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).
Friction in pivots and the functionality of a hydraulic steering damper, focusing on oil viscosity.
| Identifier | ExFiles\Box 154\3\ scan0011 | |
| Date | 17th February 1927 | |
| Oy6-E-21727 -2- February 17, 1927. 2. Friction in Pivots. There are two schemes for increasing this, one a multi-plate clutch loaded by the weight of the car, and the other a similar clutch loaded by a spring. Both clutches have three friction faces. Hives reports neither is quite equal in results to the spring-loaded cross-steering tube, and the one without the spring is definitely unsatisfactory as it tends to lock when shunting. 3. Hydraulic Steering Damper. This is considered rather more effective than friction in the pivots but so far inferior to the friction in cross steering tube. The basic trouble is the varying viscosity of the oil. To lighten the steering for shunting it is essential to provide a "leak" in the instrument. This has been established at .048" diameter. This is such a size that at a nominal temperature (65°F.{Mr Friese}) the valve will just lift for the smallest "joggles" of the front wheels, but any slower movement will force oil through the leak only. (A valve is used apparently as a limit to the maximum loads which can be thrown on the damper.) Derby have proved that the resistance to motion with an orifice, is proportional to the viscosity of the liquid and varies almost directly as the speed of flow. Their best oil varies in viscosity in the ratio of 1 to 6, between 90° F.{Mr Friese} and 40° F which they consider a normal atmospheric range. With any oil we know, and for our atmospheric range of 100° F.{Mr Friese} to zero the ratio will be nearly infinity. When the oil is nearly "set" it does not mean that the instrument is rigid, any more than with a Lovejoy shock absorber. It merely means that to shunt the car sufficient effort must be exerted to open the valves, and that the steering will then be free (due to vacuum within the instrument) till the heat of the engine warms up the oil. But the variation in viscosity (unless perhaps the instrument can be brought to a standard temperature by mounting near the engine) means great changes in the amount of damping. | ||