Abstract: A lockup clutch in a hydrodynamic torque converter has an axially movable piston which can be pressed against a contact face of a flange of the converter housing in a switching position via at least one friction facing. At least one of the structural component parts of the flange of the converter housing or the piston serves as a carrier for a deformation element axially arranged between it and the other structural component part. The deformation element is connected with the carrier on at least one radial side and is in a working connection with the carrier at least at the other radial side via an elastic supporting device. The deformation element extends at least within the area of extension of the friction facing.

Abstract: A clutch disk is provided with a cushioning plate 16 to prevent an eccentric abrasion of its friction facings. The clutch disk does not use rivets and has a cushioning function. The clutch disk includes a pair of friction facings 15a and 15b and a cushioning plate 16. The cushioning plate 16 includes in a fixing part 16a, a plurality of first installation parts 16b, a plurality of second installation parts 16c, a plurality of first connecting parts 16d, and a plurality of second connecting parts 16e. The first installation parts 16b have first friction facings 15a installed thereon. The first installation parts 16b with their first friction facings 15a extend from the fixing part 16a to an outer circumferential side of the cushioning plate 16. The second installation parts 16c have second friction facings 15b installed thereon.

Abstract: A clutch is provided with an input section for inputting driving force in to the clutch, an output section for outputting driving force from the clutch, a shifting device for shifting one of the input section and the output section against the other one between an engaging position where the driving force is transmitted by the engagement of the input section with the output section and a releasing position where the driving force is intercepted by releasing the one from the other; and a shock easing member provided to at least one of the input section and the output section, for ease shock caused by the shifting.

Abstract: The linings are fixed on fixing zones (4a, 4b) of the blades (3a, 3b) constituting the disc peripheral region (2) by one or several adhesive beads (9) extending in the proximity of the edges of each of said fixing zones (4a, 4b), inside the latter. The invention is applicable to motor vehicle clutches.

Abstract: An elastic member made of, for instance, a rubber material, is fixed to a piston member of a lockup clutch. A wet friction facing is fixed to the elastic member. The elastic member provides a cushioning effect when the lockup clutch is engaged for controlled slippage.

Abstract: A single revolution clutch with an auto-home feature. This feature, added to the single revolution clutch, provides a mechanical home position stop. It utilizes the motion of the case to accomplish this. Whenever the clutch is energized, the case is pulled in, or the 1 mm gap is closed. The control ring has an additional single home detent on the opposite side to the one or more detents normally found on the single revolution clutch. The case has a tab feature, which can be punched out of the case itself, or can be tacked on as an additional piece of metal or plastic. This tab feature, seen as an "L" shape from the side, will move with the case. When the case is energized and closes its 1 mm gap, the normal detents on both the control ring and the case, spin free of each other. However, the "L" tab now moves closer to the single home tab on the other side of the control ring, and locks the control ring within one revolution of rotation or less.

Abstract: A clutch pad assembly 10 includes a first friction portion 31, a second friction portion 32 and a cushioning plate 35. The first friction portion 31 has a first core plate 34 and a first friction member 35 fixed to the first core plate 34. The second friction portion 32 has a second core plate 36 spaced in the disk axial direction from the first core plate 34, and a second friction member 37 fixed to the second core plate 36. The cushioning plate 35 has a cushioning portion 40 disposed between the first and second core plates 34 and 36. The second core plate 36 has an engagement portion 47 engaged with the cushioning portion 40. In an alternate embodiment, a clutch pad assembly 10 includes a pair of annular friction members 131 and 132, cushioning plate 133 and a pair of core plates 134 and 136. The cushioning plate 133 has a plurality of cushioning portions 141, 142 arranged between the paired friction members 131 and 132.

Abstract: A friction clutch with a flywheel and a clutch housing has the flywheel and clutch housing connected to one another by means of a preferably cylindrical wall located in the radially outer portion of the clutch housing. The cylindrical wall can extend in a ring-shaped manner around the axis of rotation of the flywheel. The clutch housing encloses a clutch plate with friction linings in the radially outer area, and an application plate or pressure plate can be pressed toward the clutch plate by means of an application spring. The friction linings can be guided or extended radially outwardly up to directly next to the cylindrical wall, to make possible, with a specified friction surface, a minimum ratio of outside diameter to inside diameter on the friction linings. The friction linings can be connected to the clutch disc without the interposition of a lining spring system.

Abstract: In a first embodiment, a friction engagement portion 3 of clutch disk assembly includes a driven plate 20 fixed to a clutch plate 5, a cushioning plate 21, first and second sintered alloy pads 22 and 23, and rivets 32. The cushioning plate 21 has a corrugated form allowing elastic deformation. The first sintered alloy pad 22 is arranged at the cushioning plate 21. The second sintered alloy pad 23 is fixed to the driven plate 20 having an outer peripheral edge bent for fixing the second sintered alloy pad 23. The rivet 32 has an end engaged with the second sintered alloy pad 23, is axially movable, and has the other end for fixing the cushioning plate 21 and the first sintered alloy pad 22. In a second embodiment, a pair of first and second cushioning plates 120 and 121 are opposed to each other at an outer peripheral portion of the clutch disk assembly. Sintered alloy pads 122 and 123 fixed at outer surfaces of the first and second cushioning plates 120 and 121.

Abstract: A disc with friction liners for a mechanical clutch. The blades of the disc include, in the region of each zone (4) in which a friction liner is fixed, a slightly raised portion (1), which prevents overflow of the adhesive on to the bending zones (10) that join the central portion (4) to supplementary engagement zones (7).

Abstract: A clutch disk for a friction clutch, especially for internal combustion engines, with a hub, two friction disks which are arranged concentric to the hub and are connected thereto. A plurality of facing spring elements are connected with the friction disks so as to be rotationally fixed relative thereto, and are provided between the friction disks in the circumferential direction. The facing spring elements are curved in a wavy manner and nested against one another in pairs such that they exert a force on the friction disks in the axial direction. The facing spring elements which are nested against one another are designed so that their ends which are directed in the circumferential direction are located at a distance from one another in the no-load state of the clutch.

Abstract: A modular clutch includes a flywheel 2, a clutch cover assembly 3 and a clutch disk assembly 4, which form a single module that in one embodiment is installed directly onto the crankshaft of an engine, and in an alternate embodiment is attached to a flex plate. The modular clutch is configured to be installed and replaced as a unit. The clutch cover assembly 3 has a clutch cover 21, a pressure plate 22 and diaphragm spring 23. The clutch disk assembly 4 has a clutch engagement portion 31 made of a metallic sintered body.

Abstract: An elastic member made of, for instance, a rubber material, is fixed to a piston member of a lockup clutch. A wet friction facing is fixed to the elastic member. The elastic member provides a cushioning effect when the lockup clutch is engaged for controlled slippage.

Abstract: A frictionally engaging clutch disc assembly includes portions which define alignment holes which are employed during assembly of the clutch disc assembly. A tooling jig having alignment pins are engaged in the alignment holes such that the various portions of the clutch disc assembly arc accurately positioned with respect to one another during construction of the clutch disc assembly.

Abstract: In a first embodiment, a friction engagement portion 3 of clutch disk assembly includes a driven plate 20 fixed to a clutch plate 5, a cushioning plate 21, first and second sintered alloy pads 22 and 23, and rivets 32. The cushioning plate 21 has a corrugated form allowing elastic deformation. The first sintered alloy pad 22 is arranged at the cushioning plate 21. The second sintered alloy pad 23 is fixed to the driven plate 20 having an outer peripheral edge bent for fixing the second sintered alloy pad 23. The rivet 32 has an end engaged with the second sintered alloy pad 23, is axially movable, and has the other end for fixing the cushioning plate 21 and the first sintered alloy pad 22. In a second embodiment, a pair of first and second cushioning plates 120 and 121 are opposed to each other at an outer peripheral portion of the clutch disk assembly. Sintered alloy pads 122 and 123 fixed at outer surfaces of the first and second cushioning plates 120 and 121.

Abstract: A lock-up clutch for a hydrodynamic torque converter which includes at least one piston which can be displaced in the axial direction and can be connected to the converter housing by means of at least one friction zone, which piston defines, by means of the side which faces the converter housing, a chamber in which, when the lock-up clutch is active, the pressure is lower than the pressure in the converter circuit, and which, in the vicinity of a friction zone, has at least one channel for the flow of hydraulic fluid from the converter circuit. The quantitative flow of hydraulic fluid is a function of the pressure exerted by the converter. The lock-up clutch further includes at least one friction zone which has at least one friction lining, whereby the lock-up clutch has a total of at least two friction linings of different axial dimensions which, in the event of different pressures acting in the converter, come into at least partial effective connection with the matching friction surfaces.

Abstract: The multiplate clutch for an automatic transmission includes a composite separator plate that reduces chatter and the frequency of vibrations transmitted through the separator plate. The separator plate includes a first rigid steel member, a second rigid steel member, and a layer of a viscoelastic material bonded between the two rigid members. The separator plate has projections extending from the first and second rigid members and the viscoelastic layer to engage a rotating drum or a splined shaft. Each of the rigid members has a thickness of between 0.010 to 0.090 inches, and the viscoelastic layer has a thickness of between 0.001 to 0.005 inches.

Abstract: A friction clutch for a motor vehicle, which friction clutch has friction surfaces on the centrifugal mass and on the application plate, whereby the clutch disc is provided with friction lining rings which have an essentially constant material thickness over their radial extent or dimension. The matching friction surfaces extend at least in one radial direction beyond the friction surfaces, and are riveted to a carrier in this area.

Abstract: A clutch friction wheel for a motor vehicle includes a friction disc which comprises two support elements, each carrying a friction liner fixed to the peripheral portion of the support element, which is extended radially inwardly by a central fastening portion of the support element. A resilient progressive action element or spring is interposed between the inner faces, facing towards each other, of the peripheral portions of the two support elements, and is fixed to at least one of the latter. A locating element is interposed between the inner faces of the central fastening portions and is fixed to the latter. The friction disc is made as a pre-formed unitary sub-assembly, and bayonet fitting means are interposed between the central fastening portion of one of the support elements and the locating element.

Abstract: A method for automated assembly of a frictionally engaging clutch disc subassembly, employing a tooling jig in conjunction with appropriately configured subassembly friction facings and cushioning plate, whereby need for post-manufacture rotational balancing is eliminated.

Abstract: A wet multidisk friction clutch is constructed of a plurality of driving friction disks connected to an input shaft and a plurality of driven friction disks connected to an output shaft and arranged alternately with said driving friction disks, whereby power is selectively transmitted by frictional engagement between said driving friction disks and said driven friction disks. Each of said driving friction disks comprises a metal core and friction linings applied on opposite sides of said metal core and is partly cut off in a radial direction to define end portions, thereby forming a partly-open annular shape.

Abstract: A carbon-carbon composite material formed from a fibrous substrate and a matrix. The fibrous substrate has a carbon fiber base which acts as a reinforcement, a coarse texture and large sized cavities. The matrix includes pyrocarbon layers coating the fibrous substrate and a carbon based cellular structure dividing the large sized cavities of the substrate into small cavities having open porosity.

Abstract: A liner support disc for supporting friction liners, adapted to constitute a clutch friction wheel, especially for a motor vehicle, of the kind comprising a central portion and a peripheral portion divided into radial blades for receiving the friction liners, with each of the blades being joined integrally to the central portion through a foot, and comprising at least one support zone which is generally parallel to the mean plane of the central portion, for contact with at least one of the friction liners and for fastening of the latter. In a clutch friction wheel, the liners lie on either side of the peripheral portion.

Abstract: This invention relates to a clutch disc for a friction clutch in which the connection between the hub and the friction linings is made by several leaf-spring-like elements distributed over the circumference, which elements are fastened in their central area to the hub, are essentially tangential to the axis of rotation and run at some radial distance from the axis of rotation in both directions, and are connected by means of their terminal areas to the friction linings.

Abstract: A friction clutch for a transmission of a motor vehicle generally will have a clutch disc, and the clutch disc will be provided with friction linings for engaging the friction clutch with a rotating engine flywheel. The friction rings can be provided, on both surfaces thereof with trough-shaped depressions, to reduce the weight of the clutch disc. The trough-shaped depressions can essentially be rectangular or square, with rounded corners and with connecting surfaces which are steeply diagonal, or curved with a large radius of curvature.

Abstract: A friction material facing and carrier assembly (10) for a clutch driven plate in which at least one annular friction facing (20A) is secured to the carrier (11) by stripes (24A, 24B, 24C, 24D) of adhesive elastomeric material which are coaxial with the facing. The carrier plate includes circular rows (15, 16, 17) of perforations (14) and the stripes of adhesive are located on the circular lands (25, 26, 27, 28) either side of and between adjacent rows of perforations. The stripes of adhesive may be joined together to provide a continuous stripe of adhesive which extends from the radially inner margin of the facing to the radially outer margin of the facing.

Abstract: It is proposed to mount single, cylindrical or polyhedron sintered friction elements (1) at the cantilevered ends of resilient metal plates (2); the metal plates are attached to a base platen (3) in such a way that each end of the plates acts as an independently movable bracket adapted to absorb any deformation induced by thermal forces, thereby enabling a uniform contact pressure to be exerted between the single friction elements and the brake disc.

Abstract: In the liner support disc adapted to constitute a clutch friction wheel, especially for a motor vehicle, of the kind comprising a central portion (16) and a peripheral portion divided into radial blades (672) alternating in the circumferential direction with a series of radial tongues (671) in the same plane as the central portion (16) of the liner support disc, in which the blades (672) have, joined by bent portions (421), a central support zone (423) and two peripheral support zones (422) on either side of the zone (423), the peripheral zones (422) being offset axially with respect to the central zone (423), at least some of the tongues (671) have at least one support zone (622) offset axially towards the central zone of the blades (672) by virtue of a connecting bent portion (621).

Abstract: A friction clutch, especially for a motor vehicle, has a clutch friction wheel which includes a liner support disc having a central portion and a peripheral portion which is divided into blades, with friction liners being carried on both sides of the support disc and secured to these blades. At least some of the blades of the liner support disc are of tripod type, having at least one central support surface zone and two peripheral support surface zones. The central zone is connected firstly to the central portion of the support disc through a tangential fold, and secondly to the peripheral zones of the blade through oblique folds.

Abstract: A clutch plate wherein a hub carries and is surrounded by a disc which, in turn, carries and is surrounded by an annulus of pairs of partially overlapping resilient sector-shaped carriers for two annular friction linings. The carriers are disposed axially between the friction linings and each such carrier has a flat portion as well as a set of substantially radially extending tongues which are partly cut out and project from the flat portion. The friction linings are fastened to the carriers by stepped rivets, and such rivets further serve to fix the carriers of each pair to each other in axially stressed condition.

Abstract: A friction clutch wherein a pressure plate is axially movably but non-rotatably coupled to a cover and is biased by a diaphragm spring to urge the friction linings of a clutch disc against a flywheel which is driven by the engine of a motor vehicle. The diaphragm spring is tiltable relative to a seat which is carried by the cover, and a second spring is provided to bias a portion of the seat against the diaphragm spring. The latter can be moved axially of the flywheel to compensate for wear upon the friction linings, particularly when the flywheel is idle or is driven at a relatively low speed.

Abstract: A friction pad for use in a friction engagement device such as a brake or clutch. The friction pad includes a friction lining, a sensor and an actuator. The sensor senses an operating condition such as pressure applied to the friction lining and emits a signal that is directly or indirectly sent to the actuator. The actuator changes shape in response to the signal and thereby causes a change in the structure of the friction pad.

Abstract: A clutch friction wheel for a motor vehicle clutch comprises a support having slotted lobes projecting radially from an inner portion of the support. Friction pads are arranged back-to-back on either side of each lobe. Springs are interposed between two associated friction pads. The springs consist of profiled fins such as to define a wavy support having, for contact with one friction pad of each pair, a central zone having free circumferential end portions, and, for contact with the other friction pad of the same pair, marginal portions. One of these marginal portions projects from and is integral with the inner portion of the support.

Abstract: There is disclosed a frictional member, or ring, which is substituted for the conventional friction linings and marcel of an automotive clutch. The frictional ring is preferably a monolithic member which has recesses that receive support brackets which attach the frictional ring to the clutch disc. Preferably, the frictional ring includes spring biased islands which permit a phased or progressive engagement of the disc between the pressure plate and flywheel.

Abstract: A dry friction clutch plate is of the kind having a metallic support plate with ring-shaped friction pads arranged on either side of it. A ring-shaped compression element is arranged between the friction pads, this ring-shaped element being of a cellular material. The cellular material is a deformable material having open and/or closed cavities or pores such as to cause the thickness of the ring-shaped compression element to be reduced when the clutch plate is subjected to compressive stresses, and to cause it to revert to its original thickness on the removal of the compressive stresses.

Abstract: A motor vehicle clutch disc includes a metal carrier sheet; an elastomer intermediate layer facing the metal carrier layer; a clutch lining facing the elastomer intermediate layer; and a composite binder bonding first surface regions of the elastomer intermediate layer to the metal carrier sheet and to the clutch lining by chemical sorption. Areas of the first surface regions are less than areas of the metal carrier sheet and the clutch lining facing the elastomer intermediate layer. The elastomer intermediate layer is of hydrated nitrile rubber or a fluoroelastomer. The elastomer intermediate layer has an elasticity of non-linear spring characteristics and is effective in a direction perpendicular to the plane of the clutch disc. The elastomer intermediate layer has unbonded, second surface regions facing the metal carrier sheet and the clutch lining.

Abstract: A friction material facing (20) and carrier (11) assembly in which the facing (20) is secured to the carrier (11) by a plurality of concentric circular stripes (24A, 24B, 24C) of adhesive (24). Each stripe (24A, 24B, 24C) is interrupted at a single point on the circle to form a gap (25A, 25B, 25C) between the beginning and end of each circle of adhesive. The end of one circle may be joined to the beginning of the adjacent circle so as to form a continuous stripe of adhesive (24) from the inner margin to the outer margin of the facing (20).

Abstract: A progressive engagement clutch having a compressible clutch plate assembly mounted between the clutch flywheel and pressure plate. The clutch plate assembly has a pair of outer clutch plates, a center wave spring plate coaxially mounted on a hub for axial movement relative to one another and to the hub, and clutch facings on the outer sides of the outer plates engagable with clutch facings on the flywheel and pressure plate. During clutch engagement, the clutch plate assembly and its spring are progressively compressed between the flywheel and pressure plate until the clutch plates are finally firmly gripped between the flywheel and pressure plate to permit torque transmission through the clutch without chattering, excessive stress on the clutch or transmission coupled to the clutch, and other problems associated with conventional clutches.

Abstract: A friction pad for use in a friction element used in a friction engagement device such as a brake or clutch. The friction element includes a carrier and a plurality of friction pads circumferentially spaced about the carrier. The pads may have a modular construction whereby pad portions are releasably secured to support portions. The pads may also be releasably secured to the carrier. Various friction pad constructions are contemplated including constructions in which the secondary support portion includes a membrane and the primary support portion includes a cylindrical member extending between the membrane and the friction pads. A continuous friction pad ring may be substituted for the discrete friction pads. The carrier may be provided with locator pins in the pad receiving bores to orient the pads properly. The carrier may have cuts and grooves formed therein to provide a flexible or even beam mounted support for the friction pads.

Abstract: A friction material and carrier assembly for a clutch driven plate, the assembly being intended for rotation about an axis and comprising a carrier (4), first and second arrays of friction material (20, 22) disposed on opposite sides of the carrier (4) each array of friction material being disposed about a respective locus substantially centered on the axis. The first and second arrays of friction material are secured to the carrier by means of first and second adhesive bonds, respectively. The second adhesive bond (24) is of elastomeric material providing resilient cushioning relative to the carrier (4) (in an axial direction of the assembly) for the second array of friction material (22), and the first adhesive bond (23) is substantially non resilient providing no or substantially no cushioning relative to the carrier (4) (in an axial direction of the assembly) for the first array of friction material (20) than is provided by the second adhesive bond for the second array of friction material.

Abstract: A friction facing material and carrier assembly (2) to form a part of a driven plate of a friction clutch. The assembly (2) comprises a circular carrier plate (4) with resilient flexible paddles (14) at its periphery. Two annuli of friction material constituting friction facings (20,22) are each bonded by silicone rubber to opposite sides of the paddles. The silicon rubber on each side of the paddles is in the form of substantially continuous circular concentric strips of rubber substantially centered on axis (X) about which the assembly (2) is intended to rotate. The concentric strips (24A, 24B, 24C, 24D, 24E), bonding the friction facing (20) to one side of the paddles (14), are each preferably opposite the gap between two adjacent concentric stripes of rubber bonding the friction facing (22) to the other side of the paddles.

Abstract: A torque converter and clutch assembly incorporates a selectively engageable clutch pressure plate which enforces frictional engagement between a clutch disc, mounted on the pressure plate, and the input shell of the torque converter. An elastomer lined compliant interface is disposed intermediate the pressure plate and the clutch disc for the purpose of permitting surface configuration compliance between the input shell and the clutch disc as well as between the clutch disc and the pressure plate.

Abstract: A clutch wheel for a plate type friction clutch comprises a clutch disc carrying a plurality of friction pads spaced coaxially around it. Each friction pad consists of two pad elements arranged back to back and movable axially with respect to each other against the action of a Belleville ring inserted between them. This axial movement is controlled within predetermined limits by abutment means consisting of cooperating elements of the two friction pads, or of at least one of the friction pads and the clutch disc. The Belleville ring is precompressed in such a way that, within the limits of the axial movement defined by the abutment means, it works only on a part of its characteristic curve in which the reaction force which it exerts is substantially constant.

Abstract: This invention relates to a friction clutch member of the kind having two friction pads which are fixed on annular support members which lie facing each other in the axial direction. A resilient progressive engagement member is interposed between the two friction pads, and includes a plurality of projecting bosses of resilient material, each boss being hollow in the middle and delimited at least over a major part of its periphery by a band of resilient material. The invention is especially applicable to automotive vehicles.

Abstract: A friction disc, in particular for a motor vehicle clutch, comprises a carrier member in the form of a simple thin metal radial disc, with a plurality of friction pads distributed on the carrier disc coaxially with it. Each friction pad is fastened to the carrier disc by at least one fastening member, and is in the form of two pad portions arranged respectively on either side of the carrier disc. The carrier disc is formed with windows, with each friction pad being mounted in line with a respective one of these windows, in such a way that it can at least partially engage in the window at its periphery. The window defines a tongue which is fixed with respect to the carrier disc and extends into the window, and the fastening member, or each fastening member, for each friction pad is secured to the corresponding tongue.

Abstract: A clutch driven disc assembly includes a ventilated support plate and friction element to reduce the build up of heat during use. The support plate includes a plurality of radially extending paddles. A pair of friction elements are secured to the opposed sides of each of the paddles. Each paddle has a plurality of generally parallel slots formed therethrough. The slots may extend generally radially or generally circumferentially relative to the paddle. Each of the friction elements includes a corrugated backing plate having a friction facing secured thereto. The corrugations define a plurality of raised channels in the backing plate. The raised channels are formed such that they are aligned with the slots formed through the support plate when the friction elements are secured to the paddle. Such alignment provides a plurality of channels for the passage of air therethrough as the driven disc assembly rotates during use.

Abstract: An adjustable rotary slip clutch comprising a driving portion, a driven portion, an annular cavity defined between the driving portion and the driven portion, a plurality of friction clutch elements of generally conical configuration mounted within the annular cavity, at least one of the friction elements mounted to the driving portion for rotation therewith, an at least one of the friction elements mounted to the driven portion for rotation therewith, and an arrangement for sealing the cavity to maintain lubricant therein.

Abstract: The invention relates to the construction of friction rings for clutch discs which peripherally have a substantially uniform material thickness and, in the region of the riveting, have groove-shaped, substantially radially extending indentations which are open to the front side, project on the rear side and rest on the wave crests of the lining carriers.

Abstract: The present invention relates to a friction clutch of the kind having two friction pads coaxial with each other and adhesively bonded or moulded on to annular supports which are arranged to face each other in the axial direction.In accordance with the invention, a progression element is interposed between the two friction pads, this progression element comprising a plurality of protuberances of resilient material, some at least of which are secured to the supports, with the protuberances delimiting channels between them and having a surface at their outer periphery which is of greater circumferential length than the surface with which they are provided at their inner periphery.

Abstract: A friction facing material and carrier assembly (2) for inclusion in a clutch driven plate. The assembly (2) comprises a metal carrier plate (4) having resiliently pliable spokes or paddles (14) at its outer periphery. Two annuli (20, 22) of friction material forming facings are bonded to opposite sides of the paddles (14) by a respective layer of an elastomeric material, for example a silicone rubber. Each elastomeric layer is in the form of a spiral stripe extending substantially continuously from the outer to the inner periphery of the respective friction facing. For example, the facing (22) is bonded by an elastomeric spiral having three turns (24A, 24B) and 24C. Preferably in a complete assembly (2), both spirals of elastomeric material are of the same hand with turns of one spiral opposite gaps between adjacent turns of the other spiral.