Abstract:
An input shaft for a hybrid transmission includes a cylindrical hollow shaft portion having internal and external surfaces. The internal surface defines an internal cavity coaxial with the hollow shaft portion and has a splined portion configured to allow power to be transferred to the hollow shaft portion. The input shaft may further include a freeze plug press-fit in the internal cavity, configured to fluidly seal the inner cavity in embodiments with a cavity extending throughout the input shaft. The splined portion may be a broached spline. A method of manufacturing a hybrid powertrain includes forming a hollow transmission input shaft and press-fitting a plug into it, such that the shaft is internally fluid sealed. The shaft is mated to the transmission which may then be filled with fluid and tested for operability. The shaft may be dry-mated to an engine output member for common rotation therewith.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of prior application Ser. No. 12/252,707, filed Oct. 16, 2008, which claims the benefit of U.S. Provisional Application No. 61/041,933, filed Apr. 3, 2008, both of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to vehicular drivetrains, and more particularly, to transmissions for hybrid and hybrid-type vehicles. 
       BACKGROUND OF THE INVENTION 
       [0003]    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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    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. 
         [0009]    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 
         [0010]    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 
         [0011]    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. 
         [0012]    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. 
         [0013]    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 
       [0014]    An input shaft for a hybrid transmission is provided. The input shaft includes a hollow shaft portion having an internal surface and an external journal surface. The internal surface defines an internal cavity coaxial with the hollow shaft portion. The internal surface has a splined portion configured to be dry-mated such that power may be transferred to the hollow shaft portion from an engine output member or test rig output member. The external journal surface is fluidly sealed by an input seal. 
         [0015]    The input shaft may further include a freeze plug press-fit in the internal cavity, configured to fluidly seal the inner cavity in embodiments with a cavity extending throughout the input shaft. The splined portion may be a broached spline. 
         [0016]    A method of manufacturing a hybrid powertrain is also provided. The method includes forming a hollow transmission input shaft and press-fitting a plug into the hollow transmission input shaft, such that the hollow transmission input shaft is internally fluid sealed. An input seal is installed in a transmission. The hollow transmission input shaft is then mated to the transmission, such that the input seal externally fluidly seals the hollow transmission input shaft, and the transmission is substantially complete. 
         [0017]    The transmission may then be tested for operability by simulating engine output conditions and transmission operation conditions. The transmission or an assembled engine may then be transported to a common facility. The hollow transmission input shaft may be dry-mated to an engine output member, such that the hollow transmission input shaft and the engine output member are capable of common rotation. 
         [0018]    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 
         [0019]      FIG. 1  is a schematic representation of a powertrain into which one embodiment of the present invention may be incorporated; and 
           [0020]      FIG. 2  is a schematic cross section of the dry-mating interface between the engine output and transmission input shown schematically in  FIG. 1 . 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0021]    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 . 
         [0022]    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. 
         [0023]    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. 
         [0024]    The fluid in transmission  20  is pressurized by a main pump  22 , which is directly or indirectly driven by rotation of the engine  12 . The pressurized fluid may be used for such functions as cooling, lubrication, and, in some cases, operation of torque transfer devices. 
         [0025]    The transmission  20  may utilize one or more planetary gear sets (not shown), and may utilize one or more clutches or other torque transfer devices (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. 
         [0026]    The motors  28  and  30  are operatively connected to a battery  32 , an energy storage device, such that the battery  32  can accept power from, and supply power to, the first and second motors  28  and  30 . A control system  34  regulates power flow among the battery  32  and the motors  28  and  30  as well as between the motors  28  and  30 . 
         [0027]    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. 
         [0028]    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 concepts of the present invention. 
         [0029]    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 during periods of regenerative braking While the engine  12  is shut down, the main pump  22  is not being driven, 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. 
         [0030]    Referring now to  FIG. 2 , there is shown one possible embodiment of a portion of the powertrain  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 .  FIG. 2  shows only the upper half of transmission  20 . Input shaft  18  is symmetrical about an axis  21 , as are many of the other rotating members of transmission  20 . 
         [0031]    The engine  12  shown in  FIG. 2  is transferring power through an engine output  14 , which may be a crank shaft, a damper hub, or another shaft-type output capable of transferring power to the transmission  20 . In this embodiment, power is transferred to the transmission  20  by a hollow, internally-splined input shaft  18 . The input shaft  18  has internal dry splines  40  which may be mated to external dry splines  42  on the engine output  14 . Splines  40  and  42  are maintained as dry splines by sealing them against pressurized transmission fluid contained in the transmission  20 . 
         [0032]    Dry splines, as opposed to wet splines, are not continuously in fluid communication with transmission fluid or engine oil, and are not replenished with fluid or grease from the transmission  20  or the engine  12 . Dry splines may, however, have grease applied to one or both sets of splines  40  and  42  before installation. Such pre-installation grease assists in the dry-mating process and may provide any necessary lubrication for the life of the parts. Furthermore, an exterior seal  43  may be included to assist in retaining grease in the splined area for the life of the transmission  20 . Exterior seal  43  may be located on the exterior surfaces between the input shaft  18  and engine output  14 . 
         [0033]    In the embodiment shown in  FIG. 2 , 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. Additionally, other seals could be used to plug the internal cavity  46  against transmission fluid, such as (without limitation) a seal which plugs the internal cavity  46  by threading into the walls of the internal cavity  46  or a seal configured to fit into a sealing groove (not shown) machined into the surface of the internal cavity  46 . 
         [0034]    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 may be pulled through the internal cavity  46  to cut the internal dry splines  40 . This broaching process may be via a keyway broach, multiple keyway broach, involute spline broach, a rotary broach, or any other suitable spline broaching tool known to those having ordinary skill in the art. Because the internal dry splines  40  are broached, there may be a significant cost improvement over having to shape the splines to manufacture the input shaft  18 . 
         [0035]    Opposite the internal cavity  46  of the input shaft  18  is an outer edge, the input shaft journal  48 , which also must be sealed against pressurized transmission fluid in order to retain pressure within transmission  20 . An input seal  50  and a bushing  52  ride against the input shaft journal  48 —instead of riding against a damper or the engine output  14 —and accomplish sealing of the input shaft journal  48 . 
         [0036]    The input seal  50  and bushing  52  can therefore be installed along with the input shaft  18 , which reduces the opportunity for cutting or damaging the seals and bushings during assembly of the transmission. The input seal  50  and bushing  52  may be installed as the final components of the transmission  20  as a first facility or a dedicated transmission facility, and the engine  12  may be completely assembled at a second facility or dedicated engine facility. 
         [0037]    The input seal  50  and bushing  52  do not have to be in contact with the engine output  14  or test equipment used to test operability of the transmission  20  by simulating the engine output  14  and operating conditions for the engine, transmission, and powertrain. This allows testing during or after the manufacturing process of the transmission  20  and prior to final assembly of the drivetrain  10 . Mating the engine output  14  to the input shaft  18  with dry splines allows a one-time, one-step engagement of the input shaft journal  48  to the input seal  50  and bushing  52 —because mating of the engine  12  to the transmission  20  does not involve contact with the input seal  50  and bushing  52 . The final assembly of the drivetrain  10  may occur at either of the first or second facilities, or at a third facility, such as a dedicated drivetrain facility or a final assembly facility. 
         [0038]    By using the input seal  50  and freeze plug  44  to seal the input shaft  18 , and by using dry splines  40  and  42  to mate the input shaft  18  to the engine output  14 , the engine  12  and transmission  20  are connected at a single, dry interface point (having only, possibly, pre-installation grease). In the manufacturing process, this allows dry-mating of 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. 
         [0039]    The detailed description and the drawings or figures are supportive and descriptive of the invention, but the scope of the invention is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments exist for practicing the invention defined in the appended claims.