GB2561681A

GB2561681A - Hydraulic damper

Info

Publication number: GB2561681A
Application number: GB1802722.7A
Authority: GB
Inventors: Jolley Paul
Original assignee: TRANSP FOR LONDON
Current assignee: TRANSP FOR LONDON
Priority date: 2017-02-28
Filing date: 2018-02-20
Publication date: 2018-10-24
Also published as: GB201802722D0; GB201703177D0

Abstract

A hydraulic damper 10 is provided; the hydraulic damper 10 being suitable for damping a hinged closure, such as a door. The hydraulic damper 10 comprises; an orifice 18 for restricting flow of a working fluid 16; and an orifice forming member 36 which forms the orifice 18. The orifice forming member 36 is movable in a first direction towards a first internal surface 40 of the damper, and in a second direction towards a second internal surface 42 of the damper, thereby to decrease the size of the orifice 18, depending on the applied force. The damping coefficient of the hydraulic damper 10 is thereby increased as an increasing force is applied to the hydraulic damper 10 under compression and under tension. A hinged closure incorporating the hydraulic damper 10, and a method of damping such a hinged closure using the hydraulic damper 10 are also disclosed.

Description

(54) Title of the Invention: Hydraulic damper Abstract Title: A hydraulic damper (57) A hydraulic damper 10 is provided; the hydraulic damper 10 being suitable for damping a hinged closure, such as a door. The hydraulic damper 10 comprises; an orifice 18 for restricting flow of a working fluid 16; and an orifice forming member 36 which forms the orifice 18. The orifice forming member 36 is movable in a first direction towards a first internal surface 40 of the damper, and in a second direction towards a second internal surface 42 of the damper, thereby to decrease the size of the orifice 18, depending on the applied force. The damping coefficient of the hydraulic damper 10 is thereby increased as an increasing force is applied to the hydraulic damper 10 under compression and under tension. A hinged closure incorporating the hydraulic damper 10, and a method of damping such a hinged closure using the hydraulic damper 10 are also disclosed.

FIG.1

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

1/10

1605 18

CM

2/10

LO ο

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-----VARIABLE

----FIXED

FIG.2

3/10

1605 18 ζχ

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V

4/10

1605 18

FIG.4C

5/10

FIG.5

6/10

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co

FIG.6

7/10

1605 18

FIG.7

8/10

1605 18

FIG.8B

9/10

1605 18

FIG.9A

102

FIG.9B

10/10

1605 18

FIG.10B

HYDRAULIC DAMPER

The present invention relates to a hydraulic damper, and in particular but not exclusively to a hydraulic damper for use in controlling the movement of a hinged closure such as a door.

Known hydraulic dampers comprise a cylinder having a cylinder bore which accommodates a piston. The piston acts on a working fluid which is contained within the cylinder. The cylinder is divided into two chambers separated by a damping orifice. When an external force is applied to the damper, the piston slides within the cylinder and forces the working fluid through the damping orifice. The passage of the fluid through the damping orifice dissipates kinetic energy, thereby providing the damping effect.

Hydraulic dampers may be used in any situation where it is desired to control the speed of a moving object. A typical application of a hydraulic damper is in controlling the movement of a door. In this case the hydraulic damper is connected between the door and the door frame or other fixed object such as a wall. The damper provides a damping force which prevents the door from opening or closing too rapidly.

In some situations a door may be subject to high forces which are not part of the normal door opening/closing force. For example, fire doors in underground transport systems may be subject to high wind forces due to passing trains. Balcony doors on high rise buildings, and doors in coastal regions are also often subject to high wind forces. However in these cases there remains a need for the door to be opened safely by a person. A standard damper with a damping coefficient sized for the high wind force would make the door very difficult to open and slow to move under the force provided by a person.

It would therefore be desirable to provide a hydraulic damper which can withstand large intermittent forces, but still allow actuation by a relatively low force.

According to one aspect of the present invention there is provided a hydraulic damper having a damping coefficient which increases as an increasing force is applied to the damper.

The present invention may provide the advantage that, by providing a hydraulic damper with a damping coefficient which increases as an increasing force is applied to the damper, the hydraulic damper may be able to withstand large intermittent forces, but still allow actuation by a relatively low force.

Preferably the damper exhibits a non-linear relationship between force applied to the damper, and damper actuation speed. For example, the damper may have a damping coefficient which is substantially constant below a predetermined threshold, and which increases above the threshold. The non-linear relationship between force and damper actuation speed may be exhibited under tension, or under compression, or both. In the latter case, the non-linear relationship under tension may be the same as under compression, or different.

The damper may comprise a cylinder, and a piston arranged to slide within the cylinder so as to displace a working fluid. Preferably, the damper comprises an orifice for restricting flow of the working fluid. The cylinder may be separated into two chambers, and movement of the piston may force the working fluid through the orifice from one chamber to the other.

Preferably the damper is arranged such that the size of the orifice decreases as an increasing force is applied to the damper. This may allow the damper to use standard fluids and may avoid the need for any active control.

The damper may comprise an orifice forming member which forms the orifice.

The orifice may be formed between an external surface of the orifice forming member, and an internal surface of the damper. The orifice forming member may be disc-shaped. For example, when viewed axially (i.e. in the direction of movement of the piston) the orifice forming member may have a circular profile. However other shapes are also possible, depending for example on the shape of the cylinder and the desired form of the orifice.

The orifice may be annular. For example, the orifice may be in the form of an annular gap around the radially outwards edge of the orifice forming member.

One or more of the radially outwards edges of the orifice forming member may be chamfered. The chamfered edges may face corresponding sloping surfaces of the damper. This may help to increase the surface area of the orifice, and thus may facilitate accurate adjustment of the size of the orifice.

Preferably the orifice forming member is movable in order to change the size of the orifice. For example, the orifice forming member may be moveable axially within the cylinder, that is, in the same direction or along the same axis as the piston. This may allow the size of the orifice to be varied.

Preferably the damper comprises an elastic device which is operable to resist movement of the orifice forming member. The elastic device may be any device or combination of devices which exhibit elastic deformation. For example, the elastic device may be at least one spring, such as a helical spring or a leaf spring, or other element such as a rubber block.

Preferably the damper is arranged such that the elastic device deforms when a force above a predetermined threshold is applied to the damper. This may allow the size of the orifice to vary once the force applied to the damper is above the threshold. However, the damper may be arranged such that the piston is able to move when a force below the threshold is applied to the damper. This may allow a non-linear relationship between force and damper actuation speed to be achieved.

The orifice forming member may be connected to the elastic device by means of a rod. In this case the rod may comprise a flange which engages with the elastic device. This may allow the elastic device to apply an opposing force to the orifice forming member.

The elastic device may be located within a housing (e.g. a spring housing). This may serve to contain the elastic device, and allow the elastic device to apply a force to the orifice forming member.

Preferably the orifice forming member is movable in a first direction towards a first internal surface of the damper, and in a second direction towards a second internal surface of the damper. Thus the size of the orifice may be adjustable when the damper is under compression and under tension. This may allow a non-linear relationship between force and damper actuation speed to be achieved in both directions.

According to another aspect of the present invention there is provided a hydraulic damper comprising an orifice for restricting flow of a working fluid, and an orifice forming member which forms the orifice, wherein the orifice forming member is movable in a first direction towards a first internal surface of the damper, and in a second direction towards a second internal surface of the damper, thereby to increase a damping coefficient of the damper as an increasing force is applied to the damper under compression and under tension.

The damper may comprise at least one, and preferably two elastic devices, such as two springs. In the latter case each of the elastic devices may be operable to resist movement of the orifice forming member. One of the elastic devices may compress in the first direction and the other elastic device may compress in the second direction. Alternatively a single elastic device may be used, which may apply a force in either direction.

The relationship between force and damper actuation speed may be the same under compression as under tension, or different, for example by selecting the spring constants of the springs as appropriate.

In one embodiment, the damper comprises two (or more) elastic devices, both of which are operable to resist movement of the orifice forming member in one direction of travel. In this case, one elastic device may be actuated when a force applied to the damper is above a first threshold, and the other elastic device may be actuated when a force applied to the damper is above a second threshold.

This can allow further control over the change in damping coefficient as a function of force.

In one arrangement, the two elastic devices may be connected in parallel, and one elastic device may be arranged to deform (extend or compress) through a predetermined distance before the other elastic device is actuated.

In another arrangement, the two elastic devices may be connected in series, and one elastic device may have a lower spring constant than the other.

If desired, a plurality of elastic devices may be provided for each direction of travel (compression and tension). In all of the above arrangements, each elastic device may comprise or more springs, and/or another elastic element.

Preferably the cylinder is separated into two chambers which are in fluid communication with each other via the damping orifice. Preferably movement of the piston forces the working fluid through the orifice from one chamber to the other. The cylinder is typically cylindrical, although other shaped cross sections such as square or hexagonal could be used instead.

In one embodiment of the invention, the orifice is separate from the piston. In this embodiment, the orifice may be formed between the orifice forming member and an internal surface of the cylinder. Movement of the piston may change the volume of the cylinder occupied by the working fluid, thereby forcing the working fluid through the orifice. An accumulator may be provided to accommodate the changing volume of working fluid in the cylinder.

In this embodiment, the piston may be connected to a first external connection means, and the orifice forming member may be connected to a second external connection means. For example, where a rod is used to connect the orifice forming member to the elastic device, the rod may also be connected to the external connection means. The external means may be any means which allows a force to be applied to the damper, such as a connecting eye.

In another embodiment of the invention the orifice is located in the piston. In this embodiment, the orifice may be formed between the orifice forming member and an internal surface of the piston. Movement of the piston may force working fluid through the orifice from one side of the piston to the other. This may avoid the need to provide a separate accumulator.

In this embodiment, the elastic device may be located in the piston. For example, the elastic device may be located in a housing within the piston. The orifice forming member may engage with the elastic device for example by means of a rod with a flange.

In this embodiment, the piston may be connected to a first external connection means, and the cylinder may be connected to a second external connection means.

In any of the above arrangements the damper may be arranged for use with a hinged closure such as a door.

According to another aspect of the invention there is provided a hinged closure comprising a damper in any of the forms described above. The hinged closure may be for use in environments which are subject to large intermittent forces, but where actuation by a relatively low force is required. For example, the hinged closure may be a door for use in situations where large intermittent wind forces are experienced, but actuation by a human being is required.

According to another aspect of the invention there is provided a method of damping a hinged closure using a hydraulic damper, the method comprising increasing a damping coefficient of the hydraulic damper as an increasing force is applied to the closure.

Preferred features of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows parts of a hydraulic damper in one embodiment of the invention;

Figure 2 is a graph showing variation of piston velocity with piston force; Figure 3 shows parts of a hydraulic damper in another embodiment of the invention;

Figures 4A, 4B and 4C show various different damping orifice profiles; Figure 5 illustrates the concept of a two-stage spring arrangement;

Figure 6 is a graph showing variations of piston velocity with applied force; Figures 7A to 7C illustrate one embodiment of a two-stage spring mechanism;

Figures 8A and 8B illustrate another embodiment of a two-stage spring mechanism;

Figures 9A and 9B show an example of a hydraulic damper being used with a door located in a wall; and

Figures 10A and 10B show an example of a damper being used with a door located at the end of a corridor;

Overview

It is known to use hydraulic dampers to control the speed at which a door is opened or closed. Typically the damper is used to prevent the door from slamming shut, and to provide end of travel cushioning. The damper may be used either on its own, or else in conjunction with a door opening/closing mechanism.

Known hydraulic dampers operate by forcing a working fluid through a damping orifice. The passage of the fluid through the damping orifice dissipates kinetic energy, which provides the damping effect. The amount of damping provided by a hydraulic damper is known as the damping coefficient, and is defined by the equation:

F = -cv where F = force, c = damping coefficient and v = velocity.

The majority of dampers have a substantially constant damping coefficient. However other dampers are arranged such that the damping coefficient can be varied. This generally requires manual adjustment, or else electronics or specialized fluids.

In embodiments of the present invention, a hydraulic damper is provided in which the damping coefficient varies in dependence on the force on the damper. In preferred embodiments, the damper has a high damping coefficient at high forces and a low damping coefficient at low forces. When used to control the movement of a door, the hydraulic damper can allow the door to withstand large intermittent forces caused by, for example, high wind speeds, but still allow actuation of the door by a person using a relatively low force.

Variable orifice

Figure 1 shows parts of a hydraulic damper in one embodiment of the invention.

In this embodiment the damper is provided with a variable orifice which is separate from the piston.

Referring to Figure 1, the damper 10 comprises a cylinder 12, piston 14, working fluid 16, damping orifice 18 and accumulator 20. The cylinder is divided into two chambers 22, 24 which are in fluid communication with each other via the damping orifice 18. The piston 14 is located within the first chamber 22, and is able to slide axially within the chamber, within the limits imposed by the size of the chamber. As the piston moves, the working fluid 16 is forced in one direction or the other through the damping orifice 18. A bladder 32 within the accumulator 20 expands and contracts as appropriate to accommodate fluid flows.

The hydraulic damper 10 is connected externally via connecting eyes 26, 28.

The first external connecting eye 26 is connected to one side of the piston 14 via piston rod 30, which passes through an end wall of the cylinder 12. The other side of the piston 14 interfaces with the working fluid 16. The piston 14 is provided with one or more piston seals 15 in order to prevent the working fluid from escaping past the piston.

In the arrangement of Figure 1, the damping orifice 18 is formed by an intermediate section 34 of the cylinder on one side (the radially outwards side), and an orifice forming member 36 on the other side (the radially inwards side). The intermediate section 34 is located between the first chamber 22 and the second chamber 24. The interior of the intermediate section 34 has a first sloping surface 40 which faces one side of the orifice forming member 36, and a second sloping surface 42 which faces the other side of the orifice forming member 36. The orifice forming member 36 is disc-shaped (when viewed axially), with a first chamfered edge 44 which faces the first sloping surface 40, and a second chamfered edge 46 which faces the second sloping surface 42.

The damping orifice 18 is formed by the gap between the first chamfered edge 44 and the first sloping wall 40, and the second chamfered edge 46 and the second sloping wall 42. When the orifice forming member 36 is in its neutral position, the gap is of approximately the same width around the orifice forming member.

The orifice forming member 36 is connected to the second connecting eye 28 via a rod 38. The rod 38 and the orifice forming member 36 are able to slide axially within the damper, although as will be explained this only takes place when a relatively high force is applied. One or more seals 39 are provided at the interface between the rod 38 and the wall of the second chamber 24, to prevent the working fluid from escaping.

The rod 38 also passes through a spring housing 48. The spring housing accommodates two springs 50, 52. A flange 54 on the rod 38 sits between the two springs 50, 52. Thus each of the springs 50, 52 engages with a wall of the housing 48 on one side, and with the flange 54 on the other side.

In order for the rod 38 and the orifice forming member 36 to slide axially within the damper it is necessary for one or other of the springs 50, 52 to be compressed, depending on the direction of movement. However the spring constant of the springs 50, 52 is relatively high, so that a relatively high force is required to compress them (for example, relatively high compared to a normal actuation force such as that applied by a human when opening a door).

In operation of the hydraulic damper 10, a contracting or expanding force is applied via the connecting eyes 26, 28. As long as the applied force is below a certain threshold as determined by the spring constants of the springs 50, 52, little or no compression of the springs 50, 52 takes place. As a consequence, there is little or no movement of the rod 38 and orifice forming member 36. In this case the size of the damping orifice 18 is approximately the same on either side of the orifice forming member 36.

However, provided the applied force is sufficient to overcome resistive forces in the damper, the piston 14 is caused to slide within the cylinder 12. This forces the working fluid 16 through the damping orifice 18. The damping orifice 18 restricts the flow of fluid, and thus controls the velocity at which the cylinder moves in response to the force. Thus, when a relatively low force is applied to the damper, the damper operates with a substantially constant damping coefficient, as determined by the size of the damping orifice in the neutral position.

As an increasingly high force is applied to the damper, the velocity of the working fluid through the damping orifice increases, thus increasing the resistive force. This causes an increasingly high opposing force to be applied to one of the springs 50, 52 via the flange 54, depending on whether the damper is under compression or tension. Once the applied force exceeds a certain threshold the spring starts to be compressed. This causes the orifice forming member 36 to move axially, such that one of its chamfered edges 44, 46 is closer to the corresponding sloping surface 40, 42 than would otherwise be the case. This causes the size of the damping orifice to decrease, thereby restricting further the flow of fluid from one chamber to the other. As a consequence of the restricted flow, more kinetic energy is dissipated and the damping coefficient increases.

Thus the hydraulic damper show in Figure 1 has a force dependent damping coefficient by virtue of the variable damping orifice. When a relatively high force is applied to the damper, one of the springs compresses and restricts the flow of the working fluid from one side to the other. This restriction is dependent on the force applied to the damper, that is, the greater the force, the greater the restriction. As the restriction increases, the damping coefficient increases. This causes a non-linear relationship between force and damper actuation speed, greatly reducing movement under high load.

The force dependent damping effect will work whether the damper is under tension or compression. In Figure 1, fluid flows are shown when the damper is under tension. Fluid flows are in the opposite direction when the damper is under compression.

Figure 2 is a graph showing variation of piston velocity with piston force in one embodiment. In the graph of Figure 2, the line 56 shows the variation of piston velocity with piston force for a hydraulic damper with a force dependent damping coefficient. As can be seen from Figure 2, in this embodiment the piston velocity increases with piston force up to a force of around 400 N. However, as the force increases above 400 N, the velocity decreases, and approaches zero at a force of around 1000 N. For comparison, the line 58 shows the variation of piston velocity with piston force for a standard damper with a fixed damping coefficient.

It will be appreciated that the values shown in Figure 2 are given as an example only, and the damping properties of the damper may be varied to suit the circumstances. This may be achieved, for example, by varying the spring coefficients of the springs 50, 52, and/or by changing the profile of the orifice forming member 36 and/or the sloping surfaces 40, 42.

In some embodiments, if a sufficiently high force is applied, the orifice forming member 36 comes into contact with one of the sloping surfaces 40, 42, thereby closing the orifice 18. In this case the velocity of travel will approach zero at high force. In other embodiments, a gap is left between the first chamber and the second chamber even under very high force. This may be achieved, for example, by providing a stop for the flange 54, or by providing channels in the orifice forming member 36 or the sloping surfaces 40, 42. In this case the final velocity of the damper at high force will be determined by the size of the gap.

The damper may be arranged such that the damping coefficient varies in a similar way under both tension and compression. Alternatively, the damping coefficient for a given force may be different depending on whether the damper is under tension or compression. This may be achieved by varying the spring coefficients of the springs 50, 52, and/or by changing the profile of the orifice forming member 36 and/or the sloping surfaces 40, 42. This may be useful in situations where a large intermittent force is expected in one direction but not the other, or where unequal forces are expected in opposite directions. If desired, the non-linear relationship between force and damper actuation speed may be provided in one direction only, in which case one or other of the springs 50, 52 may be dispensed with.

Moving orifice

Figure 3 shows parts of a hydraulic damper in another embodiment of the invention. In this embodiment the variable damping orifice is contained within the piston.

Referring to Figure 3, the damper 60 of this embodiment comprises cylinder 62, piston 64, working fluid 66, damping orifice 68 and accumulator 70. The cylinder 62 is divided into two chambers 72, 74 which are in fluid communication with each other via the damping orifice 68. The piston 64 is located within the cylinder 62, and is able to slide axially within the limits imposed by the size of the cylinder. As the piston moves, the working fluid 66 is forced in one direction or the other through the damping orifice 68. A bladder 82 within the accumulator 70 expands and contracts as appropriate to accommodate fluid flows.

The hydraulic damper 60 is connected externally via connecting eyes 76, 78.

The first external connecting eye 76 is connected to the piston 64 via a piston rod 80 which passes through a wall of the cylinder 62. One or more seals 75 are provided between the piston rod 80 and the cylinder 62, to prevent the working fluid from escaping. The second external connecting eye 78 is connected to the cylinder 62.

In the arrangement of Figure 3, the damping orifice 68 is contained within the piston 64. The damping orifice 68 is formed between a first section 84 of the piston on one side, and an orifice forming member 86 on the other. The first section 84 of the piston has a first sloping surface 90 which faces one side of the orifice forming member 86, and a second sloping surface 91 which faces the other side of the orifice forming member 86. The orifice forming member 86 has a first chamfered edge 92 which faces the first sloping surface 90, and a second chamfered edge 93 which faces the second sloping surface 91. The damping orifice 68 is formed by the gap between the first chamfered edge 92 and the first sloping wall 90, and the second chamfered edge 93 and the second sloping wall 91.

A second section 94 of the piston is located inside the first section 84, and is connected to it by means of radially extending arms (not shown in Figure 3). The radially extending arms are formed such that the first section 84 and second section 94 of the piston move in unison. However gaps between the arms allow the working fluid 66 to flow freely between the first section 84 and second section

94.

The second section 94 of the piston includes a spring housing. The spring housing accommodates two springs 95, 96. The orifice forming member 86 is connected to the inside of the spring housing by means of connecting rod 88.

One or more seals 99 are provided at the interface between the rod 88 and the wall of the second section 94, to prevent the working fluid from entering the interior of the spring housing.

The connecting rod 88 includes a flange 98 which sits between the two springs

95, 96. Thus each of the springs 95, 96 engages with a wall of the spring housing 94 on one side, and with the flange 98 on the other side. The rod 88 and the orifice forming member 86 are able to slide axially with respect to the piston 64. In order for this to happen, it is necessary for one or other of the springs 95, 96 to be compressed, depending on the direction of movement. However the spring constant of the springs 95, 96 is relatively high, so that a relatively high force is required to compress them.

In operation of the hydraulic damper 60, a contracting or expanding force is applied via the connecting eyes 76, 78. As long as the applied force is below a certain threshold as determined by the spring constants of the springs 95, 96, little or no compression of the springs 95, 96 takes place. As a consequence, there is little or no movement of the rod 88 and orifice forming member 86. In this case the size of the damping orifice 68 is approximately the same on either side of the orifice forming member 86.

However, provided the applied force is sufficient to overcome resistive forces in the damper, the piston 64 is caused to slide within the cylinder 62. This forces working fluid 66 from one side of the piston to the other, through the damping orifice 68. The damping orifice 68 restricts the flow of fluid, and thus controls the velocity at which the cylinder moves in response to the force. Thus, when a relatively low force is applied to the damper, the damper operates with a substantially constant damping coefficient, as determined by the size of the damping orifice 68 in the neutral position.

If on the other hand a relatively high force is applied to the damper, then pressure from the moving hydraulic fluid causes one or other of the springs 95, 96 to compress, depending on the direction of movement. This causes the orifice forming member 86 to move axially, such that one of its chamfered edges 92, 93 is closer to the corresponding sloping surface 91, 92 than would otherwise be the case. This causes the size of the damping orifice 68 to decrease, thereby restricting further the flow of fluid from one chamber 72, 74 to the other. As a consequence of the restricted flow, more kinetic energy is dissipated and the damping coefficient increases.

Thus the hydraulic damper of Figure 3 has a force dependent damping coefficient by virtue of the variable damping orifice. In this embodiment the orifice forming member is actuated by the pressure from the moving hydraulic fluid, rather than by an external force transmitted by a rod as in the embodiment of Figure 1.

When a relatively high force is applied to the damper, one of the springs compresses and restricts the flow of the working fluid from one side of the piston to the other. This restriction is dependent on the force applied to the damper, that is, the greater the force, the greater the restriction. As the restriction increases, the damping coefficient increases. This causes a non-linear relationship between force and damper actuation speed, greatly reducing movement under high load.

In the arrangement of Figure 3 the variable damping orifice is contained within the piston. The total quantity of working fluid within the cylinder 62 therefore remains the same regardless of the position of the piston. As a consequence, the external accumulator 20 of Figure 1 is not required. However in this embodiment a small internal accumulator 70 comprising a bladder 82 is provided, in order to accommodate the hydraulic fluid displaced by piston rod 80 as the damper compresses.

The hydraulic damper shown in Figure 3 may have, for example, a variation of piston velocity with piston force as shown in Figure 2. As with the first embodiment, in the second embodiment the parameters of the damper may be adjusted to suit the circumstances by, for example, varying the spring coefficients of the springs 95, 96, and/or by changing the profile of the variable orifice.

Figures 4A, 4B and 4C show various different damping orifice profiles. Figure 4A shows the damping orifice profile used in the embodiments of Figures 1 and 3. In this arrangement the orifice forming member has chamfered edges which face sloping surfaces on the inside of the cylinder or piston in order to form the damping orifice. In these embodiments, both sides of the orifice forming member (in an axial direction) are substantially frustoconical in shape. However other shapes may be used as appropriate.

Figure 4B shows an alternative arrangement in which the orifice forming member has flat surfaces which face flat surfaces on the inside of the cylinder or piston in order to form the damping orifice. Figure 4C shows another alternative arrangement in which two orifice forming members are provided on either side of an internal protrusion on the cylinder or piston in order to form the damping orifice. Various other different arrangements will be apparent to the skilled person.

Two-stage mechanism

Figure 5 illustrates the concept of a two-stage spring arrangement in another embodiment of the invention. In this embodiment, two different spring mechanisms are provided for each direction of travel. As a consequence, the damper encounters two different spring constants, depending on the force applied to the damper. This can provide additional control over the variation in damping coefficient with force.

In the arrangement of Figure 5, the hydraulic damper includes cylinder 12, orifice forming member 36, rod 38 and spring housing 48. Each of these elements functions in a similar way to the corresponding element described above with reference to Figure 1, and accordingly is not described further. However, in the arrangement of Figure 5, two separate spring mechanisms are provided for each direction of travel.

Referring to Figure 5, the spring housing 48 accommodates first spring mechanism 112, second spring mechanism 114, third spring mechanism 116 and fourth spring mechanism 118. Each spring mechanism may be a single spring, or two or more springs. Alternatively, any other elastic element capable of storing mechanical energy, such as one or more elastic bands or elastic blocks, may be used as well or instead. The spring mechanisms may be arranged to apply an appropriate force under compression or extension, or some combination of the two.

A flange 120 is provided on the rod 38, inside the spring housing 48. The flange 120 has a stepped design, with a radially inward part 121 and a radially outward part 122. The radially inward part 121 is longer in the axial direction than the radially outward part 122. In addition, two spring guides 123, 124 are provided, one on either side of the flange 120. The spring guides are annular, and are located against the inside surface of the spring housing 48. The spring guides 123, 124 are arranged such that they can move axially within the spring housing 48. The spring guides are arranged to engage with the radially outwards part 122 of the flange 120 when the appropriate force is applied to the damper, as will be explained below.

In the arrangement of Figure 5, the first spring mechanism 112 is provided between one end wall of the spring housing 48 and one side of the radially inward part 121 of the flange 120; the second spring mechanism 114 is provided between the other end wall of the spring housing 48 and the other side of the radially inward part 121 of the flange 120; the third spring mechanism 116 is provided between one end wall of the spring housing 48 and the first spring guide 123; and the fourth spring mechanism 118 is provided between the other end wall of the spring housing 48 and the second spring guide 124.

In operation, a contracting or expanding force is applied to the hydraulic damper in a similar way to that described above in the previous embodiments. As long as the applied force is below a certain threshold as determined by the spring constants of first spring mechanism 112 or the second spring mechanism 114, little or no compression of the relevant spring mechanism takes place. As a consequence, there is little or no movement of the rod 38 and orifice forming member 36. In this case the size of the damping orifice 18 is approximately the same on either side of the orifice forming member 36. Thus, when a low force is applied to the damper, the damper operates with a substantially constant damping coefficient, as determined by the size of the damping orifice 18 in the neutral position.

As an increasing force is applied to the damper, the velocity of the working fluid through the damping orifice increases, thus increasing the resistive force. This causes an increasing opposing force to be applied to one of the spring mechanisms 112, 114 via the flange 120, depending on whether the damper is under compression or tension. Once the applied force exceeds a certain threshold (as determined by the spring constant of the relevant one of the spring mechanisms 112, 114) the spring mechanism starts to be compressed (or extended). This causes the orifice forming member 36 to move axially, thereby decreasing the size of the damping orifice 18, and restricting further the flow of fluid from one chamber to the other. As a consequence of the restricted flow, more kinetic energy is dissipated and the damping coefficient increases.

As the spring mechanism 112 or 114 is compressed (or extended), the flange 120 moves in an axial direction within the spring housing 48. Under a relatively low force, the spring mechanism is only compressed by a relatively small amount, and there is a relatively small amount of travel of the flange 120. However, as the applied force is increased, the spring mechanism is further compressed and the flange 120 moves axially until the radially outwards part of the flange 120 comes into contact with one of the spring guides 123, 124. At this point, the compressive force of the relevant one of the spring mechanism 116 or 118, as well as that of the relevant one of the spring mechanism 112 or 114, needs to be overcome before the flange can travel any further. Thus, when the force is below a second threshold (as determined by the combined spring constant of one of the spring mechanisms 112, 114, and one of the spring mechanisms 116, 118), there is no further travel of the flange 120. As a consequence, while the applied force is below the second threshold, there is no further closure of the orifice 18, and therefore no further increase in the damping coefficient.

However, once the applied force exceeds the second threshold, the force of the radially outwards part 122 of the flange 120 against the relevant spring guide 123, 124 causes the relevant spring mechanism 116, 118 (together with the corresponding spring mechanism 112, 114) to start to be compressed. This causes the orifice forming member 36 to move further, thereby further decreasing the size of the damping orifice 18, and further restricting the flow of fluid from one chamber to the other. As a consequence, once the second threshold is exceeded, the damping coefficient again increases.

In some embodiments, if a sufficiently high force is applied, the orifice forming member closes the orifice 18. In this case the velocity of travel will approach zero at high force. In other embodiments, a gap is left between the first chamber and the second chamber even under very high force. In this case the final velocity of the damper at high force will be determined by the size of the gap.

Thus, the hydraulic damper of Figure 5 has a force dependent damping coefficient which depends on the spring constants of both the spring mechanisms 112, 114, and the spring mechanisms 116, 118. This can allow greater control over the variation in damping coefficient with force. For example, if the damper is fitted to a door, then a low force may allow relatively free movement of the door, a medium force more restricted (lower velocity) movement of the door, and a high force only very limited (very low velocity) movement of the door.

In the arrangement of Figure 5, the damper has a variable orifice which is separate from the piston, in a similar way to the damper shown in Figure 1. However, a similar two-stage spring arrangement could be used with the moving orifice damper arrangement described above with reference to Figure 3.

Figure 6 is a graph showing variations of piston velocity with applied force. In the graph of Figure 6, the line 57 shows the variation of piston velocity with piston force for a hydraulic damper with the two-stage spring arrangement. For comparison, the line 56 shows the variation of piston velocity with piston force for a hydraulic damper with a single-stage spring arrangement, and the line 58 shows the variation of piston velocity with piston force for a standard damper with a fixed damping coefficient.

Referring to Figure 6, in the two-stage spring arrangement, the piston velocity increases with piston force in a roughly linear manner up to a force of around 3N. As the applied forces increased above this amount, the increase in piston velocity flattens off as one of the first and second spring mechanisms 112, 114 is compressed. Once the applied force reaches a value of about 7N, there is a slight increase in piston velocity with piston force. This is due to the fact that further closure of the orifice is resisted by one of the third and fourth spring mechanisms 116, 118. Once the applied force reaches a value of about 10N, the relevant one of the third and fourth spring mechanism 116, 118 starts to be compressed, thereby further closing the orifice, and causing the piston velocity to start decreasing with increasing force.

Figures 7A to 7C illustrate one embodiment of the two-stage spring mechanism. Referring to Figures 7, the spring mechanisms in this embodiment comprise first spring 132, second spring 134, third spring 136 and fourth spring 138. The first spring 132 is located radially inwards of (parallel to) the third spring 136, and the second spring 134 is located radially inwards of (parallel to) the fourth spring 138. The first spring 132 is provided between one end wall of the spring housing 48 and one side of the radially inward part of the flange 120; the second spring 134 is provided between the other end wall of the spring housing 48 and the other side of the radially inward part of the flange 120; the third spring 136 is provided between one end wall of the spring housing 48 and the first spring guide 122; and the fourth spring 138 is provided between the other end wall of the spring housing 48 and the second spring guide 124.

The first and second springs 132, 134 will typically have a lower spring constant than the third and fourth springs 136, 138. However, this is not necessarily the case, and it would also be possible for the first and second springs 132, 134 to have the same or a higher spring constant than the third and fourth springs 136,

138. Furthermore, the spring constants of the first and second springs may be the same or different; and similarly the spring constants of the third and fourth springs may be the same or different

Figure 7A illustrates the damper in the neutral position. Under low load, only the central spring 132 or 134 compresses, providing small resistance to motion.

Figure 7B illustrates the damper at the limit of the single spring compression. Once the flange 120 on the central rod 38 comes into contact with the spring guide 124, it is necessary for the outer spring 138 to be compressed before any further movement of the flange can take place.

Figure 7C illustrates the damper under double spring compression. Here, the inner spring 134 and the outer spring 138 both actuate, providing a greater resistance to loading.

Figures 8A and 8B illustrate another embodiment of the two-stage spring mechanism. Referring to Figures 8, the spring mechanisms comprise first spring 142, second spring 144, third spring 146 and fourth spring 148. In this embodiment the first spring 142 and the third spring 146 are located next to (in series with) each other, and the second spring 144 and the fourth spring 146 are located next to (in series with) each other. The first and second springs 142, 144 have a lower spring constant than the third and fourth springs 146, 148.

Figure 8A illustrates the damper in the neutral position. Under low load, the shorter softer spring 144 compresses most, providing small resistance to motion.

Figure 8B illustrates the damper at the limit of single spring compression. Once the softer spring has compressed to its limit, only the harder spring can compress, increasing the resistance to motion.

If desired, three or more spring mechanisms could be provided for each direction of travel, in order to further modify the variation of damping coefficient with force. Furthermore, the various spring arrangements described above may be used together in any appropriate combination.

The hydraulic dampers disclosed herein have particular application in controlling the movement of doors, gates, hatches, flaps and other such hinged closures. For example, fire doors in underground transport systems are often subject to high wind forces due to passing trains, but still need to be opened safely by people using low force. The disclosed damper provides a high damping force when force on it is high, restricting movement to a safe rate. When a low force is applied, the damping force is much less, allowing a person to open the door at a reasonable rate. By contrast, a standard damper, with a damping coefficient sized for the high wind force would be very slow and difficult to move under the force provided by a person.

Figures 9A and 9B show an example of the hydraulic damper 10 being used with a door 100 located in a wall 102. In this example the damper is connected between the wall 102 and an arm 104 on the door. Figure 9A shows the door in its closed state and Figure 9B shows the door in its open state.

Figures 10A and 10B show an example of the damper 10 being used with a door 106 located at the end of a corridor. In this case the corridor may connect, for example, two platforms in an underground train station. In this example the damper 10 is connected between the door 106, and a wall 108 of the corridor. Figure 10A shows the door in its closed state and Figure 10B shows the door in its open state.

It will be appreciated that the hydraulic dampers disclosed herein may be used in any situation where a large intermittent force is expected, but actuation by a low force is also required. For example, the hydraulic dampers may be used to control the movement of lids, covers, machine guards, hatches, windows, gates, vehicle doors, ramps, beds, tables, swinging loads, lever arms and any type of hinged closure. If desired, the damper may be used in combination with an opening/closing mechanism.

Claims

1. A hydraulic damper having a damping coefficient which increases as an increasing force is applied to the damper.

2. A damper according to claim 1, wherein the damper exhibits a non-linear relationship between force applied to the damper, and damper actuation speed.

3. A damper according to claim 1 or 2, wherein the damper has a damping coefficient which is substantially constant when the applied force is below a predetermined threshold, and which increases when the applied force is above the threshold.

4. A damper according to any of the preceding claims, wherein the damper comprises a cylinder, and a piston arranged to slide within the cylinder so as to displace a working fluid.

5. A damper according to any of the preceding claims, wherein the damper comprises an orifice for restricting flow of a working fluid.

6. A damper according to claim 5 when dependent on claim 4, wherein the cylinder is separated into two chambers, and movement of the piston forces the working fluid through the orifice from one chamber to the other.

7. A damper according to claim 5 or 6, wherein the damper is arranged such that the size of the orifice decreases as an increasing force is applied to the damper.

8. A damper according to any of claims 5 to 7, the damper comprising an orifice forming member which forms the orifice.

9. A damper according to claim 8, wherein the orifice is formed between an external surface of the orifice forming member and an internal surface of the damper.

10. A damper according to claim 8 or 9, wherein the orifice forming member is disc-shaped.

11. A damper according to any of claims 8 to 10, wherein the orifice is annular.

12. A damper according to any of claims 8 to 11, wherein at least one radially outwards edge of the orifice forming member is chamfered.

13. A damper according to any of claims 8 to 12, wherein the orifice forming member is movable in order to change the size of the orifice.

14. A damper according to claim 13, wherein the damper comprises an elastic device which is operable to resist movement of the orifice forming member.

15. A damper according to claim 14, wherein the elastic device comprises at least one spring.

16. A damper according to claim 14 or 15, wherein the damper is arranged such that the elastic device deforms when a force above a predetermined threshold is applied to the damper.

17. A damper according to claim 16 when dependent on claim 4, wherein the damper is arranged such that the piston is able to move when a force below the threshold is applied to the damper.

18. A damper according to any of claims 14 to 17, wherein the orifice forming member is connected to the elastic device by means of a rod.

19. A damper according to claim 18, wherein the rod comprises a flange which engages with the elastic device.

20. A damper according to any of claims 14 to 19, wherein the elastic device is located within a housing.

21. A damper according to any of claims 8 to 20, wherein the size of the orifice is adjustable when the damper is under compression and under tension.

22. A damper according to any of claims 8 to 21, wherein the orifice forming member is movable in a first direction towards a first internal surface of the damper, and in a second direction towards a second internal surface of the damper.

23. A hydraulic damper comprising an orifice for restricting flow of a working fluid, and an orifice forming member which forms the orifice, wherein the orifice forming member is movable in a first direction towards a first internal surface of the damper, and in a second direction towards a second internal surface of the damper, thereby to increase a damping coefficient of the damper as an increasing force is applied to the damper under compression and under tension.

24. A damper according to any of claims 8 to 23, wherein the damper comprises at least one elastic device operable to resist movement of the orifice forming member.

25. A damper according to claim 24, wherein the damper comprises two elastic devices, and wherein one elastic device is actuated when the damper is in compression and the other elastic device is actuated when the damper is in tension.

26. A damper according to any of claims 8 to 25, wherein the damper comprises two elastic devices, both of which are operable to resist movement of the orifice forming member in one direction of travel.

27. A damper according to claim 26, wherein one elastic device is actuated when a force applied to the damper is above a first threshold, and the other elastic device is actuated when a force applied to the damper is above a second threshold.

28. A damper according to claim 26 or 27, wherein the two elastic devices are connected in parallel, and one elastic device is arranged to deform through a predetermined distance before the other elastic device is actuated.

29. A damper according to claim 26 or 27, wherein the two elastic devices are connected in series, and one elastic device has a lower spring constant than the other.

30. A damper according to any of claims 8 to 29 when dependent on claim 4, wherein the orifice is formed between the orifice forming member and an internal surface of the cylinder.

31. A damper according to claim 30, wherein the piston is connected to a first external connection means, and the orifice forming member is connected to a second external connection means.

32. A damper according to any of claims 8 to 29 when dependent on claim 4, wherein the orifice is formed between the orifice forming member and an internal surface of the piston.

33. A damper according to claim 30, wherein movement of the piston forces working fluid through the orifice from one side of the piston to the other.

34. A damper according to claim 32 or 33, wherein at least one elastic device is located in the piston.

35. A damper according to any of claims 32 to 34, wherein the piston is connected to a first external connection means, and the cylinder is connected to a second external connection means.

36. A damper according to any of the preceding claims for use with a hinged closure such as a door.

37. A hinged closure comprising a damper according to any of the preceding claims.

38. A hinged closure according to claim 37, for use in environments which are subject to large intermittent forces, but where actuation by a relatively low force is required.

39. A method of damping a hinged closure using a hydraulic damper, the method comprising increasing a damping coefficient of the hydraulic damper as an increasing force is applied to the closure.

Intellectual

Property

Office

Application No: GB1802722.7 Examiner: Mr Kevin Hewitt