JPH05321768A - Exhaust gas circulating device of diesel engine - Google Patents

Abstract

PURPOSE:To improve the operability of an exhaust gas circulating device by arranging a valve body of an exhaust gas circulating control valve closer to the exhaust passage side than the valve seat, providing a spring to energize the valve body in the valve- opening direction, and increasing the opening of an intake throttle valve in response to the suction negative pressure. CONSTITUTION:A valve body 41 to be connected to a diaphragm 45 of an exhaust gas circulating control valve 4 is arranged closer on the exhaust passage 2 side than a valve seat 42, and a spring 48 to energize this valve body 41 in the valve-opening direction is provided. An intake throttle valve 8 is interposed upstream of a merging part between an intake passage 1 and an exhaust gas circulating passage 3, and springs 62, 69 to energize this intake throttle valve 8 in the valve-opening direction are provided. The opening of the intake throttle valve 8 is increased in response to the suction negative pressure caused downstream of the intake throttle valve 8. A constant pressure control mechanism 50 to adjust the suction negative pressure to a constant value in the operation range where the engine speed is not less than the specified value is provided. This arrangement allows the correct exhaust gas circulating control without being affected by the rise of the exhaust gas pressure or the rise of the suction negative pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a diesel engine exhaust gas recirculation system.

[0002]

2. Description of the Related Art In order to control the amount of exhaust gas recirculation according to engine operating conditions, a diaphragm type exhaust gas recirculation control valve is provided in an exhaust gas recirculation passage connecting an intake passage and an exhaust passage of an engine. Some are equipped with a negative pressure control valve that adjusts the signal negative pressure introduced into the diaphragm chamber of the recirculation control valve via a step motor (for example, the actual opening 6
3-198458, gazette).

This type of exhaust gas recirculation control valve is provided with a spring for urging a valve element connected to the diaphragm in a valve closing direction, and a signal negative pressure introduced into the diaphragm chamber via the negative pressure control valve is increased. Along with this, the valve body is moved in the valve opening direction against the spring. Since the negative pressure control valve controls the opening degree of the exhaust gas recirculation control valve so that the pressure in the exhaust gas recirculation passage becomes a predetermined value, when the pressure in the exhaust gas recirculation passage becomes higher than the predetermined value, the negative pressure control valve outputs a signal negative pressure. When the exhaust gas recirculation control valve opening is decreased by weakening it, while the pressure in the exhaust gas recirculation passage drops below a predetermined value, the negative pressure control valve pressure is increased to increase the signal negative pressure and the exhaust gas recirculation control valve opening is increased. The exhaust pressure in the passage is adjusted to a predetermined value.

However, in such a conventional exhaust gas recirculation system, the valve body of the diaphragm type exhaust gas recirculation control valve is arranged on the intake passage side with respect to the valve seat interposed in the exhaust gas recirculation passage, and the exhaust passage Since the exhaust pressure of the engine works in the valve opening direction, the diesel engine equipped with a supercharger and a trap for collecting particulates will be in the fully closed position or at a small closed position when the exhaust pressure increases significantly. There is a possibility that the valve element, which should be in the open position, may lift more than necessary from the valve seat against the biasing force of the spring, resulting in an excessive amount of exhaust gas recirculation.

Further, conventionally, there is one in which an intake throttle valve is provided upstream of a confluence portion of the intake passage with the exhaust gas recirculation passage to suck the exhaust gas recirculation gas from the exhaust gas recirculation passage by negative suction pressure. Since the opening of the throttle valve was controlled in stages, the intake negative pressure could not be finely controlled, and the opening of the exhaust gas recirculation control valve was small when the engine was running at high engine speed with a small amount of exhaust gas recirculation. On the other hand, the suction negative pressure generated on the downstream side of the intake throttle valve becomes large, and the negative pressure introduced from the exhaust gas recirculation passage to the negative pressure control valve becomes excessive, which may impair the closing performance of the negative pressure control valve. was there. As a countermeasure against this, it is necessary to increase the spring constant of the spring that biases the diaphragm of the negative pressure control valve in opposition to the negative pressure, or to increase the amount of spring deflection. However, when the spring constant of the spring is increased, there is a problem that the amount of change in the spring load per step of the step motor that adjusts the spring load of the spring increases, and precise control cannot be performed. Further, when the flexure amount of the spring is increased, it is necessary to increase the pitch of the screw that converts the rotation of the step motor into the expansion / contraction direction of the spring or increase the rotation speed of the step motor, and the negative pressure control valve becomes large. There was a problem.

The present invention focuses on the above problems and aims to improve the operability of the exhaust gas recirculation device.

[0007]

According to the present invention, an exhaust gas recirculation passage connecting an intake passage and an exhaust passage of an engine, a diaphragm type exhaust gas recirculation control valve interposed in the exhaust gas recirculation passage,
A step motor is used to detect the signal pressure in the diaphragm chamber of the exhaust gas recirculation control valve by detecting the pressure in the exhaust gas recirculation passage between the exhaust gas recirculation control valve and the merging portion of the exhaust gas recirculation valve and setting this pressure to a predetermined value. In a diesel engine exhaust gas recirculation system including a diaphragm-type negative pressure control valve that is adjusted via a valve body, the valve body connected to the diaphragm of the exhaust gas recirculation control valve is arranged on the exhaust passage side of the valve seat, and the valve body is opened. A spring for urging in the valve direction is provided, and an intake throttle valve is provided upstream of a confluence portion of the intake passage with the exhaust gas recirculation passage, and a spring for urging the intake throttle valve in the closing direction is provided. , In response to intake negative pressure generated on the downstream side of the intake throttle valve, the opening degree of the intake throttle valve is increased and the intake negative pressure is adjusted to a constant value in an operating range where the engine speed is equal to or higher than a predetermined value. Providing a pressure control mechanism.

[0008]

[Function] The opening of the exhaust gas recirculation passage is basically determined by the pressure of the exhaust gas recirculation passage introduced to the negative pressure control valve, and when the pressure in the exhaust gas recirculation passage exceeds a predetermined value, the negative pressure control valve weakens the signal negative pressure. When the opening degree of the exhaust gas recirculation control valve decreases and the pressure in the exhaust gas recirculation passage falls below a predetermined value, the negative pressure control valve increases the signal negative pressure to increase the opening degree of the exhaust gas recirculation control valve, and The pressure is adjusted to a predetermined value.

On the other hand, the intake throttle valve produces an intake negative pressure at the confluence portion of the intake passage with the exhaust gas recirculation passage, so that the exhaust gas recirculation amount according to the differential pressure between the intake negative pressure and the exhaust gas recirculation passage exhaust pressure. Is obtained.

In the low rotational speed range, the intake throttle valve is biased by the spring and held at a constant opening, so that the intake negative pressure gradually increases in accordance with the rotational speed. The exhaust gas recirculation amount increases, and the exhaust gas recirculation rate can be kept substantially constant while keeping the number of steps of the step motor provided in the negative pressure control valve constant. The control range of the exhaust gas recirculation rate can be expanded.

In the high engine speed range, the exhaust recirculation rate can be kept small by adjusting the intake negative pressure generated in the intake passage to a constant value by the intake throttle valve via the equal pressure control mechanism. Also,
Since the suction negative pressure is maintained at a constant value even at high speed,
Unlike the conventional example, it is not necessary to increase the spring load of the spring that urges the diaphragm of the negative pressure control valve, and the amount of change in the spring load per step of the step motor can be reduced to achieve precise control. Further, the amount of flexure of the spring for urging the diaphragm is reduced, and the negative pressure control valve can be downsized.

Although the opening of the exhaust gas recirculation control valve is basically determined by the pressure of the exhaust gas recirculation passage introduced to the negative pressure control valve, the valve body connected to the diaphragm of the exhaust gas recirculation control valve is located closer to the exhaust passage than the valve seat. By arranging and arranging a spring for urging the valve element in the valve opening direction, the exhaust pressure in the exhaust passage acts in the valve closing direction, so the exhaust pressure is significantly increased and the exhaust valve is in the fully closed position. The valve body should lift from the valve seat,
Alternatively, the valve body, which should be in the small opening position, is prevented from being lifted more than necessary from the valve seat, and the exhaust gas recirculation amount can be accurately controlled according to the engine operating conditions.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an outline of an exhaust gas recirculation system,
An exhaust gas recirculation passage 3 that connects the exhaust passage 2 of the diesel engine 9 and the intake passage 1 is provided, and a diaphragm type exhaust gas recirculation control valve 4 is interposed in the exhaust gas recirculation passage 3. A signal negative pressure passage 5 is connected to the diaphragm chamber 46 of the exhaust gas recirculation control valve 4, and a negative pressure from the vacuum tank 7 is introduced into the signal negative pressure passage 5 through the negative pressure passage 31 and the orifice 35, and at the same time, a negative pressure is given. Connected to the pressure control valve 6,
The degree of opening of the exhaust gas recirculation control valve 4 is controlled by appropriately diluting the negative pressure introduced into the diaphragm chamber 46 of the exhaust gas recirculation control valve 4 by the negative pressure control valve 6.

In the exhaust gas recirculation control valve 4, a valve body 41 which can be seated on a valve seat 42 formed in the middle of the exhaust gas recirculation passage 3 is arranged on the exhaust passage 2 side of the valve seat 42, that is, on the upstream side of the exhaust gas recirculation passage 3. To be done. The valve seat 42 has a conical seat surface 42a.
While the valve body 41 is also formed with a conical seat surface 41a, the valve body 41 is lifted to the upstream side with respect to the valve seat 42 so that a gap 40 is formed between the two.
The opening area of is changed, and the exhaust gas recirculation amount is adjusted.

In the exhaust gas recirculation control valve 4, the valve body 41 has the rod 4
3 is connected to the diaphragm 45. The inside of the casing 44 is covered by the diaphragm 45.
6 and the back pressure chamber 47. In this embodiment, the back pressure chamber 47 is defined.
Atmospheric pressure is introduced through the hole 49 into the.

The diaphragm 45 has a diaphragm chamber 4
A predetermined spring load is applied by the spring 48 interposed in the compressed state in 6 to urge the valve body 41 in the valve opening direction. That is, as the signal negative pressure guided to the diaphragm chamber 46 increases, the diaphragm 45 draws the valve body 41 toward the valve seat 42 while compressing the spring 48.
It is supposed to sit down.

As shown in FIG. 2, the negative pressure control valve 6 has a lower diaphragm valve section 32 which controls a basic negative pressure according to the pressure of the exhaust gas recirculation passage 3, and a control characteristic of the lower diaphragm valve section 32. It is roughly divided into an upper step motor 33 for changing to.

The diaphragm valve portion 32 includes a casing 34.
A diaphragm 35 disposed inside is mainly used, and a discharge pressure chamber 36 and a dilution chamber 37 are defined by the diaphragm 35.

An orifice 30 is provided on the intake passage 1 side, that is, on the downstream side of the exhaust gas recirculation control valve 4 in the exhaust gas recirculation passage 3, and the pressure therebetween is introduced into the exhaust pressure chamber 36 from the passage 52 via the orifice 11. ..

A predetermined spring load is applied to the diaphragm 35 by a spring 38 which is interposed in a pressure-exhaust chamber 36 in a compressed state, and the valve body 3 is provided on the dilution chamber 37 side.
9 is attached.

Atmospheric pressure is introduced from the hole 51 into the dilution chamber 37, and the port 1 communicating with the signal negative pressure passage 5 is provided.
0 opens toward the valve body 39, and the port 10 opens the valve body 39.
It is designed to be opened and closed by.

On the other hand, the step motor 33 includes a pair of stators 13 fixed to the casing 12 and a bearing 1.
The rotor 16 is rotatably supported via the rotors 4 and 15. This step motor 33 is
The rotation angle is controlled stepwise by applying a predetermined pulse signal from the control unit 80 to the coil.

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, 19
Is a plunger guided by the guide member 18 so as to be non-rotatable and slidable in the axial direction. The plunger 19 has a male screw 20 formed on an upper portion thereof, which is screwed to the female screw 17 of the rotor 16. ing. That is,
The plunger 19 is configured to linearly move in the axial direction according to the rotation angle of the step motor 33. A disk-shaped spring seat 21 is provided at the lower end of the plunger 19.
Is fixed.

Reference numeral 22 is an intermediate member for transmitting the operation of the plunger 19 to the diaphragm 35. This intermediate member 22
Is composed of a disk-shaped spring seat portion 22a and a push rod portion 22b extending from one side portion of the spring seat portion 22a in the axial direction of the plunger 19, and the push rod portion 22b is the upper surface of the dilution chamber 37 of the casing 34. It is arranged so as to penetrate the portion. An auxiliary spring 23 is interposed between the spring seat portion 22a and the spring seat 21 in a compressed state, whereby the push rod portion 22b of the intermediate member 22 is pressed against the upper retainer 24 of the diaphragm 35. ..

The step motor 33 makes one rotation in four steps, and in this embodiment, the operating range is defined in 32 steps of 0 to 32. FIG. 2 shows a state in which the number of steps of the step motor 33 is at an appropriate intermediate value, and the tip of the plunger 19 and the intermediate member 22 are apart from each other to some extent. In this state, the differential pressure between the exhaust pressure and the intake pressure acts on the diaphragm 35, and is biased in the closing direction by the set spring 38 and in the opening direction by the auxiliary spring 23. Therefore, the port 10 is opened when the differential pressure becomes larger than the pressure (valve closing pressure) determined by the spring load of both springs 38 and 23, and the port 10 is closed when the differential pressure becomes small.

Since the spring load of the auxiliary spring 23 changes according to the position of the spring seat 21 supporting the upper end of the auxiliary spring 23, when the step motor 33 rotates and the spring seat 21 moves upward, the valve closing thereof is performed. When the spring seat 21 moves downward, the valve closing pressure decreases. That is, the step motor 33
It is possible to correct the opening / closing characteristics of the port 10 by controlling the rotation angle, and thereby to make the final EGR amount a desired characteristic. FIG. 3 illustrates the characteristic of the valve opening pressure obtained corresponding to the number of steps of the step motor 33.

A butterfly type intake throttle valve 8 is provided in the intake passage 1 upstream of the confluence portion of the exhaust gas recirculation passage 3.
A rotary shaft 57 of the intake throttle valve 8 is linked to the rotary shaft 57 of the intake throttle valve 8 as a constant pressure control mechanism 50 for the intake throttle valve 8 that adjusts the intake negative pressure to a constant value in response to the intake negative pressure in an operating range where the engine speed is equal to or higher than a predetermined value. 61 is connected, a spring 62 for urging the intake throttle valve 8 in the valve closing direction is connected to the swing end of the link 61, and the intake throttle valve 8 is rotated in the valve opening direction against the spring 62. The diaphragm device 63 to be driven is the rod 5
Connected via 8.

In the diaphragm device 63, the inside of the casing 64 is surrounded by the diaphragm 65 and the diaphragm chamber 6
6 and the back pressure chamber 67. In this embodiment, the back pressure chamber 6
Atmospheric pressure is introduced into 7 through hole 68. Diaphragm chamber 6
6, the pressure in the intake passage 1 downstream of the intake throttle valve 8 is introduced via the intake negative pressure introduction passage 71.

The diaphragm 65 has a diaphragm chamber 66.
A predetermined spring load is applied to the intake throttle valve 8 in the valve closing direction by the spring 69 interposed therein in a compressed state. Therefore, the diaphragm device 63 rotates the intake throttle valve 8 in the opening direction against the springs 62 and 69 when the suction negative pressure introduced into the diaphragm chamber 66 rises above a predetermined value, and the intake throttle valve 8 is rotated. The suction negative pressure generated on the downstream side of is adjusted to a constant value.

In the diaphragm chamber 66, the suction negative pressure introducing passage 71 and the negative pressure passage 31 communicating with the vacuum tank 7 are selectively connected via a three-way solenoid valve 72. The diaphragm device 63 is configured to forcibly fully open the intake throttle valve 8 against the spring 62 and the spring 69 by introducing a negative pressure from the vacuum tank 7 into the diaphragm chamber 66.

Next, the exhaust gas recirculation control valve 4 and the intake throttle valve 8
The control of the exhaust gas recirculation amount using is explained. The control unit 80 is composed of a microcomputer, to which an engine speed detection signal Ne, a cooling water temperature detection signal Tw representative of the engine temperature, etc. are input, and these information are taken in according to a prestored program to perform arithmetic processing. Then, the exhaust gas recirculation amount is controlled via the negative pressure control valve 6 and the three-way solenoid valve 72.

Next, this control operation will be described with reference to the flowchart of FIG.

First, in step 10, the engine speed N
Various data of operating conditions such as e, engine load Tq, and cooling water temperature Tw are read.

Next, the process proceeds to step 20 and step 1
Based on the control map shown in FIG. 5, it is judged from the data read at 0 whether the current operating condition is the exhaust gas recirculation region.

If it is determined in step 20 that the exhaust gas is not in the exhaust gas recirculation region, the process proceeds to step 60, and the three-way solenoid valve 72 is connected to the diaphragm chamber 66 of the diaphragm device 63.
The intake throttle valve 8 is held at the fully open position by switching to a position where the negative pressure passage 31 is connected to the position.

Then, in step 70, the maximum number of steps is output to the step motor 33 of the negative pressure control valve 6,
The exhaust gas recirculation control valve 4 is fully closed to stop the exhaust gas recirculation.

If it is determined in step 20 that the exhaust gas is in the exhaust gas recirculation region, the process proceeds to step 30, and the three-way solenoid valve 72 is placed at a position where the suction negative pressure introducing passage 71 is connected to the diaphragm chamber 66 of the diaphragm device 63. To switch. As a result, the diaphragm device 63 adjusts the opening degree of the intake throttle valve 8 in response to the intake negative pressure to control the intake negative pressure.

Then, the process proceeds to step 40 and step 10
Based on the control map shown in FIG. 5, the basic step number Bstp of the step motor 33 is read based on the control speed map shown in FIG. 5 from the data of the engine speed Ne and the load Tq read in step (4), and based on the control map shown in FIG. The lower the EGR amount is, the smaller the EGR amount is increased (the number of steps is increased), the correction coefficient Ktw is read, and the step number STEPN of the step motor 33 is set to ST.
After calculating with the formula of EPN = Bstp × Ktw, the process proceeds to step 50 and outputs the step number STEPN to the step motor 33. By using the correction coefficient Ktw, the exhaust gas recirculation amount in the cold state is reduced to stabilize the combustion.

In this way, according to the negative pressure control valve 6,
Depending on the rotation angle of the step motor 33, the diaphragm 35
The urging force acting on changes. The opening of the exhaust gas recirculation control valve 4 is determined by the pressure of the exhaust gas recirculation passage 3 guided to the negative pressure control valve 6, and as shown in FIG. 7, the lower the engine speed Ne and the lower the load Tq, the more the exhaust gas recirculation. The rate is increasing.

On the other hand, in the operating range where the engine speed is equal to or lower than the predetermined value X, the diaphragm device 63 holds the intake throttle valve 8 at the predetermined opening regulated by the stopper by the urging force of the springs 62 and 69. On the other hand, as shown in FIG. 8, the suction negative pressure increases with the engine speed, so the exhaust gas recirculation amount increases with the increase of the intake air amount, and the stepping motor 33 provided in the negative pressure control valve The exhaust gas recirculation rate can be kept substantially constant while keeping the number constant, and the change in the number of steps with respect to the required exhaust gas recirculation rate can be reduced.

In the high engine speed range in which the engine speed exceeds the predetermined value X, the diaphragm device 63 resists the biasing force of the spring 62 and the spring 69 by the suction negative pressure introduced into the diaphragm chamber 66. The opening degree of 8 is gradually increased to adjust the suction negative pressure to a constant value.

When the pressure in the exhaust gas recirculation passage 3 is constant,
As shown by hatching in FIG. 8, the exhaust gas recirculation amount increases until the engine speed reaches a predetermined value X, and is kept constant thereafter. On the other hand, the amount of fresh air sucked through the intake throttle valve 8 increases with the engine speed as shown by the one-dot chain line in FIG. It is kept constant until it reaches X, and gradually decreases in a rotation speed range where it rises above a predetermined value X.

As a result, it is not necessary to increase the spring load of the spring 36 that urges the diaphragm 35 of the negative pressure control valve 6 in opposition to the suction negative pressure, and the step motor 33
The amount of change in the spring load per step can be reduced for precise control. Further, the negative pressure control valve 6 can be downsized by reducing the amount of bending of the spring 36.

When the engine operation is stopped, the intake throttle valve 8 is closed by the urging force of the spring 62 and the spring 69, and is kept at a predetermined opening regulated by the stopper.

Further, the diaphragm 4 of the exhaust gas recirculation control valve 4
The valve body 41 connected to the valve 5 is arranged closer to the exhaust passage 2 than the valve seat 42, and a spring 48 for urging the valve body 41 in the valve opening direction.
Since the exhaust pressure in the exhaust passage 2 is increased by providing the
Works in the valve closing direction. Therefore, even when the exhaust pressure is significantly increased during high supercharging of the diesel engine or regeneration of the trap, the valve body 41, which should be in the fully closed position, is prevented from being lifted from the valve seat 42, and exhaust gas recirculation is reliably performed. It is possible to prevent the valve body 41, which should be stopped or in the small opening position, from being lifted more than necessary from the valve seat 42, and the exhaust gas recirculation amount can be accurately controlled according to the engine operating conditions.

When the engine is stopped, the valve body 41 of the exhaust gas recirculation control valve 4 is moved to the valve seat 4 by the urging force of the spring 48.
Hold at a position away from 2. As a result, it is possible to prevent the valve body 41 and the valve seat 42 from sticking due to an adhesive substance such as carbon that has entered the exhaust gas recirculation passage 3, and the operability of the exhaust gas recirculation control valve 4 can be favorably maintained.

Next, another embodiment shown in FIG. 11 is provided with a suction piston 81 which faces the intake passage 1 and slides in the vertical direction as an intake throttle valve.

A negative pressure chamber 82 is defined on the upper surface of the suction piston 81 as an equal pressure control mechanism 90 for adjusting the suction negative pressure to a constant value in response to the suction negative pressure in an operating range where the engine speed is equal to or higher than a predetermined value. Then, the suction piston 8 is placed in the negative pressure chamber 82.
A suction negative pressure is introduced from a hole 83 opened at the tip of the No. 1 unit.

A spring 84 for urging the suction piston 81 in the direction of narrowing the intake passage 1 is interposed. The suction piston 81 has a stopper portion 81a that restricts its downward movement. In the operating range where the engine speed is equal to or lower than a predetermined value, the suction piston 81 is stopped by the gravity of the suction piston 81 and the urging force of the spring 84. Is held at the minimum opening position where it abuts 81a,
The suction negative pressure increases as the engine speed increases, and the exhaust gas recirculation amount increases as the intake air amount increases.

In a high engine speed range where the engine speed rises above a predetermined value, the suction negative pressure acting on the upper surface of the suction piston 81 is balanced by the gravity of the suction piston 81 and the urging force of the spring 84. It automatically moves upward and adjusts the suction negative pressure to a constant value.

In order to completely stop the exhaust gas recirculation, a solenoid valve 8 is provided in the signal negative pressure passage 5 to cut off communication with the negative pressure control valve 6.
5 are provided.

Also in this embodiment, since the suction negative pressure is adjusted to a constant value via the suction piston 81 at the time of high rotation, the diaphragm 3 of the negative pressure control valve 6 faces the suction negative pressure.
It is not necessary to increase the spring load of the spring 36 that biases the spring 5, and the amount of change in the spring load per step of the step motor 33 can be reduced to achieve precise control.
Further, the negative pressure control valve 6 can be downsized by reducing the amount of bending of the spring 36.

[0054]

As described above, according to the present invention, the exhaust gas recirculation passage connecting the intake passage and the exhaust passage of the engine, the diaphragm type exhaust gas recirculation control valve interposed in the exhaust gas recirculation passage, and the exhaust gas recirculation control are provided. The signal negative pressure introduced to the diaphragm chamber of the exhaust gas recirculation control valve is adjusted via a step motor in order to detect the pressure in the exhaust gas recirculation passage between the valve and the confluence portion with respect to the intake air passage and bring this pressure to a predetermined value. In a diesel engine exhaust gas recirculation system including a diaphragm type negative pressure control valve, a valve body connected to the diaphragm of the exhaust gas recirculation control valve is arranged on an exhaust passage side from a valve seat, and the valve body is attached in a valve opening direction. A spring for urging is provided, and an intake throttle valve is provided upstream of a confluence portion of the intake passage with the exhaust gas recirculation passage, and a spring for urging the intake throttle valve in a closing direction is provided. At the same time, in response to the suction negative pressure generated on the downstream side of the intake throttle valve, the opening degree of the intake throttle valve is increased and the suction negative pressure is adjusted to a constant value in the operating range where the engine speed is equal to or higher than a predetermined value. Since a pressure control mechanism is provided, it is not affected by the rise in exhaust pressure or suction negative pressure.
Exhaust gas recirculation control can be performed accurately.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an exhaust gas recirculation device showing an embodiment of the present invention.

FIG. 2 is a sectional view of the negative pressure control valve.

FIG. 3 is a characteristic diagram of valve opening pressure of the negative pressure control valve.

FIG. 4 is a flow chart of exhaust gas recirculation amount control.

FIG. 5 is a control map of the negative pressure control valve.

FIG. 6 is a control map of a correction coefficient Ktw according to the cooling water temperature.

FIG. 7 is a characteristic diagram of the exhaust gas recirculation rate.

FIG. 8 is a characteristic diagram of intake negative pressure, exhaust gas recirculation amount, fresh air amount, and maximum exhaust gas recirculation amount.

FIG. 9 is a schematic configuration diagram of an exhaust gas recirculation device showing another embodiment.

[Explanation of symbols]

 1 intake passage 2 exhaust passage 3 exhaust gas recirculation passage 4 exhaust gas recirculation control valve 5 signal negative pressure passage 6 negative pressure control valve 8 intake throttle valve 9 diesel engine 41 valve body 42 valve seat 45 diaphragm 46 diaphragm chamber 50 equal pressure control mechanism 63 diaphragm Device 71 Negative pressure introduction passage 80 Control unit

Claims (1)

[Claims] 1. An exhaust gas recirculation passage connecting an intake passage and an exhaust passage of an engine, a diaphragm type exhaust gas recirculation control valve interposed in the exhaust gas recirculation passage, and a merging portion for the exhaust gas recirculation control valve and the intake passage. And a diaphragm type negative pressure control valve for detecting the pressure in the exhaust gas recirculation passage between them and adjusting the signal negative pressure introduced into the diaphragm chamber of the exhaust gas recirculation control valve through a step motor so as to bring this pressure to a predetermined value. In an exhaust gas recirculation device for a diesel engine, a valve body connected to a diaphragm of the exhaust gas recirculation control valve is arranged on a side of an exhaust passage from a valve seat, and a spring for urging the valve body in a valve opening direction is provided, and the intake air An intake throttle valve is provided upstream of the confluence portion of the passage with the exhaust gas recirculation passage, and a spring for urging this intake throttle valve in the valve closing direction is provided and at the downstream side of the intake throttle valve. A constant pressure control mechanism is provided for increasing the opening degree of the intake throttle valve in response to the generated intake negative pressure and adjusting the intake negative pressure to a constant value in an operating range where the engine speed is equal to or higher than a predetermined value. Exhaust gas recirculation system for diesel engines.