Hydraulic antivibration supports

A hydraulic antivibration support comprises first and second rigid strength members, an elastomer body which has a thick wall interconnecting the two rigid strength members and which defines a portion of a working chamber, and a thin wall of elastomer which defines a portion of a compensation chamber that is connected to the working chamber via a narrow channel, the two chambers and the narrow channel being filled with a liquid. The support includes an abutment having no portion that projects into the working chamber from the inside surface of the thick wall of the elastomer body.

The invention relates to antivibration supports designed to be interposed, 
for damping and connection purposes, between two rigid elements such as 
the chassis and the engine of a vehicle, to damp vibratory motion between 
the two rigid elements, essentially along a main vibration direction. 
BACKGROUND OF THE INVENTION 
More particularly, the invention relates to an antivibration support of the 
kind in question, comprising: 
first and second rigid strength members suitable for being secured to 
respective ones of the two rigid elements to be united, the second 
strength member being a base plate which extends in a general plane 
substantially perpendicular to the main vibration direction; 
an elastomer body having a thick wall that connects the two rigid strength 
members together and that has an inside surface defining part of a working 
chamber, said thick wall being substantially bell-shaped, extending along 
the main vibration direction from a peripheral base secured to the second 
strength member to a crown secured to the first strength member, the 
elastomer body also including a freely deformable thin elastomer wall 
which is integrally formed with the thick wall of said elastomer body and 
which defines part of a compensation chamber in communication with the 
working chamber via a narrow channel, the two chambers and the narrow 
channel being filled with a liquid, the base plate having a "support" face 
secured in sealed manner to the elastomer body to co-operate therewith in 
defining the two chambers and the narrow channel; and 
abutment means for limiting relative movement of the first and second 
strength members towards each other parallel to the main vibration 
direction in order to avoid completely crushing the working chamber. 
Document EP-A-0 236 199 describes an example of such a hydraulic 
antivibration support. 
In that document, the abutment means are constituted by a boss of the 
elastomer body projecting into the working chamber parallel to the main 
vibration direction, the boss co-operating with a portion of the second 
strength member to limit movements of the first strength member towards 
the second strength member. 
The present inventors have discovered that such a boss is liable to disturb 
proper operation of the antivibration support at high frequency, in 
particular at around 400 Hz, where the dynamic stiffness of the support 
becomes too great. 
OBJECTS AND SUMMARY OF THE INVENTION 
A particular object of the invention is to mitigate that drawback. 
To this end, according to the invention, in a hydraulic antivibration 
support of the kind in question the abutment means do not include any 
portion that projects into the working chamber from the inside surface of 
the thick wall of the elastomer body. 
In preferred embodiments of the invention, use is made of one or more of 
the following dispositions: 
the first strength member is an elongate member extending along an axis 
perpendicular to the main vibration direction, the base plate including a 
zone that is occupied neither by the working chamber nor by the 
compensation chamber and facing a corresponding zone of the first strength 
member, and the abutment means include an abutment member which is 
interposed between said two zones of the base plate and of the first 
strength member in order to limit movements of the first strength member 
towards the base plate along the main vibration direction; 
the abutment member is an elastomer block belonging to the elastomer body 
and integrally formed therewith; 
the elastomer block is secured to the base plate; 
the base plate includes a boss which projects into the working chamber to 
limit movements of the first strength member towards the base plate along 
the main vibration direction, said boss thus constituting the 
above-mentioned abutment means; 
the boss is constituted by a stamping formed in the base plate; 
the working chamber and the compensation chamber are juxtaposed in 
non-concentric manner on the support face of the base plate; and 
the thin wall of elastomer is bell-shaped, extending along the main 
vibration direction from a peripheral base secured to the base plate to a 
crown that is free, said thin wall being connected via a portion only of 
its base to the thick wall of the elastomer body.

MORE DETAILED DESCRIPTION 
In the first embodiment of the invention, shown in FIGS. 1 to 3, the 
antivibration support comprises two rigid metal strength members 1 and 2 
that are connected together by an elastomer body 3. 
The first strength member 1 is tubular in the example shown, having a 
longitudinal axis X. More generally, the first strength member 1 could be 
in the form of an elongate member that is solid or hollow, and of section 
that is circular or otherwise. 
The second strength member 2 is a plate referred to below as a base plate, 
it is generally plane in shape, at least in parts, and it extends parallel 
to the axis X of the first strength member. 
The elastomer body 3 is secured to the first strength member 1 by 
vulcanization. It has a substantially bell-shaped thick wall 4 which 
extends along a direction Z (in which vibratory motion between the two 
strength members is to be damped) from a crown that is secured to the 
first strength member 1 to a peripheral base 4.sub.1 secured to the base 
plate 2. The direction Z is perpendicular to the axis X and to the general 
plane of the base plate 2, and it may be vertical, for example. 
The thick wall 4 has sufficient compression strength to support a static 
load applied to the first strength member 1 parallel to the axis Z and 
directed towards the base plate. This load may be greater than 15 kg, for 
example, and in general is much greater than 15 kg. 
The peripheral base 4.sub.1 of the thick wall 4 is secured in sealed manner 
to the base plate 2, thereby defining a working chamber A. In the example 
shown, the chamber A is of rectangular horizontal section, but it could be 
of some other shape, in particular it could be circular or oval in 
horizontal section. 
The elastomer body 3 also includes a flexible thin wall 5 which is 
juxtaposed to the thick wall 4 and is integrally formed therewith. 
The thin wall 5 is bell-shaped, having a peripheral base 5.sub.1 which is 
secured in sealed manner to the base plate 2, thereby defining a 
compensation chamber B. 
The chamber B is rectangular in horizontal section in the example shown, 
but it could have some other shape. 
The walls 4 and 5 preferably do not have any common portion between the 
chambers A and B, other than the connection via their bases 4.sub.1 and 
5.sub.1. 
The two chambers A and B communicate via a narrow channel C in the form of 
a groove formed in the face of the elastomer body 3 which is applied 
against the base plate 2, the edges of the groove being in sealed contact 
against the base plate 2. 
The chambers A and B and the narrow channel C are filled with liquid. When 
the two strength members 1 and 2 are subjected to relative vibratory 
motion, the thick wall 4 of the elastomer body deforms, thereby causing 
the volume of the working chamber A to vary. These variations in volume 
cause liquid to be transferred between the chambers A and B via the narrow 
channel C, the variations in volume of the working chamber A being 
compensated by complementary variations of the compensation chamber B 
whose thin wall 5 is easily deformable. 
In the vicinity of a particular frequency, which is generally less than 20 
Hz and which depends essentially on the dimensions of the narrow channel C 
and on the density of the liquid moving in said narrow channel, a 
resonance phenomenon occurs in the narrow channel C which, in association 
with headlosses in said narrow channel, causes a high degree of damping of 
the vibration between the two strength members 1 and 2. 
In the example shown, the elastomer body 3 is molded onto a perforated 
plate 6 disposed on the face of the elastomer body which is in contact 
with the base plate 2. Thus, the base plate 2 may be secured to the 
elastomer body by crimping tabs 6a of the perforated plate 6 onto the base 
plate 2, or possibly by crimping said base plate onto said perforated 
plate 6. 
The perforated plate 6 includes a groove or gutter 7 which accurately 
defines the shape of the narrow channel C. 
The antivibration support of FIGS. 1 to 3 also includes a metal arch 8 
which is rigidly secured to the base plate 2. The arch 8 surrounds the 
first strength member 1 and the elastomer body 3, and it extends parallel 
to the axis X. 
In the example shown, the arch 8 is a folded plate which covers all of the 
elastomer body so as to protect it from shocks from foreign bodies. This 
is advantageous insofar as the thin wall 5 is fragile and exposed beside 
the thick wall 4. 
The arch 8 includes two lateral extensions 8.sub.1 on respective sides of 
the elastomer body 3. Each of these lateral extensions covers a portion of 
the perforated plate 6 which itself overlies the second strength member. 
In addition, in each of the extensions 8.sub.1, all three elements are 
pierced by a respective hole 16. 
The holes 16 enable the antivibration support to be secured to a rigid part 
by means of screws or bolts (not shown), while also providing additional 
fastening between the various portions of the antivibration support by 
clamping the extensions 8.sub.1 onto the plate 6 and the second strength 
member 2. 
To co-operate with the arch 8, the elastomer body 3 includes a first boss 9 
which extends parallel to the direction Z from the first strength member 1 
and away from the base plate 2. This boss 9 is adapted to come into 
abutment against the top portion of the arch 8, thereby limiting the 
displacement of the first strength member going away from the base plate 
2. 
The elastomer body also has lateral bosses 11 and 12 that are substantially 
diametrically opposite about the first strength member 1, and that are 
adapted to come into abutment against the arch 8 whenever the first 
strength member is moved substantially perpendicularly to the axis X and 
to the direction Z. 
The first strength member 1 also includes a projecting zone 1a and the base 
plate 2 includes a zone 2a beneath said zone 1a of the first strength 
member, the zone 2a being occupied neither by the working chamber nor by 
the compensation chamber. 
An elastomer block 50 is placed in this zone 2a of the base plate, which 
block is preferably integrally formed with the elastomer body 3 and is 
also preferably secured to the base plate 2, the block 50 being molded 
over the perforated plate 6. 
The elastomer block 50 limits movements of the first strength member 1 
towards the base plate 2 parallel to the main vibration direction Z. 
This makes it possible to avoid having a boss projecting from the inside 
surface 4.sub.2 of the elastomer body where it defines the working chamber 
A, given that such a boss would reduce the effectiveness of the 
antivibration support at high frequency, particularly at about 400 Hz. 
The variant of FIGS. 4 and 5 is similar to the embodiment of FIGS. 1 and 3. 
It is therefore not described in detail below, and only the differences 
between this variant and the embodiment of FIGS. 1 to 3 are explained. 
In the variant shown in FIGS. 4 and 5, the device does not have the 
elastomer block 50, instead the base plate 2 has a boss 60 which may be 
made by stamping, in particular, and which projects into the working 
chamber A to limit movements of the first strength member 1 towards the 
base plate 2 along the main vibration direction Z. 
As in the embodiment of FIGS. 1 to 3, this makes it possible to avoid using 
a boss projecting from the inside surface 4.sub.2 of the elastomer body 
that defines the working chamber A, given that such a boss would reduce 
the effectiveness of the antivibration support at high frequency, in 
particular in the region of 400 Hz.