York leads in one-upmanship
Page 28
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by Trevor Longcroft
A DUAL-PURPOSE trailer suspension offering either single or tandem-axle operation has been introduced by the York Trailer Co Ltd.
When fully laden the full tandem is used, but when the bogie Is loaded to the capacity of its trailing axle only, the leading axle may be lifted. This eliminates tyre scrub and the power It consumes, extending tyre life and improving fuel economy.
By fitting the suspension to a 32-tonner that covers 80,450km (50,000 miles) per year and runs at 24.4 tonnes (24 tons) gcw for 50 per cent of the time, York estimates that up to £148 a year can be saved on tyres and up to £67 can be saved on fuel. On a 160,900km (100,000 miles) covered basis, at the same load factor, the estimated savings jump to £297 and £134 respectively.
Tyre savings are based on a net tyre cost of £85, a 160,900km (100,000 miles) life on single-axle trailers and a 112,630km (70,00 mile) life for tandems.
Fuel cost savings have been calculated using a typical 40.3 litres/I0Okm (7.0mpg) fuel consumption for 32-tonners at 47p per gallon of derv.
Two tests were completed running with the single-axle with a set of readings being achieved with the trailer being loaded with 3 tonnes and 9 tonnes of ballast respectively. Compared with the typical consumption both showed a fuel saving of around 4 per cent.
Dubbed the Hobo, the new tandem/single suspension is available in close coupled or widespread form. Compared with existing designs it is up to 220kg (4cwt) heavier. Specifying the suspension will add £340 to the price of a new trailer.
The design of the suspension linkage eliminates axle hop, providing more efficient braking with all four wheels being kept in contact with the road surface.
Control system
The basic control system has a two-position hand-valve for either single or tandem operation. The trailer should be loaded with both axles hearing. Once loaded, the lever is shifted to the single-axle position and the action completed by the aft-powered lifting gear. If the axle either refuses or is reluctant to lift, tandem operation must be selected to prevent overloading.
Automatic selection of either single or tandem axle is available with an optional weight sensing valve. Costing a further £40 it includes a threeposition hand valve, "single," " sense " and "tandem."
For loading the lever is set to "sense" and the sensing valve will either lift or lower the leading axle, depending on its initial position, according to the weight on the bogie. Once loading is completed the lever is set to the appropriate setting to lock the axles in position.
Better ride
The choice of either single or tandem-axle running also provides for a better ride at light laden conditions. The results are less jostling for unladen bodies and tanks with a corresponding reduction in vibration damage and metal fatigue.
The leading axle is lifted by two 406mm (16in) diameter air bags located between chassis cross-members and the two arms of a prefabricated "T" member. The tail of the "T" is linked to the axle.
When the bags are inflated the "T" member which is directly above the axle is raised along with the axle. The leading axle is lifted through 89mm (3.5in), the lift being doubled by an opposite shift of the trailing axle via the suspension leakage. The leading axle' wheels are raised 188mm (7.0in) from the ground, though the trailer platform is lifted 89mm (3.5in).
When the front axle is raised its suspension linkage is locked solidly against the chassis leaving a simple rear axle and suspension only.
Air for the system is drawn from the trailer emergency line and the system has its ov.n separate reservoir. The emergency line is protected against any fault occurring in the Hobo air circuits.