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All wheels driven on artic road/site tractor
Page 22
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• Operators of semi-trailer dumpers, heavy-duty articulated tippers and plant-carrying low-loaders frequently used on site operation can now specify a tractive unit with a greater traction capability than ever before. The machine has been developed by Unipower Ltd, Aintree Rod, Petivale, Middx, for gross combination weights up to 28 tons.
It is the first British heavy-duty articulated tractor, equipped as standard with front wheel drive, to offer normal roadgoing performance at speeds of 50 mph or more.
Many features of the new 4 by 4 artic tractor have figured over the past five years in Unipower's Invader range of 4 by 4 rigid off-road chassis. This latest extension to the Invader range is intended for use on and off the public road; its specification conforms fully to Construction and Use Regulations, at a plated weight of 28 tons.
Considerable attention has been paid to achieving optimum axle loadings on the 10ft 6in. wheelbase chassis, so that the front axle contributes its full part towards the overall tractive effort. Working in conjunction with the trailer dumper manufacturers. Unipower has based its axle loading calculations on an imposed trailer king-pin load of 9.3 tons. The York Big D fifth-wheel is normally Located 21in. forward of the rear axle centre-line, so that the front axle accepts almost 16 per cent of the coupling load. This results in front and rear axle loadings of 4.95 and 9.47 tons respectively.
Traction is further assisted by the fitting of sand and gravel tread tyres all round. Those at the front are 12.00-20, 16 ply units, while at the rear 18-22.5 wide-singles minimize the mud pick-up problem and reduce tare weight. Taxation weight in normal trim is 5 tons 10÷cwt.
Fifth-wheel height on the new tractor is 54.5in. — only 2in. above standard, which suits the majority of semi-trailer dumpers and tippers now on the market.
Power for the latest Invader comes from a Perkins V8.510 engine, developinkk 170 bhp (gross) at 2800 rpm. driving fliVugh an Eaton SMA-542 five-speed synchromesh geiavbox (ratios: 7.65; 4.3; 2.51; L48 and 1 to'l) to a Thornycroft two-speed auxiliary transfer gearbox separately mounted amidships. High ratio is a direct drive, while the low range incorporates a 1.63 to 1 reduction.
On hard surfaces, at normal roadg_ojpg speeds, the front axle drive can be readily disengaged by means of an air-operated sliding-mesh gear, thereby cutting wear and friction losses, as well as improving directional stability at higher road speeds.
Maudslay axles are employed front and rear, with an overall reduction of 6.25 to 1 giving a maximum level road speed of 53 mph. Both have spiral-level primary gears and double-helical secondary reduction gearing. On the front axle assembly the swivel carriers are bolted to the axle casing. They house the Tracta constant-velocity joints. Plated axle weights are 6 tons front, and 10 tons rear. A cross differential lock is an option in the rear axle, giving a positive drive to at least three wheels in any situation.
Full-air braking is provided with three-line trailer connections. All wheels are equipped with Clayton Dewandre type 30 lock actuators for parking and secondary braking. The front brakes are of particularly generous diameter at 17in., with a shoe width of 4in. At the rear the drum dimensions are 15.5in. by 6in.
Chassis frame longitudinals are parallel 10.5in. by 3im channels with internal flitch reinforcement. Power-assistance is incorporated as standard in the 2.47 to 1 reduction cam and roller steering gear. All electrical equipment is to 24 volt standard.
Road vehicle standards of comfort are provided for the crew in the Unipower tractive unit. The cab is based on a pressed steel shell built by Motor Panels (Coventry) Ltd, with step-over-wheel entry and a one-piece curved windscreen.
The first of the new units has been completed for Cross (Southall) Ltd, where it is used on bulk haulage work, in conjunction with two semi-trailer dumpers built by Neville Truck Equipment Ltd, of Kirby-in-Ashfield, Notts. One is a single-axle Uni-dump machine with special removable extruded aluminium side extensions increasing its capacity from 15 to 29 cu yd. The other is a Tandem-Dump unit whose basic 18 cu yd. body can be similarly extended to 36 cu yd.