Fluid-pressure and analogous brake systems – Multiple control – Fluid and electric
Reexamination Certificate
2001-10-31
2003-12-16
Lavinder, Jack (Department: 3683)
Fluid-pressure and analogous brake systems
Multiple control
Fluid and electric
C303S014000, C303S006010, C303S009610
Reexamination Certificate
active
06663192
ABSTRACT:
The invention relates to an architecture for a hydraulic braking system adapted to aircraft having landing gear with braked wheels.
BACKGROUND OF THE INVENTION
In general, an airplane is fitted with a main hydraulic circuit, said hydraulic circuit being arranged to feed the braking actuators of wheels carried by main landing gear units, said actuators being in the form of brakes each comprising a first series of “rotor” disks constrained to rotate with the wheels and associated with a second series of “stator” disks that are prevented from rotating, the disks in the two series alternating along the axis of rotation of a wheel and being pressed against one another by pistons mounted to slide in a hydraulic ring and actuated by means of hydraulic fluid under pressure delivered by the main hydraulic circuit of the aircraft. This pressure of the disks against one another then generates friction because the rotor disks are rotating with the wheel while the stator disks are prevented from rotating. This dissipates the kinetic energy of the aircraft in the form of the heat that is generated by the friction, thus slowing down the aircraft.
Braking is a critical function for an aircraft, and if braking fails completely, e.g. on landing, then there is an unacceptably high likelihood of passenger lives being at risk, not to mention the possibility of the aircraft itself being damaged. Furthermore, safety requirements lead to aircraft systems being designed so as to ensure that mere breakdown of any one system (e.g. the main hydraulic circuit) cannot lead to a catastrophe.
Thus, as a general rule, aircraft are fitted with an emergency hydraulic circuit whose hydraulic fluid is applied to the brakes in the event of the main hydraulic circuit failing. There are two approaches to brake design. In a first variant the brakes have dual cavities, i.e. their rings carry two series of pistons, a first series being actuated by the main hydraulic circuit, while the second series is actuated by the emergency hydraulic circuit. The two circuits are thus kept apart all the way to the final actuators. In a second variant, each brake has a single cavity only, i.e. only one series of pistons which can be fed selectively from one or other of the circuits via a shuttle valve which is generally situated in the wheel well and which delivers hydraulic fluid to the brake from whichever circuit is under the greater pressure. The advantage of this configuration is that the brake rings are simplified, as is the hydraulic pipework that extends along the landing gear itself, since a single pipe per brake then suffices.
Given the size and weight of the commercial aircraft presently under consideration, manufacturers have been constrained to consider using large numbers of main landing gear units, for example two wing units and one or two fuselage units.
This increase in the number of landing gear units leads to a corresponding increase in the amount of pipework required for the two braking circuits, particularly since each wing or fuselage landing gear unit is expected to be fitted with at least six wheels. This increase number of pipes and associated increase in pipework length due to the large size of the aircraft leads to an economically unacceptable penalty in the weight breakdown of the aircraft.
OBJECTS AND SUMMARY OF THE INVENTION
In order to simplify and lighten the braking system of such an aircraft, the invention proposes an architecture for a hydraulic braking system suitable for an aircraft of the type having at least one group of main landing gear units, each landing gear unit comprising a determined number of wheels each provided with a hydraulically actuated brake, the or each landing gear group being associated with a hydraulic circuit provided with hydraulic equipment and adapted to deliver hydraulic fluid under pressure to all of the brakes of the landing gear group, the hydraulic fluid being pressurized by at least one aircraft pressure generator system associated with an aircraft hydraulic fluid supply. According to the invention, accumulators are connected on the or each circuit in sufficient number for each accumulator to feed two pairs of brakes, each pair of brakes being mounted on a distinct landing gear unit, and an electrically-driven pump being arranged to maintain a predetermined pressure level in all of the accumulators of the circuit in question.
Thus, failure of any one circuit affects only a single landing gear group, and the brakes carried by the landing gear in another group continue to be fed normally by the other circuit. In the event of one of the circuits failing, e.g. due to pipework breaking or to the pressure generator system failing, then the accumulators, assisted where appropriate by the electrically-driven pump, take over to maintain sufficient pressure to provide braking that is acceptable for passenger safety. If these means also should fail, the aircraft would still retain braking ability on the other landing gear group, which is not possible with prior architectures. In addition, this architecture enables the hydraulic pipework to be simplified considerably, since there is no need to take pipes from both circuits to each landing gear unit. This architecture also makes it possible to make use of single-cavity brakes, which are lighter in weight and less complex than dual-cavity brakes.
Naturally, the landing gear groups should be organized in symmetrical manner so that total failure of any one circuit will not cause the remaining braking capacity to be asymmetrical, since that would make the pilot's work much more difficult. For example, one landing gear group could be a wing group and another could be a fuselage group, each group having its own feed circuit. It will be understood that under such circumstances the architecture would not be implemented in aircraft having only two wing landing gear units each organized as a separate group, since under such circumstances the failure of one circuit would make braking highly asymmetrical which would be difficult to control.
In an emergency, the pressure available for the brakes comes from the associated accumulator whose capacity must be sufficient to enable the brakes connected to the corresponding circuit to be operated. Under normal circumstances, pressure is maintained in the accumulator by the pressure generator system of the hydraulic circuit. In an emergency, this pressure is maintained by the electrically-driven pump. In addition, the accumulator can be used for the parking brake, i.e. for preventing the aircraft from moving when it is stationary and its engines are not running. Furthermore, since the electrically-driven pump is driven by a motor that is electric, it is not sensitive, a priori, to hydraulic breakdowns.
The failure of any one accumulator involves only two pairs of wheels, each pair being situated on a different landing gear unit, which means that the aircraft retains significant braking capacity, since only four brakes are lost out of a total of about twenty. It is thus possible to clear an aircraft for takeoff even if it has a faulty accumulator.
For safety reasons, each accumulator is advantageously fitted with an overpressure relief valve.
Thus, in the event of pressure in an accumulator becoming excessive, the valve opens and allows a certain quantity of hydraulic fluid to escape into the aircraft's fluid supply, thereby allowing the pressure to drop down to a safety threshold of the accumulator.
Also for safety reasons, the accumulator is fitted with a check valve on the line connecting it to the circuit so as to prevent it from discharging into the circuit in the event of the pressure in the circuit falling.
Still for safety reasons, provision is made for the electrically-driven pump to be associated with its own supply of hydraulic fluid.
Thus, if the aircraft's fluid supply is not available, it is still possible to make use of the pump's fluid supply for braking purposes.
Finally, in an emergency, in order to avoid emptying the pump's fluid supply into the aircraft&a
Bourguet Vincent
Hamzeh Walid
Lavinder Jack
Messier-Bugatti
Pezzlo Benjamin A
Sughrue & Mion, PLLC
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