Fig. 27. Rear axle. Service and Emergency Brake.
Combined Service and Emergency Brake.—Fig. 27 represents a standard type of service and emergency brake, each of the internal expanding type. As both are inclosed in a drum they are absolutely free from dirt and dust, and the construction shown eliminates rattling of the parts.
The wheel bearing is also represented by the annular ball-bearing type of construction, in which the balls are unusually large, and therefore, capable of taking great weight and high speed without undue wear.
CHAPTER V
THE DIFFERENTIAL
The Meaning of Differential.—This is a term used to designate the difference in the turning movement of two wheels on opposite ends of an axle. For various reasons they do not turn at the same rate of speed, particularly in turning corners, where the outer wheel must travel a greater distance than the inner wheel.
If both wheels are fixed to the shaft the latter would be submitted to a torque, or one of the wheels would slip, and thus be destructive of tires.
On the other hand, if one wheel should be loose, then, as power is applied to the shaft, the tractive action would be on one wheel only, and this would be bad practice, and frequently cause the wheel to slip, and thus unduly increase the wear of the tire.
The differential is made up of a system of gears, which are so arranged that one wheel may turn independently of the other, and at the same time the effective driving power is utilized by each.
Various forms of this mechanism have been developed. While the differential is an exceedingly simple piece of mechanism, it is not such an easy matter to describe its operation, so that the principle will be explained by a series of illustrations.
Equalizer Bar.—Examine Fig. 28. Let A be an equalizer bar, mounted on the end of a thrust bar B, by a pivot C, so the ends will swing back and forth freely. A horizontal bar D is hinged at each end of the equalizer, which bars project forwardly parallel with each other and these are provided with right-angled bends E E, simply for convenience in describing the operation.