Abstract:
A transmission is provided that utilizes a unique packaging scheme for torque-transmitting mechanisms and gear drive members in order to minimize the overall axial length of the transmission. Specifically, the transmission may include a clutch housing that is connected for common rotation with a transmission input member. A rotatable hub member may be connected for common rotation with both the clutch housing and a gear member, thereby connecting the gear member for common rotation with the input member. Preferably, the rotatable hub member is connected to the clutch housing by the reaction plates that extend from the clutch housing. First and second torque-transmitting mechanisms may be packaged within the clutch housing.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a transmission having a rotatable hub member that connects a gear member to a clutch housing that rotates with an input member.  
       BACKGROUND OF THE INVENTION  
       [0002]     Wide ratio transmissions such as seven or eight speed transmissions offer several advantages including improved vehicle acceleration performance and potentially improved fuel economy over four, five and six speed transmissions. However, increasing the number of speed ratios presents challenges in packaging additional clutches, drive mechanisms for the various gear members, and hydraulic circuit feed paths, and in insuring an overall axial length that is acceptable.  
       SUMMARY OF THE INVENTION  
       [0003]     A transmission is provided that utilizes a unique packaging scheme for torque-transmitting mechanisms and gear drive members in order to minimize the overall axial length of the transmission. Specifically, the transmission may include a clutch housing that is connected for common rotation with a transmission input member. A rotatable hub member may be connected for common rotation with both the clutch housing and a gear member, thereby connecting the gear member for common rotation with the input member. Preferably, the rotatable hub member is connected to the clutch housing by the reaction plates that extend from the clutch housing.  
         [0004]     First and second torque-transmitting mechanisms may be packaged within the clutch housing. The torque-transmitting mechanisms have friction plates that are selectively engagable with at least some of the reaction plates to thereby connect the input member with respective different gear members. The rotatable hub member may be packaged between the first and second torque-transmitting mechanisms, minimizing required axial packaging space and thereby the overall axial length of the transmission.  
         [0005]     In one aspect of the invention, one of the torque-transmitting mechanisms packaged radially inward of the rotatable clutch housing is selectively engagable to connect for common rotation with the clutch housing a member of a planetary gear set that is spaced axially from the rotatable clutch housing. Two other planetary gear sets are located between the planetary gear set and the clutch housing. By locating the first torque-transmitting mechanism radially inward of the clutch housing adjacent the second torque-transmitting mechanism rather than adjacent the planetary gear set member that it selectively connects with the clutch housing, common hydraulic feed may be utilized for the two torque-transmitting mechanisms, eliminating the need to route hydraulic feed to the axial location of the planetary gear set.  
         [0006]     In referring to first, second and third planetary gear sets in this description and in the claims, these sets may be counted “first” to “third” in any order in the drawings (i.e., left to right, right to left, etc.). Additionally, the first, second or third members of each planetary gear set may be counted “first” to “third” in any order in the drawings (i.e., top to bottom, bottom to top, etc.) for each gear set.  
         [0007]     In another aspect of the invention, additional torque-transmitting mechanisms may be supplied to obtain up to eight forward speed ratios and three reverse speed ratios. Preferably, a center support of the transmission housing is utilized to provide torque reaction and hydraulic feed for at least some of the additional torque-transmitting mechanisms. The invention also provides a minimum content transmission that obtains seven forward speed ratios utilizing only five torque-transmitting mechanisms. This transmission includes a first interconnecting member that continuously interconnects a first member of the first planetary gear set with the first member of the second planetary gear set and a second interconnecting member that continuously interconnects the second member of the second planetary gear set with the first member of the third planetary gear set. Additionally, the third member of the second planetary gear set is continuously connected with a stationary member such as the transmission housing.  
         [0008]     Three reverse speed ratios may be obtained by the minimum content transmission described above by adding a selectable one-way hydraulic clutch actuatable to ground one of the members of the planetary gear sets to the stationary member.  
         [0009]     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic cross-sectional representation of a first embodiment of a powertrain including a transmission having three planetary gear sets and seven torque-transmitting mechanisms with two of the torque-transmitting mechanisms packaged within a rotatable clutch housing connected with an input member and having a gear member connected with the input member via the rotatable clutch housing;  
         [0011]      FIG. 2  is a truth table depicting some of the operating characteristics of the transmission shown in  FIG. 1 ;  
         [0012]      FIG. 3  is a chart depicting other operating characteristics of the transmission shown in  FIG. 1 ;  
         [0013]      FIG. 4  is a schematic cross-sectional representation of a second embodiment of a powertrain having a transmission utilizing five torque-transmitting mechanisms to achieve seven forward speed ratios as well as a selectable one-way clutch to obtain three reverse speed ratios;  
         [0014]      FIG. 5  is a truth table depicting some of the operating characteristics of the powertrain shown in  FIG. 4 ;  
         [0015]      FIG. 6  is a chart depicting other operating characteristics of the powertrain of  FIG. 4 ; and  
         [0016]      FIG. 7  is a schematic cross-sectional representation of the selectable one-way clutch used in the transmission of  FIG. 4 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Referring to the drawings, wherein like reference numerals represent the same or corresponding components through the several views, shown in  FIG. 1 , a powertrain  10  having a convention engine and torque converter  12 , a planetary transmission  14  and a convention final drive mechanism  16 . Only the top half of the transmission  14  is depicted.  
         [0018]     The planetary transmission  14  includes an input member or shaft  17  continuously connected with the engine and torque converter  12 , a planetary gear arrangement  18 , and an output member or shaft  19  continuously connected with the final drive mechanism  16 .  
         [0000]     Packaging of Drive Member  
         [0019]     A rotatable clutch housing  20  is continuously connected with the input member  17  and rotates therewith. A plurality of reaction plates  22  extend radially inward from the clutch housing  20 . The clutch housing  20  is annular, forming a generally C-shaped channel. A rotatable hub member  24  is connected for common rotation with at least one of the plates  22  such that the hub member  24  rotates commonly with the clutch housing  20  and the input member  17 . The hub member  24  may also be referred to as a drive member.  
         [0020]     The planetary gear arrangement  18  includes three planetary gear sets  30 ,  40  and  50 . The planetary gear set  30  includes a sun gear member  32 , a ring gear member  34 , and a planet carrier member  37  (referred to as a second gear member in the claims). As used in the claims, a “gear member” may be a sun gear member, a ring gear member a carrier member or a pinion gear. The planet carrier member  37  rotatably supports a plurality of pinion gears  39  that are disposed in meshing relationship with both the sun gear member  32  and the ring gear member  34 .  
         [0021]     The planetary gear set  40  includes a sun gear member  42 , a ring gear member  44 , and a planet carrier member  47 . The planet carrier member  47  rotatably supports a plurality of pinion gears  49  that are disposed in meshing relationship with both the sun gear member  42  and the ring gear member  44 .  
         [0022]     The planetary gear set  50  includes a sun gear member  52  (referred to as a first gear member in the claims), a ring gear member  54 , and a planet carrier member  57  (refereed to as a third gear member in the claims). The planet carrier member  57  rotatably supports a plurality of pinion gears  59  that are disposed in meshing relationship with both the sun gear member  52  and the ring gear member  54 .  
         [0023]     The rotatable hub member  24  is continuously connected with the sun gear member  52 . Thus, the sun gear member  52  is connected for common rotation with the input member  17  via the rotatable hub member  24 , and the clutch housing  20 .  
         [0024]     The transmission  14  also includes seven torque-transmitting mechanisms  60 ,  62 ,  64 ,  66 ,  67 ,  68  and  69 . The torque-transmitting mechanisms  60 ,  62  and  64  are brakes, while the torque-transmitting mechanisms  66 ,  67 ,  68  and  69  are rotating clutches.  
         [0025]     The input shaft  17  is continuously connected with the sun gear member  52  via the clutch housing  20  and the rotatable hub member  24 . The output shaft  19  is continuously connected with ring gear member  34 . An interconnecting member  70  continuously interconnects the ring gear member  44  and the carrier member  57 . An interconnecting member  72  continuously connects the sun gear member  32  and the carrier member  47 . An interconnecting member  72  is. a sleeve shaft. The sun gear member  42  is continuously grounded to the transmission housing  80  via a center support member  82  which extends from the transmission housing  80 . The support member  82  may be integral with or a unitary part of the transmission housing  80  or may be a separate component. The transmission housing  80  may also be referred to as a stationary member or a casing.  
         [0026]     The carrier member  37  is selectively connectable with the transmission housing  80  via the brake  60 . The ring gear member  54  is selectively connected to the transmission housing  80  via the brake  62 . The carrier member  47  is selectively connectable with the transmission housing  80  through the brake  64 . The carrier member  37  is selectively connectable to the sun gear member  32  and with the carrier member  47  via the clutch  66 . The carrier member  47  is selectively connectable with the ring gear member  54  via the clutch  67 . The carrier member  37  is selectively connectable with the input member  17  via the clutch  68 . The carrier member  57  is selectively connectable with the input member  17  via the clutch  69 .  
         [0000]     Clutch Packaging Arrangement  
         [0027]     As shown in  FIG. 1 , both the first and second clutches  68 ,  69  are packaged radially inward of and enveloped by the clutch housing  20 . The clutch  68  includes friction plates  76  that are selectively engagable with reaction plates  22  on a first side of the hub member  24  (the right side in  FIG. 1 ) via selective hydraulic actuation of the apply piston  122 . The friction plates  76  are connected for common rotation with the carrier member  37  via sleeve shaft  74  which rotates about a center axis of rotation C. The interconnecting member  72  which is also a sleeve shaft, rotates concentrically with the sleeve shaft  74 . In fact, the input member  17  and the output member  19 , the planetary gear sets  30 ,  40  and  50  as well as the rotating portions of the torque-transmitting mechanisms rotate concentrically about the axis C.  
         [0028]     The clutch  69  includes friction plates  78  which are connected for common rotation with the carrier member  57 . The friction plates  78  are selectively engagable with reaction plates  22  on an opposite, second side of the hub member  24  (the left side in  FIG. 1 ). Thus, selective hydraulic actuation of an apply piston  126  engages the clutch  69  such that driving power from the input member  17  is relayed to the carrier member  57  via the clutch housing  20 .  
         [0000]     Hydraulic Feed and Torque Reaction  
         [0029]     The torque-transmitting mechanisms are clustered near one another to allow common hydraulic feed paths for supplying hydraulic fluid to selectively engage the torque-transmitting mechanisms. Integration of hydraulic feed to the torque-transmitting mechanisms minimized machining costs and simplifies componentry and assembly. For instance, the torque-transmitting mechanisms  60 ,  62 ,  64 ,  66  and  67  are fed hydraulic fluid via channels formed in the center support  82 . A valve body and electronic controller (not shown) are positioned to feed hydraulic fluid from a fluid source such as a pump through channel  84  formed through the transmission casing  80 . Channel  86  formed in support  82  aligns with channel  84 . Channel  86  may be formed, bored or otherwise machined through the support  82 . Channel  83  extends from channel  86  to allow hydraulic fluid to pressurize piston  110  when engagement of brake  62  is desired. Similarly channel  88  extends from channel  84  to allow hydraulic fluid flow to either piston  112  to allow selective engagement of brake  64  or to pressurize piston  108  to allow selective engagement of brake  60 . Internal valves (not shown) are positioned within one or more of the channels  83 ,  84 ,  86  and  88  to selectively open when flow through one of the channels to cause engagement of one of the pistons is desired. Because reaction plates for brakes  60 ,  62  and  64  are splined to an axially extending portion of the center support member  82 , the center support member  82  acts as a torque reaction member when any of the brakes  60 ,  62  or  64  is applied.  
         [0030]     Channel  90  runs axially and is in fluid communication with channel  86 . Channels  92 A,  92 B,  92 C and  92 D are formed machined or otherwise provided in an axially extending portion of the center support  82  in fluid communication with channel  90 . Channels  94 A and  94 B are formed in rotatable hub member  93  such that channel  94 A aligns axially with channel  92 A and channel  94 B aligns axially with channel  92 B. Thus, selective engagement of clutch  66  is achieved by fluid flow through channels  84 ,  86 ,  90 ,  92 B and  94 B to pressurize piston  114 , thereby engaging clutch  66 . Fluid flow through channel  92 A and channel  94 A controls pressure in a balance dam formed between piston  114  and dam member  116 . Similarly, fluid through channels  84 ,  86 ,  90 ,  92 C and  94 C pressurizes piston  118  to selectively engage clutch  67 . Pressure through channels  84 ,  86 ,  90 ,  92 D and  94 D controls pressure in a balance dam chamber formed between piston  118  and dam member  120 .  
         [0031]     Hydraulic feed for clutches  68  and  69  is similarly integrated. Hydraulic feed from the valve body, fluid source and electronic controller (not shown) is provided through channel  96  to channel  98  and channel  100  all of which are formed or otherwise machined in the transmission casing  80 . Channels  102 A,  102 B and  102 C radially extend from channel  100  and axially align with channels  104 A,  104 B and  104 C respectively formed in the clutch housing  20 . When engagement of the clutch  68  is desired, internal valves within the channels allows fluid flow through channel  102 B and channel  104 B to pressurize apply piston  122  and thereby engage the clutch  68 . When selective engagement of clutch  69  is desired, the internal valves direct fluid flow from channels  96 ,  98  and  100  through channels  102 C and  104 C to pressurize apply piston  126 . Fluid may be directed through channels  102 A and  104 A into a chamber formed between dam member  124  and apply piston  122  to counteract fluid pressure in the apply chamber formed between pistons  122  and  126  or the chamber formed between the clutch housing  20  and apply piston  126 .  
         [0000]     Establishment of Multiple Speed Ratios  
         [0032]     The input shaft  17  is continuously connected with the sun gear member  52  through the clutch housing  20  and hub member  24 . The ring gear member  44  is continuously connected with the carrier member  57  through the interconnecting member  70 . The sun gear member  32  is continuously connected with the carrier member  47  through the interconnecting member  72 . The sun gear member  42  is continuously grounded to the transmission housing  80  through the center support  82 .  
         [0033]     The carrier member  37  is selectively grounded to the transmission housing  80  through the brake  60 . The ring gear member  54  is selectively grounded to the transmission housing  80  through the brake  62 . The carrier member  47  and the sun gear member  32  (via the interconnecting member  72 ) are selectively grounded to the transmission housing  80  through the brake  64 . The carrier member  37  is selectively connectable with the sun gear member  32  through the clutch  66 . The carrier member  47  and the sun gear member  32  are selectively connectable with the ring gear member  54  through the clutch  67 . The input member  17  is selectively connectable with the carrier member  37  through the clutch  68 . The input member  17  is selectively connectable with the carrier member  57  (and thereby with the ring gear member  44  via the interconnecting member  70 ) through the clutch  69 .  
         [0034]     As shown in the truth table of  FIG. 2 , the torque-transmitting mechanisms  60 ,  62 ,  64 ,  66 ,  67 ,  68  and  69  are selectively engagable in combinations of two to provide eight forward speed ratios and three reverse speed ratios.  
         [0035]     The third reverse (Reverse # 3 ) speed ratio is established with the engagement of the brakes  60  and  62 . The brake  60  connects the carrier member  37  with the stationary transmission housing  80  and the brake  62  connects the ring gear member  54  with the transmission housing  80 . The sun gear member  52  rotates at the same speed as the input shaft  17 . The carrier member  57  rotates at the same speed as the ring gear member  44 . The ring gear member  54  does not rotate. The carrier member  57  rotates at a speed determined from the speed of the sun gear member  52  and the ring gear/sun gear tooth ratio of the planetary gear set  50 . The carrier member  47  rotates at the same speed as the sun gear member  32 . The sun gear member  42  does not rotate. The carrier member  47  rotates at a speed determined from the speed of the ring gear member  44  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The carrier member  37  does not rotate. The ring gear member  34  rotates at the same speed as the output shaft  19 . The ring gear member  34 , and therefore the output shaft  19 , rotates at a speed determined from the speed of the sun gear member  32  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The numerical value of the third reverse (Reverse # 3 ) speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  30 ,  40  and  50 .  
         [0036]     The second reverse (Reverse # 2 ) speed ratio is established with the engagement of the brake  60  and the clutch  67 . The brake  60  grounds the carrier member  37  to the transmission housing  80 , and the clutch  67  connects the carrier member  57  (and the sun gear member  32  via the interconnecting member  72 ) with the ring gear member  54 . The sun gear member  52  rotates at the same speed as the input shaft  17 . The carrier member  57  rotates at the same speed as the ring gear member  44 . The ring gear member  54 , the carrier member  47  and the sun gear member  32  rotate at the same speed. The ring gear member  54 , and therefore the sun gear member  32 , rotates at a speed determined from the speed of the carrier member  57 , the speed of the sun gear member  52  and the ring gear/sun gear tooth ratio of the planetary gear set  50 . The carrier member  37  does not rotate. The ring gear member  34  rotates at the same speed as the output shaft  19 . The ring gear member  34 , and therefore the output shaft  19 , rotates at a speed determined from the speed of the sun gear member  32  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The numerical value of the second reverse (Reverse # 2 ) speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  30  and  50 .  
         [0037]     The first reverse (Reverse # 1 ) speed ratio is established with the engagement of the brake  60  and the clutch  69 . The brake  60  grounds the carrier member  37  to the transmission housing  80 , and the clutch  69  connects the carrier member  57  with the sun gear member  52  and thereby with the input shaft  17 . The planetary gear set  50  and the ring gear member  44  rotate at the same speed as the input shaft  17 . The carrier member  47  rotates at the same speed as the sun gear member  32 . The sun gear member  42  does not rotate. The carrier member  47  rotates at a speed determined from the speed of the ring gear member  44  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The carrier member  37  does not rotate. The ring gear member  34  rotates at the same speed as the output shaft  19 . The ring gear member  34 , and therefore the output shaft  19 , rotates at a speed determined from the speed of the sun gear member  32  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The numerical value of the first reverse (Reverse # 1 ) speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  30  and  40 .  
         [0038]     The first forward speed ratio is established with the engagement of the brake  62  and the clutch  66 . The brake  62  grounds the ring gear member  54  to the transmission housing  80 , and the clutch  66  connects the sun gear member  32  with the carrier member  37 . The sun gear member  52  rotates at the same speed as the input shaft  17 . The carrier member  57  rotates at the same speed as the ring gear member  44 . The ring gear member  54  does not rotate. The carrier member  57  rotates at a speed determined from the speed of the sun gear member  52  and the ring gear/sun gear tooth ratio of the planetary gear set  50 . The sun gear member  42  does not rotate. The carrier member  47  and the planetary gear set  30  rotate at the same speed as the output shaft  19 . The carrier member  47 , and therefore the output shaft  19 , rotates at a speed determined from the speed of the ring gear member  44  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The numerical value of the first forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  40  and  50 .  
         [0039]     The second forward speed ratio is established with the engagement of the clutches  66  and  67 . The clutch  66  connects the sun gear member  32  with the carrier member  37 , and the clutch  67  connects the carrier member  47  with the ring gear member  54 . The sun gear member  52  rotates at the same speed as the input shaft  17 . The carrier member  57  rotates at the same speed as the ring gear member  44 . The ring gear member  54 , the carrier member  47  and the planetary gear set  30  rotate at the same speed as the output shaft  19 . The ring gear member  54 , and therefore the output shaft  19 , rotates at a speed determined from the speed of the carrier member  57 , the speed of the sun gear member  52  and the ring gear/sun gear tooth ratio of the planetary gear set  50 . The numerical value of the second forward speed ratio is determined utilizing the ring gear/sun gear tooth ratio of the planetary gear set  50 .  
         [0040]     The third forward speed ratio is established with the engagement of the clutches  66  and  69 . The clutch  66  connects the sun gear member  52  with the carrier member  57 , and the clutch  69  connects the carrier member  57  with the sun gear member  52  and the input shaft  17 . The planetary gear set  50  and the ring gear member  44  rotate at the same speed as the input shaft  17 . The carrier member  47  and the planetary gear set  30  rotate at the same speed as the output shaft  19 . The sun gear member  42  does not rotate. The-carrier member  47 , and therefore the output shaft  19 , rotates at a speed determined from the speed of the ring gear member  44  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The numerical value of the third forward speed ratio is determined utilizing the ring gear/sun gear tooth ratio of the planetary gear set  40 .  
         [0041]     The fourth forward speed ratio is established with the engagement of the clutches  66  and  68 . The clutch  66  connects the carrier member  37  with the sun gear member  32 , and the clutch  68  connects the input shaft  17  and sun gear member  52  with the carrier member  37 . In this configuration, the planetary gear set  30  and the output shaft  19  rotate at the same speed as the input shaft  17 . The numerical value of the fourth forward speed ratio is 1.00.  
         [0042]     The fifth forward speed ratio is established with the engagement of the clutches  68  and  69 . The clutch  68  connects the carrier member  37  with the sun gear member  52 , and the clutch  69  connects the sun gear member  52  with carrier member  57 . The planetary gear set  50 , the ring gear member  44  and the carrier member  37  rotate at the same speed as the input shaft  17 . The carrier member  47  rotates at the same speed as the sun gear member  32 . The sun gear member  42  does not rotate. The carrier member  47  rotates at a speed determined from the speed of the ring gear member  44  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The ring gear member  34  rotates at the same speed as the output shaft  19 . The ring gear member  34 , and therefore the output shaft  19 , rotates at a speed determined from the speed of the carrier member  37 , the speed of the sun gear member  32  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The numerical value of the fifth forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  30  and  40 .  
         [0043]     The sixth forward speed ratio is established with the engagement of the clutches  67  and  68 . The clutch  67  connects the carrier member  47  with the ring gear member  54 , and the clutch  68  connects the carrier member  37  with the sun gear member  52 , and therefore with the input shaft  17 . The sun gear member  52  and the carrier member  37  rotate at the same speed as the input shaft  17 . The carrier member  57  rotates as the same speed as the ring gear member  44 . The ring gear member  54  and the carrier member  47  rotate at the same speed as the sun gear member  32 . The ring gear member  54 , and therefore the sun gear member  32 , rotates at a speed determined from the speed of the carrier member  57 , the speed of the sun gear member  52  and the ring gear/sun gear tooth ratio of the planetary gear set  50 . The ring gear member  34  rotates at the same speed as the output shaft  19 . The ring gear member  34 , and therefore the output shaft  19 , rotates at a speed determined from the speed of the carrier member  37 , the speed of the sun gear member  32  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The numerical value of the sixth forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  30  and  50 .  
         [0044]     The seventh forward speed ratio is established with the engagement of the brake  62  and the clutch  68 . The brake  62  grounds the ring gear member  54  with the transmission housing  80 , and the clutch  68  connects the carrier member  37  with the sun gear member  52  and therefore with the input shaft  17 . The sun gear member  52  and the carrier member  37  rotate at the same speed as the input shaft  17 . The carrier member  57  rotates at the same speed as the ring gear member  44 . The ring gear member  54  does not rotate. The carrier member  57  rotates at a speed determined from the speed of the sun gear member  52  and the ring gear/sun gear tooth ratio of the planetary gear set  50 . The carrier member  47  rotates at the same speed as the sun gear member  32 . The sun gear member  42  does not rotate. The carrier member  47  rotates at a speed determined from the speed of the ring gear member  44  and the ring gear/sun gear tooth ratio of the planetary gear set  40 . The ring gear member  34  rotates at the same speed as the output shaft  19 . The ring gear member  34 , and therefore the output shaft  19 , rotates at a speed determined from the speed of the carrier member  37 , the speed of the sun gear member  32  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The numerical value of the seventh forward speed ratio is determined utilizing the ring gear/sun gear tooth ratios of the planetary gear sets  30 ,  40  and  50 .  
         [0045]     The eighth forward speed ratio is established with the engagement of the brake  64  and the clutch  68 . The brake  64  grounds the carrier member  47  to the transmission housing  80 , and the clutch  68  connects the carrier member  37  with the sun gear member  52 , and therefore with the input shaft  17 . The carrier member  37  rotates at the same speed as the sun gear member  52  and the input shaft  17 . The sun gear member  32 , the planetary gear set  40  and the carrier member  57  do not rotate. The ring gear member  34  rotates at the same speed as the output shaft  19 . The ring gear member  34 , and therefore the output shaft  19 , rotates at a speed determined from the speed of the carrier member  37  and the ring gear/sun gear tooth ratio of the planetary gear set  30 . The numerical value of the eighth forward speed ratio is determined utilizing the ring gear/sun gear tooth ratio of the planetary gear set  30 .  
         [0046]     As set forth above, the engagement schedule for the torque-transmitting mechanisms of the transmission  14  of  FIG. 1  is shown in the truth table of  FIG. 2 . The truth table of  FIG. 2  also provides an example of speed ratios that are available utilizing the following ring gear/sun gear tooth ratios: N R1 /N S1= 1.75 (value of the tooth ratio of the planetary gear set  30 ); N R2 /N S2 = 1.84 (value of the tooth ratio of the planetary gear set  40 ); and N R3 /N S3 =2.25 (value of the tooth ratio of the planetary gear set  50 ). The chart of  FIG. 3  describes the ratio steps attained utilizing these sample tooth ratios. For example, the step ratio between the first and second forward speed ratios is 1.81, while the step ratio between the first reverse speed ratio (Reverse # 1 ) and the first forward speed ratio is −0.54. It should be noted that both the single and double step forward ratio changes as well as the reverse ratio changes are of the single transition variety.  
         [0047]      FIG. 4  shows another embodiment of a powertrain  200  having a planetary transmission  214  and a planetary gear arrangement  218 . The transmission  214  is the same as the transmission  14  of  FIG. 1  expect that brake  64  is removed and brake  60  is replaced with a selectable one-way clutch (SOWC)  161 . With the elimination of brake  64 , only seven forward speed ratios are achieved. The SOWC  161  is utilized in each of the three reverse speed ratios, as indicated in the truth table of  FIG. 5 . As described above for the transmission  14  of  FIG. 1 , those skilled in the art will understand from the truth table of  FIG. 5  how the speed ratios are established through the planetary gear sets  30 ,  40  and  50 . Assuming the same tooth ratio values described above with respect to the transmission  14  in  FIG. 1 , the ratio steps indicated in  FIG. 6  may be achieved. According to a preferred embodiment of the present invention, the SOWC  161  is a mechanical diode-based SOWC. It should be appreciated, however, that according to alternate embodiments the mechanical diode-based SOWC  161  may be replaced with other selectable one-way clutches. The SOWC  61  is potentially a lower cost option than a friction based torque-transmitting mechanism and avoids spin losses associated with hydraulically applied friction based torque-transmitting mechanisms.  
         [0048]     As shown in  FIG. 4 , the SOWC  161  includes a first and second race  226 ,  228 . The SOWC  161  and the races  226 ,  228  are shown in more detail in  FIG. 7 , which is a schematic cross-sectional view taken at the arrows indicated in  FIG. 4 . The first race  226  is connected for common rotation with a hub member  233  that is connected to the carrier member  37 . The second race  228  is grounded to the transmission housing  80 . The first race  226  is configured to selectively either spin relative to the second race  228  (i.e., freewheel), or lock-up as a single grounded unit. Referring to  FIG. 7 , the first race  226  defines first and second recessed portions  232 ,  234  adapted to respectively retain first and second struts  236 ,  238 , and first and second springs  240 ,  242 . The second race  228  defines first and second engagement shoulders  244 ,  246  each adapted to engage one of the first and second struts  236 ,  238  to lock-up the clutch  161 .  
         [0049]     When the first and second springs  240 ,  242  are in a compressed position, the struts  236 ,  238  are retracted within the recessed portions  232 ,  234  of the race  226  such that the shoulders  244 ,  246  are not engaged and the first race  226  freewheels in both clockwise and counter-clockwise directions. When the first and second springs  240 ,  242  are in an extended position, the struts  236 ,  238  protract from their respective recessed portions  232 ,  234  and respectively engage the first and second engagement shoulders  244 ,  246  such that the SOWC  161  locks-up in both clockwise and counter-clockwise directions. Additionally, by compressing one of the springs  240 ,  242  and extending the other, the SOWC  161  can be locked-up in one direction and freewheel in the opposite direction.  
         [0050]     The springs  240 ,  242  are configured to push the struts  236 ,  238  into engagement with the shoulders  244 ,  246  such that in the steady state position the SOWC  161  is locked-up in both directions. Therefore, for purposes of releasing the SOWC  161 , a selector plate  248  (shown in both  FIGS. 4 and 7 ) is provided. The selector plate  248  is adapted to selectively translate and engage one of the struts  236 ,  238  such that the engaged strut is pushed toward its respective recessed portion  232 ,  234  and out of engagement with its respective shoulder  244 ,  246 . As an example, the selector plate  248  may be translated into engagement with strut  236  thereby compressing the spring  240  and retracting the strut  236  out of engagement with the shoulder  244  such that race  226  is rotatable in a clockwise direction relative to race  228 . Conversely, the selector plate  248  may be translated into engagement with strut  238  thereby compressing the spring  242  and retracting the strut  238  out of engagement with the shoulder  246  such that race  226  is rotatable in a counter-clockwise direction relative to race  228 .  
         [0051]     According to a preferred embodiment, the selector plate  248  is hydraulically translatable using a conventional hydraulic device such as the hydraulic actuator  230 . The hydraulic actuator  230  includes a return spring  231  adapted to push the selector plate  248  into engagement with one of the struts  236 ,  238  such that SOWC  161  is mechanically biased into a one-way operational mode. Hydraulic actuation of the selector plate  248  by the actuator  230  overcomes the return spring  231  and translates the selector plate  248  into a position between the struts  236 ,  238  such that the SOWC  161  is locked in both directions. In this manner, the SOWC  161  is hydraulically engaged with the actuator  230  and mechanically released with the return spring  231 .  
         [0052]     Thus, the transmission  214  of  FIG. 4  achieves seven forward speed ratios utilizing only five torque-transmitting mechanisms and also achieves three reverse speed ratios by utilizing the torque-transmitting mechanisms in combination with the SOWC  161 .  
         [0053]     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.