CA2020909A1 - Process and apparatus for the release of a prestress initially applied to a mechanism such as a bearing on board a space vehicle - Google Patents

Process and apparatus for the release of a prestress initially applied to a mechanism such as a bearing on board a space vehicle

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Publication number
CA2020909A1
CA2020909A1 CA 2020909 CA2020909A CA2020909A1 CA 2020909 A1 CA2020909 A1 CA 2020909A1 CA 2020909 CA2020909 CA 2020909 CA 2020909 A CA2020909 A CA 2020909A CA 2020909 A1 CA2020909 A1 CA 2020909A1
Authority
CA
Canada
Prior art keywords
prestress
shape memory
memory material
release
spacer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
CA 2020909
Other languages
French (fr)
Inventor
Jean-Pierre Schoeffter
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Airbus Group SAS
Original Assignee
Airbus Group SAS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Airbus Group SAS filed Critical Airbus Group SAS
Priority to CA 2020909 priority Critical patent/CA2020909A1/en
Publication of CA2020909A1 publication Critical patent/CA2020909A1/en
Abandoned legal-status Critical Current

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Abstract

DESCRIPTIVE ABSTRACT

In space vehicles, mechanisms such as ball bearings (14, 14') are subject to an initial preload or prestress enabling them to with-stand the vibrations caused by the launch and without leading to any clearance or play. A member (34) made from a shape memory material e.g. makes it possible under the effect of its elongation, to release said preload when the vehicle is in the operational mode. The con-trol of the release can take place by means of a heating resistor (36), whose energization leads to the member (34) clearing its shape change temperature.

(Fig. 1) SP 5675.69 GP

Description

P~OCESS AND APPARATUS FOR THE RELEASE OF A PRESrRESS INITIALLY
.. .. ~
APPLIED TO A MECHANI9M SUCH AS A BEARING ON ~oA~D A SPACE VEHICLE

DESCRIPrION

The invention relates to a process ar~ an apparatus for releas m y a prestress or preload initially applie~ between the moving parts of a mechanisrn such as a bearing on board a space vehicle, when the latter is in the cperational mcde.

Space vehicles such are artificial satellites and orbiting stations have equipment such as solar panels, antennas, etc., which incor-porate mechanisms penmitting relative rr~ov~nents between the parts forming thern when the vehicle is in orbit. These mechanisms are usually ball bearings, but can also comprise screw-nut syst~ns and bearings of various types.

During the launch of space vehicles, said mechanisms are subject to high mechanical stresses. In the case of ball bearings, the stresses are transmitted fn~n one ring to the other whilst passing through the balls. The presence or creation of clearances during said phase would therefore lead to shocks between the balls and the rings, leading to surface deterioration and in the long tenm to an unsatis-factory operation and then a deterioration of the bearing. Thus, it is conventional practice to apply a preload or prestress to said mechanisn to avoid any clearance or play occurring therein at the tIme of launch.

~owever, sai~ preload or prestress is limited to a minimum value, so as not to have an excessively disadvantageous effect on the mechanism under operational conditions. Thu5, under these conditions, only a prestress approximately ten times lower than that to be applie~ during the launch is really necessaryO Thus, when the vehicle is in the cperational m~de, any increase in the prestress no~mally leads to an increase in the resistant torque of the mechan-ism, operational irregularities linked with the fluctuation of saidtorque and a limitation to the service lifeO

SP 5675.69 GP
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Therefore, in practice, the prestress or prelo~d c~pplied to the mechanisms is the result of a compramise between contradictory requirements at the time of la m ch c~ld during the flight of the space vehicle. Thus, in the particular case of a ball bearing, the latter is dimensioned by determuning the static forces representing the vibrational loads which it underg æ s during launch a~d then to said bearing is applied a minimum prestress, which is approximately equal to one third of these static forces. This prestress must be accur-ately applied (approximately 20%), which makes it necessary to use sensitive strain gauges c~nd leads to a difficult, long and expensive procedure. This method also requires interfaces, which are not always compatible.

In view of the fact that to these mechanisms is applied a limited prestress, the risks of creating clearances during launch are not completely eliminated in the presence of high forces, Consequently, it is also standard practice to place between the moving parts of the mechanisms or between the components connected thereto, a rigid member by which part of the loads produced during launch are transmitted. When the space vehicle is under operational conditions, said rigid member must be broken by means of a pyrotechnic control.

The present invention consequently relates to a process and an appar-atus making it possible m a particularly simple and non-constraining manner, to release the prestress applied during launch to the mech-anisms, such as ball bearings on board space vehicles, when saidvehicles arrive in the operational mcde, which makes it possible on the one hand to make said prestress limit-free and consequently avoid any risk of deterioration to the mechanisms during the launch phase and on the other hand limit the prestress in the cperational mode without it being necessary to use a rigid member linked with a pyro-technic control.

According to the invention this problem is solved by means of an 5P 5675.69 GP

_ 3 _ 2 ~

apparatus for the release of a prestress or preload initially applied by prestressing or preload m g means between the moving paYts of a mechanism on board a space vehicle, when the latter is in the oper-atialal mcde, characterized m that it comprises a member made frcn a shape memory material associated with the prestress or preload means, so as to control a rele~se of the prestress or preload applied be-tween said parts under the effect of a change to its shape, when clearing a phase change temperature of the shape memory material.

It is pointed out that a shape memory material is a matexial having two stable crystalline phases, respectively an austenitic and a martensitic phase, as a function of whether its temperature is above or below the structural txansformation temperature characteristic of said material. When the material is in the martensitic phase and is exposed to a mechanical stress, it is plastically deformed and retains said deformation for as long as the temperature remains below its structural transformation temperature. As scon as the temperature exceeds this thxeshold, the structure beccmes austenitic again and the material reassumes its initial shape.

m e shape change of the material prcduced by the clearing of the phase change temperature may in particular consist of an elongaticn.
The member made fm m the shape menory material then acts as a jack, which is adjusted prior to launch to a size such that a high pre-stress is applied to the mechanism by the prestressing means. The heating of the material, which can be ensured either by a heating means such as an electrical resistor positioned in the vicinity of the shape memory material member, or by means of solar energy, elong-ates the said member, which has the effect of releasing the prestress applied to the mechanism.

The invention also relates to a process for the release of a pre stress or preload initially applied between moving parts of a mech-anism carried on board a space vehicle when the latter is in the operational mode, character~zed in that it consists of controlling SP 5675.69 GP

2~J?~
a shape change of a member made from a shape memory material associ-ated with said mechanism, so as to bring about a release of the prestress applied between the parts by m2Xing æaid member clear a phase change temperature of the shape memory material.

The invention is described in greater detail hereinafter relative to non-limitative e~bodiments and the attached drawings, wherein show:
Fig. 1 A lcngitudinal sectional view of a hinge or joint on board a space vehicle ha~ing two ball bearin~s to which is applied an axial preslless or preload, said arrange-ment being provided with an apparatus according to the invention for releasing said prestress or preload and which is shcwn in its initial inactive state.
Fig. 2 A view comparable to fig. 1, in which the prestress release apparatus is shown in its actuated state.

The joint shcwn in fig. 1 is e.g. the joint of a solar panel of a satellite or orbiting station. This joint ccmprises a spindle 10, which is assumed to be fixed in the represented embodi~ent, as well as an outer sleeve 12 mounted so as to rotate on the spindle 10 via two ball bearings, 14, 14'. Each of the bearings 14, 14' respecti~ely comprises an inner r m~ 16, 16', an outer ring 18, 18' and balls 20, 20' rolling between the rings.

The inner rings 16, 16' are mounted on the spindle 10 between a shoulder lOa shaped onto the latter and a tubular spacer 22 arranged coaxially ar wnd the spindle 10. The opposite end of said spacer 20 is positioned facing a nut 24 screwed onto a threaded end lOb of the spindle 10, a thrust washer 26 being interposed between the n~lt 24 and tne spacer 22.

The nut 24 and the threa~ed end lOb of the sp mdle 10 consequently constitute the precha~ging or prestressing means by means of which an axial prech~rye or prestress can be applied to the fixed inner rings 16, 16' of the bearings 14, 14'. A tubular spacer 28 placed SP 5675.69 GP

_ 5 _ 2~2~

between the rings 16, 16' ensures the transfer of said prestress from one ring to the other.
The outer rotary rings 18, 18' are mcNnted in the outer sleeve 12 between a shculder 12a and a nut 30 screwed into a reamed end 12b of the sleeve. A tubular spacer 32 is also placed between the outer rings 18, 18'.

The strucbure described hereinbefore is of a conventional nature, with the exception of the tubular spacer 22, the thrust washer 26 be m g normally in direct contact with the irmer ring 16' of the bearing 14', According to the invention, to said structure is added a supplementary part constituted by a second tubular spacer 34, which is made from a shape memory material and which is positioned coaxially within the spacer 22 around a reduced diameter portion lOc of the spindle 10 on which is formed the threaded end lOb. More specifically, the tubular spacer 34 is placed between a shoulder lOd of the spir~le 10 located in a plane adjacent to the end face of the inner ring 16' on which bears the spacer 22 and a shoulder 22a formed in said spacer in the vicinity of the washer 26.

In the position illustrated in fig. 1 and which correspcnds to the ground fitting position of the joint and which remains unchanged throughout the launch of the space vehicle on which said joint is carried, an axial clearance Jl exists between the spacer 34 and the shoulders lOd and 22a. Consequently, the prestress obtained by tightening the nut 24, which is transmitted by the spacer 22 to the inner rings 16' and 16 of the bearings 14' and 14 is not supported by the shape memory material spacer 34O

The shape memory material for producing the tubular spacer 34 is chosen as a function of the conditions of use, taking acccunt more particularly of the phase change temperature Gf the alloy. In a non-linitative manner, it is possible to use for the purposes of the SP 5675.69 GP

mvention shape memory materials in the form of iron-based allcys (Fe-C, Fe-Cr, Fe-Ni...), cuprcus alloys or noble metals (Cu-Zn, Cu-Sn, Cu-Al, Cu-Zn-Al, Cu-Zn-Al-Ni, Cu-Al-Ni, Ag-Cd, Au-Cd,~..), allcys based on titanium and/or nickel (Ni-Ti, Ni-Ti-Fe, Ni-Al, ...) and certain pure metals (Cn, Ti, Na)~

In the embodiment illustrated in the drawings, the heating of the shape memory material tubular spacer3~ up to its transformation temperature is obtained by means of a heating device e.g. constituted by an electrical resistor 36 directly wound ara~nd the spacer 34.
Electrical conductors 38 make it possible to connect sa;~ resistor 36 to a not shcwn pcwer supply carried on the space vehicle, via a not shown switch, which is open at the time of launch.

When said switch receives a closing instruction, the spacer 34 made from the shape memory material is heated to a temperature ab we its structural transformation temperature. Therefore the structure of said material again becomes austenitic, which has the effect of making it reassume its initial shape which, in this case, corresponds to a greater length of the spacer 34.

As illustrated in fig. 2, an adequate dimensioning of the components of the assembly has the effect, during the elongation of the spacer 34, of bringing abcut a penmanent elongation of the reduced diameter portion lOc of the spindle 10, as a result of the spacer 34 bearing against the shoulders lOd and 22a. Under these conditions, the prestress initially applied to the inner rings of the bearings via the spacer 22 is released and a clearance ~2 appears between the spacer 22 and the mner rings 16, 16' of the bearings.

In the e~bcdiment illustrated in figs. 1 and 2, said clearance J2 is eliminated by positioning, during installation, at least one elastic washer 40 or any technically eguivalent means, between the inner ring 16' and the spacer 22. Under the cperational conditions, said elastic washer 40 maintains a slight axial prestress or preload, SP 5675.69 GP

- 7 - 2~2~

which has the effect of eliminating the clearance J2.

In order to facilitate the elongation of the reduced diameter portion lOc of the spindle 10, sald portion lOc is advantageously machined at lOe over part of its length, in order to further reduce its cross-section and as illustrated in the drz~ings.

Ir. a not shcwn variantt the heating of the shape memory material isobtained withwut using the electric pcwer of the satellite, by orienting the latter following its placing in orbit, m such a way that the material is heated by solar pcwer.

In an arrangement which is the reverse of that describeA hereinbefore, i.e. m which the rotary spindle is mounted in a fixed sleeve via one or more bearings, an identical stxucture is used in order to initially appl~ an axial prestress or preload to the outer ring of the bearings.

If in future a shape memory material becomes available, which has mechanical characteristics enabling it to support the prestress applied, e.g. by means of the nut 24, it could be directly used for producing the spacer 22~ The clearing of the phase change temper-ature of this material would then directly eliminate the prestress by a length reduction of said spacer.

As a result of the apparatus accor~ing to the invention, simple and small means are used for bring mg about a release ~f the prestress initiaLly applied to mechanisms such as bearings or nut-screw systems on board space vehicles, as soon as the latter are in the operational mode. The risks of creating clearances in these mechanisms during launch are consequently eliminated, because a significantly higher prestress than previously can then be applied. Moreover, the elim-ination of the limitation to said prestress makes it possible to significantly simplify the prestress application procedure~ which now only requires an accuracy of + 100~. It is also pcssible to 2 ~
avoid the need for interposing a rigi~ member during launch and of breaking said member following launch by means of a pyrotechnic control, which obviates all the disadvantages inherent in such a system. Fina Uy, the elimination of the prestress in the operational mode, or the application of a very low prestress significantly increases the reliability of the mechanisms.

Moreo~er, the advantages inherent in shape memory materials are added thereto. Thus, the reliability of a mechanism ccn~rolled in this way is total, its cperation prcducing neither shocks, nor pollution and its cverall dimensions are very small.

Obviously the invention is not limited to the embcdiment described in exemplified manner hereinbefore and instead ccvers all variants thereof. As has already been observed, its application is not linited to ball bearings. In addition, the structure of the pre-stressing means can also differ from that described, as can the shapeof the shape memory material p rt. Finally, the relative rotation between the two parts of the mechanism can be unlimited or, on the oontrary, can be limited to angles below 360~

SP 5675.69 GP

Claims (10)

1. Apparatus for the release of a prestress or preload initially applied by prestressing or preloading means between the moving parts of a mechanism on board a space vehicle, when the latter is in the operational mode, said apparatus comprising a member made from a shape memory material associated with the prestress or preload means, so as to control a release of the presetress or preload applied between said parts under the effect of a change to its shape, when clearing a phase change temperature of the shape memory material.
2. Apparatus according to claim 1, wherein the mechanism comprises at least one bearing having a fixed ring and a rotary ring between which are placed the rolling members, the prestressing means acting on the fixed ring via a first tubular spacer, so as to initially apply an axial prestress to said fixed ring.
3. Apparatus according to claim 2, wherein the shape memory material member is a second tubular spacer arranged coaxially to the first spacer, the clearing of the phase change temperature having the effect of elongating the second spacer and of transferring the pre-stress from the fixed ring to the second tubular spacer.
4. Apparatus according to claim 2, wherein the prestressing means act on said parts via elastic means.
5. Apparatus according to claim 4, wherein the elastic means are interposed between the first tubular spacer and the fixed ring of the bearing.
6. Apparatus according to claim 2, wherein the fixed ring is an inner ring of the bearing mounted on a fixed spindle, the prestressing means incorporating a nut screwed onto a threaded end of said spindle traversing the first tubular spacer.
7. Apparatus according to claim 2 also comprising heating means SP 5675.69 GP

located in the vicinity of said shape memory material member.
8. Process for the release of a prestress initially applied between the moving parts of a mechanism carried on a space vehicle, when the latter is in the operational mode, comprising controlling a shape change of a shape memory material member associated with said mech-anism, so as to obtain a release of the prestress applied between the parts by making said member clear a phase change temperature of the shape memory material.
9. Process according to claim 8, wherein said member is made to clear the phase change temperature of the shape memory material by heating said member with the aid of heating means located in the vicinity thereof.
10. Process according to claim 8, wherein said member is made to clear the phase change temperature of the shape memory material by heating the member by solar power.

SP 5675.69 GP
CA 2020909 1990-07-11 1990-07-11 Process and apparatus for the release of a prestress initially applied to a mechanism such as a bearing on board a space vehicle Abandoned CA2020909A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CA 2020909 CA2020909A1 (en) 1990-07-11 1990-07-11 Process and apparatus for the release of a prestress initially applied to a mechanism such as a bearing on board a space vehicle

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CA 2020909 CA2020909A1 (en) 1990-07-11 1990-07-11 Process and apparatus for the release of a prestress initially applied to a mechanism such as a bearing on board a space vehicle

Publications (1)

Publication Number Publication Date
CA2020909A1 true CA2020909A1 (en) 1992-01-12

Family

ID=4145453

Family Applications (1)

Application Number Title Priority Date Filing Date
CA 2020909 Abandoned CA2020909A1 (en) 1990-07-11 1990-07-11 Process and apparatus for the release of a prestress initially applied to a mechanism such as a bearing on board a space vehicle

Country Status (1)

Country Link
CA (1) CA2020909A1 (en)

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