (when the exhaust valve 9 is stopped in a closed state). A region C is a plot region of data obtained when both the intake valve 8 and the exhaust valve 9 of the first and fourth cylinders 2A and 2D are stopped in the closed state.

  As shown in FIG. 12, the region A exists in the upper left region of FIG. 12 where the ratio of the secondary intensity SP2 is large. This is because in the region A, the intake / exhaust valves 8 and 9 of all the cylinders are driven to open and close, so the intensity of the frequency component with 180 ° CA as one cycle, that is, the ratio of the secondary intensity SP2 increases. On the other hand, the region C exists in the lower right region of FIG. 12 where the ratio of the primary intensity SP1 is large. This is because, in region C, only the intake and exhaust valves 8 and 9 of the two cylinders (second and third cylinders 2B and 2C) of the four cylinders are driven to open and close, so the frequency component with 360 ° CA as one cycle This is because the strength, that is, the ratio of the primary strength SP1 increases.

  On the other hand, the region B exists in an intermediate region between the region A and the region C described above. In the region B, the intake valves 8 and exhaust valves 9 of the second and third cylinders 2B and 2C and the intake valves 8 of the first and fourth cylinders 2A and 2D are driven to open and close. Because the exhaust valves 9 of the cylinders 2A and 2D are stopped in the closed state, the primary strength SP1 and the secondary strength SP2 increase accordingly. That is, when only the intake valve 8 is opened and closed while the exhaust valve 9 is closed in the first and fourth cylinders 2A and 2D, the gas compressed in the exhaust stroke of the cylinders 2A and 2D is taken into account as described above. This is because the blowback that flows back into the intake passage 30 occurs as the valve 8 opens, and this blowback contributes to the increase in the secondary strength SP2, and both the primary strength SP1 and the secondary strength SP2 increase.

  Note that FIG. 12 does not show data when only the exhaust valves 9 of the first and fourth cylinders 2A and 2D are driven to open and close (when the intake valve 8 is stopped in a closed state). The plot area in this case is basically the same as the plot area C when both the intake valve 8 and the exhaust valve 9 are closed.

  According to FIG. 12, the area A and the area B partially overlap each other, but the area C is completely separated (independent) from the areas A and B. For this reason, a straight line passing between the areas A and B and the area C can be set as a straight line P in FIG. When the slope of the straight line P is a and the intercept of the vertical axis is b, on the straight line P, the primary intensity SP1 and the secondary intensity SP2 satisfy the formula “SP2 = a × SP1 + b”. On the other hand, in the area A and the area B located on the upper left side of the straight line P, the relationship between the primary intensity SP1 and the secondary intensity SP2 can be expressed by an equation “SP2> a × SP1 + b”. In the region C located on the lower right side, the relationship between the primary intensity SP1 and the secondary intensity SP2 can be expressed by an equation “SP2 <a × SP1 + b”.

  Assuming that the value defined by the linear function (SP2 = a × SP1 + b) representing the straight line P is the intake valve determination threshold value, the intake valve determination threshold value is compared with the secondary strength SP2, thereby deactivating the first cylinder (first, It can be determined whether or not the intake valves 8 of the fourth cylinders 2A, 2D) have returned to normal. That is, the secondary strength SP2 is larger than the intake valve determination threshold (a × SP1 + b), that is, the relationship “SP2> a × SP1 + b” is established. Either in the state of the region A being driven to open or close, or in the state of the region B where only the intake valve 8 of the deactivated cylinder is normally driven to open or close (the exhaust valve 9 is stopped in the closed state) Therefore, it can be determined that at least the intake valve 8 of the idle cylinder has returned to normal. Conversely, when the secondary strength SP2 is smaller than the intake valve determination threshold value (a × SP1 + b), that is, when the relationship of “SP2 <a × SP1 + b” is established, the intake valve 8 of the idle cylinder has failed to return. It can be determined that the valve is stopped with the valve closed.

  Therefore, in the present embodiment, the intake valve return determination unit 53 acquires the intake pressure detected by the intake pressure sensor SN3 over a predetermined period including the intake stroke of the idle cylinder, and performs spectrum analysis on the acquired intake pressure data. Thus, the primary intensity SP1 and the secondary intensity SP2 are specified. If the secondary strength SP2 is greater than the intake valve determination threshold (a × SP1 + b), it is determined that the intake valve 8 has returned to normal, and the secondary strength SP2 is determined to be the intake valve determination threshold (a × SP1 + b). In the following cases, it is determined that the intake valve 8 has failed to return.

(5) Control operation when returning from reduced-cylinder operation to full-cylinder operation Next, the control operation performed when switching from reduced-cylinder operation to full-cylinder operation will be described in detail with reference to the flowcharts of FIGS. . Assuming that the control according to this flowchart is started, it is assumed that the engine is in a reduced cylinder operation.

  As shown in FIG. 13, during the reduced-cylinder operation of the engine, the operation request determination unit 51 of the ECU 50 reduces the cylinder based on the engine load and the rotational speed specified from the accelerator opening sensor SN4, the crank angle sensor SN1, and the like. It is determined whether or not there is a request to switch from operation to all-cylinder operation (step S1). For example, when the operation request determination unit 51 shifts from an operation condition suitable for reduced-cylinder operation (an operation condition with relatively low load and rotation speed) to an operation condition in which the load or rotation speed is increased to perform all-cylinder operation. Then, it is determined that there is a request for switching from the reduced cylinder operation to the all cylinder operation.

  When it is determined YES in step S1 and a request for switching to all-cylinder operation is confirmed, the valve control unit 52 of the ECU 50 performs the intake and exhaust valves 8 and 9 in the idle cylinders (first cylinder 2A and fourth cylinder 2D). Is returned to the valve stop mechanism 25a of the S-HLA 25 (step S2). In other words, the valve control unit 52 causes the valve stop mechanism 25a of the S-HLA 25 to open and close the intake / exhaust valves 8 and 9 of the deactivated cylinders that have been stopped in the closed state during the reduced cylinder operation. A control signal for switching from the unlocked state to the locked state is output (step S2).

  Next, the valve control unit 52 determines whether or not to return from the exhaust valve 9 first by the return command in step S2 (step S3). Specifically, the determination in step S3 is performed as follows.

  5 and 6, the period indicated by Tex indicates that the opening / closing operation is resumed first (in the order of the exhaust valve 9 → the intake valve 8) from the exhaust valve 9 if a return command is issued within the period. Hereinafter, this is referred to as a first period Tex. Further, the period indicated by Tin indicates that the opening / closing operation is resumed first (in the order of the intake valve 8 → the exhaust valve 9) after the intake valve 8 if a return command is issued within the period. This is called the second period Tin. The first period Tex and the second period Tin are determined in consideration of the operation delay time Ta necessary for the valve stop mechanism 25a to actually switch to the locked state from the return command. Specifically, the period from immediately after the time when the operation delay time Ta is traced back from the valve opening start timing q0 of the intake valve 8 to the time when the operation delay time Ta is traced back from the valve opening start timing p of the exhaust valve 9 is The first period Tex is used. In addition, the period from immediately after the time when the exhaust valve 9 starts from the valve opening start time p by the operation delay time Ta to the time when the intake valve 8 starts from the valve opening start timing q1 by the operation delay time Ta is the second time. The period is Tin.

  Then, when the return command is issued within the first period Tex, the valve control unit 52 determines that the opening / closing operation is resumed first from the exhaust valve 9, and the return command is issued within the second period Tin. If it is determined that the opening / closing operation is resumed from the intake valve 8, it is determined. For example, in the case of FIG. 5, since the output time ts of the return command is included in the first period Tex, it is determined that the opening / closing operation is restarted first from the exhaust valve 9, and in the case of FIG. Is included in the second period Tin, it is determined that the opening / closing operation is restarted first from the intake valve 8.

  Note that the determination as described above is performed individually for the first cylinder 2A and the second cylinder 2D, which are idle cylinders. That is, in the first cylinder 2A and the second cylinder 2D having a phase difference of 360 ° CA, the relative positions of the periods Tex and Tin with respect to the output time ts of the return command are shifted by 360 ° CA. The determination results may differ between the cylinders 2A and 2D. Therefore, the valve control unit 52 considers the above phase difference between the valve whose opening / closing operation is restarted first in the first cylinder 2A and the valve whose opening / closing operation is restarted first in the fourth cylinder 2D, respectively. Judge individually.

  Further, the first and second periods Tex and Tin shown in FIGS. 5 and 6 are not fixed, and actually depend on the engine speed and the progress of engine warm-up (hydraulic oil temperature). Various changes. This is because if the engine speed is different, the crank angle traveling per unit time is different, and if the hydraulic oil temperature is different, the operation delay time Ta is different. The valve control unit 52 identifies the periods Tex and Tin based on various conditions such as the engine rotation speed and the temperature of the hydraulic oil at the output time ts of the return command, and makes a determination using these.

  When the return order of the intake / exhaust valves 8 and 9 is determined by the above procedure, one of the processes (first and second determination processes) shown in steps S4 and S5 is executed according to the result. The That is, when it is determined as YES in step S3 and it is predicted that the opening / closing operation is restarted first after the exhaust valve 9, the first determination process shown in step S4 is executed, and NO is determined in step S3. When it is determined and the opening / closing operation is predicted to be resumed first after the intake valve 8, the second determination process shown in step S5 is executed.

  FIG. 14 is a subroutine showing a specific procedure of the first determination process, and FIG. 15 is a subroutine showing a specific procedure of the second determination process. As described above, the process of step S3 for determining the return order of the intake / exhaust valves 8 and 9 is performed individually for each idle cylinder (first and fourth cylinders 2A and 2D). The determination process 2 is also performed individually for each idle cylinder. For example, when it is predicted that the opening / closing operation is resumed first from the exhaust valve 9 for both the first cylinder 2A and the fourth cylinder 2D, the first determination process is executed for both the cylinders 2A, 2D. . Further, for example, when the opening / closing operation is predicted to be restarted first from the exhaust valve 9 in the first cylinder 2A, and the opening / closing operation is predicted to be restarted first from the intake valve 8 in the fourth cylinder 2D, The first determination process is executed for the first cylinder 2A, and the second determination process is executed for the fourth cylinder 2D. However, in the following description, it is not particularly limited which of the first cylinder 2A and the fourth cylinder 2D is to be controlled. For this reason, the cylinder may be simply referred to as a deactivated cylinder in the sense that it is either the first cylinder 2A or the fourth cylinder 2D.

  First, the first determination process executed when the opening / closing operation is restarted first after the exhaust valve 9 will be described with reference to FIG. When the first determination process is started, the exhaust valve return determination unit 54 of the ECU 50 identifies the intake pressure fluctuation associated with the first opening of the intake valve 8 of the idle cylinder based on the detected value of the intake pressure sensor SN3. The process which performs is performed (step S10). That is, as shown in FIG. 5, the detection is made by the intake pressure sensor SN3 during a predetermined period w1 sandwiching the valve opening start timing q1 of the intake valve 8 when the idle cylinder reaches the first time after the output time ts of the return command. For example, based on the waveform of the intake pressure, an increase range or rate of increase of the intake pressure as shown in FIG. 8, for example, is calculated and specified as a change in intake pressure.

  Next, the exhaust valve return determination unit 54 determines whether or not the pressure fluctuation (the pressure fluctuation of the first intake air) specified in step S10 is smaller than a predetermined threshold β (FIG. 9) (step S11). ).

  When it is determined YES in step S11 and it is confirmed that the pressure fluctuation of the first intake is smaller than the threshold value β, the exhaust valve return determination unit 54 opens the intake valve 8 of the idle cylinder for the second time. A process of specifying the accompanying intake pressure fluctuation based on the detected value of the intake pressure sensor SN3 is executed (step S12). That is, as shown in FIG. 5, the intake pressure sensor SN3 detects a predetermined period w2 sandwiching the valve opening start timing q2 of the second intake valve 8 in which the idle cylinder reaches after the return command output time ts. The intake pressure is examined, and the intake pressure fluctuation is specified based on the waveform of the intake pressure.

  Next, the exhaust valve return determination unit 54 determines whether or not the pressure fluctuation (the pressure fluctuation of the second intake air) specified in step S12 is smaller than the threshold value β (step S13).

If it is determined YES in step S13, that is, if it is confirmed that both the first and second intake air pressure fluctuations specified in steps S10 and S12 are smaller than the threshold value β, the exhaust valve is returned. The determination unit 54 inputs “1” indicating that the exhaust valve 9 has returned to normal to an exhaust valve state flag F1 _i (i is 1 or 4) for indicating success or failure of the exhaust valve 9 (step) S14). Since the subscript _i of the exhaust valve state flag F1 _i is 1 or 4, there are two types of F1 _i , F1 ₁ and F1 ₄ . F1 ₁ is a flag for the first cylinder 2A, F1 ₄ is a flag for the fourth cylinder 2D. Therefore, when the pressure variation <beta for the first cylinder 2A is confirmed, "1" is input to the exhaust valve state flag F1 ₁ for the first cylinder 2A, the pressure variation for the fourth cylinder 2D <beta confirmation is the case was a "1" is input to the exhaust valve state flag F1 ₄ for the fourth cylinder 2D.

On the other hand, if it is determined NO in step S11 or step S13, that is, if it is confirmed that one of the first and second intake pressure fluctuations is equal to or greater than the threshold value β, the exhaust valve return determination unit 54 Inputs “0”, which means that the exhaust valve 9 has failed to return, to the exhaust valve state flag F1 _i (step S15).

  Here, in the first determination process shown in FIG. 14, the processes of the following steps S <b> 16 to S <b> 19 are executed in parallel with the processes of steps S <b> 10 to S <b> 15 described above. That is, when the first determination process starts, the intake valve return determination unit 53 of the ECU 50 executes a process of performing a spectrum analysis on the intake pressure detected by the intake pressure sensor SN3 over a predetermined period including the intake stroke of the deactivated cylinder ( Step S16). That is, as shown in FIG. 5, the intake pressure sensor SN3 performs a period w3 of 360 ° CA in total including the intake stroke that the idle cylinder first meets after the output time ts of the return command and the subsequent compression stroke. By examining the detected intake pressure and performing spectrum analysis of the waveform of the intake pressure, the frequency component intensity (primary intensity) SP1 with 360 ° CA as one cycle and the frequency component with 180 ° CA as one cycle Strength (secondary strength) SP2.

  Next, the intake valve return determination unit 53 uses the primary intensity SP1 and the secondary intensity SP2 specified in step S16 to determine whether the relationship of “SP2> a × SP1 + b” is satisfied, that is, 1 It is determined whether the secondary intensity SP2 is larger than the intake valve determination threshold value (a × SP1 + b) defined by the linear function of the secondary intensity SP1 (step S17).

When it is determined YES in step S17 and it is confirmed that the secondary strength SP2 is larger than the intake valve determination threshold value (a × SP1 + b), the intake valve return determination unit 53 indicates success or failure of the return of the intake valve 8. Therefore, “1” indicating that the intake valve 8 has returned to the normal state is input to the intake valve state flag F2 _i (i is 1 or 4) (step S18). The use of the intake valve state flag F2 _i (i is 1 or 4) is the same as that of the exhaust valve state flag F1 _i described above. That is, when the relationship of "SP2> a × SP1 + b" was confirmed for the first cylinder 2A, the "1" is input to the intake valve state flag F2 ₁ for the first cylinder 2A, the fourth cylinder 2D "SP2> If the relation of a × SP1 + b "is confirmed," 1 "is input to the exhaust valve state flag F2 ₄ for the fourth cylinder 2D.

On the other hand, when it is determined NO in step S16 and it is confirmed that the secondary intensity SP2 is equal to or smaller than the intake valve determination threshold value (a × SP1 + b), the intake valve return determination unit 53 determines the intake valve state flag F2 _i. Then, “0”, which means that the intake valve 8 has failed to return, is input (step S19).

  Next, a second determination process executed when the opening / closing operation is restarted first after the intake valve 8 will be described with reference to FIG. When the second determination process is started, the exhaust valve return determination unit 54 of the ECU 50 identifies the intake pressure fluctuation caused by the second opening of the intake valve 8 of the idle cylinder based on the detected value of the intake pressure sensor SN3. The process which performs is performed (step S20). That is, as shown in FIG. 6, the intake pressure sensor SN3 detects for a predetermined period w2 sandwiching the valve opening start timing q2 of the second intake valve 8 where the idle cylinder reaches after the output time ts of the return command. The intake pressure is examined, and the intake pressure fluctuation is specified based on the waveform of the intake pressure.

  Next, the exhaust valve return determination unit 54 determines whether or not the pressure fluctuation (the pressure fluctuation of the second intake air) specified in step S20 is smaller than the threshold value β (step S21).

If it is determined YES in step S21 and it is confirmed that the pressure fluctuation of the second intake air is smaller than the threshold value β, the exhaust valve return determination unit 54 determines the exhaust valve state flag F1 _i (i is 1 or 1). In 4), “1” indicating that the exhaust valve 9 has returned to normal is input (step S22). Specifically, when the pressure variation <beta for the first cylinder 2A has been confirmed, "1" to the exhaust valve state flag F1 ₁ for the first cylinder 2A is input, the pressure variation for the fourth cylinder 2D <beta There when it is confirmed, "1" is input to the exhaust valve state flag F1 ₄ for the fourth cylinder 2D.

On the other hand, if it is determined NO in step S21 and it is confirmed that the pressure fluctuation of the second intake air is smaller than the threshold value β, the exhaust valve return determination unit 54 sets the exhaust valve state flag F1 _i to the exhaust valve state flag F1 _i. “0” indicating that 9 failed to return is input (step S23).

  Here, in the second determination process shown in FIG. 15, the processes of the next steps S24 to S27 are executed in parallel with the processes of steps S20 to S23 described above. That is, when the second determination process starts, the intake valve return determination unit 53 of the ECU 50 executes a process of performing a spectrum analysis on the intake pressure detected by the intake pressure sensor SN3 over a predetermined period including the intake stroke of the deactivated cylinder ( Step S24). That is, as shown in FIG. 6, the intake pressure sensor SN3 performs a period w3 of 360 ° CA in total including the intake stroke that the idle cylinder first meets after the output time ts of the return command and the subsequent compression stroke. By examining the detected intake pressure and performing spectrum analysis of the waveform of the intake pressure, the frequency component intensity (primary intensity) SP1 with 360 ° CA as one cycle and the frequency component with 180 ° CA as one cycle Strength (secondary strength) SP2.

  Next, the intake valve return determination unit 53 uses the primary intensity SP1 and the secondary intensity SP2 specified in step S24 to determine whether or not the relationship of “SP2> a × SP1 + b” is satisfied, that is, 1 It is determined whether or not the secondary intensity SP2 is larger than the intake valve determination threshold value (a × SP1 + b) defined by the linear function of the secondary intensity SP1 (step S25).

When it is determined YES in step S25 and it is confirmed that the secondary intensity SP2 is larger than the intake valve determination threshold value (a × SP1 + b), the intake valve return determination unit 53 determines the intake valve state flag F2 _i ( i is 1 or 4), and “1”, which means that the intake valve 8 has returned to normal, is input (step S26). Specifically, if the relationship of "SP2> a × SP1 + b" was confirmed for the first cylinder 2A, "1" is input to the intake valve state flag F2 ₁ for the first cylinder 2A, the fourth cylinder 2D when the relationship of "SP2> a × SP1 + b" is checked for, "1" is input to the exhaust valve state flag F2 ₄ for the fourth cylinder 2D.

On the other hand, when it is determined NO in step S16 and it is confirmed that the secondary intensity SP2 is equal to or smaller than the intake valve determination threshold value (a × SP1 + b), the intake valve return determination unit 53 determines the intake valve state flag F2 _i. In addition, “0” indicating that the intake valve 8 has failed to return is input (step S27).

When the return determination of the intake valve 8 and the exhaust valve 9 for the deactivated cylinder is completed by the first and second determination processes as described above, the flow proceeds to step S6 in FIG. In step S6, the combustion control unit 55 of the ECU 50 multiplies the values of the exhaust valve state flags F1 ₁ and F1 _{4 and} the values of the intake valve state flags F2 ₁ and F2 ₄ to obtain “1”. Determine whether or not. Note that YES (F1 ₁ × F1 ₄ × F2 ₁ × F2 ₄ = 1) in the determination of step S6 means that the exhaust valve state flag F1 ₁ for the first cylinder 2A and the exhaust valve for the fourth cylinder 2D. a status flag F1 _4, an intake valve state flag F2 ₁ for the first cylinder 2A, since the intake valve state flag F2 ₄ for the fourth cylinder 2D it is meant that either is "1", the suspendable cylinder All the intake valves 8 and exhaust valves 9 of the (first and fourth cylinders 2A, 2D) have returned to normal. On the other hand, NO (F1 ₁ × F1 ₄ × F2 ₁ × F2 ₄ = 0) in the determination in step S6 means that at least one of the flags F1 ₁ , F1 ₄ , F2 ₁ , F2 ₄ is “0”. This means that there are some of the intake valves 8 and exhaust valves 9 of the deactivated cylinders (first and fourth cylinders 2A, 2D) that have failed to return.

  When it is determined YES in step S6 and it is confirmed that all of the intake valves 8 and exhaust valves 9 of the deactivated cylinder have returned to normal, the combustion control unit 55 shifts the engine from the reduced cylinder operation to the all cylinder operation ( Step S7). That is, by operating the injector 12 and the spark plug 13 of the idle cylinder to restart the fuel injection and ignition, the cylinders 2A to 2D are brought into a state where combustion is performed. In FIGS. 5 and 6, the resumption of fuel injection is indicated by ▼ marked with “INJ”, and the resumption of ignition is indicated by ▼ marked with “IG”.

  On the other hand, when it is determined as NO in step S6 and it is confirmed that there is an unsuccessful recovery among the intake valve 8 and the exhaust valve 9 of the deactivated cylinder, the combustion control unit 55 performs the reduced-cylinder operation of the engine. Is maintained (step S8). That is, the operation of the injector 12 and the spark plug 13 of the idle cylinder is stopped to prohibit the combustion injection and ignition, and the state where the combustion is not performed in the idle cylinder (first and fourth cylinders 2A and 2D) is maintained.

(6) Operation, etc. As described above, in this embodiment, when a return command is output to the valve stop mechanism 25a in response to a request for switching from reduced-cylinder operation to all-cylinder operation, the idle cylinder (first, first, Based on the result of spectral analysis of the intake pressure detected over a predetermined period including the intake stroke of the four cylinders 2A, 2D), it is determined whether or not the intake valve 8 of the deactivated cylinder has returned to the normal state in the openable / closable state. At the same time, based on the pressure fluctuation of the intake air before and after the timing when the intake valve 8 of the deactivated cylinder starts to open, it is determined whether or not the exhaust valve 9 of the deactivated cylinder has returned to the normal state. Then, when the normal return of the intake valve 8 is confirmed and the normal return of the exhaust valve 9 is confirmed, the fuel supply to the idle cylinder is resumed, and the engine operation is changed from the reduced cylinder operation to the all cylinder operation. Can be switched. According to such a configuration, there is an advantage that switching from the reduced-cylinder operation to the all-cylinder operation can be performed safely and appropriately by accurately determining the states of both the intake valve 8 and the exhaust valve 9. .

  That is, in the above embodiment, the success or failure of the return of the exhaust valve 9 is determined based on the pressure fluctuation of the intake air before and after the timing when the intake valve 8 of the deactivated cylinder starts to open. Is unsuccessful in return, the gas in the deactivated cylinder is compressed during the exhaust stroke and then blown back to the intake passage 30 as the intake valve 8 is opened (the intake pressure fluctuates thereby). By utilizing this, it is possible to reliably recognize that the exhaust valve 9 has failed to return. Further, the success or failure of the return of the intake valve 8 is determined by performing a spectrum analysis of the intake pressure over a predetermined period including the intake stroke of the idle cylinder. Therefore, if the intake valve 8 of the idle cylinder fails to return, By utilizing the fact that the periodicity different from the normal state of the valve 8 appears in the waveform of the intake pressure, it is possible to reliably recognize that the intake valve 8 has failed to return.

  Only when it is confirmed that both the intake valve 8 and the exhaust valve 9 have returned to normal by the highly accurate determination as described above, the supply of fuel to the idle cylinder is resumed. Switching from operation to all-cylinder operation can be performed safely and appropriately. For example, when the supply of fuel to the deactivated cylinder is resumed even though the exhaust valve 9 has failed to return, the high-temperature exhaust gas generated by the combustion in the deactivated cylinder flows backward through the intake passage 30, so-called It is expected that a backfire will occur and have a significant impact on the engine. In addition, when the supply of fuel to the deactivated cylinder is resumed even though the intake valve 8 has failed to return, misfire occurs due to insufficient intake in the deactivated cylinder, and the supplied fuel is wasted. It is assumed that On the other hand, according to the above-described embodiment, the fuel supply or the like is not resumed unless both the intake valve 8 and the exhaust valve 9 have returned to normal, so that it can be safely and appropriately reduced without causing backfire or misfire. It is possible to switch from tube operation to all tube operation.

  Here, in the engine of the above-described embodiment, when both the intake valve 8 and the exhaust valve 9 fail to return (when the valve is stopped in the closed state), the gas in the deactivated cylinder is originally taken into the intake passage. Since the phenomenon of blowing back to 30 cannot occur, the intake pressure does not increase greatly as the intake valve 8 opens. For this reason, even if both the intake valve 8 and the exhaust valve 9 fail to return, the pressure fluctuation does not increase, and it is not recognized that the exhaust valve 9 has failed to return. However, even in such a case, since it is determined that at least the intake valve 8 has failed to return by spectral analysis of the intake pressure, fuel supply to the deactivated cylinder is not resumed, and in an inappropriate situation. It is possible to reliably prevent the switching to the all-cylinder operation.

  Further, in the above embodiment, in order to confirm the normal return of the exhaust valve 9, the intake pressure fluctuation over and around the time when the intake valve 8 of the idle cylinder starts to open is compared with a predetermined threshold β (FIG. 9). When the pressure fluctuation is smaller than the threshold value β, it is determined that the exhaust valve 9 has returned to normal. Therefore, the success or failure of the return of the exhaust valve 9 is determined by a simple procedure that simply compares the pressure fluctuation with the threshold value β. can do.

  In particular, in the above embodiment, when the opening / closing operation is resumed in the order of the exhaust valve 9 and the intake valve 8 in response to the return command, as shown as the first determination process in FIG. A determination is made to compare the pressure fluctuation of the intake air before and after the timing when the valve 8 starts to open (q1 in FIG. 5) with the threshold value β (steps S10 and S11). However, even if it is confirmed in this determination that the pressure fluctuation is smaller than the threshold value β (when the determination in step S11 is YES), it is not determined that the exhaust valve 9 has returned to normal at that time. A determination is made to compare the pressure fluctuation of the intake air before and after the timing (q2 in FIG. 5) when the intake valve starts opening for the second time after the return command with the threshold value β (steps S12 and S13). Then, when it is confirmed in this determination that the pressure fluctuation is smaller than the threshold value β (when the determination in step S13 is YES), it is determined for the first time that the exhaust valve 9 has returned to normal (step S14). According to such a configuration, for example, even if the internal pressure of the deactivated cylinder before the return command is reduced because the duration of the reduced-cylinder operation is relatively long, the exhaust valve 9 has returned to normal due to that reason. And the accuracy of the return determination can be further improved.

  That is, while the engine is in the reduced cylinder operation, in the idle cylinder, the piston 11 reciprocates while both the intake valve 8 and the exhaust valve 9 are closed. As the gas leaks to the outside through a gap with the inner wall of the chamber 10, the internal pressure of the idle cylinder gradually decreases. For this reason, if the duration of the reduced cylinder operation is relatively long, the internal pressure of the idle cylinder considerably decreases during the reduced cylinder operation, so that the exhaust valve 9 fails to return (therefore, the exhaust cylinder 9 fails to return). Even if the gas is compressed during the exhaust stroke), the intake pressure fluctuation that occurs when the intake valve 8 starts to open for the first time after the return command does not increase sufficiently. For this reason, when the return determination of the exhaust valve 9 is performed only based on the pressure fluctuation of the intake air before and after the first opening timing of the intake valve 8 (q1 in FIG. 5), the reduced cylinder as described above It is expected that the accuracy of the return determination of the exhaust valve 9 will decrease due to the decrease in the internal pressure of the deactivated cylinder due to gas leakage during operation. Therefore, in this embodiment, even if the pressure variation of the intake air accompanying the opening of the first intake valve 8 is smaller than the threshold value β, it is not determined that the exhaust valve 9 has returned to normal at that time, and 2 By examining the pressure fluctuation of the intake accompanying the opening of the intake valve 8 for the first time and comparing it with the threshold value β, the return determination of the exhaust valve 9 is performed again. In this manner, in a state where sufficient intake air is introduced into the idle cylinder by opening the first intake valve 8, the return determination of the exhaust valve 9 is performed based on the intake pressure fluctuation accompanying the second opening of the intake valve 8. When the operation is performed, the conditions of the internal pressure of the idle cylinder before the pressure fluctuation occurs can be made uniform, so that the accuracy of the return determination can be further increased.

  On the other hand, when the opening / closing operation of the intake valve 8 and the exhaust valve 9 is resumed in this order by the return command, the intake valve 8 is opened for the second time after the return command, as shown as the second determination processing in FIG. Is determined to compare the pressure fluctuation of the intake air before and after the time (q2 in FIG. 6) with the threshold β (steps S20 and S21), and it is confirmed in this determination that the pressure fluctuation is smaller than the threshold β. If so (if the determination in step S21 is YES), it is determined that the exhaust valve 9 has returned to normal. According to such a configuration, it is erroneously determined that the exhaust valve 9 has failed to return due to a change in intake pressure caused by the intake valve 8 restarting the opening / closing operation before the exhaust valve 9. Therefore, the accuracy of the return determination of the exhaust valve 9 can be ensured satisfactorily.

  That is, when the opening / closing operation is resumed in the order of the intake valve 8 and the exhaust valve 9, when the intake valve 8 starts to open for the first time after the return command, the intake valve 8 is compressed because the exhaust valve 9 is closed until just before that. The gas in the idle cylinder is blown back to the intake passage 30. For this reason, if the return determination of the exhaust valve 9 is made based on the intake pressure fluctuation accompanying the first opening of the intake valve 8, the intake valve 8 may have returned before the exhaust valve 9. In spite of the pressure fluctuation caused by the cause, there is a possibility that it is erroneously determined that the exhaust valve 9 has failed to return based on the pressure fluctuation. On the other hand, in the above embodiment, since the first opening of the intake valve 8 is overlooked, the return determination of the exhaust valve 9 is performed when the intake valve 8 is opened for the second time. An erroneous determination can be avoided, and the accuracy of the return determination of the exhaust valve 9 can be ensured satisfactorily.

  Further, in the above embodiment, in order to confirm the normal return of the intake valve 8, the intake pressure during a predetermined period including the intake stroke of the idle cylinder is subjected to spectrum analysis, and the primary frequency component having a cycle of 360 ° CA is analyzed. An intensity (primary intensity) SP1 and an intensity (secondary intensity) SP2 of a secondary frequency component having a period of 180 ° CA are specified, and the secondary intensity SP2 is defined by a linear function of the primary intensity SP1. Is greater than the intake valve determination threshold (a × SP1 + b), it is determined that the intake valve 8 has returned to normal. According to such a configuration, the change period (180 ° CA) of the intake pressure that appears when the intake valve 8 returns to normal is shorter than the change period (360 ° CA) when the return fails. By utilizing this, the success or failure of the return of the intake valve 8 can be accurately determined.

  In addition, instead of comparing each value of the primary intensity SP1 and the secondary intensity SP2 with the threshold value, the threshold value (intake valve determination threshold value) defined by the primary function of the primary intensity is compared with the secondary intensity value. Since it did in this way, the precision of the return | restoration determination of the intake valve 8 can be ensured favorable irrespective of the difference in the driving | running conditions of an engine, etc. That is, even if the state of the intake valve 8 (whether it has returned to normal or failed) is the same, for example, if the engine operating conditions (rotation speed, load, etc.) are different, the values of the primary strength SP1 and the secondary strength SP2 Can vary. For this reason, if the values of the primary intensity SP1 and the secondary intensity SP2 are directly compared with a specific threshold value, it is considered that the influence due to the difference in operating conditions as described above cannot be removed, and the determination accuracy is lowered. . On the other hand, in the above embodiment, the primary function (SP2 = a × SP1 + b) that defines the correlation between the primary intensity SP1 and the secondary intensity SP2 is used as a threshold value. And the success or failure of the return of the intake valve 8 can be determined with higher accuracy.

  In the above embodiment, in the graph of the spectrum analysis shown in FIG. 12, the plot region C obtained when the intake valve 8 of the deactivated cylinder fails to return, and obtained at least when the intake valve 8 returns normally. A straight line P (SP2 = a × SP1 + b) used as an intake valve determination threshold is set between the plot areas A and B. As shown in FIG. 16, for example, as a straight line P ′ (SP2 = c × SP1 + d), The intake valve determination threshold value may be set so that only the exhaust valve 9 fails to return and the intake valve 8 passes through the inside of the plot region B obtained when it returns to normal. In this way, for example, when data such as the point X in the region B is obtained, the secondary strength SP2 is equal to or lower than the intake valve determination threshold value even though the intake valve 8 originally returns to normal. When the relationship of (SP2 <c × SP1 + d) is satisfied, it is determined that the intake valve 8 has failed to return, and resumption of fuel injection or the like is prohibited. However, since the region B is a plot region obtained when the exhaust valve 9 fails to return, there is no problem even if resumption of fuel injection or the like is prohibited. Rather, by setting the intake valve determination threshold as described above, whether the return of the exhaust valve 9 is successful is determined based on whether the intake air is blown back (intake pressure fluctuation) and determination using the spectrum analysis of the intake pressure Therefore, the possibility of missing the return failure of the exhaust valve 9 can be made closer to zero.

  Further, in the above embodiment, in order to confirm the normal return of the intake valve 8, the intake pressure detected over a period of 360 ° CA including the first intake stroke after the return command is subjected to spectrum analysis. During the 360 ° CA detection period, engine operating conditions may change significantly. When such changes in operating conditions occur, the intake pressure changes due to the influence, which may affect the results of spectrum analysis. Therefore, in order to further improve the accuracy of the return determination of the intake valve 8, the change tendency of the intake pressure caused by the change in the operating condition as described above is captured, and a value obtained by removing the change tendency from the actually detected intake pressure is obtained. Spectral analysis is desirable. Here, as the change tendency of the intake pressure, for example, a value obtained by linearly approximating a plurality of detected values of the intake pressure detected by the intake pressure sensor SN3 by the least square method can be adopted.

  Moreover, although the said embodiment demonstrated the example which applied the control apparatus of this invention to the 4-cylinder gasoline engine, the form of the engine which can apply the control apparatus of this invention is not restricted to this. For example, a multi-cylinder engine other than four cylinders such as 6 cylinders or 8 cylinders may be targeted, and another type of internal combustion engine such as a diesel engine, an ethanol fuel engine, or an LPG engine may be targeted.

  Furthermore, the number of idle cylinders during reduced-cylinder operation may be changed according to engine operating conditions. For example, in the case of a 6-cylinder engine, it is conceivable to switch between a reduced-cylinder operation in which 3 cylinders are deactivated and a reduced-cylinder operation in which 2 cylinders are deactivated according to the operating state of the engine. When switching from one of these two types of reduced-cylinder operation to all-cylinder operation in which all six cylinders operate, it is also possible to determine whether or not the intake valve of the deactivated cylinder has returned to normal. Spectral analysis can be used.

  For example, in a 6-cylinder engine as described above, the frequency component with 120 ° CA as one cycle is strong during all-cylinder operation with all six cylinders operating, and 240 ° CA is with one cycle during reduced-cylinder operation with three cylinders deactivated. And the frequency component with 360 ° CA as one cycle becomes strong during the reduced-cylinder operation in which the two cylinders are deactivated (in this case, the so-called two-explosion / one-burn combustion mode). Therefore, the intensity of the frequency component having 360 ° CA as one cycle is represented as a primary function, and the frequency component having 240 ° CA or 120 ° CA as one cycle is represented as a high-order strength, which is expressed by a linear function of the primary intensity. If the intake valve determination threshold is compared with the high-order intensity, it can be determined whether or not the intake valve has returned to normal based on the comparison.

DESCRIPTION OF SYMBOLS 1 Engine main body 2A-2D Cylinder 8 Intake valve 9 Exhaust valve 12 Injector 25a Valve stop mechanism 52 Valve control part 53 Intake valve return determination part 54 Exhaust valve return determination part 55 Combustion control part

Claims (5)

A plurality of cylinders, a plurality of intake valves provided at a rate of one or more per cylinder to control the introduction of intake air into each cylinder, and one per cylinder to control gas discharge from each cylinder A plurality of exhaust valves provided at a ratio of one or more and a plurality of injectors for supplying fuel to each cylinder, all-cylinder operation for supplying fuel to all cylinders from the injector and burning, An apparatus for controlling an engine that can be switched between a reduced-cylinder operation for stopping the supply of fuel to the deactivated cylinder in order to make the cylinder a deactivated cylinder,
A valve stop mechanism that maintain the closed state stops the opening and closing operation of the intake and exhaust valves in the stopped cylinders during the reduced-cylinder operation,
A valve control unit that outputs a return command to the valve stop mechanism and restarts the opening and closing operations of the intake valve and the exhaust valve when there is a request for switching from the reduced cylinder operation to the all cylinder operation;
After the return command, based on the result of spectrum analysis of the intake pressure detected over a predetermined period including the intake stroke of the deactivated cylinder, it is determined whether or not the intake valve of the deactivated cylinder has returned to a normally open state. An intake valve return determination unit for determining;
After the return command, it is determined whether or not the exhaust valve of the idle cylinder has returned to a normal state based on the pressure fluctuation of the intake air before and after the timing when the intake valve of the idle cylinder starts to open. An exhaust valve return determination unit that
When the intake valve return determination unit confirms normal return of the intake valve and the exhaust valve return determination unit confirms normal return of the exhaust valve, the injector is inactivated to resume combustion in the deactivated cylinder. An engine control device comprising: a combustion control unit that resumes fuel supply to the cylinder. The engine control device according to claim 1,
The engine control device according to claim 1, wherein the exhaust valve return determination unit determines that the exhaust valve of the deactivated cylinder has returned to normal when the pressure fluctuation of the intake air is smaller than a predetermined threshold value. The engine control device according to claim 2,
When the opening / closing operation of the exhaust valve and the intake valve is resumed in this order by the return command from the valve control unit, the exhaust valve return determination unit extends before and after the timing when the intake valve starts to open for the first time after the return command. Even if the pressure fluctuation of the intake air is specified and the pressure fluctuation is smaller than the threshold value, it is not determined that the exhaust valve has returned to normal at that time, and the intake valve starts to open for the second time after the return command. An engine control device characterized by identifying pressure fluctuations of intake air before and after the timing, and determining that the exhaust valve has returned to normal if the pressure fluctuations are smaller than the threshold value. The engine control device according to claim 2 or 3,
When the opening / closing operation of the intake valve and the exhaust valve is resumed in the order of the return command from the valve control unit, the exhaust valve return determination unit extends before and after the timing when the intake valve starts to open for the second time after the return command. A control apparatus for an engine characterized by identifying pressure fluctuation of intake air and determining that the exhaust valve has returned to normal if the pressure fluctuation is smaller than the threshold value. In the engine control device according to any one of claims 1 to 4,
The intake valve return determination unit is configured to analyze a first-order intensity that is the intensity of a first-order frequency component having a predetermined crank angle as a period and a higher-order frequency component having a shorter period than the predetermined crank angle, by spectral analysis of the intake pressure. The higher-order intensity that is the intensity is specified, and when the higher-order intensity is greater than the intake valve determination threshold defined by the linear function of the primary intensity, it is determined that the intake valve has returned to normal. An engine control device characterized by that.

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