Patent Publication Number: US-10763731-B2

Title: Resolver stator

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2017-068133 filed on Mar. 30, 2017 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The disclosure relates to a stator of a resolver, especially to a structure of the stator. 
     2. Description of Related Art 
     There is a known resolver that detects a rotational position of a rotor such as a motor rotor rotating about an axis. For example, a resolver provided in a motor includes a resolver rotor that rotates together with a rotor of the motor, and a resolver stator that is disposed around the resolver rotor and is disposed so as to be fixed to a stator of the motor. By detecting a rotational position of the resolver rotor with respect to the resolver stator, it is possible to detect a position of the rotor of the motor with respect to the stator. 
     The resolver stator is fixed to a structure to which the stator of the motor is fixed, such as a case of the motor. To position the resolver stator with respect to the case, a knock pin can be used. In Japanese Unexamined Patent Application Publication No. 2015-023622 (JP 2015-023622 A) described below, a resolver stator ( 30 ) that is positioned with respect to a motor case ( 18 ) by using a knock pin ( 50 ) is described. The resolver stator ( 30 ) has a resin cover member ( 40 ) that covers a stator coil ( 38 ). In the cover member ( 40 ), a stopper part ( 58 ) is provided at a position corresponding to a rear end of the knock pin ( 50 ). The stopper part ( 58 ) suppresses the knock pin ( 50 ) from coming off. The reference numerals stated above in the parentheses are used in reference literature 1 below, and are not related to the reference numerals used in description of an embodiment of the application concerned. 
     SUMMARY 
     In a case where a metallic member, such as a metallic cover that covers a core of a resolver stator, is provided adjacent to the core, and the member suppresses a knock pin from coming off, and when a distance between the member and the knock pin is short, peripheral electromagnetic noise received by the knock pin enters the core of the resolver stator through the cover, and noise can be mixed with an output signal from the resolver. 
     The disclosure restrains a knock pin from coming off, and also restrains electromagnetic noise from entering from the knock pin. 
     As an example aspect of the present disclosure is a resolver stator that is mounted on a target structure including a knock pin, the target structure having a hole, a portion of the knock pin being disposed in the hole. The resolver stator includes: a stator core that has an engaging groove configured to be engaged with the knock pin, and the stator core includes a yoke; and a resolver cover covering the yoke in a central axis direction of the resolver cover, the resolver cover being made from metal and having a first cutout, the first cutout being disposed such that the first cutout overlaps at least a part of an end surface of the knock pin engaged with the engaging groove, in the central axis direction. 
     As an example aspect of the present disclosure is a resolver stator that is mounted on a target structure including a knock pin, the target structure having a hole, a portion of the knock pin being disposed in the hole. The resolver stator includes: a stator core having an engaging groove configured to be engaged with the knock pin; and a metallic fixing plate that is screwed and joined to a bolt configured to pass through the target structure and the stator core from a back surface of the target structure, the fixing plate being configured to sandwich and fix the stator core together with the target structure. The fixing plate has a second cutout, and the second cutout is disposed such that the second cutout overlaps at least a part of an end surface of the knock pin engaged with the engaging groove, in a central axis direction of the fixing plate. 
     An area of the first cutout may be 40% or smaller of an area of the knock pin end surface. An area of the second cutout may be 40% or smaller of an area of the knock pin end surface. 
     The first cutout may be disposed in the resolver cover such that the first cutout is separated from the knock pin end surface. The second cutout may be disposed in the fixing plate such that the second cutout is separated from the knock pin end surface. 
     A clearance between the knock pin end surface and the first cutout may be smaller than a length of the portion at which the knock pin is disposed in the hole. A clearance between the knock pin end surface and the second cutout may be smaller than a length of the portion at which the knock pin is disposed in the hole. 
     Since the knock pin facing part faces only a part of the knock pin end surface, it is possible to restrain entrance of electromagnetic noise from the knock pin while the knock pin is suppressed from coming off. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a sectional view of a schematic structure of a resolver according to the disclosure and of a periphery of the resolver; 
         FIG. 2  is a view of a resolver stator and a periphery of the resolver stator, the view being taken in the direction of arrows II and showing a state where a resolver cover is removed; 
         FIG. 3  is a view of the resolver stator with the resolver cover mounted in  FIG. 2 ; and 
         FIG. 4  is a view of another form of a resolver cover. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the disclosure is described with reference to the drawings.  FIG. 1  is a sectional view of a resolver  12  provided in a motor  10 . Only a structure of the motor  10  in a periphery of the resolver  12  is shown. 
     The motor  10  includes a motor rotor  14 , and a motor stator  16  that is arranged so as to surround the motor rotor  14 . The motor rotor  14  is joined to a rotor shaft  18  that serves as an output shaft of the motor  10 , and the motor rotor  14  and the rotor shaft  18  rotate integrally. Both the motor rotor  14  and the motor stator  16  are housed in a motor case  20 . The motor case  20  includes an end case  24 . In the end case  24 , a bearing  22  is disposed. The bearing  22  supports the rotor shaft  18  so that the rotor shaft  18  is able to rotate. Although  FIG. 1  shows a first end of the rotor shaft  18  only, a second end of the rotor shaft  18  is also supported by a bearing so that the rotor shaft  18  is able to rotate. The motor stator  16  includes a motor coil  26 , and a motor stator core  28  around which the motor coil  26  is wound, and the motor stator  16  is fixed to the motor case  20 . 
     The resolver  12  includes a resolver rotor  30  fixed to the rotor shaft  18 , and a resolver stator  32  that is mounted and fixed onto the motor case  20 , especially onto the end case  24 . The resolver rotor  30  has an elliptical plate shape, and a center of rotation of the elliptical resolver rotor  30  is located on an axis of rotation of the rotor shaft  18 . As the rotor shaft  18  rotates, the resolver rotor  30  also rotates integrally. The resolver rotor  30  is formed by laminating electrical steel sheets in a direction of the axis of rotation. The resolver stator  32  has a generally circular shape, and is disposed so as to surround an outer periphery of the resolver rotor  30 . Further, the resolver stator  32  is disposed so that the resolver stator  32  is housed radially inward of a plurality of arc walls  34  provided in the end case  24  (see  FIG. 2  and  FIG. 3 ). The arc walls  34  are disposed on the same circumference about the axis of rotation of the rotor shaft  18 , and an outer peripheral side surface of the resolver stator  32  comes into contact with inner wall surfaces of the arc walls  34 . Thus, a position of the resolver stator  32  in the radial direction is decided. 
     The resolver stator  32  includes a stator core  40 , and resolver coils  42 . The stator core  40  has a circular yoke portion (yoke)  36 , and teeth  38  that extend inwardly from an inner periphery of the yoke portion  36 , and the resolver coils  42  are mounted so that the resolver coils  42  are wound around the teeth  38 . The stator core  40  is formed by laminating electrical steel sheets in a direction of an axis of rotation of the resolver rotor  30 . The plurality of teeth  38  is disposed on the inner periphery of the yoke portion  36  along a circumferential direction. 
     The resolver coils  42  include three kinds of coils that are an excitation coil and two detecting coils. The two detecting coils are mounted on the two teeth  38 , respectively, the two teeth  38  being disposed at intervals of electric angle of 90° of the motor  10 . When alternating current is applied to the excitation coil, current is induced in the two detecting coils. 
     When the resolver rotor  30  rotates with rotation of the rotor shaft  18 , a gap between an outer peripheral surface of the elliptical resolver rotor  30  and distal ends of the teeth of the stator core  40  changes periodically. Therefore, current induced in the detecting coil changes periodically. From the changes of current flowing in the detecting coils, a rotational position of the resolver rotor  30  with respect to the resolver stator  32  is calculated. Since the resolver stator  32  is fixed to the motor case  20 , and the resolver rotor  30  rotates integrally with the motor rotor  14 , the resolver  12  is able to detect a rotational position of the motor rotor  14  based on the motor case  20 . 
     A shape of the resolver rotor  30  is not limited to the above-mentioned ellipse, and may be any shape as long as a gap between the outer peripheral surface of the resolver rotor  30  and the distal ends of the teeth of the stator core  40  changes periodically with rotation. For example, the resolver rotor  30  may have a disk shape having a center that is displaced from the center of rotation. 
     At least a part of the resolver coil  42  is housed in a coil case  44 . In the resolver  12 , the coil case  44  has a circular shape along the stator core  40 , and is disposed on the front and back of the stator core  40 . The coil case  44  may be made from resin. 
     A resolver cover  46  is disposed on a surface on the opposite side of the end case  24  so that the resolver cover  46  covers the yoke portion  36  of the resolver stator  32 . In other words, the resolver cover  46  covers the yoke portion  36  in a central axis direction of the resolver cover  46 . A material for the resolver cover  46  is metal, and may be steel in particular. The resolver cover  46  has a circular plate shape that corresponds to the yoke portion  36 , and a flange  48  is provided in an inner peripheral edge of the resolver cover  46 . The flange  48  comes into contact with an outer peripheral surface of the coil case  44 . Further, outer peripheral edges of the resolver cover  46  and the yoke portion  36  coincide with each other, and both of the outer peripheral edges are in contact with the inner wall surfaces of the arc walls  34 . In the resolver cover  46 , a boss portion  50  having a tapped hole is provided. A threaded portion of a bolt  52  is screwed into the tapped hole of the boss portion  50 . The bolt  52  penetrates from a back surface of the end case  24 . In the end case  24 , a through-hole  54  for the bolt  52  to pass through is formed, and a long hole  56  for the bolt  52  to pass through is also formed in the stator core  40  (see  FIG. 2 ). The long hole  56  extends in a circumferential direction, and thus allows the resolver stator  32  to move in an angular range in the circumferential direction. Once the bolt  52  is fastened, the stator core  40  is sandwiched between the resolver cover  46  and the end case  24  and fixed to the motor case  20 . The resolver  12  is fixed by using the three bolts  52 . As described above, the resolver cover  46  functions as a fixing plate that sandwiches and fixes the stator core  40  together with the motor case  20 . 
       FIG. 2  and  FIG. 3  are views of the resolver stator  32  and a periphery of the resolver stator  32  seen from a direction of arrows II shown in  FIG. 1 .  FIG. 2  shows a state in which the resolver cover  46  is removed. Hereinafter, description is given with reference to  FIG. 1 , and  FIGS. 2, 3 . 
     In the stator core  40 , an engaging groove  60  is provided. The engaging groove  60  is engaged with a knock pin  58  that is erected from the end case  24 . The engaging groove  60  is formed radially inwardly from the outer peripheral edge of the yoke portion  36 , and is also provided over an entire thickness direction of the yoke portion  36  (a direction along an axis of rotation of the motor rotor). The knock pin  58  is inserted in a joining hole (hole)  62  provided in the end case  24 , and is erected so that one end of the knock pin  58  projects from the end case  24 . The knock pin  58  has a columnar shape and a material thereof may be metal, particularly steel. Dimensions of the knock pin  58  and the engaging groove  60  in the circumferential direction are set so that a clearance is made between the knock pin  58  and the engaging groove  60 . Thus, it is possible to move the resolver stator  32  slightly in the circumferential direction in a state where the bolt  52  is loosened a little bit and the resolver stator  32  is temporarily fixed. Accordingly, it is possible to make fine adjustments of a position of the resolver stator  32  in the circumferential direction. 
     At a position of the resolver cover  46 , the position corresponding to the knock pin  58  and the engaging groove  60 , a cutout (a first cutout, a second cutout)  64  is provided inwardly from the outer peripheral edge of the resolver cover  46 . A bottom edge  64   a  of the cutout  64  extends in the circumferential direction, and the cutout  64  is formed so that the bottom edge  64   a  goes across an end surface  58   a  of the knock pin  58 . Thus, the resolver cover  46  faces a part of the knock pin end surface  58   a , and the remaining part of the knock pin end surface  58   a  is exposed without being covered by the resolver cover  46 . That is, the part of the resolver cover  46 , the part facing the knock pin (a knock pin facing part), faces only a part of the knock pin end surface  58   a . In the other words, the cutout  64  is disposed such that the cutout  64  overlaps at least a part of an end surface of the knock pin  58   a  engaged with the engaging groove  60 , at the center axial direction of the resolver cover  46 . 
     Since the resolver cover  46  faces the knock pin end surface  58   a , the knock pin  58  is suppressed from coming off from the joining hole  62 . Even when the knock pin  58  is fixed to the joining hole  62  by press fitting, it is still conceivable that the knock pin  58  comes off depending on conditions. For example, when the motor case  20  is made from an aluminum alloy, and the knock pin  58  is made from general steel, the knock pin  58  can be in a loose-fit state due to thermal expansion caused by heat generation in the motor. A coefficient of thermal expansion of an aluminum alloy is larger than that of general steel, and, when temperature becomes high, an inner diameter of the joining hole  62  expands and becomes larger than an outer diameter of the knock pin  58 . Therefore, these fitting dimensions are changed from a close-fit state to a loose-fit state, thus causing looseness. Therefore, it is possible that the knock pin  58  comes off. In a case where the motor  10  is installed in a vehicle, there are instances where the knock pin becomes loose due to vibration of the vehicle. In order to address falling of the knock pin  58 , the part that faces the knock pin end surface  58   a  is provided in the resolver cover  46 . Thus, this part presses the end of the knock pin  58  and suppresses the knock pin  58  from coming off. A clearance between the knock pin end surface  58   a  and the resolver cover  46  that faces the knock pin end surface  58   a  is set to be smaller than a depth at which the knock pin  58  is embedded in the joining hole  62 . Accordingly, it is possible to suppress the knock pin  58  from coming off. 
     When current flows in the motor coil  26  disposed in the periphery of the resolver  12 , a fluctuating magnetic field is generated in a periphery, and, there are instances where the magnetic field influences a magnetic flux induced in the stator core  40 . Because the resolver cover  46  is made from metal, an outside magnetic field caused by the motor  10  may be blocked to some extent. Meanwhile, there are instances where the knock pin  58  functions like an antenna and amplifies noise that is caused by an outside magnetic field. The noise can enter the stator core  40  through the resolver cover  46 . The noise degrades detection accuracy for a rotational position of the motor rotor  14 . 
     In the resolver  12 , since the resolver cover  46  faces only a part of the knock pin end surface  58   a , an amount of noise that enters is reduced. Since an area where the resolver cover  46  and the knock pin end surface  58   a  face each other is small, it is possible to reduce noise entering the resolver cover  46  from the knock pin  58  in comparison with a case where the resolver cover  46  faces the entire knock pin end surface  58   a . An area where the knock pin end surface  58   a  and the knock pin facing part face each other, that is, each an area of the first cutout and the second cutout is 40% or smaller of the overall area of the knock pin end surface  58   a . Further, it is preferred that the resolver cover  46  is separated from the knock pin end surface  58   a . As the resolver cover  46  is separated from the knock pin end surface  58   a , entry of noise is also restrained. 
       FIG. 4  is a view of another form for restraining entry of noise. In this form, a shape of a resolver cover is different from that of the foregoing resolver cover  46 . The rest of the structure is similar to that described in the foregoing. The resolver cover  66  in this form has a separated portion  68 , instead of the foregoing cutout  64 . The separated portion  68  is bent and separated further from a knock pin end surface  58   a  in an axis direction of a knock pin than the rest of the resolver cover  66 . Thus, a distance between the knock pin end surface  58   a  and the resolver cover  66  becomes longer. Therefore, compared to a flat resolver cover without the separated portion  68 , noise entering the resolver cover  66  from the knock pin  58  is reduced. In this case, a distance between the knock pin end surface  58   a  and the separated portion  68  of the resolver cover  66  facing the knock pin end surface  58   a  is set to be smaller than a depth at which the knock pin  58  is embedded into a joining hole  62 . Thus, it is possible to suppress the knock pin  58  from coming off.