Patent ID: 7553226

Claim:
A grain cleaning system for a combine harvester, comprising a frame supporting a grain pan and an upper sieve, the grain pan being operative to receive grain and chaff separated from the other crop residue by a threshing mechanism and being reciprocable relative to the frame in order to propel the grain and chaff towards the sieve, and the sieve being reciprocable relative to the frame and being connected to the frame by front and rear support arms that are pivotably secured to the frame and to the sieve, wherein the front support arms have different geometries from the rear support arms such that when the sieve is reciprocated relative to the frame, the vertical component of oscillation is greater at the front end than at the rear end of the sieve, wherein in the mean positions of the front and rear support arms during a cycle oscillation of the upper sieve, the front and rear support arms are inclined to the vertical at different angles from one another, wherein, in their mean positions, the front and rear support arms are both inclined forwardly of the vertical, further wherein, in their mean positions, the front support arms are inclined forwardly at a larger angle to the vertical than the rear support arms.