GB1599565A

GB1599565A - Shock absorber

Info

Publication number: GB1599565A
Application number: GB7320/78A
Authority: GB
Original assignee: Quiri & Cie Usines
Current assignee: Quiri & Cie Usines
Priority date: 1977-02-23
Filing date: 1978-02-23
Publication date: 1981-10-07
Also published as: DE2807717B2; DE2807717A1; DE2807717C3

Description

(54) SHOCK ABSORBER (71) We, SOCIETE DES USINES QUIRI & CIE, a French Body Corporate, of BP 40 - 67 042 Strasbourg Cedex, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a shock absorber comprising a hydraulic piston-and-cylinder unit, mainly designed to avoid deterioration of ducts in thermonuclear power stations in the case of very small earthquakes.

Ducts of large cross-section supported at regular intervals have their own resonant frequency. When subjected to vibratory movements close to the resonance frequency, these ducts risk being broken owing to the amplitude of the movements. Accidents thus caused inevitably result in severe damage due to the pressure of the fluid and its nature, i.e. aggressive vapours or liquids, radioactive substances or fluids. This is a permanent danger, a reality which is unfortunately confirmed in all the cases in which vibrations are generated, in particular seismic movements.

One can mention installations having a large development of pipes, and in particular atomic power stations, where the permanent risk of rupture of the pipe systems is a matter of concern for the population in view of the frightening consequences which might result.

Double-acting oil-pressure shock absorbers already exist which are located between a wall and the pipe system in places where the pipes may bend to a substantial extent, in order to modify the resonance frequency of the system, and thus avoid rupture. These shock absorbers include a preset self-locking device which increases the shock absorbing effect, up to locking, in proportion as one comes near to the resonance frequency. These shock absorbers avoid damage due to: earthquakes; water hammers; violent shocks and thrusts occurring as a result of safety valves being discharged or rupture of pipes.

Of course, these shock absorbers permit slow displacements due to different expansion rates. Since they are double-acting these shock absorbers react indifferently to traction or to compression.

have properties of sensitivity, sturdiness, and have properties of sensitivity, studiness, and short time of response. They are designed to function in hot, humid, and irradiated locations, and are particularly suitable for protecting pipes in nuclear power stations.

Although these shock absorbers have undeniable qualities, unfortunately they also have side effects such as cavitation phenomenon, danger of polluting the oil in contact with the outside, and above all compensation of volume variation following expansion of the oil due to an increase in temperature.

The present invention provides a shock absorber comprising a double-acting hydraulic piston-and-cylinder unit, the unit comprising a hollow liquid-tight body defining a longitudinal space subdivided into a variable-volume front chamber and a variable-volume rear chamber by a crosshead which is longitudinally movable in the said space, the cross-head being rigid with a piston rod extending from the rear of the body through a stuffing member, the front and rear chamber communicating with each other via two opposed check valves in series which are each held open by biassing means and which each close automatically when the speed of the hydraulic fluid through the valve in opposition to its biassing means reaches a given value, the body containing a gas-filled volume compensation capsule.

The following description illustrates in detail all the preferred technical features of the invention, the description being given by way of non-limiting example with reference to the accompanying drawings, in which: Figure 1 is a longitudinal cross sectional view generally showing the internal consti tution of a shock absorber; Figure 2 is a longitudinal cross sectional view showing in detail the internal construction of the cross-head; Figure 3 is a longitudinal cross sectional view of a variant showing a shock absorber with an external chamber having seat in a cylinder-like arrangement for capsules; Figure 4 is a cross sectional view taken along the line VI-VI of the shock absorber shown in Figure 3; Figure 5 is a diagrammatic longitudinal cross sectional view of a cylindrical-capsule compensation reservoir, Figure 6 is a diagrammatic perspective view of a volume-compensation capsule for an annular chamber; Figure 7 is a diagrammatic perspective view of another volume-compensation capsule for an annular chamber; Figure 8 is a diagrammatic longitudinal cross sectional view of a self-locking shock absorber with a spirally rigid compensation capsule; Figure 9 is a diagrammatic longitudinal cross sectional view of a self-locking shock absorber with a longitudinally open or closed cylindrical compensation capsule.

The shock absorber illustrated in Figures 1 and 2 comprises a piston-and-cylinder unit 1 having one of its ends fixed to a pin 2 provided on a support 3 rigid with a base 4 assumed to be fixed, such as a foundation or wall. The body 5 of the unit 1 is substantially cylindrical and is closed at one of its ends by a stuffing member 6 having a central extension 7 locating a guide ring 8 for the piston rod 9 of the unit 1. The unit 1 has its other end mechanically connected to an articulated support 10 secured to a duct, pipe, or the like to be protected, by means of a holding collar 11. The piston rod 9 is mechanically connected at its end to a cross-head 12 and extends through the guide ring 8 and an inner seal 13 and an outer seal 14.

The cross-head 12 has a substantially cylindrical volume with a front face 15 provided with a central extension 16 arranged to provide a shock absorbing action at the end of the forward stroke by engagement with small clearance in a recess 17 formed in the centre of the bottom of the inner chamber of the unit. The cross-head 12 has its rear face defined by a body 18 having a central recess 19 which engages with the extension 7 of the body of the stuffing member 6 to provide in a similar manner a shock absorbing action at the end of the rearward stroke.

The periphery of the cross-head 12 has two pairs of metal piston-rings 20 angularly displaced so that each slot is diametrically opposite, the segments being held in position by a pin. This assembly feature ensures minimum leaks. Oil-tightness is also improved by means of decompression slots or grooves 21 formed in the peripheral surface of the cross-head.

The cross-head 12 has an internal cavity 22 which serves as a compensation chamber and which has a longitudinal section approximately in the shape of a U. This chamber contains a capsule 23 which is deformable in the same way as bellows and is filled with a pressurized gas. The capsule 23 has a corrugated lateral surface 24, a front wall 25 slightly inclined to avoid the sticking phenomenon due to a film of oil being present between it and the front end surface of the chamber, and a rear wall 26 which is tubular in shape and has a longitudinal U-section the base of which serves as a bottom copper for the bellows and the limbs of which form a slide surface for the corrugations of the lateral surface 24.

The tubular rear wall 26 has at its rear end a shoulder 27 to which the rear edge 28 of the bellows is fixed by welding thereby ensuring perfect gas-tightness.

The rear part of the bellows extends in the annular space between the inside of the cross-head 12 and the outside of the tubular wall 26. The capsule 23, at its end adjacent to the piston rod 9, is located in an annular cavity 29 which permits the compensation chamber to be cleaned by means of a purging means termed a nozzle in the following description.

The cross-head 12 comprises two flap valves, i.e. a front valve 30 located inside the front face at the position of the front extension 16, and a rear valve 31 located in the rear body 18 of the cross-head. The flap valves are of a monoblock kind having a body 32 which defines in a passage 33 in the cross-head a seat 34 for the valve member, the body having its base 35 screwed into the cross-head. Each flap valve also has a spring 36 for opening the valve, and a casing 37 which serves as an abutment for the delimits the stroke of the valve member. The casing is inserted into a partly screw-threaded bore and is fixed by tightening the base 35 of the valve in the screw threaded part.

These valves are particularly advantageous owing to their low sensitivity to the viscosity of the hydraulic liquid (oil), which improves the response time. Should a sudden movement occur in the forward or rearward direction of movement of the cross-head 12, the valve 30 or 31 (respectively) will automatically close at a predetermined level of liquid flow speed, thereby ensuring a severe shock absorbing action.

Since the valves are kept open by their respective springs at flow speeds below the predetermined level, they permit free displacement of the cross-head 12 during slow movements, in particular small displacements due to thermal expansion of the duct or pipe.

After the blocking of either valve 30 or 31 in response to a shock, in order to still permit displacement of the cross-head inside the cylinder, the cross head has (except in the case of special applications) nozzles such as 38 and 39. The nozzles also enable the shock absorber to compensate for the oil volume variation due to variations in temperature when the valves are closed.

It should also be noted that the body of the stuffing member is mounted on the body of the unit by way of screws 40 and fluid-tightness is ensured by a metal ring seal 41 which is insensitive to temperature variation and to radiations.

The peripheral surface of the cross-head 12 has been subjected to a surface treatment which prevents seizing as a result of friction at high frequencies of vibration.

The general configuration of the unit is such that it enables easy cleansing and correct operation even in the case in which a small amount of air is present.

Thus, the operation of the shock absorber is always correct since the average air pocket accidentally formed could not come into contact with the valves.

When the piston rod is suddenly stressed to move in a direction the valve in question is rapidly closed and is kept closed until a force is applied to it.

In the embodiment in which nozzles 38, 39 are provided, locking is not absolute since the possibility exists of a small inovement due to liquid flow occurring through the nozzles. The locking remains constant until the movement is modified or until discharged.

Should the movement change direction, the valve in question opens and the same applies to the other valve. During slow movement, the two valves remain open owing to the action of their respective springs.

Oil freely circulates from one chamber of the unit to the other through the cross-head by passing through the valves and (to a lesser extent) the nozzles.

Volume variations due to movements of the piston rod or to change in temperature are absorbed by the metal capsule, which is compressed or extended; the volume surplus is transferred to or from the inside of cross-head either through the valves or through the nozzles should the valves be closed.

The oil used is a high viscosity oil which results in small leaks through the metal seals on the cross-head and in rapid closing of the valves.

It is possible to design variants having an angular chamber 42 (Figure 8 or 9) coaxial with the front and rear chambers separated by the cross-head, the chamber 42 being for example formed between the body of the unit and an outer wall 43, the chamber 42 being delimited by a fitting member 44 and communicating with the front and rear chambers via respective opposed check valves which are each held open by biassing means and which each close automatically when the speed of the hydraulic fluid through the valve in opposition to its biassing means reaches a given value.

The annular chamber may have a substantially cylindrical volume-compensation capsule 46 having inner and/or outer longitudinal ribs or undulations 47 and a longitudinal slot (Figure 6), or transverse ribs or undulations 48 (Figure 7).

A particular compensation capsule (Figure 8) has a tube wound in the annular chamber 42 in the form of a helix 49, the turns being mounted free to move one with respect to the other by means of seperations 50.

Of course, the capsule of Figure 7 requires a compression plate 51 in contact with the side face of the capsule generally constituted by the closing crown of its undulations, and against which the expansion pressure is applied.

Figures 3 to 5 show an embodiment comprising a ring of capsules 52, shown in Figure 4. Each capsule is a metal cylindrical capsule having on its side surface small undulations 53 and is filled with an inert gas, such as nitrogen inside a metal casing. In the illustrated example, the body of the piston-and-cylinder unit has a succession of cylindrical longitudinal cavities 54 coaxial with the unit, arranged in a cylinder and having in their inner volume a succession of capsules 52 connected in series by welding their end neck 55.

These cavities 54 arranged in a cylinder communicate with a conduit 56 connecting two check valves 57 and 58 by way of an annular chamber 59 delimited by an annular groove and a closing member 60 articulated to a member 61.

Similarly, the outer end of the piston rod 62 of the cross-head 63 of the unit is articulated by means of a pin 64 to a support 65 having a base 66 secured to the conduit or pipe to be protected.

Each valve has a valve element kept in the opened position by a spring 67 whose opening stroke is limited by an abutment 68. The valve also has a compensation nozzle 69 enabling movements at slow speed due to normal expansion.

The operation is very simple.

In any case, the compensating device, independently of the way in which it is embodied, i.e. shell or capsule, absorbs the different variations in volume of the hydraulic fluid, independently of the operation of the shock absorber mostly due to variations in the ambient temperature by taking advantage of the compression of the metal diaphragm or the outer surfaces of the capsules on the gas contained therein.

The effect thus produced is found to be practically independent of the location of the compensation device.

The multiple advantages thus obtained are: considerable protection from the environment, particularly radioactivity; avoidance of cavitation during forward stroke of cross-head; locking of valves by rapid but small stroke of cross-head; confinement of oil in a closed space.

The specific design and working characteristic consisting in the incorporation of the volume-compensation capsule in the cross-head results in numerous qualities and multiple advantages as well as substantial improved performance being obtained. Thus, the area of the cross-head can be maximised, in order to obtain, with respect to the conventional technology: a service pressure which is reduced by a quarter; a stiffness or rigidity which is approximately four times greater; a smaller weight.

Thus, there is obtained: a longer useful life because as the working pressure decreases the fatigue of the elements is also reduced; a better resistance to radiations due to the use of metal seals in substitution for elastomeric seals, and to the use of a metal compensation capsule; no risk of pollution to the outside since the unit is pressurized with no contact with the ambient air; structure of monoblock kind without welding, which ensures great mechanical reliability; owing to this structure, the volume of oil to be thermally compensated is smaller, i.e. a smaller dead volume; leaks are reduced owing to the small operating pressure and the use of metal dynamic seals.

WHAT WE CLAIM IS: 1. A shock absorber comprising a double-acting hydraulic piston-and-cylinder unit, the unit comprising a hollow liquidtight body defining a longitudinal space subdivided into a variable-volume front chamber and a variable-volume rear chamber by a cross-head which is longitudinally movable in the said space, the cross-head being rigid with a piston rod extending from the rear of the body through a stuffing member, the front and rear chambers communicating with each other via two opposed check valves in series which are each held open by biassing means and which each close automatically when the speed of the hydraulic fluid through the valve in opposition to its biassing means reaches a given value, the body containing a gas-filled volume-compensation capsule.

2. A shock absorber as claimed in claim 1, in which the capsule is contained in a chamber which communicates with the front chamber and the rear chamber via the respective valves, each valve closing automatically when the flow of hydraulic fluid into the capsule-containing chamber through that valve in opposition to its biassing means reaches a given value.

3. A shock absorber as claimed in claim 1 or 2, in which the front of the crosshead has a central extension which, at the end of the forward stroke, enters a recess in the front end of the front chamber.

4. A shock absorber as claimed in any of claims 1 to 3, in which the rear of the cross-head has a central recess which, at the end of the rearward stroke, receives a central extension of the stuffing member.

5. A shock absorber as claimed in any of claims 1 to 4, in which the periphery of the cross-head has two pairs of pistonrings, the rings of each pair having slots which are arranged diametrically opposite each other, the rings being held in position by a pin.

6. A shock absorber as claimed in any of claims 1 to 5, in which the front and rear chambers communicate with each other via nozzles in parallel withy the valves.

7. A shock absorber as claimed in any of claims 1 to 6, in which the cross-head is hollow and defines an internal chamber containing the gas-filled volume-compensation capsule, the internal chamber communicating with the front and rear chambers via the valves.

8. A shock absorber as claimed in claim 1 or 2, in cluding a plurality of volumecompensation chambers containing a plurality of gas-filled volume-compensation capsules and being disposed in a circular formation about the longitudinal axis of the unit.

9. A shock absorber as claimed in claim 1 or 2, in which the capsule is contained in an annular chamber surrounding the front and rear chambers.

10. A shock absorber as claimed in claim 9, in which the capsule is in the form of a hollow cylinder.

11. A shock absorber as claimed in claim 10, in which the hollow cylinder has longitudinal ribs and a longitudinal slot.

12. A shock absorber as claimed in claim 10, in which the hollow cylinder has transverse ribs.

13. A shock absorber as claimed in claim 9, in which the capsule is in the form of a helix.

14. A shock absorber as claimed in claim 1, substantially as described with reference to any of the embodiments illustrated in the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The effect thus produced is found to be practically independent of the location of the compensation device. The multiple advantages thus obtained are: considerable protection from the environment, particularly radioactivity; avoidance of cavitation during forward stroke of cross-head; locking of valves by rapid but small stroke of cross-head; confinement of oil in a closed space. The specific design and working characteristic consisting in the incorporation of the volume-compensation capsule in the cross-head results in numerous qualities and multiple advantages as well as substantial improved performance being obtained. Thus, the area of the cross-head can be maximised, in order to obtain, with respect to the conventional technology: a service pressure which is reduced by a quarter; a stiffness or rigidity which is approximately four times greater; a smaller weight. Thus, there is obtained: a longer useful life because as the working pressure decreases the fatigue of the elements is also reduced; a better resistance to radiations due to the use of metal seals in substitution for elastomeric seals, and to the use of a metal compensation capsule; no risk of pollution to the outside since the unit is pressurized with no contact with the ambient air; structure of monoblock kind without welding, which ensures great mechanical reliability; owing to this structure, the volume of oil to be thermally compensated is smaller, i.e. a smaller dead volume; leaks are reduced owing to the small operating pressure and the use of metal dynamic seals. WHAT WE CLAIM IS:

1. A shock absorber comprising a double-acting hydraulic piston-and-cylinder unit, the unit comprising a hollow liquidtight body defining a longitudinal space subdivided into a variable-volume front chamber and a variable-volume rear chamber by a cross-head which is longitudinally movable in the said space, the cross-head being rigid with a piston rod extending from the rear of the body through a stuffing member, the front and rear chambers communicating with each other via two opposed check valves in series which are each held open by biassing means and which each close automatically when the speed of the hydraulic fluid through the valve in opposition to its biassing means reaches a given value, the body containing a gas-filled volume-compensation capsule.