WO2000001956A1

WO2000001956A1 - Anti-vibration apparatus

Info

Publication number: WO2000001956A1
Application number: PCT/GB1999/001264
Authority: WO
Inventors: Pascal Tournier
Original assignee: Draftex Industries Limited
Priority date: 1998-07-07
Filing date: 1999-04-23
Publication date: 2000-01-13
Also published as: GB2339259A; GB2339259B; GB9814761D0

Abstract

An engine mount for use in a vehicle comprises a pin (20) for connection to the engine and a support plate (22) for connection to the chassis or body of the vehicle. The support plate (22) defines an aperture with a turned-down edge (24). A stiff but resilient cone-shaped hollow support (30), made of rubber preferably, supports the engine from the support plate (22) and flexes in response to engine vibrations. The rubber support (30) defines a chamber (32) which is closed off by a base plate (34) but is open to a resonator (38), the chamber (32) and the resonator (38) being filled with hydraulic fluid. The resonator (38) comprises a longitudinally extending passageway (39) having a plurality of flexibly walled volumes (40, 42, 44, 46, 48) in the form of bellows turns which are positioned at respectively different predetermined positions along the length of the passageway (39) for providing the passageway (39) with correspondingly different resonant frequencies for the hydraulic fluid which oscillates along the passageway in response to engine vibrations. In this way, the resonator (38) causes damping at corresponding frequencies.

Description

ANTI- VIBRATION APPARATUS

The invention relates to a vibration damping arrangement, comprising an elongate

passageway containing hydraulic fluid, means for causing the fluid to oscillate along the

passageway in response to the vibrations, and means defining at least one flexible walled

volume open to the passageway to provide the passageway with a corresponding resonant

frequency for the fluid oscillating along the passageway whereby to damp or reduce the

transmission of the vibrations at that frequency.

The invention also relates to an engine mount, for supporting the engine of a vehicle

relative to the chassis or body of the vehicle and for damping vibrations of the engine

relative to the chassis or body, comprising a first rigid element for connection to the

engine, a second rigid element for connecting to the chassis or body, support means made

of stiff resilient material extending between the two elements for relatively supporting

them and flexing in response to the vibrations, and an enclosure partly defined by and

within the support means and filled with hydraulic fluid, the enclosure including an

elongate passageway along which the fluid oscillates in response to the vibrations and

having a resonant frequency dependent on the length of the passageway to cause damping

of the vibrations of that frequency.

The invention further relates to mounting apparatus for mounting part of the engine or transmission of a vehicle relative to the chassis or body thereof, comprising first and

second rigid elements for respective connection to the said part of the engine or

transmission and to the chassis or body for relative vibration therewith, support means

comprising stiff resilient material extending between the two elements for relatively

supporting them and flexing alternately in first and second opposite directions in response

to the vibrations, means defining a first flexibly walled chamber mounted between the

support means and a first part of the first element so as to be compressed by flexing of the

support means in the first direction and to expand in response to flexing of the support

means in the second direction, means defining a second flexibly walled chamber mounted

between the support means and a second part of the first rigid element so as to be

compressed by flexing of the support means in the second direction and to expand in

response to flexing of the support means in the first direction, and an elongate

passageway between and interconnecting the two chambers, the two chambers and the

passageway being filled with hydraulic fluid which oscillates along the passageway in

response to the vibrations at a resonant frequency dependent on the length of the

passageway whereby to damp vibrations at that frequency.

Such arrangements, engine mounts and mounting apparatus are shown, for example, in

EP-A-0 012 638. There is shown an engine mount having a working chamber filled with

hydraulic fluid which also fills passageways leading from the working chamber to

terminate in flexible walled volumes in the form of thin- walled lateral chambers. In such

an engine mount, fluid is pumped to and fro along the passageways by the flexing of a stiff rubber support which forms part of the wall of the working chamber and flexes with

the vibrations to be damped. The passageways provide a resonant frequency for the

oscillating fluid, the resilient frequency being dependent on various parameters including

the dimensions of each passageway.

Another such engine mount is shown, for example, in EP-A-0 277 056. In this known

arrangement, fluid in the working chamber flows to and fro, according to the flexing of

a rubber support forming part of the wall of the working chamber along an elongate tube¬

like passageway which extends away from the body of the engine mount to terminate in

a bulb having a flexible wall. Again, the resonant frequency for the oscillating fluid in

the passageway depends on various parameters including the dimensions of the

passageway.

According to the invention, the known form of arrangement as first set forth above is

characterised in that the flexible walled volume is positioned intermediate the ends of the

passageway between two relatively stiff-walled portions thereof.

According to the invention, the known form of first engine mount as first set forth above

is characterised by means defining at least one flexible-walled volume connected to the

passageway at a predetermined position along its length and between its ends to provide

the passageway with a predetermined resonant frequency for the oscillating fluid to cause

damping of the vibrations at that frequency. According to the invention, the known form of mounting apparatus as first set forth above

is characterised by means defining at least one flexible walled volume connected to the

passageway at a predetermined position intermediate its ends to provide the passageway

with a corresponding further resonant frequency for the oscillating fluid to cause damping

of the vibrations at a corresponding frequency.

Anti- vibration apparatus, in the form of hydroelastic mounts for mounting or limiting the

movement of the engine or other part of a motor vehicle, and embodying the invention,

will now be described, by way of example only, with reference to the accompanying

diagrammatic drawings in which:

Figure 1 is a cross-section through one of the engine mounts having a resonant conduit

or passageway containing hydraulic fluid responsive to vibrations;

Figure 2 is a diagram for explaining the operation of the resonant conduit or passageway

of Figure 1;

Figure 3 corresponds to Figure 1 but shows a modification;

Figure 4 corresponds to Figure 1 but shows a further modification; Figure 5 is a cross-section through a modified form of a resonant conduit or passageway;

Figure 6 is a cross-section on the line VI- VI of Figure 7 through another of the engine

mounts having a resonant conduit or passageway:

Figure 7 is an underside view of the engine mount of Figure 5 but with some parts

removed;

Figure 8 is a cross-section through a detail of another of the engine mounts;

Figure 9 is an end view of another of the engine mounts; and

Figure 10 is a cross-section through another form of the apparatus constructed as a

movement limiter.

The vibration damping apparatus of Figure 1 is in the form of an engine mount for

supporting the engine of the vehicle from the body or chassis of the vehicle. The engine

mount comprises a rigid metal bolt or pin 20 which use is in rigidly attached to the engine

by means of a suitable bracket. In addition, the engine mount incorporates a rigid metal

support plate 22 having an aperture with a turned-down edge 24 and holes 26 by means

of which the plate is bolted to the chassis or body of the vehicle. The pin 20 is rigid with a metal bush 28 to which is bonded a cone-shaped rubber support 30 which defines a

hollow chamber 32 and whose generally circular base is bonded to the turned-down edge

24 of the plate 22. A rigid base plate 34 is sealingly attached to the turned-down edge 24

of the aperture in the plate 22 and closes off the chamber 32 except for a through hole 36.

Hole 36 connects with the interior of a flexible elongate resonator 38 comprises a

relatively stiff- walled passageway 39 interrupted by flexible walled volumes formed by

spaced flexible bellows turns 40,42,44,46,48 of progressively increasing diameter as

shown.

The chamber 32 and the resonator 38 are filled with suitable hydraulic fluid.

The rubber support 30 supports the static weight of the engine with respect to the body

or chassis of the vehicle and flexes resiliently in response to vibratory movements of the

engine. Such vibrations may be of low frequency and relatively large amplitude, such as

caused by movements of the engine as the vehicle is subjected to changes in the contour

or curvature of the road. Instead, they can be higher frequency and of lower amplitude

such as caused by the moving parts within the engine (e.g. when the engine is running at

idling speed).

In response to the vibrations, therefore, the flexing of the rubber support 30 produces a

pumping action on the hydraulic fluid which thus oscillates within the resonator 38 in

dependence on the frequency of the vibration. The bellows turns 40,42,44,46,48 provide the resonator with correspondingly different

resonant frequencies for the oscillating fluid within the passageway 39. Accordingly, the

resonator 38 acts on the fluid to cause damping at corresponding frequencies of vibration.

The operation will be described in more detail with reference to Figure 2 which

illustrates, in diagrammatic form, the mechanical operations taking place within the

engine mount.

As shown in Figure 2, a plate A is assumed to be vibrating to and fro in the direction of

the arrows shown. The vibrations are transmitted by a spring B to a piston C acting on

hydraulic fluid within a chamber D.

The vibrations of the plate A correspond to the vibrations of the engine in the engine

mount of Figure 1. As already explained, these vibrations cause flexing of the rubber

support 30 (corresponding to the spring B in Figure 2), and produce a pumping action on

the fluid within the chamber 32 (corresponding to the action of the piston C on the fluid

in the chamber D of Figure 2). As shown in Figure 2, the fluid is thus pumped to and fro

along the passageway E which corresponds to the passageway 39 of resonator 38 of

Figure 1, except that the passageway E of Figure 2 is shown as only having two bellows

turns F and G instead of the several bellows turns of Figure 1. When the vibrations have a relatively high frequency (and, generally, relatively low

amplitude), the to and fro movement of the hydraulic fluid within the passageway E takes

place along only a restricted part of its length indicated at H. The flexible bellows turns

F act at this frequency, causing the required damping.

However, at lower frequencies of vibration, when the vibrations have larger amplitude,

the to and fro movement of the fluid extends along the whole length of the passageway

E as shown by the arrow I, and the larger diameter bellows turns G come into operation

to produce the required damping.

At intermediate vibration frequencies, that is, between the high frequency vibrations

causing the fluid movement H and the low frequency vibrations causing the fluid

movement I, the fluid will move to and fro along respectively intermediate lengths of the

resonator and will be affected by the appropriate intermediate bellows turn shown in

Figure 1.

Therefore, the bellows turns are positioned and arranged so that they provide respectively

different resonant frequencies for the fluid oscillating in the passageway 39, thus

providing damping of the vibrations at these frequencies.

In order to protect the resonator 38 shown in Figure 1, it is desirable in practice to encase it within a cover shown dotted at 50.

The resonator 38 can be formed in a single piece by blow extrusion or blow injection.

The operation of the resonator 38 can be adjusted to produce the required damping

characteristics by appropriate adjustment of various parameters:

(a) the ratio of the cross-section of the chamber 32 to the cross-section of the

passageway 39;

(b) the length of the passageway 39;

(c) by varying the cross-section of the passageway 39 along its length;

(d) by varying the number, position, size and flexibility of the bellows turns.

Items in Figure 3 corresponding to items in Figure 1 are similarly referenced.

In Figure 3, the wall defining the working chamber 32 is itself provided with a flexible

wall 51 which acts in the same way as the flexible bellows turns of the resonator 38 of

Figure I . The flexible wall 51 has a relatively large width portion 51 A which acts to

provide dynamic damping at relatively high frequencies. A relatively lesser width portion 5 IB acts to provide dynamic damping at lower frequencies, such as corresponding to

engine idling. The resonator shown at 52 acts at still lower frequencies.

In effect, for a certain rate of flow of the fluid caused by the pumping action of the rubber

support 30, the speed of the fluid flow depends on the cross-sectional area of each part

of the flow path. The inertia of the fluid is a function of the square of its flow rate, and

consequently a variation of the cross-sectional area produces a strong variation of the

inertia of the fluid.

Figure 4 corresponds to Figure 3 and items corresponding to those in the preceding

Figures are similarly referenced. In the arrangement shown in Figure 4, the resonator 53

has bellows arrangements 54 and 55 connected in parallel to the passageway 39, instead

of in series with it, but acting in the same way at relatively high frequencies. A resonator

56 acts at lower frequencies.

Figure 5 shows how the resonator 53 in Figure 4 can be modified to provide a branched

arrangement with two passageways 39A and 39B and a "Y" junction 57.

In Figures 6 and 7, items corresponding to those in other Figures are correspondingly

referenced. In Figure 6, the working chamber 32 is closed off by a plate 58 which is

apertured at 59 to connect with one end of a helical conduit 60 formed in a block 61. The

helical conduit 60 is connected to two bellows 62 and 63 at intervals along its length. These bellows are omitted from Figure 7 (but shown dotted there), and Figure 7 shows

the shape of the conduit 60. When the vibrations have a relatively high frequency (and,

generally, relatively low amplitude), the to and fro movement of the hydraulic fluid along

the conduit 60 in response to the pumping action of the rubber support 30 takes place

along only a restricted part of its length. The flexible bellows turns 62 act at this

frequency, causing the required damping.

the to and fro movement of the fluid extends along a greater length of the conduit 60, and

the larger diameter bellows turns 63 come into operation to produce the required

damping.

The arrangements shown in the various Figures can be used with advantage in engine

mounts (or similar supports) which are required to provide strong damping. In such

cases, particularly where the engine mounts are dimensionally small, very high pressure

variations can occur in the fluid. In such cases, the fluid may vaporise or any gas bubbles

entrained in the fluid may expand considerably, causing the support to act pneumatically

instead of hydraulically and thus with reduced damping. However, a resonator of the type

described can be used to provide two different resonant frequencies at which damping

occurs instead of only a single resonant frequency. One of the two resonant frequencies

is above and the other below the single resonant frequency. This enables the frequency band for high damping to be enlarged without requiring a very high fluid pressure.

Figure 8 shows a modification in which the flexible bellows in the passageway 39 of the

engine mount of Figure 1 is replaced with a flexible membrane 64 to form a Helmotz

resonator.

Figure 9 shows another of the vibration damping arrangements but in an axi-symmetrical

form. Here, a rigid metal bush 65 is adapted to be rigidly connected to the engine, and

an outer rigid metal circular casing 66 is adapted to be secured to the chassis or body of

the vehicle, such as by an U-shaped clamp (not shown). The bush 65 is bonded to a yoke

made of stiff rubber 67 which extends radially outwardly in opposite directions and is

bonded to the inside surface of the casing 66. The rubber yoke 67 defines diametrically

opposite hollow spaces 68 and 69, each containing a flexible-walled hollow chamber

70,72. Chambers 70,72 may be made of flexible plastics material. They are connected

by a passageway 74 which incorporates flexible bellows arrangements 76 and 78. The

chambers 70,72 are filled with hydraulic liquid which also fills the passageway 74 and

the bellows arrangements 76,78.

When vibrations of the engine take place in the directions of the arrow shown in Figure

9, the bush 65 oscillates in these directions with reference to the casing 66, thus

compressing and expanding the chambers 70,72 alternately. The hydraulic fluid is thus

pumped to and fro between the two chambers at a corresponding frequency along the passageway 74.

At low frequencies, damping is effected by the passage of the liquid along the complete

length of the passageway 74 from one chamber 70 or 72 to the other.

At higher frequencies, with lower amplitude vibrations, the fluid does not flow along the

full length of the passageway 74 between the two chambers. Instead, it flows from each

chamber to the adjacent flexible bellows arrangements 76,78 which produces the required

damping effect, in the manner explained with reference to Figures 1 to 7.

The arrangement shown in Figure 9 could instead be used as one end of an engine-

movement restraining link - for connecting a point on the engine to a point on the vehicle

chassis or body to prevent undue movement of the engine in response to changes in

engine torque.

Figure 10 shows vibration-damping arrangement in the form of a movement-limiter such

as for limiting movement of the engine of a vehicle relative to the chassis or body of the

vehicle, or for similarly limiting movement of some other part of the vehicle such as its

gearbox or transmission. A central rigid metal boss 80 has a hole 82 by means of which

it can be bolted to an arm 84 rigid with the engine or other part. Rubber stops 86 and 88

engage respective fixed parts 90 and 92 of an element rigid with the vehicle body or

chassis. The rubber stops 86 and 88 are integrated in the chambers 98 and 100. They can be bonded to or simply in contact with the boss 80.

Each rubber support 86,88 is enclosed within a respective flexible cover or bellows 94,96.

The cover 94 defines a chamber 98 having an outer part 98A connected via bores 98B

through the rubber support 86 to an inner part 98C. Cover 96 defines a similarly arranged

chamber 100. Chambers 98 and 100 are filled with an hydraulic liquid which also fills

a passageway 102 extending through the boss 80 and a side channel 104 which terminates

in a flexible bellows 106.

Instead, parts 90 and 92 can be fixed to or part of the engine and the part 80 can be fixed

to the chassis or body of the vehicle. In such a configuration, the bellows 94,96 are less

subjected to the high temperature of the engine.

Vibration of the engine or other supported part in the direction of the arrows shown

causes resilient flexing of the rubber supports 86,88 and thus alternate compression and

expansion of the chambers 98 and 100. The hydraulic fluid is thus pumped to and fro

along the passageway 102, the movement of the fluid being damped by the bellows

arrangement 106 in the manner already explained.

Claims

1. A vibration damping arrangement, comprising an elongate passageway

(39,E,60,74,102) containing hydraulic fluid, means (30,67,86,8) for causing the fluid to

oscillate along the passageway (39,E,60,74,102) in response to the vibrations, and means

defining at least one flexible walled volume (40,42,44,46,F,51,54,55,62,63,64,76,78,106)

open to the passageway to provide the passageway with a corresponding resonant

frequency for the fluid oscillating along the passageway

(40,42,44,46,F,51 ,54,55,62,63,64,76,78, 106) whereby to damp or reduce the transmission

of the vibrations at that frequency, characterised in that the flexible walled volume

(40,42,44,46,F,51,54,55,62,63,64,76,78,106) is positioned intermediate the ends of the

passageway (39,E,60,74, 102) between two relatively stiff-walled portions thereof.

2. An arrangement according to claim 1, characterised in that the passageway

(39,E,60,74,102) is terminated in another flexible walled volume

(48,G, 52,56,63, 70,72,94,96) to provide the passageway with another corresponding

resonant frequency for the fluid oscillating along the passageway (39,E,60,74,102)

whereby to damp the vibrations at that frequency.

3. An arrangement according to claim 1 or 2, characterised in that there are at least

two of the flexible walled volumes (40,42,44,46,54,55,78,78) open to the passageway (39,E,60,74,102), at positions intermediate the ends of the passageway (39,E,60,74,102),

each volume being positioned at a respective predetermined position therealong to

provide the passageway (39,E,60,74,102) with correspondingly different resonant

frequencies for the fluid oscillating along the passageway whereby to damp the vibrations

at those frequencies.

4. An arrangement according to any preceding claim 1, characterised in that the

flexible walled volume (40,42,44,46,F,51,54,55,62,63,64,76,78,106) or at least one of the

flexible walled volumes (40,42,44,46,F,51,54,55,62,63, 64,76,78,106) comprises at least

one bellows turn.

5. An arrangement according to any one of claims 1 to 3, characterised in that the

flexible walled volume or at least one of the flexibly walled volumes comprises a flexible

membrane (64).

6. An arrangement according to any preceding claim, characterised in that the

passageway (39,E,60,74, 102) is relatively stiff-walled, and the or each volume

(40,42,44,46,F, 51,54,55,62,63,64,76,78,106) intermediate the ends of the passageway

(39,E,60,74, 102) interrupts the stiff walls of the passageway (39,E,60,74, 102).

7. An arrangement according to any one of claims 1 to 5, characterised in that the

passageway is relatively stiff- walled and the flexible walled volume (54, 106) or at least one of the volumes (54,106) intermediate the ends of the passageway

(40,42,44,46,F,51,54,55,62,63,64,76,78,106) is positioned in a respective stiff-walled

passage (39B,104) connected in parallel with the passageway (39,102).

8. An arrangement according to any preceding claim, characterised in that the

elongate passageway (60) is helical.

9. An arrangement according to any preceding claim for damping vibration between

two relatively vibratable rigid members, characterised by first and second rigid elements

(20,22;84,90,92) for respective connection to the rigid members to vibrate therewith and

stiff resilient support means (30,86,88) extending between the rigid elements

(20,22;84,90,92) and relatively supporting them and resiliently flexing in response to the

vibrations, the means for causing the fluid to oscillate along the passageway (39,102)

comprising means responsive to the flexing of the support means.

10. An arrangement according to claim 9, characterised in that the passageway forms

part of an enclosure (32,100) filled with the fluid.

11. An arrangement according to claim 10, characterised in that the enclosure is partly

defined by the support means (30,86,88).

12. An arrangement according to any one of claims 1 to 6, characterised by means defining two flexible-walled chambers (70,72,94,96) connected by the passageway, the

means for causing the fluid to oscillate along the passageway (74,102) in response to the

vibrations comprising means for respectively and altematingly compressing and

expanding the chambers (70,72,94,96) in response to the vibrations.

13. An arrangement according to claim 12, for damping vibration between two

relatively vibratable rigid member, comprising first and second rigid elements (66,65) for

respective connection to the rigid members to vibrate therewith, and support means (67)

made of stiff resilient material and extending from the second rigid element (65) to first

and second parts of the first rigid element (66) for relatively supporting the two elements

and resiliently flexing in first and second opposite directions in response to the vibrations,

one of the chambers (70) being mounted between the second rigid element (65) and the

first part of the first rigid element (66) so as to be compressed in response to vibration in

the first direction and expanded in response to vibration in the second direction, and the

other chamber (72) being mounted between the second rigid element (65) and the second

part of the first rigid element (66) so as to be compressed by vibration in the second

direction and expanded by vibration in the first direction.

14. An arrangement according to claim 13, characterised in that the first element

embraces an area including the second element.

15. An arrangement according to claim 14, characterised in that the first element (66) encircles the area and the second element (65) is mounted substantially at the centre of

the area so that the first and second directions extend oppositely along a diameter of the

area and the support means (67) extends radially and transverse to the diameter to define

two spaces positioned at opposite ends of the diameter in which are respectively located

the two chambers (70,72).

16. An arrangement according to claim 12, for damping vibration between two

relatively vibratable rigid members, characterised by first and second rigid elements

(90,92; 80) for respective connection to the rigid members to vibrate therewith, in that the

second element (80) is positioned between first and second spaced parts (90,92) of the

first element for movement in response to the vibrations towards each part in turn and

simultaneously away from the other, and by first and second support means (86,88) made

of stiff resilient material and respectively extending between the second rigid (80)

element and the first part (90) of the first rigid element and between the second rigid

element (80) and the second part (92) of the first rigid element for supporting the two

rigid elements (80,90,92) relative to each other and for resiliently flexing in response to

the vibrations.

17. An arrangement according to claim 16, characterised in that one chamber (98) is

defined between the second rigid element (80) and the first part (90) of the first rigid

element and the other chamber ( 100) is defined between the second rigid element (80) and

the second part (92) of the first rigid element.

18. An arrangement according to claim 17, characterised in that the chambers

(98,100) are respectively and at least partly defined by the respective support means

(86,88).

19. An arrangement according to any one of claims 16 to 18, characterised in that the

passageway (102) extends between the chambers through the second rigid element (80).

20. An engine mount, for supporting the engine of a vehicle relative to the chassis or

body of the vehicle and for damping vibrations of the engine relative to the chassis or

body, comprising a first rigid element (20,65) for connection to the engine, a second rigid

element (22,66) for connecting to the chassis or body, support means (30,67) made of stiff

resilient material extending between the two elements (20,65 ;22,66) for relatively

supporting them and flexing in response to the vibrations, and an enclosure (32,70,72)

partly defined by and within the support means (30,67) and filled with hydraulic fluid, the

enclosure including an elongate passageway (39,60,74) along which the fluid oscillates

in response to the vibrations and having a resonant frequency dependent on the length of

the passageway (39,60,74) to cause damping of the vibrations of that frequency,

characterised by means defining at least one flexible-walled volume

(40,42,44,45,54,55,60,62, 64,70,78) connected to the passageway (39,60,74) at a

predetermined position along its length and between its ends to provide the passageway

(39,60,74) with a predetermined resonant frequency for the oscillating fluid to cause

damping of the vibrations at that frequency.

21. An engine mount according to claim 20, characterised in that there are a plurality

of the flexible walled volumes (40,42,44,46,54,55,76,78) connected to the passageway

(39,74) at respectively different predetermined positions along its length and between its

ends for providing the passageway with corresponding different predetermined resonant

frequencies for the oscillating fluid to cause damping of the vibrations at corresponding

frequencies.

22. An engine mount according to claim 20 or 21 , characterised in that the passageway

(39,60,74) is relatively stiff-walled and the or each flexible walled volume

(40,42,44,46,54,55,60,62, 64,70,78) interrupts the stiff wall.

23. An engine mount according to claim 20 or 21 , characterised in that the passageway

(39,60) is relatively stiff- walled and the or each flexibly walled volume (54,62,63,64) is

positioned in a respective stiff-walled passage (39B) connected in parallel to the

passageway (39,60).

24. An engine mount according to any one of claims 20 to 23, characterised in that the

flexibly walled volume or one of the flexibly walled volumes is defined by a flexible

membrane (64).

25. An engine mount according to any one of claims 20 to 24, characterised in that the

passageway (60) is helical.

26. An engine mount according to any one of claims 20 to 25, a further flexibly walled

volume (48,56,70 or 72) which terminates the passageway.

27. An engine mount according to any one of claims 20 to 26, characterised in that the

or each flexibly walled volume (40,42,44,46,48,56,76,78) is defined by one or more

bellows turns.

28. An engine mount according to any one of claims 20 to 27, characterised by a

substantially rigid protective cover (50) enclosing the passageway (39).

29. Mounting apparatus for mounting part of the engine or transmission of a vehicle

relative to the chassis or body thereof, comprising first and second rigid elements

(66,65,90,92,80) for respective connection to the said part of the engine or transmission

and to the chassis or body for relative vibration therewith, support means (67,86,88)

comprising stiff resilient material extending between the two elements (66,65;90,92,80)

for relatively supporting them and flexing alternately in first and second opposite

directions in response to the vibrations, means defining a first flexibly walled chamber

(70,98) mounted between the support means (67,86,88) and a first part of the first element

(66,90,92) so as to be compressed by flexing of the support means (67,86,88) in the first

direction and to expand in response to flexing of the support means (67,86,88) in the

second direction, means defining a second flexibly walled chamber (72,100) mounted

between the support means (67,86,88) and a second part of the first rigid element (66,90,92) so as to be compressed by flexing of the support means (67,86,88) in the

second direction and to expand in response to flexing of the support means (67,86,88) in

the first direction, and an elongate passageway (74,102) between and interconnecting the

two chambers (70,72,98,100), the two chambers (70,72,98,100) and the passageway

(74,102) being filled with hydraulic fluid which oscillates along the passageway in

passageway (74,102) whereby to damp vibrations at that frequency, characterised by

means defining at least one flexible walled volume (76,78,106) connected to the

passageway (74,102) at a predetermined position intermediate its ends to provide the

passageway with a corresponding further resonant frequency for the oscillating fluid to

cause damping of the vibrations at a corresponding frequency.

30. Mounting apparatus according to claim 29, characterised in that the first rigid

element (66) is generally circular and the second rigid element (65) is mounted

substantially centrally thereof, the support means (67) extending radially in opposite

directions from the second rigid element (65) to the first rigid element (66) so that the first

and second directions extend oppositely along a diameter extending transverse to the

radial directions, the first and second parts of the first element (66) comprising portions

thereof positioned at opposite ends of the diameter, and the support means (67) defining

two spaces positioned at opposite end portions of the diameter, the two flexibly walled

chambers (70,72) being respectively mounted within the spaces.

31. Mounting apparatus according to claim 29, characterised in that there are at least

two of the flexibly walled volumes (76,78) connected to the passageway (74) intermediate

its ends, the flexibly walled volumes (76,78) being connected thereto at respectively

different predetermined positions along the length of the passageway (74) to provide the

passageway with correspondingly different resonant frequencies for the oscillating fluid

to cause damping of the vibrations at correspondingly different frequencies.

32. Apparatus according to claim 29, characterised in that the passageway (102)

extends through the second rigid element (80).

33. Apparatus according to any one of claims 29 to 32, characterised in that the or each

flexibly walled volume (76,78,106) is defined by one or more bellows turns.