TORSIONAL VIBRATION DAMPER

Abstract: A torsional vibration damper has a rotational axis (X) and an annular housing (1) having inner and outer members (3, 4). The housing has an annular channel (5) in which an inertia member (6) is received. The channel has axially extending walls (8, 9) and is closed by an annular cover plate (14) to retain the inertia member (6). The inner edge of the cover plate (14) is received in a rabbet (13) in the inner channel wall and is joined to the wall by means of a weld. The inner and outer members (3, 4) are connected by an annular weld (12) at a central hub. The weld (12) may extend between two radial extremes which are separated by a distance substantially greater than the thickness of weld (12). The damper is easier to manufacture and assemble and has greater structural integrity.

Description: TORSIONAL VIBRATION DAMPER The present invention relates to a torsional vibration damper and more particularly, but not exclusively, to such a damper used to limit the torsional vibrations in an internal combustion engine. Torsional vibration dampers are used to limit the torsional vibrations that occur in a crankshaft of an internal combustion engine. Such dampers generally comprise an annular inertia member disposed within an annular chamber in a housing. A space between a wall of the chamber and the inertia member is filled with viscous damping fluid and the resistance to shear of the fluid between the chamber wall and the inertia member provides a damping effect. One method of manufacturing this type of damper utilises a sheet metal fabrication construction. The housing of such dampers generally comprises a two-part construction. Typically each part comprises central radial flange by which the damper is attached to the crankshaft and an outer region which is shaped to form the chamber. The parts are connected together such that the radial flanges are substantially coterminous and overlie one another and the outer regions combine to define the chamber. One known torsional damper comprises a three component housing. The first two components are assembled to form a common radial flange (as described above) and an outer region in the form of an annular channel. The annular inertia member is received in the channel and a third component being a cover plate is fitted to cover the channel and seal the inertia member therein. The channel has an annular reservoir in which the viscous damping fluid is retained. Such an arrangement is simpler to manufacture than a two-component housing and is particularly advantageous in that a first component forming an outer wall of the channel can be made to a standard size whereas the second component can be made to various sizes to accommodate different sized annular inertia members for different damping criteria. The cover plate is simply placed on the top edge of the walls of the channel and is fixed thereto at the junction between the walls and the cover plate by means of an electron beam weld or the like. When the damper is operational the joints between the channel walls and the cover plate are subject to a relatively large amount of stress. In order to counteract this it has been known to increase the structural integrity by adding a large annular fillet weld in a corner of the channel at the flange where the first and second components meet. The use of a large fillet weld creates distortion in the shape of the housing as a result of the significant heat produced in the welding process. Moreover, the fillet weld has to be machined to form the annular reservoir for the viscous damping fluid resulting in an increase in the manufacturing time and complexity. It is an object of the present invention to obviate or mitigate the aforesaid disadvantages. According to a first aspect of the present invention there is provided a torsional vibration damper having a rotational axis and comprising a housing having at least three parts, at least two of which define an annular channel in which an inertia member is received, wherein the channel has axially extending walls and is closed by a third part of the housing defining an annular cover at least one edge of which is received in a rabbet in one of said walls and is joined to the wall by means of a weld. The channel preferably has radially inner and outer walls and the rabbet is in the inner wall. The first and second parts of the housing are preferably connected at a central flange by means of a weld whose path extends between two radial extremities separated by a distance substantially greater than the weld thickness. Conveniently at least one of the channel walls is deformed to provide a damping material reservoir between it and the inertia member. Preferably the inner channel wall is stepped to form a wall of the reservoir Alternatively the inner channel wall may comprise a first wall portion defined by a first part of the housing and a second wall portion defined by a second part of the housing. The first and second wall portions may be radially offset to form the step. According to a second aspect of the present invention there is provided a torsional vibration damper having a rotational axis and comprising a housing having two parts defining an annular channel in which an inertia member is received, wherein the housing parts are joined at a central flange by means of a weld whose path extends between two radial extremities separated by a distance substantially greater than the weld thickness. The weld is preferably continuous and its path comprises a plurality of arcs at an outer periphery of the flange, adjacent arcs being joined by a radially inward path. In one preferred embodiment the radially inward path comprises an arcuate path joining diametrically opposite points on adjacent arcs. Alternatively the weld may comprise a plurality of separate paths which may be in the form of centrally offset circles. Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diametral sectioned view of a first embodiment of - the present invention; Figure 2 is a diametral sectioned view of a second embodiment of the present invention; Figure 3 is a diametral sectioned view of a third embodiment of the present invention; Figure 4 is a diametral sectioned view of a fourth embodiment of the present invention; Figure 5 is a fragmentary sectional view of a joint between a cover plate and a channel wall of present invention; and Figures 6 to 8 are schematic illustrations showing alternative welding configurations according to the invention. Referring now to the drawings Figures 1 to 4 show torsional vibration dampers embodying the present invention. Each damper has a central rotational axis X and comprises a housing assembly (indicated generally by reference numeral 1) having a central radial flange 2 by which the damper is attached to a crankshaft (not shown) of an internal combustion engine (not shown). In each of the embodiments of figures 1 to 4 the same reference numerals are used to designate features which are common to all embodiments. The housing is constructed from sheet metal and comprises three principal components: inner and outer members 3,4 and cover plate 14. When assembled the members 3,4 form the central flange 2 and a peripheral annular channel 5 in which an annular inertia member 6 is rotatably housed. The annular inertia member 6 is rectangular in cross section and has associated bearings 7 for radial and axial positioning. The annular channel 5 is defined between two concentric inner and outer axially extending walls 8,9 and is closed by an annular cover plate 14 sealingly welded thereto in order to retain the inertia member 6 and viscous damping fluid present in the space between inertia member 6 and the walls of the enclosed channel 5. In the embodiment shown in figure 1 the outer member 4 of the housing 1 is circular with an upstanding peripheral wall forming the outer axially extending channel wall 8. The inner member is similarly shaped with an upstanding wall forming the outer axially extending channel wall 9. Base walls 10,11 of the inner and outer members 3,4 are fixed together by annular welds 12 to form the flange 2. The free end of the inner wall 9 has an external rabbet 13 within which the inner edge of the cover plate 14 is received (see figure 5). The cover plate 14 is placed over the channel 5 so that its outer edge sits on the end of the outer channel wall 8 and its inner edge is seated in the rabbet 13 of the inner channel wall 9 and is fixed there by means of annular electron beam, laser or similar non-filler type welds 15. Towards the flange 2 of the damper the inner channel wall 9 is inwardly stepped so as to form a groove 14a in a lower portion of the channel. The region between the groove 14a and the annular inertial member 6 acts as a reservoir 15a for the viscous damping fluid. The damper shown in figure 2 differs from that described in relation to figure 1 in that there is provided a circular flange strengthening plate 16 between the inner and outer housing members 3,4. The welds 12 joining the inner and outer members 3,4 at the flange 2 also fix the strengthening plate 16 in place. In figure 3 a similar strengthening plate 17 is shown but is fixed at the flange 2 above the inner member 3. In an alternative embodiment (not shown) strengthening plates may be fixed below the outer member 4 at the flange 2. Figure 4 shows a damper in which the flange 2 is axially offset in relation to those shown in figure 1 to 3. The offset is provided by the base wall 11 of the outer member 4 having an annular axial step 18 . An inner channel wall 19 is formed partly from the upstanding wall 9 of the inner member 3 and partly from the axial step 18 in the base wall 11 of the outer member 4. The flange portion of the inner member 3 is greater in diameter than that of the outer member 4 so that when the housing 1 is assembled a viscous damping fluid reservoir 19 is provided in the lower portion of the channel by virtue of the fact that there is a greater clearance between the step 18 and the inertia member 6 than that between the upstanding wall 9 of the inner member 3 and the inertia member 6. Stiffening plates such as those described in relation to figures 2 and 3 may be used with this embodiment. In each of the four embodiments described it will be appreciated that the housing has a separate cover plate 14 which is used to enclose the channel 5. In use, the joints between the cover plate 14 and the channel walls 8,9 are subject to stress. It has been established that the joint between the cover plate 14 and inner channel wall 9 or 19 bears a significant proportion of the stress. The rabbet joint 13 provides greater sealing area, strength and load-bearing characteristics than other joints and a large part of the stress is borne by the channel wall 9 or 19 in the vicinity of the rabbet 13 rather than in the relatively weak weld. The use of an electron beam, laser or other non-filler weld reduces the heat distortion that occurs in other welding techniques. Thus costly machining operations are not required and the design of the components of the damper can be made to precise tolerances. Figures 6 to 8 show welds 12 that may be used to join the inner and outer housing members 3,4 at the flange 2. In addition to providing strength in the damper structure, the weld 12 acts to seal the members hermetically to prevent egress of the damper fluid. The figures show schematically the damper of figures 1 to 4 in plan. A central location bore 20 through which the crankshaft (not shown) may pass is circumscribed by five smaller fixing bores 21 by which damper is attached to the crankshaft. The weld 12 shown in figure 6 passes between an imaginary outer circle at the edge of the flange 2 and an imaginary inner circle passing through the centres of the fixing bores 21. The weld 12 is continuous and comprises five equi- angularly spaced arcs 22 at the edge of the flange 2, adjacent arcs being joined by radially inward U-shaped sweeps 23. Figure 7 shows a continuous weld 12' in the form of three arcs 24 at the edge of the flange 2 being joined by " arcuate sweeps 25 passing between the fixing bores 21 and interconnecting diametrically opposite points on the edge of the flange 2. Figure 8 shows three separate circles 12" of offset centres. The welding of these circles may be effected sequentially or simultaneously. Each of the welds 12, 12', 12" shown in figures 6 to 8 provide additional strength in the structure of the housing 1 by virtue of their progression in a radial direction as well as in a circumferential direction. It will be appreciated that numerous modifications to the designs described above may be made without departing from the scope of the inventions as defined in the appended claims. For example, a rabbet joint may be used on the outer channel wall instead of or in addition to that on the inner channel wall. Furthermore, the rabbet joint may be used in conjunction with a flange weld of any suitable pattern. With regard to figures 6 to 8 it will be understood that different geometrical patterns may be used provided they extend between two radial extremities. It will also be appreciated that the above described vibration damper may be used in other applications where torsional vibration of the rotating component is required, e.g. impellers or rotors.

Claims: CLAIMS 1. A torsional vibration damper having a rotational axis and comprising a housing having at least three parts, at least two of which define an annular channel in which an inertia member is received, wherein the channel has axially extending walls and is closed by a third part of the housing defining an annular cover plate at least one edge of which is received in a rabbet in one of said walls and is joined to the wall by means of a weld. 2. A torsional vibration damper according to claim 1, wherein the channel has radially inner and outer walls and the rabbet is in the inner wall. 3. A torsional vibration damper according to claim 2, wherein the first and second parts of the housing are connected at a central radial flange. 4. A torsional vibration damper according to claim 3, wherein the first and second parts are connected at the flange by means of a weld whose path extends between two radial extremities separated by a distance substantially greater than the weld thickness. 5. A torsional vibration damper according to any preceding claim, wherein at least one of the channel walls is deformed to provide a damping material reservoir between it and the inertia member. 6. A torsional vibration damper according to claim 5 when dependent on claim 2, wherein the inner channel wall is stepped to form a wall of the reservoir. 7. A torsional vibration damper according to claim 6, wherein the inner channel wall comprises a first wall portion defined by a first part of the housing and a second wall portion defined by a second part of the housing. 8. A torsional vibration damper according to claim 7, wherein the first and second wall portions are radially offset to form the step. 9. A torsional vibration damper having a rotational axis and comprising a housing having two parts defining an annular channel in which an inertia member is received, wherein the housing parts are joined at a central flange by means of a weld whose path extends between two radial extremities separated by a distance substantially greater than the weld thickness. r 10. A torsional vibration damper according to claim 9, wherein the weld is continuous. 11. A torsional vibration damper according to claim 9 or 10, wherein the weld path comprises a plurality of arcs at an outer periphery of the flange, adjacent arcs being joined by a radially inward path. 12. A torsional vibration damper according to claim 11, wherein the radially inward path comprises an arcuate path joining diametrically opposite points on adjacent arcs. 13. A torsional vibration damper according to claim 9 wherein the weld comprises a plurality of separate paths. 14. A torsional vibration damper according to claim 13, wherein the separate paths are in the form of centrally offset circles. 15. A torsional vibration damper substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: ALLPORT JOHN MARTIN, TENNANT DAVID WILLIAM HENRY, ALLPORT, JOHN, MARTIN, TENNANT, DAVID, WILLIAM, HENRY
Applicants: ALLPORT JOHN MARTIN, HOLSET ENGINEERING CO, TENNANT DAVID WILLIAM HENRY, ALLPORT, JOHN, MARTIN, HOLSET ENGINEERING CO. LTD, TENNANT, DAVID, WILLIAM, HENRY
Application year: 1996
Main classification: F16F15
IPC codes: F16F15