EP0290320A1 - Hydraulic actuator with a piston position control system - Google Patents

Abstract

Proximity sensors (36) are housed, along the stroke of the piston (4) of the jack, in through holes (34) drilled in the wall (32) of the cylinder. The piston (4) of the jack is devoid of gasket and is not damaged by its passage against the outlet of the orifices (34) opening onto the inner surface (40) of the cylinder. The output signals from the sensors (34) are applied to a device for measuring and checking (46) the position of the piston (4) in the cylinder.

Application to the control of the operation of high-voltage electric circuit breakers.

Description

The present invention relates to a hydraulic cylinder with a piston position control system.

In many applications of hydraulic actuators with a jack, it is necessary to know the position of the member actuated by the jack and for this purpose contacts, known as limit switches or passage contacts, generally influenced by the member, are used. itself or another member linked to it, for example the rod coming out of the piston.

But for certain particular applications, for example the hydraulic control of electric circuit breakers, at high voltage, it is very inconvenient and often impossible (because of the energization of certain moving parts) to install limit switches or equivalent in the immediate vicinity of the components actuated by the jack.

This is why, in order to avoid long and unreliable mechanical connections, an "image cylinder" is used on the electrical circuit breaker controls, that is to say a small auxiliary control cylinder which is supplied or purged like the main cylinder and which is therefore supposed to reproduce the maneuvers of the main cylinder, and consequently, the movements of the member actuated by the cylinder, that is to say the movable contact of the circuit breaker.

Aside from its main role, which consists in indicating the open or closed position of the circuit breaker, this "image cylinder" also has the function of controlling certain automatic safety operations of the circuit breaker. It must therefore be very safe to operate, which means that its manufacture is delicate and therefore costly, to avoid the risk of a false indication. On the other hand, it has the drawback of requiring an additional hydraulic circuit, which can be a source of hydraulic fluid leaks.

In addition, in modern circuit breaker controls, we would like to be able to control the actual response and operating times in service of the circuit breaker's mobile contact. We know that the maneuver times are very short and of the order of a few hundredths of a second. These times are checked when the equipment is received, but once it has been put into service, it is no longer possible to check whether the initial performance is well preserved. On the other hand, it would be very important to be able to verify that these operating times are indeed constant and reproducible, this in particular in the case of circuit breakers with several poles in series in which the operations must be absolutely simultaneous. Finally, the electrical technicians take into account the time of exit of the mobile contact compared to the fixed contact, time which is obviously only a fraction of the total time of movement of the mobile contact and want to know the speed curves of the mobile contact.

Of course, an "image cylinder", which has by no means the same inertia as the main cylinder and the movable members that it operates, cannot give any valid indication of the various operating characteristics in service.

The object of the present invention is to remedy the drawbacks and insufficiency of the control systems used up to now, such as, in particular, the "image cylinders".

The present invention makes it possible to produce a control system which detects the position of the piston itself during its stroke in the jack, the position detection being able to be made not only at the two end positions, but also in a plurality of intermediate positions.

Until now, it has not been possible to accommodate piston position sensors in a cylinder, in the immediate vicinity of the passage of the piston. Indeed, conventional cylinders, for circuit breaker controls, operate at a very high pressure, of the order of 300 to 400 bar, which requires perfect sealing of the piston in the cylinder. The piston has a seal of a very elaborate type, most often a composite seal called "spring", and the inner surface of the cylinder is perfectly ground and lapped so as not to wear or damage the seal. It is of course not possible to place one or more detectors close to the piston in the thickness of the wall of the cylinder, because the irregularities which would result therefrom in the surface of the cylinder would destroy the lining.

However, the present inventor has recently found that it is possible to build differential cylinders, in particular for the control of circuit breakers, in which the piston does not have a tight seal and in which the piston actuates or carries a sealed valve which closes the main chamber of the jack at the end of the piston stroke. The leak which exists around the piston, due to the absence of a seal on the piston, cannot therefore gain the volume of the cylinder situated below the piston, when the latter has reached its end of travel.

Such a differential cylinder, with piston devoid of seal, was described in French patent application No. 87.04.134 filed March 25, 1987 in the name of the same inventor.

The present invention applies to a differential hydraulic cylinder of this type.

The subject of the invention is a cylinder of the aforementioned type characterized: in that a plurality of through holes are drilled in the wall of the cylinder of the cylinder, over the extent of the piston stroke; in that a displacement sensor is arranged in each of said orifices, with its detection member facing the interior of the cylinder so as to be influenced by the passage of the piston; and in that a tight closure is provided between the sensor and the exterior surface of the cylinder to restore the integrity of the tightness of the cylinder at high pressure.

The surface finish of the interior surface of the cylinder is thus destroyed by the through holes, but this is without disadvantage since the piston does not carry a fragile seal.

Proximity sensors, in particular inductive sensors, are preferably used, which are influenced by the passage of the metal piston opposite the orifice in which the sensor is housed. Of course, the sensors themselves are subjected to the high pressure (300 to 400 bar) prevailing in the cylinder of the cylinder, but there are types of sensor designed to operate in high pressure environments, for example 500 bar.

Inductive sensors have a built-in electrical switch which provides an analog output signal on the output cables which can be amplified and processed before being applied to control instruments which indicate the position of the piston in the cylinder and, by Consequently, the position of the actuated member, in particular the movable contact of a circuit breaker.

• La figure 1 est une vue axiale d'un vérin hydraulique différentiel suivant l'invention.
• La figure 2 est une vue en coupe transversale, suivant le plan II - II de la figure 1 à plus grande échelle.

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

• Figure 1 is an axial view of a differential hydraulic cylinder according to the invention.
• Figure 2 is a cross-sectional view, along the plane II - II of Figure 1 on a larger scale.

The jack represented in FIG. 1 is of the type described in the aforementioned patent application and it comprises a cylinder 2 preferably in the form of a casting, a piston 4 devoid of seal, a piston rod 6 which is coupled to the movable contact of a circuit breaker (not shown) and a valve device 8 for closing the intake / bleed orifice 10 of the jack in the low end position (position shown on the right half of the figure) of the piston 4.

In the embodiment shown, the actuator also comprises a end-of-travel damping system in which the closing valve is constituted by a floating ring 8 which has two sealing lips 12-12 ′ and whose central bore 14 cooperates with a damping pin 16 carried by the piston 6. Such a damping system, with a floating ring simultaneously forming a double-sealing closing valve at the end of the piston stroke, has been described in the application for French patent N ° 87.05.198 filed on April 13, 1987 in the name of the same inventor.

As is known in hydraulic controls for circuit breakers with differential actuators, the annular chamber 18 of the actuator (above the piston 6) is permanently connected to the high pressure source constituted by an oleopneumatic accumulator 20. The main chamber 22 of the cylinder (below the piston 6) is selectively connected, by a 3-way valve 24, or to the high pressure (by the line 26 and by a transfer line 28, which preferably came from the foundry with the cylinder 2 of the cylinder), or to the purge to a low pressure tank 30. Such a hydraulic control for circuit breaker, with differential cylinder, has been described for example in French patent No. 2,317,532 (or US patent No. 4,026. 523).

According to the invention, a plurality of through holes 34 are drilled in the wall 32 of the cylinder 2 at several levels on the stroke of the piston. In the embodiment of FIG. 1, only three orifices have been represented, one at each end of the piston stroke and an intermediate, but, of course, if we want a greater number of detection points for the passage position of the piston it is possible to pierce more than three orifices, on the same generator of the cylinder or, preferably on different generators.

In each of the orifices 34, a proximity sensor 36 is housed whose detection face 38 (see FIG. 2) is flush with the interior surface 40 of the cylinder 2. Sealing means, such as seals 42-42 ′ ensure the closure tight of the orifices 34 at the high pressure prevailing in the cylinder of the jack, after the installation of the sensors 36 in their housing.

For the sake of clarity of the drawing, FIG. 1 shows only two of the orifices 34 fitted with their sensor 36, the mounting of a sensor in its housing being shown in more detail in the sectional view of FIG. 2.

The electrical output of each sensor is via a two-wire cable 44, all these cables arriving at means 46 for controlling and / or recording and / or displaying the movements of the piston 6 and, optionally, the speed curves .

As seen in particular in Figure 2, the holes 34 open into the inner surface 40 of the cylinder of cylinder 2, which breaks the integrity of this surface. But since the piston 6 is devoid of a seal applied in a sealed manner against the interior surface of the cylinder, the non-continuity of this surface is without drawback. On the contrary, with a conventional cylinder, the seal of the piston would be damaged with each passage of the piston in front of the orifices and would be quickly destroyed.

As a proximity sensor, it is advantageous to use inductive sensors with micro-switch, intended to operate in a high pressure environment, such as those marketed by the company HONEYWELL CONTROL SYSTEMS LTD under the reference series 921, 922, 926 which can operate under a pressure of 500 bar.

Other types of sensors could be used, for example capacitive or, again, mechanical.

The detection system according to the invention has the advantage that it is directly integrated into the jack itself and that it does not require any mounting or connection on site other than the connection of the sensor output cables to the control.

Such integration is important because modern technology increasingly provides for the production of complete assemblies which are assembled and adjusted in the factory.

Not only, thanks to the invention, it is possible to remove, in the circuit-breaker controls, the conventional image jack, the drawbacks of which have been pointed out in the foregoing, but also, the performances can be precisely controlled. circuit breakers upon commissioning, then periodically thereafter.

Of course, the detection system according to the invention, by means of its control apparatus 46, indicates the open or closed position of the circuit breaker, ensures safety interlocks with the other devices associated with the circuit breaker (for example disconnectors) , and prohibits the "pumping" phenomena of the circuit breaker in the event of tripping on latching (closing on short-circuit) if the closing order is maintained.

In addition, the system according to the invention makes it possible to carry out various measurements which were not possible with an image jack, as we have seen in the foregoing, or even with mechanical connections or linkages taken directly on the mobile member actuated by the jack. In fact, due to the length and the play in these mechanical connections, the measurements were completely imprecise, if only as a result of the forces and elastic deformations appearing in these mechanical connections during the operations of the circuit breakers which are very brutal.

This is how it is now possible, with the detection system according to the invention, to measure and record with precision the time for leaving the movable contact outside the fixed contact after the issuance of the order. engagement, to determine the speed curve of the movable contact, which is very important in particular in the case of self-blowing circuit breakers with SF 6, and to check the proper functioning of the end-of-stroke damping.

Claims (6)

1) Differential hydraulic cylinder, in particular for controlling high voltage electric circuit breakers, of the type in which the piston of the cylinder is devoid of gasket ensuring the tightness of the piston with respect to the internal surface of the cylinder of the cylinder, characterized in that the wall (32) of the cylinder (2) is pierced with a plurality of through holes (34) over the extent of the stroke of the piston (4); in that a displacement sensor (36) is housed in each of said orifices (34), with its sensitive detection member (38) turned towards the inside of the cylinder (2) so as to be influenced by the passage of the piston (4) opposite the corresponding orifice (34); in that sealing means (42-42 ′) are provided between each sensor and the wall (32) of the cylinder to ensure the integrity of the seal the cylinder at the high pressure prevailing in said cylinder; and in that the output links (44) of the sensors are connected to an apparatus (46) for monitoring the position of the piston (4) in the cylinder (2). 2) Cylinder according to claim 1, characterized in that the sensors (36) are proximity sensors, without physical contact with the piston (4) in the passage of the latter in front of the corresponding orifice (34). 3) Cylinder according to claim 2, characterized in that proximity sensors (36) are inductive sensors resistant to high hydraulic pressures of the order of 300 to 400 bar. 4) Cylinder according to one of claims 1 to 3, characterized in that the aforementioned orifices (34) are drilled on the same generator of the cylinder (2). 5) Cylinder according to one of claims 1 to 3, characterized in that the aforementioned orifices (34) are drilled on several generatrices of the cylinder (2). 6) Cylinder according to any one of the preceding claims, characterized in that the cylinder (2) of the cylinder is a piece from foundry.

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