Patent Description:
Aircraft systems often use hydraulic power to transmit force to a mechanical component to move that component, for example. For example, many aircraft have one or more retractable landing gear that can be extended or retracted by appropriate transmission of hydraulic fluid to hydraulic actuators mechanically coupled to the landing gear.

Many such hydraulic aircraft systems are powered from a central hydraulic power source. That source may, for example, comprise an electric pump powered by the aircraft engines to generate hydraulic pressure.

In some aircraft, the central hydraulic power source may provide a source of hydraulic pressure for multiple hydraulic aircraft systems. For example, the central hydraulic power source may provide hydraulic power for the landing gear and for powering hydraulic brakes.

For a hydraulic system that performs a critical function (such as unlocking the landing gear), a backup mechanism may be provided. For example, the backup mechanism may be an alternate hydraulic system, a hand-crank, compressed air (nitrogen), a pyrotechnic or a free-fall (i.e. gravity driven) system. In the case of an alternate hydraulic system, a dedicated backup source of hydraulic pressure may be used to provide hydraulic pressure to perform those critical functions if a main source of hydraulic pressure fails.

The present application discloses an improvement to such an alternate hydraulic system.

<CIT> discloses a hydraulic system for aircraft in which devices to be operated by the system are powered by a backup source of hydraulic pressure in the event of a pressure failure from their normal source of hydraulic pressure. A primary accumulator is connected to landing gear actuators. A secondary accumulator is connected through a valve to the main landing gear wheel brake mechanisms and is also connected to the landing gear actuators. Should the primary accumulator no longer supply the landing gear actuators, the pilot can manually operate an emergency valve in order to direct fluid pressure from the secondary accumulator to operate the landing gear actuators.

<CIT> discloses fluid pressure operated systems for use in controlling services such as undercarriages, brakes, steering mechanisms and flaps, in multi-engine aircraft. The systems comprise two or more pumps, each of which normally provides fluid pressure to a part of the system. Each pump can provide fluid pressure to the remainder of the system if one or more of the other pumps is not operating.

A first aspect of the present invention provides a hydraulic system for an aircraft, the hydraulic system comprising: a backup hydraulic pressure source to provide hydraulic pressure to a brake in the event of a failure condition of a primary hydraulic brake pressure source; and a landing gear backup system to provide hydraulic pressure to enable extension and/or retraction of landing gear; and a controller arranged to detect a failure condition of the primary landing gear hydraulic pressure source, wherein, in response to the detected failure condition, the controller is arranged to transmit an activation signal to a valve arranged to fluidically couple the backup hydraulic pressure source to the landing gear backup system, to provide hydraulic pressure to the landing gear backup system from the backup hydraulic pressure source.

Optionally, the backup hydraulic pressure source is an accumulator arranged to receive a supply of pressurised hydraulic fluid from a primary hydraulic pressure source.

Optionally, the primary hydraulic pressure source is a hydraulic system powered by the aircraft.

Optionally, the landing gear comprises a landing gear lock arranged to hold the landing gear in a retracted state, and wherein the backup hydraulic pressure is to provide hydraulic pressure to deactivate the landing gear lock in the event of a failure condition of the primary landing gear hydraulic pressure source.

Optionally, the landing gear comprises a landing gear door lock arranged to hold a landing gear door in a closed state, and wherein the backup hydraulic pressure is to provide hydraulic pressure to deactivate the landing gear door lock in the event of a failure condition of the primary landing gear hydraulic pressure source.

Optionally, the respective failure conditions are a reduction of hydraulic pressure from the respective hydraulic pressure sources, beyond a specified threshold.

Optionally, the respective failure conditions are a spike in the hydraulic pressure from the respective hydraulic pressure source, beyond a specified threshold.

A second aspect of the present invention provides an aircraft comprising the hydraulic system according to the first aspect of the present invention.

A third aspect of the present invention provides a method of operating an aircraft hydraulic system comprising a backup hydraulic pressure source to provide hydraulic pressure to a brake in the event of a failure condition of a primary hydraulic brake pressure source and a landing gear backup system to provide hydraulic pressure to enable extension and/or retraction of landing gear in the event of a failure condition of a primary landing gear hydraulic pressure source.

The method comprises: detecting, by a controller, a failure condition of a primary landing gear hydraulic pressure source; and, in response to detecting a failure condition of the primary landing gear hydraulic pressure source, providing hydraulic pressure to the landing gear backup system from the backup hydraulic pressure source.

A fourth aspect of the present invention provides a computer program which, when executed by a processor in a hydraulic system comprising a backup hydraulic pressure source to provide hydraulic pressure to a brake in the event of a failure condition of a primary hydraulic brake pressure source and a landing gear backup system to provide hydraulic pressure to enable extension and/or retraction of landing gear, causes the processor to perform the method of the third aspect.

Also provided is a hydraulic system for an aircraft, configured to: provide hydraulic pressure to a brake of the aircraft from a hydraulic pressure source in the event of a reduction of a primary hydraulic brake pressure; and provide hydraulic pressure to a landing gear backup system, from the hydraulic pressure system of the aircraft in the event of a reduction of a primary landing gear hydraulic pressure.

<FIG> illustrates major elements of an exemplary landing gear arrangement <NUM> for an aircraft, which forms part of a Landing Gear Extension/Retraction System (LGERS). The landing gear arrangement <NUM> generally comprises a shock strut <NUM> (for example, an oleo-pneumatic shock strut) having a main fitting <NUM> attached to the aircraft (for example to a wing or to the aircraft fuselage) and a slider <NUM> (or post), which can slide into the main fitting <NUM> against the pressure of a fluid or fluids to form a shock absorbing element. A torque link assembly <NUM> couples the main fitting <NUM> to a torque link lug structure <NUM> at a lower end of the slider <NUM>. The torque link lug structure <NUM> also pivotally connects the shock strut <NUM> to a bogie beam assembly <NUM>, which supports at least one wheel 114f at the front of the landing gear arrangement <NUM> and at least one wheel 114r at the rear of the landing gear arrangement <NUM>. Typically there are two or more wheels at each end of the bogie beam assembly <NUM>.

Each wheel 114f, 114r comprises a wheel brake <NUM> for providing a retardation function (under the control of the pilot) while the aircraft is on the ground. Other retardation functions available to the aircraft may be provided by one or more of thrust reversers, ground spoilers, and/or lift dumpers, for instance, and may generally be referred to herein as 'braking'. Braking by wheel braking is provided by the wheel brakes <NUM> and is typically initiated when sustained ground contact has occurred.

The landing gear arrangement <NUM> comprises an up-lock roller <NUM> arranged to engage a landing gear up-lock (not shown) when the landing gear is in a retracted position. The landing gear arrangement <NUM> may also comprise a down-lock roller (not shown for clarity) arranged to engage a landing gear down-lock (not shown) when the landing gear is in an extended position.

The landing gear arrangement <NUM> also comprises a door <NUM> (shown schematically with a dashed line) which opens from the aircraft (for example, from the aircraft fuselage, or an underside of the wing) to enable extension of the landing gear arrangement <NUM> for landing, and closes to the aircraft to conceal the landing gear arrangement <NUM> during flight. The door <NUM> may comprise an up-lock (not shown for clarity) for holding the door <NUM> in a closed position and/or a down-lock (not shown for clarity) for holding the door <NUM> in an open position.

<FIG> is a simplified schematic diagram of a prior art hydraulic system <NUM> for providing hydraulic power to a landing gear arrangement, such as the landing gear arrangement <NUM> described above with reference to <FIG>.

The hydraulic system <NUM> is, in normal operation, powered by a central hydraulic power source <NUM>. The hydraulic system <NUM> also includes a landing gear backup system <NUM> and a backup braking system <NUM>.

The landing gear backup system <NUM> is for providing hydraulic pressure to enable extension and/or retraction of landing gear arrangement <NUM> in the event of a failure of the primary hydraulic power source <NUM> to provide hydraulic pressure to the landing gear arrangement <NUM>.

The landing gear backup system <NUM> comprises an alternative power pack <NUM>, which may be engaged to provide hydraulic pressure to the landing gear arrangement <NUM> in the event of a failure of the primary hydraulic power source <NUM> to provide sufficient hydraulic pressure to the landing gear arrangement <NUM>. In particular, in some examples, the alternative power pack <NUM> may comprise a hydraulic pump with a supply of hydraulic fluid to provide hydraulic power to at least gear up-locks <NUM> and door up-locks <NUM>, so that in the event of a failure of the primary hydraulic power source <NUM> to provide hydraulic power to the landing gear arrangement <NUM>, the doors <NUM> can be opened and the landing gear arrangement <NUM> can be moved to its extended position.

The landing gear backup system <NUM> comprises a landing gear backup controller <NUM> arranged to detect a failure condition of the primary hydraulic power source <NUM>. For example, the landing gear backup controller <NUM> may comprise a pressure sensor for sensing a pressure provided by the primary hydraulic power source <NUM> and a processor to receive a pressure signal (indicated by the dashed arrow 214a) and evaluate the pressure signal. The processor may be programmed to send a control signal (indicated by the dashed arrow 214b) to activate the alternate power pack <NUM> in the event that a sensed pressure falls below a threshold pressure, for example.

The backup braking system <NUM> is for providing hydraulic pressure to enable braking of the aircraft in the event of a failure of the primary hydraulic power source <NUM> to provide sufficient hydraulic pressure to a system providing a retardation function. For example, in relation to the landing gear arrangement <NUM> depicted in <FIG>, the backup braking system <NUM> may be arranged to provide hydraulic pressure to enable operation of the wheel brakes <NUM> while the aircraft is on the ground.

In the example shown in <FIG>, the backup braking system <NUM> comprises an accumulator <NUM>, a backup braking selector valve <NUM>, and a backup braking servo valve <NUM>. In some embodiments, the backup braking selector valve <NUM> and the backup braking servo valve <NUM> may be different from a primary selector valve and servo valve. In other embodiments, the backup braking selector valve <NUM> and the backup braking servo valve <NUM> may be the same valves used by the primary hydraulic system but powered, in the event a failure of the primary hydraulic power source, from a backup hydraulic source.

The accumulator <NUM> is a pressure storage reservoir in which hydraulic fluid is held under a hydraulic pressure generated by an external source. In particular, the accumulator <NUM> is selected to provide a sufficient volume of pressurised hydraulic fluid to operate a brake <NUM> (or brakes) in the event of a failure of the primary hydraulic power source <NUM> to provide sufficient hydraulic pressure to the brake <NUM>.

In the example shown in <FIG>, the external source is the primary hydraulic power source <NUM>, which, in normal use, maintains a predetermined hydraulic pressure for a predetermined volume of hydraulic fluid in the accumulator <NUM>.

The backup brake system <NUM> comprises a backup braking controller <NUM> arranged to detect a failure condition of the primary hydraulic power source <NUM>. For example, the backup braking controller <NUM> may comprise a pressure sensor for sensing a pressure provided by the primary hydraulic power source <NUM> and a processor to receive a pressure signal (indicated by the dashed arrow 224a) and evaluate the pressure signal. The processor may be programmed to send a control signal (indicated by the dashed arrow 224b) operate the backup braking selector valve <NUM> to operate the brake <NUM> in the event that a sensed pressure falls below a threshold pressure, for example. Thus, in the event of a failure of the primary hydraulic power source <NUM> to provide sufficient hydraulic pressure to the brake <NUM>, the accumulator <NUM> provides hydraulic pressure via the backup braking selector valve <NUM> and the backup braking servo valve <NUM>, which in turn apply the brake <NUM> (such as a wheel brake <NUM> or brakes).

In some examples, the backup braking controller <NUM> may be implemented in the same hardware and/or software as the landing gear backup controller <NUM>.

<FIG> is a simplified schematic diagram of a hydraulic system <NUM> for providing hydraulic power to a landing gear arrangement, such as the landing gear arrangement <NUM> described above with reference to <FIG>, according to an embodiment of the invention.

Similar to the hydraulic system <NUM> described above with reference to <FIG>, the hydraulic system <NUM> shown in <FIG> comprises a primary hydraulic power source <NUM>, an accumulator <NUM>, backup braking selector valve <NUM> and backup braking servo valve <NUM>, which each operate, as described above with reference to <FIG>, to apply a brake <NUM> (such as a wheel brake <NUM> or brakes).

In the embodiment shown in <FIG>, the hydraulic system <NUM> comprises a valve <NUM>. An input of the valve <NUM> is fluidically connected to the accumulator <NUM>. An output of the valve <NUM> is fluidically connected to the landing gear arrangement <NUM>. In particular, in the example shown in <FIG>, the output of the valve <NUM> is fluidically connected to gear up-locks <NUM> and door up-locks <NUM>, such as those described above with reference to <FIG>.

The hydraulic system <NUM> comprises a controller <NUM> arranged to detect a failure condition of the primary hydraulic power source <NUM>. For example, the controller <NUM> may comprise a pressure sensor for sensing a pressure provided by the primary hydraulic power source <NUM> and a processor to receive a pressure signal (indicated by the dashed arrow 304a) and evaluate the pressure signal.

In the event that there is a failure of the primary hydraulic power source <NUM>, the processor may be programmed to determine that a sensed pressure of the primary hydraulic power source <NUM> falls below a threshold pressure, for example. However, in contrast to the hydraulic system <NUM> shown in <FIG>, the controller <NUM> is arranged to send a control signal (indicated by the dashed arrow 304b) to operate the valve <NUM> to provide a transmission path for hydraulic fluid between the accumulator <NUM> and the landing gear. For example, the valve <NUM> may be opened to provide hydraulic pressure from the accumulator <NUM> to the gear up-locks <NUM> and the door up-locks <NUM>.

In the event of a failure of the primary hydraulic power source <NUM>, hydraulic fluid may no longer be supplied to the accumulator <NUM>, or the primary hydraulic power source <NUM> may not be able to maintain a specified pressure of hydraulic fluid in the accumulator <NUM> (since hydraulic fluid in the accumulator may leak, for example). Therefore, the accumulator <NUM> is selected to provide a sufficient volume of hydraulic fluid, pressurised to a sufficient pressure, to provide hydraulic power to both the brake <NUM> and the landing gear arrangement <NUM> (i.e. the gear up-locks <NUM> and the door up-locks) in the event of a failure of the primary hydraulic power source <NUM>. This enables the hydraulic system <NUM> to provide backup hydraulic power to both the brake <NUM> and the landing gear arrangement <NUM> from a single source of hydraulic power (i.e. the accumulator <NUM>), which reduces the number of components required to provide backup hydraulic power, and thus saves cost and weight.

<FIG> is a flow diagram illustrating a method <NUM> of operating an aircraft hydraulic system, such as the hydraulic system <NUM> described above with reference to <FIG>; that is, a hydraulic system comprising a backup hydraulic pressure source to provide hydraulic pressure to a brake in the event of a reduction of a primary hydraulic brake pressure and a landing gear backup system to provide hydraulic pressure to enable extension and/or retraction of landing gear.

At block <NUM>, a failure condition of a primary landing gear hydraulic pressure source is detected. For example, a reduction or spike in the pressure supplied by the primary hydraulic power source <NUM> may be detected by a pressure sensor and the detected pressure may be evaluated by the controller <NUM>, as described above with reference to <FIG>.

At block <NUM>, in response to detecting a failure condition of the primary landing gear hydraulic pressure, the hydraulic system provides hydraulic pressure to the landing gear backup system from a backup hydraulic pressure source. The failure condition could be, for example, a reduction in hydraulic pressure or an increase (e.g. a spike) in hydraulic pressure). For example, as described above with reference to <FIG>, the controller <NUM> of the hydraulic system <NUM> may send a control signal to operate the valve <NUM> to provide a transmission path for hydraulic fluid between the accumulator <NUM> and the landing gear arrangement <NUM>. For example, the valve <NUM> may be opened to provide hydraulic pressure from the accumulator <NUM> to the gear up-locks <NUM> and the door up-locks <NUM>.

Although in the hydraulic systems <NUM>, <NUM> described above with reference to <FIG> and <FIG>, a single primary hydraulic power source is described, it will be understood that some embodiments of the invention, may include multiple primary (i.e. main) sources of hydraulic pressure for which the respective backup pressures source of hydraulic pressure provides backup hydraulic power. In particular, the LGERS and the braking system may each have a dedicated primary source of hydraulic power, with the hydraulic system disclosed with reference to <FIG> providing a backup source of hydraulic power in the event of a failure of the primary source of hydraulic power of the LGERS, a failure of the primary source of hydraulic power of the braking system, or a failure of both the primary source of hydraulic power of the LGERS and the primary source of hydraulic power of the braking system.

In some embodiments, hydraulic system <NUM> described above with reference to <FIG> may be installed in a vehicle. Referring to <FIG>, there is shown a schematic side view of an example of a vehicle according to an embodiment of the invention. In the example of <FIG>, the vehicle is an aircraft <NUM>. The aircraft <NUM> may comprise one or more hydraulic systems, such as the hydraulic system <NUM> described above with reference to <FIG>. In other embodiments, the vehicle may be other than an aircraft, such as a road vehicle, a rail vehicle, a watercraft or a spacecraft.

The above embodiments are to be understood as illustrative examples of the invention. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments, without departing from the scope of the appended claims. Furthermore, modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claim 1:
A hydraulic system (<NUM>) for an aircraft (<NUM>), the hydraulic system (<NUM>) comprising:
a backup hydraulic pressure source (<NUM>) to provide hydraulic pressure to a brake (<NUM>) in the event of a failure condition of a primary hydraulic brake pressure source (<NUM>); and
a landing gear backup system to provide hydraulic pressure to enable extension and/or retraction of landing gear (<NUM>) in the event of a failure condition of a primary landing gear hydraulic pressure source;
characterised by a controller (<NUM>) arranged to detect a failure condition of the primary landing gear hydraulic pressure source,
wherein, in response to the detected failure condition, the controller (<NUM>) is arranged to transmit an activation signal (304b) to a valve (<NUM>) arranged to fluidically couple the backup hydraulic pressure source (<NUM>) to the landing gear backup system, to provide hydraulic pressure to the landing gear backup system from the backup hydraulic pressure source (<NUM>).