GB2624231A

GB2624231A - Sheave assembly

Info

Publication number: GB2624231A
Application number: GB2216872.8A
Authority: GB
Inventors: Black Nicholas; Delaperriere Antoine; Walker James
Original assignee: Rigging Projects Ltd
Current assignee: Rigging Projects Ltd
Priority date: 2022-11-11
Filing date: 2022-11-11
Publication date: 2024-05-15
Also published as: WO2024100415A1; GB202216872D0

Abstract

A sheave assembly 112 has a hub 108 with an inner opening, an insert 156 and a plurality of rolling elements 120, such as ball bearings. Around the hub a sheave defines an annular space 115 for the rolling elements to rotatably mount the sheave on the hub. The hub has a radially extending aperture (148 fig.6) between the inner opening and the annular space to receive the rolling elements whilst assembling the sheave assembly. The insert is configured to be removed and inserted radially from within the inner opening. The annular space is bounded by an outer race 116 provided by the sheave and an inner race 126. The inner race is defined by a surface provided by the hub and by a continuous surface of the insert which is shaped to fill the aperture when the insert is mounted in the aperture. The insert may be secured by a fastener 180 passing through apertures 170 and (154 and 162 fig. 6).

Description

Sheave Assembly

FIELD OF THE INVENTION

The present invention relates to a sheave assembly, a sheave block comprising a sheave assembly, and a method of assembling a sheave assembly.

BACKGROUND TO THE INVENTION

Sheaves or pulley wheels are used on sailing vessels to guide movement of flexible lines (for example ropes or cables, such as stays, sheets or halyards), often under load. A sheave comprises a rotatable wheel or ring having an outer circumferential groove for receiving part of the line.

A sheave may be mounted for rotation on a shaft, with a plain bearing formed by contact between the shaft and the side of a central hole through the sheave. In some applications, a sheave forms part of a sheave assembly in which the sheave is mounted on, or comprises, the outer ring of a radial bearing, with rolling elements such as ball bearings set between the sheave and an inner ring to allow the sheave to rotate on the inner ring.

In such arrangements, typically the rolling elements are inserted into a space between the outer ring and the inner ring in an axial direction (i.e., parallel to an axis of rotation of the sheave). The rolling elements may be fed axially into the space through one or more notches or cut-away side wall portions of the inner ring or outer ring. The rolling elements may be retained between the inner and outer rings by annular snap rings or seals subsequently secured to sides of the inner ring or outer ring. In some instances, the rolling elements are inserted by forcing the rolling elements axially between the inner and outer rings, temporarily deforming the inner and/or outer rings to accept the rolling elements therebetween.

A problem with these arrangements is that the resulting sheave assembly may -2 -perform poorly if subjected to any axial load, as the rolling elements may contact the notches in use, resulting in undesirable noise and a reduction in efficiency and reliability.

WO 201 2/1 27394 Al discloses a sheave assembly having an insert applied radially from within an inner ring of the sheave assembly. The insert has appendages which project through holes in the inner ring to reduce a radial distance between the inner ring and the outer ring to improve axial retention of the outer ring on the inner ring by the rolling elements.

It is against this background that the present invention is devised.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a sheave assembly comprising: a hub having an inner opening; an insert; a plurality of rolling elements; and a sheave arranged coaxially around the hub to define an annular space for receiving the plurality of rolling elements for rotatably mounting the sheave on the hub; wherein: - the hub comprises a radially extending aperture which extends between the inner opening and the annular space, the aperture being sized to receive the rolling elements therethrough for inserting the rolling elements into the annular space from the inner opening during assembly of the sheave assembly; - the insert is removably mountable in the aperture and is configured to be removed and inserted radially from within the inner opening; -the annular space is bounded by an outer race provided by the sheave and an inner race; - the inner race being defined by a surface provided by the hub and by a -3 -continuous surface of the insert, said continuous surface being shaped to fill the aperture when the insert is mounted in the aperture.

In this way, the continuous surface of the insert provides a bearing contact surface of the inner race within the periphery of the aperture. With this arrangement, larger rolling elements and/or a greater number of rolling elements can be used and other parts of the sheave assembly can be manufactured to finer tolerances, thereby improving the performance of the sheave assembly. The continuous surface of the insert minimises interruption of a bearing contact surface of the inner race and reduces the presence of features which might otherwise become contaminated with dirt or debris. In this way, friction between the rolling elements and the inner race is reduced and the efficiency and reliability of the sheave assembly is improved.

Preferably the insert is a single-piece insert. In this way the strength and rigidity of the insert (and of the hub when the insert is mounted in the aperture) is improved.

Preferably the continuous surface of the insert spans a width of a bearing contact surface of the inner race in a direction parallel to an axis of rotation of the sheave.

Preferably the continuous surface of the insert comprises a saddle surface.

Preferably the continuous surface of the insert comprises a convex curvature in a direction perpendicular to the axis of rotation of the sheave assembly and a concave curvature in a direction parallel to the axis of rotation of the sheave assembly.

The inner race may comprise at least two parallel raceways extending circumferentially around the hub, each raceway providing a respective bearing contact surface. In this case preferably the aperture intersects each of the raceways. In such embodiments the raceways may be separated by a circumferential ridge, and the continuous surface of the insert may provide a portion of the ridge and a portion of the bearing contact surface of each raceway within the aperture. -4 -

Preferably the continuous surface of the insert and the surface provided by the hub have a common cross-sectional profile.

In some embodiments the insert is secured in the aperture by a fastener which extends parallel to an axis of rotation of the sheave. In such embodiments the insert may comprise a bore which extends through the insert for receiving the fastener.

Alternatively, or in addition, the hub may comprise a circumferentially extending groove in an inner surface of the inner opening and the insert is secured in the aperture by a retaining ring which engages with the circumferential groove.

The retaining ring and the insert may be a unitary body.

The aperture may have a stadium-shaped cross-section. The aperture may have a circular or oval cross-section.

Also provided is a sheave block comprising a sheave assembly according to the firsts aspect of the invention and a pair of cheek plates disposed on opposite sides of the sheave assembly.

In embodiments of the sheave block in which the insert is secured in the aperture by a fastener which extends parallel to an axis of rotation of the sheave, preferably a fastener extends through a hole in at least one of the cheek plates and into the insert to secure the insert in the aperture and to secure the at least one cheek plate to the hub.

The cheek plates may be formed from a composite sandwich material having a skin comprising a fibre reinforced polymer material and a core comprising a thermoplastic polymeric material.

The fibre reinforced polymer skin may comprise one or more of carbon fibre, flax fibre, and hemp fibre. -5 -

The thermoplastic polymer core may comprise a plastics material. Preferably the thermoplastic polymer core comprises polyethylene terephthalate.

In some embodiments of the sheave block, part of a surface of the hub defining the inner opening comprises a planar surface or saddle surface arranged to engage with a strop for securing the sheave block to a supporting structure in use.

The hub and/or insert may be formed from metal. The insert may be formed from a plastics material.

The rolling elements may be formed from a ceramic material, steel (such as stainless steel or chrome steel), a plastics material, or other suitable material.

According to a second aspect of the invention there is provided a method of assembling a sheave assembly according to the first aspect of the invention, the method comprising: from within the inner opening, inserting the plurality of rolling elements into the annular space through the radially-extending aperture; mounting the insert in the aperture to close the aperture; and securing the insert in the aperture. -6 -

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which like reference numerals are used for like features and in which: Figure 1 is a perspective view of a sheave block comprising a sheave assembly according to a first embodiment of the invention; Figure 2 is a perspective exploded view of the sheave block of Figure 1; Figure 3 is a perspective view of a sheave of the sheave block of Figure 1; Figure 4 is a perspective view of a hub of the sheave block of Figure 1; Figure 5 is a side view of the hub of Figure 4; Figure 6 is a perspective view of the hub and a removable insert of the sheave block of Figure 1; Figure 7 is a perspective view of the hub and the removable insert of the sheave block of Figure 1, showing the insert mounted in the hub; Figure 8 is a side view of the insert of the sheave block of Figure 1; Figure 9 is a cross-sectional axial view of the sheave block of Figure 1; Figure 10 is a cross-sectional side view of the sheave block of Figure 1; Figures 11 and 12 are perspective views of a sheave assembly according to a second embodiment of the invention; -7 -Figure 13 is a perspective exploded view of the sheave assembly of Figures 11 and 12; Figure 14 is a cross-sectional axial view of the sheave assembly of Figures 11 and 12; and Figure 15 is a cross-sectional radial view of the sheave assembly of Figures 11 and 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a sheave assembly and a sheave block comprising a sheave assembly. The sheave assembly comprises a removable insert for allowing rolling elements (such as bearing balls) to be inserted into the sheave assembly during assembly.

The sheave assembly of the present invention is arranged to be attached to a supporting structure such as a retaining structure on part of a sailing vessel. The sheave assembly is arranged to provide a rotating sheave or pulley wheel for guiding and allowing movement of a flexible line whilst resisting load in a loading direction generally away from the supporting structure to which the sheave assembly is attached. Accordingly, in this specification, the terms proximal, proximally and related terms refer to a position or direction towards the point of attachment of the sheave assembly to a supporting structure (e.g. towards the bottom in Figure 1). Similarly, the terms distal, distally and related terms refer to a position or direction generally away from the supporting structure (e.g. towards the top in Figure 1) which is also a loading direction of the sheave assembly.

Figures 1 to 10 show a sheave block 100 according to a first embodiment of the invention. The sheave block 100 comprises a sheave assembly 102 and a shell or cheek assembly 104. The sheave assembly 102 comprises a sheave or pulley -8 -wheel 106 and a central hub 108. The sheave 106 is rotatably mounted on the central hub 108. The cheek assembly 104 comprises a pair of side plates or cheek plates 110 and a spacer 112. The cheek plates 110 are arranged on opposite lateral sides (e.g. opposite axial ends) of the sheave assembly 102 such that the central hub 108 and sheave 106 are disposed between the cheek plates 110. The cheek plates 110 are secured to the central hub 108 such that the sheave 106 rotates with respect to the central hub 108 and the cheek plates 110. Each of the cheek plates 110 is elongate and extends away from the sheave assembly 102 towards a proximal end or head end 114 of the sheave block 100. The spacer 112 is disposed between the cheek plates 110 proximate the head end 114 and the cheek plates are secured to the spacer 112, as described further below. With this arrangement the cheek plates 110 are spaced apart from one another on opposite sides of the sheave assembly 102 to define a space 115 between the sheave 106, the cheek plates 110 and the spacer 112 for receiving part of a line such as a rope (not shown).

In use, the line contacts and wraps part way around the sheave 106 and at least part of the line extends distally away from the sheave block 100.

In use, the sheave block 100 is attached to a supporting structure (such a cleat, eye, track car or the like on the deck of a sailing vessel (not shown)) with the proximal end 114 closest to the supporting structure and the sheave assembly 102 furthest from the supporting structure. In particular, the sheave block 100 is secured to the supporting structure using a strop (not shown) which passes through an opening extending through the cheek plates 110 and the central hub 108 and extends proximally away from the sheave block 100. The cheek plates 110 are also secured to the strop proximate the proximal end 114 of the block 100 so as so retain the proximal end 114 of the block 100 closest to the supporting structure. With this arrangement, because the cheek plates 110 are fixed with respect to the central hub 108, an orientation of the hub 108 is fixed or limited with respect to the loading direction of the sheave block 100. In use, load is applied to the sheave 106 in a distal direction.

As can be seen most clearly in Figures 2 and 3, the sheave 106 (which may also be -9 -termed a pulley or outer ring) is generally annular and comprises an outer circumferential groove for receiving part of a flexible line such as a rope. An inner circumferential side of the sheave comprises an outer bearing race 116. The outer race 116 faces radially inwards. In this embodiment, the outer race 116 comprises a pair of circumferential grooves or raceways 118 each having a generally semi-circular cross-sectional profile for receiving a plurality of rolling elements (which in this embodiment are bearing balls 120). The sheave 106 is arranged to be mounted for rotation on the central hub 108. The sheave 106 is arranged to rotate about an axis of rotation A (as shown in Figure 1) of the sheave assembly 102 (which in this embodiment can also be considered an axis of rotation of the sheave block 100). It will be appreciated that in other embodiments, the outer race may not be integrally formed with the sheave and the outer race may be provided by a separate component such as a ring on which the sheave may be mounted.

Referring additionally to Figures 4, 5, 6, and 7, the central hub 108 comprises a generally annular body having a central opening or inner opening 124. The central hub 108 is coaxial with the axis A of the sheave assembly 102. The central opening 124 opens at opposite axial ends of the central hub 108. An outer circumferential surface of the central hub comprises part of an inner race or inner ring 126 of the sheave assembly 102. The inner race 126 faces radially outwards. The inner race 126 is arranged to provide a contact surface for the rolling elements 120 set between the central hub 108 and the sheave 106, for rotatably mounting the sheave 106 on the hub 108. In this embodiment, the inner race 126 comprises a pair of circumferential grooves or raceways 128 which extend around the central hub 108.

Each raceway 128 has a generally semi-circular cross-sectional profile for receiving the bearing balls 120. Each raceway 128 provides part of a bearing contact surface of the central hub 108. An outer diameter of the hub 108 is sized to fit with clearance in the sheave 106, so that in use a circumferential space or annular space 130 is provided between the inner race 126 and the outer race 116. The plurality of bearing balls 120 are received in the annular space 130 for rotatably mounting the sheave 106 coaxially on the hub 108. The balls 120 run in the raceways 118, 128 provided in each of the inner race 126 and the outer race 116. In this embodiment, an even -10 -separation between the balls 120 is maintained by a generally annular bearing cage or separator 132 which fits in the annular space 130. The cage 132 comprises a circumferential wall having a plurality of circular holes 134 therethrough, each hole sized to receive a bearing ball 120.

Referring in particular to Figures 4 and 5, the central hub annular body 108 comprises a proximal, first portion 136, and a distal, second portion 138 opposite the first portion 136. A middle region 140 of the proximal portion 136 has an increased thickness between the central opening 124 and the inner race 126 compared with a thickness in distal regions of the proximal portion 136 either side of the middle portion 140. In use, the proximal portion 136 bears more load than the distal portion 138. Under load, the sheave 106 is urged distally so that a majority of the load is transferred from the sheave 106 to the hub 108 via bearing balls 120 bearing on the inner race 126 at the proximal portion 136 of the hub 108. In this way, a thickness of part of the annular body of the hub 108 is increased where load on the central hub 108 is greatest. A distal surface or radially inner surface 142 of the middle portion 140 also provides a contact surface for the strop in use. The distal surface 142 comprises a generally planar portion 144 and radiused or blended edge portions 146 disposed between the planar portion 144 and open ends of the central opening 124. In use, the planar portion 144 allows space for two or more lengths of the strop to bear against the distal surface 142 without being urged together under load, thus reducing rubbing or chafing between parts of the strop. The chamfered edge portions 146 also act to reduce chafing of the strop on the central hub 108.

Referring also to Figure 6, the central hub 108 comprises a bore or aperture 148 which extends radially between the central opening 124 and the inner race 126. The aperture 148 is disposed in the distal portion 138. The aperture 148 opens at the outer circumferential surface of the hub 108 and thus interrupts the inner race 126. In this way the aperture 148 intersects the inner race to define a periphery 155 of the aperture. In this way, a portion of the inner race 126 is absent due to the aperture 148. The periphery 155 of the aperture 148 can be considered to define a lacuna in the inner race 126. The aperture 148 is sized to receive rolling elements (e.g. the bearing balls 120) therethrough during assembly of the sheave block 100. In this embodiment, the aperture 148 has a generally stadium-shaped cross section. A major diameter of the aperture 148 (i.e. along a length of the stadium-shaped cross section) extends parallel to the axis of rotation A, and perpendicular to a direction of travel of the balls 120 along each raceway. A thickness of part of the central hub 108 between the central opening 124 and the inner race 126 is increased around the aperture 148, as can be seen most clearly in Figures 4 and 5. This increased thickness region around the aperture 148 provides a convex surface 150 which protrudes into the central opening 124. The aperture 148 and convex surface 150 are diametrically opposite the thicker middle region 140 of the proximal portion 136 and with this arrangement, the central opening 124 of the hub 108 has a generally kidney-shaped cross-section.

The proximal portion 136 of the hub 108 comprises a pair of protruding semi-annular lips 152 disposed on opposite axial ends of the hub 108. Each lip 152 extends part way around a circumference of the central opening 124 and protrudes away from the hub 108 parallel to the axis A. Each lip 152 is arranged to engage with part of a respective one of the cheek plates 110. A pair of fastener holes 154 are provided at opposite axial ends of the central hub 108 proximate the aperture. Each fastener hole 154 extends from an axial end of the hub 108 and opens into the aperture 148.

Referring in particular to Figures 6, 7 8 and 9, the sheave assembly 100 further comprises an insert 156 arranged to fit in the aperture 148. In this embodiment the insert is a single-piece insert or unitary body. The insert 156 is arranged to restore the portion of the inner race 126 interrupted by the aperture 148. Accordingly, the insert 156 has a cross-sectional profile which matches a cross-sectional profile of the inner race 126. A radially outwardly facing surface (which in this embodiment is a distal surface 158) of the insert 156 comprises a pair of saddle-shaped contact surfaces 160. The distal surface 158 provides a continuous, uninterrupted surface of the insert 156. The saddle surfaces 160 are spaced apart by a bridge portion disposed between the saddles 160. The saddle contact surfaces 160 are shaped so as to complete each of the grooved inner raceways 128 when the insert 156 is -12 -mounted in the aperture 148. A curvature of the distal surface 158 of the insert 156 matches a curvature of the contact surfaces provided by the raceways 128 of the inner race 126. The continuous distal surface 158 of the insert 156 and a surface of the hub together define the inner race 126. The contact surfaces 160 of the insert 156 and raceways 128 together provide a continuous bearing contact surface of the inner race 126. In this way, a contact surface of the insert 156 and a contact surface of the central hub 108 together define a bearing surface of the inner race 126. The insert 156 is shaped and sized to be a close fit in the aperture 148 so that there is minimal interruption of the contact surface of each raceway 128 when the insert 156 is in place, as can be seen in Figure 7. The distal surface 158 fills the aperture 148 when the insert 156 is mounted in the aperture 148. The insert 156 comprises a fastener bore 162 which extends through the insert 156 in a direction parallel to the axis of rotation A of the sheave assembly 102. The fastener bore 162 is arranged to align with and register with the fastener holes 154 of the central hub 108.

With reference to Figures 2 and 10, each cheek plate 110 comprises a distal end opening 166 through the cheek plate 110 proximate a distal end of the cheek plate 110. The distal end opening 166 is aligned with the central opening 124 of the hub 108. A proximal portion of each distal end opening 166 has a larger diameter than a distal portion of the opening 166, such that shoulders 168 are formed between the two portions of the opening 166. The increased diameter proximal portion is shaped to receive a respective one of the protruding lips 152 on each end of the central hub 108 and ends of each lip 152 are arranged to abut one of the shoulders 168. In this way, relative rotation between the central hub 108 and the cheek plates 110 is prevented.

Each cheek plate 110 further comprises a fastener hole 170 which extends through the cheek plate 110 proximate a distal edge of the distal end opening 166. Each fastener hole 170 is arranged to align with a respective fastener hole 154 in the central hub 108. Each fastener hole may be reinforced (for example with a metal insert). A proximal portion or head portion 172 of each cheek plate 110 has an increased thickness relative to a middle portion of the cheek plate between the -13 -proximal portion 172 and the sheave assembly 102. Each proximal portion 172 comprises a plurality of blind bores 174 which open towards the other of the cheek plates 110. Proximate the proximal end 114 of the sheave block 100, the cheek plates 110 are secured to, and spaced apart by, the spacer 112, which is disposed between the cheek plates 110. The spacer 112 comprises a block having a plurality of bores 176 which open towards the cheek plates. The bores 174 of the cheek plates 100 and the bores 176 of the spacer 112 are arranged to align when the sheave block 100 is assembled, and pins 178 (or other suitable fasteners) inserted into the bores 174, 176 are arranged to secure the cheek plates 110 to the spacer 112. For example, the pins 178 may be an interference fit in the bores 174, 176 of the spacer 112 and cheek plates 110.

The cheek plates of the sheave block may be formed from metal. Advantageously, in some embodiments, the cheek plates are formed from a composite material, in particular a thin-wall or sandwich structure composite material. In a preferred embodiment, the cheek plates are formed from a sandwich structure composite material comprising a carbon fibre reinforced polymer (CFRP) outer material or skin and a PET (polyethylene terephthalate) polymer core material. To form the cheek plates, PET balls or pellets are pressed between CFRP sheets in a mould under suitable heat and pressure. The use of balls of the core material allows the core material to conform to the three-dimensional structure of the cheek plates during manufacture of the cheek plates. Under heat and pressure, consolidation of the PET balls and CFRP occurs to form the composite sandwich material. The PET balls expand as they are heated, which helps to increase the pressure during moulding, to improve consolidation of the sandwich structure. The resulting material is considerably lighter than a solid CFRP structure but still strong enough to withstand loads in use. For example, cheek plates made using the sandwich material may be approximately 60% lighter than cheek plates made from solid CFRP material without a core. In some embodiments, regions of the cheek plates which are subjected in use to higher load (than other parts of the cheek plates may be reinforced). For example, the proximal portions of the cheek plates, and parts of each cheek plate disposed between the proximal portion and the distal end opening, may be subject -14 -to compressive forces in use from the strop. The strop is passed through the distal end openings and extends over the cheek plates to secure the sheave block in use, such that the cheek plates may be compressed and urged towards each other by the strop in use. Accordingly, at least some of these regions of the cheek plates may have a thickened skin, or be formed from only CFRP (or other fibre reinforced polymer material) without a core material. Additionally, or alternatively, these regions may comprise a reinforcing element or insert, such as a metal or fibre reinforcing element disposed between or embedded in the skin structure or solid CFRP structure.

In other embodiments, instead of CFRP, another fibre reinforced polymer material may be used for the skin of the sandwich structure, such as a glass fibre reinforced polymer, flax fibre reinforced polymer, or hemp fibre reinforced polymer material. It will be appreciated that other materials may be used for the core material, such as other suitable polymeric plastics materials. It will also be appreciated that the composite sandwich material cheek plates described above could also be used in sheave blocks and with sheave assemblies other than those described here.

During assembly of the sheave block 100, the hub 108 is inserted into the sheave 106 and the bearing cage 132 is inserted into the annular space 130 between the inner and outer races 126, 116. Subsequently, bearing balls 120 are fed or inserted into the annular space 130 from within the central opening 124, via the aperture 148. Each bearing ball 120 is located in a respective hole in the bearing cage 132 and each ball 120 contacts the raceways 128, 118 of the inner and outer races 126, 116.

Once all the balls 120 have been inserted, the insert 156 is inserted into the aperture 148 from within the central opening 124 to complete the inner race 126 and to prevent the balls 120 from escaping. An annular sealing member 125 is provided on each axial end face of the sheave 106, between the sheave 106 and a respective one of the cheek plates 110, to prevent ingress of contaminants (e.g. water, grit) into the annular space 130. Each sealing member 125 is seated in an annular recess or rebate on the sheave 106.

-15 -The cheek plates 110 are located on opposite sides of the sheave assembly 102 and a fastener 180 is inserted through the fastener hole 170 in each cheek plate 110. Each fastener 180 extends through a respective fastener hole 154 of the hub 108 and into the fastener bore 162 of the insert 156. Each fastener 180 thus extends through a cheek plate 110, through part of the hub 108 and into the insert 156. In this way, the cheek plates 110 are secured to the hub 108 and the insert 156 is secured in the aperture 148. In some embodiments, a single fastener may be inserted to extend through both cheek plates, both fastener holes in the hub, and through the insert. The proximal portions of the cheek plates 110 are secured to the spacer 112 by the pins 178, thereby securing the cheek plates 110 together. In alternative embodiments, the sheave block may be provided as deck block or cheek block in which one or more fasteners secure the sheave assembly to a deck with the cheek plates extending parallel to the surface of the deck.

With the arrangements described above, once the sheave block is assembled, the sheave 106 is mounted for rotation on the hub 108 and is axially retained on the hub 108 by contact of the bearing balls 120 with the raceways 128, 118. Because the insert 156 is located in the distal portion 138 of the central hub 108, opposite to the load-bearing proximal portion 136, the bearing contact surfaces 160 of the insert 165 are subject to considerably less load than the inner race 126 in the proximal portion 136. In this way, the insert 156 and fasteners 180 which secure the insert 156 in place are not subject to potentially damaging loads. Also, any interruption of the bearing contact surface between the edge of the aperture 148 and the insert 156 will have little or no effect on the operation or efficiency of the sheave assembly 102, since this region of the bearing contact surface is subject to very little load.

When load is applied to the sheave 106 in the loading direction, a clearance gap opens between the balls 120 and the inner and/or outer race proximate the distal portion 138, such that substantially no load is applied to the distal portion 138 and insert 156. Accordingly, the insert may be formed (e.g. 3D printed) from lightweight material such as a plastics material. Because each contact surface 160 of the insert 156 spans a full width of one of the raceways 128, a majority of an edge of the insert 156 is located away from a centre line of each raceway 128. Since the bearing balls mostly contact the raceway 128 close to the centre line of the raceway 128 in use, disruption to the rolling of the balls 120 on the raceway 128 is minimised.

A sheave assembly according to a second embodiment of the invention is shown in Figures 11 to 15. In this embodiment, the sheave assembly 202 comprises a plain sheave assembly or standalone sheave assembly suitable for mounting on a shaft. For example, the sheave assembly 202 of this second embodiment may be used in a sheave box such as a through-deck sheave box, or as a masthead sheave.

The sheave assembly 202 comprises a sheave or outer ring 206, and a central hub or inner ring 208. The sheave 206 is substantially the same as the sheave 106 of the first embodiment, being generally annular and comprising an inwardly facing outer race 216. The central hub 208 is similar to the central hub 108 of the first embodiment and only differences will be described in detail. In use, the sheave 206 is rotatably mounted on the hub 208, with a plurality of rolling elements (not shown in Figures 11 to 15) disposed in an annular space 230 between the sheave 206 and the hub 208. The rolling elements are located in holes in a cage or separator 232, substantially the same as the cage 132 described above in relation to the first embodiment.

The central hub 208 comprises an annular body 222 having a central opening 224 with a circular cross section. The central opening is arranged to receive part of a shaft. The hub 208 comprises an outwardly facing inner race 226, a radially extending aperture 248, and an insert 256 arranged to fit in the aperture 248. In this second embodiment, the hub 208 comprises an inwardly facing circumferential groove 290 which extends around an inner circumference of the hub 208. The circumferential groove 290 intersects the aperture 248. The circumferential groove 290 is sized to receive a retaining ring.

In this embodiment, the insert 256 does not have a fastener bore extending through it, but instead the insert 256 is provided with a retaining ring 292 (which may also be referred to as a retaining clip or locating ring) which is arranged to fit in the -17 -circumferential groove 290 in order to secure the insert 256 in the central hub 208. The retaining ring 292 comprises first and second resilient members 294, 296 which extend from opposite sides of the insert 256. The resilient members 294, 296 are curved and extend away from the insert 256 to form an incomplete ring shape such that ends of the resilient members 294, 296 furthest from the insert 256 do not meet.

In this embodiment, the insert 256 and retaining ring 292 are a unitary body. To assemble the sheave assembly, the insert 256 is inserted into the central opening 224 and the resilient members 294, 296 of the retaining ring 292 are flexed radially inward to fit the retaining ring into the central opening 224. The insert 256 is located in the aperture 248 and the retaining ring 292 is slotted into the circumferential groove 290. The resilient members 294, 296 of the retaining ring are biased radially outwards into the circumferential groove 290 to secure the insert 256 in the central hub 208.

The central opening 224 is arranged to receive part of a shaft or pin (not shown) to mount the central hub 208 on the shaft or pin, for retaining the sheave assembly 200. For example, the sheave assembly 200 may be mounted on a pin in a sheave box. In use, a rotational orientation of the central hub 208 may be fixed with respect to a loading direction of the sheave assembly 200. In particular, the central hub 208 may be fixed such that a distal portion 238 of the central hub 208, in which the insert 256 is located, is disposed distally (that is, towards the loading direction) and an opposite proximal side 236 of the central hub 208 is disposed furthest from the loading direction. With this arrangement, similarly as described above in relation to the first embodiment, the proximal side of the hub 236 is subject to a majority of the load resulting from load applied to the sheave 206 in the loading direction, and the insert 256 is subject to considerably less load (or substantially no load). In order to fix the rotational orientation of the central hub 208, the hub may comprise an antirotation feature (not shown), such as a groove for receiving a spline of a splined shaft, or any other suitable feature for preventing rotation of the hub with respect to a shaft or pin on which the hub is mounted.

It will be appreciated that the retaining ring mechanism for securing the insert in the -18 -hub as described above could be used in the sheave assembly and sheave block of the first embodiment. Similarly, the fastener arrangement used for securing the insert in the hub in the first embodiment could be used in the sheave assembly of the second embodiment.

It will also be appreciated, that in some applications, the distal orientation of the insert is not essential. For example, where the load applied to the sheave is sufficiently low that any risk of damage to the bearing balls and/or insert, or reduced efficiency, is minimised, the insert need not be located on a distal side of the hub.

In some embodiments of the present invention, the aperture could have a different shape, for example, where a single bearing raceway is used. In this case, the insert may comprise a single saddle shaped contact surface. It will also be appreciated that other types of rolling elements other than ball bearings could be used, such as conical or cylindrical rolling elements, roller bearings, needle bearings and the like.

Further modifications and variations not explicitly described above may also be contemplated without departing from the scope of the invention as defined in the appended claims.

Claims

-19 -CLAIMS1. A sheave assembly comprising: a hub having an inner opening; an insert; a plurality of rolling elements; and a sheave arranged coaxially around the hub to define an annular space for receiving the plurality of rolling elements for rotatably mounting the sheave on the hub; wherein: -the hub comprises a radially extending aperture which extends between the inner opening and the annular space, the aperture being sized to receive the rolling elements therethrough for inserting the rolling elements into the annular space from the inner opening during assembly of the sheave assembly; -the insert is removably mountable in the aperture and is configured to be removed and inserted radially from within the inner opening; - the annular space is bounded by an outer race provided by the sheave and an inner race; - the inner race being defined by a surface provided by the hub and by a continuous surface of the insert, said continuous surface being shaped to fill the aperture when the insert is mounted in the aperture.
A sheave assembly according to Claim 1, in which the insert is a single-piece insert.
3. A sheave assembly according to Claim 1 or Claim 2, in which the continuous surface of the insert spans a width of a bearing contact surface of the inner race in a direction parallel to an axis of rotation of the sheave.
4. A sheave assembly according to any preceding claim, in which the continuous surface of the insert comprises a saddle surface.-20 -6. 7. 8. 10. 11. 12. 13.
A sheave assembly according to any preceding claim, in which the inner race comprises at least two parallel raceways extending circumferentially around the hub, each raceway providing a respective bearing contact surface.
A sheave assembly according to Claim 5, in which the aperture intersects each of the raceways.
A sheave assembly according to Claim 6, in which the raceways are separated by a circumferential ridge, and the continuous surface of the insert provides a portion of the ridge and a portion of the bearing contact surface of each raceway within the aperture.
A sheave assembly according to any preceding claim, in which the continuous surface of the insert and the surface provided by the hub have a common cross-sectional profile.
A sheave assembly according to any preceding claim, in which the insert is secured in the aperture by a fastener which extends parallel to an axis of rotation of the sheave.
A sheave assembly according to Claim 9, in which the insert comprises a bore which extends through the insert for receiving the fastener.
A sheave assembly according to any one of Claims 1 to 8, in which the hub comprises a circumferentially extending groove in an inner surface of the inner opening and the insert is secured in the aperture by a retaining ring which engages with the circumferential groove.
A sheave assembly according to Claim 11, in which the retaining ring and the insert are a unitary body.
A sheave assembly according to any preceding claim, in which the aperture -21 -has a stadium-shaped cross-section.
14. A sheave block comprising a sheave assembly according to any preceding claim and a pair of cheek plates disposed on opposite sides of the sheave assembly.
15. A sheave block according to Claim 14 when dependent on Claim 9 or on any claim dependent upon Claim 9, in which the fastener extends through a hole at least one of the cheek plates and into the insert to secure the insert in the aperture and to secure the at least one cheek plate to the hub.
16. A sheave block according to Claim 14 or 15, in which the cheek plates are formed from a composite sandwich material having a skin comprising a fibre reinforced polymer material and a core comprising a thermoplastic polymeric material.
17. A sheave block according to any one of Claims 14 to 16, in which the fibre reinforced polymer skin comprises one or more of carbon fibre, flax fibre, and hemp fibre.
18. A sheave block according to any one of Claims 14 to 17, in which the thermoplastic polymer core comprises polyethylene terephthalate.
19. A sheave block according to any one of Claims 14 to 18, in which part of a surface of the hub defining the inner opening comprises a planar surface or saddle surface arranged to engage with a strop for securing the sheave block to a supporting structure in use.
20. A method of assembling a sheave assembly according to any preceding claim, the method comprising: from within the inner opening, inserting the plurality of rolling elements into the annular space through the radially-extending aperture; -22 -mounting the insert in the aperture to close the aperture; and securing the insert in the aperture.