Method for controlling an actuator via the slope of the consumed current; corresponding braking device, braked wheel and aircraft

Abstract

The invention relates to a method for controlling at least one actuator (4) comprising a translatably movable piston (4.2) and an electric motor (4.1) for moving the piston (4.2) between a first position set back from a stop and a second position of contact with the stop, the method comprising the step of controlling the power supply to the electric motor (4.1) via speed feedback control of the piston (4.2) by determining, in real time, a current consumed by the electric motor (4.1) in order to detect arrival of the piston (4.2) in the contact position, characterized in that the detection of the contact position comprises the step of determining a slope of change in the current consumed by the electric motor (4.1) as the piston moves and the step of detecting an increase in the slope corresponding to the arrival of the piston (4.2) in the contact position. The invention also relates to a braking device, to a braked wheel and to an aircraft for implementing this method.

Description

[0001] Description

[0002] Title of the invention: Method for controlling an actuator by the slope of the current consumed; corresponding braking device, braked wheel and aircraft

[0003] The present invention relates to the field of braking of vehicle wheels, such as aircraft wheels.

[0004] BACKGROUND OF THE INVENTION

[0005] An aircraft landing gear typically comprises a telescopic strut acting as a shock absorber, with a housing equipped at one end with means for articulating the housing to an aircraft structure, and a rod that slides within the housing and protrudes from its other end. A shaft (axle or spindle) is fixed to one free end of the rod, and wheels are mounted to pivot on the shaft.

[0006] An aircraft wheel typically consists of a rim surrounded by a tire and connected by a disc to a hub mounted to rotate on the shaft.

[0007] Friction braking systems are known to consist of a stack of brake discs housed in an annular space extending between the rim and the hub. These discs alternate between rotors, which rotate with the wheel, and stator discs, which are fixed relative to the wheel's support shaft. The braking system also includes hydraulic or electromechanical actuators with a body mounted on an actuator carrier and a piston (or pusher) that can be moved axially within the body to apply a pressing force to the stack of discs, thereby generating a braking torque to slow the wheel's rotation.

[0008] In current electric braking systems, the control logic for the electric motors of electromechanical actuators implements a position control system for the actuator piston using a transfer function that relates the required braking force to the piston's position relative to a reference position. To implement this actuator control logic, it is necessary to detect the piston's contact with the stack of discs, which determines the reference position. However, it is important to remember that as the discs wear, the length of the disc stack decreases, and it is essential to know the position at which the piston makes contact with the disc stack, because it is from this reference position that the piston can exert the pressing force.

[0009] It is known to detect the contact position by measuring the instantaneous current consumption Iq by the actuator's electric motor and to detect an increase Alq relative to a reference current Iq no_load taken at the beginning of the piston's movement, when it is moving "unloaded." This detection mode is also used in other operating phases of the actuator, particularly during piston retraction phases up to a rear mechanical stop. Unloaded movement corresponds to the piston's extension or retraction stroke before it comes into contact with the stack of discs or the rear mechanical stop. Figure 1 shows the ideal instantaneous current consumption by the motor of such an actuator during the piston stroke up to the position of contact between the piston and the stack of discs. This control mode works very well when the current consumed Iq remains equal to the reference current Iq no_loadas long as the piston moves without load. However, in certain situations (for example, in the case of air overpressure in internal spaces within the actuator whose volume varies with piston movement), the current Iq increases during the piston's unloaded movement, instead of remaining constant and equal to the reference current Iq. no_load This increase causes the current consumed by the motor to exceed the threshold Iq+ΔIq defined relative to the reference current Iq no_loadThis allows the system to detect contact between the piston and the brake disc stack or the rear mechanical stop. This can lead to an unintended detection of the contact. Figure 2 shows the instantaneous current consumption by the motor over the piston stroke up to the point of contact with the brake disc stack in the specific situations described above. The detected contact position is then earlier than the actual contact position: this can result in a longer braking distance because the piston will be further from the brake disc stack than expected when braking is initiated.

[0010] SUBJECT OF THE INVENTION

[0011] The invention is intended, in particular, to remedy at least partially the aforementioned drawbacks.

[0012] SUMMARY OF THE INVENTION

[0013] To this end, the invention provides a method for controlling at least one actuator comprising a piston that moves in translation and an electric motor for moving the piston between a first position retracted from a stop and a second position in contact with the stop. The method includes the step of controlling the power supply to the electric motor via a speed control system for the piston by determining in real time the current consumed by the electric motor to detect when the piston reaches the contact position. Detecting the contact position includes the step of determining the slope of the current consumed by the electric motor during the piston's movement and the step of detecting an increase in the slope corresponding to the piston reaching the contact position.

[0014] Free movement of the piston refers to a movement during which the piston theoretically does not apply any force to an external mechanical element. This is also called no-load movement.

[0015] Thus, contact detection is not performed by monitoring the current threshold exceeding the reference current measured at the beginning of the no-load stroke, as in the prior art. With the method of the invention, a slope of current variation is determined during piston movement. When the piston moves no-load to the point of contact, the current follows a shallow slope; when the piston reaches the point of contact, the current slope increases rapidly due to the increased effort the motor must exert to overcome the mechanical reaction at the point of contact. By monitoring this slope, and more specifically by detecting a change in this slope, it is then possible to detect the contact of the piston with the stack of discs or the mechanical stop of the piston's movement during its no-load stroke. Therefore, the focus is not on the current value itself, but on its evolution.It is not necessary to store reference current values ​​in memory.

[0016] Depending on optional features, used individually or in whole or in combination:

[0017] - the current consumed is averaged over a sliding window before determining the slope of evolution of the current consumed;

[0018] - the current consumed is subjected to low-pass filtering before determining the slope of evolution of the current consumed;

[0019] The invention also relates to a braking device comprising an electronic control unit, a stack of discs, and at least one actuator comprising a piston that moves in translation and an electric motor connected to the electronic control unit for moving the piston between a retracted position in which the piston is not in contact with the stack of discs and a braking position in which the piston exerts a pressing force on the stack of discs. The electronic control unit is arranged to implement the method of the invention. According to optional features, used individually or in whole or in combination:

[0020] - the contact position corresponds to the piston coming into contact with the stack of discs;

[0021] - the electronic control unit is arranged to, after detecting the contact position, control the power supply of the electric motor via a position control according to a position setpoint determined according to a transfer function linking the position of the piston to a press force; - the piston is in contact with a rear mechanical stop when it is in the retracted position and the contact position corresponds to a contact of the piston with the rear mechanical stop.

[0022] The invention also relates to a braked wheel comprising such a braking device, and an aircraft equipped with such a wheel.

[0023] Other features and advantages of the invention will become apparent from the following description of a particular and non-limiting embodiment of the invention.

[0024] BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Reference will be made to the attached drawings, among which:

[0026] [Fig. 1] is a diagram representing the theoretical instantaneous current consumption by the motor of a braking device actuator over the piston stroke until it comes into contact with the stack of discs;

[0027] [Fig. 2] is a diagram representing the actual instantaneous current consumption by the motor of an actuator over the piston stroke until it comes into contact with the stack of discs;

[0028] [Fig. 3] is a front view of an aircraft according to the invention;

[0029] [Fig. 4] is a half-view of a braked wheel of this aircraft, in section along the central axis of the wheel;

[0030] [Fig. 5] is a diagram showing in parallel, on the one hand, the actual instantaneous current consumption by the motor of an actuator over the piston stroke until it comes into contact with the stack of discs (as in Figure 2) and, on the other hand, the slope of evolution of the instantaneous current consumption over this stroke;

[0031] [Fig. 6] is a flowchart illustrating the implementation of the process of the invention.

[0032] DETAILED DESCRIPTION OF THE INVENTION Figure 3 represents an aircraft 100 comprising landing gear 101.

[0033] Each of the landing gear 101 comprises a leg having an end here provided with two coaxial shafts 102 on each of which is mounted to pivot at least one wheel 103, each shaft 102 having a central axis defining an X axis of rotation of the wheel 103 which it carries.

[0034] At least one of the wheels 103 comprises, in a manner known per se, a hub 104 mounted to pivot on the shaft 102 and a rim 105 connected to the hub 104 by a disc 106. The rim 105 and the hub 104 define between them an annular space 107 having one end closed by the disc 106 and one end open towards the outside of the wheel 103 forming an entrance to the annular space 107. The rim 105 is encircled by a tire 108 received between two lips 109 of the rim 105.

[0035] According to the invention, at least one of the wheels 103 of each landing gear 101 is equipped with a braking device generally designated as 1, shown in Figure 4. The braking device 1 comprises a stack of braking discs 2 which is housed in the annular space 107 and which alternately comprises rotor discs 2.1 linked in rotation with the rim 105 of the wheel 103 and stator discs 2.2 fixed relative to the shaft 102 supporting the wheel 103. In the example shown, two end stator discs 2.2 frame two rotor discs 2.1 arranged on either side of a central stator disc 2.2. More precisely, the stator discs 2.2 are carried by a torque tube 3 to which they are rotationally connected. The torque tube 3 is here fixed to a flange 102's extending outwards from the shaft 102 and is therefore fixed relative to the leg of the lander 101. The rotor discs 2.1 are mounted in the rim 105 to be movable along the X axis and the stator discs 2.2 are mounted on the torque tube 3 to be movable along the X axis. The translational guidance of the rotor discs 2.1 and the stator discs 2.2 is ensured by ribs fixed respectively to the rim 105 and the torque tube 3. The torque tube 3 has an end close to the web 106 which carries an externally projecting heel 3' against which the stator disc 2.2 of the end closest to the web 106 bears, the heel 3' forming a stop to the axial displacement of the stack of discs 2.

[0036] The braking device 1 also includes electromechanical actuators 4, each comprising a body mounted in an actuator-carrying ring 5 fixed to the collar 102'. Each actuator 4 comprises an electric motor 4.1 and a piston or pusher 4.2 that can be moved axially within the body to apply a pressing force on the stack of discs 2 against the heel 3' so as to generate a braking torque to slow the rotation of the wheel 103 around the shaft 102. Each piston 4.2 is thus movable between a retracted position in which the piston 4.2 bears against a rear mechanical stop not visible in Figure 4 and is not in contact with the stack of discs 2, and a braking position in which the piston 4.2 exerts a pressing force on the stack of discs 2. The stack of discs 2 comprises a force plate 2.3 applied against the stator disc 2.2. The end closest to the actuator-carrying ring 5 distributes the braking force over the entire surface of the discs. The electric motors 4.1 are connected to an electronic control unit 6. The electronic control unit 6 comprises a power stage and a control stage, including, for example, a processor and memory containing a program executable by the processor. The program is configured to control the electric motors 4.1 in a manner known per se, based on braking instructions issued by the pilot of the aircraft 100 using a brake control instrument located in the cockpit of the aircraft 100, or issued by a central control unit of the aircraft 100, for example, in the case of an unmanned aircraft such as a drone. In a manner known per se, the electronic control unit 6 is thus configured to control the power supply to the electric motor 4.1 of each actuator 4 via a position control of the piston 4.2 of said actuator 4 by using a transfer function relating the required braking force and the position of the piston 4.2 relative to a reference position of the piston 4.2 corresponding to the contact position of the piston 4.2 with the stack of discs 2.

[0037] Thus, to control the electric motors 4.1 according to the braking instructions, the electronic control unit 6 must detect the contact position of the piston 4.2 with the stack of discs 2. This contact position constitutes the reference position but depends on the wear of the discs in the stack. Indeed, before braking, for example when the landing gear 101 is extended prior to landing, or before a taxiing phase prior to takeoff, the piston 4.2 of each actuator 4 is brought into the contact position (within one operating range) in order to apply the pressing force as quickly as possible.

[0038] The determination of the contact position will now be described. The control unit 6 measures the instantaneous current consumption by the electric motor 4.1 to detect when the piston 4.2 reaches the contact position.

[0039] In Figure 5, the top diagram shows the instantaneous power consumption of one of the electric motors 4.1 to move the piston 4.2 between the retracted position and the contact position. At t0, the piston 4.2 is in its retracted position, and the electronic control unit 6 begins to supply current to the electric motor 4.1. The current initially increases rapidly, without the piston 4.2 moving, because it is necessary to overcome the inertia of the electric motor 4.1 (rotor) and piston 4.2 assembly, before decreasing just as rapidly once this assembly is set in motion: this is called the inertia peak. The current consumed Iq then stabilizes at a value Iq no_loadcorresponding to an unloaded movement, the current consumption can either remain at this value (the slope of the current consumption curve is zero) or increase steadily (the slope of the current consumption curve is greater than zero but constant) until piston 4.2 reaches the contact position. Figure 5 illustrates this second case, and the slope of the current consumption curve is shown in the diagram below Figure 5. When piston 4.2 reaches the contact position, the upper diagram shows a sharp increase in instantaneous current consumption, and therefore, the lower diagram shows a sharp increase in the slope. The slope is compared to a predetermined slope threshold, and when the slope exceeds this threshold, the control unit 6 considers piston 4.2 to be in its contact position.

[0040] In practice, and also referring to Figure 6, the electronic control unit 6 measures in real time the current Iq consumed by the electric motor 4.1 while it controls the electric motor 4.1 to move the piston 4.2 towards the stack of discs 2 via speed control based on a constant setpoint. After detecting the crossing of a current peak corresponding to the inertia peak, the control unit 6 activates the contact detection procedure and calculates the average current Iq consumed over a sliding window, taking into account the motor speed Vm (step El) in order to limit the effect of occasional torque increases related to the position of the permanent magnets in the electric motor 4.1 (cogging torque). The duration of the window (here approximately 50 ms) is determined in a way that is known to itself based on the characteristics of the actuator and the speeds used.The average Iqm from the averaging step is then subjected to low-pass filtering (Iqm' - step E2) before being derived (step E3) to obtain the slope p of the current consumed Iq by the electric motor 4.1. The slope p thus determined is compared to a slope threshold Sp stored in the control unit 6 (step E4), and the contact position is considered reached when the slope p is greater than or equal to the slope threshold Sp (step E5). The current measurement signals are discretized here for digital processing. The low-pass filter cleans the signal to eliminate any remaining discontinuities and suppress any unwanted noise. The filter settings depend on the characteristics of the electrical network and its electromagnetic environment.

[0041] Regardless of the circumstances, in situations where the current Iq changes during no-load movement, the slope p of the current Iq variation remains small, i.e., always below the slope threshold Sp. Conversely, when the piston 4.2 comes into contact with the stack of discs 2, the slope p becomes more significant until it exceeds the slope threshold Sp. The invention makes it possible to observe the value of this slope p and it is possible, by using the slope threshold Sp, to distinguish a true contact from a simple variation of the current during the movement of the piston 4.2. The control unit 6 therefore monitors the occurrence of a significant change in the slope of the current and does not use, as in the prior art, the current as a representation of the force applied by the piston 4.2 by monitoring the crossing of a threshold by the instantaneous value of the current.

[0042] The slope threshold Sp can have a single, factory-set value stored in memory, or several values ​​depending, for example, on the temperature or another parameter measurable by the electronic control unit, allowing the selection of the appropriate value. It is also possible to define the slope threshold Sp periodically or for each piston stroke 4.2, as the sum of the current slope after the inertia peak and a correction value, or as the product of the current slope after the inertia peak and a correction coefficient.

[0043] The contact detection method according to the invention has been described here during the exit phase of piston 4.2. It is obviously possible to use it also during the retraction phase of piston 4.2, from the position in contact with the stack of discs 2 towards the position in contact with the rear mechanical stop, to detect the arrival of piston 4.2 in contact with the rear mechanical stop.

[0044] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0045] In particular, the braking device may have a different structure than that described.

[0046] The number of discs in the disc stack can be more or less significant.

[0047] The electronic control unit can be a microcontroller, an ASIC, an FPGA...

[0048] Applying one or more filters (moving average, low-pass, etc.) is very advantageous. The type and number of filters applied depend on the application.

[0049] The invention is not limited to a single actuator but applies to a plurality of actuators installed on a wheel and a plurality of wheels (one or more) equipped with actuators and installed on the aircraft.

[0050] The invention is applicable to all types of vehicles: land, sea, air, space... piloted or unpiloted...

Claims

DEMANDS 1. Method of controlling at least one actuator (4) comprising a piston (4.2) movable in translation and an electric motor (4.1) for moving the piston (4.2) between a first position withdrawn from a stop and a second position in contact with the stop, the method comprising the step of controlling the power supply to the electric motor (4.1) via a speed control of the piston (4.2) by determining in real time a current consumed by the electric motor (4.1) to detect an arrival of the piston (4.2) in the contact position, characterized in that the detection of the contact position comprises the step of determining a slope of evolution of the current consumed by the electric motor (4.1).1) during the movement of the piston and, after observing a crossing of an intensity peak corresponding to an inertia peak, the step of activating a contact detection procedure by detecting an increase in the slope corresponding to the arrival of the piston (4.2) in contact position, the slope of evolution of the current consumed is obtained after calculating an average (Iqm) of the current consumed (Iq) over a sliding window.

2. A method according to claim 1, wherein the current consumed is averaged taking into account the speed of the motor in order to limit an effect of point increases in torque related to a position of permanent magnets in the electric motor.

3. A method according to any one of the preceding claims, wherein the current consumed is subjected to low-pass filtering before determining the slope of evolution of the current consumed.

4. Braking device comprising an electronic control unit (6), a stack of discs (2) and at least one actuator (4) comprising a piston movable in translation and an electric motor (4.1) connected to the electronic control unit (6) to move the piston (4.2) between a retracted position in which the piston is not in contact with the stack of discs and a braking position in which the piston (4.2) exerts a pressing force on the stack of discs (2), the electronic control unit (6) being arranged to implement the method according to any one of the preceding claims.

5. Braking device according to claim 4, wherein the contact position corresponds to the piston (4.2) being in contact with the stack of discs (2).

6. Braking device according to claim 5, wherein the electronic control unit is arranged to, after detection of the contact position, control the supply of the electric motor (4.1) via a position control as a function of a position setpoint determined according to a transfer function linking the position of the piston to a pressure force.

7. Braking device according to claim 4, wherein the piston (4.2) is in contact with a rear mechanical stop when it is in the retracted position and the contact position corresponds to a contact of the piston (4.2) with the rear mechanical stop.

8. Aircraft braked wheel, comprising a rim (105) and a hub (104) connected to the rim (105) by a web (106) defining an annular space (107), and a device according to any one of claims 4 to 7, the stack of discs (2) comprising rotor discs (2.1) rotationally linked to the rim (105) and stator discs (2.2) rotationally linked to a torque tube (3) relative to which the rim (105) is rotationally movable.

9. Aircraft comprising at least one landing gear equipped with at least one braked wheel according to claim 8.

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