Stepping motor, electric valve, and motor monitoring device

Abstract

[Problem] To improve accuracy of detecting a magnetic flux of a rotor magnet by a magnetic sensor. [Solution] A stepping motor 12 in the present embodiment is of a claw pole type, including: a stator 30 having coils 31, 32; a cylindrical case 14 which is fitted inside the stator 30 and partially protrudes from one end surface of the stator 30; a rotor 20 which is rotatably housed in the case 14 and has a magnet; and a magnetic sensor 50 which is disposed so as to overlap the one end surface of the stator 30 and is configured to be able to detect a magnetic flux directed in a tangential direction of a circle centered on the rotor 20.

Description

Stepping motors, motor-operated valves, and motor monitoring devices

[0001] The present disclosure relates to a stepping motor, an electric valve driven by the stepping motor, and a motor monitoring device that monitors the state of the stepping motor.

[0002] A known conventional stepping motor is a claw-pole stepping motor in which a cylindrical case housing a rotor protrudes from one end face of a stator. Also known is a stepping motor of this type that has a magnetic sensor disposed on one end face of the stator to detect the magnetic flux of the rotor magnet. The detection results of the magnetic sensor are used, for example, to monitor the operation of the rotor (see, for example, Patent Document 1).

[0003] JP 2021-110395 A (see paragraph

[0026] )

[0004] However, in the conventional stepping motors described above, the accuracy with which the magnetic sensor detects the magnetic flux of the rotor magnet is low, and there is a need to develop a technology to improve this detection accuracy.

[0005] A first aspect of the presently disclosed invention is a claw-pole stepping motor including a stator having a coil, a cylindrical case fitted inside the stator and partially protruding from one end face of the stator, a rotor rotatably housed in the case and having a magnet, and a magnetic sensor arranged over the one end face of the stator and configured to detect magnetic flux oriented in a tangent direction of a circle centered on the rotor.

[0006] FIG. 1 is a side cross-sectional view of a valve device according to a first embodiment of the present disclosure. FIG. 2 is a diagram showing magnetic flux generated in a stepping motor when a rotor rotates. FIG. 3 is a block diagram showing the electrical configuration of the valve device. FIG. 4 is a block diagram showing the control configuration of a motor control circuit. FIG. 5 is an enlarged cross-sectional view of a stepping motor according to a second embodiment.

[0007] 1 to 4, a valve device 10 according to a first embodiment of the present disclosure will be described. The valve device 10 includes an electric valve 11 driven by a stepping motor 12, and a wiring board 80. Hereinafter, in describing the components of the valve device 10, the "upper side and lower side in FIG. 1" will be simply referred to as the "upper side and lower side."

[0008] The stepping motor 12 is, for example, a two-phase claw-pole stepping motor, and includes a rotor 20 inside a cylindrical case 14 and a stator 30 outside. The stator 30 has a stack 31S, in which an A-phase coil 31 wound around a bobbin 31A is surrounded by a yoke 31K, and a stack 32S, in which a B-phase coil 32 wound around a bobbin 32A is surrounded by a yoke 32K, stacked and fixed with resin, forming an overall cylindrical shape. Multiple claw poles 31P, 32P provided on each yoke 31K, 32K are aligned circumferentially on the inner periphery of each stack 31S, 32S (not shown). A connecting portion 30C extends from the side of the stator 30 and is bent upward at a right angle. Multiple pin-shaped terminal fittings 30K for energizing the coils 31, 32 protrude upward from the top surface of the connecting portion 30C.

[0009] The case 14 has a cylindrical wall 14W with an outer shape that fits perfectly inside the stator 30. The upper end of the cylindrical wall 14W is closed by a lid 14A, and the lower end is provided with a bottom wall 14B that is bent inward at a right angle from the cylindrical wall 14W. The rotation support part 15 is fixed to and passes through the center of the bottom wall 14B. A disk 14P protrudes from the lower end of the case 14 to reinforce the connection between the case 14 and the rotation support part 15, and the lower surface of the stator 30 is placed on the disk 14P. A portion of the case 14 protrudes upward from the upper end surface of the stator 30.

[0010] The rotation support portion 15 is formed by joining multiple cylindrical parts, with a central hole 15A penetrating through the center. The portion of the rotation support portion 15 that protrudes downward from the case 14 forms the valve body 13, with part of the central hole 15A serving as the flow path 13R. Specifically, the central hole 15A is narrowed toward the lower end of the valve body 13 to form a valve seat 24, and the inside of the valve seat 24 serves as the valve port 23. A branch hole 15T that communicates with the central hole 15A from the side is provided in the valve body 13 above the valve seat 24. The branch hole 15T and the portion of the central hole 15A below where it joins with the branch hole 15T form the flow path 13R.

[0011] The upper and lower ends of the central hole 15A above the junction with the branch hole 15T form bearings 15J1 and 15J2, and a screw hole 15N is provided between the bearings 15J1 and 15J2.

[0012] The rotor 20 comprises a cylindrical rotor body 20H with an upper and lower end that is slightly smaller than the inner diameter of the case 14, and a central shaft 21 that penetrates and is fixed to the upper end wall of the rotor body 20H. The upper outer surface of the portion of the central shaft 21 that is located inside the rotor body 20H is rotatably supported by the bearing portion 15J1 of the rotation support portion 15, and a male screw portion 21N provided below it is threaded into the screw hole portion 15N of the rotation support portion 15. As a result, the rotor 20 is rotatably supported by the rotation support portion 15 and moves up and down as the rotor 20 rotates.

[0013] The lower part of the central shaft 21 has a hollow structure with an open bottom end, and the base end of the needle-shaped valve element 16 is fitted inside this structure in a slidable but retained state. A compression coil spring 18S housed in the central hole 21A biases the valve element 16 in the direction of protruding from the central shaft 21. As a result, the valve element 16 moves up and down together with the rotor 20, and the bottom end of the valve element 16 approaches and moves away from the valve seat 24, thereby changing the flow rate of the fluid that can pass through the flow path 13R.

[0014] A screw guide 19G, formed by spirally wound wire, is fixed to the upper part of the central shaft 21 so as to rotate integrally with the central shaft 21. A stopper 19A, formed by spirally wound wire with a larger diameter and shorter length than the screw guide 19G, is threadedly engaged with the outer surface of the screw guide 19G. A pair of stopper abutment portions 19S1, 19S2 are provided at both ends of the screw guide 19G, and the stopper 19A abuts against the pair of stopper abutment portions 19S1, 19S2 to prevent it from coming off the screw guide 19G. Furthermore, a rotation restriction bar 90A extends parallel to the central shaft 21 from the inner surface of the upper end of the case 14 and is positioned to the side of the screw guide 19G, with a portion of the stopper 19A abutting against the rotation restriction bar 90A. Rotation limiting mechanism 19K, which includes screw guide 19G, stopper 19A, and rotation restricting bar 90A, causes stopper 19A to move linearly along rotation restricting bar 90A as rotor 20 rotates. When rotor 20 rotates in one direction, as shown in Figure 1, stopper 19A abuts against one stopper abutment portion 19S1, positioning rotor 20 at one end of its rotatable range, and when rotor 20 rotates multiple times in the other direction from that end position, stopper 19A abuts against the other stopper abutment portion 19S2, positioning rotor 20 at the other end of its rotatable range.

[0015] In this embodiment, one end position of the rotatable range of the rotor 20, where the rotor 20 is positioned by the stopper abutment portion 19S1, is set as the origin position. When the rotor 20 is located at the origin position, the valve element 16 abuts against the valve seat 24, fully closing the valve hole 23, resulting in a closed position. The other end position of the rotatable range is the fully open position. At the origin position, the compression coil spring 18S is slightly deflected.

[0016] In this embodiment, the stopper abutment portion 19S1 that positions the rotor 20 at the home position is provided inside the case 14, but it may also be provided outside the case 14. For example, the rotor 20 may be positioned at the home position by the valve element 16 abutting against the valve seat 24 as a stopper. In this case, it is preferable that the valve element 16 is fixed so as not to slide relative to the central shaft 21. In this embodiment, when the rotor 20 is located at the home position, the valve element 16 may be slightly separated from the valve seat 24, allowing a small amount of fluid to pass through the valve hole 23.

[0017] The rotor body 20H is a magnetic body, and as shown in Fig. 2, is magnetized so that south and north poles are arranged alternately in the circumferential direction, and each magnetic pole extends parallel to the rotation axis of the rotor 20. Also, as shown in Fig. 1, when the rotor 20 is disposed at the origin position, the top surface of the rotor 20 is located at the same height as the top surface of the stator 30. Then, as the rotor 20 moves away from the origin position, the top surface of the rotor 20 moves upward above the top surface of the stator 30.

[0018] When current is applied to the coils 31 and 32, the multiple claw poles 31P arranged circumferentially on the inner peripheral surface of the stack 31S are divided into north and south poles and arranged alternately in the circumferential direction, and the same is true for the inner peripheral surface of the stack 32S. Then, by switching the current pattern for the coils 31 and 32 using a known excitation method such as 1-2 phase excitation or 1 phase excitation, magnetic flux extends inside the stator 30 to connect the claw poles 31P and 32P of the stator 30 with the magnetic poles of the rotor 20, causing repulsion and attraction, etc., and driving the rotor 20 to rotate in any direction.

[0019] A magnetic sensor 50 is attached to the upper end face of the stator 30. Here, FIG. 2 conceptually illustrates, with dashed lines and thick solid lines, the magnetic flux around the rotor 20 on the end face of the stator 30 (more specifically, the upper region of the end face of the stator 30) when the stepping motor 12 is viewed from above. On the end face of the stator 30, the influence of the magnetic force of the claw poles 31P, 32P of the stator 30 is suppressed, and the magnetic flux (see the thick solid lines in FIG. 2 ) connecting adjacent N and S poles arranged alternately in the circumferential direction of the rotor 20 extends in a curved manner. Specifically, the magnetic flux extending from the N pole of the magnet of the rotor 20 toward the outside in the radial direction of the stator 30 splits into two, which flow in opposite circumferential directions, then turns radially again and flows toward the S poles on either side of the N pole. Furthermore, in a claw-pole stepping motor such as the stepping motor 12 of this embodiment, excitation of the coils 31 and 32 generates magnetic flux that penetrates the inside of the coils 31 and 32 (which is also the inside of the stator 30). The magnetic flux that penetrates the coils 31 and 32 extends in the radial direction on the end face of the stator 30, as shown by the dashed lines in FIG. 2.

[0020] In contrast, magnetic sensors in conventional stepping motors are configured to detect magnetic flux from the magnet of rotor 20 that is oriented in the radial direction of stator 30, and therefore detect even magnetic flux due to excitation of coils 31 and 32, resulting in low detection accuracy. In contrast, magnetic sensor 50 of stepping motor 12 of this embodiment is attached so as to be able to detect magnetic flux of vector components oriented in the tangent direction of a circle centered on rotor 20, in order to suppress the influence of magnetic flux due to excitation of coils 31 and 32.

[0021] Specifically, the magnetic sensor 50 is, for example, a Hall element having a structure in which a plurality of terminals 50T extend from an element body 50H. As shown in Fig. 2, the planar shape of the element body 50H is, for example, an irregular shape with chamfered corners at both ends of one long side of a rectangle. The plurality of terminals 50T are arranged in a row along the longitudinal direction of one end face of the irregular shape of the element body 50H and extend parallel to each other.

[0022] The magnetic sensor 50 detects only magnetic flux of a vector component (hereinafter referred to as a "specific vector component") that is oriented in a direction perpendicular to both sides of the short side of the element body 50H (hereinafter referred to as the "detection axis direction" as appropriate), and does not detect magnetic flux in the opposite direction or a different direction. The magnetic sensor outputs a binary signal indicating whether the magnetic flux density of the specific vector component is equal to or greater than a preset reference value. Specifically, when the magnetic flux density of the specific vector component is equal to or greater than the reference value, the detection signal is turned on, and when the magnetic flux density of the specific vector component is less than the reference value, the detection signal is turned off. In the case of a detection signal that switches between HIGH and LOW, HIGH means "on" and LOW means "off."

[0023] The magnetic sensor 50 in this embodiment is a Hall element, but is not limited to this and may be, for example, a GMR element (giant magnetoresistive element), an AMR element (anisotropic magnetoresistive element), a TMR element (tunneling magnetoresistive element), etc.

[0024] As shown in FIG. 1 , the magnetic sensor 50 is held by a sensor holder 51 fixed to the upper surface of the stator 30. The sensor holder 51 is, for example, placed on the upper surface of the stator 30 and has a rectangular parallelepiped main body 51H extending radially of the stator 30. The holder main body 51H has a rectangular parallelepiped sensor housing space 52 that is open to the bottom and the end face facing the case 14. As shown in FIG. 2 , the end face facing the case 14 is curved so as to fit exactly on the outer surface of the case 14. Furthermore, as shown in FIG. 1 , a plurality of through holes 53 are formed above the sensor housing space 52 and aligned radially of the stator 30. A fixing piece 51T is provided on the end face of the holder main body 51H opposite the case 14, extending from its lower edge. As shown in FIG. 2 , a mounting hole 51A penetrating vertically is formed in the center of the width of the fixing piece 51T, and a pair of positioning protrusions 51B protrude from the bottom surface of the fixing piece 51T. A pair of positioning protrusions 51B are fitted into a pair of positioning holes (not shown) formed in the stator 30, and screws B (see Figure 1) passed through the mounting holes 51A are tightened into screw holes (not shown) formed in the stator 30, thereby fixing the sensor holder 51 to the stator 30.

[0025] The magnetic sensor 50 has multiple terminals 50T that pass through multiple through-holes 53 from the sensor housing space 52 side relative to the sensor holder 51, and the element body 50H fits snugly into the sensor housing space 52. The sensor holder 51 is fixed to the stator 30, preventing the magnetic sensor 50 from slipping out of the sensor housing space 52. The magnetic sensor 50 is three-dimensionally positioned by the sensor holder 51 and fixed around the case 14 with its detection axis facing the tangential direction (i.e., the circumferential direction) of a circle centered on the case 14. In this embodiment, the detection axis is positioned so that the magnetic flux of a specific vector component detected by the magnetic sensor 50 is a vector component that faces, for example, clockwise when the stepping motor 12 is viewed from above, of the tangential direction of the circle centered on the case 14. That is, in this embodiment, of the magnetic flux indicated by the thick solid line in FIG. 2 , only the magnetic flux with an arrow pointing clockwise is detected by the magnetic sensor 50.

[0026] The structure of the sensor holder 51 is not limited to the one described above, and may have any shape as long as it can fix the magnetic sensor 50 to the stator 30 or the case 14. The sensor holder 51 may also be fixed to the stator 30 or the case 14 with an adhesive.

[0027] The plurality of terminals 50T of the magnetic sensor 50 and the plurality of terminal fittings 30K of the stator 30 extend to a position above the upper surface of the case 14. Then, they are passed through through holes 80A of a wiring board 80 disposed above the case 14 and soldered thereto.

[0028] 3 are mounted on wiring board 80. A CPU 83A included in motor control circuit 83 executes a control program, causing motor control circuit 83 to function as command receiving unit 41, rotation control unit 42, motor monitoring device 40, etc., shown in FIG.

[0029] The rotation control unit 42 controls the operation of the rotor 20. Specifically, immediately after power is applied to the motor control circuit 83, the rotation control unit 42 performs initialization processing on the stepping motor 12 and sets the current position of the rotor 20 to the origin position. Furthermore, when the command receiving unit 41 receives an external signal that is, for example, a target valve opening or a target flow rate of the motor-operated valve 11, sets a target rotation amount, a target rotation speed, etc. based on the received signal and stores the set value in memory 83B, the rotation control unit 42 provides a control signal to the motor drive circuit 82 so that the rotor 20 rotates from the current position by the target rotation amount stored in the memory at the target rotation speed.

[0030] An example of the initialization process performed by the rotation control unit 42 will now be described. The memory 83B of the motor control circuit 83 pre-stores a target rotation amount for initialization, a target rotation speed for initialization, and other information. When power is applied to the motor control circuit 83, the rotation control unit 42 provides a control signal to the motor drive circuit 82 so that the rotor 20 rotates in one direction from its current position by the target rotation amount for initialization at the target rotation speed for initialization. The motor drive circuit 82 then excites the coils 31 and 32 in response to the provided control signal. The target rotation amount for initialization is greater than the amount of rotation of the rotor 20 permitted by the rotation limiting mechanism 19K. The rotation limiting mechanism 19K forcibly stops the rotor 20 while the rotor 20 is being rotated by the target rotation amount for initialization. When the motor drive circuit 82 finishes exciting the coils 31 and 32 by the target rotation amount for initialization, the current position of the rotor 20 is set to the origin position.

[0031] The motor monitoring device 40 includes a stoppage determination unit 43 , a rotational speed detection unit 44 , a stoppage abnormality determination unit 45 , a speed abnormality determination unit 46 , and an abnormality processing unit 47 .

[0032] The stoppage determination unit 43 determines whether the rotor 20 is stopped or not, for example, based on whether the aforementioned binary signal output by the magnetic sensor 50 is maintained at either on or off for a predetermined reference time or longer.

[0033] The rotational speed detection unit 44 detects the rotational speed of the rotor 20 from the period of the change in the output of the magnetic sensor 50, which alternates between on and off. For example, in this embodiment, the output of the magnetic sensor 50 turns on only when a magnetic flux oriented clockwise in the tangential direction of a circle centered on the case 14 passes through the magnetic sensor 50. Therefore, if the number of north magnetic poles in the circumferential direction of the rotor 20 is m, the rotor 20 will have rotated 360 degrees when the detection signal of the magnetic sensor 50 has switched exactly m times from immediately after the first switching. The rotational speed detection unit 44 then measures, for example, the time t1 from immediately after the detection signal of the magnetic sensor 50 first switched until, for example, a preset number p of switchings have occurred, and calculates the rotational speed n based on the following equation.

[0034] n=p / (m・t1)

[0035] The rotational speed detection unit 44 may detect the rotational speed using a formula other than the above, and the rotational speed may be expressed in any unit. The rotational speed detected by the rotational speed detection unit 44 may also include a substitute value that can be converted into a rotational speed, even if it differs from the rotational speed commonly accepted in society. For example, the rotational speed detection unit 44 may be configured to detect the time required to rotate a predetermined fixed amount of rotations as a substitute value for the rotational speed. Furthermore, when the detection signal of the magnetic sensor 50 alternately switches between on and off repeatedly, the rotational speed detection unit 44 may detect the rotational speed of the rotor 20 based on the length of the on period or the off period.

[0036] The stop abnormality determination unit 45 acquires the determination result from the stop determination unit 43 and also acquires a stop determination signal from the rotation control unit 42 to determine whether the rotor 20 is operating and stopped in accordance with the control signal from the rotation control unit 42. Specifically, when the rotation control unit 42 outputs a control signal to the motor drive circuit 82 to stop the rotor 20 in order to maintain the motor-operated valve 11 at a predetermined valve opening, the stop determination signal indicating that stop control is in progress is provided from the rotation control unit 42 to the stop abnormality determination unit 45. Furthermore, when the rotation control unit 42 outputs a control signal to the motor drive circuit 82 to rotate the rotor 20 in order to change the valve opening of the motor-operated valve 11, the stop determination signal indicating that rotation control is in progress is provided from the rotation control unit 42 to the stop abnormality determination unit 45. Then, when the content of the stop determination signal matches the determination result by the stop determination unit 43, the stop abnormality determination unit 45 determines that there is no abnormality, and when they do not match, the stop abnormality determination unit 45 determines that there is an abnormality, and outputs each determination result to the abnormality processing unit 47.

[0037] When the abnormality processing unit 47 receives a determination result indicating the presence of an abnormality from the stop abnormality determination unit 45, it outputs an abnormality notification signal to the outside to notify the fact. Then, for example, the abnormality is notified by an external monitor or a warning light. Note that when the valve device 10 of the present embodiment is mounted on a vehicle, for example, and the abnormality notification signal is transmitted to the ECU of the vehicle, the transmission may be performed using an on-vehicle communication means.

[0038] Furthermore, when the abnormality processing unit 47 notifies the rotation control unit 42 of the determination result that an abnormality has occurred, the rotation control unit 42 stops outputting the control signal to the motor drive circuit 82 as necessary. This prevents the coils 31 and 32 from overheating, shorting, or other problems.

[0039] When the rotation control unit 42 performs the initialization process, the stop abnormality determination unit 45 may determine that the rotor 20 has stopped, and the excitation of the coils 31, 32 may be terminated before the excitation of the coils 31, 32 for the target rotation amount for initialization is completed. Such a configuration reduces power consumption.

[0040] Speed ​​abnormality determination unit 46 acquires the detection result from rotation speed detection unit 44, and also acquires a speed determination signal indicating the target rotation speed of rotor 20 being controlled by rotation control unit 42. Speed ​​abnormality determination unit 46 then determines the presence or absence of an abnormality based on whether the actual rotation speed of rotor 20 detected by rotation speed detection unit 44 matches the target rotation speed within a predetermined error range, and outputs the determination result to abnormality processing unit 47. Then, abnormality processing unit 47 performs the same processing as when stop abnormality determination unit 45 determines that an abnormality exists.

[0041] The configuration of this embodiment has been described above. The configuration of this embodiment provides the following advantages. Specifically, in the stepping motor 12 of this embodiment, the magnetic sensor 50 disposed on one end surface of the stator 30 is configured to detect magnetic flux oriented in the tangential direction of a circle centered on the rotor 20 (case 14). Therefore, compared to conventional magnetic sensors that detect only magnetic flux oriented radially of the rotor 20, the influence of magnetic flux due to excitation of the coils 31 and 32 on the detection results of the magnetic sensor 50 is reduced, improving the detection accuracy of the magnetic sensor 50. As a result, the motor monitoring device 40, which uses the detection results of the magnetic sensor 50, can more accurately monitor whether the rotor 20 of the stepping motor 12 is stopped and detect the rotational speed of the rotor 20. Based on these determination and detection results, the operation of the stepping motor 12 and the motor-operated valve 11 can be monitored more accurately than in the past.

[0042] Second Embodiment Figure 5 shows the main components of a stepping motor 12V according to a second embodiment of the present disclosure. The stepping motor 12V is equipped with two magnetic sensors 50. These two magnetic sensors 50 are arranged so that the phases of the detection signals output when the rotor 20 rotates are shifted from each other, and the amount of phase shift is a magnitude other than an integer multiple of half the electrical angle period of the detection signals output by the magnetic sensors 50. According to the configuration of this embodiment, the direction of rotation of the rotor 20 can be detected based on which of the phases of the detection signals output by the two magnetic sensors 50 changes cyclically first.

[0043] While the magnetic sensor 50 of the above embodiment outputs a binary signal indicating whether or not a magnetic flux density of a specific vector component equal to or greater than a reference value has been detected, the magnetic sensor 50 may output a detection value whose magnitude varies depending on the detected magnetic flux density. Furthermore, while the element body of the magnetic sensor 50 outputs the detection result in the first embodiment, the magnetic sensor 50 may be configured to include the element body and a signal processing circuit on the wiring substrate 80, and the signal processing circuit may output the binary signal or a detection value whose magnitude varies depending on the magnetic flux density.

[0044] In the above embodiment, the magnetic sensor 50 is held by the sensor holder 51. However, the magnetic sensor 50 may be fixed directly to the stator 30 or the case 14 without using the sensor holder 51. In this case, for example, a part of the stator 30 may be molded with resin, and the resin part may be cut out to house the magnetic sensor 50.

[0045] In the motor monitoring device 40 of the first embodiment, whether the rotor 20 is stopped or not and the rotational speed of the rotor 20 are detected. However, the motor monitoring device 40 may also be provided with a rotational acceleration detection unit that detects the rotational acceleration of the rotor 20 based on the output of the magnetic sensor 50, and a rotation amount detection unit that detects the amount of rotation of the rotor 20 based on the output of the magnetic sensor 50.

[0046] Although the stepping motor 12 in the above embodiment is a two-phase claw-pole type, the stepping motor 12 may be a three-phase or more claw-pole type.

[0047] In the above embodiment, a motor monitoring device 40 is shown that monitors the stepping motor 12 of the electric valve 11, but the configuration of the motor monitoring device 40 may also be applied to a motor monitoring device that monitors a stepping motor that is a driving source other than the electric valve 11.

[0048] <Supplementary Notes> Below, the group of features extracted from the above embodiment will be explained, indicating, as necessary, the effects, etc. Note that, for ease of understanding, the corresponding configurations in the above embodiment will be indicated in parentheses as appropriate below, but these group of features are not limited to the specific configurations indicated in parentheses.

[0049] [Feature 1] A claw-pole stepping motor (12) including: a stator (30) having coils (31, 32); a cylindrical case (14) fitted inside the stator (30) and partially protruding from one end face of the stator (30); a rotor (20) rotatably housed in the case (14) and having a magnet; and a magnetic sensor (50) arranged over the one end face of the stator (30) and configured to be capable of detecting magnetic flux oriented in a tangential direction of a circle centered on the rotor (20).

[0050] [Feature 2] The stepping motor (12) according to Feature 1 is used as a drive source for an electric valve (11), and includes: a rotation support part (15) that rotatably supports the rotor (20); threaded engagement parts (15N, 21N) that are provided on the rotor (20) and the rotation support part (15) and that are threadedly engaged with each other to linearly move the rotor (20) as the rotor (20) rotates; and a stopper (19A) that positions the rotor (20) at one end in the linear movement direction.

[0051] [Feature 3] An electric valve (11) including: the stepping motor (12) according to Feature 2; a valve element (16) that moves linearly together with the rotor (20); a valve body (13) having a valve seat (24) to which the valve element (16) approaches and moves away from; and a flow path (13R) formed in the valve body (13) and including a valve port (23) surrounded by the valve seat (24).

[0052] [Feature 4] A motor monitoring device (40) that acquires a detection result by the magnetic sensor (50) as a detection signal in order to monitor the state of the stepping motor (12) according to Feature 1 or 2, and that includes a stop determination unit (43) that determines whether the rotor (20) is stopped based on whether the detection signal has changed.

[0053] [Feature 5] A motor monitoring device (40) that acquires a detection result from the magnetic sensor (50) as a detection signal to monitor the state of the stepping motor (12) according to Feature 1 or 2, the motor monitoring device (40) including a rotational speed detection unit (44) that detects the rotational speed of the rotor (20) from a period of change in the detection signal.

[0054] [Feature 6] In order to monitor the state of the stepping motor (12) according to Feature 1 or 2, a motor monitoring device (40) obtains a detection result from the magnetic sensor (50) as a detection signal, which is an on / off signal indicating whether or not the detected magnetic flux is greater than a preset reference value, and the motor monitoring device (40) includes a rotational speed detection unit (44) that detects the rotational speed of the rotor (20) based on the length of an on period or an off period when the detection signal changes periodically.

[0055] In the stepping motor of Feature 1, the magnetic sensor placed on top of one end face of the stator is configured to be able to detect magnetic flux oriented in the tangential direction of a circle centered on the rotor. Therefore, compared to conventional stepping motors in which the magnetic sensor detects only magnetic flux oriented in the radial direction of the rotor, the influence of magnetic flux due to excitation of the coil on the detection results of the magnetic sensor is reduced, improving the detection accuracy of the magnetic sensor.

[0056] According to Features 2 and 3, the operation of the motor-operated valve can be monitored more accurately than before. Furthermore, the motor monitoring device according to Feature 4 can monitor whether the rotor of the stepping motor is stopped with higher accuracy than before. Furthermore, the motor monitoring devices according to Features 5 and 6 can detect the rotation speed of the rotor with higher accuracy than before.

[0057] Although the present specification and drawings disclose specific examples of the technology included in the scope of the claims, the technology described in the claims is not limited to these specific examples, but also includes various modifications and variations of the specific examples, and also includes parts of the specific examples taken out alone.

[0058] REFERENCE SIGNS LIST 11 Motor-operated valve 12, 12V Stepping motor 13 Valve body 13R Flow path 14 Case 15 Rotation support portion 16 Valve element 19A Stopper 20 Rotor 23 Valve port 24 Valve seat 15N, 21N Threaded portion 30 Stator 31, 32 Coil 40 Motor monitoring device 43 Stop determination portion 44 Rotational speed detection portion 50 Magnetic sensor

Claims

1. A claw-pole stepping motor comprising: a stator having a coil; a cylindrical case fitted inside the stator and partially protruding from one end face of the stator; a rotor rotatably housed in the case and having a magnet; and a magnetic sensor arranged over the one end face of the stator and configured to be able to detect magnetic flux oriented in a tangent direction of a circle centered on the rotor.

2. A stepping motor as claimed in claim 1, which is used as a drive source for an electric valve, and which comprises: a rotation support part that rotatably supports the rotor; a screw-fitting part that is provided on the rotor and the rotation support part and screws together to move the rotor linearly as it rotates; and a stopper that positions the rotor at one end in the linear movement direction.

3. An electric valve comprising: the stepping motor according to claim 2; a valve element that moves linearly together with the rotor; a valve body having a valve seat to which the valve element approaches and moves away; and a flow path formed in the valve body and including a valve port surrounded by the valve seat.

4. A motor monitoring device that obtains the detection results from the magnetic sensor as a detection signal in order to monitor the state of the stepping motor described in claim 1 or 2, and that is equipped with a stoppage discrimination unit that determines whether the rotor is stopped or not based on whether the detection signal has changed.

5. A motor monitoring device that obtains the detection results from the magnetic sensor as a detection signal in order to monitor the state of the stepping motor according to claim 1 or 2, and that includes a rotational speed detection unit that detects the rotational speed of the rotor from the period of change in the detection signal.

6. A motor monitoring device for monitoring the state of a stepping motor according to claim 1 or 2, which obtains the detection results from the magnetic sensor as a detection signal, which is an on / off signal indicating whether the detected magnetic flux is greater than a preset reference value, and which is equipped with a rotational speed detection unit that detects the rotational speed of the rotor based on the length of the on or off period when the detection signal changes periodically.

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