JPH065052B2 - 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 ratio supplied to the engine cylinder at a stoichiometric air-fuel ratio, when the air-fuel ratio control device fails, the air-fuel mixture becomes lean or rich. In this case, if the air-fuel mixture becomes extremely 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 notice Since the engine is not noticed that an abnormality is occurring, the operation of the engine is continued as it is, and as a result, a large amount of 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 it is determined whether the air-fuel ratio control device is out of order. A failure diagnosis device for making a judgment has already been proposed by the present applicant (Japanese Patent Laid-Open No. Sho 61-242).
63-100255).

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, if a failure diagnosis is performed at this time, 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 of the present invention 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 be below the engine temperature at which the carburetor will not generate percolation. The failure diagnosis is started when the voltage drops.

[Problems to be solved by the invention]

However, the carburetor is not cooled by the cooling water as strongly as the engine itself, but is only 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 vaporizer 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 percolation, and in such a case, if the failure diagnosis is performed, there is a problem that a misdiagnosis is made.

[Means for solving problems]

In order to solve the above-mentioned problems, according to the present invention, the air-fuel ratio is feedback-controlled based on the output signal of the oxygen concentration detector arranged in the engine exhaust passage as shown in the block diagram of the invention of FIG. In a carburetor-equipped internal combustion engine equipped with an air-fuel ratio control device, temperature detection means for detecting the engine temperature,
Failure determination means for determining whether or not the air-fuel ratio control device has a failure based on the feedback control signal, and the engine after the engine temperature becomes equal to or higher than a predetermined set temperature based on the output signal of the temperature detection means. Failure occurs while the engine continues to operate after the engine temperature exceeds the set temperature based on the determination result of the continuous operation determination means that determines whether or not the engine is continuously operating. A failure discrimination prohibition means for prohibiting the failure discrimination by the discrimination means 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. When the air bleed control valve 11 is output from the electronic control unit 30, it is controlled based on a control current. 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 _{2 in the} exhaust manifold 4
The 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. A water temperature sensor 15 that generates an output voltage proportional to the engine cooling water temperature is attached to the draft book 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 is connected to 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. The output port 36 is connected on the one hand to the air bleed control valve 11 via a drive circuit 41 and on the other hand 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 0.
The O ₂ sensor 1 is compared with the reference voltage Vr of about 45 volts.
If the output voltage V of 3 is higher than Vr, it is judged to be rich, and if it is higher than Vr, it is judged to be lean.

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, when it is determined in step 50 that it is rich, the routine proceeds to step 55, where it is determined whether or not the lean-to-rich inversion was performed between the previous processing cycle and 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 inverted, the routine proceeds to step 57, where the integral value K is added to I,
Go to step 53. In step 53, I is output to the output port 36.

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 AMX, and if the air-fuel mixture continues to become lean 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. This flag is set when the engine cooling water temperature is higher than a predetermined temperature as described later. on the other hand,
When the starter switch 21 is turned off, the routine proceeds to step 63, where it is judged if the flag is set.
When the starter switch 21 is switched from on to off, the flag has been reset, so the routine proceeds to step 64. In step 64, 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 65, where the timer is set and then it proceeds to step 62, and when it is not switched from on to off, the routine proceeds to step 66. At step 66, it is judged if a fixed time has elapsed since the timer was set. When the fixed time has not elapsed, that is, when the fixed period has not elapsed after the engine has started, the routine proceeds to step 62, and when the fixed period has elapsed after the engine has started, the step 67.
Proceed to. In step 62, the cooling water temperature T is determined from the output signal of the water temperature sensor 15 to a preset temperature, for example 70 ° C.
Is higher than the above. If T> 70 ° C., the flag is set in step 68 to complete the post-processing cycle. Once the flag is set, it remains set as long as the engine continues to operate. By the way, when the flag is set, the processing routine is completed immediately through step 63. Therefore, once the flag is set, the failure diagnosis is not performed while the operation is continued for the period thereafter. That is, when the engine cooling water temperature T is higher than 70 ° C. at the time of starting the engine, the temperature of the carburetor 3 is considerably high, and at this time, percolation may occur. Furthermore,
Even if the engine cooling water temperature T decreases thereafter, the temperature of the carburetor 3 does not necessarily decrease accordingly, and therefore, even if the engine cooling water temperature T becomes 70 ° C. or less, percolation may occur. . Therefore, when the engine is started, the engine cooling water temperature T
When the temperature exceeds 70 ° C., the subsequent failure diagnosis is prohibited in order to prevent erroneous diagnosis due to the occurrence of barcolation. When the temperature is determined to be T70 ° C. in step 62, the process proceeds to step 69 without setting the flag.

On the other hand, if it is determined in step 66 that the predetermined time has elapsed since the engine was started, the routine proceeds to step 67, where 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 70, where the flag is set, and as a result, failure diagnosis is prohibited as long as the engine continues to operate. That is, 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. Furthermore, even if the engine cooling water temperature T decreases thereafter, the temperature of the carburetor 3 does not necessarily decrease accordingly, and therefore, even if the engine cooling water temperature T becomes 95 ° C. or less, percolation may occur. There is. Therefore, when the engine cooling water temperature T becomes 95 ° C. or higher after a lapse of a certain time after the engine is started, the subsequent failure diagnosis is prohibited in order to prevent erroneous diagnosis due to occurrence of percolation. It should be noted that the cooling water temperature of 95 ° C at which percolation is considered to occur after the engine has started for a certain period of time after starting the engine is higher than the cooling water temperature of 70 ° C at which percolation is likely to occur immediately after the engine starts because the vehicle has been operating for a certain period of time after engine startup. This is because the carburetor 3 is cooled by the traveling wind and the temperature of the carburetor 3 is lowered.

When it is determined that the temperature is T95 ° C. in step 67, the process proceeds to step 69. Therefore, the process proceeds to Step 69 before the engine has started and before a certain engine has passed, and the cooling water temperature T is 70.
When the temperature of the cooling water does not rise above 95 ° C., and when the cooling water temperature does not rise above 95 ° C. after a certain time has passed after the engine was started.

In steps 69, 71, 72 and 73, it is determined whether or not the operating state is one in which a failure diagnosis should be made. If the diagnosis is made in steps 74 and 75 and there is a failure, the warning lamp 22 is turned on in step 76. . That is, in step 69, it is determined whether the cooling water temperature T is 60 ° C. or lower. T <60
In the case of ° C, the processing cycle is completed, so that 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 choking effect, and therefore failure diagnosis is not performed in order to avoid erroneous diagnosis. Therefore, when a certain period of time has not passed after the engine was started, the failure diagnosis is performed only when 60 ° C. <T70 ° C., and once T <70 ° C., the failure diagnosis is not performed. On the other hand, when a certain period of time has passed after the engine was started, 6
Failure diagnosis is performed only when 0 ° C. <T95 ° C., and once T> 95 ° C., failure diagnosis is not performed.

At step 71, it is judged from the output signal of the throttle sensor 12 whether the throttle opening θ is 10 ° or less, and at 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 the range is within the range, and in step 73, it is determined from the output signal of the rotational speed sensor 20 whether or not the rotational speed N is within the range of 1500 r.pm <N <3000 r.p.m6. These steps 71, 72,
As can be seen from 73, fault diagnosis is not performed in order to avoid misdiagnosis in the low air-intake region where air bleed sensitivity is low and in the high-speed region where an 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 76, it is determined whether or not the state of IMIN or IMAX has passed for 10 seconds or longer, for example, and if 10 seconds or more has passed, it is determined that the air-fuel ratio control system has failed, and the routine proceeds to step 76, where the warning lamp 22 is turned on. It is turned on.

〔The invention's effect〕

Since the failure diagnosis is stopped in the operating state where percolation may occur in the carburetor even if the engine temperature decreases, it is possible to prevent erroneous diagnosis of the failure diagnosis.

[Brief description of drawings]

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.
The drawings are diagrams showing changes in the output signal of the O ₂ sensor and the control current, and 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 equal to or higher than a predetermined set temperature based on an output signal of the temperature detection means. After that, the engine continues to operate after the engine temperature exceeds the set temperature based on the determination result of the continuous operation determination means for determining whether the engine is continuously operating or not. A failure diagnosis device for an air-fuel ratio control system, comprising failure determination prohibition means for prohibiting failure determination by the failure determination means during operation.