Although the following description is provided with almost exclusive reference to domestic elevators, it will be appreciated from the foregoing and the description of the invention hereunder provided that the elevator of the invention may be provided in environments other than domestic environments, and furthermore the components of the invention may simply be enlarged to allow the elevator to be used in alternate environments.

Currently, the majority of domestic elevators are hydraulically driven. The elevator cabin is securely attached to the upper free end of a ram, the piston end of which is provided within a cylinder into which hydraulic fluid, most commonly oil, is introduced under pressure. The cylinder is rigidly secured to the base of the elevator shaft in which the cabin travels, and a screw pump, which may also be provided in the shaft, but is more commonly in a location remote from the shaft to reduce noise transmission within the premises in which the elevator is installed, communicates through piping with an inlet port commonly provided at the base of the cylinder.

The compressibility of oil necessitates a valve/venting arrangement which controls the flow rate oil into the cylinder. This is essential when it is considered that the compression of the oil within the cylinder is often significant enough to result in an appreciable increase or decrease in the height of the elevator cabin adjacent a particular floor when persons alight from or step into the cabin.

Such a valve arrangement or other suitable fluid compression compensation system is commonly employed to prevent the unnecessary alarming of passengers within the elevator. The problem is further exacerbated by the fact that the compressibility characteristics of oil depend on its ambient temperature. In many cases, complex electronics is required to control a compensating mechanism which communicates with the pump motor to control the flow rate of oil into and from the cylinder to ensure that the elevation of the cabin above a certain datum level is not adversely affected by a sudden increase or decrease in the load carried by the cabin, and also to ensure that the acceleration and deceleration of the cabin proximate a floor are gradual.

In elevators of the type described above, the combination of an oil screw pump together with an fluid compressibility compensating arrangement usually necessitates a large housing which is remote from the elevator shaft, and the size of this housing unit often presents a construction and/or a location problem. These problems are exacerbated when it is considered that the diameter of the cylinders and pistons contained therein are often of the order of 30cm or more, and therefore the volume of fluid required to effect the actuation of the pistons and ultimately the elevator cabin is concomitantly large. This necessitates that the screw pump draws oil from a tank which must be of sufficient capacity to ensure that the required extent of travel of the cabin can be achieved. Accordingly, the screw pump is commonly submerged within the tank and surrounded by the oil, which presents a pump design problem because oil ingress into the pump must be prevented, except in the region of the oil inlet.

It must be pointed out at this stage that this configuration for lift cabin actuation is inherently disadvantaged because a specific hydraulic cylinder has to be manufactured for each and every elevator installation, and each cylinder must be provided with a specific screw pump together with a fluid compressibility compensation mechanism in communication with, and commonly provided within a tank of sufficient capacity to ensure effective operation of the elevator. Henceforth, elevator design and installation has heretofore been inherently complex.

The use of oil as a fluid is further disadvantaged in that oil is flammable and presents a fire hazard, especially in domestic installations, and therefore stringent British and European standards require compliance as regards ventilation and temperature control at the location of the screw pump and tank. These requirements necessarily increase the cost of the installation.

A further disadvantage of the elevator configuration described above arises from the fact that the elevator cabin is supported by what is essentially a strut in static engineering terms, in the form of a piston ram. Henceforth, not only is the likelihood of compressive failure to be assessed at the design stage, but also the possibility that the ram may buckle must be assessed. To ensure that the ram fails by neither of these mechanisms in practice, large factors of safety are built into the cylinder, piston and ram during their construction resulting most simply in an increased diameter thereof.

It will be appreciated that the overall cost of the elevator is increased both at the design stage as further calculations are required, and at the manufacturing stage because more material is required to construct the cylinder. A larger cylinder in turn necessitates a larger tank from which oil is pumped into said cylinder and a larger pump to effect the same speed elevation of the cabin.

Furthermore, it has been shown that a larger capacity cylinder reduces the efficiency of the fluid compressibility compensation device, and in some cases it is necessary to add weight to the cabin to ensure the correct operation of the compensation device.

The extent of travel of many elevators requires the use of a telescopic piston arrangement comprising a cylinder from which a telescopic ram extends in a number of predetermined sections. It will be appreciated that these are costly devices, and any marginal increase in their diameter gives rise to a disproportionate increase in their cost.

It is an object of the invention to provide an elevator configuration which substantially mitigates the abovementioned disadvantages.

According to the present invention there is provided an elevator construction comprising an hydraulic piston and cylinder arrangement and an elevator cabin adapted to move within a shaft of a building, said piston being provided with a ram which is optionally telescopic, characterised in that the ram is secured to a fixed location in the upper region of the shaft, the cylinder and piston arrangement depending therefrom and in that the cylinder is secured to the cabin, the introduction of fluid into the cylinder causing the cylinder, and thus the cabin to rise relative to the fixing of the ram.

Preferably the ram is telescopic.

Preferably the fluid is introduced to the cylinder through a fluid inlet port in the ram.

The configuration described above is of particular advantage over existing elevator configurations when it is considered firstly that the propensity for the ram to fail by buckling is removed because the ram now carries only tensile forces. Henceforth, reduced diameter components can be used in the construction of the piston and cylinder arrangement without compromising the safety of the device. Furthermore, slight lateral movement of the cabin can be tolerated far more effectively when the ram is in tension-such movement was previously of great concern to designers because it increased the probability of buckling failure when the ram was in compression.

Secondly, the increased flexibility of the piston and cylinder arrangement provided by the reduced dimensions allows for the mass production of such arrangements, and the possibility of providing piston and cylinder arrangements which satisfy range of operating conditions, such as load carrying capacity and required extension. Such flexibility has heretofore been unachievable. The elevator configuration of the invention allows a single cylinder and piston arrangement to be used for elevator shafts of different depths with little modification.

A specific embodiment of the invention is now described by way of example only with reference to the accompanying diagrams wherein: Figure 1 shows a sectional view of a telescopic cylinder and piston arrangement for use in the invention; Figure 2 shows a perspective schematic view of the elevator configuration according to the invention; Figures 3A, 3B shows sectional views of the cylinder of Figure 1 at different extensions, and Figure 4 shows a schematic representation of a circuit diagram indicating the fluid transfer system with the pump of the invention used in conjunction with a telescopic hydraulic cylinder to actuate an elevator cabin.

Referring firstly to Figure 1, there is shown a telescopic cylinder and piston arrangement 2 provided with an outer cylinder 4, an intermediate cylinder 6 which has a piston head 8 and a cylinder body 10 in which is disposed a further piston head 12 attached to an inner ram 14. The inner ram 14 is provided at one end with attachment means 16 through which may pass a bolt, pin or the like (not shown) by which the piston and cylinder arrangement may secured to a suitable location within a lift shaft. A further attachment means 17 is provided on a base portion 44 of the outer cylinder for securing same to an elevator cabin. In accordance with the invention, this location is in the upper region of the lift shaft and the piston and cylinder arrangement 2 depends from said location as shown clearly in Figure 2.

Outer cylinder 4, cylinder body 10, and inner ram 14 are provided with fluid inlet ports 18,20,22 respectively through which fluid passes to effect the overall extension and contraction of the arrangement. In one embodiment the majority of the fluid is introduced through port 22 and flows into a cavity 24 defined therein by the walls of the ram 14. Said cavity 24 is in communication with a valve arrangement 26 and additionally fluid passage 28 which links the cavity 24 with a further cavity 30 defined by the walls of the intermediate cylinder 6. An annular seal 32 contacts the inner walls of said intermediate cylinder to prevent fluid in the cavity 30 from escaping into a lower cavity 34 bounded by the intermediate cylinder walls, the piston head 8, and the lower region of the valve arrangement 26.

The cavity 34 communicates through a fluid passage 36 with a cavity 38 defined by the walls of the outer cylinder 4. A further annular seal 40 provided on the piston head 8 of the intermediate cylinder 6 to prevent fluid leakage from the cavity 38 into a lower cavity 42 defined by the walls of the outer cylinder, its base 44 and the lower surface of the piston head 8.

It will be instantly appreciated from the above that the actuation of the piston and cylinder arrangement 2 is in opposite manner to conventional piston and cylinder arrangement. In the arrangement of Figure 2, hydraulic pressure is exerted on the upper surfaces of the piston heads 8,12 on annular surfaces 46,48 thereof around the intermediate cylinder 6 and the ram 14 respectively, and on further annular surfaces 50,52 provided in the upper regions of the intermediate cylinder 6 and the outer cylinder 4. In a conventional piston and cylinder arrangement, fluid is commonly introduced at the base of the cylinder and exerts pressure on the entire face of a piston disposed within the cylinder to effect actuation thereof.

Henceforth, as fluid is introduced into the cavity 24, it is urged both through the fluid passage 28 into the cavity 30. The valve 26 operates to ensure that the fluid flow rates into the cavity 30 and into the cavity 38 through fluid passage 36 from cavity 34 are balanced such that extension and retraction of the piston and cylinder arrangement is smooth and that during such extension and retraction, both intermediate cylinder 6 and outer cylinder 4 move proportionate distances to effect such smooth motion. Additionally, valve 26 acts to prime the cylinder with fluid when the entire arrangement is in its fully retracted position due to the abutment of valve main stem 27 with piston 8.

It should be mentioned that according to the invention, the ram 14 is fixed whereas the intermediate cylinder 6 and the outer cylinder 4 can be displaced relative thereto, and therefore the increase in the volume of fluid in the cavities 30,34 (and 38 which cavity is effectively the same as cavity 34 because of the communication betwixt same at 36) serves to increase the distance between surfaces 46 and 50, and 48 and 52 respectively thus decreasing the overall length of the piston and cylinder arrangement. This retraction of the piston and cylinder arrangement is shown clearly in Figures 3A and 3B.

It should also be noted that the cylinder retraction is effected by means of equal displacement when fluid is entered into cavity 24 through interconnecting port 28 into cavity 30 thus retracting the cylinder.

Referring now to Figure 2, which it is to be emphasised is schematic to facilitate the understanding of the invention, a piston and cylinder arrangement 60 depends from a universal beam section 62 to which a ram 64 is secured by suitable means not shown. The piston and cylinder arrangement 60 is ideally of the type described above in relation to Figure 1. The ram 64 is provided with a piston head (not shown) disposed within an intermediate cylinder 66, which is in turn provided with a piston head disposed within an outer cylinder 68. Hydraulic fluid is introduced into the ram 64 through a fluid inlet port 70.

The outer cylinder is provided with a mounting 72 on which seats or to which is secured by suitable means an elevator cabin 74 capable of vertical movement within an elevator shaft indicated generally by 74 in which said cabin is disposed. A front portion 76 of the shaft is provided intermittently with sliding doors 78 through which persons enter and exit the lift cabin 74, which is itself provided with sliding doors (not shown) in the portion thereof facing the said portion 76.

As fluid is introduced by pumping or other suitable means into the ram 64, the intermediate cylinder 66 and outer cylinder 68 rise in unison and the overall length of the piston and cylinder arrangement 60 is reduced as described above. This retraction causes the elevator cabin 74 to be raised relative to the universal beam 62 within the shaft 74.

It is to be noted that the hydraulic actuation of the piston and cylinder arrangements described is superior to that of conventional arrangements because the effective area over which the hydraulic pressure acts, being the annular surfaces described in relation to Figure 1, is less than the piston head surface in a conventional arrangement. Henceforth the ability of the cylinder according to the invention to raise and lower greater cabin loads is improved because of the greater hydraulic (mechanical) advantage achieved.

Referring finally to Figure 4, there is shown a fluid transfer system 100 comprising a fluid transfer unit 102 of the type described in greater detail in our co-pending patent application No.

GB9826455.9 and having a compressible fluid 104 provided therein to aid expulsion of hydraulic fluid 106 also provided therein. The hydraulic fluid 106 passes through a stop valve 108 and/or optionally an emergency lowering valve 110 which may be manually operated with a lever 112. The fluid then passes through a pressure compensated fixed flow control valve 114 and into a telescopic pulling cylinder 116 of the type described both above and in more detail in our co-pending patent application No. GB9826452.6.