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).
Automotive spring rates, suspension flexibility, and the practical application of high flexibility springs combined with Oil Springs.
| Identifier | ExFiles\Box 46\1\ Scan133 | |
| Date | 3rd June 1919 guessed | |
| -2- Many American built cars make use on the front of springs of approximately 600# to the inch for supporting a total sprung weight of 900#, the initial compression of this spring consequently being 1 1/2". Should the front wheels of a car with this spring fall into a hole 1 1/2" deep, the spring in expanding practically gives up its entire support against the frame of the car, the body mass consequently following the axle and spring into the hole. If this same car were equipped with springs of 200# to the inch, the wheels when encountering the bottom of the hole 1 1/2" deep would still maintain through the 200# spring a lifting support to the frame of 600# to the inch. Comparing the above actions it will be seen that whereas the stiffer spring has virtually given up all support, the more flexible spring has yielded only 33% of its total support against the body mass. Conversely the same effect is experienced with the wheel passing over a bump of 1 1/2", the pressure exerted to displace the sprung mass by the 600# spring being three times that of the 200# spring. The ideally perfect suspension, which of course, it is impossible to obtain, would allow freedom of movement of the wheels and unsprung parts without change of reaction of the springs against the frame or sprung mass. This, of course, would require springs of infinite length or infinite flexibility. With such springs no movement of axle would have any tendency to displace the sprung or body mass. What is desired is to obtain a form of suspension which will allow freedom of movement of the wheels and unsprung mass with the least possible change of reaction against the sprung mass. It is readily seen that this change of reaction becomes less with the increased flexibility of the spring used. It is perfectly practical by the use of leaves of proper grades or thickness and proper variation of gauges to procure springs of high flexibility which will give a fibre strain when under their greatest deflection well within their elastic limit, and at the same time procure a spring with a life far in excess of that obtained from the average spring which is made use of in this country today. The question which arises is how is it practical to use these high flexibility springs and protect the car from damage? After many years of experimenting and a reasonable number of Oil Springs having been placed upon the market for the past four years, we believe that practical results can be obtained through the use of the Oil Springs, provided the manufacturer of the car will consider the combined reaction of the spring and Oil Spring to give the required results and not simply treat the Oil Spring as a snubber to be attached to a spring suspension which in itself cannot give proper balance or comfort to the passengers. | ||