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).
Technical analysis of spring, damper, and valve performance in a vehicle's suspension system.
| Identifier | WestWitteringFiles\V\December1930-February1931\ Scan195 | |
| Date | 30th January 1931 | |
| -3- up to about 3 ft/sec. on the rear axle of a spring controlled passage in the shape of an annular leak of length .100 and various areas depending on the number of the valves fitted. Actually for the valve recommended by Delcos for the front of the 40/50 it is .016 sq.ins. The leak is controlled by a very low rating spring as all the compression loads on the dampers are exceedingly low for slow axle movements. When the valve has lifted 1037 1/16 of an inch, a very high rating spring takes charge. So stiff is the second spring that the valve after this point has an appreciable pressure velocity, as is shewn clearly on Sheet 3 and Sheet 7. There is very little lost movement over high frequency small strokes (Sheets 1 and 4) unless specially produced by large leaks in the H.P. valve on dampers for the rear (Sheet 11). They certainly shew no signs of having more air in the damper than we do. The effect of extremes of temperature is not very marked on the low pressure poundages. High Pressure Valve. This is also a masked valve and the main opening does not take place until it is .025 or so, off its seat. It has two leaks - (1) A permanent leak consisting of a groove up its stem. This of course is effective on both the high and low pressure strokes. (2) An annular leak which comes into operation as soon as the valve lifts, presumably really only the minimum working clearance for the mask. The actual valve opening is on the sleeve valve principle and owing to the high rating of the control spring there is a very high pressure velocity factor. This is clearly indicated on Sheets 6 & 7, the maximum pressure on the front damper rising from 150 lbs/sq.in. at an axle velocity of .27 ft/sec. to 750 lbs/sq.in. at an axle velocity of 1.25 ft/sec. You will recollect that all the original Phantom 11 cars were fitted with dampers having dynamic restrictions which gave this type of pressure velocity increase and the riding was considered by all to be very good. The Delco people have obtained the result very much more simply than we did but with the disadvantage (which we avoided) that their pressure velocity increase can vary over 300% with temperature over the extreme range likely to be encountered in service (Sheet 5). However, for the average owner the results they achieve must be considered to be a very good compromise. It is obvious that the only reason why they can use such high ball pin loads (over 300 lbs/sq.in. Sheet 3) without passenger discomfort is because of their pressure velocity factor and low rate of pressure rise particularly over small axle movements. The rate of pressure rise is blocking up the leaks in the valve stem, the effect of | ||