1 November 1996

Prototype linkage is a challenger for 3-point

TO attempt a redesign of the tractors three-point linkage would appear to be a brave move. Virtually unchanged in principle since Harry Ferguson developed it some 60 years ago, it has stood the test of time remarkably well.

But now theres a new kid on the block. Well, there could be.

Still in its prototype build, the system being developed by Richard Price of Pontypool-based Chavtrac aims to combine the advantages of operating trailed implements with those offered by having them fully mounted.

His reasoning goes like this: Trailed implements – a set of harrows, for example – are able to follow a tractor during bends putting only minimal strain on the tractor. Any appreciable turn with a mounted implement when it is in the ground puts considerable stress on the tractor and implement.

So whats Mr Prices solution? For a start, a four-wheel steer machine is required and one which has a fairly advanced control system.

The companys Chavtrac 410 workhorse is equipped with a number of electronically activated steering modes – two-wheel, four-wheel, opposite and, designed for this purpose, a variable rear-steer mode.

With the linkage arms, plus lift rams, fixed rigidly to the rear of the chassis so they can only move up or down, any slight turn of the tractor would inflict severe structural stresses on an attached implement.

But with the rear wheels turning a set percentage of the front wheels it is possible to turn on full lock, with the implement still in the ground, without, says Mr Price, causing any problems.

"Its all about turning radius," he explains. "As the front wheels turn, the rear set turn in the same direction but only so far as to reduce any sideways pull on the implement."

The subject of a Small firms Merit Award for Research and Technology (SMART), Mr Price envisages the finished design will mean a complete integration between tractor and implement.n

Turning on full lock with an implement still in the ground is not a good idea – usually. Steering the rear wheels in the same direction, but not to such a steep angle, is designed to reduce the strain imposed on the implement. (Inset) Linkage detail. Note the rigid attachment which allows no lateral movement of the linkage arms whatsoever.