New Features in Latest Trolleybuses
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Series-Dynamic Control a Salient Point in Six New Sixwheeled Vehicles for Newcastle FOLLOWING the successful operation of the vehicles already in service, the Associated Equipment Co., Ltd., Southall, Middlesex, recently received from the Newcastle-on-Tyne Transport Department an order for a further six A.E.C.-English Electric six-wheeled trolleybuses. , These vehicles have a special distinction inasmuch as they embody a patented system of seriesdynamic control, and they are among the first trolleybuses of this type to be put into commission.
Realizing that the air-brake system should be of the highest efficiency, an A.E.C. patented design of combined reservoir unit is fitted. The arrangement incorporates the reservoir, governor, check valve and buffer chamber as a complete unit assembly.
The recent-design of high-lift brake cams and the self-locking independent adjusters for all camshaft levers must also be mentioned, as these enable the liners, in. thick, to be worn out completely without any re-splining of levers. Careful attention has been paid to the arrangement of the application for the front brakes, in order that braking Will not affect steering, or vice versa. This has been effected by mounting the air cylinders directly over hollow king-pins, through which the piston rods operate directly on to the camshaft levers.
Specially designed for heavy trolleybus duty, the worm gears have fl-in. centres and three four-star differentials are incorporated. The importance of a clear gangway, free from worm-cover obstruction, has not been overlooked, and this has been obtained by offsetting the worm gear to the near side. Fully floating axles are provided with bellows gland-type oil seals. The position of the motor ensures that a low floor height is obtained as well as a short straight-line transmission.
A Renown Chassis.
The chassis itself is of the standard Renown type with an 18-ft, 7-in, wheelbase, and ventilated disc wheels with 10,50 by 20 low-pressure tyres are fitted all round. Tubular cross-members rigidly brace the frame, which is inswept at the front to provide a small turning circle. The rear of the chassis is dropped to provide a low platform and bodies of 30 ft. overall length, for seating up to 74 passengers, can be accommodated.
The electrical equipment of the new vehicles is of the series-dynamic type which has been specially developed by the English Electric Co. to meet the requirement of providing a stable, easily manipulated electric brake without returning heavy currents to the line. Such an undesirability may be due to the use of mercury arc rectifiers in the substations, or to the particular method of sectionalizing the, overhead. or to the traffic headway requirement being such that it is uncertain whether one or more vehicles on a section will be taking power when other vehicles of the same section will be regenerating current to the line.
The English Electric Co. makes use of a compound motor having a shunt field which is relatively light._ A strong series field allows the well-known advantages of the series motor to be retained, and the light shunt winding is used only for rheostatic braking purposes. This provides a rheostatic brake which can be applied at all speeds without risk of 'flashing over the motors or overstressing the transmission.
The rate of retardation is closely similar to that obtained with a regenerative motor, but no current is returned to the line and high voltages across the armature are absent in the case of the series-dynamic motor.
The new vehicles are also • arranged for operation from the battery.