Emergency braking method for an aircraft

#The invention relates to an emergency braking method for an aircraft.

#Aircraft, such as commercial airplanes of large size for transporting passengers, are known that include a main braking circuit and an emergency braking circuit suitable for use in the event of a failure of the main braking circuit. Those circuits are completely segregated and each of them requires a large number of passive hydraulic components such as accumulators, filters, and active hydraulic components such as gates, valves, and servo-valves, adapted to deliver braking pressure in proportion to a braking setpoint determined by a braking computer, in particular as a result of the pilot acting on the brake pedals. In addition to those two circuits, the aircraft is generally fitted with a parking brake device adapted to hold the aircraft stationary, after a parking selector has been operated by the pilot, by applying and maintaining a given pressure (the brake feed pressure, usually delivered by an accumulator) in the brakes while the aircraft is stationary, e.g. by using a bistable valve.

#Although that architecture is very safe, it is complex and it is often not possible to envisage using it on smaller aircraft, such as regional airplanes or business airplanes. Aircraft of this size often have only one braking circuit, and a “progressive” parking brake that can also be used for emergency braking. The parking brake is controlled by a lever that is mechanically connected to the slide of a proportional valve so that the pilot can perform emergency braking by moving the lever between a “0%” position in which the brakes are at the aircraft return pressure, and a “100%” position in which the brakes are at the aircraft feed pressure. The lever can be blocked in the 100% position in order to provide a parking brake. Nevertheless, the mechanical connection, which takes place via cables, pulleys, connecting rods, requires a considerable length of time to install, needs numerous supports in the structure of the aircraft, and gives rise to regular maintenance actions (verification, tension adjustment, greasing, . . . ).

#The invention can be better understood in the light of the following description of a particular implementation of the invention given with reference to the figures of the accompanying drawing, in which:

#FIG. 1 is a diagram of the hydraulic circuit including a two-state valve that is used for performing emergency braking of the invention;

#FIG. 2 is an electric circuit diagram showing how the valve used in the FIG. 1 hydraulic circuit is controlled using a progressive parking brake lever; and

#FIG. 1 shows a hydraulic circuit suitable for implementing emergency braking of the invention. This emergency braking circuit is additional to a main braking circuit, that is not shown. In this example, the aircraft has two brakes 1A and 1B associated with braked wheels 2A and 2B having brakes that are connected to the outlet port 3 of a two-state slide valve 4 having a rest state that is stable (as shown in FIG. 1) in which the slide of the valve 4 connects the outlet port 3 to a return port 5, and an active state in which the slide of the valve 4 connects the outlet port 3 to a feed port 6. A coil 7 forces the slide of the valve 4 to take up the active state when the coil 7 is powered by a control voltage, and a spring 8 returns the slide of the valve 4 to the rest state when the coil 7 is no longer powered.

#According to the invention, the coil 7 is powered so that the pressure delivered to the brakes 1A and 1B via the outlet port 3 is a function of the position of a lever 10 operated by the pilot of the aircraft. For this purpose, the position of the lever 10 in this example is measured by means of a potentiometer 11 having its output transmitted to an electronic card 12 having means for processing the signal that are adapted to generate a control signal 13 for a first selector 14 that selectively connects a first terminal of the coil 7 either to ground 15 or else to a direct current (DC) voltage source (in this example of 28 volts (VDC)).

#In this example, the electronic card 12 is adapted to perform a pulse-width modulation (PWM) method as shown in FIG. 3. When the lever 10 is raised by the pilot from an initial “0%” position, the selector 14 applies voltage to the coil 7 for a first determined time ΔT, thereby directing hydraulic fluid to fill the cavities of the brakes 1A and 1B. Thereafter, for each successive period T, the electronic card 12 determines an open time τ which in this example is a function of the position of the lever 10 in the range from its 0% position to its 100% position, corresponding to the maximum stroke of the lever, with this being done in application of a proportional relationship, for example. The valve 4 then connects the outlet port 3 to the feed port 6 for a length of time τ, and connects the outlet port 3 to the return force 5 for the complementary length of time T−τ, thereby determining an open duty ratio R=τ/T. The mean pressure seen by the brake is a function of the open duty ratio R and it increases as this open ratio increases between the return pressure and the feed pressure. Thus, using a simple two-state valve, control is thus obtained that is proportional to the position of the lever 10. The pilot can then perform manual braking, and can vary its magnitude at will by acting on the lever 10, specifically in the event of the main braking circuit failing.