Steyr Antriebstechnik, an independent supplier of transmissions for agric tractors and trucks, has developed a Continuously Variable Transmission (CVT) on the basis of a hydrostatic mechanical power split.
The intelligence of the S-Matic is based on a splitting of power from the drive unit into a mechanical and a hydrostatic part. This takes place at the transmission entry. The continuously variable transmission modulation is accomplished by the variable displacement pump, which is “back to back” assembled to the fixed displacement motor.
By adjusting the swash plate, variable rotational speed results at the hydrostat motor output, which is between the maximum opposite and equal speed and direction to the purely mechanically driven gears. Both of the power parts are brought together in the summary planetary gear, where the revolutions coming directly from the engine and the hydrostatic rotational speed are superimposed.
In order to achieve sufficient transmission spread and to limit the hydrostatic power component, the S-Matic gear system operates with four mechanical transmission ranges. To minimize frictional losses, all clutches are designed as dog clutches. Shifting from one range to the next one is done at synchronuous speed. All transmission functions are controlled electronically.
The result is a continuously variable output speed from vehicle standstill to maximum speed.
Major advantages of this driveline system are:
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Fully automized drive train from the engine to wheels
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Highest driver's comfort, no shifting required
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Save operation under all driving conditions by permanent torque connection (geared neutral)
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Smooth vehicle acceleration from standstill to maximum speed
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Very good overall efficiency by keeping the hydrostatic power portion at low level
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Easy to operate by controlling engine and transmission by vehicle electronics.