Patent Publication Number: US-2007101806-A1

Title: Engine misfire identification device for internal combustion engine and hybrid vehicle equipped with the same

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an engine misfire identification device for an internal combustion engine and a hybrid vehicle equipped with the engine misfire identification device. More specifically the invention pertains to an engine misfire identification device mounted on a hybrid vehicle equipped with an internal combustion engine and a motor, as well as to a hybrid vehicle equipped with the internal combustion engine, the motor, and the engine misfire identification device.  
      2. Description of the Prior Art  
      One proposed engine misfire identification device cuts off the fuel supply to all of multiple cylinders in an engine for a preset time period during a load operation of the engine and sequentially allows the fuel supply to one of the multiple cylinders to identify a misfired cylinder (see, for example, Japanese Patent Laid-Open Gazette No. 2000-248989). Another proposed engine misfire identification device is mounted on a hybrid vehicle and controls the operation of a motor to minimize a variation in rotation speed of an engine during a load operation of the engine to enhance the accuracy of engine misfire identification (see, for example, Japanese Patent Laid-Open Gazette No. 2001-271695). Still another proposed engine misfire identification device controls the operation of a motor to drive an engine at a preset fixed rotation speed during a stop of a vehicle to reduce a fluctuating factor of engine output and enhance the accuracy of engine misfire identification (see, for example, Japanese Patent Laid-Open Gazette No. 2001-268711).  
     SUMMARY OF THE INVENTION  
      In the general hybrid vehicle, the engine is driven intermittently or is driven in a specific operation range for the enhanced energy efficiency. It is accordingly difficult to perform engine misfire identification at an appropriate frequency. Any of the prior art techniques described above may be adopted for the engine misfire identification. Execution of the engine misfire identification regardless of the driver&#39;s operation request of the hybrid vehicle or regardless of the state of the hybrid vehicle (especially the state of charge of a battery) may result in a failed response to the driver&#39;s operation request or may worsen the state of the hybrid vehicle.  
      The engine misfire identification device of the invention for identifying a misfire in an internal combustion engine, the hybrid vehicle equipped with the engine misfire identification device, and the corresponding engine misfire identification method of identifying a misfire in the internal combustion engine thus aim to enhance the frequency of engine misfire identification of the internal combustion engine mounted on the hybrid vehicle. The engine misfire identification device of the invention for identifying a misfire in an internal combustion engine, the hybrid vehicle equipped with the engine misfire identification device, and the corresponding engine misfire identification method of identifying a misfire in the internal combustion engine also aim to perform suitable engine misfire identification of the internal combustion engine according to the state of the hybrid vehicle. The engine misfire identification device of the invention for identifying a misfire in an internal combustion engine, the hybrid vehicle equipped with the engine misfire identification device, and the corresponding engine misfire identification method of identifying a misfire in the internal combustion engine further aim to perform engine misfire identification in a wide operation range of the internal combustion engine.  
      In order to attain at least part of the above and the other related objects, the engine misfire identification device of the invention for identifying a misfire in an internal combustion engine, the hybrid vehicle equipped with the engine misfire identification device, and the corresponding engine misfire identification method of identifying a misfire in the internal combustion engine have the configurations discussed below.  
      The present invention is directed to an engine misfire identification device to identify a misfire in an internal combustion engine mounted on a hybrid vehicle. The hybrid vehicle includes: an internal combustion engine; a first motor that is used for motoring the internal combustion engine and for power generation with output power of the internal combustion engine; a second motor that has power output capability of outputting a driving power, and an accumulator unit that receives and transmits electric power from and to the first motor and the second motor. The engine misfire identification device includes: a state detection module that detects a state of said hybrid vehicle; an engine misfire identification pattern specification module that, when an instruction of engine misfire identification is given, specifies an executable engine misfire identification pattern based on the instruction of engine misfire identification and the detected state of said hybrid vehicle; and an engine misfire identification module that performs engine misfire identification of the internal combustion engine according to the specified engine misfire identification pattern.  
      When an instruction of engine misfire identification is given, the engine misfire identification device of the invention specifies the executable engine misfire identification pattern based on the given instruction of engine misfire identification and the state of the hybrid vehicle. The engine misfire identification device then performs engine misfire identification of the internal combustion engine according to the specified engine misfire identification pattern. The engine misfire identification for the internal combustion engine is thus performed according to the engine misfire identification pattern specified based on the state of the vehicle and based on the given instruction of engine misfire identification. This arrangement enables engine misfire identification in a wide operation range of the internal combustion engine, while enhancing the frequency of engine misfire identification for the internal combustion engine.  
      In one preferable application of the engine misfire identification device of the invention, the instruction of engine misfire identification includes multiple different instructions of engine misfire identification caused by multiple different factors. The engine misfire identification pattern specification module specifies the engine misfire identification pattern based on a factor causing one of the multiple instructions of engine misfire identification. The engine misfire identification for the internal combustion engine is thus performed according to the engine misfire identification pattern specified based on the factor causing one of the multiple instructions of engine misfire identification. The multiple different instructions of engine misfire identification may include at least one of an instruction caused by elapse of at least a preset time period since a last engine misfire identification, an instruction caused by a drive of at least a preset distance since the last engine misfire identification, an instruction caused by system activation of the hybrid vehicle, an instruction caused by requirement for operation of the internal combustion engine, and an instruction caused by an operator&#39;s preset engine misfire identification operation.  
      In one preferable embodiment of the engine misfire identification device of the invention, the state detection module detects a charge-requirement state that requires charging the accumulator unit. In response to detection of the charge-requirement state of the accumulator unit by the state detection module, the engine misfire identification pattern specification module sets an engine misfire identification pattern in a specific range with preference to charging the accumulator unit. This arrangement gives preference to the charge state of the accumulator unit and thus effectively prevents overcharge or over-discharge of the accumulator unit.  
      In another preferable embodiment of the engine misfire identification device of the invention, the state detection module measures a vehicle speed of the hybrid vehicle. The engine misfire identification pattern specification module sets an operation range of the internal combustion engine according to the measured vehicle speed and specifies the engine misfire identification pattern in the set operation range. This arrangement ensures the engine misfire identification in the suitable operation range of the internal combustion engine corresponding to the vehicle speed and thus effectively prevents the driver or any passenger on the hybrid vehicle from feeling uncomfortable due to the engine misfire identification in the unsuitable operation range of the internal combustion engine against the vehicle speed.  
      In still another preferable embodiment of the engine misfire identification device of the invention, the state detection module detects an operating state of the internal combustion engine. In response to detection of a load operation state of the internal combustion engine by the state detection module, the engine misfire identification pattern specification module sets an engine misfire identification pattern with stop of fuel supply to one of multiple cylinders in the internal combustion engine. In response to detection of a motoring state of the internal combustion engine with no fuel supply, the engine misfire identification pattern specification module sets an engine misfire identification pattern with fuel supply to and ignition in one of the multiple cylinders in the internal combustion engine. This arrangement effectively avoids unnecessary operations of the internal combustion engine.  
      The present invention is directed to a hybrid vehicle including: the internal combustion engine; a first motor that is used for motoring the internal combustion engine and for power generation with output power of the internal combustion engine; a second motor that has power output capability of outputting a driving power, an accumulator unit that receives and transmits electric power from and to the first motor and the second motor, a state detection module that detects a state of said hybrid vehicle; an engine misfire identification pattern specification module that, when an instruction of engine misfire identification is given, specifies an executable engine misfire identification pattern based on the instruction of engine misfire identification and the detected state of said hybrid vehicle; and an engine misfire identification module that performs engine misfire identification of the internal combustion engine according to the specified engine misfire identification pattern.  
      When an instruction of engine misfire identification is given, the hybrid vehicle of the invention specifies the executable engine misfire identification pattern based on the given instruction of engine misfire identification and the state of the hybrid vehicle. The engine misfire identification device then performs engine misfire identification of the internal combustion engine according to the specified engine misfire identification pattern. The engine misfire identification for the internal combustion engine is thus performed according to the engine misfire identification pattern specified based on the state of the vehicle and based on the given instruction of engine misfire identification. This arrangement enables engine misfire identification in a wide operation range of the internal combustion engine, while enhancing the frequency of engine misfire identification for the internal combustion engine.  
      In one preferable application of the hybrid vehicle of the invention, the instruction of engine misfire identification includes multiple different instructions of engine misfire identification caused by multiple different factors, and said engine misfire identification pattern specification module specifies the engine misfire identification pattern based on a factor causing one of the multiple instructions of engine misfire identification. The multiple different instructions of engine misfire identification include at least one of an instruction caused by elapse of at least a preset time period since a last engine misfire identification, an instruction caused by a drive of at least a preset distance since the last engine misfire identification, an instruction caused by system activation of said hybrid vehicle, an instruction caused by requirement for operation of the internal combustion engine, and an instruction caused by an operator&#39;s preset engine misfire identification operation.  
      In one preferable application of the hybrid vehicle of the invention, said state detection module detects a charge-requirement state that requires charging the accumulator unit, and in response to detection of the charge-requirement state of the accumulator unit by said state detection module, said engine misfire identification pattern specification module sets an engine misfire identification pattern in a specific range with preference to charging the accumulator unit. In another preferable application of the hybrid vehicle of the invention, said state detection module measures a vehicle speed of said hybrid vehicle, and said engine misfire identification pattern specification module sets an operation range of the internal combustion engine according to the measured vehicle speed and specifies the engine misfire identification pattern in the set operation range. In another preferable application of the hybrid vehicle of the invention, said state detection module detects an operating state of the internal combustion engine, and in response to detection of a load operation state of the internal combustion engine by said state detection module, said engine misfire identification pattern specification module sets an engine misfire identification pattern with stop of fuel supply to one of multiple cylinders in the internal combustion engine, in response to detection of a motoring state of the internal combustion engine with no fuel supply, said engine misfire identification pattern specification module setting an engine misfire identification pattern with fuel supply to and ignition in one of the multiple cylinders in the internal combustion engine.  
      In one preferable application of the hybrid vehicle of the invention, said hybrid vehicle further includes: a three shaft-type power input output module that is linked to three shafts, an output shaft of the internal combustion engine, a driveshaft linked with an axle of said hybrid vehicle, and a rotating shaft of the first motor, and inputs and outputs power from and to a residual one shaft based on powers input from and output to any two shafts among the three shafts.  
      The present invention is directed to an engine misfire identification method of identifying a misfire in an internal combustion engine mounted on a hybrid vehicle. The hybrid vehicle includes: the internal combustion engine; a first motor that is used for motoring the internal combustion engine and for power generation with output power of the internal combustion engine; a second motor that has power output capability of outputting a driving power, and an accumulator unit that receives and transmits electric power from and to the first motor and the second motor. The engine misfire identification method includes the steps of: when an instruction of engine misfire identification is given, specifying an executable engine misfire identification pattern based on the instruction of engine misfire identification and a state of said hybrid vehicle; and performing engine misfire identification of the internal combustion engine according to the specified engine misfire identification pattern.  
      The engine misfire identification method of identifying a misfire in an internal combustion engine of the invention, when an instruction of engine misfire identification is given, the engine misfire identification device of the invention specifies the executable engine misfire identification pattern based on the given instruction of engine misfire identification and the state of the hybrid vehicle. The engine misfire identification device then performs engine misfire identification of the internal combustion engine according to the specified engine misfire identification pattern. The engine misfire identification for the internal combustion engine is thus performed according to the engine misfire identification pattern specified based on the state of the vehicle and based on the given instruction of engine misfire identification. This arrangement enables engine misfire identification in a wide operation range of the internal combustion engine, while enhancing the frequency of engine misfire identification for the internal combustion engine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  schematically illustrates the configuration of a hybrid vehicle equipped in one embodiment of the invention;  
       FIG. 2  schematically shows the structure of an engine mounted on the hybrid vehicle of the embodiment;  
       FIG. 3  is a flowchart showing an engine misfire identification instruction routine executed by a hybrid electronic control unit included in the hybrid vehicle of the embodiment;  
       FIG. 4  is a flowchart showing an engine misfire identification routine executed by an engine ECU included in the hybrid vehicle of the embodiment;  
       FIG. 5  is a flowchart showing an engine misfire identification drive control routine executed by the hybrid electronic control unit;  
       FIG. 6  shows one example of a torque demand setting map;  
       FIG. 7  is an alignment chart showing torque-rotation speed dynamics of respective rotational elements of a power distribution integration mechanism included in the hybrid vehicle of the embodiment;  
       FIG. 8  schematically illustrates the configuration of another hybrid vehicle in one modified example; and  
       FIG. 9  schematically illustrates the configuration of still another hybrid vehicle in another modified example. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      One mode of carrying out the invention is discussed below as a preferred embodiment.  FIG. 1  schematically illustrates the construction of a hybrid vehicle  20  with a power output apparatus mounted thereon in one embodiment of the invention. As illustrated, the hybrid vehicle  20  of the embodiment includes an engine  22 , a three shaft-type power distribution integration mechanism  30  that is linked with a crankshaft  26  functioning as an output shaft of the engine  22  via a damper  28 , a motor MG 1  that is linked with the power distribution integration mechanism  30  and is capable of generating electric power, a reduction gear  35  that is attached to a ring gear shaft  32   a  functioning as a drive shaft connected with the power distribution integration mechanism  30 , another motor MG 2  that is linked with the reduction gear  35 , and a hybrid electronic control unit  70  that controls the whole power output apparatus.  
      The engine  22  is an internal combustion engine that consumes a hydrocarbon fuel, such as gasoline or light oil, to output power. As shown in  FIG. 2 , the air cleaned by an air cleaner  122  and taken in via a throttle valve  124  is mixed with the atomized fuel injected by a fuel injection valve  126  to the air-fuel mixture. The air-fuel mixture is introduced into a combustion chamber via an intake valve  128 . The introduced air-fuel mixture is ignited with spark made by a spark plug  130  to be explosively combusted. The reciprocating motions of a piston  132  by the combustion energy are converted into rotational motions of a crankshaft  23 . The exhaust from the engine  22  goes through a catalytic conversion unit  134  (filled with three-way catalyst) to convert toxic components included in the exhaust, that is, carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx), into harmless components, and is discharged to the outside air.  
      The engine  22  is under control of an engine electronic control unit  24  (hereafter referred to as engine ECU  24 ). The engine ECU  24  is constructed as a microprocessor including a CPU  24   a , a ROM  24   b  that stores processing programs, a RAM  24   c  that temporarily stores data, input and output ports (not shown), and a communication port (not shown). The engine ECU  24  receives, via its input port, diverse signals from various sensors that measure and detect the operating conditions of the engine  22 . The signals input into the engine ECU  24  include a crank position from a crank position sensor  140  detected as the rotational position of the crankshaft  26 , a cooling water temperature from a water temperature sensor  142  measured as the temperature of cooling water in the engine  22 , an in-cylinder pressure Pin from a pressure sensor  143  located in the combustion chamber, a cam position from a cam position sensor  144  detected as the rotational position of a camshaft driven to open and close the intake valve  128  and an exhaust valve for gas intake and exhaust into and from the combustion chamber, a throttle valve position from a throttle valve position sensor  146  detected as the opening or position of the throttle valve  124 , an air flow meter signal AF from an air flow meter  148  located in an air intake conduit, and an intake air temperature from a temperature sensor  149  located in the air intake conduit. The engine ECU  24  outputs, via its output port, diverse control signals and driving signals to drive and control the engine  22 . The signals output from the engine ECU  24  include driving signals to the fuel injection valve  126 , driving signals to a throttle valve motor  136  for regulating the position of the throttle valve  124 , control signals to an ignition coil  138  integrated with an igniter, and control signals to a variable valve timing mechanism  150  to vary the open and close timings of the intake valve  128 . The engine ECU  24  establishes communication with the hybrid electronic control unit  70  to drive and control the engine  22  in response to control signals received from the hybrid electronic control unit  70  and to output data regarding the operating conditions of the engine  22  to the hybrid electronic control unit  70  according to the requirements.  
      The power distribution and integration mechanism  30  has a sun gear  31  that is an external gear, a ring gear  32  that is an internal gear and is arranged concentrically with the sun gear  31 , multiple pinion gears  33  that engage with the sun gear  31  and with the ring gear  32 , and a carrier  34  that holds the multiple pinion gears  33  in such a manner as to allow free revolution thereof and free rotation thereof on the respective axes. Namely the power distribution and integration mechanism  30  is constructed as a planetary gear mechanism that allows for differential motions of the sun gear  31 , the ring gear  32 , and the carrier  34  as rotational elements. The carrier  34 , the sun gear  31 , and the ring gear  32  in the power distribution and integration mechanism  30  are respectively coupled with the crankshaft  26  of the engine  22 , the motor MG 1 , and the reduction gear  35  via ring gear shaft  32   a . While the motor MG 1  functions as a generator, the power output from the engine  22  and input through the carrier  34  is distributed into the sun gear  31  and the ring gear  32  according to the gear ratio. While the motor MG 1  functions as a motor, on the other hand, the power output from the engine  22  and input through the carrier  34  is combined with the power output from the motor MG 1  and input through the sun gear  31  and the composite power is output to the ring gear  32 . The power output to the ring gear  32  is thus finally transmitted to the driving wheels  63   a  and  63   b  via the gear mechanism  60 , and the differential gear  62  from ring gear shaft  32   a.    
      Both the motors MG 1  and MG 2  are known synchronous motor generators that are driven as a generator and as a motor. The motors MG 1  and MG 2  transmit electric power to and from a battery  50  via inverters  41  and  42 . Power lines  54  that connect the inverters  41  and  42  with the battery  50  are constructed as a positive electrode bus line and a negative electrode bus line shared by the inverters  41  and  42 . This arrangement enables the electric power generated by one of the motors MG 1  and MG 2  to be consumed by the other motor. The battery  50  is charged with a surplus of the electric power generated by the motor MG 1  or MG 2  and is discharged to supplement an insufficiency of the electric power. When the power balance is attained between the motors MG 1  and MG 2 , the battery  50  is neither charged nor discharged. Operations of both the motors MG 1  and MG 2  are controlled by a motor electronic control unit (hereafter referred to as motor ECU)  40 . The motor ECU  40  receives diverse signals required for controlling the operations of the motors MG 1  and MG 2 , for example, signals from rotational position detection sensors  43  and  44  that detect the rotational positions of rotors in the motors MG 1  and MG 2  and phase currents applied to the motors MG 1  and MG 2  and measured by current sensors (not shown). The motor ECU  40  outputs switching control signals to the inverters  41  and  42 . The motor ECU  40  communicates with the hybrid electronic control unit  70  to control operations of the motors MG 1  and MG 2  in response to control signals transmitted from the hybrid electronic control unit  70  while outputting data relating to the operating conditions of the motors MG 1  and MG 2  to the hybrid electronic control unit  70  according to the requirements.  
      The battery  50  is under control of a battery electronic control unit (hereafter referred to as battery ECU)  52 . The battery ECU  52  receives diverse signals required for control of the battery  50 , for example, an inter-terminal voltage measured by a voltage sensor (not shown) disposed between terminals of the battery  50 , a charge-discharge current measured by a current sensor (not shown) attached to the power line  54  connected with the output terminal of the battery  50 , and a battery temperature Tb measured by a temperature sensor  51  attached to the battery  50 . The battery ECU  52  outputs data relating to the state of the battery  50  to the hybrid electronic control unit  70  via communication according to the requirements. The battery ECU  52  calculates a state of charge (SOC) of the battery  50 , based on the accumulated charge-discharge current measured by the current sensor, for control of the battery  50 .  
      The hybrid electronic control unit  70  is constructed as a microprocessor including a CPU  72 , a ROM  74  that stores processing programs, a RAM  76  that temporarily stores data, a timer  78  that counts time, and a non-illustrated input-output port, and a non-illustrated communication port. The hybrid electronic control unit  70  receives various inputs via the input port: an ignition signal from an ignition switch  80 , a gearshift position SP from a gearshift position sensor  82  that detects the current position of a gearshift lever  81 , an accelerator opening Acc from an accelerator pedal position sensor  84  that measures a step-on amount of an accelerator pedal  83 , a brake pedal position BP from a brake pedal position sensor  86  that measures a step-on amount of a brake pedal  85 , a vehicle speed V from a vehicle speed sensor  88 , and the on-off condition of the engine misfire identification switch SWj corresponding to the driver&#39;s on-off operation of the engine misfire identification switch  89  that performs engine misfire identification for the purpose of maintenance. The hybrid electronic control unit  70  communicates with the engine ECU  24 , the motor ECU  40 , and the battery ECU  52  via the communication port to transmit diverse control signals and data to and from the engine ECU  24 , the motor ECU  40 , and the battery ECU  52 , as mentioned previously.  
      The hybrid vehicle  20  of the embodiment thus constructed calculates a torque demand to be output to the ring gear shaft  32   a  functioning as the drive shaft, based on observed values of a vehicle speed V and an accelerator opening Acc, which corresponds to a driver&#39;s step-on amount of an accelerator pedal  83 . The engine  22  and the motors MG 1  and MG 2  are subjected to operation control to output a required level of power corresponding to the calculated torque demand to the ring gear shaft  32   a . The operation control of the engine  22  and the motors MG 1  and MG 2  selectively effectuates one of a torque conversion drive mode, a charge-discharge drive mode, and a motor drive mode. The torque conversion drive mode controls the operations of the engine  22  to output a quantity of power equivalent to the required level of power, while driving and controlling the motors MG 1  and MG 2  to cause all the power output from the engine  22  to be subjected to torque conversion by means of the power distribution integration mechanism  30  and the motors MG 1  and MG 2  and output to the ring gear shaft  32   a . The charge-discharge drive mode controls the operations of the engine  22  to output a quantity of power equivalent to the sum of the required level of power and a quantity of electric power consumed by charging the battery  50  or supplied by discharging the battery  50 , while driving and controlling the motors MG 1  and MG 2  to cause all or part of the power output from the engine  22  equivalent to the required level of power to be subjected to torque conversion by means of the power distribution integration mechanism  30  and the motors MG 1  and MG 2  and output to the ring gear shaft  32   a , simultaneously with charge or discharge of the battery  50 . The motor drive mode stops the operations of the engine  22  and drives and controls the motor MG 2  to output a quantity of power equivalent to the required level of power to the ring gear shaft  32   a.    
      The description regards an engine misfire identification process to identify a misfire in the engine  22  mounted on the hybrid vehicle  20 .  FIG. 3  is a flowchart showing an engine misfire identification instruction routine executed by the hybrid electronic control unit  70 . This instruction routine is triggered by system activation of the hybrid vehicle  20  or by the driver&#39;s operation of an engine misfire identification switch  89  to turn on an engine misfire identification switch SWj and is further executed repeatedly at preset time intervals (for example, at every several hours)  
      In the engine misfire identification instruction routine of  FIG. 3 , the CPU  72  of the hybrid electronic control unit  70  first inputs various data required for instruction of engine misfire identification, that is, a frequency of system activation Nj of the hybrid vehicle  20  since the last engine misfire identification, an elapsed time Tj since the last engine misfire identification, the on-off condition of the engine misfire identification switch SWj corresponding to the driver&#39;s on-off operation of the engine misfire identification switch  89 , the state of the engine  22 , the vehicle speed V from the vehicle speed sensor  88 , and the state of charge SOC of the battery  50  (step S 100 ). The frequency of system activation Nj since the last engine misfire identification and the elapsed time Tj since the last engine misfire identification are entered, for example, by reading the last count of the frequency of system activation Nj and the count of the elapsed time Tj on a timer  78  from the storage of the RAM  76 . The state of the engine  22  is defined by entries of the operation or non-operation of the engine  22  and the loading state of the engine  22 . The state of charge SOC of the battery  50  is computed from the accumulated charge-discharge current of the battery  50  and is received from the battery ECU  52  by communication.  
      After the data input, the CPU  72  specifies whether the engine misfire identification switch SWj is off or on (step S 110 ). In response to the on condition of the engine misfire identification switch SWj (step S 110 : No), there is a requirement of engine misfire identification for the purpose of maintenance. The CPU  72  thus gives the engine ECU  24  an instruction of engine misfire identification across the whole operable range of the engine  22  in the hybrid vehicle  20  (step S 120 ). The CPU  72  then exits from this engine misfire identification instruction routine of  FIG. 3 . In this state, the hybrid vehicle  20  does not run but stops. The thorough engine misfire identification is accordingly performed for the purpose of maintenance over the whole operable range of the engine  22  with a sequential variation in drive point of the engine  22 . In this embodiment, the engine misfire identification for the purpose of maintenance is referred to as maintenance-based engine misfire identification pattern.  
      In response to the off condition of the engine misfire identification switch SWj (step S 110 : Yes), on the other hand, the CPU  72  makes a comparison between the frequency of system activation Nj from the last engine misfire identification and a preset reference number Nref and a comparison between the elapsed time Tj since the last engine misfire identification and a preset reference time Tref (step S 130 ). When the frequency of system activation Nj is not greater than the preset reference number Nref and when the elapsed time Tj is not longer than the preset reference time Tref (step S 130 ; No), there is no requirement of engine misfire identification. The CPU  72  thus immediately terminates this engine misfire identification instruction routine of  FIG. 3 . When the frequency of system activation Nj is greater than the preset reference number Nref or when the elapsed time Tj is longer than the preset reference time Tref (step S 130 : Yes), on the other hand, there is a requirement of engine misfire identification. The CPU  72  accordingly identifies the state of the engine  22  (step S 140 ). In a stop state of the engine  22  (step S 140 ), the CPU  72  specifies no urgent need of the immediate restart of the engine  22  for engine misfire identification and thus terminates the engine misfire identification instruction routine of  FIG. 3 .  
      In a load operation state of the engine  22  (step S 140 ), the state of charge SOC of the battery  50  is compared with a preset upper charge level Shi (step S 150 ). When the state of charge SOC of the battery  50  is not less than the preset upper charge level Shi (step S 150 : No), the engine misfire identification may cause overcharge of the battery  50 . The CPU  72  accordingly specifies no requirement of engine misfire identification and exits from this engine misfire identification instruction routine of  FIG. 3 . When the state of charge SOC of the battery  50  is less than the preset upper charge level Shi (step S 150 : Yes), on the other hand, the CPU  72  specifies requirement of engine misfire identification and sets a reference upper rotation speed Nmax of the engine  22  based on the vehicle speed V (step S 160 ). The CPU  72  then gives the engine ECU  24  an instruction of engine misfire identification in a range to the reference upper rotation speed Nmax in the load operation state of the engine  22  (step S 170 ) and exits from this engine misfire identification instruction routine of  FIG. 3 . The reference upper rotation speed Nmax represents a maximum rotation speed of the engine  22  allowed for engine misfire identification and is set to a greater value with an increase in vehicle speed V. Such setting is because the engine misfire identification in the operation of the engine  22  at a higher rotation speed than the normal rotation speed against the vehicle speed may cause the driver to feel something is wrong. In this embodiment, the engine misfire identification in the range to the reference upper rotation speed Nmax in the load operation state of the engine  22  is referred to as load-operation-state engine misfire identification pattern.  
      In a motoring state of the engine  22  (step S 140 ), the state of charge SOC of the battery  50  is compared with a preset lower charge level Slow (step S 180 ). When the state of charge SOC of the battery  50  is less than the preset lower charge level Slow (step S 180 : No), the engine misfire identification may cause over-discharge of the battery  50 . The CPU  72  accordingly specifies no requirement of engine misfire identification and exits from this engine misfire identification instruction routine of  FIG. 3 . When the state of charge SOC of the battery  50  is not less than the preset lower charge level Slow (step S 180 : Yes), on the other hand, the CPU  72  specifies requirement of engine misfire identification and sets the reference upper rotation speed Nmax of the engine  22  based on the vehicle speed V (step S 190 ). The CPU  72  then gives the engine ECU  24  an instruction of engine misfire identification in a range to the reference upper rotation speed Nmax in the motoring state of the engine  22  (step S 200 ) and exits from this engine misfire identification instruction routine of  FIG. 3 . The reference upper rotation speed Nmax in the motoring state of the engine  22  is set to a smaller value than the reference upper rotation speed Nmax in the load operation state of the engine  22 . Such setting is because the high rotation speed in the motoring state of the engine  22  may cause the driver to feel uncomfortable. In this embodiment, the engine misfire identification in the range to the reference upper rotation speed Nmax in the motoring state of the engine  22  is referred to as motoring-state engine misfire identification pattern.  
      The engine ECU  24  receives the instruction of engine misfire identification given by the hybrid electronic control unit  70  according to the engine misfire identification instruction routine of  FIG. 3  and executes an engine misfire identification routine shown in the flowchart of  FIG. 4 . In the engine misfire identification routine of  FIG. 4 , the CPU  24   a  of the engine ECU  24  sets a target rotation speed Ne* of the engine  22  and specifies load operation or non-load operation of the engine  22  (step S 300 ). The target rotation speed Ne* of the engine  22  is set as multiple different rotation speeds selected from the whole operable range of the engine  22  in the hybrid vehicle  20  in the maintenance-based engine misfire identification pattern. The target rotation speed Ne* is set as at least one rotation speed selected from the range to the reference upper rotation speed Nmax in the load-operation-state engine misfire identification pattern or in the motoring-state engine misfire identification pattern.  
      According to the specification of the load operation or non-load operation of the engine  22  (step S 310 ), the CPU  24   a  performs engine misfire identification in the load operation state of the engine  22  (step S 320 ) or engine misfire identification in the motoring state of the engine  22  (step S 330 ). The engine misfire identification routine is then terminated. The engine misfire identification in the load operation state of the engine  22  is based on a variation in rotation speed (rotation change) of the crankshaft  26 , which is computed from the crank position detected by the crank position sensor  140  attached to the crankshaft  26  when the fuel supply is sequentially cut off to one of the multiple cylinders in the operation of the engine  22  at the target rotation speed Ne*. The engine misfire identification in the motoring state of the engine  22  is based on a rotation change of the crankshaft  26  when fuel injection and ignition are performed sequentially with regard to one of the multiple cylinders in the motoring state of the engine  22  at the target rotation speed Ne*. When there are multiple different target rotation speeds Ne*, the engine misfire identification in the load operation state of the engine  22  or the engine misfire identification in the motoring state of the engine  22  is repeated with regard to all the target rotation speeds Ne*. The engine misfire identification process is not characteristic of the present invention and is thus not specifically described in detail here.  
      The hybrid vehicle  20  is under drive control during engine misfire identification in the load-operation-state engine misfire identification pattern or in the motoring-state engine misfire identification pattern.  FIG. 5  is an engine misfire identification drive control routine executed by the hybrid electronic control unit  70  during engine misfire identification. This drive control routine is repeatedly executed at preset time intervals, for example, at every several hours.  
      In the engine misfire identification drive control routine of  FIG. 5 , the CPU  72  of the hybrid electronic control unit  70  first inputs various data required for control, that is, the accelerator opening Acc from the accelerator pedal position sensor  84 , the vehicle speed V from the vehicle speed sensor  88 , rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2 , the target rotation speed Ne* of the engine  22 , and an input limit Win and an output limit Wout of the battery  50  (step S 400 ). The target rotation speed Ne* of the engine  22  is that used in the engine misfire identification in the load operation state of the engine  22  at step S 320  or in the engine misfire identification in the motoring state of the engine  22  at step S 330  in the engine misfire identification routine of  FIG. 4  and is received from the engine ECU  24  by communication. The rotation speeds Nm 1  and Nm 2  of the motors MG 1  and MG 2  are computed from the rotational positions of the respective rotors in the motors MG 1  and MG 2  detected by the rotational position detection sensors  43  and  44  and are received from the motor ECU  40  by communication. The input limit Win and the output limit Wout of the battery  50  are set based on the battery temperature Tb of the battery  50  measured by the temperature sensor  51  and the state of charge SOC of the battery  50  and are received from the battery ECU  52  by communication.  
      After the data input, the CPU  72  sets a torque demand Tr* to be output to the ring gear shaft  32   a  or the drive shaft linked to the drive wheels  63   a  and  63   b  as a required torque for the hybrid vehicle  20 , based on the input accelerator opening Acc and the input vehicle speed V (step S 410 ). A concrete procedure of setting the torque demand Tr* in this embodiment stores in advance variations in torque demand Tr* against the accelerator opening Acc and the vehicle speed V as a torque demand setting map in the ROM  74  and reads the torque demand Tr* corresponding to the given accelerator opening Acc and the given vehicle speed V from this torque demand setting map. One example of the torque demand setting map is shown in  FIG. 6 .  
      The CPU  72  calculates a target rotation speed Nm 1 * of the motor MG 1  from the input target rotation speed Ne* of the engine  22 , the rotation speed Nr (=Nm 2 /Gr) of the ring gear shaft  32   a , and a gear ratio ρ of the power distribution integration mechanism  30  according to Equation (1) given below, while calculating a torque command Tm 1 * of the motor MG 1  from the calculated target rotation speed Nm 1 * and the current rotation speed Nm 1  of the motor MG 1  according to Equation (2) given below (step S 420 ):
 
 Nm 1*= Ne *·(1+ρ)/ρ− Nm 2/( Gr ·ρ)  (1)
 
 Tm 1*=Previous  Tm 1*+ k 1( Nm 1*− Nm 1)+ k 2∫( Nm 1*− Nm 1) dt   (2)
 
 Equation (1) is a dynamic relational expression of the rotation elements included in the power distribution integration mechanism  30 .  FIG. 7  is an alignment chart showing torque-rotation speed dynamics of the respective rotation elements included in the power distribution integration mechanism  30 . The left axis ‘S’ represents the rotation speed of the sun gear  31  that is equivalent to the rotation speed Nm 1  of the motor MG 1 . The middle axis ‘C’ represents the rotation speed of the carrier  34  that is equivalent to the rotation speed Ne of the engine  22 . The right axis ‘R’ represents the rotation speed Nr of the ring gear  32  (ring gear shaft  32   a ) obtained by dividing the rotation speed Nm 2  of the motor MG 2  by a gear ratio Gr of the reduction gear  35 . Two upward thick arrows on the axis ‘R’ in  FIG. 7  respectively show a torque that is directly transmitted to the ring gear shaft  32   a  when the torque Te is output from the engine  22  in steady operation at a specific drive point of the target rotation speed Ne* and the torque Te, and a torque that is applied to the ring gear shaft  32   a  via the reduction gear  35  when a torque Tm 2 * is output from the motor MG 2 . The engine  22  is not driven during the engine misfire identification in the motoring state of the engine  22 . The torque Te is thus based on the friction of the engine  22  and is applied in a reverse direction. Equation (1) is readily introduced from the alignment chart of  FIG. 7 . Equation (2) is a relational expression of feedback control to drive and rotate the motor MG 1  at the target rotation speed Nm 1 *. In Equation (2) given above, ‘k 1 ’ in the second term and ‘k 2 ’ in the third term on the right side respectively denote a gain of the proportional and a gain of the integral term. 
 
      After calculation of the target rotation speed Nm 1 * and the torque command Tm 1 * of the motor MG 1 , the CPU  72  calculates a lower torque restriction Tmin and an upper torque restriction Tmax as minimum and maximum torques output from the motor MG 2  according to Equations (3) and (4) given below (step S 430 ):
 
 T min=( W in− Tm 1*· Nm 1)/ Nm 2  (3)
 
 T max=( W out− Tm 1*· Nm 1)/ Nm 2  (4)
 
 The lower torque restriction Tmin and the upper torque restriction Tmax are respectively given by dividing a difference between the input limit Win of the battery  50  and power consumption (power generation) of the motor MG 1 , which is the product of the torque command Tm 1 * and the input current rotation speed Nm 1  of the motor MG 1 , and a difference between the output limit Wout of the battery  50  and the power consumption (power generation) of the motor MG 1  by the input current rotation speed Nm 2  of the motor MG 2 . The CPU  72  then calculates a tentative motor torque Tm 2 tmp to be output from the motor MG 2  from the torque demand Tr*, the torque command Tm 1 * of the motor MG 1 , the gear ratio ρ of the power distribution integration mechanism  30 , and the gear ratio Gr of the reduction gear  35  according to Equation (5) given below (step S 440 ):
 
 Tm 2 tmp =( Tr*+Tm 1*/ρ)/ Gr   (5)
 
 The CPU  72  limits the tentative motor torque Tm 2 tmp to the range between the calculated lower torque restriction Tmin and upper torque restriction Tmax to set a torque command Tm 2 * of the motor MG 2  (step S 450 ). Setting the torque command Tm 2 * of the motor MG 2  in this manner restricts the torque demand Tr* to be output to the ring gear shaft  32   a  or the driveshaft within the range between the input limit Win and the output limit Wout of the battery  50 . Equation (5) is readily introduced from the alignment chart of  FIG. 7 . 
 
      The CPU  72  then sends the torque commands Tm 1 * and Tm 2 * of the motors MG 1  and MG 2  to the motor ECU  40  (step S 460 ) and exits from this engine misfire identification drive control routine. The motor ECU  40  receives the torque commands Tm 1 * and Tm 2 * and performs switching control of the switching elements included in the respective inverters  41  and  42  to drive the motor MG 1  with the torque command Tm 1 * and the motor MG 2  with the torque command Tm 2 *. This drive control enables the hybrid vehicle  20  even during the engine misfire identification to be driven with the torque demand Tr* output in the range of the input limit Win and the output limit Wout of the battery  50 .  
      The hybrid vehicle  20  of the embodiment specifies the engine misfire identification pattern based on the instruction of engine misfire identification or the state of the engine  22 . The engine misfire identification of the engine  22  is thus performed in the suitable engine misfire identification pattern according to the instruction of engine misfire identification or the state of the engine  22 . The hybrid vehicle  20  of the embodiment gives an instruction of engine misfire identification over the whole operation range of the engine  22  in response to the on condition of the engine misfire identification switch SWj, while giving an instruction of engine misfire identification based on the frequency of system activation Nj since the last engine misfire identification or an instruction of engine misfire identification based on the elapsed time Tj since the last engine misfire identification. The engine misfire identification is performed in the suitable engine misfire identification pattern according to the state of the engine  22 . This arrangement enables the engine misfire identification across the wide operation range of the engine  22  and enhances the frequency of misfire identification of the engine  22 . The hybrid vehicle  20  of the embodiment sets the reference upper rotation speed Nmax for the engine misfire identification as the upper limit of the operation range of the engine  22  according to the vehicle speed V and specifies the suitable engine misfire identification pattern in the range to the reference upper rotation speed Nmax. This arrangement ensures the engine misfire identification in the suitable operation range of the engine  22  corresponding to the vehicle speed V and thus effectively prevents the driver or any passenger on the hybrid vehicle  20  from feeling uncomfortable due to the engine misfire identification in the unsuitable operation range of the engine  22  against the vehicle speed V.  
      In the hybrid vehicle  20  of the embodiment, the engine misfire identification in the load operation state of the engine  22  is based on a rotation change of the crankshaft  26  when the fuel supply is sequentially cut off to one of the multiple cylinders in the operation of the engine  22  at the target rotation speed Ne*. The engine misfire identification in the motoring state of the engine  22  is based on a rotation change of the crankshaft  26  when fuel injection and ignition are performed sequentially with regard to one of the multiple cylinders in the motoring state of the engine  22  at the target rotation speed Ne*. This arrangement allows the engine misfire identification according to the state of the engine  22  and thus desirably avoids unnecessary operations of the engine  22 .  
      The hybrid vehicle  20  of the embodiment specifies the engine misfire identification pattern according to the state of charge SOC of the battery  50 , thus effectively preventing overcharge or over-discharge of the battery  50 . Even during the engine misfire identification, the hybrid vehicle  20  of the embodiment is drivable with the torque demand Tr* output corresponding to the driver&#39;s depression amount of the accelerator pedal  83  in the range of the input limit Win and the output limit Wout of the battery  50 .  
      The hybrid vehicle  20  of the embodiment sets the engine misfire identification pattern according to the state of charge SOC of the battery  50 . When the state of charge SOC indicates a requirement for immediate charge of the battery  50 , the hybrid vehicle  20  may give preference to charging the battery  50  and may not perform the engine misfire identification. The engine misfire identification is prohibited, for example, when the state of charge SOC of the battery  50  is lower than a preset reference charge level.  
      In the hybrid vehicle  20  of the embodiment, the engine misfire identification in the load operation state of the engine  22  is based on a rotation change of the crankshaft  26  when the fuel supply is sequentially cut off to one of the multiple cylinders in the operation of the engine  22  at the target rotation speed Ne*. The engine misfire identification in the motoring state of the engine  22  is based on a rotation change of the crankshaft  26  when fuel injection and ignition are performed sequentially with regard to one of the multiple cylinders in the motoring state of the engine  22  at the target rotation speed Ne*. The engine misfire identification is, however, not restricted to this technique but may be performed by any other technique.  
      The hybrid vehicle  20  of the embodiment gives an instruction of engine misfire identification over the whole operation range of the engine  22  in response to the on condition of the engine misfire identification switch SWj, while giving an instruction of engine misfire identification based on the frequency of system activation Nj since the last engine misfire identification or an instruction of engine misfire identification based on the elapsed time Tj since the last engine misfire identification. One possible modification may omit the instruction of engine misfire identification based on the frequency of system activation Nj since the last engine misfire identification or the instruction of engine misfire identification based on the elapsed time Tj since the last engine misfire identification. Another possible modification may additionally give an instruction of engine misfire identification based on the drive of or over a preset reference distance since the last engine misfire identification, an instruction of engine misfire identification in response to requirement for operation of the engine  22 , or an instruction of engine misfire identification in response to repetition of auto stop and auto restart of the engine  22  by a preset number of times.  
      The hybrid vehicle  20  of the embodiment sets the reference upper rotation speed Nmax, which is the upper limit of the operation range of the engine  22  for the engine misfire identification, based on the vehicle speed V and performs the engine misfire identification in the range to the reference upper rotation speed Nmax. One possible modification may omit the specification of the operation range of the engine  22  for the engine misfire identification based on the vehicle speed V.  
      In the hybrid vehicle  20  of the embodiment, the power of the motor MG 2  is subjected to gear change by the reduction gear  35  and is output to the ring gear shaft  32   a . In one possible modification shown as a hybrid vehicle  120  of  FIG. 8 , the power of the motor MG 2  may be output to another axle (that is, an axle linked with wheels  64   a  and  64   b ), which is different from an axle connected with the ring gear shaft  32   a  (that is, an axle linked with the wheels  63   a  and  63   b ).  
      In the hybrid vehicle  20  of the embodiment, the power of the engine  22  is output via the power distribution integration mechanism  30  to the ring gear shaft.  32   a  functioning as the drive shaft linked with the drive wheels  63   a  and  63   b . In another possible modification of  FIG. 9 , a hybrid vehicle  220  may have a pair-rotor motor  230 , which has an inner rotor  232  connected with the crankshaft  26  of the engine  22  and an outer rotor  234  connected with the drive shaft for outputting the power to the drive wheels  63   a ,  63   b  and transmits part of the power output from the engine  22  to the drive shaft while converting the residual part of the power into electric power.  
      The technique of the invention is applicable to identify a misfire in an engine mounted on a hybrid vehicle of any other configuration, which is different from any of the hybrid vehicle  20  of the embodiment and the hybrid vehicles  120  and  220  of the modified examples.  
      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.  
      The disclosure of Japanese Patent Application No. 2005-217719 filed Jul. 27, 2005 including specification, drawings and claims is incorporated herein by reference in its entirety.