FLUID-DAMPED RESILIENT BUSH

Abstract: A fluid-damped resilient bush, e.g. for use in a vehicle suspension comprises an outer sleeve (11) and an intermediate sleeve (12) between which a rubber bush (13) is moulded as a one-piece moulding. Cavities (36, 38) are formed between the intermediate sleeve and an inner member (10), which is mounted within the one-piece moulding and sealed to the one-piece moulding by axially separate annular areas of the moulding which engage but are not bonded to the inner member. The cavities communicate with one another and are filled with damping fluid, the arrangement being such that displacement of the outer sleeve relative to the inner member causes displacement of fluid between the cavities.

Description: This invention relates to a fluid-damped resilient bush, such as may be used as a component in a vehicle suspension. It is known to manufacture a fluid-damped bush in which an inner rigid member and an outer rigid member have a resilient insert bonded to both members, the insert containing cavities which intercommunicate and are filled with liquid, the arrangement being such that relative displacement of the inner and outer members reduces the volume of one cavity and increases the volume of the other cavity with a resulting flow of liquid between the cavities, usually through a restricted passage, and thereby damping the relative movement of the two members. It is known also from EP-A-9120 to manufacture a fluid-damped bush comprising an outer sleeve, an inner member and a resilient member located between and bonded to one of the outer sleeve and inner member with provision for at least two cavities arranged to contain damping fluid and to communicate with one another, said resilient member being bonded also to an intermediate sleeve located between the outer sleeve and the inner member. The present invention provides a fluid-damped resilient bush which can be economically manufactured by arranging that the resilient member is moulded between and bonded to each of an outer sleeve and an intermediate sleeve as a one-piece moulding, that the outer sleeve is surrounded at least partially by and bonded to a moulded rubber outer covering portion, and that an inner member is mounted within the one-piece moulding and sealed thereto by axially separate annular areas of the one-piece moulding engaging but not bonded to the inner member, cavities being formed between the one-piece moulding and the inner member. Embodiments of the invention will now be described with reference to the accompanying drawings in which:- Figure 1 is a plan view of a resilient bush in accordance with the invention; Figure 2 is a section on the line II-II of Figure 1; Figure 3 is a section on the line III-III of Figure 1; Figure 4 is a section on the line IV-IV of Figure 3; Figure 5 is a plan view of an alternative resilient bush in accordance with the invention; Figure 6 is a section on the line VI-VI of Figure 5; Figures 7, 8 and 9 are sections corresponding to Figure 2 showing alternative embodiments of the invention; Figure 10 is a section corresponding to Figure 3 (but viewed in the opposite direction) showing a further alternative embodiment of the invention; Figure 11 is an axial section through a one-piece moulding comprising an outer sleeve, intermediate sleeve and resilient rubber member of a bush in accordance with another embodiment of the invention; Figure 12 is a section on the line XII-XII of Figure 11, showing the bush assembly including an inner member; Figure 13 is a section corresponding to Figure 11, showing the bush assembly including an inner member, and Figure 14 is an axial section through a further alternative resilient bush in accordance with the invention. The resilient bush shown in Figures 1 to 4 comprises an inner rigid member 10, an outer metal sleeve 11, and an intermediate sleeve 12. Between the outer sleeve and the intermediate sleeve a rubber resilient member 13 is bonded to the intermediate sleeve and outer sleeve so as to cushion relative movement between these components and thus between the outer sleeve and the inner member 10 to which the intermediate sleeve 12 is firmly secured. The axis of the bush is indicated by the line A of Figure 2, and the inner member 10 contains a socket 15 of complex shape which is designed to receive a complementarily shaped shaft end to form part of the sub-frame mounting system of a motor car suspension, the bush being mounted on the vehicle body by a suitable clamp engaging the outer sleeve 11 via a moulded rubber outer covering portion 17 bonded to the outer sleeve. In order to compensate for deflection of the inner member under static load when installed in the vehicle, the centre lines A, A′ of the inner member in the appropriate planes (see Figures 1 and 3) are displaced slightly (in the unstressed state of the bush) from the central plane of the outer sleeve 11 (in which the section II-II is taken). Thus under normal static load the inner member is centralised within the outer sleeve and the resilient member 13 is pre-stressed. The resilient member is of rubber (which term is used herein to embrace any suitable elastomeric material) and is conveniently moulded in one operation to provide both the resilient member 13 and the outer covering 17, both suitably bonded to the outer and the intermediate metal sleeves and thus forming a unit for assembly with the inner member in a further operation. In order to achieve required stiffnesses in different planes, the outer sleeve 11 is shaped as indicated by dotted lines in Figure 1, and in Figure 4, to provide selected thicknesses of rubber in different areas of the space thus formed between the intermediate and outer sleeves. Additionally, pockets 20, 21; 22, 23 and axial holes 25, 26, 27, 28 extending throughout the resilient member, (see Figure 4) are provided for further modification of its stiffness in local areas. The intermediate sleeve 12 is provided with a thin lining layer 30 of rubber on its inner surface for sealing engagement with unbroken annular surfaces 32, 34 of the inner member 10, and sealed cavities 36, 38 are thus formed between the intermediate sleeve and recessed parts of the inner member 10. Openings 40, 42 in the intermediate sleeve 12 communicate with the respective cavities 36, 38 and are sealed by the adjacent portions of the resilient member 13 which cover the areas of the openings and in the unstressed condition of the bush are substantially coplanar with the openings. The two cavities 36, 38 are filled with a suitable liquid and intercommunication between the cavities is established by means of a groove 45 in the outer surface of the inner member 10. As previously described, the outer sleeve, resilient member and intermediate sleeve are manufactured as a single bonded unit, and assembly may be effected by immersing this unit in liquid and inserting the inner member 10. The sealing surfaces 32, 34 of the inner member are tapered to provide good sealing engagement with the thin rubber layer 30 (which may be internally ribbed to improve the seal) and assembly is completed by pressing the inner member 10 into the intermediate sleeve 12 until the adjacent end 46 of the sleeve engages a flange 47 on the inner member 10, following which the other end 48 of the sleeve is crimped into a groove 49 in the inner member 10 to provide a permanently secured and sealed assembly. The end 50 of the member 10 may be made sufficiently long to provide an effective primary seal for a liquid-filling stage, following which the assembly may be removed from the liquid for the final pressing and crimping operation. By this means a pre-pressurisation of the liquid may be achieved. When relative movement of the inner member 10 and outer sleeve 11 takes place, particularly transverse deflection in a direction along the line B of Figure 4, the rubber in the portion of the resilient member adjacent one of the openings is caused to bulge towards or into its respective cavity and thus to displace fluid from the cavity, through the passage formed by the groove 45, into the other cavity which will then be enlarged by outward bulging (relative to the cavity) of its adjacent portion of the resilient member. The cross-sectional area of the groove 45 is selected to provide optimum damping at a required frequency of relative movement of the inner member and the outer sleeve. The embodiment illustrated in Figures 5 and 6 is similar in most respects to that described with reference to Figures 1 - 4, and will not be described in detail. The modified feature consists of the provision of gaps 60, 61 between radially outer and inner portions of the resilient member in the regions adjacent the cavities, with the effect of providing lost-motion before the damping effect of the liquid-filled cavities and their connecting passage is brought into action. Thus for relative movement at low amplitudes (usually associated with higher frequencies) there is low damping and consequently reduced noise transmission, whilst at higher amplitudes (usually at lower frequencies) the lost-motion is taken up and the liquid-filled cavities and connecting groove operate to provide damping. Figure 7 shows an alternative to the groove 45 : instead, a drilling 70 in the inner member connects the two cavities. Figure 8 shows an alternative position for a connecting groove 80 formed as a notch in a shoulder region of the inner member. Figure 9 shows an alternative means for securing together the inner member and the intermediate sleeve, using a stop ring 90 which is a press-fit on the inner member. Figure 10 shows an alternative arrangement in which the liquid in the cavities may be pre-pressurised on assembly into a suitable clamp on the vehicle. In this arrangement an opening 100 is formed in the outer sleeve, aligned with an opening in the intermediate sleeve, and a protrusion 101 of the resilient member stands proud of the opening 100 so that when a constricting clamp is fixed around the assembly the protrusion 101 is forced inwardly to pre-pressurise the liquid in the cavities. The liquid-damped resilient bush shown in Figures 11-13 comprises an inner rigid member 120 (not shown in Figure 11), an outer metal sleeve 121 and an intermediate sleeve 122. Between the outer sleeve and the intermediate sleeve a rubber resilient member 123 is bonded to the intermediate sleeve and outer sleeve so as to cushion relative movement between these components and thus between the outer sleeve and the inner member 120 to which the intermediate sleeve 122 is firmly secured. The rubber member 123, the outer sleeve 121 and the intermediate sleeve 122 are made as a one-piece moulding. The rubber member 123 covers the whole of the inner surfaces of the outer sleeve 121 and the intermediate sleeve 122, so that when the tapered inner member 120 is inserted (see Figure 13) annular ribbed rubber sealing areas 126, 127 and 128 are presented to the inner member. Recesses 130,132 moulded into the rubber member 123 provide cavities 134,136 which are filled with a suitable liquid on assembly and are permanently sealed, apart from a restricted connecting passageway which may be formed, for example, by a grooved or rebated portion of the inner member groove (not shown) extending between, and opening into, the two cavities. The inner member is press-fitted into the intermediate sleeve 122, and is then retained in position by the bending-over of tabs 141-145 on the intermediate sleeve into engagement with corresponding notches 150,151 at the adjacent end of the inner member. In the arrangement of Figures 11 to 13, the cavities extend deeply into the rubber member 123, the intermediate sleeve having wide 'windows' to enable large cavities 134,136 to be provided. 'Bump stops' 155,157 projecting into the cavities are formed in the rubber moulding, and a rubber covering 158 is provided around the outer surface of the outer sleeve 121 during the moulding operation. Figure 14 shows a variation in the design of the bush of Figures 11 - 13 : lower axial and radial stiffness is achieved by shaping the end walls 160, 162 of the resilient rubber member 164 to an annular corrugated form so as to permit easier deflection. Also, the bump stops are omitted from the design of Figure 14. The various forms of liquid-damped bushes as described above have the advantage that they can be economically manufactured, the process entailing only a single rubber/metal moulding operation followed by a simple assembly operation, providing an efficient permanently liquid-filled bush, at low cost.

Claims: A fluid-damped resilient bush comprising an outer sleeve (11,121), an inner member (10,120) and a resilient member (13,123) located between and bonded to one of the outer sleeve and the inner member with provision for at least two cavities (36,38; 134,136) arranged to contain damping fluid and to communicate with one another, said resilient member (13,123) being bonded also to an intermediate sleeve (12,122) located between the outer sleeve (11,121) and the inner member (10,120), characterised in that the outer sleeve (11,121) is at least partially surrounded by and bonded to a moulded rubber outer covering portion (17) and is bonded also to said resilient member (13,123), the resilient member (13,123) being moulded between and bonded to each of the outer sleeve and an intermediate sleeve (12,122) as a one-piece moulding (11,12,13; 111,122,123) and the inner member being mounted within the one-piece moulding and sealed thereto by axially separate annular areas (30,126,127) of the one-piece moulding engaging but not bonded to the inner member, the cavities being formed between the one-piece moulding and the inner member. A bush according to claim 1 wherein the intermediate sleeve has a rubber lining (30). A bush according to claim 2 characterised in that the rubber lining (30) is internally ribbed. A bush according to any one of claims 1 to 3 characterised in that the inner member has tapered sealing surfaces (32,34) for engagement with the intermediate sleeve. A bush according to any one of claims 1 to 4 characterised in that a groove (45) is formed in the inner member to provide communication between the cavities. A bush according to claim 5 characterised in that the groove is formed as a notch (80) in a shoulder region of the inner member. A bush according to any one of claims 1 to 4 characterised in that a drilling (70) is provided in the inner member to connect the two cavities. A bush according to any one of claims 1 to 7 characterised in that the intermediate sleeve has openings (40,42) communicating with said cavities and said openings are sealed by the resilient member or members, whereby relative movement of the outer sleeve towards the opening of the intermediate sleeve adjacent one of the cavities causes bulging of a portion of the resilient member towards or into the said one cavity and thereby displaces fluid from the said one cavity into the other cavity. A bush according to any one of claims 1 to 8 characterised in that the inner member and the intermediate sleeve are secured together by the crimping of an end (48) of the intermediate sleeve into a groove (49) formed in the inner member. A bush according to any one of claims 1 to 8 characterised in that the inner member and the intermediate sleeve are secured together by a stop ring (90) press-fitted to the inner member. A bush according to any one of claims 1 to 10 characterised in that the intermediate sleeve comprises tabs (141 - 145) at one end which are bent-over to engage the adjacent end of the inner member. A bush according to any one of claims 1 to 11 characterised in that as considered in cross-section in a plane perpendicular to a longitudinal axis of the bush one of said axially spaced sealing surfaces (32,34) is larger in cross-section than the other. A bush according to any one of claims 1 to 12 characterised in that gaps (60,61) are provided between radially outer and inner portions of the resilient member in the region adjacent the cavities, to provide lost-motion before the damping effect of the connected liquid-filled cavities is brought into action. A bush according to any one of claims 1 to 13 characterised in that an opening (100) is formed in the outer sleeve, aligned with an opening in the intermediate sleeve, and a protrusion (101) of the resilient member stands proud of the opening in the outer sleeve so that the protrusion can be forced inwardly to pre-pressurise the liquid in the cavities. A bush according to any of the preceding claims characterised in that an end wall (160,162) of the resilient rubber member is of annular corrugated form so as to permit easier deflection. A bush according to any one of the preceding claims characterised in that the resilient member comprises bump stops (155,157) which project into the cavities (134,136).

Inventors: COURT, PETER THOMAS
Applicants: BTR PLC
Application year: 1988
Main classification: F16F13
IPC codes: F16F13