Patent Description:
Shock absorbing devices are used in a wide variety of vehicle suspension systems for controlling motion of the vehicle and its tires with respect to the ground and for reducing transmission of transient forces from the ground to the vehicle. Shock absorbing struts are a common component in most aircraft landing gear assemblies. Shock struts control motion of the landing gear, and absorb and damp loads imposed on the gear during landing, taxiing, braking, and takeoff.

A shock strut generally accomplishes these functions by compressing a fluid within a sealed chamber formed by hollow telescoping cylinders. The fluid generally includes both a gas and a liquid, such as hydraulic fluid or oil. One type of shock strut generally utilizes an "air-over-oil" arrangement wherein a trapped volume of gas is compressed as the shock strut is axially compressed, and a volume of oil is metered through an orifice. The gas acts as an energy storage device, similar to a spring, so that upon termination of a compressing force the shock strut returns to its original length. Shock struts also dissipate energy by passing the oil through the orifice so that as the shock absorber is compressed or extended, its rate of motion is limited by the damping action from the interaction of the orifice and the oil.

Functionality and performance of a landing gear shock strut depends on internal gas and oil levels. Gas pressure and oil volume may be maintained within a design envelope to ensure that the landing gear functionality is within an acceptable range. <CIT> describes the automated inspection of aircraft landing gear internal fluid levels and <CIT> describes a dual stage, stroke-activated, mixed fluid gas shock strut servicing monitoring system. Operations performed by a controller of the monitoring system may comprise: receiving a primary chamber temperature sensor reading, receiving a primary chamber pressure sensor reading, receiving a shock strut stroke sensor reading, receiving a secondary chamber pressure sensor reading, receiving a secondary chamber temperature sensor reading. It may be ensured that a set of data is associated to a landing or a takeoff or any other event that has caused a shock strut to travel between <NUM> to <NUM>.

The matter for which protection is sought is defined by the appended claims. A method for monitoring a dual-stage shock strut is disclosed, comprising measuring a first primary chamber pressure of a primary gas chamber of the dual-stage shock strut when the dual-stage shock strut is in a first state, measuring a first secondary chamber pressure of a secondary gas chamber of the dual-stage shock strut when the dual-stage shock strut is in the first state, measuring a shock strut stroke when the dual-stage shock strut is in the first state, measuring a first ambient temperature corresponding to that of the dual stage shock strut when the dual stage shock strut is in the first state, measuring a second primary chamber pressure of the primary gas chamber when the dual-stage shock strut is in a second state, measuring a second secondary chamber pressure of the secondary gas chamber when the dual-stage shock strut is in the second state, measuring a second ambient temperature corresponding to that of the dual stage shock strut when the dual stage shock strut is in the second state, and determining a servicing condition of the shock strut based upon at least the first primary chamber pressure, the first secondary chamber pressure, the shock strut stroke, the first ambient temperature, the second primary chamber pressure, the second secondary chamber pressure, and the second ambient temperature; wherein the secondary gas chamber is separated from the primary gas chamber via a separator piston.

In various embodiments, the first state comprises the dual-stage shock strut in a static position, before a take-off event, and supporting a weight of an aircraft, and the second state comprises the dual-stage shock strut in a weight-off-wheel position within a second pre-determined duration after the take-off event.

According to the invention, the first ambient temperature is measured using a temperature sensor in close proximity to the dual-stage shock strut.

In various embodiments, the temperature sensor is located in a wheel well of the aircraft.

In various embodiments, the shock strut stroke is measured manually.

In various embodiments, the shock strut stroke is measured via a sensor.

In various embodiments, the servicing condition comprises at least one of a primary chamber gas volume, a secondary chamber gas volume, a primary chamber oil volume, and a secondary chamber oil volume.

In various embodiments, the servicing condition is determined by solving a set of equations in table <NUM>.

In various embodiments, the second ambient temperature measurement associated with the second state is measured within a pre-determined duration before the take-off event, and the pressure measurement associated with the second state is measured after the take-off event.

A method for monitoring a dual-stage shock strut is disclosed, comprising calculating a servicing condition of the dual-stage shock strut based upon a first primary chamber pressure when the dual-stage shock strut is in a first state, a first secondary chamber pressure when the dual-stage shock strut is in the first state, a shock strut stroke when the dual-stage shock strut is in the first state, an ambient temperature corresponding to that of the shock strut, a second primary chamber pressure when the dual-stage shock strut is in a second state, and a second secondary chamber pressure when the dual-stage shock strut is in the second state. The calculating comprises calculating a primary gas volume in the first state, calculating a primary gas volume in the second state, calculating a secondary gas volume in the first state, calculating a secondary gas volume in the second state, calculating a primary oil volume in the first state, calculating a primary oil volume in the second state, calculating a secondary oil volume in the first state, calculating a secondary oil volume in the second state, calculating a first number of moles of gas dissolved in an oil in the first state, and calculating a second number of moles of gas dissolved in an oil in the second state.

In various embodiments, the calculating includes solving an equation <MAT> <MAT>, wherein <MAT> is the first secondary chamber pressure, <MAT> is the second secondary chamber pressure, <MAT> is a gas volume in a secondary chamber of the dual-stage shock strut in the first state, <MAT> is a gas volume in the secondary chamber of the dual-stage shock strut in the second state, Z is a compressibility factor, R is a universal gas constant, T̂a is at least one of the ambient temperature or a second ambient temperature, and T̂b is at least one of the ambient temperature or the second ambient temperature.

In various embodiments, the calculating includes solving an equation Vtot_primary - AP<NUM> × <MAT> in response to the shock strut stroke being greater than or equal to an activation stroke of the dual-stage shock strut, wherein Vtot_primary is a total internal volume of a primary chamber of the dual-stage shock strut in a fully extended position, AP<NUM> is an area of a primary piston of the dual-stage shock strut, Ŝa is the shock strut stroke of the dual-stage shock strut, AP<NUM> is an area of a separator piston of the dual-stage shock strut, Sactivation is the activation stroke of the dual-stage shock strut, <MAT> is a gas volume in the primary chamber of the dual-stage shock strut in the first state, and <MAT> is a volume of oil in the primary chamber of the dual-stage shock strut in the first state.

In various embodiments, the calculating includes solving an equation Vtot_primary - AP<NUM> × <MAT> in response to the shock strut stroke being less than the activation stroke of the dual-stage shock strut, wherein Vtot_primary is the total internal volume of a primary chamber of the dual-stage shock strut in a fully extended position, AP<NUM> is the area of the primary piston of the dual-stage shock strut, Ŝa is the shock strut stroke of the dual-stage shock strut, <MAT> is the gas volume in the primary chamber of the dual-stage shock strut in the first state, and <MAT> is the volume of oil in the primary chamber of the dual-stage shock strut in the first state.

A shock strut monitoring system is disclosed, comprising a controller and a tangible, non-transitory memory configured to communicate with the controller, the tangible, non-transitory memory having instructions stored thereon that, in response to execution by the controller, cause the controller to perform operations comprising receiving, by the controller, a first shock strut pressure, receiving, by the controller, a second shock strut pressure, receiving, by the controller, a shock strut stroke, receiving, by the controller, a first temperature, receiving, by the controller, a third shock strut pressure, receiving, by the controller, a fourth shock strut pressure, receiving, by the controller, a second temperature, and calculating, by the controller, a servicing condition of a dual-stage shock strut. The calculating the servicing condition comprises calculating, by the controller, a primary gas volume in a first state, calculating, by the controller, a primary gas volume in a second state, calculating, by the controller, a secondary gas volume in the first state, calculating, by the controller, a secondary gas volume in the second state, calculating, by the controller, a primary oil volume in the first state, calculating, by the controller, a primary oil volume in the second state, calculating, by the controller, a secondary oil volume in the first state, calculating, by the controller, a secondary oil volume in the second state, calculating, by the controller, a first number of moles of gas dissolved in an oil in the first state, and calculating, by the controller, a second number of moles of gas dissolved in an oil in the second state.

In various embodiments, the first shock strut pressure comprises a first primary chamber pressure when the dual-stage shock strut is in a first state.

In various embodiments, the second shock strut pressure comprises a first secondary chamber pressure when the dual-stage shock strut is in the first state.

In various embodiments, the shock strut stroke comprises a shock strut stroke when the dual-stage shock strut is in the first state.

In various embodiments, the first temperature comprises an ambient temperature corresponding to that of the shock strut.

In various embodiments, the third shock strut pressure comprises a second primary chamber pressure when the dual-stage shock strut is in a second state.

In various embodiments, the fourth shock strut pressure comprises a second secondary chamber pressure when the dual-stage shock strut is in the second state.

In various embodiments, at least one of the first shock strut pressure and the second shock strut pressure and at least one of the first temperature and the second temperature are measured using a single, integrated pressure/temperature sensor mounted to the shock strut.

In various embodiments, the instructions further cause the controller to perform operations comprising further comprising sending, by the controller, the shock strut servicing condition to a display.

The forgoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated herein otherwise, the matter for which protection is sought being defined by the appended claims.

The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made in accordance with this disclosure and the teachings herein without departing from the scope of the disclosure, the matter for which protection is sought being defined by the appended claims.

Aircraft landing gear systems in accordance with the present disclosure may comprise a dual-stage, stroke-activated, mixed gas/fluid shock strut (shock strut). A shock strut may comprise various fluids such as oil and gas. Performance of the shock strut may be evaluated by monitoring aspects of the shock strut, including gas temperature, gas pressure, and shock strut stroke of the shock strut under various conditions of the shock strut and aircraft. Shock strut stroke may refer to a shock strut piston position.

Gas curves used as springs in aircraft landing gear are typically calculated based upon a static test, where the shock strut is slowly compressed and decompressed, causing the pressure of the gas to slowly change in a manner to allow heat dissipation during the process. However, during operation of a vehicle, such as an aircraft for example, the shock strut may rapidly stroke causing rapid pressure changes in the gas, such as nitrogen for example, and allowing the gas to more freely move into and out a fluid, such as oil for example. During these rapid pressure changes (caused by stroking the shock absorber quickly), the oil constantly remains saturated with nitrogen. In contrast, when slowly changing the pressure during a static test, the nitrogen is not as free to go into and out of the oil and therefore can leave the oil and nitrogen in an un-balanced state; either over-saturated or under-saturated. Traditionally measured gas curves start at the fully extended position and stroke to the fully compressed condition and then back to the fully extended position. Assuming the gas and oil are at balance (oil fully saturated) at the start, as the strut is compressed and pressure increased, the oil becomes more under saturated as the higher pressure drives more nitrogen into solution, but the slow change prevents it. Systems and methods disclosed herein, take into account gas absorption and desorption in the fluid (e.g., gas entrainment within the fluid) resulting in more accurate measurements of shock strut servicing conditions, such as gas volume and oil volume. Systems and methods disclosed herein may accurately calculate a shock strut servicing condition, taking into account gas absorption and desorption in the fluid, without the need for a position sensor. In various embodiments, systems and methods disclosed herein allow for determining shock strut servicing conditions using a temperature sensor located externally from the shock strut (e.g., at another location of the aircraft such as in the wheel well, coupled to the fuselage, or coupled to a wing).

The following nomenclature in table <NUM> corresponds to various equations and parameters described in the present disclosure:.

The following equations in table <NUM> correspond to various methods described in the present disclosure:.

With reference to <FIG>, an aircraft <NUM> in accordance with various embodiments may include landing gear such as landing gear <NUM>, landing gear <NUM> and landing gear <NUM>. Landing gear <NUM>, landing gear <NUM> and landing gear <NUM> may generally support aircraft <NUM> when aircraft is not flying, allowing aircraft <NUM> to taxi, take off and land without damage. Landing gear <NUM> may include shock strut <NUM> and wheel assembly <NUM>. Landing gear <NUM> may include shock strut <NUM> and wheel assembly <NUM>. Landing gear <NUM> may include shock strut <NUM> and nose wheel assembly <NUM>. Aircraft <NUM> may comprise a controller <NUM>. Landing gear <NUM> may be in communication with controller <NUM> and may send information to controller <NUM>, for example, shock strut pressure and temperature information.

In various embodiments, controller <NUM> may comprise one or more processors. Controller <NUM> may comprise hardware having a tangible, non-transitory memory configured to communicate with controller <NUM> and having instructions stored thereon that cause controller <NUM> to perform various operations as described herein.

System program instructions and/or controller instructions may be loaded onto a non-transitory, tangible computer-readable medium having instructions stored thereon that, in response to execution by a controller, cause the controller to perform various operations. The term "non-transitory" is to be understood to remove only propagating transitory signals per se from the claim scope and does not relinquish rights to all standard computer-readable media that are not only propagating transitory signals per se. Stated another way, the meaning of the term "non-transitory computer-readable medium" and "non-transitory computer-readable storage medium" should be construed to exclude only those types of transitory computer-readable media which were found in In Re Nuijten to fall outside the scope of patentable subject matter under <NUM> U. <NUM><NUM>.

In various embodiments, a monitoring system for a dual-stage, stroke-activated, mixed gas fluid shock strut is provided herein. A functional schematic view of such a shock strut is presented in <FIG>, <FIG>.

With reference to <FIG>, a dual-stage, stroke-activated, mixed gas/fluid shock strut (shock strut) <NUM> is illustrated, in accordance with various embodiments. Shock strut <NUM> may be similar to shock strut <NUM> of <FIG>. Shock strut <NUM> may comprise a strut cylinder <NUM> and a strut piston <NUM>. Strut piston <NUM> may be operatively coupled to strut cylinder <NUM> as described herein. Strut cylinder <NUM> may be configured to receive strut piston <NUM> in a manner that allows the two components to telescope together and absorb and dampen forces transmitted thereto. In various embodiments, a liquid, such as a hydraulic fluid and/or oil may be located within strut cylinder <NUM>. Further, a gas, such as nitrogen or air, may be located within strut cylinder <NUM>. Strut cylinder <NUM> and strut piston <NUM> may, for example, be configured to seal such that fluid contained within strut cylinder <NUM> is prevented from leaking as strut piston <NUM> translates relative to strut cylinder <NUM>.

Shock strut <NUM> may consist of a low pressure, primary chamber <NUM> in which oil and gas can mix. In this regard, a volume of gas (also referred to herein as a primary chamber gas volume) <NUM> and a volume of oil (also referred to herein as an oil volume) <NUM> may be contained within primary chamber <NUM>. In this regard, the portion of primary chamber <NUM> containing the volume of gas <NUM> may be referred to herein as a primary gas chamber <NUM>. Similarly, the portion of primary chamber <NUM> containing the oil volume <NUM> may be referred to herein as an oil chamber <NUM>. Dashed line <NUM> represents the level of the oil volume <NUM>, or the interface between the oil chamber <NUM> and the primary gas chamber <NUM>, with shock strut <NUM> in the fully extended position. Stated differently, the oil volume <NUM> may be located below dashed line <NUM> and the volume of gas <NUM> may be located above dashed line <NUM>. In this regard, the interface between the oil chamber <NUM> and the primary gas chamber <NUM> may move relative to primary chamber <NUM> depending on the position of strut piston <NUM> relative to strut cylinder <NUM>. Shock strut <NUM> may further consist of a high pressure, secondary gas chamber <NUM>. Secondary gas chamber <NUM> may be separated from primary gas chamber <NUM> via a separator piston <NUM>. An orifice support tube <NUM> may be positioned within primary chamber <NUM>. Orifice support tube may at least partially define secondary gas chamber <NUM>. Separator piston <NUM> may be positioned within orifice support tube <NUM> and may be configured to translate relative thereto. In various embodiments, separator piston <NUM> may be positioned outside of orifice support tube <NUM>. <FIG> illustrates separator piston <NUM> at a minimum compression stroke (also referred to herein as being "bottomed out"). In various embodiments, separator piston <NUM> may be located at a minimum compression stroke when shock strut <NUM> is in the fully extended position (i.e., at a shock strut stroke <NUM> of zero). An orifice plate <NUM> may be coupled to orifice support tube <NUM>. Metering pin <NUM> may translate with strut piston <NUM> with respect to orifice plate <NUM>.

In various embodiments, shock strut <NUM> may be installed onto a landing gear of an aircraft. During a landing event, shock strut <NUM> may be compressed wherein strut piston <NUM> translates into strut cylinder <NUM>. During the landing, the shock strut may initially function as a single-stage, mixed fluid gas shock strut by metering oil through orifice plate <NUM> and compressing the primary chamber gas volume <NUM>. The primary gas chamber <NUM> compression may continue until the secondary gas chamber <NUM> is mechanically activated. As illustrated in <FIG>, this occurs when metering pin <NUM> reaches, and mechanically engages, the separator piston <NUM> at a secondary gas chamber activation stroke <NUM> (Sactivation), of between zero and the maximum shock strut stroke. Separator piston <NUM> may translate towards second end <NUM> in response to metering pin <NUM> engaging separator piston <NUM>. Once the secondary gas chamber <NUM> is activated, further compression of the shock strut may compress the gas in the secondary gas chamber <NUM>, as illustrated in <FIG> illustrates shock strut <NUM> in a compressed position, or at a shock strut stroke <NUM>.

In various embodiments, alternate dual-stage, stroke-activated, mixed gas/fluid shock strut designs may be provided wherein the high pressure, secondary gas chamber <NUM> is activated in response to the strut piston <NUM> contacting a separator piston that is located externally from orifice support tube <NUM>.

With reference to <FIG>, a dual-stage, stroke activated, mixed fluid gas shock strut arrangement (shock strut arrangement) <NUM> is illustrated, in accordance with various embodiments. Shock strut arrangement <NUM> may include shock strut <NUM> and a monitoring system <NUM> Monitoring system <NUM> may comprise various sensing elements for measuring various parameters and providing measurements to a monitoring algorithm. Monitoring system <NUM> may comprise a pressure sensor (also referred to herein as a first sensor) <NUM> installed on the primary gas chamber <NUM> to measure gas pressure within primary gas chamber <NUM>. It is contemplated herein that, although described herein as a pressure sensor <NUM>, it is contemplated herein that an integrated pressure/temperature sensor may be used in place of pressure sensor <NUM> in order to measure both temperature and pressure within primary gas chamber <NUM>, in accordance with various embodiments. Monitoring system <NUM> may comprise a pressure sensor (also referred to herein as a second sensor) <NUM> installed on the secondary gas chamber <NUM> to measure gas pressure within secondary gas chamber <NUM>. Although described herein as a pressure sensor <NUM>, it is contemplated herein that an integrated pressure/temperature sensor may be used in place of pressure sensor <NUM> in order to measure both temperature and pressure within secondary gas chamber <NUM>. Monitoring system <NUM> may comprise a position sensor (also referred to herein as a stroke sensor) <NUM> configured to measure the stroke of shock strut <NUM>. However, in various embodiments, position sensor <NUM> may be omitted and the stroke of shock strut <NUM> may be measured manually (e.g., by hand).

Monitoring system <NUM> may further comprise a temperature sensor <NUM>. Temperature sensor <NUM> may be installed in close proximity to shock strut <NUM>. For example, temperature sensor <NUM> may be installed within a wheel bay of an aircraft. With momentary reference to <FIG>, a temperature sensor <NUM> may be installed within wheel bay <NUM> of aircraft <NUM>. In this regard, temperature sensor <NUM> may be similar to temperature sensor <NUM> of <FIG>. It is further contemplated that temperature sensor <NUM> may be installed in other locations of aircraft <NUM> (see <FIG>) in close proximity to shock strut <NUM>, including the fuselage, the wings, etc. Temperature sensor <NUM> may measure the ambient temperature <NUM>, wherein the temperature of shock strut <NUM> and the fluids contained therein are assumed to be equal to or approximately equal to the ambient temperature <NUM>.

In various embodiments, shock strut temperatures of the present disclosure may be measured indirectly using an ambient temperature to estimate fluid temperatures. In various embodiments, shock strut temperatures of the present disclosure may be directly measured using an integrated pressure/temperature sensor (e.g., sensors <NUM>, <NUM>). In this regard, the present disclosure contemplates various methods for determining a shock strut fluid temperature.

Pressure sensor <NUM> may measure primary chamber gas pressure <NUM> (P̂gas-<NUM>). Pressure sensor <NUM> may measure secondary chamber gas pressure <NUM> (P̂gas-<NUM>). Stroke sensor <NUM> may directly or indirectly measure shock strut stroke <NUM> (<NUM>). In various embodiments, shock strut stroke <NUM> (Ŝ) is measured manually, for example using a caliper or a ruler. Temperature sensor <NUM> may measure ambient temperature <NUM> (T̂). Primary chamber gas pressure <NUM> (P̂gas-<NUM>), secondary chamber gas pressure <NUM> (P̂gas-<NUM>), shock strut stroke (Ŝ), and ambient temperature <NUM> (T̂) may be referred to herein as sensor readings.

Monitoring system <NUM> may be devised assuming that the sensors comprise a minimum sampling frequency of between <NUM> and <NUM> in accordance with various embodiments, between <NUM> and <NUM> in accordance with various embodiments, or about <NUM> in accordance with various embodiments, wherein the term "about" in this regard may mean ± <NUM>.

With reference to <FIG>, monitoring system <NUM> may comprise a controller <NUM> and a tangible, non-transitory memory <NUM> configured to communicate with the controller <NUM>. The tangible, non-transitory memory <NUM> may have instructions stored thereon that, in response to execution by the controller <NUM>, cause the controller <NUM> to perform various operations as described herein. Monitoring system <NUM> may comprise a visual display <NUM>. Visual display <NUM> may be in electronic communication with controller <NUM>. As described herein, controller <NUM> may issue or send a servicing message <NUM>. Servicing message <NUM> may be displayed on visual display <NUM>. In various embodiments, servicing message <NUM> may comprise an indication of a quantity of oil or gas in shock strut <NUM> based upon the sensor readings. In various embodiments, servicing message <NUM> may comprise a current and/or a voltage signal. Controller <NUM> may be in electronic communication with pressure sensor <NUM> and pressure sensor <NUM>.

In various embodiments, controller <NUM> may receive a shock strut status signal <NUM> indicating a state of the shock strut <NUM>. In various embodiments, controller <NUM> may detect, via shock strut status signal <NUM>, that shock strut <NUM> is in a first state, such as before a take-off event (i.e., before aircraft <NUM> (see <FIG>) has taken off, with weight on wheels (WONW) (i.e., with shock strut <NUM> supporting the weight of the aircraft), and in a static position). In various embodiments, controller <NUM> may detect, via shock strut status signal <NUM>, that shock strut <NUM> is in a second state, such as after a take-off event (i.e., after aircraft <NUM> (see <FIG>) has taken off, with weight off wheels (WOFFW), and in a static position). In various embodiments, shock strut status signal <NUM> is based on an internal pressure of shock strut <NUM> whereby controller <NUM> determines a stroke position of shock strut <NUM> for determining whether the shock strut is supporting the weight of an aircraft. For example, the internal pressure of shock strut <NUM> may be greater in a WONW state than in a WOFFW state. In various embodiments, shock strut status signal <NUM> is based on a stroke of shock strut <NUM> whereby controller <NUM> determines whether the shock strut is supporting the weight of an aircraft. For example, the shock strut stroke may be greater in a WONW state (e.g., a compressed position) than in a WOFFW state (e.g., fully extended position). In this manner, controller <NUM> may take pressure, position, and/or temperature measurements of shock strut <NUM> based on a status of the shock strut status signal <NUM>. For example, in response to shock strut status signal <NUM> indicating a change from a WONW condition to a WOFFW condition of shock strut <NUM>, controller <NUM> may take pressure and temperature measurements of shock strut <NUM> in the second state.

In various embodiments, controller <NUM> may comprise one or more controllers. For example, a first controller may receive sensor information and a second controller may perform the calculations or transmit sensor information to other systems as described herein.

With reference to <FIG>, a method <NUM> for monitoring a shock strut is provided, in accordance with various embodiments. Method <NUM> includes measuring a first shock strut pressure before a take-off event (step <NUM>). Method <NUM> includes measuring a second shock strut pressure before the take-off event (step <NUM>). Method <NUM> includes measuring a shock strut stroke before the take-off event (step <NUM>). Method <NUM> includes measuring a temperature (step <NUM>). Method <NUM> includes measuring a third shock strut pressure after the take-off event (step <NUM>). Method <NUM> includes measuring a fourth shock strut pressure after the take-off event (step <NUM>). Method <NUM> includes determining a servicing condition of the shock strut (step <NUM>).

With combined reference to <FIG>, <FIG>, and <FIG>, step <NUM> may include measuring primary chamber gas pressure <NUM> ( <MAT>) in a first state, such as before a take-off event (i.e., before aircraft <NUM> (see <FIG>) has taken off, with weight on wheels (WONW) (i.e., with shock strut <NUM> supporting the weight of the aircraft), and in a static position) via pressure sensor <NUM>. For example, step <NUM> may be performed before push-back onto a runway. In various embodiments, step <NUM> is performed within thirty minutes before push-back onto a runway. In various embodiments, step <NUM> is performed within sixty minutes before take-off of the aircraft. Step <NUM> may include measuring secondary chamber gas pressure <NUM> ( <MAT>) before the take-off event via pressure sensor <NUM>. Step <NUM> may be performed under similar conditions as step <NUM>. In various embodiments, step <NUM> and step <NUM> are performed at substantially the same time. In various embodiments, step <NUM> is performed within five minutes of step <NUM>. In various embodiments, step <NUM> and step <NUM> are performed simultaneously. Step <NUM> may include measuring a shock strut stroke (Ŝa) before the take-off event. Step <NUM> may be performed under similar conditions as step <NUM> and step <NUM>. Step <NUM> may be performed using a measuring device, such as a ruler for example, to manually measure shock strut stroke <NUM>. However, in various embodiments, shock strut stroke (Ŝa) may be measured automatically using stroke sensor <NUM>. In this regard, primary chamber gas pressure <NUM> ( <MAT>), secondary chamber gas pressure <NUM> ( <MAT>), and shock strut stroke (Ŝa) may be measured before take-off under static conditions and stored (e.g., in memory <NUM>) for later use. In various embodiments, shock strut stroke (Ŝa) may be entered manually into controller <NUM> using an input device such as a keyboard for example.

In various embodiments, step <NUM> may include measuring ambient temperature <NUM> (T̂) using temperature sensor <NUM>. In various embodiments, step <NUM> is performed before take-off to measure temperature (T̂a). In various embodiments, step <NUM> is performed after take-off to measure temperature (T̂b). In various embodiments, step <NUM> is performed both before take-off to measure temperature (T̂a) and again after take-off to measure temperature (T̂b) (see <FIG> and <FIG>). However, In various embodiments, step <NUM> is performed once either before take-off to measure temperature (T̂a) or after take-off to measure temperature (T̂b), wherein the measured temperature (T̂) is used for both temperature (T̂a) and temperature (T̂b), under the assumption that the temperature inside of shock strut <NUM> does not substantially change between step <NUM> and step <NUM>.

In various embodiments, with combined reference to <FIG>, <FIG>, and <FIG>, step <NUM> may include measuring primary chamber gas pressure ( <MAT>) in a second state, such as after a take-off event (i.e., after aircraft <NUM> (see <FIG>) has taken off, with weight off wheels (WOFFW), and in a static position) via pressure sensor <NUM>. In various embodiments, step <NUM> is performed within thirty minutes after push-back onto a runway. In various embodiments, step <NUM> is performed within ten minutes after take-off. In various embodiments, step <NUM> is performed within thirty minutes after take-off. Step <NUM> may include measuring secondary chamber gas pressure <NUM> ( <MAT>) after the take-off event via pressure sensor <NUM>. Step <NUM> may be performed under similar conditions as step <NUM>. In various embodiments, step <NUM> and step <NUM> are performed at substantially the same time. In various embodiments, step <NUM> is performed within five minutes of step <NUM>. In various embodiments, step <NUM> and step <NUM> are performed simultaneously. In various embodiments, the shock strut stroke (Ŝb) of shock strut <NUM> is known after the take-off event. For example, the shock strut <NUM> may be in a fully extended position where the shock strut stroke Ŝb is zero or shock strut <NUM> may be in a known compressed position. In this regard, primary chamber gas pressure ( <MAT>) and secondary chamber gas pressure ( <MAT>) may be measured after take-off under static conditions and stored (e.g., in memory <NUM>) for use in determining a servicing condition of shock strut <NUM> (i.e., calculating the levels of fluids in shock strut <NUM>).

Having measured <MAT>, and <MAT>, step <NUM> may include determining a servicing condition of shock strut <NUM> (i.e., calculating the levels of fluids in shock strut <NUM>). Step <NUM> may include solving the ten equations in table <NUM>. Equations <NUM> through <NUM> may be solved by controller <NUM>. Step <NUM> involves solving the provided set of ten equations with ten unknown values, as provided in table <NUM>, using any suitable method for solving a system of equations. Furthermore, after solving the system of equations, as provided in table <NUM>, the unknown parameters (unknown parameters <NUM>-<NUM>), as provided in table <NUM> become known. In this regard, step <NUM> includes solving for the primary chamber gas volume (Vgas_<NUM>), the secondary chamber gas volume (Vgas_<NUM>), the primary chamber oil volume (Voil_<NUM>), and the secondary chamber oil volume (Voil_<NUM>). These calculated parameters may be compared with known threshold values to determine whether shock strut <NUM> needs servicing with gas and/or oil.

With reference to <FIG>, a method <NUM> for monitoring a shock strut is provided, in accordance with various embodiments. Method <NUM> includes receiving a first shock strut pressure (step <NUM>). Method <NUM> includes receiving a second shock strut pressure (step <NUM>). Method <NUM> includes receiving a shock strut stroke (step <NUM>). Method <NUM> includes receiving a temperature (step <NUM>). Method <NUM> includes receiving a third shock strut pressure (step <NUM>). Method <NUM> includes receiving a fourth shock strut pressure (step <NUM>). Method <NUM> includes calculating a shock strut servicing condition (step <NUM>).

With combined reference to <FIG> and <FIG>, step <NUM> may include receiving, by controller <NUM>, primary chamber gas pressure ( <MAT>). Step <NUM> may include receiving, by controller <NUM>, secondary chamber gas pressure ( <MAT>). Step <NUM> may include receiving, by controller <NUM>, shock strut stroke (Ŝa). Step <NUM> may include receiving, by controller <NUM>, ambient temperature (T̂). Step <NUM> may include receiving, by controller <NUM>, primary chamber gas pressure ( <MAT>). Step <NUM> may include receiving, by controller <NUM>, secondary chamber gas pressure ( <MAT>). Step <NUM> may include calculating, by controller <NUM>, a servicing condition of shock strut <NUM>. In various embodiments, step <NUM> includes solving, by controller <NUM>, the system of equations as provided in Table <NUM> herein.

With respect to <FIG>, elements with like element numbering, as depicted in <FIG>, are intended to be the same and will not necessarily be repeated for the sake of clarity.

With reference to <FIG>, a method <NUM> for monitoring a shock strut is provided, in accordance with various embodiments. In various embodiments, method <NUM> is similar to method <NUM> of <FIG>, except that method <NUM> includes measuring a first ambient temperature associated with a first state and a second ambient temperature associated with a second state. In this regard, method <NUM> includes measuring a first temperature (step <NUM>) and measuring a second temperature (step <NUM>). In various embodiments, step <NUM> is performed both before take-off to measure temperature (T̂a). In various embodiments, step <NUM> is performed after take-off to measure temperature (T̂b). In various embodiments, step <NUM> is performed within a pre-determined duration before take-off to measure temperature (T̂b), such that the second temperature is equal to, or substantially equal to, the temperature of shock strut <NUM> at the time that step <NUM> and step <NUM> are performed.

With reference to <FIG>, a method <NUM> for monitoring a shock strut is provided, in accordance with various embodiments. In various embodiments, method <NUM> is similar to method <NUM> of <FIG>, except that method <NUM> includes receiving a first ambient temperature associated with a first state and a second ambient temperature associated with a second state. In this regard, method <NUM> includes receiving a first temperature (step <NUM>) and receiving a second temperature (step <NUM>). In various embodiments, step <NUM> is performed both before take-off to measure temperature (T̂a). In various embodiments, the temperature associated with step <NUM> is measured after take-off to measure temperature (T̂b). In various embodiments, the temperature associated with step <NUM> is measured within a pre-determined duration before take-off to measure temperature (T̂b), such that the second temperature is equal to, or substantially equal to, the temperature of shock strut <NUM> at the time that the third shock strut pressure of step <NUM> and the fourth shock strut pressure of step <NUM> are measured.

In various embodiments, method <NUM> and/or method <NUM> may be performed on-board an aircraft in real time or during pre-determined intervals. In this regard, the measurements associated with method <NUM> and/or method <NUM> may be stored on-board an aircraft and/or may be transmitted to an off-aircraft system for processing and determining landing gear shock strut fluid levels.

Claim 1:
A method for monitoring a dual-stage shock strut (<NUM>), comprising:
measuring (<NUM>) a first primary chamber pressure of a primary gas chamber (<NUM>) of the dual-stage shock strut (<NUM>) when the dual-stage shock strut (<NUM>) is in a first state:
measuring (<NUM>) a first secondary chamber pressure of a secondary gas chamber (<NUM>) of the dual-stage shock strut (<NUM>) when the dual-stage shock strut (<NUM>) is in the first state:
measuring (<NUM>) a shock strut stroke when the dual-stage shock strut (<NUM>) is in the first state:
measuring (<NUM>) a first ambient temperature corresponding to that of the dual stage shock strut when the dual stage shock strut is in the first state using a temperature sensor (<NUM>) installed on the fuselage or the wings of an aircraft (<NUM>);
measuring a second primary chamber pressure of the primary gas chamber (<NUM>) when the dual-stage shock strut (<NUM>) is in a second state;
measuring a second secondary chamber pressure of the secondary gas chamber (<NUM>) when the dual-stage shock strut (<NUM>) is in the second state;
measuring a second ambient temperature corresponding to that of the dual stage shock strut (<NUM>) when the dual stage shock strut (<NUM>) is in the second state using the temperature sensor (<NUM>);
determining (<NUM>) a servicing condition of the shock strut (<NUM>) based upon at least the first primary chamber pressure, the first secondary chamber pressure, the shock strut stroke, the first ambient temperature, the second primary chamber pressure, the second secondary chamber pressure, and the second ambient temperature; and
wherein the secondary gas chamber (<NUM>) is separated from the primary gas chamber (<NUM>) via a separator piston