JPH08165949A - Fuel injection timing control device for internal combustion engine - Google Patents

Abstract

(57) [Summary] [Purpose] To accurately control the fuel injection timing so that optimum combustion can be obtained according to the operating conditions. [Structure] The intake pipe pressure value detected by the intake pipe pressure sensor (6) is subjected to a first-order difference, and the intake flow reaches the maximum flow velocity from the time when the value becomes minimum, and the steady flow starts from the time when the intake changes from negative to positive. The timing is calculated, and the difference of the second floor is calculated. The moment when the intake valve is opened is calculated from the time when the value becomes the minimum, and the operation state is detected from the values of the throttle opening sensor (7) and the crank angle sensor (8). Then, the fuel is injected at the optimum time to inject the fuel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection timing control system for an internal combustion engine.

[0002]

2. Description of the Related Art It is known to change the fuel injection timing according to the operating condition of an engine. For example, JP-A-60-15
Japanese Patent No. 0459 discloses that the variable valve timing mechanism changes the opening / closing timing of the intake valve according to the operating state, and changes the fuel injection timing in synchronization with the valve opening timing.

[0003]

However, the optimum injection timing differs depending on the operating conditions, and for example, at the time of high load where the main purpose is to improve output, it is preferable to inject fuel at the initial stage of valve opening when the intake flow velocity becomes maximum. However, at the time of high rotation, which should be noted due to the improvement of exhaust emission, it is rather preferable to inject in the middle of the valve opening period when the flow of intake air becomes a steady flow. Therefore, it is not possible to obtain optimum combustion according to the operating state simply by synchronizing with the opening timing of the intake valve. In view of the above problems, it is an object of the present invention to provide a fuel injection control device capable of accurately controlling the fuel injection timing so that optimal combustion can be obtained according to operating conditions.

[0004]

According to claim 1 of the present invention, as a means for solving the above-mentioned problems, as shown in FIG. Operating state detecting means, fuel injection optimum intake state selecting means for selecting an intake state optimal for injecting fuel with respect to the engine operating state detected by the engine operating state detecting means, and during an opening period of the intake valve. The intake state detecting means for detecting a change in the actual intake state in the intake pipe and the actual intake state detected by the intake state detecting means are used to inject the fuel selected by the fuel injection optimum intake state selecting means. There is provided a fuel injection timing control device for an internal combustion engine, which comprises fuel injection timing adjusting means for adjusting the fuel injection timing so as to inject fuel at the time when the optimum intake state is achieved. According to claim 2, as shown in FIG. 1B, the intake state detecting means further differentiates the intake pressure detected by the intake pressure detecting means and the intake pressure detecting means to calculate the intake flow velocity. There is provided a fuel injection timing control device for an internal combustion engine, characterized by comprising intake pressure differential calculation means.

[0005]

According to the first aspect of the present invention, the optimum intake state for injecting fuel with respect to the engine operating state detected by the engine operating state detecting means is selected by the fuel injection optimum intake state selecting means. The intake state detecting means detects a change in the actual intake state in the intake pipe during the opening period of the intake valve. Then, the fuel injection timing adjusting means adjusts the fuel injection timing so that the fuel injection timing matches the time when the actual intake state becomes the optimal intake state for fuel injection. In the second aspect of the present invention, the change in the intake state is detected by differentiating the intake pressure.

[0006]

Next, an embodiment of the present invention will be described. In this embodiment, since the change of the intake state is obtained from the first-order differential value and the second-order differential value of the intake pipe pressure value, its principle is shown in FIG.
Will be described with reference to. 2A shows the intake pipe pressure P detected by the intake pipe pressure detection means.
2B shows the change of 1 in FIG. 2A.
It is a curve connecting the derivative values. 2C is a curve connecting the second-order differential values of FIG. 2A.

Generally, the equation of state of gas can be expressed by PV = GRT, where P is pressure, V is volume, G is mass, T is temperature, and R is gas constant. Here, considering the volume of a minute portion of the intake air in which the intake pipe pressure detecting means is provided, the pressure fluctuation P ′ of this portion can be expressed as follows by differentiating the above equation of state. The symbol "'" represents the first derivative. P ′ = G′RT / V (1) Then, when the pressure P changes as shown in (A) of FIG.
P'is as shown in FIG.

Here, the weight flow rate of gas per unit time that is sucked into the cylinder through the intake valve is gc, and the weight amount of gas per unit time that flows into the volume of the minute portion upstream of the intake valve. When the flow rate is gp, the equation (1) becomes as follows. P ′ = RT (gp−gc) / V (2) When the intake valve 2 is closed, gc = 0, gp≈
Since it is 0, P′≈0 and the pressure fluctuation is small. At the moment when the intake valve 2 opens, gc has a positive value, while
Since gp does not immediately become the same value as gc due to the inertia of the gas in the intake pipe, it is small, so the left side of equation (2) becomes negative and the pressure drops, and the state of "a" part in (B) of FIG. Become.

Here, the timing at which the intake valve 2 opens can be strictly determined from the timing at which gc becomes positive from 0 and the differential value gc 'of gc shows a large value (positive value). Therefore, if the equation (2) is further differentiated to obtain P ″ = RT (gp′−gc ′) / V (3), the timing of the change of the second derivative of the pressure P, specifically, the negative It can be accurately detected from the timing at which the extreme value of is indicated, that is, “b” in FIG.
The point indicated by is the intake valve opening timing. The symbol "" represents the second derivative.

Therefore, the intake valve opens at point b in FIG. 2 (C), and the intake flow velocity becomes maximum at point a in FIG. 2 (B). This steady flow condition is
In the above equation (2), “gp” and “gc” become equal, there is no pressure fluctuation, and P ′ becomes 0 (zero).
Therefore, in FIG. 2B, it can be said that the point “c” at which the curve of the first-order differential value first intersects with the horizontal axis 0 (zero) is the moment when the steady flow state is reached. This timing can be obtained by obtaining a point where the first-order differential value of the pressure becomes a positive value for the first time after the intake flow velocity becomes maximum, that is, after the point a in FIG.

As described above, the intake valve opening timing can be obtained from the second derivative of the intake pipe pressure, and the maximum flow velocity timing and the steady flow timing can be obtained from the first derivative. Since the above differentiation is performed by a difference calculation in an actual computer, it is expressed as a difference in the following description of the embodiments.

FIG. 3 is a diagram showing the configuration of an embodiment of the present invention. Reference numeral 1 is an engine body, 2 is an intake valve, 3 is an exhaust valve, 4 is an intake pipe, and 5 is a fuel injection valve. 6 is an intake pipe pressure sensor, 7 is a throttle opening sensor, and 8 is a crank angle sensor. The ECC 100 includes an input interface 101, an A / D converter 102, a CP
It is composed of a U 103, a RAM 104, a ROM 105, an output interface 106 and the like.

Since the intake pipe pressure sensor 6 detects the pressure in the intake pipe, it serves as intake pressure detecting means in the present invention.
The output is input through the input interface 101 and the A / D converter 102, and is stored in the RAM 104 as time-series data synchronized with the signal of the crank angle sensor 8. Throttle opening sensor 7 and crank angle sensor 8
Since the throttle opening and the engine speed, which are indicators of the driving state, are detected from the above, these two sensors serve as a driving state detecting means.

The CPU 103 selects the optimum intake state for fuel injection according to the operating conditions detected by the throttle opening sensor 7 and the crank angle sensor 8 which are the operating state detecting means. Of the intake pipe pressure stored in the RAM 104, the first-stage difference value and the second-stage difference value are further calculated to detect the intake state, which serves as an intake pressure differential calculating means. It searches the time when the intake state becomes the optimum intake state for injecting fuel according to the operating condition, and thus serves as a fuel injection optimum intake state timing search means. The fuel injection timing adjusting means also serves as the fuel injection timing adjusting means.

Next, the operation of the ECC 100 will be described with reference to the flowchart. Steps 101 to 107 show the operation of recording the intake pipe pressure signal as time series data in the RAM during one engine cycle, and at the sampling interval ts between the reference pulses generated once per engine cycle. It is captured. here,
The recorded pressure signal values are P (1) to P (n).

Steps 108 to 111 show the operation for obtaining the first-order difference value of the pressure signal value. Based on the pressure signal value recorded in the RAM as described above, DP (i ) = P (i + 1) -P (i)
Seeking by. Therefore, P (1) to P (n)
To DP (1) = P (2) −P (1)
(N-1) = P (n) -P (n-1) can be obtained.

Steps 112 to 115 show the operation of obtaining the second difference value by subtracting the first difference value of the pressure signal value obtained as described above as follows. DDP (i) = DP (i + 1) -DP (i) = {P (i + 2) -P (i + 1)}-{P (i + 1) -P (i)} Therefore, in P (1) to P (n) On the other hand, DDP
(1) = DP (2) −DP (1) to DDP (n−
2) = DP (n) -DP (n-1) is obtained.

In step 116, the planned valve opening time AVO stored in the ROM in advance and which maximizes the engine performance.
p is read as the crank angle (° CA) from the reference pulse, and in step 117, the engine speed N at that time is read.
Read E.

In step 118, the planned valve opening timing AVOp (° CA) set in step 116 is set to 6 × NE ×
It is divided by ts to obtain the number of samplings from the reference angle at which the planned valve opening timing is. Where 6 × NE × ts
The reason for dividing by is as follows. The unit of rotation speed NE is r
Since it is pm, that is, the number of revolutions per minute, first, the number of revolutions per second is obtained by NE / 60, and this is multiplied by 360 °, that is, 360 × NE / 60
= 6 × NE, the rotation angle per second (° C
A) is obtained. Therefore, 6 × NE × ts, which is obtained by multiplying this by the sampling time ts whose unit is expressed in seconds, is
The sampling interval will be indicated by the rotation angle (° CA). Therefore, the value iVO obtained by dividing the planned valve opening timing AVOp indicated by the crank angle (° CA) by 6 × NE × ts
p indicates the planned valve opening timing by the sampling number from the reference pulse position.

Next, steps 119 to 124
Is a step for obtaining an actual valve opening moment, and is for obtaining a point where the second-order differential value indicated by “b” in FIG. In a certain range before and after the planned valve opening timing iVOp indicated by the sampling number from the reference pulse position, a sampling number having the smallest second-order difference value of the pressure is searched for, and the point of the sampling number is searched. This is the actual valve opening timing. That is, step 1
IVOp-kb from the reference pulse position shown in FIG.
Starting from the second sampling point, the second-order difference value at that time is set to the minimum value of the initials, and the second-order difference value at the next sampling point is compared in magnitude to determine the smaller one as the new minimum value. The work is repeated until the iVOp + kbth sampling point shown in step 123, and as shown in step 124, the sampling point imi showing the minimum value from the iVOp-kbth sampling point to the iVOp + kbth sampling point.
Let n _b be the sampling number iVOa that is the actual valve opening timing. In the above, kb is an integer selected empirically. As described above, the calculation time is shortened by limiting the search range to a certain range before and after the planned valve opening timing.

Steps 125 to 132 are steps for determining the time when the suction flow velocity becomes maximum. The suction flow velocity is maximized at the point indicated by “a” in FIG. 2B, and is the point at which the first-order differential value of the intake pipe pressure is minimized. Similar to finding the point where the second-order difference value is the minimum, a sampling number that minimizes the first-order difference value of the pressure is searched for in a certain range, and the point of the sampling number is set as the maximum flow velocity period. Is. Here, since the timing at which the intake flow velocity becomes maximum is always after the moment when the intake valve is opened, the starting point of the search is the iVO at which the above second-order difference value is the minimum.
Let iVOp + 1 which is the next point of p. Then, the operation of setting the first-order difference value at that time as the initial minimum value and sequentially comparing the magnitude with the second-order difference value at the next sampling point and setting the smaller one as the new minimum value is shown in step 129. Repeat until iVOp + kath sampling point, and as shown in step 131,
The sampling points imin _a and the sampling number count iWX having the maximum flow rate time showing the minimum value therebetween. In the above, ka is an empirically selected integer.
Then, in step 131, conversely to that performed in step 118, the sampling number iWX of the maximum flow velocity time obtained in step 131 is multiplied by 6 × NE × ts to obtain the crank angle (° CA). The actual maximum flow velocity timing AWX indicated by is calculated.

Steps 132 to 134 are the sampling number iWS at the timing when the intake air becomes a steady flow.
(B) in FIG. 2 is to obtain a constant first-order differential value, and the sampling number iW is the maximum flow velocity period.
Starting from iWX + 1, which is the next sampling number of X, the point where the first-order difference value DP (i) becomes positive for the first time thereafter is taken as the sampling number iWS at the timing when the intake air becomes a steady flow. And step 1
At 35, iWS is converted into a crank angle (° CA) value AWS, and the processing is ended.

Next, FIG. 9 is a map showing the optimum fuel injection timing according to the operating condition. First, since a large amount of fuel is sent in during high load operation, it is indicated that fuel is injected when the intake air has the maximum flow velocity in order to sufficiently mix this with air to increase combustion efficiency and to fully demonstrate engine performance. Has been done. On the other hand, since the amount of intake air is small during low-medium-speed, low-speed operation, it is necessary to inject fuel at the moment when the intake valve opens when the pressure change is maximum so that fuel can be prevented from sticking to the intake port or intake valve. It is shown. Further, it is shown that fuel is injected during a steady flow in which intake air is stable in order to stabilize exhaust gas purification performance during high-speed operation at low and medium loads.

FIG. 10 is based on the map shown in FIG.
6 is a flowchart for selecting whether to perform fuel injection timing at the valve opening instant, when intake air has a maximum flow velocity, or when intake air has a steady flow according to the operating state. In step 201, the engine speed NE and the accelerator opening ACC are read, and in step 202, the accelerator opening ACC read in step 201 is the predetermined judgment value AC on the map of FIG.
If it is C1 or more, it is determined to be a high load state and step 20 is performed.
In step 3, a command is issued to set the fuel injection start timing to AWX that maximizes the flow velocity, and if it is the following, it is determined to be in a medium to low load state and the routine proceeds to step 204, where the rotational speed is previously set on the map of FIG. It is determined whether the rotation speed is higher or lower than the predetermined determination value NE1, and if the rotation speed is high, the process proceeds to step 205 to issue a command to set the fuel injection start timing to AWS that maximizes the flow velocity, and if the rotation speed is low, step 206. Then, a command is issued to set the fuel injection start timing to the valve opening instant AVO, and the process ends.

Next, as shown in FIG. 11, since the command determined as described above is indicated by the crank angle (° CA) from the reference pulse signal generation point, this is exhausted B
It is a flowchart which sets to the counter which makes DC a count start point. In step 301, the crank angle ACA between the exhaust BDC and the reference pulse signal generation point is added to the command indicated by the crank angle (° CA) from the reference pulse signal generation point, and the value of each command is added to the exhaust BDC. Crank angle (° CA) from ASOi. In step 302, ASOi is divided by 6 × NE to obtain the time value TSO.
i is converted to i, and in step 303, TSOi is set in the injection valve energization counter, and the process ends.

As described above, according to the present embodiment, the intake pipe pressure is subjected to the first-order difference, and the time when the value becomes minimum and the time when the intake air reaches the maximum flow velocity are obtained, and thereafter, the value is changed from the negative value to the positive value. From the point of change, the time when the steady flow is obtained can be obtained, and the second-order difference can be obtained to accurately capture the opening moment of the intake valve from the time when the value becomes the minimum. Depending on the operating state at that time, the above It is possible to inject the fuel at the optimum timing of the three timings.

[0027]

According to the first aspect of the present invention, the fuel injection timing can be accurately controlled so that optimum combustion can be obtained according to the operating condition. According to the second aspect, the fuel injection timing can be accurately controlled so that the optimum combustion can be obtained according to the operating state by differentiating the intake pressure without providing other detecting means. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing a concept of control of each claim of the present invention, (A) is a block diagram showing a concept of control of claim 1 of the present invention, and (B) is a claim of the present invention. It is a block diagram which shows the concept of 2 control.

FIG. 2 is a diagram for explaining characteristics of intake pipe pressure,
(A) is time-series data of intake pipe pressure. (B) is a first-order derivative of (A). (C) is 2 (A)
It is a differential.

FIG. 3 is an overall schematic view of an embodiment of the present invention.

4 is a flow chart for explaining the operation of the control circuit of the embodiment of FIG.

5 is a flow chart for explaining the operation of the control circuit of the embodiment of FIG.

6 is a flow chart for explaining the operation of the control circuit of the embodiment of FIG.

7 is a flowchart for explaining the operation of the control circuit of the embodiment of FIG.

8 is a flow chart for explaining the operation of the control circuit of the embodiment of FIG.

9 is a flowchart for explaining the operation of the control circuit of the embodiment of FIG.

FIG. 10 is a map showing an optimum intake state for injecting fuel with respect to an operating state.

11 is a flow chart for explaining the operation of the control circuit of the embodiment of FIG.

[Explanation of symbols]

 1 ... Engine 2 ... Intake valve 3 ... Exhaust valve 4 ... Intake pipe 5 ... Fuel injection valve 6 ... Intake pipe pressure sensor 7 ... Throttle opening sensor 8 ... Crank angle sensor 100 ... Engine control computer (ECC) 101 ... Input interface 102 ... A / D converter 103 ... CPU 104 ... RAM 105 ... ROM 106 ... Output interface

[Procedure amendment]

[Submission date] March 8, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a block diagram showing a concept of control of each claim of the present invention, (A) is a block diagram showing a concept of control of claim 1 of the present invention, and (B) is a claim of the present invention. It is a block diagram which shows the concept of 2 control.

FIG. 2 is a diagram illustrating characteristics of intake pipe pressure.

FIG. 3 is an overall schematic view of an embodiment of the present invention.

4 is a flow chart for explaining the operation of the control circuit of the embodiment of FIG.

5 is a flow chart for explaining the operation of the control circuit of the embodiment of FIG.

6 is a flow chart for explaining the operation of the control circuit of the embodiment of FIG.

7 is a flowchart for explaining the operation of the control circuit of the embodiment of FIG.

8 is a flow chart for explaining the operation of the control circuit of the embodiment of FIG.

9 is a flowchart for explaining the operation of the control circuit of the embodiment of FIG.

FIG. 10 is a map showing an optimum intake state for injecting fuel with respect to an operating state.

11 is a flow chart for explaining the operation of the control circuit of the embodiment of FIG.

[Explanation of Codes] 1 ... Engine 2 ... Intake valve 3 ... Exhaust valve 4 ... Intake pipe 5 ... Fuel injection valve 6 ... Intake pipe pressure sensor 7 ... Throttle opening sensor 8 ... Crank angle sensor 100 ... Engine control computer (ECC) 101 ... Input interface 102 ... A / D converter 103 ... CPU 104 ... RAM 105 ... ROM 106 ... Output interface

Claims (2)

[Claims] 1. A fuel injection timing control device for an internal combustion engine, comprising: engine operating state detecting means for detecting an engine operating state; and fuel injection for the engine operating state detected by the engine operating state detecting means. For selecting the optimum intake state for the fuel injection, the intake state detecting means for detecting the actual intake state in the intake pipe during the opening period of the intake valve, and the actual state detected by the intake state detecting means. Of the fuel injection optimum intake state timing searching means for searching a time when the intake state of the fuel injection becomes the optimum intake state selected by the fuel injection optimum intake state selecting means, and fuel at the time searched by the fuel injection optimum intake state timing selecting means. And a fuel injection timing adjusting means for injecting the fuel. 2. The fuel injection timing control device according to claim 1, wherein the intake state detecting means includes an intake flow rate differential calculating means for calculating an intake flow rate by differentiating the intake pressure.