Performance, Durability and Applications of a Fast Switching Valve

In the late 1980’s first experiments with switching converters were done at Linz University. One main open problem was the lack of fast switching valves. First measurements were done with servo or fast control valves at frequencies up to 100Hz or with switching valves with lower frequencies of about 20 Hz. Servo valves are much too expensive and 20 Hz operation creates too much pulsation and jerky motion. Digital and switching hydraulics is successfully established for some special applications in the automotive area. The valves used in these applications are optimized with respect to cost under the given limited lifetime requirements; their nominal flow rates are very low. This paper gives an overview of lifetime tests of a fast 3/2 way solenoid actuated spool type switching valve. The valve features a very compact design for ease of integration, a nominal flow rate of 10 l/min @ 5 bar pressure loss, a switching time of approximately 1 to 2 ms, a powerful yet compact solenoid, and an integrated wave spring for spool actuation. For getting such fast switching times a high coil current is needed requiring an advanced electronics, which for a better usability is integrated an part of the valve. The onboard microcontroller controls the current and measures the voltage of the solenoid. The main challenging part for a standard valve is the lifetime. For an application running at repeating frequency of 100Hz it takes less than 12 days to reach more than 100 Mio load cycles. Today most of the hydraulic suppliers do not specify themaximum load cycles. 129 At the end of the paper an overview about possible applications for a fast switching valve is given.