GB1575307A

GB1575307A - Hydraulic lifting apparatus including a hydropneumatic spring arrangement

Info

Publication number: GB1575307A
Application number: GB1516976A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-02-25
Filing date: 1977-02-25
Publication date: 1980-09-17

Description

(54) HYDRAULIC LIFTING APPARATUS INCLUDING A HYDRO-PNEUMATIC SPRING ARRANGEMENT (71) I, MARTIN RICHARD PACK ER, a British Subject, of 3 Cherington Close, Handforth, Wilmslow, Cheshire, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns hydraulic lifting apparatus including a hydro-pneumatic spring arrangement of the kind (hereinafter called "of the kind described") comprising a hydro-pneumatic accumulator the liquid side of which is connected to the cylinder of a hydraulic ram.

In such apparatus it is normal for the liquid connection between the accumulator and the ram to be permanently-open circuit, so that the ram is constantly subjected to the influence of the accumulator.

The present invention is based upon the appreciation that the characteristics of or operation of the ram can be modified in a very simple way by acting upon or controlling the said liquid connection, and that by appropriate development of this possibility one can produce equipment which is of particular utility in certain operations from the environment in which it is employed.

Pursuant hereto the invention provides hydraulic lifting apparatus comprising loadcarrying means adapted for a load to be suspended therefrom, a ram connected to the load-carrying means for up-and-down movement of the load relative to the apparatus to cause corresponding relative movement between a piston and a cylinder of the ram, a hydropneumatic accumulator connected by its fluid side to the cylinder of the ram by way of a valve, and having its gas side connected to a source of pressurised gas, a fluid store coupled with the cylinder of the ram by a respective valve, a pump connected to the load-carrying means and adapted, upon said up-and-down movement of the load to pump fluid from a reservoir to the fluid store, and control means responsive to a control effect, to operate to close the valve between the accumulator and the ram, and to open the valve between the fluid store and the ram, thereby to cause actuation of the ram by fluid from the store.

The apparatus of the invention may be a device used in an environment wherein the motion of waves influences working operation, for example the loading or unloading of a supply ship or barge, or the like, at a stationary off-shore structure. Accordingly the said means may be adapted to sense up and down movement of a floating body.

In such a practical use, the apparatus will, for example, be incorporated into, or attached to a load-carrying cable of, a crane in such a way that the spring arrangement operates to ensure that the load-carrying cable of the crane is maintained under a near constant slight tension even though the load rises and falls with a wave motion relative to the crane, e.g. by means of the load being in a floating boat or vessel.

It will readily be understood that it would be quite practical to adopt a mode of operation in which a signal is generated to close the valve in the connection between the accumulator and the ram when the load has been raised substantially to a maximum height at the crest of a wave, so that the load will no longer be able to fall again with the wave motion but will be taken up and supported by the crane.

In order that the invention may be fully understood, it will be described further, by way of example, with reference to the accompanying drawing in which the single figure is a schematic diagram illustrating a preferred embodiment of lifting apparatus constructed in accordance with the invention.

As shown in the drawing, the preferred apparatus of the invention comprises a sealed housing, indicated generally at 10, from which a ram piston rod 11 of a hydraulic lifting ram 12 projects vertically downwards, this rod 11 having a hook 13 on its lower end for carrying a load as indicated schematically at 14. Space 15 in cylinder 16 of the ram 12, below ram piston 17, is connected via a compensate valve 18 to the liquid side of a hydro-pneumatic accumulator 19, the gas side of which is connected to a high-pressure nitrogen source 20.

It will readily be understood that, with the accumulator 19 having an appropriate volumetric capacity, and with the housing 10 suspended from the cable of a crane (not shown) mounted in a stationary environment such as an offshore oil rig, and with a rising and falling load 14 (such as an item of cargo on a ship, not shown, alongside the rig) connected to the hook 13, the accumulator 19 operates to ensure that the piston 17 and hook 13 are caused to rise and fall in synchronism with the rise and fall of the load 14, maintaining a substantially constant tension in the crane cable from which the housing 10 is suspended.

For deriving energy from the wave motion causing the load (and ship) to rise and fall, the piston rod 11 is connected mechanically to a piston rod 21 of a heaving pump indicated generally by numeral 22. This mechanical connection is shown as being by way of an extended cross bar 23 in the drawing, but it has been illustrated in this way simply for ease of understanding in the diagrammatic drawing. In practice, the heaving pump 22 will be positioned closely adjacent the hydraulic lifting ram 16, and there will be only a short mechanical connection therebetween.

Space 24 below pump piston 25 in pump cylinder 26 is connected, by way of a non-return valve 27, to space 28 beneath store piston 29 of an energy store cylinder 30. In turn, space 31 in the store cylinder 30 above the store piston 29 is connected to a nitrogen cylinder 32 whereby the piston 29 is loaded with nitrogen at very high pressure.

Store piston rod 33 projects downwards out of the cylinder 30 and has an actuator cam or lobe 34 on its bottom end.

The space 28 below the store piston 29 is, in turn, connected by way of a lift valve 35 in the space 15 in the cylinder 16 of the lifting ram 12 below the lifting piston 17.

A sealed hydraulic fluid reservoir 36, embodying a pressurising bladder 37 filled with nitrogen at a relatively low pressure thereby to impose a correspondingly low pressure on the fluid contained therein, is connected in the space 24 below the pump piston 25 by way of a non-return valve 38.

Also embodied in the compensator, in a manner which will be evident from consideration of the drawing and the following description of the operation of the compensator, are a normally-closed "store-full" valve 39, an intermediate valve 40 effective to prevent fluid flow from the store-full valve 39 to a normally-closed wave top valve 41 when the pump piston 25 is moving downwards to supply pressure to said valve 40, a lift decay valve 42, a reset valve 43, a variable pilot decay choke or throttle 44 and a lift decay choke or throttle 45.

The wave top valve 41 is adjustable in its vertical disposition according to wave height, as will readily be understood from the following description, so that upon each rising of the load 14 and corresponding movement of the pump rod 21, at the top of the rising movement, a wave cam 46 on the pump rod 21 engages with and actuates the wave top valve 41.

Assuming the housing 10 to be suspended substantially stationarily as described, and the load 14 to be rising and falling as already described above, the heaving pump 22 will, of course, draw low pressure hydraulic fluid from the reservoir 36 and supply it into the store cylinder 30 thereby causing the store piston 29 gradually to rise, the rod 33 rising correspondingly. Upon the store cylinder 30 becoming full, the cam or lobe 34 actuates the store-full valve 39 to open the latter thereby enabling fluid to flow via the intermediate valve 40 (whilst the latter is not held closed by pressure from the pump 22) to the wave top valve 41.The spring loading of the valve 40 is sufficient to overcome the suction pressure created in the pump chamber 24 by the reservoir 36, but is insufficient to overcome the pressure generated by the pump 22 against the back pressure created by the gas pressure in the chamber 31.

Upon the next rising of the load 14 and corresponding movement of the pump rod 21, at the top of the rising movement, the wave cam 46 on the rod 21 actuates the wave top valve 41, thereby to open the latter and permit fluid to flow to the lift valve 35 which in turn opens the space 28 in the energy store cylinder 30 to the space 15 in the ram cylinder 16. The wave top valve 41 also supplies fluid to the compensated valve 18 to close off the space 15 from the accumulator 19.

Thus, it will readily be understood that upon the energy store, represented by the cylinder 30, becoming effectively filled with energy derived from the wave motion by way of the heaving pump 22, the store-full valve 39 is actuated and makes the apparatus ready for lifting the load 14. Then, as soon as the load 14 rises to the apex of its wave motion, the wave top valve 41 operates to interrupt the connection between the accumulator 19 and the ram 12, so that the action 12 is modified to prevent the load falling again concomitant with a falling portion of the wave motion and simultaneously to release energy into the space 15 in the cylinder 16 of the ram 12 so as to raise the hook 13 and load 14 relatively to the wave motion therebelow.

Accordingly, the apparatus operates automatically: (a) firstly to enable the load 14 to follow the wave motion of whatever is supporting it; (b) simultaneously to supply energy to the energy store, this energy being derived freely from the wave motion; and (c) upon the energy store becoming adequately charged, to arrest the reciprocation of the piston 17 of the ram 12 at a wave top; (d) and also to supply energy to the ram 12 from an external source, thereby to ensure that the load is lifted from the wave top position.

Lifting of the load having been effected automatically at the top of a wave, the load can then be appropriately manoeuvred in the usual way with the crane and can be deposited where required.

The opening of the valve top valve 41 by the cam 46 when the store 30 is full serves, of course, also to supply fluid to the lift decay valve 42 which, accordingly, permits slow decay of pressure from the space 15 of the cylinder 16 of the lifting ram 12 to commence simultaneously with opening said space 15 to the energy store cylinder 30, so that upon the load having been raised off the top of a wave by the force derived from the energy store 30 and whilst the load is being manoeuvred by conventional operation of the crane. the piston 17 of the lifting ram 12 will fall back slowly to its lowermost position. This can, of course, be dealt with in the operation of the crane.

It will be understood that when the lifting ram piston 17 and the load 14 are raised by the energy derived from the energy store 30, the reset valve 43 will be closed by reason of it being engaged by the wave cam 46.

However, upon the piston 17 falling back as above discussed, and the rod 21 being lowered correspondingly, the reset valve 43 eventually becomes open (when the wave cam 46 disengages therefrom) whereupon the lift decay valve 42 is open and the entire apparatus is reset and is ready for a next subsequent lifting operation which can take place in the manner above discussed.

Naturally, the invention is not confined to the precise details of the foregoing example, and variations may be made thereto.

In the described embodiment, the wave top valve 41 is adjustable in height, relative to the position of the cam 46 on the piston rod 21, but of course it would be equally possible to arrange for the cam 46 to be adjustable axially along the piston rod 21 to ensure that the wave top valve 41 is opened only at the top of the stroke of the rod 21, in correspondence with the crests of the waves acting on the load 14.

Naturally, it would be possible to make the cam 46 and/or the wave top valve 41 self-adjusting automatically according to the prevailing wave heights during use of the apparatus. Thus, for instance, the valve 41 could be mounted so as to tend to sink to a lowermost or rest position and to be displaceable upwards, against the influence of a damper whose effect progressively increases with increase in height of the valve 41, upon being engaged by the cam 46, so that the cam 46 will tend to nudge the valve 41 upwards into an operative position correlated to wave height. Naturally, a reverse arrangement in which the cam 46 is displaceable downwards on the piston rod 21 from an uppermost position against the effect of a damper, can be employed to the same effect.

Obviously, the invention is not confined to wave motion compensators and can be applied to any hydraulic lifting apparatus wherein modification of or arresting of spring action of an accumulator and ram is required for any purpose, and the arrangement can include means for sensing any variable parameter and to close off the connection between the accumulator and the ram when that parameter reaches a predetermined value.

WHAT 1 CLAIM IS: 1. Hydraulic lifting apparatus comprising load-carrying means adapted for a load to be suspended therefrom, a ram connected to the load-carrying means for upand-down movement of the load relative to the apparatus to cause corresponding relative movement between a piston and a cylinder of the ram, a hydropneumatic accumulator connected by its fluid side to the cylinder of the ram by way of a valve, and having its gas side connected to a source of pressurised gas, a fluid store coupled with the cylinder of the ram by a respective valve, a pump connected to the loadcarrying means and adapted, upon said up-and-down movement of the load to pump fluid from a reservoir to the fluid store, and control means responsive to a control effect, to operate to close the valve between the accumulator and the ram, and to open the valve between the fluid store and the ram, thereby to cause actuation of the ram by fluid from the store.

2. Apparatus as claimed in claim 1 wherein the control means is adapted to operate only when the fluid store is full.

3. Apparatus as claimed in claim 1 or 2 wherein the pump is a piston pump, the control effect being the movement of the piston of the pump into an end position

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. portion of the wave motion and simultaneously to release energy into the space 15 in the cylinder 16 of the ram 12 so as to raise the hook 13 and load 14 relatively to the wave motion therebelow. Accordingly, the apparatus operates automatically: (a) firstly to enable the load 14 to follow the wave motion of whatever is supporting it; (b) simultaneously to supply energy to the energy store, this energy being derived freely from the wave motion; and (c) upon the energy store becoming adequately charged, to arrest the reciprocation of the piston 17 of the ram 12 at a wave top; (d) and also to supply energy to the ram 12 from an external source, thereby to ensure that the load is lifted from the wave top position. Lifting of the load having been effected automatically at the top of a wave, the load can then be appropriately manoeuvred in the usual way with the crane and can be deposited where required. The opening of the valve top valve 41 by the cam 46 when the store 30 is full serves, of course, also to supply fluid to the lift decay valve 42 which, accordingly, permits slow decay of pressure from the space 15 of the cylinder 16 of the lifting ram 12 to commence simultaneously with opening said space 15 to the energy store cylinder 30, so that upon the load having been raised off the top of a wave by the force derived from the energy store 30 and whilst the load is being manoeuvred by conventional operation of the crane. the piston 17 of the lifting ram 12 will fall back slowly to its lowermost position. This can, of course, be dealt with in the operation of the crane. It will be understood that when the lifting ram piston 17 and the load 14 are raised by the energy derived from the energy store 30, the reset valve 43 will be closed by reason of it being engaged by the wave cam 46. However, upon the piston 17 falling back as above discussed, and the rod 21 being lowered correspondingly, the reset valve 43 eventually becomes open (when the wave cam 46 disengages therefrom) whereupon the lift decay valve 42 is open and the entire apparatus is reset and is ready for a next subsequent lifting operation which can take place in the manner above discussed. Naturally, the invention is not confined to the precise details of the foregoing example, and variations may be made thereto. In the described embodiment, the wave top valve 41 is adjustable in height, relative to the position of the cam 46 on the piston rod 21, but of course it would be equally possible to arrange for the cam 46 to be adjustable axially along the piston rod 21 to ensure that the wave top valve 41 is opened only at the top of the stroke of the rod 21, in correspondence with the crests of the waves acting on the load 14. Naturally, it would be possible to make the cam 46 and/or the wave top valve 41 self-adjusting automatically according to the prevailing wave heights during use of the apparatus. Thus, for instance, the valve 41 could be mounted so as to tend to sink to a lowermost or rest position and to be displaceable upwards, against the influence of a damper whose effect progressively increases with increase in height of the valve 41, upon being engaged by the cam 46, so that the cam 46 will tend to nudge the valve 41 upwards into an operative position correlated to wave height. Naturally, a reverse arrangement in which the cam 46 is displaceable downwards on the piston rod 21 from an uppermost position against the effect of a damper, can be employed to the same effect. Obviously, the invention is not confined to wave motion compensators and can be applied to any hydraulic lifting apparatus wherein modification of or arresting of spring action of an accumulator and ram is required for any purpose, and the arrangement can include means for sensing any variable parameter and to close off the connection between the accumulator and the ram when that parameter reaches a predetermined value. WHAT 1 CLAIM IS:

1. Hydraulic lifting apparatus comprising load-carrying means adapted for a load to be suspended therefrom, a ram connected to the load-carrying means for upand-down movement of the load relative to the apparatus to cause corresponding relative movement between a piston and a cylinder of the ram, a hydropneumatic accumulator connected by its fluid side to the cylinder of the ram by way of a valve, and having its gas side connected to a source of pressurised gas, a fluid store coupled with the cylinder of the ram by a respective valve, a pump connected to the loadcarrying means and adapted, upon said up-and-down movement of the load to pump fluid from a reservoir to the fluid store, and control means responsive to a control effect, to operate to close the valve between the accumulator and the ram, and to open the valve between the fluid store and the ram, thereby to cause actuation of the ram by fluid from the store.

when the fluid store is full.

4. Apparatus as claimed in claim 3 herein the control comprises a store full valve and a respective valve associated with the piston of the pump, which valves, when open, permit liquid under pressure to flow to and operate the valve between the accumulator and the ram and the valve between the fluid store and the ram.

5. Apparatus as claimed in any preceding claim wherein the cylinder of the ram is connected back to the reservoir by way of a decay valve to permit fluid to return to the reservoir from the ram after actuation of said ram by fluid from the store.

6. Apparatus as claimed in claim 4 wherein the control further includes reset valve means also associated with the piston of the pump and operative, in a predetermined position of said piston, to open the valve between the accumulator'and the ram, to close the valve between the fluid store and the ram, and to close the bleed valve.

7. Hydraulic lifting apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.