AND CONTROL METHOD FOR POWER OUTPUT DEVICE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a power output device and a control method for the power output device and, more particularly, to control at the time of starting an internal combustion engine.

2. Description of Related Art

[0002] In an existing art, a power output device is mounted on a hybrid vehicle, or the like. The power output device includes an engine; a planetary gear that connects a crankshaft of the engine to a carrier and that connects a ring gear to a drive shaft mechanically coupled to an axle; a generator that inputs or outputs power to or from a sun gear of the planetary gear; and an electric motor that inputs or outputs power to or from the drive shaft. At the time of starting the engine, fluctuations in torque at the time of the engine start are computed, and an output torque from the electric motor is corrected on the basis of the computed result. By so doing, torque fluctuations of the drive shaft that serves as a final output shaft are corrected.

[0003] Japanese Patent Application Publication No. 2005-30281 (JP 2005-30281 A) describes a controller. The controller executes drive control over an electric power input/output device such that an engine is cranked when a command to start the engine is issued while an electric motor is being subjected to drive control so as to output a required torque to a drive shaft in a state where the operation of the engine is stopped, executes drive control over the electric motor such that the required torque is output to the drive shaft while cancelling a torque applied to the drive shaft as reaction force as a result of cranking the engine, controls the operation of the engine such that the engine is started, and controls the electric motor such that the electric motor outputs a torque smaller by a predetermined torque than a torque that should be output from the electric motor in a predetermined period of time that includes an initial combustion timing of the engine. The predetermined torque is set on the basis of an operation parameter of the engine, which includes at least one of an intake pressure, an intake air temperature and a throttle opening degree at the time of initial ignition of the engine. Specifically, a relationship between an initial combustion torque and an operation parameter, such as an intake pressure and an intake air temperature, in various states is obtained through an experiment, the relationship is stored in a ROM as a map, and an initial combustion torque is derived as a predetermined torque using the detected operation parameter and the map.

[0004] Incidentally, when a torque that is applied to the drive shaft as reaction force as a result of cranking the engine is cancelled, it is required to accurately evaluate the torque serving as reaction force; however, the torque serving as reaction force pulsates as a result of passing through a top dead center (TDC) at the time of cranking the engine, so there is a problem that it is not always sufficient to just set a predetermined torque on the basis of the operation parameter, such as an intake pressure, an intake air temperature and a throttle opening degree.

SUMMARY OF THE INVENTION

[0005] The invention provides a device that further highly accurately evaluates a torque applied to a drive shaft as reaction force at the time of a start of an internal combustion engine and then cancels the torque, thus making it possible to suppress a torque shock generated when starting the internal combustion engine, and a control method for the device.

[0006] An aspect of the invention provides a power output device that outputs power to a drive shaft. The power output device includes: an internal combustion engine that outputs power to the drive shaft; an electric motor that outputs power to the drive shaft; an electric cranking device that performs cranking for starting the internal combustion engine; and a controller that is configured to, at the time of starting the internal combustion engine from a state where operation of the internal combustion engine is stopped, control the electric motor using a rotation speed of the internal combustion engine, at the time point at which a crank position at the time of the cranking falls within a predetermined range from a top dead center and the rotation speed of the internal combustion engine falls within a predetermined range from a predetermined resonance frequency band, and using an elapsed time from the time point, to cancel a reaction torque that acts on the drive shaft as the electric cranking device cranks the internal combustion engine.

[0007] Another aspect of the invention provides a control method for a power output device that outputs power to a drive shaft. The power output device includes: an internal combustion engine that outputs power to the drive shaft; an electric motor that outputs power to the drive shaft; and an electric cranking device that performs cranking for starting the internal combustion engine. The control method includes: determining whether a crank position of the internal combustion engine falls within a predetermined range from a top dead center; determining whether a rotation speed of the internal combustion engine falls within a predetermined range from a predetermined resonance frequency; acquiring the rotation speed of the internal combustion engine at an estimation start timing; accumulating an elapsed time from the estimation start timing; and when the crank position at the time of the cranking falls within the predetermined range from the top dead center and the rotation speed of the internal combustion engine falls within the predetermined range from the predetermined resonance frequency band, at the time of starting the internal combustion engine from a state where operation of the internal combustion engine is stopped, controlling the electric motor on the basis of the accumulated time and the rotation speed such that a reaction torque that acts on the drive shaft as the electric cranking device cranks the internal combustion engine is cancelled.

[0008] The reaction torque that occurs at the time when the electric cranking device cranks the internal combustion engine is not constant, and the magnitude of the reaction torque varies before and after the top dead center (TDC) of the internal combustion engine, so the reaction torque pulsates. Then, with the above-described power output device and the control method for the power output device, focusing on the case where the crank position of the internal combustion engine at the time of cranking falls within the predetermined range from the top dead center, a reaction torque as a result of the cranking is estimated or predicted using the rotation speed of the internal combustion engine at that time point and the elapsed time from that time point, and the electric motor is controlled such that the reaction torque is cancelled. Then, the reaction torque as a result of the cranking propagates to the drive shaft within the predetermined range from the resonance frequency band of the crankshaft of the internal combustion engine, so, focusing on the case where the crank position of the internal combustion engine at the time of the cranking falls within the predetermined range from the top dead center and the rotation speed of the internal combustion engine falls within the predetermined range from the resonance frequency band of the crankshaft, the electric motor is controlled using the rotation speed of the internal combustion engine at that time point and the elapsed time from that time point. Therefore, the torque shock which is generated at the time of starting the engine can be effectively suppressed.

[0009] In addition, in the power output device, the controller may be configured to control the electric motor using pulsation amounts of the reaction torque before and after the top dead center at the time of the cranking, the pulsation amounts being estimated by using the rotation speed of the internal combustion engine and the elapsed time.

[0010] In addition, in the power output device, the controller may be configured to acquire the pulsation amount with the use of a preset and prestored relationship among the rotation speed of the internal combustion engine, the elapsed time and the pulsation amount.

[0011] In addition, in the power output device and the control method, the controller may be configured to control the electric motor with a torque that is obtained by subtracting the reaction torque from a torque of the electric motor corresponding to a required torque of the drive shaft, and the reaction torque may be obtained by adding a pulsation amount to a predetermined torque.

[0012] The power output device according to the aspect of the invention may be, for example, mounted on a hybrid vehicle. In addition, the electric motor in the power output device according to the aspect of the invention may be formed of a so-called motor generator (MG). In addition, the electric cranking device in the power output device according to the aspect of the invention may be formed of a so-called motor generator (MG) as in the case of the electric motor.

[0013] According to the above-described power output device and the control method for the power output device, it is possible to highly accurately cancel a reaction torque as a result of cranking the internal combustion engine with the use of the electric motor, so it is possible to effectively suppress a torque shock as the internal combustion engine is cranked.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a configuration view of a power output device according to an embodiment of the invention;

FIG. 2 is a relevant configuration view of FIG. 1 ;

FIG. 3 is a view that shows a relationship between a crank angle and reaction torque of an engine shown in FIG. 1 ;

FIG. 4A is a nomograph that shows a dynamic relationship between rotation speeds and torques in a power distribution integration mechanism before a top dead center of the engine shown in FIG. 1 ;

FIG. 4B is a nomograph that shows a dynamic relationship between rotation speeds and torques in the power distribution integration mechanism after the top dead center of the engine shown in FIG. 1 ;

FIG. 5 is an explanatory view of a torque command generating process for a motor MG2 shown in FIG. 1;

FIG. 6 is a graph that shows a relationship between an elapsed time and a pulsation torque amount, as an example of the embodiment;

FIG. 7 is a flowchart of an engine start control routine according to the embodiment; and

FIG. 8 is a graph that shows a torque variation of the motor MG2 shown in FIG. 1.

DETAILED DESCRIPTION OF EMBODIMENTS

[0015] Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings. FIG 1 shows the configuration of a hybrid vehicle 20 on which a power output device according to the embodiment is mounted. The hybrid vehicle 20 includes an engine 22; a triaxial power distribution integration mechanism 30; a motor MG1; a speed reduction gear (or a rear planetary gear) 35; a motor MG2; and a hybrid electronic control unit (ECU) 70. The power distribution integration mechanism 30 is connected to a crankshaft 26 via a flywheel damper 28. The crankshaft 26 serves as an output shaft of the engine 22. The motor MG1 is connected to the power distribution integration mechanism 30, and is able to generate electric power. The speed reduction gear (rear planetary gear) 35 is connected to a ring gear shaft 32a that serves as a drive shaft connected to the power distribution integration mechanism 30. The motor MG2 is connected to the speed reduction gear 35. The hybrid ECU 70 comprehensively controls the power output device.

[0016] The engine 22 is an internal combustion engine that outputs power using fuel, such as gasoline, and is controlled by an engine ECU 24 to which signals are supplied from various sensors that detect operating states of the engine 22. A crank angle Θ, an intake air temperature Ta, an intake pressure Va, an opening degree of a throttle valve 23d, a coolant temperature Tw, and the like, are supplied from the engine ECU 24. The crank angle Θ is output from a crank position sensor 23a attached to the crankshaft 26. The intake air temperature Ta is output from an intake air temperature sensor 23b attached to an intake system. The intake pressure Va is output from a negative pressure detection sensor 23c. The opening degree of the throttle valve 23d is output from a throttle position sensor 23e. The coolant temperature Tw is output from a coolant temperature sensor 23f attached to a cooling system of the engine 22. The engine ECU 24 communicates with the hybrid ECU 70, controls the operation of the engine 22 through a control signal from the hybrid ECU 70, and, where necessary, outputs data about the operation states of the engine 22 to the hybrid ECU 70.

[0017] The power distribution integration mechanism 30 includes a sun gear 31, a ring gear 32, a plurality of pinions 33 and a carrier 34. The sun gear 31 is an external gear. The ring gear 32 is an internal gear and is arranged concentrically with the sun gear 31. The plurality of pinions 33 are in mesh with the sun gear 31 and in mesh with the ring gear 32. The carrier 34 holds the plurality of pinions 33 such that the pinions 33 are rotatable and revolvable. The power distribution integration mechanism 30 is formed as a planetary gear mechanism (planetary gear) that includes the sun gear 31, the ring gear 32 and the carrier 34 as rotating elements and that performs differential action.

[0018] In the power distribution integration mechanism 30, the crankshaft 26 of the engine 22 is coupled to the carrier 34, the motor MGl is coupled to the sun gear 31, and the speed reduction gear 35 is coupled to the ring gear 32 via the ring gear shaft 32a. When the motor MGl functions as a generator, power from the engine 22, input from the carrier 34, is distributed between the sun gear 31 and the ring gear 32 at its gear ratio; whereas, when the motor MGl functions as an electric motor, power from the engine 22, input from the carrier 34, and power from the motor MGl, input from the sun gear 31, are integrated and output to the ring gear 32. The power output to the ring gear 32 is output from the ring gear shaft 32a to drive wheels 63a and 63b of a vehicle via a gear mechanism 60 and a differential gear 62.

[0019] The motors MGl and MG2 each are a synchronous motor generator that is able to function as a generator and as an electric motor. The motor MGl exchanges electric power with a battery 50 via an inverter 41, and the motor MG2 exchanges electric power with the battery 50 via an inverter 42. Power lines 54 are formed as a positive electrode bus and a negative electrode bus that are shared by the inverters 41 and 42. The power lines 54 connect the inverters 41 and 42 to the battery 50. The power lines 54 allow electric power generated in any one of the motors MGl and MG2 to be consumed in the other one of the motors. The battery 50 is charged by electric power generated from any one of the motors MGl and MG2 or discharged due to insufficient electric power in any one of the motors MGl and MG2. When electric power consumed in and electric power output from the motors MGl and MG2 are balanced, the battery 50 is not charged or discharged.

[0020] The motors MGl and MG2 each are subjected to drive control by a motor ECU 40. Signals required to execute drive control over the motors MGl and MG2 are supplied to the motor ECU 40. The signals, for example, include signals from rotational position detection sensors 43 and 44 and currents applied to the motors MGl and MG2. The rotational position detection sensors 43 and 44 respectively detect rotation positions of rotors of the motors MGl and MG2. The currents applied to the motors MGl and MG2 are respectively detected by current sensors. The motor ECU 40 outputs switching control signals to the inverters 41 and 42. The motor ECU 40 communicates with the hybrid ECU 70, executes drive control over the motors MGl and MG2 through control signals from the hybrid ECU 70, and, where necessary, outputs data about the operation states of the motors MGl and MG2 to the hybrid ECU 70.

[0021] The battery 50 is controlled by a battery ECU 52. Signals required to control the battery 50 are supplied to the battery ECU 52. The signals, for example, include a terminal voltage from a voltage sensor, a charge/discharge current from a current sensor, a battery temperature Tb from a temperature sensor 51. The voltage sensor is attached between terminals of the battery 50. The current sensor is attached to the power line 54 connected to the output terminal of the battery 50. The temperature sensor 51 is attached to the battery 50. The battery ECU 52, where necessary, outputs data about the state of the battery 50 to the hybrid ECU 70. In addition, the battery ECU 52 computes a remaining level (SOC) on the basis of an accumulated value of charge/discharge current detected by the current sensor in order to control charging and discharging of the battery 50.

[0022] The hybrid ECU 70 is formed as a microprocessor that includes a CPU 72. The hybrid ECU 70 includes a ROM 74, a RAM 76, input/output ports and a communication port in addition to the CPU 72. The ROM 74 stores process programs. The RAM 76 temporarily stores data. An ignition signal, a shift position SP, an accelerator operation amount Acc, a brake pedal position BP, a vehicle speed V, and the like, are supplied to the hybrid ECU 70 via the input port. The ignition signal is output from an ignition switch 80. The shift position SP is output from a shift position sensor 82 that detects the operating position of a shift lever 81. The accelerator operation amount Acc is output from an accelerator pedal position sensor 84 that detects the depression amount of an accelerator pedal 83. The brake pedal position BP is output from a brake pedal position sensor 86 that detects the depression amount of a brake pedal 85. The vehicle speed V is output from a vehicle speed sensor 88. The hybrid ECU 70 is connected to the engine ECU 24, the motor ECU 40 and the battery ECU 52 via the communication port, and exchanges various control signals and data with the engine ECU 24, the motor ECU 40 and the battery ECU 52.

[0023] The hybrid vehicle 20 computes a required torque to be output to the ring gear shaft 32a that serves as the drive shaft on the basis of the accelerator operation amount Acc, corresponding to the driver's depression amount of the accelerator pedal 83, and the vehicle speed V, and controls the engine 22, the motor MG1 and the motor MG2 such that a required power corresponding to the required torque is output to the ring gear shaft 32a. Specifically, the hybrid vehicle 20, for example, includes the following modes. In a first mode, the engine 22 undergoes operation control such that a power corresponding to a required power is output from the engine 22, and the motors MG1 and MG2 undergo drive control such that the whole of power output from the engine 22 is converted to torque by the power distribution integration mechanism 30, the motor MG1 and the motor MG2 and then output to the ring gear shaft 32a. In a second mode, the engine 22 undergoes operation control such that a power corresponding to the sum of a required electric power and an electric power required to charge or discharge the battery 50 is output from the engine 22, and the motors MG1 and MG2 are controlled such that the whole or part of power output from the engine 22 is subjected to torque conversion through the power distribution integration mechanism 30, the motor MG1 and the motor MG2 while the battery 50 is charged or discharged and then a required power is output to the ring gear shaft 32a. In a third mode, the operation of the engine 22 is stopped, and the motor MG1 and the motor MG2 are controlled such that a power corresponding to a required electric power of the motor MG2 is output to the ring gear shaft 32a.

[0024] With the above configuration, next, the operation at the time of starting the engine 22 that is stopped in operation will be described. FIG. 2 shows the configuration of a relevant portion of the power output device within the configuration shown in FIG. 1. The carrier 34 is coupled to the crankshaft 26 of the engine 22 via the flywheel damper 28, and the sun gear 31 and the ring gear 32 are in mesh with the pinions held by the carrier 34. The motor MG1 is coupled to the sun gear 31, the speed reduction gear 35 is coupled to the ring gear 32 via the ring gear shaft, and the motor MG2 is coupled to the speed reduction gear 35. When the engine 22 is cranked with a torque Tg of the motor MGl that functions as an electric cranking device to start the engine 22, a reaction torque pulsates as the engine 22 passes through a top dead center (TDC). In the drawing, a pulsation 100 of the reaction torque is indicated by a directional arrow. The pulsation of the reaction torque propagates to the ring gear 32 via the carrier 34, and generates a torque shock. Then, the pulsation of the reaction torque is estimated, and a torque command to the motor MG2 is generated such that the motor MG2 outputs an oscillation suppression component that cancels the pulsation.

[0025] FIG. 3 shows a relationship between the crank angle Θ and reaction torque of the engine 22. Focusing on any one of cylinders in the case where the engine 22 is a four-cycle multi-cylinder engine, as the engine 22 is cranked, the focusing cylinder repeats four strokes, that is, intake, compression, expansion and exhaust strokes. The pressure in the cylinder is high in the compression stroke and is low in the expansion stroke. A pressure variation in the cylinder acts on the crankshaft 26 as a reaction torque via a corresponding piston. A slight pressure variation also occurs in the intake stroke and the exhaust stroke, but it is smaller than that in the compression stroke and the expansion stroke and can be ignored. The reaction torque that acts on the crankshaft 26 propagates to the ring gear shaft 32a that serves as the drive shaft via the power distribution integration mechanism 30, so a torque pulsation based on a pressure variation in the cylinder appears in the ring gear shaft 32a. The reaction torque that acts on the ring gear shaft 32a on the basis of a pressure variation in the cylinder acts in a direction to suppress the rotation of the engine 22 when the intended cylinder is within the range from a bottom dead center (BDC) to a top dead center (TDC) in the compression stroke, and acts in a direction to facilitate the rotation of the engine 22 when the intended cylinder is within the range from the TDC to the BDC in the expansion stroke. Thus, in order to cancel such a pulsation of the reaction torque, within the range from the BDC to the TDC in the compression stroke, that is, before the TDC, a torque in the direction to facilitate the rotation of the engine 22 should be applied with the use of the motor MG2, and, within the range from the TDC to the BDC in the expansion stroke, that is, after the TDC, a torque in a direction to suppress the rotation of the engine 22 should be applied to the motor MG2. In the multi-cylinder engine 22, it is possible to obtain a torque that should be applied to the ring gear shaft 32a by combining such a torque in one cylinder by the number of cylinders.

[0026] FIG. 4A and FIG. 4B are nomographs that show a dynamic relationship between rotation speeds and torques of the rotating elements (the sun gear 31, the ring gear 32 and the carrier 34) of the power distribution integration mechanism 30 when the engine 22 is cranked to be started. FIG. 4A is a nomograph before the top dead center (TDC). FIG. 4B is a nomograph after the top dead center (TDC). As shown in FIG. 4A, before the TDC, a compression reaction force is output to the shaft of the carrier 34, the rotation speed of the engine 22 is hard to increase, an inertia term, that is, the proportion of inertia based on the mass of the rotor of the motor MG1, decreases among destinations to which the torque Tg of the motor MG1 is distributed, and the absolute value of a direct torque in the ring gear shaft 32a of the ring gear 32 increases. In the graph, a reaction force -1/pxTg due to the torque Tg of the motor MG1 is indicated by a downward arrow on the ring gear shaft, and the amount of the direct torque is indicated by hatching. Here, p denotes the gear ratio of the power distribution integration mechanism 30.

[0027] On the other hand, as shown in FIG. 4B, after the TDC, an expansion reaction force is output to the shaft of the carrier 34, the rotation speed of the engine 22 tends to increase because of the action of the expansion reaction force, the proportion of the inertia term of the motor MG1 relatively increases among destinations to which the torque Tg of the motor MG1 is distributed, and the absolute value of the direct torque in the ring gear shaft 32a of the ring gear 32 reduces. When FIG. 4A is compared with FIG. 4B, it is to be noted that the direct torque within the reaction torque -1/pxTg is relatively smaller in FIG. 4B than in FIG. 4A. In this way, before and after the TDC, the magnitude (absolute value) of the direct torque increases or reduces, so a pulsation occurs.

[0028] In the present embodiment, by taking into consideration that the amount of pulsation of the direct torque is due to a compression pulsation during cranking and the compression pulsation is inverted before and after the TDC depending on a crank angle (or the degree of compression of air in a combustion chamber), and, in addition, by taking into consideration that propagation of a direct torque pulsation of the drive shaft occurs at an engine rotation speed around a resonance frequency band (resonance rotation speed band) because the crankshaft 26 of the engine 22 is coupled to the carrier 34 via the flywheel damper 28, the amount of pulsation of the direct torque is estimated as follows. That is, it is assumed that estimation of the amount of pulsation is started when the crank position of the engine 22 is around the TDC and the rotation speed of the engine 22 is around the resonance frequency band, and the rotation speed of the engine 22 at the estimation start timing is acquired. In addition, an elapsed time from the estimation start timing is measured by a timer. Then, the amount of pulsation of the direct torque at that time point is estimated using the engine rotation speed at the estimation start timing and the elapsed time from the estimation start timing. Specifically, the amounts of pulsation of the direct torque at various engine rotation speeds and elapsed times are obtained in advance through an experiment, or the like, and are stored in the ROM 74 as a map. Then, the amount of pulsation of the direct torque based on the acquired engine rotation speed and the acquired elapsed time may be read from the map. The estimated amount of pulsation of the direct torque and a temporary estimated direct torque are added together to be computed as an estimated direct torque, and a final torque command is generated by subtracting the estimated direct torque from a torque command to the motor MG2.

[0029] FIG. 5 schematically shows the process of generating a torque command to the motor MG2, executed in the hybrid ECU 70. When the hybrid ECU 70 determines that the crank angle of the engine 22 is around the TDC because the crank angle falls within a predetermined range and determines that the rotation speed Ne of the engine 22 is around the resonance frequency band because the rotation speed Ne falls within a predetermined range, the hybrid ECU 70 starts estimating the amount of pulsation, and derives an estimated amount of pulsation of a direct torque, corresponding to a current engine rotation speed Ne and an elapsed time from the start of estimation, using the map prestored in the ROM 74, the current engine rotation speed Ne and the elapsed time. On the other hand, the hybrid ECU 70, as well as the above-described JP 2005-30281 A, estimates a direct torque corresponding to the intake pressure, the intake air temperature and the throttle opening degree. The estimated direct torque corresponds to the corrected torque T in JP 2005-30281 A. A relationship between an estimated direct torque and an operation parameter, such as the intake pressure of the engine 22, is obtained in advance through an experiment, and is stored in the ROM 74 as a map. Alternatively the estimated direct torque may be set as 1/pxTg for simplification.

[0030] The torque Tg of the motor MGl is determined from a preset relationship between the torque command to the motor MGl and the rotation speed of the engine 22 at the time of starting the engine 22, and is, specifically, determined on the basis of the rotation speed of the engine 22 and the crank angle. Then, the estimated direct torque and the derived amount of pulsation of the direct torque are added together to obtain a final estimated direct torque. When the estimated direct torque is computed as described above, a final torque command Tm2 to the motor MG2 obtained by subtracting the estimated direct torque from the torque command to the motor MG2, required to meet the required torque, is output. Note that the torque command Tm2tmp to the motor MG2, required to meet the required torque, is specifically computed from a required torque Tr*, a torque command Tml* to the motor MGl and the gear ratio p of the power distribution integration mechanism 30 by the following mathematical expression.

Tm2tmp = (Tr*+Tml */p)Gr

Here, Gr is the gear ratio of the speed reduction gear 35. Of course, the torque of the motor MG2 is limited within the range of input/output limits Win and Wout of the battery 50, so, for example, when the torque command Tm2tmp to the motor MG2 exceeds a torque upper limit Tmax determined from the output limit Wout of the battery, the torque command value of the motor MG2 is limited to Tmax, and the final torque command Tm2 to the motor MG2 is generated by subtracting the estimated direct torque from the limited value.

[0031] FIG. 6 shows an example of the map stored in the ROM 74 of the hybrid ECU 70, that is, an example of the map that defines the relationship among the rotation speed of the engine 22, the elapsed time from the estimation start timing and the amount of pulsation of the direct torque. In the graph, the abscissa axis represents an elapsed time (msec) from the estimation start timing, the ordinate axis represents a direct torque pulsation amount (Nm), and values at various rotation speeds of the engine 22 are shown. The map is shown in the form of graph; however, of course, the map may be shown in the form of table by a combination of engine rotation speed, elapsed time and pulsation amount.

[0032] Note that, as can be understood from the above description, the estimated direct torque is derived from the map that defines the relationship between the operation parameter, such as the intake pressure of the engine 22, and the estimated direct torque, and the estimated direct torque pulsation amount is derived from the map that defines the relationship between the rotation speed of the engine 22, the elapsed time and the estimated direct torque pulsation amount, so it is applicable that the relationship among the operation parameter, such as the intake pressure of the engine 22, the rotation speed of the engine 22, the elapsed time and the final estimated direct torque is defined as a map or a table and then a final estimated direct torque is directly derived with the use of the map or table.

[0033] FIG. 7 shows a flowchart of an engine start control routine executed by the hybrid ECU 70 in the present embodiment. The routine is executed when a command to start the engine 22 is issued.

[0034] First, the hybrid ECU 70 determines whether the process of starting the engine 22 is being executed (S101). When the process of starting the engine 22 is not being executed, an estimation start determination flag is set to an off state as a default (S 106).

[0035] On the other hand, when the process of starting the engine 22 is being executed, subsequently, it is determined whether the crank angle of the engine 22 (the engine 22 is abbreviated as ENG in the flowchart for the sake of convenience) is around the TDC because the crank angle falls within the predetermined range, the engine rotation speed is around the resonance frequency band because the engine rotation speed falls within the predetermined range and the estimation start determination flag remains in the off state (S 102). Here, the predetermined range that is a threshold for determining whether the crank angle is around the TDC may be appropriately set, and may be, for example, set to a crank angle of five degrees (°CA), a crank angle of ten degrees (°CA), or the like, with respect to the TDC. In addition, the predetermined range that is a threshold for determining whether the engine rotation speed is around the resonance frequency band may also be similarly appropriately set. Of course, in S102, instead of determining whether the crank angle falls within the predetermined range and the engine rotation speed falls within the predetermined range, it may be determined whether the difference between the crank angle and the TDC falls within a predetermined allowable range and the difference between the engine rotation speed and the resonance frequency band falls within an allowable range. Note that the crank angle is detected by the crank position sensor 23 a attached to the crankshaft 26.

[0036] Note that the process of S I 02 is, in short, the process of determining whether the crank position is the TDC and the engine rotation speed is the resonance frequency band, and is intended to determine with allowances of differences within the predetermined ranges. Thus, to put it briefly, it is determined whether the crank position is the TDC and the engine rotation speed is the resonance frequency band.

[0037] When affirmative determination is made in S 102, that is, the crank angle is around the TDC because the crank angle falls within the predetermined range, the rotation speed of the engine 22 is around the resonance frequency band because the rotation speed falls within the predetermined range and the estimation start determination flag is in the off state, the hybrid ECU 70 sets this time point as the estimation start timing, acquires the rotation speed of the engine 22 at this time point and starts a time measuring timer from 0, and further sets the estimation start determination flag from the off state to an on state (S 103). On the other hand, when the crank angle falls outside the predetermine range, when the engine rotation speed falls outside the predetermined range or when the estimation start determination flag is not in the off state, the process of S103 is not executed.

[0038] Subsequently, the hybrid ECU 70 determines whether the estimation start determination flag is in the on state (S 104). Then, when the estimation start determination flag is in the on state, an elapsed time from the estimation start timing is accumulated (S 105). That is, an elapsed time value measured by the time measuring timer is acquired. On the other hand, when the estimation start determination flag is not in the on state but in the off state, the time measuring timer is cleared and returned to zero (S 107).

[0039] As described above, when the crank angle is around the TDC and the engine rotation speed is around the resonance frequency band, the engine rotation speed is acquired, and the elapsed time from the estimation start timing is acquired. After that, the hybrid ECU 70 derives the pulsation amount of the direct torque using the engine rotation speed and the elapsed time, estimates a final direct torque, and generates a torque command to the motor MG2, required to cancel the direct torque that incorporates the pulsation amount (S 108).

[0040] Note that, after starting the engine 22, in the routine that repeats the processes in S 101 and the following steps again, negative determination is made in the determination process of S 101, so the estimation start determination flag is set from the on state to the off state (S 106). In this case, no reaction torque as a result of cranking occurs, so the torque command to the motor MG2 is a torque command corresponding to the required torque.

[0041] FIG. 8 shows a temporal variation in the torque of the motor MG2 in the present embodiment. In the graph, the abscissa axis represents time, and the ordinate axis represents the torque of the motor MG2. In the graph, the solid line indicates a torque in the case where a pulsation amount is not taken into consideration, and the broken line indicates a torque in the case where a pulsation amount is taken into consideration and is the torque of MG2 in the present embodiment. The pulsation amount of the reaction torque that occurs at the time of cranking the engine 22 is also reliably cancelled by the torque of the MG2, so a torque shock at the time of the engine start is effectively suppressed, and drivability further improves.