Patent Publication Number: US-2016244040-A1

Title: Insert molded article, manufacturing method for protective cover having sensor holder part, and manufacturing method for bearing device including the protective cover

Description:
TECHNICAL FIELD 
     The present invention relates to a cup-shaped protective cover that is press-fitted into an outer ring of a bearing to cover a magnetic encoder, more specifically to a protective cover having a sensor holder part holding a magnetic sensor opposed to the magnetic encoder. 
     BACKGROUND ART 
     An antilock brake system widely used in automobiles for efficient and safety braking without wheel lock detects the rotation speeds of wheels by a rotation speed detector (wheel speed sensor), calculates the acceleration and the deceleration and estimates the vehicle speed and the slip ratio by a controller, and drives an actuator to control the brake fluid pressure based on the calculation and estimation results, for example. 
     Bearing devices including such a rotation speed detector in a rolling bearing for supporting automobile wheels (hub bearing) are also widely used. Such a bearing device may be structured such that a magnetic encoder having N poles and S poles alternately arranged at constant intervals in the circumferential direction is fitted to the inner ring of a bearing, a magnetic sensor for detecting the rotation of the magnetic encoder is attached to the outer ring so as to be opposed to the magnetic encoder, and a protective cover covering the magnetic encoder from the inner side to protect the magnetic encoder is press-fitted into the inner end portion of the outer ring (for example, refer to Patent Document 1). 
     The protective cover keeps the magnetic encoder from getting hit by pebbles, mud water, or the like and prevents damage to the magnetic encoder. In addition, the protective cover eliminates the need for a seal member on the outer side of the magnetic encoder, which decreases a sliding resistance to reduce rotation torque of the bearing device. 
     In addition, to eliminate a troublesome work of adjusting the air gap between the magnetic encoder and the magnetic sensor, the protective cover having the sensor holder part for holding the magnetic sensor may be configured such that a boss part composed of a synthetic resin is integrally joined to part of the bottom of a cup-shaped main part (cap) formed in a cup shape by press working on a non-magnetic steel plate, and a nut is integrally joined to the boss part to fix the magnetic sensor (for example, refer to Patent Document 2). 
     CITATION LIST 
     Patent Literatures 
     Patent Document 1: JP-A No. 2011-084265 
     Patent Document 2: JP-A No. 2013-117455 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the structure of the protective cover having the sensor holder part as described in Patent Document 2, the boss part composed of a synthetic resin is generally adhered to part of the bottom of the cup-shaped main part (cap). Therefore, even when minute dimples are formed on the adhesion surface of the bottom, the fixing strength between the cup-shaped main part and the boss part may become lower due to long-term use and depending on usage environments, resulting in dropping of the boss part with reduction in reliabilty. 
     In light of the foregoing circumstances, to solve the problem, an object of the present invention is to provide an insert molded article that maintains high reliability over the long term, a manufacturing method for a protective cover having a sensor holder part, and a manufacturing method for a bearing device including the protective cover, by increasing fixing strength between an insert article and a synthetic resin through insert molding. 
     Solution to Problem 
     To solve the foregoing problem, an insert molded article according to the present invention is an insert molded article in which an insert article and a synthetic resin are integrated, wherein through hole is formed in a joint surface of the insert article relative to the synthetic resin, and the synthetic resin has a wrap-around portion extending radially outward from the joint surface through the through hole (claim  1 ). 
     According to this configuration, the synthetic resin of the insert molded article has the wrap-around portion extending radially outward through the through hole of the insert article, whereby the insert article and the synthetic resin are mechanically joined to each other. Accordingly, the fixing strength between the insert article and the synthetic resin becomes high to ensure high reliability of joint between the insert article and the synthetic resin over the long term. 
     In addition, to solve the foregoing problem, an insert molded article according to the present invention is an insert molded article in which an insert article and a synthetic resin are integrated, wherein the insert article is cup-shaped, the cup shape has a side portion of the bottom smaller in diameter than a side portion of the cup shape to form a step connecting to a bottommost part, the smaller-diameter side portion has a concave or a convex, and the synthetic resin has a step covering portion that covers the step portion (claim  2 ). 
     According to this configuration, the step covering portion of the synthetic resin covers the step formed by the bottommost portion and the smaller-diameter side portion of the insert article, and the synthetic resin engages with the concave or the convex formed in the smaller-diameter side portion, whereby the insert article and the synthetic resin are mechanically joined to each other. Accordingly, the fixing strength between the insert article and the synthetic resin becomes high to ensure high reliability of joint between the insert article and the synthetic resin over the long term. 
     To solve the foregoing problem, a manufacturing method for a protective cover having a sensor holder part according to the present invention is a manufacturing method for a protective cover for use in a bearing device including: an inner ring with an inner ring track surface on an outer periphery; an outer ring with an outer ring track surface on an inner periphery; a bearing having a rolling element rolling between the inner ring track surface and the outer ring track surface; a magnetic encoder that is positioned at one axial end of the bearing, fixed to the inner ring, and has N and S poles alternately arranged at regular intervals in an circumferential direction; and a magnetic sensor that is opposed to the magnetic poles of the magnetic encoder to detect rotation of the magnetic encoder, wherein the protective cover has: a cup-shaped main part that is formed in a cup shape from a non-magnetic steel plate, positioned at the one axial end of the bearing, and press-fitted into the outer ring; and a synthetic resin sensor holder part that is integrally joined to the cup-shaped main part while holding a nut for attaching the magnetic sensor, the cup-shaped main part having a through hole in a bottom, and the manufacturing method includes: a press working step of forming the cup-shaped main part by press working; and an injection molding step of setting the nut and the cup-shaped main part as insert articles into a metal mold, tightening the mold, charging molten plastic into a cavity to perform injection molding to form a wrap-around portion extending radially outward on an inner side of the bottom through the through hole at the sensor holder part integrated with the nut and the cup-shaped main part (claim  3 ). 
     By press-fitting the protective cover manufacture by the foregoing manufacturing method into the outer ring of the bearing with the magnetic encoder fixed to the inner ring, the protective cover is axially positioned with respect t the magnetic encoder, and the magnetic sensor is axially positioned and held with respect to the protective cover by the sensor holder part of the protective cover, whereby the air gap between the magnetic sensor and the magnetic encoder is completely adjusted. 
     This eliminates the need for a troublesome work of adjusting the air gap between the magnetic encoder and the magnetic sensor. 
     In addition, according to the manufacturing method, by the injection molding with the nut and the cup-shaped main part as insert articles, the wrap-around portion extending radially outward on the inner side of the bottom of the cup-shaped main part through the through hole of the bottom is formed at the synthetic resin sensor holder part integrated with the nut and the cup-shaped main part. 
     Therefore, in the protective cover manufactured by the foregoing manufacturing method, the cup-shaped main part and the sensor holder part are mechanically joined to each other. This increases the fixing strength between the cup-shaped main part and the sensor holder part to ensure high reliability of joint between the cup-shaped main part and the sensor holder part over the long term. 
     It is preferred that the manufacturing method includes at least one of a vulcanization and adhesion step of vulcanizing and adhering an endless seal body to a periphery of the through hole in the cup-shaped main part and an adhesive application step of applying a thermoset adhesive to the periphery (claim  4 ). 
     According to the manufacturing method, even when the through hole is formed in the bottom of the cup-shaped main part, the vulcanization and adhesion step or the adhesive application step allows the seal body or the adhesive layer on the periphery of the through hole intervenes between the cup-shaped main part and the sensor holder part to retain airtightness of the protective cover. 
     It is also preferred that the bottom of the cup-shaped main part has a disc portion as a bottommost portion, a cylindrical portion extending axially from an outer edge of the disc portion, and an annular portion extending radially outward from an axial end edge of the cylindrical portion, and the sensor holder part has a portion covering the disc portion and the cylindrical portion (claim  5 ). 
     According to the manufacturing method, the bottom of the cup-shaped main part formed at the press working step has the disc portion as an bottommost portion, the cylindrical portion extending axially from the outer edge of the disc portion, and the annular portion extending radially outward from the axial end edge of the cylindrical portion, and the sensor holder part formed at the injection molding step has the portion covering the step formed by the disc portion with the through hole of the cup-shaped main part and the cylindrical portion extending axially from the outer edge of the disc portion. Accordingly the protective cover manufactured by the manufacturing method has the effect of retaining some degree of airtightness even without having to provide the vulcanization and adhesion step or the adhesive application step, thereby achieving reduction in manufacturing costs. 
     To solve the foregoing problem, a manufacturing method for a protective cover having a sensor holder part according to the present invention is a manufacturing method for a protective cover for use in a bearing device including: an inner ring with an inner ring track surface on an outer periphery; an outer ring with an outer ring track surface on an inner periphery; a bearing having a rolling element rolling between the inner ring track surface and the outer ring track surface; a magnetic encoder that is positioned at one axial end of the bearing, fixed to the inner ring, and has N and S poles alternately arranged at regular intervals in an circumferential direction; and a magnetic sensor that is opposed to the magnetic poles of the magnetic encoder to detect rotation of the magnetic encoder, wherein the protective cover has: a cup-shaped main part that is formed in a cup shape from a non-magnetic steel plate, positioned at the one axial end of the bearing, and press-fitted into the outer ring; and a synthetic resin sensor holder part that is integrally joined to the cup-shaped main part while holding a nut for attaching the magnetic sensor, the bottom of the cup-shaped main part has a disc portion as a bottommost portion, a cylindrical portion extending axially from an outer edge of the disc portion, and an annular portion extending radially outward from an axial end edge of the cylindrical portion, the cylindrical portion having a concave or a convex, and the manufacturing method includes: a press working step of forming the cup-shaped main part by press working; and a injection molding step of setting the nut and the cup-shaped main part as insert articles into a metal mold, tightening the mold, charging molten plastic into a cavity to perform injection molding to form a step covering portion covering a step formed by the disc portion and the cylindrical portion at the sensor holder part integrated with the nut and the cup-shaped main part (claim  6 ). 
     By press-fitting the protective cover manufactured by the foregoing manufacturing method into the outer ring of the bearing with the magnetic encoder fixed to the inner ring, the protective cover is axially positioned with respect to the magnetic encoder, and the magnetic sensor is axially positioned and held with respect to the protective cover by the sensor holder part of the protective cover, whereby the air gap between the magnetic sensor and the magnetic encoder is completely adjusted. 
     This eliminates the need for a troublesome work of adjusting the air gap between the magnetic encoder and the magnetic sensor. 
     In addition, according the manufacturing method, by the injection molding with the nut and the cup-shaped main part as insert articles, the step covering portion covering the step formed by the disc portion and the cylindrical portion of the cup-shaped main part is formed at the synthetic resin sensor holder part integrated with the nut and the cup-shaped main part. The synthetic resin of the sensor holder part engages with the concave or the convex formed in the cylindrical portion of the cup-shaped main part. 
     Therefore, in the protective cover manufactured by the foregoing manufacturing method, the cup-shaped main part and the sensor holder part are mechanically joined to each other. This increases the fixing strength between the cup-shaped main part and the sensor holder part to ensure high reliability of joint between the cup-shaped main part and the sensor holder part over the long term. 
     Further, a manufacturing method a bearing device according to the present invention is a manufacturing method for a bearing device including: an inner ring with an inner ring track surface on an outer periphery; an outer ring with an outer ring track surface on an inner periphery; a bearing having a rolling element rolling between the inner ring track surface and the outer ring track surface; a magnetic encoder that is positioned at one axial end of the bearing, fixed to the inner ring, and has N and S poles alternately arranged at regular intervals in an circumferential direction; and a magnetic sensor that is opposed to the magnetic poles of the magnetic encoder to detect rotation of the magnetic encoder, wherein the manufacturing method includes a step of press-fitting the protective cover manufactured by the manufacturing method for the protective cover having the sensor holder part into the outer ring (claim  7 ). 
     Advantageous Effects of Invention 
     According to the insert molded article, the manufacturing method for a protective cover having a sensor holder part, and the manufacturing method for a bearing device including the protective cover according to the present invention described above, the synthetic resin (sensor holder part) of the insert molded article (protective cover) and the insert article (cup-shaped main part) are mechanically joined to each other. Accordingly, the fixing strength between the insert article and the synthetic resin becomes large to produce the significantly advantageous effect of ensuring high reliability of joint between the insert article and the synthetic resin over the long term. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a partial vertical cross-sectional view of a bearing device including a protective cover with a sensor holder part according to a first embodiment of the present invention; 
         FIG. 2  is an enlarged perspective vertical cross-sectional view of main components of the protective cover with the sensor holder part according to the first embodiment of the present invention to which a magnetic sensor is attached; 
         FIG. 3  is a vertical cross-sectional view of an example of an injection metal mold; 
         FIG. 4  is a partial vertical cross-sectional view of a bearing device including a protective cover with a sensor holder part according to a second embodiment of the present invention; 
         FIG. 5  is an enlarged perspective vertical cross-sectional view of main components of the protective cover with the sensor holder part according to the second embodiment of the present invention to which a magnetic sensor is attached; 
         FIG. 6  is a partial vertical cross-sectional view of a bearing device including a protective cover with a sensor holder part according to a third embodiment of the present invention; 
         FIG. 7  is an enlarged perspective vertical cross-sectional view of main components of the protective cover with the sensor holder part according to the third embodiment of the present invention to which a magnetic sensor is attached; 
         FIG. 8  is a partial vertical cross-sectional view of the same; and 
         FIG. 9  is a vertical cross-sectional view of an example of an injection metal mold. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments illustrated in the accompanying drawings but includes all of embodiments satisfying the requirements described in the claims. 
     First Embodiment 
     A bearing device  11  according to a first embodiment of the present invention illustrated in the partial vertical cross-sectional view of  FIG. 1  includes a magnetic encoder  16 , a protective cover  1 , and a magnetic sensor A arranged at one axial end of the bearing, and a seal member  15  arranged at the other axial end of the bearing, and others, in addition to a bearing with an inner ring  12  rotating relative to an outer ring  13 . 
     The bearing has the inner ring  12  with an inner ring track surface  12 A on the outer periphery the outer ring  13  with an outer ring track surface  13 A on the inner periphery, and rolling elements  14 ,  14 , . . . rolling between the inner ring track surface  12 A and the outer ring track surface  13 A, and others. 
     The magnetic encoder  16  has N and S poles alternately arranged at regular intervals in the circumferential direction, and is fixed to the inner ring  12  by a support member  17  positioned at the one axial end of the bearing. 
     The protective cover  1  is attached to the outer ring  13  to seal the one axial end of the bearing and has a sensor holder part  8  holding the magnetic sensor A. 
     The magnetic sensor A attached to the sensor holder part  8  of the protective cover  1  is opposed to the magnetic encoder  16  to detect the rotation of the magnetic encoder  16 . 
     At the bearing device  11  illustrated in  FIG. 1 , a cup-shaped main part  1 A of the protective cover  1  is press-fitted into the outer ring  13  of the bearing in which the magnetic encoder  16  is fixed to the inner ring  12 , whereby the protective cover  1  is axially positioned with respect to the magnetic encoder  16 . 
     The magnetic sensor A is axially positioned and held with respect to the protective cover  1  by the sensor holder part  8  of the protective cover  1 , and an air gap between the magnetic sensor A and the magnetic encoder  16  is completely adjusted. 
     This eliminates a troublesome work of adjusting the air gap between the magnetic encoder  16  and the magnetic sensor A. 
     As illustrated in the partial vertical cross-sectional view of  FIG. 1  and the enlarged perspective vertical cross-sectional view of main components of  FIG. 2 , the protective cover  1  according to the first embodiment of the present invention has the cup-shaped main part  1 A formed in a cup shape by press working of a non-magnetic steel plate and the synthetic resin sensor holder part  8  that is integrally joined to the cup-shaped main part  1 A while holding a nut  10  to which an attachment bolt B for attachment of the magnetic sensor A is screwed. 
     The protective cover  1  is an insert molded article, and the cup-shaped main part  1 A and the nut  10  are insert articles. 
     The cup-shaped main part  1 A is composed of a first cylindrical portion  2  press-fitted into the outer ring  13 , a second cylindrical portion  3  that is smaller in diameter than the first cylindrical portion  2 , connects to an end edge of the first cylindrical portion  2 , and has an outer peripheral surface to which a seal body  7  is vulcanized and adhered, an annular portion  4  that connects to an end edge of the second cylindrical portion and extends radially inward, a third cylindrical portion  5  that connects to an inner-side end edge of the annular portion  4  and extends axially, and a disc portion  6  connecting to an end edge of the third cylindrical portion  5 . The disc portion  6  (the bottom of the cup-shaped main part  1 A) has a through hole  6 A. 
     The bottom of the cup-shaped main part  1 A has the disc portion  6  as a bottommost portion, a third cylindrical portion  5  extending axially from an outer edge of the disc portion  6 , the annular portion  4  extending radially outward from an axial end edge of the third cylindrical portion  5 , and a step C (see  FIG. 2 ) formed by the disc portion  6  and the third cylindrical portion  5  extending axially from the outer edge of the disc portion  6 . 
     The sensor holder part  8  integrated with the cup-shaped main part  1 A has a base portion  8 A holding the nut  10  and a wrap-around portion  8 B that extends radially outward at the inner side of the cup-shaped main part  1 A through the through hole  6 A of the disc portion  6 . The base portion  8 A has a portion covering the disc portion  6  and the third cylindrical portion  5 . 
     An endless seal body S intervenes between the cup-shaped main part  1 A and the sensor holder part  8  around the through hole  6 A. 
     The seal bodies  7  and S are elastic bodies such as synthetic rubbers and can be formed of one of rubbers such as nitrile rubber (NBR), hydrogenated nitrite rubber (HNBR), acrylic rubber (ACM), ethylene-acrylic rubber (AEM), fluorine rubber (FKM, FPM), and silicone rubber (VMQ) or an appropriate blend of two or more of these rubbers. 
     Next, a manufacturing method for the protective cover  1  having the sensor holder part  8  will be described. 
     &lt;Press Working Step&gt; 
     At a press working step, the cup-shaped main part  1 A constituting the protective cover  1  is formed from an austenitic stainless-steel plate material by press working, for example. 
     &lt;Vulcanization and Adhesion Step&gt; 
     At a vulcanization and adhesion step, the seal body  7  is vulcanized and adhered to the outer peripheral surface of the second cylindrical portion  3  of the cup-shaped main part  1 A shaped at the press working step, and the endless (for example, annular) seal body S is vulcanized and adhered around the through hole  6 A of the disc portion  6 . 
     Alternatively, at an adhesive application step of applying a thermoset adhesive around the through hole  6 A of the disc portion  6 , instead of the seal body S, may be performed, or both the vulcanization and adhesion step of vulcanizing and adhering the seal body S and the adhesive application step of applying the thermoset adhesive may be performed. 
     &lt;Injection Molding Step&gt; 
     In an injection mold illustrated in the vertical cross-sectional view of  FIG. 3 , first, the nut  10  as an insert article is set on a support shaft  21  of a fixed mold  18 . 
     The cup-shaped main part  1 A as an insert article having undergone the press working step and the vulcanization and adhesion step is set in a movable mold  19 . 
     Next, while the fixed mold  18  and the movable mold  19  are mounted on an injection molding machine and are tightened, molten plastic is injected through a sprue and charged from a gate  20  into a cavity between the fixed mold  18  and the movable mold  19 . 
     Next, the molten plastic is cooled and solidified, and then the movable mold  19  is opened to remove the insert molded article. 
     In the protective cover  1  having undergone the injection molding step as described above (see  FIGS. 1 and 2 ),the synthetic resin is entered into a circumferential groove  10 A of the nut  10  to retain the nut  10 , and a wrap-around portion  8 B in which the synthetic resin wraps around the disc portion  6  radially outward through the through hole  6 A is formed. Accordingly, the cup-shaped main part  1 A and the sensor holder part  8  are mechanically joined to each other. 
     One or both of the seal body S and the adhesive layer intervene between the cup-shaped main part  1 A and the sensor holder part  8  around the through hole  6 A of the disc portion  6 , thereby to keep the airtightness of the protective cover  1 . 
     The base portion  8 A of the sensor holder part  8  has the portion covering the disc portion  6  and the third cylindrical portion  5  (the step C illustrated in  FIG. 2 ) to produce the effect of keeping airtightness to some degree without the seal body S and the adhesive layer. Accordingly, the seal body S or the adhesive layer may not be provided depending on the required specifications. 
     Second Embodiment 
     In a bearing device  11  and a protective cover  1  according to a second embodiment of the present invention illustrated in the partial vertical cross-sectional view of  FIG. 4  and the protective cover  1  according to the second embodiment of the present invention illustrated in the enlarged perspective vertical cross-sectional view of main components of  FIG. 5 , the components with the same reference signs as those in the first embodiment illustrated in  FIGS. 1 and 2  are the components identical or equivalent to the components in the first embodiment, and descriptions thereof will be omitted. 
     A cup-shaped main part  1 A of the protective cover  1  in the second embodiment is composed of a first cylindrical portion  2  press-fitted into the outer ring  13 , a second cylindrical portion  3  that is smaller in diameter than the first cylindrical portion  2 , connects to an end edge of the first cylindrical portion  2 , and has an outer peripheral surface to which a seal body  7  is vulcanized and adhered, and a disc portion  6  connecting to an end edge of the second cylindrical portion  3 . The disc portion  6  (the bottom of the cup-shaped main part  1 A) has a through hole  6 A. 
     Accordingly, the cup-shaped main part  1 A in the second embodiment does not have the step C in the first embodiment illustrated in  FIG. 2 , which allows simplification of the processing process of the cup-shaped main part  1 A with reduction in manufacturing costs of the protective cover  1 . 
     According to the configuration of the protective cover  1  in the first and second embodiments, the synthetic resin sensor holder part  8  of the protective cover  1  as an insert molded article has the wrap-around portion  8 B extending radially outward through the through hole  6 A of the bottom of the cup-shaped main part  1 A as an insert article, whereby the cup-shaped main part  1 A and the sensor holder part  8  are mechanically joined to each other. 
     Accordingly, the fixing strength between the cup-shaped main part  1 A and the sensor holder part  8  becomes large to produce the significantly advantageous effect of ensuring high reliability of joint between the cup-shaped main part  1 A and the sensor holder part  8  over the long term. 
     The technique for mechanically joining the cup-shaped main part  1 A and the sensor holder part  8  in the protective cover  1  as described above is also applicable to insert molded articles other than the protective cover  1  in which the insert article and the synthetic resin are integrated by insert molding. 
     Specifically, a through hole is formed in a joining surface between an insert article and a synthetic resin, and a wrap-around portion extending radially outward from the joining surface through the through hole is formed in the synthetic resin. 
     Third Embodiment 
     In a bearing device  11  and a protective cover  1  according to a third embodiment of the present invention illustrated in the partial vertical cross-sectional view of  FIG. 6  and the protective cover  1  according to the third embodiment of the present invention illustrated in the enlarged perspective vertical cross-sectional view of main components of  FIG. 7  and the partial vertical cross-sectional view of  FIG. 8 , the components with the same reference signs as those in the first embodiment illustrated in  FIGS. 1 and 2  are the components identical or equivalent to the components in the first embodiment, and descriptions thereof will be omitted. 
     The cup-shaped main part  1 A of the protective cover  1  in the third embodiment has concaves  9 ,  9 , . . . formed in the outer peripheral surface of the third cylindrical portion  5  by pressing the third cylindrical portion  5  with a punch or the like from the outside and thus does not have the through hole  6 A in the first embodiment. 
     The sensor holder part  8  has the base portion  8 A holding the nut  10  and a step covering portion  8 C covering the step C formed by the disc portion  6  and the third cylindrical portion  5 . The synthetic resin of the sensor holder part  8  is entered into the concaves  9 ,  9 , . . . to integrate the sensor holder part  8  with the cup-shaped main part  1 A. 
     Next, a manufacturing method for the protective cover  1  having the sensor holder part  8  will be described. 
     &lt;Press Working Step&gt; 
     At a press working step, the cup-shaped main part  1 A constituting the protective cover  1  is formed from an austenitic stainless-steel plate material by press working, for example. 
     &lt;Vulcanization and Adhesion Step&gt; 
     At a vulcanization and adhesion step, the seal body  7  is vulcanized and adhered to the outer peripheral surface of the second cylindrical portion  3  of the cup-shaped main part  1 A shaped at the press working step. 
     Alternatively, an adhesive application step of applying a thermoset adhesive to a joint surface of the cup-shaped main part  1 A relative to the synthetic resin may be performed to improve the joint strength between the cup-shaped main part  1 A and the synthetic resin. 
     &lt;Injection Molding Step&gt; 
     In an injection mold illustrated in the vertical cross-sectional view of  FIG. 9 , first, the nut  10  as an insert article is set on a support shaft  21  of a fixed mold  18 . 
     The cup-shaped main part  1 A as an insert article having undergone the press working step and the vulcanization and adhesion step is set in a movable mold  19 . 
     Next, while the fixed mold  18  and the movable mold  19  are mounted on an injection molding machine and are tightened, molten plastic is injected through a sprue and charged from a gate  20  into a cavity between the fixed mold  18  and the movable mold  19 . 
     Next, the molten plastic is cooled and solidified, and then the movable mold  19  is opened to remove the insert molded article. 
     In the protective cover  1  having undergone the injection molding step as described above (see  FIGS. 6 to 8 ), the synthetic resin is entered into a circumferential groove  10 A of the nut  10  to retain the nut  10 . In addition, the sensor holder part  8  has the step covering portion  8 C covering the step C of the cup-shaped main part  1 A, and the synthetic resin of the sensor holder part  8  is entered into the concaves  9 ,  9 , . . . formed in the outer peripheral surface of the third cylindrical portion  5  of the cup-shaped main part  1 A. Accordingly, the cup-shaped main part  1 A and the sensor holder part  8  are mechanically joined to each other. 
     As illustrated in  FIGS. 6 to 8 , the concaves  9 .  9 , . . . are formed in the outer peripheral surface of the third cylindrical portion  5  to produce convexes in the inner peripheral surface of the third cylindrical portion  5 . Accordingly, even in the presence of an undercut portion, the movable mold  19  illustrated in  FIG. 9  has smaller-diameter portions D, D, . . . at positions corresponding to the convexes, which facilitates setting of the cup-shaped main part  1 A to the movable mold  19  and removal of the protective cover  1  from the movable mold  19 . 
     According to the configuration of the protective cover  1  in the third embodiment, the synthetic resin sensor holder part  8  covers the step C formed by the disc portion  6  as a bottommost portion of the cup-shaped main part  1 A as an insert article and the third cylindrical portion  5  extending axially from the outer edge of the disc portion  6 , and the sensor holder part  8  engages with the concaves  9 ,  9 , . . . formed in the third cylindrical portion  5 , whereby the cup-shaped main part  1 A and the sensor holder part  8  are mechanically joined to each other. 
     Accordingly the fixing strength between the cup-shaped main part  1 A and the sensor holder part  8  becomes large to ensure high reliability of joint between the cup-shaped main part  1 A and the sensor holder part  8  over the long term. 
     In the case described above, the concaves  9 ,  9 , . . . are formed in the outer peripheral surface of the third cylindrical portion  5  as a smaller-diameter side portion of the cup-shaped main part  1 A. Alternatively, convexes may be formed in the outer peripheral surface of the third cylindrical portion  5 . In this case, there is no need for the diameter-reduced portions D, D, . . . in the movable mold  19  illustrated in  FIG. 9 . 
     The technique for mechanically joining the cup-shaped main part  1 A and the sensor holder part  8  in the protective cover  1  as described above is also applicable to insert molded articles other than the protective cover  1  in which the insert article and the synthetic resin are integrated by insert molding. 
     Specifically, an insert article is formed in a cup shape, the bottom of the cup shape is provided with a step having a side portion that is smaller in diameter than a side portion of the cup shape and connects to the bottommost portion, concaves or convexes are formed in the smaller-diameter side portion, and the synthetic resin has a portion covering the step (the bottommost portion and the smaller-diameter side portion). 
     REFERENCE SIGNS LIST 
     
         
           1  Protective cover (insert molded article) 
           1 A Cup-shaped main part (insert article) 
           2  First cylindrical portion 
           3  Second cylindrical portion 
           4  Annular portion 
           5  Third cylindrical portion (smaller-diameter side portion) 
           6  Disc portion (bottommost portion) 
           6 A Through hole 
           7  Seal body 
           8  Sensor holder part (synthetic resin) 
           8 A Base portion 
           8 B Wrap-around portion 
           8 C Step covering portion 
           9  Concave 
           10  Nut (insert article) 
           10 A Circumferential groove 
           11  Bearing device 
           12  Inner ring 
           12 A Inner ring track surface 
           13  Outer ring 
           13 A Outer ring track surface 
           14  Rolling element 
           15  Seal member 
           16  Magnetic encoder 
           17  Support member 
           18  Fixed mold 
           19  Movable mold 
           20  Gate 
           21  Support shaft 
         A Magnetic sensor 
         B Attachment bolt 
         C Step 
         D Diameter-reduced portion 
         S Seal body