Patent ID: 8572938

Claim:
An agricultural combine ( 100 ) comprises a combine vehicle ( 102 ) on which a harvesting head ( 104 ) is mounted, said harvesting head ( 104 ) supported on a feederhouse ( 112 ) pivotally coupled to the front of the combine vehicle ( 102 ), said harvesting head ( 104 ) supported by a plurality of hydraulic cylinders ( 114 ) coupled to and between the feederhouse ( 112 ) and a chassis ( 106 ) of the combine vehicle ( 102 ) to support the harvesting head ( 104 ), said cylinders ( 114 ) being coupled to a hydraulic circuit ( 116 ) further comprising a closed center hydraulic pump ( 110 ), said pump ( 110 ) having a variable displacement, wherein said displacement is controllable by application of hydraulic fluid to a control line ( 200 ) of said pump ( 110 ), said pump ( 110 ) defining an input port coupled to a hydraulic reservoir ( 202 ) to receive hydraulic fluid therefrom, said pump further defining an output port, said hydraulic circuit ( 116 ) further comprising a hydraulic lift valve ( 206 ) fluidly coupled to the outlet port of said pump ( 110 ) to receive hydraulic fluid therefrom, said hydraulic lift valve ( 206 ) being further coupled to the cylinders ( 114 ) and selectively operable to supply hydraulic fluid thereto from said pump ( 110 ), wherein said hydraulic circuit ( 116 ) further comprises an electro-hydraulic control arrangement including an electronic control unit ( 310 ), a pressure sensor ( 308 ) coupled for sensing the pressure in said cylinders ( 114 ) and operable for generating an electrical pressure signal representative of the sensed pressure, with the pressure signal being connected to said electronic control unit, an electrically responsive pressure control valve ( 304 ), said electronic control unit being electrically coupled to said pressure control valve and being operable for sending an electrical pressure command signal corresponding to said electrical pressure signal to said pressure control valve, said pressure control valve ( 304 ) being coupled to said control line ( 200 ) of said pump ( 110 ) to signal said pump ( 110 ) to generate a pressure substantially equal to the hydraulic pressure in the cylinders ( 114 ) at least when the hydraulic lift valve ( 206 ) is closed, and said pressure control valve ( 304 ) being coupled to the output port of the pump ( 110 ) and to the reservoir ( 202 ) and, for establishing a cylinder float mode, being selectively coupleable to said cylinders ( 114 ) for maintaining a commanded hydraulic pressure in said cylinders ( 114 ) over a range of cylinder positions.