Brake wear measurement system and method

A brake measurement system comprising a measurement mechanism for measuring brake wear operatively coupled to a moveable member of a brake assembly is provided. The system further includes a displacement sensor and a visual indicator. The displacement sensor is operatively coupled to the measurement mechanism, wherein movement of the moveable member is converted by the measurement mechanism into a displacement sensed by the displacement sensor. The visual indicator is operatively connected to the measurement mechanism, wherein the visual indicator displays the movement of the moveable member and consequently the wear of the brake stack at a point on the exterior of an aircraft brake housing for inspection.

FIELD OF INVENTION

This invention generally relates to braking systems, and more particularly, to electronic brake control systems for aircraft.

BACKGROUND OF THE INVENTION

Prior art aircraft brake systems often employ wear pin indicators to measure overall wear of the brake disk stack. Brake wear is indicated by the length of the pin relative to a reference plate. This system generally requires a visual inspection of the pin to determine wear. However, the wear pin is typically installed as part of the brake assembly inside the aircraft wheel making visual inspection difficult. Such installation and inspection is also potentially difficult because of the harsh environment created by the aircraft braking system and the closed system created when the brake assembly is installed inside the wheel. Therefore, a longstanding need exists to provide for visual brake wear measurement on the exterior of the aircraft brake and to exhibit greater precision.

SUMMARY OF THE INVENTION

In various embodiments, the aircraft brake wear measurement systems comprise a measurement mechanism operatively coupled to a moveable member (e.g., a pressure plate and/or piston head) of a brake assembly. A displacement sensor is operatively coupled to the measurement mechanism. Movement of the moveable member is converted by the measurement mechanism into a displacement sensed by the displacement sensor.

The displacement sensor may be fitted with a scraper that engages the measurement mechanism and removes contaminants and debris from a measured surface of the measurement mechanism. The brake wear measurement system may further comprise a mechanical calibration mechanism that interfaces with the measurement mechanism providing for single point calibration. In an embodiment, the displacement sensor is fitted with a connector, enabling communication of the displacement sensor to a brake control system (or other aircraft system). The measurement mechanism may further comprise a visual indicator that is capable of being inspected on the exterior of an aircraft brake housing when the brake wear measurement system is installed. The measurement mechanism may be configured in any manner which allows the displacement sensor to be configured to measure linear, rotational, and/or angular displacement, for example, a twisted spline, drill bit, rack and pinion assembly, cable and pulley system assembly, hinge, spring, spring loaded cable and threaded bolt assembly, cam and lever assembly, spring loaded lever assembly, pneumatic cylinder, and/or bent wear pin or other geometries.

DETAILED DESCRIPTION

The brake wear measurement system uses a displacement sensor and a visual indicator capable of being inspected on the exterior of an aircraft brake housing. The use of a displacement sensor and visual indicator allows the wear of the aircraft brakes to be captured and reported electronically in a central location and physically inspected with no or minimal disassembly of the aircraft brake system. In one embodiment, the brake wear system makes use of at least two brake wear monitoring devices, particularly a displacement sensor and a visual indicator, to provide redundancy. The system allows for inspection of aircraft brake stack wear during daytime, nighttime, and/or when the aircraft is not powered on, without any (or with minimal) removal or disassembly of the aircraft wheel or aircraft brake.

Further, since a primary use of the brake wear measurement system is in conjunction with aircraft brakes, a feature of the system is the ability to tolerate the harsh wheel and brake environment. In particular, temperature and non-axial vibration levels are often very high in aircraft brake systems. Because of these harsh environmental conditions and general best practices in the aerospace industry, various embodiments are configured with low profiles to minimize weight and/or the impact of vibration loads. These embodiments allow the aircraft brake measurement system to conform, for example, with space constraints when installed with the aircraft brakes in the brake housing. The incorporation of a visual indicator on the exterior of the aircraft brake housing also provides the ability to measure brake stack wear at a more convenient location. In an embodiment, the displacement sensor may be mounted outside of the aircraft brake housing, and may measure brake stack wear mechanically communicated by a visual indicator. For example, the visual indicator may be fitted with a cable, wire, rod, or similar structure that mechanically communicates brake stack wear to a displacement sensor and allows for visual inspection of brake stack wear in a convenient location. The brake wear measurement systems described herein are robust in meeting various design requirements, including such harsh environmental requirements.

Preliminarily, an aircraft brake generally comprises a wheel disc that is coupled to and turns with an aircraft wheel, a brake stack that applies a frictional stopping force to the wheel disc, a pressure plate that applies a force to the brake stack causing the brake stack to contact the wheel disc, and a piston which drives the pressure plate into the brake stack causing the brake stack to apply a frictional braking force to the wheel disc. As designed, the brake stack wears as it applies a frictional braking force to the wheel disc.

In various embodiments, brake stack wear can be monitored by evaluating the displacement between a moveable member (e.g., a pressure plate or piston head) and a reference point. The reference point may be any fixed structure in the brake system, such as a piston support or piston housing. As the brake stack applies a braking force, the stack becomes thinner and the distance between the moveable member and the reference point increases proportionally to the amount of brake stack wear. The wear of the brake stack is monitored so the brake stack can be serviced when brake stack wear reaches a specified wear point. A brake wear measurement system may be installed with the aircraft brake in an aircraft brake housing.

In an embodiment, the brake wear measurement system comprises a measurement mechanism in combination with a displacement sensor, a mechanical calibration mechanism, and a visual indicator to evaluate brake stack wear. The measurement mechanism is operatively coupled to a pressure plate and/or a piston head and is in communication with a displacement sensor that measures displacement. The visual indicator is attached to a free end of the measurement mechanism and is operatively coupled to the measurement mechanism. The mechanical calibration mechanism is coupled to the displacement sensor of the aircraft brake and provides for single point calibration of the measurement mechanism. In this embodiment, the visual indicator passes through the aircraft brake housing, allowing the visual indicator to be inspected without (or with minimal) internal inspection of the aircraft brake housing.

In accordance with various embodiments, the brake wear measurement mechanism is any structure configured to measure the distance from a reference point to a moveable member, where the distance moved by the moveable member is proportional to the amount of wear of a brake stack. Exemplary embodiments (described below in more detail) depict various types of measurement mechanisms that may be attached to a moveable member. These measurement mechanisms may include, for example, a twisted spline geometry, a drill bit, a rack and pinion assembly, a cable and pulley system assembly, a hinge, a spring, a spring loaded cable and threaded bolt assembly, a cam and lever assembly, a spring loaded lever assembly, a pneumatic cylinder, and/or a bent wear pin.

In accordance with various embodiments, the displacement sensor is any apparatus configured to capture a change in movement. In this regard, the displacement sensor measures movement of a measurement mechanism (discussed above) or may partially or fully replace the measurement mechanism by remotely sensing a change in the position of a moveable member from a reference point. Exemplary embodiments described below measure movement of the measurement mechanism. The movement measured by the displacement sensor may be linear, rotational, or angular movement. This movement may be captured by a sensor, such as a linear variable differential transformer, rotary variable differential transformer, or potentiometer. In general, selection of the appropriate displacement sensor may depend on various factors, including the geometry of the measurement mechanism, orientation of the measurement mechanism to the displacement sensor, environmental factors, and the like.

In accordance with various embodiments, the displacement sensor may further comprise a mechanical calibration mechanism. The mechanical calibration mechanism may be configured such that calibration of the brake wear measurement system may be performed independently from the aircraft electrical system. In one embodiment, the mechanical calibration mechanism is coupled to the displacement sensor and engages the measurement mechanism to provide single point calibration, preventing the measurement mechanism from moving. This allows a known reference point to be established for the brake wear measurement system. In response to the measurement mechanism being coupled to the brake pressure plate and the displacement sensor being at the known reference point, the mechanical calibration mechanism may be disengaged from the measurement mechanism and fixed to the displacement sensor. Fixing the mechanical calibration mechanism to the displacement sensor fully or partially prevents the mechanism from interfering with the brake wear measurement system or aircraft brake system, while in operation.

In accordance with various embodiments, the displacement sensor may further comprise an interface bushing fitted with a scraper. The interface bushing and scraper may be installed such that the scraper fully or partially clears contaminants and debris from the leading edge or surface of the measurement mechanism that is tracked by the displacement sensor as the measurement mechanism is displaced. The interface bushing and scraper may be coupled to the sensor such that the scraper remains in place with limited or no backlash. This coupling allows the measured portion of the measurement mechanism to interface effectively with the displacement sensor and fully or partially prevents binding, jamming, contamination, and the like.

Referring toFIG. 1, and in accordance with an embodiment, brake wear measurement system10comprises a piston12, a support member14, a head16, a pressure plate18, a measurement mechanism20, a measured surface50, a hole22, a displacement sensor24, an interface bushing52, a scraper54, a mechanical calibration mechanism56, a connector26, a visual indicator46, and a brake housing48. Head16of piston12or other type actuator is configured to apply pressure to pressure plate18in order to exert a controllable braking force on the brake stack (not shown). As the brake stack wears, the stack becomes thinner and the distance between pressure plate18and piston12/support14increases.

Brake wear is measured by measuring the displacement between the reference of displacement sensor24and brake pressure plate18. The geometry of measurement mechanism20is such that, as pressure plate18moves linearly, measurement mechanism20is displaced along a linear, angular, or rotational path. In various embodiments, linear, angular, or rotational measurement may be taken by displacement sensor24depending on its orientation to measurement mechanism20. The motion of measurement mechanism20also causes visual indicator46to move a proportional distance, displaying the amount of wear of the brake stack and allowing visual inspection on the exterior of aircraft brake housing48. In an embodiment, outputs of displacement sensor24and visual indicator46are proportional to the absolute linear displacement of brake pressure plate18, which is proportional to the wear of the brake stack.

In accordance with an embodiment, brake wear measurement system10includes measurement mechanism20which is attached at one end to pressure plate18. At another end, measurement mechanism20may be connected to visual indicator46. Visual indicator46is installed as part of brake wear measurement10, such that visual indicator46protrudes through brake housing48. Measurement mechanism20extends away from pressure plate18and through a hole22in support14. Hole22is sized such that measurement mechanism20may freely move linearly through hole22. In various embodiments, brake wear measurement system10further comprises a displacement sensor24. Displacement sensor24is aligned axially with hole22, such that measurement mechanism20passes through displacement sensor24.

In accordance with an embodiment, brake wear measurement system10includes mechanical calibration mechanism56which is operatively coupled to displacement sensor24. Mechanical calibration mechanism56is capable of being attached to measurement mechanism20, such that mechanical calibration mechanism56fixes measurement mechanism20at a specified calibration point. In response to the calibration point being established, mechanical calibration mechanism56is removed from measurement mechanism20and partially or fully fixed in place on displacement sensor20, such that mechanical calibration mechanism56does not interfere with the aircraft brake or brake wear measurement system10while in operation.

In accordance with an embodiment, displacement sensor24may be secured to the piston housing12and/or support14via a bracket or the like so as to extend away from the piston housing12and/or support14in a plane parallel to the pressure plate18. In such embodiments, hole22may be eliminated.

In accordance with an embodiment, measurement mechanism20may be configured with a twisted spline geometry, such as a twisted flat piece of metal, in a region which communicates with displacement sensor24. Displacement sensor24may be configured to include scraper54coupled to an interface bushing52. Interface bushing52interfaces with measured surface50to partially or fully clear debris and contaminates. Displacement sensor24may also be configured to include one or more engagement members30, as shown inFIG. 2, configured to engage and/or follow one of more measured surface50of measurement mechanism20as measurement mechanism20passes linearly therethough. As the brake stack wears, measurement mechanism20moves in the linear direction (e.g., up/down in relation toFIG. 1) with pressure plate18. The twisted spline geometry of measurement mechanism20converts the linear displacement of measurement mechanism20into an angular displacement that is measured by displacement sensor24. In this manner, the output of displacement sensor24is proportional to the linear displacement of the measurement mechanism20, and thus, that of pressure plate18. The linear displacement of pressure plate18in turn represents an amount of brake stack wear.

With reference now toFIG. 3, and in accordance with an embodiment, measurement mechanism20may be configured similar to a drill bit. In such an embodiment, displacement sensor24and interface bushing52may be coupled to scraper54and configured to partially or fully clear contaminants and debris from measured surface50of measurement mechanism20. Engagement member30may be installed in displacement sensor24, such that engagement member30tracks the linear movement of the drill bit along measured surface50. The linear motion of the drill bit is converted into an angular displacement that is measured by displacement sensor24.

With reference now toFIG. 4, and in accordance with an embodiment, measurement mechanism20is configured as a geared rack that travels along a guide34and is operatively coupled to a pinion gear32. Pinion gear32is operatively coupled to displacement sensor24. Measurement mechanism20is operatively coupled to pressure plate18. Movement of pressure plate18causes linear movement of measurement mechanism20and forces pinion gear32to rotate. As discussed above, the linear movement of pressure plate18is proportional to brake stack wear. Consequently, the movement of measurement mechanism20and resulting rotation of pinion gear32are proportional to brake stack wear. Displacement sensor24measures the rotation of pinion gear32.

With reference toFIG. 5, and in accordance with an embodiment, measurement mechanism20is configured as a cable connected to pressure plate18and a pulley system36. As shown, pulley system36is configured with two pulleys, however, more pulleys may be used. Pulley system36is operatively coupled to displacement sensor24. As such, linear movement of pressure plate18causes measurement mechanism20to move, forcing pulley system36to contract. This contraction is proportional to the linear movement of pressure plate18and consequently, is proportional to brake stack wear. The connection between pulley system36and displacement sensor24allows displacement sensor24to measure the movement of pressure plate18, by way of the contraction of pulley system36.

With reference toFIG. 6, and in accordance with an embodiment, brake wear measurement mechanism20is configured as a slotted hinge, wherein the hinge comprises at least two hinge members operatively coupled at a pivoting joint. One hinge member is connected to pressure plate18and another hinge member is connected to displacement sensor24. As pressure plate18compresses the brake stack, measurement mechanism20expands in proportion to the displacement of pressure plate18. The expansion of measurement mechanism20is measured by displacement sensor24. Given that the displacement of pressure plate18is proportional to brake stack wear, and that elongation of measurement mechanism20is proportional to the displacement of pressure plate18, displacement sensor24is able to measure the total wear of the brake stack.

With reference toFIG. 7, and in accordance with an embodiment, brake wear measurement mechanism20is configured as a spring and scissor jack mechanism. In various embodiments, the spring may be an accordion style spring, a cylindrical spring, a torsion spring, or any other device suitable for communicating displacement. One free end of the spring is connected to pressure plate18and another free end of the spring is connected to displacement sensor24. Further, one free end of the scissorjack mechanism is connected to pressure plate18and one free end of the scissor jack mechanism is connected to displacement sensor24. Linear movement of pressure plate18causes measurement mechanism20to expand, causing a displacement by the spring and the scissorjack mechanism to be communicated to displacement sensor20which is proportional to the linear displacement of pressure plate18and brake stack wear. Displacement sensor24is thus able to evaluate the spring displacement and determine brake stack wear.

With reference toFIG. 8, and in accordance with an embodiment, measurement mechanism20is configured as a spring loaded cable. In this embodiment, measurement mechanism20is connected to a cable carrier38and pressure plate18. Cable carrier38is fixed on a threaded rod42. Threaded rod42is installed in a carrier40, which allows threaded rod42to rotate along its threads through carrier40when measurement mechanism20is displaced by pressure plate18. Carrier40is also fixed to housing/support14. Threaded rod42is operatively connected to displacement sensor24, allowing displacement sensor24to measure the displacement of threaded rod42in carrier40, which is proportional to the linear movement of measurement mechanism when it is acted upon by pressure plate18. Displacement sensor24is therefore able to measure the displacement of threaded rod42, which is proportional to brake stack wear.

With reference toFIG. 9, and in accordance with an embodiment, measurement mechanism20is configured as a cam and lever assembly. Measurement mechanism20is fixed at a pivot point44to brake wear measurement system10and operatively connected to pressure plate18and displacement sensor24. Linear movement of pressure plate18causes measurement mechanism20to rotate about pivot point44, such that the cam, which is coupled to the lever, communicates the rotational displacement of the lever to displacement sensor24. This rotation communicates the wear of the brake stack through the linear displacement of pressure plate18to displacement sensor24.

With reference toFIG. 10, and in accordance with an embodiment, measurement mechanism20is configured as a spring loaded lever assembly. Measurement mechanism20is coupled at a pivot point44to housing14of brake wear measurement system10and operatively connected to pressure plate18and displacement sensor24. Linear movement of pressure plate18causes measurement mechanism20to rotate about pivot point44, such that the rotation of the lever compresses displacement sensor24. This rotation communicates the wear of the brake stack through the linear displacement of pressure plate18to displacement sensor24.

With reference toFIG. 11, and in accordance with an embodiment, measurement mechanism20is configured as a pneumatic cylinder. Measurement mechanism20is operatively connected to pressure plate18and pneumatically connected to a pneumatic cylinder46. Pneumatic cylinder46is operatively connected to displacement sensor24. Movement of pressure plate18causes a proportional movement of measurement mechanism20. This movement causes a pressure change in pneumatic cylinder46that is measured by displacement sensor24and is proportional to brake stack wear.

With reference toFIG. 12, and in accordance with an embodiment, measurement mechanism20is configured as a bent wear pin. Measurement mechanism20is operatively connected to pressure plate18and displacement sensor24. Displacement sensor24may be connected to measurement mechanism20around a point where measurement mechanism20becomes angled. Measurement mechanism20moves linearly with pressure plate18. As measurement mechanism20moves with pressure plate18, displacement sensor24tracks the linear displacement along the angled portion of measurement mechanism20. The total linear displacement of the brake stack, which is proportional to the linear movement of pressure plate18and measurement mechanism20, is communicated to displacement sensor24as a change in measured angle.

In accordance with various embodiments, the output of displacement sensor24may be an electrical signal that is provided via a connector26to a remaining portion of the overall brake system (not shown). The output of displacement sensor24represents the brake wear and may be utilized by the system to provide an indication as to when the brake stack should be replaced, serviced, and/or the like. Exemplary displacement sensors24suitable for use in brake wear measurement system10are commercially available from Moog Components Group, located at 1501 North Main Street, Blacksburg, Va., 24060, and marketed as “low cost brushless pancake resolvers”. Other types of known displacement sensors24may also be used.

In various embodiments, measurement mechanisms such as those described above may also be attached to the piston head16, and thus provide an indication of the position of the piston head16and/or brake position.

Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the invention. The scope of the invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.