Abstract:
A transmission includes provisions to mount two accessory drive units and to transmit power to the accessory drive units from an engine. The accessories are driven by an accessory drive gear that is coupled to a torque converter impeller as opposed to a turbine such that power is provided to the accessories regardless of the selected gear state or vehicle speed. The accessory drive gear also transmits power to an off-axis transmission pump. In one embodiment, power is transferred to the accessories via idler gears that is supported by the transmission housing and is present even when no accessory is installed. In another embodiment, the idler gear is supported by the accessory drive unit and is only present when the accessory is installed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application Ser. No. 61/976,236 filed Apr. 7, 2014, the disclosure of which is hereby incorporated in its entirety by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to the field of automatic transmissions for motor vehicles. More particularly, the disclosure relates to a transmission having an accessory drive. 
       BACKGROUND 
       [0003]    Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse movement. Some types of engines, however, are capable of operating efficiently only within a narrow range of speeds. Consequently, transmissions capable of efficiently transmitting power at a variety of speed ratios are frequently employed. Transmission speed ratio is the ratio of input shaft speed to output shaft speed. When the vehicle is at low speed, the transmission is usually operated at a high speed ratio such that it multiplies the engine torque for improved acceleration. At high vehicle speed, operating the transmission at a low speed ratio permits an engine speed associated with quiet, fuel efficient cruising. 
         [0004]    Most transmission are equipped with a torque converter or other type of launch device. When the vehicle is stationary or moving very slowly, the gearbox input speed is less than the minimum operating speed of the engine. A launch device transmits torque from the engine to the gearbox input while permitting the engine to rotate at an acceptable speed. A torque converter includes an impeller driven by the engine and a turbine driving the gearbox input. Torque is transferred from the impeller to the turbine hydro-dynamically. 
         [0005]    Some types of vehicles need substantial amounts of power to run accessories in addition to the power required to propel the vehicle. These vehicles may use one or more accessory drive units, which may be called power take-off units, mounted to the transmission to provide this accessory power. If the accessory drive is connected to the turbine, then it only rotates when the vehicle is moving. Although this is acceptable for some types of accessories, other types of accessories require power when the vehicle is stationary. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    A transmission includes a transmission case, a primary drive gear fixed to an input shaft, and a first transmission pump drive gear meshing with the primary drive gear. The first transmission pump drive gear is configured to transmit power from the input shaft to a transmission pump, for example, via a second transmission pump gear and a pump shaft. The transmission case has provisions, such as bosses, to support a first accessory drive unit such that a first accessory drive gear meshes with the primary drive gear. The transmission case may include further provisions to support a second accessory drive unit such that a second accessory drive gear meshes with the primary drive gear. In some embodiments, the first and second accessory drive gears may be supported by the transmission when the accessory drive units are not present. 
         [0007]    In some embodiments, a transmission includes a primary drive gear fixed to an input shaft, a pump drive gear meshing with the primary drive gear and configured to transmit power to a transmission pump, and a first idler gear meshing with the primary drive gear. The transmission may also include a second idler gear meshing with the primary drive gear. The pump drive gear, first idler gear, and second idler gear may be supported by a front support mounted to the transmission case. Alternatively, the first idler gear may be supported by a first accessory drive mounted to the transmission case. The transmission may also include a gear box having a plurality of hydraulically actuated shift elements configured to establish various speed ratios in response to fluid pressure supplied by the transmission pump. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic diagram of a vehicle powertrain with two accessory drives. 
           [0009]      FIG. 2  is an end view cross section of the transmission and accessory drives of  FIG. 1 . 
           [0010]      FIG. 3  is a cross section of the transmission of  FIGS. 1 and 2  showing the transmission pump drive mechanism. 
           [0011]      FIG. 4  is a cross section of a first embodiment of the transmission and one of the accessory drives of  FIGS. 1 and 2  showing the accessory drive mechanism. 
           [0012]      FIG. 5  is a cross section of a second embodiment of the transmission and one of the accessory drives of  FIGS. 1 and 2  showing the accessory drive mechanism. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
         [0014]    An exemplary vehicle powertrain  10  is illustrated schematically in  FIG. 1 . In  FIG. 1 , solid lines represent mechanical connections such as shafts or fixed ratio gearing. Engine  12  generates mechanical power by burning fuel. Transmission  14  transmits the power to differential  16  at a shaft speed suited to current vehicle needs, which may be faster or slower than the shaft speed at which engine  12  generates the power. Differential  16  reduces the shaft speed by a fixed final drive ratio and transmits the power to left and right driving wheels  20  and  22 , allowing for slight speed differences between the wheels as the vehicle turns a corner. 
         [0015]    Transmission  14  may include a torque converter  24  or other launch device and a gearbox  26 . Torque converter  24  includes impeller  30  which is fixed to the engine crankshaft and turbine  32  which is fixed to the gearbox input shaft. Torque is transferred hydro-dynamically from impeller  30  to turbine  32  when impeller  30  rotates faster than turbine  32 . Bypass clutch  34  may be engaged to transfer torque by friction from impeller  30  to turbine  32  to reduce the power loss inherent in the hydro-dynamic power transfer. Gearbox  26  includes a number of hydraulically actuated shift elements. Gearbox  26  establishes different speed ratios by engaging various subsets of the shift elements. Pressurized fluid to engage the shift elements is provided by transmission pump  28 . Some of the power generated by engine  12  is used to drive transmission pump  28 , reducing the power delivered to differential  16 . In order to maximize the percentage of power delivered to differential  16  and thus reduce the amount of fuel consumed by engine  12 , it is desirable to minimize the power consumption of transmission pump  28 . 
         [0016]    Accessories  36  and  38  are power consuming devices added by vehicle operators, typically after purchasing the vehicle. These accessories are mounted to the transmission structure using mounting provisions that may be provided by the transmission manufacturer. Accessories  36  and  38  are powered by the engine indirectly through the transmission. Some types of accessories require power only when the vehicle is moving, other types require power only when the vehicle is stationary, and yet other types require power in both circumstances. 
         [0017]    For example, the vehicle engine can provide power for various tools at remote worksites by way of transmission mounted electric generators, hydraulic pumps, and air compressors. These accessories are only utilized when the truck is in park. A transmission mounted refrigeration compressor must work while the vehicle is travelling and while the vehicle is parked. When a truck is used for snow removal, a transmission mounted accessory may provide the power to raise and lower the snowplow. The driver would like to be able to raise and lower the plow while moving, while stopped with the vehicle in gear, and while in park. 
         [0018]      FIG. 2  is a cross sectional end view of transmission  14  with accessory drives  36  and  38  attached. Transmission housing  62  includes provisions for mounting the accessory drives in the proper locations. Specifically, accessory drive  36  is bolted to bosses  37  and accessory drive  38  is bolted to bosses  39 . When either accessory drive is not installed, a cover may be bolted to the respective bosses.  FIG. 3  is a cross section through section AA of  FIG. 2  showing the gears driving transmission pump  28 .  FIG. 4  is a cross section through section BB of  FIG. 2  showing the gears driving accessory drive  36 . The gears driving accessory drive  38  are similar to those driving accessory drive  36 . 
         [0019]      FIG. 3  is a cross section of a portion of the transmission showing the transmission pump drive. Many parts are axisymmetric with respect to the centerline at the top of  FIG. 2 . Engine  12  (not shown) is located to the left and drives impeller  30 . Turbine shaft  50  is fixed to turbine  32  and extends to the right to drive gearbox  26  (not shown). A stationary front support assembly is assembled separately and bolted to transmission case  62 . The front support assembly includes a rear half  52  with a number of fluid passageways that transport fluid from the valve body to the turbine shaft. The rear half  52  of the front support assembly extends to the left to support the torque converter stator  54 . The front support assembly also includes a front half  60  that bolts to transmission case  62  and also to the rear half  52 . Impeller shaft  56  is a hollow shaft that extends between the front half  60  and the rear half  52  of the front support assembly to connect impeller  30  to primary drive gear  58 . The front support assembly also includes transmission pump drive idler gear  64  which is supported between the front half  60  and rear half  52  and meshes with primary drive gear  58 . Transmission pump drive main gear  66  meshes with transmission pump drive idler gear  64  and drives off-axis transmission pump  68 . Off-axis transmission pumps are typically more efficient than on-axis transmission pumps because the packaging space available off-axis imposes fewer constraints on transmission pump design optimization. The improved transmission pump efficiency more than offsets the small power loss resulting from the transmission pump drive gear meshes. 
         [0020]      FIG. 4  is a cross section of a portion of the transmission showing an accessory drive installed. The accessories, like transmission pump  28 , are driven by the impeller shaft  56  via primary drive gear  58 . The first idler shaft  80  is supported in the front support assembly between front half  60  and rear half  52 . The first accessory drive idler gear  82  rotates about idler shaft  80  on a set of needle bearings  84  and meshes with the primary drive gear  58 . Needle bearing  84  may be a caged needle bearing or a full complement needle bearing. In the embodiment illustrated in  FIG. 4 , first idler gear  80  is installed into the front support assembly before the front support assembly is installed in the transmission. Thus, first idler gear  80  is present even when the accessory drive  36  is not installed. Accessory drive housing  86  is bolted to transmission case  62 . When accessory drive  36  is not installed, a cover may be bolted to transmission case  62  in its place. The second accessory drive idler shaft  88  is supported by accessory drive housing  86 . The second accessory drive idler gear  90  rotates about idler shaft  88  on a set of needle bearings  92  and meshes with the first accessory drive idler gear  82 . In the illustrated embodiment, the accessory load is driven by gear  94  which meshes with second accessory drive idler gear  90 . In other embodiments, the accessory load may be driven by a gear that meshes directly with the first accessory drive idler gear or additional gear stages may be present. The second accessory drive is structured similarly but is bolted to the opposite side of the transmission. 
         [0021]      FIG. 5  is a cross section showing an alternative accessory drive installation. In the embodiment illustrated in  FIG. 5 , first accessory idler shaft  80 ′ is supported by accessory housing  86  rather than the front support assembly. In the embodiment of  FIG. 5 , idler shaft  80 ′, first accessory drive idler gear  82 , and needle bearings  84  are not present until an accessory drive is installed. 
         [0022]    In the accessory drive installations of  FIGS. 4 and 5 , power for the accessories is provided via the impeller. Therefore, power is available any time the engine is running. Power is available regardless of whether the gearbox is in neutral, park, reverse, or a forward gear. Power is available both when the vehicle is stationary and when the vehicle is moving. 
         [0023]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.