Abstract: A tractor implement draft force control system in which desired and actual implement draft force values are compared to provide a draft force error signal. The system is responsive to the error signal to control the working depth and hence the draft force of the implement. A deadband operates on the error signal to render error signals within the deadband ineffective to control the working depth of the implement and a deadband control means adjusts the width of the deadband so that the deadband width is maintained dependent on components of the error signal above a predetermined frequency. Thus the system can be arranged not to respond to high frequency spurious components of the draft force signal but is able to respond to the lower frequency components of this signal which are representative of the true draft force variations.

Abstract: A system for the control of a fluid flow control valve which controls the supply of fluid to an actuator to control the movement of a component such as a tractor implement hitch in response to a selected operating parameter such as hitch position or draft force. The system enables the desired value of the selected parameter to be set and this desired value is compared with the actual sensed value of the parameter to provide a parameter error signal. A start-up control function is provided to improve the initial speed of response of the system. The start-up control function is arranged on each detection of a parameter error signal to apply a start-up signal to the valve to initiate movement of the component and, if no movement results, to increase the start-up signal until movement of the component is detected whereupon the increase in the start-up signal is stopped and the magnitude of the signal applied to the valve is dependent on the parameter error signal so as to tend to reduce the error signal to zero.

Abstract: An electronic tractor hitch control system in which the position of an implement hitch relative to a tractor can be set using a main control operable by a tractor operator from his normal location on the tractor and can also be set using a secondary control located at a location remote from the normal operator's location, such as on the rear of the tractor fenders. The system is arranged so that any implement position signal set using the secondary control is opposed by a smaller hitch positioning signal generated within the system so that the speed of movement of the hitch in response to hitch positions set using the secondary control is moderated. The system also includes circuitry for detecting short circuits in parts of the system located in vulnerable locations.