GB1596573A

GB1596573A - Mechanical shock arrester

Info

Publication number: GB1596573A
Application number: GB374078A
Authority: GB
Original assignee: Pacific Scientific Co
Current assignee: Pacific Scientific Co
Priority date: 1977-03-10
Filing date: 1978-01-31
Publication date: 1981-08-26
Also published as: FR2383360A1; CA1080758A; FR2383360B1; JPS53118674A; JPS5736450B2; DE2810510A1

Description

(54) MECHANICAL SHOCK ARRESTER (71) We, PACIFIC SCIENTIFIC COM- PANY, a corporation organized under the laws of the State of California, United States of America, of 1346 South State College Boulevard, Anaheim, State of California 92803, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to apparatus for limiting acceleration of two relatively moving members to a predetermined threshold, and more particularly, to an improved all mechanical shock arrester or motion snubbing device.

In U.S.A. Patent No. 3,876,040, there is described an acceleration sensitive motion snubber that is particularly useful in snubbing motion which occurs from earthquakes or other rapidly accelerating forces. Such devices permit slow acceleration such as that which occurs due to temperature changes but will prevent rapid acceleration while stili permitting continued movement at the lower acceleration levels. The device shown in U.S.A. Patent No. 3,876,040 is particularly useful in connection with atomic energy electric generating plants because it is highly reliable and is not affected by radiation, as are hydraulic snubbers.

The present invention relates to improvements in an acceleration sensitive mechanical shock arrester of the general type de scribe in the above-mentioned patent. Such shock arrester has been very successful.

particularly in the smaller sizes. however.

with struts for handling exceedingly large loads such as that which might be imposed on struts attached directly to major components within a nuclear reactor, the design shown in the above-mentioned patent can become larger than desired when having adequate strength. Thus, the present invention employs arrangements which are more compact and also highly reliable.

In accordance with one aspect of the invention, a motion snubbing device comprises a pair of members mounted for movement relative to each other. a pair of inertia elements mounted to be freely rotated, means connecting said members to said elements so that relative movement of said members in one direction will drive one of said inertia elements and relative movement of said members in an opposite direction will drive the other inertia element, and means interconnecting said inertia elements in a manner such that rotating either of the elements below a predetermined acceleration threshold causes such element to rotate the other inertia element, and attempting to rotate said other inertia element above said threshold initiates braking action on said elements and said members which limits acceleration to said threshold.

In accordance with another aspect of the invention, a motion snubbing device comprises a pair of members mounted for relative movement with respect to each other: and acceleration sensitive means connected to said members for limiting movement of either of the members relative to the other member, in either of two opposite directions, to a predetermined threshold acceleration rate, said acceleration sensitive means including a pair of rotatably mounted inertia members and means responsive to said relative movement in one direction for rotating one of said inertia elements and responsive to said relative movement in the opposite direction for rotating the other one of said elements, means inter connecting said inertia elements in a manner such that rotation of the element being driven by said relative movement will further rotate the other one of said elements so long as the rotational acceleration is below said threshold, and attempted acceleration above said threshold will cause the inertia element driven by the other inertia elements to lag because of its inertia, and means responsive to said lagging movement preventing acceleration beyond said threshold.

In one form of the invention, the inertia elements are cylindrical and are mounted coaxially with two of their ends in face to face relation. Motion is transmitted between the inertia elements by means of a coil spring which surrounds the interfacing portions of the elements. If the force applied to the inertia elements exceeds a predetermined acceleration threshold, the inertia of the element being driven by the coil spring will cause that element to impose a lagging force on the spring which in turn will cause it to increase its diameter so that it will brake against a surrounding housing wall. This braking action prevents acceleration beyond the threshold.

In another form of the invention, the axial length of a strut employing the acceleration sensitive means has been minimized. A very short strut is needed in certain applications such as interconnecting fuel rod support tubes in a nuclear reactor. In such an axially short snubbing device, the inertia elements are made axially short so that they are disc shaped. The drive shaft for rotating the inertia elements is formed with high lead threads on opposite ends which cooperate with members to be attached to the fuel rod tubes or other structure whose motion is to be arrested. These connecting members are slidably mounted for axial movement in the ends of a housing containing the inertia elements and the slidable mounting arrangement prevents rotation of the connecting members. The threaded connections between the members and the shaft are such that moving the connecting members towards each other will produce rotation of the shaft in one direction and moving the connecting members away from each other will rotate the shaft in the opposite direction. This is preferably accomplished by having the threads on opposite ends of the shaft extend in opposite directions. Thus, both connecting members and both ends of the shaft are involved in converting axial movement of the device into rotation of the inertia elements.

In a presently preferred embodiment of the invention, axial movement of a fixed shaft on one strut member is transferred to the other member by being translated into rotation of a nut: the nut in turn transfers the rotation and the axial load directly to an inertia element which transfers the axial load through ball bearings to the other strut member. Interengaging portions of the strut member surround the inertia members which increases the strength of the strut enabling it to handle lateral or side loads better than with a strut of reduced diameter.

The invention will be further described, by way of example, with reference to the accompanying drawings in which: Fig. I is a longitudinal view through the longitudinal axis of a strut embodying one form of the invention; Fig. 2 is a cross-sectional view on line 2-2 of Fig. 1; Fig. 3 is a cross-sectional view on line 33 of Fig. I; Fig. 3a is a side elevational view illustrating the connection between an inertia element and the spring; Fig. 4 is a cross-sectional view on line 4-4 of Fig. 1; Fig. 5 is a longitudinal view through the longitudinal axis of a strut embodying another form of the invention; Fig. 6 is a view of the strut of Fig. 5 on line 66; Fig. 7 is a cross-sectional view of the strut of Fig. 5 on line 7-7; Fig. 8 is a cross-sectional view of the strut of Fig. 5 on line 8-8; Fig. 9 is a schematic perspective view illustrating the strut of Fig. 5 in use; and Fig. 10 is a longitudinal sectional view of a preferred embodiment of the present invention.

Referring now to Fig. 1, the shock arrester shown includes a pair of support or connecting members 10 and 12 which are telescopically mounted on each other for relative axial reciprocation. These support members are formed of several different components which are rigidly connected to move as a unit. Thus, the support members 10 and 12 each include an end tongue 14 and 16, respectively, which are adapted to be connected to the structures whose relative motion is being arrested. The tongue 14 is threadably attached to a heavy disc shaped end plate 18 which in turn is attached to a tubular or cylindrical housing 20.

Attached to the other end of the housing 20 is an end plate or flange 22 formed integral with a tube 24. The flange 22 is positioned against an annular shoulder in the housing wall 20 and is axially held in this position by a retaining ring 26. The flange 22 is also rotationally fixed with respect to the housing wall 20 by means of a series of pins 28, one of which is shown in Fig. 1.

The other end of the tube 24 is threaded to a tubular sleeve 30 which slid ably receives an elongated support tube 32, which is threadably attached to the tongue 16 of the support member 12. Threadably attached to the interior of the other end of the tube 32 is a tubular nut 34 which has an outwardly extending flange on one end that has a plurality of radially extending lugs 36, as seen in Fig. 4. These lugs fit within axially extending grooves formed between splines 38 on the interior of the tube 24 which is attached to the support assembly 10. Thus, it can be seen that the telescopic movement of the assemblies 10 and 12 occurs by the tube 32 axially sliding within the tube 24 and its sleeve 30. The cooperation between the nut lugs 36 and the splined interior 38 of the tube 24 prevents rotation of the assemblies 10 and 12. The strut is shown in its fully telescoped position with the end of the sleeve 30 engaging the interior end wall of the tongue 16.

The interior of the tubular nut 34 is formed with a high-lead thread which mates with a high-lead thread formed on the exterior of the shaft 40 which extends within the tube 32 and into the housing 20. The portion of the shaft extending into the housing 20 has a section 42 with a slightly reduced diameter on which is threadably mounted a tubular load transfer member 44.

The member 44 is rotationally and axially locked on the shaft by means of a plug sleeve 46 which is forced between an axially ridged bore in the member 44 and an axially ridged section 48 formed on the shaft 40.

As seen from Fig. 1, the shaft through its load transfer member 44 is rotatably mounted within the housing 20 on the support assembly 10. This is accomplished by means of a schematically illustrated bearing 50 which extends between the inner end of the tube 24 and an annular shoulder 52 formed on one end of the load transfer member 44. Similarly. a bearing 54 is positioned between the interface of the end plate 18 and an annular shoulder 56 formed on the other end of the load transfer member 44.

The tip 58 of the shaft 40 is also rotatably mounted in the end plate 18; however, the axial load on the strut is carried on the bearings 50 and 54.

Between the housing wall 20 and the load transfer member 44. there is formed an annular cavity in which is positioned a pair of ring shaped or annularly shaped inertia elements 60 and 62. As may be seen from Fig. I. these members are identical and they are axially aligned within the cavity. However. they are mounted in opposed relation with the end face of one closely positioned adjacent the similar end face of the other. A suitable roller bearing unit 64 is positioned in recesses formed in the opposing end faces to facilitate the rotation of the inertia elements with respect to the other. The inertia element 60 is further rotatably mounted by a roller bearing 66 positioned between the inner wall of the element 6t) adjacent its axially outer end and the exterior of the tube 24 adjacent its end within the housing 20. Similarly. a bearing 68 is positioned between the inner wall of the inertia element 62 adjacent its axially outer end and the exterior of a cylindrical axial projection 18a on the end plate 18.

A coil spring 70 surrounds the portions of the inertia elements 60 and 62 adjacent their opposing ends. An annular recess 63 is formed in the elements 60 and 62 for receiving the spring. As may be seen from Fig. 1 the coil spring 70 is closely spaced from the surrounding housing wall 20. A shallow annular recess 72 may be formed in the wall 20 for receiving the coil spring with the desired spacing, although it is not critical.

The ends of the coil spring 70 are interconnected to the inertia elements 61 and 62 so that rotation of one inertia element will rotate the other element through the spring.

More specifically one end 70a of the spring, as shown in Fig. 3a, engages a radial shoulder 62a formed on the inertia element 62. The shoulder 62 is created by forming the end wall 62b of the recess 63 in the inertia element 62 so that it conforms to the spirally sloping end surface of the spring 70. The other end of the spring 70 is similarly, though reversely, positioned with respect to the inertia element 60.

The load transfer member 44 is formed with a plurality of axially and radially extending teeth or ribs 74 as may be seen in Figs. 2 and 3 which define spaces between them. The inertia element 60 is similarly formed with inwardly extending ribs or teeth 76 which fit within the grooves defined between the teeth 74 on the load transfer nut; however, the grooves between the teeth 74 and the grooves between the teeth 76 are larger than the teeth positioned therein so that in the position shown in Fig. 2, one edge of each tooth 74 is engaged with one edge of each tooth 76 but the other edges of the teeth are spaced circumferentially a distance greater than the width of the teeth.

Referring to Fig. 3, the inertia element 62, being identical to the element 60 also has inwardly extending teeth 78 which engage the teeth 74. However, in this instance, it is the other edge of each tooth 74 which engages the edge of the teeth 78. This occurs because of the reversal of the elements 60 and 62. The location of the teeth 76 and 78 on the inertia elements is circumferentially oriented or related to the location of the radial shoulders on the inertia elements that are engaged by the ends of the coil spring 70 so that the load transfer nut teeth 74 are oriented with respect to the inertia element teeth as shown in Figs. 2 and 3.

Operation When an axial force is applied to the strut causing it to become shorter or longer, the axial force is applied to the shaft 40 by means of the nut 34. The high-lead threads of the nut and shaft will produce rotation of the shaft as the strut members 10 and 12 are axially moving relative to each other. The rotation of the shaft 40 of course, rotates the load transfer member 44 which is attached thereto. Relative axial motion of the strut members in one direction will produce counterclockwise rotation, and the teeth 74 on the load transfer member 44 will engage and drive the teeth 76 formed on the inertia element 60 as shown in Fig. 2. However, referring to Fig. 3, it can be seen that the load transfer member does not drive the inertia element 62 with a counterclockwise rotation because the teeth 74 would tend to move away from the teeth 78.

Rotation of the inertia element 60 in a counterclockwise direction also rotates the coil spring 70 since the end of the spring engages the shoulder on the inertia element to cause such rotation. Rotation of the coil spring 70 in turn drives the inertia element 62 through the end 70a of the spring 70 engaging the shoulder 62a as shown in Fig. 3a. So long as the acceleration of the telescoping movement of the strut and the resulting rotation of the shaft and load transfer member is slow, the inertia element 62 simply follows the movement of the inertia element 60 and the relationship of the components remains as illustrated in the drawings. Thus, the strut can accommodate slow movement such as that produced by the thermal expansion and contraction of the components and structures to which the strut is attached.

However, if the relative movement received by the strut approaches a predetermined acceleration threshold, the inertia of the inertia element 62 which is being rotated through the coil spring 70 will cause the element to lag rotationally because of the resiliency of the spring. This lagging rotation can be further understood by referring to Fig. 3 and visualizing the teeth 74 moving in a counterclockwise direction away from the teeth 78. The lagging movement of the inertia element 62 introduces a force or load which tries to compress the spring 70 along its spiral axis which causes the diameter of the coils to expand and frictionally engage the inner surface of the housing wall 20. This frictional engagement produces a braking action which limits the acceleration of the inertia elements, which in turn brakes or restricts the rotation of the load transfer member and the shaft 40. Referring to Fig. 3, the width of the slots between the teeth is such that the lagging movement of the inertia element 62 can be accommodated without the teeth 78 interfering with the teeth 74.

When the accelerating force attempting to cause movement beyond the acceleration threshold is snubbed. the coil spring can relax and return the inertia element 62 to its normal position in relation to the load transfer member 44 as shown in Fig. 3. The telescoping movement of the strut does not stop with this braking action produced by the coil spring and the inertia elements. Instead, the motion continues but at an acceleration rate which is below the predetermined threshold.

If the telescoping force on the strut is such as to produce rotation of the shaft 40 in the opposite or clockwise direction, the operation of the strut is the same with the exception that the inertia element 62 becomes the element positively or directly driven by the load transfer member 44 and the inertia element 60 is driven through the coil spring.

More specifically, the teeth 74 on the load transfer member 44 positively drive the teeth 78 on the inertia element 62 as shown in Fig.

3. This force is then in turn transferred to the coil spring 70 by virtue of the shoulder 62a on the inertia element shown on Fig. 3a engaging the end of the coil spring 70. The spring then drives the element 60. Thus, it can be seen that the load transfer member positively drives either of the inertia elements depending upon the direction of rotation but it only positively or directly drives one of them at a time, and the element not directly driven by the load transfer member is instead rotated by means of the coil spring.

Enihodirneni of'Figs. 5 to 9 The embodiment of figs. 5 to 9 is similar to that of the embodiment of Figs. I to 4 in that its employs a pair of inertia elements selectively driven by a rotating shaft and interconnected by a coil spring. However. the structure is otherwise greatly modified and simplified to form a very compact and axially short strut 79 having a minimum number of parts.

There is shown a tubular or cylindrical housing 80 clamped between a pair of end plates 82 and 83 by a plurality of bolts 84 extending through the corners of the plates.

Attached to and extending outwardly from the end of each plate is a pair of guide pins 86. A pair of identical support or attachment members 88 is slidably mounted on the guide pins 86 for axial movement while being prevented from rotation. The members 88 are each provided with a pair of bores 89 for receiving the guide pins 86. The members 88 are further provided with an opening 90 through which connection is made to the structure whose motion is being snubbed or arrested. Each of the members 88 is further provided with a tubular extension 92 which extends into the end plates 82 and 83. The tubular extensions are internally threaded to mate with the threads on the end of a shaft 94 which extends through the housing coaxial with the cylindrical wall 80. The threads on the tubular extensions 92 and on the ends of the shaft 94 are of the high-lead type so that axial movement of the members 88 will produce rotation of the shaft. Note from Fig.

5 that the threads on one end of the shaft are left-hand and the threads on the other end of the shaft are right-hand. With this arrange ment, the end members 88 can have the same pitch internal thread and movement of the members 88 towards each other will produce rotation of the shaft 94 in one direction and movement of the members 88 away from each will rotate the shaft 94 in the opposite direction.

Positioned within the housing 80 is a pair of inertia elements 96 and 98 which have a generally tubular or ring shape surrounding the shaft 94. The inertia elements 96 and 98 are rotatably mounted, but this is accomplished without the use of any roller or ball bearings, The inertia elements 96 and 98 are identical in shape and are axially aligned.

However, they are positioned with their similar faces in opposing relation. A washer or ring shaped spacer 100 extends between these opposing faces to give them a slight clearance and keep the inertia element 96 and 98 on the relative center of the shaft 94.

The housing is also thereby centrally positioned between the members 88. The other axial ends of the inertia elements are formed with axially extending tubular portions 102 which fit within sockets 104 formed in the end plates 82 and 83. The tubular portions 102 and the sockets 104 provide bearing surfaces for the inertia elements which rotationally and axially position the elements.

A spirally shaped coil spring 106 is positioned within annular recesses formed on the exterior of the inertia elements adjacent the opposing faces. The ends of the coil spring engage shoulders, (not shown) on the inertia elements in a manner similar to that explained in connection with the embodiment of Figs. 1 to 4. The outer periphery of the coil spring 106 is closely spaced from the inner surface of the cylindrical wall 80.

A load transfer or collar 108 is fixed to the central section of the shaft 94 to rotate with the shaft. As with the arrangement of Figs. 1 to 4. the load transfer collar 108 is provided with a plurality of radially extending teeth 110 which cooperate with radially extending teeth formed on the inertia elements 96 and 98. More specifically, the teeth 110 of the load transfer collar are oriented to drivingly engage the teeth 112 of the inertia element 96 when the load transfer collar is rotated in a counterclockwise direction as viewed in Fig.

7. By contrast. the teeth 110 will drive the teeth 114 on the inertia element 98 when the load transfer collar 108 is rotated in the opposite or clockwise direction as shown in Fig. 8.

Operation It will be apparent that movement of the end members 88 towards each other will permit the members 88 to slide towards the end plates on the guide pins 86. This movement will rotate the shaft 94 in one direction due to the threads on the shaft and the members 88. If the motion is in, say, a counterclockwise direction, the load transfer collar 108 will positively drive or rotate the inertia element 96 in a counterclockwise direction as shown in Fig. 7. Element 96 will in turn rotate element 98 by means of the coil spring 106. So long as the acceleration remains below a predetermined threshold, the inertia elements will simply rotate as the strut telescopes. However, if acceleration reaches the predetermined threshold, the inertia element 98 will lag by virtue of its resilient connection through the coil spring and will cause the coil spring diameter to expand and frictionally engage the cylindrical wall 80 producing a braking action on movement.

As with the embodiment of Figs. 1 to 4, movement of the strut members in the opposite direction will produce the opposite rotation of the shaft 94. This in turn will cause the load transfer collar 108 to drive the other inertia element 98 by movement in the clockwise direction as shown in Fig. 8. The inertia element 96 then becomes the element driven through the coil spring 106 and the combination of the spring and the element 106 will sense the acceleration threshold to prevent acceleration beyond the threshold.

The device in Fig. 5 is particularly useful in situations wherein there is very limited axial space in which to position a snubber.

An example of this is in connection with the fuel rod guide tubes within a power generating nuclear reactor, It has been determined that it is desirable from a safety standpoint to interconnect the fuel rod tubes with devices which will snub or arrest rapidly oscillating forces such as that which might occur during an earthquake. The amount of relative movement which the device will be subjected to as a result of normal thermal changes is quite small. and thus the travel of the attachment members 88 with respect to the housing is limited, as determined by the guide pins X6 and retaining rings 116 positioned on the exterior of the tubular extension 92 on the attachment members 88.

The snubbing device of Fig. 5 is shown in Fig. 9 connected to such nuclear reactor fuel rod tubes. More specifically, there is shown a mounting bracket or structure 120 attached to a plurality of vertically oriented, closely spaced, parallel fuel rod tubes 122. The attachment bracket 120 has an outwardly extending lug 124 as best seen in Fig. 6, on which is mounted a stud 130. The snubbing device is positioned so that the stud 130 extends through the hole 90 in the connecting member 88. A suitable retaining element 132 fitting over the stud is shown on the other end of the device in Fig. 5. Thus, - several snubbing devices 79 may be attached between a group of fuel rod tubes as shown in Fig. 9 to provide the necessary capability for preventing the fuel rods from whipping violently and dangerously during rapid movement such as that in an earthquake.

Emhodintent of Figure 10 Fig. 10 shows a variation of the arrangement shown in Figs. I to 4. The form of the invention shown in Fig. 10 is a production model and hence, is presently the preferred form. The shock arrester shown includes a pair ,of strut members 210 and 212 which are telescopically mounted on each other for relative axial reciprocation. These strut members are formed of several different components which are rigidly connected to move as a unit. Thus, the support member 210 includes an end tongue (not shown) adapted to be connected to the structure whose relative motion is being arrested. Such tongue is threadably attached to a heavy disc-shaped end plate 218 which in turn is threaded to a tubular or cylindrical housing or casing 220 having inner bearing surfaces 220a and 220b. Fixed to the end plate 218 is an elongated shaft 240 which extends through a central opening in the end plate 218 and is threaded on the exterior of an enlarged head which mates with internal threads formed on the bore through the end plate. A retaining element 243 further locks the shaft in position.

The support member 212 includes an enlarged tongue 216 which is formed with an end plate 217. Surrounding the end plate and sliding within the tubular casing 220 is an elongated tubular housing member 224. The housing 224 is axially fixed to the end plate by a flange 224a which is captured between a shoulder 217a on the end plate and a retaining ring 226. This arrangement permits the tongue 216 to be rotated for alignment purposes in mounting. The other end of the tube 224 is threaded on its interior and mates with a tubular bearing support member 228.

The bearing support member 228 includes an enlarged end portion or plate which mates with the tube 224 and further includes a tubular portion of reduced diameter which surround the shaft 240. Pinned in a recess in the right end of the bearing support member 228 is a spline follower 230 having a plurality of circumferentially spaced grooves which slidably mate with axially extending spline teeth 241 on the exterior of the shaft 240.

This spline teeth and groove arrangement permits axial movement of one strut member relative to the other but prevents relative rotation.

On the other end of the bearing support member 228 is positioned a bearing race 242, which is held in place by a retaining ring 244.

Thus, it can be seen that the bearing support member 228 along with the bearing race 242 and the spline follower 230 are fixed to the tubular member 224 which is attached to the mounting tongue 216. In addition the strut member 212 includes a bearing support member 246 on the strut left end which is threadably attached to internal threads on a recess in the support plate 217. This bearing support member 246 like the support member 228 carries a bearing race 248 on the exterior surface of the inner end of the member and is held in position by a retaining ring 250. Thus, the strut member 212 forms a closed end structure which can slide axially relative to the strut member 210.

Positioned within the housing 224 is a torque transfer nut 254 which is threadably mounted on the threads 243 on the shaft 240.

The threads on the shaft and the mating threads on the torque transfer nut 254 are of the high-lead type such that axial movement of the shaft 240 relative to the transfer nut will cause the nut to rotate.

Surrounding the transfer nut 254 and extending within the annular space formed by the bearing supports 246 and 228 in similar screw or pin 273 extends into a hole in the inertia element 258.

In operation of the strut of Fig. 10, the overall result obtained is similar to that of the strut in Fig. 1. However, there are a number of operational and structural differences that provide certain advantages. The strut is shown in its most fully collapsed position. If a tension load is applied to the strut, the load is transmitted directly through the shaft 240 and the torque transfer nut 254 into the shoulder 258c of the inertia element 258. The load path is through the ball bearings 265 and into the bearing support member 228, the surrounding housing 224, and the tongue 216 of the support member 212.

Since the nut 254 is axially engaging the inertia element 258 and cannot move further axially in that direction, the high lead thread connection with the shaft causes the nut 254 to rotate which in turn rotates the inertia element 258 through the friction of the interengaging axial surfaces on the nut and the inertia element 258. The inertia element 258 which is driven by the nut 254 rotates the spring 270, which in turn rotates the inertia element 256. A slight axial clearance between the nut and inertia element 256 being driven by the spring permits the spring driven element to rotate independently of the nut and the inertia element 256. When rotation of the nut 254 and the inertia elements is below a predetermined acceleration level, the rotating components have no significant effect on the telescoping movement of the strut.

However, with acceleration beyond a predetermined threshold, the inertia of the element being driven through the coil spring causes the spring to unwind a small amount such that the diameter of the spring increases causing the spring to brake against the interior of the surrounding support housing 224. thus. imposing a braking force on the telescoping strut. As soon as the accleration is braked. the spring diameter will relax to its normal condition.

With the strut in compression the load is again through the shaft and the nut but it passes from the nut through the inertia element 256 and ball bearing 264 into the strut member 212. The compression load rotates the nut which rotates the element 256, that in turn drives the element 258 through the spring 270. The braking action at the threshold acceleration is comparable to that which occurs with a tension load.

One of the advantages of the arrangement of Fig. 10 is that only a single set of large ball bearings is required for each inertia element.

Such bearings handle both the radial forces and the axial thrust forceps. The size of the bearings are such that the very large thrust components can be accommodated. The large single sets of bearing also provide considerable manufacturing convenience in that they are easier to install than the small roller bearings shown in Fig. 1.

The use of the large ball bearing en ables the nut 254 to transmit the axial load directly to one of the inertia elements and enables the nut to rotate the inertia element without the need for teeth connecting the nut to the inertia elements as in Fig. 1. This eliminates lost angular motion between the components. Also, the manufacture and assembly is simplified. Further, the number of components is minimized in that the nut 254 serves the function of translating the axial force of the strut into rotation, in combination with the shaft as well as the device which transfers the torque to the inertia elements. This is in contrast with the arrangement of Fig. 1 wherein the rotating shaft was used and one threaded member was used for rotating the shaft and a load transfer member was attached to the shaft for rotating the inertia element.

Another advantage of the arrangement of Fig. 10 is that the reciprocating strut components are of relatively large diameter throughout the length of the strut. This enables the strut to withstand lateral forces more effectively than can a strut of smaller diameter. Yet the overall size of the structure is not prohibitive in terms of installation problems in that the radial thickness of the tubular members forming the strut is not large relative to the overall diameter of the strut.

WHAT WE CLAIM IS: 1. A motion snubbing device comprising a pair of members mounted for movement relative to each other, a pair of inertia elements mounted to be freely rotated, means connecting said members to said elements so that relative movement of said members in one direction will drive one of said inertia elements and relative movement of said members in an opposite direction will drive the other inertia element, and means interconnecting said inertia elements in a manner such that rotating either of the elements below a predetermined acceleration threshold causes such element to rotate the other inertia element, and attempting to rotate said other inertia element above said threshold intiates braking action on said elements and said members which limits acceleration to said threshold.

2. A device as claimed in Claim 1 in which said inertia elements are mounted in axial alignment, with an end face of one element facing an end face of the other element, and are surrounded by a housing, and in which said element interconnecting means comprises a coil spring surrounding a portion of said elements adjacent said housing with the spring being arranged to trans

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. similar screw or pin 273 extends into a hole in the inertia element 258. In operation of the strut of Fig. 10, the overall result obtained is similar to that of the strut in Fig. 1. However, there are a number of operational and structural differences that provide certain advantages. The strut is shown in its most fully collapsed position. If a tension load is applied to the strut, the load is transmitted directly through the shaft 240 and the torque transfer nut 254 into the shoulder 258c of the inertia element 258. The load path is through the ball bearings 265 and into the bearing support member 228, the surrounding housing 224, and the tongue 216 of the support member 212. Since the nut 254 is axially engaging the inertia element 258 and cannot move further axially in that direction, the high lead thread connection with the shaft causes the nut 254 to rotate which in turn rotates the inertia element 258 through the friction of the interengaging axial surfaces on the nut and the inertia element 258. The inertia element 258 which is driven by the nut 254 rotates the spring 270, which in turn rotates the inertia element 256. A slight axial clearance between the nut and inertia element 256 being driven by the spring permits the spring driven element to rotate independently of the nut and the inertia element 256. When rotation of the nut 254 and the inertia elements is below a predetermined acceleration level, the rotating components have no significant effect on the telescoping movement of the strut. However, with acceleration beyond a predetermined threshold, the inertia of the element being driven through the coil spring causes the spring to unwind a small amount such that the diameter of the spring increases causing the spring to brake against the interior of the surrounding support housing 224. thus. imposing a braking force on the telescoping strut. As soon as the accleration is braked. the spring diameter will relax to its normal condition. With the strut in compression the load is again through the shaft and the nut but it passes from the nut through the inertia element 256 and ball bearing 264 into the strut member 212. The compression load rotates the nut which rotates the element 256, that in turn drives the element 258 through the spring 270. The braking action at the threshold acceleration is comparable to that which occurs with a tension load. One of the advantages of the arrangement of Fig. 10 is that only a single set of large ball bearings is required for each inertia element. Such bearings handle both the radial forces and the axial thrust forceps. The size of the bearings are such that the very large thrust components can be accommodated. The large single sets of bearing also provide considerable manufacturing convenience in that they are easier to install than the small roller bearings shown in Fig. 1. The use of the large ball bearing en ables the nut 254 to transmit the axial load directly to one of the inertia elements and enables the nut to rotate the inertia element without the need for teeth connecting the nut to the inertia elements as in Fig. 1. This eliminates lost angular motion between the components. Also, the manufacture and assembly is simplified. Further, the number of components is minimized in that the nut 254 serves the function of translating the axial force of the strut into rotation, in combination with the shaft as well as the device which transfers the torque to the inertia elements. This is in contrast with the arrangement of Fig. 1 wherein the rotating shaft was used and one threaded member was used for rotating the shaft and a load transfer member was attached to the shaft for rotating the inertia element. Another advantage of the arrangement of Fig. 10 is that the reciprocating strut components are of relatively large diameter throughout the length of the strut. This enables the strut to withstand lateral forces more effectively than can a strut of smaller diameter. Yet the overall size of the structure is not prohibitive in terms of installation problems in that the radial thickness of the tubular members forming the strut is not large relative to the overall diameter of the strut. WHAT WE CLAIM IS:

1. A motion snubbing device comprising a pair of members mounted for movement relative to each other, a pair of inertia elements mounted to be freely rotated, means connecting said members to said elements so that relative movement of said members in one direction will drive one of said inertia elements and relative movement of said members in an opposite direction will drive the other inertia element, and means interconnecting said inertia elements in a manner such that rotating either of the elements below a predetermined acceleration threshold causes such element to rotate the other inertia element, and attempting to rotate said other inertia element above said threshold intiates braking action on said elements and said members which limits acceleration to said threshold.

mit torque between the elements, the inertia of the spring driven element causing it to lag and increase the spring diameter so that it engages said housing to produce said braking action.

3. A device as claimed in claim I or 2 in which said members are strut members mounted for relative axial movement therebetween, and in which said means connecting said members to said elements include means for translating relative axial movement between said strut members into rotary movement of said inertia elements.

4. A device as claimed in claim 3 in which said means for translating relative axial movement into rotary movement comprises at least one high-lead screw thread connection.

5. A device as claimed in claim 3 or 4 in which said means connecting said members to said elements include a rotary drive member operative between said movement translating means and said inertia elements.

6. A device as claimed in claims 2 and 5 in which an interengaging rib and slot connection is provided between said rotary drive member and said inertia elements, said rib and groove connection permitting a limited relative angular displacement between said inertia elements and said rotary drive member.

7. A device as claimed in claimed in claims 2 and 5 in which axial thrust bearings are provided between said inertia elements and respective ones of said strut members and in which axial shoulder abutments are provided between said rotary drive member and each of said inertia elements, whereby an axial load between said strut members in one direction loads one of said shoulder abutments to enable the rotary drive member to drive the respective one of the inertia elements and an axial load in the opposite direction loads the other shoulder abutment so that the rotary drive member can drive the other inertia element.

8. A device as claimed in claim 7 in which said thrust bearings comprise ball bearings serving also as journal bearings journalling the respective inertia elements for rotation.

9. A device as claimed in claim 4 and in claim 7 or 8 in which the high-lead thread is provided between one of said strut members and said rotary drive member and in which said housing is axially fixed to the other strut member but is non-rotatable relative to said one strut member.

10. A device as claimed in claim 9 in which said housing is slidably guided in a casing fixed to said one strut member.

I I. A device as claimed in claim 4 and in any of claims 7 to 10 in which said high-lead thread includes an internal thread in said rotary drive member, and said inertia elements encircle the member having a complementary external screw thread thereon.

12. A device as claimed in claim 5 or 6 in which said movement translating means includes a shaft attached to or integral with said rotary drive member, said inertia elements encircling the rotary drive member and shaft combination.

13. A device as claimed in claim 12 in which axial thrust bearings are provided between said rotary drive member and one of said strut members and in which said movement translating means is opposite between said shaft and the other of said strut mem bers. said members being non-relatively rotatable.

14. A device as claimed in claim 4 and in claim 12. 13 or 14 in which the high-lead thread includes an external screw thread on said shaft and a mating internal screw thread on a respective one of said strut members.

15. A device as claimed in any of claims 3 to 6 or in claim 12, 13 or 14 in which one of said strut members includes a casing in which the other strut member is telescopably slidably received.

16. A device as claimed in claim 3 and in claim 12 in which said movement translating means includes high-lead threads of opposite hand between said shaft and each of said strut members.

17. A device as claimed in claim 2 and in claim 16 in which said housing is axially displaceably but non-relatively rotatably mounted on said strut members.

18. A device as claimed in claim 17 in which said inertia elements and said housing have mating bearing surfaces to position said inertia elements in said housing both axially and rotatably.

19. A device as claimed in claim 18 in which each of said inertia elements has an outwardly extending annular collar received in a corresponding socket formed in a respective end-plate of said housing, said mating bearing surfaces being on said collar and in said socket.

20. A device as claimed in claims 4 and 5 in which said rotary drive member comprises a nut and said movement translating means includes an external screw thread on a shaft mating with the internal thread in the nut, said shaft being arranged to receive axial load applied between said strut members whereby to cause said nut to rotate.

21. A device as claimed in claim 20 in which said inertia elements are annular and encircle said shaft, said nut being axially captured between opposing axial faces of said inertia elements.

22. A device as claimed in claim 21 in which said shaft forms part of one strut member and in which the inertia elements are journalled by ball bearings on the other strut member.

23. A device as claimed in claim 22 in which said other strut member has a pair of axially spaced end-plates each provided with a respective tubular bearing support with a respective one of said ball bearings mounted externally thereon, said spaced end-plates being interconnected by a housing, and in which each of said inertia elements has a tubular portion overlying a respective one of said tubular bearing supports and having a respective one of said ball bearings internally thereof.

24. A device as claimed in claim 23 in which said one strut member has an endplate to which said shaft is fixed and a tubular casing attached to said end-plate and surrounding'said housing, said housing being telescopably received in said tubular casing.

25. A motion snubbing device comprising a pair of members mounted for relative movement with respect to each other: and acceleration sensitive means connected to said members for limiting movement of either of the members relative to the other member, in either of two opposite directions, to a predetermined threshold acceleration rate, said acceleration sensitive means including a pair of rotatably mounted inertia members and means responsive to said relative movement in one direction for rotating one of said inertia elements and responsive to said relative movement in the opposite direction for rotating the other one of said elements, means interconnecting said inertia elements in a manner such that rotation of the element being driven by said relative movement will further rotate the other one of said elements so long as the rotational acceleration is below said threshold, and attempted acceleration above said threshold will cause the inertia element driven by the other inertia elements to lag because of its inertia. and means responsive to said lagging movement preventing acceleration beyond said threshold.

26. A device as claimed in claim 25 in which a housing is connected to one of said members said inertia elements being annularly shaped and being rotatably mounted within said housing with the periphery of the inertia elements being closely spaced from the interior wall of the housing and in which said means interconnecting said inertia elements comprises a coil spring surrounding said inertia elements and closely spaced from said housing, said coil spring being arranged with respect to said inertia elements in a manner such that said lagging movement causes the convolutions of said spring to increase their diameter and engage the interior of said housing to provide said braking action which limits the acceleration.

27. A device as claimed in claim 16, 17, 18 or 19 in which the strut constituted by said strut members is axially short so as to extend between two adjacent fuel rod support tubes in a nuclear power generating plant.

28. A device as claimed in claim 27 when appendant to claim 17, 18 or 19 in which attachment members are slidably mounted on respective ones of said end-plates to permit movement of said attachment members towards each other, said attachment members being adapted to be connected to said fuel rod support tubes.

29. A motion snubbing device constructed and adapted to operate substantially as herein described with reference to and as illustrated in Figs. 1 to 4 of the accompanying drawings.

30. A motion snubbing device constructed and adapted to operate substantially as herein described with reference to and as illustrated in Figs. 5 to 9 of the accompanying drawings.

31. A motion snubbing device constructed and adapted to operate substantially as herein described with reference to and as illustrated in Fig. 10 of the accompanying drawings.