DRIVETRAIN SUBASSEMBLY HAVING AN INTEGRATED SPRAG CLUTCH RACE AND GEAR SHAFT MEMBER

A drivetrain subassembly includes a clutch portion and a gear shaft portion connected by an integrated inner race/gear shaft member. The clutch portion includes a sprag clutch configured to transfer torque from an engine to a rotor system while allowing the rotor system to continue to rotate in the event of an engine failure. The inner race of the clutch portion is integrally formed with the gear shaft of the gear shaft portion of the subassembly. The gear shaft is configured to rotate about the longitudinal axis of the sprag clutch for transmitting torque from the sprag clutch to a downstream drivetrain component.

TECHNICAL FIELD

This disclosure generally relates to overrunning sprag clutches for the uni-directional transmission of torque. In one aspect, it relates to an overrunning sprag clutch having an improved output shaft configuration.

DETAILED DESCRIPTION

FIG. 1shows a schematic diagram of an example tiltrotor aircraft101. Aircraft101includes a fuselage103with attached wings105. Nacelles107are carried at the outboard ends of wings105and are rotatable between the helicopter-mode position shown and a forward-facing airplane-mode position (not shown). Nacelles107carry engines and transmissions109for powering rotor systems111in rotation. An engine may be an internal combustion engine, an electrical power source and associated motor, or any other suitable means for powering rotor system111. Each rotor system111is illustrated as having three blades113. Spinning covers115and nacelles107substantially enclose transmission109, obscuring transmission109from view inFIG. 1. The tiltrotor aircraft101includes a drive train that includes subassemblies generally indicated at301and described below for driving the rotor systems111. The drive train subassemblies301can include gearboxes, shafts, couplings, and respective sprag overrunning one-way clutches as disclosed herein.

FIG. 2shows a schematic diagram of an example rotorcraft201, which also constitutes an aircraft. Rotorcraft201has a rotor system203with multiple rotor blades205. The pitch of each rotor blade205can be manipulated in order to selectively control direction, thrust, and lift of rotorcraft201. Rotorcraft201can further include a fuselage207, anti-torque system209, and an empennage211. The rotorcraft201includes a drive train, including a subassembly generally indicated at301and described below for driving the rotor system203. The drive train subassembly301can include a gearbox, shafts, couplings, and a sprag clutch.

FIG. 3shows a cross-sectional view of an embodiment of a drive train subassembly301. The drive train subassembly301includes a clutch portion302A and a gear shaft portion302B. The clutch portion302A includes a sprag clutch303. The gear shaft portion302B includes a gear shaft309B, which is integrally formed with an inner race309A of the sprag clutch303so as to form an integrated inner race/gear shaft309A/309B member. The integration of the inner race309A and the gear shaft309B can be accomplished by forming the inner race309A/gear shaft309B together as a single component. Alternatively, in some embodiments the inner race309A can be formed separately from the gear shaft309B, and then inner race309A and gear shaft309B can be colinearly fixed together, for example by friction welding, so as to be formed into a single continuous component.

The integration of the output gear shaft309B with the inner race309A of the sprag clutch303as disclosed herein constitutes an example of a deviation from prior drive train assemblies. Traditionally, an output gear shaft would be a separate component from a sprag clutch. The sprag clutch would typically be connected to the output gear shaft via another component, such as a dog-bone shaft, that allows for axial misalignments between the output gear shaft and the sprag clutch. However, integration of the inner race309A and the output gear shaft309B into a single shaft component reduces parts count, weight, and complexity, which is desirable for aircraft applications.

The sprag clutch303includes an outer race305having a longitudinal axis307therethrough, with the inner race309A positioned concentrically within the outer race305. An annular space311is therefore present between the inner race309A and the outer race305. One or more annular sprag rows313are positioned in the annular space311radially between the inner race309A and the outer race305. The exact number and configuration of sprags is determined according to principles known in the art for designing sprag clutches. Outer race305is adapted for connection to an input shaft (not shown) at an input end318. For example, the input end318of the outer race305can be a gear, such as a spiral bevel gear in the illustrated embodiment (note that the gear teeth are not shown inFIG. 4for simplicity of the view), or can be provided with internal and/or external crowned splines (not shown) which can receive torque from the input shaft. Outer race305can be adapted for connection to an input shaft using any one of a variety of known mechanical connections. The integrated inner race309A and gear shaft309B has an output end315at a distal end of the output gear shaft309B.

The clutch portion302A includes a pair of overrunning bearings319,321positioned radially between the outer race305and the inner race309A of the sprag clutch303. The first bearing319of the pair is positioned axially between the output end315and the sprag rows313. The second bearing321is positioned axially on the opposite side of the sprag rows313from the output end315.

The sprag clutch303can be used in a variety of rotorcraft designs to transfer power from an engine to rotor system. In the illustrated embodiment, a duplex bearing assembly331is provided for supporting the subassembly301in the axial direction. Alternative embodiments can include a single-row bearing in place of the duplex bearing assembly331, depending on the input to the input end318. In the illustrated embodiment, the duplex bearing assembly331is desirable because it provides for more exact axial positioning than a single-row bearing, which is desirable for use with the spiral bevel gear on the input end318. The configuration and location of the bearing assembly331can vary depending on the loading induced by the configuration of the outer race305and the gear shaft309B. Also, depending on the input and output drive arrangements of the particular aircraft drivetrain, the loads on the bearings331can be modified such that the subassembly301can be held radially between roller bearings and axially with the duplex bearing assembly331.

In the event of an engine failure, the sprag clutch303allows the rotor system to continue to rotate faster than the engine so that the rotorcraft can perform an autorotation. In rotorcraft with more than one engine, the clutch is also used to allow one engine to be started up before the other engine(s). The input end of outer race305and output end315of the integrated inner race309A and the gear shaft309B are positioned at opposite ends of the longitudinal axis307. When the sprag clutch303is engaged and in driving mode, the outer race305and the integrated inner race309A and gear shaft309B rotate together as single shaft. However, in the event of an engine failure, the sprag clutch303is disengaged and allows the integrated inner race309A and gear shaft309B to rotate faster than the outer race305in order to allow for autorotation.

Referring now also toFIG. 4, the gear shaft portion302B of the drive train subassembly301can extend into a downstream component of the drivetrain. For example, in the illustrated embodiment, the gear shaft309B extends into a gearbox401. Since the gear shaft309B is integrally formed with the inner race309A of the sprag clutch303, the inner race309A is part of a single continuous component that also serves as the gear shaft309B that extends into the gearbox401for transmitting torque to downstream drivetrain components. The integrated inner race309A and gear shaft309B can be formed of metal, such as hardened steel, or can be formed of composite or ceramic material.

An output gear323is formed on the gear shaft309B between the sprag clutch303and the output end315. For example, in the illustrated embodiment the output gear323is a helical gear, but other types of gears can be used depending on the drivetrain configuration. Also, while the illustrated embodiment includes an integrally formed output gear323, alternative embodiments can include an output gear that is a separate component that is attached to the gear shaft309B. It will also be appreciated that the gear shaft309B can be provided with additional components (not shown) within the gearbox401, such as one or more bearings, flanges, and retaining nuts.

The embodiment of the integrated inner race309A and the gear shaft309B includes a generally cylindrical portion325A that extends from within the sprag rows313to the output gear323. The integrated inner race309A and the gear shaft309B further includes a pair of frustoconical portions325B and325C. The first frustoconical portion325B extends from the output gear323away from the input end318such that the outside diameter of the first frustoconical portion325B increases as it extends away from the output gear323. The second frustoconical portion325C extends from the sprag rows313to the bearing321such that the outside diameter of the second frustoconical portion325C decreases from the sprag rows313to the bearing321. However, it will be appreciated that the shape of the integrated inner race309A and the gear shaft309B can differ from the illustrated embodiment as desired to accommodate different drivetrain configurations.