JP2001115880A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To control an air-fuel ratio with high accuracy while suppressing the influence of disturbance. Each time a reference signal from a crank angle sensor is output a predetermined number of times C0, a feedback control amount of the air-fuel ratio by the sliding mode control is calculated, and the feedback control of the air-fuel ratio is performed using the feedback control amount. I made it. Thus, the feedback control amount is calculated and updated with the cycle of the dead time in which the exhaust gas discharged from the combustion chamber reaches the air-fuel ratio sensor, so that excessive correction during the dead time can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for feedback-controlling an air-fuel ratio of an internal combustion engine, and more particularly to a technique for performing feedback control using sliding mode control.

[0002]

2. Description of the Related Art In an internal combustion engine for a vehicle, the air-fuel ratio is generally feedback-controlled to a target value for the purpose of purifying exhaust gas and improving fuel efficiency.

For this reason, PID control (proportional / integral / differential) or the like is used so that the air-fuel ratio is sequentially detected by an air-fuel ratio sensor provided in an exhaust passage or the like and the detected air-fuel ratio converges to a target air-fuel ratio. The fuel supply amount is feedback controlled.

On the other hand, a sliding mode control is known as a highly robust control that suppresses the influence of disturbance, and is often used in robot control and the like. Feedback control of the air-fuel ratio is performed using the sliding mode control. It has been proposed to do this (Japanese Unexamined Patent Publication No. Hei 8-23271).
No. 3).

[0005]

However, as a general problem of the air-fuel ratio feedback control by the sliding mode control, the air-fuel ratio is detected from a specific component of the exhaust gas. There is a delay (dead time) between the (fuel supply amount) and the air-fuel ratio detected from the exhaust gas, and excessive correction during the dead time may be performed. If the dead time is constant, excessive correction can be suppressed by setting the calculation period of the feedback control amount in accordance with the dead time. However, the dead time greatly changes depending on the operating state of the engine, so the calculation period is set to an appropriate value. Could not be set to. For example, if the calculation cycle is set sufficiently large, excessive correction can be suppressed,
Responsiveness decreases. In practice, the calculation cycle is reduced to some extent, and the feedback gain is set to a small value to suppress overcorrection. However, a reduction in responsiveness cannot be denied, and the original function of the sliding mode control cannot be sufficiently performed. Can not demonstrate.

The sliding mode control used in the feedback control of the air-fuel ratio is very complicated and troublesome because the delay of each part of the air-fuel ratio control system including the dead time is finely modeled and designed. It requires a lot of work, has no versatility for the vehicle type and the engine, has complicated control, and requires a large amount of ROM and RAM.

In view of this point, the applicant of the present application has proposed air-fuel ratio feedback control by sliding mode control in which a switching plane is set by using a direct function switching method, and according to this, simple and highly accurate control is achieved. It became clear that we could do it.

[0008] However, although it is possible to exhibit high robustness against the influence (disturbance) of the response of the air-fuel ratio sensor and the variation of parts, etc., the problem of excessive correction due to the dead time remains as before. .

The present invention has been made in view of such a conventional problem. In the air-fuel ratio feedback control by the sliding mode control, it is possible to secure high responsiveness while suppressing the excessive correction during the dead time. The purpose is to.

[0010]

Therefore, the invention according to claim 1 is a device for feedback-controlling the air-fuel ratio of an internal combustion engine as shown in FIG. Air-fuel ratio detection means for detecting a fuel ratio, air-fuel ratio feedback control means for performing feedback control based on an air-fuel ratio detection value obtained by the air-fuel ratio detection means so as to approach the target air-fuel ratio, and feedback control in the feedback control The amount is calculated by a feedback control amount calculating unit that calculates by the sliding mode control, and the feedback control amount calculating unit calculates the amount by:
Calculation cycle control means for controlling the calculation cycle so that the calculation cycle is performed in synchronization with the stroke cycle of the engine.

According to the first aspect of the present invention, the calculation cycle control means sends the feedback control amount calculation means to the feedback control amount calculation means in synchronization with the stroke cycle of the engine based on the feedback of the sliding mode control based on the air-fuel ratio detection value by the air-fuel ratio detection means. The control amount is calculated, and the air-fuel ratio feedback control means performs feedback control of the air-fuel ratio to the target air-fuel ratio using the feedback control amount.

Here, as described above, the dead time until the exhaust gas discharged from the combustion chamber of each cylinder reaches the air-fuel ratio detecting means varies greatly depending on the operating condition. When converted in terms of, most of them are constant and there is no large deviation. That is, it is estimated that the exhaust gas reaches the air-fuel ratio detecting means several times in the exhaust stroke of another cylinder after the exhaust gas is exhausted from the combustion chamber in the exhaust stroke of a certain cylinder. Therefore, if the calculation cycle is controlled so that the control cycle, that is, the feedback control amount of the sliding mode control is calculated in synchronization with the stroke cycle of the engine, the number of calculations during the dead time can be suppressed to a certain value or less. , Excessive correction can be suppressed. Further, as a result, the feedback gain can be made sufficiently large, and high responsiveness can be ensured.

Further, the invention according to claim 2 is characterized in that the feedback control amount calculating means performs a sliding mode control using a deviation between a target air-fuel ratio and an actual air-fuel ratio detected by the air-fuel ratio detecting means as a switching function. It is characterized in that a feedback control amount is calculated.

According to the second aspect of the present invention, the feedback control amount is calculated by the sliding mode control using the switching function S as the deviation (error amount) between the target air-fuel ratio and the detected air-fuel ratio (actual air-fuel ratio). Feedback control of the air-fuel ratio is performed using the control amount. Thereby, the air-fuel ratio converges to the target air-fuel ratio while sliding on the switching plane defined as S = 0 (that is, error amount 0).

Here, the setting of the switching function S is based on a method called a direct switching function method of the sliding mode control, and a state where the switching plane (S = 0) is desired to be achieved (in this case, the air-fuel ratio is set to the target value). It is a method of defining as a function such that the air-fuel ratio is obtained. This method is characterized in that the state is not necessarily guaranteed to slide on the switching plane, but the best sliding mode control can be performed if the sliding is confirmed. That is, the switching plane is determined only by the magnitude relation between the target value and the actual value, irrespective of changes in the response of the air-fuel ratio sensor and the fuel supply device.

Then, when the sliding mode control of the air-fuel ratio was performed using the switching function set as described above, it was confirmed that the sliding on the switching plane was performed. Therefore, the feedback control by the sliding mode control can be easily and accurately performed.

In addition, since the switching function is set, a complicated operation for modeling the engine is not required, and the versatility is not affected by the variation of each vehicle type and each engine type.
The invention according to claim 3 is characterized in that the calculation cycle control means controls the calculation cycle of the feedback control amount by the feedback control quantity calculation means to be a cycle that is a multiple of the stroke cycle of the engine. According to the third aspect of the invention, it is simplest to suppress the overcorrection to several times or less even if the feedback control amount is calculated for each stroke cycle of the engine. If the calculation is performed in a cycle in which the value converted by the number is a multiple, excessive correction can be suppressed as much as possible.

Further, the invention according to claim 4 is characterized in that the calculation cycle control means variably controls a calculation cycle of the feedback control amount by the feedback control amount calculation means in accordance with an operation state of the engine. I do.

According to the fourth aspect of the present invention, the value obtained by converting the dead time by the number of stroke cycles is substantially constant,
It is thought that it changes somewhat depending on the operating conditions. For example, the volume of the exhaust passage from the combustion chamber to the air-fuel ratio
Considering how many of the exhaust volume discharged from each cylinder is filled, the value varies depending on the amount of exhaust per cylinder. Therefore, a value representing the amount of exhaust, for example, the basic fuel injection amount T
By controlling the calculation cycle, which is a multiple of the stroke cycle, variably with p or the like, more accurate control can be performed.

According to a fifth aspect of the present invention, the calculation cycle control means sets the calculation cycle of the feedback control amount by the feedback control quantity calculation means to the actual air-fuel ratio detected by the target air-fuel ratio and the air-fuel ratio detection means. It is characterized in that it is variably controlled according to the deviation from the fuel ratio.

According to the fifth aspect of the invention, for example, when the deviation is large, the response cycle is emphasized and the calculation cycle, which is a multiple of the stroke cycle, is reduced (the multiple is reduced).
When the deviation becomes smaller, the calculation cycle is increased to a cycle (a multiple of the stroke cycle) commensurate with the dead time, and control can be performed in which the deviation from the target air-fuel ratio is reduced.

In the invention according to claim 6, the calculation cycle control means controls the calculation cycle so as to calculate the feedback control amount in synchronization with a signal for detecting a predetermined stroke timing of each cylinder. It is characterized by.

According to the present invention, the feedback control amount is calculated in synchronization with a signal for detecting a predetermined stroke timing of each cylinder, so that the calculation cycle can be easily synchronized with the stroke cycle of the engine. Can be done.

Further, the invention according to claim 7 is characterized in that the signal for detecting the predetermined stroke timing of each cylinder is a reference signal output from a crank angle sensor.

According to the seventh aspect of the invention, the timing of calculating the feedback control amount can be easily determined by using the reference signal output at a predetermined stroke timing of each cylinder of the crank angle sensor provided for discriminating the rotational speed and the cylinder. Can be controlled.

The invention according to claim 8 is characterized in that the signal for detecting the predetermined stroke timing of each cylinder is a signal obtained by detecting an in-cylinder pressure.

According to the eighth aspect of the present invention, for example, a signal that increases at the compression top dead center is used as a signal for detecting a predetermined stroke timing of each cylinder according to a detection signal of an in-cylinder pressure used for knocking detection or the like. be able to.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. In FIG. 2 showing a system configuration according to one embodiment, an intake passage 12 of an engine 11 is provided with an air flow meter 13 for detecting an intake air flow rate Qa and a throttle valve 14 for controlling the intake air flow rate Qa in conjunction with an accelerator pedal. In the downstream manifold portion, an electromagnetic fuel injection valve 15 is provided for each cylinder as fuel supply means.

The fuel injection valve 15 is driven to open by an injection pulse signal from a control unit 16 containing a microcomputer, and is supplied by pressure from a fuel pump (not shown) to inject and supply fuel controlled to a predetermined pressure by a pressure regulator. . Further, a water temperature sensor 17 for detecting a cooling water temperature Tw in a cooling jacket of the engine 11 is provided, and a wide area type air for linearly detecting an air-fuel ratio of an intake air-fuel mixture in accordance with an oxygen concentration in exhaust gas in an exhaust passage 18. Fuel ratio sensor
Further, a three-way catalyst 20 is provided for purifying by oxidizing CO and HC in the exhaust gas on the downstream side and reducing NOx.

The distributor (not shown) has a built-in crank angle sensor 21.
The engine rotation speed Ne is detected by counting a crank unit angle signal output from 21 in synchronization with the engine rotation for a certain period of time, or by measuring a cycle of the crank reference angle signal.

The control unit 16
The fuel injection amount and ignition timing from the fuel injection valve 15 are calculated and controlled. Here, in the air-fuel ratio feedback control region, the fuel injection amount is calculated so as to perform the air-fuel ratio feedback control by the sliding mode control according to the present invention.

FIG. 3 is a control block diagram of the first embodiment of the air-fuel ratio feedback control by the sliding mode control. The nonlinear term calculating unit, a non-linear term U _NL feedback control amount is calculated by the following equation.

U _NL = (gain 1) · | target air-fuel ratio−actual air-fuel ratio | / (target air-fuel ratio−actual air-fuel ratio) + _{UNL (OLD)} That is, in the sliding mode control, the switching function is performed by the direct switching function method. By setting S as the switching function method S = target air-fuel ratio−actual air-fuel ratio, the switching plane S = 0 becomes a desired state, ie, actual air-fuel ratio = target air-fuel ratio, and the feedback gain increases / decreases each time the switching plane is crossed. The direction (positive / negative) is switched. The nonlinear term U _NL is calculated in this way a feedback gain decrease direction (positive or negative) is switched off換平surface as the integrated value.

Further, in the linear term calculation unit, a linear term U _L of the feedback control amount is calculated by the following equation. U _L = (Gain 2) (target air-fuel ratio - actual air-fuel ratio) / actual air-fuel ratio the linear term U _L is, for example, when the target air-fuel ratio has been switched large, adjust the speed to approach the state on the switching換平surface Is set. In other words, the larger the deviation (= target air-fuel ratio-actual air-fuel ratio) is, the larger the value is set. If the deviation approaches the switching plane quickly while approaching the switching plane, the value is reduced to a small value to suppress overshoot. To work.

[0035] Then, the linear term control amount U _L, a value obtained by adding the non-linear term control amount U _NL, median of the feedback correction coefficient α of the air-fuel ratio (a value corresponding to no feedback correction: 1.0) , And a limiter processing section performs limiter processing so as to be equal to or less than the upper limit value and equal to or greater than the lower limit value, and then outputs the result.

In the same manner as in the normal air-fuel ratio control, the basic fuel injection amount Tp calculated based on the intake air amount and the engine speed is corrected to a value corrected by various correction coefficients COEF such as water temperature. The fuel injection amount (fuel injection pulse width) Ti is calculated by multiplying the feedback correction coefficient α calculated as described above and adding the battery voltage correction amount Ts, and a drive signal (pulse) is output to the fuel injection valve 15. And inject a considerable amount of fuel.

In this way, high-precision feedback control is realized while sliding on the switching plane by the sliding mode control in which (switching plane S = error amount = 0) is set using the direct switching function method. it can.

FIG. 4 shows that the air-fuel ratio feedback control by the sliding mode control is performed at a predetermined cycle (Z in FIG. 3).
¹ is shown in a flowchart according to the first embodiment.

In step 1, various signals used for the air-fuel ratio feedback control by the sliding mode control are read. In step 2, it is determined whether a reference signal has been output from the crank angle sensor. As the reference signal, for example, a signal output near the exhaust top dead center of each cylinder is used. In this case, the output of the reference signal means the end of the exhaust stroke of the corresponding cylinder.

When it is determined that the reference signal has been output, the routine proceeds to step 3, where a feedback control amount (feedback correction coefficient α) is calculated by the sliding mode control.

In step 4, the air-fuel ratio feedback control is performed by calculating the fuel injection amount as described above using the feedback control amount calculated and updated in the cycle and outputting the fuel injection amount at a predetermined fuel injection timing.

This embodiment shows the simplest control. For example, the exhaust gas discharged from the combustion chamber of a certain cylinder is
If it reaches the air-fuel ratio sensor in three exhaust strokes,
Since the feedback control amount is calculated and updated for each stroke cycle, the excessive correction amount can be suppressed to twice the gain 1 of the nonlinear term. Further, since a large excess correction amount can be estimated in advance, the value of the gain 1 can be set in accordance with this. Thus, it is possible to perform the sliding mode control in which the deviation width from the target air-fuel ratio is reduced, and as a result, it is possible to increase the feedback gain, thereby ensuring high responsiveness.

FIG. 5 shows a flowchart of the second embodiment. Steps 11 and 12 correspond to steps 1 and 2 described above.
When the reference signal is output, the process proceeds to step 13 and the counter is counted up.
At 4, it is determined whether or not the count value C has reached a predetermined number of times C0. Here, the predetermined number C0 is set to a value (3 in the above example) obtained by converting the dead time by the number of exhaust stroke cycles.

When it is determined that the predetermined number has been reached, the process proceeds to step 15 to calculate the feedback control amount by the sliding mode control and reset the counter value C0 to 0. The air-fuel ratio control is performed using the feedback control amount.

With this configuration, a new feedback control amount is calculated based on the result of detecting the air-fuel ratio controlled using the previously calculated feedback control amount. The amount can be reduced, and the sliding mode control in which the deviation from the target air-fuel ratio is minimized can be performed. In addition, as a result, the feedback gain can be made sufficiently large, so that the responsiveness can be made sufficiently high.

FIG. 6 shows a flowchart of the third embodiment. Steps 21 and 22 correspond to steps 1 and 2 described above.
When the reference signal is output, the routine proceeds to step 23, where it is determined whether the deviation between the target air-fuel ratio and the detected actual air-fuel ratio is equal to or greater than a predetermined value.

When it is determined that the deviation is equal to or larger than the predetermined value, the process proceeds to step 24, where the feedback control amount is calculated by the sliding mode control. When it is determined that the deviation is less than the predetermined value, the routine proceeds to step 25, where a predetermined number of times C0 is set based on the basic fuel injection amount Tp. Here, the predetermined number C0 is set to a value obtained by converting the dead time by the number of times of the exhaust stroke cycle, and when the amount of exhaust per cylinder represented by the basic fuel injection amount Tp is large, Since it is considered that the number of exhaust stroke cycles required for exhaust gas to reach the air-fuel ratio sensor from the combustion chamber becomes smaller, the predetermined number of times C0
Is set by switching.

In step 26, the counter is counted up. In step 27, the count value C is set to the predetermined number of times C0.
When it is determined that the value has reached, the routine proceeds to step 24, where the feedback control amount is calculated by the sliding mode control.

In step 28, the air-fuel ratio control is executed using the feedback control amount calculated as described above. With this configuration, when the deviation is large, the feedback control amount is calculated and updated for each stroke cycle.
When higher responsiveness is obtained and the deviation is small, the calculation cycle is increased to a cycle (a multiple of the stroke cycle) commensurate with the dead time, and the cycle is switched based on the basic fuel injection amount Tp. Excessive correction during the dead time can be suppressed with higher accuracy, and control can be performed with the deviation from the target air-fuel ratio as small as possible.

In the above embodiment, the overcorrection is suppressed by a simple control that basically synchronizes the calculation cycle with the stroke cycle, as compared with the complicated control in the conventional sliding mode control. It is possible,
It is not affected by the aging of the system.
The consumption capacity of the OM and the RAM can also be reduced.

Note that, instead of the reference signal of the crank angle sensor, an in-cylinder pressure detection signal from an in-cylinder pressure sensor used for knocking detection or the like can be used. For example, a signal that increases at the compression top dead center is applied to each cylinder. It can be used as a signal for detecting a predetermined stroke time.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration and functions of the present invention.

FIG. 2 is a diagram showing a system configuration according to the embodiment of the present invention.

FIG. 3 is a control block diagram according to the embodiment;

FIG. 4 is a flowchart illustrating an air-fuel ratio feedback control routine according to the first embodiment.

FIG. 5 is a flowchart illustrating an air-fuel ratio feedback control routine according to a second embodiment.

FIG. 6 is a flowchart illustrating an air-fuel ratio feedback control routine according to a third embodiment.

[Explanation of symbols]

 11 Internal combustion engine 15 Fuel injection valve 16 Control unit 19 Air-fuel ratio sensor

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F02D 45/00 370 F02D 45/00 370Z G05B 13/00 G05B 13/00 A 21/02 21/02 Z F term (reference) 3G084 BA09 DA05 EB13 EC01 EC04 FA00 FA21 FA26 FA29 FA38 FA39 3G301 HA06 JA03 LA01 LB01 MA01 MA12 NA06 NA08 NA09 NB00 NB14 ND02 ND05 ND45 NE17 NE19 NE22 PA01Z PC01Z PC08Z PD04A PD04Z PE01Z PE03ZPE04H03 GA03H04 GA04 KA33 KA37 KA38 KA39 KA54 KA65 KA74 LA05 MA01

Claims (8)

[Claims] An apparatus for feedback controlling the air-fuel ratio of an internal combustion engine, comprising: air-fuel ratio detection means for detecting an air-fuel ratio based on a specific component in exhaust gas; Air-fuel ratio feedback control means for performing feedback control so that the air-fuel ratio approaches the target air-fuel ratio; feedback control amount calculation means for calculating a feedback control amount in the feedback control by sliding mode control; and feedback control amount calculation means An air-fuel ratio control device for an internal combustion engine, comprising: calculation cycle control means for controlling the calculation cycle so that the calculation by the calculation is performed in synchronization with the stroke cycle of the engine. 2. The feedback control amount calculating means calculates the feedback control amount by sliding mode control using a deviation between a target air-fuel ratio and an actual air-fuel ratio detected by the air-fuel ratio detecting means as a switching function. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein 3. The calculation cycle control means controls the calculation cycle of the feedback control amount by the feedback control amount calculation means to be a cycle that is a multiple of the stroke cycle of the engine. Or an air-fuel ratio control device for an internal combustion engine according to claim 2. 4. The system according to claim 1, wherein said calculation cycle control means variably controls a calculation cycle of the feedback control amount by said feedback control amount calculation means in accordance with an operation state of the engine. An air-fuel ratio control device for an internal combustion engine according to any one of the above. 5. The calculation cycle control means varies a calculation cycle of the feedback control amount by the feedback control amount calculation means according to a deviation between a target air-fuel ratio and an actual air-fuel ratio detected by the air-fuel ratio detection means. The air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 3, wherein the air-fuel ratio control device controls the air-fuel ratio. 6. The calculation cycle control means controls a calculation cycle so as to calculate the feedback control amount in synchronization with a signal for detecting a predetermined stroke timing of each cylinder. An air-fuel ratio control device for an internal combustion engine according to claim 5. 7. The air-fuel ratio control device for an internal combustion engine according to claim 6, wherein the signal for detecting the predetermined stroke timing of each cylinder is a reference signal output from a crank angle sensor. 8. The air-fuel ratio control device for an internal combustion engine according to claim 6, wherein the signal for detecting a predetermined stroke timing of each cylinder is a signal obtained by detecting an in-cylinder pressure.