JPH07166968A - Engine exhaust gas recirculation system - Google Patents

Abstract

(57) [Summary] [Object] To enhance the control response of the EGR valve in an engine exhaust gas recirculation system. [Structure] A negative pressure duty valve 7 and an atmospheric duty valve 8 that adjust the valve opening ratios of the negative pressure passage 5 and the atmosphere opening port 27 to bring the opening degree of the EGR valve 4 close to a target value set according to the operating state. In the exhaust gas recirculation device of the engine 20 provided, the absolute value of the difference between the opening degree S1 of the EGR valve 5 and the target value S2 |
A three-way switching valve 32 that selectively communicates either the negative pressure passage 5 or the atmosphere opening port 27 with the diaphragm chamber 13 when S1-S2 | is larger than the set value b is provided.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In automobile engines and the like, in order to suppress the generation of NOx which is a harmful component in exhaust gas,
A so-called exhaust gas recirculation device for recirculating an inert exhaust gas is provided in the intake pipe.

As this exhaust gas recirculation device, a conventional example is shown in FIG.
(See Japanese Patent Publication No. 63-9103), reference numeral 43 denotes an exhaust passage and an intake passage 41 of the engine.
A diaphragm type EGR valve 44 is provided in the middle of the EGR passage 43. EGR valve 4
The larger the opening degree of, the larger the exhaust gas recirculation amount recirculated to the intake passage 41 via the EGR passage 43.

The diaphragm chamber 53 of the EGR valve 44 communicates with the negative pressure passage 45 via the electromagnetic valve 47 and also communicates with the atmosphere opening port 49 via the electromagnetic valve 48. EGR valve 4
No. 4 opens the valve against the return spring 59 as the negative pressure introduced into the diaphragm chamber 53 becomes stronger.

A lift sensor 50 for detecting the opening degree of the EGR valve 44 is provided, and the output from the lift sensor 50 is sent to the control unit 51. The control unit 51 includes an engine speed sensor 61 and a load sensor 62.
A target value of the opening degree of the EGR valve 44 is calculated from the detected values of the above, etc. according to a preset map 60, and the solenoid valves 47, 48 are opened so that the opening degree detected by the lift sensor 50 approaches the target value. Adjust the valve ratio.

By the way, there is a possibility that the EGR valve 44 may remain open due to malfunction of the solenoid valves 47 and 48, and a larger amount of exhaust gas recirculation than the target value may flow. As a countermeasure against this, the solenoid valve 4 is installed in the diaphragm chamber 53 of the EGR valve 44.
8 is provided with a solenoid valve 52 that communicates with the atmosphere opening port 49, and the control unit 51 detects the detected EGR.
When the opening degree of the valve 44 exceeds the reference value and exceeds the reference value, the solenoid valve 52 is opened, atmospheric pressure is introduced into the EGR valve 44, and the return spring 59 is forcedly closed by the urging force of the return spring 59. , Has a fail-safe function.

[0007]

However, in such a conventional apparatus, the EGR valve 44 is adjusted by adjusting the valve opening ratio of each solenoid valve 47, 48 to adjust the pressure introduced into the diaphragm chamber 53. Has a problem that the opening / closing operation of the EGR valve 44 is delayed under operating conditions in which the target opening value of the EGR valve 44 changes abruptly. .

Further, when the opening degree of the EGR valve 44 becomes larger than the target value, the electromagnetic valve 52 is controlled to be opened, so that the EGR valve 44 can be quickly closed. In the case where the opening degree of the EGR valve 44 becomes smaller than the target value, there is no means for opening the EGR valve 44 promptly, and the exhaust gas recirculation amount is temporarily insufficient to reduce the NOx reduction rate. There is room for improvement.

In view of the above problems, it is an object of the present invention to provide an exhaust gas recirculation device having a high control response.

[0010]

According to the present invention, an EGR passage connecting an exhaust passage and an intake passage of an engine, a diaphragm type EGR valve interposed in the middle of the EGR passage, and an EGR valve in a diaphragm chamber of the EGR valve are provided. Of the valve operating pressure passage that guides the pressure that drives the valve in the valve closing direction, the valve operating pressure passage that guides the pressure that drives the EGR valve in the valve opening direction into the diaphragm chamber, and the valve operating pressure passage and the valve operating pressure passage that close the valve. EGR by adjusting the valve opening ratio
First pressure adjusting means for bringing the opening of the valve close to a target value set according to the operating state, and a valve closing working pressure passage in the diaphragm chamber when the opening of the EGR valve exceeds the target value and is larger than the set value. If the opening of the EGR valve exceeds the set value and is smaller than the target value, the valve opening operating pressure passage is connected to the diaphragm chamber, and the absolute value of the difference between the EGR valve opening and the target value is less than or equal to the set value. In this case, the second pressure adjusting means for blocking both the communication of the valve closing operation pressure passage and the valve opening operation pressure passage with respect to the diaphragm chamber is provided.

[0011]

When the absolute value of the difference between the opening degree of the EGR valve and the target value is equal to or less than the set value, the second pressure adjusting means shuts off both the communication of the valve closing operation pressure passage and the valve opening operation pressure passage to the diaphragm chamber. By doing so, the first pressure adjusting means adjusts the valve opening ratio of the valve closing operating pressure passage and the valve opening operating pressure passage to bring the opening degree of the EGR valve close to the target value set according to the operating state.

When the opening degree of the EGR valve is smaller than the target value by more than the set value during the valve opening operation in which the opening degree target value of the EGR valve suddenly changes, the diaphragm chamber is connected to the diaphragm chamber via the second pressure adjusting means. By communicating the valve-opening operating pressure passage, the valve-opening operating pressure is instantly introduced into the diaphragm chamber bypassing the first pressure adjusting means, and the EGR valve opens against the biasing force of the return spring or the like. It is possible to obtain sufficient control response by shortening the time required for By increasing the speed at which the EGR valve opens, it is possible to prevent the exhaust gas recirculation amount from becoming insufficient during the process of opening the EGR valve, and to keep the NOx emission amount low.

When the opening degree of the EGR valve exceeds the set value and is larger than the set value during the closing operation in which the opening degree target value of the EGR valve changes abruptly, the EGR valve opens to the diaphragm chamber via the second pressure adjusting means. By communicating the valve-closing operating pressure passage, the valve-closing operating pressure bypasses the first pressure adjusting means and is instantaneously introduced into the diaphragm chamber, and the return spring or the like urges the valve closing operating pressure to E.
Sufficient control responsiveness is obtained by shortening the time taken for the GR valve to close. As a result, the EGR valve can be promptly closed at the time of sudden acceleration in which exhaust gas recirculation is desired to be stopped promptly, and it is possible to prevent an increase in smoke emission amount and a deterioration in drivability.

[0014]

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 device provided in a diesel engine. An EGR passage 23 that connects the exhaust passage 22 and the intake passage 21 of the engine 20 is provided, and a diaphragm type EGR is provided in the middle of the EGR passage 23.
The valve 4 is interposed. As the opening degree of the EGR valve 4 increases, the exhaust gas recirculation amount recirculated to the intake passage 21 via the EGR passage 23 increases.

The diaphragm chamber 13 of the EGR valve 4 serves as a valve opening operating pressure passage for introducing an operating pressure when the EGR valve 4 is opened.
A negative pressure passage 5 that communicates with the negative pressure duty valve 7 is provided therein. The EGR valve 4 is opened against the return spring 29 as the negative pressure introduced into the diaphragm chamber 13 becomes stronger.

An atmosphere opening port 27 communicating with the diaphragm chamber 13 via the atmosphere duty valve 8 is provided as a valve closing operation pressure passage for introducing an operation pressure when the EGR valve 4 is closed. The EGR valve 4 is configured to be closed by the biasing force of the return spring 29 as the negative pressure introduced into the diaphragm chamber 13 becomes weaker.

A negative pressure duty valve 7 and an atmospheric duty valve 8 are provided as first pressure adjusting means for adjusting the valve opening ratios of the negative pressure passage 5 and the atmosphere opening port 27 with respect to the diaphragm chamber 13. The negative pressure introduced from the vacuum pump 31 to the diaphragm chamber 13 of the EGR valve 4 is controlled by controlling the valve opening time ratio of the duty control valves 7 and 8.
The opening degree of the EGR valve 4 is adjusted by appropriately diluting with the atmospheric pressure introduced from 7.

A three-way switching valve 32 is provided as a second pressure adjusting means for selectively connecting either the negative pressure passage 5 or the atmosphere opening port 27 to the diaphragm chamber 13.

The three-way switching valve 32 has two solenoids 3
A spool 35 that slides through 3, 34 is provided.

When both solenoids 33 and 34 are not energized, the spool 35 is held in the closed position shown by the biasing force of the return spring, and the diaphragm chamber 1
The communication between the negative pressure passage 5 and the atmosphere opening port 27 for 3 is cut off.

When one of the solenoids 33 is energized, the spool 35 is held at the position moved to the right in the figure, and the negative pressure passage 5 is communicated with the diaphragm chamber 13.

When the other solenoid 34 is energized, the spool 35 is held in the position moved leftward in the figure, and the atmosphere opening port 27 is opened to the diaphragm chamber 13.
Are communicated.

A lift sensor 3 for detecting the opening degree of the EGR valve 4 is provided, and the output from the lift sensor 3 is sent to the control unit 11. Control unit 11
Is a target value S1 of the opening degree of the EGR valve 4 calculated according to a preset map 9 from detected values such as the engine speed and the load (control lever opening degree of the fuel injection pump), and is detected by the lift sensor 3. So that the opening S2 approaches the target value S1 via the negative pressure duty valve 7, the atmospheric duty valve 8 and the three-way switching valve 32, respectively.
The opening degree of is controlled.

The flowchart of FIG. 2 shows a program executed by the control unit 11 for controlling the opening degree of the EGR valve 4, which is executed at regular intervals.

First, in step 1, various data of engine operating conditions such as engine speed and control lever opening are read.

Next, in step 2, the target value S1 of the opening of the EGR valve 4 is calculated according to the engine speed and the control lever opening based on the map 9 shown in FIG. 3 stored in advance.

Next, at step 3, the opening S2 detected by the lift sensor 3 is read.

Next, in step 4, the difference S (= S1-S) between the opening S2 detected by the lift sensor 3 and the target value S1.
2) is calculated.

Next, the difference S calculated in step 5 is calculated.
Is larger than the set value a. If the difference S
Is determined to be less than or equal to the set value a, the detected opening S2
And the target value S1 substantially coincide with each other, this routine ends.

If it is determined that the difference S is larger than the set value a, the routine proceeds to step 6, where the negative pressure duty valve 7 and the atmospheric duty valve 8 are set so that the detected opening S2 approaches the target value S1. The opening of the EGR valve 4 is controlled via each of them.

Next, the difference S calculated in step 7 is calculated.
Is greater than the set value b. If the difference S
If it is determined that is larger than the set value b, step 9
Then, one solenoid 33 is energized, the spool 35 is held in the position moved to the right in the drawing, and the negative pressure passage 5 is communicated with the diaphragm chamber 13.

In this way, the negative pressure from the vacuum pump 31 bypasses the negative pressure duty valve 7 and is guided to the diaphragm chamber 13 of the EGR valve 4, so that the negative pressure in the diaphragm chamber 13 instantly increases and a return is made. Spring 2
The time required for the EGR valve 4 to open against 9 is shortened, and sufficient control responsiveness is obtained. By increasing the speed at which the EGR valve 4 opens, it is possible to prevent the exhaust gas recirculation amount from becoming insufficient in the process of opening the EGR valve 4, and
The x emission amount can be kept low.

If it is determined that the difference S is smaller than the set value b, the process proceeds to step 8 and it is determined whether the calculated difference S is smaller than the set value -b. If it is determined that the difference S is greater than or equal to the set value -b, that is, if the absolute value | S1-S2 | of the difference S between the detected opening S2 and the target value S1 is smaller than the set value b, the three-way switching valve 32 is held in the closed position, and the opening degree of the EGR valve 4 is controlled only through the negative pressure duty valve 7 and the atmospheric duty valve 8.

If it is determined that the difference S is smaller than the set value -b, the routine proceeds to step 10, the other solenoid 34 is energized, the spool 35 is held in the position moved leftward in the drawing, and the diaphragm is moved. The atmosphere opening port 27 communicates with the chamber 13.

In this way, the atmospheric pressure bypasses the atmospheric duty valve 8 and is guided to the diaphragm chamber 13 of the EGR valve 4, so that the pressure of the diaphragm chamber 13 instantly rises to the atmospheric pressure, and the EGR valve 4 is turned on. Sufficient control responsiveness can be obtained by shortening the time taken to close the valve. As a result,
It is possible to quickly close the EGR valve 4 at the time of sudden acceleration when it is desired to quickly stop the exhaust gas recirculation, and it is possible to prevent an increase in smoke emissions and a deterioration in drivability.

[0037]

As described above, according to the present invention, the EGR passage connecting the exhaust passage and the intake passage of the engine, the diaphragm type EGR valve interposed in the middle of the EGR passage, and the EGR passage are provided.
Valve operating pressure passage that leads to the pressure that drives the EGR valve in the valve closing direction into the diaphragm chamber, and valve opening operating pressure passage that leads to the pressure into the diaphragm chamber that drives the EGR valve in the valve opening direction Adjust the valve opening ratio of the passage and the valve opening pressure passage
In an exhaust gas recirculation system for an engine, which comprises a first pressure adjusting means for bringing the opening of the GR valve closer to a target value set according to the operating state, when the opening of the EGR valve exceeds the target value and is larger than the set value. To communicate the valve-closing operating pressure passage with the diaphragm chamber, and to communicate the valve-opening operating pressure passage with the diaphragm chamber when the opening of the EGR valve exceeds the target value and is smaller than the set value.
Since the second pressure adjusting means is provided for blocking both the communication of the valve closing operation pressure passage and the valve opening operation pressure passage to the diaphragm chamber when the absolute value of the difference between the opening degree of the EGR valve and the target value is equal to or less than the set value. A sufficient control responsiveness can be obtained during the operation in which the target opening value of the EGR valve changes rapidly, and it is possible to prevent the emission amount of NOx or smoke from increasing during the process of opening and closing the EGR valve.

[Brief description of drawings]

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

FIG. 2 is a flowchart similarly showing a control example.

FIG. 3 is a characteristic diagram of an example of control data.

FIG. 4 is a system diagram of an exhaust gas recirculation device showing a conventional example.

[Explanation of symbols]

 4 EGR Valve 5 Negative Pressure Passage (Valve Opening Pressure Passage) 7 Negative Pressure Duty Valve (First Pressure Adjusting Means) 8 Atmospheric Duty Valve (First Pressure Adjusting Means) 11 Control Unit 13 Diaphragm Chamber 20 Diesel Engine 21 Intake Passage 22 Exhaust passage 23 EGR passage 27 Atmosphere opening (valve closing pressure passage) 32 Three-way switching valve (second pressure adjusting means)

Claims (1)

[Claims] 1. An EG connecting an exhaust passage and an intake passage of an engine
An R passage, a diaphragm type EGR valve installed in the middle of the EGR passage, a valve closing working pressure passage for guiding pressure for driving the EGR valve in a closing direction to a diaphragm chamber of the EGR valve, and an EGR valve for the diaphragm chamber. The opening degree of the EGR valve is set according to the operating state by adjusting the valve opening ratio of the valve opening pressure passage for guiding the pressure to drive in the valve opening direction and the valve closing pressure passage and the valve opening pressure passage. If the opening of the EGR valve is larger than the target value and the opening of the EGR valve is larger than the target value, the opening of the EGR valve is set above the target value by communicating the valve closing pressure passage with the diaphragm chamber. If the absolute value of the difference between the opening of the EGR valve and the target value is less than or equal to the set value, the valve opening operating pressure passage and the valve opening operating pressure passage for the diaphragm chamber are opened. Second that both shuts off the communication of the working pressure passage Exhaust gas recirculation system for an engine, characterized in that a pressure regulating means.