Title of Invention

VEHICLE LEAP SPRING BUSHES

Abstract

An improved bush for use in mounting of leaf springs for vehicles is described comprising support ribs located on the outer cylindrical face thereof, for engagement with the inside surface of the non-circular portion of the leaf eye. Said engagement provides support for the bush in said non-circular portion, unlike as in conventional mountings, and reduces the wear and tear and provides extended life thereof Different embodiments are described wherein said ribs comprise a single rib extending substantially over the whole length of the bush or a segmental construction. Being well supported, bushes of the invention can be made of plastics unlike conventional bushes. This lowers costs and allows for matching of expected bush life and leaf life under different working conditions. PRICE: THIRTY RUPEES

Full Text

This invention relates to leaf springs used in suspensions of road, rail and other vehicles. More specifically, this invention relates to the bushes that are used in the mounting of leaf springs upon vehicle bodies, chasses and frames. Leaf springs are widely used in the suspensions of automotive vehicles such as cars, three-wheelers, buses, trunks and lorries. They are also used in rail vehicles such as locos, tankers, wagons and passenger carriages. They are furthermore, used in tractors, trailers, tracked vehicles and earth-moving veliicles. They are also used in manually powered road vehicles such as for example, cycle-rickshaws. The bushes of this invention have potential application in all the vehicles mentioned hereinabove. In the interests of clarity, consistency and conciseness the following definitions/confirmations are followed in the specification and claims hereinbelow: (i) The term 'leaf spring' is intended to cover all other terms by which it is referred to, such as. for example, laminated plate springs and laminated springs; (ii) The term 'bush' is intended to cover all other tenns by which it is referred to such as for example. 'bushing'; (iu) The term 'spring eye' is intended to cover all other expressions by which it is referred to , such as for example, 'spring hole'; (iv) The term 'hanger' is intended to cover all other expressions by which it is referred to such as for example, 'bracket', 'hinge' and 'pin joint'; (v) The term 'leaf in the context of a leaf spring is intended to cover all other terms by which it is referred to, such as for example, strips and blades; (vi) References to a 'longitudinal' mounting of a leaf spring or a leaf spring suspension implies that it is aligned generally parallel to the longitudinal axis of the vehicle. Likewise, a transverse mounting thereof implies that it is generally horizontal and aligned substantially perpendicular to said vehicle longitudinal axis; (vii) References to the front and rear of a leaf spring imply that it is aligned generally longitudinally as mentioned in (vi) and that the former is ahead of the latter along the direction of the said longitudinal axis going from the rear tow'ards the front of the vehicle: (viii) A leaf spring suspension essentially comprises one or more leaf springs and. in addition, may have other springing elements and also other elements such as location rods/bars and the like. When a leaf spring suspension comprises a single leaf spring without any of said additions, the expressions 'leaf spring" and 'leaf spring suspension mean the same. Vehicle suspensions are two types independent and dependent. .A widely used depcndeni suspension comprises a beam having asles located at each end with wheels monntable (hereupon, the vechicle body, chassis or frame being mounted upon said beam through two longitudinal leaf spnngs located one each on each side of the vechile longitudinal. alternatively the vehicle body, chassis or frame may be mounted through a single transyerse lea!" spring instead of said two longitudinal ones. Beam axle suspensions of the former type are widely used in conunercial \ chicles and also considerably m passenger cars. Independent suspensions may also comprise a leaf spring. A mono-leaf spring comprise just single leaf whereas a mulltiple-leaf spring comprises a stack of leaves, the lengths of succcss leaves in acid stack becoming greater going either up or down the stack. In the most common arrangement. the longest leaf is located at the lop of the stack. The leaves in leaf spring may be flat or may be slightly arched, that is. generally elliptical in shape. The arching may be positive or negative. Mosty. howere the leaf are half-ellipitcal and the arching is such that the lea\ es are convex to the ground. Quarter- and full-elliptical springs are also used. Altliough, there is a great di\ ersit\ in leaf spring configurations, the arrangement or metliod of mounting thereof upon their respecti\ e ^ chicle bodies, frames or cliasses is essentially the same and the minor adaptations, required if any to suit a particular configuration can be simple carried out by a person of average skill in the art. Therefore, in the interests of clarity and conciseness, the mounting of leaf springs will be hereindescribed only with reference to one common configuration, namely, a half-elliptical longitudinal leaf spring. The ends of the longest leaf located at the top of the stack are forged into circles so as to form spring eyes. The front spring eye is mounted upon the front hanger while the rear spring eye is mounted upon the rear hanger not directly but through a spring shackle. Each said hanger comprises essentially two trunnions that may be separate or integral with each other. The two trunnions of a hanger have a hole each and said two trunnion holes he on a horizontal axis perpendicular to the longitudinal axis of the vehicle. During assembly, the front spring eye is aligned with said trunnion holes and a pin is passed through said holes and the spring eye. The pin is secured in position by a fastening means. Alternatively, the pin may have a bolthead and screwed portion for securing the assembly. Interposed between said pin and inside surface of said front spring eye is a bush that provides the bearing surface on its outside and inside cylindrical faces. Said outside and inside cylindrical faces engage respectively the inside surface of said spring eye and the pin surface and transmit the vehicle weight/load through said spring eye to the vehicle axles and thence to the wheels. Said faces of the bush also provide the bearing surface for the relative motion which takes place between the pin and the spring eye as the vehicle encounters the unevennesses of the road surface during motion. The rear hanger is similar in construction to the front hanger and the mounting of the upper end the spring shackle thereupon is similar to the mounting of the front spring eye upon the front hanger. The upper end of the spring shackle is ahgned with the tnmnion holes and the mounting is fastened by means of a pin similar to the one used in the front spring eye mounting. Interposed between the said pin and said shackle is a hollow cylindrical bush which provides the bearing surfaces and is similar to the bush employed in the front spring eye mounting described hereinabove. To distinguish the said hollow cylindrical bush used in the mounting of the upper end of a shackled from the bushes of prior art and invention used in the spring eye mountings, the former is referred to further herein as the bearing sleeve. the rear spring eye is mounted upon the lower end of the sprmg shackle. The rear spring eye is aligned between the holes provided at the lower end of said sliackle and is fastened by means of a pin similar to that used in spring eye mountings described hereinabove. A hollow cylindrical bush is interposed between the pin and the spring eye and provides the bearing surfaces for the transmission of the static vehicle load to the ground and also the dynamic loads arising out of the motion of the vehicle and consequent flexing of the leaf spring. As the leaf spring flexes there is a change in its span as the rear end thereof moves forwards and backwards in a horizontal longitudinal direction, litis motion of the rear end of the leaf spring is accommodated by the spring shackle. Having described the feature of vehicle leaf spring mountings it should be mentioned that within the design context described several variations are possible and are used in practice in vehicles, which variations are marginal to the basic design unity of the various types of mountings. For example, the spring shackle and/or the bushes may be in two parts or that said bushes may have collars or flanges for location and/or fixing or the bushes may be split In another design the front hanger comprises a pin extending from the the vehicle frame or chassis, upon which the spring eye and bush are mounted. The bushes of this invention have applications in all aforesaid mountings and are easily and simply adapted for such use by a person of average skill in the art. These comments apply to both said bushes and bearing sleeves. Spring eyes, which are formed by means of either rolling or forging of the leaf ends are substantially circular except in the comer formed by the turned-back leaf end and the adjacent leaf portion. Said comer, which is substantially triangular in profile, that is, in the shape of a substantially triangular prism, runs across the full width of the leaf. Said comer is referred to hereinbelow as the 'spring eye comer'. Leaf spring mounting bushes, during operation, are subject to static loads arising out of the weight of the vehicle and its contents and to several dynamic loads that arise due to such factors as the flexing of the leaf spring caused by movement of the vehicle, the acceleration and braking of the vehicle and the forces that arise out of the transmission of power to the wheels and the cornering of the vehicle. Under the effect of these forces, the bush material suffers distortion and creep flow wherever the body of the bush remains unsupported as at said spring eye comers. It will be observed that the outer cylindrical face of the bush is in engagement with the spring eye substantially all around except in the region of said spring eye comer and the bulk of the distortions and creep flow in bush material occur precisely in this region. Considerations and analysis of bush distortions and creep flow caused in the region of spring eye comers does not appear to have done in the prior art and is novel. Potential metallic materials for bushes are common alloys of one or more of the following: Copper, Tin, Lead, Antimony, Zinc, Aluminium, Nickel and a few others. These alloys have a greater or lesser tendency towards distortions and flow tmder compression. In fact, a certain amount of malleability is desirable in bush materials so that they flow somewhat under compression and allow for small misalignments in assemblies. The drawbacks/disadvantages of bush distortions are: i. lower bush life and consequent higher vehicle nmning costs; ii. increased transmission of noise and vibration to the vehicle body; and iii. increased lubricant consumption. It is the object of this invention to provide a bush wherein said distortions and creep flow are minimised and said drawbacks/disadvantages are reduced or eliminated. In the bushes of this invention, this is achieved in a novel way by providing support for the bush in the region of said spring eye comers. According to the invention, therefore, there is provided a bush, for the mounting of leaf springs upon vehicle bothes, frames or chasses, comprising a hollow cylindrical portion, said portion being characterised in having one or more support ribs that are disposed longitudinally thereon and that provide support thereto by engagement with the sides of the comer of the eye of the said leaf spring, wherein it is mounted. The said support ribs are located parallel to the longitudinal axis of the bush and at regular spacings. The number of ribs required will depend on the width of the leaves. In practice, a very wide range of leaf widths are used so that there may be one, two or three or more of said support ribs associated with a bush. The support ribs may be attached to the surface of said hollow cylindrical portion by fasteners or alternatively may be integrally cast therewith. If the bush is made of plastics it may moulded integral with the support ribs. There is no record in prior art of plastics being used as a material of construction of said bushes. This invention provides for the use of plastics bushes and this is a novel development. A conventional bush of the prior art but made in plastics would suffer far greater distortion and possible failure due to its lower strength in contrast to the metallic materials used for bushes. Being well-supported by support ribs the bushes of the invention therefore, open up the possibility of the use of a new set of materials, that is, plastics which provide the following advantages: i. lower cost, and ii. matching of mean bush Ufe with mean leaf life particularly in reference to Indian road conditions. This invention has conducted trials and experimented with several plastics such as DELRIN, a polyacclal plastic, TEFLON(polytetrafluoroethylene) and >fYLON, a polyamide. In another embodiment of the mvention a single support rib is provided, which rib extends for the full length of said hollow cyhndrical portion. The advantages of a single support rib runnmg said full length is that it can be formed integral with said hollow cylindrical portion by the process of moulding/casting or by extrusion. This advantage is particularly relevant if the material of construction is chosen to be plastics as the process of extrusion can be used for manufacture of said bushes leading to cost benefits. In the third embodiment the bush comprises a single rib extending for said full length and the material of construction is plastics. Plastics bushes offer the advantage of low cost as compared to conventional bush material, say, phosphor bronze. However, in comparison the service life of plastics bushes is lesser but still overall, the cost advantage prevails. In addition, the use of plastics offers the prospect of matching the average service lives of bushes and leaves and obtain a further cost advantage. This is particularly relevant in reference to Indian road conditions. The average service life of a bush is an important criterion in so far as it is advantageous to match the service life of the bush and that of the leaf spring on which it is installed. This is because, whenever a leaf spring change becomes necessary perforce new bushes have to be fitted. This invention has matched the average service lives of various plastics bushes with average service lives of the leaf springs of different makes of vehicles on Indian roads specifically with reference to Indian road conditions. For example, a DELRIN(poIyacetal plastic) bush proved to be a very good match for a particularly widely used make of lorry chassis in India. From the point of view of several factors such as strength, dimensional stability, abrasion resistance and temperature resistance and coefficient of action the polyacetal bush has proved to be the most advantageous. The invention will now be described in detail hereinbelow particularly with reference to the accompanying drawings wherein: Fig. 1 shows the assembly of the front end mounting of a leaf spring; Fig. 6 shows the elevation and end view of the bush of the invention having two support ribs; and Fig. 7 shows the elevation and end view of a bush of the invention having a single fullU length support rib. Reference numeral 1 in Figs. 1 and 2 denotes the front spring eye of the leaf spring, which is formed by forging the end 2 of the uppermost leaf into a circle. The front hanger 3 that is rigid with the vehicle chassis 4 comprises two trunnion-like ends 5, whose holes 6 lie on a horizontal axis which is perpendicular to the vehicle longitudinal axis. The spring eye 1 during assembly is aligned with holes 6 and pin 7 is placed in position and fastened by fastening means 8. Interposed between the spring eye surface and the pin surface is the prior art bush 9 which provides the bearing surface for relative movement between the said spring eye 1 and pin 7, said relative motion being caused by the flexing of the leaf spring. It will be observed that the bush 9 is unsupported in the region of the spring eye comer, 10. In Figs. 3 and 4, the rear spring eye 11 is mounted on the lower end 12 of spring shackle 13, and the other parts of the mounting assembly are: rear end 14 of the uppermost leaf, vehicle chassis 4, holes 15, pin 16, bush 17, spring eye comer 18 and fastening means 19. This mounting is smilar to the front end mounting described with reference to Figs. I and 2. Also, shown in Figs. 3 and 4 is the mounting of the upper end 20 of spring shacke 13, upon rear hanger 21. The rear hanger 21 comprises trumnion hke ends 22 having holes 23 between which the upper end 21 of spring shackle is aligned and the pin 24 put in position. Around pin 24 is the said bearing sleeve that provides the bearing surface for relative motion between the shackle 13 and pin 24. The assembly is fastened by means fastening means 26. The rear hanger is mouinted upon chassis 4 through fastening means 27. This mounting is also similar to that described with reference to Figs. 1 and 2. ig. 5 highlights the end 2, 14 of a leaf spring and shows the spring eye I, 11 the spring eye comer 10,18 the pin 7, 16 and the bush 9,17. one embodiment of the bush of the invention is shown in Fig. 6 wherein the cylindrical portion 28 of the ush is provided with two numbers of support ribs 29. The embodiment of the bush of the invention down in Fig. 7 comprises the cylindrical portion 30 having a single support rib 31 extending substantially the full length of the bush. I claim: A bush, for the mounting of leaf springs upon vehicle bodies, frames or chasses, comprising a hollow cylindrical portion, said portion being characterised in having one or more support ribs that are disposed longitudinally thereon and that provide support thereto by engagement with the sides of the comer of the eye of the said leaf spring, wherein it is mounted. The bush as claimed in the preceding claim 1 and having a single support rib extending over substantially the full length of the said hollow cylindrical portion. The bush as claimed in any of the preceding claims 1 and 2 and made from Delin , a polyacetal plastic. A bush for the mounting of leaf springs upon vehicle bodies, chasses or frames substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. A leaf spring suspension system of a vehicle incorporating one or more bushes as claimed in any of the preceding claims 1 to 4.

Documents:

1444-mas-1996 abstract.pdf

1444-mas-1996 claims.pdf

1444-mas-1996 correspondence -others.pdf

1444-mas-1996 correspondence -po.pdf

1444-mas-1996 description (complete).pdf

1444-mas-1996 drawings.pdf

1444-mas-1996 form-1.pdf

1444-mas-1996 form-62.pdf