The F.W.D. Brake - booster: The Editor, THE COMMERCIAL MOTOR.
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127171 a recent number of your excellent paper we notice that in the resume of recentpatents you have included our toggle brake gear. Unfortunately, in describing this, the main feature has been
lost sight of, which is the effect of the toggle linkage increasing the pull on the brakes as the pressure is applied.
Although primarily intended as a compensating gear, the arrangement was designed so that, with an even pressure on the hand-brake lever, the pressure on the brake shoes gradually increased, so that, inversely, whilst taking up the clearance between the shoes and drums a quick action is obtained, whilst after the clearance haS been taken up the action slows down, with a .corresponding increase in brake pressure. We are enclosing a blue print herewith, Which shows the action of the brake in the form of a curve. [We have reproduced this.—En.] As you will see from this, assuming a 10 to 1 leverage between hand lever and axle-brake lever, with the normal linkage we get the two horizontal lines showing 100 lb. pull on the hand lever and 1,000 lb. pull on the axle-brake lever. With the toggle Mechanism, however, with the same horizontal line at 100 lb. we start with
a pressure on the brakes of less than 500 lb, and finish up with slightly more than 2,500 lb: The linkage is so designed that the horizontal line at 3,000 lb. and the curve for the toggle mechanism cross at approximately the point where clearance has been taken up, so that, starting from the point where Clearance has been taken up, we increase from the same pull of 1,000 lb. to a maxitnum of 2,500 lb.
We hope that all this is quite clear to you, and that it may be of some interest. —Yours faithfully, For the Four Wheel Drive Lorry Co., Ltd.,
C. F. CLEAVER, Director.
Slough, Bucks.