This invention relates to a buffer in particular for use in the well of an elevator or lift. It is common practice to install one or more buffers at the bottom of such a well in order to cater for certain types of malfunction that occasionally occur during operations of elevators.

Various designs of elevator exist. In many of them a lift car is suspended from a pulley wheel by way of a cable connected to a heavy counterweight on the opposite side of the pulley wheel to that of the lift car. An electric motor causes controlled raising and lowering of the lift car the mass of which is rendered essentially "neutral" by reason of its connection, via the cable, to the counterweight. An electric or mechanical brake selectively acts on the lift car, pulley wheel or electric motor (depending on the precise elevator design) in order to arrest the lift car at a chosen height corresponding to a floor or storey of the construction in which or adjacent which the elevator is installed. When so restrained the lift car is at a correct height for entry and/or exit of passengers or goods.

The support cables of elevator lift cars are capable of supporting masses many times that of a full lift car, and the cables and other parts of the elevator in most countries must undergo regular safety inspections. Therefore the chance of an accident arising in which the cable fails completely such that the lift car falls under gravity is exceedingly remote; and generally the maximum vertical speed attained by a lift car is determined by the rotational speed of the motor. The essentially force-balanced nature of cable-supported elevators indeed is the primary reason that their lift cars move at the same speed whether ascending or descending. It is however known for the cables sometimes to stretch, or for the brakes or the control electronics of an elevator to become defective such that the lift car does not stop at precisely the correct height at each floor.

Such an occurrence may be merely inconvenient, if it results in a step between the floor of the lift car and the floor of the storey next to which it has stopped.

A more serious problem arises when the position of the lift car is sufficiently far from its intended halt adjacent a floor that a release switch for the lift car door(s) is not activated on arresting of the lift car. In consequence it may be impossible for a person inside the lift car to exit without assistance from outside. Of potentially the greatest concern is the possibility of an impact occurring when, for one of the above-stated reasons, a lift car descends too far into the elevator well at the lowermost extent of its travel.

In many buildings the base of an elevator well is formed from concrete or another hard material. If a lift car were to impact such a base as a result of cable stretching or brake/control electronics malfunction the lift car could become damaged.

Moreover the resulting jolting or jarring inside the lift car could injure passengers or damage goods carried by the elevator. Even if no physical injuries to persons or animals occur during such an impact the fear of a catastrophic elevator well accident is strongly developed in many people. Therefore any kind of uncontrolled jolting of an elevator lift car can cause quite severe psychological trauma and anxiety.

For the foregoing reasons it is known to install an elongate buffer extending upwardly from the base of an elevator well for the purpose of dissipating the energy of a lift car that descends too far below its intended lowermost halt.

The lift car typically includes a plate secured to its underside that is aligned with the free upper end of the buffer so that in the event of excessive descent of the lift car the plate engages the buffer and compresses it. Such action causes dissipation of the lift car kinetic energy in a predictable manner that minimises jolting inside the lift car and also minimises the risk of damage to the lift car itself.

One type of buffer that is widely known is a so-called hydraulic buffer.

Such buffers are used in elevator wells and also, in a more heavily engineered form, on railway vehicles and as buffer stops (called bumpers in the US) at the ends of railway tracks. A hydraulic buffer whether used in an elevator well or in railway applications typically includes a cylindrical casing protruding from which is one end of a piston the other end of which lies inside the casing. A cap terminates the protruding end of the piston and when impacted by e.g. an elevator car converts the resulting force into linear motion of the piston towards a position retracted inside the casing.

During this action the piston forces an hydraulic oil through a throttling nozzle following opening of valves in a fluid flow path. The throttling of fluid damps the motion of the piston in accordance with known physical principles such that the lift car is brought to rest smoothly and progressively, without it suffering any damage or jolting.

The known designs of elevator well buffer are, as stated, intended to accommodate non- catastrophic impacts of the kinds discussed above. In view of this it is normally the case that the buffers are designed to be used multiple times. To this end many known buffer designs include restoring springs the purpose of which is to cause movement of the piston back to its extended position after an impact has been absorbed and the lift car raised away from the buffer. Following operation of the spring in such a buffer it is ready for re-use.

The springs can adopt many forms and generally they act on the piston inside the casing referred to above. Some of the spring designs are complex, and include gas compression chambers that are activated in the event of an impact occurring. The complexity of known restoring spring arrangements tends to add weight and cost to the buffer designs. Furthermore the throttling valve and nozzle assemblies often are complex and therefore relatively expensive to manufacture.

The provision of expensive and/or complex components in railway buffers and buffer stops may be justified in terms of the usage duty of such buffers. On the other hand it is harder to justify high levels of cost, complexity and mass in elevator buffers in particular. This is not least because such buffers are intended to operate only very infrequently, in cases of defects arising as explained above.

Moreover there is general pressure in at least some sectors of the construction industry to reduce the costs of building components.

Thus there is a need to produce an effective elevator well buffer that provides good performance when required while giving cost savings that may result from specifying an infrequent usage duty.

A further problem of elevator buffers relates to instability of the piston during activation. In many countries regulations state that the piston may deviate only minimally from a straight longitudinal travel. It therefore is desirable to stabilise the piston against non- longitudinal movement.

In a relatively long buffer it may be possible to provide sleeves that overlap inside the buffer to stabilise the rod of the piston over all or most of its travel against unwanted side-to-side movement.

In an elevator buffer however the space does not usually exist to provide the long overlapping stabiliser elements in an economical fashion.

As alternative it is possible simply to construct the buffer with very high precision and to close tolerances. This however is also expensive and may add to the weight of the buffer. Both these penalties may be unacceptable in a low-cost elevator buffer design. In accordance with the invention in a broad aspect there is provided a buffer comprising a casing defining a hollow container for hydraulic fluid; a hollow, hydraulic fluid reservoir adjacent to the container; a displacement member extending between the exterior of the buffer and the interior of the reservoir via a first aperture in the reservoir; and a spring acting between the displacement member and the remainder of the buffer, the displacement member being moveable inside the reservoir between a first position in which the displacement member is extended relative to the exterior of the casing; and a second position in which the displacement member is relatively retracted inside the reservoir, the spring urging the displacement member towards the first position and the reservoir including one or more further apertures via which on movement of the displacement member from the first position to the second position hydraulic fluid flows from the reservoir to the container in a manner damping movement of the displacement member; wherein the displacement member includes a free end that is remote from the reservoir; wherein the spring is a coil spring acting between the said free end and the casing or an element connected to the casing; and wherein the interior of the buffer includes a stabiliser that inhibits non-longitudinal movement of the displacement member in a manner that increases with increasing movement of the displacement member towards the second position. An advantage of this arrangement is that it may be constructed cheaply and as an item that is relatively light in weight. This is partly because the spring being configured to act between the free end of the displacement member and the casing (or an element connected thereto) is provided in the form of a conventional coiled spring that may be readily sourced at low cost.

Furthermore the specified location of the spring means that it is not necessary to locate any parts of the spring inside the casing or reservoir. This in turn means that the construction of the buffer may be made economical since it is not required for example to provide expensive sealing that isolates the chamber of a gas spring from that of an hydraulic damping mechanism. This furthermore means that the diameter of the buffer (if, as in the preferred embodiment described below, it is constructed in a cylindrical form) may be minimised as much as possible while taking account of the performance requirements of the buffer. This reduces the amounts of material (i.e. steel in the preferred embodiments) needed in manufacture of the buffer, thereby further reducing its cost and weight.

It does not matter that the spring is in practice exposed on the exterior of the device since an elevator buffer normally is not accessible to users of the elevator (so there is no danger of interference by users); and moreover the coiled spring will be functional even after a long period of inactivity in an exposed position.

Preferably the casing and the reservoir respectively are or include hollow cylinders and the diameter of the interior of the casing exceeds that of the exterior of the reservoir, the reservoir lying at least partly inside the casing so that the container is an annulus surrounding the reservoir over at least part of its length.

Such an arrangement is advantageously compact. Moreover the construction of the components, and especially the reservoir, as cylinders means they can withstand high stresses, especially those that arise during operation of the buffer. Conveniently the casing and the reservoir are concentric with and extend parallel to one another and the reservoir lies substantially entirely inside the casing. This arrangement further assists in conferring compactness and lightness on the buffer.

In a preferred embodiment of the invention the displacement member is a cylindrical piston part of which is slideably received inside the reservoir so as to be in fluid- displacing communication with an interior wall of the reservoir such that movement of the displacement member towards the second position causes positive displacement of fluid via the one or more further apertures.

This arrangement significantly simplifies the buffer of the invention compared with the prior art.

In particular the reservoir may as a result be configured as a metering tube in which there are no moving parts, with the aperture(s) open all the time. This means there is no need in the buffer of the invention for the relatively expensive metering valves that are known in the prior art devices.

Conveniently the stabiliser includes an annular collar encircling the rod or piston, the diameter of the collar being variable; and the rod or piston includes connected thereto one or more first actuator surfaces that on movement of the rod or piston towards the second position are engageable with the collar to cause expansion of the collar, such expansion being resisted by one or more further surfaces lying externally of the collar so as to inhibit non-longitudinal movement of the piston.

Preferably the annular collar is formed from two or more annulus segments that on engagement by the one or more first actuator surfaces are expandable away from one another.

In a preferred embodiment of the invention the or each first actuator surface is or includes one or more chamfers.

Preferably the collar includes one or more receipt surfaces including a chamfer that is engageable by a said actuator surface.

Conveniently the collar is restrained against longitudinal movement by one or more shoulders opposing forces applied to the collar by the or each first actuator surface.

Preferably the collar includes one or more reaction surfaces that is engageable by one or more further actuator surfaces, the location of engagement between the one or more reaction surfaces and the further actuator surfaces causing expansion of the collar at a location that is spaced longitudinally along the piston from the location of engagement by the or each said first actuator surface.

Conveniently the or each first actuator surface and/or the or each further actuator surface is formed as an actuator surface annulus encircling the rod or piston.

It is preferable that the diameter of at least one said actuator surface annulus is variable.

Also preferably the buffer of the invention includes one or more discontinuities in a said actuator surface annulus that permit variation of its diameter.

In order to provide for effective sealing and hence positive displacement of hydraulic fluid as aforesaid, in preferred embodiments of the invention the piston includes inside the reservoir one or more piston rings in slideable, fluid-displacing contact with the said interior wall of the reservoir.

The piston rings may be manufactured from any of a range of suitable materials, as would occur to the worker of skill in the art.

Conveniently the interior of the reservoir is elongate and includes a plurality of the further apertures that define a spaced series extending along the reservoir, the displacement member on moving towards the second position sequentially obscuring the further apertures of the series such that the damping of the movement of the displacement member increases as the displacement member moves towards the second position.

This formation of the further apertures beneficially renders the buffer of the invention self- regulating in the sense that high-energy impacts tend to compress the displacement member further into the reservoir than low-energy ones. During the attenuation of an impact the displacement member covers and blocks off successively more of the further apertures in the series. This progressively reduces the aggregate further aperture area via which hydraulic fluid is displaced by the displacement member. The damping effect of the buffer thereby increases the further the displacement member is compressed.

In more detail in a preferred embodiment of the invention the further apertures define a spiral pattern, of the further apertures, disposed about a periphery of the reservoir. The spacings between the further apertures from one another vary along the length of the reservoir.

These aspects of the further aperture patterns mean firstly that the hydraulic fluid is displaced evenly on all sides of the reservoir. This in turn evens out the stresses experienced by the displacement member and the wall of the reservoir.

Secondly the preferred further aperture pattern means that the damping effect increases by varying increments as the displacement member travels along the reservoir. The resulting, progressive nature of the increases in the damping effect means that the designs of the reservoir and displacement member may be simplified and may result from relatively straightforward engineering calculations while being useable to damp a range of lift car masses. Advantageously the plurality of further apertures extends vertically in use of the buffer between a lowermost and at least one uppermost further aperture; and when the displacement member occupies its first, extended position the container contains hydraulic fluid to a level above the or each uppermost further aperture. The volume of the container (as dictated principally by its diameter) may be chosen to give rise to this filling level of hydraulic fluid. In a preferred embodiment the filling level is chosen so that the or each uppermost further aperture is not normally used appreciably for displacement of fluid during a compression stroke of the displacement member. Instead, as described herein, the or each uppermost further aperture beneficially is available for the purpose of re-charging of the reservoir on extension of the displacement member under the action of the spring following an impact.

In order to facilitate this effect optionally the or each uppermost, further aperture of the series is larger than the remaining apertures thereof.

In a preferred embodiment of the invention the reservoir and the casing are coterminous with one another at at least one end whereby the piston protrudes directly from the reservoir to the exterior of the casing via the first aperture. Moreover optionally the free end includes secured thereto a flange and the spring acts between the flange and the casing; and further optionally the flange includes a skirt that encircles the spring at a first end and the casing includes a reduced-diameter portion that a second end of the spring, opposite the first end, encircles, the arrangement being such as to retain the spring captive relative to the buffer.

The foregoing features assist in providing a compact construction that is relatively inexpensive to manufacture and assemble.

Preferably the buffer of the invention includes a switch secured on the casing and a switch actuator secured to the displacement member such that on movement of the displacement member from the first position towards the second position the switch actuator operates the switch.

Such a switch provides for enhanced safety of operation of the buffer. The switch may be connected to a circuit that in the event of compression of the buffer cuts power to the elevator motor. This in turn in many designs of elevator automatically activates the elevator brake e.g. through release of an electromagnetic brake retainer.

Conveniently the switch actuator is or includes an elongate rod extending from the displacement member towards the switch so as to engage the switch in a manner causing its operation on movement of the displacement member towards the second position.

This feature of the invention may be designed so as advantageously to ensure that only a small amount of compression of the buffer is required in order to activate the switch and in turn cut the motor power. There now follows a description of a preferred embodiment of the invention, by way of non-limiting example, with reference being made to the accompanying drawings in which:

Figure 1 is a longitudinally sectioned view of a buffer illustrating some basic features of the invention;

Figure 2 is a similar view to Figure 1 , illustrating certain optional features of the invention.

Figure 3 illustrates in partly sectioned view a stabiliser forming part of the invention;

Figures 4A and 4B show operation of the Figure 3 arrangement together with additional, optional features of the invention; and

Figure 5 shows in plan view an annular collar forming part of the stabiliser shown in Figures 3 and 4. Referring to the figures, a buffer 10 comprises a hollow, essentially constant cross- section, cylindrical, metal (e.g. steel) outer casing 11 the hollow interior 12 of which defines a container for hydraulic fluid (that is not visible in the drawing).

Casing 11 is defined by a cylinder wall 11a; a metal base plate 13 at an in use lowermost end of the buffer 10 and a metal end cap 14 that in use terminates its upper end.

End cap 14 includes a flanged skirt portion 14a the flange 14b of which mates with the upper end of the cylinder wall 11a in a fluid-retaining manner. The remainder of skirt portion 14a is of reduced diameter compared with the outer diameter of cylinder wall 11a. The purpose of this reduced diameter portion of skirt portion 14a is to accommodate a coil spring 16 in a manner described in more detail below. A hollow, essentially constant cross-section, cylindrical upright metering tube 17 lies inside casing 11 so as to be concentric therewith and to extend between the base plate 13 and end cap 14 within the interior of the buffer 10. The hollow interior of the metering tube 17 defines a reservoir for hydraulic fluid. The metering tube 17 may be made from for example a metal such as a steel that is capable of withstanding the significant hoop stresses that may arise during operation of the buffer 10. Other materials than the metals indicated for the components are possible within the scope of the invention. The worker of skill in the art will be aware of viable alternatives.

The metering tube 17 is sealed at its lowermost end by a steel disc 17a fitted with a plastic (or similar material) seal 17b. As an alternative to this composite construction it is possible to consider e.g. a welded metal plate omitting the plastic seal for the purpose of sealing the lowermost end of metering tube 17.

A displacement member in the form of an elongate, circular cross-section piston 18 extends lengthwise relative to the buffer 10.

Piston 18 is in the pre-use condition of the buffer shown in Figure 1 received partly within the interior of metering tube 17 with a major part of its length protruding externally of the buffer 10 via a through-going aperture 19 formed in the uppermost face of end cap 14. The piston by reason of the coterminous construction of the upper end of casing 11 and metering tube 17 protrudes essentially directly from the interior of the reservoir to the exterior of the buffer 10 via aperture 19. A seal such as an elastomeric seal 21 encircles the shank of piston 18 in the vicinity of aperture 19 so as to retain within the container defined by casing 11 any hydraulic fluid therein.

At its lowermost end piston 18 terminates in a piston head 22 that is slidingly sealingly in contact with the interior wall of the reservoir defined inside metering tube 17. Sliding sealing of piston head 22 in metering tube 17 is achieved through the use of one or more annular piston rings 23a, 23b received in corresponding, complementary grooves 24a, 24b that extend around the perimeter of piston head 22. The piston rings may be made of any of a range of materials that are known to be suitable for the purpose of providing sliding seals of the kind described above. In the preferred embodiment of the invention they are made from cast iron that is machined appropriately to provide the desired oil control effects.

More than the two piston rings 23a, 23b may be provided if desired. In theory it is also possible to provide only a single piston ring, but the use of two such rings as shown in preferred. As shown in Figure 1 the piston head 22 above the piston rings 23 is formed including annular lands 42 defined by annular grooves machined into the surface of piston head 22. The lands 42 and piston rings 23 between them provide for predictable leakage flow of hydraulic fluid across the piston head 22 in the upward direction, giving rise to adequate levels of sliding sealing at reasonable cost.

At its uppermost, free end outside the reservoir piston 18 terminates in a top plate 26 that in essence is a metal or other rigid material circular disc extending horizontally. The diameter of the top plate 26 is substantially the same as the outer diameter of casing 11. Top plate 26 includes a downwardly depending, annular skirt 27 that extends a short distance towards casing 11. The top plate 26 is retained rigidly captive on the free end of piston 18 by way of a spring washer 29 a projecting collar 29a of which is resiliently snap-fitted into an annular groove 31 formed adjacent the end of piston 18. Spring washer 29 as a result presents a downwardly projecting, v-section annulus 29b that is received in an annular depression 32 formed in the upper surface of top plate 26. Spring 26 urges the depression 32 into contact with v-section annulus 29b so as to form a rigid, robust yet low cost retaining mechanism for the top plate 26. The coils of spring 16 are of a constant diameter along its length. The coil diameter is chosen such that at its in use lowermost end the spring 16 may seat snugly over the reduced diameter portion defined by end cap 14 so that its lowermost coil bears against an outwardly directed flange 14b extending from the lowermost end of skirt 14a.

At its uppermost end the spring 16 bears as illustrated against the underside of top plate 26 and is restrained against lateral movement by the skirt 27. Over its length the spring 16 encircles the portion of piston 18 that protrudes on the exterior of the casing 11.

It will thus be apparent that the spring 16 acts between the displacement member represented by piston 18 and the remainder of the buffer by way of contact with the end cap 14. Any tendency of the piston 18 to compress into the interior of metering tube is resisted by the force of the spring so acting; although this force is not responsible for the damping effect that the buffer 10 is capable of exhibiting.

On the contrary, the buffering effect leading to dissipation of impact energy experienced by the top plate in a manner described in more detail hereinbelow is the result of the construction of the metering tube 17.

Metering tube 17 is formed including extending along its length a series of multiple further, through-going apertures arranged in a spiral pattern extending down the metering tube 17 and of which four 28a, 28b, 28c, 28d are labelled in Figure 1. In other embodiments of the invention in which the lengths of the metering tube 17 and piston 18 differ from those illustrated there may be more or fewer of the further apertures 28a, 28b, etc than those shown.

In the preferred embodiment of the invention the spiral pattern of the apertures is arranged such that there is a increasing density of the apertures, and hence a larger area via which fluid may flow, towards the lower end of the metering tube 17. The aim of this aspect of the invention is to provide an optimised performance of the buffer 10 when used with a range of lift car masses. Each of the further apertures 28 is formed as a throttling nozzle extending from the interior of metering tube 17 and opening into the container so that any fluid forced by action of the piston 18, as described below, via the further apertures undergoes a per se known energy-dissipating throttling process.

In preparation for use of the buffer 10, during its final assembly, the container and the metering tube 17 are filled, via a filler plug 34 (visible in Figure 2) that releasably closes an opening in the end cap 14, with a hydraulic fluid such as an oil (not shown) to a depth just above the piston rings 23. Since the further apertures 28 permit fluid communication between the reservoir and the container the levels of oil in these two chambers become equal on filling of the buffer with oil. Following filling of the container and reservoir via this means, the filling opening may be closed eg. by way of a threaded, plastic plug that if desired may include a downwardly depending dipstick 36 for the purpose of checking the filling level of the buffer. In this regard, it is important to ensure that the buffer is filled to the correct level. If insufficient hydraulic oil is added such that the level of the oil is below one of the sets of further apertures 28, such apertures would not provide any damping function during operation of the device until the piston rings 23 descend to reach the oil level.

On the other hand, it is necessary to ensure that in the container defined by casing 11 a volume of gas (ie. air) exists above the level of hydraulic fluid since during operation of the buffer such fluid is displaced from the reservoir defined by metering tube 17 into the container defined by casing 11. If the latter was filled entirely with (incompressible) hydraulic fluid, during the operation the buffer would lock up immediately allowing no further piston travel. Such an event may result in the casing 11 being excessively pressurised and encountering stresses beyond those for which it was designed.

Once the filling activity is complete the buffer is essentially ready for use. It thereafter is typically bolted in place in the well of an elevator, for example by way of threaded studs that are cast into the (typically) concrete material of the well bottom so as to protrude upwardly. Apertures formed in the base plate 13 in a pattern coinciding with the pattern of the studs permit the use of nut and washer combinations to secure the buffer 10 in the orientation shown in the figures.

In the event of a lift car descending sufficiently far in the well that its underside contacts the top plate 26 this causes compression of the buffer 10 so that the piston retracts into the reservoir defined by metering tube 17.

During this action of course such retraction only would occur in the event of the force imparted by the lift car exceeding the force of spring 16. The latter force, however, is of a relatively low value since as explained below the primary purpose of spring 16 is to restore the piston 18 to the extended position visible in Figure 1 following removal of the lift car from its upper end.

Assuming that, as explained, the force imparted by the lift car is sufficient to cause compression of the buffer the piston head 22 moves downwardly inside the reservoir.

By reason of the effect of the piston rings 23a, 23b and lands 42 this causes the piston head 22 to force oil in the reservoir via the apertures 28a, 28b, 28c, 28d outwardly from the reservoir into the container.

The design of each aperture 28 is, as stated, such as to provide for throttling of the hydraulic fluid during this process. Therefore the energy of the impact of the lift car is dissipated in a perse known manner by energy conversion.

As is apparent from Figure 1 , when in its fully extended condition the piston seals the reservoir at a height only a very short distance above the uppermost apertures 28a. In consequence only a very small movement of piston 18 in a downward direction as a result of an imparted force causes the sealing rings 23 to pass, and seal off from the hydraulic fluid in the reservoir, the uppermost apertures 28a such that thereafter no fluid is throttled via those further apertures notwithstanding further motion of the piston 18 towards the bottom of the buffer 10. As a result very shortly after initiation of the movement of the piston 18 the number of sets of further apertures 28 is reduced, such that a lesser number than the maximum is available for the throttling of hydraulic fluid.

This in turn means that following passage of the piston rings 23a, 23b downwardly past the uppermost set of further apertures 28a the resistance to flow of hydraulic fluid in the buffer increases progressively in consequence of the spiral pattern of the further apertures 28.

Further movement of the piston 18 in a downward direction subsequently causes similar covering of increasingly more of the further apertures 28, with the result that the resistance to flow increases further. One may then see that additional, downward movement of the piston 18 sequentially causes further increases in the flow resistance until the piston head 22 finally forces hydraulic fluid via only the lowermost further aperture(s) 28d shown in the figure.

As a result of this arrangement the resistance of the buffer to an applied, downwardly acting force increases as the amount of compression increases. In other words, the buffering effect of the buffer 10 automatically increases in proportion to the applied force magnitude.

As the hydraulic fluid is forced via the apertures 28 into the reservoir the level of fluid therein rises into the air volume described above. Since air is compressible the air volume in the container is able to accommodate this increase in the amount of hydraulic fluid.

Obviously not all forces applied to the top plate 26 would be sufficient to compress the buffer such that only the lowermost further aperture set 28d eventually is operational. In cases of lesser forces an equilibrium position may be reached before the piston head 22 covers and closes off the further apertures sets 28c or even 28b as appropriate.

Following removal of the lift car from the top plate 26 the force of spring 16 acts to stroke the piston 18 back to its fully extended position as shown in Figure 1.

During this process it may be possible for some of the hydraulic fluid to re-enter the reservoir via the further apertures sets 28d, 28c and 28b; although in view of the viscosity of a typical hydraulic fluid only a partial refilling of the reservoir would be achieved via these routes.

On the other hand the average diameter of each further aperture in uppermost set 28a is greater than that of each further aperture in the sets 28b, 28c and 28d. In consequence when the spring 16 strokes the piston 18 such that the sealing rings 23a, 23b pass in an upward direction to above the level of the uppermost further aperture set 28a the hydraulic fluid in the container that had been transferred there by the compression stroke of the buffer may freely flow under gravity back into the reservoir until the levels in the container and reservoir once again are equal. Clearly by reason of being defined as enlarged apertures the uppermost further aperture set 28a offers relatively little resistance to the flow of hydraulic fluid during the downward (compressive) stroke of the piston 18. This however is of little effect on the overall resistance to compression provided by the buffer, since as stated after only a very short travel in the downward direction of the piston 18 the uppermost further aperture set 28a becomes covered by the sealing rings 23a, 23b such that no further hydraulic fluid is forced via them during the remainder of the downward piston motion.

One optional refinement of the invention is the incorporation of venting apertures 33 providing gas communication between the upper ends of the reservoir and container. As a result any gas in the upper end of the container may during buffer compression be vented into the region of the reservoir behind the downwardly advancing piston head 22 (this effect being possible by reason of the shank 18a of the piston 18 being of lesser diameter than that of the piston head 22). As a result there is a reduced requirement for the buffer 10 to accommodate gas compression forces, by reason of there existing a relatively large volume constituted by parts of the container and reservoir respectively into which gas may migrate as the level of hydraulic fluid rises in the container.

Figure 2 shows a buffer that is very similar to the Figure 1 embodiment, but omitting the venting apertures 33. The Figure 2 arrangement on the other hand includes some further optional features of the invention. Figure 2 illustrates the plastics filler plug 34 referred to above, that is threadedly receivable into an opening in end cap 14. Depending downwardly from the lowermost end of the filler cap 34 into the interior of the container is a hydraulic fluid level dipstick 36 that as stated may be employed for the purpose of checking filling of the buffer to the correct depth with hydraulic fluid. As is apparent from Figure 2, the lowermost, free end of the dipstick includes an indicator portion 36a that in use terminates at the optimum hydraulic fluid level as described above when the filler cap 34 is screwed into its aperture in the end cap 14.

Yet a further option is in the form of a flange ring 37 that encircles the end cap 14 in the vicinity of skirt 4a so as to rest on the upper face of flange 14b.

The spring 16 urges the flange ring 37 into firm contact with the flange 14b on assembly of the buffer 10. Flange ring 37 supports in cantilevered fashion on one side of the buffer 10 a switch box 38 containing an electromechanical switch. A switch actuator rod 39 projects downwardly from the skirt 27 of top plate 26 so as to enter into the switch box 38 from above via an aperture formed in its uppermost surface.

Switch actuator rod 39 includes at its lowermost end a switch actuator member 41 that is positioned to engage and operate a switch in the switch box 38 on commencement of the downward compressive movement of the piston 18.

Such operation of the switch may trip a relay that instantaneously cuts power to the lift motor and/or activates a lift brake. In consequence the buffer 10 of the invention may readily include enhanced safety features that become operational almost instantaneously after compression of the buffer 10 commences.

As is apparent from Figure 2, the length of switch actuator rod 39 is approximately equal to that of the piston 18. In consequence the flange plate 37 includes an aperture via which the switch actuator 39 may be guided ensuring activation of the switch and thereby accommodating further downward movement of the piston 18 after activation of the switch.

Referring now to Figures 3 to 5 there is shown an arrangement by which stabilisation of the piston rod 18 against unwanted lateral or other non-longitudinal movement may be effected in accordance with the invention.

The buffer 10 of Figures 3 to 5 is similar to that of Figures 1 and 2 in terms of its overall arrangement and functioning. At its in use upper end however the buffer 10 is modified to include a stabiliser 43.

Stabiliser 43 operates on movement of the piston rod 18 towards the second position defined herein. Stabiliser 43 is constituted by an annular collar 44 that in preferred embodiments of the invention is machined from a lightweight metal such as "De/r/n", "Kemetar or an aluminium alloy having a relatively high modulus of elasticity. Other materials however, including non-metals, are possible when constructing the collar 44. As shown in Figure 5, which is a plan view of collar 44, the collar is in the preferred embodiment of the invention formed from two semi-annular segments 44a, 44b that when placed adjacent one another as shown define the full annulus 44. Preferably the annulus segments 44a, 44b are machined from a solid annulus, although other methods of forming annulus 44 are possible. Moreover it is possible to form the annulus 44 from a greater number of the segments 44a, 44b than the two shown.

Regardless of the precise design of the collar 44 the fact that the segments 44a, 44b define a dividing line means that the diameter of the collar 44 may be increased by spreading the segments 44a, 44b apart from one another. In the preferred embodiment of the invention such spreading is effected by first 46 and (optional) further 47 actuator surfaces.

The actuator surfaces 46, 47 are formed as respective annular wedges that each encircle the piston rod 18 as illustrated in Figures 3 and 4.

More specifically, the first actuator surface 46 is defined as an inclined chamfer 48 that in the view visible in Figures 3 and 4 is inclinedly downwardly directed.

In preferred embodiments of the invention the annuli 46a, 47a defining the wedge surface 46, 47 are also segmented, eg. formed from two split, semi-annular halves; or possibly from a greater member of part-annular segments. This means that the inner diameters of these annuli 46a, 47a may be shrunk during operation of the buffer to take up any gap that would otherwise exist between the inner surfaces of the annuli and the rod 18. This arrangement assists in improving the lateral stability of the buffer 10.

The buffer 10 however would enjoy improved stability even if the annuli defining actuator surfaces 46, 47 were of fixed diameter and were completely rigid. Such an arrangement, in which each of the annuli is formed as or is assembled to be a one-piece item, is within the scope of the invention.

Another variant within the scope of the invention also involves forming the annuli defining the actuator surfaces 46, 47 as one-piece items that each include a through-going slot cut through the material of the respective annulus 46a, 47a to permit variability of the inner and outer diameters of the annuli 46a, 47a while avoiding the potential assembly inconvenience of having to assemble the annuli 46a, 47a from separate, part-annular segments. In such an embodiment the material of the annuli 46a, 47a would be resiliently deformable at least to a limited extent. In such an embodiment the annuli, or at least one of them, may be made from a plastics material (although metals are also possible). Combinations of the different types are at least theoretically possible in one and the same buffer 10.

The first actuator 46 encircles rod 18 at a location permitting engagement of the chamfer

48 with a corresponding, upwardly facing chamfer 49 defined at the upper end of collar 44.

As is apparent from Figures 3 and 4 movement of rod 18 towards its second (retracted) position that transmits a force to the first actuator 46 drives the aforesaid chamfers 48,

49 into binding engagement with one another.

This causes a wedging effect to arise that in turn expands the collar 44 through separation of the collar segments 44a, 44b.

The collar segments 44a, 44b resultingly engage on their radially outer surfaces a sleeve 51 that is fixed in the open, upper end of the container 12. The wedging action between the rod 18, first actuator 46, collar 44 and sleeve 51 rigidifies the containment of the rod 18 in non-longitudinal directions thereby stabilising it in an effective manner that occupies only a relatively short length in the buffer 10. At its lowermost (as shown) end sleeve 51 includes an inwardly directed shoulder 52. The lower end of collar 44 bears against shoulder 52 which thereby inhibits downward movement of collar 44 under the influence of downwardly acting forces transmitted from the downwardly moving rod 18 via the first actuator 46. The sleeve 51 is itself prevented from moving downwardly by reason of being threadedly engaged with top plate 61 of the buffer 10. An outer flange 53 bears against the top plate 61 in a manner trapping an annular seal 62 that assists in making the device leak- proof. Other sealing arrangements however are possible within the scope of the invention.

The buffer 10 of Figures 3 and 4 illustrated includes a further actuator 47 that is an optional feature. Further actuator 47 is of essentially the same design as first actuator 46 except that it is installed in an inverted orientation so that its inclined chamfer 54 is upwardly directed as shown.

In the illustrated embodiment of the invention collar 44 is formed including at its lower end including a downwardly facing, inclined chamfer 56.

The arrangement is such that on downward movement of the collar 18 occasioned by the influence of first actuator 46 the lower chamfers 54, 56 are driven into binding engagement as illustrated.

This action provides an expanding force acting on the collar 44 at its lower end. Therefore if the features of the further actuator surface (chamfer) 54 and the chamfer 56 are present expansion of the collar 44 may be occasioned evenly at its upper and lower ends. The use of the two actuators 46, 47 is not mandatory however; and it is possible to effect expansion of the collar using only a single pair of engaging located at an upper end of sleeve 51 , at a lower end or part-way along the sleeve chamfers if desired. At its upper end sleeve 51 is formed including a pre-tensioner that is also optional.

The pre-tensioner takes the form of an inner annulus 57 secured by way of a laterally acting grub screw 58 as illustrated in the otherwise open upper end of sleeve 51. Inner annulus imparts a downwardly acting force to first actuator 46, thereby providing a certain expanding force that acts on the collar 44 thereby driving it moderately firmly into the sleeve 51. The inner annulus also simply prevents the parts described in relation to Figures 3 to 5 from falling out of the open upper end of the buffer 10.

Figures 4A and 4B show the stabiliser 43 when the piston rod 18 is respectively in its first (Figure 4A) and second (4B) positions.

Figures 4A and 4B also illustrate another optional feature of the invention in the form of intermediate spring flange 59. Flange 59 is fixed part-way along piston rod 18. In consequence it is possible to construct the buffer 10 including a long piston rod 18 without having to install a spring 16 of commensurate length. As illustrated, the intermediate flange 59 permits the use of two springs 16a, 16b each of which extends over roughly half the length of the piston rod 18 when the latter occupies its first position.

As shown, spring 16a extends between cap 14 of buffer 10 and the intermediate flange 59; and spring 16b extends from intermediate flange 59 and top plate 26. The flange edges, the edge of cap 14 and the edge of top plate 26 are shaped to retain the coil springs 16a, 16b. The flange and spring arrangement cheaply provides a stable arrangement. Overall the buffer of the invention represents a significant advance in the art of elevator buffer arrangements. Although its use has been described herein in connection with a cable-suspended lift car, it will be apparent that such a buffer readily could find use in other types of lift car such as but not limited to those supported on hydraulic rams or other mechanisms.

Furthermore, the buffer may be manufactured in a range of lengths and diameters in order to suit the precise application under consideration; and a range of materials may, as stated herein, be considered for the manufacture of the components parts. The listing or discussion of an apparently prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.