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).
Detailed explanation of the design, function, and manufacturing of air-spring suspension systems.
Identifier | ExFiles\Box 43\3\ Scan021 | |
Date | 28th September 1923 guessed | |
[PAGE 16] AIR-SPRINGS AND RIDING-QUALITY FIG. 23—INDICATOR-CARD MADE ON THE CONVENTIONAL CROSBY STEAM-ENGINE INDICATING DEVICE This Card Shows the Characteristic Pressure Increase as the Air-Spring is Compressed under Load washer is absolutely tight and no leakage occurs, except for the gradual seepage that is present in some degree in all cups, the pressure on the lower cup-washer will remain constant, but, if there is a slight leak, the extra oil will build-up in the air chamber that opens into the annular space between the two cups and compress the trapped air in it. The action is then similar to that of an ordinary air-chamber pump. The piston moving up and down gives the necessary drop in pressure in the acts as a rebound check. The outer shell of the air-spring is bolted to the frame of the car, and the lower end of the piston-rod is connected to the existing steel spring. The air-spring of late design is a development of the elementary spring shown in Fig. 22. This spring has two cup-washers, and is designed so that an air chamber opens into the annular space between the two washers. Either packing is capable of taking the full load, but the design is intended primarily to use only the upper washer as the packing that takes the continuous variable loads that are present in the pressure chamber when the spring is in operation. The pressure chamber is subject to loads that will vary from 25 to 150 lb. per sq. in. in ordinary use. The lower washer is generally under a constant pressure of 25 lb. per sq. in. If the upper FIG. 25—TYPICAL INDIRECT-ACTING REAR AIR-SPRING This Spring Is Substantially the Same as the Original Invention of George West-inghouse in 1911. The Guide d and Outer Member a Is Permanently Bolted to the Frame, The Cylinder or Sliding Moving Member b Is Supported by the Column of Oil Pressure Under the Air Dome, c Is the Cup-Leather Seal and d is the Piston That Is Attached to the End of Oil Passing Back and Forth from the Lower Chamber to the Upper and Is Designed as an Extra Precaution To Take Care of Any Oil Leakage That Gets By the Cup Packing Its Duty Is To Return it to the Upper Pressure-Chamber FIG. 24—APPARATUS USED IN OBTAINING THE INDICATOR-CARD REPRODUCED IN FIG. 23 This Crosby Device is Located at the Left and is Connected in the Conventional Steam-Engine Method. A Hydraulic Jack Was Used in Compressing Both the Air and the Steel Springs at the Same Time when Getting the Reading. This Accounts for the Wavy Line on the Up-Stroke as Shown on the Indicator-Card carrying chamber, and, if sufficient oil has leaked by the upper cup to build-up a pressure that is greater than the decreasing pressure in the upper chamber on the full back-stroke of the air-spring, the oil will be forced back by the edges of the upper cup-washer into the pressure chamber. In this construction a pumping action occurs only with leakage and the top cup-washer takes all the hard knocks, leaving the lower one as the last line of defense. Even with a poor upper cup-washer, the lower one is protected from the full force of the changing pressures above, and it is also apparent that the effective pres- [PAGE 17] AIR-SPRINGS AND RIDING-QUALITY FIG. 26—ASSEMBLING A DIRECT-ACTING AIR-SPRING The Workman Has the Cylinder in His Right Hand and Is Preparing To Slip It Over the Piston-Head That Holds the Two Cup-Washers. The Springs Are First Assembled as a Unit in the Cylinder and Then Assembled in the Guide or Outside Member That Is Bolted to the Bracket on the Frame of the Car FIG. 27—VIEW SHOWING TESTING DEPARTMENT The Air-Springs Are Set in Racks under Pressure and Closely Observed for Leakage, Either Oil or Air During the Various Stages of Their Assembly at the left in a horizontal position. An ordinary hydraulic jack on rollers was utilized to compress both the air-spring and the steel spring. The stepping-up action of the jack is reflected in the trembling compression-line. Fig. 25 shows an earlier type of air-spring than the direct-acting type that has just been described. It has stood the test of time and is still being manufactured. The view shows the air-spring in collapsed position. Actually, for riding conditions, the spring will be pumped-up so that the cylinder or piston is in mid-position. The main elements of this spring are the cylinder b, to which the steel spring is connected, and the outer shell a and inner parts d, all as one element attached rigidly to the frame of the car. The interior is filled with sufficient oil to keep the cup-washer c covered at all times. The partition between the upper and the lower chamber contains the pump and pump body. Oil completely fills the lower chamber at all times and fills the upper chamber partly. A compression stroke of the cylinder drives the oil through the bypasses in the pump body into the upper chamber, compressing the air. On the return stroke, the oil is forced back by the air-pressure into the lower chamber. Any oil that leaks past the cup-washer is trapped in the annular reservoir above it, whence it is caught up by the pump and returned to the pressure chamber. The pump consists of a closely fitting plunger in the pump body, directly connected to a flapper valve that is actuated by the flow of oil back and forth from one chamber to another. This pump, though entirely different in every way from that used in the direct-acting spring, is there for the same purpose, namely, to act as a secondary line of defense in the event that the cup-washer is not absolutely tight. The important points on air-spring design, therefore, are to (1) Build it to maintain the pressure required to support the load (2) Proportion the spring so that it has ample capacity for any load it is intended to carry (3) Design the air-spring so that it is easily applicable to the average automobile MANUFACTURE Manufacturing an air-spring is a precision job. It is necessary to work to close limits and yet secure a certain freedom of movement for all moving parts under working conditions. A rigid inspection of material and on the top cup-washer is cut down by the fact that pressure is present on the under side. An air-spring of this type is commonly known as a “direct-acting” spring; that is, it has a compression curve that is practically isothermal. Fig. 23 shows an indicator-card taken with the air-spring connected to a steel spring and the load applied at the axle location. The trembling line is the up-stroke; the straight line is the return stroke as the load is released. Fig. 24 illustrates the apparatus used in getting this last curve. The indicator-card instrument is shown | ||