Spring devices – Resilient shock or vibration absorber – Including energy absorbing means or feature
Reexamination Certificate
1998-10-29
2001-08-21
Graham, Matthew C. (Department: 3613)
Spring devices
Resilient shock or vibration absorber
Including energy absorbing means or feature
C267S293000
Reexamination Certificate
active
06276671
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulically damped mounting device. Such a mounting device usually has a pair of chambers for hydraulic fluid, connected by a suitable passageway, and damping is achieved due to the flow of fluid through that passageway.
2. Summary of the Prior Art
In EP-A-0172700, a hydraulically damped mounting device of the “bush” type was disclosed which damped vibration between two parts of a piece of machinery, e.g. a car engine and a chassis. In a bush type of hydraulically damped mounting device, the anchor for one part of the vibrating machinery is in the form of a hollow sleeve, and the other anchor part is in the form of a rod or tube extending approximately centrally and coaxially of the sleeve. Resilient walls then interconnect the central anchor part and the sleeve to act as a resilient spring for loads applied to the mounting device. In EP-A-1072700, the resilient walls also defined one of the chambers (the “working chamber”) in the sleeve, which chamber was connected via the elongate passageway to a second chamber (the “compensation chamber”) bounded at least in part by a bellows wall which was effectively freely deformable so that it could compensate for fluid movement through the passageway without itself resisting that fluid movement significantly.
In GB-A-2291691, the arrangement disclosed in EP-A-1072700 was modified by providing a bypass channel from the working chamber to the compensation chamber. Under normal operating conditions, that bypass channel was closed by part of the bellows wall bounding the compensation chamber. At high pressures, however, the bellows wall deformed to open the bypass channel, thereby permitting fluid from the working chamber to pass directly into the compensation chamber without having to pass through the full length of the passageway.
In both EP-A-1072700 and GB-A-2291691, the resilient walls extended generally axially along the interior of the mount. Those walls therefore formed axially elongate blocks of e.g. rubber material which were configured to achieve the desired static spring requirements. The material of the block was deformed primarily in shear, to give maximum durability. As the resilient walls also formed walls of the working chamber, the axial ends of the working chamber were closed with material being integral with the resilient walls. In practice, however, the spring effect of those ends walls was small, so that the spring characteristic of the mount could be determined by the axially extending resilient walls.
SUMMARY OF THE INVENTION
The present invention departs from this, by locating the resilient walls at axially spaced apart locations. This is thus a departure from the arrangements in EP-A-1072700 and GB-A-2291691, in which the main spring effect is provided by axially extending, circumferentially spaced, resilient walls. The resilient walls of the present invention thus define an enclosed space within the sleeve which extends circumferentially around the central anchor part, which space is axially bounded by the resilient walls.
It is then necessary to divide that space into two chambers, and connect those two chambers with a passageway, to form the hydraulic mounting device of the bush type. To provide that division, the present invention proposes that axially extending walls extend between the central anchor part and the sleeve. Unlike the axially extending walls of the known arrangements, those walls do not need to provide a spring effect, since the spring effect is provided by the axially spaced resilient walls. Therefore, it is not necessary for those axially extending walls to be bonded to the sleeve and/or central anchor part. Instead, they may make abutting, un-bonded, contact.
This is significant, because it then permits a bypass to be formed between the chambers without the need for a separate bypass channel, as in GB-A-2291691. By suitably selecting the abutment force of the axial walls against the sleeve and/or central anchor part, a pressure-sensitive seal is achieved. For pressures below a suitable level, the integrity of that seal will be achieved by the force of abutment. For higher pressures, however, the seal will be broken, thereby providing a path around the axial walls between the two chambers.
A further advantage of this arrangement is that tensile stresses are less likely to occur in the axial extending walls. In known hydraulically damped mounting devices of the bush type, there is a risk that the resilient walls may be put under tensile stress at their bonding to the sleeve so reducing durability of the mounting device. Since the axially extending walls are not bonded to the sleeve, in the present invention, such tensile stresses cannot occur and thus the durability is improved.
Thus, the present invention may provide a hydraulically damped mounting device having
a first anchor part;
a second anchor part in the form of a hollow sleeve containing the first anchor part, such that the first anchor part extends axially of the sleeve;
first and second resilient walls interconnecting the first and second anchor parts, the first and second resilient walls being spaced apart so as to define an enclosed space within the sleeve extending circumferentially around the first anchor part and axially bounded by the first and second resilient walls; and
first and second deformable walls, each extending axially between the first and second resilient walls at circumferentially spaced locations, so as to divide the enclosed space into first and second chambers for hydraulic fluid; and
a passageway interconnecting the first and second chambers for flow of hydraulic fluid therethrough;
wherein the first and second deformable walls each have an edge forced into abutting, unbonded contact with the sleeve or first anchor part. Thus the axial walls can form seals between said first and second chambers below a predetermined pressure of hydraulic fluid, the seals being released at pressures above the predetermined pressure.
Preferably, the resilient walls are in the shape of hollow frusto-cones, with their frustums at the central anchor part and their bases at the sleeve. The resilient walls thus operate in shear under load. They preferably extend substantially completely around the central anchor part.
It may be noted that, with the present invention, it is not necessary to provide a bellows wall to bound one of the chambers. Instead, each chamber is axially bounded by a part of the resilient walls, and the two chambers separated by the axial walls. It is, however, possible for only one of the chambers (the working chamber) to be bounded in this way and the other chamber to be bounded by a compensation chamber, as in EP-A1072700 and GB-A-2291691.
Although it is possible for the axial walls to be simple flaps, it is preferable for them to be hollow and more preferably with a V-shaped cross section, with the base of the “V” being in contact with the sleeve. Providing such hollow axial walls allows tuning of the dynamic stiffness of the mount independent of the static stiffness. Where the axial walls are hollow in this way, it may be necessary to provide voids in the resilient walls at the point where those resilient walls meet the axial walls.
The hydraulic mounting device may also be formed such that the first anchor part is offset transversely from the longitudinal axis of the second anchor part. This permits the hydraulic mounting to bear greater loads in certain transverse directions.
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patent: 43 32 367
Fursdon Peter Michael Trewhella
West John Philip
Avon Vibration Management Systems Limited
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Graham Matthew C.
Rodriguez Pamela J.
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