Interlocking gearwheels have an unequalled high efficiency. Hydraulics, on the other hand, have an unequalled high amount of operating comfort. You can examine how the two principles interact with each other in a customary tractor gearbox here.

The next picture points to an important catchphrase, 'performance-splitting'. Pretty much directly at the output of the engine, a part of the performance is transferred through a simple gearwheel drive to the compact hydrostatic unit, whose output shaft meshes with the inside ring-gear of a planetary set. The direct connection is to its sun wheel. The planetary wheel carrier-plate is connected with the rear axle.

Let's begin with the so-called 'active shutdown'. This describes a completely switched torque transfer, which is only prevented by the hydraulic unit. In its internal workings are two axial piston pumps, like those we know which are found in certain air-conditioner compressors.

The mechanical displacement-pump is the one driven by the input shaft. This means, its swash plate can be moved at an angle to two both sides. If it stands vertical to the shaft, then the delivery is zero. Depending on the tilt direction, the closed oil-circuit to the constant motor, moves it in the one or the other direction.

Active idling means, that the hydrostat creates on its drive shaft, exactly the RPM of the through-shaft, only in the opposing direction, so that the movement at the rear, towards the planetary wheel carrier-plate, is precisely balanced out. This is stationary, can however, through the smallest adjustment to the displacement-motor and with the slightest increase of the RPM, be driven with the maximum torque.

For tractors having up to 74 kW (100 HP), this one planetary set is sufficient and can, through the hydrostats, cover all regions up to 50 km/h infinitely. What is important, is that at a certain operating point, the output shaft is fixed. This would then be the operating point with the highest efficiency.

Here you can see a complete TERRAMATIC gearbox. This gearbox, designed for lower performance tractors, is a cooperation between the tractor manufacturer, Lindner (Lintrac), the gearwheel factory Friedrichshafen (ZF) and Bosch Rexroth for the hydraulic unit. It is manufactured in the ZF-factory in the Upper-Austrian town of Steyr. 10/14