Abstract: A steering control system for a tracked vehicle includes an engine driven variable displacement steering pump which drives a hydraulic motor. A control system senses steering wheel position, vehicle speed, engine speed and forward/reverse vehicle direction. As a function of these sensed inputs, a control signal is generated and is used to control the swashplate angle of an engine-driven variable displacement pump which drives a steering motor which drives a differential track drive mechanism. The control system also determines a ratio of motor speed to vehicle speed and generates a powerboost signal when the ratio exceeds a threshold value. The powerboost signal is communicated to the engine controller which causes the engine to increase its power output. This modifies the engine fuel delivery curve based on the steering system power requirement and increases the power available for turning the vehicle.

Abstract: A four-wheel drive tractor with front and rear frame structures joined for articulation about a generally upright pivot has a split change speed-transmission. The first section of the transmission is supported on the front frame structure of the tractor and provides direct drive and overdrive speed ratios. A second section of the transmission is supported on the rear frame structure of the tractor and has a plurality of forward and reverse transfer ratios. A power take-off on the rear frame structure of the tractor is driven by the drive between the first and second sections of the transmission and includes selectively engageable and disengageable clutch means. An interlock between the clutch means and the first section of the transmission shifts the first section of the transmission to and/or holds the first section of the transmission in its direct drive condition whenever the PTO clutch is engaged. In this manner damage to any PTO driven implement coupled to the tractor as a result of overspeed is avoided.