By way of example and to facilitate the understanding of the invention, in the accompanying drawings:
By referring to the figures, it is seen that according to a first embodiment of the invention, the hydraulic jack comprises a piston 1 that moves in a cylinder that consists of two co-axial tubes 2 and 3 that provide between them a cylindrical annular space 4.
Said annular space 4 is connected to a compressed gas source 6 through a non-return valve 7, such that the chamber 4 is a closed, airtight space, whereby the pressure of the gas is permanent.
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When compressed hydraulic fluid is introduced into one or the other of the chambers 8 or 9, located on both sides of the piston, which does not comprise a seal, this liquid will intervene between the wall 2 of the cylinder and the outside wall of the piston 1 by creating a counter-pressure that neutralizes the deformation of said wall 2.
If reference is made to
To prevent this, it is advantageously possible to arrange a slight leakage from one to the other of the chambers by a very slight play allowing the presence of a film of oil (or another hydraulic fluid) or else by a spiral groove.
The deformation of the inside tube 2 is based on the thickness of the wall of this tube, the metal that is used, and the pressure of the gas that is blown into the space 4. These parameters are set based on the usage for which the jack is designed.
The extent of the locking force of the piston 1 is based on the pressure of the gas and the size of the surfaces in contact. These parameters will also be set based on the usage for which the jack is designed.
It is therefore possible, thanks to this arrangement:
In addition, it turns out that it becomes possible to produce a jack that is equipped with a piston without a seal because as soon as the pressure of the fluid eliminates the tight clamping of the tube 2 on the piston 1, the latter can move freely, which makes it possible to allow a very slight play between the piston 1 and the tube 2.
With a jack according to
The object of the variant that is illustrated in
In these figures, the same elements bear the same references.
At each of its ends, the piston 1 bears sealing segments 25-26 that are similar to the segments that are used in the internal combustion engines.
Two annular grooves 20 and 21, which are connected to one another via a pipe 22, which communicates with the chambers 8 and 9 of the jack via the anti-return valves 23 and 24 in reversed positions, are provided in these two groups of sealing segments 25 and 26.
The operation of this jack is described below.
In “locked” position (
The piston 1 is then wedged by the tight clamping exerted by the pressure of the gas and can no longer move.
In
The sealing segments 25 and 26 allow one another a slight leakage at the beginning of the exerting of pressure: this leakage, being added to the introduction of compressed liquid via the grooves 20 and 21, facilitates the appearance of a compressed oil film between the wall of the piston 1 and that of the tube 2.
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The piston 30, carried by a rod 31, can slide into a cylinder 32. The piston is hollow and comprises a chamber 32 that is filled with a compressed neutral gas. The wall 30a that surrounds the chamber 33 is relatively thin and deformable: under the action of the pressure of the gas that is found in the chamber 33, this wall 30a deforms and is applied against the inside wall of the cylinder 32 such that the piston is locked.
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To facilitate the forward motion of the compressed hydraulic fluid between the wall 30a and the inside wall of the cylinder, it is possible to engrave small grooves on the wall 30a that facilitate the forward motion of the compressed hydraulic fluid.
In all of the examples that are described, the chambers 4 or 33 are permanently pressurized, closed, airtight spaces, but it is also possible to use a non-return valve such as the valve 7 of the
It is also possible to replace the gas under a set pressure by variable compressed gas or fluid that is controlled by an outside circuit that is connected to the jack.
This type of jack will be used in all of the cases where a jack should hold a load without changing position for a very long period.
By way of nonlimiting example, such a jack can advantageously be used for the positioning of a mobile radar, such that, once the radar is regulated, its position is kept constant.
In all of the examples that are shown, the locking of the piston is achieved by the fact that the gas-filled chamber is airtight and permanently filled with compressed gas, but it is quite obvious that it is possible to achieve the unlocking either by neutralizing the gas pressure via a suitable valve or by replacing the gas pressure by a variable and controlled gas or fluid pressure.
The jack consists of a cylinder 20, into which a piston 21 that is integral with a rod 22 slides.
The piston 21 comprises an annular chamber 23 whose annular wall 24, in contact with the inside wall of the cylinder 20, is elastically deformable.
This annular chamber 23 is linked with the chamber 25 of an hydraulic accumulator 26, placed inside the piston 21.
A mechanical means, constituted by a rod 27 that slides inside the rod 22 of the piston 21, can push back the moving element of the accumulator 26 against its spring 29.
The movement of this rod 27 can be caused by any suitable device, but in the example shown, it is caused by a small piston 28, integral with the rod 27, controlled hydraulically.
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Number | Date | Country | Kind |
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60/07819 | Sep 2006 | FR | national |