Electrohydraulic proportional actuator apparatus

#1. Field of the Invention

#This invention relates to electrohydraulic actuator systems and, more particularly, to such systems for positioning the nozzle of an associated turbine.

#2. Description of the Prior Art

#A better understanding of the present invention may be had from a consideration of the following detailed description, taken in conjunction with the accompanying drawing, in which:

#FIG. 1 is a front elevational view, partially broken away, of one particular arrangement in accordance with the present invention;

#FIG. 2 is a similar view of a portion of the device of FIG. 1, showing a particular modification thereof;

#Referring to FIG. 1, a particular linear servoactuator 10 in accordance with the invention is shown comprising a main body or housing 12 which houses a four-way hydraulic valve 14, a proportional solenoid 16 and a piston 18. A follow-up linkage 20 connects the proportional solenoid 16 and piston 18, thus providing an output which is linearly proportional to the electrical signal input solenoid.

#The hydraulic valve 14 has an inlet line 22 for connection to a supply of pressurized fluid (not shown) and an outlet 24 for connection to a fluid return line. Internal fluid lines 26 and 28 connect from the valve 14 to opposite sides of the piston 18 within its cylinder 30. A spool 32 is mounted to move laterally within the valve chamber 34 to admit pressurized fluid from the inlet 22 to a selected one of the internal lines 26, 28. Another internal line 36 connects the portion of the chamber 34 on the right-hand side of the spool 32 with the portion of the chamber on the left-hand side of the spool 32 to which the outlet 34 is connected.

#The solenoid 16 comprises a coil 40 attached to a core 42 which is movable within the housing 12 in sealing relationship provided by a seal 44. The solenoid 16 has a plunger 46 shown with a central port 48. The plunger 46 is connected to the spool 32 by means of a link 50. The proportional solenoid is loaded by a compression spring 52 extending between adjacent faces of the coil 40 and the plunger 46 to provide a feedback force. The direct connection between the solenoid plunger 46 and the valve spool 32 via the link 50 provides zero backlash and simultaneously accommodates the close clearance of the spool valve. The plunger 46 operates in the fluid return passage of the servoactuator body, thus providing minimum operating force for plunger 46 and the valve spool 32. The hydraulic seal 44 for the solenoid is at the outer diameter of the coil 40, and the force for follow-up motion is provided by the piston 18. Since the valve 14 has a high-pessure gain, the error introduced to overcome seal friction is very small.