Abstract:
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. A first interconnecting member continuously interconnects the third member of the first planetary gear set with a stationary member, a second interconnecting member continuously interconnects the first member of the second planetary gear set with the stationary member, a third interconnecting member continuously interconnects the third member of the second planetary gear set with the first member of the third planetary gear set, and a fourth interconnecting member continuously interconnects the third member of the third planetary gear set with a third member of the fourth planetary gear set. The torque transmitting devices may include clutches.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/917,115 filed on May 10, 2007. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     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 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     A typical multiple speed transmission uses a combination of torque transmitting devices, 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. 
     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 
     In an aspect of the present invention a transmission is provided. The transmission includes an input member, an output member first, second, third and fourth planetary gear sets each having first, second and third members, first, second, third, and fourth interconnecting members and five torque-transmitting mechanisms. The first interconnecting member continuously interconnects the third member of the first planetary gear set with a stationary member. The second interconnecting member continuously interconnects the first member of the second planetary gear set with the stationary member. The third interconnecting member continuously interconnects the third member of the second planetary gear set with the first member of the third planetary gear set. The fourth interconnecting member continuously interconnects the third member of the third planetary gear set with a third member of the fourth planetary gear set. The five torque-transmitting mechanisms are selectively engageable to interconnect one of the first, second, and third members with another of the first, second, and third members. The torque-transmitting mechanisms are 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. 
     In another aspect of the present invention a first of the five torque transmitting mechanisms is selectively engageable to interconnect the second member of the second planetary gear set with the second member of the fourth planetary gear set. 
     In yet another aspect of the present invention a second of the five torque transmitting mechanisms is selectively engageable to interconnect the second member of the third planetary gear set with the second member of the fourth planetary gear set. 
     In yet another aspect of the present invention a third of the five torque transmitting mechanisms is selectively engageable to interconnect the second member of the third planetary gear set with the second member of the first planetary gear set. 
     In yet another aspect of the present invention a fourth of the five torque transmitting mechanisms is selectively engageable to interconnect the first member of the fourth planetary gear set with the third member of the fourth planetary gear set. 
     In yet another aspect of the present invention a fifth of the five torque transmitting mechanisms is selectively engageable to interconnect the first member of the first planetary gear set with the first member of the fourth planetary gear set. 
     In yet another aspect of the present invention the first, the second, the third, the fourth, and the fifth torque transmitting mechanisms are clutches. 
     In yet another aspect of the present invention the first members are sun gears, the second members are carrier members, and the third members are ring gears. 
     In yet another aspect of the present invention the input member is continuously interconnected with the second member of the second planetary gear set and the output member is continuously interconnected with the second member of the first planetary gear set. 
     In still another aspect of the present invention a transmission is provided. The transmission includes an input member, an output member, a first, second, third and fourth planetary gear sets each having first, second and third members, a first, second, third and fourth interconnecting members and a first, second, third, fourth and fifth torque-transmitting mechanisms. The input member is continuously interconnected with the second member of the second planetary gear set, and the output member is continuously interconnected with the second member of the first planetary gear set. The first interconnecting member continuously interconnects the third member of the first planetary gear set with a transmission housing. The second interconnecting member continuously interconnects the first member of the second planetary gear set with the transmission housing. The third interconnecting member continuously interconnects the third member of the second planetary gear set with the first member of the third planetary gear set. The fourth interconnecting member continuously interconnects the third member of the third planetary gear set with a third member of the fourth planetary gear set. The first torque-transmitting mechanism is selectively engageable to interconnect the second member of the second planetary gear set with the second member of the fourth planetary gear set. The second torque-transmitting mechanism is selectively engageable to interconnect the second member of the third planetary gear set with the second member of the fourth planetary gear set. The third torque-transmitting mechanism is selectively engageable to interconnect the second member of the first planetary gear set with the second member of the third planetary gear set. The fourth torque-transmitting mechanism is selectively engageable to interconnect the first member of the fourth planetary gear set with the third member of the fourth planetary gear set. The fifth torque-transmitting mechanism is selectively engageable to interconnect the first member of the first planetary gear set with the first member of the fourth planetary gear set. The torque-transmitting mechanisms are 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. 
     In still another aspect of the present invention a transmission is provided. The transmission has an input member, an output member, a first, second, third and fourth planetary gear sets each having a sun gear, a carrier member, a ring gear, first, second, third and fourth interconnecting members and first, second, third, fourth, and fifth torque-transmitting mechanisms. The input member is continuously interconnected with the carrier member of the second planetary gear set, and the output member is continuously interconnected with the carrier member of the first planetary gear set. The first interconnecting member continuously interconnects the ring gear of the first planetary gear set with the stationary member. The second interconnecting member continuously interconnects the sun gear of the first planetary gear set with the stationary member. The third interconnecting member continuously interconnects the ring gear of the second planetary gear set with the sun gear of the third planetary gear set. The fourth interconnecting member continuously interconnects the ring gear of the third planetary gear set with ring gear of the fourth planetary gear set. The first torque-transmitting mechanism is selectively engageable to interconnect the input member and the carrier member of the second planetary gear set with the carrier member of the fourth planetary gear set. The second torque-transmitting mechanism is selectively engageable to interconnect the carrier member of the third planetary gear set with carrier member of the fourth planetary gear set. The third torque-transmitting mechanism is selectively engageable to interconnect the carrier member of the third planetary gear set with the carrier member of the first planetary gear set. The fourth torque-transmitting mechanism is selectively engageable to interconnect the sun gear of the fourth planetary gear set with the ring gear of the fourth planetary gear set. The fifth torque-transmitting mechanism is selectively engageable to interconnect the sun gear of the first planetary gear set with sun gear of the fourth planetary gear set. The torque-transmitting mechanisms are 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. 
     Further 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 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a lever diagram of an embodiment of an eight speed transmission according to the present invention; 
         FIG. 2  is a diagrammatic view of an embodiment of an eight speed transmission according to the present invention; and 
         FIG. 3  is a truth table presenting the state of engagement of the various torque transmitting clutches in each of the available forward and reverse speeds or gear ratios of the transmission illustrated in  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     At the outset, it should be appreciated that the embodiments of the eight speed automatic transmission of the present invention have an arrangement of permanent mechanical connections between the elements of the four planetary gear sets. For example, a first component or element of a first planetary gear set is permanently coupled to a ground or the transmission housing. A first component or element of a second planetary gear set is also permanently coupled to a ground or the transmission housing. A second component or element of the second planetary gear set is permanently coupled to a second component or element of the third planetary gear set. Finally, a first component or element of the third planetary gear set is permanently coupled to a first component or element of a fourth planetary gear set. 
     Referring now to  FIG. 1 , an embodiment of an eight 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 represents a planetary gear set wherein the three basic mechanical components of the planetary gear set are each represented by a node. Therefore, a single lever contains three nodes: one for the sun gear, one for the planet gear carrier, and one for the 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 are presented as interleaved fingers. 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. 
     The transmission  10  includes an input shaft or member  12 , a first planetary gear set  14  having three nodes: a first node  14 A, a second node  14 B and a third node  14 C, a second planetary gear set  16  having three nodes: a first node  16 A, a second node  16 B and a third node  16 C, a third planetary gear set  18  having three nodes: a first node  18 A, a second node  18 B and a third node  18 C, a fourth planetary gear set  20  having three nodes: a first node  20 A, a second node  20 B and a third node  20 C and an output shaft or member  22 . 
     The second node  14 B of the first planetary gear set  14  is coupled to the output member  22 . The third node  14 C of the first planetary gear set  14  is coupled to a ground or transmission housing  50 . The first node  16 A of the second planetary gear set  16  is also coupled to the ground or transmission housing  50 . The second node  16 B of the second planetary gear set  16  is coupled to the input member  12 . The third node  16 C of the second planetary gear set  16  is coupled to the first node  18 A of the third planetary gear set  18 . The third node  18 C of the third planetary gear set  18  is coupled to the third node  20 C of the fourth planetary gear set  20 . 
     A first clutch  26  selectively connects the second node  16 B of the second planetary gear set  16  and the input member  12  to the second node  20 B of the fourth planetary gear set  20 . A second clutch  28  selectively connects the second node  18 B of the third planetary gear set  18  to the second node  20 B of the fourth planetary gear set  20 . A third clutch  30  selectively connects the second node  18 B of the third planetary gear set  18  to the second node  14 B of the first planetary gear set  14 . A fourth clutch  32  selectively connects the third node  20 C of the fourth planetary gear set  20  to the first node  20 A of the fourth planetary gear set  20 . A fifth clutch  34  selectively connects the first node  20 A of the fourth planetary gear set  20  to the first node  14 A of the first planetary gear set  14 . 
     Referring now to  FIG. 2 , a stick diagram presents a schematic layout of the embodiment of the eight speed transmission  10  according to the present invention. In  FIG. 2 , the numbering from the lever diagram of  FIG. 1  is carried over. The clutches and couplings are correspondingly presented whereas the nodes of the planetary gear sets now appear as components of planetary gear sets such as sun gears, ring gears, planet gears and planet gear carriers. 
     For example, the planetary gear set  14  is a planetary gear set that includes a sun gear member  14 A, a planet gear carrier member  14 B and a ring gear member  14 C. The sun gear member  14 A is connected for common rotation to a first shaft or interconnecting member  52 . The planet gear carrier member  14 B rotatably supports a set of planet gears  14 D (only one shown) and is connected for common rotation with a second shaft or interconnecting member  54  and output shaft  22 . The planet gears  14 D are configured to intermesh with the sun gear member  14 A and the ring gear member  14 C. The ring gear member  14 C is permanently connected to ground or transmission housing  50  through a third shaft or interconnecting member  56 . 
     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). 
     The planetary gear set  16  is a planetary gear set that includes a sun gear member  16 A, a planet carrier member  16 B that rotatably supports a set of planet gears  16 D and a ring gear member  16 C. The sun gear member  16 A is permanently connected to ground or transmission housing  50  through a fourth shaft or interconnecting member  58  in order to restrict the sun gear member  16 A from rotating relative to the ground or transmission housing  50 . The planet carrier member  16 B is connected for common rotation with input shaft or member  12 . The ring gear member  16 C is connected for common rotation with the fifth shaft or interconnecting member  60 . The planet gears  16 D are configured to intermesh with both the sun gear member  16 A and the ring gear member  16 C. 
     The planetary gear set  18  is a planetary gear set that includes a sun gear member  18 A, a ring gear member  18 C and a planet carrier member  18 B that rotatably supports a set of planet gears  18 D. The sun gear member  18 A is connected for common rotation with fifth shaft or interconnecting member  60 . The ring gear member  18 C is connected for common rotation with a sixth shaft or interconnecting member  62 . The planet carrier member  18 B is connected for common rotation with a seventh shaft or interconnecting member  64  and an eighth shaft or interconnecting member  66 . The planet gears  18 D are configured to intermesh with both sun gear member  18 A and ring gear member  18 C. 
     The planetary gear set  20  is a planetary gear set that includes a sun gear member  20 A, a ring gear member  20 C and a planet carrier member  20 B that rotatably supports a set of planet gears  20 D. The sun gear member  20 A is connected for common rotation with a ninth interconnecting member  68 . The ring gear member  20 C is connected for common rotation with a tenth shaft or interconnecting member  70  and with sixth shaft or interconnecting member  62 . The planet carrier member  20 B is connected for common rotation with an eleventh shaft or interconnecting member  72 . The planet gears  20 D are configured to intermesh with both the sun gear member  20 A and the ring gear member  20 C. 
     The torque-transmitting mechanisms or clutches  26 ,  28 ,  30 ,  32  and  34  allow for selective interconnection of the shafts or interconnecting members, members of the planetary gear sets and the housing. For example, the first clutch  26  is selectively engageable to connect the eleventh interconnecting shaft or member  72  to the input member  12 . The second clutch  28  is selectively engageable to connect the eighth interconnecting member  66  to the eleventh interconnecting member  72 . The third clutch  30  is selectively engageable to connect the second interconnecting shaft or member  54  to the seventh interconnecting member  64 . The fourth clutch  32  is selectively engageable to connect the ninth interconnecting shaft or member  68  to the tenth interconnecting shaft or member  70 . The fifth clutch  34  is selectively engageable to connect the first interconnecting shaft or member  52  to the ninth interconnecting shaft or member  68 . 
     Referring now to  FIGS. 2 and 3 , the operation of the embodiment of the eight speed transmission  10  will be described. It will be appreciated that 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. 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  26 , second clutch  28 , third clutch  30 , fourth clutch  32 , and fifth clutch  34 ), as will be explained below.  FIG. 3  is a truth table presenting the various combinations of torque-transmitting mechanisms 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 . 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. 
     To establish reverse gear, the third clutch  30 , the fourth clutch  32 , and the fifth clutch  34  are engaged or activated. The third clutch  30  connects the second interconnecting shaft or member  54  to the seventh interconnecting member  64 . The fourth clutch  32  connects the ninth interconnecting shaft or member  68  to the tenth interconnecting shaft or member  70 . The fifth clutch  34  connects the first interconnecting shaft or member  52  to the ninth interconnecting shaft or member  68 . Likewise, the eight forward ratios are achieved through different combinations of clutch engagement, as shown in  FIG. 3 . 
     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 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 engaged or activated in both gear states will remain engaged or activated. 
     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. Such variations are not to be regarded as a departure from the spirit and scope of the invention.