Hybrid vehicle and control method of the same

In a hybrid vehicle 20, when a deceleration demand based on accelerator-off is made in selecting an S position that allows arbitrary selection of shift positions SP1 to SP6, and fuel cut cannot be prohibited from a state of a battery 50, an engine 22 and motors MG1 and MG2 are controlled so that a driving force based on a torque demand Tr* is outputted with the fuel cut (Steps S410, S420, S360 to S400). When the deceleration demand based on the accelerator-off is made in selecting the S position, and the fuel cut can be prohibited from the state of the battery 50, the engine 22 and the motors MG1 and MG2 are controlled so that the engine 22 substantially performs self-sustaining operation at a target rotation speed Ne0 and a driving force based on the torque demand Tr* is outputted (Steps S340 to S400).

TECHNICAL FIELD

The present invention relates to a hybrid vehicle and control method of the hybrid vehicle.

BACKGROUND ART

A conventionally known hybrid vehicle includes a motor generator placed between a torque converter that transmits power of an internal combustion engine to a drive shaft and an automatic transmission (for example, see Patent Document 1). In this hybrid vehicle, control is performed to prevent fuel cut of the internal combustion engine when it is determined that a temperature of a catalyst is higher than a predetermined criterion value in order to prevent degradation of the catalyst caused by being exposed to lean atmosphere at high temperatures. When a deceleration demand based on accelerator-off is made but the fuel cut is prohibited from a temperature state of the catalyst, a regenerative braking force is generated by a motor generator and regenerative electric power is accumulated in an accumulator unit such as a secondary battery in order to compensate for a reduction in the degree of deceleration caused by the prohibition of the fuel cut. In the hybrid vehicle, if there is a possibility that the regenerative electric power by the motor generator is not accumulated in the accumulator unit according to a state of the accumulator unit when the catalyst is at a high temperature and the deceleration demand based on accelerator-off is made, a required braking force is generated by a hydraulic brake instead of the regenerative braking force by the motor generator. In a vehicle which has an internal combustion engine as an only driving source and an automatic transmission with a manual transmission mode as an option, known techniques relating to the fuel cut include a technique of reducing a fuel cut rotation speed in selecting the manual transmission mode as compared with in selecting an automatic transmission mode (for example, see Patent Document 2), and a technique of increasing a fuel cut return rotation speed for restarting fuel supply in selecting the manual transmission mode as compared with in selecting an automatic transmission mode (for example, see Patent Document 3), in terms of making a so-called engine brake more effective, improving fuel consumption, or improving riding comfort or driving feeling.

DISCLOSURE OF THE INVENTION

In the above described hybrid vehicle, the internal combustion engine can be operated at an arbitrary operation point. Thus, in recent years, to meet various needs of drivers, it has been proposed to apply, to a hybrid vehicle, a shift device that can arbitrarily set a desired operation condition among a plurality of operation conditions that define, in different manners, settable ranges of a required driving force required for driving and operation point constraints for determining a target rotation speed of an internal combustion engine corresponding to the required driving force, by changing shift positions. Such a shift device is applied to the hybrid vehicle, and a rotation speed of the internal combustion engine with fuel cut at the time of a deceleration demand such as in an accelerator-off state is changed, and thus a braking force corresponding to the selected shift position can be generated by an engine brake. However, when a driver is allowed to select an arbitrary shift position (operation condition), fuel cut may be frequently performed unless the fuel cut is prohibited according to a state of a catalyst. If the fuel cut is frequently performed, a large amount of air is fed to an exhaust gas purifying catalyst, and thus oxygen may attach to the catalyst to reduce NOx purifying performance of the catalyst.

Thus, a hybrid vehicle and a control method thereof according to the present invention has an object to prevent a reduction in purifying performance of an exhaust gas purifying catalyst when arbitrary selection of an operation condition that defines a settable range of a required driving force required for driving is allowed. The hybrid vehicle and the control method thereof according to the present invention has another object to satisfactorily prevent a reduction in purifying performance of the exhaust gas purifying catalyst to improve emission.

At least part of the above and the other related demands is attained by a hybrid vehicle and control method of the hybrid vehicle having the configurations discussed below.

The present invention is directed to a hybrid vehicle including: an internal combustion engine; a purifying unit including a catalyst for purifying exhaust gas exhausted from the internal combustion engine; and electric power-mechanical power input output mechanism that is connected to a first axle that is any one of axles and an output shaft of the internal combustion engine and can input and output power to the first axle and the output shaft with input and output of electric power and mechanical power; an electric motor that can input and output power to the first axle or a second axle that is any one of axles different from the first axle; an accumulator unit that can supply and receive electric power to and from the electric power-mechanical power input output mechanism and the electric motor; a fuel supply stop determination module that determines whether a stop of fuel supply to the internal combustion engine can be prohibited based on a state of the accumulator unit; an operation condition setting module that sets any one of a plurality of operation conditions that define, in different manners, settable ranges of a required driving force at least required for driving as an operation condition for execution, and allows a driver to select an arbitrary operation condition under a predetermined condition; a required driving force setting module that sets the required driving force according to the set operation condition for execution; and a control unit that controls the internal combustion engine, the electric power-mechanical power input output mechanism, and the electric motor so that a driving force based on the set required driving force is outputted with the stop of the fuel supply, when a deceleration demand is made in a state where the operation condition setting module allows selection of the arbitrary operation condition, and the fuel supply stop determination module determines that the stop of the fuel supply cannot be prohibited, and controls the internal combustion engine, the electric power-mechanical power input output mechanism, and the electric motor so that the internal combustion engine substantially performs self-sustaining operation at a predetermined rotation speed and a driving force based on the set required driving force is outputted, when the deceleration demand is made and the fuel supply stop determination module determines that the stop of the fuel supply can be prohibited.

In the hybrid vehicle, the driver can arbitrarily select any one of the plurality of operation conditions that define the settable ranges of the required driving force at least required for driving under the predetermined condition. When the deceleration demand is made in the state where the driver is allowed to select the arbitrary operation condition, and the stop of the fuel supply to the internal combustion engine cannot be prohibited from the state of the accumulator unit, the internal combustion engine, the electric power-mechanical power input output mechanism, and the electric motor are controlled so that the driving force based on the set required driving force is outputted with the stop of the fuel supply to the internal combustion engine. When the deceleration demand is made in the state where the driver is allowed to select the arbitrary operation condition, and the stop of the fuel supply to the internal combustion engine can be prohibited from the state of the accumulator unit, the internal combustion engine, the electric power-mechanical power input output mechanism, and the electric motor are controlled so that the internal combustion engine substantially performs the self-sustaining operation at the predetermined rotation speed and the driving force based on the set required driving force is outputted. Specifically, in the state where the driver is allowed to select the arbitrary operation condition, the fuel supply is easily stopped when the deceleration demand is made from the relationship with the required driving force based on the selected operation condition. Without any measure, the stop of the fuel supply causes a large amount of air to be fed to the exhaust gas purifying catalyst, and oxygen may attach to the catalyst to reduce purifying performance. Thus, when the deceleration demand is made in the state where the driver is allowed to select the arbitrary operation condition, the driving force based on the required driving force is obtained with the substantial self-sustaining operation of the internal combustion engine without the stop of the fuel supply, except the case where the stop of the fuel supply to the internal combustion engine has to be prohibited from the state of the accumulator unit. This can prevent a reduction in purifying performance of the catalyst caused by the stop of the fuel supply, and thus improve emission. The substantial self-sustaining operation of the internal combustion engine includes operation without an output of power (torque) from the internal combustion engine, and operation with a slight output of power (torque) from the internal combustion engine.

In one preferable embodiment of the hybrid vehicle of the invention, the deceleration demand includes a deceleration demand due to an accelerator operation state being an accelerator-off state, and a deceleration demand due to the accelerator operation state staying in an accelerator-on state and an accelerator opening being reduced. When these deceleration demands are made, the fuel supply to the internal combustion engine is generally stopped. In such a case, the driving force (braking force) based on the required driving force is obtained with the substantial self-sustaining operation of the internal combustion engine without the stop of the fuel supply, except the case where the stop of the fuel supply to the internal combustion engine has to be prohibited from the state of the accumulator unit. This can prevent a reduction in purifying performance of the catalyst, and thus improve emission.

In another preferable embodiment of the hybrid vehicle of the invention, the fuel supply stop determination module determines that the stop of the fuel supply can be prohibited when an amount of charge left in the accumulator unit is a predetermined upper limit value or less, or when charge allowable electric power that is electric power allowed for charging the accumulator unit and is set based on the state of the accumulator unit is a predetermined charge limit value or less. This allows more proper determination of whether the stop of the fuel supply to the internal combustion engine can be prohibited based on the state of the accumulator unit.

In still another preferable embodiment of the hybrid vehicle of the invention, the upper limit value and the charge limit value is determined based on electric power inputted and outputted by the electric power-mechanical power input output mechanism and the electric motor when the required driving force at the time of the deceleration demand is obtained with the substantial self-sustaining operation of the internal combustion engine without the stop of the fuel supply. The upper limit value and the charge limit value as thresholds are thus determined to allow the prohibition of the stop of the fuel supply to the internal combustion engine to be canceled at appropriate timing and prevent degradation by overcharge of the accumulator unit.

In still another preferable embodiment of the hybrid vehicle of the invention, the operation condition setting module is a shift setting module that sets a shift position for execution among a plurality of shift positions according to a driver's shift operation, the plurality of operation conditions correspond to the plurality of shift positions, and the plurality of shift positions include a sequential shift position that allows the driver to select an arbitrary shift position.

In still another preferable embodiment of the hybrid vehicle of the invention, an operation condition that the driver is allowed to select when the sequential shift position is selected defines a settable range of the required driving force and an operation point constraint for determining a target rotation speed of the internal combustion engine corresponding to the required driving force, and the control unit controls the internal combustion engine, the electric power-mechanical power input output mechanism, and the electric motor so that the internal combustion engine is operated at the target rotation speed set based on the operation point constraint and a driving force based on the set required driving force is outputted with the stop of the fuel supply, when the deceleration demand is made and the fuel supply stop determination module determines that the stop of the fuel supply cannot be prohibited.

In still another preferable embodiment of the hybrid vehicle of the invention, the electric power-mechanical power input output mechanism includes a three shaft-type power input output module that is connected to the first axle, the output shaft of the internal combustion engine, and a rotatable third shaft, and inputs and outputs power determined based on power inputted and outputted to any two shafts among the three shafts to a remaining shaft, and a generator that can input and output power to the third shaft.

The present invention is also directed to a control method of a hybrid vehicle including: an internal combustion engine; a purifying unit including a catalyst for purifying exhaust gas exhausted from the internal combustion engine; an electric power-mechanical power input output mechanism that is connected to a first axle that is any one of axles and an output shaft of the internal combustion engine and can input and output power to the first axle and the output shaft with input and output of electric power and mechanical power; an electric motor that can input and output power to the first axle or a second axle that is any one of axles different from the first axle; an accumulator unit that can supply and receive electric power to and from the electric power-mechanical power input output mechanism and the electric motor; and an operation condition setting module that sets any one of a plurality of operation conditions that define, in different manners, driving force setting constraints for determining ranges of a required driving force at least required for driving as an operation condition for execution, and allows a driver to select an arbitrary operation condition under a predetermined condition. The control method including the step of: (a) controlling the internal combustion engine, the electric power-mechanical power input output mechanism, and the electric motor so that a driving force based on the required driving force set according to the set operation condition for execution is outputted with the stop of the fuel supply to the internal combustion engine, when a deceleration demand is made in a state where the operation condition setting module allows selection of the arbitrary operation condition, and the stop of the fuel supply to the internal combustion engine cannot be prohibited from a state of the accumulator unit, and controlling the internal combustion engine, the electric power-mechanical power input output mechanism, and the electric motor so that the internal combustion engine substantially performs self-sustaining operation at a predetermined rotation speed and a driving force based on the required driving force set according to the set operation condition for execution is outputted, when the deceleration demand is made and the stop of the fuel supply can be prohibited from the state of the accumulator unit.

When the driver can arbitrarily select any one of the plurality of operation conditions that define the settable range of the required driving force at least required for driving as in the hybrid vehicle to which the method is applied, in the state where the driver is allowed to select the arbitrary operation condition, the fuel supply is easily stopped when the deceleration demand is made from the relationship with the required driving force based on the selected operation condition. The stop of the fuel supply causes a large amount of air to be fed to the exhaust gas purifying catalyst, and oxygen may attach to the catalyst to reduce purifying performance. Thus, as in the method, when the deceleration demand is made in the state where the driver is allowed to select the arbitrary operation condition, the driving force based on the required driving force is obtained with the substantial self-sustaining operation of the internal combustion engine without the stop of the fuel supply, except the case where the stop of the fuel supply to the internal combustion engine has to be prohibited from the state of the accumulator unit. This can prevent a reduction in purifying performance of the catalyst, and thus improve emission.

In one preferable embodiment of the control method of the hybrid vehicle of the invention, the deceleration demand includes a deceleration demand due to an accelerator operation state being an accelerator-off state, and a deceleration demand due to the accelerator operation state staying in an accelerator-on state and an accelerator opening being reduced.

In another preferable embodiment of the control method of the hybrid vehicle of the invention, the control method further including the step of: (b) determining whether the stop of the fuel supply to the internal combustion engine can be prohibited based on the state of the accumulator unit, and the step (b) includes determining that the stop of the fuel supply can be prohibited when an amount of charge left in the accumulator unit is a predetermined upper limit value or less, or when charging allowable electric power that is electric power allowed for charging the accumulator unit and is set based on the state of the accumulator unit is a predetermined charge limit value or less.

In still another preferable embodiment of the control method of the hybrid vehicle of the invention, the upper limit value and the charge limit value are determined based on electric power inputted and outputted by the electric power-mechanical power input output mechanism and the electric motor when the required driving force at the time of the deceleration demand is obtained with the substantial self-sustaining operation of the internal combustion engine without the stop of the fuel supply.

In still another preferable embodiment of the control method of the hybrid vehicle of the invention, the operation condition setting module is a shift setting module that sets a shift position for execution among a plurality of shift positions according to a driver's shift operation, the plurality of operation conditions correspond to the plurality of shift positions, and the plurality of shift positions include a sequential shift position that allows the driver to select an arbitrary shift position.

In still another preferable embodiment of the control method of the hybrid vehicle of the invention, an operation condition that the driver is allowed to select when the sequential shift position is selected defines a settable range of the required driving force and an operation point constraint for determining a target rotation speed of the internal combustion engine corresponding to the required driving force, and the step (a) includes controlling the internal combustion engine, the electric power-mechanical power input output mechanism, and the electric motor so that the internal combustion engine is operated at the target rotation speed set based on the operation point constraint and a driving force based on the set required driving force is outputted with the stop of the fuel supply, when the deceleration demand is made and the fuel supply stop determination module determines that the stop of the fuel supply cannot be prohibited.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the best mode for carrying out the present invention will be described by an embodiment.

FIG. 1is a schematic block diagram of a hybrid vehicle according to an embodiment of the present invention. The hybrid vehicle20inFIG. 1includes an engine22, a three shaft-type power distribution and integration mechanism30connected to a crankshaft26as an output shaft of the engine22via a damper28, a motor MG1that is connected to the power distribution and integration mechanism30and can generate electric power, a reduction gear35mounted to a ring gear shaft32aas a drive shaft connected to the power distribution and integration mechanism30, a motor MG2connected to the reduction gear35, and a hybrid electronic control unit (hereinafter referred to as a hybrid ECU)70that controls the entire power output device.

The engine22is configured as an internal combustion engine that can output power using hydrocarbon fuel such as gasoline or gas oil. As is seen fromFIG. 2, in the engine22, air cleaned by an air cleaner122is taken into an intake port via a throttle valve124and gasoline is injected from a fuel injection valve126to mix intake air and gasoline, the air/fuel mixture is sucked into a combustion chamber via an intake valve128and fired by electric spark from an ignition plug130, and reciprocating motion of a piston132pushed down by energy of the firing is converted into rotation motion of the crankshaft26. Exhaust gas from the engine22is exhausted to the outside via a purifying device134including an exhaust gas purifying catalyst (three way catalyst) for purifying harmful components such as carbon monoxide (CO), hydrocarbon (HC), or nitrogen oxides (NOx). The exhaust gas purifying catalyst in the purifying device134is preferably constituted by an oxidation catalyst such as platinum (Pt) or palladium (Pd), a reduction catalyst such as rhodium (Rh), and a promoter such as ceria (CeO2). In this case, CO or HC contained in exhaust gas is cleaned into water (H2O) or carbon dioxide (CO2) by the action of the oxidation catalyst, and NOx contained in the exhaust gas is cleaned into nitrogen (N2) or oxygen (O2) by the action of the reduction catalyst.

The engine22thus configured is controlled by an engine electronic control unit (hereinafter referred to as an engine ECU)24. As shown inFIG. 2, the engine ECU24is configured as a microprocessor mainly including a CPU24a, a ROM24bthat stores a processing program, a RAM24cthat temporarily stores data, and unshown input and output ports and communication ports. To the engine ECU24, for example, a crank position from a crank position sensor140that detects a rotational position of the crankshaft26, cooling water temperature from a water temperature sensor142that detects temperature of cooling water of the engine22, pressure in a cylinder from a pressure sensor143for detecting pressure in a cylinder that is pressure in a combustion chamber, a cam position from a cam position sensor144that detects a rotational position of a cam shaft that opens and closes the intake valve128and an exhaust valve that supply and exhaust air to and from the combustion chamber, a throttle position from a throttle valve position sensor146for detecting a position of the throttle valve124, a signal from an airflow meter148provided in an intake pipe, intake air temperature from a temperature sensor149also provided in the intake pipe, and a catalyst floor temperature Tcat from a temperature sensor135provided in the purifying device134are input via the input port. From the engine ECU24, various control signals for driving the engine22, for example, a drive signal to the fuel injection valve126, a drive signal to a throttle motor136that adjusts the position of the throttle valve124, a control signal to an ignition coil138integrated with an igniter, and a control signal to a variable valve timing mechanism150that can change opening and closing timing of the intake valve128are output via the output port. The engine ECU24communicates with the hybrid electronic control unit70, and controls operation of the engine22by a control signal from the hybrid ECU70and outputs data on an operation state of the engine22to the hybrid ECU70as required.

The power distribution and integration mechanism30has a sun gear31that is an external gear, a ring gear32that is an internal gear and is arranged concentrically with the sun gear31, multiple pinion gears33that engage with the sun gear31and with the ring gear32, and a carrier34that holds the multiple pinion gears33in such a manner as to allow free revolution thereof and free rotation thereof on the respective axes. Namely the power distribution and integration mechanism30is constructed as a planetary gear mechanism that allows for differential motions of the sun gear31, the ring gear32, and the carrier34as rotational elements. The carrier34, the sun gear31, and the ring gear32in the power distribution and integration mechanism30are respectively coupled with the crankshaft26of the engine22, the motor MG1, and the reduction gear35via ring gear shaft32a. While the motor MG1functions as a generator, the power output from the engine22and input through the carrier34is distributed into the sun gear31and the ring gear32according to the gear ratio. While the motor MG1functions as a motor, on the other hand, the power output from the engine22and input through the carrier34is combined with the power output from the motor MG1and input through the sun gear31and the composite power is output to the ring gear32. The power output to the ring gear32is thus finally transmitted to the driving wheels63aand63bvia the gear mechanism60, and the differential gear62from ring gear shaft32a.

Both the motors MG1and MG2are known synchronous motor generators that are driven as a generator and as a motor. The motors MG1and MG2transmit electric power to and from a battery50via inverters41and42. Power lines54that connect the inverters41and42with the battery50are constructed as a positive electrode bus line and a negative electrode bus line shared by the inverters41and42. This arrangement enables the electric power generated by one of the motors MG1and MG2to be consumed by the other motor. The battery50is charged with a surplus of the electric power generated by the motor MG1or MG2and is discharged to supplement an insufficiency of the electric power. When the power balance is attained between the motors MG1and MG2, the battery50is neither charged nor discharged. Operations of both the motors MG1and MG2are controlled by a motor electronic control unit (hereafter referred to as motor ECU)40. The motor ECU40receives diverse signals required for controlling the operations of the motors MG1and MG2, for example, signals from rotational position detection sensors43and44that detect the rotational positions of rotors in the motors MG1and MG2and phase currents applied to the motors MG1and MG2and measured by current sensors (not shown). The motor ECU40outputs switching control signals to the inverters41and42. The motor ECU40communicates with the hybrid ECU70to control operations of the motors MG1and MG2in response to control signals transmitted from the hybrid ECU70while outputting data relating to the operating conditions of the motors MG1and MG2to the hybrid ECU70according to the requirements.

The battery50is under control of a battery electronic control unit (hereafter referred to as battery ECU)52. The battery ECU52receives diverse signals required for control of the battery50, for example, an inter-terminal voltage measured by a voltage sensor (not shown) disposed between terminals of the battery50, a charge-discharge current measured by a current sensor (not shown) attached to the power line54connected with the output terminal of the battery50, and a battery temperature Tb measured by a temperature sensor51attached to the battery50. The battery ECU52outputs data relating to the state of the battery50to the hybrid ECU70or the engine ECU24via communication according to the requirements. The battery ECU52calculates a state of charge (SOC) of the battery50, based on the accumulated charge-discharge current measured by the current sensor, for control of the battery50.

The hybrid ECU70is constructed as a microprocessor including a CPU72, a ROM74that stores processing programs, a RAM76that temporarily stores data, and a non-illustrated input-output port, and a non-illustrated communication port. The hybrid ECU70receives various inputs via the input port: an ignition signal from an ignition switch80, a gearshift position SP from a gearshift position sensor82that detects the current position of a gearshift lever81, an accelerator opening Acc from an accelerator pedal position sensor84that measures a step-on amount of an accelerator pedal83, a brake pedal position BP from a brake pedal position sensor86that measures a step-on amount of a brake pedal85, and a vehicle speed V from a vehicle speed sensor88. The hybrid ECU70communicates with the engine ECU24, the motor ECU40, and the battery ECU52via the communication port to transmit diverse control signals and data to and from the engine ECU24, the motor ECU40, and the battery ECU52, as mentioned previously.

In the hybrid vehicle20in the embodiment, shift positions SP of a shift lever81includes a parking position used in parking, a reverse position for backward driving, a neutral position, and a normal drive position for forward driving (hereinafter referred to as a D position), and further includes a sequential shift position (hereinafter referred to as an S position), an up-shift indication position, and a down-shift indication position. When the D position is selected as a shift position SP, the hybrid vehicle20in the embodiment is driven and controlled so that the engine22is efficiently operated. When the S position is selected as a shift position SP, a ratio of a rotation speed of the engine22to a vehicle speed V can be changed, for example, in six stages (SP1to SP6) mainly in deceleration. In the embodiment, when the driver sets the shift lever81in the S position, the shift position SP is set to SP5in a fifth stage, and a shift position sensor82detects that the shift position SP is SP5. Thereafter, when the shift lever81is set to the up-shift indication position, the shift position SP is shifted up one stage a time, while when the shift lever81is set to the down-shift indication position, the shift position SP is shifted down one stage at a time, and the shift position sensor82outputs the present shift position SP according the operation of the shift lever81.

In the hybrid vehicle20thus configured according to the embodiment, operation of the engine22and the motors MG1and MG2is controlled so that a torque demand Tr* to be outputted to the ring gear shaft32aas the drive shaft is calculated based on the accelerator opening Acc corresponding to the depression amount of the accelerator pedal83by the driver and the vehicle speed V, and power corresponding to the torque demand Tr* is outputted to the ring gear shaft32a. Operation control modes of the engine22and the motors MG1and MG2include: a torque conversion operation mode in which the operation of the engine22is controlled so that power corresponding to the power demand is outputted from the engine22, and the motor MG1and the motor MG2are driven and controlled so that all of the power outputted from the engine22is torque converted by the power distribution and integration mechanism30and the motors MG1and MG2and outputted to the ring gear shaft32a; a charge-discharge operation mode in which the operation of the engine22is controlled so that power corresponding to the sum of the power demand and electric power required for charging and discharging the battery50is outputted from the engine22, and the motor MG1and the motor MG2are driven and controlled so that all or part of the power outputted from the engine22with the charge and discharge of the battery50is torque converted by the power distribution and integration mechanism30and the motors MG1and MG2, and the power demand is outputted to the ring gear shaft32a; and a motor operation mode in which operation is controlled so that the operation of the engine22is stopped and power corresponding to the power demand is outputted from the motor MG2to the ring gear shaft32a.

Next, operation of the hybrid vehicle20in the embodiment, particularly, operation of the hybrid vehicle20when the driver selects the S position as the shift position SP will be described. Operation of the hybrid vehicle20in selecting the S position will be herein described for the case where the accelerator operation state is the accelerator-on state and the case where the accelerator operation state is the accelerator-off state.

FIG. 3is a flowchart showing an example of a drive control routine performed by the hybrid ECU70when the driver selects the S position as the shift position SP, and the accelerator operation state is the accelerator-on state. This routine is repeatedly performed every predetermined time (for example, every few milliseconds) when the accelerator operation state is the accelerator-on state. When the drive control routine inFIG. 3is started, the CPU72of the hybrid ECU70first performs a processing for inputting data required for control such as the accelerator opening Acc from the accelerator pedal position sensor84, the vehicle speed V from the vehicle speed sensor88, rotation speeds Nm1and Nm2of the motors MG1and MG2, the shift position SP from the shift position sensor82, charge-discharge power demand Pb* to be charged and discharged by the battery50, the state of charge (SOC) of the battery50, and the input and output limits Win and Wout of the battery50(Step S100). In this case, the rotation speeds Nm1and Nm2of the motors MG1and MG2calculated based on rotational positions of rotors of the motors MG1and MG2detected by the rotational position detection sensors43and44are inputted from the motor ECU40by communication. The charge-discharge power demand Pb* and the state of charge (SOC) are inputted from the battery ECU52by communication. The input limit Win as charging allowable electric power that is electric power allowed for charging the battery50and the output limit Wout as discharging allowable electric power that is electric power allowed for discharging the battery50set based on the battery temperature Tb of the battery50detected by the temperature sensor51and the state of charge SOC of the battery50are inputted from the battery ECU52by communication. The input and output limits Win and Wout of the battery50can be set in such a manner that basic values of the input and output limits Win and Wout are set based on the battery temperature Tb, an output limit correction coefficient and an input limit correction coefficient are set based on the state of charge (SOC) of the battery50, and the set basic values of the input and output limits Win and Wout are multiplied by the correction coefficients.FIG. 4illustrates an example of a relationship between the battery temperature Tb and the input and output limits Win and Wout, andFIG. 5illustrates an example of a relationship between the state of charge (SOC) of the battery50and the correction coefficients of the input and output limits Win and Wout.

After the data input processing in Step S100, the torque demand Tr* to be outputted to the ring gear shaft32aas the drive shaft connected to the drive wheels63aand63b, and the power demand P* required for the entire vehicle in driving are set based on the inputted accelerator opening Acc, vehicle speed V and shift position SP (Step S110). In the embodiment, a relationship between the accelerator opening Acc, the vehicle speed V and the shift position SP, and the torque demand Tr* are previously determined and stored in the ROM74as a torque demand setting map that defines a settable range of a required driving force, and when the acceleration opening Acc, the vehicle speed V and the shift position SP are provided, the torque demand Tr* corresponding thereto is derived from the map and set. In the embodiment, among the cases where the shift position SP is the D position and the shift positions SP1to SP6, the torque demand Tr* is set under the same constraint in the accelerator-on state, while the torque demand (braking torque) Tr* set at the accelerator opening Acc of 0% (accelerator-off) differs.FIG. 6shows an example of the torque demand setting map. In the embodiment, the power demand P* is set as the sum of the set torque demand Tr* multiplied by a rotation speed Nr (=Nm2/Gr) of the ring gear shaft32a, the charge-discharge power demand Pb* to be charged and discharged by the battery50, and a loss Loss.

Then, it is determined whether the set power demand P* is a predetermined threshold Pref or more (Step S120). The threshold Pref used herein is a lower limit or near the lower limit of power in a range that allows relatively efficient operation of the engine22, determined based on characteristics of the engine22and the motor MG2for determining whether power (torque) is to be outputted to the engine22. When it is determined in Step S120that the power demand P* is the threshold Pref or more, the power demand P* is outputted to the engine22, and a tentative target rotation speed Netmp and tentative-target torque Tetmp of the engine22are set based on the power demand P* (Step S130). Herein, the tentative target rotation speed Netmp and the tentative target torque Tetmp are set based on an operation line for efficiently operating the engine22and the power demand P*.FIG. 7shows an example of the operation line of the engine22and an example of a correlation curve between the tentative target rotation speed Netmp and the tentative target torque Tetmp. As shown inFIG. 7, the tentative target rotation speed Netmp and the tentative target torque Tetmp can be calculated from an intersection between the operation line and the correlation curve showing a constant power demand P* (Netmp×Tetmp). The tentative target rotation speed Netmp and the tentative target torque Tetmp are thus set, and then a lower limit engine rotation speed Nemin as a lower limit value of the rotation speed of the engine22is set based on the shift position SP inputted in Step S100(Step S140). The lower limit engine rotation speed Nemin is previously determined as a minimum rotation speed that allows a sufficiently broad range of increase and decrease of power from the engine22and allows quick increase and decrease of the power in order from the shift position SP1to the shift position SP6, and stored in ROM74. In the entire vehicle speed range or when the vehicle speed V is less than a predetermined value, the lower limit engine rotation speed Nemin may be determined based on the shift position SP and the vehicle speed V. In this case, a map for determining a relationship between the shift position SP, the vehicle speed V, and the lower limit engine rotation speed Nemin may be previously prepared and stored in the ROM74.

After the lower limit engine rotation speed Nemin is set, the lower limit engine rotation speed Nemin is compared with the tentative target rotation speed Netm set in Step S130(Step S150). When the tentative target rotation speed Netmp is the lower limit engine rotation speed Nemin or more, it is determined that the range of increase and decrease of the power from the engine22is sufficiently broad and quick increase and decrease of the power is allowed, the tentative target rotation speed Netmp set in Step S130is set as the target rotation speed Ne* of the engine22, and the tentative target torque Tetmp set in the Step S130is set as the target torque Te* of the engine22(Step S160). On the other hand, when the tentative target rotation speed Netmp is less than the lower limit engine rotation speed Nemin, the lower limit engine rotation speed Nemin set in Step S140is set as the target rotation speed Ne* of the engine22so that the range of increase and decrease of the power from the engine22becomes sufficiently broad and quick increase and decrease of the power is allowed, and the target torque Te* (P*/Ne*) of the engine22is calculated from the set target rotation speed Ne*(=Netmp) and the power demand P* and set as the target torque Te* of the engine22(Step S170). Thus, when the S position is selected as the shift position SP, the target rotation speed Ne* of the engine22is the lower limit rotation speed Nemin determined for each of the shift positions SP1to SP6or more, thereby allowing quick response to driver's acceleration and deceleration demand.

The target rotation speed Ne* and the target torque Te* of the engine22as engine commands are thus set, then a target rotation speed Nm1* of the motor MG1is calculated based on the set target rotation speed Ne*, the rotation speed Nr (=Nm2/Gr) of the ring gear shaft32a, and a gear ratio ρ of the power distribution and integration mechanism30by the following formula (1), and a torque command Tm1* of the motor MG1is calculated based on the calculated target rotation speed Nm1* and the present rotation speed Nm1by the following formula (2) (Step S180). The formula (1) is a dynamic relational expression of a rotating element of the power distribution and integration mechanism30.FIG. 8is an alignment chart illustrating a dynamic relationship between a rotation speed and torque of each rotating element of the power distribution and integration mechanism30in the accelerator-on state. InFIG. 8, an S-axis on the left indicates a rotation speed of the sun gear31that matches the rotation speed Nm1of the motor MG1, a C-axis indicates a rotation speed of the carrier34that matches the rotation speed Ne of the engine22, and an R-axis indicates a rotation speed Nr of the ring gear32obtained by dividing the rotation speed Nm2of the motor MG2by the gear ratio Gr of the reduction gear35. Two bold arrows on the R-axis indicate torque including torque Tm1outputted from the motor MG1and applied to the ring gear shaft32a, and torque including torque Tm2outputted from the motor MG2and applied to the ring gear shaft32avia the reduction gear35. The formula (1) for calculating the target rotation speed Nm1* of the motor MG1can be easily derived using the relationship of the rotation speed in this alignment chart. In the formula (1), ρ is the gear ratio of the power distribution and integration mechanism30(the number of teeth of the sun gear31/the number of teeth of the ring gear32). In the formula (2), “k1” in the second term on the right side is a gain of a proportional term, and “k2” in the third term on the right side is a gain of an integral term.
Nm1*=Ne*·(1+ρ)/ρ−Nm2/(Gr·ρ)  (1)
Tm1*=lastTm1*+k1(Nm1*−Nm1)+k2∫(Nm1*−Nm1)d(2)

When the torque command Tm1* is set, a deviation between the output limit Wout or the input limit Win of the battery50inputted in Step S100by the following formulas (3) and (4) and power consumption of the motor MG1obtained by multiplying the set torque command Tm1* of the motor MG1by the present rotation speed Nm1of the motor MG1is divided by the rotation speed Nm2of the motor MG2to calculate torque restrictions Tmax and Tmin as upper and lower limits of torque that may be outputted from the motor MG2(Step S190). Further, tentative motor torque Tm2tmpas torque to be outputted from the motor MG2is calculated using the torque demand Tr*, the torque command Tm1*, the gear ratio ρ of the power distribution and integration mechanism30, and the gear ratio Gr of the reduction gear35by the following formula (5) (Step S200), and the calculated tentative motor torque Tm2tmpis restricted by the torque restrictions Tmax and Tmin to set a torque command Tm2* of the motor MG2(Step S210). The torque command Tm2* of the motor MG2is thus set to allow the torque demand Tr* outputted to the ring gear shaft32ato be set as torque basically restricted within the range of the input and output limits Win and Wout of the battery50. The formula (5) can be easily derived from the alignment chart inFIG. 8. The target rotation speed Ne* and the target torque Te* of the engine22, and the torque commands Tm1* and Tm2* of the motors MG1and MG2are thus set, and the target rotation speed Ne* and the target torque Te* of the engine22as the engine commands are transmitted to the engine ECU24, the torque commands Tm1* and Tm2* of the motors MG1and MG2are transmitted to the motor ECU40(Step S220), and the routine is once finished. The engine ECU24having received the target rotation speed Ne* and the target torque Te* performs control to obtain the target rotation speed Ne* and the target torque Te*. The motor ECU40having received the torque commands Tm1* and Tm2* performs switching control of switching elements of the inverters41and42so that the motor MG1is driven by the torque command Tm1* and the motor MG2is driven by the torque command Tm2*.
Tmax=(Wout*−Tm1*·Nm1)/Nm2  (3)
Tmin=(Win−Tm1*·Nm1)/Nm2  (4)
Tm2tmp=(Tr*+Tm1*/ρ)/Gr(5)

On the other hand, for example, when the driver suddenly reduces the accelerator opening Acc from a relatively high state (for example, a substantially fully opened state) to a relatively low state (for example, about 5%), and the deceleration demand is made due to the accelerator opening being reduced with the accelerator operation state being the accelerator-on state, the power demand P* required for the entire vehicle is set to a relatively low value in Step S110, and thus it is sometimes determined in Step S120that the power demand P* is less than the threshold Pref. In such a case, it is first determined whether the state of charge SOC of the battery50inputted in Step S100is a predetermined upper limit value SOC1or less (Step S230). When the state of charge SOC is the upper limit value SOC1or less, it is determined whether the input limit Win of the battery50inputted in Step S100is a predetermined charge limit value Win1or less as charging electric power (Step S240). The upper limit value SOC1used in Step S230and the charge limit value Win1used in Step S240are determined based on electric power inputted and outputted by the motors MG1and MG2when the required driving force at the time of deceleration demand is obtained with substantial self-sustaining operation of the engine22without fuel cut as described later.

When the state of charge SOC is the upper limit value SOC1or less, and the input limit Win of the battery50is the charge limit value Win1or less, a command for continuing the firing of the engine22is set as an engine command, and the target rotation speed Ne* of the engine22is set to a rotation speed Ne0at the time of continuation of the firing so that the engine22substantially performs the self-sustaining operation without any output of torque (Step S250). In the embodiment, the rotation speed Ne0is, for example, a rotation speed (800 to 1000 rpm) in idling. Then, calculation is performed based on the set target rotation speed Ne* (=Ne0) and the rotation speed Ne of the engine22inputted in Step S100by the following formula (6), and the torque command Tm1* of the motor MG1is set for causing the rotation speed Ne of the engine22to reach the target rotation speed Ne* (=Ne0) with the firing being continued (Step S260). The formula (6) is a relational expression in feedback control for causing the rotation speed Ne of the engine22to reach the target rotation speed Ne* with the firing being continued. In the formula (6), “k1” in the first term on the right side is a gain of a proportional term, and “k2” in the second term on the right side is a gain of an integral term. To continue the firing of the engine22, the gains k1and k2are set to smaller values than when relatively high torque is outputted from the engine22.

The torque command Tm1* is thus set, and then the torque command Tm2* of the motor MG2is set using the set torque command Tm1* (Steps S190to S210), the engine commands (the firing command and the target rotation speed Ne*) are transmitted to the engine ECU24, the torque commands Tm1* and Tm2* are transmitted to the motor ECU40(Step S220), and the routine is once finished. For continuing the firing of the engine22when the deceleration demand is made in the accelerator-on state, the motor MG1is driven and controlled as described above, thereby allowing the rotation speed Ne of the engine22to be quickly reduced to the target rotation speed Ne* (=Ne0) without fuel cut, and allowing deceleration of the hybrid vehicle20. In this case, the engine ECU24sets the opening of the throttle valve124to a low value so as to ensure intake air in an amount that causes no misfire.FIG. 9is an alignment chart illustrating a dynamic relationship between a rotation speed and torque of each rotating element of the power distribution and integration mechanism30when firing of the engine22is continued in the accelerator-on state. As is seen fromFIG. 9, when the engine22is operated at the rotation speed Ne0, slight driving torque is outputted from the engine22, and the driving torque is applied to the ring gear shaft32aas the output shaft. Thus, the motor MG2outputs torque obtained by subtracting the driving torque from the torque based on the torque demand (braking torque) Tr*.
Tm1*=k1·(Ne*−Ne)+k2∫(Ne*−Ne)·dt(6)

If the firing of the engine22is continued when the accelerator opening Acc is suddenly reduced in the accelerator-on state with the vehicle speed V being high as shown by the dash-double-dot line inFIG. 9, the rotation speed of the engine22needs to be abruptly reduced to the target rotation speed Ne0by the motor MG1, which increases electric power regenerated by the motor MG1. Thus, depending on the state of charge SOC of the battery50or the value of the input limit Win of the battery50set based on the state of charge SOC, there is a possibility that the electric power regenerated by the motor MG1cannot be accumulated in the battery50when the engine22substantially performs the self-sustaining operation without the fuel cut. Thus, when it is determined in Step S230that the state of charge SOC of the battery50is less than the upper limit value SOC1, or it is determined in Step S240that the input limit Win of the battery50is less than the charge limit value Win1as the charging electric power, it is determined that the fuel cut cannot be prohibited, and a command for performing the fuel cut for temporarily stopping fuel injection to the engine22is set (Step S270), and the torque command Tm1* of the motor MG1is set to zero (Step S280). Then, the torque command Tm2* of the motor MG2is set using the set torque command Tm1* (=0) (Steps S190to S210), the engine command (fuel cut command) is transmitted to the engine ECU24, and the torque commands Tm1* and Tm2* are transmitted to the motor ECU40(Step S220), and the routine is once finished. The fuel cut is thus performed to allow the rotation speed of the engine22to be quickly reduced and allow deceleration of the hybrid vehicle20.FIG. 10is an alignment chart illustrating a dynamic relationship between a rotation speed and torque of each rotating element of the power distribution and integration mechanism30when the fuel cut is performed in the accelerator-on state.

As described above, in the hybrid vehicle20of the embodiment, when the deceleration demand in the accelerator-on state is made in the state where the shift position SP is set to the S position and arbitrary selection (manual selection) of the shift positions SP1to SP6that define settable ranges of the torque demand Tr* required for driving is allowed, and it is determined that the fuel cut cannot be prohibited based on the state of the battery50, that is, the state of charge SOC and the input limit Win, the engine22and the motors MG1and MG2are controlled so that the driving force based on the set torque demand Tr* is outputted with the fuel cut of the engine22(Steps S270, S280, S190to S220). When the deceleration demand in the accelerator-on state is made in the state where the shift position SP is set to the S position, and it is determined that the fuel cut can be prohibited based on the state of charge SOC and the input limit Win of the battery50, the engine22and the motors MG1and MG2are controlled so that the engine22substantially performs the self-sustaining operation at the target rotation speed Ne0and the driving force based on the set torque demand Tr* is outputted (Steps S250, S260, S190to S220).

Next, operation of the hybrid vehicle20will be described when the driver selects the S position as the shift position SP, and the accelerator operation state is the accelerator-off state.FIG. 11is a flowchart showing an example of a drive control routine performed by the hybrid ECU70when the driver selects the S position as the shift position SP and the accelerator operation state is the accelerator-off state. This routine is also repeatedly performed every predetermined time (for example, every few milliseconds) when the accelerator operation state is the accelerator-off state. When the drive control routine inFIG. 11is started, the CPU72of the hybrid ECU70first performs a processing for inputting data required for control such as the vehicle speed V from the vehicle speed sensor88, the rotation speeds Nm1and Nm2of the motors MG1and MG2, the shift position SP from the shift position sensor82, the charge-discharge power demand Pb* to be charged and discharged by the battery50, the state of charge (SOC) of the battery50, and the input limit Win of the battery50(Step S300). The input procedure of each data is the same as in the routine inFIG. 3. After the data input processing in Step S300, the torque demand (braking torque) Tr* to be outputted to the ring gear shaft32aas the drive shaft connected to the drive wheels63aand63b, and the power demand P* required for the entire vehicle in driving are set based on the vehicle speed V and the shift position SP (Step S310). In the embodiment, the torque demand Tr* is set by deriving the torque demand Tr* when the accelerator opening Acc corresponding to the vehicle speed V and the shift position SP is 0%, from the torque demand setting map inFIG. 6. The power demand P* is set as in the routine inFIG. 3. Then, it is determined whether the state of charge SOC of the battery50inputted in Step S300is the predetermined upper limit value SOC1or less (Step S320). When the state of charge SOC is the upper limit value SOC1or less, it is determined whether the input limit Win of the battery50inputted in Step S300is the predetermined charge limit value Win1or less (Step S330). The upper limit value SOC1and the charge limit value Win1are the same as those in the routine inFIG. 3.

When the state of charge SOC is the upper limit value SOC1or less, and the input limit Win of the battery50is the charge limit value Win1or less, a command for continuing the firing of the engine22is set as an engine command (Step S340), and the target rotation speed Ne* of the engine22is set to a rotation speed Ne0at the time of continuation of the firing so that the engine22substantially performs the self-sustaining operation without any output of the torque (Step S350). The rotation speed Ne0is, for example, a rotation speed (800 to 1000 rpm) in idling as in the routine inFIG. 3. Then, calculation is performed based on the set target rotation speed Ne* (=Ne0) and the rotation speed Ne of the engine22inputted in Step S300by the following formula (6), and the torque command Tm1* of the motor MG1is set for causing the rotation speed Ne of the engine22to reach the target rotation speed Ne* (=Ne0) with the firing being continued (Step S360). When the torque command Tm1* is set, a deviation between the input limit Win of the battery50inputted in Step S300and power consumption of the motor MG1obtained by multiplying the set torque command Tm1* of the motor MG1by the present rotation speed Nm1of the motor MG1is divided by the rotation speed Nm2of the motor MG2to calculate a torque restriction Tmin as a lower limit of torque that may be outputted from the motor MG2(Step S370). Further, tentative motor torque Tm2tmpas torque to be outputted from the motor MG2is calculated using the torque demand Tr*, the torque command Tm1*, the gear ratio ρ of the power distribution and integration mechanism30, and the gear ratio Gr of the reduction gear35as in Step200in the routine inFIG. 3(Step S380), and the calculated tentative motor torque Tm2tmpis restricted by the torque restriction Tmin to set a torque command Tm2* of the motor MG2(Step S390). The torque command Tm2* of the motor MG2is thus set to allow the torque demand Tr* outputted to the ring gear shaft32ato be set as torque basically restricted by the input limit Win of the battery50. The engine command (the firing command and the target rotation speed Ne*) and the torque commands Tm1* and Tm2* of the motors MG1and MG2are set, and then the engine commands are transmitted to the engine ECU24, the torque commands Tm1* and Tm2* of the motors MG1and MG2are transmitted to the motor ECU40(Step S400), and the routine is once finished.

For continuing the firing of the engine22when the deceleration demand based on accelerator-off is made, the motors MG1and MG2are driven and controlled as described above, thereby allowing the rotation speed Ne of the engine22to be quickly reduced to the target rotation speed Ne* (=Ne0) without fuel cut, and allowing a braking force to be generated by regeneration of the motor MG2to decelerate the hybrid vehicle20. Also in this case, the engine ECU24sets the opening of the throttle valve124to a low value so as to ensure intake air in an amount that causes no misfire.FIG. 12is an alignment chart illustrating a dynamic relationship between a rotation speed and torque of each rotating element of the power distribution and integration mechanism30when the firing of the engine22is continued in the accelerator-off state. When the engine22is operated at the rotation speed Ne0in the accelerator-off state, slight driving torque is outputted from the engine22to the ring gear shaft32aas the output shaft as shown inFIG. 12, and thus the motor MG2outputs the sum of torque based on the torque demand (braking torque) Tr* and torque for canceling the driving torque.

Also in the accelerator-off state, if the firing of the engine22is continued when the accelerator opening Acc is suddenly reduced in the accelerator-on state with the vehicle speed V being high as shown by the dash-double-dot line inFIG. 12, the rotation speed of the engine22needs to be abruptly reduced to the target rotation speed Ne0by the motor MG1, which increases electric power regenerated by the motor MG1. As is seen fromFIG. 6, in the accelerator-off state, the set torque demand Tr* increases as the braking force with increasing vehicle speed or lowering shift position SP (toward the SP1side), and thus the regenerative braking force required for the motor MG2increases, which increases electric power inputted from the motor MG2to the battery50. Thus, depending on the state of charge SOC of the battery50or the value of the input limit Win of the battery50set based on the state of charge SOC, there is a possibility that the electric power regenerated by the motor MG1cannot be accumulated in the battery50when the engine22substantially performs the self-sustaining operation without the fuel cut.

Thus, when it is determined in Step S320that the state of charge SOC of the battery50is less than the upper limit value SOC1, or it is determined in Step S330that the input limit Win of the battery50is less than the charge limit value Win1as the charging electric power, it is determined that the fuel cut cannot be prohibited, and a command for performing the fuel cut for temporarily stopping fuel injection to the engine22is set (Step S410), and the target rotation speed Ne* of the engine22is set based on the shift position SP and the vehicle speed V so that the engine brake provides part of the braking force (Step S420). In the embodiment, for the selection of the S position, the relationship between the shift positions SP including SP1to SP6, the vehicle speed V, and the target rotation speed Ne* of the engine22is previously determined, and stored in the ROM74as the target rotation speed setting map as an operation point constraint in selecting the S position, and when the shift position SP and the vehicle speed V are provided, the target rotation speed Ne* of the engine22corresponding to the shift position SP and the vehicle speed V is derived from the map and set.FIG. 13illustrates an example of the target rotation speed setting map used in selecting the S position. The target rotation speed Ne* of the engine22is thus set, then the processings in Steps S360to S400described above are performed, and the routine is once finished. Thus, the fuel cut is performed when the deceleration demand based on the accelerator-off is made, and the motors MG1and MG2are driven and controlled as described above, thereby allowing braking torque (direct torque=−1/ρ·Tm1*) by the engine brake from the engine22and the braking force by regeneration of the motor MG2to be outputted to the ring gear shaft32aas the drive shaft, and thus reducing electric power inputted to the battery50by the regeneration of the motor MG2. Particularly, when the vehicle speed V is relatively high and the shift position SP is on the lower side, relatively high braking torque is set as the torque demand as is seen fromFIG. 6, and the target rotation speed Ne* of the engine22is set to a relatively high value as is seen fromFIG. 13, and the rotation speed of the engine22is maintained at the high value by motoring of the motor MG1to the like, thereby reducing the load on the motor MG2.FIG. 14is an alignment chart illustrating a dynamic relationship between a rotation speed and torque of each rotating element of the power distribution and integration mechanism30when the fuel cut is performed in the accelerator-off state.

As described above, in the hybrid vehicle20of the embodiment, when the deceleration demand based on the accelerator-off is made in the state where the shift position SP is set to the S position and arbitrary selection of the shift positions SP1to SP6is allowed, and it is determined that the fuel cut cannot be prohibited based on the state of the battery50, that is, the state of charge SOC and the input limit Win, the engine22and the motors MG1and MG2are controlled so that the driving force based on the set torque demand Tr* is outputted with the fuel cut of the engine22(Steps S410, S420, S360to S400). When the deceleration demand in the accelerator-off state is made in the state where the shift position SP is set to the S position, and it is determined that the fuel cut can be prohibited based on the state of charge SOC and the input limit Win of the battery50, the engine22and the motors MG1and MG2are controlled so that the engine22substantially performs the self-sustaining operation at the target rotation speed Ne0and the driving force based on the set torque demand Tr* is outputted (Steps S340to S400).

As described above, in the hybrid vehicle20of the embodiment, when the deceleration demand in the accelerator-on state or the deceleration demand based on the accelerator-off is made in the state where the shift position SP is set to the S position and arbitrary selection of the shift positions SP1to SP6is allowed, the driving force (braking force) based on the torque demand Tr* is obtained with the substantial self-sustaining operation of the engine22without the fuel cut except the case where the fuel cut has to be prohibited based on the state of the battery50, that is, the state of charge SOC and the input limit Win. Specifically, when the driver is allowed to arbitrarily select the shift positions SP1to SP6, and the deceleration demand in the accelerator-on state due to the sudden reduction in the accelerator opening Acc or the deceleration demand based on the accelerator-off is made, the fuel cut is generally performed, thus a large amount of air is fed to the exhaust gas purifying catalyst in the purifying device134, and thus oxygen may attach to the catalyst to reduce NOx purifying performance. Thus, the driving force (braking force) based on the torque demand Tr* is obtained with the substantial self-sustaining operation of the engine22without the fuel cut except the case where the fuel cut has to be prohibited from the state of the battery50. This can prevent a reduction in purifying performance of the exhaust gas purifying catalyst caused by a large amount of air being fed to the purifying device134because of the fuel cut, and thus improve emission.

As described above, the upper limit value SOC1and the charge limit value Win1as the thresholds are determined based on the electric power inputted and outputted by the motors MG1and MG2when the torque demand Tr* at the time of deceleration demand is obtained with the substantial self-sustaining operation of the engine22without the fuel cut, and it is determined that the fuel cut can be prohibited when the state of charge SOC of the battery50is the upper limit value SOC1or less, or the input limit Win as the charging allowable electric power set based on the state of the battery50is the charge limit value Win1or less. Thus, it can be properly determined whether the fuel cut can be prohibited based on the state of the battery, and the prohibition of the fuel cut can be canceled at proper timing to prevent degradation by overcharge of the battery50.

The hybrid vehicle20of the embodiment has been described in which the shift positions of the shift lever81include the S position that allows the driver to arbitrarily select the shift positions SP1to SP6, but the present invention is not restrictively applied to this. Specifically, in the case where the shift positions SP of the shift lever81include a brake position that is selected, for example, in driving on a downhill at a relatively high speed, and has a settable range of a driving force corresponding thereto having a lower limit of a power range lower than in the D position, the drive control routine inFIG. 3or11may be performed when the brake position is selected.

The embodiment discussed above is to be considered in all aspects as illustrative and not restrictive. There may be many modifications, changes, and alterations without departing from the scope or spirit of the main characteristics of the present invention. The scope and spirit of the present invention are indicated by the appended claims, rather than by the foregoing description.

Specifically, in the hybrid vehicle20of the embodiment, the ring gear shaft32aas the drive shaft and the motor MG2are connected via the reduction gear35that reduces the rotation speed of the motor MG2and transmits the rotation speed to the ring gear shaft32a. However, instead of the reduction gear35, for example, a transmission may be used that has two transmission stages of High and Low or three or more transmission stages, and changes the rotation speed of the motor MG2and transmits the rotation speed to the ring gear shaft32a.

In the hybrid vehicle20of the embodiment, the power of the motor MG2is decelerated by the reduction gear35and outputted to the ring gear shaft32a. However, as a hybrid vehicle120of a variant shown inFIG. 15, power of a motor MG2may be changed in speed by a transmission65and transmitted to an axle (an axle connected to wheels63cand63dinFIG. 15) different from an axle connected to a ring gear shaft32a(an axle connected to drive wheels63aand63b).

In the hybrid vehicle20and20B of the embodiment, the power of the engine22is output via the power distribution integration mechanism30to the ring gear shaft32afunctioning as the drive shaft linked with the drive wheels63aand63b. In another possible modification ofFIG. 16, a hybrid vehicle220may have a pair-rotor motor230, which has an inner rotor232connected with the crankshaft26of the engine22and an outer rotor234connected with the drive shaft for outputting the power to the drive wheels63a,63band transmits part of the power output from the engine22to the drive shaft while converting the residual part of the power into electric power.

INDUSTRIAL APPLICABILITY

The present invention is applicable in production industries of vehicles.