JP5397291B2 - Start control device for turbocharged engine - Google Patents

Description

  The technology disclosed herein relates to a start control device for an engine with a turbocharger, and particularly relates to control at the time of starting an automatically stopped engine.

  For example, Patent Document 1 describes a control device for an engine with a turbocharger. This control device eliminates the deterioration of the startability of the vehicle as a result of an increase in engine back pressure and an increase in engine pumping loss due to a delay in the increase in rotation of the turbocharger when the vehicle starts. Therefore, the wastegate valve interposed on the bypass passage that bypasses the turbine on the exhaust passage of the engine is fully opened for a predetermined period when the vehicle starts. In other words, in this control device, the back pressure of the engine is reduced by bypassing the turbine that can become exhaust resistance in the low engine speed range, thereby reducing the pumping loss of the engine and improving the startability of the vehicle accordingly. I am doing so.

  In addition, the turbocharger is configured in series with two turbochargers, a relatively small turbocharger and a relatively large turbocharger, in order to increase output. A configuration (so-called two-stage turbo configuration) is known. In this two-stage turbo configuration, two large and small turbines are arranged in series on the exhaust passage of the engine, and two bypass passages are provided so as to bypass each turbine. A regulation valve (on the bypass path of the small turbine) and a waste gate valve (on the bypass path of the large turbine) are interposed on the road.

JP-A-8-170541

By the way, for the purpose of reducing fuel consumption and CO ₂ emission, for example, the engine is automatically stopped if a predetermined stop condition is satisfied during a temporary stop of the vehicle, and the engine is restarted if a predetermined start condition is satisfied. A so-called idle stop system is known. Therefore, it is conceivable to apply such an idle stop system to the aforementioned turbocharged engine.

  Here, as the engine start condition, for example, a start condition accompanied by a vehicle start request, which is established when the driver performs an accelerator operation, and a state of charge (SOC) of the battery, for example, decreases. There are two types of starting conditions that are established by a request on the vehicle side but not accompanied by a start request, such as the necessity of starting the compressor of the air conditioner.

  Among these, when a start condition not accompanied by a vehicle start request is satisfied, the start of the engine is completed in a short time, and after the start is completed, a start request due to the driver's accelerator operation or the like is made. It is desirable to wait in preparation. On the other hand, when the start condition accompanied by the start request is satisfied, the start of the vehicle must be started and accelerated immediately after the start is completed as well as the start of the engine is completed in a short time. From the viewpoint of improving the start acceleration performance at that time, it is desirable that the turbocharging is started early. Thus, when starting the engine when the start condition is satisfied, the request differs depending on whether or not a start request is made.

  The technology disclosed herein has been made in view of such a point, and the purpose thereof is related to restart control of an engine with a turbocharger, depending on whether or not a start request is made when a start condition is satisfied. The goal is to optimize the starting control.

  The technology disclosed herein is a turbocharged engine having a so-called two-stage turbo configuration, including first and second turbochargers including first and second turbines arranged in series on an exhaust passage. First and second bypass passages for bypassing the first and second turbines when a start condition with a start request is satisfied and when a start condition without a start request is satisfied We decided to make the valve control different.

  In other words, when the start condition with the start request of the vehicle is satisfied, after the engine start is completed, the turbocharger is started at an early stage to improve the start acceleration performance, so that it is disposed relatively upstream on the exhaust passage. The back pressure of the first turbine is reduced to increase the differential pressure before and after the first turbine, thereby quickly increasing the rotational speed of the first turbine from the 0 (zero) rotation among the first and second turbines. For this purpose, valve control is performed in which the first valve on the first bypass path that bypasses the first turbine is closed after the engine start condition is satisfied, while the second valve on the second bypass path that bypasses the second turbine is opened. Run.

  On the other hand, when start conditions that do not require a vehicle start request are satisfied, there is no request to start turbocharging early, but it is necessary to respond promptly when a start is requested after engine start is completed Therefore, the system waits in a state where both the first and second turbines are rotated. For this purpose, valve control is performed to close both the first and second valves after the engine start condition is satisfied.

  Specifically, an engine start control device for a turbocharged engine disclosed herein includes an engine mounted on a vehicle, a fuel injection valve that injects fuel into a combustion chamber of the engine, and an exhaust passage of the engine. A first turbocharger including a first turbine disposed relatively upstream, a second turbocharger including a second turbine disposed relatively downstream, and the first A normally open first valve provided on a first bypass path that bypasses the turbine, a normally open second valve provided on a second bypass path that bypasses the second turbine, and a predetermined stop When the condition is satisfied, the engine is stopped, and when a predetermined start condition is satisfied, predetermined start control is performed to burn the fuel supplied into the combustion chamber through the fuel injection valve. And a start control means for starting the engine.

  The start control means closes the first valve after the start condition is satisfied and executes the start control when the start condition with the vehicle start request is satisfied, and completes the start of the engine. The first valve control for closing the second valve is executed when a predetermined time elapses. On the other hand, when a start condition that does not require a start of the vehicle is satisfied, the start condition is After the establishment, the second valve control for closing both the first and second valves is executed.

  Here, each of the first valve and the second valve may be a valve whose opening degree can be adjusted. In this case, “closing the valve” includes not only fully closing the valve, The opening may include a predetermined opening on the closing side.

  According to this configuration, when the start condition with the start request of the vehicle is satisfied, the start control for starting the engine by supplying the fuel into the combustion chamber of the engine and burning it is executed. And with this start control, the 1st valve on the 1st bypass way which bypasses the 1st turbine arranged on the relatively upstream side on the exhaust passage of an engine is closed. The first valve may be closed at the start of engine start control, or may be closed after completion of engine start. On the other hand, the second valve on the second bypass passage that bypasses the second turbine disposed on the relatively downstream side is closed when a predetermined time elapses after the start of the engine is completed. That is, after the start condition is satisfied, the first valve can be closed and the second valve can be opened in a transitional period from when the engine start is completed until a predetermined time elapses. Since this state can bypass the second turbine downstream of the first turbine, the back pressure of the first turbine is reduced and the differential pressure across the first turbine is increased. This is advantageous in that the number of revolutions of the first turbine is quickly increased from zero with the start of the engine, and after the start of the engine is completed, supercharging by the first turbocharger is started early. become. That is, the start acceleration performance can be improved.

  On the other hand, when a start condition that does not require a vehicle start request is established, the first valve on the first bypass path and the second valve on the second bypass path are closed together with the execution of the start control. Here, the timing of closing the first and second valves may be set as appropriate after the start condition is satisfied, for example, immediately after the start condition is satisfied (that is, at the start of engine start control) Immediately after the start-up is completed. By closing the first and second valves, each of the stopped first and second turbines can start rotating as the engine is started. Each of the second turbines can be put on standby in a rotating state. This is advantageous in quickly responding to a start request when a start request is made after completion of engine start.

  The first valve may be configured to be closed when the engine is in a low rotation range, and to be opened in other regions. Here, “opening the valve” includes opening the valve to a predetermined opening on the opening side in addition to fully opening the valve.

  That is, the first turbocharger may be a relatively small turbocharger that performs supercharging mainly when the engine is in a low rotation range. In other words, the first valve is closed in the low engine speed range and the small turbocharger is driven to improve the start-up characteristic, while the first valve is operated when the engine is in the middle or high engine speed range. By opening and bypassing the first turbine, the exhaust resistance can be reduced. This configuration also allows the first turbine to be small and low-inertia, so that, as described above, when the engine start condition that requires a start request is satisfied, the first turbine can be quickly increased from 0 rpm. It becomes even more advantageous.

  The engine is a diesel engine, and the start control means injects fuel during an expansion stroke following main injection that injects fuel in the vicinity of compression top dead center when a start condition involving a start request of the vehicle is satisfied. The post injection control for performing the post injection may be further executed.

  Performing post-injection during the expansion stroke can be advantageous in increasing exhaust energy and quickly increasing the rotational speed of the first turbine. In other words, when the start condition with the vehicle start request is established, the first valve control described above is combined with the post-injection control, so that supercharging by the first turbocharger can be started early and sufficient supercharging can be performed. The start acceleration performance can be further enhanced by securing the pressure.

  As described above, according to the start control device for an engine with a turbocharger, when the start condition with the vehicle start request is satisfied, the engine start control is performed together with the engine start control, and then the engine start is performed. During the transition period until the predetermined time elapses, the first valve is closed and the second valve is opened, thereby increasing the differential pressure across the first turbine and increasing the rotational speed of the first turbine. Can be quickly increased from 0 rotation. As a result, the supercharging by the first turbocharger can be started at an early stage, and the start acceleration performance immediately after completion of the engine start can be improved. On the other hand, when the start condition without the vehicle start request is established, both the first and second turbines are turned on after the start of the engine is completed by closing both the first and second valves together with the execution of the engine start control. Since it can be made to stand by in the state where it is rotating, it is advantageous in promptly responding to a start request made after completion of engine start.

It is the schematic which shows the structure of the diesel engine with a turbocharger. It is a block diagram concerning a control device of a diesel engine. It is an example of the operation | movement map of a small and a large sized turbocharger. It is a flowchart which concerns on the engine start control which PCM performs. (A) Start request restart execution flag, (B) Engine speed, (C) Complete explosion flag, (D) Post injection execution flag, (E) Regulate valve opening, (F) according to one embodiment It is a time chart which shows an example of a change of a waste gate valve opening degree, (G) small turbine rotational speed, and (H) large turbine rotational speed.

  Hereinafter, a start control device for an engine with a turbocharger will be described with reference to the drawings. The following description of the preferred embodiment is merely exemplary in nature. 1 and 2 show a schematic configuration of an engine 1 that employs a control device according to an embodiment. The engine 1 is a diesel engine mounted on a vehicle, and includes a cylinder block 11 provided with a plurality of cylinders 11a (only one is shown), a cylinder head 12 disposed on the cylinder block 11, An oil pan 13 is disposed below the cylinder block 11 and stores lubricating oil. In each cylinder 11a of the engine 1, a piston 14 is fitted and removably fitted. A top surface of the piston 14 is formed with a cavity that defines a deep dish combustion chamber 14a. The piston 14 is connected to the crankshaft 15 via a connecting rod 14b. The cylinder block 11 is provided with a water temperature sensor SW1 that detects the temperature of engine cooling water.

  In the cylinder head 12, an intake port 16 and an exhaust port 17 are formed for each cylinder 11a, and an intake valve 21 and an exhaust valve that open and close the opening of the intake port 16 and the exhaust port 17 on the combustion chamber 14a side. 22 are arranged respectively. In the valve systems that drive these intake and exhaust valves 21 and 22, respectively, a hydraulically operated variable mechanism that switches the operation mode of the exhaust valve 22 between a normal mode and a special mode on the exhaust valve side (see FIG. 2 below). VVM (Variable Valve Motion). Although detailed illustration of the configuration of the VVM 71 is omitted, two types of cams having different cam profiles, a first cam having one cam peak and a second cam having two cam peaks, and the first cam When a lost motion mechanism that selectively transmits the operating state of one of the first and second cams to the exhaust valve is included, and the operating state of the first cam is transmitted to the exhaust valve 22 The exhaust valve 22 operates in a normal mode in which the valve is opened only once during the exhaust stroke, whereas when the operating state of the second cam is transmitted to the exhaust valve 22, the exhaust valve 22 is in the exhaust stroke. In addition, the valve operates in a special mode in which the exhaust is opened twice so that the valve is opened during the intake stroke. Switching between the normal mode and the special mode of the VVM 71 is performed by hydraulic pressure supplied from an engine-driven hydraulic pump (not shown), and the special mode can be used in the control related to the internal EGR. In order to enable switching between the normal mode and the special mode, an electromagnetically driven valve system that drives the exhaust valve 22 by an electromagnetic actuator may be employed.

  The cylinder head 12 is provided with an injector 18 for injecting fuel and a glow plug 19 for warming intake air and improving fuel ignitability when the engine 1 is cold. The injector 18 is disposed so that its fuel injection port faces the combustion chamber 14a from the ceiling surface of the combustion chamber 14a, and is configured to directly inject and supply fuel to the combustion chamber 14a near the top dead center of the compression stroke. It has become.

  An intake passage 30 is connected to one side of the engine 1 so as to communicate with the intake port 16 of each cylinder 11a. On the other hand, an exhaust passage 40 for discharging burned gas (exhaust gas) from the combustion chamber 14a of each cylinder 11a is connected to the other side of the engine 1. The intake passage 30 and the exhaust passage 40 are provided with a large turbocharger 61 and a small turbocharger 62 that supercharge intake air.

  An air cleaner 31 that filters intake air is disposed at the upstream end of the intake passage 30. On the other hand, a surge tank 33 is disposed near the downstream end of the intake passage 30. The intake passage 30 downstream of the surge tank 33 is an independent passage branched for each cylinder 11a, and the downstream end of each independent passage is connected to the intake port 16 of each cylinder 11a. The surge tank 33 is provided with a supercharging pressure sensor SW2 that detects the pressure of air supplied to the combustion chamber 14a.

  Between the air cleaner 31 and the surge tank 33 in the intake passage 30, an intake air temperature sensor SW 3 that detects the temperature of the intake air in order from the upstream side, and compressors of large and small turbochargers 61 and 62 described later in detail. 61a, 62a, a supercharged air temperature sensor SW4 for detecting the temperature of the air compressed by the compressors 61a, 62a, an intercooler 35 for cooling the air compressed by the compressors 61a, 62a, and the cylinders 11a. And a throttle valve 36 for adjusting the amount of intake air into the combustion chamber 14a. The throttle valve 36 is basically fully opened, but is fully closed when the engine 1 is stopped so that no shock is generated.

  The upstream portion of the exhaust passage 40 is constituted by an exhaust manifold having an independent passage branched for each cylinder 11a and connected to the outer end of the exhaust port 17 and a collecting portion where the independent passages gather. Yes.

  On the downstream side of the exhaust manifold in the exhaust passage 40, the turbine 62b of the small turbocharger 62, the turbine 61b of the large turbocharger 61, and exhaust for purifying harmful components in the exhaust gas in order from the upstream side. A purification device 41 and a silencer 42 are provided.

The exhaust purification device 41 includes an oxidation catalyst 41a and a diesel particulate filter (hereinafter referred to as a filter) 41b, which are arranged in this order from the upstream side. The oxidation catalyst 41a and the filter 41b are accommodated in one case. The oxidation catalyst 41a has an oxidation catalyst carrying platinum or platinum added with palladium or the like, and promotes a reaction in which CO and HC in the exhaust gas are oxidized to produce CO ₂ and H ₂ O. Is. The oxidation catalyst 41a constitutes a catalyst. The filter 41b collects particulates such as soot contained in the exhaust gas of the engine 1. The filter 41b may be coated with an oxidation catalyst. Further, an exhaust temperature sensor SW5 that detects the temperature of the exhaust gas that has passed through the oxidation catalyst 41a is disposed between the oxidation catalyst 41a and the filter 41b.

  A portion of the intake passage 30 between the surge tank 33 and the throttle valve 36 (that is, a portion on the downstream side of the small compressor 62a of the small turbocharger 62), the exhaust manifold and the small turbocharger in the exhaust passage 40. The portion between the turbocharger 62 and the small turbine 62 b (that is, the upstream portion of the small turbocharger 62 from the small turbine 62 b) is an exhaust gas recirculation for recirculating a part of the exhaust gas to the intake passage 30. They are connected by a passage 50. The exhaust gas recirculation passage 50 is provided with an exhaust gas recirculation valve 51a for adjusting the recirculation amount of the exhaust gas to the intake passage 30 and an EGR cooler 52 for cooling the exhaust gas with engine cooling water. It includes a passage 51 and a cooler bypass passage 53 for bypassing the EGR cooler 52. The cooler bypass passage 53 is provided with a cooler bypass valve 53 a for adjusting the flow rate of the exhaust gas flowing through the cooler bypass passage 53.

  Further, as shown in FIG. 2, the engine 1 is provided with two crank angle sensors SW6 and SW7 for detecting the rotation angle of the crankshaft 15. The engine speed (rotation speed) is detected based on the detection signal output from one crank angle sensor SW6, and the crank angle is detected based on the detection signal out of phase output from both crank angle sensors SW6 and SW7. The position is detected. The engine 1 includes an accelerator opening sensor SW8 that detects an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown) of the vehicle, and a brake pedal sensor that detects an operation of a brake pedal (not shown) of the vehicle. SW9, clutch pedal sensor SW10 for detecting the operation of the vehicle clutch pedal (not shown), shift lever sensor SW11 for detecting the operation of the vehicle shift lever (not shown), and the speed of the vehicle Is provided with a vehicle speed sensor SW12 for detecting.

  Here, the configuration of the large turbocharger 61 and the small turbocharger 62 will be described in detail.

  The large turbocharger 61 has a large compressor 61 a disposed in the intake passage 30 and a large turbine 61 b disposed in the exhaust passage 40. The large compressor 61a is disposed between the air cleaner 31 and the intercooler 35 in the intake passage 30 (specifically, between the intake air temperature sensor SW3 and the supercharged air temperature sensor SW4). On the other hand, the large turbine 61b is disposed between the exhaust manifold and the oxidation catalyst 41a in the exhaust passage 40.

  The small turbocharger 62 has a small compressor 62 a disposed in the intake passage 30 and a small turbine 62 b disposed in the exhaust passage 40. The small compressor 62 a is disposed on the downstream side of the large compressor 61 a in the intake passage 30. On the other hand, the small turbine 62 b is disposed on the upstream side of the large turbine 61 b in the exhaust passage 40.

  That is, in the intake passage 30, a large compressor 61a and a small compressor 62a are arranged in series from the upstream side, and in the exhaust passage 40, a small turbine 62b and a large turbine 61b are arranged in series from the upstream side. Has been. The large and small turbines 61b and 62b are rotated by the exhaust gas flow, and the large and small turbines 61a and 62a connected to the large and small turbines 61b and 62b are rotated by the rotation of the large and small turbines 61b and 62b, respectively. Each operates. An intermediate pressure sensor SW13 for detecting the pressure of intake air supercharged by the large compressor 61a is provided between the large compressor 61a and the small compressor 62a in the intake passage 30.

  The small turbocharger 62 is relatively small, and the large turbocharger 61 is relatively large. That is, the large turbine 61 b of the large turbocharger 61 has a larger inertia than the small turbine 62 b of the small turbocharger 62.

  The intake passage 30 is connected to a small intake bypass passage 63 that bypasses the small compressor 62a. The small intake bypass passage 63 is provided with a small intake bypass valve 63 a for adjusting the amount of air flowing to the small intake bypass passage 63. The small intake bypass valve 63a is configured to be in a fully closed state (normally closed) when no power is supplied.

  On the other hand, the exhaust passage 40 is connected to a small exhaust bypass passage 64 that bypasses the small turbine 62b and a large exhaust bypass passage 65 that bypasses the large turbine 61b. The small exhaust bypass passage 64 is provided with a regulating valve 64a for adjusting the exhaust amount flowing to the small exhaust bypass passage 64, and the large exhaust bypass passage 65 has an exhaust amount flowing to the large exhaust bypass passage 65. A wastegate valve 65a for adjusting the pressure is provided. Both the regulating valve 64a and the waste gate valve 65a are configured to be in a fully open state (normally open) when no power is supplied.

  The small turbocharger 62 is the first turbocharger, the large turbocharger 61 is the second turbocharger, the small exhaust bypass passage 64 is the first bypass passage, and the large exhaust bypass passage 65 is In the second bypass path, the regulating valve 64a constitutes the first valve, and the wastegate valve 65a constitutes the second valve.

  The large turbocharger 61 and the small turbocharger 62 are integrated into a single unit including the intake passage 30 and the exhaust passage 40 in which the large turbocharger 61 and the small turbocharger 62 are arranged, thereby forming a supercharger unit 60. doing. The supercharger unit 60 is attached to the engine 1. The outlet of the intake passage 30 of the supercharger unit 60 is connected to the upstream end of the intercooler 35 via a rubber hose 30a. That is, the intercooler 35 is attached to the vehicle body, and vibration different from that of the supercharger unit 60 attached to the engine 1 occurs. Therefore, the vibrations of the supercharger unit 60 and the intercooler 35 are absorbed by the rubber hose 30a so that they do not affect each other. For the same reason, the downstream end of the intercooler 35 and the upstream portion of the throttle valve 36 of the intake passage 30 are also connected via a rubber hose 30b.

  The turbocharged engine 1 configured as described above is controlled by a powertrain control module (hereinafter referred to as PCM) 10. The PCM 10 includes a microprocessor having a CPU, a memory, a counter timer group, an interface, and a path connecting these units. The PCM 10 constitutes a control device. As shown in FIG. 2, the PCM 10 receives detection signals from the sensors SW1 to SW13, performs various calculations based on these detection signals, determines the state of the engine 1 and the vehicle, and responds accordingly. Control signals are output to the injector 18, the valve-operated VVM 71, and actuators of various valves. The PCM 10 outputs a control signal to the injector 18 and the starter motor 72 when the engine 1 is started, and also outputs a control signal to the glow plug 19 as necessary. Further, the PCM 10 outputs a control signal to a regulator circuit 73 built in an alternator connected to the crankshaft 15 by a timing belt or the like, thereby controlling the amount of power generation corresponding to the electric load of the vehicle and the voltage of the vehicle battery. Execute.

  The PCM 10 controls the operations of the large and small turbochargers 61 and 62 when the engine is operating. Specifically, the PCM 10 controls the openings of the small intake bypass valve 63a, the regulator valve 64a, and the wastegate valve 65a to the openings set according to the operating state of the engine 1, respectively.

  Specifically, the PCM 10 has a low load and low rotation side region A (engine load is smaller than a predetermined load (smaller as the engine speed increases)) in the map having the engine speed and the engine load as parameters shown in FIG. ), Both the large and small turbochargers 61 and 62 are operated by setting the small intake bypass valve 63a and the regulating valve 64a to an opening other than fully open and the wastegate valve 65a to be fully closed. Let On the other hand, in the high load and high rotation side region B (region where the engine load is larger than the predetermined load), the small turbocharger 62 becomes exhaust resistance, so the small intake bypass valve 63a and the regulating valve 64a are fully opened. The small turbocharger 62 is bypassed and only the large turbocharger 61 is operated by setting the waste gate valve 65a to an opening close to the fully closed state. The waste gate valve 65a is slightly opened to prevent over-rotation.

In the present embodiment, the PCM 10 automatically stops the engine 1 when a predetermined automatic stop condition is satisfied for the purpose of reducing fuel consumption, suppressing CO ₂ emission, and the like, and then the predetermined restart condition is satisfied. So-called idle stop control is performed so that the engine 1 is sometimes restarted.

  Specifically, the PCM 10 stops the fuel injection by the injector 18 when the automatic stop condition is satisfied. For example, the temperature of the engine coolant detected by the water temperature sensor SW1 is equal to or higher than a predetermined temperature, and the depression operation of the brake pedal determined based on the detection signal of the brake pedal sensor SW9 continues for a predetermined time, and the vehicle speed sensor SW12 It can be set as an automatic stop condition that the vehicle speed determined based on the detection signal is equal to or lower than a preset very low speed (for example, 2 to 5 km / h) and the vehicle is substantially stopped. At the time of this automatic stop, the engine 1 is stopped at a piston position suitable for restarting the engine 1 by performing both opening / closing control of the throttle valve 36 and alternator control through the regulator circuit 73. .

  Thereafter, when the restart condition is satisfied, the PCM 10 starts supplying fuel to each cylinder 11a, applies assist torque to the engine 1 by driving the starter motor 72, and restarts the engine 1 by the combustion ( Starting control means). As described above, the engine 1 is characterized in that although the assist torque is applied, the restart time is extremely short because the restart is basically performed by combustion. For example, based on the detection signal from the accelerator opening sensor SW8 or the clutch pedal sensor SW10 that the remaining capacity of the vehicle battery is reduced and charging is necessary, the operation of the compressor of the air conditioner is required. The restart condition may be that an accelerator operation or a clutch operation is detected by a passenger. Among these, the fact that the remaining capacity of the vehicle battery has decreased and charging has become necessary, and that the operation of the compressor of the air conditioner has been required can be said to be a start condition without a start request, conversely, The detection of the accelerator operation or the clutch operation can be regarded as a start condition accompanied by a start request.

  When the engine 1 is restarted, the PCM 10 performs the valve control of the regulating valve 64a and the wastegate valve 65a described above when the start condition with the start request is satisfied and when the start condition without the start request is satisfied. It is different. Below, the control which concerns on restart of the engine 1 by PCM10 is demonstrated, referring the flowchart of FIG. 4, and the time chart of FIG. Here, the order of each step in the flow of FIG. 4 is for convenience of explanation, and it is of course possible to change the order as appropriate or to execute the steps in parallel in time. is there.

  First, in step ST1 of the flow of FIG. 4, it is determined whether or not a restart condition for the engine 1 is satisfied. As described above, the restart condition includes a restart condition with a start request and a restart condition without a start request. If the restart condition is not satisfied in step ST1 (NO), step ST1 is repeated, and if the restart condition is satisfied (YES), the process proceeds to step ST2.

  In step ST2, execution of restart control is started. That is, fuel supply to each cylinder 11a is started. With this combustion start, as shown in FIG. 5B, the engine speed gradually increases while fluctuating. In the following step ST3, it is determined whether or not there is a start request. When there is a start request (YES), the process proceeds to step ST4. When there is no start request (NO), the process proceeds to step ST9. Transition. Here, as shown in FIG. 5A, when there is a start request, the start request restart execution flag is turned ON (see the solid line).

  In step ST4 when there is a start request, post-injection control for performing post-injection for injecting fuel during the expansion stroke is executed following main injection for injecting fuel near the compression top dead center (FIG. 5D). (See also solid line in figure). Therefore, the post-injection control is started when the start condition of the engine 1 is established and the start control of the engine 1 is started. The post-injection control increases the exhaust energy as will be described later without increasing the engine speed. In subsequent step ST5, the regulating valve 64a is energized and closed (see the solid line in FIG. 5E). As a result, the regulator valve 64a is closed immediately after the start condition is satisfied. However, considering that the starter motor 72 is being driven at this timing, the regulator valve 64a is operated, for example, for starting the engine 1 described later. It may be closed after completion. Here, the regulating valve 64a may be set to a predetermined opening degree on the fully closed or closed side. On the other hand, the wastegate valve 65a is not energized and remains fully open (normally open) (see the solid line in FIG. 5F). Thus, since the large turbine 61b can be bypassed by performing the first valve control that closes the regulating valve 64a and opens the wastegate valve 65a, the back pressure of the small turbine 62b is reduced, and the back pressure of the small turbine 62b is reduced. The differential pressure before and after increases. This quickly increases the rotation speed of the small turbine 62b from 0 rotation, as exemplified by the solid line in FIG. In addition, the broken line of FIG.5 (G) is an example of the change of the rotation speed of the small turbine 62b when not implementing 1st valve | bulb control so that it may mention later. On the other hand, since the large turbine 61b can be bypassed as described above, the increase in the rotational speed of the large turbine 61b becomes slow as shown in FIG.

  Then, after completion of restart of the engine 1 (in other words, after complete explosion) in step ST6, it is determined whether or not a predetermined time has elapsed. The complete explosion determination may be performed based on, for example, the engine speed. After the complete explosion of the engine 1, the complete explosion flag is turned on (see FIG. 5C), while the start request restart flag is set. It is turned off (see FIG. 5A).

  If the predetermined time has not elapsed after the complete explosion (NO), step ST6 is repeated. On the other hand, when the predetermined time has elapsed (YES), the process proceeds to step ST7. Here, step ST6 is a step for determining whether or not the rotation speed of the small turbine 62b is equal to or higher than the predetermined rotation speed and the rotation of the small turbine 62b is in a stable state after the complete explosion of the engine 1. For this reason, the “predetermined time” may be set in advance through experiments or the like, for example, as a time that allows the rotation of the small turbine 62b to be in a stable state. Here, the rotational stability of the small turbine 62b is determined based on the elapsed time after the complete explosion. However, the parameters are not limited to the time as long as the parameters can determine the rotational stability of the small turbine 62b. Parameters can be employed.

  In step ST7 where the predetermined time has elapsed after the complete explosion and the rotation of the small turbine 62b has been stabilized, the post-injection control is terminated (see the solid line in FIG. 5D), and in the subsequent step ST8, the waste gate valve The power supply 65a is energized and closed (that is, a predetermined opening on the fully closed or closed side, see also the solid line in FIG. 5F). Thus, all the start control of the engine 1 when the start condition with the start request is satisfied is completed. In this case, as indicated by a solid line in FIG. 5 (G), since the rotational speed of the small turbine 62b is increased early, supercharging by the small turbocharger 62 is early in starting acceleration after the start of the engine 1 is completed. To begin. At the same time, by continuing the post-injection or the like until the rotation of the small turbine 62b is stabilized, a sufficient boost pressure can be secured and the start acceleration performance after the restart of the engine 1 can be enhanced.

  On the other hand, in step ST9 which has shifted to step ST3 because there is no start request, the post injection control in step ST4 described above is not performed (see the broken line in FIG. 5D). Further, the closing control of the regulating valve 64a in step ST5 is not performed (see the broken line in FIG. 5E). Then, after the restart of the engine 1 is completed, the second valve control for closing the regulating valve 64a and the waste gate valve 65a is executed. This closing timing means that when the inrush current is generated due to the drive of the starter motor 72 from the start of the start control of the engine 1 to the complete explosion, the other control is not performed as much as possible. As described above, the engine 1 is basically restarted by combustion, and the starter motor 72 is only used supplementarily. Therefore, the engine 1 is regulated immediately after the restart condition of the engine 1 is established. Each of the valve 64a and the wastegate valve 65a may be closed. In addition, the regulating valve 64a and the waste gate valve 65a are respectively set to a predetermined opening degree on the fully closed or closed side (see broken lines in FIGS. 5E and 5F).

  Thus, when the engine 1 is restarted without a start request, the rotational speeds of both the small turbine 62b and the large turbine 61b gradually increase as shown by the broken lines in FIGS. 5 (G) and (H). After the complete explosion of the engine 1, it becomes a predetermined rotational state, and it becomes possible to prepare for a start request that can occur thereafter.

  As described above, in the above configuration, when the start condition of the engine 1 accompanied by the start request is satisfied, the regulating valve 64a is in a transition period from the start of the start control of the engine 1 until a predetermined time elapses after the complete explosion. On the other hand, by opening the wastegate valve 65a, the differential pressure across the small turbine 62b during this transition period can be increased. This makes it possible to quickly increase the rotation speed of the small turbine 62b from 0 rotation, as indicated by a solid line in FIG. As a result, the supercharging by the small turbocharger 62 can be started early after the start of the engine 1 is completed, and after the start of the engine 1 is completed as when the start condition with the start request is satisfied, In a situation where the vehicle starts and accelerates immediately, the start acceleration performance can be improved. In this case, since the small turbine 62b has relatively small inertia, it is advantageous in increasing the rotational speed from zero rotation.

  Further, at that time, by combining the post injection control, the rotational speed of the small turbine 62b can be increased more rapidly by increasing the exhaust energy.

  Further, the waste gate valve 65a is opened until a predetermined time elapses after the engine 1 is completely exploded, and the post injection control is also continued until a predetermined time elapses after the engine 1 is completely exploded. By doing so, it becomes possible to reach the rotational speed of the small turbine 62b to a stable rotation at an early stage, and at the time of start acceleration after the start of the engine 1 is completed, a sufficient supercharging pressure is secured and the start acceleration performance is improved. Further improvement can be achieved.

  On the other hand, when the start condition of the engine 1 without a start request is satisfied, unlike the above, there is no request for early start of supercharging by the turbocharger. There is no need to increase it quickly. On the other hand, in this case, both the small turbine 62b and the large turbine 61b are rotated to a predetermined rotational speed in preparation for the driver's start request being made after the start of the engine 1 is completed. It is preferable to keep it. Therefore, when the start condition of the engine 1 without a start request is established, the regulator valve 64a and the wastegate valve 65a are both closed, and after the start of the engine 1 is completed, both the small turbine 62b and the large turbine 61b are It can be in the state rotated to the predetermined rotation speed. In this case, post-injection is unnecessary, and it is advantageous in terms of fuel efficiency by not performing such unnecessary post-injection.

  The control of the regulating valve 64a and the wastegate valve 65a is not limited to application to a diesel engine as in this embodiment, but can also be applied to idle stop control of a gasoline engine with a turbocharger. is there.

1 engine 10 PCM (starting control means)
14a Combustion chamber 18 Injector (fuel injection valve)
40 Exhaust passage 61 Large turbocharger (second turbocharger)
61b Large turbine (second turbine)
62 Small turbocharger (first turbocharger)
62b Small turbine (first turbine)
64 Small exhaust bypass passage (first bypass passage)
64a Regulating valve (first valve)
65 Large exhaust bypass passage (second bypass passage)
65a Wastegate valve (second valve)

Claims (3)

An engine mounted on the vehicle,
A fuel injection valve for injecting fuel into the combustion chamber of the engine;
A first turbocharger including a first turbine disposed relatively upstream on the exhaust passage of the engine and a second turbocharger including a second turbine disposed relatively downstream. A machine,
A normally open first valve interposed on a first bypass path that bypasses the first turbine;
A normally open second valve interposed on a second bypass path bypassing the second turbine;
The engine is stopped when a predetermined stop condition is satisfied, and when the predetermined start condition is satisfied, a predetermined start control is performed to burn the fuel supplied into the combustion chamber through the fuel injection valve. Starting control means for starting
The start control means includes
When the start condition with the vehicle start request is satisfied, the start control is executed, the first valve is closed after the start condition is satisfied, and a predetermined time has elapsed after the start of the engine is completed. While performing a first valve control to close the second valve,
A turbocharger that executes a second valve control that closes both the first and second valves after the start condition is satisfied, together with the execution of the start control, when a start condition that does not accompany the vehicle start request is satisfied Engine start control device. The engine start control device according to claim 1,
The first valve is a start control device for an engine with a turbocharger that is configured to be closed when the engine is in a low rotation range and open in other regions. The engine start control device according to claim 1 or 2,
The engine is a diesel engine;
The start control means performs post-injection control for performing post-injection for injecting fuel during an expansion stroke following main injection for injecting fuel in the vicinity of compression top dead center when a start condition with a start request for the vehicle is satisfied. An engine start control device for a turbocharger that further executes

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