12 June 1998

Steyr box gives stepless speed

By Peter Hill

A HYDRO-MECHANICAL trans- mission which gives tractor drivers stepless speed control instead of fixed ratio gears, is undergoing intensive field testing in Austria.

The Steyr S-Matic gearbox has been developed by the drivelines division of engineering group Steyr-Daimler-Puch.

Its pioneering customer will be tractor maker Case-Steyr. Together, they are field-testing prototype tractors to refine the components, fine-tune the system electronics and evaluate its advantages and features.

"Components involved are relatively simple. Our aim was to use off-the-shelf items where possible," explains Franz Konig of Steyr Antriebstechnik. "Most development has gone into the software that monitors and controls the system."

The main attraction of any continuously variable transmission is that the driver does not have to worry about finding the best gear and engine speed combination for different tasks and changing draft loads. Electronics automatically find the best settings.

The S-Matic system allows drivers to select priorities, such as running the engine at peak power and torque, running the engine at speeds designed for best economy or at set ground or pto speeds.

"The system will adjust itself to cope with changes in load to meet the drivers requirements," says Mr Konig. "It is simpler for the operator to get maximum efficiency and output from his tractor and he can concentrate on implement control and, especially during road travel, on steering and driving safely."

Like Fendts Vario transmission, S-Matic uses hydrostatic and mechanical drive components with epicyclic gear units blending the output from both.

Unlike the Vario design, however, four auto-change range gears are used to achieve sufficient speed coverage, in contrast to the Varios specially-developed wide-angle hydraulic pumps and motors.

"We rely more on mechanical drive components to ensure a high level of power delivery efficiency but with the hydrostatic units providing easy driving characteristics and speed variability," says Mr Konig.

Providing the test programme goes well, Case-Steyr expects series production of tractors using the S-Matic transmission to begin within the next couple of years.

Despite new UK distribution, certain Steyr models will still be available through Case dealers.

Left: The S-Matic transmission is very compact and power efficient, claims Franz Konig, drivelines specialist at Steyr Antriebstechnik.

Right: Prototype control layout for Case-Steyr CVT tractors selects forward/reverse and speed with linkage and spool valve controls positioned nearby on the arm rest mounted layout.