Patent Publication Number: US-2015080170-A1

Title: Continuously variable transmission with chain output

Description:
FIELD 
     The present disclosure relates to automatic transmissions and more particularly to a continuously variable transmission having a chain driven output. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     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. 
     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 
     A continuously variable transmission for a motor vehicle is provided. The CVT includes an input member, an output member, a first planetary gear set having first, second, and third members, wherein the first member is interconnected with the input member, a brake connected to the second member of the first planetary gear set, a clutch interconnected between one of the first member, second member, and third member of the first planetary gear set and another one of the first member, second member, and third member of the first planetary gear set, a belt and pulley assembly connected to the third member of the first planetary gear set and the output member, a chain drive interconnected to the output member, and a final drive unit interconnected to the chain drive. 
     In one embodiment of the present invention, engagement of the brake provides a Reverse speed ratio and engagement of the clutch provides a forward speed ratio. 
     In another embodiment of the present invention, the clutch is selectively engageable to connect the first member of the first planetary gear set with the second member of the first planetary gear set. 
     In another embodiment of the present invention, the clutch is selectively engageable to connect the first member of the first planetary gear set with the third member of the first planetary gear set. 
     In another embodiment of the present invention, the clutch is selectively engageable to connect the second member of the first planetary gear set with the third member of the first planetary gear set. 
     In another embodiment of the present invention, the first member of the first planetary gear set is a ring gear, the second member of the first planetary gear set is a carrier member, and the third member of the first planetary gear set is a sun gear. 
     In another embodiment of the present invention, the final drive unit includes a second planetary gear set having a first member, a second member, and a third member, wherein the first member is interconnected to the chain drive and the third member is fixed for rotation to a stationary member. 
     In another embodiment of the present invention, the first member of the second planetary gear set is a sun gear, the second member of the second planetary gear set is a carrier member, and the third member of the second planetary gear set is a ring gear. 
     In another embodiment of the present invention, the brake is a band brake. 
     In another embodiment of the present invention, the band brake, the output member, and the final drive unit are each disposed on separate, parallel axes of rotation, and the transmission includes a transmission housing which cooperates with the band brake to define a space adjacent the band brake and radially inwards of the transmission housing, and the chain drive is at least partially disposed within the space when the transmission is operating. 
     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 
       The drawings described herein are for illustration purposes only and is not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic diagram of a powertrain according to the principles of the present invention; 
         FIG. 2A  is a is a diagrammatic illustration of an embodiment of a gear set according to the principles of the present invention; 
         FIG. 2B  is a is a diagrammatic illustration of an embodiment of a gear set according to the principles of the present invention; 
         FIG. 2C  is a is a diagrammatic illustration of an embodiment of a gear set according to the principles of the present invention; 
         FIG. 2D  is a is a diagrammatic illustration of an embodiment of a gear set according to the principles of the present invention; 
         FIG. 3A  is a schematic diagram of a front view layout of a transmission of the powertrain; and 
         FIG. 3B  is a schematic diagram of a side view layout of the transmission. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     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 flexplate (not shown) or other connecting device or a starting device  15  such as a hydrodynamic device or launch clutch. 
     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 or member  20  and a transmission output shaft or member  22 . Connected between the transmission input shaft  20  and the transmission output shaft  22  is a gearbox  24  and pulley assembly  26  that cooperate to provide forward and reverse speed or gear ratios between the transmission input shaft  20  and the transmission output shaft  22 . The transmission input shaft  20  is functionally interconnected with the engine  12  through the starting device  15  and receives input torque or power from the engine  12 . The transmission output shaft  22  is preferably connected with a chain driven final drive unit  28 . The transmission output shaft  22  provides drive torque to the chain driven final drive unit  28 . 
     The transmission input shaft  20  is connected to the gearbox  24 . The gearbox  24 , as well as a portion of the final drive unit  28 , is illustrated in a lever diagram format. A lever diagram is a schematic representation of the components of a mechanical device such as an automatic transmission. Each individual lever represents a planetary gear set wherein the three basic mechanical components of the planetary gear are each represented by a node. Therefore, a single lever contains three nodes: one for the sun gear, one for the planet gear carrier, and one for the ring gear. In some cases, two levers may be combined into a single lever having more than three nodes (typically four nodes). For example, if two nodes on two different levers are interconnected through a fixed connection they may be represented as a single node on a single lever. The relative length between the nodes of each lever can be used to represent the ring-to-sun ratio of each respective gear set. These lever ratios, in turn, are used to vary the gear ratios of the transmission in order to achieve an appropriate ratios and ratio progression. Mechanical couplings or interconnections between the nodes of the various planetary gear sets are illustrated by thin, horizontal lines and torque transmitting devices such as clutches and brakes are presented as interleaved fingers. Further explanation of the format, purpose and use of lever diagrams can be found in SAE Paper 810102, “The Lever Analogy: A New Tool in Transmission Analysis” by Benford and Leising which is hereby fully incorporated by reference. 
     For example, the gearbox  24  includes a planetary gear set  30  that includes a first node  30 A, a second node  30 B, and a third node  30 C. The first node  30 A is coupled to the transmission input shaft  20 . The third node  30 C is connected to a transfer shaft or member  32  that is coupled to the pulley assembly  26 . A clutch  34  selectively connects the transmission input member  20  and the first node  30 A of the planetary gear set  30  with the second node  30 B of the planetary gear set  30 . A brake  36  selectively connects the second node  30 B of the planetary gear set  30  to a stationary member or the transmission housing  16 . The brake  36  is preferably a band brake in order to minimize axial space, as will be discussed in greater detail below. In a preferred embodiment, the first node  30 A corresponds to a ring gear, the second node  30 B corresponds to a planet carrier member, and the third node  30 C corresponds to a sun gear. In an alternate embodiment, the clutch  34  is replaced by a clutch  34 ′, indicated by dashed lines in  FIG. 1 . The clutch  34 ′ selectively connects the transmission input member  20  and the first node  30 A of the planetary gear set  30  with the third node  30 C of the planetary gear set  30 . In another alternate embodiment, the clutch  34  is replaced by a clutch  34 ″, indicated by dashed lines in  FIG. 1 . The clutch  34 ″ selectively connects the second node  30 B of the planetary gear set  30  with the third node  30 C of the planetary gear set  30 . By engaging the clutch  34 , the gearbox  24  transfers engine torque to the transfer shaft  32  and the pulley assembly  26  in a forward speed ratio. By engaging the brake  36  with the clutch  34 , the gearbox  24  transfers the engine torque to the transfer shaft  32  and the pulley assembly  26  in a reverse speed ratio. 
     Turning to  FIGS. 2A-D , stick diagrams present schematic layouts of embodiments of the gearbox  24  according to the present invention. In  FIGS. 2A-D  the numbering from the lever diagram of  FIG. 1  are carried over. The clutches and couplings are correspondingly presented whereas the nodes of the planetary gear sets now appear as components of planetary gear sets such as sun gears, ring gears, planet gears and planet gear carriers. 
     For example, in  FIG. 2A , the gear set  30  includes a ring gear member  30 A, a planet carrier member  30 B, and a sun gear member  30 C. The planet carrier member  30 B rotatably supports a set of planet gears  30 D (only one of which is shown). The planet gears  30 D are each configured to intermesh with both the ring gear member  30 A and the sun gear member  30 C. The sun gear member  30 C is connected for common rotation with the transfer shaft  32  and to the clutch  34 ′. The planet carrier member  30 B is connected to the brake  36 . The ring gear member  30 A is connected for common rotation with the input shaft  20  and the clutch  34 ′. The clutch  34 ′ is selectively engageable to connect the transfer shaft  32  and the sun gear  30 C with the input shaft  20  and the ring gear  30 A. The brake  36  is selectively engageable to connect the carrier member  30 B with the transmission housing  16  in order to restrict relative rotation of the carrier member  30 B. 
     In  FIG. 2B , the gear set  30  is a compound planetary gear set and includes a ring gear member  30 B, a planet carrier member  30 A, and a sun gear member  30 C. The planet carrier member  30 A rotatably supports a set of planet gears  30 D (only one of which is shown) and  30 E (only one of which is shown). The planet gears  30 D are each configured to intermesh with both the sun gear member  30 C and the planet gears  30 E. The planet gears  30 E are configured to intermesh with both the planet gears  30 D and the ring gear  30 B. The sun gear member  30 C is connected for common rotation with the transfer shaft  32  and to the clutch  34 ″. The planet carrier member  30 A is connected to the input shaft  20 . The ring gear member  30 B is connected for common rotation with the clutch  34 ″ and the brake  36 . The clutch  34 ″ is selectively engageable to connect the transfer shaft  32  and the sun gear  30 C with the ring gear  30 B. The brake  36  is selectively engageable to connect the ring gear  30 B with the transmission housing  16  in order to restrict relative rotation of the ring gear  30 B. 
     In  FIG. 2C , the gear set  30  is a compound planetary gear set and includes a ring gear member  30 B, a planet carrier member  30 A, and a sun gear member  30 C. The planet carrier member  30 A rotatably supports a set of planet gears  30 D (only one of which is shown) and  30 E (only one of which is shown). The planet gears  30 D are each configured to intermesh with both the sun gear member  30 C and the planet gears  30 E. The planet gears  30 E are configured to intermesh with both the planet gears  30 D and the ring gear  30 B. The sun gear member  30 C is connected for common rotation with the transfer shaft  32  and to the clutch  34 ′. The planet carrier member  30 A is connected to the input shaft  20  and the clutch  34 ′. The ring gear member  30 B is connected for common rotation with the brake  36 . The clutch  34 ′ is selectively engageable to connect the transfer shaft  32  and the sun gear  30 C with the carrier member  30 A and the input shaft  20 . The brake  36  is selectively engageable to connect the ring gear  30 B with the transmission housing  16  in order to restrict relative rotation of the ring gear  30 B. 
     In  FIG. 2D , the gear set  30  is a compound planetary gear set and includes a ring gear member  30 B, a planet carrier member  30 A, and a sun gear member  30 C. The planet carrier member  30 A rotatably supports a set of planet gears  30 D (only one of which is shown) and  30 E (only one of which is shown). The planet gears  30 D are each configured to intermesh with both the sun gear member  30 C and the planet gears  30 E. The planet gears  30 E are configured to intermesh with both the planet gears  30 D and the ring gear  30 B. The sun gear member  30 C is connected for common rotation with the transfer shaft  32 . The planet carrier member  30 A is connected to the input shaft  20  and the clutch  34 . The ring gear member  30 B is connected for common rotation with the brake  36  and the clutch  34 . The clutch  34  is selectively engageable to connect the input shaft  20  and the carrier member  30 A with the ring gear  30 B. The brake  36  is selectively engageable to connect the ring gear  30 B with the transmission housing  16  in order to restrict relative rotation of the ring gear  30 B. 
     Returning to  FIG. 1 , 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 transfer member  32  and may be integrally formed with the transfer member  32 . The first sheave  40 A is moveable axially relative to the second sheave  40 B by a hydraulic control system (not shown) 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. 
     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 shaft or member  22  or may be integrally formed with the transmission output shaft or member  22 . The first sheave  42 A is moveable axially relative to the second sheave  42 B by a hydraulic control system (not shown) 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. 
     A torque transmitting belt or chain  44  having a V-shaped cross section is mounted between the first pulley pair  40  and the second pulley pair  42 . Drive torque communicated from the transfer shaft  32  is transferred via friction between the sheaves  40 A and  40 B and the belt  44 . 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 A towards sheave  42 B 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  44 , the belt  44  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  44  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  44  to assure torque is transferred from the pulleys  40 ,  42  to the belt  44 . 
     The transmission output shaft  22  is interconnected with or includes a first spur gear or drive sprocket  46 . A transfer chain or chain drive  48  is engaged or otherwise meshed with the drive sprocket  46  and engaged or otherwise meshed with a second spur gear or driven sprocket  50 . The driven sprocket  50  is interconnected with a final drive planetary gear set  52  either directly or via a shaft or member  54 . 
     The final drive planetary gear set  52  includes a first node  52 A, a second node  52 B, and a third node  52 C. The first node  52 A is coupled to the driven sprocket  50 . The third node  52 C is connected to a fixed or stationary member such as the transmission housing  16 . The second node  52 B is interconnected to other final drive components (not shown) that may include a differential, drive axles, and vehicle road wheels. In a preferred embodiment, the first node  52 A corresponds to a sun gear, the second node  52 B corresponds to a planet carrier member, and the third node  52 C corresponds to a ring gear. The final drive planetary gear set  52  transfers the drive torque from the carrier  52 B to the final drive components that includes the differential, axle shafts, and road wheels. 
     Turning to  FIGS. 3A and 3B , schematic diagrams illustrate the axial and radial layout of the transmission  14  on three primary axes “A”, “B”, and “C”. During operation of the transmission  14 , the chain  48  flexes radially outwardly, indicated by dashed lines  48 ′. As best seen in  FIG. 3A , this flexing of the chain  48  radially overlaps the outer diameter of the brake  36 . If the brake  36  is a typical plate clutch the chain  48  would not have the space to freely flex since the plate clutch has a relatively large axial presence. However, configuring the brake  36  as a band brake creates an axial space  60  which is defined by the axial end of the brake  36  and the housing  16 . This axial space  60  allows the chain  48  to flex into the same radial plane as the brake  36  without contacting the brake  36 . 
     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.