GB2300461A

GB2300461A - Compression loaded torsional device

Info

Publication number: GB2300461A
Application number: GB9609323A
Authority: GB
Inventors: Iii Edward J Arlt; David Snider
Original assignee: Continental Emsco Co
Current assignee: Oil States Industries Inc
Priority date: 1995-05-05
Filing date: 1996-05-03
Publication date: 1996-11-06
Anticipated expiration: 2016-05-03
Also published as: NO961798D0; GB9609323D0; GB2300461B; NO961798L

Abstract

A torsional coupling 300 for transmitting torque in a direction about a longitudinal axis 345 of the torsional coupling includes a plurality of torsional springs 10, outer couplings 305, inner couplings 310, and torque drive couplings 315,320. Each torsional spring 10 includes an outer ring, an outer elastomeric ring, an intermediate ring, an inner elastomeric ring, and an inner ring operably coupled to and coaxially positioned with respect to one another. The elastomeric rings include inner and outer surfaces which are elliptically shaped in the plane transverse to the longitudinal axis of the torsional spring with the elliptical shapes of the inner elastomeric ring positioned at a different orientation from the elliptical shapes of the outer elastomeric ring. Adjacent torsional springs are operably coupled to and coaxially positioned with respect to each other by means of the outer couplings. Pairs of adjacent torsional springs are in turn operably coupled to and coaxially positioned with respect to each other by means of the inner couplings. The torque drive couplings are operably coupled to the torsional coupling assembly at opposite ends thereof to thereby permit the torsional coupling to store, release, or transmit torque.

Description

COMPRESSION LOADED TORSIONAL DEVICE This invention relates generally to compression loaded devices and, more specifically relates to compression loaded elastomeric devices utilized as springs or couplings.

Increased oil consumption has led to exploration and drilling in difficult geographic locations that were previously considered to be economically unfeasible.

As is to be expected, drilling under these difficult conditions leads to problems that are not present under more ideal conditions. For example, an increasing number of exploratory wells are being drilled in deep water, offshore locations in an attempt to locate more oil and gas reservoirs. These exploratory wells are generally drilled from floating vessels, leading to a set of problems peculiar to that environment.

As in any drilling operation, offshore drilling requires that drilling fluid must be circulated through the drill bit to cool the bit and to carry away the cuttings. This drilling fluid is normally delivered to the drill bit through the drill string and returned to the floating vessel through an annulus formed between the drill string and a large diameter pipe, commonly known as a riser. The riser typically extends between a subsea well-head assembly and the floating vessel and is sealed against water intrusion.

The lower end of this riser is connected to the well-head assembly adjacent the ocean floor, and the upper end usually extends through a centrally located opening in the hull of the floating vessel. The drill string extends longitudinally through the riser and into earth formations lying below the body of water, and drilling fluid circulates downwardly through the drill string, out through the drill bit, and then upwardly through the annular space between the drill string and the riser, returning to the vessel.

As these drilling operations progress into deeper waters, the length of the riser and, consequently, its unsupported weight also increases. Riser structural failure may result if compressive stresses in the elements of the riser exceed the metallurgical limitations of the riser material. Riser tensioning systems are typically used to avoid this type of riser failure.

Riser tensioning systems are installed onboard the vessel. The systems apply an upward force to the upper end of the riser, usually by means of cable, sheave, and pneumatic cylinder mechanisms connected between the vessel and the upper end of the riser. In addition, buoyancy or ballasting elements may also be attached to the submerged portion of the riser. These usually are comprised of syntactic foam elements or individual ballast or buoyancy tanks formed on the outer surface of the riser sections. The ballast or buoyancy tanks are capable of being selectively inflated with air or ballasted with water by using the floating vessel's air compression equipment. These buoyancy devices create upwardly directed forces in the riser, and thereby, compensate for the compressive stresses created by the riser's weight.

Both types of these mechanisms suffer from inherent disadvantages. Hydraulic and pneumatic tensioning systems are large, heavy, and require extensive support equipment, such as, air compressors, hydraulic fluid, reservoirs, piping, valves, pumps, accumulators, electrical power, and control systems. The complexity of these systems necessitate extensive and frequent maintenance with their attendant high cost.

Oil exploration and drilling in remote geographic locations has further led to the transport of petroleum by supertankers which are often too large to maneuver within most harbors and shipping channels. Consequently such ships often must load and offload their cargo at specially designed moorings in deep water. When a boat or other vessel is moored to an offshore drilling platform or offshore oil and gas pipeline offloading mooring by means of a wire rope or other flexible but relatively inelastic line, it is conventional to provide the line with some type of device for maintaining the line taut while allowing a predetermined amount of resilient elongation in order to allow relative movement between the vessel and its mooring.

Prior art line compensators have utilized a variety of energy absorbing devices to maintain a resilient S-shaped bend in the line that stretches into a more elongated S-shape as tensile forces are applied to the line. Such line compensators utilize a variety of linear and torsional elastomeric spring elements. The elastomeric torsional spring elements of the prior art have been limited to shear dominated designs by employing a plurality of elastomeric members of circular cross-section. Such shear dominated designs are characterized by limited load and fatigue capacity as well as susceptibility to catastrophic failure.

The increased reliance upon offshore oil and gas exploration has further led to the operation of marine drives of oil and gas transport vessels in extreme operating conditions. In service, the drive shafts of such marine drives may be subjected to unpredictable loadings. If a sudden high loading is applied to the shaft, the shaft could be permanently damaged by the high torsional stresses placed on the shaft.

Such drive shafts also typically undergo oscillatory loadings, i.e., loadings which are greater or less than the mean load on the shaft. Oscillatory loadings can create undesirable stresses and high noise levels during shaft operation.

To protect a drive shaft from these unpredictable and oscillatory loadings, a torsional coupling typically is inserted in the shaft to provide a resilient interface between the powered or input portion of the shaft and the driven or output portion of the shaft. Such conventional torsional coupling devices often utilize an elastomeric material as an interface to absorb unpredictable or oscillatory loadings placed on the shaft, to reduce noise levels, and to allow for slight misalignments, axial displacements, or angularities between the input and output shaft portions.

The use of elastomers for such springs and couplings has conventionally been limited to shear dominated designs because no simple and effective means of satisfying the functional requirements with a compression dominated device was available. Such shear dominated devices are characterized by limited load and fatigue capacity as well as susceptibility to catastrophic failure.

The present invention is directed to overcoming or minimizing one or more of the problems set forth above.

In accordance with a first aspect of the present invention, there is provided a torsional spring that includes an outer rigid member, an elastomeric member, and an inner rigid member operably coupled to and coaxially positioned with respect to one another. The elastomeric member includes inner and outer surfaces which are elliptically shaped in the plane transverse to the longitudinal axis of the torsional spring.

In accordance with a second aspect of the present invention, there is provided a torsional spring that includes an outer rigid member, an outer elastomeric member, an intermediate rigid member, an inner elastomeric member, and an inner rigid member speratively coupled to and coaxially positioned with respect to one another.

The elastomeric members include inner and outer surfaces which are elliptically shaped in the plane transverse to the longitudinal axis of the torsional spring with the elliptical shapes of the inner elastomeric member positioned at a different orientation from the elliptical shapes of the outer elastomeric member.

In accordance with a third aspect of the present invention, there is provided a torsional coupling that includes a plurality of torsional springs, outer couplings, inner couplings, and torque drive couplings. Each torsional spring includes an outer rigid member, an elastomeric member, and an inner rigid member operably coupled to and coaxially positioned with respect to one another. The elastomeric member includes inner and outer surfaces which are elliptically shaped in the plane transverse to the longitudinal axis of the torsional spring. Adjacent torsional springs are operably coupled to and coaxially positioned with respect to each other by means of the outer couplings. Pairs of adjacent torsional springs are in turn operably coupled to and coaxially positioned with respect to each other by means of the inner couplings.The torque drive couplings are operably coupled to the torsional coupling assembly at opposite ends thereof to thereby permit the torsional coupling to store, release, or transmit torque.

In accordance with a fourth aspect of the present invention, there is provided a riser tensioner including a pair of torsional couplings positioned in parallel.

In accordance with a fifth aspect of the present invention, there is provided a line compensator including a pair of torsional couplings positioned in parallel.

In a accordance with a sixth aspect of the present invention, there is provided a marine drive including a torsional coupling inserted in the drive shaft to provide a resilient interface between the powered or input portion of the shaft and the driven or output portion of the shaft.

Ie accordance with a final aspect of the present invention there is provided a motor mount that incorporates a torsional spring.

The present invention will become more fully understood from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings in which: FIG. 1 is a perspective view including a one quarter cross section of a first embodiment of a torsional spring; FIG. 2 is a cross sectional view taken in a plane perpendicular to the longitudinal axis of the first embodiment of a torsional spring illustrated in FIG. 1; FIG. 3 is a cross sectional view taken in a plane perpendicular to the longitudinal axis of the first embodiment of a torsional spring illustrating the loading conditions for the elastic member when the inner rigid member is rotated with respect to the outer rigid member; FIG. 4 is a perspective view including a one quarter cross section of a second embodiment of a torsional spring;; FIG. 5 is a cross sectional view taken in a plane perpendicular to the longitudinal axis of the second embodiment of a torsional spring illustrated in FIG. 4; FIG. 6 is a cross sectional view taken in a plane perpendicular to the longitudinal axis of a third embodiment of a torsional spring; FIG. 7 is a perspective view of a torsional coupling; FIG. 8 is an exploded view of the torsional coupling; FIG. 9 is a cross sectional view of the torsional coupling taken in a midline plane parallel to the longitudinal axis of the torsional coupling incorporating the first embodiment of the torsional spring; FIG. 10 is a cross sectional view of the torsional coupling taken in a midline plane parallel to the longitudinal axis of the torsional coupling incorporating the second embodiment of the torsional spring;; FIG. 11 is a perspective view of a riser tensioner assembly utilizing torsional couplings; FIG. 12 is an exploded view of a riser tensioner utilizing a pair of torsional couplings; FIG. 13 is a cross sectional view taken in a midline plane parallel to the longitudinal axis of the torsional couplings of the riser tensioner; FIG. 14 is a perspective view of a particularly preferred embodiment of the riser tensioner; FIG. 15 is a cross sectional view taken in a midline plane perpendicular to the longitudinal axis of the particularly preferred embodiment of the riser tensioner; FIG. 16 is a perspective view of a line compensator utilizing torsional couplings; FIG. 17 is an exploded view of the line compensator; FIG. 18 is a cross sectional view taken in a midline plane parallel to the longitudinal axis of the torsional couplings of the line compensator;; FIG. 19 is a perspective view of a marine drive utilizing a torsional coupling; FIG. 20 is a cross sectional view taken in a midline plane parallel to the longitudinal axis of the torsional coupling illustrating the connection of the torsional coupling to the powered and driven shafts; FIG. 21 is a perspective view of a motor mount utilizing a torsional spring; and FIG. 22 is a cross sectional view taken in a plane perpendicular to the longitudinal axis of the torsional spring illustrating the attachment of the torsional spring, support shaft, and the mounting bracket.

Turning now to the drawings and referring initially to FIGS. 1 and 2, a first embodiment of a torsional spring 10 is illustrated. The torsional spring 10 includes an outer rigid member 15, an elastic member 20, and an inner rigid member 25. The outer rigid member 15, elastic member 20, and the inner rigid member 25 are operably coupled and coaxially positioned with respect to each other.

The outer rigid member 15 includes an outer surface 30 and an inner surface 35. The outer surface 30 may be of any shape in a plane transverse to a longitudinal axis 40 of the torsional spring 10. In a preferred embodiment, the outer surface 30 is circularly shaped in the plane transverse to the longitudinal axis 40 of the torsional spring 10 and further includes attachment means facilitating the transmission of torque to or from the torsional spring 10. In a preferred embodiment, the attachment means provides points of attachment equally distributed about the outer surface 30. In a particularly preferred embodiment, the attachment means comprises a plurality of grooves 45 aligned with the longitudinal axis 40 of the torsional spring 10. The inner surface 35 may be oblong shaped in the plane transverse to the longitudinal axis 40 of the torsional spring 10.An oblong shape is any shape which is longer in a first direction than it is in a second direction approximately perpendicular to the first direction. In a preferred embodiment, the inner surface 35 is elliptically shaped in the plane transverse to the longitudinal axis 40 of the torsional spring 10.

The inner rigid member 25 includes an outer surface 50 and an inner surface 55. The outer surface 50 may be oblong shaped in the plane transverse to the longitudinal axis 40 of the torsional spring 10. In a preferred embodiment, the outer surface 50 is elliptically shaped in the plane transverse to the longitudinal axis 40 of the torsional spring 10. The inner surface 55 may be of any shape within the plane transverse to the longitudinal axis 40 of the torsional spring 10. In a preferred embodiment, the inner surface 55 is circularly shaped in the plane transverse to the longitudinal axis 40 of the torsional spring 10 and further includes attachment means facilitating the transmission of torque to or from the torsional spring 10. In a preferred embodiment, the attachment means provides points of attachment equally distributed about the inner surface 55.In a particularly preferred embodiment, the attachment means comprises a plurality of grooves 60 aligned with the longitudinal axis 40 of the torsional spring 10.

The elastic member 20 is positioned between the outer rigid member 15 and the inner rigid member 25. The shape of the elastic member 20 is determined by the annular volume defined by the inner surface 35 of the outer rigid member 15 and the outer surface 50 of the inner rigid member 25. In a preferred embodiment, the elastic member 20 is coupled to the inner surface 35 of the outer rigid member 15 and the outer surface 50 of the inner rigid member 25. The elastic member 20 may be composed of any resilient material such as, for example, natural or synthetic rubber.

In a preferred embodiment, the elastic member 20 is composed of an elastomeric material with the inner and outer rigid members 25 and 15 composed of metal or composite materials. The particular materials selected for a specific application will vary in a known manner as a function of the loading conditions, operating environment, and types and levels of vibration. In a particularly preferred embodiment, for subsea applications, the elastic member 20 is comprised of nitrile or natural rubber.

In a preferred embodiment, attachment of the elastic member 20 to the inner and outer rigid members 25 and 15 utilizes conventional elastomeric molding and bonding processes. In a preferred embodiment, the torsional spring 10 is formed by high pressure transfer or injection molding of the elastomeric material of the elastic member 20 into the circumferential annular space defined by the inner surface 35 of the outer rigid member 15 and the outer surface 50 of the inner rigid member 25. In the preferred embodiment, the high pressures are maintained throughout the curing process to avoid shrinkage of the elastomeric material. The required high pressures will vary as a function of the specific elastomeric material selected with typical pressures ranging from about 1500 to 6000 p.s.i.

Referring to FIG. 3, the operation of the torsional spring 10 will now be described. In operation, a torque is applied to the torsional spring 10 about the longitudinal axis 40 of the torsional spring 10 which results in relative rotation of the inner rigid member 25 with respect to the outer rigid member 15. Relative rotation of the inner rigid member 25 with respect to the outer rigid member 15 places the elastic member 20 in compression in the approximate regions C and in tension in the approximate regions T.

Conventional torsional springs, which utilize elastomers, incorporate designs in which the elastomeric members are placed in shear during relative rotation of inner and outer rigid members. Such conventional designs employ an elastic member having inner and outer surfaces which are cylindrical. The shear dominated devices are characterized by limited load and fatigue capacity as well as susceptibility to catastrophic failure. In contrast, the torsional spring 10 provides a compression dominated device by means of the oblong, and preferably elliptical, shapes of the inner surface 35 of the outer rigid member 15 and the outer surface 60 of the inner rigid member 25 in the plane transverse to the longitudinal axis 35 of the torsional spring 10.Such a compression dominated device exhibits extended fatigue life and load capacity as well as fail safe operational characteristics as compared with shear dominated devices In a preferred embodiment, the aspect ratio (the ratio of the major diameter to the minor diameter) of the elliptical shapes of the torsional spring 10 are adjusted to either increase or decrease the effective spring rate of the torsional spring 10.

Increasing the aspect ratio of the elliptical shapes will increase the effective spring rate, while decreasing the aspect ratio of the elliptical shapes will decrease the effective spring rate. Similarly, the size and type of elastomeric material utilized in the elastic member 20 may be varied to achieve the desired dynamic characteristic for the torsional spring 10.

Referring now to FIGS. 4-5, a second embodiment of the torsional spring 100 which utilizes a plurality of elastic members is illustrated. The second embodiment of the torsional spring 100 includes an outer rigid member 105, an outer elastic member 110, an intermediate rigid member 115, an inner elastic member 120, and an inner rigid member 125. The outer rigid member 105, outer elastic member 110, intermediate rigid member 115, the inner elastic member 120, and the inner rigid member 125 are operably coupled to and positioned coaxially with respect to each other.

The outer rigid member 105 includes an outer surface 130 and an inner surface 135. The outer surface 130 may be of any shape in a plane transverse to a longitudinal axis 140 of the torsional spring 100. In a preferred embodiment, the outer surface 130 is circularly shaped in the plane transverse to the longitudinal axis 140 of the torsional spring 100 and further includes attachment means for facilitating the transmission of torque to or from the torsional spring 100. In a preferred embodiment, the attachment means provides points of attachment equally distributed about the outer surface 130. In a particularly preferred embodiment, the attachment means comprises a plurality of grooves 145 aligned with the longitudinal axis 140 of the torsional spring 100.The inner surface 135 may be oblong shaped at a first orientation (where the orientation of the oblong shape is determined by the orientation of the major axis of the oblong shape) in the plane transverse to the longitudinal axis 140 of the torsional spring 100. In a preferred embodiment, the inner surface 135 is elliptically shaped at-a first orientation in the plane transverse to the longitudinal axis 140 of the torsional spring 100.

The intermediate rigid member 115 includes an outer surface 150 and an inner surface 155. The outer surface 150 may be oblong shaped at the first orientation in the plane transverse to the longitudinal axis 140 of the torsional spring 100. In a preferred embodiment, the outer surface 150 is elliptically shaped at the first orientation in the plane transverse to the longitudinal axis 140 of the torsional spring 100. The inner surface 155 may be oblong shaped at a second orientation in the plane transverse to the longitudinal axis 140 of the torsional spring 100. In a preferred embodiment, the inner surface 155 is elliptically shaped at the second orientation in the plane transverse to the longitudinal axis 140 of the torsional spring 100.

The inner rigid member 125 includes an outer surface 160 and an inner surface 165. The outer surface 160 may be oblong shaped at the second orientation in the plane transverse to the longitudinal axis 140 of the torsional spring 100. In a preferred embodiment, the outer surface 160 is elliptically shaped at the second orientation in the plane transverse to the longitudinal axis 140 of the torsional spring 100. The inner surface 165 may be of any shape in the plane transverse to the longitudinal axis 140 of the torsional spring 100. In a preferred embodiment, the inner surface 165 is circularly shaped in the plane transverse to the longitudinal axis 140 of the torsional spring 100.In a preferred embodiment, the inner surface 165 is circularly shaped in the plane transverse to the longitudinal axis 140 of the torsional spring 100 and further includes attachment means for facilitating the transmission of torque to or from the torsional spring 100. In a preferred embodiment, the attachment means will provide points of attachment equally distributed about the inner surface 165. In a particularly preferred embodiment, the attachment means comprises a plurality of grooves 170 aligned with the longitudinal axis 140 of the torsional spring 100.

The outer elastic member 110 is positioned between the outer rigid member 105 and the intermediate rigid member 115. The shape of the outer elastic member 110 is determined by the annular volume defined by the inner surface 135 of the outer rigid member 105 and the outer surface 150 of the intermediate rigid member 115.

In a preferred embodiment, the outer elastic member 110 is coupled to the inner surface 135 of the outer rigid member 105 and the outer surface 150 of the intermediate rigid member 115.

The inner elastic member 120 is positioned between the intermediate rigid member 115 and the inner rigid member 125. The shape of the inner elastic member 120 is determined by the annular volume defined by the inner surface 155 of the intermediate rigid member 115 and the outer surface 160 of the inner rigid member 125. In a preferred embodiment, the inner elastic member 120 is coupled to the inner surface 155 of the intermediate rigid member 115 and the outer surface 160 of the inner rigid member 125.

The inner and outer elastic members 110 and 120 may be composed of any resilient material such as, for example, natural or synthetic rubber. In a preferred embodiment, the inner and outer elastic members 110 and 120 are composed of an elastomeric material with the outer rigid member 105, the intermediate rigid member 115, and the inner rigid member 125 composed of metal or composite materials. The particular materials selected for a specific application will vary in a known manner as a function of the loading conditions, operating environment, and types and levels of vibration. In a particularly preferred embodiment, for subsea applications, the inner and outer elastic members 110 and 120 are composed of nitrile or natural rubber.

Attachment of the elastic members 110 and 120 to the outer rigid member 105, intermediate rigid member 115, and inner rigid member 125 utilizes conventional elastomer molding and bonding processes. In a preferred embodiment, the torsional spring 100 is formed by high pressure transfer, or injection, molding of the elastomeric material of the elastic members 110 and 120 into the annular volumes defined by the inner surfaces 135 and 155 of the outer rigid member 105 and the intermediate rigid member 115 respectively and the outer surfaces 150 and 160 of the intermediate rigid member -115 and the inner rigid member 125 respectively. In the preferred embodiment, the high pressures are maintained throughout the curing process to avoid shrinkage of the elastomeric material.The required high pressures will vary as a function of the specific elastomeric material selected with typical pressures ranging from about 1500 to 6000 p.s.i.

In a preferred embodiment, the first orientation of the elliptical shapes will be different from the second orientation of the elliptical shapes. In a particularly preferred embodiment, the orientation of the elliptical shapes will be approximately 90 degrees out of phase with one another.

More generally, in a preferred embodiment, the torsional spring 100 includes an outer rigid member, an inner rigid member, N- 1 intermediate rigid members, and N elastic members defined by the rigid members. In the preferred embodiment, the outer rigid member includes an inner elliptical surface at a first orientation, the inner rigid member includes an outer elliptical surface at an Nth orientation, and each of the intermediate rigid members include inner and outer elliptical surfaces. In the preferred embodiment, the outer elliptical surface of an ith intermediate rigid member is at an ith orientation and the inner surface of the ith intermediate rigid member is at an i+lth orientation. In the preferred embodiment, the N elastic members include a 1st elastic member, 2nd through N-lth elastic members, and an Nth elastic member.In the preferred embodiment, the 1st elastic member is coupled to the inner elliptical surface of the outer rigid member and to an outer elliptical surface of a 1 sot intermediate rigid member, the Nth elastic member is coupled to an inner elliptical surface of the N-lth intermediate rigid member and to the outer elliptical surface of the inner rigid member, and an ith one of the 2nd through N-lth elastic members is coupled to an inner elliptical surface of an i-lth intermediate rigid members and to an outer elliptical surface of an ith intermediate rigid member. In a particularly preferred embodiment, for a plurality of elastic members of number N, the orientations of adjacent pairs of elliptical shapes are approximately 180/N degrees out of phase.

In an exemplary embodiment, for N=3, the torsional springs 100 includes an outer rigid member, an inner rigid member, two intermediate rigid members, and three elastic members defined by the rigid members. In the exemplary embodiment, the outer rigid member includes an inner elliptical surface at a 1 sot orientation, the inner rigid member includes an outer elliptical surface at a 3rd orientation, and both of the intermediate rigid members include inner and outer elliptical surfaces.In the exemplary embodiment, the outer elliptical surface of the 1st intermediate rigid member is at the 1st orientation and the inner surface of the 1st intermediate rigid member is at a 2nd orientation, and the outer elliptical surface of the 2nd intermediate rigid member is at the 2nd orientation and the inner surface of the 2nd intermediate rigid member is at a 3rd orientation. In the exemplary embodiment, the three elastic members include a 1 st, 2nd, and 3rd elastic member.In the exemplary embodiment, the 1st elastic member is coupled to the inner elliptical surface of the outer rigid member and to an outer elliptical surface of the 1 sot intermediate rigid member, the 2nd elastic member is coupled to an inner elliptical surface of the 1st intermediate rigid member and to an outer elliptical surface of the 2nd intermediate rigid member, and the 3rd elastic member is coupled to the inner elliptical surface of the 2nd intermediate rigid member and to the outer elliptical surface of the inner rigid member. In the exemplary embodiment, the 1st and 2nd orientations and the 2nd and 3rd orientations are sixty degrees out of phase.

In operation, a torque is applied to the torsional spring 100 about the longitudinal axis 140 of the torsional spring 100 which will result in relative rotation of the inner rigid member 125 with respect to the outer rigid member 105. Relative rotation of the inner rigid member 125 with respect to the outer rigid member 105 will then place the elastic members 110 and 120 in compression and in tension in analogous fashion to that illustrated in FIG. 3 for the torsional spring 10.

In another preferred embodiment, additional elastic members are added to the torsional spring 100, interspersed with additional intermediate rings, to increase the stroke length of the torsional spring 100. In this manner, the stroke length of the torsional spring 100 may be adjusted to virtually any desired amount thereby resulting in an extremely efficient, reliable, and compact structure.

Referring to FIG. 6, a third embodiment of a torsional spring 200 is illustrated which is especially adapted for unidirectional operation. The torsional spring 200 includes an outer rigid member 205, a first elastic member 210, a second elastic member 915, and an inner rigid member 220. The outer rigid member 205, elastic members 210 and 215, and the inner rigid member 220 are operably coupled and coaxially positioned with respect to each other.

The outer rigid member 205 includes an outer surface 225 and an inner surface 230. The outer surface 225 may be of any shape in a plane transverse to a longitudinal axis 235 ofthe torsional spring 200. In a preferred embodiment, the outer surface 225 is circularly shaped in the plane transverse to the longitudinal axis 235 of the torsional spring 200 and further includes attachment means facilitating the transmission of torque to or from the torsional spring 200. In a preferred embodiment, the attachment means will provide points of attachment equally distributed about the outer surface 225. In a particularly preferred embodiment, the attachment means comprises a plurality of grooves 240 aligned with the longitudinal axis 235 of the torsional spring 200.The inner surface 230 may be oblong shaped in the plane transverse to the longitudinal axis 235 of the torsional spring 200. In a preferred embodiment, the inner surface 230 is elliptically shaped in the plane transverse to the longitudinal axis 235 of the torsional spring 200.

The inner rigid member 220 includes an outer surface 245 and an inner surface 250. The outer surface 245 may be oblong shaped in the plane transverse to the longitudinal axis 235 of the torsional spring 200. In a preferred embodiment, the outer surface 245 is elliptically shaped in the plane transverse to the longitudinal axis 235 of the torsional spring 200. The inner surface 250 may be of any shape within the plane transverse to the longitudinal axis 235 of the torsional spring 200. In a preferred embodiment, the inner surface 250 is circularly shaped in the plane transverse to the longitudinal axis 235 of the torsional spring 200 and further includes attachment means facilitating the transmission of torque to or from the torsional spring 200. In a preferred embodiment, the attachment means will provide points of attachment equally distributed about the inner surface 250.In a particularly preferred embodiment, the attachment means comprises a plurality of grooves 255 aligned with the longitudinal axis 235 of the torsional spring 200.

The elastic members 210 and 215 are positioned between the outer rigid member 205 and the inner rigid member 220 to provide a reaction torque when placed in compression due to rotation of the outer rigid member 205 with respect to the inner rigid member 220 in a single direction 260. In this manner, the torsional spring 200 provides a unidirectional spring. The shape of the elastic members 210 and 215 are further determined by the annular volume defined by the inner surface 230 of the outer rigid member 220 and the outer surface 245 of the inner rigid member 220. In a preferred embodiment, the elastic members 210 and 215 are in intimate contact with and attached to the inner surface 230 of the outer rigid member 205 and the outer surface 245 of the inner rigid member 220.The elastic members 210 and 215 may be composed of any resilient material such as, for example, natural or synthetic rubber.

In a preferred embodiment, the elastic members 210 and 215 are composed of an elastomeric material with the inner and outer rigid members 205 and 220 composed of metal or composite materials. In a preferred embodiment, the particular materials selected for a specific application will vary in a known manner as a function of the loading conditions, operating environment, and types and levels of vibration. In a particularly preferred embodiment, for subsea applications, the elastic members 210 and 215 are comprised of nitrile or natural rubber.

In a preferred embodiment, attachment of the elastic members 210 and 215 to the inner and outer rigid members 205 and 220 utilizes conventional elastomeric molding and bonding processes. In a preferred embodiment, the torsional spring 200 is formed by high pressure transfer or injection molding of the elastomeric material of the elastic members 210 and 215 into the circumferential annular volume defined by the inner surface 230 of the outer rigid member 205 and the outer surface 245 of the inner rigid member 220. In the preferred embodiment, the high pressures are maintained throughout the curing process to avoid shrinkage of the elastomeric material. The required high pressures will vary as a function of the specific elastomeric material selected with typical pressures ranging from about 1500 to 6000 p.s.i.

The torsional spring 200 may further include intermediate rigid members with additional sets of elastic members to increase the stroke length of the torsional spring 200 as previously discussed in connection with the torsional spring 100. The torsional springs 10, 100, and 200 may also be further utilized as torsional couplings with an input member coupled to the inner or outer rigid member and with an output member coupled to the outer or inner rigid member.

Referring to FIGS. 7-10, a torsional coupling 300 utilizing a plurality of torsional springs will now be described. The torsional coupling 300 receives an input torque at a first end and provides an output or reaction torque at a second end. The torsional coupling 300 utilizes a plurality of torsional springs which may comprise any torsional spring. In several preferred embodiments, the torsional springs of the torsional coupling 300 will comprise the torsional springs 10, 100, or 200.

In one preferred embodiment illustrated in FIGS. 7-9, the torsional coupling 300 includes a plurality of torsional springs 10, outer couplings 305, inner couplings 310, a first torque drive coupling 315, and a second torque drive coupling 320. The plurality of torsional springs 10, outer couplings 305, inner couplings 310, first torque drive coupling 315, and second torque drive coupling 320 are operably coupled and coaxially positioned with respect to one another. In another preferred embodiment, as illustrated in FIG. 10, the torsional coupling 300 includes a plurality of torsional springs 100, outer couplings 305, inner couplings 310, a first torque drive coupling 315, and-a second torque drive coupling 320.In yet another preferred embodiment, for an application requiring unidirectional loading conditions, the torsional coupling 300 includes a plurality of torsional springs 200, outer couplings 305, inner couplings 310, a first torque drive coupling 315, and a second torque drive coupling 320.

Each outer coupling 305 includes an outer surface 325, a first inner surface 330, a second inner surface 335, and an inner spacer 340. The outer surface 325 may be of any shape in a plane transverse to the longitudinal axis 345 of the torsional coupling 300. In a preferred embodiment, the outer surface 325 is circularly shaped in the plane transverse to the longitudinal axis 345 of the torsional coupling 300. The first inner surface 330 may be of any shape in the plane perpendicular to the longitudinal axis 345 of the torsional coupling 300 and will include attachment means facilitating the transmission of torque to and from the outer coupling 305.In a preferred embodiment, the first inner surface 330 is circularly shaped in the plane transverse to the longitudinal axis 345 of the torsional coupling 300 and includes attachment means that provides points of attachment equally distributed about the first inner surface 330. In a particularly preferred embodiment, the attachment means comprises a plurality of splines 350 aligned with the longitudinal axis 345 of the torsional coupling 300. The second inner surface 335 may be of any shape in the plane perpendicular to the longitudinal axis 345 of the torsional coupling 300 and will include attachment means facilitating the transmission of torque to and from the outer coupling 305.In a preferred embodiment, the second inner surface 335 is circularly shaped in the plane transverse to the longitudinal axis 345 of the torsional coupling 300 and includes attachment means that provides points of attachment equally distributed about the second inner surface 335. In a particularly preferred embodiment, the attachment means comprises a plurality of splines 355 aligned with the longitudinal axis 345 of the torsional coupling 300. The inner spacer 340 is positioned between the first inner surface 330 and the second inner surface 335 and provides spacing between adjacent torsional springs 10 in the direction of the longitudinal axis 345 of the torsional coupling 300.The inside diameter of the inner spacer 340 is less than the inside diameters of the first and second inner surfaces 330 and 335.-The inner spacer 340 may be of any shape in the plane perpendicular to the longitudinal axis 345 of the torsional coupling 300. In a preferred embodiment, the inner spacer 340 is circularly shaped in the plane perpendicular to the longitudinal axis 345 of the torsional coupling 300.

Pairs of torsional springs 10 are operably coupled and coaxially aligned with each other by the outer couplings 305 by the interlocking arrangement of the grooves 45 of the outer rigid members 15 of the torsional springs 10 and the splines 350 and 355 of the outer couplings 305. An outer coupling 305 and a pair of torsional springs 10 operably coupled and coaxially aligned with each other by the outer coupling 305 comprise a torsional spring assembly 360. The torsional spring assemblies 360 comprise the basic element of the torsional coupling 300. The torsional coupling 300 may comprise any number of torsional spring assemblies 360 depending upon the operational requirements of the torsional coupling 300. Adjacent torsional spring assemblies 360 are operably coupled to and coaxially aligned with each other by the inner couplings 310.

Each inner coupling 310 includes a first outer surface 365, a second outer surface 370, an outer spacer 375, and an inner surface 380. The first outer surface 365 may be of any shape in the plane transverse to the longitudinal axis 345 of the torsional coupling 300 and will include attachment means facilitating the transmission of torque to and from the inner coupling 310. In a preferred embodiment, the first outer surface 365 is circularly shaped in the plane transverse to the longitudinal axis 345 of the torsional coupling 300 and includes attachment means that provides points of attachment equally distributed about the first outer surface 365. In a particularly preferred embodiment, the attachment means comprises a plurality of splines 385 aligned with the longitudinal axis 345 of the torsional coupling 300.The second outer surface 370 may be of any shape in the plane transverse to the longitudinal axis 345 of the torsional coupling 300 and will include attachment means facilitating the transmission of torque to and from the inner coupling 310. In a preferred embodiment, the second outer surface 370 is circularly shaped in the plane transverse to the longitudinal axis 345 of the torsional coupling 300 and includes attachment that provides points of attachment equally distributed about the second outer surface 370.

In a particularly preferred embodiment, the attachment means comprises a plurality of splines 390 aligned with the longitudinal axis 345 of the torsional coupling 300. The outer spacer 375 is positioned between the first outer surface 365 and the second outer surface 370 and provides spacing between adjacent torsional spring assemblies 360 in the direction of the longitudinal axis 345 of the torsional coupling 300. The outside diameter of the outer spacer 375 is greater than the outside diameters of the first and second outer surfaces 365 and 370. The outer spacer 375 may be of any shape in the plane perpendicular to the longitudinal axis 345 of the torsional coupling 300. In a preferred embodiment, the outer spacer 375 is circularly shaped in the plane perpendicular to the longitudinal axis 345 of the torsional coupling 300.The inner surface 380 may be of any shape in a plane transverse to the longitudinal axis 345 of the torsional coupling 300. In a preferred embodiment, the inner surface 380 is circularly shaped in the plane transverse to the longitudinal axis 345 of the torsional coupling 300. In a particularly preferred embodiment, the inside diameter of the inner surface 380 is selected to permit the passage of a circular support shaft. In this manner, a torsional coupling 300 comprised of a plurality of torsional spring assemblies 360 may be supported by the circular support shaft to minimize radial deflections of the torsional coupling 300 in operation.

The first torque drive coupling 315 includes a first outer surface 395, a front attachment plate 400, a second outer surface 405, and an inner surface 410. The first outer surface 395 may be of any shape in a plane perpendicular to the longitudinal axis 345 of the torsional coupling 300. In a preferred embodiment, the first outer surface 395 is circularly shaped in the plane perpendicular to the longitudinal axis 345 of the torsional coupling 300 to facilitate axial alignment of the torsional coupling 300 in operation. The front attachment plate 400 includes a plurality of attachment points for rigid attachment of the first torque drive coupling 315 to an input or an output member. In a preferred embodiment, the plurality of attachment points will be equally distributed about the front attachment plate 400.In a particularly preferred embodirsent, the plurality of attachment points will comprise a plurality of threaded bores 415. The second outer surface 405 may of any shape in a plane perpendicular to the longitudinal axis 345 of the torsional coupling 300 and will include attachment means facilitating the transmission of torque to and from the first torque drive coupling 315. In a preferred embodiment, the second outer surface 405 is circularly shaped in the plane transverse to the longitudinal axis 345 of the torsional coupling 300 and includes attachment means that provides points of attachment equally distributed about the second outer surface 405. In a particularly preferred embodiment, the attachment means comprises a plurality of splines 420 aligned with the longitudinal axis 345 of the torsional coupling 300.The inner surface 410 may be of any shape in a plane transverse to the longitudinal axis 345 of the torsional coupling 300. In a preferred embodiment, the inner surface 410 is circularly shaped in the plane transverse to the longitudinal axis 345 of the torsional coupling 300. In a particularly preferred embodiment, the inside diameter of the inner surface 410 is selected to permit the passage of a circular support shaft. In this manner, a torsional coupling 300 comprised of a plurality of torsional spring assemblies 360 may be supported by the circular support shaft to minimize radial deflections of the torsional coupling 300 in operation. Where a support shaft is present, a lubricant such as, for example, a lightweight oil may be used to provide easy rotation of the torsional coupling 300 about the support shaft.

The second torque drive coupling 320 includes a first outer surface 425, a second outer surface 430, and an inner surface 435. The first outer surface 425 may be of any shape in a plane perpendicular to the longitudinal axis 345 of the torsional coupling 300 and will include attachment means facilitating the transmission of torque to and from the second torque drive coupling 320. In a preferred embodiment, the first outer surface 425 is circularly shaped in the plane transverse to the longitudinal axis 345 of the torsional coupling 300 and includes attachment means that provides points of attachment equally distributed about the first outer surface 425. In a particularly preferred embodiment, the attachment means comprises a plurality of splines 440 aligned with the longitudinal axis 345 of the torsional coupling 300.The second outer surface 430 may be of any shape in a plane perpendicular to the longitudinal axis 345 of the torsional coupling 300 and will include attachment means facilitating the transmission of torque to and from the second torque drive coupling 320. In a preferred embodiment, the second outer surface 430 is circularly shaped in the plane transverse to the longitudinal axis 345 of the torsional coupling 300 and includes attachment means that provides points of attachment equally distributed about the second outer surface 430. In a particularly preferred embodiment, the attachment means comprises a plurality of splines 445 aligned with the longitudinal axis 345 of the torsional coupling 300. The inner surface 435 may be of any shape in a plane transverse to the longitudinal axis 345 of the torsional coupling 300.In a preferred embodiment, the inner surface 435 is circularly shaped in the plane transverse to the longitudinal axis 345 of the torsional coupling 300. In a particularly preferred embodiment, the inside diameter of the inner surface 435 is selected to permit the passage of a circular support shaft. In this manner, a torsional coupling 300 comprised of a plurality of torsional spring assemblies 360 may be supported by the circular support shaft to minimize radial deflections of the torsional coupling 300 in operation.

Where a support shaft is present, a lubricant such as, for example, a lightweight oil may be used to provide easy rotation of the torsional coupling 300 about the support shaft.

The torque drive couplings 315 and 320 permit the torsional coupling 300 to be utilized for the transmission of torque about the longitudinal axis 345 by means of the interlocking arrangement of the grooves 60 of the inner rings 25 of the torsional springs 10 and the splines 420 and 445 of the torque drive couplings 315 and 320.

Other interlocking means may be substituted for the arrangement of grooves and splines. In a preferred embodiment, the interlocking arrangement provides a rigid coupling in a circumferential manner.

The torsional coupling 300 may be configured for use with a single torsional spring assembly 360 or with a plurality of torsional spring assemblies 360. More generally, in a preferred embodiment, for a torsional coupling 300 including a plurality of torsional spring assemblies 360, the torsional coupling 300 will include a first torque drive coupling 310, a plurality of torsional spring assemblies 360 of number N, a plurality of inner couplings 310 of number N-l, and a second torque drive coupling 320. In the preferred embodiment, the first torque drive coupling 310 will be operably coupled to the 1st torsional spring assembly 360 and the second torque drive coupling 320 will be operably coupled to the Nth torsional spring assembly.

Referring to FIGS. 11-13, a riser tensioner assembly 500 including a plurality of torsional couplings 300 will now be described. The riser tensioner assembly 500 provides an upward vertical force on a riser 505 which places the riser 505 in tension thereby preventing structural failure of the riser 505 which would otherwise occur due to the compressive force created by the weight of the riser 505. The riser tensioner assembly 500 includes a plurality of riser tensioners 510 arranged about the riser 505 and rigidly mounted on a fixed structure 515. The fixed structure 515 may be a platform supported by the ground or a floating platfo:rm. In a preferred embodiment, the riser tensioners 510 will be spaced at equal angle.s in a plane perpendicular to the longitudinal axis of the riser 505.A bracket 520 rigidly attached to the riser 505, using conventional mechanical attachment methods, permits pivotal connection of the riser tensioners 510 to the riser 505 by means of connecting pins 525 and bores 527 located in the bracket 520.

Each of the riser tensioners 510 include a pair of mounting brackets 530, a support arm 535, a support shaft 540 integral to the support arm 535, and a pair of torsional couplings 300. The mounting brackets 530 are rigidly mounted upon the fixed structure 515 by means of mounting bolts 540 or other similar rigid attachment which pass through mounting holes 545. The mounl:ing brackets 530 also include a plurality of mounting holes 550 to permit attachment of the torsional couplings 300 by a plurality of screws 555. The mounting brackets 530 further include a bore 560 for supporting the support shaft 540 and the first outer surface 395 of the first torque drive coupling 315 of the torsional coupling 300. A lubricant such as, for example, a lightweight oil may be used to provide easy rotation of the torsional coupling 300 about support shaft 540.Alternatively, a conventional ball bearing assembly may also be provided between the torsional coupling 300 and the support shaft 540. The torsional couplings 300 are connected at one end to the mounting brackets 530 and at another end to the support arm 530. Connection of the torsional couplings 300 to the mounting brackets 530 is provided by the threaded bores 415 of the first torque drive couplings 315 of the torsional couplings 300. Connection of the torsional couplings 300 to the support arm 540 is provided by the splines 445 of the second torque drive couplings 320. The support arm 535 includes inner c.ylindrical surfaces 565 and 570 that each include a plurality of grooves 575 and 580 which interlock with the splines 445 of the second torque drive couplings 320 of the torsional couplings 300.The support shaft 540 of the support arm 535 passes through the bores 560 of the mounting brackets 530 and the torsional couplings 300. The support arm 535 further includes a forked end 585 with bores 590 and 595. The bores 590 and 595 of the forked end 585 permit the pivotal connection of the support arm 535 to the bracket 520 by the pin 525.

The riser tensioner assembly 500 is assembled to provide an vertical force upon the riser 505 thereby placing it in tension. In one preferred embodiment, the riser tensioners 510 are first connected to the riser 505 with each of the support arms 535 elevated at the same slight upward angle relative to a horizontal plane 585. The riser 505 is supported by a crane, winch, or other similar device while the forked ends 585 of the support arms 535 of the riser tensioners 510 are pivotally connected to the bracket 520 of the riser 505 by the pins 525. The riser 505 is then lowered into its final position thereby pivoting all ofthe support arms 535 toward the horizontal plane 580 and placing the torsional springs 10, 100, or 200 of the torsional couplings 300 in compression and tension.The resulting reaction torque of the torsional couplings 300 provides an upward vertical force on the riser 505 placing it in tension. The magnitude of the initial upward angle of the support arms 535 will vary as a function of the dimensions of the riser 505 (i.e. its weight) and the specific configuration of the torsional couplings 300, thereby providing an upward force upon the riser 505 when it is pivotally attached to the support arms 530 thereby placing the torsional springs of the toFsional couplings 300 in compression.

In another preferred embodiment, the riser tensioners 510 are first assembled with each of the support arms 535 elevated at the same slight upward angle relative to a horizontal plane 585. The riser 505 is then positioned near its final position while supported by a crane, winch, or other similar device. The forked ends 585 of the support arms 535 of the riser tensioners 510 are then pivotally connected to the bracket 520 of the riser 505 by pivoting the support arms 535 downward using weights or other mechanical means until the bores 590 and 595 of the forked ends 585 are aligned with the bores 527 of the bracket 520. The pins 525 are then inserted to pivotally connect the support arms 535 to the bracket 520.The riser 505 is then lowered into its final position thereby further pivoting all of the support arms 535 toward the horizontal plane 580 and placing the torsional springs 10, 100, or 200 of the torsional couplings 300 in compression and tension. The resulting reaction torque of the torsional couplings 300 provides an upward force on the riser 505 placing it in tension. The magnitude of the initial upward angle of the support arms 535 will vary as a function of the dimensions of the riser 505 (i.e. its weight) and the specific configuration of the torsional couplings 300, thereby providing an upward force upon the riser 505 when it is pivotally attached to the support arms 530 thereby placing the torsional springs of the torsional couplings 300 in compression.

Referring to FIGS. 14-15, a particularly preferred embodiment of the riser tensioner 510 will now be described. In the particularly preferred embodiment, a pretensioning mechanism 905 is provided that permits a vertical load to be applied to the riser 505 after connection of the support arm 535 to the bracket 520. The pretensioning mechanism 905 includes a pair of adjustment plates 910 and 915, which are capable of partial rotation about the shaft 540 and extend radially outward adjacent the mounting brackets 530 on opposite ends of the riser tensioner 510. The first torque drive couplings 315 of the torsional couplings 300 are connected to the adjustment plates 910 and 915, instead of the mounting brackets 530, by means of a rigid connection such as, for example, threaded bolts. In a preferred embodiment, the connection of the adjustment plates to the first torque drive couplings are made by well known welding or brazing processes. The adjustment plates 910 and 915 further include central bores 930 which permit passage the support shaft 540 and the first torque drive couplings 315.

A linkage 935 is pivotally connected to each of the adjustment plates 910 and 915 that rotates the adjustment plates 910 and 915 about the shaft 540 to thereby apply a torque to the torsional couplings 300. The linkage 935 includes a tie-rod sleeve 940 connected to the adjustment plates 910 and 915 by a swivel arrangement 945, a tie-rod 950 connected at a first end portion to the tie-rod sleeve 940 and at a second end portion to a pinned bracket 955. The pinned brackets 955 are in turn rigidly mounted onto the fixed structure 515 using conventional means such as, for example, mounting bolts. The second end portion of the tie-rod 950 embodies a larger diameter machined rod section 960 which provides a swivel pin arrangement to permit rotation of the tie rod 950.Preferably, the connection between the tie-rod 950 and the tie-rod sleeve 940 takes the form of the tie-rod 950 being threaded and extending through a borehole in the tie-rod sleeve 940 with a pair of nuts 965 and 970 on either side of the sleeve.

The connection between the tie rod 950 second end portion and the pinned bracket 955 takes the form of a pinned swivel joint.

The pretensioning mechanism 905 is used to increase the preload of the torsional springs 10, 100, or 200 of the torsional couplings 300 by adjusting the linkage 935 to increase the length of the tie rods 950, thereby causing the adjustment plates 910 and 915 to rotate about the shaft 540. The rotation of the adjustment plates 905 and 910 about the shaft 540 in turn applies a torque to the torsional couplings 300 which, by way of the support arm 535, apply an upward vertical force to the riser 505.

The pretensioning mechanism 905 permits the riser tensioner 510 to be used to apply an upward vertical force to the riser 505 after the initial connection of the riser tensioner 510 to the riser or at a later point as operating conditions may warrant.

In a particularly preferred embodiment, the torsional couplings 300 utilized in the riser tensioners 510 will utilize the unidirectional torsional springs 200, oriented to be in compression once the riser tensioner assembly 500 is assembled, since the required loading conditions for the riser tensioner assembly 500 are unidirectional.

Referring to FIGS. 16-18, a line compensator 600 including a plurality of torsional couplings300 will now be described. The line compensator 600 utilizes a plurality of torsional couplings 300 to maintain a resilient S-shaped bend in a line 605 that stretches into a more elongated S-shape as tensile forces are applied to the line 605. The line 605 may include any approximately inelastic flexible line such as, for example, a mooring rope, a chain, or a wire rope cable.

The line compensator 600 includes a pair of support brackets 610, a pair of torsional couplings 300, a pulley assembly 615, and a support shaft 620 integral to the pulley assembly 615. Each of the support brackets 610 are rigidly mounted upon a fixed structure 625 by means of mounting bolts 630 or other similar rigid attachment which pass through mounting holes 635 positioned in a supporting foot 640. The mounting brackets 610 also include a plurality of mounting holes 645 to permit attachment of the torsional couplings 300 by a plurality of screws 650. The support brackets 610 further include a bore 655 for supporting the support shaft 620 and the first outer surface 395 of the first torque drive coupling 315 of the torsional coupling 300.A lubricant such as, for example, a lightweight oil may be used to provide easy rotation of the torsional coupling 300 about the support shaft 620. Alternatively, a conventional ball bearing assembly may also be provided between the torsional coupling 300 and the support shaft 620. The torsional couplings 300 are connected at one end to the support brackets 610 and at another end to the pulley assembly 615.

Connection of the torsional couplings 300 to the support brackets 610 is provided by the threaded bores 415 of the first torque drive couplings 315 of the torsional couplings 300. Connection of the torsional couplings 300 to the pulley assembly 615 is provided by the splines 445 of the second torque drive couplings 320. The pulley assembly 615 includes inner cylindrical surfaces 660 and 665 that each include a plurality ef grooves 670 and 675 which interlock with the splines 445 of the second torque drive couplings 320 of the torsional couplings 300. The support shaft 620 of the pulley assembly 615 passes through the bores 655 of the support brackets 610 and the torsional couplings 300.

The line compensator 600 is assembled with the longitudinal axis 680 of the pulley assembly 615 at a predetermined orientation. In a preferred embodiment, the predetermined orientation of the longitudinal axis 680 of the pulley assembly 615 is approximately vertical. The line 605 is then fed through the pulley assembly 615 supported by a first pulley 685 and a second pulley 690 forming an S-shaped curve within the interior of the pulley assembly 615. The line is fed by a winch 695 at one end and is connected to a ship, or other floating vessel, at another end. The line 605 is placed in tension by operation of the winch 685 which reels in the line 605 thereby deflecting the pulley assembly 615 slightly from the initial predetermined orientation which in turn deflects the torsional springs 10, 100, or 200 of the torsional couplings 300.The torsional couplings 300 then provide a reaction torque which, by means of the pulley assembly 615, places the line 605 in tension. Where the line 605 is connected to a ship, or other floating vessel, the current and/or wave action will also deflect the pulley assembly 615 thereby creating a reaction torque in the torsional couplings 300. The line compensator 600 by means of the torsional couplings 300 maintains the line 605 in tension and further absorbs motion of the ship, or other similar floating vessel, caused by currents and/or wave action. The torsional couplings 300 may comprise the torsional springs 10, 100, or 200. In a preferred embodiment, the torsional couplings 300 will comprise the torsional springs 10 or 100 due to the bidirectional nature of the loading conditions for the line compensator 600.

Referring to FIGS. 19-20, a marine drive 700 including a torsional coupling 300 will now be described. The marine drive 700 include an engine 705, a transmission 710, an input or powered shaft 715, a torsional coupling 300, an output shaft or driven shaft 720, and a support bearing 735. The engine 705 may be any prime mover such as, for example, a diesel or gasoline engine, or an electric motor.

The transmission 710 may be any conventional transmission such as, for example, a hydrostatic transmission. The powered shaft 715 receives an input torque from the engine 705 by way of the transmission 710. The powered shaft 715 transmits the input torque to the torsional coupling 300 rigidly connected to the end of the driven shaft 715. The rigid attachment of the torsional coupling 300 to the end of the powered shaft 715 may be provided by any conventional means for attaching a pair of in-line rotating members.In a preferred embodiment, the rigid attachment of the torsional coupling 300 to the end of the powered shaft 715 is provided by an inner surface 740 including a plurality of grooves 745 aligned with the longitudinal axis of torsional coupling 300 and provided on the end of the powered shaft 715 which interlock with the plurality of splines 445 provided on the second torque coupling 320 of the torsional coupling 300. The torsional coupling 300 in turn transmits the input torque to the driven shaft 720 which is rigidly attached to the opposite end of the torsional coupling 300. The rigid attachment of the torsional coupling 300 to the end of the driven shaft 720 may be provided by any conventional means for attaching a pair of in-line rotating members for the transmission of torque.In a preferred embodiment, the rigid attachment of the torsional coupling 300 to the end of the driven shaft 720 is provided by a face plate 750 provided on the end of the driven shaft 720 including a plurality of holes 755 permitting a plurality of bolts 760 to be connected with the plurality of threaded bores 415 provided on the first torque coupling 315 of the torsional coupling 300. The torsional coupling 300 in turn transmits the input torque to the driven shaft 720 which is rigidly attached to the opposite end of the torsional coupling 300. The driven shaft 720 is rotably supported by a conventional support bearing 735. The driven shaft 720 in turn transmits the input torque to an output device such as, for example, a propeller of a ship or other floating vessel.

The torsional coupling 300 transmits the input torque from the engine 705 to the output device, absorbs and attenuates vibrations in the marine drive 700, and absorbs and attenuates unpredictable and/or oscillatory loading conditions. The torsional coupling 300 may comprise torsional springs 10, 100, or 200. In a preferred embodiment, the torsional coupling 300 will comprise the torsional springs 10 or 100 due to the bidirectional nature of the loading conditions for the marine drive 700.

Referring now to FIGS. 21-22, a motor mount 800 including a torsional spring 805 will now be described. The motor mount 800 includes a mounting bracket 810, a torsional spring 805, a support shaft 815, and a motor bracket 820 affixed to a motor 825. A plurality of motor mounts 800 may be used to support the motor 825. In a preferred embodiment, four motor mounts 800 are equally positioned about the motor 825 with two supporting the front half of the motor 825 and two supporting the rear half of the motor 825. The torsional spring 805 may be any torsional spring. In a preferred embodiment, the torsional spring 805 will comprise the torsional springs 10, 100, or 200. In a particularly preferred embodiment, the torsional spring 805 will comprise the torsional springs 10 or 100 due to the bidirectional loading conditions for the motor mount 800.The mounting bracket 805 is rigidly attached using conventional means to the chassis of a powered vehicle such as, for example, an automobile or truck. The mounting bracket includes a support arm 830 that includes an opening 835 for receiving the torsional spring 805. The opening 835 may be of any shape provided it interlocks with the outer surface of the torsional spring 805. In a preferred embodiment, the opening 835 is a right circular cylinder and includes a plurality of splines 840 for locking the outer surface of the torsional spring 805. The mounting bracket 805 may oriented to place the longitudinal axis 845 of the torsional spring 805 in a predetermined orientation.In a preferred embodiment, the mounting bracket 805 is oriented to place the longitudinal axis 845 of the torsional spring 805 approximately in a horizontal direction and also approximately parallel to a longitudinal axis 850 of the motor 825. In this manner, the motor mount 800 permits the motor 825 to move in the longitudinal direction by means of the sliding fit provided by the splines and grooves. The support shaft 815 is supported by the inner rigid member of the torsional spring 805 and further includes attachment means for interlocking with the inner rigid member of the torsional spring 805.In a preferred embodiment, the attachment means will comprise a plurality of splines 855 that interlock with the grooves provided in the inner rigid member of the torsional spring 805. Th support shaft 815 is rigidly attached to the motor 820 by the motor bracket 820. The motor bracket 820 is in turn rigidly attached to the motor 825 using conventional means.

The motor mount 800 supports the motor 825, absorbs and attenuates vibrations generated by the motor 825, provides a reaction torque to the torque generated by the motor 825 in operation, and absorbs and attenuates vibrations and shock loads generated in normal operation of the motor vehicle thereby protecting the motor 825.

A compression loaded torsional spring has been described which has further utility in torsional couplings that may then be advantageously employed in riser tensioners, line compensators, and marine drives. If properly designed and sized, elastomeric spring and coupling assemblies possessing tremendous load and stroke capacity may be modularly assembled. Any number of elastomeric disks may be combined to achieve virtually any desired performance characteristics. Where utilized in the form of a torsional coupling in a marine drive the present device will provide shock and vibration protection to the prime mover as well as noise attenuation.

Whether used as a spring or as a coupling, the present device will be virtually maintenance free for its entire operational life. Loading of the elastomeric elements in compression in the plane transverse to the longitudinal axis of the device will allow extended fatigue life and greatly enhanced reliability.

The present device used in the form of a torsional coupling offers the further advantage of fail-safe operation. Even if all of the elastomeric material is destroyed, the device will continue to transmit torque about its longitudinal axis.

While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Claims

CLAIMS:

1. A torsional spring comprising: an outer rigid member having an inner oblong surface; an inner rigid member having an outer oblong surface; and an elastic member coupled to said inner oblong surface and to said outer oblong surface.

2. The torsional spring of claim 1, wherein said elastic member is comprised of an elastomeric material.

3. The torsional spring of claim 2, wherein said inner and outer rigid members are comprised of metal.

4. The torsional spring of claim 2, wherein said inner and outer rigid members are comprised of a composite material.

5. The torsional spring of claim 1, wherein said inner surface of said outer rigid member +s elliptical, and wherein said outer surface of said inner rigid member is elliptical.

6. The torsional spring of claim 1, wherein rotation of said inner rigid member with respect to said outer rigid member places said elastic member predominately in compression.

7. A torsional spring comprising: a outer rigid member; an elastic member coupled to said outer rigid member; and an inner rigid member coupled to said elastic member wherein rotation of said inner rigid member with respect to said outer rigid member places said elastic member predominately in compression.

8. The torsional spring of claim 7, wherein said outer rigid member includes an inner oblong surface, wherein said inner rigid member includes an outer oblong surface, and wherein said elastic member is coupled to said oblong surfaces.

9. The torsional spring of claim 8, wherein said oblong surfaces are elliptical.

10. A torsional spring comprising: an outer rigid member including an inner oblong surface at a first orientation; an intermediate rigid member including inner and outer oblong surfaces at a second orientation and at said first orientation respectively; a first elastic member coupled to said inner oblong surface of said outer rigid member and to said outer oblong surface of said intermediate rigid - member; an inner rigid member including an outer oblong surface at said second orientation; and a second elastic member coupled to said inner oblong surface of said intermediate rigid member and to said outer oblong surface of said inner rigid member.

11. The torsional spring of claim 10, wherein said oblong surfaces are elliptical.

12. The torsional spring of claim 10, wherein said first and second orientations are out of phase.

13. The torsional spring of claim 12, wherein said first and second orientations are approximately 90 degrees out of phase.

14. A torsional spring comprising: an outer rigid member including an inner oblong surface at a 1st orientation; an inner rigid member including an outer oblong surface at an Nth orientation; N-l intermediate rigid members, wherein each said intermediate rigid member includes inner and outer oblong surfaces, and wherein said outer oblong surface of an ith intermediate rigid member is at an ith orientation and said inner surface of said ith intermediate rigid member is at an i+lth orientation; a 1 sot elastic member coupled to said inner oblong surface of said outer rigid member and to an outer oblong surface of a 1st intermediate rigid member; an Nth elastic member coupled to an inner oblong surface of an N-lth intermediate rigid member and to said outer oblong surface of said - inner rigid member;; and 2nd through N-lth elastic members, wherein an ith one of said 2nd through N 1 th elastic members is coupled to an inner oblong surface of an i-lth intermediate rigid members and to an outer oblong surface of an ith intermediate rigid member.

15. The torsional spring of claim 14, wherein said oblong surfaces are elliptical.

16. The torsional spring of claim 14, wherein said ith orientation and said i+lth orientation are out of phase.

17. The torsional spring of claim 16, wherein said ith orientation and said i+lth orientation are approximately 180/N degrees out of phase.

18. A torsional coupling comprising: a first torque drive coupling including an outer surface adapted for transmitting or receiving torque; a first torsional spring including inner surface and outer surfaces, wherein said inner surface is coupled to said outer surface of said first torque drive coupling; a first outer coupling including a first inner surface coupled to said outer surface of said first torsional spring and a second inner surface; a second torsional spring including inner and outer surfaces, wherein said outer surface is coupled to said second inner surface of said first outer coupling; and a second torque drive coupling including an outer surface coupled to said inner surface of said second torsional spring adapted for transmitting or receiving torque.

19. The torsional coupling of claim 18, wherein each said torsional spring comprises: a outer rigid member; an elastic member coupled to said outer rigid member; and an inner rigid member coupled to said elastic member; wherein rotation of said inner rigid member with respect to said outer rigid member places said elastic member in tension and in compression.

20. The torsional coupling of claim 19, wherein said outer rigid member includes an inner oblong surface, wherein said inner rigid member includes an outer oblong surface, and wherein said elastic member is coupled to said oblong surfaces.

21. The torsional coupling of claim 20, wherein said oblong surfaces are elliptical.

22. A torsional coupling comprising: a first torque drive coupling including an outer surface adapted for transmitting or receiving torque; a first torsional spring including inner and outer surfaces, wherein said inner surface is coupled to said outer surface of said first torque drive coupling; a first outer coupling including a first inner surface coupled to said outer surface of said first torsional spring and a second inner surface; a second torsional spring including inner and outer surfaces, wherein said outer surface is coupled to said second inner surface of said first outer - coupling; a first inner coupling including a first outer surface coupled to said inner surface of said second torsional spring and a second outer surface;; a third torsional spring including inner and outer surfaces, wherein said inner surface is coupled to said second outer surface of said first inner coupling; a second outer coupling including a first inner surface coupled to said outer surface of said third torsional spring and a second inner surface; a fourth torsional spring including inner and outer surfaces, wherein said outer surface is coupled to said second inner surface of said second outer coupling; and a second torque drive coupling including an outer surface coupled to said inner surface of said fourth torsional spring adapted for transmitting or receiving torque.

23. The torsional coupling of claim 22, wherein each said torsional spring comprises: a outer rigid member; an elastic member coupled to said outer rigid member; and an inner rigid member coupled to said elastic member; wherein rotation of said inner rigid member with respect to said outer rigid member places said elastic member in tension and in compression.

24. The torsional coupling of claim 23, wherein said outer rigid member includes an inner oblong surface, wherein said inner rigid member includes an outer oblong surface, and wherein said elastic member is coupled to said oblong surfaces.

25. Tbe torsional coupling of claim 24, wherein said oblong surfaces are elliptical.

26. A torsional coupling comprising: N torsional spring assemblies, each said torsional spring assembly comprising: a first torsional spring including inner and outer surfaces; a second torsional spring including inner and outer surfaces; and an outer coupling including a first inner surface coupled to said outer surface of said first torsional spring and a second inner surface coupled to said outer surface of said second torsional spring;; N- 1 inner couplings, wherein each said inner coupling includes a first outer surface and a second outer surface, and wherein said first outer surface of an ith inner coupling is coupled to said inner surface of said second torsional spring of an ith torsional spring assembly and said second outer surface of said ith inner coupling is coupled to said inner surface of said first torsional spring of an i+lth torsional spring assembly; and a first torque drive coupling including an outer surface coupled to said inner surface of said first torsional spring of a first torsional spring assembly adapted for transmitting and receiving torque; and a second torque drive coupling including an outer surface coupled to said inner surface of said second torsional spring of a Nth torsional spring assembly adapted for transmitting and receiving torque.

27. The torsional coupling of claim 26, wherein each said torsional spring comprises.

a outer rigid member; an elastic member coupled to said outer rigid member; and an inner rigid member coupled to said elastic member; wherein rotation of said inner rigid member with respect to said outer rigid member places said elastic member in tension and in compression.

28. The torsional coupling of claim 27, wherein said outer rigid member includes an inner oblong surface, wherein said inner rigid member includes an outer oblong surface, and wherein said elastic member is coupled to said oblong surfaces.

29. The torsional coupling of claim 28, wherein said oblong surfaces are elliptical.

30. A riser tensioner adapted for mounting between platform and a riser, and for applying a generally upward force to said riser, comprising: first and second spaced apart Supports adapted for being supported relative to said platform in spaced-apart relation; a shaft coupled to each of said supports and extending therebetween; a support arm having a first end coupled to said shaft and a second end adapted for being coupled to said riser; a first torsional coupling including a plurality of elastic members operably coupled to one another and having a first end coupled to said first support and a second end coupled to said support arm; and a second torsional coupling including a plurality of elastic members operably coupled to one another having a first end coupled to said second support and a second end coupled to said support arm; wherein rotation of said support arm about said shaft places said elastic members in tension and in compression.

31. A riser tensioner adapted for mounting between platform and a riser, and for applying a generally upward force to said riser, comprising: first and second spaced apart supports adapted for being supported relative to said platform in spaced-apart relation; a shaft coupled to each of said supports and extending therebetween; a support arm having a first end coupled to said shaft and a second end adapted for being coupled to and applying said generally upward force to said riser; a first torsional coupling including a plurality of elastic members operably coupled to one another and having a first end coupled to said first support and a second end coupled to said support arm;; a second torsional coupling including a plurality of elastic members operably coupled to one another having a first end coupled to said second support and a second end coupled to said support arm; and a pretensioner device coupled to said first and second torsional couplings adapted for applying a bias to said torsional couplings whereby said generally upward force applied to said riser is enhanced; wherein rotation of said support arm about said shaft places said elastic members in tension and in compression.

32. A line compensator adapted for providing a tensile load on an inelastic flexible line extending between a platform or other rigid structure and a floating vessel comprising: first and second spaced apart supports adapted for being supported relative to said platform in spaced-apart relation; a shaft coupled to each of said supports and extending therebetween; a pulley assembly coupled to said shaft and including a first end and a second end adapted for being coupled to said inelastic line; a first torsional coupling including a plurality of elastic members operably coupled to one another and having a first end coupled to said first support and a second end coupled to said pulley assembly; and a second torsional coupling including a plurality of elastic members operably - coupled to one another having a first end coupled to said second support and a second end coupled to said pulley assembly; wherein rotation of said pulley assembly about said shaft places said elastic members in tension and in compression.

". A motor mount adapted for supporting a motor within a chassis of a motor vehicle comprising: a mounting bracket adapted for being supported by said chassis of said motor vehicle; a torsional spring coupled to said mounting bracket, said torsional spring comprising: an outer rigid member; an elastic member coupled to said outer rigid member; and an inner rigid member coupled to said elastic member; wherein rotation of said inner rigid member with respect to said outer rigid member places said elastic member in tension and compression; a support shaft coupled to said torsional spring; and a motor bracket adapted to be attached to said motor and coupled to said support shaft.

34 A torsional coupling including at least one torsional spring as defined in any one of claims 1 to 17.

35 A riser tensioner including at least one torsional coupling as defined in any one of claims 18 to 30.

36 A line compensator including at least one torsional coupling as defined in any one of claims 18 to 30.

37 A marine drive including at least one torsional coupling as defined in any one of claims 18 to 30.

38 A motor mount including at least one torsional spring as defined in any one of claims 1 to 17.

39 A torsional spring substantially as herein described either with reference to FIGS. 1 to 3, FIGS. 4 and 5, or FIG. 6.

40 A torsional coupling substantially as herein described with reference to FIGS.

7 to 10.

41 A riser tensioner assembly utilizing torsional couplings substantially as herein described with reference to FIGS. 11 to 15.

42 A line compensator utilizing torsional couplings substantially as herein described with reference to FIGS. 16 to 18.

43 A marine drive utilizing a torsional coupling substantially as herein described with reference to FIGS. 19 and 20.

44 A motor mount utilizing a torsional spring substantially as herein described with reference to FIGS. 21 and 22.