Pulley Number:7,367,277 from the United States Patent and Trademark Office (PTO) owispatent A pulley comprising a first pulley wheel and a second pulley wheel and a ratchet acting between the two pulley wheels. When substantially equal force is applied to each pulley wheel in use on a rope tail side causing the pulley wheels to rotate, a low gear ratio is achieved through a rope, chain or the like acting on a load through a block. When one pulley wheel is prevented from rotating and a force is applied to the other pulley wheel in use on a rope tail side causing it to rotate, then a higher gear ratio is achieved through a rope or chain or the like acting on a load through a block. When force is applied to the first wheel on a rope tail side and the second pulley wheel is allowed to rotate, then a still higher ratio is achieved in use through a rope, chain or the like acting on a load through a block. In another embodiment, the pulley comprises a first pulley wheel, a second pulley wheel and means to prevent relative rotation of the pulley wheels in one direction, the pulley wheels being able to rotate relative to each other in the other direction. In another embodiment, the pulley comprises a first pulley wheel, a second pulley wheel and means acting between the pulley wheels such that, a force acting to rotate the first pulley wheel in a first direction imparts a corresponding force to rotate the second pulley wheel in a second, opposite direction.<H Pulley, , Pulley, 7367277.html, Patent, pto, 7367277

Title: Pulley

Abstract: A pulley comprising a first pulley wheel and a second pulley wheel and a ratchet acting between the two pulley wheels. When substantially equal force is applied to each pulley wheel in use on a rope tail side causing the pulley wheels to rotate, a low gear ratio is achieved through a rope, chain or the like acting on a load through a block. When one pulley wheel is prevented from rotating and a force is applied to the other pulley wheel in use on a rope tail side causing it to rotate, then a higher gear ratio is achieved through a rope or chain or the like acting on a load through a block. When force is applied to the first wheel on a rope tail side and the second pulley wheel is allowed to rotate, then a still higher ratio is achieved in use through a rope, chain or the like acting on a load through a block. In another embodiment, the pulley comprises a first pulley wheel, a second pulley wheel and means to prevent relative rotation of the pulley wheels in one direction, the pulley wheels being able to rotate relative to each other in the other direction. In another embodiment, the pulley comprises a first pulley wheel, a second pulley wheel and means acting between the pulley wheels such that, a force acting to rotate the first pulley wheel in a first direction imparts a corresponding force to rotate the second pulley wheel in a second, opposite direction.

Patent Number: 7,367,277 Issued on 05/06/2008 to Bowman

Inventors: Bowman; George (London SE11 4DB, GB)
Appl. No.: 11/233,654

Filed: September 23, 2005

Foreign Application Priority Data


Sep 23, 2004 [GB]			0421249.4

Current U.S. Class: 114/102.12 ; 474/67

Current International Class: B63H 9/04 (20060101); F16H 9/10 (20060101)

Field of Search: 114/102.12

References Cited [Referenced By]

U.S. Patent Documents


4440354	April 1984	Kobayashi et al.

Primary Examiner: Sotelo; Jes s D
Attorney, Agent or Firm: St. Onge Steward Johnston & Reens LLC

Claims

What is claimed is:

1. A pulley comprising a first pulley wheel and a second pulley wheel, the pulley including means acting between the two pulley wheels such that: when substantially equal force is applied to each pulley wheel in use on a rope tail side causing the pulley wheels to rotate, then a low gear ratio is achieved through a rope or chain acting on a load through a block; when one pulley wheel is prevented from rotating and a force is applied to the other pulley wheel in use on a rope tail side causing it to rotate, then a higher gear ratio is achieved through a rope or chain acting on a load through a block; and, when force is applied to the first wheel on a rope tail side and the second pulley wheel is allowed to rotate, then a still higher ratio is achieved in use through a rope or chain acting on a load through a block.

2. A pulley as claimed in claim 1, wherein the means acting between the pulley wheels prevents relative rotation of the pulley wheels in one direction, the pulley wheels being able to rotate relative to each other in the other direction.

3. A pulley as claimed in claim 2, wherein the means to prevent relative rotation of the pulley wheels in one direction comprises a ratchet mechanism.

4. A pulley as claimed in claim 3, wherein the ratchet mechanism is a load-activated ratchet system so that the ratchet operates only when the load on one pulley wheel reaches a certain level.

5. A pulley as claimed in claim 4, wherein part of the ratchet mechanism is resiliently moveable under load to activate the load-activated ratchet mechanism.

6. A pulley as claimed in claim 1, wherein the first pulley wheel is arranged to grip a rope or chain reaved around the pulley less well than the second pulley wheel.

7. A pulley as claimed in claim 1, wherein the first pulley wheel is arranged to prevent a rope or chain reaved around the pulley from slipping relative to the pulley wheel when both tails of the rope or chain coming from the pulley wheel are under tension, the pulley wheel being arranged to allow the rope or chain to slip relative to the pulley wheel when one or both tails of the rope are not under tension.

8. A pulley as claimed in claim 7, wherein the second pulley wheel is arranged to prevent a rope or chain from slipping around the pulley wheel.

9. A pulley as claimed in claim 1 wherein at least one pulley wheel is arranged for use with rope, a plurality of intrusions are offset on opposite sides of a circumferential groove in said pulley wheel to create a serpentine path for the rope.

10. A pulley as claimed in claim 1 wherein at least one pulley wheel is grooved around its circumference, the inner surface of the groove consists of a series of facets.

11. A pulley as claimed in claim 1, wherein the pulley has a frame and the frame defines an opening aligned with the second pulley wheel to enable a rope or chain to be fed around substantially the whole circumference of the second pulley wheel.

12. A pulley as claimed in claim 11, wherein the frame carries means for jamming the rope or chain.

13. A pulley as claimed in claim 1, further comprising a brake to resist rotation of at least one pulley wheel.

14. A pulley as claimed in claim 13, wherein urging means is provided to urge the pulley wheel and the brake together.

15. A pulley as claimed in claim 14, wherein the urging means comprises an elastomeric bush mounted axially of the pulley wheel.

16. A pulley as claimed in claim 1, wherein the first pulley wheel and the second pulley wheel have a common axis of rotation.

17. A pulley as claimed in claim 16, wherein the first pulley wheel and the second pulley wheel each rotate about a common axle.

18. A pulley as claimed in claim 1, wherein one pulley wheel has a larger effective radius for rope around the pulley wheel than the other.

19. A pulley as claimed in claim 1, wherein the means acting between the pulley wheels imparts, when a rotational force is applied to the first pulley wheel, an opposite counter-rotational force on the second pulley wheel such that in the absence of a force on the second pulley wheel opposite to the counter-rotational force, a rotational force applied to the first pulley wheel causes the first pulley wheel to rotate and the second pulley wheel to counter-rotate.

20. A pulley comprising a first pulley wheel, a second pulley wheel and means to prevent relative rotation of the pulley wheels in one direction, the pulley wheels being able to rotate relative to each other in the other direction, wherein the means to prevent relative rotation of the pulley wheels in one direction comprises a ratchet mechanism.

21. A pulley as claimed in claim 20, wherein the ratchet mechanism is a load-activated ratchet system so that the ratchet operates only when the load on one pulley wheel reaches a certain level.

22. A pulley as claimed in claim 21, wherein part of the ratchet mechanism is resiliently moveable under load to activate the load-activated ratchet mechanism.

23. A pulley as claimed in claim 20, wherein the first pulley wheel is arranged to grip a rope or chain reaved around the pulley less well than the second pulley wheel.

24. A pulley as claimed in claim 20, wherein the first pulley wheel is arranged to prevent a rope or chain reaved around the pulley from slipping relative to the pulley wheel when both tails of the rope or chain coming from the pulley wheel are under tension, the pulley wheel being arranged to allow the rope or chain to slip relative to the pulley wheel when one or both tails of the rope are not under tension.

25. A pulley as claimed in claim 20, wherein the second pulley wheel is arranged to prevent a rope or chain from slipping around the pulley wheel.

26. A pulley as claimed in claim 20 wherein at least one pulley wheel is arranged for use with rope, a plurality of intrusions are offset on opposite sides of a circumferential groove in said pulley wheel to create a serpentine path for the rope.

27. A pulley as claimed in claim 20 wherein at least one pulley wheel is grooved around its circumference, the inner surface of the groove consists of a series of facets.

28. A pulley as claimed in claim 20, wherein the pulley has a frame and the frame defines an opening aligned with the second pulley wheel to enable a rope or chain to be fed around substantially the whole circumference of the second pulley wheel.

29. A pulley as claimed in claim 28, wherein the frame carries means for jamming the rope or chain.

30. A pulley as claimed in claim 20, further comprising a brake to resist rotation of at least one pulley wheel.

31. A pulley as claimed in claim 30, wherein urging means is provided to urge the pulley wheel and the brake together.

32. A pulley as claimed in claim 31, wherein the urging means comprises an elastomeric bush mounted axially of the pulley wheel.

33. A pulley as claimed in claim 20, wherein the first pulley wheel and the second pulley wheel have a common axis of rotation.

34. A pulley as claimed in claim 20, wherein the first pulley wheel and the second pulley wheel each rotate about a common axle.

35. A pulley as claimed in claim 20, wherein one pulley wheel has a larger effective radius for rope around the pulley wheel than the other.

36. A pulley comprising a first pulley wheel, a second pulley wheel and means acting between the pulley wheels such that, a force acting to rotate the first pulley wheel in a first direction imparts a corresponding force to rotate the second pulley wheel in a second, opposite direction.

37. A pulley as claimed in claim 36, wherein, when the second pulley wheel is prevented from rotating, the force acting to rotate the first pulley wheel causes the first pulley wheel to rotate but not the second pulley wheel.

38. A pulley as claimed in claim 37, wherein, when a force is acting to rotate the second pulley wheel in the same direction as the first pulley wheel, the force acting to rotate the first pulley wheel causes the first pulley wheel to rotate, and the force acting to rotate the second pulley wheel causes the second pulley wheel to rotate in the same direction as the first pulley wheel.

39. A pulley as claimed in claim 36, wherein means is provided to allow the first and second pulley wheels to slip relative to each other under low load conditions.

40. A pulley as claimed in claim 36, wherein the means acting between the two pulley wheels is a gear means.

41. A pulley as claimed in claim 40, wherein the gear means includes a plurality of pinions, said first and second pulley wheels including means for engaging said pinions.

42. A pulley as claimed in claim 41, wherein each of the means for engaging the pinions is a continuous track.

43. A pulley as claimed in claim 42 wherein the continuous tracks lie out of the major plane of respective pulley wheels.

44. A pulley as claimed in claim 43, wherein the pinions are frustoconical rollers.

45. A pulley as claimed in claim 44, wherein the rollers are made of elastomeric material.

46. A pulley as claimed in claim 41, wherein the means for engaging the pinions are gear wheels having gear teeth.

47. A pulley as claimed in claim 46, wherein the pinions are held by a carrier, the carrier being rotatable.

48. A pulley as claimed in claim 47, wherein the pinions extend substantially radially from the axis of rotation of the carrier.

49. A pulley as claimed in claim 47, wherein the first pulley wheel, the second pulley wheel and the carrier have a common axis of rotation.

50. A pulley as claimed in claim 41, wherein the number of pinions provided obeys the following formula: the total number of gear teeth on the two gear wheels divided by the number of pinions equals an integer.

51. A pulley as claimed in claim 41, wherein the pinions are angled.

52. A pulley as claimed in claim 36 further including a frame, wherein the carrier is arranged such that, in a first state, it can rotate relative to the frame in one direction only, but, in a second state, it can rotate relative to the frame in both directions.

53. A pulley as claimed in claim 52, wherein one of the carrier and the frame of the pulley carries a ratchet and the other of the carrier and the frame of the pulley carries a pawl.

54. A pulley as claimed in claim 53, wherein there is provided a quick-release for the ratchet and pawl.

55. A pulley as claimed in any of claims 52, wherein the frame is provided with means for feeding rope or chain to the pulley wheels.

56. A pulley as claimed in claim 55, wherein the means for feeding comprises two opposed wheels for each pulley wheel.

57. A system comprising a pulley having a first pulley wheel and a second pulley wheel, the pulley including means acting between the two pulley wheels such that: when substantially equal force is applied to each pulley wheel in use on a rope tail side causing the pulley wheels to rotate, then a low gear ratio is achieved through a rope or chain acting on a load through a block; when one pulley wheel is prevented from rotating and a force is applied to the other pulley wheel in use on a rope tail side causing it to rotate, then a higher gear ratio is achieved through a rope or chain acting on a load through a block; and, when force is applied to the first wheel on a rope tail side and the second pulley wheel is allowed to rotate, then a still higher ratio is achieved in use through a rope or chain acting on a load through a block, the system further comprising a rope or chain.

58. A system as claimed in claim 57, wherein the rope or chain is wound around the pulley wheels in opposite directions.

59. A system as claimed in claim 58, wherein the first pulley wheel and the rope have a friction coefficient such that the ratio of tension between the two ends of the rope when reaved around the first pulley wheel is greater than half the highest gearing ratio of the system.

60. An expanded system comprising a pulley having a first pulley wheel and a second pulley wheel, the pulley including means acting between the two pulley wheels such that: when substantially equal force is applied to each pulley wheel in use on a rope tail side causing the pulley wheels to rotate, then a low gear ratio is achieved through a rope or chain acting on a load through a block; when one pulley wheel is prevented from rotating and a force is applied to the other pulley wheel in use on a rope tail side causing it to rotate, then a higher gear ratio is achieved through a rope or chain acting on a load through a block; and, when force is applied to the first wheel on a rope tail side and the second pulley wheel is allowed to rotate, then a still higher ratio is achieved in use through a rope or chain acting on a load through a block, the expanded system further comprising a rope or chain and at least one block.

61. A boat having an expanded system comprising a pulley having a first pulley wheel and a second pulley wheel, the pulley including means acting between the two pulley wheels such that: when substantially equal force is applied to each pulley wheel in use on a rope tail side causing the pulley wheels to rotate, then a low gear ratio is achieved through a rope or chain acting on a load through a block; when one pulley wheel is prevented from rotating and a force is applied to the other pulley wheel in use on a rope tail side causing it to rotate, then a higher gear ratio is achieved through a rope or chain acting on a load through a block; and, when force is applied to the first wheel on a rope tail side and the second pulley wheel is allowed to rotate, then a still higher ratio is achieved in use through a rope or chain acting on a load through a block, the expanded system further comprising a rope or chain and at least one block.

62. A pulley comprising a first pulley wheel, a second pulley wheel, a frame mounting the first and second pulley wheels and means acting between the pulley wheels such that, a force acting to rotate the first pulley wheel in a first direction imparts a corresponding force to rotate the second pulley wheel in a second, opposite direction, and an anchor point for attachment of the pulley being provided on the frame.

63. A pulley comprising a first pulley wheel, a second pulley wheel, a frame mounting the first and second pulley wheels, means acting between the pulley wheels to prevent relative rotation of the pulley wheels in one direction, wherein the pulley wheels being able to rotate relative to each other in the other direction, wherein one pulley wheel has a larger effective radius for rope around the pulley wheel than the other, and an anchor point for attachment of the pulley being provided on the frame.

64. A pulley comprising a first pulley wheel, a second pulley wheel and means to prevent relative rotation of the pulley wheels in one direction, the pulley wheels being able to rotate relative to each other in the other direction, wherein at least one pulley wheel is arranged for use with rope, a plurality of intrusions are offset on opposite sides of a circumferential groove in said pulley wheel to create a serpentine path for the rope.

65. A pulley comprising a first pulley wheel, a second pulley wheel and means to prevent relative rotation of the pulley wheels in one direction, the pulley wheels being able to rotate relative to each other in the other direction, wherein at least one pulley wheel is grooved around its circumference, the inner surface of the groove consists of a series of facets.

66. A pulley comprising a first pulley wheel, a second pulley wheel and means to prevent relative rotation of the pulley wheels in one direction, the pulley wheels being able to rotate relative to each other in the other direction, further comprising a brake to resist rotation of at least one pulley wheel.

Description

This application claims priority of British Patent Application No. 0421249.4 filed on Sep. 23, 2004.

FIELD OF THE INVENTION

The present invention relates to a pulley which can be used as an improved type of differential pulley, and is particularly but not exclusively concerned with use in sailing, mountaineering and industry, and more particularly for use with a mainsheet for controlling the angle of a mainsail on a sailing boat, or for the kicking strap or boom vang on a sailing boat or any other rope handling application on a sailing boat.

BACKGROUND OF THE INVENTION

FIG. 1 shows a known differential pulley 10. Differential pulleys are used to lift heavy loads because they achieve a high gear ratio. A standard differential pulley 10 consists of two pulley wheels 12, 14 of different radii R, r which are fast with one another to rotate as one about a common axle. The differential pulley 10 is fixed in position so as not to move. A continuous chain 16 is run around both pulley wheels 12, 14 in opposite directions to create two hanging loops 18, 20. A moveable pulley block 22, which is connected to a load 24, is placed in a first hanging loop 18, and the load 24 is raised or lowered by pulling or releasing respectively a length of the second hanging loop 20. When the load 24 is being raised or lowered, the two pulley wheels 12, 14 rotate as one around the common axle and, because the chain 16 is reaved in opposite directions around each wheel 12, 14, the chain 16 winds upon one pulley wheel as it unwinds from the other. A high gear ratio is achieved because the pulley wheels 12, 14 have different radii. It is important that the chain 16 does not slip on the pulley wheels 12, 14, and so the pulley wheels 12, 14 have lugs (not shown) to engage the chain links and thereby prevent slipping.

The known differential pulley 10 achieves a single high power gear ratio which is determined by the radii of the two pulley wheels 12, 14, and it is not possible to achieve multiple gear ratios from a single known differential pulley 10. However, there are applications where more than one gear ratio is desired.

On a sailing boat 30, for example as shown in FIG. 2, when the mainsail 32 is being controlled, it is advantageous to be able to use a high gear ratio when large forces are acting on the mainsail 32, or when fine control of the position of the mainsail 32 is required. It is also advantageous to be able to trim the sail position quickly when maneuvering, and this requires that the pulley system 34 for the mainsheet 36 is configurable to have more than one gear ratio, preferably having at least one high power gear ratio and one low power gear ratio. The known differential pulley would not be useful for such applications. In the known boat shown in FIG. 2 the mainsheet pulley system acts between the boom 38 and a transverse spar 40 across the boat 30. A pulley system 42 is also used on the known boat 30 for the vang 44 or kicking strap to the boom 38.

Two-speed mainsheet block and tackle systems provide mainsail control with two gear ratios. For example, a mainsheet pulley system as shown in FIG. 3 with gear ratios of 4:1 and 16:1 are commercially available. Two-speed continuous mainsheet block and tackle systems, as shown in FIG. 4, having for example gear ratios of 2:1 and 4:1, 3:1 and 6:1, and 4:1 and 8:1 are also commercially available, for example, the Harken system 330 2-speed mainsheet system. However, only two gear ratios are possible with these block and tackle systems, and furthermore, the available gear ratios from a single system are relatively close to one another, thus preventing both very fine tuning and quick trimming of a mainsail with a single mainsheet system.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a pulley comprising a first pulley wheel and a second pulley wheel, the pulley including means acting between the two pulley wheels such that: when substantially equal force is applied to each pulley wheel in use on a rope tail side causing the pulley wheels to rotate, then a low gear ratio is achieved through a rope, chain or the like acting on a load through a block; when the first pulley wheel is prevented from rotating and a force is applied to the second pulley wheel in use causing it to rotate, then a higher gear ratio is achieved through a rope or chain and the like acting on a load through a block; and, when force is applied to the first wheel on a tail side and the second pulley wheel is allowed to rotate, then a still higher ratio is achieved in use through a rope, chain or the like acting on a load through a block.

In this way, a single pulley which can have three increasing gear ratios in a system is achieved, and so low-power quick trimming and high-power fine tuning of a load may be achieved, which may be at widely differing gear ratios, and an intermediate ratio is also available, which is particularly useful for controlling the position of a mainsail on a sailing boat, or for tightening a boom vang.

In one embodiment, the means acting between the pulley wheels prevents relative rotation of the pulley wheels in one direction, the pulley wheels being able to rotate relative to each other in the other direction. In this way the pulley wheels are not fixed to rotate as one about a common axis, as in the known differential pulley, but the pulley wheels may rotate in a direction opposite from one another, and may rotate as one. As such, the potential to achieve more than one gear ratio exists. A low power gear ratio may be achieved when the pulley wheels rotate relative to one another, and a high power gear ratio may be achieved when the second pulley wheel and the first pulley both rotate as one.

In another embodiment, the means acting between the pulley wheels imparts, when a rotational force is applied to the first pulley wheel, an opposite counter-rotational force on the second pulley wheel such that in the absence of a force on the second pulley wheel opposite to the counter-rotational force, a rotational force applied to the first pulley wheel causes the first pulley wheel to rotate and the second pulley wheel to counter-rotate. In this way, in use, a rope or chain or the like can be reaved in the same direction around the pulley wheels to create a differential system.

According to another aspect of the invention there is provided a pulley comprising a first pulley wheel, a second pulley wheel and means to prevent relative rotation of the pulley wheels in one direction, the pulley wheels being able to rotate relative to each other in the other direction.

In this way, the first pulley wheel and the second pulley wheel are not fixed to rotate as one on a common axle, as in the known differential pulley, but the pulley wheels may rotate in a direction opposite from one another, and may rotate as one. As such, the potential to achieve more than one gear ratio exists. A low-power gear ratio may be achieved when the pulley wheels rotate relative to one another, and a high-power gear ratio may be achieved when the second pulley wheel and the first pulley both rotate as one.

The means to prevent relative rotation of the pulley wheels in one direction may take any suitable form and may comprise a ratchet mechanism. The means acting between the pulley wheels may be a simple ratchet system or a load activated ratchet system where the ratchet operates only when the load on one pulley wheel reaches a certain level. In this way the pulley wheels can freely rotate in either direction under low-load conditions allowing the pulley to run out more freely. The ratchet may be an internal ratchet. Part of the ratchet may be resiliently moveable under load to activate the load-activated ratchet mechanism. Preferably, a mount for part of the rotate mechanism is resiliently moveable.

Preferably, the first pulley wheel is arranged to grip a rope, chain or the like reaved around the pulley less well than the second pulley wheel. Preferably, the first pulley wheel is arranged to prevent a rope, chain or the like reaved around the pulley from slipping relative to the pulley wheel when both tails of the rope, chain or the like coming from the pulley wheel are under tension, the pulley wheel being arranged to allow the rope, chain or the like to slip relative to the pulley wheel when one or both tails of the rope are not under tension. The first pulley wheel may be arranged so that in use, the friction between the pulley wheel and the rope or the like is such that the ratio of tension between two ends of a rope reaved around the pulley wheel is greater than half the gearing ratio of the differential system. In this way, the pulley wheel will grip the rope when under load, but the pulley wheel will be able to slip with respect to the rope when outgoing tension is released allowing quick release of the pulley. The pulley wheel may be drum shaped so that in use, a rope may be passed all the way around it at least once or even around it several times.

Preferably, the second pulley wheel is arranged to prevent a rope, chain or the like from slipping around the pulley wheel. In this way, the rope should not slip relative to the pulley wheel regardless of whether or not the rope tails coming from the pulley wheel are under tension.

At least one pulley wheel may be grooved around its circumference and may have a substantially V-shaped groove. Preferably, the pulley wheel has at least one intrusion into the groove and may have a plurality of intrusions. Where the pulley wheel is arranged for use with rope, the intrusions may be offset on opposite sides of the groove to create a serpentine path for the rope. The intrusion or intrusions may be achieved by providing holes or rebates in the walls defining the groove. The inner surface of the groove of the pulley wheel may consist of a series of facets, for example between four and eleven facets. Preferably there are eight facets. With a suitable number of facets on the first pulley wheel, this enables the required friction force between the pulley wheel and rope under tension while allowing free movement when tension on the rope is released.

A resisting means may be provided to resist rotation of at least one pulley wheel, preferably the second pulley wheel. The means may be a brake. Urging means may be provided to urge the pulley wheel and the resisting means together. The urging means may take any suitable form and may comprise means to urge the pulley wheel against the resisting means. The urging means may include an elastomeric member. The elastomeric member may comprise a bush mounted axially of the pulley wheel. The bush may axially mount both pulley wheels, preferably through a common bearing.

Preferably, the first pulley wheel and the second pulley wheel have a common axis of rotation. Preferably, the first pulley wheel and the second pulley wheel each rotate about an axle which more preferably is a common axle. In this way, the pulley is simple to construct.

The pulley wheels may have the same radius, but in a preferred embodiment, one pulley wheel has a larger effective radius of the rope around the pulley wheel than the other pulley wheel, which may provide differential gearing.

The pulley suitably has a frame. Preferably, the frame defines an opening aligned with the second pulley wheel which, in use, enables a rope, chain or the like to be fed around substantially the whole circumference of the second pulley wheel. Both ends of the rope, chain or the like may pass through the opening. In this way, the friction between the second pulley wheel and rope is increased so as to reduce the likelihood of the rope or pulley wheel slipping.

The frame may carry means suitable for jamming the rope, chain or the like. Preferably, the means suitable for jamming the rope is a cam cleat. In this way, means for jamming the rope is conveniently located on the pulley and is a known, readily available device.

Preferably, an anchor point is provided on the pulley, more preferably on the frame. In this way, the pulley may be attached and removed from a fixed anchorage. The pulley may comprise means to allow the pulley to be bolted directly to a fixed object, such as the deck or a spar of a sailing boat. A shackle may be provided for attaching to the anchor point. Where the pulley includes a frame, the frame may define at least one flat side cheek, and means may be provided to mount the pulley with the flat side cheek flat against a flat fixed object such as the deck of a boat. The frame may be provided with holes for allowing the pulley to be fixed to an object with screws or the like.

According to another aspect of the invention there is provided a system comprising a pulley according to the preceding aspect of the invention, and a rope, chain or the like wound around the pulley wheels, the rope, chain or the like being wound on the pulley wheels in opposite directions.

The system preferably includes rope. Preferably, the first pulley wheel and rope have friction coefficients such that the ratio of tension between two ends of a rope reaved around the pulley wheel is greater than half the gearing ratio of the differential system. In this way, the pulley wheel will grip the rope when under load, but the pulley wheel will be able to slip with respect to the rope when outgoing tension is released allowing quick release of the pulley.

According to a further aspect of the invention there is provided an expanded system comprising a system according to the preceding aspect of the invention and a block, the rope, chain or the like being wound around the pulley wheels and block.

According to another aspect of the invention there is provided a pulley comprising a first pulley wheel and a second pulley wheel, wherein the first pulley wheel and the second pulley wheel communicate with each other, such that, a force acting to rotate the first pulley wheel in a first direction imparts a corresponding force to rotate the second pulley wheel in a second, opposite direction.

According to a further aspect of the invention there is provided a pulley comprising a first pulley wheel and a second pulley wheel, wherein the first pulley wheel and the second pulley wheel communicate with each other, such that, a force acting to rotate the first pulley wheel in a first direction imparts a corresponding force to rotate the second pulley wheel in a second opposite direction, and wherein, when the corresponding force is greater than any opposing forces on the second pulley wheel, the force acting to rotate the first pulley wheel causes the first pulley wheel to rotate, and the corresponding force acting to rotate the second pulley wheel causes the second pulley wheel to counter-rotate.

In this way, the first pulley wheel and second pulley wheel can be caused to rotate in opposite directions, in the absence of sufficient opposing forces. In use, a rope or chain or the like can be run in the same direction over both pulley wheels to form a hanging loop, into which a moveable block may be placed, and, in this way, a differential type pulley can be achieved without the requirement that the rope is run in opposite directions around each pulley wheel.

Preferably, when the second pulley wheel is prevented from rotating, the force acting to rotate the first pulley wheel causes the first pulley wheel to rotate but not the second pulley wheel. In this way, the pulley acts as a standard single block; the first pulley wheel rotates and the second pulley wheel remains stationary. In use, a system including the pulley, a rope or chain or the like fed around the pulley and a movable pulley block can create a low gear ratio, for example of 2:1. The lower power gear ratio is suitable for quick trimming.

Preferably, when a force is acting to rotate the second pulley wheel in the same direction as the first pulley wheel is prevented from rotating, the force acting to rotate the first pulley wheel causes the first pulley wheel to rotate, and the net force acting to rotate the second pulley wheel causes the second pulley wheel to rotate in the same direction as the first pulley wheel. In this way, both pulley wheels rotate in the same direction. In use, a system including the pulley, a rope or chain or the like fed around the pulley and a pulley block can create a still lower power gear ratio, for example of 1:1, in addition to the gear ratio of 2:1, for even quicker trimming.

Preferably, the first pulley wheel and the second pulley wheel communicate via a gear means, such that a gearing ratio exists between the first pulley wheel and the second pulley wheel. In this way, when the first and second pulley wheels rotate in opposite directions, a differential relationship may be achieved. Preferably, the gearing ratio between the first pulley wheel and the second pulley wheel is between 1:1 and 1:3, preferably between 1:1 and 1:2. In a preferred embodiment the gear ratio is 44:49. In this way, a high differential gear ratio of 19.6:1 may be achieved.

Preferably, the first pulley wheel is provided with a first rack or first gear wheel and the second pulley wheel is provided with a second rack or second gear wheel. Preferably, the racks are substantially concentric, and preferably are concentric with the rotational axis of the first and/or second pulley wheels. Preferably, the racks are bevelled. In this way, a pinion may easily engage between the racks to communicate therebetween. The term "rack" means a rack in the sense of a rack-and-pinion but the rack does not necessarily have gear teeth, but provides a surface for engagement with a pinion or the like.

Preferably, there is provided a plurality of pinions (e.g. three pinions) to engage between the first and second racks. Preferably, the pinions are bevelled and are shaped to complement the first and second racks. Preferably, the pinions are located at substantially the same distance from the axis of rotation. Preferably, the pinions are held in a carrier. Preferably, the pinions extend substantially radially from the carrier. Preferably, the carrier is concentric with the racks. The carrier may be rotatable. In particular, the carrier may normally be arranged to rotate with respect to the racks in at least one direction. Preferably, the carrier is allowed to rotate in both directions, and may be arranged to allow rotation in only one direction in one state and in both directions in another state. In this way, the first and second pulley wheels may rotate in both directions and in use, for example when the pulley is used on a boat for the kicking strap, the kicking strap can be quick released.

Typically, the carrier, the first pulley wheel and the second pulley wheel each rotate about an axle.

Typically, the first and second pulley wheels each include means for engaging the pinions, such as a continuous track. The continuous track may be toroidal. The means for engaging the pinions may be concentric with each other. The continuous track of the first pulley wheel may have a larger radius than the continuous track of the second pulley wheel. The continuous track of the first pulley wheel may be on the surface of a notional sphere. The continuous track of the second pulley wheel may be on the surface of a concentric notional sphere of a different apical angle.

In one embodiment, the first and second racks have gear teeth. Preferably, the first rack has a different number of teeth from the second rack. Preferably, the racks have similar radii. Preferably, the first and second racks have between 30 and 50 gear teeth. The first rack may have 49 gear teeth, and the second rack may have 44 gear teeth. In this way, a differential gear ratio of 44:49 exists between the pulley wheels and in use a system gear ratio of 19.6:1 is achieved.

In this embodiment, the pinions have gear teeth. Each pinion preferably has the same number of gear teeth. Preferably, the number of pinions provided is calculated from the following formula: the total number of gear teeth divided by the number of pinions should equal an integer. For a gear ratio of 44:49, the number of pinions is preferably 3, because 93 is divisible by 3. In this way the teeth of the rack and pinion will mesh together properly. Preferably still, the number of gear teeth on each rack divided by the number of gear teeth on a pinion should equal a non-integer number. In this way, more even wear on the gear teeth is achieved.

In another embodiment, the racks and pinions engage using frictional gearing. Preferably, the racks are frictional gear tracks. Preferably, the gear track of the first pulley wheel has a larger radius than the gear track of the second pulley wheel. Preferably, the pinions are frustoconical rollers, which may be made of elastomeric material. In this way, the pulley may be cheaper to manufacture. Preferably, the pinions are angled to engage the gear track on the first pulley wheel and the second pulley wheel. Preferably, means is provided to allow the first and second pulley wheels to slip relative to each other under low load conditions. In this way, in use a rope can be run out.

Preferably, each pulley wheel includes means to prevent a rope, chain or the like from slipping around the pulley wheel. Each pulley wheel may be grooved around its circumference. The groove may be V-shaped, and there may be at least one intrusion into the groove. Preferably, each pulley wheel has a plurality of intrusions. Where the pulley wheels are arranged for use with rope, the intrusions may be offset on opposite sides of the groove to create a serpentine path for the rope. The intrusion or intrusions may be achieved by providing holes or rebates or facets in the walls defining the groove.

The pulley wheels may have any suitable radii and preferably have substantially the same radii. In this way, the pulley may be more uniform in size and shape and its weight and rope lead angles may be more balanced.

Preferably, the pulley is held in a frame. Preferably the frame is provided with an anchor point. The frame may be provided with means for feeding rope to the pulley wheels, where, preferably, the means for feeding the rope comprises at least one wheel, and may comprise two opposed wheels for each pulley wheel.

Preferably one of the carrier and the frame of the pulley includes a ratchet and the other of the carrier and the frame of the pulley includes a pawl. Preferably, the carrier includes/carries the ratchet, and the frame includes/carries the pawl. Preferably, there is provided a quick-release for the ratchet system. In this way, in use a rope can be run out.

Above are set out preferred and/or optional features. These can be combined, singly or in any combination, with any of the aspects of the invention, unless the context demands otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a differential pulley of the prior art;

FIG. 2 is a perspective view of a sailing boat of the prior art showing a mainsheet and vang in use;

FIG. 3 is a perspective view of a 2.times. purchase mainsheet system of the prior art;

FIG. 4 is a perspective view of a two-speed mainsheet system of the prior art;

FIG. 5 is a perspective view of the pulley of the first embodiment of the invention in a system showing a rope and pulley block;

FIGS. 6a and 6b are perspective views of the pulley of FIG. 5;

FIG. 7 is a side elevation of the pulley of FIG. 5;

FIG. 8 is a front end elevation of the pulley of FIG. 5 in cross-section taken through the points A-A shown in FIG. 7;

FIG. 9 is an front end elevation of the pulley of FIG. 5;

FIG. 10 is a side elevation in cross-section taken through the points B-B shown in FIG. 9;

FIG. 11 is a side elevation in cross-section taken through the points C-C shown in FIG. 9;

FIG. 12 is an rear end elevation of the pulley of FIG. 5;

FIG. 13 is a side elevation in cross-section taken through the points D-D shown in FIG. 12;

FIG. 14 is a first exploded perspective view of the pulley of FIG. 5;

FIG. 15 is a second exploded perspective view of the pulley of FIG. 5;

FIG. 16 is a front perspective view of the pulley of the second embodiment of the invention in a system showing a rope and pulley block;

FIG. 17 is a side elevation of the pulley of the second embodiment of the invention in a system showing a rope and pulley block;

FIG. 18 is a front elevation of the pulley of the second embodiment of the invention in a system showing a rope and pulley block;

FIGS. 19a and 19b are perspective views of the pulley of FIG. 16;

FIG. 20 is a side elevation of the pulley of FIG. 16;

FIG. 21 is a front end elevation in cross-section taken through the points A-A of the pulley of FIG. 20;

FIG. 22 is a front end elevation of the pulley of FIG. 16;

FIG. 23 is a side elevation in cross-section taken through the points B-B of the pulley of FIG. 22;

FIG. 24 is a front end elevation of the pulley of FIG. 16;

FIG. 25 is a side elevation in cross-section taken through the points C-C of the pulley of FIG. 24;

FIG. 26 is a first exploded perspective view of the pulley of FIG. 16;

FIG. 27 is a second exploded perspective view of the pulley of FIG. 16;

FIG. 28 is a front perspective view of the pulley of the second embodiment of the invention in another system showing a rope and fiddle block

FIG. 29 is a rear perspective view of the pulley of the second embodiment of the invention in the system of FIG. 28;

FIG. 30a is a front end elevation of the pulley of the third embodiment of the invention;

FIG. 30b is a side elevation in cross-section taken through the points C-C of the pulley of FIG. 30a under no external load;

FIG. 30c is a side elevation in cross-section taken through the points CII-CII of the pulley of FIG. 30a under applied external load;

FIG. 31a is a front end elevation of the pulley of the third embodiment of the invention;

FIG. 31b is a side elevation in cross-section taken through the points B-B of the pulley of FIG. 31a under no external load;

FIG. 31c is a side elevation in cross-section taken through the points BII-BII of the pulley of FIG. 31a under applied external load;

FIG. 32 is a first exploded perspective view of the pulley of FIG. 30a;

FIG. 33 is a second exploded perspective view of the pulley of FIG. 30a;

FIG. 34a is a side elevation of the pulley of the fourth embodiment of the invention;

FIG. 34b is an end elevation in cross-section taken through the points A-A of the pulley of FIG. 34a;

FIG. 35a is an end elevation of the pulley of FIG. 34a;

FIG. 35b is a side elevation in cross-section taken through the points B-B of the pulley of FIG. 35a under low-load conditions;

FIG. 35c is a side elevation in cross-section taken through the points B-B of the pulley of FIG. 35a under high-load conditions;

FIG. 36a is an end elevation of the pulley of FIG. 34a;

FIG. 36b is a side elevation in cross-section taken through the points C-C of the pulley of FIG. 36a under low-load conditions;

FIG. 37 is a first exploded perspective view of the pulley of FIG. 30;

FIG. 38 is a second exploded perspective view of the pulley of FIG. 30;

FIG. 39 is a side perspective view of the pulley of the fifth embodiment of the invention in a system showing a rope and pulley block;

FIGS. 40a and 40b are perspective views of the pulley of FIG. 39;

FIG. 41a is a side elevation of the pulley of FIG. 39;

FIG. 41b is an end elevation in cross-section taken through the points A-A of the pulley of FIG. 41a;

FIG. 42a is an end elevation of the pulley of FIG. 39;

FIG. 42b is a side elevation in cross-section taken through the points B-B of the pulley of FIG. 42a;

FIG. 43 is a first exploded perspective view of the pulley of FIG. 39;

FIG. 44 is a second exploded perspective view of the pulley of FIG. 39;

FIG. 45 is a perspective view of the carrier of the pulley of FIG. 39;

FIG. 46 is a side perspective view of the pulley of the sixth embodiment of the invention in a system showing a rope and pulley block;

FIG. 47 is a side elevation of the pulley of FIG. 46;

FIG. 48 is an end elevation in cross-section taken through the points A-A of the pulley of FIG. 47;

FIG. 49 is a front end elevation of the pulley of FIG. 46;

FIG. 50 is a side elevation in cross-section taken through the points B-B of the pulley of FIG. 49;

FIG. 51 is a first exploded perspective view of the pulley of FIG. 46;

FIG. 52 is a second exploded perspective view of the pulley of FIG. 46;

FIG. 53 is a perspective view of the carrier of the pulley of FIG. 46;

FIG. 54 is a perspective view of a sailing boat showing a pulley system of the present invention.

FIGS. 55 to 61 show several alternative pulley wheels.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 5 to 15, a pulley 110 of the first embodiment of the invention comprises a first pulley wheel 112, a second pulley wheel 114 and a frame 116. The first and second pulley wheels 112, 114 are held within the frame on respective axles 118a, 119a so that the pulley wheels 112, 114 are concentric and adjacent.

The rope 148 in the pulley system may be a standard sailing rope such as made by Marlow Ropes, for example a three strand core rope with a braid cover. The rope is in a continuous loop.

The frame 116 comprises two side plates 118, 119 joined together by three tie bars 120, 121, 122. Tie bar 122 is located at a first end of the pulley 110 and is broader than tie bars 120, 121 which are located at a second opposite end of the pulley 110. Tie bar 122 has a cylindrical anchor point 124 fixed to it, which may be attached to a fixed object such as the deck of a sailing boat by a shackle (not shown). Tie bar 120 is located toward the front end of the pulley 110 and defines an aperture suitable for feeding a rope onto the second pulley wheel 114. Tie bar 121 is located toward the rear end of the pulley 110 and defines an aperture suitable for feeding a rope onto the first pulley wheel 112.

Side plate 118 has an axle 118a which extends into the frame 116. The first pulley wheel 112 is mounted via a cylindrical bearing 123 on the axle 118a. Side plate 119 has an axle 119a which extends into the frame 116, and the second pulley wheel 114 is mounted via a cylindrical bearing 123 on the axle 119a. Two mounting arms 126, 127 attach to and lie against the outside surface of each respective side plate 118, 119, extending outward to join a short distance from the frame 116. A cam cleat 128 is attached to the mounting arms 126, 127 at the point at which they join, such that a rope may be fed through the cam cleat 128 onto the first pulley wheel 112.

The first pulley wheel 112 is drum shaped allowing in use a rope to be passed around it several times and may have a rope radius of 38 mm.

The second pulley wheel 114 has a substantially V-shaped groove running around its circumference. Moreover, to increase the grip of the wheel 114 on a rope, the side walls of the groove have holes drilled in them, the holes in one wall being offset from the holes in the other wall. The holes increase grip on a rope and because they are offset they cause a rope to snake as it feeds around the groove of the pulley wheel 114, again increasing friction and grip. It is important that, in use, a rope does not slip relative to the second pulley wheel 114. The second pulley wheel 114 may have a rope radius of 30 mm.

Referring in particular to FIGS. 8 to 15, the first pulley wheel 112 defines an internal cylindrical ratchet 132 which is located within the pulley wheel 112 on the side adjacent the second pulley wheel 114.

The second pulley wheel 114 has a cylindrical protrusion 136 with two pawls 138 fitted thereto by torsion springs (not shown). The protrusion 136 protrudes from the second pulley wheel 114 at a side adjacent the first pulley wheel 112 and is shaped to fit into the internal ratchet 132 of the first pulley wheel 112. The pawls 138 are arranged to engage with the ratchet 132. The ratchet mechanism is designed so that the pulley wheels 112, 114 are prevented from rotating relative to each other in one direction, but are able to rotate relative to one another in the other direction.

In use, as shown in FIG. 5, a continuous rope 148 runs through the cam cleat 128, around the first pulley wheel 112 about 11/4 times, then to a standard block 150 which is attached to a load (not shown), and back around the second pulley wheel 114. The rope 148 is reaved in opposite directions around the first and second pulleys 112, 114 and forms a free loop 149.

A first gear ratio of 1:1 is obtained by pulling simultaneously both free ends of the loop 149. In this way, the pulley wheels 112, 114 turn in opposite directions. Friction between the rope 148 and first pulley wheel 112 prevents the rope from slipping. The ratchet mechanism allows the pulleys 112, 114 to turn in opposite directions.

A second gear ratio of 2:1 is obtained by securing the length of the loop 149 from the first pulley wheel 112 in the cam cleat 128 and pulling on the other length from the second pulley wheel 114. In this way, the first pulley wheel 112 is prevented from moving while the second pulley wheel 114 turns as the rope is pulled. Again, friction between the rope 148 and first pulley wheel 112 prevents the rope from slipping. The ratchet mechanism allows the second pulley wheel 114 to turn relative to the first pulley wheel 116 in this direction. Alternatively, the length of the loop 149 from the second pulley wheel may be fixed and the same 2:1 ratio can be achieved by pulling on the rope from the first pulley wheel.

A third, high power, gear ratio of 9.5:1 is obtained by pulling on the free length of the loop 149 from the first pulley wheel 112 and allowing the other length of the loop 149 to run out freely. The first pulley wheel 112 turns as the free end of the loop 149 is pulled. The second pulley wheel 114 is impelled to turn in the same direction as the first pulley wheel 112 by the rope 148. In this way, the pulley wheels 112, 114 rotate in the same direction due to the forces acting on them from the free length of the rope and the load. The second pulley wheel 114 is prevented from rotating relative to the first pulley wheel 112 in this direction by the ratchet mechanism, and so the second pulley wheel 114 cannot overtake the first, despite the force from the load, as transmitted by the rope 148, compelling it to do so. However, the force from the load, as transmitted by the rope 148, generates a torque on the first pulley wheel 112 through the ratchet mechanism. The torque urges the first pulley wheel 112 to rotate faster in the same direction, and it is important that the pulley wheel 112 does not slip relative to the rope 148 in normal use. To prevent slippage, sufficient friction must be generated between the first pulley wheel 112 and the rope 148. In this embodiment a drum-shaped pulley wheel 112 is used with the rope being reaved around it about 11/4 times. The friction between the first pulley wheel 112 and the rope 148 reaved around it should ideally be such that the ratio of tension between the two ends of the rope 148 is greater than half the high gear ratio. In this way both pulley wheels 112, 114 turn together in the same direction and the difference in radii of the pulley wheels 112, 114 creates a differential. A high power gear ratio is achieved in a similar way to the known differential pulley.

If the free ends of the rope 148 are released, the friction around the first pulley wheel 112 is reduced and the rope may slip. A quick release of the pulley 110 is achieved in this way.

Referring to FIG. 54, the pulley 110 is shown in a system fitted to a boat 30. A system including the pulley 110 is fitted between a boom 38 and a spar 40. Another system including the pulley is fitted between the boom 38 and the foot of the mast 39 as a vang 44.

Referring to FIGS. 16 to 29, a pulley 210 of the second embodiment of the invention comprises a first pulley wheel 212, a second pulley wheel 214 and a frame 216. The first and second pulley wheels 212, 214 are held within the frame on respective axles 218a, 219a so that they are concentric and adjacent.

The frame 216 comprises two side plates 218, 219 joined together by two upper tie bars (not shown) and a central bar (not shown). The two upper tie bars are located at a first end of the pulley 210, with one located toward the front and the other located toward the rear of the pulley 210 passing through apertures 208 in the side plates 218, 219. An anchor point 224 is fixed to the frame 216 between the two upper tie bar apertures 208 being received in opposed undercut recesses 215 in the side plates 218, 219 of the frame 216 so as to project radially away from the pulley wheels 212, 214.

Referring particularly to FIGS. 26 and 27, side plate 218 has an axle boss 218a which extends into the frame 216. The first pulley wheel 212 is mounted via a short cylindrical bearing 217 on the axle boss 218a. Side plate 219 has an axle boss 219a which extends into the frame 216, and the second pulley wheel 214 is mounted via a cylindrical bearing 211 on the axle boss 219a. Each axle boss 218a, 219a has a central aperture 213 to receive the central tie bar to connect the side plates 218, 219 together. Axle boss 218a defines an axial recess 218b at its inner end. Axle boss 219a has an inwards step to define a narrower diameter end portion 219b to be received in the recess 218b in the end of axle boss 218a.

Referring particularly to FIG. 22, the first pulley wheel 212 has a substantially V-shaped groove running around its circumference. The innermost surface of the groove 222 is faceted and has a octagonal profile. The groove 222 is narrowest at the point where two of the eight facets 223 meet. The side walls of the groove 222 bow out between the points where the eight facets meet. The first pulley wheel 212 has a rope radius of 38 mm.

The second pulley wheel 214 also has a substantially V-shaped groove running around its circumference. However, to increase the grip of the wheel 214 on a rope, the side walls of the groove have holes drilled in them, the holes in one wall being offset from the holes in the other wall. The holes increase grip on a rope and because they are offset they cause a rope to snake as it feeds around the groove of the pulley wheel 214, again increasing friction and grip. It is important that, in use, a rope does not slip relative to the second pulley wheel 214. The second pulley wheel 214 has a rope radius of 30 mm.

Referring in particular to FIGS. 22 to 27, and particularly FIGS. 23, 26 and 27, the first pulley wheel 212 defines an internal cylindrical ratchet 232 which is located within the pulley wheel 212 on the side adjacent the second pulley wheel 214. The second pulley wheel 214 has a substantially cylindrical protrusion 236 with two pawls 238 fitted thereto by torsion springs (not shown). The protrusion 236 protrudes from the second pulley wheel 214 at a side adjacent the first pulley wheel 212 and is shaped to fit into the internal ratchet 232. The pawls 238 are arranged to engage with the ratchet 232. The ratchet mechanism is designed so that the pulley wheels 212, 214 are prevented from rotating relative to each other in one direction, but are able to rotate relative to one another in the other direction.

Two mounting arms 226, 227 attach to and lie against the outside surface of each respective side plate 218, 219, extending outward to join a short distance from the frame 216. Each arm 226, 227 is in the form of a strip, a first end of which lies coplanar with and against the side surface of the frame casing 216, and which is bent through substantially a right angle at the other end. Each arm is bent in the same direction. Thus, the arm 226 adjacent the first pulley wheel 212 is bent outwards, and the other arm 227 is bent inwards. A cam cleat 228 is attached to the mounting arms 226, 227 at their bent ends, such that a rope may be fed through the cam cleat 228 onto the first pulley wheel 212, the cam cleat 228 in this way being aligned with the first pulley wheel 212.

In use, as shown in FIGS. 16, 17 and 18, a continuous rope 248 runs around the first pulley wheel 212 of the pulley 210, around a pulley wheel 260 of a normal block 262 which is attached to a load (not shown), then around the second pulley wheel 214 of the pulley 210.

A first gear ratio of 1:1 is obtained by pulling simultaneously both lengths of the loop 258 entering the pulley 210. This causes the first pulley wheel 212 and the second pulley wheel 214 to turn in opposite directions. In this situation, the ratchet mechanism allows the pulleys 212, 214 to turn in opposite directions. The three pulley wheels 212, 214, 260 work together to achieve the 1:1 gear ratio.

A second gear ratio of 2:1 is obtained by securing the rope 248 in the cam cleat 228 and pulling on the loop 258 from the second pulley wheel 214. In this way, pulley wheels 214, 260 rotate as the rope 248 is pulled and pulley wheel 212 is prevented from rotating as the rope 248 is jammed in the cam cleat 228. The pulley wheel 260 rotates slowly. In this situation, the ratchet mechanism allows the second pulley wheel 214 to turn relative to the first pulley wheel 212 in this direction only. The two pulley wheels 214, 260 work together thus a 2:1 gear ratio is achieved.

A third high power gear ratio of is obtained by pulling on the free length of the loop 258 from the first pulley wheel 212 and allowing the other length to run out freely. In this way, the pulley wheels 212, 214 rotate in the same direction. The second pulley wheel 214 is prevented from rotating relative to the first pulley wheel in this direction by the ratchet mechanism, and so the second pulley wheel 214 cannot overtake the first. The difference in radii of the pulley wheels 212, 214 creates a differential and a high power gear ratio of 9.5:1 is achieved in a similar way to the known differential pulley. As in the first embodiment, the first pulley wheel 212 must not slip relative to the rope 248 in use in this way. In this embodiment, a grooved pulley wheel 212 is used instead of a drum-shaped pulley wheel 112, and the rope is reaved around the grooved pulley wheel 212 along about 1/4 of the wheel's circumference. Ideally, to prevent slippage in this system, the total friction between the rope 248 and the pulley wheel 212 should be such that the ratio of tension between the two ends of the rope 248 is greater than half the high gear ratio. Therefore, as there is less contact between the rope 248 and pulley wheel 212 of this embodiment, the friction coefficient must be greater than that of the first embodiment. The faceted grooved pulley wheel 212 of this embodiment achieves a sufficiently high friction coefficient.

If the free end of the rope 248 through the cam cleat 228 is released, the friction around the first pulley wheel 214 is reduced and the rope may slip. A quick release of the load attached to the pulley 210 is achieved in this way.

FIGS. 28 and 29 show an alternative arrangement of use. Here, a continuous rope 248 runs through a cam cleat 228 attached to a standard fiddle block 252, around a first pulley wheel 250 of the fiddle block 252, then to and around the first pulley wheel 212 of the pulley 210, which is attached to a load (not shown), then around a second pulley wheel 254 of the fiddle block 252, around the second pulley wheel 214 of the pulley 210 and through a feed 256 in the fiddle block 252. The rope 248 is reaved in the opposite direction around the first and second pulley wheels 212, 214. A free loop 258 is formed in the rope 248 at the fiddle block 252.

A first gear ratio of 2:1 is obtained by pulling simultaneously both lengths of the loop 258 entering the fiddle block 252. This causes the fi