Control of pump for hydraulic front wheel drive

A hydrostatic transmission system of the type comprising a load, a hydraulic motor operably associated with said load, a variable displacement pump having means operable to vary the displacement thereof in response to a pump displacement command signal, said pump receiving input torque from a source of motive power, said system characterized by:

• (a) means for determining anticipated motor flow to said hydraulic motor and generating an anticipated motor flow signal corresponding thereto;
• (b) means for generating a pressure command signal corresponding to commanded pump pressure;
• (c) means for sensing actual motor flow to said hydraulic motor;
• (d) processor means for calculating pump flow and comparing pump flow to said actual motor flow to determine system leakage;
• (e) processor means for modifying said anticipated motor flow signal to compensate for said system leakage and generate said pump displacement command signal;
• and
• (f) said processor means to compensate for said system leakage includes means operable to receive a motor speed signal, and calculate a leakage gain signal.

A vehicle propel system of the type comprising a pair of primary propel wheels adapted to receive input torque from a vehicle engine by means of a primary transmission, and a pair of secondary propel wheels receiving input torque from a hydrostatic transmission including a wheel motor operatively associated with each secondary propel wheel, and a variable displacement pump having means operable to vary the displacement thereof in response to a pump displacement command signal;

• characterized by:
• (a) means for determining anticipated motor flow to said wheel motors and generating an anticipated motor flow signal corresponding thereto;
• (b) means for generating a pressure command signal corresponding to commanded pump pressure;
• (c) means for sensing actual motor flow to said wheel motors for said secondary propel wheels;
• (d) processor means for calculating pump flow and comparing pump flow to said actual motor flow to determine system leakage;
• (e) processor means for modifying said anticipated motor flow signal to compensate for said system leakage and generate said pump displacement command signal;
• and
• (f) said processor means to compensate for said system leakage includes means operable to receive motor speed signals, and calculate a leakage gain signal.