New Features in London's Latest Trolleybuses
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IT is now generally well known that London Transport is carrying out a big conversion scheme in the metropolitan area which involves the replacement of certain tramways by trolleybuses, and, in connection with this development, the Associated Equipment Co., Ltd., is supplying 252 trolleybuses, work on which is now actively proceeding. The scheme involves the replacement of over 90 mites of tramways route and is equivalent to one-quarter of the total of routes now served by electric tramcars.
The new vehicles, which are all of the six-wheeled type with wheelbases of IS ft. 7 ins., follow closely the design of the experimental unit put into service some 12 months ago by London Transport. An outstanding feature is that, despite the fitting of additional electrical equipment, the weight of the chassis has been reduced so effectively that it is possible for a 70-seater body to be accommodated. Actually, the chassis, complete with full regenerative equipment, motor generator and battery-shunting apparatus, weighs no more than 4 tons 12 cwt. 3 qrs.
A new and important development found in these trolleybuses is the use of batteries for propulsion in the event of the overhead supply failing, when the bus can be run under its own power to a less-congested thoroughfare, for reversing should the normal turning circle provided by the overhead equipment be unavailable, and for moving in the depot without the need for changing the trolley from one overhead set of wires to another. '
The chassis frame is of channel' sestion, with a maximum depth of 11-i
ins., and it is swept up over the front and rear axles; the laden frame height is 1 ft. 11 ins.
• The rear axles are of the fully floating type, with underslung worms, the forward-axle worm housing carrying 'a third differential through which the rearmost axle is driven by means of a short propeller shaft. The rear-axle ratio is 10.33 to 1. The rear axles are attached to cantilever springs, 4 ft. 9 ins, long, which swivel at their centres on large steel castings riveted to the frame side members and connected by a large-diameter cross-tube.
Compressed air cylinders of A.E.C. design form part of the system 'for operating the brakes on the front and rear wheels. A 5-cubic ft. compressor, driven by a 500-volt motor, which is mechanically and electrically insulated from the chassis, maintains a pressure of 85 lb. per sq, in, in a steel' airreservoir of 750 cubic ins. capacity. The vibration and noise of this unit, -formerly the subject of criticism, have been overcome in the new chassis by placing the unit •on special rubber Mountings and by utilizing the frame cross tubeas a Silencer fci,T, the intake.. . Particular' attentiOU has been given' to the layout of the air system, with the object of reducing the number of
rubber connections. An interesting feature is the leading of the exhaust from the air brake over the resistances, which are situated in front of the frame, the effect being that each time the brakes are used a stream of air is directed over them, thus improving heat dissipation.
The electrical equipment is of the English Electric electro-magnetic remote-control type. The motor develops 80 h.p. at 550 volts, and is supported within the chassis side members on a resilient mounting. The foot-operated master controller, which is of the drum type, is located under the driver's seat. A motor generator supplies the 24-volt lighting set and charges the nickel-iron batteries. Other features of the electrical equipment are the fitting of " double band " radio choke coils, a lightning arrester, lightweight-type trolley bases, and slider beads.
A component of particular interest is the patented multiple testing plug, designed to protect passpngers and stall from any electrical leakage.
Most of the 70-seater bodies for these new vehicles are being built by Metropolitan Carnrnell Weymann Motor, Bodies, Ltd., and are of the company's patented metal construction.