[0001]The present invention constitutes a torque detection device used in an electrical power steering device of a vehicle, to a yoke cover to be assembled to the two electromagnetic yokes facing in the axial direction. Background technique [0002]An electric power steering apparatus for a vehicle, detected by the torque detector steering torque generated by the operation of the steering wheel by the driver (torque sensor), the steering burden of the driver by applying a steering assist force by the motor to a steering system it is intended to mitigate (e.g., see Patent documents 1-3). 　In the example shown in partial cut-away side view of FIG. 10, is aimed to reduce the force required of the electric motor 30 to operate the steering wheel 21 as the source of auxiliary power (e.g., see Patent Document 1). 　Here, explaining the example of Figure 10 the steering device of a vehicle, the rotation of the steering wheel 21 is transmitted to the input shaft 23 of the steering gear unit 22, the pair of left and right tie rods 24 and 24 with the rotation of the input shaft 23 by being pushed and pulled, the steering angle is applied to the front wheels. Steering wheel 21 is supported on the rear end portion of the steering shaft 25, the steering shaft 25 is fixed to the vehicle body is rotatably supported by the steering column 26. The front end of the steering shaft 25 is connected to the rear end of the intermediate shaft 28 via a universal joint 27, the front end of the intermediate shaft 28 is connected to the input shaft 23 via a universal joint 29. [0003] 　Then, cross-sectional view of FIG. 11, and with reference to the enlarged view of FIG. 12, an example of a more specific structure of the electric power steering apparatus. Steering column 26a is a inner column 31 and the outer column 32 are those comprising a combination of full length to be contracted during the secondary collision, it is supported on the vehicle body. A steering shaft 25a that is rotatably supported inside the steering column 26a is a lower shaft 33 and upper shaft 34, to permit torque transmission, and, comprising a combination of full length to be contracted at the time of a secondary collision. The rear end portion of the upper shaft 34 protruding from the rear end opening of the outer column 32, a steering wheel 21 (see FIG. 10) is fixed. The front end portion of the inner column 31, the housing 35 is coupled fixed, the front half portion of the lower shaft 33 is inserted inside the housing 35. Inside the housing 35, the front side of the lower shaft 33 is an input shaft, an output shaft 36 is rotatably supported by a pair of ball bearings 37 and 38. The output shaft 36 and lower shaft 33 are linked via a torsion bar 39. The front end portion of the output shaft 36 projecting from the front end opening of the housing 35, the universal joint 27 (see FIG. 10) is coupled. [0004] 　The rear end portion of the output shaft 36, the cylindrical portion 40 is provided. The outer peripheral surface of the cylindrical portion 40, the circumferential groove 41 is provided over the entire circumference in the circumferential direction. In contrast, on the inner peripheral surface of the cylindrical portion 40, the female stopper portion 42 of the concave-convex shape in the circumferential direction is provided. On the other hand, the front end portion of the outer peripheral surface of the lower shaft 33, the outer diameter (diameter of the circumscribed circle) is smaller than near the front end portion, the male stopper 43 of the uneven shape is provided in the circumferential direction. The male stopper portion 43, and the female stopper portion 42, can be recess-projection engaging a relative rotation in a predetermined angle range. Thus, excessive twisting prevention of the torsion bar 39 is achieved. 　Lower shaft 33 is made of steel as a magnetic metal, the front end portion close of the outer peripheral surface of the lower shaft 33, the torque detecting concave and convex portion 44 of the concave-convex shape in the circumferential direction is provided. The outer diameter side of the torque detecting concave and convex portion 44, the cylindrical torque-detecting sleeve 45 made of non-magnetic metal having conductivity such as an aluminum alloy is arranged. Proximal end of the torque detection sleeve 45 is fitted on the cylindrical portion 40 fixed. In this state, in order to position and preventing deformation in the axial direction of the torque detection sleeve 45, the edge portion of the base end portion of the torque detection sleeve 45 is crimped to the circumferential groove 41. The portion of the torque detection sleeve 45 located on the outer diameter side of the torque detecting concave and convex portion 44, a plurality of window holes 46a, 46b are provided. The outer diameter side of the torque detecting concave and convex portion 44 and a torque detecting sleeve 45, the torque detector 47 fixed fitted into the housing 35 is arranged. [0005] 　The rear end portion of the output shaft 36, the worm wheel 48 is fixedly fitted, the worm wheel 48, worm 49 which is rotatably supported by the housing 35 is engaged. Worm wheel 48 and the worm 49 constituting a worm reduction gear 50. 　The housing 35, the electric motor 30 (see FIG. 10) is supported fixed, the output shaft of the electric motor 30, the proximal end portion of the worm 48, is coupled to torque transmission. 　If the electric power steering apparatus configured as described above, by the driver operates the steering wheel 21, the torque is steering force to a steering shaft 25a is applied, depending on the direction and magnitude of the torque only minute, the torsion bar 39 is twisted elastically. Accordingly, by the circumferential positional relationship between the torque detecting concave and convex portion 44 and the torque-detecting sleeve 45 varies, the impedance change occurs in the coil constituting the torque detection unit 47. Therefore, based on this impedance variation, it can detect the direction and magnitude of the torque. Electric motor 30 generates auxiliary power corresponding to the detection result of the torque. The auxiliary power after being increased by the worm reduction gear 50, is imparted to the output shaft 36. As a result, the force required for the driver to operate the steering wheel 21 is reduced. [0006] 　Next, partial cross-sectional perspective view of FIG. 13, and with reference to the exploded perspective view of FIG. 14 will be described torque sensor 47 constituting a torque detecting device of Patent Document 3. 　Torque detecting unit 47, a torque detecting concave and convex portion 44 formed in the lower shaft 33, the detection coil 13a and 13b of the pair disposed inside the housing 35, the torque detection sleeve disposed therebetween and a 45. 　The outer periphery of the torque detecting sleeve 45 is surrounded by an electromagnetic yoke 15a and 15b for holding the coil bobbin 18 detection coil 13a and 13b of the same standard are wound. That is, the detection coils 13a, 13b are arranged coaxially with the torque-detecting sleeve 45, the detection coil 13a surrounds the first window row portion consisting of the window hole 46a, the detection coil 13b and the second consisting of the window hole 46b surrounding the Madoretsu part. [0007] 　Furthermore, the torque detecting section 47, the coil 13a, 13b are two coil bobbin 18 having the same shape that are wound respectively, used facing each other. 　The lateral end of the flange portion 18b of the coil bobbin 18, the terminal mounting portion 18e constituting the coil-side connector connectable to a board-side connector is formed and positions the terminal mounting portions 18e on the upper end portion of the coil bobbin 18 the perpendicular line passing through the center of the coil bobbin 18 in the state as a symmetric axis, the position of the line symmetry, regulating portion 18d is formed. 　Restricting portion 18d includes a base portion in which a part of the flange portion 18b is protruded radially outwardly, the base portion to one region obtained by equally dividing the circumferential direction, formed to protrude toward the outside in the axial direction of the coil bobbin 18 It was composed of the convex portion. In other words, the two coil bobbins 18, in a state of arranging the flange portion 18b so as to face on the same axis, both the regulating portion 18d is abutted in the circumferential direction, and the structure in which the relative position of the rotation angle direction is determined going on. 　Terminal mounting part 18e is a substantially rectangular parallelepiped member which projects further radially outward from the side surface upper portion of the flange portion 18b, the upper surface thereof, two terminal 18f for connecting the board side connector is press-fitted It is. These two coil terminals 18f are disposed parallel to, and is fixed so as to protrude from the upper surface of the terminal mounting portion 18e radially outward. 　Furthermore, on one side portion of the terminal mounting portion 18e, plate-like guide portion 18g projecting further radially outward from the upper surface of the terminal mounting portion 18e is formed. [0008] 　Electromagnetic yoke 15a and 15b is a member of the same shape, a cylindrical portion 15d fitted around the coil bobbin 18, a ring-shaped bottom portion 15e formed at an end portion facing axially outward as it is fixed to the coil bobbin 18 are composed of the inner diameter of the bottom portion 15e has a inner diameter the same size as the cylindrical portion of the coil bobbin 18 (groove portion 18c). 　The electromagnetic yoke 15a and 15b, the end portion opposite to the bottom portion 15e of the cylindrical portion 15d, 3 one recess 15c are spaced apart by a predetermined angle in the circumferential direction. 　Here, one of the yoke cover 14 is a substantially ring-shaped member, in its outer peripheral surface, three projections 14a are spaced apart by a predetermined angle in the circumferential direction. 　Yoke cover 14, the electromagnetic yoke 15a, in a state in which is fitted the protrusion 14a to the recess 15c and 15b, are pressed into the inner diameter of the opposing two electromagnetic yokes 15a, both of 15b the cylindrical portion 15d. 　When press-fitting the yoke cover 14 electromagnetic yoke 15a, a 15b, projections 14a are recesses 15c, since it is abutted engaged with 15c, the electromagnetic yoke 15a, the relative position of the press-fitting direction of the yoke cover 14 relative 15b is regulated (press-fit depth is restricted). 　The configuration of the yoke cover 14 as described above, the torque detecting device of Patent Document 3, with respect to the torque detecting device of Patent Document 2, reduction of component count and electromagnetic yoke 15a, press-fit the number of yoke cover 14 to 15b It has achieved a reduction. CITATION Patent Document [0009] Patent Document 1: WO 2014/199959 Patent Publication Patent Document 2: WO 2004/018987 pamphlet Patent Document 3: JP 2014-122869 JP Summary of the Invention Problems that the Invention is to Solve [0010] 　Projections 14a formed on one of the yoke cover 14 in the torque detecting device of Patent Document 3, in order to have the function of a pair of detection coils 13a, 13b interval regulations to restrict the axial length (issuing a precision) there is a need. [0011] 　Here, when performing a precision stamping punching of the yoke cover 14 (fine blanking), both of the electromagnetic yoke 15a, press-fit is possible becomes accurate smooth shear plane outer diameter portion of the thickness of the 15b is formed in a direction entirely, accurate smooth shearing surface in radial leading end surface of the protrusion 14a is formed in the thickness direction over the entire surface. 　Therefore, since the sagging vent radially distal end surface of the protrusion 14a is not formed, the axial length of the protrusion 14a is restricted. 　However, when manufacturing the yoke cover by precision punching, it requires high accuracy and high rigidity press mold, pressing force and inverse keep pressing the material of the blank portions other than directly required press drive force to the machining force ( since the die cushion) is required, the cycle time is slow along with the structure of the press machine becomes complicated. 　Thus, productivity with cost of manufacturing the yoke cover is increased is reduced [0012] 　Further, if carried out by general punching pressing a punching of the yoke cover, does not perform any special processing such as precision punching, it is possible to suppress the increase and decrease in the productivity of the manufacturing cost. 　However, when manufacturing a yoke cover with common punching press working, the working surface, possible other highly accurate smooth shearing surface, since fracture surface and vent sag is formed, pressed to both electromagnetic yoke it becomes difficult to form a highly accurate smooth shear plane becomes. 　Moreover, vent anyone radially distal end surface of the protrusion of the yoke cover is formed, there is a sag D vent the protrusion 1a of the yoke cover 1 as shown in enlarged longitudinal sectional view of FIGS. 7 (a) since a large radius of curvature R of the punching sag D is in a state, when pressed into an electromagnetic yoke 11a as shown in enlarged longitudinal sectional view of FIG. 8 (a), the inner surface of the recess 11c of the electromagnetic yoke 11a protrusion 1a since the radial contact length H1 between the axial end surface 10A of the shorter, not enough contact area. 　Thus, the axial length of the projection of the yoke cover, can not be regulated so as to satisfy the accuracy required. [0013] 　In terms of the yoke cover in the torque detecting device of Patent Document 3 as described above, but in which there is a feature of reducing such components number, to regulate the axial length of the protruding portion without increasing the manufacturing cost I see that there is room for improvement. [0014] 　An object of the present invention is to regulate the axial length of the protruding portion without increasing the manufacturing cost of the one yoke cover that fits is pressed into the two electromagnetic yokes constituting a torque detecting device . Means for Solving the Problems [0015] 　Yoke cover according to the present invention, because of the problem solving, impedance changes depending on the torque generated in the rotary shaft, a detection coil in a pair, to detect the torque based on the output voltage of the detecting coil constituting a torque detecting apparatus, as sandwiched between two electromagnetic yoke facing each other in the axial direction, one yoke for holding the two electromagnetic yoke the two electromagnetic yoke to the inner diameter of the cylindrical portion is Meawasa of a cover, 　the projecting radially outward from the inner diameter of the electromagnetic yoke, the two engage in opposite circumferential direction a plurality of recesses formed in an end portion of the electromagnetic yoke abutted against the circumferential direction a plurality of projections It stepped surface in the axial direction end faces of the parts, and / or that the stepped surface is formed radially distal end surface of the protrusion and wherein (claim 1). [0016] 　According to such a yoke cover, the axial length of the engaged with a plurality of circumferential recesses and abut against the plurality of circumferential protrusions of the electromagnetic yoke is regulated by the stepped surface, the inner surface of the recess of the electromagnetic yoke and a sufficient contact area is secured between the axial end faces of the projections of the yoke cover. 　Moreover, the area of the stepped-down surface which is formed on the projecting portion of the yoke cover is small, by forming an appropriate processing method stepped surface by selecting, it is possible to suppress an increase in manufacturing cost of the yoke cover. 　Therefore, without increasing the manufacturing cost of the one yoke cover that fits it is pressed into the two electromagnetic yokes constituting a torque detecting apparatus, the axial length of the protrusion of the yoke cover so as to satisfy the accuracy required It is can be regulated. [0017] 　Here, preferably the stepped surface is the push processed pressing surface. 　According to such a configuration, since the formation by the pressing process the stepped surface does not perform a special process, such as precision punching, further increases the effect of suppressing the increase in the manufacturing cost of the yoke cover . [0018] 　Torque detecting apparatus according to the present invention, the impedance changes according to torque generated in the rotary shaft, a detection coil in a pair, a torque detector for detecting the torque based on the output voltage of the detecting coil are those provided with the yoke cover (claim 3). [0019] 　Electric power steering apparatus according to the present invention, an electric power steering apparatus for applying a steering assist force to a steering system of a vehicle, and the torque detector for detecting steering torque input to the steering mechanism, the torque detecting device in on the basis of the detected steering torque, in which a motor control unit for driving and controlling the electric motor to impart the steering assist force (claim 4). [0020] 　Method for producing a yoke cover according to the present invention, because of the problem solving, impedance changes depending on the torque generated in the rotary shaft, a detection coil in a pair, the torque based on the output voltage of the detecting coil constituting a torque detecting device for detecting, as sandwiched between two electromagnetic yoke facing each other in the axial direction, for holding the two said is Meawasa the inner diameter of the cylindrical portion of the electromagnetic yoke two electromagnetic yoke a one manufacturing process of the yoke cover, 　the projecting radially outward from the inner diameter of the electromagnetic yoke, engages abutment in engagement with the two electromagnetic yoke opposing end circumferential direction a plurality of recesses formed in the the the axial end surface of is a plurality of circumferential projections, and / or the radial leading end surface of the projecting portion is pressed processed to have a pressing step to regulate the axial length of the protrusions The characters (claim 5). [0021] 　According to the manufacturing method of the yoke cover, the axial length of the engaged with a plurality of circumferential recesses and abut against the plurality of circumferential protrusions of the electromagnetic yoke is restricted by the pressing process, the recess of the electromagnetic yoke the inner surface and a sufficient contact area between the axial end faces of the projections of the yoke cover is secured. 　Therefore, since not performed special processing such as precision punching, without increasing the manufacturing cost, it can be restricted axial length of the protrusion of the yoke cover so as to satisfy the accuracy required. [0022] 　Method of manufacturing an electric power steering apparatus according to the present invention is a manufacturing method of an electric power steering apparatus for applying a steering assist force to a steering system of the vehicle, constituting a torque detecting apparatus for an electric power steering apparatus, in the axial direction the inner diameter of the cylindrical portion of the two electromagnetic yokes facing each other, is intended to include the step of Awa fit the yoke cover manufactured by the manufacturing method (claim 6). Effect of the invention [0023] 　As described above, according to the yoke cover and the manufacturing method thereof according to the present invention, the axial engages the circumferential direction a plurality of concave portions abutted circumferential direction a plurality of protrusions of the electromagnetic yoke length press working or the like It is restricted by the stepped surface formed by, since the sufficient contact area between the axial end faces of the projections of the inner surface and the yoke cover the recess of the electromagnetic yoke is ensured, without increasing the manufacturing cost, are required so as to satisfy the accuracy that a marked effect of being able to regulate the axial length of the protrusion of the yoke cover. BRIEF DESCRIPTION OF THE DRAWINGS [0024] It is a perspective view of the yoke cover according to the embodiment of FIG. 1 the present invention. [FIG. 2] (a) is a plan view of the yoke cover, is an arrow sectional view taken along line X-X of (b) is (a). [FIG 3] (a) is a plan view of an electromagnetic yoke, is an arrow Y-Y cross-sectional view of (b) is (a). FIG. 4 is an exploded perspective view of the yoke cover and two electromagnetic yoke. [Figure 5] is a front view showing a state where press-fitting the yoke cover the inner diameter of the cylindrical portion of the two electromagnetic yokes, other components that constitute the torque detecting apparatus is omitted. [Figure 6] is an explanatory view showing an example of a manufacturing method of a yoke cover according to the preferred embodiment of the present invention, showing (a) shows a first punching step, (b) a second punching step. [Figure 7] is an enlarged longitudinal sectional view, (a) represents protrusion formed on the outer peripheral surface of the yoke cover by punching press work, (b) is shows a protrusion axial end face is pressed processed there. [Figure 8] is an enlarged longitudinal sectional view showing a state where press-fitting the yoke cover the electromagnetic yoke, (a) shows the example in which a yoke cover does not press working protrusions, (b) the axial direction of the protrusion It shows an example using a pressure processed yoke cover the end faces. [Figure 9] is an enlarged longitudinal sectional view, (a) represents projections is radially distal end surface is pressed processing, (b) shows a protrusion axial end surface and the radial leading end surface is pressed processed ing. Is a partial cut-away side view of FIG. 10 steering system. 11 is a cross-sectional view of an electric power steering apparatus. FIG. 12 is an enlarged view of the left end upper half in FIG. 10. 13 is a partial cross-sectional perspective view of the torque detector. FIG. 14 is an exploded perspective view of the torque detector shown by omitting the detection coil. DESCRIPTION OF THE INVENTION [0025] 　Next will be described an embodiment based on the accompanying drawings of the present invention, the present invention is, all embodiments meet the requirements referred to in the invention is not limited to that shown in the accompanying drawings forms claims including is Dressings. [0026] 　Yoke cover of the present invention has the same function as the yoke cover constituting a torque detecting device of Patent Document 3 (yoke cover 14 of FIG. 13 and FIG. 14), the two electromagnetic yoke facing each other in the axial direction as sandwiched, the inner diameter of the cylindrical portion of the two electromagnetic yokes are those Meawasa. 　The torque detecting device of the present invention has the same function as the torque detecting device of Patent Document 3 (torque detecting apparatus comprising a torque detecting portion 47 of FIG. 13), opposite directions in response to torque generated in the rotary shaft to, or impedance changes in the same direction, a detection coil in a pair, and detects the torque based on the output voltage of the detection coil. 　Furthermore, the electric power steering apparatus of the present invention are those having the same function as the electric power steering apparatus of Patent Document 1, and the torque detector for detecting steering torque input to the steering mechanism, the torque detecting device in on the basis of the detected steering torque, in which a motor control unit for driving and controlling the electric motor to impart the steering assist force. [0027] 　Perspective view of FIG. 1, and as shown in a plan view and a cross-sectional view of FIG. 2 (b) in FIG. 2 (a), the yoke cover 1 according to the embodiment of the present invention is a substantially ring-shaped member, its outer peripheral surface F, the first cylindrical surface 2a is formed on the first circumferential portion F1 of the three, first from the first circumferential portion F1 to second circumferential portion F2 of the three positions shifted in the circumferential direction 2 cylindrical surface 2b is formed. The first cylindrical surface 2a and the second cylindrical surface 2b are alternately arranged in the circumferential direction. 　Here, first circumferential portion F1 and the second circumferential portion F2 and the protruding portion 1a forms a first cylindrical surface 2a and the second cylindrical surface 2b may if two or more places. 　The yoke cover 1 of the present embodiment, the circumferential equal intervals in the three projections 1a are formed, projecting portion 1a adjacent, between 1a, first cylindrical surface 2a and the second cylindrical surface 2b is one It is formed. 　Further, the planar portion 5 is formed between the projecting portion 1a, the first cylindrical surface 2a and the second cylindrical surface 2b adjacent between 1a. 　Furthermore, the planar portion 6 between the projecting portion 1a and the first cylindrical surface 2a is planar portion 7 is formed between the projecting portion 1a and the second cylindrical surface 2b. 　The planar portions 5, 6 and 7 may be a rather may be a curved surface, a surface located radially inward from imaginary cylindrical surface including a first cylindrical surface 2a and the second cylindrical surface 2b plane . [0028] 　Here, formed on the outer peripheral surface F of the yoke cover 1, the protrusion 1a and the first cylindrical surface 2a and the second cylindrical surface 2b are those formed, for example, by punching press work, and the first cylindrical surface 2a second cylindrical surface 2b is a shear plane formed by changing the punching direction by punching press process. The first cylindrical surface 2a at a position deviated one axial direction to the (downward in FIG. 1), the second cylindrical surface 2b is formed at a position offset to the other axial (upward in FIG. 1). 　Further, since the first cylindrical surface 2a is sheared surfaces formed by press punching, punching sag 3a in the axial direction of the one (lower in Fig. 1) close to the R-shape of the first cylindrical surface 2a is, first cylindrical axial direction of the other surface 2a fracture surface 4a to close (upper in Fig. 1) is formed. [0029] 　Similarly, the second cylindrical surface 2b is, since changing the punching pressing and punching direction to form a first cylindrical surface 2a is a shear plane formed by punching press work, one axial direction of the second cylindrical surface 2b fracture surface 4b to close (downward in FIG. 1), vent sagging 3b of R shape is formed axially of the other of the second cylindrical surface 2b to close (upper in Fig. 1). 　Here, fracture surface 4a from the upper edge of the first cylindrical surface 2a toward the upward (from the upper edge of the first cylindrical surface 2a as the distance in the axial direction) outer diameter decreases gradually tapered a surface, fracture surface 4b is tapered to an outer diameter toward downward from the lower end edge of the second cylindrical surface 2b (as the distance from the lower edge of the second cylindrical surface 2b in the axial direction) gradually decreases which is the surface. 　Further formed, axial end surfaces of the protrusion 1a, i.e. the pressing surface A on the lower surface in FIG. 1 and 2 (b) is, the pressing surface B on the upper surface of FIG. 1 and 2 (b), the pressing process It is. [0030] 　Plan view and FIG. 3 a cross-sectional view of (b) in FIG. 3 (a), and as shown in the exploded perspective view of FIG. 4, two electromagnetic yokes 11a to the yoke cover 1 is pressed, 11b are members of the same shape a is composed of a coil bobbin (not shown) and a cylindrical portion 11d fitted around a ring-shaped bottom portion 11e formed at an end portion facing axially outward when secured to the coil bobbin. 　The electromagnetic yoke 11a, 11b is on the opposite side of the end portion and the bottom portion 11e of the cylindrical portion 11d (an end portion of the yoke cover 1 side), along with three recesses 11c circumferentially equal intervals is formed, adjacent recesses 11c, 11c notch 11f is formed between the. Recess 11c and the notch portion 11f are alternately arranged in the circumferential direction. In Figure 4, but is longer than the circumferential length of the recess 11c circumferential length of the notch 11f, these large and small does not matter. 　Here, the cutout portion 11f, the coil bobbin terminal mounting portion (coil bobbin 18 see FIG. 14) (see the terminal mounting portion 18e of FIG. 14) is engaged. [0031] 　Exploded perspective view of FIG. 4 other components that constitute the torque detecting apparatus shown omitted, and as shown in the front view of FIG. 5, the yoke cover 1 two electromagnetic yokes 11a, 11b of the cylindrical portion 11d of when press-fitting the inner diameter, the first cylindrical surface 2a of the three positions with fitted is pressed into the electromagnetic yoke 11a, a second cylindrical surface 2b of the three is fitted is pressed to the electromagnetic yoke 11b. 　The first cylindrical surface 2a of the yoke cover 1 is fitted to the inner surface of the engaging protrusion G1 electromagnetic yoke 11a, the inner surface a second cylindrical surface 2b of the yoke cover 1 is engaged protrusion G2 electromagnetic yoke 11b It fits into. Further, the protruding portion 1a of the yoke cover 1 is engaged electromagnetic yoke 11a, the concave portion 11c of the 11b, the 11c. 　Electromagnetic yoke 11a and the yoke cover 1 as shown in FIG. 4, when pressed into 11b, unplug sagging 3a of R shape in the yoke cover 1, since there is a 3b (see also FIG. 1), the press-fitting is improved. [0032] 　When assembled in this way two electromagnetic yokes 11a, a yoke cover 1 to 11b, since the first cylindrical surface 2a and the second cylindrical surface 2b of the yoke cover 1 has a high smooth shear plane precision, the electromagnetic yoke 11a, 11b of the cylindrical portion 11d, a stable firm holding power was in a state of fitted by press-fitting the yoke cover 1 to the inside diameter of 11d has occurred. 　Here, the press-fitting depth when the yoke cover 1 is pressed electromagnetic yoke 11a, and 11b, the protrusion 1a and the electromagnetic yoke 11a of the yoke cover 11 as shown in FIG. 5, the recess 11c of 11b, restricted by the 11c is, depth of less than half the thickness of the yoke cover 1 is pressed. That is, the protrusion 1a is concave 11c, 11c to engage the pressing surface A, since B is abutted, electromagnetic yoke 11a, the relative position of the press-fitting direction of the yoke cover 1 is the (pressed depth regulation of 11b is restricted). 　Incidentally, the yoke cover 1 and the electromagnetic yoke 11a, the fitting between 11b, electromagnetic yoke 11a and the yoke cover 1, an electromagnetic yoke 11a in a state assembled to 11b, since it becomes a state where 11b can not move relatively, pressed (interference fit) may be a fit middle instead. [0033] 　Next, a method for manufacturing the yoke cover 1. 　Method for manufacturing a yoke cover 1 (see FIGS. 1 and 2 of the present embodiment) performs punching press working, first punching step and second punching step, as well as having a pressing step of pressing processed projections 1a . 　The first punching step is to plate, two electromagnetic yokes 11a, a first cylindrical surface 2a to be press-fitted into one 11a of 11b, so as to form a plurality of first circumferential portion F1 Nisen section of the outer peripheral surface F to, those formed by press punching a first cylindrical surface 2a. 　The second punching step, the relative said plate member through the first punching step, two electromagnetic yokes 11a, a second cylindrical surface 2b to be press-fitted to the other 11b of 11b, the first circumferential direction of the outer peripheral surface F so as to form a portion F1 as a plurality of second circumferential portion F2 Nisen cross section circumferentially displaced, that the second cylindrical surface 2b, is formed by punching press process of varying the first punching step and the punching direction it is. 　Further, the pressing step, relative to the plate material through the first punching step and the second punching step is intended to press machining a predetermined portion of the projections 1a to regulate the axial length of the protruding portion 1a . [0034] 　Next, an example of a method of manufacturing the yoke cover 1 according to the embodiment of the present invention. (First punching step) 　as shown in the illustration of FIG. 6 (a), performing a punching press working with respect to the plate material by the first punching die 8a is a hatched portion in FIG. (For example, FIGS. 6 (a) punching the surface side from the back side). 　The first cutting die 8a, together has a recess forming the projecting portion 1a, has an arc portion R1 and the linear portion S1, S2, S3,. 　Thus, the plate, protrusions 1a, first cylindrical surface 2a is shear plane, punching sag 3a and broken surface 4a, and flat portions 5, 6 and 7 are formed (see FIGS. 1 and 2). [0035] (Second punching step) 　as shown in the illustration of FIG. 6 (b), performing a punching press working with respect to the plate member by the second punching die 8b is a hatched portion in FIG. (For example, and FIG. 6 (b) punching from the surface side to the back side). 　Second cutting die 8b has a circular arc portion R2. 　Therefore, the plate member, a second cylindrical surface 2b, punching sag 3b and fracture surface 4b is formed a shear plane (see FIGS. 1 and 2). 　Further, since the same time punching the outer and inner diameter 1b of the yoke cover 1 by the second punching die 8b, it can be secured in the outer inner diameter accuracy (concentricity). [0036] 　In the above description, the example of forming the protrusion 1a in the first punching step, may be formed a protrusion 1a in the second punching step. [0037] 　As shown in enlarged longitudinal sectional view of FIG. 7 (a), the projection portion 1a formed in the first punching step and second punching step, the punching press working, highly accurate smooth shear plane S other, fracture surface E and vent sag D is formed. The radius of curvature R is large the punching shear drop D, since the securing of the plane is difficult, the contact surface between the inner surface of the recess 11c of the electromagnetic yoke becomes difficult to secure in a state where there is a vent sag D. 　Therefore, by performing a pressing step described below to regulate the axial length of the protruding portion 1a (put the accuracy of the axial length). [0038] (Pressing step) 　, as shown in FIG. 7 enlarged longitudinal sectional view of (b), the axial end surface 10A of the projecting portion 1a, and 10B to press machining, the axial end surface 10A, the 10B, precisely finished pressed forming a surface a, B. 　Whereby the axial length of the distal portion of the protrusion 1a L2 is smaller than the axial length L1 of the inner diameter side portion of the yoke cover 1 (L2