Electric Brakes on Semi-trailer
Page 78
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ABULK-CEMENT semi-trailer built by R. A. Dyson and Co., Ltd., Liverpool, 8, for operation in Norway, has been equipped with Warner electric brakes. The semi-trailer is a hopper unit, drawn by a Leyland Beaver prime mover. Electric brakes have been used to obviate freezing troubles caused by the , low temperatures in which the outfit will work,
The Warner electric brake is essentially a mechanical internal-band brake actuated by an electro-magnetic clutch. Reference to the accompanying illustration shows the make-up of a brake unit.
B is the magnet, mounted on the backplate (A). The armature (C) is bolted inside the brake drum (E) and is kept in constant light contact with the magnet by means of flat springs. When currentis passed through the electro-magnetic eon the armature clings to the magnet and starts it turning.
Band Brake
Lug F is attached to the magnet, and is forced against the end of. the brake band (D), thus pressing it against Ihe drum. The brake band floats in its support to allow a self-servo effect. '
• The greater the currenf passing through. the magnet,' the tighter the band .will wrap itself 'into, the drum Ev.entually ' the magnet slips on the ' ai•mature to prevent the wheel from 'hacking unless an emergency application is made.
./s rheostatic controller, linked to the tractor's brake 'pedal; controls the Current in the magnet. _ A hand-operated "controller is also supplied to give semi-trailer braking alone.
A synchronizing unit is incorporated in the tractor braking system, so that the time at which the semi-trailer brakes come into effect, relative to the tractor brakes, can be set to suit requirements. Usually the semi-trailer brakes are set to come on slightly before the tractor brakes.
Another control is provided to allow the driver to reduce or increase the maximum braking effect according to whether the semi-trailer is laden or empty.
The Warner electric brake is designed to operate at 6v. and the amount of current required for maximum braking is 3 amp. per brake. An emergency break-away connection ensures that should the semi-trailer become detached. a dry battery on the semi-trailer will apply the brakes.
The brakes, which are an American design, are made in Great Britain by the Patent Lighting Co., Ltd., Eden Works, Uxbridge Road, Hayes, Middx.