Patent Publication Number: US-2004055800-A1

Title: Drive apparatus for hybrid vehicle

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to a drive apparatus for a vehicle which has an engine and a motor which also serves as a generator, power to drive the vehicle being produced by either the engine alone or by both the engine and the motor, the power of the engine and the motor being transmitted via a transmission to a differential assembly.  
       [0002] Honda R&amp;D Technical Review Vol. 12 No. 2 (October 2000) discloses a drive apparatus for a hybrid vehicle where an engine is connected to a belt-type continuously variable transmission via a motor-generator and damper which are disposed behind an output-shaft end of an engine. Japanese Patent Provisional Publication No. 2000-289475 discloses a drive apparatus for a hybrid vehicle wherein a motor-generator is disposed between an engine and an automatic transmission, and starting of the engine is performed by the motor-generator.  
       SUMMARY OF THE INVENTION  
       [0003] However, there is a requirement for enough drive torque to start an engine, especially during extremely low outdoor temperatures when engine friction is large, and since starting of the engine is carried out by a starter generator located directly behind an output-shaft end portion of an engine, a large starter generator is necessary. With a large starter generator, the axial dimension, or length, of the drive apparatus is necessarily large. Also, a high-cost starter generator must be used, which is a cost burden.  
       [0004] It is therefore an object of the present invention to provide a drive apparatus for a hybrid vehicle which is compact and can be provided at a lower cost.  
       [0005] An aspect of the present invention resides in a drive apparatus for a hybrid vehicle, the drive apparatus comprising an internal combustion engine, a damper connected on one side thereof to a rear of the engine, a motor-generator connected on one side thereof to another side of the damper, the motor-generator being capable of starting the engine, a clutch connected on one side thereof to another side of the motor-generator, a transmission connected to the internal combustion engine via the damper, the motor-generator, and the clutch, and a starter motor connected to the damper, the starter motor being capable of starting the engine.  
       [0006] Another aspect of the present invention resides in a drive apparatus for a vehicle, the vehicle comprising an engine and a transmission, the drive apparatus comprising a battery, damping means for reducing transmitted vibration, the damping means being disposed behind the engine, restarting means for restarting the engine under a predetermined set of conditions, the restarting means also serving to charge the battery, the restarting means being disposed behind the damping means, engaging means for allowing or interrupting power flow from the engine, the engaging means being disposed behind the restarting means, normal starting means for starting the engine under conditions other than the predetermined set of conditions, and control means for controlling the engine, the normal starting means, the restarting means, the engaging means, and the transmission.  
       [0007] A further aspect of the present invention resides in a drive system for a hybrid vehicle, the hybrid vehicle comprising an engine, and a clutch which allows or interrupts transmission of power from the engine to a transmission, the drive system comprising a motor-generator which is connected from a rear thereof to the transmission, the motor-generator being both capable of driving the engine as a starter motor and of generating electrical power, a damper which is joined at one end thereof via an elastic member thereof to an input shaft which supports the motor-generator and at another end thereof to an output shaft of the engine, a starter motor which is connected to the engine, and a control system which detects a speed of the vehicle, a state of a brake switch, and a temperature of oil in the transmission, and which determines execution of an idle-stop function to temporarily stop the engine, the control system executing the idle-stop function if a set of idle-stop conditions including the vehicle speed being 0 km/h, the brake switch being in an ON state, and the oil temperature being within a predetermined range are met, the engine being started with the motor-generator when the brake pedal is released during execution of the idle-stop function. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008]FIG. 1 is a block diagram showing a drive apparatus for a vehicle according to a first embodiment of the present invention.  
     [0009]FIG. 2 is a cross-sectional view of the drive apparatus of FIG. 1.  
     [0010]FIG. 3A is a block diagram of a drive apparatus according to the related art showing occurrence of torsional vibration.  
     [0011]FIG. 3B is a block diagram of a drive apparatus according to the present invention showing an effect of torsional vibration being reduced.  
     [0012]FIG. 4 is a graph showing a relationship between resonance level and frequency.  
     [0013]FIG. 5 is a cross-sectional view showing a drive apparatus for a vehicle according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0014] Referring to FIGS.  1  to  4 , there is discussed a first embodiment of a drive apparatus for a hybrid vehicle in accordance with the present invention.  
     [0015] As shown in FIG. 1, the hybrid vehicle comprises an internal combustion engine  70  and a motor-generator  20 . Motor-generator  20  is connected to an output shaft of engine  70  via damper  10 . A belt-type continuously variable transmission (CVT)  40  is connected to motor-generator  20  via a multi-plate-type magnetic clutch  30  and a forward/back selector mechanism  60 . Power transmitted to CVT  40  is outputted to wheels  48  via a reduction mechanism  80  and a differential assembly  45 . A starter motor  15  is connected to damper  10 , and an oil pump  50  is connected to motor-generator  20 . A control valve unit  90  is connected to both oil pump  50  and CVT  40 .  
     [0016] Explained more specifically with reference to FIGS. 1 and 2, a drive apparatus comprises a first case member  1 , a front cover  1   a  which is bolted to first case member  1 , damper  10  joined at one end thereof to the output shaft at a rear or crank end of engine  70 , and motor-generator  20  joined to another end of damper  10  so as to be behind damper  10 . Damper  10  and motor-generator  20  are contained in first case member  1  on a side of front cover  1   a  which is nearest engine  70 . Magnetic clutch  30  is disposed on the other side of front cover  1   a  and is thus connected to a rear of motor-generator  20 . CVT  40  is located behind magnetic clutch  30 , and is connected to magnetic clutch  30  via forward/back selector switch  60 . Rotational torque thus flows from engine  70  to damper  10  and continues through motor-generator  20  to magnetic clutch  30 . Rotational torque next continues through forward/back selector mechanism  60  and onto CVT  40 . Magnetic clutch  30  engages or disengages to respectively allow or interrupt flow of rotational torque. Front cover  1   a  is made of a magnetic material such as iron, and serves to prevent magnetic force of motor-generator  20  from affecting magnetic clutch  30 . Also, an outer diameter of damper  10  and an outer diameter of magnetic clutch  30  are respectively less than an outer diameter of a rotor  21  of motor-generator  20 .  
     [0017] A shaft stator  4  is bolted to a second case member  2 . Shaft stator  4  comprises a dividing wall portion  4   a  which separates magnetic clutch  30  and forward/back selector mechanism  60 , a shaft support portion  4   b  which supports a first input shaft  31  to be rotatable, a drum support portion  4   c  which axially supports forward/back selector mechanism  60  on an outer circumference thereof, and a chain sprocket support portion  4   d  which supports a driven chain sprocket  43   b  used in driving oil pump  50 . A drive chain sprocket  43   a  is supported to be rotatable around shaft support portion  4   b , and drives driven chain sprocket  43   b  via a chain  43   c.    
     [0018] With reference to FIG. 2, damper  10  comprises an outer member  10   c  which is directly connected to an engine output shaft  73 , an inner member  10   d  which is directly connected to first input shaft  31 , and a spring  10   e  which is disposed between outer member  10   c  and inner member  10   d . Inner member  10   d  is thus joined to outer member  10   c  via spring  10   e . An outer circumference ring gear  10   b  is disposed on an outer circumference of outer member  10   c , and meshes with starter motor  15  only when starter motor  15  is used to drive engine  70 . Starter motor  15  is a normal 12V starter, and starts engine  70  in the same manner as in a conventional car. A damper spline hub  10   a  is disposed on an inner circumference of inner member  10   d , and is splined to an input-shaft spline hub  31   a  which is splined to first input shaft  31 . Rotor  21  of motor-generator  20  is fixed to input-shaft spline hub  31   a  by press-fitting, and a stator  22  is fixed to first case member  1  by press-fitting. Thus, elements including damper spline hub  10   a  and input-shaft spline hub  31   a , and first case member  1 , can be easily exchanged as required, according to the highest output power available with a particular engine.  
     [0019] First input shaft  31  is supported to be rotatable by front cover  1   a  via bearing  31   b . First input drum  32   a  of magnetic clutch  30  is joined to first input shaft  31  to form an integral body.  
     [0020] Magnetic clutch  30  comprises a main clutch  37 , a pilot clutch  34  having a smaller diameter than main clutch  37 , a cam mechanism  36 , and an electromagnet  35 . Pilot clutch  34  is made to engage by an attraction force of electromagnet  35 . Engagement force of pilot clutch  34  is changed by cam mechanism  36  into axial-direction thrust to increase torque. Main clutch  37  then engages due to the axial-direction thrust increased by cam mechanism  36 . Leakage flux of motor-generator  20  is absorbed by front cover  1   a , therefore the clutch torque of pilot clutch  34 , which is made to engage by attraction force of electromagnet  35 , is not affected.  
     [0021] Main clutch  37  comprises a first input drum  32   a , a second input drum  32   b  which is splined to first input drum  32   a  to be slidingly movable in the axial direction, a main clutch hub  32   c  which is splined to a second input shaft  41 , and a set of clutch plates  32   d . A rotor  33  is splined to an inner circumference of second input drum  32   b  to be slidingly movable in the axial direction.  
     [0022] Electromagnet  35 , which makes pilot clutch  34  engage, is fixed to rotor  33 , and rotor  33  comprises an oil pump drive tooth  33   a  at a tip end thereof which is fitted into drive chain sprocket  43   a . Engine drive power is transmitted through, and in order of, first through damper  10 , first input shaft  31 , first input drum  32   a , second input drum  32   b , rotor  33 , and drive chain sprocket  43   a , regardless of the state of engagement of magnetic clutch  30 . Thus, when engine  70  is driving, i.e., when there is output rotation from engine  70 , drive chain sprocket  43   a  is driven, resulting in oil pump  50  also being driven, so that fluid line pressure is maintained.  
     [0023] Magnetic clutch  30  is joined at an output end thereof to second input shaft  41 , and forward/back selector mechanism  60  is also disposed on second input shaft  41 . Forward/back selector mechanism  60  comprises a planetary gearset which comprises a ring gear  61  joined to second input shaft  41 , a carrier  62 , and a sun gear  63  joined to a transmission input shaft  42 . A reverse brake  64  is disposed on an outer circumference of carrier  62 , reverse brake  64  being fixable to a transmission case, and a forward clutch  65  is disposed inside forward/back selector mechanism  60 , forward clutch  65  being capable of fixably coupling ring gear  61  and sun gear  63 .  
     [0024] Referring to FIG. 1, CVT  40  is connected at a drive pulley thereof to forward/back selector mechanism  60 . Reduction mechanism  80  is connected to a driven pulley of CVT  40 , and differential assembly  45  is connected to reduction mechanism  80 . The speed of rotation which is output from forward/back selector mechanism  60  is changed by CVT  40 , and is output via reduction mechanism  80  and differential assembly  45  to wheels  48 .  
     [0025] Control valve unit  90  is hydraulically connected to oil pump  50  and CVT  40 , and controls line pressure of CVT  40  with oil pump  50  acting as a source of line pressure. A drive apparatus according to the present invention also comprises a control system which controls the states of various elements of a vehicle. The control system comprises CVT control unit  91  (hereafter, ATCU  91 ) as a transmission control unit which outputs command signals to control valve unit  90 , and a hybrid control unit  92  (hereafter, HEV-CU  92 ) which functions to effect vehicle drive control. A battery  93  is connected to HEV-CU  92 .  
     [0026] Signals are sent to ATCU  91  from a primary rotation sensor  91   a  which detects a number of rotations of input rotation of CVT  40 , from a secondary rotation sensor  91   b  which detects a number of rotations of output rotation of CVT  40 , from an oil temperature sensor  91   c , and from control valve unit  90 . A command signal is then sent to control valve unit  90 , and shift control, i.e., gear shift is performed according to the running condition of a vehicle.  
     [0027] Signals are sent to HEV-CU  92  from a throttle sensor  71  which detects a degree of opening of a throttle  70   a , from an engine sensor  72  which detects a number of rotations of engine rotation of engine  70 , from a brake sensor  94  which detects the depressed state of the brake pedal, and from a steer angle sensor  95  which detects a steer angle. Throttle sensor  71  is disposed on engine  70  and is electronically controlled. A signal is also sent from battery  93  which indicates a state of charge (SOC) thereof. HEV-CU  92  controls the state of drive of engine  70  as well as the state of drive of starter motor  15  and motor-generator  20 , and also controls the state of engagement of magnetic clutch  30 . ATCU  91  and HEV-CU  92  are linked by an intercommunication system, whereby necessary signals are mutually sent and received, in order to effect drive control appropriate to the running condition of a vehicle.  
     [0028] Reduction of torsional vibration made possible by the present invention will now be explained with reference to FIGS. 3A and 3B, wherein torsional vibration is represented by a zigzagged line. With reference to FIG. 3A, torsional vibration occurring in the related art is output from an engine and a large-size motor-generator. The torsional vibration is then transmitted via a damper to a vibration receiving side. In contrast, with the present invention as shown in FIG. 3B, torsional vibration is output from an engine and then transmitted via a damper to a small-size motor-generator. Torsional vibration then continues on to a vibration receiving side.  
     [0029] Referring to FIG. 4, it can be seen that the resonance level of torsional vibration which is transmitted within a practical-use frequency zone is large in an instance where a large-size motor-generator is directly connected to an output shaft of an engine, as with the related art. However, with the present invention, by providing starter motor  15  and motor-generator  20  separately, a smaller motor-generator can be provided, and by providing damper  10  between engine  70  and small-size motor-generator  20 , a large reduction in resonance level is achieved in the practical-use frequency zone.  
     [0030] By providing starter motor  15  separately for normal engine starting, such as when launching a vehicle, a hybrid vehicle can be equipped with a smaller-size motor-generator. This allows the drive apparatus to have a more compact design, and also results in a reduction in cost.  
     [0031] Operation of a drive apparatus according to the present invention will now be explained. Under conditions where a large amount of driving force is required, such as when a vehicle is accelerating or when climbing an inclined surface, motor-generator  20  assists engine  70  in moving a vehicle. This is achieved by motor-generator  20  providing driving force that is combined with a driving force of engine  70 . Under different conditions where there is enough driving force being output from engine  70 , such as when running at a constant low speed or when traveling down an inclined surface, motor-generator  20  functions as a generator to charge battery  93 . Also, when the vehicle temporarily stops during normal running and given certain conditions, idle-stop control is effected. Idle-stop control is implemented in a vehicle as a way of improving fuel efficiency, and when a set of prescribed conditions is met, idle-stop control then functions to stop engine  70 . Once the vehicle is again made to proceed, engine  70  is quickly restarted. This set of conditions is set forth in the following discussion of the difference between normal engine starting and engine restarting under idle-stop control.  
     [0032] Normal engine starting is performed by starter motor  15 . Often, normal starting of an engine is performed under such conditions as oil temperature being less than optimal. When the oil temperature is low, this results in a high oil viscosity, which increases load during starting of an engine. Therefore, starter motor  15  is a normal 12V starter motor used for starting engine  70  under such conditions.  
     [0033] Idle-stop control is effected to stop an engine if each of the following conditions has been met when a vehicle is running. 
     [0034] 1) vehicle speed=0 km/h  
     [0035] 2) brake switch is ON  
     [0036] 3) steer angle=0° 
     [0037] 4) not R range  
     [0038] 5) oil temperature is within predetermined range 
     [0039] A state of the brake switch is determined from brake sensor  94 , a steer angle from steer angle sensor  95 , and a temperature of oil in the transmission from oil temperature sensor  91   c . A speed of the vehicle is determinable from secondary rotation sensor  91   b , and a range of the transmission from primary rotation sensor  91   a . Thus, among the above prerequisites, the temperature of the oil in the transmission also factors into the determination by the control system as to whether to effect idle-stop control or not. By determining that the temperature of the oil is within a predetermined range, it is determined that the viscosity of the oil is such that a large load will not be encountered when starting engine  70 , and therefore, engine  70  can be restarted with relatively little effort. Therefore, it is not necessary for motor-generator  20  to be a large-size motor-generator capable of driving a heavier load, and thus, according to the present invention, motor-generator  20  is designed with a small and compact structure.  
     [0040] Therefore, for any other set of conditions where the above criteria are not met, including temperature of oil in the transmission being outside the predetermined range, engine starting is deemed to be normal engine starting, and is  20  performed by starter motor  15 .  
     [0041] The flow of operation of idle-stop control will now be explained, particularly as regards the manner in which oil temperature factors into idle-stop control. 
     [0042] 1) ATCU  91  has received a signal from secondary rotation sensor  91   b  indicating the vehicle is stopped, and a signal from primary rotation sensor  91   a  indicating the transmission is in a range other than reverse to meet conditions 1 and 2.  
     [0043] 2) ATCU  91  sends corresponding flag signals to HEV-CU  92 .  
     [0044] 3) ATCU  91  receives a signal from oil temperature sensor  91   c  indicative of the temperature of the oil in the transmission.  
     [0045] 4) ATCU  91  determines that the oil temperature is within a predetermined range to meet condition 5.  
     [0046] 5) ATCU  91  sends a corresponding flag signal to HEV-CU  92 .  
     [0047] 6) HEV-CU  92  has received a signal from steer angle sensor  95  indicating the steer angle is  0  degrees, and a signal from brake sensor  94  indicating the brake pedal is being depressed to meet conditions 3 and 4.  
     [0048] 7) Idle-stop control is effected by HEV-CU  92 . Engine  70  is stopped as a result.  
     [0049] 8) Eventually, when a driver releases the brake, HEV-CU  92  receives a signal from brake sensor  94  indicating the brake pedal has been released, which is interpreted as the driver&#39;s intention to make the vehicle proceed once again.  
     [0050] 9) HEV-CU  92  then sends command signals to magnetic clutch  30  to engage and to motor-generator  20  to commence driving engine  70 . 
     [0051] Also, by provision of magnetic clutch  30 , torque above a predetermined level is not transmitted due to current control. Thus, even if a sudden surge of torque should occur immediately after combustion is complete in engine  70 , the vehicle is able to resume running smoothly. Also, following engine restarting, transmitted engine output torque is maintained at a reduced level by magnetic clutch  30  until an amount of oil enough to prevent belt-slippage as well as to secure forward clutch pressure is achieved by pump  50 . The durability of CVT  40  is assured by this measure.  
     [0052] A second embodiment according to the present invention will now be explained with reference to FIG. 5. In the second embodiment, a dry bearing  74 , not present in the first embodiment, is disposed in an end of engine output shaft  73  such that dry bearing  74  is connectable with first input shaft  31 . Other than dry bearing  74 , all elements and reference numbers of the first embodiment are the same. Referring to FIG. 5, an end of first input shaft  31  which is nearest engine  70  is extended axially, and passes through dry bearing  74  to be supported by dry bearing  74 . Therefore, first input shaft is supported at both ends thereof, at one end by bearing  31   b , and at another end by dry bearing  74 . By supporting first input shaft  31  at two points in this manner, a space between rotor  21  and stator  22  of motor-generator  20  can be regulated with precision. The efficiency of motor-generator  20  is improved in this manner.  
     [0053] Thus, according to a first embodiment of a drive apparatus according to the present invention, by disposing damper  10  between starter motor  15  and motor-generator  20 , a resonance point is lowered, i.e., vibration is reduced, within a practical-use frequency zone. Also, by providing motor-generator  20  and a normal 12V starter motor for starter motor  15  separately, engine starting can be performed by starter motor  15  when there is a large engine load, and by motor-generator  20  when there is a light load. Motor-generator  20  is thus designed with a smaller size, and therefore the driving apparatus is more compact and can be provided at lower cost.  
     [0054] Also, by disposing outer circumference ring gear  10   b  on an outer circumference of outer member  10   c  of damper  10  to mesh with starter motor  15 , a starter motor layout commonly found in vehicles is maintained. It is therefore only necessary to change the transmission unit of a vehicle.  
     [0055] By providing magnetic clutch  30 , clutch engagement control is executed electrically, and controllability is thus improved. Also, by disposing front cover  1   a  made of magnetic material between motor-generator  20  and magnetic clutch  30 , leakage flux of motor-generator  20  is prevented from affecting engagement force of magnetic clutch  30 .  
     [0056] Further, by providing electromagnetically-controlled pilot clutch  34  and cam mechanism  36  which changes engagement force of pilot clutch  34  to axial-direction thrust, a large engagement force to be applied to main clutch  37  is achieved with a small electromagnetic force.  
     [0057] Also, by setting the outer diameter of rotor  21  of motor-generator  20  larger than the respective outer diameters of main clutch  37  and damper  10 , stator  22  of motor generator  20  overlaps magnetic clutch  30  and damper  10  in the radial direction around the respective outer circumferences thereof, and the dimension of the drive apparatus is therefore shortened in the axial direction. Also, by disposing stator  22  of motor-generator  20  around the respective outer circumferences in the radial direction, a diameter of rotor  21  is large. That is, since a rotational inertia of rotor  21  is proportional to the square of the radius thereof, a large rotational inertia is gained through rotor  21  having a large diameter. The result is that torsional vibration is reduced with greater effect.  
     [0058] By providing idle-stop control to stop engine  70  under a specific set of conditions, fuel efficiency is improved.  
     [0059] And according to a second embodiment of the present invention, by extending a tip end of first input shaft  31  to be supported via dry bearing  74  inside an end of the output shaft of engine  70 , first input shaft  31  is supported at two points. This allows the space between rotor  21  and stator  22  to be regulated with precision, and improves the efficiency of motor-generator  20   
     [0060] This application is based on a prior Japanese Patent Application No. 2002-276726. The entire contents of Japanese Patent Application No. 2002-276726 with a filing date of Sep. 24, 2002 are hereby incorporated by reference.  
     [0061] Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. For example, although the embodiments of the present invention were described as applied to a belt-type continuously variable transmission, the present invention is also applicable to a gear-type conventional transmission. The scope of the invention is defined with reference to the following claims.