Abstract:
The technique of the invention sets a relationship between the throttle opening (corresponding to the accelerator opening), the vehicle speed, and the target torque of a drive shaft, so as to enable a greater braking torque to be output in a working status of a cruise control system than a braking torque, which is output to the drive shaft in a full closed position of the accelerator opening in a non-working status of the cruise control system. This arrangement ensures output of a sufficient braking force to the drive shaft even under the condition of a relatively large drive load applied to the drive shaft, for example, during a downslope run, thus enabling the vehicle speed to be certainly kept at a preset level under the control of the cruise control system.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a power output apparatus and a movable body with a power output apparatus mounted thereon.  
           [0003]    2. Description of the Prior Art  
           [0004]    A type of proposed power output apparatus has a constant speed control system that keeps the revolving speed of a drive shaft at a preset level (for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 1-114547). A cruise control system mounted on an automobile, for example, automatically regulates, in response to a driver&#39;s setting of a desired vehicle speed, the throttle opening of an engine without any operation of an accelerator pedal, so as to keep the vehicle speed at a preset level.  
           [0005]    In a non-working status of the cruise control system, the driver can operate an accelerator pedal and a brake pedal according to the conditions of a road or another driving path (that is, the loading applied to wheels), for example, a slope, to regulate the vehicle speed to a desired level. The cruise control system in a working status, on the other hand, may not sufficiently handle the situation of a relatively large load applied to an axle, for example, during a drive on a steep slope, and fail to keep the vehicle speed at the preset level. While the vehicle runs on a relatively steep downslope, the vehicle speed may significantly exceed the preset level due to an insufficient braking force output to the axle.  
         SUMMARY OF THE INVENTION  
         [0006]    The object of the present invention is thus to provide a power output apparatus that certainly keeps the revolving speed of a drive shaft at a preset level. The object of the invention is also to certainly keep the travelling speed of a movable body with the power output apparatus mounted thereon at a preset level.  
           [0007]    In order to achieve at least a part of the aforementioned objects, the power output apparatus and the movable body with power output apparatus mounted thereon of the present invention are structured as follows.  
           [0008]    A power output apparatus of the present invention includes: a power output unit that outputs power to a drive shaft; and a controller that drives and controls the power output unit to make a power according to an accelerator opening output to the drive shaft, sets a wider power output range, in response to setting of a revolving speed, than a possible power output range according to the accelerator opening in the drive control, and drives and controls the power output unit to keep a revolving speed of the drive shaft at the preset revolving speed by output of a power in the preset power output range.  
           [0009]    The power output apparatus of the invention sets a wider power output range, in response to setting of a revolving speed, than a possible power output range according to the accelerator opening, and drives and controls the power output unit to keep the revolving speed of the drive shaft at the preset revolving speed by output of a power in the preset power output range. The arrangement of setting the wider power output range in response to setting of the revolving speed than the possible power output range according to the accelerator opening enables a power to be output to the drive shaft corresponding to each of diverse loads applied to the drive shaft. This arrangement enables the revolving speed of the drive shaft to be certainly kept at the preset revolving speed. Here the ‘power’ includes a negative power, that is, a braking force.  
           [0010]    In one preferable application of the power output apparatus of the invention, the controller sets, in response to setting of the revolving speed, a power output range to possibly output a greater braking force than a braking force output to the drive shaft in a full closed position of the accelerator opening. In one embodiment of this application, the power output unit includes an internal combustion engine that functions as a power source, and a transmission, for example, a continuously variable transmission, which changes speed of a power from the internal combustion engine and outputs the speed-changed power to the drive shaft. The controller utilizes a rotational resistance of the internal combustion engine due to regulation of a change gear ratio set in the transmission, so as to enable the greater braking force to be output to the drive shaft. In another embodiment of this application, the power output unit includes a motor that functions as a power source to output a power to the drive shaft and generates electric power in response to input of a power from the drive shaft. The controller utilizes a braking force due to regenerative control of the motor, so as to enable the greater braking force to be output to the drive shaft.  
           [0011]    A movable body of the present invention includes: a power output unit that outputs power to a drive shaft; and a controller that drives and controls the power output unit to make a power according to an accelerator opening output to the drive shaft, sets a wider power output range, in response to setting of a travelling speed, than a possible power output range according to the accelerator opening in the drive control, and drives and controls the power output unit to keep a travelling speed of the drive shaft at the preset travelling speed by output of a power in the preset power output range.  
           [0012]    The movable body of the invention sets a wider power output range, in response to setting of a travelling speed, than a possible power output range according to the accelerator opening, and drives and controls the power output unit to keep the travelling speed at the preset travelling speed by output of a power in the preset power output range. The arrangement of setting the wider power output range in response to setting of the travelling speed than the possible power output range according to the accelerator opening enables a power to be output to the drive shaft corresponding to each of diverse loads applied to the drive shaft. This arrangement enables the travelling speed to be certainly kept at the preset travelling speed. Here the ‘power’ includes a negative power, that is, a braking force.  
           [0013]    In one preferable application of the movable body of the invention, the controller sets, in response to setting of the travelling speed, a power output range to possibly output a greater braking force than a braking force output to the drive shaft in a full closed position of the accelerator opening. In one embodiment of this application, the power output unit includes an internal combustion engine that functions as a power source, and a transmission, for example, a continuously variable transmission, which changes speed of a power from the internal combustion engine and outputs the speed-changed power to the drive shaft, and the controller utilizes a rotational resistance of the internal combustion engine due to regulation of a change gear ratio set in the transmission, so as to enable the greater braking force to be output to the drive shaft. In another embodiment of this application, the power output unit includes a motor that functions as a power source to output a power to the drive shaft and generates electric power in response to input of a power from the drive shaft, and the controller utilizes a braking force due to regenerative control of the motor, so as to enable the greater braking force to be output to the drive shaft. In still another embodiment, the movable body is a vehicle.  
           [0014]    A method of controlling a power output unit of the invention outputs power to a drive shaft, the method driving and controlling the power output unit to make power according to an accelerator opening output to the drive shaft, setting a wider power output range, in response to setting of a revolving speed, than a possible power output range according to the accelerator opening in the drive control, and driving and controlling the power output unit to keep a revolving speed of the drive shaft at the preset revolving speed by output of a power in the preset power output range.  
           [0015]    The method of the invention sets a wider power output range, in response to setting of a revolving speed, than a possible power output range according to the accelerator opening, and drives and controls the power output unit to keep the revolving speed of the drive shaft at the preset revolving speed by output of a power in the preset power output range. The arrangement of setting the wider power output range in response to setting of the revolving speed than the possible power output range according to the accelerator opening enables a power to be output to the drive shaft corresponding to each of diverse loads applied to the drive shaft. This arrangement enables the revolving speed of the drive shaft to be certainly kept at the preset revolving speed. Here the ‘power’ includes a negative power, that is, a braking force.  
           [0016]    In one preferable application of the method of the invention, the method sets, in response to setting of the revolving speed, a power output range to possibly output a greater braking force than a braking force output to the drive shaft in a full closed position of the accelerator opening. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 schematically illustrates the construction of a power output apparatus  20  in one embodiment of the present invention;  
         [0018]    [0018]FIG. 2 is a flowchart showing a drive control routine executed by a hybrid ECU  70  in the power output apparatus  20  of the embodiment;  
         [0019]    [0019]FIG. 3 is a map showing a relationship between accelerator opening A, vehicle speed V, and target torque To*;  
         [0020]    [0020]FIG. 4 is a flowchart showing a cruise control-state drive control routine executed by the hybrid ECU  70  in the power output apparatus  20  of the embodiment;  
         [0021]    [0021]FIG. 5 is a map showing a relationship between throttle opening S (accelerator opening A), vehicle speed V, and target torque To*. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    One mode of carrying out the invention is discussed below as a preferred embodiment. FIG. 1 schematically illustrates the construction of a power output apparatus  20  in one embodiment of the present invention. The power output apparatus  20  of the embodiment is constructed to output power, for example, to driving wheels of a hybrid vehicle. The power output apparatus  20  includes an engine  22 , a planetary gear unit  30  linked with a crankshaft  24  i.e. an output shaft of the engine  22 , a motor  40  connected with the planetary gear unit  30  for power generation, a CVT  50  as a continuously variable transmission connected with the planetary gear unit  30  and coupled with driving wheels  66   a  and  66   b  via a differential gear  64 , and a hybrid electronic control unit (hereafter referred to as hybrid ECU)  70  for controlling the respective constituents of the whole power output apparatus  20 .  
         [0023]    The engine  22  is an internal combustion engine that uses a hydrocarbon fuel, such as gasoline or light oil, to output power. A starter motor  26  is linked with the crankshaft  24  of the engine  22  via a belt  28  to generate electric power, which is to be supplied to auxiliary machines (not shown), and start the engine  22 . An engine electronic control unit (hereafter referred to as engine ECU) takes charge of operation control of the engine  22 , for example, fuel injection control, ignition control, and intake air flow regulation. The engine ECU  29  communicates with the hybrid ECU  70  to control operations of the engine  22  in response to control signals transmitted from the hybrid ECU  70  while outputting data relating to driving conditions of the engine  22  according to the requirements.  
         [0024]    The planetary gear unit  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 , and a carrier  35  that holds a first pinion gear  33  engaging with the sun gear  31  and a second pinion gear  34  engaging with the first pinion gear  33  and the ring gear  32  in such a manner as to allow free revolution thereof and free rotation thereof on the respective axes. The planetary gear unit  30  allows for differential motions of the sun gear  31 , the ring gear  32 , and the carrier  35  as rotational elements. The crankshaft  24  of the engine  22  is coupled with the sun gear  31  of the planetary gear unit  30 . A rotating shaft  41  of the motor  40  is coupled with the carrier  35  of the planetary gear unit  30 . Output power is transmittable between the engine  22  and the motor  40  via the sun gear  31  and the carrier  35 . The carrier  35  and the ring gear  32  are linked with an input shaft  51  of the CVT  50  respectively via a clutch C 1  and a clutch C 2 . The clutch C 1  and the clutch C 2  in a coupling state prohibit differential motions of the three rotational elements, the sun gear  31 , the ring gear  32 , and the carrier  35  and cause the crankshaft  24  of the engine  22 , the rotating shaft  41  of the motor  40 , and the input shaft  51  of the CVT  50  to function as an integral rotating body. The planetary gear unit  30  also has a brake B 1  that fixes the ring gear  32  to a casing  39  and prohibits rotation of the ring gear  32 .  
         [0025]    The motor  40  is a known synchronous motor generator, which is actuated both as a generator and as a motor, and transmits electric power to and from a secondary battery  44  via an inverter  43 . The motor  40  is driven and controlled by a motor electronic control unit (hereafter referred to as motor ECU)  49 . The motor ECU  49  receives input of various signals required for drive and control of the motor  40  and various signals required for management of the secondary battery  44 , and outputs a switching control signal to the inverter  43 . The input includes, for example, a signal from a rotational position detection sensor  45  that detects the rotational position of a rotor in the motor  40 , a phase current applied to the motor  40 , which is measured by a current sensor (not shown), an inter-terminal voltage measured by a voltage sensor  46  disposed between terminals of the secondary battery  44 , a charge-discharge current measured by a current sensor  47  attached to a power line from the secondary battery  44 , and a battery temperature measured by a temperature sensor  48  attached to the secondary battery  44 . The motor ECU  49  calculates a state of charge (SOC) of the secondary battery  44 , based on the accumulated charge-discharge current measured by the current sensor  47  and the inter-terminal voltage measured by the voltage sensor  46 , for management of the secondary battery  44 . The motor ECU  49  communicates with the hybrid ECU  70  to drive and control the motor  40  in response to control signals from the hybrid ECU  70  while outputting data relating to the driving conditions of the motor  40  and the state of the secondary battery  44  to the hybrid ECU  70 .  
         [0026]    The CVT  50  has a primary pulley  53  that has a variable groove width and is linked with the input shaft  51 , a secondary pulley  54  that also has a variable groove width and is linked with an output shaft  52  as a drive shaft, a belt  55  that is spanned over the grooves of the primary pulley  53  and the secondary pulley  54 , and a first actuator  56  and a second actuator  57  that vary the groove widths of the primary pulley  53  and the secondary pulley  54 . The variation of the groove widths of the primary pulley  53  and the secondary pulley  54  by means of the first actuator  56  and the second actuator  57  results in changing the speed of a power from the input shaft  51  in a stepless manner. The stepless speed-changed power is output to the output shaft  52 . A CVT electronic control unit (hereafter referred to as CVTECU)  59  regulates the change gear ratio set in the CVT  50 . The CVTECU  59  receives a revolving speed Ni of the input shaft  51  measured by a revolving speed sensor  61  attached to the input shaft  51  and a revolving speed No of the output shaft  52  measured by a revolving speed sensor  62  attached to the output shaft  52 , and outputs driving signals to the first actuator  56  and the second actuator  57 . The CVTECU  59  communicates with the hybrid ECU  70  to regulate the change gear ratio set in the CVT  50  in response to control signals transmitted from the hybrid ECU  70 , while outputting data relating to the driving conditions of the CVT  50  to the hybrid ECU  70  according to the requirements.  
         [0027]    The hybrid ECU  70  is constructed as a microprocessor including a CPU  72 , a ROM  74  that stores processing programs, a RAM  76  that temporarily stores data, and an input-output port and a communication port (not shown). The hybrid ECU  70  receives input of various data and instruction signals via the input port. The input includes, for example, the revolving speed Ni of the input shaft  51  transmitted from the revolving speed sensor  61 , the revolving speed No of the output shaft  52  transmitted from the revolving speed sensor  62 , a gearshift position SP transmitted from a gearshift position sensor  81  that detects the operating position of a gearshift lever  80 , an accelerator opening A transmitted from an accelerator pedal position sensor  83  that measures the step-on amount of an accelerator pedal  82 , a brake pedal position BP transmitted from a brake pedal position sensor  85  that measures the step-on amount of a brake pedal  84 , and a vehicle speed V measured by a vehicle speed sensor  86 . The input also includes instruction signals from a cruise control switch  88  that gives an activation command to actuate a cruise control system (constant speed drive) as well as instructions for diverse operations (for example, setting the vehicle speed, speed reduction control, speed-up control, restoration of control, and cancellation of control) in the working status of the cruise control system. The hybrid ECU  70  outputs driving signals to the clutches C 1  and C 2  and the brake B 1  via the output port. The hybrid ECU  70  is connected with the engine ECU  29 , the motor ECU  49 , and the CVTECU  59  via the communication port to transmit data and various control signals to and from the engine ECU  29 , the motor ECU  49 , and the CVTECU  59 , as mentioned previously.  
         [0028]    The following describes the operations of the power output apparatus  20  of the embodiment thus constructed, especially the operations of the power output apparatus  20  in the working status of the cruise control system. The description first regards the basic operations of the power output apparatus  20  in the non-working status of the cruise control system, and then the operations of the power output apparatus  20  in the working status of the cruise control system. FIG. 2 is a flowchart showing a drive control routine executed by the hybrid ECU  70  of the power output apparatus  20  in the non-working status of the cruise control system. This routine is repeatedly carried out at preset time intervals while the clutches C 1  and C 2  are in the coupled state and the brake B 1  is in the released state, that is, while the crankshaft  24  of the engine  22 , the rotating shaft  41  of the motor  40 , and the input shaft  51  of the CVT  50  are rotated as an integral rotating body.  
         [0029]    When the program enters the drive control routine, the CPU  72  of the hybrid ECU  70  first receives the required signals for control, for example, the accelerator opening A from the accelerator pedal position sensor  83 , the vehicle speed V from the vehicle speed sensor  86 , the revolving speed Ni of the input shaft  51  from the revolving speed sensor  61 , the revolving speed No of the output shaft  52  from the revolving speed sensor  62 , and the state of charge (SOC) of the secondary battery  44  (step S 100 ). The CPU  72  determines a target torque To* of the output shaft  52  functioning as the drive shaft, based on the input accelerator opening A and vehicle speed V (step S 102 ). The procedure of this embodiment experimentally or otherwise specifies the relationship between the accelerator opening A, the vehicle speed V, and the target torque To* in advance and stores the relationship in the form of a torque map in the ROM  74 . The target torque To* corresponding to the input accelerator opening A and vehicle speed V is read from the torque map. FIG. 3 shows a torque map showing the relationship between the accelerator opening A, the vehicle speed V, and the target torque To*.  
         [0030]    After determination of the target torque To*, the CPU  72  multiplies the target torque To* by the revolving speed No of the output shaft  52  input at step S 100  (or the revolving speed of the output shaft  52  calculated from the vehicle speed V based on a gear ratio of the differential gear  64 ) to calculate a power required for the output shaft  52  (required power Po) (step S 104 ). The CPU  72  then sets a target power Pe* of the engine  22  and a target power Pm* of the motor  40  to cover the calculated required power Po (step S 106 ). The target powers Pe* and Pm* are set based on the magnitude of the required power Po and the state of charge (SOC) of the secondary battery  44 , in order to satisfy an equation of Po=Pe*+Pm*.  
         [0031]    After setting the target power Pe*, the CPU  72  sets a target torque Te* of the engine  22 , which ensures efficient drive of the engine  22 , and a target revolving speed Ni* of the input shaft  51 , based on the setting of the target power Pe* (step S 108 ). The CPU  72  divides the target power Pm* by the target revolving speed Ni* to calculate a target torque Tm* of the motor  40  (step S 110 ), and controls the engine  22  to attain the target torque Te*, the motor  40  to attain the target torque Tm*, and the CVT  50  to rotate the input shaft  51  at the target revolving speed Ni* (step S 112 ). The program then exits from this routine. According to the concrete procedure of controlling the engine  22 , the motor  40 , and the CVT  50 , the hybrid ECU  70  outputs the target torque Te*, the target torque Tm*, and the target revolving speed Ni* as control signals respectively to the engine ECU  29 , the motor ECU  49 , and the CVTECU  59 . The engine ECU  29  controls the engine  22  to output a torque equal to the target torque Te*. The motor ECU  49  controls the motor  40  to output a torque equal to the target torque Tm*. The CVTECU  59  controls the CVT  50  to rotate the input shaft  51  at the target revolving speed Ni*.  
         [0032]    This is the basic operations of the power output apparatus  20  in the non-working status of the cruise control system. The operations of the power output apparatus  20  of the embodiment in the working status of the cruise control system are discussed below. FIG. 4 is a flowchart showing a cruise control-state drive control routine executed by the hybrid ECU  70  in the power output apparatus  20  of the embodiment. This routine is repeatedly carried out at preset time intervals in response to a driver&#39;s operation of the cruise control switch  88  to set the cruise control system in the working status, while the clutches C 1  and C 2  are in the coupled state, the brake B 1  is in the released state, and the vehicle speed is within a predetermined range.  
         [0033]    When the program enters the cruise control-state drive control routine, the CPU  72  of the hybrid ECU  70  first reads required signals for control, for example, a preset vehicle speed V* set by the driver&#39;s operation of the cruise control switch  88 , the observed vehicle speed V from the vehicle speed sensor  86 , and observed the revolving speeds Ni and No from the revolving speed sensors  61  and  62  (step S 200 ). The CPU  72  then calculates a difference ΔV (=V*−V) between the preset vehicle speed V* and the observed vehicle speed V (step S 202 ), sets a throttle opening S, which corresponds to the accelerator opening A, to cancel the difference ΔV (step S 204 ), and determines a target torque To* of the output shaft  52  based on the throttle opening S (accelerator opening A) and the vehicle speed V according to a cruise control-state torque map (step S 206 ). The determination of the target torque To* follows a similar procedure to that of the processing at step S 102  in the routine of FIG. 2. The throttle opening S is one-to-one mapped to the accelerator opening A. The procedure experimentally or otherwise specifies a relationship between the throttle opening S, the vehicle speed V, and the target torque To* in advance and stores the relationship in the form of a cruise control-state torque map in the ROM  74 . The target torque To* corresponding to the input throttle opening S and vehicle speed V is read from the cruise control-state torque map. FIG. 5 shows a cruise control-state torque map showing the relationship between the throttle opening S (accelerator opening A), the vehicle speed V, and the target torque To*.  
         [0034]    At vehicle speeds of not lower than a specific vehicle speed making a creep torque equal to zero, the braking force in a throttle valve OFF position in the map for the cruise control-state drive control routine (shown by the solid line in FIG. 5) is set greater than the braking force in an accelerator OFF position (throttle valve OFF position) in the map for the drive control routine in FIG. 2 (shown by the broken line in FIG. 5). The range of a braking torque possibly output to the output shaft  52  in the working status of the cruise control system is set wider than the range of a braking torque possibly output to the output shaft  52  through an operation of the accelerator pedal in the non-working status of the cruise control system. This allows for output of a braking torque corresponding to a relatively large load in the driving direction applied to the output shaft  52 . For example, when the vehicle in the working status of the cruise control system runs on a downslope having a preset or greater gradient (for example, a gradient of −10%), the braking force corresponding to the load in the driving direction applied to the output shaft  52  due to the downslope may not be output to the output shaft  52  and cause the vehicle to be accelerated over the preset vehicle speed. In such cases, the driver should step on the brake pedal to reduce the speed of the vehicle. Output of the braking force corresponding to the load in the driving direction applied to the output shaft  52  due to the downslope effectively prevents the vehicle from being accelerated to have the vehicle speed V exceeding the preset vehicle speed V* and keeps the vehicle speed V at the level of the preset vehicle speed V*.  
         [0035]    After determination of the target torque To* of the output shaft  52 , the CPU  72  multiplies the target torque To* by the revolving speed No to calculate a required power Po for the output shaft  52  (step S 208 ). The required power Po of a positive value functions as a driving power, while the required power Po of a negative value functions as a braking power. The CPU  72  then sets the target power Pe* of the engine  22  and the target power Pm* of the motor  40  to make the output of the engine  22  and the output of the motor  40  cover the calculated required power Po (step S 210 ). The procedure of the embodiment sets the target powers Pe* and Pm* to satisfy an equation of Po=Pe*+Pm*. The settings of the target powers Pe* and Pm* may have any ratio. When the braking power is required as the target power Po, the engine  22  utilizes a friction torque produced by the downshift control of the change gear ratio in the CVT  50  to output the braking power, while the motor  40  utilizes the regenerative torque to output the braking power. Setting a greater share ratio of the motor  40  effectively ensures recovery of the braking energy and enhances the energy efficiency of the whole apparatus.  
         [0036]    After setting the target power Pe* of the engine  22 , the CPU  72  calculates a target torque Te* of the engine  22  from the target power Pe* and sets the revolving speed of the input shaft  51  to a target revolving speed Ni* to attain the target power Pe* (step S 212 ). The CPU  72  divides the target power Pm* by the target revolving speed Ni* to calculate a target torque Tm* of the motor  40  (step S 214 ), and controls the engine  22  to attain the target torque Te*, the motor  40  to attain the target torque Tm*, and the CVT  50  to rotate the input shaft  51  at the target revolving speed Ni* (step S 216 ). The program then exits from this routine.  
         [0037]    In the power output apparatus  20  of the embodiment, the range of the braking force possibly output to the output shaft  52  in the working status of the cruise control system is set to be greater than the range of the braking force possibly output to the output shaft  52  by the accelerator opening A in the non-working status of the cruise control system. Even when a relatively large driving load is applied to the output shaft  52  in the working status of the cruise control system, this arrangement enables a sufficiently large braking force comparable to the relatively large driving load to be output to the output shaft  52 . Under the control of the cruise control system, the vehicle speed is thus desirably kept at the driver&#39;s preset vehicle speed V*. The power output apparatus  20  of the embodiment carries out the downshift control of the CVT  50  functioning as the continuously variable transmission to continuously regulate the friction torque output from the engine  22  to the output shaft  52 . Such continuous regulation effectively prevents an abrupt change of the revolving speed Ni of the input shaft  51  while outputting the braking force to the output shaft  52 , thus ensuring the favorable drivability.  
         [0038]    As discussed above, in the power output apparatus  20  of the embodiment, the range of the braking force possibly output to the output shaft  52  in the working status of the cruise control system is set to be greater than the range of the braking force possibly output to the output shaft  52  by the accelerator opening A in the non-working status of the cruise control system. Additionally the range of the driving force possibly output to the output shaft  52  in the working status of the cruise control system may be set to be greater than the range of the driving force possibly output to the output shaft  52  by the accelerator opening A in the non-working status of the cruise control system.  
         [0039]    The power output apparatus  20  of the embodiment outputs the braking force to the drive shaft as the combination of the friction torque of the engine  22  caused by the downshift control of the change gear ratio in the CVT  50  with the regenerative torque caused by the regenerative control of the motor  40 . One possible modification may utilize either one of the downshift control and the regenerative control to output the braking force to the drive shaft.  
         [0040]    The power output apparatus  20  of the embodiment has the CVT  50  working as the continuously variable transmission. The transmission is, however, not restricted to the continuously variable transmission but may be a stepped speed gear.  
         [0041]    The power output apparatus  20  is applied to the hybrid vehicle in the embodiment discussed above. The application is, however, not restricted to the hybrid vehicle. The principle of the invention is applicable to any of various automobiles with an internal combustion engine that outputs the power to a drive shaft via a transmission, any of electric vehicles with a motor generator that transmits the power to and from a drive shaft, and other moving bodies like boats, ships, and aircraft. The automobile with the transmission and the internal combustion engine utilizes the rotational resistance of the internal combustion engine caused by the downshift control of the transmission to output the required braking force to the drive shaft. The electric vehicle with the motor generator utilizes the braking force caused by the regenerative control of the motor generator to output the required braking force to the drive shaft.  
         [0042]    The above embodiments are to be considered in all aspects as illustrative and not restrictive. There may be many modifications, change, and alterations without departing from the scope or sprit of the main characteristics of the present invention. All changes within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.