Patent ID: 9618017
Date: 2017-04-11
CPC Classifications: E02F,F15B

Claim:
1. A hydraulic system for a construction machine, comprising: a variable displacement hydraulic pump connected to an engine; an attachment operation device and a swing operation device outputting operation signals in proportion to operator's operation amounts; at least one attachment actuator connected to a discharge flow path of the hydraulic pump to be driven by the operation of the attachment operation device; a first control valve installed in the discharge flow path and shifted to control a start, a stop, and a direction change of the actuator in response to the operation of the attachment operation device; a swing motor connected to a flow path branched from the discharge flow path to be driven by the operation of the swing operation device; a second control valve installed in the flow path and shifted to control a start, a stop, and a direction change of the swing motor in response to the operation of the swing operation device; a first pressure compensation valve installed on a downstream side of the discharge flow path to have an opening amount that is controlled by a difference between a maximum load sensing pressure and a pressure on the downstream side of the discharge flow path; a second pressure compensation valve installed on the downstream side of the flow path to have an opening amount that is controlled by a difference between the maximum load sensing pressure and a pressure on the downstream side of the flow path; a pressure sensor detecting a discharge pressure of the hydraulic pump; a maximum load pressure sensor detecting a pressure of a maximum load sensing pressure line; an attachment operation amount detection means for detecting the operation amount of the attachment operation device; a swing operation amount detection means for detecting the operation amount of the swing operation device; and a control unit receiving an input of detection values of the pressure sensor of the hydraulic pump, the maximum load pressure sensor, the attachment operation amount detection means, and the swing operation amount detection means, and outputting a control signal for controlling a discharge flow rate of the hydraulic pump, wherein one of output ports of the first pressure compensation valve is connected to the attachment actuator through a spool of the first control valve, and another of the output ports thereof is connected to the maximum load sensing pressure line, and wherein one of output ports of the second pressure compensation valve is connected to the swing motor through a spool of the second control valve, and another of the output ports thereof is not connected to the maximum load sensing pressure line, but is connected to a swing load pressure sensor for detecting a load pressure of the swing motor.