JP3074408B2 - Engine air-fuel ratio control device - Google Patents

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 engine in which a linear air-fuel ratio sensor is provided upstream of a catalyst device provided in an exhaust passage and a λ air-fuel ratio sensor is provided downstream.

[0002]

2. Description of the Related Art An O ₂ sensor is provided in an exhaust passage of an engine, and it is determined whether the air-fuel ratio of the engine is rich or lean based on whether a detection signal of the O ₂ sensor is higher or lower than a predetermined slice level. An air-fuel ratio control device for an engine that performs feedback control of the air-fuel ratio of the engine based on the determination is conventionally known. In such air-fuel ratio control apparatus, O as ₂ sensor, although the stoichiometric air-fuel ratio output voltage as a boundary is usually to use a .lamda.o ₂ sensor having a characteristic of switching on and off, for example lean burn (Riban) In order to realize the above, a linear O ₂ having a characteristic that the output voltage changes linearly with respect to the air-fuel ratio
Sometimes a sensor is used. In that case, the linear O
_{The two} sensors are arranged as close as possible to the combustion chamber on the upstream side of the catalyst device provided in the exhaust passage.

Incidentally, the linear O ₂ sensor requires calibration because of large variations among the sensors. Therefore, it has been proposed to calibrate the linear O ₂ sensor by comparing it with the output of a λO ₂ sensor provided downstream of the catalyst device. The λO ₂ sensor has a stoichiometric air-fuel ratio of 1
Because accurately detect 4.7, .lamda.o ₂ sensor can detect the displacement of the linear O ₂ sensor by viewing the output of the linear O ₂ sensor when detecting the 14.7. Note that λ
O is a _two sensor which was used in the air-fuel ratio detection, for example, in JP-61-234241 discloses, in addition to the upstream side of the catalytic converter is provided separately O ₂ sensor in the downstream side, O ₂ sensor of the downstream A so-called double O ₂ sensor system has been proposed in which the control characteristic of the air-fuel ratio feedback control by the upstream O ₂ sensor is corrected by the output of the sensor.

[0004]

However, in the case of an air-fuel ratio control device using a linear O ₂ sensor, the above-mentioned double O ₂ sensor system cannot be applied as it is, and the λO _{Even if two} sensors are provided and the linear O ₂ sensor is calibrated by comparing with the output,
Due to the effect of the O ₂ storage effect of the catalyst device, the output difference between the upstream and downstream O ₂ sensors is slightly affected by the degree of deterioration of the catalyst, which makes it difficult to perform accurate calibration. there were. That is, the timing at which the linear O ₂ sensor and the λO ₂ sensor detect the same air-fuel ratio is shifted due to the O ₂ storage effect of the catalyst device.
_{Even if two} sensors detect an air-fuel ratio of 14.7, the linear O
₂ Sensors may detect different air-fuel ratios,
There is a concern about incorrect calibration.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is intended for use in calibrating a linear air-fuel ratio sensor provided upstream of a catalyst device with a λ air-fuel ratio sensor provided downstream.
An object of the present invention is to prevent an erroneous calibration from being performed by a purifying action of a catalyst device.

[0006]

According to the present invention, the responsiveness of feedback control is deliberately deteriorated, and the air-fuel ratio fluctuation is increased in the same manner as the responsiveness of the linear air-fuel ratio sensor upstream of the catalytic converter is deteriorated. Then, paying attention to the point that the O ₂ storage effect of the catalyst device cannot be sufficiently obtained and the effect of the catalytic action will not be obtained, creating a situation where the air-fuel ratio fluctuation before the catalyst becomes large when the linear air-fuel ratio sensor is calibrated This enables accurate calibration of the sensor, and the configuration is as shown in FIG. That is, an air-fuel ratio control device for an engine according to the present invention includes a linear air-fuel ratio sensor provided upstream of a catalyst device provided in an exhaust passage of the engine, and a λ air-fuel ratio sensor provided downstream of the catalyst device. An air-fuel ratio control device for controlling the air-fuel ratio of the engine to a target air-fuel ratio based on the output of the linear air-fuel ratio sensor. Purification of catalyst device due to large fluctuation in fuel ratio
Control constant changing means for changing the control constant of the feedback control by the air-fuel ratio feedback control means so as to protrude beyond the window; and linear air based on the output of the λ air-fuel ratio sensor when the control constant is changed by the control constant changing means. A linear air-fuel ratio sensor output calibrating means for calibrating the output of the fuel ratio sensor is provided.

Here, the control constant to be changed in order to increase the fluctuation of the air-fuel ratio is a feedback delay which delays the judgment of the output of the air-fuel ratio sensor, and the control delay is increased by the control constant changing means when the linear air-fuel ratio sensor is calibrated. Is good.

[0008]

When the linear air-fuel ratio sensor is calibrated, for example, a feedback delay that delays the determination of the output of the air-fuel ratio sensor is added to increase the swing width of the air-fuel ratio fluctuation of the exhaust gas flowing into the catalyst device, thereby increasing the purification window of the catalyst device. Protruding
In this way, the output of the linear air-fuel ratio sensor is calibrated based on the output of the λ air-fuel ratio sensor obtained at that time. By doing so, the output difference between the air-fuel ratio sensors on the upstream and downstream sides of the catalyst device is accurately set without being affected by the purification action of the catalyst device, and thereby the calibration of the linear air-fuel ratio sensor is performed accurately. Will be

[0009]

Embodiments will be described below with reference to the drawings.

FIG. 2 is an overall system diagram of an embodiment of the present invention. In this embodiment, an intake valve 4 for opening and closing an intake port 3 and an exhaust valve 6 for opening and closing an exhaust port 5 are arranged in a combustion chamber 2 of the engine 1. An intake passage 7 of the engine 1 is provided with an injector 8 for fuel injection near the intake port 3, a throttle valve 10 upstream of the surge tank 9, and furthermore, an intake air amount upstream of the surge tank 9. Air flow sensor 11 for measuring
Is provided. The upstream side of the air flow sensor 11 is connected to an air cleaner 12.

An exhaust passage 13 connected to the exhaust port 5 is provided with a catalyst device 14 for purifying exhaust gas. An upstream side (front side) and a downstream side (rear side) of the catalyst unit 14 are provided with an exhaust gas. A linear O ₂ sensor 15 and a λO ₂ sensor 16 for detecting oxygen concentration are provided. Here, the linear O ₂ sensor 15 detects the air-fuel ratio (A /
F) has the characteristic that the output voltage changes linearly with the change of F), while the λO ₂ sensor 16 has the characteristic that the output voltage switches on and off at the stoichiometric air-fuel ratio (A / F = 14.7). Have

The combustion air enters the intake passage 7 from the air cleaner 12 and is sucked into the combustion chamber 2 through the intake valve 4 together with the fuel injected by the injector 8. Also,
The exhaust gas after the combustion flows out into the exhaust passage 13 through the exhaust port 5 and is discharged through the catalyst device 14.

The injector 8 is controlled by a control unit 17 constituted by a microcomputer. The control unit 17 includes an intake air amount signal from the air flow sensor 11, an engine speed signal from a crank angle sensor 18 attached to the distributor, a water temperature signal from a water temperature sensor 19 provided in a cooling water jacket of the engine 1, output signals of the linear O ₂ sensor 15 and .lamda.o ₂ sensor 16 are inputted. And
The fuel injection amount and the like are calculated based on the calculated values and output to the injector 8 and the like.

The control of the air-fuel ratio of the engine of this embodiment is as follows.
This is performed by performing feedback control of the fuel injection amount based on the output of the linear O ₂ sensor 15 disposed on the front side of the catalyst device 14. That is, the amount of fuel injection is basically the amount of intake air detected by the air flow sensor 11, is set based on the engine speed calculated from the crank angle signal, the linear O ₂ sensor 15
Is determined based on whether the output is higher or lower than a predetermined slice level, and the feedback correction amount of the fuel injection amount is calculated based on the determination.

The output of the linear O ₂ sensor 15 is, for example, every time the engine starts and runs once.
Is calibrated by the output of the λO ₂ sensor 16 disposed on the rear side of the sensor. This calibration was performed by forcibly increasing the feedback delay of the air-fuel ratio detection by the linear O ₂ sensor 15, thereby increasing the period and amplitude of the air-fuel ratio fluctuation on the front side of the catalyst device 14. calibrating the linear O ₂ sensor 15 based on the output difference of the linear O ₂ sensor 15 and .lamda.o ₂ sensor 16.

FIGS. 3 and 4 show the control characteristics at the time of performing the above-mentioned calibration. FIG. 3 (a) shows the output characteristics of the linear O ₂ sensor 15 during normal feedback control. FIG. 4B shows the corrected output characteristics of the sensor 15 at the time of calibration, respectively.
4A shows the output characteristics of the air-fuel ratio (A / F) corresponding to the sensor output, and FIG. 4B shows the output characteristics of the air-fuel ratio when the sensor 15 is calibrated. FIG.
(A) and (b) show the purification window of the catalyst device 14 by two parallel straight lines. Linear O ₂ sensor 1
When the feedback delay is forcibly increased during the calibration of 5, the period of the sensor output becomes longer as shown in FIG. 3 (b), and the fluctuation of the air-fuel ratio becomes longer as shown in FIG. 4 (b). It becomes long and the swing width becomes large, and the cleaning window protrudes. Therefore, the purifying ability of the catalyst device 14 is reduced, and the residual O ₂ on the rear side of the catalyst device 14 is reduced.
Is hardly affected by the purification rate of the catalyst device 14, and the output difference between the linear O ₂ sensor 15 and the λO ₂ sensor 16 can be accurately detected.

Next, the control of this embodiment will be described with reference to the flowchart of FIG. In addition, S1 to S10 indicate each step.

This flow is executed when the linear O ₂ sensor 15 is calibrated. When the flow is started, first, in step S1, the linear O ₂ sensor 15 on the front side receives λ =
1 control, that is, whether or not feedback control to the stoichiometric air-fuel ratio is being performed.
To determine whether the execution condition of the calibration of the linear O ₂ sensor 15 is satisfied. The execution condition of the calibration is, for example, a preset condition such as executing the calibration once per one drive after starting the engine.

The calibration execution condition is determined in S2 is directly returns when not satisfied, on the other hand, in the case that has been satisfied, at S3, increasing the feedback delay of the linear O ₂ sensor 15. Then, in S4, it is determined whether or not the cycle of the linear O ₂ sensor output has become larger than a predetermined value (K).
In the following cases, the feedback delay of the linear O ₂ sensor 15 is further increased in S5, and the process returns to S3.
When it exceeds the predetermined value K, the process proceeds to the next step.

In the next step, the output difference between the linear O ₂ sensor 15 and the λO ₂ sensor 16 is detected in S6, and then the linear O ₂ sensor 1 is detected based on the output difference in S7.
5 is calibrated. Then, in S8, it is determined whether or not the calibration has been completed, and if not, the process returns to S6 to execute the steps of S6 and S7 again. On the other hand, if the calibration has been completed, the process proceeds to S9. The feedback delay of the linear O ₂ sensor 15 is returned to the original, and the routine returns.

If the determination in S1 is NO, that is, the linear O
_{When the two} sensors 15 are not executing the λ = 1 control, the process proceeds to S10, where the lean control of the linear O ₂ sensor 15 is executed in S10 and the process returns.

According to this embodiment, the output difference between the linear O ₂ sensor 15 on the front side and the λO ₂ sensor 16 on the rear side can be accurately detected regardless of the purification rate of the catalyst device. The calibration of the linear O ₂ sensor 15 can be accurately performed using the output difference as a correction amount.

In the above embodiment, by increasing the feedback delay of the linear O ₂ sensor,
Although the air-fuel ratio fluctuation of the exhaust gas flowing into the catalyst device is increased, other means for increasing the air-fuel ratio fluctuation include, for example, a feedback gain, an I value, and a P value.
Various means such as changing a feedback control constant such as a value are possible.

[0024]

The present invention is constructed as described above. Therefore, when the linear air-fuel ratio sensor provided on the upstream side of the catalyst device is calibrated by the λ air-fuel ratio sensor provided on the downstream side, purification of the catalyst device is performed. It is possible to prevent erroneous calibration from being performed by the action, and to perform accurate calibration.

[Brief description of the drawings]

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

FIG. 2 is an overall system diagram of an embodiment of the present invention.

FIG. 3 is an output characteristic diagram of the linear O ₂ sensor in the embodiment.

FIG. 4 is a characteristic diagram showing air-fuel ratio fluctuation in the embodiment.

FIG. 5 is a flowchart for executing the control of the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 8 Injector 13 Exhaust passage 14 Catalyst device 15 Linear O ₂ sensor 16 λO ₂ sensor 17 Control unit

Continuation of the front page (56) References JP-A-3-258947 (JP, A) JP-A-3-175129 (JP, A) JP-A-61-234241 (JP, A) JP-A-64-53038 (JP) JP-A-1-121538 (JP, A) JP-A-64-53046 (JP, A) JP-A-58-174142 (JP, A) JP-A-4-124438 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) F02D 41/14 310

Claims (2)

(57) [Claims] 1. A linear air-fuel ratio sensor provided upstream of a catalyst device provided in an exhaust passage of an engine, a λ air-fuel ratio sensor provided downstream of the catalyst device, and an output of the linear air-fuel ratio sensor. a air-fuel ratio control system for an engine having an air-fuel ratio feedback control means for feedback controlling the air-fuel ratio of the engine to the target air-fuel ratio based on, it increases the air-fuel ratio fluctuation of the exhaust gas flowing into the catalytic converter
Control means for changing the control constant of the feedback control by the air-fuel ratio feedback control means so as to protrude beyond the purification window of the catalyst device, and the λ empty in a state where the control constant is changed by the control constant change means. An air-fuel ratio control device for an engine, comprising a linear air-fuel ratio sensor output calibrating means for calibrating the output of the linear air-fuel ratio sensor based on the output of the fuel ratio sensor. 2. The control constant to be changed to increase the fluctuation of the air-fuel ratio is a feedback delay that delays the determination of the output of the air-fuel ratio sensor. The control delay is increased by the control constant changing means when the linear air-fuel ratio sensor is calibrated. The engine air-fuel ratio control device according to claim 1.