JPH051372B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air-fuel ratio control device for a multi-cylinder engine.

(Industrial application field) Conventionally, exhaust sensors such as O ₂ sensors are installed in the engine exhaust system to detect the air-fuel ratio of the intake system from the concentration of exhaust components, and supply air to the intake system accordingly. Engine air-fuel ratio control techniques that perform closed-loop (feedback) control of the air-fuel ratio are well known.

However, in the above-mentioned closed-loop control of the air-fuel ratio, there is a time delay between detecting the air-fuel ratio supplied to the intake system in the exhaust system, and in order to avoid sudden fluctuations in the air-fuel ratio, there is a time delay in detecting the air-fuel ratio supplied to the intake system. The air-fuel ratio adjusting means is controlled according to the integral signal.
Therefore, the actual air-fuel ratio fluctuations do not remain constant with respect to the set value, for example, the stoichiometric air-fuel ratio, but cause a hunting phenomenon in which they periodically fluctuate up and down around this set value, and during idling etc. This hunting fluctuation in the air-fuel ratio poses the problem of torque fluctuations, that is, rotational fluctuations, and if a three-way catalyst is installed in the exhaust system, there is a risk that the exhaust purification performance will drop due to the three-way atmosphere. be.

Therefore, in order to improve the hunting phenomenon of the closed-loop control described above, a multi-cylinder engine is divided into a first cylinder group and a second cylinder group, and the first cylinder An exhaust sensor is disposed in the exhaust system of each cylinder group, and the first cylinder group is controlled in a closed loop by an integral signal based on the output of the exhaust sensor, while the second cylinder group is controlled by inverting the integral signal for the first cylinder group. A technique has been proposed in which air-fuel ratio control is performed in an opposite phase state. In this technique, the fluctuations in the air-fuel ratio of the first cylinder group and the second cylinder group are reversed so that they cancel each other out, thereby suppressing the hunting phenomenon.

However, in the above-mentioned prior art, the second cylinder group is not substantially subjected to closed-loop control based on the detection of the air-fuel ratio supplied to its intake system, but is simply controlled by the first cylinder group.
The air-fuel ratio is simply controlled in a phase opposite to the first cylinder group based on the assumption that the air-fuel ratio will fluctuate in the same way as the cylinder group. Due to system accuracy errors, intake system filling efficiency errors, etc., for example, even if the same fuel injection signal is output to multiple fuel injection valves, there will be differences in the amount of fuel actually injected. As a result, the air-fuel ratio control in the second cylinder group may be controlled to an air-fuel ratio that is far from the target value, resulting in a significant decrease in control accuracy, and the original purpose of closed-loop control of the air-fuel ratio may not be fully achieved. This results in deterioration in combustibility, fuel efficiency, and emission performance.

(Object of the Invention) In view of the above circumstances, the present invention provides an air-fuel ratio control system for a multi-cylinder engine that improves control accuracy and improves the hunting phenomenon associated with closed-loop control. The purpose of this invention is to provide a control device.

(Structure of the Invention) The air-fuel ratio control device of the present invention includes a first cylinder group and a second cylinder group.
Exhaust sensors are provided in the exhaust systems of the cylinder groups, and both cylinder groups are provided to perform closed-loop control using integral signals based on the respective exhaust sensor outputs. The air-fuel ratio is controlled by correcting the first integral signal for the first cylinder group and the second integral signal for the second cylinder group to have opposite phases based on a signal related to the reversal timing. This is a characteristic feature.

FIG. 1 is an overall configuration diagram for clearly showing the configuration of the present invention.

The multi-cylinder engine E is divided into two cylinder groups, a first cylinder group 1 and a second cylinder group 2, and a first exhaust system extracts exhaust gas corresponding to the first cylinder group 1 and the second cylinder group 2. 3 and a second exhaust system 4 are connected to each other, and both exhaust systems 3 and 4 meet on the downstream side, and a catalyst device 5 is interposed therebetween.

The first exhaust system 3 and the second exhaust system 4 include a first exhaust sensor 6 and a second exhaust sensor 7 such as an O ₂ sensor that detects the component concentration of exhaust gas discharged from the respective cylinder groups 1 and 2. are arranged respectively.

On the other hand, a fuel supply device 8 that supplies fuel to the first and second cylinder groups 1 and 2 is provided, and a first air-fuel ratio that adjusts the air-fuel ratio supplied to the first cylinder group 1 with respect to the fuel supply device 8. Adjustment means 9 and second cylinder group 2
A second air-fuel ratio adjusting means 10 for adjusting the air-fuel ratio supplied to the second air-fuel ratio is provided.

The first air-fuel ratio adjustment means 9 and the second air-fuel ratio adjustment means 10 are connected to the first exhaust sensor 6 and the second air-fuel ratio adjustment means.
It is controlled by a control means that receives the detection output of the exhaust sensor 7, and this control means includes a closed loop control means 11, a reversal detection means 12, and an integral signal correction means 13.

The closed loop control means 11 controls the first air-fuel ratio adjusting means 9 in response to a first integral signal based on the first exhaust sensor 6, and controls the second air-fuel ratio adjusting means 9 in response to a second integral signal derived from the second exhaust sensor 7. It controls the fuel ratio adjusting means 10.

Further, the reversal detection means 12 detects signals related to the reversal of the first integral signal, the second integral signal, and the second integral signal by the closed loop control means 11 from the first and second integral signals or from the first and second integral signals. This is detected from the detection outputs of the two exhaust sensors 6 and 7.

Further, based on the signal from the reversal detection means 12, the integral signal correction means 13 adjusts the first integral signal so that the increasing and decreasing directions of the first integral signal and the second integral signal are in opposite phases.
At least one of the integral signal and the second integral signal is corrected.

By using the above-mentioned control means, for example, when there is an output fluctuation (comparison output) of the first exhaust sensor 6 and the second exhaust sensor 7 as shown in A and B in FIG. 2, that is, an air-fuel ratio fluctuation, both of them are controlled. The reversal timing and period are different between rich detection and lean detection, and correspondingly, the first integral signal and the second air-fuel ratio for the first air-fuel ratio adjusting means 9 as shown in C and D in FIG. the second for the adjusting means 10;
An integral signal is created, but if left as is, a hunting phenomenon will occur, so for example, the second
As shown in E in FIG. 2, the second integral signal to the air-fuel ratio adjusting means 10 basically corresponds to the output of the second exhaust sensor 7, and the phase of the increase and decrease corresponds to the first integral signal. The signal is corrected so that it has a phase opposite to that of the signal, and closed-loop control with a phase opposite to that of the signal is performed.

As a result, closed-loop control is performed in the first and second cylinder groups 1 and 2 according to the outputs of the first and second exhaust sensors 6 and 7, respectively, and increases and decreases in the first and second cylinder groups 1 and 2 are performed. The phase is adjusted so that the direction becomes an integral signal with an opposite phase, thereby improving control accuracy through closed loop control and suppressing hunting through opposite phase correction.

The multi-cylinder engine E is a 6-cylinder or 8-cylinder V-type engine, with one bank serving as the first cylinder group 1 and the other bank serving as the second cylinder group.
The present invention is applicable to various multi-cylinder engines, such as those with a cylinder group 2, or those with an in-line 4 to 8 cylinder engine divided into two, a first cylinder group 1 and a second cylinder group 2.

The fuel supply device 8 and the first and second air-fuel ratio adjusting means 9, 10 are equipped with a fuel injection amount calculation section, and the fuel supply device 8 and the first and second air-fuel ratio adjusting means 9, 10 are equipped with a fuel injection amount calculation section and adjust the air-fuel ratio by adjusting the fuel injection amount from the fuel injection valve. injection type,
Alternatively, a carburetor system may be used in which the supplied air-fuel ratio is adjusted by adjusting the amount of bleed air in the carburetor.

Furthermore, the correction in which the increasing/decreasing directions of the first integral signal and the second integral signal are in opposite phases is performed by looking at the time t when both are in the same phase, and correspondingly increasing or decreasing the first or second integral signal.
By increasing or decreasing the integral constant (gain) of the integral signal, the air-fuel ratio fluctuation is temporarily controlled by the first or second exhaust sensor 6, 7.
one that changes and shifts the phase regardless of the output, or the first or second exhaust sensor output, i.e. the first
Or, when one of the second integral signals is inverted, the phase is shifted by maintaining the control state of one until the other is inverted in the opposite direction,
A system that maintains one control in response to the time difference t is appropriately adopted.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

Figure 3 shows the specific configuration. The multi-cylinder engine E, which is a V-type 6-cylinder engine, is connected to one bank B1.
is divided into a first cylinder group 1 and the other bank B2 is divided into a second cylinder group 2. A first exhaust system 3 is connected to the exhaust port 16 of each cylinder C1 of the first cylinder group ₁ , and a first exhaust system 3 is connected to the exhaust port 16 of each cylinder C1 of the first cylinder group 1. The second exhaust system 4 is connected to the exhaust port 16 of each cylinder C ₂ of the cylinder C 2 , and a catalyst device 5 (three-way catalyst) is provided downstream from the merging portion. Further, the first exhaust system 3 and the second exhaust system 4 are respectively provided with a first exhaust sensor 6 and a second exhaust sensor 7 such as an O ₂ sensor.

On the other hand, an intake system 18 that supplies intake air is connected to the intake port 17 of each cylinder C ₁ and C ₂ of the first and second cylinder groups 1 and 2. This intake system 18
is equipped with an air cleaner 19 at the upstream end, an air flow sensor 20 for measuring the amount of intake air is interposed downstream of the air cleaner 19, and a first intake passage for the first cylinder group 1 is installed downstream of the air flow sensor 20. 18a and the second intake passage 18 for the second cylinder group 2
It is branched into b. The first and second intake passages 18a, 18b are connected to throttle valves 21, 2, respectively.
The downstream portion of the cylinder 2 is configured as a surge tank, and this surge tank is communicated with each cylinder C ₁ and C ₂ through an independent intake passage. Note that the two throttle valves 21 and 22 are synchronously opened and closed to the same opening degree.

A first fuel injection valve 23 for supplying fuel to each cylinder C1 of the first cylinder group 1 is disposed in the first intake passage 18a, and a first fuel injection valve 23 for supplying fuel to each cylinder _C1 of the first cylinder group 1 is disposed in the second intake passage 18b. The second supplying fuel to cylinder C ₂
Fuel injection valves 24 are respectively provided. A control signal from a control unit 25 (microcomputer) is outputted to the first and second fuel injection valves 23 and 24 according to the operating state, and from this first fuel injection valve 23 to the first cylinder group 1, And the fuel injection amount, that is, the air-fuel ratio, respectively supplied from the second fuel injection valve 24 to the second cylinder group 2 is controlled.

This control unit 25 includes the first
Exhaust gas component concentration signals, that is, detected air-fuel ratio signals are input from the exhaust sensor 6 and the second exhaust sensor 7, and an intake air amount signal from the air flow sensor 20 and the rotation speed sensor 26 are input as signals for detecting the operating state of the engine. The engine rotation speed signal from the engine speed sensor 27 and the coolant temperature signal from the water temperature sensor 27 are respectively input.

The control unit 25 includes a fuel supply device 8 that supplies fuel to the first and second cylinder groups 1 and 2 in FIG. 2nd cylinder group 1,
the first and second adjusting the air-fuel ratio supplied to the second
The air-fuel ratio adjusting means 9 and 10 are configured, and
This control unit 25 has the functions of the closed loop control means 11, the reversal detection means 12, and the integral signal correction means 13 shown in FIG. Phase correction control is performed so that the phase is opposite.

Next, the operation of the control unit 25 will be explained using the flowchart shown in FIG.

First, after starting (step S1 shown in FIG. 4) and initializing to reset the timer t and flag F, the intake air amount Q
and engine rotation speed N (S2, S3),
Based on these, a basic injection pulse T ₀ to be output to the first and second fuel injection valves 23 and 24 corresponding to the required fuel amount is calculated (S4). Also, step S5,
In S6, temperature correction based on the detection of the water temperature sensor 27 or other correction coefficients such as starting, acceleration correction, etc. C ₀
, and calculate the corrected injection pulse Ti.

Next, the comparison outputs E ₁ and E ₂ of the first exhaust sensor 6 and the second exhaust sensor 7 are read (S7, S
8). These comparison outputs E ₁ and E ₂ output a 1 signal when the detected air-fuel ratio is richer than the set air-fuel ratio, and output an O signal when the detected air-fuel ratio is lean.
It outputs a signal.

The comparison output E ₁ of the first exhaust sensor 6 and the comparison output E ₂ of the second exhaust sensor 7 are compared in step S9, and it is determined whether they are in the same phase as 1 or 0, and are in the same phase. If (YES), a flag F, which will be described later, is set to 1 in step S10, and then the timer t is counted. This timer t is for counting the time when both are in the same phase.

If the determination in step S9 is NO and the phases are opposite, it is determined whether flag F has been reset (S14). When this flag F is set to 1, it indicates that the integral constant Ibo used when obtaining the second integral signal for the second cylinder group 2 has not been corrected, and when it is reset to 0, it indicates that it has been corrected. It is something. Above step S1
If the determination in step 4 is YES and there is no correction (when the phase starts from the same phase and becomes an opposite phase), the flag F is reset (S15), and the comparison output _E2 of the second exhaust sensor 7 is registered in the memory at step S16. It is determined whether the detected air-fuel ratio is the same as the previous comparison output E ₂ m, that is, whether the detected air-fuel ratio has reversed from the lean side to the rich side or from the rich side to the lean side with respect to the set air-fuel ratio. It is determined whether this state of opposite phase is caused by an inversion of the output of the first exhaust sensor 6 or an inversion of the output of the second exhaust sensor 7.

If this judgment is YES, the second exhaust sensor 7
Since the reversal of the output of the first exhaust sensor 6 is delayed by the period t with respect to the reversal of the output, the reversal timing of the second integral signal based on the output of the second exhaust sensor 7 is delayed and the output of the first exhaust sensor 6 is reversed. In order to match the reversal timing, in step S17, the integral constant Ibo is corrected to a smaller value by subtracting a correction value obtained by multiplying the time t of the timer by the coefficient C from the reference integral constant Ibo. On the other hand, when the above determination is NO, the reversal of the second exhaust sensor 7 output is delayed by the period t with respect to the reversal timing of the first exhaust sensor 6 output. 2 In order to advance the reversal timing of the integral signal to match the reversal timing of the first exhaust sensor 6 output, a correction value obtained by multiplying the time t of the above-mentioned timer by the coefficient C is added to the integral constant Ibo and the reference integral constant Ibc in step S18. The value is corrected to a larger value.

After the above-mentioned integral constant Ibo is corrected, the timer t is reset in step S19, and the memory of the second comparison output _E2 is rewritten ( _S22 ). 1 cylinder group 1
It is determined whether or not the air-fuel ratio is rich (S23), and if it is rich (YES), the correction coefficient _C1 is calculated by subtracting the integral constant Iao so that the supplied air-fuel ratio shifts to the lean direction (S24). , in the case of lean (NO), the correction coefficient _C1 is calculated by adding the integral constant Iao so that the supplied air-fuel ratio shifts to the rich direction (S
25). Based on this, a first integral signal for closed loop control of the first cylinder group 1 is obtained.

Next, the process proceeds to step S26, where it is determined whether the air-fuel ratio of the second cylinder group 2 is rich or not from the comparison output _E2 of the second exhaust sensor 7, and if it is rich (YES), the supplied air-fuel ratio is in the lean direction. A correction coefficient C ₂ is calculated by subtracting the corrected integral constant Ibo so that the air-fuel ratio shifts to the rich direction (S27). The correction coefficient _C2 is calculated by adding the integral constant Ibo (S28). Based on this, the second
A second integral signal for closed loop control of the cylinder group 2 is obtained.

The correction coefficient C ₁ (first integral signal) obtained in step S24 or S25 and step S27
Alternatively, the final injection pulse T ₁ for the first cylinder group 1 and the final injection pulse T ₂ for the second cylinder group 2 are determined based on the correction coefficient C ₂ (second integral signal) determined in S28 (S29, S30); In response to this, in step S31, the first fuel injection valve 23 of the first cylinder group 1 and the second fuel injection valve 24 of the second cylinder group 2 are
outputs a fuel injection pulse to inject a predetermined amount of fuel to control the air-fuel ratio in a closed loop, and also corrects the integral constant Ibo of the second integral signal so that the phases of the two match opposite phases. to correct.

After the integral constant Ibo is corrected, the flag F is reset in step S15, so the determination in step S14 becomes NO, and the process moves to step S20, where the comparative output of the second exhaust sensor 7 is reset.
Determine whether E ₂ is reversed or not; if not reversed (YES)
In this case, closed-loop control is performed using the corrected integral constant Ibo, while in the case of reversal (NO), closed-loop control is performed by returning this integral constant Ibo to the reference value Ibc.

In the above reverse phase control, if either the output of the first exhaust sensor 6 or the output of the second exhaust sensor 7 is reversed first and becomes the same phase state, the determination in step S9 becomes YES and flag F is set. It is set as an uncorrected state (S10), and the timer t starts counting in step S11, and the comparison output of the second exhaust sensor 7 determines whether or not _E2 has been reversed (S12). returns the integral constant Ibo to its reference value.

Therefore, when the same phase is achieved by the above control routine, the period of the same phase is counted by timer t, and the integral constant of the second integral signal is determined based on the value.
Ibo is corrected, and the air-fuel ratio change is made faster or slower to achieve an opposite phase state, thereby achieving an opposite phase, and closed loop control is performed on both cylinder groups 1 and 2 to maintain this opposite phase state.

In addition, the integral constants Iao and Ibo used when calculating the first and second integral signals in the flowchart may have different values depending on whether the air-fuel ratio is shifted to a rich direction or a lean direction.

(Effects of the Invention) According to the present invention, both the first cylinder group and the second cylinder group perform closed-loop control using integral signals based on the outputs of the exhaust sensors of the respective exhaust systems,
At the same time, the control accuracy for the target value of the air-fuel ratio supplied to the first cylinder group and the second cylinder group is improved, and at the same time, correction control is performed so that the first cylinder group and the second cylinder group are controlled in a closed loop with opposite phases. It is possible to suppress the hunting phenomenon, stabilize the engine speed during idling operation, and improve emission performance.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram to clarify the structure of the present invention, Fig. 2 is a characteristic diagram showing an example of correction of an integral signal together with an exhaust sensor output and an integral signal, and Fig. 3 is a specific structural example of the present invention. FIG. 4 is a flowchart illustrating the operation of the control unit in FIG. 3. E...Multi-cylinder engine, 1...First cylinder group, 2
...Second cylinder group, 3...First exhaust system, 4...Second
Exhaust system, 6...First exhaust sensor, 7...Second exhaust sensor, 8...Fuel supply device, 9...First air-fuel ratio adjustment means, 10...Second air-fuel ratio adjustment means, 11...
...Closed loop control means, 12...Reversal detection means, 1
3... Integral signal correction means, 23... First fuel injection valve, 24... Second fuel injection valve, 25... Control unit.

Claims (1)

[Claims] 1 The cylinders of the engine are divided into a first cylinder group and a second cylinder group, a first exhaust system is provided corresponding to the first cylinder group, and a second exhaust system is provided corresponding to the second cylinder group. In addition, in a multi-cylinder engine equipped with a fuel supply device that supplies fuel to the first and second cylinder groups, the component concentration of the exhaust gas disposed in the first exhaust system and discharged from the first cylinder group is determined. a first exhaust sensor that detects a component concentration of exhaust gas that is disposed in the second exhaust system and that detects a component concentration of exhaust gas discharged from a second cylinder group; a first air-fuel ratio adjustment means for adjusting the air-fuel ratio; a second air-fuel ratio adjustment means for adjusting the air-fuel ratio supplied to the second cylinder group; and a first air-fuel ratio adjustment according to a first integral signal based on the first exhaust sensor output. a second exhaust sensor based on the second exhaust sensor output;
closed-loop control means for controlling the second air-fuel ratio adjustment means in response to the integral signal; reversal detection means for detecting a signal related to reversal of the first integral signal and the second integral signal; and based on the signal of the reversal detection means. An air-fuel ratio control device for a multi-cylinder engine, comprising an integral signal correcting means for correcting at least one of the integral signals so that the increasing and decreasing directions of the first integral signal and the second integral signal are in opposite phases.