New Fault Tolerant Hydraulic Valve for Safety Critical Applications

The paper deals with a new concept hydraulic spool valve. The new patented valve presents a secondary rotary type actuator connected to a sleeve interposed between the spool and the valve body, thus composing a roto-translating valve. The sleeve presents holes that can be moved and positioned partially or totally overlapped to the valve ports, thus allowing a secondary metering, that can be controlled according to the spool position. The valve port area is then related to the movement of the spool, and to the rotary movement of the cylinder, controlled by a different type of motors. The valve port area is the result of two actuators position, and the resulting control is linearly depending by two PWM signals, both controlled by a microcontroller based unit. Due to the valve structure, the metering control precision is virtually quadratic in respect to the traditional valve spool position electronic control, due to the concurrency of two electronically controlled actuators. Similar considerations could be done for the valve speed, due to the concurrent speed of two different actuators. Another big advantage is the lack of need of special spool design for different applications, due to the possibility offered by the two actuators control. The valve can realize both basic logic functions (AND, OR), and advanced control techniques; moreover in term of safety it offers a fail operational characteristic, in reason of an operational redundancy and functional diversity.