AU2010201738A1 - Misalignment-tolerant Coupling - Google Patents

Abstract

- 4 A misalignment-tolerant coupling transmitting rotation between a driving shaft and a driven shaft; said coupling providing for both angular and/or parallel misalignment 5 between said driving shaft and said driven shaft, characterized in that said coupling includes first and second constant velocity coupling elements and mounted at respective outer ends of a common linking shaft. - 14 hI ~ W ' jat. Al, Z*' Ar ; AV T D o . zoo" V~ -. -.. y.'a:: N.,,.,. N

Description

P100/009 Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Invention Title MISALIGNMENT-TOLERANT COUPLING The invention is described in the following statement including the best method of performing it known to us: Our Ref: 102011 - 2 MISALAIGNMENT-TOLERANT COUPLING The present invention relates to couplings between rotating shafts and, more particularly, to couplings 5 allowing for misalignment between such shafts. BACKGROUND Numerous articles and industry research over the years have demonstrated the need for accurate shaft alignment 10 when transferring the power from a driving to a driven rotating shaft. The evidence indicates that good shaft alignment provides improvements in bearing life, reductions in energy loss and improved machine reliability. As most of the known forms of shaft couplings are generally radially 15 stiff, misalignment exceeding the manufacturer's limited operating range (typically less than l1 angular) results in large side loads imposed on the rotating shafts. While the methods to achieve "good" alignment are varied, the most popular and common form used today is with 20 laser tools. In practice the system must be stopped and electrically isolated for safety reasons. A laser beam projected along one of the shafts and a sensor mounted to the other shaft, provide a reading of the relative misalignment of the two shafts. The readout then displays 25 the necessary corrections in positions, for example by means of shims and/or adjusting bolts to accurately align - 3 the two shafts. Typical accuracies achievable by this means are within 0.1mm. A problem with this alignment method is that the shafts must be stopped, the system made safe and flanges 5 and/or taper lock bushes removed, before the laser equipment can be applied and the results obtained. The entire process may take up hours to rectify the misalignment, especially if "soft foot" conditions are encountered in any of the mounting feet of the driving and 10 driven equipment. Apart from energy losses and strain on bearings, misalignment between shafts causes vibration, sometimes leading to a loosening of the mountings of the equipment, with possibly serious damage resulting. 15 It is an object of the present invention to address or at least ameliorate some of the above disadvantages. 20 Notes 1. The term "comprising" (and grammatical variations thereof) is used in this specification in the inclusive sense of "having" or "including", and not in the exclusive sense of "consisting only of". 25 2. The above discussion of the prior art in the Background of the invention, is not an admission that any - 4 information discussed therein is citable prior art or part of the common general knowledge of persons skilled in the art in any country. BRIEF DESCRIPTION OF INVENTION 5 Accordingly, in one broad form of the invention, there is provided a misalignment-tolerant coupling transmitting rotation between a driving shaft and a driven shaft; said coupling providing for both angular and/or parallel misalignment between said driving shaft and said driven 10 shaft, characterized in that said coupling includes first and second constant velocity coupling elements and mounted at respective outer ends of a common linking shaft. Preferably, allowable said parallel misalignment is up to 15 8mm. Preferably, allowable said angular misalignment is up to 6 degrees. Preferably, said first and second constant velocity coupling elements include at least one Rzeppa type ball 20 joint couplings. Preferably, both said first and second constant velocity couplings are Rzeppa type ball joint couplings. Preferably, said Rzeppa type ball joint couplings are plunging Rzeppa type ball joint couplings.

- 5 Preferably, respective inner races of said first and second constant velocity coupling elements are secured to said respective outer ends of said common linking shaft. Preferably, respective outer races of said first and 5 second constant velocity coupling elements are connected to respective first and second adaptor bosses. Preferably, each of said outer races is clamped between its respective said adaptor boss and a bolting plate; bolts passing from said adaptor boss through holes in 10 said outer race to engage threaded holes in said bolting plate. Preferably, said first and second adaptor bosses are adapted for connection respectively to flanges of shaft bushes mounted to said driving shaft and said driven 15 shaft; said adaptor bosses being provided with projecting location spigots and/or spigot accepting sockets. Preferably, said shaft bushes are taper lock bushes. Preferably, said adaptor bosses of said driving shaft and said driven shaft are provided with taper lock bushes in 20 a plurality of shaft sizes. Preferably, said coupling has sufficient axial contraction freedom of movement to allow insertion of said coupling between said flanges of said shaft bushes. Preferably, one or more spacer rings may be interposed 25 between one of said adaptor bosses and the adjoining shaft bush flange; said spacer rings causing axial - 6 displacement of a said outer race relative to said inner race of a said Rzeppa type coupling element, thereby moving balls of said coupling element to a different wear inducing position within cooperating grooves of said 5 outer and inner race. Preferably, said coupling is protected from ingress of contaminants by a flexible protective boot; said flexible boot provided with integral securing structures adapted for clamped retention between elements comprising said 10 first and second adaptor bosses and said bolting plates. Preferably, circumferential features of said protective flexible protective boot provide reference points; said reference points assuming distorted positions proportional to said misalignment; said distortion 15 providing a means for assessment of allowable misalignment limits of said coupling. Preferably, a template provides assessment of said distortion; said template including reference lines and a reference zone for comparison with said distorted 20 positions of said reference points. In another broad form of the invention, there is provided a method of minimizing side loads on misaligned driving and driven shafts; said method including the steps of interposing a misalignment-tolerant coupling comprising 25 two constant velocity coupling elements interconnected by - 7 a common linking shaft; said method further including the steps of: (a) securing shaft bushes at ends of said driving and driven shafts at a separation distance equal to outer 5 face to outer face distance of adaptor bosses of said misalignment-tolerant coupling, (b) axially contracting said coupling so as to pass projecting spigots of said adaptor bosses between flanges of said shaft bushes, 10 (c) bolting said adaptor bosses to said flanges. Preferably, assessment of whether degree of misalignment between said driving and said driven shaft is within allowable limits is made by means of a template applied to a protective flexible boot of said coupling. 15 In another broad form of the invention, there is provided a mis-alignment tolerant coupling between a rotating drive shaft and a rotating driven shaft; said coupling including first and second constant velocity couplings located at respective outer ends of a common linking 20 shaft; said mis-alignment tolerant coupling providing for both angular and parallel misalignment. Preferably, said first and second constant velocity couplings are Rzeppa type ball joint couplings. Preferably, respective inner rings of said first and 25 second constant velocity couplings are secured to said respective outer ends of said common linking shaft.

Preferably, respective outer rings of said first and second constant velocity coupling are connected to respective first and second adaptor bosses; said adaptor bosses adapted for connection respectively to said 5 rotating drive shaft and said rotating driven shaft. Preferably, said adaptor bosses are provided with projecting location spigots and/or spigot accepting sockets; said location spigots and/or sockets mating with corresponding sockets and/or spigot accepting sockets 10 provided in respective said driving shaft and said driven shaft adaptor bosses; said adaptor bosses of said coupling secured to said adaptor bosses of said driving and driven shafts by securing bolts. Preferably, said coupling has sufficient axial 15 contraction freedom of movement to allow insertion of said coupling between said adaptor bosses of said driving shaft and said driven shaft. Preferably, said adaptor bosses of said driving shaft and said driven shaft are provided with taper lock bushes in 20 a plurality of shaft sizes. Preferably, said coupling is protected from ingress of contaminants by a flexible boot; said flexible boot provided with integral securing structures adapted for clamped retention between elements comprising said first 25 and second adaptor bosses.

- 9 Preferably, said flexible boot includes annular ridges; said annular ridges deforming from a regular spacing and angular position commensurate with the degree of angular and parallel offset between said driving shaft and said 5 driven shaft; said distortion providing visible comparison with a gauge for assessment of the degree of said angular and parallel offset within allowable limits. In yet another broad for of the invention, there is provided a method of accommodating misalignment between a 10 driving shaft and a driven shaft; said method including the steps of: (a) interposing a coupling between said driving shaft and said driven shaft; (b) connecting a first constant velocity coupling 15 element of said coupling to said driving shaft, (c) connecting a second constant velocity coupling element of said coupling to said driven shaft, wherein said first and second constant velocity couplings are interconnected by a common linking shaft. 20 Preferably, said first and second constant velocity couplings are Rzeppa type couplings. In still another broad form of the invention, there is provided a method of interlinking a misaligned rotating driven shaft and driven shaft; said method including the 25 steps of: - 10 (a) connecting a first adaptor boss of a coupling to said driving shaft, (b) Connecting a second adaptor boss of said coupling to said driven shaft, 5 wherein respective said adaptor bosses are connected to outer cages of respective Rzeppa type constant velocity couplings interconnected by a common linking shaft; inner cages of said Rzeppa type couplings connected at respective outer ends of said common linking shaft. 10 BRIEF DESCRIPTION OF DRAWINGS 15 Embodiments of the present invention will now be described with reference to the accompanying drawings wherein: Figure 1 is a general perspective view of a preferred embodiment of the coupling of the present invention with 20 shaft coupling bosses and a protective flexible boot removed for clarity, Figures 2A to 2C are perspective views of the coupling of Figure 1 showing the types of misalignment provided for, Figure 3 is a cross section view of the coupling of 25 Figures 1 and 2 including the protective flexible boot and its preferred method of retention, - 11 Figure 4 is a fragmentary view of the coupling of Figures 1 to 3 showing a detail of the retention method for the protective flexible boot of the coupling, Figure 5 is a sectioned partial view of the coupling 5 of Figures 1 to 3 showing the mounting of one end of the coupling to a taper lock bush, Figure 6 is a sectioned partial view of the main components of one end of the coupling, Figure 7 is a sectioned portion of the protective 10 flexible boot showing differential distortion of the boot convolutions as an indicator of shaft misalignment, Figure 8 is a view of a first preferred form of a template for application to the distorted convolutions of the protective flexible boot, 15 Figure 9 is a view of a second preferred form of the template of Figure 8. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 20 The present invention is for a new type of rotating shafts coupling that is radially "soft" and designed to significantly reduce the alignment setup time for applications such as motor driven pumps. The coupling of the invention comprises two torsionally stiff but radially 25 "soft" coupling elements mounted on a common connecting shaft. The coupling elements to be described are - 12 preferably, though not limited to, constant velocity Rzeppa type ball joints. The proven nature of the Rzeppa type coupling produces constant velocity output at any moderate shaft angle and the combination of two such couplings at a 5 given separation provides full angular and offset displacement possibilities between the two rotating shafts. Features of the coupling include: * True constant velocity power transfer at angles up to 6 degrees and up to 8mm parallel offset 10 misalignment between shafts, a Caters for angular, parallel offset and combinations of these, * Minimises loss of energy as a result of misalignment, 15 * Provides retention of protective flexible boot without need of external bands or clamps, * Allows "cartridge" style insertion of the coupling between fixed flanges, obviating need for removal or loosening of driving and driven 20 shaft flanges, @ Allows for integration with taper lock bushes into end flanges for common shaft sizes. The key feature of the coupling of the present invention is its ability to transfer rotation with the 25 input and output shafts misaligned either angularly or - 13 offset or a combination of both, without the penalty of inducing significant side loads on either shaft. The result is a coupling which does not require precise alignment of the shafts. Furthermore the same gains in energy 5 efficiency, bearing and seal life and reliability, can be achieved as with accurate laser guided shaft alignment, without the need for lengthy down time, Literature studies and tests indicate that at misalignment angles of up to 6a, the loss of energy through friction in a Rzeppa type joint 10 is less than 0.25%. With reference to Figure 1, the coupling 10 according to the invention includes two constant velocity coupling elements 12 and 14 fixed at respective outer ends of a common splined linking shaft 16 at a separation "X". These 15 constant velocity coupling elements 12 and 14 are constructed in the manner of Rzeppa type ball joints. As can be seen from Figures 2A to 2C, the Rzeppa joints of coupling elements 12 and 14 allow parallel shaft axes misalignment as shown in Figure 2A, angular misalignment as 20 shown in Figure 2B or a combination of offset and angular misalignment as shown in Figure 2C Referring now also to Figure 3, each Rzeppa type ball joint of the coupling elements 12 and 14, comprises an outer ring, or race 18 and an inner ring, or race 20, 25 between which is located an annular cage 22. The bore of inner ring 20 is splined (as best seen in Figure 6) and - 14 secured in position on a splined linking shaft 16 by circlips 21. Outer race 18 and inner race 20 are provided with complementary, radially distributed grooves 24 and 26 respectively. Located between each complementary pair of 5 grooves is a ball 28. Balls 28 are retained in apertures 30 in the annular cage 22. It will be understood from Figure 6, that as the angle between the axes of the outer race 18 and inner race 20 changes, the ball 24 rolls in its complementary grooves 24 and 26, constrained by the cage 10 22. The arrangement is such, that as the outer race 18 and inner race 20 rotate in opposite directions to each other about the coupling centre, the balls 24 are caused to move to a position in grooves 24 and 26 at which the centres of 15 the balls lie on a plane at the bisector of the angle between the axes of the outer and inner races. Thus the centres of the balls define the homokinetic plane of the coupling. As a coupling element rotates, the balls oscillate in their grooves for each rotation of the 20 coupling element but maintain their location on the bisector of the angle between the outer and inner race axes. Thus the balls and the retaining cage continuously rotate about the coupling centre in the homokinetic plane. Since it is the balls through which torque is transmitted 25 between the outer and inner races, the condition for constant velocity transfer by the coupling elements 18 and - 15 20 between a driving shaft, the linking shaft 16 and the driven shaft, is satisfied. Referring again to Figure 3, each of the coupling elements 12 and 14 is clamped between an adaptor boss 30 5 and 32 respectively, and bolting plates 34 and 36. Securing bolts 33 (visible for coupling element 12 only) pass through holes 35 provided in the outer races 18 and 20, to engage threaded holes 37 in the bolting plates 34 and 36. Adaptor bosses 30 and 32 are provided with bolt holes 37 10 (visible for adaptor boss 32 only) and projecting location spigots 38. As shown in Figure 5, these adaptor bosses may be coupled to suitable shaft bushes 40, for example taper lock bushes, mounted at the ends of the driving and driven 15 shafts (not shown) such that their flanges are separated by a distance equal to the outer face to outer face distance of the two adaptor bosses 30 and 32. Axial freedom of the coupling 10 is such as to provide sufficient contraction to allow fitment within the flanges 42 of pre-fitted shaft 20 hubs, permitting quick and easy insertion of the cartridge like coupling assembly. When the shafts of a motor and a driven device are out of alignment, the coupling 10 provides power transfer through the inner races, balls and outer races of the two 25 coupling elements 12 and 14. Due to the relative angle imposed by the misalignment, the balls must roll along the - 16 grooves of the inner and outer races as is described in Rzeppa ball joint literature and as is well known to those skilled in the relevant art, However, in practice, whenever the coupling 10 operates between shafts which have no, or 5 virtually no angular or offset misalignment, the movement of the balls in their grooves will be nil or negligible and so wear is not distributed. Instead the balls are forced to create wear only through point contact with the surfaces of the grooves. Although the coupling will remain operable 10 indefinitely, resulting wear may cause unacceptable backlash For this reason, the coupling elements 12 and 14 of the invention are, preferably, so-called "plunging"' Rzeppa joints which allow both angular rotation between the axes 15 of the outer race 18 and inner race 20, as well as axial displacement of one race relative to the other. By interposing at service intervals during the life of the coupling, one or more spacers 44, between one of the adaptor bosses (adaptor boss 30 in Figure 5) and the shaft 20 bush flange 42, the resulting axial displacement of the outer race relative to the inner race moves the contact points of balls 24 to a different locations along the grooves 24 and 26. This significantly extends the service life of the coupling. 25 A particular feature of the design of the adaptor bosses 30 and 32, and the bolting plates 34 and 36, as - 17 shown in Figure 4, is that their opposing peripheries 46 and 48 are shaped to act as retainers for integral securing structures 50 at each end of a protective flexible boot 52, as best seen in the enlarged sectioned view of Figure 4. By 5 this means the boot 52 is secured to the coupling elements 12 and 14 without the need for external clamps, bands or the like. As well as providing a protection against dust and contaminants, and containment for lubricant, the protective 10 boot 52 of the coupling 10 is so configured as to provide an indication of the limits of angular and offset misalignment which the coupling can accommodate. Referring again to Figure 3, preferably, the boot 52 includes two circumferential valleys 54 and 55 and one circumferential 15 ridge 58. Reference point "B" takes up a distorted position proportional to the misalignment between the axes of the two adaptor bosses 30 and 32 at either end of the coupling, when attached to the flanges 42 of the driving and driven shaft bushes 40. As indicated in Figure 3, the shoulders 20 "A" and "C" and the apex of central circumferential ridge "B" provide reference points against which a template may be applied to ensure misalignment limits are not exceeded. As shown in Figure 7, when an angle exists between the axes of the two adaptor bosses 30 and 32, the distances y1 25 between reference points "A" and "B", and y2 between reference points "B" and "C" are unequal.

- 18 Figures 8 and 9 show two preferred forms of a template by means of which the degree of distortion of the flexible boot 52 can be assessed, and thus that the misalignment between the shafts is within limits. In the case of the 5 flat template 60 shown in Figure 8, the template is placed along the boot 52 at that location around the periphery of the boot where the separation between points "A" and "C" is a maximum, and so that reference lines A and C of the template contact the boot at reference points "A" and "C". 10 If reference point "B" falls within the hatched "Reference Zone for B", the misalignment between the axes is within limits. The cylindrical form of the template of Figure 9 is similarly applied with the template rotated until reference lines A and C are coincident with reference points "A" and 15 "C" of the boot 52. Again if point "B" lies within the reference zone for B, the angle is within limits The above describes only some embodiments of the present invention and modifications, obvious to those 20 skilled in the art, can be made thereto without departing from the scope of the present invention.

Claims (20)

1. A misalignment-tolerant coupling (10) transmitting rotation between a driving shaft and a driven shaft; said coupling providing for both angular and/or 5 parallel misalignment between said driving shaft and said driven shaft, characterized in that said coupling includes first and second constant velocity coupling elements (12) and (14) mounted at respective outer ends of a common linking shaft (16). 10

2. The coupling of claim 1 wherein allowable said parallel misalignment is up to 8mm.

3. The coupling of claim 1 wherein allowable said angular misalignment is up to 6 degrees.

4. The coupling of claim 1 wherein said first and second 15 constant velocity coupling elements (12) and (14) include at least one Rzeppa type ball joint coupling.

5. The coupling of claim 1 wherein both said first and second constant velocity couplings are Rzeppa type ball joint couplings. 20

6. The coupling of claim 4 or 5 wherein said Rzeppa type ball joint couplings are plunging Rzeppa type ball joint couplings.

7. The coupling of any previous claim wherein respective inner races (20) of said first and second constant 25 velocity coupling elements are secured to said - 20 respective outer ends of said common linking shaft (16) .

8. The coupling of any previous claim wherein respective outer races (18) of said first and second constant 5 velocity coupling elements are connected to respective first and second adaptor bosses (30) and (32).

9. The coupling of claim 8 wherein each of said outer races (18) is clamped between its respective said adaptor boss and a bolting plate (34) or (36); bolts 10 (33) passing from said adaptor boss through holes in said outer race (18) to engage threaded holes (37) in said bolting plate.

10. The coupling of claim 8 or 9 wherein said first and second adaptor bosses (30) and (32) are adapted for 15 connection respectively to flanges (42) of shaft bushes (40) mounted to said driving shaft and said driven shaft; said adaptor bosses being provided with projecting location spigots (38) and/or spigot accepting sockets. 20

11. The coupling of claim 10 wherein said shaft bushes are taper lock bushes.

12. The coupling of any one of claims 8 to 11 wherein said adaptor bosses (30) and (32) of said driving shaft and said driven shaft are provided with taper lock bushes 25 in a plurality of shaft sizes. - 21

13. The coupling of any previous claim wherein said coupling has sufficient axial contraction freedom of movement to allow insertion of said coupling between said flanges (42) of said shaft bushes (40). 5

14. The coupling of any previous claim wherein, one or more spacer rings (44) may be interposed between one of said adaptor bosses (30) or (32) and the adjoining shaft bush flange; said spacer rings causing axial displacement of a said outer race (18) relative to 10 said inner race (20) of a said Rzeppa type coupling element, thereby moving balls (28) of said coupling element to a different wear inducing position within cooperating grooves (24) and (26) of said outer and inner race.

15 15. The coupling of any one of claims 9 to 14 wherein said coupling is protected from ingress of contaminants by a flexible protective boot (52); said flexible boot provided with integral securing structures (50) adapted for clamped retention between elements 20 comprising said first and second adaptor bosses (30) and (32) and said bolting plates (34) and (36).

16. The coupling of claim 15 wherein circumferential features (54,55,58) of said protective flexible protective boot (52) provide reference points (A,B,C); 25 said reference points assuming distorted positions proportional to said misalignment; said distortion - 22 providing a means for assessment of allowable misalignment limits of said coupling.

17. The coupling of claim 15 or 16 wherein a template (60) provides assessment of said distortion; said template 5 including reference lines and a reference zone for comparison with said distorted positions of said reference points.

18. A misalignment-tolerant coupling (10) transmitting rotation between a driving shaft and a driven shaft; 10 said coupling providing for both angular and/or parallel misalignment between said driving shaft and said driven shaft, characterized in that said coupling includes first and second constant velocity coupling elements (12) and (14) mounted at respective outer 15 ends of a common linking shaft (16); said first and second constant velocity couplings including at least one Rzeppa type coupling.

19. A method of minimising side loads on misaligned driving and driven shafts; said method including the 20 steps of interposing a misalignment-tolerant coupling (10) comprising two constant velocity coupling elements (12) and (14) interconnected by a common linking shaft (16); said method further including the steps of: 25 (a) securing shaft bushes (40) at ends of said driving and driven shafts at a separation distance equal to outer face to outer face distance of adaptor bosses (30) and (32) of said misalignment-tolerant coupling, (b) axially contracting said coupling so as to pass 5 projecting spigots (38) of said adaptor bosses between flanges of said shaft bushes, (c) bolting said adaptor bosses to said flanges.

20. The method of claim 19 wherein assessment of whether degree of misalignment between said driving and said 10 driven shaft is within allowable limits is made by means of a template (60) applied to a protective flexible boot (52) of said coupling.