EP1972798B1 - Device for controlling the position of an actuator by a servo-valve with position memory in the event of a breakdown - Google Patents

Abstract

The device has control chambers (62, 64) of a cylinder (60) connected with usage outlets (U1, U2) of a hydraulic distributor (20) with low pressure or high pressure. Bearings (54, 56) of a slide (52) of an actuator e.g. fuel metering valve (50), are subjected to the high and low pressures on two sides of the bearing respectively. A dynamic seal (70) assures sealing between the bearings and the cylinder, where the seal produces dynamic friction between the bearing and the cylinder based on a difference between the pressures on the sides of the bearing.

Description

Background of the invention

The invention relates to controlling the position of an actuator by means of an electrically controlled servo valve.

A particular field of application of the invention is that of the position control of actuators used in aeronautical engines, in particular for the metering of fuel or for the adjustment of vanes of variable angle valves or flaps of valves. nozzles in gas turbine engines.

For such applications, it is required to "freeze" the position of a controlled member in the event of an electrical fault at the servovalve control, to ensure safe operation and to be able to regain the position occupied before the failure. when it has been corrected.

Servo-valves said to memory position in case of failure (or "fail freeze") are well known. In particular, reference may be made to the document FR 2,818,331 . In this document, the servovalve comprises a dispenser which, in the event of an electrical control failure, comes into a position in which dispenser utilization ports connected to control chambers of the actuator are closed. A drift from the "frozen" position of the actuator is difficult to avoid due to leakage of the hydraulic fluid contained in the control chambers.

Object and summary of the invention

The object of the invention is to provide an electrically controlled servo valve actuated device in which the position of the actuator can be frozen in the event of an electrical failure without substantial risk of drift.

• une servo-valve à commande électrique comprenant un distributeur hydraulique ayant au moins un orifice d'alimentation haute pression, au moins un orifice d'échappement à basse pression, et au moins deux orifices d'utilisation, chaque orifice d'utilisation pouvant être relié à la haute pression ou à la basse pression en fonction de la position commandée d'un tiroir du distributeur hydraulique, et
• un actionneur comprenant un tiroir portant au moins deux paliers et pouvant coulisser dans un cylindre, l'actionneur ayant deux chambres de commande reliées à des orifices d'utilisation respectifs du distributeur de la servo-valve et situées chacune d'un côté d'un palier respectif et une chambre intermédiaire reliée à la haute ou basse pression et située entre les autres côtés des paliers,
• le tiroir du distributeur hydraulique étant amené, en cas de panne de commande électrique, dans une position de sécurité dans laquelle il provoque l'immobilisation du tiroir de l'actionneur sensiblement dans sa position à l'instant de la panne,
  dispositif dans lequel :
• dans la position de sécurité du tiroir du distributeur hydraulique, les chambres de commande de l'actionneur sont amenées par leur liaison avec les orifices d'utilisation du distributeur à une même pression basse ou haute opposée à celle régnant dans la chambre intermédiaire de sorte que chaque palier du tiroir de l'actionneur est alors soumis à la haute pression sur un côté et à la basse pression sur l'autre côté, et
• l'étanchéité entre chacun desdits paliers du tiroir de l'actionneur et le cylindre de celui-ci est assurée par un joint dynamique produisant un effort de frottement entre palier et cylindre fonction de la différence entre les pressions exercées des deux côtés du palier.

This goal is achieved through a device comprising:

• an electrically operated servo valve comprising a hydraulic distributor having at least one high pressure supply port, at least one low pressure exhaust port, and minus two use ports, each service port being connectable to high pressure or low pressure depending on the controlled position of a spool of the hydraulic distributor, and
• an actuator comprising a slide bearing at least two bearings and slidable in a cylinder, the actuator having two control chambers connected to respective operating ports of the servo valve distributor and each located on one side of a respective bearing and an intermediate chamber connected to the high or low pressure and located between the other sides of the bearings,
• the hydraulic distributor spool being brought, in the event of an electrical control failure, into a safety position in which it causes the immobilization of the actuator spool substantially in its position at the moment of failure,
  device in which:
• in the safety position of the hydraulic distributor spool, the control chambers of the actuator are brought by their connection with the dispenser utilization ports at the same low or high pressure opposite to that prevailing in the intermediate chamber so that each bearing of the actuator spool is then subjected to high pressure on one side and low pressure on the other side, and
• the seal between each of said bearings of the actuator spool and the cylinder thereof is provided by a dynamic seal producing a friction force between bearing and cylinder depending on the difference between the pressures exerted on both sides of the bearing.

Advantageously, the intermediate chamber of the actuator is connected to the high pressure and, in its safety position, the dispenser spool connects the dispenser use ports with the low pressure.

Thus, the locked position of the actuator slide is not influenced by leaks. Low leakage of the seals does not change the value of the pressure differential that applies to the dynamic seals and thus the friction force that "freezes" the position of the actuator slide.

The invention is particularly applicable to a fuel flow control device in an aeronautical engine, the fuel metering actuator with an intermediate chamber connected to a high pressure fuel source and having an outlet orifice whose passage section is a function of the position of the actuator slide.

In such an application, the dynamic seals also offer the advantage of avoiding leakage of the metered fuel flow.

Brief description of the drawings

• la figure 1 illustre schématiquement un dispositif à servo-valve et actionneur selon un mode de réalisation de l'invention ;
• les figures 2A et 2B sont des vues de détail en coupe à échelle agrandie d'un type de joint dynamique utilisable pour assurer l'étanchéité entre tiroir et cylindre de l'actionneur de la figure 1,
• la figure 3 montre une relation entre l'intensité d'un courant électrique de commande de la servo-valve et différents points de fonctionnement ; et
• les figures 4A à 4F sont des vues montrant très schématiquement des configurations d'un distributeur hydraulique de la servo-valve de la figure 1 pour différents points de fonctionnement de la figure 3.

The invention will be better understood on reading the description given below, by way of indication but without limitation, with reference to the appended drawings in which:

• the figure 1 schematically illustrates a servo valve and actuator device according to one embodiment of the invention;
• the Figures 2A and 2B are detailed sectional views on an enlarged scale of a type of dynamic seal that can be used to seal between the spool and the cylinder of the actuator of the figure 1 ,
• the figure 3 shows a relationship between the intensity of an electric control current of the servo valve and different operating points; and
• the Figures 4A to 4F are views very schematically showing configurations of a hydraulic distributor of the servo valve of the figure 1 for different operating points of the figure 3 .

Detailed description of embodiments

One embodiment of the invention will be described with reference to Figures 1 to 3 and 4A-4F as part of the application to fuel metering (flow control) for an aircraft engine fuel injection system.

The figure 1 schematically shows a servo valve device 10 controlling an actuator 50 forming a fuel metering device.

The servo valve 10 is electrically controlled and comprises an electric motor member, for example an electric torque motor 12, a hydraulic distributor 20 and associated hydro-mechanical elements (hydraulic potentiometer and mechanical counter-reaction) which form the control unit. piloting 14 of the distributor 20.

The hydraulic distributor 20, a particular embodiment of which is described below, comprises a slide movable in linear translation in a cylinder. The distributor 20 comprises orifices connected to a double high-pressure supply (HP) and an exhaust (or low-pressure tarpaulin return BP), use outlets U1, U2 connected to the metering device 50 and piloting inlets P1, P2 opening in control chambers located at the ends of the distributor 20. The control inputs P1, P2 are connected to the control member 14, the pressures applied by it on the inputs P1, P2 acting in opposition to one of the other to control the movement of the dispenser drawer. The hydraulic fluid used can be the fuel.

The fuel dispenser 50 comprises a slide 52 bearing two bearings 54, 56 and slidable in a cylinder 60. The bearings 54, 56 share the internal volume of the cylinder 60 in two control chambers 62, 64 located at the ends of the cylinder 60 and in an intermediate chamber 66, between the bearings 54, 56. The control chambers 62, 64 are connected by control lines to the use outputs U1, U2.

The intermediate chamber 66 is connected by a supply port 66a to the HP high pressure supply (high pressure fuel supply source) and a service port 66b to a fuel injection line. The degree of closure of the use port 66b by the bearing 56 determines the metered flow.

A servo valve / fuel metering assembly as described above is known per se.

In the event of a fault in the electrical excitation of the servo valve, the hydraulic distributor spool comes into a position in which the same pressure, in this case the low pressure, is available on the operating outputs U1 and U2. Each bearing 54, 56 of the dispenser 50 is then subjected, on one side to the low pressure and, on the other side, to the high pressure.

The tightness between the bearings 54, 56 and the cylinder 60 is achieved by means of dynamic joints producing a friction force between bearing and cylinder as a function of the difference between the pressures exerted on the two sides of each of the bearings. Thus, in the event of a failure of electrical excitation of the servo valve, this difference in pressure is maximum (difference between HP and BP), so the friction force is also maximum. The position of the slide 52 at the time of failure can be maintained without risk of substantial drift, so that the fuel flow is frozen at its value at the moment of failure.

The Figures 2A and 2B show in more detail an embodiment of such a dynamic seal 70. In known manner, it comprises an O-ring 72 housed in a groove 74 formed in the inner wall of the cylinder 60, and a ring 76 housed at least partly in the groove 74, bearing on the seal 72. The seal 72 is an elastomer, for example Viton ^® . The Figure 2A shows the seal 70 when the pressures applied on both sides thereof are equal or slightly different. Under the effect of a high pressure difference between the two sides of the seal 70 ( Figure 2B ), the seal is deformed and exerts on the ring 76 a force tending to increase the force exerted on the adjacent bearing (for example the bearing 54). The ring 76 is preferably made of a material with a low coefficient of friction, for example polytetrafluoroethylene (PTFE). Of course, alternatively, the housing groove of the seal could be formed in the bearing.

The use of dynamic seals also makes it possible to improve the seal between the bearings 54, 56 and the cylinder 60 during normal operation of the metering device, by reducing the requirements of dimensional tolerances.

An example of a variation of the fuel flow rate as a function of the intensity of an excitation current of the electric motor unit 12 is shown on FIG. figure 3 .

Operating points A, B, C, D, E and F correspond respectively to the maximum flow rate (A), the steady state (B), the limits of a minimum flow range (CD) and the limits (AB) of the "freeze" range, when the intensity of the excitation current becomes too low or zero.

The Figures 4A to 4F show the positions of the slide valve 22 of the hydraulic distributor relative to the cylinder 40 of the same distributor 20 for the different operating points A to F, respectively, positions controlled by the control member 14 under the action of the electric motor member 12.

In the position A, the drawer 22 is at a first end of its stroke in the cylinder 40, the positive difference between the pressures prevailing in the control chambers 31, 32 at the ends of the cylinder being maximum. The control chambers 31, 32 are delimited by the ends of the cylinder 40 and respective bearings 23, 24 carried by the slide 22. The use output U2 (which here comprises two separate bores formed in the wall of the cylinder 40) is in communication with the low pressure BP via a chamber BP 33 which is located between the bearing 23 and a bearing 25 and in which opens the exhaust port. The utilization output U1 is in communication with the high pressure HP via the control chamber 31.

In the position B, the slide 22 closes the use exit U1 by the bearing 23 and the two bores forming the utilization exit U2 by the bearing 25 and a bearing 26.

In positions C and D, the drawer 22 puts the use output U2 into communication with the high pressure via an HP chamber 35 located between the bearings 24 and 26 while the use outlet 31 opens in the chamber BP 33.

In the positions E and F, the drawer 22 puts the BP chamber 33 in communication with the use outlet U1 and with the utilization outlet U2 via a passage 29 formed in the drawer 22 and connecting the chamber BP 33 to a chamber 34 located between the bearings 25 and 26. In the position F, the slide 22 is at the other end of its stroke in the cylinder 40.

Of course, the operating profile of the figure 3 and the internal arrangement of the distributor of the servo-valve described above are given merely by way of example, other forms being possible since in the event of failure of electrical excitation of the servo valve 10 the Hydraulic distributor slide 20 comes into a safety position in which, in this case, the use outlets U1 and U2 are both at low pressure to "freeze" the position of the metering device 50.

The invention is of course applicable to hydraulic actuators other than fuel dispensers for aeronautical engines, since the position of the actuator can be "frozen" by application in two control chambers thereof a pressure (BP or HP) opposite to that prevailing in an intermediate chamber with dynamic seal between the intermediate chamber and each of the control chambers.

Claims (4)

1. Actuator position control device comprising:

   - an electrically controlled servo-valve (10) comprising a hydraulic distributor (20) having at least one high pressure (HP) supply hole, at least one low pressure (LP) outlet and at least two use holes (U1, U2), each use hole being connectable to high pressure or low pressure, depending on the controlled position of a slide of the hydraulic distributor and

   - an actuator (50) comprising a slide (52) carrying at least two stages (54, 56) and being capable of sliding in a cylinder (60), the actuator having two control chambers (62, 64) connected to respective use holes (U1, U2) of the servo-valve distributor and each situated on one side of a respective stage and an intermediate chamber (66) connected to high or low pressure and situated between the other sides of the stages,

   - the hydraulic distributor slide (22) being taken, in the event of electrical control failure, to a safety position in which it causes the immobilization of the actuator slide substantially in its position at the moment of the failure, wherein

   - in the safety position of the hydraulic distributor slide (22), the actuator control chambers (62, 64) are taken, via their connection with the distributor use holes (U1, U2), to the same low or high pressure opposed to that applying in the intermediate chamber (66) so that each actuator slide stage (54, 56) is then subjected to high pressure on one side and to low pressure on the other side, and

   - sealing between each of the said stages (54, 56) of the actuator slide and the actuator cylinder (60) is carried out by a dynamic seal (70) producing a frictional force between stage and cylinder, depending on the difference between the pressures exerted on the two sides of the stage.
2. Device according to claim 1, wherein the actuator intermediate chamber (66) is connected to high pressure (HP) and, in its safety position, the distributor (20) slide connects the distributor use holes (U1, U2) to low pressure (LP).
3. Fuel flow control device in an aeronautical engine, comprising a position control device according to claim 1, in which the actuator (50) forms a fuel metering unit, the intermediate chamber (66) being connected to a high pressure fuel source and having an outlet hole, of which the cross section of flow is a function of the actuator slide valve position.
4. Aeronautical engine comprising a control device according to any of claims 1 to 3.

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