JPH0329568Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an exhaust gas recirculation device for an engine, and particularly to an exhaust gas recirculation device that recirculates exhaust gas even when the engine is idling.

(Prior art) In automobile engines, a portion of the exhaust gas is generally recirculated to the intake system in order to reduce NOx in the exhaust gas, but in the case of diesel engines, For example, as disclosed in Japanese Unexamined Patent Publication No. 57-41453, this exhaust gas recirculation may be performed even during idle to reduce NOx.

However, if the idling state continues for a long time and exhaust gas recirculation continues during that time, the engine temperature will gradually drop and the water vapor component in the exhaust gas will condense and form water, which will mix with the sulfur dioxide gas in the exhaust gas. A problem arises in that they combine to generate sulfuric acid. As a result, the exhaust passage, cylinder liner, etc. corrode, reducing the durability and reliability of the engine.

On the other hand, if exhaust gas recirculation is completely stopped during idle, the problem of NOx emissions mentioned above will occur, and the heating effect of the intake air due to exhaust gas recirculation will not be obtained, and the combustion temperature will decrease as the compression pressure decreases. As a result, emissions of unburned components such as HC and CO increase.

(Purpose of the invention) The present invention addresses the above-mentioned problems in diesel engines that perform exhaust gas recirculation during idling, and reduces NOx even when idling continues for a long time. The purpose is to prevent the problem of corrosion of cylinder liners etc. due to sulfuric acid, and the problem of emissions of HC, CO, etc. due to a decrease in combustion temperature.

(Structure of the invention) That is, the present invention provides an exhaust gas recirculation passage between the intake passage and the exhaust passage, and also installs an exhaust recirculation control valve in the passage to direct a part of the exhaust gas to the operating state of the engine. In a diesel engine exhaust recirculation device that recirculates the air to the intake passage according to the
The engine is characterized by comprising an idle detection means for detecting an idle state of the engine, and an exhaust recirculation control means for operating the exhaust recirculation control valve to control exhaust recirculation during idling.

This exhaust gas recirculation control device maintains the control valve in an open state to perform normal exhaust gas recirculation until a predetermined time has elapsed after the engine is in an idle state, and also maintains the control valve in an idle state after the elapse of the predetermined time. When this continues, the control valve is opened and closed intermittently or its opening degree is reduced to continue the exhaust gas recirculation at a reduced amount than the normal exhaust gas recirculation amount. This results in
In addition to reducing NOx even when idling,
Emissions of unburned components such as HO and CO are also suppressed, resulting in good exhaust performance.

In particular, if the idling state continues for a long time, exhaust gas recirculation will continue even after a predetermined amount of time has elapsed, with a reduced amount compared to the normal amount, which may cause the engine temperature to drop excessively. This prevents the condensation of water or the generation of sulfuric acid caused by a drop in engine temperature and the accompanying corrosion of cylinder liners, etc., and also reduces the intake air temperature or combustion temperature by exhaust gas recirculated into the intake passage. As a result, combustibility is maintained well and generation of HC, CO, etc. is inhibited, and deterioration of exhaust performance is avoided.

(Example) Hereinafter, an example of the present invention will be described. still,
This example is for a diesel engine.

As shown in FIG. 1, an engine 1 includes an intake passage 2 that supplies intake air to the combustion chamber of each cylinder, and an exhaust passage 3 that discharges exhaust gas generated by combustion to the outside.
An exhaust gas recirculation passage 4 is provided between the exhaust passage 3 and the intake passage 2 to recirculate part of the exhaust gas into the intake passage 2, and an exhaust gas recirculation amount is provided in the passage 4. An exhaust gas recirculation control valve (hereinafter referred to as EGR valve) 5 is installed. A negative pressure diaphragm type actuator 6 for operating the EGR valve 5 is provided, and a negative pressure pump (not shown) and the actuator 6 are also provided.
A first negative pressure control valve 8 is installed in the negative pressure introduction passage 7 between the EGR valve 5 and the EGR valve 5. The opening degree is now controlled.

On the other hand, the exhaust gas recirculation passage 4 in the intake passage 2
An intake throttle valve 9 is provided on the upstream side of the opening, and a negative pressure diaphragm type actuator 10 for opening and closing the intake throttle valve 9 is provided. A second negative pressure control valve 12 is installed in the negative pressure introduction passage 11 that introduces negative pressure into the actuator 10, and the opening degree of the intake throttle valve 9 is controlled according to the state of negative pressure introduced into the actuator 10. It is becoming more and more common.

However, EGR is activated via the actuator 6.
Control signals A and B are sent from the control unit 13 to the first negative pressure control valve 8 that controls the valve 5 and the second negative pressure control valve 12 that controls the intake throttle valve 9 via the actuator 10. It's becoming like that. The control unit 13 also includes a rotation sensor 15 provided in the fuel injection pump 14.
a rotation signal C from the engine 1, a load signal D from the accelerator position sensor 16 that detects the position of the accelerator pedal linked to the control lever position of the pump 14, and the engine 1.
The water temperature signal E from the water temperature sensor 17 provided in the water jacket is inputted, and the control signals A and B are outputted according to the operating state of the engine 1 based on these input signals C, D, and E. I'm starting to do that. Here, the fuel injection pump 14
is for pumping fuel to fuel injection nozzles (not shown) provided in each cylinder of the engine 1,
The injection amount is set according to the rotational speed of the pump 14 (corresponding to the engine rotational speed) and the accelerator position.

Next, the operation of this embodiment will be explained according to the flowchart shown in FIG.

First, the control unit 13 inputs the water temperature signal E from the water temperature sensor 17 shown in FIG. 1 according to steps S ₁ and S ₂ in FIG. Determine whether the water temperature T is 80°C or higher. and,
If the temperature T is 80°C or higher, then step _S3 ,
Input the rotation signal C from the rotation sensor 15 according to _S4 , detect the engine rotation speed N based on the signal C, and determine whether or not the rotation speed N is 3000 RPM or less. Further, in step _S5 , the load signal D from the accelerator position sensor 16 is input. The accelerator position indicated by this load signal D and the engine speed N determine the fuel injection amount of the fuel injection pump 14 shown in FIG. 1, but the fuel injection amount depends on the indicated average effective pressure in the fuel chamber. Therefore, the indicated mean effective pressure Pe can be determined from the above-mentioned accelerator position and engine rotational speed N. and,
The control unit 13 determines in step _S6 whether or not this indicated mean effective pressure Pe is less than or equal to a predetermined value _P1 , and when it is less than or equal to the predetermined value P1, the control unit ₁₃ performs steps _S7 to _S8 .
~ Perform exhaust recirculation control using _S15 . In other words, the cooling water temperature T is 80°C or higher, and the engine rotation speed N
is 3000 RPM or less, and the indicated average effective pressure
Exhaust gas recirculation control is performed when Pe is less than or equal to a predetermined value _P1 . In this case, this exhaust gas recirculation control is performed as follows both during normal operation and when the engine 1 is idling.

First, during normal operation, the control unit 13 executes steps _S7 to _S8 , and determines whether the indicated mean effective pressure Pe is greater than a predetermined value _P2 (< _P1 ). Then, the pressure P is a predetermined amount
When the load is relatively high, which is greater than _P2 , steps _S8 to _S9 are executed to output a control signal A to the first negative pressure control valve 8 to open the EGR valve 5 shown in FIG. When the pressure Pe is less than the predetermined amount P ₂ and the load is low, steps S ₈ to S ₁₀ and S ₁₁ are performed.
and outputs a control signal A to the first negative pressure control valve 8 to open the EGR valve 5, and outputs a control signal B to the second negative pressure control valve 12 to open the intake throttle valve 9. do. Therefore, as shown in FIG. 3, when the operating region of the engine 1 is in a relatively high load region in which the above-mentioned exhaust gas recirculation control is performed, a relatively small amount of gas is When the exhaust gas is recirculated from the exhaust passage 3 to the intake passage 2 and is in a low load area,
At the same time as the EGR valve 5 opens, the intake throttle valve 9 in the intake passage 2 closes and the intake negative pressure around the opening of the exhaust gas recirculation passage 4 increases, allowing a large amount of exhaust gas to be recirculated to the intake passage 2. Become. In this way, exhaust gas recirculation is performed in a predetermined region in accordance with the load during normal operation of the engine 1. The reason for increasing the amount of exhaust gas recirculation at low loads is that in the case of diesel engines, the excess air ratio relative to the fuel injection amount is extremely large at low loads, so unless a large amount of exhaust gas is recirculated, the desired effect (NOx This is because the reduction effect) cannot be obtained, and the load exceeds the specified value (indicated mean effective pressure Pe is P ₁ or more).
The reason why exhaust gas recirculation is not performed in the high load range is that if exhaust gas recirculation is performed in such a region, the combustion condition will deteriorate significantly and smoke will occur.

On the other hand, when the engine is idling, the control unit 13 starts from step _S7 .
Exhaust gas recirculation control during idling is performed by _S12 to _S15 . That is, in step _S12 , the control signal A is output to the first negative pressure control valve 8 to open the EGR valve 5, and in step _S13 , the control signal A is output to the first negative pressure control valve 8 to open the EGR valve 5.
A predetermined time t ₀ is set in a timer built in.
Then, in step _S14 , it is determined whether or not the elapsed time t since the idle state has passed has passed _this predetermined time _t0 .
As indicated by the symbol x in the figure, the EGR valve 5 is kept open to perform continuous exhaust gas recirculation, as in normal operation (as indicated by the symbol y). Therefore, even during idling, a required amount of exhaust gas is recirculated to the intake passage 2, and the amount of NOx discharged is reduced.

However, when the time t after entering the idle state has passed the predetermined time _t0 , the control unit 13 executes steps _S14 to _S15 ,
A control signal A is output to the first negative pressure control valve 8 so as to open and close the EGR valve 5 intermittently. Therefore,
The EGR valve 5 is opened and closed at predetermined intervals as indicated by the symbol z in FIG. 4, and the amount of exhaust gas recirculation is reduced from before the elapse of the predetermined time _t0 . As a result, the NOx reduction effect of exhaust gas recirculation is maintained even when the idle state continues for a long time, and moisture is generated due to a drop in engine temperature when a large amount of exhaust gas recirculation is performed for a long time. In addition, the generation of sulfuric acid accompanying this is prevented, and the emission of HC, CO, etc. due to the reduction in combustion temperature when exhaust gas recirculation is completely stopped is also prevented.

Here, in this embodiment, when a predetermined time _t0 has passed since the idle state, the EGR valve 5
Although the exhaust gas recirculation amount is reduced by intermittently opening and closing the EGR valve, the exhaust gas recirculation amount may be reduced by reducing the opening degree of the EGR valve.

(Effects of the invention) As described above, according to the invention, in the exhaust recirculation system for a diesel engine that performs exhaust gas recirculation even during idling, normal exhaust recirculation is performed until a predetermined period of time has elapsed after the idling state. At the same time, after a predetermined period of time has elapsed, the amount of recirculation is reduced to perform exhaust recirculation, so the NOx reduction effect is maintained even when the engine remains idle for a long time, and the engine temperature decreases. This prevents the generation of sulfuric acid and the accompanying corrosion of cylinder liners, etc., and also prevents the emission of HC, CO, etc. due to the reduction in combustion temperature. This ensures the durability and reliability of the engine, and improves the exhaust performance during idling.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention: Fig. 1 is a control system diagram, Fig. 2 is a flowchart showing the operation, Fig. 3 is an explanatory diagram of the area where exhaust gas recirculation is controlled, and Fig. 4 is the EGR valve. FIG. 3 is a time chart showing the operation of FIG. DESCRIPTION OF SYMBOLS 1... Engine, 2... Intake passage, 3... Exhaust passage, 4... Exhaust recirculation passage, 5... Exhaust recirculation control valve (EGR valve), 13... Exhaust recirculation control means (control unit), 15... ...Idle detection means (rotation sensor).

Claims (1)

[Scope of utility model registration request] An exhaust recirculation device for a diesel engine, comprising an exhaust recirculation passage provided between an intake passage and an exhaust passage, and an exhaust recirculation control valve in the passage,
an idle detection means for detecting an idle state of the engine; and when the idle state of the engine is detected by the means, a predetermined amount of exhaust gas is recirculated until a predetermined time has elapsed, and also after the predetermined time has elapsed. and an exhaust recirculation control means for controlling the exhaust recirculation control valve so that the exhaust recirculation continues at a reduced amount below the predetermined amount when the idle state continues. Device.