Abstract:
A vane air motor is disclosed which is configured to prevent grease in a radial bearing from leaking into a rotor chamber. The vane air motor has a motor housing ( 20 ) having a rotor chamber, a rotor ( 22 ) with vanes ( 24 ) disposed in the rotor chamber, a first end wall ( 16 ) of the motor housing equipped with a radial bearing ( 50 ) rotatably supporting a support shaft portion ( 28 ) of the rotor, and a casing contiguously joined to the motor housing to form a compressed air supply chamber ( 44 ) together with the first end wall to supply compressed air into the rotor chamber through an air supply hole ( 46 ) formed in the first end wall. The first end wall has communication means ( 16 - 5, 16 - 6  and  16 - 7 ) for supplying compressed air from the compressed air supply chamber to the side of the first radial bearing closer to the rotor.

Description:
RELATED APPLICATIONS 
     This application is a continuation of PCT/JP2010/050019 filed on Jan. 5, 2010, which claims priority to Japanese Application No. 2009-002306 filed on Jan. 8, 2009. The entire contents of these applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vane air motor usable as driving means for pneumatic grinders and so forth. 
     2. Description of the Related Art 
     Conventionally, a vane air motor has a motor housing having a circular cylindrical inner peripheral surface defining a rotor chamber in the motor housing and a rotor eccentrically and rotatably installed in the motor housing and having vanes. The rotor has an output shaft portion projecting from one end surface of the rotor along the axis of rotation of the rotor. The output shaft portion is rotatably supported by an end wall of the motor housing. The rotor further has a support shaft portion projecting from the other end surface of the rotor in coaxial relation to the output shaft portion. The support shaft portion is rotatably supported by another end wall of the motor housing. The vane air motor further has a governor having a shaft-shaped rotating member coaxially secured to the support shaft portion to rotate together with the support shaft portion. When the shaft-shaped rotating member is rotated at a number of revolutions greater than a predetermined one, the governor limits a compressed air supply flow path supplying compressed air into the rotor chamber to suppress the number of revolutions of the rotor. 
     The output shaft portion and the support shaft portion are supported by radial bearings provided in the end walls, respectively, of the housing. The radial bearings comprise inner races secured to the output and support shaft portions, respectively, outer races provided radially outward of the respective inner races, and spherical or circular cylindrical rolling members provided between respective combinations of inner and outer races. 
     The motor housing and the governor are enclosed by a casing of a pneumatic grinder or the like to which the vane air motor is attached, and compressed air to be supplied into the rotor chamber is supplied through a compressed air supply chamber formed around the governor by the casing and through an air supply hole formed in the motor housing (Patent Literature 1 noted below). 
     Patent Literature: Patent Literature 1: Japanese Patent Application Publication No. 2001-9695 
     In the vane air motor having the above-described structure, the pressure in the compressed air supply chamber, in which the governor is disposed, is higher than in the rotor chamber in which the rotor is disposed. The rotor chamber and the compressed air supply chamber are divided from each other by the end wall of the motor housing which end wall receives the support shaft portion of the rotor extending therethrough and supports it by means of the radial bearing. Therefore, the above-noted difference in pressure causes grease in the radial bearing to gradually leak into the rotor chamber. Grease entering the rotor chamber adheres to vane end portions near the above-described end wall. Because of its high viscosity, the grease hinders smooth radial movement of the blades relative to the rotor. However, such does not occur at the radial bearing in the other end wall of the motor housing, and no grease adheres to vane end portions near the other end wall. Consequently, each blade is inclined between one end and the other end thereof. For this reason, the distal edge of each vane is pressed against the cylindrical wall surface with a stronger force at one end of the distal edge near the above-described other end wall than the other end of the same, and it is likely that the one end of the distal edge of the vane will become worn or broken. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve the above-described problem. 
     The present invention provides a vane air motor comprising a motor housing having a cylindrical wall with a circular cylindrical inner peripheral surface and first and second end walls attached to the opposite ends, respectively, of the cylindrical wall, to thereby define a rotor chamber in the motor housing. The vane air motor further comprises a rotor provided in the motor housing to extend along an axis of rotation parallel to and spaced from the center axis of the cylindrical inner peripheral surface. The rotor has an output shaft portion extending through the second end wall and a support shaft portion extending into the first end wall. Further, the vane air motor comprises vanes fitted to the rotor, first and second radial bearings attached to the first and second end walls, respectively, to rotatably support the support shaft portion and the output shaft portion, respectively, and a casing contiguously joined to the motor housing to form a compressed air supply chamber together with the first end wall to supply compressed air into the rotor chamber through an air supply hole formed in the first end wall. The first end wall has an end wall portion having an inner end surface abutting against an end surface of the cylindrical wall to define the rotor chamber together with the cylindrical inner peripheral surface of the cylindrical wall and an outer end surface opposite to the inner end surface in the axial direction of the rotor. The end wall portion further has a circular cylindrical hole extending through the first end wall in the axial direction of the rotor to receive the support shaft portion of the rotor therethrough. The first end wall further has a circular cylindrical wall portion extending from the outer end surface into the compressed air supply chamber opposite to the rotor chamber to define a bearing-housing recess housing the first radial bearing. The cylindrical wall portion has an inner peripheral surface to which an outer peripheral surface of an outer race of the first radial bearing is fitted and secured. The first radial bearing comprises the outer race, an inner race fitted and secured to an outer peripheral surface of the support shaft portion in coaxial relation to the outer race, and a plurality of rolling members provided between the outer race and the inner race. The first end wall has a communication groove extending from an end surface of the cylindrical wall portion to the outer end surface of the end wall portion along the inner peripheral surface of the cylindrical wall portion. 
     In this vane air motor, a communication groove is provided to extend from an end surface of the cylindrical wall portion to the outer end surface of the end wall portion along the inner peripheral surface of the cylindrical wall portion. Therefore, the air pressure in the compressed air supply chamber is transmitted as far as the side of the radial bearing closer to the rotor chamber through the communication groove, so that a substantially uniform air pressure acts on both the front and rear of the radial bearing (i.e., both sides of the radial bearing that are closer to the rotor chamber and the compressed air supply chamber, respectively), thereby making it possible to prevent the above-described leakage of grease from the radial bearing into the rotor chamber. Accordingly, it is possible to prevent the above-described problem that grease entering the rotor chamber adheres to the end portions of the vanes and causes the vanes to be inclined, resulting in that only one end of the vane distal edge slides against the cylindrical wall surface of the rotor chamber and is eventually worn excessively or broken. 
     Specifically, the outer end surface of the end wall portion may have a communication recess communicating with the communication groove. The communication recess is facing the radial bearing. More specifically, the communication recess may have an annular recess formed on the outer end surface of the end wall portion to extend circumferentially along the outer end surface radially outward of the cylindrical hole, and a radial recess formed on the outer end surface to extend radially from the annular recess to communicate with the communication groove. The purpose of this structure is to surely transmit the air pressure to the side of the radial bearing closer to the rotor chamber. 
     The vane air motor according to the present invention may comprise, in addition to the above-described constituent elements, a governor having a shaft-shaped rotating member secured to an end of the support shaft portion in coaxial relation thereto to rotate together with the support shaft portion. When the shaft-shaped rotating member is rotated at a number of revolutions greater than a predetermined one, the governor limits an air supply flow path provided in the casing to supply compressed air into the compressed air supply chamber to suppress the number of revolutions of the rotor. The shaft-shaped rotating member of the governor may have a flange extending radially of the shaft-shaped rotating member. The flange has an annular surface placed in close proximity to an end surface of the outer race remote from the rotor chamber. With this structure, when the shaft-shaped rotating member of the governor rotates in response to the rotation of the rotor, the flange rotates in close proximity to the outer race. Therefore, it is possible to prevent the air pressure of compressed air in the compressed air supply chamber from acting directly between the inner and outer races of the radial bearing, and hence possible to reduce the above-described leakage of grease. 
     Further, in the present invention, the end wall portion of the first end wall may have a radial hole extending through the end wall portion radially outward from the wall surface of the cylindrical hole and opening on the outer peripheral surface of the end wall portion to communicate with the atmosphere. With this structure, even if grease leaks from the radial bearing toward the rotor chamber, the grease can be discharged to the outside before reaching the rotor chamber. 
     An embodiment of the vane air motor according to the present invention will be explained below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal sectional side view of a vane air motor according to the present invention. 
         FIG. 2  is a sectional side view of a first end wall defining a rotor chamber of the vane air motor shown in  FIG. 1 . 
         FIG. 3  is an end view of the first end wall shown in  FIG. 2 . 
         FIG. 4  is an enlarged sectional side view of the first end wall having a radial bearing installed therein. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a pneumatic grinder (polishing machine)  12  having a vane air motor  10  according to the present invention. 
     The vane air motor  10  has a motor housing  20  having a cylindrical wall  14  with a circular cylindrical inner peripheral surface and first and second end walls  16  and  18  provided at the opposite ends, respectively, of the cylindrical wall  14 . The motor housing  20  has a rotor chamber  19  formed therein. The vane air motor  10  further has a rotor  22  eccentrically provided in the rotor chamber  19 , a plurality of vanes  24  fitted to the rotor  22 , and a support shaft portion  28  and an output shaft portion  26  that extend from the opposite ends of the rotor  22  along the axis of rotation of the rotor  22  and that are supported by the first and second end walls  16  and  18 , respectively. The vane air motor  10  has a governor  30  attached to an end of the support shaft portion  28 . The output shaft portion  26  is drivably connected to a rotating shaft  36  of a disk-shaped abrasive member  32  through a bevel gear  34 . 
     The rotating shaft  36 , the vane air motor  10  and the governor  30  are housed in a casing  38  of the pneumatic grinder  12 . The casing  38  comprises a plurality of casing parts  38 - 1  to  38 - 3 . The casing part  38 - 3  receives compressed air through a hose  40  connected to an air pump (not shown). The received compressed air is supplied into a compressed air supply chamber  44  through a communicating hole  42  extending through the casing part  38 - 3 . The compressed air supply chamber  44  is formed around the governor  30  by the casing part  38 - 3  and the first end wall  16 . The compressed air is further supplied into the rotor chamber  19  through air supply holes  46  and  48  provided at an upper position (as seen in the figure) of the first end wall  16  and the cylindrical wall  14 , respectively, to act on the vanes  24 , thereby causing the rotor  20  to rotate, and thus rotationally driving the abrasive member  32 . The compressed air having acted on the vanes  24  is discharged into the atmosphere through exhaust holes  49 . 
     The first end wall  16  is, as shown clearly in  FIG. 4 , provided with a circular cylindrical hole  60  communicating with the rotor chamber  19  and receiving the support shaft portion  28  therethrough and a bearing-housing recess  62  formed contiguous with the cylindrical hole  60  at the side of the first end wall  16  remote from the rotor chamber  19 . A radial bearing  50  is provided in the bearing-housing recess  62 . The radial bearing  50  has an inner race  52  secured around the support shaft portion  28 , an outer race  54  secured in the bearing-housing recess  62  at a position radially outward of the inner race  52 , and bearing balls  56  provided between the inner race  52  and the outer race  54 . The radial bearing  50  rotatably supports the support shaft portion  28 . Similarly, the second end wall  18  has a circular cylindrical hole  64  receiving the output shaft portion  26  therethrough, a bearing-housing recess  66 , and a radial bearing  68 . 
     The governor  30  has a shaft-shaped rotating member  70  coaxially secured to the end of the support shaft portion  28 , a sleeve  72  slidably provided around the shaft-shaped rotating member  70 , a pin  74  provided to extend diametrically through the shaft-shaped rotating member  70 , a coil spring  76  provided between the pin  74  and the sleeve  72  to urge the sleeve  72  leftward as seen in the figure, and a ball  78  housed in a radial hole provided in the shaft-shaped rotating member  70 . The ball  78  is engaged with a tapered surface provided on the sleeve  72  and pressed radially by the urging force of the coil spring  76 . When the rotor  20  is rotated at a number of revolutions greater than a predetermined one, together with the shaft-shaped rotating member  70 , the ball  78  moves radially outward by centrifugal force, thus urging the tapered surface of the sleeve  72  to be displaced rightward as seen in the figure. A coned disk spring  80  is provided at a position adjacent to a right-end surface of the shaft-shaped rotating member  70  so as to extend across the compressed air supply chamber  44  near the right end of the latter. The coned disk spring  80  has an air inlet hole  82  formed in the center thereof to introduce compressed air passed through the communicating hole  42  of the casing part  38 - 3  into the compressed air supply chamber  44 . When the sleeve  72  is displaced rightward as stated above, the sleeve  72  closes the air inlet hole  82  of the coned disk spring  80  to suppress the supply of compressed air into the rotor chamber  19 , thereby suppressing the rotation of the rotor  22 . The shaft-shaped rotating member  70  of the governor  30  is provided with a flange  86  extending radially of the rotating member  70 . A surface of the flange  86  that faces the radial bearing  50  is placed in close proximity to an end surface of the outer race  54  of the radial bearing  50  so that the pressure of compressed air in the compressed air supply chamber  44  acts on the inside of the radial bearing  50  after it has been reduced, thereby suppressing grease in the radial bearing  50  from being pushed out toward the rotor chamber  19 . 
     In the present invention, the following means is further provided to prevent grease in the radial bearing  50  from being pushed out into the rotor chamber  19  by the effect of compressed air in the compressed air supply chamber  44 . 
     That is, as shown in  FIGS. 2 to 4 , the first end wall  16  has an end wall portion  16 - 3  having an inner end surface  16 - 1  abutting against the end surface of the cylindrical wall  14  to define the rotor chamber  19  together with the cylindrical inner peripheral surface of the cylindrical wall  14 . The end wall portion  16 - 3  further has an outer end surface  16 - 2  opposite to the inner end surface  16 - 1 . Further, the first end wall  16  has a circular cylindrical wall portion  16 - 4  extending axially from the end wall portion  16 - 3  to define the bearing-housing recess  62 . The first end wall  16  has a pair of communication grooves  16 - 5  extending from the end surface of the cylindrical wall portion  16 - 4  to the outer end surface  16 - 2  of the end wall portion  16 - 3  along the inner peripheral surface of the cylindrical wall portion  16 - 4 . The communication grooves  16 - 5  allow the air pressure in the compressed air supply chamber  44  to be transmitted to the side of the radial bearing  50  closer to the rotor chamber  19 . Further, in the present invention, the first end wall  16  has an annular recess  16 - 6  and a pair of radial recesses  16 - 7  on the outer end surface  16 - 2  of the end wall portion  16 - 3 . The annular recess  16 - 6  is formed around the cylindrical hole  60 . The radial recesses  16 - 7  extend radially from the annular recess  16 - 6  to communicate with the communication grooves  16 - 5 , respectively. 
     With the above-described structure, the air pressure in the compressed air supply chamber  44  is applied on both the front and rear of the radial bearing  50  (i.e. both sides of the radial bearing  50  that are closer to the rotor chamber  19  and the compressed air supply chamber  44 , respectively), thereby suppressing grease from being pushed out of the radial bearing  50  toward the rotor chamber  19 . 
     Further, in the present invention, the end wall portion  16 - 3  of the first end wall  16  is provided with a radial hole  84  extending radially from the cylindrical hole  60  and opening on the outer peripheral surface of the end wall portion  16 - 3 , so that grease that may be pushed out slightly from the radial bearing  50  flows out through the radial hole  84  to the outside of the cylindrical wall  14  having the rotor chamber  19 . 
     The vane air motor  10  according to the present invention, which has the above-described structure, will make it possible to prevent leakage of grease from the radial bearing into the rotor chamber, which has been experienced with the conventional vane air motor. Further, in the vane air motor, a flange is provided on the shaft-shaped rotating member of the governor, and an annular surface of the flange is placed in close proximity to the end surface of the outer race. Because the annular surface rotates at a high speed relative to the end surface of the outer race, it forms a large flow path resistance with respect to a flow path through which the compressed air in the compressed air supply chamber formed around the governor passes to reach the radial bearing through the area between the annular surface and the end surface, whereby suppress grease in the radial bearing is suppressed from being pushed out into the rotor chamber by the compressed air. Accordingly, it is possible to prevent the problem that grease entering the rotor chamber adheres to the end portions of the vanes and causes the vanes to be inclined, resulting in that only one end of the vane distal edge slides against the cylindrical wall surface of the rotor chamber and is eventually worn excessively or broken.