Abstract:
A multiple speed power transmission comprising: four epicyclic gearing assemblies each having first, second, and third rotating elements with specified interconnections, an input shaft connected to one of the rotating elements, an output shaft, two rotating clutches releasably connecting the input shaft to rotating elements, and four brakes selectively holding rotating elements against rotation. Clutches and brakes are applied in combinations of two to produce eight forward ratios and one reverse ratio.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to the field of automatic transmissions for motor vehicles. More particularly, the invention pertains to a kinematic arrangement of gearing, clutches, brakes, and the interconnections among them in a power transmission. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0002]      FIG. 1  is a schematic diagram of a transmission according to a first embodiment of the present invention which produces eight forward and one reverse speed ratios. 
           [0003]      FIG. 2  is a table showing the proposed tooth numbers for the gears of the transmission illustrated in  FIG. 1 . 
           [0004]      FIG. 3  is a table indicating the states of the clutches and resulting speed ratio of the transmission in  FIG. 1  when the gears have the number of teeth indicated in  FIG. 2 . 
           [0005]      FIGS. 4-6  are schematic diagrams of alternative embodiments which differ from the embodiment of  FIG. 1  with respect to the structure of the torque converter assembly. 
           [0006]      FIGS. 7-8  are schematic diagrams of alternative embodiments which differ from the embodiment of  FIG. 1  with respect to the structure of the first planetary gear set and its connections to other components. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0007]    A transmission according to a first embodiment of the present invention is illustrated in  FIG. 1 . The transmission contains four simple planetary gear set assemblies  20 ,  30 ,  40 , and  50 . Each simple planetary gear set assembly has a sun gear, a ring gear with an internal mesh, a planet carrier, and a set of planet gears supported for rotation on the carrier and meshing with both the sun gear and ring gear. A recommended number of gear teeth for each of these gears is shown in  FIG. 2 . 
         [0008]    Gearbox input shaft  10  is driven by the vehicle&#39;s engine via torque converter assembly  100 . The third sun gear  42 , is fixed to gearbox input shaft  10 . The first carrier  26  is connected to the second sun gear  32 . The second carrier  36  is connected to the third ring gear  44 . The first ring gear  24 , third carrier  46 , and fourth ring gear  54  are mutually connected. A gearbox output shaft  12  drives the vehicle wheels, preferably via a driveshaft, a differential assembly, and rear axle shafts. Gearbox output shaft  12  is fixed to the fourth carrier  56  and the second ring gear  34 . A transmission case  14  provides support for the gear sets, input shaft, and output shaft. 
         [0009]    Clutches  60  and  62  and brakes  64 ,  66 ,  68 , and  70  are preferably hydraulically actuated friction clutches which releasably connect two elements when hydraulic pressure is applied and disconnect those elements when the hydraulic pressure is released. Clutch  60  releasably connects gearbox input shaft  10  to the first sun gear  22 . Clutch  62  releasably connects gearbox input shaft  10  to the first ring gear  24 , third carrier  46 , and fourth ring gear  54 . Brake  64  releasably connects the first sun gear  22  to the transmission case  14 . Brake  66  releasably connects the fourth sun gear  52  to the transmission case  14 . Brake  68  releasably connects the first carrier  26  and second sun gear  32  to the transmission case  14 . Brake  70  releasably connects the second carrier  36  and the third ring gear  44  to the transmission case  14 . One way clutch  72  is a passive device which allows the second carrier  36  and third ring gear  44  to rotate freely in a positive direction but prevents rotation in the opposite direction. 
         [0010]    Torque converter assembly  100  comprises an impeller  104  that is driven by the transmission input shaft  102 , stator  108 , and turbine  106 . The stator  108  is connected to the transmission case  14  by a one way clutch  110 . When the turbine is substantially slower than the impeller, the one way clutch holds the stator stationary and it provides a reaction torque to create torque multiplication between the impeller and turbine. The one way clutch overruns when the turbine speed is near or greater than the impeller speed. Lock-up clutch  112  connects the turbine to the impeller eliminating the hydrodynamic losses of the torque converter. In  FIG. 1 , the turbine is connected to gearbox input shaft  12  via a spring  114 . This spring isolates the gearbox and driveline from the torque pulses produced by the engine while transmitting the average torque. A torque converter assembly with a spring in this location is commonly called a turbine damper. 
         [0011]    The transmission ratio is selected by applying hydraulic pressure to two of the clutches and brakes as indicated in  FIG. 3 . 
         [0012]    The transmission is prepared for forward motion in first gear by applying brake  66 . While the vehicle is at rest, turbine  106 , gearbox input shaft  10 , and all gear set components are stationary. The engine drives impeller  104 , which circulates fluid toroidally among the impeller, stator, and turbine. This fluid flow pattern produces a torque on the turbine shaft and gearbox input shaft  10 . One way clutch  72  provides a reaction at ring gear  44 . Clutch  66  provides another reaction at sun gear  52 . Thus, a multiple of the input torque is transferred to output shaft  12 , accelerating the vehicle. 
         [0013]    In this condition, one way clutch  72  will overrun if an attempt is made to transmit power in the opposite direction. If engine braking behavior is desired, it is necessary to also apply friction brake  70 . Optionally, one way clutch  72  may be omitted and friction brake  70  applied for both directions of power transfer. 
         [0014]    Lock-up clutch  112  may be applied any time the speed of gearbox input shaft  10  is within the engine&#39;s operating range. Preferably, it is applied as soon as possible and remains engaged as long as possible in order to minimize transmission parasitic losses. 
         [0015]    To shift to second gear, brake  68  is progressively engaged, maintaining brake  66  fully applied. As the torque capacity of brake  68  increases, one way clutch  72  will overrun. If one way clutch  72  is omitted, brake  70  must be progressively released as brake  68  is engaged. 
         [0016]    To shift from second to third gear, brake  64  is progressively engaged while brake  68  is progressively released. To shift from third to fourth gear, clutch  60  is progressively engaged while brake  64  is progressively released. To shift from fourth to fifth gear, clutch  62  is progressively engaged while clutch  60  is progressively released. Brake  66  is maintained in the fully applied state through all of these transitions. 
         [0017]    To shift from fifth to sixth gear, clutch  60  is progressively engaged while brake  66  is progressively released. Sixth gear is a direct drive gear. To shift from sixth to seventh gear, brake  64  is progressively engaged while clutch  60  is progressively released. To shift from seventh to eighth gear, brake  68  is progressively engaged while brake  64  is progressively released. Clutch  62  is maintained in the fully applied state through all of these transitions. 
         [0018]    Downshifting to a lower gear is accomplished by reversing the steps described above for the corresponding upshift. 
         [0019]    The transmission is operated in reverse by applying clutch  60  and brake  70 . 
         [0020]      FIGS. 4 ,  5 , and  6  illustrate alternate embodiments that differ from the above embodiment with respect to the construction and function of torque converter assembly  100 . These embodiments are operated in the same fashion as the previous embodiment. 
         [0021]    In the embodiment of  FIG. 4 , a relatively narrow shaft  116  runs through the center of the gearbox inside gearbox input shaft  10 , which is hollow. Shafts  116  and  10  are connected to each other as far from the input end of the transmission as feasible. The diameter of shaft  116  is selected just large enough to withstand the maximum anticipated turbine torque (with an appropriate safety factor). As a result of its small diameter and relatively long length, shaft  116  has considerable torsional compliance and provides isolation from engine pulses (which was accomplished by spring  114  in the embodiment of  FIG. 1 ). In this embodiment, turbine  106  is connected to shaft  116  as opposed to shaft  10 . The remaining components and their interconnections are identical to the embodiment of  FIG. 1 . 
         [0022]    The embodiment of  FIG. 5  also uses a narrow shaft  116  to provide isolation from engine pulses. In this embodiment, however, the turbine is connected to gearbox input shaft  10  and lock-up clutch  112  releasably connects transmission input shaft  102  to shaft  116 . Shaft  116  may be designed to withstand engine torque as opposed to turbine torque which is typically much higher. As a result, it has more compliance and provides better isolation. 
         [0023]    In the embodiment of  FIG. 6 , lock-up clutch  112  is located within the gearbox portion and releasably connects the narrow shaft  116  to gearbox input shaft  10 . Turbine  106  is connected to gearbox input shaft  10 . Shaft  116  is connected to transmission input shaft  102 . The fluid that actuates clutch  112  may be fed through output shaft  12 . 
         [0024]      FIGS. 7 and 8  illustrate alternate embodiments which differ with respect to the previous embodiments with respect to the construction of the first gear set and its connections. Torque converter assembly  100  is not shown in these Figures. Any of the variations of torque converter illustrated in  FIGS. 1 ,  4 ,  5 , and  6  and described above could be utilized with the gearbox structures illustrated in  FIGS. 7 and 8 . The embodiments illustrated in  FIGS. 7 and 8  are operated in the same fashion as the embodiment illustrated in  FIG. 1  which is described above. 
         [0025]    A transmission according to another embodiment of the present invention is illustrated in  FIG. 7 . The transmission contains one compound planetary gear set assembly  80  and three simple planetary gear set assemblies  30 ,  40 , and  50 . The compound planetary gear set assembly has a sun gear, a ring gear with an internal mesh, a planet carrier, an inner set of planet gears supported for rotation on the carrier and meshing with the sun gear, and an outer set of planet gears supported for rotation on the carrier and meshing with both one of the inner planet gears and the ring gear. 
         [0026]    The third sun gear  42 , is fixed to gearbox input shaft  10 . The first ring gear  84  is connected to the second sun gear  32 . The second carrier  36  is connected to the third ring gear  44 . The first carrier  86 , third carrier  46 , and fourth ring gear  54  are mutually connected. Output shaft  12  is fixed to the fourth carrier  56  and the second ring gear  34 . A transmission case  14  provides support for the gear sets, input shaft, and output shaft. 
         [0027]    Clutch  60  releasably connects gearbox input shaft  10  to the first sun gear  82 . Clutch  62  releasably connects gearbox input shaft  10  to the first carrier  86 , third carrier  46 , and fourth ring gear  54 . Brake  64  releasably connects the first sun gear  82  to the transmission case  14 . Brake  66  releasably connects the fourth sun gear  52  to the transmission case  14 . Brake  68  releasably connects the first ring gear  84  and second sun gear  32  to the transmission case  14 . Brake  70  releasably connects the second carrier  38  and the third ring gear  44  to the transmission case  14 . One way clutch  72  allows the second carrier  36  and third ring gear  44  to rotate freely in a positive direction but prevents rotation in the opposite direction. 
         [0028]    A transmission according to another embodiment of the present invention is illustrated in  FIG. 8 . The transmission contains one compound planetary gear set assembly  90  and three simple planetary gear set assemblies  30 ,  40 , and  50 . The third sun gear  42 , is fixed to gearbox input shaft  10 . The first ring gear  94  is connected to the second sun gear  32 . The second carrier  36  is connected to the third ring gear  44 . The first sun gear  92 , third carrier  46 , and fourth ring gear  54  are mutually connected. Output shaft  12  is fixed to the fourth carrier  56  and the second ring gear  34 . A transmission case  14  provides support for the gear sets, input shaft, and output shaft. 
         [0029]    Clutch  60  releasably connects gearbox input shaft  10  to the first carrier  96 . Clutch  62  releasably connects gearbox input shaft  10  to the first sun gear  92 , third carrier  46 , and fourth ring gear  54 . Brake  64  releasably connects the first carrier  96  to the transmission case  14 . Brake  66  releasably connects the fourth sun gear  52  to the transmission case  14 . Brake  68  releasably connects the first ring gear  94  and second sun gear  32  to the transmission case  14 . Brake  70  releasably connects the second carrier  38  and the third ring gear  44  to the transmission case  14 . One way clutch  72  allows the second carrier  36  and third ring gear  44  to rotate freely in a positive direction but prevents rotation in the opposite direction. 
         [0030]    A transmission embodiment according to this invention contain four epicyclic gearing assemblies, each with three members that rotate around a common axis. In each epicyclic gearing assembly, the speeds of the three elements are linearly related. The second rotating elements is constrained to rotate at a speed which is a weighted average of the speeds of the first and third elements. The weighting factors are determined by the configuration of the epicyclic gearing assembly and the ratios of the numbers of gear teeth. In  FIG. 1 , all four epicyclic gearing assemblies are simple planetary gearsets. In  FIGS. 7 and 8 , one of the epicyclic gearing assemblies is a compound planetary gearset. Other types of epicyclic gearing assemblies, such as coplanar gear loops as described in U.S. Pat. Nos. 5,030,184 and 6,126,566, are known and may be substituted without departing from the present invention. 
         [0031]    In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that alternate embodiments can be practiced otherwise than as specifically illustrated and described.