Abstract:
A vehicle transmission includes an input member, an output member, a plurality of gear sets, first and second clutches, first and second actuators, and first and second bearings. The plurality of gear sets is disposed between the input member and the output member. The first and second clutches are selectively engaged to rotationally couple first and second pairs of the plurality of gear sets. The first and second actuators each have a stationary cylinder bore and a piston disposed in the stationary cylinder bore, where the pistons are substantially rotationally stationary. The first bearing is disposed between the first clutch and the nonrotating piston of the first actuator and the second bearing is disposed between the second clutch and the nonrotating piston of the second actuator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/529,800 filed on Aug. 31, 2011. The disclosure of the above application is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to transmissions, and more particularly to transmissions having clutch actuation assemblies with multiple hydraulic pistons. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0004]    Automatic transmissions provide a plurality of forward and reverse speeds or gear ratios by selectively actuating one or more brakes or clutches. A concentric slave cylinder assembly having concentric piston rings is often used to actuate two clutches that are located near each other, such as in a dual clutch transmission have two input shafts that each provide a subset of the available gear ratios. Each of the two input shafts is selectively coupled to an engine by use of one of these clutches. The radial stacking of the pistons results in a high linear speed of the outer actuator piston. To accommodate the high linear speed of the outer piston, bearings having high losses and rotating pistons are often used in the concentric slave cylinder assembly. The rotating seals used to accommodate rotating pistons have unfavorable fluid leakage characteristics and the high loss bearings contribute to in higher spin losses in the transmission. Thus, there is a need for a new and improved clutch actuation assembly that has improved bearing loss and fluid leakage characteristics. 
       SUMMARY 
       [0005]    A vehicle transmission includes an input member, an output member, a plurality of gear sets, first and second clutches, first and second actuators, and first and second bearings. The plurality of gear sets is disposed between the input member and the output member. The first and second clutches are selectively engaged to rotationally couple first and second pairs of the plurality of gear sets. The first and second actuators each have a stationary cylinder bore and a piston disposed in the stationary cylinder bore, where the pistons are substantially rotationally stationary. The first bearing is disposed between the first clutch and the nonrotating piston of the first actuator and the second bearing is disposed between the second clutch and the nonrotating piston of the second actuator. 
         [0006]    In another aspect of the present invention, the first actuator and the second actuator are axially separated and at least partially aligned in a radial direction. 
         [0007]    In yet another aspect of the present invention, a diameter of the nonrotating piston of the first actuator is substantially the same as a diameter of the nonrotating piston of the second actuator. 
         [0008]    In yet another aspect of the present invention, the plurality of gear sets includes four planetary gear sets. 
         [0009]    In yet another aspect of the present invention, the vehicle transmission further includes first, second, third, and fourth brakes. 
         [0010]    In yet another aspect of the present invention, the vehicle transmission further includes an interconnecting member continuously connecting a first rotary member and a seventh rotary member. The plurality of gear sets further includes first, second, third, and fourth planetary gear sets. The first and a second planetary gear set each have a first, a second, and a third member. Each of the first, second, and third members is included in one of the first rotary member, a second rotary member, a third rotary member, and a fourth rotary member, and two of the members of the first planetary gear set are directly separately connected with two of the members of the second planetary gear set to form the first and the second rotary members and the fourth rotary member is directly connected to the input member. The third and a fourth planetary gear set each have a first, a second, and a third member. Each of the first, second, and third members is included in one of a fifth rotary member, a sixth rotary member, the seventh rotary member, and an eighth rotary member. Two of the members of the third planetary gear set are directly separately connected with two of the members of the fourth planetary gear set to form the fifth and sixth rotary members and the sixth rotary member is directly connected to the output member. 
         [0011]    In yet another aspect of the present invention, the first clutch is selectively engageable to connect the fourth rotary member with the fifth rotary member. 
         [0012]    In yet another aspect of the present invention, the second clutch is selectively engageable to connect the fourth rotary member with the eighth rotary member. 
         [0013]    In yet another aspect of the present invention, the first brake is selectively engageable to connect the third rotary member with a stationary member. 
         [0014]    In yet another aspect of the present invention, the second brake is selectively engageable to connect the second rotary member with the stationary member. 
         [0015]    In yet another aspect of the present invention, the third brake is selectively engageable to connect the first rotary member, the interconnecting member, and the seventh rotary member with the stationary member. 
         [0016]    In yet another aspect of the present invention, the fourth brake is selectively engageable to connect the fifth rotary member with the stationary member. 
         [0017]    In yet another aspect of the present invention, the third member of the first planetary gear set and the third member of the second planetary gear set form the first rotary member, the second member of the first planetary gear set and the second member of the second planetary gear set form the second rotary member, the first member of the first planetary gear set forms the third rotary member, the first member of the second planetary gear set forms the fourth rotary member, the third member of the third planetary gear set and the third member of the fourth planetary gear set form the fifth rotary member, the second member of the third planetary gear set and the second member of the fourth planetary gear set form the sixth rotary member, the first member of the third planetary gear set forms the seventh rotary member, and the first member of the fourth planetary gear set forms the eighth rotary member. 
         [0018]    In yet another aspect of the present invention, the first members of the first, second, third, and fourth planetary gear sets are sun gears, the second member of the first planetary gear set and the second member of the second planetary gear set are combined to form a single ring gear, the second member of the third planetary gear set and the third member of the fourth planetary gear set are ring gears, the third member of the first planetary gear set and the third member of the second planetary gear set are combined to form a single carrier member, and the third member of the third planetary gear set and the second member of the fourth planetary gear set are carrier members. 
         [0019]    A clutch actuation assembly includes a first piston assembly and a second piston assembly. The first piston assembly includes a piston, an apply member, and a bearing. The second piston assembly includes a piston, an apply member, and a bearing. The piston of the first piston assembly is axially separated from and at least partially aligned with the piston of the second piston assembly in a radial direction. 
         [0020]    In another aspect of the present invention, the bearing members are disposed between the respective apply member and piston of the first and second piston assemblies at an inner radial portion of the piston members. 
         [0021]    In yet another aspect of the present invention, the apply members are rotationally coupled with and axially translatable through a hub of the first and second clutches. 
         [0022]    In another embodiment of the present invention, a transmission having four planetary gear sets representable by a first lever and a second lever each having four nodes is provided. The transmission includes a first clutch and a second clutch each selectively connectable between an input member and a node of the second lever. The transmission includes a clutch actuation assembly to actuate the first and second clutches. The clutch actuation assembly includes a first piston assembly and a second piston assembly. The first piston assembly includes a piston, an apply member, and a bearing. The second piston assembly includes a piston, an apply member, and a bearing. The piston of the first piston assembly is axially separated from and at least partially aligned with the piston of the second piston assembly in a radial direction. 
         [0023]    In another embodiment of the present invention, a transmission having and input and first, second, third, and fourth planetary gear sets each having a sun gear, a carrier member, and a ring gear is provided. The transmission includes a first clutch selectively engageable to rotationally couple the input member with the carrier member of the third planetary gear set and a second clutch selectively engageable to rotationally couple the input member with the sun gear of the fourth planetary gear set. The clutch actuation assembly includes a first piston assembly and a second piston assembly. The first piston assembly includes a piston, an apply member, and a bearing. The second piston assembly includes a piston, an apply member, and a bearing. The piston of the first piston assembly is axially separated from and at least partially aligned with the piston of the second piston assembly in a radial direction. 
         [0024]    Further features, aspects, and advantages of the present invention will become apparent by reference to the following description and appended drawings wherein like reference numbers refer to the same component, element or feature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0026]      FIG. 1A  is a lever diagram of a vehicle transmission including a clutch actuation assembly according to an embodiment of the present invention; 
           [0027]      FIG. 1B  is a lever diagram of a vehicle transmission including a clutch actuation assembly according to an embodiment of the present invention; 
           [0028]      FIG. 2  is a schematic diagram of an embodiment of a vehicle transmission including a clutch actuation assembly in accordance with an embodiment of the present invention; 
           [0029]      FIG. 3  is a truth table presenting the state of engagement of the various torque transmitting elements in each of the available forward and reverse speeds or gear ratios of the transmission illustrated in  FIG. 2 ; and 
           [0030]      FIG. 4  is a cross-section view of a clutch actuation assembly in accordance with an embodiment of the present invention. 
       
    
    
     DESCRIPTION 
       [0031]    Referring now to  FIG. 1A , an embodiment of a nine speed transmission  10  is illustrated in a lever diagram format. A lever diagram is a schematic representation of the components of a mechanical device such as an automatic transmission. Each individual lever with three nodes represents a planetary gear set wherein the three basic mechanical components of the planetary gear set are each represented by a node. Therefore, the three nodes of a three node lever each represent one of a sun gear, a planet gear carrier, and a ring gear. The relative length between the nodes of each lever can be used to represent the ring-to-sun ratio of each respective gear set. These lever ratios, in turn, are used to vary the gear ratios of the transmission in order to achieve appropriate ratios and ratio progression. Mechanical couplings or interconnections between the nodes of the various planetary gear sets are illustrated by thin, horizontal lines and torque transmitting devices such as clutches and brakes are presented as interleaved fingers. If the device is a brake, one set of the fingers is grounded. Furthermore, multiple gear sets sharing common connections may be combined into a lever having more nodes. For example, two three-node gear sets that share two common connections may be combined into a single four node lever. Further explanation of the format, purpose and use of lever diagrams can be found in SAE Paper 810102, “The Lever Analogy: A New Tool in Transmission Analysis” by Benford and Leising which is hereby fully incorporated by reference. 
         [0032]    The transmission  10  includes an input shaft or member  12  and a first lever  11  that represents a combination of a first planetary gear set and a second planetary gear set. Thus, two fixed connections are present between the components of the first and second planetary gear set. The first lever  11  includes a first node A, a second node B, a third node C, and a fourth node D. A second lever  13  represents a combination of a third planetary gear set and a fourth planetary gear set. Thus, two fixed connections are present between the components of the third and fourth planetary gear set. The second lever  13  includes a first node E, a second node F, a third node G, and a fourth node H. The first node A of the first lever  11  is connected for common rotation with the input shaft or member  12 . The second node F of the second lever  13  is connected for common rotation with an output shaft or member  22 . The third node C of the first lever  11  is connected for common rotation with the fourth node H of the second lever  13 . 
         [0033]    A first clutch  26  selectively connects the first node A of the first lever  11  with the third node G of the second lever  13 . A second clutch  28  selectively connects the first node A of the first lever  11  with the first node E of the second lever  13 . The first and second clutches  26 ,  28  are actuated by a dual clutch actuation assembly  29 , as will be described below. 
         [0034]    A first brake  30  selectively connects the fourth node D of the first lever  11  to a stationary member or a transmission housing  40 . A second brake  32  selectively connects the second node B of the first lever  11  to the stationary member or transmission housing  40 . A third brake  34  selectively connects the third node C of the first lever  11  and the fourth node H of the second lever  13  to the stationary member or transmission housing  40 . A fourth brake  36  selectively connects the third node G of the second lever  13  to the stationary member or transmission housing  40 . In the example provided the clutches  26 ,  28  and brakes  30 ,  32 ,  34 ,  36  are friction clutches each having first friction members interleaved with second friction members. It should be appreciated that other torque transmitting mechanisms, such as dog clutches, selectable one-way clutches, and bands may be incorporated without departing from the scope of the present invention. 
         [0035]    Referring now to  FIGS. 1A and 1B , wherein like numbers refer to like components, a transmission  10 ′ is represented by an example of a three node lever diagram that corresponds to the four node diagram of  FIG. 1A . The lever diagram of the transmission  10 ′ has four levers each with three nodes. Each of the three node levers represents a planetary gear set having a sun gear, a ring gear, and a planetary gear carrier. In the example provided, a first gear set  11 A and a second gear set  11 B have two continuous connections between each other so that they can be represented by the first lever  11  of  FIG. 1A . A third gear set  13 A and a fourth gear set  13 B have two continuous connections between each other so that they can be represented by the second lever  13  of  FIG. 1A . 
         [0036]    Referring now to  FIG. 2 , a stick diagram presents a schematic layout of an embodiment of a nine speed transmission  100  according to the present invention. More specifically, the schematic diagram of  FIG. 2  is an example of a planetary gear set configuration according to the four node lever diagram describing the transmission  10  of  FIG. 1  and like numbers refer to like components. The clutches, brakes, and couplings are correspondingly presented whereas the nodes of the levers  11 ,  13  are now represented by components of planetary gear sets such as sun gears, ring gears, planet gears and planet gear carriers. For example, the first lever  11  of  FIG. 1  is now represented by a first planetary gear set  114  and a second planetary gear set  116  that are combined to form a planetary gear set assembly  127 . The second lever  13  is now represented by interconnected planetary gear sets  120 ,  121 . Planetary gear set assembly  127  includes sun gear members  114 B/ 116 B and  116 A, a ring gear member  118 A, and a planet gear carrier member  114 A that rotatably supports a first set of planet gears  129  (only one of which is shown) and a second set of planet gears  131  (only one of which is shown). The planet gears  129  are long pinion gears that have a first end  129   a  and a second end  129   b.  The planet gears  129  are each configured to intermesh with both the sun gear member  114 B/ 116 B at the first end  129   a  and intermesh with the ring gear member  118 A and the second set of planet gears  131  at the second end  129   b.  The second set of planet gears  131  are each configured to intermesh with both the sun gear member  116 A and the first set of planet gears  129 . The sun gear member  114 B/ 116 B is coupled to an interconnecting member or shaft  132 . The ring gear member  118 A is coupled to an interconnecting member of shaft  134 . The planet carrier member  114 A is coupled to an interconnecting member or shaft  136  and an interconnecting member or shaft  138 . Sun gear member  116 A is connected for common rotation with the input shaft  12  and an interconnecting member or shaft  140 . 
         [0037]    Planetary gear set  120  includes a sun gear member  120 A, a ring gear member  120 C, and a planet gear carrier member  120 B that rotatably supports a plurality of planet gears  120 D (only one of which is shown). The sun gear member  120 A is connected for common rotation with the interconnecting member  138 . The carrier member  120 B is connected for common rotation with an interconnecting member or shaft  142  and an interconnecting member or shaft  144 . The ring gear member  120 C is connected for common rotation with an interconnecting member or shaft  146 . The planet gears  120 D are each intermeshed with both the sun gear member  120 A and the ring gear member  120 C. 
         [0038]    Planetary gear set  121  includes a sun gear member  121 A, a ring gear member  121 C, and a planet gear carrier member  121 B that rotatably supports a plurality of planet gears  121 D (only one of which is shown). The sun gear member  121 A is connected for common rotation with an interconnecting member or shaft  148 . The carrier member  121 B is connected for common rotation with the interconnecting member  146  and the output shaft  22 . The ring gear member  121 C is connected for common rotation with the interconnecting member  144 . The planet gears  121 D are each intermeshed with both the sun gear member  121 A and the ring gear member  121 C. 
         [0039]    The first clutch  26  selectively connects the interconnecting member  140  with the interconnecting member  142 . The second clutch  28  selectively connects the interconnecting member  140  with the interconnecting member  148 . The first brake  30  selectively connects the interconnecting member  132  to the housing  40  in order to restrict rotation of the member  132 . The second brake  32  selectively connects the interconnecting member  134  to the housing  40  in order to restrict rotation of the member  134 . The third brake  34  selectively connects the interconnecting member  136  with the housing  40  in order to restrict rotation of the member  136 . The fourth brake  36  selectively connects the interconnecting member  144  with the housing  40  in order to restrict rotation of the member  144 . 
         [0040]    Referring now to  FIG. 3 , a truth table presenting the various combinations of torque transmitting mechanisms that are activated or engaged to achieve the various gear states of transmission  100  is shown. Actual numerical gear ratios of the various gear states are also presented although it should be appreciated that these numerical values are exemplary only and that they may be adjusted over significant ranges to accommodate various applications and operational criteria of the transmission  100 . An example of the gear ratios that may be obtained using the embodiments of the present invention are also shown in  FIG. 3 . Of course, other gear ratios are achievable depending on the gear diameter, gear teeth count and gear configuration selected. 
         [0041]    Referring now to  FIG. 4 , wherein like reference numbers refer to like components, a cross sectional view of the dual clutch actuator assembly  29  is shown in the transmission  100 . It should be appreciated that the clutch actuator assembly  29  may be incorporated in other transmissions without departing from the scope of the present invention. The clutch actuator assembly  29  includes a first piston assembly  202  and a second piston assembly  204  for actuating the first and second clutches  26 ,  28 . The first piston assembly  202  is axially separated from and at least partially aligned with the second piston assembly  204  in a radial direction. 
         [0042]    The first piston assembly  202  includes a piston  210 , an apply member  212 , a bearing  214 , a spring  215 , and a cylinder  216 . The piston  210  is disposed in the cylinder  216  formed in a separating member  217  connected to a stationary housing member  218 . The separating member  217  projects radially outward from the housing member  218  near an axial midpoint of the housing member  218 . The piston  210  seals against the cylinder  216  and forms a hydraulic chamber  220  in combination with the separating member  217  for actuation of the first piston assembly  202 . The apply member  212  rotates with a hub  221  of the clutches  26 ,  28  that is rotationally coupled with the input member  12 . The apply member  212  includes a first end  222  adjacent the piston  210  and a second end  224  adjacent the first clutch  26 . The second end  224  slides axially through an opening in the hub  221  to compress or release the clutch  26 . The bearing  214  is disposed between the first end  222  of the apply member  212  and an inner radial portion of the piston  210  to allow relative rotation between the stationary piston  210  and the rotating apply member  212 . The spring  215  is disposed between the apply member  212  and the hub  221  to bias the apply member  212  away from the clutch  26 . 
         [0043]    The second piston assembly  204  includes a piston  230 , an apply member  232 , a bearing  234 , a spring  235 , and a cylinder  236 . The piston  230  opposes a back side of the separating member  217  and the piston  230  is substantially aligned with the piston  210  along a radial direction from an axis of the transmission  100 . Additionally, the bearing  234  is disposed at a radial distance from the axis of the transmission that is substantially similar to that of the bearing  214 . The piston  230  is disposed in the cylinder  236  that is formed in the stationary housing member  218 . The piston  230  seals against the cylinder  236  and forms a hydraulic chamber  240  in combination with the housing member  218  for actuation of the second piston assembly  204 . The apply member  232  rotates with the hub  221  of the clutches  26 ,  28  and includes a first end  242  adjacent the piston  230  and a second end  244  adjacent the second clutch  28 . The second end  244  slides axially through an opening in the hub  221  to compress or release the clutch  28 . The bearing  234  is disposed between the first end  242  of the apply member  232  and an inner radial portion of the piston  230  to allow relative rotation between the stationary piston  230  and the rotating apply member  232 . In the example provided, the bearing  234  is a low loss thrust ball type bearing. The spring  235  is disposed between the apply member  232  and the hub  221  to bias the apply member  232  away from the clutch  28 . 
         [0044]    Because the second piston assembly  204  is axially separated from the first piston assembly  202 , the piston  230  has a large cross section without interfering with the piston  210  to allow reduced pressure requirements for a given torque requirement of the clutch  28 . Additionally, the bearing  234  is disposed relatively close to an axis of rotation of the transmission  100 . Accordingly, the linear speed difference between the apply member  232  and the piston  230  is reduced relative to radially stacked concentric slave cylinders, and therefore the piston  210  may remain non-rotating and may include non-rotating seals to provide favorable hydraulic fluid leakage characteristics from the chamber  240 . 
         [0045]    Referring now to  FIGS. 2 and 4 , the operation of the clutch actuation assembly  29  will be described. When actuation of the first clutch  26  is desired, a pressurized hydraulic fluid is directed to the chamber  220 . The hydraulic fluid presses the piston  210  away from a base of the cylinder  216 . The piston  210  presses the first end  222  of the apply member  212  through the bearing  214 . The second end  224  of the apply member  212  compresses the first clutch  26  to rotationally couple the hub  221  and input member  12  to the carrier member of the planetary gear set  120 . To release the clutch  26  and allow rotation between the input member  12  and the carrier member of the planetary gear set  120 , the hydraulic fluid is evacuated from the chamber  220  and the spring  215  presses the apply member  212  and the piston  210  away from the clutch  26 . 
         [0046]    When actuation of the second clutch  28  is desired, a pressurized hydraulic fluid is directed to the chamber  240 . The hydraulic fluid presses the piston  230  away from a base of the cylinder  236 . The piston  230  presses the first end  242  of the apply member  232  through the bearing  234 . The second end  244  of the apply member  232  compresses the second clutch  28  to rotationally couple the hub  221  and input member  12  to the sun gear of the planetary gear set  121 . To release the clutch  28  and allow rotation between the input member  12  and the sun gear of the planetary gear set  121 , the hydraulic fluid is evacuated from the chamber  240  and the spring  235  presses the apply member  232  and the piston  230  away from the clutch  28 . 
         [0047]    The present invention provides several beneficial attributes. For example, the assembly provides beneficial spin loss characteristics and a low loss bearing is incorporated due to the low linear speed of the outer bearing. Additionally, the stationary pistons employ non-rotating seals to provide favorable oil leakage characteristics and hydraulic pressure requirements. 
         [0048]    The description of the invention is merely exemplary in nature and variations that do not depart from the general essence of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.