Dual toroidal cavity type continuously variable transmission

Abstract: A toroidal type continuously variable transmission (10) includes first and second parallel toroidal transmission units (12, 14) which are both mounted on a common center transmission shaft (26). The center transmission shaft (26) is axially movable, and the input cone disc (16, 20) of each transmission unit (12, 14) is mounted on the center transmission shaft (26) through ball splines (30, 32) in such a manner as to enable torque transmission and relative axial motion between each disc (16, 20) and the shaft (26). The center transmission shaft (26) transmits, from the input disc (16) of the first unit (12) to the input disc (20) of the second unit (14), not only an input torque inputted to the input disc (16) of first unit (12) through a loding cam mechanism (42), but also the an axial thrust load produced by the loading cam mechanism (42).

Description: The present invention relates to a toroidal type continuously variable transmission (CVT), and more specifically to a toroidal transmission having two toroidal cavities around a common axis (often called a dual cavity type). JP-A-62-258255 discloses one conventional example. A toroidal transmission of this example has a first toroidal cavity formed between input and output discs of a first toroidal transmission unit, and a second toroidal cavity between input and output discs of a second unit. The first and second toroidal cavities are equal in size, coaxial with each other and axially spaced from each other. In this conventional example, the input discs of both units are mounted on a torque shaft, and drivingly connected with each other by the torque shaft. A loading cam mechanism for producing an axial thrust load in accordance with an input torque is provided at the side of the input disc of the first unit, and the thrust load is transmitted to the input disc of the second unit by an axially movable tension rod. The torque shaft is hollow, and the tension rod is arranged coaxially in the hollow torque shaft. The dual cavity type toroidal transmission of this conventional example requires two separate coaxial shafts, the torque shaft and tension rod for transmission of torque and transmission of thust load. This conventional transmission design, therefore, increases the number of required component parts, requires an additional machining process for forming coaxial shafts, and complicates the assembly process with the result of cost increase. A toroidal type continuously variable transmission according to the preamble of Claim 1 is known from GB-A-431199. In this document the cam-faced torque ring and the loading nut are both mounted on the same end of the centre shaft. SUMMARY OF THE INVENTION It is the object of the present invention to provide a dual toroidal cavity type continuously variable transmission, in which the phase difference between the rotations of the first and second outside discs is minimised, which can be designed very compactly and which is easy to assemble. This object is solved according to the invention by a continuously variable transmission according to claim 1. Preferred embodiments of the invention are subject matter of the sub-claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of a toroidal type continuously variable transmission according to one embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows one embodiment of the present invention. A toroidal type continuously variable transmission (CVT) 10 of this embodiment includes a first toroidal transmission unit 12 and a second toroidal transmission unit 14, which are arranged side by side around a common axis C. The first toroidal unit 12 has first input and output discs 16 and 18 which have opposite toroid surfaces confronting each other and forming a first toroidal cavity. Similarly, the second toroidal unit 14 has second input and output discs 20 and 22 forming a second toroidal cavity. Each toroidal unit has an intervening rolling member which comprises at least two power rollers 24 installed in the toroidal cavity. In each toroidal unit, the power rollers 24 are in frictional contact with the toroidal surfaces of the input and output discs 16 and 18 or 20 and 22. In this embodiment, each of the first and second toroidal units 12 and 14 has two power rollers 24 which are symmetrically arranged with respect to the axis C, as disclosed in the above-mentioned JP-A-62-258255. The power rollers 24 are inclined by one or more control valves and actuators (not shown) in accordance with an operating condition such as a vehicle operating condition, as disclosed in Japanese Utility Model Provisional Publication No. 63-92859. In each toroidal unit, the power rollers 24 transmit power from the input disc to the output disc by rolling, and continuously vary a transmission ratio between output and input speeds by inclining. Fig. 1 shows only one power roller 24. All the discs 16, 18, 20 and 22 are mounted on asingle torque transmission center shaft 26. The axis of the center transmission shaft 26 is coincident with the above-mentioned common axis C. The center shaft 26 is hollow, and it is supported on a transmission housing 28 in such a manner that the center shaft 26 is axially movable, to a limited extent, with respect to the housing. The center shaft 26 has a first end which is a lefthand end as viewed in Fig. 1 and a second right hand end. The first toroidal unit 12 is mounted on the first lefthand half of the center shaft 26 between the first end and the middle of the center shaft. The second toroidal unit 14 is mounted on the second righthand half of the center shaft 26 between the second end and the middle of the center shaft 26. Among the discs 16, 18, 20 and 22, the first input disc 16 is closest to the first lefthand end of the center shaft 26, and the second input disc 20 is the closest to the second righthand end of the center shaft 26. The first and second output discs 18 and 22 are disposed between the first and second input discs 16 and 20. Therefore, the input discs 16 and 20 of this embodiment are outside discs, and the output discs 18 and 22 are inside discs. The outside first input disc 16 is mounted on the center shaft 26 through a first ball spline coupling 30 so that the first input disc 16 is not rotatable relative to the center shaft 26, but it is axially slidable relative to the center shaft 26. Similarly, the outside second input disc 20 is mounted on the center shaft 26 through a second ball spline coupling 32 so that the second input disc 20 is not rotatable relative to the center shaft 26 but it is axially slidable. The first and second input discs 16 and 20 are engaged with the center shaft 26 through the ball spline couplings 30 and 32, respectively, so that the first and second input discs 16 and 20 rotate together with the center shaft 26. The first and second input discs 16 and 20 are axially movable on the center shaft 26 to a limited extent. Each of the first and second ball spline couplings 30 and 32 is a coupling means for coupling coaxial shafts for power transmission therebetween. In this embodiment, each coupling means comprises splines and balls for making the relative axial motion between the shafts smooth. An output gear (terminal member) 34 is rotatably mounted on the center shaft 26 through appropriate bearing means, and the first and second output discs 18 and 22 are splined to the output gear 34. A torque transmitted from the first input disc 16 to the first output disc 18, and a torque transmitted from the second input disc 20 to the second output disc 22 are both transmitted to the output gear 34, and power is taken out through the output gear 34. The output gear 34 is rotatably supported by the housing 28 through ball bearings 38 and 40. The toroidal transmission 10 further includes a loading cam mechanism 42 serving as a first loading means. The loading cam mechanism 42 is disposed next to the first input disc 16 around the first lefthand end of the center shaft 26. The loading cam mechanism 42 is designed to produce an axial pushing force (thrust load) in accordance with an input torque. The loading cam mechanism 42 has a loading cam disc 44 shaped like a flange, and loading rollers 46 which are confined between a cam surface 44a of the loading cam member 44 and an outside surface of the first input disc 16. The loading rollers 46 are supported by a support plate 46a disposed between the loading cam member 44 and the first input disc 16. The loading cam member 44 is rotatably mounted on the center shaft 26 so that a relative rotation therebetween is possible, and engaged through a thrust bearing 48 with a flange 26a formed in the first lefthand end of the center shaft 26. A leftward pusing force applied on the loading cam member 44 is transmitted through the thrust bearing 48 and the flange 26a to the center shaft 26. The loading cam mechanism 42 of this embodiment has at least one pin hole 47 which extends axially through the loading cam member 44, and the support plate 46a, into the first input disc 16. When the loading cam mechanism 42 is assembled, a knock pin (not shown) is inserted in the pin hole 47. A torque input shaft 50 is rotatably received through a needle bearing 52 in the first lefthand end of the hollow center shaft 26. The input shaft 50 is coaxial with the center shaft 26. The input shaft 50 has a flange 54 which rotates with the input shaft 50 as a unit. The flange 54 is connected with the loading cam member 44 through a coupling means 56 shaped like splines. A first disc spring 58 is disposed through a spacer 60 and a needle bearing 62 between the first input disc 16 and the loading cam member 44. The first disc spring 58 of this embodiment is a combination of Belleville springs (initially coned disc springs). A biasing force of the first disc spring 58 is parallel to the pushing force produced by the loading cam mechanism 42. A second disc spring 68 for preloading is mounted on the second righthand end of the center transmission shaft 26. The second disc spring 68 is also a combination of Belleville springs, and serves as a second loading means. A loading nut 64 and a lock nut 66 are screwed firmly on the second right hand end of the center transmission shaft 26. The loading nut 64 prevents the first toroidal unit 12 and the second toroidal unit 14 from being axially extracted from the center shaft 26. The second disc spring 68 is disposed between a flange 64a of the loading nut 64 and the second input disc 20. A spacer 70 is interposed between the second input disc 20 and the second disc spring 68. The second disc spring 68 applies a biasing force on the second input disc 20, and a reaction force due to this biasing force is applied through the loading nut 64 to the center transmission shaft 26. The toroidal transmission 10 of this embodiment is operated as follows: A torque from a prime mover such as an engine of a motor vehicle is first inputted to the torque input shaft 50. This input torque is transmitted from the input shaft 50 through the coupling means 56 to the loading cam member 44, so that the loading cam member 44 and the first input disc 16 rotate relative to each other. This relative rotation between the cam member 44 and the first input disc 16 causes the loading rollers 46 to be compressed between the loading cam member 44 and the first input disc 16 by the action of the cam mechanism 42. In this way, the loading rollers 46 are compressed between the cam member 44 and the first input disc 16, and the torque is transmitted from the cam member 44 to the first input disc 16. The force pressing the loading rollers 46 between the cam member 44 and te first input disc 16 is increased in proportion to the input torque, and this force acts also as a force (thrust load) pushing the first input disc 16 rightwardly toward the second end of the center transmission shaft 26. The torque of the first input disc 16 is transmitted through the first ball spline coupling 30 to the center transmission shaft 26, and further transmitted from the center transmission shaft 26 through the second ball spline coupling 32 to the second input disc 20. The torque transmitted to the first input disc 16 is transmitted through the power rollers 24 to the first output disc 18. At the same time, the torque transmitted to the second input disc 20 is transmitted through the power rollers 24 to the second output disc 22. In each of the first and second toroidal units 12 and 14, power is transmitted from the input disc to the output disc through the power rollers 24 which are rolling about an inclinable axis. The axial thrust force produced by the loading cam mechanism 42 pushes the first input disc 16 rightwardly toward the first output disc 18. At the same time, the reaction force of the this axial thrust force is transmitted through the thrust bearing 48 to the transmission shaft 26. Therefore, the transmission shaft 26 is axially moved, and applies a leftward axial force to the second input disc 20 through the loading nut 64 and the second disc spring 68. In the toroidal transmission 10 of this embodiment, the single transmission shaft 26 alone is used for transmitting a torque between the first and second input discs 16 and 20, and transmitting a thrust load produced by the loading cam mechanism 42. The single transmission shaft 26 can perform the functions of both the torque shaft and tension rod of the conventional design. The toroidal transmission 10 of this embodiment can reduce the number of required component parts, simplify the structure, and facilitate the forming and assembly processes. The first and second input discs 16 and 20 are engaged with the transmission shaft 26 through the ball splines 30 and 32 in such a manner that the first and second input discs 16 and 20 and the transmission shaft 26 all rotate together. Therefore, the toroidal transmission 10 of this embodiment can transmit torque efficiently with no phase difference in the rotational direction between the first and second input discs 16 and 20. The ball splines 30 and 32 enable the first and second input discs 16 and 20 to move smoothly in the axial direction with respect to the transmission shaft 26, so that the thrust load of the loading cam mechanism 42 is transmitted smoothly. In each of the toroidal units 12 and 14, the thrust load produced by the loading cam mechanism 42 acts to push the input disc 16 or 20 toward the output disc 18 or 22, and enables the power rollers 24 to transmit power without slippage. The second disc spring 68 is interposed between the center transmission shaft 26 and the second input disc 20 which are so engaged by the ball spline coupling 32 as to prevent a relative rotation therebetween. Therefore, the second disc spring 68 rotates together with the center transmission shaft 26 and the second input disc 20, and the friction surfaces of these members are made immune from wear. When the loading cam mechanism 42 is assembled, a knock pin is inserted in the pin hole 47 to effect an initial alignment of the loading cam mechanism 42, which helps prevention of the preload of the second disc spring 68 from being decreased when the loading cam mechanism 42 is displaced. The knock pin is extracted from the hole 47 after the assembly process. In the toroidal transmission of this embodiment, torque is inputted to the outside discs 16 and 20, and taken out from the inside discs 18 and 22 through the output gear 34. However, the opposite arrangement is possible in which torque is inputted through the output gear 34 to the inside discs 18 and 22, and taken out from the outside discs 16 and 20.

Claims: A toroidal type continuously variable transmission comprising: a center transmission shaft (26) having first and second shaft ends; first and second outside discs (16, 20) which are mounted on and coupled with said shaft in such a manner as to permit said first and second outside discs to move axially relative to said shaft and to prevent relative rotation between said shaft and each of said first and second outside discs, said first outside disc being located near said first end of said shaft, and said second outside disc being located near said second shaft end; an inside disc member (18, 22) which is rotatably mounted on said shaft between said first and second outside discs, said inside disc member having a first portion forming a first toroidal cavity with said first outside disc, and a second portion forming a second toroidal cavity with said second outside disc; said outside discs being arranged as input or output elements and said inside disc member being arranged as output or input elements respectively; first and second rolling members (24), said first rolling member being installed in said first toroidal cavity for transmitting power between said first outside disc and said inside disc member, and said second rolling member being installed in said second toroidal cavity for transmitting power between said second outside disc and said inside disc member; a loading means (42, 44, 46, 48, 58, 68, 64, 66) for loading each of said first and second outside discs toward said inside disc member, said loading means comprising a cam mechanism (42) comprising a loading cam member (44) rotatably mounted on said shaft between said first outside disc and said first shaft end of said shaft, a thrust bearing (48) disposed between said cam member and said first shaft end of said shaft, a preloading disc spring (68), and a loading nut (64) disposed behind said preloading disc spring; and said shaft being axially movable relative to a housing (28) of said transmission so that an axial thrust load produced by each of said first and second loading means is transmitted by said shaft; characterized in that said inside disc member comprises a first inside disc (18) having said first portion defining said first toroidal cavity and a second inside disc (22) having said second portion defining said second toroidal cavity, said first and second inside discs being separate from each other; and in that to facilitate the assembly said loading nut (64) is screwed on said second shaft end of said shaft, and said preloading disc spring (68) is mounted on said shaft (26) between said loading nut and said second outside disc (20). A transmission according to Claim 1 wherein said loading cam mechanism (42) comprises loading rollers 46 pressed between said cam member (44) and said first outside disc (16), and said loading rollers 46 and said thrust bearing (48) are placed radially so that said thrust bearing is surrounded by said loading rollers. A transmission according to one of Claims 1 and 2 wherein said loading means comprises a first side disc spring (58) which is disposed between said loading cam member (44) and said first outside disc (16), in an axially depressed recess formed in the central portion of the first outside disc (16). A transmission according to one of Claims 1-3 wherein said first outside disc (16) is coupled with a first portion of said shaft (26) by a first spline coupling means (30) which is provided radially between a radially outwardly facing external surface of said first portion of said shaft and a radially inwardly facing internal surface of said first outside disc, and said second outside disc (20) is coupled with said shaft by a second spline coupling means (32) which is provided radially between a radially outwardly facing external surface of a second portion of said shaft and a radially inwardly facing internal surface of said second outside disc. A transmission according to Claim 4 wherein said first spline coupling (30) comprises balls confined between the external surface of said first portion of said shaft and the internal surface of said first outside disc, and said second spline coupling (32) comprises balls confined between the external surface of said second portion of said shaft and the internal surface of said second outside disc. A transmission according to one of Claims 1-5 wherein said transmission further comprises a middle terminal member (34) which is disposed axially between said first and second inside discs (18, 22) and drivingly connected with said first and second inside discs. A transmission according to Claim 6 wherein said middle terminal member (34) is rotatably supported by an inwardly projecting portion of said housing (28) of said transmission, said inwardly projecting portion of said housing being located axially between said first and second inside discs (18, 22). A transmission according to Claim 7 wherein said middle terminal member is an output gear (34) which is supported by said projecting portion of said housing (28) through two bearings (38, 40) disposed on both sides of said output gear. A transmission according to one of Claims 6-8 wherein said middle terminal member (34) is mounted on said shaft (26), which is hollow and has at least one radial hole extending radially from the interior hollow portion thereof to the outside cylindrical surface thereof, said middle terminal member is formed with a wide annular internal groove which faces inwardly toward the radial hole of said shaft and which is so wide in the axial direction that the radial hole always open into the wide groove of said middle terminal member when said shaft moves axially relative to said middle terminal member (34). A transmission according to one of Claims 1-9 wherein said transmission further comprises an input shaft (50) having one end on which said shaft (26) is mounted through a needle bearing (52). A transmission according to one of Claims 1-10 wherein said cam mechanism (42) is arranged to cause said shaft (26) to move axially relative to said housing of said transmission by applying, on said first end (26a) of said shaft, an axial force which is increased with increase in a torque transmitted through said cam mechanism. A transmission according to Claim 11 wherein said loading cam member (44) of said cam mechanism (42) is formed with an axial pin hole (47), and said first outside disc (16) is formed with an axial pin hole (47) for determining a relative position between said cam member (44) and said first outside disc with a pin to be inserted in said axial holes (47) when assembling said transmission. A transmission according to Claim 12 wherein said cam mechanism further comprises a support plate (46a) for supporting the loading rollers, said support plate being placed between said cam disc (44) and said first outside disc (16), and formed with an axial pin hole (47) which is aligned during assembly with said axial pin holes of said cam disc and said first outside disc. A transmission according to Claim 12 wherein said first end of said shaft (26) is formed with an outward flange (26a) which is an integral part thereof, and there is disposed, between said outward flange (26a) and said cam member (44), said thrust bearing (48) comprising balls sandwiched between two axially spaced races.

Inventors: NAKANO MASAKI, NAKANO, MASAKI
Applicants: NISSAN MOTOR, NISSAN MOTOR CO., LTD.
Application year: 1989
Main classification: F16H15
IPC codes: F16H15