JP5058961B2 - Manufacturing method of magnetostrictive torque sensor - Google Patents

Description

  The present invention relates to a method of manufacturing a magnetostrictive torque sensor that is optimal for detecting the steering torque of an electric power steering apparatus for an automobile.

  The electric power steering device is a support device that assists a steering force by interlocking a motor when a driver operates a steering wheel (steering handle) while driving an automobile. In the electric power steering apparatus, a motor control unit uses a steering torque signal from a steering torque detection unit that detects a steering torque generated in a steering shaft by a steering wheel of a driver, and a vehicle speed signal from a vehicle speed detection unit that detects a vehicle speed. Based on the control operation of the (drive control circuit), the assisting motor that outputs the auxiliary steering force is PWM-driven to reduce the driver's steering force.

  For example, if the steering torque is TH and the coefficient of the assist amount AH is a constant kA, AH = kA × TH. Therefore, if the pinion torque as a load is TP, TP = TH + AH to TH = TP / (1 + kA) Become. Therefore, the steering torque TH is reduced to 1 / (1 + kA) and (kA ≧ 0) of the pinion torque TP. As a steering torque detection unit in such an electric power steering apparatus, a magnetostrictive torque sensor is known in addition to a torsion bar type that uses a twist of a torsion bar provided between input and output shafts of a pinion.

  As an example of a magnetostrictive torque sensor, for example, a surface of a steering shaft connected to a steering wheel is provided with a Ni-Fe plated magnetostrictive film at two upper and lower positions, respectively, to give magnetic anisotropies in opposite directions, and to have a predetermined axial direction width. When the steering torque acts on the magnetostrictive film, the reverse magnetostrictive characteristics generated based on the magnetic anisotropy are applied to the steering shaft using the AC resistance of the coil disposed around the magnetostrictive film. Some detect torque.

  FIG. 17 is a schematic diagram of the magnetostrictive torque sensor 300. The magnetostrictive torque sensor 300 includes a magnetostrictive film 302 formed around the steering shaft 301, a magnetostrictive film 303 formed below the magnetostrictive film 302 with a space therebetween, and a minute gap in the vicinity of the magnetostrictive films 302 and 303. And a detection coil 306 provided corresponding to the magnetostrictive film 302 and a detection coil 307 provided corresponding to the magnetostrictive film 303. An excitation voltage supply source 305 is connected to the excitation coil 304.

  In the magnetostrictive torque sensor 300 shown in FIG. 17, when torque acts on the steering shaft 301, torque also acts on the magnetostrictive films 302 and 303. A magnetostrictive effect is generated in the magnetostrictive films 302 and 303 according to this torque. Therefore, a high-frequency AC voltage (excitation voltage) is supplied from the excitation voltage supply source 305 to the excitation coil 304, and a change in the magnetic field due to the magnetostriction effect of the magnetostrictive films 302 and 303 corresponding to the torque is detected by the detection coils 306 and 307. Detect as. Based on this change in impedance, the torque applied to the steering shaft 301 can be detected. In addition to detecting as a change in impedance, it can also be detected as a change in induced voltage. Below, the case where it detects by the change of an impedance is demonstrated.

  FIG. 18 is a diagram showing magnetostriction characteristics. The horizontal axis represents the steering torque applied to the steering shaft 301, and the vertical axis represents the impedance detected by the detection coils 306 and 307 when an AC voltage is applied to the excitation coil 304. A curve C110 indicates a change in impedance detected by the detection coil 306, and a curve C111 indicates a change in impedance detected by the detection coil 307.

  Since the anisotropy is given to the magnetostrictive film, the impedance detected by the detection coil 306 increases as the steering torque changes from negative to positive. When the steering torque becomes a positive value T1, the impedance becomes a peak value. When the steering torque is T1 or more, the torque decreases. Also, the detected value by the detection coil 307 takes a peak value when the steering torque is a negative value −T1, and decreases when the absolute value of the steering torque increases.

  As shown in FIG. 18, the steering torque-impedance characteristic obtained by the detection coil 306 and the steering torque-impedance characteristic obtained by the detection coil 307 are substantially convex. In addition, the steering torque-impedance characteristic (curve C110) obtained by the detection coil 306 and the steering torque-impedance characteristic (curve C111) obtained by the detection coil 307 are magnetic anisotropies that are opposite to each other at two locations above and below the magnetostrictive film. Therefore, the characteristic curves are almost symmetrical with respect to the vertical axis passing through the points where the characteristic curves intersect.

  A straight line L10 indicates a value obtained by subtracting the characteristic curve C111 detected by the detection coil 307 from the characteristic curve C110 detected by the detection coil 206, and the value becomes zero when the steering torque is zero. The magnetostrictive torque sensor 300 outputs a detection signal corresponding to the direction and magnitude of the input torque by using a region regarded as a substantially constant gradient near the torque neutral point. Further, the steering torque can be detected from the values of the detection coils 306 and 307 by utilizing the characteristic of the straight line L10.

FIG. 19 is a flowchart of a conventional method for manufacturing a magnetostrictive torque sensor. In the conventional magnetostrictive torque sensor, a step of machining a pinion at the lower end of the steering shaft (step S101), a step of quenching the pinion (step S102), a step of tempering the pinion (step S103), and a magnetostrictive film are provided. (Step S104), applying a torsion torque (step S105), heating the magnetostrictive film (step S106), cooling the magnetostrictive film (step S107), and removing the torsion torque. The process (step S108) to perform and the process (step S109) to heat-process again (for example, refer patent document 1). In the case where a plurality of magnetostrictive films are provided as shown in FIG. 3, magnetic anisotropy is imparted by steps S105 to S108 for each.
Japanese Patent No. 3730234

  The method for imparting anisotropy to the magnetostrictive film applied to the steering shaft is to heat the magnetostrictive film by high-frequency heating while applying torque to the steering shaft, to creep the magnetostrictive film, and then to apply the torque while applying the torque. And the magnetostrictive film is cooled to room temperature and then the torque is removed to give anisotropy to the magnetostrictive film. The characteristic of the impedance value that is the output with respect to the torque input from the steering shaft thus obtained is the maximum value on the positive side of the steering torque as shown by the curve C110 for the detection coil 306, as shown in FIG. The detection coil 307 has a substantially convex curve having a maximum value P2 on the negative side of the steering torque as shown by a curve C111. The value of the steering torque that takes the maximum value of this characteristic curve changes depending on the magnitude of the torque that is applied when anisotropy is applied, and the steering torque value that takes the maximum value of the two curves as the applied torque increases. The difference grows. For example, when the applied torque for increasing anisotropy is made larger than when the characteristic curves C110 and C111 shown in FIG. 18 are obtained, the characteristic curves become curves C210 and C211. At this time, the detected value by the detection coil 306 increases in impedance as the steering torque changes from negative to positive, and when the steering torque becomes a positive value T2, the impedance becomes the maximum value P12, and the steering torque is T2 or more. Then it decreases. The value detected by the detection coil 307 has a maximum impedance P22 when the steering torque is a negative value −T2, and decreases when the absolute value of the steering torque increases. A value obtained by subtracting the characteristic curve C211 detected by the detection coil 307 from the characteristic curve C210 detected by the detection coil 206 is a straight line L20, which is smaller than the slope of the straight line L10. This is because the slope and linearity of the bottom of the impedance characteristic are small. As shown in FIG. 18, in the neutral position, P12 and P22 have a smaller inclination and smaller linearity than P1 and P2. For this reason, when the torque applied when anisotropy is applied is increased, the gradient of the impedance output with respect to the torque input to the steering shaft becomes smaller than when the torque is small. Therefore, as shown in FIG. 20, the gain represented by the ratio between the output value and the input value becomes smaller as the applied torque increases when the anisotropy is applied. When the heating temperature is different, the amount of anisotropy and the state of creep of the magnetostrictive film change, and the gain changes depending on the heating temperature, as shown in FIG. However, in the manufacturing process, it is difficult to manage all the torque and heating temperature applied to the steering shaft when giving these anisotropies, and the manufacturing is complicated. As a result, it has been difficult to provide a wide range of torque sensors having high rigidity, high linearity, and small variations among sensors. Therefore, a method for suppressing variation in gain has been desired.

  In view of the above problems, an object of the present invention is to provide a method for manufacturing a magnetostrictive torque sensor in which variation in gain is suppressed.

  The method of manufacturing a magnetostrictive torque sensor according to the present invention is configured as follows in order to achieve the above object.

The first magnetostrictive torque sensor manufacturing method (corresponding to claim 1) includes two steps: a step of providing a magnetostrictive portion with magnetic anisotropy provided on a rotating shaft, and a change in magnetostrictive characteristics around the magnetostrictive portion . A step of arranging a multi-turn coil ; and at least two output voltages from each of the two multi-turn coils , and a voltage width corresponding to an increase in the absolute value of the torque corresponding to each of the at least two output voltages. So that each of at least two output voltages can be accommodated in the corresponding setting range of at least two setting ranges even if the absolute value of the torque is changed . And a gain adjustment step of adjusting a gain in the CPU of at least two output voltages .

The second magnetostrictive torque sensor manufacturing method (corresponding to claim 2) is preferably the above-described method. Preferably, each of the two multi-turn coils is connected with a coil element used as a resistor in series with a connection portion of the coil. In the gain adjustment step, the output voltage from each of the two multi-turn coils is the output voltage from each of the connection portions of the two multi-turn coils, and the gain in the CPU of at least two output voltages Is adjusted by a gain setting device .
The third magnetostrictive torque sensor manufacturing method (corresponding to claim 3) is preferably the above-described method, wherein the two coils and the two coil elements corresponding to the two multi-turn coils are preferably It has the same coil characteristic .
The fourth magnetostrictive torque sensor manufacturing method (corresponding to claim 4) is characterized in that, in the above method, preferably, the gain adjusting step is performed after the rotating shaft is assembled to the gear box of the electric power steering apparatus. It is attached.

  According to the present invention, the gain is set so that the output gain from the multi-turn coil falls within a setting range in which the width increases in accordance with the absolute value of the torque, and the gain is adjusted after the magnetostrictive torque sensor is assembled to the gear box. In the magnetostrictive torque sensor that heats the magnetostrictive film in a state where torque is applied, further gives the anisotropy by removing the torque after cooling, and detects the magnetic characteristic change of the magnetostrictive film by the detection coil, Even when the applied torque and the heating temperature are changed to change the amount of anisotropy and the state of creep of the magnetostrictive film, the variation in the torque sensor output can be reduced.

  As a result, management during the process of adding anisotropy can be reduced, and an excellent torque sensor with high rigidity, high linearity and little variation from sensor to sensor can be easily manufactured and widely provided. can do.

  In addition, gain adjustment is performed by a combination of a steering shaft having a magnetostrictive film, a coil, and a detection circuit, so that variations in the gain of the coil and the detection circuit can be corrected, and the accuracy of the coil and electronic components can be simplified. It becomes. As a result, an excellent torque sensor having high rigidity, high linearity and little variation among sensors can be manufactured at low cost, and can be provided more widely.

  DESCRIPTION OF EMBODIMENTS Preferred embodiments (examples) of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is an overall configuration diagram of an electric power steering apparatus according to a first embodiment of the present invention. The electric power steering device 10 is configured to give an auxiliary steering force (steering torque) to a steering shaft 12 a connected to the steering wheel 11. The steering shaft 12a is connected to the steering shaft 12b via a universal shaft joint 12c. The upper end of the steering shaft 12a is connected to the steering wheel 11, and the pinion 13 is attached to the lower end of the steering shaft 12b. A rack shaft 14 provided with a rack gear 14a meshing with the pinion 13 is disposed. A rack and pinion mechanism 15 is formed by the pinion 13 and the rack gear 14a. Tie rods 16 are provided at both ends of the rack shaft 14, and front wheels 17 are attached to the outer ends of the tie rods 16.

  A motor 19 is provided via a power transmission mechanism 18 for the steering shaft 12b. The power transmission mechanism 18 is formed by a worm gear 18a and a worm wheel 18b. The motor 19 outputs a rotational force (torque) that assists the steering torque, and applies this rotational force to the steering shafts 12 b and 12 a via the power transmission mechanism 18.

  A steering torque detector (steering torque sensor) 20 is provided on the steering shaft 12b. The steering torque detection unit 20 detects the steering torque applied to the steering shafts 12a and 12b when the steering torque generated by the driver operating the steering wheel 11 is applied to the steering shafts 12a and 12b. Reference numeral 21 denotes a vehicle speed detection unit that detects the vehicle speed of the vehicle, and reference numeral 22 denotes a control device constituted by a computer. The control device 22 takes in the steering torque signal T output from the steering torque detection unit 20 and the vehicle speed signal V output from the vehicle speed detection unit 21, and uses the information related to the steering torque based on the information related to the vehicle speed. A drive control signal SG1 for controlling the rotation operation is output. The rack and pinion mechanism 15 and the like are housed in a gear box 24 (see FIGS. 2 and 3) not shown in FIG.

  The electric power steering device 10 is configured by adding a steering torque detection unit 20, a vehicle speed detection unit 21, a control device 22, a motor 19, and a power transmission mechanism 18 to a normal steering system configuration.

  When the driver operates the steering wheel 11 to steer in the traveling direction during the traveling operation of the automobile, the rotational force based on the steering torque applied to the steering shafts 12 a and 12 b is transmitted to the rack shaft via the rack and pinion mechanism 15. 14 is converted into a linear motion in the axial direction, and the traveling direction of the front wheel 17 is changed through the tie rod 16. At this time, at the same time, the steering torque detector 20 attached to the steering shaft 12b detects the steering torque corresponding to the steering by the driver at the steering wheel 11 and converts it into an electrical steering torque signal T. A steering torque signal T is output to the control device 22. In addition, the vehicle speed detection unit 21 detects the vehicle speed of the vehicle, converts it into a vehicle speed signal V, and outputs the vehicle speed signal V to the control device 22.

  The control device 22 generates a motor current for driving the motor 19 based on the steering torque signal T and the vehicle speed signal V. The motor 19 driven by the motor current causes an auxiliary steering force to act on the steering shafts 12 b and 12 a via the power transmission mechanism 18. By driving the motor 19 as described above, the steering force applied by the driver to the steering wheel 11 is reduced.

  FIG. 2 shows a specific configuration of the main part of the mechanical mechanism of the electric power steering apparatus 10 and the electric system. A part of the left end portion and the right end portion of the rack shaft 14 is shown in cross section. The rack shaft 14 is housed in a cylindrical housing 31 arranged in the vehicle width direction (left-right direction in FIG. 2) so as to be slidable in the axial direction. Ball joints 32 are screwed to both ends of the rack shaft 14 protruding from the housing 31, and left and right tie rods 16 are connected to these ball joints 32. The housing 31 includes a bracket 33 for attaching to a vehicle body (not shown), and includes stoppers 34 at both ends.

  Reference numeral 35 denotes an ignition switch, 36 denotes an in-vehicle battery, and 37 denotes an AC generator (ACG) attached to the vehicle engine. The AC generator 37 starts power generation by the operation of the vehicle engine. Necessary electric power is supplied from the battery 36 or the AC generator 37 to the control device 22. The control device 22 is attached to the motor 19. Reference numeral 38 denotes a rack end that contacts the stopper 34 when the rack shaft is moved. Reference numeral 39 denotes a dust seal boot for protecting the inside of the gear box from water, mud, dust, and the like.

  FIG. 3 is a cross-sectional view taken along line AA in FIG. In FIG. 3, the specific structure of the support structure of the steering shaft 12b, the steering torque detector 20, the power transmission mechanism 18, and the rack and pinion mechanism 15 is clearly shown.

  In the housing 24 a forming the gear box 24, the steering shaft 12 b is rotatably supported by two bearing portions 41 and 42. A rack and pinion mechanism 15 and a power transmission mechanism 18 are housed inside the housing 24a, and a steering torque detector 20 is additionally provided at the top. Magnetostrictive films 20u and 20d are formed on the steering shaft 12b, and coils 20r, 20s, 20r ', and 20s' are provided so as to be surrounded by the yoke portion 20y.

  The upper opening of the housing 24a is closed with a lid 43, and the lid 43 is fixed with bolts. The pinion 13 provided at the lower end portion of the steering shaft 12b is located between the bearing portions 41 and 42. The rack shaft 14 is guided by a rack guide 45 and is urged by a compressed spring 46 and pressed against the pinion 13 side. The power transmission mechanism 18 is formed by a worm gear 18a fixed to a transmission shaft 48 coupled to an output shaft of the motor 19 and a worm wheel 18b fixed to a steering shaft 12b. The steering torque detector 20 is attached to the lid 43.

  As shown in FIG. 3, the steering torque detector 20 includes magnetostrictive films 20u and 20d provided at two locations around a steering shaft (shaft) 12b made of a ferromagnetic material such as iron, and magnetization of the magnetostrictive films 20u and 20d. Coil 20r, 20r ′ for detecting the change of the coil and coils 20s, 20s ′ used as resistors.

  A yoke portion 20y is provided on the outer periphery of the coils 20r and 20r 'and the coils 20s and 20s'. The steering torque detection unit 20 is provided in the steering gear box 24, detects the steering torque acting on the steering shaft 12b, and the detected value is input to the control device 22 to appropriately assist the motor 19 with auxiliary steering. It is supplied as a reference signal for generating torque. Reference numeral 20x denotes a detection circuit.

  The steering torque detection unit 20 used here is a magnetostrictive torque sensor, and as shown in FIG. 3, magnetostrictive films having magnetic anisotropy, for example, Ni—Fe plating are provided on the surface of the steering shaft 12 b at two locations on the upper and lower sides. (20u and 20d) are provided with a predetermined axial width so as to have anisotropy in the reverse direction, respectively, and the reverse magnetostrictive characteristics generated when steering torque acts on the magnetostrictive films 20u and 20d are expressed by the magnetostrictive films 20u and 20d. The detection is performed by using the AC resistance of the coils 20s and 20s ′ arranged around the periphery.

  The control device 22 of the electric power steering device 10 uses the steering torque signal T from the steering torque detection unit 20 and the vehicle speed signal V from the vehicle speed detection unit 21 to PWM the assisting motor 19 that outputs auxiliary steering force. Driven to reduce the steering force of the driver.

  With reference to FIG. 4, the manufacturing method of the magnetostrictive torque sensor which concerns on this invention is demonstrated. FIG. 4 is a flowchart showing a method for manufacturing a magnetostrictive torque sensor. In the magnetostrictive torque sensor, a step of processing a pinion at the lower end of the steering shaft (step S11), a step of quenching the pinion (step S12), a step of applying a magnetostrictive film (step S13), and applying a torsion torque. A step (step S14), a step of heat-treating the magnetostrictive film (step S15), a step of cooling the magnetostrictive film (step S16), a step of removing torsion torque (step S17), and a step of heat-treating again (step S16). Step S18), a step of arranging multiple winding coils and connecting the detection circuit (Step S19), a step of assembling the rotating shaft to the gear box (Step S20), and a gain adjustment unit provided in the detection circuit It consists of the process (step S21) to adjust.

Each step will be described below.
Step S11: The pinion 13 is processed at the lower end of the steering shaft 12b.
Step S12: The pinion 13 is quenched.
Step S13: The magnetostrictive films 20u and 20d are plated on the steering shaft 12b. In the plating process, the magnetostrictive material is applied with a predetermined film thickness (for example, 30 μm).
Step S14: After plating, a torsion torque Tq (applying the upper part of the steering shaft 12b in the counterclockwise direction and the lower part in the clockwise direction) is applied to apply stress to the circumferential surface of the steering shaft 12b. Here, the torsion torque Tq applies a torsion torque Tq that is larger than the torsion torque Tq that is applied during the conventional manufacturing. For example, 75 N · m is applied as the torsion torque Tq to the conventional torsion torque Tq of 70 N · m.
Step S15: The magnetostrictive film 20u is surrounded by a coil while the torsion torque Tq is applied, a high-frequency current is passed through the coil, and the magnetostrictive film 20u is heated.
Step S16: After the heat treatment, it is naturally cooled.
Step S17: After cooling, the torsion torque Tq is removed. Here, the preload torque (torsion torque remaining on the steering shaft 12b) is about −60 N · m.
Step S18: After removing the twisting torque Tq, the heat treatment is performed again. In the heat treatment again, the heat treatment is performed for 2 hours at a temperature equal to or higher than the use temperature in the situation where the steering torque detector 20 is used, for example, 200 ° C. Here, the preload torque is about −55 N · m.
Step S19: After the reheating process, a multi-turn coil is arranged at a position corresponding to the magnetostrictive films 20u and 20d, and a detection circuit is connected.
Although only the magnetostrictive film 20u has been described here, the magnetostrictive film 20d is also provided with magnetic anisotropy by the steps S14 to S17. However, the directions of torsional torque are different from each other.
Step S20: The rotating shaft is assembled to the gear box.
Step S21: The gain is adjusted by a gain adjustment unit provided in the detection circuit.

  FIG. 5 is a diagram showing the application of the torsion torque Tq and the temperature change during the period from the torsion torque application process to the torsion torque removal process. A rectangular line indicates torque, and a broken line indicates temperature. FIG. 6 is a view showing the steering shaft 12b in the heat treatment process. The steering shaft 12b is heated by applying a high-frequency current to the coil by applying a twisting torque Tq of 75 N · m. As shown in FIG. 6, the heat treatment is performed with respect to the magnetostrictive film 20u, which is a portion for heat-treating the coil 50. ] For a while. As a result, the temperature reaches 300 ° C. after tu seconds. At this time, the heating is stopped, that is, the supply of current is stopped and the cooling is performed. When the temperature drops to a predetermined temperature (for example, after te seconds), the torsion torque Tq is released.

  FIG. 7 is a diagram showing the steering shaft 12b in the process of performing the heat treatment again. The steering shaft 12b is heated by passing a high frequency current through the coil. As shown in FIG. 7, the heat treatment is performed with respect to the magnetostrictive films 20 u and 20 d and the pinion 13, which are parts for heat treatment of the coils 50 and 51, respectively. This is done by applying a current for several minutes. Here, the current is adjusted so that the temperature becomes 200 ° C.

  FIG. 8 is a diagram showing step S19 in which multiple winding coils are arranged at positions corresponding to the magnetostrictive films 20u and 20d after the reheating process, and a detection circuit is connected, and step S20 in which the rotating shaft is assembled to the gear box. The lid 43 is disposed so that the coils 20r, 20s, 20r ′, and 20s ′ are disposed around the magnetostrictive films 20u and 20d of the steering shaft 12b, and the steering shaft 12b is mounted on the housing that forms the gear box 24 with two bearing portions. 41, 42.

  FIG. 9 is a diagram illustrating a circuit configuration of the detection circuit 20x of the torque sensor. In the torque sensor 20, magnetostrictive films 20u and 20d are deposited so as to have opposite magnetic anisotropies at two locations on the steering shaft (shaft) 12b. These magnetostrictive films 20u and 20d act as a magnetic characteristic changing portion in which the magnetic characteristics change according to the torque when a torque is applied to the steering shaft 12b. In this circuit, coils 20r 'and 20s are provided around the magnetostrictive film to detect changes in magnetization of the magnetostrictive films 20u and 20d as a change in inductance when torque is applied to the steering shaft (shaft) 12b. In this circuit, coil elements 20r and 20s 'are connected in series with the coils 20r' and 20s. An excitation circuit 52 including a switching element (not shown) for applying a voltage at a predetermined cycle and a constant voltage source (not shown) connected to the two series circuits formed of a coil and an element are provided. is doing.

  Further, in this circuit, detection terminals 53 and 54 are provided from the connection portions of the coils 20r and 20r 'and the coils 20s and 20s' in order to detect voltage changes at both ends of the coils 20r' and 20s. Furthermore, the voltage changes detected from the two detection terminals 53 and 54 are inverted and rectified to rectify and output DC voltage, and the DC voltages output from the inverting rectifiers are amplified. Amplifying sections 65 and 66 are provided. In addition, this circuit includes a gain adjustment unit 67 including a CPU that outputs the output from each of the amplification units 65 and 66 by multiplying a set gain, and the difference between two DC voltages output from the gain adjustment unit 67. Is provided.

  Next, the operation of the torque sensor configured as described above will be described. The switching element (not shown) of the excitation circuit 52 is repeatedly turned on and off at a predetermined cycle and measured.

  When a switching element (not shown) is turned on / off, a current flows through a circuit including the resistors 20r 'and 20s' and the coils 20r and 20s, and the voltages at the terminals 53 and 54 change. At this time, the inductance of the coil is L (μ). A DC voltage is output from the inverting rectifiers 63 and 64. The output voltage shows different values depending on the difference in inductance L (μ). The inductance L (μ) depends on the magnetic permeability μ of the magnetostrictive film, and the magnetic permeability μ changes when the torque acts on the magnetostrictive film. Therefore, the steering torque can be detected by measuring this voltage. it can.

  The amplifying units 65 and 66 amplify those DC voltages and input them to the CPU. The gain adjustment unit 67 of the CPU multiplies the DC voltage input with a preset gain and outputs the result as VT1 and VT2. Further, VT3 obtained by calculating the difference between VT1 and VT2 is output by the calculation unit 68. By adjusting the gain adjusting unit 67 after the steering shaft 12b is assembled to the gear box 24, it is possible to detect torque while suppressing gain variation.

  FIG. 10 shows a gain setting device when the gain adjustment unit 67 sets the gain. FIG. 10 is a diagram when the gain setting device 70 is set up with the steering wheel 11 attached to the steering shaft 12b of the electric power steering device shown in FIG. The gain setting device 70 includes a steering torque measuring amplifier 71, a torque signal monitor 72, and a gain setting writing device 73. The steering torque measurement amplifier 71 measures the steering torque from the steering wheel 11 of the electric power steering apparatus, amplifies the measured value, and outputs it to the torque signal monitor 72. The torque signal monitor 72 monitors signals from the steering torque measurement amplifier 71 and signals VT1, VT2, and VT3 from the torque sensor 20. The gain setting writing device 73 adjusts the gain adjusting unit 67 based on the signal from the steering torque measuring amplifier 71 monitored by the torque signal monitor 72 and the signal from the torque sensor 20 to set the gain.

  The gain is set as follows. The torque signal monitor 72 records the output of the torque sensor 20 and the output from the steering torque measurement amplifier 71 using the gain setting device 70 shown in FIG. Next, the gain of the output (reference) of the steering torque measurement amplifier 71 and the output gain of the torque sensor 20 are compared, and a gain ratio is calculated to obtain a torque sensor gain adjustment value. Next, the torque sensor gain adjustment value is written into the CPU 67 of the detection circuit 20X using the gain setting writing device 73. The CPU 67 outputs a gain adjustment value signal, and the control device 22 performs control based on the gain adjustment value signal and the torque signal VT3.

  FIG. 11 is a graph showing the relationship of the torque detection voltage with respect to the torque before and after the gain adjustment unit 67 is adjusted and set by the gain setting device 70. 11A shows the relationship between the torque and the torque detection voltage before the gain is adjusted and set, and FIG. 11B shows the relationship between the torque and the torque detection voltage after the gain is adjusted and set. The gain setting writing device 73 causes the gain adjustment unit 67 of the CPU so that the relationship between the steering torque and the torque sensor signals VT1 and VT2 (straight line L80 and straight line L81) falls within the setting ranges R80 and R81 shown in FIG. Adjust and set the gain. FIG. 11B is a graph showing the relationship between torque and torque detection voltage after gain adjustment and setting. As shown in FIG. 11 (b), after the gain adjustment and setting, since it is bilaterally symmetrical, it is only necessary to look at the right torque. By adjusting and setting the gain in this way, the gain is set for each torque value even if the gain changes due to variations in applied torque when anisotropy is given to the magnetostrictive film. As shown in FIG. 11B, the relationship between the torque and the torque detection voltage can be obtained.

  As described above, in the manufacturing method according to the present invention, the variation is less than when adjusting the torque sensor alone. Even if the torque sensor alone is perfectly adjusted, an error factor (for example, a left / right difference due to gear meshing) due to gear engagement occurs when it is actually mounted on a vehicle. Therefore, by adjusting the gain in such a manner that it is mounted on the gear box, it is possible to adjust with high accuracy including these. As a result, a magnetostrictive torque sensor having good detection accuracy can be obtained.

FIG. 12 is a schematic view of an electric power steering apparatus according to the second embodiment of the present invention.
The electric power steering device 110 includes a steering system 120 that extends from a steering handle 121 of the vehicle to steering wheels (for example, front wheels) 131 and 131 of the vehicle, and an auxiliary torque mechanism 140 that applies auxiliary torque to the steering system 120.

In the steering system 120, a torque transmission shaft 124 is connected to a steering handle 121 (steering member) via a steering shaft 122 and universal shaft joints 123 and 123, and a rack shaft 126 is connected to the torque transmission shaft 124 via a rack and pinion 125. The left and right steering wheels 131 and 131 are connected to both ends of the rack shaft 126 via ball joints 127 and 127, tie rods 128 and 128, and knuckles 129 and 129.
The rack and pinion 125 includes a pinion 132 provided on the torque transmission shaft 124 and a rack 133 formed on the rack shaft 126.

  When the driver steers the steering handle 121, the left and right steering wheels 131, 131 can be steered by the steering torque via the rack and pinion 125, the rack shaft 126, and the left and right tie rods 128, 128.

  As described above, the electric power steering apparatus 110 transmits the steering torque according to the steering of the steering handle 121 to the rack shaft 126 via the rack and pinion 125, thereby steering wheels 131 and 131 via the rack shaft 126. Is to steer.

  The auxiliary torque mechanism 140 detects the steering torque of the steering system 120 applied to the steering handle 121 by the magnetostrictive torque sensor 141, generates a control signal by the control unit 142 based on the torque detection signal, and steers based on the control signal. In this mechanism, an auxiliary torque (motor torque) corresponding to the torque is generated by the electric motor 143 and the auxiliary torque is transmitted to the rack shaft 126 via the ball screw 144.

  The motor shaft 143 a of the electric motor 143 is a hollow shaft that surrounds the rack shaft 126. The ball screw 144 is a power transmission mechanism including a screw portion 145 formed on a portion of the rack shaft 126 excluding the rack 133, a nut 146 assembled to the screw portion 145, and a number of balls (not shown). The nut 146 connects the motor shaft 143a.

  According to the electric power steering apparatus 110, the steering torque transmitted to the torque transmission shaft 124 is detected by the magnetostrictive torque sensor 141, and the steering torque for steering the steering handle 121 is transmitted via the torque transmission shaft 124 and the rack and pinion 125. Can be transmitted to the rack shaft 126. The steering wheels 131 and 131 can be steered by the rack shaft 126 by a combined torque obtained by adding the auxiliary torque of the electric motor 143 to the steering torque of the driver.

FIG. 13 is an overall configuration diagram of an electric power steering apparatus according to the second embodiment of the present invention, and shows a left end portion and a right end portion in cross section. 14 is a cross-sectional view taken along line 3-3 of FIG.
As shown in FIGS. 13 and 14, the electric power steering apparatus 110 includes a torque transmission shaft 124, a rack and pinion 125, an electric motor 143, a ball screw 144, and a magnetostrictive torque sensor 141 in the vehicle width direction (left and right in FIG. 13). In the housing 151 extending in the direction).

The housing 151 is assembled into one elongated gear box by bolting one end surfaces of the generally tubular first housing 152 and second housing 153 together. The second housing 153 also serves as a motor case in the electric motor 143.
The first housing 152 is configured such that the upper opening is closed with a lid 154, and the upper end portion, the longitudinal center portion, and the lower end portion of the torque transmission shaft 124 are rotatably supported via the upper, middle, and lower three bearings 155 to 157. , Which is set vertically, and includes a rack guide 158.

  The rack guide 158 regulates the movement of the rack shaft 126 in the longitudinal direction of the torque transmission shaft 124 and also regulates the movement of the rack shaft 126 in the direction in which the pinion 132 and the rack 133 are disengaged from each other. Can be slidably supported in the axial direction.

Next, details of the torque transmission shaft 124 will be described with reference to FIGS. 14 and 15.
15A to 15D are configuration diagrams of a torque transmission shaft according to the present invention, FIG. 15A shows an exploded structure of the torque transmission shaft 124, and FIG. 15B is a cross-sectional view of the assembled state of the torque transmission shaft 124. The structure is shown, (c) shows the cross-sectional structure taken along the line cc of (b), and (d) shows the appearance of the assembled state of the torque transmission shaft 124.

  As shown in FIG. 15, the torque transmission shaft 124 includes a torque side shaft 161 and a pinion shaft 162 arranged coaxially with each other, and the torque side shaft 161 and the pinion shaft 162 are fitted and connected to each other. It is characterized by comprising a separate member.

  The torque side shaft 161 and the pinion shaft 162 are made of a ferromagnetic material such as steel (including nickel chrome molybdenum steel), that is, a magnetic material.

  The torque side shaft 161 has a substantially hexagonal flange portion 161a at one end and a cylindrical shaft having a fitting hole 165 (that is, a hollow portion 165), that is, a hollow shaft, in a direction perpendicular to the shaft. Two pin holes 166 and 166 passing through the fitting hole 165 are provided. As shown in FIG. 15C, the fitting hole 165 is a through-hole having a polygonal cross section such as a regular hexagon formed at the center of the torque side shaft 161 having a circular cross section. The two pin holes 166 and 166 are respectively arranged in the vicinity of both end portions of the torque side shaft 161.

  The pinion shaft 162 (that is, the action shaft 162) includes a supported portion 162c, a pinion 132, a jig hook portion 162b, a flange portion 162a, a supported portion 169, and a fitting shaft portion 163 from one end to the other end. These are solid shafts arranged in this order and integrally formed. These members 132, 162 a, 162 b, 162 c, 163, 169 are arranged coaxially with respect to the pinion shaft 162. As shown in FIG. 14, the supported portion 162 c at the lower end is a portion that is supported by a lowermost bearing 157, and the supported portion 169 is a portion that is supported by a bearing 156 at the intermediate portion.

  More specifically, the pinion shaft 162 includes a pinion 132 formed at one end, an elongated fitting shaft portion 163 having a small diameter extending from the other end surface toward the fitting hole 165, and the pinion 132 and the fitting shaft portion 163. A supported part 169 formed on the outer peripheral surface between the base end and a substantially circular flange part 162a and a jig hook part 162b formed between the pinion 132 and the supported part 169 are provided. . The jig hanging portion 162b is a portion for hanging a jig to be described later.

  The fitting shaft portion 163 is a portion longer than the entire length of the torque side shaft 161, penetrates the fitting hole 165, and has a universal shaft joint 123 (see FIG. 1) at a tip portion protruding from the fitting hole 165. There is a connecting portion 168 for connecting to. The connection part 168 consists of serrations, for example.

  Further, the fitting shaft portion 163 includes two fitting flange portions 163a and 163a formed in the vicinity of both end portions in the longitudinal direction, and a jig hook formed between the fitting flange portion 163a and the connecting portion 168. Part 163b. The jig hanging portion 163b is a portion for hanging a jig to be described later.

  The fitting flanges 163a and 163a are ring-shaped members having the same cross-sectional shape as the fitting hole 165 as shown in FIG. 15 (c), and project so as to surround the outer periphery of the fitting shaft portion 163. In addition, there are pin holes 164 and 164 penetrating in a direction perpendicular to the axis. The positions of the pin holes 164 and 164 in the fitting flange portions 163a and 163a are set to positions that match the pin holes 166 and 166 in the torque side shaft 161, respectively. The diameter of the fitting hole 165 is set smaller than the diameter of the supported portion 169.

The assembly procedure of the torque transmission shaft 124 is as follows.
First, a pilot hole having a slightly smaller diameter than those of the pin holes 166 and 166 is formed at the position of the pin holes 166 and 166 on the torque side shaft 161. At this time, the pinion shaft 162 does not have the pin holes 164 and 164 or the pilot holes.

Next, in a disassembled state of the torque transmission shaft 124, the bearing 156 (see FIG. 14) is fitted to the supported portion 169 of the pinion shaft 162, and the inner race of the bearing 156 is applied to the end surface of the flange portion 162a. Thus, the bearing 156 can be attached to the pinion shaft 162 by fitting.
Next, the fitting shaft portion 163 is press-fitted and fitted into the fitting hole 165, and the bearing 156 is sandwiched between the two flange portions 161a and 162a.

Next, upper pin holes 164 and 166 and lower pin holes 164 and 166 penetrating with the fitting shaft portion 163 are opened at the position of the lower hole of the torque side shaft 161.
Next, the pins 167 and 167 are press-fitted into the pin holes 164, 164, 166 and 166, respectively. As a result, as shown in FIGS. 15B and 15C, the torque side shaft 161 and the pinion shaft 162 are integrally connected to each other by the pins 167 and 167 and assembled into one torque transmission shaft 124. be able to. Thus, the assembly work of the torque transmission shaft 124 is completed.

The torque side shaft 161 and the pinion shaft 162 regulate relative rotation and axial movement.
As is clear from the above description, the torque side shaft 161 is a hollow shaft, and the pinion shaft 162 is a solid shaft that is fitted to the hollow shaft. The pinion shaft 162 is preferably a hollow shaft rather than a solid shaft for weight reduction.

  In addition, the cross-sectional shape of the fitting hole 165 and the fitting collar parts 163a and 163a is not limited to a polygonal cross section, and may be a circular cross section. A circular cross section is easier to manufacture, easier to manage the fitting accuracy, and easier to fit.

  The steering torque transmitted from the steering handle 121 (see FIG. 12) to the pinion shaft 162 via the connecting portion 168 is also transmitted from the pinion shaft 162 to the torque side shaft 161 via the pins 167 and 167.

Next, details of the magnetostrictive torque sensor 141 will be described with reference to FIGS.
As shown in FIG. 3, the magnetostrictive torque sensor 141 is provided with magnetostrictive films 171 and 172 made of plated layers whose magnetostrictive characteristics change according to the torque on the surface of the torque transmission shaft 124 on which torque acts from the outside. Around the magnetostrictive films 171 and 172, a detection unit 173 that electrically detects the magnetostrictive effect generated in the magnetostrictive films 171 and 172 is provided.

  More specifically, the torque side shaft 161 has a substantially constant distance di (that is, a predetermined distance di) in the longitudinal direction of the shaft and is formed at two locations on the outer peripheral surface over the entire circumference. Magnetostrictive films 171 and 172 are provided. The directions of magnetostriction in the magnetostrictive films 171 and 172 are opposite to each other. As a matter of course, the torque side shaft 161 has a non-magnetostrictive portion 179 between the first magnetostrictive film 171 and the second magnetostrictive film 172 where no magnetostrictive film exists. The two magnetostrictive films 171 and 172 may be one continuous magnetostrictive film.

  The magnetostrictive films 171 and 172 are films made of a material having a large change in magnetic flux density with respect to a change in strain. For example, a Ni—Fe alloy film formed on the outer peripheral surface of the torque side shaft 161 by vapor phase plating. It is. The thickness of this alloy film is desirably about 5 to 20 μm. The thickness of the alloy film may be less than or greater than this. The magnetostriction direction of the second magnetostrictive film 172 is different from the magnetostriction direction of the first magnetostrictive film 171 (has magnetostriction anisotropy).

  Ni-Fe-based alloy films tend to increase the magnetostriction effect when the Ni content is approximately 20% by weight and approximately 50% by weight, so that the magnetostriction effect tends to increase. Is preferably used. For example, as the Ni—Fe-based alloy film, a material containing 50 to 60% by weight of Ni and the rest being Fe is used. The magnetostrictive films 71 and 72 may be ferromagnetic films, such as permalloy (Ni; about 78% by weight, Fe; remaining) or supermalloy (Ni; 78% by weight, Mo; 5% by weight, Fe; remaining). ). Here, Ni is nickel, Fe is iron, and Mo is molybdenum.

As shown in FIG. 14, the detection unit 173 includes cylindrical coil bobbins 174 and 175 that pass through the torque side shaft 161, a first multilayer solenoid coil 176 and a second multilayer solenoid coil 177 wound around the coil bobbins 174 and 175. And a magnetic shielding back yoke 178 surrounding the first and second multilayer solenoid winding coils 176 and 177.
The first and second multilayer solenoid coils 176 and 177 are detection coils. Hereinafter, the first multilayer solenoid coil 176 will be referred to as the first detection coil 176, and the second multilayer solenoid coil 177 will be referred to as the second detection coil 177.

  Torsion generated in the torque side shaft 161 in accordance with the steering torque can be magnetically detected by the first and second detection coils 176 and 177.

  The above description is summarized as follows. The torque side shaft 61 is appropriately referred to as “hollow shaft 61”, and the pinion shaft 62 is appropriately referred to as “solid shaft 62”, “action shaft 62”, or “rotating shaft 62”.

  Next, a manufacturing method of the magnetostrictive torque sensor 41, particularly, a manufacturing method of the torque transmission shaft 124 and the magnetostrictive films 171 and 172 having the above-described configuration will be described.

  The torque transmission shaft 124 and the magnetostrictive films 171 and 172 are manufactured by the steps shown in FIG. 15 and the next FIG. FIGS. 16A to 16E are explanatory views showing a first method for manufacturing a torque transmission shaft and a magnetostrictive film according to the present invention. However, the bearing 156 (see FIG. 14) is omitted in FIG.

First, as shown in FIG. 15A, a hollow shaft 161 having magnetostrictive films 171 and 172 provided on the outer peripheral surface, which is a torque transmission shaft 124, and a solid shaft 162 fitted to the hollow shaft 161, One member is prepared (shaft preparation process).
Next, as shown in FIGS. 15B to 15C, the solid shaft 162 is press-fitted into the hollow shaft 161 and connected to each other with pins 167 and 167 (shaft connecting step). As a result, the torque transmission shaft 124 shown in FIG. 15D can be manufactured.

  Next, as shown in FIG. 16, the magnetostrictive films 171 and 172 are set for a preset time, for example, in a state where a predetermined constant torque is applied to at least one of the hollow shaft 161 and the solid shaft 162. Heat treatment is performed for 3 seconds or more (external force application step and heating step).

Specifically, first, as shown in FIG. 16A, a jig hooking portion 162b (or a jig hooking portion 162b) having the first jig 201 at one end portion of the solid shaft 162. And the flange portion 162a).
Further, the second jig 202 is hung on both the jig hooking part 163b (or the jig hooking part 163b and the connecting part 168 (serration 68)) provided at the other end of the solid shaft 162.

  Next, as shown in FIG. 16B, a heating device, for example, an induction hardening device 203 is set on the first magnetostrictive film 171. The induction hardening apparatus 203 includes a heating coil 204 that surrounds the first magnetostrictive film 171 and a power supply apparatus 205 that supplies high-frequency AC power to the heating coil 204.

Next, the second jig 202 is twisted in the clockwise direction R1 and the first jig 201 is twisted in the counterclockwise direction R2 opposite to the second jig 202. In this way, a preset positive torque is applied to the solid shaft 162. The magnitude of this torque is preferably about 30 to 100 Nm. A torque larger than this may be used.
Since the hollow shaft 161 is configured such that its rotation relative to the solid shaft 162 is restricted, a preset positive torque can be applied to the hollow shaft 161 (external force applying step). As a result, a positive torque is also applied to the first magnetostrictive film 171.

Next, as shown in FIG. 16 (b), the first magnetostrictive film 171 (particularly the surface and the surface layer portion) was preset while applying torque by the first and second jigs 201 and 202. It heats with the induction hardening apparatus 203 over time (heating process). The heating time is preferably about 3 to 5 seconds. It may be longer than this. The heating temperature is preferably about 400 ° C.
Next, as shown in FIG. 16C, after the first magnetostrictive film 171 is cooled to a temperature lower than the heated temperature, the twisting work of the first and second jigs 201 and 202 is performed. Stop and remove torque (external force release process).
In the heating step, when the heating time of the first magnetostrictive film 171 by induction hardening is set to about 3 to 5 seconds, the first magnetostrictive film 171 can be sufficiently cooled only by the outside temperature. Since the heating temperature of the first magnetostrictive film 171 is about 400 ° C., the first magnetostrictive film 171 may be cooled to a temperature lower than that.

Next, as shown in FIG. 16D, the induction hardening device 203 is set on the second magnetostrictive film 172.
Next, contrary to the previous time, the second jig 202 is twisted counterclockwise R2 in the figure, and the first jig 201 is twisted counterclockwise in the figure R1 opposite to the second jig 202. In this way, a preset negative torque is applied to the solid shaft 162. The magnitude of this torque is preferably about 30 to 100 Nm. A torque larger than this may be used.
Since the hollow shaft 161 is configured such that its rotation relative to the solid shaft 162 is restricted, a preset negative torque can also be applied to the hollow shaft 161 (external force applying step). As a result, negative torque is also applied to the second magnetostrictive film 172.

Next, as shown in FIG. 16 (d), the second magnetostrictive film 172 (especially the surface and the surface layer portion) was preset while applying torque by the first and second jigs 201 and 202. It heats with the induction hardening apparatus 203 over time (heating process). The heating time is preferably about 3 to 5 seconds. It may be longer than this. The heating temperature is preferably about 400 ° C.
Next, as shown in FIG. 16E, after the second magnetostrictive film 172 is cooled to a temperature lower than the heated temperature, the twisting work of the first and second jigs 201 and 202 is performed. Stop and remove torque (external force release process).
In the heating step, when the heating time of the second magnetostrictive film 172 by induction hardening is set to about 3 to 5 seconds, the second magnetostrictive film 172 can be sufficiently cooled only by the outside temperature. Since the heating temperature of the second magnetostrictive film 172 is about 400 ° C., the second magnetostrictive film 172 may be cooled to a temperature lower than that.
As a result, the direction of magnetostriction in the first and second magnetostrictive films 171 and 172 can be accurately and easily tilted in the direction in which torque is applied.

  Thus, according to this manufacturing method, first, the solid shaft 162 (action shaft 162) is press-fitted into the hollow shaft 161 provided with the magnetostrictive films 171 and 172 on the outer peripheral surface thereof, thereby being connected to each other. The torque transmission shaft 124 is manufactured. The magnetostrictive films 171 and 172 affected by the press-fitting and connection are distorted, and the distortion remains as it is.

  On the other hand, in this manufacturing method, the magnetostrictive films 171 and 172 are then applied over a preset time in a state where a preset torque is applied to at least one of the solid shaft 162 and the hollow shaft 161. Heat treatment (heat treatment) is performed. After the heat treatment is completed, the magnetostrictive films 171 and 172 are cooled to a temperature lower than the heated temperature, and the torque applied to at least one of the solid shaft 162 and the hollow shaft 161 is removed.

  Thus, creep can be generated in the magnetostrictive films 171 and 172 by performing heat treatment for a predetermined time in a state where torque is applied to the magnetostrictive films 171 and 172. Creep is a phenomenon in which when a material is heated at a constant temperature under a constant load (including torque), the strain of the material increases with time.

  That is, it is possible to reduce or eliminate strain remaining in the magnetostrictive films 171 and 172 by skillfully utilizing creep generated by performing heat treatment on the magnetostrictive films 171 and 172. In addition, by applying heat treatment to the magnetostrictive films 171 and 172 while applying torque, permanent deformation can be newly applied to the magnetostrictive films 171 and 172 by using creep. As a result, the direction of magnetostriction in the magnetostrictive films 171 and 172 can be accurately and easily tilted in the direction in which torque is applied. That is, the magnetostriction anisotropy between the first magnetostrictive film 171 and the second magnetostrictive film 172 can be set.

  Next, after the reheating treatment, a multi-turn coil is disposed at a position corresponding to the magnetostrictive films 171 and 172, and a detection circuit similar to the detection circuit shown in FIG. 9 of the first embodiment is connected. The torque transmission shaft 124 is assembled to the gear box. The gain is adjusted by a gain adjusting unit provided in the detection circuit. This gain adjustment is performed in the same manner as in the first embodiment using the gain setting device shown in FIG. 10 described in the first embodiment.

  In the embodiment of the present invention, the connection structure between the hollow shaft 161 and the solid shaft 162 is not limited to the connection by the pin 67, but may be the connection by press fitting or the connection by screws. .

  The configurations, shapes, sizes, and arrangement relationships described in the above embodiments are merely shown to the extent that the present invention can be understood and implemented, and the numerical values and the compositions (materials) of the respective configurations are as follows. It is only an example. Therefore, the present invention is not limited to the described embodiments, and can be variously modified without departing from the scope of the technical idea shown in the claims.

  The present invention is used as a method for manufacturing a magnetostrictive torque sensor for detecting a steering torque of an electric power steering apparatus. It is also used as an electric power steering device used for automobiles and the like.

1 is an overall configuration diagram of an electric power steering apparatus according to a first embodiment of the present invention. The principal part of the mechanical mechanism of an electric power steering apparatus and the concrete structure of an electric system are shown. It is the sectional view on the AA line in FIG. It is a flowchart which shows the manufacturing method of a magnetostrictive torque sensor. It is the figure which showed the application of the torsion torque Tq and the temperature change from the torsion torque provision process to the torsion torque removal process. It is a figure which shows a heat processing process. It is a figure which shows the process of heat-processing again. It is a figure which shows the process of arrange | positioning a multiple winding coil, connecting a detection circuit, and the process assembled | attached to a gear box. It is a figure which shows the circuit structure of a detection circuit. It is a figure which shows the setup of a gain setting apparatus. 6 is a graph showing a relationship of torque detection voltage with respect to torque before and after the gain adjustment unit 67 is adjusted and set by the gain setting device 70; It is a schematic diagram of the electric power steering apparatus which concerns on the 2nd Embodiment of this invention. It is a whole block diagram of the electric power steering device which concerns on the 2nd Embodiment of this invention. FIG. 14 is a sectional view taken along line 3-3 in FIG. 13. It is a block diagram of the torque transmission shaft which concerns on the 2nd Embodiment of this invention. It is explanatory drawing which shows the 1st manufacturing method of the torque transmission shaft and magnetostrictive film which concern on the 2nd Embodiment of this invention. It is a schematic diagram of a magnetostrictive torque sensor. It is a figure which shows a magnetostriction characteristic. It is a flowchart which shows the manufacturing method of the conventional magnetostrictive torque sensor. It is a graph which shows the change of the gain to the applied torque when giving anisotropy. It is a graph which shows the change of the gain to heating temperature when giving anisotropy.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 11 Steering wheel 12a, 12b Steering shaft 19 Motor 20 Steering torque detection part 20u Magnetostrictive film 20d Magnetostrictive film 20r Coil 20s Coil 20x Detection circuit 22 Control apparatus 24 Gear box 67 Gain adjustment part 70 Gain setting apparatus

Claims (4)

Providing a magnetostrictive portion provided with magnetic anisotropy on the rotation axis;
Arranging two multiple winding coils for detecting a change in magnetostriction characteristics around the magnetostrictive portion;
There are at least two output voltages from each of the two multi-turn coils , and at least two setting ranges in which the voltage width increases in accordance with an increase in the absolute value of the torque corresponding to each of the at least two output voltages. Have
Each of the at least two output voltages is stored in a corresponding setting range of the at least two setting ranges even if it changes in response to the increase in the absolute value of the torque . A gain adjustment step for adjusting the gain in the CPU ;
A method of manufacturing a magnetostrictive torque sensor, comprising: Each of the two multi- turn coils is configured by connecting a coil element used as a resistor in series to a connection portion of the coil,
In the gain adjustment step, the output voltage from each of the two multi-turn coils is an output voltage from each of the connecting portions of the two multi-turn coils, and the at least two output voltages in the CPU The method according to claim 1 , wherein the gain is adjusted by a gain setting device . 3. The method of manufacturing a magnetostrictive torque sensor according to claim 2, wherein each of the two coils and the two coil elements corresponding to the two multi- turn coils has the same coil characteristics .   The method of manufacturing a magnetostrictive torque sensor according to claim 1, wherein the gain adjusting step is performed after the rotating shaft is assembled to a gear box of an electric power steering apparatus.

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