Spring devices – Resilient shock or vibration absorber – Including energy absorbing means or feature
Utility Patent
1999-09-03
2001-01-02
Butler, Douglas C. (Department: 3613)
Spring devices
Resilient shock or vibration absorber
Including energy absorbing means or feature
C267S141200, C267S140120
Utility Patent
active
06168144
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulically damping elastomer bearing having an outer bearing sleeve, an elastomer element arranged therein, and a bearing core which is held by the said elastomer element and extends axially parallel or coaxially through the bearing sleeve, with chambers formed between the bearing core and the bearing sleeve and filled with fluid.
Hydraulically damping elastomer bearings are being increasingly used in vehicle construction. In the vehicle chassis area in particular, there is a demand not only for frequency-selective damping at very small vibration amplitudes but also increasingly for a greater damping of individual shocks, as occur for example when driving over potholes and transverse joints.
DE 43 07 559 A1 describes a flexible bearing bush which comprises an outer cylindrical bearing sleeve and an inner part held inside by a horizontally extending elastomer element. For the additional damping of vibrations of great amplitudes, impact absorbers which are moulded onto the elastomer element and also consist of the same material are provided. Fluid-filled chambers interconnected via channels are formed between the elastomer element and the outer bearing sleeve. In the known arrangement, between the bearing core and the moulded-on impact absorber, a cavity extends parallel to the longitudinal axis of the bearing core and is open towards the outside, so that when there are vibrations of great amplitude both the impact-absorbing distance between the bearing bush and the impact absorber and the distance formed by the cavity have to be overcome before progressive damping commences. How damping proceeds thereafter depends on the material properties of the elastomer and consequently cannot be determined exactly. What is more, dirt can get into the open cavity and adversely affect the damping characteristics by keeping the distance constant.
The present invention is based on the object of providing a hydraulically damping elastomer bearing in such a way that, for damping vibration amplitudes which go beyond a precisely definable deflection magnitude, a damping with specific progressive damping characteristics takes place.
This object is achieved by a hydraulically damping elastomer bearing between the bearing core and the inside wall of the bearing sleeve there is arranged in at least one of the chambers a substantially inflexible, hydraulically supported displacement element, which in the unloaded state is at a predetermined distance from a reference surface and between the displacement element and a component bearing the latter there is formed a displacement chamber of small height between the displacement surfaces, which chamber is in communication with one of the further chambers via at least one throttling orifice.
To be regarded as the major advantages of the elastomer bearing according to the invention are that, when there are vibrations of an amplitude which exceeds a certain magnitude, an exactly determinable progressive damping takes place, since the displacement element itself is inflexible and the damping produced by the hydraulic support of the displacement element can be set very exactly by the cross section of the throttling orifice. Depending on the configuration of the displacement element, very flat arrangements which take up only little installation space can be realized, without influencing the damping characteristics themselves.
It is regarded as an advantageous development of the present invention that the displacement element is arranged on the bearing core and the reference surface is formed on the inside wall of the bearing sleeve. In this case, depending on the design conditions and the likely directions of loading, a plurality of displacement elements may be provided, it being regarded as particularly expedient for there to be two displacement elements which lie on a common transverse axis of the bearing core and are consequently arranged diametrically.
According to a preferred embodiment, on the bearing core there is provided a hollow with a conical surface, in which a conical lateral surface of the displacement element is located, and the displacement chamber is formed between these surfaces. Such a configuration achieves the effect that the conical seating permits a self-centering of the displacement element, so that the damping function is ensured even if force is introduced eccentrically. It is also advantageous that the conical surface of the hollow and the conical lateral surface of the displacement element have different angles with respect to a plane orthogonal to the axis of symmetry, the angle of the conical surface of the hollow being greater than the angle of the conical lateral surface of the displacement element. In this way the effect is achieved that on the outer edge of the displacement chamber there is a smaller distance between the displacement element and the bearing core than towards the center of the displacement chamber, so that an annular gap acting as a throttling orifice is formed between these parts on the peripheral edge of the displacement chamber. This annular gap is increasingly reduced as the vibration amplitude takes effect, so that the damping force increases and, finally, the peripheral edge of the displacement element bears against the conical surface of the hollow.
The angle of the conical surface should, wherever possible, be <40° and is preferably about 30°. It has proven to be particularly suitable for the difference between the angles of the conical surface and the conical lateral surface to be between 1° and 5°, preferably about 2°.
To produce a further-increasing progressive damping after a first phase of the damping operation, it is advantageous to arrange an elastomeric layer between the damping element and the component bearing the latter. In this case, the surface of the displacement chamber lying opposite the displacement element is preferably formed on an elastomer coating. This elastomeric layer makes it possible for the displacement element to be moved further into the hollow once the annular gap has closed, the peripheral edge of the displacement element pressing into the elastomeric layer. In order that fluid can continue to flow out of the displacement chamber into the further chamber in spite of the closed annular gap, at the upper edge of the hollow there is provided at least one radial clearance, through which the displacement chamber is in communication with one of the further chambers. It is of course possible here for two radial clearances to be arranged diametrically.
In a preferred way, the distance between the displacement surfaces is dimensioned such that the maximum travel of the displacement element is about 1 mm. In this case, a great damping can be produced over a short distance. Depending on the design deflection, that is to say depending on the required damping forces for a specific application for the elastomer bearing, the displacement surface acted upon can be correspondingly dimensioned. For automotive engineering applications, it is regarded as advantageous for the displacement area acted upon to be >200 mm
2
and preferably between 300 mm
2
and 500 mm
2
.
To keep the displacement element in a defined position when the bearing is not subjected to any loading, it is advantageous for a cylindrical depression with an elastomer layer provided at least partially on its cylinder wall to be arranged centrally in the hollow. A rotationally symmetrical continuation, which protrudes into the depression, is moulded onto the displacement element. In this case, the elastomer layer has a radially inwardly directed bead, which engages in a radial groove in the continuation. In order that no self-contained cushion of hydraulic fluid can be produced within the depression, it is also advantageous to arrange in the elastomer layer extending along the cylinder wall at least one channel which extends approximately from the bottom of the cylinder space into the displacement chamber. In order that no undetermined conditions with respect
Butler Douglas C.
Daimler-Chrysler AG
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Talavera Melanie
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