ELASTOMERIC MOUNTING

Abstract: An elastomeric mounting (40) suitable for providing a low frequency suspension for a road vehicle cab comprises an annular elastomeric diaphragm (46) shaped to deform by both bending and shear over a normal working range to accommodate relative longitudinal movement between two members (41,42) between which the diaphragm is located. A fluid chamber (66) is defined by an annular space between two tubular rigid members (41,42) and bounded axially by said elastomeric diaphragm (46) and an annular seal (65). Said fluid chamber (66) contains fluid damping means, preferably in the form of orifices provided within a buffer means (54) which restrains relative radial movement of the rigid members (41,42).

Description: This invention relates to an elastomeric mounting and in particular, though not exclusively, to an elastomeric mounting suitable for use in providing a low frequency suspension for a vehicle cab. A vehicle cab suspension, especially a road vehicle cab suspension, usually is required, for operator comfort, to exhibit low frequency and low stiffness characteristics over a wide range of dynamic deflections under normal cab loading conditions. Elastomeric material commonly is used in seeking to meet this requirement and it is known to provide a vehicle cab suspension comprising a pair of tubular metal members arranged co-axially one within the other and interconnected by an annular element of elastomeric material bonded to the tubular members. The annular elastomeric element is orientated such that the normal load of the cab acts in a direction parallel with the longitudinal axis of the tubular members and in consequence vertical movement of the cab relative to the vehicle body is accommodated by shear deflection of the elastomeric material. Whilst the resulting suspension can provide a satisfactory performance it suffers the disadvantage of needing to be of large dimensions in order to allow for the magnitude of shear deflection necessary to accommodate the desired large range of dynamic deflection under normal cab loading conditions. The problem of achieving an efficient use of space is addressed by GB-A-1583963 which describes a particular type of hollow liquid spring comprising a body of resilient rubber and having built-in damping. One of the constructions disclosed by GB-A-1583963 is further described by DE-U-7709267. That construction may be regarded as an elastomeric mounting comprising a pair of rigid members arranged to define an annular space therebetween, an annular first element of elastomeric material located in said annular space and arranged to extend between and serve to interconnect said rigid members, the annular element of elastomeric material being of a shape which deforms by both shear and bending movements in the event of relative longitudinal movement of the rigid members, a second element of elastomeric material in the form of an annular seal spaced from said annular first element and arranged to extend between and be sealed to said rigid members, and integral damping means arranged within said chamber to provide a damping effect additional to that provided by the annular element of elastomeric material during relative longitudinal movement of the rigid members, said damping means being comprised by a fluid-filled annular chamber defined at least in part by the inner and outer rigid members and by said first and second elements of elastomeric material and a restrictor for movement through the fluid during relative longitudinal movement of the rigid members thereby to create a damping effect, said restrictor being comprised by annular elastomeric buffer means within said chamber, secured to one of the confronting surfaces of the inner and outer rigid members, for restricting relative radial movement of the rigid members. In accordance with the present invention it is provided that said buffer means is arranged to slide in fluid sealing engagement over the other of said confronting surfaces of the inner and outer rigid members, and is provided with at least one series of circumferentially spaced orifices for restrictive flow of fluid therethrough. The annular element of elastomeric material preferably is shaped and arranged such that when load is applied in said longitudinal direction the annular elastomeric element deforms from an initially unstressed condition by buckling and shear movement to exhibit a regressive stiffness characteristic. The buffer means may be secured to one of the rigid members by bonding or as a friction fit. The buffer means may be in the form of an annular body of elastomeric material which incorporates an annular reinforcement layer of substantially inextensible material thereby to permit the bush to be secured to a rigid member as a friction fit by virtue of compression of elastomeric material of the bush lying between the reinforcement layer and said rigid member. Preferably the annular chamber is filled with a substantially incompressible fluid. An orifice may be defined by a through-bore in the body of the buffer means or it may be defined by one or more spaces between a periphery of the annular buffer means and one of the confronting surfaces of the inner and outer rigid members relative to which the buffer means moves during the aforementioned relative longitudinal movement. The annular element of elastomeric material preferably comprises between its inner and outer peripheries an annular section the thickness of which, as considered in the longitudinal direction, is less than the thickness of the element, in said direction, at at least one of the inner and outer peripheral regions. Preferably, as considered in a longitudinal cross-sectional plane, the minimum thickness of the annular element in said longitudinal direction is less than one half and more preferably less than or equal to one third of the thickness of the element as considered in a direction transverse of the longitudinal direction. It is further preferred that the surfaces of the rigid members to which the annular element of elastomeric material is secured, e g by bonding, be offset in the longitudinal direction when the mounting is in an unstressed condition. Particularly suitable shapes for the annular element of elastomeric material for providing a regressive stiffness characteristic include shapes in which one of the longitudinally facing surfaces is of a substantially C-shape in cross-section. The above and other features of the invention will now be described, by way of example, with reference to the accompanying drawings in which:- Figure 1 is a longitudinal sectional view of an integrally damped elastomeric mounting of the present invention when in an unstressed condition; Figure 2 is a longitudinal sectional view of the mounting of Figure 1 shown in situ with part of a vehicle cab and body structure and in a fully deflected condition, and Figure 3 is an end view in the direction of arrow III of Figure 2. In the embodiment of the present invention shown in Figures 1 to 3 an elastomeric mounting 40 for a vehicle cab suspension comprises an inner cylindrical metal tube 41 and an outer metal tube 42 which surrounds and is spaced from the inner tube over part of the length of the inner tube. The outer tube 42 is of a two-part spun or pressed metal construction. One part 42a comprises a cylindrical shaped portion 43 from an upper end of which, as viewed in Figure 1, extends a radially outwardly directed flange 44. The other part 42b has a cylindrical portion 45a for surrounding a lower end of the cylindrical portion 43 of the first part 42a and a frustoconical shaped abutment flange 45b extends radially inwardly and downwardly from a lower end of the portion 45a. The tubes 41,42 are interconnected by an annular load-bearing rubber diaphragm 46 typically formed of non-reinforced natural rubber. A radially inner surface 47 of the diaphragm is bonded to the inner tube 41 and a radially outer region 48 is bonded to the flange 44 and neighbouring upper end of the cylindrical portion 43 of the outer tube 42. The thickness of the diaphragm in the longitudinal (vertical) direction of Figure 1 at the point of minimum thickness of the diaphragm in said direction is substantially equal to one third of the radial thickness of the diaphragm as considered between the confronting surfaces of the tubes 41,42. The diaphragm 46 is of a shape which results in it experiencing both buckling and shear deformation when subject to an applied load which causes the inner tube to move downwardly relative to the outer tube, i e from the relative orientation of Figure 1 to that of Figure 2. Associated with the buckling and shear deformation is a regressive load-deflection (i e stiffness) characteristic. That is, under increasing applied load from a condition of zero applied load the stiffness decreases, but later increases as the diaphragm and its integral buffer 53 (described in more detail below) make contact with a top overload plate 70 (see Figure 2). To assist in achieving a suitable buckling and shear deformation characteristic the diaphragm 46 is generally C-shaped in half cross-section as viewed in Figures 1 and 2. The downwardly facing surface 49 of the diaphragm is of a concave shape in cross-section and a central portion 50 of the surface 49 lies vertically above the outwardly extending flange 44 at least in the unstressed condition shown in Figure 1. It is preferred also, as shown in Figure 1, that the bonded radially inner surface 47 does not extend below the level of the outwardly extending flange 44, the tube surfaces to which the diaphragm is bonded thus being offset in the vertical, longitudinal direction when in an unloaded condition as shown in Figure 1. Although the diaphragm is of generally C-shape in half cross-section it is not essential that its upper and lower surfaces each be of a C-shape. The radially outer region 52 of the upper surface 51 of the diaphragm 46 is formed integrally with an enlarged longitudinally thickened buffer portion 53 for a purpose which will be described in more detail below. To provide a suitable radial compliance characteristic a buffer bush 54 is mounted on the inner tube 41. The bush 54 comprises an inner metal support ring 55 and an outer reinforcing ring 56. An annular element 57 of natural rubber is bonded to the rings. Radially outwards of the ring 56 is an annular natural rubber band 58 bonded to the ring 56 and formed in its upper surface 59 with a series of four uniformly circumferentially spaced pockets 60. In the base of each pocket 60 there is formed a through bore the longitudinal axis of which is parallel with the longitudinal axes of the inner and outer rigid members. A rigid disc 62 having a central orifice 63 is provided in each through bore. The radially outermost region of the band 58 defines an annular lip seal 64 for fluid-tight sliding movement over the inner surface of cylindrical portion 43 of the outer tube 42 during normal use of the mounting (i e in the absence of high radial load). A thin flexible reinforced diaphragm seal 65 is formed integrally with the annular element 57 of the buffer bush 54 and extends between the rigid members to assist in providing a fluid-tight seal therebetween. A radially outer part of the diaphragm seal 65 is located in and secured by compression on assembly to an annular crevice defined by a lower end surface of the portion 45a of the outer tube 42a and an inwardly facing surface of the outer tube part 42b. A radially inner part of the diaphragm seal extends from a thin cylindrical downwardly extending portion of the element 57, the downwardly extending portion being bonded to the inner support ring 55. The upper end of the inner support ring is bonded to the load bearing diaphragm 46. The outer rigid member 42, inner rigid member 41 supporting the inner ring 55, annular load bearing diaphragm 46 and diaphragm seal 65 define an annular chamber 66 which is wholly fitted with oil or other incompressible fluid. Figure 2 shows the elastomeric mounting 40 of Figure 1 secured to vehicle body structure plates 70,71 by means of a bolt 72 extending through the inner tube 51 and to a vehicle cab structure 73 by means of bolts (not shown) extending through the outer flange 44. An annular buffer ring 74 is attached to an upper surface of the lower body structure plate 71 to confront the frusto-conical shaped abutment flange 45 and thereby provide resistance to rebound movement of the mounting. The mounting 40 is designed in relation to the intended applied load such that under normal static load conditions the lip seal 64 lies substantially mid-way between the ends of the inner surface of the outer member 42 over which it slides in sealing contact (in the absence of high radial load). When the mounting is subject to dynamic conditions causing relative movement of the inner and outer members the incompressible fluid will be urged to flow through the orifices 63 and thereby provide a damping effect additional to the resiliency of the load bearing diaphragm 46. High vertical deflection of the inner tube downwards relative to the outer tube is resisted by increasing stiffness of the annular load bearing diaphragm and subsequently the effect of the bump buffer 53. The relative movement of the inner and outer tubes is damped by the effect of fluid flow through the orifice 63, hysteretic damping of the diaphragm 46 and friction between the seal 64 and outer tube 42. Any rebound movement arising in spite of the damping effect is resisted by the increasing stiffness of the load bearing diaphragm 46 and the effect of the buffer ring 74 as shown in the fully deflected rebound condition of Figure 2. The load bearing diaphragm need not have the longitudinal cross-sectional shape shown in Figure 1; it may be of an alternative cross-sectional shape. In general, for a more regressive load-deflection curve the bending deformation experienced by the diaphragm is more significant, and the degree of bending deformation is a function of the ratio of the thickness of the diaphragm in the longitudinal direction and the thickness in a transverse direction.

Claims: An elastomeric mounting (40) comprising a pair of rigid members (41,42) arranged to define an annular space therebetween, an annular first element of elastomeric material (46) located in said annular space and arranged to extend between and serve to interconnect said rigid members (41,42), the annular element of elastomeric material (46) being of a shape which deforms by both shear and bending movements in the event of relative longitudinal movement of the rigid members, a second element of elastomeric material (65) in the form of an annular seal spaced from said annular first element (46) and arranged to extend between and be sealed to said rigid members (41,42), integral damping means (63) arranged within said chamber to provide a damping effect additional to that provided by the annular element of elastomeric material (46) during relative longitudinal movement of the rigid members, said damping means being comprised by a fluid-filled annular chamber (66) defined at least in part by the inner and outer rigid members (41,42) and by said first (46) and second (65) elements of elastomeric material and a restrictor (62) for movement through the fluid during relative longitudinal movement of the rigid members (41,42) thereby to create a damping effect, said restrictor (62) being comprised by annular elastomeric buffer means (54) within said chamber and secured to one of the confronting surfaces of the inner and outer rigid members (41,42) for restricting relative radial movement of the rigid members (41,42), characterised in that said buffer means (54) is arranged to slide in fluid sealing engagement over the other of said confronting surfaces of the inner and outer rigid members (41,42), and is provided with at least one series of circumferentially spaced orifices (63) for restrictive flow of fluid therethrough. An elastomeric mounting according to claim 1 characterised in that said orifices (63) for restricted flow of fluid therethrough are defined by spaces between a periphery of the annular elastomeric buffer means (54) and one of said confronting surfaces of the inner and outer rigid members (41,42). An elastomeric mounting according to claim 1 or claim 2 characterised in that the elastomeric buffer means (54) is comprised at least in part by elastomeric material of or integral with said annular element (46) of elastomeric material. An elastomeric mounting according to any one of the preceding claims characterised in that the annular element (46) of elastomeric material is shaped to deform from an initially unstressed condition in response to applied load in said longitudinal direction by a combination of buckling and shear movements to exhibit a regressive stiffness characteristic. An elastomeric mounting according to any one of the preceding claims characterised in that annular first element (46) of elastomeric material is secured to surfaces (47,48) of the rigid members which are offset in the longitudinal direction when the mounting is in an unstressed condition. An elastomeric mounting according to any one of the preceding claims characterised in that one of the longitudinally facing surfaces (49,51) of the annular first element is of a substantially C-shape in crosssection. An elastomeric mounting according to any one of the preceding claims characterised in that as considered in a longitudinal cross-sectional plane the minimum thickness of the annular first element (46) in said longitudinal direction is less than one half of the thickness of the element as considered in a direction transverse of the longitudinal direction. An elastomeric mounting according to any one of the preceding claims characterised in that annular first element (46) of elastomeric material comprises between its inner and outer peripheries an annular section the thickness of which, as considered in said longitudinal direction, is less than the thickness of the element, in said direction, at at least one of the inner and outer peripheral regions. An elastomeric mounting according to any one of the preceding claims characterised in that orifices of a series (63) are comprised by through-bores provided in the body of the buffer means (54). An elastomeric mounting according to claim 9 characterised in that a rigid disc (62) having a central orifice (6,63) is provided in said through-bore.

Inventors: COLFORD, TERENCE HARRY
Applicants: DUNLOP LIMITED
Application year: 1987
Main classification: F16F13
IPC codes: F16F13