Patent ID: 9441646
Filing Date: 2016-09-13
CPC Classification: E02F,F15B

Claim Text:
1. A hydraulic system of a construction machine comprising an emergency control unit for an electric hydraulic pump, the hydraulic system comprising: first and second electric hydraulic pumps, which are pressure control type variable capacity pumps; a plurality of main control valves configured to selectively control a flow of working oil discharged from the first and second electric hydraulic pumps; a plurality of working machines and first and second travel motors driven by the working oil supplied from corresponding main control valves among the plurality of main control valves; a straight travel control valve configured to set a supply path of the working oil supplied to the first and second travel motors; an electronic control unit configured to control the quantity of outlet flow of the working oil of the first and second electric hydraulic pumps by outputting pressure control electric signals for the first and second electric hydraulic pumps based on flow signals of the first and second electric hydraulic pumps and an operation signal of a joystick; and the emergency control unit configured to output the predetermined pressure control electric signals for the first and second electric hydraulic pumps when the electronic control unit fails to operate, wherein the emergency control unit is configured to selectively control the quantity of outlet flow of the first and second electric hydraulic pumps according to the amount of load of the working machines, and wherein when the amount of load of the working machine is a low load, the emergency control unit is configured to output the predetermined pressure control electric signal with the same pressure for the first and second electric hydraulic pumps, and when the amount of load of the working machine is a high load, the emergency control unit is configured to output the predetermined pressure control electric signal with pressure, which is higher than that of the case of the low load, for one pump between the first and second electric hydraulic pumps.