JPH065054B2 - Failure diagnosis device for air-fuel ratio control system - Google Patents

Description

The present invention relates to an air-fuel ratio control system failure diagnosis device.

[Conventional technology]

In an internal combustion engine equipped with an air-fuel ratio control device for maintaining the air-fuel mixture supplied to the engine cylinder at a stoichiometric air-fuel ratio,
If the air-fuel ratio controller fails, the air-fuel mixture becomes lean or rich. In this case, if the air-fuel mixture becomes very lean, the engine output will drop, so the driver will notice that something is wrong, but if the air-fuel mixture becomes slightly lean or too rich, the driver will be abnormal. The engine continues to operate because it is not noticed that
It causes a problem that CO, HC or NO _x is emitted. In order to solve such a problem, it is judged whether the air-fuel mixture is lean or rich based on the feedback control signal, and whether the air-fuel ratio control device is malfunctioning or not is judged by it. A failure diagnosis device adapted for discrimination has already been proposed by the present applicant (Japanese Patent Laid-Open No. 63-1002).
See No. 55).

However, in an internal combustion engine with a carburetor, when the carburetor temperature rises, so-called percolation occurs, and fuel is discharged into the intake passage, so that the air-fuel mixture becomes rich. Therefore, at this time, if the failure diagnosis is performed, it is determined that the air-fuel ratio control device is out of order even though the air-fuel ratio control device is not out of order, thus causing a problem of erroneous diagnosis.

In order to solve such a problem, the applicant has already proposed a failure diagnosis device that detects the engine temperature that changes in relation to the carburetor temperature and prohibits the failure diagnosis while the engine temperature is high. (See JP-A-63-259146). In this failure diagnosis device, if the engine temperature decreases, the carburetor temperature will also decrease, and in such a case, the engine temperature will drop to below the engine temperature at which the carburetor will not generate percolation. When it does, the failure diagnosis is started.

[Problems to be solved by the invention]

However, unlike the engine itself, the carburetor is not cooled strongly by the cooling water temperature, but is simply cooled by the running wind of the vehicle flowing around the carburetor, so once the carburetor temperature becomes high, the engine temperature drops. However, the carburetor temperature does not drop immediately. That is, even if the engine temperature actually drops, the carburetor temperature does not necessarily drop with it. Therefore, even if the engine temperature is lowered, the carburetor may still generate the percolation, and in such a case, there is a problem that misdiagnosis is made when the failure diagnosis is performed.

[Means for solving problems]

In order to solve the above problems, according to the present invention, as shown in the configuration diagram of the invention of FIG. 1, the air-fuel ratio is fed back based on the output signal of the oxygen concentration detector 13 arranged in the engine exhaust passage. In an internal combustion engine with a carburetor equipped with an air-fuel ratio control device for controlling, a temperature detection means 100 for detecting the engine temperature, and a failure determination means for determining whether or not the air-fuel ratio control device has a failure based on a feedback control signal. 101
And an elapsed time calculation means 102 for calculating an elapsed time after the engine temperature has dropped to a temperature equal to or lower than a predetermined set temperature based on an output signal of the temperature detection means 100, and an elapsed time calculation means 1
A failure discrimination prohibition means 103 for prohibiting the failure discrimination by the failure discrimination means 101 until the elapsed time exceeds a predetermined time based on the calculation result of 02 is provided.

〔Example〕

Referring to FIG. 2, 1 is an engine body, 2 is an intake manifold, 3 is a variable venturi type carburetor, and 4 is an exhaust manifold. The variable venturi type carburetor 3 includes an intake passage 5, a suction piston 6, a fuel passage 7 that opens into the intake passage 5, and a throttle valve 8, and a fuel passage 7 is formed by a needle 9 attached to the suction piston 6. The amount of fuel supplied from the inside to the intake passage 5 is controlled. An air bleed passage 10 is connected to the fuel passage 7,
An air bleed control valve 11 is provided in the air bleed passage 10.
Are placed. The air bleed control valve 11 is controlled based on a control current output from the electronic control unit 30. When the control current supplied to the air bleed control valve 11 increases, the amount of air bleed supplied from the air bleed passage 10 into the fuel passage 7 increases, and thus the air-fuel mixture supplied into the engine cylinder becomes thin. On the other hand, when the control current supplied to the air bleed control valve 11 decreases, the amount of air bleed supplied from the air bleed passage 10 into the fuel passage 7 decreases, and thus the air-fuel mixture supplied into the engine cylinder becomes rich. Become.

The electronic control unit 30 comprises a digital computer, and ROMs connected to each other by a bidirectional bus 31.
(Read-only memory) 32, RAM (random access memory) 33, CPU (microprocessor) 34,
It has an input port 35 and an output port 36. A throttle sensor 12 that generates an output voltage proportional to the throttle opening is attached to the throttle valve 8, and the output voltage of the throttle sensor 12 is input to an input port 35 via an AD converter 37. O for exhaust manifold 4
_{The 2} sensor 13 is attached, and the output signal of the O ₂ sensor 13 is input to the input port 35 via the AD converter 38. Further, a negative pressure sensor 14 that generates an output voltage proportional to the negative pressure in the intake manifold 2 is attached to the intake manifold 2, and the output voltage of the negative pressure sensor 14 is input to an input port 35 via an AD converter 39. Is entered. Further, a water temperature sensor 15 that generates an output voltage proportional to the engine cooling water temperature is attached to the engine body 1, and the output voltage of the water temperature sensor 15 is input to the input port 35 via the AD converter 40. Further, the input port 35 has a rotation speed sensor 20 for generating an output pulse proportional to the engine rotation speed, and a starter switch 21 for operating the starter motor.
Are connected. The output port 36 is, on the one hand, a drive circuit 41.
Is connected to the air bleed control valve 11 via, and on the other hand is connected to the warning lamp 22 via a drive circuit 42.

FIG. 4 shows changes in the output voltage V of the O ₂ sensor 13. O
_{2 When the} sensor 13 is rich in air-fuel mixture, that is, when it is rich
An output voltage of about 0.9 V is generated, and an output voltage of about 0.1 V is generated when the air-fuel mixture is lean, that is, lean. The output voltage V of the O ₂ sensor 13 is compared with a reference voltage Vr of about 0.45 V in the CPU 34. If the output voltage V of the O ₂ sensor 13 is higher than Vr, it is judged to be rich, and if it is lower than Vr, it is lean. It is judged that there is.

FIG. 3 shows a routine for calculating the control current I of the air bleed control valve 11 which is performed based on the determination of lean or rich.

Referring to FIG. 3, first, at step 50, it is judged if lean or not. When it is lean, the routine proceeds to step 51, where it is judged whether or not it has been reversed from rich to lean between the previous processing cycle and the current processing cycle. If it is inverted, the routine proceeds to step 52, where the skip value A is subtracted from I, and the routine proceeds to step 53. If not inverted, the routine proceeds to step 54, where I is the integral value K (K) <<
A) is subtracted, and the process proceeds to step 53. On the other hand, step 5
When it is determined that the vehicle is rich in 0, step 5
The routine proceeds to step 5 and it is determined whether or not the lean-to-rich inversion was performed from the previous processing cycle to the current processing cycle. If it is inverted, the routine proceeds to step 56, where the skip value A is added to I, and the routine proceeds to step 53. If not reversed, the routine proceeds to step 57, where the integral value K is added to I, and the routine proceeds to step 53. In step 53, I is output port 3
6 is output.

Therefore, as shown in FIG. 4, when I changes from rich to lean, I rapidly decreases by the skip value A and then gradually decreases, and when I changes from lean to rich, it rapidly increases by the skip value A and then gradually. Increase. By the way, I calculated in each step 52, 54, 56, 57 of FIG.
I output to the air bleed control valve 11 is a pulse duty ratio, which is supplied to the air bleed control valve 11 with a continuous pulse which is generated at regular intervals and whose pulse width changes according to the duty ratio. The air bleed control valve 11 is controlled to an opening degree according to the average current of this continuous pulse, and thus I
Is referred to as the control current of the air bleed control valve 11. The control current I capable of controlling the air-fuel ratio is between the minimum value MIN and the maximum value MAX in FIG. 4, and during the feedback control, the normal control current I moves up and down in the middle between MIN and MAX.
However, if the air-fuel mixture continues to become rich for some reason, I reaches MAX, and if the air-fuel mixture continues to become rich for some reason, I reaches MIN. Therefore, it is possible to judge the abnormality of the air-fuel ratio control device depending on whether I becomes MAX or MIN.

Next, the fault diagnosis method according to the present invention will be described with reference to FIGS. 5 and 6. The routines shown in FIG. 5 and FIG. 6 are executed by interruption at regular time intervals.

Referring to FIGS. 5 and 6, first, at step 60, it is judged if the starter switch 21 is on or not. If it is on, the routine proceeds to step 61, where the flag is reset and then the step 62. Proceed to. As will be described later, this flag is reset when the engine cooling water temperature is higher than a predetermined temperature. On the other hand, when the starter switch 21 is turned off, step 6
In step 3, it is determined whether or not the starter switch 21 has been switched from ON to OFF between the previous processing cycle and the current processing cycle. When it is switched from on to off, the routine proceeds to step 64, where the timer I is set and then it proceeds to step 62, and when it is switched from on to off, the routine proceeds to step 65. In step 65, it is determined whether or not the fixed time determined by the timer I has elapsed since the timer I was set. When the fixed time has not passed, that is, when the fixed period has not passed after the engine instruction, the process proceeds to step 62, and when the fixed period has passed after the engine starts, the process proceeds to step 66. In step 62, it is judged from the output signal of the water temperature sensor 15 whether or not the cooling water temperature T is higher than a predetermined set temperature, for example, 70 ° C.
If T> 70 ° C., the flag is set in step 67 and the post-processing cycle is completed.

As will be described later, failure diagnosis is prohibited while the flag is set, and failure diagnosis is started when the flag is reset. When the cooling water temperature T is higher than 70 ° C. at the time of starting the period, the temperature of the carburetor 3 is also considerably high, and at this time, percolation may occur.
Therefore, at this time, the flag is set and the failure diagnosis is prohibited.

On the other hand, if it is determined in step 65 that a certain time has passed after the machine-to-machine instruction, the process proceeds to step 66, in which the cooling water temperature T
Is higher than a predetermined set temperature, for example, 95 ° C. or not. If T> 95 ° C., the routine proceeds to step 68, where a flag is set, and thus failure diagnosis is prohibited. When the engine cooling water temperature T is higher than 95 ° C. after a lapse of a certain time after the engine has been started, the temperature of the carburetor 3 is also considerably high, and therefore there is a possibility that percolation occurs at this time. Therefore, at this time, the flag is set and the failure diagnosis is prohibited.

When it is determined that the temperature is T70 ° C. in step 62, that is, when it is determined that the temperature is T70 ° C. when the engine is started, the process proceeds to step 69, and in step 66, T
When it is determined that the temperature is 95 ° C., that is, when it is determined that the temperature is T95 ° C. after a lapse of a certain time after the engine is started, the process proceeds to step 69. At step 69, it is judged if the flag is set. When the flag is reset, that is, when the engine is started, T> 70 ° C
If not, or if T> 95 ° C. has not been reached after a certain period of time has passed after the engine was started, the routine proceeds to step 70. In steps 70, 71, 72 and 73, it is judged whether or not the operation state is one in which a failure diagnosis should be performed. If the failure is diagnosed in steps 74 and 75 and the failure occurs, the warning lamp 22 is turned on in step 76. To be done. That is, step 70
Then, it is determined whether the cooling water temperature T is 60 ° C. or lower. If T <60 ° C., the treatment cycle is completed and therefore no fault diagnosis is carried out in this case. In the case of T <60 ° C., the air-fuel mixture may be excessively rich due to the choke action, and therefore, failure diagnosis is not performed to avoid misdiagnosis. Therefore, when a certain period has not elapsed after the engine has started, failure diagnosis is performed only when 60 ° C. <T70 ° C., and when a certain period has elapsed after the engine has started, failure diagnosis is performed only when 60 ° C. <T95 ° C. It should be noted that the cooling water temperature of 95 ° C at which percolation is considered to occur after a certain period of time has elapsed since the engine was started is higher than the cooling water temperature of 70 ° C at which percolation is likely to occur immediately after the engine is started. This is because when the vehicle is driven after a certain period of time, the carburetor 3 is cooled by the traveling wind and the temperature of the carburetor 3 is lowered.

In step 71, it is judged from the output signal of the throttle sensor 12 whether the throttle opening θ is 10 ° or less, and in step 72, the negative pressure P is -80 mmHg <P <-350 mmHg from the output signal of the negative pressure sensor 14. It is determined whether or not it is in the range, and in step 73, it is determined from the output signal of the rotation speed sensor 20 whether or not the rotation speed N is in the range of 1500 r.pm <N <3000 r.pm <. As can be seen from these steps 71, 72, 73, failure diagnosis is not performed in order to avoid misdiagnosis in the low intake air region where the air bleed sensitivity is low and the high speed region where the output air-fuel ratio is required.

At step 74, it is judged if the control current I is in the range of MIN <I <MAX. Next, at step 75, it is judged if the state of IMIN or IMAX has passed for 10 seconds or longer, for example. If 10 seconds or more has passed, it is determined that the air-fuel ratio control system is out of order and the routine proceeds to step 76 where the warning lamp 22 is turned on. It is turned on.

On the other hand, when it is determined in step 69 that the flag is set, it is determined whether or not step 77 is passed before proceeding to step 77. Step 7 for the first time
When passing 7, the timer II is set in step 78 and the processing cycle is completed. In the next processing cycle, the routine proceeds from step 77 to step 79, and it is judged whether or not a fixed time determined by the timer II has elapsed. If the fixed time has not passed, the processing cycle is completed, and if the fixed time has passed, the routine proceeds to step 80, where the flag is reset. If the flag is reset, the routine proceeds from step 69 to step 70, where failure diagnosis is performed.

T> 70 ° C when a certain time has not passed since the engine was started
If so, the flag is set, and when the temperature reaches T70 ° C, the process proceeds from step 69 to step 77.
After a certain period of time has elapsed since then, failure diagnosis is started. On the other hand, after a certain time has passed after the engine was started, T
If it becomes> 95 ° C, the flag is set, then T95
When the temperature reaches ℃, the process proceeds from step 69 to step 77.
The failure diagnosis is started after a lapse of a certain time after reaching 95 ° C. That is, even if the cooling water temperature T decreases, the temperature of the carburetor 3 does not necessarily decrease accordingly, and therefore even if the cooling water temperature T becomes 70 ° C. or lower, or 95 ° C. or lower, the carburetor 3
There is a possibility that percolation is occurring because the temperature is still high. Therefore, if the failure diagnosis is performed at this time, there is a possibility of misdiagnosis. Therefore, the cooling water temperature T is 70 ° C.
The failure diagnosis is prohibited for a certain period of time until the temperature of the carburetor 3 drops below the temperature of 95 ° C. or below, thereby preventing misdiagnosis.

〔The invention's effect〕

Misdiagnosis due to occurrence of percolation can be prevented by starting the failure diagnosis after a lapse of a fixed time after the engine temperature becomes lower than a preset set temperature.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the invention, FIG. 2 is an overall view of an internal combustion engine, FIG. 3 is a flowchart for calculating a control current, and FIG. 4 is an output signal of an O ₂ sensor. Diagrams showing changes in control current, FIGS. 5 and 6 are flowcharts for executing the failure diagnosis processing. 3 ... Vaporizer, 7 ... Fuel passage, 10 ... Air bleed passage, 11 ... Air bleed control valve, 13 ... O ₂ sensor, 15 ... Water temperature sensor.

Claims (1)

[Claims] 1. A temperature detector for detecting an engine temperature in an internal combustion engine with a carburetor, comprising an air-fuel ratio control device for feedback-controlling an air-fuel ratio based on an output signal of an oxygen concentration detector arranged in an engine exhaust passage. Means, a failure determination means for determining whether or not the air-fuel ratio control device has a failure based on a feedback control signal, and an engine temperature up to a predetermined set temperature or less based on an output signal of the temperature detection means. Elapsed time calculating means for calculating the elapsed time after the reduction, and a failure for prohibiting the failure determination by the failure determining means until the elapsed time exceeds a predetermined time based on the calculation result of the elapsed time calculating means. A failure diagnosis device for an air-fuel ratio control system equipped with a discrimination prohibition means.