JPS633238A - Diagnostic device for air fuel ratio feedback controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To obtain a system which is free of misjudgement due to a disturbance factor by detecting the air fuel ratio representative value of air fuel ratio feedback control. CONSTITUTION:This diagnostic device is equipped with air fuel ratio detector 1 and an air fuel ratio control means 2 which performs feedback control over an air fuel ratio according to an air fuel ratio signal from the detector 1. Then, an air fuel ratio representative value detecting means 3 detects the air fuel ratio representative value of the air fuel ratio feedback control. Further, an abnormal decision area detecting means 4 decides the abnormality of the air fuel ratio feedback control which is not affected by disturbance. In this abnormal decision area, an abnormality decision means 5 decides whether or not the feedback control is abnormal or not from the detected value of the air fuel ratio representative value. Therefore, it is judged whether or not an air fuel ratio sensor is in a rich or lean abnormal state in an operation area where the operation is easily affected by disturbance, so the abnormal state of a feedback system is accurately decided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention is for abnormality diagnosis in a device that performs feedback control of an air-fuel ratio set by an internal combustion engine in response to an air-fuel ratio signal from an air-fuel ratio detector (for example, 02 sensor). Regarding equipment.

[Conventional technology]

An abnormality diagnosis system has been proposed that turns on a warning light or stores an abnormality flag in a computer by detecting an abnormality in a feedback system in an internal combustion engine that performs feedback control of an air-fuel ratio. This abnormality diagnosis system detects a feedback signal representing the air-fuel ratio, and determines that an abnormality is occurring when the value falls below a lower limit value or exceeds an upper limit value for a predetermined period of time. For example, see Japanese Patent Application Laid-Open No. 57-62944.

[Problem that the invention seeks to solve]

In an air-fuel ratio feedbank control device, particularly in an air-fuel ratio feedback control device using an air-bleed carburetor, the base air-fuel ratio varies depending on disturbance factors 1 such as the properties of the fuel used, ambient temperature, and altitude. For example, fuel mixed with alcohol becomes lean, when the ambient temperature is high it becomes rich due to the generation of fuel vapor, and when driving at high altitudes the air pressure becomes low and it becomes rich. In this case, even if the feed pack system is normal, the representative value of the air-fuel ratio may exceed the upper limit or lower limit for a predetermined period of time. In this case, the feedback system may erroneously determine that it is abnormal even though it is normal.

An object of the present invention is to provide a system that does not cause erroneous judgments due to disturbance factors.

[Means for solving problems]

According to the present invention, as shown in FIG. 1, in an internal combustion engine equipped with an air-fuel ratio detector 1 and an air-fuel ratio control means 2 that performs feedback control of the air-fuel ratio according to an air-fuel ratio signal from the air-fuel ratio detector 1, Means 3 for detecting a representative air-fuel ratio value in air-fuel ratio feedback control; Abnormality determination area detection means 4 for detecting an operating range for determining an abnormality in air-fuel ratio feedback control without the influence of disturbance; A diagnosis WZ is provided which includes means 5 for determining whether or not the feedbank control is abnormal based on the detected value.

[Embodiment] In FIG. 2, 10 is a main body of an internal combustion engine, 12 is an intake pipe, 14 is an intake manifold, 16 is a carburetor, 18 is an exhaust manifold, and 20 is a distributor.

The carburetor 16 has a primary passage 20 and a secondary passage 2.
2, a primary throttle valve 24, a secondary throttle valve 26, and a float chamber 28. The float chamber 28 is opened into the primary passage 20 through a primary nozzle 30 and into the secondary passage 22 through a secondary nozzle 31 .

An air bleed passage 32 is installed in the primary nozzle 30. Air bleed control valve 3 on air bleed passage 32
4 will be installed. The carburetor is set to have a rich base air-fuel ratio, and is fed to the stoichiometric air-fuel ratio by air bleed.

controlled.

36 indicates a control circuit, in which air bleed control valve 34
This is to generate a signal that opens and closes the air-fuel ratio so that the air-fuel ratio reaches a predetermined value. The control circuit 36 is configured as a microcomputer system, and includes a central processing unit (CPU).
) 38, a read only memory (ROM) 40, a random access memory 42, an analog-to-digital converter 44, an input/output port 46, and a bus 48.

Each sensor is connected to the A/D converter 44, and operating condition signals are applied thereto. That is, an air-fuel ratio sensor (for example, 02 sensor 50) is installed in the exhaust manifold 18, and an air-fuel ratio signal Ox is obtained. A water temperature sensor 52 is installed in the engine body, and a signal corresponding to the engine cooling water ATHW is obtained. The throttle sensor 53 obtains a signal TH corresponding to the opening degree of the primary throttle valve 24. - On the other hand, a sensor 54 for taking out an ignition pulse or a crank angle pulse is installed in the distributor 20, and this sensor 54 is connected to the input/output port 46 so that the engine speed N can be determined. The input/output boat 46 is connected to an air bleed control valve drive circuit 56. A control air-fuel ratio parameter signal I, for example, a pulse signal, is applied to the drive circuit 56, and by changing the pulse width (duty ratio), the opening degree of the air bleed control valve 34 is changed, and the amount of air bleed is controlled. can be done. In addition, the input/output boat 46
is connected to the indicator light 57.

FIG. 3 explains how the abnormality determination area is set for the combination of the throttle valve opening and engine speed as operating conditions in the embodiment of the present invention. The region FBZ surrounded by the broken line is the region where air-fuel ratio feedback control is executed, and the engine speed is Nl (
Between 1,300 rpm) and N3 (4,000 rpm), the throttle valve opening becomes P2 (-
85NMHg) and the idle opening. That is,
When the engine is in the FBZ region and the feedbank is working normally, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio.

The lean abnormality determination area is the R5 area DZL, which is a higher load area than P2 at the upper limit of the feedback area and the rotational speed is between N2 (200 rpm) and N3. That is, in this region DZL, since air-fuel ratio feedback control is not performed, the air-fuel ratio is a base air-fuel ratio richer than the stoichiometric air-fuel ratio, for example, about 13. Therefore, disturbance factors (e.g.
Even if the air-fuel ratio deviates from the base value to the lean side due to the adoption of alcohol fuel, it will be at most about 14, and in this case, as long as the feedback system is normal, the 02 sensor 50 should generate a rich signal. Conversely,
When the lean signal from the air-fuel ratio sensor 50 continues in this DZL region, it can be determined that the feedback system is abnormal.

On the other hand, DZR is the range in which rich abnormality of the feedback system is determined, and the intake pipe negative pressure is between P3 and Pl, and the engine speed is between N2 and N3. That is, the load in the feedback region is set to a relatively high region (medium load region).

This is the change in air-fuel ratio with respect to the amount of air bleed ΔA/F
This is an area with high bleed sensitivity.

That is, in this air-fuel ratio control system, feedback is performed by controlling the air-fuel ratio to increase or decrease by changing the amount of air bleed, but the bleed sensitivity is high in the medium load range (for example, P = 150 mmHg) as shown in Fig. 3. As the load becomes smaller (for example, P=300 mmHg), it becomes smaller.

When the bleed sensitivity becomes small, if the base air-fuel ratio becomes rich due to disturbance factors, even if the air bleed amount is increased by feed hack control, it will not be reflected in the air-fuel ratio. A signal appears. On the other hand, in the medium load range where the bleed sensitivity is high, the amount of air bleed is immediately reflected in the air-fuel ratio, so the air-fuel ratio sensor 50 outputs a rich signal, and if it continues, it can be accurately determined that there is a rich abnormality. When the load exceeds the intake pipe negative pressure P3, the secondary throttle valve 26 of the carburetor starts to open, and since there is no air bleed passage in this secondary system, the bleed sensitivity decreases again. Exclude.

Hereinafter, how the air-fuel ratio control incorporating the above-described abnormality determination area is performed will be explained using a flowchart.

FIG. 5 shows an air-fuel ratio feedback routine, and it is assumed that the conor routine is executed at predetermined intervals. In step 50, it is determined whether the feedback condition indicated by FBZ in FIG. 3 is met. If the feedback condition is not met, the process proceeds to step 52, where the opening parameter I of the bleed control valve applied to the drive circuit of the bleed control valve 34 is fixed at a value of 1 min, which corresponds to fully closed. At this time, the bleed control valve 34 is fully closed, and since no air bleed is performed, the air-fuel ratio is fixed at the base value (rich).

When the feedback condition is met, the process proceeds from step 50 to step 54, where the signal of the 02 sensor is rich (Ox=1
) or not (Ox=0). If it is rich, the process proceeds to step 56, where the bleed control valve opening parameter 1 is incremented by ΔI. Therefore, the opening degree of the bleed control valve increases, and the amount of bleed air is increased, thereby correcting the air-fuel ratio toward the lean side.

In step 58, it is determined whether l>Imax, and if the determination is affirmative, the process proceeds to step 60, where it is fixed at I-11IaX.

When lean, proceed from step 54 to step 62,
(2) is decremented by ΔI. Therefore, the opening degree of the air bleed control valve 34 becomes smaller, and the amount of bleed air is reduced. Therefore, the air-fuel ratio is corrected toward the rich side. In steps 64 and 66, guard processing is performed to fix I=Imin.

FIG. 6 shows a diagnostic routine, which is also executed at regular intervals. In step 70, it is determined whether the water temperature THW is greater than a predetermined value T)IWQ.

When the temperature is cold, the process proceeds to step 72 and 0 is entered in the counter C. This counter C is in the abnormality judgment area (DZR or D
This is to measure the elapsed time since entering ZL).

After warming up, the process proceeds from step 70 to step 74, where it is determined whether or not the rich abnormality determination area DZR is reached.

If the engine is in the rich abnormality determination area DZR, the process proceeds to step 76, where it is determined whether the air-fuel ratio parameter I is at Imax. If Yes, proceed to step 78,
Counter C is incremented. In step 80, it is determined whether C≧cX.

Here, the value 01 is the value of the counter C corresponding to the duration of time during which the 02 sensor output value remains at 1 max, in order to determine that the 02 sensor is rich abnormally. If the air-fuel ratio sensor has a rich abnormality, the process proceeds from step 80 to step 8.
2, and after c'''c1 is set, the rich abnormality flag XR is set in step 84. In step 86, the indicator lamp 57 is turned on.

When the engine is in the lean abnormality determination area DZL, the process proceeds from step 74 to step 88 to step 90;
It is determined whether the air-fuel ratio parameter I=Imin. Yes
s, the counter C is incremented in step 92, and in step 92 it is determined whether C≧02. Here, the value 02 is the value of the counter C corresponding to the duration of time that the 02 sensor output value is stuck to I win in order to determine that the 02 sensor is lean abnormal. If the air-fuel ratio sensor is lean abnormal, step 94 to step 96
After c=c2, the lean abnormality flag XL is set to 1 in step 98. Then step 86
The indicator light 57 is turned on.

FIG. 7 is a timing diagram illustrating the invention in detail. The air-fuel ratio parameter ■ is fed back at an intermediate value under normal conditions (A). When a rich abnormality occurs, the counter C is stuck at I max and starts incrementing from time t1 when entering the DZR region, and the rich abnormality flag XR is set at time t2 when c=c1. - On the other hand, in the lean abnormality, the counter C sticks to Illl1n and starts incrementing from time t3 when entering the DZL region, and c ” c
2, the lean abnormality flag FL is set to 1.

〔effect〕

According to this invention, since the rich abnormality or lean abnormality of the air-fuel ratio sensor is determined in an operating range that is not easily affected by disturbances, it is possible to accurately determine the abnormal state of the feedback system.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of the present invention. FIG. 2 is a diagram showing an embodiment of the invention. FIG. 3 is a diagram illustrating the determination range of lean abnormality and rich abnormality. FIG. 4 is a diagram illustrating how the air bleed amount-air bleed intensity characteristic changes depending on the magnitude of the intake pipe negative pressure. FIGS. 5 and 6 are flowcharts illustrating the operation of the control circuit of the present invention. FIG. 7 is a timing diagram illustrating the invention in detail. DESCRIPTION OF SYMBOLS 10... Engine body, 14... Intake manifold, 16... Carburizer, 18... Exhaust manifold, 20... Distributor, 32... Air bleed passage, 34... Air bleed control valve , 44... Control circuit, 52... O2 sensor, 53... Throttle sensor.

Claims (1)

[Claims] In an internal combustion engine comprising an air-fuel ratio detector and an air-fuel ratio control means for feedback-controlling the air-fuel ratio according to an air-fuel ratio signal from the air-fuel ratio detector, means for detecting a representative value of the air-fuel ratio in air-fuel ratio feedback control; , an abnormality determination area detection means for detecting an operating range for determining an abnormality in the air-fuel ratio feedback control that is not affected by disturbance, and a means for determining whether or not the feedback control is abnormal from a detected value of the air-fuel ratio representative value in the abnormality determination area. A diagnostic device consisting of: