A BUSH ASSEMBLY The present invention relates to a bush assembly for receiving and coupling a transmission shaft to a transmission component, such as a pulley, sprocket, flange coupling or the like. More speci ically, the present invention relates to a bush assembly which is suitable for receiving and coupling a transmission shaft to a plastic transmission component.

In the past it has been known to couple pulleys, sprockets, flange couplings and other transmission components for relatively high torque applications to transmission shafts by means of tapered, longitudinally split, contractible bushes, of the type disclosed in U.K. Patent No. 592912. In these known taper bush assemblies the bush, which is generally comprised of mild steel or cast iron, is positioned co-axially between the hub of a pulley or other transmission component and a shaft. A plurality of locking screws or bolts are then screwed into locking holes provided around the perimeter of the bush, parallel with the hub axis, to effect a wedging action between the hub of the pulley and the shaft.

These known taper bush assemblies are not generally considered suitable for use with relatively lightweight plastics transmission components and are usually used with transmission components made of mild steel or cast iron. The relatively high co pressive forces exerted by

the bush assembly on the hub of a plastics transmission component would, over a period of time, tend to cause the hub to "creep" or deform. Should the hub deform the assembly would loosen on the transmission shaft, until eventually, and particularly under conditions of high torque, the transmission component would start to slip. Indeed, precisely because of this tendency to deform when coupled to transmission shafts by conventional bush assemblies of the type described above,- plastic transmission components have been restricted in use to relatively low torque applications.

Unfortunately, relatively stronger materials able to resist deformation by the compressive forces exerted by the bush assembly tend to have a relatively large mass and in many applications this can be disadvantageous. Great care must be exercised to ensure that the bush assembly and the transmission component are properly balanced on the shaft and this is difficult where they are particularly heavy. In vibration sensitive applications involving relatively flexible structures' an out of balance transmission component rotating on the end of a shaft can cause enough vibration to make effective operation impossible. A further disadvantage associated with the conventional tapered bush systems referred to hereinabove is that the locking screws are prone to freeze in the

locking holes making de-wedging of the split, tapered bush for disassembly difficult. It is known to provide split, tapered bushes which make provision for de- wedging, but these have an increased tendency to suffer an out of balance moment.

It is an object of the present invention to provide a bush assembly for receiving and coupling a transmission shaft to a transmission component which does not subj'ect the hub of the transmission component to any radially acting compressive forces.

It is a further object of the present invention to provide a bush assembly for receiving and coupling a transmission shaft to a plastics transmission component.

It is yet another object of the present invention to provide a bush assembly for receiving and coupling a transmission shaft to a transmission component which is easily assembled and disassembled.

According to the present invention there is provided a bush assembly for receiving and coupling a transmission shaft to a transmission component, compri-ses a transmission.component having a hollow hub, an annular bush member having a tapered inner bore, engagement means for engaging the transmission component with the annular bush member, a contractible, inner sleeve member having a tapered outer surface and an inner bore adapted, in use, to receive the transmission shaft, which inner sleeve member is

received in the tapered inner bore of the annular bush member with the tapered outer surface thereof contacting the tapered inner bore of the annular bush member, and means for forcibly drawing the annular bush member towards the transmission component, thereby effecting contraction of the inner sleeve member onto the shaft and engagement of the engagement means between the annular bush member and the transmission component.

The provision of such a bush assembly ensures that no radially ^' acting co pressive forces are exerted on the transmission component itself which can accordingly be made -from relatively lightweight materials, such as plastics, without risk of "creep" or deformation occurring during its working.life. The annular bush member is effectively coupled to the shaft through the inner sleeve member, and torque is transmitted between the annular bush member and the transmission component by the engagement means.

Preferably, the inner sleeve member is provided with a longitudinal slot which permits it to contract or expand about its longitudinal axis.

Preferably, the engagement means comprises inter- engageable slots and teeth carried by the annular hub member and the transmission component respectively. As the annular hub member is drawn towards the transmission component these mesh together to provide a positive coupling between the ^' two bush assembly elements.

Preferably, further engagement means are provided between the annular bush member and the inner sleeve member in the form of further inter-engageable slots and teeth which mesh together as the tapered inner bore of the annular bush member is forcibly drawn over the tapered outer surface of the inner sleeve member. These inter-engageable slots and teeth serve to enhance the coupling between the inner sleeve member and the annular bush member, thereby ensuring that torque is effectively transmitted between the two bush assembly elements.

Preferably, the means for drawing the annular ^' bush member towards the transmission component comprises locking screws or bolts which are secured through the annular bush member in captive nuts carried by the transmission component or by a facing member on the opposite side of the transmission component.

In a preferred embodiment of the present invention the bush assembly comprises a pair of annular bush members, each of which is received in a respective end of the hub of the transmission component, and the inner sleeve member defines a barrel taper - that is to say the outer surface of the inner sleeve member defines two tapered portions, each of which diverges outwardly from a respective end of the inner sleeve member towards the middle thereof. A plurality of captive nuts are carried by one of the annular bush members and correspondingly positioned holes are provided in the other annular bush

member through which locking bolts or screws can be introduced. As the locking bolts or screws are screwed into the captive nuts the two annular bush members are brought together and each is forced to slide over a 5 respective one of the two tapered surfaces of the inner sleeve member, thereby causing it to contract onto the shaft. At the same time the transmission component is trapped between the two annular bush members and is inter-engaged therewith by the engagement means which may 10 be provided between either one, or both, of the annular bush members and the transmission component.

Conveniently, each of the annular bush members comprises a flange at the outer end thereof which locates the annular bush member against the end of the hub of the 15 transmission component. Conveniently a recess is formed in the end of the transmission component hub to receive the flange. The slots and teeth of the engagement means are provided, respectively, around the perimeter of the said recess and the said flange. Moreover, the combined 20 axial length of the two annular bush members is, preferably, equal to the axial length of the hub of the transmission component. This allows the ends-of the two annular -bush members to be buttressed up against each other when the locking screws or bolts are fully 25. tightened.

In an alternative embodiment of the present invention the inner sleeve member comprises an integral

flange at one end which locates against the outer end of the hub of the transmission component. Captive nuts are provided in the flange of the inner sleeve member and correspondingly positioned holes are provided in the annular bush member, or, indeed, visa versa. In much the same way as described above, the locking screws or bolts are screwed into the captive nuts and the annular bush member is drawn towards the inner sleeve member thereby causing the inner sleeve member to contract about the shaft and tightly coupling it thereto. In order to allow the inner sleeve member to close about the shaft the longitudinal slot provided therein is extend through the flange. The transmission component is, of course, trapped between the annular bush member and the flange of the inner sleeve member, and is inter-engaged with the annular bush member by the aforesaid engagement means. Engagement means may also be provided between the transmission component and the flange of the inner sleeve member. In yet another embodiment of the present invention one end of the hub of the transmission component is partially closed so as to allow the shaft to pass • therethrough, but retain the inner sleeve member therein. The other end of the hub is open to receive the inner sleeve member. Means, preferably in the form of locking screws or bolts and captive nuts, are provided to forcibly draw the annular bush member towards the

transmission component and in the manner described above this has "the effect of closing the inner sleeve about the shaft. In this embodiment the annular bush member is actually secured to the transmission component by the locking screws or bolts, however, torque is transmitted between the two bush assembly elements by the aforesaid engagement means. It will be apparent that the inner sleeve member is prevented from sliding along the shaft as the annular bush member is drawn towards the transmission component by the partially closed end of the transmission component hub.

Preferably, the transmission component is comprised of a plastics material and the inner sleeve and the annular hub members are comprised of a glass filled composite. However, it should be appreciated that the bush assembly of the present invention may be comprised of alternative materials.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Eig 1 shows an exploded view of a bush assembly embodying the present invention for receiving and coupling a transmission shaft to a pulley; Eig 2 shows an enlarged section through the upper half of the assembled bush assembly of Pig 1 along lines 1-1.

Referring to Fig.l of the accompanying drawings there .

is shown a pulley 2 having a hollow, central hub which is open at both ends to allow the pulley 2 to be mounted on and coupled to a shaft 5« To each side of the pulley 2 and axially slidable along the shaft 3 there is provided an annular bush member 4, 5« A plurality of captive nuts

6 are provided in annular bush member 4 and an equal number of correspondingly positioned through holes 7 are provided in annular bush member 5 through which locking screws or bolts 8 can be screwed into the captive nuts 6 to draw the two annular members 4 and 5 together. An inner sleeve member 9 is also mounted on the shaft 3 between the two annular bush members 4 and 5- This inner sleeve member 9 comprises an axially extending slot 16 in i which allows it to contract and expand about its longitudinal axis.

A circular recess is formed in each end of the pulley hub which thereby defines an annular abutment surface 10. A plurality of open ended slots 11 are formed around the perimeter of each recess.

Each annular bush member 4, 5 has an integral annular flange 12 at one thereof (i,e, the outer end) which can be received in and forms a close fit with a respective one of the recesses formed in the end of the pulley hub. Around the perimeter of this flange 12 there

are provided a plurality of teeth 13 _. corresponding in number, position and size to the .slots 11 around the perimeter of the aforesaid recess. When each annular bush member 4, 5 is inserted in a respective end of the pulley hub these teeth 13 are received in the slots 11, thereby inter-engaging the annular bush member 4, 5 with the pulley 2. The axial length of each annular bush member 4, 5 is approximately half the axial length of the pulley hub. Thus, when the two annular bush members 4 and 5 are drawn together by the locking screws or bolts 8 referred to hereinabove the integral flanges 12 each abut against a respective one of the annular abutment surfaces 10 and the inner ends of the annular bush members 4 and 5 meet in the middle of the pulley hub and buttress up against each other.

Each annular bush member 4, 5 has a tapered inner bore therein, which can best be seen in Pig. 2. This taper diverges from the flanged end of the bush member towards the other end thereof. At the inner end of this tapered bore, that is to say the end remote from the flange 12, there are-provided a plurality of open ended slots 15.

The inner sleeve member 9 comprises an axial slot in one side thereof, as indicated by reference 16, and defines an inner cylindrical bore, indicated by reference 17, of slightly greater diameter than the shaft 3« The outer surface of the inner sleeve member 9 comprises a

"barrel" or double taper - that is to say it tapers outwardly from each end towards the middle. Thus, two oppositely disposed tapered surfaces 18 and ^' 19 are provided over the outer surface of the inner sleeve member 9»

Around the middle of the inner sleeve member 9 there are provided a plurality of teeth 20, corresponding in number and position to the slots 15 in the inner tapered bores of the annular bush members 4 and 5» These teeth 20 have an axial length twice that of the axial length o ^" the slots 1 , but otherwise are of the same dimensions. When the bush assembly of the present invention is assembled the teeth 20 engage in the slots 15 and inter-engage the bush members 4 and 5 with the inner sleeve member 9-

Assembly of the bush assembly to receive and couple the shaft 3 to the pulley 2 will now be described.

Initially, a first annular bush member 4 is slide onto the shaft 3 _> followed by the inner sleeve member 9 and the pulley 2. Then the other annular bush member 5 is slide onto the shaft 3 on the other side of the pulley 2 from the first annular bush member 4« The locking screws 8 are inserted in the through holes 7 in the annular bush member 5 and are screwed into the captive nuts 6 carried by the annular bush member 4- As the locking screws 8 are tightened the two annular bush members 3 and 4 are drawn together into the open ends of the pulley hub, thereby

forcing the tapered inner bore of each annular bush member 4, 5 to slide up over a respective one of the tapered outer surfaces 18, 19 of the inner sleeve member 9- Due to the wedging action effected by forcing the 5 inner sleeve member into the tapered inner bores of the two annular bush members 4 and 5 the inner sleeve member 9 is forced to contract around the shaft 3 and effectively couples the shaft 3 to the two annular bush members 4 and _. . This couple is enhanced by the 10 arrangement of teeth 20 and slots 15, which inter-engage with each other as the two annular bush members 4 and 5 are drawn together.

As the annular bush members 4 and 5 are drawn together the integral annular flanges 12 at the outer 15 ends thereof are drawn into a respective one of the recesses provided in the open ends of the pulley hub 2 • Simultaneously, the teeth 13 around the perimeter of the flange 12 are received in the open ended slots 11 formed around the perimeter of the 20 ^' recess. Inter-engagement of the teeth 13 and the slots 11 provides an effective couple between the annular bush members 4 and 5 and the pulley 2. However, it will be readily appreciated that this couple does not result in any radially acting 25. compressive forces being applied to the pulley hub.

Torque is transmitted between the annular bush members 4 and 5 and the pulley 2 through the teeth 13 and the slots

11, and as such should deformation occur between these it cannot, except in the most extreme circumstances, result in the bush assembly loosening on the shaft 3 and slipping. As the annular bush members 4 and 5 are finally tightened together by the locking screws or bolts 8, trapping the pulley 2 therebetween, the integral flange of each annular bush member 4, 5 abuts against the annular abutment surface 10 provided in each end of the pulley hub. This further enhances the couple between the annular bush members 4 and 5 and the pulley 2. Additionally, the inner ends of the annular bush members 4 and 5 meet at the middle of the pulley hub buttressing up against each other and providing an effectively integral bush assembly.

In order to disassemble the bush assembly according to the present invention the locking screws or bolts 8 are simply unscrewed from the captive nuts 6 holding them in position and the annular bush members 4 and 5 are pulled away from the pulley. Removal of the locking screws or bolts 8 is very much simpler than in conventional bush assemblies as the locking screws or ^' bolts are not themselve-s required to effect any wedging action. As such they are not as likely to become frozen in position. With a conventional tapered bush assembly two sets of tapped holes are provided in the tapered bush. One set of these holes allows the assembly to be

locked on a transmission shaft, whilst the second set allows it to be delocked or slackened. In order to effect delocking of the assembly locking screws are removed from the first set of holes and then screwed into the second set. As the screws are tightened the transmission component is "jacked off" the tapered bush. With the bush assembly of the present invention it is not necessary to jack the transmission component off the bush. Simply by loosening the locking screws the assembly is released. With the bush assembly of the present invention the pulley may, as indicated above, be comprised of a plastics material as it will not be subjected to high compressive loads which might cause it to "creep" or deform. The plastics material may be chosen to have a relatively low mass, making it ideally suitable for relatively high torque applications where it is essential that the transmission component effect the minimum of out of balance moment. However, the bush assembly is by no means restricted to being used with plastics transmission components. Conveniently, the inner sleeve member 9 and the annular hub members 4 and 5 are comprised of a glass filled composite which is hard enough to resist deformation at the site of the wedged tapered surfaces. However, here again other materials may be used instead. The bush assembly of the present invention may also be fitted to a shaft having a standard keyway. In this respect, the split 16 in the inner sleeve member 9 can be

located around the key such that the assembly is locked in position and may resist the torque against the key.