Background of the Invention

[0001] The present invention relates to a torque coupling and method of manufacturing a torque coupling.

Description of the Prior Art

[0002] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0003] Traditionally torque couplings have used a combination of keys and keyways or splines. A keyway is made of recesses formed in rotary bodies, such as shafts, gears, or the like. The keyway is designed to receive a key, which engages the recess in each rotary body, thereby preventing relative rotation of the bodies. Similarly, splines are typically formed as raised ridges on one of the rotary bodies, which then engage corresponding recesses provided on the other rotary body.

[0004] Splines and keyways are typically manufactured by cutting the rotary members in a direction parallel to the shaft axis, making it difficult to manufacture such arrangements using rotary cutting machines. As a consequence, such elements are typically made using specialised equipment, which makes manufacture time consuming and expensive. This also makes manufacturing such arrangements to a high degree of tolerance difficult. Furthermore, splines, keys and keyways, typically have square edges, which result in points of weakness in the coupling, which in turn limits the amount of torque that can be transmitted as well as limiting the lifespan of such couplings. Problems of splines and other similar arrangements are known in the art and will not therefore be discussed further.

[0005] A number of other attempts have been made to provide improved torque couplings. [0006] US2083092 describes a screw comprising a head having a socket the cross contour of which consists of a series of alternating concave and convex arcs equally spaced and tangentially joining each other all about the circle.

[0007] However, this arrangement is difficult to manufacture. Furthermore, the arrangement uses small and hence weak arcs, meaning the arrangement can only be used in low torque applications. A further issue is that the arrangement is purposefully designed to include significant clearance between male and female members, which can in turn lead to issues such as noise and vibration in use. This also means that whilst multiple convex arcs are provided, in practice many of these are not in contact with concave arcs in the other part of the coupling, weakening the overall strength of the arrangement. Consequently, this is only suitable for low powered torque coupling applications such as use as a socket head for a cap screw and thread.

[0008] US4938731 describes a rotatable coupling having a male member and a female member each rotatable about central axes. The male member has lobes and the female member cavities for mutual engagement. The male lobes terminate in wedge-shaped portions, the edges of which lie in a common plane. The female terminates in a flat bottom surface.

[0009] This arrangement is designed to allow quick alignment and as a consequence requires chamfers to assist with this function. However, chamfers lead to weakening of the coupling function, which in turn reduces efficiency in performance and the magnitude of torque that can be transmitted. Furthermore, the arrangement utilised by the document involves male and female members designed to be attached to a shaft, which in turn weakens their ability to transmit torque.

[0010] US5279190 describes a torque transmitting or coupling arrangement for a fastener drive system or the like, wherein the respective externally configured and internally configured components are provided with a series of mating, elliptically curved flutes and lobes. In both the externally and internally configured components, the flutes and lobes are defined by a first series of elliptically curved surfaces which alternate with a second series of elliptically curved surfaces, with the respective surfaces merging smoothly and generally tangentially to define the alternating flutes and lobes on each said component. One of the components, either the externally configured or the internally configured component will preferably have the flutes and lobes thereon generated from ellipses of substantially equal dimension. The other component, of necessity, will have the flutes and lobes generated from ellipses of differing dimensions.

[0011] The arrangement typically leads to a single point of contact between a lobe and flute, which in turn results in a weak coupling. This is further exacerbated by large gaps between the male and female portions, which are required to allow easy mating of the male and female portions, needed as this is designed for repeated use as part of a fastener or the like. However, this in turn further weakens the arrangement, making it suitable for low power applications only. Finally, the arrangement includes undercuts between the lobes and flutes leading to lips on edge of lobes, which provides a further point of weakness.

[0012] US3584667 describes a torque-transmitting or coupling arrangement and tools for same that consist of a body portion having a first series of similar arcuately curved surfaces with their , centres of curvature located at the corners of a regular hexagon and which surfaces are disposed outwardly of such centres with respect to the axis of the body. A second series of surfaces curved oppositely to those of the first series and alternating therewith extend substantially to the sides of said hexagon midway between the corners thereof while the ends of the second series merge tangentially with adjacent ends of the first series.

[0013] This arrangement results in drawbacks similar to those discussed above, and in particular results ih a relatively weak connection, which is prone to failure and only capable of transmitting small forces.

[0014] US5551811 describes a tool assembly comprising two components, adapted to be coaxially coupled together. The components share a common longitudinal axis so that a motion drive transmitted to the first of the two is transmitted to the second. The components afe formed with interfitting male and female coupling members, each coupling member being formed with at least two terminal lobe portions and central, symmetrically disposed portion inset with respect to its associated lobe portions. The central and lobe portions of the male coupling member mate with the central and lobe portions of the female coupling member, forming a mating pair of lobe portions. The coupling members are formed, adjacent each mating pair of lobe portions, with respective surfaces, at least one of which is curved. Upon relative rotational displacement of the components about the common axis, at least one pair of surfaces abuts in such a manner that an angle defined between a tangent to the curved surface at the point.

[0015] However, in this instance, the insets are large, making the lobes relatively small and hence weak. Furthermore, the profile of male member is different to that of female member so that gaps arise between the male and female members, which as previously described leads to noise, inefficient operation and inherent structural weaknesses.

[0016] US3857152, which is similar to US3803872, describes a toothed (spline) coupling for torque transmission between rotatable members comprises a sleeve formed as an internal gear (toothed body) snugly receiving an externally toothed wheel. However, this is an involute spline arrangement and includes splines having straight edges, which leads to inherent structural weaknesses, and a corresponding limit on transmittable torque.

[0017] US2687025 describes a tooth coupling for connecting shafts that are subject to angular misalignment, comprising an internally toothed member and an externally toothed member, the internally toothed member having longitudinally straight teeth which extend parallel to an axis, the externally toothed member having teeth whose opposite sides are longitudinally convex conical surfaces, opposite sides of spaced teeth of said externally toothed member, which teeth lie with a single quadrant, being parts of a common conical surface whose axis is perpendicular to and intersects the axis of said externally toothed member

[0018] This arrangement is designed to allow flexibility between shafts and is not designed for strength. Furthermore, the arrangement uses teeth having straight edges and therefore discontinuities, leading to inherent structural weaknesses.

[0019] US2002003985 describes a driven tool that includes a driven part which is rotatably driven by a drive part. The driven part and the drive part are coaxially arranged one inside of the other. The drive part and the driven part are conical as viewed in a longitudinal section plane containing the axis. The driven part includes driven teeth projecting generally radially with respect to the axis and received in respective radially-open recesses formed in the drive part. Each of the driven teeth makes contact with a wall of the respective recess at first and second contact places which are respectively situated on opposite sides of a generally radial line of symmetry of the driven tooth. The contact places are operable to transmit a drive force from the drive part to the driven part in respective directions of rotation.

[0020] The arrangement is designed to have gaps between male and female members, which in turn leads to issues including noise, inefficiencies and low torque limits. Additionally, the teeth include undercuts, further weakening the strength of the teeth.

[0021] US4073160 describes a high performance coupling intended to transmit a torque from a motor element to a driven element, each of the two elements having at least two teeth symmetrical in relation to the axis of rotation and having generatrices parallel to this axis, each tooth being constituted by flat surfaces symmetrical in relation to their bisecting plane and being connected by curved surfaces, characterized in that each tooth is provided with at least four flat surfaces, with at least two drive generatrices for a given direction of rotation and with at least two different angles of attack. This new coupling finds its application in the field of screws and nuts, and the corresponding spanners, and also for transmission connections and couplings and the necessary tools.

[0022] Gaps are provided between male and female members, which in turn leads to issues including noise, inefficiencies and low torque limits, whilst straight edges on the teeth lead to inherent structural weaknesses.

Summary of the Present Invention

[0023] In a first broad form the present invention provides a torque coupling including:

a) a first rotary member including a male coupling portion, the male coupling portion having a male body arranged on a first rotary member axis, the male body including at least two circumferentially spaced male lobes extending radially outwardly from the male body and being interconnected by male recesses, the male recesses and male lobes defining a continuous outer male surface; and, b) a second rotary member arranged coaxially with the first rotary member, the second rotary member including a female coupling portion having a female body including at least two circumferentially spaced female lobes extending radially inwardly from the female body and being interconnected by female recesses, the female recesses and female lobes defining a continuous inner female surface, the inner female surface and outer male surface being of a complimentary shape so that the male lobes align with the female recesses and the female lobes align with the male recesses.

[0024] Typically a centre of any male recess arc is positioned radially outwardly of a boundary formed by the shortest tangent between two adjacent male lobes.

[0025] Typically an innermost point of each male recess is positioned radially outwardly of a line connecting centers of closest arcs in adjacent male lobes.

[0026] Typically the lobes and recesses are arranged without an undercut.

[0027] Typically the lobes and recesses include segments having an arcuate or linear shape, and wherein arcuate segments of recesses and lobes meet at a point which lies on a line joining the centers of their respective circles.

[0028] Typically each segment joins a next segment with a coincident tangent.

[0029] Typically a width of each male recess is at least one of:

a) less than a width of the male lobes;

b) not less than 60% of the width of the male lobes; and,

c) not less than 80% of the width of the male lobes.

[0030] Typically a width of each female lobe is at least one of:

a) less than a width of the female recess;

b) not less than 60% of the width of the female recess; and,

c) not less than 80% of the width of the female recess.

[0031] Typically male recess widths and male lobe widths are measured between transition points between the male recesses and male lobes.

[0032] Typically the inner female surface and outer male surface are provided in contact over at least 90% of their surface area.

[0033] Typically the coupling potions include three lobes and three recesses.

[0034] Typically the lobes are equally spaced such that the male and female coupling portions are rotationally symmetric. [0035] Typically the lobes are unequally spaced such that the male and female coupling portions are rotationally asymmetric.

[0036] Typically the male and female coupling portions are integrally formed with the first and second rotary members, respectively.

[0037] Typically the torque coupling includes a sleeve arranged coaxially with the first and second rotary members and being positioned between the female and male coupling portions.

[0038] Typically the sleeve includes:

a) a number of circumferentially spaced inner sleeve lobes extending radially inwardly and being interconnected by inner sleeve recesses, the inner sleeve recesses and inner sleeve lobes defining a continuous inner sleeve surface, the inner sleeve surface and outer male surface being of a complimentary shape so that the male lobes align with the inner sleeve recesses and the inner sleeve lobes align with the male recesses.

b) a number of circumferentially spaced outer sleeve lobes extending radially outwardly from the sleeve and being interconnected by inner sleeve recesses, the inner sleeve recesses and inner sleeve lobes defining a continuous outer sleeve surface, the outer sleeve surface and inner female surface being of a complimentary shape so that the outer sleeve lobes align with the female recesses and the female lobes align with the outer sleeve recesses.

[0039] In a second broad form the present invention provides a method of manufacturing a torque coupling, the method including:

a) cutting a first rotary member so as to define a male coupling portion, the male coupling portion having a male body arranged on a first rotary member axis, the male body including at least two circumferentially spaced male lobes extending radially outwardly from the male body and being interconnected by male recesses, the male recesses and male lobes defining a continuous outer male surface; and, b) cutting a second rotary member so as to define a female coupling portion having a female body including at least two circumferentially spaced female lobes extending radially inwardly from the female body and being interconnected by female recesses, the female recesses and female lobes defining a continuous inner female surface, the inner female surface and outer male surface being of a complimentary shape so that the male lobes align with the female recesses and the female lobes align with the male recesses.

[0040] Typically the method includes using at least one of:

a) a rotary cutting machine; and,

b) a computer numerical controlled tooling apparatus.

[0041] In a third broad form the present invention provides a torque coupling including: a) a first rotary member including a male coupling portion, the male coupling portion having a male body arranged on a first rotary member axis, the male body including at least two circumferentially spaced male lobes extending radially outwardly from the male body and being interconnected by male recesses, the male recesses and male lobes defining a continuous outer male surface; b) a second rotary member arranged coaxially with the first rotary member, the second rotary member including a female coupling portion having a female body including at least two circumferentially spaced female lobes extending radially inwardly from the female body and being interconnected by female recesses, the female recesses and female lobes defining a continuous inner female surface; c) a sleeve arranged coaxially with the first and second rotary members and being positioned between the male and female coupling portions, the sleeve including a sleeve body having:

i) a number of circumferentially spaced inner sleeve lobes extending radially inwardly and being interconnected by inner sleeve recesses, the inner sleeve recesses and inner sleeve lobes defining a continuous inner sleeve surface, the inner sleeve surface and outer male surface being of a complimentary shape so that the male lobes align with the inner sleeve recesses and the inner sleeve lobes align with the male recesses; and,

ii) a number of circumferentially spaced outer sleeve lobes extending radially outwardly from the sleeve and being interconnected by inner sleeve recesses, the inner sleeve recesses and inner sleeve lobes defining a continuous outer sleeve surface, the outer sleeve surface and inner female surface being of a complimentary shape so that the outer sleeve lobes align with the female recesses and the female lobes align with the outer sleeve recesses.

[0042] In a fourth broad form the present invention provides a method ,of manufacturing a torque coupling, the method including:

a) cutting a first rotary member to define a male coupling portion, the male coupling portion having a male body arranged on a first rotary member axis, the male body including at least two circumferentially spaced male lobes extending radially outwardly from the male body and being interconnected by male recesses, the male recesses and male lobes defining a continuous outer male surface; b) cutting a second rotary member to define a female coupling portion having a female body including at least two circumferentially spaced female lobes extending radially inwardly from the female body and being interconnected by female recesses, the female recesses and female lobes defining a continuous inner female surface;

c) cutting a sleeve body to define:

i) a number of circumferentially spaced inner sleeve lobes extending radially inwardly and being interconnected by inner sleeve recesses, the inner sleeve recesses and inner sleeve lobes defining a continuous inner sleeve surface, the inner sleeve surface and outer male surface being of a complimentary shape so that the male lobes align with the inner sleeve recesses and the inner sleeve lobes align with the male recesses; and,

ii) a number of circumferentially spaced outer sleeve lobes extending radially outwardly from the sleeve and being interconnected by inner sleeve recesses, the inner sleeve recesses and inner sleeve lobes defining a continuous outer sleeve surface, the outer sleeve surface and inner female surface being of a complimentary shape so that the outer sleeve lobes align with the female recesses and the female lobes align with the outer sleeve recesses.

[0043] in a fifth broad form the present invention seeks to provide a torque coupling including a male body including at least two circumferentially spaced male lobes extending radially outwardly from the male body and being interconnected by male recesses to define a continuous outer male surface and a female body including at least two circumferentially spaeed female lobes extending radially inwardly from the female body and being interconnected by female recesses, the female recesses to define a continuous inner female surface of a complimentary shape to the outer make surface so that the male lobes align with the female recesses and the female lobes align with the male recesses. .

Brief Description of the Drawings

[0044] An example of the present invention will now be described with reference to the accompanying drawings, in which: -

[0045] Figure 1A is a schematic cross sectional end view through the line A- A' of a male coupling portion of a first example of a torque coupling;

[0046] Figure IB is a schematic cross sectional side view through the line B-B' of the male coupling portion of Figure 1 A;

[0047] Figure 1C is a schematic cross sectional end view through the line C-C of a female coupling portion of the first example of a torque coupling;

[0048] Figure ID is a schematic cross sectional side view through the line D-D' of female coupling portion of Figure 1C;

[0049] Figure IE is a schematic cross sectional side view of the first example of the torque coupling;

[0050] Figure 2A is a schematic cross sectional end view through the line E-E' of a male coupling portion of a second example of a torque coupling;

[0051] Figure 2B is a schematic cross sectional side view through the line F-F' of the male coupling portion of Figure 2A;

[0052] Figure 2C is a schematic cross sectional end view through the line G-G' of a sleeve of the second example of a torque coupling;

[0053] Figure 2D is a schematic cross sectional side view through the line H-H' of the sleeve of Figure 2C;

[0054] Figure 2E is a schematic cross sectional end view through the line Ι-Γ of a female coupling portion of the second example of a torque coupling;

[0055] Figure 2F is a schematic cross sectional side view through the line J- J' of the female coupling portion of Figure 2F;

[0056] Figure 2G is a schematic cross sectional view of the second example of the torque coupling; [0057] Figure 3 A is a schematic cross sectional end view of a sleeve of a third example of a torque coupling;

[0058] Figure 3B is a schematic cross sectional side view of the third example of the torque coupling; ^"

[0059] Figure 4A and 4B are schematic perspective views of a fourth example of a torque coupling in exploded and constructed states respectively;

[0060] Figure 5 is a schematic view of an example of a male coupling portion for illustrating features of the torque coupling;

[0061] Figures 6A and 6B are schematic end views of example male coupling portions illustrating different segment shapes;

[0062] Figures 7A to 7C are schematic end views of example male coupling portions;

[0063] Figures 8 A and 8B are schematic end views of example coupling portions illustrating a lobe undercut;

[0064] Figures 9A and 9B are schematic end views of examples of part of a male coupling portion illustrating different recess widths;

[0065] Figure 10 is a schematic end view of an example of male and female coupling portions having different profiles;

[0066] Figures 11A and 1 IB are schematic end views of example male coupling portions showing relative lobe and recess positions;

[0067] Figures 12A to 121 are schematic diagrams of coupling arrangements used in comparative testing;

[0068] Figure 13 A is a graph of the measured load versus the measured crosshead displacement for the coupling arrangements of Figures 12A to 121; and,

[0069] Figure 13B is a graph of the calculated applied torque versus the calculated angle of rotation for the coupling arrangements of Figures 12 A to 121.

Detailed Description of the Preferred Embodiments

[0070] A first example of a torque coupling will now be described with reference to Figures lA to IE.

[0071] In this example, the torque coupling 100 includes first and second rotary members 110, 130, including respective male and female coupling portions 120, 140. The first and second rotary members 110, 130 define respective first and second axes 11 1, 131, which in use are arranged coaxially.

[0072] The rotary members 1 10, 130 can be any form of bodies that are capable of undergoing rotation and between which it is desirable to transmit torque. In one example, the rotary members 1 10, 130, are drive shafts, but this is not essential and other forms of rotary member, such as gears or the like, can be used, as will be described in more detail below.

[0073] The male coupling portion 120 has a male body 121 arranged on a first axis 111 of the first rotary member 110. The male body 121 includes at least two circumferentially spaced male lobes 122 (with three being shown in this example for the purpose of illustration), the male lobes 122 extending radially outwardly from the male body 121 and being interconnected by male recesses 123. The male lobes and recesses 122, 123 define a continuous outer male surface.

[0074] The female coupling portion 140 includes a generally annular shaped female body 141 including at least two circumferentially spaced female lobes 142 (with three being shown in this example for the purpose of illustration), extending radially inwardly from the female body 141. The female lobes 142 are interconnected by female recesses 143, with the female lobes and recesses 142, 143 defining a continuous inner female surface.

[0075] The inner female surface and outer male surface are of a complimentary shape so that when the male and female coupling portions 120, 140 are engaged, as shown in Figure IE, the male lobes 122 align with the female recesses 143 and the female lobes 142 align with the male recesses 123. In this configuration, the torque coupling allows torque to be transferred between the first and second rotary members 110, 130.

[0076] Accordingly, the above described arrangement using lobes and recesses provides a torque coupling that can replace the need for keyways and spline members in torque couplings.

[0077] By providing the outer male surface and inner female surface as continuous surfaces, and in particular, by avoiding discontinuities in the surfaces, this allows the torque coupling to handle greater torque loads. In particular, discontinuities such as sharp edges, can lead to structural weaknesses and hence potential points of failure within torque couplings, thereby reducing the torque that can be transmitted by the coupling.

[0078] Furthermore, by providing continuous surfaces this allows the male and the female coupling portions to be created utilising rotary cutting machines. In particular, this allows the male and female coupling portions to be manufactured by cutting material from the first and second rotary members utilising an appropriate cutting machine such as a computer numerical control (CNC) tooling apparatus. This allows the male and female coupling portions to be made integrally as part of the rotary members, improving the strength of the torque coupling and increasing the magnitude of torque that can be transferred.

[0079] Use of a computer controlled tooling apparatus also allows the male and female portions to be manufactured with a high degree of accuracy. This can be used to minimise gaps between the male outer surface and female inner surface, which in turn maximises contact between the surfaces. Providing a high surface contact area ensures close fit between the male and female members, in effect allowing the torque coupling to function as a single unit once the male and female coupling portions are engaged. The high total contact surface area therefore helps prevent relative movement of the male and female coupling portions, which in turn minimises vibration and noise generated by the torque coupling, as well as reducing lateral movement of the rotary members. This ensures the efficient transmission of torque between the first and second rotary members 110, 130 thereby maximising the effectiveness of the torque coupling, whilst increasing the life span of the torque coupling.

[0080] In one particular example, the male and female coupling portions are arranged to ensure that the outer male surface and inner female surface are in contact over at least 90% of their surface areas, although it will be appreciated that other arrangements coupled be used depending on the application.

[0081] To help further maximise the coupling, ends of the coupling portions and the rotary members are typically perpendicular to the rotary member axes, as shown in Figure IE, thereby maximising the contact area of the male outer and female inner surfaces. [0082] Utilising a three lobe arrangement similar to that described above ensures self centring of the torque coupling, thereby leading to greater stability at higher RPM, although alternative lobe configurations can be used, as will be described in more detail below.

[0083] The above described arrangement also spreads load evenly between the male and female lobes, further increasing the life span of the device and maximising the torque loads thai: can be transmitted.

[0084] A number of further features will now be described in more detail.

[0085] A second example of a torque coupling will now be described with reference to Figures 2 A to 2G. For the purpose of this example, similar reference numerals increased by 100 are used to refer to features similar to those described above with respect to the first torque coupling and these features will not therefore be described in detail.

[0086] Thus, in this example, first and second rotary members 210, 230 are provided having respective male and female coupling portions 220, 240. The male coupling portion 220 includes a male body 221 having male lobes 222 interconnected by male recesses 223, whilst the female coupling portion 240 includes a female body 241 having female lobes 242 interconnected by female recesses 243.

[0087] In this example, the torque coupling further includes a sleeve 250 including a generally annular shaped sleeve body 251. The sleeve body 251 includes a number of circumferentially spaced inner sleeve lobes 252 extending radially inwardly from the sleeve body 251 and being interconnected by inner sleeve recesses 253, so that the inner sleeve recesses 253 and inner sleeve lobes 252 define a continuous inner sleeve surface. The inner sleeve surface and outer male surface of the male coupling portion 220 are of a complimentary shape so that the male lobes 222 align with the inner sleeve recesses 253 and the inner sleeve lobes 252 align with the male recesses 223, in use.

[0088] The sleeve 250 further includes a number of circumferentially spaced outer sleeve lobes 254 extending outwardly from the sleeve body 251 and being interconnected by inner sleeve recesses 255. The outer sleeve recesses 255 and outer sleeve lobes 254 define a continuous outer sleeve surface which is a complimentary shape to the inner female surface of the female coupling portion 240, so that the outer sleeve lobes 254 align with the female recesses 243, whilst the female lobes 242 align with the outer sleeve recesses 255.

[0089] Accordingly, it will be appreciated that the second torque coupling is substantially similar to the first torque coupling, albeit with an intermediate sleeve 250 positioned between the male and female coupling portions 220, 240. Otherwise the torque coupling functions in substantially the same manner as that described above and will not therefore be described in any detail.

[0090] The use of an intermediate sleeve can provide a number of benefits, and in particular can be used to help interconnect first and second rotary members in arrangements other than the end to end arrangements described above, as will now be described with reference to Figures 3 A and 3B. For the purpose of this example, similar reference numerals are used to the example of Figures 2A to 2G increased by 100 are used to feature those described above with respect to the first torque coupling and these features will not therefore be described in further detail.

[0091] In this example, the sleeve 350 includes inner sleeve lobes and recesses 352, 353 and outer sleeve lobes and recesses 354, 355. The sleeve body is formed from three separate sleeve body portions 351.1, 351.2, 351.3, so that the sleeve can be separated before fitting to the male coupling portion 320. The sleeve 350 has an outer radius greater than that of the first rotary member 310, so that the first rotary member 310 and sleeve 350 can be inserted into the female coupling portion 340 of the second rotary member 330. Once in place, the female coupling portion 340 will prevent the sleeve body portions 351.1, 351.2, 351.3 from separating in use, allowing the sleeve to perform as described above with respect to the second example.

[0092] This arrangement allows the first male coupling portion 320 to be provided away from an end of the first rotary member 310, allowing a gear wheel or other similar second rotary member 330 to be mounted along from an end of the first rotary member 310. Accordingly, this arrangement can be used to allow gear wheels to be easily mounted at intermediate positions along a shaft, or other similar rotary member.

[0093] A fourth example of a torque coupling is shown in Figures 4A and 4B. [0094] In particular, this coupling includes first and second rotary members 410.1, 410.2 which include respective male coupling portions 420.1, 420.2. An intermediate body 460 is provided including a female coupling portion 470, allowing the male coupling portions 420.1, 420.2 to be inserted therein, so that the intermediate body 460 interconnects the first and second rotary members 410.1, 410.2.

[0095] In this example, the male coupling portions 420.1, 420.2 can also include a respective aperture extending along the axis of the rotary members 410.1, 410.2, through the male coupling portions 420.1 , 420.2. This allows a bolt 480 to be inserted therein for engagement with the first and second rotary members 410.1, 410.2. Accordingly, it will be appreciated that this allows the first and second rotary members 410.1, 410.2 to be securely connected so as to prevent relative axial movement, in use.

[0096] An example of terminology utilised to describe certain features of the torque coupling will now be described with reference to Figure 5.

[0097] In this example, a male coupling portion 520 includes male lobes and recesses 522, 523. The male recesses 523 are formed from a continuous arc segment of a circle 514 whilst the male lobes 522 include a portion formed from an arc of a circle 513, with the lobes 522 being formed from two connected arcs, as will be described below. In any event, a transition point 524 is defined where the male lobes and male recesses 522, 523 meet, with the transition point 524 being coincident with a line 515 drawn between the centres of the respective circles 513, 514. By having the transition point coincident with the line 515, this avoids discontinuities occurring where the lobes and recesses meet, assisting with manufacture and improving the strength of the torque coupling, as previously described.

[0098] As apparent from the above example, the lobes 622 and recesses 623 can be made of respective segments which can include curved, arcuate or straight profiles, as will now be described with reference to Figures 6A and 6B.

[0099] In the example of Figure 6A, the lobes 622 and recesses 623 are formed from respective segments 622.1, 622.2, 622.3, 623.1 , 623.2, 623.3, which include straight segments 622.2, 623.1, 623.3 and curved segments 622.1, 622.3, 623.2. In this arrangement, it will be appreciated that the transition point between the lobes and recesses will typically be coincident with the segments 623.1, 623.3, and these could therefore be considered as part of the lobes, but are described as recess segments for ease of description.

[0100] In contrast, in the example of Figure 6B all of the lobe and recess segments 622.1, 622.2, 622.3, 623.1, 623.2, 623.3, are curved. It will be appreciated from this that a variety of different configurations for the segments can therefore be provided.

[0101] In the case of adjacent curved arc segments, these meet at a point which lies on a line joining the centres of their respective circles, as described for example with respect to the transition point between the lobes and recesses in Figure 5. This ensures the segments join smoothly to form one continuous path, with each segment joining the next with a coincident tangent. This avoids the presence of discontinuities in the outer male surface and inner female surface, which as described above assists in machining of the male and female coupling portions.

[0102] It will be appreciated from the above that any number of segments can be provided, as long as each segment joins at a tangent to the adjacent segments.

[0103] An optimal number of lobes for the torque coupling is three lobes arranged symmetrically within a circular frame work as shown for example in Figure 7A. However, any number of lobes and corresponding number of recesses can be provided and the use of three lobes is for the purpose of example only.

[0104] Furthermore, symmetry is not critical in the arrangement and asymmetric shapes can be used for the male and female coupling portions, as long as the male and female coupling portions are of complimentary shape. Examples of asymmetric shapes are shown in Figures 7B and 7C.

[0105] It will be appreciated that in the event that the male and female coupling portions are rotationally symmetric, this can be used to allow rotary members to be coupled together with different relative orientations. However, in the event that asymmetric coupling portions are provided, this will mean that the rotary members can only be successfully interconnected with one particular relative orientation, which can be useful in certain applications.

\ [0106] In one example, the torque coupling is arranged so that the male recesses do not undercut the male lobes. An example of an undercut is shown at 802 in Figure 8A, in which the surface of the male recess 823 extends beyond a tangent 801 extending from the widest part of an adjacent lobe 822. The presence of an undercut reduces the strength of the lobes by making the lobe have a thinner width radially inwardly of the widest point of the lobe, meaning the lobe can be more easily sheared under high torque due to the lever advantage by the recess area of the female member. Additionally, the presence of an undercut makes machining of the lobe and recesses difficult thereby complicating manufacture.

[0107] An undercut can be avoided by reducing the depth ^" of the male recess 823, as shown at 803 in Figure 8B. It will be appreciated that the female lobes and recesses have a similar profile.

[0108] The widths of the lobes and recesses are selected so that the male lobes and female lobes have similar load bearing capabilities. This reduces the likelihood of failure occurring in one of the male or female coupling portions, and thereby maximises the torque load that can be transferred for any given size (and in particular diameter and length) of the torque coupling.

[0109] In one example, the preferred profile of the torque coupling is such that the width of the male recess is less than width of the male lobes but typically not less than 60% of the width of the male lobes and more preferably not less than 80% of the width of the male lobes. The female lobes are also complementarily sized, so that the width of the female lobes is less than width of the female recesses, but typically not less than 60% of the width of the female recesses and more preferably not less than 80% of the width of the female recesses. In this regard, the width of the lobes and recesses are typically measured between the transition points with adjacent lobes and recesses.

[0110] In the example of Figure 9A a male coupling portion 920 includes male recesses 923 having a width of 0.52 of the male lobes 922. In this example, the width of the female lobes of the corresponding female coupling portion will be small, leading to a risk that these will shear. [0111] In contrast, in the arrangement of Figure 9B the male coupling portion 920 includes a male recess having a width of 0.96 of the width of the male lobe, which ensures relatively equal widths for the male, and female lobes, reducing the chance of lobe shear, thereby increasing the maximum torque that can be transferred.

[0112] As previously described, the male outer surface and female inner surface should generally be of complementary shapes, as will now be described with reference to Figure 10.

[0113] In this example, male and female coupling portions 1020, 1040 have different outer male and inner female surface shapes, and as a result, there are gaps in either the lobe or recess sections, meaning the male and female coupling portions are only in contact over a relatively small area 1000. This in turn leads to increased forces on the points of contact between the male and female coupling portions, which can lead to defamation and ultimately failure of the lobes.

[0114] As a result, a reduction in contact between the two members will, for the same amount of torque increase surface stress leading to deformation and early failure of the coupling portions. This also decreases the maximum lateral load that the torque coupling can withstand.

[0115] Further explanation of the preferred relative position of the recesses and lobes will now be described with reference to Figures 11A and 1 IB.

[0116] In the example of Figure 11 A, a centre 1 101 of the male recess arc 1102 is positioned radially outwardly of a boundary 1103, formed by the shortest tangent between two adjacent male lobes 1 104, 1105. In this arrangement, the recess 1102 also extends beyond a boundary 1106 connecting centres 1107, 1108 of the closest arcs in the adjacent male lobes 1104, 1105. However, this arrangement weakens the adjacent male lobes by increasing the lobe redial length. As a result, mechanical lever advantage results in a high lateral force on the radially outward end of the lobe, meaning the lobe is more likely to shear at high torque loads.

[0117] Accordingly, as shown in Figure 1 IB, a centre 1 111 of the male recess arc 1112 is positioned radially inwardly of the boundary 1113, formed by the shortest tangent between two adjacent male lobes 11 14, 1115, whilst the recess 1 1 12 is provided radially outwardly of the boundary 1 1 16 connecting centres 1117, 1118 of the closest arcs in the adjacent male lobes 1 114, 1 1 15. This ensures that the lobes retain their strength maximising the torque that can be transferred by the torque coupling.

[0118] It will be further appreciated that the load bearing capability of the torque coupling will depend on a number of factors including the material from which the rotary members, and hence couplings are formed, as well as the size, and in particular the length and diameters of the male and female coupling portions, and that these parameters can therefore be selected as required.

[0119] Accordingly, the above described torque coupling can provide significant improvements in design and performance compared to traditional arrangements, such as keyway and spline members. The improvements can arise from a number of features, which may be provided independently, or in conjunction.

[0120] In one example, the torque coupling provides an optimal profile maximising the torque that can be transmitted and reducing noise and vibrations. The arrangement can also provide self-centring effects, minimising uneven wear, providing greater stability at high RPM and maximising lifespan.

[0121] The profile is typically configured to negate the need for complex internal profiles which are not machine-able on the majority of mills. This allows for the coupling portions to be machined allow for more accurate a precision fit, reducing gaps between the male and female members.

[0122] Consequently, once the two members of the coupling are engaged, the torque coupling performs as if it was a single unit. In one example, the contact area between the two members is over 90% of the total surface area, resulting in minimal movement between the two members, increasing the lifespan of the device, minimizing noise in operation and enhancing performance.

[0123] In one example, the load on the interface between the two members is evenly spread around the whole of the surface between the two members, further increasing the lifespan of the device, and maximising the load that can be handled by the torque coupling. This also allows greater axial loads to be accommodated. [0124] In contrast to this, traditional machining techniques, such as the use of keyway cutters or the like, have poor precision, produce low quality surface smoothness, and are inconsistent in surface machining, especially in regard to internal surfaces. Furthermore, even CNC machines are unable to satisfactorily produce splines on internal surfaces, meaning these arrangements can only be manufactured on uncommon, very specialised and expensive equipment, making the manufacturing process more expensive.

[0125] To demonstrate the effectiveness of the design, comparative testing was performed on various torque transmission coupling designs by the University of Queensland. Testing was performed on prior art coupling designs, including traditional keyways, splines (coarse & fine and square & involute), hex (a six flat sided hexagonal coupling), torx (corresponding to US3584667) and tri-lobe, to those according to the above described arrangement (hereinafter referred to as "The Shamrock").

[0126] A purpose built rig was designed to comparatively test the load displacement characteristics of each coupling design with the use of an Instron 5584 universal test machine. The rig provides a means for converting the crosshead displacement of the Instron 5584 into torsional loading of the shaft/plate coupling.

[0127] The results provide a comparison of common coupling designs against the above described arrangements. Whilst, the measured torque values are specific to the test rig, the materials used for the plates and shafts and the size of the couplers, it will be appreciated that as these factors remain constant between the tests on different samples, then the results provide a good comparative analysis.

[0128] A total of 10 samples were tested, with the plates into which the shafts were coupled being made from Grade 300 structural steel plate. The shafts used for each test were made from K1045 medium carbon steel. These are common materials used to manufacture machine components. The designs tested are shown in Figures 12A to 121, which respectively show the Shamrock, Torx, Hex, Tri Lobe, Keyway, Spline Involute Fine, Spline Square Fine, Spline Involute Coarse, Spline Square Coarse arrangements, respectively. Information regarding the samples and their dimensions is set in table 1 below. Table 1 : Testing sample geometries and loading rate

[0129] The test was displacement controlled with a constant crosshead speed of 5 mm/min for all samples except for Shamrock 1, which corresponds to testing of The Shamrock design at 10 mm/min, whereas The Shamrock 2 was tested at 5 mm/min, to evaluate the sensitivity to cross head displacement rate.

[0130] The crosshead was allowed to displace up to approximately 170-175 mm. This translates to approximately 40° of rotation between the side plates and the centre plate.

[0131] The crosshead displacement and the direct tension applied were measured and recorded. The plots of each sample are shown in Figure 13 A. By using the following two formulas, the results were converted into angular rotation versus applied torque and plotted again in Figure 13B.

Torque (N. m) = Load (N) x Lever Arm (m) eql

Angular Rotation (°) = Extension (m) x 180° eq2

Lever Arm (m) x π [0132] The performance of the different coupling designs can be seen by comparing the properties of the Shamrock to the other coupler types tested. The two main aspects of comparison are:

1. The stiffness (elastic component) of the coupling in this arrangement.

2. The load at onset of permanent (plastic) deformation of the coupling in this arrangement.

[0133] The stiffness is most easily identified/described as the slope (or steepness) of the load/displacement curve (Figure 13A) prior to permanent (plastic) deformation. This is commonly known as the elastic deformation. If the loading is elastic, the components will return to their original position with no damage when the load is removed. The steeper the slope, the stiffer the coupling. In Figure 13 A, the elastic region occurs for the first 5-10 mm of cross head displacement.

[0134] The load-displacement curves of the different couplings shown of Figure 13A above fall into three groups according to their stiffness. The groups and their relative stiffness are:

1. The tri-lobe and keyway which have the lowest stiffness.

2. The splines and the torx which have the highest stiffness.

3. The Shamrock and hex which show stiffness values between that of (i) and (ii).

[0135] The onset of permanent deformation can be identified on the load-displacement curves above as the region where the curve transitions from the steep straight region to the less steep horizontal region. This transition marks the change between non-permanent (elastic) deformation and permanent (plastic) deformation. The load at which this transition occurs is an indication of the strength of the coupling.

[0136] The load-displacement curves of the different couplings shown of Figure 13A above fall into three groups according to their load at the onset of permanent deformation. The groups and their relative loads are:

1. The tri-lobe and keyway which have the lowest permanent deformation onset loads.

2. The splines and the torx which have the highest permanent deformation onset loads. 3. The Shamrock and hex which permanent deformation onset loads between (i) and (ii).

[0137] The three groups of couplings are the same for both the stiffness and the permanent deformation onset loads suggesting that these two aspects are related in this test. Both are highly dependent on the cross sectional area and radial distance from centre of material engaged by the coupling. The more material engaged and the further out from the centre, the stiffer and the higher the permanent deformation onset load is.

[0138] It will also be noted that the Spline and Tri-Lobe arrangements tended to fail before reaching the 40° angular displacement, indicating that these arrangements are more likely to undergo catastrophic failure during excess loading, which is undesirable.

[0139] The comparative test performed demonstrates that the Shamrock design performs better than the tri-lobe and keyway designs and similarly to the hex design. Whilst the Shamrock is not as strong as the spline and Torx arrangements as plastic deformation commences at lower applied torques, critically, the Shamrock is less likely to undergo catastrophic failure than spline arrangements. Furthermore, in comparison to the Torx configuration, even as the Shamrock deforms, it continues to be able to support an increasing load, whereas the load capabilities of the Torx arrangement decrease. This means, in the event that Torx arrangement is unduly stressed, this will significantly weaken its ability to transmit torque and will again lead to more likely failure. Additionally, the spline and Torx arrangements are more difficult and costly to manufacture due to their complexity.

[0140] Finally, in comparing the shamrock to the keyway, a 0.25° offset point was recorded in order to quantify the elastic limit. The Shamrock specimen sustained a 0.97 kNm load before plastic deformation which is more than twice the 0.46 kNm load sustained by the keyway.

[0141] Accordingly, the above tests confirm that the Shamrock performs at least as well if not better than most competing arrangements, whilst generally being significantly easier to manufacture.

[0142] Throughout this specification and claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers.

[0143] Persons skilled in the art will appreciate that numerous variations and modifications will become apparent. All such variations and modifications which become apparent to persons skilled in the art, should be considered to fall within the spirit and scope that the invention broadly appearing before described.