FR2954742A1 - Parking braking managing method for braking system of aircraft, involves comparing real change of position of push-pull rod with theoretical change of position of rod, and selecting table for which theoretical change is close to real change - Google Patents

Abstract

The method involves establishing direct parking braking adjustment tables e.g. high energy level tables, corresponding to vehicle braking situations. One of the tables is selected and applied to friction elements i.e. disks (11), during preset initial application time. Parking braking force is adjusted. Real change of a position of a push-pull rod (13) is compared with theoretical change of the position of the push-pull rod from the tables after the table application time is equal to the initial time. Another table, for which the theoretical change is close to the real change, is selected.

Description

The invention relates to a method for managing park braking in a vehicle braking system equipped with electric brakes. BACKGROUND OF THE INVENTION The vehicle electric brakes, in particular an aircraft, generally comprise at least one electric actuator which comprises a pusher actuated by an electric motor for selectively applying a force on friction elements of the brake.

In order to block the vehicle, for example when it is stationary in a parking lot, the actuator pusher is placed in a position in which it exerts on the friction elements a controlled force and then blocks the pusher in this position so that it continues to exercise a park force on the friction elements, which allows to cut the power of the engine and thus reduce the power consumption of the brake. However, given the dimensional variations of the brake components as a function of temperature, the park force varies over time and it is therefore necessary to provide an adjustment of the position of the pusher. It is known, in particular documents US Pat. No. 6,959,794 and FR 2,880,603, to perform an adjustment of the park force applied at given times by using a force sensor mounted on one of the components of the system. braking and ensuring the maintenance of the force at a constant value by means of a closed loop acting on the position of the pusher according to the value of the effort. This adjustment can still be done by implementing a so-called return to zero process comprising the steps of: unlocking the pusher, retracting the pusher to zero effort and then advancing it again until it exerts the required force which is measured from one of the operating parameters of the actuator, for example the supply current of the electric motor of the actuator. These two means are energy consumers, which poses a problem insofar as during parking braking the braking system is fed only by the vehicle battery. It is also known from the document US Pat. No. 6,959,794 to adjust the position of the pusher according to a so-called direct adjustment table which causes a variation of the pusher's position as a function only of the time elapsed since the parking braking. In order for the parking brake to remain effective whatever the circumstances, it is then necessary for the adjustment table to correspond to compensation for the effects of an emergency brake, that is to say a situation in which a strong Expansion of the components occurs shortly after the park brake is applied. This expansion causes in particular a very significant elongation of the torsion tube which carries the discs. The pusher being rusted in a fixed position relative to the torsion tube, an elongation of the torsion tube causes a decrease in the braking force. To compensate for this decrease it is therefore necessary to provide a direct adjustment table ensuring a displacement of the pusher significantly in the direction of a tightening. Since the adjustment is the same regardless of the circumstances preceding the parking brake, there is a risk that in some cases adjustments may be made at a frequency or level that is too high, so that these adjustments are unnecessary, and in particular after braking at very low energy for which the thermal expansion of the torsion tube will be very low. These unnecessary adjustments help to prematurely age the actuators.

OBJECT OF THE INVENTION The subject of the invention is a method of managing park braking which provides park brake force, minimizing the risk of premature aging of the actuator. BRIEF DESCRIPTION OF THE INVENTION With a view to achieving this object, a method of managing park braking in a vehicle braking system equipped with at least one electric brake comprising at least one electromechanical actuator which comprises a pusher actuated by an electric motor for selectively applying a force on friction elements of the brake, characterized in that the method comprises the steps of: - establishing a series of direct adjustment tables of the parking braking corresponding to situations braking at different energy levels, - during park braking, to carry out a selection of a direct adjustment table in relation to a braking situation preceding the braking of the park, - to adjust the direct way a park brake force according to the selected direct adjustment table. Thus, by selecting the adjustment table according to a preceding braking, it is possible to apply the adjustment which will lead to respect the minimal effort of park without risking to induce in the brake significant efforts during cooling of the brake, which helps to increase the service life of the actuators. In particular, one benefits from the reduction of the adjustment frequency and / or the level of effort of each adjustment after low intensity braking inducing only weak thermal expansions. According to a first embodiment of the method according to the invention, the selection of a direct adjustment table is made in relation to a history of the braking operations carried out over a period of time preceding the putting into park braking. This makes it possible to anticipate precisely the dimensional variations of the braking structure. According to a second embodiment of the method according to the invention, it comprises the steps of: selecting a first direct adjustment table and applying it for a predetermined initial application time; - make a first adjustment; - Make a comparison of a real change of position of the pusher with a change of the theoretical position of the pusher emerging from the direct adjustment tables after an application time equal to the initial application time; selecting a second direct adjustment table for which the theoretical change of position of the pusher is the closest to the real position change. Thus, the choice of the second direct adjustment table is made by comparison with actual data which takes into account all the features of the braking system in question.

According to another aspect of the invention in relation to the two aforementioned embodiments, for each braking according to a given energy level, different direct adjustment tables are established according to different ambient temperatures and during the selection of a table of direct adjustment is taken into account the ambient temperature. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood in the light of the description which follows with reference to the figures of the appended drawings in which: FIG. 1 is a schematic view of an aircraft comprising several braked wheels; - Figure 2 is a sectional view of a wheel equipped with an electric actuator brake; FIG. 3 is a graph of the evolution over time of the park force of an actuator without adjustment for different levels of braking energy; FIG. 4 is a graph illustrating the production of a table; direct adjustment. - Figure 5 is a graph of the evolution over time of the position of the pusher and the corresponding park force of an actuator according to the second embodiment of the method of the invention. DETAILED DESCRIPTION OF THE INVENTION The method of the invention is detailed herein in application to an aircraft A such as that illustrated in FIG. 1, which here comprises four braked wheels numbered 1 to 4 carried by landing gear 15. Of course, The invention applies to an aircraft having any number of braked wheels. One of these braked wheels is illustrated in FIG. 2. Each of the wheels comprises a rim 5 adapted to receive a tire (not shown here) and rotatably mounted on an axle 6 carried by one of the aircraft's aircraft. the aircraft. On the axle 6 is mounted a ring 7 carrying actuators 8. On the ring 7 is fixed a torsion tube 9 which extends into the rim 5 to end with a support 10. The ring 7, and therefore the tube torsion 9, are stopped in rotation with respect to the axle 6 by stop means not shown here. Between the support 10 and the actuators 8 extends a stack of disks 11 composed of rotors which are integral in rotation with the rim 5 and stators which are integral in rotation with the torsion tube 9.

Each of the actuators 8 comprises a body 12 in which a pusher 13 is mounted to move linearly facing the stack of discs 11 under the action of an electric motor contained in the body 12, in order to apply to the stack of 11 disks a controlled pressure force which, by inducing frictional forces between the rotors and the stators of the stack of disks, contributes to slowing the rotation of the rim 5, and thus to braking the aircraft A. Each of actuators 8 comprises a locking member 14 adapted to block the pusher 13 in the position where it is during the activation of the locking member 14. The braking system comprises a control module 50 adapted to operate the actuators 8 of the brakes is in a controlled mode for which each of the actuators is controlled to selectively apply a force on the associated stack of disks 11 in response to a braking instruction, or in a park mode in which ac 8 are locked in a position by means of the locking member 14 for which the push 13 exerts on the pile of disks 11 associated with a park force. In the park mode, the park effort is thus held without the help of the electric motor, which makes it possible to cut off the power supply of the latter. To switch to the park mode, when the aircraft is in the parking lot, the control module 50 first controls the pushers 13 of the actuators 8 so that they apply to the stack of disks 11 associated a controlled effort equal to a force and the control module 50 activates the locking members 14 to block the push-buttons 13. The power supply of the electric motors of the actuators can then be cut off. The pushers 13 thus blocked continue to exert on the piles of discs 11 a park effort that immobilizes the aircraft. However, as has been pointed out in preamble the relative expansion of the components of the braking system, and in particular the relative expansion of the torsion tube 9 and the discs 11 causes variations in the force actually applied. FIG. 3 illustrates these variations according to four curves Enl, En2, En3, and En4 which correspond to increasing levels of energy of the braking preceding immediately the putting in park braking. For example, the curve Enl corresponds to a braking of low energy level, for example when traveling at low speed with mainly a final braking to stop the vehicle. The curve En2 corresponds to a braking of energy level a little higher, for example when traveling at low speed with successive braking before final braking. The curve En3 corresponds to a braking of high energy level, for example when the vehicle is stopped several times in succession in a reduced time. The curve En4 corresponds to a braking of maximum energy level as it results from a sudden stop of the vehicle while it was launched at full speed. In the graph of FIG. 3, the changes in the time of the park force E exerted by one of the actuators 8 on the associated stack of disks 11 are represented. The time t0 corresponds to the moment when the pusher 13 of the actuator is blocked by the locking member 14 in a position in which it exerts a force equal to the nominal force Enom park. As explained above, the park force E tends to decrease under the effect of the dilations. In the example illustrated in FIG. 3, the braking curves of energy levels En1 and En2 remain between the value of the minimum required effort Emin and the value of the nominal force Enom. In both cases it is therefore not necessary to make an adjustment. On the other hand, with regard to the En3 and En4 braking curves, if the park force is allowed to evolve according to the expansions, it can be seen from FIG. 3 that it will fall below a minimum value. Emin necessary to prevent the vehicle from moving.

According to the invention, a series of direct park brake adjustment tables are established which correspond to braking situations at different energy levels. Each direct adjustment table comprises, at determined times, a direct correction of the position of the pusher so as to reduce the park brake force to a value close to or equal to the nominal force Enom in a direction of increase of the park brake force when the adjustment has to compensate for a reduction of the park brake force due to an expansion of the brake, and so as to reduce the park brake force to a value close to or equal to the minimum effort Emin in the sense of a reduction of the park brake force when the adjustment has to compensate for an increase in the park brake force due to a retraction of the brake. By way of example, FIG. 4 illustrates the development of a direct adjustment table for the energy level park brake curve En3. In this figure the evolution of the position of the pusher has been shown in solid lines while the evolution of the corresponding park brake force is shown in dashed line. At the initial moment t0 the pusher is in the position p0 to which corresponds a nominal brake force Enom. From the force curve of Figure 3 we determine the time t1 for which the stress curve reaches the minimum effort level Emin. A command is inserted in the direct adjustment table so that at this moment the pusher is maneuvered in a direction of increasing the effort until the push reaches the position p1 for which the effort of park brake is equal to the nominal effort Enom. This position is reached at the instant t2 from which the evolution of the park brake force continues along the corresponding part of the curve En3 of FIG. 3. From the curve En3 of FIG. determines the time t3 for which, taking into account the shape of the curve of FIG. 3, the park brake force again reaches the nominal value Enom. A control is inserted in the direct adjustment table so that at this moment the pusher is retracted until reaching a position p2 for which the parking brake force reaches the minimum value Emin. This position is reached at time t4 from which the evolution of the park brake force continues along the corresponding part of the curve En3 of FIG. 3. A new retraction control of the pusher is inserted into the table from the direct adjustment at time t5 for which the park brake force reaches a new nominal value Enom. At this moment the push is again retracted until the moment t6 at which it reaches the position p3 this time just necessary for the park brake force to be brought back to a value such as when the brake temperature has become stable the park brake force is substantially equal to the nominal force Eom. For the sake of clarity of the drawing, the time differences between the instants t1-t2, t3-t4, and t5-t6 have been intentionally exaggerated in FIG. 4. A direct adjustment table is established analogously for different braking energy levels. Preferably for each level of braking energy different direct adjustment tables are developed for different ambient temperatures. According to the invention, the park braking management method comprises the step of performing, during park braking, a selection of a direct adjustment table in relation to a braking situation preceding braking. park and adjust a park brake force directly according to the selected direct adjustment table. According to a first preferred embodiment of this method, a history of the energy levels of the braking operations carried out prior to the park braking is established, and the selection of an adjustment table is carried out according to this history. braking, preferably also taking into account the ambient temperature. For this purpose the vehicle is preferably equipped with a thermoprobe 70. When the braking history determines an intermediate energy level between two direct adjustment tables, the direct adjustment is preferably carried out according to the table d. direct adjustment of energy level immediately higher. FIG. 5 illustrates a second mode of implementation of the method according to the invention. According to this embodiment, a first direct adjustment table, preferably a high energy level table and more precisely the highest energy level direct adjustment table, is selected and applied for a period of time. predetermined initial application time. The first table can be selected using the first embodiment detailed above. In the example illustrated in FIG. 5, the first selected direct adjustment table corresponds to the energy level braking curve En4 of FIG. 3 and the initial application time is the time between the instant t0 and a moment t'1 for which the park brake force is equal to the minimum force Emin (see FIG. 3). In the illustrated example for which the braking conditions prior to braking park corresponds to the energy curve En3, the park brake force actually reached is the force E21 given by the curve of En3 energy. At this moment a first adjustment is made, for example here according to a method of return to zero, that is to say comprising the steps of: unlocking the pusher 13; - Push back the pusher 13 until it is no longer in contact with the stack of disks 11; - Advancing the pusher 13 to a position for which the parking brake force reaches the nominal value Enom as illustrated by the moment t'2 in Figure 5. The actual change in position of the pusher is then compared with that the theoretical positional changes as they emerge from the direct adjustment tables after an application time equal to the initial application time. The second direct adjustment table selected is that for which the actual change of position of the pusher is identical to the theoretical change of position. Direct adjustments are then made according to the direct adjustment table selected as illustrated in FIG. 5. The method described above can be applied to all the actuators of the aircraft, either one by one or simultaneously. In the latter case, however, it will be ensured that the total effort generated by all the actuators of the aircraft does not fall below a minimum that would call into question the immobility of the aircraft. Naturally, the invention is not limited to the embodiments described and alternative embodiments can be made without departing from the scope of the invention as defined by the claims. In particular The method of the invention is applicable to brakes provided with actuators in position. To exert a park force E on this type of actuator, the pusher 13 is brought into contact with the disk stack 11, a contact position of the pusher 13 is raised, and the pusher 13 is moved from this contact position of a given distance corresponding to the desired controlled effort given a stiffness of the brake. Although it was indicated that during an adjustment stage, the fleet effort is raised to its nominal level, other strategies can be implemented, such as raising the park effort to a slightly higher level. greater than the nominal force in order to reduce the number of adjustment steps. Conversely, rather than establishing the adjustment tables with reference to the Enom effort, one can consider making adjustments to an intermediate effort between Enom and Emin, even if it means increasing the frequency of the adjustments. Indeed, high force adjustments (Enom) are more likely to damage the actuator than more adjustments to less effort. It is also possible to provide different direct adjustment tables depending on the weight of the vehicle, the minimum effort threshold being lowered when the vehicle is empty or in partial load.

Claims (4)

REVENDICATIONS1. A method of managing a parking brake in a vehicle braking system equipped with at least one electric brake comprising at least one electric actuator (8) which comprises a pusher (13) actuated by an electric motor for selectively applying a force on friction elements (11) of the brake, the method comprising the steps of: - establishing a series of direct park brake adjustment tables corresponding to braking situations at different energy levels, - of during park braking, to carry out a selection of a direct adjustment table in relation to a braking situation preceding park braking, and to directly adjust a park braking force according to the direct adjustment table selected; characterized in that it comprises the steps of: - selecting a first direct fit table and applying it for a predetermined initial application time; - to make a first adjustment; to make a comparison of a real change of position of the pusher with a theoretical change of position of the pusher emerging from the direct adjustment tables after a time of application equal to the initial application time; and - to select a second direct adjustment table for which the theoretical change of position of the pusher is the closest to the actual change of position. The method of claim 1, wherein the first direct fit table is a high energy level table. The method of claim 2, wherein the first direct fit table is the highest energy level table. 4. Method according to claim 1 characterized in that it comprises the steps of: - establishing for each level of energy braking different tables of direct adjustment as a function of ambient temperature, and - to make the selection of the direct adjustment table according to the ambient temperature measured during park braking.