" Safety-first " Tanker
Page 51
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A.E.C. Tanker Fitted with Power Steering and Exhaust Brake Spells Safety for Liquid Loads AN A.E.C. Mammoth Major Mk. Ill eight-wheeled 3,600-gallon tanker, operated by Shell-Mex and B.P., Ltd., has been experimentally equipped with several devices -to assist the safe transportation of liquid loads and to reduce the fatigue and worry of the driver.
The most noteworthy feature is the latest type of Manes power-steering gear, but the tanker also embodies exhaust braking, an all-alloy cab with sliding doors and a tank lined with Epikote, a new form of durable and chemically resistant synthetic resin.
The power steering is manufactured by_the Adamant Engineering Co., Ltd., Luton, under licence from the Gemmer Manufacturing to., Detroit, U.S.A. It was first described in The .Commercial Motor on March 19, 1954, and is an integral unit which incorporates a standard Marles cam-and-double-roller gearbox. A gear ratio of 24.7 to 1 is used, instead of the standard 32 to I.
Power assistance is provided regardless of pressure applied at the steering wheel, thus,giving stable conditions of steering and reducing the transference of road shocks. The system consists of an engine-driven positive-displacement oil pump, combining a small reservoir and a flow-control valve, and the gear itself, connection being by copper pipes.
The column shaft is connected to the worm shaft by spur gearing, and when the wheel is turned the column gear is displaced slightly in relation to the worm shaft because of the resistance of the road, thus actuating the valves and operating the power piston.
There is no delay with this system, because of the constant flow of the oil throUghout the gear at two gallons per minute, this being governed by the flowcontrol valve. The reaction valves are set to blow off at 650 p.s.i., which is equal to a rim pressure of 18 lb., giving a torque of 2,000 lb.-ft. at the rocker _shaft.
Following a trial run with the laden tanker, a representative of The Commercial Motor reports that the . steering was at all times positive, with no trace of wander at high speeds, and the light action was particularly beneficial when negotiating roundabouts and sharp corners. Despite the front bogie loading of over 7 tons, the steering was lighter than that on most current private cars, without creating a
sense of remoteness from the road wheels. Even on snow-covered surfaces there was no tendency for skidding to OCC111% By disconnecting the oil supply to the power gear it was possible to make a direct comparison between the steering characteristics with and without assistance, and at the same time to verify that, should the power fail, the vehicle was still manageable despite the high steering ratio.
A second test with this gear was made on a Leyland Royal Tiger chassis with a front-axle load of 41 tons. At speeds up to 50 m.p.h. the chassis was quite stable on a wet road and the sole physical steering effort required was that needed to overcome the column friction.
The Ashanco exhaust brake, as recommended by A.E.C., Ltd., consists of a butterfly valve in the exhaust system which is electritally operated by a pad on the brake pedal. Thus the exhaust brake is operated before the main system is applied. Proof of its effectiveness was afforded descending a snow-covered hill of 1 in 5 in second gear at 7 m.p.h. without the use of the air brakes.