WO2011119053A1

WO2011119053A1 - A clutch

Info

Publication number: WO2011119053A1
Application number: PCT/NZ2011/000039
Authority: WO
Inventors: John Darcey Bradley; Roger William Herbert Dunkley
Original assignee: Fastec Ltd
Priority date: 2010-03-26
Filing date: 2011-03-25
Publication date: 2011-09-29
Also published as: NZ584247A

Abstract

A clutch includes a throw arrangement configured to use radial motion of one or more throws for transmission of power via the clutch to a driven element. The clutch may convert radial motion of the throws into axial motion of some clutch components. This axial motion causes one or more friction elements to engage so as to transmit power to a driven element. The clutch may include one or more biasing elements which resist outward radial motion of the throws. The biasing element or elements may provide a desired time lag and/or a desired number of revolutions of the throw assembly between power being applied to the clutch and power being transmitted to the driven element. An adjustment element may be provided to allow alteration of a clearance within the clutch in order to allow adjustment of a time lag between power being applied to the clutch and maximum power being transmitted to the driven element.

Description

A CLUTCH

FIELD OF THE INVENTION The invention relates to clutches, in particular to soft start clutches. BACKGROUND TO THE INVENTION

Clutches are used in various applications for engaging and disengaging an output element (usually called the driven element) from a power source.

Centrifugal clutches generally include a shaft which is connected to a motor crankshaft or other power source. A number of centrifugal weights are arranged to move outwards as the shaft rotates and engage with the inside surface of a housing which surrounds the shaft, enabling transmission of power from the shaft to the housing. Friction elements may be provided between the centrifugal weights and the housing. Such clutches are used in reel lawn mowers and some light vehicles.

On start-up, the rate of rotation of the shaft increases and at some point the centrifugal weights are forced outwards to make contact with the driven housing. However, it is not feasible to adjust the point in the start-up operation at which the transfer of power to the driven element occurs. Furthermore, existing clutches generally transition from off to on with immediate engagement. Other forms of clutch, such as magnetic hysteresis, electromagnetic or hydraulic clutches, are prohibitively expensive for many applications.

It is an object of the invention to provide an improved clutch or at least to provide the public with a useful choice. SUMMARY OF THE INVENTION

In a first aspect the invention provides a clutch including:

a throw assembly arranged to rotate about a rotation axis, rotation of the throw assembly being driven by power input to the clutch;

a friction element; and

a driven element;

wherein:

the throw assembly includes: a biasing element; and one or more throws configured to move radially, outward radial motion of the throws being caused by rotation of the throw assembly;

outward radial motion of the throws causes engagement between the friction element and the driven element, thereby transmitting power to the driven element; and

the biasing element resists outward radial motion of the throws and has properties selected so as to provide a desired time lag and/or a desired number of revolutions of the throw assembly between power being applied to the clutch and power being transmitted to the driven element.

In a second aspect the invention provides a clutch including:

a friction element;

a driven element;

wherein the throw assembly includes:

one or more throws configured to move radially, outward radial motion being caused by rotation of the throw assembly;

one or more cooperating surfaces, the throws and the cooperating surfaces being configured to convert outward radial motion of the throws caused by rotation of the throw assembly into axial motion of at least part of the clutch; and one or more biasing elements configured to resist outward radial motion of the throws;

and wherein said axial motion causes engagement between the friction element and the driven element, thereby transmitting power to the driven element.

In a third aspect the invention provides a clutch including:

a friction element;

a driven element; and

an adjustment element;

wherein:

the throw assembly includes one or more throws configured to move radially, outward radial motion of the throws being caused by rotation of the throw assembly; outward radial motion of the throws causes engagement between the friction element and the driven element, thereby transmitting power to the driven element; and

the adjustment element can be adjusted to alter clearances within the clutch, so as to alter a degree of slippage and therefore a time lag between power being applied to the clutch and power being fully transmitted to the driven element.

In this specification the term "radial motion" means motion towards or away from the axis of the clutch. Radial motion can therefore be inward motion towards the axis or outward motion away from the axis.

In this specification the term "axial motion" means motion along or parallel to the axis of the clutch. BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 is an exploded view of a clutch according to one embodiment;

Figure 2 is an assembled view of the clutch of Figure 1 ;

Figure 3 is a side view of the main spindle of the clutch in Figure 1 ;

Figure 3A is a plan view of the spindle of Figure 3;

Figure 4 is a side view of a friction element in the clutch of Figure 1 ;

Figure 5 shows the driven element of the clutch of Figure 1 ;

Figure 6 is a side view of a friction element housing, from the clutch of Figure

1 ;

Figure 6A is a plan view of the friction element housing of Figure 6;

Figure 7 is a side view of a throw housing, from the clutch of Figure 1 ;

Figure 7A is a plan view of the throw housing of Figure 7;

Figure 8 is a side view of a throw, from the clutch of Figure 1 ;

Figure 8A is a plan view of the throw of Figure 8;

Figure 9 shows the biasing element of the clutch of Figure 1 ;

Figure 10 is a side view of a throw cover plate, from the clutch of Figure 1 ;

Figure 10A is a plan view of the throw cover plate of Figure 10;

Figure 11 is a side view of an adjustment nut, from the clutch of Figure 1 ;

Figure 11A is a plan view of the nut of Figure 11 ;

Figure 12 is an exploded view of a clutch according to another embodiment;

Figure 13 is an assembled view of the clutch of Figure 12;

Figure 14 is an exploded view of a clutch according to a further embodiment;

Figure 15 is an assembled view of the clutch of Figure 14;

Figure 16 shows a friction element from the clutch of Figure 14;

Figure 17 shows a clutch according to yet another embodiment;

Figure 18 shows a clutch according to a further embodiment;

Figure 19 shows a clutch according to another embodiment; Figure 19A shows a direct drive disc according to one embodiment;

Figure 20 shows a clutch removal tool;

Figure 21 shows an alternative embodiment of friction element housing;

Figure 21 A is a plan view of the friction element housing of Figure 21 ;

Figure 21 B is a side view of the friction element housing of Figure 21 ;

Figure 22 is a plan view of an alternative embodiment of throw housing;

Figure 23 shows an alternative embodiment of throw housing and contact surface;

Figure 24 is an exploded view of a further embodiment;

Figure 25 shows the main spindle of the embodiment of Figure 24;

Figure 26 is a perspective view of a throw from the embodiment of Figure 24;

Figure 27 is a top view of the throw of Figure 26;

Figure 28 is a side view of the throw of Figure 26;

Figure 29 is a perspective view of the throw housing of the embodiment of

Figure 24;

Figure 30 is a plan view of the throw housing of Figure 29; and

Figure 31 is a cross-section through a cover plate of the embodiment of Figure

24. DETAILED DESCRIPTION

Figure 1 is an exploded view and Figure 2 is an assembled view of a clutch 1 according to one embodiment.

The clutch 1 includes a main spindle 2, shown in detail in Figures 3 and 3A. Figure 3 is a side elevation, while Figure 3A is a plan view from the end of the spindle 2. The main spindle 2 serves to support the other elements of the clutch and also to transmit power, as will become clear below.

The main spindle 2 is configured to receive power input to the clutch from a motor crankshaft or the like. The spindle 2 includes a flange 3 and a shaft 4. The shaft 4 includes a round section 5 and a square section 6 on which other components of the clutch reside. The square section 6 includes four machined flats 7, which are dimensioned such that rounded sections 8 remain. These rounded sections are threaded in a region 9 near the end of the shaft 4.

Alternatively, the shaft 4 may include flats 7 and rounded sections 8 along its entire length. In general, at least part of the length of the shaft 4 must have a non-circular cross-section allowing it to engage with cooperating non-circular holes in some of the clutch elements riding on the shaft, such that those elements are driven in rotational motion by the rotating shaft.

The spindle may include a central bore 10.

The inner face of the flange 3 is formed with a recess 12 which carries a first friction element 14. The friction element 14 is shown in detailed cross-section in Figure 4. The friction element 14 may have an outer diameter 15 such that it sits within the recess 12 and an inner bore 16 with a diameter 17 such that it rides freely on the circular section 5 of the main spindle 2, or on the rounded sections 8 if those sections extend the full length of the shaft 4.

The friction element may be of any suitable material, including proprietary materials. Different materials may be suitable for different applications and suitable materials will be known to skilled readers. The first friction element and the second friction element (described below) are preferably free running elements not fixed to any contact surface.

A driven element 18 is positioned between the first friction element 14 and a second friction element 19. In the embodiments of Figures 1 to 16 the driven element 18 is in the form of a pulley, as shown in detail in Figure 5. The pulley 18 includes a substantially v-shaped recess 20 around its periphery, to receive a belt for transmitting power output from the clutch to a load. The pulley 18 also includes a central bore 21 with a diameter 22 such that the pulley rides freely over the circular section 5 of the main spindle 2.

The driven element 18 may be formed from cast iron, which has good wear resistance. If other materials (such as steel or aluminium) are used, a bronze or PTFE bushing may be used in the bore 21 to contact the surface of the main spindle 2.

Suitable pulleys include universal A, B & M section pulleys and their variants. Duplex or triplex pulleys may be used where appropriate.

The second friction element 19 may be generally similar to the first friction element 14, except that its inner and outer diameters are such that it is received in a recess formed in a friction element housing 25. The friction element housing 25 is shown in detail in Figures 6 and 6A. Figure 6 is a cross-section and Figure 6A is a plan view of the friction element housing 25.

These figures clearly show the recess 26 for receiving the second friction element 19. The friction element housing includes a central square hole 27 which fits over the four flats 7 of the main spindle 2.

On the rear side of the friction element housing, a detent groove 28 is formed. The function of this groove will become clear below. The clutch also includes a throw assembly 30. The throw assembly includes a throw housing 31 , a number of throws 32, a throw retention and/or biasing means 33 and a throw cover plate 34.

The throw housing 31 is shown in detail in Figures 7 and 7A. The throw housing has a central square hole 37, which is sized for a running clearance over the four flats 7 of the main spindle 2. The throw housing 31 therefore rotates with the main spindle 2.

In the embodiment shown, the clutch includes four throws 32. The throw housing 31 therefore includes four slots 38 which, in the assembled clutch, each receive a throw 32.

Each slot 38 allows radial movement of the throw retained in that slot. However, the base 39 of each slot slopes to form a surface which cooperates with the throw, such that radial movement of the throw also causes axial movement of the throw (or some other part of the throw assembly). The slope, indicated by the angle a in Figure 7, may be in the range 12.5 to 17°, preferably around 15°. Alternatively, the angle a may be in the range 10 to 15°, preferably around 13°. This second range would provide a smoother progression to full transmission on start-up. However, adjustment of the clutch is finer with a smaller angle and other modifications may be necessary, such as reduction in the thread pitch of the adjustment nut 58, described below.

The throw housing 31 also includes a peripheral groove 41 which, in the assembled clutch retains the throw biasing means 33.

Finally, the throw housing 31 includes a number of tapped holes 42 which allow the various components of the throw assembly to be fastened together, as will become clear below.

Figures 8 and 8A show a throw 32. Each throw 32 includes a throw body 45 with a projecting contact region 46. The throws may be formed from bronze or other suitable materials. Preferably the material chosen has a low coefficient of friction. The contact region 46 could be coated with polytetrafluoroethylene (PTFE). The contact region 46 could be formed by embedding a steel ball bearing in a bronze block, for improved friction properties. An outer face 47 of each throw is formed with a groove 48 for locating the throw biasing element 33, which is shown in figure 9. The biasing element 33 may be a resilient or elastic ring, such as a standard O-ring. The O-ring may be formed from rubber or nitrile or silicon rubber, fluorocarbon rubber (such as Vitron), polypropylene rubber, ethylene propylene rubber, neoprene, polyurethane or other suitable materials. Alternatively a steel extension spring could be formed in a ring.

The magnitude of the force applied by the biasing means to the throws will depend on the material of the ring, the cross-section of the ring and the resting diameter of the ring. An annular extension spring could also be used.

Figures 10 and 10A show the throw cover plate 34 in detail. The cover plate includes a number of slots 50 which co-operate with the slots 38 in the throw housing 31 , to allow movement of the throws. A central square hole 51 rides on the square flats 7 of the main spindle 2. Countersunk holes 52 align with the tapped holes 42 in the throw housing, such that the components of the throw assembly can be fastened together using threaded fasteners. An inner face 54 of the throw cover plate is tapered at an angle a corresponding to the angle of the tapered surfaces 39 in the throw housing's slots 38.

Figure 2 clearly shows the assembled throw assembly 30, with the tapered surfaces of the throw housing 31 and throw cover plate 34 parallel and separated by a distance corresponding to the height of the throw bodies. The throws are therefore contained but allowed to move radially between the cooperating surfaces in the throw housing and the inner face 54 of the throw cover plate. The contact region 46 of each throw protrudes through the slot 50 in the throw cover plate, to contact the surface of the friction element housing 25.

Figure 2 also shows the biasing means 33 residing within the slot 41 of the throw housing 31. Finally, the clutch includes an adjustment nut 58, as shown in detail in figures 11 and 11 A. The adjustment nut 58 has an internal thread 59 which engages with the external thread 9 on the end of the main spindle 2. The adjustment nut has another threaded hole 60 for receiving a set screw (not shown) which engages with one of the flats 7 on the main spindle 2 to lock the position of the adjustment nut 58. The pitch of the thread 9 on the main shaft 4 may be designed such that the clutch can be assembled, the nut hand-tightened and then backed off to the next flat 7. The set screw is then tightened to fix the position of the adjustment nut. With a pitch of about 2mm this has been found to provide a suitable clearance between the various clutch elements for some applications.

In use, the clutch starts from a stationary position. When a motor connected to the main spindle 2 is started, the spindle 2 begins to rotate. The throw assembly 30, adjustment nut 58 and friction element housing 25 engage with the flats 7 on the main spindle 2. These elements therefore rotate with the spindle, driven by power input to the clutch. The friction element 14, 19 and the driven element 18 reside on the circular section 5 of the main spindle 2 and an external load is connected to the driven element 18 via a belt or the like. These elements, or at least the driven element 18, therefore do not rotate in the initial start-up phase.

As the throw assembly 30 rotates, the throws 32 are forced outwards, in centrifugal motion caused by rotation of the throw assembly. This outward radial motion of the throws 32 is in part converted into axial motion of the throws by the tapered cooperating surfaces 39 of the throw housing 31. The contact regions 46 therefore force the friction element housing 25 to move along the main spindle 2, thereby forcing together the friction element housing, friction elements 14, 19, driven element 18 and the flange 3 of the main spindle 2. This causes rotational motion to be transmitted through the flange 3 and the friction element housing 19 to the driven element 18. The outward radial motion of the throws is resisted by the biasing element 33. The magnitude of this resistance is a function of the properties of the biasing element, including its elasticity, material and dimensions (including cross-sectional dimensions and resting diameter). The magnitude of the resistance can therefore be adjusted by selecting different biasing elements with different sets of properties. This allows a desired time lag and/or a desired number of revolutions of the throw assembly to be achieved between power being applied to the clutch and the throws reaching a point where power is transmitted to the driven element, simply by selecting appropriate biasing element properties.

When the throws reach a maximum displacement from the axis of the clutch, the contact regions 46 engage in the detent groove 28 of the friction element housing 25. This effectively provides a slight impediment to movement of the throws back towards the axis of the clutch. This also accurately positions the throws in a designed position for full transmission of power to the driven element, preventing undesirable radial oscillation.

The detent groove also acts as a useful indicator of the clutch clearances. If the throws do not engage with the detent groove then insufficient clearance has been allowed. The clearances can then be adjusted using the adjustment nut 58.

However, if the speed of the clutch slows sufficiently (which may be caused by a great load applied to the driven element 18) the inertia of the throws and the impediment of the detent groove will not be large enough to resist the inward force applied by the biasing element 33. The throws will therefore move back towards the axis of the clutch. This will release the engagement with the driven element 18.

The speed of the driving elements of the clutch can then pick up again, causing the throws once again to move outwards to cause engagement with the driven element 18. This is advantageous, since it provides an automated mechanism for applying drive to high loads without stalling a power source.

When a power source is switched off, the throws automatically return to their innermost positions under the force from the biasing means 33, such that the clutch is again ready to receive power from the power source.

Furthermore, the adjustment nut does not simply have one correct setting. Adjustment of the adjustment nut 58 allows the clearances between the clutch elements to be adjusted.

As the throws move outwards and the friction elements engage with the driven element there is a degree of slippage, such that power is not fully transmitted to the driven element. When the clearances are very low, this slippage will be minimal. When the clearances are too high (and this may depend on the nature of the load), there will be excessive slippage such that full power is never transmitted. However, the degree of slippage can be adjusted by adjusting the clearances using the adjustment nut 58. This contributes to the soft-start capabilities of the Applicant's clutch. The throws move outwards and the friction elements engage with the driven element. When the load is large, slippage will prevent full transmission of power to the load, while the load is brought up to speed. Over a time period, the speed of the load will increase and the slippage will decrease until there is full transmission of power from the clutch to the load.

Thus the adjustment nuts allows adjustment of clearances and the degree of slippage within the clutch and therefore allows adjustment of a time lag between power being applied to the clutch and maximum power being transmitted to the driven element. Again, this helps to prevent stalling or overloading of a power source when used with a large load.

Figures 12 and 13 show a second embodiment which is functionally similar to the embodiment of figures 1 to 11. The main spindle 2, friction elements 14, 19 and driven element 18 are similar to the corresponding elements of figures 1 to 11.

However, in this embodiment the friction element housing is incorporated into the throw housing 65. The throw housing 65 therefore includes all elements of the throw housing 31 of figures 1 to 11 but also includes a recess 66 for receiving the second friction element 19. In addition, the throw assembly has been reversed so that the contact regions 46 of the throws 32 project to the left, as shown. Finally, the adjustment nut 67 is formed with a flange 68 in which a detent groove 69 is formed to receive the contact regions 46 of the throws at their maximum displacement. In this embodiment, a spare O-ring 70 may be stored on the adjustment nut 67.

In this embodiment, radial motion of the throws 32 causes the throw housing 65 to move along the shaft 4 of the main spindle 2, forcing the throw housing 65, friction elements 14, 19, driven element 18 and the flange 3 of the main spindle 2 together. This causes transmission of rotational motion to the driven element 18.

As no separate friction element housing is required, this embodiment may provide a more compact clutch. Figures 14 to 16 show a further embodiment, in which two throw assemblies are used. Each throw assembly is identical to that of figures 12 and 13. The contact regions of one set of throws engage with the flange 3 of the main spindle 2 while those of the other set of throws engage with the flange 68 of the adjustment nut 67. Here a detent groove is formed in the flange 68 and a further detent groove is formed in the flange 3 of the main spindle 2. A friction element 71 is positioned on each side of the driven element 18. Each friction element 71 includes two layers of friction material 72, as shown in figure 16. These layers 72 are separated by a bonded, resilient compression material 73. This provides a smoother transmission of power to the driven element 18.

In this embodiment, the shaft of the main spindle preferably has flats 7 and rounded sections 8 extending along its entire length.

Figure 17 shows a further embodiment in which power is output by a direct drive mechanism, rather than by a pulley and belt. This embodiment is similar to that of figures 1 to 11 , except that the driven element is a disc 75 rather than a pulley 18. The disc 75 rides on the circular part 5 of the main spindle 2 in the same manner as the pulley 18. However, the periphery of the disc 75 includes a number of tapped holes 76 which align with countersunk holes 77 in a direct drive housing 78.

A Taperlock sleeve 80 is fitted to the end of the direct drive housing 78. A male Taperlock shaft can be inserted into this sleeve for transmission of power from the clutch. Thus, when power is transmitted from the main spindle 2 to the driven disc 75, the entire housing 78 rotates and drives rotational motion of a shaft (not shown) connected to the Taperlock sleeve 80. This shaft may be connected to a load.

Taperlock sleeves such as that shown allow output shafts with a range of shaft diameters to be driven by the clutch. Figure 18 shows yet a further embodiment, which is similar to that of Figure 13, except that a direct drive disc 75, housing 78 and Taperlock sleeve 80 are used instead of a pulley 18.

Figure 19 shows another embodiment similar to that of Figures 12 and 13. However, the pulley 18 has again been replaced with a disc 75, connected to a housing 78 and Taperlock sleeve 80. In this embodiment the power source 81 is connected to the end of the shaft 4 opposite the flange 3, and the housing 78 encloses the flange 3. This is in contrast to the embodiments of Figures 17 and 18 and significantly reduces the size of the housing 78. The outer surface of the disc 75 may be formed with one or more protrusions 79, as shown in Figure 19A, to form a keyed connection with corresponding recesses or cut-outs (not shown) in the housing 78.

Figure 20 shows an extraction tool 82 for removing the clutch from an input shaft. Removing the clutch by pulling or levering by hand on the clutch components may damage or misalign those components. Therefore, the tool 82 is configured to align precisely with the clutch. The tool 82 includes a body 83 with a number of holes 84 (preferably four or more) which align with tapped holes 85 in the adjusting nut. With the body securely fastened to the adjusting nut, a force can be applied to the body 83 using a bolt 87 which cooperates with a threaded hole in the body 83. Thus, the clutch can be pulled from an input shaft without risking damage to the clutch.

Figures 21 , 21 A and 21 B show an alternative friction element housing 90, which has an overall shape similar to the friction element housing 25 but includes a number of venting channels 91 formed in its surface. Each channel 91 communicates with the periphery of the housing 90 via one or more openings 92. These channels 91 and openings 92 serve to dissipate heat build up in the friction element housing and/or friction element. Heat build up in the clutch components is undesirable and can be a problem where a number of start-up processes are performed using the clutch in a short time period. The channels 91 and openings 92 may also help to prevent build up of particles between the components, which can tend to glaze the mating metal surfaces. Similar venting arrangements can be used in the various friction element housings described herein.

Figure 22 shows an alternative embodiment of throw housing 95, which is generally similar to the throw housing 31 except that the bases of the slots 96 include a relieved area 97 to reduce the contact area of the throw and the base of the slot. Relieved area 97 is lowered such that the throw will ride only on the surrounding area 98. This smaller contact area reduces friction and therefore allows smoother travel of the throws. Again, such relieved slots could be used in any of the throw housings described herein.

In any of the embodiments described herein the surface which the throws contact (e.g. the surface of the friction element housing 25 in Figure 2, the surface of the flange 68 in Figure 12, the surface of the flange 3 in Figure 14 etc) may be ground to a fine finish. This also reduces friction and contributes to smoother movement of the throws. Improved smoothness leads to improved performance, in particular allowing the throws to engage in a more controlled fashion and to disengage reliably when the power is reduced. Figure 23 shows an alternative throw housing 100 in which the throw slots 101 are not angled, but extend straight outwards from the centre of the throw housing 100. The main spindle 2 differs from other spindles described above in that the flange 3 is formed with an angled surface 102. As the throws travel directly outwards in the slots 101 , they ride along the angled surface 102, thereby forcing the throw housing 100 axially away from the surface 102. The skilled reader would understand that the clutch configurations described above could be adapted to use these parallel slots 101 and angled contact surfaces 102.

The angle of the surface 102 may again be in the range 12.5 to 17°, preferably around 15°. Alternatively, the angle may be in the range 10 to 15°, preferably around 13°.

The angled surface 102 need not be straight, but could include a slight curve or change in angle to provide desired properties. For example, the surface 102 could be curved to provide less resistance to movement of the throws near the outward most point of the throw travel range. This would assist in release of the throws when power is reduced.

Figures 24 to 31 show yet another embodiment of clutch.

A main spindle 200 is shown in detail in Figure 25 and includes a flange 203 and a shaft with a round section 205 and a hexagonal section 206. The hexagonal section includes six machined flats. First and second friction elements 214, 219 are positioned on either side of a driven element 218, which in the embodiment shown is in the form of a pulley. The pulley 218 rides on a bush 220 (formed for example from bearing bronze) which itself sits over the round section 205 of the main spindle 200.

The throw assembly 230 of this embodiment includes a throw housing 231 , a number of throws 232 and first and second ramp plates (or cover plates) 233, 234. For clarity only one throw is shown separate from the throw housing in the exploded view of Figure 24, with the five other throws 232 being shown in position in the throw housing 231.

A single throw is shown in detail in Figures 26 to 28. In this embodiment the throws are formed as small blocks with two generally trapezoidal faces 240 and other generally square or rectangular faces. Each throw may have a rectangular or square hole 241 formed in it for receiving rollers 244 (Figure 24). A bore 245 in the top of the throw receives one end of a spring 246. The other end of each spring 246 either is received in a bore in the throw housing or in/on a small bush 247 which can be formed with or attached to the throw housing by any suitable means.

Figures 29 and 30 show the throw housing in detail. The throw housing 231 includes a central hexagonal hole 250 which is sized for a running clearance over the hexagonal section of the main spindle 200. Six slots 251 receive the throws, with the springs 246 (discussed above but not shown in Figures 29 and 30) biasing the throws inwards towards the centre of the throw housing 231. Thus in this embodiment each throw is biased inwards by its own biasing element.

Each ramp or cover plate 233, 234 is formed with a number of ramps 252, as shown in Figure 24. A cross section through one of these ramps is shown in Figure 31, showing the ramp inclining at an angle a. This angle is preferably in the range 1 to 10°, preferably 1 to 5°, ideally around 3°.

This angle is preferably the same as the angle of the throw faces. This arrangement of throws and ramps distributes the pressure evenly, reducing the chance of the throws being held by pressure in their outermost position when the clutch disengages.

The throws roll along the ramps 252 on the rollers 244, thereby reducing the effects of friction on operation of the clutch. A larger number of rollers could be used to further reduce the effects of friction. In the preferred embodiment the rollers are simple cylinders and are held in place only by the assembly of the clutch (i.e. they need not be secured to the throws). An adjustment nut 255 mounts to the end of the main spindle 200.

The skilled reader will understand that the throw arrangement of this embodiment can be used or adapted for use with many of the configurations of Figures 1 to 23. A clutch according to any of the above embodiments may be connected to a power source and a load. When the power source is started, power is not transmitted to the load. However, after some time lag the throws will move outwards, forcing axial movement of at least part of the throw housing. This in turn will cause engagement with the driven element and power will be transmitted to the load. The time lag can be controlled by appropriate selection of biasing element 33. The Applicant's clutch therefore allows this time lag to be controlled, such that the point in a starting operation at which power is applied to the load can be controlled. Furthermore, the Applicant's clutch prevents stalling of a power source during starting. This is particularly beneficial where high inertial loads such as compressors or pumps are to be driven.

This is especially true where such loads are to be driven from a domestic or mains power source. The Applicant's FasTec Soft Start controller allows three phase motors to be powered from a domestic single phase power supply with no inrush current or heating of the motor armature. However, with high inertial loads the current load required would ordinarily be too great for the starting unit. By using the Applicant's clutch, the motor is permitted to reach a high (possibly maximum) speed over a time period or number of revolutions which depends on the properties of the biasing element. Full power transfer is achieved when the throws have moved to the outermost position. Therefore, in combination with a suitable controller, the Applicant's clutch enables high inertial loads to be driven from mains power sources.

As is clear from the several embodiments disclosed, the components of the Applicant's clutch can be arranged in several different configurations.

In addition, the number of throws can be altered. Throws could be arrange in a tiered manner, each throw housing having an inner series of slots for an inner tier of throws and an outer series of slots for an outer tier of throws. Each tier could have a separate biasing element. Larger numbers of throws, or tiered throws, may be useful in applications where larger power outputs are required. The size of the throws can be adapted to different applications. In general heavier throws will move radially outwards more readily than lighter throws.

The overall size of the clutch may also be adapted to particular applications.

The Applicant's clutch uses simple and easily manufactured or readily available components.

O-rings of many different sizes, cross-sections and resting diameters are readily available and cheap. Different O-rings can be used to provide different time lags, suitable for different applications, power sources or loads.

Similarly, where biasing elements other than O-rings are used their characteristics can be selected to provide the required operation of the clutch.

Adjustment of the clutch clearances allows a degree of slippage to be adjusted, contributing to the soft-start capabilities of the clutch.

While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of the Applicant's general inventive concept.

Claims

CLAIMS:

1. A clutch including:

i. a throw assembly arranged to rotate about a rotation axis, rotation of the throw assembly being driven by power input to the clutch;

ii. a friction element; and

iii. a driven element;

wherein:

a. the throw assembly includes: one or more biasing elements; and one or more throws configured to move radially, outward radial motion of the throws being caused by rotation of the throw assembly;

b. outward radial motion of the throws causes engagement between the friction element and the driven element, thereby transmitting power to the driven element; and

c. the biasing element or elements resist outward radial motion of the throws and has or have properties selected so as to provide a desired time lag and/or a desired number of revolutions of the throw assembly between power being applied to the clutch and power being transmitted to the driven element.

2. A clutch as claimed in claim 1 wherein the biasing element is an annular biasing element which engages with an outer surface of each throw so as to exert a force on each throw towards an axis of the clutch.

3. A clutch as claimed in claim 2 wherein the annular biasing element is a resilient ring.

4. A clutch as claimed in claim 3 wherein the resilient ring is formed from rubber, nitrile or silicon rubber, fluorocarbon rubber, polypropylene rubber, ethylene propylene rubber, neoprene or polyurethane.

5. A clutched as claimed in claim 3 or 4 wherein the properties of the resilient ring include material, cross-section and resting diameter.

6. A clutch as claimed in any preceding claim wherein the throw assembly includes one or more cooperating surfaces, the throws and the cooperating surfaces being configured to convert outward radial motion of the throws caused by rotation of the throw assembly into axial motion of at least part of the throw assembly, said axial motion causing engagement between the friction element and the driven element.

7. A clutch as claimed in claim 6 wherein the throw assembly also includes: a throw housing incorporating the cooperating surfaces; and a throw cover plate attached to the throw housing and having inclined surfaces parallel to the cooperating surfaces, the distance between the cooperating and inclined surfaces corresponding to a height of the throws, such that the throws are contained and move radially between those surfaces.

8. A clutch as claimed in claim 7 wherein the throw housing includes a slot for each throw, each throw sliding within a slot and a cooperating surface forming the base of the slot.

9. A clutch as claimed in claim 7 or 8 wherein the throw cover plate includes a number of apertures allowing a contact region of each throw to protrude.

10. A clutch as claimed in claim 7, 8 or 9 wherein the throw housing has a peripheral groove configured to locate the biasing element.

11. A clutch as claimed in any one of claims 6 to 10 wherein the cooperating surfaces are inclined with respect to a plane normal to the clutch axis.

12. A clutch as claimed in claim 11 wherein the cooperating surfaces are inclined with respect to a plane normal to the clutch axis by an angle in the range 12.5 to 17 degrees.

13. A clutch as claimed in claim 12 wherein the angle is around 15 degrees.

14. A clutch as claimed in claim 6 wherein the throw assembly includes a throw housing having radially extending slots in which the throws are located and move, the throw assembly also including at least one cover plate having a ramp surface, wherein outward radial motion of the throws applies an axial force to the ramp surface.

15. A clutch as claimed in claim 14 wherein the throw assembly includes two such cover plates, one on each side of the throw housing.

16. A clutch as claimed in any preceding claim wherein each throw has one or more rollers reducing frictional resistance to radial motion of the throws.

17. A dutch as claimed in claim 1 wherein the biasing elements comprise one or more springs.

18. A clutch as claimed in any preceding claim including a main spindle extending along the axis of the clutch and configured to receive power input to the clutch, the main spindle having a non-circular cross-section along at least part of its length and at least one component of the throw assembly having a central bore with a shape matching with the non-circular cross-section, such that the throw assembly is driven in rotational motion by the main spindle.

19. A clutch as claimed in claim 18 wherein the driven element rides freely on the main spindle.

20. A clutch as claimed in claim 18 or 19 including a friction element housing configured to house a first friction element and a flange on the main spindle configured to house a second friction element, wherein the driven element is located between the first and second friction elements, and wherein radial motion of the throws causes the friction element housing to move towards the flange, pushing the friction elements against the driven element for transmission of rotational motion to the driven element.

21. A clutch as claimed in any preceding claim wherein the driven element is formed from cast iron.

22. A clutch as claimed in any preceding claim wherein the driven element is a pulley configured to drive a belt for connection to a load.

23. A clutch as claimed in any one of claims 1 to 21 wherein the driven element is a disc configured to drive a housing which is arranged to drive a shaft connected to a load.

24. A clutch as claimed in any preceding claim wherein the throws each include a throw body with a raised contact region extending from the throw body.

25. A clutch as claimed in any preceding claim wherein the throws are formed substantially from bronze.

26. A clutch as claimed in any preceding claim including two friction elements positioned on either side of the driven element.

27. A clutch as claimed in any preceding claim wherein each friction element includes two layers of friction material around an inner layer of resilient cushioning material.

28. A clutch including:

ii. a friction element;

iii. a driven element;

wherein the throw assembly includes:

a. one or more throws configured to move radially, outward radial motion of the throws being caused by rotation of the throw assembly;

b. one or more cooperating surfaces, the throws and the cooperating surfaces being configured to convert outward radial motion of the throws caused by rotation of the throw assembly into axial motion of at least part of the clutch; and

c. one or more biasing elements configured to resist outward radial motion of the throws;

29. A clutch as claimed in claim 28 wherein each biasing element has properties selected so as to provide a desired time lag between power being applied to the clutch and power being transmitted to the driven element.

30. A clutch as claimed in claim 28 or 29 wherein the biasing element is an annular biasing element which engages with an outer surface of each throw so as to exert a force on each throw towards an axis of the clutch.

31. A clutch as claimed in claim 30 wherein the annular biasing element is a resilient ring.

32. A clutch as claimed in claim 31 wherein the resilient ring is formed from rubber, nitrile or silicon rubber, fluorocarbon rubber, polypropylene rubber, ethylene propylene rubber, neoprene or polyurethane.

33. A clutched as claimed in claim 29 wherein the properties of the resilient ring include material, cross-section and resting diameter.

34. A clutch as claimed in any one of claims 28 to 33 wherein the cooperating surfaces are inclined with respect to a plane normal to the clutch axis.

35. A clutch as claimed in claim 34 wherein the cooperating surfaces are inclined with respect to a plane normal to the clutch axis by an angle in the range 12.5 to 17 degrees.

36. A clutch as claimed in claim 35 wherein the angle is around 15 degrees.

37. A clutch as claimed in claim 28 wherein the throw assembly includes a throw housing having radially extending slots in which the throws are located and move, the throw assembly also including at least one cover plate having a ramp surface, wherein outward radial motion of the throws applies an axial force to the ramp surface.

38. A clutch as claimed in claim 37 wherein the throw assembly includes two such cover plates, one on each side of the throw housing.

39. A clutch as claimed in any one of claims 28 to 38 wherein each throw has one or more rollers reducing frictional resistance to radial motion of the throws.

40. A clutch as claimed in claim 28 wherein the biasing elements comprise ope or more springs.

41. A clutch as claimed in any one of claims 28 to 36 wherein the throw assembly also includes: a throw housing incorporating the cooperating surfaces; and a throw cover plate attached to the throw housing and having inclined surfaces parallel to the cooperating surfaces, the distance between the cooperating and inclined surfaces corresponding to a height of the throws, such that the throws are contained and move radially between those surfaces.

42. A clutch as claimed in claim 41 wherein the throw housing includes a slot for each throw, each throw sliding within a slot and a cooperating surface forming the base of the slot.

43. A clutch as claimed in claim 41 or 42 wherein the throw cover plate includes a number of apertures allowing a contact region of each throw to protrude.

44. A clutch as claimed in any one of claims 41 to 43 wherein the throw housing has a peripheral groove configured to locate the biasing element.

45. A clutch as claimed in any one of claims 28 to 44 including a main spindle extending along the axis of the clutch and configured to receive power input to the clutch, the main spindle having a non-circular cross-section along at least part of its length and at least one component of the throw assembly having a central bore with a shape matching the non-circular cross-section, such that the throw assembly is driven in rotational motion by the main spindle.

46. A clutch as claimed in claim 45 wherein the driven element rides freely on the main spindle.

47. A clutch as claimed in claim 45 or 46 including a friction element housing configured to house a first friction element and a flange on the main spindle configured to house a second friction element, wherein the driven element is located between the first and second friction elements, and wherein radial motion of the throws causes the friction element housing to move towards the flange, pushing the friction elements against the driven element for transmission of rotational motion to the driven element.

48. A clutch as claimed in any one of claims 28 to 47 wherein the driven element is formed from cast iron.

A clutch as claimed in any one of claims 28 to 48 wherein the driven element is a pulley configured to drive a belt for connection to a load.

A clutch as claimed in any one of claims 28 to 48 wherein the driven element is a disc configured to drive a housing which is arranged to drive a shaft connected to a load.

51. A clutch as claimed in any one of claims 28 to 50 wherein the throws each include a throw body and a raised contact region extending from the throw body.

52. A clutch as claimed in any one of claims 28 to 51 wherein the throws are formed substantially from bronze.

53. A clutch as claimed in any one of claims 28 to 52 including two friction elements positioned on either side of the driven element.

54. A clutch as claimed in any one of claims 28 to 53 wherein the or each friction element includes two layers of friction material around an inner layer of resilient cushioning material.

55. A clutch including:

ii. a friction element;

iii. a driven element; and

iv. an adjustment element;

wherein: the throw assembly includes one or more throws configured to move radially, outward radial motion of the throws being caused by rotation of the throw assembly;

the adjustment element can be adjusted to alter clearances within the clutch, so as to alter a degree of slippage and therefore a time lag between power being applied to the clutch and maximum power being transmitted to the driven element.