JP2000337172A - Exhaust gas recirculation device of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the initial excessive exhaust gas recirculation by the effect of an exhaust pressure at the same time when the exhaust gas recirculation is started at an early stage when an exhaust shutter valve is opened. SOLUTION: When an exhaust shutter valve (b) is closed to improve a heating performance, the exhaust gas recirculation is stopped as the exhaust pressure is high. As the exhaust shutter valve (b) is opened slowly to avoid a torque sudden change, the exhaust pressure change becomes gentle, but the opening (step number) (e) of the exhaust gas recirculation control valve is corrected to a small value at the initial stage and increased so as to be a target opening #VSTEP gradually. The excessive exhaust gas recirculation is not generated by the effect of the exhaust pressure before the exhaust shutter valve (b) is fully opened and the target exhaust gas recirculation rate can be obtained from the initial stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas recirculation device for a diesel engine, and more particularly to an exhaust gas recirculation device for a diesel engine having an exhaust shutter valve in an exhaust passage.

[0002]

2. Description of the Related Art In order to reduce NOx contained in exhaust gas of a diesel engine, a part of the exhaust gas, which is an inert gas, is recirculated from an exhaust system to an intake system so as to suppress the maximum temperature during combustion. An exhaust gas recirculation device is conventionally known. In this system, for example, an exhaust gas recirculation control valve using a step motor is interposed in an exhaust gas recirculation passage from the exhaust system to the intake system. The rate is controlled (see, for example, JP-A-9-4521).

[0003] Also, there is known a diesel engine for an automobile which is provided with an exhaust shutter valve in an exhaust passage in order to promote warm-up in a cold state or to improve the performance of a vehicle compartment heater. The exhaust shutter valve is opened and closed automatically, for example, according to operating conditions or by a driver's switch operation. When the exhaust shutter valve is closed, the back pressure of the exhaust system of the engine increases. Therefore, the required fuel injection amount increases, and the cooling water temperature rises quickly (see, for example, Japanese Patent Application Laid-Open No. 5-71367).

[0004] Generally, in the exhaust gas recirculation valve provided with such an exhaust shutter valve, the exhaust shutter valve is located downstream of a branch portion of the exhaust gas recirculation passage. The exhaust pressure acting on the exhaust gas increases, making it difficult to accurately control the exhaust gas recirculation rate. Therefore, when the exhaust shutter valve is closed, the exhaust gas recirculation is generally stopped.

That is, when the engine is operated in the exhaust gas recirculation region, the exhaust gas recirculation is stopped and started in conjunction with the closing and opening of the exhaust shutter valve.

[0006]

The exhaust shutter valve can be simply switched between an open position and a closed position. For example, when the engine is cold, the vehicle is started with the exhaust shutter valve closed. Then, when the exhaust shutter valve is subsequently opened, the back pressure acting on the exhaust system decreases, so that the engine torque suddenly increases, which may cause the occupant to feel a torque step. . In particular, when the switching from the closed state to the open state is automatically executed according to the engine operating conditions such as the rotation speed, the load, and the cooling water temperature, a torque step occurs at a timing unintended by the driver, so that it is easy to give a sense of incongruity.

For this reason, it has been considered that the opening operation of the exhaust shutter valve is moderated by using an orifice or the like to suppress the feeling of a step in the torque. In this manner, the opening operation of the exhaust shutter valve is slowed. If this is not the case, the reduction of the exhaust pressure on the upstream side is substantially delayed, so that when the exhaust gas recirculation is started simultaneously with the start of the switching, there is a possibility that excessive exhaust gas recirculation is temporarily performed.

That is, when the exhaust shutter valve is switched from the closed state to the open state and the exhaust gas recirculation is started at the same time, a large amount of exhaust gas recirculation exceeds a predetermined exhaust gas recirculation rate determined by the operating conditions, and soot generation and the like are prevented. May invite.

[0009]

SUMMARY OF THE INVENTION Accordingly, the invention according to claim 1 is characterized in that an exhaust shutter valve for reducing a passage area is interposed in an exhaust passage, and an exhaust system is provided upstream of the exhaust shutter valve to an intake system. An exhaust gas recirculation passage is connected to the exhaust gas recirculation passage, and when the exhaust shutter valve is closed, the exhaust gas recirculation is stopped via an exhaust gas recirculation control valve provided in the exhaust gas recirculation passage. When the shutter valve is opened from a closed state, an opening correction means is provided for limiting the opening of the exhaust gas recirculation control valve so as to gradually increase toward a target opening.

In the present invention, the exhaust shutter valve is provided with an opening speed reducing means such as an orifice for slowing the opening operation of the valve body from the closed position to the open position. It is suitable for.

That is, the exhaust shutter valve is in the closed position, for example, when the engine is in a cold state and in a predetermined low-speed, low-load region. As a premise of the opening / closing control of the exhaust shutter valve, a changeover switch operated by a driver may be provided, and the exhaust shutter valve may be operated only when the switch is ON. In this state, the exhaust gas recirculation control valve is closed, and the exhaust gas recirculation is stopped. When the operating condition of the engine deviates from the predetermined condition, the exhaust shutter valve is switched to the open position. For example, the exhaust shutter valve changes from closed to open due to an increase in load, an increase in the number of revolutions, an increase in the temperature of the cooling water, and the like. According to the second aspect, when the switching from the closed position to the open position is performed, the opening operation of the valve element is made slower by the opening speed reducing means in order to avoid a sudden torque fluctuation.

When the engine operating condition is within a predetermined exhaust gas recirculation region when the exhaust shutter valve opens, the exhaust gas recirculation control valve opens simultaneously with the opening operation of the exhaust shutter valve, and the exhaust gas recirculation starts. At this time, the target opening of the exhaust gas recirculation control valve is determined by the engine operating conditions. However, in the present invention, the opening does not suddenly increase to this target opening, but the opening gradually increases and gradually increases to the target opening. Reach. That is, the opening degree of the exhaust gas recirculation control valve is initially limited to a small value and gradually increases so as to correspond to a gradual decrease in exhaust pressure accompanying the switching of the exhaust shutter valve from the closed position to the open position.
Accordingly, an excessive amount of exhaust gas does not recirculate due to the effect of the high exhaust pressure, and an appropriate amount of exhaust gas recirculation can be performed from the beginning of the exhaust gas recirculation.

According to a third aspect of the invention, which is dependent on the first and second aspects, the intake throttle valve is provided at a position upstream of the junction of the exhaust recirculation passage of the intake passage, and the opening operation of the exhaust shutter valve is performed. And a delay means for giving an appropriate delay time to the closing operation of the intake throttle valve. The intake throttle valve closes in a predetermined region in the exhaust gas recirculation region, and realizes a high exhaust gas recirculation rate by increasing the negative pressure on the intake side. When the intake throttle valve is closed first at the beginning of the start of the process, the pressure difference between the front and the rear of the exhaust gas recirculation passage increases, which promotes the excessive exhaust gas recirculation described above. Therefore, according to the third aspect of the present invention, the closing operation of the intake throttle valve is slightly delayed to avoid its influence.

[0014]

In the exhaust gas recirculation apparatus for a diesel engine according to the present invention, excessive exhaust gas recirculation at the beginning of the exhaust gas recirculation start which becomes a problem when the exhaust shutter valve is slowly opened in order to suppress a sense of torque difference. Thus, an appropriate amount of exhaust gas recirculation along the target recirculation rate can be obtained from the beginning of the exhaust gas recirculation associated with the opening operation of the exhaust shutter valve. Accordingly, it is possible to start the exhaust gas recirculation at an early stage and to suppress the NOx while avoiding an increase in soot due to excessive exhaust gas recirculation.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is an explanatory view showing the construction of an embodiment of an exhaust gas recirculation apparatus according to the present invention, wherein 1 denotes a diesel engine, 2 denotes an intake passage, and 3 denotes an exhaust passage. The exhaust passage 3 is provided with an exhaust shutter valve 4 including a butterfly valve type valve element 4a and a negative pressure actuator 4b. When the negative pressure VAC is introduced through a three-way solenoid valve 5 from a negative pressure pump (not shown) serving as a negative pressure source, the negative pressure actuator 4b closes the valve body 4a, and opens the atmosphere through the three-way solenoid valve 5. When connected to the passage 6, the valve 4a is set to the open position. here,
An orifice (not shown) having an appropriate diameter is interposed in the atmosphere passage 6 in order to restrict the introduction of the atmosphere and slow the opening operation of the valve body 4a.

The intake passage 2 is provided with, for example, a hot-wire type air flow meter 9 for detecting a flow rate of fresh air taken in from the outside via an air cleaner 8, and is located upstream of the intake collector 10. An intake throttle valve 11 for reducing the intake passage area at the time of exhaust gas recirculation is provided. The intake throttle valve 11 has a negative pressure actuator (not shown), and closes when a negative pressure VAC is introduced by switching the electromagnetic valve 12 and opens when the vacuum valve is opened to the atmosphere.

Between the exhaust passage 3 and the intake passage 2,
An exhaust gas recirculation passage 13 is provided. One end of the exhaust gas recirculation passage 13 is connected to the exhaust passage 3 at a position upstream of the exhaust shutter valve 4, and the other end is connected to the intake collector 10. The exhaust gas recirculation passage 13 is provided with an exhaust gas recirculation control valve 14 whose opening can be variably controlled continuously (strictly, in many steps) by a step motor.

In FIG. 1, reference numeral 21 denotes a fuel injection nozzle, 22 denotes a glow plug, 23 denotes a water temperature sensor, 24 denotes a rotation speed sensor for detecting an engine rotation speed, and 25 denotes an accelerator opening for detecting an amount of depression of an accelerator pedal. , Respectively. The exhaust gas recirculation control valve 14, the three-way solenoid valve 5 for the exhaust shutter valve 4, the solenoid valve 12 for the intake throttle valve 11, and the like are controlled by a control unit 26. The detection signals of various sensors such as a rotation speed sensor 24, an accelerator opening sensor 25, and an air flow meter 9 are input.

The exhaust shutter valve 4 basically includes an engine speed, a fuel injection amount Q, a cooling water temperature,
Is controlled based on the That is, the engine speed and the fuel injection amount Q are in a predetermined low-speed, low-load side closed region as shown in FIG.
° C) or less, the exhaust shutter valve 4 is closed, and otherwise opened. In the driver's seat,
A warm-up switch (not shown) that is manually operated is provided, and the exhaust shutter valve 4 is operated only when the warm-up switch is ON.

Therefore, when the engine is operating in the closed region of FIG. 2 during a cold period, the exhaust shutter valve 4 is in the closed position. When entering the open area or when the cooling water temperature becomes equal to or higher than a predetermined temperature, the three-way solenoid valve 5 is switched by the control signal of the control unit 26,
Atmosphere is introduced into the negative pressure chamber actuator 4b, and the valve body 4
a opens. At this time, the introduction of the atmosphere is slowed down by the orifice, so that the valve body 4a is gradually opened.

On the other hand, the exhaust gas recirculation is controlled according to a target exhaust gas recirculation rate determined by operating conditions. FIG. 3 shows an example of the characteristic of the target exhaust gas recirculation rate. Further, while the exhaust shutter valve 4 is closed, the exhaust gas recirculation is stopped regardless of the operating conditions. That is, the exhaust gas recirculation control valve 14 is kept in the fully closed state. Then, when the exhaust shutter valve 4 changes from the closed state to the open state, if the exhaust shutter valve 4 is switched within the exhaust recirculation region shown in FIG. At the beginning of the recirculation, the opening degree of the exhaust gas recirculation control valve 14 is initially small and gradually increases so as to offset the slow opening operation of the valve body 4a, that is, the slow decrease of the exhaust pressure.

The intake throttle valve 11 is controlled to open and close according to the characteristics shown in FIG. 4 when the exhaust gas is being recirculated. That is, the intake throttle valve 11 closes on a part of the exhaust gas recirculation region on the low-speed low-load side where the exhaust gas recirculation rate is high. Here, when the exhaust gas recirculation is started along with the opening operation of the exhaust shutter valve 4, if the operating condition is in the intake throttle valve closing region of FIG. 4, the intake throttle valve 11 is closed with the start of the exhaust gas recirculation. However, if the intake throttle valve 11 is closed while the exhaust pressure is high without the exhaust shutter valve 4 being completely closed, the differential pressure across the exhaust recirculation passage 13 increases, and excessive exhaust is recirculated. Therefore, the intake throttle valve 11 is closed with a slight delay.

FIG. 5 is a flow chart showing the flow of the exhaust gas recirculation control executed by the control unit 26, in particular, the flow of the exhaust gas recirculation control accompanying opening and closing of the exhaust shutter valve 4. This will be described below. This routine is repeatedly executed at regular intervals, for example.

First, in step 1, it is determined whether or not the exhaust shutter valve 4 controlled by another routine (not shown) is in a closed state. If “YES” here, the process proceeds to a step 2 wherein the opening degree (VSTE) of the exhaust gas recirculation control valve 14 is
P) is set to 0, exhaust gas recirculation is stopped, and the intake throttle valve 11 is opened. Further, the flag F is reset to 0, and a series of routines is ended. Therefore, while the exhaust shutter valve 4 is closed, the state in which the exhaust gas recirculation is stopped is continued.

If the answer to step 1 is NO, the process proceeds to step 3, where the previous state of the exhaust shutter valve 4 is determined.
Here, if the exhaust shutter valve 4 was closed last time, this indicates that the exhaust shutter valve 4 has just been switched from the closed state to the open state, and the process proceeds to step 4 and subsequent steps. From the next time, the process proceeds from step 3 to step 11. This corresponds to switching of the three-way solenoid valve 5, and as described above, the exhaust shutter valve 4 actually opens slowly.

In step 4, the timer TM indicating the time elapsed since the switching is reset, and in step 5, the correction coefficient K is set to an initial value K1. The initial value K1 of the correction coefficient K is an appropriate value less than 1, for example, 0.4
It is set to about, but may be 0. Or you may make it read from a predetermined map according to driving conditions. In this case, since the exhaust pressure increases as the engine speed increases, it is desirable to reduce the initial value K1 on the high speed side.

Then, the program proceeds to a step S6, wherein based on the operating conditions, mainly the engine speed and the fuel injection amount Q corresponding to the load, the exhaust gas recirculation control valve target opening ΔVSTEP in accordance with the target exhaust gas recirculation rate. Set. This target opening ♯VSTE
P is actually shown as the number of steps of the step motor in the exhaust gas recirculation control valve 14. Then, in step 7, the target opening ♯VSTEP is multiplied by the correction coefficient K, and the opening VS, which is the number of steps to be actually output, is obtained.
Ask for TEP. Therefore, in the first time, the exhaust gas recirculation control valve 14 is controlled to the opening degree VSTEP along the initial value K1 of the correction coefficient K. In step 8, the correction coefficient K is set to 1
Is determined, and if it is less than 1, the routine proceeds to step 9, where a small amount ΔK is added to the correction coefficient K, and the correction coefficient K
Is gradually increased.

From the next time, step 3 to step 11
In step 11, it is determined whether the operating condition at that time is the open region or the closed region of the intake throttle valve 11 (see FIG. 4). If it is in the open region, the routine proceeds to step 12, where the intake throttle valve 11 is opened. On the other hand, if it is in the closed region, it is determined in step 13 whether or not the value of the timer TM has reached TM1 corresponding to a predetermined delay time. Keep open. When the predetermined value TM1 is reached, the routine proceeds to step 14, where the intake throttle valve 11 is closed. In addition,
The delay time due to TM1 is set such that the intake throttle valve 11 closes before the valve body 4a of the exhaust shutter valve 4 reaches the fully open position.

In the next step 15, it is determined whether or not the flag F is "1". If not, the flow returns from step 15 to step 6. That is, steps 6 to 9 are repeated until F = 1. As described above, since the correction coefficient K gradually increases in step 9, the actual output opening VSTEP is calculated as follows: target opening ♯VSTE
It gradually approaches P. Then, the correction coefficient K is 1
Is reached, the process proceeds from step 8 to step 10, where the flag F is set to 1. At this stage, the actual opening VS
TEP is equal to the target opening degree ♯VSTEP.

When the flag F becomes 1 as described above, thereafter, the process proceeds from step 15 to step 16 to shift to normal exhaust gas recirculation control. In this normal exhaust gas recirculation control, for example, as in step 6, the number of steps of the step motor along the target exhaust gas recirculation rate is allocated to a map, and the corresponding number of steps is read out based on the operating conditions. Open-loop control may be used, or a method of feedback-controlling the opening degree of the exhaust gas recirculation control valve 14 so that the flow rate of fresh air detected by the air flow meter 9 becomes a target flow rate obtained from the target exhaust gas recirculation rate. Can also be used.

FIG. 6 shows the state of each part when the exhaust shutter valve 4 is opened. The three-way solenoid valve 5 changes from ON to OFF as shown in FIG. Thus, the exhaust shutter valve 4 gradually changes from the closed state to the open state as shown in FIG. Then, the exhaust pressure gradually decreases as shown in (d), and the torque changes gently as shown in (c). If you do not have an orifice,
The opening changes abruptly as indicated by the broken line, causing a sudden change in torque.

On the other hand, when the operating condition is in the exhaust gas recirculation region, the exhaust gas recirculation is started at the same time. However, as shown in FIG. After opening stepwise to the opening determined by the value K1, the opening gradually opens with the passage of time, and reaches the target opening ΔVSTEP when the exhaust pressure is sufficiently reduced. Therefore, excessive exhaust gas recirculation is not caused by the influence of exhaust pressure.
As shown in (f), an appropriate exhaust gas recirculation rate can be obtained before the exhaust shutter valve 4 is completely opened. In addition,
As shown by the broken lines in (e) and (f), when the opening of the exhaust gas recirculation control valve 14 is not corrected, the exhaust gas recirculation is temporarily excessively affected by the high exhaust pressure.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing a configuration of an exhaust gas recirculation device according to the present invention.

FIG. 2 is a characteristic diagram showing a control region for opening and closing an exhaust shutter valve.

FIG. 3 is a characteristic diagram showing characteristics of a target exhaust gas recirculation rate.

FIG. 4 is a characteristic diagram showing a control region for opening and closing an intake throttle valve.

FIG. 5 is a flowchart showing the flow of exhaust gas recirculation control.

FIG. 6 is a time chart showing a state change of each part when the exhaust shutter valve is opened.

[Explanation of symbols]

 4 Exhaust shutter valve 11 Intake throttle valve 13 Exhaust recirculation passage 14 Exhaust recirculation control valve 26 Control unit

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) F02M 25/07 570 F02M 25/07 570C 580 580B 580F 35/10 311 35/10 311E F-term (Reference) 3G062 AA01 BA00 CA04 DA04 EA11 EB10 EC17 FA08 GA01 GA04 GA06 GA08 GA22 3G065 AA09 CA12 DA02 DA06 EA04 FA02 FA12 GA05 GA10 GA14 GA46 GA47 3G084 AA01 BA19 BA20 CA04 DA04 DA10 EB12 EC07 FA08 FA10 FA20 FA33 FA37 3G092 AA09 DG09 GA11 GB01 HA01Z HD07X HD09X HD09Z HE01Z HE08Z HF08Z 3G301 HA02 HA13 JA11 JA25 KA14 KB01 LA00 LC04 LC07 MA15 NB06 NC02 ND02 NE03 NE22 PA04Z PD14Z PD15A PE01Z PE08Z PF03Z

Claims (3)

[Claims] An exhaust shutter valve for reducing a passage area is interposed in an exhaust passage, and an exhaust recirculation passage leading to an intake system is connected upstream of the exhaust shutter valve to close the exhaust shutter valve. In the exhaust gas recirculation device for a diesel engine, wherein the exhaust gas recirculation is stopped via an exhaust gas recirculation control valve disposed in the exhaust gas recirculation passage, the exhaust gas recirculation is performed when the exhaust shutter valve is opened from a closed state. An exhaust gas recirculation device for a diesel engine, comprising an opening correction means for limiting an opening of a control valve to gradually increase toward a target opening. 2. The exhaust gas recirculation of a diesel engine according to claim 1, wherein the exhaust shutter valve includes an opening speed reducing means for slowing an opening operation of the valve element from a closed position to an open position. apparatus. 3. An apparatus in which an intake throttle is provided at a position upstream of an exhaust recirculation passage merging portion of an intake passage, wherein an appropriate delay time is given to the closing operation of the intake throttle valve accompanying the opening operation of the exhaust shutter valve. The exhaust gas recirculation device for a diesel engine according to claim 1 or 2, further comprising a delay unit.