JPH0868361A - Exhaust gas reflux device for engine - Google Patents

Abstract

PURPOSE: To provide an exhaust gas reflux device for an engine which provides a proper EGR rate from a low load area. CONSTITUTION: An exhaust gas reflux device for an engine comprises a diaphragm type press control (BPT) valve 6 to dilute an inlet negative pressure, guided to the diaphragm chamber 8 of an EGR valve 5, with an atmospheric pressure; an EGR gas pressure passage 14 to guide an EGR gas pressure P on the exhaust pipe 3 side from the EGR valve 5 of the EGR passage 4 to the diaphragm chamber 11 of a BPT valve 6; and a first solenoid valve 21, serving as a BOT cut means, to cut off an atmospheric pressure guided to the diaphragm chamber 8 of the EGR valve 5 through a BPT valve 6 according to an operation condition.

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 a conventional exhaust gas recirculation system, there is a system of exhaust pressure control (BPT) which controls the exhaust gas recirculation amount by the exhaust pressure of the exhaust pipe (see Japanese Utility Model Laid-Open No. 54-79320).

This exhaust pressure control (BPT) type exhaust gas recirculation system is an EGR connecting an exhaust pipe and an intake pipe of an engine.
A diaphragm type EGR valve is provided in the middle of the passage, and a diaphragm type BPT valve for diluting the suction negative pressure introduced into the diaphragm chamber of the EGR valve with the atmospheric pressure is provided. The EGR gas pressure P ₂ on the exhaust pipe side is introduced from the EGR valve in the EGR passage into the diaphragm chamber of the BPT valve.

In the BPT valve, the degree to which the negative pressure introduced to the EGR valve is diluted with the atmospheric pressure as the EGR gas pressure P ₂ rises is reduced, and the opening degree of the EGR valve is increased to increase the opening degree of the EGR passage. Feedback control is performed so that the EGR gas pressure P ₂ is kept constant. When the EGR gas pressure P ₂ of the EGR passage is kept constant, the differential pressure between the EGR gas pressure P ₂ and the exhaust pressure P ₁ of the exhaust pipe, the exhaust gas recirculation amount is proportional to the exhaust pressure P _1. Since the exhaust pressure P ₁ has a correlation with the intake air amount of the engine, the exhaust gas recirculation amount increases as the intake air amount increases, and the EGR rate is kept substantially constant.

[0006]

However [0007], in the exhaust gas recirculation system of the conventional exhaust pressure control (BPT) method, the exhaust pressure P ₁ is lower than the working pressure P ₀ which is BPT valve starts to lift Since the EGR valve remains closed in the load range, there is a problem that exhaust gas recirculation cannot be performed.

It is an object of the present invention to provide an exhaust gas recirculation system for an engine, which focuses on the above problems and which can obtain an appropriate EGR rate even in a low load range.

[0008]

An exhaust gas recirculation system for an engine according to claim 1, wherein an EGR passage connecting an exhaust pipe of the engine and an intake pipe, a diaphragm type EGR valve interposed in the middle of the EGR passage, A negative pressure passage that guides the suction negative pressure generated in the intake pipe to the diaphragm chamber of the EGR valve, a diaphragm-type BPT valve that dilutes the suction negative pressure that is guided to the diaphragm chamber of the EGR valve with atmospheric pressure, and an EGR in the diaphragm chamber of the BPT valve. An EGR gas pressure passage that guides the EGR gas pressure P ₂ on the exhaust pipe side from the EGR valve in the passage, and a BPT cut means that shuts off the atmospheric pressure introduced to the diaphragm chamber of the EGR valve via the BPT valve according to operating conditions; Equipped with.

According to another aspect of the engine exhaust gas recirculation system of the present invention, an EGR passage connecting an engine exhaust pipe and an intake pipe, and E
A diaphragm type EGR valve installed in the middle of the GR passage, a negative pressure passage for guiding a suction negative pressure generated in the intake pipe to the diaphragm chamber of the EGR valve, and a suction negative pressure introduced to the diaphragm chamber of the EGR valve at atmospheric pressure. A diaphragm type BPT valve for dilution, an EGR gas pressure passage for guiding the EGR gas pressure P ₂ on the exhaust pipe side from the EGR valve in the EGR passage to the diaphragm chamber of the BPT valve, and a BP depending on operating conditions.
Under operating conditions in which the BPT cut means for shutting off the atmospheric pressure introduced to the diaphragm chamber of the EGR valve via the T valve and the atmospheric pressure shut off for the atmospheric pressure introduced to the diaphragm chamber of the EGR valve via the BPT valve by the BPT cut means, Negative pressure adjusting means for adjusting the suction negative pressure introduced into the diaphragm chamber of the EGR valve via the pressure passage.

In the exhaust gas recirculation system for an engine according to a third aspect of the present invention, in the invention according to the second aspect, an atmospheric pressure diluting passage for appropriately guiding the atmospheric pressure to the negative pressure passage is connected as the negative pressure adjusting means.

In the exhaust gas recirculation system for an engine according to a fourth aspect, in the invention according to the third aspect, an atmospheric pressure diluting passage for appropriately guiding the atmospheric pressure to the negative pressure passage is connected as negative pressure adjusting means, and A fixed throttle is installed in the middle of the atmospheric pressure dilution passage.

[0012]

In the exhaust gas recirculation system for an engine according to claim 1, the degree to which the BPT valve dilutes the negative pressure introduced to the EGR valve with the atmospheric pressure as the EGR gas pressure P ₂ increases becomes smaller. , EGR valve opening is increased, and feedback control is performed so that the EGR gas pressure P ₂ in the EGR passage is kept constant. EGR gas pressure P in the EGR passage
When ₂ is kept constant, the differential pressure between the EGR gas pressure P ₂ and the exhaust pressure P ₁ of the exhaust pipe, the exhaust gas recirculation amount is proportional to the exhaust pressure P _1. Since the exhaust pressure P ₁ has a correlation with the intake air amount of the engine, the exhaust gas recirculation amount increases as the intake air amount increases, and the EGR rate is kept substantially constant.

When the atmospheric pressure introduced into the diaphragm chamber of the EGR valve via the BPT valve is shut off by the BPT cutting means according to the operating condition, the opening of the EGR valve is controlled by the negative pressure passage without being affected by the operation of the BPT valve. It is controlled by the suction negative pressure derived from. As a result, exhaust gas recirculation can be performed from a low load range where the BPT valve does not operate. As a result, the fuel efficiency of the engine is reduced and NO
The emission of x can be suppressed.

In the exhaust gas recirculation system for an engine according to a second aspect of the present invention, the BPT cut means is used to E
Under operating conditions in which the atmospheric pressure introduced into the diaphragm chamber of the GR valve is shut off, the negative pressure adjusting means adjusts the suction negative pressure introduced into the diaphragm chamber of the EGR valve via the negative pressure passage, and the EGR rate becomes excessive. Can be suppressed.

In the exhaust gas recirculation system for an engine according to a third aspect of the present invention, the suction negative pressure introduced into the diaphragm chamber of the EGR valve via the negative pressure passage is introduced into the atmospheric pressure dilution passage connected to the negative pressure passage. It is possible to suppress the EGR rate from becoming excessive by appropriately diluting with.

In the exhaust gas recirculation system for an engine according to a fourth aspect, the suction negative pressure introduced into the diaphragm chamber of the EGR valve through the negative pressure passage is introduced through a fixed throttle provided in the atmospheric pressure dilution passage. It is possible to prevent the EGR rate from becoming excessive by appropriately diluting it with the atmospheric pressure.

[0017]

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

As shown in FIG. 1, an EGR passage 4 connecting the exhaust pipe 3 and the intake pipe 2 of the engine is provided.
A diaphragm type EGR valve 5 is provided in the middle of the process.

The EGR valve 5 has a diaphragm chamber 8
The valve is opened against the return spring 19 as the negative pressure introduced to the valve becomes stronger. As the opening degree of the EGR valve 5 increases, the exhaust gas recirculation amount recirculated to the intake pipe 2 via the EGR passage 4 increases.

A BPT negative pressure passage 24 that connects the diaphragm chamber 8 of the EGR valve 5 and the VC port 18 of the intake pipe 2 is provided, and the EGR valve 5 is connected via the BPT negative pressure passage 24.
There is provided a BPT valve 6 for appropriately diluting the negative pressure introduced to the diaphragm chamber 8 with the atmospheric pressure.

The VC port 18 is an intake throttle valve 1
In the vicinity of 7, the intake throttle valve 17 located at the idle position is positioned upstream of the front end and opens to the intake pipe 2. At the VC port 18, atmospheric pressure is generated during idling,
Negative pressure is generated in the low and medium load range.

The BPT valve 6 has a diaphragm chamber 1
1 through the EGR gas pressure passage 14 to the EG of the EGR passage 4
The EGR gas pressure P _{2 in the} EGR passage 4 is introduced through communication between the R valve 5 and the orifice 13.

The BPT valve 6 is used for the EGR of the EGR passage 4.
As the gas pressure P ₂ rises, the opening degree decreases, that is, the degree of diluting the negative pressure introduced to the EGR valve 5 with the atmospheric pressure decreases, and the opening degree of the EGR valve 5 increases. Feedback control is performed so that the EGR gas pressure P ₂ in the EGR passage 4 is kept constant.

Thus, when the EGR gas pressure P _{2 in} the EGR passage 4 is kept constant, P ₂ and the exhaust pressure P in the exhaust pipe 3
Due to the pressure difference from ₁ , the amount of exhaust gas recirculated through the orifice 13 is proportional to the exhaust pressure P ₁ . Since the exhaust pressure P ₁ has a correlation with the intake air amount of the engine, the exhaust gas recirculation amount increases as the intake air amount increases, and the EGR rate is kept substantially constant.

The present invention is provided with BPT cutting means for shutting off the atmospheric pressure introduced to the diaphragm chamber 8 of the EGR valve 5 via the BPT valve 6 according to the operating conditions. That is, an exhaust pressure control (BPT) system that adjusts the exhaust gas recirculation amount via the BPT valve 6 according to the operating conditions via the BPT cut means, and an exhaust gas recirculation amount by the suction negative pressure without using the BPT valve 6. The suction negative pressure control (VC) system to be adjusted is switched.

As the BPT cutting means, the EGR valve 5
A VC negative pressure passage 20 that connects the diaphragm chamber 8 and the VC port 18 of the intake pipe 2 is provided. The VC negative pressure passage 20 includes a first solenoid valve 21 and a second solenoid valve 22.
Are installed respectively.

The first solenoid valve 21 is connected to the VC negative pressure passage 20 and B to the diaphragm chamber 8 of the EGR valve 5.
It has two positions for communicating either one of the PT negative pressure passages 24.

The second solenoid valve 22 closes the VC negative pressure passage 20 at a position where the VC negative pressure passage 20 communicates with the atmosphere release port 23, at a position where the VC negative pressure passage 20 and the atmosphere release port 23 are disconnected from each other. Further, it has a position for disconnecting the communication between the atmospheric pressure dilution passage 26 and the BPT negative pressure passage 24.

A control unit 30 for switching the positions of the first and second solenoid valves 21, 22 is provided. The control unit 30 switches the positions of the first and second solenoid valves 21 and 22 according to the contents of a preset map as shown in FIG. 2 based on the detected values of the engine speed Ne, the load, the cooling water temperature and the like.

The control unit 30 controls the second solenoid valve 22 to V in the area A including the idle time.
The C solenoid valve 21 is switched to a position where the atmosphere opening port 23 is communicated with the negative pressure passage 20, and the first solenoid valve 21
To the diaphragm chamber 8 of the EGR valve 5 and the VC negative pressure passage 2
Hold 0 in the position where it communicates. This makes E
The GR valve 5 is fully closed by the atmospheric pressure being introduced into the diaphragm chamber 8, and the exhaust gas recirculation is stopped.

In the low speed / low load region B, the second solenoid valve 22 is connected to the VC negative pressure passage 20 and the atmosphere opening port 23.
Of the EGR valve 5 to the diaphragm chamber 8 of the EGR valve 5
Hold the VC negative pressure passage 20 in a position to communicate with
Switch to suction negative pressure control (VC) system.

In the medium-speed / medium-load region C, the second solenoid valve 22 is closed in the middle of the VC negative pressure passage 20 to switch the communication between the atmospheric pressure dilution passage 26 and the BPT negative pressure passage 24, and the first solenoid valve 22 is switched to the first position. Solenoid valve 21
Is held at a position where the BPT negative pressure passage 24 communicates with the diaphragm chamber 8 of the EGR valve 5, and the exhaust pressure control (BPT) system is switched.

The switching from the suction negative pressure control (VC) system to the exhaust pressure control (BPT) system is performed at operating points where the EGR rates obtained by both systems are equal. The switching from the exhaust pressure control (BPT) system to the suction negative pressure control (VC) system is performed at an operating point having a predetermined hysteresis on the low speed and low load side.

As a negative pressure adjusting means for adjusting the negative pressure introduced from the VC negative pressure passage 20 to the diaphragm chamber 8 of the EGR valve 5, an intermediate portion of the VC negative pressure passage 20 is located upstream of the intake throttle valve 17 of the intake pipe 2. An atmospheric pressure dilution passage 26 that communicates with each other is provided, and an orifice (fixed throttle) 27 is provided in the middle of the atmospheric pressure dilution passage 26.

With the above construction, the operation will be described.

By switching to the exhaust pressure control (BPT) system in the medium load range where the BPT valve 6 is sufficiently lifted, the exhaust gas recirculation amount proportional to the exhaust pressure P ₁ is obtained by the operation of the BPT valve 6, and the throttle valve The EGR rate according to the opening degree of 17 is kept substantially constant as shown by the solid line in FIG. 3, and the characteristic of continuing the suction negative pressure control (VC) method having the orifice 27 is shown by the one-dot chain line in FIG. As described above, it is possible to prevent the EGR rate from becoming excessive or insufficient.

[0037] In the exhaust pressure control (BPT) scheme, the lower load region than the working pressure P ₀ exhaust pressure P ₁ is the BPT valve 6 starts lifting, because remains EGR valve 5 is closed, EGR rate Figure As indicated by the broken line in Fig. 3, there is a problem that the exhaust valve recirculation cannot be performed in the low load region because the throttle valve 17 rises after the opening degree becomes considerably large.

Therefore, by switching to the suction negative pressure control (VC) system in the low load region where the BPT valve 6 does not lift sufficiently, the opening degree of the EGR valve 5 is controlled without being affected by the operation of the BPT valve 6. To do. As a result, the EGR rate can be raised from a load range in which the opening of the throttle valve 17 is sufficiently small as shown by the solid line in FIG. That is, the hatched area in FIG. 3 is the EGR area enlarged by the present invention.

Under the operating condition switched to the suction negative pressure control (VC) system, E is supplied through the orifice 27.
The negative pressure introduced to the GR valve 5 is appropriately diluted with the atmospheric pressure, and the negative pressure generated in the VC port 18 is high even in a low load range.
The orifice 2 can be controlled by suppressing the opening degree of the GR valve 5.
As a characteristic in the case of not having No. 7, it is possible to suppress the EGR rate from becoming excessively large as shown by a two-dot chain line in FIG. As a result, it is possible to suppress NOx emissions while ensuring the operational stability of the engine.

By switching the exhaust pressure control (BPT) system and the suction negative pressure control (VC) system in this way, the degree of freedom in setting the EGR rate can be expanded, and the operation stability of the engine can be ensured while reducing fuel consumption. As a result, it becomes possible to suppress NOx emissions effectively.

[0041]

As described above, the exhaust gas recirculation system for an engine according to claim 1 includes an EGR passage connecting the exhaust pipe and the intake pipe of the engine, and a diaphragm type EGR valve interposed in the middle of the EGR passage. , A negative pressure passage for guiding the negative suction pressure generated in the intake pipe to the diaphragm chamber of the EGR valve, and the EG
A diaphragm type BPT valve for diluting the suction negative pressure introduced into the diaphragm chamber of the R valve with atmospheric pressure, and an EGR gas pressure passage for guiding the EGR gas pressure P ₂ on the exhaust pipe side from the EGR valve of the EGR passage into the diaphragm chamber of the BPT valve When,
Since it has a BPT cut means for shutting off the atmospheric pressure introduced to the diaphragm chamber of the EGR valve via the BPT valve according to the operating conditions, it is possible to perform exhaust gas recirculation from a low load range where the BPT valve does not operate. Fuel consumption of the engine is reduced and NOx emission is suppressed.

An exhaust gas recirculation system for an engine according to a second aspect of the present invention includes an EGR passage connecting an exhaust pipe and an intake pipe of the engine, and E
A diaphragm type EGR valve installed in the middle of the GR passage, a negative pressure passage for guiding a suction negative pressure generated in the intake pipe to the diaphragm chamber of the EGR valve, and a suction negative pressure introduced to the diaphragm chamber of the EGR valve at atmospheric pressure. A diaphragm type BPT valve for dilution, an EGR gas pressure passage for guiding the EGR gas pressure P ₂ on the exhaust pipe side from the EGR valve in the EGR passage to the diaphragm chamber of the BPT valve, and a BP depending on operating conditions.
Under operating conditions in which the BPT cut means for shutting off the atmospheric pressure introduced to the diaphragm chamber of the EGR valve via the T valve and the atmospheric pressure shut off for the atmospheric pressure introduced to the diaphragm chamber of the EGR valve via the BPT valve by the BPT cut means, Since the negative pressure adjusting means for adjusting the suction negative pressure introduced to the diaphragm chamber of the EGR valve through the pressure passage is provided, the exhaust gas recirculation is performed so that an appropriate EGR rate can be obtained from a low load range where the BPT valve does not operate. This makes it possible to increase the degree of freedom in setting the EGR rate, reduce fuel consumption of the engine, and effectively suppress NOx emissions.

In the exhaust gas recirculation system for an engine according to a third aspect of the present invention, the suction negative pressure introduced into the diaphragm chamber of the EGR valve through the negative pressure passage is introduced into the atmospheric pressure dilution passage connected to the negative pressure passage. It is possible to suppress the EGR rate from becoming excessive by appropriately diluting with.

In the exhaust gas recirculation system for an engine according to a fourth aspect, the suction negative pressure introduced into the diaphragm chamber of the EGR valve through the negative pressure passage is introduced through a fixed throttle provided in the atmospheric pressure dilution passage. It is possible to prevent the EGR rate from becoming excessive by appropriately diluting it with the atmospheric pressure.

[Brief description of drawings]

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

FIG. 2 is a map similarly showing control characteristics.

FIG. 3 is a diagram showing a relationship between a throttle valve opening and an EGR rate.

[Explanation of symbols]

 2 intake pipe 3 exhaust pipe 4 EGR passage 5 EGR valve 6 BPT valve 8 diaphragm chamber 11 diaphragm chamber 13 orifice 14 EGR gas pressure passage 17 throttle valve 20 VC negative pressure passage 21 first solenoid valve 22 second solenoid valve 24 BPT negative pressure Passage 26 Atmospheric pressure dilution passage 27 Orifice 30 Control unit

Claims (4)

[Claims] 1. An EGR passage connecting an exhaust pipe and an intake pipe of an engine, a diaphragm type EGR valve interposed in the middle of the EGR passage, and a negative pressure for introducing an intake negative pressure generated in the intake pipe into a diaphragm chamber of the EGR valve. The EGR gas pressure P ₂ on the exhaust pipe side from the EGR valve of the EGR passage to the passage and the diaphragm type BPT valve that dilutes the suction negative pressure introduced to the diaphragm chamber of the EGR valve to the atmospheric pressure. An exhaust gas recirculation system for an engine, comprising: a gas pressure passage; and a BPT cut means for shutting off the atmospheric pressure introduced to the diaphragm chamber of the EGR valve via the BPT valve according to operating conditions. 2. An EGR passage connecting an exhaust pipe and an intake pipe of an engine, a diaphragm type EGR valve interposed in the middle of the EGR passage, and a negative pressure for introducing an intake negative pressure generated in the intake pipe into a diaphragm chamber of the EGR valve. The EGR gas pressure P ₂ on the exhaust pipe side from the EGR valve of the EGR passage to the passage and the diaphragm type BPT valve that dilutes the suction negative pressure introduced to the diaphragm chamber of the EGR valve to the atmospheric pressure. A gas pressure passage, a BPT cut means for shutting off the atmospheric pressure introduced to the diaphragm chamber of the EGR valve via the BPT valve according to the operating condition, and an EGR via the BPT valve by the BPT cut means.
A negative pressure adjusting means for adjusting the suction negative pressure introduced into the diaphragm chamber of the EGR valve under an operating condition in which the atmospheric pressure introduced into the diaphragm chamber of the valve is shut off. Exhaust gas recirculation system for engines. 3. The exhaust gas recirculation system for an engine according to claim 2, wherein as the negative pressure adjusting means, an atmospheric pressure diluting passage for appropriately guiding the atmospheric pressure is connected to the negative pressure passage. 4. A negative pressure adjusting means, wherein an atmospheric pressure dilution passage for appropriately introducing atmospheric pressure to the negative pressure passage is connected, and a fixed throttle is provided in the middle of the atmospheric pressure dilution passage. 3. An engine exhaust gas recirculation device according to item 3.