Abstract:
The invention provides measurement equipment for measuring the inflation pressure of a tire of a vehicle wheel  1 , the equipment comprising:
       a body  16  defining an internal volume;   a communication orifice  19  for putting the inside volume of the body  16  into communication with an inflation chamber situated between a rim  2  and a tire of the wheel and containing an inflation gas;   an indicator member  25  slidably mounted in the body  16  so as to define a gastight separation between a first chamber  26  containing a given quantity of a reference gas and a second chamber  27  into which the communication orifice  19  leads, such that the indicator member  25  is subjected to opposing pressures that exist in each of the chambers; and   position-identification means  30  for identifying the position of the indicator member in the body.

Description:
[0001]    The invention relates to equipment for measuring the inflation pressure of a tire of a vehicle wheel. 
       BACKGROUND OF THE INVENTION 
       [0002]    Most modern aircraft have landing gear that includes measurement means for measuring values of parameters that are monitored in order to ensure that the landing gear is used under conditions that enable predetermined safety, maintenance, and operating cost targets to be reached. By way of example, the parameters that are measured may be brake temperature, carbon disk wear when the brakes are carbon disk brakes, the pressure and the temperature of shock absorbers in the landing gear, the pressure of the gas inflating the tires of wheels, etc. 
         [0003]    The gas pressure in the tires of wheels of an aircraft constitutes a parameter that is particularly critical, and it needs to be monitored regularly. On takeoff, a tire that is under-inflated, or indeed over-inflated, presents a major risk of bursting and projecting debris that might damage various pieces of equipment of the aircraft. In addition, regular use of tires that are under-inflated or over-inflated leads to premature wear of the tires, and thus to large extra operating costs. 
         [0004]    It is nowadays mandatory to measure the pressure of each tire of an aircraft&#39;s wheels before each flight. For this purpose, it is either possible to provide the aircraft with onboard means enabling pressure to be measured continuously and enabling pressure measurements to be transmitted to the cockpit, or else to take measurements manually during maintenance operations while the airplane is on the ground. In both situations, use is made of a duct provided in the rim of each wheel, similar to that used for inflating the tire, which duct serves to put the inside of the tire into communication with a pressure sensor. 
         [0005]    The measured pressure value is naturally highly dependent on the temperature of the gas, which itself depends on outside temperature, and which may be influenced to a large extent by energy from a braking operation prior to taking the measurement, etc. 
         [0006]    It is thus essential either to correct the pressure measurement as a function of temperature, or to define thresholds that depend on temperature beyond which the tire needs to be reinflated or deflated. For this purpose, it is necessary to measure or to evaluate the temperature of the tire when measuring its pressure, thereby making onboard means more complex or lengthening the time taken for maintenance operations. An estimate of the inflation pressure of a tire can thus be obtained very simply on the basis of the position of an indicator member. 
       OBJECT OF THE INVENTION 
       [0007]    An object of the invention is to enable the pressure of a tire to be measured without requiring a correction to be made as a function of temperature. 
       SUMMARY OF THE INVENTION 
       [0008]    In order to achieve this object, the invention provides measurement equipment for measuring the inflation pressure of a tire of a vehicle wheel, the equipment comprising:
       a body defining an internal volume;   a communication orifice for putting the inside volume of the body into communication with an inflation chamber situated between a rim and a tire of the wheel and containing an inflation gas;   an indicator member slidably mounted in the body so as to define a gastight separation between a first chamber containing a given quantity of a reference gas and a second chamber into which the communication orifice leads, such that the indicator member is subjected to opposing pressures that exist in each of the chambers; and   position-identification means for identifying the position of the indicator member in the body.       
 
         [0013]    Thus, since the reference gas and the inflation gas are raised to temperatures that are substantially equal by virtue of their proximity, the effects of those temperatures on the opposing pressures exerted on the indicator member are very close and therefore they compensate. As a result, the position of the indicator member in the body does not depend on temperature. The pressure in the tire can thus be deduced simply from the position of the indicator member in the body without any need to correct the measurement of tire pressure as a function of temperature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention can be better understood in the light of the following description given with reference to the figures of the accompanying drawings, in which: 
           [0015]      FIG. 1  is a fragmentary section view of a wheel of an aircraft undercarriage fitted with pressure measurement equipment of the invention; 
           [0016]      FIG. 2   a  is a longitudinal section view of pressure measurement equipment of the invention in a first embodiment, a piston of the equipment being in a retracted position; 
           [0017]      FIG. 2   b  is a longitudinal section view of pressure measurement equipment of the invention in a first embodiment, the piston of the embodiment being in an extended position; 
           [0018]      FIGS. 3   a  and  3   b  are longitudinal section views of pressure measurement equipment of the invention in a second embodiment and in a variant of the second embodiment; and 
           [0019]      FIGS. 4 and 5  are longitudinal section views of pressure measurement equipment in third and fourth embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    With reference to  FIG. 1  and in conventional manner, a wheel  1  of an aircraft undercarriage has a rim  2  made up of two half-rims  3  receiving a tire  4  (represented diagrammatically by dashed lines). The rim  2  is rotatably mounted by means of conical roller bearings  5  in this example (only one bearing is visible). Between the rim  2  and the tire  4  of the wheel  1  there extends an inflation chamber  6  filled with an inflation gas, generally nitrogen. Pressure measurement equipment  7  of the invention is installed on one of the half-rims  3  in order to measure the inflation pressure that exists inside the inflation chamber  6 . The pressure measurement equipment  7  is screwed into an assembly orifice  8  that defines tapping  9 . 
         [0021]    It should be observed that at this point that since the pressure measurement equipment is designed to be screwed directly to the rim, it is necessary to install it before inflating the tire (and to wait for the tire to be deflated before unscrewing it). It is naturally possible to make provision for using intermediate equipment having a valve that is permanently screwed to the rim, thus making it possible to install and remove the measurement equipment without deflating the tire. 
         [0022]    In order to put the inflation chamber  6  into communication with the measurement equipment  7 , the rim  2  has a duct  12  with a first end  13  leading into the inflation chamber  6  and a second end  14  leading into the assembly orifice  8 . The duct  12 , similar to the ducts that are used for inflating the tires, serves to put the inflation chamber  6  into communication with the pressure measurement equipment  7  so that the equipment is subjected to an inflation pressure close to the pressure that exists inside the inflation chamber. 
         [0023]    With reference to  FIGS. 2   a  and  2   b , the pressure measurement equipment  7  in a first embodiment comprises a body  16  projecting from the rim  2  and an assembly endpiece  17  that is threaded in part in order to co-operate with the tapping  9  in the assembly orifice  8 . 
         [0000]    The assembly endpiece  17  has a sealing gasket  18 , in this example an O-ring, serving to provide sealing between the duct  12  and the outside of the wheel in order to prevent the tire  4  from deflating when the pressure measurement equipment  7  is installed. An opening  19  is made in the assembly end so as to enable a certain quantity of inflation gas to penetrate into the inside of the body  16  via the duct  12 . 
         [0024]    The body  16  defines an inside volume in which a piston  25  is mounted to slide in sealed manner, providing a leaktight separation between a first chamber  26  and a second chamber  27 . Movement of the piston  25  is limited by a sleeve  22  mounted stationary in the inside volume of the body  16 . In order to provide sealing between the first chamber  26  and the second chamber  27 , the piston  25  is provided with a sealing gasket  28 , in this example an O-ring. The piston  25  is also secured to the sleeve  22  via a bellows  23  that extends in an annular space  24  defined between the sleeve  22  and the body  16 . The bellows  23  serves to prevent any exchange of gas between the first chamber  26  and the second chamber  27  of the body  16 . 
         [0025]    The first chamber  26  of the body  16  is prefilled with a given quantity of a reference gas (e.g. nitrogen or helium). Pre-filling is performed prior to mounting the measurement equipment on the wheel rim (e.g. during manufacture of the measurement equipment). By means of the bellows  23 , the quantity of reference gas contained in the first chamber is kept constant. 
         [0026]    The second chamber  27 , into which the opening  19  leads, becomes filled with inflation gas when the tire of the wheel is inflated, such that when the tire is inflated the pressure inside the second chamber is equal to the inflation pressure of the tire. 
         [0027]    The piston  25  is then subjected to opposing pressures as exerted by the reference gas and by the inflation gas. The piston  25  then takes up a position depending on the value of the inflation pressure. It is thus possible to determine the value of the inflation pressure by determining the position of the piston  25 . 
         [0028]    It should be observed at this point that since the inflation gas and the reference gas are taken to temperatures that are substantially identical as a result of their proximity, the effects of such temperatures on the opposing pressures exerted on the piston  25  are very close and they compensate each other. The position of the piston  25  in the body  16  therefore does not depend on temperature, and as a result there is no need to correct the measurement of tire pressure. 
         [0029]    Thus, in  FIG. 2   a , the piston  25  is shown in a so-called “retracted” position corresponding to an inflation pressure that is great enough for the inflation pressure to push back the piston  25  so that it comes to bear against the sleeve  22 , whereby the volume of the first chamber  26  is at a minimum while the volume of the second chamber  27  is at a maximum. 
         [0030]    Conversely, in  FIG. 2   b , the piston  25  is shown in a so-called “extended” position corresponding to an inflation pressure that is small enough to allow the pressure exerted by the reference gas to push back the piston  25  into abutment against the end of the body  16 , such that the volume of the first chamber  26  is at a maximum and the volume of the second chamber  27  is practically zero. 
         [0031]    Naturally, if the tire is properly inflated, then the piston  25  finds an equilibrium position that is intermediate between those two extreme positions. 
         [0032]    In order to determine the position of the piston  25 , a linear variable differential transformer (LVDT) type sensor  30  is used that is made up of a metal rod  31  secured to the piston  25  of the bellows  23 , and of a hollow measurement element  23  of external outside shape. In the measurement element  32  there are arranged three coils on a common axis: one primary coil  33  and two secondary coils  34  and  35 . The coils  33 ,  34 , and  35  are electrically connected to an electrical module  36  (the electrical connections are not shown in order to simplify the figure), which module has generator means  37  for applying a voltage to the primary coil  33 , and measurement means  38  for measuring the voltages on the secondary coils  34  and  35 , which voltages depend on the extent to which the metal rod  31  is pushed into the measurement element  32 , and thus on the position of the piston  25 . 
         [0033]    The electrical module  36  is also connected to an antenna  40  of the measurement equipment  7  and includes transmitter means  41  arranged to format the measurements performed by the linear movement sensor  30  and to transmit them over a radio connection via the antenna  40 . This data is transmitted to communications equipment  42  situated on the aircraft or brought up to the proximity of the wheel  1  by an operator on the ground. 
         [0034]    It should be observed that an electrical power supply for the electrical module  36  and the linear movement sensor  30  can be provided by various means that are not shown herein, e.g. by transmitting electrical energy over a radiofrequency connection, or by means of a battery fitted to the measurement equipment  7 , or indeed by energy generator means (e.g. means for transforming vibration into electrical energy, or indeed a tachometer generator that provides the speed of rotation of the main wheels). 
         [0035]    Reference is made to  FIG. 3   a  in which numerical references for elements in common have one hundred added thereto, the figure showing a second embodiment comprising measurement equipment  107  that no longer has a linear movement sensor but rather a contact detector  143 . The contact detector  143  is placed at the end of a measurement element  132  and is for detecting contact with a rod  131  secured to a piston  125 . The piston  125 , the rod  131 , and the contact detector  143  are arranged in such a manner that the rod  131  comes into contact with the contact detector  143  when the piston  125  is in a retracted position. The contact signal is then transmitted to an electrical module  136 . Thus, in this second embodiment, a situation is detected in which the inflation pressure is greater than a predetermined threshold. By way of example, the measurement equipment may be dimensioned in such a manner that the contact signal is issued so long as the inflation pressure is greater than a minimum pressure below which it is appropriate to ensure a maintenance operation for reinflating the tire. The maintenance operation is thus decided on when the contact signal is no longer issued. 
         [0036]      FIG. 3   b  shows a variant of the second embodiment of the measurement equipment  207  of the invention. In this variant, the enclosure equipment  207  is provided with a first contact detector  243 , similar in arrangement and kind to the contact detector  143  described above, serving to issue a first contact signal to an electrical module  236 , and with a second contact detector  244  delivering a second contact signal to the electrical module  236  indicating that the piston is in an extended position. Thus, in this variant of the second embodiment, a first situation is detected in which the inflation pressure is greater than a first predetermined threshold, and a second situation is detected in which the inflation pressure is less than a second predetermined threshold. By way of example, the measurement equipment may be dimensioned in such a manner that the first signal and the second signal are issued respectively when the inflation pressure is above and below a maximum pressure and above and below a minimum pressure, beyond which it is appropriate to call for a maintenance operation to deflate or to reinflate the tire. 
         [0037]    With reference to  FIG. 4  and in a third embodiment, the measurement equipment  307  of the invention includes a dial comparator  345 . The dial comparator comprises a body  346 , a dial  347 , and a comparator rod  348 . The rod of the comparator  348  is in contact with a tip  349  of a rod  331  secured to the piston  325 . The comparator rod  348  is arranged to slide in the body  346  to an extent that depends on the position of the tip  349  of the rod  331  and thus on the inflation pressure of a tire. The dial  347  has a scale and a pointer (not shown in the drawings) with the angular position of the pointer depending on the linear position of the rod and providing a visual indication that is representative of the inflation pressure of the tire. 
         [0038]    With reference to  FIG. 5  and a fourth embodiment, measurement equipment  407  of the invention comprises a body  416  having a transparent window  450  (e.g. made of transparent plastics material) that is marked with a scale  451 . The transparent portion  450  is arranged in such a manner that a piston  425  of position that depends on the inflation pressure of a tire is visible through the transparent portion  450 , so that, depending on the position of the piston, the scale  451  provides an indication representative of the inflation pressure. 
         [0039]    The measurement equipment of the invention in the third and fourth embodiments provides a visible indication of the inflation pressure that can be seen by an operator on the ground. It should be observed that in these embodiments, it is necessary for the measurement equipment to be mounted on a face of a rim that gives easy visible access to the equipment. In addition to its simplicity and its robustness, the measurement equipment in the third and fourth embodiments of the invention presents the advantage of not requiring any electrical power supply since it operates entirely mechanically. 
         [0040]    The invention is not limited to the particular embodiments described above, but on the contrary covers any variant coming within the ambit of the invention as defined by the claims. 
         [0041]    Although the measurement equipment is provided with bellows, it is possible to use other means for preventing gas exchange between the chambers in the body, e.g. one or more additional gaskets mounted on the piston. 
         [0042]    Although particular position-identification means are described (a linear movement sensor, a contact detector, a dial comparator, a window), it is also possible to use other position-identification means in order to identify the position of the piston. In particular, it is possible to replace an LVDT sensor by any type of passive sensor of linear movement, which may be of inductive, capacitive, or potentiometer type, etc. It is also possible to replace the contact detector by a proximity detector. Finally, it is possible to replace the dial comparator or the window with other visual indicator means, e.g. an indicator that changes color depending on pressure (by way of example, provision could be made for an indicator that takes on a green color when the value of the inflation pressure is normal, and a red color when it is abnormally low). 
         [0043]    Although particular arrangements are described for the position-indicator means, for the electrical module, for the antenna, and for other elements of the equipment, the invention naturally applies to other arrangements of such elements. For example, the coils and the rod of the LVDT may be positioned inside the chamber that is filled with inflation gas, or the electrical module may be situated in said chamber or in the chamber filled with the reference gas.