GB2426284A - Hydraulic door closer having hydraulic fluid path control means - Google Patents

Abstract

A door closer 10 includes an anchor assembly 12 for mounting in one of a door frame 13 or within the thickness of the door 15, an actuator assembly 14 an operating member 22 coupled by a linkage 25 to the anchor assembly 12, a resilient driving apparatus 35 and a damping mechanism 40 operatively connected to the operating member 22. The damping mechanism 40 includes a cylinder 41 contains hydraulic fluid and a piston rod 46 carrying a piston 45 which divides the cylinder 41 into first and second chambers 48, 49. There is a flow path through the piston 45 from the first chamber 48 to the second chamber 49 via a variable throttling device 54, 55, 60, 61 which restricts fluid flow through the flow path to control operating member 22 movement. The throttling device 54, 55, 60, 61 includes at an axial end 52 of the piston 45, a collector groove 54 which communicates with one or more axially extending passages 51 through the piston 45, and a control groove 60 which communicates with the collector groove 54. The throttling device further includes a closure element 55 located at the axial end 52 of the piston 45. The closure element 55 includes an orifice which is aligned with the control groove 60 of the piston axial end 52 at a desired position to vary the length of the flow part to control the rate of hydraulic fluid flow through the flow path. A door closer including a piston with a peripheral seal is also disclosed.

Description

Title: Door Closer

Description of Invention

This invention relates to a door closer and more particularly to a door closer of the kind having an anchor assembly for mounting on a door frame or door, an actuator assembly for mounting within the thickness of the door or door frame which door is hinged at a hinged door edge, for movement between open and closed conditions relative to the door frame, an operating member coupled by a flexible or articulated linkage to the anchor assembly and being mounted for a range of movement between a retracted position and an extended position, a resilient driving apparatus arranged to exert a driving force on the operating member to drive the operating member towards the retracted position to draw the door into its closed condition relative to the frame, and a damping mechanism operatively connected to the operating member to damp and control movement of the operating member at least in a direction towards the retracted position.

Such a door closer is described in our previous patent GB-A-2044840.

It is known to provide such a door closer with a damping mechanism including a cylinder containing hydraulic fluid, a piston rod carrying a piston which divides the cylinder into first and second chambers, a flow path through the piston from the first chamber to the second chamber via a variable throttling device which restricts fluid flow though the flow path to control operating member movement, as the piston and cylinder relatively move. In one embodiment described in our prior patent application WO-A-9605397, the piston includes passages therethrough and the piston has a collector groove provided in an axial end thereof which communicates with the passages. The throttling device further includes a disc located at an axial end of the piston, the relative rotational positions of the piston and disc plate controlling the extent of restriction to hydraulic fluid flow though the flow path.

According to a first aspect of the present invention we provide a door closer including an anchor assembly for mounting in one of a door frame and within the thickness of the door, an actuator assembly for mounting in the other of within the thickness of the door and the door frame, with the door being hinged at the door edge, for movement between open and closed conditions relative to the door frame, an operating member coupled by a linkage to the anchor assembly and being mounted for a range of movement between a retracted position and an extended position, a resilient driving apparatus arranged to exert a driving force on the operating member to drive the operating member towards the retracted position to draw the door into its closed condition relative to the door frame, and a damping mechanism operatively connected to the operating member to damp and control movement of the operating member at least in a direction towards the retracted position, the damping mechanism including a cylinder containing hydraulic fluid, a piston rod carrying a piston which divides the cylinder into first and second chambers, and there being a flow path through the piston from the first chamber to the second chamber via a variable throttling device which restricts fluid flow through the flow path to control operating member movement, as the piston and cylinder relatively move, the throttling device including at an axial end of the piston, a collector groove which communicates with one or more axially extending passages through the piston, and a control groove which communicates with the collector groove, and the throttling device further including a closure element located at an axial end of the piston and the closure element including an orifice which is aligned with the control groove of the piston axial end at a desired position by relatively rotating the piston and closure element, to vary the length of the flow path to control the extent of restriction to hydraulic fluid flow though the flow path.

Thus the present invention obviates the need to provide a disc with the control groove as the control groove is provided in the axial end of the piston. It will be appreciated that the control groove needs to be very accurately formed, typically by etching where the disc is thin, and thus not needing to provide the disc with control groove, represents a significant cost saving, offset only by providing the control groove in the axial end of the piston.

In a first embodiment, the piston is connected to a piston rod assembly including first and second rod parts, the piston being secured relative to the first rod part and the closure element to the second rod part, the rod parts being relatively rotatable by rotating the adjustment member. For example the first rod part may be fixed relative to the door or frame in which the actuator assembly is mounted, such that in use, the cylinder moves with the operating member, the second rod part being rotatable to rotate the closure member to effect throttling adjustment. The second rod part preferably is arranged co- axially within the first rod part, and extends outwardly of the door or frame to a position at or adjacent the hinged door edge, where an end portion of the second rod part provides the adjustment member. Typically the adjustment member has a screwdriver slot or other formation to receive a tool at or adjacent to the hinged door edge, whereby the adjustment member is

rotatable.

A seal may be provided between the first and second piston rod parts to prevent any possible leakage of hydraulic fluid from the chambers between the piston rod parts. Such a seal may be provided by a pair of sealing elements, such as "o" rings, spaced axially along the piston rod assembly, thus additionally to guide the inner and outer piston rod parts.

Preferably, the cylinder includes a resiliently biased cylinder closure which closes the end of the cylinder remote from the piston, but is axially moveable against the resilient biasing when the door is opened, to reduce resistance of the damping mechanism to door opening.

In another embodiment, the piston is connected to a piston rod which is secured relative to the operating member to move relative to the cylinder with the operating member, the cylinder being fixed relative to the door or frame in which the actuator assembly is mounted, the adjustment member being mounted within the cylinder and having a formation to receive a tool from at or adjacent the hinged door edge, whereby the adjustment member is rotatable in the cylinder, the adjustment member and one of the piston and closure element, having respective formations which are interengagable when the piston and closure element are moved to a position adjacent to the adjustment member, to effect relative rotation of the piston and closure element. For example, the closure element may be provided at an outermost end of the piston and may have a projecting formation or a recess formation, whilst the adjustment member has a corresponding recess formation or projecting formation which may be interengaged when the piston and closure element are moved relatively along the cylinder to adjacent the adjustment member.

The adjustment member may be provided on a resiliently biased cylinder closure which closes the end of the cylinder remote from the piston, but is axially moveable against the resilient biasing when the door is opened, to reduce resistance of the damper to door opening.

In each case, during door opening, a relief flow path for the hydraulic fluid from the second chamber to the first chamber may be established through the axially extending passage or passages of the piston, by the closure element being moveable axially relative to the piston to so that fluid is not throttled.

Thus the closure element may be resiliently biased towards the piston, e. g. by a spring washer acting on the piston or closure element, to provide throttling as the piston and cylinder relatively move as the operating member is retracted, and the resilient biasing being overcome as the piston and cylinder relatively move as the operating member is extended.

In one embodiment, the peripheral seal seals with a first axial portion of an internal cylinder wall to prevent fluid flowing from the first chamber to the second chamber past the periphery of the piston as the piston and cylinder relatively move though a primary range of movement, and the internal cylinder surface includes a circumferentially extending recess in a second axial portion of the internal cylinder wall, relative movement of the piston and cylinder towards an end range of movement of the operating member, bringing the peripheral seal into registry with the recess to permit fluid to flow from the first chamber to the second chamber past the periphery of the piston, to relieve the damping, and wherein the recess includes a frusto-conical surface of the internal cylinder wall which increases in diameter in the direction of movement of the piston as the operating member moves towards its retracted position, the half cone angle being less than 3 .

Thus by virtue of the provision of the recess in the internal cylinder wall, as the operating member is urged towards a fully retracted position, damping will be relieved so that the door kicks closed during its end range of movement.

However it has been found that if the door is urged to its closed condition by a user, such that the piston and cylinder may then relatively axially be moved by the resilient driving apparatus without the weight of the door resisting such relative movement, as the piston and recess become aligned, hydraulic pressures in the first and second chambers to either side of the piston, may too rapidly equalise, which can result in the creation of an unwanted "popping" noise, It has been found that by arranging for the frusto-conical surface to have a half cone angle of less than 3 and more preferably, about 2.5 or even 2 where the axial length of the cylinder allows this, pressure equalisation is less rapid, resulting in the creation of no or at least less noise.

According to a second aspect of the invention we provide a door closer including an anchor assembly for mounting in one of a door frame and within the thickness of the door, an actuator assembly for mounting in the other of within the thickness of the door and the door frame, with the door being hinged at the door edge, for movement between open and closed conditions relative to the door frame, an operating member coupled by a linkage to the anchor assembly and being mounted for a range of movement between a retracted position and an extended position, a resilient driving apparatus arranged to exert a driving force on the operating member to drive the operating member towards the retracted position to draw the door into its closed condition relative to the door frame, and a damping mechanism operatively connected to the operating member to damp and control movement of the operating member at least in a direction towards the retracted position, the damping mechanism including a cylinder containing hydraulic fluid, a piston rod carrying a piston which divides the cylinder into first and second chambers, and there being a flow path from the first chamber to the second chamber via a throttling device which restricts fluid flow through the flow path to control operating member movement, and the piston including a peripheral seal which seals with a first axial portion of an internal cylinder wall to prevent fluid flowing from the first chamber to the second chamber past the periphery of the piston as the piston and cylinder relatively move as the operating member is driven towards its retracted position through a primary range of movement, and the internal cylinder wall including a circumferentially extending recess in a second axial portion of the internal cylinder wall, relative movement of the piston and cylinder towards an end range of movement of the operating member, bringing the peripheral seal into registry with the recess to permit fluid to flow from the first chamber to the second chamber past the periphery of the piston, to relieve the damping, and wherein the recess includes a frusto-conical surface of the internal cylinder wall which increases in diameter in the direction of movement of the piston as the operating member moves towards its retracted position, the half cone angle being less than 3 .

Embodiments of the invention will now be described with reference to the accompanying drawings in which:- FIGURE 1 is a side illustrative view of a door closer in accordance with the invention; FIGURE 2a is a more detailed side view of a damper mechanism of the door closer of figure 1 when the door is in a closed condition; FIGURE 2b is the damper mechanism of figure 2a but when the door is in an open condition; FIGURE 3a is an enlarged side detail of a piston and piston rod assembly of the damper mechanism of figures 2a and 2b; FIGURE 3b is an end view of the piston of figure 3a; FIGURE 4 is a side view of an alternative damper mechanism in accordance with the invention.

Referring to figures 1 to 3, a door closer 10 includes an anchor assembly 12 which in this example, is provided in a door frame 13, and an actuator assembly 14 mounted within the thickness of a door 15, with the door 15 being hinged to the door frame 13 at a door edge, for movement between a fully closed condition (as seen in figures 1) and a fully open condition.

The anchor assembly 12 includes an anchor plate 16 which is secured to an edge of the door frame 13, and an adjustable plate 18, the position of which can be adjusted relative to the anchor plate 16 via one or more screws 19, to adjust the door closer 10.

The actuator assembly 14 includes a housing 20 which mounts an operating member 22 which includes a cross head 24 to which a pair of linkages 25 are connected. The linkages 25 are substantially identical and are arranged symmetrically relative to the cross head 24, about a door closer axis A. Each linkage 25 includes a rigid part 26 connected to the cross head 24, and an articulated part 27 provided by a plurality of articulated links. The articulated part 27 extends to and is connected to the adjustable plate 18 of the anchor assembly 12.

In another example, instead of an articulated part 27, the linkages 25 may have flexible members, or the entire linkages 25 may be flexible and/or articulated, as desired. The linkages 25 permit the door 15 to be hinged open to its open condition as hereinafter described.

As the door 15 is opened, the cross head 24 of the operating member 22 is moved by the linkages 25, from the retracted position shown in figure 1 to an extended position in which the linkages 25 are extended from the actuator assembly 14, and the cross head 24 is closer to the door 15 edge.

The actuator assembly 14 includes a door edge plate 30 which is secured at the door 15 edge, and includes a pair of passages 31, 32 through which the linkages 25 pass, the linkages 25 then passing though passages 33, 34 of the anchor plate 16, to the adjustable plate 18, where they are secured.

Between the door edge plate 30 and the cross head 24, wound about each linkage 25, is a resilient operating member driving apparatus provided by a coil compression spring 35, which may include oppositely wound sections with a core member 36 between the coil sections, the coil spring 35 becoming compressed as the operating member 22 is moved to its extended position as the door 15 is opened, so that when the door 15 is released, the action of the springs 35 will urge the cross head 24 back to its retracted position, to draw the door 15 closed.

Movement of the operating member 22 back to its retracted position as seen in figure 1, is however resisted by a damping mechanism 40 which is connected to the cross head 22 and to the door edge plate 30. The damping mechanism 40 of figure 1 is shown in more detail in figures 2a and 2b.

The damping mechanism 40 includes a cylinder 41 which is secured to the cross head 22, e.g. by a threaded sleeve and nut and bolt arrangement as shown at 42 in figures 2a and 2b, and a piston 45 connected to, and carried on a piston rod assembly 46, the piston 45 and cylinder 41 relatively moving with the piston 45 inside the cylinder 41, as the operating member 22 moves between its retracted and extended positions. The piston 45 divides the cylinder into a first chamber 48 and a second chamber 49, the chambers 48, 49 being filled, with hydraulic fluid, there being a throttled flow path from the first chamber 48 to the second chamber 49 as the operating member 22 moves from the extended to the retracted position (figure 2b to figure 2a position), and there being a much lesser resistance flow path for fluid from the second chamber 49 to the first chamber 48, as the operating member 22 moves from its retracted to its extended position. At the piston's extreme positions shown in figure 2a and 2b, the volume of the first chamber 48 in figure 2a and second chamber 49 in figure 2b, are virtually nil.

The piston 45 includes a peripheral seal 50 provided by an "o" ring or pipped seal or the like, in a circumferential groove of the piston 45, and a plurality of axially extending passages 51, four in this example. At a first axial end 52 of the piston 45 facing the second chamber 49 towards the cross head 24, there is provided a closure element which in this example is a plate 55, the piston 45 and closure plate 55 being received in a rebate 56 between a nut 57 at the end of the piston rod assembly 46, and a shoulder 58 thereof, and the piston and closure plate 55 being urged together by a spring washer 59 which in the example shown, is provided between a second axial end 53 of the piston opposite to the first axial end 52, and the shoulder 58.

As seen in figure 3b, the first axial end 52 of the piston 45 includes a circular collector groove 54 into which the four axially extending passages 51 open, the collector groove 54 thus collecting hydraulic fluid passing through the passages 51 of the piston 45. The first axial end 52 of the piston 45 further includes a control groove 60 which extends only circularly, and includes a connection part 61 which extends to the control groove 60. The control groove 54 is of relatively large capacity, whereas the control groove 60, including the connection part 61 is of small capacity.

The piston 45 and closure plate 55 are urged together by the spring washer 59 so that the closure plate 55 closes the collector 54 and control 60 grooves, but the closure plate 55 has an orifice 62 provided by a notch in its periphery in this example, which may be aligned with the control groove 54, at a desired position dependent upon the relative rotational positions of the piston 45 and closure plate 55.

Thus with the closure plate 55 and piston 45 urged together, a throttled flow path for hydraulic fluid flowing from the first chamber 48 to the second chamber 49 when the operating member 22 is extended, is provided through the axially extending passages 51, into the collector groove 54, then via the connection part 61 into the control groove 60, and then via the notch 62 into the second chamber 49. By adjusting the relative rotational positions of the closure plate 55 and piston 45, the notch 62 may be brought into registry with the control groove 60 at different positions so that the length of the flow path may be varied to vary the extent of throttling and hence the damping effect of the damping mechanism 40 as the operating member 22 is moved by the springs 35 to its retracted position.

The piston rod assembly 46 includes first and second rod parts 70, 71 arranged concentrically with the second rod part 71 within the first rod part 70.

The first rod part 70 is fixed relative to the door edge plate 30 of the actuator assembly 14, but the second rod part 71 may be rotated relative to the first rod part 70 to rotate the closure plate 55 relative to the piston 45. This may be achieved as an outermost part of the second rod part 71 provides an adjustment member 73 having a screwdriver or other formation 74 in its end, for engagement with a screwdriver or other tool. The adjustment member 73 is accessible when the door 15 is hinged open, from the door edge, and the closure plate 55 may thus be adjusted in situ, to vary the damping effect of the damping mechanism 40.

Between the first and second rod parts 70, 71, there is a seal, provided in this example by a pair of sealing elements being "o" rings 75, 76 provided in respective peripheral grooves of the second rod part 71, the seal preventing the passage of hydraulic fluid from the second chamber 49 between the rod parts 70, 71.

It can be seen from figure 3a that the adjustment member 73 is in threaded engagement with a corresponding thread provided in the end of the first rod part 70, the seal 75, 76 and threads effectively preventing the second rod part 71 turning and thus rotating the closure plate 55 other than when required by use of a tool.

Inside the cylinder 41, between the piston 45 and the cross head 24 there is a resiliently biased cylinder closure 78 which closes the end of the cylinder 41 at the cross head 24 end, but is axially moveable against a resilient biasing force provided by a spring 79. This serves both to accommodate any air which may be present in the second chamber 49, and so that when the door is opened, resistance of the damping mechanism 40 to door opening is reduced.

However, resistance to door opening is relieved in the main, by virtue of the closure plate 55 and piston 45, which normally are urged together by the spring washer 59, becoming separated. During door 15 opening, the piston 45 will be urged by differential pressures in the first and second chambers 48, 49 against the spring washer 59, so that the closure plate 55 will lift off the first axial end 52 of the piston 45 and thus permit the substantially unconstrained flow of fluid though the axially extending passages 51 of the piston 45, from the second 49 to the first chamber 48.

It will be appreciated that if desired, instead of damping being relieved in this way, this may be otherwise achieved, for example only, by providing a passage external to the cylinder 41 with a one way valve which permits substantially unthrottled flow from the second 49 to the first passage 48 only.

Desirably, over an end range of movement of the door 15 to its closed condition, damping is relieved, so that the door 15 "kicks" into its fully closed condition. This is achieved in the door closer 10 of the invention by the provision of a circumferentially extending recess 80 in the internal cylinder wall 81, as best seen in figures 2a and 2b. As the piston 45 moves relative to the cylinder 41 relatively away from the cylinder closure 78, as the door 15 is drawn towards its fully closed condition, the piston 45 with its peripheral seal after passing along a first axial portion of the cylinder 41 in which the seal seals with the inside cylinder wall 81 and the piston 45 and cylinder 41 relatively move through a primary range of movement in which damping is effected, will move into registry with the recess 80, at a second axial portion of the cylinder wall 81. At this point, due to differential pressures in the first and second chambers 48, 49, because the diameter of the recess 80 is greater than that of the seal 50 of the piston 45, fluid may flow past the peripheral seal 50 from the first chamber 48 to the second chamber 49 thus to relieve damping. The recess 80 includes a frusto-conical surface lead-in part 82, the diameter of which increases in the direction of movement of the piston 45 towards the retracted position, and a cylindrical recess section 83 in which the piston 45 sits when the operating member 22 is in its fully retracted condition, with the door 15 fully in its closed condition.

The frusto-conical surface lead-in part 82 preferably has a half cone angle of about 2 -2.5 , but in any event of less than 3 , so that the equalisation of hydraulic pressures between the first and second chambers 48, 49 occurs non abruptly. This cone angle has been found to be particularly important to alleviate any risk of unwanted noise generation as could otherwise occur, for example for greater cone angles, in the event that the door 15 is urged closed by a user (which is permitted by the geometry of the linkages 25 and the springs 35 etc.) in which case the operating member 22 will continue to be urged towards its retracted position, but without the resistance of the weight of the door 15, and the piston 45 and cylinder 41 will continue relatively to move. It has been found that particularly in this case, as the piston 45 enters the recess 80, loud undesirable noises can be generated as the fluid pressures in the first and second chamber 48, 49 equalise, which problem is substantially reduced or overcome by arranging for the half cone angle of the frusto-conical lead-in surface part 82 to be less than 3 .

If desired, the recess 80 may only have a frusto-conical surface 82 and no cylindrical recess section 83 i.e. the frusto-conical surface 82 may extend over the entire length of the recess 80.

Referring now to figure 4 in which similar references are used for components similar to those shown in the previous figures, there is shown an alternative embodiment of the invention.

In this arrangement, the cylinder 41 of the damping mechanism 40 is secured to the door edge plate 30, and the piston 45 is carried on a piston rod 46 which is secured to the cross head 24 of the operating member 22. The closure plate 55 is provided on a first axial end 52 of the piston 45 which faces the door edge plate 30. Within the cylinder 41 there is a resiliently biased cylinder closure 78, but this includes a generally central axially extending opening 90 in which an adjustment member 73 is accommodated. The adjustment member 73 includes a stem 91 which extends towards the door edge plate 30, in which there is an opening 74 to receive a screwdriver or other elongate tool so that the adjustment member 73 can be rotated with respect to the cylinder 41. The adjustment member 73 further includes a head 95, with a frusto-conical edge 96 which seats with a frusto conical seat 97 of the cylinder closure 78 to provide a fluid tight seal. An "o" ring or like seal (not shown) may be provided between the stem 91 of the adjustment member 73 and the cylinder closure 78, so that fluid is prevented from escaping between the adjustment member 73 and the stem 91.

The head 95 includes one or more, two in the present example, projections which are pins 98 which extend axially towards the closure plate 55 and the piston 45. The closure plate 55 in this example, includes a pair of recesses 99 which may receive the pins 98 when the piston 45 is moved in the cylinder 41 to a position adjacent to the cylinder closure 78. The piston 45 itself cannot be rotated and is fast with the piston rod 46 which is secured to the cross head 24, but the closure member 55 may be rotated relative to the piston 45 to effect adjustment of the damping effect of the damping mechanism 40, when the operating member 22 is in its fully extended position, corresponding to the door 15 being moved substantially to its fully open condition, by accessing the adjustment member 73 from the door edge via an opening 92 in the door edge plate 30.

If desired, in another embodiment in which the closure plate 55 and piston 45 are oppositely located on the piston rod 46, the piston 45 may have the recesses 99 for receiving the pins 98, or the pins 98 may be provided on the piston 45 or closure plate 55 and recesses 99 by the head 95.

Alternative interengaging formations on the piston or closure plate and head 95 could be provided.

In each embodiment, the damping effect of the damping mechanism 40 may be adjusted in situ, by accessing an adjustment member 73 from the door edge, by relatively rotating the closure plate 55 and piston 45 to vary the length of the throttled fluid flow path for the fluid from the first to the second chamber 48, 49 of the cylinder 41.

Various modifications may be made without departing from the scope of theinvention. For example, in accordance with the first aspect of the invention, a throttled flow path for fluid from the first to the second chamber 48, 49 during door closing, may be provided by other means to those described, provided that an adjustment member 73 may be accessed from at or adjacent the door edge. Where the anchor assembly 12 is provided within the thickness of the door 15 and the actuator assembly 14 in the door frame 13, the adjustment member 73, although in the frame 13, would still be accessible from adjacent the door edge.

In the example described, a pair of springs 35 and linkages 25 are provided, although the invention may be applied where a single or more than two linkages and springs 35 are provided. The geometry of the door closer 10 may be different to that shown, in that the damping mechanism 40 need not be provided along the door closer axis A as shown, but may be provided spaced from, but preferably parallel to the axis A. The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims (19)

1. A door closer including an anchor assembly for mounting in one of a door frame and within the thickness of the door, an actuator assembly for mounting in the other of within the thickness of the door and the door frame, with the door being hinged at the door edge, for movement between open and closed conditions relative to the door frame, an operating member coupled by a linkage to the anchor assembly and being mounted for a range of movement between a retracted position and an extended position, a resilient driving apparatus arranged to exert a driving force on the operating member to drive the operating member towards the retracted position to draw the door into its closed position relative to the door frame, and a damping mechanism operatively connected to the operating member to damp and control movement of the operating member at least in a direction towards the retracted condition, the damping mechanism including a cylinder containing hydraulic fluid, a piston rod carrying a piston which divides the cylinder into first and second chambers, and there being a flow path through the piston from the first chamber to the second chamber via a variable throttling device which restricts fluid flow through the flow path to control operating member movement, as the piston and cylinder relatively move, the throttling device including at an axial end of the piston, a collector groove which communicates with one or more axially extending passages through the piston, and a control groove which communicates with the first collector groove, and the throttling device further including a closure element located at an axial end of the piston and the closure element including an orifice which is aligned with the control groove of the piston axial end at a desired position by relatively rotating the piston and closure plate, to vary the length of the flow path to control the extent of restriction to hydraulic fluid flow through the flow path.

2. A door closer according to claim I wherein the piston is connected to a piston rod assembly including first and second rod parts, the piston being secured relative to the first rod part and the closure plate to the second rod part, the rod parts being relatively rotatable by rotating the adjustment member.

3. A door closer according to claim 2 wherein the first rod part is fixed relative to the door or frame in which the actuator assembly is mounted, such that in use, the cylinder moves with the operating member, the second rod part being rotatable to rotate the closure element to effect throttling adjustment.

4. A door closer according to any one of the preceding claims wherein the adjustment member has a formation to receive a tool at or adjacent to the hinged door edge whereby the adjustment member is rotatable.

5. A door closer according to any one of claims 2 to 4 wherein the second rod part is arranged co-axially within the first rod part, and extends towards the hinged door edge, an end portion of the second rod part providing the adjustment member.

6. A door closer according to claim 5 wherein a seal is provided between the first and second piston rod parts to prevent leakage of hydraulic fluid from the chambers, between the piston rod parts.

7. A door closer according to claim 6 wherein the seal is provided by a pair of sealing elements spaced axially along the piston rod assembly, thus additionally to guide the inner and outer piston rod parts.

8. A door closer according to any one of the preceding claims wherein the cylinder includes a resiliently biased cylinder closure which closes the end of the cylinder remote from the piston, but is axially moveable against the resilient biasing when the door is opened, to reduce resistance of the damping mechanism to door opening.

9. A door closer according to claim I wherein the piston is connected to a piston rod which is secured relative to the operating member to move relative to the cylinder with the operating member, the cylinder being fixed relative to the door or frame in which the actuator assembly is mounted, the adjustment member being mounted within the cylinder and having a formation to receive a tool from at or adjacent the hinged door edge, whereby the adjustment member is rotatable in the cylinder, the adjustment member and one of the piston and closure element, having respective formations which are interengagable when the piston and closure element are moved to a position adjacent to the adjustment member, to effect relative rotation of the piston and closure element.

10. A door closer according to claim 9 wherein the closure element is provided at an axial end of the piston and has a projecting formation or a recess formation, whilst the adjustment member has a corresponding recess formation or projecting formation which are interengageable when the piston and closure element are moved relatively along the cylinder to adjacent the adjustment member.

11. A door closer according to claim 9 or claim 10 wherein the adjustment member is provided on a resiliently biased cylinder closure which closes the end of the cylinder remote from the piston, but is axially moveable against the resilient biasing when the door is opened, to reduce resistance of the damper to door opening.

12. A door closer according to any one of the preceding claims wherein during door opening, a relief flow path for the hydraulic fluid from the second chamber to the first chamber is established through the axially extending passage or passages of the piston, by the closure element being moveable axially relative to the piston to so that fluid is not throttled.

13. A door closer according to claim 12 wherein the closure element is resiliently biased towards the piston to provide throttling as the piston and cylinder relatively move as the operating member is retracted, and the resilient biasing being overcome as the piston and cylinder relatively move as the operating member is extended.

14. A door closer according to any one of the preceding claims wherein the piston includes a peripheral seal which seals with a first axial portion of an internal cylinder wall to prevent fluid flowing from the first chamber to the second chamber past the periphery of the piston as the piston and cylinder relatively move through a primary range of movement, and the internal cylinder surface includes a circumferentially extending recess in a second axial portion of the internal cylinder wall, relative movement of the piston and cylinder towards an end range of movement of the operating member, bringing the peripheral seal into registry with the recess to permit fluid to flow from the first chamber to the second chamber past the periphery of the piston, to relieve the damping, and wherein the recess includes a frusto-conical surface of the internal cylinder wall which increases in diameter in the direction of movement of the piston as the operating member moves towards its retracted position, the half cone angle being less than 3 .

15. A door closer according to claim 14 wherein the half cone angle of the frusto-conical surface is about 2.5 .

16. A door closer including an anchor assembly for mounting in one of a door frame and within the thickness of the door, an actuator assembly for mounting in the other of within the thickness of the door and the door frame, with the door being hinged at the door edge, for movement between open and closed conditions relative to the door frame, an operating member coupled by a linkage to the anchor assembly and being mounted for a range of movement between a retracted position and an extended position, a resilient driving apparatus arranged to exert a driving force on the operating member to drive the operating member towards the retracted position to draw the door into its closed condition relative to the door frame, and a damping mechanism operatively connected to the operating member to damp and control movement of the operating member at least in a direction towards the retracted position, the damping mechanism including a cylinder containing hydraulic fluid, a piston rod carrying a piston which divides the cylinder into first and second chambers, and there being a flow path from the first chamber to the second chamber via a throttling device which restricts fluid flow through the flow path to control operating member movement, and the piston including a peripheral seal which seals with a first axial portion of an internal cylinder wall to prevent fluid flowing from the first chamber to the second chamber past the periphery of the piston as the piston and cylinder relatively move as the operating member is driven towards its retracted position through a primary range of movement, and the internal cylinder wall including a circumferentially extending recess in a second axial portion of the internal cylinder wall, relative movement of the piston and cylinder towards an end range of movement of the operating member, bringing the peripheral seal into registry with the recess to permit fluid to flow from the first chamber to the second chamber past the periphery of the piston, to relieve the damping, and wherein the recess includes a frusto-conical surface of the internal cylinder wall which increases in diameter in the direction of movement of the piston as the operating member moves towards its retracted position, the half cone angle being less than 3 .

17. A door closer according to claim 16 having any of the features of any one of claims Ito 15.

18. A door closer substantially as hereinbefore described with reference to and/or as shown in the accompanying drawings.

19. Any novel feature or novel combination of features described herein and/or as shown in the accompanying drawings.