Abstract:
A gear actuation mechanism for an automatic transmission, comprising: a motor; first and second gear actuation shafts; means of selecting one power path from each of two sets of power paths in response to rotation of the first and second actuation shafts, respectively; and means of alternately driveably connecting the motor to either the first gear actuation shaft or the second gear actuation shaft.

Description:
BACKGROUND OF THE INVENTION 
     This invention is in the field of gear actuation mechanisms for automatic transmissions. The invention is particularly suited for gear actuation of dual clutch automatic transmissions. 
     In a dual clutch automatic transmission, it is necessary to select at most one even gear and at most one odd gear at any particular time. For maximum operational flexibility, it is desirable for the choices of odd gear and even gear to be independent. Typically, this is accomplished by providing two independent gear actuation mechanisms, including two motors. The motors and associated circuitry account for a substantial fraction of the costs of the actuation systems. Therefore, it is desirable to have one motor rather than two. 
     A well know actuation system uses a single motor to turn a single drum which actuates both even and odd gears. However, that system does not allow even and odd gears to be selected independently. For example, when sixth gear is selected, the only odd gears available would be fifth or seventh. Third gear cannot be selected, so a direct shift from sixth gear to third gear is impossible. 
     This invention uses a planetary gear set to multiplex a single motor, such that the motor is alternately connected to one of two independent drums. One drum actuates the odd gears and the other actuates the even gears. Although only one drum may be moved at a time, all positions on each drum are available independent of the position of the other drum. 
     Furthermore, the invention takes advantage of the relationship between the clutch state and the need to change gears to determine which of the two drums should be driven by the motor. Specifically, the odd gear is never changed while driving in an odd gear and the even gear is never changed while driving in an even gear. Therefore, the motor drives the even drum whenever the odd clutch is engaged and drives the odd drum whenever the even clutch is engaged. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an end view of a first embodiment of the gear actuation mechanism. 
         FIG. 2  is a sectional view through section A-A in  FIG. 1 . 
         FIG. 3  is a sectional view through section B-B in  FIG. 1 . 
         FIG. 4  is a sectional view through section C-C in  FIG. 1 . 
         FIG. 5  is an end view of a second embodiment of the gear actuation mechanism. 
         FIG. 6  is a schematic representation of a typical dual clutch transmission. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is an actuation system for a dual clutch transmission or transaxle. Before describing the actuation system in detail, the general structure and operation of a typical dual clutch transmission will be described. 
       FIG. 6  illustrates the structure of a typical rear wheel drive dual clutch transmission. Front wheel drive dual clutch transaxles have similar structure and operation, except that the output shaft is on a different axis from the input shaft. In this document, the term “transmission” should be understood to include both rear wheel drive transmissions and transverse mounted transaxles. Input shaft  100  is driven by the vehicle engine. Output shaft  102  drives the vehicle wheels, preferably via a differential. Clutch  110  connects input shaft  100  to the odd gear intermediate shaft  104  whenever the clutch is applied and disconnects them whenever the clutch is disengaged. Similarly, clutch  112  connects input shaft  100  to the even gear intermediate shaft  106  whenever the clutch is applied and disconnects them whenever the clutch is disengaged. Even gear intermediate shaft  106  is a hollow shaft that is concentric with odd gear intermediate shaft  104 . 
     Gears  126 ,  128 ,  130 ,  132 ,  134 , and  136  provide several different selectable power paths between the odd gear intermediate shaft  104  and countershaft  108 , each with a different speed ratio. One of the power paths is selected by moving synchronizers  150  and  152  to appropriate positions. To engage first gear, synchronizer  150  is moved leftward to couple gear  132  to shaft  108 . To engage third gear, synchronizer  150  is moved rightward to couple gear  134  to shaft  108 . To engage seventh gear, synchronizer  152  is moved leftward to couple gear  130  to shaft  104 . Gears  142  and  144  provide a continuously engaged power path from countershaft  108  to output shaft  102 . Moving synchronizer  152  to the right engages fifth gear, which is a direct drive gear, by coupling shaft  104  to output shaft  102 . When both synchronizers  150  and  152  are in the neutral position, no power flows between shaft  104  and shaft  102  and no speed relationship is enforced. 
     Gears  114 ,  116 ,  118 ,  120 ,  122 , and  124  provide several different selectable forward gear power paths between the even gear intermediate shaft  106  and countershaft  108 , each with a different speed ratio. To engage second gear, synchronizer  148  is moved leftward to couple gear  124  to shaft  108 . To engage fourth gear, synchronizer  146  is moved rightward to couple gear  116  to shaft  106 . To engage sixth gear, synchronizer  146  is moved leftward to couple gear  114  to shaft  106 . Gears  138 ,  140 , and an idler gear which is not shown provide a selectable reverse gear power path from even gear input shaft  106  to countershaft  108 . Moving synchronizer  148  to the right engages reverse by coupling gear  140  to shaft  108 . When both synchronizers  146  and  148  are in the neutral position, no power flows between shaft  106  and shaft  102  and no speed relationship is enforced. 
     To prepare the vehicle for a launch from stationary in a forward direction, first gear is selected as described above and both clutches are set at zero torque capacity. In response to accelerator pedal movement, clutch  110  is gradually engaged. Launch in reverse is similar, except that reverse gear is selected and clutch  112  is gradually engaged. 
     Whenever the vehicle is moving in an odd numbered gear, clutch  110  will be engaged and power will flow via one of the odd power paths to the output shaft. Clutch  112  will be disengaged and no power flows through any of the even power paths. To prepare for a shift into an even numbered gear, synchronizers  146  and  148  are positioned to select the desired gear as described above. Then, clutch  112  is gradually engaged while clutch  110  is gradually disengaged, transferring the power flow to the even gear power path. Similarly, a shift from an even gear to an odd gear is accomplished by selecting the odd gear while all power flows through an even power path and then gradually engaging clutch  110  while gradually disengaging clutch  112 . 
     The present invention provides a mechanism for adjusting the positions of synchronizers or other couplers to engage the desired power paths.  FIG. 1  is an end view of a first embodiment of the gear actuation mechanism.  FIG. 2  is a sectional view through section A-A in  FIG. 1 . A planetary gear set includes a sun gear  14 , a ring gear  16 , a planet carrier  18 , and a set of planet gears  20 . The planet gears are supported for rotation by the planet carrier and mesh with the sun gear and ring gear. The sun gear and planet gears each have  12  external teeth and the ring gear has  36  internal teeth. A gear actuator motor  10  drives sun gear  14  via shaft  12 . Carrier  18  has  24  external teeth which mesh with the  36  external gear teeth of gear  22 . When ring gear  16  is held stationary, each revolution of motor  10  results in ¼ revolution of carrier  18  and ⅙ revolution of gear  22 . 
     Gear  22  is connected to the even actuator drum  26  by actuation shaft  24 . Even actuator drum  26  has two grooves  28  and  30  with the axial location of the grooves varying along the circumference of the drum. A fork (not shown) extends into groove  28  and positions synchronizer  146 . Another fork extends into groove  30  and positions synchronizer  148 . The rotational position of the drum determines the positions of the forks and synchronizers. The axial location of each groove around the circumference is selected such that particular positions of the drum correspond to each desired odd gear state. 
     Ring gear  16  has  36  external teeth which mesh with the  24  gear teeth of gear  32 . Gear  32  is connected to gear  34  which has  12  teeth. Gear  34  meshes with gear  36  which has  36  teeth. When carrier  18  is held stationary, each revolution of motor  10  results in ⅓ revolution of ring gear  16 , ½ revolution of gears  32  and  34 , and ⅙ revolution of gear  36 . Gear  36  is connected by actuation shaft  38  to odd actuator drum  40 . Drum  40  has two grooves,  42  and  44 , which guide forks that determine the positions of synchronizers  150  and  152 . 
     The remainder of the mechanism functions to hold either ring gear  16  or planet carrier  18  stationary. Motor  10  may then be used to adjust the position of either drum  26  or drum  40 , depending upon which element is held. In a first embodiment, the selection of which element to hold stationary is determined by the states of the clutches. 
     Motor  64  drives shaft  66  which moves trolley  68  left or right. Translation of trolley  68  adjusts the torque capacity of clutch  110  through a mechanism which is not illustrated. Examples of such a mechanisms can be found in U.S. Pat. Nos. 6,679,362 and 7,073,649. The torque capacity is zero at the position shown and increases as the trolley is moved to the right. There is some additional travel available to the left of this position which is used to select which drum will be rotated by motor  10 . Similarly, motor  50  drives shaft  52  which moves trolley  54  left or right. Trolley  54  is shown at the rightmost limit of its travel. As it is moved to the left, the first portion of its travel is used to select which drum will be rotated by motor  10  and the remainder or the travel is used to control the torque capacity of clutch  112 . 
     Linkages  72  and  58  are supported for rotation about pin  60 . Pin  70  attached to trolley  68  engages groove  74  causing linkage  72  to rotate about pin  60  as the trolley is moved. Similarly, pin  56  engages groove  62  causing linkage  58  to rotate as trolley  54  moves. Grooves  74  and  62  are L-shaped such that the movement of the linkages occurs while the trolleys move through the first portion of their travel and the linkages are stationary during the torque capacity adjustment portion of the travel. 
       FIGS. 3 and 4  are sectional views through sections B-B and C-C in  FIG. 1 , respectively. Pins  78  and  82  are supported by the transmission case  76 . When trolley  68  is in the torque capacity adjustment portion of its travel, linkage  72  moves to the position illustrated in  FIG. 3 . An inclined surface on linkage  72  pushes pin  78  into one of a set of holes  48  in gear  36 . These holes  48  are positioned to correspond to desired odd gear states such as first, third, fifth, seventh, and neutral. When trolley  68  is moved to the leftmost stop, linkage  72  rotates such that pin  78  is pushed out of the hole by spring  80 , allowing gear  36  to rotate. Similarly, when trolley  54  is at the rightmost position of its travel, linkage  58  moves to the position shown in  FIG. 4 . In this position, the linkage allows spring  84  to push pin  82  away from gear  22 . Whenever trolley  54  is moved into the torque capacity adjusting portion of its travel, the inclined surface on linkage  58  pushes pin  82  into one of a set of holes  46  in gear  22 . These holes correspond to desired even gear states second, fourth, sixth, reverse, and neutral. An added feature of this mechanism is that the clutch is mechanically precluded from engaging whenever the corresponding drum is not in a position associated with a well defined gear state. 
     A skilled mechanism designer would be able to create a number of alternate mechanical linkages between the clutch actuators and the gear actuation shafts to satisfy the function of holding the gear actuation shaft stationary whenever the corresponding clutch is applied. Any such mechanism should be considered an equivalent to the corresponding mechanism described above. 
     To prepare the transmission for a forward launch, motor  64  is engaged to move trolley  68  all the way to the left stop and motor  50  is engaged to move trolley  54  to the beginning of the torque capacity adjustment portion of its travel. In this configuration, gear  22  and planet carrier  18  are held stationary. Then, motor  10  is engaged to rotate drum  40  to the position corresponding to first gear. Once thus configured, motor  64  is used to adjust the torque capacity of clutch  110  in response to the accelerator pedal position. 
     When the vehicle is driving in an odd gear, the transmission is prepared for a shift into an even gear by engaging motor  50  to position trolley  54  at its stop. In this configuration, gears  36 ,  34 ,  32 , and ring gear  16  are held stationary. Motor  10  is then engaged to move drum  22  to the position corresponding to the desired even gear. To complete the shift, motors  50  and  64  are used in a coordinated fashion to gradually increase the torque capacity of clutch  112  while decreasing the torque capacity of clutch  110 . Similarly, to prepare for a shift into an odd numbered gear, trolley  68  is moved all the way to the left stop and then motor  10  is engaged to select the desired odd gear. 
     In a second embodiment, which is depicted in  FIG. 5 , the selection of which element to hold stationary is determined by an independent control signal. In response to this independent control signal, solenoid  86  moves pin  88  left or right. When pin  88  is moved to the right, as depicted, gear  22  in held stationary and motor  10  is used to move drum  40 . When pin  88  is moved to the left, gear  36  is held stationary and motor  10  is used to move drum  26 . Alternatively, the control signal could be hydraulic as opposed to electrical in which case pin  88  would be driven by a piston.