Self-propelled chaff cutter

A chaff cutter (1) comprises a relatively wide chopping drum (6) arranged under a driver cabin (5) and an obliquely upwardly extending ejector shaft (7) behind the cabin. To adapt a stream of chopped crop material to the narrower cross-section of an ejector elbow (13) connected to the shaft (7) and to convey the material through the elbow, an accelerator (8) is arranged at the junction of shaft and elbow and preferably comprises two rotors (9, 9') rotatable about horizontal axes (10, 10') parallel to the direction of travel of the chaff cutter. The rotors (9, 9') are arranged symmetrically to the width of the ejector shaft (7) and, in their lower regions, the peripheral surfaces (14, 14') and end faces (11, 11 min ) thereof extend into a rectangular opening of the shaft (7). The rotors (9, 9') are driven in opposite sense through a drive (18) derived from the motor (15) of the chaff cutter.