Trailer tugs that turn Dn a sixpence
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Dy R. D. Cater \IOVEL DESIGNS DEMONSTRATED 11 When ML Industrial Products Ltd., of ;lough, Bucks, demonstrated two of their railer handling units at Tilbury Docks last veek, it was their manoeuvrability that mpressed me most.
The two machines, one a pedestrian:ontrolled motorized fifth-wheel, and the )ther a fully fledged hydraulic-lifting fifthvheel tractor, handled semi-trailers in closer barters than I have ever before witnessed.
The smaller of the two is called the Mini -Iorse 2C and comprises a motorized threevheeled bogie powered by a Coventry /ictor 8 hp single-cylinder, air-cooled liesel engine, driving through a centrifugal :hitch, a pre-set overload-clutch, a threepeed gearbox and a spiral bevel differential. t is mounted on four small-diameter solid ubber-tyred wheels, the front steering vheels being carried on a short common pindle through a head-stock type of steerng gear.
This vehicle will accept an imposed cad of 3 tons and it has a drawbar pull of 8,0001b when the load is imposed. While t is designed for use, (close-handling semiraiders up to 10 tons gross trailer weight) t has been known to move an aircraft weighing 32 tons. It has a lightweight Davies fifth-wheel mounted upon a framework giving a fifth-wheel height of 50 in. ihree hydraulic brakes, one on the transnission shaft and one at each rear wheel, ire powered by a master cylinder mounted m the headstock. This is connected via pushrod to the tiller, the brakes being applied by depressing the tiller.
As the transmission is centrifugally 3perated, and the throttle lever is springoaded, in the event of the operator ;tumbling a reduction in engine speed cuts Dut the drive and the weight of the tiller applies the brakes.
The ML Tug Horse proved to be a most versatile vehicle capable of turning in a circle of only 16.5ft. This permits it to turn 'like comfortably inside most of the roll-on/ roll-off ferry ships at present in service.
It is powered by a Ford Super Major :ractor diesel engine producing 67.5 bhp, and driving through a Brockhouse torque :onverter. This assembly gives the machine hree speeds in forward and reverse. Ihe vehicle is of three-wheel configuration aid again utilizes a headstock arrangement o carry the close-mounted front wheels, which steer through an arc of 160 deg. Steering is hydraulically power assisted.
At a maximum road speed of 15 mph the vehicle will handle semi-trailers of up to 40 tons gross trailer weight. During the demonstration a full-pressure brake stop from the maximum speed produced a Tapley meter reading of 22 per cent.
The final-drive assembly is as used in the Super Major tractor, but none of the load stresses are absorbed by the actual axle casing. Instead, two castings with hollow stub axles are mounted directly onto the chassis of the vehicle. The hub assemblies are carried on these stubs and the half-shafts pass through the casings into a driving plate on the outsides of the hubs. The driving plates are bolted to the hubs through a series of Metalastik bushes, forming a limited cush-drive.
I noticed during the demonstration that the driver was getting a fair shaking up. This is because the vehicle has no suspension. When I commented upon this, Mr. V. A. Benning, chief development engineer, told me that the company was about to experiment with a suspension seat which should overcome the problem.
The fifth-wheel is hydraulically raised and lowered over a range of 21in. and up to a maximum height of 67 in. The coupling-jaw lock is controlled from the driving seat by an air pressure system and a clearly marked scale, showing the height of the fifth-wheel at any given time, is provided.
Although the vehicle demonstrated was a prototype it performed extremely well, its biggest advantage over other vehicles of its type being the ability to turn about in a very small space.