BACKGROUND TO THE INVENTION One type of continuously variable transmission uses an input shaft that provides a variable reciprocating motion by means of an appropriate linkage. The reciprocating motion is used to rotate a one-way clutch around an output shaft and the clutch is arranged to grip the output shaft when rotated in one direction and to release it when rotated in the other direction. The rotation when the clutch does not grip the output shaft is to reposition the clutch in readiness for a further gripping cycle.

Variable speeds of output shaft rotation can be achieved depending on the degree of reciprocation selected. A number of such one way clutches arranged to operate sequentially on an output shaft can result in a continuous speed of rotation of the shaft for any given degree of reciprocation selected as each clutch in turn grips, rotates and releases the output shaft.

However, such continuously variable transmissions are unable to provide overrun torque transmission through the device due to the inherent nature of the one way clutches employed, which will freewheel when the load starts to overrun the prime mover since the one way clutches can only transmit torque in the driving direction of rotation.

Cone clutches use a drum with a frusto conical inner gripping surface. In one typical application the drum is secured to an output shaft and a contact plate with a conical outer surface is moved coaxially along the shaft to engage the drum.

The drum is secured to a prime mover and is rotated by it. The conical surfaces of the drum and plate have the same angle in relation to the shaft, which enable them to form a tight grip upon contact.

Upon contact the plate and drum lock together and motion from the prime mover is transmitted through the contact plate to the shaft. Substantial lateral force is required to release the plate from the drum. A lower cone angle of the drum and plate results in a higher gripping force between them, which makes higher torque transmission possible. Unfortunately this also results in a higher required force to release the plate from the drum. Practically most cone clutches have a minimum angle of about 12 degrees, since conical angles less than this tend to require a lateral release force that is unacceptably high.

The limitation on the minimum cone angle therefore limits the maximum possible torque transmission of the clutch.

OBJECT OF THE INVENTION It is an object of this invention to provide a conical clutch that alleviates at least some of the above-mentioned problems and that can be used in continuously variable transmissions.

SUMMARY OF THE INVENTION In accordance with this invention there is provided a clutch including at least first and second members; the first member having a frusto conical gripping surface located coaxially around a shaft; the second member having a base and at least one gripping formation with a complementarily shaped gripping surface, the formation being movably secured to the base to be movable between a supported position and an unsupported position; at least one of the members being secured to the shaft to be axially movable along the shaft between an engaged position and a disengaged position, and the other member being rotatably securable around the shaft, and one of the members being rotatable by a prime mover; wherein movement of the axially movable member into the engaged position causes the formation gripping surface and the frusto conical gripping surface to engage with the formation being in the supported position; and wherein movement of the axially movable member to the disengaged position causes movement of the formation to the unsupported position and the formation gripping surface and the frusto conical gripping surface to disengage, thereby enabling selective motion transfer from the prime mover to the shaft.

There is further provided for the second member to be axially movable along the shaft and for the first member to be rotatably securable around the shaft.

There is further provided for the gripping formation to be rotatably secured to the base and to be rotatable between the supported position and the unsupported position.

There is further provided for the gripping formation to be supported by the base, and for the gripping formation to be biased to the supported position.

There is further provided for a recess in the base to provide the support for the gripping formation, for the gripping formation to be axially movable along its axis of rotation, and for the axial movement of the gripping formation to be bounded by edges of the recess.

There is still further provided for a plurality of gripping formations to be evenly spaced around the shaft.

There is also provided for the contact area between the gripping formation gripping surface and the frusto conical gripping surface to have a boundary that includes a line or point of greatest radial distance of the contact area from the shaft; for the rotational point of the gripping formation to lie on a radial line extending from the shaft which intersects the conical gripping surface at a point of intersection; and for the point of intersection to have a radial distance greater than the greatest radial distance of the line or point of the contact area with the greatest radial distance from the shaft.

There is further provided for the part of the gripping formation gripping surface that corresponds with the line of greatest radial distance of the contact area from the shaft to be beveled, thereby leaving the operatively outermost corners of the gripping formation free of contact with the frusto conical gripping surface.

The invention also provides for the gripping formation of the second member to be at least partly located between transmission faces, for the transmission faces to form part of a transmission member, for the transmission member to be securable to the shaft, for the first and second members to be rotatably securable around the shaft.

There is still further provided for the gripping drum conical angle relative to the shaft axis to be less than 12 degrees, preferably between about 3 and 7 degrees.

There is also provided for the first member to be driven by the prime mover.

A further feature of the invention provides for the gripping formation to be engageable with the shaft and for movement of the axially movable member into the engaged position to cause the formation gripping surface to grip the shaft, thereby enabling selective motion transfer from the prime mover to the shaft.

A further feature of the invention provides for a clutch comprising a drive hub securable around a shaft, a gripping drum located at least partly around the shaft, and connecting means to releasably connect the drive hub and the gripping drum; the gripping drum being rotatable by a prime mover, the connecting means including an actuated hub located at least partly around the shaft and adapted to be engageable with the drive hub and the gripping drum; whereby actuation of the actuated hub causes the actuated hub to engage with the drive hub and the gripping drum, thereby connecting the gripping drum and the drive hub to enable rotation of the output shaft.

The invention also provides for a continuously variable transmission comprising a reciprocating device adapted to be moved by at least one prime mover, and the gripping drum to be connected to the reciprocating device to be rotated thereby.

There is also provided for the reciprocating device to be a variable reciprocating device and for an amount of reciprocation to determine an effective ratio of transmission of the continuously variable transmission.

The invention also provides for the connecting means to include at least one elongate member pivotally secured to the actuated hub at a first end thereof and extending from the actuated hub, for the drive hub to include engaging

formations, and for each elongate member to be engageable with a drive hub engaging formation at a second end of the elongate member.

There is also provided for biasing means to urge the second end of each elongate member into engagement with a drive hub engaging formation.

The invention also provides for each drive hub engaging formation to be defined by a slot having at least two sidewalls in the drive hub, and for the elongate member to slidingly engage the slot between the two sidewalls, for the elongate member to abut the first sidewall upon torque transmission from the gripping drum to the shaft in a first direction of rotation and for the elongate member to abut the second sidewall upon torque transmission from the gripping drum to the shaft in the same first or a second direction of rotation, thereby enabling torque transmission from the gripping drum to the shaft in either directions of rotation.

The invention also provides for the elongate member to abut the second sidewall upon torque transmission from the shaft to the gripping drum in the first direction of rotation, and for the elongate member to abut the first sidewall upon torque transmission from the shaft to the gripping drum in the second direction of rotation, thereby providing overrun torque transmission for the shaft.

There is also provided for the elongate members to be spaced around the actuated hub.

The invention further provides for the actuated hub to be axially movable relative to the shaft, for the elongate members to describe an effective diameter around the actuated hub, for movement of the actuated hub towards the drive hub to cause the effective diameter to increase and the elongate members to engage the gripping drum, and for movement of the actuated hub away from the drive hub to cause the effective diameter to decrease and the elongate members to disengage the gripping drum.

The invention further provides for the elongate member to engage the gripping drum at the second end of the elongate member, and for a friction lining to be removably secured to the second end of the elongate member.

The invention also provides for movement of the actuated hub toward the drive hub to be timed to coincide with rotation of the gripping drum by the variable reciprocating device in a driven direction thereby timing connection of the gripping drum and drive hub to rotate the shaft in the driven direction of rotation, and for movement of the actuated hub away from the drive hub to coincide with rotation of the gripping drum by the variable reciprocating device in a non-driven direction thereby timing disconnection of the gripping drum and drive hub to not rotate the shaft in the non-driven direction of rotation.

A further feature of the invention provides for the clutch to include an adjustable travel limit, whereby movement of the actuated hub is limited by the travel limit thereby limiting the contact force between the gripping drum and the elongate member.

The invention also provides for the travel limit to comprise an annular ring removably secured to the drive hub, and for the amount of movement limitation of the actuated hub to be adjustable by adjusting the thickness of the annular ring, and for the thickness of the annular ring to be adjustable by securing annular rings of differing thickness to the drive hub.

A still further feature of the invention provides for the shaft to be rotatable by a prime mover, and for actuation of the above described actuated hub to cause the connecting means to engage with the drive hub and the gripping drum, thereby connecting the shaft and the gripping drum to enable rotation of the gripping drum.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described below by way of example only and with reference to the accompanying drawings in which: Figure 1 is a part sectional view of a first embodiment of a clutch according to the invention; Figure 2 is detail of the biasing means of the clutch shown in Figure 1; Figure 3 is an end view through the clutch of Figure 1; Figure 4 is detail of the clutch gripping formation of Figure 1's upper edge showing it's beveling ; Figure 5 is a part sectional view of a second embodiment of a clutch according to the invention; Figure 6 is an end view of a third embodiment of a clutch according to the invention, operating around a shaft; and Figure 7 is a part sectional view through the clutch of Figure 6 operating around an output shaft.

DETAILED DESCRIPTION OF THE DRAWINGS A clutch according to the invention is generally indicated in figure 1 by numeral (1). The clutch includes a drive hub (2) and a gripping drum (3) both coaxially located around a shaft (4). The gripping drum (3) is rotatably connected to a prime mover (not shown), and is located freely rotatable around the shaft (4) by means a set of bearings (5). The gripping drum (3) inner surface (6) is conically shaped at a predetermined angle (7) relative to the shaft axis (8).

The drive hub (2) includes an actuated hub (9) and a gripping formation (10).

The actuated hub (9) is rotatably located around the shaft (4) by means of a set of bearings (11) and is coaxially movable with the shaft (4) by an actuation member (not shown).

The gripping formation (10) is rotatably secured (12) at a first end (13) to the actuated hub (9). The first end (13) is profiled to be freely rotatable in a complementarily shaped slot (14) in the actuated hub (9). The second end (15) of the formation (10) is supported on its one side (16) by a support face (17) of the actuated hub (9). The second end (15) also includes a gripping surface (18) that substantially matches the conical gripping surface (6) of the gripping drum (3).

This means the second end gripping surface (18) has the same angle (7) relative to the shaft axis (8) as the gripping drum inner surface (6) and the formation gripping surface (18) has a profile to substantially match the conical inner surface (6) of the gripping drum (3).

The drive hub (2) includes biasing means that urges the gripping formation (10) towards the support (17) of the actuated hub (9), as is shown in Figure 2. The biasing means includes a cylindrical pin (19) secured to the actuated hub (9). A coil spring (20) is located around the pin (19), which urges rotation of the formation (10) around rotation axis (12). This biases the second end (15) towards the support face (17) of the actuated hub (9).

The coil spring (20) tension is predetermined to provide the correct amount of bias in relation to the release of the gripping formation (10) from the gripping drum (3), as will be explained further on.

A transmission segment (21) is keyed (22) to the shaft (4). The transmission segment (21) includes two faces (23A, 23B) between which the gripping formation (10) is located. This is shown in detail in Figure 3, which also shows that four gripping formations (10) are located around the shaft (4), with four transmission segments (21) spaced between them.

Each unsupported side (24) of a gripping formation second end (15) is freely located between but closely bounded by its surrounding transmission segments

(23A, 23B). As can be seen in Figure 1, a substantial part of the cross sectional area of the formation (10) is located between the transmission segments (21).

An important aspect of the drive hub design is the imaginary perpendicular radial line (25) that extends from the shaft through the gripping formation rotation axis (12) and the imaginary point (26) where this imaginary line (25) intersects with the gripping drum inner surface (6). The drive hub (2) is suitably arranged that a line (27) drawn from the point of the gripping area between the formation (10) and the gripping drum inner surface (6) that is radially the furthest away from the shaft axis (8) is either coincident with or further into the drum (3) cone than the imaginary point (26) relative to the actuated hub (9). In other words, the perpendicular radius of the imaginary point (26) from the shaft axis (8) is equal to or larger than the radius of the line (27) of the mentioned contact area with the largest radius.

Another important aspect is the profile of the formation gripping surface (18).

The surface (18) is shaped to substantially match the conical shape of the gripping drum (3) inner surface (6). However, the operatively upper edge (28) of the formation (10) includes and corresponds with the previously defined line of the contact area between the formation (10) and the gripping drum inner surface (6) with the greatest radius from the shaft (8). As shown in Figure 4, the sides (29) of this edge (28) are suitably profiled to provide a beveled edge such that the no part of the gripping formation (10) outermost edge is positioned further out of the drum (3) cone than the imaginary line (25) described above.

The above two important aspects contribute to the release of the formation (10) from the gripping drum (3), which will be explained further on.

When torque is applied to the gripping drum (3) and the actuated hub (9) is moved towards the gripping drum (3), the gripping formation (10) engages the gripping drum (3) inner surface (6). Since the gripping formation (10) gripping

surface (18) and the gripping drum inner surface (6) are complementary in shape, these surfaces engage through frictional contact and torque is transmitted from the prime mover through the gripping drum (3) and drive hub (2) connection to the shaft (4) as a function of any actuating force appropriately applied to the drive hub (2) along the shaft (4) axis of rotation (8).

Release of the drive hub (2) from the gripping drum (3) is accomplished by moving the drive hub (2) away from the gripping drum (3). The frictional contact that has been established between the gripping drum inner surface (6) and the formation gripping surface (18) tends to resist attempts to remove the formation (10) from the gripping drum (3). This causes the formation (10) to rotate around the rotation axis (12) and away from the support (17) of the actuated hub (2), against the coil spring bias (19).

Since the radius of the imaginary point (26) from the shaft axis (8) is equal to or larger than the radius of the line (27) of the formation-gripping drum contact area with the greatest radius, and the operatively upper edge (28) of the formation (10) has been suitably profiled as described above the contact between the formation (10) and the inner surface (6) is easily broken. Any rotation of the gripping formation (10) about its axis of rotation (12) as a consequence of axial withdrawal of drive hub (2) from the drum (3) cone will encourage release of frictional contact between the gripping formation (10) gripping surface (18) and the drum (3) cone (6). After contact has been broken between the inner surface (6) and the formation (10), the coil spring (19) bias immediately urges the formation (10) back towards its support (17) on the actuated hub (2). This immediately repositions the drive hub (2) for subsequent torque transmission.

The clutch (1) is capable of transmitting torque in the driven direction and is also capable of providing overrun torque transmission. The driven torque transmission and the overrun torque transmission are both achieved by means of the transmission segments (21) that closely bound the gripping formation (10).

As can be seen from Figure 3, each transmission segment (21) has two faces, a driven (23A) and an overrun face (23B). The same applies for the formation, which also has driven (10A) and overrun faces (10B). When torque is transmitted from the prime mover to the shaft (4), contact is maintained between the respective driven faces (23A, 10A). When the shaft (4) is overrunning the prime mover contact is rapidly established between the overrun faces (10B, 23B), and the prime mover then restrains the shaft (4) overrun.

It will be readily appreciated that there other embodiments of conical clutches that still fall within the scope of this invention.

The configuration described above is for a clutch with a cone angle (7) of 6 degrees. his is substantially lower than the practical minimum cone angle of about 12 degrees for conventional conical clutches and allows for a dramatic increase in torque transmission. As mentioned before it is not possible to use a cone angle of less than about 12 degrees for a conventional cone clutch since this leads to practical lockup or jamming of the clutch during disengagement.

With the present invention it is possible to use radically smaller cone angles, even as small as 3 degrees and possibly smaller without hub disengagement lockup.

A second embodiment of a clutch according to the invention is shown in Figure 5.

In this embodiment there are no separate transmission segments. Instead, the gripping formation (30) is received in a suitable recess (not shown) in the actuated hub (31). In this instance the actuated hub (31) is movable on a spline (32) on the shaft (33). The gripping formation (30) is still biased (not shown) towards the supported position on the actuated hub (31) and since it is received within the recess between two opposing faces (not shown) the clutch still provides torque transmission in both drive and overrun directions of rotation.

A third embodiment of a clutch according to the invention is shown in Figures 6 and 7.

As shown in Figures 6 and 7, the clutch comprises a drive hub (41), a gripping drum (43), and connecting means (45,46). The drive hub (41) is securable around a shaft and in this embodiment it is secured around an output shaft (42).

The gripping drum (43) is located around the shaft (42). The gripping drum (43) is rotatable around the shaft (42) by a prime mover (not shown). The connecting means (45,46) includes an actuated hub (45) that is adapted to be engageable with the drive hub (41) and the gripping drum (43). Actuation of the actuated hub (45) causes the actuated hub (45) to engage with the drive hub (41) and the gripping drum (43), thereby connecting the gripping drum (43) and the drive hub (41) to enable rotation of the shaft (42).

The connecting means (45,46) also includes a spigot (46) that is pivotally connected to the actuated hub (45) at a first end (46a) of the spigot (46). The first end (46a) connects to the actuated hub (45) in a complimentarily shaped recess (45a). The second end (46b) of the spigot (46) includes a cylindrical pin (46c) around which a radial spring (47) is secured at a first end (47a) thereof.

The radial spring (47) is secured to the drive hub (41) at its other end (47b). The radial spring (47) draws the spigot (46) towards the drive hub (41) to slidingly abut it. The contact area (not shown) of the drive hub (41) is complimentarily shaped to the contact area (not shown) of the spigot (46) where they abut.

The gripping drum (43) is concentric with the drive hub (41) and the shaft (42), and is free to rotate around both. The actuated hub (45) is rotatably mounted such that it is free to rotate but not necessarily to be radially constrained around an extended hub (44) of the drive hub (41) and shaft (42) axis of rotation.

As can be readily observed in Figure 7, when the actuated hub (45) is moved towards the drive hub (41), i. e. towards the right hand side of Figure 7, the angle

of inclination of the spigot (46) against the drive hub (41) will change until the spigot (46) outer end (48) comes into contact with the gripping drum (43) inner surface (49).

When sufficient axial force is applied to the actuated hub (45) a resulting force will be applied between the spigot (46) outer end (48) and the gripping drum (43) inner surface (49), which facilitates transmission of the required torque between the drive hub (41) and the gripping drum (43) without slippage.

Torque is transferred from the spigot (46) outer end (48) to the drive hub (41) by means of suitably arranged engagement of the spigot (46) torque transmission faces (50) with drive hub (41) radial splines (51). A shown in Figure 6, each spigot moves between two radial splines (51). Each spline (51) has two torque transmission faces (51 a) proximate the spigots (46). This arrangement facilitates axial movement of the actuated hub (45) in order to operate the radial extension and retraction of all the spigots (46), which consequently grip or release the gripping drum (43) inner surface (49).

The spigot (46) outer ends (48) each may have a frictional lining (not shown) removably secured thereto. This frictional lining provides for a controlled and increased coefficient of friction between the spigot (46) outer end (48) and the gripping drum (43) inner surface (49). The frictional lining can be replaced if it is worn.

The clutch also includes a travel limit for the actuated hub (45), which comprises am annular ring (52) that is removably secured to the drive hub (41). As can be seen in Figure 7, the actuated hub can be moved axially towards the drive hub (41) until it abuts the annular ring (52). By controlling the thickness of the ring (52), the amount of travel of the actuated hub (45) can be controlled. This effectively limits the amount of radial movement of the spigots (46) thereby

controlling the frictional contact force between the spigots (46) and the gripping drum (43) inner surface (49).

The arrangement as described is thus capable of transmitting a predetermined torque in either direction of rotation without slippage between the spigot (46) outer ends (48) and the gripping drum (43) inner surface (49) when a suitable force is applied axially to the actuated hub (45) acting towards drive hub (41), i. e. towards the right hand side, as shown in Figure 7.

By mechanical or other timing means, the clutch (60) can be caused or actuated to timeously grip the gripping drum (43) to coincide with the required portion of reciprocating motion imparted by a reciprocating device (not shown) to either the gripping drum (43) or the output shaft (42). By utilising a suitable number of suitably arranged clutches (60) suitably sequentially actuated to operate upon a suitably arranged output shaft or shafts (42) continuous transmission of either driving or overrun torque can be achieved for any degree of reciprocation imparted by the reciprocating device.

It is also clear from the drawings that the clutch (60) provides for overrun torque transmission. As can be seen in Figure 6, when the gripping drum (43) is rotated clockwise by the prime mover engagement of the spigots (46) with the inner surface (49) of the gripping drum (43) causes torque to be transmitted to the radial splines (51) located clockwise to the spigots (46), which in turn causes the output shaft (42) to be rotated clockwise. If the output shaft (42) overruns the prime mover contact between the spigots (46) and the splines (51) clockwise to the spigots (46) will be lost. Instead, the splines (51) counter clockwise to the spigots (46) will come into contact with the spigots (46), thereby transmitting torque from the output shaft (42) to the prime mover. This will cause the prime mover to brake the overrun rotation of the output shaft (42) to the point where the rotational speeds of the output shaft (42) and prime mover are matched.