WO2022075091A1

WO2022075091A1 - Variable valve control device

Info

Publication number: WO2022075091A1
Application number: PCT/JP2021/035054
Authority: WO
Inventors: 亮草壁; 裕介木原; 匡行猿渡
Original assignee: 日立Astemo株式会社
Priority date: 2020-10-08
Filing date: 2021-09-24
Publication date: 2022-04-14
Also published as: JPWO2022075091A1; JP7361224B2; CN116096990A

Abstract

An exhaust valve phase changing unit provided in this variable valve control device outputs an instruction for changing the phase of an exhaust valve through an exhaust valve phase variable mechanism on the basis of a state change of an engine. In addition, the exhaust valve phase changing unit advances the central phase of the exhaust valve to a first angle which is further toward an advanced side than the bottom dead center of an expansion stroke until the engine is stopped after a fuel supplied to the engine has been cut by the control of an engine control device.

Description

Variable valve controller

The present invention relates to a variable valve control device.

Conventionally, a hybrid vehicle equipped with a traction motor and an engine has been provided. Two types of hybrid systems are known: a parallel hybrid system in which electricity and gasoline are used in combination, and a series hybrid system in which only a motor is used during driving and the engine is used only for power generation.

In the parallel hybrid system, the engine is stopped in the low load operating range where the thermal efficiency of the engine is low, and the vehicle runs only with the motor, and in the driving range where the thermal efficiency of the engine is high and the medium load or higher, the vehicle runs alone. 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 mounted on the vehicle is monitored, and when the battery capacity falls below a predetermined lower limit, the engine operates and rotates the generator to generate electricity and charge the battery. Driving is done. Then, when the battery capacity exceeds the upper limit value, the operation of stopping the engine is performed. In this way, in the series hybrid type vehicle, the engine is repeatedly stopped and started, so that the frequency of stopping and starting the engine is higher than that of a general internal combustion engine vehicle.

In this way, in the engine for hybrid vehicles used in each hybrid system, the frequency of stopping and starting the engine is high in order to reduce fuel consumption. In recent years, in order to further reduce fuel consumption, "fuel cut" is implemented in which fuel injection is cut during a period in which torque when stopping the engine is unnecessary. However, since the engine rotates by inertia during this fuel cut, unburned air (fresh air) is sucked 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 to 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, so that the three-way catalyst is in a state of excess oxygen. In this state, the purification efficiency of nitrogen oxides (NOx) of the three-way catalyst is lowered. Therefore, when the engine is restarted, the oxygen stored in the three-way catalyst is removed by increasing the fuel injection ratio so that the operating air-fuel ratio becomes smaller than the theoretical mixture ratio and supplying surplus fuel. "Enrich control" may be implemented.

In this enrichment control, there was a problem that fuel consumption deteriorated because excess fuel was injected, and HC and PN increased due to combustion in a state of excess fuel, resulting in deterioration of exhaust gas. Especially in the engine for hybrid vehicles, the frequency of stopping and starting the engine is high, so that the fuel consumption and the deterioration of the exhaust are greatly affected by the fuel cut.

As a technique for suppressing a decrease in purification efficiency of a three-way catalyst in a fuel cut operation, for example, Patent Document 1 states that "when the fuel cut detecting means detects a fuel cut, the intake valve is opened earlier. The technique of controlling the advance angle of the valve opening timing variable means is disclosed.

Japanese Unexamined Patent Publication No. 10-11234

The technology disclosed in Patent Document 1 reduces the amount of fresh air sucked into the cylinder during the intake stroke, reduces the amount of fresh air discharged to the exhaust pipe, and suppresses oxygen storage of the three-way catalyst. It was thought that it could be done. Especially in the fuel cut operation, by advancing the phase of the intake valve to the exhaust stroke and shortening the valve opening period of the intake stroke, the amount of fresh air sucked into the cylinder in the intake stroke is reduced, thereby reducing the exhaust pipe. It was thought that the amount of fresh air discharged to the gas could be reduced to suppress the oxygen storage of the three-way catalyst.

If the phase of the intake valve is advanced in this way and the period from opening to closing is set in the exhaust stroke, the intake valve and the exhaust valve will open during the exhaust stroke. Therefore, the air sucked into the cylinder from the intake pipe and the exhaust pipe is in a state of being blown back to the intake pipe and the exhaust pipe by the piston rising, and it is possible to suppress the discharge of fresh air to the exhaust pipe.

However, in the method disclosed in Patent Document 1, there is a transient period in which the intake valve opens and closes during the intake stroke from the start of operation to the advance side of the phase of the intake valve until the target position is reached. .. Since the intake valve is open in the intake stroke during this transition period, the fresh air sucked into the cylinder during the intake stroke is discharged to the exhaust pipe, whereby oxygen is stored in the three-way catalyst.

In addition, when restarting the engine, engine motoring is performed with the intake valve advanced for decompression (venting of gas) that suppresses fluctuations in engine speed due to air compression of the piston immediately after starting the engine. To. However, when the rotation speed rises and shifts to the first explosion cycle, the operation opposite to the above-mentioned operation (the operation in which the intake valve is retarded and returns to the initial position before returning to the original intake stroke) is performed. .. Therefore, fresh air is similarly discharged to the exhaust pipe even during the transient period when the intake valve phase of the first explosion is reached.

After changing the phase of the intake valve to the target position in this way, it is possible to suppress the discharge of fresh air to the exhaust pipe, but during the transition period during the phase change, the fresh air is discharged to the exhaust pipe and oxygen is added to the three-way catalyst. It is stored. Therefore, before the engine rotation is stopped or when the engine rotation is restarted, enrichment control for removing oxygen from the three-way catalyst is required. When enrichment control is performed, wasteful fuel is injected, so that CO ₂ emissions may increase, or PN and HC may increase due to an increase in rich air-fuel mixture.

The present invention has been made in view of such a situation, and an object of the present invention is to prevent enrichment injection when the engine is restarted.

The present invention is a variable valve control device that controls a variable valve timing control mechanism that can change the phase of an exhaust valve provided in the exhaust pipe of an engine, through a variable valve timing control mechanism based on a change in the state of the engine. It is provided with an exhaust valve phase changing unit that outputs an instruction for changing the phase of the exhaust valve. The exhaust valve phase changing unit advances the central phase of the exhaust valve from the bottom dead center of the expansion stroke between the time when the fuel supplied to the engine is cut by the control of the engine control device and the time when the engine is stopped. Advance to the first angle on the side.

According to the present invention, the central phase of the exhaust valve is advanced to the first angle between the time when the fuel supplied to the engine is cut and the time when the engine is stopped. , The fresh air discharged to the exhaust pipe when the engine is started flows back into the cylinder. Therefore, the amount of fresh air supplied to the three-way catalyst is reduced, and enrichment injection does not have to be performed when the engine is restarted, so that deterioration of fuel efficiency and exhaust gas can be suppressed.
Issues, configurations and effects other than those described above will be clarified by the following description of the embodiments.

It is a schematic diagram which shows the structural example of the engine which concerns on 1st Embodiment of this invention. It is a control block diagram which shows the internal structure example of the valve mechanism of the ECU and the engine which concerns on 1st Embodiment of this invention. It is a figure which shows the example of the profile of the intake valve and the exhaust valve at the time of the engine power generation operation which concerns on 1st Embodiment of this invention. The relationship between the engine speed and the amount of NOx detected in the tail pipe when the intake valve and the exhaust valve according to the first embodiment of the present invention are operated with a general profile is shown in chronological order. It is a graph. It is a figure which shows the example of the profile of the intake valve and the exhaust valve at the time of transition to the fuel cut operation of the engine which concerns on 1st Embodiment of this invention. It is a figure which shows the example of the integrated value of the fresh air amount of fresh air supplied to a three-way catalyst from after the fuel cut which concerns on the 1st Embodiment of this invention to the time when an engine is stopped. It is a figure which shows the example of the profile of the intake valve and the exhaust valve which concerns on the modification of 1st Embodiment of this invention, and the example of the schematic diagram of an engine. The exhaust valve is closed when the central phase of the exhaust valve is maintained at the second angle from the time when the rotation of the engine according to the first embodiment of the present invention is stopped until the next fuel injection is started. It is a figure which shows the example of a valve timing. It is a figure which shows the example of the profile of the intake valve and the exhaust valve which concerns on the 2nd Embodiment of this invention, and the example of the schematic diagram of an engine. It is a figure which showed the relationship between the time which concerns on the 2nd Embodiment of this invention, the engine speed, the closing time of an exhaust valve, and the opening time of an intake valve. It is a figure which shows the example of the time-series change of the phase of the exhaust valve and the intake valve which concerns on 3rd Embodiment of this invention.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the attached drawings. In the present specification and the drawings, components having substantially the same function or configuration are designated by the same reference numerals, and duplicate description will be omitted.

[First Embodiment]
FIG. 1 is a schematic diagram showing a configuration example of the engine 100 according to the first embodiment of the present invention.
In the series hybrid vehicle, the engine 100 used only for power generation is configured to include a traction motor 50 for traveling the vehicle. The engine (engine 100) is started when the charge capacity (referred to as "battery capacity") of the battery 111 mounted on the vehicle becomes less than a specified value. On the contrary, when the charge capacity (referred to as "battery capacity") of the battery 111 exceeds the specified value, the engine (engine 100) is stopped.

The engine 100 is configured as a 400cc in-line 3-cylinder naturally aspirated engine per cylinder. A combustion chamber is formed by a cylinder head 1 provided in the engine 100, a cylinder block 2, and a piston 3 inserted in the cylinder block. The piston 3 is connected to the crank shaft 5 via a connecting rod 4. The crank angle sensor 6 provided in the vicinity of the crank shaft 5 can detect the engine speed. Further, the traction motor 50 is installed coaxially with the crank shaft 5. As described above, the engine (engine 100) is provided with a motor (traction motor 50) capable of rotating the engine (engine 100) under the control of the engine control device (ECU 25). Then, the traction motor 50 rotates the engine 100 by rotating the crank shaft 5.

The intake pipe 7 and the exhaust pipe 8 are connected toward the combustion chamber of one cylinder, and the intake valve 9 and the exhaust valve 10 are provided so as 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 12, and a crank pulley connected to the crank shaft 5 are provided on the side of the engine 100 and are connected via a timing belt. .. As a result, the intake cam 11 and the exhaust cam 12 are rotated by the rotation of the crank shaft 5 during the operation of the engine 100. The intake cam pulley and the exhaust cam pulley are set so that the intake cam 11 and the exhaust cam 12 rotate once when the crank shaft 5 rotates twice.

The intake cam 11 and the exhaust cam 12 are provided with a variable valve timing control mechanism (hereinafter, VTC) 40 (see FIG. 2 to be described later). The VTC (Valve Timing Control) 40 can change the phase of the intake valve (intake valve 9) provided in the intake pipe (intake pipe 7) of the engine (engine 100). Further, the VTC 40 can change the phase of the exhaust valve (exhaust valve 10) provided in the exhaust pipe (exhaust pipe 8) of the engine (engine 100). Further, the crank shaft 5 is provided with a motor generator (not shown) that acts as a generator during power generation and as a motor when the engine 100 is started or stopped. The VTC 40 is a hydraulic type, and the ECU (Engine Control Unit) 25 can change the phase of the intake valve 9 and the exhaust valve 10 to an advance angle or a retard angle by rotating a motor provided in the VTC 40.

An injector 13 is provided on the intake side of the combustion chamber, and a spark plug 14 and an ignition coil 15 are provided on the upper part of the combustion chamber. The fuel is stored in the fuel tank 16 and sent to the high-pressure fuel pump 18 by the feed pump 17 through the fuel pipe. The high-pressure fuel pump 18 is driven by the exhaust cam 12, and the boosted fuel is sent to the common rail 19. A fuel pressure sensor 20 is installed on the common rail 19 so that the fuel pressure (referred to as "fuel pressure") can be detected. 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 to each cylinder from the collector 21. Further, a throttle valve 27 capable of changing the amount of air sucked into the cylinder is provided on the upstream side of the collector. 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 of the three-way catalyst 22. A temperature sensor 23 is provided on the three-way catalyst 22 to detect the temperature of the three-way catalyst 22. Further, a tail pipe (not shown) is provided downstream of the three-way catalyst 22.

The cylinder block 2 is provided with a water temperature sensor 26 that measures the temperature (water temperature) of the water flowing around the cylinder block 2. The water temperature and engine speed signals are input to the ECU 25. The ECU 25 controls the on / off of fuel injection and the phase of the VTC 40 based on various information obtained from the signals input from each sensor.

Next, an internal configuration example and an operation example of the ECU 25 and the VTC 40 will be described below.
FIG. 2 is a control block diagram showing an internal configuration example of the valve mechanism of the ECU 25 and the engine 100. The engine control device (ECU 25) controls an engine (engine 100) provided with a variable valve timing control mechanism (VTC40) capable of changing the phase of the intake valve (intake valve 9). The ECU 25 executes the engine control method according to the present embodiment to control the engine 100 provided with the VTC 40.

The ECU 25 includes a CPU (Central Processing Unit) 30, a RAM (Random Access Memory) 31, and a ROM (Read Only Memory) 32.
The ECU 25 includes a primary voltage detected by a voltage sensor (not shown) of the ignition coil 15, a secondary current detected by a current sensor (not shown) of the ignition coil 15, and an accelerator opening sensor 113 (see FIG. 1). Detected accelerator depression information (accelerator opening), angle information detected by the crank angle sensor 110 (crank angle), engine 100 rotation speed, throttle valve opening from throttle valve 27, battery voltage sensor 112 (see FIG. 1). ) Detects an input signal such as the battery voltage (battery capacity) is input.

The input information of each sensor input to the ECU 25 is temporarily stored in the RAM 31, and the CPU 30 performs arithmetic processing according to a predetermined control program. Variables and parameters generated during the arithmetic processing of the CPU 30 are temporarily written in the RAM 31, and these variables and parameters are appropriately read by the CPU 30. However, an MPU (Micro Processing Unit) may be used instead of the CPU 30.

The ROM 32 permanently records programs, data, and the like necessary for the CPU 30 to operate, and is used as an example of a computer-readable non-transient recording medium that stores a program executed by the ECU 25. The control program that describes the content of the arithmetic processing performed by the CPU 30 is written in advance in the ROM 32, and is appropriately read and executed by the CPU 30. Further, the phase change information storage unit (ROM 32) has a reference position of the phase of the exhaust valve (exhaust valve 10) before the state change of the engine (engine 100) and the exhaust valve after the state change of the engine (engine 100). The target position of the phase of the (exhaust valve 10) is stored as the phase change information of the exhaust valve (exhaust valve 10). Further, the phase change information storage unit (ROM 32) has a reference position of the phase of the intake valve (intake valve 9) before the state change of the engine (engine 100) and the intake valve after the state change of the engine (engine 100). The target position of the phase of the (intake valve 9) is stored as the phase change information of the intake valve (intake valve 9). However, the non-volatile storage may be provided in the ECU 25, and the phase change information updated through the network may be stored in the non-volatile storage.

The control program executed by the CPU 30 realizes the functions of the state determination unit 300, the exhaust valve phase changing unit 303, the intake valve phase changing unit 302, and the motor control unit 304 shown in the figure.
The ECU 25 according to the present embodiment controls, for example, to cut the fuel supplied to the engine 100 when the ECU 25 is instructed to stop the engine 100 by a VCU (Vehicle Control Unit) (not shown). The start of fuel cutting is performed prior to stopping the engine (engine 100) when the charge capacity of the battery (battery 111) used for driving the vehicle (hybrid vehicle) exceeds a specified value.

Further, the ECU 25 restarts the engine 100 when the driver depresses the accelerator while the engine 100 is stopped and the fuel is cut. Therefore, the state determination unit (state determination unit 300) determines the state change of the engine (engine 100) and outputs the determination result. The state change of the engine (engine 100) includes that the fuel supplied to the engine (engine 100) is cut due to the stop of the engine (engine 100). Further, the change in the state of the engine (engine 100) includes the restart of the engine (engine 100) from the state in which the fuel is continuously cut.

The variable valve control device (variable valve control device 301) is provided in the exhaust valve (exhaust valve 10) provided in the exhaust pipe (exhaust pipe 8) of the engine (engine 100) and the intake pipe (intake pipe 7). It controls a variable valve timing control mechanism (VTC40) that can change the phase of the intake valve (intake valve 9). The variable valve control device 301 includes an intake valve phase changing unit 302 and an exhaust valve phase changing unit 303. The variable valve control device 301 is an intake valve according to, for example, a change in the state of the engine 100 such that the ECU 25 starts a fuel cut to stop the engine 100 or restarts the engine 100 based on the battery capacity. The phase of at least one of 9 and the exhaust valve 10 is changed, and the valve opening / closing timing is changed.

The intake valve phase changing unit (intake valve phase changing unit 302) is an intake valve (intake valve 9) through a variable valve timing control mechanism (intake valve phase variable mechanism 41 of VTC 40) based on a state change of the engine (engine 100). Outputs an instruction to change the phase of. Here, the intake valve phase changing unit (intake valve phase changing unit 302) has a reference position of the phase of the intake valve (intake valve 9) before the state change of the engine (engine 100) and the state of the engine (engine 100). The phase of the intake valve (intake valve 9) is changed based on the phase change information in which the target position of the phase of the intake valve (intake valve 9) after the change is set and the state change of the engine (engine 100). It is good to output the instruction for. Therefore, the intake valve phase change unit (intake valve phase change unit 302) is the phase change information read from the phase change information storage unit (ROM 32) and the engine (engine 100) determined by the state determination unit (state determination unit 300). Refer to the state change of. The control by which the intake valve phase changing unit 302 changes the phase of the intake valve 9 will be described later in the second embodiment.

The exhaust valve phase changing unit (exhaust valve phase changing unit 303) passes through the variable valve timing control mechanism (exhaust valve phase variable mechanism 42 of VTC 40) based on the state change of the engine (engine 100) to exhaust valve (exhaust valve 10). Outputs an instruction to change the phase of. Here, the exhaust valve phase changing unit (exhaust valve phase changing unit 303) has a reference position of the phase of the exhaust valve (exhaust valve 10) before the state change of the engine (engine 100) and the state of the engine (engine 100). The exhaust valve (exhaust valve 10) is set based on the phase change information of the exhaust valve (exhaust valve 10) in which the target position of the phase of the exhaust valve (exhaust valve 10) is set after the change, and the state change of the engine (engine 100). It is advisable to output an instruction for changing the phase of the valve 10). Therefore, the exhaust valve phase change unit (exhaust valve phase change unit 303) is the phase change information read from the phase change information storage unit (ROM 32) and the engine (engine 100) determined by the state determination unit (state determination unit 300). Refer to the state change of.

Then, the exhaust valve phase changing unit (exhaust valve phase changing unit 303) is operated from the time when the fuel supplied to the engine (engine 100) is cut by the control of the engine control device (ECU 25) until the engine (engine 100) is stopped. In the meantime, the central phase (central phase 401) of the exhaust valve (exhaust valve 10) is moved to the first angle (first angle 405) (see FIG. 5) on the advance side of the bottom dead point of the expansion stroke. Advance the angle. This instruction is output to the exhaust valve phase variable mechanism 42 of the VTC 40.

The VTC 40 has an intake valve phase variable mechanism 41 and an exhaust valve phase variable mechanism 42.
The intake valve phase variable mechanism 41 opens and closes the intake valve 9 at a predetermined time by variably controlling the intake valve phase of the intake valve 9 based on the instruction of the intake valve phase changing unit 302. The intake valve phase variable mechanism 41 can change the phase of the intake valve 9 to an advance angle or a retard angle by driving the intake cam 11 based on the instruction of the intake valve phase change unit 302. In the following description, it is assumed that the intake valve phase changing unit 302 changes the phase of the intake valve 9 to an advance angle or a retard angle.

The exhaust valve phase variable mechanism 42 opens and closes the exhaust valve 10 at a predetermined time by variably controlling the exhaust valve phase of the exhaust valve 10 based on the instruction of the exhaust valve phase changing unit 303. The exhaust valve phase variable mechanism 42 can change the phase of the exhaust valve 10 to an advance angle or a retard angle by driving the exhaust cam 12 based on the instruction of the exhaust valve phase change unit 303. In the following description, it is assumed that the exhaust valve phase changing unit 303 changes the phase of the exhaust valve 10 to an advance angle or a retard angle.

Further, the motor control unit 304 included in the CPU 30 controls the operation of the traction motor 50.

<Relationship between the phase of the intake valve and exhaust valve and the lift amount>
Next, the timing of changing the phase of the exhaust valve 10 (valve opening / closing timing) and the changed phase of the exhaust valve 10 will be described with reference to FIGS. 3 to 7. The horizontal axis of FIGS. 3, 5 and 7 shows how the stroke changes in the order of expansion stroke, exhaust stroke, intake stroke, and compression stroke, and the vertical axis shows the intake valve 9 and the exhaust valve 10. The lift amount of is shown.

FIG. 3 is a diagram showing an example of profiles of the intake valve 9 and the exhaust valve 10 during engine power generation operation. Each profile of the intake valve 9 and the exhaust valve 10 shown in the figure represents the opening / closing timing, the phase change, and the lift amount of the intake valve 9 and the exhaust valve 10.

In FIG. 3, the change in the phase of the intake valve 9 is represented by the intake valve profile 9a, and the change in the phase of the exhaust valve 10 is represented by the exhaust valve profile 10a. For example, the lift amount of the intake valve 9 is set to 11 mm, and the working angle is set to 190 deg. Further, for example, the lift amount of the exhaust valve 10 is set to 10 mm, and the working angle is set to 200 deg. Further, the valve closing time of the intake valve 9 is set near the bottom dead center (BDC: Bottom Dead Center), and the valve closing time of the exhaust valve 10 is set near the top dead center (TDC: Top Dead Center). As shown in FIG. 3, when the engine 100 is being driven, the exhaust valve profile 10a changes in the exhaust stroke, and the intake valve profile 9a changes in the intake stroke. The intake valve profile 9a and the exhaust valve profile 10a do not almost overlap each other. The phase position of the intake valve 9 represented by the intake valve profile 9a and the phase position of the exhaust valve 10 represented by the exhaust valve profile 10a are referred to as "reference positions".

For example, it is assumed that the engine 100 is operating at the power generation point because the battery capacity of the engine 100 is below the lower limit after warming up under the condition that the hybrid vehicle is running. At this time, the engine 100 is operating according to the intake valve profile 9a and the exhaust valve profile 10a shown in FIG. That is, the intake valve phase changing unit 302 controls the phase so that the intake valve 9 operates according to the intake valve profile 9a. Further, the exhaust valve phase changing unit 303 controls the phase so that the exhaust valve 10 operates according to the exhaust valve profile 10a. In this state, the injector 13 injects fuel adjusted so that the air-fuel ratio of the fuel becomes "14.5" with respect to the fresh air amount of the air sucked into the combustion chamber in the intake stroke.

The fuel injection timing is, for example, 60 deg ATDC in the intake stroke, and a uniform air-fuel mixture is formed in the combustion chamber after a period from the intake stroke to the compression stroke. The air-fuel mixture is ignited at the best fuel economy ignition timing in the latter half of the compression stroke, and the combustion pressure pushes the piston 3 to rotate the crank shaft 5. When the crank shaft 5 rotates, a motor generator (not shown) connected to the crank shaft 5 also rotates to generate electric power, and the battery 111 is charged with electric power.

The hybrid vehicle stops due to a signal, traffic jam, etc., and when the battery capacity exceeds the upper limit, charging is stopped, and the engine 100 starts the stop process under the control of the ECU 25. At this time, since engine torque is not required, the ECU 25 cuts the fuel supplied to the engine 100. At this time, the ECU 25 controls to turn off the fuel injection signal to the injector 13, and stops the fuel supply to the combustion chamber. Therefore, the fuel injection from the injector 13 to the combustion chamber is stopped.

FIG. 4 is a graph showing the relationship between the engine speed when the intake valve 9 and the exhaust valve 10 are operated with a general profile and the amount of NOx detected in the tail pipe in chronological order.

When the charge amount of the battery 111 exceeds the threshold value, the engine speed starts to decrease at the timing t21 under the control of the ECU 25. Here, a fuel cut timing t22 is provided between the timing t21 and the timing t23 at which the engine is stopped. Further, in a hybrid vehicle, the negative pressure of the engine 100 may be used to secure the brake pressure of the hybrid vehicle. For example, in a series hybrid system or a parallel system hybrid vehicle, if the stop section of the engine 100 is long, the traction motor 50 may perform motoring 52 to idle the engine 100 in order to generate a negative pressure of the brake.

In addition, the battery capacity of the hybrid vehicle decreases as the traveling state becomes longer due to the electric power supplied from the battery 111. When the battery capacity decreases, it is necessary to charge the battery 111. Therefore, the ECU 25 controls to increase the rotation speed of the engine 100 at the timing t24. However, the ECU 25 does not inject fuel in the motoring section 53 started at the timing t24, but controls the traction motor 50 to raise the engine speed to a predetermined value 56.

Then, the ECU 25 controls so that fuel injection is not performed in the range of the section 51. Therefore, when the engine 100 is moved according to the intake valve profile 9a and the exhaust valve profile 10a shown in FIG. 3, the three-way catalyst 22 is used in the section where the engine 100 is stopped, the section where the engine is motorized, and the section where the engine 100 is started. Fresh air is supplied, and the inside of the three-way catalyst 22 becomes in a state of excess oxygen. In the three-way catalyst 22, when the A / F, which is the ratio of air and fuel, changes from a stoichiometric state of 14.7 to an excess oxygen state, the NOx purification efficiency becomes higher than that of the stoichiometric air-fuel ratio (stoikiometry). descend. As a result, the NOx emission amount 54 increases at the timing of restarting the engine 100.

Here, with reference to FIG. 5, the details of the operation of the variable valve control device 301 according to the first embodiment will be described. The variable valve control device 301 according to the first embodiment controls the operation of the exhaust cam 12 through the exhaust valve phase variable mechanism 42 by having the exhaust valve phase changing unit 303, and adjusts the phase angle of the exhaust valve 10. change.

FIG. 5 is a diagram showing an example of profiles of the intake valve 9 and the exhaust valve 10 at the time of transition to the fuel cut operation of the engine 100 according to the first embodiment. The horizontal axis and the vertical axis of the profile shown on the upper side of FIG. 5 are the same as the horizontal axis and the vertical axis of the profile shown in FIG. Further, on the lower side of FIG. 5, the operation state of the intake valve 9 and the exhaust valve 10 defined by the profile shown on the upper side of FIG. 5 is shown for each timing (1) to (4). Of the intake pipe 7 and the exhaust pipe 8 shown on the lower side of FIG. 5, and the schematic diagram of the combustion chamber, the pipe on the left side is referred to as the intake pipe 7, and the pipe on the right side is referred to as the exhaust pipe 8. Further, in the timings (1) to (4), the vertical stripe region represents the fresh air of the intake pipe 7, and the horizontal stripe region represents the fresh air or the exhaust gas of the exhaust pipe 8. The arrows in the figure indicate the direction of movement of fresh air.

As shown in FIG. 4, the exhaust valve phase variable mechanism 42 sets the central phase 401 of the exhaust valve 10 in FIG. 5 between the fuel cut timing t22 of the engine 100 and the timing t23 when the engine 100 is stopped. The engine is advanced to the first angle 405, which is on the advance side of the bottom dead center (BDC) 402 of the expansion stroke shown. At this time, the exhaust valve 10 operates according to the exhaust valve profile 10b changed from the exhaust valve profile 10a. The phase position of the exhaust valve 10 represented by the exhaust valve profile 10b is referred to as a "target position". As a result, the variable valve control device 301 causes fresh air to flow back into the cylinder from the exhaust pipe 8, suppresses the fresh air supplied to the three-way catalyst 22 when the fuel is cut, and discharges NOx when the engine 100 is restarted. The amount can be suppressed.

Here, the operation of the intake valve 9 and the exhaust valve 10 in each stroke will be described. The opening / closing timing of the exhaust valve 10 is controlled according to the exhaust valve profile 10b.
In the expansion stroke, the piston 3 begins to descend in the section 403 where the exhaust valve 10 is closed. Then, after the section 403, the exhaust valve 10 starts to open. At the timing (1) of the expansion stroke, the pressure inside the exhaust pipe 8 becomes atmospheric pressure, the pressure inside the combustion chamber (inside the cylinder) becomes negative, and only the exhaust valve 10 is opened. Therefore, due to the pressure difference between the exhaust pipe 8 and the cylinder, fresh air containing the exhaust gas discharged to the exhaust pipe 8 in the previous cycle flows back into the cylinder. Then, the cylinder is filled with fresh air containing the exhaust gas discharged in the cycle before the exhaust pipe 8. In the expansion stroke, the pressure in the cylinder recovers to the atmospheric pressure, and the differential pressure between the pressure in the cylinder and the pressure in the exhaust pipe 8 disappears.

After the expansion stroke BDC, the piston 3 rises at the timing (2) of the exhaust stroke. Further, in the exhaust stroke, only the exhaust valve 10 is in a state of being opened, and the intake valve 9 is in a state of being closed. Therefore, the fresh air in the cylinder is not sucked from the intake pipe 7, and the fresh air or the exhaust gas in the cylinder is discharged to the exhaust pipe 8 again. Then, the exhaust valve 10 closes on the advance side of the top dead center (TDC) of the intake stroke. Therefore, when the exhaust gas flows into the cylinder from the exhaust pipe 8, the EGR (Exhaust Gas Recirculation) rate increases. However, when there is a lot of fresh air in the exhaust pipe 8, the fresh air is trapped in the cylinder, so that the EGR rate does not increase.

Here, the EGR rate is a value defined by the following mathematical formula (1) and represents the ratio of the exhaust gas to the intake air amount.
EGR rate [%] = (F0-FA) / F0 × 100 ... (1)
F0 [l / min] is the amount of intake air before EGR is introduced. FA [l / min] is the amount of intake air when EGR is introduced.

When the exhaust valve 10 is closed in the middle of the exhaust stroke, the pressure in the cylinder becomes high because the air in the cylinder is compressed by the rise of the piston 3 in the section 404 where the piston 3 rises. After the exhaust stroke TDC, at the timing (3) of the intake stroke, the piston 3 starts descending. As shown in the intake valve profile 9a, the intake valve 9 is opened as the piston 3 descends. Here, since the pressure of the intake pipe 7 is lower than the pressure in the cylinder, the exhaust gas in the cylinder flows back to the intake pipe 7 due to the pressure difference between the cylinder and the intake pipe 7.

At the timing (4), which is the latter half of the intake stroke, the piston 3 is further lowered with the exhaust valve 10 closed. Therefore, in the section where the exhaust valve 10 is closed, the air existing in the cylinder is expanded and a negative pressure is formed in the cylinder. When the piston 3 descends, exhaust gas and fresh air flow into the cylinder from the intake pipe 7. After the intake stroke BDC, the intake valve 9 closes.

Next, in the compression stroke, the piston 3 rises and the in-cylinder volume becomes smaller. However, since both the intake valve 9 and the exhaust valve 10 are closed, the air in the cylinder stays. Next, when the piston 3 descends in the expansion stroke, since there is no fresh air sucked from the intake pipe 7, the air in the cylinder expands again and a negative pressure is formed.

In the section 403 where the exhaust valve 10 is open, the pressure inside the cylinder is negative, so the exhaust gas or fresh air from the exhaust pipe 8 is discharged at the moment when the exhaust valve 10 is opened as the piston 3 descends. A lot of it flows in. Therefore, as the engine 100 rotates, exhaust gas and / or fresh air flows into the cylinder. After that, when the intake valve 9 is opened, a part of the exhaust gas, fresh air, or both of the exhaust gas flowing into the cylinder is discharged to the intake pipe 7.

Next, when the opening / closing timing of the exhaust valve 10 is changed by using the variable valve control device 301, the engine speed after the fuel cut and the integrated value of the fresh air amount supplied to the three-way catalyst 22 are calculated. The relationship between the above will be described with reference to FIG.

FIG. 6 is a diagram showing an example of an integrated value of the amount of fresh air supplied to the three-way catalyst 22 after the fuel is cut until the engine 100 is stopped. The horizontal axis of FIG. 6 represents the engine speed [time] until the engine 100 stops after the fuel is cut, and the vertical axis represents the integrated value [mg] of the fresh air supplied to the three-way catalyst 22. .. The dotted line 501 in the figure shows the integrated value of the fresh air amount when the phase of the exhaust valve 10 changes in the exhaust valve profile 10a shown in FIG. Further, the alternate long and short dash line 502 shows the integrated value of the fresh air amount when the phase of the exhaust valve 10 changes in the exhaust valve profile 10b shown in FIG. Further, the solid line 503 shows the integrated value of the fresh air amount when the phase of the exhaust valve 10 changes at the exhaust valve closing timing shown in FIG. 8 to be described later.

First, the integrated value of the fresh air amount when the engine rotation is stopped according to the intake valve profile 9a and the exhaust valve profile 10a shown in FIG. 3 will be described with reference to the dotted line 501.
In this profile, fresh air flows into the cylinder from the intake pipe 7 in the intake stroke, and fresh air in the cylinder is discharged to the exhaust pipe 8 in the exhaust stroke. Therefore, as shown by the dotted line 501, the amount of fresh air supplied to the three-way catalyst 22 increases according to the engine speed after the fuel is cut.

Next, when the central phase 401 of the exhaust valve 10 is moved to the advance side after the fuel cut timing t22 shown in FIG. 4 by the control according to the profile according to the first embodiment (exhaust valve profile). 10b) will be described.

The timing 504 shown in FIG. 6 indicates that the central phase 401 of the exhaust valve profile 10b shown in FIG. 5 has advanced to the vicinity of the bottom dead center of the expansion stroke. After the fuel is cut, the fresh air in the cylinder and the exhaust pipe 8 is supplied to the three-way catalyst 22 until the timing 504. However, when the central phase 401 changes to the advance angle side from the bottom dead center 402 of the expansion stroke, fresh air, exhaust gas, or both of the exhaust pipe 8 rather than the fresh air flowing into the cylinder from the intake pipe 7 The amount of backflow inward is larger. At this time, as shown in the range 505 along the alternate long and short dash line 502 in FIG. 6, the integrated value of fresh air supplied to the three-way catalyst 22 starts to decrease. As a result, the amount of fresh air supplied to the three-way catalyst 22 when the engine 100 is stopped becomes the amount of fresh air supplied to the three-way catalyst 22 by the conventional control shown by the dotted line 501. It decreases in comparison.

In the variable valve control device 301 according to the first embodiment described above, the central phase 401 of the exhaust valve profile 10a is advanced to the first angle 405 which is the advance angle side of the bottom dead center 402 of the expansion stroke. .. As a result, the fresh air supplied to the three-way catalyst 22 is suppressed, and the fresh air stored in the three-way catalyst 22 can be significantly reduced. Therefore, the oxygen excess of the three-way catalyst 22 at the time of restarting the engine 100 Can be reduced. Further, since fresh air is not stored in the three-way catalyst 22, NOx emissions at the time of restarting the engine 100 can be suppressed. Further, since the enrichment control can be suppressed by reducing the supply of fresh air to the three-way catalyst 22, for example, HC and PN can be suppressed, and fuel consumption can be improved by suppressing unnecessary fuel injection.

<Control to throttle the throttle valve opening>
Next, various modifications relating to the operation control of the exhaust valve 10 according to the first embodiment of the present invention will be described.
First, an example in which the ECU 25 controls to throttle the opening degree of the throttle valve 27 before or after the fuel cut will be described. Here, before or after the fuel cut is, for example, between the timings t21 and t23 shown in FIG.

The engine control device (ECU 25) according to the first embodiment is a throttle valve (ECU 25) provided upstream of an intake pipe (intake pipe 7) provided with an intake valve (intake valve 9) before or after cutting fuel. Control is performed to throttle the opening degree of the throttle valve 27). For example, the ECU 25 reduces the opening area of the intake pipe 7, which is a fresh air flow path, by reducing the opening degree of the throttle valve 27 after the timing t21 when the engine speed decreases as shown in FIG. Control to be. By controlling the ECU 25 to narrow the opening degree of the throttle valve 27, the fresh air flowing into the cylinder from the intake pipe 7 is reduced. The pressure in the intake pipe 7 and the pressure in the cylinder become lower than the atmospheric pressure (exhaust pipe), and the pressure difference between the exhaust pipe 8 and the cylinder becomes large. Therefore, the amount of exhaust gas and / or fresh air flowing back from the cylinder to the intake pipe 7 and backflow from the exhaust pipe 8 to the cylinder can be increased, and the fresh air supplied to the three-way catalyst 22 can be increased. Decreases. As a result, the integrated value of the fresh air supplied to the three-way catalyst 22 can be further suppressed in combination with the effect of reducing the fresh air to the three-way catalyst 22 by advancing the exhaust valve profile 10a. Then, the ECU 25 maintains the throttle valve 27 in a throttled state until just before the restart of the engine 100. Therefore, the effect of reducing NOx emissions when the engine 100 is restarted is enhanced.

If the timing at which the ECU 25 throttles the opening degree of the throttle valve 27 is before the fuel cut shown in the timing T22, the amount of decrease in fresh air supplied to the cylinder and the exhaust pipe 8 can be increased. However, even if the timing at which the ECU 25 throttles the opening degree of the throttle valve 27 is after the fuel cut, it is possible to reduce the fresh air supplied to the inside of the cylinder and the exhaust pipe 8.

<Control with the central phase of the exhaust valve as the center position of the expansion stroke>
Next, an example in which the variable valve control device 301 controls the central phase 401 of the exhaust valve 10 as the center position of the expansion stroke will be described.

FIG. 7 shows an example of profiles of the intake valve 9 and the exhaust valve 10 and an example of a schematic diagram of the engine 100 according to the modified example of the first embodiment. FIG. 7 shows how the central phase 401 of the exhaust valve 10 is controlled to be advanced to the second angle 701, which is a substantially center position of the expansion stroke. An example of the profile is shown on the upper side of FIG. 7, and the operation of the intake valve 9 and the exhaust valve 10 is shown on the lower side of FIG. 7. The details of the exhaust valve profile 10d shown in the figure will be described later.

The variable valve control device 301 according to the modified example of the first embodiment of the present invention is an exhaust valve during the period from the fuel cut timing t22 shown in FIG. 4 to the timing t23 when the rotation of the engine 100 is stopped. Control is performed to advance the central phase 401 of 10. Specifically, the exhaust valve phase changing unit (exhaust valve phase changing unit 303) cuts the fuel supplied to the engine (engine 100) by the engine control device (ECU 25) until the engine (engine 100) is stopped. In the meantime, the central phase (central phase 401) of the exhaust valve (exhaust valve 10) is advanced to the second angle (second angle 701) which is a substantially center position of the expansion stroke. As a result, the central phase 301 of the exhaust valve profile 10a overlaps with the central phase of the exhaust valve profile 10c having the central phase at the center position of the expansion stroke. The phase position of the exhaust valve 10 represented by the exhaust valve profile 10c is also referred to as a “target position”.

Here, the operation of the intake valve 9 and the exhaust valve 10 whose opening / closing timing is controlled according to the intake valve profile 9a and the exhaust valve profile 10c will be described with reference to the schematic diagram shown on the lower side of FIG.

First, as shown in the timing (1), the exhaust valve 10 starts to open after the compression stroke TDC according to the exhaust valve profile 10c. At this time, since the pressure in the cylinder is higher than that in the exhaust pipe 8, fresh air in the cylinder, exhaust gas, or both are discharged to the exhaust pipe 8.

When the piston 3 descends in the expansion stroke, the pressure in the cylinder becomes lower than the pressure in the exhaust pipe 8. Therefore, as shown in timing (2), exhaust gas, fresh air, or both flow into the cylinder from the exhaust pipe 8. After the expansion stroke BDC, the exhaust valve 10 closes. In the exhaust stroke, the piston 3 rises with the intake valve 9 and the exhaust valve 10 closed, so that the pressure inside the cylinder increases.

In the intake stroke, the intake valve 9 opens. At this time, the pressure in the intake pipe 7 is lower than the pressure in the cylinder. Therefore, as shown in the timing (3), the exhaust gas in the cylinder and / or fresh air flows back to the intake pipe 7. As the piston 3 further lowers in the latter half of the intake stroke, the pressure in the intake pipe 7 becomes higher than that in the cylinder. Therefore, as shown in the timing (4), the exhaust gas of the intake pipe 7 and / or the fresh air re-inflow into the cylinder.

As described above, the variable valve control device 301 (exhaust valve phase changing unit 303) controls the opening / closing timing of the intake valve 9 and the exhaust valve 10 according to the intake valve profile 9a and the exhaust valve profile 10c of FIG. By this control, the section in which the exhaust valve 10 is opened in the expansion stroke becomes wider than the section in which the exhaust valve 10 is opened as shown in FIG. Further, the section in which the exhaust valve 10 is closed in the exhaust stroke is wider than the section in which the exhaust valve 10 is closed as shown in FIG. As a result, the exhaust gas easily flows back into the cylinder from the exhaust pipe 8, and the backflow rate of air increases.

Therefore, as shown in the solid line 503 of FIG. 6, the integrated value of the amount of air supplied to the three-way catalyst 22 is compared with the integrated value of the amount of air shown by the alternate long and short dash line 502 showing the result of the profile shown in FIG. It becomes smaller. As a result, the variable valve control device 301 can suppress the amount of air supplied to the three-way catalyst 22 when the fuel is cut, and can enhance the effect of suppressing the amount of NOx emissions when the engine 100 is restarted.

<Control to maintain the central phase of the exhaust valve 10 at the center position of the expansion stroke>
Next, an example in which the variable valve control device 301 controls to maintain the central phase 401 of the exhaust valve 10 at the center position of the expansion stroke will be described. In the exhaust valve phase changing section (exhaust valve phase changing section 303), after the central phase (center phase 401) of the exhaust valve (exhaust valve 10) reaches the second angle (second angle 701), the engine (engine 100) The engine (engine 100) restarts until the rotation of the engine (engine 100) stops, and the rotation speed of the engine (engine 100) reaches a predetermined value of 56 (see FIG. 4). The second angle (second angle 701) is maintained until it rises. The period until the rotation speed of the engine (engine 100) rises to the predetermined value 56 may be read as the period after the rotation of the engine 100 is stopped and before the next fuel injection is started.

FIG. 8 shows the closing timing of the exhaust valve 10 when the central phase 401 of the exhaust valve 10 is maintained at the second angle 701 from the time when the rotation of the engine 100 is stopped until the time when the next fuel injection is started. It is a figure which shows the example of. In FIG. 8, the engine speed [rpm] and the exhaust valve closing timing [deg. A graph showing the relationship with [ATDC] in chronological order is shown. In FIG. 8, the same parts as those in FIG. 4 will be described with reference to the same reference numerals.

The variable valve control device 301 controls the central phase 401 of the exhaust valve 10 to be maintained at the second angle 701 until the engine 100 is stopped. Therefore, as shown on the lower side of FIG. 7, the variable valve control device 301 can increase the amount of exhaust gas and / or fresh air flowing back from the exhaust pipe 8, and is supplied to the three-way catalyst 22. The amount of fresh air can be reduced. By such phase control of the exhaust valve 10, there is an effect that the amount of air flowing back from the exhaust pipe 8 into the cylinder can be maximized.

Further, the variable valve control device 301 controls the central phase 401 of the exhaust valve 10 to maintain the second angle 701 even when the motoring 52 is performed to generate the brake negative pressure in the range of the section 51. do. The variable valve control device 301 can increase the amount of exhaust gas and / or fresh air flowing back from the exhaust pipe 8 and reduce the amount of air supplied to the three-way catalyst 22 even in such control.

Further, at the timing t25 when the fuel cut is completed and the fuel injection is restarted, air for burning the fuel injected into the cylinder is required. Therefore, the variable valve control device 301 gradually retards the phase of the exhaust valve 10 within the motoring section 53 or before the motoring section 53, as shown in the timing 601. Then, the variable valve control device 301 may be controlled so that the phase of the exhaust valve 10 is retarded to at least the exhaust valve profile 10d shown in FIG. 7 by the timing t25 when the fuel injection is started. The phase position of the exhaust valve 10 represented by the exhaust valve profile 10c is also referred to as a “target position”.

Further, the phase in which the variable valve control device 301 retards the exhaust valve 10 is determined by the EGR rate of the internal EGR that causes the exhaust gas to flow back from the exhaust pipe 8 by adjusting the opening / closing timing of the intake valve 9 and the exhaust valve 10. .. Therefore, the variable valve control device 301 may determine the amount of retard angle of the exhaust valve 10 so that the EGR rate of the internal EGR is 30% or less. This is because it is generally known that when the EGR rate exceeds 30%, it becomes difficult for the fuel to burn.

Therefore, the engine control device (ECU 25) calculates the EGR rate of the internal EGR. Then, the exhaust valve phase changing unit (exhaust valve phase changing unit 303) determines the amount of retarding the phase of the exhaust valve (exhaust valve 10) based on the EGR ratio. At this time, the variable valve control device 301 controls the valve closing time of the exhaust valve 10 to approach the top dead center of the exhaust stroke until the timing t25 when the fuel cut is completed and the combustion is injected, as shown in FIG. conduct. By this control, the EGR ratio of the internal EGR in the cylinder is reduced at the timing t25 when the fuel injection is started, so that the combustion stability is improved. As a result, the ECU 25 can stably restart the engine 100, and can achieve both NOx reduction and stability of restartability.

<Countermeasures when the VTC response of the exhaust valve 10 is slow>
Here, a case where the response of the exhaust valve phase variable mechanism 42 included in the VTC 40 is slow will be examined. Even if the exhaust valve phase changing unit 303 tries to change the phase of the exhaust valve 10 by using such an exhaust valve phase variable mechanism 42, from the fuel cut timing t22 shown in FIG. 8 to the timing t23 when the engine 100 is stopped. In the meantime, the phase of the exhaust valve 10 may not be completely moved to the substantially center position (second angle 701) of the expansion stroke.

In this case, the motor control unit 304 controls the operation of the traction motor 50 to rotate the engine 100 on the traction motor 50. Then, the exhaust valve phase changing unit (exhaust valve phase changing unit 303) advances the valve closing timing of the exhaust valve (exhaust valve 10) from the top dead center before the fuel is cut. For example, the exhaust valve phase changing unit 303 may control the phase of the exhaust valve 10 to move to the second angle 701. By this control, the exhaust valve phase changing unit 303 can reliably move the phase of the exhaust valve 10 to a substantially center position of the expansion stroke in which the amount of exhaust gas and air flowing into the cylinder from the exhaust pipe 8 becomes large. The amount of air supplied to the three-way catalyst 22 can be suppressed. As a result, the ECU 25 can reduce the amount of NOx emissions when the engine 100 is restarted.

<Electric exhaust valve phase variable mechanism>
In the hydraulic exhaust valve phase variable mechanism 42, the responsiveness when the phase of the variable valve mechanism is changed is lowered when the hydraulic pressure is low, such as when the rotation speed of the engine 100 is low or when the engine 100 is restarted. It may be difficult to control the target position. Therefore, the exhaust valve phase changing unit 303 can improve the responsiveness of the phase change of the exhaust valve 10 by using the electric exhaust valve phase changing mechanism 42.

For example, if the exhaust valve phase variable mechanism 42 is an electric type, the exhaust valve phase changing unit 303 changes the phase of the exhaust valve 10 by rotating a motor (not shown) provided in the exhaust valve phase variable mechanism 42. It is possible. The speed at which the electric exhaust valve phase variable mechanism 42 changes the phase of the exhaust valve 10 is, for example, 200 degCA per second, which is higher than the speed at which the hydraulic exhaust valve phase variable mechanism 42 changes the phase of the exhaust valve 10. Is also fast.

By making the exhaust valve phase variable mechanism 42 electric in this way, the exhaust valve phase changing unit 303 can accurately control the phase of the exhaust valve 10 after the fuel is cut, and the exhaust pipe 8 is inserted into the cylinder. The amount of inflowing exhaust gas and air can be increased, and the amount of air supplied to the three-way catalyst 22 can be suppressed. Further, when the engine 100 is restarted, the electric exhaust valve phase variable mechanism 42 quickly retards the phase of the exhaust valve 10, so that combustion after the fuel cut is completed can be stabilized.

[Second Embodiment]
Next, the variable valve control device and the variable valve control method according to the second embodiment of the present invention will be described with reference to FIGS. 1, 2, 9, and 10. The difference between the second embodiment and the first embodiment is that after the fuel is cut, the intake valve phase changing unit 302 advances the phase of the exhaust valve 10 in addition to the control that the exhaust valve phase changing unit 303 advances the phase of the exhaust valve 10. The purpose is to control the phase of the intake valve 9 to be retarded.

FIG. 9 shows an example of profiles of the intake valve 9 and the exhaust valve 10 according to the second embodiment of the present invention and an example of a schematic diagram of the engine 100. In FIG. 9, the phase of the exhaust valve 10 is advanced and the exhaust valve profile 10a is changed to the exhaust valve profile 10b, and the phase of the intake valve 9 is retarded and the intake valve profile 9a is changed to the intake valve profile 9b. It is shown how it is done. An example of the profile is shown on the upper side of FIG. 9, and the operation of the intake valve 9 and the exhaust valve 10 is shown on the lower side of FIG.

<Control to advance the exhaust valve 10 and retard the intake valve 9>
The intake valve phase changing unit (intake valve phase changing unit 302) included in the variable valve control device 301 according to the second embodiment and capable of controlling the phase of the intake valve 9 is controlled by the engine control device (ECU 25). From the time when the fuel supplied to the engine (engine 100) is cut until the engine (engine 100) is stopped, the valve opening start time of the intake valve (intake valve 9) is stepwise from the top dead point of the intake stroke. Has the function of retarding. As a result, the variable valve control device 301 causes fresh air and / or exhaust gas to flow back into the cylinder from the exhaust pipe 8, suppresses the amount of air supplied to the three-way catalyst 22 at the time of fuel cut, and restarts the engine 100. It becomes possible to suppress the amount of NOx emitted at the time of starting.

The details of the variable valve control device 301 according to the second embodiment will be described. Here, it is assumed that the opening / closing timing of the intake valve 9 is controlled according to the intake valve profile 9b, and the opening / closing timing of the exhaust valve 10 is controlled according to the exhaust valve profile 10b. The phase position of the intake valve 9 represented by the intake valve profile 9b is also referred to as a “target position”.

In the section 403 where the exhaust valve 10 is closed in the expansion stroke shown in FIG. 9, the pressure in the cylinder becomes negative as the piston 3 descends. At this time, since the pressure in the cylinder is higher than that in the exhaust pipe 8, when the exhaust valve 10 is opened as shown in timing (1), the pressure difference between the cylinder and the exhaust pipe 8 and the piston 3 are lowered. By doing so, fresh air or exhaust gas in the exhaust pipe 8 flows into the cylinder.
At the timing of the exhaust stroke (2), the intake valve 9 is closed and the exhaust valve 10 is opened. Therefore, as the piston 3 rises, the exhaust gas in the cylinder is discharged to the exhaust pipe 8. The exhaust valve 10 closes in the latter half of the exhaust stroke.

In the first half of the intake stroke, both the intake valve 9 and the exhaust valve 10 are closed. In the latter half of the intake stroke, the exhaust valve 10 is closed, and the intake valve 9 whose valve phase is retarded according to the intake valve profile 9b is opened. When the piston 3 descends in the intake stroke, the pressure in the cylinder becomes lower than the pressure in the intake pipe 7. Therefore, as shown in the timing (3), when the intake valve 9 is opened while the piston 3 is descending, a slight amount of air flows in from the intake pipe 7 due to the pressure difference.
The intake valve 9 starts to open immediately before the intake stroke BDC. The intake valve 9 is also opened when the piston 3 rises in the compression stroke. Therefore, as shown in the timing (4), the air and the exhaust gas in the cylinder flow back to the intake pipe 7 as the piston 3 rises. In this way, the intake valve phase changing unit 302 included in the variable valve control device 301 retards the phase of the intake valve 9, and the exhaust valve phase changing unit 303 advances the phase of the exhaust valve 10, whereby the exhaust pipe 8 is connected. Exhaust gas and / or fresh air flow back into the intake pipe 7.

In the variable valve control device 301 according to the second embodiment described above, the intake valve phase changing unit 302 retards the phase of the intake valve 9, so that the exhaust gas in the cylinder and fresh air or fresh air are generated in the compression stroke. Both of them flow back to the intake pipe 7. Therefore, the exhaust valve phase changing unit 303 included in the variable valve control device 301 according to the first embodiment is supplied to the three-way catalyst 22 as compared with the case where only the phase of the exhaust valve 10 is changed. The air volume can be further reduced. As a result, even if the ECU 25 does not control the fuel cut, the NOx emission amount at the time of restarting the engine 100 can be suppressed.

<Control to change the opening timing of the intake valve and the closing timing of the exhaust valve>
Next, the variable valve control method of the intake valve 9 and the exhaust valve 10 performed by the variable valve control device 301 from the fuel cut to the restart of the engine 100 will be described.
FIG. 10 is a diagram showing the relationship between the time according to the second embodiment of the present invention, the engine speed, the closing time of the exhaust valve 10, and the opening time of the intake valve 9. FIG. 10 shows a time-series change in the phases of the exhaust valve 10 and the intake valve 9 according to the second embodiment. Further, in FIG. 10, examples of three types of intake valve profiles are represented by solid lines, broken lines, and alternate long and short dash lines.

The profile 901 shown by the solid line at the valve opening timing (1) of the intake valve 9 represents an example of the intake valve profile.
As described above, when the engine speed starts to decrease at the timing t21, the fuel is cut at the timing t22. After the fuel cut timing t22, the exhaust valve phase changing unit 303 advances the valve closing timing of the exhaust valve 10, and the intake valve phase changing unit 302 controls to retard the valve opening timing of the intake valve 9. .. As a result, the valve opening time of the intake valve 9 was 180 deg after top dead center. It is retarded to ATDC. Here, when the responsiveness of the intake valve 9 is slow, the valve opening timing of the intake valve 9 is 180 deg after top dead center by the timing t23 when the rotation of the engine 100 is stopped. It may not be possible to move to ATDC.

However, the variable valve control device 301 not only advances the closing timing of the exhaust valve 10, but also controls the valve opening timing of the intake valve 9 to be retarded from the top dead center. Compared with the control of changing only the phase of the exhaust valve 10 according to the embodiment, the backflow of air from the exhaust pipe 8 can be increased, and the supply of air to the three-way catalyst 22 can be suppressed.

Further, the intake valve phase changing unit 302 may be provided with a section 904 in which the intake valve 9 is maintained in a retarded state after the rotation of the engine 100 is stopped. Therefore, in the intake valve phase change unit (intake valve phase change unit 302), the rotation of the engine (engine 100) causes the intake valve (intake valve 9) to open at a retarded angle from the top blind point of the intake stroke. After the engine is stopped, the engine (engine 100) is restarted and maintained until the rotation speed of the engine (engine 100) rises to a predetermined value (predetermined value 56). As a result, even if the ECU 25 (motor control unit 304) drives the traction motor 50 to perform the motoring 52 during the section 904 as shown in the chart at the top of FIG. 10, the three-way catalyst 22 is reached. The amount of air can be suppressed. Therefore, the effect of suppressing the NOx emission amount when the engine 100 is restarted can be further enhanced.

<Variable valve control method shown in the valve opening timing (1) of the intake valve>
Next, with reference to the valve opening timing (1) of the intake valve 9 shown in FIG. 10, another example of the variable valve control method performed by the variable valve control device 301 will be described using the profile 903 of the intake valve 9. do.

As shown in the profile 903 of the intake valve 9, the intake valve phase changing unit 302 sets the valve opening timing of the intake valve 9 after the fuel cut timing t22 to the advance side of the bottom dead center of the intake stroke which is TDC + 180 deg. It may be moved to a certain intake valve opening time 907. As a result, the time required from the timing t24 when the engine speed increases to the timing t26 when the intake valve opening timing completes the movement to the TDC can be shortened. As a result, the ECU 25 can control to start fuel injection at a timing earlier than the timing t25. Then, when the engine 100 is restarted, the intake valve phase changing unit 302 advances the phase of the intake valve 9, and the exhaust valve phase changing unit 303 supplies the three-way catalyst 22 in the process of retarding the phase of the exhaust valve 10. You will be able to suppress the freshness that is created.

<Variable valve control method shown in the valve opening timing (2) of the intake valve>
Next, another example of the variable valve control method according to the second embodiment of the present invention will be described with reference to the valve opening timing (2) of the intake valve 9 shown at the bottom of FIG. Here, the profile 902 represented by a broken line at the valve opening time (2) of the intake valve 9 at the bottom stage represents another example of the intake valve profile.

In the profile of the intake valve 9 shown in the profile 902 of the intake valve 9, the intake valve phase changing unit 302 sets the valve opening start time of the intake valve 9 later than the TDC at the timing t27 before the fuel cut timing t22. The angle is started and the phase of the intake valve 9 is moved to the intake valve opening time 906. In this way, the intake valve phase change unit (intake valve phase change unit 302) retards the valve opening timing of the intake valve (intake valve 9) from the top dead center of the intake stroke before the fuel is cut. .. By performing this pre-operation, the time required for the valve opening timing of the intake valve 9 to complete the movement (TDC + 180 deg) after the fuel cut timing t22 can be shortened by the time 905. As a result, the effect of suppressing the fresh air supplied to the three-way catalyst 22 is enhanced, and the responsiveness of the intake valve phase variable mechanism 41 can be relaxed.

From the time when the engine speed starts to decrease at the timing t21 to the time when the engine 100 is stopped at the timing t23, the traction motor 50 of the ECU 25 (motor control unit 304) is the motoring 55 (the uppermost stage of FIG. 10). It may be controlled to start (the chart of the broken line shown in). By providing the section of the motoring 55, the traction motor 50 can smoothly perform the motoring 55 as compared with the case where the ECU 25 performs the motoring 52 again after the engine 100 is stopped once.

<Countermeasures when there is a large amount of fresh air or exhaust gas backflow from the exhaust pipe to the intake pipe>
In the variable valve control device 301 according to the second embodiment described above, exhaust gas, fresh air, or both can flow back from the exhaust pipe 8 to the intake pipe 7 via the inside of the cylinder. However, if the backflow of air from the exhaust pipe 8 to the intake pipe 7 increases, fresh air will flow back into the intake pipe 7 in addition to the exhaust gas. However, at the timing t25 when the fuel cut is completed and the fuel is injected, fresh air for burning the fuel in the cylinder is required. Therefore, the intake valve phase changing unit 302 changes the phase of the intake valve 9 to the advance side in the section 910 in which the engine 100 is rotated by the traction motor 50 before the timing t25, so that fresh air is generated in the cylinder. It is good to control it so that it flows in. By such control, the fresh air required for combustion is secured in the cylinder at the timing t25 when the fuel is injected. Therefore, it is possible to suppress the amount of fresh air supplied to the three-way catalyst 22 and to stably restart the engine 100.

Further, the variable valve control device 301 according to the second embodiment may perform the fuel cut after the valve opening timing of the intake valve 9 is retarded from the top dead center of the intake stroke before the fuel cut. The intake valve phase changing unit 302 delays the opening timing of the intake valve 9 from the top dead center of the intake stroke in advance, so that the intake valve 9 retards after the fuel is cut, and the intake valve 9 The time it takes to complete the move can be shortened. As a result, the amount of air supplied to the three-way catalyst 22 can be suppressed while the intake valve 9 is moving.

<Electric intake valve phase variable mechanism>
In the hydraulic intake valve phase variable mechanism 41, the responsiveness when the phase of the variable valve mechanism is changed is lowered when the hydraulic pressure is low, such as when the rotation speed of the engine 100 is low or when the engine 100 is restarted. It may be difficult to control the target position. Therefore, the intake valve phase change unit 302 can improve the responsiveness of the phase change of the intake valve 9 by using the electric intake valve phase variable mechanism 41.

For example, if the intake valve phase variable mechanism 41 is an electric type, the intake valve phase changing unit 302 changes the phase of the intake valve 9 by rotating a motor (not shown) provided in the intake valve phase variable mechanism 41. It is possible. The speed at which the electric intake valve phase variable mechanism 41 changes the phase of the intake valve 9 is 200 degCA per second, which is faster than the speed at which the hydraulic intake valve phase variable mechanism 41 changes the phase of the intake valve 9. ..

By making the intake valve phase variable mechanism 41 electric in this way, the intake valve phase changing unit 302 can accurately control the phase of the intake valve 9 after the fuel is cut, and the exhaust pipe 8 is inserted into the cylinder. The amount of inflowing exhaust gas and fresh air can be increased, and the amount of air supplied to the three-way catalyst 22 can be suppressed. Further, when the engine 100 is restarted, the electric intake valve phase variable mechanism 41 quickly advances the phase of the intake valve 9, so that combustion after the fuel cut is completed can be stabilized.

[Third Embodiment]
Next, the variable valve control device and the variable valve control method according to the third embodiment of the present invention will be described with reference to FIGS. 1, 2, and 11. The difference between the third embodiment and the first embodiment is that the motor control unit 304 provides a section in which the engine 100 is rotated by the traction motor 50 after the fuel is cut, so that the exhaust valve phase changing unit 303 is the exhaust valve. The point is that control is performed to suppress the amount of retardation of the phase of 10.

FIG. 11 is a diagram showing an example of a time-series change in the phases of the exhaust valve 10 and the intake valve 9 according to the third embodiment of the present invention. In FIG. 11, the same components or locations as those in FIGS. 1 and 8 will be described with reference to the same reference numerals.

<Control to secure the backflow cycle by motoring and suppress the amount of air to the three-way catalyst 22>
The variable valve control device 301 according to the third embodiment provides a motoring section 101 after the fuel is cut at the timing t22 and before the engine 100 is stopped at the timing t23. In the motoring section 101, after the central phase 401 of the exhaust valve 10 reaches the first angle 405 (see FIG. 5) or the second angle 701 (see FIG. 7), the motor control unit 304 sets the traction motor 50. This is a section in which the rotation of the engine 100 is maintained by rotating the engine 100.

As described above, in the engine control device (ECU 25), the central phase (center phase 401) of the exhaust valve (exhaust valve 10) is set to the first angle (first angle 405) by the exhaust valve phase changing unit (exhaust valve phase changing unit 303). ) Is reached, a motoring section (motoring section 101) for driving the motor (traction motor 50) to rotate the engine (engine 100) is provided. For example, the motoring section 101 is started immediately after the central phase 401 of the exhaust valve 10 reaches the first angle 405 at the timing t29.

Further, when the phase of the exhaust valve 10 is changed by the exhaust valve profile 10a shown in FIG. 3, the ECU 25 detects the amount of fresh air entering the cylinder by the air flow sensor attached upstream of the throttle valve 27. Then, the ECU 25 can estimate the amount of fresh air supplied to the three-way catalyst 22 based on the amount of fresh air detected by the airflow sensor. Therefore, the ECU 25 calculates in advance the amount of fresh air supplied to the three-way catalyst 22. Then, the ECU 25 supplies the fresh air amount that flows back from the exhaust pipe 8 into the cylinder according to the fresh air amount calculated in advance to the three-way catalyst 22 from the fuel cut to the restart of the next engine 100. It is advisable to determine the time of the motoring section 101 so as to exceed the air volume.

Here, an example in which the exhaust valve phase changing unit 303 controls the exhaust valve closing timing by the profile of the exhaust valve 10 shown in FIG. 11 will be examined. The exhaust valve phase changing unit 303 starts moving the phase of the exhaust valve 10 in the retard direction at the fuel cut timing t22. Then, the valve opening start timing of the exhaust valve 10 is −180 deg. Fresh air is supplied to the three-way catalyst 22 in the section up to the timing t28 when the ATDC is reached, that is, the central phase 401 of the exhaust valve 10 comes to the advance angle side from the top dead center of the expansion stroke. Further, when the engine is restarted, the central phase 401 of the exhaust valve 10 is 180 de. Fresh air is supplied to the three-way catalyst 22 in the section 102 from the time when the ATDC is reached to the timing t25 when the phase movement of the exhaust valve 10 is completed.

Therefore, the ECU 25 estimates the amount of fresh air supplied to the three-way catalyst 22 based on the amount of fresh air detected by the airflow sensor as described above. Then, the ECU 25 sets the time of the motoring section 101 and the exhaust valve so that the estimated amount of fresh air supplied to the three-way catalyst 22 is equal to or greater than the amount of fresh air flowing back from the exhaust pipe 8 into the cylinder. It is advisable to determine at least one of the target values for the amount of advance of the phase of 10.

In the variable valve control device 301 according to the third embodiment described above, the amount of exhaust gas and air flowing into the cylinder from the exhaust pipe 8 increases due to the provision of the motoring section 101. Therefore, the integrated value of the amount of air supplied to the three-way catalyst 22 can be suppressed.

It should be noted that the present invention is not limited to the above-described embodiments, and it goes without saying that various other application examples and modifications can be taken as long as they do not deviate from the gist of the present invention described in the claims.
For example, each of the above-described embodiments describes the configurations of the apparatus and the system in detail and concretely in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to those including all the described configurations. Further, it is possible to replace a part of the configuration of the embodiment described here with the configuration of another embodiment, and further, it is possible to add the configuration of another embodiment to the configuration of one embodiment. It is possible. Further, it is also possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.
In addition, the control lines and information lines indicate what is considered necessary for explanation, and do not necessarily indicate all the control lines and information lines in the product. In practice, it can be considered that almost all configurations are interconnected.

3 ... Piston, 7 ... Intake pipe, 8 ... Exhaust pipe, 9 ... Intake valve, 10 ... Exhaust valve, 22 ... Three-way catalyst, 25 ... ECU, 30 ... CPU, 40 ... VTC, 100 ... Engine, 111 ... Battery, 300 ... state determination unit, 301 ... variable valve control device, 302 ... intake valve phase change unit, 300 ... state determination unit, 301 ... variable valve control device, 302 ... intake valve phase change unit, 303 ... exhaust valve phase change unit, 304 ... Motor control unit, 401 ... Center phase

Claims

It is a variable valve control device that controls a variable valve timing control mechanism that can change the phase of the exhaust valve provided in the exhaust pipe of the engine.
An exhaust valve phase changing unit for outputting an instruction for changing the phase of the exhaust valve through the variable valve timing control mechanism based on the state change of the engine is provided.
The exhaust valve phase changing unit sets the central phase of the exhaust valve to the bottom dead center of the expansion stroke between the time when the fuel supplied to the engine is cut by the control of the engine control device and the time when the engine is stopped. A variable valve control device that advances to the first angle, which is on the advance side.
The exhaust valve phase changing unit sets the central phase of the exhaust valve at a substantially central position of the expansion stroke between the time when the engine control device cuts the fuel supplied to the engine and the time when the engine is stopped. The variable valve control device according to claim 1, which advances to a certain second angle.
The exhaust valve phase changing unit restarts the engine after the central phase of the exhaust valve reaches the second angle, until the rotation of the engine is stopped, or after the rotation of the engine is stopped. The variable valve control device according to claim 2, wherein the second angle is maintained until the engine speed rises to a predetermined value.
The variable valve control device according to claim 1, wherein the exhaust valve phase changing unit advances the valve closing timing of the exhaust valve from the top dead center before the fuel is cut.
The engine control device calculates the EGR ratio of the internal EGR and calculates it.
The variable valve control device according to claim 1, wherein the exhaust valve phase changing unit determines an amount of retarding the phase of the exhaust valve based on the EGR rate.
The engine is provided with a motor capable of rotating the engine under the control of the engine control device.
The engine control device is provided with a motoring section for driving the motor to rotate the engine after the central phase of the exhaust valve reaches the first angle by the exhaust valve phase changing unit. The variable valve control device described.
The variable valve control device controls the variable valve timing control mechanism capable of changing the phase of the intake valve provided in the intake pipe of the engine.
It is provided with an intake valve phase changing unit that outputs an instruction for changing the phase of the intake valve through the variable valve timing control mechanism based on the state change of the engine.
The intake valve phase changing unit sets the valve opening start time of the intake valve on the intake stroke between the time when the fuel supplied to the engine is cut by the control of the engine control device and the time when the engine is stopped. The variable valve control device according to claim 1, wherein the angle is gradually retarded from the dead center.
The variable valve control device according to claim 7, wherein the intake valve phase changing unit retards the valve opening timing of the intake valve from the top dead center of the intake stroke before the fuel is cut.
The intake valve phase changing unit is in a state where the valve opening timing of the intake valve is retarded from the top dead center of the intake stroke, the engine is restarted after the rotation of the engine is stopped, and the engine of the engine is operated. The variable valve control device according to claim 8, wherein the variable valve control device is maintained until the rotation speed rises to a predetermined value.
The variable valve control device according to claim 1, wherein the engine control device narrows the opening degree of a throttle valve provided upstream of an intake pipe provided with an intake valve before or after cutting the fuel.