Preventing Fire
Page 45
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Following an Accident
An Interesting Automatic Mechanism that Switches off Current and Turns off Petrol in the Event of a Mishap
IT is generally supposed that most fires which occur following a road accident are 'started by an electric spark, either from the ignition circuit or from the breakage and short circuiting of a low-tension lead. Working on this theory, Mr. B. Dixon-Bate, a well-known ttailer manufacturer of Chester, has developed an automatic mechanism, the purpose of which is to overcome this
The Dixon-Bate Safeguard 'Control, as it is called, incorporates two bobweights, one of which can move in a fore-and-aft direction, whilst the other is arranged to swing laterally. These two weights are coupled up to a toggle mechanism in such a manner that if either of them swings from its normal position, it trips the toggle, and thus allows the switch mechanism to be operated. By reason of the two weights, the Safeguard Control comes into action either in the event of a head-on collision, or if the vehicle be overturned.
• The Effect of a Sudden Stop.
Inside an aluminium box is a toggle joint, to one lever of which there is attached a suitable weight. Should the vehicle be stopped suddenly, as in a collision, the inertia of this weight carries the toggle over dead centre, so that it collapses under the influence of a coil spring. As it collapses, it operates the switch lever.
So much for a head-on crash; in other forms of accident, the impact is more of a glancing blow, resulting sometimes in the vehicle being overturned. The second pendulum, therefore, has its axis at right angles to the axes of the toggle joint, Should this pendulum swing through an arc of more than 20 degrees, a cam (which rotates with it) releases a spring-loaded bell-crank lever which pushes the toggle over its dead centre.
The switch is then operated in the same way as in a head-on collision. In each case, suitable clearances ensure
that there is no movement of the switch until the toggle is properly tripped.
Turning to the electrical side of the device, this incorporates four distinct switches. Above the box in which the operating gear is located, there is an arm pivoted on a ball bearing. At one end of this arm are two knife switches. When the device comes into action, one of these earths the dynamo positive terminal and the other earths the magneto, if the ignition system happens to be of this type.
At the shorter end of this arm there is a set of really heavy contacts in the main battery positive lead. Normally, this switch is closed so that the battery circuit is completed, but when the Safeguard Control comes into action, this lead is interrupted. Alongside it is another smaller switch, the purpose of which is to interrupt the coil-ignition circuit. Finally, there is a push-pull cable which connects the petrol tap to the device so that also the fuel supply is cut off. • In Case of Accident.
The various switches are substantial, so that, in the ordinary way, they are unlikely to affect the various circuits in which they are fitted. Should an accident occur, however, the result would appear to •be most complete. Simultaneously, the ignition, whether by coil • or by magneto, or by both, is cut off, the battery is isolated, and, in case the engine is still rotating by the momentum of the flywheel, the dynamo positive terminal is safely earthed. At the same time, any possibility of a. considerable flow of petrol from the carburetter is also prevented.
By means of a neat dashboard control which can be obtained with a lock incorporated in it, the Dixon-Bate Safeguard Control can be used to put the entire power unit of the vehicle out of action when it is left parked. Furthermore, it can be used as a main battery switch when such a device is desirable.