JP2002188493A - Exhaust emission control system for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent self-ignition combustion of exhaust particulates collected on an exhaust particulate filter and also the dissolution loss or fracture of the filter, when an exhaust temperature is higher than a prescribed one and an engine is in a speed-reducing operation state. SOLUTION: The exhaust particulate filters 5 and 6 are mounted on branched exhaust passages 7 and 8 of an exhaust passage 2 to control the emission of exhaust gas from a diesel engine 1. For this purpose, an exhaust emission control system is provided with an exhaust temperature sensor 23, a speed reduction operation-detecting means for the engine 1, an intake throttle valve 16 and an EGR control valve 15. When the exhaust temperature T is higher than the prescribed value Tc and the engine 1 is in the speed reduction operation state, the intake throttle valve 16 is throttled and at the same time, the EGR control valve is fully opened temporarily.

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 a diesel engine having an exhaust particulate filter mounted on an exhaust passage.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Application Laid-Open No. 7-286512, an exhaust particulate filter for collecting exhaust particulates has been employed in diesel engines for purifying exhaust gases.

However, in a diesel engine equipped with an exhaust particulate filter, when the exhaust temperature rises to a high temperature of 600 ° C. or more and the amount of oxygen in the exhaust increases, the collected exhaust particulates cause self-ignition combustion. This causes problems such as melting of the exhaust particulate filter and damage due to thermal stress.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to prevent trapped exhaust particulates from igniting and burning even when the exhaust temperature is equal to or higher than a predetermined value and the engine is in a deceleration operation state. It is an object of the present invention to provide a diesel engine exhaust purification device for preventing the occurrence of exhaust gas.

[0005]

In order to solve the above-mentioned problems, the present invention provides an exhaust gas purifying apparatus for a diesel engine having an exhaust particulate filter mounted on an exhaust passage, wherein exhaust temperature detecting means for detecting exhaust temperature, A deceleration operation detecting means for detecting a deceleration operation state of the engine and an intake throttle means for restricting intake air in the intake passage when the exhaust gas temperature is equal to or higher than a predetermined value and the engine is in a deceleration operation state.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, exhaust temperature detecting means for detecting exhaust temperature, decelerating operation detecting means for detecting a decelerating operation state of an engine, and intake throttle means for restricting intake air in an intake passage are provided. Is greater than or equal to a predetermined value and the engine is in a deceleration operation state, the intake throttle means throttles intake air in the intake passage. Therefore, the amount of oxygen in the exhaust gas is reduced, the self-ignition combustion of the collected exhaust particulates is prevented, and the erosion and breakage of the exhaust particulate filter are avoided.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, an exhaust brake valve 3 is provided in the exhaust passage 2 of a diesel engine 1 so as to be openable and closable. Downstream of the exhaust path 2, two exhaust particulate filters 5, 6 into which exhaust gas selectively flows in by a switching valve 4 provided at a branch portion are provided in the middle of the branch exhaust paths 7, 8. The actuator 4a switches the switching valve 4 by the output of the electronic control unit 12. The outlet sides of the branch exhaust passages 7 and 8 join the exhaust passage 9. Each of the exhaust particulate filters 5 and 6 collects exhaust particulates in the exhaust. When one of the exhaust particulate filters 6 is clogged, the switching valve 4 shuts off the introduction of exhaust gas into the exhaust particulate filters 6. The exhaust particulate filter 6 is incinerated by heating the exhaust particulate filter 6, so-called regeneration of the exhaust particulate filter 6 is performed. During regeneration of the exhaust particulate filter 6, exhaust gas is introduced into the other exhaust particulate filter 5, and the exhaust particulate in the exhaust is collected.

The exhaust particulate filters 5 and 6 are formed by sandwiching a non-woven fabric or felt made of ceramic fiber between two wire meshes into a tubular body having a petal cross section.
When the exhaust gas passes from the outer peripheral side to the inner peripheral side of the cylindrical body, exhaust particulates in the exhaust are collected. To regenerate the exhaust particulate filters 5, 6, at least one of the above-described wire meshes is energized from the heating wires 10, 11 to act as a heater, thereby burning the exhaust particulate.

The clogging of the exhaust particulate filters 5, 6 is caused by the pressure P detected by the pressure sensors 21, 22 disposed upstream and downstream of the exhaust particulate filters 5, 6, respectively.
Electronic control unit 12 based on the difference between P1, P2 or ratio P2 / P1
Is calculated by The exhaust temperature T is detected by the temperature sensor 23.

The EGR passage 13 of the EGR device is connected to an inlet 13
a is connected to an intermediate portion between the position where the exhaust brake valve 3 is provided and the position where the exhaust particulate filters 5 and 6 are provided.
3b is connected to the intake path 14. The opening of the EGR control valve 15 provided in the EGR passage 13 is controlled by the electronic control unit 12.

An intake throttle valve 16 is provided in the intake passage 14 so as to be openable and closable. The intake throttle valve 16 acts to throttle the intake air in conjunction with the closing operation of the exhaust brake valve 3 during the operation of the exhaust brake, and the region where the self-ignition combustion of the collected exhaust particulates, that is, the exhaust temperature T becomes a predetermined value Tc. As described above, the intake air is throttled when the engine 1 is in the deceleration operation state. The throttle degree of the intake throttle valve 16 in the self-ignition combustion region of the exhaust particulates is set smaller than the throttle degree at the time of operating the exhaust brake. This is to prevent the engine 1 from stopping (stalling). The throttle operation of the intake throttle valve 16 is performed by a step motor 17 controlled by the electronic control unit 12. The operating state of the engine 1 is detected by a load sensor 18 and a rotation speed sensor 19.

FIG. 2 shows the intake throttle valve 16, the switching valve 4, and the EGR
5 is a flowchart of a control program for controlling a control valve 15 by an electronic control device 12 including a microcomputer. In FIG. 2, P11 to P17 represent each step of the control program. This program is repeatedly executed at predetermined time intervals. The control program is started in P11, and the exhaust temperature T, the engine load L, and the engine speed V are read in P12. P13
And the exhaust temperature T of the engine 1 becomes a predetermined value Tc (for example, 600 ° C.).
It is determined whether or not this is the case. If the exhaust temperature T is equal to or higher than the predetermined value Tc, the process proceeds to P14, and if the exhaust temperature T is less than the predetermined value Tc, the process returns to P12. In P14, it is determined whether or not the operation state of the engine 1 is the deceleration operation. If the vehicle is decelerating, proceed to P15. If not, return to P12. In P15, the intake throttle valve 16 is set to a light throttle degree. That is, the throttle amount is set to be smaller than the throttle amount when the exhaust brake is operated. Next, the EGR control valve 15 is temporarily fully opened in P16, and the process ends in P17.

As described above, when the exhaust temperature T of the engine 1 is equal to or higher than the predetermined value Tc and the engine 1 is in a deceleration operation state, the intake air is throttled by the intake throttle valve 16 to supply fresh air having a large amount of oxygen. To reduce the amount of oxygen in the exhaust. Therefore, the self-ignition combustion of the exhaust particulate collected by the operating exhaust particulate filter 5 is prevented.

Further, at the same time, the EGR control valve 15 is temporarily fully opened and the exhaust gas is recirculated to the intake passage 14, so that the amount of fresh air in the intake air becomes smaller, and the self-ignition combustion of the exhaust particulates is further enhanced. It is surely prevented.

[0015]

As described above, according to the present invention, in an exhaust gas purifying apparatus for a diesel engine having an exhaust particulate filter mounted in an exhaust path, an exhaust temperature detecting means for detecting an exhaust temperature and a deceleration for detecting a deceleration operation state of the engine. When the engine is in a deceleration operation state when the exhaust gas temperature is equal to or higher than a predetermined value and the engine is in a deceleration operation state, the operation detection means and the intake throttle means for restricting the intake air in the intake passage are provided. Self-ignition combustion is prevented, and erosion of the exhaust particulate filter is prevented.

Since the intake throttle valve is throttled and the EGR control valve is temporarily fully opened, the prevention of self-ignition combustion of exhaust particulates and the prevention of erosion and breakage of the exhaust particulate filter are further ensured.

[Brief description of the drawings]

FIG. 1 is an overall system diagram of an exhaust gas purifying apparatus for a diesel engine according to the present invention.

FIG. 2 is a flowchart of a control program for preventing the exhaust particulate filter from being melted or damaged by the electronic control unit.

[Explanation of symbols]

1: diesel engine 2: exhaust path 3: exhaust brake valve 4: switching valve 4a: actuator 5: exhaust particulate filter 6: exhaust particulate filter 7: branch exhaust path
8: Branch exhaust path 9: Exhaust path 10: Heating lead 1
1: heating wire 12: electronic control unit 13: EGR passage 14: intake path 15: EGR control valve 16: intake throttle valve 18: engine load sensor 19: engine speed sensor 21: exhaust pressure sensor 22: exhaust pressure sensor 2
3: Exhaust gas temperature sensor

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Claims (4)

[Claims] An exhaust gas purifying apparatus for a diesel engine having an exhaust particulate filter mounted in an exhaust passage, an exhaust temperature detecting means for detecting an exhaust temperature, a deceleration operation detecting means for detecting a decelerated operation state of the engine, and An exhaust gas purifying apparatus for a diesel engine, further comprising intake throttle means for restricting intake air in an intake passage when the engine is in a deceleration operation state at a predetermined value or more. 2. The exhaust purifying apparatus for a diesel engine according to claim 1, wherein said intake throttle means is an intake throttle valve of an exhaust brake device. 3. The throttle valve according to claim 2, wherein an exhaust throttle amount of the intake throttle valve when the exhaust temperature is equal to or higher than a predetermined value and the engine is in a deceleration operation state is smaller than an intake throttle amount when the exhaust brake is operated. Exhaust purification system for diesel engine. 4. An EGR control valve of an EGR control device, wherein when the exhaust gas temperature is equal to or higher than a predetermined value and the engine is in a deceleration operation state, the EGR control valve of the EGR control device is temporarily fully opened when the intake throttle means restricts intake air. The exhaust gas purifying apparatus for a diesel engine according to any one of claims 1 to 3.