Abstract:
A dual clutch transmission is provided including a transmission input member, a first output member, a first, second, third and fourth gear sets, a first and second countershafts, and a first and second sleeve shafts. In operation, the first countershaft is engaged to the first sleeve shaft or the second countershaft is engaged to the second sleeve shaft, at least one of the first and second gears of the first and second gear sets is engaged to at least one of the first and second sleeve shafts, and at least one of the first and second gears of the third and fourth gear sets is engaged to at least one of the first and second countershafts to establish at least eight forward speed ratios between the transmission input member and the output shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/327,636 filed on Dec. 3, 2008 and as such, claims priority thereto under 35 U.S.C. §120. 
    
    
     FIELD 
     The present disclosure relates to a powertrain and transmission for a motor vehicle and more particularly to a hybrid powertrain and dual clutch transmission for a motor vehicle. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     Within the motor vehicle automatic transmission art, the dual clutch transmission (DCT) is a relative newcomer. A typical dual clutch transmission configuration includes a pair of mutually exclusively operating input clutches which drive a pair of layshafts or countershafts disposed on opposite sides of an output shaft. One of each of a plurality of pairs of constantly meshing gears which define the various forward gear ratios is freely rotatably disposed on one of the layshafts and the other of each pair of gears is coupled to the output shaft. A plurality of dog clutches selectively couple one of the gears to the layshaft to achieve a forward gear ratio. After the dog clutch is engaged, the input clutch associated with the active layshaft is engaged. 
     Dual clutch transmissions are known for their sporty, performance oriented shift characteristics. They typically exhibit good fuel economy due to good gear mesh efficiency and ratio selection flexibility in design. The dog clutches have low spin losses which also contributes to overall operating efficiency. 
     However, dual clutch transmissions have several unique design considerations. For example, because of the torque throughput during launch and the heat that can be generated during slip, the input clutches must be of a relatively large size. The size requirement applies as well to the cooling system which must be able to dissipate relatively large quantities of heat. Finally, because such transmissions typically have many sets of axially aligned gears, their overall length may be problematic in some platform configurations. 
     The present invention is directed not only to providing a dual clutch automatic transmission have reduced axial length but also to such a transmission for incorporation into a hybrid powertrain. 
     SUMMARY 
     The present invention provides a dual clutch transmission including a transmission input member, a first output member, a first, second, third and fourth gear sets, a first and second countershafts, and a first and second sleeve shafts. The first, second, third and fourth gear sets each have a first, second and third gears. The first and second gears are each intermeshed with the third gear. The third gears of the first and second gearsets are rotatably fixed to the transmission input member. The third gears of the third and fourth gearsets are rotatably fixed to the first output member. The first and second countershafts are disposed parallel to the transmission input member. The first gears of the third and fourth gear sets are each rotatably supported by and selectively engagable to the first countershaft. The second gears of the third and fourth gearsets are each rotatably supported by and selectively engagable to the second countershaft. The first and second sleeve shafts are disposed parallel to the transmission input member. The first gears of the first and second gear sets are each rotatably supported by and selectively engagable to the first sleeve shaft. The second gears of the first and second gearsets are each rotatably supported by and selectively engagable to the second sleeve shaft. The first sleeve shaft is selectively engageable to the first countershaft, and the second sleeve shaft is selectively engageable to the second countershaft, to establish at least eight forward speed ratios between the transmission input member and the output shaft at least one of the first countershaft is engaged to the first sleeve shaft and the second countershaft is engaged to the second sleeve shaft, at least one of the first and second gears of the first and second gear sets is engaged to at least one of the first and second sleeve shafts, and at least one of the first and second gears of the third and fourth gear sets is engaged to at least one of the first and second countershafts. 
     In another example of the present invention, the dual clutch transmission further includes an electric motor having input shaft and an output shaft. The output shaft is coupled to the transmission input member. 
     In yet another example of the present invention, the dual clutch further includes an input clutch having an input shaft and an output shaft coupled to the input shaft of the electric motor. 
     In yet another example of the present invention, the electric motor is bi-directional and provides a reverse speed ratio. 
     In yet another example of the present invention, the dual clutch transmission further includes four dog clutches. A first of the four dog clutches selectively connects at least one of the first gears of the first and second gearsets to the first sleeve shaft. A second of the four dog clutches selectively connects at least one of the second gears of the first and second gearsets to the second sleeve shaft. A third dog of the four dog clutches selectively connects at least one of the first gears of the third and fourth gearsets to the first countershaft. A fourth of the four dog clutches selectively connecting at least one of the second gears of the third and fourth gears sets to the second countershaft. 
     In yet another example of the present invention, the dual clutch transmission further includes two multiple disc clutches. A first of the two multiple disc clutches selectively connects the first countershaft to the first sleeve shaft. A second of the two multiple disc clutches selectively connects the second countershaft to the second sleeve shaft. 
     In yet another example of the present invention, the first sleeve shaft is disposed coaxial to and at least partially covers the first countershaft and the second sleeve shaft is disposed coaxial to and at least partially covers the second countershaft. 
     In yet another example of the present invention, the dual clutch transmission further includes a differential and a second and a third output shafts. The differential is coupled to the first output member. The second and third output shafts are disposed parallel to the transmission input member and drivingly connected to the differential. 
     Further features and advantages of the present invention will become apparent by reference to the following description and appended drawings wherein like reference numbers refer to the same component, element or feature. 
    
    
     
       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, top plan view of a dual clutch automatic transmission according to the present invention; 
         FIG. 2  is a schematic, end elevational view of a dual clutch automatic transmission according to the present invention taken along line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is a truth table presenting the various states of the two countershaft clutches and four dog clutches in the dual clutch transmission which achieve eight forward speeds or gear ratios; 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     Referring now to  FIGS. 1 and 2 , a dual clutch automatic transmission according to the present invention is illustrated and generally designated by the reference number  10 . The dual clutch automatic transmission  10  includes a housing  12  which receives, supports and protects the various components of the automatic transmission  10 . An input shaft or member  14  receives drive torque from a prime mover such as a gasoline, Diesel or flexible fuel engine (not illustrated) and connects to and drives an input clutch  16 . The input clutch  16  which is preferably disposed within a bell housing  13  secured to the front of the transmission housing  12  selectively engages to provide drive torque from the prime mover to a clutch output shaft or member  18  that drives an electric motor  20 . The electric motor  20  includes an armature  22  coupled to a main transmission input shaft  24 . The electric motor  20  may be an induction motor or more preferably a permanent magnet or brushless DC motor. The main transmission input shaft  24  is coupled to and directly drives a first input drive gear  26  and a second input drive gear  28 . The first input drive gear  26  is in constant mesh with a first input gear  34  which is freely rotatably disposed upon a first (odd) quill or drive tube  40  and a second input gear  42  which is freely rotatably disposed upon a second (even) quill or drive tube  50 . The first input gear  34  is active when first and fifth gears have been selected and the second input gear  42  is active when second and sixth gears have been selected. Also freely rotatably disposed on the first quill or drive tube  40  and spaced from the first input gear  34  is a third input gear  36  which is in constant mesh with the second input drive gear  28 . A fourth input gear  44  is freely rotatably disposed on the second quill or drive tube  50 , spaced from the second input gear  42  and in constant mesh with the second input drive gear  28 . The third input gear  36  is active when third and seventh gears have been selected and the fourth input gear  44  is active when fourth and eighth gears have been selected. 
     Between the first input gear  34  and the third input gear  36  is a first dog clutch  38 . The first dog clutch  38  is conventional and operates to positively connect either the first input gear  34  or the third input gear  36  to the first quill or drive tube  40 . Depending upon the sophistication of the control system and logic, the first dog clutch  38  and other dog clutches referenced below may be equipped with synchronizers to synchronize the speed of the elements of the dog clutches before they are engaged. Associated with the first dog clutch  38  is an operator and shift fork assembly  39  which axially and bi-directionally translates the first dog clutch  38  along the first quill or drive tube  40  and which may be either electric, hydraulic or pneumatic. Likewise, between the second input gear  42  and the fourth input gear  44  are a second dog clutch  48  and optional synchronizers. The second dog clutch  48  and the optional synchronizers are also conventional and operate to first synchronize and then positively connect the second input gear  42  or the fourth input gear  44  to the second quill or drive tube  50 . An electric, hydraulic or pneumatic operator and shift fork assembly  49  is associated with the second dog clutch  48 . 
     The first quill or drive tube  40  is connected to and directly drives an input of a first countershaft clutch assembly  52 . The first countershaft clutch assembly  52  is preferably a multiple disc or plate friction clutch pack having an electric, hydraulic or pneumatic operator (not illustrated) which selectively connects the first quill or drive tube  40  to a first (odd) layshaft or countershaft  60 . Similarly, the second quill or drive tube  50  is connected to and directly drives an input of a second countershaft clutch assembly  54 . The second countershaft clutch assembly  54  is also preferably a multiple disc or plate friction clutch pack actuated by an electric, hydraulic or pneumatic operator (not illustrated) which selectively connects the second quill or drive tube  50  to a second (even) layshaft or countershaft  70 . 
       FIG. 1  presents the first and second countershaft clutch assemblies  52  and  54  within the housing  12 . So located, the clutch assemblies  52  and  54  will typically be wet plate clutches. It should be appreciated that an equally viable alternate construction comprehends a wall or bulkhead  56  (shown in phantom) which separates the first and second countershaft clutch assemblies  52  and  54  from the other components of the transmission  10  within a dedicated compartment or housing, to allow them to operate as dry plate clutches, to keep clutch debris from contaminating the oil within the transmission housing  12  and to facilitate their easy service by avoiding the need to remove the engine or transmission  10  from the vehicle. 
     Freely rotatably disposed on the first layshaft or countershaft  60  is a first output gear  62  which is in constant mesh with a first driven output gear  84  which is secured to and rotates with a cage or housing  86  of a differential assembly  90 . Also freely rotatably disposed on the second layshaft or countershaft  70  is a second output gear  72  which is also in constant mesh with the first driven output gear  84  of the differential assembly  90 . The first output gear  62  is active when fifth or seventh gear is selected and the second output gear  72  is active when sixth or eighth gear is selected. Spaced from the first output gear  62  and also freely rotatably disposed on the first countershaft  60  is a third output gear  64  which is in constant mesh with a second driven output gear  88  secured to the housing  86  of the differential assembly  90 . Spaced from the second output gear  72  and freely rotatably disposed on the second countershaft  70  is a fourth output gear  74  which is in constant mesh with the second driven output gear  88 . The third output gear  64  is active when first and third gears have been selected and the fourth output gear  74  is active when second and fourth gears have been selected. 
     Between the first output gear  62  and the third output gear  64  is a third dog clutch  66  and optional synchronizers. The third dog clutch  66  and optional synchronizers are conventional and operate to first synchronize and then connect either the first output gear  62  or the third output gear  64  to the first countershaft  60 . An electric, hydraulic or pneumatic operator and shift fork assembly  68  is associated with the third dog clutch  66 . Likewise, between the second output gear  72  and the fourth output gear  74  is a fourth dog clutch  76  and optional synchronizers. The fourth dog clutch  76  and optional synchronizers are conventional and operate to first synchronize and then connect either the second output gear  72  of the fourth output gear  74  to the second countershaft  70 . An electric, hydraulic or pneumatic operator and shift fork assembly  78  is associated with the fourth dog clutch  76 . 
     The differential assembly  90  and specifically the cage or housing  86  is driven through either the first driven gear  84  or the second driven gear  88 , as noted. The differential assembly  90  includes four bevel gears (not illustrated) within the housing  86  disposed in pairs on two perpendicular axes. An opposed (co-axial) pair of the bevel gears are idler gears and the gears of a second opposed pair of bevel gears are coupled to and drive a first output shaft  92  and a second, coaxial output shaft  94 . The output shafts  92  and  94  may be coupled to drive wheels through universal joints (all not illustrated). 
     It should be understood that reverse gear may be provided by any one of a number of alternate means. For example, the input clutch  16  may be disengaged and the electric motor  20  may be energized to rotate in reverse and drive through a low speed (high ratio) gear such as first or second gear. Alternatively, an additional (idler) gear and clutch (not illustrated) may be incorporated into the automatic transmission  10  to operate in conjunction with, for example, the input gear  34  and the output gear  64  on the first countershaft  60 . 
       FIG. 3  is a truth table presenting a clutching scheme for the dual clutch automatic transmission  10 . An “X” in a row for a particular speed or gear ratio indicates that the actuator and countershaft clutch or the actuator and dog clutch associated with the gear indicated by the column heading are activated and engaged. It will therefore be appreciated that for each forward gear or speed ratio two gears on either the first countershaft  60  or the second countershaft  70  will be engaged and active. For example, in first gear, the first input gear  34  and the third output gear  64  on the first (odd) countershaft  60  will be active and in second gear the second input gear  42  and the fourth output gear  74  on the second (even) countershaft  70  will be active. 
     The foregoing description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention and the following claims.