JP4020117B2 - Exhaust gas recirculation control device for diesel engine - Google Patents

Description

  The present invention relates to an exhaust gas recirculation (hereinafter referred to as EGR) control device for a diesel engine.

As a conventional EGR control device for a diesel engine, there is one disclosed in, for example, Patent Document 1. In this system, the opening degree of the EGR control valve is controlled so that the actual measurement value and the target value coincide with each other, thereby suppressing the control opening degree from decreasing due to carbon adhesion to the valve body (Patent Literature). 1).
Japanese Unexamined Patent Publication No. 57-44760

  However, generally, even under the same operating conditions for each engine, the intake air flow varies due to variations in the intake system, and the opening of the intake throttle valve that changes the opening area of the intake passage in multiple stages also varies. As a result, the intake air flow rate during EGR control also varies.

  For this reason, if the control is performed with the preset target value, the smoke discharge characteristic deteriorates on the high load side, the EGR amount is not appropriate even during EGR control, the NOx reduction effect is reduced, and the smoke discharge characteristic is reduced. There was a problem of inviting deterioration.

  The present invention has been made in view of such a conventional problem. EGR of a diesel engine in which proper EGR control is performed by correcting various control amounts during EGR control according to the variation. An object is to provide a control device.

For this reason, as shown in FIG.
An exhaust gas recirculation passage branched from the exhaust passage of the diesel engine and joined to the intake air passage, an exhaust gas recirculation control valve interposed in the exhaust gas recirculation passage, and an intake air passage upstream of the junction of the exhaust gas recirculation passage A passage opening area control means for controlling the passage opening area, an exhaust gas recirculation control valve control means for controlling the opening degree of the exhaust gas recirculation control valve according to the engine operating state, and an intake air flow rate provided in the intake passage. In an exhaust gas recirculation control device for a diesel engine comprising an intake air flow rate detection means,
Detected by the intake air flow rate detecting means when the opening area of the intake passage is controlled to a predetermined value by the passage opening area control means based on the operating state in the operating state where fuel supply to the engine is stopped A comparison means for comparing the intake air flow rate with a target intake air flow rate set based on the engine operating state under the conditions;
When the target intake air flow rate is larger than the detected intake air flow rate, the opening degree of the exhaust gas recirculation control valve is decreased, and when the target intake air flow rate is smaller than the detected intake air flow rate, the exhaust gas recirculation control valve is opened. A control amount correction amount setting means for setting and storing a correction amount for correcting the control amount of the opening degree of the exhaust gas recirculation control valve so as to increase the degree ,
It is characterized by including.

According to the first aspect of the invention, when the fuel supply is stopped, the intake passage opening area is controlled to a predetermined value, and the target intake air flow rate and the actual intake air flow rate set based on the engine operating state at that time are When the target intake air flow rate is larger than the detected intake air flow rate, the opening degree of the exhaust gas recirculation control valve is decreased, and when the target intake air flow rate is smaller than the detected intake air flow rate, the exhaust gas recirculation control By setting a correction amount for correcting the control amount of the exhaust gas recirculation control valve so as to increase the valve opening, and correcting the control amount using this correction amount, The influence can be reduced.

Embodiments of the present invention will be described below with reference to the drawings.
In FIG. 1 showing the configuration of one embodiment, an air flow meter 23 and an intake throttle valve 3 for detecting an intake air flow rate are provided in an intake passage 1 connected to an engine body 100. Similarly, an EGR passage 5 branched from the exhaust passage 4 connected to the engine body 100 and joined to the intake passage 1 downstream of the intake throttle valve 3 is connected, and an EGR control valve 6 is interposed in the EGR passage 5. Has been. The EGR amount is controlled by adjusting the opening of the intake throttle valve 3 and the EGR control valve 6 so that the air flow meter output stored in advance in the engine control unit 7 is obtained.

The opening degree of the intake throttle valve 3 is such that negative pressure generated by a vacuum pump (not shown) is negatively controlled by the first solenoid valve 12 and the second solenoid valve 13 via the negative pressure passages 9, 10, 11. Thus, switching control is performed in three stages of fully open, half open, and fully closed.
Specifically, when the energization of both the first solenoid valve 12 and the second solenoid valve 13 is OFF, the atmospheric pressure is introduced into the pressure chamber 3A of the intake throttle valve 3 and the intake throttle valve 3 is fully opened. When the first solenoid valve 12 is turned on and the second solenoid valve 13 is turned off, the pressure obtained by diluting the negative pressure from the vacuum pump in the atmosphere is introduced into the pressure chamber 3A, and the intake throttle valve 3 is opened halfway. When the first solenoid valve 12 and the second solenoid valve 13 are both ON, the negative pressure from the vacuum pump is directly introduced into the pressure chamber 3A, and the intake throttle valve 3 is fully opened. Set to position.

  On the other hand, the EGR control valve 5 is equipped with a lift sensor 24 for detecting the opening degree (the lift amount of the valve body), and the opening degree of the EGR control valve 5 is set so that the negative pressure generated by the vacuum pump is reduced to the negative pressure passage 9, 14 is sent to the duty control valve 8 through 14 to increase or decrease the duty ratio, thereby appropriately introducing the atmosphere to dilute the signal negative pressure, thereby detecting the actual opening degree with the lift sensor 15 in advance. The feedback control is performed so that the opening degree stored in FIG.

  The opening control of the intake throttle valve 3 and the EGR control valve 6 is performed when the control unit 7 controls the first solenoid valve 12 and the second solenoid valve based on the engine operating state, for example, the engine rotational speed, the load, and the coolant temperature. 13 and the duty control valve 8 are controlled.

  FIG. 3 is a block diagram showing details of the control unit 7. The CPU 71, ROM 72, RAM 73, and input / output circuit (hereinafter referred to as I / O) 74 are included. The I / O 74 includes a rotational speed sensor 21 that detects an engine rotational speed N, an accelerator opening sensor 22 that detects an accelerator opening (accelerator pedal depression amount), an air flow meter 23 that detects an intake air flow rate, and the EGR control valve 5. Outputs such as a lift sensor 24 for detecting the opening degree, a water temperature sensor 25 for detecting the cooling water temperature, and a fuel temperature sensor 26 for detecting the fuel temperature are input. The CPU 71 fetches information from the I / O 74 according to a program stored in the ROM 72 and performs arithmetic processing to control the fuel injection amount and fuel injection timing, the fuel injection pump 31, the duty control valve 8, and the first solenoid valve 12. Then, data that is a control amount for controlling the second electromagnetic valve 13 is set in the I / O 74, whereby the fuel injection amount, the fuel injection timing, the EGR amount, and the intake air flow rate are controlled. The RAM 73 is used to temporarily save data related to the arithmetic processing of the CPU 71.

An example of each control will be described with reference to the flowcharts of FIGS. Here, in the present invention, the fuel injection amount and the target opening values of the intake throttle valve 3 and the EGR control valve 5 are corrected according to various variations in the intake system.
Step (denoted as S in the figure. The same applies hereinafter) In 310, various operating conditions such as engine speed Ne, accelerator opening Acc, air flow meter output Va, EGR control valve opening Le, cooling water temperature Tw, fuel temperature Tf, etc. Read data.

  Next, at step 320, based on the characteristics shown in FIGS. 6 to 11 stored in the ROM 72 based on the engine speed Ne and the accelerator opening Acc, the basic injection amount QN, the basic injection timing ITN, Air flow rate GaN, basic EGR valve opening degree LeN or basic duty ratio DpN, and intake valve control signals Vs1, Vs2 are calculated.

Next, at step 330, based on the value of the accelerator opening Acc read at step 310, it is determined whether or not the accelerator is fully opened, that is, is in a full load state. If the accelerator is not fully opened, the process proceeds to step 410 and later described. If it is determined in step 330 that the accelerator is fully open, the process proceeds to step 340, and the difference between the basic air flow rate (target air flow rate) GaN read in step 320 and the actually detected air flow rate Ga ( ΔGa which is GaN-Ga) is calculated.
In step 350, based on the value of ΔGa calculated in step 340, for example, based on the characteristics of FIGS. 12 to 17 stored in the ROM 72, the corrected fuel injection amount ΔQ, the corrected air flow rate ΔGae, the corrected EGR valve The opening degree ΔLe or the correction duty ratio ΔDp is calculated.

  Here, for example, when ΔGa is a positive value and large, that is, the larger the shortage amount of the actual air flow rate Ga with respect to the target air flow rate GaN, the more easily the carbon discharge amount increases due to the shortage of air. Therefore, the corrected fuel injection amount ΔQ is set to a large negative value, and for the same reason, the corrected air flow rate ΔGae is set to a large positive value to increase the air flow rate, and the corrected EGR valve opening ΔLe and the corrected duty ratio ΔDp are set. Is set to a large negative value in order to reduce and correct the excess EGR rate due to air shortage. On the contrary, when the actual air flow rate Ga is larger than the target air flow rate GaN, it is set so that correction in the reverse direction is performed.

Finally, in step 360, the corrected fuel injection amount ΔQ, the corrected air flow rate ΔGae, the corrected EGR valve opening degree ΔLe, and the corrected duty ratio ΔDp are stored at predetermined addresses, and the process is terminated.
On the other hand, if it is determined in step 330 that the accelerator is not fully opened, the routine proceeds to step 430, where the fuel cut state such as when the engine brake is operated is based on the values of the engine speed Ne and the accelerator opening Acc read in step 310. It is determined whether or not. If it is not in the fuel cut state, this routine is terminated.

If it is determined in step 430 that the fuel is cut, the process proceeds to step 440. For example, the solenoid valve control signals Vs1, Vs2 are set so that the intake throttle valve opening corresponds to the engine speed N when the accelerator opening Acc = 15%. To control the intake throttle valve opening. Next, in step 450, the air flow meter output Va is read again.
Next, in step 460, a difference ΔGa between the target value GaN of the air flow rate stored in the ROM 72 and the actual air flow rate Ga is calculated.

Next, in step 470, based on the value of ΔGa calculated in step 460, the corrected EGR valve opening degree ΔLe or the corrected duty ratio ΔDp is calculated based on the characteristics shown in FIGS. In this characteristic, since the intake throttle valve 3 is throttled, a correction amount for ΔGa (absolute value) is set larger than the characteristics shown in FIGS.
Finally, in step 480, the corrected EGR valve opening degree ΔLe or the corrected duty ratio ΔDp is stored at a predetermined address, and this routine is terminated.

In this way, the fuel injection amount, the intake air flow rate, and the EGR control valve opening are corrected for variations in the intake system such as the intake air flow rate and intake throttle valve opening, so that the smoke emission characteristics and the NOx reduction performance by EGR can be achieved. It can be maintained well .

The block diagram which shows the structure and function of this invention. The system block diagram of the EGR control apparatus which concerns on one Example of this invention. The block diagram which shows the internal structure of the control unit of an Example same as the above. The flowchart which shows the front | former stage of the control routine of an Example same as the above. The flowchart which shows a back | latter stage similarly. The characteristic diagram of basic injection quantity. The characteristic diagram of basic injection timing. The characteristic diagram of basic air flow rate. The characteristic view of the basic EGR control valve opening. The characteristic diagram of basic duty ratio. ON-OFF characteristic diagram of solenoid valve. The characteristic figure of correction | amendment injection amount. The characteristic figure of correction | amendment air flow rate. The characteristic view of the correction opening degree of an EGR control valve. The characteristic figure of the correction | amendment duty ratio of an EGR control valve. The characteristic view of the correction opening degree of the EGR control valve in a fuel cut state. The characteristic figure of the correction | amendment duty ratio of an EGR control valve same as the above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Intake passage 3 Intake throttle valve 4 Exhaust passage 5 EGR passage 6 EGR control valve 7 Control unit 8 Duty control valve
12 First solenoid valve
13 Second solenoid valve
15 Lift sensor
23 Air flow meter

Claims (2)

An exhaust gas recirculation passage branched from the exhaust passage of the diesel engine and joined to the intake air passage, an exhaust gas recirculation control valve interposed in the exhaust gas recirculation passage, and an intake air passage upstream of the junction of the exhaust gas recirculation passage A passage opening area control means for controlling the passage opening area, an exhaust gas recirculation control valve control means for controlling the opening degree of the exhaust gas recirculation control valve according to the engine operating state, and an intake air flow rate provided in the intake passage. In an exhaust gas recirculation control device for a diesel engine comprising an intake air flow rate detection means,
Detected by the intake air flow rate detecting means when the opening area of the intake passage is controlled to a predetermined value by the passage opening area control means based on the operating state in the operating state where fuel supply to the engine is stopped A comparison means for comparing the intake air flow rate with a target intake air flow rate set based on the engine operating state under the conditions;
When the target intake air flow rate is larger than the detected intake air flow rate, the opening degree of the exhaust gas recirculation control valve is decreased, and when the target intake air flow rate is smaller than the detected intake air flow rate, the exhaust gas recirculation control valve is opened. A control amount correction amount setting means for setting and storing a correction amount for correcting the control amount of the opening degree of the exhaust gas recirculation control valve so as to increase the degree ,
An exhaust gas recirculation control device for a diesel engine, characterized by comprising: The exhaust gas recirculation control valve is composed of a duty-type control valve whose opening degree is controlled by a pressure adjusted by diluting a signal negative pressure introduced into the negative pressure introduction chamber by an atmosphere whose introduction time ratio is duty controlled. the control amount correction amount setting means, the diesel engine according to claim 1, characterized in that to set the correction amount of the control amount for correcting the opening degree of the exhaust gas recirculation control valve by modifying the duty ratio Exhaust gas recirculation control device.

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