Abstract:
A multiple speed power transmission, comprising an input shaft; a transmission case; a co-planar gear set; a rear epicyclic gearing assembly with four rotating members; a first clutch connecting the output of the co-planar gear set to the fourth rotating member; a second clutch connecting the output of the co-planar gear set to the first rotating member; a third clutch connecting the input shaft to the third rotating member; a first brake holding the fourth rotating member against rotation; a second brake holding the third rotating member against rotation; and an output shaft connected to the second rotating member.

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 two reverse speed ratios. 
           [0003]      FIG. 2  is a table showing 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]      FIG. 4  is a schematic diagram of a transmission according to a second embodiment of the present invention which produces seven forward and one reverse speed ratios. 
           [0006]      FIG. 5  is a table showing proposed tooth numbers for the gears of the transmission illustrated in  FIG. 4 . 
           [0007]      FIG. 6  is a table indicating the states of the clutches and resulting speed ratio of the transmission in  FIG. 4  when the gears have the number of teeth indicated in  FIG. 5 . 
           [0008]      FIG. 7  is a schematic diagram of a transmission according to a third embodiment of the present invention which produces eight forward and two reverse speed ratios. 
           [0009]      FIG. 8  is a table showing the proposed tooth numbers for the gears of the transmission illustrated in  FIG. 7 . 
           [0010]      FIG. 9  is a table indicating the states of the clutches and resulting speed ratio of the transmission in  FIG. 7  when the gears have the number of teeth indicated in  FIG. 8 . 
           [0011]      FIGS. 10 and 11  are cross sectional views of a co-planar gear set. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]    This invention utilizes co-planar gear sets similar to those described in U.S. Pat. Nos. 5,030,184 and 6,126,566. For clarity, an example of a co-planar gear set is illustrated in  FIGS. 10 and 11  and described below. Sun gear  12 , carrier  10 , and ring gear  14  are typically supported for rotation around centerline  18 , although in some applications one of them may be held against rotation. Eccentric gear  16  is supported by carrier  10  for rotation about centerline  20 . Centerline  20  rotates around centerline  18  along with carrier  10 . Internal gear teeth on eccentric gear  16  engage external gear teeth on sun gear  12 . External gear teeth on eccentric gear  16  engage internal gear teeth on ring gear  14 . The rotational speed of ring gear  14  is a weighted average of the rotational speeds of sun gear  12  and carrier  10 , with the weighting factors determined by the numbers of teeth. The name co-planar gear set is used even in embodiments wherein the components do not all occupy a single plane, such as the embodiment illustrated in  FIG. 11 . 
         [0013]    A transmission according to a first embodiment of the present invention is illustrated schematically in  FIG. 1 . Input shaft  30  is driven by the vehicle engine, preferably via a torque converter. Output shaft  32  drives the vehicle wheels, preferably via a differential. 
         [0014]    A front co-planar gear set  36  includes a sun gear with external gear teeth  38 , a ring gear with internal gear teeth  40 , a carrier  42 , and an epicyclic gear  44  supported by the carrier. Internal gear teeth  46  of the eccentric gear engage the external teeth  38  of the sun gear. External gear teeth  48  of the eccentric gear engage the internal teeth  40  of the ring gear. The sun gear is held against rotation by transmission case  34 . Carrier  42  is driveably connected to the input shaft  30 . 
         [0015]    A rear epicyclic gearing assembly  50  includes a planetary gear set and a second co-planar gear set. The planetary gear set includes a sun gear with external gear teeth  52 , a ring gear with internal gear teeth  54 , a carrier  56 , and a set of planet gears  58  supported by the carrier and meshing with the sun gear and ring gear. The second co-planar gear set includes a sun gear with external gear teeth  60 , a ring gear with internal gear teeth  62 , and an epicyclic gear  64  supported by carrier  56  which is shared with the planetary gear set. Internal gear teeth  66  of the eccentric gear engage the external teeth  60  of the sun gear. External gear teeth  68  of the eccentric gear engage the internal teeth  62  of the ring gear. The ring gears of both the planetary gear set and the second co-planar gear set are driveably connected to the output shaft  32 . 
         [0016]    The rear epicyclic gearing assembly has four members that each rotate as a unit around the transmission axis. The first member is the sun gear of the co-planar gear set. The second member is the combination of the ring gear of the planetary gear set and the ring gear of the co-planar gear set. The third member is the shared carrier  56 . The fourth member is the sun gear of the planetary gear set. The kinematic constraints of planetary gear sets and co-planar gear sets are such that the second and third members rotate at speeds that are weighted averages of the speeds of the first and fourth members, with the weighting factors determined by the numbers of teeth. The weighting factors are such that the speed of the second member is between the speeds of the first and third members and the speed of the third member is between the speeds of the second and fourth members. 
         [0017]    Clutches  70 ,  72 ,  74 , and  76  and brakes  78  and  80  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  70  releasably connects gearbox input shaft  30  to the sun gear of the planetary gear set. Clutch  72  releasably connects the ring gear of the front co-planar gear set to the sun gear of the planetary gear set. Clutch  74  releasably connects the ring gear of the front co-planar gear set to the sun gear of the second co-planar gear set. Clutch  76  releasably connects gearbox input shaft  30  to the carrier of the planetary gear set and second co-planar gear set. Brake  78  releasably connects the sun gear of the planetary gear set to the transmission case  34 . Brake  80  releasably connects the carrier of the planetary gear set and second co-planar gear set to the transmission case  34 . 
         [0018]    The transmission ratio is selected by applying hydraulic pressure to two of the clutches and brakes as indicated in  FIG. 3 . The transmission is prepared for forward motion in first gear by applying clutch  74  and brake  80 . To transition to second gear, brake  80  is progressively released while brake  78  is progressively engaged. To transition from second gear to third gear, brake  78  is progressively released while clutch  72  is progressively engaged. To transition from third gear to fourth gear, clutch  72  is progressively released while clutch  70  is progressively engaged. To transition from fourth gear to fifth gear, clutch  70  is progressively released while clutch  76  is progressively engaged. Clutch  74  is maintained in the engaged state while operating in the first five forward gears. To transition from fifth gear to sixth gear, clutch  74  is progressively released while clutch  70  is progressively engaged. To transition from sixth gear to seventh gear, clutch  70  is progressively released while clutch  72  is progressively engaged. To transition from seventh gear to eighth gear, clutch  72  is progressively released while brake  78  is progressively engaged. Clutch  76  is maintained in the engaged state while operating in gears five through eight. 
         [0019]    The transmission is prepared for reverse motion by applying clutch  72  and brake  80 . If desired, the transmission can be shifted into a second reverse ratio by progressively releasing clutch  72  while progressively engaging clutch  70 , maintaining clutch  80  in the engaged state. 
         [0020]    A transmission according to a second embodiment of the present invention is illustrated schematically in  FIG. 4 . Input shaft  30  is driven by the vehicle engine, preferably via a torque converter. Output shaft  32  drives the vehicle wheels, preferably via a differential. A rear epicyclic gearing assembly is as described above for the first embodiment. 
         [0021]    A front co-planar gear set  36  includes a sun gear with external gear teeth  38 , a ring gear with internal gear teeth  40 , a carrier  42 , and an epicyclic gear  44  supported by the carrier. Internal gear teeth  46  of the eccentric gear engage the external teeth  38  of the sun gear. External gear teeth  48  of the eccentric gear engage the internal teeth  40  of the ring gear. Carrier  42  is driveably connected to the input shaft  30 . 
         [0022]    Clutches  72 ,  74 , and  76  and brakes  78 ,  80 , and  82  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  72  releasably connects the ring gear of the front co-planar gear set to the sun gear of the planetary gear set. Clutch  74  releasably connects the ring gear of the front co-planar gear set to the sun gear of the second co-planar gear set. Clutch  76  releasably connects gearbox input shaft  30  to the carrier of the planetary gear set and second co-planar gear set. Brake  78  releasably connects the sun gear of the planetary gear set to the transmission case  34 . Brake  80  releasably connects the carrier of the planetary gear set and second co-planar gear set to the transmission case  34 . Brake  82  releasably connects the sun gear of the front co-planar gear set to the transmission case  34 . 
         [0023]    The transmission ratio is selected by applying hydraulic pressure to three of the clutches and brakes as indicated in  FIG. 6 . The transmission is prepared for forward motion in first gear by applying clutch  74  and brakes  80  and  82 . To transition to second gear, brake  80  is progressively released while brake  78  is progressively engaged. To transition from second gear to third gear, brake  78  is progressively released while clutch  72  is progressively engaged. To transition from third gear to fourth gear, clutch  72  is progressively released while clutch  76  is progressively engaged. Brake  82  is maintained in the engaged state while operating in the first four forward gears. To transition from fourth gear to fifth gear, brake  82  is progressively released while clutch  72  is progressively engaged. Clutch  74  is maintained in the engaged state while operating in the first five forward gears. To transition from fifth gear to sixth gear, clutch  74  is progressively released while brake  82  is progressively engaged. To transition from sixth gear to seventh gear, clutch  72  is progressively released while brake  78  is progressively engaged. Clutch  76  is maintained in the engaged state while operating in gears four through seven. 
         [0024]    The transmission is prepared for reverse motion by applying clutch  72  and brakes  80  and  82 . 
         [0025]    A transmission according to a third embodiment of the present invention is illustrated schematically in  FIG. 7 . Input shaft  90  is driven by the vehicle engine, preferably via a torque converter. Output shaft  92  drives the vehicle wheels, preferably via a differential. 
         [0026]    A front co-planar gear set  96  includes a sun gear with external gear teeth  98 , a ring gear with internal gear teeth  100 , a carrier  102 , and an epicyclic gear  104  supported by the carrier. Internal gear teeth  106  of the eccentric gear engage the external teeth  98  of the sun gear. External gear teeth  108  of the eccentric gear engage the internal teeth  100  of the ring gear. The carrier is held against rotation by transmission case  94 . The sun gear is driveably connected to the input shaft  90 . 
         [0027]    A rear epicyclic gearing assembly  110  includes first sun gear  112 , second sun gear  122 , first ring gear  114 , second ring gear  116 , third ring gear  124 , first carrier  118  and second carrier  126 . A first set of planet gears with external gear teeth  120  and  121  is supported by the first carrier  118 . Gear teeth  120  mesh with both the first sun gear  112  and first ring gear  114 . Gear teeth  121  mesh with the second ring gear  116 . Preferably, the number of gear teeth at  120  and  121  are identical and the number of gear teeth on ring gears  114  and  116  are identical. When this is the case, the speed of ring gear  114  and ring gear  116  will always be equal. Alternatively, the planet gears could be stepped in which case the speed of ring gear  114  and ring gear  116  would differ slightly. Carrier  118  extends radially between ring gear  114  and ring gear  116  and it driveably connected to both ring gear  124  and output shaft  92 . Ring gear  116  is driveably connected to carrier  126 . A second set of planet gears  128  is supported by carrier  126  and meshes with both sun gear  122  and ring gear  124 . 
         [0028]    The rear epicyclic gearing assembly has at least four members that each rotate as a unit around the transmission axis. The first member is sun gear  112 . The second member is the combination of carrier  118  and ring gear  124 . The third member is ring gear  116  and carrier  126 . The fourth member is sun gear  122 . The kinematic constraints of planetary gear sets are such that the second and third members rotate at speeds that are weighted averages of the speeds of the first and fourth members, with the weighting factors determined by the numbers of teeth. The weighting factors are such that the speed of the second member is between the speeds of the first and third members and the speed of the third member is between the speeds of the second and fourth members. If the first set of planet gears are stepped pinions, then ring gear  114  is a fifth member with a speed that is between the speeds of the second and fourth members. 
         [0029]    Clutches  130 ,  132 ,  134 , and  136  and brakes  138  and  140  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  130  releasably connects gearbox input shaft  90  to sun gear  122 . Clutch  132  releasably connects the ring gear of the front co-planar gear set to sun gear  122 . Clutch  134  releasably connects the ring gear of the front co-planar gear set to sun gear  112 . Clutch  136  releasably connects gearbox input shaft  90  to ring gear  116  and carrier  126 . Brake  138  releasably connects sun gear  122  to the transmission case  94 . Brake  140  releasably connects ring gear  114  to the transmission case  94 , which constrains the speed of ring gear  116  and carrier  126  to a value equal to or near zero. 
         [0030]    The transmission ratio is selected by applying hydraulic pressure to two of the clutches and brakes as indicated in  FIG. 9 . The transmission is prepared for forward motion in first gear by applying clutch  134  and brake  140 . To transition to second gear, brake  140  is progressively released while brake  138  is progressively engaged. To transition from second gear to third gear, brake  138  is progressively released while clutch  132  is progressively engaged. To transition from third gear to fourth gear, clutch  132  is progressively released while clutch  130  is progressively engaged. To transition from fourth gear to fifth gear, clutch  130  is progressively released while clutch  136  is progressively engaged. Clutch  134  is maintained in the engaged state while operating in the first five forward gears. To transition from fifth gear to sixth gear, clutch  134  is progressively released while clutch  130  is progressively engaged. To transition from sixth gear to seventh gear, clutch  130  is progressively released while clutch  132  is progressively engaged. To transition from seventh gear to eighth gear, clutch  132  is progressively released while brake  138  is progressively engaged. Clutch  136  is maintained in the engaged state while operating in gears five through eight. 
         [0031]    The transmission is prepared for reverse motion by applying clutch  132  and brake  140 . If desired, the transmission can be shifted into a second reverse ratio by progressively releasing clutch  132  while progressively engaging clutch  130 , maintaining clutch  140  in the engaged state. 
         [0032]    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.