GB2172373A - Load lifting and support device - Google Patents

Abstract

A load lifting and support device comprising a chamber bounded by walls and two ends which has a piston 24, movable barrier means 30 and a valve 23 located therein which define four compartments. The first compartment 28 is defined by the piston and one end of the chamber (and is filled with a gas). The second compartment 29, which is defined by the piston and the valve, and the third compartment 32, which is defined by the valve and the barrier means, and both filled with a substantially incompressible material. The fourth compartment 33, which is defined by the barrier means and the other end of the chamber, is filled with a gas under pressure. The device is particularly useful as a height adjustment device for chairs and other pieces of furniture. To raise the height, the valve 23 is opened and the gas pressure in compartment 33 lifts the chair. With the valve closed the load is supported by the incompressible fluid in compartment 29. This may be a gel, a thixotropic material or a rheopectic material. The movable barrier may be a floating piston in an adjacent or concentric cylinder. <IMAGE>

Description

SPECIFICATION Load lifting and support device This invention relates to a load lifting and support device and, in particular, to a load lifting and support device which can be incorporated into a piece of furniture, such as a chair, so that its height can be readily adjusted.

It is already known to incorporate gas cylinders having a high internal pressure into, for instance, office chairs to act as height adjustment devices and, indeed, it is estimated that three million chairs are equipped in this way in the UK alone.

In use as a chair height adjustment device, the gas pressure in a cylinder of this type is required to fulfil two roles. First, it must be capable of adjusting the height of the chair and, secondly, it must be able to support the combined weight of the chair seat and its occupant. The force required to lift a chair seat is about 40 Ibs (18 Kg) whereas the force required to support a heavy man and a chair seat could be about 300 Ibs (136 Kg). Thus, it is clear that it is the second "support" role which requires the utilisation of considerable gas pressure and, for this reason, present designs of gas cylinder can have a internal pressure of about 700 p.s.i. (4.8 x 106Pa). Indeed, the high pressure combined with the stroke requirements of such cylinders means that gas cylinders of this type may have a stored energy comparable to that of a powerful air rifle.

The high pressure and amount of stored energy in such gas cylinders makes these cylinders potentially dangerous. For instance, any failure in the cylinder may result in the piston in the cylinder shooting upwards at high velocity or, if the cylinder is taken apart without excercising proper caution, gas under high pressure may be explosively released. Such failures have already resulted in deaths and serious injuries. Also, final safe disposal of these cylinders at the end of their working lives has proved a problem.

It is thus an object of the present invention to provide a load lifting and support device which does not require the utilisation of gas under such dangerously high pressure for efficient operation; thereby removing the risk of serious injury in case of failure of the device and facilitating safe disposal of the device at the end of its working life.

According to the invention there is provided a load lifting and support device comprising a chamber bounded by walls and two ends having a piston, movable barrier means and valve means located therein which define first, second, third and fourth compartments of the chamber; the first compartment, which is defined by the piston and the first end of the chamber being open or closed; the second compartment, which is defined by the piston and the valve means, being filled with a substantially incompressible fluid; the third compartment which is defined by the valve means and the movable barrier means, being filled with a similar material to the second compartment, and the fourth compartment, which is defined by the movable barrier means and the second end, being filled with a gas under pressure, the pressure of the gas being sufficient to force the incompressible fluid through the open valve and thus move the piston away from the valve against a force on the piston which does not exceed a predetermined value, whereby, when the valve is closed, any force on the piston is borne via the incompressible fluid by the chamber walls and the valve.

The movable barrier means may be a free piston or a diaphragm and the substantially incompressible fluid may be a liquid or a gel, or a thixotropic material may be used. The latter would have the advantage of reducing any tendancy to leakage.

Rheopectic material may also be used which would have the advantage of increasing the damping of the system.

It is preferred that the valve means comprises a restrictor valve which limits the rate at which the substantially incompressible fluid flows from the second compartment to the third compartment and vice-versa.

Embodiments of the invention will now be described with reference to the accompanying drawings in which : Figure 1 is a schematic diagram of one embodiment of the invention; and Figure 2 is a schematic diagram of a second embodiment of the invention.

Referring to Figure 1 of the drawings, a load lifting and support device 1 is shown comprising a chamber in the form of an actuator cylinder 2 and a reservoir cylinder 3 located side by side. Cylinders 2 and 3 are joined at one end by a tube containing a valve 5 and at the other end by an open connection 6. Valve 5 has a small orifice to restrict flow of liquid through the valve.

Actuator cylinder 2 contains a piston 7 having a piston rod 9. A seat 10 is supported on the end of piston rod 9 remote from piston 7. Seat 10 is capable of bearing a weight W.

Piston 7 effectively divides cylinder 2 into two compartments 11 and 12. Compartment 11 contains a gas under pressure and compartment 12 contains a liquid.

Reservoir cylinder 3 contains a free piston 13 which effectively acts as a movable barrier dividing cylinder 3 into two compartments 14 and 15. Compartment 14, which communicates with compartment 11 via open connection 6, contains a gas under pressure whereas compartment 15, which communicates with compartment 12 via tube 4 and 5, contains a liquid.

In use, with no weight W located on seat 10, valve 5 is opened which allows liquid to flow at a controlled rate from compartment 15 to compartment 12 or vice-versa. On opening valve 5, the pressurised gas in compartments 11 and 14 expands thus forcing free piston 13 downwards which, in turn, causes liquid to flow through open valve 5 from compartment 15 to compartment 12.

Since liquid is substantially incompressible, the flow of liquid into compartment 12 causes piston 7 to rise so that the increased volume of liquid in cylinder 2 can be accommodated and thus, in turn, causes seat 10 to rise. When seat 10 has risen to the desired height, valve 5 is closed thus fixing seat 10 at the desired height. When a weight W is placed on seat 10, the height of seat 10 remains constant because it is supported by the liquid in compartment 12 which cannot be compressed.

When it is desired to lower seat 10, valve 5 is opened and the downward force exerted by seat 10 and weight W then forces piston 7 downwards which, in turn, causes liquid to flow through valve 5 from compartment 12 to compartment 15. This flow of liquid into compartment 15 causes free piston 13 to rise so that the increased volume of liquid in cylinder 3 can be accommodated and thus causes compression of the gas in compartments 11 and 14. When the seat 10 has been lowered by the desired amount, valve 5 is closed and seat 10 is again supported by the liquid in compartment 12.

Referring to Figure 2, a load lifting and support device 20 is shown comprising an actuator cylinder 21 located vertically above and coaxial with a reservoir cylinder 22. Cylinders 21 and 22, which are of different diameters, are joined by a valve 23.

Valve 23 has a small orifice to restrict flow of liquid through the valve.

Actuator cylinder 21 contains a piston 24 having a piston rod 26. A seat 27 is supported on the end of piston rod 26 remote from piston 24. Seat 27 is capable of bearing a weight W.

Piston 24 effectively divides cylinder 21 into two compartments 28 and 29. Compartment 28 contains a gas under pressure and compartment 29 contains a liquid.

Reservoir cylinder 22 contains a diaphragm 30 which is fixed at its edges to the upper rim 31 of cylinder 22. Diaphragm 30 acts as a barrier dividing cylinder 22 into two compartments 32 and 33.

Compartment 32, which communicates with compartment 29 through valve 23 is filled with liquid whereas compartment 33 contains a gas under pressure.

In operation, with no weight W on seat 27, valve 23 is opened which allows liquid to flow at a controlled rate from compartment 32 to compartment 29 or vice-versa. On opening valve 23, the pressurised gas in compartment 33 expands thus pushing diaphragm 30 upwards. This causes liquid to flow from compartment 32 through open valve 23 into compartment 29 which, in turn, forces piston 24 to rise so that the increased volume of liquid in compartment 29 of cylinder 21 can be accommodated and this, in turn, causes seat 27 to rise. When seat 27 has risen to the desired height, valve 23 is closed thus fixing seat 27 at the desired height.

When a weight W is placed on seat 27, the height of seat 27 remains unchanged because the combined weight of W and the seat is supported by the liquid in compartment 29 which is incompressible.

When it is desired to lower seat 27, valve 23 is opened and the downward force exerted by seat 27 and weight W forces piston 24 downwards which, in turn, forces liquid to flow through valve 23 from compartment 29 to compartment 32. This flow of liquid into compartment 32 causes diaphragm 30 to bow downwards to accommodate the increased volume of liquid and thus causes compression of the gas in compartment 33. Once the seat has descended to the desired level, valve 23 is closed and seat 27 is again supported by the liquid in compartment 29.

From the foregoing description of the preferred embodiments, it is apparent that the weight of the seat and the weight W is supported by the liquid and that the gas merely serves to lift the unloaded seat. Thus, it is unnecessary to have gas under such a high pressure as in known gas cylinders and, in practice, a gas pressure of approximately one seventh of that existing in conventional devices has been found sufficient to fulfil the unloaded seat lifting function.

Of course, the pressure in the liquid will be exactly which it was in the gas for equal support cyi- inder internal diameters. However, since liquids are to all intents and purposes incompressible, they do not possess stored energy in the way that a compressed gas does and they do not expand when the pressure is released. Thus, liquids under high pressure are not as potentially dangerous as gases under high pressure and failure in devices according to the invention will not present the same risk of serious injury as conventionai "all-gas" devices.

Moreover, the provision of a restrictor valve in the liquid part of the system ensures that the liquid never flows at a high rate and thus limits the rate at which the actuating piston can travel.

It should be noted that, although the present invention has been described in terms of its use as a height adjustment device for a chair or similar piece of furniture, it could be used in any situation where it is necessary to raise a relatively small load and then support a larger load at a selected height. For instance, it could also be used to raise the boot covers and tailgates of cars and then hold the boot cover or tailgate in the open position.

It will of course be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope and spirit of the invention.

For instance, in the first embodiment, cylinders 2 and 3 have been shown standing side by side for the sake of clarity but they could be located concentrically. Also, the provision of open connection 6 is optional and its absence does not affect the operation of the deivce. In both embodiments, compartments 11 and 28 are described as being filled with gas under pressure. However, this gas could be at atmospheric pressure or, indeed, these compartments could be open to the atmosphere without affecting the operation of the device.

When a gel-like material or a thixotropic material is used, this may have the added advantage that a small amount thereof may form a seal above the piston.

The predetermined value of the force which is mentioned above is to be predetermined in accordance with the intended use of the device. For example, if it is to be used in a chair, a predetermined force is to be selected which depends on the weight of the seat borne by the device, which may for example be of the order of 15,20, or 25 kg.

It has been found that if the piston rod is pulled up rapidly or pulled up manually beyond its normal range of adjustment, a vacuum is created between the upper surface of the fluid and the lower surface of the piston. The presence of a vacuum at this point may allow some of the fluid to evaporate and this may take some time to recondense. Consequently, when a weight is subsequently applied to the piston rod, the weight is not immediately rigidly supported at the desired height but, in fact, may drop slightly because of the presence of the evaporated fluid between the piston and fluid thus producing "sponginess" in the system.

This "sponginess" may be overcome by having the piston rod merely resting on the piston rather than attached to it so that when the rod is pulled upwards, the piston remains on top of the fluid and thus no vacuum is created between the piston and fluid. This arrangement will not affect the normal operation of the device as previously described, however, an alignment device will be required to ensure that the free piston rod does not stray from its course and thus buckle.

Stops may be located within the chamber so that the piston can never be pulled beyond its normal range of adjustment.

Claims (11)

1. A load lifting and support device comprising a chamber bounded by walls and two ends having a piston, movable barrier means and valve means located therein which define first, second, third and fourth compartments of the chamber; the first compartment, which is defined by the piston and the first end of the chamber being open or closed; the second compartment, which is defined by the piston and the valve means, being filled with a substantially incompressible fluid; the third compartment, which is defined by the valve means and the movable barrier means, being filled with a similar material to the second compartment, and the fourth compartment, which is defined by the movable barrier means and the second end, being filled with a gas under pressure, the pressure of the gas being sufficient to force the incompressible fluid through the open valve and thus move the piston away from the valve against a force on the piston which does not exceed a predetermined value, whereby, when the valve is closed, any force on the piston is borne via the incompressible fluid by the chamber walls and the valve.

2. A device according to Claim 1 in which the movable barrier means comprises a diaphragm.

3. A device according to Claim 1 in which the movable barrier means comprises a free piston.

4. A device according to any preceding claim in which the substantially incompressible fluid is a thixotropic material.

5. A device according to any one of Claims 1 to 3 in which the substantially incompressible fluid is a gel.

6. A device according to any one of Claims 1 to 3 in which the substantially incompressible fluid is a liquid.

7. A device according to any one of Claims 1 to 3 in which the substantially incompressible fluid is a rheopectic material.

8. A device according to any preceding claim in which the valve means comprises a restrictor valve, which limits the rate at which the substantially incompressible fluid flows from the second compartment to the fluid compartment and viceversa.

9. A load lifting and support device substantially as hereinbefore described and with reference to the accompanying drawings.

10. An article of furniture including a load lifting and support device according to any preceding claim.

11. A variable-height seat chair in which the height of the seat is controlled by a device according to any of Claims 1-8.