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New Braking Systems for Cars hia.y •

14th September 1962
Page 91
Page 91, 14th September 1962 — New Braking Systems for Cars hia.y •
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Indicate Important Trends

Rear-wheel anti-locking device from Lockheed and a Dunlop self-servo disc brake for frontwheel application

ESICiNED for application to the rear wheels of private cars; an antiking system has been developed by the ;khccd company which ensures that vehicle continues to move in a straight : during an emergency stop when full king force is applied. Although the nt wheels may lock, the rear wheels vide maximum braking effort without king, and the greater effective friction ween the rolling tyres and the road vents the tail of the vehicle slewing mays. Application to the rear 'wheels y promotes simplicity and reduces t, and it is pertinent that no auxiliary ossure system is required.

rhe sensing or control unit of the proypc device is belt-driven from a pulley .unted behind the rear universal joint the propeller shaft (which enables )erimental applications to be made ,h the iniaimum complexity), and is :d in conjunction with a vacuumcrated servo unit which is connected to dmple type of vacuum reservoir con

trolled by manifold Pressure. A flywheel in the sensing unit -tends to Overrdn the, drive pulley when the mean deceleration of the two wheels exceeds a critical maximum rate, and this displaces a cam plate' and opens a spring-loaded plunger Valve located between • an atmospheric intake_ and the upper chamber 'of: the servo. A diaphragm in the -serve -is normally held in its extended position by a coil Spring against the vacuum 'oni. the lower side, but as soon as air is admitted to the upper chamber the vacuum is sufficient to move the diaphragm downwards: A diaphragm-operated plunger is in contact with a non-return ball valve which is normally held open to allow free transfer of fluid from the hydraulic .master cylinder of the main brake system

to the rear brake line. When air is admitted to the upper chamber, however, the ball drops back on to its seat and isolates the rear brake line from the master cylinder, whilst the effective • volume of the line is increased by movement of the plunger. In this way pressure is relieved in the brake line without loss of fluid to the main system.

BLEED FROM MASTER CYLINDER.

A member of the staff Of The Commercial Motor; Who drove i'car equipped with the system, cdnfirms the validity of the makers' claims. Full brake application resulted in the Vehicle skidding in a straight line with only the front wheels locked, . whereas all the wheels locked when the systdm Was not in use and it was impossible to prevent severe tail slewing. According to the makers, overall braking efficiency is increased by the complete prevention of rear-wheel skidding.,

Self-servo Disc

Sclf-energization by wedge action is a feature of a new Dunlop hydraulically operated disc brake, known as the S type, which is designed for front-wheel applications, the scope of the, brake in its existing form being indicated by its

suitability , vehicles based on private-car 'chassis in the .1.5-'2.5-litre class. The servo factor is about 2 to 1, and the brake can, therefore, he employed in place of two-leading-shoe equipment without an external servo, brakes of the latter type being inherently selfenergizing.

In contrast to conventional disc brakes, the two operating cylinders of the calliper mechanism are so arranged that their axes' are located at 45 degrees to the disc, the thrust of the pads being in the same general direction as the forward rotation of the disc. In conformity with the shape of the housing, each pad is angled at its apex to provide a wedge between the disc and the housing, the perpendicular centre lines of the inclined faces lying approximately, on the axes of the cylinders When pressure is applied to the pistons, the drag force created by disc rotation tends to wedge the pads between the disc and the housing and this produces a reaction that augments the force derived from .the hydraulic cylinder pressure.

An essential feature of the design is the use of DU dry-type low-friction plates between the pads and the housing, which affords freedom from the slip-stick problem. A fade-free friction material is employed and adjustment of the pads is automatic. The pads are easily replaced.

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