Use of the universal-joint for transmitting power mechanically through an angle has been traced back to about 300 years before Cardan's period and about 400 years before a patent on a universal-joint was granted to Robert Hooke in 1664. The first reference to use of this type of joint is found in a manuscript by Wilars de Honecort, a thirteenth-century architect.
A peculiarity of the universal-joint is that, as the two shafts which it unites are rotated when at an angle to each other, it imparts to the driven shaft a non-uniform rotational velocity which becomes very erratic as the angle between the shafts approaches 90 deg. This action has been analyzed by many writers by different methods, two such analyses being cited by the author of the present paper.
To secure uniformity of velocity of the two shafts by the use of a pair of universal-joints, the driving and the driven shaft must form equal angles with the intermediate shaft and the axes of the joint yokes on the ends of the intermediate shaft must lie in the same plane. With such an arrangement, the universal-joint is so highly efficient at small angles that the loss of power in transmission can be detected only by delicate and accurate instruments. The theoretically correct arrangement of a double-jointed propeller-shaft in a car having a torque-arm is shown.
Many typical examples of patented universal-joint design on which much inventive effort has been expended are given, together with descriptive text. Basic ideas embodied in some of these are in use in various types of universal-joints now offered in the market and that have been used for years in motor-vehicles. The more prominent of these joints are illustrated and described.
The author classifies universal-joints into three general divisions: grease lubricated, oil lubricated, and non-lubricated. An ideal sought by some engineers is a joint that will perform its function satisfactorily with no lubrication or other attention, and that will have a life equal to that of the vehicle in which it is installed.
A type of joint that is distinguished by a uniform driving relation between the engine and the driving wheels has a series of steel balls held in races milled in opposite faces of the jaws of the yokes. Such rolling balls add a supplemental principle to that of the universal-joint. Live-rubber balls give a cushioning effect that is highly desirable in some applications.
Flexible-disc joints, which are in a class by themselves, have been greatly improved by special construction of the fabric-and-rubber discs and by the method of holding them to the spiders on the shaft ends.


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