Method for securing a parking function in an aircraft braking system

Abstract

The invention relates to a method for securing a parking function of a hydraulic braking circuit (1) supplying brakes (12a, 12b) of braked wheels (11a, 11b) carried by landing gear of an aircraft, the hydraulic circuit comprising a parking solenoid valve (13) having a service port connected to the brakes (12a, 12b) and a supply port connected, in the rest position, to a hydraulic return (102) of the aircraft, the parking solenoid valve (13) being controllable in order to connect the supply port to a pressure source (101, 2) so as to selectively transmit, to the brakes of the aircraft, a pressure that is sufficient to cause the brakes to operate, thus immobilising the aircraft, which method comprises a step of arranging, in series with the parking solenoid valve (13), a protective solenoid valve (20) allowing, when at rest, pressure to be supplied to the brakes via the parking solenoid valve, and which protective solenoid valve can be controlled to prevent pressure from being supplied to the brakes via the parking solenoid valve; and a step of controlling the protective solenoid valve (20) at least in a situation where a failure of the parking solenoid valve can induce undesired braking.

Description

[0001] METHOD FOR SECURING A PARKING FUNCTION IN AN AIRCRAFT BRAKING SYSTEM

[0002] The invention relates to hydraulic braking circuits for aircraft comprising a parking function.

[0003] BACKGROUND OF THE INVENTION

[0004] Figure 1 illustrates a hydraulic braking circuit 1 for an aircraft known per se operating from a hydraulic generation 100 comprising a pressure source 101 and a return reservoir 102. The hydraulic braking system comprises:

[0005] - a secondary pressure source in the form here of an accumulator 2 supplied by the pressure source 101 and associated with a non-return valve 4 and a pressure limiting valve 5;

[0006] - a pressure sensor 3 for monitoring the pressure level in the accumulator 2;

[0007] - a solenoid valve 6 making it possible to selectively supply one or more servovalves 7a, 7b each applying an adjusted pressure to pistons of hydraulic brake crowns 12a, 12b equipping wheels 11a, 11b carried by landing gears of the aircraft to brake said wheels;

[0008] - pressure sensors 10a, 10b each arranged on a brake supply line 12a, 12b to measure the pressure in the brakes;

[0009] - hydraulic fuses 9a, 9b each arranged on a brake supply line 12a, 12b making it possible to avoid total loss of hydraulic supply in the event of breakage of the supply lines downstream of the fuses;

[0010] - at least one braking control unit 14 which controls the solenoid valve 6 and controls the servovalves 7a, 7b independently of one another by means of electrical signals corresponding to the desired pressure in each brake in response to a braking instruction generated by the pilot or other systems of the aircraft;

[0011] - tachometers 17a, 17b for measuring the rotation speed of each braked wheel necessary for the anti-skid function provided by the braking control unit 14;

[0012] - non-return valves 15 to prevent pressurization of the brakes in the event of an increase in pressure on the return line to the hydraulic generation reservoir.

[0013] Such a braking system includes a parking function to activate the brakes to immobilize the aircraft in parking when it is stationary. This function is achieved by:

[0014] - shuttle valves 8a, 8b placed on the brake supply lines to allow the imposition of a parking pressure in the brakes 12a, 12b via the service port of a parking solenoid valve 13 having a supply port connected in the rest position to the return 102 of the supply, and being controllable to connect the supply port to the pressure source 101 and / or to the accumulator 2, so as to transmit the supply pressure directly to the brakes via the shuttle valves 8;

[0015] - a parking brake control unit 16 controlling the parking solenoid valve 13 according to the driver's request to apply parking pressure in the brakes 12a, 12b.

[0016] Aviation regulations require that aircraft braking systems be designed so that no single failure can lead to a catastrophic event. Below are two examples of scenarios in which a catastrophic event could occur: 1 / During the takeoff phase, the involuntary application of pressure above a certain threshold in a certain number of brakes leads to an increase in the takeoff distance, or even prevents the aircraft from reaching the minimum speed for takeoff, with the resulting risk of exceeding the end of the runway.

[0017] 2 / During the landing phase, the involuntary application of pressure above a certain threshold in the brakes causes the wheels concerned to lock, resulting in the tire bursting. The loss of at least one tire on one of the braked wheels has the effect of increasing the braking distance, with the tire bursting on all the braked wheels risking taking the aircraft beyond the runway threshold.

[0018] To avoid such scenarios, the aircraft system commonly includes a three-way / two-position safety solenoid valve 6 located upstream of the servovalves 7a, 7b to connect the hydraulic supply port of these servovalves either with the pressure source 101 and the accumulator 2 when the safety solenoid valve 6 is commanded, or with the return 102 when the safety solenoid valve 6 is at rest. During critical phases on the ground, such as takeoff, the brake control unit 14 does not apply any electrical command to the safety solenoid valve 6 and the servovalves 7a, 7b as long as the pilot or another system does not request to brake the aircraft. This type of architecture avoids inadvertently pressurizing the brakes via the servovalves 7a, 7b, which constitutes a catastrophic event.

[0019] It should be noted, however, that the parking solenoid valve 13 is always hydraulically supplied to its supply port as long as the external hydraulic generation 100 is in service or the hydraulic accumulator 2 is filled, which is always the case for the aircraft during taxiing, takeoff, landing operations, but also during flight phases. Consequently, the parking solenoid valve 13 must be designed so that it cannot experience any simple failure that could lead to unwanted pressurization of the brakes via the shuttle valves 8a, 8b. Satisfying this constraint involves complex design and integration choices, such as the use of an electric motor type actuator, which has the disadvantage of being expensive, bulky, and heavy. In addition, this solution requires a device for controlling the electric motor(s) of the solenoid valve 13, which can be integrated into the parking brake control unit 16.

[0020] SUBJECT OF THE INVENTION

[0021] The invention aims to propose a simple method for securing the park function, preventing any simple breakdown from leading to a catastrophic event.

[0022] SUMMARY OF THE INVENTION

[0023] With a view to achieving this aim, a method is proposed for securing a parking function of a hydraulic braking circuit supplying brakes of braked wheels carried by landing gear of an aircraft, the hydraulic circuit comprising a parking solenoid valve having a service port connected to the brakes and a supply port connected in the rest position to a hydraulic return of the aircraft, the parking solenoid valve being controllable to connect said supply port with a pressure source so as to selectively transmit to the brakes of the aircraft sufficient pressure to cause the actuation of the brakes ensuring the immobilization of the aircraft, the method of the invention comprising the steps of: arranging in series with the parking solenoid valve a protection solenoid valve allowing, at rest, the supply of pressure to the brakes via the parking solenoid valve,and which is controllable to prohibit the supply of brake pressure via the parking solenoid valve; control the protection solenoid valve at least in a situation where a failure of the parking solenoid valve may induce unwanted braking.,

[0024] The presence of the protection solenoid valve allows for cases of simple failure of the parking solenoid valve to be accepted while ensuring that these simple failures cannot lead to catastrophic situations, a possible simple failure of the parking solenoid valve being neutralized by the actuation of the protection solenoid valve which prevents unwanted application of pressure in the brakes.

[0025] The control of the protection solenoid valve intervenes in a situation of failure of the solenoid valve, either curatively when the unwanted braking has already occurred, which makes the aircraft controllable on the ground again, or preventively to prevent any unwanted braking that may occur.

[0026] This arrangement makes it possible to considerably simplify the design of the park solenoid valve, which can then be satisfied with a simple solenoid actuation rather than one based on electric motors. This arrangement also makes it possible to simplify the installation of the park solenoid valve within the aircraft, but also to reduce its mass and size, while improving the safety of the aircraft.

[0027] According to a particular implementation of the method of the invention, the protection solenoid valve is arranged upstream of the park solenoid valve, between the latter and a pressure source.

[0028] Preferably, the protection solenoid valve is of the three-way / two-position type.

[0029] According to another particular implementation of the method of the invention, functional tests are carried out to detect a possible failure by successively controlling and cancelling the park solenoid valve and the protection solenoid valve.

[0030] Preferably then, pressure information from a pressure sensor placed on a hydraulic line between the park solenoid valve and the protection solenoid valve is used.

[0031] Also preferably, functional tests are performed each time the aircraft is started up.

[0032] According to a particular mode of implementation of the method of the invention, the control of the protection solenoid valve is developed taking into account the following information:

[0033] • a rotation speed of each braked wheel;

[0034] • information on the sinking of the aircraft's landing gear with braked wheels;

[0035] • information on locking in the deployed position of each of the landing gears equipped with braked wheels.

[0036] According to a particular embodiment of the method of the invention, a switch is placed on an electrical line carrying the control of the protection solenoid valve, the switch being normally closed, and controllable to be open, thus preventing any possible control of the protection solenoid valve.

[0037] According to a particular embodiment of the method of the invention, the protection solenoid valve is of the two-way / two-position type. According to a particular embodiment of the invention, the protection solenoid valve is arranged downstream of the parking solenoid valve, between the latter and the brakes.

[0038] BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The invention will be better understood in light of the following description of embodiments of the invention, with reference to the figures of the appended drawings, among which:

[0040] [Fig. 1] Figure 1, already commented on, is a diagram of an aircraft hydraulic braking circuit according to the prior art;

[0041] [Fig. 2] Figure 2 is a diagram of a hydraulic braking circuit according to a first embodiment of the invention;

[0042] [Fig. 3a] Figure 3a is the beginning of a flowchart describing the test logic for verifying the correct operation of the equipment providing parking braking; [Fig. 3b] Figure 3b is the end of the flowchart started in Figure 3a;

[0043] [Fig. 4] Figure 4 is an extract from a diagram of a hydraulic braking circuit according to a second embodiment of the invention;

[0044] [Fig. 5] Figure 5 is a diagram of a hydraulic braking circuit according to a third embodiment of the invention.

[0045] DETAILED DESCRIPTION OF THE INVENTION

[0046] A first particular embodiment is now detailed with reference to Figure 2. In this figure, the elements common to those of Figure 1 bear the same numerical references and will not be detailed here. According to the invention, a protection solenoid valve 20 is arranged in series with the park solenoid valve 13, here upstream of the latter. In the illustrated embodiment, the protection solenoid valve 20 is a three-way / two-position solenoid valve, the supply port of which is, in the rest position, connected to the pressure source 101 and to the accumulator 2, while the service port is connected to the supply port of the park solenoid valve 13. The protection solenoid valve 20 is thus interposed between the pressure source 101 (and the accumulator 2) and the park solenoid valve 13.In the rest position illustrated here, the protection solenoid valve 20 is normally conductive and connects its supply port with its service port so that the park solenoid valve 13 is supplied with pressure. When it is commanded, the protection solenoid valve 20 connects its service port to its return port connected to the return 102 of the hydraulic circuit so that the park solenoid valve 13 is no longer supplied with pressure.

[0047] To monitor the operation of the assembly, a pressure sensor 21 is placed on the hydraulic line connecting the protection solenoid valve 20 to the park solenoid valve 13, enabling the following monitoring to be carried out:

[0048] • If the protection solenoid valve 20 is controlled, if the park solenoid valve 13 is not controlled, and if the pressure sensor 21 detects a pressure greater than a certain threshold, for example a threshold of 50 bars, then information is sent to the aircraft maintenance system indicating that the protection solenoid valve 20 is in a stuck-open failure mode. • If the protection solenoid valve 20 is not controlled, if the pressure sensor 21 detects a pressure less than a certain threshold, for example 50 bars, and if the pressure of the accumulator 2, measured by means of the pressure sensor 3, indicates a value greater than its pre-charge value, for example 100 bars, then information is sent to the aircraft maintenance system indicating that the protection solenoid valve 20 is in a stuck-closed failure mode.

[0049] The protection solenoid valve 20 is controlled according to the conditions in which the aircraft operates, and more particularly the conditions in which untimely pressurization of one or more brakes would lead to unfortunate consequences for the aircraft or the passengers. Conversely, the protection solenoid valve 20 may not be controlled in the conditions for which actuation of the parking brake by the pilot is permitted, for example when the aircraft is stationary, or without major consequences, for example during taxiing or any other phase in which it is deemed that the protection provided by the protection solenoid valve is not essential.

[0050] In order to minimize the electrical energy consumption for controlling the protection solenoid valve 20, it is preferably controlled only in the phases where the pressurization of one or more brakes by the parking solenoid valve 13 would be critical for the aircraft or its passengers. Another strategy, but less optimal in terms of electrical energy consumption, consists of controlling the protection solenoid valve 20 only in the phases where the parking solenoid valve 13 needs to be controlled.

[0051] The control order of the protection solenoid valve 20 is preferably generated by the braking control unit 14, and is determined from measurement information and observations of states coming from sensors installed on the braking system but also from information coming from other systems, such as the landing gear extension / retraction system 22, or the aircraft navigation system providing in particular the speed and altitude of the aircraft.

[0052] According to a particular embodiment of the invention, the information taken into account for the preparation of the control order for the protection solenoid valve 20 is as follows:

[0053] • the rotation speed of each braked wheel by means of their respective tachometers 17;

[0054] • information on the depression of each landing gear of the aircraft provided by the extension / retraction system 22;

[0055] • information on locking in the deployed position of each of the landing gears equipped with braked wheels provided by the extension / retraction system 22. Preferably, the logic instructions implemented within the braking control unit 14 are as follows:

[0056] • If all the landing gears are not deployed and locked then: the protection solenoid valve 20 is not controlled (this condition is encountered when the aircraft is in flight with the landing gears retracted);

[0057] • If at least one landing gear is locked in the deployed position then:

[0058] If all the landing gears are not depressed then: the protection solenoid valve 20 is controlled (this condition is encountered when the aircraft is on approach to land or just after takeoff); If at least one landing gear is depressed and if the rotation speed of at least one braked wheel is greater than or equal to a threshold speed Vc then: the protection solenoid valve 20 is controlled (this condition is encountered when the aircraft is in the taxiing phase at a speed greater than or equal to Vc);

[0059] If at least one landing gear is pressed and if the rotation speed of all the braked wheels is lower than the threshold speed Vc then: the protection solenoid valve 20 is not controlled (this condition is encountered when the aircraft is stationary or in the taxiing phase at a speed lower than a threshold speed Vc).

[0060] The threshold speed Vc is defined so that in the event of untimely braking the consequences for the aircraft are not critical, for example a speed Vc of 20 Kts, which makes it possible to reduce the control time of the protection solenoid valve 20 and thus limit the electrical consumption.

[0061] According to another embodiment, the logic instructions implemented within the braking control unit 14 are as follows:

[0062] • If the extension / retraction control lever is in the extension position then:

[0063] If all landing gears are not down then: the protection valve is commanded (condition when the aircraft is on approach to land or just after takeoff);

[0064] If at least one landing gear is pressed and if the aircraft speed is greater than or equal to speed Vc then: the protection valve is controlled (condition when the aircraft is in the taxiing phase at a speed greater than or equal to Vc);

[0065] If at least one landing gear is pressed and if the aircraft speed is lower than speed Vc then: the protection valve is not controlled (condition when the aircraft is stationary or in the taxiing phase at a speed lower than Vc);

[0066] • If the extension / retraction control lever is in the retracted position then: the protection valve is not commanded (condition when the aircraft is in flight with the landing gear retracted);

[0067] • If the extension / retraction control lever is in the extension position then:

[0068] If the aircraft speed is greater than or equal to speed Vc then: the protection valve is controlled (condition when the aircraft is in the taxiing phase at a speed greater than or equal to Vc);

[0069] If the aircraft speed is lower than the speed Vc then: the protection valve is not controlled (condition when the aircraft is stationary or in the taxiing phase at a speed lower than Vc).

[0070] According to a particular arrangement of the invention, the protection solenoid valve 20 is controlled when the aircraft is stationary in the event that the parking solenoid valve 13 is blocked in the open position in order to be able to depressurize the brakes and thus allow the aircraft to be towed.

[0071] According to another particular arrangement of the invention, an electrical switch 23 is arranged on an electrical line carrying the control of the protection solenoid valve 20, the electrical switch 23 being controllable by the parking brake control unit 16. The switch 23 is normally closed. However, the driver can force the opening of this switch by controlling it via the parking brake control unit 16, which prevents any possible control of the protection solenoid valve 20, so that the parking solenoid valve 13 is thus supplied with pressure. This situation can occur in the event of a failure of the braking circuit, leading the driver to attempt emergency braking using the parking brake. The opening of the switch 23 ensures that, despite a command generated by the braking control unit 14, the protection solenoid valve 20 is in its rest position ensuring the supply of pressure to the parking solenoid valve 13.Alternatively, the electrical switch 23 can be operated directly by maintenance personnel, for example to force activation of the parking brake in the event of a failure of the parking brake control unit 16 or for ground tests of the protection solenoid valve 20.

[0072] Monitoring the proper operation of the electrical switch 23 and the protection solenoid valve 20 is carried out during a functional test. This test can be carried out by observing the variation in the pressure level measured by the pressure sensor 21. Before controlling the park solenoid valve 13, the pressure must be below a given threshold, for example 50 bars. It is arranged so that controlling the park solenoid valve 13 causes the switch 23 to open, which returns the protection solenoid valve 20 to the rest position if it was not already there, causing an increase in the pressure measured by the pressure sensor 21 above a certain threshold, for example 100 bars. In the event that this pressure level is not reached, information is sent to the maintenance system indicating that the switch 23 is stuck in the closed position.

[0073] The flowchart of figures 3a and 3b describes an example of a functional test sequence for detecting the failure of one of the components performing the protection function of the parking solenoid valve 13. In the initial state, the parking solenoid valves 13 and protection 20 are not controlled (they can however be faulty by being stuck open or closed). During the functional tests, the two solenoid valves are successively controlled and de-controlled according to a sequence depending on the pressure in the brakes (greater than a threshold pressure Ps or on the contrary lower than a minimum pressure Pm, with typically Ps=100 bars, Pm=5 bars). If the parking solenoid valve 13 is not faulty, it must in fact be controlled to detect pressure in the brakes (unless of course the braking circuit itself is faulty).The illustrated sequence makes it possible to identify faults in the park solenoid valve 13, the protection solenoid valve 20, and the switch 23. This sequence is executed, for example, each time the aircraft is started, so that the pilot is informed of a possible fault before it can cause an unfortunate consequence.

[0074] According to an alternative implementation of the invention illustrated in Figure 4, the three-way / two-position protection solenoid valve 20 is replaced by a two-way / two-position protection solenoid valve 20'. This alternative solution offers the advantage of removing a leak path between the supply port and the return port, which makes it possible to optimize the sizing of the hydraulic accumulator. A pressure sensor 21' is preferably arranged between the two solenoid valves to assist in fault detection.

[0075] According to another variant implementation of the invention illustrated in Figure 5, the protection solenoid valve 20'' is positioned still in series with the park solenoid valve 13, but this time downstream of the latter. A pressure sensor 21'' is preferably arranged between the two solenoid valves to help detect faults.

[0076] According to yet another variant implementation of the invention, the pressure sensors 10a, 10b used for the anti-skid function are used directly to provide a pressure measurement making it possible to monitor the correct operation of the park 13 and protection 20 solenoid valves, thus avoiding the installation of the pressure sensor 21.

[0077] The protection provided by the protective solenoid valve 20, in combination or not with the controlled switch 23, therefore makes it possible to prevent a simple failure of the parking solenoid valve 13 from leading to an unwanted braking situation or any other catastrophic situation. It is therefore possible to be satisfied with a single-actuated parking solenoid valve.

[0078] 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.

[0079] In particular, although the examples illustrated here relate to aircraft with two brakes, it goes without saying that the invention applies to aircraft having a greater number of brakes.

Claims

CLAIMS 1. Method for securing a parking function of a hydraulic braking circuit (1) supplying brakes (12a, 12b) of braked wheels (11a, 11b) carried by landing gear of an aircraft, the hydraulic circuit comprising a parking solenoid valve (13) having a service port connected to the brakes (12a, 12b) and a supply port connected in the rest position to a hydraulic return (102) of the aircraft, the parking solenoid valve (13) being controllable to connect said supply port with a pressure source (101, 2) so as to selectively transmit to the brakes of the aircraft a pressure sufficient to cause the actuation of the brakes ensuring the immobilization of the aircraft, the method being characterized in that it comprises the steps of: arranging in series with the parking solenoid valve (13) a protection solenoid valve (20; 20';20'') allowing at rest the supply of pressure to the brakes via the parking solenoid valve, and which is controllable to prohibit the supply of pressure to the brakes via the parking solenoid valve; control the protection solenoid valve at least in a situation where a failure of the parking solenoid valve may induce unwanted braking.; 2. Method according to claim 1, in which the protection solenoid valve (20; 20') is arranged upstream of the park solenoid valve (13), between the latter and a pressure source (101,2).

3. Method according to one of claims 1 or 2, in which the protection solenoid valve (20; 20'') is of the type three-way / two-position.

4. Method according to claim 1, in which functional tests are carried out to detect a possible failure by successively controlling and deactivating the park solenoid valve (13) and the protection solenoid valve (20; 20'; 20'').

5. Method according to claim 4, in which pressure information from a pressure sensor (21; 21'; 21'') arranged on a hydraulic line between the park solenoid valve (13) and the protection solenoid valve (20; 20'; 20'') is used.

6. Method according to claim 4, in which the functional tests are carried out each time the aircraft is started up.

7. Method according to claim 1, in which the control of the protection solenoid valve (20; 20'; 20'') is developed taking into account the following information: • a rotation speed of each braked wheel; • information on the sinking of the aircraft's landing gear with braked wheels; • information on locking in the deployed position of each of the landing gears equipped with braked wheels.

8. Method according to claim 1, in which a switch (23) is arranged on an electrical line carrying the control of the protection solenoid valve (20), the switch being normally closed, and controllable to be open, thus preventing any possible control of the protection solenoid valve (20; 20'; 20'').

9. Method according to claim 1, in which the protection solenoid valve (20') is of the two-way / two-way type positions.

10. Method according to claim 1, in which the protection solenoid valve (20'') is arranged downstream of the parking solenoid valve (13), between the latter and the brakes.

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