GB2165617A - Tunable viscous spring mount - Google Patents

Abstract

A viscous spring damper particularly adapted for supporting an automobile engine is provided. The damper comprises a first fluid chamber 42 including a first wall portion defined by an elastomeric journal 28 and a second fluid chamber 44 including a second wall portion defined by an elastomeric diaphragm 50. A restrictor plate 40 is interposed between the fluid chambers and includes a main fluid port 64 and an auxiliary fluid port 66 for communicating fluid between the chambers. First and second elastomeric flaps 74, 76 are oppositely disposed about the main fluid port. The flaps are selectively tensioned and spaced from the restrictor plate to seal the main fluid port against fluid flow upon deflection of the flaps against the port in response to a preselected shock amplitude and frequency. The flaps are independently tensioned and spaced from the restrictor plate to possess the capability of having distinct natural frequencies and to seal the fluid port upon distinct amplitude deflections and frequencies during damper compression and rebound. The main fluid port is sized so that the flaps may be receptively deflected into the port upon sufficient compression of a fluid chamber to substantially limit the pressure in the chamber. <IMAGE>

Description

SPECIFICATION Tunable viscous spring mount Background of the Invention The present invention relates generally to shock absorbers. More particularly, it relates to shock absorbers of the type which are mounted to vehicles and which use both an elastomeric shear spring and the flow of fluid through a restricted orifice for absorbing shock, structural leveling and energy dissipation.

As automobile design has tended to favor smaller, more energy-efficient vehicles having reduced weight and engine power requirements, the resulting automobiles have been particularly subject to disadvantageous vibrational problems such as harder rides and engine vibration detectable in the passenger compartment. These problems have arisen from such design factors as integral frame and automobile cab construction whereby riding shocks to the frame are directly transmitted to the passenger compartment. In addition, the smaller engines are oftentimes inherently unbalanced and when they are mounted to the integral frame they transmit their vibrations directly to the cab.Such typical constructions generate several types of vibration which are loosely segregated into low frequency, high amplitude vibrations (i.e., a stationary car with the engine idling or a moving car going over a bump) and high frequency, low amplitude vibrations (i.e., the vibrations generated by a motor operating at highway speeds being generally less than plus or minus 0.1 millimeter).

The theory of vibration transmissibility as it applies to engine mounts seeks to generally provide high damping at low frequencies (up to 20 Hz) and low damping at high frequencies (above 20 Hz). Accordingly, various forms and types of engine mounts have heretofore been suggested which provide substantial hydraulic damping only above a predetermined amplitude of vibration oscillation. These various forms and types of engine mounts have met with varying degrees of success. It has been found that the defects present in such prior engine mounts are such that the mounts are of limited economic and practical value.

A typical prior engine mount construction employs opposed armatures associated by an elastomeric member housing an hydraulic fluid.

The elastomeric member operates as a shear spring. A means for partitioning the fluid chamber in the interior of the elastomeric shear spring is provided to segregate the interior into at least two fluid chambers. The partition usually includes an orifice for providing a restricted flow of fluid communication between the chambers. A valve is associated with the restricted orifice to close the orifice upon a preselected pressure differential between the fluid chambers. This pressure differential is generated as a result of vibration or shock being incurred by the device.

A particular problem with such constructions is that they are not susceptible for selective tuning to adjust the valve operation. The valve possesses a natural frequency which defines one set of operational characteristics of the engine mount only. Such an engine mount will usually be designed for one particular type of vehicle structure and lacks the versatility to be applied for efficient operation to a variety of vehicle designs.

Another problem with prior art engine mount constructions is that the valve usually has only a single natural frequency which affects the damping response identically both during mount compression and rebound. Oftentimes it is highly desirable to have a different operating response between compression and rebound to provide smoother vibration transmission or damping.

Yet another problem with prior art engine mounts occurs when the valve seals fluid flow under a relatively high differential pressure and pressure continues to increase in the fluid chambers. Since the chambers have only limited means for relieving the pressure differential, the mount can become undesirably stiff.

The present invention contemplates a new and improved device which overcomes the above referred to problems and others to provide a new viscous spring mount with a tunable flapper valve which is simple in design, economical to manufacture, readily adaptable to a plurality of vehicle types having a variety of structural and dimensional characteristics, easy to tune and install and which provide improved engine vibration isolation and damping.

Brief Summary of the Invention In accordance with the present invention, there is provided a viscous spring engine mount including a deflection amplitude and frequency dependent flapper valve. The engine mount includes a fluid flow restrictor plate interposed between first and second fluid chambers. The first fluid chamber includes a first wall portion generally defined by an elastomeric journal. The second fluid chamber includes a second wall portion generally defined by an elastomeric diaphragm. The restrictor plate includes a main fluid port and an auxiliary fluid port for communicating fluid between the chambers.First and second elastomeric flaps are spaced from the restrictor plate and oppositely disposed about the main fluid port whereby the flaps are selectively tensioned to seal the main fluid port against fluid flow upon deflection of the flaps against the port in response to a preselected shock amplitude and frequency to the engine mount.

In accordance with another aspect of the present invention, the elastomeric flaps com prise elongated bands including fastening means for locating the bands a preselected clearance from the main fluid port. The bands are sized to at least engage the port upon deflection of the bands into engagement with the restrictor plate.

In accordance with another aspect of the present invention, the first and second flaps are tuned to have distinct natural frequencies to effect a different damping response of the mount during compression than during rebound.

in accordance with a further aspect of the present invention, the flaps are received in the first and second fluid chambers respectively and each flap is free to deflect both away from and into the port.

In accordance with still a further aspect of the present invention the elastomeric diaphragm defining the second fluid chamber has a central portion comprising a rigid and variable mass.

One benefit obtained by use of the present invention is an engine mount which provides improved viscous spring damping.

Another benefit obtained from the present invention is an engine mount having an amplitude and frequency dependent hydraulic valve which is selectively tunable to provide high or low damping at a preselected vibrational amplitude and frequency.

Other benefits and advantages of the subject new engine mount will become apparent to those skilled in the art upon a reading and understanding of this specification.

Brief Description of the Drawings The invention may take physical form in certain parts and arrangements of parts, the preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein: Figure 1 is a cross-sectional view of an engine mount formed in accordance with the present invention; Figure 2 is a cross-sectional view of the engine mount of Fig. 1 rotated 90"; Figure 3 is a cross-sectional view taken along line 3-3 of Fig. 1; and Figure 4 is a cross-sectional view taken along line 4-4 of Fig. 1.

Detailed Description of the Invention Referring now to the drawings wherein the showings are for purposes of illustrating the preferred embodiment of the invention only and not for purposes of limiting same, the figures show a viscous spring damper 10 particularly useful as an engine mount. The damper 10 includes first and second opposed armatures 12, 14 which are adapted for fastening to an engine and an automobile chassis (not shown) respectively. The first armature 12 generally comprises a piston including a first portion 16 preferably constructed of a strong and durable material such as a metal, and a second portion 18 protruding therefrom comprising a threaded extension adapted for fastening to an engine. A locating protrusion 20 is provided for mating reception in a bore (not shown) for locking the piston 12 against rotational movement after assembly to the engine and frame.

The second armature 14 preferably comprises a metallic plate defining a damper bottom wall and includes conventional fastening means 24 for fastening the damper to an engine frame.

The side wall of the damper 10 comprises a cylindrically configured annulus 26 and an elastomeric journal 28. Annulus 26 is preferably constructed of a strong and durable material such as steel and includes a flange 30 which is chemically bonded to the journal 28.

The elastomeric journal tapers from flange 30 towards the piston 12 for attachment to the piston with conventional chemical bonding techniques. The innermost end 34 of journal 28 comprises an annular flange 34 engaging a shoulder 36 of flange 30. Resting upon journal flange 34 is a partition plate 40 which substantially divides the damper interior into a first fluid chamber 42 and a second fluid chamber 44. A conventional hydraulic fluid is received in the fluid chambers. The partition plate 40 operates as a means for fluid flow restriction between the first and second fluid chambers to effect the viscous spring damping action of the invention as will hereinafter be more fully discussed.

Interposed between the partition plate 40 and the second armature 14 is an elastomeric diaphragm 50 which is positioned and sealed at an annular bead 52 with a cylindrical ring 54. The bead 52 is compressed between plate 14 and ring 54 to define a selectively pressurizable gas chamber 56. Preferably, a plate 58 forms a top wall of the elastomeric diaphragm 50 to enhance the strength of the diaphragm over this portion and to, more importantly, allow the mass of the diaphragm to be varied. This construction causes greater or lesser propensity for diaphragm 50 to oscillate at a specific frequency. In particular, it facilitates diaphragm movement and thus fluid flow near its natural frequency. This feature is advantageous in providing optimum fluid damping at desired frequency by the flap construction described hereinafter.

The general operation of communicating fluid chambers through a means for fluid flow restriction in combination with a selectively pressurizable gas chamber to provide an advantageous viscous spring damper is more fully discussed in U.S. Patent No. 4,352,487.

The partition plate 40 comprises an as sembly having an elastomeric flap associated with a main fluid port that is spaced from the port a preselected distance and stressed to a preselected strain whereby the flap exhibits a particular natural frequency. The flap operates to seal the port upon amplitude deflection to the damper in excess of a predetermined amount.

With particular reference to Figs. 3 and 4, it may be seen that partition plate 40 includes a main fluid port 64 and an auxiliary fluid port 66. Main fluid port 64 may comprise a single aperture or a plurality of fluid apertures. In the embodiment illustrated, two apertures are shown. It is important that the main fluid port 64 provide a substantially greater fluid accessway between the fluid chambers than the auxiliary port 66. It has been found that to operate as a proper viscous spring damper, the ratio of the main port area that is sealed by the flap to the auxiliary port cross-sectional area must be at least 5 to 1, although when the damper 10 is employed as an engine mounting assembly for present size automobiles, the ratio preferably falls in the range of 40 to 50 to 1.

With continued reference to Figs. 3 and 4, it may be seen that auxiliary port 66 presents a tortuous flow path to fluid between the fluid chambers. Fluid may enter the auxiliary port from the main fluid chamber only at a portion of the port channel 68 which is radially innermore than the elastomeric journal flange 34.

That portion of the auxiliary port which runs with the flange 34 is sealed against the first fluid chamber 42 by the flange. Fluid from the auxiliary port 66 is communicated to the second fluid chamber from a portion of the port 66 cut in partition plate 40 that is open to the second fluid chamber (Fig. 4).

With reference to all the figures, associated with plate 40 are first and second elastomeric flaps 74, 76 which are fastened to the plate 40 at their terminal end portions with conventional fastening means 78. The flaps 74, 76 comprise elastomeric bands which are oppositely disposed about the main fluid port 64.

The flaps are selectively tensioned and selectively spaced from the plate 40 whereby the flaps operate to seal the main fluid port against fluid flow upon deflection of the flaps against the port in response to a preselected shock amplitude and frequency to the damper 10. The selective spacing 82 comprising the distance between the flap and the plate allows fluid to freely pass through the main fluid port until such time as the flap is urged or dragged into engagement with the plate to seal the main fluid port 64. In addition, the greater the tension placed upon the flaps 74, 76 the less susceptible the flaps will be to deflection against the plate. It is a feature of the present invention that each flap may be independently spaced and stressed such that the flaps will possess distinct natural frequencies.This permits the present invention to effect a different damping response on compression than on rebound.

More particularly, it may be seen that the first fluid chamber 42 includes a first wall portion defined by the elastomeric journal 28 which allows compression or expansion of first chamber 42 dependent upon forces applied to the damper 10. Similarly, the second fluid chamber 44 includes a second wall portion defined by the elastomeric diaphragm 50 to allow expansion and contraction of the second fluid chamber in accordance with the expansion or contraction of the diaphragm 50 and the gas chamber 56. Upon a compression force being applied to the damper 10, fluid in the first fluid chamber 42 will be urgued toward the second fluid chamber 44 through both the main fluid port 64 and the auxiliary fluid port 66.Upon a sufficient amplitude of shock or vibration to the damper 10, such that the pressure in the first chamber 42 causes the first elastomeric flap 74 to be urged into engagement with the plate 40, the main fluid port will be sealed against fluid flow from the first fluid chamber into the port 64 by first flap 74. The flaps are sized to at least engage the port 64 upon deflection of the flaps into engagement with the plate 40.

While the first elastomeric flap 74 is thus urged into sealing engagement, the second elastomeric flap 76 is being urged away from the partition plate 40 since the pressure in the first fluid chamber is greater than the pressure in the second fluid chamber. On the rebound from this deflection, the opposite in deflection will occur to the flaps 74, 76. The fluid will be drawn from the second fluid chamber 44 towards the first fluid chamber 42 and will urge the second elastomeric flap 76 toward plate 40 while urging the first elastomeric flap 74 away from the plate 40.When the first flap 74 is both spaced and tensioned differ ently than the second flap 76, the amount of pressure differential which will cause the first flap 74 to seal the main fluid port on compression will be different from the amount of differential pressure which will cause the second elastomeric flap 76 to seal the main fluid port. This provides a selective and independent tuning feature to the invention.

It is a common objective of mounting devices to provide a low natural frequency for the suspended mass associated therewith (i.e., the engine) in order to most effectively isolate the vibrations generated. This objective can result, however, in excessive deflection of the suspended mass near its natural frequency if insufficient damping is provided by the mount.

The mount of the present invention provides this desired damping by including separately tunable flaps for sealing of main ports and by optimizing flow characteristics by using an appropriate mass 58 as part of diaphragm 50.

Another design consideration of engine mounting assemblies generally is that it is important to obtain low stiffness of the mounting device at high frequency. The present in vention limits the stiffness of the device by substantially limiting the pressure which may be exerted on the fluid chambers 74, 76.

More particularly, when the device 10 is subjected to a high amplitude deflection such that there is a high pressure differential between the fluid chambers 42, 44 and the main fluid port 64 is sealed against fluid flow, the elastomeric flaps 74, 76 may still deflect or bulge into the fluid port 64 to expand the effective volume of the chamber beyond plate 40. This bulging action limits the pressure of the chambers and keeps the stiffness of the damper lower than if no bulging action were free to occur.

The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon the reading and understanding of the specification. It is my intention to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims (12)

1. A viscous spring damper comprising a first fluid chamber including a first wall portion defined by an elastomeric journal; a second fluid chamber including a second wall portion defined by an elastomeric diaphragm; a restrictor plate interposed between said fluid chambers including a main fluid port and an auxiliary fluid port for communicating fluid between the chambers; and first and second elastomeric flaps selectively oppositely disposed about the main fluid port, said flaps being selectively tensioned and selectively spaced from the restrictor plate whereby the flaps operate to seal the main fluid port against fluid flow upon deflection of the flaps against the port in response to a preselected shock amplitude or frequency to the damper.

2. The damper as defined in Claim 1 wherein the elastomeric flaps comprise elongated bands including fastening means for locating the bands a preselected clearance from the main fluid port, said bands being sized to at least engage the port upon deflection of the bands into engagement with the restrictor plate.

3. The damper as defined in Claim 1 wherein said first and second elastomeric flaps are independently tensioned and spaced from the restrictor plate.

4. The damper as defined in Claim 3 wherein said first elastomeric flap is tensioned to have a first natural frequency and said second elastomeric flap is tensioned to have a second natural frequency, said first natural frequency being different from said second natural frequency.

5. The damper is defined in Claim 1 wherein said main fluid port is sized for receptive deflection of an elastomeric flap whereby compression of a fluid chamber to a generally predetermined pressure deflects the flap into the port to substantially limit the pressure within the chamber.

6. The damper as defined in Claim 1 wherein said elastomeric diaphragm includes a selectively variable mass portion to provide a preselected diaphragm natural frequency.

7. An engine mounting assembly including a deflection amplitude and frequency dependent flapper valve having: a means for fluid flow restriction interposed between first and second fluid chambers and including a fluid port; and, an elastomeric flap associated with said port and spaced from said port a preselected distance and stressed to a preselected strain whereby said flap seals said port upon a preselected deflection to the assembly.

8. The assembly as defined in Claim 7 wherein said flap is dimensioned to cover the extent of said port upon deflection of the flap against said means for fluid flow restriction.

9. The assembly as defined in Claim 8 wherein a pair of said elastomeric flaps are oppositely spaced about said port.

10. The assembly as defined in Claim 9 wherein said flaps are received in said first and second fluid chambers respectively and each flap is free to deflect both away from and into the respective port.

11. The tunable viscous spring mount substantially as described herein with reference to the accompanying drawings.

12. A viscous spring damper comprising first and second fluid chambers each having a wall portion defined by elastomeric material, means providing for restricted fluid flow between said first and second chambers via a fluid flow port, and tunable flapper valve means associated with said port for determining the fluid flow therethrough in the event of a predetermined pressure differential between said chambers.