WO2015028797A1

WO2015028797A1 - Continuously variable transmission

Info

Publication number: WO2015028797A1
Application number: PCT/GB2014/052603
Authority: WO
Inventors: Romeo Petrica GLOVNEA; Colin Alexander BELL; Daniel RISZCZUK
Original assignee: The University Of Sussex
Priority date: 2013-08-29
Filing date: 2014-08-28
Publication date: 2015-03-05
Also published as: GB201315336D0

Abstract

A continuously variable transmission (1) comprising: one or more driving members (5) coupled to an input shaft (7), wherein one or more of the driving members (5) are movable; a first carriage assembly (11) comprising one or more intermediary elements (13) disposed circumferentially at least partially within the first carriage assembly (11), wherein each of the intermediary elements (13) has a rotational axis that can be displaced in relation to the first carriage assembly (11); and a second carriage assembly (17) coupled to an output shaft (3), the second carriage assembly (17) comprising a second carriage member (18) and one or more movable driven members (19), wherein the intermediary elements (13) are configured to transmit rotational motion between the driving: members (5) and the driven members (19), the second carriage member (18) being substantially annular and comprising one or more wedging surface features (28), wherein the wedging surface features (28) comprise one or more profiled surfaces (29) that are configured to displace the driven members (19) upon movement of the second carriage member (18) in relation to the driven members (19).

Description

Continuously Variable Transmission

This invention relates to a continuously variable transmission and particularly, but not exclusively relates to a constant-power continuously variable transmission that automatically adjusts the transmission ratio in response to the resistive torque applied to an output shaft of the continuously variable transmission.

Background Continuously vaHafele transmission (CVT) are used in a wide variety of machines across a broad range of Industries, For example, CVTs may be used in milling machines, aircraft, agricultural machinery and passenger vehicles. Known variants of the CVT include cone-drive CVTs, variable-diameter pulley CVTs, magnetic CVTs and roller CVTs amongst others.

Over recent years, the use of CVTs has been particularly focused within the automotive industry. The use of a CVT in a vehicle may have a number of benefits, including an improvement in fuel efficiency. A powertrain of a vehicle that incorporates a CVT permits the engine to operate substantially at maximum load by continuously varying Its transmission ratio to meet instantaneous loading conditions. Specifically, the CVT provides an infinite number of torque-speed conditions within a predetermined range of transmission ratios, which is set by the internal geometry of the CVT. in this manner, the CVT allows the engine to operate substantially at its optimum brake specific fuel consumption (6SPC) rate. it is desirable therefore to maintain the power transmitted acros the CVT at a constant level, i.e. a constant power (CP-CVT, in order to sustain engine operation at the optimum 8 SFC rate. This may be achieved by the CP-CVT automatically adjusting the transmission ratio in accordance with the required output torque. Th degree by which the power deviates from the constant level depends upon the geometry of the components internal to the CP-CVT and the type of loads that those components, are placed under.

In general, the loads within the CP-CVT are transmitted through e!astohydrodynamle (END) traction between drive members, with a toroidal-drive layout being best suited to the automotive industry due to higher torque capacity and lower operating noise. It is known to provide the CP-CVT with a toroidal-drive and a ball-screw coupling between an output shaft and a driven output disc. However, du to the inherent geometry of the ball-screw coupling, the. relationship between the output torque and the transmission ratio is fixed, It is desirable, therefore, to provide the CP-CVT with meanso obtain any desired or predetermined relationship between the output torque and the transmission ratio.

The present invention seeks to address these issues.

Statements of Invention

According to a first aspect of the present invention there is provided a continuously variable transmission comprising; one or more driving members coupled to an input shaft, wherein one or more of the driving members are movable; a firs carriage assembly, comprising on or more intermediary elements disposed clreomferentially at least partially within the first carriage assembly, wherein each of the intermediary elements has a rotational axis that can b displaced in relation to the first carriage assembly: and a second carriage assembly coupled to an output shaft, the second carriage assembly comprising a second carriage member and one or more movable driven members, wherei the intermediary elements ar configured to transmit rotational motion between the driving members and the drive members, the second carriage member comprising on or more wedging surface features, wherein the wedging surface features comprise ope or more profiled surfaces that are configured to displace the driven members upon movement of the second carriage member in relation to the driven members.

The profiled surface may comprise one or more ramped and/or curved surfaces. The movement of the second carriage member with respect to the driven members is caused by the application of a resistive torque to the output shaft. The form of the profiled surfaces may correlate to a predetemiined relationship between output torque and transmission ratio of the continuously variable transmission.

The second carriage assembly may further comprise one or mors recesses wherein the profiled surfaces are provided one or more wails of each of the recesses, The second carnage assembly may comprise one or more protruding members, Tlie profiled surfaces may be provided on the one or more protruding members 8, The protruding members may extend axiaily or radially from the second carriage member. Th protruding members ma extend at least partially around the inner circumference of the second carriage member. The protruding members may be integral to the second carriage assembly. The ^'protruding members may be at least partially wedge-shaped.

The wedging surface features may extend circumferentiaily around the second carriage members so as to form an arc on a surface of the second carriage member that subtends an angle less than or equal to 360 degrees.

The second carriage assembly may further comprise one or more roller elements disposed between the driven members and the profiled surfaces. The roller elements may be configured to operafiveiy transfer the movement of the. second carriage member to th movement of the driven members, The roller element may fee cylindrical. The roller elements may be configured to operate as a cam, for example., the roller elements may be elliptical in cross section or cylindrical in cross section with an off-centre axis of rotation. In this manner, the form of the profiled surfaces and/or the form of the roller elements may be selected in order to obtain a desired relationship between output torqu and the transmission ratio.

According to a second_, aspect .of the present invention there is provided a continuously variable transmission comprising: one or more driving members coupled to an input shaft, wherein one of more of the driving members are movable:; a first carriage assembly comprising one or more intermediary elements disposed eircu ferenflaily at least partially within the first carriage assembly, wherein each of the Intermediary elements has a rotational axis that can b displaced In relation to the first carriage assembly: and a second carriage assembly coupled to an output shaft, the second carriage assembly comprising a second carriage member and one or more movable driven members, wherein the intermediary elements are configured to transmit rotational motion between the driving members and the driven members, th second carriage member comprising one or more profiled surfaces that are configured to displace the driven members upon movement of the second carriage member in relation to the driven members, wherein the second carriage assembly furthe comprises one or more roller element disposed between the driven members and the profiled surfaces, the roller elements configured to operatively transfer the movement of the second carriage mem e to the movement of the driven members.

The roller elements may engage th protruding member by way of a line contact As line contacts are able to transmit much large forces than the point contacts, the present invention is advantageous over known ball-screw type mechanisms that may foe used in CVTs. Furthermore, fric iona! forces, and hence wear rates, may be reduced between the roller elements and the protruding members. According to a third aspect of the present invention there is provided a continuously variable transmission comprising: one or mor driving members coupled to an input shaft, wherein one or more of the driving members are movable a first carriage assembly comprising first carriage member and one or more intermediary elements, the first, carriage member configured to hold the intermediary elements, the intermediary elements disposed drcumferentially at least partially within the first carriage assembly, wherein each of the intermediary elements has a rotational axis that can be displaced i relation to the first carriage assembly and a second carriage assembly coupled to an output shaft, the second carriage assembly comprising one or more movable driven members, wherein the intermediary elements are configured to transmit rotational motion between the driving members and the driven members, the continuously variable transmission further comprising a clutch mechanism configured such that when the dutch mechanism Is engaged the first carriage member is unable to rotate and when the clutch. Is disengaged the first carriage member is able to rotate. The clutch mechanism ma be configured such that when the first carriage assembly is unable to rotate rotational motion is transmitted from the driving members to the driven members through the intermediary elements and when the first carriage assembly is able to rotate rotational motion is not transmitted from the driving members to the driven members, in thi manner, a neutral drive position is provided when the clutch mechanism Is disengaged.

The clutch mechanism ma be operated hydrauiicaliy, pneumatically or magnetically. The clutch mechanism may be a multi-disc wet clutch. According to a fourth aspect of the present invention there is provided a continuously variable transmission comprising: one or more driving members coupled to an input •Shaft, wherein one or mo of the driving members are movable; a first carriage assembly comprising one or more intermediary elements disposed circumferentiaiiy at least partially within t e first carriage assembly, wherein each of the intermediary elements has a rotational axis that can foe displaced in relation^' to the first carriage assembly; and a second carriage assembly coupled to an output shaft, the second carriage assembly comprising a second carriage member and one or more movable driven members, wherein; the intermediary elements are configured to transmit rotational motion between the driving member and the driven members, the first carriage assembly further comprising a firs carriage member and one or more bearing elements, wherein the bearing elements are disposed between the carriage member and the intermediary elements, the bearing elements comprising one or more textured surfaces that in use reduce friction between the bearing elements and the intermediary elements. The bearing elements may comprise one or mor appropriately shaped surface features configured suc that, consequent to the relative motion between th intermediary elements and the bearing elements, a hydrodynamlc bearing force is generated in a film of lubricating fluid disposed between the Intermediary elements and the bearing elements,

The bearing elements may further comprise one or more textu ed surfaces that in use reduce friction between the bearing elements and the intermediary elements, The textured- surfaces may comprise a plurality of surface features, e g, dimples, depressions, recesses or protrusions, which are configured to reduce the friction force generated between the textured surface and the intermediary elements. The surface features of the textured surface may be arranged radially, circularly or in any other appropriate arrangement.

The bearing elements and/or the Intermediary elements may comprise one or more surface coatings, e g, diamond-like carbon or titanium nitride, or may be subject to on or more surface treatments, e.g. nitridirtg, to lowe friction and improve wear characteristics

According to a fifth aspect of the present invention there is provided a continuousl variable transmission comprising: one or more driving members coupled to an Input shaft, wherein one or more of the driving members are movable; a first carriage 8

assembly comprising one or more intermediary elements disposed elreurnferentlaliy at least ^'partially within the. first carriage assembly, wherein each of the intermediary elements has a rotational axis that can be displaced In relation to the first carriage assembly; and a second carriage assembly coupled to an output shaft,_, the second carriage assembiy comprising a second carriage member and one or more movable driven members, wherein the intermediary elements are configured to transmit rotational motion between the driving members and the driven members, the second carriage assembly further comprises one or more fin elements extending from the second carriage assembly, the fin elements in use configured to displace a lubricating fluid of the continuously variable transmission for the. purpose of providing the lubricating fluid to the. driven members, the first carriage assembly and the driving members.

The second carriage assembly may further comprise openings that extend through the second carriage assembly. The openings may extend radially and/or axially through the second carriage assembiy. The openings may fluidiealiy connect the outside of the second carriage assembly to the inside of the second carriage assembly.

According to the- first second, third, fourt and fifth aspects of the present invention, the continuously variable transmission may comprise any of the additional features as set out below.

The continuously variable transmission according to the any aspect of the present invention, wherein an axiai position of the drive members may determine: an axial position ,a radial position and/or an angular orientation of the rotational axis of the intermediary elements in relation to the first carriage member; and an a i l position of the movable driving member's. The respectiv positions of the driven members, the intermediary elements and the moveable driving members may determine the transmissio ratio of the continuously variable transmission,

The continuously variable transmission may furthe comprise a housing. The housing may support the input shaft and/or the output shaft. The housing may be filled with the lubricating fluid. An elastohydrodynamic lubricating fluid film ma be disposed between the driven members., the intermediar elements and the driven members. Thus, as the driving members, the intermediary elements and the driven members rotate relative to each other, power may be transmitted between- the driving members, the Intermediary elements and the driven members b way of shear stress generated in the a astohydrodynamic lubricating fluid film.

The one or more driving members may biased towards the intermediary elements. The one or more driven members are biased away from the intermediary elements.

The first and second carriage assemblies may be concentric to the input shaft The first and second carriage assemblies may be rotata le. The driving and or the driven elements may be axially and/o radially moveable.

The driving and/or driven members^' may comprise one or more at least partially formed eonloai and/o curved surfaces that contact the intermediary elements. The intermediate element may be balls, The continuously variable transmission may comprise one or more ancillar pumps, Trie ancillary pumps may be configured to circulate the lubricating fluid around the continuously variable transmission.

To avoid Unnecessary duplication of effort and repetition of text in the specification, certain features are described in relation to only one or several aspects or embodiments of the invention. However, it is to be understood that, where it is technically possible, features described In relation to any aspect or embodiment of the invention may also be. used with any other aspect or embodiment of the invention. L st of Figures

Figure 1 shows a cross section of a continuously variable transmission comprising protruding members configured to displace t e driven members.

Figures 2a and 2b show partial cross sections of the continuously variable transmission configured for low speed -high torque and high speed - low torque operating conditions respectively.

Figure 3 shows a partial cross section of a second carriage assembly of the continuousl variable transmission.

Figures 4a and 4b show partial cross sections of the continuously variable transmission with the clutch in an engaged and disengaged position respectively. Figure 5 shows a partial cross section of the continuously variable transmission showing an input shaft, -a first carriage assembly and the second carriage assembly.

Detailed Descriptio

A continuous variable transmission (CVT) 1 according to the present invention is shown In figure 1 , The CVT 1 is able to adjust automatically the transmission ratio as a function of the resistive torque applied to the output shaft 3 by changing the relative positions of components Internal to the CVT 1.

Figure 1 shows a cross section of the CVT 1 comprising one or more driving members 5 coupled to an input shaft 7 that is supported by a CVT housing 9, wherein one or more of the driving members 5 are axiai y movable driving members 5a and one or more of the driving members 5 are axiaiSy fixed driving members 5b, The driving members 5 may comprise one or more at least partially conical and/or curved surfaces. In the embodiment shown in figure 1, the movable driving members 5a comprise a partially toroidal-shaped disc and the fixed driving members 5b comprise a partially conical disc. In an alternative example (not shown), the driving member 5b may be a partially toroidal-shaped disc.

The CVT 1 further comprises a first carriage assembl 11 comprising one or more intermediary elements 13 disposed cireumferentially at least partially withi the first carriage assembly 11. Each of the intermediary elements 13 has a rotational axis that can be displaced in relation to the first carriage assembly 11. The intermediary elements 13 may be spherical in form and may be solid or hollow. The first carriage assembly 11 may further comprise a first carriage member 15 configured to hold the Intermediary elements 13. The first carriage assembly 11 may be concentric, to the input shaft 7 and may be configured to rotate about the input shaft 7. In the example shown in figures 1, the first carnage assembly 11 is unable to rotate about the input shaft 7. As a result,, the first carriage member 5 holds the intermediary members 13 in circumferential position about the input shaft 7 and permits each of the intermediary elements 13 to rotate about independent rotational axes.

The CVT 1 further comprises a second, carriage assembly 17 fixed to the output shaft 3, The output shaft 3 is supported by the CV housing 8 and Is coaxial to the input shaft 7, In an alternative example (not shown), the output shaft 3 may be arranged sueh that the rotational axis of the output shaft 3 is different to the rotational axis of the input shaft 7, The output shaft 7 may be coupled to the second carriage assembly 17 toy way of a geared or belt-driven coupling, The second carriag assembly 17 comprises a second carriage member 18 and one or more movable driven members 19. The driven members 19 may comprise one or more at least partially formed conical and/or curved surfaces. _.In the example shown in figure 1, each of the driven members 19 comprises a partially conical disc. The second carriage assembly 17 may be concentric to th Input shaft 7 and may be configured to rotate about the first carriage assembly 11.

The intermediary elements 13 are configured to transmit rotational motion between the driving member 5 and the driven members 19, In this manner, rotational motion may be transferred from the Input shaft 7 to the output shaft 3 by virtue of the interaction between the driving members 5_S the intermediary elements 13 and the driven members 9, Specifically, rotational motion may be transferred du to the shearing of the eiastohydrodyoamio lubricating fluid film in the contacts betwee the driving members 5, the intermediary elements 13 and the driven members 10, The example shown in figure 1 depicts a double-cage CVT 1, in which there a e two sets of driving members 6, intermediary elements 13 and driven members 18 arranged back-to-back. This has the advantage of doubling the number of eiasto ydrodynamic contacts, which therefore improves the torque transferred between the Input shaft 7 and output shaft 3. ft is appreciated, however, that the CVT 1 according to the present invention may comprise a single-cage CVT 1, i.e. a CVT 1 comprising a single set of driving members 5, intermediary elements 13 and driven members 19 configured to transfe rotational motion from the input shaft 7 to the output shaft 3,

For the example shown in figure 1 , the second carnage member 18 is substantially annular and comprises one or more wedging surface features 28, wherein the wedging surface features 28 comprise one or more profiled surfaces 27 that are configured to displace the driven members 19 upon movement of the second carriage member 18 in relation to the driven members 19. As shown in figure 1 , wedging surface features 28 comprise the profiled surfaces 27 provided on opposite sides of ^'wedge-shaped protruding members 29, which are formed on or attached to a radially inner side of the second carriage member 18, In an alternative example (not shown), the second carriage member 18 may comprise one or more wedge-shaped recesses. The profited surfaces 27 m y be provided on one or more wails of each of the recesses such that the wails of the recesses are configured to displace the driven members 19 upon movement of the second carriage member 18 in relation to the driven members 19.

The movement of the second carriage member 18 with respect to the driven members 19 may be caused b the application of a resistive torque to the output shaft 3, For example, upon application of a resistive torque to the output shaft 3, the second carriag member 18 acts to displace the driven members 19 by virtue of the movement of the profiled surfaces 2? relative to the driven members ,

For the exampl shown in figur 1, the second carriage assembly 1? is fixed to the output shaft 3 such that th resistive torque applied to the output shaft 3 is directly transferred to the second carriage member 18. Upon the application of the resistive torque, a rotational movement of the second carriage member IS relative to the driven members 19 acts to displac axsaiiy the driven members 19 by virtue of the movement of the profiled surfaces 27. In this manner, art axial position of the driven members 9 further determines: 1) an axial and a radial position of the intermediary elements 13 in relation to the first carriage assembly 11; il) an angular position of the rotational axis of the intermediary elements 13; and ill) an axial position of the movable driving members Sa, The relative positions of the driven members 19. th intermediary elements 13 and the moveable driving members -5a, therefore, determine the transmission ratio of the CVT 1.

The CVT may be further configured such that the movable driving members 5a are biased towards the intermediary elements 13, In a similar manner, the driven members 19 ma be biased away from the intermediary elements 13. for example, as shown in figure 1, one or more first biasing elements 21 e.g. a first spring, may be configured to displace the movable driving members 5a towards the intermediary elements 13 and one or more second biasing elements 23, e.g, a second spring, may be configured to displace the driven members 19 away from the intermediary elements 13, i.e. the first and second biasing elements 21, 23 are configured to displace the driven members 19 and the movable driving members Sa in directions opposite to the displacement caused by the movement of the profiled surfaces 27, Figures 2a and 2b tiepict low speed - high torque and high speed ~ Sow torque operational configurations of the CVT 1 respectively. Figure 2a shows a partial cross section of the CVT 1 operating at a low rotational speed with a high resistive torque applied to the output shaft 3_< for example during start-up or heavy load conditions. The second carriage member 18. the driven members 19, the Intermediary elements 13 and th m v b e ^' driving members 5a are in first positions with the first and second biasing elements 21 , 23 in compressed states. During start-up or heavy load conditions, the second carriage member 18 moves into the first position such that the profiled surfaces 27 acts to displace axialiy the driven members IS towards the . intermediar elements 13. Consequently, the partially conical surfaces of the driven elements 19 act to displace the intermediary elements 13 axialiy and radially inwards towards the driving members 5. As a result, the movable driving members 5a are displaced axialiy along the input shaft away from the fixed driving members 5b by virtue of the configuration of the partially conical surface of the fixed driving members 5b and the partially toroidal surface of th movable driving member Sa. Consequently there Is a reduced transmission ratio between th input shaft 7 and the output shaft 3.

Figure 2b shows a partial cross section of th CVT 1 operating at a higher rotational speed with a lower resistive torque applied to the output shaft 3. The second carnage member 18, the driven members 19, the intermediary elements 13 and the movable driving mem ers 5a are in second positions with the first and second biasing elements 21 _; 23 in less compressed states. During high speed operating conditions, when the resistive torque applied to the output shaft is lower, the biasing forces of th first and second biasing elements 2 , 23 act to displace axialiy the movable driving members 5a and the driven members 19 respectively. Consequently, the Intermediary elements 13 are displaced axialiy and radially outwards such that the transmission ratio automatically adjusts in response to the chang in resistive torque and operational speed, The positions of the driven members 1.9, the Intermediary elements 13 and the movable drive members 5a are controlled by a balance of forces imparted by the resistive torque to the output shaft 3 and the biasing force of the first and second biasing elements 21 , 23. As such, the transmission ratio automatically increases in response to a decreased resistive torque and, conversely, the transmission ratio automatically decreases in response to an increased resistive torque. Eac of the profiled surfaces 2? may comprise one or more ramped and/or curved surfaces configured to determine the degree by which the driven mem e s 18 are displaced consequent to the movement of the second carriage assembl 17, i.e. the degree by which the driven members 19 are displaced consequent to the resistive torque applied to the output shaft 3. For example, the profiled surface 27 may comprise a single planar ramp, multiple planar ramps, a single curved surface, multiple curved surfaces or any combination thereof. The form of the profiled surfaces 27 may be selected dependent upon the desire displacement °^ ^ driven members 19 consequent to the application of th resistive torque to the output shaft "3, i.e. the form of the profiled surfaces 27 may correlate to a predetermined relationship between output torque and transmission ratio of the CV7 1 , In this manner, the form of the profiled surfaces 2? may be selected dependent upon the desired rate of change of the transmission ratio consequent to the application of a resistive torque to the output shaft 3. Appropriate geometry of the profiled surfaces may therefore be selected in response to the intended application of the CVT 1 ,

As mentioned above, the second carriage assembly 17 may further comprise one or more protruding members 29 that extend from the second carriage member 18, The protruding member 28 may extend axial!y and/or radially from the second carriage member S and ma extend at least partially around the inner circumference of the second carriage member 18. The protruding members 29 may be Integral to the second carriage member 18 or alternatively may be fixed to the second carriage member 18 using any appropriate means, e.g. fasteners. The one or more profited surfaces 27 of the second carriage assembly 17 may be provided on the protruding members 29, in the example shown in figures 1 to 4b, the protruding members 29 are provided circumferentiaify around an inner surface of the second carriage member IS: and are wedge-shaped, extending radially inwards towards th first carriag assembly 11. figure 3 shows a partial cross section of the second carriage assembly 17 removed from the CVT 1. The protruding members 29 are configured to rotate with the carriage assembly 18 such that, upon application of the resistive torque, the wedge-shaped protruding members 29 rotate relative to the driven members 18, The protruding members 29 are each provided with the said profiled surfaces 27 that are configured to displace the driven members 19. it may be appreciated from the example shown i figures 1 to 4b that the resistive torque acts to drive the wedge-shaped protruding member between the two sets of driven members 19, thereby causing the axial displacement of the driven members 19. It may also be appmoiated how the form of the profiled surfaces 27 may be selected in order to displace the driven members 10 by the desired amount consequent to a predetermined rotation of the second carriage member 18. For example, if the profiled surfaces 27 comprise single planar ramped surfaces, as shown in figure 3, there w ll be a linear relationship between resistive torque and displacement of the driven member 19,

The second carriage assembly 17 may further comprise one or more roller elements 31 disposed between the driven members 19 and the profiled surfaces 27. The roller elements 31 ma be configured to engage the profiled surfaces 27 and to operatively transfer the rotational movement of th profiled surfaces 27 to the axial movement of the driven members 19. Th roller elements 3 may be cylindrical such that they roll over the profiled surfaces 27 as the profited surfaces 27 rotate with the second carriage member 18, The roller elements 31 may be configured to operate as a cam, for example, the roller elements 31 may be elliptical in cross section or cylindrical in cross section with an off-centre axis of rotation. In this manner, the desired relationship between output torque and the transmission ratio may be selected as a function of the form of the roller elements 31 and/or the form of the profiled surfaces 27,

The roller elements 31 may engage the protruding members 27 by way of a line contact. As line contacts are able to transmit much large forces than point contacts, the present invention is advantageous over known ball-screw type mechanisms that may be used in GVTs. Furthermore, frictional forces, and hence wear rates, may be reduced between the roller elements 31 and the profiled surfaces 27 due to Improved distribution of forces, i.e. lower contact pressures, Figures 4a and 4b show partial cross sectional views of the CVT 1 , which may further comprise a clutch mechanism 33 configured such that when th clutch mechanism 33 i engaged, as shown in figure 4a, the first carriage member 15 is unable to rotate and when the clutch mechanism 33 is disengaged, as show in figure 4b, the first carriag member 15 is able to rotate. The clutch mechanism 33 may foe configured such that -when the first carriage member 15 is unable to rotate, rotational motion is transmitted from th driving members 5 to the driven members 19 through the intermediary elements 13 by way of e!astohydrodynamic. traction. Conversely, when the first carriage member 15 is- able to rotate, rotational motion is not transmitted from the driving members 5 to the driven members 19. Instead, the intermediary elements 13 roll over the partially conical surface of the driven members 19, thereby causing the first carriage member 15 to rotate about the input shaft 7, In this manner, a neutral drive position is provided when the clutch mechanism 33 is disengaged, in the example shown in figures 1 to 4b the clutch mechanism Is a multi-disc wet dutch operated by a clutch lever 35. However, In an alternative example (not shown), the clutch mechanism 33 may be of any other appropriate type and may be operated, for example, hydrauiicaliy, pneumatically or magnetically.

Figure 5 show a cross sectional view perpendicular to th rotational axis of the input shaft 7 of the CVT 1. The first carriage assembly 11 may further comprise one or more bearing elements 37 disposed between the first carriage member 15 and the intermediary elements 13. The bearing elements 37 may comprise one or more surfaces that are substantially conformal to the surfaces of the intermediary elements 13. The bearing elements 37 ma be configured to constrain the Intermediary elements 13 In relation to the first carriage assembly 11 and permit the intermediary elements 13 to rotate about their independent rotational axes, The bearing elements 37 may comprise one or more appropriately shaped surface features configured such that, consequent to the relative motion between the Intermediary elements 13 and the bearing elements 37, a hydrodynamlc bearing force is generated in a film of lubricating fluid; which is disposed between the intermediary elements 13 and the bearing elements 37.

The bearing elements 37 may comprise one or more textured surfaces 39 that in use reduce friction between the bearing elements 37 and the intermediary elements 13, The textured surfaces 39 may comprise a plurality of surface features, e.g. dimples, which are configured to reduce the friction force generated between the textured surface 39 and the intermediary elements 13. The surf ce features of the textured surface 39 ma be arranged radially, circularly or in any other appropriat arrangement.

The bearing elements 37 and/or the intermediar elements 13 may further comprise one or mor surface coatings, e.g. diamond-like carbo or titanium nitride, or may be subject to one or mor surface treatments, e.g. nitridlng, to reduce friction and to improve wear characteristics. These surface coating -and/or treatments may also be applied to any of the components of the CVT 1 a described herein.

The second carriage assembly 17 may further comprise one or more fin elements 41 that extend a iaily and/or radially from the second carriage assembly 17. The fin elements 41 may be configured in use to displace the lubricating fluid around the CVT housing 9 for the purpose of distributing the lubricating fluid to the internal components of the CVT 1- Specifically, the fin elements 41 may be configured to provide an improved supply of lubricating fluid to th driven members 19, the Intermediary elements 13 and the driving members 5 to ensure adequate elastohydredynarnic lubrication between the rotating components. In the example shown in figure 1 and 5, the fin elements 41 are provided on the outer circumference of the second carriage member 18 and extend radially outwards towards the CVT housing 9. In another exampl {not shown), the fin elements 41 may be provided on any other rotating feature of the CVT, for example the first carriage assembly _.11 such that the lubricating fluid is better distributed about the CVT housing 9,

In the absence of the fin elements 41 , the lowest allowable level of lubricating fluid within the CVT bousing 9 would be the centre of the lowest positioned intermediary element 13, The fin elements 41 function to pick up and distribute lubricating fluid from the cavity between the second carriage assembly 17 and the CVT housing 9, In this manner, the total volume of lubricating fluid may be reduoed,

The second carnage assembly 17 may further comprise one or more openings 43 that extend radially and/or axially through the second carriage member 18.. The openings 43 may be configured to fluidicaliy connect the outside of the second carriage assembly 17 to the inside of the second carriage assembly 17 for the purpose of providing better lubrication to the first carriage assembly 17 and the driving members 5- Reference Numerals

1 Continuously variabl ^'transmission 3 Output shaft

5 Driving member

5a Movable driving member 5b Fixed driving member

7 nput shaft

9 CVT housing

11 First carriage assembly

13 intermediary elements

15 First carnage member

17 Second carriage assembly

18 Second carriage member 19 Driven mem bers

21 First biasing element

23 Second biasing element

2? Profiled surface

28 Wedging surface features 29 Protruding members

31 Roller elements

33 Clutch mechanism

35 Clutch lever

37 Bearing element

39 Textured surface

41 Fin elements

43 Openings

Claims

1. A continuously variable transmission comprising:

one or more driving members coupled to an input shaft, wherein one or more of the driving members ar movable;

a first carriage assembly comprising one or more intermediary elements disposed circumferentially at least partially within the first carriage assembly, wherein each of the intermediary elements has a rotational axis that can he displaced in relation to the first carriage assembly; and

a second carriage assembly coupled to an output shaft, the second carriage assembly comprising a second carriage member and one or more movable driven members, wherein the intermediary elements are configured to transmit rotational motion between the driving member and the driven members_.,

the second carriage member being substantially annular and comprising one or more wedging surface features, wherein the wedging surface features comprise one or more profiled surfaces that are configured to displace the driven members upon movement of the second carriage member in relation to the driven members.

2. A continuously variable transmission according to claim 1 , wherein the second carriage assembly further comprises one or more roller elements disposed between the driven members and the profiled surfaces, th roller elements configured to operative^ transfer the movement of the second carriage member to the movement of the driven members.,

3. A continuously variable transmission according to claim 2, wherei the roller elements are c lindrical .

4. A continuously variable transmission according to claim 2 or 3, wherein the roller elements are configured to operate as cams,

5. A continuously variable transmission according to an of the preceding claims, wherein the first carriage assembly further comprises a first carriage member, and ^•the continuously variable transmission further comprises a clutch mechanism configured such that when the clutch mechanism is engaged the first carriage member is- unable to rotate and when the clutc Is disengaged the first carriage member Is able to rotate.

6. A continuously variable transmission according to claim 5_; wherein when the first carriage assembly is unable to rotate rotational motion is transmitted f rom the driving members to the driven members through the intermediary elements and when the first carriage assembly is able to rotate rotational motion is not transmitted from the driving members to the driven members,

7, A continuously variable transmission according to claim: 5 or 6, wherein the clutch mechanism: is operated hydraulieaSiy, pneumatically or magnetically.

8. A continuously variable transmission according to any of the preceding claims, wherein the first carriage assembly further comprises one o more bearing elements disposed between the first carriage member and the intermediary elements, the bearing: elements comprising one or more textured surfaces that in use reduce friction between the bearing elements and the intermediary elements.

9. A continuously variable transmission according to any of the preceding claims, wherein the second carriage assembly further comprises one or more fin elements extending from the second carriage assembly, the fin elements configured to displace a lubricating fluid of the continuously variable transmission upon rotation of the second carriage assembly.

10. A continuously variable transmission according to any of the preceding claims, wherein the second carriage assembly comprises one o more protruding members.

11. A continuously variable transmission according to claim t0, wherein the protruding members extend axlaiiy and/or radially from the second carriage member, 12, A continuously variable transmission according to claim 10 or 11, wherein the protruding members extend at least partially around the inner circumference of the second carriage member.

13, A .continuously variable transmission according to any of claims 10 to 12, wherein the protruding members are integral to the second carriage assembly.

14, A continuously variable transmission according to any of claims 10 to 13, wherein trie protruding members are at least partially wedge-shaped,

15, A continuously variable transmission according to any of claims 10 to 14, wherein the profiled surfaces ar provided on the one or more protruding members,

10. A continuously variable transmission according to any of th preceding claims, wherein an axial position of the driven members determines:

an angular orientation and radial position of the rotational axis of the intermediary elements in relation to the first carriage assembly; and an axial position of the movable driving members,

17, A continuously variable transmission according to claim 16, wherein the relative positions of the driven members, the Intermediary elements and the moveable driving members determine- th transmission ratio of the continuously variable transmission,

13, A continuously variable transmission according to any of the preceding claims, wherein the wedging surface features extend circumferentlaliy around the second carnage members so as to form an arc that subtends an angle less than or equal to 360 degrees,

19, A continuously variable transmission according to any of the preceding claims, wherein the second carriage assembly further comprises one or more recesses, wherein one or more wails of each of the recesses comprise the wedging surface features.

S

20, A continuously variable transmission according any of the preceding claims, wherein the profited surface comprises one or more ramped and/or curved surfaces.

21^', A continuously variable transmission according to any of the preceding claims, wherein movement of the second carnage member with respect to the driven members is caused by the application of a resistive torque to the output shaft,

22. A continuously variable transmission according to any of the preceding claims, wherein the form of the profiled surfaces correlates to a predetermined relationship between output torque and transmission ratio of the continuously variable transmission.

23, A continuously variable transmission according to any of the preceding claims, wherein the one or more of the movable driving members are biased towards the intermediary elements.

24. A continuously variable transmission · according to any of the preceding claims, wherein the one or more driven members are biased away from the intermediary elements.

25, A continuously variable transmission according to an of the preceding claims, wherein the first and/or second carriage assemblies are concentric to th input-

2.6. A continuously variable transmission according to any of the preceding claims, wherein the first and/or second carriage assemblies are rotatabie about the input shaft.

27, A continuously variable transmission according to any of the preceding claims, wherein the driving and/o driven members comprise- one or more at least partially formed conical and/or curved surfaces that contact the intermediary elements,

28, A continuously varia le transmission according to any of th preceding claims, wherei the intermediate- elements are balls.

29. A continuousl variable transmission according to any of the preceding claims, •wherein the second carriage assembly further comprises one or more openings that extend axiaiiy and/or radially through the second carriage assembly, wherein the openings are configured to fluidicaily connect a region radially outside the second carriage assembly to a region radially inside the second carriage assembly,

30. A continuously variable transmission comprising:

one or more . driving members coupled to an input shaft, wherein one or0 more of the driving members are movable;

a first carriage assembly comprising one or more intermediary elements disposed eircumferentiaily at least partially within the first carriage assembly, wherein each of the intermediary elements has a rotational axis that can be displaced in relation to the first carriage assembly; and

S a second carriage assembly coupled to an output shaft, the second carriage assembly comprising a second carriage member and one or more movable driven members, wherein the intermediary elements are configured to transmit rotational motion between the driving members and the driven members,

0 the second carnage member being substantially annular and comprising one or more profiled surfaces that are configured to displace the driven members upon movement of the second carriage member in relation to the driven members, and

the second carriage assembly further comprises one or more roller elements disposed between the driven members and: the profiled surfaces, the roller element configured to operatively transfer the movement of the second carriage member to the movement of the driven members .

3 A continuously variable transmission comprising;

one or more driving members coupled to an input shaft, wherein one or more of the driving members are movable;

a first carriage assembly comprising a first carriage member and one or more Intermediary elements, the first carriage member configured to hold the intermediary elements, the Intermediary elements disposed circumferential!y at least partially within the first carriage assembly, wherein each of the intermediary elements has a rotational axis mat can be displaced m -relation to the first carriage assembly; and

a second carriage assembly coupled to an output shaft, the second carriage assembly comprising a second carriage member and one or more movable driven members, wherein the intermediary elements are configured to transmit rotational motio between the driving members and the driven members,

the continuously variable transmission further comprising a clutch mechanism configured such that when the clutch mechanism is engaged the first carriage member is unable to rotate and when the clutch Is disengaged the first carriage member is able to rotate. , A continuously variable transmission comprising:

first carriage assembly comprising one or more intermediar elements disposed cireumferenflally at least partially within the first carriage assembly, wherein each of the Intermediary elements has a rotational axis that can be displaced in relation to the first carnage assembly; and

a second carriage assembly coupled to an output shaft, the second carriage assembly comprising a second carriage member and one or more movable driven members, wherein the intermediary elements are configured to transmit rotational motion between the driving members: and the driven members,

the first carriage assembly further comprising a first carriage member and one or more bearing elements, wherein the bearing elements are disposed betwee the first carriage member and the intermediary elements, the bearing elements comprising one or more textured surfaces that in use reduce friction between the bearing elements and the Intermediary elements, , A continuously variable transmission comprising:

a first carriage assembly comprising on or more intermediary elements disposed circumferential!⁴/ at least partially within the first carnage assembly, wherein each of the intermediary elements has a rotational axis that can be displaced, in relation to the first carriage assembly; and

a_. second carriage assembly coupled to an output shall, the second carriag assembly comprising a second carriage member and one or more movable driven members, herein the intermediary elements are configured to tfa.ns.mif rotational motion between the driving members and the driven members,

the second carriage assembly further comprising one or more fin elements extending from the second carriage assembly, the fi elements configured to displace a lubricating fluid of the continuously variable transmission upon rotation of the second carriage assembly, , A continuously variable transmission as described herein, and. with reference to and as shown in the accompanying drawings.