A Finger-tip Emergency Brake
Page 42
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MHE ideal emergency brake, or
"dead man's brake," as it is sometimes called, has yet to be discovered, the difficulty being that the driver of a toad vehicle has much to occupy his attention and it seems unfair to eve him another matter to attend to, such as holding a brake 41 the " off " position. In exploring the possibilities of providing an emergency brake the Harris Motor Co., Burslein, Stoke-on-Trent, has evolved a scheme which could be used in a number of ways. The design of the system calls for an hydraulic reservoir, from which pressure may be
tapped, for application of the brake pedal, merely by opening and closing a valve—an action which could be readily coupled up to a small lever attached to the steering-wheel boss where it is readily reached by the driver's left or. right hand.
As arranged on a test car which we tried last week, the valve is held in a closed position by the driver maintaining a grip on a ring situated beneath the steering-wheel rim. By releasing the ring the brakes are applied.
Driven from the car propeller shaft is a two-cyliudered oil pump equipped with ball valves; it is operated by cams. This Pump charges a container M a pressure of 150 lb. per sq. in. (this figure could be modified), a spring meanwhile being compressed to allow a reaction to be given upon a ram for application of the brakes.
The drawing-indicates two springs in the accumulator, and the energy stored in the springs can be released through the medium of the oil, which is, of course, working under the same pressure as that exerted by the springs.
The system works quite well on the road and although it was fitted to an old ear on which only rear brakes were used, the system was powerful enough to cause skidding of the rear wheels on wet road surfaces. Down a hill of a gradient of about 1 in 5 the car was pulled up to rest from 25 m.p.h. in about 100 ft. and until the ring beneath the steering wheel was pulled up the position on the decline was maintained. We actually made eight stops in .3 of a mile without the efficiency of the system falling to any noticeable extent, the pressure being maintained in the accumulator throughout this rather severe test. With four-wheel brakes it should be possible considerably to improve on the figures quoted, whilst the inclusion of a " gate" type of valve would make the system progressive in action and would place it directly under the control of the driver.