Abstract:
A transmission unit for a hybrid vehicle has a single-shaft structure wherein the input from an electromagnetic clutch to a motor and a CVT is effected through a single input shaft. The input shaft is supported by first and second bearing members on both sides of the CVT, and a third bearing member provided between the input shaft and a first partition wall. Each of the first and second bearing members is fit in a hole of the housing in a manner to prevent radial motion of the input shaft, whereas the third bearing member is surrounded by a clearance for allowing radial motion of the input shaft relative to the housing. In the clearance, there is provided a seal member for preventing passage of foreign objects from the clutch chamber into the motor chamber.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a transmission unit to be installed in a hybrid vehicle combining an engine and a motor, to obtain a driving force. 
     With improved fuel economy and lower emissions, hybrid vehicles benefit conservation of global environment and savings of limited resources. In a hybrid vehicle, a motor is arranged in series or parallel to an engine to assist the engine output and to serve as a generator for converting kinetic energy of the vehicle to electrical energy on deceleration. 
     A published Japanese patent application Publication (Kokai) No. 2000-9213 shows an apparatus for a hybrid vehicle. This apparatus includes a clutch chamber  101  defined by a first housing  113  and a first partition  116 , a motor chamber  102  defined by a second housing  114 , the first partition  116  and a second partition  117 , and a transmission chamber  103  defined by a third housing  115  and the second partition  117 , as shown in FIG.  6 . The rotation of the engine is input to an electromagnetic clutch  110  in the clutch chamber  101 , and the output of the electromagnetic clutch  110  is transmitted to a motor  111  in the motor chamber  102  and a transmission  112  in the transmission chamber  103  through an input shaft  100 . 
     This input shaft  100  is rotatably supported by a bearing at each of support portions  120  and  121  which are provided in the third housing  115  and the second partition  117 , respectively in a manner not to allow run-out and off-center deviation of the input shaft  100 . On the sliding surface between the first partition  116  and the input shaft  100 , there is provided a seal member  122  to prevent entrance into the motor chamber  102 , of abrasion powder abraded from an electrode blush at a slip ring (or collector ring)  110   a  for supplying electric current to the electromagnetic clutch  110  in the clutch chamber  101 , and moisture permeating from the joint surface between the engine and the transmission unit A. 
     SUMMARY OF THE INVENTION 
     The apparatus of the above-mentioned Japanese Publication has the following problems. 
     The clutch chamber  101  and the motor chamber  102  are in the dry state with no lubrication by oil. Therefore, the seal member provided therebetween requires the addition of a lubricating structure, specifically at its seal lip portion (to prevent powder produced by abrasion). 
     When a bearing requiring no lubrication structure is used as a seal member, the input shaft  100  is supported at three support points  120 ,  121  and  122  by the three bearings, as shown in FIG.  5 A. In this three-point support structure including the bearing, as the seal member  122 , rigidly supporting the input shaft without allowing radial motion, stress concentration is liable to occur at each support portions  120 ,  121  and  122  in the case of whirling motion of the input shaft  100  due to vibrations produced by the transmission  112 . Consequently, the durability of the input shaft  100  and the bearings is decreased. (FIG. 5A shows the wavelike form of the input shaft exaggeratedly to illustrate the stress concentration.) 
     Moreover, when the support portions  120 ,  121  and  122  are to be assembled in this order, without providing a portion for absorbing the accumulated tolerance of constituent parts, as shown in FIG. 5C, the assembly operation of the third bearing portion  122  becomes unfeasible. 
     To improve the performance of the motor  111 , the clearance between a rotor and a stator is set small, and there is a need for providing a predetermined clearance in addition to a part for absorbing the accumulated tolerance. 
     It is therefore an object of the present invention to provide a transmission unit for a hybrid vehicle which is capable of sealing an opening between a clutch chamber and a motor chamber without requiring a lubricating structure and without deteriorating the durability. 
     According to the present invention, a transmission unit for a hybrid vehicle comprises: 
     a unit housing defining a first dry chamber containing an electromagnetic clutch, a second dry chamber containing a motor, and a hydraulic wet chamber containing a transmission mechanism, and comprising a partition wall separating the first and second dry chambers; 
     an input shaft extending through the first dry chamber, the second dry chamber and the wet chamber, to input rotation from the electromagnetic clutch to the motor and the transmission mechanism; 
     first and second bearing members supporting the input shaft rotatably at first and second support points spaced from each other in the wet chamber, in a manner to prevent radial motion of the input shaft relative to the unit housing; 
     a third bearing member provided between the partition wall and the input shaft with a clearance interposed between the third bearing member and the partition wall, to allow radial motion of the input shaft relative to the unit housing; and 
     a seal member provided in the clearance, for preventing passage of foreign matters from the first dry chamber to the second dry chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view showing a drive system of a hybrid vehicle according to one embodiment of the present invention. 
     FIG. 2 is a sectional view of a transmission unit having a belt type continuously variable transmission (CVT) in the hybrid vehicle of the embodiment. 
     FIG. 3 is an enlarged sectional view of a third bearing portion in the transmission unit of FIG.  2 . 
     FIG. 4 is a schematic view of the transmission unit of FIG.  2 . 
     FIGS. 5A,  5 B and  5 C are views for illustrating operations of an input shaft support structure according to the embodiment. 
     FIG. 6 is a schematic view showing an input shaft support structure of a related art. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows the arrangement of main units of a hybrid vehicle according to the embodiment of the invention. 
     The drive system shown in FIG. 1 includes a transmission unit  1 , an engine  2 , a B motor  3  for acting as a generator/starter, an inverter  4 , a battery  5 , an electric power steering  6 , a hybrid control unit  7 , and a chain  8 . 
     In the transmission unit  1 , there are provided an electromagnetic clutch  11 , an A motor  15  for acting as a driving motor, and a continuously variable transmission (CVT)  13 . The A motor  15  also acts as a regenerative motor for regeneration of energy during deceleration and braking. A C motor  9  is for driving an electric oil pump. The C motor  9  can drive the oil pump properly even in a motor drive mode in which the vehicle is driven only by the motor and the engine cannot supply sufficient power to drive the oil pump (especially to obtain a pulley pressure of the CVT  13 ). For the same reason, the power steering  6  is assisted by the motor. 
     The B motor  3  serving as generator/starter is mounted on the engine block and connected with the engine  2  through the chain  8 . The B motor  3  acts as a generator in normal operation, and acts as a starter in a starting operation. Control units  7   a ,  7   b ,  7   c ,  7   d , and  7   e  for the battery  5 , motors  3  and  15 , engine  2 , clutch  11  and CVT  13  are independent, and controlled integrally by the hybrid control unit  7 . 
     The hybrid drive system is operated as follows. The hybrid drive system in the embodiment is a parallel type. The A motor  15  assists the engine  2  which is fuel economy oriented rather than output. The CVT  13  also acts as a coordinator so that the engine operates at the optimum fuel consumption point. The clutch  11  is an electromagnetic clutch. When the clutch is in OFF state, the vehicle is operated only by the A motor  15 . The clutch control unit  7 d controls the ON/OFF state of the clutch  11  automatically and optimally under the command of the hybrid control unit  7 . 
     &lt;Starting Up the System&gt; 
     When starting up the system, the B motor  3  functions as a starter to start the engine  2 . 
     &lt;Starting/Low-Speed Operation&gt; 
     In a starting operation or a low-speed operation at low load where the fuel consumption rate of the engine  2  is low, the engine  2  stops and the vehicle is driven only by the A motor  15 . If the load is heavy (the throttle opening is large), the engine  2  starts up immediately, the clutch  11  turns on, and the vehicle is driven by both the engine  2  and the A motor  15 . 
     &lt;Normal Running Operation&gt; 
     The vehicle runs mainly by the engine  2 . In this case, the operation on the best fuel consumption line is achieved by adjusting the engine speed under the shift control of the CVT  13 . 
     &lt;At Heavy Loads&gt; 
     During operation in a heavy load region where the driving force is deficient even if the engine  2  generates the maximum output, electrical energy is supplied from the battery  5  to the A motor  15  actively to enhance the whole driving force. 
     &lt;Decelerating&gt; 
     When the vehicle is decelerated, the supply of fuel to the engine  2  is cut off. Simultaneously, the A motor  15  functions as a generator to convert a part of kinetic energy to electrical energy and store the electrical energy in the battery  5 . Thus, kinetic energy that used to be thrown away is recovered. 
     &lt;Reverse Operation&gt; 
     A reverse gear is not provided in the CVT  13 . Therefore, to operate the vehicle in reverse, the clutch  11  is opened and the A motor  15  is rotated in the reverse direction. The vehicle is driven only by the A motor  15 . 
     &lt;Stopping&gt; 
     When the vehicle is stopped, the engine  2  stops except for the case of need to charge the battery  5 , to operate the air compressor, or for warming-up. 
     FIG. 2 shows, in section, the transmission unit  1  having the belt type continuously variable transmission (CVT)  13 . In FIG. 2, an engine output shaft  10  is connected with the electromagnetic clutch  11  and an electrode member  11   a  is provided for supplying power to this electromagnetic clutch  11 . The output side of the electromagnetic clutch  11  is connected with a transmission input shaft  12 . At the end of the input shaft  12 , there is provided a driving pulley  14  of the CVT  13 . The A motor  15  for operating the vehicle is disposed axially between the driving pulley  14  and the electromagnetic clutch  11 . 
     The A motor  15  includes a rotor  16  fixed to the input shaft  12  and a stator  17  fixed to the housing. The A motor receives power supply from the battery  5  to drive the input shaft  12 . When the vehicle is decelerated, the A motor functions as a generator based on the torque of the input shaft  12 . 
     The CVT  13  includes the foregoing driving pulley  14 , a driven pulley  18 , and a belt  19  for transmitting the torque from the driving pulley  14  to the driven pulley  18 . The driving pulley  14  includes a fixed conical plate  20  for rotating integrally with the input shaft  12 , and an adjustable conical plate  22  disposed opposite the fixed conical plate  20  to form a V-shaped pulley groove. The adjustable conical plate  22  is movable in the axial direction of the input shaft  12  by the hydraulic pressure in a driving pulley cylinder chamber  21 . The driven pulley  18  is mounted on a driven shaft  23 . The driven pulley  18  includes a fixed conical plate  24  for rotating integrally with the driven shaft  23 , and an adjustable conical plate  25  disposed opposite the fixed conical plate  24  to form a V-shaped pulley groove. The adjustable conical plate  25  is movable in the axial direction of the driven shaft  23  by the hydraulic pressure in a driven pulley cylinder chamber  32 . 
     On the driven shaft  23 , a driving gear  26  is secured. The driving gear  26  is engaged with an idler gear  28  on an idler shaft  27 . A pinion  29  provided on the idler shaft  27  is engaged with a final gear  30 . The final gear  30  drives drive shafts leading to drive wheels (not shown) through a differential  31 . 
     The torque inputted from the engine output shaft  10  is transmitted to the CVT  13  through the electromagnetic clutch  11  and the input shaft  12 . The torque of the input shaft  12  is transmitted to the differential  31  through the driving pulley  14 , the belt  19 , the driven pulley  18 , the driven shaft  23 , the driving gear  26 , the idler gear  28 , the idler shaft  27 , the pinion  29 , and the final gear  30 . 
     The thus-constructed transmission can vary the rotating ratio or speed ratio between the driving pulley  14  and the driven pulley  18  by moving the adjustable conical plates  22  and  25  of the driving pulley  14  and the driven pulley  18  in the axial direction to vary the contacting radii with the belt  19 . The CVT control unit  7   e  varies the groove width of the V-shaped pulley groove of each of the driving pulley  14  and the driven pulley  18  by controlling the hydraulic pressure for the driving pulley cylinder chamber  21  or the driven pulley cylinder chamber  32 . 
     The transmission housing is composed of a second housing  41  and a first housing  42  which are placed end to end in the axial direction, and joint together. The second housing  41  encloses the CVT  13  and the A motor  15 . The first housing  42  encloses the electromagnetic clutch  11 . The inside of the second housing  41  is partitioned into a transmission chamber  43  having the CVT  13  therein, and a motor chamber  44  having the A motor therein, by a second partition  45 . 
     The first housing  42  extends axially from a first axial end to which the engine is joined, to a second axial end to which the second housing  41  is joined. The first housing  42  includes a first partition  46  at the second axial end. In the assembled state in which the housings  41  and  42  are joined together, the motor chamber  44  is defined axially between the second partition  45  and the first partition  46 . A clutch chamber  47  is defined axially between the first partition  46  and the engine  2  joined to the first axial end of the first housing  42 . 
     The stator  17  of the A motor  15  is fixed in the motor chamber  44  by shrinkage fit to simplify the structure. A cooling-water jacket  48  is formed around the stator  17  in the second housing  41  to circulate cooling water for efficient cooling of the A motor  15 . 
     FIG. 3 shows the structure for supporting the input shaft in the embodiment. 
     FIG. 3 is an enlarged sectional view of a third bearing  53 . A front cover  66  is fixed to the first partition  46  to form a first partition wall separating the motor chamber  44  and the clutch chamber  47 . Between the front cover  66  and the input shaft  12 , there are provided the third bearing  53  filled with grease and a resolver rotor  61  for rotating with the input shaft  12 . On the motor chamber&#39;s side of this front cover  66 , there are provided a resolver stator  62  for detecting the rotational position of the A motor  15 , and a magnetic shield plate  63  for preventing the effect of the magnetic field generated due to the A motor  15  on the resolver stator  62  and the resolver rotor  61 . 
     In the clutch chamber  47 , there is provided the electrode member  11   a  for supplying power to the electromagnetic clutch  11 . Electrode terminals  65  of the electrode member  11   a  supply power by being pressed and contacted by slip rings  64  for rotating with the engine output shaft  10 . 
     The third bearing  53  includes an inner race  54  fixed to the input shaft  12 , an outer race  56  held unrotatable relative to the first partition wall ( 46 ,  66 ) by at least one stopper member  58 , balls  55 , a cage or retainer  60  for retaining the balls  55 , and a sealing plate  60   a  for sealing grease filled in the third bearing  53 . The stopper member  58  is a stopper pin in this example. The stopper member  58  extends radially and is engaged in a hollow portion formed in the front cover  66  in a manner to allow radial motion of the outer race  56 . 
     The outer race  56  is formed with at least one pin hole  56   b  for holding the stopper pin  58  for fixing the outer race  56  in the rotational direction, and an O-ring groove  56   a  for holding an O-ring  57  for sealing abrasion powder or water. The outer race  56  has an outside cylindrical surface facing radially outward. The pin hole  56   b  and the ring groove  56   a  are formed in the outside cylindrical surface of the outer race  56 . The ring groove  56   a  is located axially between the pin hole  56   b  and the clutch chamber  47 . The pin hole  56   b  is located axially between the ring groove  56   a  and the second bearing  52 . 
     A clearance  59  is formed between the outer race  56  of the third bearing  53  and the first partition wall ( 46 ,  66 ). The outer race  56  is surrounded by the clearance  59 . The front cover  66  forming the first partition wall is formed with a hole having an inside cylindrical surface surrounding, and facing toward, the outside cylindrical surface of the outer race  56 . The clearance is formed radially between the outside cylindrical surface of the outer race  56  and the inside cylindrical surface of the front cover  66 . 
     The transmission unit for a hybrid vehicle in the embodiment is operated as follows. FIG. 4 is a skeleton diagram showing the configuration of the embodiment. When the engine starts up and the electromagnetic clutch turns on, the input shaft  12  rotates and the rotation is transmitted to the motor and the transmission. The clutch chamber  47  and the motor chamber  44  are dry chambers, and the transmission chamber  43  is a wet chamber lubricated by oil. When the input shaft  12  vibrates by the vibration generated in the transmission chamber  43 , the vibration is transmitted to the third bearing  53 . In this case, the clearance  59  formed between the outer race  56  of the third bearing  53  and the first partition  46  permits radial motion of the input shaft  12  to the extent determined by the radial dimension of the clearance  59 . The O ring  57  and the ring groove  56   a  are so designed as to hold sealing contact of the O ring  57  with the inside cylindrical surface of the hole in the front cover  66  while permitting the radial motion of the input shaft  12 . Thus, the third bearing portion allows vibrations. 
     FIG. 5A illustrates the stress concentration in a three-point support structure supporting the input shaft  12  at three support points  120 ,  121  and  122 . FIG. 5B illustrates the support structure according to the embodiment. Unlike the three-point support structure of FIG. 5A, the clearance  59  in the support structure of FIG. 5B functions to prevent stress concentration at each support point by allowing vibrations at the third support point ( 53 ). Therefore, the support structure of FIG. 5B provides stable input rotation to the A motor  15  and the CVT  13 , and improves the durability of the input shaft  12  and each bearing  51 ,  52  or  53 . Moreover, center deviation due to tolerance of the input shaft  12  accumulated after setting up is allowed by the clearance  59  to simplify the setting up. 
     The clutch chamber  47  and the motor chamber  44  are dry, so that the lubrication for the third bearing  53  is not feasible. However, the third bearing  53  does not require lubrication because the outer race  56  is held unrotatable relative to the first partition wall, the rolling elements  55  reduce friction in the relative rotation between the input shaft  12  and the first partition wall, and the grease is confined in the third bearing  53 . 
     There is provided, between the outer race  56  of the third bearing  53  and the front cover  66 , the stopper pin or locking pin  58  for preventing rotation of the outer race  56 . The input shaft  12  rotates as a unit with the inner race  54 , and the outer race  56  is fixed in the rotational direction to the front cover  66  of the first partition wall. Thus, the third bearing  53  supports the input shaft  12  rotatably, and the O-ring  57  is durable between the front cover  66  and the outer race  56  held unrotatable. 
     Further, the O ring  57  can reliably prevent passage of powder produced by abrasion between the electrode terminals  65  and slip rings  64  of the electromagnetic clutch  11 , and moisture permeating through the joint surface between the engine and the transmission unit. 
     The clearance  59  is annular at least when the input shaft  12  is located correctly at the center of the circular hole formed in the front cover  66 . The clearance  59  is sized to absorb the eccentricity of the input shaft  12  caused by tolerances of parts of the assembly, and thereby facilitate the assembly process. 
     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. The scope of the invention is defined with reference to the following claims.