Patent ID: 7553408

Claim:
In a vehicle hydraulic system having a component lube circuit, a pump supplying hydraulic fluid from a sump to a first and a second hydraulic control circuit, a filter circuit comprising: a first filter circuit outlet connected to a inlet of the lube circuit; a sump line connected to the sump; a second filter circuit outlet connected to an inlet of the pump; a suction filter between the sump line and the second filter circuit outlet; a suction bypass filter connected in series with a suction bypass valve between the sump line and the second filter circuit outlet; a return filter connected to an outlet of the first control circuit; a return line connected between the return filter and the first filter circuit outlet; a return bypass filter connected in series with a return bypass valve between an outlet of the first control circuit and the return line; a pressure responsive backpressure valve having an outlet connected to the second filter circuit outlet, having an inlet and a pressure sensing pilot line both connected to an outlet of the return filter, and having a valve member biased by a spring to a normally closed position and movable to an open position in response to pressure in the pilot line; and an orifice in the return line; and a pressure sense line having one end connected to the return line between the orifice and the first filter circuit outlet, and having a second end connected to the valve member in opposition to the pilot line.