US1846045A - Recoil check - Google Patents

Description

Feb 23, 1932 R. W, ALBERTSON HECOIL CHECK biled- Dec. 5, 1925 Patented Feb. 23, 1932 UNITED STATES RUSSELL W. ALBERTSON, OF FORT ATKNSON, WISCONSIN RECOIL CHECK Application filed December 5, 1925. Serial No. yI"3,30.

This invention relates to improvements in recoil checks of a type particularly adapted for motor vehicles.

Broadly speaking, it is the principal object of this invention to provide a n ovel and improved recoil check in which initial d1s pincement between the parts connected thereby is substantially unopposcd but in which the checking action is proportioned to the extent ot displacement and thereby to the torce ofthe recoil. t will be understood that the torce with which a spring supported body will be caused to recoil will depend upon the extent of the displacement. Most recoil checls exert a constant retarding eiiect on the recoil and consequently do not discriminate in eti'ect between a severe shock and a light shock. It is my purpose to provide two relatively movable members in a structure so organized to permit ot' substantially unretarded relative movements of said inembers in one direction while checking their recoil or opposite movement to an extent which will be directly dependent upon the extent of the displacement and will consequently be proportioned in a manner hereinafter described to the torce with which the recoil tends to occur.

lt is also my purpose to provide a device in which the checking action is gradiuiliy i'lecreased as the parts approach their nor-- mal positions.

I am aware that various attempts have been made more or less successfully to proportion the checking action to the displace nient. lt is, however, my object to produce this result more dependahly than has heretofore been possible and by a principle newly realized. in this iield, whereby the arcuate angle and area of trictional surfaces in contact actually varied in exactly the desired proportion while maintaining like pressures at all points of contact. By adopting this principle I have succeeded in proportioning thc checking torce to the displacement while eliminating the possibility that the recoil check inigl'it fail to respond to a succession of short, sharp shocks and I have produced a device which is dependably effective.

Further objects oi? the invention conteniplate the provision oi a simple compact device provided with means for its ready adjustment, the provision ot' a device wherein the friction brake mechanism has a mechanical advantage over the cable which actuates it so that greater sensitiveness is achieved with less wear on the parts7 the provision of means for eliminating slap and rattle during the operation of the parts, and the provision oi a device which can be `constructed to in# clude all of the aforementioned advantages and is nevertheless enclosed in a substantially tightcase in which the non-frictional parts can be'packed in grease and which lends itself to attachment with great facility to motor vehicles.

ln the drawings:

Figure i is a side elevation of an embodiment of this invention applied to the frame and axle of a motor vehicle but having its cover plate removed to expose its interior construction.

Figure 2 is a section taken on line 2-2 ot Figure l showing the cover piate in place.

Figure 3 is a detail `View taken on the sec tion through the drum indicated at 3-3 in Figure 2.

Figure 4i is an enlarged detail showing airagn'ient of the friction drum to illustrate the relieved periphery thereof.

Like parts are identified by the saine ref- @rence characters throughout the several views- 1While the casing in which my improved recoii check is housed may be of any desired character, nevertheless I prefer the construction illustrated for reasons which will be made apparent in the discussion of the functions of the several parts. The casing 5 shown in the accompanying `drawings includes a wail t5 ot ovoid outline and an out wardiy projecting wall 7 extending about the perimeter ot wall 6 and integrally connected therewith. A boss at 8 and a stud at 9 are inode tubular to support the shaft 10 upon which the moving parts of the device are rotatable. A cross pin ll is preferably used to lrey the shaft l() against rotation so that it is rigidly connected with the casing shell 5. Journalled upon the shaft 10 is a rotor l5 sin preferably provided with a roller bearing 14 fitted therein.

The rotor includes differentially diametered drum portions 16 and 17 to be described later. A thrust nut 18 threaded to shaft 10 bears against the bearing 14 and has been found to be adapted to take end thrust without'noise. Fine threads are used to connect nut 18 with shaft 10 so that a very accurate acglustment is possible. A pin 18 is used to secure the parts in the desiredadjustment.

The casing shell V5 and the rotor 15 are provided with complementary arcuate ribs 19 and 20, respectively. The extent of these ribs is shown in Figure 3, and it will be observed that they are not quite annular but are provided with spaced ends 21 and 22, thetwo ribs being alike in this particular. These ribs provide seats for the ends of the torsion spring. 25 which has hooked extremities 26, each of which is engaged about one of the ends of one of the arcuate ribs above referred to.

In practice, the spring 25 is maintained under torsion tending to rotate drum 15 upon the axis shaft 10 of the casing shell. A cover plate 27 conforming in outline to the casing shell and provided with a circular opening receiving the drum portion 16 lof rotor 15 is secured to the casing and encloses drum portion 17 and the friction brake mechanism hereinafter to be described.` A rubber gasket at- 28 makes a substantially grit-proof closure between the cover plate 27 and the shoulder 29 of the rotor. A flange 30 on the cover plate embraces the periphery of wall 7 of the casing and -makes a tight joint therewith. A boss 31 cast integr"L ily with the wall portion 6 ofthe casing is adapted to receive a screw 32 whereby the cover plate is detachably secured in place.

The drum portion 16 of the device may be made concentric with shaft 10 and is adapted to have wound thereon a vtension member 35 which, for the purposes of the present disclosure, comprises steel cable having at its free end a headed fitting 36 adapted to be engaged by a clamp member 37 on the axle 38 of the vehicle. At its other end the cable 35 carries a fitting 39 of the peculiar form best shown in Figure 3 and so designed as to provide a bent arm 40 which may be manipulated t irough anopening l1 in drum portion 1G of the rotor and is adapted to interlock with the rotor in such a manner that it cannot be withdrawn from opening 41 as long as 'the tension member 35exerts a pull substantially tangential with reference to the rotor. The torsion of spring 25 keeps the cable 35 constantly under tension so that when the casing 5 ('wliicn is understood to be bolted to the vehicle frame) approaches the vehicle axle 38 the torsion spring will rotate the rotor '15 to wind cable 35 on drum surface 16 and thereby to take up all slack therein. The extent of rotation permitted to the rotor 15 by cable 35 will obviously be proportioned to the extent to which the vehicle frame and axle approach each other.

While it is broadly immaterial whether the drum surface 16 be concentric or eccentric with reference to the'axle shaft 10 it is very important to the present invention that the brake drum surface 17 be provided with a peripheral portion of reduced radius. For the purposes of this invention the otherwise concentric periphery of the brake drum 17 is relieved at 113 to provide a peripheral portion of less radius and of substantially greater than 90 extent in the present embodiment of the invention. The peripheral extent of the relieved portion 43 of the brake drum is preferably so determined as to approximate the maximum range of rotor displacement.

Interacting Vwith the friction drum surface 1 17 is a shoe 50 which may be slightly flexible but which, comparatively speaking, is rather rigid. 1n practice this shoe has been satisfactorily made of a band 51 of 16 gage steel faced at`52 with a leather lining. The friction shoe is concentric with the axis of shaft 10 and is anchored at 53 to the interior of wall 7 of the Casing shell 5. At its free end the shoe 50 is connected with a yoke'55 which is slidable upon a screw 56. The angle of convergence between the sides of wall 7 of the casing is so determined that the head 57 of screw 56 will be in plane Contact with the exterior surface of wall 7, whereby the screw may be readily rotated in the aperture 58 in said wall. A nut 59 is threaded upon screw 56, and a compression spring 60 coiled about screw 56 is confined between nut 59 and the end of yoke 55. By rotating screw 56 it is possible toadjust the tension exerted Aby spring 60 upon the friction shoe 50, and obviously such tension will be determinative in a general way of the pressure with which the leather facing 52 will initially be forced into contact with the periphery of, drum portion 17 of the rotor. The band 51 has an arcuate form concentric with shaft 10, and its slight degree of pliability is adequate to enable itto accommodate itself to the surface of friction drum 17 sufficiently to distribute over such drum the pressure to which it is subjected by spring 60. l The flexibility of band 51, however, is not vsuch as tov cause such band to deviate materially'frorn its original arcuate form'whenthe relieved portion 'its l second factor varies at a variable rat-e.

43 of the drum passes therebcneath. It is obvious, therefore, that there will be no fric tion whatever between the shoe and that part of the relieved periphery 43 of the drinn which underlies the lining 52 of the shoe 50.

lf desired, the device may be designee to cnsnre against deviation of the band from its normal arcuate form. This may be done by interrupting tle continuity of relieved portion 43 with a bearing protubcranee li" corresponding in radius to the brake surface 1T. This supports the brake band or shoe and facilitates pre-calculati m of the operation of the device by keeping the shoe inflesed and thus allowing spring GO to remain at constant tension. The spring (SO tends to bccome overloaded in any event and it is desirable to lreep it under as nearly constant tension as possible.

It has long been lrnown that a. shoe which is anchored rigidly at one of its ends and is rcsiliently anchored at the other end about a friction drum will bind itself upon the drum when the periphery of the drum rotates away from the anchored end of the shoe, whereas when the drum rotates toward the anchored end of the shoe the initial frj'zctional Contact between the drum and shoe will cause the shoe to yield and leave the drum practically free for its subsequent rotation in that direction. ln the present device the springl GO yieldably anchors one end of shoe 50 and, conscqnently, when the rotor l5 is turned in a clockwise direction viewed in Figure l nn der torsion of spring 25, its rotation will be practically nnopposed by any friction between the drum and the shoe 50. lWhen, hmvever, the drum is caused to be rotated counter-clockwise by recoil in the vehicle spri ng which is interposed between the frame and axle to which the drum casing and cable are respectively connected, the result will be to draw shoe aga-inst its positive an chorage at 53, whereby it will be caused to bind on the periphery of the friction drum l? and to check 'the recoil.

In a general way the binding effect in the presentdevice will be proportioned to:-1, the initial tension of spring 2, the arcuate l angle of contact between the band and drum;

and 25, the area of contact; el, the character of the frictionally related surfaces. The first and fourth factors are constant during normal operation of the present device. The The third factor varies at a substantially constant rate.

It will be remembered that in the normal position of the parts as shown in Figure l,

` the relieved portion i3 of the friction drum underlies a comparatively large extent of the shoe 50. The area of friction surface between the drum and shoe is at a minimum in this position of the parts. lf displacement now occurs between casing and the parte to which cable 35 is connected the drum will rotate in a clockwise direction, and while the drum encounters no material degree of friction in opposition to this clockwise rota-l tion, nevertheless it will be observed that the angle of contact and also the potential friction area is being increased in exactly the proportion in` which displacement occurs be` tween the parts. angie and area is produced by the movement of the relieved portion 43 of the drum out from under the friction surface of the shoe 50. At the maximum displacement to which the parts areordinarily subject the relieved por.- tion of the drum will have passed wholly from beneath the friction surface of the shoe, and the drum will be in a position for frictional contact with the entire length of the friction surface of the shoe. It is particularly to be noted that the arcuate space between the end 61 of the line 52 and the end 62 of such lining is so calculated that the relieved portion 43 of the drum will not pass beneath end G2 of the lining until it has left end 61 thereof.

finer displacement has occurred and a greater. or less portion of the relieved periliiheryt3 of the drum has passed from beneath the shoe 50 the recoil will take place and, from the above discussion, it will` be ap preciated that such recoil will be opposed by tl e oinding of the shoe on the periphery of the drum. The degree of opposition to the recoil or counter-clockwise rotation of the friction drum will be in a general way proportionate to the original displacement. lt will not, however, be exactly proportioned to the displacement but will tend to increase more rapidly than 'the value of the displace ment and with a constantly increasing factor. Se far as the area of surfaces in frictional contact concerned, the binding effect and con sequent checking action will. probably be directly proportional. As` the` included" angle of frictional contact increases, however, there is an increasing factor of potential checking action due to the development of a snubbing effect.

lt follows from the foregoing remarks that the recoil check herein described will offer comparatively little resistance to recoil when 'the displacement has been slight, butthat a high resistance will be initially offered to recoil when` the displacement has been greater, Ubv'iously, the high resistance which is in v offered subsequent to a comparatively displacement decreases as the displacenient decreases and reaches a minimum value when the parts have been restored to their normal positions.

@ne situation remains to be considered. If

the displacement of the drum is so excessive as to bring the relieved portion 43 thereof beneaththe free end 62 of the shoe the result will be that when recoil commences the de- Ubviously, the increase in CLL vice will not act initially with its maximum retarding eect. This is desirable since in cases of extreme shock the retarding effect would be too severe if it were increased in the proportion which the increase follows during the normal operation of the parts. The construction illustrated, however, is such `that when the parts exceed their normal displacement the area of the friction surface becomes 1 decreased, and during recoil the resistance will be somewhat below the maximum at first and will reach the maximum when the parts reach their maximum normal displacement. This action of the checking device results in gradually absorbing the. shock and after the present embodiment of the invention the friction surface of the drum and also that of the shoe each `has an arcuate extent of approximately two-thirds of the entire periphery of the drum. These proportions need not be adhered to but have been found satisfactory in practice.

The length of tension member is preferably so adjusted that the relieved portion of the drum will, in the normal stationary positions of the parts, underlie the fixedly anchored end of the brake. The reasons for this have already been explained. It may be said, however, that the eective length of the tension member or cable may readily be varied through the simple expedient of providing a number vof apertures 41 in drum portion 16. This not only provides means for fitting the length of the cable to the dis-- tance in any given installation between a vehicle axle and vehicle frame but, furthermore, the adjustment of the cable provides means for taking care of variations in the stiffness of the vehicle springs. It will be obvious that if the cable is `so adjusted as to increase its length over that indicated in Figure 1 so that the drum is permitted to rotate clockwise, the change in initial position of the drum will increase the initial intensity of the checking action of the device. The construction illustrated is such that a minimum checking action will occur during those minor os-.

l checking action throughout the range of operation of the device. It is well known in the art that the adjustment of the tension of such springs affords means for controlling the braking effect which will be exerted by the shoe when the drum rotates from the fixed anchorage of the shoe toward its yieldable anchorage.

While the device thus far disclosed is a complete and operative structure, for the purposes of this invention I prefer to add one or more stops shown at as comprising studs projecting inwardly from the casing 5. These stops positively limit the releasing movement of intermediate portions of the band. Because of wide variations in leather thickness, I prefer in practice to adjust each stop separately by making it in the form of a screw which will be turned down tight on the band and an interposed shim. A shim .005 inch more or less will be satisfactory considering the self-compacting quality of the leather used. The shim is now withdrawn and the screw sheared off to leave the stu-d 7G, or inner end of the screw in the desired position as indicated by experiment. Stops 70, however, serves to relieve the device of an annoying slap to which other recoil checks are subject upon such occasions as are frequently encountered in practice where a series of shocks reach the device to cause it to act several times in quick succession. Under suchcircumstances the friction band or shoe of the ordinary recoil check frequently leaves the drum to such an extent that when the slack is taken up there is a pronounced slap very annoying to the operator of a vehicle equipped with such a device. By using a stop 70 extending into close proximity to the band I have overcome the objectionable slap without in any way interfering with the operation of the device.

In stating the objects of this invention I mentioned the fact that I desired to give the friction mechanism a mechanical advantage over the'tension device or cable 85. The desired result is accomplished by making the drum portion 16 of the rotor somewhat smaller than the friction surface 17. frictional resistance on surface 17 to check a given amount of recoil than would be necessary if the surface 17 corresponded in its radius to surface 16 of the rotor. At the same time, the sensitiveness of the `device is increased inasmuch as a comparatively slight movement of cable will produce a correspondingly increased linear travel on the surface of friction drum 17. It is furthermore to be noted that the shoulder between the two drums co-operates to good purpose with the closure plate Q7 to exclude foreign matter from the interior of the casing. It is very important that water be excluded because water changes the frictional characteristic of the leather or other brake lining employed at 52 on the friction shoe. The fact It takes lessthat the two drums l? and 16 are integrally connected in a common hollow rotor affords desired room for a torsion spring of ample size for the operation of the device.

l claim:

l. ln a device of the character described, the combination of two relatively movable members of substantially fixed contour hav ing partially overlapping friction surfaces in their normal positions, means for maintaining said members in frictional engagement, means for mounting said members for relative movement aforesaid while maintaining such frictional engagement, and means for moving one of said members with respect to the other whereby to vary the extent of overlap between the respective friction surfaces of said members.

2. ln a device of the character described, the combination with a rotor having a braking surface, of a shoe frictionally bearing on such surface, such surface being relieved to provide a portion of said rotor out of contact with said shoe and of a length such as to be adapted to be spanned thereby, whereby the rotation of said rotor is adapted to vary the included angle of frictional contact between the braking surface of said rotor and that of said shoe.

3. In a device of the character described, the combination with a braking shoe providing a discontinuous braking surface, of a rotor supported for oscillation adjacent said surface and provided with a portion of such extent that some part thereoef will underlie said surface in all positions of said rotor in contact frictionally with said .surface and a relieved portion spaced from said surface, the oscillation of said rotor being ladapted to vary the frictional area of contact between said rotor and said shoe.

el. In a device of the character described, the combination with a member having a peripheral surface with portions at different radial distances from its center, of a brake shoe operatively associated for frictional contact with said member and supported by relatively yieldable and fixed anchorages at its respective ends in such a manner as to leave said member substantially fr-ee for rotation in one direction while opposing a variable frictional resistance to the rotation of said member in the other direction.

5. In a device of the character described, the combination with a friction drum member and another member, said members being arranged for relative movement, of a friction shoe connected with said other member and supported in operative engagement with said drum, and means anchoring said shoe to oppose frictionally the relative rotation` between said members in one direction while permittingr the free rotation between said members in the opposite direction, the said drum member having peripheral portions at varying radial distances from its center, whereby to vary the effect of said shoe in opposing relative rotation between said members in said first mentioned direction.

6. ln a device of the character described, the combination with a drum having its periphery divided into friction and nonfriction surfaces of differing radii, of a friction band encircling said drum and provided at one end with a comparatively fixed anchorage and at the other ene with a comparatively veilding anchorage, together with means for producing relative rotation between said drum and band.

7. ln a device of the character described, the combination with a drum having a discontinuous peripheral friction surface and an intermediate peripheral surface of lesser radius and a housing for said drum, said drum and said housing being relatively rotatable, of a friction strap anchored withinsaid housing passed about saiddrum and yieldably connected again with said housing, whereby said strap is adapted to permit substantially unrestrained rotation between said drum and housing in onedirection and to frictionally oppose relative rotation in the opposite direction to an extent generally proportionate to the extent of the original rotation.

8. In a device of the character described, the combination with a drum member having a peripheral friction surface interrupted by a surface of lesser radius and a housing member for said drum, one of said members being adapted for connection with a motor vehicle axle and the other with a motor vehicle frame in a manner adapted to produce relative rotation between said members cominensurate with displacement occurring between said aXle and frame, of torsion means operable to produce relative rotation `between said members in one direction, a friction shoe operatively co-acting with said drum and provided with a fixed anchorage to said casing at the end toward which a given point on said drum moves after frictionally contacting said shoe during the relative rotation between said members, and a yieldable anchorage for the other end of said shoe.

9. In a device of the character described, the combination with a pair of relatively movable members having complementary friction surfaces in operative contact and partially overlapping in the normal positions of said members, of a spring housed within and acting upon one of said .members and adapted to produce relative movement between said members in a `direction such as to increase the extent to which said surfaces overlap, means for maintaining said surfaces in operative frictional contact throughout the extent of their overlap, and means acting positively upon one of said members in opposition to said spring to restore said members to their said normal positions.

CII

10. In a device of the character described, the combination with a rotor provided with la discontinuous peripheral braking surface, of an arcuate shoe provided with a discontinuous braking surface complementary to that of said rotor and in contact therewith insofar as said surfaces overlap, variable means normally maintaining said rotor in a position in which its braking surface partially overlaps the friction surface of said shoe, and a spring acting o-n said rotor to increase the extent of frictional contact between said surface when said means fails to operate to maintain said rotor in its aforesaid normal position.

11. In a device of the character described, the combination witha rotor provided with a discontinuous peripheral braking surface, of a-V shoe complementary to said rot-or and provided with a discontinuous friction surface in contact with said braking surface insofar as said surfaces overlap, said shoe having one of its ends rigidly anchored and another of its ends yieldably anchored together with means acting to produce relative rotation between said shoe and said rotor and adapted to maintain said rotor in a position wherein the friction surface of said shoe will partially overlap the braking surface of said rotor, the yieldable anchorage for said shoe being so disposed as to release said shoe from binding engagement with said rotor when said rotor moves in a direction to increase the extent to which said surfaces overlap.

12.. In a device of the character described, t-he combination with a rotor having a discontinuous braking surface relieved throughout a material portion of the periphery of said rotor,y of a shoe complementary to said rotorand provided with a discontinuous friction surface in overlapping engagement with a part of said braking surface in the norma-.l position of the parts, and a spring normally acting to maintain said surfaces in contact, said shoe having a. suiiicient rigidity to. span the cut-away portion of said rotor and having'sufcient flexibility to be drawn by said spring into conformity with the b-raking surface of said rotor'.

13. In a device of the vcharacter described, the combination with a relatively fixed casing, of a rotor operatively mounted for rotation with respect to said casing and having a drum portion in said casing withv a part of its periphery reduced in radius and a concentric drum portion exterior of said casing, acover plate for said casing applied to said rotor intermediate its drum portions aforesaid, friction means applied to said drum portion within said casing and productive of resistance proportionate to the degree of contact therewith in the rotation of the drum portion exterior to said casing.

14. In a device of the character described, the combination with a relatively fixed cas` ing, of a rot-or operatively mounted for rotation with respect to said casing and having a relieved friction drum portion in said casing and a winding drum portion exterior to said casing, a. cover plate for said casing applied to said rotor intermediate its drum portions aforesaid, friction means applied to said drum portion within said casing and productive of resistance proportionate to the degree of contact therewith in the rotation of the drum, and actuating means applied to said drum portion exterior to said casing, said actuating means comprising a cable drawn upon said winding drum portion and adapted when subject to tension to rotate said rotor in one direction, said rotor being provided interiorly with a torsion spring housed between said rotor and said casing and tending to rotate sai-d rotor opposite to the` direction in whichsaidrotoris turned by said cable.

15. In a device of the character described, the combination with a shallow casing and an axle shaft therein, of a hollow drum having portions of different diameters and operatively mounted for rotation on said shaft, the larger portion of said drum being housed within said casing and the smaller portion of said drum being exposed exteriorly of said casing, a brake shoe rigidly connected at one of its ends with the interior of said casing and extending about said drum toV a, resiliently yieldableanchoragey of` its other end to said casing, a torsion spring. connected with said casing and the outer end of said drum and housed within said drum, and tension means opposing the'action of said spring and wound upon said drum in a direction to rotate it from the fixed end of said shoe toward the resilient anchorage thereof, the larger portion of said drum being relieved whereby to affordclearance between a por-- tion of its periphery and an overlying portion of said shoe, an area of surface infric-- tional contact between said shoe and said drum being variable in accordance with the position of rotation of said drum.

16. In a device of the character described, the combination with a drum having approximately one-third of its periphery cut away to reduce its radius and having the remainder of its periphery substantially concentric with its axis, a shoe provided with a friction surface substantially the arcuate extent of the concentric portion of the periphery of said drum, means supporting said shoe in a position affording operative frictional contact between said surface and the periphery of said' drum, and means for producingrelative rotation between said shoe and said drum, said rotation beingV adapted to vary the a-ngle of friction contact between saidshoe and said drum by varyingthe ex- Clt tent to which the friction surface of said shoe overlaps the concentric peripheral portion of said drum.

l?. In a device of the character described, the combination With a drum having approximately one-third of its periphery cut away to reduce its radius and having the remainder of its periphery substantially concentric with its axis, a shoe provided With a friction surface substantially the arcuate extent of the concentric portion of the periphery of said drum, means supportingr said shoe in a position alfording operative frictional contact between said surface and the periphery of said drum, and means for producing relative rotation 'between said shoe and said drum, said rotation being adapted to vary the area of friction contact between said shoe and said drum by varying the extent to Which the friction surface of said shoe overlaps the concentric peripheral portion of said drum, said means beingl adapted to maintain said drum and said shoe normally in relative position such as to maintain a minimum degree of such overlap.

18. In a device of the character described, the combination with a casing, of a friction shoe having an arcuate extent of approximately 211: and provided at its opposite ends with relatively fixed and relatively yieldable anchorage to said casing, a drum positioned within said slice and provided with a periphe 'al friction surface substantially corresponding in extent to that of said shoe and relieved throughout the remainder of its periphery to avoid contact With said shoe, and means for actuating said drum to oscillate it with reference to said shoe, said means being adjusted normally to maintain said drum in a position in which a minimum port-ion of its periphery Will overlap the frictional surface of said shoe, the relieved portion of the periphery of said drum underlying the end of said shoe Which is provided With a fixed anchorage whereby any displacemeiit of said drum will increase the opposition to a movement of said drum from said fixed anchorage toward said yieldable anchorage.

19. In, a device of the character described, the combination with a drum having' a peripheral friction surface interrul'ited by a relieved portion of less radius, of a shoe conforming' to the friction surface portion of said drum and adapted to span the relieved portion thereof, said shoe being provided with a relatively lixed and a relatively yieldable anchorage at its respective ends, a tori-tion spring actingn on said drum in a direction to rotate it toward the fixed anchorage of said shoe, and positive motion transmitting connections acting,` on said nrum in a direction to rotate it from the fixed anchorage toward the yieldable ancho-rage of said shoe, said connections being normally so adjusted that When the parts are at rest substantially the entire relieved portion of said drum Will underlie that end of said shoe adjacent its fixe-d anchorage.

20. A recoil check comprising the combination of relatively rotatable parts having relatively discontinuous friction surfaces adapted for interaction in opposition to the relative movement of said parts toward a predetermined relative position, said surfaces being so disposedy with reference lto said position that their mutua-l overlap varies generally proportionately With displacement throughout a tgiven range of relative rotation to and from said position and generally in versely as the displacement in excess of .aid

range. w

2l. A recoil check comprising thecombination of relatively rotatable parts having relatively discontinuous friction surfaces adapted for interaction in opposition to the relative movement of said parts toward a predetermined relative position, said surfaces being so disposed with reference to said position that their mutual overlap varies generally proportionately kwith displacement throughout a given range of relative rotation to and from said position and generally inversely as the displacement in excess of said range, the frictional resistance to relative movement toward said position being approximately in accordance With overlap of said surfaces whereby such resistance vvill progressively increase in approaching said range and progressively decrease within said range.

22. A friction check comn'ising the combination of a rotatable member having a discontinuous friction surface, and an arcuate shoe member having a complementary discontinuous friction surface and mounted to oppose drum rotation frictionally, the extent and posit-ions of said surfaces being so determined that their maximum degree of overlap will occur intermediate the extremes of possible relative movement.

23. T he combination with relative rotatable members, of an arcuate surface on one thereof, a friction shoe in pressure engagement about said surface and anchored at one of its ends to the other of said members, whereby frictionally to oppose relative rotation of said members in one direction, and one of said members having a contour for relieving the degree of initial opposition offeredby said shoe when said members have exceeded a predetermined displacement.

24. The combination With relatively rotatable members and a spring tending to rotate them from a predetermined initial p0sition, of a curved peripheral surface limited in arcuate extent upon one of said members, and a friction shoe under tension about said surface and anchored at" one of its ends to the other of said members, whereby frictionllO ally to oppose relative rotation of said members toward said position only, said shoe and surface having relatively little overlap in said posit-ion and being of such relative extent as to reach a maximum degree of overlap before reaching maximum displacement from said position.

25. The combination With a rotatable member having its periphery relieved to provide a discontinuous friction surface concentric with the axis of rotation of said member and of relatively greater radius than adjacent portions ofthe periphery thereof, of a relatively fixed housing, a flexible brake shoe anchored at on-e end Within said housing encircling a portion of said member and yieldably connected at its other end with said housing, said shoe being extended about only a portion of said member, tension means adapted to rotate said member in opposition to the friction of said shoe, and a spring connected between said member and said housing adapted to rotate said member in the opposite direction, said tension means being so adjusted as to maintain the relieved portion of said member normally Within the compass of said shoe and in a position to pass from beneath said shoe upon rotation of said member by said spring.

26. The combination Wit-h a rotatable member having its periphery relieved to provide a discontinuous friction surface concentric With the axis of rotation of said member and of relatively greater radius than adjacent portions of the periphery thereof, of a relatively fixed housing, a flexible brake shoe anchored at one end Within said housing encircling a portion of said member and yieldably connected at its other end with said housing, said shoe being extended about only a portion of said member, tension means adapted to rotate said member in opposition to the friction of said shoe, and a spring connected between said member and said housing adapted to rotate said member in the opposite direction, said tension means being so adjusted as to maintain the relieved portion of said member normally Within the compass of said shoe and in a position to pass from beneath said shoe upon rotation of said member by said spring, the proportion and arrangement of the parts being such that in an extreme rotative position of such member under the action of such spring, the

- relieved portion of said member Will pass beneath another portion of said shoe.

27. A recoil check comprising the combination of relatively rotatable members, and means for frictionally opposing rotation of said members toward a predetermined relative position, said means and a member being frictionally engaged and mutually spaced for a predetermined.peripheral extent Whereby to be adapted to produce a frictional opposition variable in intensity according to the displacement of said members and adapted toI reach a maximum intermediate the range of possible displacement. l

28. A friction check comprising members relatively rotatable between a neutral position and an extreme position, and means opposing a variable frictional resistance to the movement of said members toward said neutral position and controlled in the relative movement of said members, said means andone of said members having partially relieved frictionally engageable surfaces angularly positioned for a maximum engagement at an intermediate point in relative rotative movement of saidmembers and operatively adapted to afford frictional opposition reaching a maximum at said point, whereby `said members in their extreme positions Will be opposed by frictional resistance gradually increasing to said maximum and thence decreasing toWard a "minimum in approaching said neutral position. l

RUSSELL W. ALBERTSON.V

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