Hybrid vehicle

A control device is configured to control an engine to be started and stopped such that when a hybrid vehicle is required to output a vehicular required power smaller than an engine starting threshold value the control device operates to stop the engine and use only a motor generator to cause the vehicle to travel and when the vehicular required power exceeds the threshold value the control device operates to start the engine and use both the engine and the motor generator to cause the vehicle to travel. The engine starting threshold value is set to be higher when at least one of an amount of lifting the intake valve and a working angle on the intake valve controlled by a VVL device provided to the engine is small than when at least one of the amount and the angle is large.

This nonprovisional application is based on Japanese Patent Application No. 2013-233888 filed on Nov. 12, 2013 with the Japan Patent Office, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a hybrid vehicle, and more specifically to controlling a hybrid vehicle including an internal combustion engine having a variable valve actuation device for varying an actuation characteristic of an intake valve.

Description of the Background Art

A variable valve actuation device is generally known for varying an actuation characteristic of an intake valve of an internal combustion engine. Some variable valve actuation devices are configured to be capable of varying at least one of an amount of lifting an intake valve and a working angle on the intake valve. The variable valve actuation device allows an internal combustion engine to have a modified operational characteristic.

For example, Japanese Patent Laying-Open No. 2005-299594 discloses an internal combustion engine including a variable valve actuation device. More specifically, when the engine is automatically stopped, provided that the engine is restarted, the variable valve actuation device operates to allow an intake valve to be worked by a working angle increased to obtain a maximum decompression effect. Furthermore, when the engine is manually stopped and starting it at low temperature and doing so at high temperature are both expected, the variable valve actuation device operates to allow the intake valve to be worked by a working angle reduced to be smaller than when the engine is automatically stopped.

SUMMARY OF THE INVENTION

When a hybrid vehicle including an internal combustion engine having a variable valve actuation device travels at low speed, at a small load, and/or the like, the hybrid vehicle may stop the internal combustion engine and use only a traction motor's driving force to travel. When the hybrid vehicle thus travels, and requires the internal combustion engine's driving force depending on how the hybrid vehicle travels, the internal combustion engine that is currently stopped is started while the hybrid vehicle is travelling. When the internal combustion engine is started with the intake valve worked by a large working angle, a portion of air taken into a cylinder is returned out of the cylinder, which provides a decompression effect, however, a reduced amount of air is taken in, and the internal combustion engine provides a poorer torque response than when the internal combustion engine is started with the intake valve worked by a small working angle.

The impaired torque response results in reduced driving force, which may be compensated via a control by the traction motor's torque. This control requires previously increasing the internal combustion engine's driving force before a battery outputs excessive electric power as the traction motor consumes more electric power. If the internal combustion engine is timed to start invariably earlier regardless of what working angle is applied to the intake valve in starting the internal combustion engine, however, travelling with the internal combustion engine stopped and the traction motor's driving force alone used is reduced more than necessary, resulting in impaired fuel efficiency.

The present invention has been made in order to address such an issue, and it contemplates a hybrid vehicle having a variable valve actuation device for varying an actuation characteristic of an intake valve, that can reduce/prevent impaired fuel efficiency caused by starting an internal combustion engine.

The present invention in one aspect provides a hybrid vehicle comprising an internal combustion engine, a power storage device, a first rotating electric machine, and a control device. The internal combustion engine has a variable valve actuation device for varying an actuation characteristic of an intake valve. The power storage device is chargeable. The first rotating electric machine receives electric power supplied from the power storage device to generate driving force to cause the hybrid vehicle to travel. The control device is operative in response to a vehicular required power that the vehicle is required to output being smaller than a threshold value for stopping the internal combustion engine and allowing a driving force of the first rotating electric machine to be used to cause the vehicle to travel, and the control device is operative in response to the vehicular required power exceeding the threshold value for starting the internal combustion engine and allowing a driving force of the internal combustion engine and the driving force of the first rotating electric machine to be both used to cause the vehicle to travel. The variable valve actuation device is configured to be capable of selecting a first state and a second state allowing the intake valve to be lifted in a larger amount and/or worked by a larger working angle than the first state does. The control device performs a process to increase the threshold value to be higher when the first state is selected than when the second state is selected.

In the present hybrid vehicle when the intake valve is lifted in a small amount and/or worked by a small working angle the internal combustion engine is started with higher torque response than when the intake valve is lifted in a large amount and/or worked by a large working angle, and accordingly, the internal combustion engine can output a rapidly increasing torque. Accordingly, in starting the internal combustion engine, the internal combustion engine can be timed to start later by increasing a threshold value for vehicular required power at which starting the internal combustion engine is required (i.e., an engine starting threshold value) without increasing electric power output from the power storage device to increase a driving force to be compensated for by an output of the first rotating electric machine. As a result, a range allowing the vehicle to travel with the internal combustion engine stopped and the rotating electric machine's driving force alone used can be larger than when the engine starting threshold value is set invariably regardless of in what amount the intake valve is lifted and by what working angle the intake valve is worked, and the vehicle can thus reduce/prevent impaired fuel efficiency. The hybrid vehicle having the variable valve actuation device for varying the actuation characteristic (an amount of lift and/or a working angle) of the intake valve, can thus reduce/prevent impaired fuel efficiency caused by starting the internal combustion engine.

Preferably, the hybrid vehicle further comprises a second rotating electric machine coupled with an output shaft of the internal combustion engine and usable to start the internal combustion engine. In starting the internal combustion engine when the first state is selected the control device controls the second rotating electric machine, while cranking the internal combustion engine, to increase a rate that is applied to increase a rotational speed of the second rotating electric machine to be a rate higher than that applied when the second state is selected.

Increasing the rate applied to increase the second rotating electric machine's rotational speed can reduce/prevent preventing the internal combustion engine's rotational speed from increasing.

Preferably, when the variable valve actuation device is switched from the second state to the first state during a start control of the internal combustion engine, the control device controls the second rotating electric machine, while cranking the internal combustion engine, to increase the rate that is applied to increase the rotational speed of the second rotating electric machine to be a rate higher than that applied when the second state is selected.

When at least one of the amount of lifting the intake valve and the working angle on the intake valve is varied to be small in an engine start control, accordingly increasing a rate applied to increase the second rotating electric machine's rotational speed can reduce/prevent preventing the internal combustion engine's rotational speed from increasing.

Preferably, the control device performs the process when the internal combustion engine's start shock is permitted.

Accordingly, when the internal combustion engine's start shock is not permitted the above process is not performed. Reducing the internal combustion engine's start shock can thus be prioritized.

Preferably, the variable valve actuation device is configured to be capable of switching the actuation characteristic of the intake valve to any one of a first characteristic, a second characteristic allowing the intake valve to be lifted in a larger amount and/or worked by a larger working angle than when the actuation characteristic is the first characteristic, and a third characteristic allowing the intake valve to be lifted in a larger amount and/or worked by a larger working angle than when the actuation characteristic is the second characteristic.

This allows the intake valve to be lifted in an amount and worked by a working angle that are limited to three actuation characteristics, and the engine's operation state can be controlled via a control parameter adapted in a shorter period of time. Furthermore, this also allows an actuator to have a simpler configuration.

Preferably, the variable valve actuation device is configured to be capable of switching the actuation characteristic of the intake valve to any one of a first characteristic and a second characteristic allowing the intake valve to be lifted in a larger amount and/or worked by a larger working angle than when the actuation characteristic is the first characteristic.

This allows the intake valve to be lifted in an amount and worked by a working angle that are limited to two actuation characteristics, and the engine's operation state can be controlled via a control parameter adapted in a further shorter period of time. Furthermore, the actuator is allowed to have a further simpler configuration.

A major advantage of the present invention lies in a hybrid vehicle having a variable valve actuation device for varying an actuation characteristic of an intake valve, that can reduce/prevent impaired fuel efficiency caused by starting an internal combustion engine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter reference will be made to the drawings to describe the present invention in embodiments more specifically. Note that, in the figures, identical or corresponding components are identically denoted and will not be described repeatedly.

First Embodiment

FIG. 1is a block diagram generally showing a configuration of a hybrid vehicle having a control device applied thereto according to a first embodiment of the present invention. With reference toFIG. 1, a hybrid vehicle1includes an engine100, motor generators MG1and MG2, a power split device4, a speed reducer5, a driving wheel6, a power storage device B, a power control unit (PCU)20, and a control device200.

Hybrid vehicle1travels as driven by a driving force output from at least one of engine100and motor generator MG2. Engine100generates driving force which is in turn split by power split device4for two paths. One path transmits driving force via speed reducer5to driving wheel6, and the other path transmits driving force to motor generator MG1.

Power storage device B is a chargeably and dischargeably configured electric power storage element. Power storage device B for example includes a rechargeable battery such as a lithium ion battery, a nickel metal hydride battery or a lead acid battery, or a cell of a power storage element such as an electric double layer capacitor.

Power storage device B is connected to a PCU20provided for driving motor generators MG1and MG2. Power storage device B supplies PCU20with electric power for generating force to drive hybrid vehicle1. Furthermore, power storage device B stores electric power generated by motor generators MG1, MG2. Power storage device B outputs 200 V for example.

PCU20receives direct current (DC) electric power from power storage device B and converts the received dc electric power into alternating current (AC) electric power to drive motor generators MG1and MG2. PCU20also receives AC electric power generated by motor generators MG1and MG2and converts the received AC electric power into DC electric power to charge power storage device B therewith.

Control device200calculates vehicular required power based on an accelerator pedal position signal indicative of an open degree of the accelerator pedal operated, and the vehicle's travelling state, and control device200controls force, as based on the calculated vehicular required power, to drive engine100and motor generator MG2. Specifically, for a vehicular required power smaller than a threshold value, control device200stops engine100and uses the driving force of motor generator MG2to cause the vehicle to travel as an EV, whereas for a vehicular required power exceeding the threshold value, control device200starts engine100and uses both the driving force of engine100and the driving force of motor generator MG2to cause the vehicle to travel as an HV.

FIG. 2shows a configuration of engine100shown inFIG. 1. With reference toFIG. 2, engine100takes in air from via an air cleaner102. How much amount of air is taken in is adjusted by a throttle valve104. Throttle valve104is an electronically controlled throttle valve driven by a throttle motor312.

An injector108injects fuel towards an air intake port. At the air intake port, the fuel is mixed with air and thus introduced into a cylinder106.

While the present embodiment will be described with engine100implemented in the form of a port injected engine with injector108having an injection port provided in the air intake port, port injecting injector108and in addition thereto a direct injection injector may also be provided to inject fuel directly into cylinder106. The direct injection injector may alone be provided.

Cylinder106receives the air-fuel mixture, which is ignited by an ignition plug110and thus combusted. The combusted air-fuel mixture, or exhaust gas, is purified by a three-way catalyst112and subsequently discharged outside the vehicle. As the air-fuel mixture is combusted, a piston114is pushed down and a crankshaft116thus rotates.

Cylinder106has a head or top portion provided with an intake valve118and an exhaust valve120. When and in what amount cylinder106receives air is controlled by intake valve118. When and in what amount cylinder106exhausts exhaust gas is controlled by exhaust valve120. Intake valve118is driven by a cam122. Exhaust valve120is driven by a cam124.

Intake valve118is lifted in an amount and worked by a working angle, as controlled by a variable valve lift (VVL) device400, as will be described hereinafter more specifically. Exhaust valve120may also be similarly lifted and worked. Furthermore, a variable valve timing (VVT) device may be combined with VVL device400to control timing when the valve should be opened/closed.

Control device200controls a throttle angle θth, timing when to provide ignition, timing when to inject fuel, the amount of fuel to be injected, the intake valve's operating condition (timing when to open/close the valve, the amount of lift, the working angle, and the like) to allow engine100to achieve a driving state as desired. Control device200receives signals from a cam angle sensor300, a crank angle sensor302, a knock sensor304, and a throttle angle sensor306.

Cam angle sensor300outputs a signal indicating a cam's position. Crank angle sensor302outputs a signal indicating the rotational speed of crankshaft116(or the engine's rotational speed) and the angle of rotation of crankshaft116. Knock sensor304outputs a signal indicating how engine100vibrates in intensity. Throttle angle sensor306outputs a signal indicating throttle angle θth.

FIG. 3represents a relationship, as implemented in VVL device400, between a valve's displacement in amount and crank angle. With reference toFIG. 3, for the exhaust stroke, exhaust valve120opens and closes, and for the intake stroke, intake valve118opens and closes. Exhaust valve120displaces in an amount represented by a waveform EX, and intake valve118displaces in amounts represented by waveforms IN1and IN2.

The valve's displacement in amount indicates an amount by which intake valve118is displaced from its closed position. The amount of lift indicates an amount by which intake valve118is displaced when the valve peaks in how much in degree it is opened. The working angle is a crank angle assumed after intake valve118is opened before it is closed.

Intake valve118has an actuation characteristic varied by VVL device400between waveforms IN1and IN2. Waveform IN1corresponds to a minimal amount of lift and a minimal working angle. Waveform IN2corresponds to a maximal amount of lift and a maximal working angle. In VVL device400, a larger amount of lift is accompanied by a larger working angle.

FIG. 4is a front view of VVL device400serving as an exemplary device that controls an amount of lifting intake valve118and a working angle on intake valve118. With reference toFIG. 4, VVL device400includes a driving shaft410extending in one direction, a support pipe420that covers driving shaft410circumferentially, and an input arm430and a rocking cam440disposed in alignment on an outer circumferential surface of support pipe420in a direction along the axis of driving shaft410. Driving shaft410has a tip with an actuator (not shown) connected thereto to cause driving shaft410to provide rectilinear motion.

VVL device400is provided with a single input arm430associated with a single cam122provided for each cylinder. Input arm430has opposite sides provided with two rocking cams440associated with a pair of intake valves118, respectively, provided for each cylinder.

Support pipe420is formed in a hollowed cylinder and disposed in parallel to a cam shaft130. Support pipe420is secured to a cylinder head and thus prevented from axially moving or rotating.

Support pipe420internally receives driving shaft410to allow driving shaft410to slide axially. Support pipe420has an outer circumferential surface provided thereon with input arm430and two rocking cams440to be rockable about an axial core of driving shaft410and also prevented from moving in a direction along the axis of driving shaft410.

Input arm430has an arm portion432projecting in a direction away from the outer circumferential surface of support pipe420, and a roller portion434rotatably connected to a tip of arm portion432. Input arm430is provided to allow roller portion434to be disposed at a position allowing roller portion434to abut against cam122.

Rocking cam440has a nose portion442in a generally triangular form projecting in a direction away from the outer circumferential surface of support pipe420. Nose portion442has one side having a recessed, curved cam surface444. Intake valve118is provided with a valve spring, which is biased to apply force to in turn press against cam surface444a roller rotatably attached to a rocker arm128.

Input arm430and rocking cam440rock together about the axial core of driving shaft410. Accordingly, as cam shaft130rotates, input arm430that abuts against cam122rocks, and as input arm430thus moves, rocking cam440also rocks. This motion of rocking cam440is transmitted via rocker arm128to intake valve118to thus open/close intake valve118.

VVL device400further includes a device around the axial core of support pipe420to vary a relative phase difference between input arm430and rocking cam440. The device that varies the relative phase difference allows intake valve118to be lifted in an amount and worked by a working angle, as modified as appropriate.

More specifically, input arm430and rocking cam440with an increased relative phase difference allow rocker arm128to have a rocking angle increased relative to that of input arm430and rocking cam440and intake valve118to be lifted in an increased amount and worked by an increased working angle.

In contrast, input arm430and rocking cam440with a reduced relative phase difference allow rocker arm128to have a rocking angle reduced relative to that of input arm430and rocking cam440and intake valve118to be lifted in a reduced amount and worked by a reduced working angle.

FIG. 5is a partial perspective view of VVL device400.FIG. 5shows VVL device400partially exploded to help to clearly understand its internal structure.

With reference toFIG. 5, input arm430and two rocking cams440, and an outer circumferential surface of support pipe420define a space therebetween, and in that space, a slider gear450is accommodated that is supported to be rotatable relative to support pipe420and also axially slideable. Slider gear450is provided slideably on support pipe420axially.

Slider gear450as seen axially has a center provided with a helically right handed splined helical gear452. Slider gear450as seen axially also has opposite sides provided with helically left handed splined helical gears454s, respectively, with helical gear452posed therebetween.

An internal circumferential surface of input arm430and two rocking cams440that defines the space that has slider gear450accommodated therein, is helically splined to correspond to helical gears452and454. More specifically, input arm430is helically right handed splined to mesh with helical gear452. Furthermore, rocking cam440is helically left handed splined to mesh with helical gear454.

Slider gear450is provided with an elongate hole456located between one helical gear454and helical gear452and extending circumferentially. Furthermore, although not shown, support pipe420is provided with an elongate hole extending axially and overlapping a portion of elongate hole456. Driving shaft410, inserted in support pipe420, is integrally provided with a locking pin412to project through those portions of elongate hole456and the unshown elongate hole which overlap each other.

Driving shaft410is coupled with an actuator (not shown), and when the actuator is operated, driving shaft410moves in its axial direction, and accordingly, slider gear450is pushed by locking pin412and helical gears452and454move in a direction along the axis of driving shaft410concurrently. While helical gears452and454are thus moved, input arm430and rocking cam440splined and thus engaged therewith do not move in the axial direction. Accordingly, input arm430and rocking cam440, helically splined and thus meshed, pivot about the axial core of driving shaft410.

Note that input arm430and rocking cam440are helically splined in opposite directions, respectively. Accordingly, input arm430and rocking cam440pivot in opposite directions, respectively. This allows input arm430and rocking cam440to have a relative phase difference varied to allow intake valve118to be lifted in a varying amount and worked by a varying working angle, as has been previously described. Note that the VVL device is not limited to such a form as described above. For example, the VVL device may be a VVL device which electrically drives the valve, a VVL device which hydraulically drives the valve, or the like.

Control device200controls by how much amount the actuator that causes driving shaft410to move in rectilinear motion should be operated to control the amount of lifting intake valve118and the working angle on intake valve118.

FIG. 6illustrates an operation provided when intake valve118is lifted in a large amount and worked by a large working angle.FIG. 7illustrates an operation provided when intake valve118is lifted in a small amount and worked by a small working angle. With reference toFIGS. 6 and 7, when intake valve118is lifted in a large amount and worked by a large working angle, intake valve118is timed to close late, and accordingly, engine100is operated in the Atkinson cycle. More specifically, the intake stroke is performed to allow cylinder106to take in air, which is partially returned outside cylinder106, and accordingly, the compression stroke is performed with the air compressed by a reduced force, i.e., with a reduced compressive reaction. This allows the engine to be started with reduced vibration. However, a reduced compression ratio is provided resulting in poor ignitability.

In contrast, when intake valve118is lifted in a small amount and worked by a small working angle, intake valve118is timed to close early, and accordingly, a raised compression ratio is provided. This can improve ignitability for low temperature. However, an increased compressive reaction is provided resulting in the engine vibrating more when it starts. Furthermore, when intake valve118is lifted in a small amount and worked by a small working angle, improved engine torque response is provided, as will be described hereinafter.

FIG. 8is a timing plot for illustrating a difference in engine torque response depending on a characteristic of intake valve118. InFIG. 8, the axis of abscissa represents time and the axis of ordinate represents the engine's rotational speed.FIG. 9is a graph for illustrating a difference in engine torque depending on a characteristic of intake valve118. InFIG. 9, the axis of abscissa represents the engine's rotational speed and the axis of ordinate represents engine torque. InFIGS. 8 and 9, a solid line corresponds to a small amount of lift and a small working angle, and a broken line corresponds to a large amount of lift and a large working angle.

With reference toFIG. 8andFIG. 9, when the engine's rotational speed is in a lower range, a smaller amount of lift and a smaller working angle allow a larger engine torque to be output than a larger amount of lift and a larger working angle do. The larger amount of lift and the larger working angle allow a portion of air taken in the cylinder to be returned out of the cylinder. In contrast, the smaller amount of lift and the smaller working angle allow intake valve118to be closed earlier, and accordingly, a larger amount of air to be introduced, and engine100can thus output an increased torque.

In contrast, when the engine's rotational speed is in a higher range, a larger amount of lift and a larger working angle allow a larger engine torque to be output than a smaller amount of lift and a smaller working angle do. This is because the larger amount of lift and the larger working angle allow air's inertia force to be exploited to introduce a larger amount of air.

Accordingly, when engine100's rotational speed is raised to a rotational speed targeted in starting the engine, i.e., to a prescribed value NA, a smaller amount of lift and a smaller working angle, allowing a larger engine torque to be output for a low rotation range, allow the engine's rotational speed to be rapidly increased. In contrast, a larger amount of lift and a larger working angle allow only a small engine torque to be output for the low rotation range, resulting in impaired engine torque response.

Accordingly, when engine100is to be started, intake valve118may be lifted in an increased amount to start engine100with reduced engine start shock. This allows a decompression effect to be exploited to reduce vibration caused in starting the engine, and the vehicle can thus be comfortable to ride in.

Lifting intake valve118in an increased amount to start engine100, however, results in reduced engine torque response, and this entails using motor generator MG2's torque to compensate for a driving force until engine100has been completely started. This requires previously enhancing engine100's driving force before power storage device B outputs excessive electric power as motor generator MG2consumes large electric power. However, timing engine100to start invariably earlier regardless of what working angle is applied to intake valve118in starting engine100reduces travelling as an EV more than necessary, resulting in impaired fuel efficiency.

In the present embodiment, in starting engine100when intake valve118is lifted in a small amount and/or worked by a small working angle, a process is performed to increase a vehicular required power for starting engine100to be larger than when intake valve118is lifted in a large amount and/or worked by a large working angle. Hereinafter, this will be described more specifically.

FIG. 10is a functional block diagram for illustrating a start control that theFIG. 1control device200performs. Each functional block shown inFIG. 10is implemented by processing done by control device200via hardware or software.

With reference toFIG. 10, control device200includes a travelling control unit201, a motor control unit202, an engine control unit203, and a valve control unit204.

Travelling control unit200calculates vehicular required power based on an accelerator pedal position signal, the vehicle's travelling state and/or the like, and controls the operation states of engine100and motor generators MG1and MG2, as based on the calculated vehicular required power. Specifically, when the engine is stopped, and the vehicular required power as calculated exceeds an engine starting threshold value, travelling control unit201generates a signal for starting engine100and outputs the signal to engine control unit203.

Herein, travelling control unit201sets the engine starting threshold value in response to a signal received from valve control unit204and indicating an amount of lifting intake valve118and a working angle on intake valve118. Specifically, if engine100's start shock is not permitted or intake valve118is lifted in a large amount and worked by a large working angle, travelling control unit201sets the engine starting threshold value to a prescribed value X. In contrast, if engine100's start shock is permitted and intake valve118is lifted in a small amount and worked by a small working angle, travelling control unit201sets the engine starting threshold value to a prescribed value Y.

Note that prescribed values X and Y are values used to determine whether it is necessary to start engine100to satisfy vehicular required power and that prescribed value Y is a value larger than prescribed value X. Thus when engine100's start shock is permitted and intake valve118is lifted in a small amount and worked by a small working angle, engine100is timed to start later and travelling as an EV is thus more easily continued than when engine100's start shock is not permitted or intake valve118is lifted in a large amount and worked by a large working angle.

Note that engine100's start shock is permitted in restarting engine100when: hybrid vehicle1is traveling at high vehicular speed; when VVL device400has failed (e.g., when it is inoperable with intake valve118lifted in a small amount and/or worked by a small working angle); when fuel efficiency is prioritized (e.g., when an eco-mode is selected to prioritize fuel efficiency); when acceleration is prioritized (e.g., when the accelerator pedal is operated in a maximum amount); and/or the like. In such cases, it is more important to operate engine100in a desired operational state than to reduce engine100's start shock. Accordingly, engine100's start shock is permitted to allow priority to be given to operating engine100in the desired operational state.

Furthermore, travelling control unit201calculates the engine's required power based on vehicular required power and outputs the engine's required power as calculated to engine control unit203.

Engine control unit203receives the engine's required power from travelling control unit201and accordingly sets a target value for an operating point of engine100. The operating point of engine100is determined by the engine's rotational speed and torque. Engine control unit203outputs to travelling control unit201and valve control unit204a signal indicating the target value for the operating point of engine100.

Valve control unit204receives the target value from engine control unit203and accordingly regulates an amount of lifting intake valve118and a working angle on intake valve118. Valve control unit204generates a signal VLV for controlling VVL device400and outputs the generated signal to VVL device400. Valve control unit204outputs to travelling control unit201a signal indicating an amount of lifting intake valve118and a working angle on intake valve118.

When starting engine100, travelling control unit201calculates a target value for a rotational speed of motor generator MG1to crank engine100. Once engine100is cranked, travelling control unit201calculates a target value for a rotational speed of motor generator MG1to allow engine100to have an operating point maintained at a desired operating point. Travelling control unit201outputs the target value for the rotational speed of motor generator MG1, as calculated, to motor control unit202.

Motor control unit202generates an instruction for controlling PCU20to allow motor generator MG1to have a rotational speed indicated by the target value received from travelling control unit201, and motor control unit202outputs the generated instruction to PCU20.

FIG. 11is a flowchart for illustrating a process that theFIG. 1control device200follows to perform the start control. TheFIG. 11flowchart is implemented by periodically executing a program previously stored in control device200.

Alternatively, some steps may be performed via constructed dedicated hardware (or electronic circuitry). This also applies to the flowcharts shown inFIG. 17andFIG. 18described hereinafter.

With reference toFIG. 11, control device200in Step (S)100determines whether engine100is currently stopped. If it is determined that engine100is currently not stopped (NO in S100), the subsequent steps are not performed and the control returns to the main routine. If it is determined that engine100is currently stopped (YES in S100), control device200determines whether engine start shock is permitted (S110).

If it is determined that the engine start shock is not permitted (NO in S110), control device200sets the engine starting threshold value to prescribed value X (S120). If it is determined that the engine start shock is permitted (YES in S110), control device200determines whether intake valve118is lifted in a small amount and worked by a small working angle (S130).

If it is determined that intake valve118is lifted in a large amount and worked by a large working angle (NO in S130), control device200sets the engine starting threshold value to prescribed value X (S120). If it is determined that intake valve118is lifted in a small amount and worked by a small working angle (YES in S130), control device200sets the engine starting threshold value to prescribed value Y larger than prescribed value X (S140).

Subsequently, in S150, control device200determines whether vehicular required power is larger than the engine starting threshold value. If it is determined that the vehicular required power is equal to or smaller than the engine starting threshold value (NO in S150), the subsequent steps are not performed and the control returns to the main routine. If it is determined that the vehicular required power is larger than the engine starting threshold value (YES in S150), control device200generates a signal for starting engine100and outputs the generated signal to PCU20and engine100(S160).

FIG. 12is timing plots for illustrating how theFIG. 1control device200performs the start control. InFIG. 12, the axis of abscissa represents time and the axis of ordinate represents vehicular required power, the output of power storage device B, the engine's output, the engine's rotational speed, and the amount of lifting intake valve118and the working angle on intake valve118. Note that a solid line corresponds to a small amount of lift and a small working angle and an alternate long and short dashed line corresponds to a large amount of lift and a large working angle.

With reference toFIG. 12, engine100is stopped at time t0for the sake of illustration. For the large amount of lift and the large working angle, the vehicular required power exceeds the engine starting threshold value (of prescribed value X) at time t1, and accordingly, starting engine100starts. The large amount of lift and the large working angle are accompanied by low engine torque response, and this entails using motor generator MG2's output to compensate for a shortage of the engine's output relative to the vehicular required power. As a result, the torque of motor generator MG2required is increased. This entails previously enhancing the engine's output before power storage device B provides an output exceeding a discharging limit value as motor generator MG2's torque is increased. Accordingly, an engine starting threshold value is set to time engine100to start earlier.

For the small amount of lift and the small working angle, in contrast, the vehicular required power exceeds the engine starting threshold value (of prescribed value Y) at time t2, and accordingly, starting engine100starts. The small amount of lift and the small working angle are accompanied by high engine torque response, and the torque of motor generator MG2required is reduced. This provides a margin to an output of power storage device B relative to the discharging limit value, and accordingly, an engine starting threshold value is set to time engine100to start later.

Thus for the small amount of lift and the small working angle a larger engine starting threshold value is set than for the large amount of lift and the large working angle, and a range allowing the vehicle to travel as an EV can thus be increased. Impaired fuel efficiency can thus be reduced/prevented.

Thus, in the first embodiment, in starting engine100when intake valve118is lifted in a small amount and/or worked by a small working angle control unit200performs a process to increase a vehicular required power for starting engine100to be larger than when intake valve118is lifted in a large amount and/or worked by a large working angle.

When intake valve118is lifted in a small amount and/or worked by a small working angle engine100is started with higher torque response than when intake valve118is lifted in a large amount and/or worked by a large working angle. Accordingly, engine100can output a rapidly increasing torque to contribute to reducing an output of motor generator MG2. This allows engine100to be started with motor generator MG2consuming reduced electric power, which can provide a margin to electric power output by power storage device B and thus allows engine100to be timed to start later. As a result, travelling as an EV can be increased and impaired fuel efficiency can be reduced/prevented. Hybrid vehicle1having VVL device400for varying an actuation characteristic (i.e., an amount of lift and/or a working angle) of intake valve118, can thus reduce/prevent impaired fuel efficiency caused by starting engine100.

Furthermore, engine100started with high torque response can achieve a rapidly increasing rotational speed and accordingly have its operating point rapidly shifted to that allowing good fuel efficiency. This can prevent engine100from being operated at an operating point providing impaired fuel efficiency and thus allows hybrid vehicle1to achieve better fuel efficiency. Furthermore, as engine100can have a rotational speed increasing at an increased rate, engine100can provide a rapidly increasing power to contribute to enhanced acceleratability. Furthermore, when intake valve118is lifted in a large amount and/or worked by a large working angle, engine100is timed to start relatively early, and power storage device B can thus be prevented from outputting excessive electric power.

Furthermore, in the first embodiment, control device200performs the above process when engine100's start shock is permitted. This allows priority to be given to reducing/preventing impaired fuel efficiency, rather than reducing engine100's start shock. In contrast, when engine100's start shock is not permitted the above process is not performed. This allows priority to be given to reducing engine100's start shock.

Note that intake valve118may be lifted in an amount and worked by a working angle which vary steplessly or discretely (or in steps).

FIG. 13represents a relationship between the valve's displacement in amount and crank angle, as implemented by a VVL device400A that can vary intake valve118's actuation characteristic in three levels. VVL device400A is configured to be capable of varying the actuation characteristic to be any one of first to third characteristics. The first characteristic is represented by a waveform IN1a. The second characteristic is represented by a waveform IN2aand corresponds to a larger amount of lift and a larger working angle than the first characteristic. The third characteristic is represented by a waveform IN3aand corresponds to a larger amount of lift and a larger working angle than the second characteristic.

FIG. 14represents an operating line of an engine100A including VVL device400A having theFIG. 13actuation characteristic. InFIG. 14, the axis of abscissa represents the engine's rotational speed and the axis of ordinate represents engine torque. Note that inFIG. 14, alternate long and short dashed lines indicate torque characteristics corresponding to the first to third characteristics (IN1a-IN3a). Furthermore, inFIG. 14, a circle indicated by a solid line indicates an isometric fuel efficiency line. The isometric fuel efficiency line indicates connected points equal in fuel consumption, and a point closer to the center of the circle corresponds to more enhanced fuel efficiency. Engine100A is basically operated on an engine operating line indicated inFIG. 14by a solid line, for the sake of illustration.

Herein, a range R1indicates a low rotational speed range, for which reducing a shock caused when the engine starts is important. Furthermore, exhaust gas recirculation (EGR) is ceased and the Atkinson cycle is applied for enhanced fuel efficiency. To do so, the third characteristic (IN3a) is selected as the actuation characteristic of intake valve118to provide an increased amount of lift and an increased working angle. A range R2indicates a medium rotational speed range, for which the EGR is applied to introduce exhaust gas in an increased amount for enhanced fuel efficiency. To do so, the second characteristic (IN2a) is selected as the actuation characteristic of intake valve118to provide an intermediate amount of lift and an intermediate working angle.

In other words, when intake valve118is lifted in a large amount and worked by a large working angle (i.e., the third characteristic is selected), enhancing fuel efficiency via the Atkinson cycle, rather than via the EGR, is prioritized. In contrast, when a medium amount of lift and a medium working angle are selected (i.e., the second characteristic is selected), enhancing fuel efficiency via the EGR, rather than via the Atkinson cycle, is prioritized.

A range R3indicates a high rotational speed range, for which intake inertia is exploited to introduce a large amount of air into the cylinder to provide an increased actual compression ratio for better output performance. To do so, the third characteristic (IN3a) is selected as the actuation characteristic of intake valve118to provide an increased amount of lift and an increased working angle.

When engine100A is operated in the low rotational speed range at a large load; engine100A is started at cryogenic temperature; or a catalyst is warmed up, the first characteristic (IN1a) is selected as the actuation characteristic of intake valve118to provide a reduced amount of lift and a reduced working angle. Thus an amount of lift and a working angle are determined depending on how engine100A is operated.

FIG. 15is a flowchart for illustrating a process that control device200A that controls VVL device400A having theFIG. 13actuation characteristic follows to perform a start control. With reference toFIG. 15, S100-S120and S140-S160are similar to theFIG. 11flowchart, and accordingly, will not be described repeatedly.

In S110if it is determined that the engine start shock is permitted (YES in S110), control device200A determines whether intake valve118's actuation characteristic is the first characteristic (S135).

If it is determined that intake valve118's actuation characteristic is not the first characteristic (NO in S135), control device200A sets the engine starting threshold value to prescribed value X (S120). If it is determined that intake valve118's actuation characteristic is the first characteristic (YES in S135), control device200A sets the engine starting threshold value to prescribed value Y larger than prescribed value X (S140).

This allows intake valve118to be lifted in an amount and worked by a working angle that are limited to three actuation characteristics, and engine100A's operation state can be controlled via a control parameter adapted in a period of time shorter than required when intake valve118is lifted in a steplessly varying amount and worked by a steplessly varying working angle. Furthermore, a torque that an actuator requires to vary the amount of lifting intake valve118and the working angle on intake valve118can be reduced and the actuator can thus be reduced in size and weight. The actuator can thus be produced at a reduced cost.

FIG. 16represents a relationship between the valve's displacement in amount and crank angle, as implemented by a VVL device400B that can vary intake valve118's actuation characteristic in two levels. VVL device400B is configured to be capable of varying the actuation characteristic to be any one of first and second characteristics. The first characteristic is represented by a waveform IN1b. The second characteristic is represented by a waveform IN2band corresponds to a larger amount of lift and a larger working angle than the first characteristic.

This allows intake valve118to be lifted in an amount and worked by a working angle that are limited to two actuation characteristics, and engine100's operation state can be controlled via a control parameter adapted in a further shorter period of time. Furthermore, the actuator is allowed to have a simpler configuration. Note that intake valve118may not be lifted in an amount or worked by a working angle that are limited to an actuation characteristic varying between two or three levels, and intake valve118may be lifted in an amount or worked by a working angle with an actuation characteristic varying between four or more levels.

Second Embodiment

In the present embodiment, in starting engine100when intake valve118is lifted in a small amount and/or worked by a small working angle a rate applied to increase motor generator MG1's rotational speed is increased to be a rate higher than when intake valve118is lifted in a large amount and/or worked by a large working angle.

FIG. 17is a flowchart for illustrating a process that a control device200B of the present invention in the second embodiment follows to perform a start control. Note that the remainder in configuration of control device200B according to the second embodiment is similar to that according to the first embodiment.

With reference toFIG. 17, S100-S120, S130-S140, and S150-S160are similar to the first embodiment, and accordingly, will not be described repeatedly. In S120, the engine starting threshold value is set to prescribed value X, and in response, control device200B sets to a prescribed value S a rate applied to increase motor generator MG1's rotational speed (S125).

In S140, the engine starting threshold value is set to prescribed value Y, and in response, control device200B sets to a prescribed value T larger than prescribed value S a rate applied to increase motor generator MG1's rotational speed (S145). Note that prescribed values S and T are values set depending on a rate applied in starting engine100to increase motor generator MG1's rotational speed. More specifically, engine100has an output shaft coupled with a shaft of rotation of motor generator MG1, and accordingly, prescribed values S and T are set to avoid preventing the engine's rotational speed from increasing.

When intake valve118is lifted in a small amount and worked by a small working angle, high engine torque response is provided and the engine's rotational speed rapidly increases, and accordingly, prescribed value T is set to be a value larger than prescribed value S. Control device200B in starting engine100controls motor generator MG1according to a rate, as set, applied to increase motor generator MG1's rotational speed.

Thus, in the second embodiment, in starting engine100when intake valve118is lifted in a small amount and/or worked by a small working angle control device200B controls motor generator MG1to increase a rate that is applied to increase motor generator MG1's rotational speed to be a rate higher than when intake valve118is lifted in a large amount and/or worked by a large working angle. Increasing the rate applied to increase motor generator MG1's rotational speed can reduce/prevent preventing engine100's rotational speed from increasing.

Third Embodiment

A third embodiment will be described for varying an amount of lifting intake valve118and a working angle on intake valve118after starting engine100is started.

FIG. 18is a flowchart for illustrating a process that a control device200C of the present invention in the third embodiment follows to perform a start control. Note that the remainder in configuration of control device200C according to the third embodiment is similar to that according to the first embodiment.

With reference toFIG. 18, control device200C in S200determines whether the engine is currently being started. Note that the engine being currently being started means a period of time after cranking engine100is started before engine100is operated at a desired operating point, under an engine start control.

If it is determined that the engine is currently not being started (NO in S200), the subsequent steps are not performed the control returns to the main routine. If it is determined that the engine is currently being started (YES in S200), control device200C determines whether the engine start shock is permitted (S210).

If it is determined that the engine start shock is not permitted (NO in S210), control device200C sets to prescribed value S a rate applied to increase motor generator MG1's rotational speed (S220). If it is determined that the engine start shock is permitted (YES in S210), control device200C determines whether intake valve118is lifted in a small amount and worked by a small working angle (S230).

If it is determined that intake valve118is lifted in a large amount and worked by a large working angle (NO in S230), control device200C sets to prescribed value S the rate applied to increase motor generator MG1's rotational speed (S220). If it is determined that intake valve118is lifted in a small amount and worked by a small working angle (YES in S230), control device200C sets to prescribed value T larger than prescribed value S the rate applied to increase motor generator MG1's rotational speed (S240).

Control device200C in starting engine100controls motor generator MG1according to a rate, as set, applied to increase motor generator MG1's rotational speed.

FIG. 19is timing plots for illustrating how control device200C of the present invention in the third embodiment performs a start control. InFIG. 19, the axis of abscissa represents time and the axis of ordinate represents vehicular required power, the output of power storage device B, the engine's output, the engine's rotational speed, the rate applied to increase motor generator MG1's rotational speed, and the amount of lifting intake valve118and the working angle on intake valve118.

With reference toFIG. 19, at time t3engine100is stopped and a large amount of lifting intake valve118and a large working angle on intake valve118are applied for the sake of illustration. At time t4, vehicular required power exceeds the engine starting threshold value (of prescribed value X), and accordingly, starting engine100starts. As starting engine100is started with intake valve118lifted in the large amount and worked by the large working angle, the engine's output and rotational speed gradually increase.

At time t5, when the amount of lifting intake valve118and the working angle on intake valve118are varied to be small, enhanced engine torque response is provided, and accordingly, a rate applied to increase motor generator MG1's rotational speed is set to be high. This steeply increases the engine's output and rotational speed.

Thus, in the third embodiment, in starting engine100when at least one of the amount of lifting intake valve118and the working angle on intake valve118is varied to be small control device200C controls motor generator MG1to increase a rate that is applied to increase motor generator MG1's rotational speed to be a rate higher than that applied when intake valve118is lifted in a large amount and/or worked by a large working angle. Starting engine100with at least one of the amount of lifting the intake valve and the working angle on the intake valve varied to be small, and accordingly, increasing a rate applied to increase motor generator MG1's rotational speed, can reduce/prevent preventing engine100's rotational speed from increasing.

While the above embodiments have been described for a case with the amount of lifting intake valve118and the working angle on intake valve118both varied, the present invention is also applicable to a case with the amount of lifting intake valve118alone varied and a case with the working angle on intake valve118alone varied. A configuration that can vary either the amount of lifting intake valve118or the working angle on intake valve118can be as effective as that which can vary both the amount of lifting intake valve118and the working angle on intake valve118. Note that the configuration that can vary either the amount of lifting intake valve118or the working angle on intake valve118can be implemented via well known technology.

While the above embodiments have been described in connection with a series/parallel type hybrid vehicle capable of splitting the motive power of engine100by power split device4and thus transmitting the split motive power to driving wheel6and motor generators MG1and MG2, the present invention is also applicable to hybrid vehicles of other types. More specifically, the present invention is for example also applicable to a so-called series type hybrid vehicle that uses engine100only to drive motor generator MG1and generates vehicular driving force only by motor generator MG2, a hybrid vehicle recovering only regenerated energy of kinetic energy that is generated by engine100as electrical energy, a motor-assisted hybrid vehicle using an engine as a main driving force source and assisted by a motor as required, and the like. Furthermore, the present invention is also applicable to a hybrid vehicle which allows a motor to be disconnected and travels by the driving force of the engine alone.

Note that, in the above, engine100corresponds in the present invention to one embodiment of an internal combustion engine and motor generator MG2corresponds in the present invention to one embodiment of a first rotating electric machine. Furthermore, motor generator MG1corresponds in the present invention to one embodiment of a second rotating electric machine and VVL device400corresponds in the present invention to one embodiment of a variable valve actuation device. Furthermore, in the present invention, “when a first state is selected” indicates intake valve118being lifted in a small amount and/or worked by a small working angle, and “when a second state is selected” indicates intake valve118being lifted in a large amount and/or worked by a large working angle.

While the present invention has thus been described in embodiments, the embodiments may be combined in configuration, as appropriate.