Trencher power control system

Claim 1

A trencher control system which varies the vehicle drive speed so as to maintain a preset torque on the digging chain as the digging conditions vary, comprising: a prime mover; a drive means connecting the prime mover to the digging chain; a variable displacement pump means driven by the prime mover; a stroker control means attached to the pump means to control the pump displacement level, including a stroker control cylinder having at least one working chamber defined by a piston in said cylinder which is spring-biased toward a neutral zero flow position; a charge pump connected to said chambers of the cylinder, a fixed orifice positioned between the charge pump and each chamber; a drain line connecting each chamber to drain, a solenoid controlled valve means positioned in each of said drain lines which varies the pressure level in said chambers; a vehicle drive motor connected to the drive wheels of the trencher, said motor being driven by said pump means; RPM sensing means on the prime mover; an electronic control means which controls the solenoid of the valve means, the control means receives a signal from the prime mover RPM sensing means and compares the signal with an adjustable reference, if the signal received is less than the reference, the control means signals the solenoid to decrease the pressure level in the working chamber and decrease the pump displacement; if the signal is greater than the reference, the control means signals the solenoid to increase the pressure level in the working chamber and increase the pump displacement and further load the prime mover, whereby the control means maintains the prime mover at its peak torque output regardless of changes in the digging conditions.