Abstract:
A multi-speed transmission includes a first power transmission module driven by an input shaft. A second power transmission module is driven by the first power transmission module. A third power transmission module is driven by the second power transmission module and drives an output shaft. Each power transmission module includes an actuation mechanism and a planetary gearset. Each actuation mechanism controls the output of its respective planetary gearset to one of a first gear ratio and a second gear ratio. One of the actuation mechanisms includes a clutch and a spring biasing a member to rotate and cause a corresponding actuation of the clutch. The clutch causes two members of the respective planetary gearset to rotate at substantially the same speed and provide the first gear ratio. The actuation mechanism selectively restricts the member from rotating and prevent actuation of the clutch to provide the second gear ratio.

Description:
This application claims the benefits of U.S. Provisional Application No. 60/984,829, filed Nov. 2, 2007. 
    
    
     FIELD 
     The present disclosure generally relates to automatic transmissions for vehicles. More particularly, multi-speed power shift transmissions having multiple epicyclic units are disclosed. 
     BACKGROUND 
     Many vehicles have been equipped with a power train including an engine and a multi-speed transmission. The multi-speed transmission allows torque to be transferred from the engine through a wide range of vehicle speeds. The engine operates through its torque range a number of times corresponding to the number of forward speed ratios that are available in the transmission. 
     A variety of manufacturers have provided three speed and four speed automatic transmissions. Other transmissions have been constructed or described in publications suggesting six, seven or eight speed automatic transmissions. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio changes substantially imperceptible to the operator under normal vehicle acceleration. However, previously known transmissions providing six or more forward speed gear ratios are relatively complex, heavy and difficult to package because of their relatively large size. Furthermore, these transmissions are relatively expensive to construct due to the complex machining of multiple fluid passageways required to actuate multiple hydraulically operated brakes and clutches found within the automatic transmissions. 
     SUMMARY 
     A multi-speed transmission includes an input shaft, an output shaft, and a first power transmission module driven by the input shaft. A second power transmission module is driven by the first power transmission module. A third power transmission module is driven by the second power transmission module and drives the output shaft. Each power transmission module includes an actuation mechanism and a planetary gearset. Each actuation mechanism is operable to control the output of its respective planetary gearset to one of a first gear ratio and a second gear ratio. One of the actuation mechanisms includes a clutch and a spring biasing a member to rotate and cause a corresponding actuation of the clutch. The clutch causes two members of the respective planetary gearset to rotate at substantially the same speed and provide the first gear ratio. The actuation mechanism is operable to selectively restrict the member from rotating and prevent actuation of the clutch to provide the second gear ratio. 
     In another form, a multi-speed transmission includes an input shaft, an output shaft and a first power transmission module driven by the input shaft. A second power transmission module is driven by the first power transmission module and drives the output shaft. Each power transmission module includes an actuation mechanism and a planetary gearset. Each actuation mechanism is operable to control the output of its respective planetary gearset to one of a first gear ratio and a different second gear ratio. One of the actuation mechanisms includes a ball ramp mechanism biased to actuate a clutch without external input. The clutch causes two members of the respective planetary gearset to rotate at substantially the same speed to provide the first gear ratio. The actuation mechanism is operable to restrict the ball ramp mechanism and prevent actuation of the clutch to provide the second gear ratio. 
     In another form, a multi-speed transmission includes an input shaft, an output shaft and a first planetary gearset outputting one of a gear ratio equal to 1 or a gear ratio less than 1 and being driven by the input shaft. A second planetary gearset outputs one of a gear ratio equal to 1 or a gear ratio greater than 1 and is driven by the first planetary gearset. A third planetary gearset outputs a gear ratio equal to 1 or a gear ratio greater than 1, is driven by the second planetary gearset and drive the output shaft. A biasing mechanism causes the second planetary gearset to output the gear ratio equal to 1. A brake counteracting the biasing mechanism causes the second planetary gearset to output the gear ratio greater than 1. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       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 cross-sectional view of a seven speed automatic transmission; 
         FIG. 2  is a gear ratio, ratio step and shift chart relating to the seven speed transmission depicted in  FIG. 1 ; 
         FIG. 3  is an enlarged fragmentary cross-sectional view of a power transmission module shown in  FIG. 1 ; 
         FIG. 4  is an enlarged fragmentary cross-sectional view of another power transmission module shown in  FIG. 1 ; 
         FIG. 5  is a cross-sectional view showing a band brake actuation mechanism; 
         FIG. 6  is a cross-sectional view of a ten speed automatic transmission; 
         FIG. 7  is a gear ratio, ratio step and shift chart relating to the ten speed transmission depicted in  FIG. 6 ; and 
         FIG. 8  is a cross-sectional view depicting a two-piece transmission housing. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     A multi-speed epicyclic power shift transmission  10  is depicted in  FIG. 1 . Transmission  10  includes an input shaft  12 , a first power transmission module  14 , a second power transmission module  16 , a third power transmission module  18  and an output shaft  20 . A reverse gearset  22  is also provided and at least partially supported on a countershaft  24 . A shift mechanism  26  is provided to allow a user to selectively place transmission  10  in one of a forward drive, a reverse drive or a neutral mode. In the forward drive mode, power is transferred from the vehicle engine to rotate output shaft  20  in a first direction. In the neutral mode, power is not transferred to output shaft  20 . In the reverse drive mode, output shaft  20  rotates in an opposite direction from the forward drive mode rotational direction. Transmission  10  is arranged to provide seven forward speeds and one reverse speed. As will be described in greater detail, many similar automatic transmission may be constructed implementing the inventive concepts of the present disclosure. As such, it is contemplated that seven, eight, nine, ten, eleven and twelve speed power shift transmissions having a single input shaft are within the scope of the present disclosure. 
     First power transmission module  14  is arranged as an overdrive module selectively providing one of an overdrive ratio of 0.75:1 when in the active mode or a direct drive ratio of 1:1 when operating in an inactive mode. Second power transmission module  16  is arranged as a gear reduction unit providing a reduction ratio of 2.86:1 when in an active mode or a direct drive ratio of 1:1 when in an inactive mode. Third power transmission module  18  is arranged as a gear reduction unit providing a reduction ratio of 1.61:1 when in an active mode or a direct drive ratio of 1:1 when in an inactive mode. By selectively operating each of first, second and third power transmission modules  14 ,  16 ,  18  in one of the active or inactive modes previously mentioned, seven forward speeds having relatively small drive ratio steps therebetween may be provided. It should be appreciated that the particular gear ratio provided by any one power transmission module may be other than the examples provided without departing from the scope of the present disclosure. In particular, other individual power transmission module gear ratios may be combined to provide a different overall final drive ratio range more suitable for another application. The ease of creating different planetary gearsets leads to assembling various power transmission modules having different gear ratios without great expense. 
       FIG. 2  depicts a shift chart providing exemplary final drive ratios that may be obtained by selectively activating one of first, second and third power transmission modules  14 ,  16 ,  18 . As previously implied, a power transmission module will be considered active when a ratio other than the direct drive ratio of 1:1 is being transferred. Accordingly, a first gear final drive ratio of 4.51:1 is provided when second power transmission module  16  and third power transmission module  18  are in the active mode while first power transmission module  14  is in the inactive mode. Operation of transmission  10  provides various other final drive ratios as will be described hereinafter. 
       FIG. 1  shows an optional wet clutch  30  selectively drivingly interconnecting first input shaft  12  with an auxiliary shaft  32 . Clutch  30  includes a hub  34  fixed for rotation with auxiliary shaft  32 . A drum  36  is fixed for rotation with input shaft  12 . A plurality of interleaved friction plates  38  may be selectively forced into contact with one another to transfer torque between hub  34  and drum  36 . It is contemplated that at least some torque is transferred through clutch  30  at all times of operation of transmission  10 . Through the use of clutch  30  in this manner, transmission  10  may be directly coupled to an engine (not shown) thereby alleviating the need for a torque converter. 
     First power transmission module  14  includes a planetary gearset  40  having a sun gear  42  rotatably supported on input shaft  12 , a ring gear  44  and a plurality of pinion gears  46  meshingly engaged with ring gear  44  and sun gear  42 . A carrier  48  rotatably supports pinion gears  46 . One portion of carrier  48  is fixed to or integrally formed with input shaft  12 . A drum  50  is fixed for rotation with sun gear  42 . An actuation clutch  52  selectively drivingly couples drum  50  to a housing  54  to restrict rotation of drum  50 . Power transmission module  14  may be placed in the active mode by actuating clutch  52  to act as a brake restricting sun gear  42  from rotation. Power flows through first transmission module  14  input at carrier  48  and output at ring gear  44 . A drive plate  56  drivingly interconnects ring gear  44  and second power transmission module  16 . Accordingly, when clutch  52  is transferring torque, first power transmission module  14  transfers power at an overdrive ratio. 
     In the inactive mode of operating first power transmission module  14 , clutch  52  is released and does not transfer torque. Sun gear  42  is allowed to rotate relative to housing  54 . A one-way clutch  58  interconnects carrier  48  and ring gear  44 . One-way clutch  58  allows relative rotation of carrier  48  relative to ring gear  44  in a first direction but restricts relative rotation between the two components in an opposite direction. Accordingly, when a direct drive ratio of 1:1 is desired, one-way clutch  58  assures that ring gear  44  and carrier  48  rotate at the same speed in the same direction such that the torque magnitude input to carrier  48  equals the torque magnitude output by ring gear  44 . 
     Depending on the direction of torque transfer, power transmission modules  14 ,  16  and  18  operate in one of a drive mode and a coast mode. In the drive mode, torque is being provided from the vehicle engine and transferred across the power transmission module toward output shaft  20 . In the coast mode, torque is being provided by a vehicle driveline (now shown) to output shaft  20  and transferred toward the vehicle engine. It has been discovered that many vehicle operators desire some magnitude of engine braking when the engine throttle is released. Engine braking may occur during coast mode operation. With reference to first power transmission module  14 , one-way clutch  58  is overrunning during the drive mode of operation. In the coast mode of operation, one-way clutch  58  reacts torque and causes carrier  48  to rotate at the same speed as ring gear  44 . 
       FIG. 3  depicts an enlarged view of second power transmission module  16  including a planetary gearset  60  and an actuation mechanism  62 . Actuation mechanism  62  includes a ball ramp actuator  64  and a friction plate clutch  66 . Actuation mechanism  62  is selectively operable to place second power transmission module in one of the active and inactive modes. A direct drive ratio of 1:1 may be achieved by causing sun gear  68  and ring gear  74  to rotate at the same speed. Actuation mechanism  62  is configured to provide the direct drive 1:1 ratio when in the inactive mode. 
     Planetary gearset  60  includes a sun gear  68  supported for rotation on a center shaft  70 . Center shaft  70  is rotatably supported by input shaft  12  and a stub shaft  72 . Planetary gearset  60  also includes a ring gear  74  and a plurality of pinion gears  76  in meshed driving engagement with sun gear  68  and ring gear  74 . A carrier  78  rotatably supports pinion gears  76 . Carrier  78  is supported for rotation on center shaft  70  and is arranged as the output of second power transmission module  16  being continuously drivingly coupled to third power transmission module  18 . As previously mentioned, the input to second power transmission module  16  is provided by drive plate  56  driving sun gear  68   
     Ball ramp actuator  64  includes a torsional spring  80  applying a torque to a rotary plate  82 . Ball ramp actuator  64  also includes a reaction plate  84  and a plurality of balls  86  positioned between rotary plate  82  and reaction plate  84 . At least one of rotary plate  82  and reaction plate  84  includes tapered grooves  88 ,  90  in receipt of balls  86 . Relative rotation between rotary plate  82  and reaction plate  84  causes a change in the spacing between an outer surface  92  of reaction plate  84  and an outer surface  94  of rotary plate  82 . 
     A brake  96  includes a brake drum  100  fixed for rotation with rotary plate  82  and a band  102  selectively engageable with brake drum  100  to restrict rotary plate  82  from rotation. When second power transmission module  16  is in the inactive mode, band  102  is not engaged brake drum  100 . Accordingly, torsional spring  80  causes rotary plate  82  to rotate relative to reaction plate  84  and space apart outer surface  92  and outer surface  94  relative to one another. Because reaction plate  84  is axially fixed, rotary plate  82  axially translates to actuate clutch  66 . Clutch  66  includes a plurality of inner plates  104  fixed for rotation but axially moveable relative to sun gear  68  as well as a plurality of outer clutch plates  106  fixed for rotation with ring gear  74 . When ball ramp actuator  64  is actuated by torsion spring  80 , clutch  66  acts to fix sun gear  68  for rotation with ring gear  74  and provide a direct drive 1:1 ratio through second power transmission module  16 . When band  102  is disengaged from brake drum  100  and second power transmission module  16  is operating in an inactive direct drive mode, one-way clutches  110  and  112  are overrunning. 
     Band  102  is placed in frictional engagement with brake drum  100  when a gear reduction ratio is desired from second power transmission module  16 . Second power transmission module  16  is now in the active drive mode. By restricting brake drum  100  from rotation relative to housing  54 , rotary plate  82  is also restricted from rotating relative to reaction plate  84 . At this time, the axial spacing between outer surface  92  and outer surface  94  is minimized such that a force is not imparted to clutch  66 . Ring gear  74  may rotate relative to sun gear  68 . One-way clutch  110  reacts torque provided from ring gear  74 . One-way clutch  112  is overrunning. Therefore, a drive reduction exists between sun gear  68  and carrier  78 . Up until this point, operation of second power transmission module  16  has been discussed in view of transferring torque from sun gear  68  to carrier  78  in the drive mode. As previously mentioned, it may be desirable to transfer torque in the coast mode of operation where output shaft  20  functions as the input and input shaft  12  functions as the output. In particular, it may be desirable to provide some level of engine braking via the driveline and transmission  10 . Specifically, when second power transmission module  16  operates in the inactive coast mode, one-way clutch  112  prevents ring gear  74  from overrunning sun gear  68 . At the same time one-way clutch  110  is overrunning. 
     When second power transmission module  16  operates in the active coast mode of operation, carrier  78  acts as an input while sun gear  68  acts as an output. One-way clutch  112  is in an overrunning condition while one-way clutch  110  reacts torque from ring gear  74 . 
     Third power transmission module  18  is depicted in  FIGS. 1 and 4  and includes a planetary gearset  120  and an actuator  122 . Actuator  122  includes a ball ramp actuator  124  and a friction plate clutch  126 . Planetary gearset  120  includes a sun gear  130  supported for rotation on stub shaft  72 , a ring gear  132  and a plurality of pinion gears  134  in driving meshed engagement with sun gear  130  and ring gear  132 . A carrier  136  supports pinion gears  134  for rotation. Third power transmission module  18  is configured such that ring gear  132  is the input and carrier  136  provides the output when operating in the drive mode. 
     Third power transmission module  18  is configured substantially similarly to second power transmission module  16  in that actuator  122  causes third power transmission module  18  to provide a direct drive 1:1 ratio when in the inactive mode and provides a reduced gear output when in the active mode. The direct drive 1:1 ratio is provided by restricting ring gear  132  from rotating relative to sun gear  130 . A drive plate  138  drivingly interconnects carrier  78  of second power transmission module  16  with ring gear  132  of third power transmission module  18 . A rotary spring  140  rotates a rotary plate  142  relative to a reaction plate  144  of ball ramp actuator  124 . Relative rotation between the plates causes a plurality of balls  146  to run up ramps and axially separate rotary plate  142  from reaction plate  144 . An axial force acts on friction clutch  126  to fix sun gear  130  and ring gear  132  to one another. A one-way clutch  148  and a one-way clutch  150  are overrunning when third power transmission module  18  is in the inactive drive mode providing a direct 1:1 ratio. When in the inactive coast mode, carrier  136  becomes the input and ring gear  132  becomes the output of third power transmission module  18 . At this time, one-way clutch  148  prevents sun gear  130  from overrunning ring gear  132 . One-way clutch  150  is overrunning during this mode of operation. 
     To operate third power transmission module  18  in the active or gear reduction mode, a band  152  is engaged with a brake drum  154 . Brake drum  154  is fixed to rotary plate  142 . Accordingly, engagement of band  152  with brake drum  154  restricts rotation of rotary plate  142  relative to reaction plate  144 . Friction clutch  126  does not transfer torque and sun gear  130  may rotate relative to ring gear  132 . In the active drive mode of operation, one-way clutch  148  is in an overrunning mode while one-way clutch  150  reacts torque to restrict sun gear  130  from rotating. When third power transmission module  18  operates in the active coast mode, one-way clutch  150  continues to transfer torque and one-way clutch  148  continues to be in an overrunning mode of operation. Band  152  remains engaged with brake drum  154  to hold the ball ramp actuator  124  off such that torque is not transferred through clutch  126 . 
       FIG. 5  shows an exemplary band actuation mechanism  160  operable to selectively engage band  152  with drum  154 . A first end  162  of band  152  is coupled to housing  54  by an adjustment mechanism  164 . Adjustment mechanism  164  includes a threaded rod  166  and a nut  168 . Threaded rod  166  may be translated to move first end  162  to a desired location. Once first end  162  is at the desired position, nut  168  may be tightened to fix the axial location of threaded rod  166  and first end  162 . A second end  170  of band  152  is fixed to an arm  172  selectively moveable by an electromechanical device  174 . Electromechanical device  174  is operable to move arm  172  between at least two positions corresponding to the band engaged and band disengaged from the brake drum positions. Accordingly, electromechanical device  174  may be constructed as a simple solenoid or may include an electric motor operable to move arm  172  to a variety of desired positions. It is contemplated that electromechanical device  174  be relatively small because the torque transfer between band  152  and brake drum  154  is relatively low having a magnitude less than 100 lb-ft. Alternatively, arm  172  may be selectively moved between two positions by a simple hydraulic device in lieu of electromechanical device  174 . Furthermore, band  102  may be selectively engaged or disengaged with brake drum  100  via a band actuation mechanism substantially similar to band actuation mechanism  160 . 
     Referring once again to  FIG. 1 , shift mechanism  26  of transmission  10  includes a shift fork  180  supported on a shift rail  182 . Shift rail  182  is axially moveable relative to and supported by housing  54 . Shift fork  180  is fixed to shift rail  182  and translates therewith. A shift collar  184  is in splined engagement with a hub  186  fixed for rotation with stub shaft  72 . Shift collar  184  is axially moveable relative to hub  186  between one of three positions, namely, a reverse position, a neutral position and a forward position. In the neutral position, shift collar  184  is clear of adjacent elements and torque is not transferred through collar  184 . When collar  184  is moved to the reverse position by axial translation of shift rail  182  and shift fork  180 , shift collar  184  engages a first drive sprocket  188  of reverse gearset  22 . Reverse gearset  22  also includes a driven sprocket  192  drivingly coupled to drive sprocket  188  via a chain  194 . Driven sprocket  192  is fixed for rotation with countershaft  24 . A reverse drive gear  196  is also fixed for rotation with countershaft  24 . Reverse drive gear  196  is in meshed engagement with a reverse driven gear  198  fixed for rotation with output shaft  20 . 
     To transmit torque through transmission  10  and provide a forward drive gear ratio, shift rail  182  and shift fork  180  are axially translated to cause shift collar  184  to drivingly engage reverse driven gear  198 . Torque transfers from stub shaft  72  through hub  186 , collar  184 , reverse driven gear  198  and output shaft  20 . 
     A parking pawl  200  is selectively engageable with a parking gear  202  splined to output shaft  20 . Parking pawl  200  is moveable between a retracted position shown in  FIG. 1  and an advanced position where parking pawl  200  engages parking gear  202  to restrict output shaft  20  from rotation. With reference to  FIG. 2 , a first forward transmission drive ratio of 4.5:1 may be achieved by placing second power transmission module  16  and third power transmission module  18  in the active modes while leaving first power transmission module in the inactive mode. A first gear to second gear shift may be achieved by switching third power transmission module  18  to the inactive mode by releasing band  152  from brake drum  154 . A second to third gear up shift is achieved by activating first power transmission module  14  and leaving second power transmission module  16  active as well. A third to fourth gear shift entails inactivating first power transmission module  14  and second power transmission module  16  and activating third power transmission module  18 . To complete a fourth to fifth forward gear up shift, third power transmission module  18  remains active and first power transmission module  14  is also activated. Sixth gear is a direct drive ratio of 1:1. Accordingly, each of first, second and third power transmission modules  14 ,  16 ,  18  are inactive. Seventh gear is an overdrive gear and may be provided by activating only first power transmission module  14 . 
       FIG. 6  depicts a 10-speed automatic transmission  300  substantially similar to transmission  10 .  FIG. 4  illustrates the module concept well including previously described input shaft  12 , first power transmission module  14 , second power transmission module  16 , third power transmission module  18 , output shaft  20 , reverse gearset  22 , countershaft  24 , shift mechanism  26  and wet clutch  30  from transmission  10 . An additional three forward gear ratios may be obtained by positioning a fourth power transmission module  302  downstream from third power transmission module  18 . Fourth power transmission module  302  is substantially similar to third power transmission module  18  except that the size of certain components within the planetary gearset have been changed to provide a gear reduction ratio of 1.5:1 compared to the gear reduction ratio of 1.61:1 provided by third power transmission module  18 . Accordingly, the elements of fourth power transmission module  302  will be identified with the reference numerals of third power transmission module  18  including a prime suffix. 
       FIG. 7  is an element chart indicating which of the first through fourth power transmission modules  14 ,  16 ,  18 ,  302  are placed in an active mode to obtain the desired final drive ratio. Through the use of the proposed module ratios, a first gear ratio of 6.38:1 is provided. Because of the magnitude of this ratio, a torque converter may be eliminated. In addition, a final drive gear reduction unit may be configured with a reduced reduction ratio, such as 3.90 to 3.00:1. Furthermore, due to the modular nature of transmissions  10  and  300 , the overall size and weight of these transmissions is greatly reduced. The cost of manufacturing transmissions  10  and  300  may also be reduced due to the elimination of a need for hydraulic fluid passageways acting on elements of the power transmission modules. 
       FIG. 8  depicts yet another feature of power transmissions  10  and  300  in that housing  54  may be split along a centerline  304  about which input shaft  12  and output shaft  20  rotate. Accordingly, two case halves, one of which is shown in  FIGS. 1 and 4  are defined. A plurality of webs  306  may be integrally formed with housing  54  or subsequently positioned therein. Webs  306  define pockets or cavities in receipt of the various power transmission modules. During assembly of any one of the transmissions envisioned by the present disclosure, the power transmission modules along with their associated shafts may be assembled and subsequently dropped into one of the transmission housing halves  54 . Assembly is completed by fixing the opposite transmission housing half to the prior half. 
     Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations may be made therein without departing from the spirit and scope of the disclosure as defined in the following claims.