GB2381560A

GB2381560A - A CVT arrangement

Info

Publication number: GB2381560A
Application number: GB0220357A
Authority: GB
Inventors: Donald Rae
Original assignee: DKT ENGINEERING Ltd
Current assignee: DKT ENGINEERING Ltd
Priority date: 2001-08-31
Filing date: 2002-09-02
Publication date: 2003-05-07
Anticipated expiration: 2022-09-02
Also published as: WO2003019045A1; GB2381560B; GB0121162D0; GB0220357D0

Abstract

A CVT arrangement 10 has levers 30,31,32,33 pivotally coupled at one end to a rotatable output shaft 16 via one-way clutches 34 and positioned at their other ends on a cam shaft like input member 14 in such a way that rotation of the input member 14 causes the levers 30,31,32,33 to pivot about the clutches 34 and turn the output shaft 16. The distance between the input 14 and output 16 is variable so as to alter the amount the levers 30,31,32,33 turn the output 16 and so alter the gear ratio.

Description

A' 2381 560

GEARING ARRANGEMENT

FIELD OF THE INVENTION

This invention relates to a gearing arrangement, and in particular but not exclusively to a variable ratio gearing arrangement.

5 BACKGROUND OF THE INVENTION

Gearing of one form or another is present in the majority of machines, including bicycles, motor vehicles and tractors. Most modern bicycles produced for recreational use include derailleur gearing. While such 10 gearing is relatively efficient, in that it involves minimal losses, the gear mechanism is exposed and liable to accidental damage. Care is also required when changing gears, and difficulties may be experienced if a gearchange is attempted under load.

15 In modern motor vehicles, gearboxes are becoming increasingly sophisticated. However, modern gearboxes remain bulky and contribute significantly to the mass of the vehicle. Furthermore, such gearboxes absorb a significant amount of power. This latter disadvantage is 20 particularly true of conventional "automatic" gearboxes.

Various proposals have been made to produce "step less" or continuously variable gearboxes, that is gearboxes

in which there is no discernable step-change between ratios. However, such gearboxes have not been adopted on a large scale, and do not overcome many of the disadvantages of conventional gearboxes.

5 It is among the objectives of embodiments of the present invention to obviate or mitigate these disadvantages. SUMMARY OF THE INVENTION

According to a first aspect of the present invention 10 there is provided a gearing arrangement comprising; an input member; a rotating output member; and a lever member having a pivot axis, one end of the lever member being coupled to the input member and the 15 other end of the lever member being coupled to the output member via a one-way clutch arrangement such that movement of the input member induces reciprocal movement of said lever member and rotation of the output member, the coupling between the input member and the lever member 20 being configurable to vary the degree of movement of the lever member, and thus the angle of rotation of the output member, induced by a predetermined degree of movement of the input member.

Thus, by controlling the configuration of the coupling 25 between the input member and the lever member the gear DO lanes I 11 1 1111 ' 111 - ' no: 1111$ 1 11'1 111 1111 1 1 111 11 111 1 51 11 1111111 11 11 11111 B1 111

ratio provided by the arrangement may be varied.

Preferably, the changes in the configuration of the coupling may be effected in infinitely small increments, such that changes in gear ratio may be effected in a 5 "stepless" manner.

Preferably, the pivot axis of the lever member corresponds to the axis of rotation of the output member, though in other embodiments the pivot axis may be spaced from the output member axis.

10 Preferably, the input member is rotatable. The input member may reciprocate, but preferably is adapted to be driven to rotate in one direction or the other.

Preferably, the one way clutch is a mechanical clutch arrangement, such as a sprag, index or roller clutch, or a 15 ratchet. Alternatively, other non-mechanical clutch forms may be utilised, including variable configuration clutches which permit the direction of drive transfer to be varied.

Preferably, the coupling between the input member and the lever member is in the form of a cam profile on the 20 input member engaging a follower surface of the lever member. With such a coupling, variation in gearing may be effected by varying the distance, along the length of the lever member, between the point of contact between the input member and the lever member follower surface, and the 25 lever member pivot axis. Conveniently, this is achieved by translation of one of the input member or the output member

relative to a housing which provides mounting for the parts of the arrangement. Of course other coupling configurations may be utilized, including a crank arrangement on the input member, which crank member may 5 permit translation of the input member relative to the lever member pivot axis, or may incorporate a variable throw arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present invention will 10 now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective schematic representation of a gearing arrangement in accordance with a preferred embodiment of the present invention; 15 Figure 2 is a perspective view of an input camshaft of the gearing arrangement of Figure 1; Figures 3a, 3b, 3c and 3d are sectional views of the camshaft of Figure 2 and illustrating the relative positioning of the cams on the shaft; 20 Figures 4a and 4b are plan and end view of an input cog of the gearing arrangement of Figure 1; and Figures 5a and 5b are side and plan views of a lever arm and clutch of the gearing arrangement of Figure 1.

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DETAILED DESCRIPTION OF THE_ DRAWINGS

Reference is first made to Figure 1 of the drawings, which is a perspective view from above of a gearing arrangement 10 in accordance with a preferred embodiment of 5 the present invention. The illustrated embodiment is intended for use in a relatively low power machine, such as a bicycle or moped and includes a housing 10 which provides mounting for a rotating input member 14 and a rotating output member 16. The housing 10 is illustrated as being 10 open, however it will be recognised that the housing would normally enclose and protect the inner workings of the arrangement. Reference is now also made to Figures 2, 3 and 9 of the drawings, which illustrate features of the input member 15 19. In particular, Figure 2 illustrates a cam shaft 18 which forms the mason element of the member 14 and features four circular cams 20, 21, 22, 23 which are each offset a common distance from the axis of the shaft 18.

Furthermore, the cams are positioned at 90 angular 20 spacings from one another, as is apparent from Figures 3a to 3d. The cam shaft 18 is coupled to an input cog 26, as illustrated in Figures 4a and 9b of the drawings, the cog 26 being mounted externally of the housing 12.

The output member 16 is mounted towards the opposite 25 end of the housing 12 from the input member 14 and comprises a shaft 28 coupled to an output cog (not shown)

mounted externally of the housing 12. Four levers 30, 31, 32, 33 are coupled to the output shaft 28 via respective one-way clutches 34, one of the levers 30 being illustrated in Figures 5a and 5b of the drawings. As may be seen from 5 Figure 1, the free end of each lever 30, 31, 32, 33 rests on a respective cam 20, 21, 22, 23 of the input member 14.

Thus, as the input member rotates 14 in direction A, the free ends of the levers 30, 31, 32, 33 rise and fall, in a reciprocal manner, as indicated by arrow B. Due to the 10 provision of the clutches 34 between the levers 30, 31, 32, 33 and the output shaft 28, this reciprocal movement of the levers 30, 31, 32, 33 induces rotation of the output shaft 28 in direction C. It has been found that by providing four cams 20, 21, 15 22, 23 operating in combination with four levers 30, 31, 32, 33, it is possible to achieve substantially continuous rotation of the output shaft 28 in response to rotation of the input member 14.

The degree of rotation of the shaft 28 induced by 20 rotation of the input member 14 is related to the throw of the cams 20, 21, 22, 23, indicated as dimension D in Figures 3a, and also the length of the lever arm E, that is the distance between the contact point between each cam and lever, and the lever pivot axis, which in this example 25 corresponds to the axis of rotation of the output shaft 28.

Figure 1 illustrates the gearing arrangement 10 __,__ - _ I 1all llllllla lll llll llllll111 11111-'1 El1 11

configured to provide its lowermost ratio, that is to provide a relatively low speed but high torque output. In the illustrated arrangement 10, the gear ratio may be changed by varying the length of the lever arm E, which may 5 be achieved by moving the output member 16 towards the input member l4, and thus shortening the lever arm E. In the illustrated embodiment, this is made possible by the mounting of the output member 16 between supports 36 (only one shown) which are movable along side members of the 10 housing 12. Such movement may be achieved by any convenient arrangement.

As will be apparent to those of skill in the art, this arrangement allows the gear ratio between the input and output members 19, 16 to be varied in infinitely small 15 increments, and without step changes. Accordingly, changes in gear ratio may be achieved smoothly and easily, without requiring use of a clutch-type arrangement to disengage the gearing arrangement 10 from the prime mover, and without reducing the power or loading being applied through the 20 arrangement lo.

Those of skill in the art will recognise that the gearing arrangement 10 provides a simple and effective arrangement of providing a continuously variable gear ratio in a very simple and compact arrangement. Where the 25 application requires, two or more gearing arrangements may be provided in series, to provide an appropriate range of

ratios. Those of skill in the art will further recognise that the illustrated arrangement 10 is merely exemplary of the present invention, and that the same objectives may be 5 achieved by using a variety of different configurations.

For example, in other embodiments the output member may be fixed relative to the housing, while the input member is movable relative to the housing to vary the gear ratio obtained. In other embodiments a crank shaft and 10 connecting rod arrangement may be utilised rather than a cam shaft and lever arrangement, variations in gear ratio being achieved by provision of a variable throw crank shaft or a coupling between the crank shaft and the connecting rods which permits relative movement of the crank shaft and 15 the connecting rods to vary the distance between the crank shaft and the output member, or more particularly the pivot axis of the connecting rods. Furthermore, the above embodiment features four cams and levers, and those of skill in the art will recognise that other numbers of cams 20 and levers may be utilized. In other embodiments, particularly where higher speeds are likely to be experienced, if levers are employed, there is a possibility that the levers will not follow the cams. In such cases a poi;-down lever t.0 may be provided, as shown in claim 25 dotted outline in Figure 5a.

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Claims

1. A gearing arrangement comprising; an input member; a rotating output member; and 5 a lever member having a pivot axis, one end of the lever member being coupled to the input member and the other end of the lever member being coupled to the output member via a one-way clutch arrangement such that movement of the input member induces reciprocal movement of said 10 lever member and rotation of the output member, the coupling between the input member and the lever member being configurable to vary the degree of movement of the lever member, and thus the angle of rotation of the output member, induced by a predetermined degree of movement of IS the input member.

2. A gearing arrangement as claimed in claim 1, wherein the variation in the degree of movement of the lever member is effected in infinitely small increments.

20

3. A gearing arrangement as claimed in claim 1 or 2, wherein the pivot axis of the lever member corresponds to the axis of rotation of the output member.

4. A gearing arrangement as claimed in claim 1 or 2, wherein the pivot axis of the lever member is spaced from the output member axis.

5. A gearing arrangement as claimed in any preceding 5 claim, wherein the input member is rotatable.

6. A gearing arrangement as claimed in any preceding claim, wherein the input member can reciprocate.

7. A gearing arrangement as claimed in any one of claims 1 to 5, wherein the input member is adapted to be driven to 10 rotate in one direction.

8. A gearing arrangement as claimed in any preceding claim, wherein the one-way clutch is a mechanical clutch arrangement.

9. A gearing arrangement as claimed in any preceding 15 claim, wherein the one-way clutch is a sprag clutch.

10. A gearing arrangement as claimed in any one of claims 1 to 8, wherein the one-way clutch is an index clutch.

11. A gearing arrangement as claimed in any one of claims 1 to 8, wherein the one-way clutch is a roller clutch.

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12. A gearing arrangement as claimed in any one of claims 1 to 8, wherein the one-way clutch is a ratchet.

13. A gearing arrangement as claimed in any one of claims 1 to 7, wherein the one-way clutch is a non-mechanical 5 clutch.

14. A gearing arrangement as claimed in claim 13, wherein the nonmechanical clutch is a variable configuration clutch.

15. A gearing arrangement as claimed in any preceding 10 claim, wherein the coupling between the input member and the lever member is in the form of a cam profile on the input member engaging a follower surface of the lever member.

16. A gearing arrangement as claimed in claim 15, wherein 15 variations in the degree of movement of the lever member may be effected by varying the distance, along the length of the lever member, between the point of contact between the input member and the lever member follower surface, and the lever member pivot axis.

20

17. A gearing arrangement as claimed in claim 16, wherein the distance between the point of contact between the input

member and the lever member follower surface is varied by translation of one of the input member or the output member relative to a housing which provides mounting for the parts of the arrangement.

5

18. A gearing arrangement as claimed in any one of claims 1 to 14, wherein the coupling between the input member and the lever member is in the form of a crank arrangement on the input member, which crank arrangement permits translation of the input member relative to the lever 10 member pivot axis.

19. A gearing arrangement as claimed in claim 18, wherein the crank arrangement incorporates a variable throw arrangement.

20. A gearing arrangement substantially as described 15 herein and shown in the accompanying representations.

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