From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Article by Granville Bradshaw discussing the pros and cons of different independent front suspension systems.
| Identifier | ExFiles\Box 161\1\ scan0130 | |
| Date | 15th July 1938 | |
| July 15th, 1938. The Autocar. 117. TECHNICAL PROBLEMS DISCUSSED BY GRANVILLE BRADSHAW STEERING WITH INDEPENDENT SPRINGING—No. 2 LAST week we discussed the solid front axle and its effect upon the steering. Let us now study the effect with independent springing so that we can form our own opinions. The mechanism of independent suspension, if well designed, must be powerful and yet it must ensure that both front wheels have the greatest freedom of steering control. In no circumstances must they be compelled by incorrect radius arms or links ever to work in opposition to one another or to strain sideways or, jointly or severally, to promote lateral thrust between themselves, the road or the chassis. A number of independent front springing systems, and particularly some Continental ones, have glaring faults in this direction. Their designers appear to have thought chiefly in terms of securing a minimum of unsprung weight. Let us study a few types at random without fear or favour. (Perhaps I may say here that my technical activities are not connected with any motor firm or any make of car; therefore, I can claim to be unbiased except from purely technical considerations.) The sketches are mere diagrams and are not intended to represent any specific make. Fig. 1 is independent springing of a kind. The road wheel has a bad radius of action, as shown by the arrow, and it will move outwards as it rises. Let me repeat what I said last week. A wheel that is travelling forwards will not freely run outwards unless its bearing is turned outwards. You cannot push a rotating wheel sideways. The wheels in Fig. 1 will, therefore, run crab fashion, skidding all the time they are rotating. Which wheel is now going to take steering control? You may be certain that the driver will not know which way the car will swerve until it has already done so. And what will be the life of the tyres? Fig. 2 is better, but its radius action is not yet perfect and there is no great saving in unsprung weight. The springs are badly positioned because the unsprung weight (the wheel) has a leverage over the spring and a transverse leaf spring (which I have shown by dotted lines) would be better. You cannot have more sprung weight than the total weight of the car, so why not place the whole of it straight on top of the unsprung weight? Fig. 3, in my opinion, is good. If one must be frank, it is almost identical with the motor cycle front fork standardised for twenty years or more. It employs coil springs which are fundamentally rapid where necessary and one can provide powerful links taking stresses in all directions. Large and accessible bearings and a design readily acceptable to the application of shock absorbers are further advantages. The springs are widely spaced, but are not quite the widest possible where they are attached to the body. The wheels will rise practically vertically, but, due to the radius action of the links, they are bound to move inwards a little when they rise. Fig. 4, I think, completes the picture and should correct everything to within the finest limits. The links are irregular, so that, whilst the lower ones tend to bring the wheels closer together, the upper links will pull the top just the right amount closer still. This pushes out the tyre at the lower periphery and, by correcting the error, will ensure that the treads of both wheels (where they are in contact with the road) will rise and fall in a vertical line and with a complete absence of side-thrust. The springs are now placed wider and higher where they are attached to the chassis so as to give more control over the unsprung member. Correcting the Errors. Fig. 5 is a diagram in plan of a type popular with torsion springs. It can be likened to a bicycle crank—the front wheel carried where the pedal is and the spring fitted inside the bottom bracket. It has a curious action. The whole of the steering can be sprung, which is its greatest advantage. The rise and fall of the cranks slightly alter the caster effect of the steering, but not much. The cranks (which are in line with the front wheels) are affected by the torque of braking, i.e., the springing is altered as the brakes are applied. Braking will lift the front of the car unless separate means are provided for accommodating this torque. The springs can be reasonably wide apart to prevent body roll, but there are restrictions, as you will observe. It is a sound system, and if I were to hazard any criticism it would be that theoretically I do not like the load being carried through the crank arm to the spring, and I, personally, feel happier when I see the car's weight sitting straight on to the spring and with the link mechanism looking after the movement of the wheel and nothing else. [Image Captions] Five fundamental types of independent suspension discussed in this article. To the left (Fig. 1) is perhaps the simplest type. Fig. 2 (below left), is an improvement using either coil springs or a transverse spring (dotted line). (Above, centre) Fig. 3. A type which utilises the principle of the motor cycle front fork. (Above, right) Fig 4, in which compensation is introduced by linkage angles. (Right) Fig. 5. The torsion-bar type. ROLLING THRUST. CENTRE OF GRAVITY. | ||