JP2014178178A - Magnetic shield member and torque detection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost magnetic shield member exhibiting a high magnetic shield effect.SOLUTION: A first magnetic shield plate 53 is arranged between a substrate 50 and a second magnet 52, which shields a magnetic flux extending from the second magnet 52 toward first and second magnetic sensors 61, 62. The characteristics of a magnetic flux density passing through the first magnetic shield plate 53 from the second magnet 52 for a thickness of the first magnetic shield plate 53 are characterized in that the magnetic flux density passing through the first magnetic shield plate 53 is decreased gradually as the first magnetic shield plate 53 is increased in thickness, and that a degree of change of the magnetic flux density passing through the first magnetic shield plate 53 is decreased when the thickness of the first magnetic shield plate 53 is equal to or greater than a first predetermined value. The thickness of the first magnetic shield plate 53 is set to be the predetermined value.

Description

  The present invention relates to a torque detection device used for a magnetic shielding member, an electric power steering device, and the like.

Torque detection devices used in electric power steering systems (EPS) and the like detect torque applied to the input shaft by detecting the torsion angle of the torsion bar that connects the input shaft and output shaft. It is configured to calculate.
As this type of torque detection device, the one disclosed in Patent Document 1 below has already been proposed. Specifically, the input shaft and the output shaft are coaxially connected via a torsion bar. A short cylindrical first magnet is connected to the input shaft so as to be integrally rotatable, and a short cylindrical second magnet is connected to the output shaft so as to be integrally rotatable. Between the first magnet and the second magnet, a plurality of input shaft rotation angle detection magnetic sensors for detecting magnetic flux from the first magnet, and a plurality of output shafts for detecting magnetic flux from the second magnet, respectively. A magnetic sensor for detecting the rotation angle is arranged. In addition, a first magnetic shielding member for blocking the magnetic flux from the second magnet to the magnetic sensor for detecting the input shaft rotation angle is disposed between the magnetic sensor for detecting the input shaft rotation angle and the second magnet. ing. In addition, a second magnetic shielding member for blocking the magnetic flux from the first magnet to the magnetic sensor for detecting the output shaft rotation angle is disposed between the magnetic sensor for detecting the output shaft rotation angle and the first magnet. ing.

JP 2012-163492 A

Generally, a magnetic shielding member has a greater magnetic shielding effect as the thickness increases. However, increasing the thickness of the magnetic shielding member increases the cost.
An object of the present invention is to provide a magnetic shielding member having a high magnetic shielding effect and a low cost, and a torque detection device including the same.

  In order to achieve the above object, the invention according to claim 1 is arranged between the magnet (52 or 51) and the electronic component (61, 62 or 63, 64), and blocks magnetic flux from the magnet toward the electronic component. The magnetic shielding member (53 or 54) of the magnetic shielding member has a magnetic flux density characteristic from the magnet passing through the magnetic shielding member with respect to the thickness of the magnetic shielding member. The magnetic flux density that passes through the shielding member gradually decreases, and when the thickness of the magnetic shielding member exceeds a predetermined value, the degree of change in the magnetic flux density that passes through the magnetic shielding member is reduced. And a magnetic shielding member having a thickness of the predetermined value. In addition, although the alphanumeric character in parentheses represents a corresponding component in an embodiment described later, of course, the scope of the present invention is not limited to the embodiment. The same applies hereinafter.

According to the present invention, the thickness of the magnetic shielding member can be set to the minimum value among the thicknesses that can provide a high magnetic shielding effect. Thereby, a magnetic shielding member having a high magnetic shielding effect and low cost can be realized.
The invention according to claim 2 is a torque detecting device (11) for detecting torque by detecting a torsion angle of the torque detecting shaft (10), wherein the torque detecting device (11) can be rotated integrally with one end of the torque detecting shaft. The connected short cylindrical first magnet (51or52), the short cylindrical second magnet (52or51) connected to the other end of the torque detection shaft so as to be integrally rotatable, the first magnet, A plurality of first rotations arranged between the second magnet and detecting a magnetic flux from each of the first magnets to detect a first rotation angle that is a rotation angle of the one end of the torque detection shaft. A magnetic sensor (61, 62 or 63, 64) for detecting an angle, and disposed between the first magnet and the second magnet, respectively detecting a magnetic flux from the second magnet, and To detect the second rotation angle that is the rotation angle of the other end A plurality of second rotation angle detection magnetic sensors (63, 64 or 61, 62) and the first magnet and the second magnet, and from the second magnet for detecting the first rotation angle. A first magnetic shielding member (53or54) for blocking a magnetic flux directed to the magnetic sensor, and disposed between the first magnet and the second magnet, for detecting the second rotation angle from the first magnet. A magnetic flux density from the second magnet passing through the first magnetic shielding member with respect to the thickness of the first magnetic shielding member, and a second magnetic shielding member (54 or 53) for interrupting the magnetic flux toward the magnetic sensor The magnetic flux density passing through the first magnetic shielding member gradually decreases as the thickness of the first magnetic shielding member increases, and the thickness of the first magnetic shielding member is a first predetermined value. When the value exceeds the value, the first magnetic shielding member is passed through. The degree to which magnetic flux density changes can have a characteristic that decreases, the thickness of the first magnetic shield is the first predetermined value is a torque detector.

According to this invention, it is possible to set the thickness of the first magnetic shielding member to the minimum value among the thicknesses that can provide a high magnetic shielding effect. Thereby, the torque detection apparatus provided with the 1st magnetic shielding member with a high magnetic shielding effect and low cost is realizable.
According to a third aspect of the present invention, the first magnetic shielding member is disposed between the plurality of first rotation angle detection magnetic sensors and the second magnet, and is viewed from the first magnet side. The arc is formed in an arc shape having a width around the central axis of the second magnet, and the length of the arc passing through the center of the width of the first magnetic shielding member is the thickness of the first magnetic shielding member. The torque detection according to claim 2, wherein the torque detection is determined to have a constant magnetic flux density from the second magnet that passes through the first magnetic shielding member when the first predetermined value or more is reached. Device.

In this configuration, the length of the arc passing through the width center of the first magnetic shielding member is increased, and the magnetic flux density passing through the first magnetic shielding member is increased when the thickness of the first magnetic shielding member is equal to or greater than the first predetermined value. It becomes possible to set to the minimum value of the length not to be performed. Thereby, the torque detection apparatus provided with the 1st magnetic shielding member with a high magnetic shielding effect and low cost is realizable.
According to a fourth aspect of the present invention, the characteristic of the magnetic flux density from the first magnet that passes through the second magnetic shielding member with respect to the thickness of the second magnetic shielding member is an increase in the thickness of the second magnetic shielding member. Accordingly, the magnetic flux density passing through the second magnetic shielding member gradually decreases, and the magnetic flux density passing through the first magnetic shielding member when the thickness of the second magnetic shielding member exceeds a second predetermined value. The torque detecting device according to claim 2, wherein the torque detecting device has a characteristic that a degree of change of the torque becomes small, and a thickness of the second magnetic shielding member is the second predetermined value.

According to this configuration, it is possible to set the thickness of the second magnetic shielding member to the minimum value among the thicknesses that can provide a high magnetic shielding effect. Thereby, the torque detection apparatus provided with the 2nd magnetic shielding member with a high magnetic shielding effect and low cost is realizable.
According to a fifth aspect of the present invention, the second magnetic shielding member is disposed between the plurality of second rotation angle detection magnetic sensors and the first magnet, and viewed from the second magnet side. The arc is formed in an arc shape having a width around the central axis of the first magnet, and the length of the arc passing through the center of the width of the second magnetic shielding member is the thickness of the second magnetic shielding member. 5. The torque detection according to claim 4, wherein the length is determined such that a magnetic flux density from the first magnet passing through the second magnetic shielding member is constant when the second predetermined value or more is reached. Device.

In this configuration, the length of the arc passing through the width center of the second magnetic shielding member is increased, and the magnetic flux density passing through the second magnetic shielding member is increased when the thickness of the second magnetic shielding member is equal to or greater than the second predetermined value. It becomes possible to set the value to the minimum value of the length not to be performed. Thereby, the torque detection apparatus provided with the 2nd magnetic shielding member with a high magnetic shielding effect and low cost is realizable.
According to a sixth aspect of the present invention, there is provided first calculation means (65Aor65B) for calculating the first rotation angle based on output signals of the plurality of first rotation angle detection magnetic sensors, and the plurality of second rotations. Based on the output signal of the magnetic sensor for angle detection, the second calculation means (65 Bor65A) for calculating the second rotation angle, the first rotation angle calculated by the first calculation means, and the second calculation means The torque detection device according to any one of claims 2 to 6, further comprising torque calculation means (65C) for calculating a torque based on the second rotation angle calculated by.

FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering device to which a torque detection device according to an embodiment of the present invention is applied. FIG. 2 is a schematic diagram showing an electrical configuration of the motor control ECU. FIG. 3 is a schematic diagram schematically showing the configuration of the electric motor. FIG. 4 is a graph showing a setting example of the q-axis current command value I _q ^* with respect to the detected steering torque Th. FIG. 5 is a schematic diagram schematically showing the configuration of the torque sensor. 6A is a schematic view of the first magnetic shield plate 53 viewed from the first magnet 51 side, and FIG. 6B is a schematic view of the second magnetic shield plate 54 viewed from the second magnet 52 side. FIG. 7 is a schematic diagram showing the configuration of the first magnet and the arrangement of the first magnetic sensor and the second magnetic sensor. FIG. 8 is a schematic diagram showing the output signal waveforms of the first magnetic sensor and the second magnetic sensor and the magnetic poles detected by the first magnetic sensor. FIG. 9 is a schematic diagram for explaining an experimental method performed to determine the thickness and length of the first magnetic shield plate. 10 is an arrow view seen from the direction of arrow B in FIG. FIG. 11 is a graph showing experimental results.

Hereinafter, embodiments of the present invention applied to an electric power steering apparatus will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering device to which a torque detection device according to an embodiment of the present invention is applied.
The electric power steering apparatus 1 includes a steering wheel 2 as a steering member for steering the vehicle, a steering mechanism 4 that steers the steered wheels 3 in conjunction with the rotation of the steering wheel 2, and steering by the driver. And a steering assist mechanism 5 for assisting. The steering wheel 2 and the steering mechanism 4 are mechanically coupled via a steering shaft 6 and an intermediate shaft 7.

  The steering shaft 6 includes an input shaft 8 connected to the steering wheel 2 and an output shaft 9 connected to the intermediate shaft 7. The input shaft 8 and the output shaft 9 are connected via a torsion bar (torque detection shaft) 10 so as to be relatively rotatable on the same axis. That is, when the steering wheel 2 is rotated, the input shaft 8 and the output shaft 9 rotate in the same direction while rotating relative to each other.

  A torque sensor (torque detection device) 11 is provided around the steering shaft 6. The torque sensor 11 detects the steering torque applied to the steering wheel 2 based on the relative rotational displacement amount of the input shaft 8 and the output shaft 9. The steering torque detected by the torque sensor 11 is input to a motor control ECU (Electronic Control Unit) 12.

  The steered mechanism 4 includes a rack and pinion mechanism including a pinion shaft 13 and a rack shaft 14 as a steered shaft. The steered wheel 3 is connected to each end of the rack shaft 14 via a tie rod 15 and a knuckle arm (not shown). The pinion shaft 13 is connected to the intermediate shaft 7. The pinion shaft 13 rotates in conjunction with the steering of the steering wheel 2. A pinion 16 is connected to the tip of the pinion shaft 13.

  The rack shaft 14 extends linearly along the left-right direction of the automobile (a direction orthogonal to the straight-ahead direction). A rack 17 that meshes with the pinion 16 is formed at an intermediate portion in the axial direction of the rack shaft 14. By the pinion 16 and the rack 17, the rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. The steered wheels 3 can be steered by moving the rack shaft 14 in the axial direction.

When the steering wheel 2 is steered (rotated), this rotation is transmitted to the pinion shaft 13 via the steering shaft 6 and the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into an axial movement of the rack shaft 14 by the pinion 16 and the rack 17. Thereby, the steered wheel 3 is steered.
The steering assist mechanism 5 includes an electric motor 18 for generating a steering assist force, and a speed reduction mechanism 19 for transmitting the output torque of the electric motor 18 to the steering mechanism 4. In this embodiment, the electric motor 18 is a three-phase brushless motor. The speed reduction mechanism 19 includes a worm gear mechanism that includes a worm shaft 20 and a worm wheel 21 that meshes with the worm shaft 20. The speed reduction mechanism 19 is accommodated in a gear housing 22 as a transmission mechanism housing.

The worm shaft 20 is rotationally driven by the electric motor 18. The worm wheel 21 is coupled to the output shaft 9 so as to be rotatable in the same direction as the output shaft 9. The worm wheel 21 is rotationally driven by the worm shaft 20.
When the worm shaft 20 is rotationally driven by the electric motor 18, the worm wheel 21 is rotationally driven, and the steering shaft 6 (output shaft 9) rotates. The rotation of the steering shaft 6 is transmitted to the pinion shaft 13 via the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. Thereby, the steered wheel 3 is steered. That is, the wheel 3 is steered by rotating the worm shaft 20 by the electric motor 18.

The rotation angle of the rotor of the electric motor 18 (rotor rotation angle) is detected by a rotation angle sensor 25 such as a resolver. The output signal of the rotation angle sensor 25 is input to the motor control ECU 12. The electric motor 18 is controlled by a motor control ECU 12 as a motor control device.
FIG. 2 is a schematic diagram showing an electrical configuration of the motor control ECU 12.

  The motor control ECU 12 drives the electric motor 18 according to the steering torque Th detected by the torque sensor 11, thereby realizing appropriate steering assistance according to the steering situation. The motor control ECU 12 includes a microcomputer 40, a drive circuit (inverter circuit) 31 that is controlled by the microcomputer 40 and supplies electric power to the electric motor 18, and a current detection unit 32 that detects a motor current flowing through the electric motor 18. It has.

  The electric motor 18 is, for example, a three-phase brushless motor, and includes a rotor 100 as a field and U-phase, V-phase, and W-phase stator windings 101, 102, and 103, as schematically shown in FIG. And a stator 105. The electric motor 18 may be of an inner rotor type having a stator opposed to the outside of the rotor, or may be of an outer rotor type having a stator opposed to the inside of a cylindrical rotor.

Three-phase fixed coordinates (UVW coordinate system) are defined in which the U, V, and W axes are taken in the direction of the stator windings 101, 102, and 103 of each phase. Further, a two-phase rotational coordinate system (dq coordinate system) in which the d axis (magnetic pole axis) is taken in the magnetic pole direction of the rotor 100 and the q axis (torque axis) is taken in a direction perpendicular to the d axis in the rotation plane of the rotor 100. The actual rotating coordinate system) is defined. The dq coordinate system is a rotating coordinate system that rotates with the rotor 100. In the dq coordinate system, since only the q-axis current contributes to the torque generation of the rotor 100, the d-axis current may be set to zero and the q-axis current may be controlled according to the desired torque. The rotation angle (electrical angle) θ- _S of the rotor 100 is the rotation angle of the d axis with respect to the U axis. The dq coordinate system is an actual rotating coordinate system according to the rotor angle θ- _S . By using this rotor angle θ- _S , coordinate conversion between the UVW coordinate system and the dq coordinate system can be performed.

  The microcomputer 40 includes a CPU and a memory (ROM, RAM, non-volatile memory, etc.), and functions as a plurality of function processing units by executing a predetermined program. The plurality of function processing units include a current command value setting unit 41, a current deviation calculation unit 42, a PI (proportional integration) control unit 43, a dq / UVW conversion unit 44, and a PWM (Pulse Width Modulation) control unit. 45, a UVW / dq conversion unit 46, and a rotation angle calculation unit 47.

The rotation angle calculation unit 47 calculates the rotation angle of the rotor of the electric motor 18 (electrical angle; hereinafter referred to as “rotor angle θ _S ”) based on the output signal of the rotation angle sensor 25.
The current command value setting unit 41 sets a current value to be passed through the coordinate axes of the dq coordinate system as a current command value. Specifically, the current command value setting unit 41 refers to a d-axis current command value I _d ^* and a q-axis current command value I _q ^* (hereinafter, collectively referred to as “two-phase current command value I _dq ^* ”). ) Is set. More specifically, the current command value setting unit 41 sets the q-axis current command value I _q ^* to a significant value and sets the d-axis current command value I _d ^* to zero. More specifically, the current command value setting unit 41 sets the q-axis current command value I _q ^* based on the steering torque (detected steering torque) Th detected by the torque sensor 11.

A setting example of the q-axis current command value I _q ^* for the detected steering torque Th is shown in FIG. For the detected steering torque Th, for example, the torque for steering in the right direction is a positive value, and the torque for steering in the left direction is a negative value. The q-axis current command value I _q ^* is a positive value when an operation assisting force for rightward steering is to be generated from the electric motor 18, and the operation assisting force for leftward steering from the electric motor 18 is When it should be generated, it is a negative value. The q-axis current command value I _q ^* is positive for a positive value of the detected steering torque Th and negative for a negative value of the detected steering torque Th. When the detected steering torque Th is zero, the q-axis current command value I _q ^* is zero. The q-axis current command value I _q ^* is set so that the absolute value of the q-axis current command value I _q ^* increases as the absolute value of the detected steering torque Th increases.

The two-phase current command value I _dq ^* set by the current command value setting unit 41 is given to the current deviation calculation unit 42.
The current detection unit 32 detects the U-phase current I _U , the V-phase current I _V, and the W-phase current I _W (hereinafter collectively referred to as “three-phase detection current I _UVW ”) of the electric motor 18. To do. The three-phase detection current I _UVW detected by the current detection unit 32 is given to the UVW / dq conversion unit 46.

The UVW / dq converter 46 converts the three-phase detection current I _UVW (U-phase current I _U , V-phase current I _V and W-phase current I _W ) in the UVW coordinate system detected by the current detector 32 into the dq coordinate system. _Are transformed into two-phase detection currents I _d and I _q (hereinafter collectively referred to as “two-phase detection current I _dq ”). For this coordinate conversion, the rotor angle θ _S calculated by the rotation angle calculation unit 47 is used.

The current deviation calculation unit 42 calculates a deviation between the two-phase current command value I _dq ^* set by the current command value setting unit 41 and the two-phase detection current I _dq given from the UVW / dq conversion unit 46. More specifically, the current deviation calculation unit 42 calculates the deviation of the d-axis detection current I _d with respect to the d-axis current command value I _d ^* and the deviation of the q-axis detection current I _q with respect to the q-axis current command value I _q ^* . To do. These deviations are given to the PI control unit 43.

The PI control unit 43 performs a PI calculation on the current deviation calculated by the current deviation calculation unit 42 to thereby provide a two-phase voltage command value V _dq ^* (d-axis voltage command value V _d ^* and a d-axis voltage command value to be applied to the electric motor 18. q-axis voltage command value V _q ^* ) is generated. The two-phase voltage command value V _dq ^* is given to the dq / UVW converter 44.
The dq / UVW conversion unit 44 performs coordinate conversion of the two-phase voltage command value V _dq ^* into the three-phase voltage command value V _UVW ^* . For this coordinate conversion, the rotor angle θ _S calculated by the rotation angle calculation unit 47 is used. The three-phase voltage command value V _UVW ^* includes a U-phase voltage command value V _U ^* , a V-phase voltage command value V _V ^*, and a W-phase voltage command value V _W ^* . This three-phase voltage command value V _UVW ^* is given to the PWM control unit 45.

The PWM control unit 45 includes a U-phase PWM control signal, a V-phase PWM control signal having a duty corresponding to the U-phase voltage command value V _U ^* , the V-phase voltage command value V _V ^*, and the W-phase voltage command value V _W ^* , respectively. A W-phase PWM control signal is generated and supplied to the drive circuit 31.
The drive circuit 31 includes a three-phase inverter circuit corresponding to the U phase, the V phase, and the W phase. The power elements constituting the inverter circuit are controlled by a PWM control signal supplied from the PWM control unit 45, whereby a voltage corresponding to the three-phase voltage command value V _UVW ^* is set to the stator winding 101 of each phase of the electric motor 18. , 102, 103.

The current deviation calculation unit 42 and the PI control unit 43 constitute a current feedback control unit. By the action of the current feedback control means, the motor current flowing through the electric motor 18 is controlled so as to approach the two-phase current command value I _dq ^* set by the current command value setting unit 41.
FIG. 5 is a schematic diagram schematically showing the configuration of the torque sensor 11.

A short cylindrical first magnet (multipolar magnet) 51 is connected to the input shaft 8 so as to be integrally rotatable. The first magnet 51 is fixed to the input shaft 8 while being fitted to the outer peripheral surface of the input shaft 8. A short cylindrical second magnet (multipolar magnet) 52 is connected to the output shaft 9 so as to be integrally rotatable. The second magnet 52 is fixed to the output shaft 9 in a state of being fitted to the outer peripheral surface of the output shaft 9.
A substrate 50 is disposed between the first magnet 51 and the second magnet 52. The substrate 50 is arranged in parallel with these magnets 51 and 52 so as not to interfere with the input shaft 8, the output shaft 9 and the torsion bar 10. The substrate 50 is attached to a housing (not shown) in which the magnets 51 and 52 and the substrate 50 are accommodated and supported by the vehicle body.

  A first magnetic sensor 61 and a second magnetic sensor 62 that detect magnetic flux from the first magnet 51 are attached to the surface (the upper surface in FIG. 5) of the substrate 50 facing the first magnet 51. These magnetic sensors 61 and 62 are used to detect the rotation angle of the input shaft 8 (the rotation angle of the end of the torsion bar 10 on the side to which the input shaft 8 is connected). These magnetic sensors 61 and 62 are arranged to face the annular end face of the first magnet 51 facing the substrate 50 (second magnet 52).

  A third magnetic sensor 63 and a fourth magnetic sensor 64 for detecting the magnetic flux from the second magnet 52 are attached to the surface (the lower surface in FIG. 5) facing the second magnet 52 of the substrate 50. These magnetic sensors 63 and 64 are used to detect the rotation angle of the output shaft 9 (the rotation angle of the end of the torsion bar 10 on the side where the output shaft 9 is connected). These magnetic sensors 63 and 64 are arranged to face the annular end face of the second magnet 52 facing the substrate 50 (first magnet 51) side.

  Between the board | substrate 50 and the 2nd magnet 52, the 1st magnetic shielding board (magnetic shielding member) 53 for interrupting | blocking the magnetic flux which goes to the 1st and 2nd magnetic sensors 61 and 62 from the 2nd magnet 52 is arrange | positioned. ing. Between the board | substrate 50 and the 1st magnet 51, the 2nd magnetic shield board (magnetic shielding member) 54 for interrupting | blocking the magnetic flux which goes to the 3rd and 4th magnetic sensors 63 and 64 from the 1st magnet 51 is arrange | positioned. ing. Each of the magnetic shield plates 53 and 54 is made of SPCC (cold rolled steel plate). Each of the magnetic shield plates 53 and 54 is attached to the substrate 50 via a spacer (not shown), for example.

  FIG. 6A is a schematic view of the first magnetic shield plate 53 viewed from the first magnet 51 side. In FIG. 6A, the first magnet 51, the substrate 50, the second magnetic shield plate 54, and the third and fourth magnetic sensors 63 and 64 are omitted. The first magnetic shield plate 53 has a circular arc shape with a width centered on the central axis of the second magnet 52 when viewed from the first magnet 51 side. The first and second magnetic sensors 61 and 62 are disposed in the center of the first magnetic shield plate 53 as viewed from the first magnet 51 side.

  FIG. 6B is a schematic view of the second magnetic shield plate 54 viewed from the second magnet 52 side. In FIG. 6B, the second magnet 52, the substrate 50, the first magnetic shield plate 53, and the first and second magnetic sensors 61 and 62 are omitted. The second magnetic shield plate 54 has an arc shape with a width centered on the central axis of the first magnet 51 when viewed from the second magnet 52 side. The third and fourth magnetic sensors 63 and 64 are disposed in the center of the second magnetic shield plate 54 when viewed from the second magnet 52 side.

  The length L1 of the first magnetic shield plate 53 is defined as the length of an arc passing through the center of the width of the first magnetic shield plate 53, as shown in FIG. 6A. Similarly, the length L2 of the second magnetic shield plate 54 is defined as the length of an arc passing through the center of the width of the second magnetic shield plate 54, as shown in FIG. 6B. The thickness D1 (see FIG. 5) and length L1 of the first magnetic shield plate 53 and the thickness D2 (see FIG. 5) and length L2 of the second magnetic shield plate 54 are set to predetermined sizes, respectively. Has been. A method for determining these sizes will be described later.

  The first and second magnetic sensors 61 and 62 output sinusoidal signals V1 and V2 having a phase difference with each other according to the rotation of the first magnet 51, respectively. The third and fourth magnetic sensors 63 and 64 output sinusoidal signals V3 and V4 having a phase difference with each other according to the rotation of the second magnet 52, respectively. In addition, as each magnetic sensor 61-64, what was equipped with the element which has the characteristic which an electrical characteristic changes with the effect | actions of a magnetic field, such as a Hall element and a magnetoresistive element (MR element), can be used, for example. In this embodiment, Hall elements are used as the magnetic sensors 61 to 64.

The output signals V1, V2, V3, V4 of the magnetic sensors 61, 62, 63, 64 are input to a torque calculation ECU 65 for calculating the steering torque applied to the input shaft 8. The magnet 51, 52, the magnetic shield plates 53, 54, the magnetic sensors 61, 62, 63, 64, and the torque calculation ECU 65 constitute the torque sensor 11.
The torque calculation ECU 65 includes a microcomputer. The microcomputer includes a CPU and a memory (ROM, RAM, nonvolatile memory, etc.), and functions as a plurality of function processing units by executing a predetermined program. The plurality of function processing units include a first rotation angle calculation unit 65A, a second rotation angle calculation unit 65B, and a torque calculation unit 65C.

The first rotation angle calculator 65A calculates the rotation angle (electrical angle θ1) of the input shaft 8 based on the output signals V1 and V2 of the first and second magnetic sensors 61 and 62. The second rotation angle calculator 65B calculates the rotation angle (electrical angle θ2) of the output shaft 9 based on the output signals V3 and V4 of the third and fourth magnetic sensors 63 and 64.
The torque calculation unit 65C is based on the rotation angle θ1 of the input shaft 8 detected by the first rotation angle calculation unit 65A and the rotation angle θ2 of the output shaft 9 detected by the second rotation angle calculation unit 65B. A steering torque Th applied to the input shaft 8 is calculated. Specifically, the steering torque Th is calculated based on the following equation (1), where K is the spring constant of the torsion bar 10 and N is the number of magnetic pole pairs provided in each of the magnets 51 and 52.

Th = {(θ1-θ2) / N} × K (1)
Since the operation of the first rotation angle calculation unit 65A and the operation of the second rotation angle calculation unit 65B are the same, only the operation of the first rotation angle calculation unit 65A will be described in detail.
FIG. 7 is a schematic diagram showing the configuration of the first magnet 51 and the arrangement of the first and second magnetic sensors 61 and 62.

  The first magnet 51 includes five pairs of magnetic poles (M1, M2), (M3, M4), (M5, M6), (M7, M8), (M9, M10) arranged at equal angular intervals in the circumferential direction. have. That is, the first magnet 51 has ten magnetic poles M1 to M10 arranged at equal angular intervals. The magnetic poles M <b> 1 to M <b> 10 are arranged at an angular interval (angular width) of 36 ° (electrical angle 180 °) with the central axis of the input shaft 8 as the center. The magnitude of the magnetic force of each of the magnetic poles M1 to M10 is substantially constant.

The two magnetic sensors 61 and 62 are arranged to face the annular end face of the first magnet 51 facing the second magnet 52 side. These magnetic sensors 61 and 62 are arranged at an angular interval of 9 ° (45 ° in electrical angle) with the central axis of the input shaft 8 as the center.
A direction indicated by an arrow in FIG. 7 is a positive rotation direction of the input shaft 8. When the input shaft 8 is rotated in the forward direction, the rotation angle of the input shaft 8 is increased. When the input shaft 8 is rotated in the reverse direction, the rotation angle of the input shaft 2 is decreased. As shown in FIG. 8, the magnetic sensors 61 and 62 output sinusoidal signals V1 and V2 whose phases are shifted from each other by 90 degrees as the input shaft 8 rotates. Note that the rotation angle [deg] on the horizontal axis in FIG. 8 represents a mechanical angle.

  Assuming that the output signals V1 and V2 of the magnetic sensors 61 and 62 are sine wave signals and the rotation angle of the input shaft 8 is θ1 (electrical angle), the output signal V1 of the first magnetic sensor 61 is V1 = A1. It is expressed as sin θ1, and the output signal V2 of the second magnetic sensor 62 is expressed as V2 = A2 · cos θ1. A1 and A2 each represent an amplitude. Assuming that the amplitudes A1 and A2 are equal to each other, the rotation angle θ1 of the input shaft 8 is calculated based on the following equation (2).

θ1 = tan ⁻¹ (V1 / V2) (2)
The second rotation angle calculation unit 65B also calculates the rotation angle θ2 of the output shaft 9 based on the output signals V3 and V4 of the third and fourth magnetic sensors 63 and 64 by the same operation. However, when the steering wheel 2 is in the neutral position and no steering torque is applied to the steering wheel 2, the rotation angle θ1 of the input shaft 8 calculated by the first rotation angle calculation unit 65A and the second rotation angle are calculated. The relative positions of the magnetic poles between the first magnet 51 and the second magnet 52, and the first and second so that the rotation angle θ2 of the output shaft 9 calculated by the calculation unit 65B has the same value. The relative positions of the magnetic sensors 61 and 63 and the third and fourth magnetic sensors 63 and 64 are set.

Next, a method for determining the thickness D1 and the length L1 of the first magnetic shield plate 53 will be described. The thickness D1 and the length L1 of the first magnetic shield plate 53 are determined by experiments. Hereinafter, this experimental method will be described.
Samples of a plurality of first magnetic shield plates 53 having different lengths L1 and thicknesses D1 were prepared. Specifically, a plurality of samples X having a length L1 of 40 [mm] and a different thickness D1, a plurality of samples X having a length L1 of 25 [mm] and a different thickness D1, and a length L1 of 10 A plurality of samples X having different thicknesses D1 in [mm] were prepared. And the characteristic of the magnetic flux density which passes the sample with respect to thickness D1 was investigated for every sample from which length L1 differs.

  FIG. 9 is a schematic diagram for explaining the experimental method. 10 is an arrow view seen from the direction of arrow B in FIG. However, the substrate 50 is omitted in FIG. As shown in FIGS. 9 and 10, the first magnet 51 and the second magnetic shield plate 54 are removed from the torque sensor 11. Further, the sample X is disposed between the substrate 50 and the second magnet 52. The distance H between the sample X and the substrate 50 is set to 1 [mm]. One magnetic sensor S is arranged at a position facing the center of the sample S on the surface of the substrate 50 opposite to the surface on the second magnet 52 side. Based on the output of the magnetic sensor S, the magnetic flux density [T] from the second magnet 52 passing through the sample X is detected. The same experiment is repeated with sample X replaced.

The outer diameter of the second magnet 52 is 41 [mm]. The magnetic flux density of the second magnet 52 is 0.04 [T]. The sample material of the first magnetic shield plate 53 is SPCC (cold rolled steel plate).
FIG. 11 is a graph showing experimental results.
A broken line a in FIG. 11 is a graph showing the characteristics of the magnetic flux density [T] passing through the sample X with respect to the thickness D1 for the sample X having a length L1 of 40 [mm]. The broken line b is a graph showing the characteristic of the magnetic flux density [T] passing through the sample X with respect to the thickness D1 for the sample X having a length L1 of 25 [mm]. The broken line c is a graph showing the characteristic of the magnetic flux density [T] passing through the sample X with respect to the thickness D1 for the sample X having a length L1 of 10 [mm].

  In each sample X having a different length L1, the magnetic flux density passing through the sample X gradually decreases as the thickness D1 increases. When the thickness D1 of each sample X reaches a predetermined value A or more (in this example, 0.35 [mm] or more), the amount of change in magnetic flux density passing through the sample X is small. That is, even if the thickness D1 of each sample X is larger than the predetermined value A, the magnetic flux density passing through the sample X hardly decreases. Therefore, the thickness D1 of the first magnetic shield plate 53 is determined to be the predetermined value A (0.35 [mm] in this example). Thereby, the thickness D1 of the 1st magnetic shield board 53 can be set to the minimum value among the thickness in which a high magnetic shielding effect is acquired. Thereby, the 1st magnetic shielding board 53 with a high magnetic shielding effect and low cost is realizable.

  Further, in the sample X having the length L1 of 40 [mm], even when the thickness D1 of the sample X is equal to or larger than the predetermined value A, the sample X slightly increases as the thickness D1 of the sample X increases. The magnetic flux density passing through is reduced. In the sample X having a length L1 of 10 [mm], when the thickness D1 of the sample X is equal to or greater than the predetermined value A, the magnetic flux passing through the sample X is slightly increased as the thickness D1 of the sample X increases. The density is increasing. In the sample X having a length L1 of 25 [mm], when the thickness D1 of the sample X is equal to or greater than the predetermined value A, the magnetic flux density passing through the sample X is constant even if the thickness D1 of the sample X increases. . Therefore, the length L1 of the first magnetic shield plate 53 is set such that the magnetic flux density passing through the sample X is constant when the thickness of the sample X is not less than the predetermined value A (25 in this example). [mm]). Thereby, the length D1 of the first magnetic shield plate 53 is set to the minimum value of the lengths in which the magnetic flux density passing through the sample X does not increase when the thickness D1 of the sample X is equal to or greater than the predetermined value A. Can be set. Thereby, the 1st magnetic shielding board 53 with a high magnetic shielding effect and low cost is realizable.

  The thickness D2 and the length L2 of the second magnetic shield plate 54 are also determined by the same method as the thickness D1 and the length L1 of the first magnetic shield plate 53. In this embodiment, the characteristics of the first magnet 51 and the second magnet 52 are substantially the same, the characteristics of the magnetic sensors 61 to 64 are substantially the same, and the first magnet 51 and the second magnetic shield plate 54. Is approximately the same as the distance between the second magnet 52 and the first magnetic shield plate 53. Therefore, the thickness D2 and the length L2 of the second magnetic shield plate 54 are set to the same values as the thickness D1 and the length L1 of the first magnetic shield plate 53, respectively.

  As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented in another embodiment. For example, the method of calculating the rotation angle of the input shaft 8 based on a plurality of magnetic sensors that detect magnetic flux from the first magnet 51 may be a method other than the above-described calculation method. Further, the method for calculating the rotation angle of the output shaft 9 based on a plurality of magnetic sensors for detecting the magnetic flux from the second magnet 52 may be a method other than the calculation method described above.

Further, the number of magnetic sensors used for calculating the rotation angle of the input shaft 8 may be three or more. Similarly, the number of magnetic sensors used for calculating the rotation angle of the output shaft 9 may be three or more.
In the above-described embodiment, Hall elements are used as the magnetic sensors 61 to 64. However, any element having a characteristic in which electrical characteristics change due to the action of a magnetic field may be a magnetoresistive element (MR element) or the like. Elements other than Hall elements may be used.

The present invention can also be applied to devices other than the electric power steering device.
In addition, various design changes can be made within the scope of matters described in the claims.

  DESCRIPTION OF SYMBOLS 8 ... Input shaft, 9 ... Output shaft, 10 ... Torsion bar (torque detection shaft), 11 ... Torque sensor (torque detection device), 51 ... First magnet, 52 ... Second magnet, 53 ... First magnetic shield plate 54 ... second magnetic shield plate, 61-64 ... magnetic sensor (electronic component), 65A ... first rotation angle calculation means, 65B ... second rotation angle calculation means, 65C ... torque calculation means

Claims (6)

A magnetic shielding member disposed between a magnet and an electronic component for blocking a magnetic flux from the magnet toward the electronic component;
The magnetic flux density characteristic from the magnet passing through the magnetic shielding member with respect to the thickness of the magnetic shielding member is such that the magnetic flux density passing through the magnetic shielding member gradually decreases as the thickness of the magnetic shielding member increases. Then, when the thickness of the magnetic shielding member becomes a predetermined value or more, the magnetic flux density passing through the magnetic shielding member has a characteristic that the degree of change is small,
A magnetic shielding member whose thickness is the predetermined value. A torque detection device that detects torque by detecting a torsion angle of a torque detection shaft,
A short cylindrical first magnet coupled to one end of the torque detection shaft so as to be integrally rotatable;
A short cylindrical second magnet coupled to the other end of the torque detection shaft so as to be integrally rotatable;
In order to detect a magnetic flux from each of the first magnets and to detect a first rotation angle, which is a rotation angle of the one end of the torque detection shaft, between the first magnet and the second magnet. A plurality of magnetic sensors for detecting the first rotation angle;
It is arrange | positioned between the said 1st magnet and the said 2nd magnet, each detects the magnetic flux from the said 2nd magnet, and detects the 2nd rotation angle which is a rotation angle of the said other end part of the said shaft for torque detection. A plurality of magnetic sensors for detecting the second rotation angle,
A first magnetic shielding member disposed between the first magnet and the second magnet and configured to block a magnetic flux from the second magnet toward the first rotation angle detection magnetic sensor;
A second magnetic shielding member disposed between the first magnet and the second magnet and configured to block a magnetic flux from the first magnet toward the second rotation angle detection magnetic sensor;
The characteristic of the magnetic flux density from the second magnet passing through the first magnetic shielding member with respect to the thickness of the first magnetic shielding member is that the first magnetic shielding member increases as the thickness of the first magnetic shielding member increases. The magnetic flux density passing through the member gradually decreases, and when the thickness of the first magnetic shielding member exceeds a first predetermined value, the degree of change in the magnetic flux density passing through the first magnetic shielding member is reduced. A torque detection device having characteristics, wherein the thickness of the first magnetic shielding member is the first predetermined value. The first magnetic shielding member is disposed between the plurality of magnetic sensors for detecting the first rotation angle and the second magnet, and is viewed from the first magnet side, and the central axis of the second magnet Is formed in an arc shape having a width centered on
The length of the arc passing through the width center of the first magnetic shielding member is the second length that passes through the first magnetic shielding member when the thickness of the first magnetic shielding member is equal to or greater than the first predetermined value. The torque detection device according to claim 2, wherein the torque detection device is determined to have a constant magnetic flux density from the magnet.   The characteristic of the magnetic flux density from the first magnet that passes through the second magnetic shielding member with respect to the thickness of the second magnetic shielding member is that the second magnetic shielding member increases as the thickness of the second magnetic shielding member increases. The magnetic flux density that passes through the member gradually decreases, and when the thickness of the second magnetic shielding member exceeds a second predetermined value, the degree of change in the magnetic flux density that passes through the first magnetic shielding member is reduced. 4. The torque detection device according to claim 2, wherein the torque detection device has characteristics, and the thickness of the second magnetic shielding member is the second predetermined value. 5. The second magnetic shielding member is arranged between the plurality of magnetic sensors for detecting the second rotation angle and the first magnet, and is viewed from the second magnet side, and the central axis of the first magnet Is formed in an arc shape having a width centered on
The length of the arc passing through the width center of the second magnetic shielding member is such that the first magnetic shielding member passes through the second magnetic shielding member when the thickness of the second magnetic shielding member is equal to or greater than the second predetermined value. The torque detection device according to claim 4, wherein the torque detection device is determined to have a constant magnetic flux density from the magnet. First calculation means for calculating the first rotation angle based on output signals of the plurality of first rotation angle detection magnetic sensors;
Second calculating means for calculating the second rotation angle based on output signals of the plurality of second rotation angle detection magnetic sensors;
The torque calculation means of calculating torque based on the first rotation angle calculated by the first calculation means and the second rotation angle calculated by the second calculation means. The torque detection apparatus as described in any one.

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