Safer Braking

Press, Volume CI, Issue 30005, 14 December 1962, Page 11

Safer Braking

A DEVICE designed to stop "the rear brakes of a car locking in an emergency stop, particularly on slippery surfaces, has been produced in Britain by research engineers of the Lockheed Hydraulic Brake Company. The device has been greeted by experts as an important step in braking safety. Each year a number of road accidents occur that are directly attributable to skids caused by excessive brake pressure locking the wheels in an emergency. A locked wheel has no directional stability and consequently the vehicle takes the least line of resistance. That, due to road camber or uneven tyres, frequently results in it crossing the path of oncoming vehicles, or hitting roadside obstacles.

To overcome these hazards, it is desirable to have a braking system that automatically prevents wheel lock and yet permits the best possible levels of braking to be maintained consistent with the road surface. It is known that many skidding accidents are caused by the large angular deviations of the car that frequently occur when the rear wheels lock. Should only the front wheels lock, the car will continue to travel in a substantially straight line, and although steering control is lost' the risk of a collision resulting from the car

gyrating is virtually eliminated. The system now in the process of development consist basically of a single inertia type skid sensing device driven off the differential input drive flange, and a vacuum servo to regulate the rear brake pressure in response to the requirements of the sensing device. Should the rear wheels begin to lock the function of the servo unit is to isolate the brakes from the master cylinder and increase the volume of the rear brake system, thus reducing the fluid pressure and so relieving the brakes. Tests during development have shown that with the rear brakes controlled by this system the car will consistent stop straight on a variety of surfaces even though the front wheels are locked. When braking on dangerous wet, slippery surfaces the device gives reduced stopping distances compared with the four-wheel locked condition. This, is an additional safety feature but one that is secondary to that of ensuring that a vehicle will brake in a straight line and not slew into oncoming traffic.