Abstract:
A multiple speed transmission includes first and second concentric input shafts, an output shaft, an auxiliary shaft, a first clutch for driveably connecting and disconnecting the first input shaft, and a second clutch for driveably connecting and disconnecting the second input shaft. First pairs of mutually engaged gears include a first member supported on the first input shaft, and a second member supported on the output shaft. Second pairs of mutually engaged gears includes a first member supported on the second input shaft, and second member supported on the output shaft. A gear wheel, supported on the auxiliary shaft, engages a gear of a second pair on the second input shaft. A planetary gearset includes a ring gear driveably engaged with a member of the first pair on the first input shaft. The carrier of the gearset is held against rotation in reverse drive and released in forward drive.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to an automated gear transmission, more particularly to a dual-clutch transmission having two input shafts arranged mutually essentially concentrically for use in a motor vehicle. 
   Various automated gear transmissions, dual-clutch transmissions for motor vehicles, are known from the prior art. Of these, numerous embodiments include two concentric input shafts and two output shafts for driving the vehicle. It is also known from DE 199 44 879 A1, that an embodiment with two input shafts arranged essentially concentrically to each other may be provided with only one output shaft for mechanical design simplification and to reduce the transmission&#39;s installation space requirement. Disclosed in that publication is a dual-clutch transmission intended for a motor vehicle and comprising two mutually concentric input shafts and one output shaft, with the first and second input shafts being each connectable to a drive shaft via first and second clutches, respectively. The first input shaft is engageable with the output shaft via at least one first pair of gear wheels, whereas the second input shaft is engageable with the output shaft via at least one second pair of gear wheels. In order to achieve an advantageously compact design for front longitudinal mounting in the engine compartment of a motor vehicle, it is intended that the first input shaft should be in the form of a solid shaft while said second input shaft should be of hollow shaft design. The first input shaft should be arranged within the second input shaft. The input shafts and output shaft should each be disposed in a direction essentially parallel to the longitudinal axis of the vehicle, while the first and second clutch should be arranged radially relative to each other. 
   One embodiment of this arrangement comprises seven forward speeds. Preferably, a separate auxiliary shaft is provided for implementing a reverse gear. According to further design features, the first input shaft carries the respective gear wheels for the seventh, fifth, third and first speeds, in that order, while the second input shaft may carry the respective gear wheels for the second, fourth and sixth speed, in that order. Provision is made in this arrangement for the first and third speed, fourth and sixth speed, fifth and seventh speed, and second and reverse speed to share a common sliding sleeve in each case for selective shifting of the above-mentioned speeds. This feature is intended to achieve a particularly compact design of the dual-clutch transmission. The two clutches may be in the form of multi-plate clutches, whereby a compact radial clutch with a clutch housing is said to be implemented. Depending on how the clutches are configured in this arrangement, the radially inward or radially outward clutch may be designed as a start-up clutch. 
   A dual-clutch transmission of the above design is alleged to lend itself to compact installation in a front longitudinal configuration in the engine compartment of a motor vehicle, given that the first input shaft is a solid shaft while the second input shaft is in the form of a hollow shaft, one being arranged within the other. Moreover, there is said to be provided only one output shaft extending, like the input shafts, in the longitudinal direction of the vehicle. It is stated to be a decisive feature that the necessary clutches are arranged radially and no longer sequentially relative to each other, whereby the requisite installation space in the vehicle&#39;s longitudinal direction is said to be minimized. 
   A particular disadvantage of this known embodiment of a dual-clutch transmission for a motor vehicle is that the design integration of the reverse speed into said transmission should be improved. Overlap of the individual speed-change gears will regularly occur due to the defined gear positions associated with the integration of the reverse speed. As a result of these defined gear positions in a dual-shaft powershift transmission, a normal reverse speed—as implemented via an axially displaceable sliding gear wheel—cannot be achieved without overlap, or a poor transmission ratio of the individual speed-change gears, or without negatively affecting the transmission dimensions. 
   SUMMARY OF THE INVENTION 
   The transmission of this invention integrates the reverse speed such that all overlap of the individual speed-change gears is eliminated. The transmission meets or improves requirements regarding the transmission ratio of the individual change-speed gears and the use of packaging space. In addition, the transmission improves service durability and reliability, and is simple and inexpensive to manufacture. 
   The transmission includes two concentric input shafts, a solid shaft surrounded by a hallow, sleeve shaft. Various meshing gear pairs on the input shafts and the output shaft produce the forward speeds. For reverse drive, torque is transmitted from an input shaft by a member of one of these gear pairs to an auxiliary shaft, where reverse speed is produced by a planetary gear set supported on the auxiliary shaft. The ring gear of the planetary gear set has gear teeth that are engaged with another member of one of those gear pairs. In this way, reverse speed torque is transmitted from the ring gear through one of these gear pairs to the output shaft, with one of the gears acting as an idler. This arrangement saves space and reverses the rotational direction of the output, as required for reverse drive. To perform this dual function, the ring gear has both external and internal teeth. 
   The gear wheel mounted on the second input shaft that transmits torque to the auxiliary shaft is the gear wheel for the fourth speed or sixth speed. Thus, torque for driving the vehicle in reverse is transmitted from an input shaft in a simple manner via the fourth or sixth speed gear to the reverse-speed gear wheel on the auxiliary shaft. 
   The gear wheel, mounted on the first input shaft that is engaged with the ring gear of the planetary gear set for torque transmission to the output shaft, is a third speed gear or a fifth speed gear. Thus, torque is transmitted to the output shaft via the ring gear and the third or fifth speed gear. In this condition, with the clutch disengaged, the third or fifth speed gear on the first input shaft becomes an idler gear serving to transmit torque for the reverse speed. For this to take place, third or fifth gear must be engaged, respectively, so that the torque can be transmitted to the output shaft. 
   Another advantage of the transmission is the synchronized process of bringing the planet carrier of the planetary gear set into form-fitting, non-slip engagement with the housing to produce reverse drive. 
   An additional space saving feature is the use of a common sliding selector sleeve on respective couplers or synchronizes to produce the first and fifth speeds, an other sleeve for the third and sixth speeds, and another sleeve for the fourth and second speeds. 
   A multiple speed transmission according to this invention that accomplishes these advantages includes first and second concentric input shafts, an output shaft, an auxiliary shaft, a first clutch for driveably connecting and disconnecting the first input shaft, and a second clutch for driveably connecting and disconnecting the second input shaft. First pairs of mutually engaged gears include a first member supported on the first input shaft, and a second member supported on the output shaft. Second pairs of mutually engaged gears includes a first member supported on the second input shaft, and second member supported on the output shaft. A gear wheel supported on the auxiliary shaft engages a gear of a second pair on the second input shaft. A planetary gearset includes a ring gear driveably engaged with a member of the first pair on the first input shaft. The carrier of the gearset is held against rotation in reverse drive and released in forward drive. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other advantages of the present invention will become apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
       FIG. 1  is a schematic view of an automated gear transmission according to the invention; 
       FIG. 2  is a view of the automated gear transmission of  FIG. 1  showing the rotational directions of all gear wheels when the transmission produces reverse drive; 
       FIG. 3  is a side view of  FIG. 4  showing the arrangement of the shafts and the pitch circles of the gear wheels; and 
       FIG. 4  is a schematic cross section of the automated gear transmission of  FIGS. 2 and 3 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawings, there is illustrated in  FIG. 1  an automated gear transmission  10  according to the invention. The transmission  10 , designed particularly as a dual-clutch transmission, includes two input shafts  11 ,  12  arranged essentially mutually concentrically, and an output shaft  13 . The first input shaft  11  is a solid shaft. The second input shaft  12  is a hollow shaft. The first input shaft  11  is arranged, over a portion of its longitudinal extent, inside second input shaft  12 , as illustrated in  FIG. 1 . The first input shaft  11  and second input shaft  12  are each driveably connected to an input, such as the crankshaft of an engine or another drive shaft (not shown), via a first clutch  14  and a second clutch  15 , respectively. The first input shaft  11  is engageable with the output shaft  13  through at least one of first pairs of gear wheels  16 , and the second input shaft  12  is engageable with the output shaft  13  through at least one of second pairs of gear wheels  17 . The first output shaft  11  is engageable with the output shaft  13  via three pairs of gear wheels  16  for the first, third and fifth speeds, and the second input shaft  12  is engageable with the output shaft  13  via three pairs of gear wheels  17  for the second, fourth and sixth speeds. In addition, the automated gear transmission  10  according to the invention includes a separate auxiliary shaft  18  to provide for reverse drive speed. 
   Referring again in particular to the illustration in  FIG. 1  of the drawings, the transmission  10  transmits torque to the auxiliary shaft  18 . A gear wheel  19 , provided on the separate auxiliary shaft  18  for implementing reverse drive, is engageable with a gear wheel  20  on the second input shaft  12 . Gear wheel  20  is a member of a second gear pair. A planetary gear set  21  is arranged on the auxiliary shaft  18  to reverse the direction of rotation for the reverse speed. The ring gear  22  of the planetary gear set  21  transmits torque to the output shaft  13  through its engagement with a gear wheel  23 , which is mounted on the first input shaft  11 . The reverse speed is engaged via a planet carrier  24  of the planetary gear set  21 . Thus, the transmission  10  integrates the reverse speed such that all overlap of the individual speed-change gears is eliminated. Since the reverse gear wheel is in mesh only with the input shafts  11 ,  12 , this reverse gear wheel can be positioned around the input shafts  11 ,  12  at an angle of approximately 180°. Only a single shaft distance between the reverse gear and the input shaft co-determines the transmission ratio of the two reverse gear wheels, which preferably mesh with the fixed gear for the third and fourth speeds. This arrangement also has the particular advantage of reducing interdependencies among the gear ratio, shaft distance, and pitch circle radii. 
   The gear wheel  19  is secured to the auxiliary shaft  18  and is engaged with the gear wheel  20  on the second input shaft  12 . Preferably, gear wheel  20  is the gear wheel for the fourth speed. Thus, the torque for moving the vehicle in reverse is transmitted via the fourth speed gear wheel on the second input shaft to the fixed reverse speed gear wheel  19  on the auxiliary shaft  18 . Alternatively, the gear wheel  20  on the input shaft  12  is the gear wheel for the sixth speed. A reversal of the sense of rotation and the necessary gear ratio reduction are then achieved via the planetary gear set  21  on the auxiliary shaft  18 . 
   Moreover, in the embodiment of the automated gear transmission  10  according to the invention illustrated in the drawings, the gear wheel  23  mounted on the first input shaft  11  for engagement with the outer ring gear  22  of the planetary gear set  21  for torque transmission to the output shaft  13  is the third speed gear. Thus, torque is transmitted to the output shaft via the ring gear  22  and via the third speed gear  23  on the input shaft  11  when the third gear is engaged. In this condition, with the clutch disengaged, the third speed gear  23  on the input shaft  11  becomes an idler gear serving to transmit torque for the reverse speed. For this to take place, third gear must be engaged so that the torque can be transmitted. 
   In an alternative solution for the automated gear transmission  10  according to the invention, the gear wheel  23  mounted on the first input shaft  11  for engagement with the ring gear  22  of the planetary gear set  21  is the fifth speed gear. 
   Thus, as mentioned above, in the illustrated embodiment of the automated gear transmission  10  according to the invention, the gear wheel  23  mounted on the solid first input shaft  11  for engagement with the ring gear  22  of the planetary gear set  21  is an idler gear which serves to transmit torque for the reverse speed. 
   Moreover, in the illustrated embodiment, the gear wheel  20  is secured to input shaft  12  for engagement with the gear wheel  19  on the auxiliary shaft  18 . The gear wheel  23  is secured to input shaft  11  for engagement with the ring gear  22 , and is designed as a fixed gear; although, when clutch  14  of the solid input shaft is disengaged, the fixed-type third speed gear  23  becomes an idler gear. 
   Shifting into reverse is achieved via the planet carrier  24  of the planetary gear set  21  by bringing planet carrier  24  into form-fitting, non-slip engagement with the housing  25 , which is fixed against rotation. Thus, through the stationary planet carrier  24  of the planetary gear set  21 , a reversal of the rotational direction of the auxiliary shaft  18  is achieved in a known manner via the sun gear  30  and the fixed planet gears  31 , which, turning against the direction of the sun gear  30 , act on the ring gear  22 . Reference is made here in particular to  FIG. 2 , which shows the directions of rotation of the gears relevant for transmission of the reverse speed, with “L” denoting the counterclockwise direction and “R” the clockwise direction (viewed from the input toward the clutch) when the reverse speed is engaged. Thus, counterclockwise rotation of the auxiliary shaft  18  is converted, via the sun gear  30  of the planetary gear set  21 , its planet carrier  24  (now stationary), and the fixed planet gears  31  turning against the direction of said sun gear  30 , into clockwise rotation of the ring gear  22 . The process of bringing the planet carrier  24  of the planetary gear set  21  into form-fitting, non-slip engagement with the housing  25  is preferably synchronized. 
   In order to achieve a particularly compact design, there is provided common sliding sleeve  26  on the synchronizers or couplers for the first and fifth speeds, for the third and sixth speeds, and for the fourth and second speeds, respectively. The common sliding sleeve selects engagement of the aforementioned speeds. These three sliding sleeves  26  on their respective couplers or synchronizers, are schematically illustrated in  FIGS. 1 and 2  of the drawing. The slanted lines on these sleeves  26  indicating synchromesh engagement of the selected gear for each respective speed and the output shaft  13 . 
   In addition to the foregoing, the ring gear  22  of the planetary gear set  21  has both internal and external teeth. The planetary gear set  21  provides a reversal of the rotational direction, in addition to the gear ratio reduction. 
   In  FIG. 2 , which indicates the directions of rotation of the gear wheels relevant to the transmission of the reverse speed, the second input shaft  12  and gear wheel  20  are shown to rotate clockwise. Gear wheel  20  meshes with the gear wheel  19  on the auxiliary shaft  18 , which rotates in the opposite direction, i.e., counterclockwise. It follows that the auxiliary shaft  18  will also rotate in a counterclockwise direction, with the planetary gear set  21  producing a reversal of rotation with respect to its ring gear  22 , which rotates clockwise. The ring gear  22  meshes with the gear wheel  23  on the first input shaft  11 ; therefore, gear wheel  23  rotates counterclockwise. Because gear wheel  23  is secured to the first input shaft  11  and functions as an idler gear when the clutch  14  of the solid input shaft is disengaged, the first input shaft  11  rotates counterclockwise with the gear wheel  23  when the reverse speed is engaged. The gear wheel  23  meshes with the mating third speed gear on the output shaft (which mating third speed gear is generally referred to by the numeral  16  herein), causing this mating gear to turn in the opposite direction, i.e., clockwise. It is therefore via this mating gear that the torque is transmitted to the output shaft  13  when the reverse speed is engaged. Further downstream, the direction of rotation of output shaft  13  is again reversed via a second pair of gear wheels  32  mounted, respectively, on the output shaft  13  and on a differential gear unit  27 . The gear wheel arranged on the differential gear unit  27  of this gear wheel pair  32 , will rotate counterclockwise. From the differential gear unit  27 , the drive shafts  28  and  29  extend to the driving wheels of the vehicle. 
   The three gear wheels  16  on the first input shaft  11  each mesh in a known manner with the corresponding mating gear wheels  16  for the first, third and fifth speed, and the three gear wheels  17  on the second input shaft  12  each mesh in a known manner with the corresponding mating gear wheels  17  for the second, fourth and sixth speed on the output shaft  13 . 
     FIGS. 3 and 4  illustrate the transmission  10  in the form of a simplified schematic cross section showing the pitch circles of the gear wheels. Identified in  FIG. 4  are the two input shafts  11 ,  12  with the three gear wheels  16  for the first, third and fifth speed, respectively, on the first input shaft  11 ; the three gear wheels  17  for the second, fourth and sixth speed, respectively, on the second input shaft  12 ; and the output shaft  13  carrying the corresponding three mating gears  16  for the first, third and fifth speed, respectively, and the three mating gears  17  for the second, fourth and sixth speed, respectively. Also identified are three sliding coupler sleeves  26  of the synchronizers or couplers on the output shaft  13 , and the gear wheel pair  32  for transmitting the torque to the differential gear unit  27 . Located above the two input shafts  11 ,  12 , are the auxiliary shaft  18  for providing the reverse speed and carrying the gear wheel  19 , which meshes with the fourth speed gear wheel  20  mounted on the second input shaft  12 . The planetary gear set  21  is arranged on the auxiliary shaft  18  to reverse the rotational direction for the reverse speed, with the planet carrier  24  of said planetary gear set  21  being in form-fitting, non-slip engagement with the housing  25 ; and the ring gear  22  co-operating with the third speed gear wheel  23  on the first input shaft  11  so as to transmit the torque to the output shaft  13  when the reverse speed is engaged. The pitch circles in  FIG. 4  illustrate specifically the arrangement of the individual input shafts  11 ,  12 , the output shaft  13 , and the auxiliary shaft  18  for the reverse speed, as well as the manner in which the individual gear wheels mesh. The pitch circles of these gear wheels have not been individually referenced with specific numerals for this purpose. 
   As mentioned above, the embodiments represented are merely given by way of example to illustrate the invention, which is not limited to these embodiments, but may be variously modified or otherwise expressed. Thus, the automated gear transmission according to the invention may, in particular, be of different structure and have a deviating number of speeds, e.g., five speeds or four speeds. Different arrangements of the input shafts  11 , the output shaft  13 , the gear wheels carried by any of these shafts, and the auxiliary shaft  18  with its planetary gear set  21  are likewise conceivable. 
   In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.