LOW FREQUENCY TORSIONAL SPRING-DAMPER

Abstract

The disclosed invention is a novel method for constructing a LSTSD that simultaneously yields the following advantages over conventional designs: (1) the elastomer is not mold-bonded to the two metallic extremities; (2) the amount of elastomer is relatively smaller compared to conventionally constructed devices; (3) the device only allows the torsional direction to be spring loaded; (4) there is some damping inherently present in the system; (5) the device does not disintegrate on failure of the elastomeric element; and (6) the device is serviceable in the field without disengaging from the rotating shaft. Such a LSTSD when used in a TVI or a TVA would reduce its cost while improving its structural and modal integrity and enabling its serviceability in the field.

Claims

1. A Low Stiffness Torsional Spring-Damper (LSTSD), comprising: a hub including, a first cylindrical Inner Diametric surface (ID) that is radially most proximate to the axial centerline of the LSTSD (CL); a second cylindrical Outer Diametric surface (OD) that is radially most distal to the CL; a first planar annular surface that connects the ID and OD; a second planar annular surface that connects the ID and OD and is axially opposed to the first planar annular surface; and the first and second planar annular surfaces include a plurality of axially through openings (openings); a tubular split bushing (bush) including, a first cylindrical surface radially proximate to the CL that is a non-slippery surface and is received by the OD of the flange as a press-fit; a second cylindrical surface radially distal to the CL that is a slippery surface; bounded axially by two planar annular surfaces; and having a split across the tubular wall that enables bush to be radially flexed during installation; an axisymmetric ring including, a first ID radially proximate to the CL, further including, a radially oriented rectangular recessed channel (channel) disposed radially distal to the CL receiving the OD of the bush as a slip fit for enabling rotation; and two opposing circumferentially bounding ledges on either axial periphery preventing axial motion of the bush after assembly relative to the ring; a second axis-symmetric surface radially distal to the CL; and two axially opposing annular surfaces bounding the first and the second axis-symmetric surfaces of the ring, each further including a plurality of axially oriented holes a plurality of grooved headed-pegs (pegs) including, a cylindrical head (head) with a radially oriented groove; and a cylindrical end that is smaller in diameter than the head and is received by the plurality of axially oriented holes present in the ring; a plurality of O-rings that pass twin-fold through the openings in the hub and are stretched and loaded onto the grooves in the pegs on either axial periphery of the ring; thereby creating a LSTSD that mounts onto the rotating shaft by the first ID surface of the hub only allowing spring loaded torsional motion between the hub and the ring, and enabling the replacement of a damaged spring without disassembly of the LSTSD from the rotating shaft.

2. The LSTSD defined in claim 1 where the hub has alternate geometry of the structure disposed between its ID and OD including but not limited to I-beam, C-Channel, Trapezoidal, or Z shaped cross-sectional shapes.

3. The LSTSD defined in claim 1 where the elastomer O-rings have various cross-sections including but not limited to square, rectangular, triangular, or elliptical shapes.

4. The LSTSD defined in claim 1 where the spring includes a plurality of elastomer cables that are looped on each end.

5. The LSTSD defined in claim 1 where the spring includes a plurality of metallic extension springs that are looped on each end.

6. The LSTSD defined in claim 1 where the bush is replaced by a bearing, including but not limited to roller ball bearing, needle bearing, roller thrust bearing etc. The channel present in the ring for receiving the bush is eliminated, and the bearing press-fits on to the OD surface of the hub and the ID surface of the ring.

7. The LSTSD defined in claim 1 where the pegs have alternate geometry than a grooved headed pin, including any shape that allows the mounting and retention of the spring during operation.

8. The LSTSD defined in claim 1 where the pegs have male threads on their narrow ends that are received by female threads on the axial holes present in the ring.

9. The LSTSD defined in claim 1 where the pegs are not oriented parallel to the CL.

10. The LSTSD defined in claim 1 where the ring and pegs are monolithic. For example, the ring is a stamped component with axially protruding tabs replacing the pegs, the tabs having any shape that allows the mounting and retention of the spring during operation.

11. The LSTSD defined in claim 1 where the bush mounts as a press-fit into the ring and a slip-fit onto channel located on OD of the hub and is disposed radially proximate to the CL.

12. The LSTSD defined in claim 1 where the axial holes and pegs are located in the hub and the openings are located in the ring; thereby, reversing the radial orientation of the spring.

13. A Torsional Vibration Isolator employing the LSTSD defined in claim 1.

14. A Torsional Vibration Absorber employing the LSTSD defined in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is a partial cross-section illustrating the internal structure of a conventional TVI.

[0022] FIG. 2 is a partial cross-section illustrating the internal structure of a conventional TVA.

[0023] FIG. 3 is a partial cross-section illustrating the internal structure of an embodiment of the invention where a plurality of elastomeric O-rings is employed as the LSTSD.

[0024] FIG. 4 is an illustration of an embodiment of the invention where a plurality of metallic extension springs is employed as the LSTSD.

DETAILED DESCRIPTION

[0025] FIG. 3 illustrates an embodiment of the invention that comprises of hub (hub) 1, a tubular split-bushing (bush) 4, an axis-symmetric ring (ring) 3, a plurality of elastomeric O-rings (spring) 2, and a plurality of grooved headed-pegs (pegs) 5.

[0026] Hub 1 is radially most proximate to the CL of the LSTSD and includes a radially proximate tubular nose 11, and a radially distal tubular flange 14. Nose 11 and flange 14 are radially connected on their respective OD and ID by a central tubular rib 12. The ID 111, of nose 11 is rigidly mounted onto the rotating shaft most often via a press-fit condition. Rib 12 has a plurality of through axial openings 13 that allow the passage of the spring 2 axially through rib 12.

[0027] The OD 141 of flange 14, receives ID 41 of bush 4. ID 41 is the non-slippery surface of bush 4 and has a press-fit with OD 141. The bush is tubular with a split through is axial length at one point circumferentially (split) 43. Split 43 may be either parallel or angular to the CL. Split 43 is to facilitate the loading of the bush 4 into the channel defined for accepting it on its OD 42 and its axial extremities. The channel present in ring 3 includes two opposing circumferential ledges at both axial extremities (ledges) 33 and ID 31. OD 42 is the slippery surface of bush 4 and has a slip-fit with ID 31 of channel in ring 3.

[0028] It must be appreciated that the geometric shape of hub 1 is flexible, the only three necessary features being ID 111 that interfaces with the rotating shaft, the OD 151 that interfaces with bush 4, and a plurality of through axial openings 13 in its central region.

[0029] Additionally, it must be appreciated that bush 4 can be replaced with any other type of bearing including but not limited to, roller ball bearing, needle bearing, roller thrust bearing etc. If a bearing is used instead of bush 4 then a channel need not be formed in ring 3 by ID 31 and ledges 33. The bearing can now have a press fit on ID 31 of ring 3, and OD 141 of hub 1. Also, a plurality of bushings and/or bearings may be used for accomplishing the same objective as bush 4.

[0030] The radially most distal axisymmetric surface 32 ring 3 may be cylindrical, include a single or set of circumferential belt grooves, include a set of axially or radially oriented gear or sprocket teeth, or be of any other intended shape to interact with external machinery. Ring 3 on both its axial peripheries includes a plurality of axially oriented blind holes 34. Each hole 34 receives the narrow cylindrical end 52 of a peg 5. Axially opposing the narrow cylindrical end 52, each peg 5 has a head 51 with a diameter larger than that of the narrow cylindrical end 52 including a circumferential groove 53.

[0031] Spring 2 includes a plurality of elastomer O-rings that are threaded through the openings 13 present in hub 1 in twin fold, stretched and looped around grooves 53 on each peg 5 on either axial periphery of ring 3. The geometry of the openings 13 is such that they allow spring 2 to axially pass through hub 1.

[0032] The inventor recognizes that the plurality of pegs 5 and ring 3 can be unified into a single component. For example, ring 3 could be a metallic stamping where pegs 5 are formed by bending tabs into the desired shape. Peg 5 geometry can vary infinitely to any shape that allows spring 2 to be looped around and be retained during operation. Similarly the inventor recognizes that the geometry of groove 53 in peg 5 can have several possible configurations including but not limited to angled grooves, semi-circumferential grooves, grooves with non-circular cross-sections, or even no grooves. Also pegs 5 need not have their axes parallel to the CL.

[0033] The inventor also recognizes that spring 2 need not be limited to a plurality of elastomer O-rings but can include several other constructions such as elastomer cables with twin loops, or elastomer rings of various cross-sectional shapes including but not limited to square, rectangular, triangular, or elliptical cross-sectional shapes. Furthermore, it is possible to have several looping configurations that would yield different stiffness and damping for spring 2. For example, a single O-ring 2 looping across more than one pegs 5 located on ring 3, or even a composite looping combination (e.g. where a few O-rings loop across more than one pegs 5 located on ring 3 while remaining O-rings loop across only one peg 5 located on ring 3).

[0034] Although there are several possible methods of assembling the LSTSD, a suggested method is to: (1) mount the pegs 5 onto ring 3; (2) radially squeeze and install bush 4 into the channel in Ring 3; (3) mount hub 1 into the subassembly thus obtained via a press-fit; (4) mount spring 2 onto the sub-assembly thus obtained by looping the O-rings around grooves 53 in pegs 5 and threading them twin fold through the axial openings 13 in hub 1.

[0035] The advantages of the disclosed invention over conventional constructions are hereby elaborated: First, the need for mold-bonding has been eliminated completely (thereby enhancing cost-effectiveness and ease of manufacturing). Second, the volume of elastomer used is considerably smaller than that used in conventional designs; for example, in one arrangement the volumetric reduction was approximately 80% (thereby enhancing cost-effectiveness). Third, due to the presence of the bush, the invention allows only the torsional degree of freedom to be active (thereby enhancing modal stability). Fourth, due to the use of elastomeric springs, the device has viscous damping inherent to the material (thereby enhancing its NVH performance). Fifth, due to the novel design, a failure of the elastomer does not disintegrate the entire device; the metallic bush joint is mechanically more robust (thereby enhancing its safety characteristics). Lastly, the part can easily be serviced without disassembly from the rotating shaft by pulling out the failed O-rings and replacing them with new O-rings.

[0036] FIG. 4 illustrates an embodiment of the invention that comprises of identical components and construction as the embodiment illustrated in FIG. 3 except where the elastomer O-ring based spring 2 is here replaced by metallic extension springs 2a with double end loops. In this embodiment, the viscous damping is replaced by coulomb damping provided by the friction in springs 2b during operation.