Hydraulic actuator 202 (e.g. for aircraft landing gear) having extension 206 and retraction chamber 208, and bypass line 222 having flow restrictor 224 and bypass valve 226 (e.g. in series) connecting the two chambers. Valve is made from temperature-responsive shape-changing material (e.g. phase change material PCM, shape-memory alloy) defining a port 226c’ which opens when temperature is below threshold (zero Celsius). Different temperature-sensitive material with different contraction expansion rate may be used. Phase-changed material may be contained in an annular wall 226d, and transition from solid to liquid from -15 to -25 degrees. Flow restrictor may have 4 to 14 mm2 cross-sectional area. Valve status sensor may sense valve position or hydraulic fluid parameter in the bypass line. The bypass line may be external to the hydraulic ram connecting to the hydraulic lines 216, 218, within the wall of the hydraulic ram housing, or within the moveable piston 204.
Hydraulic actuator
2025-06-18
Patent
Electronic Resource
English