USRE21908E

USRE21908E - Shock absorber

Info

Publication number: USRE21908E
Authority: US
Priority date: 1938-06-10
Publication date: 1941-09-30
Also published as: GB521261A; FR847267A; US2214038A

Description

- E. w L. BEECHER SHOCK ABSORBER- Qriginal Filed June 10,, 1938 flag-wt 6. 86801958 ATTORNEY J ing fit in the hydraulic shock absorber I working or pressure cylinder and a reservoir tor.

' and effectively sealed against Reissued Sept. 30, 1941- UNITED STATES PATENT OFFlCE SHOCK ABSORBER Eugene L. Beecher, Cleveland Heights Ohio, as-

signor to The Gabriel Company, Cleveland. Ohio, a corporation of Ohio Original No. Serial No.

2,214,038, dated September 10,1940, 212,995, June 10, 1938. Application for reissue October 12, 1940, Serial No. 380,970 g 13 Claims. ,(Cl. 188-88) This invention relates to a shock absorber and particularlyto a fluid shock absorber.

A shock absorber embodying the present invention may be employed with a variety of machines or apparatus to snub or check the velocity of movement between two relatively movable parts thereof, but inasmuch as the shock absorber oi the present invention has particular adaptability and utility when used in motor vehicles, it will be so described herein.

It will also be understood that although the invention is shown applied to a direct double acting hydraulic shock absorber, certain or all of its features might be employed in pneumatic shock absorbers or other types or hydraulic shock absorbers and his not the intention to limit the invention to the first named type.

An object of the invention is to provide a hydraulic shock absorber which is quiet and eillcient in operation. I

Another object is shock, absorber improved valve means for conto provide in a hydraulic,

so constructed that a pneumatic pressure head will be built up in the reservoir during the relative movement of the piston in thecylinder in one direction, and said pressure head will act-to force oil or liquid from the reservoir into the working cylinder during the, relative movement of the piston and cylinder in the opposite direction. Another object is to provide in a fluid shock absorber improved means for assembling and locking a closure member in one end oi the pressure or working cylinder thereof. Another object is to provide in a direct acting shock absorber improved means for preventing the aspiration of oil or air around the piston rod where it extends through a closure at one end or trolling the displacement of the oil or other liquid in the working or pressure chamber from one side of the piston to the opposite side thereof during the operation oi the shock absorber-and which valve means is free oi all hissing, whistling, rattling or other sounds.

A further object of the invention is to provide 'in a fluid shock absorber an improved and novel piston, as well as improved and novel valve means for controlling the passage of iiuid from one sideto the otherside oi the piston during its movement in one direction and which piston is so constructed that it need have only a sliding workcyllnder in which .it operates, as distinguished from a close iit therein, which iact, together with the iact that the piston does not contact the cylinder wall throughout the entire circumierential area of the piston, reducesthe friction between the p ton and cylinderand consequently the wear on these parts.

A further object is to provide a direct acting oi the type having a the oil or liquid in communication with said cyland reservoir are adequately the escape of oil or dust, dirt and that said cylinder liquid therefrom or the entrance of other foreign matter the A still further object is to provide a hydraulic shock absorber of the type having a working or pressure cylinder and a reservoir for the oil or liquid in communication the pressure or working cylinder, in combination with improved means for collecting such oil ioam as may be created at said end of the cylinder and utilizing this foam and the pressure in the cylinder to provide pressure lubrication for the piston rod and its bearing in the cylinder closure.

Further and additional objects and advantages not hereinbeiore referred to will become apparent hereinafter during the detailed description which is to follow or an embodiment of the invention.

Referring to the accompanying drawing 11- lustrating said embodiment of the invention.

Fig. 1 is a substantially central longitudinal sectional view through the shock absorber.

Fig. 2 is a transverse sectional view taken substantially on line 2-2 of Fig. 1 looking in the direction of the arrows.

Fig. 3 is a transverse sectional view through I the working or pressure cylinder and the piston and is taken substantially on line 3-3 of Fig. 1

looking in the direction 0! the arrows.

Fig. 4 is a detached fragmentary elevational view of the lower end oi the pressure or working cylinder 01' the shock absorber, and

Fig. 5 ms transverse sectional view through the pressure or working cylinder and the piston inder, and which shock absorber-is so constructed and is taken substantially on line H of Fig. 1"

looking in the direction of the arrows.

The shock absorber embodying the present in-' vention and illustrated in the accompanying drawing is shown as or the direct double acting hydraulic type and comprises a cylindrical casing III which has relative telescoping movement within a cylindrical housing II that is spaced radially outwardly irom the casing'll.

. The upper end of the housing II is closed by an invertedcup-shaped closure or cap member I! and is provided on its outer side with an eye II therewith, and which is to which the piston rod or the shock absorber (not shown) may be connected, respectively, to

the frame and axle of the vehicle in any suitable manner so as to extend outwardly therefrom in parallel relation and pass through the eyes 13 and I6. These pins or rods may be operatively connected with the eyes l3 and It by suitable means well known in the art, wherefore relative movement between the frame. and axle of the vehicle will cause relative telescoping movement" between the casing Ill and housingilas will be well understood.

The pressure or working cylinder I! of the shock absorber is disposed within the casing II] in spaced concentric relationship therewith, so that thespace defined by the casing Ill, cylinder I 1, closure member l5 and closure member for the upper end of the casing (later to be referred 'to) constitutes a reservoir l8 for the oil or liquid in the shock absorber.

The lower end of the cylinder ll extends into the cup-shaped member l5 and is secured thereto by the end pressure caused by the spinning over of the upper end of the casing Ill. The cylinder l'l upwardly of its lower end has secured therein a closure plate l9. s I

In order to provide an efficient and. economical way for assembling and locking the closure plate I! in position said plate has its circumference provided with serrations, wherefore the plate can be positioned in the cylinder and then 7 the lower end of the cylinder can be contracted and an annular serrated groove formed therein adjacent the closure plate IS, with the. result that the serratio is of the plate and groove interlock and the plate is held in sealing relationship with the inner wall of the cylinder. The cylinder 11 below the serrated groove 20 is provided with one or more openings 2| placing that portion of the cylinder below the closure plate I! in communication with the reservoir I8.

The closure plate l9 may be provided with a centrally disposed opening surrounded by an internally threaded boss 22 and into which a threaded plug 23 is screwed, said plug being provided with a small centrally located opening 24 for a purpose later to be explained. The closure plate I 9 also may have secured to its inner side an inwardly projecting finger 25 that cooperates with an adjustable part carried by the piston for the purpose of adjusting the tension of a valve spring as will later be explained.

The upper or high pressure end of the cylinder I1 is closed by a plug member 25 which fits into the cylinder and is suitably secured in position therein, it being noted that the upper edge of the cylinder is'turned inwardly over the outer side of-"the plug member. provided with a centrally disposed opening arranged concentrically with a counterbore on the inner side of the member and in which is located a flanged portion of an elastic sleeve 21. The

sleeve 21 is held in position by a thin plate 28 secured to the inner side of the member 26 by suitable means, such as the integral rivet-like portions 26a that extend through openingsv in The member 28 is the plate 28 and then have their ends upset against the plate.

The piston rod l4 extends through the central opening in the member 26 and through the elastic sleeve 21. The elastic sleeve 21 tightly grips the piston rod and acts as a seal to prevent oil and air working out of *thecylinder I1 along thepiston rod H. In other words, the

elastic sleeve 21 eliminates likelihood of any uncontrolled air passages between the piston rod and the wall of the opening in the member 26. If such passages existed the result would be an atomization of oil foam through the passages to the outside of the cylinder, and this would cause an undesirable hissing or whistling noise in the operation of the shock absorber. The elastic sleeve 21 will always tightly grip the piston rod, and-even though considerable clearance should eventually be. present between the rod and the wall of the opening in the member 26 due to wear of the parts, the sleeve will still adequately function as a seal to close the passage around the piston.

The plate 28 has its circumference terminating slightly inwardly of the circumference of the member 25, while said member 28 is provided adjacent its inner side and on its circumference with circularly spaced inclined notches 29 that merge at their upper ends into small grooves 30. The grooves 30 have their upper ends in communication with an annular channel 3| formed in the circumference of the member 26 substantially midway between the outer and inner ends of the member. Communicating with the channel 3| are a pluralityof circumferentially spaced radially extending small passages or bores 32 that terminate in the central opening of the member 26, see Fig. 2. The purpose of the notches 29, grooves 30, channel 3| and bores or passages 32 will be pointed outhereinafter.

The upper end 01' the casing I0 is closed by a closure member 33 mounted in the. casing and suitably connected thereto. The closure member 33 is provided with inwardly extending portions 34 that contact with the upper end of the cylinder IT, as clearly shown in Fig. l. The

member 33 is also provided with a centrally shown in Fig. 1, but since this particular detail forms no part of the present invention it is not believed necessary to describe the same further- The piston rod ll has secured to its lower end a piston 33 and said piston on its lower side is provided with a cylindrical recess 39 at theinner end of which is a centrally located extension 40 that surrounds the lower end of the piston rod and is lock d thereto. A transverse opening II is formed in the piston rod H above the piston and communicates with a longitudinally extending passage 42 that extends to the lower end of the piston rod and is in communication with the recess 33 in thepiston. An externally threaded cup-shaped plug 43 is screwed into the recess 39 '01 the piston and the tension of a relatively fstiff coil spring 43b 2 mounted in the recess 3! and having one of its ends abutting against the bottom of the cup-shaped plug 43 serves to lock the plug in its different adjusted positions.

Rigidly connected to the bottom of the plug a plurality of longitudinally extending relatively II is a centrally disposed pin 44 that extends.

upwardly into .the passage 42 in the piston rod.

. .A small coil spring 45 surrounds the pin 44 and has its upper end abutting against a plate valve 45 that is slidably mounted on the pin N and is held by the spring it normally seated against the lower end of the piston rod and seals the passage .42. 1

broad grooves 54 which are spaced circumferenftially of the piston and which, as clearly indicated in Figs. 1 and 5, are of gradually diminishing depth from a point substantiallymidway of their ends to their upper ends. The grooves 54,

- however, at their upper ends are not of such This arrangementofthe pin 44' and valve 46 possesses a decided advantage. Flap valves .ordinarily .have a tendency to crack open on one side first, with the result that in order to accommodate the volume of expelled fluid the if the valves had opened evenly.- This sidewise opening movement of the valves causes valve flutter and often produced in shock absorbers thumping noises. The use of adequate guides for the valves may correct this fault, but the guides cause objectionable weight to be introduced'into'the shock absorber.

(movement of the valves sidewise is more than' In the present construction the pin 44 has a relatively large diameter, and since it extends into the passage 42 an annular space is provided between the pin and the wall of the passage. Therefore the valve It has an exposed pressure area of annular shape and located substantially near'the circumference of the valve, wherefore there will be an even pressure distribution on the valve 45 and the latter will move to and from its seat in parallel relation to the axis of the pin 44. Also since the area of the valve is reduced by the area of the pin M a much lighter spring pressure is required for the expelled volume of oil.

. A ring 41 also'surrounds the pin II and is for the purpose of preventing acomplete collapse of the spring II when the valve It is moved to 'closed position upon manual adjustment. The

movement of the valve under pressure of the oil is only a few thousandths of an inch.

The plug member 43 is provided with a plurality of openingsna which can beeengaged by. the finger I! on the closure member i9 when the piston-is in its most inward position, so that rel-' ative rotation between the cylinder l1 and the piston will cause the member 48 to be screwed inwardly or outwardly of the recess 39. with a resultant change .in the tension of the spring I! and 'consequentlyin the pressure required for.

opening. the valve 4].

A flexible cup packing ring 48, preferably formed of leather, is arranged onthe upper. side of. the piston 88 and is held in position thereon bytmeans of a plate I! that has a plurality of openings 50' formed therein and through which extend integral pin-like portions If formed on.

the upper side of the piston SI. A small passage cates with one; ofthe openings'lll, wherefore the space in the cylinder above the piston-is in constant communication with the recess 3! and the space in the cylinder below the piston. A small It extends through the piston u andcominunidepth as to allow the flexible cup packing 48 to j be forced into the grooves by the pressure of the fluid inthe upper part of the cylinder during the operation of the shock absorber, but are so proportioned as to back up the cup packing and prevent such an occurrence. The aspect or phase of the piston construction last'described can be used in hydraulic, pneumatic or other types of fluid shock absorbers.

' Assuming that the shock absorber of the construction shown in Fig. l and which has Just been described hasits opposite ends connected to the axle and frame of a motor vehicle, it will be understood that relative movement of the axle andframe toward each other will cause a relative downward movement of the piston 38 in the cylinder l1 and, of course, a compression of the vehicle springs. During this relative downward movement of the piston 38 in the cylinder H the oil or liquid below the piston can flow through the passage 52 in the piston to the opposite side thereof. Also oil will flow through the grooves H in the periphery of the piston: and its pressure,

will cause it to pass between the flexible cup packing ring 48 and the wall of the cylinder. In addition, some of the oil below the piston and at least in an amount equivalent to the oil displaced by the piston rod ll as'the piston moves inwardly of the cylinderwill flow through the opening 24 in the plug 23 and hence through the openings Ziintothereservoir l8. This oil flowing into the reservoir. I8 produces. a compression of the air in the reservoir above the oil level and since the upper end of the casing i 0 is thoroughly sealed a relatively high pneumatic pressure head is established at the upper side of the reservoir.

It is desirable in designing shock absorbers to provide for an increasing built-up resistance at or near the end of the compression or impact stroke, so that when the shock absorbers are installed onan automobilethe axle will be prevented in its upward movement under load impacts from "bottoming" against the frame of the vehicle. I v

It is contemplatedin constructing shock absorbers embodying the present-invention to build intothe shock. absorbers suitable pneumatic pressure heads to provide the desired increasing.

resistance at or near the impact or compression stroke of the shock absorbers. This may be accomplished as follows:

In finally assembling the shock absorbers the pistons thereof are extended with relation to'the cylinders to themaximum limit of their extended movement. The correct amount of oil is then introduced into the cylinders and the reserve or reservoir chambers, such that the oil in the reservoir chambers extends well up into said chambers and thus forms therein an'oil piston and a pneumatic compression chamber above the oil piston. Then while, the shock absorbersare ,in the extended position they are hermetically I sealed, with the result that the pneumaticcompressionchambers above the oil pistons in the reservoir chambers are then at atmospheric pres-'- sure. It will be appreciated that different effects of the increasing resistance at or near-the end of 3 Y The piston 38 is provided on its periphery with I the compression stroke can be obtained by varying the amount of oil introduced into the shock absorber, since the height of the oil in the reservoir or reserve chambers will change the effectof the pneumatic compression chambers located above the oil pistons.

It will .be understood that if it is desired to cause the pneumatic compression chamber to be at less than atmospheric pressure when the piston and cylinder are in the fully extended position that then the hermetical sealing'of the shock absorber need not be made at the fully extended position. On the other hand, if it is desired to have a pneumatic compression chamber which in the fully extended position is at greater than atmospheric pressure, then gas forming chemicals might be introduced into the shock absorber,

to bring about this eil'ect.

It will be understood that when the piston rod moves into the cylinder under an impact stroke,

oil is displaced and flows into-the reservoir cham- I her and causes the oil therein to rise into the space which forms the pneumatic compression chamber. This raises the pressure of air or gas and results in a pneumatic resistance which supplements the hydraulic resistance, and eventually as the end of the impact or collapsing strok approaches the pneumatic resistance will have been built up to a resistance greater than the hydraulic resistance and will act-to prevent bottoming of the axle.

In installing shock absorberson automobiles it is the general practice to allow more recoil stroke ithan compression or impact stroke in the normal or riding position. Therefore, on a shock absorber having a total stroke or six inches, for

example, the piston could be moved approximately four inches on the recoil stroke and two inches on the compression or impact stroke and the pneumatic compression chamber would be considerably above atmospheric pressure at the normal riding position. 7

' It will be noted that in addition to the piston being provided with a fixed passage through which the oil can flow from one side of the pis ton to the other during its movement in either direction, it is also provided with valve means for allowing a greater flow of oil from one side of the piston to the other when the piston is moving downwardly in the cylinder, that is toward the low pressure'end than is the case when it is moving upwardly toward the high pressure end.

This valve means being formed of the flexible cup packing l8 and the grooves 54 is highly ellicient, and since there are no movable metal parts the valve means is totally quiet in operation. In addition, the piston 38 only has portions of its periphery in engagement with the wall of thecylinder, that is the portions'intermediate the grooves 54, wherefore friction between the piston and cylinder is at a minimum thus reducing the relative wear between the parts.' Likewise, because of the use of the flex-- ible cup packing 48 his unnecessary to provide as close or tight a fit between the piston and cylinder as would ordinarily be the case.

As the piston moves upwardly in the cylin- "der any oil foam or emulsification of the oil above the piston caused by the compression of the entrained air therein will-pass through the grooves 29 and into the annular chamber 3! in the member'26.- In other words, the chamber II will act as a collecting chamber '1 r 011' foam and the pressures in the cylinder and in the chamber 3| will cause small quantities of, this oil foam to be forced under pressure through the small passages or bores 32 against the piston rod I, thus providing forced or pressure lubrication for the rod. During the downward movementof the piston in the cylinderQoil which has accumulated I in the chamber II will be drawn backlnto the cylinder.

From the foregoing a hydraulic shock absorber embodying the pres- When the axle and the frame of the vehicle start to separate or move away. from each other" under the recoil actionv of the vehicle spring, the piston 38, of course, moves relatively upwardly in the cylinder l-I. As the piston moves upwardly the pneumatic pressure head in the reservoir acts on the oil therein to force the same through the opening I4 and into the cylinder below the piston, thus eliminating any tendency for a vacuum to be created below the piston in the lower 1 end of the cylinder. The oil in the cylinder above the piston as the piston moves upwardly can at first only now to the lower side of the piston the pressure of the oil in the flexible cup-shaped pecking 48 causes said packing to tightly engage the wall of the cylinder and prevent any flow of 011 between the packing and the cylinder'and e oftheoil in the mains seated until the pro in the opening 41 upper end of the cylinder a and passage ll reaches a predetermined point sumcient to ovorcome'the tension of the spring through the passage n, it being understood that through thegrooves I. Also during this upward Q movement of the piston the plate valve 40 rewhereupon the valve it will unseat and allow this high prcssureoil to now from the passage '42 to the other side otthe piston. As previously stated, the tension of the spring ll can be nd-,

iusted without the necessity of removing the iston from the cylinder by" merely enema v fliigerllofthecloniromember llinanopenins' "a of the plug member 0. and then relatively ent invention will be quiet and eflicient in 013- eration and that the valve means for controlling the displacement of the oil or other liquid in the working or pressure chamber from one side of I the pistonto the opposite side thereof will be free of. hissing. Whistling, rattling or other sounds. 'It will alsobe seen that the piston is of improved and novel construction, as well as the valve means associated therewith for controlling the passage of fluid thereby in one direction.

The construction of the piston and valve means is such that the piston need-have only a sliding working lit in the cylinder as distinguished from A a close flt' therein, which fact together with the fact that the piston does not contact the cylinder, wall throughout the entire circumferential area of the piston reduces the friction between the piston and cylinder and consequently thewear on these parts;

Although a preferred embodiment of the in-- vention has been illustrated and described here- 1 in, it will be understood that the invention is susceptible of various modificationsand adaptations within the scope of the appended claims.

Having thusdescribed my invention, I claim: '1. A hydraulic shock absorber comprising relatively reciprocablecylinder and pistonmembers; said piston memberlbeing' provided with a passage extending between the opposite ends" there- 01', a flexible cup shapod packing ring carried by we piston and overlying one end of menu sage and having its wall 'portlon e suing the lit will have been seen that i cylinder, a closure plug der provided with a centrally dis cylinder wall whereby said ring seals said passage during movement of the piston in one direction, said piston being provided with a second and constantly open passage extending therethrough, said piston also being provided with a a piston relatively reciprocablein said cylinder and provided with a rod extending through said centrally disposed opening, said closurepiug being provided intermediate. its ends with an anthird passage therethrough, and a spring controlled valve sealing said third passage when the pressure of the liquid therein is below a predetermined point during movement 01' said piston in said one direction.

2. A shock'absorber comprising a cylinder, a

nular peripheral groove torming a chamber and with a port extending radially from said central 4 opening to said chamber, said closure plug also piston relatively reciprocable therein and provided with a peripheral passage extending from end to end thereof and having a portion adjacent one end of said piston or gradually diminishing depth, and a flexible cup-shaped packing ring mounted on said end of said piston and being provided with'a relatively small passage placing said chamber'in communication with said cylinder.

8., A hydraulic shock absorber comprising a cylinder, a closure plug for one end of the cylinder and provided with a centrally disposed opening and with an elastic sleeve extending 1m wardly oi the cylinder and aligned with said opening, a piston relatively reciprocable in said overlying the end 01 said portion of. said passage and having its wall portion engaging the cylinder wall. whereby said ring seals said passage during movement of the piston in one direction.

3. A shock absorber comprising a cylinder, a piston relatively reciprooable therein and provided with aplurality of oircumferentially spaced peripheral grooves extending from end to end of the piston and of gradually diminishing depth adjacent one end of the latter, and a flexible cupshaped packing ring mounted on said end of said piston and overlying said grooves and having its wall portion engaging the'cylinder wall whereby said ring seals said grooves during movement oi the piston in one direction.

- 4. A hydraulic shock absorber comprising a cylinder, 9. piston relatively reciprocable therein and provided with a plurality of circumferentially spaced peripheral grooves extending irom end to end of the piston, a flexible cup-shaped packing ring mounted on one end said piston and overlying one end of said grooves and having its wall portion engaging the cylinder wall whereby said ring seals said grooves during movement oi the piston in one direction, said piston being provided with passages therethrough one of which is constantly open and another normally closed, and a spring controlled valve sealing said last named passage when the pressure of the liquid therein is below a predetermined point.

5. A shock absorber comprising a cylinder, a

- piston relatively reciprocable therein and pro-- vided witha plurality of longitudinal peripheral recesses oi! relatively broad width extending irom end to end oi the piston and spaced circumferentially thereof, said recesses being of gradually diminishing depth toward one end of said piston, and a flexible cup-shaped packing ring mounted on said end of said piston and overlying the end of said recesses and'having its wall portion engaging ring seals said recesses piston in one direction.

during movement 01 the 6. A hydraulic shock absorber comprisinga plug at one o! munication with said cylinder.

'7. A hydraulic shock absorber comprising a at one end of said cylincylinder and provided with a piston rodextending through said sleeve and said opening, said closure plug being provided intermediate its ends with an annular peripheral groove forming a chamber and with a port extending radially from said opening to said chamber, said closure plug also being provided with a'relatively small peripheral passage placing said chamber in communication with said cylinder.

9; A shock absorber comprising relatively reciprocable cylinder and piston members, a closure member for one end of said cylinder and provided on its circumference with serrations, said cylinder having formed therein adjacent said closure member an internal annular serrated groove the serrations 01 said groove and said closure member being interlocked to retain the latter inposition.

10. In a hydraulic shock absorber, a cylinder, a piston relatively movable in the cylinder and provided with a passage'extending through it and having at one of its ends a valve seat, a

, pin carried bysaid piston and extending into said one end of said passage, and providing a predetermined annular space between the periphery oi the pin and the wall of the passage, a disk valve mounted on said pin, and a spring acting on said valve, and maintaining the same normally seated against said valve seat.

11. In a direct acting hydraulic shock ah- I sorber, an elongated cylinder, a piston reciprocable therein, a rod extending into the cylinder the cylinder wall whereby said at one end thereof Ior actuating the piston, a reservoir having restricted communication with the cylinder adjacent its other end and into which liquid is forced by movement of said rod into the cylinder, said pistonhaving peripheral grooves extending from end to end thereof for flowing liquid past the piston upon movement of the latter toward saidother end 0'! the cylinder, aflexible cup-shaped packing mounted on the piston and overlying oneend of said grooves and having its annular wall portion engaging the cylinder wall whereby said packing seals said grooves during movement oi the piston toward said one end of the cylinder,-said piston also having a constantly open passage of restricted size therein placing in communication the cylinder. posed opening, 12. In a direct with each other the portions of the cylinder on opposite sides of the piston and a third passage of relatively larger size also connecting said cylinder portions with each other, and a spring controlled valve sealing said third passage during movementof the piston toward said other end of the cylinder and adapted to be unseated by apredetermined pressure of the liquid during movement oi! the piston toward said one end of acting hydraulic shock abgrooves during movement of the said one end of ,the cylinder.

sorber. an elongated cylinder, a piston reciprocable therein, a rod extending into the cylinder at one end thereof for actuatingth'cpiston, a

reservoir having restricted communication with the cylinder adjacent itssother end and into which liquid is forced by movement of said rod into the cylinder, said piston having peripheral grooves extending from end to end thereof and of gradually diminishing depth for flowing liquid past the piston upon movement 0! the latter 10 toward said other end ot-the cylinder, and a flexible cup-shaped packing mounted on the piston and overlying one end oi. said grooves and having its annular wall portion engaging the cylinder wall whereby said packing seals said piston toward 13. A hydraulic shock absorber comprising relatively reciprocable cylinder and piston members, said piston member being arranged in and contacting said cylinder and being provided with a passage therethrough which has one of its ends terminating at the periphery of the piston, said piston also being-provided with a second and constantly open passage therethrough. said passages placing the portions of the cylinder on opposite sides oi'said piston in communication passage, means associated with one of said membars and providing a third passage placing the portions of the cylinder on opposite sides 0! the piston in communication with each other, and a spring controlled valve sealing said third passage when the pressure oi theliquid therein is 20 below a predetermined point.