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 Autocar' magazine discussing the effects of frame distortion on engine and gearbox wear.
| Identifier | ExFiles\Box 75\3\ scan0232 | |
| Date | 4th March 1911 | |
| THE AUTOCAR, March 4th, 1911. 291 The Effect of Frame Distortion on Wear. By A.{Mr Adams} W. Reeves. A consideration of the claims of the single unit system of combined engine and gear box as being a means whereby wear and distortion in engine and transmission mechanism due to frame deflection can be completely nullified. THE Note in The Autocar of the 25th ult., dealing with this subject set the writer thinking. Why is it that at the present stage of automobile engineering such an obviously defective mechanical arrangement as the method of rigidly attaching the motor and gear box to the frame still exists to the extent it does? Everyone who has any knowledge of the subject whatsoever openly admits that all frames must, of necessity, give or distort to a certain extent. As pointed out in the leader above referred to, flexibility within suitable limits is a real virtue in a frame, for it cannot be gainsaid that without such flexibility there is sure to be trouble arising from localisation of vibration, causing consequent crystallisation and fracture of the material. We know very well what happens if the radiator be rigidly and immovably attached to a motor car frame in a position where it is possible for deflection to occur, the experience being that no radiator ever made can be prevented from leaking due to the straining action of the frame deflection. Therefore, irrespective of whether engine and gear box be connected by means of a truly flexible coupling or not, if the motor unit be rigidly coupled to the frame by means of four or six feet in the common manner, and likewise if the gear box be coupled to the frame more or less similarly, it is patent to everybody that the frame deflections are being taken and absorbed by these units respectively. In other words, in addition to their legitimate functions the motor and gear box are compelled to perform the additional functions of frame stiffeners. This point was never more aptly illustrated to the writer than some time ago when the bearers supporting the motors in a number of London motor 'buses commenced suddenly to break away, and one engine actually dropped clean through the frame owing to the loss of all its supports. A Frequent Cause of Noisy Gears. Likewise in regard to the gear box. There is not the slightest possible shadow of doubt that the reason why the gears on so many cars become noisy after a certain amount of use is that the gear box has become distorted due to the methods of attachment now under condemnation. The facts, then, are as follows: It is of no use whatsoever providing perfectly flexible joints between the motor unit and transmission unit if these units themselves are rigidly connected to the frame in the common manner—it merely means that external dis-alignment between the two units is provided for, but the internal disalignment of the units themselves has been completely ignored, and it is hard to say which is the greater of the two evils. In mentioning a perfectly flexible connection between the motor and transmission gear the writer is perfectly well aware that one has to travel far in an investigation of the point before one finds it really carried out. The “barrelled square” arrangement coupling is a barbarous relic of the early days of motor engineering, yet, on the other hand, if a sound pair of universal joints be arranged for, the question of their lubrication has to be considered, also the necessity for their being completely enclosed to prevent a shower of oil being continually thrown out from them. Also to obtain sufficient room for their insertion in the design it often means that the transmission unit must be pushed further backwards towards the rear wheels, with the disadvantage that for a complete examination of the transmission gears the body has to be lifted every time—unless access can be obtained by lifting the rear floor boards, in which case the bodywork usually suffers. Unbalanced Transmission. There is one other feature that must not be missed, and that is the weight of all rotating parts should always be kept as low as possible. This is an axiom which no modern designer dare neglect, and it is probably unnecessary to enlarge upon the reasons therefor; suffice it to say, the inertia of heavy rotating parts in connection with modern high speed motors is responsible for a vast number of ills and a very great amount of vibration. In one particular car which the writer recently experimented upon, the vibration of the car as a whole when the motor was running by itself with the clutch thrown out was extraordinarily less than was the case when the transmission was running. This transmission had large and heavy universal joints both to back and front ends of the gear box, combined with a heavy foot brake drum, all of which, by the way, had been completely ignored as regards correct running balance. However, it is always an easy matter to be destructive but not quite so easy to be constructive, and to the design of motor cars this applies with extraordinary truth. Therefore we will now consider the steps to be taken to eliminate the above bad points. The Three-point Suspended Composite Unit. We must do so by starting off once again with a compliment to the foresight of Mr. Lanchester. This time in regard to the system known as unit construction of engine and gear box. Now, unfortunately, this system has been very severely handicapped by the unconsidered manner in which it has been attempted in very many instances. Primarily it was argued that, given a unit construction supported at three points in the frame, there was always constant alignment and, in fact, a really ideal job. Unfortunately, however, as in so many cases, the friends of the system wounded it by their kindness. As a start, clutch troubles arose in just exactly the same manner and for the same reason that clutch troubles have often arisen in the older type of construction, these troubles being due to lack of concentricity of the male portion of the clutch with the female portion, due to disalignment between motor and transmission gear box. The unwise friends of the unit construction said, “Here we have a system which allows us to dispense with all universal joints and in which alignment is constant,” yet in actual practice this was coupled with a gear box having ball bearings and a motor with its crankshaft running upon plain bearings—the fact that the crankshaft had to be bedded in place, and that adjustments were of course made as found necessary, due to the wear of main journal bearings, whilst no wear was appreciable upon the ball bearings carrying the transmission-shafts, was lost sight of. These facts were quite sufficient to cause very bad alignment in the transmission-shafting in relation to the crankshaft, and the opponents of the unit system therefore said that the Handwritten text: X962 | ||