TURBINE DRIVESHAFT FOR RAM AIR TURBINE

Abstract

A driveshaft for an aircraft ram air turbine includes a tubular body and a flange. The tubular body defines an axis of rotation and includes a forward portion and a frusto-conical portion located rearward of the forward portion. The flange adjoins the forward portion of the tubular body opposite the frusto-conical portion, and has a forward face and an opposite rear face. A ratio of an outer diameter of the forward portion of the tubular body to an inner diameter of the forward portion of the tubular body is in a range of approximately 1.423 to 1.425.

Description

BACKGROUND

The present invention relates generally to driveshafts and their manufacture, and more particularly to driveshafts for use in housings and/or gearboxes of ram air turbines (RATs) and their method of manufacture.

RATs are used on aircraft to provide an emergency power supply to power a generator, hydraulic pump, etc. When not in use, the RAT is generally stowed within the aircraft fuselage. When the aircraft is in flight, the RAT can be deployed to generate power as turbine blades of the RAT spin in oncoming airflow around the aircraft. The RAT can be deployed as a secondary or emergency system when power is unavailable from primary systems of the aircraft.

Driveshafts used in RAT drivetrains are subject to many requirements. The RAT driveshaft must be reliable and it must be able to mate with necessary drivetrain components and be able handle the torque loads to which it will be subjected. Due to the fact that most RATs protrude outward from an aircraft's fuselage in a cantilevered manner, RATs and their subcomponents are subject to a significant amount of vibration and bending. Moreover, the rotational nature of RAT drivetrains can introduce torsional resonance issues. However, because positioning of the RAT in the aircraft must account for numerous other aircraft design factors, the location of the RAT and its subcomponents is highly constrained, which greatly limits design options for the geometry and dimensions of the RAT drivetrain and its driveshafts. Weight of RAT components is also an important design consideration.

SUMMARY

A driveshaft for an aircraft ram air turbine according to the present invention includes a tubular body and a flange. The tubular body defines an axis of rotation and includes a forward portion and a frusto-conical portion located rearward of the forward portion. The flange adjoins the forward portion of the tubular body opposite the frusto-conical portion, and has a forward face and an opposite rear face. A ratio of an outer diameter of the forward portion of the tubular body to an inner diameter of the forward portion of the tubular body is in a range of approximately 1.423 to 1.425.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a ram air turbine (RAT) according to the present invention.

FIG. 2 is an enlarged perspective view of a portion of the RAT of FIG. 1.

FIG. 3 is a cross-sectional view of the portion of the RAT of FIG. 2, taken along line 3-3 of FIG. 2.

While the above-identified drawing figures set forth embodiments of the invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the invention. The figures may not be drawn to scale Like reference numbers have been used throughout the figures to denote like parts.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view of a ram air turbine (RAT) 10 for use with an aircraft (not shown). For simplicity, FIG. 1 is shown without cross-hatching. The RAT 10 includes a turbine assembly 12, a strut 14, a generator 16, and a drivetrain (or driveline) 18 that includes a strut driveshaft 20 and turbine driveshaft 22. The strut 14 provides structural support of the RAT 10 and helps support the turbine assembly 12. In the illustrated embodiment, the strut 14 has a hollow and generally cylindrical shape. Moreover, in the illustrated embodiment, the generator 16 is positioned at a proximal end of the strut opposite the turbine gearbox assembly 12. It should be noted that the generator 16 is merely one form of power conversion device that can be used with the RAT 10, and is shown merely by way of example and not limitation. For instance, a hydraulic pump can be used in place of or in addition to the generator 16 in further embodiments. The drivetrain 18 includes suitable shafts and gearing to provide a mechanical connection between the turbine assembly 12 and the generator 16, in order to transmit rotational energy (torque) to the generator 16, as explained further below.

In the illustrated embodiment, the turbine assembly 12 includes turbine blades 24, a hub 26, and a locking mechanism 28. The turbine assembly 12 can further include additional components as desired, such as suitable pitch or speed control mechanisms located within the hub 26. The turbine blades 24 are secured to the hub 26, and can have adjustable pitch in some embodiments. During operation, the turbine blades 24 can interact with airflows to produce rotation of the hub 26. In one embodiment, the turbine assembly 12 is configured to have an operating range of approximately 3,800-5,000 RPM (or 63.33-83.33 Hz).

The hub 26 is secured to the turbine driveshaft 22, which rotates at the same speed as the hub 26. The turbine driveshaft 22 is part of the drivetrain 18 and extends into a gearbox 30, which can be located aft of the hub 16 and the turbine blades 24. The gearbox 30 can be secured to and supported by a distal end of the strut 14. The gearbox 30 contains suitable gearing of the drivetrain 18 to provide a gear ratio to operate the strut driveshaft 20. The locking mechanism 28 can be configured to selectively insert a plunger into a mating feature (e.g., opening) in the turbine driveshaft 22 to selectively stop rotation of the turbine driveshaft 22, the hub 26, and other components engaged therewith.

The strut driveshaft 20 is part of the drivetrain 18, and is positioned at least partially within the strut 14. The strut driveshaft 20 can directly engage the generator 16.

The RAT 10, in the illustrated embodiment, is configured to be selectively deployable from fuselage of the aircraft using suitable actuators (not shown). When deployed, the RAT 10 presents the turbine assembly 12 to airflow passing the aircraft, and can be used to generate desired forms of power using kinetic energy from rotation of components of the turbine assembly 12 produced by the passing airflow. The RAT 10 can be deployed in-flight to provide emergency or secondary power. Because the general configuration and use of RATs is well known, further discussion here is unnecessary.

FIG. 2 is an enlarged perspective view of a portion of the RAT 10, and FIG. 3 is a cross-sectional view of the portion of the RAT 10, taken along line 3-3 of FIG. 2. As shown in the illustrated embodiment, the strut driveshaft 20 extends into the gearbox 30 and is rotatably supported relative to the gearbox 30 by two bearing sets 32. A pinion gear 34 is attached to a distal end of the strut driveshaft 20, and can be positioned in between the bearing sets 32.

In the illustrated embodiment, the turbine driveshaft 22 extends through the gearbox 30, and is rotatably supported relative to the gearbox 30 by two bearing sets 36. A ring gear 38 is attached to the turbine driveshaft 22, and meshes with the pinion gear 34 to transmit power between the turbine driveshaft 22 and the strut driveshaft 20 at a desired gear ratio. Splines 40 can be provided in the turbine driveshaft 22 to form a “back drive” connection for external tooling to be attached to the RAT 10 to rotate the drivetrain 18 for maintenance and safety inspection purposes. A pair of diametrically opposed openings 42 can be provided in the turbine driveshaft 22 to allow engagement with a locking member (e.g., plunger or pin) of the locking mechanism 28.

The turbine driveshaft 22 includes a flange 50 that can interface with the hub 26. The flange 50 can be secured to the hub 26 with suitable bolts at or near a perimeter of the flange 50. The flange 50 has a forward face (to the left in FIG. 3) that can be arranged at an angle of approximately2° (+/−0.25°) relative to an axis of rotation A, and has a rear face (to the right in FIG. 3) that can be arranged at approximately 9° (+/−0.25°). In this way the flange 50 can taper from a thicker inner diameter portion to a thinner outer diameter portion. The inner diameter portion of the flange 50 at a base of the taper can have a wall thickness of approximately 2.240 cm (0.882 inches). Extending rearward from the flange 50 of the turbine driveshaft 22 is a body portion that is tubular in shape with a hollow interior cavity. An axial length L of the body portion of the turbine driveshaft 22 can be approximately 22.715 cm (8.943 inches). The tubular body portion of the turbine driveshaft 22 can include a frusto-conical portion 54 (also called the shaft cone), which can be located approximately 6.78 cm (2.67 inches) rearward from the flange 50, with the turbine driveshaft 22 being substantially cylindrical in shape between the flange 50 and the frusto-conical portion 54. The frusto-conical portion 54 creates space to accommodate one of the bearing sets 32 and the distal end of the strut driveshaft 20. The frusto-conical portion 54 can be arranged at approximately 14° (+/−0.5°) relative to the axis A. A hub pilot diameter Ø1 can be defined adjacent to the forward face of the flange 50, and can be approximately 18.001 cm (7.090 inches). An outer diameter Ø2 of the body of the turbine driveshaft 22 at the forward bearing set 36 can be approximately 7.117 cm (2.802 inches) and a corresponding inner diameter Ø3 can be approximately 4.994 cm (1.966 inches), resulting in a corresponding wall thickness of approximately 2.123 cm (0.836 inches).

In one embodiment, a ratio of the outer diameter Ø2 of the body of the turbine driveshaft 22 to the corresponding inner diameter Ø3 can be in the range of approximately 1.423 to 1.425. In one embodiment, a ratio of the outer diameter Ø2 of the body of the turbine driveshaft 22 to the hub pilot diameter Ø1 can be in the range of approximately 1.359 to 1.380. Further, in one embodiment, a ratio of the inner diameter Ø3 of the body of the turbine driveshaft 22 to the hub pilot diameter Ø1 can be in the range of approximately 0.954 to 0.968.

Certain dimensions of the turbine driveshaft 22 are critical to performance. In addition to the angles of the front and rear faces of the flange 50 mentioned above, thicknesses of particular portions of the turbine driveshaft are significant. Ratios of the various dimensions discussed above can also be significant. Together, the combination of these design parameters of the turbine driveshaft 22 produces desirable vibration performance.

During operation, the RAT 10 is subject to various forces, including torques, vibration and bending. The turbine driveshaft 22, in particular, must be able to transmit suitable torque loads, and must have geometry and size characteristics that allow portions of it to fit within the gearbox 30 and engage with other components of the RAT 10. For instance, the turbine driveshaft 22 should be able to interface with existing hubs 26 and interface with the locking mechanism 28. Because the turbine assembly 12 is subject to a variety of forces during operation, bending moments can be imparted to the turbine driveshaft 22. It has been discovered that lateral movement of the turbine driveshaft 22 in a direction in and out of the page as shown in FIG. 3 can cause displacement between the pinion gear 34 and the ring gear 38, which leads to torque ripples through the drivetrain 18. Torque ripple is an increase and decrease in torque transmission over time. The harmonic response characteristics of the RAT can cause amplified lateral movment of the turbine driveshaft through twisting of the RAT strut. By increasing the lateral stiffness of the turbine driveshaft 22, these large amplifications can be moved outside of the operating range of the RAT and subsequently torque ripple can be reduced.

Any relative terms or terms of degree that used herein, such as “substantially”, “approximately”, “about”, “essentially”, “generally” and the like, should be interpreted in accordance with and subject to any applicable definitions or limits expressly stated herein. In all instances, any relative terms or terms of degree used herein should be interpreted to broadly encompass any relevant disclosed embodiments as well as such ranges or variations as would be understood by a person of ordinary skill in the art in view of the entirety of the present disclosure, such as to encompass ordinary manufacturing tolerance variations and the like.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A driveshaft for an aircraft ram air turbine, the driveshaft comprising:

a tubular body that defines an axis of rotation and that includes a forward portion and a frusto-conical portion located rearward of the forward portion; and

a flange adjoining the forward portion of the tubular body opposite the frusto-conical portion, the flange having a forward face and an opposite rear face,

wherein a ratio of an outer diameter of the forward portion of the tubular body to an inner diameter of the forward portion of the tubular body is in a range of approximately 1.423 to 1.425.

2. The driveshaft of claim 1 and further comprising:

a hub pilot located adjacent to the forward face of the flange, wherein a ratio of the outer diameter of the forward portion of the tubular body to the hub pilot diameter is in the range of approximately 1.359 to 1.380.

3. The driveshaft of claim 1, wherein a length of the tubular body, measured in an axial direction, is approximately 22.715 cm (8.943 inches).

4. The driveshaft of claim 1, wherein the frusto-conical portion is arranged at approximately 14° with respect to the axis.

5. The driveshaft of claim 1, wherein the forward face of the flange is arranged at approximately 2° with respect to the axis, and wherein the rear face of the flange is arranged at approximately 9° with respect to the axis.

6. The driveshaft of claim 1 and further comprising:

a hub pilot located adjacent to the forward face of the flange, wherein the hub pilot has a diameter of approximately 18.001 cm (7.090 inches), wherein a length of the tubular body, measured in an axial direction, is approximately 22.715 cm (8.943 inches), wherein the frusto-conical portion is arranged at approximately 14° with respect to the axis, wherein the forward face of the flange is arranged at approximately 2° with respect to the axis, and wherein the rear face of the flange is arranged at approximately 9° with respect to the axis.

7. A driveshaft for an aircraft ram air turbine, the driveshaft comprising:

a tubular body that defines an axis of rotation and that includes a forward portion and a frusto-conical portion located rearward of the forward portion; and

a flange adjoining the forward portion of the tubular body opposite the frusto-conical portion, the flange having a forward face and an opposite rear face,

wherein the frusto-conical portion is arranged at approximately 14° with respect to the axis, and

wherein the rear face of the flange is arranged at approximately 9° with respect to the axis.

8. The driveshaft of claim 7, wherein the forward face of the flange is arranged at approximately 2° with respect to the axis.

9. The driveshaft of claim 7, wherein an outer diameter of the forward portion of the tubular body is approximately 7.117 cm (2.802 inches) and an inner diameter of the forward portion of the tubular body is approximately 4.994 cm (1.966 inches).

10. The driveshaft of claim 7 and further comprising:

a hub pilot located adjacent to the forward face of the flange, wherein the hub pilot has a diameter of approximately 18.001 cm (7.090 inches).

11. The driveshaft of claim 7, wherein a length of the tubular body, measured in an axial direction, is approximately 22.715 cm (8.943 inches).

12. The driveshaft of claim 7, wherein the frusto-conical portion is arranged at approximately 14° with respect to the axis.

13. The driveshaft of claim 7 and further comprising:

a hub pilot located adjacent to the forward face of the flange, wherein the hub pilot has a diameter of approximately 18.001 cm (7.090 inches), wherein a length of the tubular body, measured in an axial direction, is approximately 22.715 cm (8.943 inches), wherein the frusto-conical portion is arranged at approximately 14° with respect to the axis, wherein the forward face of the flange is arranged at approximately 2° with respect to the axis, wherein an outer diameter of the forward portion of the tubular body is approximately 7.117 cm (2.802 inches), and wherein an inner diameter of the forward portion of the tubular body is approximately 4.994 cm (1.966 inches).

14. A ram air turbine assembly for an aircraft, the assembly comprising:

a turbine subassembly having a rotatable hub;

a gearbox positioned adjacent to the hub;

a strut positioned adjacent to the gearbox, wherein the strut supports the gearbox;

a power conversion device; and

a drivetrain operably connected between the turbine subassembly and the power conversion device, the drivetrain having a turbine driveshaft attached to the hub and located at least partially within the gearbox, the turbine driveshaft including: a tubular body that defines an axis of rotation and that includes a forward portion and a frusto-conical portion located rearward of the forward portion; and a flange adjoining the forward portion of the tubular body opposite the frusto-conical portion, the flange having a forward face and an opposite rear face, wherein a ratio of an outer diameter of the forward portion of the tubular body to an inner diameter of the forward portion of the tubular body is in a range of approximately 1.423 to 1.425.

15. A method of installing a driveshaft in an aircraft ram air turbine, the method comprising:

providing a driveshaft having a tubular body that includes a forward portion and a frusto-conical portion located rearward of the forward portion, and a flange adjoining the forward portion of the tubular body opposite the frusto-conical portion, the flange having a forward face and an opposite rear face, wherein a ratio of an outer diameter of the forward portion of the tubular body to an inner diameter of the forward portion of the tubular body is in a range of approximately 1.423 to 1.425;

positioning the driveshaft at least partially within a gearbox; and

operatively engaging the driveshaft in a drivetrain that extends between a turbine and a power conversion device.