Abstract:
A transmission unit for a hybrid vehicle includes a housing formed with a water jacket for cooling a stator of a motor. The water jacket includes a hollow annular passage having a water inlet and a water outlet. The water jacket has at least one uneven or depressed portion for avoiding an adjacent component. At the uneven portion, the cross sectional shape of the flow passage is varied gradually and smoothly so that the cross-sectional area of the flow passage remains constant. The water jacket further includes an inflow passage extending in a tangential direction to the water inlet, and an outflow passage extending in a radial direction from the water outlet.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    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.  
           [0002]    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 and to serve as a generator for converting kinetic energy of the vehicle to electrical energy on deceleration.  
           [0003]    A published Japanese patent application Publication (Kokai) No. 9(1997)-329228 shows a conventional transmission having a planetary gear system. This transmission is designed to add a motor without changing the basic layout of a conventional transmission to reduce the manufacturing cost. The transmission of this example includes, as shown in FIG. 7A, a torque converter chamber  101  defined by a first housing  113  and a first partition  116 , a planetary gear 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 . Rotation from the engine is inputted to a torque converter  110  in the torque converter chamber  101 , the output from the torque converter  110  is inputted the planetary gear system in the planetary gear chamber  102  and further to a transmission  112  in the transmission chamber  103 .  
           [0004]    When a motor is disposed in the planetary gear chamber without changing the basic layout, a water jacket formed around the motor is effective to cool the motor having the coil heated by repetition of drive and generation.  
           [0005]    A published Japanese patent application Publication (Kokai) No.2000-9213 shows an apparatus having an electromagnetic clutch in the torque converter chamber  101  and a motor in the planetary gear chamber  102 , as shown in FIG. 7A.  
         SUMMARY OF THE INVENTION  
         [0006]    However, the space for the water jacket is limited because, as shown in FIGS. 7A and 7B, a transmission input shaft  120 , a driven shaft  121 , an idler shaft  123  and a differential  124  are arranged with proper distances between adjacent axes. FIG. 8 shows a front view of the housing of the transmission unit of FIG. 7B. As shown in FIG. 8, a motor receiving portion  231  for receiving the motor is surrounded by a driven pulley receiving portion  232  for a driven pulley, a differential receiving portion  233  for a differential, and a parking support receiving portion  234  for a parking pole support.  
           [0007]    An object of the present invention is to provide a transmission unit for a hybrid vehicle, having a water jacket to cool a motor efficiently. Another object is to provide a transmission unit in which a water jacket is formed compactly without the need for changing a layout of a conventional design. Still another object is to provide an annular water jacket designed to improve the cooling performance by holding the flow rate uniform all round the circumference.  
           [0008]    According to the present invention, a transmission unit for a hybrid vehicle, the transmission unit comprises a unit housing which comprises;  
           [0009]    a first section (such as an item  42 ) defining a clutch chamber for containing an electromagnetic clutch;  
           [0010]    a second section (such as an item  41   a ) defining a transmission chamber for containing a transmission; and  
           [0011]    a third section (such as an item  41   b ) defining a motor chamber for containing a motor comprising a rotor and a stator, and a water jacket for circulation of water to cool the stator.  
           [0012]    The water jacket comprises an annular passage extending around the motor chamber, and comprising a water inlet for introducing the coolant into the annular passage, a water outlet for discharging the coolant from the annular passage, and a depressed or uneven portion which is depressed to form a space for receiving an adjacent component of the transmission unit, and which has a cross sectional shape varied gradually so that a flow sectional area remains uniform. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a schematic view showing a hybrid drive system of a hybrid vehicle according to one embodiment of the present invention.  
         [0014]    [0014]FIG. 2 is a sectional view of a transmission unit having a belt type continuously variable transmission (CVT) in the hybrid drive system of the embodiment.  
         [0015]    [0015]FIG. 3 is a front view of a second housing in the transmission unit of FIG. 2.  
         [0016]    [0016]FIG. 4 is a view showing the outline of a water jacket in the transmission unit of FIG. 2.  
         [0017]    [0017]FIG. 5 is a development of the outer periphery of an A motor receiving portion in the transmission unit of FIG. 2.  
         [0018]    FIGS.  6 A˜ 6 D are simulation views for illustrating flow rates in water jackets of various shapes.  
         [0019]    [0019]FIGS. 7A and 7B are sectional views for comparing a conventional transmission unit with a transmission unit modified for a hybrid vehicle.  
         [0020]    [0020]FIG. 8 is a front view of a ho-using of the transmission unit of FIG. 7B. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    The following is explanation on one embodiment according to the present invention, based on the drawings.  
         [0022]    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 .  
         [0023]    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.  
         [0024]    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 controlled in an integrated manner by the hybrid control unit  7 .  
         [0025]    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 .  
         [0026]    &lt;Starting up the System&gt; 
         [0027]    When starting up the system, the B motor  3  functions as a starter to start the engine  2 .  
         [0028]    &lt;Starting/Low-speed Operation&gt; 
         [0029]    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 .  
         [0030]    &lt;Normal Running Operation&gt; 
         [0031]    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 .  
         [0032]    &lt;At Heavy Loads&gt; 
         [0033]    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.  
         [0034]    &lt;Decelerating&gt; 
         [0035]    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.  
         [0036]    &lt;Reverse Operation&gt; 
         [0037]    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 .  
         [0038]    &lt;Stopping&gt; 
         [0039]    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.  
         [0040]    [0040]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 .  
         [0041]    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 .  
         [0042]    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 .  
         [0043]    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 .  
         [0044]    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 .  
         [0045]    The thus-constructed transmission can vary the 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 .  
         [0046]    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  has a housing section  41   a  enclosing the CVT  13  and a housing section  41   b  enclosing 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  15  therein, by a second partition  45 .  
         [0047]    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 .  
         [0048]    The stator  17  of the A motor  15  is fixed in the motor chamber  44  by shrinkage fit to simplify the structure. A 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 .  
         [0049]    [0049]FIG. 3 shows the second housing  41 , as viewed from the engine&#39;s side. In this example, the water jacket  48  is formed in the section  41   b  of the second housing  41 .  
         [0050]    The second housing  41  includes a motor receiving portion  61  for receiving the A motor  15 , a driven pulley receiving portion  63  for receiving the driven pulley  18 , an idler shaft receiving portion  64  for receiving the idler shaft  27 , a differential receiving portion  65  for receiving the differential, and a parking support receiving portion  62  for forming a parking pole support. Reference numerals  71  and  72  denote water inlet and water outlet.  
         [0051]    [0051]FIG. 4 shows the contour of the water jacket  48 . An inflow passage  73  extends in a tangential direction of the water jacket  48 , and an outflow passage  74  extends in a radial direction of the water jacket  48 . The water jacket  4  includes an annular passage extending around the motor chamber  44 . The annular passage is divided into first and second arc passages  75  and  76 . The first arc passage  75  extends from the water inlet  71  to the water outlet  72  in a clockwise direction as viewed in FIG. 4. The second arc passage  76  extends from the water inlet  71  to the water outlet  72  in a counterclockwise direction as viewed in FIG. 4. The first arc passage  75  is longer than the second arc passage  76 . The flow direction in the first arc passage  75  near the water inlet  71  is substantially coincident with the flow direction in the inflow passage  73 . The flow direction in the second arc passage  76  near the water inlet  71  is approximately perpendicular to the flow direction in the inflow passage  73 .  
         [0052]    The first and second arc passages  75  and  76  are connected together to form the annular passage extending in a circle. The inflow passage  73  extends along a tangent to the circle. The outflow passage  74  extends in a diametral direction of the circle. The inflow passage  73  is substantially perpendicular to the direction of the outflow passage  74 . In this example, the location of the water inlet  71  is away from, but near the diametrically opposite position of the water outlet  72 .  
         [0053]    In general, a long passage has a greater flow resistance than a short passage. Therefore, in this example, the bend formed at the water inlet  71  between the inflow direction in the inflow passage  73  and the circumferential flow in the first arc passage  75  is made obtuse and nearly straight to reduce energy loss. The bend formed at the water inlet  71  between the inflow direction in the inflow passage  73  and the circumferential flow in the second arc passage  76  is made relatively sharp to increase energy loss. Thus, the water jacket  48  can make the flow resistances of the first arc passage  75  and the second arc passage  76  substantially equal to each other, and thereby hold the flow rate in each of the first and second arc passages  75  and  76  substantially equal to that in the other.  
         [0054]    [0054]FIG. 5 shows the water jacket  48  in a developed state. The cross sectional area of the annular passage is uniform while the cross sectional shape of the flow passage is varied to avoid the differential receiving portion  65 , the driven pulley receiving portion  63  and the parking support receiving portion  62 . This arrangement is advantageous to the flexibility in design and the compactness of the structure. In the example shown in FIG. 5, the first arc passage  75  (1ST) of the water jacket  48  has a depressed portion for the differential receiving portion  65  and a depressed portion for the driven pulley receiving portion  63 , and the second arc passage  76  (2ND) has a depressed portion for the parking support receiving portion  62 .  
         [0055]    [0055]FIGS. 6A, 6B,  6 C and  6 D show the results of flow velocity simulation in water jackets different in slope and angle of corner of projections in the flow passage formed by the depressed portions. Each figure show a region having a flow velocity of 0.6 (m/sec) or higher (hereinafter referred to as M region). In a first model shown in FIG. 7A, the M region in the first arc passage  75  is narrow in a certain section. This means that the flow rate in the first arc passage  75  is lower than that in the second arc passage  76 . Therefore, the water jacket of FIG. 6A is unable to cool the entirety of the A motor  15  evenly. In second and third models shown in FIGS. 6B and 6C, the flow rates in the first and second arc passages  75  and  76  are substantially equal. However, the water jackets FIGS. 6B and 6C are unable to make enough room for the driven pulley receiving portion  63 .  
         [0056]    In a fourth model shown in FIG. 6D, the M region appears about equally in both of the first and second arc passages  75  and  76 , and the flow rates in both passages are substantially equal. The water jacket of FIG. 6D is able to cool the A motor  15  adequately. This embodiment employs the design of FIG. 6D.  
         [0057]    The flow passage resistance is determined by the shape of the passage, and reduced by varying the sectional shape of the passage smoothly. Thus, the water jacket of this embodiment can ensure the flow velocity of flow, and hence the cooling performance.  
         [0058]    The water inlet and outlet  71  and  72  are positioned approximately at two diametrically opposite positions so as to confront each other across the A motor  15 . The flow in the inflow passage  73  is divided at the inlet  71  into a first circumferential flow through the first arc passage  75  and a second circumferential flow through the second arc passage  76 . The first and second arc passages  75  and  76  are so designed as to hold the flow rate in each of the first and second arc passages  7  equal to the flow rate in the other, to achieve stable cooling effect.  
         [0059]    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.