Aircraft braking method including dynamic correction of braking commands

Abstract

A method for braking at least one wheel of an aircraft, the wheel being provided with a brake having at least one brake actuator, the method comprising the steps of: based on a braking set point (C f ) to generate the braking command (C om ); estimating wheel speed; applying a dynamic correction to the braking command, the dynamic correction being a function of the braking command and the wheel speed (V(t)), the dynamic correction comprising generating a corrected braking command (C corr ), and subsequently when the wheel speed becomes less than a predetermined speed threshold, the step of reducing the corrected braking command, with the result that the corrected braking command becomes less than the braking command.

Description

[0001] The invention relates to the field of aircraft braking methods involving dynamic correction of braking commands. Background of the Invention

[0003] Modern aircraft, such as airplanes or helicopters, conventionally have a ground braking system for certain so-called "braking" wheels of the aircraft. The braking system comprises one or more braking computers which arm one of the braking wheels.

[0004] Each brake comprises at least one friction member, for example made of steel or carbon, and one or more brake actuators, which are either hydraulic actuators (hence the term "hydraulic brake system") or electromechanical actuators (hence the term "electric brake system").

[0005] In the case of aircraft, each brake typically includes several actuators and a stack of carbon discs.

[0006] In the case of helicopters, patent FR 3007096 B1 describes a brake in which a single disc rotates with the brake wheel, the disc being associated with a caliper which overlaps the disc and whose jaws receive two pads, one of which is movably mounted so as to be able to clamp the disc between the two pads with the aid of a single brake actuator.

[0007] When the pilot of the aircraft depresses the brake pedal located in the cockpit, a so-called manual brake set point is generated, which depends on the deflection applied to the brake pedal. This manual brake set point is transmitted to a brake computer, which generates a manual brake command based on the manual brake set point. Likewise, when braking is commanded by an automatic brake function, the automatic brake set point is transmitted to a brake computer, which generates an automatic brake command.

[0008] Manual or automatic braking commands are used to control the brake actuators, with the result that each brake acts on the associated braking wheel, the braking torque braking the braking wheel and thus decelerating the aircraft.

[0009] Purpose of the Invention

[0010] The object of the present invention is to optimize the braking command with the aim of limiting the risk of damaging the structure of the brake while maintaining the overall intended braking performance. SUMMARY OF THE INVENTION

[0011] In order to achieve this object, a method for braking at least one wheel of an aircraft is proposed, the wheel being provided with a brake having at least one brake actuator, the method comprising the following steps:

[0012] generating a braking command based on a braking set point;

[0013] estimating and / or measuring wheel speed;

[0014] 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 steps of generating a corrected braking command greater than the braking command when the wheel speed is greater than or equal to a predetermined speed threshold, and then 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;

[0015] A brake actuator controlling the brakes of the wheels is controlled by using the corrected brake commands.

[0016] An extensive analysis based on the results of numerous braking tests made it possible to observe that during braking, when a constant braking command is used, the level of braking torque actually applied by the brakes to the wheels is directly related to the wheel speed. The braking torque actually applied by the brakes to the wheels is greater at low speeds and less at high speeds.

[0017] Therefore, at high speeds, the performance of prior art braking methods is not optimal, and at low speeds there is a risk of damaging the braking equipment.

[0018] In contrast, in the braking method according to the invention, a dynamic correction is applied that depends on the brake command and the wheel speed. The dynamic correction makes it possible to compensate the brake command at high speeds and thus improve the braking performance, and to limit the brake command at low speeds and thus extend the service life of the aircraft's brakes and reduce the risk of damage to the brake's structure, in particular the rotor structure.

[0019] Furthermore, a braking method is proposed, such as the one just described, in which the dynamic correction consists in multiplying the braking command by a correction factor that depends on the braking command and the wheel speed.

[0020] Furthermore, a braking method is proposed, such as the one just described, in which, for a given braking command, the correction factor has a constant value that depends only on the given braking command when the wheel speed is greater than or equal to a predetermined speed threshold.

[0021] Furthermore, a braking method is proposed, such as the one just described, in which the constant value is an increasing function of the braking command.

[0022] Additionally, a braking method, such as the one just described, is proposed in which the correction factor is limited by a minimum correction factor and a maximum correction factor.

[0023] Additionally, a braking method, such as the one just described, is proposed wherein, for a given braking command, when the wheel speed is less than a predetermined speed threshold, the correction factor is an increasing linear function of the wheel speed.

[0024] Additionally, a braking method is proposed, such as the one just described, in which the slope of the linear function is an increasing function of the braking command.

[0025] Furthermore, a braking method such as the one just described is proposed, wherein the value of the correction coefficient at zero wheel speed is a decreasing function of the braking command. Furthermore, a braking method such as the one just described is proposed, wherein the linear function passes through the same point defined by the predefined wheel value and the predefined coefficient value regardless of the braking command.

[0026] Additionally, a braking method, such as the one just described, is proposed, wherein the predefined coefficient value is equal to 1.

[0027] The present invention will best be understood from the following description of specific non-limiting embodiments of the invention.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Reference will be made to the accompanying drawings, in which:

[0030] Figure 1 is a graph including a brake torque curve as a function of time;

[0031] Figure 2 is a graph including a brake torque curve as a function of wheel speed;

[0032] Figure 3 represents an electric brake system in which the braking method according to the invention is implemented;

[0033] Figure 4 Shows the steps of the braking method according to the present invention;

[0034] Figure 5 Represents a limitation / compensation functional unit;

[0035] Figure 6 is a diagram of a curve including a correction factor as a function of wheel speed.

[0036] Detailed description of the invention

[0037] In the scope of the development of a new electric brake system for a helicopter, a large number of brake tests have been carried out and, in particular, the results of these tests have been extensively analyzed.

[0038] refer to Figure 1 These analyses make it possible to observe that during braking, when a constant braking force command (manual or automatic) is used to control the brake actuator of the wheel brake, the braking torque Cfreinage Increases during braking.

[0039] refer to Figure 2 , these analyses also make it possible to show the actual applied braking torque C freinage Directly related to the wheel speed. The braking torque actually applied by the brakes to the wheels is greater at low speeds and lower at high speeds. This evolution of the braking torque conveys the variation of the braking efficiency coefficient "μ" with speed.

[0040] During braking with a constant braking force command, the variation of the braking torque is not optimal. In fact, at high speeds, the observed average braking torque is constant, but far from the maximum admissible braking torque. A greater braking force would make it possible to use the remaining margin and improve the braking performance. At low speeds, when the wheel speed decreases, the average braking torque increases and can become greater than the maximum admissible braking torque. This situation carries the risk of causing fracture of the structural components of the brake. The greater the braking force command, the more the risk increases.

[0041] refer to Figure 3 The invention is implemented here in an electric braking system 1 of a helicopter, the purpose of which is to optimize the braking torque in order to reduce the risk of damaging the brake structure and maintain the required performance level.

[0042] The helicopter comprises two front wheels and two main wheels. The two main wheels are brake wheels 2.

[0043] The electric brake system 1 comprises two brakes 3 , each associated with one wheel 2 .

[0044] Each brake 3 comprises a brake actuator as an electromechanical actuator, as well as a disc, a caliper and a pad. The brake actuator acts on a movable pad to clamp the disc between two pads.

[0045] Each brake 3 thus generates a braking torque in order to brake the associated wheel 2 .

[0046] The brakes can be commanded by brake pedals 4 located in the cockpit of the helicopter. Each brake pedal 4 is connected to a pressure sensor 5 which measures the deflection of the associated brake pedal 4.

[0047] The electric brake system 1 further comprises a brake computer 6 which is connected to the pressure sensor 5 .

[0048] Now, refer to Figure 4 and Figure 5 The braking method according to the present invention is described in more detail.

[0049] When the helicopter pilot depresses the brake pedal 4 to brake the helicopter, the associated pressure sensor 5 measures the deflection of the brake pedal 4 and generates a braking setpoint C f .

[0050] The brake computer 6 acquires the brake set point C f , and based on the braking set point C f To generate a preliminary braking command C for the brake 3 of the wheel 2 prél . Preliminary braking command C prél Here is the force command.

[0051] like Figure 4 As can be seen in FIG. 1 , according to the first predetermined curve 7, the preliminary braking command C prél Depends on the braking set point C f (and therefore depends on the measurement of deflection).

[0052] The brake computer 6 responds to the preliminary brake command C prél The process is performed with the implementation of a plurality of functional units, which include, among others, a slope limiter 10 and a limiter / compensator 11 .

[0053] Initial brake command C prél is applied to the input of the slope limiter 10. The slope limiter 10 makes it possible to limit the force peak which occurs at the start of braking, when the brake actuator applies the braking force.

[0054] Therefore, a braking command C is generated at the output of the slope limiter 10. om .

[0055] Braking command C om It is therefore applied to a first input E1 of the limiter / compensator 11. The limiter / compensator 11 comprises a second input E2 via which the speed V(t) of the wheel 2 is acquired in real time.

[0056] The speed V(t) of the wheel 2 is estimated based on a measurement of the helicopter ground speed. Of course, the wheel speed 2 can be obtained differently, for example by measuring the wheel speed 2 directly by means of a tachometer mounted on the wheel 2 .

[0057] Limiter / compensator 11 for braking command C om Apply dynamic correction.

[0058] The purpose of dynamic correction is to ensure that the brake 3 responds to the braking command C om A braking torque is applied to wheel 2 which is substantially constant regardless of wheel speed 2. The dynamic correction is a function of the braking command and wheel speed 2.

[0059] At the beginning of braking, when the speed V(t) of the wheel 2 is greater than or equal to a predetermined speed threshold, the dynamic correction includes generating a braking command C greater than om The corrected braking command C corr .

[0060] Subsequently, when the speed V(t) of the wheel 2 becomes less than a predetermined speed threshold, the dynamic correction consists in reducing the corrected braking command C corr , the result is the corrected braking command C corr becomes less than the braking command C om .

[0061] The corrected braking command C is generated at the output S of the limiter / compensator 11. corr .

[0062] Dynamic correction consists in changing the braking command C om Multiply by the correction factor C c , which depends on the braking command C om and the speed V(t) of wheel 2.

[0063] Thus, therefore:

[0064] C corr =C c (C om ,V(t))x C om ,

[0065] Among them C corr is the corrected braking command, C om is the braking command, V(t) is the wheel speed 2, and C c (C om , V(t)) depends on the braking command C om And the correction coefficient of the speed V(t) of the wheel 2.

[0066] refer to Figure 6 , for a given braking command C om , when the speed V(t) of the wheel 2 is greater than or equal to the predetermined speed threshold S v When the correction factor C c has a constant value that depends only on the given braking command C om This constant value is the braking command C om An increasing function of .

[0067] Curve portion 15 corresponds to the maximum braking command, curve portion 16 corresponds to the minimum braking command, and curve portion 17 corresponds to an intermediate braking command between the maximum braking command and the minimum braking command. Here, the minimum braking command is a braking command below which no dynamic correction is achieved, and the maximum braking command is a braking command above which no dynamic correction is achieved.

[0068] It can be seen that the maximum correction coefficient C corresponding to the maximum braking command cmax Greater than the intermediate correction coefficient C corresponding to the intermediate braking command cint , which itself is greater than the minimum correction factor C corresponding to the minimum braking command cmin Therefore, the correction factor C c Subject to minimum correction factor C cmin and the maximum correction factor C cmax This makes it possible to avoid corrector malfunctions leading to too low or too high corrected braking commands.

[0069] For a given braking command C om , when the speed V(t) of the wheel 2 is less than the predetermined speed threshold S v When the correction factor C c It is a linear increasing function of wheel speed 2.

[0070] The slope of the linear function is the braking command C om An increasing function of .

[0071] from Figure 6 It can be seen that the gradient of the linear function 19 corresponding to the maximum braking command is greater than the slope of the linear function 20 corresponding to the intermediate braking command, which itself is greater than the gradient of the linear function 21 corresponding to the minimum braking command.

[0072] It should also be noted that at zero speed V(t), the correction factor C c The value is the braking command C om A decreasing function.

[0073] Therefore, for the maximum braking command, the correction factor C at zero speed V(t) is c The value 22 is less than the correction coefficient C at zero speed V(t) for the intermediate braking command c The value of 23, which itself is less than the correction coefficient C at zero speed V(t) for the minimum braking command c The value is 24.

[0074] It can also be seen that, regardless of the braking command, the linear functions 19, 20, 21 will pass through the same point P, which is determined by the predefined wheel speed value V p and the predefined correction factor value C cp definition.

[0075] For example, the predetermined speed threshold S v This predetermined speed threshold may be influenced by the value of the braking command and the predetermined wheel speed value.

[0076] Correction factor Ccp The predefined value of is equal to 1 here.

[0077] Therefore, the corrected braking command C corr is converted into a position set point C ons According to the second predetermined curve 25, the position set point C ons Depends on the corrected brake command. Position set point C ons is the linear position value of the button of the brake actuator of the wheel 2 brake 3. The brake computer 6 uses the measurement of the linear position provided by the position sensor located on the brake actuator and implements the slave 26 to command the linear position of the button of the brake actuator.

[0078] Therefore, the brake computer 6 uses the corrected brake command C corr To control the brake actuator of the wheel 2 brake 3.

[0079] It should be noted here that the braking method according to the invention does not implement torque or force slave. The braking command and the corrected braking command are force commands, but no torque or force measurement is performed. Therefore, the braking method according to the invention does not require any torque or force sensor.

[0080] It is also stipulated that the implementation of this technical solution requires two separate steps.

[0081] During a first step, the characterization of a large number of constant braking force command braking test data files makes it possible to model the evolution of torque with speed and, therefore, to identify the speed threshold S v The model is independent of the initial braking speed.

[0082] In S v Below, the average torque increases as the speed decreases. Therefore, this increase must be limited and a limiting function must be implemented.

[0083] In S v Above, the stability of the average torque is acceptable. However, the average torque is less than the total average braking torque (due to the above phenomenon). Therefore, it must be increased to compensate for the performance degradation caused by the limiting function. Therefore, the compensation function is implemented.

[0084] In a second step, once the model is built, correction coefficients are established in order to dynamically adapt to the wheel speed, but also to the braking command, since the level of compensation and / or limitation to be applied depends on the request of the pilot or the avionics.

[0085] Of course, the invention is not limited to the described embodiments but comprises any variant coming within the field of the invention such as defined in the claims.

[0086] Here, it is described that the brake computer generates a brake command to be sent to the wheel, and the brake command is corrected according to a dynamic correction, which is a function of the brake command and the wheel speed. Of course, the brake command can be an overall command sent to several wheels. Likewise, the speed used can be a speed representative of the (measured or estimated) speeds of several wheels (e.g., an average of the speeds of these wheels).

[0087] The architecture of the braking system implementing the invention can of course differ from that presented here. The braking system is not necessarily an electric braking system, but can be, for example, a hydraulic braking system (in which case the correction is made according to the hydraulic pressure rather than to the braking command intended to be converted into a position setpoint).

Claims

1. A method for braking at least one wheel (2) of an aircraft, the wheel being provided with a brake (3) having at least one brake actuator, the method comprising the following steps: Based on the braking set point (C f ) to generate the braking command (C om ); Estimating and / or measuring wheel speed (V(t)); A dynamic correction is applied to the braking command, the dynamic correction being a function of the braking command and the wheel speed (V(t)), the dynamic correction comprising: v ) generates a corrected braking command (C corr ), and subsequently when the wheel speed becomes less than the predetermined speed threshold, the step of reducing the corrected braking command, with the result that the corrected braking command becomes less than the braking command; controlling the brake actuator of the brake of the wheel by using the corrected brake command, The dynamic correction includes multiplying the braking command by a correction factor (C c ), the correction factor depends on the braking command (C om ) and the wheel speed (V(t)).

2. The method according to claim 1, characterized in that For a given braking command, when the wheel speed (V(t)) is greater than or equal to the predetermined speed threshold (S v ), the correction coefficient (C c ) has a constant value which depends only on the given braking instruction.

3. The method according to claim 2, characterized in that The constant value is the braking command (C om ) is an increasing function.

4. The method according to claim 1, characterized in that The correction factor (C c ) is determined by the minimum correction factor (C cmin ) and the maximum correction factor (C cmax ) to restrict.

5. The method according to claim 1, characterized in that For a given braking command, when the wheel speed (V(t)) is less than the predetermined speed threshold (S v ), the correction coefficient (C c ) is an increasing linear function of the wheel speed (V(t)).

6. The method according to claim 5, characterized in that The slope of the linear function is the braking command (C om ) is an increasing function.

7. The method according to claim 5, characterized in that At zero wheel speed, the correction factor (C c ) is the braking command (C om ) is a decreasing function.

8. The method according to claim 5, characterized in that Regardless of the braking command (C om )) the linear function passes through the same point (P) determined by the predefined wheel speed value (V p ) and predefined coefficient values.

9. The method according to claim 8, characterized in that The predefined coefficient value is equal to 1.

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