TORSIONAL VIBRATION DAMPER

Abstract: A torsional vibration damper, for example for a driven place of a friction clutch, comprises first and second rotatable members in the form of a radially directed annular element (33) arranged between two radially directed annular elements (29, 31) of ferromagnetic material. The first and second rotatable members are coupled together and movable angularly with respect to each other about a common axis of rotation. A magnetic circuit passes through both members and includes gaps (34, 35) between the members across which magnetic fields are established. A viscous magnetic fluid is held in the gaps by the magnetic fields and provides viscous damping of relative angular movement between the members.

Description: TORSIONAL VIBRATION DAMPER The invention relates to torsional vibration dampers. The invention is concerned particularly but not exclusively with torsional vibration dampers for use in conjunction with internal combustion engines. Such torsional vibration dampers are frequently incorporated in the driven plates of friction clutches through which drive is transmitted from the engine but they may be installed in other arrangements. There is an increasing tendency to solve various drive line vibration problems with torsional vibration dampers. Such torsional vibration dampers are generally made from a number of components which are all movable relative to each other and which are subject to wear and deterioration, particularly under the arduous conditions associated with friction clutches. A typical torsional vibration damper comprises first and second rotatable members coupled together and movable angularly with respect to each other about a common axis of rotation and friction damping means operative between the two members to provide damping of the relative angular movement between the members. Friction damping is normally employed due to its ease of implementation but other forms of damping such as viscous fluid damping can be employed. Normally, a torsional vibration damper also incorporates resilient means operative between the members to provide further control over relative angular movement therebetween but such resilient means is not absolutely fundamental to all kinds of torsional vibration damper. A further problem associated with some automobiles is that during the periods when the transmission drive is under no load, rotary oscillations occur in the gearbox producing a phenomenon known as idle-rattle. In order to damp out the vibrations which generate idle-rattle it is known to utilise a friction clutch driven plate in which the torque load through the driven plate passes through two sets of damping springs arranged in series with each other. Very light loads applied to the driven plate are taken through soft auxiliary vibration damping springing. When the limited angular movement controlled by the auxiliary damping springing has been taken up, normal drive load passes through a set of main torsion damping springs. In this way, very light damping is provided over a limited range of movement for very light loads and this arrangement tends to prevent idle-rattle. Such a driven plate is known from French Patent Publication No. 1 501 465. Viscous damping is attractive in many situations where primary and/or auxiliary vibration dampers are employed due to its velocity dependent degree of damping. However, containment of a suitable viscous fluid normally requires complex seals which must remain effective in a possibly hostile environment for a long period of time with the result that there are many applications where in the past viscous damping has been impractical. An object of the present invention is to provide a simplified viscous torsional vibration damper. In accordance with one aspect of the present invention there is provided a torsional vibration damper comprising first and second rotatable members coupled together and movable angularly with respect to each other about a common axis of rotation, a magnetic circuit passing through both members and comprising a gap between the members across which a magnetic field is established, and a viscous magnetic fluid held in the gap by the magnetic field and providing viscous damping of relative angular movement between the members. Preferably one of the members carries an annular permanent magnet. Preferably one member incorporates a radially directed annular element of ferromagnetic material, the other member incorporates two radially directed annular elements of ferromagnetic material arranged axially one on each side of the first mentioned element, the magnetic field passes across two gaps between the elements, and magnetic fluid is provided in both gaps. The two elements may extend radially inward and be joined together outwardly thereof to provide an inwardly directed annular groove to constrain escape of magnetic fluid under the influence of centrifugal force. Any part of the groove remote from said gaps may be filled with a non-magnetic material to further constrain the magnetic fluid. The viscous magnetic fluid preferably comprises a suspension of ferrite in a base liquid which may, for example, be a mineral oil or a silicone-based oil. According to another aspect of the present invention there is provided a clutch driven plate comprising a hub, a friction facing carrier mounted on the hub coaxially therewith and capable of limited angular rotation about the hub, and a torsional vibration damper as defined hereinabove acting between the hub and the friction facing carrier. According to a further aspect of the present invention there is provided a clutch driven plate comprising a hub incorporating an inner flange, an outer flange mounted on the inner flange coaxially therewith and capable of limited angular rotation about the hub, a friction facing carrier mounted on the hub coaxially therewith and capable of limited angular rotation relative to the hub and to the outer flange, and a torsional vibration damper as defined hereinabove acting between the outer flange and the hub. Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a diagrammatic cross-sectional view through a friction clutch driven plate incorporating a torsional vibration damper; Figure 2 is a corresponding view of part of the driven plate on a larger scale showing further details of the damper; Figures 3 to 5 together show details of a modification of the damper shown in Figures 1 and 2; and Figure 6 is a diagrammatic cross-sectional view through a friction clutch driven plate incorporating a torsional vibration damper in the form of an idle-rattle damper. The driven plate shown in Figure 1 incorporates an annula hub 11 having internal splines 12 intended for engagemen with a splined input shaft to a gearbox. Hub 1 incorporates an integral radial flange 13. A friction facing carrier is constituted by two side plate 14 and 15 arranged one to each side of the flange 13 an held together by stop pin rivets 16 which unite the sid plates together with clearance therebetween for the flang 13. The friction facing carrier also carries a series o spring steel segments 17 around the outer periphery of th side plate 14 and these segments in turn carry two frictio facings 18 and 19. The hub 11 with its flange 13 and the friction facin carrier with its friction facings constitute first an second rotatable members coupled together and movabl angularly with respect to each other about a common axis o rotation. Low friction bearing elements 21 and 2 themselves provide relative radial location between the tw members. In conjunction with axially directed sprin loading provided by a belville spring 23, the bearin elements 21 and 22 also provide relative axial locatio between the members. -7 - Circumferentially directed resilient elements constitute by coil springs 24 are arranged in mutually aligned apertures in the flange and side plates, namely apertures 25 in the flange and apertures 26 and 27 in side plates 14 and 15 respectively. Side plate 14 incorporates an inward annular step 28 near its inner periphery providing an inwardly directed annular element 29. The side plate 14 and in particular element 29 is of a magnetic material such as mild steel. An annular magnet 31 is secured by half sheared lugs 20 and clips 30 to the side plate 14 in such a position that it forms a second inwardly directed annular element spaced from the element 29 and also forms an inwardly directed annular groove 32 between the elements 29 and 31. An outwardl directed annular element 33 is carried by the hub 11 for rotation therewith and extends outward between the tw elements 29 and 31 with gaps 34 and 35 between adjacen elements. For assembly purposes, element 33 must of cours be positioned between elements 29 and 31 before they ar secured together. Also, to enable the side plate 14 to b mounted on the hub after elements 29 and 31 have bee joined together, element 33 is arranged to be splined t the hub 11 on splines 37. It .is located axially against a end face of the bearing element 22 and held in position by a circlip 38. Element 33 is also of ferromagnetic material. A magnetic fluid is introduced into the gaps 34 and 35 in such quantities as to bridge the gaps substantially as shown. The fluid is held in position by magnetic fields in the gaps arising from the magnet 31 and its associated magnetic circuit including shoulder 28, element 29, gap 34, element 33 and gap 35. The magnet or element 31 is magnetised radially as indicated by references N and S to provide magnetic flux around this circuit and magnetic fields across the gaps. In use, torque from an internal combustion engine is transmitted through the friction facings 18 and 19 to the carrier and from the carrier to the hub 11 with its flange 13. The main driving torque is transmitted through the resilient elements 24, deflecting these elements and causing relative angular displacement between the carrier and hub. Spring lengths and aperture lengths may be such that some springs come into effect immediately while others come into effect only after some movement. Torsional vibrations associated with the engine and its transmission of power result in vibratory angular displacement between the carrier and the hub. Shear action in the magnetic fluid in gaps 34 and 35 provides viscous damping between the carrier and the hub and thereby tends to damp out the vibratory angular displacement between these two members. The degree of damping provided by the magnetic fluid can be varied to meet requirements by the characteristics of the fluid, by the strength of the magnet and by the width and other dimensions of the gaps. The magnetic fluid may be, for example, a colloidal suspension of ferrite in any suitable base liquid that has a low vapour pressure and therefore does not evaporate. Suitable liquids include mineral oils and silicone-based oils. The viscous nature of the fluid itself can be varied by selecting a base liquid of suitable viscosity and by selecting the quantity and nature of the magnetic particles suspended .in the base liquid. The width of the gaps between the annular element 33 and the magnet element 31 and annular element 29 are preferably in the range up to 0.5mm, for example 0.25ram, but can be varied as mentioned above to provide the required degree of damping. The torsional vibration damper as shown and incorporated in a friction clutch driven plate is in a typical application rotated at speeds of up to 7000 rpm. The substantial centrifugal force may be sufficient in some cases to throw the magnetic fluid outward away from the gaps 34 and 35. With a suitable magnetic circuit and the inwardly directed annular groove 32 .confining the magnetic fluid, the arrangement may be such that the fluid is retained near to the gaps 34 and 35 and is returned to them by magnetic attraction as the rotational speed decreases. An alternative arrangement is to fill or substantially fill the free part of the annular groove 32 outward of the element 33 with a non-magnetic material. If the non-magnetic material is a relatively highly viscous material, the element 33 may extend radially outwardly into the non-magnetic material to provide increased damping. The fact that the magnetic fluid may bear against the non-magnetic material can also influence the degree of damping in such a manner that it varies with rotational speed. Of course, if the magnetic fluid is thrown out beyond the gaps 34 and 35 by centrifugal force, the degree of damping again varies with rotational speed. In the drawings the surfaces of the elements 29, 31 and 33 defining the gaps 34 and 35 are shown as being smooth. As an alternative, they may be provided with local roughness or larger irregularities to vary the degree of damping. Figures 3, 4 and 5 taken together show details of a modified annular element to replace element 33 and magnet to replace the magnet 31. Figure 3 shows the annular element 41 in elevation and Figure 5 shows the magnet 42 in elevation. Figures 3 and 5 show the faces of these components which in practice are positioned adjacent each other as shown in Figure 4, which shows both elements in cross section, taken on lines A-A and B-B of Figures 3 and 5 respectively. The viscous magnetic fluid is not shown in Figure 4. The magnet 42 shown in Figure 5 is generally annular and corresponds in most respects to the magnet 31 but incorporates four castellations 43 projecting from one face at regular intervals around its periphery. The castellations act as magnetic pole pieces, tending to concentrate magnetic field in their vicinity. The annular element 41 corresponds in most respects to the annular element 33 of Figures 1 and 2 but on its face directed towards the magnet carries a series of raised ribs. There is an outer rib 44 and an inner rib 45 at each of four angular positions around the annular element. These ribs project towards the magnet 42. The relative angular positions between the castellations 43 on the one hand and the ribs 44 and 45 on the other hand is such that during relative movement which is to be damped out, the degree of overlap varies. The result of this is a variation in the strength of the magnetic field and thus of the degree of damping dependent on the relative angular position of the members. The relative positions of the castellations 43 and of the ribs 44 and 45 may be varied to suit the required variations in damping with angular movement. For example, it might be desirable to provide a central region of relative movement with very little damping and an increasing degree of damping with increasing angular movement. In a further modification ribs such as 44 and 45 may also be provided on the opposite face of the annular member 41 and there may also be further castellations with which these ribs co-operate. Although it is not shown in the drawings and is not needed in all embodiments of the invention, we have found that it may be desirable in some instances to provide means for centering the intermediate element 33 between the rotatable members. The centering may be accomplished by suitable resilient biasing of the intermediate element or the rotatable members. In the driven plate shown in Figures 1 to 5, there are only two relatively rotatable members but in some driven plates there are - three relatively rotatable members with relatively stiff main damping between one pair and relatively flexible damping between another pair. In such a case ' , viscous damping with magnetic fluid as described above may be used in either or both of these situations. For example Figure 6 shows a driven plate with viscous damping with magnetic fluid providing relatively flexible damping for suppressing idle-rattle. The driven plate shown in Figure 6 incorporates an annular hub 111 having internal splines 112 intended for engagement with a splined input shaft to a gearbox. Hub 111 incorporates an integral inner flange 113 which is provided with radially outwardly protruding teeth. An outer flange 114 is mounted on inner flange 113 by means of radially inwardly protruding teeth which permit angular movement of up to about 6° between the flanges 113,114. A friction facing carrier is constituted by two side plates 115 and 116 arranged one to each side of the outer flange 114 and held together by stop pin rivets 117 which unite the side plates with clearance therebetween for the flange 114. The friction facing carrier also carries a series of spring steel segments 118 around the outer periphery of the side plate 115 and these segments in turn carry two friction facings 119 and 120. The hub 111 with its inner flange 113 constitutes a first rotatable member, the outer flange constitutes a second rotatable member, and the friction facing carrier with its friction facings constitutes a third rotatable member. The rotatable members of the driven plate are coupled together and are movable angularly with respect to each other about a common axis of rotation. A low friction bearing element 121, in conjunction with axially directed spring loading provided by a belville spring 122 and a circlip 123, provides relative radial location of the side plates 115,116. Circu ferentially directed primary resilient elements constituted by coil springs 124 are arranged in mutually aligned apertures in the outer flange 114 and side plates 115,116, namely aperture 125 in the outer flange and apertures 126 and 127 in the side plates 115 and 116 respectively. Side plate 116 incorporates an outward annular step 128 providing an enlarged space between the o.uter flange 114 and the side plate. Positioned within the space is a control plate 129 which is provided with a lug 130 engaging with the aperture 125 in the outer flange so that the control plate 129 rotates with the outer flange 114. An intermediate plate 131 closely surrounds the hub 111 and is mounted on splines formed on the hub and held in place by a circlip 132. Windows 133 and 134 are provided in the control plate 129 and the intermediate plate 131 respectively and circumferentially directed auxiliary resilient elements consituted by coil springs 135 are arranged in the windows 133,134. Springs 135 are softer than springs 124. A stepped annular plate 136 is secured to control plate 129 to form a first rotatable member of the damper with an axially polarised annular magnet 137 being located between the annular plate 136 and the control plate 129. Annular plate 136 and control plate 129 are made of a ferromagnetic material such as mild steel. An outwardly directed annular element 138 comprising a second rotatable member of the damper is carried by hub 111 for rotation therewith and extends outward between the two plates 129, 136 with gaps between adjacent components. Element 138 is splined to the hub 111 and is located axially by a circlip 139. Element 138 is also of ferromagnetic material. A magnetic fluid is introduced into the gaps between the components 129,138 and 136,138 in such quantity as to bridge the gaps. The fluid is held in position by magnetic fields in the gaps arising from the magnet 137 and its associated magnetic circuit. In use, when a light load or small displacement is applied to the carrier this is transmitted through springs 124 to outer flange 114 and control plate 129, and from control plate 129 through auxiliary springs 135 to intermediate -16- plate 131 and hub 111. Because the springs 135 are mu softer than springs 124 there is direct drive witho compression of the springs 124 and the initial angul movement occurs between hub 111 and outer flange 114 und the control of auxiliary springs 135. Torsional vibratio under conditions of light loading, such as those whi cause idle-rattle, result in vibratory angular displaceme between the outer flange and the hub and shear action the magnetic fluid provides viscous damping between t outer flange and the hub and thereby tends to damp out t vibratory angular displacement between these two member This is the situation for movement up to 3° in eith direction as allowed by the co-operating teeth of the inn and outer flanges. After this movement of 3° in eith direction, no further relative rotation can occur betwe the hub and the outer flange so that further deflection controlled by the springs 124.

Claims: CLAIMS 1. A torsional vibration damper comprising first an second rotatable members (29,31,33 or 133,136,138) couple together and movable angularly with respect to each othe about a common axis of rotation, a magnetic circuit passin through both members and comprising a gap (34,35) betwee the members across which a magnetic field is established and a viscous magnetic fluid held in the gap by th magnetic field and providing viscous damping of relativ angular movement between the members. 2. A torsional vibration damper as claimed in Claim wherein one of the members carries an annular permanen magnet (31 or 137) . 3. A torsional vibration damper as claimed in Claim or Claim 2 wherein one member incorporates a radiall directed annular element (33 or 138) of ferromagneti material, the other member incorporates two radiall directed annular elements (29,31 or 133,136) o ferromagnetic material arranged axially one on each side o the first mentioned element, the magnetic field passe across two gaps between the elements, and magnetic fluid i provided in both gaps. 4. A torsional vibration damper as claimed in Claim 3 wherein the two elements extend radially inward and are joined together outwardly thereof to provide an inwardly directed annular groove to constrain escape of magnetic fluid under the influence of centrifugal force. 5. A torsional vibration damper as claimed in Claim 4 wherein a part of the groove remote from said gaps is filled with a non-magnetic material to further constrain the magnetic fluid. 6. A torsional vibration damper as claimed in any one of Claims 1 to 5, wherein the viscous magnetic fluid comprises a suspension of ferrite in a base liquid. 7. A torsional vibration damper as claimed in Claim 6. wherein the base liquid comprises a mineral oil or a silicone-based oil. 8. A clutch driven plate comprising a hub (11), a friction facing carrier mounted on the hub coaxially therewith and capable of limited angular rotation about the hub, and a torsional vibration damper as claimed in any one of Claims 1 to 7 acting between the hub and the friction facing carrier. 9. A clutch driven plate comprising a hub (111) incorporating an inner flange (113), an outer flange (114) mounted on the inner flange coaxially therewith and capable of limited angular rotation about the hub, a friction facing carrier mounted on the hub coaxially therewith and capable of limited angular rotation relative to the hub and to the outer flange, and a torsional vibration damper as claimed in any one of Claims 1 to 7 acting between the outer flange and the hub.

Inventors: BAINBRIDGE WILFRED NICHOLAS, BAINBRIDGE, WILFRED, NICHOLAS
Applicants: AUTOMOTIVE PRODUCTS PLC
Application year: 1987
Main classification: F16F15
IPC codes: F16F15