Electrohydraulic propeller governor

Proposed is a hydraulically controlled variable pitch propeller system for air, land or water craft, comprising an engine, an engine controller, a rotating propeller featuring at least two propeller blades (16), for the pitch control of which a propeller governor (30) is provided connecting the propeller (10) via at least one hydraulic line and comprising a governor body (32) housing a control spool (46) the position of which is determined by the cooperation of flyweights (40) rotating by means of the engine and a variably biased governor spring (48) supported by the control spool (46). In accordance with the invention, the propeller governor (30) comprises an electric motor (58) which sets the preload of the governor spring (48) for the desired rpm and is electrically connected to the engine controller.

RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. 119 to German Patent Application No. 10 2008 004 196.3, filed Jan. 11, 2008, which is hereby incorporated by reference.

The invention relates to a hydraulically controlled variable pitch propeller system for air, land or water craft having the features as set forth in the preamble of claim1.

One such propeller system is known in practice to comprise an engine for powering a propeller having at least two variable pitch propeller blades. This is done by means of fixed controller consequently forming a propeller governor as a hydraulic means with which the pitch of the propeller blades can be adapted to the operating mode in each case. Existing propeller governors comprise an arm acting on a governor spring for positioning a control spool, the spring being supported by the spool. The position of the control spool dictates the pressure acting on a servo piston for varying the pitch of the propeller blades. The adjusting arm of the propeller governor is mechanically connected to a control lever in the cockpit of the aircraft for manual control by the pilot. This means that the pilot has the task of defining propeller RPM. Existing propeller governors thus work mechanically and hydraulically in combination, their activating control being mechanical.

More advanced engines for powering the propeller often require engine power and RPM to be controlled electronically as a function of a variety of parameters to optimize performance in any required operating condition. This is not possible with existing propeller governors working mechanically and hydraulically in combination.

The invention is based on the object of defining a hydraulically controlled variable pitch propeller system of the type as recited at the outset which is provided with a propeller governor permitting activation control of the propeller system with optimized ease of operation.

This object is achieved by the hydraulically controlled variable pitch propeller system having the features as set forth in claim1.

In accordance with the invention there is consequently provided a hydraulically controlled variable pitch propeller system for air, land or water craft, comprising an engine, an engine controller, a rotating propeller featuring at least two propeller blades, for the pitch control of which a propeller governor is provided connecting the propeller via at least one hydraulic conduit and comprising a governor housing a control spool the position of which is determined by the cooperation of flyweights powered rotating by means of the engine and a variably biased governor spring supported by the control spool. The propeller governor comprises an electric motor which sets the bias of the governor spring and is electrically connected to the engine controller.

Engineering a propeller system in accordance with the invention eliminates the need of a mechanical connection from a cockpit control to the governor usually mounted on the engine. Instead the governor spring and thus the hydraulic pressure for pitch control can be handled by Full Authority Digital Engine Control (FADEC), i.e. the engine controller commands are translated from the electric motor into actuation of the propeller governor. This considerably enhances ease of operation of an aircraft since it permits a single power lever control of the air, land or water craft involved, thus relieving the strain on the pilot or operator.

The control representing the propeller governor engineered in accordance with the invention now permits control of the propeller being fully electronic so that also fuel consumption can be optimized in keeping with the output of the engine as selected in each case. Where aircraft are concerned this also includes various parameters such as air density, external temperature and flight speed, in which also variations in engine and propeller RPM play an important role.

In one special embodiment of the propeller system the electric motor acts via a lever arm on a bearing block for the governor spring. By means of the lever arm an increase or reduction in the transmission ratio of the positioning action exerted by the electric motor, particularly when linear, may occur. In this case a mechanical means is provided for communicating the control commands from the electronic engine controller via the electric motor to the biased governor spring responsible for governing propeller RPM differing as a function of the bias.

For flexibility in installing the governor in the region of an engine casing the governor may feature a rotatable head for mounting the electric motor and the lever arm.

To limit the RPM of the propeller to a maximum and/or minimum RPM it is of advantage when the lever arm cooperates with at least one stop defining a minimum and/or a maximum RPM of the propeller, i.e. the stops for the lever arm ensuring that engine RPM remains safe even when the electronic input of the engine malfunction.

Preferably, the stops are engineered adjustable. More particularly, each stop may be formed by a stopscrew penetrating the header housing accommodating the lever arm. Preferably the stopscrews are arrested from turning out of place to prevent unwanted positioning of each stop. The stopscrews permit setting the values limiting propeller RPM on the outside of the governor, i.e. without requiring the casing of the controller to be opened up.

Preferably the electric motor is secured to the header housing accommodating the lever arm.

To perform feathering of the propeller blades, particularly on a multi-engine aircraft, i.e. to minimize drag with the engines stopped, the governor of the propeller system in accordance with the invention preferably comprises a solenoid valve, opening of which reduces the hydraulic pressure acting on a servo piston so that system pressure is effectively rendered zero and the propeller blades automatically feather due to the effect of the springs and counterweights. On a return from feathering this solenoid valve is closed.

To always ensure an adequate supply of hydraulic pressure for example in flight, to start the engine after feathering, it is provided for to advantage that the propeller system in accordance with the invention comprises an oil accumulator with an additional solenoid valve that fluidly communicates with the governor so that opening of the solenoid valve reduces the pitch of the propeller blades to ensure reliable engine starting in flight.

On a multi-engine air, land or water craft it may be desired to synchronize propeller blade RPM. This is achievable by digital engine control cooperating with the electric or servo motors of the governors assigned to each propeller constituting Full Authority Digital Engine Control (FADEC) or an external electronic control.

Further advantages and advantageous aspects of the subject matter of the invention read from the description, the drawing and the claims.

Referring now toFIG. 1there is illustrated a hydraulically controlled variable pitch propeller assembly comprising a propeller hub12and at least two propeller blades16each assigned bearings14. Provided at each propeller blades16is a flyweight18which together with springs17feathers the corresponding propeller blades16. For powered rotation of the propeller10, the propeller hub12is connected to an engine of an aircraft or other vehicle.

Provided furthermore in the propeller hub12is a servo piston20by means of which the pitch of the propeller blades16can be varied. Displacement of the servo piston20occurs hydraulically. For this purpose a cylinder space in which the servo piston20is guided and hydraulically connected to a propeller governor30serving as a control shown in detail inFIGS. 2 to 4.

The propeller governor30comprises a governor body32made of metal and a governor head34with a head housing36. The governor body32contains a gear pump34which uses hydraulic fluid, pumped from the engine, to increase the servo pressure between 18 and 42 bar. To vary the pitch of the propeller blades16the servo piston20is moved by this servo pressure.

Furthermore included in the governor body32is a drive shaft37powered by the engine via a coupling member38and which drives flyweights40arranged in a governor space42. The flyweights40are pivotally mounted on a rotating plate44connected to the drive shaft37.

Axially sliding, guided in the drive shaft37is a valve or control spool46, which controls the servo pressure supplied to the servo piston20in the hub12of the propeller10.

At its end facing away from the coupling member38the control spool46is biased by means of a governor spring48. The governor spring48is supported at one end by a support50connecting the control spool46and at its other end by a bearing sleeve52, at the position which dictates the preload of the governor spring48.

The bearing sleeve52installed in the governor head34is connected to a lever arm54pivotally mounted at an axis56which can be moved by means of an electric motor58fitted to the governor head34. The electric motor58connected to an engine controller has an axially displaceable or translationally working shaft60acting on the lever arm54so that when pivoted it displaces the bearing sleeve52supporting the governor spring48and changing the preload of the spring.

Provided furthermore at the governor head34are two setscrews62,64penetrating a cover66of the governor head34and of which the setscrew62forms a mechanical stop for the lever arm54defining a minimum RPM of the propeller10, and the setscrew64forming a mechanical stop for the lever arm54defining a maximum RPM of the propeller, or vice-versa.

Configured furthermore in the governor body32is a pressure-relief valve70which can be set to a desired servo pressure in the range between 18 and 42 bar which opens to dump hydraulic fluid in case of overpressure from the propeller governor30.

Configured furthermore at the propeller governor30is a solenoid valve capable of dumping the pressure in the hydraulic line to the servo piston20, when actuated automatically feather the propeller blades16by the effect of the counterweights and springs17assigned to the propeller blades16.

Provided furthermore at a sidewall of the body32is a port74for connecting a hydraulic accumulator provided with an additional solenoid valve which can the propeller blades16return from feathering into the operating condition. By opening the solenoid valve, hydraulic pressure is moving the piston20in the hub12of the propeller10.

It will be assumed, of course, that the governor as described, can also be used with propellers not engineered for feathering.