GB2590094A - Method of manufacturing and servicing an aircraft shock absorber - Google Patents

Method of manufacturing and servicing an aircraft shock absorber Download PDF

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Publication number
GB2590094A
GB2590094A GB2010669.6A GB202010669A GB2590094A GB 2590094 A GB2590094 A GB 2590094A GB 202010669 A GB202010669 A GB 202010669A GB 2590094 A GB2590094 A GB 2590094A
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GB
United Kingdom
Prior art keywords
hydraulic fluid
shock absorber
inner cavity
gas
cavity
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB2010669.6A
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GB2590094B (en
GB202010669D0 (en
Inventor
Zantner Tobias
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Liebherr Aerospace Lindenberg GmbH
Original Assignee
Liebherr Aerospace Lindenberg GmbH
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Publication date
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Publication of GB202010669D0 publication Critical patent/GB202010669D0/en
Publication of GB2590094A publication Critical patent/GB2590094A/en
Application granted granted Critical
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64C—AEROPLANES; HELICOPTERS
    • B64C25/00—Alighting gear
    • B64C25/32—Alighting gear characterised by elements which contact the ground or similar surface 
    • B64C25/58—Arrangements or adaptations of shock-absorbers or springs
    • B64C25/60—Oleo legs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64C—AEROPLANES; HELICOPTERS
    • B64C25/00—Alighting gear
    • B64C25/32—Alighting gear characterised by elements which contact the ground or similar surface 
    • B64C25/58—Arrangements or adaptations of shock-absorbers or springs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64F—GROUND OR AIRCRAFT-CARRIER-DECK INSTALLATIONS SPECIALLY ADAPTED FOR USE IN CONNECTION WITH AIRCRAFT; DESIGNING, MANUFACTURING, ASSEMBLING, CLEANING, MAINTAINING OR REPAIRING AIRCRAFT, NOT OTHERWISE PROVIDED FOR; HANDLING, TRANSPORTING, TESTING OR INSPECTING AIRCRAFT COMPONENTS, NOT OTHERWISE PROVIDED FOR
    • B64F5/00—Designing, manufacturing, assembling, cleaning, maintaining or repairing aircraft, not otherwise provided for; Handling, transporting, testing or inspecting aircraft components, not otherwise provided for
    • B64F5/10—Manufacturing or assembling aircraft, e.g. jigs therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64F—GROUND OR AIRCRAFT-CARRIER-DECK INSTALLATIONS SPECIALLY ADAPTED FOR USE IN CONNECTION WITH AIRCRAFT; DESIGNING, MANUFACTURING, ASSEMBLING, CLEANING, MAINTAINING OR REPAIRING AIRCRAFT, NOT OTHERWISE PROVIDED FOR; HANDLING, TRANSPORTING, TESTING OR INSPECTING AIRCRAFT COMPONENTS, NOT OTHERWISE PROVIDED FOR
    • B64F5/00—Designing, manufacturing, assembling, cleaning, maintaining or repairing aircraft, not otherwise provided for; Handling, transporting, testing or inspecting aircraft components, not otherwise provided for
    • B64F5/40—Maintaining or repairing aircraft
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64F—GROUND OR AIRCRAFT-CARRIER-DECK INSTALLATIONS SPECIALLY ADAPTED FOR USE IN CONNECTION WITH AIRCRAFT; DESIGNING, MANUFACTURING, ASSEMBLING, CLEANING, MAINTAINING OR REPAIRING AIRCRAFT, NOT OTHERWISE PROVIDED FOR; HANDLING, TRANSPORTING, TESTING OR INSPECTING AIRCRAFT COMPONENTS, NOT OTHERWISE PROVIDED FOR
    • B64F5/00—Designing, manufacturing, assembling, cleaning, maintaining or repairing aircraft, not otherwise provided for; Handling, transporting, testing or inspecting aircraft components, not otherwise provided for
    • B64F5/60—Testing or inspecting aircraft components or systems
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B21/00—Common features of fluid actuator systems; Fluid-pressure actuator systems or details thereof, not covered by any other group of this subclass
    • F15B21/04—Special measures taken in connection with the properties of the fluid
    • F15B21/044—Removal or measurement of undissolved gas, e.g. de-aeration, venting or bleeding

Landscapes

  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • General Engineering & Computer Science (AREA)
  • Fluid-Damping Devices (AREA)

Abstract

A method of manufacturing and servicing a shock absorber for an aircraft landing gear. The shock absorber has an inner cavity filled with pressurized gas and hydraulic fluid. The method comprises venting the inner cavity 110, filling hydraulic fluid to a desired value 120, degassing of the hydraulic fluid, and repressurising the cavity with gas 140. Degassing hydraulic fluid may be by applying a vacuum in the inner cavity 130a, or mechanical agitation in the inner cavity of the vented shock absorber (130b, figure 2). A method of servicing such shock absorbers comprises mechanically agitating the shock absorber (e.g. using landing gear retraction cycle), measuring the pressure in the inner cavity, and where required, topping up the pressure of the inner cavity. The gas may be nitrogen. Hydraulic oil may be used as hydraulic fluid.

Description

Liebherr-Aerospace Lindenberg GmbH Lindenberg, DE Method of manufacturing and servicing an aircraft shock absorber The invention relates to a method of manufacturing and servicing a shock absorber for landing gear of aircraft. The method in accordance with the invention is in particular used in the manufacture and thus in the first filling of a shock absorber as well as in maintenance with a removed shock absorber with a new filling and in the servicing of the shock absorber in the installed state on the aircraft.
Shock absorbers having an inner cavity are typically used in aircraft landing gear, with said inner cavity being filled both with pressurized gas and with a hydraulic fluid and being divided into two chambers that communicated with one another through a small aperture. The gas portion is compressed on a touching down of the aircraft and cushions the shock while the hydraulic fluid absorbs the shock. Nitrogen is typically used as the gas. A hydraulic oil is typically used as the hydraulic fluid.
The shock absorbers are serviced periodically and/or as required over the operating life of the vehicle. This is necessary since the pressurized gas can gradually escape due to smaller leaks, whereby the pressure in the shock absorber drops and the response behavior changes. Smaller fluid leaks can also occur that make the refilling of hydraulic fluid necessary.
If the gas and the fluid are not separated in the shock absorbers, but are rather present together in one and the same cavity, a certain portion of the gas dissolves in the hydraulic fluid. This results in inaccuracies in the refilling of gas or of hydraulic fluid.
It is proposed against this background, in EP 2 937 591 A2 always to apply a gas pressure that is a little higher than the desired gas pressure on the refilling of hydraulic fluid to compensate pressure losses due to the dissolving of gas in the hydraulic fluid. The degree of the increase depends on the volume of the supplied hydraulic fluid and on the total gas volume and is here determined using a forecasting formula to estimate the amount of the solution of gas per volume unit of the hydraulic fluid.
However, the problem also remains with such a procedure that the degree of saturation of the gas in the existing hydraulic fluid is not known, which results in inaccuracies. This problem can only be avoided with the framework of the method known from the prior art by a replacement of the total hydraulic fluid. The inaccuracies resulting therefore otherwise have to be accepted.
It is the object of the invention to provide a method of servicing an aircraft shock absorber that avoids these disadvantages.
Against this background, the invention relates to a method of servicing a shock absorber for a landing gear of aircraft, wherein the shock absorber has an inner cavity that is filled both with a pressurized gas and with a hydraulic fluid and wherein the method comprises the following steps: Venting the cavity; filling in hydraulic fluid up to the reaching of a desired value degassing of the hydraulic fluid. and repressurizing the cavity with gas.
Provision is therefore made in accordance with the invention that as part of a servicing procedure in which hydraulic fluid is to be refilled, the cavity is first vented, with gas escaping from the cavity and a lower pressure, preferably environmental pressure, being adopted in the cavity.
Furthermore, hydraulic fluid should then be filled in up to the reaching of a desired value i.e. hydraulic fluid lost as part of the preceding use of the shock absorber should be replaced A central idea of the invention is the degassing of the hydraulic fluid. A state should therefore be established in which the hydraulic fluid contains no or hardy any dissolved gas before the cavity is filled with gas again and pressurized. The problem is thus avoided that an unknown degree of saturation of the gas in the hydraulic fluid results in inaccuracies without a complete replacement of the hydraulic fluid having been necessary.
The method serves the servicing both with respect to the filling level of the hydraulic fluid and with respect to the gas pressure.
The order of the steps is such that the venting of the cavity is necessarily at the start and the repressurizing of the cavity is necessarily at the end of the described step sequence.
In an embodiment, the degassing of the hydraulic fluid takes place by the application of a vacuum in the inner cavity of the shock absorber. The inner cavity of the shock absorber can therefore be at least partially evacuated using a vacuum pump, for example. Since the gas solubility decreases as the pressure drops, the dissolved gas consequently escapes from the hydraulic fluid. The application of a vacuum works independently of whether the aircraft is raised from the ground or is at least supported during the servicing or whether this is not the case. The pressure in the inner cavity can be lowered, for example, to less than 300 mbar, preferably less than 100 mbar, and further preferably less than 10 mbar. The applied vacuum can here be maintained for a specific time period, for example for at least 10 minutes or preferably at least 15 minutes.
In another embodiment variant, the degassing of the hydraulic fluid takes place by a mechanical agitation of the vented shock absorber. The gas solubility is also already greatly reduced by the venting and the simple lowering of the pressure within the cavity and the dissolved gas can escape from the hydraulic fluid. The kinetics of this escape are greatly improved by the agitation. The mechanical agitation can preferably be achieved by using the carrying out of at least one retraction cycle at the landing gear. This works when the aircraft is raised from the ground or is at least supported during the servicing.
In a further embodiment, the agitation can also take place in interaction with the application of a vacuum, whereby the respective effects are amplified.
Provision can be made as part of the repressurizing that the pressure in the cavity is increased to a value that is above the pressure desired for operation. Provision can therefore be made to prevent a pressure loss due to the dissolving of gas in the hydraulic fluid that is substantially free of gas after the degassing by the application of a higher pressure than the desired nominal pressure.
The invention further relates to a method of servicing a shock absorber for a landing gear of aircraft, wherein the shock absorber has an inner hollow space that is filled both with pressurized gas and with a hydraulic fluid, said method comprising the following steps: mechanically agitating the shock absorber; measuring the pressure in the inner cavity of the shock absorber; and, where necessary, topping up the pressure of the inner cavity of the shock absorber.
The method does not the servicing with respect to the filling level of the hydraulic fluid, but rather only with respect to the gas pressure. Disruptive factors are minimized by the mechanical agitation of the non-vented shock absorber upstream of the pressure measurement.
The mechanical agitation is preferably carried out using the carrying out of at least one retraction cycle at the landing gear. It is also a requirement here that the aircraft is raised from the ground or is at least supported during the servicing.
The gas used is preferably nitrogen A hydraulic oil is preferably used as the hydraulic fluid.
Further details and advantages of the invention result from the following embodiment described with reference to the Figures. There are shown in the Figures: Figure 1: a flow chart for the carrying out of a method in accordance with the invention in a first embodiment; Figure 2: a flow chart for the carrying out of a method in accordance with the invention in a second embodiment; and Figure 3: a flow chart for the carrying out of a method in accordance with the invention for servicing only with respect to the gas pressure.
Figure 1 shows a flow chart for the carrying out of a method in accordance with the invention for servicing a shock absorber for a landing gear of aircraft in a first embodiment.
The shock absorber to be serviced comprises, as customary in aircraft shock absorbers, an inner cavity that is filled both with a pressurized gas and with a hydraulic fluid. The continuous servicing is necessary since both the gas and the hydraulic fluid can gradually escape due to smaller leaks, whereby the response behavior of the shock absorber changes.
The cavity is vented in a first method step 110. The gas escapes from the cavity in this process and environmental pressure is adopted in the cavity.
In a second step 120, fresh hydraulic fluid is added in to the existing hydraulic fluid until a desired filling level is reached. The reaching of the desired filling level can be achieved by flushing with hydraulic oil at a specific position. The setting of the position takes place via so-called service terminal. A different desired filling level is to be set depending on the temperature. Different service terminals are provided for this purpose that each corresponding to the desired filling level at a specific temperature. This means that the respective desired filling level can be set by applying the associated service terminal in dependence on the temperature. The service terminals can here have a specific color corresponding to a temperature value or range associated with them. The service engineer can thus easily recognize which service terminal he should select to set the specific desired filling level corresponding to the temperature.
In a third step 130a, the hydraulic fluid now filled to nominal is degassed. This step serves to remove gas still dissolved in the old portion of the hydraulic fluid. Since namely the gas and the fluid are not separated in the shock absorbers and are rather present together in one and the same cavity, gas dissolves in the hydraulic fluid during operation.
The degassing takes place in step 130a by the application of a vacuum in the inner cavity of the shock absorber in that a vacuum pump is connected to a connection provided for this purpose. The vacuum applied is lower than a specific value, for example 10 mbar, and is maintained for at least 10 minutes. Since the gas solubility decreases as the pressure drops, the dissolved gas consequently escapes from the hydraulic fluid. The application of a vacuum works independently of whether the aircraft is raised from the ground or is at least supported during the servicing or whether this is not the case.
Finally, in step 140, the inner cavity is pressurized again by filling in gas. Provision is made here that the pressure is increased to a value that is a defined degree above the pressure desired for operation to prevent a pressure loss to be expected by gas dissolving in the hydraulic fluid substantially free of gas after the degassing.
Figure 2 shows a flow chart for the carrying out of a method in accordance with the invention for servicing a shock absorber for a landing gear of aircraft in an alternative embodiment.
The only difference from the method in accordance with Figure 1 is that in step 130b the degassing does not take place by applying a vacuum, but rather by mechanical agitation in the vented, i.e., not pressurized, state of the shock absorber. The agitation is here achieved using the carrying out of at least one retraction cycle at the landing gear while the aircraft has been raised from the ground. The gas solubility in the hydraulic fluid is also already greatly reduced at environmental pressure in comparison with the operating pressure and an escape of oversaturated gas is kinetically promote by the agitation.
In a further embodiment not shown separately, the measures of steps 130a and 130b of the embodiment in accordance with Figures 1 and 2 can also be combined, i.e. an agitation can take place under a vacuum, whereby the effect of the degassing is additionally amplified.
Figure 3 finally shows a flow chart for the carrying out of a method in accordance with the invention for servicing only with respect to the gas pressure.
Provision is accordingly made that first, in a first step 210, the shock absorber is subjected to mechanical agitation, as achieved in step 130b using the carrying out of at least one retraction cycle at the landing gear while the aircraft has been raised from the ground; however, unlike step 130b, in the original, pressurized state of the shock absorber.
The inner pressure in the cavity of the shock absorber is then determined by a suitable sensor. Disruptive factors are minimized by the mechanical agitation of the non-vented shock absorber upstream of the pressure measurement in accordance with step 220.
If it is below a desired value, the gas pressure is raised to the desired value in a further step 230 by topping up pressurized gas.
Advantages of the method in accordance with the invention with respect to previously known methods comprise a high accuracy in the filling of the shock absorber, a fast performability, and, as part of the method in accordance with Figure 3, the ability to check the current gas curve with high accuracy.

Claims (10)

  1. Claims A method of manufacturing and servicing a shock absorber for a landing gear of an aircraft, wherein the shock absorber has an inner cavity that is filled both with a pressurized gas and with a hydraulic fluid and wherein the method comprises the following steps: - venting the cavity; - filling in hydraulic fluid up to a reaching of a desired value; and repressurizing the cavity with gas, characterized in that the method further comprises the following step carried out between the venting and repressurizing of the cavity: degassing the hydraulic fluid.
  2. 2. A method in accordance with claim 1, characterized in that said method steps are carried out in the following order:.
  3. 1) venting the cavity; 2) filling in hydraulic fluid up to a reaching of a desired value; and 3) degassing the hydraulic fluid; and 4) repressurizing the cavity with gas 3. A method in accordance with one of the preceding claims, characterized in that the degassing of the hydraulic fluid takes place by applying a vacuum in the inner cavity of the shock absorber.
  4. 4. A method in accordance with claim 3, characterized in that the pressure in the inner cavity is lowered, for example, to less than 300 mbar, preferably less than 100 mbar, and further preferably less than 10 mbar.
  5. 5. A method in accordance with claim 3 or claim 4, characterized in that the vacuum applies is maintained for a specific time period, for example at least 10 minutes, or preferably at least 15 minutes.
  6. 6. A method in accordance with one of the preceding claims, characterized in that the degassing of the hydraulic fluid takes place by mechanical agitation in the inner cavity of the vented shock absorber.
  7. 7. A method in accordance with claim 6, characterized in that the mechanical agitation is achieved using the carrying out of at least one retraction cycle at the landing gear.
  8. A method in accordance with one of the preceding claims, characterized in that as part of the repressurizing the pressure in the cavity is increased to a value that is above the pressure desired for operation.
  9. 9. A method of servicing a shock absorber for a landing gear of aircraft, wherein the shock absorber has an inner cavity that is filled both with a pressurized gas and with a hydraulic fluid and wherein the method comprises the following steps: - measuring the pressure in the inner cavity of the shock absorber; and - where required, topping up the pressure of the inner cavity of the shock absorber, characterized in that the method further comprises the following step to be carried out before the pressure measurement: - mechanically agitating the shock absorber.
  10. 10. A method in accordance with claim 9, characterized in that the mechanical agitation is carried out using the carrying out of at least one retraction cycle at the landing gear.
GB2010669.6A 2019-07-10 2020-07-10 Method of manufacturing and servicing an aircraft shock absorber Active GB2590094B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE102019118629.3A DE102019118629B4 (en) 2019-07-10 2019-07-10 Method for manufacturing and maintaining an aircraft shock absorber

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GB202010669D0 GB202010669D0 (en) 2020-08-26
GB2590094A true GB2590094A (en) 2021-06-23
GB2590094B GB2590094B (en) 2022-04-13

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GB (1) GB2590094B (en)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB905996A (en) * 1959-09-30 1962-09-19 Rheinmetall Gmbh A process for the treatment of hydraulic fluids
US20150266569A1 (en) * 2014-03-21 2015-09-24 Goodrich Corporation Method of initializing a landing gear strut
US20170008647A1 (en) * 2015-07-10 2017-01-12 Airbus Operations Limited Landing gear shock absorber servicing
US20170130796A1 (en) * 2015-11-06 2017-05-11 Goodrich Corporation Servicing procedure for single-stage mixed fluid/gas shock strut

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19717043C2 (en) * 1997-04-23 2003-05-22 Daimler Chrysler Ag Method for dewatering and / or degassing hydraulic fluids, device for carrying out the method and use of the device
DE102014222510A1 (en) * 2014-11-04 2016-05-04 Robert Bosch Gmbh Device for degassing a hydraulic fluid
DE102016221125A1 (en) * 2016-10-26 2018-04-26 Robert Bosch Gmbh Hydraulic hybrid system

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB905996A (en) * 1959-09-30 1962-09-19 Rheinmetall Gmbh A process for the treatment of hydraulic fluids
US20150266569A1 (en) * 2014-03-21 2015-09-24 Goodrich Corporation Method of initializing a landing gear strut
EP2937591A2 (en) 2014-03-21 2015-10-28 Goodrich Corporation Method for initializing a landing gear strut
US20170008647A1 (en) * 2015-07-10 2017-01-12 Airbus Operations Limited Landing gear shock absorber servicing
EP3118111A1 (en) * 2015-07-10 2017-01-18 Airbus Operations Limited Landing gear shock absorber servicing
US20170130796A1 (en) * 2015-11-06 2017-05-11 Goodrich Corporation Servicing procedure for single-stage mixed fluid/gas shock strut

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DE102019118629A1 (en) 2021-01-14
DE102019118629B4 (en) 2024-05-23
GB2590094B (en) 2022-04-13
GB202010669D0 (en) 2020-08-26

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