Simplified aircraft braking system

Abstract

The invention relates to a hydraulic braking circuit for an aircraft comprising at least two main landing gears, each having at least one braked wheel (50L, 50R) equipped with a brake (51L, 51R), the circuit comprising a pump (1) for generating supply pressure in the hydraulic circuit; an accumulator (5) inflated by the pump to maintain parking pressure in the circuit when the pump is not activated; distribution elements (4L, 4R), one per main landing gear, for adjusting the braking pressure delivered to the associated brakes between a return pressure and the supply pressure by means of a proportional control in order to ensure differential braking; parking immobilization means (8) for bringing parking pressure to the brakes of the braked wheels in order to ensure parking braking at least when the pump is not activated;The distribution components, the pump and the parking lot immobilization means are electrically controlled by a braking logic implemented either in a dedicated braking computer, or in an aircraft flight control system, or in the electronics of one of the braking circuit components. FIGURE IN ABRIDGED DIAGRAM: Fig. 1;

Description

Title of the invention: Simplified braking circuit for aircraft

[0001] The invention relates to aircraft hydraulic braking circuits, and more particularly those adapted to light general aviation aircraft or even certain drones, large enough to justify the installation of a hydraulic circuit, but nevertheless not large enough to meet the drastic safety standards of commercial or military aviation.

[0002] BACKGROUND OF THE INVENTION

[0003] We are talking here about aircraft whose two main landing gears are equipped with braked wheels. On small aircraft, braking is controlled using pedals actuated by the pilot to generate pressure in the brakes using master cylinders. By providing a master cylinder per landing gear, it is thus possible, by identical pressure on the pedals, to ensure symmetrical braking on the wheels of the two landing gears, or by asymmetrical pressure on the pedals, to ensure differential braking making it possible in particular to steer the aircraft on the ground if the wheel of the auxiliary landing gear is left free to pivot. To immobilize the aircraft in parking, it is necessary to press the two pedals simultaneously and to actuate a parking selector making it possible to trap under pressure the fluid reaching the brakes, so as to keep them activated. These rudimentary technologies do not allow easy diagnosis of the components of the braking circuit.

[0004] On the other hand, for aircraft of a certain size, such as transport aircraft certified according to the FAR-25 or CS-25 standards, the redundancy and safety requirements are much greater. This type of aircraft is generally equipped with a main hydraulic circuit and an emergency hydraulic circuit, as well as numerous duplicated hydraulic equipment. In modern aircraft, this hydraulic equipment is electrically controlled (isolation valves, servo valves, etc.) and / or generates electrical signals (pressure sensors), and is managed by a braking computer which collects the braking orders and transforms them into instructions for the electrohydraulic equipment. This electrohydraulic equipment is well known and allows easy diagnosis of its operation.

[0005] SUBJECT OF THE INVENTION

[0006] The aim of the invention is to propose the simplest possible hydraulic braking architecture for aircraft, making it possible to ensure at least symmetrical or differential braking and fleet immobilization, with modern components of reduced size and maintenance for easy installation in a constrained environment. Summary of the invention

[0007] With a view to achieving this aim, a hydraulic braking circuit for an aircraft is proposed, comprising at least two main landing gears, each provided with at least one braked wheel equipped with a brake, the circuit making it possible to provide symmetrical or differential braking as well as parking immobilization, the circuit comprising for this purpose: - a pump to generate supply pressure in the hydraulic circuit; - an accumulator inflated by the pump to maintain park pressure in the circuit when the pump is not activated; - distribution members, at least one per main landing gear, for adjusting a braking pressure delivered to the associated brakes between a return pressure and the supply pressure by means of a proportional control in order to ensure symmetrical or differential braking; - park immobilization means for bringing park pressure into the brakes of the braked wheels in order to ensure park immobilization at least when the pump is not activated;

[0008] the distribution members, the pump and the park immobilization means being electrically controlled by a braking logic implanted either in a dedicated braking computer, or in a flight control system of the aircraft, or in electronics of one of the braking circuit equipment.

[0009] Thus, a particularly simple hydraulic circuit is used, with a minimum of equipment to ensure the current braking (symmetrical or differential) and the parking immobilization, the current braking being ensured using the distribution members, while the parking immobilization is ensured by a simple accumulator inflated by the pump, the braking logic is then very simple and can be implemented in an existing electronic component (either the aircraft flight control system, or electronics of one of the braking circuit equipment), or even, if necessary, in a dedicated braking computer. The whole thing uses modern electrically controlled components that can be easily tested, and, of course, controlled in automatic mode by an on-board or remote flight control unit.

[0010] According to a first particular embodiment of the invention, the distribution members are servovalves supplied with pressure by the pump, the hydraulic circuit comprising an isolation valve interposed between the pump and the servovalves to selectively connect a supply port of the servovalves to the return and thus prevent untimely braking during unwanted actuation of the servovalves.

[0011] According to a particular aspect of the invention, the park immobilization means have a parking valve interposed between the accumulator and the brakes to isolate the brakes from the accumulator while the pump is activated, or to connect the accumulator and the brakes to bring the accumulator pressure into the brakes.

[0012] In the case of single-cavity brakes, then, the parking immobilization means comprise shuttle valves arranged at the inlet of the brakes to receive the pressure either from the pump or from the accumulator.

[0013] In the case of two-cavity brakes, one of the cavities is connected to the associated distribution member, and the other of the cavities is connected to the parking valve.

[0014] According to a second particular embodiment of the invention, the distribution members are valves with two operating modes, including a first operating mode in which the pressure delivered to the brake is adjustable by means of a proportional control between the return pressure and the supply pressure, and a second bistable operating mode comprising a parking immobilization position subjecting the brakes to the parking pressure, thus forming the parking immobilization members, and an isolation position in which the brakes are at the return pressure.

[0015] The use of this type of member makes it possible to eliminate the isolation and park valves, which considerably simplifies the circuit. The accumulator will then advantageously be placed in series with the pump, so that it ensures the arrival of the park pressure at the inlet of the distribution members when the pump is no longer activated, thus ensuring the immobilization of the park while the said distribution members are placed in the stable park immobilization position.

[0016] The invention also relates to an aircraft comprising such a braking circuit. Brief description of the drawings

[0017] The invention will be better understood in light of the following description of particular embodiments of the invention, with reference to the figures of the appended drawings, among which:

[0018] [Fig-1] [Fig. 1] is a schematic diagram of a hydraulic braking circuit of an aircraft according to a first particular embodiment of the invention;

[0019] [Fig.2] [Fig.2] is a schematic diagram of a hydraulic braking circuit of an aircraft according to a second embodiment of the invention;

[0020] [Fig.3] [Fig.3] is a schematic diagram of a hydraulic braking circuit of an aircraft according to a third embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] In Figures 1 to 3, identical elements have a reference number increasing by one hundred. Thus, for example, elements 1, 101, 201, respectively in Figures 1, 2, 3, are identical. To simplify the figures, the return hydraulic circuit has not been shown, the returns from each piece of equipment being represented by vent-shaped symbols and all leading to a tank on the aircraft from which the pump draws the fluid.

[0022] According to a first particular embodiment illustrated in [Fig.l], the hydraulic circuit of the invention is intended to supply the brakes 5IL and 51R of two braked wheels 50L, 50R carried respectively by left and right main landing gears of the aircraft. The hydraulic braking circuit comprises: - a pump 1 driven here by an electric motor 2 powered by the aircraft's electrical circuit. The pump 1 is for example activated by generating a discrete electrical activation signal BCT when the aircraft is about to land, to enable it to brake when it has landed. The pump 1 can also be activated on the ground for maintenance tests, or even in flight, before landing, to carry out reliability tests and check whether the braking circuit is functional; - an isolation valve 3 which isolates the rest of the braking circuit from pump 1 by keeping it on the return, to avoid any untimely braking, and which connects the rest of the circuit to pump 1 via a main branch 30 in response to the generation of a discrete electrical signal BRAKE; - proportional distribution members, in this case servovalves 4L, 4R supplied by pump 1 via the main branch 30 of the hydraulic circuit, to adjust a braking pressure respectively in the brakes 5 IL, 51R in response to proportional electrical braking orders LB, RB by which it is possible to carry out differential braking if the signals LB, RB are different, or symmetrical braking if the signals LB, RB are identical; - an accumulator 5 inflated by the pump 1 via a non-return valve 6, and the pressure of which is limited by a pressure relief valve 7; - a bistable parking valve 8 which isolates the brakes 5IL, 5IR from the accumulator 5, and which connects the brakes 5IL, 51R to the accumulator 5 via an auxiliary branch 31 in response to the generation of a discrete electrical signal PARK. This ensures that the parking remains operational even when the pump 1 is stopped, and particularly when the aircraft is stationary on the tarmac.

[0023] Thus, the braking circuit of the invention is particularly simple and comprises only standard electrohydraulic equipment found in more complex aircraft hydraulic circuits. This simple circuit is sufficient to provide symmetrical or differential braking, as well as parking braking. It is even possible to provide emergency braking in the event of a malfunction of the pump or servovalves in operating the park valve 8 to force pressure from the accumulator 5 into the brakes, which allows emergency braking of the aircraft.

[0024] It will be noted that the brakes 5 IL, 51R are here single-cavity brakes. Shuttle valves 9L, 9R are arranged at the inlet of the brakes 5 IL, 51R, to receive the pressure either from the pump 1 via the servovalves 4L, 4R, or from the accumulator 5. Of course, if the brakes 51L, 51R have two cavities, the shuttle valves 4L, 4R can be dispensed with by distributing the pressures coming from the servovalve or the accumulator in two separate cavities. In this case, the parking brake can be used either to compensate for a failure of the servovalves and provide emergency braking, or in addition to the action of the servovalves (so-called "brake boost" function), in order to increase the braking torque, for example in the case of a landing at high weight or on a short runway. Of course, the pressure delivered by the accumulator 5 via the park valve 8 is not regulated, unlike the pressure delivered by the associated servovalve.

[0025] This hydraulic circuit requires only three discrete electrical commands (BCT, PARK, BRAKE), and two proportional commands (LB, RB). These electrical commands are here generated by a braking logic which, given the simplicity of the braking circuit, is very simple and requires little memory space and computing resources. Thus, and according to an important aspect of the invention, this logic is implemented directly in the flight control computer of the aircraft, which avoids the use of a dedicated braking computer. To generate the electrical braking commands, the flight control computer receives, if the aircraft is piloted by a pilot: - electrical signals from right and left pedals operated by the pilot; - where applicable, if a co-pilot is present, electrical signals from right and left pedals operated by the co-pilot; - a discrete two-state electrical signal from a park selector.

[0026] Alternatively, if the aircraft is remotely controlled (drone), the braking logic receives equivalent radio signals. As a further alternative, the braking logic can be programmed to automatically generate the electrical braking commands by means of an intelligent braking and guidance algorithm based on knowledge of the runway and the tarmac on which the aircraft is operating, or can provide braking assistance by modulating the braking commands, for example to avoid wheel lock.

[0027] To monitor the correct operation of the hydraulic braking circuit, it is equipped here with various pressure sensors, including: - a pressure sensor 10 downstream of the isolation valve 3, to measure the inlet pressure of servovalves 4L, 4R from pump 1; - a pressure sensor 11 downstream of the parking valve 8, to measure the brake input pressure from the accumulator 5; - pressure sensors 12L, 12R downstream of servovalves 4L, 4R to measure the brake input pressure from servovalves 4L, 4R.

[0028] These sensors allow the braking logic to perform various tests by opening or closing valves 3, 8 and operating servovalves 4L, 4R, to check the correct operation of this equipment, and by warning the driver if a malfunction is detected. These sensors can also be used for fault detection, maintenance assistance, or closed-loop feedback control. If necessary, simple pressure switches may be sufficient.

[0029] This circuit can easily be adapted to an aircraft with four independent wheels (one servovalve per brake) or paired wheels (the same servovalve controlling a pair of brakes).

[0030] A second particular embodiment of the hydraulic braking circuit is illustrated in [Fig. 2]. Equipment identical to that previously mentioned can be seen, in particular the pump 101 and its motor 102, the accumulator 105, the pressure relief valve 107. It can be seen that the non-return valve 106 is now placed upstream of a branch leading to the accumulator 105 allowing the latter to be inflated by the pump 101, so that the accumulator is directly in communication with the rest of the hydraulic circuit via the main branch 130, the auxiliary branch having been removed here.

[0031] According to an original aspect of the invention, the main branch 130 here supplies two dual-mode distribution members 114L, 114R capable of operating according to two operating modes: - a proportional operating mode in which the distribution members 114L, 114R work in a conventional manner to adjust a braking pressure respectively in the brakes 5 IL, 51R in response to proportional electrical braking orders LB, RB by which it is possible to carry out differential braking if the signals LB, RB are different, or symmetrical braking if the signals LB, RB are identical; - a bistable operating mode in which the distribution members 114L, 114R are placed stably in the parking position in response to a discrete electrical signal PARK and in which the brakes are connected directly to the main branch 130 of the hydraulic circuit, so that the pressure of the accumulator 105 is applied in the brakes 51L, 51R to ensure parking immobilization, or are placed by default in an isolation position in which the brakes are put on return.

[0032] The dual-mode distribution members 114L, 114R are, for example, of the type described in document FR-A-3082503 with pulse width modulation (PWM) control, i.e. fundamentally bistable valves, but which can be used as proportional opening valves thanks to PWM control.

[0033] The dual-mode distribution members 114L, 114R therefore make it possible to carry out both parking immobilization and current braking and constitute both the distribution members and the means of parking immobilization. These distribution members are advantageously provided with their own electronics, which can therefore house the braking control logic. It will be sufficient to ensure that the electronics of the distribution members can have access to the signals from the pedals and the parking selector, as well as to the signals from the pressure sensors, for example, via the aircraft data bus. This arrangement further simplifies the installation of the braking circuit in the aircraft.

[0034] It will be noted that this hydraulic braking circuit does not include an isolation valve or a parking valve, which makes it a particularly simple circuit.

[0035] The absence of an isolation valve does not allow protection against untimely braking by the hydraulic circuit alone. If such protection were required, it is possible to organize it electronically, for example by cutting off all electrical power to the distribution members until the aircraft has been rolling on the ground for a few seconds after landing, the time for the wheels to start rotating. Another means of securing against untimely braking consists of providing sensors linked to the pedals (contactor or proximity sensor, etc.), segregated and independent of the sensors used to transmit the braking commands. The transmission of a discrete signal is then carried out as soon as the pedals are pressed beyond a certain threshold, characterizing the pilot's desire to brake.It is also possible to use signals from the switches mounted on the landing gears indicating that they are sinking during landing, or to use a signal from one of the flight computers, capable of determining the phases where braking is required or not, and for example prohibiting any braking during the take-off run (characterized by the fact that the aircraft is on the ground, accelerating, at high speed).

[0036] According now to a third particular embodiment illustrated in [Fig.3], the advantages of the first and second particular embodiments are now combined. In this figure, the hydraulic circuit is in all respects identical to that of [Fig.l], with two differences: - the 4L, 4R servovalves have been replaced by dual-mode distribution elements 214L, 214R, identical to those described in relation to [Fig.2]; - due to the presence of these dual-mode organs, isolation valve 3 has become useless, and is therefore removed.

[0037] This provides a parking immobilization which is activated by means of the parking valve 208, and which can be used as emergency braking in the event of failure of one of the distribution members 214L, 214R.

[0038] The invention is not limited to what has just been described, but on the contrary encompasses any variant falling within the scope defined by the claims.

[0039] In particular, although the braking logic here is simple to the point of being able to be easily housed either in a flight computer of the aircraft (or several to achieve redundancy), or in the electronic card of the distribution members, it will more generally be possible to house this logic in any card of one of the electrohydraulic equipments of the hydraulic braking circuit of the invention, or even in a dedicated braking computer.

[0040] Although here the pump is driven by a dedicated electric motor, so that it is possible to stop the pump in flight, it will also be possible to have the pump driven by the aircraft's powertrain.

Claims

Claims

1. Hydraulic braking circuit for an aircraft comprising at least two main landing gears each comprising at least one braked wheel (50L, 50R) equipped with a brake (5IL, 51R), the circuit making it possible to provide symmetrical or differential braking as well as parking immobilization, the circuit comprising for this purpose: - a pump (1; 101; 201) for generating a supply pressure in the hydraulic circuit; - an accumulator (5; 105; 205) inflated by the pump to maintain a parking pressure in the circuit when the pump is not activated; - distribution members (4L, 4R; 114L, 114R; 214L, 214R), at least one per main landing gear, for adjusting a braking pressure delivered to the associated brakes between a return pressure and the supply pressure by means of a proportional control in order to provide symmetrical or differential braking; - means of immobilizing the park (8; 114L, 114R;208) to bring the parking pressure into the brakes of the braked wheels in order to ensure parking immobilization at least when the pump is not activated; the distribution members, the pump and the parking immobilization means being electrically controlled by a braking logic implemented either in a dedicated braking computer, or in a flight control system of the aircraft, or in electronics of one of the equipment of the braking circuit.;

2. Hydraulic braking circuit according to claim 1, in which the distribution members are servovalves (4L, 4R), the hydraulic circuit comprising an isolation valve (3) interposed between the pump and the servovalves to selectively connect a supply port of the servovalves to the return and thus prevent untimely braking during unwanted actuation of the servovalves.

3. Hydraulic braking circuit according to claim 1, in which the parking immobilization means comprise a parking valve (8; 208) interposed between the accumulator (5; 205) and the brakes (5IL; 51R) to isolate the brakes from the accumulator while the pump is activated, or to connect the accumulator and the brakes to bring the accumulator pressure into the brakes to ensure at least parking braking when the pump is not activated.

4. Hydraulic braking circuit according to claim 3, in which the brakes are of the single-cavity type, the parking immobilization means comprising shuttle valves (9L, 9R; 209L, 209R) arranged at the inlet of the brakes to receive either the pressure from the pump (1; 201) via the distribution members (4L, 4R; 214L, 214R), or the pressure from the accumulator (5; 205) via the parking valve (8; 208).

5. Hydraulic braking circuit according to claim 3, in which the brakes are of the two-cavity type, one of the cavities receiving the pressure from the pump (1; 201) via the associated distribution member (4L, 4R; 214L, 214R), the other of the cavities receiving the pressure from the accumulator (5; 205) via the parking valve (8; 208).

6. Hydraulic braking circuit according to claim 1, in which the distribution members are valves (114L, 114R; 214L, 214R) with two operating modes, including a proportional operating mode in which the pressure delivered to the associated brake is adjustable by means of a proportional control between the return pressure and the supply pressure, and a bistable operating mode comprising a parking braking position subjecting the associated brake to the parking pressure, and an isolation position in which the brakes are subjected to the return pressure, so that said distribution members also form the parking immobilization members.

7. A hydraulic braking circuit according to claim 6, wherein the proportional operating mode is achieved by means of pulse width modulation control.

8. Hydraulic circuit according to claim 6, in which the accumulator (105) is inflated by the pump (101) via a non-return valve (106) placed upstream of a bypass leading to the accumulator.

9. Hydraulic braking circuit according to claim 1, comprising pressure sensors (12L, 12R) for measuring a pressure downstream of the distribution members.

10. Hydraulic braking circuit according to claim 1, comprising pressure sensors (12L, 12R; 112L, 112R; 212L, 212R) for measuring a pressure downstream of the distribution members.

11. A hydraulic braking circuit according to claim 2, comprising a pressure sensor (10) for monitoring the pressure downstream of the isolation valve (3).

12. Hydraulic braking circuit according to claim 3, comprising a pressure sensor (11; 211) for monitoring the pressure downstream of the park valve (8; 208).

13. Hydraulic braking circuit according to claim 6, controlled by braking logic installed in an electronic card of the distribution members (114L; 114R) or in a dedicated braking computer.

14. Aircraft comprising landing gears provided with braked wheels each equipped with a brake connected to a hydraulic braking circuit according to any one of the preceding claims.

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