Hydraulic system

A hydraulic system comprising:

• a variable displacement hydraulic pump configured to discharge hydraulic oil and comprising a swash plate;
• a swash plate angle sensor configured to measure an angle of the swash plate;
• a swash plate drive piston having a large diameter section and a small diameter section and configured to move the swash plate of the hydraulic pump in response to a change in pressure applied to the large diameter section;
• a swash plate control hydraulic line for supplying a portion of the hydraulic oil discharged by the hydraulic pump to the large diameter section;
• a control valve installed on the swash plate control hydraulic line to control a flow rate of the hydraulic oil supplied to or discharged from the large diameter section;
• an electronic proportional pressure reducing valve configured to generate pilot pressure that is to be delivered to one side of the control valve;
• an operation device configured to generate an operation signal;
• a control device configured to control the electronic proportional pressure reducing valve according to the operation signal from the operation device and angle information from the swash plate angle sensor;
• a drain line connected to the control valve;
• and
• a valve control hydraulic line branched from the swash plate control hydraulic line upstream of the control valve and provided to deliver pressure to the other side of the control valve,
• wherein the pilot pressure generated by the electronic proportional pressure reducing valve under control of the control device and delivered to one side of the control valve comprises:
• a first pilot pressure lower than the pressure applied to the other side of the control valve through the valve control hydraulic line,
• a second pilot pressure higher than the pressure applied to the other side of the control valve through the valve control hydraulic line, and
• a third pilot pressure higher than the second pilot pressure.