Redundant hydraulic system

A method for operating an hydraulically driven actuator of a redundant hydraulic system, the method comprises:

• providing the hydraulic system that comprises a hydraulic actuator;
• a first pilot-operated directional control valve connected to the hydraulic actuator and a second pilot-operated directional control valve also connected to the hydraulic actuator;
• first and second fail-safe solenoid-controlled pilot valves operatively connected to the first pilot-operated directional control valve, and third and fourth fail-safe solenoid-controlled pilot valves operatively connected to the second pilot-operated directional control valve;
• energizing a solenoid of the first fail-safe solenoid-controlled pilot valve for displacing an associated pilot spool forwards, such that a flow passage opens that supplies pilot pressure fluid from a redundant pilot pressure fluid supply system to a first longitudinal end of a flow control spool of the first directional control valve, and such that high-pressure hydraulic fluid from an external hydraulic fluid pressure source is routed to a first chamber of the hydraulically driven actuator via the first directional control valve, and substantially simultaneously energizing a solenoid of the third fail-safe solenoid-controlled pilot valve for displacing an associated pilot spool forwards, such that a flow passage opens that supplies the pilot pressure fluid from the redundant pilot pressure fluid supply system to a first longitudinal end of a flow control spool of the second directional control valve, and such that the high-pressure hydraulic fluid from the external hydraulic fluid pressure source is routed to said first chamber of the hydraulically driven actuator via the second directional control valve;
• and
• stopping energizing the solenoid of the first fail-safe solenoid-controlled pilot valve, and substantially simultaneously stopping energizing the solenoid of the third fail-safe solenoid-controlled pilot valve, wherein subsequent rearwards motion of a plunger of the solenoid of the first fail-safe solenoid-controlled pilot valve automatically causes opening of a normally closed internal drain passage in the first fail-safe solenoid-controlled pilot valve for enabling automatic drainage of the pilot pressure fluid supplied from the pilot pressure fluid supply system in the event the associated pilot spool is stuck in an actuated state, and wherein subsequent rearwards motion of a plunger of the solenoid of the third fail-safe solenoid-controlled pilot valve automatically causes opening of a normally closed internal drain passage in the third fail-safe solenoid-controlled pilot valve in the event the associated pilot spool is stuck in an actuated state,
• wherein the redundant pilot pressure fluid supply system having a first pilot pressure fluid supply line and a second pilot pressure fluid supply line configured for supplying pilot pressure fluid to the first to fourth fail-safe solenoid-controlled pilot valves,
• wherein the first pilot pressure fluid supply line is connected to a first input port of a shuttle valve and the second pilot pressure fluid supply line is connected to a second input port of the shuttle valve, and an inlet port of each of the first to fourth fail-safe solenoid-controlled pilot valves is connected to an outlet port of the shuttle valve, and
• wherein the redundant pilot pressure fluid supply system comprises a first pressure reducing valve configured for supplying the pilot pressure fluid to the first pilot pressure fluid supply line, and a second pressure reducing valve configured for supplying the pilot pressure fluid to the second pilot pressure fluid supply line.

A hydraulic system for activating a hydraulic consumer having a first consumer port and a second consumer port, the system comprising:

• a valve assembly having a pressure source inlet port, a reservoir port, a first pilot-operated directional control valve and a second pilot-operated directional control valve, each pilot-operated directional control valve including:
• a first port fluidly connected to the pressure source inlet port, a second port fluidly connected to the reservoir port, a third port fluidly connected to the first consumer port, a fourth port fluidly connected to the second consumer port, and a pilot operated flow control spool arranged in a spool bore,
• a first fail-safe solenoid-controlled pilot valve operably connected to the first directional control valve and configured for driving the flow control spool in a first direction,
• a second fail-safe solenoid-controlled pilot valve operably connected to the first directional control valve and configured for driving the flow control spool in a second direction,
• a third fail-safe solenoid-controlled pilot valve operably connected to the second directional control valve and configured for driving the flow control spool in the first direction,
• a fourth fail-safe solenoid-controlled pilot valve operably connected to the second directional control valve and configured for driving the flow control spool in the second direction, and
• a pilot pressure fluid supply system having a first pilot pressure fluid supply line and a second pilot pressure fluid supply line configured for supplying pilot pressure fluid to the first to fourth fail-safe solenoid-controlled pilot valves,
• wherein each of the fail-safe solenoid-controlled pilot valves has an internal drain passage that is normally closed and is configured to automatically open upon subsequent rearward motion of a plunger of the solenoid of each fail-safe solenoid-controlled pilot valve for enabling automatic drainage of the pilot pressure fluid supplied from the pilot pressure fluid supply system in the event a pilot spool of the associated fail-safe solenoid-controlled pilot valve is stuck in an actuated state,
• wherein the first pilot pressure fluid supply line is connected to a first input port of a shuttle valve and the second pilot pressure fluid supply line is connected to a second input port of the shuttle valve, and an inlet port of each of the first to fourth fail-safe solenoid-controlled pilot valves is connected to an outlet port of the shuttle valve, and
• wherein the redundant pilot pressure fluid supply system comprises a first pressure reducing valve configured for supplying the pilot pressure fluid to the first pilot pressure fluid supply line, and a second pressure reducing valve configured for supplying the pilot pressure fluid to the second pilot pressure fluid supply line.