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).
Analysis of shock absorber performance, discussing indicator cards, temperature effects, leakage, and oil compressibility calculations.
| Identifier | ExFiles\Box 152\1\ scan0075 | |
| Date | 12th January 1933 guessed | |
| - 6 - that in the absence of an indicator, cards No's 391 & 410 would be almost exactly rectangular in form. The cards taken at high temperatures show that under these conditions a little leakage occurs round the rotor. The result of this is that the rotor movement necessary to reach a given pressure is roughly double that at the lower temperatures. Of this delay in reaching the maximum pressure, approximately one half may be ascribed to the presence of the indicator, and the other half is the true leakage effect. Therefore, in the absence of the indicator the form of the card at, say 65°C, would be approximately that actually recorded at 20°C. In other words the true shape of the card with a 4" stroke at 70 double strokes/min, and at a temperature of 65°C is approximately that shown on cards No's 371 & 390, and similarly with a 1" stroke at 440 double strokes/min. the true shape of the card is approximately that of card No. 391 or card No.410. It is felt that these results are eminently satisfactory and that such shock absorbers should give particularly good results on the road. At the beginning of the test the adjusting screws were set so as to give a load of little more than a 100 lbs at the end of an 8 1/2" lever. The actual figure is about 108 lbs as the average of the two sides. The cards taken show that at the highest temperature this falls to about 90 lbs at the lower speed, and 97 lbs at the higher. These figures could of course be raised by altering the adjusting screws, but in view of the very serious distortion caused by the presence of the indicator, it was considered that there would be no gain in doing so at the present stage. Another matter which must affect the shape of the indicator card is the compressibility of the oil in the working chamber of the shock absorber. No figures are available for this, but it is probably not greatly different from that for the compressibility of the fuel oil used in Diesel engines. An average figure for this is, that a given volume of fuel is reduced by .6 x 10^-4 of its volume for each atmosphere of pressure. The total volume of the working chamber is π/4 x 2.875^2 x 1.5 = 9.75 cu.ins. Assume half of this to be the volume of oil in one side of the chamber at the beginning of the working stroke = 4.87 cu.ins. If the maximum pressure is 800 lbs/sq.in., or say 54 atmos., the reduction of volume would be (4.87 x 54 x .6) / 10^4 = .0158 cu.ins. | ||