Aircraft braking procedure with dynamic brake fault correction

Description

[0001] The invention relates to the field of aircraft braking methods, comprising dynamic correction of the braking control. BACKGROUND OF THE INVENTION

[0002] A modern aircraft, for example an airplane or a helicopter, typically has a ground braking system for certain so-called "braked" wheels of the aircraft. The braking system includes one or more braking computers and brakes, each of which equips one of the braked wheels.

[0003] Each brake comprises at least one friction member, made for example of steel or carbon, and one or more braking actuators which are hydraulic actuators (in which case we speak of a "hydraulic braking system") or electromechanical actuators (in which case we speak of an "electric braking system").

[0004] In the case of an aircraft, each brake typically consists of several actuators and a stack of carbon discs.

[0005] In the case of a helicopter, patent FR 3 007 096 B1 describes a brake with a single rotating disc with the braked wheel, the disc being associated with a caliper which straddles the disc and whose jaws receive two pads, one of which is mounted movably to be able to pinch the disc between the two pads by means of a single braking actuator. EP2853487A1 discloses a system for an aircraft which determines whether a strong braking condition and a high speed condition exist and implements different braking profiles. 1

[0006] When an aircraft pilot presses a brake pedal located in the cockpit, it produces a so-called manual braking instruction which depends on the deflection applied to the brake pedal. This manual braking instruction is transmitted to the braking computer which generates a manual braking command from the manual braking instruction.

[0007] Similarly, when braking is controlled by an automatic braking function, an automatic braking instruction is transmitted to the braking computer which generates an automatic braking command.

[0008] The brake control, whether manual or automatic, is used to control the brake actuators so that each brake exerts a braking torque on the associated braked wheel which brakes the braked wheel and thus slows the aircraft. SUBJECT OF THE INVENTION

[0009] The object of the invention is to optimize braking control, with the aim of limiting the risks of damage to the structure of the brakes while maintaining the expected overall braking performance. SUMMARY OF THE INVENTION

[0010] In order to achieve this goal, a method is proposed for braking at least one wheel of an aircraft, the wheel being provided with a brake comprising at least one braking actuator, comprising the steps of: generating a braking command from a braking setpoint; estimating and / or measuring a wheel speed; applying a dynamic correction to the braking command, the dynamic correction being a function of the braking command and the wheel speed, the dynamic correction comprising the step of producing a corrected braking command greater than the braking command when the wheel speed is greater than or equal to a predetermined speed threshold, then the step of reducing the corrected braking command when the wheel speed becomes lower than the predetermined speed threshold, such that the corrected braking command becomes lower than the braking command; controlling the braking actuator of the wheel brake using the corrected braking command.

[0011] Extensive analyses, based on the results of numerous braking tests, have shown that, during braking, when a constant braking control is used, the level of braking torque actually exerted by the brake on the wheel is directly linked to the wheel speed. The braking torque actually exerted by the brake on the wheel is greater at low speed and lower at high speed.

[0012] Thus, at high speed, the performance of the prior art braking methods is not optimal, and at low speed, there is a risk of damage to the brake equipment.

[0013] On the contrary, in the braking method according to the invention, a dynamic correction is applied which depends on the braking command and the wheel speed. The dynamic correction makes it possible to compensate for the braking command at high speed, and therefore to improve the braking performance, and to limit the braking command at low speed, and therefore to increase the service life of the aircraft brakes and to reduce the risk of damage to the brake structure, in particular that of the rotor.

[0014] A braking method such as that just described is further proposed, in which the dynamic correction consists of multiplying the braking command by a correction coefficient which depends on the braking command and the wheel speed.

[0015] We further propose a braking method such as that which has just been described, in which, for a given braking command, when the wheel speed is greater than or equal to the predetermined speed threshold, the correction coefficient has a constant value which depends solely on the given braking command.

[0016] Further, a braking method such as that just described is proposed, in which the constant value is an increasing function of the braking command.

[0017] We further propose a braking method such as that which has just been described, in which the correction coefficient is bounded by a minimum correction coefficient and by a maximum correction coefficient.

[0018] A braking method such as that just described is also proposed, in which, for a given braking command, when the wheel speed is below the predetermined speed threshold, the correction coefficient is an increasing linear function of the wheel speed.

[0019] We further propose a braking method such as that just described, in which the slope of the linear function is an increasing function of the braking command.

[0020] A braking method such as that just described is further proposed, in which a value of the correction coefficient, at zero wheel speed, is a decreasing function of the braking command.

[0021] We further propose a braking method such as that just described, in which, whatever the braking command, the linear function passes through the same point defined by a predefined wheel speed value and a predefined coefficient value.

[0022] We further propose a braking method such as that just described, in which the predefined coefficient value is equal to 1.

[0023] The invention will be better understood in light of the following description of a particular non-limiting embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Reference will be made to the attached drawings, including: there figure 1 is a graph comprising curves of braking torque as a function of time; the figure 2 is a graph comprising curves of braking torque as a function of wheel speed; the figure 3 represents an electric braking system in which the braking method according to the invention is implemented; the figure 4 represents steps of the braking method according to the invention; the figure 5 represents a limiter / compensator functional block; the figure 6 is a graph including curves of a correction coefficient as a function of wheel speed. DETAILED DESCRIPTION OF THE INVENTION

[0025] As part of the development of a new electric braking system for a helicopter, numerous braking tests were carried out, and particularly in-depth analyses were carried out on the results of these tests.

[0026] In reference to the figure 1 , these analyses have shown that, during braking, when a constant braking force control (manual or automatic) is used to control the braking actuator of a wheel brake, the braking torque C braking actually exerted by the brake increases during braking.

[0027] In reference to the figure 2 , these analyses also showed that the level of braking torque C braking actually exerted is directly linked to the wheel speed. The braking torque actually exerted by the brake on the wheel is greater at low speed and lower at high speed. This change in braking torque reflects a variation in the braking efficiency coefficient "µ" as a function of speed.

[0028] The variation in braking torque during constant force control braking is not optimal.

[0029] Indeed, at high speeds, the average braking torque observed is constant but far from the maximum permissible braking torque. A greater braking force would allow the remaining margin to be used and improve braking performance. At low speeds, the average braking torque observed increases as the wheel speed decreases, and may become greater than the maximum permissible braking torque. This situation risks causing the failure of a structural component of the brake. The higher the braking force command, the greater the risk.

[0030] In reference to the figure 3 , the invention is implemented here in an electric braking system 1 of a helicopter, with the aim of optimizing the braking torque to reduce the risk of damage to the brake structure, and to maintain the expected level of performance.

[0031] The helicopter has two nose wheels and two main wheels. The two main wheels are braked wheels.

[0032] The electric braking system 1 comprises two brakes 3 each associated with one of the wheels 2.

[0033] Each brake 3 includes a brake actuator which is an electromechanical actuator, as well as a disc, a caliper, and pads. The brake actuator acts on a movable pad to pinch the disc between the two pads.

[0034] Each brake 3 thus produces a braking torque to brake the associated wheel 2.

[0035] Braking can be controlled by brake pedals 4 located in the helicopter cockpit. Each brake pedal 4 is connected to a deflection sensor 5 which measures a deflection of the associated brake pedal 4.

[0036] The electric braking system 1 further comprises a braking computer 6 which is connected to the depression sensors 5.

[0037] The braking method according to the invention will now be described in more detail, with reference to: figures 4 et 5 .

[0038] When a helicopter pilot presses a brake pedal 4 to brake the helicopter, the associated deflection sensor 5 measures a deflection of the brake pedal 4 and thus produces a braking instruction C f .

[0039] The braking computer 6 acquires the braking instruction C f and generates, from the braking instruction C f , a preliminary braking command C prél for the brake 3 of a wheel 2. The preliminary braking command C prél is here a force command.

[0040] As seen on the figure 4 , the preliminary braking command C prél depends on the braking setpoint C f (and therefore on the deflection measurement) according to a first predetermined curve 7.

[0041] The braking computer 6 performs processing on the preliminary braking command C prel. The processing involves the implementation of a plurality of functional blocks, which in particular comprise a slope limiter 10 and a limiter / compensator 11.

[0042] The preliminary braking command C prel is applied to an input of the slope limiter 10. The slope limiter 10 makes it possible to limit a peak force occurring, at the start of braking, at the time of application of the braking force by the braking actuator.

[0043] A braking command C om is thus generated at the output of the slope limiter 10.

[0044] The braking command C om is then applied to a first input E1 of the limiter / compensator 11. The limiter / compensator 11 includes a second input E2 via which it acquires, in real time, a speed V(t) of the wheel 2.

[0045] This speed V(t) of wheel 2 is here estimated from a measurement of the ground speed of the helicopter. Of course, the speed of wheel 2 could be obtained differently, for example by directly measuring the speed of wheel 2 using a tachometer mounted on wheel 2.

[0046] The limiter / compensator 11 applies a dynamic correction to the braking command C om .

[0047] The purpose of dynamic correction is to ensure that brake 3 exerts on wheel 2, in response to the braking command C om , a braking torque which is effectively constant regardless of the speed of wheel 2.

[0048] Dynamic correction is a function of the brake command and the speed of wheel 2.

[0049] Dynamic correction consists, at the start of braking, when the speed V(t) of wheel 2 is greater than or equal to a predetermined speed threshold, in producing a corrected braking command C corr greater than the braking command C om .

[0050] Then, when the speed V(t) of wheel 2 becomes lower than the predetermined speed threshold, the dynamic correction consists of reducing the corrected braking command C corr so that the corrected braking command C corr becomes lower than the braking command C om .

[0051] The corrected braking command C corr is produced on output S of limiter / compensator 11.

[0052] The dynamic correction consists of multiplying the braking command C om by a correction coefficient C c which depends on the braking command C om and the speed V(t) of wheel 2.

[0053] So we have: C corr = C c C om , V t × C om , where C corr is the corrected brake command, C om is the brake command, V(t) is the speed of wheel 2 and C c (C om , V(t)) is the correction coefficient which depends on the brake command C om and the speed V(t) of wheel 2.

[0054] In reference to the figure 6 , for a given braking command C om , when the speed V(t) of wheel 2 is greater than or equal to the predetermined speed threshold S v , the correction coefficient C has a constant value which depends only on the given braking command C om . This constant value is an increasing function of the braking command C om .

[0055] Curve portion 15 corresponds to a maximum braking command, curve portion 16 to a minimum braking command, and curve portions 17 to intermediate braking commands between the maximum braking command and the minimum braking command. Here, the minimum braking command is the braking command below which the dynamic correction is not implemented, and the maximum braking command is the braking command above which the dynamic correction is not implemented.

[0056] We can clearly see that the maximum correction coefficient C cmax , corresponding to the maximum braking command, is greater than the intermediate correction coefficients C cint , corresponding to the intermediate braking commands, which are themselves greater than the minimum correction coefficient C cmin , corresponding to the minimum braking command.

[0057] The correction coefficient C c is therefore limited by the minimum correction coefficient C cmin and by the maximum correction coefficient C cmax, which prevents a fault in the corrector from leading to a corrected braking command that is too weak or too strong.

[0058] For a given braking command C om , when the speed V(t) of wheel 2 is lower than the predetermined speed threshold S v , the correction coefficient C c is an increasing linear function of the speed of wheel 2.

[0059] The slope of the linear function is an increasing function of the braking command C om .

[0060] We see on the figure 6that the slope of the linear function 19, corresponding to the maximum braking command, is greater than the slopes of the linear functions 20, corresponding to the intermediate braking commands, which are themselves greater than the slope of the linear function 21, corresponding to the minimum braking command.

[0061] We also note that a value of the correction coefficient C c , at zero speed V(t), is a decreasing function of the braking command C om .

[0062] Thus, the value 22 of the correction coefficient C c at zero speed V(t), for the maximum braking command, is lower than the values ​​23 of the correction coefficient C c at zero speed V(t), for the intermediate braking commands, which are themselves lower than the value 24 of the correction coefficient C c at zero speed V(t), for the minimum braking command.

[0063] We also see that, whatever the braking command, the linear function 19, 20, 21 passes through the same point P defined by a predefined wheel speed value V p and a predefined correction coefficient value C cp .

[0064] The predetermined speed threshold S v is for example equal to 11m / s. The predetermined speed threshold can be influenced by the value of the brake command and by the predefined wheel speed value.

[0065] The value of the predefined correction coefficient C cp is here equal to 1.

[0066] The corrected braking command C corr is then transformed into a position setpoint C ons . The position setpoint C ons depends on the corrected braking command according to a second predetermined curve 25. The position setpoint C ons is a linear position value of the pusher of the braking actuator of the brake 3 of the wheel 2. The braking computer 6 uses measurements of this linear position, provided by a position sensor located on the braking actuator, and implements a servocontrol 26 to control the linear position of the pusher of the braking actuator.

[0067] The braking computer 6 therefore controls the braking actuator of brake 3 of wheel 2 using the corrected braking command C corr.

[0068] It should be noted here that the braking method according to the invention does not implement torque or force control. The braking command and the corrected braking command are force controls, but no torque or force measurement is carried out. The braking method according to the invention therefore does not require a torque or force sensor.

[0069] It is also specified that the implementation of the technical solution required two distinct stages.

[0070] In a first step, the characterization of numerous data files from braking tests with constant braking force control made it possible to construct a model of the evolution of the torque as a function of the speed, and made it possible to identify the speed threshold S v . This modeling is independent of the initial braking speed.

[0071] Below S v , the average torque increases as the speed decreases. It is therefore necessary to limit this increase, and a limiter function is implemented.

[0072] Above S v , the stability of the average torque is acceptable. However, the average torque is lower than the overall average braking torque (due to the previous phenomenon). It must therefore be increased to compensate for the reduction in performance due to the limiter function. A compensator function is therefore implemented.

[0073] In a second step, once the model was established, the correction coefficient was constructed in order to adapt dynamically to the wheel speed, but also to the braking command, because the level of compensation and / or limiter to be applied is dependent on the request made by the pilot or the avionics.

[0074] 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.

[0075] It has been described here that the braking computer produces a braking command to a wheel, and that the braking command is corrected according to a dynamic correction which is a function of the braking command and the wheel speed. The braking command could of course be a global command to several wheels. Similarly, the speed used could be a speed (measured or estimated) representative of the speed of several wheels (for example an average of the speeds of these wheels).

[0076] The architecture of the braking system in which the invention is implemented may of course be different from that presented here. The braking system is not necessarily an electric braking system, but could be, for example, a hydraulic braking system (in which case the correction is, for example, carried out on the hydraulic pressure and not on a braking command intended to be transformed into a position instruction).

Claims

1. Method for braking at least one wheel (2) of an aircraft, the wheel being provided with a brake (3) having at least one braking actuator, comprising the steps of: generating a braking command (Com) on the basis of a braking setpoint (Cf); estimating and / or measuring a wheel speed (V(t)); applying a dynamic correction to the braking command, the dynamic correction being a function of the braking command and of the wheel speed (V(t)), the dynamic correction comprising the step of producing a corrected braking command (Ccorr) greater than the braking command when the wheel speed is greater than or equal to a predetermined speed threshold (Sv), and then the step of reducing the corrected braking command when the wheel speed becomes less than the predetermined speed threshold, with the result that the corrected braking command becomes less than the braking command; controlling the braking actuator of the brake of the wheel by using the corrected braking command.

2. Braking method according to claim 1, wherein the dynamic correction consists of multiplying the braking command by a correction coefficient (Cc) which depends on the braking command (Com) and on the wheel speed (V(t)).

3. Braking method according to claim 2, wherein, for a given braking command, when the wheel speed (V(t)) is greater than or equal to the predetermined speed threshold (Sv), the correction coefficient (Cc) has a constant value which depends only on the given braking command.

4. Braking method according to claim 3, wherein the constant value is an increasing function of the braking command (Com).

5. Braking method according to claim 2, wherein the correction coefficient (Cc) is limited by a minimum correction coefficient (Ccmin) and by a maximum correction coefficient (Ccmax).

6. Braking method according to claim 2, wherein, for a given braking command, when the wheel speed (V(t)) is less than the predetermined speed threshold (Sv), the correction coefficient (Cc) is an increasing linear function of the wheel speed ((V(t)).

7. Braking method according to claim 6, wherein the slope of the linear function is an increasing function of the braking command (Com).

8. Braking method according to claim 6, wherein a value of the correction coefficient (Cc), at zero wheel speed, is a decreasing function of the braking command (Com).

9. Braking method according to claim 6, wherein, whatever the braking command (Com), the linear function passes through one same point (P) defined by a predefined wheel speed value (Vp) and a predefined coefficient value.

10. Braking method according to claim 9, wherein the predefined coefficient value is equal to 1.