Abstract:
In a measuring device for the measurement of the brake torque on an aircraft landing gear, a connecting element that is transversally loaded by said brake torque is provided with measuring elements which produce a measuring signal in function of a deformation of said connecting element. In one of two preferred variants, said measuring elements are attached to the surface of a cavity in said connecting element, and in the second preferred embodiment, a corresponding sensor is introduced into said connecting element as a whole, said sensor being so designed that deformations affect its enclosure and deform the latter as well.

Description:
FIELD OF THE INVENTION  
       [0001]    The present invention relates to a device for measuring the brake torque in a vehicle undercarriage in which the brake torque is transmitted to said vehicle undercarriage by a bar-shaped member and said bar-shaped member is loaded transversally by said brake torque. The invention further relates to a sensor for such a device. 
       PRIOR ART  
       [0002]    The brakes of aircraft consist of stacks of mutually interleaved brake disks that are pressed against each other by hydraulic or electric actuators. One of the stacks is connected to the respective wheel. The other stack is connected to the stationary part of the landing gear for receiving the brake torque. In order to transmit the brake torque, i.e. the torque that appears when the brakes are activated, to the landing gear, the latter stationary stack is non-rotatably locked to the landing gear in a suitable manner. Generally, this is achieved by a fastening device that is arranged on the stationary stack eccentrically with respect to the axis of the wheel, in the simplest case a bore. A bolt serves for connecting the stationary stack to the landing gear directly or via a torque takeout arm. This bolt is highly stressed by the torque in the transversal direction and is consequently made of a high-strength material. Since its diameter is generally relatively large, it is hollow in order to reduce its weight. 
         [0003]    For various reasons it is desirable to measure the momentary braking action. To this end, U.S. Pat. No. 4,474,060 suggests designing the bushing that is normally arranged between the mentioned bolt and the respective receiving opening, as a torque sensor. However, the disadvantage of this solution is that it involves a modification of the elements which serve for force transmission, thereby causing considerable expenditures for the certification of this solution. The certification is relatively time-consuming and costly and may furthermore be required, in the extreme case, for each aircraft type separately. 
         [0004]    Similar problems in the measurement of the brake torque may also be encountered in other types of vehicles whose braking systems are similar to those of aircraft. 
       SUMMARY OF THE INVENTION  
       [0005]    It is therefore an object of the present invention to provide a device for measuring the brake torque in a vehicle undercarriage, wherein the device can be mounted without substantial interventions in the transmission path of the brake torque. 
         [0006]    This is accomplished by a device for measuring the brake torque in a vehicle undercarriage in which the brake torque is transmitted to said vehicle undercarriage by a bar-shaped member and said bar-shaped member is loaded transversally by said brake torque, wherein said bar-shaped member is essentially hollow and said measuring means are located in the interior of said bar-shaped member. The following claims indicate preferred embodiments and sensors for use in the device. 
         [0007]    Accordingly, the principle of the invention consists in providing the bolt that serves for transmitting the brake torque with means for measuring its deformation. The arrangement is based upon the observation that by the arising great forces, the bolt is deformed to an extent that allows a measurement. More specifically, the measuring device can be arranged in the interior of the hollow bolt. One possibility thereof is its direct attachment to the surface of the bolt, e.g. in the form of strain gauges. 
         [0008]    Another possibility consists in an indirect coupling. To this end, the bolt is provided with a sensor that is inserted therein in a suitable manner so as to contact the interior of the bolt so closely that it is deformed along with the bolt during braking. In its interior, the sensor is provided with strain gauges or the like to detect the arising tensions and/or deformations. Furthermore, in both cases, evaluating electronics may additionally be provided for conditioning the measuring signals locally. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]    The invention shall be explained in more detail by means of preferred exemplary embodiments and with reference to figures. 
           [0010]      FIG. 1  schematic illustration of an aircraft landing gear (bogie); 
           [0011]      FIG. 2  longitudinal section of a bolt with a first embodiment of the measuring device; 
           [0012]      FIG. 3  longitudinal section in analogy to  FIG. 2  of a second embodiment of the invention; 
           [0013]      FIG. 4  cross-section according to IV-IV in  FIG. 3  in unstressed condition; and 
           [0014]      FIG. 5  cross-section as in  FIG. 4  in stressed condition. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0015]      FIG. 1  shows the basic structure of an aircraft landing gear  1 . On a landing gear strut  2 , a bogie train  4  is mounted by a pivot  3 . The bogie train supports wheels  5 . Wheels  5  are provided with brakes  6  that are actuatable by (e.g. hydraulic) actuators  7 . The stationary disk stack of brake  6  has a lever  8  with a bore  9 . A torque arm  12  is fastened to bore  9  as well as to an attachment point  10  and transmits the brake torque from brake  7  to landing gear  1  during brake application. 
         [0016]    The depicted basic construction of an aircraft landing gear corresponds to the state of the art for larger aircraft. Alternatively, instead of using torque arm  12 , it is also common, especially in smaller aircraft, to transmit the torque from the brake directly to the landing gear, e.g. by a direct bolt connection. 
         [0017]      FIG. 2  shows a longitudinal section of the connection between brake torque arm  12  and the stationary part  14  of brake  6 , the above-mentioned lever  8  being considered as belonging to stationary part  14 . 
         [0018]    Bolt  16  extends through bore  9  in lever  8  as well as through a bore  15  at the end of brake torque arm  12 . Bolt  16  is made of a high-strength material and is largely hollow to reduce its weight. However, during brake application, it is still noticeably deformed. For example, a deformation of 4/10 mm (0.4 mm) has been observed in a bolt having an internal diameter of 50 mm. 
         [0019]    In order to measure this deformation, strain gauges  18 ,  20  are attached to the inner wall of bolt  16 . More specifically, strain gauges  18 ,  20  are arranged such that their measuring directions form an angle of approx. 45° with longitudinal axis  22  of bolt  16 . They are furthermore arranged symmetrically to the plane that is parallel to axis  22  and perpendicular to the brake torque (arrow  24 ). This arrangement allows a measurement of the shearing strain. At the same time, this arrangement allows separating the deformation of bolt  16  that results from the brake forces from other causes such as vibrations and shocks. 
         [0020]    If two strain gauges are used, they may form part of a half-bridge arrangement. Preferably, however, a second pair (not shown) is provided opposite strain gauge pair  18 ,  20  to form a full measuring bridge. To this end, as the case may be, an antiparallel configuration or an inverted arrangement (mirrored on the plane perpendicular to longitudinal axis  22 ) will be used. Due to the spatial proximity of strain gauges  18 ,  20  it is possible to prefabricate them as a unit with the correct mutual alignment of the measuring directions. Suitable circuits are known in the art per se. 
         [0021]    For the function of the measuring arrangement it is important that the strain gauges are in the correct position relative to the action of brake torque  24 . For this purpose, a ring  26  may be mounted on stationary part  14 . A pin  28  is pushed through this ring  26  and bolt  16  and is secured in a suitable manner, thereby locking bolt  16  against rotation. 
         [0022]    On a circuit board  31  inserted in the same recess  30  in bolt  16  where strain gauges  18 ,  20  are located, a circuit for driving strain gauges  18 ,  20  and evaluating their signals is provided. Recess  30  is sealed by a plate  32  in order to protect circuit board  31  and strain gauges  18 ,  20  from environmental influences. In the center of the latter there is an electric connector  34 , here a threaded connector, to which the power supply and signal lines for the measuring arrangement are connected. 
         [0023]    Thus, the entire measuring device can be attached to bolt  16  without requiring a recertification of this safety-relevant part. Due to the fact that strain gauges are used which are designed for the measurement of the shearing strain and pairs of which can thus be prefabricated in the required configuration, providing a bolt  16  with these strain gauges while maintaining their correct orientation with respect to one another and to bolt  16  is simplified. Moreover, two pairs of strain gauges may be used which form a measuring full bridge. 
         [0024]    A different attachment of the measuring device is shown in the embodiment of  FIG. 3 . The parts that correspond to  FIG. 2 , such as brake torque arm  12 , stationary brake part  14 , and the orientation means for the measuring device including ring  26  and pin  28 , are designated by the same reference numerals and have the same functions. In this embodiment, a sensor  38  is inserted into bolt  16  whose enclosure  39  is adapted to the internal diameter of bolt  16  and is slightly press-fitted such that it is deformed along with bolt  16 . In the present embodiment, the enclosure is provided with four projections  40  (see  FIGS. 4 ,  5 ). The projections have a rounded cross-section and are regularly distributed over the circumference of sensor enclosure  39 , i.e. at a mutual angle of 90°. More specifically, sensor  38  is preferably arranged in bolt  16  such that the connecting lines between opposed projections  40  are parallel or perpendicular to brake torque  24  in order to obtain an optimum transmission of the deformation to sensor enclosure  39 . 
         [0025]    As appears in  FIG. 3 , projections  40  only extend over a part of the total length of sensor  38 . More particularly, they are provided at the junction between stationary brake part  14  and torque arm  12 . For support purposes, further such projections are provided at the enclosure end and are traversed by orientation pin  28 . 
         [0026]    Enclosure  39  of sensor  38  has to be sufficiently flexible to follow the deformation of bolt  16 . For the same reason, projections  40  have to be sufficiently rigid relative to enclosure  39  as a whole to transmit this deformation to enclosure  39  as completely as possible. 
         [0027]    In the interior of the enclosure, strain measuring means  42 ,  44  are arranged, more particularly in the form of strain gauges. More specifically, strain gauges  42 ,  44  are arranged such that they are sensitive to an angular strain or a compression strain of the surface, i.e. a deformation in parallel to the circumference in the plane perpendicular to longitudinal direction  22  of bolt  16 . This arrangement is based on the observation that bolt  16  is subject to both an axial strain or compression strain and an ovalization, i.e. during brake application, the cross-section of bolt  16 , which is normally circular in the unstressed condition, becomes oval. 
         [0028]    For a better detection of this ovalization, four sets of strain gauges  42 ,  44  are regularly distributed over the circumference. 
         [0029]    The sensor again contains a circuit board  31  with a conditioning circuit, and at one end of the sensor, a connector  34  for the electric connection of the sensor is provided. 
         [0030]    From the preceding description, numerous modifications are accessible to those skilled in the art without leaving the scope of the invention as defined by the claims. In particular, it is conceivable: 
         [0031]    to use other strain measuring elements than strain gauges; 
         [0032]    a different fixating arrangement than pin  28  and ring  26  for defining the orientation of the measuring elements relative to brake torque  24 ; 
         [0033]    to use a greater number of measuring elements while possibly omitting an orientation device (ring  26 , pin  28 ) and providing a corresponding evaluation of the signals in order to obtain a measurement in any angular orientation of the measuring arrangement with respect to torque  24 . 
         [0034]    A brake torque measuring device (strain gauges  18 ,  20 ; sensor  38 ) is additionally or alternatively mounted in another location where a suitable connecting element is situated which is transversally loaded by the braking force respectively by the corresponding torque, e.g. in attachment point  10  or in the bolt that connects the stationary brake part to the landing gear in landing gears having no torque arm  12 . 
         [0035]    The measuring means that are directly attached to bolt  16  measure the strain respectively compression strain directly, i.e. they are e.g. arranged opposite each other in the direction of force  24 . 
         [0036]    A support (disk, wall portion) on which the measuring means are located is arranged in the bolts or in sensor  38 . The measuring means deliver a signal in function of the deformation of the support.