Patent Abstract:
A family of hybrid electric transmission arrangements share a common center housing, rear housing, two electric machines, power-split planetary gearset, and torque multiplication gearset. One arrangement additionally utilizes an overdrive gearset and an overdrive clutch. Another arrangement additionally utilizes two clutches and a brake to implement three operating modes. Since the components that differ between the two arrangements use the same general packaging space and all shift elements are hydraulically controlled via a front housing, the design of the front housing is also similar.

Full Description:
TECHNICAL FIELD 
     This disclosure relates to the field of hybrid transmissions for motor vehicles. More particularly, the disclosure pertains to the structure and support of components in a hybrid electric transmission. 
     BACKGROUND 
     Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse movement. Most types of internal combustion 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. 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. 
     In an effort to reduce fuel consumption, some transmissions are designed to utilize substantial amounts of energy storage in addition to liquid fuel burned in an internal combustion engine. Most commonly, the energy storage takes the form of electric batteries. The transmission diverts power to the batteries and utilizes power from the batteries using one or more reversible electric machines, such as synchronous motors or induction motors. A vehicle that uses traditional liquid fuel and also includes electrical storage is called a hybrid electric vehicle (HEV). When the vehicle includes provisions to charge the electric batteries from an external source, the vehicle is called a plug-in hybrid electric vehicle (PHEV). 
     One hybrid transmission configuration is a power-split hybrid. A power-split hybrid includes two electric machines. One of the electric machines is typically called the generator and the other is typically called the motor, although both are reversible electric machines. A planetary gearset distributes power from an internal combustion engine between the generator and the transmission output. The motor drives the transmission output. When the internal combustion engine is off, the motor can propel the vehicle using energy stored in the battery. During braking, the motor can converter vehicle kinetic energy to electrical energy for storage in the battery for later use. In some operating modes, the planetary gearset sends a portion of the power from the engine to the output via a mechanical power flow path and sends the remainder of the power to the generator which converts it to electrical power. The electrical power may be stored in the battery for later use, sent to the motor to supplement the power transferred via the mechanical power flow path, or some combination of the two. In other operating modes, typically associated with high vehicle speeds, the planetary gearset may draw power from the generator and send power from both the generator and the internal combustion engine to the output via the mechanical power flow path. The electrical energy to drive the generator in these modes may be drawn from the battery, from the motor, or from some combination of the two. Due to recirculation of power through the mechanical power flow path, the motor, and the generator, efficiency in these operating modes tends to be lower. 
     SUMMARY OF THE DISCLOSURE 
     A transmission includes an output, a first electric machine, and a first planetary gearset. The output is supported on a front side of a center housing while a stator of the first electric machine is fixed to the center housing and a rotor of the first electric machine is supported on a rear side of the center housing. A sun of the first planetary gearset is fixedly coupled to the rotor of the first electric machine, a carrier of the first planetary gearset is fixedly coupled to the output, and a ring of the first planetary gearset is fixedly held against rotation. The first planetary gearset may be located on the front side of the output. A rear housing may support rotor of a second electric machine. The rotors of the first and second machines may rotate about the same axis. A second planetary gearset may be located axially between the first and second rotors and radially inside the first and second stators. A sun of the second planetary gearset may be fixedly coupled to the rotor of the second electric machine. A carrier of second planetary gearset may be fixedly coupled to an input. A ring of the second planetary gearset may be fixedly coupled to an intermediate shaft. A front housing may support the input shaft and convey pressurized fluid to at least one hydraulically actuated clutch. One embodiment includes a third planetary gearset having a sun gear coupled to the front housing, a carrier coupled to the input, and a ring gear coupled to the output. Two of the planetary gearset elements may be fixedly coupled while the third is selectively coupled by the hydraulically actuated friction clutch. In a second embodiment, one friction clutch selectively couples the intermediate shaft to the output, another friction clutch selectively couples the intermediate shaft to the sun of the first planetary gearset, and a friction brake selectively holds the intermediate shaft against rotation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a first hybrid electric transmission arrangement. 
         FIG. 2  is a cross sectional view of a rear portion of the hybrid electric transmission arrangement of  FIG. 1 . 
         FIG. 3  is a cross sectional view of a front portion of the hybrid electric transmission arrangement of  FIG. 1 . 
         FIG. 4  is a schematic diagram of a second hybrid electric transmission arrangement. 
         FIG. 5  is a cross sectional view of a front portion of the hybrid electric transmission arrangement of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     Two elements are fixed to one another if they are directly fastened together without intermediate parts. The elements may be fixed by spline connections, welding, press fitting, machining from a common solid, bolts, or other means. A group of elements are fixedly coupled to one another if they are constrained to rotate, or to not rotate, at the same speed about the same axis in all operating conditions. Elements may be fixedly coupled via intermediate parts. Slight variations in rotational displacement between fixedly coupled elements can occur such as displacement due to lash or shaft compliance. In contrast, two elements are selectively coupled by a clutch when the clutch constrains them to rotate, or not rotate, at the same speed about the same axis whenever the clutch is fully engaged and they are free to rotate at distinct speeds in at least some other operating condition. A clutch that holds an element against rotation by selectively coupling the element to a stationary housing may be called a brake. A group of elements are coupled if they are either fixedly coupled or selectively coupled. 
     A first power-split hybrid electric transmission is illustrated schematically in  FIG. 1 . Input  10  is driven by an internal combustion engine. Output  12  drives the vehicle wheels via a differential on an offset axis. Power may be transferred from output  12  to the differential by a chain and sprocket or by axis transfer gearing. Motor  14  includes a stator  16  fixedly and a rotor  18 . Stator  16  is held against rotation by transmission case  20 , which is mounted to vehicle structure. Gearset  22  includes a sun gear  24  fixedly coupled to rotor  18 , a ring gear  26  fixedly held against rotation, a carrier  28  fixedly coupled to output  12 , and a set of planet gears  30  supported for rotation with respect to carrier  28  and meshing with both sun gear  24  and ring gear  28 . Generator  32  includes a stator  34  and a rotor  36 . Simple planetary gearset  38  includes a sun gear  40  fixedly coupled to rotor  36 , a ring gear  42  fixedly coupled to intermediate shaft  44 , a carrier  46  fixedly coupled to input  10 , and a set of planet gears  48  supported for rotation with respect to carrier  46  and meshing with both sun gear  40  and ring gear  42 . Intermediate shaft  44  is fixedly coupled to output  12  via carrier  28 . 
     Motor  14  drives output  12  via planetary gearset  22 , which provides torque multiplication. When the internal combustion engine is off, motor  14  can propel the vehicle using energy stored in a battery. During braking, motor  14  can converter vehicle kinetic energy to electrical energy for storage in the battery. Planetary gearset  38  distributes power from input  10  between generator  32  and output  12 . Planetary gearset  38  also establishes a speed relationship among rotor  36 , input  10 , and intermediate shaft  44 . A controller can adjust the speed of rotor  36  by adjusting the electrical current to stator  34 . By adjusting the speed of rotor  36 , the controller can vary the speed ratio between input  10  and output  12  to any desired value between lower and upper limits. In some operating modes, in which rotor  36  rotates in the same direction as input  10 , planetary gearset  38  sends a portion of the input power to output  12  and sends the remainder of the power to generator  32  which converts it to electrical power. The electrical power may be stored in the battery for later use, sent to motor  14  to propel the vehicle, or some combination of the two. In other operating modes, in which rotor  36  and input  10  rotate in the opposite directions, planetary gearset  38  may draw power from generator  32  and send power from both generator  32  and input  10  to the output  12 . The electrical energy to drive generator  32  in these modes may be drawn from the battery, from motor  14 , or from some combination of the two. 
     The hybrid electric transmission of  FIG. 1  also provides a fixed overdrive operating mode. Simple planetary gearset  50  includes a sun gear  52  fixedly held against rotation, a ring gear  54 , a carrier  56  fixedly coupled to input  10 , and a set of planet gears  58  supported for rotation with respect to carrier  56  and meshing with both sun gear  52  and ring gear  54 . Clutch  60  selectively couples ring gear  58  to output  12  via carrier  28 . When clutch  60  is engaged, out  12  is constrained to rotate at a fixed multiple of the speed of input  10 . Power may be transferred from input  10  to output  12  via gearset  50  and clutch  60  without use of either generator  32  or motor  14 . This direct mechanical power transfer is more efficient than converting a portion of the power to electrical form in one electric machine and then back to mechanical form in the other electrical machine. Although the engine may be slightly less efficient because the engine speed is not optimized, there are many circumstances in which the overall efficiency is improved by use of the fixed ratio operating mode. While operating in this fixed ratio mode, generator  32  and/or motor  14  may be used to add power for improved performance or to divert some power to the battery for later use. 
       FIG. 2  shows a cross section of a rear portion of a transmission according to the arrangement illustrated schematically in  FIG. 1 . Rear refers to the side opposite the end of the transmission through which the input shaft extends. Front refers to the side toward the end through which the input extends. A center housing  62  supports a number of the components. A housing is a single piece of the transmission structure. Typically, a housing is formed by casting or forging metal into a shape close to the final desired shape, but having some additional material in certain areas. Then, excess material is removed in critical areas using more precise types of machining in order to produce a finished housing having low part-to-part variation with respect to critical dimensions. A transmission case may include multiple housings fastened together with removable fasteners such as bolts. This makes the housings easier to produce and permits assembly of components into areas that would be inaccessible if the transmission case were manufactured in a single piece. Output  12  is supported for rotation by center housing  62  on a front side of center housing  62 . Output  12  may be a sprocket meshing with chain  64  to transfer power to the differential assembly on another axis. Stator  16  is fixed to center housing  62  on a rear side of center housing  62 . Motor shaft  66  is supported for rotation by center housing  62  and extends from the front side to the rear side of center housing  62 . Rotor  18  is welded to rotor shaft  66  on the rear side of center housing  62  while sun gear  24  is splined to rotor shaft  66  on the front side of center housing  62 . 
     Rear housing  68  is bolted to flange  70  of center housing  62 . A leg of rear housing  68  supports generator shaft  72  for rotation. In some embodiments, the split line between center housing  62  and rear housing  68  may be shifted toward the front such that stator  34  is fixed to rear housing  68  instead of center housing  62  to reduce part-to-part variability of the air gap distance between stator  34  and rotor  36 . Stator  34  is fixed to center support  62  and rotor  36  is welded to generator shaft  72 . Sun gear  40  is splined to generator shaft  72 , carrier  46  is splined to input shaft  10 , and ring gear  42  is splined to intermediate shaft  44 . Planetary gear set  38  is nested inside rotors  18  and  36  to reduce axial length. 
       FIG. 3  shows a cross section of a front portion of a transmission according to the arrangement illustrated schematically in  FIG. 1 . Front housing  76  is bolted to center housing  62  through flange  76  of center housing  62  and flange  78  of front housing  72 . Carrier  28  is splined to output  12 , intermediate shaft  44 , and clutch housing  80  of clutch  60 . Sun gear  52  is splined to a leg of front housing  74 . Carrier  56  is splined to input shaft  10 . Ring gear  54  is splined to a hub of clutch  60 . Front housing  74  is also fixed to valve body  82 . Front housing  74  defines fluid passageways  84  that carry fluid from valve body  82  to clutch  60 . One passageway carries fluid to an apply chamber. To engage clutch  60 , the fluid is this passageway is pressurized forcing a piston to compress a clutch pack. A second passageway carries unpressurized fluid to a balance chamber. 
     A second power-split hybrid electric transmission is illustrated schematically in  FIG. 4 . Parts that are common with the transmission of  FIG. 1  are labeled with the same reference number. Unlike the transmission of  FIG. 1 , intermediate shaft  44  is not fixedly coupled to output  12 . Clutches  86  and  88  and brake  90  provide the modes of operation. Clutch  86  selectively couples intermediate shaft  44  to sun gear  24 . Engaging clutch  86  selects a low mode. In low mode, the mechanical power flow path from power-split gearset  38  utilizes gearset  22  to provide torque multiplication. Clutch  88  selectively couples intermediate shaft  44  to output  12 . Engaging clutch  88  selects a high mode, which functions the same as the transmission of  FIG. 1  with clutch  60  disengaged. Brake  90  selectively holds intermediate shaft  44  against rotation. Engaging brake  90  selects a series mode. In series mode, there is no mechanical power flow path from power-split gearset  38  to the output. Rotor  36  is constrained to rotate at fixed multiple of the speed of input  10 . Generator  32  converts all of the input power into electrical power. Motor  16  provides all of the power to propel the vehicle, using some combination of stored electrical power from the battery and electrical power from generator  32 . 
     The rear portion of the transmission of  FIG. 4  is identical to the rear portion of the transmission of  FIG. 1  as shown in  FIG. 2 .  FIG. 5  shows a cross section of a front portion of a transmission according to the arrangement illustrated schematically in  FIG. 4 . Parts that are common with the transmission of  FIG. 3  are labeled with the same reference number. Intermediate shaft  44  is splined to clutch housing  92 . Front housing  74  includes a series of fluid passageways  84  from valve body  82  to various shift elements One passageway carries fluid to an apply chamber of clutch  86 . Another passageway carries fluid to an apply chamber of clutch  88 . A third passageway carries unpressurized fluid to balance chambers of clutches  86  and  88 . A fourth passageway carrier fluid to an apply chamber of brake  90  which is integrated into the front housing  74 . 
     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.

Technology Classification (CPC): 8