GB2325720A

GB2325720A - Hydraulically damped mounting device

Info

Publication number: GB2325720A
Application number: GB9818457A
Authority: GB
Inventors: Michael Peter Trewhela Fursdon; Andrew Paul Smith; Martin Andrew Shaw; John Philip West; Trevor Howard Johnson
Original assignee: Avon Vibration Management Systems Ltd
Current assignee: Avon Vibration Management Systems Ltd
Priority date: 1995-12-08
Filing date: 1996-11-26
Publication date: 1998-12-02
Anticipated expiration: 2016-11-26
Also published as: GB2307965A; GB9624628D0; GB2325720B; GB9818457D0; GB2307965B

Abstract

A hydraulically damped mounting device of known construction comprises first and second relatively vibratable anchor parts. The anchor parts are interconnected by a deformable wall which itself partially bounds a working chamber for hydraulic fluid. A compensation chamber is also provided interconnected to the working chamber by a passageway (101) for the flow of hydraulic fluid. The invention constitutes the shape of the passageway (101), which is a 'flattened'spiral; that is a spiral such that half the maximum diameter (d max ) is greater than the maximum radius (r max ) in the direction perpendicular to the maximum diameter (d max ). Such a passage way has advantages in terms of packaging the device, and providing room (120) for eg a second passage, whilst maintaining a desired passageway (101) length.

Description

HYDRAULICALLY DAMPED MOUNTING DEVICE 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.

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.

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 other 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.

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.

Fig. 1 of the accompanying drawings shows one example of a "cup and boss" type of mounting device, and has been disclosed in our UK patent application No.

2282430. The mounting device is for damping vibration between two parts of a structure(not shown), and has a boss 1 connected via a fixing bolt 2 to one of the parts of the structure, and the other part of the structure is connected to a generally U-shaped cup 4. A resilient spring 5 of e.g. rubber interconnects the boss 1 and the cup 4. A partition 7 is also attached to the cup 4 adjacent the ring 6, and extends across the mouth of the cup 4. Thus, a working chamber 8 is defined within the mount, bounded by the resilient spring 5 and the partition 7.

The interior of the partition 7 defines a convoluted passageway 9 which is connected to the working chamber 8 via an opening 10 and is also connected via an opening 11 to a compensation chamber 12. Thus, when the boss 1 vibrates relative to the cup 4 (in the vertical direction in Fig. 1), the volume of the working chamber 8 will change, and hydraulic fluid in that working chamber 8 will be forced through the passageway 9 into, or out of, the compensation chamber 12. This fluid movement causes damping. The volume of the compensation chamber 12 needs to change in response to such fluid movement, and therefore the compensation chamber 12 is bounded by a flexible wall 13.

The above structure is generally similar to that described in EP-A-0115417, and the manner of operation is similar. In EP-A-0115417, the partition supported a diaphragm which acted as a boundary between fluid in the working chamber and a gas pocket. In the arrangement shown as Fig. 1, there is an annular diaphragm 50 which is convoluted. That diaphragm 50 is held on the partition 7 by an upper snubber plate 22, that snubber plate 22 is held in pace by a ring 40, which is clamped to the partition 7 and to the cup 4, by a clamping ring 41. The resilient spring 5 is also connected to the ring 40. The upper snubber plate 22 has openings 21 which permits fluid in the working chamber 8 to contact the diaphragm 50.

In the arrangement shown in Fig. 1, the passageway 9 is in the form of a spiral, and the internal dimensions of that spiral are uniform.

According to the first aspect of the present invention, however, the height (in the direction of vibration) and/or the width (perpendicular to the direction of vibration) vary along the length of the passageway.

Although the present invention was developed for a spiral passageway, it should be noted that the present invention is not limited to the case where the passageway forms a perfect spiral of regularly decreasing radius around the spiral, based on a common centre of curvature.

It is applicable to spirals where the radius changes stepwise, and also spirals in which the centre of curvature is not a single point, and instead there are multiple centre of curvature. The present invention is also applicable to a "flattened" spiral, which will be discussed in more detail later.

Normally, the cross-sectional area of the passageway will be constant, to ensure a uniform damping action.

Hence, there needs to be a relationship between the variation of the height and width of the channel to ensure that the cross-sectional area is uniform.

By incorporating a passageway of varying height and/or width into a hydraulically damped mounting device, it is possible to design and manufacture the mount more efficiently. It can seen from Fig. 1 that the overall diameter of the passageway 9 in that arrangement is limited, because it must fit within the annular diaphragm 50. If the height reduces with increasing radius, it is then possible for the passageway 9 to extend under the diaphragm 50. This enables a longer passageway to be formed, or permits the mount to have a smaller transverse dimension for a given passageway length. This passageway configuration also permits the height of the mount to be reduced.

It should be noticed that the changes in height and/or width along the passageway should be smooth, so that there are no abrupt changes. The angle of taper of the walls of the passageway relative to the central line of the passageway should therefore not exceed 800. In practice, taper angles of 300 or less are preferred.

There are thus no step changes in the height/width of the passageway. Where the walls are curved relative to the centre line, the taper angle is then defined by the tangent to the wall at that point.

In principle, this restriction on taper angles should extend over the whole length of the passageway.

In practice, more abrupt changes are possible at the ends of the passageway, but the smooth changes should occur over the majority of the length of the passageway, preferably 90% of the passageway, excluding the 5% at each end.

As mentioned above, the present invention is not limited to the case where the invention is a "true" spiral. It has been realised that the use of a "flattened" spiral offers advantages in an hydraulically damped mounting device. In a flattened spiral, half the maximum diameter is greater than the maximum radius in the direction perpendicular to the maximum diameter.

Thus, the radius of the spiral does not continuously decrease, but it increases and decreases over a half turn of the spiral.

Again, such a flattened spiral is applicable not only to true spiral with a common centre of curative, but also to modified spirals in which the passageway has curved sections which do not have a common centre of curvature. Although such a flattened spiral is particularly useful in arrangements in which the internal dimensions of the passageway vary as discussed above with reference to the first aspect of the present invention, such a flattened spiral represents a second independent aspect of the present invention.

The use of such a flattened spiral has the advantage that an area is created on the partition for any purpose desired, such as the provision of a diaphragm, an additional passageway, etc.

Embodiments of the present invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: Fig 1 is sectional view through a known hydraulically damped mounting device, and has already been discussed; Fig 2 shows a partition which may be incorporated in a hydraulically damped mounting device according to the present invention; Fig 3 shows the configuration of a spiral passageway which may be used in the present invention; Fig 4 shows a schematic drawing of an alternative spiral passageway which may be used in the present invention.

Fig 2 shows a cross-section of a view of a partition 100 which may be incorporated in a hydraulically damped mounting device. The hydraulically damped mounting device may be otherwise identical to that of the arrangement shown in Fig. 1, so that the partition 100 replaces the partition 7 in the arrangement of Fig 1.

The partition 100 has a passageway 101 therein, which passageway extends from an opening 102 which will communicate with the working chamber 8, and an opening 103 which will communicate with the compensation chamber 12. As shown in Fig. 2 the partition 100 has a main partition plate 104, having a groove 105 therein, the groove 105 then being covered by a cover plate 106, thereby closing the groove 105 except at the opening 103 and thus forming the passage way 101. As in the arrangement of Fig. 1, an annular diaphragm 106 is mounted on the main partition plate 104 of the partition 100, and secured thereto by an upper snubber plate 107.

Again, there are holes 108 in the upper snubber plate 107 to permit fluid communication through the upper snubber plate 107 from the working chamber 8 to the diaphragm 106.

In the arrangement of Fig. 2, the diaphragm 106 is convoluted. The advantages of such convolutions are discussed in our UK patent application 2282430 and will not be discussed in more detail now.

As can be seen from Fig. 2, the passageway 101 has a height in the direction of vibration of the mount, which changes along the length of the passageway 101. The height is larger towards the centre of the passageway than it is at the outer regions. The passageway 101 is preferably in the form of a spiral, with the height of the passageway increasing with decreasing radius. The height decrease is preferably continuous, but may be stepwise if preferred.

However, it is desirable that the passageway 101 has a uniform cross-sectional area. Therefore, the width of the passageway 101 decreases with decreasing height except possibly immediately adjacent the openings 102 and 103. For practical purposes the passageway 101 has a centerline which sits on an approximate, though not true, spiral configuration. The cross-sectional area is constant and approximately rectangular along the length of the passageway; however the height and width of this area are continuously varying along the length of the passageway. The height of the passageway, at a point 'P' on the passageway centerline is related to the point which is regarded as the centre of the spiral by a mathematical function such as; height(h)= C1 + [(Q-R)/Q113 where R is the distance of the point P' from the centre of the spiral, and where C1, C2 and C3 are numerical constants chosen to suit the geometry required. Other mathematical functions may be used.

The width of the passageway at a point is related to the depth at the same point by the mathematical function; width = A/h where A is the cross-sectional area of the passageway (constant along length of passageway), and h is the height of the passageway.

The use of this function ensures that the changes in width and height of the passageway are smooth, as previously defined, so that there are no steps in the walls of the passageway.

The position of points on the spiral are calculated iteratively using polar coordinates, starting at 0 (the innermost point on the spiral). Each iteration represents a step of angle i along the spiral.

The procedure for calculating the position of points is set out below.

1. Let 6 (angle of starting point of spiral) = 0 2. Let R = distance from centre to start-point of spiral 3. Polar coordinates of point P = (R,0) 4. Calculate width W' of channel at point P - use procedure described above 5. Calculate spiral development factor 'F' at point P; F= (W + t)/(360/i) where t is the wall thickness between channels (constant), where i is the size of the angular step taken from each iteration.

6. Calculate polar coordinates of next point; hew = R + F 8new = 8 + i 7. Let R = hew and 8 = anew 8. Go to step 3, above and continue procedure.

The above iterative procedure is continued until sufficient length of spiral is achieved.

In such an arrangement therefore, the passageway 101 extends under the diaphragm 106, unlike the arrangement shown in Fig. 1 where the passageway is confined to the interior of the annular diaphragm 50. Thus, for a given mount size, the passageway can be longer. In practice, the present invention also permits a greater amount of partition material surrounding the passageway 101, which permits greater partition strength.

In the partition shown in Fig. 2, the spiral may be a "true" one, in which the radius increases along the spiral from the opening 102 to the opening 103, with a common centre. It is applicable to arrangements which depart from a "true" spiral, in which the passageway 101 has curved section with stepwise changes in radius, and possibly not a common centre of curvature.

Fig. 3 illustrates a partition in which the spiral is a flattened one. In such a flattened spiral, there will be maximum transverse diameter dmaX, along the long axis of the spiral and a significantly smaller transverse diameter dt in the perpendicular direction. Around the spiral, the radius both increases and decreases so that half dXX is greater than rt > X where r,,, is the maximum radius in the direction perpendicular to the direction dtnax The advantage of using such a flattened spiral is also illustrated in Fig. 3, namely at an area 120 is created in the partition 100 where there is no passageway 101. This space 120 may be used for eg. a diaphragm.

Alternatively, the space 120 may be used for a second passageway interconnecting the working and compensation chambers 8,12.

It can also be seen from Fig. 3 that the passageway 101 changes width. In the direction of the maximum transverse diameter dRx, the width is w1 whilst in the perpendicular direction (the direction of dp) the width is w2. The change in width occurs because of the manner of design of the passageway 101. It is relatively simple to design a flattened spiral by computer graphics by first forming a true spiral, and then scaling that spiral by one factor in the direction of dx and a smaller factor in the perpendicular direction. However, the width of the channel is then also changed by the scaling factor. The result in order to maintain constant cross-sectional area within the passageway 101, is that the channel height will have to vary.

Fig. 4 then illustrates a modification of the flattened spiral Fig. 3, in which the width is constant, such that w1 is equal to w2. Thus, in order to obtain the advantages of the flattened spiral, it is not necessary for the width of the channel to vary. In a further alternative, the width of the flattened spiral increases from the opening 102 to the opening 103, to enable it to pass under a diaphragm as in the arrangement of Fig. 2.

Claims

CLAIMS:

1. A hydraulically damped mounting device comprising first and second anchor parts vibratable relative to each other in a predetermined direction, a deformable wall interconnecting the first and second anchor parts, a working chamber for hydraulic fluid at least partially bounded by the deformable wall, a compensation chamber for the hydraulic fluid, and a passageway interconnecting the working and compensation chambers for flow of the hydraulic fluid therethrough between the working and compensation chambers, wherein the passageway is in the form of a spiral and wherein the spiral is such that half the maximum diameter is greater than the maximum radius in the direction perpendicular to the maximum diameter.

2. A hydraulically damped mounting device according to claim 1, wherein the passageway is in a rigid partition rigidly connected to one of the anchor parts and partially bounding the working chamber.

3. A hydraulically damped mounting device according to claim 2, wherein the partition supports a diaphragm, the diaphragm separating the hydraulic fluid in the working chamber and a gas pocket.

4. A hydraulically damped mounting device according to claim 3, wherein the diaphragm is annular.

5. A hydraulically damped mounting device according to claim 3 or claim 4, wherein the passageway extends in the partition so as to overlap the diaphragm.

6. A hydraulically damped mounting device substantially has herein described with reference to and as illustrated in Fig. 4 of the accompanying drawings.