US2543649A - Linkage for hydraulic actuators - Google Patents

Description

Feb. 27, 1951 Filed July l2, 1950 L. B. WALES ETAL LINKAGE FOR HYDRAULIC ACTUATORS 2 Sheets-Sheet l'lll 4 I t rwvem ors: g 'Lawrence vvales, W MSFOTW 0. Hodgesj b l /TherActovrwey.

Feb. 27, 1951 L.. B. WALES ETAL 2,543,649

LINKAGE FOR HYDRAULIC AcTUAToRs Filed July l2, 1950 A 2 Sheets-Sheet 2 ITM/erw tors Lawrence wales, Me rtorw O. Hodges,

Then* Attorney.

Pmntea Feb.' 21, 1951 LnvKAGE Foa HYDRAULIC Ac'rUA'roRs Lawrence B.- Wales and Merton 0. Hodlel. Mal'- blehead, Mass., assgnors to General Electric Company, a corporation of New York Application July 12, 1950, Serial No. 173.444

(Cl. 'I4-53) 7 Claims. l

This invention relates to mechanical linkage mechanism for communicating motion from a hydraulic motor to a member positioned thereby,

particularly to mechanical linkages for positioning the inlet valves of a prime mover such as a steam turbine. l

In steam turbines having capacities on the order of 15,000 kw., it is conventional practice to subdivide the first-stage nozzles into arcuate segments, with separate chambers in the steam inlet chest arranged to feed each segment, sepa-- rate valves being provided to control the admission of steam to the respective valve chest chambers. Ordinarily these valves are arranged in a row with a common actuating mechanism for opening the valves in desired sequence. A form of this mechanism which has become quite common includes a valve lift lever disposed substantially horizontally above the steam chest with one end pivoted to a fixed fulcrum supported by a bracket from the turbine casing, the other end carrying a roller cam follower engaged by a contoured cam positioned by suitable hydraulic or other motor means. The fixed fulcrum may be a common shaft passing through bushings in .the ends of the respective valve lift levers. Likewise the cams for positioning the other ends of the levers may be mounted on a common shaft rotatably positioned by the actuating motor, and

suitably contoured and oriented with respect to y each other so that the valves are opened in proper sequence and positioned as required by the turbine operating schedule. A connecting link or rod is p pted to the mid-portion of the valve lift lever and to the valve stem.

In mechanism of this type, enormous forces must be applied to the turbine valves. For instance. in a 15,000 kw. turbine, it may be necessary to apply a force as much as 10,000 lbs. in opening a given valve against full steam inlet pressure. At the same time, the governing of a steam turbine must be done quite precisely and with maximum reliability. It is therefore necessary that the linkage connecting the valve positioning motor with the valve stems be simple, extremely rugged, and. in particular, arranged to have an absolute minimum of friction in the pivot joints.

Accordingly, the object of this invention is to provide a suitable linkage for turbine valve lift mechanism of the multiple cam type with a special frictionless pivot arrangement between the connecting rod and the valve lift lever arranged so that only rolling contact occurs between the connecting rod bearing surface and the pivot. It will of course be appreciated that the invention may also be applicable to other machines where similar problems are encountered.

Other objects and advantages will be apparent from the following description taken in conneetion with the accompanying drawings in which Fig. 1 shows, partly in section. a turbine valve actuating linkage arranged in accordance with the invention; Fig. 2 is a top view of the linkage of Fig. 1; Fig. 3 is a detail view of a modified form of the valve lift lever with its special rolling contact connecting pivot; and Fig. 4 is atransverse section taken on the plane 4--4 in Fig'. 3.

In general. the special pivot arrangement which is a principal characteristic of this linkage comprisesa cylindrical pivot rod nxed to the valve lift lever and cooperating with fiat transverse parallel spaced bearing surfaces formed in the connecting rod end portion, the space between these bearing surfaces being somewhat greater than the diameter of the pivot rod so the pivot engages only one of the bearing surfaces at a given time and has pure rolling contact therewith, so that friction is reduced to the absolute minimum.

Referring now more particularly to Fig. 1, valve stem I is positioned by a pivoted connecting rod 2 the upper end of which is connected by the specially arranged rolling contact pivot shown generally at 3 to the mid-fportion of valve lift lever 4, which has its left-hand end carried on a fixed fulcrum 5, while the right-hand endA thereof is provided with a roller cam follower 6 adapted to be engaged by an actuating cam 1. The upper portion of the turbine valve inlet casing 8 supports a heavy, horizontally disposed frame plate member 9 secured by studs I0 to the inlet casing. Disposed through opening I I in casing 8 is a lower valve stem bushing I2 secured in a bore through plate 8 by means of a circumferential flange I3 engaged by a retaining ring I4 (which may be divided into two or more segments for convenience in assembly) secured by screws I5 to the frame plate 9. Cast integral with the frame member 9 is a central upwardly extending cylindrical portion IG having a anged end portion I1 carrying an upper valve stem bushing I8 secured in the frame end iiange Il by means of a flange I9 engaged by a retaining ring 20 held by suitable threaded fastenings 2 I.

As will be apparent from Fig. l, the valve stem I is constrained for linear reciprocating motion by the upper and lower bushings I8, I2, and carries on its upper projecting end portion an abutment member 22 suitably secured to the valve stem, as by being threaded thereon, and having a circumferential shoulder portion defining a spring seat 23. For biasing the stem I in the valveclosing direction, a heavy coil spring 24 is disposed with its lower end portion engaging the seat 23, while its upper end portion engages a similar seat ring 25, the latter being supported in fixed relation to the frame 9 by means of two or more radially extending projections 25a through which are disposed elongated tubular nut members 26 having a. depending portion 21, the lower end 28 of which is threadedly received on a studl 29 secured at its lower end in the flange portion I1 of the frame plate 9. The circumferential flange 23 of abutment 22 may be provided with radially extending portions having semi-circular cutouts indicated in dotted lines at 23a as cooperating with the studs 29 so that rotation of the abutment 22 is prevented by engagement of these cutout portions with the studs. While not essential to the present invention, it may be noted that the biasing force of spring 24 may be readily adjusted by turning the nuts 25 so that they move longitudinally on the threaded end of stud 29.

As will be understood from Fig. 1, the valve stem abutment 22 is provided with a pair of opposed upwardly extending ears 30 in which are fixed the respective ends of the lower connecting rod pivot 3 I. It will of course be obvious to those skilled in the art that the cooperating bore through the lower connecting rod end may be provided with a Babbitt metal lining or a suitable bronze vbushing to provide a low friction bearing surface engaging the mid-portion of the pivot 3 l The special rolling contact pivot for the upper end portion of the connecting rod will be described in more detail hereafter.

The valve lift lever 4 is preferably fabricated from steel plates by welding and consists of parallel spaced side plates 32 having welded therebetween at the left-hand end a fulcrum bushing 33 with a bronze bushing 34 or equivalent bearing means engaging the common fixed fulcrum A shaft 35. This shaft has one extreme end portion fixed in a support block 36 secured by threaded fastenings 31 to the upper end of a bracket 38, the bottom end portion of which is suitably secured by welding or bolting to the frame plate member 9.

The bearing bushing 34 of the valve lift lever is retained on the fixed fulcrum shaft 35 between the support block 35 and a retaining collar 39 (Fig. 2) which may conveniently be secured to shaft 35 by a set screw 40. It will be understood of course that the shaft 35 is extended to provide the support for the other valve lift levers (not shown) and has a suitable number of spaced support blocks corresponding to that shown at 36. Where they receive the ends of the pivot rod 4|, the side plates 32 are thickened by having welded thereto reinforcing plates 42. 'Ihe pivot rod 4I may be secured in position b y means of a set screw 43 or equivalent means.

At the right-hand end of the valve lift lever 4. a pair of bushings 44 are welded to the side plates, one of which bushings has fixed therein an end portion of the cam roller follower shaft 45, as by a set screw 44a. As may be seen in Fig. 2, the cam follower roller 6 is disposed between the support bushings 44 and is carried on the shaft 45 by suitable bearing means, which may be either a Babbitted or bronze bushing type of bearing or 4 an anti-friction bearing such as the well-known "needle-type roller bearing.

The actuating cam 1 which engages the cam roller follower 6 is carried on a shaft 41 journalled in suitable pillow blocks 48 secured to a portion 38a of the bracket 38. The motor means for rotatably positioning the cam 1 is not illustrated because it is not material to an understanding of the present invention.

The structure of the valve lift lever 4 is completed by a pair of top plate members 49, 50, which may be welded along the edges thereof to the side plates 32 and at the respective ends to the bushings 33, 44. At the left-hand side of the rolling contact pivot 3, a, bottom plate 5| is similarly welded to the edges of side plates 32. Between the pivot 3 and the right-hand end of lever 4 there is provided a downwardly extending knock-down arm" 52, the function of which will be described hereinafter. This arm may be formed integral with or welded to the side plates 32. The depending lower end portion of this knock-down lever defines a cam surface 53 adapted to be engaged by a cylindrical knock-down pin 54, which is fixed in the side of and projects axially from the cam 1.

Referring now to the rolling contact pivot at 3. it will be noted that the upper end portion 2a of connecting rod 2 is provided not with the usual cylindrical bore but a transversely elongated slot 55. The top and bottom walls of this slot form at parallel surfaces indicated at 55a, 55h, which are the bearing surfaces for the rolling contact engagement with the pivot 4I. Normally the upper bearing surface 55a is biased into engagement with the top surface of pivot 4| by the action of the main spring 24. In this condition there is a small but significant clearance space between the lower bearing surface 55h and the lower side of pivot 4I, this clearance being indicated at 56.

The method of operation described hereinafter requires that the connecting rod end portion 2a always be biased to the right relative to pivot 4I; and to this end an auxiliary coil spring 51 is provided, having one end hooked into a. hole in the top plate 49 as will be obvious from Fig. 2. The other end of coil spring 51 loops around a pin 58 threadedly received in the top of connecting rod end portion 2a. It will be apparent from Fig. l that the effect of auxiliary spring 51 is to bias the connecting rod end portion 2a to the right so that ordinarily pivot pin 4I will occupy the extreme left-hand side of slot 55 when the valve gear is in the valve-closed position, as represented by Fig. 2. As indicated above, the pivot 4i will ordinarily engage the top bearing surface 55a by reason of the bias imposed by main spring 24.

It will be seen in Fig. 2 that the reinforcing portions 42 of the lever side plates form comparatively close clearances with the adjacent side faces of the connecting rod end portion 2a, so that any rotational movement o f the connecting rod 2 about its longitudinal axis relative to pivot rod 4I is prevented.

To illustrate the method of operation, assume that the actuating cam 1 begins to rotate in the clockwise direction. with the result that roller follower 6 begins to rise. This of course means that the valve lift lever 4 begins to rotate counter-clockwise about the fixed fulcrum 5. This motion causes pivot pin 4l to bear against the upper surface 55a and raise the connecting rod 2, thus cracking" the turbine valve open.

Now if cam 1 continues to rotate clockwise its Y e contoured outer surface will cause the roller follower 5 to rise progressively andv thel'lever 4 to continue rotating in thecounter-clockwise directionaround pivot 5. `This'rotational movement of lever 4 also causes -the pivot rod 4I to rotate 5 relative to the connecting rod bearing surface 55a. This relative rotation between pivot 4I and surface 55a\`causes the cylindrical pivot toroll on the surface 55, with the result that the connecting rod end portion 2a moves to the left, against l0 the bias of coil spring 51. Because of the enormous forces transmitted. between the pivot 4I and the bearing surface 55a, the frictional resist- -ance to slipping between these surfaces prevents any slipping so that there is truerolling contact. Even in the inoperative condition,with no steam pressure on the valves, the biasing force of the main coil spring 24 will create enough static friction .between pivot 4I and bearing surface 55a that there will be no relative slipping therebetween.

It will be understood that the bearing surface 55a is sufficiently long in a transverse direction, relative to the angular travel of the valve lift lever 4, that throughout the normal movement 2;, of the valve stem vertically the pivot 4I simply rolls freely along thesurface 55a, without any slippage therebetween and without reaching the' right-hand end of the slot 55. By the time the cam 1 reaches its limiting position, with the valve 30 stem I raised to the wide-open position, the pivot 4I will have rolled along surface 55a.until it almost, but not quita-reaches the right-hand end of the slot 55.

If the cam 1 now rotates in the counter-clock- 35 wise direction, the cam roller 6 is permitted to move downwardly, the valve lift lever 4pivcts clockwise about the fixed fulcrum 5, and the heavy biasing spring 24 causes the valve spindle I to move downwardly in the valve closing direc 40 tion. This motion causes the pivot 4I to rotate in a clockwise direction, whereupon the rolling contact between pivot 4I and surface 55a effects movement ofthe connecting rod end portion 2a to the right., When the cam returns to the valve closed position, the pivot 4I will again have reached the left-hand side of slot 55, the position shown in Fig. 1.

The above-described operation in the opening and closing directions is that which normally occurs. However, this arrangement also incorporates provision for the comparatively rare case where the turbine valve stem-sticks in the open position, so that the bias of the spring 24 is not sufiicient to move it towards closed position. If this sticking persists as the cam 1 rotates counterclockwise in the closing direction, the cam follower rollervI will leave the surface of cam 1. When this happens, the weight of the valve lift lever 4 tends to move it clockwiseabout fulcrum 5, so the connecting rod 2 remaining in its elevated position due to the sticking of the valve stem I. This means that pivot 4I moves out of frictional engagement with surface 55a; and the instant this occurs,the auxiliary biasing spring 5,1 will snap the connecting rod end 2a to the right until pivot 4I occupies the left-hand portion of slot 55, as shown in Fig. 1. If rotation of cam 1 in the counter-clockwise direction now continues, with valve stem I stuck in open position, the knock- 70 down pin 54 Vwill engage the surface 53 of arm 52, thus applying a forceto the lever 4 tending to rotate it clockwise about pivot 5, so as to positively force the stem I in the valve-closing direction. l

It will be seen that, when the lever 4 is forced downwardly by engagement of the knock-down p'in 54 with the arm 52, the, clearance space 56 between the lower surface of pivot pin 4I and the bearing surface 55h closes so that the bearing engagement between pivot 4I and the lower bearing surface 55h forces the connecting rod 2 downwardly. Now las the lever 4 continues to rotate clockwise, the clockwise rotation of the pivot- 4I :follower 6 again engagesthe cam 1. During this movement, however, the pivot 4I will move out of engagement with the lower bearing surface 55h; and instantly the spring 51 will again pull the connecting rod end portion 2a to the right so that pivot 4I is returned to the left-hand side of the slot 55. Thus the next time cam 1 moves clockwise in the valve opening direction, the pivot 4I will be at the left-hand side of slot 55 and ready to roll to the right-hand side thereof as dev scribed above for the normal operation of the mechanism.

It will now be apparent that regardless of whether the cam 1 forces the lever 4 upwardly,

so that pivot 4I rolls to the right across bearing 45517. there is always true rolling contact between pivot 4I and connecting rod end portion 2a. Thus a most important source of frictional resistance in the actuating linkage is eliminated. The auxiliary biasing spring 51 serves to insure that any time contact is broken between the pivot 4I and one of the bearing surfaces 55a, 55h, the upper connecting rod end portion 2a. will be quickly moved to the right so that the pivot 4I will be in position to travel across the bearing surfaces 55a, 55b as may be required by the operating conditions.

While, theoretically at least, it would appear possible to apply this rolling contact type of pivot to the lower end of connecting rod 2 also, in practice this does not achieve sufficient improvement to warrant the additional mechanical complication because if the connecting rod 2 is of a reasonable length, the angular movement of the lower pivot 3| relative to the connecting rod is only a very few degrees so that friction at this point is of no great consequence. On the other hand, the upper connecting rod bearing has been found to be an important source of troublesome friction in turbine valve gear of this type; and the rolling contact arrangement described herein is found to effect a substantial improvement in rendering the operation of the valve actuating mechanism friction-free and reliable.

AIt will of course be apparent to those skilled in the art that the mechanical details of the connecting rod 2 and of the main and auxiliary biasing springs associated with it are susceptible to an enormous number of modifications, as are also the details ofthe valve lift lever and the means for positioning it.

The details of the rolling contact arrangement may also be considerably varied. For instance,

which the enlarged upper end of the 'connecting rod 2 is replaced by a pair of spaced abutments in the form of a lower cylindrical block 60 having a central bore threaded onto the valve spindle 2 and seating against a lock nut 6 I. The cylindrical upper abutment 62 is likewise threaded' onto the connecting rod 2 and provided with a lock nut v In this modication, the pivot pin 64 is provided with a conical bore 65 therethrough, through which the connecting rod 2 projects freely. The respective ends of pivot pin 64 are carried in. bushings ss, s1 (Fig. 4), which may conveniently be welded to the outside of the lever arm side plates 66, 69, the latter corresponding to the side plates 32 in Fig. 1. The pivot pin may be locked in one of these bushings bymeans of a set-screw,

as shown at 10 in Fig. 4. The mechanical details of the fixed fulcrum pivot 5, valve lift lever 4, cam follower roller 6, and the known-down lever 52 may be generally as described above in connection with Figs. l, 2. l

It wil be apparent that the lower face 62a of abutment 62 forms a iiat bearing surface corresponding in function to the upper bearing sur` face 55a, in Fig. l, while the upper surface 60a of the lower abutment 60 forms a bearing surface correspondingV to that identified 55h in Fig. 1. As will be apparent in Fig. 4, 'the bias of 'spring 24 ordinarily maintains the upper bearing surface 62a in contact with the -upper surface of pivot rod 64. Also, the lower surface of pivot rod 64 forms the clearance space shown at 56. It will be apparent that the magnitude of this clearance space may be readily adjusted by suitably positioning the abutments 60, 62 on the threaded portions of connecting rod 2.

The auxiliary biasing means for the upper end of connecting rod 2 consists here of a springbiased plunger 1I (Fig. 3) slidably disposed in a cylindrical recess in a cross-brace 12 which may be welded at either end to the side plates 68, 69. As will be apparent from Fig. 3, the coil spring 13 surrounds a reduced diameter portion of the plunger 1I and is disposed in the recess in crossbrace 12. The left-hand end of plunger 1| slides in the recess and engages the side of abutment 60 so as to bias it to the left. The other reducedend portion of plunger 1| projects through a hole in brace 12 and carries a stop member which may be in the form of a nut 14 threadedly received on the plunger end portion. In order to accurately limit the extent to which the'upper connecting.

rod end portion may be moved to the left by the biasing plunger 1 I, an adjustable stop is provided in the form of a cross-brace 15 weldedto the side plates 68, 69 and carrying a threaded stop member 16 provided with a lock nut 11.

Although the general function is the same, the detailed operation of this modification is different in some respects from that of Figs. 1, 2. The tapered hole 65 through the pivot pin 64 is of course so proportioned that for all positions of the lever 4 there will be no mechanical interference between connecting rod 2 and the sides of recess 65. In Fig. 3, the mechanism is shown in the valve closed position, with main spring 24 biasing the bearing surface 62a into contact with the top of pivot pin 64. When the lever 4 moves counter-clockwise about xed fulcrum 5 in the valve opening direction,A the pivot 64 rotates counter-clockwise also, with the result that rolling contact between surface 62a and pivot rod 64 causes the connecting rod 2 to approach the lefthand side of the recess 65.

Conversely. when the knock-down lever 52 is engaged to force the lever 4 clockwise in order to free a sticky valve, the pivot 64 moves downwardly to engage the bearing surface 60a whereupon the biasing plunger 1i moves the upper end of the connecting rod 2 to the left against stop 16. Thus when pivot 64 contacts the lower bearing surface 60a the clearance space between connecting rod 2 and the recess 65 will be so disposed that the pivot 64 can roll across the lower bearing surface without mechanical interference between pivot and connecting rod.

Thus in each of the above-described modifications the rolling contact pivot is so arranged that for either mode of operationethe cylindrical surface of the pivot rod rolls across one of a pair of opposed flat bearing surfaces and out of contact with the other, while auxiliary biasing means automatically move the end of the connecting rod relative to the pivot rod so that the clearance space provided therebetween will always permit such free-rollingy contact. Thus the friction at the most troublesome point in the mechanism is reduced to a minimum, even below that which would be obtainable with conventional ball or roller anti-friction bearings. At the same time this pivot joint requires no lubrication whatever since there is no relative rubbing under load.

It will be apparent to those skilled in the art that many other alterations and substitutions .of equivalents might be made, and it is desired to cover by the appended claims all such changes as fall within the true spirit and scope of the invention. v

What we claim as new and desire to secure by Letters Patent of the United States is:

l. In a mechanical linkage including a lever pivoted to a fixed fulcrum at one end thereof and having a connecting link pivoted to a spaced portion thereof, the combination of rolling contact bearing means for the connecting link pivot comprising a cylindrical pivot member fixed to the lever with the axis thereof parallel to theaxis of rotation of the lever about the fixed fulcrum, the connecting link end portion having walls delining substantially flat spaced parallel bearing surfaces disposed at opposite sides of the pivot member and substantially normal to the length of the connecting link, the spacingl between said surfaces being greater than the diameter of the pivot whereby a clearance space is defined at all times between at least one of said fiat bearing surfaces and the pivot, and means biasing the connecting link end portion relative to the pivot. whereby when the pivot is disengaged from both bearing surfaces said biasing means moves the connecting link end portion transversely tc provide a clearance space between pivot and connecting link so disposed that, upon subsequent engagement of the pivot with one of the fiat bearing surfaces, free-rolling contact may take place between pivot and bearing surface as the lever rotates about the fixed fulcrum.

2. In a mechanical linkage including a lever pivoted to a xed fulcrum at one end thereof and having a connecting link pivoted to a spaced l portion thereof, the combination of rolling contact bearing means for the connecting link pivot comprising a member fixed to the lever and having a portion forming a cylindrical bearing surface the axis of which is parallel to the axis of rotation of the lever about the fixed fulcrum, a member secured to the connecting link end portion and defining a fiat bearing surface normal to the length of the link and disposed adjacent said pivot member, and spring means biasing the connecting link end portion transversely relative to the pivot whereby, when the pivot bearing surface is disengaged from the flat bearing surface, the biasing means moves the link end portion transversely to provide a clearance space between pivot and link so disposed that. upon subsequent engagement of the pivot bearing surface with the fiat bearing surface, free-rolling contact may take place between pivot and bearing surface as the lever rotates about 'the xed fulcrum.

3. In a mechanical linkage including a lever pivoted to a fixed fulcrum at one end thereof and having Va connecting link Apivoted to a spaced portion thereofy with means for constraining the other end of the link for rectilinear movement in a direction substantially normal to the length of the lever, the combination of rolling contact bearing means for the connecting link pivot comprising a member fixed to the lever and having a cylindrical pivot bearing surface the axis of which is disposed parallel to the axis of rotation of the lever about the xed fulcrum, the connecting link end portion defining an opening through which the cylindrical pivot member is disposed, the opposed wallsof said opening defining substantially flat spaced parallel bearing surfaces disposed substantially normal to the length of the link and spaced apart a distance greater than the diameter of the cylindrical pivot bearing surface whereby a clearance space is defined at all times between at least one of said fiat bearing surfaces and the pivot bearing surface, and means biasing the connecting link end portion relative to the pivot bearing surface, whereby when the pivot is disengaged from both bearing surfaces said biasing means moves the connecting link end portion transversely to provide a clearance space between pivot and link so disposed that, upon subsequent engagement of the pivot with one of said bearing surfaces, free-rolling contact may take place between pivot and bearing surface as the lever rotates about the fixed fulcrum.

4. In a mechanical linkage including a lever pivoted to a xed fulcrum at one end thereof and having a connecting link pivoted to a spaced portion thereof with means for constraining the other end of the link for rectilinear movement in a direction generally normal to the length of the lever, main spring means biasing the link to one extreme of its range of movement and means for positioning the lever against the bias of said main spring, the combination of rolling contact bearing means for the connecting link pivot comprising a member fixed to the lever and having a cylindrical pivot bearing surface the axis of which is disposed parallel to the axis of rotation of the lever about the fixed fulcrum, the end portion of the connecting link dening an opening through which the cylindrical pivot member is disposed, opposite side walls of said opening forming flat parallel bearing surfaces disposed substantially normal to the length of the link, the spacing between said parallel bearing surfaces being slightly greater than the diameter of the cylindrical pivot member whereby a clearance space is defined at all times between at least one of said fiat bearing surfaces and the pivot bearing surface, the length of said opening transverse to the length of the link being substantially greater than the diameter of the cylindrical pivot bearing surface, and auxiliary means biasing the connecting link end portion relative to said. cylindrical pivot in a direction away fr'o'm theiixed fulcrum, whereby, when the cylindrical pivot is disengaged from both the flat bearing surfaces, said auxiliary biasing means movesthe' connecting. link end portion transversely away from the fixed fulcrum so that upon subsequent engagement of the pivot with one of the fiat bearing surfaces free-rolling contact may take place between pivot and bearing surface as the lever rotates about the fixed fulcrum. Y

5. In a mechanical linkage including a lever pivoted to a fixed 'fulcrum at one end thereof and having a connecting link pivoted to a spaced portion thereof 'with' means constraining the other end of the 'link 't'"move ina substantially rectilinear direction generally normal to the length of the lever, main spring means biasing the link in a direction away from the lever, and means for positioning the lever against the bias of the main spring, the combination of vrolling contact bearing means for the connecting link pivot comprising a member fixed to the lever and having a circumferential portion forming a cylindrical pivot bearing surface, said pivot member defining a transverse recess through which the connecting link end portion is disposed with substantial clearances between link and pivot, a pair of spaced members adjustably secured to the connecting link end portion and forming a pair of flat parallel bearing surfaces disposed adjacent diametrically opposite portions of the cylindrical pivot bearing surface, the spacing between said parallel bearing surfaces being greater than the diameter of the cylindrical pivot surface whereby a clearance space is defined at all times between at least one of the flat surfaces and the pivot, and auxiliary spring means biasing the connecting link end portion relative to the lever in the direction towards the i'lxed fulcrum, whereby, when the pivot surface is disengaged from both flat bearing surfaces, the auxiliary spring means biases the connecting link end portion transversely so as to be disposed adjacent the side of the recess in the pivot nearer the fixed fulcrum in order that upon subsequent engagement of the pivot bearing surface with one of said fiat bearing surfaces, free-rolling contact may take place between pivot and bearing surface as the lever rotates about the fixed fulcrum.

6. In a mechanical linkage including a lever pivoted at one end to a fixed fulcrum and having a connecting link pivoted to a spaced portion thereof, the combination of rolling contact bearing means for the connecting link pivot comprising a member fixed to the lever and having a circumferential portion defining a cylindrical pivot bearing surface with its axis disposed parallel to the axis of rotation of the lever about the fixed fulcrum, said pivot member delining a transverse recess through which the connecting link end portion is disposed with substantial clearances between link and pivot, the link end portion defining at least one fiat bearing surface disposed substantially normal to the length of the link and disposed adjacent said pivot member, and spring means biasing the connecting link end portion transversely relative to the pivot, whereby, when the pivot surface is disengaged from the flat bearing surface, said biasing means moves the link end portion transversely to provide a clearance space between pivot and link so disposed that, upon subsequent engagement of the pivot bearing surface with the flat bearing surface, free-boiling contact l l may take place between pivot and bearing surtace as the lever rotates about the fixed tulcrum.

7. In a mechanical linkage including a lever pivotally ilxed to a fulcrum at one end thereof and having a connecting link pivoted to a spaced portion thereof with means constraining the other en d of a link to move in a substantially rectilinear direction generally normal to the length ot'the lever. spring means biasing the link in a direction away from the lever. and means for positioning the lever in either direction, the combination of rolling contact bearing means for the connecting link pivot comprising a member iixed to the lever and having a cylindrical pivot bearing surface, said pivot member dening a transverse recess through whichan end portion of the connecting link is disposed with; substantial clearances between link and pivot, a pair of spaced members secured to the connecting link end portion and forming a pair of nat parallel bearing surfaces disposed normal to the length of the link and adjacent diametrically opposite portions of the l2 cylindrical pivot bearing surface. the spacing between said parallel bearing surfaces being greater than the diameter ot the cylindrical pivot whereby a clearance space is defined at all times between at least one of the flat surfaces and the pivot, and auxiliary spring means biasing the connecting link end portion relative to the lever transversely towards the iixed fulcrum. whereby, when the pivot surface 'is disengaged from both at bearing surfaces, the auxiliary spring means biases the connecting link end portion transversely to the side o! the recess in the pivot nearer the ilxed fulcrum in order that. upon reengagement of the pivot bearing surface with one oi' the flat bearing surfaces. free-rolling contact may take place between pivot and bearing surface `as the lever rotates about the xed fulcrum.

LAWRENCEYB. WALES, MERTON O. HODGES.

No references cited.

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