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).
Design principles and challenges of shock dampers.
| Identifier | WestWitteringFiles\V\October1930-February1931\ Scan322 | |
| Date | 10th February 1931 | |
| HS{Lord Ernest Hives - Chair}/RM.{William Robotham - Chief Engineer} FROM R.{Sir Henry Royce} (At Le CanadelHenry Royce's French residence.) R2/M10.2.31. x235. SHOCK DAMPERS. I want to warn us that we must not follow Lovejoy's without real reason. One cannot see any reason in some of the arrangements, but several things go without saying. I have always been struggling for shorter levers. Our last efforts are to limit the rear axle movement by slings. It is possible that this can be done by a very robust shock damper but it would not be possible with long levers. One imagines a second port after the main is closed by the piston and a spring loaded ball on this set to say 1000 lbs. per sq. in; assuming levers of from 8" to 10", 2" X 1000 = 2000, lever ratio 5 to 1 = 400 lbs. ball pressure for another 1" of ball travel, should bring the axle to follow the frame, but severe on frame fixing. You will remember that my advice has been to have low pressure side about 50% of the high. We all started off with one way only but had to get some damping out of the axle's upward (relative to frame) motion because we could not get enough total damping unless we did so. So that since we shall have a more robust damper with short levers we can perhaps return to 50%. I do not think for a moment these figures are of much importance but one can see that possibly there is a great advantage in having the front ones more single acting (so as not to set the car pitching) and the back ones more double acting so that the back is not so easily thrown down when the car front is thrown up. In other words we want to allow the front axle to pass freely over humps but not let the wheels fall into a hollow. I think it is quite wrong to have great variation of damping by changes of temperature or rate of axle movement (don't misunderstand me to say car speed), the reason being that we would like to let the axle follow the road which means that it must move quickly relative to the frame, but we wish to steady the car which only moves slowly - i.e. slow damping must be effective and quick damping must not be excessive. IMPORTANT IDEA!!! One must agree to some leak between the pistons so that conditions can become normal without having to lift the relief valves, but I am very afraid from experience that this should be over-done. It now seems that piston leaks can get rid of the air. (1) | ||