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Don-Bur invents lifting-deck trailer with adapting-height roof


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Transport Engineer  /  April 30, 2020

For the first time, Don-Bur has manufactured a lifting deck tri-axle trailer design with an expanding roof.

The new product, designed for a parcel delivery company, provides 7.8% more head room on the lower deck during loading, but keeps overall height to 4.5m when in transit to avoid low bridge restrictions and retain a more ideal aerodynamic profile.

Lifting deck trailers were invented by Don-Bur in the late 1980’s and continue to rise in popularity due to high payload volume and rapid turnaround at the bay without additional specialist bay equipment, the company says. The simple premise is a secondary deck that, when loaded in its lowered position to suit bay height, then rises via hydraulics to a second height, allowing another full payload to be loaded underneath it.

However, straight-frame lifting decks in particular have limited lower-deck apertures whose heights are fixed between the height of the fifth wheel and the overall height. This restriction can cause challenges during loading.

The new expanding roof overcomes this by allowing the loaded second deck to raise much higher than normal during lower deck loading. After loading and before transit, the roof and deck lower again to a position where gaps over the load are minimal.

Aerodynamically, the force of drag is directly proportional to the frontal area of the trailer. Therefore, the ability to keep the roof 350mm lower than a full-height 4.85m-high double deck reduces drag force by an estimated 661 Newtons, at 56mph. This 15.5% reduction in drag is expected to realise a 5% fuel saving, as wind resistance is thought to contribute about a third to total drag (other components being surface friction, tyre deformation and drive line resistance).

One of the most ingenious parts of the design is the roof attachment system. During part of the loading operation, the second deck has to move up and down freely and independently of the roof. However, as the deck extends upwards to generate more head height, so too does the roof to prevent the upper load being crushed. Not only that, but the roof then has to forcibly clamp back down onto the body structure, to ensure the correct lower height and prevent water ingress. Don-Bur has developed and innovative solution to this challenge and, for this reason, has applied for a patent.

The new trailer design won’t suit operators that need to carry high, indivisible payloads. There, a step-frame design may be more applicable. Instead, the new model is said to be best suited to those with lower cage heights and pallets or loose loads. It could also be used for companies that switch between operation in Northern Ireland (which has a 4,650mm overall height restriction) and the UK mainland; the latter having a 250mm potential height benefit, equivalent to an 8.6m3 volume increase.


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