An Ingenious Automatic Adjuster for Brakes
Page 52
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AN interesting and compact device -for automatically• preserving the correct adjustment in a braking system has been invented and patented by Mr. W. Halleot Hingston,
M.I.A.E., 50, Pall Mall, 4.ondon, S.W.1, who is the consulting engineer to Associated '1'2.ansmissions, Ltd., the proprietor of the Hun frey-Sandlierg free wheel.
It is necessary to explain that, in addition to the advantage of having brakes permanently in correct adjustment, such a device permits of the full -brake-pedal travel being employed for application, instead cif preserving part of the travel for wear of brake-shoe facings. This means that about double the leverage can be obtained—a point which is clearly explained by an accompanying sketch.
In Mr. Efingston's device an adjusting nut on the brake rod has a ratchet head and is turned by a pawl whenever there is the least slackness,;an important point being that full application a the brake is not needed—adjustment to thoir predetermined degree is automatically made by even 1124
slight depressions of the pedal. The accompanying drawings show the device embodied in the brake pedal, but it may equally well be placed elsewhere in the system.
-.The long ratchet nut lies in the bore of a trunnion block held between the brake pedal and a cover plate. A pawl, mounted On a forward boss on the brake pedal, would move the ratcheenut one tooth every time the pedal was depressed but for the fact that the pawl is wide enough to span not only the -ratchet but also a loose collar, adjacent to the ratchet, which makes the pawl ride clear of the ratchet teeth.
The loose collar has a notch in it, however, and by reason of a spring it tends to rotate so as to bring that notch. into coincidence with the rekaive notch on the ratchet—the condition necessary to allow the pawl to work the ratchet; but the collar is prelierderl' iiroui responding to the sprin-g, for it has, opposite to this one notch, a flat, and this is engaged by a flat-faced stop. Depression of the pedal carries the collar flat free from the stop, but before it gets free the pressure on the pedal, by overcoming a spring, grips the collar tightly between the ratchet and the front face of the trunnion block, atill preventing it from turning and so preventiug the pawl from engaging the ratchet. That, of course, is provided the brake adjustment is correct. If the brake-shoe clearance be excessive, the pedal will be depressed a little farther before brake-shoe resistance causes the overcoming of the spring. In this smaIrtime lag the collar, packing free from the stop, will have time to slip around before being gripped, and the paw) will than shift both collar and ratchet through one tooth. This partial turn of the ratchet nut on the brake rod takes up the minute slackness.
To adjust the moment of disengagement of the flat, the stop is made in the form of a bell-crank and can be adjusted by a set-screw against a spring. The arrangement of;the coil spring, the overcoming of which causes the loose collar to be gripped, is feade clear by the drawings. It can be adjusted by means of its cap nut and should be strong enough just to overcome the brake pull-off springs.