JPH06307292A - Exhaust reflux device for diesel engine - Google Patents

Abstract

PURPOSE:To prevent a phenomena wherein an exhaust reflux control valve can not be made to be fully closed in a high-speed region and also stop reflux at the time of starting by reducing the change width of exhaust pressure in an exhaust reflux passage to engine speed change. CONSTITUTION:A variable type FGR orifice 61 is interposed in the down stream than the exhaust reflux control valve 34 of an exhaust circulation passage 33, and the opening of the exhaust reflux control valve 34 is feedback-controlled by a negative pressure control valve 1 so as to make exhaust pressure P2 between both the sides constant. The target valve of the exhaust pressure P2 can be optionally set by a step motor 3 to be controlled according to an operation condition. An air intake throttle valve 45 is interposed in an air intake passage 32. The opening of the FGR orifice 61 is controlled according to an engine operation state by a negative pressure actuator 62 and two solenoid valves 63 and 64.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation system for a diesel engine, and more particularly, to a negative pressure control valve which responds to exhaust gas pressure for introducing a negative pressure into a negative pressure chamber of a diaphragm type exhaust gas recirculation control valve. The present invention relates to an improvement in an exhaust gas recirculation device that is diluted to control an exhaust gas recirculation rate to a desired characteristic.

[0002]

2. Description of the Related Art For example, as an exhaust gas recirculation device suitable for a diesel engine, an EGR orifice is provided on the downstream side of the exhaust gas recirculation passage, that is, in the vicinity of a confluence portion of an intake passage, and an exhaust pressure P ₂ between the orifice and the exhaust gas recirculation control valve. There is known a configuration in which the opening degree of the exhaust gas recirculation control valve is feedback-controlled by a negative pressure control valve so as to keep constant. Also,
In order to arbitrarily variably control the exhaust pressure P ₂ in accordance with operating conditions, etc., the substantial load of the set spring with respect to the diaphragm that defines the exhaust pressure chamber and the atmospheric chamber is changed to open the atmospheric introduction port. A negative pressure control valve capable of changing the valve pressure is disclosed in, for example, Japanese Utility Model Laid-Open No. 1-130058 and Japanese Patent Laid-Open No. 1-149558. This is because an auxiliary spring is arranged so as to oppose the set spring that urges the diaphragm in the closing direction of the atmosphere introduction port, and the position of the spring seat supporting the base end of this auxiliary spring is moved up and down by a step motor. The valve opening pressure can be adjusted. Therefore, the exhaust pressure P _{2 and} thus the exhaust gas recirculation rate can be finely controlled by the control position of the step motor.

FIG. 14 shows an example of a conventional structure of this type. An exhaust gas recirculation passage 33 is provided so as to connect an exhaust passage 31 and an intake passage 32 of an engine, and a diaphragm type is provided in the middle of the passage. The exhaust gas recirculation control valve 34 is installed. In this exhaust gas recirculation control valve 34, a tapered valve body 35 opens and closes a valve opening from the exhaust passage 31 side, and a negative pressure introduced into a negative pressure chamber 37 defined by a diaphragm 36 is the negative pressure. The valve body 35 opens when it is weaker than the urging force of the set spring 38 in the chamber 37, and closes when the urging force is overcome. The negative pressure chamber 37 communicates with the negative pressure tank 40 via a signal pressure passage 39 and a negative pressure passage 51. This negative pressure tank 40
The negative pressure of a constant pressure generated by a vacuum pump or the like (not shown) is stored in the. The tip of the signal pressure passage 39 is connected to the negative pressure control valve 1,
An atmosphere introduction port 10 (see FIG. 1) which will be described later in the negative pressure control valve 1.
(See 5)). In the negative pressure passage 51 connected to the signal pressure passage 39, a VC orifice 52 is provided closer to the negative pressure tank 40 than the junction with the signal pressure passage 39.

The exhaust gas recirculation control valve 3 in the exhaust gas recirculation passage 33
4 Downstream side and the exhaust pressure chamber 6 of the negative pressure control valve 1 (see FIG. 15)
Are communicated with each other by the exhaust pressure passage 42, and the EGR orifice 43 is provided further downstream of the exhaust gas recirculation passage 33.
Is installed. That is, the exhaust pressure P ₂ between the EGR orifice 43 and the exhaust gas recirculation control valve 34 is guided to the exhaust pressure chamber 6 described later.

Then, the exhaust gas recirculation passage 33 of the intake passage 32
A butterfly valve type intake throttle valve 45 is provided on the upstream side of the merging portion. The intake throttle valve 45 restricts the area of the intake passage when performing exhaust gas recirculation, and the opening degree thereof is controlled stepwise by a step motor 46, for example.

On the other hand, in the negative pressure control valve 1, as shown in FIG. 15, the lower diaphragm valve section 2 which controls the basic negative pressure control according to the exhaust pressure, and the control characteristic thereof are further changed to desired characteristics. It is roughly divided into an upper step motor 3 for changing.

The diaphragm valve section 2 includes a casing 4
A diaphragm 5 disposed inside is mainly used, and the diaphragm 5 separates a discharge pressure chamber 6 in a lower portion and an atmosphere chamber 7 in an upper portion. A predetermined set load is applied to the diaphragm 5 by a set spring 8 arranged in the exhaust pressure chamber 6 in a compressed state, and a valve body 9 is attached to the atmosphere chamber 7 side. An atmosphere introducing port 10 is formed in the atmosphere chamber 7 so as to face the valve body 9. This atmosphere introduction port 1
0 extends laterally and communicates with the signal pressure passage 39 described above. Although the atmosphere chamber 7 is generally open to the atmosphere through the communication hole 7a and the filter 25, the intake passage 32 is used in a supercharged engine or the like as in the example shown in FIG. There is also a case where the atmosphere is guided from the outside through the atmosphere passage 44.

On the other hand, the step motor 3 has a casing 1
A pair of stators 13 fixed to 2 and a bearing 1
The rotor 16 is rotatably supported via the rotors 4 and 15. The stepping motor 3 has its rotation angle controlled stepwise by applying a predetermined pulse signal to the coil of the stator 13, and has a configuration in which the rotor 16 makes one revolution in four steps, for example. The operating range of the total number of steps is set to 58 steps from 0 to 58, for example. The rotor 16 has a cylindrical shape, and an internal thread 17 is formed on the inner peripheral surface thereof.

Reference numeral 18 is a guide member fixed to the inner peripheral side of the bearing 15 of the casing 12, and 19 is the guide member 1 described above.
The plunger 19 is non-rotatably and axially slidably guided by 8, and has a male screw 20 formed on the upper portion of the plunger 19, which is screwed to the female screw 17 of the rotor 16. In other words, this plunger 19
Is configured to linearly move in the axial direction according to the number of steps (rotation angle) of the step motor 3. The plunger 19 is located on the center line of the diaphragm 5. A disc-shaped spring seat 21 is fixed to the lower end of the plunger 19.

Specifically, a male screw 26 is formed at the lower end of the plunger 19, and the spring seat 2 is formed there.
1 is screwed together and is fixed at an appropriate position by a lock nut 27.

Reference numeral 22 denotes an intermediate member for transmitting the operation of the plunger 19 to the diaphragm 5.
The intermediate member 22 is a disk-shaped spring seat portion 22.
a and a push rod portion 22b extending in the axial direction of the plunger 19 from one side portion of the spring seat portion 22a. The push rod portion 22b is disposed so as to penetrate the upper surface portion of the atmosphere chamber 7 of the casing 4. . Then, the spring seat portion 22a and the spring seat 21
An auxiliary spring 23 is arranged in a compressed state between the push rod portion 2 and the intermediate member 22.
The tip of 2b is in pressure contact with the retainer 24 on the upper surface of the diaphragm 5. That is, the set spring 8 and the auxiliary spring 23 are arranged to face each other with the diaphragm 5 interposed therebetween.

Next, the basic operation of the conventional exhaust gas recirculation device configured as described above will be described.

As described above, the exhaust pressure P ₂ between the EGR orifice 43 and the exhaust gas recirculation control valve 34 is always guided to the exhaust pressure chamber 6 of the negative pressure control valve 1. The differential pressure between the exhaust pressure P ₂ and the atmospheric pressure acts on the diaphragm 5 of the negative pressure control valve 1, the biasing force of the set spring 8 acts in the closing direction of the atmosphere introduction port 10, and the auxiliary spring 23
The urging force of acts on the opening direction. Therefore, when the pressure determined by the urging forces of both springs 8 and 23, that is, the pressure difference becomes lower than the valve opening pressure, the atmosphere introduction port 10 is opened,
When the pressure difference becomes higher than that, the atmosphere introduction port 10 is closed.

On the other hand, a signal negative pressure obtained by diluting the negative pressure of the negative pressure tank 40 with the atmosphere introduced from the negative pressure control valve 1 is introduced into the negative pressure chamber 37 of the exhaust gas recirculation control valve 34. here,
When the signal negative pressure is weak, the opening degree of the valve element 35 increases and the exhaust pressure P ₂ rises. Therefore, the opening degree of the atmosphere introduction port 10 in the negative pressure control valve 1 is reduced and the signal negative pressure is increased, so that the opening degree of the exhaust gas recirculation control valve 34 is reduced. Along with this, the exhaust pressure P ₂ decreases and the opening degree of the atmosphere introduction port 10 in the negative pressure control valve 1 increases, so the signal negative pressure weakens and the opening degree of the exhaust gas recirculation control valve 34 increases. As a result of repeating such an action, the exhaust pressure P ₂ is kept substantially constant. Assuming that the engine is in a completely steady state,
The opening degree of the atmosphere introduction port 10 (that is, the position of the valve body 9) and the opening degree of the exhaust gas recirculation control valve 34 in the negative pressure control valve 1 are
It can be considered that they are balanced at certain points, and a constant exhaust pressure P ₂ is obtained in that state. Then, the EGR rate (exhaust gas recirculation rate) according to the exhaust pressure P ₂
Therefore, exhaust gas recirculation is performed.

The biasing force of the auxiliary spring 23 is
Since the spring seat 21 changes depending on the position, when the step motor 3 rotates and the spring seat 21 moves up and down, the valve opening pressure changes, and as a result, the exhaust pressure P ₂ changes proportionally. In this embodiment, when the number of steps is small, the spring seat 21 descends and the EGR
The rate is high. As a result, the final exhaust gas recirculation rate characteristic can be obtained as a desired characteristic according to the engine operating conditions.
When the intake throttle valve 45 in the intake passage 32 is throttled, the throttle valve 4
Since the negative pressure is downstream of 5, the exhaust gas recirculation rate can be controlled to be higher.

[0016]

However, in the above-described conventional exhaust gas recirculation system, when the intake throttle valve 45 is opened halfway and an attempt is made to control to a small EGR amount in a high rotation range, the intake negative pressure is reduced by the intake throttle. Because it ’s getting higher,
The pressure in the exhaust gas recirculation passage 33 (exhaust gas pressure P ₂ ) also becomes a high negative pressure, and the negative pressure control valve 1 cannot completely shut off the introduction of the atmosphere. As a result, the exhaust gas recirculation control valve 34 cannot be fully closed. There is a problem. In order to cope with this, it is effective to increase the spring constant of the set spring 8 in the negative pressure control valve 1 or increase the set load, but with this, the step motor 3 is increased in size and height. It has to be torqued, which is not a good idea in terms of cost and weight.

Further, in the above-mentioned conventional structure, since the exhaust gas recirculation control valve 34 is fully opened at the time of starting when the negative pressure as the drive source of the control is not generated, a large amount of exhaust gas recirculation is made at the time of starting. However, there is a drawback that the startability is deteriorated.

Further, it is necessary to stop the exhaust gas recirculation at the time of acceleration of the diesel engine.
By controlling the number of steps of the step motor 3, the signal negative pressure applied to the exhaust gas recirculation control valve 34 is strengthened, and the exhaust gas recirculation control valve 3
Since 4 is fully closed, the responsiveness when exhaust gas recirculation is stopped is low, and exhaust gas recirculates in the initial stage of acceleration. Therefore, the HC and the smoke are likely to increase due to the decrease in the excess air ratio.

[0019]

Therefore, according to the present invention,
The EGR orifice is a variable orifice and can be fully closed. That is, the exhaust gas recirculation device for a diesel engine according to the present invention is a diaphragm type exhaust gas recirculation control which is interposed in the exhaust gas recirculation passage and is always urged in the opening direction by the urging force of the set spring arranged in the negative pressure chamber. A valve and a downstream side of the exhaust gas recirculation passage, which changes the flow passage area stepwise or continuously,
A variable EGR orifice that can be fully closed and this EG
A signal communicating with the negative pressure type drive mechanism that drives the movable part of the R orifice according to the engine operating conditions and keeps the EGR orifice fully closed when no negative pressure is applied, and the negative pressure chamber of the exhaust gas recirculation control valve. A negative pressure source that supplies negative pressure to the negative pressure type driving mechanism and communicates with the signal pressure passage through the negative pressure passage, an exhaust gas recirculation control valve in the exhaust gas recirculation passage, and the EGR orifice. A negative pressure control valve of a diaphragm type that introduces atmospheric pressure into the signal pressure passage so that the exhaust pressure is introduced to a predetermined value, and the exhaust pressure is located upstream of the exhaust gas recirculation passage connecting portion. And an intake throttle valve that changes the intake passage opening area according to the engine operating conditions.

According to a second aspect of the invention, the negative pressure type drive mechanism comprises a diaphragm type actuator and a plurality of solenoid valves. Further, it is provided with an acceleration detecting means for detecting the acceleration of the engine and a recirculation stopping means for fully closing the EGR orifice via the negative pressure type driving mechanism at the time of detecting the acceleration.

[0021]

When the engine is started with no negative pressure, the variable pressure type EGR orifice keeps the variable EGR orifice fully closed and the exhaust gas recirculation is stopped.

Further, during operation, the opening degree of the variable EGR orifice is controlled according to the engine operating conditions. In the region where the exhaust gas recirculation amount should be reduced, the opening degree of the EGR orifice is controlled to be small so that the exhaust gas recirculation passage is controlled. The exhaust pressure inside can be increased. That is, even when the intake passage area is reduced by the intake throttle valve, the pressure drop in the exhaust gas recirculation passage is suppressed by reducing the opening degree of the EGR orifice.

On the other hand, in the structure of claim 2, the EG is used during acceleration.
The R orifice is immediately fully closed, and the exhaust gas recirculation is stopped with good response.

[0024]

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

FIG. 1 shows a first embodiment of an exhaust gas recirculation system for a diesel engine according to the present invention. This exhaust gas recirculation device has the same basic configuration as the above-mentioned conventional device. That is, an exhaust gas recirculation passage 33 is provided so as to connect the exhaust passage 31 and the intake passage 32 of the engine, and a diaphragm type exhaust gas recirculation control valve 34 is interposed in the middle of the passage. The exhaust gas recirculation control valve 34 is
The tapered valve body 35 opens and closes the valve opening from the exhaust passage 31 side, and the negative pressure introduced into the negative pressure chamber 37 defined by the diaphragm 36 is set by the set spring 38 in the negative pressure chamber 37. The valve body 35 opens when it is weaker than the biasing force, and closes when the biasing force is overcome. The negative pressure chamber 37 communicates with the negative pressure tank 40 via a signal pressure passage 39 and a negative pressure passage 51. In this negative pressure tank 40, a constant negative pressure generated by a vacuum pump (not shown) is stored.
Further, the tip of the signal pressure passage 39 is connected to the negative pressure control valve 1 and opens as an atmosphere introduction port 10 in the negative pressure control valve 1. Further, in the negative pressure passage 51 connected to the signal pressure passage 39, a VC orifice 52 is provided closer to the negative pressure tank 40 than the junction with the signal pressure passage 39. Since the structure of the negative pressure control valve 1 itself is the same as that shown in FIG. 15, the description thereof will be omitted.

A butterfly valve type intake throttle valve 45 is provided upstream of the joining portion of the exhaust gas recirculation passage 33 of the intake passage 32.
Is provided. The intake throttle valve 45 can be controlled in opening degree in two stages of a fully open state and a half open state by a negative pressure actuator or a step motor (not shown).

Further, the exhaust gas recirculation control valve 3 in the exhaust gas recirculation passage 33
4 the downstream side and the exhaust pressure chamber 6 of the negative pressure control valve 1 are connected to the exhaust pressure passage 4
2 and the exhaust gas recirculation passage 33
An EGR orifice 61 is provided on the further downstream side. That is, the exhaust pressure P ₂ between the EGR orifice 61 and the exhaust gas recirculation control valve 34 is guided to the exhaust pressure chamber 6.

The EGR orifice 61 is constructed as a variable type orifice. A diaphragm type negative pressure actuator 62 is used as a negative pressure type drive mechanism for controlling the opening degree of the variable EGR orifice 61.
And two solenoid valves 63 and 64 for supplying a negative pressure to the actuator 62, and a negative pressure is supplied from a negative pressure tank 40 as a negative pressure source. Again 65
Is a control unit that outputs a control signal to the solenoid valves 63 and 64 and the step motor 3, and the control unit 65 includes a lever opening sensor 66 that detects an accelerator opening (control lever opening of the injection pump). The engine speed sensor 67 for detecting the engine speed, the water temperature sensor 68 for detecting the cooling water temperature, and other detection signals indicating engine operating conditions are input.

As shown in detail in FIG. 2, the EGR orifice 61 comprises an annular valve seat 71 and a valve body 73 fixed to a rod 72 of an actuator 62, and the valve body 73 is provided from the tip side. The three parts of the small diameter portion 73a, the large diameter portion 73b, and the flange portion 73c are integrated so that the diameters gradually increase. The large diameter portion 73b has a diameter slightly smaller than the inner diameter of the valve seat 71, and the flange portion 73c has the valve seat 71.
It is formed larger than the inner diameter. Therefore, the flange portion 73c comes into contact with the valve seat 71, so that the EGR orifice 61 is fully closed.

On the other hand, in the negative pressure actuator 62, an atmospheric pressure chamber 75 and a negative pressure chamber 76 are separated from each other by a diaphragm 74, and a vertically movable spring seat 77 is provided.
A first spring 78 is arranged between the diaphragm 79 and the diaphragm 74, and a second spring 80 is arranged between the casing 79 and the spring seat 77. The spring seat 77 is positioned at a predetermined position by the stopper 81. The pressure passage 82 for supplying the negative pressure to the negative pressure chamber 76 can communicate with the negative pressure passage 83 reaching the vacuum tank 40 via the first solenoid valve 63, and the atmospheric passage leading to the air cleaner (not shown). It is possible to communicate with 84 via both the first and second solenoid valves 63, 64. That is, the first solenoid valve 63 is a three-way solenoid valve that selectively switches the negative pressure passage 83 and the atmosphere passage 84, and the second solenoid valve 64 opens and closes the atmosphere passage 84. The first and second solenoid valves 63 and 64 are both in the atmosphere passage 8 when they are OFF.
4 is opened.

FIGS. 3 to 5 show each solenoid valve 63,
The relationship between the state of 64 and the operation of the negative pressure actuator 62 is shown. Both solenoid valves 63 and 64 are O
In the case of FF, as shown in FIG. 3, since the atmosphere passage 84 communicates with the negative pressure chamber 76 through both, the diaphragm 74
Is largely moved downward, and the EGR orifice 61 is fully closed. When the first solenoid valve 63 is ON and the second solenoid valve 64 is OFF, both the atmosphere passage 84 and the negative pressure passage 83 communicate with the pressure passage 82, as shown in FIG. 4. Therefore, an intermediate negative pressure is supplied to the negative pressure chamber 76, and the EGR orifice 61 is in a half-open state. In this half open state, only the first spring 78 is displaced, so that the intermediate position can be reliably obtained. When both the first and second solenoid valves 63 and 64 are turned on, as shown in FIG. 5, only the negative pressure passage 83 communicates with the pressure passage 82, so that a strong negative pressure is supplied to the negative pressure chamber 76. The second spring 79 is also displaced so that the EGR orifice 61 is fully opened.

Next, FIG. 6 is a flow chart showing the contents of the exhaust gas recirculation control executed by the control unit 65, and the operation of the above embodiment will be described below based on this flow chart.

First, in step 1, the lever opening sensor 66
Is read, the engine speed detected by the rotation speed sensor 67, and the cooling water temperature detected by the water temperature sensor 68 are read, and the operation range is determined in steps 2 and 3. That is, the three areas A to C shown in FIG.
To determine. The required exhaust gas recirculation rate becomes large on the low speed and low load side as shown in the figure.

In the case of the area A on the low speed / low load side,
Proceeding to step 4, the intake throttle valve 45 is half-opened and the EGR orifice 61 is fully opened. Then, in step 5, the number of steps of the step motor 3 is set based on the control map shown in FIG. As mentioned above,
The smaller the number of steps, the higher the exhaust gas recirculation rate. Therefore, in this region A, sufficient exhaust gas recirculation is provided by utilizing the intake throttle.

If the region B is on the higher speed side than the region A, the process proceeds from step 3 to step 6 and the intake throttle valve 45
Is half-opened and the EGR orifice 61 is half-opened. Then, in step 7, the number of steps of the step motor 3 is set based on the control map shown in FIG.
Note that the control map in FIG. 8 considers switching from full opening to half opening of the EGR orifice 61 in advance, and the regions A and B have a discontinuous number of steps.
By making the EGR orifice 61 half-open in this manner, the exhaust pressure P ₂ in the exhaust gas recirculation passage 33 can be kept high even on the high rotation side where the exhaust gas recirculation amount is controlled to be small. That is, the pressure drop caused by the intake throttle is small, and the exhaust gas recirculation control valve 34 can be reliably controlled to the fully closed state in accordance with the target exhaust gas recirculation ratio.

If the region C is on the high load side or the high speed side, the process proceeds from step 3 to step 8 to fully open the intake throttle valve 45 and to make the EGR orifice 61
Fully closed. As a result, the exhaust gas recirculation passage 33 is closed and the exhaust gas recirculation is stopped. Then, in step 9, FIG.
The number of steps of the step motor 3 is set based on the control map shown in FIG. The number of steps has a large value so that the exhaust gas recirculation control valve 34 is fully closed.

FIG. 9 is a characteristic diagram showing a change in the exhaust pressure P ₂ with respect to the rotational speed at a constant load L, for example, together with a change in the pressure in the intake passage 32. Further, the conventional characteristic in which the EGR orifice 61 is a fixed orifice is shown by a broken line. As is clear from this figure, by switching the EGR orifice 61 from full open to half open,
The change range of the exhaust pressure P ₂ due to the change of the rotation speed becomes small,
As a result, the variable control by the step motor 3 becomes easier and the accuracy thereof is improved.

Further, in the above structure, the EGR orifice 61 is always kept in the fully closed state when the engine is started when the negative pressure by the vacuum pump is not sufficiently generated. Therefore, it is possible to avoid deterioration of startability due to exhaust gas recirculation.

According to the above-mentioned embodiment, when the EGR orifice 61 is fully closed, the valve body 73 is seated so as to penetrate through the opening of the valve seat 71, so that it adheres to the valve body 73. The attached substances are naturally removed, and it is possible to prevent the variation of the opening area and the reduction of the exhaust gas recirculation amount due to the attached substances.

Next, the flowchart of FIG. 10 shows a different embodiment of the exhaust gas recirculation control.

In this embodiment, as shown as steps 10 and 11, the rate of change Δacc of the accelerator opening acc detected by the lever opening sensor 68 is successively calculated, and whether or not this is a predetermined value or more is determined. The acceleration state is determined by. When accelerating, the routine proceeds from step 11 to step 8 where the intake throttle valve 45 is fully opened and EG
The R orifice 61 is fully closed. As a result, the exhaust gas recirculation passage 33 is closed and the exhaust gas recirculation is stopped. Where E
Since the GR orifice 61 is driven by switching the solenoid valves 63 and 64, the exhaust gas recirculation can be stopped with extremely high responsiveness as compared with the exhaust gas recirculation stop by controlling the number of steps of the step motor 3. Therefore, the exhaust gas recirculation can be surely stopped at the time of acceleration, and the deterioration of exhaust emission and smoke can be prevented. The other steps of FIG. 10 are not different from those of FIG. 6 described above.

Next, FIG. 11 shows a second embodiment of the present invention. In this embodiment, as the negative pressure control valve 1A,
What is fixed to the constant control characteristic without using the step motor 3 is used, and the intake throttle valve 45 can control the opening degree in three stages of a fully opened state, a half opened state and a slightly opened state. By combining this opening control and the opening control of the EGR orifice 61, a plurality of stages of exhaust gas recirculation rate are obtained.

The negative pressure control valve 1A of this embodiment has the same basic structure as the diaphragm valve portion 2 of the negative pressure control valve 1 described above, and a diaphragm 92 is provided inside a casing 91.
The exhaust chamber 93 and the atmospheric chamber 94 are separated by
A predetermined set load is applied by a set spring 95 arranged in a compressed state in the exhaust pressure chamber 93, and a valve body 96 is attached to the atmosphere chamber 94 side of the diaphragm 92. Then, in the atmosphere chamber 94, the valve 9
An air introduction port 97 is formed so as to face 6. The atmosphere introducing port 97 communicates with the signal pressure passage 39, and the atmosphere chamber 94 is open to the atmosphere via the atmosphere passage 98. The exhaust pressure P ₂ in the exhaust gas recirculation passage 33 is introduced into the exhaust pressure chamber 93 through the exhaust pressure passage 42 as in the above-described embodiment.

On the other hand, the intake throttle valve 45 is driven by the negative pressure type drive mechanism shown in detail in FIG. This is basically the same structure as the drive mechanism of the EGR orifice 61, and is a diaphragm negative pressure actuator 101 linked to the intake throttle valve 45 via a rod 102, and the actuator 1
Two solenoid valves 103 for supplying negative pressure to 01,
And a negative pressure tank 40 as a negative pressure source.
The negative pressure is being supplied from. The negative pressure actuator 1
In 01, the atmospheric pressure chamber 106 and the negative pressure chamber 107 are separated by the diaphragm 105, the first spring 109 is arranged between the vertically movable spring seat 108 and the diaphragm 105, and the casing 11
The second spring 1 between 0 and the spring seat 108.
11 are provided. The spring seat 108
Is positioned at a predetermined position by the stopper 112.
The pressure passage 113 for supplying the negative pressure to the negative pressure chamber 107 is
A negative pressure passage 114 reaching the vacuum tank 40 can be communicated with via a third solenoid valve 103, and an atmosphere passage 115 leading to an air cleaner (not shown) is passed through both the third and fourth solenoid valves 103, 104. Communication is possible. That is, the third solenoid valve 103 functions as a three-way solenoid valve to selectively switch the negative pressure passage 114 and the atmosphere passage 115, and the fourth solenoid valve 1
Reference numeral 04 opens and closes the atmosphere passage 115. In addition, the third
The fourth solenoid valves 103 and 104 are both OF
At the time of F, the atmosphere passage 115 is opened.

Therefore, both solenoid valves 103, 10
If 4 is OFF at the same time, rod 1
02 is largely moved downward, and the intake throttle valve 45 is fully opened.
When the third solenoid valve 103 is ON and the fourth solenoid valve 104 is OFF, an intermediate negative pressure is supplied and the intake throttle valve 45 is in a half open state. When both solenoid valves 103 and 104 are simultaneously ON, a strong negative pressure is supplied and the intake throttle valve 45 is in a slightly opened state.

In this embodiment, as shown in Table 1 below, the intake throttle valve 4 is used for each of the operating regions A to F shown in FIG.
5 and the EGR orifice 61 are controlled in opening degree, and exhaust gas recirculation rate control is performed stepwise. That is, the negative pressure control valve 1A
It is possible to realize variable control of the exhaust gas recirculation rate, while making it extremely simple as compared with the above-described embodiment.

[0047]

[Table 1]

[0048]

As is apparent from the above description, according to the exhaust gas recirculation system for a diesel engine of the present invention, the EGR orifice in the exhaust gas recirculation passage is a variable type orifice, so that the exhaust gas recirculation due to a change in the rotational speed is performed. The change width of the exhaust pressure in the passage can be reduced, the exhaust gas recirculation control valve can be reliably controlled according to the required exhaust gas recirculation rate, and the accuracy thereof can be improved. Further, exhaust gas recirculation at the time of starting can be prevented, and deterioration of startability can be avoided.

Further, according to the second aspect of the invention, the exhaust gas recirculation can be stopped with high responsiveness by utilizing the EGR orifice, and deterioration of exhaust emission and smoke due to exhaust gas recirculation can be prevented.

[Brief description of drawings]

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

FIG. 2 is a structural explanatory view showing an EGR orifice and its drive mechanism.

FIG. 3 is an operation explanatory view of an EGR orifice (fully closed state).

FIG. 4 is an operation explanatory diagram of an EGR orifice (half open state).

FIG. 5 is an operation explanatory diagram of an EGR orifice (fully opened state).

FIG. 6 is a flowchart showing an example of control of this embodiment.

FIG. 7 is a characteristic diagram showing divisions of operating regions.

FIG. 8 is a characteristic diagram showing the number of steps in each operation region.

FIG. 9 is a characteristic diagram showing a relationship between an operating region and exhaust pressure.

FIG. 10 is a flowchart showing another example of exhaust gas recirculation control.

FIG. 11 is a structural explanatory view showing a second embodiment of the present invention.

FIG. 12 is a structural explanatory view showing a drive mechanism of an intake throttle valve.

FIG. 13 is a characteristic diagram showing the division of the operating region in the second embodiment.

FIG. 14 is a structural explanatory view showing a structure of a conventional exhaust gas recirculation device.

FIG. 15 is a cross-sectional view showing a negative pressure control valve in this exhaust gas recirculation device.

[Explanation of symbols]

 1 ... Negative pressure control valve 3 ... Step motor 32 ... Intake passage 34 ... Exhaust gas recirculation control valve 37 ... Negative pressure chamber 39 ... Signal pressure passage 40 ... Negative pressure tank 45 ... Intake throttle valve 61 ... Variable EGR orifice 62 ... Negative pressure Actuator 63 ... First solenoid valve 64 ... Second solenoid valve

Claims (2)

[Claims] 1. A diaphragm type exhaust gas recirculation control valve which is interposed in the exhaust gas recirculation passage and is constantly urged in an opening direction by an urging force of a set spring arranged in a negative pressure chamber, and a downstream side of the exhaust gas recirculation passage. The variable EGR orifice which is placed in the position where the flow passage area is changed stepwise or continuously and can be fully closed, and the movable part of the EGR orifice are driven according to the engine operating conditions, and a negative pressure is applied. The negative pressure type drive mechanism that keeps the EGR orifice fully closed in a state where the pressure does not act, the signal pressure passage communicating with the negative pressure chamber of the exhaust gas recirculation control valve, the negative pressure type drive mechanism, and the negative pressure type drive mechanism. The negative pressure source communicating with the signal pressure passage via the pressure passage, the exhaust pressure between the exhaust gas recirculation control valve of the exhaust gas recirculation passage and the EGR orifice are introduced, and the exhaust gas pressure is maintained at a predetermined level. The diaphragm-type negative pressure control valve that introduces the atmosphere into the signal pressure passage as described above, and the intake passage opening area that is located upstream of the exhaust recirculation passage connection part of the intake passage and that changes according to engine operating conditions. An exhaust gas recirculation device for a diesel engine, comprising: 2. The negative pressure type drive mechanism comprises a diaphragm type actuator and a plurality of solenoid valves, and acceleration detection means for detecting acceleration of the engine, and the negative pressure type drive mechanism at the time of detecting the acceleration. The exhaust gas recirculation device for a diesel engine according to claim 1, further comprising: a recirculation stop means for fully closing the EGR orifice.