Abstract:
A hydraulically damped mounting device has two anchor parts connected by deformable wall. A partition is associated with one of the anchor parts and defines, together with the deformable wall a working chamber for hydraulic fluid. The working chamber is connected via a passageway to a compensation chamber partially bounded by another deformable wall. The partition separates the working and compensation chambers, and the device has a diaphragm being a barrier between the hydraulic fluid and a gas. In one arrangement at least part of the passageway is formed within a cavity in the partition in which there are projections which are arranged to overlap, and so define a convoluted path for the hydraulic fluid around the projections. In another arrangement a duct to a diaphragm part is at least partially formed by a cavity within the partition, which cavity has cylindrical projections arranged one within the other and overlapping to form a convoluted path for hydraulic fluid. In a third arrangement the passageway has a branch to the diaphragm, which branch is convoluted as it passages through a cavity in the partition containing cylindrical projections.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority on British Application No. GB0806073.3, filed Apr. 3, 2008. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a hydraulically damped mounting device. Such a device usually has a pair of chambers for hydraulic fluid, connected by suitable passageway, and damping is achieved due to the flow of fluid through that passageway. 
         [0004]    2. Summary of the Prior Art 
         [0005]    EP-A-0115417 and EP-A-0172700 discussed two different types of hydraulically damped mounting devices for damping vibration between two parts of a piece of machinery, e.g. a car engine and a chassis. EP-A-0115417 disclosed various “cup and boss” type of mounting devices, in which a “boss”, forming one anchor part to which one of the pieces of machinery was connected, was itself connected via a deformable (normally resilient) wall to the mouth of a “cup”, which was attached to the other piece of machinery and formed another anchor part. The cup and the resilient wall then defined a working chamber for hydraulic fluid, which was connected to a compensation chamber by a passageway (usually elongate) which provided the damping orifice. The compensation chamber was separated from the working chamber by a rigid partition, and a flexible diaphragm was in direct contact with the liquid and, together with the partition formed a gas pocket. 
         [0006]    In EP-A-0172700 the mounting devices disclosed were of the “bush” type. In this type of mounting device, the anchor part for one part of the vibrating machinery is in the form of a hollow sleeve with the outer anchor part in the form of a rod or tube extending approximately centrally and coaxially of the sleeve. In EP-A-0172700 the tubular anchor part was connected to the sleeve by resilient walls, which defined one of the chambers in the sleeve. The chamber was connected via a passageway to a second 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. 
         [0007]    In the hydraulically damped mounting devices disclosed in the specifications discussed above, there was a single passageway. It is also known, from other hydraulically damped mounting devices, to provide a plurality of independent passageways linking the chambers for hydraulic fluid. 
         [0008]    In EP-A-0115417, there was a single diaphragm, which was configured to give a specific influence on the vibration characteristics of the hydraulically damped mounting device. Those characteristics depended on the stiffness of the diaphragm, by which is meant the change in applied pressure needed to cause unit change in the volume displaced by the diaphragm. Furthermore, the surface of the diaphragm which is in contact with the fluid in the working chamber may be covered by a snubber plate, with openings therein for fluid communication therethrough between the upper surface of the diaphragm and the rest of the working chamber, and it has been found that the size of those openings also affects the characteristics of the mount. 
         [0009]    In GB-A-2282430, a mounting device was disclosed of the “cup and boss” type, with two diaphragms. The two diaphragms were arranged to have different characteristics, such as different stiffnesses or different effective stiffnesses, due to the shape of the openings by which fluid reaches those diaphragm parts from the working chamber. GB-A-2282430 also disclosed that either or both of the diaphragms may be convoluted. 
         [0010]    One issue when producing a mount of the “cup and boss” type is to ensure that the characteristics of the passageway are appropriate. Normally, the passageway is formed in a rigid partition separating the working and compensation chambers, and thus there is limited space available within that partition for the passageway. In general, in the arrangements disclosed in EP-A-0115417 and GB-A-2282430, the passageway was formed as a spiral within the partition. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention, at its most general, seeks to modify such passageway arrangements, and, in a first aspect, proposes that at least part of the passageway is formed within a cavity in the partition in which there are projections which are arranged to overlap, and so define a convoluted path for the hydraulic fluid around the projections. 
         [0012]    Thus, according to the first aspect, there may be provided a hydraulically damped mounting device comprising two anchor parts connected by a deformable wall; a working chamber enclosed between the deformable wall and a partition rigidly associated with a first one of the anchor parts, the working chamber containing hydraulic fluid; a compensation chamber for the hydraulic fluid, the compensation chamber being at least partially bounded by a second deformable wall; a passageway between the chambers to allow fluid communication between them; and a flexible diaphragm part acting as a barrier between the hydraulic fluid and at least one gas chamber, wherein the passageway is formed in a rigid partition separating the working and compensation chambers, the partition has a hollow cavity therein having opposed surfaces defining part of the passageway therebetween, each of the opposed surfaces having a projection extending therefrom towards the other of the opposed surfaces, the free end of each projection being spaced from the surface towards which it extends, the free end of each projection being closer to the surface towards which it extends then the free end of the projection extending from the surface, whereby the projections overlap and define a convoluted path for the passageway around the projections. 
         [0013]    In the first aspect, therefore, the projections form convolutions in the passageway linking the working and compensation chambers. However, similar ideas may be applied to other fluid parts in the mounting device. For example, they may be used in a path from the working and/or compensation chamber to a diaphragm part, or to one or more diaphragm parts where there are multiple diaphragm parts. 
         [0014]    Thus, according to a second aspect, at its most general, a duct to a diaphragm part is at least partially formed by a cavity within the partition, which cavity has cylindrical projections arranged one within the other and overlapping to form a convoluted path for hydraulic fluid. 
         [0015]    Thus, according to this second aspect, there may be provided a hydraulically damped mounting device comprising two anchor parts connected by a deformable wall; a working chamber enclosed between the deformable wall and a partition rigidly associated with a first one of the anchor parts, the working chamber containing hydraulic fluid; a compensation chamber for the hydraulic fluid, the compensation chamber being at least partially bounded by a second deformable wall; a passage way between the chambers to allow fluid communication between them; and a flexible diaphragm part acting as a barrier between the hydraulic fluid and at least one gas chamber, wherein there is a duct for hydraulic fluid formed in a rigid partition separating the working and compensation chambers, and supporting the diaphragm part, the partition having a hollow cavity therein having opposed surfaces defining part of the duct therebetween, each of the opposed surfaces having a projection extending therefrom towards the other of the opposed surfaces, the free end of each projection being spaced from the surface towards which it extends, the free end of each projection being closer to the surface towards which it extends then the free end of the projection extending from the surface, the duct extending to said diaphragm part from said working or compensation chamber, the duct extending through said cavity, whereby said duct is convoluted around the projections. 
         [0016]    A third possibility is for the passageway linking the working and compensation chambers, and the duct for hydraulic fluid from the working and/or compensation chamber to the diaphragm part be linked together. In such an arrangement, the duct to the diaphragm part may be a branch in the passageway linking the working and compensation chambers. Then, in a third aspect of the invention, that branch may be made convoluted, by causing it to pass through the cavity containing the cylindrical projections. 
         [0017]    Thus, according to a third aspect of the invention, there may be provided a hydraulically damped mounting device comprising two anchor parts connected by a deformable wall; a working chamber enclosed between the deformable wall and a partition rigidly associated with a first one of the anchor parts, the working chamber containing hydraulic fluid; a compensation chamber for the hydraulic fluid, the compensation chamber being at least partially bounded by a second deformable wall; a passage way between the chambers to allow fluid communication between them; and a flexible diaphragm part acting as a barrier between the hydraulic fluid and at least one gas chamber, wherein the passageway is formed in a rigid partition separating the working and compensation chambers, the partition has a hollow cavity therein having opposed surfaces, each of the opposed surfaces having a projection extending therefrom towards the other of the opposed surfaces, the free end of each projection being spaced from the surface towards which it extends, the free end of each projection being closer to the surface towards which it extends then the free end of the projection extending from the surface, wherein said passageway has a branch extending therefrom into said cavity, and from said cavity to said diaphragm part, whereby said branch of said passageway is convoluted around said projections. 
         [0018]    Thus, in all of the above aspects, fluid passing through the cavity has to flow around the projections. In normal operation, where the mounting device vibrates vertically, it is convenient if the flow through the cavity is in the radial (horizontal) directions with the upwardly extending projection acting as a weir, and the downwardly extending projection acting as an underfall, for the fluid flow. Moreover, the discussion of the three aspects of the invention above refers to one projection extending from each opposed surface bounding the cavity, there may be additional projections extending from either or both of those surfaces. In such case, the projections form a series of weirs and underfalls for the fluid flow. 
         [0019]    Where, as in the first aspect, the cavity is part of the passageway between the working and compensation chambers, it may be convenient for the inlet from the working or compensation chamber within a radial or central position within that cavity, and for the outlet (to the compensation chamber or working chamber) to be at the periphery of the cavity. In such an arrangement, it may be then convenient if projections are cylindrical, one within the other. However, such an arrangement is not limited to the case where such cylinders are circular in cross-section. Other cross-sectional shapes may be possible, such as square, rectangular, or oval. Preferably, the cylindrical projections are concentric, although this is not essential. Moreover, although we have referred to the projections being cylindrical, their walls need not be parallel to their axes so that the projections are inclined to the surfaces from which they extend. In further alternatives, the projection may be linear or curved walls within the cavity. 
         [0020]    In a similar way, where the cavity is part of a duct or branch leading to a diaphragm, the opening from the cavity to that diaphragm may be at a central part of the cavity, and the inlet to the cavity be at a peripheral part. Again, in such an arrangement, it may be convenient to use cylindrical projections to define weirs and underfalls although the other shapes of projection discussed above may also be used. 
         [0021]    To form the cavity, it may be possible to use selective laser sintering to form a one-piece partition with the cavity therein. However, for ease of manufacture, it may be preferable for the partition to comprise at least two partition parts, with the cavity being formed between those partition parts. 
         [0022]    As was discussed above, in all three aspects of the invention, the diaphragm part acts a barrier between hydraulic fluid and a gas chamber. Means, such as a vacuum source, may be connected to that gas chamber to allow the gas therefrom to be evacuated. This forces the diaphragm against a wall of the vacuum chamber, and prevents the diaphragm from vibrating. Under such conditions, the hydraulic fluid in the duct or branch leading to that diaphragm part also cannot move, and the branch or duct is effectively blocked off. Thus, by application of vacuum to the gas chamber, the effect of the fluid movement in the duct or branch, and the vibration of the diaphragm, may be turned on and off. 
         [0023]    Moreover, in the second and third aspects of the invention, where the diaphragm part terminates the duct or branch, a further diaphragm part may be provided, preferably on the partition, which acts as a barrier between the fluid in the working chamber and a further gas pocket. Again, means such as a vacuum source may be connected to that further gas pocket, to allow it to be evacuated. In such an arrangement, by selectively applying a vacuum to the gas pocket or further gas pocket, the characteristics if the mounting device may be changed. 
         [0024]    In all the aspects discussed above, the or any diaphragm part may be annular. Such an annular diaphragm may be an incomplete annulus similar to a horse shoe, with a gap therein, to enable other components such as the passageway, to be in the gap of the annulus. 
         [0025]    Where, as in the first aspect of the invention, the passageway is convoluted around the projections, the inlet to that passageway may be provided within the innermost cylindrical projection, and the outlet lie outside the outermost cylindrical projection. Where, as in the second or third aspect, the convolutions are in a duct or branch to the diaphragm part, the inlet to that duct or branch may be outside the outermost cylindrical projection, and the outlet to the diaphragm part be within the innermost cylindrical projection. 
         [0026]    Embodiments of the present invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a cross-sectional view of a hydraulically damped mounting device being a first embodiment of the present invention; 
           [0028]      FIG. 2  is a cross-sectional view of the partition of the mounting device of  FIG. 1 ; 
           [0029]      FIG. 3  is a perspective view from below of the partition of  FIG. 2 ; 
           [0030]      FIG. 4  is a view from below of the partition of  FIG. 2 ; 
           [0031]      FIG. 5  is a perspective view from above of the partition of  FIG. 2 ; 
           [0032]      FIG. 6  is a cross-sectional view of a hydraulically damped mounting device being a second embodiment of the present invention; 
           [0033]      FIG. 7  is a cross-sectional view through the partition of the hydraulically damped mounting device of  FIG. 6 ; 
           [0034]      FIG. 8  is a perspective view, partially in section, of the partition of  FIG. 7 ; 
           [0035]      FIG. 9  is a view from below of the partition of  FIG. 7 ; 
           [0036]      FIG. 10  is a cross-sectional view from a hydraulically damped mounting device being a third embodiment of the present invention; 
           [0037]      FIG. 11  is a cross-sectional view through the partition of the hydraulically damped mounting device of  FIG. 10 ; 
           [0038]      FIG. 12  is a perspective view, partially in section, of the partition of  FIG. 11 ; 
           [0039]      FIG. 13  is a view from below of the partition of  FIG. 11 ; and 
           [0040]      FIG. 14  is a cross-sectioned view of a hydraulically damped mounting device being a fourth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0041]    A first embodiment of the present invention will now be described with reference to  FIGS. 1 to 5 . 
         [0042]    Referring first to  FIG. 1 , a hydraulically damped mounting device being a first embodiment of the invention is shown for damping vibration between two parts of a structure (not shown). For example, the mounting device may be used to damp vibration between a vehicle engine and a chassis of the vehicle. The mount has a boss  1  connectable via a fixing bolt  2  to one of the parts of the structure, and the other part of the structure is connectable to a generally U-shaped cup  4  via a further fixing bolt  5 . A resilient spring  6  of e.g. rubber interconnects the boss  1  and cup  4 . A rigid partition  7  is mounted on the cup  4  to extend across its mouth, and a bracket  8  is mounted on the partition  7 , so that the spring  6  is connected to the cup  4  via the bracket  8  and the partition  7 . 
         [0043]    A working chamber  9  is defined within the mounting device, bounded by the resilient spring  6  and the partition  7 . Moreover, within the cup  4 , there is a compensation chamber  10  bounded by a flexible wall  11 . The working chamber  9  and the compensation chamber  10  are connected by a passageway  11  within the partition  7 . The configuration of that passageway  11  will be described in more detail later. 
         [0044]    Thus, when the boss  1  vibrates relative to cup  4  (in the vertical direction in  FIG. 1 ) the volume of the working chamber  9  will change, and hydraulic fluid in that working chamber will be forced through the passageway  12  into, or out of, the compensation chamber  10 . The volume of the compensation chamber  10  needs to change in response to such fluid movement, and this is achieved by deformation of the flexible wall  11 . This movement of the hydraulic fluid damps the vibrations. 
         [0045]    In addition, the partition  7  supports an annular diaphragm  13 , one side of which is in contact with the hydraulic fluid in the working chamber  9 , and the other bounds a gas pocket  14 . 
         [0046]    The above structure is generally similar to that described in EP-A-0115417, and the manner of operation is similar. 
         [0047]    The structure of the partition  7  is illustrated in more detail in  FIG. 2 . The partition  7  has a lower plate  20  attached at its periphery to an upper body  21 , to define a cavity  22  between the body  21  and the plate  20 . The plate  20  has upstanding projections  23 ,  24  in the form of concentric circular cylinders. Similarly, the body  21  has downwardly extending concentric cylindrical projections  25 ,  26  with the projection  25  being radially inward of the projection  23 , and the projection  26  being between the projections  23  and  24 . The body  21  has an opening  27  within the confines of the cylindrical projection  25 , which opening  27  communicates with the working chamber  9 . Similarly, openings  28  are formed at the periphery of the plate  20 , communicating with the compensation chamber  10 . Thus, convoluted paths shown by arrows A to A and B to B are formed within the cavity  22 , extending between the working chamber  9  and the compensation chamber  10 . The projections  23  and  24  extending from the plate  20  extend close to, but are spaced from, the body  20 , and similarly the projections  25  and  26  extend close to, but are spaced from, the plate  20 . Thus, fluid must flow around those projections in order to pass from the working chamber  9  to the compensation chamber  10 , or vice versa, and thus may follow a longer path than the direct distance between the openings  27  and  28 . 
         [0048]      FIG. 2  also shows that the gas pocket  14  is formed by an annular recess  30  in the upper surface of the body  21 , which annular recess  30  is covered by diaphragm  13 , which itself is annular. The diaphragm  13  is then held on the body  21  by a cover  31 . 
         [0049]      FIG. 3  shows the openings  28  at the end of the passageway  11  between the working and compensation chambers  9 ,  10 .  FIG. 3  also shows the parts  32  of the plate  20  which separate those openings  28  one from the other, and which may be bonded to the body  21  of the partition  7  by ultrasonic or other welding. Similar features are also shown in  FIG. 4 , which shows a bottom view of the partition  7 . 
         [0050]    Moreover, in this embodiment the flow of fluid is different from in e.g. EP-A-0115417. In that document, the passageway between the chambers is a spiral, so that the fluid flows circumferentially around the axis of vibration of the mount, as it flows outwardly. However, in the embodiment of  FIG. 1 , the fluid flows between the opening  27  and the multiple openings  28 . Thus, the fluid flow is essentially radial, and also axial as it flows around the projections  23 ,  24 ,  25  and  26 . The projections  23  and  24  act as weirs over which the fluid flows, and the projections  25  and  26  act as underfalls under which the fluid flows, to define the convoluted path. Hence, in this embodiment, the fluid flow between the working and compensation chambers  9 ,  10  is radial and axial relative to the axes of the vibration of the mount, rather than circumferential and radial, as in arrangements where the passageway is in the form of a spiral. 
         [0051]      FIG. 5 , which is a perspective view from above of the partition  7 , shows the opening  27  by which the passageway  11  communicates with the working chamber  9 , and also the cover  31  which covers the annular diaphragm  13 . As can be seen from  FIG. 5 , that cover  31  has a series of holes  33  therein which permit fluid from the working chamber  9  to communicate with the diaphragm  13 . Also, as can be seen from  FIG. 2 , an edge  34  of the cover  31  extends over and around an upwards projection  35  on the body  21 , to seal the diaphragm  13 , and the gas pocket  14 , from the fluid in the working chamber  9 . 
         [0052]    A second embodiment of the invention will now be described with reference to  FIGS. 6 to 10 . In this embodiment, a branch in the passageway between the working and compensation chambers leads to a diaphragm. Note that components of this invention which correspond to those of the first invention are indicated by the same reference numerals, and will not be described in more detail. 
         [0053]      FIGS. 6 and 7  thus show the structure of the partition  7  in this embodiment. The partition  7  has a lower plate  50 , a main body  51  and an upper plate  52 . A cavity  53  is formed between the lower plate  50  and the body  51 . A cylindrical projection  54  projects upwardly into that cavity from the lower plate  50 . Similarly, cylindrical projections  55 ,  56  project downwardly into that cavity from the body  51 . The projection  55  has its free edge uniformly spaced from the lower plate  50 . However, the free edge of the projection  56  has a part (on the right in  FIG. 7 ) which is spaced from the plate  50 , and a part on (on the left in  FIG. 7 ) which extends to make contact with the plate  50 , and so seal the body  51  to the lower plate at that projection  56 . The body  51  has a central opening  57  and a series of further openings around the central opening  57 , within the projection  55 . The body  51  also has a bore  58   a  which extends from an opening  58  communicating with the working chamber  9  to adjacent the cavity  53 , and communicates with that cavity at a gap  59 . Thus, a fluid path is defined between the working chamber  9  and the central opening  57 , as shown by arrow  59   a  between A to A′. That path is convoluted around the projections  54 ,  55  and  56 . 
         [0054]    A diaphragm  60  is mounted on the body  51 , lying above the central opening  57 . Thus, one side of that diaphragm  60  (the lower side in  FIGS. 6 and 7 ) is in contact with hydraulic fluid axis in the cavity  53  and the openings  57  and  57   a.  The upper plate  52  then covers that diaphragm  60 , and holds the periphery of the diaphragm  60  in place. However, a gap is defined between the upper surface of the diaphragm  60  and the upper plate  52 , which communicates with an outlet duct  61 . 
         [0055]    The bore  58   a  which communicates with the working chamber  9  at opening  58 , also communicates with a passageway  62  extending around the partition  7 , and leading to the compensation chamber. 
         [0056]    That passageway  62  is shown more clearly in  FIG. 9 , which illustrates that the body  51  has a hole  63  which corresponds to the lower end of the bore  58  and a groove  64  in the lower surface of the body  51  which extends from that hole  63  around the partition  7  as shown by arrow  65  to an outlet (not shown but corresponding to the position of arrowhead  66 ) which opens into the compensation chamber  10 . Thus, there are two possible paths from the opening  58 , one path following arrow  59   a  leading to the diaphragm  60  (via the cavity  53 ) and the other leading to the compensation chamber  10  (via the groove  64 ). The latter is path A to A in  FIG. 7  with arrow  67  showing the branching to hole  63 . The path to the diaphragm  60  has a larger cross-sectional area for fluid flow than to the compensation chamber  10 . Thus, the preferential liquid flow path is to the diaphragm  60 , rather than that to the compensation chamber  10 . Hence, assuming the diaphragm  60  is free to move in the space between the body  51  and the upper plate  52 , when the boss  1  moves relative to the cup  4 , fluid from the working chamber  9  is forced along the path shown by arrow A to A′ to the diaphragm, or in the opposite direction. The diaphragm  60  vibrates to absorb such fluid movement. 
         [0057]    However, as mentioned, there is a duct  61  leading from the gas space between the diaphragm  60  and the upper plate  52 , and that duct is connected to a vacuum source. When a vacuum is applied to the duct  61 , the diaphragm  60  is forced against the upper plate  52 , so that it is locked. The fluid in the cavity  53  therefore cannot move. As a result, if the boss  1  moves relative to the cup  2 , any liquid flow must be through the passageway  62  to the compensation chamber  10 . The branch from the passageway  62  to the diaphragm  60  is thus locked off when the vacuum is applied to the duct  61 . Thus, the characteristics of the mounting device may be varied by applying a vacuum to that duct  61 . 
         [0058]    This may be used, for example, when the mounting device is used to damp vibration between an engine and a chassis of a vehicle. In this case, when the engine is in its “idle” state, the constant frequency low amplitude vibrations generated in that state may be absorbed by the diaphragm  60 . When the engine is running to drive the vehicle, however, that idle state can be locked off, by the application of a vacuum for the duct  61 . 
         [0059]      FIGS. 6 and 7  also show that there is a further diaphragm  70  mounted between the upper plate  52  and the body  51 , and which communicates with the fluid in the working chamber  9  via openings  71  in a recess  72  in the upper plate  52 . These are shown in  FIG. 8 . The diaphragm  70  thus has its upper surface in contact with hydraulic fluid from the working chamber  9 . Its lower surface is exposed to a gas pocket  73  which may also be connected to a vacuum source (not shown). Thus, in e.g. the “ride” condition of the vehicle discussed above, the diaphragm  70  may absorb high frequency low amplitude vibrations due to movement of hydraulic fluid through the opening  71 . However, that diaphragm  70  may be locked by the application of a vacuum to the gas chamber  73 , e.g. to give an altered response in different ride conditions. 
         [0060]    Note that, as can be seen from  FIGS. 6 to 8 , the projection  56  from the body  51  separates the cavity  53 , which leads to the diaphragm  60 , from the passageway  62  extending between the working and compensation chambers  9 ,  10 . Moreover,  FIGS. 6 to 8  show that the two diaphragms  60 ,  70  may be made from a single integral moulding connected at a connection  74  and held at that connection between the body  51  and the upper plate  52 . 
         [0061]    A third embodiment of the invention will now be described with reference to  FIGS. 10 to 13 . Again, corresponding parts are indicated by the same reference numerals. The third embodiment operates in a similar way to the second embodiment, where the passageway between the working and compensation chambers  9 ,  10  has a branch leading to a diaphragm. However, the structure of the partition  7  is different from that of the second embodiment. 
         [0062]    In this third embodiment, the partition  7  has a main body  80 , with a central bore  81  therein. In that bore, a cylindrical projection  82  extends upwardly, spaced from the outer walls  83  of that bore. An upper cap  84  is fitted over that bore  81 , with a downward cylindrical projection  85  extending in the space between the walls  83  of the bore and the projection  82 . The upper cap  84  has openings  85  therein (visible in  FIG. 12 ) which communicate with the working chamber  9 . A diaphragm  86  is then held between the body  80  and a lower plate  87 , that diaphragm  86  communicating with the bore  81  via openings  88 . Thus, a convoluted path is defined from the working chamber  9  to the diaphragm  86 , as illustrated by arrows A to A′ and B′. This is similar to the convoluted path between the working chamber  9  and the diaphragm  60  in the second embodiment, and has a similar effect. As in the second embodiment, the gas space between the diaphragm  86  and lower plate  87  has a duct  89  leading therefrom, to a vacuum source (not shown). 
         [0063]    Thus, again, the effect of the diaphragm  86  may be locked off by applying a vacuum to the duct  89 . As in the second embodiment, there is also a passageway  90  extending between the working and compensation chambers  9 ,  10 , defined between the body  80  and the lower plate  87 . An opening in the wall  83  of the bore  81  (the opening not being visible is  FIGS. 11 and 12  but indicated by the arrow head  90   a ) leads to that passageway  90 , that opening being shown more clearly in  FIG. 13 . The passageway  90  leads to an outlet  92   a  (in  FIGS. 11 and 12 , and indicated by the arrowhead  92  in  FIG. 13 ) to the compensation chamber  10 . Thus, when the flow path to the diaphragm  86  is locked off, by application of a vacuum to the duct  89 , fluid flows as shown by arrow  93  in the passageway  90  between the working and compensation chambers  9 ,  10 . 
         [0064]      FIGS. 10 to 12  show that, in a similar way to the second embodiment, the mounting device of the third embodiment has a second diaphragm  100  (in this case an annular diaphragm), held between the body  80  and an upper plate  101 . As can be seen in  FIG. 12 , there are openings  102  in that upper plate, to allow hydraulic fluid from the working chamber  9  to communicate with the diaphragm  100 . The diaphragm  100  thus acts to separate fluid in the working chamber  9  from a gas pocket. Although not shown in  FIGS. 10 to 13 , that gas pocket may have a duct leading to a vacuum source, as in the second embodiment. 
         [0065]    Thus, the behaviour of the third embodiment is similar to that of the second embodiment, and thus will not be described in more detail now. 
         [0066]    A fourth embodiment will now be described with reference to  FIG. 14 .  FIG. 14  shows only the partition  7  of the mounting device. Other features of the mounting device may be the same as shown in  FIG. 1 ,  6  or  10 . 
         [0067]    In the second and third embodiments, the fluid path to the diaphragm  60  was in a branch from the passageway  62 ,  90  between the working and compensation chambers  9 ,  10 . In this fourth embodiment, the duct to the diaphragm is separate from the passageway between the working and compensation chambers  9 ,  10 , but the duct to the diaphragm is convoluted in a similar way to the third embodiment. 
         [0068]    Thus, referring to  FIG. 14 , the partition  7  has a main body  120  with a passageway  121  therein which links the working and compensation chambers  9 ,  10 . In  FIG. 14 , The passageway  121  Is relatively short and straight. However, it may be in the form of a spiral, or other elongate path to achieve appropriate damping characteristics. The main body  120  supports a diaphragm  122 , held between the lower part of the main body  120  and a lower plate  123 . An airspace  124  is defined between the diaphragm  122  and the lower body  123 , with that space having a duct  125  which may lead to a vacuum source (not shown) in a similar way to the duct  89  in the third embodiment. 
         [0069]    The main body  120  has a central bore  126  therein, with a cylindrical projection  127  extending apparently in the bore  126 . An upper cap  128  is fitted over that bore  126  with openings  129  which communicate with the working chamber  9 . A cylindrical projection  130  extends downwardly from the upper cap  128 . Thus, the convoluted path is defined from the working chamber  9  to the diaphragm  122 , via the openings  129 , and around the cylindrical walls  127 ,  130 , to the centre of the bore  126 . The bore  126  communicates via openings  131  with the upper surface of the diaphragm  122 . 
         [0070]    The arrangement is thus similar to the arrangement shown in  FIG. 11 , with the structure providing a smaller function to the bore  81 , projections  82  and  85 , cap  84  and openings  85  and  88 . The fluid path formed by the convolution of the duct leading from the working chamber  9  to the diaphragm  122  in this fourth embodiment gives similar effects to the corresponding fluid path in the third embodiment. However, in this fourth embodiment, that duct is wholly separate from the passageway  121 , and therefore their characteristics can be designed (by suitable size and shape of the components to achieve appropriate characteristics. This is thus different from the third embodiment, as in the second and third embodiment, where the relative dimensions of the branch to the diaphragm and the passageway between the working and compensation chambers must be chosen to achieve appropriate preferential flow, which may limit the characteristics achievable. 
         [0071]    Note that in  FIG. 14 , in the second and third embodiments, there may be an additional diaphragm  132  held on the main body  120  by a holding ring  133  to define an air space  134  between that diaphragm  132  and the main body. That air space  134  may also have a duct  135  leading to e.g. a vacuum source. Thus, by controlling any vacuum applied to ducts  125 ,  135 , the diaphragms  122 ,  132  may be switched between vibrating and non-vibrating states in a similar way to the diaphragms of the earlier embodiments.