Abstract:
The present invention provides a method for cooling and lubricating an off-axis motor/generator of a hybrid transmission. A transmission case at least partially defines a manifold. A transmission cover is mounted to the transmission case such that the off-axis motor/generator is retained therebetween. The transmission cover at least partially defines an oil passage. Oil is transferred through the manifold and onto a bearing device so that the bearing device is lubricated. Oil is also transferred through the oil passage and onto a torque transfer device such that the torque transfer device is lubricated. A corresponding apparatus for lubricating an off-axis motor/generator of a hybrid transmission is provided is similarly provided.

Description:
TECHNICAL FIELD 
       [0001]    The present invention pertains generally to a method and apparatus for cooling and lubricating an off-axis motor/generator of a hybrid transmission. 
       BACKGROUND OF THE INVENTION 
       [0002]    A conventional electrically variable transmission (EVT) includes a two electric machines such as electric motor/generators which are located on the transmission input axis. Locating the two electric machines on the transmission input axis limits the packaging design flexibility of such machines. It may therefore be desirable to relocate one of the electric machines to an off-axis position, particularly in the case of strong hybrid power trains having large electric machines. It is well known that electric machines such as electric motor/generators require cooling and lubrication in order to maintain optimal performance. 
       SUMMARY OF THE INVENTION 
       [0003]    A method for lubricating an off-axis motor/generator of a hybrid transmission is provided. A transmission case at least partially defines a manifold. A transmission cover is mounted to the transmission case such that the off-axis motor/generator is retained therebetween. The transmission cover at least partially defines an oil passage. Oil is transferred through the manifold and onto a bearing device so that the bearing device is lubricated. Oil is also transferred through the oil passage and onto a torque transfer device so that the torque device is lubricated. A corresponding apparatus for lubricating an off-axis motor/generator of a hybrid transmission is similarly provided. 
         [0004]    The method may include transferring oil through the manifold and onto a second bearing device so that the second bearing device is lubricated. 
         [0005]    The method may include transferring oil through a hollow tube disposed along the central axis of a rotor before said transferring oil through the oil passage and onto a torque transfer device. 
         [0006]    The bearing device may be configured to rotatably support a rotor drum, and the second bearing device may be configured to rotatably support a rotor hub. 
         [0007]    The torque transfer device may be a chain or a transfer gear configured to transfer off-axis motor/generator output to a transmission output shaft. 
         [0008]    The above feature and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic sectional illustration of a hybrid transmission in accordance with the present invention; and 
           [0010]      FIG. 2  is a more detailed schematic sectional illustration of an off-axis motor/generator of the hybrid transmission of  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]    Referring to  FIG. 1 , a schematic sectional illustration of a hybrid transmission  10  is shown. The hybrid transmission  10  includes an input shaft  12  and an output shaft  14  which define a first axis of rotation  16 . The hybrid transmission  10  also includes first and second electric machines which will hereinafter be described as first and second motor/generators  20 ,  22  in accordance with the preferred embodiment. The first motor/generator  20  is referred to as an “on-axis” motor/generator because its rotor  24  defines an axis of rotation that is common with the first axis  16 . Similarly, the second motor/generator  22  is referred to as an “off-axis” motor/generator because its rotor  26  defines an axis of rotation that is distinct from the first axis  16 . 
         [0012]    A first sprocket  30  coupled to the rotor  26  is rotatable about a second axis of rotation  28 , and second sprocket  32  is rotatable about the first axis  16 . A chain  34  couples the sprockets  30  and  32  such that output from the off-axis motor/generator  22  is transferable from the second axis  28  to the first axis  16  in order to drive the transmission output shaft  14 . Although the present invention is described as incorporating a plurality of sprockets  30 ,  32  coupled by a chain  34 , other known torque transfer devices such as, for example, a transfer gear arrangement (not shown) may also be implemented to transfer torque from the off-axis motor/generator  22  to the transmission output shaft  14 . 
         [0013]    Referring to  FIG. 2 , a schematic sectional illustration of the off-axis motor/generator  22  is shown in more detail. The off-axis motor/generator  22  is retained within and secured to a transmission case  36 . A transmission cover  38  is mounted to the transmission case  36  such that the off-axis motor/generator  22  is disposed therebetween. 
         [0014]    The off-axis motor/generator  22  includes a stator  42 , a stator housing  44 , the rotor  26 , a rotor hub  48 , and a rotor drum  50 . The stator  42  is substantially annular and is configured to remain stationary relative to the stator housing  44  during operation of the motor/generator  22 . The rotor  26  is generally circumscribed by the stator  42  and is rotatable relative thereto. The rotor drum  50  is secured to a radially inner portion of the rotor  26  for unitary rotation herewith. The rotor hub  48  and rotor drum  50  may be a single piece construction as shown in accordance with the preferred embodiment or may include individual rigidly connected components. A motor cover  52  is mounted to the stator housing  44  such that the stator  42  and rotor  26  are disposed therebetween. A left side bearing  54  is adapted to rotatably support the rotor drum  50  on the stator housing  44 , and a right side bearing  56  is adapted to rotatably support the rotor drum hub  48  on the motor cover  52 . 
         [0015]    The present invention implements a fluid such as oil  60  to cool the off-axis motor/generator  22 . A pump  63  provides the cooling oil  60  to the chamber  66  through the pressure regulator valve  65 , orifice  67  and inlet  64 . The pump  63  provides lubrication oil to inlet  80  through the cooler feed limit valve  69 , cooler  62  and cooling line  71 . 
         [0016]    The coolant chamber  66  is defined between the stator housing  44  and the transmission case  36 . A first seal  70  is disposed near one axial end portion of the stator  42  between the stator housing  44  and the transmission case  36  to seal one end of the coolant chamber  66 , and a second seal  72  is disposed near the other axial of the stator  42  between the stator housing  44  and the transmission case  36  to seal the other end of the coolant chamber  66 . It is well known that the stator coils  68  are a primary source of heat during the operation of the off-axis motor/generator  22 . The proximity of the coolant chamber  66  to the stator  42  and the stator coils  68  facilitates the cooling of the motor/generator  22 . Accordingly, by circulating cool oil  60  from the cooler  62  through the coolant chamber  66 , the off-axis motor/generator  22  can be cooled such that efficiency and durability are improved. 
         [0017]    The present invention also implements the oil  60  to lubricate the off-axis motor/generator  22 . More precisely, the oil  60  is implemented to lubricate motor/generator components including the left side bearing  54 , the chain  34 , and the right side bearing  56  as will individually be described in detail hereinafter. 
         [0018]    The left side bearing  54  is preferably lubricated in the following manner. The pump  63  transfer oil  60  from the cooler  62  into the lubrication inlet  80 . Thereafter, the oil  60  is transferred from the lubrication inlet  80 , through a manifold  82 , through an oil passable  84 , and into a chamber  86 . The manifold  82  and oil passage  84  are preferably integrally defined in a wall of the transmission case  36  such as with a casting process and/or a machining process. The chamber  86  is defined between the transmission case  36  and the stator housing  44 . The oil  60  is transferred from the chamber  86 , through one or more orifices  88  and onto the left side bearing  54  such that the left side bearing  54  is lubricated. The orifices  88  are defined by the stator housing  44  and are preferably formed with a machining process. The size and quantity of orifices  88  may be varied to control the rate at which oil  60  is transferred onto the left side bearing  54 . 
         [0019]    After lubricating the left side bearing  54 , the excess oil  60  is transferred into a drum cavity  90  defined by the rotor drum  50 , through one or more exhaust holes  92  and into the chamber  94 . The exhaust holes  92  are defined by the rotor drum  50 , and the chamber  94  is defined between an end portion of the stator  42  and the motor cover  52 . The oil  60  is then transferred from the chamber  94  through a motor vent  96  defined by the motor cover  52  such that the oil  60  may be implemented for other cooling, lubrication and/or pressure requirements of the transmission  10  (shown in  FIG. 1 ). To reduce the amount of oil  60  trapped within the rotor drum  50 , the interior surface  98  is preferably conical such that the diameter defined by the interior surface  98  tapers in an axial direction becoming larger toward the exhaust holes  92 . It has been observed that an interior surface  98  having a taper angle of approximately 1 degree is sufficient to drive the oil  60  from the left side bearing  54  toward the exhaust holes  92 . 
         [0020]    Some of the oil  60  used to lubricate the left side bearing  54  is transferred into a chamber  100  as it passes from the orifice  88  onto the left side bearing  54 . To prevent excessive accumulation of oil  60  in the chamber  100 , the stator  42  includes a radially outer surface  102  defining a plurality of axial channels  104 . The axial channels  104  are in fluid communication with both the chamber  100  and the chamber  94 . Accordingly, accumulated oil  60  in chamber  100  is transferable through the axial channels  104 , into the chamber  94 , and out of the motor vent  96 . 
         [0021]    The chain  34  is preferably lubricated in the following manner. The pump  63  transfers oil  60  from the cooler  62  into the lubrication inlet  80 . Thereafter, the oil  60  is transferred from the lubrication inlet  80 , through the manifold  82 , and into a chamber  106 . The oil  60  in the chamber  106  is transferred through a channel  108 , and into a chamber tube  110 , into the oil passage  112 , through the orifice  114 , and onto the chain  34  such that the chain  34  is lubricated. The tube  110  is preferably sealed by the first and second seals  116 ,  118  disposed at axially defined ends thereof. The tube  110  is generally positioned on the central axis of the rotor drum  50  and remains stationary relative to the rotatable rotor drum  50 . The oil passage  112  and the orifice  114  are preferably integrally defined in a wall of the transmission cover  38  such as with a machining process. The size of the orifice  114  can be varied to control the rate at which oil  60  is transferred onto the chain  34 . 
         [0022]    The right side bearing  56  is preferably lubricated in the following manner. The color  63  transfers oil  60  into the lubrication inlet  80 . Thereafter, the oil  60  is transferred from the lubrication inlet  80 , through the manifold  82 , and into the chamber  106 . The oil  60  in the chamber  106  is transferred through the channel  108  defined by the tube  110 , through one or more orifices  120 , and is collected in the annulus  122 . The orifices  120  are defined by the tube  110 . The annulus  122  is formed in a radially inner surface  124  of the rotor hub  48 . Centrifugal forces generated during the rotation of the rotor hub  48  assist in the transfer of the oil  60  collected in the annulus  122  through an angled hole  126  and onto the right side bearing  56  such that the right side bearing  56  is lubricated. The angled hole  126  is defined by the rotor hub  48  such as with a machining process. After lubricating the right side bearing  56 , part of the oil  60  is exhausted into the motor chamber  94  and through the motor vent  96 , and the other part of the oil leaving the bearing  56  lubricates the chain  34  (shown in  FIG. 1 ). 
         [0023]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.