Abstract:
A multi-mode continuously variable transmission (CVT) for a motor vehicle includes a transmission input member, a transmission output member, a planetary gear set, a forward clutch, a brake, and a continuously variable unit having a first pulley, a second pulley, and an endless member wrapped around the first pulley and the second pulley. A first transfer gear set is connected to the transmission output member. A second transfer gear set is connected to the transmission output member. A dual clutch assembly is provided having a first clutch and a second clutch, wherein the first clutch selectively connects the second pulley to the first transfer gear set and the second clutch selectively connects the second pulley to the second transfer gear set. The dual clutch assembly provides two modes or ranges of continuously variable speed ratios between the transmission input member and the transmission output member.

Description:
FIELD 
       [0001]    The present disclosure relates to automatic transmissions and more particularly to a multi-mode continuously variable transmission having selectable transfer gears. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0003]    A continuously variable transmission (“CVT”) typically includes a belt and pulley system that operatively couples a rotary power source, such as an engine or electric motor, to a double gear final drive unit. The belt and pulley system generally includes first and second pairs of pulley cones having a torque transmitting belt or chain extending between the cone pairs. Each pulley cone pair includes an axially stationary pulley member and an axially movable pulley member. Each movable pulley member is axially adjustable with respect to the stationary pulley member by a hydraulic system. The hydraulic system provides primary and secondary hydraulic pressures to the respective movable pulley members to adjust the running radius of the first and second pulley cone pairs which in turn controls the output/input ratio of the continuously variable transmission. Movement of the cones steplessly or continuously varies the ratio of an input speed to an output speed. With the continuously variable transmission, small but effective ratio changes can be attained. This is in contrast to a fixed gear ratio unit where any ratio changes are step values. 
         [0004]    CVT axial length and mass significantly impact its power density and efficiency. Accordingly, there is a constant need for improved CVT designs that minimize axial length and mass while providing sufficient performance characteristics. 
       SUMMARY 
       [0005]    A multi-mode CVT is provided for a motor vehicle. In one aspect of the present invention, the CVT includes a transmission input member, a transmission output member, a planetary gear set having first, second, and third members, wherein the second member of the planetary gear set is connected to the transmission input member, a forward clutch for selectively connecting the transmission input member to the first member of the planetary gear set, a brake for selectively connecting the third member of the planetary gear set to a stationary member, and a continuously variable unit having a first pulley connected for common rotation with one of the first, second, and third members of the planetary gear set, a second pulley, and an endless member wrapped around the first pulley and the second pulley. A first transfer gear set is connected to the transmission output member. A second transfer gear set is connected to the transmission output member. A dual clutch assembly is provided having a first clutch and a second clutch, wherein the first clutch selectively connects the second pulley to the first transfer gear set and the second clutch selectively connects the second pulley to the second transfer gear set. The planetary gear set arrangement controls forward and reverse speed selections while the dual clutch assembly provides two modes or ranges of continuously variable speed ratios between the transmission input member and the transmission output member. 
         [0006]    In another aspect of the present invention, the first transfer gear set includes a first drive gear in mesh with a first driven gear, the first drive gear connected to the first clutch and the first driven gear connected to the transmission output member. 
         [0007]    In another aspect of the present invention, the second transfer gear set includes a second drive gear in mesh with a second driven gear, the second drive gear connected to the second clutch and the second driven gear connected to the transmission output member. 
         [0008]    In another aspect of the present invention, the first drive gear is co-planar with the first driven gear and the second drive gear is co-planar with the second driven gear. 
         [0009]    In another aspect of the present invention, the dual clutch includes a clutch housing, an inner clutch hub, and an outer clutch hub, wherein the first clutch is connected between the inner clutch hub and the clutch housing, and the second clutch is connected between the outer clutch hub and the clutch housing. 
         [0010]    In another aspect of the present invention, the inner clutch hub includes a flange and the first clutch is connected to the flange. 
         [0011]    In another aspect of the present invention, the inner clutch hub includes a first end portion and a second end portion each on opposite sides of the flange, and wherein the first drive gear is connected to the second end portion. 
         [0012]    In another aspect of the present invention, the first drive gear is coaxial with the inner clutch hub and the second drive gear is supported on the inner clutch hub by at least one bearing. 
         [0013]    In another aspect of the present invention, the first end portion of the inner clutch hub is disposed within the second pulley assembly. 
         [0014]    In another aspect of the present invention, the clutch housing defines inner and outer cavities, and the first clutch and flange are disposed in the inner cavity and the second clutch and outer clutch hub are disposed in the outer cavity. 
         [0015]    In another aspect of the present invention, the first pulley is connected for common rotation with the first member of the planetary gear set. 
         [0016]    In another aspect of the present invention, the first member of the first planetary gear set is a sun gear, the second member of the first planetary gear set is a planet carrier member, and the third member of the first planetary gear set is a ring gear member. 
         [0017]    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 
         [0018]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0019]      FIG. 1  is a schematic and cross-section view of a powertrain according to the principles of the present invention; and 
           [0020]      FIG. 2  is an enlarged portion of the cross-section view of the powertrain shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0022]    With reference to  FIG. 1 , a powertrain for a motor vehicle is generally indicated by reference number  10 . The powertrain  10  generally includes an engine  12  interconnected with a transmission  14 . The engine  12  may be a conventional gasoline, Diesel, or flex fuel internal combustion engine, a hybrid engine, or an electric motor, or any other type of prime mover, without departing from the scope of the present disclosure. The engine  12  supplies a driving torque to the transmission  14  through, for example, a torque converter  15 . It should be appreciated that other starting devices may be employed, such as a launch clutch. 
         [0023]    The transmission  14  is a variable diameter pulley or sheave drive continuously variable transmission (CVT). The transmission  14  includes a typically cast, metal housing  16  which encloses and protects the various components of the transmission  14 . The housing  16  includes a variety of apertures, passageways, shoulders and flanges which position and support these components. Generally speaking, the transmission  14  includes a transmission input shaft  20  and a transmission dual output transfer gear assembly (transmission output assembly)  22 . The transmission input shaft  20  is functionally interconnected with the engine  12  through the torque converter  15  and receives input torque or power from the engine  12 . Connected between the transmission input shaft  20  and the transmission output assembly  22  is a planetary gear set arrangement  24  and a continuously variable unit or pulley assembly  26 . The planetary gear set arrangement  24  and the continuously variable unit  26  cooperate to provide forward and reverse speed ratios between the transmission input shaft  20  and the transmission output assembly  22 . The transmission output assembly  22  provides two modes or ranges of speed ratios to a final drive unit  28 , as will be described below. The final drive unit  28  may include a differential, axle shafts, and road wheels (not shown). 
         [0024]    The transmission input shaft  20  is connected to the planetary gear set arrangement  24 . The planetary gear set arrangement  24  includes a planetary gear set  30  having a sun gear member  30 A, a planet carrier member  30 B, and a ring gear member  30 C. The planet carrier member  30 B rotatably supports a set of planet gears  30 D (only two of which are shown). In one example, the planetary gear set arrangement  24  is configured as a compound planetary gear set where the set of planet gears  30 D include a first subset of planet gears each configured to intermesh with the sun gear member  30 A and a second subset of planet gears each configured to intermesh with both the first subset of planet gears and with the ring gear member  30 C. In another example, the planetary gear set arrangement  24  is configured as a simple planetary gear set where the planet gears  30 D are each configured to intermesh with both the sun gear member  30 A and the ring gear member  30 C. The sun gear member  30 A is selectively connectable for common rotation with the transmission input shaft  20  by a forward clutch  32  and the sun gear member  30 A is connected for common rotation with the continuously variable unit  26 . The carrier member  30 B is connected for common rotation with the transmission input member  20 . The ring gear member  30 C is selectively connectable to the transmission housing  16  by a brake  34 . 
         [0025]    The forward clutch  32  and the brake  34  are friction, dog or synchronizer type mechanisms or the like. Engagement of the forward clutch  32  provides a forward drive torque while engagement of the brake  34  provides a reverse drive torque. 
         [0026]    The pulley assembly  26  includes a first pulley or sheave pair  40  and a second pulley or sheave pair  42 . The first pulley  40  includes a first truncated conical sheave or member  40 A and second truncated conical sheave or member  40 B in axial alignment with the first truncated conical sheave  40 A. The second sheave  40 B is directly connected for rotation with the sun gear member  30 A. The second sheave  40 B is moveable axially relative to the first sheave  40 A by a hydraulic controlled piston  43  or other actuating system. It should be appreciated that the sheaves  40 A and  40 B may be axially switched without departing from the scope of the present invention. 
         [0027]    The second pulley  42  includes a first truncated conical sheave or member  42 A and second truncated conical sheave or member  42 B in axial alignment with the first truncated conical sheave  42 A. The second sheave  42 B is directly connected for rotation with the transmission output assembly  22 . The first sheave  42 A is moveable axially relative to the second sheave  42 B by a hydraulic controlled piston  45  or other actuating system. It should be appreciated that the sheaves  42 A and  42 B may be axially switched without departing from the scope of the present invention. 
         [0028]    A torque transmitting belt or chain  46  having an approximately V-shaped cross section is mounted between the first pulley  40  and the second pulley  42 . It should be appreciated that other types of belts, including positive engagement devices, may be employed without departing from the scope of the present invention. Drive torque communicated from the transmission input shaft  20  and planetary gear set assembly  24  is transferred via friction between the sheaves  40 A and  40 B and the belt  46 . The ratio of the input pulley  40  to the output pulley  42  is adjusted by varying the spacing between the sheaves  40 A and  40 B and between the sheaves  42 A and  42 B. For example, to change the ratio between the pulleys  40  and  42 , the axial distance between sheaves  40 A and  40 B may be reduced by moving sheave  40 B towards sheave  42 A while simultaneously the axial distance between sheave  42 A and  42 B may be increased by moving sheave  42 A away from sheave  42 B. Due to the V-shaped cross section of the belt  46 , the belt  46  rides higher on the first pulley  40  and lower on the second pulley  42 . Therefore the effective diameters of the pulleys  40  and  42  change, which in turn changes the overall gear ratio between the first pulley  40  and the second pulley  42 . Since the radial distance between the pulleys  40  and  42  and the length of the belt  46  is constant, the movement of the sheaves  40 A and  42 A must occur simultaneously in order to maintain the proper amount of tension on the belt  46  to assure torque is transferred from the pulleys  40 ,  42  to the belt  46 . 
         [0029]    Turning to  FIG. 2 , the second pulley  42  of the continuously variable unit  26  transfers torque to the transmission output assembly  22 . The transmission output assembly  22  includes a dual clutch  50  connected to a first transfer gear set  52  and a second transfer gear set  54 . The dual clutch  50  includes a dual clutch housing  56  connected via a spline connection  58  to an elongated shaft portion  60  of the second sheave  42 B. The dual clutch housing  56  defines an inner housing  62  and an outer housing  64  disposed radially outward of the inner housing  62 . The inner housing  62  supports an inner clutch pack  66  and a hydraulically actuated piston  68 . The inner clutch pack  66  includes interleaved friction or reaction plates  66 A,  66 B. The plates  66 A are slidably splined or connected to the inner housing  62 . The plates  66 B are slidably splined or connected to a flange portion  70  of an inner clutch hub  72 . The hydraulically actuated piston  68  selectively engages the inner clutch pack  66  by compressing the interleaved plates  66 A,  66 B together so that torque is transferred from the dual clutch housing  56  to the inner clutch hub  72 . 
         [0030]    The outer clutch housing  64  supports an outer clutch pack  74  and a hydraulically actuated piston  76 . The outer clutch pack  74  includes interleaved friction or reaction plates  74 A,  74 B. The plates  74 A are slidably splined or connected to the outer housing  64 . The plates  74 B are slidably splined or connected to an outer clutch hub  78 . The hydraulically actuated piston  76  selectively engages the outer clutch pack  74  by compressing the interleaved plates  74 A,  74 B together so that torque is transferred from the dual clutch housing  56  to the outer clutch hub  78 . 
         [0031]    The inner clutch hub  72  includes a first end portion  72 A and a second end portion  72 B on either axial side of the flange  70 . The first end portion  72 A is supported within a cavity  79  disposed in the second sheave  42 B. The second end portion  72 B is disposed outside the cavity  79  and is supported by the transmission housing  16  via bearings  81 . 
         [0032]    The first transfer gear set  52  includes a drive gear  52 A in mesh with a driven gear  52 B. The drive gear  52 A is coaxial with the inner clutch hub  72  and is rotationally connected to the inner clutch hub  72  by a spline connection  80  disposed on the second end portion  72 B. The driven gear  52 B is coaxial with an intermediate member or transmission output member  82  and is rotationally connected to the intermediate member  82  by a spline connection  84 . 
         [0033]    The second transfer gear set  54  includes a drive gear  54 A in mesh with a driven gear  54 B. The drive gear  54 A is coaxial with the inner clutch hub  72  and is rotationally supported on second end portion  72 B of the inner clutch hub  72  by bearings  86 . The drive gear  54 A is rotationally connected to the outer clutch hub  78 . The driven gear  54 B is coaxial with the intermediate member  82  and is rotationally connected to the intermediate member  82  by a spline connection  88 . 
         [0034]    Returning to  FIG. 1 , the intermediate member  82  is connected to the final drive unit  28 . The final drive unit  28  may include a differential  90  and axles  92  that provide drive torque to a set of road wheels (not shown). During operation of the transmission  14 , engine speed and torque is supplied through the torque converter  15  to the planetary gear assembly  24 . Engagement of the forward clutch  32  and the brake  34  selectively provide forward and reverse rotations. Speed and torque is transferred from the planetary gear assembly  24  to the continuously variable unit  26  where movement of the pulleys  40 ,  42  provides a range of continuous forward or reverse speed ratios. The speed and torque output from the continuously variable unit  26  is then selectively transferred to one of the first transfer gear set  52  or the second transfer gear set  54  by selectively engaging one of the clutches  66 ,  74  of the dual clutch assembly  50 . Each of the transfer gear sets  52 ,  54  provides a step up or step down in speed ratio thus providing two modes or ranges of continuously variable forward or reverse speed ratios to the intermediate member  82 . Speed and torque are then transferred from the intermediate member  82  to the final drive unit  28  to propel the motor vehicle. 
         [0035]    The 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.