Trailer Has Its Own Power Unit
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. ANEW ZEALAND operator,
Waikato Breweries Ltd., is now
using a tractor-trailer combination in which the trailer is powered by an independent engine and transmission unit. Called the Grademaster, the trailer was built by the Tasman Manufacturing Co., the power unit being a Ford fourcylinder, 60 b.h.p. diesel engine and this drives through a Brockhouse transmission unit to the trailer rear axle.
The tractor is a Bedford KOL5 with a 330-cu.-in, diesel engine, five-speed gearbox and two-speed rear axle, Mounted on the chassis is a stainlesssteel tank, (with a capacity of 1,250 gal.) fully insulated and clad exterhally with tight alloy. A stainless-steel tank, insulated and light-alloy clad, is also mounted on the trailer, but in this case the capacity is 1,750 gal. Waikato Breweries uses the combination on beer distribution from Hamilton, N.Z., to hotels equipped with bulk storage facilities in Waiki, Tauranga, Rotarua, Palmerston North and Wellington. To keep the contents of the tanks under pressure during delivery, carbon dioxide is carried on the tractor and trailer.
When carrying a full load of 3,000 gal, of beer, the gross weight of the combination is 23-5 tons. it is said that by using the Bedford in conjunction with the powered trailer, a saving of about £1,500 is made in initial cost compared with a tractive unit tandem-axle semi trailer.
The Ford engine and Brockhouse transmission are mounted as a unit on the trailer in a compartment located amidships beneath the frame. The transmission unit is a Brockhouse T.T.T., which consists of a torque convertor driving through a two-speed epicyclic gearbox with ratios of 2-18 and 1 to 1, reverse being 2-0 to 1. Control equipment is provided which automatically selects the correct gear ratio according to the road speed of the trailer. An extra instrument panel fitted in the Bedford cab carries remote controls by which the trailer engine is started, the gears selected and the engine speed set to half or full.
The main advantage of the use of a powered trailer is said to be the great improvement in gradient performance over a similar tractor with a normal trailer. . Some of the roads on which the combination is used have very severe hills. For example, the road to Tauranga includes a climb of 1,600 ft. in four miles and the road to Wellington goes from sea level to 2,800 ft. above and includes some severe steep and winding gradients in its 360 miles, Although the maximum speed of the Bedford is 41 m.p.h., the combination averages 27 m.p.h. for the journey and is said to be faster by some two hours in the 720-mile round trip than other vehicles at the same gross weight.
Drivers are reported as commenting favourably on the ease of control of the powered trailer and on the fact that having such a unit helps high average speeds to he maintained on hills. Gear changing on the Bedford is less frequent and drivers are far less tired at the end of the journey than on normal vehicles. Other advantages are that the independently driven trailer axle makes a better traction on slippery surfaces, there is greater reliability on large hauls in the event of mechanical failure of the tractor engine as the trailer engine can be used to get the combination back to base, and as the trailer is not imposing a drag on the tractor, stability—particularly on corners—is improved.
A torque converter transmission is said to make an ideal unit for a powered trailer of this nature as it enables power to be transmitted in a very flexible way, providing an easy and automatic method of starting from rest by just engaging a gear and then raising the engine power either to half or full. The torque converting characteristic enables a large speed range to be obtained with only two speed changes, and the changes themselves are convenient for adaptation to automatic operation. In a vehicle of this nature, the changes need only be controlled on a vehicle speed basis. Other advantages are that it is impossible to stall the engine so that the units controlling the gear change do not need to be complex providing the change from low to high is not left too late as the vehicle gains speed and so oversneeds the engine by overrunning it. The Brockhouse torque converter, incidentally, transmits power back to the engine in overrun, giving a measure of engine braking.
It is intended that the Ford engine will he replaced eventually by a Bedford 300-cu.-in, diesel and plans are now being laid for making larger powered trailers using the Brockhouse T.T.T. three-speed transmission, which is a full power-shift gearbox with torque converter drive and suitable for engines of around 100 h.p.