Abstract:
The present invention relates to a torsional damper for an electrically-variable transmission. The torsional damper is equipped with a hydraulically actuable lock-out clutch to directly couple the engine to the input shaft of the transmission. The electric motors provided with the electrically-variable transmission can serve to effectively cancel out engine compression pulses when the springs of the torsional damper are locked out. When the engine is off and the torsional damper assembly is in use, an auxiliary pump is provided to pump oil to the torsional damper assembly. The lock-out clutch is hydraulically balanced by the oil supplied by the auxiliary pump. The pump is strategically mounted to the transmission housing in a manner to minimize the distance between the auxiliary pump and the transmission without affecting any vehicle ground clearance requirements.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [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 relates to an electrically-variable transmission with at least one electric motor (capable of canceling out engine vibrations) and a hydraulically actuable, selectively engageable torsional damper assembly, which is at least partially controlled by a motor driven auxiliary pump.  
       BACKGROUND OF THE INVENTION  
       [0003]     Automobile engines produce torsionals or vibrations that are undesirable to transmit through the vehicle transmission. To isolate such torsionals, torsional dampers can be implemented into the vehicle transmission. These dampers rest between the engine crankshaft and the input shaft or turbine shaft of the transmission to substantially counteract the unwanted torsionals generated by the engine. Dampers are configured with springs that have the capacity to carry maximum engine torque plus some margin above.  
         [0004]     One premise behind hybrid automobiles is that alternative power is available to propel the vehicle, thus reliance on the engine for power can be decreased, thereby increasing fuel economy. Since hybrid vehicles can derive their power from sources other than the engine, hybrid engines typically operate at lower speeds more often and can be turned off while the vehicle is propelled by the electric motors. For example, electrically-variable transmissions alternatively rely on electric motors housed in the transmission to power the vehicle&#39;s driveline. Engines in hybrid vehicles are therefore required to start and stop more often than engines in non-hybrid systems. Compression pulses are generated by the engine during starts and stops that can produce undesirable vibration in hybrid vehicles such as those having an electrically-variable transmission. Therefore, greater functionality is desirable in the damper assembly to aid the electrically-variable transmission in canceling these compression pulses.  
         [0005]     Lastly, when the internal combustion engine is not operating, pumps which derive their power from the engine are also inoperable. Where hydraulic fluid is used to govern the torsional damper, the fluid is subjected to centrifugal loading as a result of the high annular speeds at which the torsional damper rotates.  
       SUMMARY OF THE INVENTION  
       [0006]     Provided is an auxiliary pump which derives its power from an electric motor to hydraulically control a torsional damper assembly with a lock-out clutch. The lock-out clutch is piston actuated and the auxiliary pump supplies oil (or hydraulic fluid) to one side of the piston to apply the lockout clutch during predetermined conditions. The auxiliary pump also provides lube oil to other areas in the transmission, e.g., the damper vessel of the torsional damper assembly to hydraulically balance the piston when the torsional damper assembly is rotating at high speeds.  
         [0007]     In one aspect of the present invention, an adaptor housing is provided with the auxiliary pump which enables the auxiliary pump to be mounted with respect to the transmission housing in a manner to minimize the distance between the auxiliary pump and the oil pan.  
         [0008]     In another aspect of the present invention, the auxiliary pump is mounted to the transmission housing in a manner to not affect the ground clearance of the transmission and/or vehicle.  
         [0009]     More specifically, the present invention provides a powertrain having an internal combustion engine, characterized as generating compression pulses during start and/or stop modes of operation and torsionals during other modes of operation, and an electrically-variable transmission. The electrically-variable transmission includes a transmission housing and a torsional damper assembly enclosed within the transmission housing. Further provided is a damper flange, in the torsional damper assembly, rotatable with the engine, having a damper spring enabling the torsional damper assembly to absorb such engine torsionals during the other modes of operation. Also included is a lock-out clutch selectively engageable with the damper flange for locking out the damper spring. The transmission has at least one electric motor operable to selectively cancel the engine compression pulses when the damper spring is locked out. An auxiliary pump powered by an electric motor and operable to pump hydraulic fluid to the torsional damper assembly when the engine is not operating is also provided.  
         [0010]     Further provided is a method of supplying hydraulic fluid to an electrically-variable transmission with a torsional damper assembly for selectively canceling out engine generated compression pulses and torsionals. The method includes: providing a piston actuated lock-out clutch between the engine and the electrically-variable transmission; operating an electric motor in the electrically-variable transmission in a manner to cancel or reduce engine compression pulses when the torsional damper is locked out; and pumping hydraulic fluid to at least one side of the piston of the lock-out clutch to hydraulically counter balance any hydraulic fluid on the opposing side of the piston.  
         [0011]     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  
       [0012]      FIG. 1  is a schematic side view of an electrically-variable transmission (EVT) with parts broken away to show selected transmission components and an auxiliary pump mounted to the transmission;  
         [0013]      FIG. 2  is a fragmentary cross-sectional view of the EVT of  FIG. 1  taken along one side of the centerline of the front portion of the electrically-variable transmission; and  
         [0014]      FIG. 3  is a schematic cross-sectional view of the auxiliary pump and adaptor housing mounted to the transmission, which is partially cut away. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Referring to the drawings,  FIGS. 1 through 3 , wherein like characters represent the same or corresponding parts throughout the several views, there is shown in  FIG. 1 a  side view of an electrically-variable transmission  10 . The internal combustion engine  24  is characterized as generating compression pulses during start and/or stop modes of operation and torsionals during other modes of operation. The electrically-variable transmission  10  includes a transmission main housing  14  and a torsional damper assembly  26 , as shown in  FIG. 2 , enclosed within the input housing  12 . Further provided is a damper flange  38 , in the torsional damper assembly  26  rotatable with the engine  24 , having a damper spring  32  enabling the torsional damper assembly to absorb such engine torsionals during the other modes of operation. Also included is a lock-out clutch  33  selectively engageable with the damper flange  38  for locking out the damper spring  32 . The transmission has at least one electric motor (A or B as shown in  FIG. 1 ) operable to selectively cancel the engine compression pulses when the damper spring  32  is locked out. An auxiliary pump  27  (as shown in  FIGS. 1 and 3 ) is powered by an electric motor and operates to pump hydraulic fluid to the torsional damper assembly  26 , as shown in  FIG. 2 , when the engine is not operating.  
         [0016]     More specifically,  FIG. 1  displays selected components of an electrically-variable transmission  10  including the input housing  12  and main housing  14  with dual electric motors (A and B), which are indirectly journaled onto the main shaft  19  of the transmission  10  through a series of planetary gear sets (not shown). The motors (A, B) operate with selectively engaged clutches (not shown) to rotate the output shaft  20 . The oil pan  16  is located on the base of the main housing  14  and is configured to provide oil volume for the transmission  10  and its components. The projection line P-P of the oil pal  16  defines the necessary ground clearance for the vehicle, as shown in  FIG. 1 . The main housing  14  covers the inner most components of the transmission such as the electric motors (A, B), planetary gear arrangements, the main shaft  19  and two clutches (all of which are mentioned for exemplary purposes and not all are shown). Finally, the input housing  12  is bolted directly to the engine block rear face of the engine  24  (schematically represented in  FIG. 2 ) and encases the transmission components that mechanically interface with the engine  24 . Namely, the input housing  12  covers the torsional damper assembly  26  (shown in  FIG. 2 ). The input housing  12  also supports an auxiliary pump  27  (as shown in  FIGS. 1 and 3 ), which is mounted to the base of the input housing  12  and secured nestably adjacent the oil pan  16  and above the projection line P-P.  
         [0017]     The torsional damper assembly  26 , as shown in  FIG. 2 , generally functions to isolate the transmission  10  from unwanted torsionals generated by the engine  24  during operation and also to selectively aide the transmission electric motors (either A or B) in canceling engine compression pulses during starts and stops. The torsional damper assembly  26  consists of an engine side cover  28 , which is affixed to the engine crankshaft  29 . The engine side cover  28  is welded to the transmission side cover  30  at  31  and houses the damper springs  32 . The two covers ( 28  and  30 ) define a vessel  34 , which encloses the lock-out clutch  33  and a piston  50 . The torsional damper assembly  26  further houses a damper flange  38  with hub portion  40  that mates to the input shaft  18  at complementary splines  42 . The engine side cover  28  of the torsional damper assembly  26  is affixed to an engine flexplate  44 . The flexplate  44  functions to transmit to the transmission the torque produced by the engine  24  and also to absorb any thrust loads generated by the torsional damper assembly  26 . The torsional damper assembly  26  consists of a series of damper springs  32  running annularly or circumferentially between the engine side cover  28  and transmission side cover  30 . The damper springs  32  absorb and dampen the unwanted torsionals produced by the engine  24  during normal or drive mode operation. The torsional damper assembly  26  has a torque capacity equal to the maximum torque capacity of the engine plus some margin. The torsional damper assembly  26  may be configured, in part, similarly to the structure disclosed in commonly owned, U.S. Pat. No. 5,009,301, which is hereby incorporated by reference in its entirety.  
         [0018]     The electrically-variable transmission  10  is equipped with two electric motors (A and B as shown in  FIG. 1 ). Electric motor A creates a torque during start and stop that effectively cancels out the engine compression pulses caused when the engine is operating at speeds below 600 rpm (or in start and/or stop mode). The damper springs  32  of the torsional damper assembly  26  can be locked out by applying the clutch plates  36  and  37  (of the lock-out clutch  33 ) when the engine  24  is operating within a predetermined speed range. In the preferred embodiment, the torsional damper assembly  26  is effectively locked out when the engine is operating at speeds less than or equal to 600 rpm. This mode of operation is desirable because in an electrically-variable transmission either electric motor (A or B) can be used to actively cancel out engine compression pulses generated during start or stop.  
         [0019]     The lock-out clutch  33 , located inside the torsional damper assembly  26 , consists of two reaction plates  37  connected to the damper flange  38 , two friction plates  36  connected to the transmission side cover  30 , a backing plate  46  and a snap ring  48  that is attached to the damper flange  38 . The lock-out clutch  33  includes a hydraulic piston  50  which moves against the reaction plates  37  forcing them to engage the friction plates  36 . The piston  50  moves in response to oil fed into cavity  58  from an oil circuit  57 . The load is reacted at the backing plate  46  and snap ring  48  and contained by the damper flange  38 . Adjacent the piston  50  and affixed to the damper flange  38  is the damper hub  40  of the torsional damper assembly  26 , which has a cross-drilled channel  56 , to define a radially extending aperture  52  that receives oil from circuit  57 . The piston  50  is restricted from engaging with the lock-out clutch  33  and held in the disengaged position by a return spring  54 . As oil is fed between the inner diameter of the input shaft  18  and the outer diameter of a steel tub  35 , through aperture  53  in the input shaft  18  to aperture  52  in the damper hub  40 , and into channel  56  in the damper hub  40 , the pressure inside the piston cavity  58  increases, creating a load sufficient to overcome the spring force and stroke the piston  50 , thereby engaging the lock-out clutch  33 . The vessel  34  is also filled with oil from the hydraulic circuit  59  (pumped by either the auxiliary pump  27  as shown in  FIGS. 1 and 3  or the main transmission pump  55  as shown in  FIG. 1 ). The oil passes from aperture  52  through the interior of tube  35  fitted in the inner diameter of the input shaft  18  and leads through a grooved washer  41  or bushing and into the cavity or spacing  43  in the interior of vessel  34 . The oil thus received in vessel  34  travels to the right side of the piston  50 , as shown in  FIG. 2 , to counter balance the oil fed into cavity  58  on the other side of the piston  50  during predetermined modes of operation when it is desired that the clutch not be applied (i.e., engine speeds above 600 rpm).  
         [0020]     The hydraulic circuits  57  and  59 , as schematically shown in  FIG. 2 , supply oil to the piston cavity  58  and damper vessel  34  respectively; governing the lock-out clutch  33  and commanding it to engage and disengage under certain predetermined conditions. The first circuit  57  ultimately delivers hydraulic fluid supplied by the auxiliary pump  27  to the piston cavity  58 . The piston  50  inside the torsional damper assembly  26  responds to the increased pressure resulting from the oil fed through the first circuit  57  by stroking and engaging the lock-out clutch  33  to effectively lock out the damper springs  32 . When the lock-out clutch  33  is engaged the torsional damper springs  32  are deactivated or locked out so that the engine  24  is directly coupled to the input shaft  18  of the transmission  10 . This condition is only preferred for engine starts and stops (i.e., the start and/or stop modes wherein engine speeds are within the predetermined speed range: between 0 and 600 rpm).  
         [0021]     The second circuit  59 , which can obtain oil from either the main pump  55  or the auxiliary pump  27 , uses the auxiliary pump  27 , as shown in  FIGS. 1 and 3 , when the main pump  55  is not operating. The second circuit  59  supplies oil to the right side of the piston  50  (or the damper vessel  34 ) as viewed in  FIG. 2  to hydraulically balance the piston  50 . Oil travels through aperture  51  to the inner diameter of the steel tube  35 , through a grooved thrust washer  41  (or bushing) into spacing  43  and into the damper vessel  34 .  
         [0022]     When the engine is off, the main pump  55 , as shown in  FIG. 2 , which derives its power from the engine, is inoperable. Since the damper vessel  34  is unsealed, the oil inside drains from the damper vessel  34  until approximately half full when the main pump  55  and auxiliary pump  27  are not in operation. The remaining oil is forced to the perimeter of the torsional damper assembly  26  by the centrifugal loading resulting from the revolution of the input shaft  18  and torsional damper assembly  26 . Likewise, the oil remaining in the damper flange  38  is forced into the piston cavity  58  (i.e., its perimeter). Since the oil in the damper flange  38  is concentrated in the piston cavity  58  the oil in the piston cavity  58  weighs on the piston  50 . At high speeds the centrifugal loading on the oil in the piston cavity  58  may overcome the force of the return spring  54  and stroke the piston  50 . In the preferred embodiment, the pressure difference between the piston cavity  58  and the damper vessel  34  must be greater than or equal to 4 psi to overcome the return spring and 60 psi to get full torque holding capacity on the clutch  33 . This engagement of the lock-out clutch  33  and effectively locking out of the torsional damper assembly spring  32  can lead to additional wear on transmission components causing premature failure or reduced cycle life if it occurs outside of the predetermined speed range.  
         [0023]     One of the technical advantages of the present invention is that the auxiliary pump  27 , as shown in  FIGS. 1 and 3 , is configured to supply oil (or hydraulic fluid) to the torsional damper assembly  26  when the engine  24  is off, thereby providing transmission clutch pressure, damper clutch pressure and lubrication. Additionally, the auxiliary pump  27  and main pump  55  supply oil to the remaining portion of the damper vessel  34 . In a preferred embodiment, the auxiliary pump  27  is a gerotor pump driven by an electric motor C, as schematically shown in  FIG. 3 . As shown in  FIG. 1 , the auxiliary pump  27  lies nestably adjacent the oil pan  16  and above the projection line P-P of the oil pan (or an imaginary line extrapolated from the bottom of the oil pan  16 ) so that the pump  27  does not require additional ground clearance.  
         [0024]     The auxiliary pump  27  is secured to the bottom of the input housing  12  by an adaptor housing  62  which has a suction line  66  and pressure line  64 , as shown in  FIG. 3 . The adaptor housing  62  is secured to the input housing  12  through structural connectors (or bolts  65 ) and separates the auxiliary suction line  66  and auxiliary pressure line  64  which each extend between the auxiliary pump  27  and input housing  12 . The auxiliary pump  27  is mounted to the input housing  12  to be as close as possible to the oil sump and control module which are located in the oil pan  16 , as shown in  FIG. 1 , to minimize line losses on both the suction and pressure lines ( 66  and  64 , respectively as shown in  FIG. 3 ) of the pump  27 . Oil is filtered and pulled through the auxiliary suction line  66  from the oil sump (or source of oil within the oil pan  16 ) to the auxiliary pump  27 . Pressurized oil is then pushed through the adaptor housing pressure line  64 , into the transmission controller  60  (as schematically shown in  FIG. 2 ) and ultimately fed back into the input shaft  18  via the first hydraulic circuit  57 .  
         [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.