Abstract:
A transmission is provided having an input member, an output member, three planetary gear sets, four external co-planar 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. Each of the external gear sets includes first and second gears. The torque transmitting devices may include clutches and brakes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/956,822 filed on Aug. 20, 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 gear sets and a plurality of torque transmitting devices, and more particularly to a transmission having eight or more speeds, three planetary gear sets, four external 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 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. 
     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, three planetary gear sets, four external 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. Each of the external gear sets include first and second gears. The torque transmitting devices are for example clutches and brakes. 
     An embodiment of the transmission includes three planetary gear sets, four external drive gear sets, four clutches, and one brake. 
     It is thus an object of the present invention to provide a transmission having three planetary gear sets and four external drive gear sets. 
     It is a further object of the present invention to provide a transmission having at least eight forward speeds and at least one reverse. 
     It is a still further object of the present invention to provide a transmission having three planetary gear sets, four external drive gear sets, a plurality of coupling members and a plurality of torque transmitting devices. 
     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 diagrammatic view of another embodiment of an eight speed transmission according to the present invention; and 
         FIG. 4  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  FIGS. 1-3 . 
     
    
    
     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 gear set. Solid line levers represent a planetary gear set wherein the three basic mechanical components of the planetary gear set are each represented by a node. Therefore, a single planetary gear set lever contains three nodes: one for the sun gear, one for the planet gear carrier, and one for the ring gear. Dashed line levers represent a spur or external drive gear set wherein the basic mechanical components of the external drive gear set are each represented by a node. Therefore, a single external drive gear set lever contains three nodes: one for the first drive gear, one for the second drive gear, and one representing the connection between the drive gears. The relative length between the nodes of each lever can be used to represent the ring-to-sun ratio and first drive gear to second drive gear ratio of each respective gear set. These lever ratios, in turn, are used to vary the gear ratios of the transmission in order to achieve appropriate ratios and ratio progression. Mechanical couplings or interconnections between the nodes of the various planetary gear sets are illustrated by thin, horizontal lines and torque transmitting devices such as clutches and brakes are presented as interleaved fingers. Where the torque transmitting device is a brake, one set of interleaved fingers is coupled to a ground. 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 first external gear set  20  having three nodes: a first node  20 A, a second node  20 B and a third node  20 C, a second external gear set  22  having three nodes: a first node  22 A, a second node  22 B and a third node  22 C, a second external gear set  24  having three nodes: a third node  24 A, a second node  24 B and a third node  24 C, a fourth external gear set  26  having three nodes: a first node  26 A, a second node  26 B and a third node  26 C, and an output shaft or member  30 . 
     The input member  12  is coupled to the second node  14 B of the first planetary gear set  14 . The output member  30  is coupled to the third node  26 C of the fourth external gear set  26 . The first node  14 A of the first planetary gear set  14  is coupled to the first node  20 A of the first external gear set  20 . The third node  14 C of the first planetary gear set  14  is coupled to the first node  22 A of the second external gear set  22 . The third node  22 C of the second external gear set  22  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 second node  18 B of the third planetary gear set  18  and to the first node  26 A of the fourth external gear set  26 . The third node  18 C of the third planetary gear set  18  is coupled to the first node  24 A of the third external gear set  24 . 
     A first clutch  40  selectively connects the second node  14 B of the first planetary gear set  14  to the third node  24 C of the third external gear set  24 . A second clutch  42  selectively connects the first node  22 A of the second external gear set  22  to the third node  24 C of the third external gear set  24 . A third clutch  44  selectively connects the third node  20 C of the first external gear set  20  to the first node  18 A of the third planetary gear set  18 . A fourth clutch  46  selectively connects the first node  18 A of the third planetary gear set  18  to the second node  16 B of the second planetary gear set  16 . A first brake  48  selectively connects the first node  14 A of the first planetary gear set  14  to a stationary element or transmission housing  50 . 
     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 and the nodes of the external drive gear sets now appear as components of the external drive gear sets such as first and second interconnected drive gears. 
     For example, the planetary gear set  14  includes a sun gear member  14 A, a planet gear carrier member  14 B and a ring gear member  14 C. The planet gear carrier member  14 B rotatably supports a set of planet gears  14 D 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 a first shaft or interconnecting member  52 . The ring gear member  14 C is for common rotation with a second shaft or interconnecting member  54 . The planet carrier member  14 B is connected for common rotation with the input member  12 . 
     The planetary gear set  16  includes a sun gear member  16 C, a planet gear carrier member  16 B and a ring gear member  16 A. The planet gear carrier member  16 B rotatably supports a set of planet gears  16 D configured to intermesh with both the sun gear member  16 C and the ring gear member  16 A. The sun gear member  16 C is connected for common rotation with a third shaft or interconnecting member  56 . The ring gear member  16 A is connected for common rotation with a fourth shaft or interconnecting member  58 . The planet carrier member  16 B is connected for common rotation with a fifth shaft or interconnecting member  60 . 
     The planetary gear set  18  includes a sun gear member  18 C, a planet gear carrier member  18 B and a ring gear member  18 A. The planet gear carrier member  18 B rotatably supports a set of planet gears  18 D configured to intermesh with both the sun gear member  18 C and the ring gear member  18 A. The sun gear member  18 C is connected for common rotation with a sixth shaft or interconnecting member  62 . The ring gear member  18 A is connected for common rotation with a seventh shaft or interconnecting member  64  and an eighth shaft or interconnecting member  66 . The planet carrier member  18 B is connected for common rotation with a ninth shaft or interconnecting member  68  and with the fourth interconnecting member  58 . 
     The external gear set  20  includes a first gear member  20 A intermeshed with a second gear member  20 C. The first gear member  20 A is connected for common rotation with the first interconnecting member  52 . The second gear member  20 C is connected for common rotation with a tenth shaft or interconnecting member  70 . 
     The external gear set  22  includes a first gear member  22 A intermeshed with a second gear member  22 C. The first gear member  22 A is connected for common rotation with the second interconnecting member  54  and with an eleventh interconnecting member  72 . The second gear member  22 C is connected for common rotation with the third interconnecting member  56 . 
     The external gear set  24  includes a first gear member  24 A intermeshed with a second gear member  24 C. The first gear member  24 A is connected for common rotation with the sixth interconnecting member  62 . The second gear member  24 C is connected for common rotation with a twelfth shaft or interconnecting member  74 . 
     The external gear set  26  includes a first gear member  26 A intermeshed with a second gear member  26 C. The first gear member  26 A is connected for common rotation with the ninth interconnecting member  68 . The second gear member  26 C is connected for common rotation with the output member  30 . 
     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  30  is continuously connected with the final drive unit or transfer case (not shown). 
     The torque-transmitting elements or the clutches  40 ,  42 ,  44 ,  46  and brake  48  allow for selective interconnection of the shafts or interconnecting members, members of the planetary gear sets and external gear sets, and the transmission housing. For example, the first clutch  40  is selectively engageable to connect the input member  12  with the twelfth interconnecting member  74 . The second clutch  42  is selectively engageable to connect the eleventh interconnecting member  72  with the twelfth interconnecting member  74 . The third clutch  44  is selectively engageable to connect the tenth interconnecting member  70  with the seventh interconnecting member  64 . The fourth clutch  46  is selectively engageable to connect the eighth interconnecting member  66  with the fifth interconnecting member  60 . The first brake  48  is selectively engageable to connect the first interconnecting member  52  to a stationary element or the transmission housing  50  in order to restrict the first interconnecting member  52  and therefore the first gear member  20 A and the sun gear member  14 A from rotation relative to the transmission housing  50 . 
     In the particular example provided, the transmission  10  is arranged along separate axes including a first axis defined by the input member  12 , a second axis defined by the sixth interconnecting member  62  and the ninth interconnecting member  68 , and a third axis defined by the output member  30 . Accordingly, in the example provided, the interconnecting members  52 ,  54 ,  72 ,  74 , the planetary gear set  14 , the first gear member  20 A, the second gear member  24 C, the first brake  48 , and the clutches  40 ,  42  are all concentric with the input member  12 . The interconnecting members  64 ,  70 , the first gear member  26 A, the third clutch  44 , and the second gear member  20 C are concentric with the ninth interconnecting member  68  while the interconnecting members  56 ,  58 ,  60 ,  66 , the planetary gear sets  16 ,  18 , the first gear member  24 A, and the fourth clutch  46  are concentric with the sixth interconnecting member  62 . Finally, the second gear member  26 C is concentric with the output member  30 . It should be appreciated that concentric shafts may be sleeve shafts without departing from the scope of the present invention. Additionally, the transmission  10  is preferably configured for a front wheel drive vehicle. 
     Turning now to  FIG. 3 , an alternate embodiment of the transmission  10  is shown and generally indicated by reference number  100 . The transmission  100  is similar to the transmission  10  and accordingly like parts are indicated by like reference numbers. However, the second planetary gear set  16  of the transmission  100  includes a second set of planet gears  16 E supported by the planet carrier member  16 B such that the sun gear  16 C is intermeshed with the planet gears  16 D, the planet gears  16 D are intermeshed with the planet gears  16 E, and the planet gears  16 E are intermeshed with the ring gear member  16 A. Additionally, the planet carrier member  16 B is connected for common rotation with the fourth interconnecting member  58  and the ring gear member  16 A is connected for common rotation with the fifth interconnecting member  60 . All other connections, couplings, and gear sets are similar to the arrangement disclosed in the transmission  10  illustrated in  FIG. 2 . 
     Referring now to  FIGS. 2-4 , the operation of both embodiments of the eight speed transmission  10  and  100  will be described. It will be appreciated that the transmissions  10 ,  100  are capable of transmitting torque from the input shaft or member  12  to the output shaft or member  30  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  40 , second clutch  42 , third clutch  44 , fourth clutch  46 , and first brake  48 ), as will be explained below.  FIG. 4  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 transmissions  10 ,  100 . An example of the gear ratios that may be obtained using the embodiments of the present invention are also shown in  FIG. 4 . Of course, other gear ratios are achievable depending on the gear diameter, gear teeth count and gear configuration selected. 
     To establish reverse gear, the second clutch  42 , the third clutch  44 , and the first brake  48  are engaged or activated. The second clutch  42  connects the eleventh interconnecting member  72  with the twelfth interconnecting member  74 . The third clutch  44  connects the tenth interconnecting member  70  with the seventh interconnecting member  64 . The first brake  48  connects the first interconnecting member  52  to a stationary element or the transmission housing  50  in order to restrict the first interconnecting member  52  and therefore the first gear member  20 A and the sun gear member  14 A from rotation relative to the transmission housing  50 . Likewise, the eight forward ratios are achieved through different combinations of clutch and brake engagement, as shown in  FIG. 4 . 
     It will be appreciated that the foregoing explanation of operation and gear states of the eight speed transmissions  10 ,  100  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. 
     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.