Abstract: An excavator includes: a swing motor driven by oil from a swing pump coupled to a power take-off and driven by an engine; a first main oil passage connecting a first discharge port of the swing pump and a first suction port of the swing motor; a second main oil passage connecting a second discharge port of the swing pump and a second suction port of the swing motor; a neutral retention valve disposed in the first main oil passage and the second main oil passage and controlling passage of oil; a regenerative energy absorbing device coupled to the power take-off and absorbs regenerative energy generated by oil from the swing motor to the swing pump via a meter-out opening of the neutral retention valve; and a valve control section controlling an area of the meter-out opening based on a state of the regenerative energy absorbing device.

Abstract: A filter state estimation system is configured to estimate a state of a filter provided in a hydraulic circuit. The hydraulic circuit includes: the filter; a bypass channel circumventing the filter and through which an oil flows; and a valve provided in the bypass channel and configured to be opened and closed based on a differential pressure. The filter state estimation system includes: a sensor to detect that the valve is in an open state or in a closed state; a temperature sensor to detect a temperature of the oil; and a state estimating unit to estimate a state of the filter based on detection results detected by the sensor and the temperature sensor. The state estimating unit estimates the state of the filter based on the temperature of the oil which is detected by the temperature sensor when the sensor detects that the valve is in the open state.

Abstract: A filter state estimation system is configured to estimate a state of a filter provided in a hydraulic circuit. The hydraulic circuit includes: the filter; a bypass channel circumventing the filter and through which an oil flows; and a valve provided in the bypass channel and configured to be opened and closed based on a differential pressure. The filter state estimation system includes: a sensor to detect that the valve is in an open state or in a closed state; a temperature sensor to detect a temperature of the oil; and a state estimating unit to estimate a state of the filter based on detection results detected by the sensor and the temperature sensor. The state estimating unit estimates the state of the filter based on the temperature of the oil which is detected by the temperature sensor when the sensor detects that the valve is in the open state.

Abstract: An arithmetic processing portion is configured to perform a correction process for resetting an original position of the stroke position by using at least detection results of a voltage value of a first magnetic force sensor as well as a second magnetic force sensor according to the piston movement, and further not to perform the correction process to reset the original position of the stroke position by using the detection result of the first magnetic force sensor and the second magnetic force sensor right after an abutment when the piston is abutted to the stroke end based on a detection result of a stroke end abutment detecting system.

Abstract: An arithmetic processing portion is configured to perform a correction process for resetting an original position of the stroke position by using at least detection results of a voltage value of a first magnetic force sensor as well as a second magnetic force sensor according to the piston movement, and further not to perform the correction process to reset the original position of the stroke position by using the detection result of the first magnetic force sensor and the second magnetic force sensor right after an abutment when the piston is abutted to the stroke end based on a detection result of a stroke end abutment detecting system.