Rubber radial bearing

Details Rubber radial bearing Rubber radial bearing

1999-08-02

2001-11-20

Oberleitner, Robert J. (Department: 3613)

Spring devices

Resilient shock or vibration absorber

Including energy absorbing means or feature

Reexamination Certificate

active

06318708

ABSTRACT:

The invention relates to a hydraulically damping sleevelike rubber bearing.
The invention accordingly relates, in particular therefore, to a hydraulically damping sleevelike rubber bearing, especially radial rubber bearing, with different spring characteristics (F
1
, F
2
) radially perpendicular to one another. The bearing consists of an inner sleevelike connecting block (
1
) and of a likewise sleevelike cage (
2
) surrounding the latter, said block and said cage, lying axially parallel one in the other, being vulcanized or otherwise embedded in a rubber spring block (
3
). At least two diametrically opposed pumping working chambers (
4
,
5
) for a working fluid, communicating with one another via at least two overflow ducts (
6
;
21
), are designed in the rubber spring block (
3
) in such a way that said working chambers are closed off in a fluid-tight manner, radially relative to the outside, by the cylindrical inner wall (
7
) of an outer sleeve (
8
), for which purpose the rubber spring block (
3
), reinforced by the cage, is pressed under radial prestress into the outer sleeve (
8
). The at least two overflow ducts have permeability behaviors and damping behaviors which are different from one another and are in each case tuned to different amplitude ranges.
Such a sleeve bearing is known from European preliminary publication EP 0 335 007 A2. It has a throttle duct of small cross section for damping of vibrations of relatively low amplitudes, particularly of the order of magnitude of ±0.1 mm in the acoustic frequency range of approximately 40 to 200 Hz, and a second overflow duct of larger cross section, which acts as a bypass duct for this throttle duct, in which a rubber lip is provided as a bypass valve. When excessively high amplitudes (>±2 mm) act on the bearing, that is to say when a pressure gradient, increased beyond the intended operating characteristic data foreseeable for the respective use of the bearing, occurs in one of the two fluid chambers, the rubber lip opens and allows damping fluid to overflow from one chamber to the other in each case, the pressure gradient at the same time being compensated, and, if appropriate, with slight damping.
The phenomena mentioned, which act with excessively high amplitudes on the bearing, are, particularly in the field of motor vehicle technology, as a rule, either stochastic shocks and impacts or low frequency vibration-like phenomena of high amplitude, occur, for example, in the motor vehicle when it travels over undulating roads of long wavelength and, as a rule, are at frequencies of below 10 Hz, that is to say at frequencies well into the subacoustic range.
So that the forces which occur during these dynamic spring loads, and which are sometimes very considerable, can be absorbed both in conformity with the appropriate function and with as much care as possible being taken of the material of the rubber spring, bearings of this type are conventionally tuned in such a way that their fundamental resonance is placed in the range between 10 and 30 Hz, that is to say in the range between the markedly subacoustic frequencies and the lowest acoustic frequencies. For this purpose, however, it is necessary, in the case of bearings of this type, to allow for the fact that, after the resonance maximum, the dynamic spring constant of the bearing scarcely decreases appreciably toward higher frequencies. However, the higher the dynamic bearing spring constant remaining after the resonance maximum, the more permeable the bearing becomes to a passage of subsequent frequencies in the acoustic range, so that disturbing acoustic vibrations, taking the form of only insufficiently damped or even virtually undamped solidborne sound, pass through from the supporting connection to the abutment connection, that is to say from the inner sleeve to the outer sleeve or, conversely, from the outer sleeve to the inner sleeve of the rubber sleeve bearing. When such sleeve springs are used in motor vehicle construction, this leads to the acoustic discomfort in the motor vehicle being impaired to an extent which cannot be ignored.
Proceeding from this state of the art, the technical problem on which the invention is based is to improve a hydraulically damping sleevelike rubber bearing of the type explained above, to the effect that, after a subacoustic damping range, that is to say a frequency range of below approximately 10 Hz and a resonance maximum in the range of 10 to 30 Hz, the sleeve spring has, in the subsequent low acoustic frequency range at least up to a range of approximately 200 Hz, a markedly reduced dynamic bearing spring constant, as compared with the state of the art, in order to suppress the transmission of solidborne sound in this lower acoustic range.
The invention achieves this object in, that a transmission of vibrations of low amplitude through the bearing is brought about not only by throttle losses in a flow of the working fluid in a throttle duct, but essentially also due to the fact that the supporting connection piece and the abutment connection piece of the sleeve bearing are acoustically uncoupled by means of an uncoupling member.
In this case, uncoupling is carried out, in a way known per se for large-volume supporting bearings, via a loose piece which makes it possible to compensate the sound pressure between the fluid chambers of such a supporting bearing, without relevant displacements in the volume of the damping fluid occurring in the throttle duct between the working chamber and compensating chamber. In this case, the loose piece is arranged in a separate subsidiary duct to the throttle duct.
In the sleeve bearing under consideration here, the flutterable loose piece serving as an uncoupling member is arranged in one of the two overflow ducts of the sleeve bearing, that is to say either in the damping duct or, preferably, in the bypass duct. In this case, “Loose piece” means, in the usual sense, an insert part which is inserted or received in a receptacle or cage loosely, that is to say without any positive connection, so as to be limited on all sides, but freely movable within this framework, and flutterable.
If the restraint for the loose piece is designed as a cage, the wall perforations of such an uncoupling cage must have such large dimensions that they allow a throttle-free passage of the solidborne sound waves of low amplitudes which are to be uncoupled in the damping fluid of the sleeve bearing.
However, since, under some circumstances, the use of cages for restraining the loose piece when the bearing is subjected to shocks may not be entirely without its problems, the loose piece inserted in the sleeve bearing of the invention is preferably mounted flutterably in undercut structures (FIG.
3
).
The material of the loose piece itself may, in principle, be selected, as desired, from materials of relatively low density, that is to say may, for example, also be a plastic part or an aluminum sheet, but, for the present purpose, is preferably an elastomeric part, in particular an elastomeric web or an elastomeric diaphragm, in order to rule out the occurrence of rattling noises or fluttering noises of the loose piece, in particular in a cage.
According to a preferred embodiment of the invention, the uncoupling member is oriented axially parallel to the longitudinal axis of the sleeve spring and extends preferably over the axial width of the rubber spring body between two end-face sealing means, preferably two cylindrical surface sealing rings of the sleeve cage of the rubber spring. This design makes it possible, if the uncoupling member has only a small overall height in the radial direction of the sleeve spring, nevertheless to provide an effective surface which is sufficiently large for acoustic uncoupling.
If a cylindrical surface seal is used on the two end faces of the sleeve spring, the throttle duct is designed preferably in the radially outer generated surfaces of the cylindrical rings. The two part throttle ducts thus designed are connected communicatingly, again with respect to the

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