Variable valve control

Abstract

The exhaust valve phase changing unit of the variable valve control device of the present invention outputs an instruction for changing the phase of the exhaust valve through the exhaust valve phase variable mechanism according to the state change of the engine. In addition, the exhaust valve phase changing unit advances the center phase of the exhaust valve to a first angle on the advance side with respect to the bottom dead center of the expansion stroke during the period from when the fuel supplied to the engine is cut off to when the engine stops under the control of the engine control device.

Description

Technical Field

[0001] The invention relates to a variable valve control device. Background Art

[0002] Conventionally, there are hybrid vehicles equipped with a traction motor and an engine. There are two known hybrid vehicles: a parallel hybrid vehicle that uses both electricity and gasoline for running, and a series hybrid vehicle that uses only the motor for running and the engine for generating electricity.

[0003] In the parallel hybrid mode, the vehicle stops the engine in the low-load operation range where the thermal efficiency of the engine is low and runs only on the motor, and the vehicle runs only on the engine in the medium-load and above operation range where the thermal efficiency of the engine is high. In urban areas, there are a mixture of low-load and medium-load operation ranges, so the frequency of engine stopping and starting is high.

[0004] In addition, in the series hybrid mode, the battery capacity of the battery mounted in the vehicle is monitored, and when the battery capacity becomes below a predetermined lower limit, the engine is operated to rotate the generator, thereby generating electricity to charge the battery. In addition, when the battery capacity reaches above an upper limit, the engine is stopped. In this way, the engine is repeatedly stopped and started in a series hybrid vehicle, so the frequency of engine stopping and starting is higher than that of a general internal combustion engine vehicle.

[0005] Thus, the engines for hybrid vehicles used in various hybrid modes have a high frequency of stopping and starting the engine in order to reduce fuel consumption. In recent years, "fuel cut" has been implemented to further reduce fuel consumption, that is, to cut off fuel injection during the period when the engine does not require torque when stopping the engine. However, during this fuel cut, the engine rotates under inertia, so unburned air (fresh air) is sucked into the cylinder at the same valve timing as during normal driving, and then discharged to the exhaust pipe.

[0006] When the fresh air is discharged to the exhaust pipe and reaches the three-way catalyst installed in the exhaust pipe, the oxygen contained in the fresh air is stored in the three-way catalyst, so the three-way catalyst becomes in a state of excessive oxygen. In this state, the purification efficiency of the three-way catalyst for nitrogen oxides (NOx) is reduced. Therefore, when the engine is restarted, "enrichment control" is sometimes implemented, that is, the fuel injection ratio is increased in a way that the operating air-fuel ratio is less than the theoretical mixture ratio to supply excessive fuel, thereby removing the oxygen stored in the three-way catalyst.

[0007] In this enrichment control, extra fuel is injected, so fuel efficiency deteriorates. Furthermore, since combustion is performed in a fuel-excess state, HC and PN increase, resulting in a problem of deteriorating exhaust gas. In particular, in engines for hybrid vehicles, the frequency of engine stopping and starting is high, so the impact of fuel cut on fuel efficiency and exhaust gas deterioration is greater.

[0008] As a technology for suppressing the reduction in purification efficiency of the three-way catalyst during fuel cut operation, for example, Patent Document 1 discloses the following technology: "When the fuel cut detection unit detects fuel cut, the valve opening time variable unit is controlled to advance the valve opening time of the intake valve."

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 10-115234 Summary of the invention

[0012] Problem that the invention aims to solve

[0013] With the technology disclosed in Patent Document 1, it is believed that the amount of fresh air sucked into the cylinder during the intake stroke can be reduced, thereby reducing the amount of fresh air discharged to the exhaust pipe, thereby suppressing oxygen storage in the three-way catalyst. In particular, it is believed that 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 during the intake stroke can be reduced, thereby reducing the amount of fresh air discharged to the exhaust pipe and suppressing oxygen storage in the three-way catalyst.

[0014] When the phase of the intake valve is advanced in this way and the period from valve opening to valve closing is set in the exhaust stroke, the intake valve and the exhaust valve are open in the exhaust stroke. Therefore, the air sucked into the cylinder from the intake pipe and the exhaust pipe is sprayed back into the intake pipe and the exhaust pipe due to the rise of the piston, thereby suppressing the discharge of new air into the exhaust pipe.

[0015] However, in the method disclosed in Patent Document 1, there is a transition period in which the intake valve is opened and closed during the intake stroke from the start of the action of advancing the phase of the intake valve to the arrival at the target position. During this transition period, the intake valve is open during the intake stroke, so the fresh air sucked into the cylinder during the intake stroke is discharged to the exhaust pipe, thereby causing oxygen to be stored in the three-way catalyst.

[0016] Furthermore, when the engine is restarted, the engine motor is rotated with the intake valve advanced in order to achieve decompression (bleeding) to suppress the fluctuation of the engine speed caused by the air compression of the piston immediately after the engine is started. However, when the speed rises and the initial explosion cycle is entered, the opposite action to the above action is performed (the intake valve is delayed until it returns to the original intake stroke, and returns to the initial position). Therefore, fresh air is also discharged to the exhaust pipe during the transition period of the intake valve phase to the initial explosion.

[0017] In this way, after the phase of the intake valve is changed to the target position, the discharge of fresh air to the exhaust pipe can be suppressed. However, during the transition period of the phase change, fresh air is discharged to the exhaust pipe, causing oxygen to be stored in the three-way catalyst. Therefore, before the engine is stopped or when the engine is restarted, enrichment control is required to remove oxygen from the three-way catalyst. When the enrichment control is performed, useless fuel is injected, so the emission of CO2 increases and the rich mixture increases, thereby increasing PN and HC.

[0018] The present invention has been made in view of such a situation, and an object of the present invention is to avoid performing rich injection when the engine is restarted.

[0019] Technical means of solving problems

[0020] 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 on an exhaust pipe of an engine, and includes an exhaust valve phase changing unit that outputs an instruction for changing the phase of the exhaust valve through the variable valve timing control mechanism according to a change in the state of the engine. The exhaust valve phase changing unit advances the center phase of the exhaust valve to a first angle that is on the advance side relative to the bottom dead center of the expansion stroke during a period from when fuel supplied to the engine is cut off to when the engine stops under the control of an engine control device.

[0021] Effects of the Invention

[0022] According to the present invention, during the period from when the fuel supplied to the engine is cut off to when the engine is stopped, the center phase of the exhaust valve is advanced to the first angle, so that the fresh air discharged to the exhaust pipe and the fresh air discharged to the exhaust pipe when the engine is started flow back into the cylinder. Therefore, the amount of fresh air supplied to the three-way catalyst is reduced, and enriched injection is not required when the engine is restarted, so that the fuel consumption and exhaust gas degradation can be suppressed.

[0023] Other problems, structures, and effects than those described above will become clear from the following description of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1It is a schematic diagram showing a configuration example of an engine according to a first embodiment of the present invention.

[0025] Figure 2 This is a control block diagram showing an example of the internal configuration of the ECU and the valve mechanism of the engine according to the first embodiment of the present invention.

[0026] Figure 3 It is a diagram showing an example of the curves of the intake valve and the exhaust valve during the engine power generation operation according to the first embodiment of the present invention.

[0027] Figure 4 This is a graph showing in time series the relationship between the engine speed and the amount of NOx detected in the tail pipe when the intake valve and the exhaust valve are operated according to a general curve according to the first embodiment of the present invention.

[0028] Figure 5 It is a diagram showing an example of the curves of the intake valve and the exhaust valve when the engine according to the first embodiment of the present invention shifts to the fuel cut operation.

[0029] Figure 6 This is a diagram showing an example of the integrated value of the fresh air amount supplied to the three-way catalyst after the fuel cut until the engine stops according to the first embodiment of the present invention.

[0030] Figure 7 It is a diagram showing an example of a curve of an intake valve and an exhaust valve and an example of a schematic diagram of an engine according to a modification of the first embodiment of the present invention.

[0031] Figure 8 This is a diagram showing an example of the closing time of the exhaust valve when the center phase of the exhaust valve is maintained at the second angle during the period from when the engine stops to when the next fuel injection starts according to the first embodiment of the present invention.

[0032] Fig. 9 It is a diagram showing an example of a curve of an intake valve and an exhaust valve and an example of a schematic diagram of an engine according to a second embodiment of the present invention.

[0033] Fig.10 This is a diagram showing the relationship between time, engine speed, exhaust valve closing time, and intake valve opening time according to the second embodiment of the present invention.

[0034] Fig.11 It is a diagram showing an example of a time-series change in the phase of the exhaust valve and the intake valve according to the third embodiment of the present invention. DETAILED DESCRIPTION

[0035] In the present specification and the drawings, components having substantially the same function or configuration are denoted by the same reference numerals, and repeated descriptions are omitted.

[0036] [First embodiment]

[0037] Figure 1 It is a schematic diagram showing a configuration example of an engine 100 according to a first embodiment of the present invention.

[0038] The series hybrid vehicle is a structure in which an engine 100 used only for power generation is provided with a traction motor 50 for driving the vehicle. When the charge capacity (referred to as "battery capacity") of a battery 111 mounted in the vehicle is less than a predetermined value, the engine (engine 100) is started. Conversely, when the charge capacity (referred to as "battery capacity") of the battery 111 exceeds a predetermined value, the engine (engine 100) is stopped.

[0039] The engine 100 is configured as a 400cc in-line three-cylinder naturally aspirated engine. A combustion chamber is formed by a cylinder head 1 and a cylinder block 2 equipped with the engine 100, and a piston 3 inserted in the cylinder block. The piston 3 is connected to a crankshaft 5 via a connecting rod 4. A crank angle sensor 6 provided near the crankshaft 5 can detect the engine speed. In addition, a traction motor 50 is provided on the same axis as the crankshaft 5. In this way, a motor (traction motor 50) that can rotate the engine (engine 100) under the control of the engine control device (ECU 25) is provided to the engine (engine 100). Then, the traction motor 50 rotates the engine 100 by rotating the crankshaft 5.

[0040] An intake pipe 7 and an exhaust pipe 8 are connected to 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 on the upper part of the intake valve 9, and an exhaust cam 12 is provided on the upper part of the exhaust valve 10. The intake cam 11 rotates to open and close the intake valve 9, and the exhaust cam 12 rotates to open and close the exhaust valve 10.

[0041] Although not shown in the figure, an intake cam pulley connected to the intake cam 11, an exhaust cam pulley connected to the exhaust cam 12, and a crankshaft pulley connected to the crankshaft 5 are provided on the side of the engine 100, and are connected together via a timing belt. Therefore, when the engine 100 is operated, the crankshaft 5 rotates, thereby rotating the intake cam 11 and the exhaust cam 12. The intake cam pulley and the exhaust cam pulley are set so that the crankshaft 5 rotates 2 times and the intake cam 11 and the exhaust cam 12 rotate once.

[0042] The intake cam 11 and the exhaust cam 12 are provided with a variable valve timing control mechanism (hereinafter referred to as VTC) 40 (refer to the following description). Figure 2 ). The VTC (Valve Timing Control) 40 is capable of changing the phase of the intake valve (intake valve 9) provided on the intake pipe (intake pipe 7) of the engine (engine 100). In addition, the VTC 40 is capable of changing the phase of the exhaust valve (exhaust valve 10) provided on the exhaust pipe (exhaust pipe 8) of the engine (engine 100). In addition, the crankshaft 5 is provided with an electric generator (not shown) which works as a generator when generating electricity and works as a motor when starting or stopping the engine 100. The VTC 40 is set to a hydraulic type, and the ECU (Engine Control Unit) 25 can change the phase of the intake valve 9 and the exhaust valve 10 in an advanced or delayed manner by rotating the motor provided in the VTC 40.

[0043] 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 a fuel tank 16 and is sent to a high-pressure fuel pump 18 by a feed pump 17 through a fuel pipe. The high-pressure fuel pump 18 is driven by the exhaust cam 12 to send the boosted fuel to the common rail 19. A fuel pressure sensor 20 is provided on the common rail 19 to detect the fuel pressure (referred to as "fuel pressure"). The common rail 19 and the injector 13 provided on each cylinder are connected together by a fuel pipe.

[0044] An air collecting box 21 is provided upstream of the intake pipe 7. The intake pipe 7 is connected to each cylinder from the air collecting box 21. In addition, a throttle valve 27 capable of changing the amount of air sucked into the cylinder is provided on the upstream side of the air collecting box. On the other hand, a three-way catalyst 22 is provided in front 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. Furthermore, a tail pipe (not shown) is provided downstream of the three-way catalyst 22.

[0045] The cylinder block 2 is provided with a water temperature sensor 26 for measuring the temperature of water (water temperature) flowing around the cylinder block 2. Signals of the water temperature and the engine speed 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 the sensors.

[0046] Next, an internal configuration example and an operation example of the ECU 25 and the VTC 40 will be described below.

[0047] Figure 21 is a control block diagram showing an example of the internal structure of the ECU 25 and the valve mechanism of the engine 100. The engine control device (ECU 25) controls the engine (engine 100) equipped with a variable valve timing control mechanism (VTC40) that can change the phase of the intake valve (intake valve 9). The ECU 25 executes the engine control method of this embodiment to control the engine 100 equipped with the VTC 40.

[0048] The ECU 25 includes a CPU (Central Processing Unit) 30 , a RAM (Random Access Memory) 31 , and a ROM (Read Only Memory) 32 .

[0049] 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 pedal opening sensor 113 (reference Figure 1 ) detected by the accelerator pedal depression information (accelerator pedal opening), the angle information (crankshaft angle) detected by the crank angle sensor 110 and the speed of the engine 100, the throttle opening from the throttle valve 27, the battery voltage sensor 112 (reference Figure 1 ) and other input signals such as the battery voltage (battery capacity) detected by the ECU 25.

[0050] The input information of each sensor input to the ECU 25 is temporarily stored in the RAM 31 and is processed by the CPU 30 according to a predetermined control program. Variables and parameters generated during the processing of the CPU 30 are temporarily written to the RAM 31, and these variables and parameters are read out as appropriate by the CPU 30. However, an MPU (Micro Processing Unit) may be used instead of the CPU 30.

[0051] The ROM 32 continuously records programs and data required for the CPU 30 to operate, and is used as an example of a computer-readable non-transitory recording medium storing programs for execution by the ECU 25. The control program describing the contents of the calculation processing performed in the CPU 30 is written in advance in the ROM 32, and is read and executed by the CPU 30 as appropriate. In addition, the phase change information storage unit (ROM 32) stores the reference position of the phase of the exhaust valve (exhaust valve 10) before the state change of the engine (engine 100) and the target position of the phase of the exhaust valve (exhaust valve 10) after the state change of the engine (engine 100) as the phase change information of the exhaust valve (exhaust valve 10). In addition, the phase change information storage unit (ROM 32) stores the reference position of the phase of the intake valve (intake valve 9) before the state change of the engine (engine 100) and the target position of the phase of the intake valve (intake valve 9) after the state change of the engine (engine 100) as the phase change information of the intake valve (intake valve 9). However, a configuration may be adopted in which a nonvolatile storage unit is provided in the ECU 25 and the phase change information updated via a network is stored in the nonvolatile storage unit.

[0052] The control program executed by the CPU 30 realizes the functions of the state determination unit 300, the exhaust valve phase change unit 303, the intake valve phase change unit 302 and the motor control unit 304 shown in the figure.

[0053] For example, when the ECU 25 is instructed to stop the engine 100 from the VCU (Vehicle Control Unit) not shown, the ECU 25 of the present embodiment performs control to cut off the fuel supplied to the engine 100. When the charge capacity of the battery (battery 111) used for driving the vehicle (hybrid vehicle) has reached a predetermined value or more, the fuel is cut off before the engine (engine 100) is stopped.

[0054] In addition, when the driver steps on the accelerator pedal when the engine 100 is stopped and the fuel is cut off, the ECU 25 restarts the engine 100. 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 the situation that the fuel supplied to the engine (engine 100) is cut off as the engine (engine 100) stops. In addition, the state change of the engine (engine 100) includes the situation that the engine (engine 100) is restarted from the state where the fuel cut continues.

[0055] The variable valve control device (variable valve control device 301) controls a variable valve timing control mechanism (VTC 40) that can change the phase of an exhaust valve (exhaust valve 10) provided on an exhaust pipe (exhaust pipe 8) of an engine (engine 100) and an intake valve (intake valve 9) provided on an intake pipe (intake pipe 7). 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 changes the phase of at least one of the intake valve 9 and the exhaust valve 10 in accordance with a change in the state of the engine 100, such as when the ECU 25 starts fuel cut-off based on the battery capacity to stop the engine 100 or restarts the engine 100, thereby changing the opening and closing time of the valve.

[0056] The intake valve phase changing unit (intake valve phase changing unit 302) outputs an instruction for changing the phase of the intake valve (intake valve 9) by the variable valve timing control mechanism (intake valve phase variable mechanism 41 of VTC 40) according to the state change of the engine (engine 100). Here, the intake valve phase changing unit (intake valve phase changing unit 302) preferably outputs an instruction for changing the phase of the intake valve (intake valve 9) according to the phase change information for setting the reference position of the phase of the intake valve (intake valve 9) before the state change of the engine (engine 100) and the target position of the phase of the intake valve (intake valve 9) after the state change of the engine (engine 100), and the state change of the engine (engine 100). Therefore, the intake valve phase changing unit (intake valve phase changing unit 302) refers to the phase change information read from the phase change information storage unit (ROM 32) and the state change of the engine (engine 100) determined by the state determination unit (state determination unit 300). The control of changing the phase of the intake valve 9 by the intake valve phase changing section 302 will be described later in the second embodiment.

[0057] The exhaust valve phase changing unit (exhaust valve phase changing unit 303) outputs an instruction for changing the phase of the exhaust valve (exhaust valve 10) by the variable valve timing control mechanism (exhaust valve phase variable mechanism 42 of the VTC 40) according to the state change of the engine (engine 100). Here, the exhaust valve phase changing unit (exhaust valve phase changing unit 303) preferably outputs an instruction for changing the phase of the exhaust valve (exhaust valve 10) based on the phase change information of the exhaust valve (exhaust valve 10) that sets the reference position of the phase of the exhaust valve (exhaust valve 10) before the state change of the engine (engine 100) and the target position of the phase of the exhaust valve (exhaust valve 10) after the state change of the engine (engine 100), and the state change of the engine (engine 100). Therefore, the exhaust valve phase changing unit (exhaust valve phase changing unit 303) refers to the phase change information read from the phase change information storage unit (ROM 32) and the state change of the engine (engine 100) determined by the state determination unit (state determination unit 300).

[0058] Furthermore, the exhaust valve phase changing unit (exhaust valve phase changing unit 303) advances the center phase (center phase 401) of the exhaust valve (exhaust valve 10) to a first angle (first angle 405) on the advance side relative to the bottom dead center of the expansion stroke during a period from when the fuel supply to the engine (engine 100) is cut off to when the engine (engine 100) is stopped under the control of the engine control unit (ECU 25) (refer to Figure 5 ). This instruction is output to the exhaust valve phase variable mechanism 42 of the VTC 40.

[0059] The VTC 40 includes an intake valve phase variable mechanism 41 and an exhaust valve phase variable mechanism 42 .

[0060] The intake valve phase variable mechanism 41 variably controls the intake valve phase of the intake valve 9 according to the instruction of the intake valve phase changing unit 302, thereby opening and closing the intake valve 9 at a predetermined time. The intake valve phase variable mechanism 41 drives the intake cam 11 according to the instruction of the intake valve phase changing unit 302, thereby changing the phase of the intake valve 9 in an advanced or delayed manner. In the following description, the description is made in the form of the intake valve phase changing unit 302 changing the phase of the intake valve 9 in an advanced or delayed manner.

[0061] The exhaust valve phase variable mechanism 42 variably controls the exhaust valve phase of the exhaust valve 10 according to the instruction of the exhaust valve phase changing unit 303, thereby opening and closing the exhaust valve 10 at a predetermined time. The exhaust valve phase variable mechanism 42 drives the exhaust cam 12 according to the instruction of the exhaust valve phase changing unit 303, thereby changing the phase of the exhaust valve 10 in an advanced or delayed manner. In the following description, the exhaust valve phase changing unit 303 changes the phase of the exhaust valve 10 in an advanced or delayed manner.

[0062] Furthermore, the motor control unit 304 included in the CPU 30 controls the operation of the traction motor 50 .

[0063] 〈Relationship between the phase and lift of the intake and exhaust valves〉

[0064] Next, refer to Figure 3 to Figure 7 , the time (valve opening and closing time) for changing the phase of the exhaust valve 10 and the phase of the exhaust valve 10 after the change are described. Figure 3 , Figure 5 as well as Figure 7 The horizontal axis represents the change of the stroke in the order of expansion stroke, exhaust stroke, intake stroke, and compression stroke, and the vertical axis represents the lift of the intake valve 9 and the exhaust valve 10.

[0065] Figure 3 The figure shows an example of the curves of the intake valve 9 and the exhaust valve 10 during the engine power generation operation. The curves of the intake valve 9 and the exhaust valve 10 shown in the figure show the opening and closing time of the intake valve 9 and the exhaust valve 10, the change of the phase and the lift.

[0066] Figure 3 In the figure, the change in phase of the intake valve 9 is represented by the intake valve curve 9a, and the change in phase of the exhaust valve 10 is represented by the exhaust valve curve 10a. For example, the lift of the intake valve 9 is set to 11 mm, and the action angle is set to 190 degrees. In addition, for example, the lift of the exhaust valve 10 is set to 10 mm, and the action angle is set to 200 degrees. In addition, the closing time of the intake valve 9 is set near the bottom dead center (BDC: Bottom Dead Center), and the closing time of the exhaust valve 10 is set near the top dead center (TDC: Top Dead Center). Figure 3 As shown in FIG. 1 , when the engine 100 is being driven, the exhaust valve curve 10a changes during the exhaust stroke, and the intake valve curve 9a changes during the intake stroke. The intake valve curve 9a and the exhaust valve curve 10a do not substantially overlap. The phase position of the intake valve 9 shown by the intake valve curve 9a and the phase position of the exhaust valve 10 shown by the exhaust valve curve 10a are referred to as "reference positions".

[0067] For example, it is set that: under the condition that the hybrid vehicle is running, the battery capacity is below the lower limit after the engine 100 is preheated, so the engine 100 operates at the power generation point. Figure 3 The intake valve curve 9a and the exhaust valve curve 10a shown in the figure are in operation. That is, the intake valve phase changing unit 302 controls the phase so that the intake valve 9 operates according to the intake valve curve 9a. In addition, the exhaust valve phase changing unit 303 controls the phase so that the exhaust valve 10 operates according to the exhaust valve curve 10a. In this state, the fuel adjusted so that the air-fuel ratio of the fuel becomes "14.5" is injected from the injector 13 for the amount of new air sucked into the combustion chamber during the intake stroke.

[0068] The fuel injection time is, for example, 60 degrees ATDC of the intake stroke, and a uniform mixture is formed in the combustion chamber during the period from the intake stroke to the compression stroke. The mixture is ignited at the fuel-efficient ignition time at the late stage of the compression stroke, and the combustion pressure pushes the piston 3, thereby rotating the crankshaft 5. The rotation of the crankshaft 5 also causes the motor generator (not shown) connected to the crankshaft 5 to rotate and generate electricity, thereby charging the battery 111.

[0069] When the hybrid vehicle stops due to a traffic light or congestion, and the battery capacity exceeds the upper limit, charging stops, and the engine 100 starts the stop process under the control of the ECU 25. At this time, the engine torque is not required, so the ECU 25 cuts off the fuel supplied to the engine 100. At this time, the ECU 25 controls the fuel injection signal to the injector 13 to be turned off, and stops the fuel supply to the combustion chamber. Therefore, the fuel injection from the injector 13 to the combustion chamber is stopped.

[0070] Figure 4 This is a graph showing in time series the relationship between the engine speed and the amount of NOx detected in the tail pipe when the intake valve 9 and the exhaust valve 10 are operated according to a general curve.

[0071] When the charge amount of the battery 111 exceeds the threshold value, the engine speed is reduced at time t21 by the control of the ECU 25. Here, a fuel cut-off time t22 is provided between time t21 and time t23 when the engine stops. Furthermore, the hybrid vehicle may use the negative pressure of the engine 100 to ensure the braking pressure of the hybrid vehicle. For example, in a series hybrid vehicle or a parallel hybrid vehicle, if the stop interval of the engine 100 is long, the motor rotation 52 of idling the engine 100 by means of the traction motor 50 may be performed to generate the negative pressure for braking.

[0072] In addition, in a hybrid vehicle, if the state of running by the electric power supplied from the battery 111 is long, the battery capacity will decrease. When the battery capacity decreases, the battery 111 must be charged. Therefore, the ECU 25 controls to increase the rotation speed of the engine 100 at time t24. However, the ECU 25 does not perform fuel injection in the motor rotation interval 53 starting at time t24, but controls to increase the engine rotation speed to a predetermined value 56 by means of the traction motor 50.

[0073] Therefore, the ECU 25 performs control so as not to perform fuel injection within the range of the interval 51. Figure 3 When the engine 100 is operated with the intake valve curve 9a and the exhaust valve curve 10a shown in FIG. 1 , fresh air is supplied to the three-way catalyst 22 in the intervals of stopping the engine 100, rotating the engine 100 with the motor, and starting the engine 100, resulting in an oxygen-excess state in the three-way catalyst 22. In the three-way catalyst 22, if the ratio of air to fuel, i.e., A / F, changes from the ideal ratio of 14.7 to an oxygen-excess state, the NOx purification efficiency decreases compared to the theoretical air-fuel ratio (stoichiometric). As a result, the NOx emission 54 increases at the time of restarting the engine 100.

[0074] Here, reference Figure 5 The operation of the variable valve control device 301 of the first embodiment will be described in detail. The variable valve control device 301 of the first embodiment has an exhaust valve phase changing unit 303, whereby the operation of the exhaust cam 12 is controlled by the exhaust valve phase variable mechanism 42 to change the phase angle of the exhaust valve 10.

[0075] Figure 5 1 is a diagram showing an example of curves of the intake valve 9 and the exhaust valve 10 when the engine 100 according to the first embodiment shifts to the fuel cut operation. Figure 5 The horizontal and vertical axes of the curve shown on the upper side are Figure 3 The horizontal and vertical axes of the curves shown are the same. Figure 5 The lower side shows each moment (1) to (4). Figure 5 The operation of the intake valve 9 and the exhaust valve 10 is defined by the curve shown on the upper side of FIG. Figure 5 In the intake pipe 7 and exhaust pipe 8 shown on the lower side of the combustion chamber, the pipe on the left side is the intake pipe 7, and the pipe on the right side is the exhaust pipe 8. In addition, at time (1) to (4), the vertical striped area represents the fresh air of the intake pipe 7, and the horizontal striped area represents the fresh air or exhaust gas of the exhaust pipe 8. The arrows in the figure represent the moving direction of the fresh air.

[0076] like Figure 4As shown, the exhaust valve phase variable mechanism 42 advances the center phase 401 of the exhaust valve 10 to a value between the time t22 when the fuel of the engine 100 is cut off and the time t23 when the engine 100 is stopped. Figure 5 The first angle 405 shown is on the advance side compared to the bottom dead center (BDC) 402 of the expansion stroke. At this time, the exhaust valve 10 operates according to the exhaust valve curve 10b changed from the exhaust valve curve 10a. The position of the phase of the exhaust valve 10 shown by the exhaust valve curve 10b is called the "target position". As a result, the variable valve control device 301 can make the fresh air flow back from the exhaust pipe 8 into the cylinder, suppress the fresh air supplied to the three-way catalyst 22 when the fuel is cut, and thus suppress the emission of NOx when the engine 100 is restarted.

[0077] Here, the operation of the intake valve 9 and the exhaust valve 10 in each stroke will be described. The opening and closing timing of the exhaust valve 10 is controlled according to an exhaust valve curve 10b.

[0078] During the expansion stroke, the piston 3 begins to descend in the interval 403 in which the exhaust valve 10 is closed. Then, after the interval 403, the exhaust valve 10 begins to open. At the moment (1) of the expansion stroke, the exhaust pipe 8 becomes at atmospheric pressure, the combustion chamber (cylinder) becomes at negative pressure, and only the exhaust valve 10 opens. Therefore, the pressure difference between the exhaust pipe 8 and the cylinder causes the new air containing exhaust gas discharged into the exhaust pipe 8 in the previous cycle to flow back into the cylinder. As a result, the cylinder is filled with the new air containing exhaust gas discharged from the exhaust pipe 8 in the previous cycle. During the expansion stroke, the pressure in the cylinder returns to atmospheric pressure, and the pressure difference between the pressure in the cylinder and the pressure in the exhaust pipe 8 disappears.

[0079] After the expansion stroke BDC, at the time (2) of the exhaust stroke, the piston 3 rises. In addition, in the exhaust stroke, only the exhaust valve 10 is in an open state, and the intake valve 9 is in a closed state. Therefore, new air is not sucked into the cylinder from the intake pipe 7, and the new air or exhaust gas in the cylinder is discharged to the exhaust pipe 8 again. In addition, the exhaust valve 10 is closed on the advance side compared to 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 new air in the exhaust pipe 8, the new air is confined in the cylinder, so the EGR rate does not increase.

[0080] Here, the EGR rate is a value defined by the following equation (1), and represents the ratio of exhaust gas to the intake air amount.

[0081] EGR rate [%] = (F0-FA) / F0×100…(1)

[0082] F0 [l / min] is the amount of intake air before EGR is introduced

[0083] FA [l / min] is the intake air volume when EGR is introduced

[0084] When the exhaust valve 10 is closed in the middle of the exhaust stroke, the rise of the piston 3 compresses the air in the cylinder in the interval 404 where the piston 3 rises, so the pressure in the cylinder increases. After the exhaust stroke TDC, at the time (3) of the intake stroke, the piston 3 begins to descend. As shown in the intake valve curve 9a, the intake valve 9 opens as the piston 3 descends. Here, the pressure of the intake pipe 7 is lower than the pressure in the cylinder, so the pressure difference between the cylinder and the intake pipe 7 causes the exhaust gas in the cylinder to flow back to the intake pipe 7.

[0085] In the second half of the intake stroke, i.e., at time (4), the piston 3 further descends with the exhaust valve 10 closed. Therefore, in the interval in which the exhaust valve 10 is closed, the air in the cylinder expands and forms a negative pressure in the cylinder. When the piston 3 descends, exhaust gas and new air flow into the cylinder from the intake pipe 7. After the intake stroke BDC, the intake valve 9 is closed.

[0086] Next, in the compression stroke, the piston 3 rises and the cylinder volume decreases. However, since both the intake valve 9 and the exhaust valve 10 are in the closed state, the air in the cylinder is retained. Next, when the piston 3 descends in the expansion stroke, since there is no new air sucked from the intake pipe 7, the air in the cylinder expands again to form a negative pressure.

[0087] In the interval 403 where the exhaust valve 10 is closed, the pressure in the cylinder is negative pressure, so as the piston 3 descends, a large amount of exhaust gas or fresh air from the exhaust pipe 8 flows into the cylinder at the moment when the exhaust valve 10 opens. Therefore, the more the engine 100 rotates, the more exhaust gas or fresh air or both flow into the cylinder. Thereafter, when the intake valve 9 opens, a part of the exhaust gas, fresh air or both that flow into the cylinder is discharged to the intake pipe 7.

[0088] Next, refer to Figure 6 The relationship between the engine speed after fuel cut and the integrated value of the fresh air amount supplied to the three-way catalyst 22 when the opening and closing timing of the exhaust valve 10 is changed using the variable valve control device 301 will be described.

[0089] Figure 6 1 is a diagram showing an example of the integrated value of the fresh air amount supplied to the three-way catalyst 22 from after the fuel cut to when the engine 100 stops. Figure 6 The horizontal axis of the diagram represents the engine speed [time] until the engine 100 stops after the fuel cut, and the vertical axis represents the cumulative value [mg] of the amount of fresh air supplied to the three-way catalyst 22. The dotted line 501 in the diagram represents the phase of the exhaust valve 10. Figure 3The cumulative value of the fresh air amount when the exhaust valve curve 10a shown in FIG. 1 is changed. Figure 5 The cumulative value of the fresh air amount when the exhaust valve curve 10b shown in FIG. 1 is changed. In addition, the solid line 503 represents the phase of the exhaust valve 10 described later. Figure 8 The cumulative value of the fresh air amount when the exhaust valve closing time is changed is shown.

[0090] First, while referring to the point line 501, Figure 3 The integrated value of the fresh air amount when the engine cranking stopping operation is performed will be described using the intake valve curve 9a and the exhaust valve curve 10a shown in FIG.

[0091] In this curve, fresh air flows into the cylinder from the intake pipe 7 during the intake stroke, and fresh air in the cylinder is discharged to the exhaust pipe 8 during the exhaust stroke. Therefore, as shown by dotted line 501, the amount of fresh air supplied to the three-way catalyst 22 increases with the engine speed after fuel cut.

[0092] Next, the control according to the curve of the first embodiment is performed. Figure 4 A case where the center phase 401 of the exhaust valve 10 is shifted toward the advance side after the time t22 at which the fuel is cut (exhaust valve curve 10b) will be described.

[0093] Figure 6 The time 504 shown indicates Figure 5 The center phase 401 of the exhaust valve curve 10b shown in FIG. 1 is advanced to the vicinity of the bottom dead center of the expansion stroke. During the period from the fuel cutoff to the time 504, the fresh air in the cylinder and the exhaust pipe 8 is supplied to the three-way catalyst 22. However, when the center phase 401 changes toward the advance side compared to the bottom dead center 402 of the expansion stroke, the amount of fresh air or exhaust gas or both flowing back from the exhaust pipe 8 into the cylinder is greater than the amount of fresh air flowing into the cylinder from the intake pipe 7. At this time, if Figure 6 As shown in the range 505 along the single dotted line 502, the cumulative value of the fresh air supplied to the three-way catalyst 22 turns to decrease. As a result, the amount of fresh air supplied to the three-way catalyst 22 at the time when the engine 100 stops is reduced compared to the amount of fresh air supplied to the three-way catalyst 22 under the previous control as shown by the dotted line 501.

[0094] In the variable valve control device 301 of the first embodiment described above, the center phase 401 of the exhaust valve curve 10a is advanced to the first angle 405 on the advance side relative to 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, so that the excess oxygen in the three-way catalyst 22 when the engine 100 is restarted can be reduced. In addition, since the fresh air is not stored in the three-way catalyst 22, the NOx emission amount when the engine 100 is restarted can be suppressed. In addition, by reducing the fresh air supply to the three-way catalyst 22, the rich control can be suppressed, so that, for example, HC and PN can be suppressed, and the fuel efficiency can be improved by suppressing the injection of unnecessary fuel.

[0095] <Control to reduce the throttle opening>

[0096] Next, various modified examples related to the operation control of the exhaust valve 10 according to the first embodiment of the present invention will be described.

[0097] First, an example in which the ECU 25 performs control to reduce the opening of the throttle valve 27 before or after the fuel cut will be described. Here, before or after the fuel cut refers to, for example, Figure 4 Between times t21 and t23 shown.

[0098] The engine control device (ECU 25) of the first embodiment controls the opening of a throttle valve (throttle valve 27) provided upstream of an intake pipe (intake pipe 7) provided with an intake valve (intake valve 9) to be reduced before or after fuel cutoff. For example, the ECU 25 controls the opening of the throttle valve (throttle valve 27) provided upstream of an intake pipe (intake pipe 7) provided with an intake valve (intake valve 9) to be reduced. Figure 4 After the time t21 when the engine speed decreases, the opening of the throttle valve 27 is reduced, thereby reducing the opening area of ​​the flow path of the intake pipe 7 as the flow path of the fresh air. By controlling the ECU 25 to reduce the opening of the throttle valve 27, the fresh air flowing from the intake pipe 7 into the cylinder 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 increases. Therefore, the amount of exhaust gas and fresh air or both flowing back from the cylinder to the intake pipe 7 and from the exhaust pipe 8 to the cylinder can be increased, and the fresh air supplied to the three-way catalyst 22 can be reduced. As a result, combined with the effect of reducing the fresh air going to the three-way catalyst 22 by advancing the exhaust valve curve 10a, the cumulative value of the fresh air supplied to the three-way catalyst 22 can be further suppressed. In addition, the ECU 25 maintains the opening of the throttle valve 27 in a reduced state until just before the engine 100 is restarted. Therefore, the effect of reducing the NOx emission amount when the engine 100 is restarted is improved.

[0099] Furthermore, if the timing at which the ECU 25 reduces the opening of the throttle valve 27 is set before the fuel cut shown at the timing T22, the amount of reduction in the fresh air supplied to the cylinder and the exhaust pipe 8 can be increased. However, even if the timing at which the ECU 25 reduces the opening of the throttle valve 27 is after the fuel cut, the fresh air supplied to the cylinder and the exhaust pipe 8 can be reduced.

[0100] <Control that sets the center phase of the exhaust valve to the center position of the expansion stroke>

[0101] Next, an example in which the variable valve control device 301 performs control to set the center phase 401 of the exhaust valve 10 to the center position of the expansion stroke will be described.

[0102] Figure 7 An example of a graph of the intake valve 9 and the exhaust valve 10 and an example of a schematic diagram of the engine 100 according to a modification of the first embodiment are shown. Figure 7 2 shows a situation where the central phase 401 of the exhaust valve 10 is controlled to advance to the second angle 701 which is substantially the central position of the expansion stroke. Figure 7 The upper side shows an example of a curve, Figure 7 The lower side of the diagram shows the operation of the intake valve 9 and the exhaust valve 10. The exhaust valve curve 10d shown in the figure will be described in detail later.

[0103] A variable valve control device 301 according to a modified example of the first embodiment of the present invention is Figure 4 In the period from the time t22 when the fuel is cut off to the time t23 when the rotation of the engine 100 is stopped, the center phase 401 of the exhaust valve 10 is controlled to be advanced. Specifically, the exhaust valve phase changing unit (exhaust valve phase changing unit 303) advances the center phase (center phase 401) of the exhaust valve (exhaust valve 10) to the second angle (second angle 701) which is approximately the center position of the expansion stroke during the period from when the engine control unit (ECU 25) cuts off the fuel supplied to the engine (engine 100) to when the engine (engine 100) is stopped. As a result, the center phase 401 of the exhaust valve curve 10a overlaps with the center phase of the exhaust valve curve 10c which has a center phase at the center position of the expansion stroke. The position of the phase of the exhaust valve 10 shown by the exhaust valve curve 10c is also called the "target position".

[0104] Here, reference Figure 7 The schematic diagram shown below will explain the operation of the intake valve 9 and the exhaust valve 10 whose opening and closing timings are controlled according to the intake valve curve 9a and the exhaust valve curve 10c.

[0105] First, as shown at time (1), the exhaust valve 10 starts opening after the compression stroke TDC according to the exhaust valve curve 10c. At this time, the pressure in the cylinder is higher than that in the exhaust pipe 8, so the fresh air or exhaust gas in the cylinder or both are discharged to the exhaust pipe 8.

[0106] When the piston 3 descends during the expansion stroke, the pressure in the cylinder becomes lower than the pressure in the exhaust pipe 8. Therefore, as shown at time (2), the exhaust gas or the fresh air or both of them flow into the cylinder from the exhaust pipe 8. After the expansion stroke BDC, the exhaust valve 10 is closed. In the exhaust stroke, the piston 3 rises with the intake valve 9 and the exhaust valve 10 closed, so the pressure in the cylinder increases.

[0107] 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 at time (3), the exhaust gas or fresh air in the cylinder, or both, flows back into the intake pipe 7. In the second half of the intake stroke, the piston 3 further descends, causing the pressure in the intake pipe 7 to become higher than that in the cylinder. Therefore, as shown at time (4), the exhaust gas or fresh air in the intake pipe 7, or both, flows back into the cylinder.

[0108] As described above, the variable valve control device 301 (exhaust valve phase changing unit 303) is configured to Figure 7 The intake valve curve 9a and the exhaust valve curve 10c are used to control the opening and closing time of the intake valve 9 and the exhaust valve 10. Through this control, the opening interval of the exhaust valve 10 in the expansion stroke becomes shorter than that in the expansion stroke. Figure 5 The exhaust valve 10 shown in FIG. 1 has a wide opening interval. In addition, the exhaust valve 10 has a wide closing interval during the exhaust stroke. Figure 5 The exhaust valve 10 shown has a wide closing range. As a result, exhaust gas easily flows back from the exhaust pipe 8 into the cylinder, and the amount of backflow of air increases.

[0109] Therefore, if Figure 6 As shown by the solid line 503, the cumulative value of the amount of air supplied to the three-way catalyst 22 is Figure 5 As a result, the variable valve control device 301 can improve the effect of suppressing the amount of air supplied to the three-way catalyst 22 during fuel cut and suppressing the emission of NOx during restart of the engine 100.

[0110] <Control to maintain the center phase of the exhaust valve 10 at the center position of the expansion stroke>

[0111] Next, an example of the variable valve control device 301 controlling the central phase 401 of the exhaust valve 10 to maintain the central position of the expansion stroke is described. After the central phase (central phase 401) of the exhaust valve (exhaust valve 10) reaches the second angle (second angle 701), the engine (engine 100) is stopped or the engine (engine 100) is restarted after the engine (engine 100) stops rotating and the engine (engine 100) speed increases to a predetermined value 56 (reference Figure 4 ), the exhaust valve phase changing unit (exhaust valve phase changing unit 303) maintains the second angle (second angle 701). The so-called increase in the speed of the engine (engine 100) to the specified value 56 can also be called the period from when the engine 100 stops rotating to when the next fuel injection starts.

[0112] Figure 8 The diagram shows an example of the valve closing time of the exhaust valve 10 when the center phase 401 of the exhaust valve 10 is maintained at the second angle 701 during the period from when the engine 100 stops rotating to before the next fuel injection starts.

[0113] Figure 8 A graph showing the relationship between the engine speed [rpm] and the exhaust valve closing time [deg. ATDC] in a time series is shown in FIG. Figure 8 In, with Figure 4 The same parts are described using the same symbols.

[0114] The variable valve control device 301 controls the exhaust valve 10 so as to maintain the center phase 401 at the second angle 701 until the engine 100 stops. Figure 7 As shown in the lower side of , the variable valve control device 301 can increase the amount of exhaust gas or fresh air or both of them flowing back from the exhaust pipe 8, thereby reducing the amount of fresh air supplied to the three-way catalyst 22. By such phase control of the exhaust valve 10, the amount of air flowing back from the exhaust pipe 8 to the cylinder can be maximized.

[0115] Furthermore, when the motor is rotated 52 within the range 51 to generate the brake negative pressure, the variable valve control device 301 is also controlled so that the center phase 401 of the exhaust valve 10 maintains the second angle 701. The variable valve control device 301 can also increase the amount of exhaust gas or fresh air or both of them flowing back from the exhaust pipe 8 during such control, thereby reducing the amount of air supplied to the three-way catalyst 22.

[0116] In addition, at time t25 when the fuel cut is completed and the fuel injection is resumed, air is required for the fuel injected into the cylinder to be burned. Therefore, the variable valve control device 301 delays the phase of the exhaust valve 10 in stages as shown by time 601 within the motor rotation interval 53 or before the motor rotation interval 53. Furthermore, the variable valve control device 301 preferably delays the phase of the exhaust valve 10 to at least Figure 7 The exhaust valve curve 10d shown in FIG. 1 is controlled until the time t25 when the fuel injection starts. The phase position of the exhaust valve 10 shown in the exhaust valve curve 10d is also referred to as a "target position".

[0117] Furthermore, the variable valve control device 301 retards the phase of the exhaust valve 10 based on the EGR rate of the internal EGR that causes the exhaust gas to flow back from the exhaust pipe 8 by adjusting the opening and closing timing of the intake valve 9 and the exhaust valve 10. Therefore, the variable valve control device 301 can determine the retard amount of the exhaust valve 10 so that the EGR rate of the internal EGR becomes 30% or less. This is because it is known that generally when the EGR rate exceeds 30%, fuel becomes difficult to burn.

[0118] 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 phase retardation of the exhaust valve (exhaust valve 10) according to the EGR rate. At this time, the variable valve control device 301 Figure 8 In the period from the time t25 when the fuel cut ends and the fuel is injected, the closing time of the exhaust valve 10 is controlled to be close to the top dead center of the exhaust stroke. By this control, the EGR rate of the internal EGR in the cylinder is reduced at the time t25 when the fuel injection starts, so the combustion stability is improved. As a result, the ECU 25 can restart the engine 100 stably, so that NOx reduction and the stability of the restart performance can be achieved at the same time.

[0119] <Countermeasures when the responsiveness of the VTC of the exhaust valve 10 is slow>

[0120] Here, the case where the exhaust valve phase variable mechanism 42 provided in the VTC 40 has a slow response is studied. Even if the exhaust valve phase changing unit 303 attempts to change the phase of the exhaust valve 10 using such an exhaust valve phase variable mechanism 42, there is still a problem. Figure 8 In the illustrated example, the phase of the exhaust valve 10 cannot complete the movement to the substantially center position (second angle 701) of the expansion stroke during the period from time t22 when the fuel is cut off to time t23 when the engine 100 is stopped.

[0121] In this case, the motor control unit 304 controls the operation of the traction motor 50 so that the traction motor 50 rotates the engine 100. In addition, the exhaust valve phase changing unit (exhaust valve phase changing unit 303) advances the valve closing time of the exhaust valve (exhaust valve 10) compared to the top dead center before the fuel is cut off. For example, the exhaust valve phase changing unit 303 can be controlled in a manner to move the phase of the exhaust valve 10 to the second angle 701. Through this control, the exhaust valve phase changing unit 303 can reliably move the phase of the exhaust valve 10 to the approximate center position of the expansion stroke where the amount of exhaust gas and air flowing from the exhaust pipe 8 into the cylinder increases, thereby suppressing the amount of air supplied to the three-way catalyst 22. As a result, the ECU 25 can reduce the NOx emission at the time of restarting the engine 100.

[0122] 〈Electric exhaust valve phase variable mechanism〉

[0123] In the hydraulic exhaust valve phase variable mechanism 42, when the engine 100 has a low rotation speed or when the hydraulic pressure is low, such as when the engine 100 is restarted, the responsiveness of the variable valve mechanism when changing the phase may be reduced or it may be difficult to control to 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 variable mechanism 42.

[0124] For example, if the exhaust valve phase variable mechanism 42 is an electric type, the exhaust valve phase changing unit 303 can change the phase of the exhaust valve 10 by rotating a motor (not shown) provided in the exhaust valve phase variable mechanism 42. 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 faster than the speed at which the hydraulic exhaust valve phase variable mechanism 42 changes the phase of the exhaust valve 10.

[0125] In this way, by making the exhaust valve phase variable mechanism 42 electrically operated, the exhaust valve phase changing unit 303 can accurately control the phase of the exhaust valve 10 after the fuel cut, thereby increasing the amount of exhaust gas and air flowing from the exhaust pipe 8 into the cylinder and suppressing the amount of air supplied to the three-way catalyst 22. In addition, when the engine 100 is restarted, the electrically operated exhaust valve phase variable mechanism 42 quickly delays the phase of the exhaust valve 10, thereby stabilizing the combustion after the fuel cut.

[0126] [Second embodiment]

[0127] Next, refer to Figure 1 , Figure 2 , Fig. 9 as well as Fig.10, a variable valve control device and a variable valve control method according to a second embodiment of the present invention are described. The difference between the second embodiment and the first embodiment is that after the fuel is cut, in addition to the exhaust valve phase changing unit 303 controlling the exhaust valve 10 to advance the phase, the intake valve phase changing unit 302 also controls the intake valve 9 to retard the phase.

[0128] Fig. 9 An example of a schematic diagram of an engine 100 and an example of a curve of the intake valve 9 and the exhaust valve 10 according to the second embodiment of the present invention are shown. Fig. 9 2 shows a situation in which the phase of the exhaust valve 10 is advanced to change the exhaust valve curve 10a to the exhaust valve curve 10b, and the phase of the intake valve 9 is retarded to change the intake valve curve 9a to the intake valve curve 9b. Fig. 9 The upper side shows an example of a curve, Fig. 9 The lower side shows the operation of the intake valve 9 and the exhaust valve 10.

[0129] <Control of advancing the exhaust valve 10 and retarding the intake valve 9>

[0130] The intake valve phase changing unit (intake valve phase changing unit 302) capable of controlling the phase of the intake valve 9 provided in the variable valve control device 301 of the second embodiment has a function of delaying the valve opening start timing of the intake valve (intake valve 9) from the top dead center of the intake stroke in stages during the period from when the fuel supplied to the engine (engine 100) is cut off to when the engine (engine 100) is stopped by the control of the engine control device (ECU 25). As a result, the variable valve control device 301 can make the fresh air or the exhaust gas or both flow back into the cylinder from the exhaust pipe 8, suppress the amount of air supplied to the three-way catalyst 22 when the fuel is cut off, and thus suppress the emission amount of NOx when the engine 100 is restarted.

[0131] The details of the variable valve control device 301 of the second embodiment are described. Here, the opening and closing time of the intake valve 9 is controlled according to the intake valve curve 9b, and the opening and closing time of the exhaust valve 10 is controlled according to the exhaust valve curve 10b. The phase position of the intake valve 9 shown in the intake valve curve 9b is also called the "target position".

[0132] exist Fig. 9 In the expansion stroke shown, the piston 3 descends in the interval 403 when the exhaust valve 10 is closed, thereby causing the pressure in the cylinder to become negative. At this time, the pressure in the cylinder is lower than that in the exhaust pipe 8, so as shown at time (1), when the exhaust valve 10 opens, the pressure difference between the cylinder and the exhaust pipe 8 and the continuous descent of the piston 3 cause the new air or exhaust gas in the exhaust pipe 8 to flow into the cylinder.

[0133] At the time (2) of the exhaust stroke, the intake valve 9 is in a closed state and the exhaust valve 10 is in an open state. Therefore, as the piston 3 rises, the exhaust gas in the cylinder is discharged to the exhaust pipe 8. In the second half of the exhaust stroke, the exhaust valve 10 is closed.

[0134] In the first half of the intake stroke, both the intake valve 9 and the exhaust valve 10 are in a closed state. In the second half of the intake stroke, the exhaust valve 10 is in a closed state, and the intake valve 9, whose valve phase is delayed according to the intake valve curve 9b, opens. When the piston 3 descends during the intake stroke, the pressure in the cylinder becomes lower than the pressure in the intake pipe 7. Therefore, as shown at time (3), when the intake valve 9 opens while the piston 3 descends, the pressure difference causes air to flow in slightly from the intake pipe 7.

[0135] The intake valve 9 starts to open from just before the intake stroke BDC. Also, when the piston 3 rises during the compression stroke, the intake valve 9 is also in an open state. Therefore, as shown at time (4), as the piston 3 rises, the air and exhaust gas in the cylinder flow back to the intake pipe 7. In this way, the phase of the intake valve 9 is delayed by the intake valve phase changing unit 302 of the variable valve control device 301, and the phase of the exhaust valve 10 is advanced by the exhaust valve phase changing unit 303, so that the exhaust gas and the new air in the exhaust pipe 8 or both of them flow back to the intake pipe 7.

[0136] In the variable valve control device 301 of the second embodiment described above, the phase of the intake valve 9 is delayed by the intake valve phase changing unit 302, so that the exhaust gas and the fresh air in the cylinder or both of them flow back to the intake pipe 7 during the compression stroke. Therefore, compared with the case where the exhaust valve phase changing unit 303 of the variable valve control device 301 of the first embodiment changes only the phase of the exhaust valve 10, the amount of fresh air supplied to the three-way catalyst 22 can be further reduced. As a result, even if the ECU 25 does not perform the control of fuel cut, the NOx emission at the time of restarting the engine 100 can be suppressed.

[0137] <Control of changing the opening time of the intake valve and the closing time of the exhaust valve>

[0138] Next, a description will be given of a variable valve control method of the intake valve 9 and the exhaust valve 10 performed by the variable valve control device 301 during a period from fuel cut to restart of the engine 100 .

[0139] Fig.10 1 is a diagram showing the relationship among the time, the engine speed, the closing time of the exhaust valve 10, and the opening time of the intake valve 9 according to the second embodiment of the present invention. Fig.10 The time series change of the phase of the exhaust valve 10 and the intake valve 9 of the second embodiment is shown in FIG. Fig.10 In the figure, three examples of intake valve curves are shown using a solid line, a dotted line, and a dashed line.

[0140] A curve 901 indicated by a solid line in the valve opening time (1) of the intake valve 9 shows an example of an intake valve curve.

[0141] As described above, when the engine speed starts to decrease at time t21, fuel is cut off at time t22. After time t22 when the fuel is cut off, the exhaust valve phase changing unit 303 advances the closing time of the exhaust valve 10, and the intake valve phase changing unit 302 delays the opening time of the intake valve 9. As a result, the opening time of the intake valve 9 is delayed to 180 degrees ATDC after the top dead center. Here, if the responsiveness of the intake valve 9 is slow, the opening time of the intake valve 9 may not be moved to 180 degrees ATDC after the top dead center before time t23 when the rotation of the engine 100 stops.

[0142] However, the variable valve control device 301 not only advances the closing timing of the exhaust valve 10 but also uses control to delay the opening timing of the intake valve 9 compared to the top dead center. Therefore, compared with the control of only changing the phase of the exhaust valve 10 in the first embodiment, the backflow of air from the exhaust pipe 8 can be increased, thereby suppressing the supply of air to the three-way catalyst 22.

[0143] In addition, the intake valve phase changing unit 302 is preferably provided with an interval 904 for maintaining the intake valve 9 in a delayed state after the rotation of the engine 100 stops. Therefore, the intake valve phase changing unit (intake valve phase changing unit 302) maintains the state of delaying the opening time of the intake valve (intake valve 9) from the top dead center of the intake stroke during the period from when the engine (engine 100) stops rotating and the engine (engine 100) restarts until the engine (engine 100) speed increases to a prescribed value (prescribed value 56). As a result, in the interval 904, even if Fig.10 As shown in the uppermost graph, even if the ECU 25 (motor control unit 304) drives the traction motor 50 to perform the motor rotation 52, the amount of air flowing to the three-way catalyst 22 can be suppressed. Therefore, the effect of suppressing the NOx emission amount when the engine 100 is restarted can be further improved.

[0144] <Variable valve control method shown in the opening time of the intake valve (1)>

[0145] Next, refer to Fig.10 Another example of the variable valve control method performed in the variable valve control device 301 will be described using a curve 903 of the intake valve 9 as shown in the valve opening time (1) of the intake valve 9.

[0146] As shown in the curve 903 of the intake valve 9, the intake valve phase changing unit 302 can move the valve opening time of the intake valve 9 to the intake valve opening time 907 which is on the advanced side compared to the bottom dead center of the intake stroke which is TDC+180 degrees after the time t22 when the fuel is cut off. As a result, the time taken from the time t24 when the engine speed rises to the time t26 when the intake valve opening time completes the movement to TDC can be shortened. As a result, the ECU 25 can control the start of fuel injection at a time earlier than the time t25. Therefore, it is possible to suppress the supply of fresh air to the three-way catalyst 22 during the process in which the intake valve phase changing unit 302 advances the phase of the intake valve 9 and the exhaust valve phase changing unit 303 delays the phase of the exhaust valve 10 when the engine 100 is restarted.

[0147] <Variable valve control method shown in the opening time of the intake valve (2)>

[0148] Next, refer to Fig.10 Another example of the variable valve control method of the second embodiment of the present invention is described with reference to the valve opening time (2) of the intake valve 9 shown at the bottom layer. Here, the curve 902 shown by the dotted line in the valve opening time (2) of the intake valve 9 at the bottom layer represents another example of the intake valve curve.

[0149] In the curve of the intake valve 9 shown by the curve 902 of the intake valve 9, the intake valve phase changing unit 302 starts to delay the valve opening start time of the intake valve 9 from TDC at the time t27 before the time t22 when the fuel is cut, and moves the phase of the intake valve 9 to the intake valve opening time 906. In this way, the intake valve phase changing unit (the intake valve phase changing unit 302) delays the valve opening time of the intake valve (the intake valve 9) from the top dead center of the intake stroke before the fuel is cut. By performing this advance operation, the time required for the valve opening time of the intake valve 9 to complete the movement (TDC+180 degrees) after the time t22 when the fuel is cut can be shortened by the time 905. As a result, the suppression effect of the fresh air supplied to the three-way catalyst 22 is improved, and the responsiveness of the intake valve phase variable mechanism 41 can be relaxed.

[0150] Furthermore, during the period from when the engine speed starts to decrease at time t21 to when the engine 100 stops at time t23, the ECU 25 (motor control unit 304) can also cause the traction motor 50 to start the motor rotation 55 ( Fig.10 By setting the interval of the motor rotation 55, the traction motor 50 can smoothly perform the motor rotation 55 compared with the case where the ECU 25 restarts the motor rotation 52 after the engine 100 stops.

[0151] <Measures for when there is a large amount of backflow of fresh air or exhaust gas from the exhaust pipe to the intake pipe>

[0152] In the variable valve control device 301 of the second embodiment described above, exhaust gas, fresh air, or both of them can be made to flow back from the exhaust pipe 8 to the intake pipe 7 through the cylinder. However, if the amount of air flowing back from the exhaust pipe 8 to the intake pipe 7 is large, fresh air in addition to the exhaust gas will also flow back to the intake pipe 7. However, at the time t25 when the fuel cut is completed and the fuel is injected, fresh air for fuel combustion is required in the cylinder. Therefore, the intake valve phase change unit 302 preferably changes the phase of the intake valve 9 toward the advance side in the interval 910 in which the engine 100 is rotated by the traction motor 50 before the time t25, thereby controlling the fresh air to flow into the cylinder. Through such control, at the time t25 when the fuel is injected, the fresh air required for combustion is ensured in the cylinder. Therefore, it is possible to achieve both the suppression of the fresh air amount supplied to the three-way catalyst 22 and the stable restart of the engine 100.

[0153] In addition, the variable valve control device 301 of the second embodiment may delay the valve opening time of the intake valve 9 from the top dead center of the intake stroke before the fuel cut, and then perform the fuel cut. The intake valve phase changing unit 302 can shorten the time taken from the fuel cut to the intake valve 9 delaying and completing the movement of the intake valve 9 by delaying the valve opening time of the intake valve 9 from the top dead center of the intake stroke in advance. As a result, the amount of air supplied to the three-way catalyst 22 during the movement of the intake valve 9 can be suppressed.

[0154] 〈Electric intake valve phase variable mechanism〉

[0155] In the hydraulic intake valve phase variable mechanism 41, when the engine 100 has a low rotation speed or when the hydraulic pressure is low, such as when the engine 100 is restarted, the responsiveness of the variable valve mechanism when changing the phase may be reduced or it may be difficult to control to the target position. Therefore, the intake valve phase changing 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.

[0156] For example, if the intake valve phase variable mechanism 41 is an electric type, the intake valve phase changing section 302 can change the phase of the intake valve 9 by rotating a motor (not shown) provided in the intake valve phase variable mechanism 41. 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 type intake valve phase variable mechanism 41 changes the phase of the intake valve 9.

[0157] In this way, by making the intake valve phase variable mechanism 41 electrically operated, the intake valve phase changing unit 302 can accurately control the phase of the intake valve 9 after the fuel cut, thereby increasing the amount of exhaust gas and fresh air flowing into the cylinder from the exhaust pipe 8 and suppressing the amount of air supplied to the three-way catalyst 22. In addition, when the engine 100 is restarted, the electrically operated intake valve phase variable mechanism 41 quickly advances the phase of the intake valve 9, thereby stabilizing the combustion after the fuel cut.

[0158] [Third Embodiment]

[0159] Next, refer to Figure 1 , Figure 2 as well as Fig.11 , a variable valve control device and a variable valve control method according to a third embodiment of the present invention are described. The third embodiment differs from the first embodiment in that a section is provided in which the motor control unit 304 rotates the engine 100 by the traction motor 50 after the fuel is cut off, whereby the exhaust valve phase changing unit 303 controls the amount of delay of the phase of the exhaust valve 10.

[0160] Fig.11 1 is a diagram showing an example of a time-series change in the phase of the exhaust valve 10 and the intake valve 9 according to the third embodiment of the present invention. Fig.11 In, with Figure 8 , Fig.10 The same components or parts are described using the same reference numerals.

[0161] <Control of ensuring reverse circulation by motor rotation and suppressing the amount of air flowing to the three-way catalyst 22>

[0162] The variable valve control device 301 of the third embodiment provides a motor rotation section 101 during the period from the fuel cut at time t22 to the stop of the engine 100 at time t23. The motor rotation section 101 is when the center phase 401 of the exhaust valve 10 reaches the first angle 405 (refer to Figure 5 ) or the second angle 701 (reference Figure 7 ) After that, the motor control unit 304 rotates the traction motor 50 to maintain the rotation range of the engine 100.

[0163] The motor rotation section (motor rotation section 101) is set in such a way that the engine control device (ECU 25) drives the motor (traction motor 50) to rotate the engine (engine 100) after the center phase (center phase 401) of the exhaust valve (exhaust valve 10) reaches the first angle (first angle 405) by means of the exhaust valve phase changing unit (exhaust valve phase changing unit 303). For example, the motor rotation section 101 starts immediately after the center phase 401 of the exhaust valve 10 reaches the first angle 405 at time t29.

[0164] In addition, in Figure 3 When the phase of the exhaust valve 10 is changed according to the exhaust valve curve 10a shown in FIG. 1 , the ECU 25 detects the amount of fresh air entering the cylinder by means of an airflow sensor installed upstream of the throttle valve 27. Thus, the ECU 25 can infer 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 pre-calculates the amount of fresh air supplied to the three-way catalyst 22. Then, the ECU 25 preferably determines the time of the motor rotation interval 101 based on the pre-calculated amount of fresh air so that the amount of fresh air flowing back into the cylinder from the exhaust pipe 8 becomes fuel cutoff until the next restart of the engine 100 is greater than the amount of fresh air supplied to the three-way catalyst 22.

[0165] Here, the exhaust valve phase changing unit 303 is Fig.11 The example of controlling the exhaust valve closing time by using the curve of the exhaust valve 10 shown in FIG. 1 is studied. The exhaust valve phase changing unit 303 starts to move the phase of the exhaust valve 10 in the delayed direction at the time t22 when the fuel is cut off. And, fresh air is supplied to the three-way catalyst 22 in the interval from the time when the opening start time of the exhaust valve 10 reaches -180 deg.ATDC to the time t28 when the center phase 401 of the exhaust valve 10 reaches the advanced side compared with the top dead center of the expansion stroke. In addition, when the engine is restarted, fresh air is supplied to the three-way catalyst 22 in the interval 102 from the time when the center phase 401 of the exhaust valve 10 reaches 180 deg.ATDC to the time t25 when the movement of the phase of the exhaust valve 10 is completed.

[0166] Therefore, the ECU 25 estimates the fresh air amount of the fresh air supplied to the three-way catalyst 22 based on the fresh air amount detected by the airflow sensor as described above. Then, the ECU 25 preferably determines at least one of the target values ​​of the time of the motor rotation interval 101 and the advance amount of the phase of the exhaust valve 10 so that the estimated fresh air amount of the fresh air supplied to the three-way catalyst 22 becomes greater than the fresh air amount flowing back from the exhaust pipe 8 into the cylinder.

[0167] In the variable valve control device 301 of the third embodiment described above, the amount of exhaust gas and air flowing into the cylinder from the exhaust pipe 8 increases by providing the motor rotation section 101. Therefore, the accumulated value of the amount of air supplied to the three-way catalyst 22 can be suppressed.

[0168] The present invention is not limited to the above-described embodiments, and various other application examples and modified examples can of course be employed without departing from the gist of the present invention described in the claims.

[0169] For example, the above-mentioned embodiments are detailed and specific descriptions of the configurations of the device and system in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to having all the configurations described. In addition, a part of the configuration of the embodiment described here can be replaced with the configuration of other embodiments, and further, the configuration of other embodiments can be added to the configuration of a certain embodiment. In addition, other configurations can be added, deleted, or replaced to a part of the configuration of each embodiment.

[0170] In addition, the control lines and information lines are shown as those considered necessary for explanation, and not all control lines and information lines may be shown on the product. In fact, it can be considered that almost all components are connected to each other.

[0171] Explanation of symbols

[0172] 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 changing unit, 303…exhaust valve phase changing unit, 304…motor control unit, 401…center phase.

Claims

1. A variable valve control device that controls a variable valve timing control mechanism that can change the phase of an exhaust valve provided on an exhaust pipe of an engine, characterized in that: An exhaust valve phase changing unit is provided, the exhaust valve phase changing unit outputting an instruction for changing the phase of the exhaust valve through the variable valve timing control mechanism according to a change in the state of the engine, The exhaust valve phase changing unit advances the center phase of the exhaust valve to a second angle that is a substantially center position of an expansion stroke during a period from when fuel supply to the engine is cut off to when the engine is stopped under the control of an engine control device.

2. The variable valve control device according to claim 1, characterized in that: After the center phase of the exhaust valve reaches the second angle, the exhaust valve phase changing unit maintains the second angle until the engine stops rotating or the engine is restarted after the engine stops rotating and the engine speed increases to a specified value.

3. The variable valve control device according to claim 1, characterized in that: The engine control device calculates the EGR rate of the internal EGR, The exhaust valve phase changing unit determines an amount by which the phase of the exhaust valve is to be retarded according to the EGR rate.

4. The variable valve control device according to claim 1, characterized in that: The variable valve control device controls the variable valve timing control mechanism capable of changing the phase of the intake valve provided on the intake pipe of the engine. An intake valve phase changing unit is provided, the intake valve phase changing unit outputting an instruction for changing the phase of the intake valve through the variable valve timing control mechanism according to a change in the state of the engine, The intake valve phase changing unit delays the opening start timing of the intake valve stepwise from the top dead center of the intake stroke during a period from when fuel supply to the engine is cut off to when the engine is stopped under the control of the engine control device.

5. The variable valve control device according to claim 4, characterized in that: The intake valve phase changing section delays the opening timing of the intake valve from the top dead center of the intake stroke before the fuel is cut.

6. The variable valve control device according to claim 5, characterized in that: The intake valve phase changing unit maintains a state in which the opening timing of the intake valve is delayed from a top dead center of the intake stroke until the engine speed increases to a predetermined value after the engine is restarted after the engine stops rotating.

7. The variable valve control device according to claim 1, characterized in that: The engine control device reduces the opening of a throttle valve provided upstream of an intake pipe provided with an intake valve before or after the fuel is cut.

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