USRE23743E

USRE23743E - Vibration isolator

Info

Publication number: USRE23743E
Authority: US
Priority date: 1951-10-15
Publication date: 1953-11-24
Also published as: GB693545A

Description

Nov. 24, 1953 F. LAMBERT. JR. ETAL Re. 23,743

VIBRATION ISOLA'IOR Original Filed May 19, 1948 Pg- 5 Frank Lambert Char/es E. Grade 04 06 as 10 644ml. 2. 611A Deflection, Inc/2e: Age! If Reiuued Nov. 24, 1953 VIBRATION ISOLATOB Frank Lambert, Jr., West Newton, and Charles E. Crede, Winchester, Mam, acsignors to'lhe Barry Corporation, a corporatlonwi Massaehusetts Original No. 2,610,017, dated September '9, 1952,

Serial No. 27,948, May 19, 1948. Application for reissue September 24,

Claims.

1952, Serial No.

Matter enclosed in heavy brackets I: appears in the original patent but Iornu no part of thh name specification} matter printed m italics indicatec the additions made by reissue.

' isolate such equipment from any vibration which may exist at the supporting structure. Vibration i'solators, in general, are well known and 1 may be described briefly as a resilient means for supporting the equipment.

It may be determined from the theory of vibration isolation that it is required that the natural frequency of the equipment upon the isolators must be substantially lower than the frequency of the vibration which is to be isolated.

An equipment mounted upon resilient mounts has a natural frequency, and the motion of the equipment may become excessively large at resonance; i. e., when the vibration to be isolated occurs at the natural frequency of the equipment upon the isolators. It is an object of our invention, therefore, to provide a vibration isolator with a large damping capacity in order to prevent excessive excursion of the mounted equipment when operating at or near its resonant frequency.

Another object of our invention is to provide a vibration isolator whose natural frequency remains constant independently of the load al I plied to the isolator. This is advantageous when the weight or weight distribution of the mounted equipment has not been accurately predetermined or when it varies from time to time.

A further object of our invention is to provide a vibration isolator which will remain operative at extremely high and low temperatures. This requires the use of a resilient load-supporting element which remains operative throughout a wide temperature range and damping means which provides adequate damping at all temperatures.

Other objects and advantages of our invention will become apparent from the following detailed description and accompanying drawings in which:

Figure 1 is a plan view of the isolator.

Figure 2 is a section on line 22 of Figure 1 showing the isolatorin a position of mean deflection.

Figure 3 is a view similar to Figure 2 showing the isolator in a position of greatest deflection.

Figure 4 is a view similar to Figure 2 showing the load-carrying spring in an inverted position.

Figure 5 is a load-deflection curve for a spring whose natural frequency remains constant at 5 cycles per second independently of load from 0.25 to 0.75 lb.

As illustrated in Figures 1 and 2, the isolator includes an outer retaining cup "land a base' plate ll attached together by means of eyelets I3 which embody central. holes for attachment of the isolator to a supporting structure. A shallow positioning cylinder I8, is attached to the base plate II at its center. A volute spring I 1 is supported by the base plate ll and-nests within the positioning cylinder it; A central core l9 extends downwardly through the opening 20 in the top wall 22 of the retaining cup II and has a pilot 23 whichnestsin the upper coil of the volute spring 21. The core I! has rigidly attached thereto a flat upper washer Iland a dome-shaped lower washer 2i. Theflopening 2|! in the upper wall of the retaining cup H is encircled by a rubber grommet II attached to. the retaining cup ID. The central core is tapped for attachment of the mountedequipment. The upper (25) and lower (26) ,washersjare larger than the opening 20 in the retainingcup so that the mounted equipment is madecaptive; that is, it cannot escape from the supporting structure in the event offailure off the resilient parts of the isolator. V

The volute spring I! is. positioned within an enclosure formed preferablyfby a thin-walled, sphere-like member 30 made Irom rubber or other resilient material. Av boot jl l which surrounds and forms a part of the upperlofthe sphere-like member'lll flts aroundtheperiphery of the lower washer 26 and formsan airtight connection therewith. An integralperipheral flange 33 at the lower edge of the resilient member 30 is held in contact withthe base plate II by a clamp plate 34 interposed between the outer retaining cup ll and! the base; plate; [I and held in position by the eyelets It. {The spring I1 is thus contained within a flexible enclosure which is airtight except for asmall; aperture 36 in the lower washer 26. V Y a; Y

As the isolator is deflected dow wardly-from the position shown in Figure} to, the position shown in Figure 3. the volume contained: within the rubber member Ills decrease dif someof the air within the enclosure isqthus expelled through the aperture it. In a; similar manner, when the isolator is deflected upwardly. thevolume within the rubber member. vill isincreased and air is drawn inwardlythrough the. aperture 3'. The force applied to. themount ls used'part- 1y to deflect the spring l1 and partly to expel the air through the aperture It; The, energyhused to deflect the spring is stored in-ithe sprlnganrl returned to the mounted body when the spring is restored to its initial length. The energy used equipment when operating at its resonant frement and the mass of the supported body. If'the.

stiffness of the resilient element is constant, independently of deflection, the natural frequency of the system decreases as the mass of the mounted body increases. The frequency can be maintained constant, however, if the stiflness increases proportionately to the applied load. The load-deflection curve shown in Figure illustrates the required characteristics in order to maintain the natural frequency constant at 5 C. P. S. for any load between 0.25 lb. and 0.75 lb. In a volute spring, the outer coils are more flexible because they are coils of larger diameter. when these outer coils become inactive, the stiffness of the spring increases because the remaining active coils are fewer in number and smaller in diameter. The volute spring, therefore, has a stiflness which increases with load because the outer coils successively bottom. upon the supporting surface and become inactive as the deflection increases. By proper choice of the radii of the various coils and the helix angle which determines the rate at which the height of the spring increases, a spring may be designed with the characteristics shown in Figure 5. These characteristics are desirable where r the exact load on each isolator has not been predetermined or where the weight distribution 0! the mounted body changes from time to time.

Figure 4 shows .a modified form of the isolator in which the volute spring 31 is arranged with its larger coils at the top. As deflection of the isolator takes place, the larger diameter coils bottom. upon the washer I! which is attached to the central core Ill.

The accompanying drawings illustrate the preferred form of the invention, although it is to be understood that the invention is not limited to the exact details of construction shown and described, as it is obvious that various modifications thereof, within the scope of the claims, will occur to persons skilled in the art.

We claim:

[1. A vibration isolator comprising a main resilient member for carrying the load and an enclosure member for said main resilient member forming a chamber about it, said enclosure member having a resilient side wall which is symmetrical with respect to the vertical axis of the main resilient member and which is spaced outwardly a substantial distance from the main resilient member throughout substantially its en- I forming a chamber about it. said enclosure memv 4 4 her having 'a resilient side wall which is symmetrical with respect to the vertical axis of the main resilient member, which is spaced outwardly a substantial distance from the main resilient member throughout substantially its entire length and which is provided with an outwardly convex portion intermediate its ends,

said enclosure member being substantially impervious to air except for a relatively small aperture, whereby upon deflection of said main resilient member said outwardly convex portion of the side wall of the enclosure member is also deflected and air is caused to flow through said aperture, thereby causing damping to prevent excessive excursion of the mounted equipment without frictional engagement between said outwardly spaced side wall of the enclosure member and the main resilient member] 3. A vibration isolator comprising a single main resilient member for carrying the load, an enclosure member for said main resilient member having a resilient side wall and a rigid top wall and forming a chamber about the main resilient member, said side wall being symmetrical with respect to the vertical axis of the main resilient member and spaced outwardly a substantial distance from the main-resilient member throughout substantially its entire length, the upper end of said enclosure side wall being attached to said rigid top wall, a mounting stud attached to said top wall and being adapted to transmit the load to the upper end of the main resilient member, said enclosure member being substantially impervious to air, said top wall having a relatively small aperture, whereby air is caused to flow through said aperture upon deflection of said main resilient member and thereby causes damping to prevent excessive excursion of the mounted equipment without frictional engagement between said outwardly spaced side wall of the enclosure member and the main resilient member.

4. A vibration isolator comprising an outer cup having an opening in the top thereof, said cup being adapted to be secured to a. supporting structure, a single coil spring disposed within said cup for carrying the load, a stud ertending through said opening, said stud having a cross section substantially smaller than said opening, the vertical axis of said stud being substantially in alignment with the vertical axis of said spring and said spring resiliently supporting said stud, and an enclosure member for said spring forming a chamber about it, said enclosure member having a resilient side wall which is symmetrical with respect to the vertical axis of said spring and which is spaced outwardly a substantial distance from said spring throughout substantially its entire length, said enclosure member being substantially impervious to air except for a relatively small aperture, whereby air is caused to flow through said aperture upon deflection of said spring and thereby causes damping to prevent excessive e: cursion of the mounted equipment without frictional engagement between said outwardly spaced side wall of the enclosure member and said spring.

5. A vibration isolator comprising an outer cup having an opening in the top thereof, said cup being adapted to be secured to a supporting structure, a coil spring disposed within said cup for carrying the load, a stud extending through said opening, said stud having a cross section 7 substantially smaller than the opening, the-vertical axis of said stud being substantially in alignment with the vertical axis of said spring and said spring resiliently supporting said stud, and an enclosure member for said Spring forming a chamber about it, said enclosure member having a resilient side wall which is symmetrical with respect to the vertical axis of said spring and which is spaced outwardly a substantial distance from said spring throughout substantially its entire length, the outermost surface of the side wall of said enclosure member being spaced a short distance from the inner surface of the side wall of the cup under normal operating conditions but impinging with said inner surface upon lateral movement of said stud, said enclosure member being substantially impervious to air except for a relatively small aperture, whereby air is caused to flow through said aperture upon vertical or horizontal deflection of said spring and thereby causes damping to prevent excessive excursion of the mounted equipment without frictional engagement between said outwardly spaced side wall of the enclosure member and said spring.

6. A vibration isolator comprising an outer cup having an opening in the top thereof, said cup being adapted to be secured to a supporting structure, a single coil spring disposed within said cup for carrying the load, a stud extending through said opening, said stud having a cross section substantially smaller than the opening, the vertical axis of said stud being substantially in alignment with the vertical axis of said spring and said spring resiliently supporting said stud, an enclosure member for said spring forming a chamber about it and a rigid flange on said stud located within the casing and being larger than said opening whereby it limits vertical movement of said stud upwardly through said opening, said enclosure member having a resilient side wall which is symmetrical with respect to the vertical axis of said spring and which is spaced outwardly a substantial distance from said spring throughout substantially its entire length, said enclosure member being substantially impervious to air except for a relatively small aperture, whereby air is caused to flow through said aperture upon vertical deflection of said spring and thereby causes damping to prevent excessive excursion of the mounted equipment without frictional engagement between said outwardly spaced side wall of the enclosure member and said spring.

7. A vibration isolator comprising an outer cap having an opening in the top thereOf, a single main resilient member disposed within said cup for carrying the load, a stud extending through said opening, said stud having a cross section substantially smaller than said opening, the vertical axis of said stud being substantially in alignment with the vertical axis of said main resilient member and said main resilient member supporting said stud, and an enclosure member for said main resilient member forming a chamber about it, said enclosure member having a resilient side wall which is symmetrical with respect to the vertical axis of said main resilient member and which is spaced outwardly a substantial distance from said main resilient member throughout sub stantially its entire length, and which is provided with an outwardly convex portion intermediate its ends, the outermost surface of said outwardly convex portion of said enclosure member being spaced a short distance from the inner surface of the side wall of the cup under normal operating References Cited in the file of this patent or the original patent UNITED STATES PATENTS Number Name Date 943,709 Sherwood Dec. 21, 1909 2,175,405 Meredith et a1 Oct. 10, 1939 2,425,565 Robinson Aug. 12, 1947 FOREIGN PATENTS Number Country Date 511,737 Great Britain Aug. 23, 1939 540,084 Great Britain Oct. 6, 1941 Germany Dec. 17, 1931