Abstract: An assembly for hoisting and lowering a drill string of a drilling rig includes a multiple displacement hydraulic cylinder having a blind end, a rod end, and a single piston rod configured for slidable extension and retraction movement within the interior space of the cylinder. The interior space is defined by three chambers, each chamber having a port allowing switchable flow of hydraulic fluid into and out from the cylinder. The assembly also includes a pumping and switching system with hydraulic fluid connections to each port of the cylinder. The pumping and switching system is configured to switch the direction of hydraulic fluid flow through each of the ports of the three chambers, thereby providing the assembly with a plurality of hydraulic fluid flow path combinations. Each flow path combination provides a different speed-to-force ratio for extending or retracting the piston rod, thereby hoisting or lowering the drill string.

Abstract: The invention provides a system for automatic control of the drilling an oil well. The system includes an autodrilling interface enabling parameter input data to be input and enabling the display of system output data, a controller, a hydraulic control system and at least one sensor configured to the hydraulic control system. The controller receives parameter input data from the autodrilling interface and at least one sensor and provides output instructions to the hydraulic control system such that the hydraulic control system operates to control drilling based on controller instructions and sensor data.