WO2008068492A1

WO2008068492A1 - Improvements in or relating to drive systems

Info

Publication number: WO2008068492A1
Application number: PCT/GB2007/004670
Authority: WO
Inventors: Alan Neil Russell Stannah
Original assignee: Stannah Lifts Limited
Priority date: 2006-12-07
Filing date: 2007-12-06
Publication date: 2008-06-12
Also published as: GB0624436D0

Abstract

A drive unit for an hydraulic elevator or lift is provided with counterbalance means to at least partly counterbalance the load imposed by the load carrier or lift car. The drive function and the counterbalance function are effected by separate fluids and a novel sealing arrangement is provided to ensure that the separate fluids cannot mix. In another aspect the positioning of sealing arrangement, to enable ready and efficient inspection and replacement, is described.

Description

IMPROVEMENTS IN OR RELATING TO DRIVE SYSTEMS

Field of the Invention

This invention relates to drive systems. The system described herein has been developed for particular application to hydraulically powered elevators, lifts or lifting platforms but it will be appreciated that a drive system as disclosed herein could have application in a variety of alternative fields.

In the following specification the terms 'elevator', 'lift' and lifting platform may be used inter-changeably and are intended to have the same meanings.

Background to the Invention

In our pending International Patent Application No WO 2005/061361 we describe a form of hydraulic elevator and/or elevator drive unit in which the load applied to the elevator is counterbalanced, at least to some extent, by a fluid-filled chamber. The fluid-filled chamber is preferably provided in the same unit as the hydraulic ram and, although suitable seals are provided to maintain a separation between the pressurized counterbalance fluid and the pressurized hydraulic fluid, seals are mechanical components which are subject to wear and, in some instances, failure. In this type of apparatus, the seepage of counterbalance fluid into the hydraulic drive fluid could lead to uncontrolled upward movement of the elevator and, where the counterbalance fluid is a fluid other than hydraulic fluid of the same form as the drive fluid, seepage could also lead to contamination of the hydraulic drive fluid.

A further shortcoming of the apparatus already described is that the fluid-to- fluid seals are located at the bottom of the piston rod and require removal of the piston rod to enable a thorough inspection and/or replacement. It is an object of this invention to provide apparatus which will go at least some way in addressing the problems outlined above; or which will at least provide a novel and useful choice.

Summary of the Invention

Accordingly, in a first aspect, the invention provides an operating unit for a lift, said operating unit having a first chamber to receive pressurized hydraulic fluid to effect raising and lowering; a second fluid-filled chamber to at least partially counterbalance a load applied to said lift; and a sealing arrangement positioned and operable to prevent the exchange of fluids between said first and second chambers, said operating unit being characterised in that: said sealing arrangement has a first sealing component in contact with said first chamber; a second sealing component in contact with said second chamber; and a cavity between said first and second sealing components which is maintained at a pressure below the pressure in either said first chamber or said second chamber.

Preferably said cavity is vented to atmosphere.

Preferably said first chamber comprises the fluid-filled chamber of an hydraulic ram having an extending piston rod, said second chamber being arranged about said ram such that said piston rod defines, in part, said first chamber and is displaceable within said second chamber.

Preferably said first and second chambers are included in a fixed drive part, said piston rod moveably projecting from said fixed drive part, wherein said sealing arrangement is located at or adjacent to the position at which said piston rode projects from said fixed drive part.

Preferably said piston rod is tubular and has an inner wall, said sealing arrangement being mounted and configured to sealingly engage said inner wall.

Preferably a hollow filler rod is provided within said first chamber to reduce the effective volume thereof, said cavity being in communication with atmosphere via the interior of said filler rod.

Preferably the fluid within said second chamber comprises a gas.

In a second aspect, the invention provides an operating unit for a lift, said operating unit having a fixed part comprising a first chamber to receive pressurized hydraulic fluid to effect raising and lowering, and a second chamber having a fluid therein to at least partially counterbalance a load applied to said lift; said operating unit further including a sealing arrangement positioned and operable to prevent the exchange of fluids between said first and second chambers and a piston rod projecting from said fixed part, said operating unit being characterised in that:

said sealing arrangement is located at or adjacent to the position at which said piston rod projects from said fixed part.

Preferably said sealing arrangement has a first sealing component in contact with said first chamber; a second sealing component in contact with said second chamber; and a cavity between said first and second sealing components which is maintained at a pressure below the pressure in either said first chamber or said second chamber. Preferably said cavity is vented to atmosphere.

In a third aspect, the invention provides a lift having a load bearing structure and a lift operating unit as set forth above.

Many variations in the way the present invention can be performed will present themselves to those skilled in the art. The description which follows is intended as an illustration only of one means of performing the invention and the lack of description of variants or equivalents should not be regarded as limiting. Wherever possible, a description of a specific element should be deemed to include any and all equivalents thereof whether in existence now or in the future.

Brief Description of the Drawings

One operating embodiment of the invention will now be described with reference to the accompanying drawings in which:

Figure 1 : shows an elevational diagrammatic view of an hydraulic lift to which the various aspects of the invention may be applied;

Figure 2: shows a diagrammatic view of a lift drive system with reduced power requirement embodying the broad principles of the invention;

Figure 3 : shows a cross-sectional view of one embodiment of lift operating unit according to the invention.

Figure 4: shows a view similar to Figure 3, but of a modified form of operating unit according to the invention; and Figure 5: shows an enlarged view that part of the drive unit circled in Figure 4.

Detailed Description of Working Embodiment

Referring firstly to Figure 1, a typical hydraulic lift installation comprises a load carrier in the form of lift car or platform 10 supported on lift guides 12, the guides 12 being fixed to, and extending vertically upwards, in a lift shaft 14. An hydraulic ram 16, having a moving piston rod 17, is mounted on the base 18 of the lift shaft, the piston rod 17 engaging the underside of the lift car 10 so as to displace the lift car upwards and downwards in the lift shaft 14. G In order to extend piston 17 from the cylinder of ram 16, hydraulic fluid is pumped by motor/pump unit 19 drawing fluid from reservoir 20. When the lift car is required to move in the downwards direction, dump valve 21 is opened to allow the hydraulic fluid to pass directly back into the reservoir 20. Alternatively, the motor/pump unit is reversed to scavenge fluid from thes cylinder and return the same to the reservoir 20.

In the particular embodiment shown in Figure 1, the piston 17 bears directly against the lift car 10 however, as is well known in the art, the piston may displace a roping arrangement which results in the displacement of the lift car 10 with respect to the displacement of the piston 17, being multiplied. WhilstG such roping per se does not form part of this invention it can be used to advantage to increase system pressure and, thereby, allow the use of lower fluid volumes.

Indeed all that has been described above is entirely conventional as are variations thereof. For example, it is common to immerse the motor pump unit 19 within the fluid contained in reservoir 20 as is shown in Figure 2.

In the past various means have been implemented, or at least proposed, to reduce the load on the hydraulic system and, thereby, reduce the overall power requirement. The most conventional counterbalancing means comprises a simple mechanical counterweight. However, a mechanical counterweight requires its own guide rails and roping arrangement and is thus relatively expensive to implement. It can also occupy significant space in the lift shaft. Thus, attention has been diverted to the hydraulic drive system itself in the search for a more efficient overall drive system.

Turning now to Figure 2, the drive element principles of a lift drive system according to the invention are entirely conventional and, as illustrated, include an hydraulic ram 16 having a piston 17 extendible there-from and retractable therein. Hydraulic fluid from reservoir 20 is, in the conventional manner, pumped by motor/pump 19 into the cylinder 16 to extend the piston 17. When the piston 17 is to retract, the motor/pump is reversed, or suitable valving (not shown) is operated, to cause the fluid in cylinder 16 to return to the reservoir 20.

The basis for the present invention resides in providing a counterbalance chamber in which the preferred working fluid is a pressurized gas. Whilst the counterbalance chamber may be in close physical proximity to hydraulic drive components, it operates entirely independently of the drive system, in that the counterbalance chamber does not receive any fluid from reservoir 20.

As can be seen, the counterbalance chamber 22 contains a counterbalance fluid. This counterbalance fluid may be hydraulic oil but, as will be apparent from the description which follows, is more preferably, a gas. Gas within the chamber 22 is preferably supplemented by gas within a communicating auxiliary chamber 24. The greater the volume of gas within the counterbalance circuit, the less the difference of the gas pressure between when the piston 17 is fully extended and when it is fully retracted. This, in turn, means that the counterbalance force is kept substantially constant over the stroke of the piston rod 17.

Turning now to Figure 3 the counterbalance system is conveniently provided in unit with the hydraulic drive system. In such an arrangement, it is most convenient to apply the counterbalance force along the same axis as the drive force.

In the form shown, drive unit 31 comprises an outer cylinder 32 which is fixed to base member 34. Fixed to the inner surface of base 34 is a static drive cylinder 36 which may, conveniently, be located centrally within outer body 32. Located over the drive cylinder 36, and in sliding contact therewith, is a piston rod 38, the upper end of which is capped by a top cap 40. Mounting flange 42, by means of which the drive unit is attached to the lift car 10, is attached to, or formed integrally with, the top cap 40. It will be noted that, unlike the piston rod of a conventional hydraulic ram, piston rod 38 is hollow, its interior slides over the fixed drive cylinder 36, and is filled with oil. This is believed to have an advantage in the reduction of the buckling loads to which the unit 31 is subjected.

It will be appreciated that the fluid in the interior of drive cylinder 36 is essentially 'dead' fluid and, by keeping the volume of this dead fluid to a minimum, the compressibility of the drive system is also minimised. To this end, the volume of the drive cylinder (and thus the volume of working fluid) may be reduced by inserting a filler rod 43 within the drive cylinder 36. The inner lower end of piston rod 38 carries an annular slider 44 which slides over the outer surface of the drive cylinder 36 and locates the lower end of the piston rod with respect to the drive cylinder 36 yet still allows the passage of fluid between the piston rod and the fixed drive cylinder. A further slider 45 is provided which extends outwardly of the piston rod 38 and whose purpose is to support the lower end of the piston cylinder within the outer body 32.

A conventional annular seal 72, sealing against the outer surface of piston rod 38, is mounted within a collar 46 provided about the end of the outer cylinder 32 from which the piston rod projects. The collar 46 is preferably screw-fitted to the cylinder 32 for ease of assembly and/or maintenance.

To drive the lift car 10 in an upward direction, hydraulic fluid is fed under pressure, through port 48, in base member 34. Port 48 communicates with the interior of drive cylinder 36 so that incoming hydraulic fluid passes into the interior of the drive cylinder and around the outside of the filler rod 43. The hydraulic fluid then passes through a port 50 in seal block 52 and thence into the interior of piston rod 38. The increasing pressure within the piston rod 38, acting against top cap 40, causes the piston rod 38 to telescope upwardly over the drive cylinder 36, but within the outer cylinder 32.

When the lift car is to move in a downward direction, the port 48 is placed in communication with a low pressure reservoir and the fluid within the interior of the cylinders 36 and 38 pumped, or allowed to bleed, there-from.

It will be appreciated that an annular chamber 54 is defined between the inner surface of the outer cylinder 32 and the outer surfaces of the drive and piston cylinders 36 and 38 respectively. This chamber, referred to as the counterbalance chamber is used to generate the counterbalance force discussed above. In operation the counterbalance chamber 54 is charged with counterbalance fluid so that a fluid strut is formed about the hydraulic drive. The counterbalance fluid is preferably a pressurized gas, the volume of which may be supplemented by gas within a communicating auxiliary chamber 60.

According to the principles described in our published International Patent application WO 2005/061361 the slider 45 extends across the annulus defining chamber 54 to provide a sliding contact against the inner surface of outer cylinder 32. Axial ports 56 are provided in the slider 45 to allow the sections of the chamber 54, above and below the slider 45, to communicate with one another, and thus the fluid pressures in the two chamber parts, to balance.

A port 58 is preferably provided in the base member 34 of chamber 54. Leading from the port 58 is a line 59 which places the chamber 54 in communication with the interior of auxiliary chamber 60.

Counterbalance gas is compressed and/or displaced from chamber 54 into auxiliary chamber 60 as the lift lowers. More particularly, it will be noted that, as the piston rod 38 and slider 45 lowers, the volume of chamber 54 effectively reduces because the intrusion of piston rod 38 effectively reduces the width of chamber 54. The width of the annulus changes from the distance between cylindrical walls 32 and 36 to the distance between cylindrical walls 32 and 38. As the volume of chamber 54 reduces, this causes the gas within chamber 54 to be compressed and/or displaced into chamber 60.

The gas within the counterbalance circuit is preferably nitrogen as nitrogen is substantially inert. It will be appreciated, however, that other gases and fluids could be used without departing from the scope of the invention. Indeed, the counterbalance fluid may, itself, be hydraulic oil and the counterbalance circuit configured more like that described in our pending International Patent Application No. PCT/GB2006/002099.

In the event the counterbalance fluid is the same as the hydraulic drive fluid, contamination of working fluid by the counterbalance fluid may not be an issue, however any leakage of the counterbalance fluid (whatever its make-up might be) into the drive fluid could lead to uncontrolled rising of the lift. The invention is thus equally applicable to lift systems having different combinations of drive and counterbalance fluids.

During the design process the drive unit components are configured to ensure that the counterbalance fluid within chamber 54 provides a net upward component of force on the lower annular surface of piston rod 38 and thus counterbalances, at least to some extent, the downward component of force imposed by the lift car 10 and any load carried thereby.

At any time when it is desired to raise the lift, the pressurized gas within the counterbalance circuit acts in conjunction with the drive motor 19 to effect upwards displacement. It will be appreciated that this action is independent of the actual drive function in that the counterbalance fluid within chambers 54 and 60 is entirely independent of the hydraulic fluid within the drive cylinder 36 and piston rod 38.

The present invention addresses the need to provide optimum sealing between the gas and oil chambers to ensure that there is no leakage of gas into the hydraulic drive system. As described above, if appreciable leakage of pressurised gas into the hydraulic drive system were to occur, this could cause uncontrolled upward movement of the lift car, and thus have safety implications. Further, any leakage of gas into the hydraulic fluid would cause contamination of the fluid and reduce its efficiency. With this in mind, and without detracting from the need to effectively seal between the drive and counterbalance chambers, the present invention provides a novel sealing arrangement between the drive and counterbalance chambers which provides a safety back-up to minimise, if not eliminate, the possibility of pressurised gas passing from the counterbalance chamber into the hydraulic drive circuit.

5 As can be seen in Figures 3 to 5, a seal arrangement is provided within seal block 52 which provides a first sealing component 64 sealing the egress of gas from the chamber 54, and a second sealing component 66 sealing the egress of hydraulic fluid from the interior of piston rod 38. A cavity 68 is provided between the sealing components 64 and 66 and this cavity is maintained at a io pressure below the pressures of either the hydraulic fluid or of the counterbalance gas. As a consequence any leakage, particularly of the counterbalance gas, is attracted to the low pressure cavity 68 and does not pass past the sealing component 66 and into the hydraulic fluid. Further, the existence of the vented cavity 68 substantially prevents pressure build-up of i₅ any type, between the drive and counterbalance chambers, during normal operation of the lift.

In the form shown, the seal block 52 is mounted on the upper end of fixed drive cylinder 36 and includes a radial passage 70 communicating with the cavity 68. The seal block 52 is also, preferably, sealed to the filler rod 43. In 2Q the embodiment shown in Figure 3, the passage 70 communicates with the interior of the filler rod 43. The interior of filler rod 43 is, in turn, vented to atmosphere through a vent passage 62 provided in base 34 and thus the cavity 68 is effectively vented to atmosphere.

In the embodiment shown in Figures 4 & 5, the interior of the filler rod 43 5 carries the hydraulic drive oil from entry port 48 to the interior of piston rod 38 and thus the cavity 68 is vented into the annulus 74 between the exterior surface of the filler rod 43, and the interior wall of the drive cylinder 36. As can be seen, the annulus 74 is, in turn, vented to atmosphere via port 76.

Whilst two specific forms of venting arrangement have been described herein, it will be appreciated by those skilled in the art that other venting arrangements are possible without departing from the scope of the invention.

The sealing components 64 and 66 may be conventional annular sliding seals.

They may, as shown, be separate components or may be separate sealing elements on a common component. All that is important is that an area of low pressure, relative to the pressure at least in the chamber 54, is able to be created between the seal positions.

Another important aspect of the invention, shown in Figures 3 to 5, is the positioning of the seals. As can be seen, the sealing collar 46 is a screw-fit into the upper end of outer cylinder 32 and includes an annular sealing member 72. In the conventional manner the sealing member 72 forms a sliding seal with the outer surface of the piston rod 38. The internal sealing arrangement included in sealing block 52, which separates the drive and counterbalance fluids, is mounted on the upper end of both the fixed drive cylinder 36 and the filler rod 43 or, more precisely, at the location where piston rod 38 projects from the fixed part of the drive unit. If it is desired to inspect or replace any of the components mounted on sealing block 52, access to the block can be gained by unscrewing the top cap 40 from the piston rod 38, and releasing the block 52 from the drive cylinder 36. Thus all seals can be replaced without having to remove the piston rod 38, which is a considerable benefit when the drive system needs to be serviced.

To configure a drive system as described above, the empty load of the lift car 10 is calculated and the number of counterbalances, the geometry thereof, and the fluid pressures therein, determined so as to ensure the lift car 10 always imposes a small net downward force. In reality it is preferred that the counterbalance is no more than 90% of the weight of the empty lift car and, more preferably, in the range of 70 to 90% of the weight of the lift car. This ensures the lift car is able to descend under manual lowering and avoids the chance of the lift car rising under the effect of the counterbalance alone.

The lift drive system as above described is believed to have at least the following advantages:

1) Because a substantial part of the operating mass of the lift is counterbalanced, effective lift operation can be achieved using ao relatively small hydraulic drive package.

2) The drive system requires a relatively small volume of hydraulic oil to operate.

3) The provision of a fluid-based counterbalance system which is both independent of the drive fluid, and which is substantially constant ins volume, ensures a substantially constant counterbalance force throughout the lift travel. The counterbalance force is solely dependent on the gas contained within chambers 54 and 60.

4) Because of the low loading imposed on the hydraulic drive, heat and noise generation is low. o 5) The incorporation of a double seal between the drive and counterbalance fluids, with a vented cavity between the seals, ensures that gas used as the counterbalance fluid cannot migrate into, and contaminate, the hydraulic drive fluid. More importantly, pressurised gas cannot migrate into the hydraulic drive circuit and cause the lift to₅ rise in an uncontrolled manner. 6) The positioning of all the main sealing components at the location where the piston rode emerges from the fixed part of the drive unit allows ready inspection and replacement of these sealing components, and does not require the removal of the piston rod itself.

Many variations to the system above described will present themselves to those skilled in the art. For example, as stated above, the invention may be applied to lifting or support systems other than lifts or elevators and may be incorporated in other lifting systems.

Claims

Y) An operating unit for a lift, said operating unit having a first chamber to receive pressurized hydraulic fluid to effect raising and lowering; a second fluid-filled chamber to at least partially counterbalance a load applied to said lift; and a sealing arrangement positioned and operable to prevent the exchange of fluids between said first and second chambers, said operating unit being characterised in that:

said sealing arrangement has a first sealing component in contact with said first chamber; a second sealing component in contact with saido second chamber; and a cavity between said first and second sealing components which is maintained at a pressure below the pressure in either said first chamber or said second chamber.

2) An operating unit as claimed in claim 1 wherein said cavity is vented to atmosphere. s 3) An operating unit as claimed in claim 1 or claim 2 wherein said first chamber comprises the fluid- filled chamber of an hydraulic ram having an extending piston rod, said second chamber being arranged about said ram such that said piston rod defines, in part, said first chamber and is displaceable within said second chamber. o 4) An operating unit as claimed in any one of claims 1 to 3 wherein said first and second chambers are included in a fixed drive part, said piston rod moveably projecting from said fixed drive part, and wherein said sealing arrangement is located at or adjacent to the position at which said piston rod projects from said fixed drive part. 15

5) An operating unit as claimed in claim 3 or claim 4 wherein said piston rod is tubular and has an inner wall, said sealing arrangement being mounted and configured to sealingly engage said inner wall.

6) An operating unit as claimed in any one of the preceding claims wherein a hollow filler rod is provided within said first chamber to reduce the effective volume thereof, said cavity being in communication with atmosphere via the interior of said filler rod.

7) An operating unit as claimed in any one of claims 1 to 5 wherein a filler rod is provided within said first chamber and wherein the interior of said filler rod conveys said hydraulic fluid, said cavity being in communication with atmosphere by a path around the outside of said filler rod.

8) An operating unit as claimed in any one of claims 1 to 7 wherein the fluid within said second chamber comprises a gas.

9) An operating unit for a lift, said operating unit having a fixed part comprising a first chamber to receive pressurized hydraulic fluid to effect raising and lowering, and a second chamber having a fluid therein to at least partially counterbalance a load applied to said lift; said operating unit further including a sealing arrangement positioned and operable to prevent the exchange of fluids between said first and second chambers, and a piston rod projecting from said fixed part, said operating unit being characterised in that:

said sealing arrangement is located at or adjacent to the position at which said piston rod projects from said fixed part. 10) An operating unit as claimed in claim 9 wherein said sealing arrangement has a first sealing component in contact with said first chamber; a second sealing component in contact with said second chamber; and a cavity between said first and second sealing components which is maintained at a pressure below the pressure in either said first chamber or said second chamber.

11) An operating unit as claimed in claim 10 wherein said cavity is vented to atmosphere.

12) A lift having a load bearing structure and a lift operating unit as claimed in any one of claims 1 to 11.