A TORSIONAL VIBRATION DAMPER

Abstract: A torsional vibration damper (1) comprises an annular driven hub member (2) and an outer annular inertia member (3) capable of limited rotational movement relative thereto. The damper (1) has diametrically opposed variable volume pumping chamber sets (16) defined by blades (11) of the inertia member being received in cavities in the hub member. Relative movement of said hub and inertia members in a first direction decreases the volume of one of said chambers (16) and increases the volume of the other whereas relative movement in the oposite direction causing a reverse variation in the volume of the chambers (16). The variable volume chambers (16) are connected, in use, to a source of damping fluid which is pressurised by the relative movement. Each blade (11) has a planar base surface that is adjacent a planar bottom surface of each cavity. The planar surfaces enable easier and cheaper manufacturing.

Description: A TORSIONAL VIBRATION DAMPER The present invention relates to a toisional vibration dampei tor use. foi example, in damping the torsional vibrations of an engine crankshaft It is known to provide a torsional vibration damper tor an engine crankshaft in which an outer inertia member is connected to an innei hub member and is capable of limited relative rotation thereto In certain dampers of this kind damping is achieved by the presence of pumping chambers defined between the hub and the outer inertia member The chambers are formed by cavities in the inertia member being occupied by undersized blades on the hub member such that there are clearances on each side of the blade that, in use, are occupied bv engine oil Relative rotation ol the inner and outer members causes the oil to be pumped between the cavities thereby providing a damping effect Such dampers have been known as "Sandnei dampers aftei the inventor In one particular Sandner design the blade had a transverse passage that communicated with the chambers on each side ol the blade Such dampers may require the complex assembly ol many precision machine pans and expensive machining operations both of which makes them inherently expensive It is an object of the present invention to obviate or mitigate the aforesaid disadvantage According to the present invention there is provided a toisional ubration damper comprising an annular driven member, an annular inertia member coaxial with said driven member and capable of limited rotational movement relative thereto the driven and inertia members having at least one set of variable volume chambers formed by a cavity in one member receiving a protecting element horn the othei member and the chambers being arranged such that relative movement ot said driven and inertia members in a first direction decreases the volume ot one ot said chambers and increases the volume ot the other lelative movement in the opposite direction causing a reverse variation in the volume of the chambers, the variable volume chambers being connected, in use. to a source of fluid characterised in that a surface of the projecting element and an adjacent surface of the cavity aie each substantially planar The provision of the planar surfaces greatly simplifies the manufacturing operation and is feasible as a result of the relatively low angular displacement of the driven and inertia members. In a preferred embodiment the planar cavity surface is provided with a recess in which a seal is provided. The projecting element may have a through conduit to permit the passage of fluid between the variable volume chambers on each side of the projection and the conduit may be provided with a constriction. Alternatively the projecting element may have a convoluted through conduit that preferably comprises offset parallel bores interconnected by a substantially perpendicular bore. The perpendicular bore may have an extended portion that forms an exhaust conduit to provide an exhaust outlet for fluid to atmosphere. In a preferred embodiment there may be provided two sets of variable volume chambers at diametrically opposed locations Preferably there is provided at least one radial conduit in the driven member for delivering damping fluid to each of the variable volume chambers, said radial conduit having a one-way valve The radial conduit and one-way valve may be of simple and compact design in view of the present invention since a relativeh small flow of damping fluid to the variable volume chambers is required The projecting element may have at least one cooling conduit that passes adjacent at least part of the transverse conduit, although in a preferred embodiment there are two cooling conduits, one on each side of the transverse conduit and each having a substantially right angle bend, a first portion of each conduit passing adjacent the transverse conduit and a second portion directed away from the transverse conduit to an outlet. Preferably the outlet of the cooling conduit is fitted with a non-return \ alve. In addition it is advantageous if an inlet of the oi each cooling chambei is fitted with an orifice. A specific embodiment 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 sectioned side view along line AA of figure 2. Figure 2 is a sectioned front view along line BB of figure 1 , Figure 3 is a sectioned view through a blade and side plates of the embodiment shown in figure 2; Figure 4 is sectioned view along line CC of figure 3; Figure 5 is a view corresponding to that of figure 3 in relation to a first alternative embodiment of the design; Figure 6 is a sectioned view along line DD of figure 5 Figure 7 is a sectioned view through a blade and side plates of a second alternative embodiment of the design; and Figure 8 is a sectioned view along line EE of figure 7. Referring now to figures 1 and 2 of the drawings, the torsional vibration damper comprises a rotary body 1 of flat cylindrical shape having an inner hub member 2 and an outer inertia member 3 The members 2,3 normally rotate in unison, for example with the end of an engine crankshaft, but torsional vibrations in the shaft tend to produce limited relative rotation of the hub member 2 with respect to the outer inertia member 3 The damping effect is achieved by damping such relative rotation In the following description it is assumed that the vibration damper is intended for damping the torsional vibrations of an engine crankshaft using engine oil as a damping fluid. It will be appreciated, however, that alternative applications involving other damping fluids are possible. The hub member 2 has a central bore 4 for receiving the end of a crankshaft (not shown) to which a radially inward projecting flange 5 of the hub member 2 is fixed by bolts (not shown) inserted through equi-angularly spaced holes 6 (see figure 2). The hub member 2 is penetrated by two opposed pairs of parallel radial inlet flow passages 7.8 which interconnect an oil reservoir (not shown) with a damping arrangement that is described below. Engine oil is supplied under pressure through the centre of the crankshaft to the oil reservoir m the central bore 4 of the hub member 2. Each pair of radial inlet flow passages 7, 8 is connected to a cavity 9 formed in the outer periphery of the hub member 2. Each cavity 9 is substantially rectangular in section and has a planar base wall 10 in which there is a recess that houses an oil seal 10a. The outer inertia member 3 is provided with two diametrically opposed radially inward projecting blades 1 1 that are each received in a corresponding hub member cavity 9. Each blade 1 1 is secured between annular side plates 12 (not shown in figure 2 for clarity) that are fixed to opposite sides of the outer member 3 by equi- angularly spaced bolts 13. The blades 1 1 are each fixed to the side plates 12 by means of four parallel bolts 14, two on each side, each of which is received in a threaded blind bore in the blade 1 1. The side plates 12 overlap the hub member 2 and oil seals 15 are provided at the contact surfaces. The blades 1 1 are separated from the cavity walls by axial gaps defining variable volume chambers 16, 16a to the left and right respectively of each blade 1 1 as shown in figure 2. Each blade 1 1 has a planar radially inner surface 17 that is almost in contact with the planar base wall 10 of the respective cavity 9, a small clearance being provided. Referring now to figures 3 and 4, the blade 1 1 is shown fixed between the two annular side plates 12 by bolts (not shown for clarity) fitted in threaded blind bores 14a. A transverse constricted flow passage 18 traverses the blade 1 1 in a direction substantially perpendicular to the axis of rotation of the damper, thereby providing communication between the variable volume chambers 16 on each side of the blade 1 1. A constriction 19 is provided in the central portion of the How passage 18 in order to restrict the flow of oil therethrough. Cooling conduits 20, 20a are provided on each side of the blade 1 1 , each comprising a first portion 21 extending parallel and closely adjacent to one half of the constricted flow passage 18 and a second portion 22 that extends at right angles to the first portion 21 from the alongside the constriction 1 to the respective side plate 12. The first portion 21 of each cooling conduit 20. 20a extends alongside different halves of the constricted flow passage 1 thereby providing a measure of cooling along the entire length of the flow passage 18. Ends of the cooling conduits 20. 20a adjacent the side plates 12 each have a non-return valve 23, 23a and communicate with an exit boic 24. 24a in the side plates 1 that permits oil to egress to the engine sump (not shown) via a jet 25, 25a to pei it the controlled escape of oil The diametrically opposed pair of chamber sets defined by the blades 1 1 and cavities 9 constitute pumping chambers. The pumping chambers form part ol a pumping mechanism in which the blade 1 1 can be regarded as a double-acting piston sweeping a cylinder defined by the cavity The variable volume chambers 16, 16a form part of the cylinder at opposite ends of the cylinder Damping oil flows into the chambers 16.16a via the radial inlet passages 7,8 which each have simple non-return valves 27. 28 comprising a ball 29 resting on a valve seat 30 formed in the radial inlet passage 7 or 8 In operation torsional vibration of the crankshaft causes slight rotation of the hub member 2 relative to the outei inertia member 3 This movement is slight enough to permit the planar surface 17 of the blade 1 1 to move relative to the base wall 10 of the cavity 9 without interference. If the hub member 2 rotates clockwise relative the stationary outer mernbei 3 then the leading chamber 16 of each variable volume chamber pair is reduced in volume and the trailing chamber 16a is correspondingly increased in volume This causes a pumping action to ensue in which damping oil is drawn up the radial inlet passage 8 into the trailing chamber 16a through the nonreturn valve 28 The corresponding non-ieturn valve 27 in the othei radial inlet passage 7 prevents the pressurised oil in the leading chambei 16 from passing out through the radial inlet passage 7 and it is therefore forced to travel across the blade 1 1 through the transverse constricted flow passage 18 across to the other variable volume chamber 16a to fill the increased volume The transverse constπction 19 in the flow passage 18 minimises the flow through the blade 1 1 and thereby provides the damping effect, the turbulence in the damping oil occurring across the blade 1 1 In addition to oil being forced through the blade 1 1 between the v ariable volume chambers 16, 16a a small volume of oil is torced thiough the cooling conduit 20 thereby maintaining the temperature of the blade 1 1 around the constricted flow passage 18 at a relatively stable level t he oil is forced out through the non-ieturn valve 23 to the exit bore 24 in the side plate 12 where it egresses through the jet 25 and back to the engine sump. The non-return valve 23a in the other cooling conduit 20a prevents the drawing in of air during the suction that occurs when the variable volume chamber 16a is increased in volume. If the hub member 2 rotates anti-clockwise relative to the outer member 3. the chambers 16 will increase in volume whereas the chambers 16a decrease in volume. Damping oil is thus drawn up radial inlet passage 7 into chamber 16 and passes through transverse constricted flow passage 18 in the blade 1 1 in a direction opposite to that described above. Moreover, oil is forced through the opposite cooling conduit 20a and out through the exit bore 24a in other side plate 12. The majority of the oil in the variable volume chambers 16. 16a is transferred through the blade 1 1 during operation, with only a relatively small volume leaving the chambers 16, 16a via the cooling conduits 20,20a. There is therefore only a requirement for a small replacement volume to be drawn up the radial inlet passage 7,8 into the variable volume pumping chamber 16,16a during each stroke. The low volume flow rate enables the radial inlet passages 7,8 and the non-return valves 27,28 to be made compact and simple thereby reducing the manufacturing cost, future maintenance or repair expenditure and leaving space for other features to be incorporated into the damper. In particular since the flow rate is so low non-return valves without return springs may be used. It will be understood that the oil that passes through the cooling conduits 20. 20a may also provide a modicum of damping and it is the cyclical through flow of the oil around the cooling conduits 20. 20a, the chambers 16, 16a, the transverse passage 18 and the radial inlet passages 7. 8 that disposes the heat generated in the damping process. Since the relative movement between the blades 1 1 and the cavities 9 is small it is possible to design the radially inner surface 17 of each blade 1 1 and the bottom wall 10 of each cavity 9 with planar surfaces separated by a very small clearance. This design provides for simple and cheap manufacture of the blade 1 1 and cavity 9 in comparison to conventional dampers which generally have corresponding arcuate surfaces. The cavities may be formed simply by milling a fiat bottomed slot into the hub and then milling the recess in which the oil seal 10a is seated. In a first alternative configuration shown in figures 5 and 6, the cooling conduits are fitted with an inlet orifice 31 and pressure controlled non-return exhaust valves 32 to ensure that the exhaust valves are not exposed to a potentially damaging the maximum damper pressure. A second alternative embodiment of the present invention is shown in figures 7 and 8. The blade 1 1 ' has a flow passage 18' that comprises two offset parallel conduits 40 interconnected by a perpendicular bore 41, thereby defining a roughly z- shaped flow passage. Each offset conduit has an inlet/outlet damping jet 42. One end of the perpendicular bore 41 is closed whereas the other extends through the blade 1 1 ' and meets with an exit bore 43 in the side plate 12'. An exhaust jet 44 is fitted in the exit bore 43. The blade 1 1 ' has two parallel spaced through bores 45 that extend below the flow passage 18' and parallel to the perpendicular bore 41. Bolts (not shown) are received in the through bores 45 to secure the blade 1 1 " to the side plates 12'. In use oil passes across the blade I T through the flow passage 18 " and provides improved damping particularly in view of the convoluted path. Excess oil will pass along the perpendicular bore 41 and out though the exhaust jet 44. Since the pressure in the flow passage 18' between the damping jets 42 is always higher than atmosphere a non-return exhaust valve is not required in the exit bore 43. It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in the appended claims. For example, the seals 10a are optional since the clearance between the blade 1 1 and the base wall 10 of the cavity 9 may be employed to transfer oil between the chambers 16. 16a. The present invention may be used in conjunction with a tuned spring damper such as that described in our UK patent number GB2261716. our pending international patent application WO 95/23300. or the gas spring tuned damper described in GB 4014673.

Claims: CLAIMS 1 A torsional vibration damper comprising an annular driven member, an annular inertia member coaxial with said driven member and capable of limited rotational movement relative thereto, the driven and inertia members having at least one set of variable volume chambers formed by a cavity in one member receiving a projecting element from the other member and the chambers being arranged such that relative movement of said driven and inertia members in a first direction decreases the volume of one of said chambers and increases the volume of the other, relative movement in the opposite direction causing a reverse variation in the volume of the chambers, the variable volume chambers being connected, in use. to a source of fluid, characterised in that a surface of the projecting element and an adjacent surface of the cavity are each substantially planar 2 A torsional vibration damper according to claim 1 , wherein the planar surface of the cavity has a recess in which a seal is provided 3 A torsional vibration damper according to claim 1 oi 2, in which the cavity is provided in the driven member and the projecting element is provided on the inertia member 4 A torsional vibration damper according to any one of claims 1 to 3 wherein the projecting element has a through conduit to permit the passage of fluid between the variable volume chambers on each side of the projecting element 5 A torsional vibration dampei according to claim 4 wherein the conduit is a rectilinear through bore with a constriction 6. A torsional vibration damper according to claim 4, wherein the conduit is a convoluted passage. 7. A torsional vibration damper according to claim 6, wherein the conduit comprises offset parallel bores interconnected by a substantially perpendicular bore. 8. A torsional vibration damper according to claim 6 or 7, wherein an exhaust conduit is connected to the though conduit and acts to exhaust excess fluid to atmosphere. 9. A torsional vibration damper according to claim 8. when dependent on claim 7, wherein the perpendicular bore has an extended portion to form the exhaust conduit. 10. A torsional vibration damper according to any preceding claim, wherein there are two sets of variable volume chambers at diametrically opposed locations. 11. A torsional vibration damper according to any preceding claim, wherein there is provided at least one radial conduit in the driven member for delivering damping fluid to each of the variable volume chambers, said radial conduit having a one-way valve. 12. A torsional vibration damper according to any preceding claim, wherein the projecting element has at least one cooling conduit that passes adjacent at least part of the transverse conduit. 13. A torsional vibration damper according to claim 12, wherein there are two cooling conduits, one on each side of the transverse conduit and each having a substantially right angle bend, a first portion of each conduit passing adjacent the transverse conduit and a second portion directed away from the conduit to an outlet. 14. A torsional vibration damper according to claim 13, wherein the outlet of the cooling conduit is fitted with a non-return valve. 15. A torsional vibration damper according to claim 12. 13 or 14 , wherein an inlet of the or each cooling chamber is fitted with an orifice. 16. A torsional vibration damper substantially as hereinbefore described with reference to figures 1 to 4, 5 and 6. and 7 and 8 of the accompanying drawings.

Inventors: VOLLETT ERIC MALCOLM, VOLLETT, ERIC, MALCOLM
Applicants: HOLSET ENGINEERING CO, VOLLETT ERIC MALCOLM, HOLSET ENGINEERING CO. LTD., VOLLETT, ERIC, MALCOLM
Application year: 1997
Main classification: F16F15
IPC codes: F16F15