Abstract:
A device for selectively connecting a tire to a pneumatic unit of an aircraft, the tire forming part of a wheel mounted to rotate on a hollow axle of the aircraft, the device comprising a stator and a rotor that is mounted to rotate relative to the stator and that includes means enabling it to be rotated by the wheel. The stator is bell-shaped and is designed to be received as a push-fit in the axle, and includes an end wall carrying a first pneumatic port for connection to the pneumatic unit via a tube running along the inside of the axle, the rotor extending substantially inside the stator.

Description:
The invention relates to a device for connecting a tire of an aircraft wheel to a pneumatic unit of the aircraft. 
     BACKGROUND OF THE INVENTION 
     Aircraft are known that include devices for connecting the tires of wheels to an on-board pneumatic unit. The unit may be an air compressor, a nitrogen generator, or any other system enabling gas to be delivered under a pressure suitable for inflating the tires. Depending on whether the pressure made available by the pneumatic unit is greater than or less than the pressure that exists in the tire, the tire will inflate or deflate. When the aircraft is on the ground, the pneumatic unit can be connected to an external source of pressure. 
     Document GB 1 031 726 illustrates such a device, having some of its elements outside the axle. In particular, the wheel is fitted with a protective cover that covers the end of the axle and that receives an isolation valve of the tire. That disposition of the valve makes it sensitive to external impacts. Furthermore, the valve is actuated by a needle that is movable in an axial orifice of the axle. That type of device is not suitable for modern aircraft that usually have axles that are hollow. In addition, it includes a plurality of parts that are separately removable (the needle in the axle, the valve in the wheel cover), which does not facilitate maintenance thereof. 
     Document U.S. Pat. No. 2,107,405 and U.S. Pat. No. 2,685,906 disclose other devices, more particularly adapted to land vehicles. In particular, the device shown in document U.S. Pat. No. 2,685,906, which is in accordance with the introductory portion of claim  1 , is found to be advantageous in that it is entirely modular and can be removed as a whole, naturally providing the gas connections are disconnected. Nevertheless, that device projects from the wheel and is therefore exposed to impacts. 
     OBJECT OF THE INVENTION 
     An object of the invention is to provide a device for adjusting the pressure in a tire forming part of an aircraft wheel, based on the device of document U.S. Pat. No. 2,685,906, but better protected. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to the invention, there is provided a device for selectively connecting a tire to a pneumatic unit of an aircraft, the tire forming part of a wheel mounted to rotate on a hollow axle of the aircraft, the device comprising:
         a stator and a rotor mounted to rotate relative to the stator about an axis that coincides, in operation, with the axis of rotation of the wheel, and including means for enabling the wheel to drive it in rotation;   a seal that extends between the rotor and the stator to close a first chamber extending between the rotor and the stator and into which a first pneumatic port opens out, the port being carried by the stator for connecting the device to the pneumatic unit;   the rotor defining a second chamber into which a second pneumatic port opens out for connecting the device to the tire;   the rotor carrying a valve extending through a wall of the rotor separating the first and second chambers, thereby enabling the two chambers to be put selectively into pneumatic communication by opening the valve; and   the stator carrying an actuator that acts selectively on the valve in order to switch between a stable closed state and an open state.       

     According to the invention, the stator is bell-shaped, being designed to be received as a push-fit in the axle and having an end wall that carries the first pneumatic port for connection to the pneumatic unit by a pipe running inside the axle, the rotor extending substantially inside the stator. 
     Thus, the entire device is housed in the axle where it is protected from impacts. Furthermore, the disposition of the first port in the end wall makes it easier to connect the device to the pneumatic unit via a pipe running along the inside of the axle. 
     Preferably, the actuator is of the electromechanical type. Thus, using an electromechanical actuator enables the actuator to be incorporated completely within the first chamber, without any need to provide an actuator chamber in the stator or an additional pneumatic port for activating the actuator. The gas under pressure coming from the pneumatic unit can flow from the first port towards the open valve by passing through the electromechanical actuator. Nevertheless, the gas will reach the tire only if the valve is open, i.e. only if the actuator is activated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood in the light of the following description with reference to the figures of the accompanying drawings, in which: 
         FIG. 1  is a section view of a wheel mounted on an aircraft axle that is fitted with a device constituting a particular embodiment of the invention; and 
         FIG. 2  is a section view on a larger scale of the device shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , the device of the invention is shown in place on an aircraft fitted with a pneumatic generator, e.g. a compressor that receives nitrogen from an air separator system that sends the oxygen from the air to an oxygen circuit of the aircraft and the nitrogen from the air to the compressor. The aircraft has at least one wheel  1  comprising a rim  2  that carries a tire  3  and that is received to rotate about an axis of rotation X on a hollow axle  4 , by means of ball bearings  5 . The device  10  of the invention is placed in the axle  4  at the end thereof and comprises a stator  11  engaged as a push-fit in the axle  4  and fastened thereto by fastener means (not shown). The device  10  further comprises a rotor  12  rotatably mounted in the stator  11 . The device  10  is described in greater detail below with reference to  FIG. 2 . At this point it suffices to observe that the rotor  12  is caused to rotate together with the wheel by means of a finger  13  that extends to co-operate with a protective cap  14  secured to the wheel  1 . 
     With reference to  FIG. 2 , it can be seen that the stator  11  is generally bell-shaped and is designed to be engaged as a push-fit in the axle, which is drawn in dashed lines, being received almost entirely therein with the exception of an end collar that comes into abutment against the end of the axle. The stator  11  has an end wall  19  that carries a first pneumatic port  15  for connecting the device to the pneumatic unit of the aircraft, by means of a pipe  16  extending along the axle  4 . The rotor  12  is completely received within the stator and it is mounted to rotate inside the stator  11  by means of ball bearings  26 . The rotor  12  carries a second pneumatic port  17  for connecting the device to the tire via a pipe  18  that extends between the rotor  12  and the rim  2 . 
     The assembly is particularly compact and is incorporated fully within the axle, thereby protecting it against any external impact. 
     Together the stator  11  and the rotor  12  define a first chamber  20  that is closed by a lip seal  21  that is carried by the rotor  12  to co-operate with a cylindrical bearing surface  22  formed by the outside wall of an axial protrusion  28  of the stator  11  extending inside the rotor  12 . The axial protrusion  28  defines an axial housing  23  that opens into the first chamber  20  and within which an oblong electromechanical actuator  24  is engaged, the actuator being stopped axially by a ring  25 . The first pneumatic port  15  opens out into the housing  23  and thus into the first chamber  20 , given that the actuator  24  is permeable to gas and therefore does not constitute an obstacle to the passage thereof. The actuator  24  extends along the axis X in this embodiment and it possesses a terminal actuator member that is movable along said axis X. 
     Furthermore, the rotor  12  defines a second chamber  30  into which the second pneumatic port  17  opens out. The second chamber  30  is separated from the first chamber  20  by a wall  31  having a valve  32  passing therethrough along the axis of rotation X. The valve is normally closed, thereby isolating the two chambers from each other. However, it can be opened by the actuator member of the actuator  14  that pushes the stem of the valve  32  so as to open the valve and put the two chambers  20 ,  30  into pneumatic communication with each other. 
     In order to modify the pressure in the tire, it is appropriate to put the tire into communication with the pneumatic unit. To do this, the actuator  24  is actuated in such a manner as to open the valve  32  and put the chambers  20  and  30  into communication with each other, which chambers are connected respectively to the pneumatic unit and to the tire. The valve  32  is then left open for a length of time that is sufficient to enable the desired pressure to be established in the tire. 
     These operations of modifying pressure are normally performed only while the aircraft is in flight or while the aircraft is stationary on the ground. Under such conditions, the lip seal  21  is subjected to pressure only while the wheel is not revolving. This makes it easier for the lip seal  21  to be leaktight. Nevertheless, if a small leak does appear via the lip seal  21 , it suffices that the leakage flow rate is well below the inflation flow rate to ensure that the tire is nevertheless inflated. In a variant, it is possible to use any other type of sealing gasket, that is compatible with rotation, and that is capable of providing gastightness, at least while the wheel is not revolving. 
     The use of an electromechanical actuator makes it possible to avoid providing a second pneumatic source for controlling the actuator, as in the embodiment shown in FIG. 5 of document U.S. Pat. No. 2,685,906. It would be difficult to arrange two pneumatic pipes in the axle. Furthermore, the actuator can be located fully within the first chamber as in the first embodiment shown in FIG. 4 of that document, while nevertheless enabling the actuator to be controlled separately and pressure to be raised by the pneumatic unit, which is not possible in the embodiment of that FIG. 4. 
     The configuration of the device of the invention also makes it easy to incorporate a wheel revolution sensor since the rotor  12  is constrained to rotate with the wheel. Thus, a tachometer  50  is disposed in the device of the invention, having a stationary portion  51  secured to the stator  11  and a rotary portion  52  secured to the rotor  12  and extending in register with the stationary portion  51  so as to interact remotely therewith by electromagnetic means. In known manner, the electromagnetic interaction generates an electrical current in the stationary portion  51  that is proportional to the speed of rotation of the rotor  12  and thus of the wheel. It then suffices to measure the current flowing in the stationary portion  51  in order to determine the speed of rotation of the wheel. 
     Furthermore, the configuration of the device of the invention also makes it easy to incorporate a tire pressure sensor. Thus, a pressure sensor  60  is disposed on the rotor  12  to measure the pressure that exists in the second chamber  30 , and thus in the tire, since the second chamber  30  is in pneumatic connection with the tire. The pressure sensor  60  is of the radiofrequency type and it receives its electrical energy from an antenna  61  placed on the stator  11  so as to be in a position to interact remotely by electromagnetic means with the pressure sensor  60 , regardless of the angular position of the rotor  12 . In return, the pressure sensor  60  influences the impedance of the antenna  61  as a function of the pressure in the chamber  12 . It then suffices to measure the current flowing in the antenna  60  to determine the pressure in the tire, or to measure any other electrical magnitude (voltage, impedance, . . . ) relating to the antenna  60  and varying with pressure. The pressure sensor arranged in this way replaces the sensor that is usually placed directly on the wheel rim. 
     The sensors incorporated in the device of the invention are thus particularly well protected against external impacts. 
     The stationary portion  51  of the tachometer  50 , the antenna  61 , and the actuator  24  are all electrically connected to the aircraft by means of an electrical connector  70  that also extends from the end wall  19  of the stator  11 , and by means of an electric cable  71  likewise running along the axle  4 . 
     The invention is not limited to the above description, but on the contrary covers any variant coming within the ambit defined by the claims. 
     In particular, although there is shown a device having a rotor that is housed in full within the stator, it is possible, without going beyond the invention, to provide a rotor that projects a little from the stator, e.g. through the second pneumatic port that may project from the end of the stator.