JPH0689716B2 - 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, the EGR control valve may fail or become clogged, and the supply of EGR gas may continue 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 arranged in the EGR passage downstream of the EGR control valve, and when the operating state in which EGR gas should be recirculated, the EGR passage downstream of the EGR control valve 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 used when EGR gas is recirculated.
The fact that the temperature inside the gas passage rises is used.

[Problems to be solved by the invention]

However, this fault diagnosis device has a problem in that when the exhaust gas temperature is low, it is determined to be a fault even if the EGR supply control is being performed, and therefore 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. The temperature rise amount in the exhaust gas recirculation passage 8 is lower than or equal to a predetermined rise amount during a certain period of time from when the operating state of the internal combustion engine becomes the above-mentioned predetermined operation state. Sometimes exhaust gas recirculation equipment There has been provided with a determination unit 101 to determine that a failure.

[Action]

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. Exhaust gas recirculation when the temperature rise in the exhaust gas recirculation passage during a certain period of time is low and when the operating state of the internal combustion engine has reached the predetermined operating state It is determined that the 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 connected to each other 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 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. A throttle opening sensor 21 for detecting the opening of the throttle valve 5 is connected to the throttle valve 5, and the throttle opening sensor 21 is connected to the input port 15 via an AD converter 22. Further, a water temperature sensor 23 for detecting the engine cooling water temperature is attached to the engine body 1,
The water temperature sensor 23 is connected to the input port 15 via the AD converter 18. Further, a vehicle speed sensor 25 is connected to the input port 15. 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, 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 acceleration operation is performed as indicated by S _1.
Since the supply of EGR gas is stopped, the curve T in FIG.
As shown by, the temperature T has a low value. 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 the EGR gas is stopped, so that the temperature T decreases. Next, when the steady operation is performed as indicated by S ₄ , the EGR gas is recirculated so that the temperature T gradually rises. Next, when the deceleration operation is performed as indicated by S ₅ , the temperature T gradually decreases because the supply of EGR gas is stopped. Therefore, it can be seen from FIG. 3 that the temperature T rises while the EGR gas is being recirculated. Thus, if the temperature T rises after a lapse of a certain time in the operating state where the EGR gas should be recirculated, the EGR gas supply control is normally performed, and the temperature T should hardly change after the lapse of the certain time. For example, it can be determined that the EGR device is out of order.

As can be seen from FIG. 3, according to the present invention, when the operating state in which the EGR gas is to be recirculated is reached, the temperature T at that time and the temperature increase amount during the elapse of a certain time t from that time
R It is determined whether or not the device has failed. In other words, the EGR gas is immediately recirculated when the operating state is reached.
A determination is made as to whether the device is faulty. Thus
There is an advantage that it can be detected early whether or not the EGR device has failed.

On the other hand, if the amount of temperature rise within a certain period of time is less than or equal to the predetermined amount of rise, it can be basically determined that the EGR device is malfunctioning, but the amount of temperature rise within a certain period of time Is less than or equal to a predetermined amount of increase, there is a possibility of making an erroneous decision if the EGR device is immediately determined to be out of order.

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, it can be determined that the EGR device is out of order if the amount of temperature rise in this time is small. However, for example, even if the EGR gas recirculation is started while the temperature in the EGR passage 8 is being increased while the engine high load operation is continuously performed, the temperature in the EGR passage 8 hardly rises. Therefore, at this time, since the amount of temperature rise within a certain period of time is small, it is erroneously judged that the EGR device is judged to be out of order. 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 amount of temperature increase within a certain time is small when the temperature in the EGR passage 8 is low. In the embodiment, when the temperature T in the EGR passage 8 is lower than the predetermined temperature T ₀ , the increase amount of the temperature T within a certain time period is obtained, and at this time, the increase amount of the temperature T within the predetermined time period is determined. If it is smaller than the rising amount, it is judged that the EGR device is out of order.

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 it is not in the operating state in which the EGR gas should be recirculated, the routine proceeds to step 32, where the flag is reset.

On the other hand, when it is determined in step 31 that the operating state is such that the EGR gas should be recirculated, the process proceeds to step 33, and it is determined whether or not the flag is set. When it proceeds to step 33 for the first time after it is determined that the operating condition is to recirculate the EGR gas, the flag has been reset, so the process proceeds to step 34 and the temperature T is set to T ₁ . Next, at step 35, the flag is reset, and the routine proceeds to step 36. In step 36, it is judged whether or not a fixed time has elapsed since the temperature T was set to T _1, and when the fixed time has not elapsed, the processing cycle is completed. In the next processing cycle, the process jumps from step 33 to step 36, so that the temperature T ₁ is maintained as it is without being updated until a certain time has elapsed. This fixed time is indicated by t in FIG.
When a certain period of time has passed, the routine proceeds to step 37, where the temperature T is set to T ₂ . Then, in step 38, the flag is reset. Next, at step 39, the temperature T ₂
And a difference (T ₂ −T ₁ ) between the temperatures T ₁ at the start of counting for a certain period of time is larger than a predetermined certain value ΔT. 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 40, where the data for lighting the warning lamp 28 is output to the output port 16.

〔The invention's effect〕

Even if the exhaust gas temperature is low, whether or not the EGR device has failed can be early and accurately determined regardless of the operating state of the engine before the failure of the EGR device is determined.

[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, While the temperature in the exhaust gas recirculation passage detected by the exhaust gas temperature sensor is lower than a predetermined temperature and the operating state of the internal combustion engine reaches the predetermined operating state for a certain period of time A failure diagnosis device for an exhaust gas recirculation device, comprising: a determination unit that determines that the exhaust gas recirculation device has a failure when the temperature increase amount in the exhaust gas recirculation passage is equal to or less than a predetermined increase amount.