JP7324125B2 - Engine control device and engine control method - Google Patents

Description

The present invention relates to an engine control device and an engine control method for controlling an engine having a variable valve timing control mechanism capable of changing the phase of an intake valve.

BACKGROUND ART Conventionally, a hybrid vehicle provided with a traction motor and an engine has been provided. There are two known types of hybrid systems: a parallel hybrid system that uses both electricity and gasoline for driving, and a series hybrid system that uses only the motor for driving and the engine only for power generation.

In the parallel hybrid system, the engine is stopped and the vehicle runs only on the motor in the low-load operating range where the engine's thermal efficiency is low, and the vehicle runs on the engine alone in the medium-load or higher operating range where the engine's thermal efficiency is high. In urban areas, low-load and medium-load operating ranges are mixed, so the frequency of engine stop and start is high.

In the series hybrid system, the battery capacity of the battery installed in the vehicle is monitored, and when the battery capacity falls below the lower limit, the engine operates to rotate the generator to generate electricity and charge the battery. When the battery capacity reaches or exceeds the upper limit value, the engine is stopped, so the frequency of stopping and starting the engine is high.

In this way, in the hybrid engines used in each hybrid system, the frequency of stopping and starting the engine is increasing in order to reduce fuel consumption. In recent years, in order to further reduce fuel consumption, a "fuel cut operation" is implemented in which fuel injection is cut during a period when torque is not required when the engine is stopped. However, since the engine rotates due to inertia during this fuel cut operation, unburned air (fresh air) is drawn into the cylinder and then discharged to the exhaust pipe at the same valve timing as during normal driving.

When the fresh air is discharged into the exhaust pipe and reaches the three-way catalyst provided in the exhaust pipe, the oxygen contained in the fresh air is stored in the three-way catalyst, resulting in an excess oxygen state. In this state, the nitrogen oxide (NOx) purification efficiency of the three-way catalyst is lowered. Therefore, when the engine is restarted, the fuel injection ratio is increased so that the operating air-fuel ratio becomes smaller than the stoichiometric mixture ratio, and surplus fuel is supplied to remove the oxygen stored in the three-way catalyst. Enriched injection is implemented.

However, when enriched injection is performed, there is a problem that fuel consumption deteriorates due to the injection of excess fuel, and exhaust emissions deteriorate due to combustion in an excess fuel state. Especially in hybrid engines, the frequency of stopping and starting the engine is high, so fuel cut operation has a large impact on fuel consumption and exhaust emissions.

As a technique for suppressing a reduction in purification efficiency of a three-way catalyst during fuel cut operation, for example, Japanese Patent Laid-Open Publication No. 2002-200002 discloses that "when the fuel cut detection means detects a fuel cut, the opening timing of the intake valve is advanced. advance angle control of the valve opening timing variable means" is disclosed.

JP-A-10-115234

The technology disclosed in Patent Document 1 reduces the amount of fresh air taken into the cylinder during the intake stroke and reduces the amount of fresh air discharged to the exhaust pipe, thereby suppressing the storage of oxygen in the three-way catalyst. was thought to be able to In other words, when the phase of the intake valve is advanced and the period from valve opening to valve closing is set to the exhaust stroke, the intake valve and the exhaust valve are opened during the exhaust stroke. For this reason, it was thought that the air sucked into the cylinder from the intake pipe and the exhaust pipe would be blown back into the intake pipe and the exhaust pipe by the rising piston, and it would be possible to suppress the discharge of fresh air to the exhaust pipe. .

However, in reality, there is a transitional period in which the intake valve opens and closes during the intake stroke from when the phase of the intake valve starts to advance to when it reaches the target position. Since the intake valve is open during this transitional period, fresh air drawn into the cylinder from the intake pipe during the intake stroke is discharged to the exhaust pipe. Also, fuel is cut when the engine is stopped, and fresh air is discharged to the exhaust pipe during the fuel cut. Oxygen is stored in the three-way catalyst by the fresh air discharged into the exhaust pipe.

Therefore, there is a method of advancing the phase of the intake valve for the purpose of reducing the amount of fresh air discharged into the exhaust pipe during fuel cut. However, even if the exhaust of fresh air to the exhaust pipe is suppressed after switching the phase of the intake valve, the fresh air exhausted to the exhaust pipe reaches the three-way catalyst in the process of switching the phase, and oxygen is supplied to the three-way catalyst. was stored.

When restarting the engine, engine motoring is carried out with the intake valve advanced for decompression (venting gas) to suppress fluctuations in engine speed due to air compression of the piston immediately after the engine starts. be. However, when the rotation speed rises and shifts to the initial combustion cycle, the operation opposite to that described above is performed. Ejected.

After changing the phase to the target position in this way, it is possible to suppress fresh air from being discharged into the exhaust pipe, but during the transitional period during the phase change, fresh air is discharged into the exhaust pipe and oxygen is stored in the three-way catalyst. . Therefore, when the engine is restarted, an enriched injection is required to remove oxygen from the three-way catalyst. Thus, with the conventional technology, the enriched injection cannot be eliminated when the engine is restarted, resulting in deterioration of fuel consumption and exhaust gas.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object of the present invention is to eliminate the enriched injection when the engine is restarted.

The present invention is an engine control device for controlling an engine equipped with a variable valve timing control mechanism capable of changing the phase of an intake valve provided in an intake pipe, wherein the fuel supplied to the engine decreases as the engine stops. A state determination unit that determines a state change of the engine including cut, a reference position of the phase of the intake valve before the state change of the engine, and a target position of the phase of the intake valve after the state change of the engine. a phase change information storage unit for storing, as intake valve phase change information, an intermediate position between the reference position and the target position and an intermediate holding period of the phase of the intake valve held near the intermediate position; phase change information; Based on the phase change information read from the storage unit and the state change of the engine determined by the state determination unit, during the process of changing the phase of the intake valve from the reference position to the target position through the variable valve timing control mechanism, the position near the intermediate position is detected. to lower the first phase change speed for changing the phase of the intake valve at than the second phase change speed for changing the phase of the intake valve from the reference position to the intermediate position, and after the intermediate holding period elapses, the first phase change speed an intake valve phase changer that changes the phase of the intake valve from the intermediate position to the target position at a third phase change speed higher than the speed and advances the phase of the intake valve from the reference position to the target position .
Further, the present invention is an engine control device for controlling an engine having a variable valve timing control mechanism capable of changing the phase of an intake valve provided in an intake pipe, wherein the cut of fuel supplied to the engine continues. A state determination unit that determines a state change of the engine including that the engine has restarted from a state, a reference position of the phase of the intake valve before the state change of the engine, and a phase of the intake valve after the state change of the engine. a phase change information storage unit for storing, as intake valve phase change information, a target position of the intake valve, an intermediate position between the reference position and the target position, and an intermediate holding period of the phase of the intake valve held near the intermediate position; while changing the phase of the intake valve from the reference position to the target position through the variable valve timing control mechanism based on the phase change information read from the phase change information storage unit and the state change of the engine determined by the state determination unit; A first phase change speed for changing the phase of the intake valve near the intermediate position is made lower than a second phase change speed for changing the phase of the intake valve from the reference position to the intermediate position, and after the intermediate holding period elapses The phase of the intake valve is changed from the intermediate position to the target position at a third phase change speed higher than the first phase change speed, and after the decompression caused by restarting the engine is completed, the phase of the intake valve is changed from the target position. and an intake valve phase changer that retards the intake valve toward the reference position.

According to the present invention, the first phase change speed for changing the phase of the intake valve near the intermediate position is made lower than the second phase change speed for changing the phase of the intake valve from the reference position to the intermediate position. The gas in the exhaust pipe returns to the intake pipe. Therefore, when the engine is restarted, the fuel consumption can be improved and the deterioration of the exhaust gas can be suppressed by eliminating the enriched injection.
Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

1 is a schematic configuration diagram showing an example in which a control device mounted on a hybrid vehicle according to a first embodiment of the invention is applied to a series hybrid vehicle; FIG. 1 is a schematic diagram showing a configuration example of an engine according to a first embodiment of the invention; FIG. 2 is a control block diagram showing an internal configuration example of an ECU according to the first embodiment of the present invention; FIG. FIG. 4 is a diagram showing an example of profiles of an intake valve and an exhaust valve during power generation operation of the engine according to the first embodiment of the present invention; FIG. 4 is a diagram showing an example of profiles of intake valves and exhaust valves when the engine is shifted to fuel cut operation according to the first embodiment of the present invention; FIG. 4 is a diagram showing how the phase of the intake valve according to the first embodiment of the present invention is held at an intermediate position; FIG. 5 is a diagram showing an example of map information representing the relationship between the engine speed during fuel cut and the intermediate holding period stored in the ECU according to the first embodiment of the present invention; FIG. 4 is a diagram showing how an intake valve phase changing unit retards the intake valve after the ECU according to the first embodiment of the present invention starts the engine; FIG. 5 is a graph showing how the engine speed changes after the ECU according to the first embodiment of the present invention starts fuel cut; FIG. FIG. 7 is a graph showing how an intake valve phase changing unit advances the phase of the intake valve after the ECU according to the first embodiment of the present invention starts fuel cut; FIG. FIG. 4 is a diagram showing the amount of fresh air discharged to an exhaust pipe per cylinder until the phase of the intake valve according to the first embodiment of the present invention reaches the intermediate position profile. FIG. 5 is a diagram showing an operation example of an intake valve and an exhaust valve whose profile has been changed to an intermediate position according to the first embodiment of the present invention; FIG. 4 is a diagram showing how the engine speed changes after starting cranking according to the first embodiment of the present invention; FIG. 5 is a diagram showing how the phase advance amount of the intake valve 9 changes after cranking is started according to the first embodiment of the present invention; FIG. 4 is a diagram showing the amount of fresh air discharged into an exhaust pipe during four cycles with reference to the start point of phase change of the intake valve according to the first embodiment of the present invention; FIG. 4 is a diagram showing an operation example of an intake valve and an exhaust valve whose profile has been changed to a target position according to the first embodiment of the present invention; FIG. 5 is a diagram showing the amount of fresh air discharged from the exhaust pipe to the intake pipe in each cycle from the start of fuel cut to the stop of the engine according to the first embodiment of the present invention; FIG. 9 is a diagram showing an example of a profile changed near an intermediate position by an intake valve phase changer according to the second embodiment of the present invention; FIG. 10 is a diagram showing an example of the amount of air returning from the exhaust pipe to the intake pipe when the intake valve phase changing unit according to the second embodiment of the present invention is operated at a low phase change speed while the engine is stopped; be. FIG. 9 is a graph showing how the engine speed changes after an ECU according to the second embodiment of the present invention starts fuel cut; FIG. 9 is a graph showing how an intake valve phase changing unit advances the phase of the intake valve after an ECU according to the second embodiment of the present invention starts fuel cut; FIG. 10 is a diagram showing map information representing the relationship between the phase change speed and the intermediate holding period, stored in the ECU according to the third embodiment of the present invention; FIG. 12 is a diagram showing map information representing the relationship between the throttle opening degree and the intermediate holding period during fuel cut, stored in an ECU according to the fourth embodiment of the present invention;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same function or configuration are denoted by the same reference numerals, thereby omitting redundant description.

[First embodiment]
FIG. 1 is a schematic configuration diagram showing an example in which a control device according to a first embodiment of the invention is applied to a series hybrid vehicle.
Hybrid vehicle 100 according to the present embodiment is an example of a series hybrid vehicle that includes a traction motor for running and uses an engine only for power generation.

The navigation device 111 receives GPS signals transmitted on satellite radio waves from a plurality of GPS (Global Positioning System) satellites in the sky above the hybrid vehicle 100 having an internal combustion engine (engine 113) as a drive source, and measures the current position. It is possible to superimpose the current position of hybrid vehicle 100 on the map displayed on the display device in hybrid vehicle 100 and display it. Positioning of the current position by the navigation device 111 may also use a base station of a mobile phone terminal, a Wi-Fi (registered trademark) access point, or the like. Information on the current position of hybrid vehicle 100 positioned by navigation device 111 and map information including the surroundings where hybrid vehicle 100 travels and the route to the destination are output to a vehicle control unit, namely VCU (Vehicle Control Unit) 101 . be.

An accelerator opening sensor 106 and a brake switch 107 are provided in the cabin of the hybrid vehicle 100 . The accelerator opening sensor 106 detects the depression amount of the accelerator pedal, that is, the accelerator opening. A brake switch 107 detects whether or not the brake pedal is depressed.

The engine 113 is an automotive in-line three-cylinder gasoline engine using spark ignition combustion, and is an example of an internal combustion engine. This engine 113 has a starter 112 for starting the engine 113 . A crankshaft of the engine 113 is provided with a crankangle sensor 110 for detecting its rotation angle, and the other end of the crankshaft is connected to a motor generator 114 .

A generator control device, that is, a GCU (Generator Control Unit) 103 controls driving of a motor generator 114 via an inverter 115 so that the inverter 115 can charge a battery 116 with a predetermined voltage. Motor generator 114 is driven by engine 113 to generate power and charge battery 116 via inverter 115 .

A battery control unit (BCU) 104 controls charging and discharging of the battery 116 based on the required battery output from the VCU 101 . The battery 116 is provided with a battery voltage sensor 109 that measures the internal voltage of the battery 116 , and the VCU 101 constantly checks the voltage of the battery 116 .

A motor control device, that is, a MCU (Motor Control Unit) 105 controls an inverter 117 and a motor 118 based on the requested motor output from the VCU 101 . Power is supplied to the inverter 117 from an electrically connected battery 116 . Inverter 117 converts the DC power discharged from battery 116 into AC power and supplies AC power to motor 118 . Motor 118 is connected to wheel 120 via reduction gear 119 . A vehicle speed sensor 108 is also provided on the drive shaft of the wheel 120 .

Signals output from vehicle speed sensor 108 , battery voltage sensor 109 and crank angle sensor 110 are sent to VCU 101 . Signals output from the accelerator opening sensor 106 and the brake switch 107 are also sent to the VCU 101 .

The VCU 101 is installed in a vehicle (hybrid vehicle 100) that runs on the output of at least one of an internal combustion engine (engine 113) and an electric drive unit (motor 118). The VCU 101 calculates the driver's requested torque based on the output signal of the accelerator opening sensor 106 . That is, the accelerator opening sensor 106 is used as a required torque detection sensor that detects the required torque to the engine 113 and the motor 118 . The VCU 101 also determines whether or not the driver has requested deceleration based on the output signal of the brake switch 107 . The VCU 101 also calculates the remaining power amount of the battery 116 based on the output signal of the battery voltage sensor 109 . VCU 101 also calculates the rotation speed of engine 113 based on the output signal of crank angle sensor 110 . The VCU 101 calculates the optimum amount of operation of each device such as the required engine output, the required motor output, and the required battery output based on the driver's request obtained from the outputs of the various sensors and the operating state of the hybrid vehicle 100 .

The required engine output calculated by the VCU 101 is sent to an engine control unit, namely an ECU (Engine Control Unit) 2 . The ECU 102 controls the engine 113 based on the requested output from the VCU 101 . Specifically, in addition to controlling the starter 112, the ECU 102 controls an intake cam 11, an exhaust cam 12, an injector 13, a spark plug 14, an ignition coil 15 shown in FIG. 2, a throttle 26 shown in FIG. , the control of the VTC (Valve Timing Control) 40 shown in FIG. Also, the required motor output calculated by the VCU 101 is sent to the MCU 105 . Also, the battery demand output calculated by the VCU 101 is sent to the BCU 104 .

FIG. 2 is a schematic diagram showing a configuration example of the engine 113 according to the first embodiment of the invention.
In a series hybrid vehicle, the engine (engine 113) is started when the charging capacity of the installed battery 116 (referred to as "battery capacity") becomes less than a specified value. Conversely, the engine (engine 113) is stopped when the charging capacity of the battery 116 (referred to as "battery capacity") reaches or exceeds a specified value.

The engine 113 shown in FIG. 2 is configured as an in-line three-cylinder naturally aspirated engine with 400 cc per cylinder. A combustion chamber is formed by a cylinder head 1 and a cylinder block 2 of the engine 113 and a piston 3 inserted into the cylinder block 2 . Piston 3 is connected to crankshaft 5 via connecting rod 4 . A crank angle sensor 110 provided near the crankshaft 5 detects the engine speed.

An intake pipe 7 and an exhaust pipe 8 are connected toward the combustion chamber of one cylinder, and an intake valve 9 and an exhaust valve 10 are provided to open and close the opening of the combustion chamber. An intake cam 11 is provided above the intake valve 9 , and an exhaust cam 12 is provided above the exhaust valve 10 . The rotation of the intake cam 11 opens and closes the intake valve 9 , and the rotation of the exhaust cam 12 opens and closes the exhaust valve 10 .

Although not shown, an intake cam pulley connected to the intake cam 11, an exhaust cam pulley connected to the exhaust cam, and a crank pulley connected to the crankshaft 5 are provided on the side of the engine 113 and connected via a timing belt. As a result, the intake cam 11 and the exhaust cam 12 rotate as the crankshaft 5 rotates when the engine 113 operates. The intake cam pulley and the exhaust cam pulley are set so that the intake cam 11 and the exhaust cam 12 make one turn when the crankshaft 5 makes two turns.

The intake cam 11 also has a variable valve timing control mechanism (VTC) 40 (hereinafter referred to as VTC) 40 (see FIG. 3 described later) that can change the phase of the intake valve (intake valve 9) provided in the intake pipe (intake pipe 7). ) is provided. Further, the crankshaft 5 is provided with a motor generator 114 that functions as a generator during power generation and as a motor during starting and stopping of the engine 113 . The VTC 40 is electrically driven, and the ECU 102 can change the phase of the intake valve 9 to advance or retard by rotating a motor provided in the VTC 40 . The speed at which the VTC 40 changes the phase of the intake valve 9 (referred to as "phase change speed") is 300 deg CA (crank angle) per second.

An injector 13 is provided on the intake side of the combustion chamber, and an ignition plug 14 and an ignition coil 15 are provided above the combustion chamber. Fuel is stored in a fuel tank 16 and sent by a feed pump 17 to a high pressure fuel pump 18 through a fuel pipe. A high-pressure fuel pump 18 is driven by the exhaust cam 12 to send pressurized fuel to a common rail 19 . A fuel pressure sensor 20 is installed on the common rail 19 so as to detect the fuel pressure (referred to as "fuel pressure"). The common rail 19 and the injector 13 provided in each cylinder are connected by a fuel pipe.

A collector 21 is provided upstream of the intake pipe 7 . An intake pipe 7 is connected from this collector 21 to each cylinder. A throttle 26 that can change the amount of air taken into the cylinder is provided upstream of the collector 21 .

On the other hand, a three-way catalyst 22 is provided at the tip of the exhaust pipe 8, and an oxygen sensor 24 is provided downstream thereof. A temperature sensor 23 is provided in the three-way catalyst 22 to detect the temperature of the three-way catalyst 22 . The cylinder block 2 is provided with a water temperature sensor 27 that measures the temperature of water flowing around the cylinder block 2 .

Signals of water temperature and engine speed are input to the ECU 102 . The ECU 102 controls the on/off of fuel injection and the phase of the VTC 40 based on various information obtained from signals input from each sensor.

Next, an internal configuration example and an operation example of the ECU 102 will be described below.
FIG. 3 is a control block diagram showing an internal configuration example of the ECU 102. As shown in FIG. The engine control unit (ECU 102) controls an engine (engine 113) having a variable valve timing control mechanism (VTC 40) capable of changing the phase of the intake valve (intake valve 9). ECU 102 executes the engine control method according to the present embodiment to control engine 113 having VTC 40 .

The ECU 102 includes a CPU (Central Processing Unit) 30 , a RAM (Random Access Memory) 31 and a ROM (Read Only Memory) 32 .
The ECU 102 receives the primary voltage detected by the voltage sensor (not shown) of the ignition coil 15, the secondary current detected by the current sensor (not shown) of the ignition coil 15, and the accelerator depression information (not shown) detected by the accelerator opening sensor 106. accelerator opening), angle information (crank angle) detected by the crank angle sensor 110, the rotational speed of the engine 113, the throttle opening from the throttle 26, the battery voltage (battery capacity) detected by the battery voltage sensor 109, and other input signals. etc. are entered.

The input information of each sensor inputted to the ECU 102 is temporarily stored in the RAM 31, and is arithmetically processed by the CPU 30 according to a predetermined control program. Variables, parameters, etc. generated during the arithmetic processing of the CPU 31 are temporarily written in the RAM 31, and these variables, parameters, etc. are read by the CPU 31 as appropriate. However, an MPU (Micro Processing Unit) may be used instead of the CPU 31 .

The ROM 32 permanently records programs, data, and the like necessary for the CPU 31 to operate, and is used as an example of a computer-readable non-transitory recording medium storing programs executed by the ECU 102 . Therefore, a control program describing the contents of the arithmetic processing performed by the CPU 30 is written in the ROM 32 in advance, and is read out and executed by the CPU 30 as appropriate. Further, the ROM 32 stores, for example, map information 321 that defines an intermediate holding period according to the engine speed at the time of fuel cut, as shown in FIG. 7, which will be described later. However, a nonvolatile storage may be provided in the ECU 102, and the map information 321 updated through the network may be stored in the nonvolatile storage.

The phase change information storage unit (map information 321) configured in the ROM 32 stores the reference position of the intake valve (intake valve 9) before the state change of the engine (engine 113) and the reference position after the state change of the engine (engine 113). phase change information of the intake valve (intake valve 9), the target position of the intake valve (intake valve 9), the intermediate position between the reference position and the target position, and the duration of the intermediate position in a predetermined range including the intermediate position remember as

As described above, the control program executed by the CPU 30 implements the functions of the state determination unit 301 and the intake valve phase change unit 302 shown in the drawing.
For example, when the VCU 101 instructs the ECU 102 to stop the engine 113 , the ECU 102 according to the present embodiment performs control to cut the fuel supplied to the engine 113 . Fuel cut is started prior to stopping the engine (engine 113) when the charge capacity of the battery (battery 116) used to drive the vehicle (hybrid vehicle 100) reaches or exceeds a specified value.

Further, the ECU 102 restarts the engine 113 when the driver depresses the accelerator while the engine 113 is stopped and the fuel is cut. Therefore, the state determination unit 301 determines the state change of the engine (engine 113) and outputs the determination result. The change in state of the engine (engine 113) includes cutoff of fuel supplied to the engine (engine 113) as the engine (engine 113) stops. In addition, the state change of the engine (engine 113) includes restarting of the engine (engine 113) from a state in which fuel cut continues.

The intake valve phase change unit (intake valve phase change unit 302) uses the phase change information read from the phase change information storage unit (map information 321) and the engine (engine 113) determined by the state determination unit (state determination unit 301). on the way of changing the phase of the intake valve (intake valve 9) from the reference position to the target position through the variable valve timing control mechanism (VTC 40) based on the state change of the intake valve (intake valve 9) near the intermediate position. The first phase change speed for changing the phase is made lower than the second phase change speed for changing the phase of the intake valve (intake valve 9) from the reference position to the vicinity of the intermediate position, and after the intermediate holding period elapses, the second phase change speed The phase of the intake valve (intake valve 9) is changed from near the intermediate position to the target position at a third phase change speed higher than the first phase change speed. When it is determined that the fuel supplied to the engine (engine 113) is cut off as a state change of the engine (engine 113), the intake valve phase changing unit (intake valve phase changing unit 302) changes the first phase. The phase of the intake valve (intake valve 9) is advanced from the reference position to the target position at the speed, the second phase change speed or the third phase change speed. On the other hand, when it is determined that the engine (engine 113) has restarted, the intake valve phase changing unit (intake valve phase changing unit 302) changes the phase of the intake valve (intake valve 9) from the reference position to the target position. to retard the angle.

For example, based on the battery capacity, the intake valve phase changing unit 302 changes the intake valve phase according to a change in the state of the engine 113, such as when the ECU 102 starts fuel cut to stop the engine 113 or when the engine 113 is restarted. The VTC 40 is instructed to change the phase of the valve 9 . At this time, the intake valve phase changing unit 302 reads the map information 321 from the ROM 32 and performs control such as switching the timing of starting to change the phase of the intake valve 9 and the speed of changing the phase of the intake valve 9 .

The VTC 40 can change the phase of the intake valve 9 to advance or retard by driving the intake cam 11 based on an instruction from the intake valve phase changing section 302 . In the following description, it is assumed that the intake valve phase changer 302 changes the phase of the intake valve 9 to advance or retard.

In this embodiment, the ECU 102 is configured to include the state determination unit 301, the intake valve phase change unit 302, and the map information 321, but the configuration is not limited to this. For example, part or all of the state determination unit 301, the intake valve phase change unit 302, and the map information 321 may be implemented in a device other than the ECU 102.

<Relationship between intake valve and exhaust valve phases and lift amounts>
Next, the timing of changing the phase of the intake valve 9 (valve opening/closing timing) and the changed phase of the intake valve 9 will be described with reference to FIGS. 4 to 8. FIG. The horizontal axes in FIGS. 4 to 6 and 8 show how the strokes change in the order of expansion stroke, exhaust stroke, intake stroke, and compression stroke, and the vertical axes show the intake valve 9 and the exhaust valve 10. is shown.

FIG. 4 is a diagram showing an example of profiles of the intake valve 9 and the exhaust valve 10 during power generation operation of the engine 113 according to the first embodiment. Each profile of the intake valve 9 and the exhaust valve 10 shown in the following figures represents the opening/closing timing, phase change, and lift amount of the intake valve 9 and the exhaust valve 10 .

In FIG. 4, the phase change of the intake valve 9 is represented by profile 9a, and the phase change of the exhaust valve 10 is represented by profile 10a. The intake valve 9 has a lift amount of 6 mm and a working angle of 190 degrees, and the exhaust valve 10 has a lift amount of 8 mm and a working angle of 200 degrees. Further, the closing timing of the intake valve 9 is set at the bottom dead center (BDC), and the closing timing of the exhaust valve 10 is set at the top dead center (TDC). As shown in FIG. 4, when the engine 113 is running, the profile 10a of the exhaust valve 10 changes during the exhaust stroke, and the profile 9a of the intake valve 9 changes during the intake stroke. The profiles 10a, 9a are substantially non-overlapping. The phase position of the intake valve 9 represented by the profile 9a is called the "reference position".

FIG. 5 is a diagram showing an example of profiles of the intake valve 9 and the exhaust valve 10 when the engine 113 according to the first embodiment shifts to the fuel cut operation. The horizontal axis and vertical axis of FIG. 5 are the same as the horizontal axis and vertical axis of FIG.

The ECU 102 according to the first embodiment performs control to stop the engine 113 when the battery capacity reaches the upper limit value. Therefore, the ECU 102 shifts to a fuel cut operation in which fuel injection is stopped before the engine 113 is stopped.

At this time, since the engine 113 rotates due to inertia, uncombusted air (fresh air) is discharged to the exhaust pipe 8 in the state of the profile 9a. Therefore, the intake valve phase changer 302 advances the profile 9a to the stop position of the profile 9b as shown in FIG. The profile 9b is at a position advanced by 180 degrees in crank angle with respect to the profile 9a during power generation operation. Therefore, the profile 9b of the intake valve 9 and the profile 10a of the exhaust valve 10 overlap at substantially the same timing. The position of the phase of the intake valve 9 represented by this profile 9b is called the "target position".

FIG. 6 is a diagram showing how the phase of the intake valve 9 is held at the intermediate position. The horizontal axis and vertical axis in FIG. 6 are the same as the horizontal axis and vertical axis in FIG.

Intake valve phase changing unit 302 according to the present embodiment performs intermediate position control of intake valve 9 when ECU 102 performs fuel cut operation when controlling to stop engine 113 . In the intermediate position control, the intake valve phase changing unit 302 advances the intake valve 9, and when the intake valve 9 reaches the intermediate position in the middle of changing from the profile 9a to the profile 9b, a predetermined period of time (referred to as an "intermediate holding period") is reached. ) to hold the intermediate position.

When the intake valve phase changing unit 302 performs intermediate position control as described above, the phase of the intake valve 9 is held at the intermediate position over the intermediate holding period. At this time, the phase of the intake valve 9 is represented by a profile 9c. A phase position of the intake valve 9 represented by the profile 9c is called an "intermediate position".

At the target position, the gas sucked into the cylinders of the engine (engine 113) from the exhaust pipe (exhaust pipe 8) in the expansion stroke passes through the exhaust pipe (exhaust pipe 8) and the intake pipe (intake pipe 7) in the exhaust stroke. ), the opening timing of the intake valve (intake valve 9) provided in the intake pipe (intake pipe 7) and the exhaust valve (exhaust valve 10 ) overlaps with the valve opening timing. However, at the intermediate position, the opening timing of the intake valve (intake valve 9) is set to be retarded relative to the opening timing of the exhaust valve (exhaust valve 10). Also, the intermediate holding period changes depending on the rotation speed of the engine 113 at the time of fuel cut. The intermediate holding period will be described with reference to FIG.

FIG. 7 is a diagram showing an example of map information 321 stored in the ECU 102 and representing the relationship between the engine speed and the intermediate holding period during fuel cut. The horizontal axis of FIG. 7 represents the engine speed [rpm] at the time of fuel cut, and the vertical axis represents the intermediate holding period [s].

In the phase change information storage unit (map information 321), a longer intermediate holding period is defined as the rotation speed of the engine (engine 113) at the time when fuel cut is started increases. Therefore, the intake valve phase changing unit 302 acquires the intermediate holding period according to the engine speed at the time of fuel cut based on the map information 321 read from the ROM 32 shown in FIG.

Referring to FIG. 6 again, the profile 9c at the intermediate position is advanced by 150 degrees with respect to the profile 9a during power generation operation. That is, the intermediate holding position is a position advanced by 150 degrees with respect to the position of the intake valve 9 in the intake stroke before the start of the phase change. Further, as shown in the map information 321 of FIG. 7, the intake valve phase changing unit 302 determines the holding period of the intermediate position based on the engine speed immediately after the fuel cut is started, and the engine speed Control is performed so that the higher the value, the longer the intermediate holding period.

After the engine 113 stops, the engine 113 is restarted when the battery capacity becomes equal to or less than the lower limit value. At that time, the rotation of the engine 113 is started by the motor generator 114 rotating the crankshaft 5 . However, immediately after the start of the engine 113, if the air taken in during the intake stroke is compressed during the compression stroke, it will become rotational resistance and the increase in the rotational speed will fluctuate. Therefore, the intake valve phase changing unit 302 restarts the engine 113 with decompression that maintains the phase of the intake valve 9 in the state of the profile 9b.

After that, the ECU 102 controls to maintain the motor rotation speed when the engine rotation speed has increased to 1200 rpm.
FIG. 8 is a diagram showing how the intake valve phase changer 302 retards the intake valve 9 after the ECU 102 starts the engine 113. As shown in FIG.

When the ECU 102 restarts the engine 113, the intake valve phase changer 302 retards the intake valve 9 so that the intake valve 9 operates with the profile 9d. The profile 9d is positioned across the exhaust stroke and the intake stroke. A profile 9d represents the phase of the intake valve 9 set for the ECU 102 to generate the torque necessary for the engine (engine 113) to self-rotate when the engine (engine 113) first explodes. For example, the closing timing of the intake valve 9 shown in the profile 9d is set to a position retarded by 120 degrees after the top dead center.

When the profile 9d is reached, fuel is injected from the injector 13 under the control of the ECU 102, and the engine 113 is ignited for the first time. After the initial explosion, the rotation speed increases due to combustion in the engine 113, and the assist for cranking of the motor generator 114 is stopped.

Next, operation of engine 113 controlled by ECU 102 according to the present embodiment will be described. Here, the process in which the ECU 102 stops the engine 113 from the operation at the power generation point of the engine speed of 1800 rpm and the engine torque of 60 Nm, and then restarts the engine 113 will be described.

For example, under the condition that the hybrid vehicle 100 is running, the water temperature of the engine 113 is 80° C. after warming up, and the battery capacity is below the lower limit value, so the engine is operating at the power generation point. Under the engine 1800 rpm condition, which is the power generation point, the intake valve phase changer 302 operates so that the intake valve 9 and the exhaust valve 10 operate according to the profiles 9a and 10a shown in FIG. In this state, the injector 13 injects fuel so that the air-fuel ratio of the fuel to the amount of air taken into the combustion chamber in the intake stroke is "14.5".

The fuel injection timing is 60 degrees ATDC of the intake stroke, and a uniform air-fuel mixture is formed in the combustion chamber through the period from the intake stroke to the compression stroke. The air-fuel mixture is ignited at the best fuel consumption ignition timing in the latter half of the compression stroke, and the combustion pressure pushes the piston 3 to rotate the crankshaft 5 . As the crankshaft 5 rotates, the motor generator 114 connected to the crankshaft 5 also rotates to generate electric power, and the battery 116 is charged with electric power.

When the hybrid vehicle 100 stops due to traffic lights, traffic congestion, or the like, and the battery capacity reaches or exceeds the upper limit value, charging is stopped, and the engine 113 starts stop processing under the control of the ECU 102 . At this time, since the engine torque is not required, the engine enters the fuel cut operation mode. Then, the ECU 102 stops the fuel supply to the combustion chamber by turning off the fuel injection signal to the injector 13 .

Therefore, the time history of the engine speed and the phase advance amount of the intake valve 9 from the start of the fuel cut to the engine stop will be described with reference to FIGS. 9 and 10. FIG.

FIG. 9 is a graph showing how the engine speed changes after the ECU 102 starts fuel cut. The horizontal axis in FIG. 9 represents the time [s] that has elapsed after the start of fuel cut, and the vertical axis represents the engine speed [rpm].

Then, time 0.0 [s] in FIG. 9 represents the timing at which the ECU 102 started fuel cut. When the fuel cut is started, the engine rotates by inertia, and the engine speed gradually decreases.

FIG. 10 is a graph showing how the intake valve phase changer 302 advances the phase of the intake valve 9 after the ECU 102 starts fuel cut. The horizontal axis in FIG. 10 represents the time [s] that has elapsed after the start of fuel cut, and the vertical axis represents the phase advance amount [deg] of the intake valve 9 .

Time 0.0 [s] in FIG. 10 represents the timing at which the ECU 102 started fuel cut, as in FIG. The intake valve phase changing unit 302 starts control to advance the phase of the intake valve 9 at the timing when the fuel cut is started, and drives the VTC 40 . First, the ECU 102 sets a profile 9c shown as an intermediate holding position in FIG. 6 as a target value for the intermediate position. The crank angle from profile 9a to profile 9c is 150deg, and the response speed of VTC 40 is 300degCA/s.

Therefore, the profile 9a reaches the position of the profile 9c 0.5 seconds after the fuel cut is started. Incidentally, as shown in FIG. 9, the engine speed immediately before the fuel cut is 1800 rpm, and the speed after 0.5 seconds is 1780 rpm. Therefore, the profile 9c is reached in the middle of the seventh cycle. Then, the intake valve phase changing unit 302 advances the phase of the intake valve (intake valve 9) near the intermediate position (near 150 degrees) until the intermediate holding period (2.1 seconds) elapses. Let the phase change rate be zero. After the intermediate holding period has elapsed, the intake valve phase changer 302 changes the phase of the intake valve 9 to the target position at a third phase change speed higher than the first phase change speed.

Here, the amount of fresh air discharged to the exhaust pipe 8 per cylinder will be described.
FIG. 11 is a diagram showing the amount of fresh air discharged to the exhaust pipe 8 per cylinder until the phase of the intake valve 9 reaches the intermediate position profile 9c. The horizontal axis of FIG. 11 represents the cycle number (number of cycles) from the start of fuel cut, and the vertical axis represents the volume (fresh air amount) [cm ³ ] of fresh air discharged to the exhaust pipe 8 .

Immediately after the fuel cut, the closing timing of the intake valve 9 is near the bottom dead center of the intake stroke. Therefore, immediately after the fuel cut, a large amount of fresh air is drawn into the combustion chamber in the intake stroke, and after the intake valve 9 is closed, the fresh air is discharged to the exhaust pipe 8 in the exhaust stroke through the compression stroke.

However, as the phase of the intake valve 9 advances, the closing timing of the intake valve 9 approaches the top dead center of the intake stroke, so the amount of fresh air discharged to the exhaust pipe 8 gradually decreases. . Then, in the sixth cycle, the amount of fresh air discharged to the exhaust pipe 8 becomes zero, and in the seventh cycle, the amount of fresh air discharged becomes negative, and the fresh air flows from the exhaust pipe 8 to the intake pipe 7. is returned.
The volume V1 of fresh air discharged from the intake pipe 7 to the exhaust pipe 8 shown in FIG. 11 is 1411 cc. 11 also shows the volume V2 of fresh air returned from the intake pipe 7 to the exhaust pipe 8. As shown in FIG.

Here, a phenomenon in which fresh air is returned from the exhaust pipe 8 to the intake pipe 7 in the state of the eighth cycle profile 9c shown in FIG. 11 will be described.
FIG. 12 is a diagram showing an operation example of the intake valve 9 changed to the intermediate position profile 9c and the exhaust valve 10. As shown in FIG.

In the upper part of FIG. 12 profiles 9c, 10a similar to FIG. 6 are shown.
At the bottom of FIG. 12, the states of operation of the intake valve 9 and the exhaust valve 10 defined by the profiles 9c and 10a are shown for each timing (1) to (4). In the schematic diagram of the intake pipe 7, the exhaust pipe 8, and the combustion chamber shown in the lower part of FIG. In timings (1) to (4), the vertical striped area represents fresh air in the intake pipe 7, and the horizontal striped area represents fresh air in the exhaust pipe 8 or exhaust gas. The arrows in the figure represent the moving direction of the fresh air.

In the intake stroke, as shown in the profile 9c, the intake valve 9 is closed before the piston 3 descends at the beginning of the intake stroke, so little fresh air is drawn into the combustion chamber. Therefore, when the piston 3 descends after the intake valve 9 is closed, the fresh air that initially existed in the combustion chamber expands to form a negative pressure in the combustion chamber.

In the compression stroke, the piston 3 rises and the volume of the combustion chamber becomes smaller. Therefore, the initial atmospheric pressure is restored near the top dead center of the piston 3 . Next, when the piston 3 descends in the expansion stroke, the fresh air that was initially present expands again to form a negative pressure.

That is, in the expansion stroke shown at timing (1), before the exhaust valve 10 is opened, there is no fresh air taken from the intake pipe 7, so a negative pressure is formed in the combustion chamber.

During the period in which only the exhaust valve 10 is opened as indicated by timing (2), the pressure inside the exhaust pipe 8 is atmospheric pressure, and the pressure in the combustion chamber is negative. Therefore, due to the pressure difference between the exhaust pipe 8 and the combustion chamber, fresh air containing the exhaust gas that was discharged to the exhaust pipe 8 in the previous cycle is drawn into the combustion chamber. Since the period from the opening of the exhaust valve 10 to the opening of the intake valve 9 is 40 degrees, the air discharged in the previous cycle of the exhaust pipe 8 fills the combustion chamber, The pressure in the combustion chamber recovers to the same atmospheric pressure.

When the exhaust stroke starts, the piston 3 starts to rise. Here, in the exhaust stroke shown at timing (3), the intake valve 9 is also opened. Therefore, the pressure in the combustion chamber has recovered to the atmospheric pressure, and there is no pressure difference between the pressure in the combustion chamber and the pressures in the intake pipe 7 and the exhaust pipe 8 . Therefore, fresh air is not taken in from the intake pipe 7 , and fresh air that has flowed into the combustion chamber from the exhaust pipe 8 is returned to the intake pipe 7 and the exhaust pipe 8 .

During the upward movement of the piston 3 shown at timing (4), fresh air containing the air-fuel mixture of the previous cycle sucked from the exhaust pipe 8 is pushed out to the intake pipe 7 and the exhaust pipe 8, respectively. As a result, fresh air in the exhaust pipe 8 is returned to the intake pipe 7 . At timing (4), the amount of lift of the intake valve 9 is greater than the amount of lift of the exhaust valve 10, so a large amount of fresh air containing the air-fuel mixture in the previous cycle is returned to the intake pipe 7.

Here, referring to FIG. 11, from the start of fuel to the 6th cycle, fresh air with a volume V1 of 1411 cc is discharged to the exhaust pipe 8, and in the state of the profile 9c after the 8th cycle, 62 cc per cycle. Fresh air is returned from the exhaust pipe 8 to the intake pipe 7 . For example, by continuing the state of the profile 9c for 23 cycles, it is possible to return all the fresh air discharged to the exhaust pipe 8 to the intake pipe 7. Since the average rotation speed during this period is about 1700 rpm, 23 cycles correspond to 1.7 seconds.

In order to eliminate the enriched injection when the engine 113 is restarted, the amount of fresh air discharged to the exhaust pipe 8 must be zero. However, due to decompression, the intake valve phase changing unit 302 changes the phase of the intake valve 9 to the profile 9b (see FIG. 5) when the ECU 102 starts the engine 113 . Then, the intake valve phase changing unit 302 retards the phase of the intake valve 9 by 120deg from the profile 9b so that the ECU 102 causes the motor generator 114 to rotate the crankshaft 5 and the rotation speed rises to 1200 rpm for the first explosion. to change to profile 9d (see FIG. 8).

Fresh air is also discharged to the exhaust pipe 8 during the period in which the intake valve phase changing section 302 changes the phase of the intake valve 9 from the profile 9b before the first explosion to the profile 9d. Therefore, it is necessary to return combustion gas to the intake pipe 7 in addition to the fresh air discharged to the exhaust pipe 8 when the fuel is cut, in anticipation of the fresh air discharged when the engine is restarted when the engine is stopped.

When the hybrid vehicle 100 runs and the battery capacity becomes equal to or less than the lower limit value, the ECU 102 outputs a command to start the engine 113 for power generation. When the engine 113 is started, first, the crankshaft 5 is rotated by the motor generator 114 while the phase of the intake valve 9 remains at the profile 9b.

As shown in FIG. 5, in the profile 9b, when the piston 3 rises in the compression stroke, the air that has become negative pressure in the intake stroke is returned to the atmospheric pressure. Further, in the exhaust stroke, since the intake valve 9 and the exhaust valve 10 are open, the air in the combustion chamber is not compressed. Therefore, fluctuations in the engine speed caused by the piston 3 compressing the air are suppressed, and the driver does not feel uncomfortable due to vibration. Then, the intake valve phase changing unit 302 waits for the engine speed to rise to 1200 rpm by the ECU 102, and then operates the VTC 40 to change the phase of the intake valve 9 from the profile 9b to the profile 9d for initial explosion. .

Next, the influence of cranking by motor generator 114 will be described with reference to FIGS. 13 and 14. FIG.
FIG. 13 is a diagram showing how the engine speed changes after cranking is started. The horizontal axis of FIG. 13 represents the time [s] after the start of cranking, and the vertical axis represents the engine speed [rpm]. Time 0.0 [s] in FIG. 13 represents the timing at which the ECU 102 started cranking.

When the engine 113 is restarted, it takes 0.2 seconds of 3 cycles per cylinder until the rotation speed is increased to 1200 rpm by the motor generator 114 . When the engine speed reaches 1200 rpm 0.2 seconds after the engine 113 is restarted, the motor generator 114 keeps the speed at 1200 rpm. At this time, the ECU 102 changes the phase of the intake valve 9 so that the profile 9b becomes the profile 9d.

As shown in FIG. 8, in profile 9b, the closing timing of the intake valve 9 is at top dead center (TDC), and in profile 9d, the closing timing of the intake valve 9 is 120 degrees after the top dead center. Moreover, the response speed of VTC40 is 300degCA/s. Therefore, the ECU 102 can change from the profile 9b to the profile 9d in 0.4 seconds. Since the engine speed is 1200 rpm, the profile change period corresponds to 4 cycles. After reaching the profile 9d, the fuel is injected to enter the initial explosion cycle, and not fresh air but burned gas is discharged.

FIG. 14 is a diagram showing how the phase advance amount of the intake valve 9 changes after cranking is started. The horizontal axis of FIG. 14 represents the time [s] after the start of cranking, and the vertical axis represents the phase advance amount [deg] of the intake valve 9 (also called VTC phase). Time 0.0 [s] in FIG. 14 represents the timing at which the ECU 102 started cranking.

Decompression is required when the engine 113 is restarted. Therefore, the intake valve phase changing unit (intake valve phase changing unit 302) changes the phase of the intake valve (intake valve 9) from the target position to the reference position after the decompression caused by restarting the engine (engine 113) is completed. to retard. At this time, as shown in the figure, the start of restarting the engine 113 may be the same as the start of cranking.

The intake valve phase changing unit 302 does not change the phase of the intake valve 9 while keeping the profile 9b during the period from the start timing of cranking to the completion of decompression. After completing the decompression, the intake valve phase changer 302 retards the phase advance amount of the intake valve 9 from 180 [deg] to 60 [deg]. That is, when the state change of the engine (engine 113) is the start of the engine (engine 113), the intake valve phase changing unit 302 is positioned across the exhaust stroke and the intake stroke, and the engine (engine 113) At the time of the initial explosion, the phase of the intake valve (intake valve 9) is retarded to a position at which the engine (engine 113) generates torque capable of self-rotating. Then, the ECU 102 determines the initial explosion cycle at the timing when the intake valve phase changing unit 302 changes the phase advance amount of the intake valve 9 to 60 [deg].

FIG. 15 is a diagram showing the amount of fresh air discharged to the exhaust pipe 8 during four cycles with reference to the start point of phase change of the intake valve 9 .

In the first cycle during which the intake valve phase changing section 302 changes the phase of the intake valve 9, the phase of the intake valve 9 changes to near the profile 9c. At this time, the cycle is such that air returns from the exhaust pipe 8 to the intake pipe 7, but fresh air is discharged from the intake pipe 7 to the exhaust pipe 8 from the second cycle onwards.

Here, the volume V3 of air returning from the exhaust pipe 8 to the intake pipe 7 in the first cycle is 50 cc. On the other hand, the volume V4 of fresh air discharged from the intake pipe 7 to the exhaust pipe 8 in the second to fourth cycles corresponds to 500 cc. Of the volume V4, 450 cc is the amount of fresh air discharged from the intake pipe 7 to the exhaust pipe 8 when the engine 113 is started.

From this, the volume V1 of fresh air discharged from the intake pipe 7 to the exhaust pipe 8 when the fuel is cut when the engine is stopped is 1411 cc, and in the period from cranking at the start of the engine 113 to the first explosion, The volume of fresh air discharged to 8 is 450 cc, which is volume V4 (500 cc) - volume V3 (50 cc). In order to make the amount of fresh air discharged from the engine stop to the first explosion zero, 1861 cc (=1411 + 450) of air is returned from the exhaust pipe 8 to the intake pipe 7 in the profile 9c when the engine is stopped. need to leave

Here, profile 9c allows 62 cc of air to be returned per cycle. Therefore, if the profile 9c is 30 cycles and the average rotation speed of the engine 113 is 1700 rpm, 2.1 seconds are required.

Therefore, the intake valve phase changing unit 302 sets the holding period of the profile 9c to 2.3 seconds in the fuel cut for stopping the engine, and changes to the profile 9b after 2.8 seconds from the start of the fuel cut. When the profile 9b is reached, the amount of air discharged from the intake pipe 7 to the exhaust pipe 8 becomes 0, and fresh air does not flow into the exhaust pipe 8 even if the engine 113 is rotating.

Here, the phenomenon that the amount discharged from the intake pipe 7 to the exhaust pipe 8 becomes zero in the profile 9b will be described.
FIG. 16 is a diagram showing an operation example of the intake valve 9 and the exhaust valve 10 changed to the target position profile 9b.
In the upper part of FIG. 16 profiles 9b, 10a similar to FIG. 5 are shown.
At the bottom of FIG. 16, the states of operation of the intake valve 9 and the exhaust valve 10 defined by the profiles 9b and 10a are shown for each timing (1) to (4).

Also in the profile 9b shown in FIG. 16, a negative pressure is formed before the exhaust valve 10 is closed at the timing (1), similarly to the profile 9c shown in FIG. At timing (2), the exhaust valve 10 is first opened, and fresh air in the exhaust pipe 8 is drawn into the combustion.

Here, unlike the profile 9c shown in FIG. 12, the intake valve 9 is opened at an early timing 10 degrees after the opening of the exhaust valve 10 at timing (2). Therefore, at timing (3), a sufficient negative pressure remains in the combustion chamber, and fresh air is drawn into the combustion chamber through the intake pipe 7 whose valve is opened. At this time, since the exhaust valve 10 is opened first, the intake amount of fresh air from the exhaust pipe 8 is larger than the intake amount of fresh air from the intake pipe 7 .

The fresh air sucked into the combustion chamber from the intake pipe 7 and the exhaust pipe 8 is pushed out to the intake pipe 7 and the exhaust pipe 8 respectively by the upward movement of the piston 3 during the exhaust stroke shown at timing (4). At this time, the lift amount of the intake valve 9 is 6 mm, whereas the lift amount of the exhaust valve 10 is 8 mm. Therefore, a large amount of fresh air is discharged to the exhaust pipe 8 side due to pressure loss. As a result, an amount equivalent to the amount of fresh air taken in from the intake pipe 7 and the exhaust pipe 8 is returned, so that the amount of fresh air discharged to the exhaust pipe 8 is zero.

In addition, the intake valve phase changing unit 302 causes the phase of the intake valve 9 to reach the profile 9b from the profile 9c to stop the engine 113 . Therefore, the fresh air discharged to the exhaust pipe 8 from fuel cut to engine stop will be described.

FIG. 17 is a diagram showing the amount of fresh air discharged from the exhaust pipe 8 to the intake pipe 7 in each cycle from the start of fuel cut to the stop of the engine. Here, the holding period of profile 9c is controlled to be 2.3 seconds. The horizontal axis in FIG. 17 represents the cycle number from the start of the fuel cut, and the vertical axis represents the volume of fresh air discharged to the exhaust pipe 8 (fresh air amount) [cm ³ ].

From the 8th cycle to the 37th cycle, the phase of the intake valve 9 is held at the intermediate position of the profile 9c. As described above, in FIG. 15, when the intake valve phase changing unit 302 changes the phase of the intake valve 9 to the initial explosion position after cranking at the time of starting the engine 113, the new valve is returned from the intake pipe 7 to the exhaust pipe 8. A volume V3 of air and a volume V4 of fresh air discharged from the intake pipe 7 to the exhaust pipe 8 from the fuel cut when the engine is stopped to the first explosion when the engine 113 is started are shown.

FIG. 17 also shows a volume V1 of fresh air discharged from the intake pipe 7 to the exhaust pipe 8 from the start of fuel cut when the engine is stopped until the engine is stopped, and the phase of the intake valve 9 by the intake valve phase changer 302. The volume V2 of fresh air returned from the exhaust pipe 8 to the intake pipe 7 by holding it in the intermediate position is shown. Then, the ECU 102 eliminates the need to enrich the fuel injected from the initial combustion of the engine by setting the integrated value of the fresh air volume V1+V4 and the fresh air volume V2+V3 to zero. It is possible to suppress the deterioration of

The intake valve phase changing section 302 according to the first embodiment described above changes the new air discharged into the exhaust pipe 8 in the transitional period immediately after starting the phase change of the intake valve 9 when the engine is stopped. A holding period is provided for holding a constant phase (profile 9c) that allows air to be reinhaled into the combustion chamber and then returned to the intake pipe 7 . Then, after the fresh air discharged to the exhaust pipe 8 during the holding period is returned to the intake pipe 7, the intake valve phase changing unit 302 is set to the position (profile 9b) that suppresses the discharge of the fresh air to the exhaust pipe 8. make it work.

Specifically, in order to cause the fresh air discharged to the exhaust pipe 8 to be injected back into the intake pipe 7 immediately after the start of the phase change, the intake valve phase changing unit 302 changes the phase of the intake valve 9 to the target position. The state in which the opening timing of the exhaust valve 10 is more advanced than the opening timing of the intake valve 9 is maintained for a predetermined period. Then, the intake valve phase changing unit 302 changes the amount of fresh air discharged to the exhaust pipe 8 during the phase change when the engine is stopped, and the phase when the engine 113 is restarted from the decompression position to the initial explosion position. In anticipation of the amount of fresh air that is discharged when the air is exhausted, the predetermined period is set to a period in which the exhaust gas corresponding to the amount of fresh air can be returned to the intake pipe 7 in advance.

In this way, the fresh air discharged into the exhaust pipe 8 during the transitional period when the engine is stopped and the amount of combustion gas expected to be discharged into the exhaust pipe 8 during the transitional period when the engine 113 is started are combined when the engine is stopped. By returning fuel to the intake pipe 7 at this time, the ECU 102 can eliminate the enriched injection when the engine 113 is started. Further, by eliminating the enriched injection at the time of starting the engine 113, it is possible to improve the fuel consumption and suppress the deterioration of the exhaust gas.

[Second embodiment]
Next, an example of phase change control of the intake valve 9 according to the second embodiment of the present invention will be described with reference to FIGS. 18 to 21. FIG.

The configuration of the ECU 102 according to the second embodiment is the same as the configuration of the ECU 102 according to the first embodiment. However, in the ECU 102 according to the second embodiment, the intake valve phase changing unit 302 does not set the phase change speed to zero while changing the phase of the intake valve 9, and the phenomenon that air returns from the exhaust pipe 8 to the intake pipe 7 occurs. This differs from the first embodiment in that the period during which air returns from the exhaust pipe 8 to the intake pipe 7 is generated by slowing the phase change speed during the period. The advantage of operating the ECU 102 according to the second embodiment in this manner is that the phase change speed is not set to zero, so that an increase in the motor starting power can be suppressed when the operation is started.

FIG. 18 is a diagram showing an example of profiles 9d and 9e that are changed near the intermediate position by the intake valve phase changer 302 according to the second embodiment.

The intake valve phase changer 302 according to the first embodiment, as shown in FIG. was controlled to stop
On the other hand, as shown in FIG. 18, the intake valve phase changing unit 302 according to the second embodiment is set at the time when the air returns from the exhaust pipe 8 to the intake pipe 7 when the profile 9d with the phase advance amount of 140 degrees is reached. The phase change speed (first phase change speed) is made lower than the phase change speed (second phase change speed) from profile 9a to profile 9d. Then, the intake valve phase change unit 302 performs control to return to the normal phase change speed (third phase change speed) when the profile 9e of the phase advance amount of 160 degrees is reached at which air does not return from the exhaust pipe 8 to the intake pipe 7. becomes. Note that the profile 9e is at a position advanced by 10 degrees from the profile 9c shown in FIG.

Note that the amount of air discharged from the intake pipe 7 to the exhaust pipe 8 when the engine is stopped is 1411 cc (volume V1 shown in FIG. 11), and the air quantity discharged to the exhaust pipe 8 is 450 cc (volume V1 shown in FIG. 15) when the engine 113 is restarted. The sum of −50 cc of volume V3 and 500 cc of volume V4 shown in FIG. 15) is the same as in the first embodiment. Also, the target amount of air to be returned from the exhaust pipe 8 to the intake pipe 7 is 1861 cc, which is the same as in the first embodiment and the second embodiment.

Since the intake valve phase change unit 302 of the ECU 102 according to the second embodiment does not set the phase change speed to zero and continues to move at a low speed, the above-mentioned 1861 cc of air can be returned from the exhaust pipe 8 to the intake pipe 7. It is necessary to set the phase change speed (first phase change speed) as follows.

Here, the amount of air returning from the exhaust pipe 8 to the intake pipe 7 by controlling the phase change speed according to the second embodiment will be described with reference to FIG.
FIG. 19 is a diagram showing an example of the amount of air returning from the exhaust pipe 8 to the intake pipe 7 when the intake valve phase changing unit 302 operates at a low phase change speed while the engine is stopped. The horizontal axis of FIG. 19 represents the cycle number from the 6th cycle after the start of the fuel cut, and the vertical axis represents the volume of fresh air discharged to the exhaust pipe 8 (fresh air amount) [cm ³ ].

The intake valve phase changing unit 302 changes the phase of the intake valve 9 so that the phase of the intake valve 9 reaches the profile 9d in the sixth cycle. The control up to the sixth cycle after the engine is stopped by the intake valve phase changing section 302 according to the second embodiment is the same as the control of the intake valve phase changing section 302 according to the first embodiment shown in FIG. is. After that, the intake valve phase changing unit 302 reaches the position of the profile 9c where the amount of air returning from the exhaust pipe 8 to the intake pipe 7 becomes maximum in the 16th cycle. However, since the intake valve phase changing unit 302 changes the phase of the intake valve 9 at a low speed until the position of the profile 9c is reached, the amount of air returning from the exhaust pipe 8 to the intake pipe 7 gradually increases. there is

After the 16th cycle, the intake valve phase changer 302 changes the phase from the profile 9c to the profile 9e, so the amount of air returning from the exhaust pipe 8 to the intake pipe 7 gradually decreases. When the profile 9e is reached in the 26th cycle, the amount of air returning from the exhaust pipe 8 to the intake pipe 7 becomes zero.

In addition, when the period of changing from the profile 9d to the profile 9e in FIG. 19 is 20 cycles, the amount of air returning from the exhaust pipe 8 to the intake pipe 7 is 539.6 cc. From this result, in order to set the amount of air returned from the exhaust pipe 8 to the intake pipe 7 to 1861 cc, it is necessary to set the cycle for changing from the profile 9d to the profile 9e to "69".

Here, the relationship between the engine speed and the intake valve phase advance amount after the intake valve phase changing unit 302 in the second embodiment stops the engine 113 and starts fuel cut is shown in FIG. Description will be made with reference to FIG.

FIG. 20 is a graph showing how the engine speed changes after the ECU 102 starts fuel cut. The horizontal axis of FIG. 20 represents the time [s] that has elapsed after the start of fuel cut, and the vertical axis represents the engine speed [rpm].
FIG. 21 is a graph showing how the intake valve phase changing unit 302 advances the phase of the intake valve 9 after the ECU 102 starts fuel cut. The horizontal axis in FIG. 21 represents the time [s] that has elapsed after the start of fuel cut, and the vertical axis represents the phase advance amount [deg] of the intake valve 9 .

As described above, the intake valve phase changing unit 302 according to the second embodiment requires 69 cycles to return the gas from the exhaust pipe 8 to the intake pipe 7, and the control according to the first embodiment longer than the 30 cycles required. Therefore, the average rotation speed is 1600 rpm and the period of 69 cycles is 5.2 seconds. Then, as shown in FIG. 18, the phase required for the intake valve phase changer 302 to change from the profile 9d to the profile e is 20 degrees. Therefore, the phase change speed required to change the phase of 20 degrees in 5.2 seconds is 3.8 degrees CA/s.

The intake valve phase changing section 302 according to the second embodiment described above can also change the phase of the intake valve 9 at a low speed in the phase range in which the air returns from the exhaust pipe 8 to the intake pipe 7. You can get the same effect as the form. That is, the ECU 102 eliminates the enriched injection at the start of the engine 113, thereby improving fuel efficiency and suppressing deterioration of exhaust gas.

[Third Embodiment]
Next, an example of phase change control for the intake valves 9 according to the third embodiment of the present invention will be described with reference to FIG.

The configuration of the ECU 102 according to the third embodiment is the same as the configuration of the ECU 102 according to the first embodiment. However, in order to reduce the cost of the VTC 40, the intake valve phase changing unit 302 according to the third embodiment has a performance of 150 degCA/s, which is half the phase changing speed of 300 degCA/s in the first embodiment. This embodiment differs from the first embodiment in that a motor with a drop is used and this motor is operated.

If a VTC 40 employing a motor with reduced performance is used, the phase change speed will be half the phase change speed according to the first embodiment, resulting in an increase in the number of cycles at engine stop and start. For example, the number of cycles in FIG. 11 showing the state of phase change when the engine is stopped and the number of cycles in FIG. In this case, the volume V1 of the air discharged from the intake pipe 7 to the exhaust pipe 8 shown in FIG. V3 is 100 cc, and the volume V4 of the air discharged from the intake pipe 7 to the exhaust pipe 8 is 1000 cc.

Therefore, the relationship between the phase change speed and the intermediate holding period will be described.
FIG. 22 is a diagram showing an example of map information 321A stored in the ECU 102 and representing the relationship between the phase change speed and the intermediate holding period. The horizontal axis of FIG. 22 represents the phase change speed [degCA/s], and the vertical axis represents the intermediate holding period [s].

Since the phase change speed is halved, the ECU 102 sets an intermediate holding period during which the air volume of 3722 cc (=2822-100+1000) indicated by the volume V2 in FIG. 17 can be returned from the exhaust pipe 8 to the intake pipe 7. There is a need to. Therefore, the ECU 102 changes the intermediate holding period according to the phase change speed when the engine is stopped and when the engine 113 is started. In the phase change information storage section (map information 321), a shorter intermediate holding period is defined as the phase change speed of the intake valve (intake valve 9) increases.

The intermediate holding period changes depending on the engine speed immediately after the fuel cut. For this reason, the intake valve phase changing unit 302 refers to the map information 321A shown in FIG. change to an intermediate retention period.

The ECU 102 according to the third embodiment described above obtains the intermediate holding period that varies depending on the engine speed immediately after the fuel cut, and changes the intermediate holding period by changing the phase change speed. At this time, the ECU 102 controls to lengthen the intermediate holding period when the phase change speed is slow, and to shorten the intermediate holding period when the phase change speed is fast. As described above, the ECU 102 changes the intermediate holding period according to the phase change speed to eliminate the enriched injection at the start of the engine 113 in the same manner as in the first embodiment. You can get the effect of suppressing the deterioration.

[Fourth embodiment]
Next, an example of phase change control for the intake valves 9 according to the fourth embodiment of the present invention will be described with reference to FIG.

The configuration of the ECU 102 according to the fourth embodiment is the same as the configuration of the ECU 102 according to the first embodiment. However, the ECU 102 according to the fourth embodiment will explain a case where the fuel cut is started under different throttle opening conditions.

FIG. 23 is a diagram showing an example of map information 321B stored in the ECU 102 and representing the relationship between the throttle opening and the intermediate holding period during fuel cut. The horizontal axis of FIG. 23 represents the throttle opening degree [deg] at the time of fuel cut, and the vertical axis represents the intermediate holding period [s].

Since the pressure in the intake pipe 7 increases as the throttle opening increases, the volume V1 of the air discharged from the intake pipe 7 to the exhaust pipe 8 increases when the engine is stopped. Therefore, the ECU 102 needs to lengthen the intermediate holding period in accordance with the increase in the volume V1. Therefore, in the phase change information storage unit (map information 321), a longer intermediate holding period is defined as the throttle opening at the time when fuel cut is started increases.

Then, when the ECU 102 cuts the fuel, the intake valve phase changing unit 302 according to the fourth embodiment refers to the map information 321B, and determines the intermediate holding period according to the throttle opening degree at the time of the fuel cut. change.

The ECU 102 according to the fourth embodiment described above obtains the intermediate holding period that changes according to the throttle opening degree immediately after the fuel cut, and increases or decreases the intermediate holding period. At this time, the ECU 102 shortens the intermediate holding period when the throttle opening is small, and lengthens the intermediate holding period when the throttle opening is large. As described above, the ECU 102 changes the intermediate holding period according to the throttle opening degree at the time of fuel cut, thereby eliminating the enriched injection at the time of starting the engine 113 in the same manner as in the first embodiment, thereby improving the fuel efficiency. It is possible to obtain the effect of suppressing the deterioration of the exhaust gas.

[Modification]
In each of the above-described embodiments, a configuration example of the engine 113 including the VTC 40 as a variable valve timing control mechanism capable of changing the phase of the intake valve has been described. It may be an engine equipped with a VVL (Variable Valve Lift: variable valve lift mechanism).

Moreover, although the VTC 40 is a mechanism that operates electrically, it may be a mechanism that operates hydraulically. In any case, it is possible to appropriately change the phase of the intake valve 9 .

In each of the above-described embodiments, the intake valve phase changing unit 302 appropriately changes the phase of the intake valve 9 so that the ECU 102 eliminates the enriched injection. The ECU 102 may perform slightly enriched injection in consideration of the deterioration of the parts.

The present invention is not limited to the above-described embodiments, and can of course be applied and modified in various other ways without departing from the gist of the present invention described in the claims.
For example, each of the embodiments described above is a detailed and specific description of the configuration of the device and system in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to those having all the configurations described. Further, it is possible to replace part of the configuration of the embodiment described here with the configuration of another embodiment, and furthermore, it is possible to add the configuration of another embodiment to the configuration of one embodiment. It is possible. Moreover, it is also possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.
Further, the control lines and information lines indicate those considered necessary for explanation, and not all control lines and information lines are necessarily indicated on the product. In practice, it may be considered that almost all configurations are interconnected.

3 Piston 9 Intake valve 10 Exhaust valve 22 Three-way catalyst 30 CPU 40 VTC 100 Hybrid vehicle 101 VCU 102 ECU 113 Engine 116 Battery 301 ... State determination unit 302 ... Intake valve phase change unit 321 ... Map information

Claims (10)

An engine control device for controlling an engine equipped with a variable valve timing control mechanism capable of changing the phase of an intake valve provided in an intake pipe,
a state determination unit that determines a change in the state of the engine, including that fuel supplied to the engine is cut due to the stop of the engine;
a reference position of the intake valve phase before the engine state change, a target position of the intake valve phase after the engine state change, and an intermediate position between the reference position and the target position; a phase change information storage unit that stores an intermediate holding period of the phase of the intake valve held near the intermediate position in a predetermined range including the intermediate position as phase change information of the intake valve;
Based on the phase change information read from the phase change information storage unit and the state change of the engine determined by the state determination unit, the variable valve timing control mechanism changes the phase of the intake valve from the reference position to the target position. A first phase change speed for changing the phase of the intake valve near the intermediate position during the change to the position is lower than a second phase change speed for changing from the reference position to near the intermediate position. after the intermediate holding period has elapsed, the phase of the intake valve is changed from near the intermediate position to the target position at a third phase change speed higher than the first phase change speed , and the phase of the intake valve is changed to the an intake valve phase changing unit that advances the angle from a reference position to the target position . An engine control device for controlling an engine equipped with a variable valve timing control mechanism capable of changing the phase of an intake valve provided in an intake pipe,
a state determination unit that determines a state change of the engine, including restarting of the engine from a state in which fuel supply to the engine is continued;
a reference position of the intake valve phase before the engine state change, a target position of the intake valve phase after the engine state change, and an intermediate position between the reference position and the target position; a phase change information storage unit that stores an intermediate holding period of the phase of the intake valve held near the intermediate position in a predetermined range including the intermediate position as phase change information of the intake valve;
Based on the phase change information read from the phase change information storage unit and the state change of the engine determined by the state determination unit, the variable valve timing control mechanism changes the phase of the intake valve from the reference position to the target position. A first phase change speed for changing the phase of the intake valve near the intermediate position during the change to the position is lower than a second phase change speed for changing from the reference position to near the intermediate position. and after the intermediate holding period has elapsed, the phase of the intake valve is changed from near the intermediate position to the target position at a third phase change speed higher than the first phase change speed, and the engine is restarted. an intake valve phase changing unit that retards the phase of the intake valve from the target position toward the reference position after the decompression is completed.
engine controller. At the intermediate position, the opening timing of the intake valve is set to be retarded with respect to the opening timing of the exhaust valve provided in the exhaust pipe,
At the target position, the intake valve during the exhaust stroke so that the gas sucked into the cylinder from the exhaust pipe during the expansion stroke returns to the exhaust pipe and the intake pipe during the exhaust stroke. The engine control device according to claim 1 or 2 , wherein the opening timing of the exhaust valve overlaps with the opening timing of the exhaust valve. 4. The intake valve phase change unit according to claim 3 , wherein the first phase change speed for advancing the phase of the intake valve near the intermediate position is set to zero until the intermediate holding period elapses. engine controller. The start of the fuel cut is performed prior to the stop of the engine when the charge capacity of the battery used for driving the vehicle reaches or exceeds a specified value,
4. The engine control device according to claim 3 , wherein the longer the intermediate holding period is defined in the phase change information storage section, the higher the rotation speed of the engine at the time when the fuel cut is started. 4. The engine control device according to claim 3 , wherein the phase change information storage unit defines a shorter intermediate holding period as the phase change speed of the intake valve increases. 4. The engine control device according to claim 3 , wherein the longer the intermediate hold period is defined in the phase change information storage unit as the throttle opening at the time when the fuel cut is started increases. The intake valve phase changing section is positioned across an exhaust stroke and an intake stroke when the state change of the engine is restarting of the engine, and the engine is self-sustaining at the time of initial explosion of the engine. 3. The engine control system according to claim 2 , wherein the phase of the intake valve is retarded to a position where rotatable torque is generated. An engine control method for controlling an engine equipped with a variable valve timing control mechanism capable of changing the phase of an intake valve,
A process of determining a change in the state of the engine, including that the fuel supplied to the engine is cut due to the stop of the engine;
a reference position of the intake valve phase before the engine state change, a target position of the intake valve phase after the engine state change, and an intermediate position between the reference position and the target position; The phase change information read from a phase change information storage unit that stores an intermediate holding period of the phase of the intake valve held near the intermediate position in a predetermined range including the intermediate position as the phase change information of the intake valve. and a process of changing the phase of the intake valve from the reference position to the target position through the variable valve timing control mechanism based on the state change of the engine,
During the process of changing the phase of the intake valve from the reference position to the target position,
a process of lowering a first phase change speed for changing the phase of the intake valve near the intermediate position below a second phase change speed for changing from the reference position to near the intermediate position;
After the intermediate holding period has elapsed, the phase of the intake valve is changed from near the intermediate position to the target position at a third phase change speed higher than the first phase change speed , and the phase of the intake valve is changed to the reference position. and a process of advancing the angle from the target position to the target position . An engine control method for controlling an engine equipped with a variable valve timing control mechanism capable of changing the phase of an intake valve,
A process of determining a state change of the engine, including restarting of the engine from a state in which fuel supply to the engine is continued;
a reference position of the intake valve phase before the engine state change, a target position of the intake valve phase after the engine state change, and an intermediate position between the reference position and the target position; The phase change information read from a phase change information storage unit that stores an intermediate holding period of the phase of the intake valve held near the intermediate position in a predetermined range including the intermediate position as the phase change information of the intake valve. and a process of changing the phase of the intake valve from the reference position to the target position through the variable valve timing control mechanism based on the state change of the engine,
During the process of changing the phase of the intake valve from the reference position to the target position,
a process of lowering a first phase change speed for changing the phase of the intake valve near the intermediate position below a second phase change speed for changing from the reference position to near the intermediate position;
After the intermediate holding period elapses, the phase of the intake valve is changed from near the intermediate position to the target position at a third phase change speed higher than the first phase change speed, and the phase of the intake valve is changed from the vicinity of the intermediate position to the target position. and a process of retarding the phase of the intake valve from the target position toward the reference position after compression is completed.
engine control method.

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