Patent Application
20170211600
The subject matter disclosed herein generally relates to health monitoring of aircraft. More specifically, the subject disclosure relates to health assessment of hydraulic systems of an aircraft.
A leading driver of maintenance for hydraulic flight control systems is fluid leakage. This includes both external leakage that drains fluid from the stored supply, and internal leakage that reduces component efficiency and degrades system response. Current generation aircraft generally include a Leak Detection and Isolation (LDI) system that is targeted at severe leak conditions that compromise system safety. Generally speaking if the LDI system can observe the leak, enough fluid has been lost that the affected components or system lines need to be isolated by valves and backup systems engaged as required to restore aircraft control. Also, this system provides no information about internal leak conditions that may seriously degrade system performance.
The available information upon which to make decisions about hydraulic component replacement and hydraulic system servicing is currently very limited. The flight control systems on legacy aircraft are not well instrumented and leaks are generally diagnosed by visual inspection and ground check tests. Due to a limited understanding of how leak conditions affect actual system performance, maintenance practice is very conservative and component replacement may be performed before it is needed. With a better understanding of leak size, location and progression, more informed decisions can be made about component service and replacement, maintenance logistics, and hydraulic system servicing.
In one embodiment, a method of health monitoring of a hydraulic actuator includes sensing a first hydraulic fluid pressure at a first chamber of a hydraulic cylinder, the first chamber defined by a piston disposed in the cylinder and a first cylinder wall. The method further includes sensing a second hydraulic fluid pressure at a second chamber of the hydraulic cylinder, the second chamber defined by the piston and a second cylinder wall opposite the first cylinder wall. The pressures are summed to derive a pressure sum leakage estimate. An actual piston position in the hydraulic cylinder is determined and compared to an intended piston position to determine a positional error of the piston. A command-response error leakage estimate is derived from the positional error. The pressure sum leakage estimate and the command-response error leakage estimate are fused to determine an internal hydraulic fluid leakage in the hydraulic cylinder.
Additionally or alternatively, in this or other embodiments a pressure difference is calculated from the sensed first hydraulic fluid pressure and the second hydraulic fluid pressure, and a hydraulic fluid temperature is detected. The pressure sum leakage estimate and/or the command-response error leakage estimate are compensated based on the pressure difference and/or the hydraulic fluid temperature.
Additionally or alternatively, in this or other embodiments an actuator health indicator is derived from the internal hydraulic fluid leakage.
Additionally or alternatively, in this or other embodiments actuator health indicators of a plurality of actuators are aggregated into a system health indicator.
Additionally or alternatively, in this or other embodiments the internal hydraulic fluid leakage is compared to one or more previously determined internal hydraulic fluid leakages, and a degradation rate is determined based on the comparison.
Additionally or alternatively, in this or other embodiments an actuator health indicator is derived from the internal hydraulic fluid leakage and the degradation rate.
Additionally or alternatively, in this or other embodiments the positional errors of the piston are determined at a same intended piston position.
In another embodiment, a method of health monitoring of a hydraulic actuator includes sensing a first hydraulic fluid pressure at a first chamber of a hydraulic cylinder, the first chamber defined by a piston disposed in the cylinder and a first cylinder wall and sensing a second hydraulic fluid pressure at a second chamber of the hydraulic cylinder, the second chamber defined by the piston and a second cylinder wall opposite the first cylinder wall. The first hydraulic fluid pressure and the second hydraulic fluid pressure are summed to derive a pressure sum leakage, indicative of internal hydraulic fluid leakage in the hydraulic cylinder.
Additionally or alternatively, in this or other embodiments an actual piston position in the hydraulic cylinder is determined. The actual piston position is compared to an intended piston position to determine a positional error of the piston. A command-response error leakage estimate is derived from the positional error and the pressure sum leakage estimate and the command-response error leakage estimate are fused to determine the internal hydraulic fluid leakage in the hydraulic cylinder.
Additionally or alternatively, in this or other embodiments a pressure difference is calculated from the measured first hydraulic fluid pressure and the second hydraulic fluid pressure and a hydraulic fluid temperature is detected. The pressure sum leakage estimate is compensated based on the pressure difference and/or the hydraulic fluid temperature.
Additionally or alternatively, in this or other embodiments an actuator health indicator is derived from the internal hydraulic fluid leakage.
Additionally or alternatively, in this or other embodiments actuator health indicators of a plurality of actuators are aggregated into a system health indicator.
Additionally or alternatively, in this or other embodiments the internal hydraulic fluid leakage is compared to one or more previously determined internal hydraulic fluid leakages, and a degradation rate is determined based on the comparison.
Additionally or alternatively, in this or other embodiments an actuator health indicator is derived from the internal hydraulic fluid leakage and the degradation rate.
In yet another embodiment, a method of health monitoring of a hydraulic actuator includes determining an actual piston position of a piston in a hydraulic cylinder of the hydraulic actuator and comparing the actual piston position to an intended piston position to determine a positional error of the piston. A command-response error leakage estimate is derived from the positional error, indicative of an internal hydraulic fluid leakage in the hydraulic cylinder.
Additionally or alternatively, in this or other embodiments a first hydraulic fluid pressure is sensed at a first chamber of a hydraulic cylinder, the first chamber defined by the piston and a first cylinder wall and a second hydraulic fluid pressure is sensed at a second chamber of the hydraulic cylinder, the second chamber defined by the piston and a second cylinder wall opposite the first cylinder wall. The first hydraulic fluid pressure and the second hydraulic fluid pressure are summed to derive a pressure sum leakage estimate. The pressure sum leakage estimate and the command-response error leakage estimate are fused to determine the internal hydraulic fluid leakage in the hydraulic cylinder.
Additionally or alternatively, in this or other embodiments a pressure difference is calculated from the measured first hydraulic fluid pressure and the second hydraulic fluid pressure, and a hydraulic fluid temperature is detected. The pressure sum leakage estimate and/or the command-response error leakage estimate is compensated based on the pressure difference and/or the hydraulic fluid temperature.
Additionally or alternatively, in this or other embodiments an actuator health indicator is derived from the internal hydraulic fluid leakage.
Additionally or alternatively, in this or other embodiments the internal hydraulic fluid leakage is compared to one or more previously determined internal hydraulic fluid leakages and a degradation rate based on the comparison. An actuator health indicator is derived from the internal hydraulic fluid leakage and the degradation rate.
In still another embodiment, a hydraulic actuator system includes a cylinder and a piston positioned in the cylinder defining a first cylinder chamber and a second cylinder chamber, the piston operably connected to a piston shaft. A leakage detection system is operably connected to the cylinder and includes one or more pressure sensors to detect a first hydraulic fluid pressure in the first chamber and a second hydraulic fluid pressure in the second chamber. The leakage detection system is configured to sum the first hydraulic fluid pressure and the second hydraulic fluid pressure to derive a pressure sum leakage estimate, determine an actual piston position in the hydraulic cylinder, compare the actual piston position to an intended piston position to determine a positional error of the piston, derive a command-response error leakage estimate from the positional error, and fuse the pressure sum leakage estimate and the command-response error leakage estimate to determine an internal hydraulic fluid leakage in the hydraulic cylinder.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
The aircraft 10 may include many systems, such as rotor blade pitch adjustment, ailerons, landing gear and/or other systems, driven by servo-hydraulic actuators 32, an example of which is illustrated in
The first chamber 38 and the second chamber 40 include first port 50 and second port 52, respectively, which serve as inlet and outlet for hydraulic fluid 54. The flow of hydraulic fluid 54 through the first port 50 and second port 52 is controlled by a servo-valve mechanism 56 operably connected to a hydraulic fluid source (not shown) at supply port 72. Fluid is drained to the hydraulic return through return port 74. The servo-valve mechanism 56 may be electronically controlled or positioned by direct mechanical input.
To maintain the selected fluid pressures in the first chamber 38 and second chamber 40, the piston 36 includes one or more piston seals 58 located at an outer periphery of the piston 36 to seal between the piston 36 and a cylinder wall 60. The piston seals 58 are configured to prevent leakage of hydraulic fluid 54 around the piston between the first chamber 38 and the second chamber 40. Over time, however, the piston seals 58 lose effectiveness through, for example, degradation of or damage to the piston seals 58 or degradation of or damage to the cylinder wall 60. This alters the fluid pressures in the first chamber 38 and the second chamber 40, resulting in reduced performance of the actuator 32, and in some cases failure.
To detect such leakage before failure of the actuator 32, a leak detection system 62, schematically shown in
A position comparison is performed between a piston actual position 88 derived from, for example, a position sensor 108, and a piston intended position 90 derived from the servo mechanism 56, fly-by-wire device or other actuator controller. The result of the position comparison is a positional error 86 and is indicative of piston seal 58 leakage, where a relatively small positional error 86 indicates little or no leakage and a relatively large positional error 86 indicates a greater amount of leakage. The position error 86 is also influenced by the operating temperature and external load. A model 92 is used to compensate for these effects using observations of the delta pressure 78 and the fluid temperature 80, resulting in a corrected command-response leakage estimate 94.
A weighted data fusion process 96 combines the multiple leak estimates 84, 94 into a single estimated fault size 98 and, when appropriate, triggers a diagnostic flag 100 indicating maintenance attention is needed. The estimated fault size 98 can represent, for example, internal hydraulic fluid leakage. To track the progression of leakage over time, pressure sum and command response error changes may be compared to previously determined values at the data fusion algorithm 96 to arrive at a degradation rate 102. The past and current observations of compensated pressure sum 84 and the command-response leakage estimate 94 are combined with the degradation rate 102 information using weight factors that give priority to either approach based upon defined confidence metrics for the respective approaches for various leak sizes and operating conditions. The fused assessment of internal leakage is used to derive a health indicator 104, which in some embodiments is rolled up into a formulation of an aircraft or system health indicator 106, including actuator health indicators 104 from other actuators 32 in the system or other hydraulic components like pumps, valves, or fluid lines.
It should be noted that while the above description is presented such that both the pressure sum leak estimate 84 and command response leak estimates 94 are calculated, the approach is also valid in cases in which the system configuration and available data sources allow for implementation of only one of these parallel methods. In such a case the estimated fault size 98 and actuator health index 104 would be based solely upon the leakage estimate from the single approach.
Use of the above described system and method allows for quick isolation of performance issues to specific actuators 32 without the need for complex and time consuming analysis. The leakage information, through the health indicator is available in real-time.
Further, the system and method allow for problems to be addressed proactively, prior to failure of the actuator and/or before the leakage has a detrimental effect on system performance. Finally, this capability reduces the chance for aircraft maintainers to replace a healthy component before it is required by actual condition, thereby reducing the costs of unnecessary maintenance operations.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
The present application claims priority to U.S. Provisional Application 61/974,025 filed on Apr. 2, 2014, the contents of which are incorporated by reference herein in their entirely.
This invention was made with government support with the U.S. Army under Contract No. W911W6-10-2-0006. The government therefore has certain rights in this invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2015/023819 | 4/1/2015 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61974025 | Apr 2014 | US |
