A controllable support element

Abstract: An engine mount comprises a relatively stiff elastomeric member (14) having an interior defining a chamber (35) containing hydraulic liquid. The member (14) is attached to the engine (10) via a screw (18), and is attached to the vehicle body (12) via flanges (22,24). A flexible wall (32) defines a second chamber (36) and the two chambers (35,36) are connected by a restricted (e.g. helicoidal) channel (38,40,41) in a dividing wall (33). Engine vibration is transmitted to the liquid in the chamber (35) via the member (14), and damping takes place because of the resistance to the flow of liquid between the two chambers (35,36) and/or because of oscillation of the mass of the liquid in the channel (38). In addition, a flexible membrane (30) is supported by the interior wall of member (14) and urged against this wall by a leaf spring (29) and the air pressure between the interior wall of member (14) and the membrane (30) is variable. When the air pressure is increased, the membrane (30) moves away from the wall of the member (14) against the spring (29) so that the chamber (35) is now partially defined by a flexible wall, thus reducing the damping effect and the stiffness.

Description: The invention relates to a vibration-damping support for acting between two members between which it is connected in use so as to dampen transmission of vibrations between them, comprising wall means defining chamber means for containing hydraulic fluid, means responsive to the said vibrations for acting on the liquid within the chamber means so as to tend to move it, damping means resisting such movement of the fluid whereby to provide damping of the vibrations, a portion of the wall means being flexible to affect the magnitude of the vibration damping, and control means for controllably varying the flexibility of the said flexible portion of the wall means whereby to vary the magnitude of the damping, the control means comprising gas pressure means for applying controllable gas pressure between a substantially rigid surface and an adjacent surface of the said flexible portion of the wall means. Such a support is known from FR-A-2 573 156. In this known arrangement, the flexible wall portion is in the form of a flexible membrane which extends over the substantially rigid surface. The control means controllably varies the flexibility of the membrane by varying gas pressure applied between the substantially rigid surface and the membrane. In the absence of such gas pressure, the membrane lies against the rigid surface and is therefore effectively inflexible. Upon the application of such gas pressure, the flexible membrane is held away from the substantially rigid surface by the gas pressure and its flexibility is increased. With such an arrangement, though, it is important that the effective flexibility of the membrane can be rapidly varied. The invention aims to provide a solution to this problem. According to the invention, therefore, the known vibration-damping support is characterised in that the control means also includes means distinct from the flexible portion of the wall means which resiliently urges the said flexible portion of the wall means against the substantially rigid surface. In this way, the flexible wall portion is rapidly returned towards the substantially rigid surface by the resilient means, when the gas pressure is reduced, and the desired rapid change in vibration damping is achieved. Controllable anti-vibration support elements 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 support elements. Figure 2 is a partial section on the line II-II of Figure 1; Figure 3 is a schematic diagram of a control circuit for the support elements; and Figures 4A and 4B show curves for explaining the operation of the support elements. As shown in Figure 1, the support element is attached at its upper end to part of the engine 10 of a vehicle and is attached at its lower end to the body 12 of the vehicle. The support element (in conjunction with other elements which may be the same or different) supports the engine with respect to the body and, in a manner to be described, damps the vibration of the engine and reduces transmission of such vibration to the body. The support comprises an arch-shaped member which is moulded from elastomeric material and is secured to a rigid end piece 16, preferably made of metal. The piece 16 is integrally connected with a pin 18 which is in turn connected to the engine 10 such as by a screw-threaded attachment. The arch-shaped member 14 is moulded so as to incorporate a circumferentially extending metal piece 20 which is bent outwardly to form a circumferential reinforcement 22 to provide rigidity and strength. Reinforcement 22 is attached to a flange 24 forming part of a ring-shaped metal piece 26 which defines a radially inwardly directed shoulder 28. Flanges 22 and 24 are secured to each other, such as by welding, and they in turn are secured by any suitable means to the vehicle body 12. Mounted within the hollow interior under the arch-shaped piece 14 is a flexible membrane 30. This extends over the entire internal surface of the arch-shaped member 14 to provide a pneumatic chamber 31 between the piece 14 and the membrane 30. In a manner to be explained, the pressure within the chamber 31 can be varied. The membrane 30 is urged against the piece 14 by a leaf spring arrangement 29. Figure 1 shows, in its left hand half, the position adopted by the membrane 30 when the pressure in the chamber 31 is atmospheric or below atmospheric, and the membrane is consequently urged into contact with the surface of the arch-shaped piece 14 by the leaf spring arrangement 29. In its right hand half, Figure 1 shows the position adopted by the membrane 30 when the chamber 31 is pressurised above atmospheric. As shown, the pressure overcomes the force exerted by the spring arrangement 29 and urges the membrane 30 away from the piece 14. Figure 1 simultaneously shows both positions of the membrane 30. In practice, of course, the complete membrane adopts either the position shown in the left hand half of Figure 1 or its right hand half, depending on the pressure in the chamber 31. A second flexible membrane 32 is sealingly attached to the shoulder 28. A rigid channelled member 33 is mounted within the ring-shaped member 26 and supports an annular rigid plate 34. The peripheral edge of the membrane 30, and of the spring arrangement 29, are sealingly secured between the lower face of the flange 22 and the upper face of the plate 34 so as to define an upper chamber 35. Similarly, the periphery of the membrane 32 is sealed between the shoulder 28 and the lower face of the channel-shaped member 33, so as to define a lower chamber 36. The parts 30,32,33 and 34 can be crimped together in a single operation. The channel-shaped member 33 defines a circumferentially extending channel 38 and a recess 39. The chambers 35 and 36 are interconnected via the channel 38. Chamber 35 is connected to channel 38 through an opening 40 (shown dotted) and chamber 36 is connected to channel 38 through an opening 41 (also shown dotted). As shown most clearly in Figure 2, at one position on the circumference, a bore 43 is formed in which is located a ball 44 which sealingly closes off an external opening 45. The bore 43 connects with passageways 46 and 48 which also provide communication between the upper chamber 35 and the lower chamber 36. The air pressure in the space between the flexible membrane 30 and the inside surface of the arch-shaped member 14 constituting the pneumatic chamber 31 can be varied via a passageway 50 which is connected to a variable air pressure source via a control valve (not shown). The variable pressure source can be a vacuum source which can lower the pressure behind the membrane 30 to below atmospheric pressure. Instead of air, another gas could be used. The entire interior of the support element is filled with hydraulic fluid. This fluid fills the chambers 35 and 36 and also the circumferential channel 38 (recess 39 as well). Filling with hydraulic fluid is accomplished via the orifice 45 before the ball 44 is placed in position; the fluid flows through the passageways 46 and 48 into the chambers 35 and 36 and into channel 38. This filling process takes place with the support element placed on its side so that the orifice 45 is uppermost. This reduces the risk of air bubbles in the fluid. After the filling process, the ball 44 is fixed in the position shown in Figure 2 to seal of the orifice. The operation of the support element will now be described. When the air pressure behind the membrane 30 is low (below ambient pressure), the membrane is held by the spring arrangement 29 in the position illustrated in the left hand side of Figure 1. The volume of the chamber 31 is thus reduced, possibly to zero. When vibratory movement of the vehicle engine occurs, this is transmitted to the fluid via the arch-shaped member 14 which acts as a piston. The consequent oscillations of this piston cause the hydraulic fluid to oscillate within the channel 38 and between the chambers 35 and 36. Damping is produced by the hydraulic resistance to flow of fluid between the two chambers and by the effect of the fluid resonantly oscillating within the channel 38. It should be noted that the membrane 32 is very supple and freely expands and contracts in correpondence with movement of the fluid; it thus itself offers little resistance to such fluid movement and the pressure within chamber 36 is maintained substantially at atmospheric pressure. When the pressure behind membrane 30 is increased (via the passageway 50), however, the membrane 30 is forced away from the inside surface of the arch-shaped member 14, against the spring arrangement 29, as shown in the right hand side of Figure 1. The volume of chamber 35 is thus reduced and fluid is shifted into chamber 36, which expands (as explained above) without offering substantially any resistance. The damping effect which is now offered against vibrations of the vehicle engine is considerably reduced. This is because the wall of the chamber 35 is no longer substantially rigid but is more flexible - because the membrane 30 is no longer pressed against the piece 14 and is better able to vibrate in correspondence with oscillation of the hydraulic fluid. This to and fro movement is now possible because the outer surface of the membrane 30 is supported on a cushion of air and not by the substantially stiff inside surface of the arch-shaped member 14. The fluid now no longer oscillates within the channel 38 (or only oscillates therein to a small extent). The damping effect produced by such oscillation is therefore stopped or reduced. The overall damping effect produced by the support element is therefore reduced. Therefore, by controlling the pressure in the pneumatic chamber 31 (that is, between the membrane 30 and the arch-shaped member 14), the damping effect produced by the support element can be adjusted so as to provide optimum damping according to the frequency and magnitude of the vibrations. The additional interconnection between the chambers 35 and 36 which is provided by the passageways 46 and 48 modifies the total damping effect by reducing its amplitude, tending to flatten the peak of the curve which relates damping amplitude to frequency and to shift this peak towards a higher frequency. In addition, it improves the dynamic response at higher frequencies. In a modification, however, the ball 44 can be positioned (after filling the support element with hydraulic fluid) to close off the passageways 46 and 48. In this case, the interconnection between chambers 35 and 36 is only via the openings 40 and 41 and channel 38. High amplitude movements of the vehicle engine can occur due to abrupt changes in torque exerted by or on the engine - for example, when the vehicle starts or abruptly changes speed. Such large amplitude variations have a frequency within the range between 0 and 10 Hz. In order to dampen the effect of such vibrations, the support element needs to exert a strong damping force. Therefore, in this situation the pressure in pneumatic chamber 31 would be reduced to the minimum so that the membrane is in the position illustrated in Figure 1 in dashed line, thus giving maximum damping effect. As the vehicle travels along a road, the latter's irregularities will cause vertical movement of the motor on the support element and such movements can have frequencies up to about 20 Hz. Again, a relatively strong damping force is required in order to dampen these movements and therefore the pressure behind the membrane in the pneumatic chamber 31 needs to be low. When the engine is idling, it creates vibrations in the range between 15 Hz and 25 Hz. In order to avoid transmitting these vibrations, the support element needs to be more supple and the pressure in pneumatic chamber 31 is therefore increased. The various moving parts within the interior of the engine generate inertial forces producing vibrations in the range between 30 Hz and 300 Hz (or higher). In order to avoid transmitting these vibrations, the support element also needs to be supple. Again, therefore, the pressure in pneumatic chamber 31 will be increased. Figures 4A and 4B illustrate the operation graphically. The stiffness of the support element is a complex variable with a modulus K and argument d. In Figure 4A, the loss factor tan(d) is plotted on the vertical axis and vibration frequency is plotted on the horizontal axis. Curve I illustrates the ideal relationship between loss factor and vibration frequency. At low frequencies, the loss factor is maximum and remains at this maximum value until about 10 Hz, after which it falls rapidly to a minimum value which is maintained for frequencies above about 20 Hz. Curve II shows the response produced by the support element when the pressure in pneumatic chamber 31 is at its minimum value. As shown, the loss factor rises from a low value at 0 Hz to a maximum (at about 10 Hz) corresponding to the engine suspension's resonant frequency and then reduces. The peak of the curve is produced by the resonance of the fluid oscillating in the channel 38. Curve III corresponds to curve II but illustrates the case when the pressure in pneumatic chamber 31 is slightly above the minimum value. Curve IV illustrates the case when the pressure in pneumatic chamber 31 is at its maximum value. The value of loss factor is thus at its minimum level continuously. In Figure 4B, the stiffness K is plotted on the vertical axis, and, as before, vibration frequency is plotted along the horizontal axis. Again, curve I illustrates the ideal case where the resistance to movement is at its maximum value from very low frequencies (just above 0 Hz) to just above 10 Hz and then falls off rapidly to a minimum value which is maintained at frequencies above 20 Hz. Curve II illustrates the case when the pressure in pneumatic chamber 31 is at its minimum. The stiffness produced by the support element rises rapidly from a low value to a maximum value which is reached at about 15 Hz and is thereafter maintained. Curve III corresponds to Curve II but illustrates the case when the pressure in pneumatic chamber 31 is slightly above the minimum value. Curve III is generally of the same shape as Curve II except that the stiffness rises to its maximum at a lower frequency. Finally, Curve IV shows the case when the pressure in pneumatic chamber 31 is at its maximum. The resistive force exerted by the support element is at a minimum level. Figure 3 illustrates a control circuit for controlling the air pressure in pneumatic chamber 31. A transducer or sensor 50 senses the vibration to be damped. For example, it may be a vibration sensor for producing an electrical signal in dependence on the vibration (frequency and magnitude) of the vehicle engine. The resultant signal is then processed in a signal processing unit 52 which could be of any suitable type (for example, an amplifier or a micro-processor) so as to produce a control signal on a line 54 which varies according ot the magnitude and frequency of the signal produced by the transducer 50 and the resultant damping effect which is required. Control signal 54 operates an output unit 56 which correspondingly controls an electro-valve 58. This controls the pressure applied via passageway 50 behind the membrane 30. The pressure can be applied directly by a pump operated by the control signal 54. The inside surface of the arch-shaped member 14 is provided with one or more grooves 64. These provide air spaces which exist even when the pressure in pneumatic chamber 31 is reduced to its minimum. The existence of these air spaces helps to ensure that the membrane 30 is deformed away from the arch when the pressure behind it is increased. Instead of grooves, ridges could be used. Spring arrangement 29 can be made of metal or plastics, for example. The embodiment of Figures 1 and 2 uses channel 38 in which fluid oscillates to provide damping. However, any other arrangement could be used instead for damping vibrations in response to movement of the arch-shaped member 14. Examples of such other damping arrangements are: (a) a channel having a restriction within it; (b) the use of an electro-rheological fluid and a passageway passing this fluid between two electrodes which create an electric field increasing the viscosity of the fluid; (c) the use of an electromagnetic fluid and a passageway passing this fluid through a magnetic field. (d) the resonance of a dynamic damper constituted by a solid mass. In each case, an increase of pressure in the pneumatic chamber 31 would serve to divert the fluid from the particular damping arrangement.

Claims: A vibration-damping support for acting between two members between which it is connected in use so as to dampen transmission of vibrations between them, comprising wall means (14,30) defining chamber means (35,36) for containing hydraulic fluid, means (14) responsive to the said vibrations for acting on the liquid within the chamber means so as to tend to move it, damping means (38) resisting such movement of the fluid whereby to provide damping of the vibrations, a portion (30) of the wall means being flexible to affect the magnitude of the vibration damping, and control means (31,29) for controllably varying the flexibility of the said flexible portion (30) of the wall means whereby to vary the magnitude of the vibration damping, the control means comprising gas pressure means (31) for applying controllable gas pressure between a substantially rigid surface (14) and an adjacent surface of the said flexible portion (30) of the wall means, characterised in that the control means also includes means (29) distinct from the flexible portion (30) of the wall means which resiliently urges the said flexible portion (30) of the wall means against the substantially rigid surface (14). A support according to claim 1, characterised in that the gas pressure means (31) is operative in dependence on the said vibrations. A support according to claim 2, characterised in that the means for controlling the gas pressure includes transducing means (50) for producing a control signal in dependence on the magnitude and/or the frequency of the vibrations, and means (58) operative in dependence on the control signal to control the gas pressure. A support according to claim 1 or 2, characterised in that the gas pressure is variable to a value below atmospheric pressure. A support according to any preceding claim, characterised in that the said gas pressure is variable to a value above atmospheric pressure. A support according to any preceding claim, characterised in that the flexible wall portion comprises a flexible membrane (30) which extends over the substantially rigid surface (14) which is outside the chamber means (35,36). A support according to any preceding claim, characterised in that the control means includes spring means (29) within the chamber means (35,36) and acting on the wall portion (30). A support according to claim 7, characterised in that the spring means comprises leaf spring means (29). A support according to any preceding claim, characterised by a mechanical formation on one said surface to preserve a gas space between the surfaces even when the gas pressure is a minimum. A support according to any preceding claim, characterised in that the substantially rigid surface is the inner surface of a movable member (14) connected to one of the said mechanical elements (18) so as to move therewith. A support according to claim 10, characterised in that the movable member is a member (14) defining a conical surface constituting the said substantially rigid surface. A support according to any preceding claim, characterised by a mass carried by the said flexible portion of the wall means. A support according to any preceding claim, characterised in that the damping means comprises a passageway (38) for the fluid in which the fluid can resonantly oscillate. A support according to any preceding claim, characterised in that the damping means includes a fluid passageway having a restriction for the flow of fluid therein. A support according to any one of claims 1 to 12, characterised in that the damping means comprises means for subjecting the fluid to an electric or magnetic field and in that the fluid is adapted such that its flow is reduced by such field. A support according to any preceding claim, characterised in that the chamber means is divided into two parts one (35) of which includes the said flexible wall portion (30) and the other (36) of which has a volume which adjusts to the volume of hydraulic fluid in it without offering substantially any resistance to the entry of such fluid, the fluid passing between the two parts of the chamber means via the damping means (38).

Inventors: TOURNIER PASCAL, TOURNIER, PASCAL, TOURNIER, PASCAL, RESIDENCE DU BOIS ST LOUIS
Applicants: DRAFTEX IND LTD, DRAFTEX INDUSTRIES LIMITED
Application year: 1993
Main classification: F16F13
IPC codes: F16F13, B60K5