Hydraulically controlled variable pitch propeller

Proposed is a redundant hydraulically controlled variable pitch propeller for an air, land or water craft, comprising at least two propeller blades (14) mounted in a propeller hub (12) for variable pitch control by means of a hydraulically powered piston assembly (18). In accordance with the invention the piston assembly (18) comprises two mechanically interconnected servo pistons (20, 22) each assigned an independent hydraulic circuit.

RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. 119 to German Patent Application No. 10 2008 004 197.1, filed Jan. 11, 2008, which is hereby incorporated by reference.

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

Such a variable pitch propeller is known in practice which comprises a hydraulic means including a piston assembly by means of which the pitch of the propeller blades can be varied.

A variety of devices and methods are known in principle for varying the pitch of propeller blades, it usually being the case that these involve hydraulic systems provided single or dual acting by means of which the pitch can be automatically and continuously varied as to an assigned engine power, propeller RPM and flight speed. These known systems feature a servo piston, meaning that no pitch variation is possible when the hydraulic system fails. In order to prevent hazardous overspeeding, means are included to block the pitch change of the propeller blades. Known, in particular, is to install counterweights in the blade shank region of each propeller blade which, however, adds undesired weight.

Further, to prevent hazardous overspeeds on dual acting pitch change systems with a failure of the hydraulics the usual pitch control systems comprise what is called a pitch lock device, which locks the blade angle in the position which existed at the point in time of the pressure loss.

The invention is based on the object of defining a hydraulically controlled variable pitch propeller featuring a hydraulic system which ensures high operational safety of the propeller without the aforementioned safeguards.

This object is achieved in accordance with the invention by a hydraulically controlled variable pitch propeller having the features as set forth in claim1.

Consequently in accordance with the invention, a redundant hydraulically controlled variable pitch propeller system for an air, land or water craft is proposed, comprising at least two propeller blades mounted in the region of a propeller hub for variable pitch control by means of a hydraulically powered piston assembly. In accordance with the invention the piston assembly comprises two mechanically interconnected servo pistons, each assigned to an independent hydraulic circuit.

A variable pitch propeller in accordance with the invention is now possible to control a piston assembly even when one of the two independent hydraulic circuits malfunctions, so that varying the pitch of the propeller blades is still assured. This assures high safety of operation of a variable pitch propeller system without having counterweights on the blade shanks or providing a pitch lock as aforementioned. Both servo pistons are so dimensioned that in case of one hydraulic circuit malfunctions, varying the pitch of the propeller blades is possible solely by the other hydraulic circuit.

In one preferred solution of the variable pitch propeller in accordance with the invention, the two hydraulic circuits comprise a common valve assembly by means of which the two servo pistons are activated synchron with a servo pressure. This valve assembly comprises, for example, two control spools operated by a common actuator and which are positioned by the hydraulic or servo pressure in which the two pistons of the propeller assembly are arranged in the propeller hub, for changing the blade pitch.

In one special arrangement of the valve, in accordance with the invention, the valve assembly and the servo pistons are interconnected by a double-walled control tube, comprising a ring-shaped passageway assigned to one of the two hydraulic circuits and an axial passageway assigned to the other of the two hydraulic circuits.

The control tube can cooperate with the two control spools of the valve assembly, each assigned to one of the hydraulic circuits. In particular the outer tube of the double-walled control tube comprises two control ports staggered axially, one of which ports into the axial passageway and the other into the ring-shaped passageway of the control tube.

The control valve comprises in particular two independent hydraulic chambers supplied by two independent pressure sources and hydraulically connected via the control tube to pressure spaces, each assigned to one of the servo pistons, the control tube also mechanically connecting the valve assembly to the pistons of the propeller assembly.

The control valve may also comprise two control spools, each actuated independently of the other and each assigned to one of the servo pistons in supplying hydraulic fluid to the two servo pistons, each independently of the other, to maintain pitch control even when one of the hydraulic circuits fails.

The control valve is mounted normally on the gearbox of an engine for the drive of the propeller. Expediently the control tube passes through the gearbox into the propeller hub, making the hydraulic connections between the control valve and the pressure spaces for the servo pistons.

The pressurized hydraulic fluid used for the two hydraulic circuits can be supplied statically with a constant pressure by means of a pump or dynamically by means of a propeller governor.

Further advantages and advantageous aspects of the invention are shown from the description, the drawing and the claims.

Referring now toFIG. 1there is illustrated a hydraulically controlled variable pitch propeller10comprising a propeller hub12and at least two propeller blades14with assigned bearings16and of variable pitch.

Housed in the propeller hub12is a piston assembly18comprising two servo pistons20and22mechanically interconnected by a connecting tube24sited in the axis A of the propeller hub12. The servo piston20borders on a first pressure space26assigned a first hydraulic circuit. The servo piston22borders on a second pressure space28assigned a second hydraulic circuit.

Housed furthermore in the propeller hub12is a return spring30supported by a hub cover32and on which the end of the servo piston22facing away from the second pressure space28acts on the piston assembly18to preload it in an end position as shown inFIG. 1. Connected to the piston assembly18is a piston extension33varying the pitch of the propeller blades14via a pin34on actuation of the piston assembly18.

Located in the connecting tube24is a double-walled control tube36fixedly secured to the connecting tube24, comprising an outer tube38and an inner tube39whilst hydraulically communicating the pressure spaces26and28to a control valve40as shown inFIG. 2, from which it is obvious that the control valve40is mounted with a flange42to the rear of a gearbox (not shown) of the engine (likewise not shown). The double-walled control tube36consequently passes through the gearbox.

The inner tube39of the double-walled control tube36surrounds a first hydraulic passageway44assigned to the first hydraulic circuit and fluidly communicating by a transverse drilling46of the outer tube38and a transverse drilling48of the connecting tube24in alignment with the transverse drilling46, the pressure space26being assigned to the first servo piston20.

Disposed between the inner tube39and the outer tube38is a second hydraulic passageway50fluidly communicating via a transverse drilling52of the outer tube38with the pressure space28assigned to the second servo piston22.

For supplying the hydraulic passageways44and50with hydraulic fluid the outer tube38is closed off at the end facing away from the propeller hub12, comprises two further transverse drillings54and56, the latter fluidly communicating with the axial hydraulic passageway44and the transverse drilling54fluidly communicating with the hydraulic passageway50ring-shaped design.

The control valve40through which the double-walled control tube36passes comprises a two-part valve body58, a first valve body member60being assigned the first hydraulic circuit and a second valve body member62fluidly communicating with the first valve body member60being assigned the second hydraulic circuit. Each of the two valve body members60and62is provided with a servo pressure port64and66respectively fluidly communicating with a pressure source assigned to the corresponding hydraulic circuit which may be configured as a pump or also as a propeller governor. In addition, the two valve body members60and62each comprise a return port68and70respectively.

Arranged in the valve body member60is a first control spool73which communicates via control ports72with the transverse drilling56of the outer tube38of the control tube36. Located slidingly in the valve body member62is a second control spool74which communicates via control ports76with the transverse drilling54of the outer tube38of the double-walled control tube36assigned to the second hydraulic circuit.

The control spools73and74are connected by a common actuating rod78extending in the axial direction of the control valve40and slidingly positioned by means of a suitable actuator axially to position the control spools73and74. It is this positioning of the control spools73and74by means of the actuating rod78that the hydraulic pressure communicated via the hydraulic passageways44and50to the servo pistons20and22is varied so that the piston assembly18is positioned axially in varying the pitch of the propeller blades14. A reduction in the servo pressure in the pressure spaces26and28results in the servo pistons20and22being moved up to a mechanical stop80for a brake (reverse) or feathering position by the effect of the return spring30and the pitch change forces created by the propeller blades14. In the other direction a mechanical stop82in the form of a sleeve is provided which surrounds the connecting tube24and cooperates with the hub cover32of the propeller hub12.