Combine stepped threshing chamber

A combine threshing system comprising:

• (i) a rotor comprising:
• an in-feed area at a front end of the rotor;
• and
• a rotor body configured to convey material along a helical path from the front end of the rotor body to a rear end of the rotor body, and
• (ii) a substantially cylindrical threshing chamber positioned circumferentially around and spaced apart from the rotor body, the threshing chamber comprising:
• a lower portion substantially concentric with the rotor body and having an inner surface positioned at a first distance from an outer surface of the rotor body;
• and
• an upper portion comprising:
• a first inner surface substantially concentric with the rotor body and positioned at the first distance from the outer surface of the rotor body;
• and
• a second inner surface substantially concentric with the rotor body, the second inner surface being discontinuous with the first inner surface and positioned at a second distance from the outer surface of the rotor body, the second distance being greater than the first distance, wherein
• the inner surface of the lower portion occupies an area extending longitudinally from a front edge of the lower portion to a rear edge of the lower portion;
• the first inner surface of the upper portion occupies an area extending longitudinally from a front edge of the first inner surface to a rear edge of the first inner surface;
• the second inner surface of the upper portion occupies an area extending longitudinally from a front edge of the second inner surface to a rear edge of the second inner surface, and wherein
• the areas of the first and second inner surfaces of the upper portion discontinuously increase or decrease circumferentially as they extend longitudinally from the front edge of the threshing chamber to the rear edge of the threshing chamber.

A combine threshing system comprising:

• a lower portion of a substantially cylindrical threshing chamber having an inner surface positioned a first distance from a center of the threshing chamber;
• and
• an upper portion of the substantially cylindrical threshing chamber, the upper portion comprising a plurality of inner surfaces positioned at varying radial distances from a rotor body such that the varying radial distances continuously increase or decrease over about ninety degrees of the entire inner surface area of the upper portion, wherein the plurality of inner surfaces comprises:
• at least a first inner surface positioned circumferentially at a first distance from the center of the threshing chamber, and
• at least a second inner surface discontinuous with the first inner surface and positioned circumferentially at a second distance from the center of the threshing chamber, the second distance being less than the first distance.

A method for separating grain from material other than grain comprising:

• feeding crop material into a substantially cylindrical threshing chamber positioned circumferentially around a rotor body;
• conveying crop material along a helical path from a front end of the rotor body to a rear end of the rotor body and within a threshing chamber comprising:
• a lower portion substantially concentric with the rotor body and having an inner surface positioned a first distance from an outer surface of the rotor body, and
• an upper portion comprising:
• a first inner surface substantially concentric with the rotor body and positioned the first distance from the outer surface of the rotor body, and
• a second inner surface substantially concentric with the rotor body, the second inner surface being discontinuous with the first inner surface and positioned a second distance from the outer surface of the rotor body, the second distance being greater than the first distance;
• compressing the crop material between (i) the outer surface of the rotor body and the inner surface of the lower portion and (ii) the outer surface of the rotor body and the first inner surface of the upper portion;
• and
• decompressing the crop material between an outer surface of the rotor body and the second inner surface of the upper portion.