JP3969499B2 - Exhaust gas recirculation control system for two-cycle diesel engines - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas recirculation control system mainly for a two-cycle diesel engine mounted on an automobile.
[0002]
[Prior art]
Conventionally, in order to reduce NOx in exhaust gas, in a two-cycle gasoline engine, as shown in, for example, Japanese Patent Publication No. 7-116999, an exhaust gas recirculation passage that connects an air supply passage and an exhaust passage is used. 2. Description of the Related Art An exhaust gas recirculation control system (hereinafter referred to as an external EGR) that provides a valve and opens the valve under predetermined conditions to recirculate exhaust gas is known. On the other hand, in a two-cycle diesel engine, a so-called internal exhaust gas recirculation control system (hereinafter abbreviated as internal EGR) that changes the supply ratio of burned gas remaining in the combustion chamber and fresh air is known. . That is, in the internal EGR, the exhaust gas discharged from the combustion chamber to the exhaust pipe is not recirculated to the intake pipe, but the amount of scavenging delivered by the supercharger, which is a scavenging blower, is changed and left in the combustion chamber. By changing the amount of fuel gas each time, a state in which the burned gas is substantially mixed with fresh air is created, and NOx is reduced. In such a two-cycle diesel engine, a control valve is provided in a bypass passage that connects an inlet and an outlet of a supercharger attached to the air supply passage, and the scavenging amount is controlled by controlling the opening of the control valve. Change and execute the internal EGR.
[0003]
[Problems to be solved by the invention]
However, the internal EGR does not control the amount of exhaust gas circulated from the combustion chamber, but controls the amount of exhaust gas recirculated by the amount of burned gas remaining in the combustion chamber. Tend to rise. As a result, the original function of reducing NOx by lowering the maximum combustion temperature by mixing burned gas is reduced, and despite the EGR control being performed, the degree of NOx reduction is small, and the expected There was a case where the effect of could not be expected.
[0004]
The object of the present invention is to eliminate such problems.
[0005]
[Means for Solving the Problems]
In order to achieve such an object, the present invention takes the following measures. That is, the exhaust gas recirculation control system for a two-cycle diesel engine according to the present invention uses the scavenging blower to discharge the exhaust gas flowing out from the exhaust passage in the two-cycle diesel engine including the scavenging blower in order to eliminate the problem of the internal EGR. an exhaust gas recirculation passage for recirculating a first control valve provided on the exhaust gas recirculation passage, re-exhaust gases and a second control valve for controlling the amount of air to the scavenging blower in the high load region The flow rate of the exhaust gas passing through the circulation passage is controlled, and the remaining burned gas in the combustion chamber is controlled in the low load range . In this way, in the high load region, the second control valve is kept fully open, the flow rate of the exhaust gas passing through the exhaust gas recirculation passage is controlled by the opening degree control of the first control valve, and the exhaust gas discharged By recirculating the gas to the air supply passage and controlling the amount of air to the scavenging blower, the temperature in the cylinder can be controlled, the amount of NOx emission can be reduced, and in the low load range, The startability at a low temperature can be improved by holding the first control valve in the fully closed state and controlling the remaining burned gas in the combustion chamber by controlling the opening of the second control valve .
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a two-cycle diesel engine having a supply passage and an exhaust passage provided with a scavenging blower, an exhaust gas recirculation passage communicating the exhaust passage and the scavenging blower inlet side of the supply passage, and the exhaust gas recirculation passage. And a second control valve that is provided in the supply passage upstream of the communication point between the supply passage and the exhaust gas recirculation passage and controls the scavenging amount. A control valve, and in a high load range, the second control valve is kept fully open, and the flow rate of the exhaust gas passing through the exhaust gas recirculation passage is controlled by opening degree control of the first control valve. The exhaust for a two-cycle diesel engine is characterized in that in the low load range, the first control valve is held in a fully closed state, and the remaining amount of burned gas in the combustion chamber is controlled by opening control of the second control valve. It is a gas recirculation control system.
[0007]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In FIG. 1, a two-cycle diesel engine (hereinafter abbreviated as “engine”) 1 includes a supercharger 3 serving as a scavenging blower in an air supply passage 2, and exhaust gas is discharged into an exhaust passage 4 via an exhaust valve 5. This is a so-called uniflow type. That is, in this engine 1, fresh air that has flowed into the scavenging passage 7 formed around the cylinder 6 is introduced into the combustion chamber 9 from the scavenging port 8 provided on the side wall of the cylinder 6, and the exhaust valve 5 is opened. During this period, the combustion gas is scavenged into the exhaust passage 4. Fuel is injected into the combustion chamber 9 by a fuel injection valve 10, and fuel is supplied to the fuel injection valve 10 from a fuel injection pump 11.
[0008]
The air supply passage 2 includes an air cleaner 31 at the most upstream, and an intake throttle valve 16 that is a second control valve that can adjust the amount of fresh air that is not necessary for an intake system in a normal diesel engine and that is downstream of the intake passage 2. Provided, and further provided with a supercharger 3 downstream thereof. The supercharger 3 is configured to supply fresh air to the combustion chamber 9. The amount of fresh air supplied to the combustion chamber 9 is adjusted by controlling the opening of the intake throttle valve 16. The intake throttle valve 16 is controlled by an electronic control unit 15 described later, and the opening degree is controlled so as to change linearly, that is, linearly.
[0009]
The upstream side of the supercharger 3 in the air supply passage 2, that is, the inlet side of the supercharger 3 and the exhaust passage 4 communicate with each other through an exhaust gas recirculation passage 12. The exhaust gas recirculation passage 12 is provided with an EGR valve 13 as a first control valve for controlling the amount of exhaust gas passing therethrough, and EGR for cooling the exhaust gas in order to improve the reliability of the supercharger 3. A cooler 14 is attached. The opening degree of the EGR valve 13 is controlled by the electronic control unit 14 in the same manner as the intake throttle valve 16 and changes linearly. The EGR valve 13 and the intake throttle valve 16 may be combined with, for example, an electric valve that changes the opening degree by changing the duty ratio of the drive signal, a vacuum control valve, or the like to increase the lift amount of the valve body. A mechanical valve or the like that changes the opening degree by control can be used.
[0010]
The electronic control unit 15 is configured around a microcomputer, and includes a memory, an input interface, an output interface, an A / D converter, and the like. The input interface includes a rotation signal a output from the rotation speed sensor 17 that detects the engine rotation speed NE, a water temperature signal b output from the water temperature sensor 18 that detects the cooling water temperature THW, and a load for the engine 1. A depression amount signal c of the accelerator pedal 20 output from the accelerator sensor 19 is input. On the other hand, from the output interface, a signal corresponding to the injection amount determined from various conditions such as the engine speed, the amount of depression of the accelerator pedal 20 and the cooling water temperature is output to the fuel injection pump 11, and the EGR valve 13 and the intake throttle A control amount is determined for each valve 16 according to a procedure described later, and an electrical signal corresponding to the control amount is output.
[0011]
In the electronic control unit 15, data for determining the control amounts of the EGR valve 13 and the intake throttle valve 16 is created as a map using at least the engine speed NE and the load of the engine 1 as parameters. In this map, the opening degrees of the EGR valve 13 and the intake throttle valve 16 are individually adjusted, and are basically discharged to the exhaust passage 4 through the external EGR by the EGR valve 13, that is, through the exhaust valve 5. The basic opening degrees of the EGR valve 13 and the intake throttle valve 16 are set so that the exhaust gas recirculation system that recirculates the exhaust gas to the intake passage 2 via the exhaust gas recirculation passage 12 reduces NOx. It is. Specifically, the intake throttle valve 16 is set to change at a substantially constant opening with respect to changes in the engine speed and load, and the EGR valve 13 is set to a desired EGR amount. It is set based on the load and the engine speed.
[0012]
EGR control is performed using such a map, and a schematic procedure thereof is shown in FIG.
In the control, first, the engine speed NE is detected from the rotational speed signal a from the rotational speed sensor 17 (step S1). Next, the load EL of the engine 1 is detected from the depression amount signal c from the accelerator sensor 19 (step S2). Further, the coolant temperature THW is detected from the water temperature signal b from the water temperature sensor 18 (step S3). From the detected engine speed NE and load EL, a map is searched to determine a basic opening degree (step S4). Then, the basic opening value is corrected based on the detected coolant temperature THW, and the final opening degree of the EGR valve 13 and the intake throttle valve 16 is determined (step S5).
[0013]
As described above, the scavenging amount is controlled by the intake throttle valve 16 and the EGR amount is controlled by the EGR valve 13, so that the temperature in the combustion chamber 9 does not rise unlike the case of the internal EGR. Therefore, by mixing the exhaust gas with fresh air, the maximum temperature at the time of combustion is lowered, and the generation of NOx can be reduced.
In addition, the setting of the opening degree in a map may be as follows.
For example, an internal EGR and an external EGR may be selectively executed by using the intake throttle valve 16 and the EGR valve 13 independently. That is, as shown in FIG. 3, a map for setting the opening degree of the intake throttle valve 16 and the EGR valve 13 is a high load region Aa where the engine speed NE is high and the torque is large, and the engine speed NE is low. In addition, it is divided and set to a low load region Ab with a small torque. Specifically, in the high load range Aa, the opening degree is set so that the intake throttle valve 16 is kept fully open in the entire area, and only the EGR valve 13 is controlled in its opening degree. The opening of 13 is set based on the engine speed NE and the load EL. On the other hand, in the low load region Ab, the opening degree is set so that the EGR valve 13 is kept in the fully closed state throughout the entire region, and the opening degree of the intake throttle valve 16 is set based on the engine speed NE and the load EL. It is. The procedure of EGR control using such a map may be the same as that described in the above embodiment.
[0014]
Thus, by setting the opening of the intake throttle valve 16 and the EGR valve 13 in two regions depending on the operating state of the engine 1, the internal EGR and the external EGR can be switched according to the operating state. . In this case, when the opening degree of the intake throttle valve 16 is reduced at low load, the supercharger 3 rotates in accordance with the engine speed NE and generates heat. At the same time, since the amount of fresh air decreases, burned gas remains in the combustion chamber 9. Therefore, the inside of the combustion chamber 9 becomes high temperature due to the heat of the supercharger 3 and the heat of burned gas, generation of white smoke, in other words, HC can be reduced, and startability at low temperatures can be improved.
[0015]
The present invention is not limited to the embodiment described above.
In addition, the configuration of each unit is not limited to the illustrated example, and various modifications can be made without departing from the spirit of the present invention.
[0016]
【The invention's effect】
As described above, according to the present invention, the air supply passage is provided with the second control valve, the exhaust passage is provided with the first control valve, and the second control valve is kept fully open in the high load region. The flow rate of the exhaust gas passing through the exhaust gas recirculation passage is controlled by opening degree control of the first control valve, and the first control valve is held in a fully closed state in the low load region to open the second control valve. The degree of burned gas remaining in the combustion chamber is controlled by the degree control, so that the ratio of the exhaust gas to the recirculation and the fresh air can be easily changed, and the temperature in the combustion chamber can be lowered by the external EGR function. Conversely, the temperature can be increased under certain conditions. Therefore, NOx can be reduced by the external EGR function, and when the load is low, the temperature in the combustion chamber can be raised by the internal EGR function to improve startability and reduce the generation of white smoke. Can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.
FIG. 2 is a schematic flowchart showing a control procedure of the embodiment.
FIG. 3 is a graph showing a map setting concept in another embodiment of the present invention.
[Explanation of symbols]
2 ... Air supply passage 3 ... Supercharger 4 ... Exhaust passage 12 ... Exhaust gas recirculation passage 13 ... EGR valve 16 ... Intake throttle valve

Claims (1)

In a two-cycle diesel engine having an air supply passage and an exhaust passage provided with a scavenging blower, an exhaust gas recirculation passage communicating the exhaust passage and the scavenging blower inlet side of the air supply passage, and the exhaust gas recirculation passage are provided. A first control valve for controlling the flow rate of the exhaust gas, and a second control valve for controlling the scavenging amount provided in the air supply passage upstream of the communication portion between the air supply passage and the exhaust gas recirculation passage. In the high load range, the second control valve is kept fully open, and the flow rate of the exhaust gas passing through the exhaust gas recirculation passage is controlled by the opening control of the first control valve. In the exhaust gas recirculation control for a two-cycle diesel engine , the first control valve is held in a fully closed state, and the remaining burned gas in the combustion chamber is controlled by controlling the opening of the second control valve. system.

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