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 on the influence of detail, including accessibility, fuels, and lubrication, on automobile development.
| Identifier | ExFiles\Box 154a\1\ scan0008 | |
| Date | 21th October 1911 | |
| 352 MOTOR TRACTION. OCTOBER 21ST, 1911. The Influence of Detail on Automobile Development.* By L. A.{Mr Adams} Legros, M.I.Mech.E. (Concluded from page 332.) The Need for Accessibility. Accessibility is a question which has had a great influence on the design of the automobile, and in some instances may have determined the type which has set the fashion, and fashion in the automobile vehicle plays a more important part than it does in any other class of machinery within my experience. The necessity for frequent access to the engine, to its ignition gear, to its carburetter, and to its valves has ensured the placing of the engine in the front of the car where it could be quickly and most easily reached with the minimum of disturbance to the main portions of the vehicle. This fashion in position of the engine is likely to die very hard, so accustomed have we become to giving up the front of the car to the engine. Accessibility may be divided into two main heads; first, accessibility to those parts which frequently require adjustment requiring no special skill, such as the adjustment of the brakes, of the strength of the clutch spring, of the spark of the ignition devices, and the like, most of which have already been dealt with by the designer in arranging them; and second, accessibility to details requiring skilled attention. In the latter class come the overhauls of engines, gear boxes, axles, etc., and the influence of commercial and public service vehicles on this branch of the subject is only now commencing to make itself felt. The importance of being able to remove parts of a car, unit by unit, that is, engine, gear box, back axle, etc., has now become recognised by those responsible for the vehicles of public services such as those of the motor omnibus and cab companies, since the conditions of working such services are much more closely allied to those of the railway and the tramway than are the conditions of the private car or the commercial vehicle. The easy removal of these units complete, and their interchangeability with other similar units on the same class of vehicle is a large factor in economically keeping a fleet of public service vehicles upon the road. Apart from the two broad questions just mentioned, a third and very important factor is that of accessibility to the various parts by those tools used in making the adjustments. With the necessity for keeping down weight has come the reduction in the size of nuts below those selected by Whitworth for a material the use of which in automobiles only occurs in body work—reduction in the size of nuts has been accompanied by reduction in the width of flanges—the whole of the work has become more cramped and the clearance between the faces of the nut and other adjacent surfaces has been greatly reduced. To put the parts together in the first instance may require the use of special spanners, owing to the fact that the designer has not laid a scale-tracing of an ordinary spanner on his drawing and ascertained that it can be effectively used, that he has not tried the clearance between the corners of the nut and the adjacent surfaces to ascertain whether a box spanner will overcome the difficulty, or, if so, that he has not allowed for the height of the box spanner. Ignorance of these factors contributes heavily to the repair bill, especially if such inaccessibility is assisted by the super-imposition of small details, and particularly piping, which requires removal before the main parts become accessible. If these features were considered in design, bolts would often be substituted for studs, long bosses would be cast on parts to enable the nuts or bolt heads to be reached; channels would be milled across faces into which bolt heads could fit to prevent them from turning, and such parts as guardings and covers would be so made that their detachment would be dependent on very few devices, and those of kinds easily secured and readily locked. Leaving the vehicles of the present, and the position which detail has taken in their development, we may pause to ask ourselves what are the possible detail improvements which will influence the future evolution of light automobile machinery, whether for transport by earth, water, or air, and what effect will they have on the design and construction of the vehicles of the future. Fuels. Among so-called improvements may be cited solidified petrol, but it is difficult to imagine what possible advantage a solid which is troublesome to handle can have over a liquid which can be readily led from its reservoir to its destination through a pipe by gravity, or by pressure if gravity will not suffice. Among gaseous fuels acetylene has been proposed, and though this compound is to some extent endothermic, yet it has not a sufficiently high thermal value to render it a competitor of petrol, particularly as it is unsafe when compressed. It gives, however, a wider range of explosive mixture when mixed with air than the other well-known hydrocarbons, and the mixture of acetylene and air fires at a lower temperature than is the case with other gases. In considering the applications of such gases of high calorific value as acetylene or hydrogen, it is only necessary to make a rough calculation to realise that at present no saving, but, on the other hand, a great increase of weight would result were they generated on the vehicle owing to their small weight relatively to that of the compounds used in their production. Moreover, the same applies to the storage of compressed gases, which can only be considered commercially practicable in the case of town gas applied to heavy vehicles engaged on runs of but short mileage between fixed charging points. The fact that acetylene gives a larger range of explosive mixture than other well-known gases, and that the mixture fires at a lower temperature, would point to a possible saving in the weight of the ignition apparatus. This saving would, however, be but small, and affects but little the question of the total energy obtainable within a limit for the combined weight of fuel and engine. Lubrication. In the desire to reduce the weight of the transmission gear, the diameter of the shafts in the early vehicles was reduced to the minimum, and, in order to obtain the requisite area of bearing for carrying the load, the bearings in the gear box were of necessity made long. The spring of the shafts under the heavy loads to which they were subjected resulted in bending to such an extent as to reduce the thickness of the oil film locally below that necessary for efficient lubrication, with the result that in many of these earlier cars difficulties arose in maintaining the bearings in efficient order. These difficulties have been largely overcome by the use of the ball bearing, which, as it takes up less length of the shaft, reduces the effective span between the supports and diminishes the spring. But this is not the only advantage given by the ball bearing; still more important is the fact that it is capable of working satisfactorily with a greater error of alignment than is possible with a plain bearing. The ball bearing working under suitable conditions, and provided it is not overloaded in the first instance, appears capable of running almost indefinitely when immersed in an oil bath and kept free from small pieces of abraded metal. In fact, in the gear box, ball bearings generally give less trouble than on other portions of the car. Although the ball bearing has such marked advantages when treated in a suitable manner, yet under conditions less favourable, such as those of the road wheels, where a bearing may be called upon to stand excessive and obliquely applied loads, failure is much more easily produced, especially if accelerated by the penetration of water even without dirt, into the bearings as previously mentioned. The effect of water in destroying the smoothness of the surfaces leads to rapid disintegration, and once the ball bearing has begun to fail, either by the breakage of the balls, or of the race, its end occurs more rapidly than is the case with the plain bearing. Increased Motor Efficiency. The improvements in the efficiency of motors have been almost inseparably linked with improvements in carburetters; nevertheless improvements in the motor itself have certainly to no small degree contributed to the advance in the amount of power obtainable per unit of weight of motor and in the efficiency of the motor itself as a thermodynamic machine. The consumption of fuel per brake horse-power hour in the petrol motor has now been reduced to 0.63 lb. Allied to the question of efficiency is the question of * Being the Presidential Address read by L. A.{Mr Adams} Legros, M.I.Mech.E., before the Institution of Automobile Engineers on Wednesday, October 11th, 1911. | ||