GB2179603A

GB2179603A - Motorcycle rear wheel suspension

Info

Publication number: GB2179603A
Application number: GB08521003A
Authority: GB
Inventors: Paul Joseph Palmer
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-08-22
Filing date: 1985-08-22
Publication date: 1987-03-11
Also published as: GB2179603B; GB8521003D0

Abstract

A motorcycle has lateral stiffness obtained by a laterally rigid linkage interconnecting the main frame 12 and the rear wheel sub-frame 18. The linkage comprises a leaf spring 38 having one end securely anchored to the main frame 12 and the other end pivotally connected to the rear wheel sub-frame 18 through a rigid shackle 40. The main-frame 12 is pivotally connected to the sub-frame by a horizontal bearing pintle journalled in two bearings spaced apart laterally of the cycle. These two journal bearings and the shackle pivots permit the main frame 12 and the sub-frame 18 to pivot relative to one another about the horizontal axis of the pintle and this rocking movement is accompanied by flexure of the leaf spring and pivotting of the shackle, but any relative movement about a vertical axis, eg sideways or lateral swinging movement of the rear wheel sub-frame relative to the main-frame, is positively prevented by the lateral rigidity of the leaf spring/shackle linkage. The leaf spring 38 may be replaced by conventional shock absorbers (82, Figure 9A). <IMAGE>

Description

SPECIFICATION Wheeled vehicles particularly motor cycles The invention relates to wheeled vehicles and is part icularlyconcerned with motor cycles.

Over the last ten to twenty years the most usual construction for a motor cycle has been a central frame formed oftubular metal which surrounds the engine, which provides a head mountingforthefront wheel assembly and on which a trailing assembly carrying the rear wheel is pivotally mounted. Pivotal movement ofthe trailing assembly is restricted or damped by coil springs and/or shock absorbers arranged between the assembly and the central frame. Whilethisconstruction has acheived commercial acceptance and success, the machines deter ioratefairly quickly. A major contributory factor to this deterioration is wear in the bearings of the machine.In particular,the bearingformingthe pivotal mounting ofthe trailing rear wheel assembly is subject to reasonably rapid wear and the wear in this bearing permits lateral movement in a horizontal plane ofthis assembly. This permitted lateral movement can cause many difficulties and problems e.g.

lack of stability and road holding and tyre wear.

In addition the use of a swinging rearwheel assembly leads to excessive chain and sprocket wear since the centre to centre distance between the driving and driven sprockets is constantly varying as the assembly swings. This causes shock loading ofthe chain which is in turn transferred to the sprockets as impulses. Impulse loading is always accompanied by excessive wear.

Wear on a drive chain can be substantially reduced if the chain runs in an oil bath. However such oil baths have not usually been provided on motor cycles for practical reasons. Thus, although it is pos sidle to enclose the drive chain of a conventional trailing arm rear wheel assembly, allowance has to be made for the swinging movement of the assembly and this makes the chain case difficultto design and expensive to manufacture. The design difficulty stems from the requirement that the chain case has to contain a reservoir of oil and must remain oil tight over a long period of use.

The Applicant, mindfui ofthe problems and difficulties of the present day construction of motor cycles, has studied the history oftheir construction and has appreciated that a construction proposed and discarded many years ago has modern potential.

This construciton comprises a rigidly mounted rear wheel assembly somewhat like that on a pedal cycle.

A major difficulty of this construction and probably the reason why it was commercially discarded was the need to provide adequate comfort i.e. springing for the user's seat and to provide satisfactory road holding and braking.

In an article published in the edition of The Motor Cycle dated December 30, 1948, G.H. Jones made a proposal for a 250cc motor cycle which had a socalled rigid rear wheel mounting. This proposal was not taken up and it is very doubfful if even a prototype model was made. The Jones machine was centred around a novel tank construction which formed the main frame ofthe machine. The tank has two lugs mounting a tubular sleeve which passes through a large diameter bearing on top ofthe engine crankcase. The engine and the rear wheel are connected rigidly by two tubes, reasonably triangulated, on each side, and each rear fork end carries a laminated spring, thefoward free ends ofwhich are anchored in fabric lined sliders on the tank bottom.Alternativeiy, it is suggested that the free ends of the springs may be bonded in rubber, their movement allegedly being accomodated byshearstress in the rubber.

The Jones machine, if it had infactbeen made, would have suffered from the same difficulties and problems as discussed above in relation to present day motor cycle construction. Thus, even when new and in pristine condition the cycle would not have had the necessary and desirable lateral rigidity and stiffness since the spring is a sliding fit (ie there is some clearance) in the fabric lined bearing. The use of fabric or rubberto line a sliding bearing may reduce orslowdown wear between the contacting sliding surfaces but, bytheirvery nature, those materials cannot resist lateral movement due to their inherent "give".Consequently the use of a fabric or rubber lined bearing inevitably results in a greater amount of lateral play, from the first moment, over and above a bearing using metal to metal contacting surfaces.

Even after considerable use the metal to metal bearing has substantially less lateral play than the fabric or rubber lined bearing.

The Applicant have shown by mounting a leaf spring 38 cms long and 3.8 cms wide in a steel-to-steel slider bearing 7.5 cms in length, that with a sliding clearance of 0.05 mm, the lateral movement ofthe free end ofthe spring was 3 mm which increased to 8 mm when the bearing wore to give a clearance of 3.8 mm. Thus,the slider mounting of one end of the leaf spring initially offers almost no resistance to lateral movement of the other end of the leaf spring and as soon as any wear takes place and increases the clearance, offers no resistance at all. An increase in the clearance will occur quite rapidly, in the use described by Jones, since the leaf spring continuously oscillates backward and forward and the friction would cause wear.Any lateral stiffness of the Jones machine is due therefore entirely to the rigidity of the journal bearing and is not due to the slider bearing.

Consequently the Jones rearwheel mounting would soon have been able to move laterally in justthe same way as those carried by modern type swinging arms do when their mounting journal becomes worn.

It is an object ofthe present invention to provide an improved construction fora wheeled vehicle, such as a motorcycle, which not only has a high lateral stiffness or rigidity when new but retains this stiffness for a substantial lifetime.

It is a further object of the invention to provide an improved construction for a chain driven vehicle, such as a motor cycle, in which the tension in the chain can be set to an appropriate value and will not be subject to impulse variations, that is snatching during operation and in which the chain and its two sprockets can be enclosed in a casing containing oil.

Accordingly the invention provides a wheeled veh icle comprising a fore-and-aft extending main-frame to which a trailing rear wheel assembly is connected and on which a front wheel assembly is mounted characterised in that the connection between the main-frame and the rearwheel assembly comprises the combination of rotary bearing means having its axis extending laterally of the main-frame and prov- iding a hinge between the main-frame and the rear wheel assembly, with an elongate laterally rigid coupling linkage, said coupling linkage including a pivotjoint having its pivotal axis parallel to that ofthe rotary bearing so as to accomodate, by pivotal movement ofthe coupling linkage, relative rocking movement between the main-frame and the rearwheel assembly about the rotary bearing but, by reason of its lateral rigidity, preventing lateral movement therebetween.

Preferably the rearwheel assembly comprises two spaced apart sidejrames and a pintle of the rotary bearing extends through a part ofthe main-frame disposed between laterally aligned parts ofthetwo side frames and is mounted in two journal bearings spaced apartfrom but aligned with one another so as to have a common axis extending laterally ofthe main-frame.

In a preferred construction the coupling linkage comprise a shackle or other component link having two spaced elongate parallel side plates provided with aligned apertures adjacenttheirends forming aligned bearing apertures which respectively receive the shackle pins.

In this preferred construction the coupling linkage further comprises afore-and-aftextending leaf spring having one end pivotally connected to the component link by one of the shackle pins, the other end ofthe spring being rigidly anchored to the main frame or the rear wheel assembly and the other end ofthe component link being connected to the rear wheel assembly orthe main-frame.

The invention will now be further described with reference to the accompanying drawings, which are of a diagrammatic nature rather than machine drawings, and in which Figure 1 is side view ofthe presently preferred construction; Figures2 and 3 show structural details of the Figure 1 construction; Figures4and 5showdetailsofa of a modified con- struction; Figures 6,7and 8show second, third and fourth constructions somewhat similarto that of Figure 1; Figures9A, 9Band 9Cshowa fifth construction and two components used in that construction; and Figure 10 shows a sixth construction.

The motor cycle illustrated in Figure 1 comprises a rigid main-frame 12 formed of sheet metal and carry ing a tubular head bearing 14 at its fore end. The front wheel assembly 16 is mounted in this bearing. The power unit in this construction is a horizontally opposed, twin cylinder motor and is carried by the rear wheel sub-frame assembly 18. This sub4rame com- prises two complex shaped parts, one at each side of the rearwheel, each part having a basicallytriangular shaped body-portion 20 and a cantilevered arm 22.

The two arms 22 form a cradle on which the power unit is mounted and the axle of the rear wheel isjour nalled between bearings atthe apex of the struts 24,26.

As best shown in Figure 2, a bearing pintle 32 is mounted on a part of the main-frame 1 2 by two taper roller bearings 33A, 33B. The bearing 33A abuts tightly agianstthe top end of the strut 24 and acts to maintain precise alignment of the centre lines of the rearwheel assembly and the main-frame and thus of the front and rear wheels. Adjustment ofthe taper bearings is obtained via the locking nuts 35A,35B.

The pintle 32 is secured to the rear wheel assembly by nuts 37A,B and C.A substantial leaf spring 38 is securely anchored (Figure 3) at one end to the mainframe 12 by locating boit 41 which passes through a locating bore in the leaf spring 38 and U-shaped clamping bolt 43 which surrounds the spring. The forward end ofthe leaf spring 38 is pivotallyjoinedto a component link 40. The link 40 is provided as a shackle and comprises two rigid side plates and has its lower end pivotally connected to a bearing lug 42 on the power unit.

It will be seen from the foregoing description that the main-frame 12andtherearwheel assembly 18 are inter-connected by the combination ofthe bearing pintle 32 and its journal bearings 33A,33B with the coupling linkage 44 comprising leaf spring 38 and component link 40. The two bearings 33A,B and the pivotal connection between the forward end of the leaf spring and the shackle form a three point,tri- angulated suspension. The bearings of the pintle 32 permit rocking movement between the main-frame 12 and the rear wheel assembly 18 which is ac comodated byflexure of the leaf spring 38 and pivotal movement ofthe coupling.However a leaf spring is substantially inflexible laterally and any attempted relative movement between the mainframe and the rear wheel assembly in a horizontal direction, that is about a vertical axis through the centre ofthe pintie 32, is resisted by that inflexibility ofthe leaf spring. Such movement about a vertical axis can only occur if and when the bearings 33A,33B become slack due to extended use. However since those bearings are spaced apart laterally ofthe machine, the amount by which the bearing pintle can swivel in a horizontal plane is small and is prevented or at least very strongly resisted by the rigid linkage.

In the foregoing machine the seat support can be hingedly connected to the main-frame so that the angle a of the seat can be adjusted. The adjustment can be made in any convenient way (eg by placing spacer pieces between the underside of the seat and the main-frame)amd by adjusting the position ofthe footrests, the motor cycle can be tailored or "customerised" to any rider.

In a "works special" model of the foregoing machine, the rake angle 0 of the steering head, the ground clearance X and the wheel base length Y, can be altered by altering the length of the shackle to give different handling characteristics. For example, a shorter shackle reduces the rake angles 0, increases the ground clearance X and shortens the wheel base Y. The effect ofthis shorter shackle, wouid be to tend to make the motor cycle "livelier" on cornering. Converselya longer shackle increases the rake angle 6 of the steering head, decreases the ground clearance and lengthensthe wheelbase which has the effect of giving greater straight line stability.Thus by chan- ging oradjusting the component parts ofthe machine, the owner can use the same machine for different applications normally requiring different machines eg road racing, scrambling or motor cross, grass track etcetera.

The bearing pintle can be rigidly fixed to the rear wheel assembly and journalled to the main-frame as in the Figure 1 construction or the pintle can be fixed tothe main-frameand journaliedtothe rearwheei assembly. Figures 4 and 5 illustrates this second alternative. In Figures 4 and 5 the pintle 32 is rigidly fixed to the main-frame and provides two stub axles 45,47 which are received in journal bearings 49 mounted on the side4rames 20 of the rear wheel assembly 18. In this construction the leaf spring 38 is attached to the main-frame 12 by two locating bolts although the single bolt and U clamp is preferred as it only requires one hole in the spring.

The motorcycle illustrated in Figure 6 has a similar main-frame and rear wheel assembly to that of Figure 1 and those components will not be further described. This construction differs in that the leaf spring 50 is rigidly anchored to the main-frame adjacent the head bearing and extends rearwardsto a component link provided by the shackle 52. The spring is pivotally connected to the shackle 52 which, in turn, is pivotally connected to a lug 54 formed on the wall ofthe cylinder. The power unit in this cycle is a conventional single cylinder motor cycle engine. It will be again seen that in thisthird embodimentof the invention the main-frame and the rearwheel assembly are inter-connected bytwo laterally spaced bearings and a rigid laterally inflexible linkage.

The motor cycle illustrated in Figure 7 is somewhat similarto that of Figure 6 but is adapted to house a V-twin engine. In this construction the cylinder 60 is incorporated into the rearwheel assembly 18to re place the member 30 shown in Figure 1 and the lug 62 to which the shackle 52 is pivoted is on the cylinder 64.

In the motorcycle shown in Figure8the main frame 70 is generally of a shallow Y-shape and includes an upright portion 72 formed with a mounting at its lower end in which a substantial bearing pintle is mounted. The rear wheel sub-frame assembly 74 comprises two substantial side members 76 which, at their forward ends, carry the power unit 78 and between which, at their rear ends, the axle of the rear wheel isjournalled. Intermediate their lengths each of the side members 76 is formed with a journalbearing-seating 80 and the two seatings respectively receive the end portions ofthe bearing pintle.In this construction the main-frame 70 and the rearwheel assembly 74 can pivot about the generally horizontal axis of the bearing pintle but relative movement about an upright axis, that is lateral movement, is prevented by the rigidity of the leaf spring 50.

The motor cycle shown in Figure 9A,9B and 9C is somewhat different in construction in that the leaf spring used in the former constructions is replaced by conventional shock absorbers 82 from the point of view of damping out or resisting pivotal movement between the main-frame 84 and the rear wheel assembly 85 whereas the lateral stiffness formerly afforded bythe leaf spring is provided bythecoupl- ing linkage 86. This linkage is provided by the elongate double shackle 86a and 86b which is sufficiently laterally rigid to prevent movement in a horizontai plane between the main-frame and the rear wheel assembly. As shown the double shackle 86 has a pivot joint87 intermediate its length and is pivotally attached to the member 88 of the main-frame 84 and to the cantilevered ends of the two parallel side members 90 of the rear wheel assembly 85. Pivotal movement between the main-frame 84 and the rear wheel assembly 85 is accomodated by pivoting of the double shackle 86 about its three pivots, which is accompanied by an alteration of the spacing between the end pivots.

The construction shown in Figure 10 similarly comprises a double shackle 90 which is pivoted between a bearing point 92 on the upper member ofthe main-frame and a bearing lug 94 provided on the cylinder. In this construction the engine forms an integral part of the main-frame.

Claims

1. A wheeled vehicle comprising a fore-and-aft extending main-frameto which a trailing rear wheel assembly is connected and on which a front wheel assembly is mounted characterised in that the connection between the main-frame and the rear wheel assembly comprises the combination of a rotary bearing having its axis extending laterally ofthe main-frame and providing a hinge between the main-frame and the rear wheel assembly with an elongate laterally rigid coupling linkage, said coupling linkage including a pivot joint having its pivotal axis paralleltothatofthe rotary bearing so asto accomodate, by pivotal movement of the coupling linkage, relative rocking movement between the main-frame and the rearwheel assembly about the rotary bearing but, by reason of its lateral rigidity, preventing lateral movementtherebetween.

2. Awheeled vehicle as claimed in claim 1,in which a pintle ofthe rotary bearing is mounted in two journal bearings spaced apart from one another along the length of the pintle so that the main-frame and the rear wheel assembly are connected bythree pivotal bearings disposed at the apices of a triangle.

3. Awheeled vehicle as claimed in claim 2, in whichthebearing pintleextendsthrougha partof the main-frame disposed between two parts of the rear wheel assembly aligned laterally therewith.

4. Awheeled vehicle as claimed in claim 3, in which the part of the main-frame comprises an elongatetubularhousing in which the bearing pintle is journaled.

5. Awheeledvehicleas claimed in claim 3, in which the two parts of the rearwheel assembly each comprise a journal-bearing-seating, said two journal-bearing-seatings being aligned with one another and respectively receiving the projecting ends ofthebearing pintle.

6. Awheeled vehicle as claimed in any one of claims 1 to 5, in which the coupling linkage com prises a shackle.

7. Awheeled vehicle as claimed in any one of claims 1 to 6, in which the coupling linkage comprises a leaf spring.

8. Awheeled vehicle as claimed in any one of claims 1 to 5, in which the coupling linkage comprises afore-and-aftextending leaf spring having one end rigidly anchored to the main frame orthe rearwheel assembly and having its other end pivotally connected to one end of the shackle, the other end of which is pivotallyconnected directly or through a rigid membertothe rearwheel assembly orto the main frame.

9. Awheeled vehicle as claimed in any one of claims 1 to 5, in which the coupling linkage comprises two component shackles pivotally secured together to form a double shackle, the outer ends of the double shackle being respectively pivotally connected directlyorthrough a rigid membertothe main frame and the rearwheel assembly.

10. Awheeled vehicle substantially as hereinbefore described with reference to and as diagrammatically illustrated in Figures 1,2 and 3, or Figures4and 5 or Figure6 or Figure7 or Figure 8or Figures 9A,9B and 9C of the accompanying drawings.

Amendments to the claims have been filed, and have thefoliowing effect: *(a) Claims 1 and 6 above have been filed, and have been deleted ortextuallyamended.

*(b) New ortextually amended claims have been filed asfollows: *(c) Claims 7,8 and 9 above have been re-numbered as 6,7 and 8 and their appendancies corrected where necessary

1. Awheeled vehicle comprising a fore-and-aft extending main-frame to which a trailing rear wheel assembly is connected and on which a frontwheel assembly is mounted characterised in that the connection between the main-frame and the rear wheel assembly comprises the combination of a rotary bearing having its axis extending laterallyofthe main-frame and providing a hinge between the main-frame and the rearwheel assembly, with an elongate laterally rigid coupling linkage, said coupling linkage including a pivot jointcomprising a shackle mounted on a pivot pin, the pivotjoint being disposed in a position forward of the rotary bearing and having its pivotal axis parallel to that of the rotary bearing so as to accomodate, by pivotal movement ofthe coupling linkage, relative rocking movement between the main-frame and the rear wheel assembly aboutthe rotary bearing but, by reason of its lateral rigidity, preventing lateral movement therebetween.