12 March 1999

S-Matic gears are almost on market

MUCH awaited, the arrival of the Steyr automatic transmission is imminent, says Steyr-Daimler-Puch which has developed the transmission.

The S-Matic, like the Fendt Vario transmission, uses a combination of hydrostatic drive and mechanical drive – although Steyr would claim that a greater degree of its system is mechanical, when the two systems are compared.

Main elements comprise transmission electronics and sensors, planetary gears, and the hydrostatic unit. Built as a single "cartridge", the unit is designed to be integrated into a transmission housing by the tractor manufacturer.

In operation, power from the engine is split into mechanical and hydrostatic routes. By adjusting the swash plate in the hydrostatic unit, rotational speed is varied – from equal to the mechanical input at maximum speed – when the output of the transmission is 100% – to rotation at maximum speed in the opposite direction to the mechanical input – when output is zero.

Both power routes are brought together in the planetary gears. Mixed within this unit, the result is a continuously variable output rotational speed which enables a continuously variable driving speed – from standstill to maximum speed.

However, to achieve a suitable transmission spread and limit the hydrostatic input, the S-Matic incorporates four mechanical gear levels, each meshed by dog clutches – electronic control is designed to ensure that relative speeds are identical when the dog clutches are engaged.

Still undergoing field trials, Steyr-Daimler-Puch expects full production of the S-Matic to start this year.