JP4941352B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine.

  Conventionally, for example, in Patent Document 1, during cranking operation of an internal combustion engine, at least one of an exhaust valve and an exhaust throttle valve provided in an exhaust passage downstream of the exhaust valve is continuously closed. In addition, a control device for an internal combustion engine that controls at least one of a variable valve mechanism and an exhaust throttle valve is disclosed.

JP 2007-182869 A Japanese Patent Laid-Open No. 2007-100700

  If the exhaust throttle valve is closed as in the conventional control device at the time of cold start, the in-cylinder temperature (compression end temperature) can be increased by increasing the back pressure of the internal combustion engine. This makes it possible to reduce the emission of white smoke (THC) during cold start. However, if the back pressure is increased by the above-described method, the pumping loss is increased, so that the start-up of the engine speed after the first explosion becomes slow. As a result, the time until the internal combustion engine reaches the complete explosion state (the time required to complete the start-up)) is extended, and the execution time of special control performed at the start-up, such as an increase in the fuel injection amount, is extended. This leads to an increase in white smoke (THC) emissions.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a control device for an internal combustion engine that can sufficiently reduce emission of white smoke during cold start.

A first invention is a control device for an internal combustion engine,
Back pressure variable means for changing the back pressure of the internal combustion engine;
Back pressure control means for controlling back pressure using the back pressure variable means;
An initial explosion occurrence determining means for determining whether or not an initial explosion of the internal combustion engine has occurred,
The back pressure variable means corresponds to a variable nozzle for adjusting the flow rate of the exhaust gas supplied to the turbine of the turbocharger,
After determining that the first explosion has occurred, the back pressure control means performs an initial explosion that performs back pressure reduction control for controlling the opening of the variable nozzle to an opening on the opening side of the variable nozzle before the occurrence of the first explosion. viewing including the Doggy pressure control means,
The control device for the internal combustion engine further includes a complete explosion state determination means for determining whether or not the internal combustion engine has reached a complete explosion state,
The back pressure control means after the first explosion includes back pressure reduction control continuation means for continuing the back pressure reduction control from the time of occurrence determination of the first explosion to the complete explosion state,
The back pressure reduction control is characterized in that the opening of the variable nozzle is gradually opened as the engine speed after the first explosion occurs.
The second invention is a control device for an internal combustion engine,
Back pressure variable means for changing the back pressure of the internal combustion engine;
Back pressure control means for controlling back pressure using the back pressure variable means;
An initial explosion occurrence determining means for determining whether or not an initial explosion of the internal combustion engine has occurred,
The back pressure variable means corresponds to an exhaust throttle valve for limiting the flow rate of exhaust gas flowing through the exhaust passage,
After determining that the first explosion has occurred, the back pressure control means performs initial pressure reduction control for controlling the opening of the exhaust throttle valve to an opening on the opening side of the first explosion before the occurrence of the first explosion. Including post-explosive back pressure control means,
The control device for the internal combustion engine further includes a complete explosion state determination means for determining whether or not the internal combustion engine has reached a complete explosion state,
The back pressure control means after the first explosion includes back pressure reduction control continuation means for continuing the back pressure reduction control from the time of occurrence determination of the first explosion to the complete explosion state,
The control device for the internal combustion engine includes:
A variable valve mechanism for varying a valve overlap period in which an intake valve opening period and an exhaust valve opening period overlap;
A post-explosion overlap period setting means for setting a valve overlap period after reaching the complete explosion state to a longer period than before reaching the complete explosion state;
Further comprising
The back pressure reduction control is characterized by gradually opening the opening of the exhaust throttle valve as the engine speed after the first explosion increases.

According to a fifth invention , in any one of the first to fourth inventions,
The back pressure control means includes back pressure control means before the first explosion that increases the back pressure before the first explosion using the back pressure variable means.

In addition, a third aspect of the present invention, Oite the first inventions,
Controller before SL internal combustion engine, wherein an opening degree of the variable nozzle after reaching complete combustion state, after complete explosion nozzle opening is set to the closing side of the opening than before reaching the complete combustion state A degree setting means is further provided.

A fourth aspect of the present invention is the first or third inventions in Oite,
The control device for the internal combustion engine includes a variable valve mechanism that varies a valve overlap period in which an intake valve opening period and an exhaust valve opening period overlap each other;
A post-explosion overlap period setting means for setting a valve overlap period after reaching the complete explosion state to a longer period than before reaching the complete explosion state;
Is further provided.

According to the first invention, when the variable nozzle is used as the back pressure variable means , the back pressure can be reduced after it is determined that the first explosion has occurred, so that the pumping loss of the internal combustion engine can be reduced after the first explosion has occurred. Can be reduced. Thereby, compared with the case where the back pressure is increased after the first explosion occurs, the start-up time of the engine speed after the first explosion can be accelerated, and the starting time of the internal combustion engine can be shortened. For this reason, at the time of a cold start, it becomes possible to suppress suitably the increase in discharge amount of white smoke (THC). In addition, according to the present invention, the pumping loss can be satisfactorily reduced by lowering the back pressure from the time of occurrence determination of the first explosion until the complete explosion state. Thereby, it is possible to satisfactorily shorten the time from the occurrence of the first explosion to the completion of the complete explosion (time required to complete the start-up).
According to the second aspect of the present invention, when the exhaust throttle valve is used as the back pressure varying means, the back pressure can be reduced after it is determined that the first explosion has occurred. Can be reduced. Thereby, compared with the case where the back pressure is increased after the first explosion occurs, the start-up time of the engine speed after the first explosion can be accelerated, and the starting time of the internal combustion engine can be shortened. For this reason, at the time of a cold start, it becomes possible to suppress suitably the increase in discharge amount of white smoke (THC). In addition, according to the present invention, the pumping loss can be satisfactorily reduced by lowering the back pressure from the time of occurrence determination of the first explosion until the complete explosion state. Thereby, it is possible to satisfactorily shorten the time from the occurrence of the first explosion to the completion of the complete explosion (time required to complete the start-up). Furthermore, according to the present invention, the internal EGR gas amount is increased by setting the valve overlap period after the internal combustion engine reaches the complete explosion state to be longer than that before reaching the complete explosion state. be able to. As a result, the in-cylinder temperature (compression end temperature) can be increased by increasing the internal EGR gas after the complete explosion. For this reason, the white smoke (THC) can be sufficiently reduced in the cold state after the completion of the start (after the complete explosion) by combining the effect of reducing the white smoke by increasing the amount of the internal EGR gas.

According to the fifth aspect , by increasing the back pressure during cranking before the first explosion, combustion at the first explosion can be improved. As the back pressure is lowered as described above after the first explosion, the time until the internal combustion engine reaches the complete explosion state after the first explosion due to an increase in pumping loss accompanying the increase in the back pressure (until the start is completed). Time) and an increase in the execution time such as an increase in the fuel injection amount during startup can be avoided. For this reason, at the time of a cold start, it becomes possible to suppress suitably the increase in discharge amount of white smoke (THC).

According to the third invention, the opening degree of the variable nozzle after the internal combustion engine reaches the complete explosion state is set to the opening degree on the closed side as compared with the opening degree of the variable nozzle before reaching the complete explosion state. Therefore, the turbo rotation speed can be increased and the supercharging pressure can be increased. As a result, since the actual compression ratio of the internal combustion engine is increased, the in-cylinder temperature (compression end temperature) can be increased, and the emission of white smoke (THC) is suppressed when the engine is cold after the start is completed (after the complete explosion). can do.

According to the fourth aspect of the invention, the valve overlap period after the internal combustion engine reaches the complete explosion state is set to be longer than before the complete explosion state is reached, thereby increasing the internal EGR gas amount. be able to. As a result, the in-cylinder temperature (compression end temperature) can be increased by increasing the internal EGR gas after the complete explosion. For this reason, the white smoke (THC) can be sufficiently reduced in the cold state after the completion of the start (after the complete explosion) by combining the effect of reducing the white smoke by increasing the amount of the internal EGR gas.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. The system shown in FIG. 1 includes a four-cycle diesel engine (compression ignition internal combustion engine) 10. It is assumed that the diesel engine 10 is mounted on a vehicle and used as a power source. Although the diesel engine 10 of the present embodiment is an in-line four-cylinder type, the number of cylinders and the cylinder arrangement of the diesel engine in the present invention are not limited to this.

  Each cylinder of the diesel engine 10 is provided with an injector 12 that injects fuel directly into the cylinder. The injectors 12 of each cylinder are connected to a common common rail 14. In the common rail 14, high-pressure fuel pressurized by the supply pump 16 is stored. Then, fuel is supplied from the common rail 14 to the injectors 12 of each cylinder. The exhaust gas discharged from each cylinder is collected by the exhaust manifold 18 and flows into the exhaust passage 20.

  The diesel engine 10 includes a variable nozzle type turbocharger 22. The turbocharger 22 includes a turbine 22a that is operated by exhaust energy of exhaust gas, and a compressor 22b that is integrally connected to the turbine 22a and is driven to rotate by exhaust energy of exhaust gas input to the turbine 22a. ing. Furthermore, the turbocharger 22 has a variable nozzle (VN) 22c for adjusting the flow rate of the exhaust gas supplied to the turbine 22a.

  The variable nozzle 22c can be opened and closed by an actuator (not shown) (for example, an electric motor). When the opening of the variable nozzle 22c is reduced, the inlet area of the turbine 22a is reduced, and the flow rate of the exhaust gas blown to the turbine 22a can be increased. As a result, the rotational speeds of the compressor 22b and the turbine 22a (hereinafter referred to as “turbo rotational speed”) are increased, so that the supercharging pressure can be increased. Conversely, when the opening of the variable nozzle 22c is increased, the inlet area of the turbine 22a is increased, and the flow rate of the exhaust gas blown to the turbine 22a is decreased. As a result, the turbo rotation speed decreases, so that the supercharging pressure can be reduced.

  The turbine 22 a of the turbocharger 22 is disposed in the exhaust passage 20. An exhaust throttle valve 24 for limiting the flow rate of the exhaust gas flowing through the exhaust passage 20 is disposed in the exhaust passage 20 on the downstream side of the turbine 22a.

  An air cleaner 28 is provided near the inlet of the intake passage 26 of the diesel engine 10. The air sucked through the air cleaner 28 is compressed by the compressor 22 b of the turbocharger 22 and then cooled by the intercooler 30. The intake air that has passed through the intercooler 30 is distributed by the intake manifold 32 and flows into each cylinder.

  An intake throttle valve 34 is installed between the intercooler 30 and the intake manifold 32 in the intake passage 26. An air flow meter 36 for detecting the intake air amount is installed in the intake passage 26 near the downstream of the air cleaner 28.

  One end of an EGR passage 38 is connected to the intake passage 26 in the vicinity of the intake manifold 32. The other end of the EGR passage 38 is connected to the exhaust manifold 18 of the exhaust passage 20. In the present system, a part of the exhaust gas (burned gas) can be recirculated to the intake passage 26 through the EGR passage 38, that is, external EGR (Exhaust Gas Recirculation) can be performed.

  An EGR cooler 40 for cooling the exhaust gas (EGR gas) passing through the EGR passage 38 is provided in the middle of the EGR passage 38. An EGR valve 42 is provided downstream of the EGR cooler 40 in the EGR passage 38. By changing the opening degree of the EGR valve 42, the amount of exhaust gas passing through the EGR passage 38, that is, the amount of external EGR gas can be adjusted.

  Further, the system of the present embodiment includes an accelerator opening sensor 44 that detects the amount of depression of the accelerator pedal (accelerator opening) of the vehicle on which the diesel engine 10 is mounted, a water temperature sensor 46 that detects the engine coolant temperature, An intake pressure sensor 48 that detects an intake manifold pressure (intake pressure), an exhaust pressure sensor 50 that detects an exhaust manifold pressure (exhaust pressure), and an ECU (Electronic Control Unit) 60 are further provided. The ECU 60 is connected to the various sensors and actuators described above. The ECU 60 controls the operating state of the diesel engine 10 by operating each actuator according to a predetermined program based on the output of each sensor.

  FIG. 2 is a view showing a cross section of one cylinder of the diesel engine 10 in the system shown in FIG. Hereinafter, the diesel engine 10 will be further described. As shown in FIG. 2, a crank angle sensor 72 that detects a rotation angle of the crankshaft 70, that is, a crank angle, is attached in the vicinity of the crankshaft 70 of the diesel engine 10. The crank angle sensor 72 is connected to the ECU 60. The ECU 60 can also calculate the engine speed based on the detection signal of the crank angle sensor 72.

  The diesel engine 10 also includes an intake variable valve mechanism 76 that varies the valve opening characteristic of the intake valve 74 and an exhaust variable valve mechanism 80 that varies the valve opening characteristic of the exhaust valve 78. The specific configurations of the intake variable valve mechanism 76 and the exhaust variable valve mechanism 80 are not particularly limited, and the phase variable mechanism of the phase variable mechanism that continuously varies the opening / closing timing by changing the phase of the camshaft. In addition, a mechanism for driving the cam with an electric motor, an electromagnetically driven valve, a hydraulically driven valve, or the like can be used. Further, an intake cam angle sensor 82 and an exhaust cam angle sensor 84 for detecting the rotation angles of the respective cam shafts, that is, the intake cam angle and the exhaust cam angle, are arranged in the vicinity of the intake cam shaft and the exhaust cam shaft, respectively. Has been. These sensors 82 and 84 are connected to the ECU 60. The ECU 60 can also calculate the advance amount of the opening / closing timing of the intake valve 74 and the exhaust valve 78 based on the detection signals of these sensors 82 and 84.

  According to the intake variable valve mechanism 76 and the exhaust variable valve mechanism 80, a valve overlap period (hereinafter simply referred to as a “valve overlap period”) in which the valve opening period of the exhaust valve 78 and the valve opening period of the intake valve 74 overlap. ) Can be changed.

  In the system of the present embodiment configured as described above, the back pressure of the diesel engine 10 is reduced by narrowing the opening of the variable nozzle (VN) 22c of the turbocharger 22 and the opening of the exhaust throttle valve 24. Can be increased. Further, by securing the valve overlap period by the variable valve mechanisms 76 and 80, it becomes possible to increase the amount of internal EGR gas by utilizing the recirculation of the exhaust gas from the exhaust passage 20 into the cylinder.

[In-cylinder temperature rise control during cold start]
FIG. 3 is a time chart for explaining the in-cylinder temperature rise control referred to for comparison with the control in the first embodiment of the present invention. More specifically, this in-cylinder temperature increase control is a control that increases the in-cylinder temperature by increasing the back pressure of the diesel engine during cold start.

  FIG. 3A is a diagram showing how the engine speed changes when the diesel engine is started. At the start of the diesel engine, as shown in FIG. 3A, first, cranking is performed by the operation of a starter motor (not shown). Then, as the combustion of the diesel engine starts after the first explosion during cranking, the engine speed increases. After that, when the diesel engine reaches a complete explosion state (a state in which the diesel engine can stand on its own and stably), the starting operation of the diesel engine is completed. In addition, after the start operation is completed, the engine speed is maintained at the idling speed while a request for increasing the load of the diesel engine is not issued. Further, here, as shown in FIG. 3A, the period from the cranking start time (ie, the start time) to the complete explosion determination time (ie, the start time) of the diesel engine is “starting”. It is called.

  In the in-cylinder temperature rise control described with reference to FIG. 3 for comparison, as shown in FIG. 3 (B), the opening of the exhaust throttle valve or the variable nozzle, or the opening of both of these, is being started. By restricting it to a sufficiently small value, the flow rate of the exhaust gas flowing through the exhaust passage 20 is limited, and the back pressure of the diesel engine is increased. If the back pressure is increased during cranking by such a method, the in-cylinder temperature (compression end temperature) can be increased, and the combustion at the first explosion can be improved. In addition, if the back pressure is increased by the above method even after the first explosion, the in-cylinder temperature can be increased even after the first explosion, and the combustion during the cold state after the start or after the start is good. Can be.

  By the way, in the diesel engine, there is a problem that the emission amount of white smoke (THC) is easily increased by the reduction in the compression ratio particularly during cold including start-up. According to the method shown in FIG. 3, the in-cylinder temperature (compression end temperature) can be increased, so that it is possible to reduce the emission of white smoke (THC) during cold start. However, if the back pressure is increased, the pumping loss is increased, so that the start of the engine speed after the first explosion becomes slow. As a result, the time until the diesel engine reaches the complete explosion state (the time required to complete the start-up) is extended, and the execution time of special control that is performed at the start-up, such as increasing the fuel injection amount, is extended. This leads to an increase in white smoke (THC) emissions.

[Characteristics of Embodiment 1]
FIG. 4 is a time chart for explaining characteristic control executed when the diesel engine 10 is started in the cold state in the first embodiment of the present invention. The waveform indicated by the solid line in FIG. 4 is for the case where back pressure reduction control, which will be described later, of the present embodiment is accompanied, while the waveform indicated by the broken line in FIG. 4 does not involve the back pressure reduction control. This is for the control shown in FIG.

  In the present embodiment, first, during cranking, as shown in FIG. 4B, the openings of the exhaust throttle valve 24 and the variable nozzle 22c are made to be narrowed down as in the control shown in FIG. Yes.

  Furthermore, in the present embodiment, after it is determined that the first explosion has occurred during cranking, the respective opening degrees of the exhaust throttle valve 24 and the variable nozzle 22c are set according to the engine speed from before the first explosion. Also, the opening is set to the opening side. Thereby, the back pressure after the first explosion can be reduced. Here, such control is referred to as “back pressure reduction control”.

FIG. 5 is a flowchart of a routine executed by the ECU 60 in the first embodiment in order to realize the above function.
In the routine shown in FIG. 5, first, the engine speed Ne and the engine coolant temperature are read based on the outputs of the crank angle sensor 72 and the water temperature sensor 46, respectively, and the starter signal at the start is read (step 100). ).

  Next, based on the voltage signal of the starter read in step 100, it is determined whether or not the starter is being driven (step 102). As a result, if it is determined that the starter is being driven, it is then determined whether or not cranking is being performed (step 104). More specifically, in this step 104, while it is not determined that the first explosion has occurred, it is determined that cranking is being performed based on the determination result of the presence or absence of the first explosion. It is determined that the cranking is not in progress (after the first explosion). The first explosion can be detected by determining that the first explosion has occurred based on the output of the crank angle sensor 72, for example, when the change in the cycle of the crank angle signal indicates a decrease of a predetermined value or more.

  If it is determined in step 104 that cranking is being performed, the exhaust throttle valve 24 is closed to a predetermined opening, and the opening of the variable nozzle 22c is controlled to a fully closed opening (step 106). ). Thereby, the flow rate of the exhaust gas flowing through the exhaust passage 20 during cranking is limited, and the back pressure of the diesel engine 10 is increased.

  On the other hand, if it is determined in step 104 that cranking is not being performed, that is, if it can be determined that the stage is after the first explosion, the opening degrees of the exhaust throttle valve 24 and the variable nozzle 22c are the initial opening degrees. The opening is set to the opening side before the explosion occurs (during cranking) (step 108). More specifically, in this step 108, the respective opening degrees of the exhaust throttle valve 24 and the variable nozzle 22c are determined according to the engine speed after the first explosion occurs. For example, the opening degree of the exhaust throttle valve 24 and the variable nozzle 22c may be gradually opened as the engine speed after the first explosion occurs increases.

  According to the routine shown in FIG. 5 described above, during cranking, the opening of the exhaust throttle valve 24 and the variable nozzle 22c is sufficiently reduced to increase the back pressure of the diesel engine 10 and increase the in-cylinder temperature ( (Compression end temperature) can be increased, and combustion at the first explosion can be improved.

  In addition, according to the above routine, after the first explosion occurs, the respective opening degrees of the exhaust throttle valve 24 and the variable nozzle 22c are set to the opening side more open than before the first explosion according to the engine speed. (Back pressure reduction control). Thereby, the back pressure after the first explosion can be reduced. According to such back pressure reduction control, the pumping loss of the diesel engine 10 can be reduced after the first explosion occurs. Thereby, the time until the diesel engine 10 reaches the complete explosion state after the first explosion (the time required for completion of the start) and the execution time such as the increase of the fuel injection amount during the start execute the in-cylinder temperature rise control. It is possible to avoid the extension. For this reason, at the time of a cold start, it becomes possible to suppress suitably the increase in discharge amount of white smoke (THC).

  By the way, in Embodiment 1 mentioned above, when raising a back pressure during cranking, the opening degree of both the exhaust throttle valve 24 and the variable nozzle 22c is made small enough. However, the present invention is not limited to such a method, and the opening degree of either the exhaust throttle valve 24 or the variable nozzle 22c may be sufficiently reduced during cranking.

  Further, in the first embodiment described above, when reducing the pumping loss after the first explosion, the opening degree of both the exhaust throttle valve 24 and the variable nozzle 22c is set to open more open than before the first explosion. It is set to the degree. However, the present invention is not limited to such a method, and any one of the exhaust throttle valve 24 and the variable nozzle 22c may be opened after the first explosion before the first explosion.

In the first embodiment described above, the "back pressure varying means" in the variable nozzle 22c and the exhaust throttle valve 24 is the first and second inventions of the turbocharger 22, their respective equivalent to Yes. Further, when the ECU 60 executes the process of step 106 or 108, the “back pressure control means” in the first and second inventions executes the process of step 104, so that the first and second steps are executed . The “first explosion occurrence determination means” in the present invention implements the “step after the first explosion back pressure control means” in the first and second inventions by executing the processing of step 108 described above.
Further, when the ECU 60 executes the process of step 200, the “complete explosion state determination means” in the first and second inventions performs the process of step 108 while the determination of step 200 is not established. By executing continuously, the “back pressure reduction control continuation means” in the first and second aspects of the invention is realized.
Further, the ECU 60 executes the process of step 106 to realize the “back pressure control means before the first explosion” in the fifth aspect of the invention.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. 6 and FIG.
The system of the present embodiment can be realized by causing the ECU 60 to execute a routine shown in FIG. 7 described later instead of the routine shown in FIG. 5 using the hardware configuration shown in FIG.

[Characteristics of Embodiment 2]
FIG. 6 is a time chart for explaining characteristic control executed when the diesel engine 10 is started in the cold state in the second embodiment of the present invention.
As shown in FIG. 6, the control of the second embodiment is the same as the control shown in FIG. 4 in the first embodiment described above except that the control after the complete explosion determination of the diesel engine 10 is different. In other words, in the present embodiment, after it is determined that the first explosion has occurred, the opening period of each of the exhaust throttle valve 24 and the variable nozzle 22c is less than that before the first explosion occurs in order to reduce the pumping loss. It is set to be from the determination time to the time when it is determined that the complete explosion state has been reached.

  Further, in the present embodiment, after the diesel engine 10 reaches the complete explosion state, as shown in FIG. 6B, the opening of the variable nozzle 22c is set closer to the closed side than before reaching the complete explosion state. (For example, fully closed opening). Further, the opening degree of the exhaust throttle valve 24 after reaching the complete explosion state is basically set to an opening degree corresponding to the engine speed as before reaching the complete explosion state. In FIG. 6C, the opening degree of the exhaust throttle valve 24 after reaching the complete explosion state is represented by the same opening degree as that before reaching the complete explosion state. The exhaust throttle valve 24 may be opened as the number increases.

  FIG. 7 is a flowchart of a routine executed by the ECU 60 in the second embodiment in order to realize the above function. In FIG. 7, the same steps as those shown in FIG. 5 in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the routine shown in FIG. 7, if it is determined in step 104 that cranking is not being performed (that is, the stage after the initial explosion occurs), then whether or not the diesel engine 10 has reached a complete explosion state. Is determined (step 200). Here, after the start operation of the diesel engine 10 is started, it is determined that the diesel engine 10 is in a complete explosion state when the engine speed is maintained at a speed equal to or higher than the predetermined speed for a predetermined time. ing.

  If it is determined in step 200 that the diesel engine 10 has not yet reached the complete explosion state, the respective opening degrees of the exhaust throttle valve 24 and the variable nozzle 22c are set before the first explosion occurs (during cranking). ) Is set to the opening on the opening side (step 108). On the other hand, when it is determined in step 200 that the diesel engine 10 has already reached the complete explosion state, the opening of the variable nozzle 22c is closer to the closing side than before reaching the complete explosion state. (For example, fully closed opening) is set (step 202). The opening degree of the exhaust throttle valve 24 is set to an opening degree corresponding to the engine speed even after reaching the complete explosion state.

  According to the routine shown in FIG. 7 described above, the opening degree of each of the exhaust throttle valve 24 and the variable nozzle 22c varies depending on the engine speed from the initial explosion determination time to the complete explosion determination time. The opening degree is set to the opening side of the front (the back pressure reduction control). As a result, the pumping loss can be reduced as compared with cranking. Therefore, it is possible to avoid the extension of the time required to complete the start of the diesel engine 10 and the accompanying increase in the fuel injection amount increase execution time. It is possible to reduce the emission of white smoke (THC) during start-up.

  In addition, according to the above routine, after the diesel engine 10 reaches the complete explosion state, the opening degree of the variable nozzle 22c is sufficiently reduced again. Thereby, turbo rotation speed can be raised and a supercharging pressure can be raised. As a result, the actual compression ratio of the diesel engine 10 is increased, so that the in-cylinder temperature (compression end temperature) can be increased, and white smoke (THC) is discharged when the engine is cold after completion (after complete explosion). Can be suppressed.

  By the way, in Embodiment 2 mentioned above, the opening degree of the exhaust throttle valve 24 after the diesel engine 10 reaches a complete explosion state is set to the opening degree according to the engine speed. However, in the present invention, the opening of the exhaust throttle valve after reaching the complete explosion state is not limited to such a setting. For example, after the diesel engine 10 reaches the complete explosion state, the exhaust You may set the opening degree of the throttle valve 24 to the opening degree of opening side rather than reaching a complete explosion state (full opening degree as a preferable example). According to such a setting, the turbo rotational speed can be increased by lowering the exhaust pressure downstream of the turbocharger. Furthermore, by executing such control in combination with the opening degree control of the variable nozzle 22c of the second embodiment described above, the supercharging pressure can be sufficiently increased after the complete explosion.

In the second embodiment described above, the “post-combustion nozzle opening setting means” according to the third aspect of the present invention is realized by the ECU 60 executing the processing of step 202 described above.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to FIG. 8 and FIG.
The system of the present embodiment can be realized by causing the ECU 60 to execute a routine shown in FIG. 9 described later instead of the routine shown in FIG. 7 using the hardware configuration shown in FIG.

[Characteristics of Embodiment 3]
FIG. 8 is a time chart for explaining characteristic control executed when the diesel engine 10 is started in the cold state in the third embodiment of the present invention.
The control of the third embodiment is the same as the control shown in FIG. 6 in the second embodiment described above, except that the valve overlap period shown in FIG. 8D is adjusted. More specifically, in this embodiment, the valve overlap period after the diesel engine 10 reaches the complete explosion state is set to a longer period than before reaching the complete explosion state.

  FIG. 9 is a flowchart of a routine executed by the ECU 60 in the third embodiment in order to realize the above function. In FIG. 9, the same steps as those shown in FIG. 7 in the second embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the routine shown in FIG. 9, when it is determined in step 200 that the diesel engine 10 has already reached the complete explosion state, in addition to the control of the variable nozzle 22c and the exhaust throttle valve 24 described in step 202, the routine shown in FIG. The valve overlap period after the diesel engine 10 reaches the complete explosion state is set to be longer than that before the diesel engine 10 reaches the complete explosion state (step 300).

  According to the routine shown in FIG. 9 described above, the valve overlap period after the diesel engine 10 reaches the complete explosion state while achieving the effects of the routine shown in FIG. 7 described in the second embodiment. By setting the length to be longer than before reaching the complete explosion state, the amount of internal EGR gas can be increased. As a result, the in-cylinder temperature (compression end temperature) can be increased by increasing the internal EGR gas after the complete explosion. For this reason, the white smoke (THC) can be sufficiently reduced in the cold state after the completion of the start (after the complete explosion) by combining the effect of reducing the white smoke by increasing the amount of the internal EGR gas.

  In addition, according to the above routine, the opening of the variable nozzle 22c is sufficiently reduced after the complete explosion (that is, the back pressure is increased by such opening control of the variable nozzle 22c). ) Since the valve overlap period is set to be long, the internal EGR gas amount can be effectively increased. In addition, the presence of the internal EGR gas effectively increased in this way and the effect of improving the actual compression ratio due to the increase in the supercharging pressure by the opening degree control of the variable nozzle 22c described above are sufficient for the white smoke (THC). It becomes possible to reduce it.

In the third embodiment described above, the ECU 60 executes the process of step 300, thereby realizing the “overlap period setting means after complete explosion” in the fourth aspect of the invention.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure which shows the cross section of one cylinder of the diesel engine in the system shown in FIG. It is a time chart for demonstrating the in-cylinder temperature rise control referred for contrast with the control in Embodiment 1 of this invention. In Embodiment 1 of this invention, it is a time chart for demonstrating the characteristic control performed when starting a diesel engine at the time of cold. It is a flowchart of the routine performed in Embodiment 1 of the present invention. In Embodiment 2 of this invention, it is a time chart for demonstrating the characteristic control performed when starting a diesel engine at the time of cold. It is a flowchart of the routine performed in Embodiment 2 of this invention. In Embodiment 3 of this invention, it is a time chart for demonstrating the characteristic control performed when starting a diesel engine at the time of cold. It is a flowchart of the routine performed in Embodiment 3 of the present invention.

Explanation of symbols

10 Diesel engine 18 Exhaust manifold 20 Exhaust passage 22 Variable nozzle turbocharger (VNT)
22a Turbine 22b Compressor 22c Variable nozzle (VN)
24 Exhaust throttle valve 26 Intake passage 32 Intake manifold 46 Water temperature sensor 60 ECU (Electronic Control Unit)
72 Crank angle sensor 74 Intake valve 76 Intake variable valve mechanism 78 Exhaust valve 80 Exhaust variable valve mechanism

Claims (5)

Back pressure variable means for changing the back pressure of the internal combustion engine;
Back pressure control means for controlling back pressure using the back pressure variable means;
An initial explosion occurrence determining means for determining whether or not an initial explosion of the internal combustion engine has occurred,
The back pressure variable means corresponds to a variable nozzle for adjusting the flow rate of the exhaust gas supplied to the turbine of the turbocharger,
After determining that the first explosion has occurred, the back pressure control means performs an initial explosion that performs back pressure reduction control for controlling the opening of the variable nozzle to an opening on the opening side of the variable nozzle before the occurrence of the first explosion. viewing including the Doggy pressure control means,
The control device for the internal combustion engine further includes a complete explosion state determination means for determining whether or not the internal combustion engine has reached a complete explosion state,
The back pressure control means after the first explosion includes back pressure reduction control continuation means for continuing the back pressure reduction control from the time of occurrence determination of the first explosion to the complete explosion state,
The control device for an internal combustion engine, wherein the back pressure reduction control gradually opens the opening of the variable nozzle as the engine speed after the first explosion increases . Back pressure variable means for changing the back pressure of the internal combustion engine;
Back pressure control means for controlling back pressure using the back pressure variable means;
An initial explosion occurrence determining means for determining whether or not an initial explosion of the internal combustion engine has occurred,
The back pressure variable means corresponds to an exhaust throttle valve for limiting the flow rate of exhaust gas flowing through the exhaust passage,
After determining that the first explosion has occurred, the back pressure control means performs initial pressure reduction control for controlling the opening of the exhaust throttle valve to an opening on the opening side of the first explosion before the occurrence of the first explosion. viewing including the explosion back pressure control means,
The control device for the internal combustion engine further includes a complete explosion state determination means for determining whether or not the internal combustion engine has reached a complete explosion state,
The back pressure control means after the first explosion includes back pressure reduction control continuation means for continuing the back pressure reduction control from the time of occurrence determination of the first explosion to the complete explosion state,
The control device for the internal combustion engine includes:
A variable valve mechanism for varying a valve overlap period in which an intake valve opening period and an exhaust valve opening period overlap;
A post-explosion overlap period setting means for setting a valve overlap period after reaching the complete explosion state to a longer period than before reaching the complete explosion state;
Further comprising
The control device for an internal combustion engine according to claim 1, wherein the back pressure reduction control gradually opens the opening of the exhaust throttle valve as the engine speed after the first explosion increases . Controller before SL internal combustion engine, wherein an opening degree of the variable nozzle after reaching complete combustion state, after complete explosion nozzle opening is set to the closing side of the opening than before reaching the complete combustion state control apparatus for an internal combustion engine according to claim 1, further comprising a time setting means. The control device for the internal combustion engine includes a variable valve mechanism that varies a valve overlap period in which an intake valve opening period and an exhaust valve opening period overlap each other;
A post-explosion overlap period setting means for setting a valve overlap period after reaching the complete explosion state to a longer period than before reaching the complete explosion state;
Control apparatus for an internal combustion engine according to claim 1 or 3, wherein further comprising a. The back pressure control means, the back pressure before the occurrence of the initial explosion, either the back-pressure claims 1 to 4, characterized in that it comprises a before first explosion back pressure control means for increasing using a modification means 1 control apparatus for an internal combustion engine of claim wherein.

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