Abstract:
A multiple speed power transmission comprises: an epicyclic gearing assembly comprising first, second, third, and fourth rotating members with linearly related speeds; a double pinion planetary gear set with grounded carrier and input driven sun gear; two brakes; four clutches; and specified interconnections. The brakes and clutches are operated in combinations of two to produce eight forward speed ratios and at least one reverse speed ratio.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to automatic vehicular transmissions utilizing planetary gear sets and controllable clutches to obtain a suitable set of speed ratios. 
         [0002]    In a front wheel drive vehicle, the axial space available for the transmission is limited by the width of the engine compartment and the length of the engine. In addition, the trend to increase the number of ratios available generally increases the number of components required. For these reasons, it is desirable to position components concentrically with each other in order to minimize axial length. The ability to position components concentrically is limited, however, by the need to connect particular components to each other and to the transmission case. 
         [0003]    Furthermore, it is desirable for the output element to be located near the center of the vehicle, which corresponds to the input end of the gear box. An output element located toward the outside of the vehicle may require additional support structure and add length on the transfer axis. With some kinematic arrangements, however, the need to connect certain elements to the transmission case requires that the output element be so located. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    The claimed invention is a family of six and eight speed kinematic arrangements that are amenable to coaxial placement of components and also amenable to placing the output shaft near the front of the transmission. The arrangements include an epicyclic gearing assembly with four elements, a front planetary gear set with a stationary carrier, and a set of clutches and brakes. These arrangements are in the family of dual input kinematic arrangements as described in U.S. Pat. Nos. 5,106,352 and 7,699,744. One of the brakes is located internally and operates by releasably connecting one element of the epicyclic gearing assembly to the fixed carrier of the front gear set. As a result of this placement, this brake and two of the clutches may be positioned co-axially with each other and also with the epicyclic gearing assembly. Furthermore, this placement does not interfere with locating the output member at the front of the gear box. The epicyclic gearing assembly may take a number of forms, some of which would not be possible with a traditional placement of the aforementioned brake. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a schematic diagram of a transmission according to the present invention wherein the epicyclic gearing assembly is a Simpson gear set. 
           [0006]      FIG. 2  is a table showing the proposed tooth numbers for the gears of the transmission illustrated in  FIG. 1 . 
           [0007]      FIG. 3  is a table indicating the clutch state and resulting speed ratio of the transmission in  FIG. 1  when the gears have the numbers of teeth indicated in  FIG. 2 . 
           [0008]      FIG. 4  is a schematic diagram of a transmission according to the present invention wherein the epicyclic gearing assembly is a crossed ring carrier gear set. 
           [0009]      FIG. 5  is a table showing the proposed tooth numbers for the gears of the transmission illustrated in  FIG. 4 . 
           [0010]      FIG. 6  is a table indicating the clutch state and resulting speed ratio of the transmission in  FIG. 4  when the gears have the numbers of teeth indicated in  FIG. 5 . 
           [0011]      FIG. 7  is a schematic diagram of a transmission according to the present invention wherein the epicyclic gearing assembly is a Ravigneaux gear set. 
           [0012]      FIG. 8  is a table showing the proposed tooth numbers for the gears of the transmission illustrated in  FIG. 7 . 
           [0013]      FIG. 9  is a table indicating the clutch state and resulting speed ratio of the transmission in  FIG. 7  when the gears have the numbers of teeth indicated in  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    A transmission according to a first embodiment of the invention is illustrated in  FIG. 1 . A transmission housing  14  is fixed to the vehicle structure. An input shaft  10  is driven by the vehicle&#39;s engine, preferably via a launch device such as a torque converter with a lockup clutch, or via a dedicated launch clutch. Alternatively, the input shaft may be driven directly by the vehicle&#39;s engine. An output element  12  is driveably connected to the vehicle&#39;s wheels, preferably via a differential and either a set of transfer gears or a transfer chain. Output element  12  is supported by front support  52  which is fixed to the transmission housing. 
         [0015]    Front gear set  40  is a double pinion planetary gear set. Carrier  46  is fixed to the front support  52 . Sun gear  42  is fixed to input shaft  10 . A set of inner planet gears  48  is supported for rotation on carrier  46  and meshes with sun gear  42 . A set of outer planet gears  50  is also supported for rotation on carrier  46  such that each outer planet gear meshes with a corresponding inner planet gear  48 . A ring gear  44  with internal teeth meshes with each of the outer planet gears  50 . As a result of this gearing, ring gear  44  rotates in the same direction as input shaft  10  but at a reduced speed. 
         [0016]    Rear gear set  20  and middle gear set  30  are simple planetary gear sets. A set of planet gears  28  is supported for rotation on carrier  26  and meshes with both sun gear  22  and ring gear  24 . Similarly, a set of planet gears  38  is supported for rotation on carrier  36  and meshes with both sun gear  32  and ring gear  34 . Sun gear  22  and sun gear  32  are fixed to each other and to shell  56 . Carrier  26  is fixed to shell  80 . Carrier  36  and ring gear  24  are fixed to each other and to output element  12  through shell  90 . Ring gear  34  is fixed to shell  68 . 
         [0017]    Front cylinder assembly  62  is fixed to ring gear  44 . Clutch pack  70  is comprised of plates splined to cylinder assembly  62  alternating with plates splined to shell  68 . When hydraulic pressure is applied to piston  72 , the plates are forced together and torque is transferred between ring gear  44  and ring gear  34 . When the hydraulic pressure is released, ring gear  44  and ring gear  34  may rotate at different speeds with low parasitic drag. Similarly, clutch pack  64  is comprised of plates splined to cylinder assembly  62  alternating with plates splined to shell  56 . When hydraulic pressure is applied to piston  66 , torque is transferred between ring gear  44  and sun gears  22  and  32 . Pressurized fluid is routed from the control body, through front support  52 , into front cylinder assembly  62  between rotating seals. 
         [0018]    Middle cylinder assembly  54  is fixed to carrier  46 . Clutch pack  58  is comprised of plates splined to cylinder assembly  54  alternating with plates splined to shell  56 . When hydraulic pressure is applied to piston  60 , sun gear  22  and sun gear  32  are held against rotation. Pressurized fluid is routed from the control body, through front support  52 , between planet gears, into middle cylinder assembly  54 . A more traditional placement of this brake would preclude routing shell  90  to the front of the gear box and therefore require that the output be located near the center of the gear box. As a result of this placement of clutch pack  58 , output element  12  is located in the more favorable position near the front of the gear box. 
         [0019]    Rear cylinder assembly  74  is fixed to input shaft  10 . When hydraulic pressure is applied to piston  84 , clutch pack  82  transfers torque between input shaft  10  and carrier  26 . Similarly, when hydraulic pressure is applied to piston  78 , clutch pack  76  transfers torque between input shaft  10  and sun gears  22  and  32 . Clutch pack  76  and piston  78  are required for an eight speed transmission, but may be omitted in a six speed transmission. Pressurized fluid is routed from the control body, through housing  14 , into rear cylinder assembly  74  between rotating seals. 
         [0020]    When hydraulic pressure is applied to piston  88 , clutch pack  86  holds carrier  26  against rotation. One way clutch  92  passively prevents carrier  26  from rotating in the negative direction, but allows carrier  26  to rotate in the forward direction. One way clutch  92  may optionally be omitted and its function performed by actively controlling clutch  86 . 
         [0021]    This arrangement permits clutch packs  58 ,  64 , and  70  to be positioned concentrically and outside of the planetary gear sets such that they do not add to the axial length of the gearbox. Similarly, clutch packs  76 ,  82 , and  86  may be positioned concentrically with each other and outside the planetary gearing. 
         [0022]    Although clutches  64 ,  70 ,  76 , and  82  and brakes  58  and  86  have all been illustrated and described as hydraulically actuated multi-plate clutches or brakes, the invention may be practiced with alternate types of releasable connections including but not limited to dog clutches, controllable one way clutches, magnetically actuated clutches, or electrically actuated clutches. Components being fixed to one another means that the components are attached in a fashion that transfers torque and forces the components to rotate at the same speed for anticipated torque levels. Acceptable methods of fixing components to one another include but are not limited to machining from common stock, welds, spline joints, and interference fits. Some lash or torsional compliance between fixed components is permissible. 
         [0023]    If the transmission of  FIG. 1  is equipped with a launch device, then it is prepared for forward vehicle motion by engaging clutch  70 . If one way clutch  92  is omitted, then brake  86  must also be engaged. If the launch device is a torque converter, the vehicle will accelerate as soon as the brakes are released. The torque converter lock up clutch should be engaged soon after the vehicle attains a sufficient speed. On the other hand, if the launch device is a dedicated launch clutch, forward motion is effectuated by gradually engaging the dedicated launch clutch. 
         [0024]    If input shaft  10  is directly driven by the engine, then the only preparation required for forward vehicle motion is engaging brake  86  if one way clutch  92  is omitted. Forward motion is effectuated by gradually engaging clutch  70 . The remaining steps in operating the transmission are independent of the type of launch device. 
         [0025]    Once the vehicle reaches a sufficient forward speed, a shift into second gear is accomplished by gradually engaging brake  58 . As brake  58  is engaged, one way clutch  92  will over run. If one way clutch  92  is omitted, brake  86  must be gradually released while brake  58  is engaged. All remaining shifts between adjacent gears are accomplished by the coordinated engagement of one clutch or brake and release of another clutch or brake while maintaining a third clutch or brake according to the table in  FIG. 3 . In addition to these shifts, all two step shifts may be accomplished by releasing a single element, engaging another element, and maintaining one element in an engaged state. 
         [0026]    If the transmission is equipped with a launch device, then it is prepared for reverse vehicle motion by engaging clutch  64  and brake  86 . As with forward motion, if the launch device is a torque converter, the vehicle will accelerate as soon as the brakes are released. If the launch device is a dedicated launch clutch, reverse motion is effectuated by gradually engaging the dedicated launch clutch. On the other hand, if input shaft  10  is directly driven by the engine, then the transmission is prepared for reverse vehicle motion by engaging brake  86  and reverse motion is effectuated by gradually engaging clutch  64 . 
         [0027]    A transmission according to this invention comprises an epicyclic gearing assembly with four members that rotate around a common axis with speeds that are linearly related. Specifically, the second and third elements each have speeds that are a weighted average of the speed of the first and fourth elements. The speed of the second element is between the speed of the first and third elements. The speed of the third element is between the speed of the second and fourth elements. The weighting factors are determined by the configuration of the epicyclic gearing assembly and the ratios of the numbers of gear teeth. 
         [0028]    In the transmission of  FIG. 1 , the epicyclic gearing assembly corresponds to planetary gear sets  20  and  30 . The first member corresponds to ring gear  34 . The second member corresponds to the combination of carrier  36  and ring gear  24 . The third member corresponds to carrier  26 . Finally, the fourth member corresponds to the combination of sun gear  22  and sun gear  32 . 
         [0029]      FIG. 4  illustrates a transmission according to the present invention in which the epicyclic gearing assembly comprises two simple planetary gear sets  120  and  130  in a crossed ring carrier configuration. Carrier  136  is fixed to ring gear  124  and also to output element  12  through shell  90 . Carrier  126  is fixed to ring gear  134  and shell  80 . The first member corresponds to sun gear  132  which is fixed to shell  68 . The second member corresponds to the combination of carrier  136  and ring gear  124 . The third member corresponds to the combination of carrier  126  and ring gear  134 . Finally, the fourth member corresponds to sun gear  122  which is fixed to shell  56 .  FIG. 5  shows suggested tooth numbers for this embodiment and  FIG. 6  shows the resulting speed ratios. The operation of this embodiment is identical to the operation of the embodiment of  FIG. 1 . 
         [0030]      FIG. 7  illustrates a transmission according to the present invention in which the epicyclic gearing assembly is a Ravigneaux gear set  140 . A set of long planet gears  152  is supported for rotation on carrier  148  and meshes with both sun gear  142  and ring gear  146 . A set of short planet gears  150  is also supported for rotation on carrier  148  such that each short planet gear meshes with a corresponding long planet gear and with sun gear  144 . The first member corresponds to sun gear  144  which is fixed to shell  68 . The second member corresponds to ring gear  146  which is fixed to output element  12  through shell  90 . The third member corresponds to carrier  148  which is fixed to shell  80 . Finally, the fourth member corresponds to sun gear  142  which is fixed to shell  56 .  FIG. 8  shows suggested tooth numbers for this embodiment and  FIG. 9  shows the resulting speed ratios. The operation of this embodiment is identical to the operation of the embodiment of  FIG. 1 . 
         [0031]    Other types of epicyclic gearing assemblies are known and may be substituted without departing from the present invention. These other known types include but are not limited to planetary gear sets with stepped planet gears and other combinations of two simple or double pinion planetary gear sets with two connections between elements. 
         [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.