JPS63309755A - Trouble diagnosing device for air-fuel ratio controller - Google Patents

Abstract

PURPOSE:To prohibit the erroneous judgment in the case when percolation is generated in a carburetor by prohibiting the judgment of trouble of an air-fuel ratio controller in the continuous operation of an engine body after the temperature of the engine body becomes over a set value. CONSTITUTION:As for an engine body 1, a variable vneturi type carburetor 3 is installed in an intake passage 2, and an oxygen concentration sensor 13 is installed in an exhaust passage 14. An air bleed valve control valve 11 installed in a fuel passage 7 is operated on the basis of the detection signal of the detector 13, and the air-fuel ratio is feedback-controlled. In this case, after the temperature of the engine body 1 which is detected by a means A becomes over a set value, a means B judges if the engine body 1 is in the continuous operation or not. When the engine body 1 is in the continuous operation, the trouble judgement by a means D for judging the trouble of an air-fuel ratio controller on the basis of the feedback control signal is prohibited by a means C.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a failure diagnosis device for an air-fuel ratio control system.

[Conventional technology]

In an internal combustion engine equipped with an air-fuel ratio control device for maintaining the air-fuel mixture supplied into the engine cylinder at a stoichiometric air-fuel ratio, if the air-fuel ratio control device fails, the air-fuel mixture becomes lean or rich. In this case, if the air-fuel mixture becomes quite lean, the engine output will drop and the driver will notice that something is wrong, but if the air-fuel mixture becomes somewhat lean or rich, the driver will notice Since the engine does not notice that an abnormality has occurred, the engine continues to operate, resulting in the problem of a large amount of Co, HC, or NOx being discharged. In order to solve this problem, it is determined whether the air-fuel mixture is lean or rich based on the feedback control signal, and based on this, it can be determined whether the air-fuel ratio control device is malfunctioning. The present applicant has already proposed a fault diagnosis device that performs this determination (see Japanese Patent Application No. 61-243217).

However, in an internal combustion engine with a carburetor, when the carburetor temperature rises, so-called percolation occurs, and the fuel is discharged into the intake passage, resulting in an overrich mixture. Therefore, when a failure is diagnosed at this time, it is determined that the air-fuel ratio control device is malfunctioning even though the air-fuel ratio control device is not malfunctioning, resulting in a problem of misdiagnosis.

In order to solve this problem, the applicant has already proposed a fault diagnosis device that detects the engine temperature that changes in relation to the carburetor temperature and prohibits fault diagnosis while the engine temperature is high. (See Japanese Patent Application No. 62-090711). This fault diagnosis device assumes that if the engine temperature decreases, the carburetor temperature also decreases, and if we consider this, the engine temperature will drop below the engine temperature at which the carburetor will no longer generate percolation. Fault diagnosis is started when the power level drops.

[Problem that the invention seeks to solve]

However, unlike the engine itself, the carburetor is not strongly cooled by cooling water, but is only cooled by the vehicle wind flowing around the carburetor, so once the carburetor temperature reaches a high temperature, the engine temperature will drop. Even the vaporizer temperature does not drop immediately. That is, even if the engine temperature actually decreases, the carburetor temperature does not necessarily decrease accordingly. Therefore, even if the engine temperature decreases, the carburetor may still generate percolation, and if a failure diagnosis is performed in such a case, there is a problem of erroneous diagnosis.

[Means for solving problems]

In order to solve the above problems, according to the present invention, the air-fuel ratio is feedback-controlled based on the output signal of an oxygen concentration detector disposed in the engine exhaust passage, as shown in the block diagram of the invention in FIG. In an internal combustion engine with a carburetor equipped with an air-fuel ratio control device, a temperature detection means for detecting engine temperature;
failure determination means for determining whether or not the air-fuel ratio control device is malfunctioning based on a feed valve control signal; and a failure determination means for determining whether or not the air-fuel ratio control device is malfunctioning based on a feed valve control signal; Continuous operation determination means determines whether or not the engine is continuously operated after the engine temperature reaches or exceeds the set temperature based on the determination result of the continuous operation determination means. The device is equipped with a failure determination prohibition means for prohibiting failure determination by the failure determination means while the failure determination means is in use.

〔Example〕

Referring to FIG. 2, ▪ indicates the engine body, 2 indicates an intake manifold, 3 indicates a variable Henchuri carburetor, and 4 indicates an exhaust manifold. The variable Henchuri type carburetor 3 includes an intake passage 5, a suction piston 6, a fuel passage 7 opening into the intake passage 5, and a throttle valve 8. The amount of fuel supplied from the passage 7 into the intake passage 5 is controlled.

An air bleed passage 10 is connected to the fuel passage 7, and an air bleed control valve 11 is disposed within the air bleed passage 10. This air bleed control valve 11 is controlled based on a control current output from an 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 leaner. 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 richer. Become.

The electronic control unit 30 consists of a digital computer with ROMs interconnected by a bidirectional bus 31.
(read only memory) 32, RAM (random access memory) 33, CPU (microprocessor) 3
4, 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 the input port 35 via an AD converter 37. An 02 sensor 13 is attached to the exhaust manifold 4, and the output signal of the 0□ sensor 13 is input to the input port 35 via the AD converter 38. In addition, the intake manifold 2
A negative pressure sensor 14 that generates an output voltage proportional to the negative pressure inside the
is attached, and the output voltage of this negative pressure sensor 14 is input to the input port 35 via the AD converter 39. Also,
A water temperature sensor 15 that generates an output voltage proportional to the engine cooling water temperature is attached to the engine body 1.
The output voltage is input to the input port 35 via the AD converter 40. Furthermore, the input port 35 includes a rotation speed sensor 20 that generates an output pulse proportional to the engine rotation speed, and a starter switch 2 for operating the starter motor.
1 is connected. The output port 36 is connected to the drive circuit 4 on the one hand.
1 to the air bleed control valve 11 and, on the other hand, to the warning lamp 22 via a drive circuit 42 .

FIG. 4 shows changes in the output voltage ■ of the 0□ sensor 13. 0
□Sensor 13 generates an output voltage of about 0.9 volts when the air-fuel mixture is rich, that is, when it is rich, and generates an output voltage of about 0.1 volts when the air-fuel mixture is lean, that is, lean. . The output voltage ■ of the sensor 13 is compared with a reference voltage Vr of about 0.45 volts in the CPU 34,
If the output voltage V of the 02 sensor 13 is higher than Vr, it is determined that the vehicle is rich, and if it is lower than Vr, it is determined that the vehicle is lean.

FIG. 3 shows a calculation routine for the control current I of the air bleed control valve 11 based on this lean/rich determination.

Referring to FIG. 3, first, in step 50, it is determined whether the engine is lean or not. If it is lean, the process proceeds to step 51, where it is determined whether or not it has reversed from rich to lean between the previous processing cycle and the current processing cycle. If it is reversed, the process proceeds to step 52, where the skip value A is subtracted from I, and the process proceeds to step 53. If it is not inverted, the process advances to step 54 and the integral value K(K(
A) is subtracted and the process proceeds to step 53. On the other hand, if it is determined in step 50 that the fuel is rich, the process proceeds to step 55, where it is determined whether or not there has been an inversion from lean to rich between the previous processing cycle and the current processing cycle. If it is reversed, the process proceeds to step 56, where the skip value A is added to I, and the process proceeds to step 53. If it is not inverted, the process proceeds to step 57 where the integral value K is added to I, and the process proceeds to step 53. In step 53, I is output port 3.
6 is output.

Therefore, as shown in Figure 4, 1 suddenly decreases by the skip value A when changing from rich to lean, and then gradually decreases, and when changing from lean to rich, it suddenly increases by the skip value A and then gradually decreases. increase By the way, ■ calculated at each step 52, 54, 56, 57 in FIG. Continuous pulses with varying pulse widths are supplied to the air bleed control valve 11 in accordance with this duty ratio. Air bleed control valve 1
1 is controlled to an opening degree according to the average current of this continuous pulse, and therefore, 2 is called the control current of the air bleed control valve 11. The control current I that can control the air-fuel ratio is between the minimum value MIN and the maximum value MAXO in FIG. 4, and during feedbank control, the control current I normally moves up and down between MIN and MAX-. However, if the air-fuel mixture continues to become too rich for some reason, I reaches MAX, and if the air-fuel mixture continues to become too lean for some reason, I reaches MIN. Therefore, it is possible to determine whether the air-fuel ratio control device is abnormal depending on whether I has reached MAX or MIN.

Next, the fault diagnosis method according to the present invention will be explained with reference to FIGS. 5 and 6. Note that the routines shown in FIGS. 5 and 6 are executed by interrupts at fixed time intervals.

Referring to FIGS. 5 and 6, first, in step 60, it is determined whether or not the starter switch 21 is on. If it is on, the process proceeds to step 61, where the flag is reset, and then step 62 Proceed to. This flag is set when the engine cooling water temperature is higher than a predetermined temperature, as will be described later. on the other hand,
When the starter switch 21 is turned off, the process proceeds to step 63, where it is determined whether the flag is set.

When the starter switch 21 is turned from on to off, the flag has been reset, so the process proceeds to step 64. In step 64, it is determined whether the starter switch 21 was switched from on to off between the previous processing cycle and the current processing cycle. If the switch has been made from on to off, the process proceeds to step 65 and after a timer is set, the process proceeds to step 62; if the change from on to off has not been made, the process proceeds to step 66. In step 66, it is determined whether a certain period of time has elapsed since the timer was set. If the predetermined period of time has not elapsed, that is, if the predetermined period has not elapsed since the engine was started, the process proceeds to step 62, and if the predetermined period has elapsed since the engine was started, the process proceeds to step 67. In step 62, it is determined from the output signal of the water temperature sensor 15 whether the cooling water temperature T is higher than a predetermined set temperature, for example 70°C. If T>70° C., the post-processing cycle with the flag set in step 68 is completed. Once the flag is set.

Once set, this flag will remain set as long as the engine continues to operate. By the way, once the flag is set, the processing routine is immediately completed through step 63, so once the flag is set, no fault diagnosis is performed while the engine continues to operate. That is, when the engine cooling water temperature T is higher than 70°C when the engine is started, the temperature of the carburetor 3 is also quite high.
Therefore, there is a possibility that percolation is occurring at this time. Furthermore, even if the engine cooling water temperature T subsequently decreases, the temperature of the carburetor 3 does not necessarily decrease accordingly, and thus there is a possibility that percolation may occur even if the engine cooling water temperature T falls below 70°C. There is. Therefore, when the engine cooling water temperature T reaches 70° C. or higher when the engine is started, subsequent failure diagnosis is prohibited in order to prevent misdiagnosis due to the occurrence of percolation. If it is determined in step 62 that T<70°C, the process proceeds to step 69 without setting the flag.

On the other hand, if it is determined in step 66 that a certain period of time has elapsed after engine startup, the process proceeds to step 67, where the cooling water temperature T
It is determined whether or not the temperature is higher than a predetermined set temperature, for example, 95°C. If T>95°C, step 70
A flag is then set, thus inhibiting fault diagnosis as long as the engine continues to operate. That is, if the engine cooling water temperature T is higher than 95° C. after a certain period of time has elapsed after the engine has been started, the temperature of the carburetor 3 has also become considerably high, so there is a possibility that percolation is occurring at this time. Furthermore, even if the engine cooling water temperature T subsequently decreases, the temperature of the carburetor 3 does not necessarily decrease accordingly, and thus percolation does not occur even if the engine cooling water temperature T becomes 95°C or less. There is a possibility that there are. Therefore, when the engine cooling water temperature T reaches 95° C. or higher after a certain period of time has elapsed after the engine is started, subsequent failure diagnosis is prohibited in order to prevent misdiagnosis due to occurrence of percolation. Note that the cooling water temperature of 95°C, at which percolation is thought to occur after a certain period of time after engine startup, is higher than the cooling water temperature of 70°C, at which percolation is thought to occur immediately after engine startup. This is because when the engine is operated, the carburetor 3 is cooled by the wind from the vehicle, and the temperature of the carburetor 3 decreases.

If it is determined in step 67 that T-≦-95°C, the process proceeds to step 69. Therefore, proceed to step 69 before a certain period of time has elapsed after starting the engine and the cooling water temperature T has not risen above 70°C, and after a certain period of time has elapsed after starting the engine and the cooling water temperature has reached 95°C. This is when the temperature does not rise above ℃.

Steps 69.7L and 72.73 determine whether or not the operating state requires failure diagnosis, and steps 74.75
Diagnose the failure and if it is a failure, proceed to step 7.
6, the warning lamp 22 is turned on. That is, in step 69, it is determined whether the cooling water temperature T is 60° C. or lower. If T<60° C., the processing cycle is completed and therefore no fault diagnosis is performed in this case. T〈6
When the temperature is 0° C., the air-fuel mixture may be too rich due to the choke effect, so failure diagnosis is not performed to avoid misdiagnosis. Therefore, if a certain period of time has not elapsed since the engine was started, fault diagnosis is performed only when 60°C<T<70°C, and once T>70°C, fault diagnosis is not performed. - On the other hand, when a certain period of time has elapsed after the engine is started, failure diagnosis is performed only when 60°C<T<95°C, and once T>95°C, failure diagnosis is not performed.

In step 71, it is determined from the output signal of the throttle sensor 12 whether the throttle opening θ is 10' or less, and in step 72, it is determined from the output signal of the negative pressure sensor 14 that the negative pressure P is 180**Hg<P< It is determined whether or not the rotation speed N is within the range of 150 Or, p, m < N < from the output signal of the rotation speed sensor 20 in step 73.
It is determined whether or not it is within the range of 300Or, p, m.

As can be seen from these steps 71, 72, and 73, failure diagnosis is not performed in the low intake air region where air bleed sensitivity is low and in the high speed region where a high output air-fuel ratio is required to avoid misdiagnosis.

In step 74, it is determined whether the control current l is in the range of MIN<I<MAX. Next, in step 76, it is determined whether or not the state of I < M I N or IλMAX has elapsed for more than 10 seconds, for example, and if more than 10 seconds have elapsed, it is assumed that the air-fuel ratio control system has failed, and the process proceeds to step 76. , the warning lamp 22 is turned on.

〔Effect of the invention〕

Even if the engine temperature drops, the fault diagnosis is canceled when the engine is in an operating state in which percolation may occur in the carburetor, so that misdiagnosis of the fault diagnosis can be prevented.

[Brief explanation of drawings]

Figure 1 is a block diagram of the invention, Figure 2 is an overall diagram of the internal combustion engine, Figure 3 is a flowchart for calculating the control current, and Figure 4 is a flowchart for calculating the control current.
The figure is a diagram showing changes in the output signal of the 02 sensor and the control current, and FIGS. 5 and 6 are flowcharts for executing the failure diagnosis process. 3... Carburetor, 7... Fuel passage, lO
...Air bleed passage, 11...Air bleed' control valve, 13...02 sensor, 15...Water temperature sensor. Fig. 1 3... Carburetor 7... Fuel passage 1]... Air lead control valve 13... 02 sensor Fig. 3 Rich Lean Fig. 4 JP-A-1. ffG3-309755 (7) Figure 5

Claims (1)

[Claims] Temperature detection means for detecting engine temperature and feedback control in an internal combustion engine with a carburetor equipped with an air-fuel ratio control device that performs feedback control of an air-fuel ratio based on an output signal of an oxygen concentration detector disposed in an engine exhaust passage failure determination means for determining whether or not the air-fuel ratio control device is malfunctioning based on a signal; Continuous operation determining means for determining whether or not the engine is being continuously operated; and while the engine is being continuously operated after the engine temperature reaches or exceeds the set temperature based on the determination result of the continued operation determining means. A failure diagnosis device for an air-fuel ratio control system is provided with a failure determination prohibition means for prohibiting failure determination by the failure determination means.