JP2001263125A - Air-fuel ratio feedback control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the air-fuel ratio fluctuation in the purge cut of the evaporated fuel from a canister in a device for calculating a linear item and an integrated nonlinear item by sliding mode control to feedback control the air-fuel ratio to a target air-fuel ratio. SOLUTION: The nonlinear item UNL is calculated as UNL=(Gain 1)×(Actual air-fuel ratio - Target air-fuel ratio)/(|Actual air-fuel ratio - Target air-fuel ratio|)+Previous value UNL(OLD), the linear item UL is calculated as UL=(Gain 2)×(Actual air-fuel ratio - Target air-fuel ratio)/Actual air-fuel ratio, and the basic injection quantity is feedback-corrected with the added value of them. In the purge cut, an initialization of substituting the previous value UNL(OLD) by a prescribed value according to the target air-fuel ratio at that time is performed, so that the fuel corresponding to the target air-fuel ratio can be injected from just after the purge cut.

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 the air-fuel ratio of an internal combustion engine, and more particularly to a technique for feedback-controlling the air-fuel ratio of a combustion mixture to a target air-fuel ratio using sliding mode control.

[0002]

2. Description of the Related Art In an internal combustion engine for a vehicle, it is general to perform feedback control of an air-fuel ratio of a combustion mixture 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] Conventionally, a canister provided with an adsorbent such as activated charcoal adsorbs and collects evaporative fuel generated in a fuel tank of a vehicle and, under predetermined engine operating conditions, adsorbs and collects the canister. 2. Description of the Related Art There is known an evaporative fuel processing apparatus having a configuration in which fuel is purged and supplied to an intake system of an engine (for example, an intake collector).

[0006]

By the way, when the fuel adsorbed and collected in the canister is purged, the amount of fuel injected by the fuel injection valve is reduced by the amount supplied to the engine by the canister purge to reduce the target air-fuel ratio. When the purge is cut and the fuel supplied from the canister to the engine suddenly runs out as a result of feedback control to maintain the air-fuel ratio, the air-fuel ratio greatly shifts to the lean side during the feedback control response delay, causing a fluctuation. There was a problem of doing it.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and provides an apparatus for performing feedback control of an air-fuel ratio using sliding mode control, which can suppress air-fuel ratio fluctuations during purge cut with a simple configuration. The purpose is to:

[0008]

Therefore, the invention according to claim 1 is configured to calculate the air-fuel ratio feedback control amount including the linear term and the non-linear term integrated by the sliding mode control, and at the time of purging cut. ,
The non-linear term is configured to be initialized to a predetermined value.

According to this configuration, the nonlinear term due to the sliding mode control is integrated. When the purge is cut, the nonlinear term is initialized to a predetermined value, and the integration is sequentially performed from the initial value.

In the invention according to claim 2, the predetermined value is set as
The value was stored in advance for each target air-fuel ratio. According to this configuration, the non-linear term is initialized to a predetermined value selected according to the target air-fuel ratio at the time of cutting the purge, and is integrated sequentially from the initial value.

In the invention according to claim 3, the predetermined value is:
The calculation is performed according to the target air-fuel ratio. According to this configuration, the non-linear term is initialized to a predetermined value calculated according to the target air-fuel ratio at the time of the purge cut, and is sequentially integrated from the initial value.

According to a fourth aspect of the present invention, a linear term and a non-linear term are calculated by a sliding mode control using a deviation between the air-fuel ratio of the combustion air-fuel mixture and the target air-fuel ratio as a switching function. The non-linear term is calculated by integrating a feedback gain that can be switched between positive and negative according to.

With this configuration, each time the state of the air-fuel ratio crosses the switching line, the sign of the switching function is inverted, and the non-linear term, which is a value obtained by integrating the feedback gain whose sign is inverted, is calculated by the nonlinear term. The state is converged on the target air-fuel ratio while being restricted on the switching line.

According to the fifth aspect of the present invention, the absolute value of the feedback gain is variably set according to the engine operating state. According to this configuration, the engine load and
The nonlinear term of the air-fuel ratio feedback control amount is calculated using a feedback gain whose absolute value is variably set in accordance with the engine operating state such as the rotation speed.

In the invention according to claim 6, the linear term is:
The calculation is made as a value proportional to the ratio of the deviation to the air-fuel ratio of the combustion mixture. According to such a configuration,
As the state of the air-fuel ratio moves away from the switching line, a larger linear term is set in proportion to this.

[0016]

According to the first aspect of the present invention, the value of the non-linear term can be switched stepwise to a predetermined value suitable for the purge cut state at the time of purge cut, and the fluctuation of the air-fuel ratio at the time of purge cut can be suppressed. This has the effect.

According to the second aspect of the present invention, even if the target air-fuel ratio at the time of the purge cut is different, there is an effect that the target air-fuel ratio at that time can be controlled accurately around the target air-fuel ratio. Claim 3
According to the described invention, there is an effect that the nonlinear term can be initialized to a value corresponding to the target air-fuel ratio at the time of the purge cut while saving the memory capacity.

According to the fourth aspect of the invention, there is an effect that the air-fuel ratio can be constrained near the target air-fuel ratio and quickly converged to the target air-fuel ratio. According to the fifth aspect of the invention, it is possible to prevent the value of the nonlinear term from being excessively integrated during the detection delay time of the air-fuel ratio, and to reduce the amount of deviation of the actual air-fuel ratio from the target air-fuel ratio while ensuring responsiveness. Moderately small,
There is an effect that stable air-fuel ratio feedback control can be performed.

According to the sixth aspect of the present invention, there is an effect that convergence can be achieved quickly on the switching line toward the target air-fuel ratio while suppressing overshoot.

[0020]

Embodiments of the present invention will be described below. FIG. 1 is a system configuration diagram of an internal combustion engine according to the embodiment.

In FIG. 1, air is sucked into the combustion chamber of each cylinder of an internal combustion engine 1 mounted on a vehicle via an air cleaner 2, an intake passage 3, and an electronically controlled throttle valve 4 driven to open and close by a motor. Is done. An electromagnetic fuel injection valve 5 for directly injecting fuel (gasoline) into the combustion chamber of each cylinder is provided, and a mixture of air and fuel is injected into the combustion chamber by the fuel injected from the fuel injection valve 5 and the intake air. Is formed.

The fuel injection valve 5 is connected to the control unit 2
The solenoid is energized by an injection pulse signal output from 0 to open the valve and injects fuel adjusted to a predetermined pressure. The injected fuel diffuses into the combustion chamber in the case of the intake stroke injection to form a homogeneous mixture, and in the case of the compression stroke injection, forms a stratified mixture around the ignition plug 6. . The mixture formed in the combustion chamber is ignited and burned by the ignition plug 6.

However, the internal combustion engine 1 is not limited to the above-described direct injection gasoline engine, but may be an engine configured to inject fuel into the intake port. Exhaust gas from the engine 1 is discharged from an exhaust passage 7. An exhaust purification catalyst 8 is interposed in the exhaust passage 7.

Further, there is provided an evaporative fuel processing device for performing a combustion process on the evaporative fuel generated in the fuel tank 9. The canister 10 contains an adsorbent 11 such as activated carbon in a closed container.
And an evaporative fuel introduction pipe 12 extending from the fuel tank 9 is connected. Therefore, the fuel tank 9
The evaporative fuel generated in the above is guided to the canister 10 through the evaporative fuel introduction pipe 12, and is adsorbed and collected.

The canister 10 has a fresh air inlet 1
3, a purge pipe 14 is led out, and a purge control valve 15 whose opening and closing is controlled by a control signal from a control unit 20 is connected to the purge pipe 14.
Is interposed.

In the above configuration, when the purge control valve 15 is controlled to open, the suction negative pressure of the engine 1 acts on the canister 10, and the air introduced from the fresh air inlet 13 causes the adsorbent 11 of the canister 10 to act on the adsorbent 11 of the canister 10. The adsorbed fuel vapor is purged, and purge air is sucked into the intake passage 3 downstream of the throttle valve 4 through the purge pipe 14, and thereafter,
The combustion is performed in the combustion chamber of the engine 1.

The control unit 20 includes a CPU, R
A microcomputer including an OM, a RAM, an A / D converter, an input / output interface, and the like is provided. The microcomputer receives input signals from various sensors and performs arithmetic processing based on the signals.
The operation of the fuel injection valve 5, ignition plug 6, and purge control valve 15 is controlled.

As the various sensors, there are provided a crank angle sensor 21 for detecting a crank angle of the engine 1 and a cam sensor 22 for taking out a cylinder discrimination signal from a cam shaft. The rotation of the engine based on the signal from the crank angle sensor 21 is provided. The speed is calculated.

In addition, an air flow meter 23 for detecting the intake air flow rate Qa upstream of the throttle valve 4 in the intake passage 3,
An accelerator sensor 24 for detecting an accelerator pedal depression amount (accelerator opening) APS, an opening TV of the throttle valve 4
A throttle sensor 25 for detecting O, a water temperature sensor 26 for detecting the cooling water temperature Tw of the engine 1, a wide-range air-fuel ratio sensor 27 for linearly detecting the air-fuel ratio of the combustion mixture according to the oxygen concentration in the exhaust gas, and a vehicle speed VSP. Speed sensor 28 for detecting
And so on.

Here, the structure of the wide-range air-fuel ratio sensor 27 will be described with reference to FIG. Zirconia (ZrO
On a substrate 31 made of a solid electrolyte member such as 2), a + electrode 32 for measuring oxygen concentration is provided. Further, an air introduction hole 33 into which air is introduced is opened in the substrate 31,
A negative electrode 34 is attached to the air introduction hole 33 so as to face the positive electrode 32.

As described above, the oxygen concentration detecting section 35 is formed by the substrate 31, the positive electrode 32, and the negative electrode 34.
Further, an oxygen pump section 39 formed by providing a pair of platinum pump electrodes 37 and 38 on both surfaces of a solid electrolyte member 36 made of zirconia or the like is provided.

The oxygen pump section 39 is stacked above the oxygen concentration detecting section 35 via a spacer 40 formed in a frame shape of, for example, alumina, and the oxygen pump section 39 is disposed between the oxygen concentration detecting section 35 and the oxygen pump section 39. Is provided with a hollow chamber 41, and
Introducing holes 4 for introducing the exhaust of the engine into the hollow chamber 41
2 is formed on the solid electrolyte member 36 of the oxygen pump section 39.

The outer periphery of the spacer 40 is filled with an adhesive 43 made of glass to secure the hermeticity of the hollow chamber 41, and at the same time, the substrate 31 and the spacer 40 and the solid electrolyte 36.
Is fixed by bonding. Here, the spacer 4
Since the substrate 0 and the substrate 31 are simultaneously fired and bonded, the hermeticity of the hollow chamber 41 is ensured by bonding the spacer 40 and the solid electrolyte member 36. Further, the oxygen concentration detection unit 39 has a built-in heater 44 for warming up.

Then, the oxygen concentration of the exhaust gas introduced into the hollow chamber 41 through the introduction hole 42 is detected from the voltage of the + electrode 32. Specifically, an oxygen ion current flows in the substrate 31 according to the concentration difference between the oxygen in the atmosphere in the air introduction hole 33 and the oxygen in the exhaust gas in the hollow chamber 41, and accordingly, the positive electrode 32 Then, a voltage corresponding to the oxygen concentration in the exhaust gas is generated.

Then, according to the detection result, the hollow chamber 41
The value of the current flowing to the oxygen pump section 39 is variably controlled so as to keep the atmosphere in the chamber constant (for example, the stoichiometric air-fuel ratio), and the oxygen concentration in the exhaust is detected from the current value at that time.

More specifically, after the voltage of the positive electrode 32 is amplified by the control circuit 45, the voltage detection resistor 46
Is applied between the electrodes 37 and 38 to keep the oxygen concentration in the hollow chamber 41 constant.

For example, when detecting the air-fuel ratio in the lean region where the oxygen concentration in the exhaust gas is high, the outer pump electrode 3
A voltage is applied using 7 as an anode and the pump electrode 38 on the hollow chamber 41 side as a cathode. Then, oxygen (oxygen ion O ²⁻ ) proportional to the current is pumped out of the hollow chamber 41 to the outside. When the applied voltage exceeds a predetermined value, the flowing current reaches a limit value. By measuring the limit current value by the control circuit 45, the oxygen concentration in the exhaust gas, in other words, the air-fuel ratio can be detected.

Conversely, if the pump electrode 37 is used as a cathode and the pump electrode 38 is used as an anode to pump oxygen into the hollow chamber 41, detection can be performed in an air-fuel ratio rich region where the oxygen concentration in the exhaust gas is low.

The limit current is determined by the voltage detection resistor 46.
Is detected from the output voltage of the differential amplifier 47 for detecting the voltage between the terminals. When the predetermined air-fuel ratio feedback control condition is satisfied, the control unit 20 sets the air-fuel ratio (actual air-fuel ratio) detected by the air-fuel ratio sensor 27 to the target air-fuel ratio corresponding to the operating condition. The air-fuel ratio feedback control is performed by the sliding mode control according to the present invention.

FIG. 3 is a block diagram showing the air-fuel ratio feedback control by the sliding mode control. In the non-linear term calculation unit 101, a nonlinear term U _NL feedback control amount is calculated by the following equation.

U _NL = (gain 1) × (actual air-fuel ratio−target air-fuel ratio) / (| actual air-fuel ratio−target air-fuel ratio |) + _{UNL (OLD) In} the above equation, the gain 1 is predetermined. The fixed value, the target air-fuel ratio is the target value of the air-fuel ratio set according to the operating conditions at that time, and the actual air-fuel ratio is the actual air-fuel ratio at that time detected by the air-fuel ratio sensor 27, U _{NL (OLD)} Is the previous value of the nonlinear term _UNL .

In the sliding mode control in the present embodiment, the switching function S is set by the direct switching function method so that the switching function S = the actual air-fuel ratio−the target air-fuel ratio.
= 0 is the desired state, the actual air-fuel ratio = the target air-fuel ratio,
The direction of increase / decrease (positive / negative) of the feedback gain is switched every time the control line is crossed. Then, the nonlinear term _UNL is calculated as a value obtained by integrating the feedback gain for switching the increase / decrease direction (positive / negative) at the switching line S = 0.

[0043] Further, the linear term calculation unit 102, the linear term U _L of the feedback control amount is calculated by the following equation. _UL = (gain 2) × (actual air-fuel ratio−target air-fuel ratio) / actual air-fuel ratio In the above equation, the gain 2 is a predetermined fixed value.

[0044] Then, the linear term control amount U _L, a value obtained by adding the non-linear term control amount U _NL, and adds to the air-fuel ratio feedback correction coefficient median alpha (= 1.0), the addition result The limiter 103 performs limiter processing so as to be within the upper and lower limits, and outputs the final air-fuel ratio feedback correction coefficient α.

By multiplying the basic fuel injection amount Tp (basic fuel injection amount Tp corresponding to the stoichiometric air-fuel ratio) calculated according to the intake air amount and the engine speed by the air-fuel ratio feedback correction coefficient α, The fuel is injected by correcting the injection amount corresponding to the target air-fuel ratio to obtain a final fuel injection amount Ti and outputting an injection pulse signal having a pulse width corresponding to the fuel injection amount Ti to the fuel injection valve 5. Let it.

Further, a gain correction value calculating section 104 for correcting the gain 1 of the nonlinear term _UNL is provided in response to the detection delay time of the air-fuel ratio changing according to the intake air amount. Is corrected so that the smaller the intake air amount for which the delay time becomes longer, the smaller the absolute value.

Further, there is provided a non-linear term initialization section 106 for initializing the non-linear term _UNL to a predetermined value according to the judgment result of the purge cut judgment section 105. The purge cut determination unit 105 determines the timing of cutting the purge by closing the purge control valve 15 from the state where the purge from the canister 10 is performed by controlling the opening of the purge control valve 15. When the purge control valve 15 is switched from open to closed, the purge cut signal is transmitted to the non-linear term initialization unit.
Output to 106.

Upon receiving the purge cut signal, the non-linear term initialization section 106 generates the non-linear term U _NL (previous value U _NL ).
_{NL (OLD)} ) is switched to a predetermined value. The predetermined value is set to a value corresponding to the target air-fuel ratio at the time of the purge cut. Specifically, the purge cut is performed by referring to a table in which the predetermined value is stored in advance for each target air-fuel ratio. Find a value according to the target air-fuel ratio at the time, or
The predetermined value is determined by calculation based on the target air-fuel ratio at the time of the purge cut.

At the time of the purge cut, the purge fuel from the canister 10 which has been supplied to the engine 1 is cut off, thereby causing a lean variation in the air-fuel ratio during the response delay of the feedback control. Therefore, the variation of the air-fuel ratio is suppressed by changing the nonlinear term _UNL stepwise to a basic value at which the target air-fuel ratio can be obtained when the purge is stopped.

The flowchart of FIG.
_This shows an embodiment in which initialization control of _NL (previous value U _{NL (OLD)} ) is performed by referring to a table stored in advance. In step S1, a purge cut (switching of the purge control valve 15 from open to closed) is performed. ), And if it is not during the purge cut, the process proceeds to step S2, where the nonlinear term U _NL is calculated normally using the previous value U _{NL (OLD)} as it is.

On the other hand, if it is the time of the purge cut, step S
If it is determined in step 1, the process proceeds to step S3 to determine whether or not it is the first time after the purge cut determination. If it is not the first time, the process proceeds to step S2. If it is the first time, the process proceeds to step S4.

In step S4, a basic value corresponding to the target air-fuel ratio at the time of purge cut is searched by referring to a table in which the basic value of the nonlinear term _UNL is stored in advance for each target air-fuel ratio. Initialization is performed to replace the previous value _{UNL (OLD)} . As shown in FIG. 4, the basic value of the nonlinear term _UNL is 0 when the target air-fuel ratio is the stoichiometric air-fuel ratio, is larger on the rich side than the stoichiometric air-fuel ratio, and is larger on the lean side. Is set to be small.

The flowchart of FIG.
_This shows an embodiment in which initialization control of _NL (previous value U _{NL (OLD)} ) is performed by calculation according to the target air-fuel ratio, and only the processing content of step S4A is different from the flowchart of FIG.

In step S4A, the non-linear term U _NL is calculated as non-linear term U _NL = (14.7 / target air-fuel ratio) −1, and the value of the non-linear term U _NL calculated by the above equation is added to the previous value U _NL. Perform initialization to replace _(OLD) .

[0055] Note that the nonlinear term U _NL computed according to the target air-fuel ratio in the above formula, the same value from the nonlinear term U _NL retrieved from the target air-fuel ratio in step S4 in the flowchart of FIG. 4.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of an internal combustion engine according to an embodiment.

FIG. 2 is a diagram illustrating an air-fuel ratio sensor and peripheral circuits according to the embodiment.

FIG. 3 is a control block diagram showing air-fuel ratio feedback control in the embodiment.

FIG. 4 is a flowchart illustrating initialization control of a nonlinear term during purge cut according to the embodiment.

FIG. 5 is a flowchart illustrating initialization control of a nonlinear term during purge cut according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 3 ... Intake path 4 ... Throttle valve 5 ... Fuel injection valve 6 ... Spark plug 9 ... Fuel tank 10 ... Canister 14 ... Purge piping 15 ... Purge control valve 20 ... Control unit 27 ... Air-fuel ratio sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (reference) F02D 45/00 301 F02D 45/00 301L F02M 25/08 301 F02M 25/08 301J 301U F term (reference) 3G044 BA08 CA13 DA02 EA03 FA08 GA02 GA08 GA11 GA22 3G084 BA09 CA00 DA08 EB14 EB15 EC03 FA07 FA10 FA20 FA29 FA33 FA38 3G301 HA01 HA04 HA14 HA16 JA06 JA07 JA12 JA13 LA03 LB04 MA12 NA03 NA04 ND05 PA01Z PA11Z PB03ZPBZZ01 PDBZZ

Claims (6)

[Claims] An internal combustion engine provided with an evaporative fuel processing device configured to adsorb and collect evaporative fuel generated in a fuel tank in a canister and supply fuel purged from the canister to an intake system of the engine. An air-fuel ratio feedback control device that feedback-controls an air-fuel ratio of a combustion air-fuel mixture to a target air-fuel ratio, while calculating an air-fuel ratio feedback control amount including a linear term and a non-linear term integrated by sliding mode control, An air-fuel ratio feedback control device for an internal combustion engine, wherein the nonlinear term is initialized to a predetermined value when the purge is cut. 2. The air-fuel ratio feedback control device for an internal combustion engine according to claim 1, wherein the predetermined value is a value stored in advance for each target air-fuel ratio. 3. The air-fuel ratio feedback control device for an internal combustion engine according to claim 1, wherein said predetermined value is calculated according to a target air-fuel ratio. 4. A linear mode and a non-linear term are calculated by sliding mode control using a deviation between an air-fuel ratio of a combustion air-fuel mixture and a target air-fuel ratio as a switching function, and the sign is switched according to the sign of the switching function. The air-fuel ratio feedback control device for an internal combustion engine according to any one of claims 1 to 3, wherein the feedback term is integrated to calculate the nonlinear term. 5. An air-fuel ratio feedback control device for an internal combustion engine according to claim 4, wherein an absolute value of said feedback gain is set variably according to an engine operating state. 6. An air-fuel ratio feedback control system for an internal combustion engine according to claim 4, wherein said linear term is calculated as a value proportional to a ratio of said deviation to an air-fuel ratio of a combustion air-fuel mixture.