GB2136530A - Springs - Google Patents

Abstract

A spring assembly for use with motor vehicles comprises a compression type rubber spring in combination with a rigid restraining pot. The rubber spring preferably comprises a sphere or a generally cylindrical double tapered integral body 17 having an axial cavity 21 of divergent/convergent form. The pot 23 is adapted to fit over one end of the spring and enclose at least one end and the equator of the spring whereby initial flexing of the spring is not curtailed but extended flexing and bulging of the spring under increased load or shock conditions are restrained by the pot rim and sidewall. The sidewall may be open. <IMAGE>

Description

SPECIFICATION Self-damping springs This invention relates to a compression type rubber spring and, more particularly, relates to a selfdamping rubber spring assembly for use in vehicle suspension systems.

Compression type springsformed of an elastic material such as natural or synthetic rubber, such as disclosed in Canadian Patent No. 977784 issued November 11, 1975 have proven to be excellent variable rate springs in commercial vehicle suspensions as use on trucks and trailers. The spring rate of deflection adjusts to the variable load condition experienced by such vehicles and tends to maintain a relatively constant pitch frequency or frequency of vibration.

However, an undamped rubberspring provides little hysterisis for small deflections ofthe spring and vehicles incorporating these springs tend to float or bounce continuouslywhiletravelling on a road surface.The resulting small amplitudes or vertical travel, although normally harmless, can be annoying tothedriverand passengers.

Damping ofthespring can be achieved by using a rubber with increased hysterisis, i.e. a "deader" rubber, but the effect would be that the spring would take a permanent set and not return to its original shape when the load was removed, It is desirableto use a highly elastic rubber spring with an increased hysterisis. This cannot be achieved by changing the rubber mix.

It is thus necessary to add additionally damping externallytothe rubber.

Damping is normally applied parallel to the spring by means of an ancillary shock absorber. The damper thustransmitsshockthroughtothe sprung body and a compromise in its damping factor or restraint applied to the spring is necessaryto achieve a tolerable ride. However, the damper is only ideal for one load condition; it is too stifffor an empty vehicle or one with a light load, and too soft orweakto control an overload. It is thus desirable to provide damping which will adjust two load and travel conditions.

The suspension should ideally have little or no damping for very small amplitudes. This permits the suspension to be sensitive and responsive to small irregularities on the road surface such as joints in the pavement orto coarse tires. Thus as the bumps and amplitudes increase, the damping should increase and quickly bring the suspension back into the "sensitive" range. The damping device should thus adjustto the spring travel and its damping qualities should increase with deflection.

Aspring has one frequency fora given load condition, regardless ofthe deflection. In other words, ittakes the same period of time for the suspension to go through one cycle regardless ofthe amplitude.

Thusforsmalltravel oramplitude,thevertical acceleration forces on the spring body will be mild. For large amplitudes, however,the acceleration forces can be severe and damage to freight being transported can easily result.

I have found that vertical acceleration forces can be minimized or maintained constant bythe reduction of pitch frequency with increased amplitude, i.e. by variation of pitch frequency with changes in amplitude for the same load. This can be accomplished bythe application of damping to one portion of a spring in series with another portion of a spring which is lightly damped or undamped or bytwo or more springs in series with at least one ofthem undamped and at least one of them damped.

With small amplitudes, only the lightly damped or undamped portion of the spring deflects and the frequency is based upon that deflection. With larger amplitudes the damped portion is forced to deflect and the frequency is based upon the total deflection with more time taken to go through one oscillation or cycle. This increase in time decreases the acceleration and thus the vertical forces on the sprung body and freight.

The large amplitudes result in out-of-phase pitching with the heavily damped and undamped portions of the spring with each literally wishing to control the frequency. The damped and undamped portions of the springs may be "tuned"to rapidly "kill" the bouncing.

The spring assembly of the present invention, in its broad aspect, comprises an integral body of elastic material such as natural or synthetic rubber, said body having opposite end faces and a substantially circular cross-sectionthroughoutits length with an equator having a larger diameter than the diameter of the end faces, and a rigid pot for receiving a portion of said integral body therein, said pot having a substantially planar base and at least one depending sidewall sufficiently long to at least accommodate one end face and the equator ofthe integral body whereby lateral expansion ofthe integral body within the pot is controllabiy restrained during compression of the integral body.The integral body preferably is generally cylindrical with a double taperfrom the equator to the opposite end faces and the pot preferably has a circular sidewall with a rim depending from the planar base, said rim extending beyond the equator of the integral body.

The integral body may fit loosely within the pot rim wherebythe integral body can laterally expand slightly before being laterally restrained by the pot, usually first at the pot rim which may have an outwardly radiused orifice necked down to minimum diameter substantiallyopposite the equatorofthe integral body.

The present invention will now be described with reference to the accompanying drawings, in which: Figure lisa central vertical section of a known rubber spring in its unladed position; Figure 2 is a vertical section of the spring shown in Figure 1 in a loader, partially compressed condition; Figure 3 schematically illustrates a series-damped spring of the present invention in an unladen position; Figure 4 is a central vertical section of a seriesdamped rubber spring assemblyofthe present invention in an unladen position; Figure Sis a vertical section of the spring shown in Figure 4 in a loaded, partially compressed condition; Figure 6 is a central vertical section of another embodiment of a rubber spring assemblyofthe present invention; Figures 7,8 and 9 are central vertical sections of still further embodiments ofthe present invention; and Figure 10 is a graph illustrating performance of the spring assembly ofthe present invention compared to a known rubber spring.

Figures 1 and 2 show a known rubber spring 10 of generally cylindrical form which is free to laterally expand under load conditions. Although some hysterisis or molecularfriction is provided,frequency of oscillation remains substantially constant with high rates of vertical acceleration for large amplitudes.

The series-damped spring assembly 11 shown schematically in Figure 3 connected to load 12 comprises a coil spring 13 with a dash-pot or"shock absorber" 14connected to spring 13 at a point intermediate its ends such thatthe upper portion 15 is damped and the lower portion 16 is free to flex, for reasons which will become apparent as the description proceeds.

Figure 4 shows a generally cylindrical rubber spring 17formed as an integral body having a doubletaper from the equator orwaist 18to the upper and lower ends 19,20. The interior of spring 17 is hollow with an axial cavity 21 extending between the end faces 22, 22a, said cavity 21 being ofdivergentlconvergentform having a minimum cross-section at transverse planes corresponding LO the equator 18 and end faces 22, 22a wherebythe rubber spring has an increased wall thickness at the equator 18 and ends 19,20.Circular pot 23, usually formed of steel, has a flat base 24 with an outwardly convex side wall 25 and an orifice rim 26 outwardly radiused at an angle of between about 2 to about 1 into the plane ofthe side wall, preferably about 10 , necked down to a minimum reduced orifice diameter at 27 substantially opposite the equator 18 of the rubber spring. The minimum diameter of orifice 27 preferably is aboutthe same as or slightly largerthan the outside diameterofequator 18 of spring 17.

Pot 23 is placed over one end of spring 17, usually the upper end 19, and as a load 28 is applied to the spring-pot "ensemble" 29 which is fixed between the sprung and unsprung parts of a vehicle suspension, the rubber bulges outwardly and applies pressure on the inside ofthe orifice rim 26 ofthe pot, FigureS. The pot slides up and down the outside of the rubber spring, generating heat. The portion ofthe spring in the pot thus is damped and the external portion only has hysterisis damping. The percentage of the spring which is heavily damped increases with the load and with deflection.

The taper ofthe side of the rubber spring is greater than at least 20to the axis ofthe spring such that, as the pot 23 slides down the spring 17, the diameter of the rubber spring adjacentthe rim orifice will be suitable fortheouterdeflectionofthespring andthepressure between steel and the rubberwill provide the desired restraint. The side of the rubber spring is designed by the taper angle or shape to provide the correct restraint. The taper need not be a straight line and may be curved.

The interior of the pot is concave above the radiused edge of the rim orifice 27 to receive the rubber spring 17 as the spring flexes laterally under load and the rubber material flows into the void 30 surrounding the upper end 19 ofthe spring, as shown in FigureS. The portion 31 of spring 17within pot 23 thus functions as the damped portion of the spring and the portion 32 of spring 17 remaining outside of pot 23 functions as the undamped portion, the two portions cooperating asa series-damped spring.

The restraining action of the pot acting on the rubber spring stiffens the spring and prevents overstraining ofthe rubber. A stop in travel is provided when the rubber spring fills the void 30 completely since rubber is incompressible. The maximum distortion of the rubberthusiscontrolled. Heavier loads may be carried by a spring withoutthe spring suffering from permanent set end failure. Conversely, a smaller spring can be usedto handle a given load when working within a pottosaveweightandcosts.

The elimination of shock-absorbers andtheirconnections or brackets is a major advantage, again resulting in saving in weight, cost and maintenance.

The spring/pot combination is essentially mainte nance4ree for many miles oftravel. The natural settling properties of rubber will cause itto bulge into gaps worn into the rubber. The spring characteristics will thus remain constant.

With reference nowto Figure 10, the effectiveness of the spring assembly ofthe present invention compared to a rubber spring without restraining means is illustrated graphically. The curve depicted by numeral 96 represents the load deflection curve of rubber spring 10 as a load 98 (Figure 2) of 50,000 pounds was applied and then released. The area defined between the upper compression line and the lower rebound line represents the effectiveness of damping due to hysterisis or molecularfriction in the rubber spring.

The vertical line between the compression and rebound lines, having the length 100, indicates the damping force ofthe spring, e.g. about8,000 pounds.

The curve depicted by numeral 102 representsthe load deflection curve ofthe spring assembly of the present invention as a load 28 of 50,000 pounds (Figure 5) was applied and released. The vertical line between compression and rebound lines, atthe same deflection as measuredforthe rubber spring, having the length 104, indicates an improved damping force of about 20,000 pounds.

Curve 102 peaked at a lower deflection ofthespring assembly compared to curve 96 for the rubberspring in the amount indicated by numeral 1 Q6.

The embodiment of my invention shown in Figure 6 comprises a rubber spring 33, shown partially deformed by loading, inserted into pot 34 identical to pot 23 except four central aperture 36 in base 37 with interiorflange 38 forming a spigot adapted to seat in central cavity 18 of spring 33forco-axial alignment of spring 33 with pot34. A metal spigot 40 with annular base 42 is received in the opposite end of spring 33 for co-axial alignment ofthe centre of pot 34 with base 42.

The spring rubberwill provide cushioned location of the spring assembly and associated vehicle suspen sion in the horizontal plane while the spring is free to travel vertically to counter load or shock.

Figure 7 shows a series-damped spring assembly 50 in which rubber spring 52 is inserted into an open pot formed buy a ring 54 suspended below circular plate 56 parallel thereto by rigid support arms 58. The inside diameter of ring 54 defines a rim 55 which is substantially equal to or slightly largerthan the diameter of equator 60 of spring 52. This assembly functions in a manner similar to the embodiment illustrated in Figures 4-6 with the exception that the rubber material cannot be completely restrained by flexing in a closed pot.

Figure 8 shows a rubber spring 62 within a tubular pot 64which has a cylindrical side wall 66 and planar base 68. Avoid 70 is present in the upper portion ofthe potadjacentthe end 72 of spring 62 to permit flexing ofthe rubber material as the spring waist moves up and down within the rim 74 of pot 64.

Figure 9 shows a further embodiment of my invention in which a spherical rubber ball 80 is inserted into pot or like restraining receptable 82 of rectangular, preferably square, hexagonal or the like multi-faceted cross-section. The lower end 84 of sphere 80 is free to flexwhilstthe central, i.e. equator 86, and upper portions 88 are restrained within the restraining device.

Itwill be understood that modifications can be made in the embodiment of the invention illustrated and described herein without departing from the scope and purviewofthe invention as defined by the appended claims.

Claims (15)

1. A Spring assembly for a vehicle suspension comprising, in combination, an integral body of elastic material such as natural or synthetic rubber, said body having opposite end faces and a substantially circular cross-section throughout its length with an equator having a larger diameterthan the diameter of the end faces, and a rigid potfor receiving a portion of said integral bodytherein, said pot having a substantially planar base and at least one depending sidewall sufficiently long to at least accommodate one end face and the equatorofthe integral body whereby lateral expansion of the integral body within the pot is controllably restrained during compression of the integral body.

2. A spring assembly as claimed in Claim 1 which comprises a generally cylindrical integral body having a doubletaperfrom the equatorto the opposite end faces and said pot having a circular sidewall with a rim depending from the planar base, said rim extending beyondthe equator of the integral body.

3. A spring assembly as claimed in Claim 2 in which said integral body fits loosely within the pot rim wherebytheintegral body can laterally expand slightly before being laterally restrained by the pot.

4. A spring assembly as claimed in Claim 2 in which said rim has an outwardly radiused orifice necked down to minimum diametersubstantially opposite the equator of the integral body.

5. Aspring assembly as claimed in Claim 2, 3 or4 in which the sidewall is outwardly convex and in which said integral body has a taper at least 2"to the axis ofthe integral body.

6. Aspring assemblyasclaimed inClaim4in which said integral body has an axial cavity extending between said end faces, said cavity being of divergent/ convergent form having a minimum cross-section at a transverse plane corresponding to the equator.

7. Aspring assembly as claimed in Claim 6 in which the pot planar base has a central interiorflange forming a spigot depending therefrom adapted to seat within the axial cavity of the integral body for co-axial alignment of the integral body with the pot.

8. Aspring assembly as claimed in Claim 7which additionallycomprisesa rigid basewith spigot adaptedto be received in the axial cavityatthe opposite end face of the integral body for co-axial alignment therewith.

9. Aspring assembly as claimed in Claim 2,3 or4 in which said pot comprises a base having an open sidewall and a rim formed by a ring supported parallel to the base by rigid support arms.

10. A spring assembly as claimed in Claim 2,3 or4 in which said pot has a planar base and a cylindrical sidewall depending therefrom.

11. A spring assembly as claimed in Claim 1 in which said intergral body is spherical in shape.

12. A spring assembly as claimed in Claim 10 in which said pot has a multi-faceted cross-section.

13. A spring assembly as claimed in Claim 4,5 or 6 in which said rim is outwardly radiused at an angle between about 2"to about 1 5"to the plane of the pot sidewall.

14. Aspring assembly as claimed in Claim 4,5 or 6 in which said rim is outwardly radiused at an angle of about 1 0'to the plane of the pot sidewall.

15. A spring assembly substantially as herein described with reference to and as shown in figures 3 to 10 of the accompanying drawings.