Abstract:
The present invention is a device that allows the pressure inside an aircraft landing gear shock strut to be measured. A charging valve is modified by integrating a small pressure sensing device into the stem of the part such that the active diaphragm is subjected to the pressure within the charged vessel. The wires from the pressure sensing device are connected to a receptacle or connector in the bore of the stem such that a corresponding electrical receptacle may be mated for the purposes of making a measurement. The internal receptacle is designed such that the flow of air or oil is not excessively impeded and normal servicing tools do not interfere with the receptacle.

Description:
CLAIM FOR PRIORITY 
       [0001]    The present application claims priority under 35 U.S.C. § 119( e ) to U.S. Provisional Application No. 60/840,974, filed Aug. 30, 2006, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to aircraft landing systems and more particularly to a device for measuring the pressure inside a landing gear shock strut. This invention is particularly useful for retrofit applications where drilling a new hole or changing the volume of the shock strut by the addition of a normal pressure transducer is not acceptable. 
       BACKGROUND OF THE INVENTION 
       [0003]    Shock strut pressure is measured during maintenance of landing gear and other pressure vessels to ensure proper performance. The physical geometry of these pressure vessels (such as landing gear shock absorbers) determine (along with fluid and gas volumes) the behaviour and performance of the vessel. Measuring the pressure of the gas within the shock absorber is a critical task that must be performed regularly to ensure safe operation of the aircraft. This is presently performed by attaching a gauge to the external port of the charging valve, then opening the valve. This action is suboptimal because it requires a manual operation to connect and read the system, and because it involves the opening and closing of the valve (with the attendant loss of a small amount of fluid or gas). 
         [0004]    In order to reduce the amount of required maintenance, an automatic means of measuring the pressure of fluid within the shock strut is desired. Conventional approaches to this problem would involve the mounting of a pressure transducer either directly into the body of the shock strut, or the fitting of a manifold to the existing port to allow both a pressure measurement and a facility to charge (alter the quantity of fluid and gas). Both of these solutions present problems when they are applied to existing shock strut designs. Fitting a transducer into the body of the shock strut involves drilling a hole in the structure of the strut—which is generally not acceptable from a strength or fatigue perspective. Adding a manifold to the shock strut changes the amount of internal working volume, which changes the energy absorbing properties of the landing gear—which is not desirable. 
         [0005]    Many landing gears have a poppet charging valve conforming to MS28889-2/MIL-PRF-6164F. This valve allows the introduction or removal of fluid and gas from the pressure vessel. The present invention modifies this valve to include a pressure-sensing means and electrical contact means such that measurements may be made of the working fluid without interfering with the normal operation of the valve or significantly altering the volume within the pressure vessel. 
         [0006]    This modified valve can be retrofitted to any landing gear to allow pressure measurements to be made without altering the landing gear. A change in military standards from MS28889-2 to the newer performance based specification—MIL-PRF-6164F allows the certification of a modified valve to act as a replacement for existing valves. 
       SUMMARY OF THE INVENTION 
       [0007]    At the base, the design involves introducing a pressure sensitive element on one end of the valve and providing a route for the measurement wires to a connector that is mounted internally in the valve stem. The connector is configured in such a manner that it does not interfere with normal pressure charging apparatus, but a specially designed electrical connector can connect to the valve for determining the pressure either in flight or on the ground. 
         [0008]    In one aspect the present invention provides a charging valve for use in a pressure vessel in an aircraft landing gear comprising a valve stem having a first and second end and a channel extending therebetween, a pressure-sensing device received within the channel at the first end and operable to measure the pressure of the pressure vessel, and a receptacle received within the channel between the pressure-sensing device and the second end and operable to be in communication with the pressure-sensing device and configured to allow fluid to flow through the valve. 
         [0009]    In another aspect the present invention provides a charging valve for use in a pressure vessel in an aircraft landing gear comprising a valve stem having a first and second end and a channel extending therebetween, a pressure reading means connected to the first end of the valve body for reading the pressure in the pressure vessel and a receptacle received within the channel between the pressure reading means and the second end and operable to be in communication with the pressure reading means and configured to allow fluid to flow through the valve. 
         [0010]    In a further aspect the present invention provides a method of modifying a charging valve having a main body including a channel therethrough, to include a pressure measuring device for use in a pressure vessel comprising the steps of (i) placing a pressure-sensing device within the channel at the end of the valve that is in communication with the pressure vessel to allow the pressure-sensing device to measure the pressure within the vessel; (ii) connecting the pressure-sensing device to a receptacle or connector to allow for communication therebetween, the receptacle being located within the channel of the valve at the opposite end of the pressure-sensing device from the measurement end and being operable to allow for fluid to flow through the valve. The pressure-sensing device may be a pressure transducer or may include a modification to the end of the valve to form a pressure sensitive diaphragm that is gauged. 
         [0011]    In another aspect, the present invention provides a retrofit kit for use in a charging valve used with a pressure vessel comprising a pressure-sensing device sized to be received within the channel of the valve at the first end and operable to measure the pressure of the pressure vessel and a receptacle sized to be received within the channel of the valve and operable to be in communication with the pressure-sensing device and configured to allow fluid to flow through the valve. The pressure-sensing device and receptacle are as described herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention will now be described in further detail with reference to the following figures: 
           [0013]      FIG. 1  is a schematic diagram of the standard geometry of a charging valve; 
           [0014]      FIG. 2  is an exploded perspective view showing the valve stem of the present invention in two portions and the pressure-sensing device, connector and plug to be used with the valve; 
           [0015]      FIG. 3  is a perspective view of one embodiment of the receptacle of the present invention; 
           [0016]      FIG. 4  is a perspective view of an alternate embodiment of the receptacle and the second portion of the modified valve stem of the present invention; 
           [0017]      FIG. 5  is a perspective view of a further alternative embodiment of the receptacle and the second portion of the modified valve stem of the present invention; 
           [0018]      FIG. 6  is a perspective view of a further embodiment of the receptacle of the valve of the present invention; 
           [0019]      FIG. 7  is a perspective view of a further embodiment of the receptacle and the second part of the modified valve stem of the present invention; 
           [0020]      FIG. 8  is a perspective exploded view of the receptacle and plug of the valve of the present invention according to the embodiment illustrated in  FIG. 3 ; 
           [0021]      FIG. 9   a  is a perspective exploded view of the mating orientation of the receptacle and plug of the present invention; 
           [0022]      FIG. 9   b  is a perspective view illustrating the mating connection of the plug and the receptacle of  FIG. 9   a;    
           [0023]      FIG. 10  is an exploded perspective view of one embodiment of the plug construction of the present invention; 
           [0024]      FIG. 11  is a schematic showing the stem machining modifications for one embodiment of the valve of the present invention; 
           [0025]      FIG. 12  is a side cross-sectional view of the placement and connection of the pressure-sensing device of the present invention; 
           [0026]      FIG. 13  is a side cross-sectional view illustrating the welding of the pressure-sensing device during installation according to one embodiment; 
           [0027]      FIG. 14  is an exploded perspective view illustrating the plug, and the assembly of the receptacle, the pressure-sensing device, and the valve stem according to one embodiment of the present invention; 
           [0028]      FIG. 15  is a perspective view of one embodiment of the fully assembled valve of the present invention with the cap off; 
           [0029]      FIG. 16  is a cross-sectional view of an alternative embodiment of the valve of the present invention wherein the valve is modified to form a pressure sensitive diaphragm that is gauged; and 
           [0030]      FIG. 17  is a cross-sectional view of a further embodiment of the valve of  FIG. 16  in which the valve stem has been modified to include a cavity in its end. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    The present invention provides a modified charging valve having a pressure sensitive element at one end and a connector or receptacle mounted within it. The receptacle is configured to determine pressure within the valve either in flight or on the ground with minimal interference with the normal pressure charging apparatus. 
         [0032]    The modified valve of the present invention utilises the structure of known valves used in the art and incorporates within it a pressure-sensing device and a receptacle or connector that allows for pressure measurements to be made as desired without interfering with the normal operation of the valve and with minimal alteration of the volume of the working fluid within the pressure vessel. Pressure vessels and charging valves are known in the art and therefore are not described in detail herein. In an alternative embodiment, the existing end of the valve can also be modified to form a pressure sensitive diaphragm and then be gauged. 
         [0033]    The valve of the present invention will now be described in further detail with reference to the accompanying figures. 
         [0034]      FIG. 1  provides a schematic diagram of the standard valve geometry. As stated above, the present invention utilises the structure of valves known in the art. As will be described, the valve is modified to accommodate, for example, the pressure-sensing device, the receptacle and a measuring device. Generally such known valves include a main body (also referred to as a valve stem herein), that has a central channel, or bore, that extends from one end of the body to the other. The present invention incorporates the use of a pressure-sensing device and receptacle within the channel of the body, as described below. 
         [0035]    Referring to  FIG. 2 , one embodiment of the modified valve of the present invention will be described in further detail.  FIG. 2  is an exploded perspective view illustrating the components of the modified valve, indicated in the Figures at numeral  18 , which includes a valve stem  20  which is illustrated in two portions, a first portion  22  and a second portion  24 . It will be understood that the modified valve  18  of the present invention may comprise one main body that does not consist of two separate parts, however in a preferred embodiment the valve main body comprises two portions to assist in the assembly of the modified valve. The description of the modified valve will make reference to a two part valve body, however a person skilled in the art will understand that a one part valve body may also be used. The stem  20  includes an elongate channel  26  that extends through the stem  20  from one end to the other, i.e. through the first and second portions  22 ,  24 . 
         [0036]    The modified valve  18  also includes a pressure-sensing device  28  and a receptacle  30 . The modified valve  18  may optionally include a plug  32  or the plug  32  may be a separate component that is used in combination with the modified valve  18  when a pressure reading is required, discussed in further detail below. 
         [0037]    The pressure-sensing device  28  may be any pressure-sensing device or transducer that is operable to measure pressure and is sized to be received within the first portion  22  of the stem  20 . In an alternative embodiment, the channel  26  may be widened, for example by boring, to incorporate the pressure-sensing device  28 . The pressure-sensing device  28  is fixedly attached to the end of the first portion  22  by any means known in the art, for example welding, using a laser or other means, fixed using an adhesive or mechanically retained within the channel  26 . The connection of the pressure-sensing device  28  within the channel  26  may be by any means that allows the pressure-sensing device  28  to measure the pressure in the pressure vessel to which the valve  18  is attached. 
         [0038]    Examples of the type of a pressure-sensing device  28  that may be used include, but is not limited to resistive strain gauges and capacitive gauges. The modified valve  18  of the present invention may also include a temperature sensitive element (not shown). Examples of the type of temperature sensitive elements that may be used include a thermocouple and a resistance temperature detector (RTD). As will be understood by a person skilled in the art, the pressure sensing device  28  and the temperature sensing device may be an integrated piece operable to measure the pressure and temperature of the fluid within the pressure vessel. That is, the integrated pressure and temperature sensing device is preferably sized to be received within the first portion  22  of the valve stem  20 . Alternatively, the channel  26  may be widened to receive the integrated pressure and temperature sensing device. 
         [0039]    In the illustrated embodiment of  FIG. 2 , the pressure-sensing device  28  includes a series of wires  38  extending from one end which allow the pressure measurement to be communicated to an external, or internal, measuring device or plug  32  via receptacle  30 . As will be understood, if an integrated temperature and pressure sensing device are used, the combined pressure and temperature measurements may be communicated to an external, or internal, measuring device or plug  32  via the receptacle  30 . 
         [0040]    Located within the channel  26  in the second portion  24  of the stem  20  is the receptacle  30 . The receptacle  30  is operable to be in communication with the pressure-sensing device  28  and is also operable to be electrically connected to a measuring device or plug  32  at the opposite end from the connection to the pressure-sensing device  28 . The receptacle  30  is operable to communicate with the pressure-sensing device  28 , and in the illustrated embodiment, the wires  38  of the pressure-sensing device  28  are connected to the receptacle  30 . The connection of the wires  38  may be made by any means known in the art, including soldering. Thus, since the receptacle  30  is electrically connected to the pressure-sensing device  28  and the plug or measuring device  32 , it facilitates communication of a pressure reading from the pressure sensing device  28  to the plug or measuring device  32 . 
         [0041]      FIG. 3  illustrates one embodiment of the receptacle  30 , comprising a hollow cylindrical shell portion  40  within which a series of strips  42  are received. The strips  42  are connected to the interior surface of the shell portion  40  at spaced intervals. The strips  42  are attached to the shell portion  40  by any means known in the art that will withstand the environment of the valve and maintain the strips  42  in their position. The strips  42  are made from a conductive material and allow for communication between the wires  38  of the pressure-sensing device  28  and a measuring device or plug  32 . As can be seen more clearly in  FIG. 8 , the strips  42  extend outwardly past the shell portion  40  in the direction of the pressure-sensing device  28 . The wires  38  of the pressure-sensing device  28  are connected to the strips  42  by any means known in the art, for example soldering. 
         [0042]    The conductive material that is used is preferably inert to the fluid environment of the valve  18 . The illustrated embodiment shows the receptacle  30  having four spaced strips  42  within it, however the number of strips and their size and configuration may vary provided that a conductive pathway is provided from the pressure-sensing device through the receptacle  30 . 
         [0043]    As stated above, the modified valve  18  allows for pressure measurements to be taken when desired with minimal interference with the valve operation and working fluid. Therefore, it will be understood that although variations to the number and positioning of the strips  42  may be made it is preferable to minimise the obstruction of the fluid through the receptacle  30 . 
         [0044]    Referring to  FIGS. 3-7 , alternative embodiments of the receptacle  30  are illustrated. Other variations of the receptacle  30  may be used to provide an electrical connection between the pressure-sensing device  28 , and in particular the wires  38 , and the plug or measuring device  32 . As will be understood referring to  FIGS. 3-7 , the strips  42  are positioned on the receptacle  30  such as to provide sufficient separation therebetween so as to allow separation between the electrical connections on the strips  42 .  FIGS. 4 through 7  provide perspective drawings of other embodiments of the receptacle  30 . In each of these figures it will be understood that the receptacle  30  is viewed from the end that is operable to connect to plug  32 . The opposite end is connected to the wires  38  as described above. 
         [0045]    Referring to  FIGS. 4 to 7 , at the end of each of the illustrated receptacles  30  a series of apertures, indicated generally at  44 , are shown that are operable to connect to the plug  32 . In these embodiments, the plug  32  will include protrusions, not shown, that will be sized and configured to be received within the apertures  44  to provide a connection there between. 
         [0046]    Each alternative embodiment of the receptacle  30  will now be described in more detail.  FIG. 4  illustrates a receptacle  30  having a rectangular body with curved sides such as to be fittedly received within the channel  26 . This involves machining grooves in the valve stem  20  (preferably the second portion  24 ) to accommodate the receptacle  30 . In this embodiment illustrated, the apertures  44  are located within the rectangular body in a parallel line. Each aperture  44  is sized to receive a conductive strip  42 . Fluid is operable to flow on either side of the rectangle through the valve body. 
         [0047]      FIG. 5  illustrates a circular or cylindrical embodiment of the receptacle  30  that includes a pair of locking tangs  46  for holding the connector  34  within the second portion  24  of the valve stem  20 . The circular embodiment of the receptacle  30  is centrally located within the channel  26  and allows for fluid flow around the exterior circumference of the receptacle  30 . 
         [0048]      FIG. 6  illustrates a circular or cylindrical receptacle  30  that is suspended within the channel  26  by a cover  48 . It will be understood that in this embodiment the cover  48 , that extends around the connector  34  and is held within the valve shell  40  by a tab like attachment point, is preferably made from a thin metal to minimise interference with fluid flow around the connector and also to allow the minimum fluid flow rate in which the metal is susceptible to fatigue from twisting due to high fluid pressures. 
         [0049]      FIG. 7  includes an alternate embodiment of the receptacle  30 . According to the embodiment illustrated, the receptacle  30  is circular or cylindrical shaped and sized to fit within the channel  26 . The illustrated circular receptacle  30  includes a hollow passageway therefore to allow for fluid flow. The apertures  44  are located within the walls of the receptacle  30 . 
         [0050]    The plug  32  and its use will now be described in further detail. As stated above, the plug  32  may form part of the valve  18  or may be a separate unit that is used only when required. The plug  32  is operable to connect with the receptacle  30  at the opposite end from the pressure-sensing device  28 . In the illustrated embodiment, as can be seen in  FIG. 8 , the plug  32  includes a contact end that includes a series of connectors  52  having contact strips  54  that are operable to mate with the strips  42  on the receptacle  30 . The connection, or mating, of these two components can be clearly seen in  FIGS. 9A and 9B . The connection of the two parts allows for electrical contact between the pressure-sensing device  28 , the receptacle  30  and the plug  32  and therefore allows a pressure reading to be taken and communicated to a user. 
         [0051]    It will be understood that the connection point between the receptacle  30  and the plug  32  may be made by other means. For example, and as described above, in the alternative embodiments of the receptacle  30  a series of apertures  44  were provided for receiving protrusions on the plug  32  to allow for a connection between the pressure-sensing device, the receptacle  30  and the plug  32 . 
         [0052]      FIG. 10  provides an exploded perspective view of the embodiment of the plug described above, including contact strips  54  received in the connectors  52  sized to engage with the strips  42  on the receptacle  30 . 
         [0053]    As can be seen in  FIGS. 9A and 9B  the contact strips  54  of the plug  32  and the strips  42  of the receptacle  30  may be slightly curved to ensure a secure lock between the components when mated. The insulation between each mating set of contact strips is the shell portion  40  of the receptacle  30  shown in  FIG. 9A . The shell portion  40  that mounts the conductive strips is preferably a dielectric plastic material such as Delrin or PEEK. The conductive strips are therefore mounted on an insulating mount, i.e. the shell portion, when located in the conductive stainless steel of the valve stem. 
         [0054]    To ensure that the plug  32  and receptacle  30  mate in the appropriate orientation (to ensure that the correct electrical connections are made), the strips  42  and contact strips  54  may be offset radially as shown in  FIG. 10  to ensure that only one mating orientation works. Furthermore, one of the strips  42  of the receptacle  30  may be made deeper than the other strips to provide a mechanical guideway—the plug  32  would not fit into the hole in receptacle  30  unless rotated to the appropriate position. 
         [0055]    An example of the machining requirements for one embodiment of the present invention is provided in  FIG. 11 . However, it will be understood that these are merely provided as an example and are not meant to be limiting in any way. The machining requirements may be changed depending on the valve size and the configuration of the connector and pressure sending device and plug to be utilised within the valve. 
         [0056]    The valve main body or stem  20  may be modified as follows: carve a 0.04″ wide groove around the circumference of the stem 0.8″ from the left and cut the stem in half at 0.84″ starting from left of stem. As discussed above, this provides a two-part valve stem  20  that assists in the positioning and securing of the receptacle  30  to the wires  38  of the pressure-sensing device  28 . However, this is not required and the receptacle  30  may be placed within the valve body/stem  20  while the stem  20  comprises one unitary piece. 
         [0057]    Once the valve stem  20  has been divided into two pieces the first piece of the stem may be adapted to include a hole in the end facing the second stem piece with diameter 0.1170″ offset from centre with a depth of 0.6450″ using standard drill size 0.1142″+0.004/−0.001. A second hole at the opposite end (where the pressure-sensitive face of the transducer will be) may be drilled with diameter of 0.126″ and a depth of 0.1750″, using standard drill size 0.1260″+0.005/−0.001. 
         [0058]    The second half of the stem may be hollowed out to a diameter of 0.2000″ along the length of the piece. This could be done using a standard drill size 0.2008″+0.005/−0.001. 
         [0059]    In addition a cylindrical end piece  72  is machined with a diameter of 0.395″ and length 0.180″ with an offset through hole with diameter 0.15″, using a standard drill size 0.1496″+0.005/−0.001. This hole would align with the hole through the first stem piece  22 . 
         [0060]    The installation of the pressure-sensing device  28  will now be described with reference to  FIGS. 12 and 13 . 
         [0061]    In the illustrated embodiment, there were two methods that may be used to secure the pressure transducer or pressure sensing device  28  in place. Either: (i) Using Room Temperature Vulcanized rubber  56  potting compound &amp; epoxy  58 , shown in  FIG. 12  or (ii) micro laser welding  60  it in place, shown in  FIG. 13 . 
         [0062]    When following the method illustrated in  FIG. 12 , i.e. RTV  56  potting and epoxy  58 , the end piece  72  of the stem must be hermetically laser welded  62  onto the first half of the stem. The pressure-sensing device  28  is then put in place using the epoxy  58  near the lower portion of the transducer and potting  56  surrounding the head. This is to prevent residual stress caused by the epoxy curing from affecting the strain and pressure readings on the pressure-sensitive face of the transducer. 
         [0063]    If using a laser weld, as illustrated in  FIG. 13 , to install the pressure-sensing device, insert the transducer  28  into the end piece  72  until the pressure-sensitive face is flush with the surface of the end piece. Then weld  60  the two parts together around the circumference of the transducer over the existing weld left from the construction of the transducer where it protrudes from the other side of the end piece. Place the assembled end piece and transducer at the end of the first stem piece with the transducer wires extending through the stem hole. Weld  62  the end piece  72  to the first stem piece  22  around the circumference where the two parts meet. 
         [0064]    The assembly of the modified valve  18  of the present invention will now be described with reference to  FIGS. 14 and 15 . 
         [0065]    To assemble the system, the pressure-sensing device  28  should first be connected to the first portion  22  of the valve main body  20 , as described above. The wires  38  from the pressure-sensing device  28 , which protrude from the first portion of the main body  20  may be formed into one wire. The wires or wire, may then be soldered onto the receptacle  30  (e.g. onto the strips  42 ). The receptacle  30  is then placed within the second portion  24  of the main body  20  and the first and second portions are connected together. Preferably the first and second portions ( 22 ,  24 ) are hermetically laser welded together. The modified valve  18  can then be reassembled with the unmodified valve housing  74  and locking nut  76  to make the valve functional. 
         [0066]    The valve  18  may also include a cap  64 , shown in  FIG. 15 . The cap  64  fits on the end of the second portion of the valve body and provides a dust cap or seal. In one embodiment, the cap  64  may include the plug  32  which may be operable to be in communication with the receptacle  30  during the operation of the aircraft, i.e. pressure readings may be taken during operation of the aircraft whenever required. Alternatively, the cap  64  may be manually removed and the plug  32  be contained as a separate unit, for example a handheld unit, and connected to the receptacle  30  if and when a pressure reading is required. 
         [0067]    The present invention provides a modified valve according to the above description that includes a pressure-sensing means and a receptacle or connector that allows for periodic or continual communication with the pressure-sensing means. In another aspect the present invention provides a method for retrofitting a valve within a pressure vessel to incorporate a pressure-sensing device within it. In a further aspect the present invention provides a pressure-sensing retrofit device that includes a connector that may be installed in a valve to allow for pressure measuring with minimal interference with the valve. 
         [0068]    The present invention provides a standard charging valve modified to add a pressure transducer with the active diaphragm subjected to the pressure within the charged vessel. The present invention further provides an arrangement to allow the wires and connector to not interfere with the flow of gas or oil so as to not interfere with normal servicing. 
         [0069]    In a further embodiment of the present invention the existing end of the valve may be modified to form a pressure sensitive diaphragm, which is then gauged. The gauges are indicated at numeral  70  and may be attached directly into the valve stem.  FIG. 16  illustrates the inclusion of a gauge  70  in the valve stem with wires  38  extending from the gauge. The wires are as described herein and may connect in a similar manner as described above. 
         [0070]      FIG. 17  illustrates a further embodiment of the valve including the gauge in which the stem of the valve is modified to include a cavity that has been formed in one end of the valve. The cavity may be formed by machining and then welding the stem or by electro discharge machining (EDM). The strain gauge  70  may then be adhered in the cavity and the wires extend therefrom as described above. It will be understood that the gauge and wires may replace the pressure-sensing device described in the above embodiments. 
         [0071]    While this invention has been described with reference to illustrative embodiments and examples, the description should not be construed in a limiting sense. Thus, various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments. Further, all of the claims are hereby incorporated by reference into the description of the preferred embodiments. 
         [0072]    Any publications, patents and patent applications referred to herein are incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety.