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).
To Mr. E. W. Hives discussing technical issues with shock absorbers, including back pressure, temperature, and frequency variation.
| Identifier | ExFiles\Box 170\2\ img021 | |
| Date | 16th April 1931 guessed | |
| Mr. E.{Mr Elliott - Chief Engineer} W. Hives #2 It has always seemed to me that since the diagrams grow with frequency for a given stroke they should certainly show a load variation with piston velocity between the middle and ends of the stroke. (2) Back Pressure. The curves showing back pressure on the piston during its return stroke were astonishing to Delcos, and they were inclined to blame it on the indicator at first, till I told them you had had the same thing and vented the pressure circuit to escape from it. I recall that on the bench you got back pressure which grew with time until you had practically eliminated useful work. Do you attribute this back pressure to any specific thing? For example aeration of the oil or expansion of the oil under pressure due to instantaneous heating effects. Do you consider that this back pressure has any bearing on what happens on the road, or is it due to local conditions in testing which will not be reproduced on the road? I have the impression that the shock absorbers still become "hysterical" and lose their effectiveness to a certain extent when driven hard over a wavy macadam road. The old V-type without forced-filling certainly did so, and I do not feel that the horizontals are as effective in proportion to their high load settings as the R.R. To illustrate this - I have entirely failed to sell frictionless road springs, or in fact anything but putting into the springs all the interleaf friction that we can hope to maintain constant in practice. That is, we are still in the stage of believing that spring friction is essential to a good ride (particularly to keep the axles quiet). I feel that if we had shock dampers which were "on the job", we should not feel this necessity. By a new form of valve, with a "preloaded leak", we can reproduce some of the dry friction effect in the hydraulic and so get by without excessive spring friction, but I feel that we are very far from having effective dampers. (3) Temperature Variation. Delcos have not found anything like the variation with temperature which you show. Or at least anything like the variation with viscosity. I have curves showing about 5% pressure change at 550 R.P.M. between 75 and 1500 viscosity. Such variations as you show for a country with air temperatures from -15°F.{Mr Friese} to 110°F.{Mr Friese} are of course quite serious. Have you made any further tests confirming this? (4) Frequency variation. Delco tests show a slight tendency for increased maximum load at higher frequencies and at the same mean axle velocity. Your curves show a considerable falling off | ||