Abstract:
A method and apparatus for efficiently cooling and lubricating rotating components in a hybrid transmission is provided. By efficiently managing cooling flow to and between the rotating elements, flow requirements and associated pumping requirements within the drive unit are minimized. In addition, by providing a method for placing the fluid directly on the required components, spin losses associated with component contact with stray oil are reduced. Combined, the reduction in pumping and spin losses create a more efficient drive unit and an overall more efficient hybrid drive system which directly leads to higher fuel economy.

Description:
CROSS REFERENCE TO RELATED APPLICATONS  
       [0001]     This application claims the benefit of U.S. Provisional Application 60/555,141 , filed Mar. 22, 2004, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention is drawn to a method for cooling and lubricating a hybrid transmission.  
       BACKGROUND OF THE INVENTION  
       [0003]     Due to the desire for further improvements in vehicle fuel economy and reductions in emissions, there has been a strong interest in hybrid electric vehicles. Such vehicles typically incorporate a conventional internal combustion engine and one or more electric motors to assist in propulsion or energy storage depending on the mode of operation. To maximize fuel economy, each component within the system should be designed for optimal efficiency.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention provides efficient cooling and lubrication of rotating components in a hybrid transmission. By efficiently managing cooling flow to and between the rotating elements, flow requirements and associated pumping requirements within the drive unit are minimized. In addition, by providing a method for placing the fluid directly on the required components, spin losses associated with component contact with stray oil are reduced. Combined, the reduction in pumping and spin losses create a more efficient drive unit and an overall more efficient hybrid drive system which directly leads to higher fuel economy.  
         [0005]     The method of the present invention includes pumping fluid from a reservoir into a first rotating shaft. The first rotating shaft defines a flow passage through which the fluid is transferred and is preferably sealed by a first plurality of bushings. The first rotating shaft also defines a plurality of orifices through which the fluid may pass. After exiting the orifices of the first rotating shaft, the fluid is introduced into a clearance cavity between the first rotating shaft and a second rotating shaft. The clearance cavity is also preferably sealed by a second plurality of bushings. The fluid in the clearance cavity may be applied through an orifice in the second rotating shaft directly onto a planet carrier of a planet gear assembly to cool and lubricate the planet carrier. The first and second plurality of bushings may be cooled and lubricated by allowing a predetermined amount of fluid to leak across one or more bushing contact surfaces.  
         [0006]     According to a preferred embodiment of the present invention, the fluid leaked by the bushings may be implemented to cool and lubricate one or more thrust bearings.  
         [0007]     According to another preferred embodiment of the present invention, the fluid leaked by the bushings may be implemented to provide additional cooling and lubrication of the planet carrier.  
         [0008]     According to yet another preferred embodiment of the present invention, the fluid applied to the planet carrier may be redirected by a diverter to more optimally cool the planet carrier.  
         [0009]     According to still another preferred embodiment of the present invention, catchers may be implemented to catch stray fluid and thereby avoid excess spin losses.  
         [0010]     The above features 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  
       [0011]      FIG. 1  is a schematic fragmentary cross-sectional view of a hybrid electromechanical transmission in accordance with the invention;  
         [0012]      FIG. 2  is a schematic fragmentary cross-sectional view of a hybrid electromechanical transmission;  
         [0013]      FIG. 3  is a schematic fragmentary cross-sectional view of a frontward portion of the transmission of  FIG. 1 ; and  
         [0014]      FIG. 4  is a schematic fragmentary cross-sectional view of a rearward portion of the transmission of  FIG. 1 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows the upper half of a transmission  10 , in cross sectional view. The lower half of the transmission (not shown) is disposed on the opposite side of center axis  12 . First and second electric motor modules  14 ,  16 , respectively, are disposed about the center axis  12  within the transmission  10 . A main shaft  20  is longitudinally disposed, rotatable about the center axis  12 . A plurality of inner shafts, such as inner shaft  22 , are concentrically disposed about the main shaft  20 , and are likewise rotatable about the center axis. An input shaft  24  is disposed forward of the main shaft  20  and is operable for transferring power from an engine (not shown) to the transmission  10 . An output shaft  25  is disposed rearward of the main shaft  20 . The main shaft  20  and the input shaft  24  are preferably hollow to facilitate the cooling and lubrication of the transmission  10  as will be described in detail hereinafter. Engagement of one or more of a plurality of clutches included in the transmission  10  (first, second, third and fourth clutches,  26 ,  28 ,  30  and  32  respectively, being shown) interconnects one or more of first, second and third planetary gear sets  34 ,  36 , and  38 , respectively, to transfer power at varying ratios to an output member (not shown). As will be readily understood by those skilled in the art, each of the planetary gear sets includes a sun gear member, a planet carrier assembly member and a ring gear member. A fifth clutch, referred to as a lockout clutch  42 , is operable for locking out torsion isolator  44  (also referred to as damper springs) from surrounding structural elements, and to provide a direct connection between the engine and transmission.  
         [0016]     Referring to  FIG. 2 , transmission lubrication fluid  48  is transferred by a pump  49 , located in a front support  50 , from a fluid reservoir  51  into the center of the main shaft  20  and input shaft  24 , which cooperate to run the entire length of the drive unit. Bushing  52  (best shown in  FIGS. 3 ) acts to seal the fluid  48  between the input shaft  24  and main shaft  20  as they rotate and move axially relative to one another. Bushing  54  (best shown in  FIG. 4 ) acts to seal the fluid  48  between the main shaft  24  and output shaft  25  as they rotate and move axially relative to one another. The bushings  52 ,  54  are also adapted for maintaining pressure within the main shaft  20  to optimally apply the lubrication fluid  48 .  
         [0017]     To ensure lubrication fluid is delivered directly to the required locations, components used for connecting various elements of the rotating group are incorporated into the lubrication scheme of the present invention. More precisely, several of the shafts concentric with the main shaft  20 , such as sun gear shafts  34 S and  36 S (shown in  FIGS. 3 and 4 ), are used to transfer the pressurized fluid.  
         [0018]     Referring to  FIG. 3 , the clearance between the sun gear shaft  34 S and the main shaft  20  defines a clearance cavity  56 . Similarly, as shown in  FIG. 4 , the clearance between the sun gear shaft  36 S and the main shaft  20  defines a clearance cavity  58 . The main shaft  20  defines a plurality of outlet ports  60 ,  62  adapted to release the pressurized fluid from the main shaft  20  into the clearance cavities  56 ,  58 , respectively.  
         [0019]     Referring again to  FIG. 3 , bushing  52 , as well as bushings  64 ,  66  are adapted to maintain fluid pressure in the cavity  56 . Cooling and lubrication of the bushings  52 ,  64  and  66  is provided by allowing a predetermined amount of lubrication fluid  48  to leak between the bushings  52 ,  64  and  66  and their respective rotating shaft  20  or  24 . More precisely, bushing  52  is cooled and lubricated by allowing a predetermined amount of lubrication fluid  48  to leak between the bushing  52  and the input shaft  24 . Bushings  64  and  66  are cooled and lubricated by allowing a predetermined amount of lubrication fluid  48  to leak between the bushings  64 ,  66  and the main shaft  20 . The amount of bushing leakage is controllable by adjusting the fit between a given bushing and the rotating shaft inserted therein, and/or adjusting the pressure of the lubrication fluid  48 . To improve lubrication efficiency, this bushing leakage is then redirected for lubrication of other components as will be described in detail hereinafter.  
         [0020]     The sun gear shaft  34 S defines an orifice  70 . Pressurized lubrication fluid  48  is dispersed from the cavity  56  through the orifice  70  and onto the planet carrier  34 C, as shown by arrows representing fluid flow, to cool and lubricate the planet carrier  34 C. The size of the orifice  70  is preferably selected based on the cooling/lubrication needs of the planet carrier  34 C in a particular application. Additionally, the amount of fluid  48  delivered through the orifice  70  may be varied by adjusting the fluid pressure. The planet carrier  34 C is also cooled and lubricated by lubrication fluid  48  leaking from the bushings  52 ,  64  as shown by the arrows representing fluid flow in  FIG. 3 . According to a preferred embodiment, the lubrication fluid  48  leaking from bushing  52  additionally cools and lubricates a thrust bearing  53  as it is diverted to the planet carrier  34 C. Similarly, the lubrication fluid  48  leaking from bushing  64  cools and lubricates a thrust bearing  55  as it is diverted to the planet carrier  34 C.  
         [0021]     Referring to  FIG. 4 , bushing  54 , as well as bushing  72  (shown in  FIG. 3 ) and bushing  74  are adapted to maintain fluid pressure in the cavity  58  in a manner similar to that described hereinabove for cavity  56 . The bushings  54 ,  72  and  74  are cooled and lubricated by allowing a predetermined amount of lubrication fluid  48  to leak between each of the bushings and the main shaft  20 . The amount of bushing leakage is controllable by adjusting the fit between a given bushing and the rotating shaft inserted therein, and/or adjusting the pressure of the lubrication fluid  48 . To improve lubrication efficiency, this bushing leakage is then redirected for lubrication of other components as will be described in detail hereinafter.  
         [0022]     The sun gear shaft  36 S defines an orifice  76 . Pressurized lubrication fluid  48  is dispersed from the cavity  58  through the orifice  76  and onto the planet carrier  36 C, as shown the by arrows representing fluid flow, to cool and lubricate the planet carrier  36 C. The size of the orifice  76  is preferably selected based on the cooling/lubrication needs of the planet carrier  36 C in a particular application. Additionally, the amount of fluid  48  delivered through the orifice  76  may be varied by adjusting the fluid pressure. As shown in  FIG. 3 , the planet carrier  36 C is also cooled and lubricated by lubrication fluid  48  leaking from the bushings  66 ,  72  as shown by the arrows representing fluid flow. According to a preferred embodiment, the lubrication fluid  48  leaking from bushing  66  additionally cools and lubricates a thrust bearing  67  as it is diverted to the planet carrier  36 C. Similarly, the lubrication fluid  48  leaking from bushing  72  cools and lubricates a thrust bearing  69  as it is diverted to the planet carrier  36 C.  
         [0023]     Referring again to  FIG. 4 , the sun gear shaft  36 S also defines orifice  78 . Pressurized lubrication fluid  48  is dispersed from the cavity  58  through the orifice  78  and onto the planet carrier  38 C, as shown by the arrows representing fluid flow, to cool and lubricate the planet carrier  38 C. The size of the orifice  78  is preferably selected based on the cooling/lubrication needs of the planet carrier  38 C in a particular application. Additionally, the amount of fluid  48  delivered through the orifice  78  may be varied by adjusting the fluid pressure. The planet carrier  38 C is also cooled and lubricated by lubrication fluid  48  leaking from the bushing  74  as shown by the arrows representing fluid flow. According to a preferred embodiment, the lubrication fluid  48  leaking from bushing  74  additionally cools and lubricates a thrust bearing  75  as it is diverted to the planet carrier  38 C.  
         [0024]     Referring to  FIGS. 3 and 4 , a plurality of diverters  80  are preferably utilized to direct the fluid exiting the shaft orifices  70  and  76  onto the proper components. A plurality of catchers  82  are preferably implemented to minimize stray fluid which may otherwise cause excess spin losses.  
         [0025]     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.