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).
Report discussing back pressure, inter-leaf friction, temperature and frequency variation in a shock absorber or damper.
| Identifier | ExFiles\Box 170\2\ img047 | |
| Date | 23th May 1931 guessed | |
| (2) with the velocity of oil through it, then there is appreciable increase in pressure towards mid stroke as the velocity builds up. We attribute the tendency for the pressure to go on rising after mid-stroke to the K.E. of the oil keeping up the velocity through the valve up after the piston has started to slow down. We have confirmed it frequently. (2) Back Pressure. We believe this is due to the expansion of the oil and any air contained therein when work is done on it. If the piston was a perfect fit in the Delco this pressure would have no means of escape and therefore cause trouble. We make our pistons a better fit and so have to provide a separate air vent. There is no doubt unless this state of affairs is guarded against, the damper becomes hysterical, as you suggest, and we can reproduce it on our dampers on the road by blocking up the air vent when they definitely lose efficiency. With reference to the inter leaf friction which you mention, we should be interested to know whether you have had any experience with Mr. John Watson's rubber inter leaf material. We have tried to reproduce the effect of inter leaf friction by using a Hartford shock absorber set to 15 lbs. in conjunction with a hydraulic, but the results were not very convincing. (3) Temperature Variation. We are quite satisfied that the temperature variation which we shewed in our report is correct. When we were trying to get a pressure effect on our own dampers we ran into this trouble and the only way we could get over it was to use dynamic restrictions which you probably remember. You will probably be able to rig up an indicator in the same way as we have done when you will be able to check up the results yourselves. (4) Frequency Variation. Owing to the deflection on the shock absorber arm, the expansion of the cylinder etc., we do not expect the maximum load to be as high over small high frequency strokes, at the same mean velocity, as low frequency strokes. The instance we had certainly has considerable internal leakage because the pistons were a very sloppy fit in the ball. | ||