JPH05106521A - Negative pressure control valve for exhaust recirculation device - Google Patents

Abstract

PURPOSE:To regulate dispersion of control characteristics by errors for a spring constant of a set spring and an auxiliary spring easily. CONSTITUTION:An exhaust pressure chamber 6 and an open air chamber 7 are separated by a diaphragm 5, and a valve element 9 opens and closes an open air introducing port 10 corresponding to an exhaust pressure. Spring forces of a set spring 8 and an auxiliary spring 23 are applied to the diaphragm 5, and energization force of the auxiliary spring 23 can be changed by a step motor 3. For a spring seat 21, fine adjustment can be performed for an installation position for regulation of the characteristics at one control point. A variable orifice 28 is provided in a negative pressure passage 11 reaching a negative pressure source for regulation at another control point.

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 an internal combustion engine, and more particularly, to an exhaust gas recirculation rate by appropriately diluting a negative pressure introduced into a negative pressure chamber of a diaphragm type exhaust gas recirculation control valve by introducing air. The present invention relates to an improvement in a negative pressure control valve that controls 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. Then, in order to arbitrarily variably control the exhaust pressure P _{2 according} to the operating conditions and the like, the substantial load of the set spring with respect to the diaphragm is changed so that the valve opening pressure of the atmosphere introduction port can be changed. Negative pressure control valves are disclosed, for example, in Japanese Utility Model Publication No. 1-130058 and Japanese Utility Model Publication 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. For example, if the spring seat is configured to be closer to the diaphragm as the number of steps in the step motor increases, the exhaust pressure P ₂ changes as shown by the solid line a in FIG.

[0003]

In the negative pressure control valve as described above, the characteristics are varied due to the error of the spring force of the set spring and the auxiliary spring, the dimensional error of each part, etc., and therefore the adjustment is required at the time of assembly. Is.

In this case, it is relatively easy to adjust the initial mounting position of the spring seat by matching the desired characteristics (solid line B) at one point with a certain number of steps (for example, control point A in FIG. 3). can do.

However, even if the relationship between the number of steps and the exhaust pressure P ₂ is adjusted at one control point in this way, at a different number of steps (for example, control point B in FIG. 3), the set spring and the auxiliary spring are The desired characteristics may deviate due to the error of the spring constant or the hardness of the diaphragm. That is, as shown by the alternate long and short dash line (b) and the alternate long and two short dashes line (c) in FIG.

[0006]

Therefore, the present invention is directed to an exhaust pressure chamber in which exhaust pressure is introduced between an EGR orifice located downstream of an exhaust gas recirculation passage and an exhaust gas recirculation control valve located upstream thereof. And a diaphragm that separates the exhaust pressure chamber and the atmosphere chamber, and a valve body that is attached to the diaphragm and that opens and closes the atmosphere introduction port in the atmosphere chamber,
A set spring for urging the diaphragm toward the atmosphere chamber, an auxiliary spring disposed so as to oppose the set spring, and having a base end supported by a spring seat movable in the diaphragm axial direction; A step motor for controlling the position of the seat, a negative pressure passage communicating with the negative pressure source and the atmosphere introduction port, and a branched negative pressure passage leading to the negative pressure chamber of the exhaust gas recirculation control valve are provided. The negative pressure control valve of the exhaust gas recirculation device is characterized in that a variable orifice for adjusting control characteristics is provided on the negative pressure source side from the branch portion of the negative pressure passage.

Further, in particular, in the invention of claim 2, in correspondence with two control points of the step motor control position, the position of the spring seat can be adjusted for characteristic adjustment at one point, and at the other points. The variable orifice is provided for adjusting the characteristics in 1.

[0008]

In the above structure, the opening of the variable orifice is adjusted so that the exhaust pressure between the EGR orifice and the exhaust gas recirculation control valve becomes a predetermined value at a predetermined control point, that is, the number of steps at the time of assembly or inspection. To be done. In other words, assuming that the engine is in a completely steady state, it can be considered that the relative position between the valve element and the atmosphere introduction port is balanced at a certain point, and the negative pressure is passed through the atmosphere introduction port with a constant opening. A certain amount of atmosphere is introduced into the passage. Here, when the opening of the variable orifice is changed, the position where the variable orifice is balanced is changed, and the valve element approaches or separates from the atmosphere introduction port. As a result, the expansion / contraction state of the set spring and the auxiliary spring in the balanced state slightly changes, and the urging force on the diaphragm changes. Therefore, since the exhaust pressure controlled via the exhaust gas recirculation control valve increases or decreases, the variable orifice may be adjusted so that this becomes a predetermined value.

If two control points are provided and the initial position of the spring seat is adjusted at one of the control points and the variable orifice is used at the other control point, the number of steps can be reduced. It is possible to match the desired characteristics in almost the entire area.

[0010]

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

FIG. 1 is a sectional view showing the structure of a negative pressure control valve 1 according to the present invention, and FIG. 2 is a structural explanatory view showing the structure of the entire exhaust gas recirculation system using this negative pressure control valve 1.

The negative pressure control valve 1 includes a lower diaphragm valve section 2 which controls basic negative pressure control according to exhaust pressure, and an upper step motor 3 for changing its control characteristic to a desired characteristic. Is roughly divided into

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 communicates with the negative pressure passage 11 extending laterally. still,
The atmosphere chamber 7 generally includes the communication hole 7a and the filter 25.
Although it is open to the atmosphere via the, the supercharging pressure may be introduced from the intake passage in an engine with a supercharger as in the example shown in FIG.

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 32 steps from 0 to 32, 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 on the lower end portion 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. That is, the spring seat 21 can be finely adjusted in its mounting position with respect to the plunger 19.

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.

A variable orifice 28 for adjusting the control characteristic is integrally provided on the side of the diaphragm valve portion 2 on the casing 4. The variable orifice 28 is used for the passage portion 2
A tapered needle 31 screwed into a plug 30 that closes the upper surface of 9, a lock nut 32 that fixes the needle 31, and the needle 31 that is fixed in the passage portion 29.
And an orifice 33 that moves forward and backward. A connector portion 34 for connecting to a negative pressure source is provided in one of the passage portions 29 partitioned by the orifice 33, and the atmosphere introduction port 10 communicates with the other portion.
That is, this variable orifice 28 is
The negative pressure passage 11 extending from 0 to the negative pressure source is provided on the way. Further, a signal negative pressure passage 35 is branched and formed between the atmosphere introduction port 10 of the negative pressure passage 11 and the variable orifice 28, and a connector portion 36 for pipe connection is provided at an end portion of the passage 35. ..

Next, the overall structure of the exhaust gas recirculation system will be described with reference to FIG. This is an example of a configuration applied to a diesel engine, and an exhaust gas recirculation passage 43 is provided so as to connect the exhaust passage 41 and the intake passage 42 of the engine, and a diaphragm type exhaust gas is provided in the middle of the passage. A reflux control valve 44 is installed. This exhaust gas recirculation control valve 4
In No. 4, the tapered valve body 45 opens and closes the valve opening from the exhaust passage 41 side, and the negative pressure introduced into the negative pressure chamber 47 defined by the diaphragm 46 is weaker than the biasing force of the set spring 40. The valve body 45 is sometimes opened, and the valve body 45 is closed when the biasing force is overcome. The negative pressure chamber 47 is connected to the negative pressure control valve 1 via the signal negative pressure passage 35 '.
Is connected to the connector portion 36 of.

An EG having a predetermined passage cross-sectional area is provided on the downstream side of the exhaust gas recirculation passage 43, that is, near the confluence portion with the intake passage 42.
An R orifice 48 is interposed, and an exhaust pressure P ₂ between the EGR orifice 48 and the exhaust gas recirculation control valve 44 is set.
Are guided to the exhaust pressure chamber 6 of the negative pressure control valve 1 via the exhaust pressure passage 49. And the variable orifice 28 of the negative pressure control valve 1
The negative pressure tank 50 is connected to the side connector portion 34 via the negative pressure passage 11 ′. In this negative pressure tank 50, a constant negative pressure generated by a vacuum pump or the like (not shown) is stored. Further, an intake throttle valve 51 for performing a large amount of exhaust gas recirculation is provided on the upstream side of the confluence portion of the exhaust gas recirculation passage 43 of the intake passage 42. The opening degree of the intake throttle valve 51 is controlled by a step motor 52. Reference numeral 53 is a control unit that controls the step motor 3 of the negative pressure control valve 1 and the step motor 52 of the intake throttle valve 51 based on engine operating conditions such as engine speed and load.

In the illustrated example, the upstream side of the intake throttle valve 51 of the intake passage 42 is communicated with the atmosphere chamber 7 of the negative pressure control valve 1 via the intake introduction passage 54. Therefore, atmospheric pressure is normally introduced into the atmosphere chamber 7, but in the case of a supercharged engine, supercharging pressure is introduced in the supercharging region. This is in the supercharging area,
The excessive exhaust pressure acts on the exhaust pressure chamber 6 to prevent the diaphragm 5 from being damaged, and the valve body 9 from being strongly urged upward to prevent exhaust gas recirculation.

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

As described above, the exhaust pressure P ₂ between the EGR orifice 48 and the exhaust gas recirculation control valve 44 is always guided to the exhaust pressure chamber 6 of the negative pressure control valve 1. Assuming that the intake pressure upstream of the intake throttle valve 51 is the atmospheric pressure, a differential pressure between the exhaust pressure P ₂ and the atmospheric pressure acts on the diaphragm 5, and the urging force of the set spring 8 is applied to the atmosphere introduction port 10.
And the biasing force of the auxiliary spring 23 acts in the opening direction. Therefore, when the pressure determined by the urging force of both springs 8 and 23, that is, the differential pressure becomes lower than the valve opening pressure, the atmosphere introducing port 10 is opened, and when the differential pressure becomes higher than that, the atmosphere introducing port 10 is closed.

On the other hand, a signal negative pressure obtained by diluting the negative pressure of the negative pressure tank 50 with the atmosphere introduced from the negative pressure control valve 1 is introduced into the negative pressure chamber 47 of the exhaust gas recirculation control valve 44. here,
When the signal negative pressure is weak, the opening degree of the valve element 45 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 decreases and the signal negative pressure increases, so that the opening degree of the exhaust gas recirculation control valve 44 decreases. 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 44 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 44 in the negative pressure control valve 1 are
It can be considered that they are balanced at a certain point, and a constant exhaust pressure P ₂ is obtained in that state.

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, since the spring seat 21 descends when the number of steps is large,
The exhaust pressure P ₂ changes with respect to the number of steps in a tendency as shown in FIG. 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 51 of the intake passage 42 is throttled, a negative pressure is created downstream of the throttle valve 51, so that the exhaust gas recirculation rate can be controlled to be higher.

Next, the adjustment of the control characteristic of the negative pressure control valve 1 will be described. This negative pressure control valve 1 is individually tested and adjusted for its control characteristics in a test device equivalent to the exhaust gas recirculation device shown in FIG. The control characteristic is adjusted at two control points A and B as shown in FIG. 3. First, the exhaust pressure P ₂ is measured with the number of steps of the step motor 3 adjusted to the control point A. To do. Then, the mounting position of the spring seat 21 with respect to the plunger 19 is finely adjusted so that the exhaust pressure P ₂ matches the design value. Next, the number of steps is adjusted to the control point B, and the exhaust pressure P ₂ is measured in this state. Then, the exhaust pressure P ₂
It is sufficient to finely adjust the position of the needle 31 of the variable orifice 28 so as to match the design value.

That is, the gap between the valve body 9 and the atmosphere introduction port 10 is Δh (FIG. 4) when it is considered that the opening degree of the atmosphere introduction port 10 is balanced at a certain opening in the steady state.
(See), the balance point Δh varies depending on the opening of the variable orifice 28. In other words, if the variable orifice 28 is throttled, the amount of air introduced required for pressure balance is reduced, so that the gap Δh is balanced at a smaller point. On the contrary, if the variable orifice 28 is opened, it is necessary to introduce a large amount of air into the pressure balance. In other words, by moving the variable orifice 28, the gap Δh naturally changes to its balance point. Although FIG. 6 shows a change in the gap Δh that occurs when the negative pressure of the negative pressure source is changed, a similar change occurs due to a change in the opening of the variable orifice 28.

As described above, the gap Δh at the balance point
Changes, the expansion and contraction states of the set spring 8 and the auxiliary spring 23 respectively change. Therefore, the biasing force acting on the diaphragm 5 slightly changes at the balance point. FIG. 7 shows the load Pw acting on the diaphragm 5 as the sum of the urging forces of both springs 8 and 23, and as shown in the figure, it changes gently corresponding to the gap Δh.

[0029] Thus, with the change in the load Pw, because varies the characteristics of the air introduction amount to variations in exhaust pressure P _2, and finally the exhaust gas pressure P ₂ in the state in which the balance is changed. FIG. 5 shows characteristics of each part when the opening of the variable orifice 28 is reduced (broken line) and when it is increased (solid line), and the gap Δh is as shown in (A). Changes to. In response to this,
The signal negative pressure introduced to the exhaust gas recirculation control valve 44 changes as shown in (B). As described above, the smaller the signal negative pressure, the larger the opening degree of the exhaust gas recirculation control valve 44. As a result, the exhaust pressure P ₂ changes as shown in (C).

Therefore, from the above relationship, if the variable orifice 28 is adjusted so that the exhaust pressure P ₂ matches the design value at the control point B, the error of the spring constant of each spring 8, 23 and the hardness of the diaphragm 5 will be different. It is possible to adjust the desired control characteristics by absorbing the above. Strictly speaking, the exhaust pressure P at the control point A is moved by moving the variable orifice 28.
_{Since 2} changes slightly, if high accuracy is required,
After the temporary adjustment at the control point A, the necessary adjustment allowances of the variable orifice 28 and the spring seat 21 are calculated from the value of the exhaust pressure P _{2 at} the control point B, and the respective adjustments may be performed. Further, as is clear from FIG. 5, the influence of the change of the variable orifice 28 becomes larger when the number of steps is larger.
It is desirable to set the control point A for adjusting 1 to the one with a smaller number of steps and the control point B with the variable orifice 28 to the one with a larger number of steps.

Further, in the above configuration, since the needle 31 of the variable orifice 28 can be operated from the outside, it is possible to easily readjust the control characteristic with respect to secular change in a vehicle-mounted state, for example.

Although the variable orifice 28 is formed integrally with the casing 4 of the negative pressure control valve 1 in the above embodiment,
The two need not necessarily be integrated, and an independent variable orifice 28 may be provided.

[0033]

As is apparent from the above description, in the negative pressure control valve of the exhaust gas recirculation device according to the present invention, since the variable orifice for adjusting the control characteristic is provided in the negative pressure passage, the error of the spring constant, etc. It is possible to easily adjust the deviation of the control characteristic due to, and it is possible to accurately obtain the desired exhaust gas recirculation rate characteristic at various step numbers of the step motor.

In particular, two control points are set as the number of steps, and the adjustment at one point is performed by the position adjustment of the spring seat, and the adjustment at the other points is performed by the variable orifice. According to this, the desired control characteristics can be easily adjusted over the entire range of the number of steps.

[Brief description of drawings]

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

FIG. 2 is a structural explanatory view showing an exhaust gas recirculation device using this negative pressure control valve.

FIG. 3 is a characteristic diagram showing variations in control characteristics of the negative pressure control valve.

FIG. 4 is an enlarged cross-sectional view of a main part of the negative pressure control valve in a pressure balanced state.

FIG. 5 is a graph showing a case where the opening of the variable orifice is changed,
FIG. 6 is a characteristic diagram showing changes in (A) the gap Δh, (B) the negative pressure of the exhaust gas recirculation control valve, and (C) the exhaust pressure P ₂ .

FIG. 6 is a characteristic diagram showing a relationship between a negative pressure of a negative pressure source and a gap Δh.

FIG. 7 is a characteristic diagram showing a change in spring load Pw with a change in gap Δh.

[Explanation of symbols]

 1 ... Negative pressure control valve 3 ... Step motor 5 ... Diaphragm 6 ... Exhaust pressure chamber 7 ... Atmosphere chamber 8 ... Set spring 9 ... Valve body 10 ... Atmosphere introduction port 11 ... Negative pressure passage 21 ... Spring seat 23 ... Auxiliary spring 28 ... Variable orifice 31 ... Needle 35 ... Signal negative pressure passage

Claims (2)

[Claims] 1. An EGR located downstream of an exhaust gas recirculation passage
An exhaust pressure chamber into which exhaust pressure is introduced between the orifice and an exhaust gas recirculation control valve located upstream of the orifice, a diaphragm separating the exhaust pressure chamber and the atmospheric chamber, and an atmosphere attached to the diaphragm A valve body that opens and closes an indoor air introduction port, a set spring that biases the diaphragm toward the atmosphere chamber, and a spring that is arranged so as to oppose the set spring and whose base end is movable in the diaphragm axial direction. A signal negative pressure that communicates the auxiliary spring supported by the seat, the step motor that controls the position of the spring seat, the negative pressure source and the atmosphere introduction port, and reaches the negative pressure chamber of the exhaust gas recirculation control valve. In a negative pressure control valve of an exhaust gas recirculation device, which comprises a negative pressure passage having a branched passage, a control characteristic adjusting device is provided on the negative pressure source side from the branch portion of the negative pressure passage. Vacuum control valve of the exhaust gas recirculation device characterized by comprising an orifice. 2. The spring seat is configured to be positionally adjustable for the characteristic adjustment at one point corresponding to two control points of the step motor control position, and the above-mentioned for the characteristic adjustment at another point. The negative pressure control valve for an exhaust gas recirculation system according to claim 1, wherein a variable orifice is provided.