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• PREVENTION OF RUNNING BACKWARDS.

26th October 1920
Page 55
Page 55, 26th October 1920 — • PREVENTION OF RUNNING BACKWARDS.
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How the Tilling-Stevens Petrol-electric System Obviates the Ilse of Sprags or Skotches, and Makes Safety on Hills Certain.

THE NECESSITY for further effort,' on the part of chassis designers, to provide efficient niechanical preventatives against backward running on hills ha, recently received much attention in the columns of this publication.

While it is certainly true that more can be done in this direction, so far the orthodox gear-driven vehicle is con-• cerned, it is claimed that it does no-Fin the least apply in the case of the Tilling. Stevens petrol-electric chassis. In this vehicle, the problem has been obviated rather than solved, but the .fact remains that, by the adoption of an electrical transmission—as is the case with this system—running backwards out of control downhill is rendered, not only impracticable, but, scientifically impossible.

Fully to appreciate this, a review of the principles involved in the construction of the Tilling-Stevens petrol-electric chassis is necessary: • As will be seen from the accompanying illustration the chief transmission units of this chaLis consist of a four-cylinder internal-combustion engine of the usual type, an electric generator, a series-wound electric motor,

and a worm-driven back axle. The generator is coupled direct to the petrol engine, and the output of the machine is governed by the speed of the petrol engine and regulated by the throttle pedal. The electric output of the generator is transmitted by cable connections to the electric motor, the speed of the latter being affected by the loacT on the vehicle and the gradient of the route, as well as by means of resistances, operated by the resistance lever on the steering column. The motor is, in turn, coupled direct to the back axle by means of a oardan shaft and warm gearing.

An Automatic Check on Backward Running.

Reversal is obtained by means of a controller lover, also on the .steering column, which has three positions—forward, neutral, and reverse. It, is, therefore, obvious that, 'should the vehicle, when ascending a hill, have any tendency to run backward, the armature of tha motor would Devolve in the reverse direction, and it would then become transformed automatically, into an electric generator, with gravity as the psi mary source of power. The motor, which has now become a dynamo, would be generating electric current, which would flow through the chassis generator. As this would be practically a short circuit, the vehicle is held on the bill by what might be termed an electrical sprag or brake, 'whether the engine is running or not. This condition of affairs comes about with the controller lever in the forward position, but as it is never necessary to move this lever whilst running, unless it is desired to reverse the vehicle or leave it unattended, it would always be in the forward position when running uphill.

In actual practice, a Tilling-Stevens petrol-electric chassis can be stopped anywhere on the steepest hills and without the mechanical brakes being applied. Even if the engine. has stopped, the vehicle will only just crawl backwards, never -at a speed at -which it could possibly get out of hand. It will _be observed that one of the greatest usual hill-climbing dangers—changing down gems—does not even enter into the question with the petrol-electric, ae both clutch and gearbox are eliminated in this type of chassis.

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