JPH0733795B2 - Engine ignition timing control device - Google Patents

Description

The present invention relates to an engine ignition timing control device.

(Prior Art) Feedback correction of the air-fuel ratio is a correction for always maintaining the air-fuel ratio at the theoretical air-fuel ratio in the feedback control region in order to allow the three-way catalyst to function efficiently. The air-fuel ratio is detected by an oxygen sensor, and the air-fuel ratio feedback correction coefficient α is changed to control the average air-fuel ratio to the stoichiometric air-fuel ratio (Railway Japan Co., Ltd., Automotive Engineering, January 1986 issue.
See pages 110 and 111).

However, if air-fuel ratio feedback control is performed even during idling, torque fluctuations occur due to deviation from the stoichiometric air-fuel ratio, so air-fuel ratio feedback control is stopped (clamped) during idling.

(Problems to be solved by the invention) By the way, in such a device, if there is a change in intake air temperature, a slight load change, a change in rotation, etc. due to the stop of the air-fuel ratio feedback control at the time of idling, the air-fuel ratio becomes theoretical Since it shifts from the fuel ratio to the rich side or the lean side, the conversion rate of the three-way catalyst deteriorates and the emission amount of harmful gases (NOx, CO, HC) increases.

To cope with this, the air-fuel ratio feedback correction amount α
There is a method in which an ignition timing correction amount is calculated according to a deviation Δα from the average value and the basic ignition timing is corrected by this ignition timing correction amount (see Japanese Patent Laid-Open No. 62-20652).

In this system, a primary delay is applied to Δα, the value of the primary delay is synchronized with the periodic fluctuation of the torque, and the retard correction amount of the ignition timing is given in proportion to the value of the primary delay.
It is possible to eliminate the torque fluctuation caused by the fluctuation of α by the feedback control of the air-fuel ratio.

However, when the injection timing is injected relatively close to the intake stroke or when the distance from the injector to the intake valve is long, the torque fluctuation remains when approximated by the first-order lag. This is because when the injection timing is injected relatively close to the intake stroke or when the distance from the injector to the intake valve is long, the response of the first intake is delayed as shown by the dashed line in FIG. This is because the response cannot be approximated with a first-order delay.

The present invention has been made in view of such a conventional problem, and predicts a value obtained by applying a first-order delay twice to the air-fuel ratio feedback correction amount as the cylinder air-fuel ratio, so that the injection timing is set to the intake stroke. An object of the present invention is to provide a device that makes the generated torque constant at idle even when injecting relatively close to each other or when the distance from the injector to the intake valve is long.

(Means for Solving the Problems) The present invention, as shown in FIG.
And a load (for example, intake air amount Qa) respectively, sensors 31, 32 for calculating a basic injection amount Tp based on the rotational speed N and a detected value of the load, and an air-fuel ratio in exhaust gas. A sensor 34, means 35 for calculating the air-fuel ratio feedback correction amount α based on the sensor detection value, and correcting the basic injection amount Tp with this correction amount α even during idling,
Means 36 for determining the fuel injection amount Ti to be output, device 37 for injecting this injection amount Ti into the intake system, and means 38 for calculating the basic ignition timing PADV based on the rotational speed N and the detected value of the load.
And means 39 for predicting a value obtained by applying a first-order lag twice to the air-fuel ratio feedback correction amount α using predetermined weighted average coefficients X1 and Y1 as an in-cylinder air-fuel ratio for each injection or for each predetermined rotation, and this cylinder According to the predicted value FBYA of the internal air-fuel ratio, the ignition timing correction amount CTADV is obtained so that the generated torque obtained from this predicted value matches a predetermined required torque (for example, advance on the lean side and retard on the rich side. Let)
Means 40, means 41 for deciding the ignition timing ADV to be output by correcting the basic ignition timing PADV with the ignition timing correction amount CTADV, and a device for performing ignition with the signal of the determined ignition timing ADV And 42.

(Operation) When the injection timing is relatively close to the intake stroke, or when the distance from the injector to the intake valve is long,
Unlike the case where the injection timing is advanced, the response of the first intake is delayed, so that the response cannot be approximated by the first-order delay of the air-fuel ratio feedback correction amount α.

On the other hand, when the first-order delay is given to α twice in succession, the value obtained by applying the first-order delay to α twice is 1
Since the valve rises with a rising delay at the third time, even if the distance from the late injection or the injector to the intake valve is long, it is possible to approximate the response characteristic with the rising delay at the first intake.

(Embodiment) FIG. 2 is a system diagram of an embodiment.

In the figure, intake air passes from an air cleaner 2 to an intake pipe 3, and fuel is injected from an injector to each intake port of the engine 1 based on an injection signal Si. Further, the gas in the cylinder is ignited by the ignition device including the power transistor 14 receiving the ignition signal and the ignition plug 15. The gas burned in the cylinder is introduced into the catalytic converter 6 through the exhaust pipe 5, where the harmful components (NOx, CO, HC) in the combustion gas are cleaned by the three-way catalyst and discharged.

The intake air amount Qa upstream of the throttle valve is detected by a hot wire type air flow meter (engine load sensor) 7, and the flow rate is controlled by an intake throttle valve 8 which works in conjunction with an accelerator pedal. The type of the air flow meter 7 may be a hot film type, as long as it measures the amount of intake air.

The opening TVO of the throttle valve 8 is detected by a throttle valve opening sensor 9, and the rotation speed N of the engine 1 is detected by a crank angle sensor (engine rotation speed sensor) 10. Further, the cooling water temperature Tw of the water jacket is detected by the water temperature sensor 11, and the oxygen concentration in the exhaust gas is measured by the oxygen sensor (air-fuel ratio sensor) 12
Detected by. As the oxygen sensor 12, a sensor whose output suddenly changes at the stoichiometric point or a sensor having a characteristic capable of detecting a wide range of air-fuel ratios from rich to lean is used. Further, the operation of the starter motor is detected by the start switch 13.

Outputs from the air flow meter 7, the throttle valve opening sensor 9, the crank angle sensor 10, the water temperature sensor 12 and the start switch 13 are input to the control unit 20.

The control unit 20 is the means 33, 35, 36, 38-4 of FIG.
It has all functions as 1, CPU21, ROM22, RAM23 and I / O
Consists of port 24. The CPU21 fetches the external data required from the I / O port 24 according to the program written in the ROM22, and exchanges the data with the RAM23 to calculate the processing value required for the fuel injection control. I / O the processed data as needed
Output to port 24.

Signals from various sensors and switches are input to the I / O port 24, and an injection signal Si and an ignition signal are output from the I / O port 24.

ROM22 stores the calculation program in CPU21,
The RAM 23 stores data used for calculation in the form of a table or map.

3 to 5 are routines showing the contents of the CPU 21. Here, the fuel injection pulse width Ti is obtained as a value common to all cylinders, but since the ignition timing is obtained for each cylinder, the cylinder number n is added to the end of the symbols (FBYA, CTADV and ADV) representing the values relating to the ignition timing. Attach and distinguish.

First, FIG. 3 shows a routine executed in synchronization with the injection timing. This routine may be executed every predetermined number of rotations.

Cylinder discrimination is performed in S1. If the cylinder is the nth cylinder, then n is selected.

S2 is when the injection timing is advanced, and here, the predicted value FBYAn [unknown number] of the air-fuel ratio feedback correction coefficient for each cylinder is obtained from the air-fuel ratio feedback correction coefficient α [unknown number] by the following formula.

FBYAn = α × X + FBYAn ₋₁ × (1-X) ... However, in the formula, FBYAn ₋₁ means the value of the previous FBYAn. X [%] is a weighted average coefficient.

This equation uses the first-order lag of α as the predicted value FBYAn. This is because the amount of fuel that flows into the cylinder when the injection amount from the injector is increased stepwise actually increases with a first-order lag, as shown by the broken lines in FIGS. 10 and 11. In order to obtain the air-fuel ratio feedback correction coefficient during this response, it is necessary to calculate with a first-order lag.

S3 is a portion that fulfills the function of the ignition timing correction amount calculation means 40 of FIG. 1, and here, the ignition timing correction amount CTADVn [°] is calculated for each cylinder from the predicted value FBYAn by referring to the table.

Fig. 6 shows the contents of this table.
The advance amount is given when it is smaller than 1.0 (value for the required air-fuel ratio). This means that if FBYAn is less than 1.0, the air-fuel ratio of the nth cylinder is leaner than the required value and the required torque (predetermined) is not obtained, so in this case ignition This is because the required torque is generated by advancing the timing and increasing the fuel pressure.

On the contrary, when FBYAn is larger than 1.0 (the air-fuel ratio is on the rich side), the torque more than the required torque is generated for the nth cylinder. Therefore, the generated torque is requested by retarding the ignition timing. Reduce to torque.

Here, in order to obtain the ignition timing correction amount according to the air-fuel ratio deviation from the required air-fuel ratio, the cylinder air-fuel ratio is predicted in S2 for the air-fuel ratio feedback correction coefficient related to this air-fuel ratio deviation. However, the in-cylinder air-fuel ratio in the middle of response may be learned and predicted by using the oxygen sensor output. In this case, the weighted average coefficient X is corrected according to the deviation between the predicted air-fuel ratio value for each cylinder and the in-cylinder air-fuel ratio, and then the ignition timing correction amount is set for each cylinder. Further, the exhaust air-fuel ratio with respect to the in-cylinder air-fuel ratio may differ slightly due to the presence of residual gas in the cylinder, or may cause a cycle delay or exhaust pipe delay,
It is better to correct these before use.

FIG. 4 is a routine for setting the ignition timing.

In S11, it is determined whether the engine is idle or the load is low, and if so, the process proceeds to S12.

S12 is a portion that fulfills the function of the ignition timing determination means 41 in FIG. 1, and here, the basic ignition timing PADV [° BTDC] common to all cylinders is obtained by the cylinder-specific ignition timing correction amount CTADVn.

ADVn = PADV + CTADVn ... At S13, the obtained ignition timing ADVn for each cylinder is transferred to the timer of the I / O port 24. This is a set of ignition timing,
Ignition is performed for the nth cylinder at this ADVn timing.

On the other hand, if it is determined in S11 that the engine is not idle or under low load, the process proceeds to S14 and ADVn = PADV. This is because the rotation is stable in an operating range other than when the engine is idle or when the load is low, and torque fluctuations do not pose a problem so that it is not necessary to correct the ignition timing.

FIG. 5 shows a background job, which is executed once every 10 ms, for example.

S21 is a portion that fulfills the function of the basic injection amount calculation means 33 of FIG. 1, and here, from the intake air amount Qa [g / s] and the rotational speed [rpm] detected by the air flow meter, the basic value common to all cylinders. The injection pulse width Tp [ms] is calculated by the following formula.

Tp = (Qa / N) × K, where K is a constant for determining the basic air-fuel ratio.

S22 is a portion that fulfills the function of the injection amount determining means 36 of FIG. 1, and here, the synchronous injection pulse width Ti [ms] is obtained by the following equation.

Ti = Tp × COEF × α + Ts However, in the formula, COEF [anonymous number] is 1 and the sum of various increase correction coefficients, and Ts [ms] is an invalid pulse width.

Note that the air-fuel ratio feedback correction coefficient α is set in another subroutine every 1/2 revolution of the engine (1 in 4 cylinders).
It is calculated once per rotation) based on the actual air-fuel ratio obtained from the oxygen sensor output. The content of this α is publicly known.
However, it is different from the conventional example in that the air-fuel ratio feedback control is performed even during idling.

In S23, the basic ignition timing PADV [° BTDC] is obtained from the engine speed N, the basic injection pulse width Tp as the engine load, and the cooling water temperature Tw [° C] by referring to a predetermined map.

In S24, a weighted average coefficient X [%] is obtained from the cooling water temperature Tw by referring to a predetermined table. The contents of this table are
Shown in the figure. Here, X defines the rate of change of the predicted value FBYAn. This change speed largely depends on the behavior of the wall flow portion of the fuel injected from the injector to the intake port, and the wall flow portion depends somewhat on the cooling water temperature Tw, so the cooling water temperature Tw is used as a parameter.

In this way, if feedback control of the air-fuel ratio is performed even during idling, the torque during feedback control is
It fluctuates slowly at low frequencies as shown by the broken line in the figure. This is because, as shown in FIG. 8, when the air-fuel ratio A / F deviates to the rich side or the lean side under a constant ignition timing, the generated torque will be different.

At this time, when the air-fuel ratio feedback correction coefficient α for each cylinder is delayed by the above-mentioned equation in synchronization with the injection timing, the value of the first-order delay (FBYAn) also becomes a value that fluctuates periodically, and As shown by the broken line in the figure,
The phase is exactly the same as the periodic fluctuation of torque shown by the broken line. The value of FBYAn is a value that is smaller than 1.0 in the half cycle in which the torque decreases and is larger than 1.0 in the half cycle in which the torque increases (that is, the predicted value of the in-cylinder air-fuel ratio).
In proportion to the value of FBYAn, the advance angle correction value is given according to the degree of this decrease in the half cycle where the torque decreases, and conversely, in the half cycle where the torque increases, the retard angle according to the degree of this increase. When the correction value is given, the torque characteristic becomes flat as shown by the solid line in FIG. 9 when idling or at low load.

Further, an example in which the predicted value of the in-cylinder air-fuel ratio and the ignition timing correction amount calculated from this predicted value are obtained as a value common to all cylinders, not for each cylinder, are shown in FIG. 13 to FIG.
As shown in FIG. 17, FIGS. 13 to 15 show FIGS.
FIG. 16, FIG. 16 corresponds to FIG. 7, and FIG. 17 corresponds to FIG.

For example, in the case of a four-cylinder engine, as shown in FIG. 13, the predicted value FBYA of the in-cylinder air-fuel ratio common to all cylinders is obtained every 1/2 rotation, and the predicted value FBYA common to all cylinders is calculated from this predicted value FBYA. Obtain the ignition timing correction amount CTADV.

However, as for the changing speed Y [%] in S31, as shown in FIG. 16, a value smaller than the changing speed X in FIG. 7 is used.

According to this example, as shown in FIG. 17, although the torque fluctuation remains slightly as compared with the case of FIG. 9, the torque fluctuation is significantly suppressed as compared with the conventional case.

The operation of the above two examples is the same as that of the technique described in JP-A-62-20652.

When the injection timing is injected relatively close to the intake stroke (late injection), the response characteristic differs from that when the injection timing is advanced (early injection). Therefore, as described above, the air-fuel ratio feedback correction coefficient α If the in-cylinder air-fuel ratio is predicted with a first-order lag, torque fluctuation remains. In Fig. 10 and Fig. 11, the response of the fuel supply in the case of early injection is almost linear delay as shown by the broken line with respect to the stepwise increase of the injection amount (shown by the solid line). The value FBYAn can be represented by adding a weighted average to α once. However, if the distance from the injector to the intake valve is long even in the case of late injection or early injection,
Since the response of the second time is delayed, the response becomes like the one-dot chain line, so that it cannot be approximated by the first-order delay. In addition,
Both Fig. 10 and Fig. 11 show the response characteristics of the amount of fuel sucked into the cylinder when the fuel injection amount increases stepwise, and although Fig. 10 shows the horizontal axis as the number of intakes, On the other hand, it is shown as a waveform model in FIG. Also,
FIG. 12 shows examples of injection pulses for early injection and late injection.

Therefore, in the control unit 20, when the late injection or the distance from the injector to the intake valve is long, the predicted value FBYAn of the in-cylinder air-fuel ratio for each cylinder is obtained by the following formula.

FOFBYAn = α × X ₁ ＋ FOFBYAn _-1 × (1-X ₁ ) ... FBYAn = α × Y ₁ ＋ FOFBYAn × (1-X ₁ ) ... These expressions give a first-order lag to α twice in a row. Therefore, even if the latter injection or the distance from the injector to the intake valve is long, the first rise delay of the intake air shown in FIG. 11 can be accurately made.

In other words, by applying a first-order lag to α twice, it is possible to approximate the response characteristics when the late injection or the distance from the injector to the intake valve is long, and thus the distance from the late injection or the injector to the intake valve can be approximated. Is long,
It is possible to prevent torque fluctuations associated with air-fuel ratio feedback control during idling or under low load.

In addition, in, X ₁ , Y ₁ [%] is a weighted average coefficient,
In the formula, FOFBYAn [unknown number] is the value of the first-order lag for each cylinder, and FOFBYAn _-1 is the previous FOFBYAn.

Further, the characteristic of the weighted average coefficient X ₁ is a value that becomes smaller as the water temperature Tw becomes lower, similar to X shown in FIG. 7. This is because the lower the water temperature, the poorer the fuel response and the slower the response speed of the output in-cylinder air-fuel ratio predicted value with respect to the input α, and the smaller the value of the weighted average coefficient X _1. is there.

(Effects of the Invention) The present invention performs air-fuel ratio feedback correction even during idling, and uses a predetermined weighted average coefficient to perform a primary delay twice on the air-fuel ratio feedback correction amount as an in-cylinder air-fuel ratio for each injection. Or, it is decided to predict every predetermined number of revolutions, and based on this predicted value, the ignition timing is increased or decreased so that the torque generated by this predicted value matches the required torque obtained in advance, so the injection timing is compared with the intake stroke. Even when the injection is performed in close proximity to each other or when the distance from the injector to the intake valve is long, it is possible to prevent the torque fluctuation due to the air-fuel ratio feedback control during idling.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to the claims of the present invention, FIG. 2 is a control system diagram of one embodiment, FIG. 3 is a flow chart for explaining a control operation in the case of early injection, and FIGS. FIG. 6 is a flow chart for explaining the control operation of one embodiment, FIG. 6 is a view showing the characteristic of the cylinder-specific ignition timing correction amount CTADVn of this embodiment, and FIG. 7 is a characteristic of the weighted average coefficient X in the case of the early injection. FIG. 8 is a diagram showing the characteristic of the generated torque with respect to the ignition timing ADV, and FIG. 9 is a waveform diagram for explaining the action in the case of the early injection. FIG. 10 and FIG. 11 are diagrams showing the response characteristics of the above-mentioned embodiment in comparison with early injection, and FIG. 12 is a waveform diagram showing drive pulses for early injection and late injection. 13 to 15 are flow charts for explaining the control operation of another example in the case of the above-mentioned early injection, FIG. 16 is a diagram showing the characteristics of the weighted average coefficient Y of this another example, and FIG. 17 is It is a wave form diagram for explaining operation of this another example. 1 ... Engine, 3 ... Intake pipe, 4 ... Injector (fuel injection device), 7 ... Air flow meter (engine load sensor), 9 ... Throttle valve opening sensor, 10 ... Crank angle sensor (engine rotation) Number sensor), 11 ... Cooling water temperature sensor, 15 ... Spark plug, 20 ... Control unit, 31 ... Engine speed sensor, 32 ... Engine load sensor, 33 ... Basic injection amount calculation means, 34 ... Air-fuel ratio sensor, 35 ... Air-fuel ratio feedback correction amount calculation means, 36 ...
... injection amount determination means, 37 ... fuel injection device, 38 ... basic ignition timing calculation means, 39 ... in-cylinder air-fuel ratio prediction means, 40
...... Ignition timing correction amount calculation means, 41 ...... Ignition timing determination means, 42 ...... Ignition device

Claims (1)

[Claims] 1. A sensor for detecting an engine speed and a load, a means for calculating a basic injection amount based on the detected values of the engine speed and a load, a sensor for detecting an air-fuel ratio in exhaust gas, and A means for calculating the air-fuel ratio feedback correction amount based on the sensor detection value, a means for correcting the basic injection amount by this correction amount even during idling, and determining the fuel injection amount to be output, and this injection amount A device for injecting into the intake system, a means for calculating the basic ignition timing based on the detected values of the rotational speed and the load, and a value obtained by applying a primary delay twice to the air-fuel ratio feedback correction amount using a predetermined weighted average coefficient. According to the means for predicting the in-cylinder air-fuel ratio for each injection or for each predetermined rotation, and the predicted value of this in-cylinder air-fuel ratio, the generated torque obtained from this predicted value matches the predetermined required torque. Means for determining the ignition timing correction amount, means for determining the ignition timing to be output by correcting the basic ignition timing with the ignition timing correction amount, and ignition based on the determined ignition timing signal. An ignition timing control device for an engine, comprising: