Patent ID: 8347529

Claim:
A machine comprising: a chassis; a ground drive propulsion system connected to the chassis; a trencher attachment connected to the chassis, the trencher attachment including a boom that supports a material reduction tool; a control linkage and a lift control valve configured to adjust the orientation of the boom relative to the chassis and hold it in a fixed position relative to the chassis, the control linkage including a hydraulic cylinder in fluid communication with the lift control valve, the lift control valve being movable to a lock-out position wherein fluid is substantially prevented from flowing into and out of the hydraulic cylinder thereby holding the boom in the fixed position relative to the chassis; a transducer configured to measure the pressure in the hydraulic cylinder which is indicative of the force applied on the boom when the lift control valve is in the lock-out position; and a drive control unit that receives the measured pressure and is configured to automatically slow the ground speed of the trencher based at least in part on the measured pressure in the hydraulic cylinder when the lift control valve is in the lock-out position, which is independent of the pressure of hydraulic fluid that drives the material reduction tool.