Abstract:
A transmission of the present invention has an input member, an output member, four planetary gear sets, a plurality of coupling members and a plurality of torque transmitting devices. Each of the planetary gear sets includes a sun gear, a carrier member supporting a plurality of planet pinion gears and a ring gear member. The torque transmitting devices may include clutches and brakes. The torque transmitting devices are selectively engageable in combinations of at least three to establish a plurality forward speed ratios and at least one reverse speed ratio.

Description:
FIELD 
       [0001]    The invention relates generally to a multiple speed transmission having a plurality of planetary gear sets and a plurality of torque transmitting devices, and more particularly to a transmission having eight or more speeds, four planetary gear sets and a plurality of torque transmitting devices. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0003]    A typical multiple speed transmission uses a combination of friction clutches or brakes, planetary gear arrangements and fixed interconnections to achieve a plurality of gear ratios. The number and physical arrangement of the planetary gear sets, generally, are dictated by packaging, cost and desired speed ratios. 
         [0004]    While current transmissions achieve their intended purpose, the need for new and improved transmission configurations which exhibit improved performance, especially from the standpoints of efficiency, responsiveness and smoothness and improved packaging, primarily reduced size and weight, is essentially constant. Accordingly, there is a need for an improved, cost-effective, compact multiple speed transmission. 
       SUMMARY 
       [0005]    A transmission is provided having an input member, an output member, four planetary gear sets, a plurality of coupling members and a plurality of torque transmitting devices. Each of the planetary gear sets includes first, second and third members. The torque transmitting devices are for example clutches and brakes. 
         [0006]    In an embodiment of the present invention, a transmission is provided having an input member, an output member, a first, second, third and fourth planetary gear sets each having sun gears, carrier members and ring gears. 
         [0007]    In another embodiment of the present invention, the input member is continuously interconnected with the sun gear of the first planetary gear set. 
         [0008]    In yet another embodiment of the present invention, the output member is continuously interconnected with the carrier member of the fourth planetary gear set. 
         [0009]    Additionally, in another embodiment of the present invention, a first interconnecting member continuously interconnects the carrier member of the first planetary gear set with the ring gear of the second planetary gear set. 
         [0010]    In yet another embodiment of the present invention, a second interconnecting member continuously interconnects the sun gear of the second planetary gear set with the sun gear of the third planetary gear set 
         [0011]    In yet another embodiment of the present invention, a third interconnecting member continuously interconnects the carrier member of the second planetary gear set with the ring gear of the third planetary gear set. 
         [0012]    In yet another embodiment of the present invention, a fourth interconnecting member continuously interconnects the carrier member of the third planetary gear set with the ring gear of the fourth planetary gear set. 
         [0013]    Further, in still another embodiment of the present invention, a first torque transmitting device is selectively engageable to interconnect the input member and the sun gear of the first planetary gear set with the sun gear of the second planetary gear set and the sun gear of the third planetary gear set. 
         [0014]    In still another embodiment of the present invention, a second torque transmitting device is selectively engageable to interconnect the input member and the sun gear of the first planetary gear set with the carrier member of the second planetary gear set and the ring gear of the third planetary gear set. 
         [0015]    In still another embodiment of the present invention, a third torque transmitting device is selectively engageable to interconnect the carrier member of the third planetary gear set with the ring gear of the fourth planetary gear set. 
         [0016]    In still another embodiment of the present invention, a fourth torque transmitting device is selectively engageable to interconnect the ring gear of the first planetary gear set with the stationary member. 
         [0017]    In still another embodiment of the present invention, a fifth torque transmitting device is selectively engageable to interconnect the carrier member of the first planetary gear set and the ring gear of the second planetary gear set with the stationary member. 
         [0018]    In still another embodiment of the present invention, a sixth torque transmitting device is selectively engageable to interconnect the carrier member of the second planetary gear set and the ring gear of the third planetary gear set with the stationary member. 
         [0019]    In still another embodiment of the present invention, a seventh torque transmitting device is selectively engageable to interconnect the sun gear of the fourth planetary gear set with the stationary member. 
         [0020]    In still another embodiment of the present invention, the torque transmitting devices are each selectively engageable in combinations of at least three to establish at least eight forward speed ratios and at least one reverse speed ratio between the input member and the output member. 
         [0021]    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. 
     
    
     
       DRAWINGS 
         [0022]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0023]      FIG. 1  is a schematic layout of an embodiment of an eight speed transmission according to the present invention; and 
           [0024]      FIG. 2  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. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0026]    Referring now to  FIG. 1 , a stick diagram presents a schematic layout of the embodiment of the eight speed transmission  10  according to the present invention. The transmission  10  includes an input shaft or member  12 , a first planetary gear set  14 , a second planetary gear set  16 , a third planetary gear set  18 , a fourth planetary gear set  20  and an output shaft or member  22 . 
         [0027]    The planetary gear set  14  further includes a sun gear member  14 A, a ring gear member  14 C and a planet gear carrier member  14 B that rotatably supports a set of planet gears  14 D (only one of which is shown). The set of planet gears  14 D are each configured to intermesh with both the sun gear member  14 A and the ring gear member  14 C. The sun gear member  14 A is connected for common rotation with an input shaft or member  12 . The ring gear member  14 C is connected for common rotation with a first shaft or interconnecting member  44 . The planet carrier member  14 B is connected for common rotation with a second shaft or interconnecting member  46 . 
         [0028]    The planetary gear set  16  further includes a sun gear member  16 A, a ring gear member  16 C and a planet gear carrier member  16 B that rotatably supports a set of planet gears  16 D (only one of which is shown). The planet gears  16 D are each configured to intermesh with both the sun gear member  16 A and the ring gear member  16 C. The sun gear member  16 A is connected for common rotation with the third shaft or interconnecting member  48 . The ring gear member  16 C is connected for common rotation with the second shaft or interconnecting member  46 . The planet carrier member  16 B is connected for common rotation with a fourth shaft or interconnecting member  50  and with a fifth shaft or interconnecting member  52 . 
         [0029]    The planetary gear set  18  includes a sun gear member  18 A, a ring gear member  18 C and a planet gear carrier member  18 B that rotatably supports a set of planet gears  18 D (only one of which is shown). The set of planet gears  18 D are each configured to intermesh with both the sun gear member  18 A and the ring gear member  18 C. The sun gear member  18 A is connected for common rotation with the third shaft or interconnecting member  48 . The ring gear member  18 C is connected for common rotation with the fifth shaft or interconnecting member  52 . The planet carrier member  18 B is connected for common rotation with a sixth shaft or interconnecting member  54 . 
         [0030]    The planetary gear set  20  includes a sun gear member  20 A, a ring gear member  20 C and a planet gear carrier member  20 B that rotatably supports a set of planet gears  20 D (only one of which is shown). The set of planet gears  20 D are each configured to intermesh with both the sun gear member  20 A and the ring gear member  20 C. The sun gear member  20 A is connected for common rotation with a seventh shaft or interconnecting member  56 . The ring gear member  20 C is connected for common rotation with the sixth shaft or interconnecting member  54 . The planet carrier member  20 B is connected for common rotation with the output shaft or member  22 . 
         [0031]    The input shaft or member  12  is continuously connected to an engine (not shown) or to a turbine of a torque converter (not shown). The output shaft or member  22  is continuously connected with the final drive unit or transfer case (not shown). 
         [0032]    With continued reference to  FIG. 1 , transmission  10  further includes torque-transmitting mechanisms or clutches  24 ,  26 ,  28  and the brakes  30 ,  32 ,  34  and  36 . Clutches  24 ,  26  and  28  are configured to selectively interconnect the shafts or interconnecting members and the members of the planetary gear set, as will be described in detail below. The brakes  30 ,  32 ,  34  and  36  are configured to selectively interconnect the shafts or interconnecting members and members of the planetary gear sets to a transmission housing  40 , as will be described in detail below. For example, the first clutch  24  is selectively engageable to connect the input shaft or member  12  with the third shaft or interconnecting member  48 . The second clutch  26  is selectively engageable to connect the input shaft  12  with the fourth shaft or interconnecting member  50 . The third clutch  28  is selectively engageable to connect the sixth shaft or interconnecting member  54  with the seventh shaft or interconnecting member  56 . The first brake  30  is selectively engageable to connect the first shaft or interconnecting member  44  with a stationary element or the transmission housing  40  in order to prevent the first shaft or interconnecting member  44  from rotating relative to the transmission housing  40 . The second brake  32  is selectively engageable to connect the second shaft or interconnecting member  46  with a stationary element or the transmission housing  40  in order to prevent the second shaft or interconnecting member  46  from rotating relative to the transmission housing  40 . The third brake  34  is selectively engageable to connect the fifth shaft or interconnecting member  52  with the stationary element or the transmission housing  40  in order to prevent the fifth shaft or interconnecting member  52  from rotating relative to the transmission housing  40 . The fourth brake  36  is selectively engageable to connect the seventh shaft or interconnecting member  56  with the stationary element or the transmission housing  40  in order to prevent the seventh shaft or interconnecting member  56  from rotating relative to the transmission housing  40 . 
         [0033]    Referring now to  FIGS. 1 and 2 , the operation of the embodiment of the eight speed transmission  10  will be described. It will be appreciated that the transmission  10  is capable of transmitting torque from the input shaft or member  12  to the output shaft or member  22  in at least eight forward speed or torque ratios and at least one reverse speed or torque ratio with a double overdrive. Each forward and reverse speed or torque ratio is attained by engagement of one or more of the torque-transmitting mechanisms (i.e. first clutch  24 , second clutch  26 , third clutch  28 , first brake  30 , second brake  32 , third brake  34  and fourth brake  36 ), as will be explained below.  FIG. 2  is a clutch table presenting the various combinations of torque-transmitting elements that are activated or engaged to achieve the various gear states. 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  10 . Of course, other gear ratios are achievable depending on the gear diameter, gear teeth count and gear configuration selected. 
         [0034]    For example, to establish reverse gear, the third clutch  28 , the first brake  30  and third brake  34  are engaged or activated. More specifically, the third clutch  28  is engaged to connect the sixth shaft or interconnecting member  54  with the seventh shaft or interconnecting member  56 . The first brake  30  connects the first shaft or interconnecting member  44  with the stationary element or the transmission housing  40  in order to prevent the first shaft or interconnecting member  44  from rotating relative to the transmission housing  40 . The third brake  34  connects the fifth shaft or interconnecting member  52  with the stationary element or the transmission housing  40  in order to prevent the fifth shaft or interconnecting member  52  from rotating relative to the transmission housing  40 . Thus, a reverse gear ratio is established between the input member  12  and the output member  22 . 
         [0035]    A first gear is established by engaging or activating the first clutch  24 , the third brake  34  and fourth brake  36 . More specifically, the first clutch  24  is engaged to connect the input shaft or member  12  with the third shaft or interconnecting member  48 . The third brake  34  connects the fifth shaft or interconnecting member  52  with the stationary element or the transmission housing  40  in order to prevent the fifth shaft or interconnecting member  52  from rotating relative to the transmission housing  40 . The fourth brake  36  connects the seventh shaft or interconnecting member  56  with the stationary element or the transmission housing  40  in order to prevent the seventh shaft or interconnecting member  56  from rotating relative to the transmission housing  40 . Thus, a first gear ratio is established between the input member  12  and the output member  22 . 
         [0036]    A second gear is established by engaging or activating, the first clutch  24 , the third clutch  28  and third brake  34 . More specifically, the first clutch  24  is engaged to connect the input shaft or member  12  with the third shaft or interconnecting member  48 . The third clutch  28  connects the sixth shaft or interconnecting member  54  with the seventh shaft or interconnecting member  56 . The third brake  34  connects the fifth shaft or interconnecting member  52  with the stationary element or the transmission housing  40  in order to prevent the fifth shaft or interconnecting member  52  from rotating relative to the transmission housing  40 . Thus, a second gear ratio is established between the input member  12  and the output member  22 . 
         [0037]    A third gear is established by engaging or activating the first clutch  24 , the second brake  32  and fourth brake  36 . More specifically, the first clutch  24  is engaged to connect the input shaft or member  12  with the third shaft or interconnecting member  48 . The second brake  32  connects the second shaft or interconnecting member  46  with a stationary element or the transmission housing  40  in order to prevent the second shaft or interconnecting member  46  from rotating relative to the transmission housing  40 . The fourth brake  36  connects the seventh shaft or interconnecting member  56  with the stationary element or the transmission housing  40  in order to prevent the seventh shaft or interconnecting member  56  from rotating relative to the transmission housing  40 . Thus, a third gear ratio is established between the input member  12  and the output member  22 . 
         [0038]    A fourth gear is established by engaging or activating the first clutch  24 , the third clutch  28  and second brake  32 . More specifically, the first clutch  24  is engaged to connect the input shaft or member  12  with the third shaft or interconnecting member  48 . The third clutch  28  connects the sixth shaft or interconnecting member  54  with the seventh shaft or interconnecting member  56 . The second brake  32  connects the second shaft or interconnecting member  46  with a stationary element or the transmission housing  40  in order to prevent the second shaft or interconnecting member  46  from rotating relative to the transmission housing  40 . Thus, a fourth gear ratio is established between the input member  12  and the output member  22 . 
         [0039]    A fifth gear is established by engaging or activating the first clutch  24 , the third clutch  28  and first brake  30 . More specifically, the first clutch  24  is engaged to connect the input shaft or member  12  with the third shaft or interconnecting member  48 . The third clutch  28  connects the sixth shaft or interconnecting member  54  with the seventh shaft or interconnecting member  56 . The first brake  30  connects the first shaft or interconnecting member  44  with the stationary element or the transmission housing  40  in order to prevent the first shaft or interconnecting member  44  from rotating relative to the transmission housing  40 . Thus, a fifth gear ratio is established between the input member  12  and the output member  22 . 
         [0040]    A sixth gear is established by engaging or activating the first clutch  24 , the second clutch  26  and the third clutch  28 . More specifically, the first clutch  24  is engaged to connect the input shaft or member  12  with the third shaft or interconnecting member  48 . The second clutch  26  connects the input shaft  12  with the fourth shaft or interconnecting member  50 . The third clutch  28  connects the sixth shaft or interconnecting member  54  with the seventh shaft or interconnecting member  56 . Thus, a sixth gear ratio is established between the input member  12  and the output member  22 . 
         [0041]    A seventh gear is established by engaging or activating the second clutch  26 , the third clutch  28  and first brake  30 . More specifically, the second clutch  26  connects the input shaft  12  with the fourth shaft or interconnecting member  50 . The third clutch  28  connects the sixth shaft or interconnecting member  54  with the seventh shaft or interconnecting member  56 . The first brake  30  connects the first shaft or interconnecting member  44  with the stationary element or the transmission housing  40  in order to prevent the first shaft or interconnecting member  44  from rotating relative to the transmission housing  40 . Thus, a seventh gear ratio is established between the input member  12  and the output member  22 . 
         [0042]    An eighth gear is established by engaging or activating the second clutch  26 , the third clutch  28  and second brake  32 . More specifically, the second clutch  26  connects the input shaft  12  with the fourth shaft or interconnecting member  50 . The third clutch  28  connects the sixth shaft or interconnecting member  54  with the seventh shaft or interconnecting member  56 . The second brake  32  connects the second shaft or interconnecting member  46  with a stationary element or the transmission housing  40  in order to prevent the second shaft or interconnecting member  46  from rotating relative to the transmission housing  40 . Thus, an eighth gear ratio is established between the input member  12  and the output member  22 . 
         [0043]    It will be appreciated that the foregoing explanation of operation and gear states of the eight speed transmission  10  assumes, first of all, that all the clutches and brakes not specifically referenced in a given gear state are inactive or disengaged and, second of all, that during gear shifts, i.e., changes of gear state, between at least adjacent gear states, a clutch or brake engaged or activated in both gear states will remain engaged or activated. 
         [0044]    The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. For example, the present invention contemplates that multiple components, i.e. members of the planetary gear sets, maybe formed integrally with an interconnecting member or shaft to form a single member which may be rotatable or fixed. Moreover, two or more shafts or interconnecting members may be joined to form a single member or shaft. Additionally, the present invention contemplates several alternatives to increase the number of ranges and ratio spreads of the transmission  10 . More specifically, the clutched, input and output planetary components may be changed to add overdrive ranges instead of under drive ranges. The planetary gear set  20  and clutch  28  may be housed in a separate housing from a housing that houses planetary gear sets  14 ,  16  and  18 . Alternatively, planetary gear set  20  and clutch  28  may be housed in an AWD/4WD transfer case to conserve space. Such variations are not to be regarded as a departure from the spirit and scope of the invention.