Patent Publication Number: US-2013230351-A1

Title: Spline forming method for hub unit, hub unit, spline forming method for joint, and joint

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2012-046437 filed on Mar. 2, 2012 including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a hub unit, a spline forming method of forming splines in a portion of the hub unit, a joint that transmits rotary torque to the hub unit, and a spline forming method of forming splines in a portion of the joint. 
     2. Description of Related Art 
     In order to support a wheel such that the wheel is rotatable with respect to a suspension provided on a body of a vehicle, for example, a wheel support device shown in  FIG. 5  is used. The wheel support device includes a hub unit  80  and a joint  90  that transmits torque to the hub unit  80 . 
     The hub unit  80  includes a fixed ring  81 , a rotary ring  82  and rolling elements  83  that are provided between the fixed ring  81  and the rotary ring  82 . The fixed ring  81  is fixed to the suspension. The wheel is connected to the rotary ring  82 . The rolling elements  83  are arranged between the fixed ring  81  and the rotary ring  82 . Internal splines  84  are formed in the inner periphery of the rotary ring  82  of the hub unit  80 . The joint  90  has an outer ring  89 . The outer ring  89  has a tubular body portion  88  and a shaft portion  87 . The shaft portion  87  extends from the body portion  88  in the axial direction. External splines  86  that mesh with the internal splines  84  are formed on the outer periphery of the shaft portion  87  so that torque transmission between the hub unit  80  and the joint  90  is allowed. 
     When the configuration shown in  FIG. 5  is employed, many processes are required to assemble the hub unit  80  and the joint  90  together. That is, the following processes are required. First, an alignment for positioning the hub unit  80  and the outer ring  89  of the joint  90  such that the hub unit  80  and the outer ring  89  extend along the same straight line is performed (first process). The shaft portion  87  of the joint  90  is press-fitted (temporarily press-fitted) into the rotary ring  82 , and the distal end of the shaft portion  87  is protruded from an axial end face (left end face in  FIG. 5 ) of the rotary ring  82  (second process). A temporary nut (not shown) is screwed to a threaded portion  87   a  formed at the distal end of the shaft portion  87  (third process). By screwing the temporary nut to the threaded portion  87   a,  the shaft portion  87  is press-fitted (fully press-fitted) into the rotary ring  82  until no gap remains between the rotary ring  82  of the hub unit  80  and the outer ring  89  of the joint  90  (fourth process). The temporary nut is removed from the shaft portion  87  (fifth process). A nut  85  is fastened to the threaded portion  87   a  of the shaft portion  87  (sixth process), The nut  85  is fixed to the axial end face of the rotary ring  82  by crimping, or the like, to prevent loosening of the nut  85  (seventh process). As shown in  FIG. 5 , the shaft portion  87  is press-fitted into the rotary ring  82  so that the external splines  86  that extend in the axial direction mesh with the internal splines  84  that extend in the axial direction. Therefore, particularly strict dimensional control is required to form the splines  86 ,  84 . As a result, many man-hours are required also in the process of forming the splines. 
     Therefore, in order to make it easier to assemble a hub unit and a joint together, for example, a wheel support device (wheel bearing device) described in Japanese Patent Application Publication No. 2008-284920 (JP 2008-284920 A) is used. In the wheel support device, first splines are formed in an annular side face of a rotary ring of the hub unit, the annular side face being on one side of the rotary ring in the axial direction, and second splines that mesh with the first splines are formed in an annular side face of an outer ring of the joint, the annular side face being on the other side of the outer ring in the axial direction. The first splines have a plurality of spline grooves that radiate from the center side of the annular side face of the rotary ring. The second splines have a plurality of spline grooves that radiate from the center side of the annular side face of the outer ring. 
     In the case of the wheel support device described in JP 2008-284920 A, the hub unit and the joint are assembled together in the following manner. First, the hub unit and the outer ring of the joint are arranged so as to face each other in the axial direction. Then, the first splines of the hub unit and the second splines of the joint are meshed with each other. After that, the hub unit and the outer ring of the joint are fastened together with a bolt. 
     In the case of the wheel support device described in JP 2008-284920 A, it is easy to assemble the hub unit and the joint together. The first splines of the hub unit and the second splines of the joint may be formed by, for example, machining through form rolling. However, the first splines and the second splines are formed independently from each other by machining. Therefore, a backlash in the circumferential direction and a misalignment in the axial direction are likely to occur between the first splines and the second splines that are to be meshed with each other due to, for example, a manufacturing error. If there is such a backlash, or the like, abnormal noise may be generated during transmission of torque or the performance of transmission of torque may decrease. Therefore, the splines that are formed in the hub unit need to have high accuracy. In addition, the splines that are formed in the side face of the joint and that are in mesh with the rotary ring of the hub unit also need to have high accuracy. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a spline forming method for a hub unit and a spline forming method for a joint, which make it possible to form splines with high accuracy more easily than in related art, and the hub unit and the joint in which splines with high accuracy are formed. 
     An aspect of the invention relates to a spline forming method for a hub unit that includes: a fixed ring that is fixed to a vehicle body-side member; a rotary ring to which a wheel is fitted; and rolling elements that are arranged between the fixed ring and the rotary ring. The spline forming method is a method for forming splines, which are to be meshed with a joint that transmits torque to the rotary ring, in a side face of the rotary ring of the hub unit, the side face being on one side of the rotary ring in an axial direction. According to the method, spline grooves are formed in the side face by subjecting the side face to broaching. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein: 
         FIG. 1  a longitudinal sectional view that shows a wheel support device according to an embodiment of the invention; 
         FIG. 2  is a perspective view of a side face of a rotary ring of a hub unit, the side face being on one side of the rotary ring in the axial direction; 
         FIG. 3  is a sectional view taken along the line X-X in  FIG. 2 ; 
         FIG. 4  is a perspective view of a side face of an outer ring of a joint, the side face being on the other side of the outer ring in the axial direction; and 
         FIG. 5  is a sectional view that shows an example of a hub unit and an outer ring of a joint according to related art. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     An embodiment of the invention will be described with reference to the accompanying drawings.  FIG. 1  is a longitudinal sectional view that shows a wheel support device  1  that includes a hub unit  10  and a joint  30  according to one embodiment of the invention. The hub unit  10  is fitted to a suspension  2  provided on a body of a vehicle, and is used to support a wheel  3  such that the wheel  3  is rotatable with respect to the suspension  2 . The joint  30  is coupled to the hub unit  10 , and is used to transmit rotary torque to a rotary ring  12  of the hub unit  10 . The hub unit  10  and the joint  30  are fixedly coupled to each other with a bolt  4  that serves as a coupling member. 
     The lateral direction of the vehicle coincides with the axial direction of the wheel support device  1 , and the hub unit  10  and the joint  30  are provided side by side in the lateral direction of the vehicle. The hub unit  10  is provided outward of the joint  30  in the lateral direction, and the joint  30  is provided inward of the hub unit  10  in the lateral direction. In  FIG. 1 , the right side is one side in the axial direction (inner side in the lateral direction of the vehicle), and the left side is the other side in the axial direction (outer side in the lateral direction of the vehicle). 
     The hub unit  10  includes a fixed ring  11 , the rotary ring  12 , and balls (rolling elements)  13 . The fixed ring  11  is fixed to the suspension  2  with bolts (not shown). The wheel  3  is fitted to the rotary ring  12 . The balls  13  are provided between the fixed ring  11  and the rotary ring  12 . The fixed ring  11  is arranged radially outward of the rotary ring  12 , and a center line L of the rotary ring  12  coincides with the center line of the fixed ring  11 . 
     The fixed ring  11  has a tubular body portion  16  and a flange portion  17 . Raceway surfaces  14 ,  15  are formed on the inner periphery of the body portion  16 . The flange portion  17  extends radially outward from the body portion  16 . The flange portion  17  is fixed to the suspension  2 . Thus, the hub unit  10  is fixed to a vehicle body-side member. 
     The rotary ring  12  has a hollow shaft portion  19 , a flange portion  20 , and an annular inner ring member  21 . A through-hole  18  is formed at the center of the shaft portion  19 . The flange portion  20  extends radially outward from a portion of the shaft portion  19 , the portion being on the other side of the shaft portion  19  in the axial direction. The inner ring member  21  is fitted onto a portion of the shaft portion  19 , the portion being on one side of the shaft portion  19 . The through-hole  18  is formed so as to linearly extend along the center line L of the rotary ring  12 . The inner ring member  21  is fixed to the shaft portion  19  by being clinched by a large-diameter portion  22 . The large-diameter portion  22  is formed by plastically deforming an end portion of the shaft portion  19  radially outward, the end portion being on the one side of the shaft portion  19  in the axial direction. Raceway surfaces  23 ,  24  are formed on the outer periphery of the shaft portion  19  and the outer periphery of the inner ring member  21 , respectively. First splines (spline teeth)  26  are formed in a side face  25  of the large-diameter portion  22 , the side face  25  being on one side (right side in  FIG. 1 ) of the large-diameter portion  22  in the axial direction. 
     The balls  13  are arranged in the circumferential direction, and are arranged in two rows. The balls  13  arranged in one of the rows roll on the raceway surfaces  14 ,  23 , and the balls  13  arranged in the other row roll on the raceway surfaces  15 ,  24 . The balls  13  in each row are retained at equal intervals in the circumferential direction by a cage  27 . The balls  13 , the fixed ring  11  and the rotary ring  12  constitute a double-row angular contact ball bearing. 
       FIG. 2  is a perspective view of the side face  25  of the rotary ring  12  (large-diameter portion  22 ) of the hub unit  10 . The side face  25  faces one side in the axial direction (faces inward in the lateral direction of the vehicle), and is formed of an annular face that has an opening  18   a  of the through-hole  18  (see  FIG. 1 ) at its center. The first splines  26  are formed in the side face  25 . The side face  25  is a face that is perpendicular to the center line L of the rotary ring  12 . 
     The first splines  26  include a plurality of (four in the present embodiment) spline groove groups  50 ,  60 ,  50 ,  60 . The spline groove groups  50 ,  60 ,  50 ,  60  are arranged at predetermined intervals around the opening  18   a  of the through-hole  18 . In the present embodiment, the four spline groove groups  50 ,  60 ,  50 ,  60  are arranged at equal intervals of 90 degrees about an intersection P of the center line L of the rotary ring  12  with the side face  25 . That is, a pair of spline groove groups  50 ,  50  is formed in the side face  25  so as to be point-symmetric at intervals of 180 degrees about the intersection P. As the other pair of spline groove groups, a pair of spline groove groups  60 ,  60  is formed in the side face  25  so as to be point-symmetric at intervals of 180 degrees about the same point (intersection P). The spline groove groups  50 ,  60 ,  50 ,  60  have the same configuration. 
     Each of the spline groove groups  50 ,  60  has a plurality of spline grooves that are parallel to each other. That is, each of the spline groove groups  50 ,  60  includes a middle spline groove  51  and other spline grooves  52 . The spline groove  51  extends linearly in the radial direction (in one direction). The other spline grooves  52  are parallel to the spline groove  51  and extend linearly. The spline grooves  52  are formed on respective sides of the middle spline groove  51  (respective sides of the middle spline groove  51  in the rotation direction of the rotary ring  12 ). Each of the spline groove groups  50 ,  60  according to the present embodiment has the three spline grooves  51 ,  52 ,  52 . The number of the spline grooves may be changed on the basis of the magnitude of transmission torque. 
     Each of the spline grooves  51 ,  52 ,  52  is formed in the side face  25  by subjecting the side face  25  to broaching. A side face ( 25 ) that has not been subjected to broaching is a flat surface. Grooves are formed in the flat surface by performing machining with the use of a broaching tool (not shown) that is a long cutting tool, and the grooves are used as the spline grooves  51 ,  52 ,  52 . Because the broaching tool is driven linearly in its longitudinal direction, the spline grooves  51 ,  52 ,  52  formed in the side face  25  also have a linear shape. In addition, the finished sectional shape of each of the spline grooves  51 ,  52 ,  52  has substantially the same as the sectional shape of the broaching tool used in machining. That is, the sectional shape of a tooth of the broaching tool is transferred to the side face  25  of the rotary ring  12 . The broaching tool is a cutting tool that is used in a broaching machine. The broaching tool is formed of a linear metal rod, and multiple cutting blades are arranged in its longitudinal direction. Broaching is performed by reciprocating the broaching tool in the longitudinal direction. 
     Through broaching, the spline groove groups  50 ,  50  (upper and lower spline groups  50 ,  50  on respective sides of the opening  18   a  in  FIG. 2 ) arranged so as to be point-symmetric at intervals of 180 degrees are formed at the same time. That is, as shown in  FIG. 2 , the middle spline groove  51  of the upper spline groove group  50  and the middle spline groove  51  of the lower spline groove group  50  extend along the same straight line, that is, a straight line that extends in the radial direction. Therefore, it is possible to form the middle spline grooves  51  at the same time through broaching. In addition, the side spline grooves  52  of the upper spline groove group  50  and the side spline grooves  52  of the lower spline groove group  50  extend along the same straight lines (straight lines that are offset from each other by a predetermined distance in a direction perpendicular to the radial direction). With this configuration, it is possible to form the side spline grooves  52  at the same time through broaching. This simultaneous machining also applies to the spline groove groups  60 ,  60  (the right and left spline groove groups  60 ,  60  on respective sides of the opening  18   a  in  FIG. 2 ). 
       FIG. 3  is a sectional view taken along the line X-X in  FIG. 2 . As shown in  FIG. 3 , in each spline groove group  50 , a protrusion (spline protrusion)  53  that extends linearly is formed between the spline groove  51  and each spline groove  52  that are adjacent to each other. As described above, because the spline grooves  51 ,  52  are formed by broaching, the sectional shape of each of the spline grooves  51 ,  52  does not change and is therefore constant in the groove longitudinal direction, Therefore, the sectional shape of each protrusion  53  also does not change and is therefore constant in its longitudinal direction. As shown in  FIG. 3 , each spline groove group  50  has the protrusions  53  and the spline grooves  51 ,  52  that are alternately formed in the direction perpendicular to the radial direction. In  FIG. 3 , the upper spline groove group  50  is illustrated. The groove shape, including the sectional shape, shown in  FIG. 3  also applies to the lower spline groove group  50  and the right and left spline groove groups  60 ,  60 . 
     Referring back to  FIG. 1 , the joint  30  includes an inner ring  32 , an outer ring  33  and a plurality of balls  34 . The joint  30  is a constant velocity joint in the present embodiment. The inner ring  32  is fixed to an end portion of a drive shaft  31 , the end portion being on the other side of the drive shaft  31  in the axial direction. The outer ring  33  is arranged radially outward of the inner ring  32 . The balls  34  are arranged between the inner ring  32  and the outer ring  33 . The outer ring  33  has a closed-end cylindrical shape. The outer ring  33  has a tubular portion  35  and a bottom portion  36 . The tubular portion  35  has a tubular shape. The bottom portion  36  is integrated with a portion of the tubular portion  35 , the portion being on the other side of the tubular portion  35  in the axial direction. A small tubular portion  36   a  that extends toward the other side in the axial direction (outward in the lateral direction of the vehicle) is formed at the center of the bottom portion  36 . A bolt hole  37  is defined by the inner periphery of the small tubular portion  36   a.  A threaded portion  4   a  that is formed at the distal end of the bolt  4  is screwed into the bolt hole  37 . In the joint  30 , second splines (spline teeth)  39  are formed in a side face  38  of the bottom portion  36 , the side face  38  being on the other side of the bottom portion  36  in the axial direction. 
     The side face  38  of the bottom portion  36  faces the other side in the axial direction (faces outward in the lateral direction of the vehicle), and is formed of an annular face. The side face  38  has the second splines  39  that mesh with the first splines  26  (see  FIG. 2 ) formed in the hub unit  10 . That is, the second splines  39  are formed of spline protrusions that are fitted into the spline grooves  51 ,  52  shown in  FIG. 3  and spline grooves into which the protrusions  53  shown in  FIG. 3  are fitted. The second splines  39  may be formed by broaching. Alternatively, the second splines  39  may be formed by another method, such as milling. 
     As described above, the second splines  39  of the joint  30  are meshed with the first splines  26  of the hub unit  10 . When the second splines  39  and the first splines  26  are in mesh with each other, torque is transmitted between the rotary ring  12  of the hub unit  10  and the outer ring  33  of the joint  30 . According to a method of forming the splines  26 , which are to be meshed with the joint  30 , in the side face  25  of the rotary ring  12  of the hub unit  10 , the spline grooves  51 ,  52  are formed by subjecting the side face  25  to broaching as described above. With this method, the finished sectional shape (see  FIG. 3 ) of each of the spline grooves  51 ,  52  is substantially the same as the sectional shape of the broaching tool used in machining. Therefore, the finished sectional shape has high accuracy, and the machining speed is high. As a result, it is possible to form the splines with high accuracy more easily than in related art. 
     As shown in  FIG. 1 , the hub unit  10  and the joint  30  according to the present embodiment are assembled together in the following manner. First, the rotary ring  12  of the hub unit  10  and the outer ring  33  of the joint  30  are arranged so as to face each other in the axial direction. Then, the first splines  26  formed in the side face  25  of the rotary ring  12  and the second splines  39  formed in the side face  38  of the outer ring  33  are meshed with each other. After that, the hub unit  10  and the joint  30  are fastened together with the bolt  4 . In this way, in order to allow transmission of torque between the rotary ring  12  and the outer ring  33 , it is only necessary to bring the rotary ring  12  and the outer ring  33  close to each other in the axial direction, and mesh the first splines  26  of the rotary ring  12  and the second splines  39  of the outer ring  33  with each other. Therefore, assembly is easily performed. 
     The bolt  4  is a member that couples the rotary ring  12  and the outer ring  33 , which are arranged so as to extend along the same straight line, by fastening the rotary ring  12  and the outer ring  33  to each other in the axial direction. The bolt  4  has a bolt head  4   b  and a threaded portion  4   a.  The bolt head  4   b  is larger in diameter than the through-hole  18  of the rotary ring  12 . The threaded portion  4   a  is screwed into the bolt hole  37  that is formed in the outer ring  33 . The distal end portion (threaded portion  4   a ) of the bolt  4  is inserted into the through-hole  18  from the other side in the axial direction, and is screwed into the bolt hole  37 . In this way, the bolt  4  couples the rotary ring  12  to the outer ring  33  by fastening the rotary ring  12  to the outer ring  33  in the axial direction. In a state where the bolt  4  is fastened and an axial tension acts on the bolt  4 , the hub unit  10  and the joint  30  are coupled to each other and rotary torque is transmitted from the joint  30  to the hub unit  10 . 
     In the above-described embodiment, the first splines  26  having the spline grooves  51 ,  52  formed by broaching are formed in the side face  25  of the rotary ring  12  of the hub unit  10 . Alternatively, spline grooves that are formed by broaching may be formed in the joint  30 .  FIG. 4  is a perspective view of the side face  38  of the outer ring  33  of the joint  30 . The second splines  39  that are meshed with the hub unit  10  are formed in the side face  38 , and the spline grooves of the second splines  39  are formed by broaching. That is, by subjecting the side face  38  of the outer ring  33  to broaching, the spline grooves are formed in the side face  38 . 
     Particularly, in the embodiment shown in  FIG. 4 , each set of the second splines  39  includes spline grooves that are parallel to each other (as in the case of the rotary ring  12  of the hub unit  10  shown in  FIG. 2 ). That is, the second splines  39  include spline groove groups  150 ,  160 . Each of the spline groove groups  150 ,  160  has a spline groove  151  and other spline grooves  152 . The spline groove  151  extends linearly in the radial direction (in one direction). The other spline grooves  152  are parallel to the spline groove  151  and extend linearly. The spline grooves  151 ,  152  are formed by broaching. In addition, the upper and lower spline groove groups  150  in  FIG. 4  are formed in the side face  38  so as to be point-symmetric at intervals of 180 degrees about the intersection of the center line L of the outer ring  33  with the side face  38 . In addition, the right and left spline groove groups  160  are formed in the side face  38  so as to be point-symmetric at intervals of 180 degrees about the same point (the above-described intersection). The spline groove groups  150 ,  160 ,  150 ,  160  are arranged at equal intervals in the circumferential direction. 
     According to the embodiment shown in  FIG. 4 , the spline grooves  151 ,  152  are formed in the joint  30  by broaching. In this way, the finished sectional shape of each of the spline grooves  151 ,  152  is substantially the same as the sectional shape of the broaching tool used in machining. As a result, the finished sectional shape is highly accurate, and the machining speed is high. Therefore, it is possible to form the splines with high accuracy more easily than in related art. In the embodiment shown in  FIG. 4 , the first splines of the hub unit  10  that mesh with the second splines  39  of the joint  30  may be formed by broaching. Alternatively, the first splines of the hub unit  10  may be formed by another method, such as milling. 
     The wheel support device according to the invention is not limited to the one in the illustrated embodiment, and may be implemented in various other embodiments within the scope of the invention. For example, the joint  30  may be a joint other than the constant velocity joint. In the above-described embodiment, a torque transmission ring of the joint  30  is the closed-end cylindrical outer ring  33  (see  FIG. 1 ). Alternatively, a torque transmission ring may be a member that has another shape. 
     With the spline forming method for a hub unit and the hub unit according to the invention, it is possible to form the splines with high accuracy in the axial side face of the rotary ring more easily than in related art. With the spline forming method for a joint and the joint according to the invention, it is possible to form the splines with high accuracy in the axial side face of the torque transmission ring more easily than in related art.