Abstract:
A dual-clutch powershift transmission for use in a motor vehicle having an engine and a driveline includes an output shaft adapted for connection to the driveline, first and second input shafts, a first engine clutch operable for establishing a releaseable drive connection between the engine and the first input shaft and a second engine clutch operable for establishing a releasable drive connection between the engine shaft and the second input shaft. A first constant-mesh gearset is driven by the first input shaft. A second constant-mesh gearset is driven by the second input shaft. A first shift clutch releasably engages the first gearset to establish a drive connection between the first input shaft and the output shaft. A second shift clutch releasably engages the second gearset to establish a drive connection between the second input shaft and the output shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/802,454, filed on May 22, 2006. The disclosure of the above application is incorporated herein by reference. 

   FIELD 
   The present invention relates generally to transmissions for use in motor vehicles and, more particularly, to a dual-clutch automated transmission applicable for use in drive and rear-wheel drive vehicles. 
   BACKGROUND 
   Automobile manufacturers continuously strive to improve fuel efficiency. This effort to improve fuel efficiency, however, is typically offset by the need to provide enhanced comfort and convenience to the vehicle operator. For example, it is well known that manual transmissions are more fuel efficient than automatic transmissions, yet a majority of all passenger vehicles are equipped with automatic transmissions due to the increased convenience they provide. 
   More recently, “automated” variants of conventional manual transmissions have been developed which shift automatically without any input from the vehicle operator. Such automated transmissions typically include a plurality of power-operated actuators that are controlled by a transmission controller to shift traditional synchronized dog clutches. However, such automated transmissions have the disadvantage that there is a power interruption in the drive connection between the input shaft and the output shaft during sequential gear shifting. Power interrupted shifting results in a harsh shift feel which is generally considered to be unacceptable when compared to smooth shift feel associated with most automatic transmissions. To overcome this problem, automated dual-clutch transmissions have been developed which can be powershifted to permit gearshifts to be made under load. Examples of such automated manual transmissions are shown in U.S. Pat. Nos. 5,966,989 and 5,890,392. While such powershift dual-clutch transmissions overcome several drawbacks associated with conventional single-clutch automated transmissions, a need exists to develop simpler and more robust transmissions which advance the automotive transmission technology. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present disclosure provides a dual-clutch transmission and a control system for permitting automatic shifting of the dual-clutch transmission. 
   In one form of the present invention, an automated dual-clutch multi-speed transmission is adapted to transfer power from the engine to the driveline of a motor vehicle. The transmission includes a single output mesh that allows the center distance between the transaxle input shaft and the differential centerline to be easily changed. This concept also provides deep transmission ratios that, in turn, allow for short final drive ratios. A differential having a reduced ring gear diameter may be implemented to help reduce interference concerns with other chassis components such as steering gears. 
   In another form, the present invention provides a dual-clutch transmission for use in a motor vehicle having an engine and a driveline and which includes an output shaft adapted for connection to the driveline, first and second input shafts selectively drivable by the engine and first and second engine clutches. The first engine clutch is operable to establish a releasable drive connection between the engine and the first input shaft. The second engine clutch is operable to establish a releasable drive connection between the engine and the second input shaft. A first constant-mesh gearset is driven by the first input shaft. A second constant-mesh gearset is driven by the second input shaft. A third constant-mesh gearset is selectively driven by the first gearset or the second gearset. The third gearset drives the output shaft. A first shift clutch is operable to releasably drivingly couple the first gearset and the third gearset. A second shift clutch is operable to releasably drivingly couple the second gearset and the third gearset. 
   In another form, the present disclosure provides a dual-clutch transmission for use in a motor vehicle having an engine and a driveline, including an output shaft adapted for connection to the driveline, first and second input shafts, a first engine clutch operable for establishing a releasable drive connection between the engine and the first input shaft and a second engine clutch operable for establishing a releasable drive connection between the engine shaft and the second input shaft. A first constant-mesh gearset is driven by the first input shaft. A second constant-mesh gearset is driven by the second input shaft. A first shift clutch releasably engages the first gearset to establish a drive connection between the first input shaft and the output shaft. A second shift clutch releasably engages the second gearset to establish a drive connection between the second input shaft and the output shaft. 

   
     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 schematic view of a dual-clutch automated transmission according to the principles of the present disclosure; 
       FIG. 2  is a fragmentary, cross-sectional flattened view of the dual-clutch automated transmission shown in  FIG. 1 ; 
       FIG. 3  is a partial end view depicting the relative position of the rotatable shafts within the dual-clutch automated transmission shown in  FIG. 1 . 
       FIG. 4  is a diagrammatical illustration of the transmission control system adapted for use with the dual-clutch automated transmission shown in  FIG. 1 ; 
       FIG. 5  is a schematic view of a dual-clutch automated transmission according to another preferred embodiment of the present disclosure; and 
       FIG. 6  is a schematic view of a dual-clutch automated transmission according to another preferred embodiment of the present disclosure. 
   

   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. 
   With reference to  FIGS. 1 through 4  of the accompanying drawings, a dual-clutch automated transmission, hereinafter referred to as transmission  10 , will now be described. Transmission  10  is driven by the output of an engine  12  and generally includes a first engine clutch  14 , a second engine clutch  16 , a first input shaft  18 , a second input shaft  20 , a transfer shaft  22 , a reverse idler shaft  24 , a plurality of gearsets  26 , an output shaft  28 , a final drive unit  30 , and a shift control system  32 . 
   First engine clutch  14  is a hydraulically-actuated spring-apply plate-type clutch which is normally operable in its engaged state to establish a drive connection between the output of engine  12  and first input shaft  18 . Likewise, second engine clutch  16  is a hydraulically-actuated spring-apply plate-type clutch normally operable in its engaged state to establish a drive connection between the output of engine  12  and second input shaft  20 . 
   First engine clutch  14  is a multi-plate clutch having a plurality of inner clutch plates  36  fixed for rotation with first input shaft  18  and interleaved with a plurality of outer clutch plates  38  splined to a drum  40  that is fixed to engine output  12 . A first clutch actuator  42  is provided to apply a force to cause inner clutch plates  36  and outer clutch plates  38  to separate from one another and cease the transfer of torque through first engine clutch  14 . In the embodiment shown, first clutch actuator  42  is a hydraulically-actuated device that controls the magnitude of torque transferred through first engine clutch  14 . First clutch actuator  42  may also fully release first engine clutch  14  so no torque is transferred therethrough. 
   Second engine clutch  16  includes a plurality of inner clutch plates  50  in driving engagement with second input shaft  20  and interleaved with a plurality of outer clutch plates  52  splined with drum  40 . As previously described, housing  40  is fixed to engine output  12 . Second engine clutch  16  is also a normally closed clutch that transmits torque when not acted upon by an external force. In the closed condition, inner clutch plates  50  frictionally engage outer clutch plates  52  and torque is transferred between engine output  12  and second input shaft  20 . Inner clutch plates  50  and outer clutch plates  52  are axially moveable to positions spaced apart from one another where second engine clutch  16  does not transfer torque. A second clutch actuator  60  is operable to control second engine clutch  16  to selectively transfer a predetermined quantity of torque between engine output  12  and second input shaft  20  or fully release the clutch plates from one another. As will be detailed, shift control system  32  is operable to control clutch actuators  42  and  60  and, in turn, the engagement and release of engine clutches  14  and  16 . While it is contemplated that first clutch actuator  42  and second clutch actuator  60  are hydraulically operated devices, other types of power-operated actuator including electrically-powered actuators are within the scope of the present disclosure. 
   As is conventional, all of the shafts, gearset  36  and final drive unit  30  are all rotatably supported in a transmission housing  62 . The plurality of gearsets  26  includes a first gearset  70  having a first drive gear  72  fixed for rotation with first input shaft  18  that is meshed with a first speed gear  74  rotatably supported on output shaft  28 . A second gearset  76  includes a second drive gear  78  fixed for rotation with second input shaft  20  that is meshed with a second speed gear  80  rotatably supported on transfer shaft  22 . A third gearset  82  includes a third speed gear  84  rotatably supported on transfer shaft  22 , a fourth speed gear  86  rotatably supported on output shaft  28 , and a fifth speed gear  88  rotatably supported on first input shaft  18  that is in meshed engagement with third speed gear  84  and fourth speed gear  86 . Third gearset  82  also includes a reverse drive gear  90  fixed to reverse idler shaft  24  that is meshed with fifth speed gear  88 . A fourth gearset  92  includes a third drive gear  94  fixed for rotation with transfer shaft  22 , a fourth drive gear  96  fixed for rotation with output shaft  28  and a sixth speed gear  98  rotatably supported on first input shaft  18  that is meshed with third drive gear  94  and fourth drive gear  96 . It should be appreciated that fifth speed gear  88  and sixth speed gear  98  are fixed to one another to define a compound gear rotatably supported on first input shaft  18 . A fifth gearset  100  includes a fifth drive gear  102  fixed for rotation with second input shaft  20  that is meshed with a seventh speed gear  104  rotatably supported on output shaft  28 . A reverse gearset  106  includes a first reverse speed gear  108  rotatably supported on reverse idler shaft  24  that is meshed with a second reverse speed gear  110  rotatably supported on output shaft  28 . Second reverse speed gear  110  is fixed to first speed gear  74  to define a compound gear rotatably supported on output shaft  28 . 
   Final drive unit  30  includes a first output gear  112  fixed for rotation with output shaft  28  that is meshed with a second output gear  114 . A differential housing  116  is fixed to second output gear  114  for rotation therewith. Pinion gears  118  are rotatably supported by pins  119  fixed to housing  116 . A first side gear  120  is fixed to a first driveshaft  122  and meshed with each pinion gear  118 . Likewise, a second side gear  124  is fixed to a second driveshaft  126  and meshed with each pinion gear  118 . As is known, driveshafts  122  and  126  are typically used to drive a pair of front wheels in a motor vehicle. 
   To provide a compact, robust package, second input shaft  20  concentrically surrounds first input shaft  18 . Second input shaft  20  is supported at one end of housing  62  via a bearing assembly  130  and at its other end by a bearing assembly  131  supported by first input shaft  18 . First input shaft  18  is, in turn, supported at one end by a bearing assembly  132  located in housing  162  and at its other end by a bearing assembly  134  positioned within second input shaft  20 . 
   Shift control system  32  includes a plurality of electrically-actuated synchronizers which are operable for selectively coupling a selected speed gear to other speed gears, first input shaft  18 , transfer shaft  22 , reverse idler shaft  24  or output shaft  28  for establishing six forward and one reverse speed ratio drive connections. The electrically-actuated synchronizers include a first synchronizer  150  operable for selectively coupling/releasing first speed gear  74  to/from fourth speed gear  86 . First synchronizer  150  includes a first hub  152  fixed to fourth speed gear  86 , a first sleeve  154  supported for rotation with and axial sliding movement on hub  152 , a first clutch plate  156  fixed to first speed gear  74 , and a cone-type synchronizer assembly  158 . As shown in  FIG. 2 , sleeve  154  is illustrated in its neutral position. 
   Cone-type synchronizer assembly  158  is a single-cone arrangement having an outer blocker ring  162  and a reaction ring  164 . The cone torque developed between the facing conical surfaces of the blocker ring  162  and reaction ring  164  inhibits first sleeve  154  from becoming drivingly engaged with clutch plate  156  until speed synchronization between fourth speed gear  86  and first speed gear  74  is complete. Once speed synchronization has occurred, first sleeve  154  is free to move to a position engaged with first clutch plate  156 , thereby drivingly interconnecting fourth speed gear  86  and first speed gear  74 . A first synchronizer actuator  166  ( FIG. 4 ) is operable to move first sleeve  154  between the neutral and engaged positions. It is contemplated that first actuator  166  may be electrically or hydraulically powered. First synchronizer actuator  166  is in communication with a controller  168  of shift control system  32 . 
   Shift control system  32  also includes a second synchronizer  170  operable for selectively coupling/releasing second speed gear  80  to/from third speed gear  84 . Second synchronizer  170  includes a second sleeve  172  axially movable between neutral and engaged positions. A second synchronizer actuator  174  is operable to move second sleeve  172  between its neutral and engaged positions. Second synchronizer actuator  174  is also controlled by controller  168 . 
   A third synchronizer  180  is operable for selectively coupling/releasing second reverse speed gear  110  and seventh speed gear  104  to/from output shaft  28 . Third synchronizer  180  includes a bi-directionally movable third sleeve  182  movable from a central neutral position to one of two engaged positions. A third synchronizer actuator  184  is operable to move third synchronizer sleeve  182  and is in controlled by controller  168 . 
   A fourth synchronizer  186  is operable for selectively coupling/releasing second speed gear  80  to/from transfer shaft  22 . Fourth synchronizer  186  includes an axially movable fourth sleeve  188  that may be selectively positioned in a neutral position or an engaged position. A fourth synchronizer actuator  190  is operable to selectively move fourth sleeve  188  in response to control signals from controller  168 . 
   A fifth synchronizer  194  is operable for selectively coupling/releasing first input shaft  18  to/from sixth speed gear  98 . Fifth synchronizer  194  includes a fifth sleeve  196  that is axially movable between a neutral position and an engaged position. A fifth synchronizer actuator  198  is operable to move fifth sleeve  196  between its neutral and engaged positions. Fifth actuator  198  is in communication with controller  168 . 
   A sixth synchronizer  200  is operable for selectively coupling/releasing first reverse speed gear  108  to/from reverse idler shaft  24 . Sixth synchronizer  200  includes an axially slidable sixth sleeve  202 . A sixth synchronizer actuator  204  is operable to selectively move sixth sleeve  202  between a neutral position and an engaged position. Sixth synchronizer actuator  204  is controlled by and in communication with controller  168 . 
     FIG. 4  depicts shift control system  32  to include controller  168  which receives various sensor input signals, denoted diagrammatically by block  210 . Controller  168  is an electronically-controlled unit capable of receiving data from the vehicle sensors and generating output signals in response to the sensor input signals. The input signals delivered to controller  168  can include, without limitation, engine speed, throttle position, brake status, first input shaft speed, second input shaft speed, transfer shaft speed, reverse idler shaft speed and output shaft speed. Controller  168  is operable to coordinate and monitor actuation of all the electrically-controlled devices associated with shift control system  32 , so as to permit power-shifted sequential gear changes automatically without any input from the vehicle operator. As such, transmission  10  is capable of being smoothly shifted automatically without power interruption. 
   If desired, a manually-operable mode selector switch  212  can be provided to shift transmission  10  from its automatic shift mode to a manual shift mode. Mode switch  212  would, when actuated, allow a vehicle operator to shift the gear shift lever manually to effect sequential gear shifts without the use of a clutch pedal. However, controller  168  would only permit the selective gear shift to be completed if the current vehicle characteristics (i.e., engine speed, vehicle speed, etc.) permit completion of a requested shift. 
   To operate the vehicle, engine  12  is started with the gear shift lever in its PARK position. Each of first engine clutch  14  and second engine clutch  16  are in the normally engaged state with their respective drive connections completed. However, each of the power-operated synchronizers is released with each shift sleeve located in its neutral position such that no drive torque is delivered to output shaft  28 . When the vehicle operator moves the gear shift lever from the PARK position to the DRIVE position, first clutch actuator  42  is operated to place first engine clutch  14  in its open state. First synchronizer  150  is actuated to cause first sleeve  154  to drivingly interconnect first speed gear  74  and fourth speed gear  86 . Thereafter, first clutch actuator  42  is controlled to allow normally closed first engine clutch  14  to transfer torque from first input shaft  18  through first drive gear  72 , first speed gear  74 , fourth speed gear  86 , fifth speed gear  88 , sixth speed gear  98  and fourth drive gear  96  to output shaft  28  so as to establish the first forward speed ratio drive connection between first input shaft  18  and output shaft  28 . As previously described, final drive unit  30  is drivingly coupled to output shaft  28 . First engine clutch  14  may be gradually engaged to smoothly accelerate the vehicle. 
   If controller  168  determines that an up-shift is required, second clutch actuator  60  is controlled to place second engine clutch  16  in its open or released state. Second synchronizer  170  is actuated to cause second sleeve  172  to drivingly interconnect second speed gear  80  and third speed gear  84 . Controller  168  then coordinates the release of first engine clutch  14  and the re-engagement of second engine clutch  16 . Once second engine clutch  16  is re-engaged, torque is transferred from second input shaft  20  through second drive gear  78 , second speed gear  80 , third speed gear  84 , fifth speed gear  88 , sixth speed gear  98  and fourth drive gear  96  to output shaft  28  so as to establish the second forward speed ratio drive connection. Once first engine clutch  14  is completely released, controller  168  causes first synchronizer actuator  166  to return first sleeve  154  to its neutral position, thereby disconnecting first speed gear  74  and fourth speed gear  86 . The power supply to first clutch actuator  42  may be discontinued to allow first engine clutch  14  to operate in its normally closed state. At this time, transmission  10  is operable in an energy conservation mode. 
   If controller  168  determines that transmission  10  will be operated in a certain drive gear for a predetermined amount of time, each of the synchronizers associated with the gears not currently transferring torque is moved to their normally centered position. Furthermore, the engine clutch that is not transferring torque is allowed to return to its normally closed position. During this mode of operation, energy is not required to be provided to either of first clutch actuator  42  or second clutch actuator  60 . When transmission  10  is in the energy conservation mode as previously described, transmission  10  operates very similarly to a manual transmission as opposed a typical automatic transmission. Typical automatic transmissions require energy to be continuously supplied to cause the interleaved plates of the clutch packs to be forced into contact with one another to transfer torque. The normally closed clutches of transmission  10  alleviate the need for a continuous supply of hydraulic pressure or electrical energy to transfer torque at a predetermined gear ratio. It should be appreciated that transmission  10  may be operated in the energy conservation mode when operating within any one of the speed ratios. 
   Continuing the description of up-shifting transmission  10 , if controller  168  determines that a 2-3 shift is required, first clutch actuator  42  causes inner clutch plates  36  to become disengaged from outer clutch plates  38  such that torque is no longer transferred between engine output  12  and first input shaft  18 . Third synchronizer  180  is actuated to cause third sleeve  182  to drivingly interconnect second reverse speed gear  110  to output shaft  28 . A clutch-to-clutch 2-3 power shift occurs as controller  168  controls first clutch actuator  42  to engage first engine clutch  14  while second clutch actuator  60  is controlled to disengage second engine clutch  16 . Once first engine clutch  14  is engaged, power transfers from first input shaft  18  through first drive gear  72 , the compound gear including first speed gear  74  and second reverse speed gear  110  and third synchronizer  180  to output shaft  28 . 
   Other sequential shifts such as 3-4, 4-5 and 5-6 up-shifts are similarly executed by controller  168  anticipating the next shift and disengaging one of first engine clutch  14  and second engine clutch  16  to allow an appropriate synchronizer to be actuated. Accordingly, a detailed description of the shifting process will not be provided but a description of the power flow path for each drive gear follows. 
   In the fourth forward speed ratio drive connection, power flows from second input shaft  20  through second drive gear  78 , second speed gear  80 , fourth synchronizer  186 , transfer shaft  22 , third drive gear  94 , sixth speed gear  98  and fourth drive gear  96  to output shaft  28 . A fifth forward drive gear ratio is obtained by transferring torque from first input shaft  18  through fifth synchronizer  194 , sixth speed gear  98  and fourth drive gear  96  to output shaft  28 . A sixth forward drive gear ratio is provided by transferring torque from second input shaft  20  through fifth drive gear  102 , seventh speed gear  104  and third synchronizer  180  to output shaft  28 . 
   A reverse drive speed ratio torque path includes transferring torque from first input shaft  18  through first drive gear  72 , the compound gear including first speed gear  74  and second reverse speed gear  110 , first reverse speed gear  108 , sixth synchronizer  200 , reverse idler shaft  24 , reverse drive gear  90 , fifth speed gear  88 , sixth speed gear  98 , fourth drive gear  96  to output shaft  28 . One skilled in the art will appreciate that power transfer for the reverse, first, third and fifth forward drive gears are provided by torque transferred through first input shaft  18  while a torque supply for the second, fourth and sixth forward drive gears is provided by second input shaft  20 . In this manner, sequential clutch-to-clutch powershifts may occur. 
     FIG. 5  depicts an alternate embodiment dual-clutch multi-speed transmission  300 . Transmission  300  is substantially similar to transmission  10  except that a final drive unit  302  is positioned at an opposite end of output shaft  28  than depicted in  FIG. 1 . Because the remaining components of transmission  10  are substantially identical in shape and function to those previously described, like elements will retain their previously introduced reference numerals. 
   Final drive unit  302  includes a hypoid gearset having a pinion gear  304  fixed to output shaft  28 . Pinion gear  304  is in meshed engagement with a ring gear  306 . Ring gear  306  drives the housing of a differential assembly  308 . Differential assembly  308  provides torque to a pair of output shafts (not shown). By positioning final drive unit  302  rearward of each of the other transmission components, transmission  300  lends itself to a rear transaxle type application. 
     FIG. 6  depicts another alternate embodiment dual-clutch multi-speed transmission  400 . Transmission  400  is substantially similar to transmissions  10  and  300  except that a first engine clutch  402  is spaced apart from a second engine clutch  404 . Accordingly, like element will retain their previously introduced reference numerals. First engine clutch  402  is positioned at a first end of an input shaft  406  while second engine clutch  404  is positioned at an opposite end of input shaft  406 . First engine clutch  402  includes a drum housing  408  fixed for rotation with input shaft  406 . Outer clutch plates  409  are in splined engagement with housing  408 . A hub  410  is fixed to a first tubular input shaft  412 . Inner clutch plates  413  are in splined engagement with hub  410 . First tubular input stub shaft  412  encompasses a portion of input shaft  406  and is rotatable relative thereto. As described in relation to the previous embodiments, first engine clutch  402  is a normally-closed clutch operable to drivingly interconnect engine output  12  and first input stub shaft  412 . In the embodiment depicted in  FIG. 6 , first input stub shaft  412  performs the functions described in relation to first input shaft  18 . 
   Second engine clutch  404  includes a drum housing  414  coupled to the opposite end of input shaft  406 . A hub  416  is fixed to a second tubular input stub shaft  418 . Inner clutch plates  420  are coupled to hub  416  while outer clutch plates  422  are coupled to drum housing  414 . Second engine clutch  404  is a normally-closed clutch operable to drivingly interconnect engine output  12  and second input stub shaft  418 . Second input stub shaft  418  functions substantially similarly to second input shaft  20  previously described. 
   By axially spacing apart first engine clutch  402  and second engine clutch  404 , each engine clutch may be more efficiently cooled. Additionally, the relative sizes of first engine clutch  402  and second engine clutch  404  need not be dependant upon one another because second engine clutch  404  is no longer packaged within an envelope defined by first engine clutch  402 . A final drive unit  430  includes a pinion gear  432  fixed to output shaft  28 . A ring gear  434  is in meshed engagement with pinion gear  432 . A differential unit  436  is drivingly coupled to ring gear  434 . Final drive unit  430  is rearwardly positioned of each of the other components of transmission  400 . Accordingly, transmission  400  lends itself for use as a rear transaxle of a vehicle. As will be understood from comparison of the arrangement of gearset  26  in both transmissions  10  and  400 , the powershifting function and torque flow paths through the gearsets and synchronizers are identical. While the physical arrangement of the components of transmission  400  is different than that of transmission  10 , it will be appreciated that both dual-clutch powershifting automatic transmissions include the same novel packaging and torque flow arrangements. 
   Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments of the present invention. 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 department from the spirit and scope of the invention as defined in the following claims.