WO2013175209A1

WO2013175209A1 - A flexible coupling

Info

Publication number: WO2013175209A1
Application number: PCT/GB2013/051340
Authority: WO
Inventors: Graham Edward HARPIN
Original assignee: Renold Plc
Priority date: 2012-05-23
Filing date: 2013-05-22
Publication date: 2013-11-28
Also published as: GB201209060D0

Abstract

A flexible coupling (1) for transmitting torque has concentric inner (2) and outer (4) coupling members. The inner member (2) has a plurality of angularly spaced first projections (8) extending towards the outer member (4). The outer member (4) has a plurality of angularly spaced second projections (9) extending inwards towards the inner member (2). The first and second projections (8,9) define between them a plurality of pockets (11). An elastomeric coupling element (12) is disposed in each pocket (11). The coupling element (12) has a trilobe shape with a peripheral profile that is generally triangular with three sides (16), the three sides (16) being interconnected by three arcuate lobes (15). The radius of curvature of each side (16) is greater than the radius of curvature of each lobe (15).

Description

A FLEXIBLE COUPLING

The present invention relates to a flexible coupling of the kind used to interconnect machine components. Known flexible couplings of this kind are often used to connect an engine to a driven component such as, for example, a gearbox or alternator. Such couplings are substantially disc-shaped and arrange to rotate about an axis. They generally comprise a rigid inner member connected to a rigid outer annulus via elastomeric members such as rubber blocks. The inner member is typically connected to the output shaft of the engine and the outer member is bolted to the driven components. The elastomeric members afford torsional flexibility in the coupling. In particular, the elastomeric members are resiliently compressed during relative angular displacement between the inner and outer members in at least one direction about the axis of rotation. One example of a commercially available flexible coupling of the kind described above is available from Renold Hi-Tec Couplings under its DCB-GS range. The inner member has radially outwards directed projections whereas the outer member has radially inwards directed projections, the two sets of projections defining between them chambers in which elastomeric members are received. Torque is transmitted from the inner member to the outer member via the projections and the elastomeric members. The principal elastomeric members are in the form of rubber blocks of circular cross- section.

There is a continuing requirement to improve the torque capacity of such couplings. In couplings of the kind described above it is either necessary to increase the diameter of the coupling so that the elastomeric blocks are disposed at a greater distance from the axis of rotation or to increase the size of the elastomeric members. In the former instance, the size and/or mass of the coupling is increased to a point where it becomes undesirable or impractical. In the latter instance the increase in size of the elastomeric members necessitates a reduction in thickness of parts of the inner or outer members to an unacceptable degree.

It is one object of the present invention to obviate or mitigate the aforementioned disadvantages. According to the present invention there is provided a flexible coupling for transmitting torque and having an axis of rotation, the coupling comprising an inner member and a radially spaced, substantially concentric, outer member, the inner member having a plurality of angularly spaced first projections extending towards the outer member and the outer member having a plurality of angularly spaced second projections extending inwards towards the inner member, the first and second projections defining between them a plurality of pockets, a plurality of elastomeric coupling elements disposed in the pockets, at least one of the elastomeric coupling elements having a trilobe shape with a peripheral profile that is generally triangular with three sides, the three sides being interconnected by three arcuate lobes.

When torque is transmitted by the coupling any relative angular rotation of the inner and outer members in at least one direction will resiliently compress the elastomeric coupling elements. The flexible nature of the coupling accommodates angular and/or axial and/or radial misalignment of the driving and driven components between which the coupling is connected in use.

The shape of the coupling element provides for a flexible coupling with a relatively high torque capacity compared to its size, whilst maintaining a sufficient amount of torsional flexibility.

The radius of curvature of each side may be greater than the radius of curvature of each lobe. Preferably the (or each) coupling element has a rotational symmetry of 120°.

The sides of the (or each) elastomeric coupling element may be substantially convex.

The (or each) elastomeric coupling element may have opposed major faces, at least one of those major faces having a recess that may be in the form of a dimple. The recess may be, for example, circular in outline or may have a profile that is substantially the same shape as the outer profile of the elastomeric coupling element. Such a recess provides for a coupling with a lower stiffness (compared to a coupling in which the elements do not have such a recess), which may be desirable in certain applications. Each side of a given coupling element may have the same length as the other sides and may have the same radius of curvature as the other sides. In an embodiment where there is a plurality of coupling elements, each coupling element may be identical or the radius of curvature of the sides may vary between coupling elements. Each lobe of the (or each) coupling element may be of the same length and may have the same radius of curvature.

The first and/or second projections may extend in a substantially radial direction. The (or each) elastomeric coupling element is preferably disposed in a respective pocket such that a first side is in contact with an inner surface of the outer coupling member, which inner surface may be cylindrical. A first lobe, opposite the first side of the coupling element may be in contact with an outer surface of the inner coupling member, which outer surface may be cylindrical. The other two sides are preferably in contact with a respective face of the first and second projections.

The first projections may be substantially equi-angularly spaced around the inner coupling member. The second projections may be equi-angularly spaced around the outer coupling member.

The first and/or second projections may have planar surfaces for contact with sides of elastomeric coupling element.

The inner and/or outer member are preferably disc-shaped. The inner member may be penetrated by an axial bore for receipt of a rotary shaft. The first and/or second projections are preferably in the form of webs that also extend in an axial direction. The projection may be equi-angularly spaced around the respective inner or outer member. Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a front view of one embodiment of a flexible coupling according to the present invention, shown with a cover removed to reveal internal components;

Figure 2 is a front view of a second embodiment of a flexible coupling according to the present invention, shown with a cover removed to reveal internal components;

Figure 3 is a front perspective view of an elastomeric block of the coupling of figure 1 or 2;

Figure 4 is a side perspective view of the block of figure 3, shown cut-away to illustrate the cross-sectional shape; and

Figure 5 is a front perspective view of an alternative embodiment of an elastomeric block for use in place of the block of figures 1 to 4.

Referring now to figure 1 of the drawings, the flexible coupling 1 has a generally cylindrical inner coupling member 2 that is penetrated by an axial bore 3 for receiving a shaft (not shown) of a driven component (also not shown). Radially outwardly spaced from the inner member 2 is a cylindrical outer member 4 with a flange 5 extending radially from its outer peripheral surface. The flange 5 has a plurality of apertures 6 for receiving fasteners (not shown) by which the coupling is fastened to a driving component (not shown) such as, for example, a flywheel or flanged shaft. The coupling members 2, 4 are concentrically disposed for co-rotation around a rotational axis X at the centre of the axial bore 3.

Each coupling member 2, 4 has an inner and outer substantially cylindrical surface. On its outer cylindrical surface 7, the inner coupling member 2 has six thin webs 8 that project radially outwards towards the outer coupling member 4 and extend along the axial length of the inner coupling member 2. The webs 8 are substantially equi- angularly spaced around the circumference of the inner coupling member 2 in the embodiment shown in figure 1 . It will be appreciated that any suitable number and spacing of projections may be provided. The outer coupling member has six thin webs 9 that project inwardly from an inner surface 10 of the cylinder. In this particular embodiment the webs 9 are equi-angularly spaced and extend in a direction that is inclined relative to a radial line that intercepts the rotational axis X. The inner and outer coupling members 2, 4 are rotationally oriented such that their respective webs 8, 9 are angularly offset. This arrangement provides for a plurality of pockets 1 1 . Each pocket is defined in the circumferential direction between a web 8 of the inner coupling member 2 and a web 10 of the outer coupling member 4, and in the radial direction between respective cylindrical surfaces 7, 10 of the coupling members 2, 4. The inner and outer coupling members 2, 4 are resiliently interconnected by elastomeric coupling elements 12, 13 disposed in the pockets 1 1 .

In the embodiment of figure 1 the flexible coupling 1 is configured to operate in only one rotational direction and thus there are two sorts of elastomeric members 12, 13. Leading elastomeric coupling elements 12 are interspersed in the circumferential direction with trailing elastomeric blocks 13. The leading elastomeric coupling elements 12 are intended to transmit the torque from the inner coupling member 2 to the outer coupling member 4 whereas the trailing blocks 13 are not intended transmit torque in the normal direction of rotation.

In the embodiment of figure 2 the flexible coupling is configured to be bi-directional and therefore only one sort of elastomeric member is provided (identical to the leading elastomeric member of figure 1 ). In this embodiment components that are common to the first embodiment of figure 1 are given the same reference numeral but incremented by a value of 100, and are not described except in so far as they differ from their counterparts of figure 1 . Inwardly directed webs 109 of the outer coupling member 104 extend in a substantially radial direction.

Each trailing elastomeric block 13 of figure 1 is bolted or otherwise secured to a face of one of the outwardly projecting webs 8 of the inner coupling member 2. It may take any suitable shape but is typically much smaller that the leading elastomeric members 12 so as to reduce the overall size and weight of the coupling. In the embodiment shown it has a substantially planar first surface that abuts the projecting web 8 to which it is secured and an opposed surface that is approximately planar but has rounded corners, the opposed surface being for abutment with a projecting web 9 of the outer coupling member 4. Each leading elastomeric member 12, 1 12, which is shown in more detail in figures 3 and 4, comprises a block of rubber-based compound having a generally triangular profile but with the vertices rounded to as to form three lobes 15a, 15b, 15c equi- spaced around the periphery of the block. The trilobate outer profile of the block approximates a reuleaux triangle in that it has three sides 16a, 16b, 16c of equal length each defined by a curve of the same radius. However, whereas in a reuleaux triangle the sides intersect to form three vertices and all points on a given side are equi-distant from an opposite vertex, the profile of the block is modified such that the sides do not intersect to form vertices but are interconnected by rounded edges so as to form the three lobes 15a, 15b, 15c. The radius of curvature of the convex sides is greater than the radius of curvature of the three lobes 15a, 15b, 15c.

Each side 16a, 16b, 16c is of equal length and each lobe 15a, 15b, 15c is of equal length with the result that the block has rotational symmetry of 120° when viewed from the front (as depicted in figures 1 and 3).

Upper and lower major surfaces 17, 18 of the leading elastomeric members 12 each have recessed dimples 19 with a profile having substantially the same outline as the profile of the rubber block as can be seen in figures 1 and 3. It is to be understood that the shape of the dimple 19 may take any suitable form and an example of an embodiment 212 with a dimple of circular profile 219 is shown in figure 5.

It can be seen in figures 1 and 2 that each leading elastomeric coupling member 12, 212 is received in a respective pocket 1 1 , 1 1 1 . It is has a size such that its three sides 16a, 16b, 16c or 1 16a, 1 16b, 1 16c abut with surfaces of the inner and outer coupling members 2, 4, 102, 104. In particular a first side 16a, 1 16a is disposed such that it abuts the inner surface 10, 1 10 of the cylinder of the outer member 4, 104, a second side 16b, 1 16b is in contact with a planar face of a projecting web 8, 108 of the inner coupling member 2, 102 and the third side 16c, 1 16c is in abutment with a face of the inwardly directed web 9, 109 of the outer coupling member 4, 104. The respective faces of the first and second projections 8, 108, 9, 109 are arcuate towards the end where they are integrally connected to the respective cylinder of the coupling member but are substantially planar towards their free ends. A tip of the lobe 15a opposite the first side 16a is in contact with the outer cylindrical surface 7, 107 of the inner coupling member 2, 102. There are only two significant areas of the pocket 1 1 , 1 1 1 that are not filled by the respective leading elastomeric coupling element 12, 1 12. A first clearance volume 20, 120 is located between the lobe 15c, 1 15c, the inner cylindrical surface 10, 1 10 of the outer coupling member 4, 104 and the radially outer end of the web 8, 108 of the inner coupling member 2, 102. A second clearance volume 21 , 121 is provided in a region that extends between the outer cylindrical surface 7, 107 of the inner coupling member 2, 102, an end of the inwardly directed web 9, 109 of the outer coupling member, and around the first lobe 15a, 1 15a and the third side 16c, 1 16c of the block.

An annular cover plate (not shown) is fixed to the front of the coupling so as to contain the elastomeric coupling elements.

In use, the coupling is connected between driving and driven components. For example, a shaft may be secured in the bore 3, 103 of the inner coupling member 2, 102 by means of a key connection and a flywheel may be bolted to the flange 5, 105 of the outer coupling member 4, 104. Rotational movement of the flywheel is transferred to the inner member 2, 102 via the lead elastomeric coupling elements 12, 1 12, which are loaded in compression. The coupling elements 12, 1 12 are designed to provide controlled torsional flexibility and so accommodate angular, radial or axial misalignment between the driving and driven components.

The particular shape of the leading elastomeric coupling elements 12, 1 12 affords a substantial increase in torque capacity compared a conventional coupling with circular profile coupling elements. This is achieved without significant changes to the overall envelope or mass of an existing coupling. It therefore has a relatively low weight and inertia. The shape also provided for a relatively low torsional stiffness that is beneficial in certain applications.

There may be more than one coupling element 1 1 , 12, 1 12 disposed in each pocket 1 1 ,1 1 1 . There may be a row of such coupling elements extending in an axial direction in each pocket.

The dimples 19, 1 19 and the unoccupied clearance volumes 20, 120, 21 , 121 of the pockets 1 1 , 1 1 1 afford a reduction in torsional stiffness as they provide a void into which the rubber may expand during compression. In some applications the dimples 19, 1 19 may be omitted. The rotational symmetry of the leading elastomeric coupling element 12, 1 12 eliminates assembly errors in that they may be oriented in any one of three positions in order to fit within the pocket 1 1 , 1 1 1 .

The flexible coupling exhibits low noise and vibration, particularly as there is no metal to metal contact.

The flexible coupling of the present invention may be used to transmit torque between any suitable driving and driven components. For example it may be used to couple a flywheel to a rotary shaft, a flywheel to a flange of a shaft of other rotary component or to interconnect two shafts.

It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in the appended claims. For example, the precise shape and orientation of the projections of each coupling member may vary. Moreover, the sides of the trilobate coupling element may not necessarily be convex, they may, for example, be substantially planar. Furthermore, the material of the coupling elements may be of any sort that affords resilient compressibility.

The described and illustrated embodiments are to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be protected. It should be understood that while the use of words such as "preferable", "preferably", "preferred" or "more preferred" in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and embodiments lacking such a feature may be contemplated as within the scope of the invention as defined in the appended claims. In relation to the claims, it is intended that when words such as "a," "an," "at least one," or "at least one portion" are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim. When the language "at least a portion" and/or "a portion" is used the item can include a portion and/or the entire item unless specifically stated to the contrary.

Claims

A flexible coupling for transmitting torque and having an axis of rotation, the coupling comprising an inner member and a radially spaced, substantially concentric, outer member, the inner member having a plurality of angularly spaced first projections extending towards the outer member and the outer member having a plurality of angularly spaced second projections extending inwards towards the inner member, the first and second projections defining between them a plurality of pockets, a plurality of elastomeric coupling elements disposed in the pockets, at least one of the elastomeric coupling elements having a trilobe shape with a peripheral profile that is generally triangular with three sides, the three sides being interconnected by three arcuate lobes.

A flexible coupling according to claim 1 , wherein the at least one coupling element has a rotational symmetry of 120°.

A flexible coupling according to claim 1 , wherein the radius of curvature of each side is greater than the radius of curvature of each lobe.

A flexible coupling according to claim 1 , 2 or 3, wherein the sides of the at least one elastomeric coupling element is substantially convex.

A flexible coupling according to any one of claims 1 to 4, wherein the at least one elastomeric coupling element has opposed major faces, and at least one of those major faces has a recess.

A flexible coupling according to claim 5, wherein the recess is substantially circular in outline.

A flexible coupling according to claim 5, wherein the recess has a profile that is substantially the same shape as the outer profile of the at least one elastomeric coupling element.

8. A flexible coupling according to any preceding claim, wherein each side of the at least one coupling element is of the substantially the same length.

9. A flexible coupling according to any preceding claim, wherein each side of the at least one coupling element has substantially the same radius of curvature.

10. A flexible coupling according to any preceding claim, wherein each lobe of the at least one coupling element is of substantially the same length.

1 1 . A flexible coupling according to any preceding claim, wherein each lobe of the at least one coupling element has the same radius of curvature.

12. A flexible coupling according to any preceding claim, wherein the at least one elastomeric coupling element is disposed in a respective pocket such that a first side is in contact with an inner surface of the outer coupling member.

13. A flexible coupling according to claim 12, wherein a first lobe, opposite the first side of the coupling element is in contact with an outer surface of the inner coupling member.

14. A flexible coupling according to claim 13, wherein second and third sides of the at least one elastomeric coupling element are in contact with respective faces of the first and second projections.