JPS6325335A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve stability of combustion, by a method wherein, only when a combustion state fluctuation amount exceeds an allowable level determined according to a running state flucuation amount, a fuel injection amount is corrected according to a suction air-fuel ratio. CONSTITUTION:An in-cylinder pressure is measured by an engine combustion state fluctuation amount measuring means to determine a mean effective pressure shown in a diagram, and dispersion is computed to determine a fluctuation amount. By means of a running state fluctuation amount measuring means, a suction negative pressure right before closing of a suction valve is first measured, based on the measurement, a suction air amount is computed, and a fluctuation amount of an intake amount is determined as dispersion of an intake air amount. The allowable level of a combution state fluctuation amount responding to a running state fluctuation amount is searched from a map, and when the measurement exceeds the allowable level, a fuel injection amount is corrected according to a measured suction air-fuel ratio. This constitution enables proper grasping of combustion state fluctuation, caused by a suction air-fuel ratio, for correction.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a fuel injection control device for an internal combustion engine, and particularly to a technique for suppressing combustion fluctuations.

<Prior Art> As a conventional fuel injection control device for an internal combustion engine, there is one disclosed, for example, in Japanese Patent Application Laid-Open No. 58-27837.

This detects the operating state of the engine and controls the fuel injection amount based on this to control the air-fuel ratio supplied to the engine.It also detects combustion fluctuations in the engine and, if this is large, increases the fuel injection amount. This aims to reduce combustion fluctuations by enriching the supplied air-fuel ratio.

(Problem to be Solved by the Invention) However, in such a conventional fuel injection control device, when combustion fluctuations are large, it is determined that the supplied air-fuel ratio is not appropriate, and the supplied air-fuel ratio is made rich. Even though the supplied air-fuel ratio was appropriate,
Even if combustion fluctuations occur due to causes other than the air-fuel ratio, such as ignition timing or boost pressure regulator malfunction, the problem is that the supplied air-fuel ratio will become rich, which will actually worsen the combustion condition. was there.

In view of these conventional problems, the present invention provides a fuel injection control device for an internal combustion engine that can realize good drivability by correcting the fuel injection amount only when there is a high possibility that the cause of combustion fluctuation is the air-fuel ratio. The purpose is to provide

(Means for Solving the Problems) Therefore, as shown in FIG. 1, the present invention includes a combustion state variation amount measuring means for measuring the amount of variation in the combustion state of the engine;
An intake air-fuel ratio measuring means for measuring the intake air-fuel ratio taken into the cylinder, an operating state variation measuring means for measuring the amount of variation in the operating state of the engine, and a tolerance for determining the amount of combustion state variation with respect to the amount of operating state variation. The structure includes fuel injection amount correction means for correcting the fuel injection amount according to the measurement result of the intake air-fuel ratio when the intake air-fuel ratio exceeds the intake air-fuel ratio.

In other words, in addition to the combustion state fluctuation amount, the intake air-fuel ratio taken into the cylinder and the operating state fluctuation amount are measured, and only when the combustion state fluctuation amount exceeds the allowable level determined for the operating state fluctuation amount. , the combustion fluctuation is assumed to be caused by the intake air-fuel ratio, and the fuel injection amount is corrected according to the measurement result of the intake air-fuel ratio, thereby accurately suppressing the combustion fluctuation.

(Embodiment) An embodiment of the present invention will be described below. Fig. 2 shows the system configuration of a fuel injection control device.

In the figure, 1 is a crank angle sensor, which generates a crank angle signal at every predetermined crank angle. The engine speed can be calculated from this crank angle signal. 2 is an air flow meter that measures the engine intake air flow rate and outputs a corresponding voltage signal. A cylinder pressure sensor 3 detects the cylinder pressure (combustion pressure in the cylinder) and outputs a corresponding voltage signal via the charge amplifier 4. 5 is an intake negative pressure sensor;
Detects the intake negative pressure in the intake manifold and outputs a corresponding voltage signal.

6 is a control unit, CPU7゜ROM8
．． RAM9. It is composed of an A/D conversion converter and an 0r10 port 11. In this control unit 6, the various signals described above are A/D converted and read as necessary, and arithmetic processing is performed based on these signals to control the operation of the fuel injection valve 12 provided in the engine intake system.

Basically, the CPU 7 in the control unit 6 is
From the intake air flow rate Q measured by the air flow meter 2 and the engine speed N calculated based on the signal from the crank angle sensor 1, the basic fuel injection 1tT p = K-
Q/N (K is a constant) is calculated, this is corrected appropriately to set the final fuel injection amount, and a fuel injection pulse signal with a corresponding pulse width is output at a predetermined timing to activate the fuel injection valve 12. Drive.

During such control, the CPU in the control unit 6
7 also implements the present invention by executing each program shown in the flowcharts of FIGS. 3 to 7, calculating a corrected injection amount, and performing correction based on this.

FIG. 3 is a flowchart of a combustion state fluctuation amount measurement program that functions as a combustion state fluctuation amount measurement means. First, step 11 (marked as Sll in the figure) is performed.

(Similarly below), the output of the cylinder pressure sensor 3 is converted into voltage by the charge-up 4 at every predetermined crank angle (for example, 2'') indicated by the crank angle sensor l, and the voltage is converted into a voltage by the A/D converter 10. It is converted into a digital value and recorded in the RAM 9 as a measured value of cylinder pressure.

Next, in step 12, the indicated mean effective pressure Pi is calculated as a value related to the combustion state based on the measured value of the cylinder pressure.

The calculation method is to detect the cylinder pressure every time the equal volume of the combustion chamber changes, and calculate it according to the following equation (1).

However, Vh: Stroke volume θ: Crank angle Pθ: Cylinder pressure at each crank angle ΔVθ: Volume change rate at each crank angle or the cylinder pressure is detected at each predetermined crank angle, and the following formula (2) is used.
Calculate according to

Next, in step 13, the amount of variation in values related to the combustion state (
The variation amount V of the indicated mean effective pressure Pi, which is the combustion state variation amount), is calculated. This amount of variation V uses the variance of Pi obtained according to a program as shown in the flowchart of FIG.

Note that the combustion state parameters include the cylinder pressure maximum value P ssx and the cylinder pressure maximum crank angle θpHl instead of Pi.
! X may also be used. Or output torque.

The number of rotations or the like may also be used.

FIG. 5 is a flowchart of an intake air-fuel ratio measurement program that functions as an intake air-fuel ratio measurement means.
Then, the suction negative pressure is measured based on the signal from the suction negative pressure sensor 5 at a timing immediately before the intake pulp closes.

Next, in step 22, the amount of intake air taken into the cylinder is calculated based on this measured value.

The relationship between the suction negative pressure and the intake air amount can be determined theoretically and experimentally in advance, and can be calculated using a linear formula such as the following formula, for example. A and B are constants obtained theoretically and experimentally.

(Amount of intake air) = AX (Negative intake pressure) +B According to this method, a value close to the actual cylinder pressure is measured, so
When measuring the amount of intake air for each cylinder, the amount of intake air can be measured more accurately than with an air flow meter or the like.

Next, in step 23, the amount of fuel supplied to the cylinder is calculated. This method involves theoretically and experimentally determining the fuel supply amount from the fuel injection pulse width given to the fuel injection valve 12 from the previous intake stroke to the current intake stroke. Calculate using the following linear equation. C,D
is a constant obtained theoretically and experimentally.

(Fuel supply amount) = CX (Fuel injection pulse width) + D Next, in step 24, the cylinder intake air-fuel ratio is adjusted to step 2
From the calculation result in 2.23, calculate according to the following formula.

(Intake air-fuel ratio) = (Intake air amount) / (Fuel supply amount) 6th
The figure is a flowchart of a driving state variation measuring program that functions as a driving state fluctuation amount measuring means, and here the intake air amount is used as a value indicating the driving state. Step 31
Then, as in step 21 of FIG. 5, the suction negative pressure immediately before the intake valve closes is measured, and in step 32, the amount of intake air sucked into the cylinder is calculated as in step 22 of FIG.

Then, in step 33, the amount of variation in the amount of intake air is calculated as the amount of variation in the operating state.As an example, Pi in the program shown in FIG. 4 is replaced with the amount of intake air, and the variance of the amount of intake air is used.

As mentioned above, the amount of fluctuation in combustion state (the amount of fluctuation in indicated mean effective pressure), the intake air-fuel ratio, and the fluctuation in operating state! After measuring the amount of variation in intake air amount, a program for correcting the fuel injection amount shown in the flowchart of FIG. 7 is executed. This program functions as fuel injection amount correction means.

In step 41, an SL corresponding to the amount of variation in the operating state is searched from a map of allowable levels SL of the amount of variation in the combustion state depending on the amount of variation in the operating state.

Next, in step 42, the combustion state fluctuation amount is set to the allowable level SL.
If the amount of combustion state fluctuation is within the allowable level, this program is terminated.

If the amount of combustion state fluctuation exceeds the allowable level SL,
Proceeding to step 43, a rich/lean determination is made regarding the intake air-fuel ratio. If normal, exit this program.

If it is rich, the process advances to step 44. Here, if the current corrected injection amount is the correction amount of the R9 corrected injection amount as r, then in step 44, the next corrected injection amount is set as R-r, and this program is ended.

If lean, proceed to step 45. Here, the next corrected injection amount is set to R+r, and this program is ended.

The corrected injection amount thus determined is added to the regular injection amount and output. Incidentally, as a correction method, a correction coefficient may be calculated and the correction may be performed using the calculated correction coefficient.

Here, r is: ■Fixed value ■Value (function) related to the degree of rich/lean ■Lunch of a predetermined time in the past. Values related to the history of normal and lean judgments (
For example, the logic is such that a large correction is not made to the correction amount if the condition is normal a certain number of times in a row. ) etc.

Further, for R, a normal limiter is provided.

However, if the above measurement and correction control were performed for each cylinder, it would be possible to prevent a cylinder from malfunctioning if a particular cylinder in a multi-cylinder internal combustion engine malfunctions for some reason (for example, a malfunction of the spark plug or fuel injection valve). Better drivability can be ensured even when there are variations in intake air filling efficiency.

<Effects of the Invention> As explained above, according to the present invention, when the amount of fluctuation in the combustion state is at a level that is unacceptable relative to the amount of fluctuation in the operating state, the fuel injection amount is reduced only when the intake air-fuel ratio is the cause. Since the structure is designed to compensate for this, it is possible to accurately grasp and compensate for fluctuations in the combustion state caused by the intake air-fuel ratio, ensuring an appropriate intake air-fuel ratio and achieving good drivability. is obtained.

[Brief explanation of the drawing]

Fig. 1 is a functional block diagram showing the configuration of the present invention, Fig. 2 is a system diagram showing an embodiment of the present invention, Fig. 3 is a flowchart of the combustion state fluctuation measurement program, and Fig. 4 is a
A flowchart showing the aspect of combustion state fluctuation amount calculation in step 13 in the figure, FIG. 5 is a flowchart of the intake air-fuel ratio measurement program, FIG. 6 is a flowchart of the operating state fluctuation amount measurement program, and FIG. 7 is a correction injection amount calculation. It is a flowchart of the program. ■... Crank angle sensor 2... Air flow meter 3... Cylinder pressure sensor 5... Intake negative pressure sensor 6... Control unit 12... Fuel injection valve patent applicant Nissan Motor Co., Ltd. agent Patent Attorney Fujio SasashimaFigure 1 Figure 2 Φ Figure 3 Figure 4 Figure 5 Figure 6 CI one-sided Figure 7

Claims (1)

[Claims] Combustion state variation measuring means for measuring the amount of variation in the combustion state of the engine, intake air-fuel ratio measuring means for measuring the intake air-fuel ratio taken into the cylinder, and operating state variation amount for measuring the amount of variation in the operating state of the engine. It is characterized by having a measuring means and a fuel injection amount correction means for correcting the fuel injection amount according to the measurement result of the intake air-fuel ratio when the combustion state fluctuation amount exceeds an allowable level determined for the operating state fluctuation amount. A fuel injection control device for internal combustion engines.