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).
Article from the journal 'Engineering' discussing the Ljungström single-lever control for motor-cars, with accompanying diagrams.
| Identifier | ExFiles\Box 156\4\ scan0023 | |
| Date | 18th November 1927 | |
| Nov. 18, 1927.] ENGINEERING. 661 LJUNGSTRÖM SINGLE-LEVER CONTROL FOR MOTOR-CARS. CONSTRUCTED BY MESSRS. AKTIEBOLAGET SPONTAN, STOCKHOLM, SWEDEN. [Diagrams Section] Fig. 13: Motor Flywheel, Outer Sleeve in Clutch, Centrifugal Weights, (382.A.) Fig. 14: TORQUE EXPRESSED IN KG. CMS. ON VARIOUS PARTS OF THE TRANSMISSION. Labels: Turning Moment in Kg. Cms., Start, Propeller-Shaft Flywheel & Revolutions of Engine. Fig. 15: Labels: Start, Propeller-Shaft Flywheel, Propeller Shaft, Pendulum Wheel. Fig. 16: PROPELLER SHAFT RUNNING AT HALF SPEED OF ENGINE. Labels: Start, Outer Sleeve in Clutch & Prop. Shaft Flywheel, 4 Revs of Eng., Outer Sleeve in Clutch & Pendulum Wheel, Propeller-Shaft Flywheel, Additional Reaction from Stationary Flywheel Transferred to Propeller-Shaft, Engine. Fig. 17: Labels: Start, Spring Anchor on Chassis, Pendulum Wheel Carried Over by Outer Clutch Sleeve, (382.B.) Fig. 18: FIAT CAR TORQUE & TRACTIVE FORCE AT ROAD WHEELS. ORDINARY TRANSMISSION. Labels: Torque Kg. Cms., Tractive Force kgms., 1st Gear, 2nd Gear, 3rd Gear, Direct, Kilometres per Hour, (382.D.) Fig. 19: FIAT CAR WITH SPONTAN TRANSMISSION. Labels: Torque kg. Cms., Tractive Force kgms., N: 1200, N: 2300, N: 2800, Kilometres per Hour, (382.C.) Fig. 20: (382.E.) [Column 1 Text] when the parts are again brought to rest. When the engine is driving the propeller shaft, as in the above case, only the torque actually produced by the engine can be directly transmitted to the shaft. The utilisation of the additional torque produced by the action of the weights implies the existence of a suitable stationary point on which the reaction can be taken, such as the casing of the gear-box in the application described above. Since the reaction on this point must act through the anchor springs, its magnitude can be measured by suitable apparatus, and the results of such an investigation are given in Fig. 17. In the upper half of this figure, the torque due to the weights has been replotted from Fig. 16, and then reduced to the mean value shown by the undulating curve. The direct motor torque has also been plotted, and the total effective torque is thus represented by the distance between the undulating curve and the base line. In the curve in the lower half of Fig. 17, representing the torque on the anchor, the direct engine torque is not represented, as it is always positive. The two final curves, given in Figs. 18 and 19, represent the tractive force at the road wheels at various speeds, the first showing the usual curves for the Fiat car on each of the four gear-ratio speeds, and the second, the equivalent curves with the Spontan gear. The portion of the second diagram with vertical shading represents asynchronous running, while the portion with horizontal shading corresponds with the direct drive. It is particularly interesting to note that when the change over from one form of drive to the other takes place, at about 42 kilometres per hour, the speed may be decreased to about 30 kilometres per hour with the gear operating synchronously, since the weights will naturally come to rest in the outward position, and before they can be set in motion again, the force necessary to overcome the centrifugal force acting upon them in this position must be supplied by the engine. A point that should be noted in connection with these curves is that the engine is, in effect, free from the drive when the latter is moving at very low speeds, so that it can be very rapidly accelerated to give a high starting torque, with the result that the actual acceleration on the car is correspondingly high. It was stated earlier in the description of the gear, that when fitted in an actual car, the controls could be so arranged that all operations, other than that of steering, could be controlled by a single pedal. The actual arrangement of the controls is shown in Fig. 20. [Column 2 Text] The cranked lever I is keyed to the same shaft as the pedal, and, therefore, always moves with it. It is fitted with a block K¹, with a recess in which on the end of the lever K engages. The latter lever is mounted on the end of a long circular rod rigidly held at the opposite end; and serving the purpose of a brake rod G is coupled to the lever. In the position shown, the brakes are full on. To release them, the pedal is depressed, forcing the roller on the lever K out of the recess, the face on the head of the lever I being so formed that, as the pedal is further depressed, the resistance offered by the lever K is attached, gradually becomes less. At a certain point, the pedal lever reaches the throttle lever S, and, in this position, the resistance transmitted to the pedal by the torsion rod is very slight. Further movement of the pedal opens the throttle to any desired extent, and thus governs the speed of the car. To slow down the car the pedal is allowed to rise, first closing the throttle, then passing through the free-wheeling position and finally applying the brakes. To reverse the car, it is necessary to pull the lever back from the position shown in the figure, and a stirrup P, which fits over the foot, is provided on the pedal for this purpose. The act of raising the pedal causes a spring-loaded pawl X to engage with the ratchet wheel Y. The latter wheel is mounted on the end of the reversing shaft in the gear box, and when the pedal is again depressed, this shaft is turned and actuates the gear-box sleeve, reversing the gear as already explained. On completion of the reverse movement, the pedal is again pulled up by the stirrup, and again depressed. This has the effect of turning the reversing sleeve, and restoring the sleeve to the forward position. We recently had an opportunity of testing the Fiat car to which the gear has been fitted on the road, and found the designer's claim regarding the simplicity of control fully substantiated. A slight difficulty occurred, in the first instance, in letting in the clutch gently, but this could be overcome with a few minutes' practice. In spite of the fact that the car was fitted with a relatively heavy body and a small engine, the acceleration from rest was quite exceptional. We may say, in conclusion, that this gear is being shown at the Commercial Motor Exhibition, Olympia. ELECTRICITY IN THE TEXTILE INDUSTRY.—According to a quarterly publication of the British Electrical and Allied Manufacturers' Association, the textile mills do not lend themselves to easy electrification, but the contention that electrification is not borne out by the fact that in America, 63 per cent. of the textile mills are operated on this system. The corresponding figures for Great Britain are 26 per cent. or 19 per cent. for cotton alone. [Column 3 Text] PLASTIC YIELD, SHRINKAGE, AND OTHER PROBLEMS OF CONCRETE AND THEIR EFFECT ON DESIGN.* By OSCAR FABER, O.B.E., D.Sc., M.Inst.C.E. In this paper it is shown that (1) Structures of reinforced concrete with stresses inside those allowed in good practice continue to deflect without change of load or temperature, a result due partly to shrinkage and partly to plastic yield. (2) Consequently, the absence of permanent set or deflection must not be insisted on as a necessary criterion of safety where the test involves an appreciable time element. (3) This yield and shrinkage produce a large, though gradual, redistribution of stress between the steel and the concrete in a reinforced-concrete structure, of such a nature generally as to relieve the concrete and add to the steel stress. Compression steel in columns loaded at four weeks, may, at the end of a year, be stressed to 21,500 lb. per square inch, when the concrete is only stressed to 389 lb. per square inch (a result many times greater than figures as normally calculated), and if loaded earlier or left loaded longer the stress may reach higher values still, and may indeed reach the yield-point. (4) Present regulations, which take no account of these matters, leave much to be desired. (5) The deflection of reinforced-concrete beams, while only about six-tenths of the calculated deflection when the load is first applied, may amount to about six-tenths more than the calculated deflection after about six months, the final deflection then being about 2 1/2 times the original, and still increasing. (6) When the load is removed, only the initial elastic deflection disappears, the deflection due to shrinkage and plastic yield remaining as a permanent set. (7) Reinforced-concrete structures are not dangerous by reason of these phenomena when properly designed, but special care is necessary in binding compression steel, whether in beams or columns. (8) The modulus of elasticity of concrete is much greater than that specified in most regulations, but yield and shrinkage, in some cases, produce results similar to those obtained with a very low modulus. References are given to records showing that actual deformations on structures over long periods, such as a year or two, amounted to five or six times the deformation when the load was first applied. Concrete slabs designed for 300-lb. per square foot deflected 3/8 in. in three years, though standing without applied load. The values of shrinkage in concrete given by various * Abstract of a paper read before the Institution of Civil Engineers, on Tuesday, November 15, 1927. | ||