JPH02267358A - Exhaust gas recirculation control device for diesel engine - Google Patents

Abstract

PURPOSE:To control intake negative pressure to be approximately constant even after stopping EGR so as to improve warming-up performance by controlling the switching of the operation/stop of EGR and that of an intake throttle valve independently according to the engine temperature when the engine is cold, on the basis of the first and second specified temperature. CONSTITUTION:An EGR valve 7 driven by an actuator 8 is provided at the opening part 6a, to an intake passage 4, of an EGR passage 6, as well as an intake throttle valve 9 is provided more on the upstream side of the intake passage 4 than the EGR passage opening part 6a. This intake throttle valve 9 is controlled by a vacuum modulator 17 and an actuator 10 so as to keep intake negative pressure constant, thus functioning as a constant pressure control mechanism. When the cooling water temperature detected by a water temperature sensor 30 becomes lower than the first specified temperature T1, the EGR is put off and the constant pressure control is continued, and when the cooling water temperature becomes lower than the second specified temperature T2 (<T1), the constant pressure control is stopped, a switching valve 24 is changed over to the atmospheric air side, and the intake throttle valve 9 is opened to full admission.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to exhaust gas recirculation (hereinafter referred to as EG) of diesel engines.
(also referred to as R) relates to a control device.

[Conventional technology]

Conventionally, an exhaust passage and an intake passage are provided with an EGR passage that communicates with each other, and an intake throttle valve is provided upstream of the EGR passage opening of the intake passage, so that the negative pressure downstream of the intake throttle valve is kept approximately constant. An exhaust recirculation control device for a diesel engine is known in which the opening degree of an intake throttle valve is adjusted using a vacuum modulator or the like (for example, the
(Japanese Utility Model Publication No. 2-4663, Japanese Utility Model Publication No. 1983-100052), and a device that corrects the intake throttle valve to the required opening when switching the EGR valve is also known (Japanese Utility Model Publication No. 60-4).
No. 9254, Japanese Utility Model Application No. 60-49256).

(Problem to be solved by the invention) However, the above-mentioned Japanese Utility Model Publication No. 62-4663 and Japanese Utility Model Publication No. 5
In the constant pressure control of intake negative pressure as disclosed in Publication No. 5-100052, the intake negative pressure is increased over almost the entire engine speed range to increase the EGR rate (the ratio of EGR gas to intake air) and reduce NOx. However, since intake throttling, that is, constant pressure control is also turned on and off in synchronization with turning on and off of EGR, the following problems may occur.

That is, since EGR is normally stopped during the warm-up process, the intake throttle by the intake throttle valve is also stopped. However, when the intake throttle is stopped, the amount of intake air increases, and a large amount of cold air is introduced into the engine that has not yet been warmed up, causing the heat energy generated by combustion to be exhausted along with a large amount of exhaust gas. As a result, warm-up performance is impaired.

Another problem is that intake noise increases as the amount of intake air increases.

In this regard, the above-mentioned Utility Model Publication No. 60-49254.60-4925
In the device disclosed in Publication No. 6, EGR is stopped and the intake throttle valve is controlled to generate a target negative pressure when the temperature is low.

However, with this control, constant pressure control of the intake negative pressure is performed even when the engine temperature becomes low, so if the amount of fuel injection is increased, the amount of intake air may be insufficient, or the compression pressure may be insufficient. This may result in an insufficient rise in the cylinder air temperature, leading to a misfire.

The present invention has focused on the above-mentioned problems, improves warm-up performance while preventing misfires when the engine is at low temperature, and achieves excellent control by controlling the intake negative pressure path at a constant pressure within an allowable range even at low temperatures. The aim is to maximize effectiveness.

Means for Solving Problem C] The exhaust gas recirculation control device for a diesel engine according to the present invention in accordance with this object includes an EGR passage that communicates an exhaust passage with an intake passage, and has an EGR passage upstream of the EGR passage opening of the intake passage. Exhaust recirculation of a diesel engine equipped with a constant pressure control mechanism that detects negative pressure downstream of the intake throttle valve and can adjust the opening degree of the intake throttle valve to keep the negative pressure approximately constant. In the control device, the constant pressure control mechanism is configured to stop EGR when the temperature of the engine becomes equal to or higher than a first predetermined temperature, and to continue approximately constant pressure control of the intake negative pressure by the constant pressure control mechanism; is connected to a control device so as to stop the substantially constant intake negative pressure control and fully open the intake throttle valve when the temperature reaches a second predetermined temperature, which is lower than the second predetermined temperature.

(Function) In such an exhaust recirculation control device, regarding the engine temperature, there are constant pressure control that adjusts the opening of the intake throttle valve so as to keep the intake negative pressure approximately constant, and EGR on/off switching control. , are performed independently without interlocking, especially at low temperatures.

In a region where the engine temperature is lower than the first predetermined temperature and higher than the second predetermined temperature, EGR is stopped, but constant pressure control of the intake negative pressure is performed. The operation of the intake throttle valve is controlled to maintain a predetermined intake negative pressure, so when EGR is stopped, the amount of intake air is increased by that amount, thereby stabilizing combustion. However, at this time, the intake throttle is operating under constant pressure control, and the amount of intake air is appropriately throttled to improve warm-up performance and reduce intake noise and vibration. When the engine temperature becomes lower than the second predetermined temperature, the intake throttle valve is fully opened, so that a sufficient amount of intake air is secured, the compression pressure in the combustion chamber is increased, and misfires are prevented.

〔Example〕

Preferred embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show an exhaust gas recirculation control device for a diesel engine according to an embodiment of the present invention. In FIG. 0, l is the diesel engine body, 2 is a fuel injection pump, and 3 is a control device. It shows an ECU (electronic control unit). 4 is an intake passage to the engine 1, 5 is an exhaust passage from the engine 1, and an EGR passage 6 is provided which communicates the exhaust passage 5 and the intake passage 4. This EGR
An EGR valve 7 is provided at an opening 6a of the passage 6 to the intake passage 4, and the EGR valve 7 is operated by an actuator 8 having a diaphragm.

An intake throttle valve 9 is provided upstream of the EGR passage opening portion 6a of the intake passage 4. The opening degree of the intake throttle valve 9 can be adjusted by an actuator 1° having a diaphragm.

The control system for actuating actuator 8.10 is constructed as follows.

Reference numeral 11 denotes a vacuum pump, in which driving negative pressure is generated. The negative pressure from the vacuum pump 11 is EVR
EV(ii) is introduced into the negative air negative pressure regulating valve 12 and the VSV (vacuum switching pulp) 13.EVRV1
2, the introduction of negative pressure from the vacuum pump 11 to the actuator 8 is controlled.

That is, the target value of the control negative pressure to be supplied to the EGR valve actuator 8 is calculated within the ECU 3 based on information on the engine operating state inputted from various sensors. This target value is determined to be an EGR degree that provides the optimum EGR rate under the engine operating state at that time. EC
U3 converts the duty signal corresponding to the above target value to EVRV.
Give to 12. The EVRV 12 adjusts the rate at which negative pressure from the vacuum pump 11 and atmospheric pressure are introduced into the actuator 8 in accordance with the duty signal. Furthermore, during exhaust gas recirculation, the VSV 15 supplies the control negative pressure to the pressure sensor 14, and the ECU 3 corrects the duty signal based on the deviation between the actual control negative pressure detected by the pressure sensor 14 and the target value. Feedback control is performed so that the actual control negative pressure matches the target value. 5V15 supplies intake negative pressure to the pressure sensor 14 when exhaust gas recirculation is stopped.

The negative pressure downstream of the intake throttle valve 9 is introduced into the vacuum modulator 17 through the filter 16, and the opening degree of the intake throttle valve 9 can be adjusted via the vacuum modulator 17 and the actuator 10 so that the negative pressure is kept approximately constant. It has become. As shown in FIG. 2, the vacuum modulator 17 has a diaphragm valve structure, and negative intake pressure is introduced into a diaphragm chamber 19 provided with a spring 18, and another chamber 20 is communicated with the atmosphere. diaphragm 21
Negative pressure from the vacuum pump 11 is introduced into the valve body 22 of the valve body 22, and when the intake negative pressure is higher than the set value, the valve body 22 moves to the diaphragm chamber 19 side, and the negative pressure from the vacuum pump 11 is introduced into the valve body 22. is bled, the output negative pressure to the actuator 10 decreases, and the opening of the intake throttle valve 9 is adjusted in the opening direction until the intake negative pressure reaches a target value (set value). When the intake negative pressure is lower than the set value, the valve body 22
stops the negative pressure from bleeding from the vacuum pump 11,
The negative pressure from the vacuum pump 11 is directly output to the actuator 10, and the opening of the intake throttle valve 9 is adjusted in the closing direction until the intake negative pressure reaches a target value (set value). Therefore, these constitute a constant pressure control mechanism that adjusts the opening degree of the intake throttle valve 9 so as to keep the intake negative pressure substantially constant.

A VSV 23 and a VSV 24 are interposed between the vacuum modulator 17 and the actuator 10. V
The SV 23 selects either the negative pressure via the constant pressure control mechanism or the source pressure from the vacuum pump 11 as the output to the actuator 10 . (2) 5V24 selects either negative pressure from VSV23 or atmospheric pressure as the output to actuator 10.

The actuator 10 that adjusts the opening degree of the intake throttle valve 9 is
A chamber 27 divided by diaphragms 25 and 26 and communicating with the atmosphere, a chamber A 28 into which pressure from the VSV 24 is introduced, and either negative pressure or atmospheric pressure from the vacuum pump 11 switched by the VSV 13 is introduced. It has a B chamber 29. A connecting rod 30 with the intake throttle valve 9 is provided on the diaphragm 25 side, and the diaphragm 2
The intake throttle valve 9 is opened through the movement of the opening 7 and the opening 30 with the movement of the intake throttle valve 9.
The opening degree is adjusted.

A spring 31 is provided in the A chamber 28, and a seat 32
diaphragm 25 on the rod 30 side (intake throttle valve 9
(opening direction).

A stopper member 33 is provided on the A chamber 28 side of the diaphragm 26.
is provided protrudingly, and the diaphragm 25 is connected to the diaphragm 2.
When it moves to the 6 side and comes into contact with the tip of the stopper member 33, it becomes possible to restrict further movement of the diaphragm 25 toward the diaphragm 26 side, and therefore prevent the intake throttle valve 9 from operating in the closing direction below a certain opening degree. ing.

Since this stopper member 33 is provided on the diaphragm 26, it moves with the movement of the diaphragm 26. Since the B chamber 29 is provided with a spring 34 that biases the diaphragm 26 in the direction of the diaphragm 25,
When atmospheric pressure is introduced into the chamber 29, the spring 3
4, the diaphragm 26 is pressed against the seat member 32 and the stopper member 33 is held in the position shown in FIG.
When negative pressure from the vacuum pump 11 is introduced into the chamber 29, the diaphragm 2 is moved against the force of the spring 34.
6 moves in a direction to reduce the size of chamber B 29, and accordingly, stopper member 33 is also moved in the same direction. Therefore, the opening degree of the intake throttle valve 9 is controlled by the movement of the diaphragm 25 by the stopper member 33.
can be changed to a regulation position where the opening degree is even lower (for example, fully closed).

In this embodiment, the stopper member 33 is replaced by the diaphragm 26.
Although it was installed on the A chamber 28 side of the diaphragm 25,
The same function can be obtained even if it is installed on the side.

EVRV12, VSV13.15.23.24 are EC
It is operated based on a command from U3. The ECU 3 receives an accelerator opening signal as an engine load signal from a lever relationship sensor 35 attached to the fuel injection pump 2, and an engine rotational speed from an engine rotational speed sensor 36. A signal from an adjustment resistor 37 for adjusting temperature, a signal from a pressure sensor 14, and a signal from an engine water temperature sensor 38 are input. Further E
The CU 3 receives a signal from a vehicle speed sensor 39, a neutral (N) position signal 40 for a vehicle equipped with an automatic transmission, and a signal from an ignition switch 41 (engine on/off signal). The signal from the ignition switch 41 is also used as a signal for operating ■S■13. The ECU 3 further outputs a signal 42 to the near conditioner amplifier and a signal 43 to the automatic transmission.

Note that 44 represents a boost compensator for regulating the maximum value of the fuel injection amount using negative pressure, and 45 represents a fuel cut valve.

The operation of the apparatus configured as described above and the control according to the present invention will be explained.

First, the operation control of the intake throttle valve 9 will be explained with reference to Table 1 and FIGS. 3 to 6.

The opening degree of the intake throttle valve 9 is controlled via the actuator 10, and the operation of the actuator IO is controlled according to VSv13.23.
．． 24 and vacuum modulator 17. The operation mode of the intake throttle valve 9 is shown in Table 1.

When the ignition switch 41 is switched from on to off, that is, when the engine is stopped, VSV13.23.
24 are all turned off, and as shown in FIG.
, B chamber 29, a constant negative pressure from the vacuum pump 11 sufficient to move the intake throttle valve 9 is introduced (the shaded area in the figure indicates the introduction of negative pressure), and the intake throttle valve 9 is kept fully open. . Therefore, when the engine is stopped while it is running, the intake throttle valve 9 is fully closed to strongly restrict the amount of air intake, and the pressure 11 resistance of the rotating engine due to inertia is suppressed to a low level, thereby reducing shocks and vibrations. generation is suppressed and the engine is stopped quietly. At this time, the fuel supply is also cut off by the fuel cut valve 45, and combustion is stopped naturally and quietly.

During deceleration, the VSV 13 is turned on and the B chamber 29 is opened to the atmosphere, and the VSV 23.24 is turned off and negative pressure from the vacuum pump 11 is introduced into the A chamber 28. At this time, as shown in FIG. 4, the diaphragm 26
The diaphragm 2 is held in a fixed position by the diaphragm 2.
5 is held at a position that abuts the tip of a stopper member 33 that is held at a fixed position together with the diaphragm 26, and the intake throttle valve 9 is held at a half-open position. By keeping the intake throttle valve 9 half-open, a predetermined amount or more of intake air is ensured even when the load is low, and intake muffled noise during deceleration is reduced.

At full load (acceleration), VSV13.24 is turned on, atmospheric pressure is introduced into both chamber A 28 and chamber B 29, and the fifth
As shown in the figure, the intake throttle valve 9 is kept fully open.

The intake air is not substantially throttled, ensuring a sufficient amount of intake air and suppressing smoke.

In medium and low load range, VSV13.23 on, VS
V24 is turned off, the B chamber 29 is opened to the atmosphere, the output negative pressure from the vacuum modulator 17 is introduced into the A chamber 28, and the opening degree of the intake throttle valve 9 is controlled so that the intake negative pressure becomes approximately constant pressure. Ru. Vacuum modulator 17 at this time
The operation is as described above.

This constant pressure control maintains a stable intake negative pressure and prevents a shortage of intake air, so a predetermined EGR rate can be easily obtained and the target exhaust gas purification performance can be achieved.

In the low speed (low rotation speed) low load range, each VSV13.
The operating modes of 23 and 24 are the same as the modes in the low load range mentioned above. However, since atmospheric pressure is introduced into the B chamber 29 and the diaphragm 26 and the stopper member 33 are held at the fixed positions shown in FIG. 2, the negative pressure introduced into the A chamber 28 from the vacuum modulator 17 As a result, the movement of the diaphragm 25 that attempts to move the intake throttle valve 9 in the closing direction is regulated by the tip of the stopper member 33, and the intake throttle valve 9 is ultimately kept in a half-open state. Therefore, a sufficient amount of air is ensured even at low rotational speeds, and the intake negative pressure is reduced. As a result, excessive EGR rate in the low rotational speed range is prevented when constant pressure control is adopted, which has been a problem in the past.

In this way, in the above device, the opening degree of the intake throttle valve 9 can be controlled to an appropriate state depending on the engine operating state.

In the present invention, depending on the engine temperature (engine cooling water temperature) detected by the engine water temperature sensor 38, switching of F and GR operation (on) and stop (off), constant pressure control of the intake throttle valve 9, and Switching of full open control is performed as follows. In other words, when the engine coolant temperature THW detected by the sensor 38 becomes equal to or lower than the first predetermined temperature T, EGR is turned off, but the constant pressure control continues. A second predetermined temperature T where THW is lower than TI! When the temperature is below 6T, the VSV 24 is turned on and the intake throttle valve 9 is fully opened.
! is set, for example, to about 10°C.

This control is performed, for example, as shown in FIGS. 7 and 8.

FIG. 7 shows EGR control. First, step 2
At step 01, data for determining the operating state of various engines such as THW is read, and at step 202, it is determined whether or not other EGR off conditions other than THW are satisfied.
If it is true, EGR is turned off in step 203,
If other EGR off conditions are not met, it is determined in step 204 whether THW is lower than T,
If the value is lower than that, the stem 203 turns off the EGR. T.

If this is the case, EGR is turned on in step 205.

FIG. 8 shows a control flow for switching between fully opening the intake throttle valve 9 and introducing negative pressure from the vacuum modulator 17 into the actuator 10 to perform intake negative pressure path constant pressure control. performs switching control,
This control is not linked to the EGR control shown in FIG. 7, but is performed independently. First, step 301
Data such as THW is read in. Then, in step 302, it is determined whether or not a condition other than THW, that is, the intake throttle valve 9 is fully open (VSV 24 on) is satisfied. Fully open the intake throttle valve, in other words, turn off the intake throttle. If conditions other than THW are not met, it is determined in step 304 whether THW is smaller than T2, and if it is smaller than T, the intake throttle valve is fully opened (intake throttle OFF) in step 303. Tt), the intake throttle is turned on (VS
V24 off), that is, constant pressure control is performed.

Therefore, as shown in FIG. 9, the first predetermined temperature T1
If the temperature is below, EGR is stopped, but intake negative pressure constant pressure control is performed, and the amount of intake air is appropriately throttled to improve warm-up performance. When the temperature falls below T2, the intake throttle valve 9 is fully opened to ensure a sufficient amount of intake air and prevent misfires.

In addition, in the apparatus of this embodiment, control other than the control regarding THW is performed according to the control area map shown in FIG. 10, for example. Figure 10 shows the engine speed and accelerator opening (in addition to EGR activation and stop control).
This shows what has been set as a map regarding load). In Fig. 10, the shaded area is the constant pressure control area 1.
01, area 102 is the fully open area of the intake throttle valve 9, area 103 is the half open area of the intake throttle valve 9, and double hatched area 10
4, although the negative pressure from the vacuum modulator 17 is introduced into the A chamber 28 of the actuator 10 and the constant pressure control system operates, in reality, the movement is restricted by the stopper member 33 and the intake throttle valve 9 is in a half-open state. This is an area that can be preserved. EGR is turned on and off in the region between the operating boundaries 111 and 112, and the region 105 between the 0 operating boundaries 111 and 113, which is the optimum EGR rate in the constant pressure control region, is equivalent to Although the load is high, the intake throttle valve 9 is not fully open, and the intake noise can be reduced by controlling the intake throttle valve 9. Since this region is close to full load, EGR is turned off.

In the control in the constant pressure control region 101 and the region 104 (for example, on the characteristic line 114 (for example, the no-load characteristic line) in FIG. 7), the control in the low speed (low rotation speed) low load region described above is performed. In the low rotational speed range, the intake throttle valve 9 can be controlled to be fixed in a half-open state while performing EGR, and an excessive EGR rate in the low rotational speed range can be prevented.

[Effects of the Invention] As explained above, when the exhaust gas recirculation control device for a diesel engine of the present invention is used, the EGR operation and stop operation and the intake throttle operation and stop operation are performed depending on the engine temperature when the engine temperature is low. Since the switching between full open and full open is controlled independently based on the first predetermined temperature and the second predetermined temperature, the intake negative pressure path is maintained at a constant pressure even after EGR is stopped, improving warm-up performance. , vibration and noise can be reduced, and when the temperature drops further, the intake throttle valve can be fully opened to ensure a sufficient amount of intake air and prevent misfires.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of an exhaust recirculation control device for a diesel engine according to an embodiment of the present invention, FIG. 2 is an enlarged partial configuration diagram of the system shown in FIG. 1, and FIG. 3 is an intake throttle valve shown in FIG. 1. 4 is a partial configuration diagram showing a fully closed control state of the intake throttle valve. FIG. 5 is a partial configuration diagram showing a fully open control state of the intake throttle valve. A partial configuration diagram showing the intake negative pressure constant pressure control state of the throttle valve. Fig. 7 is a flow chart showing EGR control based on engine temperature. Fig. 8 is a flow chart showing intake throttling control based on engine temperature. Fig. 9 is a flow chart showing the engine cooling water temperature. FIG. 10 is a map showing an example of control of the intake throttle valve and EGR in terms of engine speed and accelerator opening. 1...Diesel engine 2...Fuel injection pump 3...ECU' (electronic control unit) as a control device 4...Intake passage 5... ...Exhaust passage 6...EGR passage 7...EGR valve 8...EGR actuator 9...
Intake throttle valve 10... Actuator 11... Vacuum pump 12... EVRV (electric negative pressure regulating valve) 13
．． 15.23.24...VSV (vacuum switching valve) 14...Pressure sensor 17...Vacuum modulator 21.25.
26...Diaphragm 32...Seat portion 33...Stock collar member 35...Lever opening sensor 36...Engine rotation speed sensor 38.・・・・・・
・Engine water temperature sensor 41...Ignition switch 45...
...Fuel cut valve T, ...First predetermined temperature Tt...Second predetermined temperature

Claims (1)

[Claims] 1. An EGR passage communicating an exhaust passage and an intake passage, and an intake throttle valve upstream of the EGR passage opening of the intake passage, detecting negative pressure downstream of the intake throttle valve and controlling the negative pressure. In the exhaust recirculation control device for a diesel engine, which is equipped with a constant pressure control mechanism that can adjust the opening degree of an intake throttle valve to keep the temperature substantially constant,
When the temperature reaches the first predetermined temperature or higher, EGR is stopped and the constant pressure control of the intake negative pressure is continued by the constant pressure control mechanism, and when the temperature falls below the second predetermined temperature, which is lower than the first predetermined temperature, the EGR is stopped. An exhaust recirculation control device for a diesel engine, characterized in that the device is connected to a control device to stop the substantially constant intake negative pressure control and fully open the intake throttle valve.