JPH03105036A - Air-fuel ratio controller of engine - Google Patents

Abstract

PURPOSE:To eliminate difference of air-fuel ratio control by properly compensating energizing quantity with respect to a heater for activation of an O2 sensor when deterioration of the O2 sensor is detected in the case that fuel supply is controlled so as to control the air-fuel ratio of mixed air based on detection information of the O2 sensor. CONSTITUTION:In an intake passage 5 of an engine 1, an air cleaner 7 and air flow meter 8 are provided at the upstream end part, and a fuel injection valve 9 is provided so as to face a combustion chamber 4 via an intake valve 2 at the downstream side. In an exhaust pipe 6, an O2 sensor 10 is provided. Fuel injection from the fuel injection valve 9 is controlled by a controller 20 based on detection signals from detectors 7, 10 and the like. In this case, deterioration information of the O2 sensor is detected by for example, a driving distance meter 21. At the detection time, energizing quantity with respect to a heater for activation of the O2 sensor 10 is compensated so as to eliminate difference of the air-fuel ratio control caused by the deterioration.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air-fuel ratio control device for an engine, and more particularly to an air-fuel ratio control device using an 02 sensor equipped with an activation heater. (Prior Art) In automobile engines, etc., in order to maintain the air-fuel ratio supplied to the combustion chamber at an optimal value, an 02 sensor is installed in the exhaust passage to detect the residual oxygen concentration in the exhaust gas. When it is detected that the residual oxygen concentration is lower than a predetermined value, it is determined that the air-fuel ratio is rich (the amount of fuel supplied is excessive compared to the amount of air! i!), and the amount of fuel supplied is corrected to reduce it. However, when the residual oxygen concentration is higher than a predetermined value, it is determined that the air-fuel ratio is lean (a state in which the amount of fuel supplied is insufficient relative to the amount of air), and the air-fuel ratio is adjusted to increase the amount of fuel supplied. Control takes place.

By the way, the 02 sensor used in this air-fuel ratio control uses an oxygen sensing element that outputs a high level voltage when the detected oxygen concentration or air-fuel ratio is above a predetermined value (or when it is below a predetermined value). is commonly used, but in order to maintain the active state of this element, it is necessary to maintain it above a certain temperature. Therefore, as shown in Japanese Patent Application Laid-open No. 60-79133, for example, this type of 02 sensor is equipped with a heater that heats the above element.
This maintains the element or sensor in an active state,
Alternatively, activation is promoted when the engine is cold, such as during startup.

(Problems to be Solved by the Invention) On the other hand, the above-mentioned 02 sensor has a property that the air-fuel ratio (reversal point) when the output voltage level is reversed gradually changes due to deterioration of the oxygen sensing element due to long-term use. Therefore, for example, if the reversal point shifts to the rich side from the normal air-fuel ratio, the actual air-fuel ratio is judged to be lean even though it is rich, and the fuel supply amount is incorrectly increased. This can lead to problems such as deterioration of the exhaust gas condition or fuel efficiency, or deterioration of the performance of the exhaust purification device.Conversely, if the reversal point shifts to the lean side, even though the actual air-fuel ratio is lean, It is determined that the engine is rich, and an erroneous reduction correction is made to the fuel supply amount, resulting in a reduction in the output performance of the engine.

The present invention addresses the above-mentioned problems in engine air-fuel ratio control using the 02 sensor, in which the reversal point of the sensor changes due to deterioration due to long-term use, and at the same time changes depending on the temperature of the sensor itself. Focusing on this, when the 02 sensor is equipped with a heater as mentioned above, this heater is used to eliminate the shift in the reversal point due to deterioration, thereby making it possible to always perform air-fuel ratio control accurately. That is the issue.

(Means for Solving the Problems) In order to solve the above problems, the present invention is characterized by the following configuration. That is, the engine air-fuel ratio control device according to the present invention has the following features:
It has an 02 sensor that detects the residual oxygen concentration in the exhaust gas, and an air-fuel ratio control means that maintains the air-fuel ratio of the air-fuel mixture at a target value by controlling the fuel supply amount according to the signal from the sensor, In a configuration in which the 02 sensor is equipped with a heater for activating the sensor, a deterioration information detection means for detecting information related to deterioration of the 02 sensor and an error in air-fuel ratio control caused by this deterioration are eliminated. The present invention is characterized in that it is provided with an energization amount correction means for correcting the energization amount to the heater.

Here, as the deterioration information of the 02 sensor, for example, the total driving time and total mileage of the vehicle can be used. (Function) According to the above configuration, for example, as the mileage of the vehicle increases, the deterioration of the 02 sensor progresses, and the air-fuel ratio (reversal point) at which the output voltage level of the sensor reverses accordingly. If it deviates to the rich side or lean side from the normal value, the energization amount correction means increases or decreases the energization amount to the heater of the 02 sensor in response to a signal from the deterioration information detection means that detects this state. . In that case, for example, if the inversion point of the 02 sensor shifts to the rich side due to deterioration, and if the inversion point shifts to the lean side at low temperatures, the energization amount correction means It operates to reduce the amount of current applied to the heater according to the following. This eliminates the shift in the reversal point due to deterioration, and the air-fuel ratio of the mixture supplied to the combustion chamber is always maintained at a predetermined value. (Examples) Examples of the present invention will be described below.

First, the control system of this embodiment will be explained with reference to FIG. 1. An engine 1 is provided with an intake passage 5 and an exhaust passage 6 that communicate with a combustion chamber 4 via intake and exhaust valves 2.3, respectively.

An air cleaner 7 and an air flow meter 8 are installed at the upstream end of the intake passage 5, and a fuel injection valve 9 is installed at the downstream end so as to face the combustion chamber 4 via the intake valve 2. . Furthermore, the air-fuel ratio of the mixture being supplied to the combustion chamber 4 is determined from a predetermined value (for example, air amount/fuel amount = 14.7) by detecting the residual oxygen concentration in the exhaust gas in the exhaust passage 6. An 02 sensor 10 is installed to detect whether the vehicle is rich or lean.

Here, the general structure of this O2 sensor 10 will be explained with reference to FIG. In addition to having an oxygen concentration detecting section 12 that protrudes, the detecting section 12 has a structure in which a cylindrical oxygen sensitive body 13 is covered with a protector 14 provided with a large number of through holes 14a. Further, although details are not shown, the oxygen sensitive body 13 includes an oxygen sensitive element made of, for example, Zr02,
It is equipped with a heater that heats and activates this. The air-fuel ratio signal a corresponding to the oxygen concentration in the exhaust gas detected by the 02 sensor 10, the air flow rate signal b from the air flow meter 7, the engine rotation speed signal C from the distributor 15, and the engine A controller 20 is provided, which receives a water temperature signal d from a water temperature sensor 16 that detects the cooling water temperature of the engine, and controls the amount of fuel injected from the fuel injection valve 9 based on these signals a to d.

This controller 20 calculates the intake air amount per intake stroke of each cylinder based on the intake air amount and engine rotation speed indicated by the signals b and c, and sets the basic fuel injection amount corresponding to this value. At the same time, this is corrected according to the engine water temperature, etc. indicated by the signal d. Further, the final fuel injection amount is set by increasing or decreasing the fuel injection amount depending on whether the air-fuel ratio is lean or rich as indicated by the signal a from the O2 sensor 10, and the fuel injection valve By outputting a fuel control signal e to 9, feedback control is performed to converge the air-fuel ratio to the predetermined value. In particular, in this embodiment, in order to eliminate errors in air-fuel ratio control caused by deterioration of the 02 sensor, the controller 10 uses an odometer 2 installed in the vehicle.
The signal f from controller 1 is input, and the controller 2
0 sets the amount of electricity to the heater built into the 02 sensor 10 based on this signal f, and outputs the energization control signal g so that the heater is energized with this amount of electricity. Next, the operation of this embodiment will be explained according to the specific operation of the controller 20.

First, the basic operation of air-fuel ratio control by the controller 20 will be explained. The operation is performed according to the flowchart in FIG.
Load. As shown in FIG. 4, this output A becomes a high level when the air-fuel ratio is richer than a predetermined value (14.7), and becomes a low level when it is leaner than a predetermined value. Based on this output level, it is determined whether the current air-fuel ratio is rich or not. If the air-fuel ratio is rich, it is determined in step S3 whether the previous output A' was also rich, and if the current air-fuel ratio is lean, the previous output A' is determined in step S4. It is determined whether or not ゛ is also lean.

Now, as shown by the symbol (A) in FIG. 4, if the air-fuel ratio changes from lean to rich, the previous output A' is lean and the current output A is rich, so the controller 20 Is it a step? 2. From S3 to step S5
is executed, and the feedback correction amount CPB of the fuel injection amount is set to a value obtained by subtracting a predetermined amount P from the previous values c and B', and at the same time, in step S6, the current output A is replaced with the previous output A'. Furthermore, in the next control cycle, both outputs A and A' become rich, so the controller 20 performs step S
2. Execute steps S3 to S7 and calculate the previous correction amount CFI.
Subtract the minute amount Δ■ from ' to obtain the current correction amount CPB. In this way, when switching from lean to rich, the feedback correction amount or fuel injection amount is reduced at once by a predetermined amount, and then further reduced gradually, as shown by the symbol (mouth) in Fig. 4. It turns out. Also, due to this weight loss correction, when the air-fuel ratio changes from rich to lean as shown by the symbol (C) in Fig. 4, the output of the sensor 10 will change to indicate that the previous output A was rich and the current output A is lean. Therefore, the controller 20 performs step S2.
Step S8 is executed from r84, and the feedback correction amount CPS is set to a value obtained by adding a predetermined amount P to the previous value CpB', and thereafter, in step S, the correction amount CFB is increased by a minute amount ΔI. Therefore, when the air-fuel ratio reverses from rich to lean, the sign (
As shown in 2>, after the above correction amount or fuel injection amount is increased by a predetermined amount at once, it is further gradually increased. By repeating such reduction and increase corrections, the air-fuel ratio is maintained at a predetermined value. By the way, as shown in FIG. 5, the 02 sensor 10 has a property that the air-fuel ratio when the output level is reversed due to deterioration of the oxygen sensing element, that is, the reversal point, gradually changes to the rich side from the predetermined value 14, 7. be. Moreover, the sensor 10
Since the deterioration of the vehicle corresponds to the mileage of the vehicle, the reversal point changes to the rich side as the mileage increases, as shown in FIG. Due to this change in the reversal point, for example, at point X shown in FIG. Corrections will be made. ? On the other hand, as shown in FIG. 7, the 02 sensor 10 has a property that the reversal point changes to the rich side as the temperature of the oxygen sensing element becomes higher. Therefore,
The controller 20 utilizes this property to perform control to prevent erroneous control caused by the above-mentioned deterioration.

This control is performed according to the flowchart in FIG.
In step S, the controller 20 first reads the output M of the odometer 21 shown in FIG.
2, . Then, in step sis, this target current IN is replaced with the energization amount iM to be energized to the heater,
In step SI4, the energization control signal g is output to the 02 sensor 10 so as to achieve this energization amount.

Next, the controller 20, in step S15,
Is the heater of sensor 10 actually energized? The actual current value I and the target current IN are compared in step S16+317. If the actual current value is smaller than the target current (■<Is), in step S18, the value obtained by adding the minute amount Δi to the current energization amount i threshold is set as the next energization amount IM+1, and the actual current value is set to the target current If it is larger (■>IN), in step S+9, the value obtained by subtracting the minute amount Δi from the current energization amount i is set as the next energization amount iM+1, and the above steps are performed so that the current of these values is energized to the heater. In S14, the energization control signal g is output.

Further, if the actual current value ■ matches the target current value IN, the controller 20 reads the output M of the odometer 21 again in step 82G, and also reads the output M of the odometer 21 in step S21.
The classification MN of the mileage indicated by the output M is the next classification MN.
If it is determined that the value has been updated to +1, step S
Execute step 1 again and set the next target current value I based on Figure 9.
Set N+1. Then, feedback control of the T4 current to the heater is performed in the same manner.

In this way, a current is supplied to the heater of the 02 sensor 10 in accordance with the distance traveled, that is, the degree of deterioration of the sensor 10. In this case, the value of the supplied current is shown in FIG. As shown, the heating temperature of the oxygen sensing element in the 02 sensor 10 decreases as the traveling distance increases. Therefore, the reversal point of the sensor 10 is corrected to the lean side according to the characteristics shown in FIG. 7, and this correction eliminates the shift of the reversal point toward the rich side due to deterioration of the sensor 10. . As a result, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 4 of the engine is always maintained at the predetermined value of 14.7. (Effects of the Invention) As described above, according to the present invention, the amount of fuel supplied to the combustion chamber is corrected to increase or decrease based on the output from the 02 sensor that detects the residual oxygen concentration in the exhaust gas. In an engine that maintains the air-fuel ratio of the air-fuel mixture at a predetermined target value, errors in air-fuel ratio control due to deterioration of the 02 sensor described above can be eliminated. As a result, even when the sensor is used for a long period of time, the air-fuel ratio is always maintained at a predetermined optimum value, and the exhaust gas condition and fuel efficiency are improved especially when the air-fuel ratio shifts to the rich side. This will prevent problems such as deterioration of the air-fuel ratio or deterioration of the performance of the exhaust gas purification device.In addition, if the air-fuel ratio shifts to the lean side due to deterioration of the 02 sensor, the engine output due to this shift will be reduced. This will prevent performance deterioration.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; Fig. 1 is a control system diagram for air-fuel ratio control, Fig. 2 is an enlarged view of the 02 sensor used in this system, and Fig. 3 shows the basic operation of air-fuel ratio control. FIG. 4 is a time chart of the same operation, FIG. 5 is an explanatory diagram of characteristic changes due to deterioration of the 02 sensor, FIG. 6 is an explanatory diagram of characteristic changes with respect to the distance traveled by the sensor, and FIG. FIG. 8 is a flowchart showing the control operation for the change in characteristics of the 02 sensor, and FIG. 9 is an explanatory diagram of a map of the target heater current used in this control. 1...Engine, 10...02 sensor, 20...
Air-fuel ratio control means, energization amount correction means (controller), 2
1...Deterioration information detection means (odometer).

Claims (1)

[Claims] (1) An O_2 sensor that detects the residual oxygen concentration in exhaust gas, and an air-fuel ratio control means that maintains the air-fuel ratio of the air-fuel mixture at a target value by controlling the fuel supply amount according to the signal from the sensor. an air-fuel ratio control device for an engine, wherein the O_2 sensor is provided with a heater for activating the sensor, a deterioration information detection means for detecting information related to deterioration of the O_2 sensor; An air-fuel ratio control device for an engine, comprising: an energization amount correcting means for correcting an energization amount to the heater so as to eliminate an error in air-fuel ratio control caused by.