Hydraulic system for work machine

A hydraulic system for a work machine, comprising:

• a first hydraulic pump to deliver operation fluid;
• a second hydraulic pump to deliver pilot fluid;
• a first hydraulic device including first and second pressure receivers to receive the pilot fluid, the first hydraulic device configured to control a flow rate of an operation fluid based on the pilot pressure applied to the first and/or second pressure receivers;
• a first manual operator configured to operate the first hydraulic device, the first manual operator including
• a first operation lever for a user to move toward one direction and another direction opposite to the one direction,
• a first operation valve configured to change first pressure of the pilot fluid in accordance with movement of the first operation lever toward the one direction, and
• a second operation valve configured to change second pressure of the pilot fluid in accordance with the movement of the first operation lever toward the another direction;
• at least one discharge fluid tube configured to drain the pilot fluid from the first operation valve and/or the second operation valve;
• and
• at least one actuating valve disposed in the at least one discharge fluid tube and configured to reduce pressure of the pilot fluid in the at least one discharge fluid tube, wherein
• the at least one actuating valve includes a pilot-operated check valve having a pressure receiver, which prevents or allows the pilot fluid to flow from the at least one discharge fluid tube through the pilot-operated check valve in accordance with pressure applied to the pressure receiver thereof.

A hydraulic system for a work machine, comprising:

• a first hydraulic pump to deliver operation fluid;
• a second hydraulic pump to deliver pilot fluid;
• a first hydraulic device including first and second pressure receivers to receive the pilot fluid, the first hydraulic device configured to control a flow rate of an operation fluid based on the pilot pressure applied to the first and/or second pressure receivers;
• a first manual operator configured to operate the first hydraulic device, the first manual operator including
• a first operation lever for a user to move toward one direction and another direction opposite to the one direction,
• a first operation valve configured to change first pressure of the pilot fluid in accordance with movement of the first operation lever toward the one direction, and
• a second operation valve configured to change second pressure of the pilot fluid in accordance with the movement of the first operation lever toward the another direction;
• at least one discharge fluid tube configured to drain the pilot fluid from the first operation valve and/or the second operation valve;
• and
• at least one actuating valve disposed in the at least one discharge fluid tube and configured to reduce pressure of the pilot fluid in the at least one discharge fluid tube, wherein
• the at least one actuating valve includes an electromagnetic switch valve configured to be switched between a first position and a second position,
• the first position preventing the pilot fluid to flow from the at least one discharge fluid tube, and
• the second position allowing the pilot fluid to flow from the at least one discharge fluid tube.

A hydraulic system for a work machine, comprising:

• a prime mover;
• a first variable displacement pump driven by the prime mover and configured to control flow rate of operation fluid;
• a second variable displacement pump driven by the prime mover and configured to control flow rate of operation fluid;
• a first manual operator having a first operation lever and a first operation valve configured to change pressure of pilot fluid applied to the first variable displacement pump in accordance with operation of the first operation lever, thereby to control the flow rate of operation fluid of the first variable displacement pump;
• a second manual operator having a second operation lever and a second operation valve configured to change pressure of pilot fluid applied to the second variable displacement pump in accordance with operation of the second operation lever, thereby to control the flow rate of the operation fluid of the second variable displacement pump;
• a first travel fluid tube connecting the first operation valve and the first variable displacement pump;
• a second travel fluid tube connecting the second operation valve and the second variable displacement pump;
• a discharge fluid tube connected to the first travel fluid tube and the second travel fluid tube and configured to drain the pilot fluid from the first travel fluid tube and the second travel fluid tube;
• an actuating valve disposed in the discharge fluid tube and configured to reduce pressure of the pilot fluid in the discharge fluid tube, the actuating valve including a relief valve having a setting pressure configured to be adjusted, which allows the pilot fluid to drain from the discharge fluid tube through the relief valve when the pressure of the pilot fluid upstream of the relief valve is greater than the setting pressure;
• a controller configured to control the actuating valve based on revolution speed of the prime mover and temperature of the operation fluid and to adjust the setting pressure of the actuating valve based on the revolution speed of the prime mover and the temperature of the operation fluid;
• and
• a proportional valve connected to a pressure-receiver of the relief valve, which is configured to adjust the setting pressure of the relief valve by changing setting pressure of the pilot fluid applied to the pressure-receiver of the relief valve.