JPH0385361A - Exhaust gas circulator of diesel engine - Google Patents

Abstract

PURPOSE:To prevent the generation of smoke by providing a first EGR valve of the opening port of large area operated at a small load, and a second EGR valve of the opening port of small area operated at a high load, and by providing a lift sensor on th second EGR valve, so as to control the amount of EGR with high accuracy at the high load. CONSTITUTION:On an EGR passage 5 by which an intake passage 3 and an exhaust passage 4 are connected together, a first EGR valve 67 of the opening port of large area operated at a high load, and a second EGR valve 7 of the opening port of small area operated at a high load are placed, and diaphragms 13, 14 at actuators 11, 12 are linked to the head of each valve rod 9, 10. Negative pressure operation chambers 19, 20 of the actuators 11, 12 are connected to a negative pressure source 26 such as a vacuum pump, through negative pressure passages 23, 24, as well as a common negative pressure passage part 25, and a solenoid valve 27 is arranged on the negative pressure passage part 25. On the second EGR valve 7, a potentiometer lift sensor 28 is provided so as to detect the amount of the lifting, whereby high accuracy control of the amount of EGR is performed according to the output thereof, at a high load.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an exhaust gas recirculation device for a diesel engine.

(Prior art) In diesel engines installed in automobiles, etc., exhaust gas recirculation (hereinafter referred to as EGR) is used to recirculate part of the exhaust gas to the intake system in order to reduce NOx in the exhaust gas and suppress the generation of smoke. That's what I mean.

) is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-352.
This has been conventionally known as described in Japanese Patent No. 55.

By the way, in the case of diesel engines, the excess air ratio is generally large, so the recirculated exhaust gas has almost no effect on engine output, especially at low loads, but as the load increases, the excess air ratio decreases, so the EGR If the amount is excessive, drivability deteriorates, such as the output decreases, and smoke becomes worse due to EGR.

Therefore, it is necessary to reduce the EGR amount as the engine load increases, and in particular, the EGR amount at high loads requires severe control depending on the engine load.

The above publication states that in order to prevent the EGR amount from becoming excessive and causing smoke due to the response delay of the EGR device during acceleration when the engine load suddenly increases,
Something like cutting is disclosed. However, this alone cannot optimally control EGR during high loads.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems, and is capable of controlling the EGR amount with high accuracy during high loads to prevent smoke generation and deterioration of drivability of a diesel engine. The purpose is to obtain a gas reflux device.

(Structure of the Invention) The present invention provides an advantage that when a single exhaust gas recirculation valve with a large opening area is used, the opening area changes rapidly with respect to the valve lift, so in a high engine load range where the amount of exhaust gas recirculation is small. Although it is difficult to perform highly accurate control, if multiple exhaust gas recirculation valves are combined and the recirculation amount is controlled by only the valve with a small opening area during high loads, it is possible to control the recirculation amount even in areas where the recirculation amount is small. This system focuses on the ability to perform highly accurate control, and its configuration is as follows. That is, the exhaust gas recirculation device for a diesel engine according to the present invention includes a first exhaust gas recirculation valve with a large opening area that operates at low loads, and a negative pressure operated type with a relatively small opening area that operates at least at high loads. A second exhaust gas recirculation valve is provided, a negative pressure regulating valve is interposed in the negative pressure passage that leads negative pressure to the negative pressure working chamber of the second exhaust gas recirculation valve, and a lift sensor is provided for controlling the amount of exhaust gas recirculation. is provided in the second exhaust gas recirculation valve.

(Function) When the load is low, the first exhaust gas recirculation valve with a large opening area operates, thereby recirculating a large amount of exhaust gas to the intake system. Further, when the load is high, the second exhaust gas recirculation valve, which has a relatively small opening area, operates, thereby finely controlling the amount of exhaust gas recirculation relative to the valve lift amount. Here, the second exhaust gas recirculation valve is actuated by the negative pressure adjusted by the negative pressure regulating valve, and at this time, the lift amount of the second exhaust gas recirculation valve is detected by the lift sensor, so that when the load is high, Accurate control of the amount of exhaust gas recirculation is performed.

(Example) Examples will be described below based on the drawings.

FIG. 1 is an overall system diagram of an embodiment of the present invention, FIG. 2 is a configuration diagram of its control system, and FIG. 3 is a structural diagram of main parts of the embodiment. In this embodiment, an intake passage 3 and an exhaust passage 4 downstream of the air cleaner 2 of the engine 1 are connected by an exhaust gas recirculation passage (EGR passage) 5, and the EGR passage 5 includes a first EGR valve 6 having a large opening area; A second EGR valve 7 with a small opening area is interposed. These E
The GR valves 6, 7 are arranged in a common casing 8 that forms part of the EGR passage 5, and each valve stem 9. At the head of the IO there is a diaphragm 13 of the actuator 11, 12, respectively.
, 14 are connected. And each diaphragm 13
, 14 are fixed to the casing 8 by being sandwiched between the edges of the cover 15.16, and coil springs 17.18
is the bottom of said cover 15, 16 and each diaphragm 13,
14 in a compressed state. Thus, within each cover 15,16 each diaphragm 13°! Negative pressure working chambers 19 and 20 are formed between each negative pressure working chamber 1 and
The negative pressure passages 23.24 connected to the negative pressure intake ports 21.22 of 9.20 are connected to a negative pressure source 26 such as a vacuum pump via a common negative pressure passage section 25. Further, a solenoid valve 27 is provided in the common negative pressure passage section 25, and a potentiometer-type lift sensor 28 is provided in the second EGR valve 7 to detect its lift amount.

The solenoid valve 27 is configured to be activated by energizing the solenoid coil 29 to leak the common negative pressure passage section 25 to the atmosphere, and is a control unit for duty-controlling the solenoid coil 29. 30 are installed. This control unit 30 includes a rotation speed signal and a load signal (fuel injection amount or accelerator opening) which are the outputs of a rotation sensor 32 and a load sensor 33 attached to a fuel injection pump 31.
is input, and the detected value of the lift sensor 28 is also input. In the control unit 30, first, the target valve lift amount (Lo) is determined by the map 34 from the engine rotation speed (N, ) and the accelerator opening degree (Ace) detected by the rotation sensor 32 and the load sensor 33; , the actual valve lift amount (L) is detected by the lift sensor 28, and the target value (L) of these valve lift amounts is determined.
The duty ratio is determined by the control logic 35 of the PI control based on the deviation between the actual value (L) and the actual value (L).

Then, energization control of the solenoid valve 27 is performed at that duty ratio, the operating negative pressure is adjusted, and the first EGR valve 6 and the second EGR valve 7 are controlled.

The valve lift characteristics of the first EGR valve 6 and the second EGR valve 7 are set as indicated by the solid lines (■) and (2) in FIG. 4(d). That is, in a region where the accelerator opening is close to zero, the first EGR valve 6. Both of the second EGR valves 7 are set at the maximum lift, with the first EGR valve 6 having a large opening area having a large maximum lift amount, and the second EGR valve 7 having a small opening area having a small maximum lift amount. As for the first EGR valve 6, as shown by the solid line (3), the lift amount decreases as the accelerator opening increases, and the lift amount becomes zero at a predetermined accelerator opening. On the other hand, for the second EGR valve 7, the solid line ■
As shown, the lift amount decreases as the accelerator opening degree increases, and the lift amount is set to be zero at an accelerator opening degree that is larger than the accelerator opening degree at which the lift amount of the first EGR valve 6 becomes zero. Note that the broken line indicates the range of error due to each variation. The lift sensor 28 operates in the region indicated by the arrow where the lift of the second EGR valve 7 changes.

By setting the lift characteristics as above, both E
The opening area of the GR valve 6.7 changes as shown in FIG. 6(c). Here, the solid line ■ represents the characteristics of the first EGR valve 6, and the solid line ■ represents the characteristics of the second EGR valve 7, respectively. The dashed line indicates the error range. Further, the difference between the exhaust pressure and the intake pressure changes as shown in FIG. Then, the overall EGR rate changes as shown by the solid line in FIG.

In FIG. 4(a), the dashed line indicates the required EGR rate corresponding to the target valve lift amount, and the broken line indicates the error range of the actual EGR rate. In this embodiment, in a low load range with a small accelerator opening, the first EGR valve 6 and the second EGR valve 7 are used together to increase the EGR rate, but in a high load range, only the second EGR valve 7 with a small opening area is used. Therefore, control with few errors is possible in a region where the EGR rate is small. In addition, the lift sensor 28
What is detected is the lift amount of the second EGR valve 7, but since the first EGR valve 6 and the second EGR valve 7 are operated by the same negative pressure, the lift amount of the second EGR valve 7 is detected by
The lift amount of the EGR valve 6 can be calculated from the lift amount of the second EGR valve 7, so that the overall EGR rate can be controlled with high precision.

Figures 5 and 6 show E in a diesel engine.
This figure shows how the emissive performance changes with respect to changes in the opening area of the GR valve under light loads (Fig. 5) and under high loads (Fig. 6). EGR at light load
Changes in smoke, No., or HC in response to changes in the opening area of the valve are gradual, but at high loads, the amount of change in response to changes in the opening area is significant.In particular, smoke becomes more pronounced as the opening area increases. To increase.

However, in this embodiment, as described above, when the load is high, the first EGR valve 6 is closed to reduce the opening area, so it is possible to prevent such an increase in smoke. Moreover, under high loads, the opening area is small and the lift change is small.
Since only the GR valve 7 is operated, highly accurate EGR control is performed.

By the way, in order to control the lift amount of the EGR valve, the rotation speed (engine rotation speed or pump rotation speed) detected by the rotation sensor 32 and the load sensor (potentiometer) 33 attached to the fuel injection pump 31 as in the above embodiment is used. When calculating the target lift amount from the map based on the fuel injection and accelerator opening, the resistance value of the potentiometer is usually set at one point between the most frequently used rotation speed and the accelerator opening. Since the pump 31 has mass-produced variations in spring constant, etc., a problem may occur in which the detected value of the accelerator opening differs from the actual value at a point other than the set point. That is, FIG. 7(a)
As shown in , when the potentiometer is set at point A and the mask curve of the prescribed injection amount passing through point A is shown by the solid line I, if the actual constant injection amount curve is the dashed line ■, then the mask curve ■ The accelerator opening will deviate from the rotation speed at other points above, making it impossible to obtain an accurate target lift amount.

In order to solve this problem, as shown in the figure, for each injection pump, the accelerator opening at another point B on the mask curve I and the dashed-dotted line
The difference Δα from the accelerator opening corresponding to the same rotation speed above is detected, and the accelerator opening correction value for the mask curve is set as shown in FIG. Then, lift control of the EGR valve is performed using the accelerator opening signal corrected using this correction value. In addition, in FIG. 7(a), the dashed line (-) indicates the equal injection amount curve (2) passing through the point B mentioned above.

The accelerator opening degree may also be corrected by detecting the rotational speed that is the same as the specified accelerator opening degree. That is, in this case, as shown in FIG. 8(a), the accelerator opening corresponding to the accelerator opening at point B on the specified injection amount curve (solid line) and the actual equivalent at that accelerator opening are The difference ΔN from the rotational speed according to the injection amount curve (-dotted chain line) is detected, and the rotational speed correction value is set as shown in FIG. 4(b) to perform correction.

What is shown in FIG. 9 is an improvement to the so-called O, sensor feedback EGR system. In this system, an EGR passage 10 communicates with an intake passage 103 downstream of an air cleaner 102 of an engine 101 and an exhaust passage 104.
5, a pump driven by motor 106! 07 is provided, and an O sensor 108 is provided in the exhaust passage, and O,
The control unit 1 controls the EGR amount according to the O1 concentration in the exhaust gas detected by the sensor lO8.
09 controls the rotation speed of the pump 107. In addition to the O concentration in the exhaust gas detected by the sensor 108, the control unit 109 receives the rotation speed signal from the rotation pickup 110 attached to the motor 106, and also receives the accelerator release signal from the fuel injection pump 111. Every time.

Signals for engine speed and fuel injection amount are input,
In addition, outside air temperature, water temperature, etc. are input. The control unit 109 controls the rotation speed of the pump 107 according to the required EGR amount according to these operating conditions. According to this, compared to the case where EGR is controlled by valve control using the difference between exhaust pressure and intake pressure, EGR during transient times such as acceleration
Control response delay can be improved. By the way, the E, which has been designed to increase responsiveness by pressurizing the pump,
The GR system can be implemented as shown in FIG. That is, in the one shown in FIG. 1O, an EGR return passage 112 is provided that communicates the exhaust passage 104 with the downstream side of the pump 107 in the EGR passage 105, and a check valve 113 is provided at the outlet of this passage 112, so that the pump 107
While keeping the pressure inside the downstream EGR passage 105 constant,
A duty solenoid valve 116 controls negative pressure supplied by a vacuum pump 115 to operate an EGR valve 114 provided at the outlet of the EGR passage 105. The duty solenoid valve 116 is controlled by a control unit 117. The control unit 117 receives the same signals as in FIG. 9 except for the pump rotation speed, and also receives the lift amount of the EGR valve 114 detected by the lift sensor 118. The present invention can also be applied to the system shown in FIG.

In addition, in the conventional O sensor feedback EGR system, an O sensor is provided in the exhaust passage, but as shown in FIG.
If a sensor 201 is provided and correction is made based on the O concentration in the recirculated exhaust gas detected by the second O sensor 201, more accurate EGR control is possible. In addition, in the conventional EGR system, 0. The concentration was detected and a controlled amount of recirculated exhaust gas was introduced into the intake air collecting section, but as shown in FIG. The sensor 301 is connected to the independent exhaust passage section 1 of each cylinder.
04a, connects the EGR passage 105 to the independent intake passage 103a of each cylinder, provides an EGR valve 302 for each cylinder, and controls the operating negative pressure for each EGR valve 302, a solenoid valve 303; lift sensor 3
04 are provided independently to perform EGR control for each cylinder, more accurate EGR control is possible. And, the EG described in these FIGS. 11 and 12
The present invention can also be applied to the R system. In addition, in FIGS. 11 and 12, parts common to those in FIG. 1O are given the same reference numerals.

(Effects of the Invention) Since the present invention is configured as described above, it is possible to accurately control the amount of EGR during high load in a diesel engine, thereby preventing the occurrence of smoke and deterioration of drivability.

[Brief explanation of drawings]

Fig. 1 is an overall system diagram of an embodiment of the present invention, Fig. 2 is a configuration diagram of a control system in the embodiment, Fig. 3 is a structural diagram of main parts of the embodiment, and Fig. 4 is a diagram of the main part of the embodiment. Control characteristic diagrams, FIGS. 5 and 6 are explanatory diagrams of emission performance in a diesel engine, FIGS. 7 and 8 are explanatory diagrams of correction control applicable to EGR control in the device of the present invention, and FIG. A system diagram showing an improved example of the 0° sensor feedback EGR system. FIGS. 10, 11, and 12 are system diagrams of examples that belong to the system shown in FIG. 9 and to which the present invention can be applied. It is. l: Engine, 5: Exhaust gas recirculation passage (EGR passage),
6: First EGR valve, 7: Second EGR valve, 19.20: Negative pressure operating chamber, 27: Solenoid valve (negative pressure regulating valve), 28:
lift sensor.

Claims (1)

[Claims] (1) A first exhaust gas recirculation valve with a large opening area that is activated during low loads, and a negative pressure operated second exhaust gas recirculation valve with a relatively small opening area that is activated at least during high loads, and the second exhaust gas recirculation valve A negative pressure regulating valve is interposed in the negative pressure passage that guides negative pressure to the negative pressure working chamber of the gas recirculation valve, and a lift sensor for controlling the amount of exhaust gas recirculation is provided in the second exhaust gas recirculation valve. Features a diesel engine exhaust gas recirculation system.