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).
Manufacturing precision, the limits of production equipment, and the critical role of lubrication in axle units.
Identifier | ExFiles\Box 114\1\ scan0082 | |
Date | 11th January 1937 guessed | |
on parallelism, squareness, and center distances of the gear axes in the machining of the parts affecting the mounting of the gears, are extraordinarily close and the cone distance positions of the gear and pinion are maintained to produce in the carrier, the tooth patterns which are exhibited on the test machine after lapping. For most of these the permissible limit is .001 of an inch and the maximum limit on cone position for the pinion in a well made unit will not exceed .0015. Precision in manufacturing is now rapidly approaching the limitations of measuring fixtures which can be regarded as falling within the category of practical production equipment. To obtain this high precision in manufacture has not been easy but the realization of the need for it and its accomplishment has been possible only by the fullest cooperation of the manufacturing and production talent, and the readiness of managements to invest heavily in the most modern equipment procurable. LUBRICATION We come now to the subject of lubrication and in any discussion of this subject we are forced to accept the concept that the lubricant is just as much a structural element in the gear unit as the steel in the gears and bearings, and that the lubrication is just as complete a functional element as the teeth on the gears; the unit will just not operate with the absence of either element. The inter-dependence of the structural elements is manifest in the capacity of the unit to transmit power: if the load capacity of the lubricant is low the capacity of the unit is limited to its break-down value; if the strength of the metal parts is low, regardless of the load capacity of the lubricant, then the power capacity of the gear unit is limited to the rupture strength of the metal. I realize that this concept is not new to you, but sometimes the reiteration of a fundamental truth brings our objectives into a clearer focus. It should hardly be necessary to say that in recent years the capacity of axle units has increased beyond the load capacity of straight mineral oils which have for so many years been regarded as the maximum standard for lubrication value. In other words axle capacity has been limited by the lubricating ability of straight mineral oils to lubricate primarily the gear teeth. Such structural elements as the housings, bearing mountings, the bearings themselves and those parts on which the gears are mounted have been increased in capacity to transmit power beyond the load carrying capacities of the lubricant to properly lubricate the gear teeth, and not only has the ability to reduce axle size or to increased power transmitting capacity been measured by the limits of lubricants, but has prevented the thought that any such thing as increasing the load capacity of lubricants could possibly exist. But the achievement of getting more and more power from engines without increasing their size and the continuous effort to lower roof-lines and floor height of automobiles has brought about the necessity of making smaller axles successfully transmit larger amounts of power. With this necessity has evaporated the compunctions about using special lubricants, and the question is now not whether a special lubricant but what kind of special lubricants can be used and how can the quality and distribution be controlled. It seems to be out of the question to ask the car owner to see to it that he does get the proper lubricant for his axle. He is told in the instruction book to obtain lubricant only from an authorized service station for his car and on the other hand he is told over the radio to buy this and that make of lubricant and he is told by the man from whom he buys his gasoline that he has a special brand of rear axle lubricant which is much better than can be obtained through authorized service. Whom is he to believe? - 7 - | ||