JP6411255B2 - Magnetostrictive torque sensor and electric power steering apparatus - Google Patents

Description

  The present invention relates to a magnetostrictive torque sensor and an electric power steering apparatus including a plurality of detection coils that detect changes in magnetic characteristics of a magnetostrictive film disposed on an outer peripheral surface of a shaft.

  2. Description of the Related Art Conventionally, an electric power steering apparatus that detects a steering torque of a steering wheel with a magnetostrictive torque sensor and drives and controls a motor based on the detected steering torque to generate a steering assist force has been widely used.

  With respect to the magnetostrictive torque sensor, for example, Patent Document 1 discloses a technical idea that suppresses fluctuations in output voltage caused by fluctuations in ambient temperature around the magnetostrictive torque sensor using a temperature correction circuit. Specifically, the output voltage corrected by adding the output voltage having the negative temperature characteristic of the magnetostrictive torque sensor and the output voltage having the positive temperature characteristic of the temperature correction circuit to cancel the negative temperature characteristic. Trying to get.

JP 09-145495 A

  In general, the magnetostrictive film has a temperature characteristic that the magnetic permeability increases as the temperature increases. Therefore, if the operating temperature of the magnetostrictive torque sensor changes, the midpoint voltage of the magnetostrictive torque sensor (the voltage at the midpoint position of the steering angle) also changes.

  Since the magnetostrictive torque sensor according to Patent Document 1 described above uses a temperature correction circuit, it is possible to correct a change in the midpoint voltage of the detection coil when the temperature of the magnetostrictive film changes uniformly. is there.

  However, in practice, a temperature difference occurs in the magnetostrictive film. Specifically, the electric power steering device extends from the passenger compartment at normal temperature to the hot engine room through the toe board, for example, a steering shaft located in the passenger compartment and a pinion located in the engine compartment. May be provided with a magnetostrictive torque sensor.

  In such a case, a temperature difference tends to occur in the axial direction of the magnetostrictive film of the magnetostrictive torque sensor. If a temperature difference occurs in the magnetostrictive film, it cannot be corrected by the temperature correction circuit as in Patent Document 1. For this reason, when the temperature difference of the magnetostrictive film is large, the deviation amount of the midpoint voltage becomes large, and the detection accuracy of the steering torque may be lowered.

  Such a problem can also occur when a magnetostrictive torque sensor is provided in the steering column (in the middle of the steering shaft). That is, for example, in cold regions and winter, the lower part of the steering shaft is locally warmed by the warm air of the air conditioner guided to the lower part of the driver's seat (under the driver's feet), and the steering shaft has a temperature difference in the axial direction. May occur. As a result, a temperature difference occurs in the axial direction also in the magnetostrictive film of the magnetostrictive torque sensor.

  The present invention has been made in consideration of such a problem, and even if a temperature difference in the axial direction occurs in the magnetostrictive film, it can suppress a decrease in detection accuracy of torque applied to the shaft. An object of the present invention is to provide a magnetostrictive torque sensor and an electric power steering device that can be used.

  In order to solve the above problems, a magnetostrictive torque sensor according to the present invention is provided with a shaft, a magnetostrictive film disposed on an outer peripheral surface of the shaft, and a magnetostrictive film provided to face the magnetostrictive film. In a magnetostrictive torque sensor including a plurality of detection coils that detect a change in magnetic characteristics and a yoke provided on an outer peripheral side of the plurality of detection coils, the plurality of detection coils are arranged in an axial direction of the shaft. A first magnetic path including a first detection coil, a second detection coil, a third detection coil, and a fourth detection coil sequentially provided along the first detection coil, the magnetostrictive film, and the yoke The change in temperature characteristic of the first impedance of the second impedance and the change in temperature characteristic of the second impedance of the second magnetic path constituted by the second detection coil, the magnetostrictive film, and the yoke are equivalent , A temperature characteristic change of a third impedance of a third magnetic path constituted by the third detection coil, the magnetostrictive film, and the yoke, and a fourth characteristic constituted by the fourth detection coil, the magnetostrictive film, and the yoke. The temperature characteristic change of the fourth impedance of the magnetic path is equivalent to each other, the temperature characteristic change of the first impedance and the temperature characteristic change of the third impedance are different from each other, and the temperature characteristic change of the second impedance is different from the temperature characteristic change of the second impedance. The fourth impedance is different from the temperature characteristic change of the fourth impedance.

  According to such a configuration, the temperature characteristic change of the first impedance and the temperature characteristic change of the third impedance are different from each other, and the temperature characteristic change of the second impedance and the temperature characteristic change of the fourth impedance are different from each other. Even when a temperature difference in the axial direction occurs in the magnetostrictive film, the change in impedance of the magnetostrictive film due to the temperature difference can be offset. Thereby, since the deviation | shift amount of a midpoint voltage can be made small, the fall of the detection accuracy of the torque applied to the shaft can be suppressed.

  In the magnetostrictive torque sensor, the yoke has a temperature characteristic change of impedance at a portion provided on the outer peripheral side of the first detection coil and a temperature characteristic of impedance at a portion provided on the outer peripheral side of the third detection coil. You may be comprised so that a change may mutually differ.

  According to such a configuration, the temperature characteristic change of the first impedance and the temperature characteristic change of the third impedance can be made different from each other using the yoke.

  In this case, the yoke may be formed of materials different from each other in a portion provided on the outer peripheral side of the first detection coil and a portion provided on the outer peripheral side of the third detection coil.

  Thereby, the temperature characteristic change of the first impedance and the temperature characteristic change of the third impedance can be made different from each other with a simple configuration.

  In the magnetostrictive torque sensor, the temperature characteristic change of the impedance of the first detection coil may be different from the temperature characteristic change of the impedance of the third detection coil.

  According to such a configuration, the temperature characteristic change of the first impedance and the temperature characteristic change of the third impedance can be made different from each other using the first detection coil and the third detection coil.

  In this case, the number of turns of the first detection coil and the number of turns of the third detection coil may be different from each other. Moreover, the dimension along the axial direction of the first detection coil and the dimension along the axial direction of the third detection coil may be different from each other.

  Thereby, the temperature characteristic change of the first impedance and the temperature characteristic change of the third impedance can be made different from each other with a simple configuration.

  In the magnetostrictive torque sensor, the dimension of the second detection coil along the axial direction may be different from the dimension of the fourth detection coil along the axial direction. Thereby, the temperature characteristic change of the second impedance and the temperature characteristic change of the fourth impedance can be made different from each other with a simple configuration.

  An electric power steering apparatus according to the present invention generates a steering assist force based on a steering wheel, a magnetostrictive torque sensor that detects a steering torque generated by steering of the steering wheel, and an output signal of the magnetostrictive torque sensor. An electric power steering apparatus comprising a motor, wherein the magnetostrictive torque sensor is the magnetostrictive torque sensor described above.

  According to such a configuration, it is possible to obtain an electric power steering device that exhibits the same effects as the magnetostrictive torque sensor described above.

  According to the present invention, even if a temperature difference in the axial direction occurs in the magnetostrictive film, the amount of deviation of the midpoint voltage can be reduced by canceling the change in impedance of the magnetostrictive film due to the temperature change. For this reason, it is possible to suppress a decrease in detection accuracy of torque applied to the shaft.

1 is a schematic diagram of an electric power steering apparatus including a magnetostrictive torque sensor according to a first embodiment of the present invention. FIG. 2 is a schematic explanatory diagram of the electric power steering device of FIG. 1. FIG. 2 is a schematic enlarged view of the magnetostrictive torque sensor of FIG. 1. FIG. 4A is a graph showing the temperature change of the magnetostrictive film when the engine is driven, and FIG. 4B shows the temperature change of the first to fourth detection coils, the first yoke, and the second yoke when the engine is driven. It is a graph. 5A is a graph showing changes in the midpoint voltage when the temperature characteristic changes of the first to fourth impedances are the same, and FIG. 5B is a graph showing the contribution of the magnetostrictive film in FIG. 5A. 5C is a graph showing contributions of the first to fourth detection coils, the first yoke, and the second yoke of FIG. 5A. 6A is a graph showing changes in the midpoint voltage of the magnetostrictive torque sensor shown in FIG. 3, and FIG. 6B shows contributions of the first to fourth detection coils, the first yoke, and the second yoke of FIG. 6A. It is a graph which shows. FIG. 7A is a first graph showing first to fourth impedances when the engine is stopped, and FIG. 7B is a first graph showing first to fourth impedances when the engine is driven. FIG. 8A is a second graph showing the first to fourth impedances when the engine is stopped, and FIG. 8B is a second graph showing the first to fourth impedances when the engine is driven. FIG. 9 is a schematic enlarged view of a magnetostrictive torque sensor according to a modification. It is a schematic diagram of the electric power steering apparatus which concerns on 2nd Embodiment of this invention. It is typical explanatory drawing of the electric power steering apparatus of FIG.

  Hereinafter, preferred embodiments of a magnetostrictive torque sensor and an electric power steering apparatus according to the present invention will be described with reference to the accompanying drawings.

(First embodiment)
The electric power steering device 12A according to the first embodiment of the present invention is applied to a vehicle such as a four-wheeled vehicle, and is configured as a so-called rack assist type electric power steering device. However, the electric power steering device 12A may be configured as a so-called column assist type or pinion assist type electric power steering device.

  As shown in FIGS. 1 and 2, the electric power steering device 12 </ b> A includes a steering wheel 14 operated by a driver, a steering shaft 16 provided on the steering wheel 14, and a steering gear mechanism 18 provided on the steering shaft 16. A steering assist mechanism 20, a magnetostrictive torque sensor 10, a detection circuit 21, and an ECU (Electronic Control Unit) 22.

  The steering shaft 16 includes an upper shaft 24 that constitutes an upper portion of the steering shaft 16 and is connected to the steering wheel 14, and a lower shaft 28 that constitutes a lower portion of the steering shaft 16 and is connected to the upper shaft 24 via a universal joint 26. And have. A universal joint 30 is provided at the lower end of the lower shaft 28.

  As shown in FIG. 2, the electric power steering device 12A extends from the passenger compartment 200 through the toe board 202 to the engine compartment 204, and the lower shaft 28 is positioned in the passenger compartment 200 to perform steering. The gear mechanism 18 is located in the engine room 204.

  The steering gear mechanism 18 includes a pinion 32 that interlocks with the steering shaft 16, a rack 38 that has rack teeth 36 that mesh with the pinion teeth 34 of the pinion 32, and a gear housing 40 that houses the pinion 32 and the rack 38.

  The rack 38 is disposed so as to be capable of reciprocating in the vehicle width direction. At both ends of the rack 38, steered wheels 44 are provided via tie rods 42. A plurality (two) of bearings 48 and 50 that pivotally support the upper and lower portions of the pinion 32 are fixed to the gear housing 40. The gear housing 40 is fixed to a subframe 208 on which the engine 206 is placed (see FIG. 2).

  The steering assist mechanism 20 is for assisting the driver's steering, and meshes with the steering assist motor 52, the worm shaft 54 connected to the rotation shaft of the motor 52, and the helical teeth of the worm shaft 54. A worm wheel 56 having teeth formed on the outer peripheral surface, an auxiliary pinion 62 having auxiliary pinion teeth 60 that mesh with auxiliary rack teeth 58 formed on the rack 38 to which the worm wheel 56 is fixed, and an auxiliary gear housing 64.

  A plurality of (two) bearings 66 and 68 that pivotally support the upper and lower portions of the auxiliary pinion 62 are fixed to the auxiliary gear housing 64. In the present embodiment, the auxiliary gear housing 64 is provided integrally with the gear housing 40.

  The magnetostrictive torque sensor 10 is provided in the steering gear mechanism 18 in a state of being positioned in the vicinity of the engine 206 in the engine room 204. Specifically, as shown in FIG. 3, the magnetostrictive torque sensor 10 includes a shaft 70 that is coaxially connected to the pinion 32, a magnetostrictive film 72 that is disposed on the outer peripheral surface of the shaft 70, and a magnetostrictive film 72. On the outer peripheral side of the bobbin 74 disposed on the outer peripheral side, the first to fourth detection coils 76, 78, 80, 82 provided on the bobbin 74, and the first to fourth detection coils 76, 78, 80, 82. A first yoke 84 and a second yoke 86, a sensor housing 88, and an urging mechanism (urging means) 90 are provided.

  The magnetostrictive film 72 is a film made of a material having a large change in magnetic permeability with respect to the change in strain. For example, the magnetostrictive film 72 is a Ni—Fe alloy film, a Co—Fe alloy film, or a Sm—Fe alloy. It consists of a film. Such a magnetostrictive film 72 is formed on the outer peripheral surface of the shaft 70 by a method such as plating.

  The magnetostrictive film 72 extends over the entire circumference on the outer circumferential surface of the shaft 70. In the magnetostrictive film 72, a first magnetostrictive portion 92 and a second magnetostrictive portion 94 having different magnetic anisotropies are provided apart from each other in the axial direction of the shaft 70. In the present embodiment, the first magnetostrictive portion 92 and the second magnetostrictive portion 94 are provided in a single magnetostrictive film 72, but the magnetostrictive film provided with the first magnetostrictive portion 92 and the second magnetostrictive portion 94 are provided. It is also possible to arrange the provided magnetostrictive films separately in the axial direction of the shaft 70.

  The bobbin 74 is integrally formed in a cylindrical shape with an insulating resin material. A shaft 70 is inserted into the inner hole of the bobbin 74, and the magnetostrictive film 72 and the bobbin 74 are opposed to each other with a gap therebetween.

  The bobbin 74 is provided with a first detection coil 76, a second detection coil 78, a third detection coil 80, and a fourth detection coil 82 sequentially from one side (above) along the axial direction of the shaft 70. .

  The first detection coil 76 and the second detection coil 78 are opposed to the first magnetostrictive region 92 through the bobbin 74, and the third detection coil 80 and the fourth detection coil 82 are in the second magnetostrictive region 94 through the bobbin 74. Opposite to. An intermediate wall 96 is formed in the center of the bobbin 74 in the axial direction, and the second detection coil 78 and the third detection coil 80 are located so as to sandwich the intermediate wall 96 from the axial direction.

  The first detection coil 76 and the second detection coil 78 detect a change in the magnetic characteristics of the first magnetostrictive portion 92, and the third detection coil 80 and the fourth detection coil 82 detect a change in the magnetic characteristics of the second magnetostrictive portion 94. To do. The first to fourth detection coils 76, 78, 80, 82 also function as excitation coils that excite the magnetostrictive film 72.

  Such first to fourth detection coils 76, 78, 80, 82 basically have a configuration described in Japanese Patent No. 4581002. Therefore, the description of the basic configuration of the first to fourth detection coils 76, 78, 80, 82 is omitted.

  In the present embodiment, the first detection coil 76 and the second detection coil 78 are configured identically, and the third detection coil 80 and the fourth detection coil 82 are configured identically. Specifically, the number of turns of the first detection coil 76 and the number of turns of the second detection coil 78 are set to be the same, and the number of turns of the third detection coil 80 and the number of turns of the fourth detection coil 82 are made the same. Is set.

  The number of turns of the first detection coil 76 is set to be smaller than the number of turns of the third detection coil 80, and the number of turns of the second detection coil 78 is set to be less than the number of turns of the fourth detection coil 82. The first to fourth detection coils 76, 78, 80, and 82 have the same dimension along the axial direction. Output signals of the first to fourth detection coils 76, 78, 80, 82 are input to the ECU 22 via the detection circuit 21.

  The first yoke 84 is formed so as to cover the first detection coil 76 and the second detection coil 78 from the outer peripheral side, and the second yoke 86 covers the third detection coil 80 and the fourth detection coil 82 from the outer peripheral side. Is formed.

  The first yoke 84 and the second yoke 86 are made of different materials. In the present embodiment, the first yoke 84 is composed of S35C, and the second yoke 86 is composed of S10C. Thereby, the impedance of the first yoke 84 can be made larger than the impedance of the second yoke 86. However, the first yoke 84 and the second yoke 86 can be made of any material as long as the impedance of the first yoke 84 is larger than the impedance of the second yoke 86.

  The sensor housing 88 is integrally formed of a resin material, and houses the magnetostrictive film 72, the bobbin 74, the first to fourth detection coils 76, 78, 80, 82, the first yoke 84, and the second yoke 86. The sensor housing 88 includes a housing body 106 formed in a cylindrical shape, and an annular wall portion 108 that extends radially inward from the housing body 106 so that one end surface of the bobbin 74 and one end surface of the first yoke 84 abut against each other. Including.

  On one end surface (upper end surface) of the sensor housing 88, an engagement protrusion 112 with which the annular seal member 110 is engaged is provided. The seal member 110 is made of rubber or the like and is pressed against the shaft 70 by a spring 114. Thereby, the sealing member 110 can prevent the lubricating oil, foreign matter, and the like from entering the inner hole of the housing body 106.

  The urging mechanism 90 urges the bobbin 74 and the second yoke 86 toward the annular wall 108 in a state where the bobbin 74 and the first yoke 84 are in contact with the annular wall 108 of the sensor housing 88. The bobbin 74, the first yoke 84, and the second yoke 86 are fixed to the sensor housing 88.

  The urging mechanism 90 includes a stop member 116 fixed to the housing body 106 and an elastic member 118 provided on the stop member 116. As the stopper member 116, for example, a circlip or a C-ring can be used. As the elastic member 118, for example, a spring member such as a wave washer can be used. However, the elastic member 118 may be rubber or the like.

  In the magnetostrictive torque sensor 10 configured as described above, a first magnetic path is formed from the first detection coil 76, the first yoke 84, and the first magnetostrictive portion 92, and the second detection coil 78, the first yoke 84, A second magnetic path is formed from the first magnetostrictive portion 92. In the magnetostrictive torque sensor 10, a third magnetic path is formed from the third detection coil 80, the second yoke 86, and the second magnetostrictive portion 94, and the fourth detection coil 82, the second yoke 86, and the second magnetostriction are formed. A fourth magnetic path is formed from the portion 94.

  In addition, since the first detection coil 76 and the second detection coil 78 are configured identically, the temperature characteristic change of the first impedance (first magnetic impedance) of the first magnetic path and the second impedance ( The change in temperature characteristic of (second magnetic impedance) is equivalent to each other. Since the third detection coil 80 and the fourth detection coil 82 are configured identically, the temperature characteristic change of the third impedance (third magnetic impedance) of the third magnetic path and the fourth impedance (fourth) of the fourth magnetic path. The change in temperature characteristics of the magnetic impedance is equivalent to each other.

  Furthermore, the first yoke 84 and the second yoke 86 are made of different materials, the number of turns of the first detection coil 76 and the number of turns of the third detection coil 80 are different, and the number of turns of the second detection coil 78 The number of turns of the fourth detection coil 82 is different from each other. Therefore, the temperature characteristic change of the first impedance and the temperature characteristic change of the third impedance are different from each other, and the temperature characteristic change of the second impedance and the temperature characteristic change of the fourth impedance are different from each other.

The detection circuit 21 calculates the first output voltage VT1 from the output signal of the first detection coil 76 and the output signal of the third detection coil 80 based on the following formula (1) and outputs the first output voltage VT1 to the ECU 22. Here, Z1 is a first impedance, and Z3 is a third impedance. V0 is a power supply voltage, and is set to V0 = 5 [V], for example.
VT1 = {Z3 / (Z1 + Z3)} × V0 (1)

Further, the detection circuit 21 calculates the second output voltage VT2 from the output signal of the second detection coil 78 and the output signal of the fourth detection coil 82 based on the following equation (2) and outputs the second output voltage VT2 to the ECU 22. Here, Z2 is the second impedance, and Z4 is the fourth impedance.
VT2 = {Z2 / (Z2 + Z4)} × V0 (2)

Then, the ECU 22 calculates the third output voltage VT3 from the first output voltage VT1 and the second output voltage VT2 input from the detection circuit 21 based on the following equation (3). Here, α is a constant, and for example, α = 1 is set.
VT3 = α (VT2-VT1) + V0 / 2 (3)

  Further, the ECU 22 calculates torque (steering torque) applied to the shaft 70 based on the third output voltage VT3, and drives and controls the motor 52 constituting the steering assist mechanism 20 based on the calculated steering torque.

  The electric power steering apparatus 12A provided with the magnetostrictive torque sensor 10 according to the present embodiment is basically configured as described above, and the operation and effects thereof will be described next.

  First, when the driver rotates the steering wheel 14, steering torque is applied to the shaft 70 of the magnetostrictive torque sensor 10. For example, a tensile force is applied to the first magnetostrictive part 92 while the second magnetostrictive part 94 is applied to the second magnetostrictive part 94. A compression force acts. As a result, the magnetic permeability of the first magnetostrictive portion 92 decreases, the inductance of the first detection coil 76 and the second detection coil 78 decreases, and the magnetic permeability of the second magnetostrictive portion 94 increases, so that the third detection coil 80 and The inductance of the fourth detection coil 82 increases.

  The output signal of the first detection coil 76 and the output signal of the third detection coil 80 are converted into the first output voltage VT1 by the detection circuit 21 and supplied to the ECU 22, and the output signal of the second detection coil 78 and the fourth detection coil The output signal 82 is converted into the second output voltage VT 2 by the detection circuit 21 and supplied to the ECU 22.

  The ECU 22 calculates the third output voltage VT3 from the difference between the first output voltage VT1 and the second output voltage VT2, calculates the steering torque, and drives and controls the steering assist motor 52. As a result, the driving force of the motor 52 is transmitted as a steering assist force to the rack 38 via the worm shaft 54, the worm wheel 56, and the auxiliary pinion 62, so that the driver's steering force is moderately assisted. Become.

  By the way, like the electric power steering apparatus 12A of the present embodiment, the pinion 32 is located in the high temperature engine room 204 and the lower part (lower shaft 28) of the steering shaft 16 is located in the room temperature 200. In this case, when the engine 206 is driven, the temperature of the magnetostrictive torque sensor 10 changes as shown in FIGS. 4A and 4B.

  Here, FIG. 4A is a graph showing the temperature change of the magnetostrictive film 72 when the engine 206 is driven. In FIG. 4A, the broken line indicates the temperature change of the first magnetostrictive region 92, and the solid line indicates the temperature change of the second magnetostrictive region 94. FIG. 4B is a graph showing temperature changes of the first to fourth detection coils 76, 78, 80, 82, the first yoke 84, and the second yoke 86 when the engine 206 is driven. In FIG. 4B, broken lines indicate temperature changes of the first detection coil 76, the second detection coil 78, and the first yoke 84, and solid lines indicate the third detection coil 80, the fourth detection coil 82, and the second yoke 86. The temperature change is shown.

  As understood from FIG. 4A, when the engine 206 is driven, the second magnetostrictive portion 94 is heated, and then the first magnetostrictive portion 92 is heated. The temperature of the first magnetostrictive portion 92 is lower than the temperature of the second magnetostrictive portion 94 at the time tb when the temperature of the first magnetostrictive portion 92 and the second magnetostrictive portion 94 is stabilized. That is, since the heat of the second magnetostrictive portion 94 is transmitted to the lower shaft 28 located in the vehicle interior 200 via the shaft 70 and the universal joint 30, the heat is transferred between the first magnetostrictive portion 92 and the second magnetostrictive portion 94. Has a predetermined temperature difference (temperature gradient).

  On the other hand, as can be understood from FIG. 4B, at the time tb when the temperatures of the first to fourth detection coils 76, 78, 80, 82, the first yoke 84, and the second yoke 86 are stabilized, the gap between these members. Does not generate a temperature difference (temperature gradient) (the temperature of these members is substantially the same).

  Thus, in a state where a predetermined temperature difference is generated between the first magnetostrictive portion 92 and the second magnetostrictive portion 94, for example, when the temperature characteristic changes of the first to fourth impedances are the same, the rudder The third output voltage (midpoint voltage) at the midpoint position of the corner changes as shown in a graph shown in FIG. 5A (a graph obtained by adding the graph shown in FIG. 5B and the graph shown in FIG. 5C).

  Here, FIG. 5A is a graph showing the change of the midpoint voltage when the temperature characteristic changes of the first to fourth impedances are the same, and FIG. 5B is a graph showing the contribution of the magnetostrictive film 72 of FIG. 5A. 5C is a graph showing contributions of the first to fourth detection coils 76, 78, 80, 82, the first yoke 84, and the second yoke 86 of FIG. 5A. That is, as shown in FIGS. 5A to 5C, the midpoint voltage at the time point tb deviates (increases) from the midpoint voltage at the time point ta when the engine 206 is stopped. Therefore, the detection accuracy of the magnetostrictive torque sensor May decrease.

  However, in the present embodiment, the first impedance and the third impedance are made different from each other, and the second impedance and the fourth impedance are made different from each other. In addition, the temperature characteristic change of the first impedance and the temperature characteristic change of the second impedance are equivalent, and the temperature characteristic change of the third impedance and the temperature characteristic change of the fourth impedance are equivalent.

  Therefore, the contribution of the impedances of the first to fourth detection coils 76, 78, 80, 82, the first yoke 84, and the second yoke 86 to the change in the midpoint voltage is corrected as shown in the graph of FIG. 6B. Can do.

  That is, the increase in the midpoint voltage due to the temperature difference of the magnetostrictive film 72 is caused by the temperature characteristic change of the impedance of the first to fourth detection coils 76, 78, 80, 82, the first yoke 84, and the second yoke 86. Can be offset. As a result, as shown in FIG. 6A, the amount of deviation between the midpoint voltage at the time point tb and the midpoint voltage at the time point ta can be reduced. Therefore, even when a temperature difference in the axial direction occurs in the magnetostrictive film 72, it is possible to suppress a decrease in the accuracy of detection of torque applied to the shaft 70.

  Next, the effect of the magnetostrictive torque sensor 10 according to the present embodiment will be described in more detail with reference to FIGS. 7A to 8B.

  First, for example, when the first yoke 84 and the second yoke 86 are made of different materials and the first to fourth detection coils 76, 78, 80, 82 are made the same, the magnetostrictive torque sensor 10 The first to fourth impedances change as shown in FIGS. 7A and 7B due to changes in the operating temperature.

  Here, FIG. 7A is a graph showing the first to fourth impedances when the engine 206 is stopped. FIG. 7B is a graph showing first to fourth impedances when engine 206 is driven. 7A and 7B, no steering torque acts on the shaft 70.

  As can be understood from FIG. 7A, when the engine 206 is stopped, no temperature difference occurs in the magnetostrictive film 72, and therefore no difference occurs in the impedance of the magnetostrictive film 72 in the first to fourth magnetic paths. However, since the impedance of the first yoke 84 and the impedance of the second yoke 86 are different from each other, a difference of ΔZ0 occurs between the first impedance and the third impedance and between the second impedance and the fourth impedance.

  On the other hand, as can be seen from FIG. 7B, during the driving of the engine 206, a temperature difference in the axial direction is generated in the magnetostrictive film 72, so that there is a difference in impedance of the magnetostrictive film 72 in the first to fourth magnetic paths. That is, the impedance of the magnetostrictive film 72 increases as the temperature increases (the fourth magnetic path side).

  However, since the temperature characteristic change of the impedance of the first yoke 84 and the temperature characteristic change of the impedance of the second yoke 86 are different from each other, the impedance change caused by the temperature change of the magnetostrictive film 72 is changed. It can be canceled by a change in the impedance of the yoke 86.

  That is, since the relationship between the first impedance and the third impedance and the relationship between the second impedance and the fourth impedance are constant regardless of the temperature difference of the magnetostrictive film 72 (ΔZa = ΔZ0, ΔZb = ΔZ0), the midpoint The voltage deviation becomes smaller. Therefore, a decrease in steering torque detection accuracy can be suppressed.

  In the example of FIGS. 7A and 7B, a difference of ΔZ1 (ΔZ0) is generated in the first impedance and the third impedance, and a difference of ΔZ2 (ΔZ0) is generated in the second impedance and the fourth impedance. Therefore, the midpoint voltage deviates from the midpoint of the power supply voltage.

  Therefore, in the present embodiment, the number of turns of the first detection coil 76 is made smaller than the number of turns of the third detection coil 80 and the number of turns of the second detection coil 78 is made smaller than the number of turns of the fourth detection coil 82. ing. As a result, as shown in FIGS. 8A and 8B, the first impedance and the third impedance can be made equal and the second impedance and the fourth impedance can be made equivalent regardless of the presence or absence of the temperature difference of the magnetostrictive film 72. it can. Therefore, the midpoint voltage is located at the midpoint of the power supply voltage.

  According to this embodiment, the temperature characteristic change of the first impedance and the temperature characteristic change of the third impedance are different from each other, and the temperature characteristic change of the second impedance and the temperature characteristic change of the fourth impedance are different from each other. Even when a temperature difference in the axial direction occurs in the magnetostrictive film 72, a change in impedance of the magnetostrictive film 72 due to the temperature difference can be offset. Thereby, since the deviation | shift amount of a midpoint voltage can be made small, the fall of the detection precision of the torque (steering torque) applied to the shaft 70 can be suppressed.

  Next, a magnetostrictive torque sensor 10a according to a modification will be described with reference to FIG. In the magnetostrictive torque sensor 10a according to the modification, elements having the same functions and effects as those of the magnetostrictive torque sensor 10 described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 9, the magnetostrictive torque sensor 10 a includes a third detection coil 130 and a fourth detection coil 132 instead of the third detection coil 80 and the fourth detection coil 82 of the magnetostrictive torque sensor 10 described above. The bobbin 74 is provided instead of the bobbin 74.

  The third detection coil 130 is formed so that the dimension along the axial direction is smaller than the dimension along the axial direction of the first detection coil 76, and the fourth detection coil 132 has a second dimension along the axial direction. The detection coil 78 is formed smaller than the dimension along the axial direction. The dimension along the axial direction of the third detection coil 130 and the dimension along the axial direction of the fourth detection coil 132 are the same.

  According to such a magnetostrictive torque sensor 10a, the temperature characteristic change of the first impedance and the temperature characteristic change of the third impedance are made different from each other with a simple configuration, and the temperature characteristic change of the second impedance and the fourth impedance are changed. The temperature characteristic change can be made different from each other. Therefore, the same effect as the magnetostrictive torque sensor 10 described above can be obtained.

  The present embodiment is not limited to the configuration described above. For example, the magnetostrictive torque sensor 10 may set the number of turns of the first to fourth detection coils 76, 78, 80, and 82 to be the same. Even in this case, as described above, since the amount of deviation of the midpoint voltage can be reduced, a decrease in detection accuracy of the magnetostrictive torque sensor 10 can be suppressed.

(Second Embodiment)
Next, an electric power steering apparatus 12B according to a second embodiment of the present invention will be described with reference to FIGS. In addition, the same referential mark is attached | subjected to the element which show | plays the same or similar function and effect as 12 A of electric power steering apparatuses which concern on 1st Embodiment, and detailed description is abbreviate | omitted.

  As shown in FIGS. 10 and 11, the electric power steering device 12B according to the present embodiment is configured as a so-called column assist type electric power steering device, and the steering column 150 is provided with the magnetostrictive torque sensors 10 and 10a described above. It has been. However, the electric power steering device 12B may be configured as a so-called rack assist type or pinion assist type electric power steering device.

  In the electric power steering apparatus 12B, the upper shaft 24 of the steering shaft 148 is accommodated in the column cover 152 that constitutes the steering column 150, and the dashboard 154 is provided at the rear of the vehicle body (driver's seat side) of the lower shaft 28. . The dashboard 154 has a blower opening 156 that guides the warm air of the air conditioner to the lower part of the driver's seat (step of the driver). That is, the warm air of the air conditioner hits the lower shaft 28 while being guided to the air blowing port 156.

  The steering gear mechanism 158 includes a rack 160 in which the above-described auxiliary rack teeth 58 (see FIG. 1) are not formed, and a gear housing 161 that houses the rack 160. The remaining configuration of the steering gear mechanism 158 is the same as that of the steering gear mechanism 18 described above.

  The steering assist mechanism 162 is provided on the steering column 150. A worm wheel 56 constituting the steering assist mechanism 162 is fitted to an assist shaft 164 connected to the lower portion of the shaft 70 of the magnetostrictive torque sensor 10, 10a. The assist shaft 164 is pivotally supported by a plurality (two) of bearings 168 and 170 fixed to the auxiliary gear housing 166.

  In the present embodiment, when supplying warm air from the air conditioner to the lower part of the driver's seat in a cold region or winter, the lower shaft 28 is locally warmed by the warm air guided to the air blowing port 156 formed in the dashboard 154. It is done. Then, a temperature difference may occur in the axial direction in the magnetostrictive film 72 of the magnetostrictive torque sensor 10, 10a located between the low temperature upper shaft 24 and the high temperature lower shaft 28.

  However, according to the present embodiment, since the electric power steering device 12B includes the magnetostrictive torque sensors 10 and 10a, the same effects as those of the first embodiment are achieved.

  Although the magnetostrictive torque sensors 10 and 10a according to the first and second embodiments described above have been described with respect to the examples including the first to fourth detection coils 76, 78, 80, 82, 130, and 132, The magnetostrictive torque sensor according to the present invention may include two detection coils (a first detection coil and a second detection coil).

  In this case, the first detection coil is disposed on the bobbin so as to face the first magnetostrictive region, and the second detection coil is disposed on the bobbin so as to face the second magnetostrictive region. And the yoke is provided in the outer peripheral side of the 1st detection coil and the 2nd detection coil. Then, the output signal of the first detection coil is converted to the first output voltage by the detection circuit, and the output signal of the second detection coil is converted to the second output voltage by the detection circuit.

  In addition, the temperature characteristic change of the first impedance of the first magnetic path composed of the first magnetostrictive region, the first detection coil, and the yoke, and the second of the second magnetic path composed of the second magnetostrictive region, the second detection coil, and the yoke. The temperature characteristic change of impedance is different from each other. According to such a configuration, even if a temperature difference along the axial direction occurs in the magnetostrictive film, the deviation amount of the midpoint voltage can be reduced, so that the accuracy of detection of the torque applied to the shaft can be reduced. Can be suppressed.

  Further, the magnetostrictive torque sensor is not limited to the example applied to the electric power steering device, and can be applied to various devices. Of course, the magnetostrictive torque sensor and the electric power steering apparatus according to the present invention are not limited to the above-described embodiments, and various configurations can be adopted without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10, 10a ... Magnetostrictive torque sensor 12A, 12B ... Electric power steering apparatus 14 ... Steering wheel 16, 148 ... Steering shaft 21 ... Detection circuit 22 ... ECU
52 ... Motor 70 ... Shaft 72 ... Magnetostrictive film 74, 134 ... Bobbin 76 ... First detection coil 78 ... Second detection coil 80, 130 ... Third detection coil 82, 132 ... Fourth detection coil 84 ... First yoke 86 ... Second yoke 88 ... sensor housing 90 ... biasing mechanism (biasing means)
92 ... first magnetostrictive region 94 ... second magnetostrictive region

Claims (8)

A shaft,
A magnetostrictive film disposed on the outer peripheral surface of the shaft;
A plurality of detection coils provided so as to face the magnetostrictive film and detecting a change in magnetic characteristics of the magnetostrictive film;
In a magnetostrictive torque sensor comprising a yoke provided on the outer peripheral side of the plurality of detection coils,
The plurality of detection coils include a first detection coil, a second detection coil, a third detection coil, and a fourth detection coil that are sequentially provided along the axial direction of the shaft,
Temperature characteristic change of the first impedance of the first magnetic path composed of the first detection coil, the magnetostrictive film, and the yoke, and the second magnetism composed of the second detection coil, the magnetostrictive film, and the yoke. The temperature characteristic change of the second impedance of the path is equivalent to each other,
A temperature characteristic change of a third impedance of a third magnetic path constituted by the third detection coil, the magnetostrictive film, and the yoke, and a fourth magnetism constituted by the fourth detection coil, the magnetostrictive film, and the yoke. The temperature characteristic change of the fourth impedance of the path is equivalent to each other,
The magnetostriction characterized in that the temperature characteristic change of the first impedance and the temperature characteristic change of the third impedance are different from each other, and the temperature characteristic change of the second impedance and the temperature characteristic change of the fourth impedance are different from each other. Type torque sensor. The magnetostrictive torque sensor according to claim 1,
The yoke is configured such that a change in impedance temperature characteristic at a portion provided on the outer peripheral side of the first detection coil is different from a change in impedance temperature characteristic at a portion provided on the outer peripheral side of the third detection coil. A magnetostrictive torque sensor. The magnetostrictive torque sensor according to claim 2,
The yoke has a magnetostrictive torque sensor in which a portion provided on the outer peripheral side of the first detection coil and a portion provided on the outer peripheral side of the third detection coil are made of different materials. . The magnetostrictive torque sensor according to any one of claims 1 to 3,
A magnetostrictive torque sensor characterized in that a change in temperature characteristic of impedance of the first detection coil and a change in temperature characteristic of impedance of the third detection coil are different from each other. The magnetostrictive torque sensor according to claim 4, wherein
A magnetostrictive torque sensor, wherein the number of turns of the first detection coil and the number of turns of the third detection coil are different from each other. In the magnetostrictive torque sensor according to claim 4 or 5,
A magnetostrictive torque sensor characterized in that a dimension along the axial direction of the first detection coil and a dimension along the axial direction of the third detection coil are different from each other. The magnetostrictive torque sensor according to any one of claims 4 to 6,
A magnetostrictive torque sensor characterized in that a dimension along the axial direction of the second detection coil is different from a dimension along the axial direction of the fourth detection coil. A steering wheel,
A magnetostrictive torque sensor for detecting a steering torque generated by steering of the steering wheel;
An electric power steering apparatus comprising: a motor that generates a steering assist force based on an output signal of the magnetostrictive torque sensor;
The magnetostrictive torque sensor, the electric power steering device, characterized in that the magnetostrictive torque sensor according to any one of claims 1-7.

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