US2628692A - Hydraulic check - Google Patents

Description

Feb. 17, 1953 G. H. HUFFERD 2,623,692

HYDRAULIC CHECK Filed July 9, 1948 5 Sheets-Sheet l 40 m- I /7a G. H. HUFFERD HYDRAULIC CHECK Feb. 17, 1953 5 Sheets-Sheet 2 Filed July 9, 1948 Feb. 17, 1953 a, H. HUFFERD 2,628,692

HYDRAULIC CHECK Filed July 9, 1948 5 Sheets-Sheet 3 21 A? H E J 4 c I I v 1 TI! I 34 Z0 [H 13/ 36 0/ z; 2 K a: 1

Feb. 17, 1953 G. H. HUFFERD 2,628,692

HYDRAULIC CHECK 620/865 H flux/m0 Patented Feb. 17, 1953 HYDRAULIC CHECK George Hiram Huflerd, Cleveland, Ohio, assignor to Houdaille-Hershey Mich., a corporation of Michigan Application, July 9, 1948, Serial No. 37,950

13 Claims.

This invention relates to an hydraulic check unit, and particularly to an improved hydraulic check. unitv adaptable for use in checking the movements of the picker stick of a loom.

Asv is well known, a loom picker stick continuously undergoes a cycle of movements involving very high rates of acceleration and deceleration at a cyclic rate approaching 180 or more cycles per minute. A picker stick is generally mounted oneachend of the lay of the loom and its path of movement is. controlled by well known linkages so that while the picker stick describes a generally pivoting movement, the top end thereof moves in a substantially straight line path. On its inward stroke, the picker stick accelerates and throws the shuttle at a very high velocity through the-warpshed to the other side of the loom where a, similar picker stick catches the shuttle and decelerates the shuttle, preliminary to throwing the shuttle, back across the loom. Since the rate of production, of any loom is determined primarily by the cyclic rate of the shuttle movements, there has been a continuous efiort to increase the rate of shuttle cycles so that present day looms operate at 180 or more picks per minute. Obviously, the acceleration and deceleration forces exerted by and upon the picker stick when operating at such high cyclic rate, are of tremendous magnitudes, hence it is of extreme importance that the movement of the picker stick be smoothly decelerated on either its inward or outward stroke in such a manner as to prevent the development of excessive forces thereon. At the same time,

the picker, stick must be accurately positioned with respect to the shuttle box, before, theshuttle time, at the same position in the shuttle box.

If, the forward or inward movement, of the picker stick is not properly controlled, then, when the shuttle is expelled from the shuttle box, the shuttle is likely to be thrown wild and thus produce defective cloth. Of course, due to the highcyclic rate of operation, it is also very essential to yieldingly bring the picker stickto rest as soon as possible after its shuttle throwing stroke has been delivered. The checking of the movement of the picker stick on its outward stroke is equally important, because the impact of the incoming shuttle must be smoothly absorbed in such manner that the shuttle will not rebound but will be brought to rest at a predetermined position in the shuttle-box. Again, such comparatively short travel of the, picker stick.

Corporation, Detroit,

It has heretofore been proposed to employ an hydraulic checking device for effecting the necessary checking actions required for proper operation of the picker stick. However, since any such checking device must necessarily be of the double acting type and furthermore, since all looms vary slightly in their operating characteristics so that independent adjustment of the checking action exerted by the hydraulic checking device in either direction of its movement is required to be made upon not only the initial assemblage of the checking device to the loom but at frequent intervals thereafter, due to variations in the loom operating characteristics produced by temperature, humidity, or wear ofcomponents, it is readily apparent that conventionally constructed, double acting hydraulic check units are not ordinarily suitable for such application.

Accordingly, it is an object of this invention to provide an improved hydraulic check unit, and particularly, a double acting hydraulic check which is unusually adaptable to checking the movements of the icker stick of a loom.

Another object of this invention is to provide an improved double acting hydraulic check, unit wherein the checking action in either direction of operation of the check may be conveniently independently adjusted, and particularly a construction wherein the effective checkin action in at least one direction of operation. may be manually varied by the simple manipulation of a control member and without requiring the disassemblage of the check or any interruption in operation of the machine tov which the checking unit is, applied.

A further object of; this invention is to, provide an hydraulic check unit of the type wherein throttling apertures in a cylinder element permit a controlled by-pass of fluid around a piston, and characterized by the formation of the peripheral portion of at least one face of the piston with a generally helical configuration, so that an axial adjustment of the checking action may be accomplished through relative rotation of the piston and the throttling ap rtures.

Still another object of this invention is the provision of an hydraulic check unit capable of effecting successive checking actions at a high cyclic rate by the by-pass of fluid around a piston element through throttling apertures a coopcrating cylinder, and particularly characterized by the; provision of an expansible fluid chamber in communication with the throttling apertures whichv chamber increases its volume automatically to accommodate any excess fluid flow through the t r ttling pertures which. does not imm diately fiow to the other side of the piston element, thereby preventing the build-up of excessive pressures in the hydraulic check units and thus eliminating unpredictable variations in the checking action when the unit is operated at a high cyclic rate.

Still another object of this invention is to provide an improved double acting hydraulic check unit for looms or similar applications wherein the effective checking force in at least one direction of operation of the check unit may be conveniently manually adjusted without requiring disassembly of the check unit or interruption of operation of the machine to which it is applied.

The specific nature of the invention as well as other objects and advantages thereof will become apparent to those skilled in the art from the detailed description of the annexed sheets of drawings which, by way of preferred example only, illustrate one specific embodiment of the invention.

On the drawings:

Figure 1 is a side elevational view of a portion of a control linkage for a picker stick of a loom which linkage embodies an hydraulic check unit constructed in accordance with this invention;

Figure 2 is a partial view of Figure l but illustrating the position of the elements of the linkage when the picker stick is positioned at its shuttle contacting or neutral position;

Figure 3 is a top plan view of the picker stick control linkage with the component thereof in the position of Figure 1;

Figure 4 is a front elevational view of Figure 1;

Figure 5 is a sectional view of an hydraulic check unit embodying this invention, taken along a plane passing through the longitudinal axis thereof;

Figure 6 is a sectional view taken on the plane VI-VI of Figure 5;

Figure '7 is a partial sectional view similar to Figure 6 but illustrating the manner in which the expansible fiuid reservoir chamber accommodates any excess of fluid being by-passed around the piston;

Figure 8 is a partial sectional view taken on the plane VIII--VIII of Figure 1;

Figure 9 is a partial sectional view taken on the plane IX-D! of Figure 1; and

Figure 10 is an axial sectional view of a modified construction of an hydraulic check unit.

As shown on the drawings:

While this invention will be particularly described and ill strated in connection with the application of an hydraulic check unit to checking the movements of a picker stick of a loom, it will be obvious to those skilled in the art that such application is merely exemplary and the hydraulic check unit embodying this invention is obviously adaptable to many other applications.

Referring to Figure 1 the n m ral III indicates the rock shaft o a loom while the numeral II indicates a conventional pi ker sti k. Picker stick II is supported for oscillating movements with respect to the rock shaft III by a linkage which controls the movement of the picker stick so that the top end of the stick traverses a substantially horizontal, straight line path. Such linka e, which is described in detail in my copending application, Serial No. 37,951, filed concurrently herewith, now Patent No. 2,566,890, may comprise a primary bracket I2, rigidly secured to the rock shaft I0, and a secondary bracket I3 which is connected to primary bracket I2 by a pair of pivoted links I4 and I5. Link Il may constitute two identical parallel link elements. The location of the pivot point of links I4 and I5, as well as the relative dimensions of such links are selected in the manner described in detail in my above referred to copending application, so that the picker stick II can move only in a path which will result in the upper end of the stick moving along the lay (not shown) in a substantially horizontal, straight line path.

Thus, primary bracket I2 constitutes an integral casting having a split cylindrical recess IZm formed therein to receive the end of a rock shaft I0 and being clamped to rock shaft III by a bolt I2e and a key I2f (Figure 8). Key I2! is disposed in a transverse aperture I2g in bracket I2 which communicates with recess IZm. Key I2f is of longitudinally tapering configuration and is drawn into engagement with shaft III by a nut I272. The surface of key I2! contacting shaft I0 is of concave configuration to provide a pair of parallel biting edges I29.

In addition, primary bracket I2 defines three spaced pivot bearings I2a, In and I2c respectively. Pivot bearing I M is located in slightly depending relationship with respect to rock shaft I0 and provides pivotal support for one end of the link I5. Pivot bearing I2a is preferably of bifurcated construction and thus surrounds the end of link I5. A pin I6 is provided for pivotally mounting link I5 in pivot bearing I2a and that portion [6a of the pin I8 which journals link I5 (Figure 9) is eccentrically formed so that limited adjustment of the effective length of link I5 may b obtained by varying the angular position of the pivot pin I6, in a manner described in more detail in my above referred to copendin application. A nut I Bb retains pivot pin I6 in position.

Pivot bearing I 2b is also of bifurcated construction and is located directly above the end of rock shaft I0 and provides pivotal support for the cylinder element 2| of an hydraulic check unit 20 to be described in more detail later.

Lastly, pivot bearing I2c is defined by a yoke shaped portion I2d of primary bracket I2 and such pivot bearing is disposed in generally triangularly spaced relationship with respect to pivot bearings I21; and I2!) and pivotally journals one end of the links I4.

The secondary bracket I3 is of generally reversed E-shaped configuration and may be convenientlv formed by a riveted assemblage of two half parts, as indicated by rivets I 3e. The back side of the upright portion of bracket I3 is suitably apertured as indicated at I3d so as to conform to and snugly partially surround the bottom portion of the picker stick II. Picker stick I I is rigidly clamped in recess I3d by a plurality of U-shaped clamps I! which are secured to secondary bracket I3 by bolts Ila.

Secondary bracket I3 likewise defines three pivot bearings which are respectively located in the ends of its arm portions. Thus, a bifurcated pivot bearing I 3a is formed in the end of the lowermost arm portion and pivotally journals the other end of link I5. A bifurcated pivot bearing I3b is mounted in the end of the top arm portion and pivotally journals the end of the piston rod 26 of the hydraulic check unit 20. Lastly, a pivot bearing I3c is provided in the end of the interbody conventional pivot pins and grease fittings];

Conventional mechanism isprovided for'producing" the required cyclic movements of the picker stick" ll. Thus, alug strap [8' is provided having a looped portion [8a surrounding the intermediate portion of picker stick H. Lug strap I8 is supported and horizontally oscillated by'an actuating link I9 which is cam driven in timed relationship to the movements oftheloom androck shaft It! in accordancewithwell known procedure. It is therefore suflicient to point out that, periodically, the lug strap I8 shifts the picker' stick- II from its extreme outward position to. its extreme inward position and in so doing; accelerates the picker stick H so rapidly that the shuttle (not shown), which is in contact with the upper end of the picker; stick II, is" violently thrown to the other side of the loom. After the shuttleis thrown, the inward movement of the picker stick H is checked by the hydraulic unit 20 in a mannerto be described and the picker stick II is brought to rest. Thereupon, a torsion spring 40, operating between secondary bracket l3 and link I5 is effective to urge the picker stick it outwardly at least to an intermediate neutral position illustrated in Figure 2 wherein a spring stop 4t carried by an arm 42 pivotall'y secured at 43 to secondary bracket [3, engages a fixed pin M transversely mounted in link I5. At this point, the picker stick II is properly positioned to receivethe initial contact by'the shuttle, when the shuttle is thrown back from the other side of the loom. The construction of the leaf" spring stop 4l is described in detail and claimed in my copending application, Serial No. 37,951. filed concurrently herewith, now Patent No. 2,566,890, and reference should be had thereto for a more detailed description.

Upon the contact of the returning shuttle with the top end of the picker stick II, the stick II is violently driven outwardly, and such outward movement must be checked by the hydraulic unit 20 to rapidly and smoothly bring the picker stick I l to rest without producing arebounding of the shuttle therefrom or permitting excessive forces to be developed in the picker stick H or any portion of its control linkage. Furthermore, the picker stick H must be brought to rest in substantially the same position each time so that the shuttle is properly positioned in the shuttle box.

As is well known, the operating characteristics of a loom vary substantially with temperature and humidity conditions as well as with wear of various component parts thereof; As a result, it is essential that the checking action exerted by the hydraulic check unit 20 be conveniently manually adjustable at least with respect to the effective checking action exerted upon the outward, or shuttle checking stroke of the picker stick llwhile the loom is operating, so that optimum conditions of checking, and hence uniform loom operation may be maintained.

Referring particularly to Figures 5 through '7, the hydraulic unit 20 embodying'this invention is seen to comprise a cylinder casing 2| having a hollow bore Zla therein closed at one end and counterbored at the other end, as indicated at 21b to receive a piston rod bearing'support'mem oer 22. At the closed end of the casing 2| an integral bearing lug 2 im isformed by which the casing is pivotally secured to pivot bearing lZb oi the primary bracket. A sleeve 23 is inserted in. the-main bore: portion 210L cylinder: casin 21 and. is rotatably adjustablesthereini. Suchradjustment may be efiected in any convenient manner, for example,.bya. pinion. 24 which. is-j'ournaled in a; generally radial extending: aperture 2 lc'provi'ded adiacentthe closed end of cylinder casing 2|- The:pinion'ztispreferably manually rotatable, such: as: by a. flexible. shaft: 25. which. is suitably co-rotatably secured) to. the. pinion 2.4; by a coupling 25a; Gear teeth 23:: are formed on the end face of sleeve. 23 and mesh with; pinion 24. Hence, upon rotation of the'flexible shaft 25 by a suitable. control knob. (not. shown) which may be located on the. machine; in. any: convenient positionxfor. the operator, the: angular position. 01 the. sleeve- 23: in. thecylinder casing: may" be varied A. piston. rod. 26 is provided which is slid'ably journaled. in a sleeve bearing insert-22a mounted in the. central bore. of the. bearing. support .ring 22. The inner endof piston rod 26. is'threaded as indicated at 26a, and av piston 21 is adjustably positioned on. such threaded. end: by a. pair. of opposed nuts 28..

The piston 21 is of generally'cup-shaped' configuration and, while'itsbottom end face. 2'la.: is substantially perpendicular to. the axis: of the piston: rod 26, thezopposite face is. shaped; so that at least: a portion; of. the periphery of such-face is generally helically' inclined. with respectjtoi the piston rod axis asrindiicated. at'2:1b.. For example, such portionl'lb may be-formedqby cutting the rim portion of piston 21: at an: acute angleto the axis of the. piston.

The entire interior of the piston. casing- 21 is filled with a. suitable hydraulicv fluid. In order to provide a controlled checking action upon relative. movements between the. piston, 21' and the bearing sleeve 23, the bearing sleeve 23 is provided with a plurality of. axially spaced throttling: apertures .29 and 30respectively; Such recesses are connected in fluid communication exteriorly of piston 2.1 in any convenient'manner, such as by the main bore 2 In of the piston. casing 2| being radially enlarged throughout. its. central portion to provide a reservoir chamber 2 lo. It is therefore apparent. that any time the piston. 21 is positioned intermediate the throttling apertures 29. and 3H, fluid will be by-passed around the piston by flow through the throttling apertures. 29 and 3B and the communicating recess or chamber 2 lo.

The effective fluid passage areas: of the throttling apertures 29 and 30 which are. exposed in any particular position. of thepistonv 21? of course determines the rate. of fiow'offiuid around the; iston and hence, determines the. effective checking action. exerted uponv the. axial movements of the piston. Such throttling apertures are therefore complexly shaped in an axial direction to: provide the desired checking characteristics required at. each particular axial position of the piston 21:. Thus. the throttling aperture 29*, which is. effective to check the inward stroke of the picker stick. ll. after the shuttle has been thrown, has a relatively short and narrow axial extension 29a so that the movementof thepiston 21. to the left as. viewed in: Figures 5? and 6 is very rapidly checked after the piston once begins to override the throttling aperture 29. In contrast, the throttling aperture 30, which effects the checking of the picker stick after it is contacted by the shuttle thrown from the other side of the loom, permits a much greater length of'travel of the iston 21- anda more gradual increase-of the 7 fluid checking action. Thus, the throttling aperture 30 is provided with a tapering axial extension 30a.

The rate of decrease of width of the throttling aperture extension 30a is, of course, proportioned according to well known design procedure to provide the desired degree of throttling at each successive axial position of the piston 21 as the piston rod 26 moves to the right as viewed in Figures and 6, so that the piston 21, and hence the picker stick and shuttle will always be stopped at substantially the same position.

As was heretofore indicated, it is practically impossible to adjust the check unit for the picker stick of a loom to exactly provide the desired checking characteristics prior to assemblage of the unit in the loom and observation of the operation of the loom. This is particularly true with respect to the checking of the outward stroke of the picker stick, wherein much greater energy forces must be absorbed and yet the picker stick must be accurately brought to rest in a predetermined relationship with respect to the shuttle box. The described construction permits a very accurate adjustment of the checking effect with respect to the axial position of the piston 2! during the outward movement of the piston rod 26, which corresponds to the outward movement of the picker stick. By rotating the sleeve 23 through the described manual adjusting mechanism, the effective angular position of the throttling aperture 30 with respect to the helically extending portion 21b of the face of piston 21 is shifted, and, as a result, a variation is effected in the amount of checking action produced at any particular axial position of the piston 21, as it moves to the right as viewed in Figures 5 and 6.

It is therefore apparent that the checking action may be accurately adjusted after the check unit is assembled to the loom and while the loom is operated, and hence variations in the operating characteristics of the loom may be readily compensated for by adjustment of the rotational position of the sleeve 23 with respect to the piston 21.

To prevent fluid leakage from the cylinder casing 2|, a sealing ring 3| is mounted in an annular groove provided in the periphery of the bearing support 22 and such ring sealingly engages the cylindrical wall of the counterbore 2|b. The bearing support block 22 is retained in assembly by a snap ring 32 which is inserted in a suitable groove provided in the outer end of counterbore 2|b. To prevent fluid leakage along the shaft of piston rod 26, a sealing unit 33 is mounted in surrounding relationship to such rod and disposed in a counterbore 22a formed in the outer end of the bearing support block 22. Such sealing unit may obviously comprise any one of several well known arrangements and will therefore not be described or illustrated in detail. The bearing support block 22 is provided with a drain aperture 22b communicating between the counterbore 22a and the reservoir chamber 2|c of the cylinder casing 2|. Hence, any fluid that is forced outwardly between the piston rod 25 and the bearing sleeve 23 will be pulled back into the reservoir chamber 2|c on the next stroke of the piston.

In the normal operation of the hydraulic check heretofore described, the fluid displaced by the axial movement of the piston will of course flow from one end to the other of the enclosed chamber through the flow paths provided by the throttling apertures 29 and 30 and the reservoir chamber 2|c. When the hydraulic check unit is employed in applications which involve relatively slow movement of the piston rod 26, such by-pass fluid flow will take place without any substantial hindrance. However, when applied to checking the movements of the picker stick of the loom, or similar applications, the acceleration of the piston rod 26 is so rapid that an excess of fluid tends to accumulate in the reservoir chamber 2|c during the movement of the piston rod in either direction, and particularly during the inward movement of the piston which corresponds to the shuttle throwing stroke of the picker stick. This is due to the fact that the movement of the piston rod is so fast that the throttling aperture which is remote from the piston position cannot immediately pass all of the fluid pumped forced into the reservoir chamber 2 lo through the active throttling aperture by the movement of the piston. Hence, the pressure of the fluid in the reservoir chamber2 lc tends to build up and such build up would adversely affect the consistency of operation of the hydraulic check. To eliminate such possibility, this invention provides a deformable wall for a portion of the reservoir chamber 2|c and such wall will yield outwardly upon any build up of pressure in the reservoir chamber 2|c to accommodate any excess of fluid which might be pumped into the chamber by the rapid movements of the piston.

Thus, the cylinder casing 2| may be provided with an integral radial protuberance 2|d which defines a bore 2|e of relatively large area. A closure element 34 is mounted in the bore 2|e and such closure element is formed of resiliently deformable material, such as rubber, and is arranged to readily expand in response to any pressure build up in the reservoir chamber 2|c to substantially increase the volume of the reservoir chamber 2 I0. Thus, the closure element may be formed in a generally cup-shaped configuration, including a relatively thick base portion 34a and annular side wall portions 34b. The top rim of the side wall portions 34b is thickened as indicated at 34c and such portions fit snugly in a suitable annular groove 2 provided in the bore 2 la. The closure 34 is retained in position in the bore 2|e by a retainer ring 35 of angular cross section which, in turn, is retained in the bore 2|e by a snap ring 36 mounted in a suitable groove provided adjacent the outer end or the bore 2 le.

With the closure element constructed as described, a relatively large increase in effective volume of the reservoir chamber 2 lo may be produced by the outward expansion of the closure element. Due to the increased thickness of the base portion 34a, the closure element will tend to flex along its side wall portions in the manner specifically illustrated in Figure 7 of the drawings.

Referring to Figure 10, there is disclosed a modification of this invention wherein the expansibility of the reservoir chamber is substantially increased. In this construction, wherein similar numerals refer to corresponding parts of the modification heretofore described, the reservoir chamber 2 lo communicates with the exterior of the cylinder casing 2| through a plurality of radial apertures 50. An expansible sleeve 5| is then mounted in surrounding relationship to the cylinder casing 2| and retained in assembly therewith by a surrounding metallic sleeve member 53. Expansible sleeve 5| is formed of rubber or rubber-like material and comprises relatively thickened portions m and Blb disposed in each axial end thereof and an intermediat thinwalled web portion 510 integrally uniting the thickened portion. Inwardly projecting ribs 51d on end portions 51a and 5lb cooperate with grooves Zip on casing 2| to anchor expansible sleeve 5| thereto. Web portion Sic is radially spaced outwardly from the periphery of cylinder casing 2| and thus defines an expansion chamber 52 therebetween. As a further featurethe bleed passage 2%, which is provided in the bearing support block 22 to bleed back fluid accumulating between the piston rod seal 33 and the base-of counterbore 22a, communicates directly with an annular groove 220 on bearing support block 22 and thence with radial apertures 54 provided in the cylinder casing 2| and thus permits the fluid to bleed directly into the expansion chamber -52.

The operation of this modification is substantially similar to that heretoLi-ore described. When an excess of fluid is pumped into the reservoir chamber 2lc due to the very rapid acceleration of the piston 21, the resulting pressure increase deforms the Web portion Me of the deformable sleeve 5| outwardly to substantially increase the volume of the expansion chamber 52. In this manner, the excess fluid is accommodated without producing any substantial increase in fluid pressure within the cylinder casing 2!.

From the foregoing description, it is apparent that this invention provides an hydraulic check unit which is of unusually simplified construction when the multiplicity of functions performed and the adjustments provided are considered. The described unit will not only accomplish smooth uniform checking of axial movements of thepiston rod in either direction at a high cyclic rate, but will positively and accurately limit the extreme axial positions of the piston rod in each cycle. Furthermore, the checking action exerted by the unit may be axially shifted with respect to the piston position while the unit is in operation. It is therefore clear that a hydraulic check unit checked in accordance with this invention permits not only improved operation, but higher speed operation of a 100m with a great reduction in wear and breakage of the loom components due to the reliable and accurate checking of the picker stick movements.

It will, of course, be understood that various details of construction may be modified through a Wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claims.

I claim as my invention:

1. An hydraulic check unit comprising means defining a generally cylindrical chamber adapted to be filled with fluid, a piston axially reciprocable in said chamber, one face of said piston having a portion ofits periphery of generally helical configuration, the cylindrical wall of said chamberhaving a throttling recess therein providing a fluid flow passage around said piston to .provide a controlled resistance to axial movement of said piston, and means fo-rrelatively angularly shifting said piston and said-chamber defining means, thereby varying the axial location of said piston at which a predetermined fluid resistance to movement of the piston is produced.

2. An hydraulic check unit comprising a hollow casing defining a cylindrical bore, a liner sleeve mounted in said bore and adapted to be filled with fluid, a piston axially reciprocable in said liner sleeve, at least a portion of one face of the piston having a periphery generally helically disposed relative to the sleeve axis, said sleeve having a throttling recess in the wall thereof providing a fluid flow passage around said piston and providin controlled resistance to axial movement of said piston, and meansfor relatively angularly shifting said piston and said sleeve, thereby varying the axial location of said piston at which a predetermined fluid resistance tomovement of the piston is produced.

.3. .An hydraulic check unit comprising a hollow casing defining a cylindrical bore adapted to be filled with fluid, a liner sleeve mounted in said bore, a piston axially reciprocable in said liner sleeve, at least a portion of one face of said piston having a periphery generally helically disposed relative to the sleeve axis, said sleeve 'havinga throttling aperture in the wall thereof, said casing bore being recessed adjacent said throttling aperture to permitfiuidflow around said piston, thereby providing a controlled resistance to axial movement of said piston, and means .for relatively angularly shifting .said piston and said sleeve, thereby varying the axial location of said piston at which a predetermined fluidresistance to movement of the piston is produced.

4. An hydraulic check unit comprising a hollow casing defining a cylindrical bore adapted to be filled with fluid, a liner sleeve mounted insaid bore, a piston axially .reciprocable in said liner sleeve, at leasta portionof oneface of saidpiston having a periphery generally helically. disposed relative to the sleeve axis, said sleeve having a throttling recess in the wall thereof permitting fluid flow around ,said piston to provide-a .controlled resistance to axial movement of said piston, and means for rotatably adjustingthe positionof said sleeveinsaid bore, therebyangularly shifting said throttling aperture with respect to said helicalportion of said piston face.

5. An hydraulic .check unit comprising .a 'hollow casing defining a cylindrical bore adapted to be filled with fluid, a liner sleeve mounted in said bore, a piston axially reciprocablein 'said'liner sleeve, at least a portion of one face of said piston having a periphery generally helically disposed relative to the sleeve axis, said sleeve having a throttling recess in "the walllthereof permitting fluid flow around said piston to provide a con trolled resistance to axial movement of said piston, said sleeve having gear teeth formed thereon, and means including a driving gear meshing with saidgear teeth for relatively angularly shifting said piston and said sleeve, there-by varying the axial location of said piston at which a predetermined fluid resistance to movement of the piston is produced.

6. An hydraulic check unit comprising a-hollow casing defining a cylindrical bore adapted to be filled with fluid, a liner sleeve mounted in said 7. An hydraulic check comprising means defining a generally cylindrical chamber adapted to be filled with fluid, a piston rod having a portion thereof axially reciprocable in said chamber, a piston secured to said piston rod portion and axially adjustable thereon, said piston having a peripheral portion of one face generally helically disposed relative to the chamber axis, the cylindrical wall of said chamber having two axially spaced throttling recesses therein respectively cooperating with the opposite faces of said piston to permit a limited flow of fluid around said piston, thereby providing a checking action in either direction of axial movement of said piston, and means for angularly shifting said chamber defining means relative to said piston, thereby permitting independent adjustment of the checking action in one direction of piston movement without effect on the checking action in the other direction of piston movement.

8. An hydraulic check unit comprising a hollow casing defining a cylindrical bore adapted to be filled with fluid, a liner sleeve mounted in said bore, a piston rod having a portion thereof axially reciprocable in said liner sleeve, a piston secured to said piston rod portion and axially adjustable thereon, said piston having a peripheral portion of one face generally helically disposed relative to the chamber axis, said liner sleeve having two axially spaced throttling recesses therein, said casing bore being additionally recessed to provide fluid communication between said throttling recesses, whereby a limited flow of fluid around said piston is permitted in either direction of movement of said piston to produce a checking action, and means for relatively angularly shifting said piston and said sleeve, thereby permitting independent adjustment of the checking n in one direction of piston movement.

'An hydraulic check unit comprising a hollow g d eflning a cylindrical bore adapted to be "ith fluid, a liner sleeve mounted in said ton rod having a portion thereof axially in said liner sleeve, a piston secured new... Q 1, V m sfixeaflefih; for relativel shifting said sleeve with respect to saidpiston, thereby permit in indepen entaadiustmentotthe he b. anistda a 9qe ain saids s nafl id assasemeaes rumass ng fl d-ar ue said ma na e. 1 m: fi n 1 aina a wa l-ap r u h said fluid passage means, rid f ieter al m H inio er in lat fi said. "aperture, aid's'l'eev'e havin 'axiallyspace'd end portions engaging said casing in sealing relation and an intermediate web portion radially spaced from said casing forming an expansible chamber in fluid communication with said wall aperture in response to increase of fluid pressure at said aperture.

11. An hydraulic check comprising a hollow casing adapted to be filled with fluid, a piston reciprocable in said casing, said casing having fluid passage means for by-passing fluid around said piston at a limited rate, said casing having a wall aperture communicating with said fluid passage means, and a disk of resiliently deformable material mounted on said casing in overlying relation to said wall aperture, said disk having portions engaging said casing in sealing relation and an intermediate web portion expansible in response to a pressure force from the inside of said casing and automatically forming a chamber accommodating fluid displaced into said fluid passage means by said piston.

12. An hydraulic check comprising casing means adapted to be filled with fluid, a sleeve in said casing means and together therewith forming an annular chamber, a piston reciprocable in said sleeve, said sleeve having throttling passages to by-pass fluid around said piston to provide a predetermined resistance to axial movement of the piston, said casing means having a wall portion made of resiliently deformable material disposed in the exterior thereof and being responsive to pressure increases in said annular chamber to produce an outward flexing of said wall portion for automatically accumulating excess fluid displaced by said piston into said annular chamber.

13. An hydraulic check comprising a hollow casing adapted to be filled with fluid, a piston reciprocable in said casing, fluid passage means in said casing for by-passing fluid around said piston at a limited rate, said casing having a resiliently deformable wall portion in the exterior thereof automatically forming an expansion chamber adjacent said fluid passage means upon displacement of fluid into said fluid passage means by said piston.

GEORGE HIRAM HUFFERD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS -48 1',569ff Great Britain Mar. 14, 1938

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