JP2721025B2 - Control method of exhaust gas recirculation control device - Google Patents

Description

The present invention relates to a control method of an exhaust gas recirculation control device mainly applied to an automobile engine.

[Related Art] In this type of exhaust gas recirculation control device, an exhaust gas recirculation control valve is disposed in an exhaust gas recirculation passage, and a negative pressure chamber communicates with an EGR port near a throttle valve by a negative pressure passage. A negative pressure switching valve is provided in the middle of the process, and the operation of the exhaust gas recirculation control valve is controlled via the negative pressure switching valve. When a part of the exhaust gas is recirculated to the intake passage, as a prior art of the present invention, for example,
As disclosed in JP-A-208659, when the engine coolant temperature reaches a set value, an exhaust gas recirculation control valve is operated to start exhaust gas recirculation.

[Problems to be Solved by the Invention] However, when the exhaust gas recirculation is started with a uniform set value in a low speed / low load region where combustion is unstable and in a high load region where the influence of misfire or the like hardly occurs. If the warm-up is insufficient, a misfire easily occurs immediately after the start of the exhaust gas recirculation in a low-speed / low-load region, and a surge or the like due to the misfire easily occurs.

Thus, if higher the set value, although it is possible to avoid such a problem, in this case, slow onset of exhaust gas recirculation in a high load region side, the amount of the NO _x is Will increase.

An object of the present invention is to solve such a problem.

[Means for Solving the Problems] The present invention employs the following means in order to achieve such an object.

That is, the control method of the exhaust gas recirculation control device according to the present invention is the control method of the exhaust gas recirculation control device configured to recirculate a part of the exhaust gas to the intake passage when the engine coolant temperature reaches a set value. The set value is increased when the engine load is reduced, and is decreased when the engine load is increased.When the engine load is in a low load range and the engine cooling water temperature is low and has not reached the set value. The exhaust gas recirculation is stopped, and the exhaust gas recirculation is started when the engine load is in a high load region and the engine cooling water temperature reaches a set value at a low temperature.

Here, the engine load refers to an intake pressure, an engine speed, an intake air amount, and the like.

[Operation] According to such a configuration, when the engine load is on the low load region side, the set value becomes large. Therefore, the warm-up is sufficiently promoted to stabilize the combustion, and then the exhaust gas is recirculated. Is performed, and the combustion instability due to the exhaust gas recirculation in the low load region where the engine cooling water temperature is low is suppressed.

On the other hand, when the engine load is on the high load region side and the engine cooling water temperature is low, the set value becomes a small value, so that even if the warm-up is slightly insufficient, the exhaust gas is quickly recirculated. , NO _X generation is suppressed.

Embodiment An embodiment of the present invention will be described below with reference to FIGS.

The engine 1 schematically shown in FIG. 1 is used for an automobile, and includes an exhaust gas recirculation control device 2 and an electronic control device 3
have.

The exhaust gas recirculation control device 2 includes an exhaust gas recirculation control valve (hereinafter, EGR passage) 4 for opening and closing an exhaust gas recirculation passage (hereinafter, referred to as an EGR passage) 4.
5), a negative pressure switching valve 6 for controlling the operation of the EGR valve 5 according to the operation range, and an EGR modulator 7.

The EGR passage 4 has an inlet 4a opened to the exhaust passage 8 and an outlet 4a.
b is opened to the intake passage 9, and the EGR valve 5 is arranged in the middle of the opening.

The EGR valve 5 includes a negative pressure chamber 5a and an atmospheric pressure side constant pressure chamber 5b.
And a valve element 5c, which constitutes a main part of the exhaust gas recirculation control device 2. The negative pressure chamber 5a is communicated with an EGR port 12 near the throttle valve 11 through a negative pressure passage 10. is there. The EGR valve 5 has a negative pressure chamber 5a and a constant pressure chamber 5a.
When the pressure difference from b exceeds a predetermined operating pressure, the valve element 5c
The passage 4 is opened, and the exhaust gas is recirculated to the intake passage 9 according to the amount of intake air.

The negative pressure switching valve 6 is a vacuum switching type three-way switching valve configured to be selectively connected to the outside air and the inside of the intake passage 9, and connects the first input port 6a to the EG.
It is connected to the R port 12, the second input port 6b is opened to the outside air through a filter, and the output port 6c is connected to the negative pressure chamber 5a side of the EGR valve 5. Then, when the electric input terminal is energized, the first input port 6a on the intake pressure side and the output port 6c communicate with each other to be in a “closed” state, and the electric input terminal is not energized. In this case, the second input port 6b and the output port 6c on the atmospheric pressure side communicate with each other to be in an “open” state.

The EGR modulator 7 adjusts the pressure introduced into the negative pressure chamber 5a of the EGR valve 5 by using the exhaust pressure.
It is arranged in a negative pressure passage 10 between a negative pressure chamber 5a of the EGR valve 5 and an output port 6c of the negative pressure switching valve 6.

On the other hand, a pressure sensor 13 is connected downstream of the outlet 4b of the EGR passage 4. The pressure sensor 13 can be selectively connected to the outside air and the inside of the intake passage 9 via a switching valve 14 for switching a pressure detection region. Specifically, the switching valve 14 is a vacuum switching type three-way switching valve substantially similar to the negative pressure switching valve 6,
The input port 14a is connected to the downstream side of the outlet 4b of the EGR passage 4, the second input port 14b is opened to the outside air through a filter, and the output port 14c is connected to the pressure sensor 13. is there. When the electric input terminal is not energized, the first input port 14a on the intake pressure side communicates with the output port 14c. When the electric input terminal is energized, the first input port 14a communicates with the atmospheric pressure side. Second input port 14b of
And the output port 14c.
Note that the first input port 14a and the output port 1
4c is held at a position where it is communicated with.

The electronic control unit 3 has a role of performing various controls including control of a fuel injection amount using signals from various sensors and the like as input information.
, Input interface 17, and output interface
It is composed of a microcomputer unit having 18. At least the input interface 17
Throttle sensor that detects the opening of the throttle valve 11
A signal a from an idle switch (not shown) provided integrally with the engine 19 and a water temperature sensor 20 for detecting an engine cooling water temperature.
, An engine rotation signal c from a crank angle sensor 22 provided in the distributor 21, and a pressure signal d from the pressure sensor 13. From the output interface 18, at least the signal e to the negative pressure switching valve 6 and the signal f to the switching valve 14
Are respectively output.

The electronic control unit 3 includes an exhaust gas recirculation control unit 2
Is controlled in accordance with the operation state of the engine 1 by the second
A program as shown schematically in FIG. First, various conditions for performing exhaust gas recirculation, for example,
After the engine 1 is started, it is determined that the engine 1 is not idling based on the engine rotation signal c from the crank angle sensor 22 and the signal a from the idle switch. Is the set value EG
R Start water temperature α (° C) is set to a specified address and step 5
Proceed to 2. As shown schematically in FIG. 3, the EGR start water temperature α is set to a small value as the intake pressure PM as an engine load increases, and to a large value as the intake pressure PM decreases. I have. Thus, in step 51, the EG is determined based on the intake pressure PM detected by the pressure sensor 13.
The R starting water temperature α will be determined. In step 52,
From the water temperature signal b from the water temperature sensor 20, it is determined whether or not the engine cooling water temperature THW has reached the EGR start water temperature α. If it is determined, the process proceeds to step 53. In step 53, the energization is turned on to the negative pressure switching valve VSV6 for controlling the EGR valve to start the exhaust gas recirculation. Note that the above control is repeatedly executed during the operation of the engine.

According to such a configuration, when the engine cooling water temperature reaches the EGR start water temperature, the electric input terminal of the negative pressure switching valve 6 is energized, the first input port 6a communicates with the output port 6c, and the negative pressure The intake pressure acts on the EGR modulator 7 and the negative pressure chamber 5a of the EGR valve 5 through the passage 10. For this reason, the EGR valve 5 opens the EGR passage 4, and a constant ratio of exhaust gas is recirculated from the EGR passage 4 to the intake passage 9 according to the negative pressure. When the engine cooling water temperature has not reached the EGR start water temperature, the power supply to the negative pressure switching valve 6 is stopped, the second input port 6b communicates with the output port 6c, and the EGR modulator is connected via the negative pressure passage 10. Atmospheric pressure acts on 7 and the negative pressure chamber 5a of the EGR valve 5. Therefore, the exhaust gas recirculation is stopped by the EGR valve 5 through the EGR passage 4.

Therefore, according to such a configuration, when the intake pressure is low and the engine load is on the low load region side, the EGR start water temperature becomes large, so that even in the warm-up operation state where the engine cooling water temperature is low, the warm-up is not performed. Promoted. Then, after the warm-up is promoted to stabilize the combustion, the exhaust gas is recirculated, so that the occurrence of misfire due to the exhaust gas recirculation can be suppressed. As a result, generation of a surge immediately after the recirculation of the exhaust gas can be effectively suppressed, and operability immediately after the recirculation of the exhaust gas can be improved.

Further, when the intake pressure increases and the engine load is on the high load range side, the EGR start water temperature has a smaller value than on the low load range side. Therefore, in the high load region side, even in the warm-up is slightly unsatisfactory state engine coolant temperature at low temperatures, will be rapidly exhaust gas recirculation is performed, generation of the NO _x in the high load range side can be suppressed.

As mentioned above, although one Example of this invention was described, it cannot be overemphasized that this invention is not limited to the said Example. For example, as shown in FIG. 4, when the intake air amount is small, the EGR start water temperature α (° C.), which is a set value, is increased, and the EGR start water temperature α is decreased with an increase in the intake air amount. You may. Alternatively, the engine load is finely determined from the engine speed and the intake pressure, and the EGR
The starting water temperature may be determined.

Further, the exhaust gas recirculation control device is not limited to the illustrated embodiment, but can be variously modified.

[Effects of the Invention] Since the present invention has the above-described configuration, the start timing of exhaust gas recirculation can be effectively adjusted according to the engine load. As a result, it is possible to suppress the occurrence of a surge after the start of the exhaust gas recirculation and obtain good operability, and when the engine shifts to a high load side, the exhaust gas recirculation is quickly performed, and NO Generation of _x can be suppressed.

[Brief description of the drawings]

1 to 3 show one embodiment of the present invention, FIG. 1 is a schematic overall configuration diagram, FIG. 2 is a flowchart diagram schematically showing a control procedure, and FIG. FIG. FIG. 4 is a view showing a control setting condition corresponding to FIG. 3 showing another embodiment of the present invention. 1 ... engine 2 ... exhaust gas recirculation control device 4 ... EGR passage 5 ... EGR valve 6 ... negative pressure switching valve 9 ... intake passage 13 ... pressure sensor 20 ... water temperature sensor α ... set value (EGR) Starting water temperature)

Claims (1)

(57) [Claims] 1. An exhaust gas recirculation control device configured to recirculate a part of exhaust gas to an intake passage when an engine cooling water temperature reaches a set value. If the engine load is in the low load range and the engine cooling water temperature is low and has not reached the set value, the exhaust recirculation is stopped, and the engine load is reduced. A control method for an exhaust gas recirculation control device, wherein the exhaust gas recirculation is started when the engine cooling water temperature reaches a set value at a low temperature in a high load region.