JPH0619821Y2 - Exhaust gas recirculation system negative pressure control valve - Google Patents

Description

TECHNICAL FIELD The present invention relates to a negative pressure control valve for an exhaust gas recirculation device in an internal combustion engine such as an automobile engine.

2. Description of the Related Art As one of methods for purifying exhaust gas of an internal combustion engine, an exhaust gas recirculation device that recirculates a part of exhaust gas to an intake passage has been conventionally known.

For example, JP-B-57-55901 discloses a diaphragm type exhaust gas recirculation control valve interposed in an exhaust gas recirculation passage,
An exhaust gas recirculation device using a negative pressure control valve that variably controls the negative pressure introduced into the negative pressure chamber of the exhaust gas recirculation control valve based on a control signal from a control unit is described. In the negative pressure control valve, the exhaust pressure chamber on the upstream side of the exhaust gas recirculation control valve and the atmospheric pressure chamber are separated from each other by a diaphragm, and the exhaust pressure chamber is exhausted so as to face the valve element on the diaphragm. An atmosphere introducing port is provided in the air pressure chamber, and the atmosphere introducing port communicates with the negative pressure passage of the exhaust gas recirculation control valve.
That is, when the exhaust pressure decreases, the atmosphere introduction port is opened to introduce the atmosphere into the negative pressure passage, and when the exhaust pressure increases, the atmosphere introduction is shut off. A signal negative pressure, for example, a suction negative pressure on the downstream side of the throttle valve, is introduced into the negative pressure chamber of the exhaust gas recirculation control valve via the negative pressure passage. Therefore, the opening degree of the exhaust gas recirculation control valve is basically determined from the relationship between the signal negative pressure and the exhaust gas pressure. That is, the basic characteristics of the exhaust gas recirculation amount are mechanically controlled.

Further, in the exhaust gas recirculation device described in the above publication, the negative pressure control valve is further provided with a plunger linked to the diaphragm via a spring and a solenoid for sucking the plunger, and a desired exhaust gas recirculation amount can be obtained. It is configured so that the characteristics can be electronically controlled. That is, by changing the suction force of the solenoid, it is possible to change the set load of the diaphragm to correct the opening / closing characteristics of the atmosphere introduction port with respect to the exhaust pressure, and thus the opening degree of the exhaust gas recirculation control valve.

However, in the conventional negative pressure control valve in which the opening / closing characteristic of the atmosphere introduction port is changed by using the solenoid as described above, the suction force of the solenoid is, for example, It is easily affected by the temperature characteristics of the coil and so stable characteristics cannot be obtained. Therefore, the final exhaust gas recirculation amount control tends to be unstable.

In order to solve the problems, the present invention corrects the opening / closing characteristics of the atmosphere introduction port by using a step motor capable of stably controlling the operation amount. That is, the negative pressure control valve of the exhaust gas recirculation device according to the present invention appropriately dilutes the signal negative pressure introduced into the negative pressure chamber of the diaphragm type exhaust gas recirculation control valve by introducing the atmosphere to obtain the desired amount of exhaust gas recirculation. A negative pressure control valve for an exhaust gas recirculation device that controls the exhaust gas, and a diaphragm that separates an exhaust pressure chamber into which exhaust pressure is introduced and an atmospheric pressure chamber, and an atmosphere introduction port in the atmospheric pressure chamber that is attached to this diaphragm. A valve body for opening and closing, a set spring for urging the diaphragm in the closing direction of the atmosphere introduction port, a step motor whose rotation angle is controlled by an output signal of the control unit, and a spring seat attached to the tip portion, In addition, it moves in the axial direction of the diaphragm in accordance with the rotation angle of the step motor, and contacts the casing side at the reference step number for positioning. And a push rod portion that abuts against the diaphragm, and has the spring seat portion facing the spring seat, and forces the diaphragm to the open position of the atmosphere introduction port at a predetermined number of steps including the reference step number. Is disposed between the spring seat and the spring seat portion of the intermediate member, which is pressed and fixed by the plunger so as to hold the diaphragm, and the diaphragm is provided with the diaphragm facing the set spring. And an auxiliary spring for urging in the opening direction.

Further, in the invention of claim 2, the control unit provides means for giving a control step number so that the plunger comes into contact with the casing side at the time of starting the internal combustion engine, and at the time of this contact, the step number is used as a reference step number for calibration. And means for doing so.

Action When the step motor is rotated, the spring seat moves in the diaphragm axial direction, and the urging force applied to the diaphragm by the auxiliary spring changes. Therefore, the opening / closing characteristics of the exhaust introduction port with respect to the exhaust pressure change. That is, the exhaust gas recirculation amount can be controlled to a desired characteristic by controlling the rotation angle of the step motor.

When the step motor is controlled to a predetermined number of steps,
The intermediate member is pressed and fixed by the plunger, and the diaphragm is forcibly held in the open position of the atmosphere introducing port via the push rod portion. As a result, the signal negative pressure introduced into the exhaust gas recirculation control valve is maintained at about atmospheric pressure.

When the step motor is controlled to the reference number of steps, the plunger abuts on the casing side and is mechanically positioned. As a result, the reference step number can be calibrated.
In claim 2, this calibration is performed every time the engine is started.

Embodiment FIG. 1 is a sectional view showing an embodiment of the negative pressure control valve 1 according to the present invention.

This negative pressure control valve 1 has a lower diaphragm valve section 2 that controls basic negative pressure control according to exhaust pressure, and an upper step motor 3 that changes its control characteristic to a desired characteristic. Be separated.

The diaphragm valve portion 2 is mainly composed of a diaphragm 5 arranged inside a casing 4, and the diaphragm 5 separates a discharge pressure chamber 6 in the lower part and an atmospheric pressure chamber 7 in the upper part. A predetermined set load is applied to the diaphragm 5 by a set spring 8 arranged in a compressed state in the exhaust pressure chamber 6, and a valve body 9 is attached to the atmospheric pressure chamber 7 side. Then, in the atmospheric pressure chamber 7, the atmosphere introducing port 10 is provided so as to face the valve body 9.
Are formed. The air introduction port 10 communicates with the negative pressure passage 11. That is, the set spring 8 biases the diaphragm 5 in the closing direction of the atmosphere introduction port 10.

On the other hand, the step motor 3 has a pair of stators 13 fixed to the casing 12 and a rotor 16 rotatably supported via bearings 14 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 rotor 16 has a cylindrical shape, and an internal thread 17 is formed on the inner peripheral surface thereof.

Reference numeral 18 denotes a guide member fixed to the inner peripheral side of the bearing 15 of the casing 12, and 19 denotes a plunger guided by the guide member 18 so as to be non-rotatable and slidable in the axial direction. 20 is formed, which is screwed onto the internal thread 17 of the rotor 16. That is, the plunger 19 is configured to linearly move in the axial direction according to the rotation angle of the step motor 3. The plunger 19 is located on the center line of the diaphragm 5. A disk-shaped spring seat 21 is fixed to the lower end of the plunger 19. Here, the tip of the plunger 19 penetrates the spring seat 21 and projects downward by a predetermined amount.

Reference numeral 22 indicates an intermediate member that transmits the operation of the plunger 19 to the diaphragm 5. The intermediate member 22 includes 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 serves as the atmospheric pressure of the casing 4. It is arranged so as to penetrate the upper surface of the chamber 7. An auxiliary spring 23 is disposed between the spring seat portion 22a and the spring seat 21 in a compressed state, whereby the tip of the push rod portion 22b of the intermediate member 22 is pressed against the retainer 24 on the upper surface of the diaphragm 5. is doing. That is, the auxiliary spring 23 is the set spring 8
The diaphragm 5 is urged toward the opening direction of the atmosphere introduction port 10 in opposition to.

FIG. 2 shows an outline of an exhaust gas recirculation device using the negative pressure control valve 1 configured as described above. In the figure, reference numeral 25 denotes a diaphragm type exhaust gas recirculation control valve interposed in the exhaust gas recirculation passage 26, and its negative pressure chamber 25
A signal negative pressure, for example, a suction negative pressure downstream of the throttle valve of the engine is introduced into a through the negative pressure passage 27. The negative pressure passage 27 is connected to the negative pressure passage 11 of the negative pressure control valve 1, and the negative pressure control valve 1 appropriately introduces the atmosphere to dilute the signal negative pressure, whereby the exhaust gas recirculation is performed. The opening degree of the control valve 25 is controlled. Further, an orifice 28 is provided upstream of the exhaust gas recirculation control valve 25 in the exhaust gas recirculation passage 26 (that is, on the exhaust manifold side), and the exhaust pressure therebetween is exhausted through the exhaust pressure passage 29 to the exhaust pressure chamber of the negative pressure control valve 1. Introduced in 6. Again 30
Is a control unit that outputs a control signal to the step motor 3 of the negative pressure control valve 1 based on engine operating conditions (for example, engine speed, load, cooling water temperature, etc.).

Next, the operation of the negative pressure control valve 1 configured as described above will be described.

The step motor 3 of the negative pressure control valve 1 makes one rotation in four steps as described above, and in this embodiment, the reference step number is 0, and the operation range is defined in 32 steps of 0 to 32. ing.

FIG. 1 shows a state in which the number of steps of the step motor 3 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,
A differential pressure between exhaust pressure and atmospheric pressure acts on the diaphragm 5, and is biased in the closing direction by the set spring 8 and in the opening direction by the auxiliary spring 23. Therefore, when the exhaust pressure becomes lower than the pressure (valve opening pressure) determined by the urging force of both springs 8 and 23, the atmosphere introducing port 10 is opened, and when the exhaust pressure becomes higher than that, the atmosphere introducing port 10 is closed. Therefore, assuming that the suction pressure used as the signal negative pressure is constant, the amount of air introduced into the atmosphere decreases as the exhaust pressure rises, and the opening degree of the exhaust gas recirculation control valve 25 increases.

Here, since the biasing force 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 3 rotates and the spring seat 21 moves upward, the opening force is increased. The valve pressure decreases, and conversely, when the spring seat 21 moves downward, the valve opening pressure increases. That is, the step motor 3
The opening / closing characteristics of the atmosphere introduction port 10 can be corrected by controlling the rotation angle of, and the final exhaust gas recirculation amount characteristics can be obtained as desired characteristics. FIG. 3 shows the characteristic of the valve opening pressure obtained corresponding to the number of steps of the step motor 3.

Further, in the above embodiment, when the number of steps of the step motor 3 is 0, which is the reference number of steps, the tip of the plunger 19 abuts on the intermediate member 22 as shown in FIG. It will be pressed against. In other words, this mechanical contact causes the plunger 19
Is restricted, that is, the zero point position of the step motor 3 is mechanically restricted. Then, in the state where the intermediate member 22 is pressed to the lower limit position in this way,
The valve body 9 is forcibly kept away from the atmosphere introducing port 10. That is, the negative pressure passage 11 is opened to the atmosphere regardless of the exhaust pressure, and the opening operation of the exhaust gas recirculation control valve 25 is prohibited. Further, as shown in FIG. 3, until the state where the predetermined number of steps including the reference number of steps, specifically, the number of steps is 3, the above-mentioned forced opening state of the atmosphere introduction port 10 is maintained and the exhaust gas recirculation is performed. Is not done.

As described above, according to the negative pressure control valve 1, the urging force acting on the diaphragm 5 changes according to the rotation angle of the step motor 3, so that stable control can be performed without being affected by the battery voltage, temperature conditions and the like. It can be carried out. Further, even when the exhaust pressure in the exhaust pressure chamber 6 fluctuates greatly, the position of the spring seat 21 does not change, and stable characteristics can always be maintained. Then, under the operating condition where the exhaust gas recirculation should be stopped, the exhaust gas recirculation can be surely stopped by setting the number of steps to 3 or less as described above, and there is no influence of pressure fluctuation of each part.

Next, exhaust gas recirculation control when the negative pressure control valve 1 is used,
In particular, the zero point correction necessary in the case of the step motor method will be described with reference to the flowchart of FIG. Fifth
The flowchart in the figure shows a control program of the negative pressure control valve 1 executed in the control unit 30. This control program is interrupted at regular time intervals, for example, every 10 ms.

In the above flowchart, S ₀ represents the target number of steps. This target step number S ₀ is set in step 6 according to the engine operating conditions during normal operation.
For example, engine speed and load (for example, basic fuel injection amount T
p) is used as a parameter and is sequentially looked up from the table map. Further, Sm indicates the monitor value of the step number, that is, the step number of the step motor 3 recognized by the control unit 30. This monitor value S
m is incremented or decremented by 1 each time the stepper motor 3 is moved one step (step 9), and the data is held in the backup memory of the control unit 30 after the engine is stopped.

As the basic control of the step motor 3, first, in step 6, the target step number S ₀ is set according to the operating conditions as described above, and in step 8, the monitor value Sm at that time is set.
Is compared with the target step number S _0, and if they do not match, the process proceeds to step 9 to drive the step motor 3 step by step. At the same time, the monitor value Sm is set to 1
You can add or subtract one by one. By repeating the above, the rotation angle of the step motor 3 is always controlled so as to follow the target step number S ₀ .

On the other hand, in the above configuration, since the sensor for detecting the actual rotation angle of the step motor 3 is not provided, the actual number of steps and the monitor value Sm recognized by the control unit 30 may be deviated for some reason. is there. Therefore, in this control program, the reference step position of the step motor 3, that is, the zero point is calibrated each time the engine is started and in the exhaust gas recirculation stop region during operation.

First, in step 1, it is determined whether or not the program is executed for the first time. Step 1 only for the first time after engine start
Then, the process proceeds to step 2, where it is determined whether the backup memory has been erased. This is because there is a possibility that the monitor value Sm in the backup memory has been erased due to removal of the battery, and the determination is made based on the state of the flag in the backup memory, for example. If the backup memory is normal, the process proceeds to step 3, the target step number S _{0 is set} to 0, and an appropriate constant A is added to the monitor value Sm. The constant A may be about 4, for example. And since it progresses from step 3 to step 9,
Here, the step motor 3 rotates one step in the direction of decreasing the number of steps.

From the next time onward, the process proceeds from step 1 to step 5 where it is determined whether the calibration completion flag is 0 or not. This calibration completion flag is cleared when the engine is stopped and is initially 0. Therefore, go from step 5 to step 8
The target step number S ₀ is kept at 0. Therefore, the step motor 3 rotates step by step toward the step number 0. Here, since the constant A is added to the monitor value Sm as described above, S ₀ = Sm (step 8)
At this stage, the stepping motor 3 is rotated extra by the rotation angle corresponding to the constant A. For example, if the number of steps when the engine is stopped (monitor value Sm) is 2,
Although it returns to the 0 point if it rotates by the number of steps 2, the step motor 3 tries to rotate by 6 steps by adding the constant A (for example, 4 steps) to the monitor value Sm. Therefore, the step motor 3 surely rotates to the lower limit position of the plunger 19, that is, the mechanically restricted position, and the actual number of steps and the monitor value Sm are assumed.
Even if and are slightly deviated, as a result of the fact that they are matched at the 0 point, the deficit is corrected. Then, the monitor value Sm is 0
When and, the starter switch is turned off (step 10), the process proceeds to step 11 and the calibration completion flag is set to 1. Therefore, after that, the routine proceeds from step 5 to step 6, the normal target step number S ₀ is set, and the rotation angle control is performed based on this target step number S ₀ .

If the backup memory has been erased at the time of starting, the process proceeds from step 2 to step 4 and the monitor value S
Set m to the constant B. This constant B may be a value close to 32, which is the maximum value of the number of steps. Therefore, in this case, the step motor 3 is rotated to some extent even after reaching the actual zero point (the lower limit position of the plunger 19) in the subsequent processing, and the zero point calibration is surely performed.

Further, in this embodiment, the target number of steps S ₀
The zero point is calibrated in the operating region where 0 is 0, that is, in the exhaust gas recirculation stop region. That is, it is determined in step 7 whether or not the target step number S ₀ is 0, and if it is 0, the process proceeds to step 12 to clear the calibration completion flag. Then, the process proceeds to step 13, and the constant A is added to the monitor value Sm as in step 3 described above. As a result, the step motor 3 rotates mechanically to the zero point, and the zero point calibration is quickly performed. Even if the 0-point calibration during operation is omitted, usually sufficient control accuracy can be maintained.

As is apparent from the above description, in the negative pressure control valve of the exhaust gas recirculation device according to the present invention, the biasing force to the diaphragm is changed according to the rotation angle of the step motor. As in the case of using a solenoid, extremely stable characteristics can be obtained without being affected by battery voltage or temperature conditions. Further, the control characteristic is not influenced by the fluctuation of the exhaust pressure acting on the diaphragm. Therefore, the final control of the exhaust gas recirculation amount can be made very stable.

Then, at the predetermined number of steps, the plunger of the step motor forcibly holds the diaphragm in the open position of the atmosphere introduction port via the intermediate member, so that the exhaust gas recirculation is surely stopped without being affected by pressure fluctuations and the like. It becomes possible.

Further, the zero point of the step motor can be easily calibrated by bringing the plunger into contact with the casing side. Moreover, according to the calibration of the second aspect, the calibration of the 0 point is performed each time the engine is started, and the accuracy is prevented from being lowered.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a negative pressure control valve according to the present invention, FIG. 2 is an explanatory view of the configuration of an essential part of an exhaust gas recirculation system using this negative pressure control valve, and FIG. FIG. 4 is a characteristic diagram showing the characteristic of the valve opening pressure in the example, FIG. 4 is a cross-sectional view of the main part showing the state when the step number of the step motor is 0, and FIG. 5 is an example of the control of the negative pressure control valve. It is a flowchart shown. 1 ... Negative pressure control valve, 3 ... Step motor, 5 ... Diaphragm, 6 ... Exhaust pressure chamber, 7 ... Atmospheric pressure chamber, 9 ... Valve body, 19 ... Plunger, 21 ... Spring seat,
22 ... Intermediate member, 23 ... Auxiliary spring.

Claims (2)

[Scope of utility model registration request] 1. A negative pressure control valve of an exhaust gas recirculation device for controlling an exhaust gas recirculation amount to a desired characteristic by appropriately diluting a signal negative pressure introduced into a negative pressure chamber of a diaphragm type exhaust gas recirculation control valve by introducing air. And a diaphragm that separates an exhaust pressure chamber into which exhaust pressure is introduced and an atmospheric pressure chamber, a valve body that is attached to this diaphragm and that opens and closes an atmosphere introduction port in the atmospheric pressure chamber, and the diaphragm described above. A set spring that urges the air inlet port toward the closing direction, a step motor whose rotation angle is controlled by the output signal of the control unit, a spring seat attached to the tip, and a diaphragm that corresponds to the rotation angle of the step motor. A plunger that moves in the axial direction and is positioned by contacting the casing side at the reference number of steps and the spring seat And a push rod portion that comes into contact with the diaphragm, and the plunger is configured to forcibly hold the diaphragm in the open position of the atmosphere introduction port at a predetermined number of steps including the reference number of steps. An intermediate member to be pressed and fixed, and an auxiliary member that is disposed between the spring seat and the spring seat portion of the intermediate member, faces the set spring, and urges the diaphragm in the opening direction of the atmosphere introduction port. A negative pressure control valve for an exhaust gas recirculation device, comprising: a spring. 2. The control unit comprises means for giving a control step number so that the plunger contacts the casing side at the time of starting the internal combustion engine, and means for calibrating the step number as a reference step number at the contact time. The negative pressure control valve of the exhaust gas recirculation device according to claim 1, further comprising: