JP2002371890A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device for an internal combustion engine capable of simultaneously keeping the drivability by preventing the air-fuel ratio shock, and improving the exhausting air characteristic. SOLUTION: This air-fuel ratio control device is provided with an air-fuel ratio feedback control coefficient calculating means for calculating a correction coefficient of the air-fuel ratio feedback control on the basis of the output of an air-fuel ratio sensor mounted on an exhausting system of the internal combustion engine, and an air-fuel ratio feedback control means for feedback controlling the air-fuel ratio of a air-fuel mixture fed to the internal combustion engine on the basis of the correction coefficient. This device further comprises a feedback gain adjusting means for adjusting the feedback gain of the correction coefficient when the correction coefficient reaches a predetermined upper limit threshold value or a lower limit threshold value, and both of the prevention of the air-fuel ratio shock and the improvement of the exhausting characteristic can be simultaneously achieved by changing the feedback gain to a smaller value when the correction coefficient is over the upper and lower threshold values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly to an air-fuel ratio control device for performing appropriate feedback control for preventing a shock due to a sudden change in the air-fuel ratio.

[0002]

2. Description of the Related Art In the air-fuel ratio control of an internal combustion engine, the air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine is controlled in accordance with the output of an air-fuel ratio sensor disposed in the exhaust system of the internal combustion engine. Maintaining good exhaust characteristics is ensured.

However, if the air-fuel ratio feedback coefficient is changed in accordance with the sudden change in the output of the air-fuel ratio sensor, a shock due to the sudden change in the output (air-fuel ratio shock) may occur and drivability may be reduced. Therefore, a method for preventing the air-fuel ratio shock by providing a limit to the feedback coefficient and preventing the feedback coefficient from changing beyond the limit value has been conventionally known.

Japanese Patent Publication No. 7-117000 discloses an air-fuel ratio feedback control in which the fuel vapor in the fuel tank is supplied during the operation of the internal combustion engine. In order to prevent the correction, a method of increasing the limit of the air-fuel ratio correction coefficient as the fuel tank internal pressure increases is disclosed.

[0005]

In the above-mentioned prior art, if the fuel injection amount is corrected by updating the feedback coefficient, the improvement of the exhaust gas characteristics is expected. Is stopped in a range narrower than the actual feedback limit (that is, the limit value), so that further improvement in exhaust gas characteristics cannot be expected. In order to address this problem, for example, even if the method of increasing the limit value disclosed in Japanese Patent Publication No. 7-117000 is applied, simply increasing the limit of the air-fuel ratio correction coefficient improves the exhaust gas characteristics, Fuel ratio shock cannot be prevented.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine which can maintain drivability and improve exhaust characteristics by preventing air-fuel ratio shock.

[0007]

According to one aspect of the present invention, there is provided an air-fuel ratio feedback control coefficient calculating means for calculating a correction coefficient for feedback control based on an output of an air-fuel ratio sensor provided in an exhaust system of an internal combustion engine; Air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine based on the correction coefficient, wherein the correction coefficient is a predetermined upper threshold value. Alternatively, there is provided an air-fuel ratio control device for an internal combustion engine further including a feedback gain adjusting means for adjusting a feedback gain of the correction coefficient when a lower threshold value is reached.

According to this aspect, in the air-fuel ratio feedback control, there is provided a feedback gain adjusting means for resetting the feedback gain even when the feedback correction coefficient reaches a threshold value provided for preventing the air-fuel ratio shock. As a result, the air-fuel ratio feedback is continued without stopping the update of the feedback correction coefficient, so that it is possible to improve the exhaust characteristics without deteriorating the followability of the air-fuel ratio and to prevent the air-fuel ratio shock.

[0009]

FIG. 1 is a diagram showing the overall configuration of an internal combustion engine (hereinafter referred to as an engine) provided with an air-fuel ratio control device according to an embodiment of the present invention.

A throttle valve 3 is disposed in the intake pipe 2 leading to the engine 1. A throttle valve opening (TH) sensor 4 is connected to the throttle valve 3, and outputs an electric signal corresponding to the opening of the throttle valve 3 and supplies it to an electronic control unit (hereinafter referred to as an ECU) 5. ECU5
Will be described later.

A fuel injection valve 6 is provided in the intake pipe 2 between the engine 1 and the throttle valve 3. Fuel injection valve 6 is E
It is electrically connected to CU5, and the valve opening time of fuel injection is controlled by a signal from ECU5. The injected fuel is mixed with air from the intake pipe 2 to form an air-fuel mixture, which is supplied to the engine 1.

The absolute pressure in the intake pipe is located downstream of the throttle valve 3.
A (PBA) sensor 7 is attached, detects an absolute pressure, and supplies it to the ECU 5 as an electric signal.

The engine 1 is provided with an engine cooling water temperature (TW) sensor 10. The TW sensor 10 is composed of a thermistor or the like, is mounted in the peripheral wall of the engine cylinder filled with cooling water, and supplies a detected water temperature signal to the ECU 5.

The engine 1 further includes an engine speed (NE)
A sensor 11 and a cylinder determination (CYL) sensor 12 are mounted. The engine speed sensor 11 outputs a pulse at a predetermined crank angle position every 180 degree rotation of the crankshaft of the engine 1.
(Hereinafter referred to as TDC pulse signal), and the cylinder determination sensor 1
2 outputs a signal pulse at a predetermined crank angle position of a specific cylinder. Both pulses are supplied to the ECU 5.

The catalytic converter 14 is an exhaust pipe 13 of the engine 1.
And purifies components such as HC, CO, and NOx in the exhaust gas. An oxygen concentration sensor 15 (hereinafter, referred to as an O2 sensor) is provided as an air-fuel ratio sensor in an exhaust pipe on the upstream side of the catalytic converter. The O2 sensor 15 detects the oxygen concentration in the exhaust gas, outputs an electric signal according to the detected value, and supplies the electric signal to the ECU 5.

The ECU 5 is composed of a computer, which stores a ROM for storing programs and data, a RAM for storing programs and data required at the time of execution to provide a calculation work area, a CPU for executing programs, and a CPU for receiving various programs. It has an input interface for processing input signals, and a drive circuit for sending control signals to valves and the like.
The signals from each of the above-mentioned sensors are received by the input interface and processed according to a program stored in the ROM. In FIG. 1, the ECU 5 is shown by functional blocks based on such a hardware configuration.

The ECU 5 includes functional blocks of an operating state detection unit 21, a feedback correction coefficient calculation unit 22, a correction coefficient determination unit 23, a feedback gain adjustment unit 24, and a feedback control unit 25.

The operating state detector 21 determines various operating states of the engine 1 based on the output of each sensor signal.

The feedback correction coefficient calculation unit 22 determines a feedback control operation area, an open loop control operation area, and the like based on various engine parameter signals such as an engine coolant temperature, an engine speed, an engine load state, and an O2 sensor activation state. Various engine operating conditions are determined, and a feedback correction coefficient KO2 is calculated by a KO2 calculation subroutine described later with reference to FIG.

The correction coefficient determining unit 23 calculates the calculated correction coefficient.
It is determined whether or not KO2 has exceeded a predetermined threshold. If not, the correction coefficient KO2 is sent to the feedback control unit 25. If it exceeds the threshold, control is passed to the feedback gain adjustment unit 24.

The feedback gain adjuster 24 recalculates the correction coefficient KO2 using a smaller gain than usual as the feedback gain.

The feedback control unit 25 receives the correction coefficient from the correction coefficient determination unit 23 or the feedback gain adjustment unit 24.
KO2 is received, and the fuel injection time Tout of the fuel injection valve 6 is calculated by the following equation in synchronization with the TDC signal pulse.

[0023]

[Equation 1] Tout = Ti × KO2 × K1 + K2 (1)

Here, Ti is a basic fuel injection time, and is determined by searching a predetermined Ti map according to the engine speed NE and the intake pipe absolute pressure PBA, for example. Also
K1 and K2 are other correction coefficients and correction variables calculated in accordance with various engine parameter signals, respectively, so that various characteristics such as fuel consumption characteristics and engine acceleration performance according to the engine operating state can be optimized. Is set to an appropriate value. The feedback control unit 25 supplies a drive signal for opening the fuel injection valve 6 to the fuel injection valve 6 based on the calculated TOUT.

FIG. 2 shows a flowchart of a subroutine for calculating the feedback correction coefficient KO2. This subroutine is executed every time a TDC signal pulse is generated in synchronization with the pulse.

First, in step 201, the O2 sensor 15
It is determined whether or not activation has been completed. Specifically, the O2 sensor 15
Is detected whether or not the output voltage has reached the activation start point Vx (for example, 0.6 V), and when the output voltage has reached Vx, it is determined that it is activated. If the determination in step 201 is NO, that is, if the activation of the O2 sensor 15 has not been completed, KO2 is set to 1.0 in step 202, and this process ends. If the determination in step 201 is YES, that is, if the activation has been completed, it is determined in step 203 whether or not the engine 1 is operating in the open-loop control operation region. The open loop control operation region refers to a full load region, a low rotation speed region, a high rotation speed region, a lean air-fuel mixture region, and the like of the internal combustion engine. If the operation is being performed in the open control operation region, the process proceeds to step 202, where KO2 is set to 1.0 and the process ends.

If it is determined in step 203 that the operation state of the engine 1 is in the feedback control operation region, feedback control is executed. In this case, the process proceeds to step 204, where it is determined whether or not the output level of the O2 sensor 15 has been inverted. In the case of YES, that is, when the output level of the O2 sensor is inverted, proportional control (P term control) is performed in the subsequent steps.

First, in step 205, it is determined whether or not the output level of the O2 sensor 15 is at a low level (LOW).
When it is at the low level, the NE-tPR table stored in a memory (not shown) in the ECU 5 is searched to obtain a predetermined time tPR corresponding to the engine speed NE (206). The predetermined time tPR is for keeping the application period of the second correction value PR, which will be described later, constant over the entire engine speed range, and is therefore set to a smaller value as the engine speed NE increases.

Next, it is determined whether a predetermined time tPR has elapsed since the last application of the second correction value PR (207). Steps
If the determination in 207 is YES, that is, when tPR has elapsed, the engine speed is obtained from the NE-PR table stored in the memory.
A second correction value PR (208) corresponding to NE is obtained. Step 207
Is NO, that is, when the predetermined time tPR has not elapsed, the NE-P table stored in the memory separately from the NE-PR table is searched to find the engine speed NE.
A first correction value P corresponding to is obtained (209). The first correction value P is set to a value smaller than the second correction value PR.

Next, the correction coefficient KO2 is calculated by adding the proportional term feedback gain Pi, ie, the first correction value P or the second correction value PR, to the correction coefficient KO2 (210).

In step 205, if the output of the O2 sensor 15 is not LOW, the first correction value P corresponding to the engine speed NE is obtained from the NE-P table as in step 209 (21).
1) The correction value (proportional term feedback gain) P is subtracted from the correction coefficient KO2 to calculate the correction coefficient KO2 (212).

In step 213, it is determined whether the calculated correction coefficient KO2 exceeds a predetermined upper limit value KO2PH. If exceeded, KO2 is set to the upper limit (21
Four). If it is less than or equal to the upper limit value, then the predetermined lower limit value KO2P
It is determined whether it is less than L (215). If so, KO2 is set to the lower limit (216). Above the lower limit, KO2 remains the same. in this way,
In the proportional control, the correction coefficient KO2 undergoes a limit check.

Subsequently, in step 217, step 210
Or calculated in 212, or in step 214 or
Using the value of the correction coefficient KO2 set to the upper and lower limit values in 216, an average value KREF of KO2 is calculated by the following equation, stored in a memory (not shown), and the process ends. The average value KREF is calculated for each operation region of the feedback control operation region corresponding to the current loop, based on a KREF calculation subroutine (not shown).

[0034]

KREFn = Cn × KO2P + (1−Cn) × KREFn ′ Here, the value KO2P is the value immediately before or immediately after the operation of the proportional term (P term).
The value of KO2, Cn, is a variable (0 <Cn <1) that is set to an appropriate value by experiment for each operation region, and KREFn 'is obtained up to the previous time in the operation region to which this loop corresponds. This is the average value of KO2P.

The value of KO2P during each P-term operation depends on the value of variable Cn.
Since the ratio with respect to KREFn changes, that is, the calculation speed of the average value KREFn changes, the optimum KREFn is set by setting this Cn value to an appropriate value according to the specifications of the target air-fuel ratio feedback device and the engine and the like. Can be obtained.

Referring again to FIG. 2, when the result of the determination in step 204 is NO, that is, when the output level of O2 sensor 15 is not inverted, integral control (I-term control) is executed in step 218 and subsequent steps. become. First, step 20
Similarly to 5, the output level of the O2 sensor 15 becomes low (LO
W) is determined (218). If the determination in step 218 is YES, that is, if the output level of the O2 sensor 15 is low, the TDC signal pulse is counted (219), and it is determined whether or not the count number NIL has reached a predetermined value NI. (220).

If NO at step 220, the correction coefficient KO2 is held at the value immediately before it (221). If YES, a new correction coefficient KO2 is calculated by adding a predetermined integral term feedback gain Δk to the correction coefficient KO2 (222).

In step 223, an upper limit threshold value KO2IH during feedback control of the feedback correction coefficient KO2 is set.
This threshold is provided to prevent shock due to a sudden change in the air-fuel ratio, and is set to a value smaller than the actual feedback limit. This KO2IH may be a preset value or may be obtained by searching a map for a value corresponding to the driving state.

Subsequently, it is determined whether the correction coefficient KO2 calculated in step 222 is larger than the upper threshold value KO2IH (224). If the determination in step 224 is NO, that is, if it is equal to or smaller than the upper threshold value, the correction coefficient KO2 is left as it is, and the process proceeds to step 226. The judgment in step 224 is YE
In the case of S, that is, if it is larger than the upper threshold, a slower than usual gain is used instead of the integral term feedback gain Δk. Specifically, the feedback correction coefficient KO2 is calculated again by the following equation (225).

[0040]

[Equation 3] KO2 = KO2 + Δk × KIH

Here, KIH is a coefficient for reducing the integral term feedback gain, and is set in advance in the range of 0 <KIH <1. Alternatively, KIH may be set by searching a value corresponding to the driving state from a map.

When the value of the correction coefficient KO2 is finally determined,
The count number NIL is reset to 0 (226). In this way, when the output of the O2 sensor 19 maintains the lean level, the correction coefficient KO2 is increased every time the TDC signal pulse is generated NI times (that is, each time the count number NIL reaches NI) in a direction to correct the lean level. The integration control is executed by adding Δk or Δk × KIH.

If the answer is NO in step 218, T
The number of DC signal pulses is counted (227), and the counted number N
It is determined whether or not IH has reached a predetermined value NI (228). If the determination in step 228 is NO, the correction coefficient KO2 is held at the value immediately before (234). If the determination in step 228 is YES, the predetermined value Δk is subtracted from the correction coefficient KO2 (22
9).

In step 230, a lower limit threshold value KO2IL of the feedback correction coefficient KO2 during integration control is set.
Similarly to the upper threshold value KO2IH described above, this KO2IL may be a preset value or may be obtained by searching a map for a value corresponding to the operating state.

Subsequently, it is determined whether the feedback correction coefficient KO2 calculated in step 229 is smaller than the lower threshold value KO2IL (231). If the determination in step 231 is NO,
That is, if it is not less than the lower threshold, the value of KO2 is left as it is, and the routine proceeds to step 233. If the determination in step 231 is YES, that is, if it is smaller than the lower threshold,
A gain slower than usual is used instead of the integral term feedback gain Δk. Specifically, the feedback correction coefficient KO2 is calculated again by the following equation (232).

[0046]

[Formula 4] KO2 = KO2-Δk × KIL

KIL is a coefficient for reducing the feedback gain, which is set in advance in the range of 0 <KIL <1 as in KIH, or set by searching a value corresponding to the operating state from a map. Is done.

When the value of the correction coefficient KO2 is determined, the count number NIH is reset to 0 (233). In this way, O2
When the output of the sensor 19 maintains the rich level, every time the TDC signal pulse is generated NI times in the direction of correcting the rich level (that is, each time the count number NIH reaches the predetermined value NI), the correction coefficient KO2 is changed to Δk or Δk. × Integral control is executed by subtracting KIL.

As described above, in the integral control, unlike the proportional control, when the correction coefficient KO2 becomes larger than the upper threshold value or becomes smaller than the lower threshold value, the feedback gain is reduced. The value is reset to a value smaller than usual, and updating of the feedback correction coefficient is continued.

FIG. 3 is a diagram comparing control by the conventional method and control by the present embodiment. In FIG. 3, (1)
2 shows the case where the feedback control according to the conventional method of limiting the correction coefficient is applied, and (2) shows the case where the feedback control according to the present embodiment shown in FIG. 2 is applied. In each of (1) and (2), (a) shows the transition of the feedback correction coefficient, and (b) shows the actual air-fuel ratio of the air-fuel mixture supplied to the engine 1.

In the control (1) of the conventional method, when the feedback correction coefficient KO2 reaches the lower threshold value KO2L at the time point A, the calculated KO2 exceeds the lower threshold value (B).
Since the air-fuel ratio is temporarily set to the rich side temporarily, the exhaust characteristic deteriorates.

On the other hand, in the control (2) according to the present embodiment, even when the feedback correction coefficient KO2 reaches the lower limit threshold value KO2L at time point A, the feedback gain is reset to a small value, but the correction coefficient KO2 is continuously updated I do. Therefore, as compared with the conventional method (1), the air-fuel ratio rich amount is greatly reduced, and it can be seen that deterioration of the exhaust characteristics can be suppressed.

[0053]

According to the present invention, even when the feedback correction coefficient reaches a threshold value provided for preventing air-fuel ratio shock, the feedback correction coefficient is updated using a smaller gain than usual as the feedback gain. Since the air-fuel ratio feedback is continued without stopping,
The exhaust characteristics can be improved without deteriorating the followability of the air-fuel ratio, and the air-fuel ratio shock can be prevented by suppressing a sudden change in the feedback correction coefficient.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an internal combustion engine including an air-fuel ratio control device according to an embodiment of the present invention.

FIG. 2 is a flowchart of a subroutine for calculating a feedback correction coefficient KO2.

FIG. 3 (1) is a diagram showing transitions of a feedback correction coefficient (a) and an actual air-fuel ratio (b) in conventional feedback control, and (2) is a feedback correction coefficient (a) in feedback control according to the present invention. FIG. 3) is a diagram showing changes in the actual air-fuel ratio (b).

[Explanation of symbols]

 1 Internal combustion engine (engine) 5 Electronic control unit (ECU) 6 Fuel injection valve 11 Engine speed sensor 15 Air-fuel ratio sensor 21 Operating state detection unit 22 Feedback correction coefficient calculation unit 24 Feedback gain adjustment unit 25 Feedback control unit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takashi Isobe 1-4-1, Chuo, Wako, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Tetsuya Ohno 1-4-1, Chuo, Wako, Saitama Inside of Honda R & D Co., Ltd. F-term in Honda R & D Co., Ltd. (reference) 3G084 BA09 DA10 DA12 EA11 EB08 EB13 FA10 FA11 FA20 FA38 FA39 3G301 JA04 JA21 LB02 MA01 NC01 NC02 ND05 NE17 NE19 PA07Z PA11Z PD02A PD02Z PE03Z PE05Z PE08Z

Claims (1)

[Claims] 1. An air-fuel ratio feedback control coefficient calculating means for calculating a correction coefficient for air-fuel ratio feedback control based on an output of an air-fuel ratio sensor provided in an exhaust system of an internal combustion engine, and an air-fuel mixture supplied to the internal combustion engine. And an air-fuel ratio feedback control means for performing feedback control of the air-fuel ratio of the internal combustion engine based on the correction coefficient, wherein the correction coefficient reaches a predetermined upper threshold value or a lower threshold value. An air-fuel ratio control device for an internal combustion engine, further comprising a feedback gain adjusting means for adjusting a feedback gain of the correction coefficient.