Abstract: A system for accelerating the front wheels of a vehicle, eg an agricultural tractor, on turning a corner, comprises steering angle sensors (21) which, via a control unit (22) enable or disable drive to the front wheels from a hydraulic motor (11). The drive from the hydraulic motor from the front wheels is via a one-way clutch (14). The hydraulic motor (11) is powered by a pump (6) driven either directly from the vehicle engine or from the main transmission.

Abstract: A transmission, particularly an agricultural tractor transmission, has a creep gear facility whereby speeds under 0.5 km per hour are possible without slipping a clutch. Planocentric gearing (20) is used for the creep gear, selectively clutchable into the transmission by means of a dog clutch (31). The planocentric gearing comprises an input eccentric (32) which runs inside an inner ring member (33) carrying external gear teeth (34). The inner ring (33), in use, oscillates within an outer ring (36) having interior gear teeth (35) with which the exterior teeth (34) mesh at one point at any given time. Pins (38) are mounted on the inner ring (33) which are received in apertures (47) in a stationary reaction member (44). The oscillating motion of the inner ring (33) is transferred to the outer ring (36) as rotation, at a reduced speed from the input, giving a reduction ratio of 10:1 or higher in a single stage. The direction of the drive is preserved from input to output.