JPS6338678A - Failure sensing unit for exhaust gas return diagnosis device - Google Patents

Abstract

PURPOSE:To prevent a faulty judgement, by prohibiting discrimination of a failure until warming up of an engine is completed when a failure of an exhaust gas return device is discriminated based on a temperature sensed by a temperature sensor disposed in an exhaust gas return passage. CONSTITUTION:A temperature sensor 7 using a thermistor is disposed downstream of an exhaust gas return valve 5 of an exhaust gas return passage 4. When a temperature sensed by a temperature sensor 7 is less than a prescribed value regardless of that it is an operating region wherein exhaust gas is returned based on values sensed by an air flow meter 10 and a crank angle sensor 12, a control circuit 13 lights a warning lamp 14 judging that an exhaust gas return device fails. Further, the diagnosis of a failure is prohibited based on a value sensed by a water temperature sensor 11 when a temperature at start is less than a first temperature which is so low that water is frozen in the vicinity of the temperature sensor 7. Then, the diagnosis of a failure is effected only when a water temperature at start is greater than a first temperature and when warming up of an engine has been completed it is greater than a second temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a failure diagnosis device for diagnosing whether or not an exhaust gas recirculation device in an automobile engine or the like is operating normally based on the temperature of an exhaust gas recirculation passage.

Conventional technologyIf the exhaust gas recirculation system of an automobile engine is out of order, it goes without saying that normal exhaust purification cannot be performed.
Generally, the failure of a car is difficult for the driver to notice, and there is a risk that the car will continue to be operated for a long time due to failure.

Therefore, as seen in Japanese Unexamined Patent Publication No. 51-94025, a temperature sensor such as a thermistor is installed in the exhaust gas recirculation passage equipped with an exhaust gas recirculation valve, and the exhaust gas recirculation system detects whether or not there is a temperature rise due to the flow of exhaust gas. Various devices have been proposed for diagnosing malfunctions. In other words, in the operating range where exhaust gas should be recirculating, it is determined based on the temperature whether or not exhaust gas is actually recirculating, and if exhaust recirculation is detected, it is diagnosed as a malfunction. It issues some kind of warning to the driver. The diagnostic range for performing the above diagnosis is, for example, in an electronically controlled fuel injection engine, using the fuel injection pulse width, especially the basic pulse width TP (calculated from the intake air amount and the engine speed) and the engine speed. It is set within the range included in the watershed.

Problems to be Solved by the Invention However, as mentioned above, when the temperature of the exhaust gas recirculation passage is detected using the W sensor, if the engine is in a cold state,
The temperature of the wall of the exhaust gas recirculation passage and the area around the temperature sensor is low, and as a result of the heat being absorbed by these, accurate temperature measurements cannot be performed. As an example, Figure 4 shows the change in detected temperature when exhaust gas recirculation is started under conditions where the outside temperature is relatively low. In the diagram, the solid line (A) indicates the actual exhaust gas temperature measured at the center of the exhaust gas recirculation passage using thermocouple 7, and the dashed line (
b) is the temperature detected by the temperature sensor in the warm-up state, and the chain double-dashed line (c) is the temperature in the cold state, the temperature detected by the fW sensor e
are shown respectively. The temperature sensor uses a thermistor and is attached to the wall of the exhaust gas recirculation passage.

As is clear from this figure, the temperature detected by the altitude sensor becomes lower than the actual exhaust gas temperature due to the external cooling effect, and the temperature decreases significantly in cold orange conditions in particular. Therefore, even though the exhaust gas is recirculating, the detected temperature may fall below the established temperature ((b) in Figure 4), which may result in a misdiagnosis.

Means for Solving the Problems Does this invention solve the above problems? In order to determine P4, a means for detecting the completion of warm-up of the engine is provided, and the diagnosis is prohibited until the warm-up is completed.

The completion of warm-up is detected based on, for example, the cooling water temperature, the ambient temperature in the engine room, or the elapsed time from the start of SVK. Diagnosis is not performed after starting until the warm-up in step 7 is completed.

Embodiment FIG. 1 is a configuration explanatory diagram showing an embodiment of the present invention, in which 1 is an engine body, 2 is an intake passage, 3 is an exhaust passage, and 4
5 indicates an exhaust gas recirculation passage that partially guides the exhaust gas from the exhaust passage 3 to the intake passage 2, and 5 indicates an exhaust gas recirculation valve that is interposed in the exhaust passage 4 and is a diaphragm type negative pressure valve. The exhaust gas recirculation valve 5 is opened and closed by the suction negative pressure 7 downstream of the throttle valve 6 and is controlled to open and close by the negative pressure acting on it through a control mechanism (not shown). is configured. Seventh, a temperature sensor 7 using a thermistor, for example, is installed in the exhaust gas recirculation passage 4 as a temperature detection means.

As shown in Figure 2, this temperature sensor 7 has a detection part 7a that protrudes into the exhaust gas recirculation passage 4 and is tightly screwed onto the wall surface of the exhaust gas recirculation passage 4. A hot water passage 8 is formed.

Constant cooling water heated by a water jacket (la) of the engine body 1 is introduced into the hot water passage 8.

A fuel injection valve 9 is disposed in the intake passage 2, and a hot wire type air 70, for example, which detects the intake nitrogen gas t2, is installed in the intake passage 2.
- A meter 10 is provided. In addition, the above-mentioned water jacket) la includes a water temperature sensor 1 as a means for detecting the completion of the warm room.
1 is installed. The reference numeral 12 denotes a crank angle sensor which is provided to detect the engine speed and emits a pulse signal at every predetermined crank angle.

The control circuit 13 uses a so-called microcomputer system, and centrally performs the injection elbow removal operation of the fuel injection valve 9, etc., and also controls the lid air recirculation system based on the detection number 4g of the m degree sensor 7. A failure diagnosis is performed on the system, and if it is determined that the song is being released, an alarm means such as an alarm lamp 14 is activated. Here, the above-mentioned failure diagnosis is not performed until the warm-up is completed in order to prevent erroneous diagnosis.

FIG. 3 is a flowchart showing a program for determining whether or not to perform the failure diagnosis 1. First, in step 1, it is determined whether the water temperature at startup is equal to or higher than the first set temperature (TWEJI). This first set temperature is set to a relatively low temperature that may cause freezing around the temperature sensor 7, for example.If the water temperature at startup is below this temperature, an error may occur even after warm-up has been completed. No diagnosis is made as it may result in a diagnosis.

If the water temperature at startup is equal to or higher than the first set temperature, then in step 2 the process waits until the water temperature rises and falls to the second set temperature (TWEJ2). This second set temperature is set to a temperature that can be considered as a precaution after warm-up has been completed, and when the cooling water temperature reaches this temperature, for safety reasons, there is a further wait for a certain period of time (Step 3).
, 5), after 7, start the diagnosis (step 6). At this stage, the area around the temperature sensor 7 is sufficiently warm, and as shown in the fourth factor, the flow of exhaust gas can be detected reliably and with good responsiveness. In particular, as mentioned above, the hot water passage 8' is located near the temperature sensor 7? : If provided, there is no risk that the temperature sensor 7 will be excessively cooled even when the outside temperature is quite low, and erroneous diagnosis can be reliably prevented. The above-mentioned diagnosis is performed, for example, by checking whether the temperature detected by the temperature sensor 7 is equal to or higher than a predetermined judgment temperature when the operating conditions are within a predetermined diagnostic range, but other diagnostic methods are also possible. be.

In the above embodiment, step 1 determines the water temperature at startup! However, the intake air temperature may be used instead.

Effects of the Invention As is clear from the above explanation, in the exhaust gas recirculation passage failure diagnosis device according to the present invention, diagnosis before completion of warm-up is prohibited, so that it is possible to prevent erroneous diagnosis when the outside temperature is low. , the reliability of diagnosis can be increased.

[Brief explanation of the drawing]

Fig. 1 is a configuration explanatory diagram showing an embodiment of the present invention, Fig. 2 is an enlarged sectional view of the vicinity of the temperature sensor, Fig. 3 is a flowchart showing a diagnostic program in this embodiment, and Fig. 4 shows that exhaust gas is recirculated. FIG. 3 is a characteristic diagram showing a comparison of changes in detected temperature when the engine is warmed up and when it is cold. 4... Exhaust recirculation passage, 5... Exhaust recirculation valve, 7...
Temperature sensor, 8... Hot water passage, 11... Water temperature sensor, 13... Control circuit, 14... Alarm lamp. Figure 1 Figure 2 D

Claims (1)

[Claims] (1) In a failure diagnosis device for an exhaust gas recirculation system that includes a temperature detection means in the exhaust gas recirculation passage and diagnoses a failure based on the detected temperature, a means for detecting the completion of warm-up of the engine is provided, and until the warm-up is completed, A failure diagnosis device for an exhaust gas recirculation device, characterized in that diagnosis is prohibited.