JPS6179828A - Exhaust gas recirculating device in diesel engine - Google Patents

Abstract

PURPOSE:To prevent compressed pressure from lowering, in an engine in which an intake-air throttle valve is disposed in an intake-air passage upstream of the opening sections of EGR passages so that it is throttled upon EGR by a predetermined amount, by decreasing the throttling degree of the throttle valve when the temperature of the engine, etc. is low. CONSTITUTION:An exhaust recirculating device recirculates a part of exhaust gas from an exhaust passage 3 into an intake-air passage 2 through first and second EGR passages 4, 5. Further, an intake-air throttle vale 14 is disposed in the intake-air passage 2 upstream of the openings of the EGR passages 4, 5. These valves 6, 7, 14 are arranged to be controlled by a control unit 18 such that the EGR valve 6 is opened upon high load operation while the EGR valve 4 is opened upon intermediate load operation, and further the throttle valve 14 is closed while the EGR valve 7 is left to be opened upon low load operation. In this arrangement, control is made such that the lower the temperature of cooling water which is detected by a water temperature sensor, the less the throttling amount of the throttle valve is made.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an exhaust gas recirculation system for a diesel engine, particularly to control during warming up of an exhaust gas recirculation system equipped with an intake throttle valve.

(Conventional technology) In automobile engines, NOx in exhaust gas
In order to reduce this, it is common practice to recirculate some of the exhaust gas back into the intake system, but in the case of diesel engines, it is also possible to draw exhaust gas into the intake system using intake negative pressure. The problem is that it can't be done. Therefore,
For example, as disclosed in Japanese Patent Application Laid-open No. 57-41453, an intake throttle valve is provided upstream of the opening of the exhaust gas recirculation passage in the intake passage, and the throttle valve is closed during exhaust gas recirculation to reduce the intake negative pressure. The exhaust gas is effectively refluxed by generating the exhaust gas.

On the other hand, in a diesel engine equipped with such an exhaust recirculation system, as described in the above publication, the engine warm-up is promoted during cold start to reduce emissions of I-(C, Go, etc.). Exhaust gas recirculation is sometimes performed in order to warm up the engine.In other words, by introducing high-temperature exhaust gas into the intake system, the intake air is heated and warmed up.
In this case, it is customary to increase the amount of exhaust gas recirculation to increase the intake air heating effect as the engine temperature decreases. Therefore, in the case where the exhaust gas is recirculated by closing the intake throttle valve as described above, the amount of throttle of the intake throttle valve is increased when the temperature is low.

However, during warm-up, if the throttle amount of the intake throttle valve is increased as the engine temperature is lower, the filling amount of the intake air decreases, the compression pressure decreases accordingly, and the temperature of the intake air due to compression [t becomes less. In other words, increasing the throttle amount of the intake throttle valve increases the heating effect of the intake air due to exhaust gas recirculation, but on the other hand, the temperature rise m of the intake air due to compression decreases.
As a result, warm-up is not performed effectively. Especially immediately after starting a FIji aircraft when the engine temperature is low,
There are cylinders that have not yet ignited, and the temperature of the exhaust gas is not high enough, so if the intake throttle valve is throttled more at this time, the intake air charge m will be reduced or compressed more than the heating effect of the intake air due to exhaust gas recirculation. The decrease in temperature increase due to the decrease in pressure exceeds the decrease, and as a result, the 81 mechanical properties are rather deteriorated.

(Object of the Invention) The present invention provides an exhaust gas recirculation device for a diesel engine in which exhaust gas recirculation is performed by closing an intake throttle valve provided in an intake passage. This prevents a decrease in compression pressure or a decrease in intake air temperature due to intake throttling, thereby effectively warming up the HC.
The purpose is to reduce emissions of carbon dioxide and CO.

(Structure of the Invention) That is, the present invention provides a di-door which is provided with an intake throttle valve on the upstream side of the opening of the exhaust gas recirculation passage in the intake passage, and configured to throttle the intake throttle valve to a predetermined opening degree during exhaust gas recirculation. In the exhaust gas recirculation device of a diesel engine, a temperature detection means for detecting a temperature related to the engine temperature or the intake air temperature is provided, and
The present invention is characterized in that it includes exhaust gas recirculation control means that reduces the amount of throttle of the intake throttle valve when the temperature detected by the detection means is low.

According to such a configuration, when the engine temperature is relatively high during warm-up, the intake air is effectively heated by exhaust gas recirculation, and when the engine is low, such as immediately after the start of warm-up, that is, the temperature of exhaust gas is If the intake air heating effect due to exhaust gas recirculation cannot be sufficiently obtained due to low will be obtained. Therefore, good heating accuracy can be obtained over a wide range from when the engine temperature is low to when the engine temperature rises to a relatively high temperature. Note that there are two methods for reducing the throttle mass of the intake throttle valve when the engine temperature or intake air temperature is low: one is to reduce the throttle m in a stepless manner as the temperature is lower, and the other is to reduce the throttling amount in stages before reaching a predetermined temperature. There is a way to change it.

(Example) Examples of the present invention will be described below.

As shown in FIG. 1, an engine 1 is provided with 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. Between the exhaust passage 3 and the intake passage 2, there is a first pipe which recirculates part of the exhaust gas into the intake passage 2. A second exhaust gas recirculation passage 4.5 is provided, and a first exhaust gas recirculation passage 4.5 for controlling the amount of exhaust gas recirculation is provided in these passages 4.5. Second reflux control valve (hereinafter referred to as EG
6.7 (referred to as R valve) is installed. A negative pressure diaphragm type actuator 8.9 for operating these EGR valves 6 and 7, respectively, is provided, and a negative pressure introduction passage 10.9 is provided between a negative pressure pump (not shown) and both actuators 8.9. 11 each have a duty control type first
．． A second negative pressure control valve 12.13 is installed, the control valve 12.
．． 13 open/close states or open/close time ratio (duty ratio)
By controlling the negative pressure within each actuator 8, 9 according to the first. The opening degree of the second EGR valve 6°7 is controlled. Here, the first EGR
The passage area when the valve 6 is fully open is smaller than the passage area when the second EGR valve 7 is fully open.

On the other hand, the first. An intake throttle valve 14 is provided on the upstream side of the opening of the second exhaust gas recirculation passage 4.5, and a negative pressure die reflex 56 type actuator 15 for driving the intake throttle valve 14 to open and close is provided. A third negative pressure control valve 17 of duty control type is also installed in the negative pressure introduction passage 16 through which negative pressure is introduced into the actuator 15 .

Therefore, the first and second
The first one controls the EGR valve 6.7. Second negative pressure control valve 12.
Control signals (duty signals) A, B, and C are sent from the control unit 18 to the third negative pressure control valve 17 that controls the intake throttle valve 14 via the intake throttle valve 13 and the actuator 15, respectively. In addition, the control unit 18 includes a rotation signal from a rotation sensor 20 provided in the fuel injection pump 19, and an accelerator position sensor 21 that detects the position of the accelerator pedal linked to the control lever position of the pump 19. A load signal E from the engine 1 and a water temperature signal F from the water temperature sensor 22 provided in the water jacket of the engine 1 are input, and based on these input signals E, F, the engine 1 is and the above control signal A,
B and C are output. Here, the fuel injection pump 19 is for pumping fuel to fuel injection nozzles (not shown) provided in each cylinder of the engine 1, and the injection m is determined by the rotational speed of the pump 19 (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 18 performs step S1 in FIG. According to S2, the water temperature signal F from the water temperature sensor 22 shown in FIG. 1 is input, and it is determined whether the cooling water temperature T in the water jacket of the engine 1 indicated by the signal F is 80° C. or higher. When the temperature T is 80° C. or higher, in other words, during normal operation of the engine 1, the rotation signal from the rotation sensor 20 is inputted in accordance with step S3.84, and the engine speed is increased based on the signal. While detecting the speed N, the rotation speed N is 900 to 3000RP
It is determined whether or not it is within the range of M, and if it is within this range, the load signal E from the accelerator position sensor 21 is further input in step S5. The accelerator position indicated by this load signal E and the engine rotation speed N
determines the fuel injection amount of one fuel injection pump shown in FIG. 1. Since the fuel injection port corresponds to the indicated average effective pressure in the combustion chamber, The average effective pressure pe will be determined. Then, in step S6, the control unit 18 determines that the indicated mean effective pressure pc is O~6.
It is determined whether or not it is within the range of K'3/cA, and when it is within this range, the exhaust gas recirculation control during normal operation is performed in steps 87 to S12. In other words, the cooling water temperature T is 8
The temperature is 0°C or higher, and the engine rotation speed N is 900 to 300
Normal exhaust gas recirculation control is performed when the indicated mean effective pressure pe is within the range of 0 PPM and within the range of 0 to 6 KCI/crA.

This control is performed as follows depending on the value of the indicated mean effective pressure Pe. That is, when the pressure pe is in the range of 5 to 6 n/ctA and the load is relatively high, the control unit 18 executes steps S7 to S8 to control the first EGR valve with a small passage area shown in FIG. A control signal A is output to the first negative pressure control valve 12 so as to open the control valve 6, and when the pressure pe is in the range of 4.5 to 51'l/crA and the load is medium, the step Sr to step S9. Execute S+o and move to the 22nd GR, which has a large passage area.
A control signal B is output to the second negative pressure control valve 13 to open the valve 7.

Furthermore, at low load when the pressure pe is within the range of O to 4.5 crA, the steps S9 to S are performed.
o, S+z to open the second EGR valve 7.
A control signal B is output to the negative pressure control valve 13, and a control signal C is output to the third negative pressure control valve 17 to close the intake throttle valve 14.
Output. Therefore, in the region where the above-mentioned exhaust gas recirculation control is performed, when the load is high, a relatively small amount of exhaust gas is recirculated from the exhaust passage 3 to the intake passage 2 through the first EGR valve 8, which has a small passage area, by the first exhaust gas recirculation passage 4. In addition, at medium loads, a relatively large amount of exhaust gas is recirculated by the second exhaust gas recirculation passage 5 through the second EGR valve 7 with a large passage area, and at low loads, the second EGR valve 7 with a large passage area is recirculated. At the same time as opening, the intake throttle valve 14 in the intake passage 2 closes and the negative pressure around the opening of the exhaust gas recirculation passage 5 increases, so that even more exhaust gas is recirculated to the intake passage 2. As a result, as shown in FIG. 3, an exhaust gas recirculation characteristic that changes stepwise according to the load is obtained.

The reason for increasing the exhaust gas recirculation m when the angle load is low is that in the case of a diesel engine, the excess air ratio relative to the fuel injection point becomes significantly large at low loads, so if a large number of exhaust gases are not recirculated, it is necessary to This is because the effect (NOx reduction effect) cannot be obtained during the period, and the reason why exhaust gas recirculation is not performed in a high load range above a predetermined load (indicated average effective pressure is 6 AV/d or more) is because exhaust gas recirculation is not performed in such a region. This is because if reflux is performed, the combustion condition will be significantly deteriorated and smoke will be generated.

However, when warming up the engine 1 when the coolant temperature T is 80° C. or lower, the control unit 18 executes steps S2 to 813 in FIG. If it is within this range, step 814~S +e
Perform exhaust gas recirculation RIJ Ill during warm-up. That is, in step S14, the first EGR valve 6 is opened, and in step S2+s, wUIiθ of the intake throttle valve 14 is set in accordance with the chilled water temperature T indicated by the signal F from the water temperature sensor 22. At this time, the cough interval degree θ is set by reading from a preset map for cold water @ temperature T, and this map is set with characteristics as shown in FIG. In other words, the lower the cooling water temperature T, the larger the opening degree θ of the intake throttle valve 14 (the smaller the throttle amount). In accordance with this characteristic, the opening degree θ of the intake throttle valve 14 is set according to the cooling water temperature T.
In step S+s, the control unit 18 sends a control signal (
Duty signal) C is output to the third negative pressure control valve 17.

As a result, the throttle amount of the intake throttle valve 14 during warm-up becomes smaller as the cold part water @ Accordingly, a high compression pressure and a sufficient temperature rise of the intake air due to this compression are obtained, and as a result, warm-up is promoted. In this case, the exhaust gas recirculation 9 is reduced due to the small throttle m of the intake throttle valve 14, but since the temperature of the exhaust gas is low when the engine is low, the intake air refill l
It is more effective to promote @machine by securing ff1 or compression pressure. When the engine temperature rises, the amount of throttle of the intake throttle valve 14 increases accordingly, increasing the amount of exhaust gas recirculation, and the intake air is effectively heated by the high-temperature exhaust gas. Warming up will be accelerated.

Here, in this embodiment, the throttle amount of the intake throttle valve 14 (
As shown in Figure 4, the lower the cooling water temperature, the lower the cooling water temperature is, the lower the opening degree is. The throttle valve may be opened and closed on the high temperature side.

(Effects of the Invention) As described above, according to the present invention, an exhaust gas recirculation device for a diesel engine configured to close an intake throttle valve provided in an intake passage during exhaust gas recirculation can be used to promote warm-up. During exhaust gas recirculation, when the engine temperature is low immediately after the start of warm-up, the required intake air filling amount or compression pressure is ensured, and this compression produces the effect of increasing the intake air temperature, and when the engine temperature rises, the exhaust gas in the This results in an intake air heating effect. As a result, good warm-up performance is obtained immediately after the start of warm-up, warm-up is promoted, and emissions of HC, co, etc. are reduced during warm-up.

[Brief explanation of drawings]

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 a characteristic diagram of normal exhaust gas recirculation control, and Fig. 4 is a diagram showing the warm-up time. FIG. 3 is a control characteristic diagram of the intake throttle valve opening degree in exhaust gas recirculation control. DESCRIPTION OF SYMBOLS 1... Engine, 2... Intake passage, 3... Exhaust passage, 4.5... Exhaust recirculation passage, 14... Intake throttle valve,
18...Exhaust recirculation control means (control unit)
, 22...Temperature detection means (water wetness sensor).

Claims (1)

[Claims] (1) An exhaust gas recirculation device for a diesel engine, which is equipped with an intake throttle valve upstream of the opening of the exhaust gas recirculation passage in the intake passage, and is configured to throttle the intake throttle valve to a predetermined opening degree during exhaust gas recirculation, the device comprising: Alternatively, a diesel engine comprising temperature detection means for detecting a temperature related to intake air temperature, and exhaust recirculation control means for reducing the throttle amount of the intake throttle valve when the temperature detected by the detection means is low. Exhaust recirculation device.