JP3262905B2 - Engine exhaust purification device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an engine, and more particularly, to prevention of deterioration of an exhaust gas purifying apparatus having a mechanism for forcibly heating when the engine is started.

[0002]

2. Description of the Related Art A catalyst for purifying exhaust gas is not activated unless it is heated to a predetermined temperature. Therefore, in order to increase the purifying capacity of the purifying device when starting the engine,
In particular, there is known an exhaust gas purifying apparatus in which a catalyst is forcibly heated when an engine is started (for example, Japanese Patent Application Laid-Open No. 4-66715).

[0003]

By the way, when the engine is cold, the engine may not start properly. If the starting is not successful, a large amount of unburned gas is discharged to the exhaust system. In addition, a large amount of unburned gasoline is discharged to the exhaust system even when the vehicle is running using heavy gasoline during a cold period.

In such a case, if the heating device is activated and the catalyst is activated within a short period of time, a large amount of unburned gasoline flows into the activated catalyst and becomes abnormal in the catalyst. The reaction takes place and the catalyst deteriorates.

[0005]

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above-mentioned drawbacks of the prior art.
It is an object of the present invention to provide an exhaust gas purifying apparatus for an engine in which an overheating state of a catalyst does not occur even if unburned components are released into exhaust gas . As shown in FIG. 1, the configuration of the present invention for this purpose is a detection method for detecting a state in which an unburned component in exhaust gas is relatively large in an exhaust purification device provided with a heating means for heating a catalyst when the engine is started. Means and before
Prohibiting means for prohibiting heating by the heating means and maintaining the inactive state of the catalyst when the catalyst is in an inactive state and the unburned component detected by the detecting means is a predetermined value or more. It is characterized by the following.

Here, the state in which the unburned components in the exhaust gas are relatively large includes, for example, a case where the engine start is poor, a case where traction control is performed, and a case where a misfire state has occurred. is there.

[0007]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 2 shows the overall configuration of the exhaust gas purifying apparatus for an engine. In the figure, 1 is an engine main body, 2 is an intake passage, and 3 is an exhaust passage. An air cleaner 4, an air flow sensor 5, a throttle valve 6, a surge tank 7,
Are provided in order. The exhaust passage 3 is provided with a first catalyst 8 as a main catalyst, and the first catalyst 8
A second catalyst 9 provided with a heating means is provided upstream of the second catalyst 9. The second catalyst 9 is provided with a temperature sensor 11 for detecting the temperature of the catalyst. Further, the second catalyst 9
A front O2 sensor 20 is provided on the upstream side of the
A rear O2 sensor 21 is provided between the catalyst 8 and the second catalyst 9.

A secondary air supply passage 12 extends from a downstream portion of the filter 4 a in the air cleaner 4 to a portion of the exhaust passage 3 between the front O 2 sensor 20 and the second catalyst 9. This secondary air supply passage 1
2, an air pump 13, an air cut valve 14, and a check valve 15 are provided in this order from the upstream side. The operating pressure of the air cut valve 14 is the negative pressure of the intake air of the engine. Therefore, a negative pressure extraction passage 16 extends from the surge tank 7 to the air cut valve 14,
A three-way solenoid valve 17 is provided in the negative pressure outlet passage 16.

In this embodiment, the secondary air is mainly used for feedback control of the inflow air-fuel ratio of the catalysts 8 and 9. That is, the operation of the three-way solenoid valve 17 is controlled by the control unit 18 using a microcomputer.
Is controlled as a signal source. Moreover, the the second catalyst 9 is heating data is provided to the battery 19 and power supply, are adapted to energization is controlled by the control unit 18.

[0010] Engine control controller (ECU) 18
Are connected to a traction controller (TRC) 32. The TRC 32 monitors the slip state of the wheels at the time of acceleration or the like, and sends a torque down signal to the engine controller 18 so that the slip does not occur. For example, the TRC 32 delays the ignition timing to reduce the engine output.

Each of the first and second catalysts 8 and 9 is a three-way catalyst. The first catalyst 8 contains platinum, palladium and cerium as catalyst components. The second catalyst 9 is a low-temperature active catalyst having high heat resistance and containing barium and zirconium as catalyst components in addition to platinum, palladium and cerium. The first catalyst 8 is formed by integrally coating a monolithic carrier made of cordierite with the above-mentioned catalyst component by alumina coating.

As shown in FIG. 3, the second catalyst 9 is loaded in a catalyst container 22 provided in the exhaust passage 3, and the catalyst carrier is made of metal and constitutes an electric heating portion 23 of a heater. are doing. The electric heating unit 23 is formed in a spiral shape on the cross section of the exhaust passage 3, and an insulating layer 24 is provided between adjacent inner and outer windings of the electric heating unit 23. That is, two independent insulating layers 24, 24 are provided in the catalyst container 22 in a spiral shape, respectively. Electrodes 25, 26 are attached to the insulating layers 24, 24, respectively. 23 are continuous at the center.

In the heating control for the catalyst according to the present embodiment, it is determined that the catalyst should not be heated when it is determined that the starting is poor. : When running is poor. : During traction control. It is. The flowchart of FIG. 4 shows this control procedure.

In step S2, it is determined whether the start key has been pressed. If the start is confirmed, in step S4, the engine coolant temperature Tw is measured by the coolant temperature sensor 30.
, The air temperature TA is input from the sensor 31 and the catalyst temperature Tc is input from the sensor 11. In step S6, it is checked whether or not conditions for energization for heating the catalyst 9 have been satisfied. Here, energization is performed when the following four conditions are met.

: The cooling water temperature is relatively low, that is, −10 ° C. <Tw <
35 ° C: the outside temperature is relatively low, that is, -10 ° C <TA <
40 ° C .: The catalyst temperature is low, that is, Tc <300 ° C .: The starter signal is on. When these conditions are not satisfied, heating is unnecessary or heating should not be performed.
Proceeding to 0, no energization is performed. On the other hand, when the conditions are satisfied, the energization is started in step S8. However, step S
It is determined whether the energization is continued at 10 or less. That is,
In step S10, a threshold α that is a function of the cooling water temperature Tw and the output voltage VB of the battery 19 is read from the map. In step S12, the time during which the starter is on is compared with the threshold value α. If the time that was on is the threshold
If it exceeds α , it is determined that the engine has failed to start. In such a case, the process proceeds to step S22 to stop energization.

FIG. 5 shows the characteristics of the threshold value α . The lower the water temperature Tw or the lower the output voltage VB of the battery 19, the more the start of the engine deteriorates. Therefore, the poor start state should be detected earlier in step S12. Therefore,
In the characteristics of FIG. 5, the value of α decreases as the water temperature Tw decreases or the output voltage VB of the battery 19 decreases. The nominal value of α is about 4 seconds.

In step S22, the power supply is stopped, and in step S24, the warm-up state of the engine is checked. The warm-up state is determined when the cooling water temperature Tw is 80 ° C. If it is not in the warm-up state, the power supply is stopped until the state becomes warm-up. Then, if it is in the warm-up state, the system is reset in step S28. When the start of the engine is normal in step S12 (YE in step S12)
S) will be described. Even if the engine starts normally, it is not preferable that the rich unburned components flow into the catalyst while the engine is cold. Therefore, detection of a misfire state is started in step S14. In the present embodiment, the state in which there is a high possibility of a misfire state is determined based on the crank angle or based on the fact that the traction control is performed by the controller 32. When the traction control is performed and the torque down signal is sent to the ECU 18, the ignition timing is delayed, and a large amount of unburned components is generated.

Therefore, when there is a possibility that a large amount of such unburned components is generated, the energization is stopped in step S22. If NO is determined in step S18, there is no possibility of abnormal combustion, so the process proceeds to step S20 to continue the energization to accelerate the activation of the catalyst. As described above, according to this embodiment, even if a large amount of unburned components is generated, the unburned components are detected in advance and the heating of the catalyst is stopped, so that abnormal combustion in the catalyst is prevented.

In the above embodiment, the detection of the unburned components is performed by detecting the failure of the engine start or the occurrence of a misfire state, or by executing the traction control. Obviously, the invention is not limited to this.

[0020]

Therefore, according to the exhaust gas purifying apparatus for an engine of the present invention, even if unburned components are released into exhaust gas,
Detects the state in advance, such a case is prohibited energization of the heating means, since the catalyst is placed in an inactive state, the occurrence of overheat state of the catalyst is prevented.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of the present invention.

FIG. 2 is a diagram showing an entire catalyst control system for an engine according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a catalyst provided with a heating device.

FIG. 4 is a flowchart illustrating a control procedure according to the embodiment.

FIG. 5 is a graph showing characteristics of a threshold α used in a control procedure of the embodiment.

Continuation of front page (72) Inventor Tetsuhiro Tanaka 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (56) References JP-A-4-31616 (JP, A) JP-A-49-1914 JP, A) JP-A-5-59936 (JP, A) JP-A-4-171234 (JP, A) JP-A-48-92714 (JP, A) JP-B-47-23607 (JP, B1) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) F01N 3/08-3/36 F02P 17/12

Claims (3)

(57) [Claims] 1. An exhaust gas purifying apparatus comprising a heating means for heating a catalyst when an engine is started, comprising: a detecting means for detecting a state in which unburned components in exhaust gas are relatively large ; and when said unburned component detected by the detection means is a predetermined value or more, the exhaust of the engine, characterized by comprising a prohibiting means for prohibiting the heating by the heating means to maintain the deactivated state of the catalyst Purification device. 2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein said detecting means determines that the unburned component is relatively large by detecting a misfire state. 3. The exhaust gas purifying apparatus for an engine according to claim 1, wherein said detecting means determines that the unburned component is relatively large when the ignition timing is delayed by a predetermined value or more.