A Disc-type Brake for Propeller Shafts
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i-no RAKES which operate by means of _Lithe friction between fixed and rotating discs pressed into contact have been employed for many years on certain private car chassis, but they have not achieved any great measure of popularity in connection with the commercial vehicle, possibly because of certain difficulties, such as warping of the discs due to overheating, which are liable to occur when the braking power has to be considerable.
In view of these circumstances it is interesting to learn that a brake of this type is embodied in the new 21-ton chassis produced by the American-La France Co., of America. This brake is on the propeller shaft, and thereforo gains the benefit of the final gear reduction, so that the, pressure between the opposing faces does not have to he excessive ; in addition it is so designed that there is a constant flow of air through the cast-steel double disc which forms the rotating member of the brake.
Reference to our illustrations will show that air spaces for cooling are also provided behind the discs which constitute the brake shoes and which have their .eentre portions cut away. Each of the partial discs thus formed is cut in the horizontal plane, the halves being each held to a cast ring by three bolts, whilst the ring itself is supported by vertical trunnion bearings on the shoe carrier. This carrier is mounted on a fulcrum pin at one end and closed in %mon, or withdrawn from, one face of ..he central double disc by a toggle device at the other end, the corresponding carrier at the other side working in a similar manner, so that the double crse is compressed between the two, or floats freely between them, as is required. The walls of the double disc are. joined
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together by curved wales, the rotation of which causes the air pumping action to which we have already referred. This rotating member is carried by splines on the gearbox shaft, along which it can fleat axially to-facilitate the equal al. gagement and freeing of the shoes, and thus to act as a type of compensating device, whilst equal pressure over the whole face of the friction material fastened to each shoe is obtained by the trunnion mounting of the discs.
Two most important claims are made for this form of brake construction, that considered to be the most vital is the
very adequate cooling obtained, the other is the large wearing surface provided, combined with great ease of re-. placement of the bonded ' asbestos.
material employed. It is stated that the four shoes can be removed and replaced in less than half an hour. . They are made from tough sheet-steel, to which the friction material is strongly riveted. Each shoe seats on lugs on its cast ring, these lugs being carefully faced so that the shoe is perfectly true. The whole arrangement' is 'carried by
heavy frame cross-member, which also ;supports the.rear end of the gearbox.