HYDRAULIC-ELASTOMERIC MOUNT

Abstract: A hydraulic-elastomeric mount is disclosed having a multi-function diaphragm 34 that in addition to forming a secondary chamber 68 also serves to provide amplitude control and multiple sealing.

Description: HYDRAULIC-ELASTOMERIC MOUNT This invention relates to a hydraulicelastomeric mount. In a typical mount such as is used for the resilient mounting of a vehicle engine, an elastomeric body is employed made of natural or synthetic rubber. Such materials have inherently low coefficients of damping, and it has been found that many of the vibratory inputs to the vehicle would be better isolated if the engine mounting system exhibited a higher coefficient of damping. It is possible to provide an increased damping coefficient by the selection of certain rubber polymers and by the use of additives, but so far this approach has proved unsatisfactory because it results in adverse affects on other properties of the rubber. Furthermore, this approach produces large damping for all vibratory inputs regardless of frequency or amplitude. There is accordingly a major desire for a cost-effective means of providing increased damping that does not limit the choice of rubber used for the elastomeric body. There is also the desire that the amount of damping be controllable as to its magnitude for vibratory inputs of various frequencies and amplitudes. Furthermore, the damping should be achieved in a manner that does not compromise the many desired features in the typical elastomeric mount design, and particularly those of major importance, such as specific stiffness ratios along the major axes and specific configurations to suit packaging space restrictions. Various mount designs have been proposed involving adding hydraulic damping. However, such mounts generally fail to meet all the design criteria, in particular damping controllability, or they are relatively complex and difficult to manufacture with a high degree of sealed integrity. An example of a prior proposal for a hydraulic-elastomeric mount is disclosed in United States Patent No. A,159,C)#l cise Salver et al). By the present invention there is provided a hydraulic-elastomeric mount comprising a pair of mounting members, a hollow elastomeric body interconnecting said zc * mounting members, an elastomeric diaphragm configured so as to close said elastomeric body and form therewith a closed cavity, a partition dividing said cavity into a primary chamber enclosed by said elastomeric body and a secondary chamber enclosed by said diaphragm, a liquid contained in: : said chambers, and an orifice through said partition interconnecting said chambers so as to permit liquid in said primary chamber to flow at a restricted rate into said secondary chamber upon contraction of said primary chamber and in the opposite direction on expansion thereof to thereby provide a damping effect, characterised in that said elastomeric diaphragm extends over the periphery of said partition and forms a seal between said chambers and atmosphere and also between said primary chamber and said secondary chamber, and that said diaphragm is configured so as to permit limited substantially free travel of said partition relative to said mounting members below a predetermined vibration amplitude of one mounting member relative to the other and to prevent such travel above such amplitude, so that flow through said orifice to effect damping does not occur until said predetermined vibration amplitude is exceeded. The present invention thereby makes available a hydraulic-elastomeric mount of a design which is potentially very simple, and easy to manufacture with excellent sealed integrity, and which is caDable of being produced as a family of mounts providing a wide range of desired characteristics to various degrees, without compromising the desired- vibrationisolating characteristics of the elastomeric body itself. In a preferred embodiment of a hydraulicelastomeric mount in accordance with the present invention, a pair of mounting members are interconnected by a hollow elastomeric body: for use as a vehicle engine mount, one of the mounting members is secured to the engine, and the other mounting member is secured to the engine-supporting structure of the vehicle, The mount includes an elastomeric diaphragm that is configured to close the elastomeric body and form therewith a closed cavity. A rigid partition is effective to divide the cavity into a primary chamber enclosed by the elastomeric body and a secondary chamber enclosed by the diaphragm. A liquid is contained in the chambers, and the partition is provided with an orifice which interconnects the chambers. The liquid is thus forced to flow at a restricted rate from the primary to the secondary chamber upon contraction of the primary chamber, and in the opposite direction on expansion of the primary chamber, to provide a damping effect as -the one mounting member is caused to vibrate relative to the other. The diaphragm is further configured to extend about and also over the periphery of the partition, and thereby form a seal between the chambers and the exterior of the < -mount as well as forming a seal between the chambers. Moreover, the diaphragm is configured to have a certain compliance at its rim to permit limited substantially free or soft travel of the partition below a predetermined vibration amplitude of one mounting member relative to the other, but prevent such relative travel above such amplitudes, so that flow through the orifice to effect damping is dependent upon the predetermined vibration amplitude. Thus in a hydraulic-elastomeric mount in accordance with the present invention the diaphragm is trifunctional, in that in addition to forming the secondary chamber it also serves to provide amplitude control and provide multiple sealing. Furthermore, the total design is such that a wide family of mounts can be made available, this being possible by designing the orifice as part of a separate and relatively movable part which is mounted on the partition with limited free travel so as to permit small inputs without damping, for further amplitude control. This design also offers a selection of orifice diameters, lengths and shapes for various types of damping responsiveness. Further extension of the family is available by varying the compliance and the durometer value of the diaphragm, and by varying the wall thickness, the shape and the durometer value of the hollow elastomeric body interconnecting the mounting members Another advantage is that the hollow elastomeric body can be formed by the use of a standard two-piece mould with no loose cores, using either injection or transfer moulding, and with little excess rubber needing to be removed. Furthermore, assembly may be simplified by the formation of the orifice, the partition and the diaphragm as one subassembly, and by the formation of the elastomeric body in a moulding operation#with one of the mounting members and a retainer as a second subassembly, which is filled with the hydraulic fluid prior to final assembly. At final assembly, the said two subassemblies may be simply brought together, with the retainer then being crimped or otherwise fixed to the other of the mounting members to retain all the parts of the mount together. In the drawings: Figure 1 is a sectional view of one embodiment of a hydraulic-elastomeric mount in accordance with the present invention; Figure 2 is a sectional view on the line 2-2 in Figure 1, in the direction of the arrows; Figure 3 is an exploded view of the mount shown in Figure 1; Figure 4 diagrammatically shows a mechanical analogy of a hydraulic-elastomeric mount in accordance with the present invention; Figures5 to 8 are graphs showing various characteristics of a hydraulicelastomeric mount in accordance with the present invention (solid-line curves) compared with those of a typical conventional mount having only an elastomeric body (dash-line curves); and Figures 9 and 10 are graphs showing various characteristics of a hydraulicelastomeric mount in accordance with the present invention, both with hydraulic fluid (solid-line curves) and without hydraulic fluid (dash-line curves). In Figures 1 to 3 of the drawings, there is shown a preferred embodiment of a hydraulic-elastomeric mount in accordance with the present invention, adapted for mounting an engine in a vehicle The mount has a generally stepped cylindrical shape, and comprises a pair of stamped sheet metal mounting members 10 and 12 which have a circular cup shaped and saucer-shaped configuration respectively. The mounting members 10 and 12 are arranged with their concave sides facing each other, and have respective studs 14 and 15 secured to the centres thereof and projecting outwardly therefrom for attachment to an engine (not shown) and to an engine-supporting member such as a frame or cradle (not shown) of the vehicle. A hollow elastomeric body 16 made of natural or synthetic rubber interconnects the mounting members 10 and 12, and for this purpose is moulded about the cup-shaped mounting member 10 and to the interior of a stamped sheet metal hollow retainer 18. The elastomeric body 16 is configured such that it essentially completely defines a hollow cavity 20 therein covering the bottom 22 and both sides of a cylindrical wall 24 of the mounting member 10 and also the inner side of a cylindrical wall 26 of the hollow retainer 18. The elastomeric body 16 thus completely covers the head 27 of the stud 14, so as to positively prevent any possible leakage therepast whilst also having extensive surface attachment to both the mounting member 10 and the hollow retainer 18. Moreover the mounting member 10, with its stud 14, elastomeric body 16 and the retainer 18 form a subassembly shown and designated as 28 in Figure 3. It will be seen that the subassembly 28 can thus be made with a conventional two-piece mould without separate, loose core pieces, using either injection or transfer moulding, and with little finishing such as flash rubber removal required. Also, directional rate control is possible by the formation of cavities or voids within the elastomeric body itself. For example the use of diametrically oppositely locatedarcuatecavities 29 as shown provides the mount with a high (hard) rate in one cross-wise direction and both a relatively soft (low) rate at low amplitudes and a nono linear high (hard) rate at high amplitudes in a direction transverse thereto (vertical and horizontal direction respectively as viewed from the top in Figure 2), such difference in rates being especially useful in isolating certain combustion engine vibrations, as is well known in the art. As is shown in Figure 3, the retainer 18 of the subassembly 28 is initially formed with an unfolded collar 30 having a scalloped edge 31 so as to receive a second subassembly 32 that comprises the other mounting member 12, an elastomeric diaphragm 34 of natural or synthetic rubber, a. stamped sheet metal circular dish-shaped partition 36 and an orifice member 37. The elastomeric diaphragm 34 has a circular rim section 38 with a radially inwardly facing internal groove 39, and the shoulder 40 on the side of the groove opposite the spanning central portion 42 of the diaphragm is flexible to receive the rim 44 of the partition 36. The partition rim 44 is thus sandwiched, as shown in Figure 1, between the shoulder 40 and the shoulder 46 on the opposite side of the groove, the latter shoulder being formed integral with and extending radially outwardly from the central portion 42 of the diaphragm to join the latter to the rim section 38 of the diaphragm. The partition 36 is positioned with its concave side facing downwardly, and has a central aperture 48 therethrough into which the orifice member 37 of elastomeric material is adapted to be inserted and retained with a slip fit. This slip fit permits limited free travel of the orifice member 37 relative to the partition 36, in addition to limited substantially free or soft travel of the latter provided by compliance of the diaphragm rim 38, and these free travels operate to prevent hydraulic damping below a predetermined low amplitude, as is described in more detail later. The lower mounting member 12 with its stud 15 is shaped with a collar 52 to receive the rim section 38 of the diaphragm 34 with the partition 36 in place and the orifice member 37 fitted to the latter, with this second subassembly 32 then adapted to be fitted into the yet-to-be-clinched collar 30 of the retainer 18 of the other subassembly 28. Sn such fitting, the lower mounting member 12 is telescopically received in the retainer collar 30 with the rim section 38 of the diaphragm pressed therebetween, whereafter the scalloped edge 31 of the retainer is clinched over the collar 52 on the lower mounting member to retain all the mount parts together as shown in Figure 1. In the assembly, the upper edge 60 of the lower mounting member 12 engages the radial shoulder 62 of the retainer collar to determine the preload on the diaphragm rim section 38, this playing an important part in amplitude control as well as sealing, as will be described in more detail later. As is seen in Figure 1, the elastomeric diaphragm 34 closes the elastomeric body 16 so as to form therewith a closed cavity generally designated 64. Furthermore, the partition 36 divides the cavity 64 into a primary chamber 66 enclosed by the elastomeric body 16, and a secondary chamber 68 enclosed by the diaphragm 34. However, prior to the closure of the cavity S4 at assembly, this cavity is substantially filled with a liquid such as a commercial anti-freeze that will not freeze in the environment of the intended usage. This-filling is readily accomplished by simply inverting the subassembly 28 and filling to a certain level 69 in the retainer 18 (see Figure 3) such that the secondary chamber 68 is thereby filled through the orifice 70 on fitting and clamping of the subassembly 32. The orifice member 37 has a central passage 70 of constant diameter which extends centrally therethrough and interconnects the chambers 66 and 68 so as to permit the liquid in the primary chamber to flow at a restricted rate into the secondary chamber upon contraction of the primary chamber, and to permit flow in the opposite direction upon expansion of the primary chamber, to thereby provide a damping effect. Upon contraction of the primary chamber 66, the wall section 72 of the elastomeric body 16 extending angularly between the mounting member 10 and the retainer 18 is caused to bulge outwardly, with the liquid therein being forced to flow through the orifice 70 into the chamber 68 to expand the latter as permitted by the elasticity of the central portion 42 of the diaphragm, Then on a reversal of amplitude resulting in expansion of the primary chamber 66, the stretched central portion 42 of the diaphragm 34 retracts and thereby contracts the secondary chamber 68, so forcing liquid to flow back through the orifice 70 into the primary chamber 66 to complete the cycle. To permit free expansion and contraction of the secondary chamber 68 as appropriate, the space between the diaphragm 34 and the lower mounting member 12 is vented to atmosphere through a plurality of radial holes 73 formed in the latter. Because the diaphragm 34 is configured at its rim section 38 to extend both around and over the rim 44 of the partition 36, not only is a seal formed between the chambers but also a double seal is formed between the chambers and the exterior, resulting in excellent sealed integrity of the mount, as will be described in more detail later. Moreover, the diaphragm rim section 38 is configured to permit limited substantially free or soft travel of the partition 36 relative to the mounting members 10 and 12 below a predetermined low vibration amplitude of one mounting member relative to the other, and to prevent such relative travel above this amplitude, so that flow through the orifice 70 to effect damping does not occur until such predetermined low vibration amplitude is exceeded. Such free travel of the partition 36 is shown in Figure 1 as being between the two phantom-line positions, and may be as much has - 1.0mum depending on the installation. This provides precise amplitude control, and is simply effected with a predetermined compliance of the diaphragm rim 38 as sandwiched between the retainer 18 and the mounting member 12. To this end, the diaphragm rim 38 is free-formed as shown in Figure 3 so as to have oppositely facing annular sealing beads 74 at the outer perimeter, and thinner but more radially extensive wall sections in the groove shoulders 40 and 46 which sandwich the partition rim 44. There is thus substantially more compliance of the sealing beads 74, which flatten at assembly to effect excellent sealing, while the partition-capturing elastomeric wall sections formed by the shoulders 40 and 46 are preloaded to a predetermined extent dependent on the amplitude responsiveness desired. Furthermore, as to sealing, there is provided in addition to the face seal beads 74 an intermediate radially projecting annular edge sealing bead 75. The edge sealing bead 75 has an interference fit with the interior of the retainer collar 30, and thereby co-operates with both of the face seal beads 74 to provide double sealing between the chambers 66, 68 and atmosphere. On the other hand, the hydraulically biased partition 36 is pressed against one or other of the elastomeric shoulders 40 and 46 of the diaphragm so as to maintain tight sealing between the chambers 66 and 68. For example, assuming that the primary chamber 66 is contracting and the hydraulic pressure therein is increasing, the partition 36 is hydraulically pressed into very tight sealing contact with the shoulder 46 while the other shoulder 40 is relaxing with such partition movement, and while the double sealing provided by the sealing beads 74 and 75 remains unaffected because of their effective isolation by reason of their radially outward location relative to the partition.. Then when the secondary chamber 68 is contracting and the hydraulic pressure therein is increasing during the remainder of each damping cycle, the partition 36 is hydraulically pressed into very tight sealing contact with the shoulder 40, to thereby maintain tightly sealed integrity between the chambers while the other shoulder 46 relaxes, and while double sealing is maintained between the chambers and atmosphere by the sealing beads 74 and 75, Accordingly, the earlier-described limited free travel of the orifice member 37, which is shown in Figure 1 as being between the phantom-line positions, operates to effectively increase the displacement of the chamber being contracted to thereby further delay damping, but not to the same extent as is possible with the much larger displaceable chamber surface of the partition 36. To further assist understanding of the mount, reference will not be made to the mechanical analogy thereof shown in Figure 4, and to the graphs in Figures 5 to 10. In the mechanical ana#ogy shown in Figure 4, the elastomeric body 16 operating alone (without hydraulic damping) has an inherent spring constant K and a coefficient of damping C, and in typical adaptation without hydraulic damping for a typical vehicle engine installation and with the shape shown would produce the characteristics.shown graphically by the dash line in each of Figures 5 to 8. For example, in Figure 5, wherein load is plotted against deflection, there would normally be a distinct transition point (feel) between a desired relatively soft rate over a majority of the deflection range and a hard rate in the remaining, large deflection range. Because the inherent damping characteristics of rubber are relatively low and substantially constant, there is essentially no damping response either to changes in frequency, as is shown in Figure 6, or to changes in amplitudes, as is shown in Figure 7. Thus damping solely with the elastomeric body cannot readily be made specific to a particularly troublesome frequency, such as one caused by vehicle structure resonance, nor can the damping readily be made specific to a particular amplitude response, as is required in a typical engine installation in which a small damping effect is desired at low amplitude and high frequency of the engine, and a large damping effect is desired at high amplitude and low frequency. Furthermore, with increasing amplitude the rubber normally softens and as a result its stiffness value falls, as is shown in Figure 8, whereas the reverse is desired to assist in amplitude control. With reference again to the mechanical analogy shown in Figure 4, the hydraulic damping arrangement in conformity with the present invention adds to the spring stiffness K and the coefficient of damping C of the elastomeric body what will be referred to as (1) a wall bulge stiffness K' resulting from the wall section 72, (2) a diaphragm stiffness K" resulting from the diaphragm central portion 42, (3) a coefficient of damping C' resulting from the primary and secondary chambers 66 and 68 and interconnecting orifice 70, and (4) free soft travel X resulting primarily from the compliance of the diaphragm rim section 38 and secondarily from the slip fit of the orifice member 37. As is shown in the mechanical analogy, the wall bulge stiffness K' is connected in series with both the diaphragm stiffness RW and the orifice damping coefficient C', which are in turn both connected in series with the free travel X . The improved result provided by the coaction of all the mount elements is shown by the solid line in each of Figures 5 to 8. For example, as is shown in Figure 5, the deflection is thereby caused to increase gradually with load throughout the deflection range, thereby avoiding any distinct transition point and eliminating a distinct transition feel As is shown in Figure 6, on the other hand, the net effective damping with the hydraulic damping C' is not relatively constant, but is bell-shaped over the frequency range, and by selection of the size of the single orifice 70 and the stiffness K' and K" of the body wall section 72 and the diaphragm central portion 42 the damping may be concentrated "tuned") at a specific frequency so as best to reduce certain troublesome vibrations in a particular installation. As is shown in Figure 7, with the effective damping no longer relatively constant relative to amplitude or frequency, and because of the free soft travel VO only a small amount of damping is provided at low amplitudes (high frequency), with the damping thereafter increasing rapidly with amplitude, and substantially levelling off to provide a large amount of damping at high amplitudes (low frequency). The very desirable advantage of minimum damping at low amplitudes is made possible primarily by the free soft travel of the partition 36 permitted by the compliance of the diaphragm rim shoulders 40 and 46, ana secondarily by the fluid displaced by the telescoping motion of the orifice member 37 in consequence of its slip fit in the partition 36. Further, by reason of the added wall bulge stiffness K' and diaphragm stiffness K" coupled with the hydraulic damping, the net effective stiffness does not fall off with amplitude, but rather increases with amplitude, as is illustrated in Figure 8. Figures 9 and 10 further illustrate the improved performance provided by a hydraulic-elastomeric mount in accordance with the present invention. In Figures 9 and 10, loss angle and dynamic rate respectively are plotted against amplitude, with a comparison of the mount with and without hydraulic fluid. As can be seen in Figure 9, without hydraulic fluid the loss angle as therein defined increases only gradually and by a very small amount with amplitude, whereas with the hydraulic fluid added the loss angle increases steeply with amplitude and by a much greater amount, for example over double the amount, as is desirable, and further this occurs in the lower half of the amplitude range, whereafter the loss angle remains relatively constant. On the other hand, as is shown in Figure lo, without hydraulic fluid the dynamic rate continues to decrease with increasing amplitude, whereas with the addition of the hydraulic fluid the dynamic rate, after an initial fall-off, remains relatively constant. The hydraulic-elastomeric mount in accordance with the present invention is thus essentially predictable and may be readily adapted and tuned to meet a specific application to give the desired spring stiffness, coefficient of damping and resulting dynamic rate calculated to est isolate a particular set of vibration conditions. Thus by the invention a cost-effective family of mounts is made available, by appropriate selection of such parameters as the durometer value of the rubber used in both the elastomeric body and the diaphragm, the wall section thickness and the angles of the elastomeric body, the¯preload of the diaphragm, and the diameter, the length and the shape of the insertable orifice.

Claims: Claims: 1. A hydraulic-elastomeric mount coericing a pair cf mountie members (10 and 12), a hollow elastomeric body (16) interconnecting said mounting members, an elastomeric diaphragm (34) configured so as to close said elastomeric body and form therewith a closed cavity (64), a partition (36) dividing said cavity (64) into a primary chamber (66) enclosed by said elastomeric body and a secondary chamber (68) enclosed by said diaphragm, a liquid contained in said chambers, and an orifice (70) through said partition interconnecting said chambers so as to permit liquid in said primary chamber (66) to flow at a restricted rate into said secondary chamber (68) upon contraction of said primary chamber and in the opposite direction on expansion thereof, to thereby provide a damping effect, characterised in that said elastomeric diaphragm (34) extends over the periphery of said partition (36) and forms a seal between said chambers (66, 68) and atmosphere and also between said primary chamber (66) and said secondary chamber (68), and that said diaphragm (34) is configured so as to permit limited substantially free travel of said partition (36) relative to said mounting members (10 and 12) below a predetermined vibration amplitude of one mounting member relative to the other and to prevent such travel above such amplitudes, so that flow through said orifice (70) to effect damping does not occur until said predetermined vibration amplitude is exceeded. 2. A hydraulic-elastomeric mount according to claim 1, characterised in that said diaphragm (34) is formed with a predetermined compliance and provides a double seal between said chambers (66, 68)and atmosphere and additionally provides alternatively pressure-biased seals between the primary and secondary chambers (66 and 68). 3. A hydraulic-elastomeric mount according to claim 2, characterised in that a rim portion (38) of the partition (36) provides the alternatively pressure-biased seals between opposite sides of the partition . and the respective chambers (66 and 68), and that said rim portion (38) forms a face seal on each side thereof and an edge seal between the face seals so as to provide said double seal between said chambers (66, 68) and atmosphere. 4. A hydraulic-elastomeric mount according to any one of claims 1 to 3, characterised in that said diaphragm (34) has in a rim portion (38) thereof an inwardly facing groove (39) receiving the peripheral region (44) of said partition (36) so as to provide said sealing, and that said rim portion (38) has shoulders (40 and 46) on the sides of said groove (39) providing compliance permitting said limited substantially free travel of said partition (36). 5. A hydraulic-elastomeric mount according to any one of claims 1 to 4, characterised in that said orifice (70) is formed in an orifice member (37) which is mounted for limited relative free travel in said partition (36) in response to pressure thereon in said chambers (66 and 68), whereby said damping effect is provided only following relative travel of said orifice member (37) in said partition (36).

Inventors: MUZECHUK, RICHARD ALLEN
Applicants: GENERAL MOTORS CORPORATION
Application year: 1983
Main classification: F16F9
IPC codes: F16F9, F16F13, B60K5