Combine harvester and driver assistance system therefor

A driver assistance system for a combine harvester that has a processing stage with an input for a crop flow, a first output for a useful flow which is obtained from the crop flow and has abundant threshed grains, and a second output for a residual flow with scarce grains, wherein at least one operating parameter of the processing stage is adjustable, wherein the driver assistance system comprises:

• an actuatable rethreshing device configured to be arranged at the second output of the processing stage, wherein the rethreshing device comprises a separating rotor, and a separating grate having a plurality of fixed segments and at least one movable segment, the at least one movable segment being equipped with friction strips and arranged opposite to a threshing bar situated at the separating rotor, wherein the at least one movable segment is movable between an active position configured for threshing grain, and an inactive position,
• a residual grain sensor configured for detecting a proportion of threshed out grain in the residual flow downstream of the rethreshing device, and
• an evaluating device which is adapted to turn the rethreshing device on and off by moving the at least one movable segment between the active position and the inactive position, to compare the proportions of threshed out grains in the residual flow when the rethreshing device is turned on and when the rethreshing device is turned off, and to adapt the at least one operating parameter of the processing stage based on the comparison.