Abstract:
A shift control apparatus for a continuously variable transmission includes a continuously variable transmission for transmitting power of an engine to a driving wheel; a shift actuator for changing a gear ratio of the continuously variable transmission; and a gear ratio controller for controlling the shift actuator such that the gear ratio of the continuously variable transmission exhibits a predetermined shift pattern. The shift controller further includes a battery monitor for detecting remaining charge of a battery charged by a generator connected to the engine, and the shift pattern is changed according to the remaining charge of the battery. The shift control apparatus ensures an operating feel similar to that during ordinary running regardless of remaining charge of a battery. A method of controlling a continuously variable transmission in a vehicle is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 USC 119 based on Japanese patent Application No. 2004-229415, filed Aug. 5, 2004. The subject matter of this priority document is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a shift controller for a continuously variable transmission. More specifically, the present invention relates to a shift controller for a continuously variable transmission including a shift actuator that changes a gear ratio regardless of engine speed. 
     2. Description of the Background Art 
     There are many known hybrid vehicles. An electric vehicle powered by a motor offers the advantage of no air pollution, reduced noise pollution, and better response to acceleration and deceleration needs as compared with conventional vehicles powered by engines. A hybrid vehicle mounted with a motor and an engine has been put into practical use as an embodiment having these benefits. 
     Three types of such a hybrid vehicle are generally known: a “series hybrid system,” a “parallel hybrid system,” and a “series-parallel combined system.” Specifically, the series hybrid system is powered solely by the motor, with the engine being used for generating electricity for recharging a battery. The parallel hybrid system uses both the motor and the engine to drive the vehicle, each being used according to a running condition and the like. The series-parallel combined system uses the foregoing two systems, one being selected for use appropriately according to the running condition. 
     In many of these hybrid vehicles, a belt-type continuously variable transmission is adopted as an automatic transmission. The belt-type continuously variable transmission includes a driving side pulley, a driven side pulley, and an endless belt. The driving side pulley is connected to an output shaft of a power source. The driven side pulley is connected to a driving shaft. The endless belt is wound around the driving side pulley and the driven side pulley. The gear ratio is changed by displacing a radius of the driving side pulley using a centrifugal force generated by rotation of the output shaft. 
     Japanese Patent Laid-open No. 2004-116672 discloses an electronically controlled belt-type continuously variable transmission in the place of a conventional belt-type continuously variable transmission. The electronic controlled belt-type continuously variable transmission includes a separate shift actuator that displaces the radius of the driving side pulley called an electronic belt converter. The electronic belt converter is capable of arbitrarily controlling its gear ratio regardless of the speed of the output shaft. 
       FIG. 9  is a diagram showing a typical shift pattern of a conventional electronic belt converter. The relation among an engine speed Ne, a vehicle speed V, and a gear ratio R of the continuously variable transmission has been previously registered. The shift pattern includes a low ratio control range, a top ratio control range, and a shift control range. In the low ratio control range, the engine speed Ne is variably controlled at a low speed range with the gear ratio R set at a predetermined low ratio Rlow. In the top ratio control range, the engine speed Ne is variably controlled at a high-speed range with the gear ratio R set at a predetermined top ratio Rtop. In the shift control range, the gear ratio is variably controlled with the engine speed Ne fixed at a boundary between the low speed range and the high-speed range. 
     There is known a system, in which power of an engine is used to drive a generator for generating electricity which, in turn, is used to charge a battery. In such a system, the more a charging current, as a result of an amount of charge still available for use in the battery or a remaining charge of the battery, the greater a driving torque for the generator. This results in the engine mechanical load increasing. Thus, a rider is required to operate the vehicle with a relatively open throttle. Therefore, to obtain running performance equivalent to that associated with a sufficient remaining charge of the battery when the remaining charge of the battery is low, a rider needs to operate the vehicle with the throttle even more open. This gives the rider an impression different from that during ordinary operation. Consequently, there is still a need for a control apparatus for a continuously variable transmission that does not give the operator the above-mentioned different impression. 
     SUMMARY OF THE INVENTION 
     The present invention provides a shift controller for a continuously variable transmission ensuring an operating feel similar to that during ordinary running regardless of the remaining charge of the battery. 
     A shift control apparatus for a continuously variable transmission includes: a continuously variable transmission for transmitting power of an engine to a driving wheel; a shift actuator for changing a gear ratio of the continuously variable transmission; and a gear ratio controller for controlling the shift actuator such that the gear ratio of the continuously variable transmission exhibits a predetermined shift pattern. 
     According to a first aspect of the present invention, the shift controller further includes a battery monitor for detecting remaining charge of a battery charged by a generator connected to the engine, and the shift pattern is changed according to the remaining charge of the battery. 
     When the remaining charge of the battery is insufficient, if the gear ratio is shifted to a lower ratio side than when the remaining charge of the battery is sufficient, insufficient torque of the engine is supplemented with the gear ratio. This occurs even if a driving torque of the generator increases as a result of an insufficient remaining charge of the battery, and a mechanical load on the engine becomes greater. This gives the rider the same operating feel as that which occurs during ordinary running. 
     According to a second aspect of the present invention, the lower the remaining charge of the battery, the lower the gear ratio is selected. Insufficient torque of the engine is supplemented by adjustment of the gear ratio even if a driving torque of the generator increases as a result of an insufficient remaining charge of the battery, and a mechanical load on the engine becomes greater. This gives the rider the same operating feel as that which occurs during ordinary running. 
     According to a third aspect of the present invention, the shift control apparatus for the continuously variable transmission is characterized in that the shift pattern includes: a low ratio control range, in which an engine speed is variably controlled at a low speed range with the gear ratio set at a predetermined low ratio; a top ratio control range, in which the engine speed is variably controlled at a high speed range with the gear ratio set at a predetermined top ratio; and a shift control range, in which the gear ratio is variably controlled with the engine speed fixed at a boundary between the low speed range and the high speed range. In the shift control apparatus, the lower the remaining charge of the battery, the more the low ratio control range is expanded to the high speed range of the engine. As a result, the gear ratio in the shift control range is shifted on a low end. This gives the rider the same operating feel as that during ordinary running regardless of the remaining charge of the battery, particularly in the medium speed running range. 
     In a fourth aspect of the present invention, the shift pattern includes: a low ratio control range, in which an engine speed is variably controlled at a low speed range with the gear ratio set at a predetermined low ratio; a top ratio control range, in which the engine speed is variably controlled at a high speed range with the gear ratio set at a predetermined top ratio; and a shift control range, in which the gear ratio is variably controlled with the engine speed fixed at a boundary between the low speed range and the high speed range. In the shift control apparatus, the lower the remaining charge of the battery, the more the gear ratio of the low ratio control range is shifted to a low ratio side. Accordingly, in the low speed running range, when the remaining charge of the battery is insufficient the gear ratio can be made lower than the gear ratio when the remaining charge of the battery is sufficient. This gives the rider the same operating feel as that during ordinary running regardless of the remaining charge of the battery particularly in the low speed running range. 
     According to a fifth aspect of the present invention, the shift pattern includes: a low ratio control range, in which an engine speed is variably controlled at a low speed range with the gear ratio set at a predetermined low ratio; a top ratio control range, in which the engine speed is variably controlled at a high speed range with the gear ratio set at a predetermined top ratio; and a shift control range, in which the gear ratio is variably controlled with the engine speed fixed at a boundary between the low speed range and the high speed range; and that the lower the remaining charge of the battery, the more the gear ratio of the low ratio control range is shifted to a low ratio side, and the more the low ratio control range is expanded to the high speed range of the engine. In the shift apparatus, the lower the remaining charge of the battery, the more the gear ratio of the low ratio control range is shifted to a low ratio side, and the more the low ratio control range is expanded to the high speed range of the engine. Accordingly, in the low speed and medium speed running range, the gear ratio when the remaining charge of the battery is insufficient can be made lower than the gear ratio when the remaining charge of the battery is sufficient, giving the rider the same operating feel as that during ordinary running for both the low and medium speed running range. 
     According to a sixth aspect of the present invention, the continuously variable transmission is a belt type continuously variable transmission having an endless belt wound around a driving side pulley and a driven side pulley; and the shift actuator changes a belt winding diameter of at least either the driving side pulley or the driven side pulley. In an existing vehicle including a belt type continuously variable transmission and a shift actuator, simply changing a control system gives the rider the same operating feel as that during ordinary running regardless of the remaining charge of the battery. 
     According to a seventh aspect of the present invention, the shift pattern is not changed during running, even if the remaining charge of the battery becomes lower than a threshold value during running. There is, therefore, no likelihood that the running feel will be changed during running. 
     For a more complete understanding of the present invention, the reader is referred to the following detailed description section, which should be read in conjunction with the accompanying drawings. Throughout the following detailed description and in the drawings, like numbers refer to like parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevational view of a hybrid vehicle according to the present invention, showing a power unit including an engine and an electric drive motor operatively connected to the rear wheel. 
         FIG. 2  is a block diagram of the system configuration of the motorcycle shown in  FIG. 1 . 
         FIG. 3  is a cross sectional view of the power unit of the motorcycle shown in  FIG. 1  showing the engine above the rear wheel, and the drive motor to one side of the rear wheel. 
         FIG. 4  is an enlarged view of the shift motor and drive motor of the power unit shown in  FIG. 3 . 
         FIG. 5  is a diagram showing a shift pattern according to the first embodiment of the present invention in which a broken line represents a shift pattern (a first pattern) when the remaining charge of the battery is sufficient, while a solid line represents a shift pattern (a second pattern) when the remaining charge of the battery is insufficient. 
         FIG. 6  is a flowchart showing shift pattern control processes. 
         FIG. 7  is a diagram showing a shift pattern according to the second embodiment of the present invention in which a broken line represents a shift pattern (a first pattern) when the remaining charge of the battery is sufficient, while a solid line represents a shift pattern (a second pattern) when the remaining charge of the battery is insufficient. 
         FIG. 8  is a diagram showing a shift pattern according to the third embodiment of the present invention in which a broken line represents a shift pattern (a first pattern) when the remaining charge of the battery is sufficient, while a solid line represents a shift pattern (a second pattern) when the remaining charge of the battery is insufficient. 
         FIG. 9  is a diagram showing a prior art shift pattern. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.  FIG. 1  is a side elevational view showing a scooter-type hybrid vehicle according to a preferred embodiment of the present invention. 
     The hybrid vehicle according to the preferred embodiment of the present invention includes a front fork  1  for journaling a front wheel WF at a point forward of a vehicle body. The front fork  1  is pivotally supported on a head pipe  2 . The front fork  1  can be steered through operation of a handlebar  3 . A down pipe  4  is fitted to the head pipe  2  so as to extend rearwardly and downwardly therefrom. An intermediate frame  5  is extended substantially horizontally from a lower end of the down pipe  4 . A rear portion frame  6  is formed rearwardly and upwardly from a trailing end of the intermediate frame  5 . 
     A vehicle body frame  10  as constructed above includes a power unit  11  including an engine and a driving motor as a power source. One end of the power unit  11  is pivotally secured to the vehicle body frame  10 . A rear wheel WR, functioning as a driving wheel, is rotatably mounted rearward and on the other end of the power unit  11 . The power unit  11  is suspended by a rear shock absorber (not shown) mounted on the rear portion frame  6 . 
     A vehicle body cover  13  covers the outer periphery of the vehicle body frame  10 . A seat  14 , on which a rider sits, is secured rearward and on a top surface of the vehicle body cover  13 . A step floor  15 , on which the rider rests his or her feet, is formed forward of the seat  14 . A storage box  100  is disposed below the seat  14 . The storage box  100  functions as a utility space for storing a helmet, luggage, and the like. 
       FIG. 2  is a block diagram showing a system configuration of the hybrid vehicle described above. The power unit  11  includes an engine  20 , an ACG starter motor  21   a , a continuously variable transmission (transmission power mechanism)  23 , a shift motor  77 , a starting clutch  40 , a driving motor  21   b , a one-way clutch  44 , and a reduction mechanism  69 . Specifically, the ACG starter motor  21   a  functions as an engine starter and generator. The continuously variable transmission  23  is connected to a crankshaft  22  and transmits power of the engine  20  to the rear wheel WR. The shift motor  77  serves as a shift actuator that changes a shift position of the continuously variable transmission  23 . The starting clutch  40  connects or disconnects transmission power between the crankshaft  22  and an input shaft of the continuously variable transmission  23 . The driving motor  21   b  functions as a motor or a generator. The one-way clutch  44  transmits power from the engine  20  and the driving motor  21   b  to the rear wheel WR, but not from the rear wheel WR to the engine  20 . The reduction mechanism  69  transmits an output from the continuously variable transmission  23  at a reduced speed to the rear wheel WR. An engine speed sensor  36  detects an engine speed Ne of the engine  20 . 
     Power from the engine  20  is transmitted from the crankshaft  22  to the rear wheel WR via the starting clutch  40 , the continuously variable transmission  23 , the one-way clutch  44 , a driving shaft  60 , and the reduction mechanism  69 . Power from the driving motor  21   b , on the other hand, is transmitted to the rear wheel WR via the driving shaft  60  and the reduction mechanism  69 . That is, according to the preferred embodiment of the present invention, the driving shaft  60  serves as an output shaft of the driving motor  21   b.    
     A battery  74  is connected to the ACG starter motor  21   a  and the driving motor  21   b . When the driving motor  21   b  functions as a motor, and when the ACG starter motor  21   a  functions as a starter, the battery  74  supplies power to the ACG starter motor  21   a  and the driving motor  21   b . When the ACG starter motor  21   a  and the driving motor  21   b  function as a generator, the battery  74  is recharged by regenerative power generated by the ACG starter motor  21   a  and the driving motor  21   b . A voltage sensor  37  detects a terminal data Vbat of the battery  74 . 
     A throttle valve  17 , for controlling the amount of intake air, is rotatably mounted in an intake pipe  16  of the engine  20 . The throttle valve  17  is rotated according to the amount of operation of a throttle grip (not shown) operated by the rider. The shift controller according to the preferred embodiment of the present invention may include a DBW (drive-by-wire) system  12 . The throttle valve  17  can thereby be automatically controlled according to the engine speed, a vehicle speed, and the like, irrespective of the operation performed by the rider. An injector  18  and a vacuum sensor  19  are disposed between the throttle Valve  17  and the engine  20 . The injector  18  injects fuel. The vacuum sensor  19  detects a negative pressure in the intake pipe. 
     A control unit  7  includes a gear ratio control portion  7   a , a battery monitoring portion  7   b , and a shift pattern registration portion  7   c . The gear ratio control portion  7   a  controls the shift motor  77  such that the gear ratio of the continuously variable transmission  23  exhibits a predetermined shift pattern. The battery monitoring portion  7   b  determines a charge state of the battery  74  based on the battery voltage Vbat detected by the voltage sensor  37 . The shift pattern registration portion  7   c  stores the shift pattern of the continuously variable transmission  23  previously registered therein. 
     The construction of the power unit  11  including the engine  20  and the driving motor  21   b  will be described with reference to  FIG. 3 . 
     The engine  20  includes a piston  25  connected to the crankshaft  22  via a connecting rod  24 . The piston  25  can slide inside a cylinder  27  disposed in a cylinder block  26 . The cylinder block  26  is disposed such that an axis of the cylinder  27  runs substantially horizontally. A cylinder head  28  is secured to the front surface of the cylinder block  26 . The cylinder head  28 , the cylinder  27 , and the piston  25  constitute a combustion chamber  20   a  for burning an air-fuel mixture. 
     The cylinder head  28  includes a valve (not shown) for controlling intake or exhaust of the air-fuel mixture to and from the combustion chamber  20   a , and a spark plug  29 . Opening or closing of the valve is controlled through rotation of a camshaft  30  journaled on the cylinder head  28 . A driven sprocket  31  is mounted on one end of the camshaft  30 . An endless cam chain  33  is wound around the driven sprocket  31  and a drive sprocket  32  disposed on one end of the crankshaft  22 . A water pump  34  for cooling the engine  20  is mounted on the one end of the camshaft  30  such that a rotational axis  35  of the water pump  34  rotates integrally with the camshaft  30 . Accordingly, rotating the camshaft  30  operates the water pump  34 . 
     A stator case  49  is connected on the right-hand side in a vehicle width direction of a crankcase  48  that journals the crankshaft  22 . The ACG starter motor  21   a  is housed in the stator case  49 . The ACG starter motor  21   a  is what is called an outer rotor type. A stator of the ACG starter motor  21   a  includes a coil  51 , which is a conductive wire wound around teeth  50  secured to the stator case  49 . An outer rotor  52  is, on the other hand, secured to the crankshaft  22 . The outer rotor  52  is of a substantially cylindrical shape covering the outer periphery of the stator. A magnet  53  is disposed on an inner peripheral surface of the outer rotor  52 . 
     The outer rotor  52  includes a fan  54   a  for cooling the ACG starter motor  21   a . When the fan  54   a  rotates in synchronism with the crankshaft  22 , cooling air is drawn-in through a cooling air intake port formed in a side surface  55   a  of a cover  55  of the stator case  49 . The cooling air is drawn-in in this manner. 
     A transmission case  59  is connected to the left-hand side, in the vehicle width direction, of the crankcase  48 . A fan  54   b , the continuously variable transmission  23 , and the driving motor  21   b  are housed in the transmission case  59 . The fan  54   b  is secured to a left end portion of the crankshaft  22 . The driving side of the continuously variable transmission  23  is connected to the crankshaft  22  via the starting clutch  40 . The driving motor  21   b  is connected to a driven side of the continuously variable transmission  23 . The fan  54   b  functions to cool the continuously variable transmission  23  and the driving motor  21   b , housed in the transmission case  59 . The fan  54   b  is disposed on the same side as the driving motor  21   b  relative to the continuously variable transmission  23 , that is, on the left-hand side in the vehicle width direction. 
     A cooling air intake port  59   a  is formed forward and on the left of the vehicle body of the transmission case  59 . When the fan  54   b  rotates in synchronism with the crankshaft  22 , an outside air is drawn in through the cooling air intake port  59   a  located near the fan  54   b . The driving motor  21   b  and the continuously variable transmission  23  are forcedly cooled by the outside air thus drawn in. 
     The continuously variable transmission  23  is a belt converter including a driving side transmission pulley  58  and a driven side transmission pulley  62  with an endless V-belt (endless belt)  63  wound therearound. The driving side transmission pulley  58  is mounted via the starting clutch  40  at a left end portion of the crankshaft  22  protruding in the vehicle width direction from the crankcase  48 . The driven side transmission pulley  62  is mounted via the one-way clutch  44  on the driving shaft  60  journaled with an axis running parallel with the crankshaft  22  on the transmission case  59 . 
     Referring to  FIG. 4  that is an enlarged view of the starting clutch  40 , the shift motor  77 , and the driving motor  21   b , the driving side transmission pulley  58  is circumferentially rotatably mounted on the crankshaft  22  via a sleeve  58   d . The driving side transmission pulley  58  includes a driving side fixed pulley half  58   a  and a driving side movable pulley half  58   c . The driving side fixed pulley half  58   a  is fixed to the sleeve  58   d . The driving side movable pulley half  58   c  is mounted on the sleeve  58   d  such that the pulley half  58   c  is axially slidable, but unable to make a circumferential rotation relative to the sleeve  58   d . A shift ring  57  is rotatably mounted via a bearing  56  to the driving side movable pulley half  58   c.    
     The shift ring  57  includes a gear  61  formed circumferentially on an outer peripheral large diameter portion thereof. The shift ring  57  also includes a trapezoidal screw  65  formed axially on an inner periphery thereof. Another trapezoidal screw  67  meshes with the trapezoidal screw  65 . The trapezoidal screw  67  is mounted so as to be circumferentially rotatable relative to the sleeve  58   d  via a bearing  66 , but unable to slide axially. 
     A worm wheel  75  meshes with the gear  61  of the shift ring  57 . Further, a worm gear  76  meshes with the worm wheel  75 . The worm gear  76  is connected to a rotational axis of a shift motor  77  for controlling the gear ratio. 
     The driven side transmission pulley  62 , on the other hand, includes a driven side fixed pulley half  62   a  and a driven side movable pulley half  62   b . The driven side fixed pulley half  62   a  is circumferentially rotatably mounted on the driving shaft  60  via a sleeve  62   d , while being restricted in its axial sliding motion relative to the driving shaft  60 . The driven side movable pulley half  62   b  is axially slidably mounted on the sleeve  62   d.    
     An endless V belt  63  is wound around each of belt grooves having substantially a V-shaped cross section formed between the driving side fixed pulley half  58   a  and the driving side movable pulley half  58   c , and between the driven side fixed pulley half  62   a  and the driven side movable pulley half  62   b.    
     A spring (elastic member)  64  is disposed on the backside (on the left-hand side in the vehicle width direction) of the driven side movable pulley half  62   b . The spring  64  urges the driven side movable pulley half  62   b  toward the driven side fixed pulley half  62   a  at all times. 
     When the gear ratio of the automatic continuously variable transmission  23  is to be changed, the shift motor  77  is driven in a direction of rotation corresponding to an upshift or downshift of the gear ratio. The driving force of the shift motor  77  is transmitted to the gear  61  of the shift ring  57  through the worm gear  76  and the worm wheel  75 . The shift ring  57  is thereby rotated. Since the shift ring  57  is in mesh with the sleeve  57   d  through the trapezoidal screws  65 ,  67 , the shift ring  57  moves to the left along the crankshaft  22 , as shown in  FIG. 4 . This results in the driving side movable pulley half  58   c  sliding toward the side of the driving side fixed pulley half  58   a . The driving side movable pulley half  58   c  then comes closer to the driving side fixed pulley half  58   a  by the amount of this sliding motion. This decreases a groove width of the driving side transmission pulley  58 . A position of contact between the driving side transmission pulley  58  and the V belt  63  is then deviated radially outwardly along the driving side transmission pulley  58 , causing the winding diameter of the V belt  63  to increase. This results in the following occurring in the driven side transmission pulley  62 . Specifically, a groove width formed by the driven side fixed pulley half  62   a  and the driven side movable pulley half  62   b  increases. That is, the winding diameter of the V belt  63  (a transmission pitch diameter) continuously varies according to the speed of the crankshaft  22 . This results in the gear ratio being automatically and steplessly varied. 
     The starting clutch  40  includes an outer case  40   a , an outer plate  40   b , a weight  40   c , a shoe  40   d , and a spring  40   e . The outer case  40   a  of a cup shape is fixed to the sleeve  58   d . The outer plate  40   b  is fixed on a left end portion of the crankshaft  22 . The shoe  40   d  is mounted on an outer peripheral portion of the outer plate  40   b  via the weight  40   c  so as to face radially outwardly. The spring  40   e  urges the shoe  40   d  radially inwardly. 
     When the engine speed, or the speed of the crankshaft  22  is equal to, or less than, a predetermined value (e.g., 3000 rpm), transmission power between the crankshaft  22  and the continuously variable transmission  23  is disconnected through the starting clutch  40 . As the engine speed increases and the speed of the crankshaft  22  exceeds the predetermined value, the centrifugal force acting on the weight  40   c  counteracts an elastic force acting radially inwardly by the spring  40   e , moving the weight  40   c  radially outwardly. This causes the shoe  40   d  to press an inner peripheral surface of the outer case  40   a  with a force of a predetermined value or more. This causes rotation of the crankshaft  22  to be transmitted to the sleeve  58   d  via the outer case  40   a . The driving side transmission pulley  58  fixed to the sleeve  58   d  is thereby driven. 
     The one-way clutch  44  includes an outer clutch  44   a , an inner clutch  44   b , and a roller  44   c . The outer clutch  44   a  is of a cup shape. The inner clutch  44   b  is internally inserted in the outer clutch coaxially therewith. The roller  44   c  allows power to be transmitted in one direction only from the inner clutch  44   b  to the outer clutch  44   a . The outer clutch  44   a  serves also as an inner rotor main body for the driving motor  21   b . The outer clutch  44   a  is formed of the same member as the inner rotor main body. 
     Power from the side of the engine  20  transmitted to the driven side transmission pulley  62  of the continuously variable transmission  23  is transmitted to the rear wheel WR by way of the driven side fixed pulley half  62   a , the inner clutch  44   b , the outer clutch  44   a  or the inner rotor main body, the driving shaft  60 , and the reduction mechanism  69 . Power from the side of the rear wheel WR generated as the vehicle is pulled by walking, during regenerative operation, or the like, on the other hand, is transmitted to the reduction mechanism  69 , the driving shaft  60 , and the inner rotor main body or the outer clutch  44   a . The power generated in the latter case is not, however, transmitted to the continuously variable transmission  23  and the engine  20 , since the outer clutch  44   a  turns idly relative to the inner clutch  44   b.    
     The driving motor  21   b  of an inner rotor type is disposed rearward of the transmission case  59 . The driving motor  21   b  uses the driving shaft  60  as its output shaft. An inner rotor  80  includes the driving shaft  60 , an inner rotor main body or the inner clutch  44   b , and a magnet. The driving shaft  60  serves also as an output shaft for the continuously variable transmission  23 . The inner clutch  44   b  is in splined engagement with the driving shaft  60  by a cup-shaped boss portion  80   b  formed at a central portion thereof. The magnet is disposed on an outer peripheral surface on an open side of the inner clutch  44   b.    
     Referring back to  FIG. 3 , the reduction mechanism  69  is disposed in a transmission chamber  70  that continues to the right-hand side at a trailing end portion of the transmission case  59 . The reduction mechanism  69  includes an intermediate shaft  73  that is journaled in parallel with the driving shaft  60  and an axle  68  of the rear wheel WR. The reduction mechanism  69  further includes a pair of first reduction gears  71  and a pair of second reduction gears  72 . The first reduction gears  71  are formed on the right end portion of the driving shaft  60  and a central portion of the intermediate shaft  73 , respectively. The second reduction gears  72  are formed on the intermediate shaft  73  and the left end portion of the axle  68 , respectively. Through such an arrangement, the speed of rotation of the driving shaft  60  is reduced at a predetermined reduction ratio. Rotation of the driving shaft  60  is then transmitted to the axle  68  of the rear wheel WR that is journaled in parallel with the driving shaft  60 . 
     In the hybrid vehicle having the arrangements as described in the foregoing, the ACG starter motor  21   a  mounted on the crankshaft  22  is used to turn the crankshaft  22  when the engine is to be started. At this time, the starting clutch  40  is not engaged, meaning that transmission power from the crankshaft  22  to the continuously variable transmission  23  is shut off. 
     When the throttle grip is operated and opened, only the driving motor  21   b  provides power as long as a throttle opening θ remains small according to the preferred embodiment of the present invention. Rotation of the driving shaft  60  through the driving motor  21   b  is not transmitted to the driven side transmission pulley  62  through the functioning of the one-way clutch  44 . The continuously variable transmission  23  can then never be driven. Accordingly, running the vehicle by driving the rear wheel WR only with the driving motor  21   b  enhances energy transmission efficiency. 
     As the throttle opening θ is made greater, the engine speed increases. When the speed of the crankshaft  22  thereafter exceeds a predetermined value (e.g., 3000 rpm), the rotational power of the crankshaft  22  is transmitted to the continuously variable transmission  23  through the starting clutch  40  and applied to the one-way clutch  44 . When the speed on an input side of the one-way clutch  44  coincides with the speed on an output side thereof, that is, the driving shaft  60 , power is switched from the driving motor  21   b  to the engine  20 . 
       FIG. 5  is a diagram showing a typical shift pattern according to the first preferred embodiment of the present invention. In  FIG. 5 , a broken line represents a shift pattern (a first pattern) when the remaining charge of the battery  74  is sufficient, while a solid line represents a shift pattern (a second pattern) when the remaining charge of the battery  74  is insufficient. 
     According to the first preferred embodiment of the present invention, if it is determined that the remaining charge of the battery is insufficient, a low ratio control range is expanded to include a high engine speed side. With an insufficient remaining charge of the battery  74 , the gear ratio is thereby made lower than the gear ratio with a sufficient remaining charge of the battery  74 , particularly in a medium speed running range. 
       FIG. 6  is a flowchart showing shift pattern control processes that change the shift pattern based on a remaining charge M of the battery  74 .  FIG. 6  mainly shows operations performed by the control unit  7 . 
     In step S 1 , the battery monitoring portion  7   b  of the control unit  7  detects the remaining charge M of the battery  74  based on the battery voltage Vbat detected by the voltage sensor  37  or a record thereof. In step S 2 , it is determined whether the vehicle is in a stationary state based on, for example, a vehicle speed V. 
     If it is determined that the vehicle is in the stationary state, the control proceeds to step S 3 . In step S 3 , the remaining charge M of the battery  74  is compared with a reference remaining charge Mref that has previously been registered as a threshold value of changing the shift pattern. If the remaining charge M of the battery  74  is lower than the reference remaining charge Mref, the control proceeds to step S 4 . In step S 4 , it is determined that the current shift pattern is the first pattern (the shift pattern indicated by the broken line in  FIG. 5 ) adopted when the remaining charge is sufficient or the second pattern (the shift pattern indicated by the solid line in  FIG. 5 ) adopted when the remaining charge is insufficient. If the current pattern is one other than the second pattern, the control proceeds to step S 5 . In step S 5 , the shift pattern is changed from the current first pattern to the second pattern. Accordingly, following this step, the gear ratio is controlled according to the second pattern indicated by the solid line in  FIG. 5 . 
     If, in step S 3 , it is not determined that the remaining charge M of the battery  74  is lower than the reference remaining charge Mref, the control proceeds to step S 6 . In step S 6 , it is determined that the current shift pattern is either the first pattern or the second pattern. If the current pattern is one other than the first pattern, the control proceeds to step S 7 . In step S 7 , the shift pattern is changed from the current second pattern to the first pattern. 
     As described in the foregoing, according to the first preferred embodiment of the present invention, the shift pattern is changed from the first pattern to the second pattern as a result of the remaining charge M of the battery  74  decreasing. Even if this happens, if charging is thereafter promoted to allow the battery  74  to recover its charge, the shift pattern is returned from the second pattern to the first pattern. Accordingly, the gear ratio is hereafter controlled according to the first pattern indicated by the broken line in  FIG. 5 . 
       FIG. 7  is a diagram showing a shift pattern according to a second preferred embodiment of the present invention. In  FIG. 7 , again, a broken line represents a shift pattern (a first pattern) when the remaining charge of the battery  74  is sufficient, while a solid line represents a shift pattern (a second pattern) when the remaining charge of the battery  74  is insufficient. 
     According to the second preferred embodiment of the present invention, if it is determined that the remaining charge M of the battery  74  is insufficient, a gear ratio in the low ratio control range Rlow is lowered further than the level when it is determined that the remaining charge M of the battery  74  is sufficient. The gear ratio when the remaining charge M of the battery  74  is insufficient is thus made to be lower than the gear ratio when the remaining charge M of the battery  74  is sufficient particularly in a low speed running range. 
       FIG. 8  is a diagram showing a shift pattern according to a third preferred embodiment of the present invention. In  FIG. 8 , too, a broken line represents a shift pattern (a first pattern) when the remaining charge of the battery  74  is sufficient, while a solid line represents a shift pattern (a second pattern) when the remaining charge of the battery  74  is insufficient. 
     According to the third preferred embodiment of the present invention, the lower the remaining charge M of the battery  74 , the more the gear ratio in the low ratio control range Rlow is shifted to the low ratio side as in the second preferred embodiment of the present invention. At the same time, the low ratio control range is expanded to include the high engine speed side as in the first preferred embodiment of the present invention. The gear ratio when the remaining charge M of the battery  74  is insufficient is thereby made to be lower than the gear ratio when the remaining charge M of the battery  74  is sufficient in both the low speed running range and the medium speed running range. 
     The present invention is not limited to the above embodiments in which the second shift pattern is selected when the remaining charge of the battery becomes insufficient. It is nonetheless appropriate that a plurality of shift patterns adopted according to the degree of insufficiency of the remaining charge of the battery is provided and the optimum shift pattern be adopted according to the remaining charge of the battery. An arrangement can thereby be made to control the shift pattern such that an even lower gear ratio can be selected when insufficiency of the remaining charge of the battery is serious. 
     Although the present invention has been described herein with respect to a limited number of presently preferred embodiments, the foregoing description is intended to be illustrative, and not restrictive. Those skilled in the art will realize that many modifications of the preferred embodiment could be made which would be operable. All such modifications, which are within the scope of the claims, are intended to be within the scope and spirit of the present invention.