Electrohydraulic valves (EHVs) operated by a torque motor are widely used in industrial applications. For example, single-stage electrohydraulic valves may be used in myriad systems and environments. One typical system and environment is the fuel control system on-board a jet-powered aircraft. No matter the specific end-use system and environment, single-stage EHVs typically include at least one nozzle that is disposed between a pressurized hydraulic fluid source and a hydraulically controlled load. Pressurized hydraulic fluid flow through the nozzle, and thus to the hydraulically controlled load, may be controlled via the torque motor.
A conventional torque motor that is used with a single-stage EHV includes a plurality of coils, an armature assembly, and a flapper. The coils are controllably energized to control the rotational position of the armature assembly. The flapper is coupled to the armature assembly and extends between the outlet of the nozzle and a flapper stop in the single-stage EHV, defining a “nozzle-flapper assembly.” The flapper in the nozzle-flapper assembly is conventionally a steel bar. By controlling the rotational position of the armature assembly, the position of the flapper relative to the nozzle outlet in the nozzle-flapper assembly is controlled and thus fluid pressure and/or flow to the hydraulically controlled device is controlled. When the EHV is used as a shut-off valve, the flapper is held against the nozzle outlet in a closed position to prevent flow of the pressurized hydraulic fluid therefrom to the hydraulically controlled device. When the flapper is off the nozzle outlet, the EHV is in an open position, permitting flow of the pressurized hydraulic flow.
Conventional nozzle-flapper assemblies exhibit limited life and excessive leakage between the flapper and the nozzle outlets even in the closed position due to wear of the flapper and/or nozzles in high vibration environments. Over time, the leakage increases as the wear increases.
Hence, there is a need for flapper assemblies for torque motors of electrohydraulic valves. In particular, there is a need for flapper assemblies that may be used in nozzle-flapper assemblies of torque motors of electrohydraulic valves, that exhibit relatively less leakage and extended operating life, and that are relatively inexpensive to manufacture. The present invention addresses at least these needs.