JPH06264826A - Exhaust gas recirculation control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To reconcile the EGR control at a constant EGR rate and the fuel consumption improvement by EGR. CONSTITUTION:The exhaust gas recirculation control device of an internal combustion engine is provided with a control negative pressure passage 9 guiding the negative pressure controlled by a BPT valve 7 keeping the back pressure applied to the valve element 61 of an EGR valve 6 constant for the EGR control at a constant EGR rate to a negative pressure operation chamber 63 of the EGR valve 6, an intake negative pressure passage 10 guiding the intake negative pressure directly to the negative pressure operation chamber 63, and a negative pressure selector valve 11 opening an intake negative pressure passage 10 in a low load area having low back pressure where the BPT valve 7 is not operated and opening a control negative pressure passage 9 on the condition of the prescribed back pressure or above that the BPT valve 7 is operated. The EGR control at a constant EGR rate and the fuel consumption improvement by EGR can be reconciled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to exhaust gas recirculation of an internal combustion engine.
The present invention relates to a control device (hereinafter referred to as “EGR”), and particularly to a technology for improving fuel efficiency in a device including a back pressure control valve for keeping an EGR rate constant.

[0002]

2. Description of the Related Art As is well known, an internal combustion engine for a vehicle is generally provided with an EGR device for returning a part of exhaust gas to an intake system under a predetermined operating condition in order to reduce NOx. In the case of an engine with a throttle valve in the intake system, EGR
It is simple to drive the EGR control valve provided in the EGR passage connecting the exhaust passage and the intake passage to control the amount in response to the intake negative pressure on the downstream side of the throttle valve. When the load is large, the valve opening becomes larger and the constant EGR rate (the ratio of the EGR flow rate to the intake air flow rate) cannot be obtained.

Therefore, a BPT valve (hereinafter referred to as a BPT valve) is provided to drive the EGR so as to keep the back pressure constant by sensing the exhaust pressure (back pressure) downstream of the EGR valve.
There is a system in which the GR ratio is obtained and thereby the EGR region is expanded (for example, Japanese Patent Laid-Open No. 63-2.
59151).

[0004]

By the way, as another purpose of performing EGR, pumping loss due to throttle resistance is reduced in a low load region where the throttle valve opening is small to improve fuel efficiency. However, in the conventional EGR control device including the BPT valve, the supply of the signal negative pressure to the EGR valve is stopped under the condition that the exhaust pressure is smaller than the back pressure to be held by the BPT valve. Therefore, when the intake air flow rate is small, that is, when the exhaust air pressure is low, that is, when the intake air flow rate is low, that is, when the exhaust pressure overlaps with the low load region, EGR cannot be performed to improve the fuel consumption. It was

Although it is possible to adjust the EGR valve to a desired opening degree by a step motor or current control, a complicated circuit and control are required, and thermal measures are required, resulting in high cost. It was The present invention has been made in view of such a conventional problem, and only by adding a relatively simple configuration, the BPT valve has a function of keeping the EGR rate constant and EGR for reducing fuel consumption by reducing throttle loss. It is an object of the present invention to provide an EGR control device for an internal combustion engine that can satisfy both of the requirements.

[0006]

For this reason, the EGR control device for an internal combustion engine according to the present invention is configured so that a part of the exhaust gas EG is exhausted under a predetermined engine operating condition of the internal combustion engine having a throttle valve in the intake system.
The EGR control valve recirculates to the intake system via the R control valve, and the EGR control valve uses the intake negative pressure downstream of the throttle valve as a drive source, and the back pressure applied to the EGR control valve is kept constant. In an EGR control device for an internal combustion engine equipped with a BPT valve for controlling dilution of intake negative pressure and atmospheric pressure introduced to a control valve, low back pressure detecting means for detecting a low back pressure condition in which the operation of the BPT valve is stopped. , The intake negative pressure passage for directly introducing the intake negative pressure to the EGR control valve and the intake negative pressure passage when the low back pressure condition is detected, and the control negative pressure passage for other times. And a negative pressure switching valve for controlling the negative pressure.

[0007]

[Operation] Under a back pressure condition above a predetermined level at which the BPT valve operates,
The control negative pressure passage is opened by the negative pressure switching valve, whereby the negative pressure controlled by the BPT valve is guided to the EGR valve so that the back pressure applied to the EGR valve is controlled to be constant, so that a wide operation is performed. EGR control with a constant EGR rate is performed over the region, and a good NOx reduction function is secured.

On the other hand, when the low negative pressure detecting means detects a low negative pressure condition in which the operation of the BPT valve is stopped, the negative pressure switching valve opens the intake negative pressure passage, whereby the EGR valve is throttled. Since a strong intake negative pressure downstream of the valve is guided as it is, EGR is performed, throttle loss of the throttle valve is reduced, and fuel consumption can be improved.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In the figure, a throttle valve 3 is provided in an intake passage 2 of an internal combustion engine 1,
An EGR passage 5 is arranged by connecting the downstream side of the throttle valve 3 of the intake passage 2 and the exhaust passage 4. The EGR passage 5
An EGR valve 6 that controls the EGR flow rate is installed in the. The EGR valve 6 has a valve body 61 connected to a diaphragm 62,
Negative pressure for driving is introduced into the negative pressure working chamber 63 partitioned by the diaphragm 62.

A BPT valve 7 for adjusting the back pressure on the downstream side of the valve body 61 of the EGR valve 6 to be constant is provided. The BP
The T valve 7 includes a pressure working chamber 71 that guides a back pressure downstream of the valve body 61.
And a negative pressure control chamber 73 partitioned from the pressure working chamber 71 by a diaphragm 72. A spring 74 for urging the diaphragm 72 toward the pressure operating chamber 71 at a predetermined set pressure is interposed in the pressure operating chamber 71, and an intake negative pressure downstream of the throttle valve 3 is provided in the negative pressure control chamber 73. A branch pipe 75 that branches off from the negative pressure introducing pipe 8 that guides the valve is disposed so that its tip opening faces a valve body 76 fixed to the central portion of the diaphragm 72. When the back pressure downstream of the EGR valve 6 becomes equal to or higher than the set pressure of the spring 74, the back pressure acts on the diaphragm 72 from the pressure working chamber 71, and the diaphragm 72
Is pushed up to close the opening of the branch pipe 75. The negative pressure introducing pipe 8 extends to the downstream side of the branch pipe 75 to extend the BP.
It serves as a control negative pressure passage 9 for guiding the negative pressure controlled by the T valve 7 to the negative pressure operating chamber 63 of the EGR valve 6. Negative pressure control room
The filter 73 communicates with the atmosphere through the filter 77. Therefore, when the opening of the branch pipe 75 is open, the intake negative pressure introduced through the negative pressure introduction pipe 8 is introduced through the branch pipe 75. The pressure diluted by the atmospheric pressure is guided to the control negative pressure passage 9, and when the opening of the branch pipe 75 is closed, the intake negative pressure is directly guided to the control negative pressure passage 9 where the BPT valve 7 The operation of will be described. When the back pressure applied to the valve body 61 of the EGR valve 6 exceeds the set pressure of the spring 74 of the BPT valve 7, the back pressure pushes up the valve body 76 together with the diaphragm 72 to close the opening of the branch pipe 75, thereby reducing the intake negative pressure. E as it is
The GR valve 6 is guided to the negative pressure operating chamber 63 to increase the opening degree of the valve body 61, thereby reducing the back pressure and reopening the branch pipe 75. By repeating this, the back pressure is kept constant. As a result, the exhaust gas recirculation amount by the EGR valve 6 is maintained at a substantially constant ratio with respect to the intake air flow rate, and the EGR rate can be maintained constant.

On the other hand, during a low load operation in which the back pressure is always less than or equal to the set pressure of the spring 74 of the BPT valve 7, the branch pipe 75 remains open and the control negative pressure passage 9 is close to the atmospheric pressure. Since negative pressure is generated, such negative pressure is E
Even if it is guided to the negative pressure working chamber 63 of the GR valve 6, the valve body 61 of the EGR 6
It does not have the function of keeping the back pressure at a predetermined value. That is, the operation of the BPT valve 7 is stopped.

On the other hand, an intake negative pressure passage 10 for guiding the intake negative pressure downstream of the throttle valve 3 directly to the negative pressure working chamber 63 is provided. An electromagnetically driven negative pressure switching valve 11 is provided which selectively opens the control negative pressure passage 9 and the intake negative pressure passage 10 to communicate with the negative pressure working chamber 63 of the EGR valve 6. The negative pressure switching valve 11 is switched by a control signal from the control unit 12. The control unit 12 has a throttle sensor 1 for detecting the opening of the throttle valve 3.
3. The signals from the vehicle speed sensor 14 for detecting the vehicle speed and the water temperature sensor 15 for detecting the cooling water temperature are input, and further E based on the signals such as the basic fuel injection amount T _{P of the} fuel supplied to the engine.
The negative pressure switching valve is detected while detecting the operating condition for performing GR.
Performs 11 switching control.

The EGR control by the control unit 12 will be described below with reference to the flow chart shown in FIG. In step (denoted as S in the figure. The same applies hereinafter) In step 1, it is determined whether or not the condition is to execute EGR. Specifically, after the water temperature detected by the water temperature sensor 15 is warmed up to a certain level or more, the vehicle speed detected by the vehicle speed sensor 14 is at a low vehicle speed below a predetermined level, and the basic fuel injection amount T
_During a partial load operation in which the torque detected by _P or the like is equal to or less than a certain value, it is detected as an EGR execution region where NO _X reduction is required within a range that does not impair operating performance.

Next, in step 2, the throttle sensor
It is determined whether the opening degree of the throttle valve 3 detected by 13 is less than or equal to a set value. Here, the set value is the EGR.
The back pressure applied to the valve body 61 of the valve 6 is set to correspond to the value when the operation of the BPT valve 7 is stopped or less. When it is determined that the opening degree θ of the throttle valve 3 is less than or equal to the set value θ ₀ , the process proceeds to step 3, where the negative pressure switching valve 7 is controlled so as to open the intake negative pressure passage 10, and it is determined that the set value exceeds the set value. If so, the routine proceeds to step 4, where the control negative pressure passage 9 is controlled to be opened.

With this control, when the back pressure exceeds the set value, the control negative pressure passage 9 is opened, and the negative pressure controlled by the BPT valve 7 is introduced to the EGR valve 6 to keep the back pressure constant. The EGR rate is kept constant and controlled. Thereby,
The NOx reduction function can be obtained in a wide operating range. When the back pressure is equal to or lower than the set value and the operation of the BPT valve 7 is stopped, the intake negative pressure passage 10 is opened, so that the intake negative pressure downstream of the throttle valve 3 is directly guided to the EGR valve 6. The EGR control can be performed by opening the valve body 61, whereby the intake pressure on the downstream side of the throttle valve 3 can be increased to reduce pumping loss, thereby improving fuel consumption.

In order to achieve both the EGR control with a constant EGR rate and the EGR control for improving fuel efficiency, the structure of the conventional EGR control device having a BPT valve is simply provided with an intake negative pressure passage and a negative pressure switching valve. It can be implemented at low cost and has excellent reliability simply by installing a new configuration.

[0017]

As described above, according to the present invention, the NOx reduction function can be ensured by performing EGR control with a constant EGR rate by the BPT valve with a simple structure, and the low load region where the BPT valve does not operate. However, by opening the EGR valve and performing EGR, pumping loss of the throttle valve can be reduced and fuel consumption can be improved.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing an EGR control routine of the above embodiment.

[Explanation of symbols]

 1 internal combustion engine 2 intake passage 3 throttle valve 4 exhaust passage 5 EGR passage 6 EGR valve 7 BPT valve 8 negative pressure introducing pipe 9 control negative pressure passage 10 intake negative pressure passage 11 negative pressure switching valve 12 control unit 13 throttle sensor 14 vehicle speed sensor 15 Water temperature sensor

Claims (1)

[Claims] 1. Under a predetermined engine operating condition of an internal combustion engine having an intake system having a throttle valve, part of exhaust gas is recirculated to an intake system via an exhaust gas recirculation control valve, and the exhaust gas recirculation control valve is the throttle valve. A back pressure control valve that uses a downstream intake negative pressure as a drive source and controls dilution of the intake negative pressure and the atmospheric pressure guided to the exhaust recirculation control valve so that the back pressure applied to the exhaust recirculation control valve is constant. In an exhaust gas recirculation control device for an internal combustion engine, the low back pressure detecting means for detecting a low back pressure condition at which the operation of the back pressure control valve is stopped, and an intake negative pressure directing an intake negative pressure to the exhaust gas recirculation control valve. A pressure passage, and a negative pressure switching valve that opens the intake negative pressure passage when the low back pressure condition is detected and opens the control negative pressure passage at other times are provided. An exhaust gas recirculation control device for an internal combustion engine, which is characterized.