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).
Technical discussion on the effects of road conditions on spring oscillation and methods of damping, including the use of friction.
| Identifier | ExFiles\Box 51\4\ Scan034 | |
| Date | 10th February 1922 guessed | |
| 4. If the road condition is reversed and we consider the effect of the car dropping off an elevation, or going into a hole, the curve shown in figure 6 will be obtained. In this case, there are two peaks to be considered. The inverted peak "B" may bring the car body against the axle and peak "C" may throw the passengers from the seats. The effect of riding over a rough road is a more or less complicated succession of the two cases considered. It will be seen that in any possible case of road jars, the riding quality of the car will be improved by adding friction to the spring action. It is of interest to note that the period of one oscillation, that is, the time represented by the distance "A" to "C", in the last curve, is a function only of the weight of the car and the elasticity of the springs. It is independent of the speed of the car, height of bump, amount of friction or other considerations. It is a well known fact that the friction normally present in an automobile spring is not sufficient to properly damp the oscillations. Additional friction must be added in some way to obtain the maximum of riding comfort. It has been proposed to increase the friction in the spring itself by additional leaves, changes in shape, no lubrication, paint, or resin between the leaves etc., but none of these expedients are really practicable. For a given elasticity of spring, the number of leaves may be increased by decreasing the thickness of the individual leaves, but questions of cost and mechanical strength and reliability prevent this being carried much if any further than present practice. The energy used up in friction is equal to the force required to overcome the friction multiplied by the distance moved. The motion between the leaves of a spring is very small and therefore the energy used is small unless the pressure between the leaves is made very large. This pressure can be increased by changes in shape, but will produce excessive wear and squeaking. The use of resin or other gummy substance between the leaves would help to some extent, but would not last long under the conditions under which an automobile spring is used. Lack of lubrication will, of course, produce excessive wear and noise. The only practical method of damping the spring oscillation is some means of absorbing energy, exterior to the spring proper. A device using friction and with as great a range of motion as can readily be obtained is by all means the simplest and best form of energy absorber. The amount of friction required will depend on the weight of car, elasticity of springs, speed and condition of road. The manufacturer of friction shock absorber should set the amount of friction to best meet the average conditions on each particular class of cars. Conditions will, however, arise in service which will require a different amount of friction, such as heavy loads, very poor roads, high speed etc., and it is very desirable that the manufacturer provide some means by which the amount of friction can be easily adjusted, and this means should include a dial by which settings can be compared. | ||