GB2028952A

GB2028952A - Longitudinally Adjustable Strut

Info

Publication number: GB2028952A
Application number: GB7908840A
Authority: GB
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1978-03-17
Filing date: 1979-03-13
Publication date: 1980-03-12
Also published as: FR2420162B1; IT7920856A0; DE2811678A1; GB2028952B; FR2420162A1; IT1110508B

Abstract

A longitudinally adjustable strut for use, mainly in the rotor head of a helicopter, provides simple manual adjustment of length with positive engagement of the parts to prevent accidental movement. The strut has a casing 4 which engages respective rod parts 12 and 14 by opposite hand threads so that rotation of the casing produces extension or retraction of the rod parts and hence the strut. A sleeve 26 engages the casing 4 telescopically and is urged by a spring 36 into the securing position shown where the sleeve interlocks with the casing and a flange 32 of the rod part 12 by means of splines (28, 30) to prevent movement. The sleeve may be slid downwardly to release the splines from flange 32 to effect adjustment by manual rotation of the casing through the sleeve. <IMAGE>

Description

SPECIFICATION A Longitudinally Adjustable Strut Primarily for Use in a Heiicopter Rotor Head This invention relates to a longitudinally adjustable strut, primarily for use as a control rod in a control linkage for a helicopter rotor head assembly.

An object of this invention is to provide a strut for manual adjustment having no loose parts and which can be constructed to have considerably reduced radial dimensions as compared with known arrangements for use in restricted spaces, such as the control rod for adjustment of the blade pitch angle in a helicopter rotor.

According to this invention there is provided a longitudinally adjustable strut with a casing having screw thread engagement with two threaded rod parts by means of opposite hand threads with a securing means for releasably interlocking the casing and a rod part, the securing means having a sleeve which is displaceable in a longitudinal direction against spring force from a retaining position in which it non-rotatably interconnects the casing and a threaded rod part to a release position in which the casing and rod part are rotatable to effect adjustment.

In the strut of the invention the automatic interlocking is ensured by a sleeve which is mounted in a longitudinally displaceable manner on the casing or on one threaded rod part and which is forced by a spring, acting longitudinally of the strut, into the retaining position, in which it is connected both with the threaded rod part and with the casing so that it cannot rotate in relation thereto. In any position of the casing, the sleeve can be moved back into the release position without difficulty, and has a slightly larger outer diameter than the casing, so that the strut can be used without difficulty in restricted spaces. The strut has no free components, which would require release and removal for adjustment and ensures reliable automatic interlocking.

Preferably the sleeve, in the released position, is separated from engagement with one threaded rod part but remains non-rotably connected with the casing, so that both the release of the securing means and the rotation of the casing can be carried out manually with one hand and without use of tools. To facilitate the manual operation still further the sleeve is advantageously arranged to form a grip which surrounds the casing in a telescopic manner and which can be rotated and slid back by hand. The splines of one threaded rod part are preferably covered, in the retaining position, by the sleeve and when pushed back into the release position they are exposed to see by a visual inspection, whether correct interlocking has taken place after the securing sleeve has been released.If the interlocking is not effected correctly the sleeve is forced against one threaded rod part towards the securing position by a spring so that the casing rotates in relation to the threaded rod part by a certain small angle only until the sleeve under the action of the spring automatically attains the securing position and again completely covers the splines of one threaded rod part.

To ensure interlocking of mutually engaging splines extending longitudinally of the strut and formed on the sleeve and the casing or one threaded rod part, the angle of rotation between the retaining positions of the casing, is made small by selection of an appropriate number of serrations.

The two threaded rod parts are preferably interconnected so that they cannot rotate in relation to each other but can move longitudinally, so that by using a single securing means both screw connections between the casing and the threaded rod parts can be made and the relative rotational position between the threaded rod parts remains unaltered over the entire adjusting range of the strut.

An embodiment according to the invention is described by way of example with reference to the accompanying drawings, wherein Figure 1 shows a side view, partly in section, of a longitudinally adjustable strut according to the invention, and Figure 2 shows a section on 2-2 of Figure 1.

The drawing shows a longitudinally adjustable strut with a rod unit 2 which when used in the control assembly in a helicopter rotor head system is positioned between the rotating swash plate and the rotor blade and serves as a linkage for control of the blade pitch angle. Adjustment of length of the control rod 2 is required for setting the tracking of the rotor and is effected by a single access aperture in a housing which surrounds the rotating control linkage parts. This is not shown in the drawing.

The rod unit 2 includes an adjusting casing 4 with threaded portions 8 and 10 which are separated from each other by a groove 6. The threading is of opposite hands in the respective sections and is engaged by two threaded rod parts 12 and 14 with threaded portions 1 6 and 1 8 respectively. By rotating the casing 4, the length of the rod unit 2 can be altered. The rod parts 1 2 and 14 are inter-connected so as to be non-rotatable but longitudinally extensible by a sliding connection formed from a slot 20 and dog 22. The extension of the parts 12 and 14 is limited by a circlip 24 at the lower end, as viewed in Figure 1, engaging the casing 4 and forming a stop against which the threaded section 1 8 of the part 14 abuts at the end of its travel.This arrangement for the unit 2 is conventional.

In order to retain the casing 4 in a selected position on the parts 12 and 14 against unwanted turning movements, the unit 2 is provided with a securing means which comprises a sleeve 26 located around and longitudinally displaceable on the casing 4. In the position shown the sleeve 26 in interlocked with the threaded part 12 thus preventing relative rotary movement. For this purpose the internal diameter of the sleeve 26 has splines 28 which extend longitudinally from the upper end of the sleeve and which, when the sleeve 26 is in the retaining position, engages both with splines 30 on a flange 32 of the part 12 and also with splines 34 formed on the outer diameter of the casing 4 in the region of the upper end of the casing as viewed in Figure 1.The length of the splines 28 is selected to ensure that over the entire range of adjustment of the control rod 4 they remain always engaged with the splines 34 when the sleeve 26 is longitudinally displaced on the casing 4.

The sleeve 26 when in the retaining position is subject to force of a helical compression spring 36 which locates in an annular recess 38 in the casing 4 and which bears on the sleeve 26 through a sliding ring 40 bearing against the lower end of the serrations 28, and also on the sleeve 4.

The displacement of the sleeve 26 is limited by a circlip 42 which, in the region of the splines 28, locates in the sleeve 26 at a distance from the upper end thereof which corresponds to the width of the flange 32. In the retaining position shown, in which the splines 30 engage over the whole length, with the splines 28 and in which they are completely covered by the sleeve 26, the circlip 42 contacts the flange 32, while the movement of the sleeve 26 in the opposite direction and against the force of the spring 36, is stopped by the circlip 42 bearing against the upper end of the casing 4.

To adjust the unit 2 the sleeve 26 is moved longitudinally on the casing 4 and in opposition to the force of the spring 36, until the splines 28 disengage from the splines 30, after which, by rotating the sleeve 26, the casing 4 is rotated as the splines 28 and 34 remain engaged even when the sleeve 26 has been slid back. When the control rod 2 is adjusted as required to the desired position, the sleeve 26 is released and returned by the spring 36 to the retaining position in which it holds the casing 4 against rotation in relation to the threaded rods 12 and 14. If the splines 28 are not aligned with the splines 30, so that the sleeve 26 cannot be slid back into the retaining position after release then this is easily observed.In such a position the sleeve 26 is rotated further until a position is reached and the sleeve 26, under action of the spring, has been moved into the retaining position. In any case the casing 4 cannot rotate farther than the next adjustment position as the sleeve 26 is engaged with the flange 32 by means of the spring 36. By selection of a sufficient number of splines 28, 30, 34, evenly arranged around the diameter, with twenty splines, as example, the angle of rotation between adjacent adjustment positions can be kept small.

In order to facilitate the operation of sliding back and rotating the sleeve 26, the upper end thereof is thickened and knurled to provide a grip.

The part 14 may have a mark 44, with graduations 46 forming a Vernier scale provided at points on the casing 4 which correspond to the engaged positions, so as to simplify the adjustment and readjustment of the unit 2.

Claims

1. A longitudinally adjustable strut with a casing having screw thread engagement with two threaded rod parts by means of opposite hand threads with a securing means for releasably interlocking the casing and a rod part, the securing means having a sleeve which is displaceable in a longitudinal direction against spring force from a retaining position in which it non-rotatably interconnects the casing and a threaded rod part to a release position in which the casing and rod part are rotatable to effect adjustment.

2. A strut in accordance with Claim 1, wherein the sleeve when in the release position, is separated from interlocking engagement with a threaded rod part while remaining engaged with the casing in a non-rotatable manner

3. A strut in accordance with Claim 1 or 2,wherein the sleeve is formed as a manual grip which surrounds the casing and is slidable telescopically in relation thereto.

4. A strut in accordance with Claim 2 or 3, wherein the means forming the interlocking connection of one threaded rod part and casing is covered over by the sleeve when the same is in the retaining position and exposed when the sleeve is slid back into the release position.

5. A strut in accordance with any one of the preceding claims, wherein splines extend in a longitudinal direction and provide engagement between the sleeve and the casing or the one threaded rod part.

6. A strut in accordance with any one of the preceding claims, wherein the two threaded rod parts are interconnected in a non-rotatable but longitudinally displaceable manner.

7. A strut constructed and arranged to function substantially as herein described with reference to and as shown in the accompanying drawings.