The present invention relates to a combine harvester. More particularly, it relates to a combine harvester having a cutting and conveyance device for crop, a threshing device for separating grain from the crop, a sieve system, and a blower system.
DE 39 06 186 A1 makes known a combine harvester of the initially stated type, which comprises a cutting and conveyance device for crop, a threshing unit for separating the grain from the crop, and a sieve system extending in the longitudinal direction of the combine harvester. A blower system is disposed upstream of the sieve system, transversely to the longitudinal direction of the combine harvester. Crop that is picked up by the cutting and conveyance device and conveyed to the combine harvester is directed to the threshing device to separate grain from the crop. The threshing device separates a large portion of the grain from the crop. The remaining crop, which comprises mainly straw and chaff, is transferred to the sieve system in order to separate out the portion of grain remaining in the crop. The blower system disposed upstream of the sieve system in the transverse direction of the combine harvester generates an air volume flow to act upon the sieve system with air, thereby assisting in the separation of heavy grains from the lighter-weight components of the crop, such as chaff and straw. The efficiency of the separation is dependent upon the consistency of the supply of the crop to the sieve system. The consistency of the supply is greatly affected when the combine harvester is in a tilted position since gravity causes crop to accumulate on the sieve system.
DE 39 06 186 A1 provides a blower system comprising a cross-flow fan which extends in the direction of travel across the entire width of the sieve system. The cross-flow fan is segmented by partition walls in order to attain a number of sectors that corresponds to the number of sieve sections of the sieve system, which are acted upon by air by the cross-flow fan. To balance the uneven crop distribution that occurs when the combine harvester is in a tilted position, the blower speed is changed in accordance with the slant.
A proven disadvantage of this blower system is that changing the blower speed has the same effect across the entire width of the sieve system. The cleaning output during the harvesting operation on the slope is clearly impaired despite a constant flow across the width of the sieve system at low throughput rates, and therefore, due to the force of gravity, the bulk phase dominates in the crop on the downhill section of the sieve system, while the flight phase dominates on the uphill section of the sieve system.