Automatic fan speed adjuster for combine harvester

A combine harvester comprising threshing and separating means, sieve means to which crop material separated by the threshing and separating means passes, cleaning means having fan means operable to blow air through the sieve means and hence clean the crop material on the sieve means, the fan means being driven by variable speed drive means, sensor means operable to sense the fore-and-aft inclination of the machine and produce a signal representative thereof, means for selecting a nominal rotational speed for the fan means during operation of the machine on level ground as a function of harvesting conditions and producing a signal representative of the nominal speed, means for combining the inclination signal and the nominal speed signal to produce a signal representative of the desired speed of the fan means as a function of the fore-and-aft inclination of the machine, means for measuring the actual rotational speed of the fan means, means for establishing a selected relationship between the fore-and-aft inclination of the combine harvester and the rotational speed of the fan means and adjusting the signal from the sensor means accordingly, such that the adjusted signal is proportional to the desired fan speed as a function of the fore-and-aft inclination, said means for establishing said selected relationship being in the form of a double potentiometer having a pair of electrical resistances and a wiper arm associated with each resistance, each said electrical resistance being coupled in series with the sensor means operable to sense the fore-and-aft inclination of the machine therebetween, said wiper arms being mechanically coupled to each other for adjustment in unison in a manner such that, upon adjustment, the wiper arms both move in the same direction relative to the centrally disposed sensor means, and control means responsive to the desired fan speed signal and the actual fan speed signal to produce a command signal for application to the variable speed drive means, whereby the rotational speed of the fan means is adjusted as a function of the fore-and-aft inclination of the machine.