WO2002050446A1

WO2002050446A1 - A one-way clutch

Info

Publication number: WO2002050446A1
Application number: PCT/IB2001/002613
Authority: WO
Inventors: Mark Parry Owen
Original assignee: Baylis, Dudley, Edward
Priority date: 2000-12-21
Filing date: 2001-12-21
Publication date: 2002-06-27
Also published as: WO2002050446B1; AU2002216307A1

Abstract

A one-way clutch (1) is disclosed. The clutch includes a sleeve (3) securable to a shaft (2) and a coaxial housing (4) having an inner right circular cylindrical gripping surface rotatable relative to the sleeve. It also includes at least one gripping shoe (6) between the sleeve and the housing with a gripping surface coaxial with the housing. The gripping shoe effective gripping surface circumference is increasable and decreasable through relative rotation of the sleeve and the housing. The clutch includes means to control (5) the increase and decrease of the gripping shoe gripping surface circumference such that when the circumference is increased the gripping surface of the gripping shoe grips the gripping surface of the housing and when the circumference is decreased the gripping shoe is released from the housing. The invention also extends to a clutch in which the gripping shoe grips the sleeve upon decrease of the gripping shoe gripping surface circumference.

Description

A ONE-WAY CLUTCH

FIELD OF THE INVENTION

This invention relates to the field of sprag clutches and one-way clutches used on rotating shafts or rotating housings.

BACKGROUND TO THE INVENTION

Rotating shafts are widely used to transmit output from a prime mover such as an electrical motor to applications such as gearboxes, hoists and so forth. In many of these applications it is important that the shaft be allowed to rotate in one direction only. In some applications the shaft is stationary but a housing is rotated around the stationary shaft. In many of these applications it is important that the housing be allowed to rotate in one direction only.

In applications such as hoists, for example, it can be critical that rotation be allowed in one direction only. If an electrical motor were to fail with a load partly lifted, the load would run back under the force of gravity. This could lead to economic loss and loss of life. Over the years, there have been attempts to provide output shafts with gripping or braking mechanisms. One-way clutches that have been developed include band-brakes, multi-element sprag clutches, chain clutches, and so forth.

Since multi element sprag clutches employ rolling line contact between the sprag elements and their inner and outer rings, the number of grip and release cycles possible before surface flaking or spalling and consequent failure occurs would be similar to that experienced in ball and roller bearings. There is some concern that multi element sprag clutches do not fulfill the requirement for multiple grip and release cycles due to the principles of operation employed which require multiple numbers of elements to simultaneously grip and release a shaft.

Further, for high transmission torques the physical size of a multi element one-way clutch can become large thus creating a bulky transmission device.

Thus the utilisation of multi element sprag clutches for multiple grip and release cycles would only provide limited operating life before major overhaul would be required, and would likely result in a bulky device which would likely exhibit random slippage.

In addition, existing multi element one-way clutches are manufactured from high strength refined materials due to the high internal contact stresses experienced during operation. This causes the cost of manufacture to be high.

Furthermore band brakes are expensive to manufacture due to the requirement for special operating profiles. They also do not present a compact operating device within an outer ring diameter for compact design considerations. Chain clutches exhibit similar problems. OBJECT OF THE INVENTION

It is an object of this invention to provide a one-way clutch for a rotatable shaft or housing that at least partly alleviates the above mentioned problems.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a one-way clutch comprising a sleeve securable to a shaft, a coaxial housing having an inner right cylindrical gripping surface rotatable relative to the sleeve; at least one gripping shoe between the sleeve and the housing having a part right circular cylindrical gripping surface coaxial with the housing; the gripping shoe effective gripping surface circumference being increasable and decreasable through relative rotation of the sleeve and the housing; and means to control the increase and decrease of the shoe gripping surface circumference such that when the circumference is increased the shoe gripping surface grips the housing gripping surface and when the circumference is decreased the gripping shoe is released from the housing gripping surface.

The invention also provides for a one-way clutch comprising a housing, a coaxial sleeve securable to a shaft having an outer right cylindrical gripping surface rotatable relative to the sleeve; at least one gripping shoe between the sleeve and the housing having a part right circular cylindrical gripping surface coaxial with the sleeve; the gripping shoe effective gripping surface circumference being increasable and decreasable through relative rotation of the sleeve and the housing; and means to control the increase and decrease of the gripping shoe circumference such that when the circumference is decreased the shoe gripping surface grips the sleeve gripping surface and when the circumference is increased the gripping shoe is released from the sleeve gripping surface. • The invention further provides for a one-way clutch comprising a sleeve securable to a shaft and a housing rotatable relative to each other with at least one gripping shoe between the sleeve and the housing, a connecting lever pivotally mounted at one end thereof with respect to one of the sleeve and the housing and pivotally and slidingly connected at another end thereof to the gripping shoe, the gripping shoe effective operating diameter being expandable and contractible and the one-way clutch including means to control the expansion and contraction of the gripping shoe, such that when the gripping shoe is expanded it is forced into gripping contact with the housing and when the gripping shoe is contracted it is released from the housing.

There is also provided for the expansion and contraction to be controlled through relative rotation of the sleeve and housing and the connecting lever being orientated relative to the sleeve and housing such that when the sleeve and housing are relatively rotated in one direction the gripping shoe is expanded and when the sleeve and housing are relatively rotated in the other direction the gripping shoe is contracted.

The invention also provides for the gripping shoe to be a radially split ring and for the ring to be expandable and contractible through a force applied between the split ends of the ring.

There is also provided for the connecting lever to be connected to the gripping shoe through slidable and rotatable slippers between the connecting lever and complimentarily shaped formations on the gripping shoe.

There is further provided for the gripping shoe to have at least two formations, one at each end thereof, a first formation at a first end of the gripping shoe being located on a smaller pitch circle diameter from the shaft centre than a second formation at a second end of the gripping shoe. The invention further provides for rotation of the sleeve in one direction to cause the connecting lever, acting through the slippers, to force the first formation to a larger effective pitch circle diameter and the second formation to a larger effective pitch circle diameter to expand the gripping shoe to grip the housing, alternatively for rotation of the housing to cause the connecting lever, acting through the slippers, to force the first formation to a smaller effective pitch circle diameter and the second formation to a smaller effective pitch circle diameter to contract the gripping shoe to grip the sleeve.

The invention also provides for a biasing means between the gripping shoe and the housing, or alternatively between the gripping shoe and the sleeve, and for the biasing means to be a spring.

The invention also provides for the connecting lever to include a centrifugal weight arranged to act on the gripping shoe at a predetermined rotational speed of the sleeve against the force of the biasing means, to cause the gripping shoe effective operating diameter to be contracted to provide a clearance between the gripping shoe and the housing, alternatively to act on the gripping shoe at a predetermined rotational speed of the housing against the force of the biasing means, to cause the gripping shoe effective operating diameter to be expanded to provide a clearance between the gripping shoe and the sleeve.

There is further provided for the gripping shoe to include engaging formations at the ends thereof for the connecting lever to act upon when rotation of the sleeve or housing causes the centrifugal weight to overcome the force of the biasing means.

A further feature of the invention provides for the gripping shoe to be configured such that the connecting levers act on the slippers through substantially the same plane in the lever, for a first end of the gripping shoe to be bifurcated and the other end complimentarily shaped, and for the connecting lever to be complimentarily shaped to be located between a bifurcated and matching end of a gripping shoe acting on the housing.

The invention further provides for a one-way clutch in which the control means includes a toggle rotatably secured to the sleeve; an actuating lever; a formation in each end of the gripping shoe a first formation acting at a first diameter about the shaft axis and a second formation acting at a smaller diameter about the shaft axis; a complimentarily shaped slipper rotatably secured in each formation, each slipper having a face complimentarily shaped to match the face of an adjacent slipper such that two opposing slippers form a pair of slippers acting upon each other at a substantially flat contact face; the toggle being rotatable by the sleeve to cause each lever to engage a pair of slippers to urge each gripping shoe gripping surface circumference to increase.

There is also provided for the one-way clutch to include biasing means between the sleeve and the lever to urge the lever to disengage from the pair of slippers; and biasing means between the gripping shoe and the sleeve to urge the gripping shoe into sliding contact with the housing gripping surface.

There is still further provided for the pair of slippers to engage each other on at most a substantial part of their mutual contact faces and for the lever to engage each slipper on a part of its face that is unengaged by the other slipper of the pair of slippers.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described by way of example only and with reference to the drawings in which FIG 1 is an end view of a first embodiment of the invention that shows a shaft around which a one-way clutch device according to the invention is located;

FIG 2 is an end view of a second embodiment of the invention that shows a shaft around which a one-way clutch suitable for high overrun shaft speeds is located;

FIG 3a is an end view of a third embodiment of the invention that shows a one-way clutch device incorporating a single plane lever;

FIG 3b shows detail of the single plane lever design of the third embodiment;

FIG 3c shows a view on sections taken through the lever of figure 3b; and

FIG 3d shows a perspective view of a single plane lever and slippers according to the third embodiment of the invention.

FIG 4 shows an end view of a fourth embodiment of the invention.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

A one-way clutch according to the invention is generally depicted by numeral (1). As shown in figure 1 the one-way clutch (1) is eatable around a shaft (2) and comprises a sleeve (3), an outer ring (4), suitably arranged levers (5), gripping shoes (6), inner self aligning slippers (7), outer self aligning slippers (8) and lever hinge pins (9). The sleeve (3) incorporates a flange (not shown) at each end of its axis of rotation. Three holes (not shown) circumferentially equally positioned around the shaft (2) and on the same pitch circle diameter around the shaft (2) central axis are arranged through both end flanges to suit lever hinge pins (9) with their central axes parallel to that of the shaft (2). A lever (5) is arranged to hinge around each lever hinge pin (9).

Each lever (5) has suitably flat faces incorporated into its shape to suit the inner self aligning slipper (7) and the outer self aligning slipper (8).

Each gripping shoe (6) has two profiled grooves (not shown), both axially aligned with the shaft (2). One groove is located in the inner end face (11) and matches the inner slipper (7) of a lever (5), and the other groove is located in the outer end face (10) and matches the outer slipper (8) of lever (5).

Therefore each lever (5) is in contact with two neighbouring shoes (6) through an inner slipper (7) and an outer slipper (8), and each shoe (6) is in contact with two levers (5) through an inner slipper (7) at its inner end face (11) and an outer slipper (8) at its outer end face (10).

Each gripping shoe is forced into contact with the outer ring (4) by means of a spring (12).

If, in the embodiment shown in figure 1 , the outer ring (4) is held firm and the shaft (2) is rotated in a clockwise direction, the sleeve (3), which is fixedly attached to the shaft (2), causes each lever hinge pin (9) to apply a force to the lever (5) inner end (13). This force will have the effect of attempting to rotate the lever (5) against the frictional resistance or drag of the gripping shoes (6) against the outer ring (4), thereby causing the lever to tend to rotate in an anti-clockwise direction. The centre of rotation of outer slipper (8) is on a pitch circle diameter around the shaft (2) that is larger than the corresponding pitch circle diameter on which the centre of rotation of inner slipper (7) lies. Attempted anti-clockwise rotation of lever

(5) will increase the circumferential distance between the grooves in inner end face (11) and outer end face (10) as a result of the tendency of the rotation to move the centre of rotation of outer slipper (8) to a large pitch circle diameter and the centre of rotation of inner slipper (7) to a larger pitch circle diameter around the shaft (2). This increase in distance occurs equally and simultaneously at all the levers, as a result of the equalization of forces acting on the gripping shoes, and tends to increase the effective circumferential length of the shoes around the shaft. The result is that the gripping shoes (6) lock into frictional non-slipping contact with the outer ring (4) thereby immediately and instantaneously resisting and holding the torque applied to the hub (3).

By suitable arrangement of the geometry of each lever (5), specifically the dimensional relationship between its inner end (13), the point of application of the torque force applied through the sleeve (3) to the lever via the lever hinge pin (9), the transfer of this force to the gripping shoes

(6) and the resulting forces applied to the outer slipper (8) and the inner slipper (7), the mechanical advantage that causes the gripping shoes (6) to grip the outer ring (4) can be arranged to ensure that the gripping torque between the gripping shoes (6) and the outer ring (4) is greater than the applied torque at the shaft (2) to such a degree that immediate and instantaneous gripping without slippage between the shoes (6) and the outer ring (4) is achieved.

If, in the embodiment shown in figure 1 , the outer ring (4) is held firm and the shaft (2) is rotated in an anti-clockwise direction the sleeve (3) causes each lever hinge pin (9) to attempt to rotate each lever (5) in a clock-wise direction thereby tending to disengage the lever flat faces from the outer slippers (8) and inner slippers (7). This consequently removes the forces applied to the gripping shoe end faces (10,11). Consequently, any strain energy applying force from the gripping shoe (6) end faces (10,11) acting as a couple to the lever (5) can only be resisted by the friction between the contacting surfaces of the linkage formed by the gripping shoes (6), the outer slippers (8), the inner slippers (7) and the levers (5). Since the frictional resistance couple is arranged by the configuration of the one-way clutch to be less than any strain energy couple applied to the lever (5), the lever (5) will rotate in a clockwise direction thereby relieving the contact pressure applied by the gripping shoes (6) upon the outer ring (4). The result is that the one-way clutch enables overrun to take place when the shaft (2) is rotated in the anti-clockwise direction of rotation.

Further, when the shaft (2) is rotated in the anti-clockwise direction of rotation the sleeve (3) operating upon the lever hinge pins (9) forces rotation of the lever (5) in such a manner as to allow or tend to cause a circumferential contraction of the effective position of the gripping shoes (6) within the outer ring (4) through the resulting removal of the forces applied to the outer self aligning slipper (8) and the inner self aligning slipper (7) thereby relieving the contact pressure applied by the gripping shoes (6) upon the outer ring (4). Consequently, the one-way clutch further enables overrun to take place when the shaft is rotated in the anticlockwise direction of rotation.

A second embodiment of the invention is shown in figure 2. This embodiment finds particular use in applications in which a one-way clutch is required to operate with relatively high overrun shaft rotational speeds in the non-gripping direction of shaft rotation.

A one-way clutch according to the second embodiment of the invention is generally depicted by numeral (21) in figure 2. As shown, the one-way clutch (21) is substantially identical to that depicted in figure (1) but has the additional features of suitably positioned centrifugal masses (33) attached to or integral with the levers (25). Further, each lever (25) has a hook protrusion (34) suitably formed to engage upon a loosely matching cavity (35) arranged at the end or end face (31) of each gripping shoe (26). Further, each gripping shoe end face (31) has a suitably formed shoe-restraining finger (36) protruding through or past the lever (25) and arranged to loosely engage in a finger-matching cavity (37) in the adjacent end or end face (30) of each gripping shoe (26)..

Upon commencement of rotation of the shaft (22) in an anti-clockwise direction, the one-way clutch (21) will allow rotation as described above. As the speed of rotation of the shaft (22) increases to a pre-determined value the centrifugal masses (33) act upon the levers (25) causing the levers (25) to rotate clockwise and inwards towards the hub (23) around lever hinge pins (29) until a rotational limit stop (not shown) is reached. The action of clockwise rotation of the levers (25) around the lever hinge pins (29) causes the hook protrusions (34) to engage with the loosely matching cavities (35) and draw the shoe end (31) away from the outer ring (24) inner surface thus creating a running clearance between gripping shoe (26) and the outer ring (24) at its inner end face (31).

As the gripping shoe (26) end face (31) is drawn inwards, as described above, the shoe restraining finger (36) acts upon the finger-matching cavity (37) and similarly draws gripping shoe (26) end (30) away from the outer ring (24) inner surface thus creating a running clearance between the outer ring (24) inner surface and the gripping shoes (26). Therefore, since both ends (30,31) of each gripping shoe (26) are drawn inwards towards the hub (23) until seated as suitably arranged upon the hub or suitably arranged seat (23), the gripping shoes (26) are maintained with a pre-determined running clearance from the outer ring (24) inner surface at all times while the shaft (22) speed of rotation is higher than the speed pre-determined for the centrifugal masses (33) to overcome the predetermined spring (32) force acting upon the gripping shoes (26) in a radial direction in order to cause frictional engagement at a predetermined lower speed of rotation of the shaft (22).

A third embodiment of the invention is shown in figures 3a, 3b and 3c. This embodiment is used for applications in which a one-way clutch is required to operate with low or near zero release torque when the gripping torque applied is reversed and with minimum lever rotational movement between the gripping position and the release position.

A one-way clutch according to the third embodiment of the invention is generally depicted by numeral (40) in figure 3a. As shown, the one-way clutch (40) is substantially similar to that depicted in figures 1 and 2 above but has the additional features of a lever (41 ) arranged to ensure practically near zero release torque upon reversal of the applied gripping torque at the hub (44). This is achieved as depicted in Figures 3b and 3c by arranging the configuration of the lever (41) to facilitate the effective application of forces applied to each lever (41) through inner self-aligning slipper (43) and outer self-aligning slipper (42) to be on a single plane, such plane having zero or near zero effective depth of section.

This is achieved by suitably arranging inner self aligning slipper (43) to act upon a middle portion of the lever and separating outer self aligning slipper (42) into two halves (42a, 42b), each half acting on outer portions of the lever (41) beside but on the same plane of action as the inner self aligning slipper (43). The design of the lever (41) is shown in perspective view in figure 3d, detail of the lever (41 ) design is shown in figure 3b and sections through the lever (41) are shown in figure 3c.

The arrangement of the gripping shoes (45) is changed to include gripping shoes that have two suitably arranged end face protrusions arranged to be acted upon by the two half self-aligning slippers (42a, 42b) which in turn are acted upon by the lever (41).

By this means any reversal or torque applied to the lever (41) by the sleeve (44) will result in the lever (41) tending to remove its contact with the inner slipper (43) and the two outer slippers (42a, 42b) without the requirement for any sliding contact action between the lever (41) and the inner slipper (43), and the lever (41) and the outer slippers (42a, 42b).

Furthermore, such reversal of torque applied to the lever (41) by the sleeve (44) will result in the lever (41) tending to remove its contact with the inner slipper (43) and the outer slippers (42a, 42b) without the requirement for any appreciable sliding or rotation of the inner slipper (43) or the outer slippers (42a, 42b) within their respective axial seating grooves positioned in gripping shoe (45) outer end face (46) and inner end face (47) or in their contact surfaces with the lever (41).

A fourth embodiment of the invention is shown in figure 4. In this embodiment the one-way clutch is generally indicated by numeral 100. As shown in figure 4 the one-way clutch (100) is beatable around a shaft (102) and comprises an sleeve (103), an outer ring (104), suitably arranged levers (105), gripping shoes (106), inner self aligning slippers (107), outer self aligning slippers (108) and toggles (109).

Three pivotal locations circumferentially equally positioned around the shaft (102) and on the same pitch circle diameter around the shaft (102) central axis are arranged on the sleeve (103) outer surface to suit toggle (109) end radius with their central axiis parallel to that of the shaft (102). Each lever (105) is arranged to be rotatably located about protrusion (110) having its central axis parallel to that of the shaft (102) when acted upon by toggle (109) upon clockwise rotation of shaft (102) and sleeve (103). Each lever (105) has suitably flat faces (116,117) incorporated into it's shape at the ends of flanges (119,120) integral with the lever (105) to engage with and act upon a predetermined portion of the inner self aligning slipper (107) and the outer self aligning slipper (108) flat faces such that the remaining portions of the flat faces of each self aligning slipper (107) and (108) are arranged to be free to engage with each other face to face.

The contact surface pressures generated can be minimised thereby facilitating the utilisation of either lower working stresses within the materials of manufacture for the items or relatively higher load carrying capacity. The lever (105) flanges (119,120) flat faces (116,117) act upon a single plane together with the plane of contact between the self aligning slippers (107, 108). This facilitates low friction release of the contacting surfaces upon removal of the torque applied to the sleeve (103) in the gripping direction.

Each flange (119,120) has a curved sectional profile that generally follows the radius of curvature of the outer ring (104) and the inner ring (103) respectively. This facilitates maximisation of the shoe ends (111 ,112) cross sectional area which protrude adjacent to each flange (119,120) and provide location for self aligning slippers (107,108) seating grooves for gripping forces transmission.

Each gripping shoe (106) has a profiled axially aligned groove situated in one end face (111) to suit an outer self aligning slipper (108) and a profiled axially aligned groove situated in the other end face (112) to suit the inner self aligning slipper (107). The profiled axially aligned grooves are located upon protrusions of the shoe ends (111 ,112). The lever (105) is arranged with integral side cheek plates to engage the toggles (109) at each side of the shoe ends (111,112). The side cheek plates are positioned at and clear of each side of the shoe ends (111,112). The shoe ends (111 , 112) are also clear of the lever (105) flanges (119,120). By such arrangement the lever (105) is free to partially rotate as a consequence of the action of the toggle (109) when the shaft (102) and sleeve (103) are rotated.

Each gripping shoe (106) is suitably forced into contact with the outer ring

(104) by means of a spring (113).

In the example shown if the outer ring (104) is held firm and the shaft (102) is rotated in a clockwise direction, the sleeve (103), which is secured to the shaft (102), causes each toggle (109) to apply a force to the lever

(105) actuated end (114).

This force will have the effect of attempting to rotate the lever (105) against protrusion (110) and also against the frictional resistance of the gripping shoes (106) against the outer ring (104) thereby causing the lever to tend to rotate thus causing a circumferential expansion of the effective position of the gripping shoes (106) within the outer ring (104) through the resulting action of the levers (105) upon the outer self aligning slippers (108) and the inner self aligning slippers (107) upon the gripping shoes end faces (112,111). The result is that the gripping shoes (106) lock into frictional non-slipping contact with the outer ring (104) thereby resisting and holding the torque applied to the sleeve (103).

By suitable arrangement of the geometry of the operating linkage formed by the toggle (109) and each lever (105), specifically the dimensional relationship between the operating angle of the toggle (109) compared with the radial, the effective length of the lever actuated end (114), the point of application of the torque force applied through the sleeve (103) to the toggle (109) via the sleeve (103), the transfer of this force to the gripping shoes (106) and the resulting forces applied to the outer self aligning slipper (108) and the inner self aligning slipper (107) as a consequence of their predetermined different pitch circle radii of action upon the shoes (106) about the shaft (102) axis of rotation, the mechanical advantage that causes the gripping shoes (106) to grip the outer ring (104) can be arranged to ensure that the gripping torque between the gripping shoes (106) and the outer ring (104) is greater than the applied torque at the shaft (102), thereby causing immediate gripping.

In the example shown if the outer ring (104) is held firm and the shaft (102) is rotated in an anticlockwise direction the sleeve (103), which is secured to the shaft (102), causes each toggle (109) to attempt to rotate each lever (105) thereby tending to disengage the lever flat faces from the outer self aligning slippers (108) and inner self aligning slippers (107). This consequently removes the forces applied to each gripping shoe end (112,111).

As a consequence any strain energy applying force from the gripping shoe ends (112,111), acting as a couple about the self aligning slipper (107, 108), can only be resisted by the friction between the contacting surfaces of the linkage formed by the gripping shoes (106), the outer self aligning slippers (108), the inner self aligning slippers (107) the levers (105) and the toggles (109). Since the frictional resistance couples about the toggle (109) and self aligning slippers (107, 108) are arranged by the configuration of the invention to be less than any strain energy couple applied through the lever (105), the lever (105) will rotate in a clockwise direction thereby relieving the contact pressure applied by the gripping shoes (106) upon the outer ring (104). Consequently the one-way clutch enables overrun to take place when the shaft (102) is rotated in the anticlockwise direction of rotation. Further, when the shaft (102) is rotated in the anticlockwise direction of rotation the sleeve (103) operating upon the toggles (109) and any retaining device such as springs (113), forces rotation of the lever (105) in such a manner as to allow or tend to cause a circumferential contraction of the effective position of the gripping shoes (106) within the outer ring (104) through the resulting removal of the forces applied to the outer self aligning slipper (108) and the inner self aligning slipper (107) thereby relieving the contact pressure applied by the gripping shoes (106) upon the outer ring (104). Consequently the one-way clutch further enables overrun to take place when the shaft is rotated in the anticlockwise direction of rotation.

The invention thus achieves the objective of a compact shaft gripping device that grips a shaft hub instantaneously, is capable of transmitting high torques whilst gripping the hub and yet is capable of instantaneous release of the gripping effort without mechanical locking or substantial internal frictional resistance to releasing effort.

It is clear that all such arrangements described can be made to operate in the mirror image opposite directions of shaft rotation to that described above.

As a consequence of the comparatively large gripping shoe surface contact area with the outer ring inner diameter, the maximum gripping surface stress on a one-way clutch according to this invention can be significantly lower for a given application than for a sprag clutch according to the prior art.

This difference in maximum contact surface stress explains why it is possible to use less expensive materials of construction and why a oneway clutch according to the invention can operate through many repeated high torque grip and release cycles without contact surface deterioration due to high contact stresses.

Further by suitable arrangement of the load bearing contact surfaces throughout the invention all operating stresses within the invention can be low in comparison to conventional multi element sprag clutches or holdbacks.

Further as a consequence of the highly compact nature of the invention holdbacks according to the invention can be manufactured with minimal volumetric dimensions which facilitate installation in restricted spaces.

The invention thus achieves the objective of an outer ring gripping device that facilitates effective gripping between a shaft hub and an outer ring substantially instantaneously, is capable of transmitting high torques whilst gripping in one rotational direction and yet is capable of substantially instantaneous release of the gripping effort without mechanical locking or substantial internal frictional resistance to releasing effort when the shaft rotational direction is reversed.

The embodiments described above are only examples of embodiments of the invention. There are other embodiments of one-way clutches according to the invention that also fall within the scope of the invention.

It is for instance possible to use any number of shoes, depending on specific applications and requirements.

It is also possible to arrange the one-way clutch so that the shoes act upon the shaft or sleeve instead of the outer ring. Such an arrangement could be used when it is necessary that the housing be rotated and the shaft is kept stationary.

Claims

1. A one-way clutch comprising a sleeve securable to a shaft; a coaxial housing having an inner right circular cylindrical gripping surface rotatable relative to the sleeve; at least one gripping shoe between the sleeve and the housing having a part right circular cylindrical gripping surface coaxial with the housing; the gripping shoe effective gripping surface circumference being increasable and decreasable through relative rotation of the sleeve and the housing; and means to control the increase and decrease of the gripping shoe gripping surface circumference such that when the gripping surface circumference is increased the gripping surface of the gripping shoe grips the gripping surface of the housing and when the circumference is decreased the gripping shoe is released from the housing.

2. A one-way clutch as claimed in claim 1 which includes a connecting lever pivotally mounted at one end thereof with respect to the sleeve and pivotally and slidingly connected at another end thereof to the gripping shoe; and the connecting lever forming part of the control means.

3. A one-way clutch as claimed in claim 2 in which the connecting lever is orientated non-radially relative to the sleeve.

4. A one-way clutch comprising a sleeve securable to a shaft having an outer right circular cylindrical gripping surface; a coaxial housing rotatable relative to the sleeve; at least one gripping shoe between the sleeve and the housing having a part right circular cylindrical gripping surface coaxial with the sleeve; the gripping shoe effective surface circumference being increasable and decreasable through relative rotation of the sleeve and the housing; and means to control the increase and decrease of the gripping shoe gripping surface circumference such that when this circumference is decreased the gripping surface of the gripping shoe grips the gripping surface of the sleeve and when the circumference is increased the gripping shoe is released from the sleeve.

5. A one-way clutch as claimed in claim 4 which includes a connecting lever pivotally mounted at one end thereof with respect to the housing and pivotally and slidingly connected at another end thereof to the gripping shoe; and the connecting lever forming part of the control means.

6. A one way-clutch as claimed in claim 5 in which the connecting lever is orientated non-radially relative to the housing.

7. A one-way clutch as claimed in any of the preceding claims in which the gripping shoe is a radially split ring.

8. A one-way clutch as claimed in claim 7 in which the radially split ring is expandable and contractible through a force applied between the split ends of the ring.

9. A one-way clutch as claimed in any of the preceding claims in which the gripping shoe includes at least two formations, a first formation at a first end of the gripping shoe located on a smaller pitch circle diameter from the shaft centre than a second formation at a second end of the gripping shoe, the connecting lever is connected to the gripping shoe through slidable and rotatable slippers between the connecting lever and the formations on the gripping shoe, and the formations are complementarily shaped to the slippers.

10. A one-way clutch as claimed in claim 9 in which rotation of the shaft in one direction causes the connecting lever to force the first formation to a larger effective pitch diameter and the second formation to a larger effective pitch diameter to increase the effective gripping shoe gripping surface circumference, and rotation of the shaft in the other direction causes the connecting lever to allow the first formation to move to a smaller effective pitch diameter and the second formation to move to a smaller effective pitch diameter to thereby decrease the effective gripping shoe gripping surface circumference.

11. A one-way clutch as claimed in any of the preceding claims which include biasing means between the gripping shoe and the housing or alternatively between the gripping shoe and the sleeve.

12. A one-way clutch as claimed in claim 11 in which the biasing means is a spring.

13. A one-way clutch as claimed in any one of claims 2 or 3 in which the connecting lever includes a centrifugal weight, and the weight is arranged to force the lever to act against the gripping shoe at a predeterminable relative speed of rotation between the sleeve and the housing to decrease the effective gripping shoe gripping surface circumference.

14. A one-way clutch as claimed in claim 13 in which the connecting lever and gripping shoes includes complementarily shaped gripping formations, and the gripping formations are arranged such that they engage when the centrifugal weight forces the lever to act against the gripping shoe, to thereby at least assist in decreasing the effective gripping shoe gripping surface circumference.

15. A one-way clutch as claimed in claim 14 in which the gripping formations include a protrusion on the connecting lever and a complementarily shaped hole in the gripping shoe.

16. A one-way clutch as claimed in any one of claims 5 or 6 in which the connecting lever includes a centrifugal weight, and the weight is arranged to force the lever to act against the gripping shoe at a predeterminable relative speed of rotation between the sleeve and the housing to increase the effective gripping shoe gripping surface circumference.

17. A one-way clutch as claimed in claim 16 in which the connecting lever and gripping shoes includes complementarily shaped gripping formations, and the gripping formations are arranged such that they engage when the centrifugal weight forces the lever to act against the gripping shoe, to thereby at least assist in increasing the effective gripping shoe gripping surface circumference.

18. A one-way clutch as claimed in claim 17 in which the gripping formations include a protrusion on the connecting lever and a complementarily shaped hole in the gripping shoe.

19. A one-way clutch as claimed in any of claims 9 to 18 in which one connecting lever acts on the slippers of adjacent gripping shoes through substantially the same plane.

20. A one-way clutch as claimed in claim 19 in which a first end of the gripping shoe is bifurcated and the second end is complementarily shaped, and for the connecting lever to be shaped to be located between a bifurcated and matching end of a gripping shoe.

21. A one-way clutch as claimed in claim 1 in which the control means includes a toggle rotatably secured to the sleeve; an actuating lever; a formation in each end of the gripping shoe; a complimentary slipper rotatably secured in the formation, the slipper having a face complimentarily shaped to the face of an adjacent slipper such that two opposing slippers form a pair of slippers; the toggle being rotatable by the sleeve to cause each lever to engage a pair of slippers to urge the gripping shoe gripping surface circumference to increase.

22. A one-way clutch as claimed in claim 4 in which the control means includes a toggle rotatably secured to the housing; an actuating lever; a formation in each end of the gripping shoe; a complimentary slipper rotatably secured in the formation, the slipper having a face complimentarily shaped to the face of an adjacent slipper such that two opposing slippers form a pair of slippers; the toggle being rotatable by the housing to cause each lever to engage a pair of slippers to urge the gripping shoe gripping surface circumference to decrease.

23. A one-way clutch as claimed in claim 21 or 22 which includes biasing means between the sleeve and the lever to urge the lever to disengage from the pair of slippers.

24. A one-way clutch as claimed in claim 21 to 23 which includes biasing means between the gripping shoe and the sleeve to urge the gripping shoe into sliding contact with the housing gripping surface.

25. A one-way clutch as claimed in any one of claims 21 to 24 in which the pair of slippers engage each other on at most a substantial part of their faces and the lever engages each slipper on a part of its face that is unengaged by the other slipper of the pair of slippers.

26. A one-way clutch substantially as herein described with reference to figure 1.

27. A one-way clutch substantially as herein described with reference to figure 2.

28. A one-way clutch substantially as herein described with reference to figures 3a, 3b, 3c, and 3d.

29. A one-way clutch substantially as herein described with reference to figure 4.