JP6094599B2 - Control device and control method for internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine that directly injects fuel into a combustion chamber and ignites a generated air-fuel mixture with a spark plug, and more particularly to a control device and control method for an internal combustion engine having a variable compression ratio mechanism.

  2. Description of the Related Art A cylinder direct injection type spark ignition internal combustion engine in which a fuel injection valve is disposed facing a combustion chamber so that fuel is directly injected into the cylinder during an intake stroke or a compression stroke is known.

  Various types of variable compression ratio mechanisms for changing the mechanical compression ratio of an internal combustion engine have been known. For example, the applicants have proposed a number of variable compression ratio mechanisms in which the piston top dead center position is displaced up and down by changing the link geometry of a multi-link piston crank mechanism. Patent Document 1 describes a variable compression ratio mechanism that similarly changes the mechanical compression ratio by displacing the cylinder position up and down with respect to the center position of the crankshaft.

  Patent Document 1 discloses control at the time of cold start in an internal combustion engine equipped with a variable compression ratio mechanism, and sets a high mechanical compression ratio by the variable compression ratio mechanism during warm-up operation of the internal combustion engine. In addition, the variable valve mechanism is controlled so that the opening timing of the exhaust valve is advanced more than after warming up and away from the exhaust bottom dead center. As a result, the exhaust temperature is raised while stabilizing the combustion during cold operation, and the catalyst is warmed up early.

  In an in-cylinder direct injection internal combustion engine in which the nozzle tip of the fuel injection valve is exposed in the combustion chamber, intergranular corrosion at the nozzle tip is easily promoted by condensed water at the time of cold start. That is, when starting from a relatively low temperature state and leaving it as idle operation as it is, moisture generated by combustion is condensed at the tip of the nozzle exposed in the combustion chamber, and the condensed water and sulfur contained in the fuel Since sulfuric acid is generated from the components, the nozzle tip corrodes. If the temperature of the nozzle tip of the fuel injection valve is high, even if condensed water adheres, it evaporates immediately, so that corrosion does not occur. Therefore, the risk of intergranular corrosion at the nozzle tip increases when the nozzle tip is in a certain temperature range.

  Although the technology of Patent Document 1 can warm up the catalyst early by raising the exhaust gas temperature, the temperature rise action of the nozzle tip exposed in the combustion chamber cannot be obtained, and the above-described intergranular corrosion of the nozzle tip is not achieved. Does not contribute to suppression.

JP 2009-74513 A

The present invention is a control device for an internal combustion engine that includes a variable compression ratio mechanism that changes a mechanical compression ratio and a fuel injection valve that directly injects fuel into a combustion chamber,
First determination means for determining whether the engine is warm-up restart or cold-start when starting;
A second determination means for determining whether or not the cooling water temperature at the start is a cryogenic start lower than a predetermined threshold set below the freezing point,
At cryogenic startup, until the elapse of a predetermined time during cryogenic starting from immediately after the start of the internal combustion engine, it is lower than the basic target compression ratio the target compression ratio causes is advanced than the basic ignition timing of the ignition timing,
During a cold start and a normal low temperature start that is not a very low temperature, the target compression ratio is reduced below the basic target compression ratio and the ignition timing is set between the start of the internal combustion engine and the predetermined time at the normal low temperature start. Perform catalyst warm-up operation that is retarded from the basic ignition timing.

  Since combustion starts early with the advance of the ignition timing, the time during which the nozzle tip of the fuel injection valve is exposed to the combustion gas becomes longer. Accordingly, the temperature at the tip of the nozzle rises early, and the temperature range in which intergranular corrosion becomes a problem can be removed early. Here, when the ignition timing is advanced, abnormal combustion such as knocking or pre-ignition is induced. However, in the present invention, the mechanical compression ratio is lowered by the variable compression ratio mechanism at the same time, so abnormal combustion is prevented. It is possible to advance the ignition timing without inviting it, and the nozzle tip temperature can be increased by such a large ignition timing advance.

  According to the present invention, the temperature of the nozzle tip of the fuel injection valve can be effectively increased at the time of cold start of the internal combustion engine, and the progress of intergranular corrosion due to moisture condensation at the nozzle tip can be suppressed. .

BRIEF DESCRIPTION OF THE DRAWINGS Configuration explanatory drawing which shows the system configuration | structure of the control apparatus of the internal combustion engine which concerns on this invention. The flowchart which shows the flow of the starting control in this Example. The characteristic view which shows the change of the combustion pressure accompanying ignition timing advance. The time chart which shows the temperature change of the nozzle tip after a cryogenic start. The time chart which shows the temperature change of the nozzle tip after a normal low temperature start.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows the system configuration of an automotive internal combustion engine 1 to which the present invention is applied. The internal combustion engine 1 is a four-stroke cycle direct injection type spark ignition internal combustion engine having a variable compression ratio mechanism 2 using, for example, a multi-link type piston crank mechanism, and is provided on the ceiling wall surface of the combustion chamber 3. A pair of intake valves 4 and a pair of exhaust valves 5 are arranged, and an ignition plug 6 is arranged in the center surrounded by the intake valves 4 and the exhaust valves 5.

  A fuel injection valve 8 that directly injects fuel into the combustion chamber 3 is disposed below the intake port 7 that is opened and closed by the intake valve 4. The nozzle tip of the fuel injection valve 8 is exposed in the combustion chamber 3. An intake passage (not shown) connected to the intake port 7 is provided with an electronically controlled throttle valve (not shown) whose opening degree is controlled by a control signal from the engine controller 9, and further upstream thereof. On the side, an air flow meter 10 for detecting the intake air amount is disposed.

  In addition, a catalyst device 13 made of a three-way catalyst is interposed in the exhaust passage 12 connected to the exhaust port 11, and an air-fuel ratio sensor 14 for detecting the air-fuel ratio is disposed upstream thereof.

  In addition to the air flow meter 10 and the air-fuel ratio sensor 14, the engine controller 9 includes a crank angle sensor 15 for detecting the engine speed, a water temperature sensor 16 for detecting the coolant temperature, and an accelerator pedal operated by the driver. Detection signals of sensors such as an accelerator opening sensor 17 that detects the amount of depression of the vehicle are input. Based on these detection signals, the engine controller 9 optimally controls the fuel injection amount and injection timing by the fuel injection valve 8, the ignition timing by the spark plug 6, the opening of a throttle valve (not shown), and the like. The cooling water temperature detected by the water temperature sensor 16 correlates with the temperature at the nozzle tip of the fuel injection valve 8, particularly the temperature at the nozzle tip at the time of engine start.

  On the other hand, the variable compression ratio mechanism 2 uses a known multi-link type piston crank mechanism described in Japanese Patent Application Laid-Open No. 2004-116434 and is rotatably supported by the crank pin 21a of the crankshaft 21. A lower link 22, an upper link 25 that connects the upper pin 23 at one end of the lower link 22 and the piston pin 24 a of the piston 24, and a control having one end connected to a control pin 26 at the other end of the lower link 22. The link 27 and a control shaft 28 that pivotally supports the other end of the control link 27 are mainly configured. The crankshaft 21 and the control shaft 28 are rotatably supported in a crankcase below the cylinder block 29 via a bearing structure (not shown). The control shaft 28 has an eccentric shaft portion 28a whose position changes with the rotation of the control shaft 28. Specifically, the end portion of the control link 27 is rotatably fitted to the eccentric shaft portion 28a. Match. In the variable compression ratio mechanism 2 described above, the top dead center position of the piston 24 is displaced up and down with the rotation of the control shaft 28, so that the mechanical compression ratio changes.

  As a drive mechanism for variably controlling the compression ratio of the variable compression ratio mechanism 2, an electric motor 31 having a rotation center axis parallel to the crankshaft 21 is disposed below the cylinder block 29. A reduction gear 32 is connected so as to be arranged in series in the direction. As the speed reducer 32, for example, a wave gear mechanism having a large speed reduction ratio is used, and the speed reducer output shaft 32 a is positioned coaxially with the output shaft (not shown) of the electric motor 31. Accordingly, the speed reducer output shaft 32a and the control shaft 28 are positioned in parallel with each other, and the first arm 33 and the control shaft 28 fixed to the speed reducer output shaft 32a are connected to each other so that both of them rotate in conjunction with each other. The fixed second arm 34 is connected to each other by an intermediate link 35.

  That is, when the electric motor 31 rotates, the angle of the speed reducer output shaft 32a changes in a form greatly decelerated by the speed reducer 32. The rotation of the speed reducer output shaft 32a is transmitted from the first arm 33 to the second arm 34 via the intermediate link 35, and the control shaft 28 rotates. Thereby, as mentioned above, the mechanical compression ratio of the internal combustion engine 1 changes. In the illustrated example, the first arm 33 and the second arm 34 extend in the same direction. Therefore, for example, when the speed reducer output shaft 32a rotates in the clockwise direction, the control shaft 28 also rotates in the clockwise direction. Although it is related, the link mechanism can also be configured to rotate in the opposite direction.

  The target compression ratio of the variable compression ratio mechanism 2 is set in the engine controller 9 based on engine operating conditions (for example, required load and engine speed), and the electric motor 31 is driven so as to realize this target compression ratio. Be controlled.

  FIG. 2 is a flowchart showing a start-up control flow executed by the engine controller 9 when the internal combustion engine 1 is started. In step 1, the temperature of the cooling water at the start is compared with a predetermined threshold value TwH, and it is determined whether it is a warm-up restart or a cold-start. If it is a warm-up restart, the process of warming the nozzle tip of the fuel injection valve 8 is not necessary, so the routine proceeds to step 4 where normal ignition timing control and compression ratio control are performed.

  If it is cold start, the process proceeds to step 2, and similarly, the coolant temperature at the start is compared with a predetermined threshold value TwL to determine whether it is a cryogenic start or a normal low temperature start. The threshold value TwL in step 2 is set at a lower temperature than the threshold value TwH in step 1, and is, for example, an appropriate temperature below the freezing point.

  If it is determined in step 2 that the coolant temperature at the start is a cryogenic start lower than the threshold value TwL, the process proceeds to step 3 where the ignition timing is advanced from the basic ignition timing and variable compression is performed. The target compression ratio of the ratio mechanism 2 is set to a compression ratio lower than the basic target compression ratio at that time. The processing of step 3, that is, the advance of the ignition timing and the reduction of the compression ratio, are terminated on the condition that a predetermined time has elapsed, and the routine proceeds to the normal control of step 4 when the predetermined time has elapsed. The predetermined time is variably set based on the cooling water temperature at the time of starting, and is set to a longer time as the cooling water temperature is lower.

  On the other hand, when the cooling water temperature is equal to or higher than the threshold value TwL in step 2, it is determined that the engine is normally started at a low temperature, and the process proceeds to step 5 to perform an operation suitable for early catalyst warm-up in the catalyst device 13 first. In the catalyst warm-up operation, for example, the target compression ratio is lowered from the basic target compression ratio, and at the same time, the ignition timing is retarded from the basic ignition timing. As a result, the exhaust temperature rises, and the catalyst quickly approaches the activation temperature. The catalyst warm-up operation is terminated on the condition that a predetermined time has elapsed, and the process proceeds to step 6 when the predetermined time has elapsed. The predetermined time is variably set based on the cooling water temperature at the time of starting, and is set to a longer time as the cooling water temperature is lower.

  In Step 6, as in Step 3, the ignition timing is advanced from the basic ignition timing at that time, and the target compression ratio of the variable compression ratio mechanism 2 is set to a compression ratio lower than the basic target compression ratio at that time. To do. The processing of step 6, that is, the advance of the ignition timing and the reduction of the compression ratio are terminated on the condition that a predetermined time has elapsed, and the routine proceeds to the normal control of step 4 when the predetermined time has elapsed. The predetermined time is variably set on the basis of the cooling water temperature at the time of start-up or the cooling water temperature at the time of shifting to Step 6, and is basically set to a longer time as these cooling water temperatures are lower.

  By performing the advance of the ignition timing in step 3 or step 6 described above, the nozzle tip of the fuel injection valve 8 in the cold state is more actively heated. FIG. 3 shows a change in the in-cylinder pressure Pi accompanying combustion in a case where the ignition timing is late (t1) and a case where the ignition timing is early (t2). As shown in the figure, combustion starts with ignition. For example, if the opening timing of the exhaust valve is the same as in t3, the nozzle tip of the fuel injection valve 8 is more advanced when the ignition timing is advanced. The time of exposure to the high-temperature combustion gas becomes longer, and the temperature of the nozzle tip rises early. At this time, if the ignition timing is advanced as described above, abnormal combustion such as knocking or pre-ignition is induced. However, in the present invention, the mechanical compression ratio is simultaneously reduced by the variable compression ratio mechanism 2. Therefore, a large ignition timing advance is possible without causing abnormal combustion, and the nozzle tip temperature can be increased by a large ignition timing advance.

  FIG. 4 shows a change in the temperature of the nozzle tip of the fuel injection valve 8 when the internal combustion engine 1 is started at an extremely low temperature, for example, −30 ° C., and left in an idle operation. Here, the risk of intergranular corrosion described above becomes very high when the temperature at the nozzle tip is between a certain upper limit temperature T1 and a certain lower limit temperature T2. For example, the upper limit temperature T1 is a temperature slightly lower than 100 ° C. which is the boiling point of water (for example, 70 ° C.), and the lower limit temperature T2 is a temperature slightly higher than 0 ° C. which is the freezing point of water (for example, 30 ° C.). is there. The characteristic shown as a comparative example in the figure is a characteristic when the idling operation is continued with the basic ignition timing and the basic target compression ratio after starting, and the temperature rise at the nozzle tip is relatively slow as shown in the figure. It stays relatively long in the temperature range (T1 to T2) where the risk of intergranular corrosion is high. In an extreme case, if the ambient atmosphere temperature is extremely low, the upper limit temperature T1 may not be exceeded in idling operation. Therefore, it is not preferable in terms of suppressing intergranular corrosion. On the other hand, the characteristic shown as an example is a characteristic when the advance of the ignition timing and the compression ratio are reduced immediately after the start at the cryogenic temperature by the process of step 3 described above. Therefore, the temperature range (T1 to T2) having a high risk of intergranular corrosion is passed in a relatively short time. Therefore, intergranular corrosion is suppressed. The duration of Step 3 described above is set according to the cooling water temperature so that the process proceeds from Step 3 to Step 4 when the temperature of the nozzle tip reaches the upper limit temperature T1.

  FIG. 5 is a time chart for normal low temperature starting, that is, when the coolant temperature at the time of starting is lower than the threshold value TwH in step 1 and above the threshold value TwL in step 2, for example, the internal combustion engine 1 is started at 10 ° C. Thereafter, the temperature change at the nozzle tip of the fuel injection valve 8 when the engine is left idle is shown. In such a normal low temperature start, the upper limit temperature T1 is reached in a relatively short time as compared with the above-mentioned cryogenic start, and therefore the risk of intergranular corrosion is relatively low. Therefore, immediately after startup, for example, the ignition timing is retarded to raise the exhaust gas temperature, and the catalyst is warmed up early. The characteristic shown as a comparative example in the figure is a characteristic when the operation is continued with the basic ignition timing and the basic target compression ratio after the catalyst warm-up is completed. As shown in the figure, when the catalyst warm-up is completed, the temperature at the nozzle tip is in the temperature range (T1 to T2) where the risk of intergranular corrosion is high, and it takes some time to exceed the upper limit temperature T1. On the other hand, the characteristic shown as an example is the characteristic when the advance of the ignition timing and the compression ratio are reduced by the process of step 6 described above after the catalyst warm-up is completed. Since the rate of temperature increase is high, the temperature range (T1 to T2) having a high risk of intergranular corrosion is passed in a relatively short time. Therefore, intergranular corrosion is further suppressed. The duration of step 6 described above is set according to the cooling water temperature so that the process proceeds from step 6 to step 4 when the temperature at the nozzle tip reaches the upper limit temperature T1.

  As mentioned above, although one Example of this invention was described, this invention is not limited to the said Example, A various change is possible. For example, in the above embodiment, the coolant temperature is detected as a temperature that correlates with the temperature of the nozzle tip of the fuel injection valve 8, but the nozzle tip such as the outside air temperature, intake air temperature, lubricating oil temperature, combustion chamber temperature, etc. It is also possible to use other temperature parameters that correlate with the temperature of In the above embodiment, the variable compression ratio mechanism 2 including a multi-link type piston crank mechanism is used. However, the present invention can be similarly applied to any type of variable compression ratio mechanism.

Claims (4)

A control device for an internal combustion engine comprising a variable compression ratio mechanism for changing a mechanical compression ratio and a fuel injection valve for directly injecting fuel into a combustion chamber,
First determination means for determining whether the engine is warm-up restart or cold-start when starting;
A second determination means for determining whether or not the cooling water temperature at the start is a cryogenic start lower than a predetermined threshold set below the freezing point,
At cryogenic startup, until the elapse of a predetermined time during cryogenic starting from immediately after the start of the internal combustion engine, it is lower than the basic target compression ratio the target compression ratio causes is advanced than the basic ignition timing of the ignition timing,
During a cold start and a normal low temperature start that is not a very low temperature, the target compression ratio is reduced below the basic target compression ratio and the ignition timing is set between the start of the internal combustion engine and the predetermined time at the normal low temperature start. A control device for an internal combustion engine that performs a catalyst warm-up operation delayed from a basic ignition timing.   At the time of the normal low temperature start, after completion of catalyst warm-up by the catalyst warm-up operation, the ignition timing is advanced from the basic ignition timing, and the operation is shifted to an operation in which the target compression ratio is lower than the basic target compression ratio. The control apparatus for an internal combustion engine according to claim 1.   The control apparatus for an internal combustion engine according to claim 1 or 2, wherein the target compression ratio when the compression ratio is lowered is set to a compression ratio that can avoid abnormal combustion due to the advance of the ignition timing. In an internal combustion engine that includes a variable compression ratio mechanism that changes a mechanical compression ratio and a fuel injection valve that directly injects fuel into a combustion chamber,
Determine whether it is warm-up restart or cold-start at the start,
It is determined whether or not the cooling water temperature at the start is a cryogenic start lower than a predetermined threshold set below the freezing point,
At cryogenic startup, until the elapse of a predetermined time during cryogenic starting from immediately after the start of the internal combustion engine, it is lower than the basic target compression ratio the target compression ratio causes is advanced than the basic ignition timing of the ignition timing,
During a cold start and a normal low temperature start that is not a very low temperature, the target compression ratio is reduced below the basic target compression ratio and the ignition timing is set between the start of the internal combustion engine and the predetermined time at the normal low temperature start. A control method for an internal combustion engine, in which a catalyst warm-up operation is performed with a retarded angle from a basic ignition timing.

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