JP2555633B2 - Exhaust gas recirculation control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas recirculation (EGR) control device, and particularly to an exhaust gas provided with a trap for collecting particulates in exhaust gas of a diesel engine or the like. The present invention relates to a gas recirculation control device.

[Conventional technology]

A particulate trap (hereinafter simply referred to as a trap) for the purpose of collecting diesel particulates that are increased by the exhaust gas recirculation control system in the exhaust system of an engine having an exhaust gas recirculation control system for the purpose of reducing NOx When equipped with, trap regeneration (reburning)
Immediately before, the exhaust pressure rises due to particulate collection, the exhaust gas recirculation amount increases, and the output decrease, fuel consumption, and particulate emission amount increase.

In order to solve this, in JP-A-57-119121,
Using the two parameters of engine speed and load, that is, the rack position of the injection pump as parameters, the desired opening of the exhaust gas recirculation control valve for all combinations thereof is obtained and stored in advance, and the engine speed and We have adopted a map-type control method in which the rack position is detected and the corresponding valve opening is read to perform control. Two such maps are prepared, and one map is used during normal engine operation (particulate collection). When the trap is regenerated, the other map is switched during trap regeneration to suppress the discharge of particulates just before trap regeneration.

However, as the trap exhaust pressure (inlet pressure) rises as particulates are trapped in the trap, the recirculation rate rises as the exhaust pressure rises (the amount of recirculated exhaust gas increases. However, in the above method, the exhaust gas recirculation control is performed with one type of map when collecting the particulates before trap regeneration, so that the exhaust pressure of the trap cannot be increased.

In order to eliminate the influence of such an increase in the exhaust pressure of the trap, in JP-A-57-206763, as shown in FIG. 4, an exhaust gas recirculation pipe 20 is provided from the downstream side of the trap 21 to the engine 22. It is recirculated to the intake pipe 23 side.

[Problems to be solved by the invention]

In such an exhaust gas recirculation control device of JP-A-57-206763, an engine is connected to a trap via an exhaust pipe, and an exhaust gas having a diameter of about 20 mm is usually provided from the outlet side of the trap to the intake pipe of the engine. Since the gas recirculation pipe needs to be routed about 2 m from the engine, the pipe length becomes too long and it is not suitable for an exhaust gas recirculation control device in terms of actual strength.

Further, as shown in FIG. 4, the outlet pressure of the trap also increases non-linearly with the exhaust gas flow rate and is not constant, so exhaust gas recirculation control according to the outlet pressure is required.

Therefore, an object of the present invention is to provide an apparatus capable of performing optimum exhaust gas recirculation control corresponding to an increase in trap exhaust pressure when trap particulate collection has progressed.

[Means for solving problems]

As means for solving the above problems, in the exhaust gas recirculation control device according to the present invention, an engine speed sensor, an engine load sensor, a particulate trap, an inlet pressure and outlet pressure sensor of the trap, A control valve provided in a pipe for recirculating exhaust gas from the inlet side of the trap, a duty ratio before collection and a recirculation rate at this time are obtained by the rotational speed, load and outlet pressure, and the recirculation rate is calculated. And a control means for controlling the control valve with a corrected duty ratio corresponding to the current inlet pressure.

[Action]

In the present invention, the engine speed, the load, the inlet pressure and the outlet pressure of the trap are constantly input to the control means, and the recirculation rate before trap collection is determined from the engine speed, the load and the outlet pressure.

For this purpose, first, the duty ratio of the recirculation control valve inserted in the exhaust gas recirculation pipe connecting the inlet side of the trap and the intake side of the engine is obtained as usual. Then, the trap pre-collection inlet pressure when trap collection is not progressing is calculated from the detected trap outlet pressure, and an appropriate re-collection is performed using the calculated pre-collection inlet pressure and the duty ratio obtained above. Calculate the circulation rate.

It is necessary to maintain this recirculation rate so that it does not rise at least even if the trap pressure advances and the inlet pressure rises. However, the above duty ratio is used when trapped particulates have not yet been trapped. It is a value, and when the trap collection progresses, it is necessary to correct this duty ratio and maintain the above recirculation rate. Therefore, the duty ratio corresponding to the actual inlet pressure with the recirculation rate kept constant is determined.

The control means controls the control valve in accordance with the duty ratio thus corrected.

〔Example〕

Embodiments of an exhaust gas recirculation control device according to the present invention will be described below.

FIG. 1 shows a hardware system configuration of an apparatus for performing exhaust gas recirculation control of an engine according to the present invention. In the figure, reference numeral 1 is a controller as a control means, which has a built-in memory composed of ROM and RAM. 2 is a duty solenoid valve (DSV) that is controlled by a control signal from the controller 1 to send the control negative pressure of the vacuum source to the exhaust gas recirculation control valve 3 for control, and 4 is provided with the recirculation control valve 3. An exhaust gas recirculation pipe connecting the exhaust side (inlet side of the trap) of the engine 5 and the intake side, 6 is a rotation speed sensor of the engine 5, 7 is a load of the engine 5, that is, a lever or throttle of the injection pump (Fig. (Not shown) load sensor for detecting the opening, 8 is a trap, 9 is an inlet pressure sensor provided on the inlet side of the trap 8 for detecting the inlet pressure, and 10 is an outlet side of the trap 8. Vignetting by sensors for detecting the outlet pressure, 11 is an exhaust silencer connected to the outlet side of the trap 8. The output signals of the sensors 6, 7, 9 and 10 are constantly read at regular intervals of the program stored in the controller 1.

FIG. 2 shows an embodiment of a flow chart of a program stored in the controller 1 executed by using the hardware configuration of FIG.

The operation of the exhaust gas recirculation control device of the present invention shown in FIG. 1 will be described below with reference to the flowchart of FIG.

The controller 1 inputs the output signals of the engine speed sensor 6 and the load sensor 7 of the engine 5 and the output signals of the inlet pressure sensor 9 and the outlet pressure sensor 10. First, the engine speed and load (injection) (Lever opening of pump)
Then, the duty ratio D _M is obtained from the map (step S1 in FIG. 2). This map is as shown in FIG. 3, and since all the data constituting the map of FIG. 3 is stored in the ROM in the controller 1, the controller 1
Can obtain the duty ratio D _M from the rotation speed and the load. The map of FIG. 3 shows the duty ratio when the trap 8 is in the uncollected state (or the trap 8 itself is not provided). The present invention is intended to correct this duty ratio according to the trapped state of the trap.

Next, the front pressure of the silencer 11, that is, the outlet pressure P ₁ of the trap 8 is detected by the sensor 10 (step S2).

Then, the inlet pressure P ₂ when the trap 8 is not in the trapped state is calculated from the detected and read outlet pressure P ₁ (step S
3). This calculation formula can be obtained from the characteristic graph of FIG. That is, the exhaust pressure characteristic of the trap with respect to the exhaust gas flow rate is as follows. Even in this case, there is a constant relationship P between the outlet pressure characteristic of the trap and the inlet pressure characteristic of the trap before the exhaust pressure rises, that is, before trapping. Since it can be seen that ₂ = kP ₁ ² (k is a constant), if the outlet pressure P ₁ is detected, the inlet pressure P ₂ before collection can be calculated. This calculation formula is also stored in the ROM in the controller 1.

When the trap inlet pressure P ₂ before trapping is obtained in this way, an appropriate exhaust gas recirculation rate before trapping is obtained from this inlet pressure P ₂ and the duty ratio D _M obtained above ( Step S4). This map is also based on the relationship between the duty ratio with the exhaust gas recirculation rate as a parameter and the trap exhaust pressure before collection, as shown in FIG.
By storing in ROM, the recirculation rate of 25% can be obtained in the example of FIG.

Thereafter, this time, the inlet pressure P ₂ ′ of the trap 8 is actually read, and the duty ratio D with respect to the measured inlet pressure P ₂ ′ with the recirculation rate obtained above maintained is stored in the ROM storing the map of FIG. Take out more (the same step S5). This is to prevent the recirculation rate corresponding to the trap inlet pressure and its duty ratio in the uncollected state from at least increasing after collection (if the recirculation rate decreases too much,
It causes an increase in NOx).

As a result, since the recirculation valve 3 is controlled with the duty ratio slightly corrected from D _M to D, an on / off signal is sent from the controller 1 to the renoid valve 2 (at the same step S
6).

As a result, a constant amount of exhaust gas can be recirculated regardless of the rise in inlet pressure.

〔The invention's effect〕

As described above, in the exhaust gas recirculation control device according to the present invention, based on the duty ratio of the recirculation control valve before the trap inlet pressure rises, the recirculation rate at that time is kept constant and the duty after the rise is increased. Since the ratio was calculated and the control valve was controlled accordingly, it is possible to always perform optimal exhaust gas recirculation control before and after trap collection, and prevent engine output drop, black smoke increase and fuel consumption drop. can do.

[Brief description of drawings]

FIG. 1 is a diagram showing a hardware configuration of an exhaust gas recirculation control device according to the present invention, and FIG. 2 is a flow chart diagram of a program showing an embodiment of an operation of the exhaust gas recirculation control device according to the present invention. FIG. 3 is a characteristic graph showing the relationship between the engine speed and the pump lever opening when the duty ratio is used as a parameter, and FIG. 4 shows the relationship between the exhaust gas flow rate and the trap exhaust pressure. FIG. 5 is a characteristic graph showing the relationship between the duty ratio and the trap exhaust pressure when the exhaust gas recirculation (EGR) rate is used as a parameter, and FIG. 6 is disclosed in Japanese Patent Laid-Open No. 57-119121. It is a system diagram which shows the conventional exhaust gas recirculation control apparatus shown by the publication. In FIG. 1, 1 is a controller, 3 is a recirculation control valve, 4 is a recirculation pipe, 5 is an engine, 6 is a rotation speed sensor,
7 is a load sensor, 8 is a trap, 9 is an inlet pressure sensor, 10
Indicates an outlet pressure sensor. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. An engine speed sensor, an engine load sensor, a particulate trap, an inlet pressure and outlet pressure sensor for the trap, and a control provided in a pipe for recirculating exhaust gas from the inlet side of the trap. The duty ratio before collection and the recirculation rate at this time are obtained by the valve, the rotation speed, the load, and the outlet pressure, and the control valve is controlled by the corrected duty ratio corresponding to the recirculation rate and the current inlet pressure. And an exhaust gas recirculation control device.