Fluid reaction surfaces (i.e. – impellers) – With control means responsive to non-cyclic condition... – With electrical means comparing and reducing error related...
Reexamination Certificate
1999-08-23
2001-03-06
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
With control means responsive to non-cyclic condition...
With electrical means comparing and reducing error related...
C416S049000, C416S003000, C416S15700A
Reexamination Certificate
active
06196797
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a governor for aircraft propellers and more specifically to electronically controlled governors which provide their own power.
Governors for variable pitch propellers are well known and usually comprise a device mounted on and driven by the engine which senses and controls propeller (RPM) by hydraulically adjusting the pitch of the propeller. A common type of governor employs a hydraulic 3-position spool valve with a flyweight type actuator connected thereto to shift the valve spool in one direction or the other as the centrifugal force of the rotating flyweights increase or decrease spring force acting on the valve member which opposes the force of the flyweights. As the propeller begins to over speed, the increasing centrifugal force on the flyweights overcomes the speeder spring and shifts the valve spool so as to allow oil to flow to a hydraulic cylinder in the propeller hub which increases the pitch of the propeller blades thus increasing torque of the propeller causing the propeller speed to slow down to maintain the original RPM setting of the governor. Mechanical governors of this type for controlling variable pitch propellers have been available on airplanes for the better part of this century. They are typically used in a constant speed propeller governing system wherein the load on the engine varies and the propeller blade must change its pitch so as to maintain a constant RPM. Propeller governors have previously been electrically actuated, as taught in U.S. Pat. Nos. 3,831,615 and 3,751,993. However, both of these patents sense speed mechanically while the present invention senses speed electrically with the use of a small generator.
The general concept of a prime mover for a vehicle driving a generator goes back to the early automotive days. Locating the generator on a rotating propeller hub to provide electrical energy for changing pitch of the blades is taught in U.S. Pat. No. 4,556,366 and U.S. Pat. No. 2,491,172. These two patents also teach using the produced electrical energy for other functions.
SUMMARY OF THE PRESENT INVENTION
The propeller governor of the present invention is similar to prior propeller governors in that it changes pitch of the blades hydraulically through a single acting cylinder located in the propeller hub having actuating links connecting the cylinder piston to the blade shank of each blade for altering the blade pitch. The governor which is engine driven also includes a hydraulic pump for producing pressurized oil for actuating the hydraulic cylinder in the propeller. Also the governor includes a hydraulic 3-position spool control valve for dispensing oil pressure acting on the piston to either increase pitch, hold pitch or reduce pitch. The directional control valve spool is positioned by a linear actuator which provides a variable force acting against a spring to maintain the propeller blade pitch to conform with an electrical signal produced by an electronic vernier RPM control. This vernier is manually set or changed by the pilot. The linear variable actuator, also referred to as a voice coil, provides a variable force depending upon the current flow in the coil of the actuator which is supplied by a linear control circuit.
Also built into the governor is an alternating current three-phase power generator having a rotor driven by the same drive shaft which drives the governor. One or more phases of the generator provides an electrical signal to the linear control circuit for the actual RPM of the governor while all three phases from the generator provide electrical power to run the linear control circuit and also provide a backup electrical supply for emergency situations when there is failure of the aircraft primary electrical power. The pilot-operated electronic vernier RPM control actuates a potentiometer which signals the linear control circuit to change the engine RPM. This electrical signal from the vernier control is compared in the linear control circuit with the RPM signal produced by the generator, and if they are different, the linear control circuit signals the voice coil to reposition the control valve spool until the signals from the manual control and the generator are identical. The three-phase AC generator has multiple functions including frequency signals which indicate the actual RPM of the engine as well as AC electrical power converted to DC for driving the linear control circuit as well as other components in the aircraft such as radios, gyros and other navigational instruments. The governor of the present invention also has application not only in constant speed propellers but also in systems which provide full-feathering, reversing and beta control. Depending upon the application, the pressurized oil can function to either increase or decrease pitch.
It is therefore the principal object of the present invention to provide a propeller governor which replaces the flyweight assembly of a mechanical governor with a generator that will produce the power for the pitch control system as well as producing a propeller RPM signal.
Another object of the present invention is to provide an electric propeller governor which also produces back up power in emergency situations.
A further object of the present invention is an electric propeller governor which includes a default mode wherein the propeller blades are forced to a minimum pitch position.
REFERENCES:
patent: 2491172 (1949-12-01), Forsyth
patent: 3575529 (1971-04-01), Bierman
patent: 3589830 (1971-06-01), Mogren et al.
patent: 3589832 (1971-06-01), Harris et al.
patent: 3751993 (1973-08-01), Davis
patent: 3831615 (1974-08-01), Hartzell
patent: 4556366 (1985-12-01), Sargisson et al.
patent: 4842484 (1989-06-01), Johnson
patent: 5415523 (1995-05-01), Muller
Bogden John M.
Davila John A.
Brown, Jr. Edward L.
Cessna Aircraft Company
Look Edward K.
McDowell Liam
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