Hydraulic control unit for best threshing yields

HAWE Hydraulik SE, Munich, has developed a new tailor-made valve bank for combine harvesters and forage harvesters. Two salient features characterize this valve bank: the possibility to control the contact pressure of the cutter bar and the option of fine and precise adjustments to the variator gearbox of the threshing unit. The solution integrates electro-proportional seated valves and proportional directional spool valves.

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If the cutter bar's weight is relieved hydraulically and not via mechanical springs, the unit will follow the soil's contour far more precisely. The cutting yield is significantly better. The contact pressure of the cutter bar is comfortably adjusted by the driver in the cabin by simple push of a button.

Where the cutter bar traverses over a recess in the ground, weight and load pressure increase as a shock valve opens up. When the unit passes over a bump in the ground the load pressure drops. The spool valve re-feeds oil and provides pressure equalization. The oil that is discharged during operations via the shock valve has to be re-supplied into the hydraulic system. To ensure that energy losses are kept at a minimum, a load sensing line prevents the pressure compensator from opening up to much.

When the farmer drives faster the threshing unit will also have to cut faster. The valve bank ensures that the threshing unit's speed is fine-tuned exactly to within a few rpm of the driving speed as well as the grain type. A hydraulic cylinder at the variator gearbox adjusts and matches the speed. Volume flow can also be set very exactly and in fine increments of minimum of 0.2 l/min.

On request, HAWE Hydraulik supplements the valve bank with a programmable logic valve control, type PLVC, as well as the axial piston pump, type V60N, and the constant motor M60N. This way the machine manufacturer receives a complete hydraulic control.