Aircraft braking system

Abstract

The present application relates to an aircraft braking system comprising a brake actuator, a main hydraulic fluid supply circuit configured to supply pressurized hydraulic fluid to the brake actuator, and a secondary hydraulic fluid supply circuit comprising a piezoelectric pump configured to supply pressurized hydraulic fluid to the brake actuator.

Description

Technical Field

[0001] This invention relates to aircraft braking systems. Aircraft braking systems typically include one or more brake actuators that are driven by a central hydraulic system during normal operation. In emergency situations, such as when the main hydraulic circuit fails, an emergency hydraulic fluid supply system is also required to drive the brake actuators. The same arrangement is also typically used to maintain sufficient pressure on the brakes when the aircraft is parked. Background Technology

[0002] Currently, emergency braking is achieved using an accumulator downstream of a check valve fed from the central hydraulic system. If the hydraulic system fails, the accumulator will hold enough fluid to allow the brake actuator to be used multiple times.

[0003] Each braking application can use a full piston volume of fluid before returning it to the central hydraulic system's storage compartment. Therefore, the requirement for multiple applications may necessitate a large accumulator. Furthermore, it limits the number of applications that can be used in emergency situations.

[0004] The same accumulator arrangement is also used to maintain sufficient pressure on the brakes when the aircraft is parked. If mechanical clearances increase, such as when the brakes are cooling, the pressure supplied by the accumulators is sufficient to maintain braking function. Summary of the Invention

[0005] According to a first aspect of the invention, an aircraft braking system is provided, the aircraft braking system comprising: a brake actuator; a main hydraulic fluid supply circuit configured to supply pressurized hydraulic fluid to the brake actuator; and a secondary hydraulic fluid supply circuit comprising a piezoelectric pump configured to supply pressurized hydraulic fluid to the brake actuator.

[0006] This provides a braking system with reduced mass, size, and / or complexity compared to known arrangements.

[0007] A piezoelectric pump may include a pumping chamber and a piezoelectric stack configured to change the volume of the pumping chamber. The piezoelectric pump may also include an electronic drive unit configured to control the piezoelectric stack, and the check valves configured on each side of the pumping chamber to control the inlet and outlet flows to the pumping chamber, respectively.

[0008] Preferably, the braking system also includes an accumulator arranged to store pressurized hydraulic fluid returning from the brake actuator, wherein a piezoelectric pump is arranged to draw hydraulic fluid from the accumulator. With this arrangement, there is no limitation on the number of strokes the brake actuator can perform when supplied by a secondary hydraulic circuit (e.g., in an emergency). Furthermore, pressurized hydraulic fluid can be supplied to the inlet of the piezoelectric pump. Additionally, the accumulator can be configured to store a fixed amount of hydraulic fluid for a single full stroke of the brake actuator. In other words, the fluid capacity of the accumulator can be equal to the capacity of the active chamber of the brake actuator. With this arrangement, the accumulator can be reduced in size and mass, thereby reducing the size and mass of the braking assembly.

[0009] Alternatively, the piezoelectric pump is configured to draw only from hydraulic fluid trapped or contained in one or more hydraulic lines downstream of the brake actuator. In other words, with this arrangement, an emergency accumulator is not required. This can provide a system with further reduced mass and size.

[0010] Optionally, the main hydraulic fluid supply circuit and the auxiliary hydraulic fluid supply circuit are in fluid communication with the brake actuator via a brake control valve, which is arranged to control the movement of hydraulic fluid into and out of the brake actuator. This arrangement reduces the number of individual brake control valves, thereby reducing the size, weight, and / or complexity of the system.

[0011] Optionally, the brake control valve is connected to the supply line of the main hydraulic circuit and the outlet of the piezoelectric pump via a first shared hydraulic line; the brake control valve is connected to the return line of the main hydraulic circuit and the inlet of the piezoelectric pump via a second shared hydraulic line; and the brake control valve is arranged to selectively connect the brake actuator to the first shared hydraulic line or the second shared hydraulic line.

[0012] Optionally, the supply line of the main hydraulic fluid supply circuit is connected to the first shared hydraulic line via a first check valve, the first check valve being arranged to control the inflow of hydraulic fluid from the main hydraulic circuit. Additionally or alternatively, the return line of the main hydraulic fluid supply circuit is connected to the second shared hydraulic line via a second check valve, the second check valve being arranged to control the outflow of hydraulic fluid returning to the main hydraulic circuit.

[0013] The supply line is a hydraulic line (e.g., a pipe or hose) arranged to deliver the incoming flow of hydraulic fluid to the brake actuator. The return line is a similar hydraulic line arranged to deliver the outgoing flow of hydraulic fluid from the brake actuator (e.g., back to the central hydraulic system). A check valve, also known as a one-way valve or non-return valve, is arranged to selectively allow hydraulic fluid to flow in one direction (i.e., towards the actuator for a first check valve and away from the actuator for a second check valve). The check valve may be a spring-loaded non-return valve.

[0014] The outlet and inlet of the piezoelectric pump can be fluidly connected to a shared supply and return line via hydraulic lines, respectively. A first check valve and a second check valve can be closed by the hydraulic pressure generated when the piezoelectric pump supplies pressurized hydraulic fluid to the brake actuator. In other words, the flow of pressurized hydraulic fluid from the pump outlet to the brake actuator serves to close the first check valve, and the flow of pressurized hydraulic fluid from the brake actuator into the piezoelectric pump inlet serves to close the second check valve.

[0015] With this arrangement, when the secondary hydraulic circuit is operating (e.g., in an emergency braking situation), the primary hydraulic circuit can be at least partially disconnected from the brake actuator (i.e., not fluidly connected). This increases the hydraulic pressure in the secondary hydraulic circuit and enables it to operate at near-closed-loop pressure.

[0016] Optionally, the accumulator is connected to the return line at a point upstream of the second check valve. In other words, the accumulator can be located at a point on the shared section between the second check valve and the brake actuator or brake control valve on the return line. With this arrangement, the accumulator can receive and store pressurized hydraulic fluid when the second hydraulic circuit is operating (i.e., when the pump supplies pressurized hydraulic fluid to the brake actuator).

[0017] Optionally, the secondary hydraulic fluid supply circuit includes: a third check valve arranged to control the inflow of hydraulic fluid into the piezoelectric pump inlet; and a fourth check valve arranged to control the outflow of hydraulic fluid from the pumping chamber outlet. The check valve, also known as a one-way valve or rectifier valve, is arranged to selectively allow hydraulic fluid to flow in one direction (i.e., toward the actuator for the fourth check valve and away from the actuator for the third check valve). The check valve may be a non-return valve. The third and fourth check valves can be closed by the hydraulic pressure generated when the main hydraulic fluid supply circuit supplies pressurized hydraulic fluid to the brake actuator. In other words, the flow of pressurized hydraulic fluid from the supply line of the main hydraulic circuit acts as a means to close the fourth check valve, which in turn closes the third check valve.

[0018] With this arrangement, when the main hydraulic circuit is operating (e.g., under "normal" braking conditions), the auxiliary hydraulic circuit can be disconnected from the brake actuator (i.e., not fluidly connected). The check valve of the main hydraulic circuit can cooperate with the check valve of the auxiliary hydraulic circuit so that at any given time only one of the main hydraulic circuit or the auxiliary hydraulic circuit is connected to the brake actuator.

[0019] Optionally, the auxiliary hydraulic fluid supply circuit is an emergency hydraulic fluid supply circuit, configured to supply pressurized hydraulic brake fluid to the brake actuator when the main hydraulic fluid supply circuit is not operational. For example, if the hydraulic pressure from the supply line is insufficient to perform the full stroke of the brake actuator, the main hydraulic fluid supply circuit can be considered not operational. This may occur when the central hydraulic system malfunctions or fails.

[0020] Alternatively, the brake actuator is configured to employ a parking brake, and the secondary hydraulic fluid supply circuit is configured to supply pressurized hydraulic fluid to the brake actuator to maintain braking force. The parking brake acts on one or more brake actuators with sufficient pressure to keep the aircraft stationary. In this arrangement, the secondary hydraulic circuit can operate independently of the primary hydraulic circuit to maintain sufficient parking brake pressure to accommodate varying mechanical clearances (such as when the aircraft braking components are cooling).

[0021] Optionally, the main hydraulic fluid supply circuit includes or is connected to a central hydraulic system. The central hydraulic system includes a hydraulic fluid storage unit and is used to supply pressurized hydraulic fluid to multiple hydraulic subsystems. The main hydraulic system's supply lines can supply hydraulic fluid from the central hydraulic system's storage unit, and the main hydraulic circuit's return lines can return hydraulic fluid to the central hydraulic system's storage unit.

[0022] Optionally, the main hydraulic fluid supply circuit and the auxiliary hydraulic fluid supply line are configured to supply pressurized hydraulic fluid to two or more brake actuators.

[0023] According to another aspect of the invention, an aircraft landing gear assembly is provided, which includes an aircraft braking system according to any of the above descriptions.

[0024] According to another aspect of the invention, an aircraft is provided that includes the aforementioned aircraft landing gear assembly.

[0025] The electronic drive unit can drive the piezoelectric stack at a predetermined frequency, causing the piezoelectric stack to alternately increase and decrease the volume of the pumping chamber. Attached Figure Description

[0026] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0027] Figure 1 This is a schematic diagram of a known aircraft braking system;

[0028] Figure 2 This is a schematic diagram of an aircraft braking system according to an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of an aircraft braking system according to an embodiment of the present invention. Detailed Implementation

[0030] Figure 1 This is a schematic diagram of a known braking system 10, which includes a main hydraulic fluid supply circuit 20 and an emergency hydraulic supply circuit 40. The main hydraulic fluid supply circuit 20 drives the brake actuator 30 during normal operation, and the emergency hydraulic supply circuit 40 drives the brake actuator 30 in emergency situations, such as when the supply line 22 of the main hydraulic circuit 20 is not working.

[0031] The actuator 30 includes a cylinder 32, within which piston and rod assemblies 34, 36 are slidably housed, such that the actuator 30 can extend and retract along the longitudinal axis A.

[0032] Cylinder 32 includes a port P for connecting actuator 30 to main hydraulic circuit 20 and auxiliary hydraulic circuit 40. The space between port P and piston 34 within cylinder 32 defines an active chamber AC (also called an extension chamber) to which hydraulic fluid, such as oil, is supplied to cause actuator 30 to extend.

[0033] Although not shown, it should be understood that the piston rod 36 of the brake actuator can be coupled to one or more brake stators. When the brake actuator extends, the one or more brake stators apply braking pressure to one or more rotors fixed to the wheel. Friction between the one or more stators and the one or more rotors applies a braking torque, which serves to slow the rotation of the wheel (or prevent the wheel from rotating when the aircraft is stationary). Of course, in practice, aircraft braking assemblies are more complex and include many other components. For example, in practice, a braking assembly for a single wheel may have multiple brake actuators. However, for the purposes of understanding the invention, a description of these components is not necessary.

[0034] During normal operation, the main hydraulic circuit 20 is operable to supply hydraulic fluid under pressure to port P of the brake actuator 30 via supply line 22. Supply line 22 can draw pressurized hydraulic fluid from a central hydraulic system (not shown).

[0035] Actuator 30 is single-acting, characterized by a single port P defining a single active chamber. A brake control valve 50 is operable to selectively connect the main supply line 22 to port P, allowing pressurized hydraulic fluid to flow into the active chamber. The hydraulic fluid entering the active chamber AC from port P forces piston 34 toward the rod 36 of housing 32 from its extended side. This causes actuator 30 to change between a first extended state and a second extended state during a first phase, which in turn applies braking force to one or more brake rotors via one or more brake stators, as described above. Brake control valve 50 enables control of the hydraulic pressure applied to the brake actuator from supply line 22, thereby enabling control of the braking torque.

[0036] Distal to the piston 34 within the housing, a resilient biasing device, such as a mechanical spring 38, is provided. In this example, this resilient biasing device is compressed as the actuator 30 extends, causing the spring 38 to provide a resilient biasing force that compresses the actuator 30 into a contracted state when fluid pressure is removed from the hydraulic supply circuit. An operable brake control valve 50 selectively connects port P to return line 24 to allow pressurized hydraulic fluid to flow out of the actuator. As the brake actuator 30 contracts, fluid is forced through port P out of the active chamber AC, and the returned fluid can return via return line 24 to, for example, a storage unit in the central hydraulic system.

[0037] In some cases, the main hydraulic circuit 20 may not provide sufficient hydraulic pressure to operate the brake actuator 30. This can happen, for example, if the central hydraulic system malfunctions.

[0038] Therefore, the braking system 10 also includes an emergency hydraulic fluid supply circuit 40, which is operable to supply pressurized hydraulic fluid to the brake actuator 30.

[0039] Figure 1 The illustrated emergency hydraulic circuit 40 includes an emergency supply line 42, which is in fluid communication with the main supply line via an emergency check valve 44. The emergency supply line 42 includes a dedicated emergency accumulator 46 located downstream of the emergency check valve 44. During normal operation, a portion of the fluid supplied by the main hydraulic circuit 20 is directed to the emergency accumulator 46 via the emergency check valve 44 and then stored under pressure in the emergency accumulator 46.

[0040] In emergency braking situations, such as when the main hydraulic circuit 20 fails or becomes inoperable, the emergency hydraulic circuit 40 can be operated to draw pressurized hydraulic fluid from the emergency accumulator 46 and supply it to port P of the brake actuator 30. It extends the brake actuator 30 in the same manner as described above. As mentioned above, when the brake actuator 30 retracts under the action of the biasing device 38, the fluid returns via the return line 24 to, for example, a storage unit in the central hydraulic system. Similar to the operation of the brake control valve 50, the emergency brake control valve 52 selectively connects the emergency accumulator 46 or the return line to port P of the brake actuator to allow hydraulic fluid to enter or leave the active chamber.

[0041] like Figure 1 As shown, the main hydraulic circuit 20 and the emergency hydraulic circuit 40 are connected to port P of the brake actuator via a reciprocating valve 60. The reciprocating valve 60 is operable to selectively connect either the main hydraulic circuit 20 or the emergency hydraulic circuit 40 to the brake actuator 30.

[0042] As will be understood, each emergency braking application (i.e., each stroke of the brake actuator) can utilize a full piston volume of fluid before returning fluid to the reservoir in the central hydraulic system. Therefore, to enable multiple applications of the brake in an emergency, the accumulator must be large enough to store the corresponding amount of hydraulic fluid (enough to achieve, for example, six full strokes). This may necessitate the use of large accumulators, thereby increasing the size and / or mass of the braking assembly. Furthermore, even with a large accumulator, the number of strokes of the brake actuator 30 that can be used in an emergency is limited.

[0043] This invention overcomes these and other disadvantages by providing a braking system in which an emergency hydraulic fluid supply circuit includes a piezoelectric pump for supplying pressurized hydraulic fluid to the brake actuator in an emergency. The inventors have discovered that the piezoelectric pump can provide sufficient hydraulic pressure and flow to drive the brake actuator while being relatively small and lightweight.

[0044] A first example of an aircraft emergency braking system according to the present invention is as follows: Figure 2 As shown in the schematic diagram. (And) Figure 1 The braking system is the same as 10. Figure 2 The braking system 100 includes a main hydraulic fluid supply circuit and an emergency (referred to herein as "secondary") hydraulic fluid supply circuit 400. The main hydraulic fluid supply circuit, represented by a supply line 220 and a return line 240, drives the brake actuator 300 under normal operation. The emergency hydraulic fluid supply circuit 400 drives the brake actuator 300 in emergency situations, such as when the main hydraulic circuit fails. Figure 2 The secondary hydraulic circuit 400 includes a piezoelectric pump 440, which is operable to draw hydraulic fluid and supply it under pressure to port P of actuator 300.

[0045] The main hydraulic fluid supply circuit and the auxiliary hydraulic fluid supply circuit are connected to port P of the brake actuator 300 via a common brake control valve 500, such that the inlet port of the brake control valve 500 can be connected to both the supply line 220 of the main hydraulic circuit and the outlet of the piezoelectric pump 440, while the outlet port of the brake control valve 500 can be connected to the return line 240 of the main hydraulic circuit and the inlet of the piezoelectric pump 440. (As mentioned above...) Figure 1 The explained operable brake control valve 500 selectively allows hydraulic fluid to flow into or out of the active chamber AC of the brake actuator. Figure 2 (The movement of the brake control valve in the direction of the arrow is shown in the image). With this arrangement, a single brake control valve can be used in both the main hydraulic circuit and the auxiliary hydraulic circuit. (Similar to...) Figure 1 Compared to existing technology systems that use separate brake control valves for the main hydraulic circuit and the auxiliary hydraulic circuit, it can reduce the size, weight and complexity of the system.

[0046] exist Figure 2 In this configuration, the main hydraulic circuit and the auxiliary hydraulic circuit are connected such that a portion 220a of the supply line immediately upstream of the brake control valve 500 is shared between the two circuits (i.e., common), and a portion 240a of the return line immediately downstream of the brake control valve 500 is also shared between the two circuits. The supply line 220 of the main hydraulic circuit can be connected to the shared portion 220a of the supply line via a check valve 222 (also known as a one-way valve), such as a spring-loaded check valve (or other pressure relief valve), the check valve being arranged to control the inflow (main supply) of hydraulic fluid from the main hydraulic circuit to the brake actuator 300.

[0047] During normal operation, when the main hydraulic fluid supply circuit is active, Figure 2 The system is related to the above. Figure 1 It operates in a largely the same manner. However, in emergency situations, such as when the main hydraulic circuit supply line 220 is not operational, pressurized hydraulic fluid is supplied to the brake actuator by the piezoelectric pump 440 of the auxiliary hydraulic circuit 400. Figure 2In this system, the piezoelectric pump 440 is arranged to draw hydraulic fluid trapped in a portion of the return line between the brake control valve 500 and the inlet of the piezoelectric pump 440 (in this example, including the aforementioned shared portion 240a of the return line and at least a portion of the return line 240 of the main hydraulic circuit). As will be understood, hydraulic fluid can be drawn from the return line after each stroke of the brake actuator 300, such that the hydraulic fluid flows effectively and continuously between the piezoelectric pump 440 and the actuator 300. Therefore, there is no limitation on the number of strokes that the brake actuator 300 can perform in an emergency (i.e., when supplied by the auxiliary hydraulic circuit 400). Furthermore, since an emergency accumulator is not required, the size and weight of the system can be significantly reduced (the small size and low weight of the piezoelectric pump mean that the removal of the accumulator can largely offset the increase in pump size).

[0048] When the secondary hydraulic circuit 400 is supplying the brake actuator (i.e., when the piezoelectric pump 440 is running), hydraulic pressure acts to close the check valve 222 connected to the main supply line 220. In this way, when the secondary hydraulic circuit 400 is running, the main hydraulic circuit is partially disconnected from the brake actuator (i.e., the supply line 220 is not in fluid communication with the brake actuator).

[0049] In some cases, there may not be enough hydraulic fluid retained in the available hydraulic lines downstream of the brake control valve 500 to allow the brake actuator 300 to complete its full stroke. Additionally, or alternatively, there may not be sufficient pressure in the return line for the piezoelectric pump 440 to operate effectively. In such cases, the braking system may preferably include an emergency accumulator from which the piezoelectric pump 440 can draw up to a full piston volume of pressurized hydraulic fluid.

[0050] An example of this braking system is as follows Figure 3 As shown. Figure 3 System 100 and the above about Figure 2 The systems described are essentially the same, except that the shared portion 240a of the return line includes a dedicated accumulator 460, which is configured to store at least a portion of the pressurized hydraulic fluid returning from the brake actuator 300 as the brake actuator 300 contracts (as described above regarding...). Figure 1 The aforementioned). Existing technology systems that directly supply actuators with emergency accumulators (such as...) Figure 1In contrast to the system described above, the emergency accumulator 460 according to the invention provides pressurized hydraulic fluid only to the piezoelectric pump 300. The piezoelectric pump 440 can then draw pressurized hydraulic fluid from the accumulator 460 to supply the brake actuator 300. In this case, the hydraulic fluid flows continuously between the piezoelectric pump 440 and the actuator 300 via the dedicated accumulator 460, thus there is no limit to the number of strokes the brake actuator 300 can perform in an emergency (i.e., when supplied by the auxiliary hydraulic circuit 400). Furthermore, the accumulator 460 only needs to store sufficient hydraulic fluid for one full stroke of the brake actuator 300, and additionally only needs to store this volume at a relatively low pressure, as it only supplies the pumping chamber of the piezoelectric pump. Therefore, the size and weight of the accumulator 460 can be reduced.

[0051] Preferably, the main hydraulic circuit supply line 240 is connected to a shared portion 240a of the return line via a second check valve 242, such as a spring-loaded check valve (or other pressure relief valve), the second check valve being arranged to control the outflow (main return) of hydraulic fluid from the actuator 300 to the main hydraulic circuit. This can increase the pressure between the accumulator 460 and the inlet of the piezoelectric pump 440. The dimensions of the return spring 38 and / or the active chamber AC of the actuator 300 can be increased to accommodate the additional pressure required for the hydraulic fluid to return via the main return line 240. When the main hydraulic circuit supplies pressurized hydraulic fluid to the brake actuator, the hydraulic pressure is used to open the first check valve 222 and the second check valve 242.

[0052] Check valves 222 and 242 can be spring-biased check valves or any suitable check valve.

[0053] The piezoelectric pump 440 of this embodiment can take any suitable form. For example, such as Figure 2 and Figure 3As shown, the piezoelectric pump may include a pair of check valves 482, 484, spaced apart from each other by a housing to define a pumping chamber 486 therebetween. One of the check valves 482 is arranged to allow hydraulic fluid to flow into the pumping chamber 486. The other check valve 484 is arranged to allow hydraulic fluid to flow out of the pumping chamber 486. The surface of the pumping chamber 486 may be formed, for example, by a movable diaphragm. The piezoelectric element 488, preferably comprising a piezoelectric stack as shown, is arranged (e.g., by moving the diaphragm) to change the pumping chamber 486 to draw fluid into the chamber from the inlet valve 482 when the chamber volume increases, and to discharge fluid from the chamber from the outlet valve 484 when the chamber volume decreases. The piezoelectric element 488 can be driven by an electronic drive unit (not shown) with an oscillating high-voltage / low-current power supply (e.g., up to 2000V) typically in the range of 200 to 2000Hz. Control can be simply turning the power on (ON) or off (OFF). The amount of fluid pumped by the pump 480 can also be regulated by the operating frequency and voltage of the piezoelectric element 488.

[0054] As will be understood, when the main hydraulic circuit is running, the hydraulic pressure will be used to close the check valve 484 of the piezoelectric pump, which in turn will close check valve 482, thus disconnecting the hydraulic pump from the brake actuator (i.e., preventing fluid communication). The check valve 222 of the main hydraulic circuit can be coordinated with the check valve 484 of the auxiliary hydraulic circuit, such that at any given time only one of the main or auxiliary hydraulic circuits is connected to the brake actuator. The check valves 482 and 484 of the piezoelectric pump can be non-return valves or any suitable check valve.

[0055] In any of the above examples, the main hydraulic circuit and / or the auxiliary hydraulic circuit can be integrally formed with the actuator 500 or can be a separate unit coupled to the actuator 500. The main hydraulic fluid supply circuit can be configured with respect to... Figure 1 Similar approaches include a central hydraulic system, or a system coupled to a central hydraulic system. Alternatively, the main hydraulic circuit can be a dedicated hydraulic fluid supply circuit, such as the hydraulic fluid supply circuit for an electro-hydraulic actuator. As will be understood, the brake actuator can be any suitable brake actuator, as described above regarding... Figure 1 The described brake actuator.

[0056] For ease of illustration, the brake actuator has been described and illustrated as a single-acting actuator. However, it will be apparent to those skilled in the art that the invention can also be applied to double-acting actuators.

[0057] Implementation of parking brake

[0058] The invention has already been described in the context of emergency braking systems in the above discussion. However, as Figure 2 and Figure 3 As shown, the aforementioned braking system is also applicable to aircraft parking brakes. Specifically, the auxiliary hydraulic circuit can be configured to maintain sufficient pressure on the brakes when the aircraft is parked, for example, by periodically activating a piezoelectric pump.

[0059] It should be noted that the above embodiments are illustrative rather than limiting of the invention, and those skilled in the art will be able to devise many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference numerals placed in parentheses should not be construed as limiting the claims. The word "comprising" does not exclude the presence of elements or steps other than those listed as a whole in any claim or specification. A singular reference to an element does not exclude a plural reference to that element, and vice versa. The various components of the invention can be implemented by means of hardware comprising several different elements. In device claims enumerating several components, several of these components may be implemented by one or the same piece of hardware. The fact that specific measures are described in mutually different dependent claims does not mean that a combination of these measures cannot be used to produce good results.

Claims

1. An aircraft braking system, comprising: Brake actuator (300); The main hydraulic fluid supply circuit (220, 240) is configured to supply pressurized hydraulic fluid to the brake actuator; and A secondary hydraulic fluid supply circuit (400) includes a piezoelectric pump (440) configured to supply pressurized hydraulic fluid to the brake actuator. The main hydraulic fluid supply circuit and the auxiliary hydraulic fluid supply circuit are fluidly connected to the brake actuator via a brake control valve (500), which is arranged to control the movement of hydraulic fluid into and out of the brake actuator. The brake control valve is connected via a first shared hydraulic line (220a) to the supply line (220) of the main hydraulic fluid supply circuit and the outlet of the piezoelectric pump. Its features are, The brake control valve is connected via a second shared hydraulic line (240a) to the return line (240) of the main hydraulic fluid supply circuit and to the inlet of the piezoelectric pump; and The brake control valve is arranged to selectively connect the brake actuator to either the first shared hydraulic line or the second shared hydraulic line.

2. The aircraft brake system of claim 1, wherein, It also includes an accumulator (460) arranged to store pressurized hydraulic fluid returned from the brake actuator (300), wherein the piezoelectric pump (440) is arranged to draw hydraulic fluid from the accumulator.

3. The aircraft brake system of claim 1, wherein, The piezoelectric pump (440) is configured to draw only from the hydraulic fluid contained in one or more hydraulic lines downstream of the brake actuator (300).

4. The aircraft braking system according to claim 1, characterized in that: The supply line (220) of the main hydraulic fluid supply circuit is connected to the first shared hydraulic line (220a) via a first check valve (222), the first check valve being arranged to control the inflow of hydraulic fluid from the main hydraulic circuit; and / or The return line (240) of the main hydraulic fluid supply circuit is connected to the second shared hydraulic line (240a) via a second check valve (242), the second check valve being arranged to control the outflow of hydraulic fluid returning to the main hydraulic circuit.

5. The aircraft brake system according to any one of claims 1 to 3, wherein, The auxiliary hydraulic fluid supply circuit (400) includes: A third check valve (482) is arranged to control the inflow of hydraulic fluid into the inlet of the piezoelectric pump (440); and A fourth check valve (484) is arranged to control the outflow of hydraulic fluid from the outlet of the piezoelectric pump.

6. The aircraft brake system according to any one of claims 1 to 3, wherein, The auxiliary hydraulic fluid supply circuit (400) is an emergency hydraulic fluid supply circuit configured to supply pressurized hydraulic braking fluid to the brake actuator (300) when the main hydraulic fluid supply circuit is not working.

7. The aircraft brake system according to any one of claims 1 to 3, wherein, The brake actuator (300) is configured to apply a parking brake, and wherein the auxiliary hydraulic fluid supply circuit (400) is configured to supply pressurized hydraulic fluid to the brake actuator to maintain braking force.

8. The aircraft brake system according to any one of claims 1 to 3, wherein, The main hydraulic fluid supply circuit includes or is connected to a central hydraulic system.

9. The aircraft brake system according to any one of claims 1 to 3, wherein, The main hydraulic fluid supply circuit and the auxiliary hydraulic fluid supply circuit are configured to supply pressurized hydraulic fluid to two or more brake actuators.

10. An aircraft landing gear assembly, the aircraft landing gear assembly comprising an aircraft braking system according to any one of claims 1 to 9.

11. An aircraft comprising the aircraft landing gear assembly according to claim 10.

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