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. The torque transmitting devices include clutches and brakes.

Description:
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 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 friction clutches, 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 
     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. 
     In one embodiment, the transmission includes an input member, an output member, first, second, third, and fourth planetary gear sets each having first, second and third members, wherein the third member of the third planetary gear set is formed on an outer surface of the first member of the second planetary gear set, wherein the third member of the third planetary gear set includes an inner surface that defines an internal cavity, wherein the first, second, and third members of the second planetary gear set are disposed within the internal cavity, and wherein the input member is continuously interconnected to the second member of the second planetary gear set and the output member is continuously interconnected to at least one of the second member of the first planetary gear set and the second member of the third planetary gear set. A first interconnecting member continuously interconnects the first member of the first planetary gear set with the second member of the fourth planetary gear set, a second interconnecting member continuously interconnects the second member of the first planetary gear set with the second member of the third planetary gear set, a third interconnecting member continuously interconnects the third member of the first planetary gear set with the third member of the second planetary gear set, and a fourth interconnecting member continuously interconnects the first member of the second planetary gear set with the third member of the third planetary gear set. A first torque transmitting mechanism is selectively engageable to interconnect the first member of the third planetary gear set with the third member of the fourth planetary gear set. A second torque transmitting mechanism is selectively engageable to interconnect at least one of the first member of the second planetary gear set and the third member of the third planetary gear set with the third member of the fourth planetary gear set. A third torque transmitting mechanism is selectively engageable to interconnect at least one of the input member and the second member of the second planetary gear set with the third member of the fourth planetary gear set. A fourth torque transmitting mechanism is selectively engageable to interconnect at least one of the third member of the first planetary gear set and the third member of the second planetary gear set with a stationary member. A fifth torque transmitting mechanism is selectively engageable to interconnect the first member of the fourth planetary gear set with the stationary member. 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 embodiment, the transmission includes an input member, an output member, first, second, third, and fourth planetary gear sets each having first, second and third members, wherein the third member of the third planetary gear set is formed on an outer surface of the first member of the second planetary gear set, wherein the third member of the third planetary gear set includes an inner surface that defines an internal cavity, wherein the first, second, and third members of the second planetary gear set are disposed within the internal cavity, and wherein the input member is continuously interconnected to the second member of the second planetary gear set and the output member is continuously interconnected to at least one of the second member of the first planetary gear set and the first member of the third planetary gear set. A first interconnecting member continuously interconnects the first member of the first planetary gear set with the second member of the fourth planetary gear set, a second interconnecting member continuously interconnects the second member of the first planetary gear set with the first member of the third planetary gear set, a third interconnecting member continuously interconnects the third member of the first planetary gear set with the third member of the second planetary gear set, and a fourth interconnecting member continuously interconnects the first member of the second planetary gear set with the third member of the third planetary gear set. A first torque transmitting mechanism is selectively engageable to interconnect the second member of the third planetary gear set with the third member of the fourth planetary gear set. A second torque transmitting mechanism is selectively engageable to interconnect at least one of the first member of the second planetary gear set and the third member of the third planetary gear set with the third member of the fourth planetary gear set. A third torque transmitting mechanism is selectively engageable to interconnect at least one of the input member and the second member of the second planetary gear set with the third member of the fourth planetary gear set. A fourth torque transmitting mechanism is selectively engageable to interconnect at least one of the third member of the first planetary gear set and the third member of the second planetary gear set with a stationary member. A fifth torque transmitting mechanism is selectively engageable to interconnect the first member of the fourth planetary gear set with the stationary member. 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 yet another embodiment, the transmission includes an input member, an output member, first, second, third, and fourth planetary gear sets each having first, second and third members, wherein the third member of the third planetary gear set is formed on an outer surface of the first member of the second planetary gear set, wherein the third member of the third planetary gear set includes an inner surface that defines an internal cavity, wherein the first, second, and third members of the second planetary gear set are disposed within the internal cavity, and wherein the input member is continuously interconnected to the second member of the second planetary gear set and the output member is continuously interconnected to the second member of the first planetary gear set. A first interconnecting member continuously interconnects the first member of the first planetary gear set with the second member of the fourth planetary gear set, a second interconnecting member continuously interconnects the first member of the third planetary gear set with the third member of the fourth planetary gear set, a third interconnecting member continuously interconnects the third member of the first planetary gear set with the third member of the second planetary gear set, and a fourth interconnecting member continuously interconnects the first member of the second planetary gear set with the third member of the third planetary gear set. A first torque transmitting mechanism is selectively engageable to interconnect at least one of the output member and the second member of the first planetary gear set with the second member of the third planetary gear set. A second torque transmitting mechanism is selectively engageable to interconnect at least one of the third member of the third planetary gear set and the first member of the second planetary gear set with the second member of the third planetary gear set. A third torque transmitting mechanism is selectively engageable to interconnect at least one of the input member and the second member of the second planetary gear set with the third member of the fourth planetary gear set. A fourth torque transmitting mechanism is selectively engageable to interconnect at least one of the third member of the first planetary gear set and the third member of the second planetary gear set with a stationary member. A fifth torque transmitting mechanism is selectively engageable to interconnect the first member of the fourth planetary gear set with the stationary member. 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 one aspect of the present invention, each of the planetary gear sets has a sun gear, carrier and ring gear members. 
     In another aspect of the present invention, the torque transmitting devices include three clutches and two brakes. 
     In yet another aspect of the present invention, the transmission is a front wheel drive transmission. 
     Further objects, 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; 
         FIG. 3  is a truth table presenting the state of engagement of the various torque transmitting mechanisms in each of the available forward and reverse speeds or gear ratios of the transmission illustrated in  FIGS. 1 and 2 ; 
         FIG. 4  is a lever diagram of an embodiment of an eight speed transmission according to the present invention; 
         FIG. 5  is a diagrammatic view of an embodiment of an eight speed transmission according to the present invention; 
         FIG. 6  is a truth table presenting the state of engagement of the various torque transmitting mechanisms in each of the available forward and reverse speeds or gear ratios of the transmission illustrated in  FIGS. 4 and 5 ; 
         FIG. 7  is a lever diagram of an embodiment of an eight speed transmission according to the present invention; 
         FIG. 8  is a diagrammatic view of an embodiment of an eight speed transmission according to the present invention; and 
         FIG. 9  is a truth table presenting the state of engagement of the various torque transmitting mechanisms in each of the available forward and reverse speeds or gear ratios of the transmission illustrated in  FIGS. 7 and 8 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     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 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 an 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. 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 input shaft or member  12  is coupled to the second node  16 B of the second planetary gear set  16 . The output shaft or member  22  is coupled to the second node  14 B of the first planetary gear set  14 . The first node  14 A of the first planetary gear set  14  is coupled to the second node  20 B of the fourth planetary gear set  20 . The second node  14 B of the first planetary gear set  14  is coupled to the second node  18 B of the third planetary gear set  18 . The third node  14 C of the first planetary gear set  14  is coupled to the third node  16 C of the second planetary gear set  16 . The first node  16 A of the second planetary gear set  16  is coupled to the third node  18 C of the third planetary gear set  18 . 
     A first clutch  26  selectively connects the first node  18 A of the third planetary gear set  18  with the third node  20 C of the fourth planetary gear set  20 . A second clutch  28  selectively connects the first node  16 A of the second planetary gear set  16  and the third node  18 C of the third planetary gear set  18  with the third node  20 C of the fourth planetary gear set  20 . A third clutch  30  selectively connects the second node  16 B of the second planetary gear set  16  and the input member  12  with the third node  20 C of the fourth planetary gear set  20 . A first brake  32  selectively connects the third node  14 C of the first planetary gear set  14  with a ground, a stationary member, or a transmission housing  40 . A second brake  34  selectively connects the first node  20 A of the fourth planetary gear set  20  with the ground, the stationary member, or the transmission housing  40 . 
     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, brakes, 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  includes a sun gear member  14 C, a ring gear member  14 A 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 sun gear member  14 C is connected for common rotation with a first shaft or interconnecting member  42  and with a second shaft or interconnecting member  44 . The ring gear member  14 A is connected for common rotation with a third shaft or interconnecting member  46 . The planet carrier member  14 B is connected for common rotation with a fourth shaft or interconnecting member  48  and with the output member  22 . The planet gears  14 D each are configured to intermesh with both the sun gear member  14 C and the ring gear member  14 A. 
     The planetary gear set  16  includes a sun gear member  16 C, a ring gear member  16 A 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 sun gear member  16 C is connected for common rotation with the second shaft or interconnecting member  44 . The ring gear member  16 A is connected for common rotation with a fifth shaft or interconnecting member  50 . The planet carrier member  16 B is connected for common rotation with the input member  12 . The planet gears  16 D each are configured to intermesh with both the sun gear member  16 C and the ring gear member  16 A. 
     The planetary gear set  18  includes a sun gear member  18 C, a ring gear member  18 A 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 sun gear member  18 C is connected for common rotation with the fifth shaft or interconnecting member  50 . The ring gear member  18 A is connected for common rotation with a sixth shaft or interconnecting member  52 . The planet carrier member  18 B is connected for common rotation with the fourth shaft or interconnecting member  48 . The planet gears  18 D each are configured to intermesh with both the sun gear member  18 C and the ring gear member  18 A. 
     The planetary gear set  20  includes a sun gear member  20 C, a ring gear member  20 A 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 sun gear member  20 C is connected for common rotation with a seventh shaft or interconnecting member  54 . The ring gear member  20 A is connected for common rotation with an eighth shaft or interconnecting member  56 . The planet carrier member  20 B is connected for common rotation with the third shaft or interconnecting member  46 . The planet gears  20 D each are configured to intermesh with both the sun gear member  20 C and the ring gear member  20 A. 
     In the preferred embodiment of the present invention, the sun gear member  18 C is integrally formed with the ring gear member  16 A of the planetary gear set  16  such that the sun gear member  18 C is located on the outer surface and the ring gear member  16 A is located on the inner surface of the same member. Moreover, the sun gear member  18 C defines an internal cavity and the planetary gear set  16  is disposed within the internal cavity (i.e., the planetary gear set  18  is radially stacked with the planetary gear set  16  such that the planetary gear set  16  is nested within the planetary gear set  18 ). However, it should be appreciated that the sun gear member  18 C and the ring gear member  16 A may be separate components connected by an interconnecting member without departing from the scope of the present invention. 
     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 torque-transmitting mechanisms or clutches  26 ,  28 , and  30  and brakes  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 sixth shaft or interconnecting member  52  with the seventh shaft or interconnecting member  54 . The second clutch  28  is selectively engageable to connect the fifth shaft or interconnecting member  50  with the seventh shaft or interconnecting member  54 . The third clutch  30  is selectively engageable to connect the input shaft or member  12  with the seventh shaft or interconnecting member  54 . The first brake  32  is selectively engageable to connect the first shaft or interconnecting member  42  and the second shaft or interconnecting member  44  with the stationary member or the transmission housing  40  in order to restrict the members  42 ,  44  from rotating relative to the transmission housing  40 . The second brake  34  is selectively engageable to connect the eighth shaft or interconnecting member  56  with the stationary member or the transmission housing  40  in order to restrict the eighth interconnecting member  56  from rotating relative to the transmission housing  40 . 
     Referring now to  FIG. 2  and  FIG. 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 with single transition sequential shifts and 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  26 , second clutch  28 , third clutch  30 , first brake  32  and second brake  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. An “X” in the box means that the particular clutch or brake is engaged to achieve the desired gear state. An “O” represents that the particular torque transmitting device (i.e. a brake or clutch) is on or active, but not carrying torque. 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 a reverse gear, the first clutch  26 , first brake  32  and second brake  34  are engaged or activated. For example, the first clutch  26  connects the sixth shaft or interconnecting member  52  with the seventh shaft or interconnecting member  54 . The first brake  32  connects the first shaft or interconnecting member  42  and the second shaft or interconnecting member  44  with the stationary member or the transmission housing  40  in order to restrict the members  42 ,  44  from rotating relative to the transmission housing  40 . The second brake  34  connects the eighth shaft or interconnecting member  56  with the stationary member or the transmission housing  40  in order to restrict the eighth interconnecting member  56  from rotating relative to the transmission housing  40 . Likewise, the eight forward ratios are achieved through different combinations of clutch and brake 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 or 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. 
     Referring now to  FIG. 4 , another embodiment of an eight speed transmission  100  is illustrated in a lever diagram format. The transmission  100  includes an input shaft or member  112 , a first planetary gear set  114  having three nodes: a first node  114 A, a second node  114 B and a third node  114 C, a second planetary gear set  116  having three nodes: a first node  116 A, a second node  116 B and a third node  116 C, a third planetary gear set  118  having three nodes: a first node  118 A, a second node  118 B and a third node  118 C, a fourth planetary gear set  120  having three nodes: a first node  120 A, a second node  120 B and a third node  120 C and an output shaft or member  122 . 
     The input shaft or member  112  is coupled to the second node  116 B of the second planetary gear set  116 . The output shaft or member  122  is coupled to the second node  114 B of the first planetary gear set  114 . The first node  114 A of the first planetary gear set  114  is coupled to the second node  120 B of the fourth planetary gear set  120 . The second node  114 B of the first planetary gear set  114  is coupled to the first node  118 A of the third planetary gear set  118 . The third node  114 C of the first planetary gear set  114  is coupled to the third node  116 C of the second planetary gear set  116 . The first node  116 A of the second planetary gear set  116  is coupled to the third node  118 C of the third planetary gear set  118 . 
     A first clutch  126  selectively connects the second node  118 B of the third planetary gear set  118  with the third node  120 C of the fourth planetary gear set  120 . A second clutch  128  selectively connects the first node  116 A of the second planetary gear set  116  and the third node  118 C of the third planetary gear set  118  with the third node  120 C of the fourth planetary gear set  120 . A third clutch  130  selectively connects the second node  116 B of the second planetary gear set  116  and the input member  112  with the third node  120 C of the fourth planetary gear set  120 . A first brake  132  selectively connects the third node  114 C of the first planetary gear set  114  with a ground, a stationary member, or a transmission housing  140 . A second brake  134  selectively connects the first node  120 A of the fourth planetary gear set  120  with the ground, the stationary member, or the transmission housing  140 . 
     Referring now to  FIG. 5 , a stick diagram presents a schematic layout of the embodiment of the eight speed transmission  100  according to the present invention. In  FIG. 5 , the numbering from the lever diagram of  FIG. 4  is carried over. The clutches, brakes, 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  114  includes a sun gear member  114 C, a ring gear member  114 A and a planet gear carrier member  114 B that rotatably supports a set of planet gears  114 D (only one of which is shown). The sun gear member  114 C is connected for common rotation with a first shaft or interconnecting member  142  and with a second shaft or interconnecting member  144 . The ring gear member  114 A is connected for common rotation with a third shaft or interconnecting member  146 . The planet carrier member  114 B is connected for common rotation with a fourth shaft or interconnecting member  148  and with the output member  122 . The planet gears  114 D each are configured to intermesh with both the sun gear member  114 C and the ring gear member  114 A. 
     The planetary gear set  116  includes a sun gear member  116 C, a ring gear member  116 A and a planet gear carrier member  116 B that rotatably supports a set of planet gears  116 D (only one of which is shown). The sun gear member  116 C is connected for common rotation with the second shaft or interconnecting member  144 . The ring gear member  116 A is connected for common rotation with a fifth shaft or interconnecting member  150 . The planet carrier member  116 B is connected for common rotation with the input member  112 . The planet gears  116 D each are configured to intermesh with both the sun gear member  116 C and the ring gear member  116 A. 
     The planetary gear set  118  includes a sun gear member  118 C, a ring gear member  118 A and a planet gear carrier member  118 B that rotatably supports a first set of planet gears  118 D (only one of which is shown) and a second set of planet gears  118 E (only one of which is shown). The sun gear member  118 C is connected for common rotation with the fifth shaft or interconnecting member  150 . The ring gear member  118 A is connected for common rotation with the fourth shaft or interconnecting member  148 . The planet carrier member  118 B is connected for common rotation with a sixth shaft or interconnecting member  152 . The planet gears  118 D each are configured to intermesh with both the ring gear member  118 A and the planet gears  118 E. The planet gears  118 E each are configured to intermesh with both the sun gear member  118 C and the planet gears  118 D. 
     The planetary gear set  120  includes a sun gear member  120 C, a ring gear member  120 A and a planet gear carrier member  120 B that rotatably supports a set of planet gears  120 D (only one of which is shown). The sun gear member  120 C is connected for common rotation with a seventh shaft or interconnecting member  154 . The ring gear member  120 A is connected for common rotation with an eighth shaft or interconnecting member  156 . The planet carrier member  120 B is connected for common rotation with the third shaft or interconnecting member  146 . The planet gears  120 D each are configured to intermesh with both the sun gear member  120 C and the ring gear member  120 A. 
     In the preferred embodiment of the present invention, the sun gear member  118 C is integrally formed with the ring gear member  116 A of the planetary gear set  116  such that the sun gear member  118 C is located on an outer surface and the ring gear member  116 A is located on an inner surface of the same member. Moreover, the sun gear member  118 C defines an internal cavity and the planetary gear set  116  is disposed within the internal cavity (i.e., the planetary gear set  118  is radially stacked with the planetary gear set  116  such that the planetary gear set  116  is nested within the planetary gear set  118 ). However, it should be appreciated that the sun gear member  118 C and the ring gear member  116 A may be separate components connected by an interconnecting member without departing from the scope of the present invention. 
     The input shaft or member  112  is continuously connected to an engine (not shown) or to a turbine of a torque converter (not shown). The output shaft or member  122  is continuously connected with the final drive unit or transfer case (not shown). 
     The torque-transmitting mechanisms or clutches  126 ,  128 , and  130  and brakes  132  and  134  allow for selective interconnection of the shafts or interconnecting members, members of the planetary gear sets and the housing. For example, the first clutch  126  is selectively engageable to connect the sixth shaft or interconnecting member  152  with the seventh shaft or interconnecting member  154 . The second clutch  128  is selectively engageable to connect the fifth shaft or interconnecting member  150  with the seventh shaft or interconnecting member  154 . The third clutch  130  is selectively engageable to connect the input shaft or member  112  with the seventh shaft or interconnecting member  154 . The first brake  132  is selectively engageable to connect the first shaft or interconnecting member  142  and the second shaft or interconnecting member  144  with the stationary member or the transmission housing  140  in order to restrict the members  142 ,  144  from rotating relative to the transmission housing  140 . The second brake  134  is selectively engageable to connect the eighth shaft or interconnecting member  156  with the stationary member or the transmission housing  140  in order to restrict the eighth interconnecting member  156  from rotating relative to the transmission housing  140 . 
     Referring now to  FIG. 5  and  FIG. 6 , the operation of the embodiment of the eight speed transmission  100  will be described. It will be appreciated that transmission  100  is capable of transmitting torque from the input shaft or member  112  to the output shaft or member  122  in at least eight forward speed or torque ratios and at least one reverse speed or torque ratio with single transition sequential shifts and 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  126 , second clutch  128 , third clutch  130 , first brake  132  and second brake  134 ), as will be explained below.  FIG. 6  is a truth table presenting the various combinations of torque-transmitting mechanisms that are activated or engaged to achieve the various gear states. An “X” in the box means that the particular clutch or brake is engaged to achieve the desired gear state. An “O” represents that the particular torque transmitting device (i.e. a brake or clutch) is on or active, but not carrying torque. 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. 6 . Of course, other gear ratios are achievable depending on the gear diameter, gear teeth count and gear configuration selected. 
     To establish a reverse gear, the first clutch  126 , first brake  132  and second brake  134  are engaged or activated. For example, the first clutch  126  connects the sixth shaft or interconnecting member  152  with the seventh shaft or interconnecting member  154 . The first brake  132  connects the first shaft or interconnecting member  142  and the second shaft or interconnecting member  144  with the stationary member or the transmission housing  140  in order to restrict the members  142 ,  144  from rotating relative to the transmission housing  140 . The second brake  134  connects the eighth shaft or interconnecting member  156  with the stationary member or the transmission housing  140  in order to restrict the eighth interconnecting member  156  from rotating relative to the transmission housing  140 . Likewise, the eight forward ratios are achieved through different combinations of clutch and brake engagement, as shown in  FIG. 6 . 
     It will be appreciated that the foregoing explanation of operation and gear states of the eight speed transmission  100  assumes, first of all, that all the clutches or 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. 
     Referring now to  FIG. 7 , another embodiment of an eight speed transmission  200  is illustrated in a lever diagram format. The transmission  200  includes an input shaft or member  212 , a first planetary gear set  214  having three nodes: a first node  214 A, a second node  214 B and a third node  214 C, a second planetary gear set  216  having three nodes: a first node  216 A, a second node  216 B and a third node  216 C, a third planetary gear set  218  having three nodes: a first node  218 A, a second node  218 B and a third node  218 C, a fourth planetary gear set  220  having three nodes: a first node  220 A, a second node  220 B and a third node  220 C and an output shaft or member  222 . 
     The input shaft or member  212  is coupled to the second node  216 B of the second planetary gear set  216 . The output shaft or member  222  is coupled to the second node  214 B of the first planetary gear set  214 . The first node  214 A of the first planetary gear set  214  is coupled to the second node  220 B of the fourth planetary gear set  220 . The first node  218 A of the third planetary gear set  218  is coupled to the third node  220 C of the fourth planetary gear set  220 . The third node  214 C of the first planetary gear set  214  is coupled to the third node  216 C of the second planetary gear set  216 . The first node  216 A of the second planetary gear set  216  is coupled to the third node  218 C of the third planetary gear set  218 . 
     A first clutch  226  selectively connects the second node  214 B of the first planetary gear set  214  and the output member  222  with the second node  218 B of the third planetary gear set  218 . A second clutch  228  selectively connects the first node  216 A of the second planetary gear set  216  and the third node  218 C of the third planetary gear set  218  with the second node  218 B of the third planetary gear set  218 . A third clutch  230  selectively connects the second node  216 B of the second planetary gear set  216  and the input member  212  with the third node  220 C of the fourth planetary gear set  220 . A first brake  232  selectively connects the third node  214 C of the first planetary gear set  214  with a ground, a stationary member, or a transmission housing  240 . A second brake  234  selectively connects the first node  220 A of the fourth planetary gear set  220  with the ground, the stationary member, or the transmission housing  240 . 
     Referring now to  FIG. 8 , a stick diagram presents a schematic layout of the embodiment of the eight speed transmission  200  according to the present invention. In  FIG. 8 , the numbering from the lever diagram of  FIG. 7  is carried over. The clutches, brakes, 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  214  includes a sun gear member  214 C, a ring gear member  214 A and a planet gear carrier member  214 B that rotatably supports a set of planet gears  214 D (only one of which is shown). The sun gear member  214 C is connected for common rotation with a first shaft or interconnecting member  242  and with a second shaft or interconnecting member  244 . The ring gear member  214 A is connected for common rotation with a third shaft or interconnecting member  246 . The planet carrier member  214 B is connected for common rotation with a fourth shaft or interconnecting member  248  and with the output member  222 . The planet gears  214 D each are configured to intermesh with both the sun gear member  214 C and the ring gear member  214 A. 
     The planetary gear set  216  includes a sun gear member  216 C, a ring gear member  216 A and a planet gear carrier member  216 B that rotatably supports a set of planet gears  216 D (only one of which is shown). The sun gear member  216 C is connected for common rotation with the second shaft or interconnecting member  244 . The ring gear member  216 A is connected for common rotation with a fifth shaft or interconnecting member  250 . The planet carrier member  216 B is connected for common rotation with the input member  212 . The planet gears  216 D each are configured to intermesh with both the sun gear member  216 C and the ring gear member  216 A. 
     The planetary gear set  218  includes a sun gear member  218 C, a ring gear member  218 B and a planet gear carrier member  218 A that rotatably supports a first set of planet gears  218 D (only one of which is shown) and a second set of planet gears  218 E (only one of which is shown). The sun gear member  218 C is connected for common rotation with the fifth shaft or interconnecting member  250 . In a preferred embodiment of the present invention, the sun gear member  218 C is integrally formed with the ring gear member  216 A of the planetary gear set  216 . The ring gear member  218 B is connected for common rotation with a sixth shaft or interconnecting member  252 . The planet carrier member  218 A is connected for common rotation with a seventh shaft or interconnecting member  254 . The planet gears  218 D each are configured to intermesh with both the planet gears  218 E and the ring gear member  218 B. The planet gears  218 E each are configured to intermesh with both the planet gears  218 D and the sun gear member  218 C. 
     The planetary gear set  220  includes a sun gear member  220 C, a ring gear member  220 A and a planet gear carrier member  220 B that rotatably supports a set of planet gears  220 D (only one of which is shown). The sun gear member  220 C is connected for common rotation with the seventh shaft or interconnecting member  254 . The ring gear member  220 A is connected for common rotation with an eighth shaft or interconnecting member  256 . The planet carrier member  220 B is connected for common rotation with the third shaft or interconnecting member  246 . The planet gears  220 D each are configured to intermesh with both the sun gear member  220 C and the ring gear member  220 A. 
     In the preferred embodiment of the present invention, the sun gear member  218 C is integrally formed with the ring gear member  216 A of the planetary gear set  216  such that the sun gear member  218 C is located on an outer surface and the ring gear member  216 A is located on an inner surface of the same member. Moreover, the sun gear member  218 C defines an internal cavity and the planetary gear set  216  is disposed within the internal cavity (i.e., the planetary gear set  218  is radially stacked with the planetary gear set  216  such that the planetary gear set  216  is nested within the planetary gear set  218 ). However, it should be appreciated that the sun gear member  218 C and the ring gear member  216 A may be separate components connected by an interconnecting member without departing from the scope of the present invention. 
     The input shaft or member  212  is continuously connected to an engine (not shown) or to a turbine of a torque converter (not shown). The output shaft or member  222  is continuously connected with the final drive unit or transfer case (not shown). 
     The torque-transmitting mechanisms or clutches  226 ,  228 , and  230  and brakes  232  and  234  allow for selective interconnection of the shafts or interconnecting members, members of the planetary gear sets and the housing. For example, the first clutch  226  is selectively engageable to connect the fourth shaft or interconnecting member  248  and the output member  222  with the sixth shaft or interconnecting member  252 . The second clutch  228  is selectively engageable to connect the fifth shaft or interconnecting member  250  with the sixth shaft or interconnecting member  252 . The third clutch  230  is selectively engageable to connect the input shaft or member  212  with the seventh shaft or interconnecting member  254 . The first brake  232  is selectively engageable to connect the first shaft or interconnecting member  242  and the second shaft or interconnecting member  244  with the stationary member or the transmission housing  240  in order to restrict the members  242 ,  244  from rotating relative to the transmission housing  240 . The second brake  234  is selectively engageable to connect the eighth shaft or interconnecting member  256  with the stationary member or the transmission housing  240  in order to restrict the eighth interconnecting member  256  from rotating relative to the transmission housing  240 . 
     Referring now to  FIG. 8  and  FIG. 9 , the operation of the embodiment of the eight speed transmission  200  will be described. It will be appreciated that transmission  200  is capable of transmitting torque from the input shaft or member  212  to the output shaft or member  222  in at least eight forward speed or torque ratios and at least one reverse speed or torque ratio with single transition sequential shifts and 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  226 , second clutch  228 , third clutch  230 , first brake  232  and second brake  234 ), as will be explained below.  FIG. 9  is a truth table presenting the various combinations of torque-transmitting mechanisms that are activated or engaged to achieve the various gear states. An “X” in the box means that the particular clutch or brake is engaged to achieve the desired gear state. An “O” represents that the particular torque transmitting device (i.e. a brake or clutch) is on or active, but not carrying torque. 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  200 . An example of the gear ratios that may be obtained using the embodiments of the present invention are also shown in  FIG. 9 . Of course, other gear ratios are achievable depending on the gear diameter, gear teeth count and gear configuration selected. 
     To establish a reverse gear, the first clutch  226 , first brake  232  and second brake  234  are engaged or activated. For example, the first clutch  226  connects the fourth shaft or interconnecting member  248  and the output member  222  with the sixth shaft or interconnecting member  252 . The first brake  232  connects the first shaft or interconnecting member  242  and the second shaft or interconnecting member  244  with the stationary member or the transmission housing  240  in order to restrict the members  242 ,  244  from rotating relative to the transmission housing  240 . The second brake  234  connects the eighth shaft or interconnecting member  256  with the stationary member or the transmission housing  240  in order to restrict the eighth interconnecting member  256  from rotating relative to the transmission housing  240 . Likewise, the eight forward ratios are achieved through different combinations of clutch and brake engagement, as shown in  FIG. 9 . 
     It will be appreciated that the foregoing explanation of operation and gear states of the eight speed transmission  200  assumes, first of all, that all the clutches or 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. 
     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.