GB2300839A

GB2300839A - A racing kart chassis with variable torsional stiffness and adjustable seating position

Info

Publication number: GB2300839A
Application number: GB9509786A
Authority: GB
Inventors: John Barry Ellis Wheeler
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-05-15
Filing date: 1995-05-15
Publication date: 1996-11-20
Also published as: GB9509786D0

Abstract

A racing kart chassis design whereby the torsional stiffness of the front part of the chassis may be easily and quickly varied by means of removable and adjustable torsion bars 12 and 13. The torsional stiffness of the rear part of the chassis may be modified by means of a special removable clamp 27, by which chassis tube 6 may be connected or disconnected. The longitudinal seat position may be quickly and easily changed by means of parallel slotted guides for all of the seat attachment points.

Description

A RACING KART CHASSIS WITH VARIABLE TORSIONAL STIFFNESS AND ADJUSTABLE SEATING POSITION This invention involves specific features used in the design of a racing kart chassis.

A racing kart is the most simple form of four-wheeled single seater racing vehicle and its design spedfications are governed by Formula regulations published internationally by the C.l.K. and nationally by the R.A.C./M.S.A. and the A.B.K.C.

The claims made in this application relate to specific areas oi the design of the chassis of the racing kart. These are: 1.Methods of varying the torsional stiffness of the chassis to enable the handling of the kart to be rnodified to suit the prevailing circuit conditions.

2 A method of simple fore/aft adjustment to the seat position which enables rapid changes to be made to the centre of gravity of the kart with driver, again for adjustirlg the handling for specific circuit conditions.

The outline chassis design regulations which govern racing kart design are described in the R.A.C. Blue Book and the pertinent clauses are as follows: N.14.1.1. Chassis must be constructed from magnetic steel tubing. Cross section free.

N.14.3. Flooring. There must be a floor rnade from rigid rnaterial that, as a minimum, stretches from the seat to the front of the Kart. It must be edged on each side by a tube or a rim to prevent the driver's feet frorn sliding off the floor.

N.14.4. Suspension. Any method of suspension, either by elastomeric material or by pivots is prohibited.

A racing Kart has no suspens. The drive to the rear wheels is provided by a chain to a rigid rear axle. There is no differential between the two rear wheels and consequently the handling of the chassis and the ability to steer efficiently with the very wide racing tyres is inherently very poor. The handling and steering is in practice facilitated by the geornetry of the front wheel kin- pins and steering, and the forces which are transmitted through the chassis from the steered wheels to the rear axle on turning the steering wheel. These forces act to lift the inside rear wheel and enable the Kart to steer and handle efficiently.

The weight of the driver accounts for approximately 50% of the overall minimum allowed weight of the vehicle. The position of the driver is therefore very critical to the handling oi the racing Kart.

The stiffness of the chassis in bending (vertical loading) and in torsion (twisting between the front and rear axles) is very critical to the handling, since it controls the forces which are transmitted frorn the front wheels to the rear, and consesuently it is normal practice to test many different chassis of different stiffness characteristics to find the best handling solution for each circuit and each prevailing temperature and weather condition.

The inventions described have been designed to make one chassis type variable to suit most differing circuit conditions.

Fig. 1 shows a pin view of a typical racing Kart which conforms to the general reguiations. The main structure of the chassis is constructed irom steel tubes, normally round in section, and normally between 28 and 34mm in diameter.

The front tube 1 provides the main front structure connecting the attachTnent points for the front wheel uprights 2 and 3.

The rear longitudinal tubes 4 and 5 provide the mounting points for the engine 8, and tubes 4, 5, 7 provide the mounts for the rear axle.

The seat is attached at its front to the centre cross tube 9, and at its sides to fixings mounted on tubes 5 and 7.

The front longitudinal tubes 10 and 11 provide the structural connection between front and rear and are normally deliberately "waisted" as illustrated to provide a controlled degree of flexibility between the front and the rear of the chassis.

Fig.1 also shows the inclusion of two additional longitudinal tubes 12 and 13 (torsion bars) which are attached to the front tube 1 at points 14 and 15, and to the centre cross tube 9 at points 16 and 17. These bars 12and13 include arms 18 and 19, which stretch outwards towards the front wheel upright attachrnent points 2 and 3. An articulating connection is made between the enclsofthearms 18 and 19 and the dassis frame near to the pints 2 and 3 by means of adjustable iength links 20 and 21. These additional bars and connections are the subject of one of the rnain elements of this invention.

The bars 12 and 13 are positioned to give clearance to the front steering attachment 22, the fuel tank and the driver's feet.

The function of the bars 12,13 is to provide additional torsional stiffness to the front part of the chassis between tubes 1 and 9.

This additional torsional stiffness is provided firstly through the attachments of the bars to the front and rear points 14,15 and 16,17 but secondly since any upward motion of the wheel attachment point 2,3 is resisted by the link 20,21 which pulls on the arm 18,19 which then stresses the bar 12,13 in torsion.

Fig. 2 shows one of the torsion bars 12,13 in detail, with adjustable arms' 18 and 19 and links 20, 21.

The advantages of providing the additional torsional stiffness by means of these additional bars are as follows: 1. The bars 12, 13 can be quickly removed and changed by unbolting the attachments 14,15,16, 17. Different diameter bars can be attached to provide different torsional stiffnesses.

2. The arms 18,19 are designed so that they cn be rotated at their attachment points to the rnin bars 12,13 (at points 23,24). The ams are assymetric to make them stiff in a vertical plane and soft, flexible in a horizontal plane.

By rotating the anne 18,19 from the stiff position to the soft position, the effectiveness of each bar 12,13 can be quickly increased or reduced.

3. The torsional stiffness of the chassis can be made assymetric (left side different from right side) either by using different orientations of the arms 18,19 on the left and right side, or by fitting different diameter bars 12,13 to the left side and right side, or both features together.

4. The torsional stiffness of the chassis can be varied without significantly changing the bending stiffness (suppleness of the chassis under the weight of the driver).

A further variation is provided by the detail design of the rearmost attachment point 16,17 of the torsion bar 12,13 to the central chassis crosstube 9 (see Fig.

4). The attachment is provided with a pivot 25 so that the attachment of the torsion bar to the chassis is stiff in torsion but articulates in the vertical direction so as not to contribute significantly to the bending stiffness oi the chassis.

The stiffness of the rear section of the chassis between the centre cross tube 9 and the rear axle is provided by the chassis tubes 4,5,6,7 (see Fig. 1 and Fig. 4).

In order to provide variation to the stiffness of the rear of the chassis, the rear longitudinal tube 6, instead of being iabricated in one piece, is stiffened locally with a weld-on steel flange 26, cut in two, and then rejoined by means of a bolted clamp 27, with two bolt holes which pass through the clamp and through the flange.This damp can then either be attached for maximum stiffness of the rear chassis construction, or detached to render the rear chassis softer with only three effective tubes 4,5,7 instead of the normal four 4,5,6,7 Since the centre of gravity and the position of the driver interacts critically with the chassis stiffness to provide the best harding characteristics, a variable seat mounting systern has been designed (see Fig. 5) whereby the four main bolting points 28,29,30,31 pbas the two or more additional rear support tube attachment points 32,33 are designed with longitudinal parallel slots 34 so that, on bosening the attachment bolts, the seat may be easily and quickly moved fore and aft wthin the slots.

Claims

A racing kart chassis design and individual components designed to be fitted to a racing kart chassis with the following specific distinguishing features: 1. A means of increasing the torsional stiffness of the front part of the kart chassis from the front cross tube to the central cross tube in front of the driver's seat by the fitting of orle or more torsion bars (tubes or members, which when twisted along their length give a measurable resistance) in addition to and inboard from the regulatory chassis perimeter tubes; these torsion bars being mounted longitudinally and attached forwards to the front crosstube and rearwards to the central cross tube; these attachments being either permmrent (nonremovable) or bolted so that they can be removed or exchanged for bars of different diameter and torsional stiffness.
2. A variation of the design described in Clairn 1 above whereby the additional torsion bars are fitted each with an arm which extends out towards the wheel upright attachment points on the chassis, these arms being connected additionally to the chassis at this extremity by means of a rod or a linkage. These arms may be either fixed permanently or removable. The attachment of these arans and links between the torsion bars and the chassis extremities gives a further increase to the stiffness of the tront part of the chassis.
3. A variation of the design described in claims 1 and 2 above, whereby the anne may be rotated to different angles, the arm being designed with a profile which is stiff in bending in one plane and soft in bending in another plane of rotation from the first plane.
4. The use of torsion bars and adjustable or non-adjustable arans as described in claims 1, 2 and 3 above in an assymetric configuration left side to right side, in order to give differing handling characteristics on left bends and right bends.
5 A variation of the design described in claims 1, 2, 3, 4 above whereby the rearmost attachment points of the torsion bars to the chassis are provided with an effective hinge in order to transmit full torsional stiffness but Sex in the vertical bending plane.
6. A rear longitudinal chassis tube which is reinforced with a longitudinal flange, divided by cutting through the flange and tube, and provided with a collar which wraps around the tube and clamps onto the flarrge. The collar may be attached for full stiffness or removed to render the chassis tube ineffective.
7. A seat mounting system whereby the two front mounting points, the two main side mounting points and the two or rnore rear support tube mounting points are provided with elongated horizontal slots, whereby the seat may be easily adjusted fore and aft by loosening the attachment bolts.
8. A racing kart chassis incorporating one )r more of the inventions substantially described herein with referçnce to Figs. 1, 2, 3, 4, 5 of the accompanying drawings.