Selective braking on wheels not provided with a drive actuator

Abstract

The invention relates to a method for braking an aircraft (11) on the ground, which aircraft comprises at least a first wheel (13a) provided with a first brake (14a) and with a drive actuator (15), and at least a second wheel (13b) provided with a second brake (14b) but not provided with a drive actuator, the method comprising the steps of: • - selecting, in order to brake the aircraft on the ground, a first braking mode or a second braking mode having a lower braking capacity; • - braking the aircraft by producing a first braking setpoint (Cl) for the first brake (14a) and a second braking setpoint (C2) for the second brake (14b) such that, if the first mode is chosen, a ratio of the first braking setpoint to the second braking setpoint is equal to a first value and, if the second mode is chosen, the ratio is equal to a second value that is lower than the first value.

Description

[0001]SELECTIVE BRAKING ON WHEELS NOT EQUIPPED WITH A DRIVE ACTUATOR The invention relates to the field of aircraft equipped with a taxiing system. BACKGROUND OF THE INVENTION It is envisaged to equip aircraft with an electric taxiing system. This system allows the aircraft to move autonomously on the ground without using its main powertrain (jet engines or propeller engines) and without external assistance. Taxiing is sometimes also referred to as "rolling". Certain wheels of such an aircraft would thus be equipped with an actuator for driving the rotation of the wheel. The drive actuators are so-called "electric" actuators (actually electromechanical) and are powered by electrical energy coming for example from the APU (for Auxiliary Power Unit). Thus, the aircraft can be rolled back to the boarding gate without the tractors,and the journey to the take-off runway can be made without the jet engines (or propeller engines). A few minutes before take-off, the jet engines are started. The aircraft takes off, operates its flight, then lands and, a few minutes after landing, which corresponds to the time needed for the jet engines to cool down, they are stopped and the aircraft is taxied to the passenger and cargo disembarkation area using the electric taxiing system. The electric taxiing system reduces fuel consumption for ground movement of the aircraft, because only the APU operates when the electric taxiing system is used. This results in economic gains, a significant reduction in carbon dioxide (CO2), nitrogen oxide (NOx) and fine particle emissions, as well as a reduction in noise in airport areas. With reference to Figure 1,for example, it is envisaged to equip with such an electric taxiing system an aircraft 1 which comprises two main landing gears 2a, 2b each carrying two wheels: an internal wheel 3a (fuselage side) and an external wheel 3b. Of course, the aircraft 1 also comprises a braking system comprising brakes 4 equipping certain so-called “braked” wheels of the aircraft 1, and a braking computer 10. Here, the braked wheels are the four wheels 3a and 3b. The electric taxiing system comprises for example a drive actuator 5 equipping each internal wheel 3a. The drive actuator 5 is integrated at the end of the axle on the side of the external half-wheel (side opposite the leg), the brake being integrated in the internal half-wheel. The internal wheels 3a are therefore each equipped with a brake 4 and a drive actuator 5 (in addition to the brake 4),and the outer wheels 3b are equipped with a brake 4 but are not equipped with a drive actuator 5. On each wheel 3b not equipped with a drive actuator, a fan 6 ensures cooling of the brake. This fan is generally called BCF (for Brake Cooling Fan). On each wheel 3a equipped with a drive actuator 5 (and a brake 4), a single fan 6 is installed,ensuring both the cooling of the brake 4 and the cooling of the drive actuator 5. There are two reasons that explain the use of a single fan 6 on this type of wheel 3a: - the integration of the drive actuator 5 at the end of the axle prevents the integration of a conventional brake fan; - the commonization of the function for these two pieces of equipment makes it possible to simplify the integration and reduce the mass compared to a configuration with two independent fans. The solution described above has the following disadvantages. The drive actuator 5 is positioned close to the brake 4. It can therefore be exposed to high temperatures when the brake 4 heats up during braking. These high temperatures can impact the reliability of the drive actuator 5. The common ventilation is activated when necessary to cool the drive actuator 5. Therefore,it can be activated on post-braking operating phases during which ventilation of the brake 4 is not desired. Indeed, to avoid oxidation of the carbon / carbon discs of the brake 4, it may be preferable not to ventilate the brake 4 when the temperature of the discs is too high. This solution can therefore reduce the reliability, efficiency and service life not only of the taxiing system but also of the braking system. OBJECT OF THE INVENTION The object of the invention is to increase the reliability, efficiency and service life of the taxiing system and the braking system of an aircraft. SUMMARY OF THE INVENTION In order to achieve this object, a method for ground braking of an aircraft is proposed which comprises at least a first wheel equipped with a first brake arranged to brake said first wheel and a drive actuator arranged to drive said first wheel in rotation,and at least one second wheel equipped with a second brake arranged to brake said second wheel but not being equipped with a drive actuator, the ground braking method comprising the steps of: - selecting, to brake the aircraft on the ground, a first braking mode, or a second braking mode having a reduced braking capacity; - braking the aircraft by producing a first braking instruction for the first brake and a second braking instruction for the second brake, such that: o if the first braking mode is selected, a ratio between the first braking instruction and the second braking instruction is equal to a first value; o if the second braking mode is selected, said ratio is equal to a second value lower than the first value. The ground braking method according to the invention therefore makes it possible to distribute the braking differently on the first wheel and on the second wheel,depending on whether the selected and commanded ground braking is a first braking mode or a second braking mode. The first braking mode corresponds to so-called “high energy” braking, and the second braking mode to so-called “low energy” braking. The invention therefore makes it possible to limit the use of the brakes equipping the wheels also provided with drive actuators of the taxiing system, and thus to reduce the duration of exposure of these drive actuators to high temperatures, and to reduce the temperatures of the brakes during the ventilation phases imposed by the need of the taxiing system. The reliability, efficiency and service life of the taxiing system and the braking system of the aircraft are therefore improved. A ground braking method as previously described is also proposed, in which the first braking instruction, in the second braking mode,is a zero setpoint. A ground braking method is further proposed as previously described, in which the first braking setpoint and the second braking setpoint, in the first braking mode, are identical. A ground braking method is further proposed as previously described, in which the selection of the first braking mode or the second braking mode comprises the steps of: - acquiring a measurement of a ground speed of the aircraft; - selecting the first braking mode or the second braking mode as a function of the ground speed of the aircraft. A ground braking method is further proposed as previously described, comprising the steps of: - comparing the ground speed of the aircraft with a first predefined threshold; - selecting the first braking mode if the ground speed is greater than the first predefined threshold,or the second braking mode if the ground speed is lower than the first predefined threshold. A ground braking method is further proposed as previously described, in which the selection of the first braking mode or the second braking mode comprises the steps of: - acquiring a measurement or an estimation of a mass of the aircraft; - selecting the first braking mode or the second braking mode as a function of the mass of the aircraft. A ground braking method is further proposed as previously described, comprising the steps of: - comparing the mass of the aircraft with a second predefined threshold; - selecting the first braking mode if the mass is higher than the second predefined threshold, or the second braking mode if the mass is lower than the second predefined threshold. A ground braking method is further proposed as previously described, comprising the steps of: - evaluating,depending on the ground speed and the mass of the aircraft, a braking energy necessary to brake the aircraft; - compare the braking energy with a third predefined threshold; - select the first braking mode if the braking energy is greater than the third predefined threshold, or the second braking mode if the braking energy is less than the third predefined threshold. A ground braking method is further proposed as previously described, in which the selection of the first braking mode or the second braking mode comprises the steps of: - acquiring an indication on a current flight phase of the aircraft; - selecting the first braking mode or the second braking mode according to said indication. A ground braking method is further proposed as previously described,wherein the selection of the first braking mode or the second braking mode comprises the steps of: - acquiring an overall braking setpoint produced by a pilot of the aircraft, the pilot being able to be a human pilot or an automatic pilot device; - selecting the first braking mode or the second braking mode according to said overall braking setpoint. A ground braking method is further proposed as previously described, further comprising the preliminary step of checking whether a braking system of the aircraft, comprising a plurality of brakes comprising the first brake and the second brake, is or is not in a nominal state, the ground braking method further comprising the step, if the braking system is not in the nominal state, of selecting the first braking mode regardless of the value of the braking parameter(s). A ground braking method is further proposed as previously described,wherein the nominal state is a state in which all brakes of the aircraft are operational. A ground braking method as previously described is further provided,in which the first wheel and the second wheel are both located on the same landing gear of the aircraft. A braking system is further provided, comprising: - a first brake arranged to brake a first wheel which is equipped with a drive actuator; - a second brake arranged to brake a second wheel which is not equipped with a drive actuator; - a braking computer comprising a processing unit in which the ground braking method as previously described is implemented. An aircraft is further provided comprising a braking system as previously described. A computer program is further provided comprising instructions which cause the processing unit of the braking computer of the braking system as previously described to execute the steps of the ground braking method as previously described. A computer-readable recording medium is further provided,on which the computer program as previously described is recorded. The invention will be better understood in light of the following description of particular non-limiting embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Reference will be made to the appended drawings, among which: [Fig. 1] Figure 1 schematically represents an aircraft of the prior art; [Fig. 2] Figure 2 schematically represents an aircraft in which the invention is implemented; [Fig. 3] Figure 3 represents steps of a braking method according to a first embodiment of the invention; [Fig. 4] Figure 4 represents steps of a braking method according to a third embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION With reference to Figure 2, the invention is here implemented in an aircraft 11 of the short or medium-haul type, which comprises two main landing gears 12a, 12b. Each main landing gear 12a,12b carries two wheels: a first wheel 13a and a second wheel 13b. The first wheel 13a is the internal wheel (located on the fuselage side) and the second wheel 13b is the external wheel. The aircraft 11 has a braking system. The braking system is here a hydraulically actuated system, but could perfectly well be a different system, for example electrically actuated. Some wheels of the aircraft, called "braked", are equipped with a brake: here these are all the wheels 13a, 13b of the main landing gears 12a, 12b. Each first wheel 13a is therefore equipped with a first brake 14a,and each second wheel 13b is therefore equipped with a second brake 14b. The brake 14a or 14b of each of these wheels comprises a crown bearing a plurality of hydraulic braking actuators. A torque tube is fixed to the crown. The torque tube extends into the rim of the wheel. The brake also comprises a stack of discs composed of rotors which are rotationally fixed to the rim of the wheel and stators which are rotationally fixed to the torque tube. The hydraulic actuators are arranged to selectively exert, upon admission of pressurized fluid, a pressing force on the discs, thus generating a braking torque to brake the wheel. The braking system also comprises a right brake pedal which allows the pilot to control the brakes of the wheels located on the right side D of the aircraft,and a left brake pedal which allows the pilot to control the brakes of the wheels located on the left side G of the aircraft 11. In Figure 2, the right side D and the left side G have been defined in a certain way, but this definition could of course be reversed. The braking system also includes a main braking circuit as well as a backup braking circuit which can be used in the event of failure of the main braking circuit. These circuits, not shown, are completely segregated and each require a significant number of passive hydraulic components such as accumulators, filters, and active hydraulic components such as valves, distributors, and servovalves. The braking system further includes a braking computer 20, which integrates a processing unit 21. The processing unit 21 comprises at least one processing component 22 (electronic and / or software), which is for example a “general-purpose” processor,a processor specialized in signal processing (or DSP, for Digital Signal Processor), or a microcontroller. The processing unit 21 then comprises memories 23, volatile and non-volatile, connected to or integrated in the processing component 22. At least one of these memories 23 forms a computer-readable recording medium,on which is recorded at least one computer program comprising instructions which cause the processing unit 21 to execute at least some of the steps of the ground braking method which will be described below. The processing component 22 can also be a programmable logic circuit such as an FPGA (for Field Programmable Gate Arrays) or an ASIC (for Application Specific Integrated Circuit). The braking computer 20 acquires global braking instructions resulting in particular from the action of the pilot on the brake pedals. The braking computer 20 receives a global braking instruction for the landing gear 12a and a global braking instruction for the landing gear 12b, which are possibly different. The braking computer 20 produces from these global braking instructions individual braking instructions associated with each brake,which allow the servovalves to be controlled, which then deliver to each brake a braking pressure proportional to the individual braking setpoint associated with it. The braking computer 20 produces a first braking setpoint C1 for each first brake 14a and a second braking setpoint C2 for each second brake 14b. The first two braking setpoints C1 are possibly different, as are the second two braking setpoints C2. The aircraft 11 further comprises a taxiing system which is here an electrically actuated system. The first wheels 13a (inner wheels) of the main landing gear are here each equipped with a drive actuator 15. Each drive actuator 15 is integrated at the end of the axle on the side of the outer half-wheel,the brake 14a being integrated into the inner half-wheel. Each drive actuator 15 is used to drive a first wheel 13a in rotation. Each drive actuator 15 is an electromechanical actuator which comprises an electric motor comprising a stator and a rotor. The drive actuator 15 here comprises a gear train and a clutch device for connecting and disconnecting the drive actuator 15 to the wheel 13a. When the drive actuator 15 is in a so-called “engaged” position, the gear train drives the first wheel 13a in rotation, thus making it possible to move the aircraft on the ground. In addition to the drive actuators 15, the taxiing system comprises a system for controlling said taxiing system (not shown), which operates in the following manner. When the pilot generates a traction command to move the aircraft 11 on the ground using the taxiing system,the piloting system generates a traction command to pilot the electric motor of the drive actuator 15 of each first wheel 13a, so that said drive actuator 15 applies to said first wheel 13a a traction motor torque intended to move the aircraft 11 on the ground. The aircraft 11 also comprises a wheel ventilation system which, for each wheel 13a, 13b of the two main landing gears 12a, 12b, comprises a fan 16. For each first wheel 13a, the fan 16 is intended to cool the first brake 14a and the drive actuator 15 equipping said first wheel 13a. For each second wheel 13b, the fan 16 is intended to cool the second brake 14b equipping said second wheel 13b. The implementation of the ground braking method according to the invention is now described. For low-energy braking (and in particular all taxiing braking),it is possible to brake less significantly on certain wheels. Indeed, the brakes are sized for significantly higher performances, and in particular for cases of overload landing braking or aborted takeoff (we speak of RTO, for Rejected TakeOff). In particular, for these low-energy brakings, it is possible to use less force on the first brakes 14a of the first wheels 13a, than on the second brakes 14b of the second wheels 13b. The processing unit 21 of the braking computer 20 therefore selects, to brake the aircraft 11 on the ground, a first braking mode, or a second braking mode having a reduced braking capacity. By "reduced braking capacity",it is understood that the deceleration capacity and the total energy that can be dissipated during braking via the second braking mode are lower than those of braking via the first braking mode. When the processing unit 21 receives a global braking instruction for the brakes 14a, 14b of each of the landing gears 12a, 12b, the processing unit 21 therefore selects and controls for braking the aircraft on the ground either a first braking mode or a second braking mode, by producing a first braking instruction C1 (individual) for the first brake 14a and a second braking instruction C2 (individual) for the second brake 14b. In the first braking mode, a ratio between the first braking instruction C1 and the second braking instruction C2 is equal to a first value. In the second braking mode, said ratio is equal to a second value lower than the first value. Here,and in a non-limiting manner: - the first braking instruction C1 and the second braking instruction C2, in the first braking mode, are identical; - the first braking instruction C1, in the second braking mode, is a zero instruction. Thus, the first value of the ratio is equal to 1, and the second value of the ratio is equal to 0. In this way, when the second braking mode is selected, for example to brake the aircraft 11 during the taxiing phases, the brakes of the wheels equipped with drive actuator 15 (i.e. the first brakes 14a) are not used and therefore do not heat up, which limits the temperatures experienced by the drive actuators 15. In addition, the ventilation, when it is activated to cool the drive actuators 15, indirectly cools only the brakes which are not used during this braking: this limits the ventilation of the hot brakes. During the taxi out phase,that is to say during taxiing before takeoff, the brakes are relatively cold after the TAT (Turn-Around Time) period, at the moment when the aircraft leaves the boarding gate. During the taxi out phase, on each main landing gear 12a, 12b, a single wheel 13b is therefore used for braking (the brake 14b of which heats up, without being ventilated because there is no drive actuator to cool). The other wheel 13a is used only for taxiing, and its brake 14a does not heat up. Similarly, during a landing, if the second braking mode is selected, and therefore if the landing braking is low-energy braking, the processing unit 21 commands braking only on the second wheels 13b not equipped with a drive actuator 15. This decorrelates the use of the braking and taxiing systems on given wheels during these braking operations. On the other hand,if the landing braking is not low energy braking, the first braking mode is selected and all four brakes are used to brake the aircraft 11. In the latter case, in the case of the taxi-in phase following landing, as all the brakes have been used, and have therefore heated up, the fact of not using all the wheels to brake during taxiing is less effective than in the taxi-out phase because the drive actuators 15 are used on first wheels 13a associated with hot brakes: the actuators 15 therefore undergo the increase in temperature of the brakes. However, the fact of not adding braking energy during taxiing (beyond the landing braking energy) nevertheless limits the temperature of the brakes 14a equipping the first wheels 13a associated with a drive actuator 15. The invention has a very positive impact on the wear of the brakes 14a, 14b. Indeed,on certain carbon / carbon composite materials used for brake discs, wear is reduced by braking on a hot brake (there is a "wear hump" on cold material). The braking method according to the invention will therefore lead to braking on hotter brakes, and will be favorable for this type of carbon. In the case of materials not having this characteristic, this method can lead to faster wear of the brakes on wheels not equipped with drive actuators (due to greater stress). However, if the integration of the drive actuators at the end of the axle requires an additional operation of dismantling this actuator to change the brake, increasing the frequency of removing the brakes on the non-equipped wheels and reducing it on the wheels equipped with drive actuators may be of interest. We will now describe in more detail, with reference to Figure 3,a first embodiment of the invention. In this first embodiment, the selection of the first braking mode or the second braking mode consists of acquiring a measurement of a ground speed of the aircraft 11, and selecting the first braking mode or the second braking mode as a function of the ground speed of the aircraft. The activation of braking on all the wheels or only on the wheels not equipped with a drive actuator is therefore managed as a function of the speed of the aircraft 11, which makes it possible to distinguish between taxiing cases (for which it is not necessary to activate all the brakes to ensure braking performance) and landing or RTO cases. The method begins with the preliminary steps E0 and E1. The processing unit 21 monitors the state of the braking system: step E0. The processing unit 21 checks whether the braking system, comprising all the brakes of the aircraft 11,and therefore the first brakes 14a and the second brakes 14b, is or is not in a nominal state: step E1. The nominal state is here a state in which all the brakes of the aircraft 11 are operational. If the braking system is not in the nominal state, the processing unit 21 controls the first braking mode (which uses both the first brakes 14a and the second brakes 14b) regardless of the value of the ground speed: step E2. Thus, if certain brakes are inhibited or faulty, all the brakes remaining operational are used. In step E1, if the braking system is in the nominal state, the processing unit 21 acquires at least one measurement of the ground speed of the aircraft 11: step E3. The measurement is carried out in real time. The measurement of the ground speed of the aircraft 11 may be a measurement produced by the tachometer(s) of one or more wheels of the aircraft 11. It may also be a speed of the aircraft 11 itself,the measurement then being produced by one or more inertial units of the aircraft 11. The processing unit 21 compares the ground speed with a first predefined threshold: step E4. If the ground speed is greater (here greater than or equal to) the first predefined threshold, the processing unit 21 selects the first braking mode to brake the aircraft 11: step E2. If the ground speed is less (here strictly) than the first predefined threshold, the processing unit 21 selects the second braking mode to brake the aircraft 11. The first brakes 14a of the first wheels 13a, each equipped with a drive actuator 15, are not used: step E5. As we have seen, the braking computer 20 receives a global braking instruction for each of the landing gears 12a and 12b. For each landing gear 12a, 12b, if the overall braking instruction is equal to X, in the case of the first braking mode,the first braking instruction C1 used for the first brake 14a and the second braking instruction C2 used for the second brake 14b are both equal to 50% of X (and therefore, as seen earlier, the ratio between the first braking instruction and the second braking instruction is equal to 1). On the other hand, in the case of the second braking mode, the first braking instruction C1 used for the first brake 14a is a zero instruction, and the second braking instruction C2 used for the second brake 14b is equal to 100% of X (and therefore, as seen earlier, the ratio between the first braking instruction C1 and the second braking instruction C2 is equal to 0). The first and second braking instructions are therefore adapted to have the same braking level on a given landing gear when braking is done on two or four wheels. The reconfiguration is therefore transparent to the pilot of the aircraft 11,which perceives the same response from the braking system for a given instruction, whether braking is done on two or four wheels. In a second embodiment, the selection of the first braking mode or the second braking mode consists of acquiring a measurement of the mass of the aircraft, and selecting the first braking mode or the second braking mode according to the mass of the aircraft. Knowledge of the mass of the aircraft makes it possible to distinguish between low-energy landings ("service landing") and high-energy landings requiring full braking capacity (normal landing, overload landing). The mass of the aircraft 11 at landing can be determined by deducting from the takeoff mass the mass of fuel consumed in flight. The mass of the aircraft 11 at takeoff can be determined in different ways. The mass can for example be determined via a system delivering, for each of the aircraft's landing gear,a signal representative of a sinking of the rod into the box. The mass can also, for example, be directly entered by the pilot of the aircraft or by the ground personnel via a human-machine interface (HMI). The mass is then determined, for example, from the empty mass of the aircraft, the mass of fuel, the weighing of freight and baggage, and a fixed mass per passenger. The ground braking method is carried out in the same way as in Figure 3, but using the mass of the aircraft. In step E4, the processing unit 21 compares the mass of the aircraft with a second predefined threshold. The processing unit 21 selects the first braking mode if the mass is greater than the second predefined threshold, or the second braking mode if the mass is less than the second predefined threshold. A third embodiment of the invention is now described with reference to Figure 4. Here, the braking parameter used by the processing unit 21,to decide whether all the brakes should be used or not, is the braking energy required to brake the aircraft 11. The method starts with the preliminary steps E10 and E11. The processing unit 21 monitors the state of the braking system: step E10. The processing unit 21 checks whether the braking system, comprising all the brakes of the aircraft 11, and therefore the first brakes 14a and the second brakes 14b, is or is not in a nominal state: step E11. If the braking system is not in the nominal state, the processing unit 21 controls the first braking mode (which uses both the first brakes 14a and the second brakes 14b) regardless of the value of the braking energy: step E12. In step E11, if the braking system is in the nominal state,the processing unit 21 acquires at least one measurement of the ground speed of the aircraft 11: step E13. The measurement is carried out in real time. The processing unit 21 also acquires at least one measurement or estimate of the mass of the aircraft: step E14. The processing unit 21 then evaluates, as a function of said mass and the ground speed, the braking energy necessary to brake the aircraft 11: step E15. The processing unit 21 compares this energy with a third predefined threshold: step E16. If the energy is greater (here greater than or equal to) the third predefined threshold, the processing unit 21 controls the first braking mode to brake the aircraft 11: step E12. If the energy is lower (here strictly) than the third predefined threshold, the processing unit 21 controls the second braking mode to brake the aircraft 11. The first brakes 14a of the first wheels 13a, each equipped with a drive actuator 15,are not requested: step E17. The selection of the first braking mode or the second braking mode could be carried out differently. The selection may for example consist of acquiring an indication on a current flight phase, and selecting the first braking mode or the second braking mode according to said indication. The flight phases are defined by an upstream system, and include taxiing, landing, takeoff phases. The acquisition of this indication makes it possible in particular to directly distinguish the taxiing phases (for which the second braking mode is selected) and the RTO phases (for which the first mode is selected). The selection could also consist of acquiring a global braking instruction produced by a pilot of the aircraft,and selecting the first braking mode or the second braking mode as a function of said overall braking instruction. The pilot of the aircraft may be a human pilot or an autopilot device. A threshold logic is therefore used on the overall braking instruction. If the pilot's instruction (pedal depression or deceleration level in automatic braking) is low, the second braking mode is selected. Beyond this threshold, the first braking mode is selected. Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims. The invention may be implemented in any type of aircraft, and not necessarily in an airplane. The aircraft in question is not necessarily of the short or medium-haul type, and may of course include a number of braked wheels per landing gear other than two. There may therefore be,for each landing gear, several first wheels each equipped with a brake and a drive actuator, and several second wheels each equipped with a brake only. It has been described here that the first braking instruction, in the second braking mode, is a zero instruction. However, in the second braking mode, the first brakes could be requested but to a lesser extent. For example, again in the case of a main landing gear comprising a single first wheel and a single second wheel, we could have: - when the first braking mode is commanded, a first braking instruction for the first brake equal to 50% of X and a second braking instruction for the second brake also equal to 50% of X (the first value of the ratio between the first and the second instruction is equal to 1); - when the second braking mode is commanded,a first braking instruction for the first brake equal to 25% of X and a second braking instruction for the second brake equal to 75% of X (the second value of the ratio between the first and the second instruction is equal to 1 / 3). In the case where, for each main landing gear, there are two first wheels and two second wheels, we could for example have: - when the first braking mode is commanded, a first braking instruction for each first brake equal to 25% of X and a second braking instruction for each second brake equal to 25% of X; - when the second braking mode is commanded, a first braking instruction for each first brake equal to 12.5% ​​of X and a second braking instruction for each second brake equal to 37.5% of X. Similarly, the first braking instruction and the second braking instruction, in the first braking mode, are not necessarily identical. We could for example have,returning to the two-wheel configuration per main landing gear: - when the first braking mode is commanded, a first braking instruction for the first brake equal to 40% of X and a second braking instruction for the second brake equal to 60% of X (the first value of the ratio between the first and second instructions is equal to 2 / 3); - when the second braking mode is commanded, a first braking instruction for the first brake equal to 25% of X and a second braking instruction for the second brake equal to 75% of X (the second value of the ratio between the first and second instructions is equal to 1 / 3). It is also noted that the distinction between a first braking mode (high energy) and a second braking mode (low energy) could be made by comparing several parameters with several predefined thresholds.,

Claims

CLAIMS 1. Method for ground braking of an aircraft (11) which comprises at least one first wheel (13a) equipped with a first brake (14a) arranged to brake said first wheel and a drive actuator (15) arranged to rotate said first wheel, and at least one second wheel (13b) equipped with a second brake (14b) arranged to brake said second wheel but not being equipped with a drive actuator, the ground braking method comprising the steps of: - selecting, to brake the aircraft on the ground, a first braking mode, or a second braking mode having a reduced braking capacity;− braking the aircraft by producing a first braking instruction (C1) for the first brake (14a) and a second braking instruction (C2) for the second brake (14b), such that: o if the first braking mode is selected, a ratio between the first braking instruction and the second braking instruction is equal to a first value; o if the second braking mode is selected, said ratio is equal to a second value less than the first value.

2. Ground braking method according to claim 1, wherein the first braking instruction, in the second braking mode, is a zero instruction.

3. Ground braking method according to one of the preceding claims, wherein the first braking instruction and the second braking instruction, in the first braking mode; braking, are identical.

4. Ground braking method according to one of the preceding claims, wherein the selection of the first braking mode or the second braking mode comprises the steps of: - acquiring a measurement of a ground speed of the aircraft (11); - selecting the first braking mode or the second braking mode as a function of the ground speed of the aircraft.

5. Ground braking method according to claim 4, comprising the steps of: - comparing the ground speed of the aircraft (11) with a first predefined threshold; - selecting the first braking mode if the ground speed is greater than the first predefined threshold, or the second braking mode if the ground speed is less than the first predefined threshold. 6.Ground braking method according to one of the preceding claims, wherein the selection of the first braking mode or the second braking mode comprises the steps of: - acquiring a measurement or an estimate of a mass of the aircraft (11); - selecting the first braking mode or the second braking mode as a function of the mass of the aircraft.

7. Ground braking method according to claim 6, comprising the steps of:. - comparing the mass of the aircraft with a second predefined threshold; - selecting the first braking mode if the mass is greater than the second predefined threshold, or the second braking mode if the mass is less than the second predefined threshold.

8. Ground braking method according to claims 4 and 6, comprising the steps of: - evaluating, as a function of the ground speed and the mass of the aircraft, a braking energy necessary to brake the aircraft; - comparing the braking energy with a third predefined threshold; - selecting the first braking mode if the braking energy is greater than the third predefined threshold, or the second braking mode if the braking energy is less than the third predefined threshold. 9.Ground braking method according to one of the preceding claims, in which the selection of the first braking mode or the second braking mode comprises the steps of: - acquiring an indication on a current flight phase of the aircraft (11); - selecting the first braking mode or the second braking mode according to said indication.

10. Ground braking method according to one of the preceding claims, in which the selection of the first braking mode or the second braking mode comprises the steps of:. - acquiring an overall braking setpoint produced by a pilot of the aircraft (11), the pilot being able to be a human pilot or an autopilot device; - selecting the first braking mode or the second braking mode as a function of said overall braking setpoint.

11. Ground braking method according to one of the preceding claims, further comprising the preliminary step of checking whether a braking system of the aircraft (11), comprising a plurality of brakes comprising the first brake (14a) and the second brake (14b), is or is not in a nominal state, the ground braking method further comprising the step, if the braking system is not in the nominal state, of selecting the first braking mode regardless of the value of the braking parameter(s).

12. Ground braking method according to claim 11, wherein the nominal state is a state in which all the brakes of the aircraft (11) are operational. 13.Ground braking method according to one of the preceding claims, wherein the first wheel (13a) and the second wheel (13b) are both located on the same landing gear of the aircraft (11).

14. Braking system comprising: - a first brake (14a) arranged to brake a first wheel (13a) which is equipped with a drive actuator (15); - a second brake (14b) arranged to brake a second wheel (13b) which is not equipped with an actuator. drive; - a braking computer (20) comprising a processing unit (21) in which the ground braking method according to one of the preceding claims is implemented.

15. Aircraft comprising a braking system according to claim 14.

16. Computer program comprising instructions which cause the processing unit (21) of the braking computer (20) of the braking system according to claim 14 to execute the steps of the ground braking method according to one of claims 1 to 13.

17. Computer-readable recording medium, on which the computer program according to claim 16 is recorded.

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