PREVENTION OF RUNNING BACKWARDS.
Page 25
If you've noticed an error in this article please click here to report it so we can fix it.
How the Tilling-Stevens Petrol-electric System Obviates the Use of Sprags or Skotches, and Makes Safety on Hills Certain.
THE NECESSITY for further effort, on the part of chassis designers, to provide efficient mechanical preventatives against backward running on hills has recently received much attention in the columns of this publication.
While it is certainly true that, more can be dtne in this direction, so far as the orthodox gear-driven vehicle is con. corned, it is claimed that it does nocin the least apply in the case of the TillingStevens 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 impraotica.ble, but scientifically impossible.
Fully to appreciate his, 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 chid transmission units of this chassis 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 gene• rator is coupled direct to the petrol engine, and the output of the machine is governed by the speed of the petrol engine and reigulated 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 tolumn. The motor is, in turn, coupled direct to the back axle by. means of a eardan shaft and worm gearing.
An Automatic Check on Backward Running.
Reversal is obtained by means of a Controller lever, also on the steering column, which Ls three positions--forward, neutral, and reverse. It is, therefore, obvious that, should the vehicle, when amending a hill, have any tendency to run backward, the armature of the motor would revolve in the reverse direction, and it would then become transformed automatically into an electric generator, with gravity as the pri 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 hill by what might be termed an electrical swag or brake, whether the engine is running or not. This condition of affairs comes abed 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 chas.sis can be stepped 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 peesibly get out of hand. It will be observed that One of the greatest usual hill-climbing dangers—changing down gears--does not even enter into the question with the petrol-electric,, as both clutch and gearbox are eliminated in this type of chassis.