Abstract:
Disclosed herein is a method and apparatus for manufacturing a tonewheel for vehicles. The present invention is capable of manufacturing a tonewheel having high precision and quality, thus enhancing the performance of the ABS, TCS, or VDC using the tonewheel.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method and apparatus for manufacturing a tonewheel, which is used as a component of a vehicle.  
       BACKGROUND OF THE INVENTION  
       [0002]     Generally, a tonewheel is a component which is mounted to a rotary object so as to sense the rotating speed of the object, such as a drive shaft or a wheel.  
         [0003]     For example,  FIG. 1  shows a tonewheel  70  which is mounted to a hub  1  of a wheel of a vehicle so as to sense the rotating speed of the wheel.  
         [0004]     That is, the tonewheel  70  is press-fitted into the hub  1  of the wheel, and is constructed as shown in  FIGS. 2 and 3 . Referring to the drawings, the tonewheel  70  includes a boss  71 , a sensing part  75 , and a coupling part  77 . The boss  71  has a cylindrical shape, and is fitted into the hub  1 . A plurality of sensing holes  73  is formed along the circumference of the sensing part  75  at regular intervals, thus forming an uneven surface. The coupling part  77  couples the boss  71  to the sensing part  75 . Such a tonewheel has the shape of a multi-stage cylinder.  
         [0005]     As shown in  FIG. 1 , a tonewheel sensor  20  is mounted to a position around the tonewheel  70 . The tonewheel sensor  20  senses the pulse generated by the sensing holes  73  of the sensing part  75  when the tonewheel  70  rotates along with the rotary object.  
         [0006]     Further, a controller mounted on a vehicle analyses the pulse transmitted from the tonewheel sensor  20 , thus allowing the rotating speed of the wheel to be checked in real time.  
         [0007]     The tonewheel  70 , the tonewheel sensor  20 , and the controller are used as essential components of an ABS (Anti-Lock Brake System), a TCS (Traction Control System), or a VDC (Vehicle Dynamic Control System).  
         [0008]     Thus, the tonewheel  70  must precisely check the rotating speed of the rotary object, such as a wheel, in real time. To this end, the sensing part  75  sensed by the tonewheel sensor  20  must have very precise flatness and a uniform sectional thickness. Further, the uniformity of the shapes and intervals of the sensing holes  73  must be very high.  
         [0009]     Unless the flatness of the sensing part  75  is precise and the sectional thickness is uniform, the uniformity of the shapes and intervals of the sensing holes  73  is lowered. This undesirably increases the defect rate of the tonewheel  70 .  
       SUMMARY OF THE INVENTION  
       [0010]     Embodiments of the present invention is to provide a method and apparatus for manufacturing a tonewheel for vehicles, which is constructed so that a sensing part has very precise flatness and uniform sectional thickness, and the uniformity of the shapes and intervals of sensing holes formed in the sensing part is very high, thus minimizing the defect rate of the tonewheel.  
         [0011]     A method of manufacturing a tonewheel for vehicles according to one embodiment of the present invention includes a shaping step of manufacturing a first semi-finished tonewheel product having a boss, a sensing part, and a coupling part, by shaping a material having a shape of a flat sheet through a progressive mold, a preliminary machining step of manufacturing a second semi-finished tonewheel product having a sensing part which has a uniform sectional thickness in a vertical direction and an outside surface of which is very precisely flat, by machining the first semi-finished tonewheel product through a strike mold; a sensing-hole machining step of manufacturing a third tonewheel product having a sensing part in which a plurality of sensing holes is formed at regular intervals in a circumferential direction of the sensing part, by machining the second semi-finished tonewheel product through a cam piercing mold; and a deformation recovery step of manufacturing a finished tonewheel product having a sensing part which has a uniform sectional thickness and has a vertical straight-line shape, by processing the sensing part of the third semi-finished tonewheel product, which is deformed to be inwardly curved at the sensing-hole machining step, through a restrike mold.  
         [0012]     An apparatus for manufacturing a tonewheel for vehicles according to another embodiment of the present invention includes a strike mold having an upper mold die and a lower mold punch to process a sensing part, having a non-uniform sectional thickness in a vertical direction, from a first semi-finished tonewheel product manufactured through a progressive mold, thus manufacturing a second semi-finished tonewheel product having a sensing part which is uniform in sectional thickness and is very precise in flatness of an outside surface; and a restrike mold having an upper mold pad, an upper mold die, and a lower mold punch to process a sensing part, deformed to be inwardly curved, from a third semi-finished tonewheel product manufactured to have a sensing hole through a cam piercing mold, thus manufacturing a finished tonewheel product having a sensing part which has a uniform sectional thickness and a vertical straight-line shape. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     For a better understanding of the nature and objects of the present invention, reference should be made to the following detailed description with the accompanying drawings, in which:  
         [0014]      FIG. 1  is a perspective view showing the use of a tonewheel;  
         [0015]      FIGS. 2 and 3  are a perspective view and a vertical sectional view of the tonewheel adapted to  FIG. 1 , respectively; and  
         [0016]      FIGS. 4 through 19  are views illustrating a method and apparatus for manufacturing a tonewheel, according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]      FIGS. 4 through 19  are views illustrating a method and apparatus for manufacturing a tonewheel, according to the present invention.  
         [0018]     As shown in  FIG. 4 , the tonewheel manufacturing method of the present invention includes a shaping step of manufacturing a first semi-finished tonewheel product  10 , a preliminary machining step of manufacturing a second semi-finished tonewheel product  30 , a sensing-hole machining step of manufacturing a third semi-finished tonewheel product  50 , and a deformation recovery step of manufacturing a finished tonewheel product  70 .  
         [0019]     As shown in  FIG. 5 , at the shaping step, a material  110  wound in a roll shape is flattened using a roller unit  120 . The flattened material  130  is processed using a progressive mold  140 , thus manufacturing the first semi-finished tonewheel product  10  having a boss  11 , a sensing part  15 , and a coupling part  17 .  
         [0020]     The material  130  is a soft steel sheet which is flattened while passing through the roller unit  120 .  
         [0021]     The progressive mold  140  is a device which performs a plurality of operations at one time while sequentially feeding the flattened material  130 . As shown in  FIG. 6 , the material  130  is processed in the progressive mold  140  by sequentially performing a slitting operation  131 , a primary drawing operation  132 , a forming operation  133 , a secondary drawing operation  134 , an inner-diameter piercing operation  135 , and a third drawing and cutting operation  136 , thus manufacturing the first semi-finished tonewheel product  10 .  
         [0022]     In this case, the number of drawing operations may be limited according to the kind of tonewheel. Of course, the forming operation may be omitted.  
         [0023]     As shown in the drawing, the first semi-finished tonewheel product  10  has only a boss  11  having a cylindrical shape, the sensing part  15 , and the coupling part  17 .  
         [0024]     Meanwhile, as shown in  FIG. 7 , in the first semi-finished tonewheel product  10  manufactured through the shaping step, the sectional thickness of the sensing part  15  is gradually changed according to the direction of the drawing operation, in consideration of the characteristics of the drawing operation performed in the progressive mold  140 .  
         [0025]     The reason for this is because the deformation and the elongation variation of the material  130  occur simultaneously due to the pressure applied by the progressive mold  140  :during the drawing operation. Consequently, the first semi-finished tonewheel product  10  is formed such that the thickness t 1  of the lower end adjacent to the material  130  is larger than the thickness t 2  of the upper end distant from the material  130 .  
         [0026]     That is, in the drawing operation, the deformation occurs at the lower end of the sensing part  15  by the progressive mold  140 , whereas the deformation and the elongation variation simultaneously occur at the upper end of the sensing part  15 . Thereby, the sensing part  15  is manufactured such that its sectional thickness is gradually changed along the direction of progression of the drawing operation.  
         [0027]     As such, when the sectional thickness of the sensing part  15  is not uniform, the flatness of the outside surface of the sensing part  15  is not precise. Thus, this increases the defect rate of a finished tonewheel product.  
         [0028]     Thus, according to the present invention, the first semi-finished tonewheel product  10  obtained through the shaping step goes through the preliminary machining step. At the preliminary machining step, the first semi-finished tonewheel product  10  is processed using a strike mold  150 , as shown in  FIG. 8 , so that a second semi-finished tonewheel product  30  having the sensing part  35 , which has a uniform sectional thickness in a vertical direction and very precise flatness on the outside surface of the sensing pad, is obtained.  
         [0029]     The strike mold  150  includes an upper mold and a lower mold. As shown in  FIG. 9 , the upper mold includes an upper mold base plate  151 , a backup plate  152 , a pusher pin  154  installed to be biased downwards by a spring  153 , an upper mold punch  155 , an upper mold pad  156 , an upper mold die  157 , and an upper mold holder  158 . The lower mold includes a lower mold punch  159 , a lifter  162  installed to be biased upwards by a spring  161 , a lower mold holder  163 , and a lower mold base plate  164 .  
         [0030]     That is, as shown in  FIGS. 9 and 10 , the first semi-finished tonewheel product  10  is seated on the lower mold punch  159 . In such a state, the upper mold of the strike mold  150  moves downwards. At this time, as shown in  FIG. 11 , the upper mold die  157  provided on the upper mold inwardly presses the outer circumferential surface of the sensing part  15  of the first semi-finished tonewheel product  10 , so that the lower end of the sensing part  15  corresponding to the thick portion t 1  is pressed by the upper mold die  157 , and the thickness of the lower end is thus reduced. A volume corresponding to the reduced thickness extends downwards from the sensing part  15 . Thereby, the overall length of the sensing part  15  is increased.  
         [0031]     As a result, the second semi-finished tonewheel product  30  having the sensing part  37 , in which the upper and lower ends have completely uniform thickness t 2  and the outside surface has very precise flatness, is manufactured. Meanwhile, the upper mold die  157  of the strike mold  150  is constructed so that a corner where a base surface  157   a  and an inside surface  157   b  meet is formed as a rounded part R 1  having a predetermined curvature. Further, the lower mold punch  159  is constructed so that a corner where an upper surface  159   a  and an outside surface  159   b  meet is formed as a rounded part R 3  having a predetermined curvature. In this case, the rounded part R 1  of the upper mold die  157  has a curvature larger than the rounded part R 3  of the lower mold punch  159 .  
         [0032]     The lower mold punch  159  is the component that seats the first semi-finished tonewheel product  10  at the preliminary machining step. Thus, the rounded part R 3  of the lower mold punch  159  may be designed to have a minimum curvature which is required simply to support the junction between the sensing part  15  and the coupling part  17 .  
         [0033]     However, the upper mold die  157  is the component that directly processes the sensing part  15  of the first semi-finished tonewheel product  10  at the preliminary machining step. Thus, the rounded part R 1  of the upper mold die  157  must be formed to have a radius of curvature which is at least several times as large as that of the rounded part R 3  of the lower mold punch  159 .  
         [0034]     The smaller the curvature of the rounded part R 1  is, the more scratches will be formed on the sensing part  35  of the second semi-finished tonewheel product  30 . Further, the flatness of the outside surface may not be precise.  
         [0035]     Thus, an intersection point P 2  is fixed at a position where a horizontal extension line L 1  of the base surface  157   a  and a vertical extension line L 2  of the inside surface  157   b  meet, and an intersection point P 3  is fixed at a position where the horizontal extension line L 1  and an extension line L 3  extending vertically from a portion of the sensing part  15  of the first semi-finished tonewheel product  10  having the thickest section meet. In this case, a point P 1  where the rounded part R 1  starts on the base surface  157   a  of the upper mold die  157  is preferably set to a point which is spaced apart from the intersection point P 3  by an interval which is two to three times as large as an interval C 1  between the intersection points P 2  and P 3  and is located along the horizontal extension line L 1  in a direction opposite the intersection point P 2 . However, the point P 1  is not limited to the above-mentioned position.  
         [0036]     Further, a point P 4  where the rounded part R 1  starts on the inside surface  157   b  of the upper mold die  157  is preferably set to a point which is spaced apart from the intersection point P 2  by an interval which is six to seven times as large as the interval C 1  between the intersection points P 2  and P 3  and is located along the vertical extension line L 2 . However, the point P 4  is not limited to the above-mentioned position.  
         [0037]     In order to prevent the upper mold die  157  from being damaged and enhance the quality of the second semi-finished tonewheel product  30  at the preliminary machining step, the entire surface of the upper mold die  157  is coated. In this case, the coating process is carried out using tin.  
         [0038]     As such, the second semi-finished tonewheel product  30 , which has been processed at the preliminary machining step, goes through a subsequent step, which is the sensing-hole machining step. At the sensing-hole machining step, as shown in  FIG. 12 , the second semi-finished tonewheel product  30  is processed using a cam piercing mold  170 , so that a third semi-finished tonewheel product  50  having a sensing part  55  in which a plurality of sensing holes  53  is circumferentially formed at regular intervals is obtained.  
         [0039]     As shown in  FIG. 13 , the cam piercing mold  170  includes an upper mold  171  and a lower mold  172 . A cam drive  173  and a press pad  178  are integrally provided on the upper mold  171  in such a way as to protrude toward the lower mold  172 . A sensing hole forming block  174  and a piercing punch  175  are provided on the lower mold  172 . The sensing hole forming block  174  functions to seat the second semi-finished tonewheel product  30  thereon. The piercing punch  175  moves rectilinearly when it contacts the cam drive  173 , thus forming a sensing hole in the second semi-finished tonewheel product  30 .  
         [0040]     Further, a lifter  176  is mounted to the lower mold  172  to be biased upwards by a spring  177 .  
         [0041]     A plurality of cam drives  173  and a plurality of piercing punches  175  are arranged along the circumference of the sensing hole forming block  174  at regular intervals.  
         [0042]     A hollow hole  174   a  is formed in the central portion of the sensing hole forming block  174  to pass through the upper and lower surfaces thereof. A plurality of slits  174   b  is formed along the outer circumference of the upper end of the sensing hole forming block  174  at regular intervals. The slits  174   b  are holes into which the piercing punches  175  are inserted. The number of slits  174   b  is equal to the number of piercing punches  175 .  
         [0043]     That is, the cam drives  173  and the piercing punches  175 , numbering the same as the sensing holes formed in the tonewheel, are provided on the circumference of the cam piercing mold  170 . Thus, when the upper mold  171  is driven once, a desired number of sensing holes is integrally formed in the sensing part of the tonewheel.  
         [0044]     Thus, as shown in  FIG. 13 , when the second semi-finished tonewheel product  30  is mounted on the sensing hole forming block  174  of the cam piercing mold  170  and the upper mold  171  moves downwards, the cam drives  173  press the piercing punches  175 . Thereby, the piercing punches  175  slide toward the sensing hole forming block  174 , as shown by the arrow in the drawing. An end of each piercing punch  175  passes through the sensing part  35  of the second semi-finished tonewheel product  30  to be located inside each slit  174   b.    
         [0045]     Consequently, the third semi-finished tonewheel product  50 , having the sensing part  55  in which a plurality of sensing holes  53  is circumferentially formed at regular intervals, is obtained from the second semi-finished tonewheel product  30 .  
         [0046]     Meanwhile, when the third semi-finished tonewheel product  50  having the sensing holes  53  is manufactured in the sensing-hole machining step, the sensing holes  53  and a portion of the sensing part  55  around the sensing holes  53  may be inwardly curved or deformed by the punching power of the piercing punches  175 , as shown in  FIG. 14 .  
         [0047]     Thus, the third semi-finished tonewheel product  50  obtained through the sensing-hole machining step is processed using a restrike mold  180 , as shown in  FIG. 15 , so that a finished tonewheel product  70  having a sensing part  75 , which is uniform in sectional thickness and has a vertical straight-line shape, is obtained.  
         [0048]     That is, the sensing part  55 , which is inwardly curved after the sensing-hole machining step has been performed, is pulled outwards during the operation using the restrike mold  180 , so that the sensing part  55  is returned to its original shape. Thereby, the finished tonewheel product  70 , having a sensing part  75  which is uniform in sectional thickness and has a vertical straight-line shape, is obtained.  
         [0049]     In this case, the restrike mold  180  is divided into an upper mold and a lower mold. As shown in  FIG. 16 , the upper mold includes an upper mold base plate  181 , a backup plate  182 , a pusher pin  184  installed to be biased downwards by a spring  183 , an upper mold punch  185 , an upper mold pad  186 , an upper mold die  187 , and an upper mold holder  188 . The lower mold includes a lower mold punch  189 , a lifter  192  installed to be biased upwards by a spring  191 , a lower mold holder  193 , and a lower mold base plate  194 .  
         [0050]     That is, after the third semi-finished tonewheel product  50  is seated on the lower mold punch  189 , as shown in  FIGS. 16 and 17 , the upper mold of the strike mold  150  is moved downwards. At this time, the upper mold pad  186 , provided on the upper mold, presses and pushes down the coupling part  57  of the third semi-finished tonewheel product  50 , as shown in  FIG. 18 . Simultaneously, the upper mold die  187  supports the outer circumferential surface of the sensing part  55  of the third semi-finished tonewheel product  50 .  
         [0051]     Thereby, the inwardly curved sensing part  55  including the sensing holes  53  is pulled outwards by the lower mold punch  189 . As a result, the finished tonewheel product  70  having the sensing part  75 , which is uniform in sectional thickness and has a vertical straight-line shape, is obtained from the third semi-finished tonewheel product  50 .  
         [0052]     Meanwhile, as shown in  FIG. 19 , the upper mold die  187  of the restrike mold  180  has a rounded part R 11  having a predetermined curvature at the corner where the base surface  187   a  and the inside surface  187   b  meet. The lower mold punch  189  has a rounded part R 13  having a predetermined curvature at the corner where an upper surface  189   a  and an outside surface  189   b  meet. The rounded part R 13  of the lower mold punch  189  has a curvature larger than the rounded part R 11  of the upper mold die  187 .  
         [0053]     The upper mold die  187  is the component that functions to simply support the outside surface of the sensing part  55  of the third semi-finished tonewheel product  50  at the deformation recovery step. Thus, the upper mold die  187  has only to be smoothly moved downwards without scratching the outside surface of the sensing part  55  when the upper mold moves downwards.  
         [0054]     Hence, the rounded part R 11  of the upper mold die  187  may have a minimum curvature that satisfies design conditions.  
         [0055]     However, the lower mold punch  189  is the component that directly restores the inwardly curved sensing part  55  of the third semi-finished tonewheel product  50  to its original state, at the deformation recovery step. Thus, the rounded part R 13  of the lower mold punch  189  must have a radius of curvature which is at least several times as large as that of the rounded part R 11  of the upper mold die  187 .  
         [0056]     The smaller the curvature of the rounded part R 13  is, the more scratches will be formed on the inner surface of the sensing part  75  of the finished tonewheel product  70 . Further, the flatness of the inner surface may not be precise.  
         [0057]     Thus, when an intersection point P 12  is fixed at a position at which a horizontal extension line L 11  of the upper surface  189   a  of the lower mold punch  189  and a vertical extension line L 12  of the outside surface  189   b  meet, a point P 11  where the rounded part R 13  starts on the upper surface  189   a  of the bottom mold  189  is preferably set to a point which is spaced apart from the intersection point P 12  by an interval which is two to three times as large as the maximum inward protruding length C 11  of the sensing part  55  on the third semi-finished tonewheel product  50  and is located along the horizontal extension line L 11 . However, the point P 11  is not limited to the above-mentioned position.  
         [0058]     Further, the point P 13  where the rounded part R 13  starts on the outside surface  189   b  of the lower mold punch  189  is preferably set to a point which is spaced apart from the intersection point P 12  by an interval which is four to five times as large as the protruding length C 11 , and is located along the vertical extension line L 12 . However, the point P 13  is not limited to the above-mentioned position.  
         [0059]     In order to prevent the upper mold die  187  from being damaged and enhance the quality of the finished tonewheel product  70  at the deformation recovery step, the entire surface of the upper mold die  187  used in the restrike mold  180  is coated. In this case, the coating process is carried out using hard chrome plating, which has hardness lower than that of tin coating used for the upper mold die  157  at the preliminary forming step.  
         [0060]     As such, when the finished tonewheel product  70  obtained through the deformation recovery step is taken out of the restrike mold  180 , the manufacture of the tonewheel  70  shown in  FIGS. 2 and 3  is completed.  
         [0061]     Thus, the finished tonewheel product  70  is manufactured through the steps of this invention such that the sensing part  75  has uniform sectional thickness and precise surface flatness. Thereby, a high degree of uniformity of the shapes and intervals of the sensing holes  73  formed in the sensing part  75  is achieved.  
         [0062]     As a result, the performance of the finished tonewheel product  70  is remarkably improved, and in addition, the performance of ABS, TCS, and VDC using the tonewheel  70  becomes superior.