GB2318850A

GB2318850A - Damper

Info

Publication number: GB2318850A
Application number: GB9622350A
Authority: GB
Inventors: R Page; John James Bushnell
Original assignee: Oleo International Ltd
Current assignee: Oleo International Ltd
Priority date: 1996-10-28
Filing date: 1996-10-28
Publication date: 1998-05-06
Also published as: GB9622350D0

Abstract

A fixed number of dampers (13) are connected between approach bridges and a high bridge by self-aligning bearing (16). Each damper (13) comprises a hydraulic capsule which includes a single-ended hydraulic cylinder (21) having a cylinder chamber provided with valving (35-38) controlling displacement of hydraulic fluid between cylinder spaces (33, 34) during extension and contraction of the cylinder (21), and pressure accumulator (39) to and from which hydraulic fluid is displaced during expansion and contraction. The valving (35-38) is operable to provide minimal resistance to slow movement of the hydraulic cylinder caused by thermal expansion and contraction of bridge parts, whilst providing significant resistance to much faster relative movement.

Description

A DAMPER This invention relates to a damper and more particularly to a damper for connecting between relatively moveable parts of a large bridge for vehicular traffic.

A large bridge for vehicular traffic comprises a fixed approach bridge at either side of the physical feature that is to be bridged and a high bridge which bridges the gap between the fixed approach bridges. The large bridge is arranged so as to allow for a certain amount of movement of the high bridge relative to the fixed approach bridges. This movement may either be very slow or very much faster1 say 100 times faster. Such very slow movement would be due to expansion or contraction caused by temperature changes. On the other hand wind and traffic surges can cause movement at a very much faster rate.

An object of this invention is to provide a damper which is operable to allow such very slow movements with as little resistance as possible whilst providing a high resistance to the movements at the very much faster rate that are caused by wind or traffic surges whereby to damp the latter. A subsidiary object of the invention is to provide such a damper which is inexpensive, is easy to install and to replace.

According to one aspect of this invention there is provided a damper comprising a single ended cylinder having a closed end wall and a piston slidable therein, the piston being at one end of a rod which extends in a fluid-tight manner through another end wall of the cylinder, the damper including one valve which is operable to provide low resistance to flow of fluid displaced from one of the cylinder chamber on either side of the piston by movement of the piston relative to the cylinder in one sense and to close when the rate of that fluid flow increases above a certain low flow rate threshold whereby to provide minimal resistance to the slow relative displacement of the piston and the cylinder in said one sense, and another valve which is normally closed and which is operable to open when that fluid flow rate increases further to exceed a certain higher threshold whereby a higher resistance to flow in said one sense and thereby a higher resistance to such relative displacement of the piston and cylinder in said one sense is provided for flows above said certain low flow rate when that relative displacement is faster and above a certain higher threshold.

Preferably the cylinder is a double acting cylinder and said one and the other valves are one pair of valves, wherein there is provided another pair of such valves which are similarly operable to provide minimal and higher resistance to relative displacement of the piston and cylinder in the opposite sense.

The valves of said one pair of valves are operable to provide resistance to fluid flow from the annular cylinder space around the rod to the larger diameter cylinder space between the piston and the dosed end wall and the valves of said other pair are operable to provide resistance to fluid flow from the larger diameter cylinder space to a fluid pressure accumulator which in turn is operable to feed fluid to the larger diameter cylinder space when the piston is moved away from the closed end wall, the certain higher threshold at which the other valve of said one pair opens being higher than that of the other valve of said other pair to the extent necessary for the force generated by fluid pressure acting on either side of the piston to be substantially the same. The one pair of valves may be in the piston. The other pair of valves may be in the closed end wall.

Conveniently, the fluid pressure accumulator comprises an annular space formed around the cylinder, there being conduit means in the cylinder providing communication between the annular space and the larger diameter cylinder space, a one-way valve in the conduit means to prevent flow through the conduit means from the larger diameter cylinder space to the annular space and resilient means operable to act on fluid in the annular space to urge it to flow to the larger diameter cylinder space through the conduit means. The resilient means may comprise gas with which the annular cylinder space is at least partially filled.

According to another aspect of this invention there is provided a bridge comprising relatively movable structural parts and damping means connected between two of the relatively movable structural parts so as to damp relative movement between those structural bridge parts, wherein the damping means comprise a hydraulic capsule which includes a singleended hydraulic cylinder having a cylinder chamber provided with valving operable to control displacement of hydraulic fluid from a respective cylinder space of the hydraulic cylinder during extension and contraction of the hydraulic cylinder, and an hydraulic fluid pressure accumulator to which hydraulic fluid is displaced from the cylinder chamber during contraction and from which hydraulic fluid is returned to the cylinder chamber during extension, the valving being operable to provide minimal resistance to slow extension and contraction of the hydraulic cylinder that is caused by thermal expansion and contraction of structural parts of the bridge whilst providing significant resistance to much faster relative movement between the structural parts of the bridge, the hydraulic cylinder, the valving and the hydraulic fluid pressure accumulator all being enclosed within a casing of the hydraulic capsule.

A bridge fitted with a number of dampers in which this invention is embodied is described now by way of example with reference to the accompanying drawings, of which; Figure 1 is a diagrammatic side view showing a damper fitted between an approach bridge and a high bridge part of a large bridge; and Figure 2 is a transverse cross section of one form of damper in which this invention is embodied.

Figure 1 shows a fixed approach bridge 10 and the adjacent end of a high bridge 11 which bridges the gap between the fixed approach bridge 10 and a similar fixed approach bridge on the other side of the stretch of water or other physical feature that is to be spanned by the bridge. There is a gap 12 between the fixed approach bridge 10 and the high bridge 11. A damper 13 is connected at one end 14 to the approach bridge 10 and at the other end 15 to the high bridge 11 by suitable self-aligning bearings shown generally at 16 at either end of the damper 13.

In practice there are a number of dampers 13 at either end of the high bridge 11. In one arrangement there are eight dampers at each end arranged in groups of four on either side of the high bridge at the respective end.

Figure 2 shows that each damper comprises a plunger 20 mounted in a cylinder 21 which is closed at one end 22. The cylinder 21 is formed by a tube 23 which is coaxially surrounded by an outer tube 24. The tube 23 is spigotted into a circular recess 25 which is formed in a yoke member 26 which forms the closed end 22 of the cylinder chamber and which is for connecting to the approach bridge 10 by the respective self-aligning bearing 16. The yoke member 26 in turn is spigotted into the outer tube 24 to which it is welded. The other end of the tube 23 is spigotted into a circular recess 27 in an annular end member 28 which in tum is spigotted into the outer tube 24 to which it may be welded or within which it may be retained by a nut member. The rod portion 29 of the plunger 20 is a sliding fit in the bore 31 of the annular member 28, suitable annular sealing arrangements being provided in the bore 31 to seal against leakage of liquid from the annular cylinder space formed around the rod 29.

The cylinder 21 is a single ended cylinder, the piston head 32 being at one end of the rod portion 29 and dividing the cylinder chamber into a larger diameter cylinder space 33 and the annular cylinder space 34 that surrounds the rod portion 29.

There are two valves 35 and 36 in the piston head 32 for controlling displacement of liquid from the annular cylinder space 34 to the larger diameter cylinder space 33 during extension of the damper 13. There are two further valves 37 and 38 in the yoke member 26 which control displacement of liquid from the larger diameter cylinder space 33 to the annular space 39 formed between the tubes 23 and 24 through suitable conduits 41 and 42 in the yoke member 26. A one-way valve 43 allows liquid to flow from the annular space 39 into the larger diameter cylinder space 33.

The valves 35 and 37 are similar creep valves. Only the valve 35 is shown in detail for convenience.

The valve 35 comprises a spring loaded shuttle valve member 44 which is slidable in a stepped through bore 45 formed in a tubular housing 46 which is screwed into a stepped bore 47 which extends through the piston head 32. The shuttle valve member 44 has a stepped external surface. The larger diameter portion 48 of the stepped external surface is at the end of the shuttle valve member 44 that is nearer to the annular cylinder space 34 and it slides in a larger diameter portion of the stepped through bore 45.

The spring 49 engages the step of the extemal surface of the valve member 44 and reacts against the step of the stepped bore 45 to urge the valve member 44 against an annular abutment 51 which is screwed into the mouth of the stepped bore 45 from the end that communicates with the annular cylinder space 34.

An angled passage is formed in the valve member 44. The angled passage comprises an axial portion 52 and a radial portion 53. The axial portion 52 opens at the larger diameter end of the valve member 44 adjacent to the annular cylinder space 34. The radial portion 53 provides communication between the axial portion 52 and the stepped through bore 45 by opening into the smaller diameter portion of the stepped external surface of the valve member 44 which is spaced from the wall of the larger diameter portion of the stepped through bore 45. The radial portion 53 includes an orifice of flow restricting dimensions which serves as a metering orifice and which allows a slow leakage of oil through the valve member 44 when the valve member 44 is seated against the annular abutment 51 by the action of the spring 49. The metering orifice provides minimal resistance to extension of the damper 13 due to expansion or contraction due to changes in temperature.

The smaller diameter end of the valve member 44 is adapted to seat on the shoulder of the stepped through bore 45 in the tubular housing 46 to close the valve 35 and prevent flow of oil through it. This occurs when the flow rate through the valve 35 increases to exceed a certain low threshold when the pressure downstream of the metering orifice in the radial passage portion 53 is reduced sufficiently as compared to that upstream thereof for the difference between the fluid pressures upstream and downstream of the valve 44 to be sufficient to overcome the loading of the spring 49.

The valve 37 is a similar creep valve which functions similarly to allow slow leakage of oil from the larger diameter cylinder space 33 through the conduit 41 into the annular space 39 when the damper 13 is caused to contract by expansion or contraction due to temperature changes.

The other valve 36 in the piston head 32 is a normally-closed relief valve.

It comprises a tubular valve housing 54 which has a stepped through bore 55 and which is screwed into a stepped through bore 56 in the piston head 32. A cup-shaped valve member 57 slides within the bore 55 in the housing 54 and has a conical nose which is formed by its closed end wall so that it tapers away from its cavity towards the annular cylinder space 34.

A spring 58 seats on the base of the cup-shaped valve member 57 within the cavity and reacts against the base of the cavity of a cup-shaped member 59 which is screwed into the stepped through bore 55. The tapered nose of the cup-shaped valve member 57 is urged by the spring 58 to seat to close an orifice 61 which is the smallest diameter portion of the stepped through bore 55 in the valve housing 54 and which is at the end thereof nearer to the annular cylinder space 34. Passages 62 through the closed end wall of the cup-shaped valve member 57 provide communication between the cavity of the cup-shaped valve member 57 and the stepped bore 55. Passages 63 in the base of the cup-shaped member 59 allow flow of oil therethrough.

The relief valve 36 is held closed by the action of its spring 58 when the creep valve 35 is open to allow slow leakage of oil through it and there is minimal resistance to extension of the damper 13 with expansion or contraction of parts of the bridge due to temperature changes. However, when the damper 13 is subjected to far greater loads which act to extend it due to the action on the bridge parts of wind and/or traffic surges, liquid is displaced from the annular cylinder space 34 through the piston head 32 to the larger diameter cylinder space 33 at a far greater rate, perhaps 100 times as great. That higher rate of flow causes the creep valve 35 to close and the relief valve 36 to open because the many times greater flow rate will overcome the greater resistance to flow through the relief valve 36 provided by the loading of the spring 58 that acts to seat the cup-shaped valve member 57. Hence, a considerably greater resistance to displacement of liquid from the annular cylinder space 34 through the piston head 32 is provided by the relief valve 34 and the loads applied to the damper 13 are thereby damped by the damper 13.

When the damper 13 contracts, slow leakage is allowed by the creep valve 37 in substantially the same way as has been described above for the creep valve 35.

The design of the relief valve 38 shown in Figure 2 is different from that of the relief valve 36 but the principle of operation is substantially the same.

In this case the valve member 64 is a mushroom valve with the spring 59 acting on the head 65 and surrounding the stem portion 66 of the valve member 64. The valve member 64 has an axially extending bore 67 which is closed at the end which forms the head 65 and which receives a guide pin 68 which is mounted in the valve housing 69 to guide the valve member 64 for reciprocal movement along its axis. The loading exerted by the spring 59 of the relief valve 38 is lower than that exerted by the spring 59 of the relief valve 36 and is selected so that the fluid pressure at which the relief valve 38 opens is lower than that at which the relief valve 36 opens so that the force generated by fluid pressure acting on either side of the piston head 32 is substantially the same despite the fact that the effective areas of the piston head 32 on either side are different.

Liquid displaced from the larger diameter cylinder space 33 to the annular space 39 compresses gas within that annular cylinder space 39 so that the annular space 39 functions as a liquid pressure accumulator. Hence, during extension of the damper 13, the compressed gas in the cylinder space 39 urges liquid through the one-way valve 43 into the larger diameter cylinder space 33 to make up the volume of liquid in the latter as is required with its enlarging volume.

A one-way valve 71 allows liquid to flow from the annular space 39 to the annular cylinder space 34 during contraction of the damper 13.

Claims

1. A damper comprising a single ended cylinder having a closed end wall and a piston slidable therein, the piston being at one end of a piston rod which extends in a fluid-tight manner through another end wall of the cylinder, the damper including one valve which is operable to provide low resistance to flow of fluid displaced from one of the cylinder spaces on either side of the piston by movement of the piston relative to the cylinder in one sense and to close when the rate of that fluid flow increases above a certain low flow rate threshold whereby to provide minimal resistance to slow relative displacement of the piston and the cylinder in said one sense, and another valve which is normally closed and which is operable to open when that fluid flow rate increases further to exceed a certain higher threshold whereby a higher resistance to flow in said one sense and thereby a higher resistance to such relative displacement of the piston and cylinder in said one sense is provided for flows above said certain low flow rate when that relative displacement is faster and above a certain higher threshold.

2. A damper according to claim 1, in which the cylinder is a double acting cylinder and said one and the other valves are one pair of valves, wherein there is provided another pair of such valves which are similarly operable to provide minimal and higher resistance to relative displacement of the piston and cylinder in the opposite sense.

3. A damper according to claim 2, wherein the valves of said one pair of valves are operable to provide resistance to fluid flow from the annular cylinder space around the piston rod to the larger diameter cylinder space between the piston and the closed end wall and the valves of said other pair are operable to provide resistance to fluid flow from the larger diameter cylinder space to a fluid pressure accumulator which in turn is operable to feed fluid to the larger diameter cylinder space when the piston is moved away from the closed end wall, the certain higher threshold at which the other valve of said one pair opens being higher than that of the other valve of said other pair to the extent necessary for the force generated by fluid pressure acting on either side of the piston to be substantially the same.

4. A damper according to any one of claims 1 to 3, wherein said one pair of valves are in said piston.

5. A damper according to claim 2, claim 3 or claim 4 when appended to claim 2, wherein said other pair of valves are in said closed end wall.

6. A damper according to claim 3 or either of claims 4 and 5 when appended to claim 3, wherein said fluid pressure accumulator comprises an annular space formed around said cylinder, there being conduit means in said cylinder providing communication between said annular space and said larger diameter cylinder space, a one-way valve in said conduit means to prevent flow through said conduit means from said larger diameter cylinder space to said annular space and resilient means operable to act on fluid in said annular space to urge it to said larger diameter cylinder space through said conduit means.

7. A damper according to claim 6, wherein said resilient means comprise gas with which said annular space is at least partially filled.

8. A bridge comprising relatively movable structural parts and damping means connected between two of the relatively movable structural parts so as to damp relative movement between those structural bridge parts, wherein the damping means comprise a hydraulic capsule which includes a single-ended hydraulic cylinder having a cylinder chamber and provided with valving operable to control displacement of hydraulic fluid from a respective cylinder space of the hydraulic cylinder during extension and contraction of the hydraulic cylinder, and an hydraulic fluid pressure accumulator to which hydraulic fluid is displaced from the cylinder chamber during contraction and from which hydraulic fluid is returned to the cylinder chamber during extension, the valving being operable to provide minimal resistance to slow extension and contraction of the hydraulic cylinder that is caused by thermal expansion and contraction of structural parts of the bridge whilst providing significant resistance to much faster relative movement between the structural parts of the bridge, the hydraulic cylinder, the valving and the hydraulic fluid pressure accumulator all being enclosed within a casing of the hydraulic capsule.

9. A damper which is operable to provide resistance to relative movement between fixed and movable parts of a bridge substantially as described hereinbefore with reference to and as shown in the accompanying drawings.

10. A bridge substantially as described hereinbefore with reference to the accompanying drawings.