Abstract:
A pump for a hybrid transmission includes an input shaft having a mating surface—which may include a flat portion—on an outer surface thereof, and a pump rotor coaxial with the input shaft. The pump rotor has an inner surface corresponding to the mating surface of the input shaft, and is directly and drivingly coupled to the input shaft for common rotation therewith. The hybrid transmission may further include an input housing and pump housing, and a pump pocket—in which the pump rotor operates—defined by the input housing, pump housing, and input shaft. The pump is configured to be testable prior to mating the hybrid transmission to an engine. The pump rotor is bounded axially by the input shaft, and a pump guide is configured to center the pump rotor, and to be installed prior to installation of the pump rotor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/041,934, filed Apr. 3, 2008, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to vehicular drivetrains, and more particularly, to transmissions for hybrid and hybrid-type vehicles. 
     BACKGROUND OF THE INVENTION 
     Internal combustion engines, particularly those of the reciprocating piston type, currently propel most vehicles. Such engines are relatively efficient, compact, lightweight, and inexpensive mechanisms by which to convert highly concentrated energy in the form of fuel into useful mechanical power. 
     Typically, a vehicle is propelled by such an engine, which is started from a cold state by a small electric motor and relatively small electric storage batteries, then quickly placed under the loads from propulsion and accessory equipment. Such an engine is also operated through a wide range of speeds and a wide range of loads and typically at an average of approximately a fifth of its maximum power output. 
     A vehicle transmission typically delivers mechanical power from an engine to the remainder of a drive system, such as fixed final drive gearing, axles and wheels. A typical mechanical transmission allows some freedom in engine operation, usually through alternate selection of five or six different drive ratios, a neutral selection that allows the engine to operate accessories with the vehicle stationary, and clutches or a torque converter for smooth transitions between driving ratios and to start the vehicle from rest with the engine turning. Transmission gear selection typically allows power from the engine to be delivered to the rest of the drive system with a ratio of torque multiplication and speed reduction, with a ratio of torque reduction and speed multiplication known as overdrive, or with a reverse ratio. 
     To operate properly, the transmission usually requires a supply of pressurized fluid, such as conventional transmission oil. The pressurized fluid may be used for such functions as cooling, lubrication, and, in some cases, operation of the torque transfer devices. The lubricating and cooling capabilities of transmission oil systems impact the reliability and durability of the transmission. Additionally, multi-speed transmissions require pressurized fluid for controlled engagement and disengagement of the torque transmitting mechanisms that operate to establish the speed ratios within the internal gear arrangement. 
     In hybrid vehicles, alternative power is available to propel the vehicle, minimizing reliance on the engine for power, thereby increasing fuel economy. Since hybrid vehicles can derive their power from sources other than the engine, engines in hybrid vehicles can be turned off while the vehicle is propelled by the alternative power source(s). For example, electrically variable transmissions alternatively rely on electric motors housed in the transmission to power the vehicle&#39;s driveline. 
     An electric generator can transform mechanical power from the engine into electrical power, and an electric motor can transform that electric power back into mechanical power at different torques and speeds for the remainder of the vehicle drive system. These functions may be combined into a single electric machine, a motor/generator. An electric storage battery used as a source of power for propulsion may also be used, allowing storage of electrical power created by the generator, which may then be directed to the electric motor for propulsion or used to power accessory equipment. 
     A series hybrid system allows the engine to operate with some independence from the torque, speed and power required to propel a vehicle, so the engine may be controlled for improved emissions and efficiency. Such a system may also allow the electric machine attached to the engine to act as a motor to start the engine. This system may also allow the electric machine attached to the remainder of the drive train to act as a generator, recovering energy from slowing the vehicle and storing it in the battery by regenerative braking. 
     An electrically variable transmission in a vehicle can simply transmit mechanical power from an engine input to a final drive output. To do so, the electric power produced by one motor/generator balances the electrical losses and the electric power consumed by the other motor/generator. By using the above-referenced electrical storage battery, the electric power generated by one motor/generator can be greater than or less than the electric power consumed by the other. Electric power from the battery can allow both motor/generators to act as motors. Both motors can sometimes act as generators to recharge the battery, especially in regenerative vehicle braking. 
     A power-split transmission can use what is commonly understood to be “differential gearing” to achieve a continuously variable torque and speed ratio between input and output. An electrically variable transmission can use differential gearing to send a fraction of its transmitted power through a pair of electric motor/generators. The remainder of its power flows through another, parallel path that is mechanical. 
     One form of differential gearing, as is well known to those skilled in this art, may constitute a planetary gear set. However, it is possible to construct this invention without planetary gears, as by using bevel gears or other gears in an arrangement where the rotational speed of at least one element of a gear set is always a weighted average of speeds of two other elements. 
     A hybrid electric vehicle transmission system may include one or more electric energy storage devices. The typical device is a chemical electric storage battery, but capacitive or mechanical devices, such as an electrically driven flywheel, may also be included. Electric energy storage allows the mechanical output power from the transmission system to the vehicle to vary from the mechanical input power from the engine to the transmission system. The battery or other device also allows for engine starting with the transmission system and for regenerative vehicle braking. 
     SUMMARY OF THE INVENTION 
     A pump for a hybrid transmission is provided. The pump includes an input shaft having a mating surface on an outer surface of the input shaft and a pump rotor coaxial with the input shaft. The pump rotor has an inner surface corresponding to the mating surface of the input shaft, and the pump rotor is directly and drivingly coupled to the input shaft for common rotation therewith, by engagement of the mating and inner surfaces. The mating surface between the input shaft and pump rotor may include a flat portion. The hybrid transmission may further include an input housing and a pump housing, and a pump pocket may be defined by the input housing, pump housing, and input shaft. The pump rotor operates in the pump pocket. 
     The pump may be configured to be tested prior to mating the hybrid transmission to an engine. The axial length of the pump rotor is less than the axial length of the input shaft, and the pump rotor is bounded axially by the input shaft. The pump may also include a pump guide configured to center the pump rotor, and configured to be installed prior to installation of the pump rotor. 
     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 
         FIG. 1  is a schematic representation of a powertrain into which one embodiment of the claimed invention may be incorporated; 
         FIG. 2  is a schematic cross section of the dry-mating interface between the engine output and transmission input shown schematically in  FIG. 1 , showing the pump rotor and pump pocket in the transmission pump housing; and 
         FIG. 3  is a schematic perspective view of the transmission input shaft and pump rotor. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , there is shown a schematic diagram of a powertrain  10  into which the claimed invention may be incorporated. The powertrain  10  includes an engine  12 , which may be any type of internal combustion engine known in the art, turning an engine output  14 , which transmits the driving power produced by the engine  12 . Driving power is then transferred through a transmission input shaft  18  into a transmission  20 . In some embodiments, a damper  16  may be interposed between the engine output  14  and the transmission input shaft  18 . Input shaft  18  is described in more detail below, with reference to  FIG. 2 . 
     Input shaft  18  may be operatively connectable to planetary gear members (not shown) or to torque transfer devices (not shown) within transmission  20 . The transmission  20  may be an electrically variable transmission, a one- or two-mode input split transmission, a two-mode transmission with input-split and compound-split, or another hybrid transmission known to those having ordinary skill in the art. 
     Transmission  20  utilizes input shaft  18  to receive power from the vehicle engine  12  and a transmission output  24  to deliver power to drive the vehicle through one or more drive wheels  26 . In the embodiment shown in  FIG. 1 , transmission  20  includes a first motor  28  and a second motor  30 . Each of the motors  28  and  30  is a motor/generator capable of both converting electric power into mechanical power and converting mechanical power into electric power. The first motor  28  may also be referred to as motor A, and second motor  30  may be referred to as motor B. 
     The fluid in transmission  20  is pressurized by a main pump  22 . The pressurized fluid may be used for such functions as cooling, lubrication, and, in some cases, operation of the torque transfer devices. Most transmission pumps are directly or indirectly driven by rotation of the engine output member—such as the engine crankshaft, engine driven damper, or torque converter assembly drive hub—to drive the pump rotor. However, the main pump  22  is driven directly by the transmission input shaft  18 . The input-driven main pump  22  will be described in more detail below, with reference to  FIGS. 2 and 3 . 
     The transmission  20  may utilize one or more planetary gear sets (not shown), and may utilize one or more clutches (not shown) to provide input split, compound split, and fixed ratio modes of operation. The planetary gear sets may be simple or may be individually compounded. 
     The motors  28  and  30  are operatively connected to a battery  32  (an energy storage device) so that the battery  32  can accept power from, and supply power to, the first and second motor/generators  28  and  30 . A control system  34  regulates power flow among the battery  32  and the motors  28  and  30 . 
     As will be apparent to those having ordinary skill in the art, the control system  34  may further control the engine  12  and operation of the transmission  20  to select the output characteristics transferred to the drive wheels  26 . Control system  34  may incorporate multiple control methods and devices. 
     As will further be recognized by those having ordinary skill in the art, battery  32  may be a single chemical battery or battery pack, multiple chemical batteries, or other energy storage device suitable for hybrid vehicles. Other electric power sources, such as fuel cells, that have the ability to provide, or store and dispense, electric power may be used in place of battery  32  without altering the claimed invention. 
     In some modes of operation for the powertrain  10 , the engine  12  may shut down or turn off completely. This may occur when the control system  34  determines that conditions are suitable for drive wheels  26  to be driven, if at all, solely by alternative power from one or both of motors  28  and  30 ; or may occur during periods of regenerative braking. While the engine  12  is shut down, the main pump  22  is not being driven by the input shaft  18 , and is therefore not providing pressurized fluid to transmission  20 . Powertrain  10  may therefore include an auxiliary pump  36 , which may be powered by the battery  32  to provide pressurized fluid to transmission  20  when additional pressure is required. 
     Referring to  FIG. 2 , there is shown one possible embodiment of a portion of the power train  10  shown schematically in  FIG. 1 . More specifically,  FIG. 2  shows a more-detailed, cross-sectional view of the area transferring power from the engine  12  to the transmission  20 . In this embodiment, the engine  12  is transferring power through an engine output  14 , which may be a crank shaft, a damper hub, or another shaft-type output member capable of transferring power to the transmission  20 . 
     As shown in  FIG. 2 , power is transferred to the transmission  20  by a hollow, internally-splined input shaft  18 .  FIG. 2  shows only the upper half of transmission  20 . Input shaft  18  is symmetrical about axis  21 , as are many of the other rotating members of transmission  20 . The input shaft  18  has internal dry splines  40  (also shown in  FIG. 3 ) which may be mated to external dry splines  42  on the engine output  14 . These splines  40  and  42  are maintained as dry splines by sealing them against pressurized transmission fluid contained in the transmission  20 . 
     Dry splines, as opposed to wet splines, are not continuously in fluid communication with transmission fluid or engine oil. Dry splines may, however, have grease applied to one or both sets of splines before installation. Such pre-installation grease assists in the dry-mating process and may provide any necessary lubrication for the life of the parts. In this embodiment, sealing against transmission fluid is accomplished with a freeze plug  44 , which is an expandable plug, press-fit into an internal cavity  46  of the input shaft  18 . However, as will be recognized by those having ordinary skill in the art, sealing could also be accomplished by an input shaft that is not completely hollow. 
     In the embodiment shown in  FIG. 2 , input shaft  18  is completely hollow, which allows the internal dry splines  40  to be manufactured as broached internal splines instead of shaped splines. As would be recognized by those having ordinary skill in the art, a broaching bar is pulled through the internal cavity  46  and cuts the internal dry splines  40 . Because the internal dry splines  40  are broached, there may be a significant cost improvement versus having to shape the splines to manufacture the input shaft  18 . 
     Opposite the internal cavity  46  of the input shaft  18  is an outer surface, the input shaft journal  48 , which also must be sealed against pressurized transmission fluid. An input seal  50  and an input housing bushing  52  ride against the input shaft journal  48  instead of a damper or the engine output  14 , and accomplish sealing the input shaft journal  48 . The input seal  50  and input housing bushing  52  can therefore be installed along with the input shaft  18 , which reduces the opportunity for cutting seals during assembly of the transmission. Furthermore, the input seal  50  and input housing bushing  52  do not have to be in contact with the engine output  14  or test equipment used to simulate the engine output  14  during the manufacturing process. This yields a one-time engagement of the input shaft journal  48  to the input seal  50  and input housing bushing  52 . 
     Main pump  22  is driven by the sealed portion of the input shaft  18 . Input shaft journal  48  is designed with one or more mating surfaces to pilot and drive a pump rotor  72 . In the embodiment shown, the mating surfaces are flats  70  (shown as a dashed or phantom line in  FIG. 2 , also shown in  FIG. 3 ). The pump rotor  72  has inner flats  71  (also shown as a phantom line in  FIG. 2 ) on an inner surface thereof. The inner flats  71  correspond to, and are configured to mate with, the flats  70 . 
     The flats  70  and inner flats  71  are configured to transfer power from the input shaft  18  to the pump rotor  72 , thereby allowing the main pump  22  to pressurize fluid in the transmission  20 . Other mating structures or surfaces may be used to directly transfer power between the input shaft  18  and the main pump  22 ; for example, without limitation: splines, keyways, polygonal shafts, et cetera. 
     The flats  70  and inner flats  71 , along with a pump guide  74 , center and guide the pump rotor  72  during assembly and operation of the main pump  22  in the transmission  20 . Pump rotor  72  and a pump slide  73  rotate and create pressure inside of a pump pocket  76  formed at least partially by the transmission input housing  78  and the pump housing  80 . The pump slide  73  allows the main pump  22  to generate variable fluid displacement and, therefore, pressure. 
     An input-driven main pump  22  with pump pocket  76  placed inside of the pump housing  80  may decrease the axial length (relative to, and as measured along, axis  21 ) of the transmission  20  and main pump  22 . Driving the main pump  22  by directly coupling it to the input shaft  18  may save greater than 5 millimeters of axial length, and allows the main pump  22  to be completely bounded within the axial length of the input shaft  18 . A pump housing bushing  82  and the input housing bushing  52  handle loads created by the main pump  22 . 
       FIG. 3  shows the input shaft  18  and pump rotor  72 . This view shows the internal dry splines  40  on the inside of input shaft  18 .  FIG. 3  also shows the flats  70  cut into the input shaft journal  48  and the inner flats  71  (the corresponding mating surface) on the pump rotor  72 . 
     By using internal dry splines  40 , the engine  12  and transmission  20  are connected at a single, dry interface point (having only pre-installation grease on the dry splines). In the manufacturing process, this allows dry-mating the input shaft  18  to the engine output  14 , which may reduce the difficulty, time, and cost of manufacturing the powertrain  10 . Furthermore, the dry-mating process allows the transmission  20  to be filled with transmission fluid prior to mating the engine  12  and transmission  20 , possibly even prior to shipping the transmission  20  to the final assembly point. Main pump  22  may also be tested—individually or as a component of the assembled transmission  20 —prior to mating of transmission  20  and engine  12 . 
     While the best modes for carrying out the claimed 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.