JPH04272460A - Exhaust gas feedback control device of diesel engine - Google Patents

Abstract

PURPOSE:To heighten the set degree of freedom of the EGR factor, and enable fine EGR control conforming to the demand from the engine. CONSTITUTION:The degree of opening of an EGR control valve 5 is feedback controlled by a pressure adjusting valve 6 so that the pressure P2 in an EGR passage 4 downstream of the EGR control valve 5 is held at a specified value, while a valve 10 is installed in the suction passage 3 to control the section area of the suction passage 3 in accordance with the engine operating conditions. According to this constitution, the EGR factor R is made variable according to the suction amount and the degree of opening of the valve 10 based upon the formula R=(A2/A1)[(gammaa/gammae)[1-{(P1-P2)/(P1-P0)}]<1/2>, where P1 is pressure upstream of valve 10, P2 is pressure in EGR passage dowstream of EGR control valve. A1 is section area of suction passage, A2 is section area of EGR passage, (g) is gravitational acceleration, and gammaa and gammae are respective specific gravities of suction air and EGR gas. This enlarges the set degree of freedom of the EGR factor and enables fine EGR control conforming to the operating conditions.

Description

[Detailed description of the invention]

0001

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

0002

2. Description of the Related Art A conventional exhaust gas recirculation (hereinafter referred to as EGR) control device for a diesel engine is disclosed in, for example, Japanese Patent Application Laid-Open No. 59-215954. To briefly explain this, a solenoid valve is provided in the supply passage of working fluid to be supplied to the EGR control valve installed in the EGR passage connected between the exhaust passage and intake passage of the engine, and the solenoid valve is controlled to adjust the fuel injection amount. The EGR amount is controlled by a pulse signal having a duty ratio determined based on the engine speed, thereby changing the EGR amount based on the engine load.

0003

[Problems to be Solved by the Invention] However, the above conventional device determines the engine load condition based on the fuel injection amount, and does not necessarily match the actual intake air amount, but rather determines the engine load condition based on the actual intake air amount. Although EGR control is performed, it is difficult to say that it is highly accurate. For this reason, there is no effect in the driving range where the amount of EGR is small, but in the driving range where the amount of EGR is large, there is a risk that the drivability and fuel will be adversely affected.

The present invention has been made in view of the above-mentioned circumstances, and enables fine control according to engine operating conditions.
It is an object of the present invention to provide an EGR control device for a diesel engine that can realize optimal EGR control in all operating regions.

[0005]

[Means for Solving the Problems] Therefore, the present invention provides an EG system in a diesel engine that branches from an exhaust passage connected to the engine body and merges into an intake passage connected to the engine body.
an R passage; an EGR control valve interposed in the EGR passage;
The EGR control valve detects the pressure in the EGR passage between the EGR control valve and the intake passage confluence part, and adjusts the pressure to a predetermined value.
EGR control valve control means that controls the opening degree of the R control valve; and passage opening area control means that is provided in the intake passage upstream of the EGR passage confluence and that varies the passage opening area according to engine operating conditions. It was composed of

[0006]

[Operation] In the above configuration, the EG downstream of the EGR control valve
By detecting the pressure in the R passage and performing feedback control so that this pressure reaches a target predetermined pressure value, it becomes possible to finely change the EGR rate according to the control principle described below. That is, as shown in FIG.
P1 is the pressure upstream of the intake orifice B (corresponding to the passage opening area control means), P0 is the pressure at the confluence of the EGR passage of the intake passage A, and P0 is the pressure upstream of the EGR orifice E in the EGR passage D downstream of the EGR control valve C. Let P2 be,
The intake air amount Qa and the EGR amount Qe are respectively Qa = A1 {2g(P1 - P0)/γa}1
/2 -(1) Qe =A2 {2g(P1 -P0
)/γe }1/2 - (2). A1 is the intake passage opening area, A2 is the EGR passage opening area, g is the gravitational acceleration, and γa and γe are the intake air and EGR, respectively.
It is the specific weight of the gas.

From formulas (1) and (2), the EGR rate is
R=(A2/A1)[(γa/γe)[1-{
(P1 - P2 ) / (P1 - P0 )}]]1/2
- (3). From equation (3), by controlling the differential pressure between P1 and P2, the following E can be obtained under the condition that the opening area of the intake passage is constant.
GR characteristics can be obtained.

(a) Control with P1 - P2 = 0 always provides a constant EGR rate. (b) In the control where P1 - P2 = constant value (≠0), the EGR rate is variable according to the amount of intake air. Here, in a diesel engine, P1 is considered to be constant at approximately atmospheric pressure, so if P2 is controlled to a predetermined value, the differential pressure P1 - P2 can be controlled to be constant at all times, and the above (a) and (b). E
GR characteristics are obtained, the degree of freedom in setting the EGR rate is increased, and detailed EGR control can be performed according to operating conditions.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. In FIG. 1 showing the first embodiment, an EGR passage 4 that branches from an exhaust passage 2 connected to an engine main body 1 and joins an intake passage 3 connected to the engine main body 1 includes an EGR passage 4 that is introduced into a negative pressure chamber 5a. A diaphragm-type EGR control valve 5 is interposed, which includes a valve body 5c that is interlocked with a diaphragm 5b that is displaced in accordance with the negative pressure generated. Reference numeral 6 denotes a pressure regulating valve as EGR control valve control means for detecting the pressure in the EGR passage 4 on the downstream side of the EGR control valve 5 and controlling the opening degree of the EGR control valve 5 to maintain the pressure at a predetermined value. , a pressure chamber 6a into which the pressure of the EGR passage 4 is introduced, an atmospheric chamber 6c defined from the pressure chamber 6a by a diaphragm 6b and communicating with the atmosphere, and a vacuum pump 7 and a negative pressure chamber 5a of the EGR control valve 5 are connected. a nozzle portion 6e that can communicate with the negative pressure passage 8 via a valve body 6d, and a spring 6f for setting the predetermined pressure.
According to the pressure introduced into the pressure chamber 6a, the valve body 6d moves up and down in the figure via the diaphragm 6b to open the negative pressure passage 8.
The opening degree of the EGR control valve 5 is controlled by controlling the amount of air introduced into the EGR control valve 5 and adjusting the dilution amount. 9 is EGR passage 4
This is an EGR orifice installed near the confluence of the intake passages.

On the other hand, on the upstream side of the EGR passage confluence of the intake passage 3, there is a control valve 1 as passage opening area control means for varying the passage opening area according to engine operating conditions.
0 is inserted. The control valve 10 is operated by a control signal from a control unit 14 based on engine operating conditions such as engine cooling water temperature, fuel injection amount, and engine speed detected by a water temperature sensor 11, a control lever sensor 12, a rotation speed sensor 13, etc., respectively. For example, the opening degree of the valve body 10B is adjusted using a stepping motor 10A.

Next, the operation will be explained with reference to FIGS. 3 and 4. First, FIG. 3 shows a case where the opening degree of the control valve 10 is constant and the intake air amount increases. Note that the intake air amount and EGR amount correspond to the sizes of the arrows in the figure. When the intake air amount increases from the state shown in (A) to the state shown in (B), the pressure loss due to the control valve 10 increases,
The pressure P0 in the intake passage downstream of the control valve 10 decreases, and the pressure P2 in the EGR passage also decreases accordingly. When this pressure P2 decreases, the diaphragm 6b of the pressure regulating valve 6 moves downward against the spring force of the spring 6a, and the valve body 6d also moves downward. This reduces the amount of dilution by air, increases the negative pressure in the load chamber 5a of the EGR control valve 5, and increases the opening degree of the EGR control valve 5. As a result, (C
) As shown in the figure, the EGR passage pressure P2 increases from the EGR amount and is balanced at a predetermined pressure value.

Further, when the intake air amount decreases, the opposite operation occurs and the pressure inside the EGR passage increases, so the opening degree of the EGR control valve 5 decreases and the EGR amount decreases. and,
In the case of FIG. 3, there is a relationship in which the EGR rate increases as the intake air amount increases, based on the above-mentioned equation (3). Figures 4(A)-(B
) shows the case where the opening degree of the control valve 10 is decreased while the intake air amount is kept constant.

When the opening degree of the control valve 10 is decreased from the state shown in FIG. (A) to the state shown in FIG. . On the other hand, control valve 1
If the 0 opening degree is increased, the EGR amount will be decreased. and,
In the case of FIG. 4, the EGR rate increases as the opening degree of the control valve 10 decreases.

FIG. 5 shows experimental data showing changes in the EGR rate when the control valve opening degree is changed. In this way, if the pressure in the EGR passage on the downstream side of the EGR control valve 5 is maintained at a predetermined value by feedback control, the EGR rate can be set more freely, which allows EGR control to be adapted to all operating ranges. It becomes possible. Furthermore, since the intake pressure is directly used as a control element, it can be controlled with high precision. Furthermore, since the EGR control valve 5 is feedback-controlled, the system has an excellent effect in that the EGR control characteristics can be prevented from changing even if it deteriorates due to heat or the like.

Next, FIG. 6 shows the main part of the second embodiment. still,
Components that are the same as those in the first embodiment shown in FIG. The present embodiment is characterized by a pressure regulating valve structure as an EGR control valve control means that detects the pressure in the EGR passage 4 and controls the operation of the EGR control valve 5. In the figure, the pressure regulating valve 20 of this embodiment includes a pressure chamber 20a that introduces the pressure of the EGR passage 4, and an atmospheric chamber 20 that communicates with the atmosphere.
0c, a diaphragm 20b that defines both chambers 20a, 20c, a valve body 20d that follows the diaphragm 20b, a nozzle portion 20e for introducing the atmosphere in the atmospheric chamber 20c into the negative pressure passage 8 via the valve body 20d, and diaphragm 20b
The first step is to include a spring 20f that urges the
The pressure regulating valve 6 is similar to the pressure regulating valve 6 of the embodiment, but is further provided with a solenoid 20g on the atmospheric chamber 20c side that sucks the diaphragm 20b upward in the figure when energized.

In this configuration, when the solenoid 20g of the pressure regulating valve 20 is in the ON state due to the output from the control unit 14, the diaphragm 20b is urged upward as shown in FIG. The amount of dilution increases, the opening degree of the EGR control valve 5 decreases, and the pressure within the EGR passage 4 decreases. This makes the EG in this case
The set pressure of the R passage 4 is set low.

When the solenoid 20g is turned from ON to OFF, the balance with the pressure (negative pressure) in the EGR passage 4 is lost, and the diaphragm 20b moves downward as shown in FIG. 7(B). Therefore, the valve body 20d also moves downward, the dilution amount decreases, and the opening degree of the EGR control valve 5 increases. When the set pressure determined by the spring 20f is reached due to an increase in the EGR amount, the stable state shown in FIG. 7(C) is reached. It should be noted that for the energization control of the solenoid 20g, duty control or the like can be applied in addition to ON-OFF control.

In this manner, the set pressure P2 of the EGR passage 4 can be varied depending on the suction force of the solenoid 20g. By varying the set pressure P2, (3
) As is clear from the equation, the EGR rate R can also be variably controlled, and by using the set pressure P2 as the basic parameter for EGR rate control, the EGR rate R can be controlled even more than in the first embodiment.
The R rate can be controlled finely.

FIG. 8 shows EGR characteristics when the pressure P2 inside the EGR passage 4 is changed.

[0020]

[Effects of the Invention] As explained above, according to the present invention, E
The configuration detects the pressure in the EGR passage downstream of the GR control valve and performs feedback control to maintain this pressure at a predetermined value, and has a function to control the amount of EGR that meets the requirements in all operating regions. Fine-grained EGR according to requests
Even in driving ranges that require a large amount of EGR, the NOX reduction effect can be obtained without deteriorating drivability and fuel efficiency.

[Brief explanation of the drawing]

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

[Fig. 2] An explanatory diagram of the control principle of the EGR control device according to the present invention

[Fig. 3] Operation explanatory diagram of the first embodiment of the present invention

[Fig. 4] Operation explanatory diagram of the first embodiment of the present invention

[Figure 5] EGR characteristic diagram of the first embodiment same as above

[Fig. 6] Main part configuration diagram of the second embodiment of the present invention

[Fig. 7] An explanatory diagram of the operation of the pressure regulating valve of the second embodiment same as above.

[Fig. 8] EGR characteristic diagram according to the pressure inside the EGR passage in the second embodiment same as above.

[Explanation of symbols]

1 Engine body
2 Exhaust passage 3 Intake passage
4 EGR passage 5 EGR control valve
6 Pressure regulating valve 7 Vacuum pump
8 Negative pressure passage 10 Control valve
11 Water temperature sensor 12 Control lever sensor
13 Rotation speed sensor 14 Control unit

Claims (1)

[Claims] 1. In a diesel engine, an exhaust recirculation passage branching from an exhaust passage connected to an engine main body and merging with an intake passage connecting to the engine main body; an exhaust recirculation control valve interposed in the exhaust recirculation passage; Exhaust recirculation control valve control means for detecting the pressure in the exhaust recirculation passage between the exhaust recirculation control valve and the intake passage confluence, and controlling the opening degree of the exhaust recirculation control valve to maintain the pressure at a predetermined value. Exhaust recirculation control for a diesel engine, comprising passage opening area control means provided in the intake passage upstream of the confluence of the exhaust gas recirculation passages and varying the passage opening area according to engine operating conditions. Device.