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(11) | EP 1 054 165 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A hydraulic actuator |
| (57) The invention relates to a hydraulic actuator comprising a chamber (1) in which a
pressurised fluid operates, which chamber (1) is closed by a diaphragm (2) having
a function of acting on at least one external body by exerting thereon a total pressure
of which the actuator is capable. The actuator has a diaphragm (2) which is fixed
to walls of the chamber (1) by a frame (3) predisposed to squeeze the diaphragm (2)
perimetrally against a corresponding seating (4) afforded in the walls. The seating
(4) is constituted by surfaces (40) having a essential characteristic of not being
perpendicular with respect to a direction of pressure of the total resultant pressure
exerted by the diaphragm (2). |
[0001] The invention relates to a hydraulic actuator. In particular, though not exclusively, it is destined to be used in machines able to exert considerable forces.
[0003] The prior art teaches practically only high-force hydraulic presses using cylinders or jacks as actuators. Usually these machines work with oil pressures which rarely go over 400 Bar.
[0004] With hydraulic cylinders or jacks equipping machines dimensioned so as to produce forces of various thousands of tons there are limits relating essentially to the sizes of diameters that can be used. At high pressures the sealing organs interpositioned between the piston and the body liner can fail. What is more, cylinders with too large a diameter can present the problem of not having the right ratios between the arm run and the bore, with a consequent risk of jamming.
[0005] For the above reasons, the prior art teaches that in order to obtain relevant forces a plurality of cylinders will almost inevitably have to be used instead of one large cylinder. This fact leads to considerable complications, both in terms of mass and general machine complexity (with consequently rather high costs). The prior art also includes realisations in which the classical arrangement as described above with mobile and sealed cylinder-piston couplings, is substituted by a system in which the mobile part is constituted by an elastic membrane which hermetically closes a chamber containing the pressurised fluid.
[0006] In these realisations the use of diaphragms associated with the use of the fluid at very high pressures presents very considerable problems.
[0007] A first of these is the difficulty of realizing an efficient seal at the perimeter constraining surfaces where the diaphragm is fixed to the mouth of the closed chamber containing the pressurised fluid.
[0008] A further problem lies in the real risk that the diaphragm, pushed by the pressurised fluid, deforms (due to extrusion) and shifts into the perimetral interstice between the piston or arm body (in contact with the external surface of the diaphragm) and the cavity the piston arm is slidingly housed in. The main aim of the present invention is to obviate the above-described drawbacks in the prior art.
[0010] These aims and advantages and others besides are all achieved by the present invention, as it is characterised in the appended claims.
[0011] Further characteristics and advantages of the present invention will better emerge from the detailed description that follows of some preferred but non-exclusive embodiment of the invention, illustrated purely by way of nonlimiting examples in the accompanying figures of the drawings, in which:
figure 1 is a section of a schematic perspective view;
figure 2 is an enlarged-scale section of a detail of figure 1;
figure 3 is an enlarged-scale section of a detail of figure 1 in a second embodiment.
[0012] The figures illustrate a hydraulic diaphragm actuator comprising a chamber 1 in which a pressurised fluid operates, which chamber 1 is closed by a diaphragm 2 whose function is to act on at least one external body by exerting thereon the maximum pressure of which the actuator is capable.
[0013] In the embodiment illustrated in more detail in figure 2, the diaphragm 2 is fixed to the walls of the chamber 1 along a perimeter which is closed by a frame 3 prediposed to perimetrally squeeze the diaphragm 2 against a corresponding seating 4 afforded on the chamber 1 walls. The seating 4 is constituted by surfaces 40 whose essential characteristic is that they are not perpendicular with respect to the direction of pressure (schematically indicated by the arrow 9) exerted by the diaphragm 2.
[0014] The frame 3 exhibits surfaces 30 by means of which it perimetrally squeezes the diaphragm 2. These surfaces 30 are parallel to the surfaces 40 of the seating 4.
[0015] The inclination of the surfaces 40 and 30 with respect to the direction of pressure indicated by arrow 9 enables the diaphragm 2 to be squeezed between the surfaces 40 and 30 with a retaining pressure which is greater than the pressure with which the most external limbs of the diaphragm are squeezed between the surfaces of the frame 3 and those of the walls of the chamber 1 which are perpendicular to the direction of the arrow 9 (which is also the direction along which the frame 3 is locked on to the walls of the chamber 1). The external surface of the diaphragm 2 is in contact with a piston 5 housed mobile and with a certain degree of play internally of a cylindrical cavity 6, produced from a generatrix which is parallel to the direction of total resultant pressure of which the actuator is capable, with an interpositioning of a layer of diaphragm protector 7 having the task of deforming by compression and closing the perimetral interstice existing between the piston 5 and the cylindrical cavity 6 in which the piston is housed freely slidingly. The protector layer, therefore, has the task of preventing the diaphragm 2 from deforming by extrusion and getting into the perimetral interstice between the piston 5 (in contact with the external surface of the diaphragm 2) and the cylindrical cavity 6 in which the piston is sliding housed.
[0016] In order to prevent dangerous friction between the diaphragm 2 and the piston 5 a thin lubricating and anti-stick layer, constituted by a leaf of teflon 8, is located between the external surface of the diaphragm 2 and the diaphragm protector 7.
[0017] At the perimetral edges of the surface facing the external surface of the diaphragm, the piston 5 exhibits concave connection surfaces 50 for accommodating the convexity of the diaphragm 2.
[0018] The embodiment of figure 3 shows a constructional variant in which with respect to the first embodiment the surfaces of the frame 3 and the walls of the chamber 1 (between which the diaphragm 2 is squeezed) are arranged differently.
[0019] In this embodiment the diaphragm 2 is still fixed to the walls of the chamber 1 along a perimeter which is closed by means of a frame 3; the frame 3 however is predisposed to perimetrally squeeze the diaphragm 2 against a corresponding seating 4' afforded on the walls. The seating 4' is principally constituted by surfaces 41 which essentially have the task of exerting a retaining action against the surfaces 31 afforded on the frame 3.
[0020] The characteristic which typifies both the surfaces 31 and 41 of the seatings 4' and the surfaces 30 and 40 of the seatings 4 is that they are not perpendicular to the direction of the resultant pressure exerted by the diaphragm 2, so that the diaphragm can be gripped with a greater pressure than that by which the diaphragm 2 itself is squeezed between the surfaces of the frame 3 and the surfaces of the chamber 1 walls, which are instead perpendicular to the direction of the arrow 9 (which is also the direction along which the frame 3 is squeezed on the walls of the chamber 1).
[0021] This possibility of multiplying the gripping pressure of the diaphragm by having it retained between inclined surfaces eliminates any oil leakage at high working pressures. Excellent results have been obtained with pressures of close on 700 Bar.
[0023] The piston 5 arm return is guaranteed by appropriate recall springs, not illustrated in the drawings.
[0024] The invention enables actuators to be made having a rectangular or square section and able to deliver exceptionally high pressures, though the actuators are actually very compact.
[0025] This ability to use actuators or jacks having square or rectangular sections, or sections which in any case coincide with the area to be pressed means that it is not necessary to use a large-thickness die plate dividing the pressure between one or more circular actuators or jacks acting on the square or rectangular area to be pressed.
[0026] The diaphragm 2 can be shaped, with the piston 5, so that the resulting form, in a perpendicular plane to the plane the pressure is exerted on, is delimited by the edges of the area on which the pressing action is to be performed. The actuator of the invention also requires a lower oil pressure than what would be necessary to develop a like pressure using a series of cylindrical jacks all applying their pressure on a single large press die plate.
1. A hydraulic actuator comprising a chamber (1) in which a pressurised fluid operates,
which chamber (1) is closed by a diaphragm (2) having a function of acting on at least
one external body by exerting thereupon a pressure corresponding to a total pressure
capacity of the actuator, characterised in that the diaphragm (2) is fixed to walls
of the chamber (1) along a closed perimeter by a frame (3) predisposed to squeeze
the diaphragm (2) perimetrally against a corresponding seating (4, 4') afforded on
the walls; at least said seating (4, 4') being constituted by surfaces (40, 41) which
are not perpendicular to a pressure direction exerted by the diaphragm (2).
2. The actuator of claim 1, characterised in that the frame (3) exhibits surfaces (30,
31) by means of which the frame (3) perimetrally squeezes the diaphragm (2); the surfaces
(30, 31) being parallel to the surfaces (40, 41) of the seating (4, 4').
3. The actuator of claim 2, characterised in that an external surface of the diaphragm
(2) is in contact with a mobile piston (5) housed with play internally of a cylindrical
cavity (6) produced from a generatrix which is parallel to a total resultant direction
of pressure of which the actuator is capable, with an interpositioning of a diaphragm
protector (7) which deforms under squeezing pressure and closes a perimetral space
existing between the piston (5) and the cylindrical cavity (6) in which the piston
(5) is housed.
4. The actuator of claim 3, characterised in that between the external surface of the
diaphragm (2) and the diaphragm protector (7) there is a thin non-stick layer of lubricant.
5. The actuator of claim 4, characterised in that the thin non-stick layer of lubricant
is constituted by a thin sheet of teflon (8).
6. The actuator of claim 5, characterised in that the piston (5) exhibits, at the perimetral
edges of a surface of the piston (5) which faces the external surface of the diaphragm
(2), concave connection surfaces (50) for affording a convex shape assumed by the
diaphragm during operation.
7. The actuator of claim 5, characterised in that the diaphragm (2) exhibits, together
with the piston (5), a shape which in a perpendicular plane to a plane in which the
pressure is totally exerted is delimited by edges of an area on which the pressure
is to be exerted.