Problems in the Design and Development of an Economical Automobile Gear-box

Abstract

The demand for still greater reductions in weight together with the general stepping-up of vehicle performance with larger power units has placed upon the transmission engineer the onus of producing a small, lightweight and compact design yet capable of giving a satisfactory life. Economy in both weight and cost has become a primary requirement, and if this is to be met, a close study must be made of all the detailed components in order that the utmost can be obtained from each pound of material used. The maximum possible life of spur and helical gears is seldom achieved, as premature tooth failure occurs through poor face comformity of the mating teeth. The causes and effects of such nonconformities, whether dimensional or resulting after heat treatment, are dealt with, and the measures that can be adopted for their correction discussed. The elimination of any tendency to corner loading and, to a finer degree, the crown shaving of the teeth enable higher basic stresses to be adopted with corresponding smaller and more economical gear trains. Investigations into syncromesh mechanisms have indicated that synchronizing efficiency depends largely on attention to certain small details. An appreciation of these points will permit of quite small diameter synchronizers functioning satisfactorily without their useful life being in any way impaired by the higher loadings involved. Syncromesh problems are treated generally with particular detailed reference to design for high performance. It is unfortunate but nevertheless axiomatic that the tendency to self-disengagement of the gears increases as the loadings and stresses of the components are increased, and no paper on the design of an efficient economical transmission could be complete without its mention. The general causes of self-disengagement are discussed together with design features which can be embodied for its avoidance. The problems generally associated with the gear train which present definite requirements, of the casing, shafts, selector mechanism, etc., are dealt with. In conclusion, descriptions of the test equipment and tests used in the development of high-duty transmissions are given. The MS. of this paper was received at the Institution on 5th February 1953. For the Report of the meeting in London, at which this paper was presented, see p. 27.