EP0287434B1 - Differential hydraulic jack, with a damping device, for operating electric breakers - Google Patents

Abstract

A differential hydraulic jack with a damping system for the control of electric circuit-breakers is provided with a floating ring which produces a damping action at the end of travel and is also provided with a damping extension stud which forms part of the jack piston and penetrates into the damping ring. No provision is made on the jack piston for any packing ring forming a seal with the jack cylinder. The damping ring carries two projecting lips constituting a double valve which forms a leak-tight seal with the bottom face of the jack piston and the internal face of the cylinder end. At the end of the travel of the piston, the damping ring forms a double sealing valve for shutting-off the supply/drain orifice of the jack.

Description

The present invention relates to a differential hydraulic cylinder for controlling electric circuit breakers, of the type in which the annular chamber of the cylinder, defined by the interior surface of the cylinder of the cylinder and by the exterior surface of the outgoing rod of the piston, is permanently connected. to a high pressure hydraulic source.

The outgoing rod of the jack is coupled to the movable contact of the circuit breaker and a supply / bleed orifice, formed in the bottom of the main chamber of the jack, can be selectively connected to said high pressure source (position "Supply") to push the piston, or to a low pressure tank ("Purge" position) to let the piston return to its initial position under the effect of the high pressure P prevailing in the annular chamber.

The first maneuver brings out the piston rod and brings the circuit breaker into the latched or closed position, while the second maneuver brings the rod back into the cylinder and brings the circuit breaker into the tripped or open position.

Such hydraulic controls of the circuit breaker, to the differential cylinder, are well known and have been described for example in French Patent ^No. 2317532 (or U.S. Patent ^No. 4,026,523).

The construction of differential cylinders, for this application, presents constructive difficulties, in particular because they must guarantee a permanent and absolute tightness, for very long periods, despite the very high hydraulic operating pressures P, of the order of 300 to 400 bar.

These jacks must therefore include at least, as shown in the aforementioned prior patent, a first seal at the passage of the outgoing rod through the bottom of the cylinder and a second seal on the piston.

This second packing, preferably of the "spring packing" type, if one wishes to obtain a perfect seal, must withstand severe operating conditions and is therefore of delicate construction.

In the French patent application ^No. 87.04.134 filed March 25, 1987 to the same inventor, there is described a differential cylinder wherein it was possible to remove this seal on the piston, thanks to the combination of the piston with a valve -closing valve for the supply / bleed orifice of the jack at the end of the jack's trigger stroke. In addition, document EP-A-250 619 (Article 54 (3) and (4) of the EPC) discloses a piston without lining associated with a complex valve system intended to ensure the quasi-permanent maintenance of the high pressure under the face of the piston. As for document FR-A-2 181 525, it shows a simple plunger without gasket but illustrates the state of the traditional technique in terms of differential piston by providing a good gasket.

Another difficulty, in the production of hydraulic cylinders for controlling electric circuit breakers, comes from the need for very effective damping of the piston limit switches. Indeed, the piston strokes to be performed in a very short time, of the order of a few hundredths of a second, the maneuvers are very brutal and it is necessary to provide for a deceleration or damping at the end of the piston stroke. This problem is all the more difficult since, in this application, there is only a very short distance (of the order of 20 to 50 mm) for effecting the damping.

Damping systems are already known for hydraulic cylinders comprising a ring mounted floating in the bottom of the cylinder of the cylinder which is engaged in an extension, or damping stud, substantially frustoconical, carried by the piston. At the end of the piston stroke, the section of the annular passage located between the inner surface of the damping ring and the aforementioned extension of the piston decreases, which produces a gradual rolling of the oil contained in the chamber. of the cylinder, between the piston and the bottom of the cylinder carrying the damping ring. This oil rolling dampens the end of the piston stroke.

An example of a floating ring for damping hydraulic cylinder is given, for example, in GB 998 753 (Parker Hannifin) and, more particularly for the specific application to the control of electric circuit breakers, in the aforementioned patent ^No. 2.317 .532.

The known floating ring damping systems function satisfactorily when they are applied to hydraulic cylinders of conventional construction, that is to say in which the piston is provided with a seal. However, care must be taken to ensure that very high overpressures, which appear in the damping chambers or "dash-pot", are not transmitted to the piston piston seals, which would otherwise be quickly put out of order.

This further complicates the construction of the cylinders, especially in the case where, as for the control of electric circuit breakers, one seeks quasi-perfect reliability and a very long service-free life.

However, these known floating ring damping systems would not be applicable to differential cylinders in which the piston does not have a seal, since they would not ensure the permanent tight closure of the supply / bleed orifice. the main chamber of the actuator at the end of the actuation stroke of the actuator. This would result in a permanent oil leak, therefore a permanent oil consumption, during all the periods when the circuit breaker is in the tripped position, which is unacceptable.

The object of the present invention is to remedy these drawbacks and to allow the production of a differential cylinder, with a ring damping system, of simple construction and of more reliable operation than in the past, the invention applying to a cylinder. of the type described in the abovementioned French patent application ^No. 87.04.134, that is to say, wherein the piston is combined with a valve-closing valve of the supply / drain orifice of the chamber main actuator, the piston positively actuating the valve of said valve to close said orifice at the end of the triggering stroke of the piston, and in which the piston is devoid of any seal.

According to the invention, the shut-off valve is constituted by a damping ring mounted floating in the bottom of the cylinder of the jack and surrounding the supply / bleed orifice, said ring having a substantially cylindrical inner surface with which comes cooperate an extension or damping stud, substantially conical, carried by the underside of the piston, to perform an oil rolling between said surface of the ring and said extension.

Said floating ring carries, on its upper annular surface, a first protruding circular lip against which the seal faces the lower face of the piston, at the end of the trigger stroke, and carries, on its lower annular surface, a second protruding circular lip which comes to bear in leaktight manner against the bottom of the cylinder of the jack, around the feed / bleed orifice, when the ring is pushed back by the piston, at the end of the triggering stroke.

The floating ring thus forms a double sealing valve, on the one hand between the piston and the ring and, on the other hand, between the ring and the cylinder bottom.

The one-piece combination of a floating ring, forming both a damping ring and a double valve ring sealing, therefore reduces the number of component parts of the cylinder, which improves cost and reliability.

• La figure 1 est une vue en coupe par un plan axial d'un vérin suivant un mode de réalisation de l'invention.
• La figure 2 est une vue partielle, à plus grande échelle, de la partie inférieure de la figure 1.
• La figure 3 est une vue en coupe diamétrale de la bague clapet/amortisseur.
• La figure 4 est une vue partielle en coupe montrant la zone de contact de la bague avec le piston et le fond de cylindre.
• La figure 5 est une vue analogue à la figure 2, montrant un mode préféré de réalisation de l'invention.

The invention will be better understood on reading the description which follows and on examining the appended drawings in which:

• Figure 1 is a sectional view through an axial plane of a cylinder according to an embodiment of the invention.
• FIG. 2 is a partial view, on a larger scale, of the lower part of FIG. 1.
• Figure 3 is a diametrical sectional view of the valve / damper ring.
• Figure 4 is a partial sectional view showing the contact area of the ring with the piston and the cylinder bottom.
• Figure 5 is a view similar to Figure 2 showing a preferred embodiment of the invention.

The differential actuator shown in FIG 1 is of the type described in the abovementioned French patent application ^No. 87.04.134.

It suffices to indicate that it comprises a cylinder 2, preferably from the foundry in a foundry part 4, in which a piston 6 slides, devoid of a gasket. The piston rod 6 is coupled to the movable contact of an electric circuit breaker not shown.

In Figure 1 there is shown in the left half, the piston 6 in its upper end position ("engaged" position of the circuit breaker) and in the right half the piston in its low position (marked 6ʹ) end travel ("tripped" position of the circuit breaker).

The piston 6 divides the interior volume of the cylinder 2 into an annular chamber 10 (above the piston) and a main chamber 12 (below the piston). The bottom of the main chamber, or bottom of the cylinder, is constituted by a screwed stopper 14 in the center of which is formed a supply / bleed orifice 16.

The annular chamber 10 is placed in permanent communication with an oleopneumatic accumulator 20 connected to an orifice 21 of the cylinder.

The feed / purge orifice 16 can be selectively placed in communication, via a 3-way valve 26, or with the accumulator 20 ("feed" position) through pipes 18-28-24 , or with a low pressure tank 32 ("purge" position) through pipes 24-30.

It should be noted that the pipe 18 is a pipe of large section, preferably from the foundry in the cylinder block 4, which ensures a high-speed oil transfer between the two chambers 10 and 12 of the jack.

The outgoing rod 8 passes through the upper plug 34 through a seal 36.

Conventionally, and as described in the aforementioned patent FR 2,317,532 (or US 4,026,523), the piston 6 carries first and second male damping members, of substantially or partially frustoconical shape or with sections storied. The first damping member 38, above the piston 6, cooperates with a damping ring 40, similar to that described in the patent cited above, to damp the high end of stroke of the piston 6.

The second damping member 42, which constitutes an extension of the piston 6, below the latter, cooperates with the ring 44 forming both a damper and a double sealing valve, according to the damping system of the present invention.

It should be recalled here that, in a differential cylinder of the type which has just been described, the absence of a gasket on the piston 6 means that there is a permanent oil leak between the outer cylindrical surface of the piston and the opposite surface of cylinder 2, when there is a pressure difference on the two faces of the piston.

At the end of the triggering stroke, low position of the piston, the piston itself, or a valve carried by the piston, comes to close sealingly and keep the supply / bleed orifice 16 closed, which is then at the low Any leak of high-pressure oil is thus prevented from leaving the cylinder of the cylinder through this orifice, as long as the piston remains in the low position.

Referring to Figure 2, which is an enlarged view of the lower part of Figure 1, the damping system follow the invention comprises the ring 44 which is mounted floating in a housing 46 where it is retained by the annular face upper part of the plug 14 and by a shoulder 48 cut in the cylinder 2. A clearance is provided in the housing so that the ring can move radially in order to center freely on the damping extension 42 of the piston 6. Such a floating mounting of a damping ring is well known and it allows an annular oil rolling passage to be obtained between the inner surface 50 of the ring 44 (see figure 3) and the extension 42 of the piston 6, producing an always reproducible damping.

As shown in FIGS. 2 and 3, the ring has, on its upper annular surface 52 a first projecting circular lip 53 and on its lower surface 56 a second identical lip 58.

The upper lip 54 forms, in cooperation with the lower annular face 60 of the piston 6, a tight seal in the end-of-travel position of the piston, while the lower lip 58 forms, in cooperation with the upper annular face 62 of the plug 14, a second waterproof seal. Thus, the damping ring 44 plays the role of a double valve ensuring the tight closure of the feed / bleed orifice 16 when the piston is in its end-of-travel position, this same ring constituting the end-of-travel stop of the piston after damping.

Preferably, the ring 44 is made of a harder metal than the piston 6 and that the plug 14 against which the lips 54, 58 bear. Thanks to the fact that, in the low position of the piston, the guides of the piston itself and of the piston rod 8 are the furthest apart, good parallelism is always obtained between the lower annular surface 60 of the piston 6 and the top of the circular lip 54, which ensures a good seal.

FIG. 2 shows the surfaces (or sections) S₁ S₂, and s respectively of the piston 6, the lips 54, 58 and the outgoing rod 8.

This figure shows the end-of-travel position for triggering the piston 6, the latter being in abutment against the ring 44. In this position the feed / purge orifice is in the purge, that is to say a low pressure P₀ substantially equal to atmospheric pressure, while in the annular chamber 10 of the cylinder reigns the permanent high pressure P₁ supplied by the accumulator 20 (Figure 1).

With the type of cylinder to which the invention applies, in which the piston does not have a gasket, the oil at pressure P₁ contained in the chamber 10 above the cylinder leaks between the cylindrical outer surface 64 of the piston 6 and cylinder 2. The pressure P₁ is therefore established above and below the ring 44 in its outer zone limited by the lips 54, 58, said lips forming, with the facing surfaces 60-62, a pressure tight barrier P₁.

In this position, the bearing force of the piston 6 on the ring is:



F₁ = P₂ (S₁-s)

Given that S prévoit is expected to be of the order of 1.5 times the section s of the rod, the support force F₁ is of the order of 0.3 (S₂xP₁)
The service pressure P₁, in the hydraulic circuit breaker controls, being of the order of 300 to 400 bar and the section S₂ of the valve being able to be of the order of 10 to 20 cm² in the most common applications, we see that the permanent closing force exerted on the valve can be very high, several tons, and ensures an absolute permanent seal, especially since the hard metal lips 54-58 imprint their imprint in the less hard metal of the piston 6 and of the plug 14.

It should be recalled here that the last part of the piston stroke, before it comes into abutment on the ring 44, is damped by the penetration of the extension 42 of the piston 6 inside the ring 44. In Figures 2 and 4, a relatively large clearance has been shown between the inner cylindrical surface 50 of the ring 44 and the outer surface 68 of the extension 42. But, in the case where energetic damping is sought, the annular interval between these two surfaces is very low, to produce an effective oil rolling and there is therefore a very high overpressure, called damping overpressure, in the main chamber of the cylinder, below the piston.

In a conventional cylinder, this overpressure (several thousand bar) is dangerous for the piston lining, which is suddenly subjected to very high pressure. On the contrary, in a cylinder according to the invention this damping overpressure is in no way dangerous, since the piston is devoid of any lining.

We will now describe the operation of the cylinder, with reference to the partial view of FIG. 4. In the position shown, the piston 6 is at the low end of travel (end of trip), the supply / purge orifice 16 is at low pressure P₀ (purge), while permanent high pressure P₁ prevails in the annular chamber of the jack. The piston 6 presses on the valve ring 44 with the force F₁ = P₁ (S₂ - s) indicated above and the pressure P₁ in the chamber 10 is also established above and below the ring 44, at the outside of the lips 54, 58, due to the non-sealing of the piston 6 in the cylinder 2. The entire area where the pressure P₁ prevails has been indicated by hatching in FIG. 4.

To carry out the reverse stroke of the jack (closing stroke), the orifice 16 is supplied under the high pressure P₁ (supply position - see figure 1, valve 24). The pressure therefore rapidly passes from the pressure P₀ to the pressure P₁: in the orifice 16; in the annular gap between the facing surfaces 50 and 68 of the ring 44 and the damping stud 42; then in space 70, below the piston 6, to the lip 54. This pressure therefore exerts on the piston 6 an upward push P × S₂ opposing the downward force F₁, and, as soon as it reaches a value P₂, called take-off pressure, such that:



P₂ × S₂ = P₁ (S₂ - s)



the piston 6 will start its interlocking stroke.

The "takeoff pressure" is therefore:



P₂ = P₁ (1 -s / S₂)



that is, in the preferred case where S₂ is of the order of 1.5 times s , P₂ is of the order of 0.33 P₁

We therefore see that we can obtain a straightforward and very rapid start of the jack since, as soon as the supply pressure reaches 33% of the high pressure P₁, the jack starts up, which is very important in the case of the control of electric circuit breakers where the response must be very fast.

Even in the case where a surface S₂ of the lips is chosen which is double the section s of the outgoing rod, the take-off occurs for a pressure P₂ equal to 50% of the high pressure P₁.

Bein heard, after "take off", that is to say as soon as the lips 54, 58 are no longer in sealed contact with the facing surfaces 60-62, the pressure P₁ is exerted on the entire surface S₁ of the piston 6 which is subjected to the normal operating force F₃ = P₁.S₁ - P₁ (S₁-s) = P₁.s, as in a conventional differential cylinder.

For certain applications, very energetic end-of-travel damping is required and, in this case, a very small annular clearance is provided between the external surface 68 of the damping stud 42 and the opposite cylindrical surface 50 of the damping ring.

In this case, this slight annular play slows down, when the supply / bleed orifice 16 is re-pressurized, the arrival of the oil under pressure in the space 70 located below the piston 6.

To increase, in this case, the speed of response, it is advantageous to provide means for recharging this space 70.

In the embodiment shown in FIG. 5, these recharging means essentially comprise a non-return valve constituted by a ball 72 and a seat 74, this seat being cut from a socket 76 screwed into a bore 78 hollowed out in the stud of 'Damping 42. One or more diametric holes 80 communicate the space located above the ball 72 with the outer surface 68 of the damping stud and, therefore, with the space 70 to be replenished.

At the time of triggering (return of the piston 6 to the low position), the high damping pressure produced below the piston keeps the non-return valve 72-74 closed by pressing the ball 72 on its seat 74, so well that the oil can escape only by rolling between the stud 42 and the ring 44.

When the supply / bleed orifice 16 is re-pressurized, the oil under pressure lifts the ball 72 and gains, by the diametrical bores 80, the space 70 under the piston 6 where the pressure is established P₂, called takeoff pressure, which was discussed in the foregoing.

It should be noted that, when the jack is in the low position (tripped position of the circuit breaker), the non-return valve 72-74 need not be sealed since the same low pressure P₀ prevails in the interval 70 and in the feed / drain hole (which is then in the drain). The non-return valve therefore has no severe production conditions.

To facilitate the replenishment of oil from the holes 80 towards the space 70, it is possible to provide an overbore of the internal cylindrical surface 50 of the ring 44 at the level of these holes 80, but, preferably, a chamfer 82 ( see Figure 3) at the upper part of the ring 44, substantially opposite the outlet of the bore 80 (indicated by broken lines in Figure 3).

To avoid any assembly error, it is advantageous to also provide a chamfer 82ʹ at the lower part of the ring 44, so that the latter can be mounted indifferently at the place or upside down.

External chamfers 84-84ʹ can also be provided to avoid any risk of the floating ring catching in its housing.

Likewise, it is simpler for the diameter of the circular lips 54 and 58 (therefore the section S₂ of these lips) to be identical, which allows mounting in any direction, but without going beyond the ambit of the invention. , one could provide lips 54 and 58 of different sections.

In a cylinder according to the invention, the section S₃ of the damping pin 42 is smaller than the section S₂ of the lips 54, 58 of the valve, but it is greater than the section s of the outgoing rod, by an amount such that the difference in section S₃ - s is sufficient for the piston 6 to surely go to the bottom of the stroke (stroke of trigger), despite the leaks between the piston and the cylinder, when tests of slow operation are performed at low flow. In the case where a valve surface S₂ of the order of 50% greater than the section s of the outgoing rod is chosen, a section S₃ is chosen for the damping stud of the order of 30% greater than the section s of the outgoing rod.

Claims (10)

1. A differential hydraulic jack for oleopneumatic control of electric circuit-breakers, comprising a cylinder (2), a piston (6) and an emergent piston-rod (8) which define within the cylinder an annular chamber (10) on one side of the piston and a main chamber (12) on the other side of the piston, said emergent piston-rod (8) being coupled with the moving contact of the circuit-breaker, said annular chamber (10) being continuously connected to a source (20) of hydraulic fluid under high pressure and said main chamber (12) being provided in the corresponding end (14) of the cylinder with a supply/drain orifice (16) for said chamber (12), a damping extension stud (60) being carried by said piston on that face which is directed toward the main chamber (12) and being adapted to cooperate with a damping ring (44) floatably mounted around the supply/drain orifice (16), said jack being characterized in that

   - the jack piston (6) is not provided with any packing ring forming a seal with the internal surface of the jack cylinder (2) ;

   - the damping ring (44) constitutes an end-of-travel stop for the jack piston (6) ;

   - said ring is provided with a first annular sealing zone (54) on its radial annular surface which is directed toward the main chamber (12) and with a second annular sealing zone (58) on its opposite radial annular surface, said first and second zones (54, 58) being adapted to form first and second valves providing a seal respectively with the aforesaid piston face (60) and with the cylinder end (14) when the piston is located at its end of travel.
2. A jack according to claim 1, wherein the first and second annular sealing zones are constituted by first (54) and second (58) circular sealing lips which project respectively from the two radial annular faces of the damping ring (44) and form an integral part of said ring.
3. A jack according to claim 2, wherein the damping ring (44) and consequently the lips (54, 58) of said ring are formed of metal having a higher degree of hardness than the metal of the jack piston (6) and the metal of the cylinder end (14).
4. A jack according to claim 2, wherein the surface area S₂ limited by the lips (54, 58) is larger than the cross-sectional area s of the emergent piston rod (8) and is preferably larger by approximately 50 % .
5. A jack according to claim 4, wherein the first lip (54) and the second lip (58) have an identical surface area S₂.
6. A jack according to anyone of claims 1 to 4, wherein means are provided for re-supply of high-pressure fluid to the annular spaces (70) located between the aforesaid piston face (60) and the opposite face (52) of the damping ring (44).
7. A jack according to claim 6, wherein the resupply means include a non-return valve (72-74) housed within the damping extension stud (42) of the jack piston (6) and radial ducts (80) pierced in said stud (42).
8. A jack according to claim 7, wherein the resupply means include a chamfer (82) cut in the internal periphery (50) of the damping ring (44) substantially opposite to the radial ducts (80).
9. A jack according to claim 8, wherein a second chamfer (82') is cut in the ring symmetrically with the chamfer (82) so as to permit symmetrical reversal of said damping ring.
10. A jack according to anyone of claims 1 to 9, wherein the cross-sectional area S₃ of the damping extension stud (42) is larger than the cross-sectional area s of the emergent piston rod (8).

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