JPH06323200A - Exhaust gas recirculation control device for diesel engine - Google Patents

Abstract

PURPOSE:To reduce NOx while preventing smoke from worsening by preventing control accuracy of exhaust gas recirculation control from decreasing due to collapsing a correlation between duty ratio and negative pressure of a negative pressure control solenoid valve. CONSTITUTION:A duty control type negative pressure control solenoid valve 18 is provided so as to variably control an opening of an exhaust gas recirculation (EGR) control valve. In order to detect a new air flow amount varied in accordance with an EGR amount, an air flowmeter 23 is provided, and based on a value obtained from a map by a detection value of the flowmeter and an operative condition, required duty ratio is set. The required duty ratio, when it is in a prescribed range, is left as output, but in the case of exceeding a lower limit value or an upper limit value, the duty ratio is fixed to the lower and upper limit values. For compensating overs and shorts of the EGR amount according to the above, injection timing of a fuel injection pump 20 is corrected.

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 device for a diesel engine, and more particularly to an exhaust gas recirculation control device for controlling the opening of a negative pressure type exhaust gas recirculation control valve via a duty control type negative pressure control solenoid valve. Regarding improvement.

[0002]

2. Description of the Related Art As an exhaust gas recirculation control device for a diesel engine, for example, in Japanese Patent Laid-Open No. 61-215426, a negative pressure type exhaust gas recirculation control valve is provided in an exhaust gas recirculation passage.
A duty control type negative pressure control solenoid valve is provided between the negative pressure chamber and the negative pressure source, and the opening degree of the exhaust gas recirculation control valve and thus the exhaust gas recirculation amount are changed by variable control of the duty ratio of the pulse signal given to the solenoid valve. The configuration is shown so that it is possible to do so. Particularly, in the device of this publication, the fresh air flow rate of the engine which changes with the exhaust gas recirculation amount is detected by an air flow meter so that the actual exhaust gas recirculation rate obtained from this fresh air flow rate matches the target exhaust gas recirculation rate. The duty ratio is feedback-controlled.

[0003]

FIG. 10 shows the relationship between the duty ratio and the negative pressure and the relationship between the negative pressure and the exhaust gas recirculation amount in the exhaust gas recirculation control device as described above. As is clear from FIG. 10, there is an upper limit DH and a lower limit DL in the range in which the negative pressure changes substantially linearly with respect to the change in the duty ratio. Even if the amount of change becomes extremely large, or conversely, the negative pressure hardly changes even if the duty ratio changes, and the control accuracy of the exhaust gas recirculation amount significantly decreases. Therefore, depending on the operating conditions, there is a possibility that the exhaust gas recirculation amount becomes insufficient and the NOx emission amount increases, or conversely, the exhaust gas recirculation amount becomes excessive and smoke increases.

[0004]

Therefore, according to the present invention,
The duty ratio of the pulse signal given to the negative pressure control solenoid valve is
The control range is limited to a stable range with high control accuracy, and the excess or deficiency of exhaust gas recirculation accompanying this is compensated by correcting the fuel injection timing. That is, as shown in FIG. 1, an exhaust gas recirculation control device for a diesel engine according to the present invention includes a negative pressure type exhaust gas recirculation control valve 1 installed in an exhaust gas recirculation passage extending from an exhaust system to an intake system of a diesel engine, Exhaust gas recirculation control valve 1
Of the negative pressure control solenoid valve 2 interposed between the negative pressure chamber and the negative pressure source and changing the negative pressure according to its duty ratio, and a parameter for detecting one or a plurality of parameters correlated with the exhaust gas recirculation amount. While outputting the detection means 3, the required duty ratio setting means 4 for setting the required duty ratio necessary to obtain the target exhaust gas recirculation amount using this parameter, and the control signal of the duty ratio according to this required duty ratio. The output means 5 for restricting the actual duty ratio to the lower limit value or the upper limit value when the required duty ratio exceeds the predetermined lower limit value or the upper limit value, and the required duty ratio exceeds the lower limit value or the upper limit value. sometimes,
An injection timing correction unit 6 that corrects the fuel injection timing according to the difference between the two is provided.

[0005]

In the parameter detecting means 3, the fresh air flow rate of the engine or the pressure in the exhaust gas recirculation passage, which has a correlation with the exhaust gas recirculation amount,
A parameter such as the pressure difference between the intake passage and the exhaust passage is detected, and the required duty ratio setting means 4 sets the required required duty ratio using this parameter. If the required duty ratio is within a predetermined stable range, the control signal of the duty ratio in accordance with the required duty ratio is a negative pressure control solenoid valve 2
Is output to. Along with this, the opening degree of the exhaust gas recirculation control valve 1 is controlled so as to reach the target exhaust gas recirculation amount.

When the required duty ratio is out of the stable range, that is, exceeds the predetermined lower limit value or upper limit value, the duty ratio of the control signal is fixed to the lower limit value or the upper limit value. As a result, the exhaust gas recirculation amount becomes insufficient or excessive, but the fuel injection timing is corrected according to the excess or deficiency, that is, the difference between the required duty ratio and the lower limit value or the upper limit value. Therefore, the increase of NOx due to the shortage of the exhaust gas recirculation amount or the increase of smoke due to the excessive exhaust gas recirculation is suppressed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 2 is a structural explanatory view showing an embodiment of an exhaust gas recirculation control device according to the present invention, in which 11 is an intake passage of a diesel engine and 12 is an exhaust passage. An exhaust gas recirculation passage 13 is formed so as to extend over the intake passage 11. A negative pressure diaphragm type exhaust gas recirculation control valve 14 is interposed in the exhaust gas recirculation passage 13. The exhaust gas recirculation control valve 14 is configured to open the exhaust gas recirculation passage 13 when negative pressure is introduced into the negative pressure chamber 14a that houses the return spring 15. Negative pressure is introduced into the negative pressure chamber 14a of the exhaust gas recirculation control valve 14 from a vacuum pump 16 serving as a negative pressure source via a negative pressure passage 17, and the negative pressure is appropriately changed. Therefore, a negative pressure control solenoid valve 18 of a duty control type is provided in the negative pressure passage 17. The negative pressure control solenoid valve 18 makes the negative pressure chamber 14a communicate with the vacuum pump 16 side when turned on, and the atmosphere introduction port 18a when turned off.
The control unit 19 is to be released to the side.
The larger the ON duty ratio of the control pulse signal given by the above, the stronger the negative pressure. In addition, the above vacuum pump 1
6 is driven by the engine output together with the fuel injection pump 20.

An intake throttle valve 22 whose opening is controlled by a step motor 21 is provided upstream of the confluence portion of the exhaust gas recirculation passage 13 of the intake passage 11. An air flow meter 23 of, for example, a hot wire type is provided at a position upstream of the intake throttle valve 22 in the intake passage 11 to detect the flow rate of fresh air taken in from the outside via an air cleaner (not shown). This air flow meter 23 measures only the flow rate of fresh air that does not include the recirculated exhaust gas flow rate. However, if the exhaust gas recirculation amount becomes large under the same operating conditions, the fresh air flow rate decreases, and conversely The smaller the recirculation amount, the greater the fresh air flow rate. That is, in this embodiment, the fresh air flow rate is focused on as a parameter having a correlation with the exhaust gas recirculation amount, and this is detected by the air flow meter 23.

The fuel injection pump 20 includes the pump 2
A rotation speed sensor 24 for detecting the rotation speed of 0 and thus the engine rotation speed is provided, and a lever opening sensor 25 for detecting the control lever opening indicating the load of the engine is provided. Reference numeral 26 is a water temperature sensor that detects the engine cooling water temperature. Detection signals from these sensors are input to a control unit 19 using a microcomputer system. In addition, the fuel injection pump 2
0 has a variable timer mechanism capable of variably controlling the injection timing. Specifically, the hydraulic pressure difference acting on both ends of the timer piston that determines the injection timing is variably controlled by the duty ratio control of the timing control valve 27, and the injection timing is controlled by forcibly sliding the timer piston. ing. The duty ratio of the control signal supplied to the timing control valve 27 is
It is also controlled by the control unit 19.

Next, FIGS. 3 and 4 are flow charts showing the contents of the exhaust gas recirculation control in the above-mentioned configuration, and the operation of the above-mentioned embodiment will be explained below based on this flow chart. The routine shown in this flowchart is repeatedly executed at regular intervals.

First, in step 1, it is determined whether the engine cooling water temperature has reached a predetermined temperature. At a temperature equal to or lower than a predetermined temperature, that is, in an unwarmed state, exhaust gas recirculation makes combustion unstable, so exhaust gas recirculation is not performed. Specifically, the intake throttle valve 2
2 is fully opened (step 2), and the negative pressure control solenoid valve 18 is turned off to fully close the exhaust gas recirculation control valve 14 (step 3).

If the warm-up is completed, steps 4 and 5
Engine speed Ne and control lever opening C detected by
Read the LV. Then, in step 6, the reference value of the EGR correlation parameter PRM, that is, the reference EGR correlation parameter PRM1 is determined based on the map assigned to the engine speed Ne and the lever opening CLV as shown in FIG. Further, at step 7, the fresh air flow rate detected by the air flow meter 23 is read as the measured EGR correlation parameter PRM2, and at step 8, the ratio K1 (= PRM2 / PRM1) between the reference EGR correlation parameter PRM1 and the measured EGR correlation parameter PRM2. Ask for. The characteristics shown in FIG. 5 are ideally set so that the two parameters match.

Next, at step 9, the opening degree of the intake throttle valve 22 is set based on the engine speed Ne and the lever opening degree CLV with reference to the characteristic map shown in FIG. The opening degree of the intake throttle valve 22 becomes smaller on the low speed and low load side so that a large amount of exhaust gas recirculation is performed on the low speed and low load side. Similarly, in step 10, the reference duty ratio D0 of the control signal of the negative pressure control solenoid valve 18 is set to the engine speed Ne and the lever opening CL.
Based on V and V, it is set with reference to the characteristic map shown in FIG. This reference duty ratio D0 also has a relatively large value in order to increase the opening degree of the exhaust gas recirculation control valve 14 on the low speed and low load side.

Then, in step 11, the required duty ratio DN is corrected with the reference duty ratio D0 corrected.
To decide. Specifically, it is calculated as DN = D0 × K1 × K2. Here, K1 is the above-mentioned parameter ratio, K2
Is a correction coefficient set based on the engine speed Ne and the lever opening CLV.

Next, the required duty ratio DN obtained as described above is compared with predetermined upper limit value DH and lower limit value DL in steps 12 and 15. Upper limit value DH
If the required duty ratio DN is larger than the required duty ratio DN, the duty ratio D actually output as the control signal is fixed to the upper limit value DH (step 13). Then, the absolute value of the difference between the required duty ratio DN and the upper limit value DH is obtained as ΔD1 (step 14). When the required duty ratio DN is smaller than the lower limit value DL, the duty ratio D actually output as a control signal is fixed to the lower limit value DL (step 1
6) And, the absolute value of the difference between the required duty ratio DN and the lower limit value DL is obtained as ΔD2 (step 17). Also,
From step 14 or step 17 to step 18
And the injection timing correction amount ΔIT is set to ΔD1 or ΔD2.
Based on. This is determined according to the characteristics shown in FIG.

Further, the required duty ratio DN is from the upper limit value DH to
If it is within the range of the lower limit value DL, the duty ratio D actually output is set to a value equal to the required duty ratio DN (step 19), and the injection timing correction amount ΔIT is set to 0 (step 20).

Next, in step 21 of FIG. 4, the basic injection timing IT0 is read. This is set based on the engine speed Ne and the lever opening CLV with reference to the map shown in FIG. Then, the injection timing correction amount ΔIT is added to the basic injection timing IT0 to determine the injection timing IT,
A control signal corresponding to this is output to the timing control valve 27 (step 22). Also step 2
In 3 and 24, the intake throttle valve opening degree determined in step 9 and the duty ratio D determined in steps 13, 16 and 19
To the step motor 21 and the negative pressure control solenoid valve 18 respectively.

As described above, in the above embodiment, as the duty ratio D of the negative pressure control solenoid valve 18, the lower limit value D shown in FIG.
Since only the stable range from L to the upper limit value DH is used, the control accuracy of the exhaust gas recirculation amount by the duty ratio D can be kept high. Further, in a region where the required duty ratio DN is equal to or higher than the upper limit value DH, the exhaust gas recirculation amount becomes insufficient, but the fuel injection timing IT is corrected to the retard side so as to compensate for this, so that NOx is generated. It can be surely suppressed. On the contrary, the exhaust gas recirculation amount becomes excessive in a region where the required duty ratio DN is equal to or lower than the lower limit value DL, but the fuel injection timing IT is corrected to the advance side correspondingly, so that the occurrence of smoke is suppressed. .

In the above embodiment, the fresh air flow rate of the engine is detected as a parameter having a correlation with the exhaust gas recirculation amount, but the present invention is not limited to this, and various other parameters are used. Can be used. Figure 1
1 is an example of the intake passage 11 and the exhaust gas recirculation passage 1.
3 is provided with an EGR orifice 31, a first pressure sensor 32 for detecting the pressure in the exhaust gas recirculation passage 13 between the EGR orifice 31 and the exhaust gas recirculation control valve 14, and a pressure in the intake passage 11 And a second pressure sensor 37 for detecting the above. The differential pressure between the two pressures is used as an exhaust gas recirculation amount correlation parameter. Further, FIG. 12 shows a configuration in which a second pressure sensor 33 that detects the pressure in the intake passage 11 and a third pressure sensor 34 that detects the pressure in the exhaust passage 12 are provided, and the differential pressure between the two pressures is exhausted. It is used as a circulation amount correlation parameter.
In addition, the pressure in the exhaust gas recirculation passage 13 detected by the first pressure sensor 32 or the pressure in the exhaust gas recirculation passage 12 detected by the third pressure sensor 34 is used alone as an exhaust gas recirculation amount correlation parameter. You can also

[0021]

As is apparent from the above description, according to the exhaust gas recirculation control device for a diesel engine of the present invention, the duty ratio of the negative pressure control solenoid valve for variably controlling the opening of the exhaust gas recirculation control valve is set to a predetermined value. Since it is regulated within the range of the lower limit value and the upper limit value of, that is, within the stable range with high control accuracy, it is possible to prevent deterioration of control accuracy. When the required value exceeds the lower limit value and the upper limit value, the fuel injection timing is corrected so as to compensate for the excess or deficiency of the exhaust gas recirculation amount, and the increase of NOx or the increase of smoke is suppressed. Therefore, under various operating conditions, the overall reduction of NOx can be achieved while preventing the deterioration of smoke.

[Brief description of drawings]

FIG. 1 is a claim correspondence diagram showing a configuration of the present invention.

FIG. 2 is a structural explanatory view showing a mechanical structure of an exhaust gas recirculation control device according to the present invention.

FIG. 3 is a flowchart showing the contents of exhaust gas recirculation control of this embodiment.

FIG. 4 is a flowchart following FIG. 3;

FIG. 5 is a characteristic diagram showing characteristics of a reference EGR correlation parameter PRM1.

FIG. 6 is a characteristic diagram showing a characteristic of an intake throttle valve opening.

FIG. 7 is a characteristic diagram showing characteristics of a reference duty ratio D0.

FIG. 8 is a characteristic diagram showing characteristics of an injection timing correction amount ΔIT.

FIG. 9 is a characteristic diagram showing characteristics of a basic injection timing IT0.

FIG. 10 is a characteristic diagram showing a relationship between a duty ratio and a negative pressure and a relationship between the negative pressure and an exhaust gas recirculation amount.

FIG. 11 is a structural explanatory view showing a different embodiment of the present invention.

FIG. 12 is a structural explanatory view showing still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Exhaust gas recirculation control valve 2 ... Negative pressure control solenoid valve 3 ... Parameter detection means 4 ... Required duty ratio setting means 5 ... Output means 6 ... Injection timing correction means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display area F02D 43/00 301 JN

Claims (1)

[Claims] 1. A negative pressure type exhaust gas recirculation control valve provided in an exhaust gas recirculation passage extending from an exhaust system to an intake system of a diesel engine, and an exhaust gas recirculation control valve provided between a negative pressure chamber and a negative pressure source. The negative pressure control solenoid valve that changes the negative pressure according to the duty ratio, the parameter detection means that detects one or more parameters that correlate with the exhaust gas recirculation amount, and the target exhaust gas recirculation amount is obtained using this parameter. Required duty ratio setting means for setting the required duty ratio necessary for the output of the control signal of the duty ratio according to the required duty ratio, and when the required duty ratio exceeds a predetermined lower limit value or upper limit value. Output means for restricting the actual duty ratio to the lower limit value or the upper limit value, and both when the required duty ratio exceeds the lower limit value or the upper limit value. Exhaust gas recirculation control device for a diesel engine, characterized by comprising, an injection timing correction means for correcting the fuel injection timing according to the difference.