The present disclosure relates to hydraulic accumulators, and more particularly to diagnosing leaks in hydraulic accumulators.
Many aircraft, for example, rotoraft, include hydraulic accumulators. Maintenance of hydraulic accumulators due to leakage of nitrogen gas charge can be a significant maintenance driver in some aircraft. Existing maintenance checks are manual, for example visual inspection. Manual maintenance checks are not always accurate, which can lead to unnecessary labor intensive re-charging of the accumulator.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved methods and systems for diagnosing leaks in hydraulic accumulators. The present disclosure provides a solution for this need.
A method for diagnosing leaks in a hydraulic accumulator includes measuring the time required to discharge the hydraulic accumulator to determine an actual discharge duration. The method includes comparing the actual discharge duration to an expected discharge duration to generate a condition indicator. The condition indicator correlates to the presence or absence of a leak.
The method can include generating a look-up table of expected discharge durations using a physics-based accumulator model that correlates expected discharge duration of a leak free accumulator to a variety of local ambient temperatures. Measuring the time required to discharge the hydraulic accumulator can include measuring elapsed time between opening of a start valve and tripping of a low-pressure switch. The method can include measuring a local ambient temperature and selecting the expected discharge duration, which corresponds to the measured local ambient temperature, from the look-up table. Comparing the actual discharge duration to the expected discharge duration can include taking the difference between the actual discharge duration and the expected discharge duration. The condition indicator can be equal to the difference between the actual discharge duration and the expected discharge duration.
It is contemplated that the method can include determining accumulator health and/or gas chamber pressure by using the local ambient temperature to select the accumulator health or gas chamber pressure from another look-up table. The method can include generating an indication of at least one of accumulator health or gas chamber pressure and transmitting the indication of at least one of accumulator health and/or gas chamber pressure to other diagnostic and prognostic tools for the purpose of further analysis The method can include selecting minimum and maximum condition indicator thresholds from another look-up table generated by a physics-based accumulator model exercised at gas chamber pressure levels corresponding to established corrective maintenance thresholds. The method can include determining whether a corrective maintenance action is required by comparing the condition indicator to the minimum and maximum condition indicator thresholds and generating an alert signaling a need for a maintenance action if the condition indicator is less than the minimum condition indicator threshold, and/or greater than the maximum condition indicator threshold.
In another aspect, a hydraulic accumulator leak assessment system includes a hydraulic accumulator having a gas chamber. A start valve is operatively connected to the hydraulic accumulator to control the release of the hydraulic charge from the hydraulic accumulator. A start valve status sensor is operatively connected to the start valve to determine whether the start valve is open or closed. A low-pressure switch is operatively connected to the gas chamber to be activated when the gas chamber pressure reaches a pre-determined threshold. A temperature sensor is operatively connected to the hydraulic accumulator to measure the local ambient temperature to which the hydraulic accumulator is exposed. A leak assessment module operatively connected to the start valve status sensor, the low-pressure switch and the temperature sensor to determine whether a leak is present in the hydraulic accumulator based on an assessment of a condition indicator corrected for the measured local ambient temperature and derived from elapsed time between opening of the start valve and tripping of the low-pressure switch.
The leak assessment module can include at least one of a look-up table and an equation. Each of the look-up table and equation can be based on a physics-based accumulator model that correlates discharge time to varied levels of pressure in the gas chamber for a variety of ambient temperatures to generate a condition indicator and temperature-dependent minimum and maximum condition indicator threshold values.
These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.
So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein:
Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a vertical takeoff and landing (VTOL) aircraft in accordance with the disclosure is shown in
As shown in
Accumulator leak assessment system 100 includes an automated accumulator diagnostic module, e.g. leak assessment module 114, described in more detail below, that alleviates the maintenance burden of traditional hydraulic accumulator systems by reducing and/or eliminating manual maintenance inspections for leaks. Accurate diagnostic indications minimize unnecessary maintenance efforts and costs due to misdiagnosis, for example, they reduce the probability of hydraulic accumulators being removed with “no fault found”. Moreover, false diagnoses of other aircraft system problems whose root cause could include a leaking hydraulic accumulator, e.g., gas path degradation of the Auxiliary Power Unit (APU) as a cause for slow APU starts, can be avoided by accurately diagnosing a leaky accumulator.
With reference now to
With continued reference to
As shown in
Method 200 includes comparing the actual discharge duration to the expected discharge duration by taking the difference between the actual discharge duration and the expected discharge duration, as indicated by box 208. The difference between the actual discharge duration and the expected discharge duration is the value of the condition indicator. Method 200 includes determining accumulator health or gas chamber pressure, as indicated by box 213, by using the ambient temperature measurement and condition indicator value to select the appropriate accumulator health or gas chamber pressure value from another look-up table, which is generated by the physics-based accumulator model and correlates the value of the condition indicator to the pressure in gas chamber 104 as a function of measured ambient temperature. Method 200 includes generating an indication of at least one of accumulator health or gas chamber pressure and transmitting the indication of accumulator health and/or gas chamber pressure to other diagnostic and prognostic tools, as indicated by box 214, for the purpose of further analysis.
With continued reference to
Method 200 includes determining whether a corrective maintenance action is required by comparing the condition indicator to the minimum and maximum condition indicator thresholds, as indicated by box 211. Method 200 includes generating an alert signaling a need for a corrective maintenance action if the condition indicator is less than or greater than the minimum and maximum condition indicator thresholds, respectively, as indicated by box 212, respectively. A condition indicator less than the minimum condition indicator threshold for the given local ambient temperature indicates that gas chamber pressure has dropped below the minimum allowable pressure, and that corrective maintenance is required. A condition indicator value above the maximum condition indicator threshold for the given local ambient temperature indicates that the gas chamber pressure is above the allowable limits, i.e. that the maintainer over-charged the accumulator. If the condition indicator is between the minimum and maximum condition indicator thresholds, no alert signaling a need for a corrective maintenance action is generated.
The methods and systems of the present disclosure, as described above and shown in the drawings, provide for systems and methods for diagnosing leaks in a hydraulic accumulator, including optimization of maintenance of hydraulic accumulators, and reduction in maintenance time and costs. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject disclosure.
This application claims benefit of U.S. Provisional Application No. 62/181,626, filed Jun. 18, 2015, the entire disclosure of which is hereby incorporated herein by reference in its entirety.
This invention was made with government support under contract number W911 W6-10-2-0006 awarded by the United States Army. The government has certain rights in the invention.
Filing Document | Filing Date | Country | Kind |
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PCT/US16/37397 | 6/14/2016 | WO | 00 |
Number | Date | Country | |
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62181626 | Jun 2015 | US |