Rotation transmission device

Abstract

A rotation transmission device having a high torque measurement resolution is provided. The rotation transmission device is provided with: a rotary-shaft unit ( 6 ) having a first and second rotary shaft ( 13, 14 ) combined so as to be coaxial and such that the end sections thereof can rotate relative to each other and a torsion bar ( 15 ) that is provided on the inner-diameter side of the first and second rotary shafts so as to be coaxial therewith, has one end section connected to the first rotary shaft ( 13 ), and has the other end section connected to the second rotary shaft ( 14 ); a first gear ( 7 ) fastened to the outer peripheral surface of the first rotary shaft ( 13 ); a second gear ( 8 ) fastened to the outer peripheral surface of the second rotary shaft ( 14 ); a coupling shaft ( 9 ) provided on the inner-diameter side of the torsion bar ( 15 ) so as to be coaxial therewith, having one end section connected to one rotary shaft ( 13 ), and having the other end section protruding from an end of the torsion bar ( 15 ) in the axial direction; a first encoder disposed and fixed on the other end of the coupling shaft ( 9 ) so as to be coaxial with the first rotary shaft ( 13 ) and having a first detected section ( 39 ); a second encoder fastened on the other end of the second rotary shaft ( 14 ) so as to be close to the first encoder and having a second detected section ( 40 ); and a sensor unit having at least one sensor ( 42 a, 42 b ) that faces the first and second detected sections ( 39, 40 ).

What is claimed is: 
     
         1 . A rotation transmission device comprising:
 a rotary-shaft unit that comprises: a first rotary shaft and a second rotary shaft that are both hollow, and together with being arranged so as to be concentric with each other, are combined so that the end sections of each are able to rotate relative to each other, and in this state are supported by a housing so as to rotate freely; and a torsion bar that is hollow and concentrically arranged on the inner-diameter side of the first and second rotary shafts, with one end section being connected to the first rotary shaft so that relative rotation is not possible, and the other end section being connected to the second rotary shaft so that relative rotation is not possible;   a first gear that is provided in the middle section in the axial direction of the outer-circumferential surface of the first rotary shaft;   a second gear that is provided in the middle section in the axial direction of the outer-circumferential surface of the second rotary shaft;   a first encoder that is fastened to one of the first and second rotary shafts so as to be concentric with that one rotary shaft, and comprising a first detected section that is magnetized so that the magnetic characteristics change in an alternating manner at a uniform pitch;   a second encoder that is fastened to the other of the first and second rotary shafts so as to be concentric with that other rotary shaft, and comprising a second detected section that is magnetized so that the magnetic characteristics change in an alternating manner at a uniform pitch; and   a sensor unit that is supported by the housing, and comprises at least one sensor that faces the first and second detected sections, and causes an output signal to change in correspondence to the change in magnetic characteristics of a portion of the first and second detected section where the at least one sensor faces.   
     
     
         2 . The rotation transmission device according to  claim 1 , wherein the torsion bar comprises a spring section, which is a portion in the middle section in the axial direction of the torsion bar that undergoes elastic torsional deformation when torque is transmitted; the dimensions of that spring section being larger than the space in the axial direction between the first and second gears. 
     
     
         3 . The rotation transmission device according to  claim 2 , wherein the spring section comprises a tube section having a wall thickness in the radial direction in the middle section in the axial direction except for the portions of the edges on both ends in the axial direction that is less than the portions of the edges on both ends in the axial direction, and is such that the inner-circumferential surface and outer-circumferential surface are single cylindrical surfaces that are concentric with each other; the ratio di/do of the inner-diameter dimension di and outer-diameter dimension do of that tube section being within the range 0.5≦di/do≦0.8. 
     
     
         4 . The rotation transmission device according to  claim 2 , wherein the spring section comprises a tube section having a wall thickness in the radial direction in the middle section in the axial direction except for the portions of the edges on both ends in the axial direction that is less than those portions of the edges on both ends in the axial direction, and is such that the inner-circumferential surface and outer-circumferential surface are single cylindrical surfaces that are concentric with each other; the ten-point average roughness Rz of that tube section being within the range Rz≦22 μm. 
     
     
         5 . The rotation transmission device according to  claim 1 , wherein the torsion bar is such that the one end section and the other end section are connected to the end sections of the first and second rotary shafts that are opposite the end sections that are combined together. 
     
     
         6 . The rotation transmission device according to  claim 1 , further comprising a coupling shaft that is arranged on the inner-diameter side of the torsion bar and arranged concentric with the torsion bar, with one end section being connected to one of the rotary shafts so that relative rotation is not possible, and the other end section protruding in the axial direction from the end section of the torsion bar; and wherein
 the first encoder is fastened to the other end section of the coupling shaft;   the second encoder is fastened to the end section on the other end section side of the coupling shaft of the other rotary shaft so at to be close to the first encoder; and   the first and second detected sections are arranged so as to be close to each other.   
     
     
         7 . The rotation transmission device according to  claim 6 , wherein a sliding bearing is provided between the inner-circumferential surface of the end section on the other end section side of the coupling shaft of the other rotary shaft and the outer-circumferential surface of the coupling shaft or a fitting cylindrical section of a metal core of the first encoder that fits on the coupling shaft. 
     
     
         8 . The rotation transmission device according to  claim 6 , wherein the coupling shaft comprises a rim section on the outer-circumferential surface of the one end section, and the coupling shaft is supported by that rim section being pressure fitted with the inner-circumferential surface of the end section on the one end side of the coupling shaft of the one rotary shaft so that relative rotation with respect to that one rotary shaft is not possible. 
     
     
         9 . The rotation transmission device according to  claim 6 , wherein
 the other rotary shaft is supported by a rolling bearing that is located between the portion of the outer-circumferential surface of the other rotary shaft that is near the end section on the other end section side of the coupling shaft and the inner-circumferential surface of the housing so as to rotate freely with respect to the housing; and   the sensor unit comprises a sensor cover and a detecting section that is fastened to and supported by the inside of the sensor cover; and by fastening the sensor cover to and supporting the sensor cover by the end section of the outer ring of the rolling bearing on the other end section side of the coupling shaft of the other rotary shaft so that the first and second encoders are located in a space inside the sensor cover, the detecting section is made to face the first and second detected sections.   
     
     
         10 . The rotation transmission device according to  claim 9 , wherein a seal device is located between the space where plural rolling bodies of the rolling bearing are located and the space on the inside of the sensor cover where the first and second detected sections are located, and functions as a partition between these spaces. 
     
     
         11 . The rotation transmission device according to  claim 6 , wherein
 the other rotary shaft is supported by a rolling bearing that is located between the portion of the outer-circumferential surface of that other rotary shaft near the end section on the other end section side of the coupling shaft and the inner-circumferential surface of the housing so as to rotate freely with respect to the housing; and   the second encoder is fastened around the outside of the end section of the inner ring of the rolling bearing on the other end section side of the coupling shaft.   
     
     
         12 . The rotation transmission device according to  claim 11  wherein
 the first and second detected sections are both cylindrical shaped; and 
 at least one end section in the axial direction of the first and second detected sections is arranged around the outer-diameter side of the end section of the other rotary shaft on the other end section side of the coupling shaft, or another part that is fastened around the outside of that end section, in a position that overlaps in the radial direction that end section of the other rotary shaft or that other part. 
 
     
     
         13 . The rotation transmission device according to  claim 1 , wherein
 the first encoder is fastened to the first rotary shaft in a position between the first and second gears in the axial direction; and   the second encoder is fastened to the second rotary shaft in a position between the first and second gears in the axial direction.   
     
     
         14 . The rotating transmission device according to  claim 1 , wherein
 the rotary-shaft unit is supported by the housing by plural rolling bearings so as to rotate freely; and   the first rotary shaft or second rotary shaft is integrally formed with the inner ring of at least one of the plural rolling bearings.   
     
     
         15 . The rotation transmission device according to  claim 1 , wherein the first rotary shaft or second rotary shaft is integrally formed with the torsion bar. 
     
     
         16 . The rotation transmission device with torque measurement device according to  claim 1 , wherein
 the sensor unit comprises a first sensor that faces the first detected section, and a second sensor that faces the second detected section; and   the first and second sensors generate output signals that change in correspondence to the change in magnetic characteristics of the portions of the first and second detected sections that the first and second sensors face.   
     
     
         17 . The rotation transmission device according to  claim 1 , wherein
 the first and second encoders are made of a magnetic material;   the first and second detected sections comprise sections with material removed and solid sections that are arranged in an alternating manner at a uniform pitch in the circumferential direction, and are arranged so as to be close to each other and overlap in the radial or axial direction;   the sensor unit comprises a stator made of a magnetic material, and plural coils that are made of one conducting wire, and is constructed so that when a driving voltage is applied to the conducting wire, the output current or the output voltage from the conducting wire is used as an output signal;   the stator comprises: plural core sections that are arranged at a uniform pitch in the circumferential direction, extend in the overlapping direction of the first and second detected sections, and the tip-end surfaces face one of the first and second detected sections from one side in the overlapping direction of the first and second detected sections; and a circular ring-shaped rim section that connects together the base-end sections of the plural core sections; and   the plural coils are fastened one by one around the plural core sections, and are such that the winding directions of coils that are adjacent in the circumferential direction are opposite each other.   
     
     
         18 . The rotation transmission device according to  claim 1 , wherein
 the first and second encoders are made of a magnetic material;   the first and second detected sections comprise sections with material removed and solid sections that are arranged in an alternating manner at a uniform pitch in the circumferential direction, and the solid sections of the first detected section and the solid sections of the second detected section are arranged in an alternating manner in the circumferential direction with a space in between each in the circumferential direction; and   the sensor unit comprises one sensor that faces the portion where the solid sections are alternatingly arranged, and that sensor generates an output signal that changes in correspondence to the change in the magnetic characteristics of the portion where the sensor faces the solid sections of the first and second detected sections are alternatingly arranged.   
     
     
         19 . The rotation transmission device according to  claim 1 , wherein
 the first and second detected sections comprise a pair of cylindrical surfaces that face each other in the radial direction or a pair of wheel surfaces that face each other in the axial direction, and are arranged so the S poles and N poles of these detected sections alternate at a uniform pitch in the circumferential direction; and   the sensor unit comprises a magnetism-detecting element or coil that is arranged between the first and second detected sections, and the output voltage or output current from that magnetism detecting unit, or the output voltage or output current from the coil is used as the output signal.