A hydraulic oil filtration apparatus 40 comprises an actuation control valve V, a pump-pressure oil passage 41, a connection oil passage 43, a tank oil passage 51, a return filter 60, a drain oil passage 53, a drain filter 70 and an aspirator structure 90. The actuation control valve V controls to charge and discharge a hydraulic actuator A such as a boom cylinder 22 and travel motors with hydraulic oil from a hydraulic pump P, which is connected through the pump-pressure oil passage 41 to the actuation control valve V The hydraulic actuator A is connected with the actuation control valve V by the connection oil passage 43, and the actuation control valve V is connected to a tank T by the tank oil passage 51, in which the return filter 60 is provided. The part of the tank oil passage 51 downstream with respect to the return filter 60 is connected to the hydraulic pump P by the drain oil passage 53, in which the drain filter 70 is provided. The aspirator structure 90 is positioned at the junction between the tank oil passage 51 and the drain oil passage 53, so that leakage oil in the drain oil passage 53 is drawn by the flow of the discharged oil through the tank oil passage 51 and led to the drain filter 70.
In a hydraulic machine, hydraulic pump failure is detected and the pump lifespan is estimated before the pump failure occurs. The discharge pressure 122, oil temperature 126, and drain filter differential pressure 120 are measured, a correlative relationship 128 between the filter differential pressure and the discharge pressure is determined, and a representative filter differential pressure 130 is calculated from this correlative relationship. Using an oil temperature-differential pressure correlation function, the representative differential pressure value 130 is corrected so that the variable component 132 caused by the oil temperature 126 is eliminated therefrom. The long-term trend and the short-term trend of the increase over time of the corrected differential pressure is calculated. A pump failure is predicted or the pump lifespan is estimated based on the degree of deviation between the long-term trend and the short-term trend.
A vehicle hydraulic system includes a lube circuit, a pump supplying hydraulic fluid from sump to first and a second hydraulic control circuits and a filter circuit. The filter circuit includes a first outlet connected to the lube circuit, a sump line, and a second outlet connected to the pump. A suction filter is connected between the sump line and second outlet. A return filter is connected to the first control circuit outlet. A return line having an orifice is connected between the return filter and the first outlet. A backpressure valve has a member, an outlet connected to the second outlet, and an inlet and pilot line connected to the return filter outlet. A pressure sense line has one end connected to the return line between the orifice and the first outlet, and a second end connected to the member in opposition to the pilot line.
