Woodward 3171A, Руководство по эксплуатации продукта, Страница: 23 / 47

Manual 26731 EM35MR1/3171A Gas Valve
Woodward 13
Chapter 3.
Description of Operation
EM35MR1 Actuator
The EM35MR1 electric actuator is comprised of a brushless dc motor, a clutch
assembly, a gearhead assembly, and an explosion-proof housing. The brushless
dc motor uses Samarium Cobalt permanent magnets bonded and sleeved to the
rotor. The high-speed motor output shaft is clutched before the gearbox
assembly. This clutch prevents damage to the motor shaft and gearbox should
an external force suddenly stop the rotation of the gearbox output shaft. The
clutch slips at 1.5 times the maximum output force of the motor/gearbox
assembly. The motor gearbox is a planetary gearbox and is used to reduce the
output speed and increase the output torque.
The control signals for the motor come from an external motor driver. The motor
driver handles motor commutation as well as closed-loop position control. The
position feedback comes from a precision resolver directly coupled to the valve
metering sleeve. This arrangement prevents any errors in sensing the desired
valve position through linkages and geartrains and results in precise position
control. Having the feedback on the valve also allows for the motor to be repaired
or replaced in the field without any loss of calibration. The entire motor assembly
is installed in a cast explosion-proof housing. The motor is heat sunk to this
external housing to allow heat generated by the motor to be effectively
transferred to the ambient environment. The output shaft of the geartrain is
supported by two roller bearings. To minimize side load to the motor, the output
shaft is directly coupled to the valve using a stainless steel torsional coupling.
The torsional coupling efficiently transmits the motor torque to the valve with very
little lost motion and is key to achieving the desired position control of the valve.
3171A Gas Valve
Actuator output shaft movement positions the gas valve metering sleeve and
resolver. Gas flow is metered at the valve through a ported rotary sleeve. Gas
enters the inlet port (P1) where it is directed through the inlet guide tube to the
rotary metering port. A spring and pressure loaded, sharp edged shoe seals
against the metering sleeve. Metered fuel is discharged at the outlet pressure.
Metered fuel is determined by valve position, inlet pressure (P1), outlet pressure
(P2), gas temperature, and gas composition.