COMBINE GROUND SPEED CONTROL SYSTEM

A combine harvester having an engine, a traction drive transmission, a header, a threshing and separating mechanism and a machine throughput control system is disclosed wherein a grain loss control loop is operable to produce a signal representative of grain loss and including a grain loss controller to which the grain loss signal and a reference grain loss signal are applied. A grain separation control loop is also provided to produce a signal representative of the grain separation in the machine. The grain loss controller is operable continuously to derive a reference grain separation signal from the grain separation signal, the grain loss signal and the reference grain loss signal. Means is also provided for algebraically summing the grain separation signal and the reference grain separation signal to produce a grain separation error signal which is used to control the machine throughput.