JP2009174493A - Supercharging device of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a supercharging device of a diesel engine capable of suppressing shock when an engine is stopped and deterioration in combustability when the engine is restarted. <P>SOLUTION: The supercharging device of a diesel engine includes an electric supercharger (34) for supercharging air in an intake passage (20) by rotating a compressor (35) disposed in the intake passage (20) by electric power, an exhaust gas recirculation passage (70) for connecting the intake passage (20) to an exhaust passage (50), an electric supercharger control means (106) for controlling operation of the electric supercharger (34) to rotate the electric supercharger (34) in reverse with respect to normal rotation when the engine is stopped, and an exhaust gas recirculation valve control means (104) for controlling an exhaust gas recirculation valve to close the exhaust gas recirculation valve disposed in the exhaust gas recirculation passage (70) when the engine is stopped. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a supercharger for a diesel engine, and more particularly, to a supercharger for a diesel engine having an electric supercharger and an exhaust gas recirculation passage disposed in an intake passage.

  Conventionally, the amount of fuel vapor that accumulates in the intake system by the fuel funnel from the fuel injection valve after the engine has stopped has an adverse effect on operability or exhaust emissions immediately after the next engine start. An engine is known in which the intake system is scavenged in the same manner as the rotation of the engine (Patent Document 1).

JP 2004-108212 A

However, even if the intake system is scavenged or not scavenged when the engine is stopped as in the engine described in Patent Document 1, the diesel engine has a high compression ratio, and the piston is compressed by air, so the engine is stopped. Sometimes a key-off shock (impact force or vibration when the engine is stopped) may occur. Such a key-off shock may be felt when the driver himself stops the engine. In particular, when performing a so-called idle stop such as an automatic stop at an intersection or the like, it is stopped by the driver's intention. Not so shock can be a big concern.
Further, there is also a problem that the combustibility at the next engine restart is deteriorated by burning the burned gas into the intake passage through the EGR passage.

  The present invention has been made to solve the above-described problems of the prior art, and is a turbocharger of a diesel engine that can suppress a shock at the time of stopping the engine and suppress deterioration of combustibility at the time of restart. An object is to provide an apparatus.

  In order to achieve the above object, according to the present invention, an electric supercharger that supercharges air in an intake passage by electrically rotating a compressor disposed in the intake passage and an intake passage and an exhaust passage are connected. A diesel engine supercharging device having an exhaust gas recirculation passage, wherein when the engine is stopped, the electric supercharger is operated so as to reversely rotate in reverse with respect to normal normal rotation. An electric supercharger control means for controlling, and an exhaust gas recirculation valve control means for controlling the exhaust gas recirculation control valve so as to close the exhaust gas recirculation control valve disposed in the exhaust gas recirculation passage when the engine is stopped. A supercharger for a diesel engine, comprising:

  In the present invention configured as described above, when the engine is stopped, the electric turbocharger is reversely rotated to suck out the air in the cylinder, and the amount of the sucked-out amount can reduce the compression work by the piston. Thus, the shock (impact force or vibration) at the time of stopping can be reduced. Furthermore, by closing the exhaust gas recirculation control valve when the engine is stopped, the deterioration of combustibility at the time of engine restart due to the combustion gas being sucked into the intake passage via the exhaust gas recirculation passage is suppressed. I can do it.

In the present invention, it is preferable that the exhaust gas recirculation control means closes the exhaust gas recirculation control valve when a predetermined period has elapsed after starting the reverse rotation of the electric supercharger by the electric supercharger control means.
In the present invention configured as described above, the exhaust gas recirculation control valve is not closed for a predetermined time at the initial start-up of the electric supercharger. Will not be generated. Thereby, the resistance of supercharging decreases, and the initial rotation of the electric supercharger can be started up smoothly. In addition, a large current flows through the motor at the initial stage of rotation of the electric supercharger, but the resistance to supercharging can be reduced without causing a sudden negative pressure while the large current flows. As a result, the load applied to the battery is reduced, and a reduction in the life of the electric supercharger can be suppressed.

In the present invention, it is preferable that the electric supercharger control means is configured to operate the electric supercharger after the predetermined time has elapsed since the start of reverse rotation of the electric supercharger until the predetermined period elapses. The electric supercharger is controlled to be smaller than the rotation speed of the supercharger.
In the present invention configured as described above, the rotational speed of the electric supercharger is made smaller during a predetermined time when the exhaust gas recirculation control valve is open than after a predetermined time when the exhaust gas recirculation control valve is closed. Therefore, the exhaust gas recirculation amount through the exhaust gas recirculation passage due to the reverse rotation of the electric supercharger can be reduced, and deterioration of combustibility after the next engine start can be minimized.

In the present invention, it is preferable that the engine further includes automatic stop control means for automatically stopping the engine when a predetermined automatic stop condition is satisfied, and the electric supercharger control means is configured when the predetermined automatic stop condition is satisfied. The electric supercharger is controlled to reversely rotate the electric supercharger, and the automatic stop control means causes the electric supercharger control means to reversely rotate the electric supercharger for a predetermined time, and then automatically stops the engine. .
In the present invention configured as described above, when the engine is automatically called so-called idle stop, the electric supercharger is reversely rotated for a predetermined time prior to the stop, so that the air in the cylinder is surely sucked out. The engine can be stopped later, thereby reducing the shock when the engine automatically stops.

Further, in the present invention, preferably, it further includes an in-cylinder pressure detecting means for detecting the in-cylinder pressure, and the electric supercharger control means is configured so that the in-cylinder pressure becomes equal to or lower than the atmospheric pressure when the engine is stopped. Control the electric supercharger.
In the present invention configured as described above, when the engine is stopped, the electric supercharger is controlled so that the in-cylinder pressure becomes equal to or lower than the atmospheric pressure. The shock when the engine is stopped can be reliably suppressed.

  According to the turbocharger for a diesel engine of the present invention, it is possible to suppress shock when the engine is stopped and suppress deterioration of combustibility during restart.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is an overall configuration diagram of a diesel engine controlled by a turbocharger for a diesel engine according to an embodiment of the present invention.
The engine body 1 is provided with a plurality of cylinders 2, and a combustion chamber 2 a is formed in these cylinders 2. In each combustion chamber 2a, an intake port 4 and an exhaust port 6 are opened, and an intake valve 8 and an exhaust valve 10 are provided in these ports. Further, a fuel injection valve 12 is provided for each combustion chamber 2a.

  An intake passage 20 that supplies air to each cylinder 2 is connected upstream of the intake port 4 and the intake valve 8, and exhaust gas is led out from each cylinder 2 downstream of the exhaust port 6 and the exhaust valve 10. An exhaust passage 50 is connected.

  A surge tank 22 and an intake manifold 24 that branches from the surge tank 22 to each intake port 4 of each cylinder 2 are formed in the intake passage 20. An air cleaner 26 is provided upstream of the intake passage 20, and an intake pipe 28 extends between the air cleaner 26 and the surge tank 22. An intake throttle valve 30 is provided downstream of the air cleaner 26 of the intake pipe 28. An intercooler 32 is disposed in the intake pipe 28.

  An electric supercharger 34 is provided between the intercooler 32 of the intake pipe 28 and the surge tank 22. The electric supercharger 34 has a compressor 35 that is directly driven by a motor 34a. An electric supercharger bypass passage 36 that bypasses the electric supercharger 34 from the intake pipe 28 and communicates with the upstream side of the surge tank 22 is provided. An electric supercharger bypass valve 38 is provided in the electric supercharge bypass passage 36. An intake shutter valve 40 is provided between the electric supercharger 34 and the electric supercharger bypass valve 38 of the intake pipe 28 and the intercooler 32.

  Next, the exhaust passage 50 includes an exhaust manifold 52 for each cylinder connected to the exhaust port 6 of each cylinder 2, an exhaust pipe 54 downstream thereof, and an exhaust purification device 56 connected downstream of the exhaust pipe 54. I have. The exhaust purification device 56 has a catalytic function and is for collecting diesel smoke exhaust particulates (PM). Specifically, the exhaust purification device 56 is disposed on the downstream side of the oxidation catalyst 56a. It is comprised by the diesel particulate filter (DPF) 56b.

An exhaust turbocharger 60 is provided between the intake passage 20 and the exhaust passage 50. The exhaust turbocharger 60 includes a turbine 62 that rotates by being driven by the energy of exhaust gas, and a compressor 66 that is connected to the turbine 62 via a shaft 64. The turbine 62 of the exhaust turbocharger 60 is provided in the exhaust pipe 54, and the compressor 66 is provided in the intake pipe 28. The exhaust turbocharger 60 supercharges the intake air in the intake pipe 28 by the rotation of the compressor 66 interlocked with the rotation of the turbine 62 by the exhaust energy. The intercooler 32 is configured to cool the air supercharged by the compressor 66.
The above-described electric supercharger 34 may be of a type in which a motor is attached to the exhaust turbocharger 60.

  A high pressure EGR passage (first EGR passage, HP-EGR passage) 70 and a low pressure EGR passage (second EGR passage, LP-EGR passage) 80 are provided between the intake passage 20 and the exhaust passage 50. ing. The first EGR passage 70 communicates between the surge tank 22 and the upstream side of the turbine 62 of the exhaust pipe 54 and a portion of the exhaust gas having a relatively high temperature and high pressure before driving the exhaust turbocharger 60. Is returned to the intake passage 20. The first EGR passage 70 is provided with an EGR valve 72 and an EGR cooler 74 on the upstream side (exhaust side) of the EGR valve 72.

  Further, the second EGR passage 80 communicates between the exhaust pipe 54 downstream of the exhaust purification device 56 and the intake pipe 28 upstream of the compressor 66 to drive the turbine 62 of the exhaust turbocharger 60. A part of the later exhaust gas having a relatively low pressure is returned to the intake passage 20. The second EGR passage 80 is provided with an EGR valve 82 and an EGR cooler 84 on the upstream side (exhaust side) of the EGR valve 82.

Next, the system of the control system of the turbocharger for the diesel engine according to the embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram of the control system of the diesel engine according to the embodiment of the present invention.
The ECU 100 is a control unit composed of a microprocessor having a CPU, a memory, a counter timer group, an interface, a bus connecting these units, and the like. Specifically, the ECU 100 includes a fuel injection valve 12, an electric supercharger 34 (34a), an electric supercharger bypass valve 38, an intake shutter valve 40, a first EGR valve (HP-EGR valve) 72, and a second EGR valve. (LP-EGR valve) 82 is connected.

  The ECU 100 functionally has a predetermined EGR opening degree in a predetermined operation region based on the combustion control unit 102 that controls the fuel injection valve 12 so as to cut fuel under predetermined conditions, as described later, and an EGR map. As described above, the EGR control unit 104 that controls the first EGR valve 72 and the second EGR valve 82 controls the electric supercharger 34 (34a) so as to obtain a predetermined rotational speed under a predetermined condition, and the electric supercharger bypass 36. The electric supercharger control unit 106 that controls the electric supercharger bypass valve 38 so as to open and close the engine and the automatic stop control unit 108 that stops the engine when a predetermined condition is satisfied are included. Here, the electric supercharger control unit 106 opens the electric supercharger bypass valve 38 of the electric supercharger bypass passage 36 when the electric supercharger 34 is not driven, and opens the electric supercharger bypass valve 38 when driven. close. Thus, when the electric supercharger 34 is not driven, the intake air is guided to the electric supercharger bypass passage 36 to reduce the intake resistance, and when the electric supercharger 34 is driven, the intake air is reliably supplied to the electric supercharger 34. To the compressor 35.

  The ECU 100 includes a vehicle speed sensor 110 that detects the vehicle speed of the vehicle, a brake sensor 112 that detects ON / OFF of the brake, an accelerator opening sensor 114 that detects the accelerator opening, and an in-cylinder pressure sensor 116 that detects the pressure in the cylinder 2. The ECU 100 receives input signals from these sensors, and each of the devices 12, 34 (34a), 38, 40, 72, 82 is received by the control units 102, 104, 106, and 108 described above. To control.

  Next, the contents of control of the turbocharger for a diesel engine according to the embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a flowchart showing a control flow of a turbocharger for a diesel engine according to an embodiment of the present invention, and FIG. 4 is a diagram showing control contents of the turbocharger for a diesel engine according to an embodiment of the present invention. FIG. 5 is a diagram of the in-cylinder pressure with respect to the crank angle obtained by the control of the turbocharger of the diesel engine according to the embodiment of the present invention. In FIG. 3, S indicates each step.

  First, as shown in FIG. 3, in S1, signals of the vehicle speed sensor 110, the brake sensor 112, the accelerator opening sensor 114, and the in-cylinder pressure sensor 116 are read. In S2, the automatic stop control unit 108 (see FIG. 2) determines whether or not a stop condition is satisfied from the values of the sensors read in S1. That is, it is determined that the stop condition is satisfied when the signal from the vehicle speed sensor 110 indicates the vehicle speed 0, the brake sensor 112 indicates that the brake is ON, and the signal from the accelerator opening sensor 114 indicates the accelerator opening 0. Note that it may be determined that the stop condition is satisfied even when the brake is OFF (for example, when the side brake is applied). If the stop condition is not satisfied in S2, the control proceeds to S3 to S10 during normal travel.

  In normal control, first, in S3, it is determined from the signal value of the vehicle speed sensor 110 whether or not the vehicle is accelerating. When it is accelerating, it progresses to S4, the electric supercharger 34 is act | operated to a normal normal rotation direction, and the bypass valve 38 is closed by S5. As a result, the intake air does not pass through the bypass 36 and is supercharged by the electric supercharger 34. On the other hand, when not accelerating, the process proceeds to S6, the electric supercharger 34 is stopped, and the bypass valve 38 is opened in S7. Thereby, supercharging by the electric supercharger 34 is not performed.

  After the control of S5 or S7, the process proceeds to S8, and it is determined whether or not it is in the EGR operating region. This is determined from a map (not shown) having the engine rotation speed (rpm) and the accelerator opening (%) as axes. If it is in the EGR operation region, the process proceeds to S9, and from the map, both or one of the first EGR valve 72 and the second EGR valve 82 is opened to a predetermined opening obtained from the map, and the EGR is operated. . If it is not in the EGR operation region, the process proceeds to S10, and both the first EGR valve 72 and the second EGR valve 82 are closed.

  Next, when the stop condition is satisfied by S2, the mode for operating the electric supercharger 34 in the reverse direction (reverse rotation) opposite to the normal mode is entered. In this mode, basically, when the engine is stopped, the electric turbocharger 34 is reversely rotated to suck out the air in the cylinder 2 and reduce the amount of compression work by the piston by that amount. It reduces the shock (impact force and vibration) generated in the engine. Further, when the engine is stopped, basically the burned gas is sucked into the intake passage 20 through the first EGR passage 70 by closing the first EGR valve 72, and the combustibility deteriorates at the time of engine restart. It suppresses.

  In this mode, first, in S11, the bypass valve 38 is closed. Next, it progresses to S12 and it is determined whether predetermined time t1 has passed since the stop condition was satisfied. The predetermined time t1 is an initial time when the motor 34a of the electric supercharger 34 rises from the rotational speed 0. t1 is approximately 1 second or less. During this time, due to the characteristics of the motor, a large current flows through the motor when the rotational speed rises, and the reverse side of the electric supercharger 34 causes the intake pipe 28 and surge on the downstream side of the electric supercharger to surge. This is the time when the negative pressure rises rapidly in the tank 22.

In S12, when it is determined that the predetermined time t1 has not elapsed since the stop condition is satisfied, the process proceeds to S13 and S14.
In S13, the electric supercharger controller 106 (see FIG. 2) causes the electric supercharger 34 to reversely rotate at a predetermined low speed. As indicated by A in FIG. 4, this is the reverse rotation of the electric supercharger 34 at a predetermined low rotational speed R1 (for example, 1000 rpm), and it is determined in S12 that the predetermined time t1 has elapsed. It will continue until In S14, the first EGR valve 72 is opened by the EGR control unit 104 (see FIG. 2). This is indicated by C in FIG. 4. By opening the first EGR valve 72 at the initial stage when the electric supercharger 34 is reversely rotated, the intake air in the cylinder 2 is drawn into the electric supercharger 34 side and the exhaust gas is also generated. The negative pressure does not rise suddenly in the intake pipe 28 or the surge tank 22 on the downstream side of the electric supercharger so as to recirculate so as not to prevent the rise of the rotational speed of the motor 34a of the electric supercharger 34. It is to make. On the other hand, since the electric supercharger 34 is rotated at a predetermined low rotational speed, a large amount of burned gas is prevented from returning to the intake passage 20 via the first EGR passage 70.

On the other hand, if it is determined in S12 that the predetermined time t1 has elapsed since the stop condition was satisfied, the process proceeds to S15 and S16.
In S15, the electric supercharger controller 106 (see FIG. 2) causes the electric supercharger 34 to reversely rotate at a predetermined high rotational speed. As shown by B in FIG. 4, this is to reversely rotate the electric supercharger 34 at a predetermined high rotational speed R2 (for example, 60000 rpm). In S17, which will be described later, the in-cylinder pressure in the cylinder 2 This is continued until the pressure falls below atmospheric pressure. In S16, the EGR control unit 104 (see FIG. 2) closes the first EGR valve 72. This is indicated by D in FIG. Thus, by rotating the electric supercharger 34 at a predetermined high rotation speed and closing the first EGR valve 72, the exhaust gas recirculation through the EGR passage 70 is stopped, and the electric supercharger 34 Air in the cylinder 2 is surely sucked out.

  By the processes of S13 and S14 or S15 and S16, the pressure in the cylinder 2 (cylinder pressure) gradually decreases as shown in FIG. In S17, the automatic stop control unit 108 (see FIG. 2) determines whether the in-cylinder pressure is equal to or lower than the atmospheric pressure. When the pressure in the cylinder 2 is larger than the atmospheric pressure, the processes in S2 to S16 are repeated to reduce the pressure in the cylinder 2. Note that the time t2 shown in FIG. 4 indicates the time from when the stop condition is satisfied until the pressure in the cylinder 2 becomes equal to or lower than the atmospheric pressure. t2 is approximately several seconds, for example, about 3 seconds or 4 seconds.

  When the pressure in the cylinder 2 becomes equal to or lower than the atmospheric pressure, it is assumed that the key-off shock (impact force or vibration when the engine is stopped) due to the engine stop is small, and the processes of S2 to S16 are ended. In S18, the electric supercharger control unit 106 (see FIG. 2) stops the operation of the electric supercharger 34, and in S19, the bypass valve 38 is opened. In S20, the combustion control unit 102 and the automatic stop control unit The fuel is cut by 108 (see FIG. 4).

  As described above, in the embodiment of the present invention, when the engine is stopped, the electric turbocharger 34 is reversely rotated to suck out the air in the cylinder 2 and reduce the amount of compression work by the piston by the sucked-out amount. It is possible to reduce the shock (impact force and vibration) when stopping. In particular, when the engine is stopped, the electric supercharger 34 is controlled so that the pressure in the cylinder 2 becomes equal to or lower than the atmospheric pressure. Can be reliably suppressed.

  Therefore, as shown in an experimental example in FIG. 5, it can be seen that the pressure in the cylinder 2 according to the present embodiment is significantly smaller than the pressure in the cylinder 2 according to the prior art. FIG. 5 also shows an example in which the electric supercharger 34 is not reversely rotated as in the embodiment of the present invention, but the intake shutter valve 40 is closed to prevent entry into the cylinder 2. Thus, the pressure in the cylinder 2 can also be reduced by closing the intake shutter valve 40. However, the reduction amount is more effective when air is actively sucked using the electric supercharger 34.

  Further, when the engine is stopped, the first EGR valve 72 is closed to suppress the deterioration of combustibility when the engine is restarted due to the combustion gas being sucked into the intake passage 20 via the first EGR passage 70. I can do it. Even if the first EGR valve 72 is open, the rotation speed of the electric supercharger 34 is made smaller than the closed time during the open predetermined time t1, so that the reverse rotation of the electric supercharger 34 is performed. By reducing the recirculation amount of the exhaust gas through the first EGR passage 70, deterioration of combustibility after the next engine start can be minimized.

  Furthermore, since the first EGR valve 72 is not closed at the predetermined time t1 when the electric supercharger 34 is initially raised, the exhaust gas does not recirculate during that time and a sudden negative pressure is not generated. Thereby, the resistance of supercharging decreases, and the initial rotation of the electric supercharger 34 can be started up smoothly. Furthermore, a large current flows through the motor 34a at the beginning of the rotation of the electric supercharger 34. However, the resistance to supercharging can be reduced without causing a sudden negative pressure during the large current flow. The load applied to the motor 34a is reduced, and a reduction in the life of the electric supercharger can be suppressed.

  Further, when the engine is automatically stopped, for example, when the engine is stopped so-called idle stop in addition to a manual stop operation by the driver, the electric supercharger 34 is reversely rotated for a predetermined time t2 prior to the stop. The engine can be stopped after the air in the air 2 is surely sucked out, so that the shock at the time of automatic engine stop can be reduced.

1 is an overall configuration diagram of a diesel engine controlled by a turbocharger for a diesel engine according to an embodiment of the present invention. FIG. 2 is a block diagram of a control system of the diesel engine according to the embodiment of the present invention. It is a flowchart which shows the control flow of the supercharging apparatus of the diesel engine by embodiment of this invention. It is a diagram which shows the control content of the supercharging apparatus of the diesel engine by embodiment of this invention. It is a diagram of the cylinder pressure with respect to the crank angle obtained by control of the supercharging device of the diesel engine by the embodiment of the present invention.

Explanation of symbols

2 cylinder 20 intake passage 34 electric supercharger 36 electric supercharger bypass passage 38 electric supercharger bypass valve 34a motor 35 compressor 40 intake shutter valve 50 exhaust passage 56 exhaust purification device 60 exhaust turbocharger 62 turbine 66 compressor 70 High pressure EGR passage 72 EGR valve 80 Low pressure EGR passage 82 EGR valve

Claims (5)

Supercharging of a diesel engine having an electric supercharger that supercharges air in an intake passage by electrically rotating a compressor disposed in the intake passage, and an exhaust gas recirculation passage connecting the intake passage and the exhaust passage A device,
An electric supercharger control means for controlling the operation of the electric supercharger so that the electric supercharger is reversely rotated reversely with respect to the normal forward rotation when the engine is stopped;
An exhaust gas recirculation valve control means for controlling the exhaust gas recirculation control valve so as to close the exhaust gas recirculation control valve disposed in the exhaust gas recirculation passage when the engine is stopped;
A supercharger for a diesel engine characterized by comprising:   2. The diesel engine according to claim 1, wherein the exhaust gas recirculation control means closes the exhaust gas recirculation control valve when a predetermined period has elapsed after the electric supercharger control means starts reverse rotation of the electric supercharger. Engine supercharger.   The electric supercharger control means is configured to rotate the electric supercharger after a predetermined time has passed since the rotation speed of the electric supercharger until a predetermined period has elapsed after starting reverse rotation of the electric supercharger. The supercharger for a diesel engine according to claim 2, wherein the electric supercharger is controlled to be smaller than the number. Furthermore, it has an automatic stop control means for automatically stopping the engine when a predetermined automatic stop condition is satisfied,
The electric supercharger control means controls the electric supercharger to reversely rotate the electric supercharger when the predetermined automatic stop condition is satisfied,
The diesel engine according to any one of claims 1 to 3, wherein the automatic stop control means automatically stops the engine after the electric supercharger control means reversely rotates the electric supercharger for a predetermined time. Supercharger. Furthermore, it has in-cylinder pressure detecting means for detecting the pressure in the cylinder,
The supercharger for a diesel engine according to any one of claims 1 to 3, wherein the electric supercharger control means controls the electric supercharger so that an in-cylinder pressure is equal to or lower than an atmospheric pressure when the engine is stopped. apparatus.

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