Abstract:
The rotation state of the bearing such as vibration is accurately sensed. 
     A plural of rollers rollably retained with a retainer are accommodated between an inner ring and an outer ring, and a sensor for sensing the rotation state of the bearing is directly attached to the outer ring. More specifically, the outer ring, having a housing attached to its outside diameter upper part, includes a radially protruding projection in the outside diameter lower part, and the sensor is attached to the end surface of the projection.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention The present invention relates to a bearing with a sensor or a roller bearing for rotatably supporting railway vehicle axles for example, and more particularly to a bearing with a sensor for sensing its rotation state. 
         [0002]    2. Description of the Related Art Roller bearings that rotatably support the axles of railway vehicles such as freight cars are specially designed and produced for railway vehicle axle applications, and generally, they are double row cylindrical roller bearings or double row tapered roller bearings. The railway vehicles, such as freight cars as mentioned above, are required to include an ABS (antilock braking system) device for each car as a safety feature for the purpose of high-speed running. 
         [0003]    There has been a bearing with a sensor attached to the bearing for sensing its rotation state during the drive of the railway vehicle so as to allow this ABS device to be mounted (see, for example, Japanese Patent Laid-Open Publication No. Hei 10-224909). 
         [0004]    The bearing with a sensor of this type has a structure shown in  FIG. 11 , wherein a plurality of tapered rollers  34  rotatably retained with a retainer  33  are accommodated between an inner ring  31  and an outer ring  32 , and an oil seal case  35  is fitted to the inside diameter end of the outer ring  32 . A sensor  36  that senses the rotation state of the inner ring  31  relative to the outer ring  32  is attached to the oil seal case  35 . 
         [0005]    The above-described bearing with a sensor disclosed in Japanese Patent Laid-Open Publication No. Hei 10-224909 has its oil seal case  35  with the sensor  36  only being fitted into the inside diameter end of the outer ring  32 , because of which the rigidity of the oil seal case  35  is low in the end portion where the sensor  36  is attached. 
         [0006]    As the sensor  36  is attached to the distal end portion of the oil seal case  35  with this component design, if the sensor  36  is a vibration sensor, it is very hard to accurately measure the vibration in the bearing. Also if the sensor  36  is a temperature sensor, it will measure the temperature of the oil seal case  35  and it is hard to sense the precise temperature of the bearing components. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention was proposed in view of the above-described problems, and its object is to provide a bearing with a sensor that can accurately sense the rotation state of the bearing such as vibration. 
         [0008]    As technical means for achieving the above object, the bearing with a sensor according to the present invention is characterized in that a plural of rollers rollably retained with a retainer are accommodated between an inner ring and an outer ring, and a sensor for sensing a rotation state of the bearing is directly attached to the outer ring. The “rotation state of the bearing” used herein means the number and direction of rotation of the inner ring, vibration of the bearing, and temperature of the outer ring. Therefore, the sensor for sensing the rotation state may be, for example, a rotary sensor, a vibration sensor, or a temperature sensor. The rollers, which are one of the bearing components, may be double row cylindrical rollers or double row tapered rollers. 
         [0009]    In the bearing with a sensor of the present invention, since the sensor for sensing the rotation state of the bearing is directly attached to the outer ring, i.e., the sensor is fixedly attached to the outer ring that has high rigidity, precise determination of the rotation state of the bearing such as vibration can be easily achieved using the sensor. 
         [0010]    The present invention is applicable to a bearing for rotatably supporting an axle of a railway vehicle, and in the case where the bearing is used for the railway vehicle axle, a housing is provided to the outside diameter upper part of the outer ring as part of the structure for attaching the bearing to the vehicle. In such a structure wherein the housing is provided to the outside diameter upper part of the outer ring, it is desirable that the sensor be arranged in the outside diameter lower part of the outer ring. With this design, the sensor can be directly attached to the outer ring easily with the housing. 
         [0011]    A possible design for attaching the sensor to the outer ring may include a radially protruding projection formed to a portion of the outside diameter of the outer ring, with the sensor being attached to the end surface of the projection. With this design, the projection formed to the outside diameter of the outer ring is stopped from rotating by making contact with the housing, whereby disconnection of wires of the sensor is prevented. 
         [0012]    According to the present invention, since the sensor for sensing the rotation state of the bearing is directly attached to the outer ring, i.e., the sensor is fixedly attached to the outer ring that has high rigidity, precise determination of the rotation state of the bearing such as vibration can be easily achieved using the sensor. As a result, the product quality and reliability are largely improved, and the bearing with a sensor has excellent safety features when used for a railway vehicle axle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]      FIG. 1  is a cross-sectional view illustrating one embodiment of a bearing with a sensor in accordance with the present invention, which is a double row tapered roller bearing with a rotary sensor provided in the lower part of an outer ring. 
           [0014]      FIG. 2  is a bottom view of  FIG. 1 . 
           [0015]      FIG. 3  is a left side view of  FIG. 1 . 
           [0016]      FIG. 4  is a cross-sectional view illustrating another embodiment of the present invention, or a bearing with a rotary sensor attached to an outer ring using a different attachment structure. 
           [0017]      FIG. 5  is a bottom view of  FIG. 4 . 
           [0018]      FIG. 6  is a left side view of  FIG. 4 . 
           [0019]      FIG. 7  is a schematic cross-sectional view illustrating yet another embodiment of the present invention, or a double row tapered roller bearing with a rotary sensor provided in the upper part of an outer ring. 
           [0020]      FIG. 8  is a left side view of  FIG. 7  without the front cover. 
           [0021]      FIG. 9  is a cross-sectional view illustrating still another embodiment of the present invention, or a bearing with a rotary sensor attached to an outer ring using a different attachment structure. 
           [0022]      FIG. 10  is a top plan view of  FIG. 9 . 
           [0023]      FIG. 11  is a schematic cross-sectional view illustrating a conventional bearing with a sensor. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]      FIG. 1  to  FIG. 10  are given for the description of one embodiment of the bearing with a sensor of the present invention used as an axle bearing of a railway vehicle such as a freight car,  FIG. 1  to  FIG. 6  illustrating one embodiment in which the sensor is attached to the outside diameter lower part of the outer ring, and  FIG. 7  to FIG. illustrating another embodiment in which the sensor is attached to the outside diameter upper part of the outer ring. The housing is not illustrated in the embodiment of  FIG. 7  to  FIG. 10 . 
         [0025]    The bearing with a sensor shown in the embodiment shown in  FIG. 1  to  FIG. 3  is mainly composed of a pair of inner rings  2  axially adjacent to each other with a spacer  1  therebetween, an outer ring  3  arranged on the outer side of the inner rings  2 , two rows of rollers  4  (tapered rollers in the drawings) interposed between the raceways of the inner rings  2  and the outer ring  3  such as to be freely rollable, and retainers  5  for retaining each row of rollers  4  circumferentially at circular pitches. This bearing is used as an axle bearing of a railway vehicle, and therefore includes a housing  13  attached to the outside diameter upper part of the outer ring  3  for mounting this bearing to the railway vehicle. 
         [0026]    Oil seal cases  7  having oil seals  6  inside are fitted to the inner circumferential surface at both ends of the outer ring  3 , and oil-cutting members  8  that are in sliding contact with the oil seals  6  are arranged on the outer side of each inner ring  2 . A front cover  9  is arranged at the shaft end and a rear cover  10  is arranged on the opposite side from the front cover  9 , with the front cover  9  being fastened to the axle  12  with a bolt  11  to securely attach the bearing to the axle  12 . 
         [0027]    In this embodiment, the outer ring  3  includes a radially protruding projection  14  in the lower part of the outside diameter thereof, and a rotary sensor  15  is attached to the end surface of this projection  14 . In this embodiment, the rotary sensor  15  is securely attached to the projection  14  of the outer ring  3  using two screws  16 . The rotary sensor  15  can be a reflection type photoelectric switch or the like, and an encoder  17  is arranged on the outer circumferential end surface of the front cover  9  opposite the light transmitting/receiving part of the sensor. 
         [0028]    With the rotary sensor  15  attached to the outer ring  3  as described above, the number of rotation of the inner ring  2  (axle  12 ), which is a rotating member relative to a stationary member or the outer ring  3 , can be measured. Since the rotary sensor  15  is firmly attached to the outer ring  3  that has high rigidity, the measurement of the number of rotation of the bearing can be made accurately with this rotary sensor  15 . Also, because the rotary sensor  15  is attached to the outside diameter lower part of the outer ring  3  where the housing  13  is not attached, the housing  13  will cause no obstruction to the attachment of the rotary sensor  15 . 
         [0029]    While this embodiment applies the structure wherein the rotary sensor  15  is securely attached to the projection  14  of the outer ring  3  with two screws  16 , other attachment structures may be applied, such as the one shown in  FIG. 4  to  FIG. 6 . In the structure shown in  FIG. 4  to  FIG. 6 , two through holes  18  and  19  are formed along the axial direction in the projection  14  of the outer ring  3  and in the flange of the rotary sensor  15 , and both ends of a U-shaped member  20  having screws at the tips are inserted into these through holes  18  and  19 , with the respective ends being fastened with nuts  21 , so that the rotary sensor  15  is securely attached to the projection  14  of the outer ring  3 . 
         [0030]    While the bearing has a rotary sensor  15  attached to the lower part of the outer ring  3  in the embodiment described above, the invention is not limited thereto, and the rotary sensor  15  can be attached to the upper part of the outer ring  3  as shown in  FIG. 7  and  FIG. 8 . The attachment structure of the rotary sensor  15  includes, similarly to the embodiment shown in  FIG. 1  to  FIG. 3 , a projection  14  radially protruding from the outside diameter upper part of the outer ring  3  and two screws  16  for securely attaching the rotary sensor  15  to the end surface of the projection  14 . 
         [0031]    In this embodiment, the housing, which is not shown, is attached to the outside diameter upper part of the outer ring  3 , and the projection  14 , which is formed to the upper part of the outside diameter of the outer ring  3  and to which the rotary sensor  15  is attached, is stopped from rotating by making contact with the housing, whereby disconnection of wires of the rotary sensor  15  is prevented. 
         [0032]    Further, in another attachment structure for the rotary sensor  15 , similarly to the embodiment shown in  FIG. 4  to  FIG. 6 , through holes  18  and  19  may be formed in the projection  14  of the outer ring  3  and in the flange of the rotary sensor  15  as shown in  FIG. 10 , and both ends of a U-shaped member  20  may be inserted into these through holes  18  and  19 , with the respective ends being fastened with nuts  21 , so that the rotary sensor  15  is securely attached to the projection  14  of the outer ring  3 . 
         [0033]    While a rotary sensor  15  is attached as a sensor for sensing the rotation state in this embodiment, a vibration sensor for sensing vibration of the bearing or a temperature sensor for sensing temperature inside the bearing other than the rotary sensor  15  may also be attached. Since these sensors are directly and fixedly attached to the outer ring  3  as mentioned above, vibration in the bearing can be measured accurately with a vibration sensor, and, temperature of the bearing components can be measured accurately with a temperature sensor.