JPH0692776B2 - Exhaust gas recirculation device failure diagnosis device - Google Patents

Description

The present invention relates to a failure diagnostic device for an exhaust gas recirculation device.

[Conventional technology]

An EGR device is known in which exhaust gas is recirculated into an intake passage through an exhaust gas recirculation (hereinafter referred to as EGR) passage in order to reduce NOx in the exhaust gas. E like this
In the GR device, an EGR control valve is usually provided in the EGR passage, and the EGR control valve controls the amount of EGR gas to be supplied into the intake passage. However, there are cases where the EGR control valve fails or is clogged, and the supply of EGR gas continues to stop. In such a case, if this is left as it is, a large amount of NOx continues to be emitted. Further, even if the supply of EGR gas is stopped in this way, the driver does not know that. Therefore, in order to judge such a failure of the EGR device, an exhaust gas temperature sensor is installed in the EGR passage downstream of the EGR control valve to recirculate the ERG gas. A failure diagnosis device is known in which it is determined that the EGR device is out of order when the temperature of the vehicle does not rise above a certain temperature.
-64623 or Japanese Utility Model Laid-Open No. 50-67220). This fault diagnosis method is E when EGR gas is recirculated.
The fact that the temperature inside the GR gas passage rises is used.

[Problems to be solved by the invention]

However, this failure diagnosis device has a problem in that when the exhaust gas temperature is low, it is diagnosed as a failure even if the EGR supply control is performed, and thus a misdiagnosis is made. On the other hand, if the upper limit value of the temperature considered to be faulty is set low, it is always determined to be normal, and thus the fault cannot be diagnosed.

[Means for solving problems]

In order to solve the above problems, according to the present invention, an exhaust gas temperature sensor 17 is arranged in an exhaust gas recirculation passage 8 of an internal combustion engine as shown in the block diagram of the invention of FIG. In the failure diagnosis device which determines the failure of the exhaust gas recirculation device from the output signal of the sensor 17, whether the operating condition of the internal combustion engine is a predetermined operating condition in which exhaust gas recirculation is being performed or not. And a temperature inside the exhaust gas recirculation passage 8 detected by the exhaust gas temperature sensor 17 when the operating state of the internal combustion engine is the above-mentioned predetermined operating state. And a determination means 102 for determining that the exhaust gas recirculation device is out of order when the temperature increase amount is lower than the predetermined increase amount.

[Work]

The temperature in the exhaust gas recirculation passage detected by the exhaust gas temperature sensor is higher than the predetermined temperature when the operating state of the internal combustion engine is the predetermined operating state in which the exhaust gas is being recirculated. When it is low and the amount of increase in this temperature is equal to or less than the predetermined amount of increase, it is determined that the exhaust gas recirculation device is out of order.

〔Example〕

Referring to FIG. 2, 1 is an engine body, 2 is an exhaust manifold, 3 is an intake manifold, 4 is an intake duct, 5 is a throttle valve provided in the intake duct 4, 6 is an air flow meter, and 7 is an intake manifold 3. , 8 is an EGR passage communicating the exhaust manifold 2 and the intake manifold 3, 9 is an EGR control valve provided in the EGR passage 8, and 10 is an electronic control unit, The exhaust gas in the exhaust manifold 2 is supplied into the intake manifold 3 via the EGR passage 8 and the EGR control valve 9.

The electronic control unit 10 is composed of a digital computer, and has a ROM (read only memory) 12, a RAM (random access memory) 13, a CPU (microprocessor) 14, and an input port 15 which are mutually connected by a bidirectional bus 11.
And an output port 16. EGR control valve 9 EGR downstream
An exhaust gas temperature sensor 17 is arranged in the passage 8, and the exhaust gas temperature sensor 17 is connected to the input port 15 via the AD converter 24. An intake air temperature sensor 19 is arranged in the intake duct 4, and the intake air temperature sensor 19 is connected to the input port 15 via the AD converter 20. Further, the throttle valve 5 has a throttle opening sensor 21 for detecting the opening of the throttle valve 5.
This throttle opening sensor 21 is connected to the AD converter 22.
Connected to the input port 15 via. In addition, the engine body 1
A water temperature sensor 23 that detects the engine cooling water temperature is attached to the water temperature sensor 23.
Connected to 15. In addition, the input port 15 has a vehicle speed sensor 25
Are connected. The output port 16 is connected on the one hand to the corresponding fuel injection valve 7 via a respective drive circuit 26 and on the other hand to a warning lamp 28 via a drive circuit 27.

Next, the fault diagnosis method according to the present invention will be described with reference to the time chart shown in FIG. V in FIG.
Is the vehicle speed, C is the count value of the counter, and T is the temperature detected by the exhaust gas temperature sensor 17. Note that FIG. 3 shows an example in which the supply of EGR gas is stopped during acceleration operation and deceleration operation. Further, FIG. 3 shows a case where the exhaust gas temperature is low such as when the engine is cold-started or when the engine is operated in a cold region. When the acceleration operation is performed as indicated by S ₁ , the supply of EGR gas is stopped, so that the temperature T becomes a low constant value as indicated by the broken line in FIG. Then, when steady operation is performed as indicated by S ₂ , the EGR gas is recirculated, so that the temperature T gradually rises. Next, when the acceleration operation is performed as indicated by S ₃ , the supply of EGR gas is stopped, and the temperature decreases at T. Next, as shown in S ₄ , when the steady operation is performed, the EGR gas is recirculated, so that the temperature T gradually rises, and when the steady operation is continued, the temperature T becomes a constant value.
Next, when the deceleration operation is performed as indicated by S ₅ , EGR
The temperature T gradually decreases because the gas supply is stopped. As described above, when the EGR gas supply control is normally performed, the temperature T changes according to the operating state of the engine.

On the other hand, the count value C of the counter is designed to increase / decrease between MIN and MAX, and the count value C is further increased in the operating state where the EGR gas should be recirculated.
It is reduced during operating conditions when the gas supply should be stopped. Therefore, it can be seen that this count value C changes following the temperature T. When the EGR gas supply control is normally performed, the temperature T rises considerably when the count value C changes from MIN to MAX. On the other hand, when the supply of EGR gas continues to be stopped, the count value C changes from MIN to MAX.
Even if it becomes, the temperature T hardly changes. Therefore, if the temperature difference between the temperature T when the count value C is MIN and the temperature T when the count value C is MAX is a certain value or more, the EGR gas supply control is normally performed, and the temperature difference is constant. If it is less than the value, it can be determined that the EGR device is out of order.

Thus, if the temperature difference between the temperature T when the count value C is MIN and the temperature T when the count value C is MAX is less than a certain value, that is, the amount of temperature increase is less than a predetermined amount of increase. If so, it can be basically judged that the EGR device has failed, but since the amount of temperature rise is less than the predetermined amount of rise, it is possible to make an erroneous decision to immediately judge that the EGR device has failed. There is a nature.

That is, if the EGR gas recirculation is started when the temperature in the EGR passage 8 is low, the temperature in the EGR passage 8 will rise considerably.
Therefore, if the amount of temperature rise at this time is small, it can be determined that the EGR device is out of order. However, for example, when the engine high load operation is continuously performed and the temperature in the EGR passage 8 is high, even if the recirculation of the EGR gas is started, the temperature in the EGR passage 8 hardly rises. Therefore, at this time, since the amount of temperature rise is small, if the EGR device is determined to be out of order, it is erroneously determined. Therefore, in order to prevent such an erroneous judgment, it is necessary to judge the failure of the EGR device based on whether or not the temperature increase amount is small when the temperature in the EGR passage 8 is low, and therefore, in the embodiment according to the present invention.
When the temperature T in the EGR passage 8 is lower than a predetermined temperature T ₀ , the increase amount of the temperature T is calculated, and when the increase amount of the temperature T is smaller than the predetermined increase amount, the EGR device fails. I try to judge that I am doing it.

4 and 5 show flowcharts for executing the failure diagnosis method described with reference to FIG. The routines shown in FIG. 4 and FIG. 5 are executed by interruption at regular time intervals. Referring to FIGS. 4 and 5, first, at step 30, the exhaust gas temperature sensor 17
The temperature T detected by the predetermined constant temperature T ₀
Is determined to be greater than or equal to. If TT ₀ , the processing cycle is completed. On the other hand, when T <T ₀ , step 31
Proceeding to step S1, the intake air temperature sensor 19, the throttle opening sensor 21, the water temperature sensor 23, the output signals of the vehicle speed sensor 25, and the fuel injection time of the fuel injection valve 7 are used to determine whether the EGR gas should be recirculated. To be determined. When the EGR gas is not in the operating state for recirculation, the routine proceeds to step 32, where the count value C is decremented by 1, and then the count value C is
If it becomes smaller than MIN, the routine proceeds to step 34, where C = MIN. Therefore, when the EGR gas is not in an operating state in which it should be recirculated, the count value C gradually decreases and the count value C
When reaches MIN, C = MIN is set thereafter.

On the other hand, when it is determined in step 31 that the EGR gas should be recirculated, the process proceeds to step 35, where C =
It is determined whether or not it is MIN. If C = MIN, the process proceeds to step 36 and the temperature T is set to T ₁ . Next, at step 37, a determination flag described later is reset. Next, at step 38, the count value C is incremented by 1.
Next, at step 39, it is judged if CMAX or not, and if C <MAX, the processing cycle is completed. on the other hand,
If it is CMAX, the routine proceeds to step 40, where C = MAX.
Therefore, when the operating state in which the EGR gas should be recirculated is C = MIN, the temperature T at that time is set to T _1, and thereafter, the step jumps from step 35 to step 38, so the count value C gradually increases. Then, when the count value C reaches MAX, C = MAX.

When C = MAX, the routine proceeds from step 40 to step 41, where it is judged if the judgment flag is set. If T ₁ is found in step 36, the determination flag has been reset, so the routine proceeds to step 42, where the temperature T is set to T ₂ . Therefore, this T ₂ indicates the temperature T when C = MAX. Next, at step 43, the judgment flag is set. Next, at step 44, it is judged if the difference (T ₂ −T ₁ ) between the temperature T ₂ when C = MAX and the temperature T ₁ when C = MIN is larger than a predetermined constant value ΔT. To be done. If T ₂ −T ₁ > ΔT, the processing cycle is completed.
On the other hand, if T ₂ −T ₁ ΔT, the routine proceeds to step 45, where the data for lighting the warning lamp 28 is output to the output port 16. After it is determined in step 44 whether T ₂ −T ₁ > ΔT, the processing cycle is completed through step 41.

〔The invention's effect〕

It is possible to accurately determine whether or not the EGR device has failed, even when the exhaust gas temperature is low, regardless of the operating state of the engine before determining the failure of the EGR device.

[Brief description of drawings]

1 is a block diagram of the present invention, FIG. 2 is an overall view of an internal combustion engine,
FIG. 3 is a time chart showing the failure diagnosis method according to the present invention, and FIGS. 4 and 5 are flowcharts for executing the failure diagnosis method according to the present invention. 2 ... Exhaust manifold, 3 ... Intake manifold, 8 ... EGR passage, 9 ... EGR control valve, 17 ... Exhaust gas temperature sensor.

Claims (1)

[Claims] 1. A failure diagnosis device, wherein an exhaust gas temperature sensor is arranged in an exhaust gas recirculation passage of an internal combustion engine and a failure of the exhaust gas recirculation device is judged from an output signal of the exhaust gas temperature sensor. Determining means for determining whether or not the operating state of the internal combustion engine is a predetermined operating state in which exhaust gas is being recirculated, and when the operating state of the internal combustion engine is the predetermined operating state, When the temperature in the exhaust gas recirculation passage detected by the exhaust gas temperature sensor is lower than the predetermined temperature and the amount of increase in the temperature is less than or equal to the predetermined amount of increase, the exhaust gas recirculation device has failed. A failure diagnosis device for an exhaust gas recirculation device, which is provided with a judgment means for judging that the exhaust gas recirculation device exists.