# ANTIVIBRATION HYDRAULIC SUPPORT
The present invention relates to anti-vibration hydraulic supports 5 intended to be interposed between two rigid elements to dampen vibrations between these two elements, essentially with respect to a main axis of vibration, and to support a previously determined static force parallel to that axis. The two rigid elements in question can be, for example, a chassis and a motor vehicle engine. Among the anti-vibration supports of this type, the invention concerns more particularly those containing: - a first and a second rigid reinforcement integrated respectively to the two rigid elements to be joined, the second reinforcement extends perpendicularly to the main axis of vibration, an elastomer body that connects to each other
the two armors; this elastomer body has a thick bell-shaped wall that extends diverging from a crest integrated to the first reinforcement to a base integrated to the second reinforcement, this wall presents, seen in section, according to a plane perpendicular to the main axis
of vibration, a contour that has four sides, substantially forming a rectangle (right angle parallelogram), the elastomer body includes, in addition an elastomer pad extending to the center of the thick bell-shaped wall forming a protrusion from from the top of this wall to the second reinforcement, this cushion has four lateral faces, each oriented towards one side of the thick bell-shaped wall, a working chamber delimited on one side by the thick bell-shaped wall and another part by a rigid wall that is integrated to the second reinforcement, and which forms a counter-stop for the aforementioned pad, a compensation chamber delimited at least partially by a flexible wall and permanently communicating with the working chamber by means of a strangulated channel, both the working chamber and the clearing chamber and the strangled channel are filled with a liquid EP-0 646 735 describes an example of an anti-vibration support as well. Supports of this type are very satisfactory, "but can in certain configurations have a relatively high dynamic stiffness for high vibration frequencies, for example of approximately 640 Hz, which decreases the filtration of vibrations at this frequency. The object of the present invention is especially to overcome this drawback. For this purpose, according to the invention, a hydraulic anti-vibration support of the kind in question is essentially characterized in that at least two of the side faces of the pad, opposite each other, have a concave shape in the whole plane that cuts them perpendicularly on the main axis of vibration that cuts them, the pad thus presents a narrow central part framed by two thicker end portions. In the preferred embodiments of the invention, optionally one and / or the other of the following arrangements can be used: the narrow central part of the pad has a first thickness while the end portions of the pad each have a second thickness thickness greater than the first thickness, with a difference greater than 5 millimeters between the first and second thicknesses; the pad has a straight section, perpendicular to the main axis of vibration that has an area greater than 150 square millimeters; the two flanks of the thick bell-shaped wall which are located facing the concave side faces of the elastomer pad, are longer than the other two sides of the said bell-shaped thick wall;
# the second reinforcement is constituted by a plate that extends according to a general plane perpendicular to the main axis of vibration and that has a face to said support, the elastomer body forming a single piece with the flexible wall delimiting the compensation chamber, and this elastomer body which is fixed hermetically on the face of the support of the second reinforcement, thereby delimiting the working chamber, the clearing chamber and the strangled channel. 10 - the second reinforcement includes a pad that forms a projection towards the working chamber with respect to the pad of the elastomer body, the pad of the filastornero body has a length substantially comprised between 2.3 and 15 2.7 cm; each side of the thick bell-shaped wall, which is arranged with respect to the concave side face of the pad of the elastomer body, is separated from the end portions of this pad by a distance which, measured perpendicularly to the main axis of the pad. vibration, is comprised appreciably between 0.8 and 1 centimeter. the pad of the elastomer body has a height, measured parallel to the main axis of
vibration, which is appreciably between 0.8 and 1.2 centimeters. Other characteristics and advantages of the invention will appear in the course of the following detailed description of one of its embodiments, given by way of example 5 without limitation with respect to the attached drawings. In the drawings: Figure 1 is a vertical section view of an anti-vibration hydraulic support according to an embodiment of the invention. 10 - Figure 2 is a sectional view according to line II-II of Figure 1, and Figure 3 is a diagram showing the dynamic stiffness of the anti-vibration support of Figure 1 compared to the dynamic stiffness of an anti-vibration support. similar equipped with a lower parallelepiped pad. In the description that follows, terms such as
"high", "low", "upper", "lower", "vertical",
"horizontal" are given as a reference to the most current position of antivibration support according to the
invention, but are not limiting. The anti-vibration hydraulic support shown in Figures 1 and 2 includes the first and second rigid metal reinforcements 1 and 2 which are joined together by an elastomer body 3 and which are intended to be
interposed between the two rigid elements (not shown) for damping and connection purposes. The first reinforcement 1 is intended to be integrated with a load to be supported, for example a drive train of a vehicle. In the example shown in the drawings, this first reinforcement has the shape of an elongated tubular member extending longitudinally along a substantially horizontal X axis. The second reinforcement 2, in itself, is a plate of generally flat shape at least in some pieces that is intended to be fixed to the chassis of the vehicle, for example, by means of fixing holes disposed in the lateral legs (not shown) of this plate, for example, as described in EP-A-0 646 735 or in document EP-A-0 709 594. This second frame 2 extends perpendicularly to a vertical axis Z representing, on the one hand , the direction of the application of the weight of the power train on the first reinforcement, and on the other hand, the main direction of the vibrations to be damped. On the other hand, the elastomer body 3 has a relatively large base 4 integrated in a sealing manner with the second reinforcement 2, especially by means of an open metal plate 5 which is submerged in said base and which has legs 6 set on the edges of the second reinforcement 2. As disclosed in the aforementioned documents EP-A-0 646 735 and EP-A-0 709 594, the lower face of the base 4 of the elastomer body is housed so as to form with the upper face of the second reinforcement 2: a working chamber A filled with liquid, which is partially delimited by a thick side wall 7 in the form of a bell extending until converging from the base 4 to a crest 8 integrated to the first reinforcement 1, this side wall 7 presents, seen in section in a horizontal plane, a rectangular contour having two large sides 9 and two small sides parallel to the X axis (or optionally four sides thereof) length), a compensation chamber B also filled with liquid, which is delimited by a thin easily deformable wall 11 belonging to the elastomer body, and a throttled channel C, which is also filled with liquid, which connects to each other, the chambers A and B and which is delimited by a groove whose shape is preferably at least partially defined by the molding 5a of the openwork plate 5. On the other hand, in order to limit the relative displacements of the first and second reinforcements 1 and 2, one against the other, the elastomer body 3 has a pad 12 which forms a downward projection in the working chamber A from the crest 8 of the elastomer body, this pad, which is preferably arranged relative to an overhang 13 supplied from the molding on the second frame 2. The pad 12 may have a height h comprised for example between 0.8 and 1.2 centimeters. Furthermore, the pad 12, seen in section in a horizontal plane, has an elongated shape parallel to the large side 9 of the side wall 7 of the working chamber and extends longitudinally between two ends 14. These two ends 14 respectively have the faces of the vertical ends 15 which are arranged relative to the small sides 10 of the side wall 7 and the pad • 12 presents on the other hand two other vertical side faces 16 which are disposed towards the large sides 9 of the side walls 7 and which each one presents a concave shape, seen in section in the whole horizontal plane that trims these lateral faces. • Thus, the two ends 14 of the pad 12 are separated from one another by a narrow central part 17 which has a thickness, the lower one, parallel to the axis X, to the thickness e2 of the ends 14. Preferably, the difference between the thicknesses e and e2 is greater than 5 millimeters, the total area of the horizontal section of pad 12 is preferably greater than 150 millimeters square. The device that has just been described works as follows: when the two reinforcements 1 and 2 are subjected to oscillations of relatively large amplitude and relatively low frequency (for example, less than 20 Hz), these oscillations cause the transfer of liquid between the chambers A and B through the strangulated channel C, and these liquid transfers tend to dampen the oscillatory movements of the fact of the losses of the load in the strangulated channel, when the two reinforcements 1 and 2 are subjected to relative vibratory movements of low amplitude and high frequency (for example higher than 20 Hz to around 650 Hz), the vibrations in question are absorbed by the flexibility of the antivibration support and are not transmitted from one armature to the other. This efficient filtering of high frequency vibrations is obtained thanks to the low dynamic rigidity of the antivibration support up to frequencies of 650 Hz, as represented by curve 18 in Figure 3. By way of comparison, curve 19 shows the stiffness dynamics of a similar antivibration support whose pad 12 does not have the narrow central part 17: it is seen that the antivibration support has a dynamic stiffness peak from around 600 Hz, so that this support does not effectively filter the vibrations beyond 600 Hz, while the anti-vibration mount of the invention filters the vibrations up to about 650 Hz. This phenomenon is due to the fact that in the absence of the narrow central part 17 of the pad 12, resonance phenomena occur at about 600 Hz in the two liquid columns located respectively between this pad 12 and the two large sides 9 of the side wall 7, each of the liquid columns extends at least over a part of the height of the pad 12, over the length 1 of this pad (for example, about 2.3 to 2. 7 centimeters) and on the width of the pad that is free between the pad and the side 7 of the side wall 7 (for example 0.8 to 1 centimeter, sensibly halfway up the pad 12). On the other hand, since the pad 12 has a narrow central part 17, the section of the liquid columns mentioned above is increased, so that the aforementioned resonance phenomenon no longer occurs. It will be noted, finally, that in the present case, the distance d2 between the end faces 15 of the pad and the small sides 10 of the side wall 7 is greater than the distance di sensibly to half the height of the pad 12 (per example, d2 can be from 1.3 to 1.5 centimeters) so that the aforementioned resonance phenomena do not occur in the liquid columns located respectively between the faces 15 and the small sides 10 of the side wall 7. However, if the faces of the 15th end in question were located closer to the small sides 10 of the side wall 1, it would be advantageous to optionally also make the end faces 15 concave to avoid the aforementioned resonance phenomena.