SPRINGING FOR SPEED.
Mr. J. G. Parry Thomas’s Idea for Improving the Suspension of Road Vehicles.
Springs and Torque Eliminated.
TN nearly all ordinary systems of suspension as A employed on motor cars, use has been made, in some form, of the original laminated spring so familiar on horse-drawn vehicles. This type of spring is open to several serious objections, chief amongst which are : — (a) Springing cannot be obtained without a considerable amount of friction between the leaves ; frequently rust and dirt accumulate to such an extent as to prevent proper freedom of action of one leaf over another and ultimately hard riding results. (b) With systems of suspension of this type, it is necessary to provide an external means to take the torque re-action of the driving and braking forces on the axles. If no such means is provided then the spring leaves are relied upon to perform the function in question and, in order that they shall be suitable and strong enough for that purpose, they have to be made stiffer than would otherwise be the case and the result is again hard riding. (c) In the case of the front axles of motor vehicles which
are equipped with the ordinary type of laminated springing, the movement is such as to cause the steering pivots continually to change position, thus affecting the steering and increasing the wear and tear of all the moving parts of the steering gear and front axles and also of the tyres. A further objection to laminated springs is their weight, which adds considerably to the unsprung weight of the axles, while they are also expensive, particularly bearing in mind the number and variety of fastenings which are required in order to effect suitable connections between the axles and the springs on one hand, and between the springs and the chassis on the other. Mr. Thomas’s own design, which he has patented, does away with these springs and objectionable features at one stroke, and his system provides definite means for taking the torque of the rear axle, and in the case of the front axle for maintaining the steering pivots always in the correct position even when front wheel brakes are
fitted. His method also prevents rolling of the vehicle when riding round corners. He claims that it generally performs its function in a more satisfactory manner than any known system of suspension and that it is comparatively cheap and simple in construction.
The springing of the vehicle is obtained by the sole use of several torsion members, and these are so disposed, relatively to each other, that the suspension arms connecting them to the axles act as torque rods and prevent rotation of the front axle and the rear axle casing.
The chassis frame is suspended on these arms which are supported on the axles by means of some kind of universal joint and spherical ball bearing. The arms are such in number and so disposed that they prevent the axles from turning and in that way act as torque rods. They are connected to the frame of the vehicle through the medium of torsion parts which act as the springs and some of them may be connected to anti-rolling rods. The detail of Mr. Thomas’s invention may best be understood if reference be made to the accompanying illustrations in which figures I, 2 and 3, show the details of this form of suspension, as applied to a front axle, and figures 4, 5 and 6 indicate how it may be applied to the rear axle. Figure 7 shows the springing arranged on a car the centre portion cf which has been removed for the sake of clearness. Referring to figures I, 2 and 3, it will be observed that there are two arms near each end of the axle, each pair of arms taking the place of one of the usual springs. The lower arm is shown in section in figure 2 ; its inner end is bolted to a flange on the end of the shaft or spindle which is so long as almost to reach to the centre of the chassis. At the end remote from the lever this shaft is splined, and the splines register with grooves cut in the interior of a torsion tube. The tube is also flanged, but is bolted to the side member of the frame. The inner spindle is enlarged somewhat at the end nearest the lever and a bush is fitted in the tube in which its enlarged end may take a bearing, suitable provision being made for
adequate lubrication at this point. The other end of the lever is attached by means of a spherical ball bearing to a bracket which is bolted to the axle and it will be appreciated that, as the axle rises and falls owing to the wheels encountering various road obstructions, the tendency is for the shaft to which the lever is coupled and the tube to which that shaft is splined, to twist and untwist, thus absorbing the shocks.
The object of securing the shaft only at its innermost end, is to ensure that, in the first place, the whole length of the shaft is utilised as a torsion member, and secondly, that the whole length of the tube surrounding it is also similarly utilised. The upper levers serve the purpose of an anti-rolling device. Each is mounted on the end of the long spindle which couples the two sets of torsion members together and thus ensures that in the event of one wheel rising or falling, its motion is to a large extent transmitted through the anti-rolling device to the wheel at the other side of the chassis.
The upper levers are connected to the cross shaft in the manner similar to that employed for the lower lever. The lever itself is bolted to a tubular part which takes a bearing in a bracket on the frame. The inside of this tubular piece is key-wayed to accommodate the splined end of the anti-rolling shaft. The outer end of the lever is coupled to the bracket on the axle by a spherical ball bearing and it is important to .note that the two levers and other connections to the frame and axle form a parallelogram so that whatever relative motion occurs between the frame and the axle there can never be any rotation of the latter. This ensures that the steering pivots are always maintained substantially in their correct positions. Moreover, if front wheel brakes are fitted to the chassis embodying this form of suspension, no additional torque member is required as the arms themselves will act jointly in that capacity and will prevent rotation of the axle when the brakes are applied. The mechanism as applied to the rear axle is precisely the same in principle as that which has been described in
relation to the front axle. The arrangement of the levers and connections in parallel form is the same, and oscillation of the rear axle, under spring movement, is thus prevented, reducing the tyre wear, a matter of equal import both to the ordinary user and to the sporting motorist. An important feature of the invention is the facility Which the construction affords for adjustment of the height of the frame above the ground. To effect such adjustment, all that is necessary is that the torsion rods should be disconnected from the tubes to which they
are splined, being then moved round a tooth or two in one direction or the other according to whether the height is to be increased or decreased.
It is also possible to vary the springing of the vehicle to which this device is fitted, merely by altering the length of the torsion members, or their diameters.
Further, in order to strengthen the springing, the antirolling members may be utilised as torsion members by splining them at their centres, and keying them to tubular members in the same way as has already been described.