JP4865685B2 - Magnetostrictive torque sensor and electric steering device - Google Patents

Description

  The present invention relates to a magnetostrictive torque sensor that detects torque based on a change in magnetic characteristics caused by magnetostriction, and an electric steering device including the magnetostrictive torque sensor.

  2. Description of the Related Art Conventionally, a so-called torsion bar type torque sensor is known as a torque sensor for detecting rotational torque acting on a shaft of a vehicle steering device or the like. In the case of this torsion bar type torque sensor, since a part of the shaft is narrowed and formed as a torsion bar, there is a risk of damage if an excessive torque is applied thereto. Therefore, in the torsion bar type torque sensor, a torsion bar is twisted more than necessary to prevent mechanically by providing a regulating member such as a pin.

By the way, in addition to the torsion bar type torque sensor, as a torque sensor for detecting torque in the rotational direction acting on the shaft, magnetostriction for detecting torque based on a change in magnetic characteristics caused by magnetostriction of a magnetostrictive element attached to the shaft. A torque sensor of the type is known (for example, see Patent Document 1).
In this type of magnetostrictive torque sensor, two magnetostrictive films having magnetic anisotropy with different directions of easy magnetization are provided on the rotating shaft, and the change in the permeability of the magnetostrictive film is detected by each of the detection coils. There is something to detect by. In the case of this magnetostrictive torque sensor, it is not necessary to form a constriction in a part of the shaft, so that sufficient strength can be obtained compared to a torsion bar type torque sensor, and as a result, there is a risk of damage due to excessive torque input. And the restriction member can be omitted.

By the way, when using the above-mentioned magnetostrictive torque sensor, it is configured to detect a failure and determine whether or not the torque sensor is operating normally at the same time as detecting the torque.
In the case of a magnetostrictive torque sensor having two magnetostrictive films, when detecting torque, a detection signal of one detection coil (hereinafter referred to as a first detection signal) and a detection signal of the other detection coil (hereinafter referred to as a first detection signal). The torque detection signal VT3 is calculated on the basis of the difference between the detection signal 2 and the detection signal 2). Further, when performing failure determination, a failure detection signal VTF is calculated based on the sum of the first detection signal and the second detection signal, and failure determination is performed based on the failure detection signal VTF. Specifically, since the first detection signal and the second detection signal are in an opposite phase relationship, the failure detection signal VTF, which has a constant value during normal operation, fluctuates for some reason and deviates from the predetermined range. It is determined that there is a fault condition. FIG. 7 shows the output characteristics when the torque detection signal VT3 is calculated based on the equation (1) and the output characteristics when the failure detection signal VTF is calculated. In equations (1) and (2), k, V0, and C are constants.
VT3 = k · (VT1-VT2) + V0 (1) Formula VTF = | VT1 + VT2 | −C (2)
JP 2006-064445 A

  However, in the above-described magnetostrictive torque sensor, the output characteristics of the two magnetostrictive films may not be symmetrical due to, for example, variations in the midpoint due to temperature drift or the like. For example, from the torque indicated by the broken line in FIG. If an excessive torque is input as in the case of the outer torque, the output of one of the two magnetostrictive films reaches the upper limit value or lower limit value of the power supply voltage first, and is constant at the upper limit value or lower limit value. There is a risk that the failure detection signal VTF may increase or decrease to make a failure determination even though it is not a failure. In the case of the graph shown in FIG. 7, an example is shown in which VT1 and VT2 first reach the lower limit value, and the failure detection signal VTF increases. When VT1 and VT2 reach the upper limit first, the failure detection signal VTF decreases.

  Therefore, the present invention provides a magnetostrictive torque sensor and an electric steering device that can improve the reliability of failure detection.

In order to solve the above-mentioned problem, the invention described in claim 1 is provided on a shaft (for example, the pinion shaft 5 in the embodiment), and has a magnetic anisotropy having different directions of easy magnetization. A first magnetostrictive film (for example, the first magnetostrictive film 31 in the embodiment) and a second magnetostrictive film (for example, the second magnetostrictive film 32 in the embodiment), and a first detection for detecting a change in magnetic characteristics of the first magnetostrictive film. Means (for example, the first detection coil 33 in the embodiment) and second detection means (for example, the second detection coil 34 in the embodiment) for detecting a change in the magnetic characteristics of the second magnetostrictive film, A magnetostrictive torque sensor for detecting torque input to the shaft based on detection results of the first detection means and the second detection means, wherein the detection signal of the first detection means and the detection of the second detection means Trust A failure detection means (for example, the electronic control unit 50 in the embodiment) that performs failure detection based on the above, a detection signal of the first detection means, and a detection signal of the second detection means are respectively set to predetermined upper limit values. Or a detection signal limiting means for limiting to a lower limit value (for example, steps S2, S6, S4, S8 or limiting circuit 62 in the embodiment), and the detection signal limiting means is a non-linear element (for example, a Zener diode 63 in the embodiment). ) comprising non-linear element, characterized that you limit the potential difference between the detection signal of the detection signal and the second detection means of the first detecting means within a predetermined range.

According to a second aspect of the present invention, in the first aspect of the invention, the detection signal limiting unit sets the upper limit value between a maximum voltage of the detection signal and a midpoint voltage of the detection signal. , and sets the lower limit value between the minimum voltage and the midpoint voltage of said detection signal.

According to the third aspect of the present invention, the steering torque is detected by a magnetostrictive torque sensor (for example, the magnetostrictive torque sensors 30 and 60 in the embodiment), and an electric motor (for example, the electric motor 11 in the embodiment is detected) according to the detected steering torque. 3), the magnetostrictive torque sensor is the magnetostrictive torque sensor according to claim 1 or 2 .

  According to the first aspect of the present invention, the detection signals of the first detection means and the second detection means for detecting the magnetic changes of the first magnetostrictive film and the second magnetostrictive film, which have different directions of easy magnetization, are detected. By limiting the upper limit value and the lower limit value by the detection signal limiting means, for example, even when an excessive torque is input, the sum of the detection signal of the first detection means and the detection signal of the second detection means is constant. Therefore, it is possible to prevent the erroneous detection by the failure detecting means and improve the reliability of the failure detection.

Furthermore, the potential difference between the detection signal of the first detection means and the detection signal of the second detection means is limited to a potential difference lower than the power supply voltage by the non-linear element, so that the detection signal of the first detection means It is possible to set an upper limit value and a lower limit value that limit the detection signal based on the detection signal of the two detection means. In addition, since the sum of the detection signal of the limited first detection means and the detection signal of the second detection means is always constant, it can be prevented from being erroneously detected as a failure due to excessive torque input. There is an effect that the reliability of failure detection can be improved.
According to the invention described in claim 2, in addition to the effect of claim 1, the upper limit value is set between the maximum voltage and the midpoint voltage of the detection signal, and the lower limit value is set to the minimum voltage and the midpoint of the detection signal. By setting it between the voltages, the detection signal can be actively limited before reaching the maximum voltage or the minimum voltage. Accordingly, it is possible to prevent erroneous detection due to excessive torque while using a single power supply circuit having a simple power supply circuit configuration, and therefore, it is possible to improve the reliability of failure detection with a small number of parts.

According to the invention described in claim 3, the magnetostrictive torque sensor for detecting steering torque of the electric dynamic steering system, despite normal, erroneously detected as a failure at the input of the excessive torque Therefore, the reliability of the electric steering device is improved.

Next, a reference example of a magnetostrictive torque sensor according to the present invention and an electric power steering apparatus for a vehicle including the same will be described with reference to the drawings.
As shown in FIG. 1, a vehicle electric power steering device (electric steering device) 100 includes a steering shaft 1 connected to a handle (steering means) 2. The steering shaft 1 is constituted by connecting a main steering shaft 3 integrally coupled to a handle 2 and a pinion shaft 5 provided with a pinion 7 of a rack and pinion mechanism by a universal joint 4.

  The lower part, the middle part, and the upper part of the pinion shaft 5 are supported by bearings 6 a, 6 b and 6 c, and the pinion 7 is provided at the lower end part of the pinion shaft 5. The pinion 7 meshes with the rack teeth 8a of the rack shaft 8 that can reciprocate in the vehicle width direction, and left and right front wheels 10, 10 as steered wheels are connected to both ends of the rack shaft 8 via tie rods 9, 9. Has been. With this configuration, a normal rack and pinion type steering operation can be performed when the steering wheel 2 is steered, and the front wheels 10 and 10 can be steered to change the direction of the vehicle. Here, the rack shaft 8, the rack 8a, and the tie rod 9 constitute a steering mechanism.

  The electric power steering apparatus 100 includes an electric motor 11 that supplies an auxiliary steering force for reducing the steering force by the handle 2, and a worm gear 12 provided on the output shaft of the electric motor 11 is connected to the pinion shaft 5. It meshes with a worm wheel gear 13 provided below the intermediate bearing 6b. In the pinion shaft 5, a magnetostrictive torque sensor 30 that detects torque based on a change in magnetic characteristics caused by magnetostriction is disposed between the intermediate bearing 6b and the upper bearing 6c.

  As shown in FIGS. 1 and 2, the magnetostrictive torque sensor 30 includes a first magnetostrictive film 31 and a second magnetostrictive film 32 that are annularly provided on the outer peripheral surface of the pinion shaft 5 over the entire circumference in the circumferential direction. The first magnetostrictive film 31 and the second magnetostrictive film 32 are arranged side by side along the axial direction of the pinion shaft 5. The first magnetostrictive film 31 and the second magnetostrictive film 32 are metal films made of a material having a large change in permeability with respect to strain, and are Ni—Fe alloy films formed by plating or the like on the outer periphery of the pinion shaft 5. Consists of.

  The first magnetostrictive film 31 is a magnetostrictive film having magnetic anisotropy, and its easy magnetization direction is set in a direction inclined about 45 degrees with respect to the axis of the pinion shaft 5. The second magnetostrictive film 32 also has magnetic anisotropy like the first magnetostrictive film 31, and its easy magnetization direction is set to a direction of 90 degrees with respect to the easy magnetization direction of the first magnetostrictive film 31. ing.

  The first magnetostrictive film 31 and the second magnetostrictive film 32 have their permeability greatly increased or decreased according to the compressive force and the tensile force when a compressive force and a tensile force are applied along the respective easy magnetization directions. When a torque of right or left rotation acts on the pinion shaft 5, a compressive force along the direction of easy magnetization acts on either the first magnetostrictive film 31 or the second magnetostrictive film 32, and the first magnetostrictive film 31. And the second magnetostrictive film 32 are subjected to a tensile force along the direction of easy magnetization. As a result, the magnetic permeability of one of the first magnetostrictive film 31 and the second magnetostrictive film 32 increases, and the magnetic permeability of the other of the first magnetostrictive film 31 and the second magnetostrictive film 32 decreases.

The first magnetostrictive film 31 is opposed to the first detection coil 33 with a predetermined gap, while the second magnetostrictive film 32 has the second detection coil 34 with a predetermined gap. Opposed.
The first detection coil 33 and the second detection coil 34 detect changes in the magnetic permeability of the first magnetostrictive film 31 and the second magnetostrictive film 32 described above. When the magnetic permeability of the first magnetostrictive film 31 changes, When the inductance of the first detection coil 33 increases or decreases and the magnetic permeability of the second magnetostrictive film 32 changes, the inductance of the second detection coil 34 increases or decreases.

The first detection coil 33 and the second detection coil 34 are each connected to a detection circuit 35.
The detection circuit 35 is supplied with power from an in-vehicle battery (not shown). A predetermined current flows through the first detection coil 33 and the second detection coil 34, and the inductance changes are in opposite phases to the torque input. Conversion circuits 38 and 39 for converting the power supply voltage (for example, 5V) into voltage signals VT1 and VT2 having the maximum value for the power supply voltage (for example, 0V) and the minimum value for the power supply reference voltage (for example, 0V) are provided. Are output to the electronic control unit 50 respectively. For convenience of illustration, in FIG. 2, a circuit for supplying a predetermined current to the first detection coil 33 and the second detection coil 34 is omitted.

  Further, the detection circuit 35 includes a differential amplifier circuit 40 that amplifies the difference between the voltage signals VT1 and VT2, and the electronic control device 50 outputs a torque detection signal VT3 that is a differential amplification signal output from the differential amplifier circuit 40. Output to. The torque detection signal VT3 is also a voltage signal that maximizes the power supply voltage, similar to the voltage signals VT1 and VT2 described above.

  The electronic control unit 50 (see FIG. 1) determines the auxiliary steering force generated by the electric motor 11 based on the torque detection signal VT3 output from the detection circuit 35, and drives the electric motor 11 based on the determined auxiliary steering force. It is something to control. Further, the electronic control device 50 is configured to detect a failure of the magnetostrictive torque sensor 30 based on the voltage signals VT1 and VT2 output from the detection circuit 35.

Specifically, the failure detection by the electronic control unit 50 is determined based on the failure detection signal VTF by calculating the failure detection signal VTF by the following equation (3) that is the same as the conventional equation (2). . In the equation (3), C is a constant.
VTF = | VT1 + VT2 | −C (3)

  Here, since the voltage signal VT1 and the voltage signal VT2 are out of phase with each other with respect to the torque input in one direction, adding the voltage signal VT1 and the voltage signal VT2 usually produces a signal output with a constant voltage. Will be obtained. In the electronic control unit 50, the normal range of the failure detection signal VTF is set in advance with both threshold values of an upper limit value and a lower limit value (not shown), and the failure detection signal VTF is out of the predetermined time. A failure is detected. That is, when one of the voltage signals VT1 and VT2 stops outputting or fluctuates significantly, it is determined that there is a failure state.

Further, in the electronic control unit 50, when the absolute value of the input torque exceeds a predetermined torque threshold, a limiting process is performed to limit the voltage signal VT1 and the voltage signal VT2 to a constant value. Is set.
Hereinafter, the restriction process by the electronic control unit 50 will be described with reference to the flowchart of FIG.

First, in step S1, it is determined whether or not the voltage signal VT1 is larger than a voltage value obtained by adding a predetermined limit value V0 to the midpoint voltage VT10 of the voltage signal VT1. If the determination result in step S1 is “Yes” (VT1> VT10 + V0), the process proceeds to step S2, and if “No” (VT1 ≦ VT10 + V0), the process proceeds to step S5.
In step S2, the voltage signal VT1 is limited to a voltage value (VT = VT10 + V0) obtained by adding the limit value V0 to the midpoint voltage VT10, and the process proceeds to step S3. Here, the midpoint voltage VT10 indicates the voltage value of the voltage signal VT1 when the input torque is “0”. Normally, for example, when the power supply voltage is 5 V, it is set to 2.5 V, which is half that voltage. The

On the other hand, in step S5, it is determined whether or not the voltage signal VT1 is smaller than a voltage value obtained by subtracting the limit value V0 from the midpoint voltage VT10. If the determination result in step S5 is “Yes” (VT1 <VT10−V0), the process proceeds to step S6. If “No” (VT1 ≧ VT10−V0), the process proceeds to step S3.
In step S6, the voltage signal VT1 is limited so as to be constant at a voltage value obtained by subtracting the limit value V0 from the midpoint voltage VT10, and the process proceeds to step S3.

Next, in step S3, it is determined whether or not the voltage signal VT2 is higher than a voltage value obtained by adding the above-described limit value V0 to the midpoint voltage VT20 of the voltage signal VT2. If the determination result in step S1 is “Yes” (VT2> VT20 + V0), the process proceeds to step S4. If “No” (VT2 ≦ VT20 + V0), the process proceeds to step S7.
In step S4, the voltage signal VT2 is limited so as to be constant at a voltage value obtained by adding the limit value V0 to the midpoint voltage VT20. Here, the midpoint voltage VT20 indicates the voltage value of the voltage signal VT2 when the input torque is “0”, as in the case of the midpoint voltage VT10 described above. Usually, for example, when the power supply voltage is 5V , Half of that is set to 2.5V.

On the other hand, in step S7, it is determined whether or not the voltage signal VT2 is lower than a voltage value obtained by subtracting the limit value V0 from the midpoint voltage VT20. If the determination result in step S7 is “Yes” (VT2 <VT20−V0), the process proceeds to step S8. If “No” (VT2 ≧ VT20−V0), the process is temporarily ended and the first Return to processing.
In step S8, the voltage signal VT2 is limited so as to be constant at a voltage value obtained by subtracting the limit value V0 from the midpoint voltage VT20, and the process is temporarily terminated and the process returns to the first process.

  Here, the above-described limit value V0 is smaller than the voltage value of the difference between the midpoint voltage VT10 (for example, 2.5 V) and the maximum value (for example, 5 V) that can be output from the voltage signal VT1, and the midpoint It is set to a voltage value (for example, about 2V) smaller than the voltage value of the difference between the voltage VT10 (for example, 2.5V) and the minimum value (for example, 0V) that can be output from the voltage signal VT1. Since voltage signal VT2 is a signal that is basically in reverse phase with voltage signal VT1 with reference to midpoint voltage VT20, limit voltage V0 is the maximum value that can be output from midpoint voltage VT20 and voltage signal VT2. And a voltage value that is smaller than the voltage value of the difference between the midpoint voltage VT20 and the minimum value of the voltage signal VT2. That is, a predetermined upper limit value for the voltage signals VT1 and VT2 on the side of the midpoint voltages VT10 and VT20 relative to the maximum and minimum values of the voltage signals VT1 and VT2 with reference to the midpoint voltages VT10 and VT20 based on the limit value V0. And a lower limit value are respectively set.

FIG. 4 shows voltage signals VT1 and VT2 when the horizontal axis is torque and the vertical axis is the voltage value (detection voltage) of the detection signal, and the power supplied to the detection circuit 35 is a single power supply (for example, 0 to 5 V). The output characteristics of the torque detection signal VT3 and the failure detection signal VTF are shown.
According to the voltage signal VT1 and the voltage signal VT2 shown in FIG. 4, when the center point voltages VT10 and VT20 (for example, about 2.5V) are changed as a reference, the time point (VT10) changes up and down by a limit value V0 (for example, about 2V). (± V0 and VT20 ± V0), the increase in the voltage value with respect to the increase in torque is stopped and limited to a constant voltage value by steps S2, S4, S6, and S8 of the above-described flowchart. As a result, even if the midpoint voltage VT10 and the midpoint voltage VT2 of the voltage signals VT1 and VT2 do not coincide with each other for some reason, the voltage values VT1 and VT2 change from the torque “0” to a predetermined torque ± Since they are simultaneously limited when they are displaced by T0, the states of opposite phases are maintained. As a result, the failure detection signal VTF that is the sum of the voltage signal VT1 and the voltage signal VT2 has a predetermined torque ± T0. The voltage value is constant even outside the range.

  In addition, although the process of step S2, S4, S6, S8 mentioned above is not performed simultaneously if description of a flowchart, the failure detection signal VTF is predetermined | prescribed so that it may not be influenced by noise etc. in the electronic controller 50. Since the failure detection is performed when the state out of the range is maintained to some extent, a series of processes of steps S1 to S8 in the flowchart shown in FIG. 3 is compared with the time required to detect the failure. It takes a moment, and can be regarded as being performed almost simultaneously. These steps S2, S4, S6, and S8 constitute detection signal limiting means.

Therefore, according to the reference example described above, the detection signals of the first detection coil and the second detection coil that respectively detect the magnetic changes of the first and second magnetostrictive films whose directions of easy magnetization are different from each other. By simultaneously limiting the upper and lower limit values of the voltage signals VT1 and VT2 in steps S2, S4, S6, and S8, the sum of the voltage signal VT1 and the voltage signal VT2 is kept constant even when an excessive torque is input. Therefore, it is possible to prevent erroneous detection of failure detection by the electronic control unit 50 and improve reliability.

  Further, the limit value V0 is a voltage between the power supply voltage (for example, 5V) and the midpoint voltage (for example, 2.5V), the reference voltage (for example, 0V) and the midpoint voltage (for example, 2.5V) of the power supply. Since the voltage signals VT1 and VT2 can be positively limited to a constant voltage before reaching the maximum and minimum power supply voltage and reference voltage, the power supply circuit configuration is simple. It is possible to prevent erroneous detection due to excessive torque while using a simple single power supply circuit (for example, 0 to 5 V, etc.), and as a result, it is possible to improve the reliability of failure detection with a small number of parts.

Next, an embodiment of the present invention will be described with reference to FIGS. In the reference example described above, the case where the voltage signals VT1 and VT2 are limited by the electronic control device 50 has been described. However, in this embodiment , the configuration for limiting the voltage signals VT1 and VT2 is only different from the reference example. The same parts will be described with the same reference numerals.

As shown in FIG. 5, the magnetostrictive torque sensor 60 in this embodiment detects the change in permeability of the first magnetostrictive film 31 and the second magnetostrictive film 32 provided around the pinion shaft 5. A coil 33 and a second detection coil 34 are provided, and the first detection coil 33 and the second detection coil 34 are connected to a detection circuit 61, respectively.

  The detection circuit 61 includes conversion circuits 38 and 39 that convert inductance changes between the first detection coil 33 and the second detection coil 34 into voltage signals VT1 and VT2 that are in opposite phases in response to torque input, respectively. Yes. The detection circuit 61 includes a differential amplifier circuit 40 that amplifies the difference between the voltage signals VT1 and VT2 converted by the converter circuits 38 and 39.

Further, between the output side of the conversion circuit 38 of the detection circuit 61 and the output side of the conversion circuit 39, a limiting circuit 62 that limits the potential difference between them within a predetermined range is interposed. The limiting circuit 62 includes two Zener diodes 63 and 63 connected in series with the cathode facing outside, and the Zener diodes 63 and 63 allow the output side of the conversion circuit 38 and the output side of the conversion circuit 39 to be connected. The potential difference between them is limited by a voltage Vz that is twice the Zener voltage (Vz / 2). Here, the Zener voltage (Vz / 2) of one Zener diode 63 is set to a voltage equivalent to the limit voltage V0 of the reference example described above. Note that what constitutes the limiting circuit 62 is not limited to the Zener diode 63 described above, and may be any non-linear element capable of limiting the voltage, for example. The position may also be on the input side of the conversion circuits 38 and 39.

FIG. 6 shows the characteristics of the voltage signals VT1, VT2, the failure detection signal VTF, and the torque detection signal VT3 when the horizontal axis is the input torque and the vertical axis is the detection voltage. As shown in FIG. 6, when the potential difference between the voltage signal VT1 and the voltage signal VT2 reaches the entire Zener voltage Vz obtained by adding the individual Zener voltages of the Zener diodes 63 and 63 (Vz / 2 in the figure). The overall Zener voltage Vz is maintained. That is, even if there is an excessive torque input, the voltage signal VT1 and the voltage signal VT2 are simultaneously limited and maintained in opposite phases, so that the failure detection signal VTF has a constant voltage value as in the reference example. It becomes.

Therefore, according to the above-described embodiment, when the potential difference between the voltage signal VT1 and the voltage signal VT2 exceeds the Zener voltage Vz, the voltage is limited by the Zener voltage Vz. Accordingly, the state in which the voltage signals VT1 and VT2 are out of phase with each other is maintained, and the failure detection signal VTF, which is the sum of the voltage signal VT1 and the voltage signal VT2 limited by the limiting circuit 62, has a constant voltage value. As a result, similarly to the reference example , it is possible to prevent erroneous detection of failure due to excessive torque input, and to improve the reliability of failure detection.

[Other Embodiments]
The present invention is not limited to application to the electric power steering apparatus of the above-described embodiment, but can also be applied to a vehicle steering apparatus of a steering-by-wire system. In the steering-by-wire system, the steering means and the steering mechanism are mechanically separated, and the steering motor provided in the steering mechanism is driven according to the steering torque acting on the steering means. This is a steering system for turning steered wheels of a vehicle, and the magnetostrictive torque sensor according to the present invention can be used for detection of steering torque acting on the steering means.

1 is an overall configuration diagram of an electric power steering device according to a reference example of the present invention. It is a schematic block diagram of the magnetostrictive torque sensor in the reference example of this invention. It is a flowchart which shows the restriction | limiting process of the voltage signals VT1 and VT2 performed with the electronic controller in the reference example of this invention. It is a graph which shows the output characteristic of voltage signal VT1, VT2 and the failure detection signal VTF in the reference example of this invention. FIG. 3 is a schematic configuration diagram corresponding to FIG. 2 in the embodiment of the present invention. 5 is a graph corresponding to FIG. 4 in the embodiment of the present invention. It is a graph equivalent to the conventional FIG.

Explanation of symbols

5 Pinion shaft (shaft)
DESCRIPTION OF SYMBOLS 11 Electric motor 30,60 Magnetostrictive type torque sensor 31 1st magnetostrictive film 32 2nd magnetostrictive film 33 1st detection coil (1st detection means)
34 Second detection coil (second detection means)
50 Electronic control device (failure detection means)
62 Limiting circuit (detection signal limiting means)
Steps S2, S6, S4, S8 Detection signal limiting means

Claims (3)

A first magnetostrictive film and a second magnetostrictive film which are provided on the shaft and have magnetic anisotropy having different directions of easy magnetization;
First detection means for detecting a change in magnetic characteristics of the first magnetostrictive film;
Second detection means for detecting a change in magnetic characteristics of the second magnetostrictive film,
A magnetostrictive torque sensor for detecting torque input to the shaft based on detection results of the first detection means and the second detection means;
Failure detection means for performing failure detection based on the detection signal of the first detection means and the detection signal of the second detection means;
Detection signal limiting means for limiting the detection signal of the first detection means and the detection signal of the second detection means to a predetermined upper limit value or lower limit value, respectively .
The detection signal limiting means is a non-linear element, and the non-linear element limits the potential difference between the detection signal of the first detection means and the detection signal of the second detection means within a predetermined range. Magnetostrictive torque sensor. The detection signal limiting means sets the upper limit value between the maximum voltage and the midpoint voltage of the detection signal, set the lower limit value between the minimum voltage and the midpoint voltage of said detection signal The magnetostrictive torque sensor according to claim 1. In the electric steering device for detecting the steering torque by a magnetostrictive torque sensor and driving the electric motor according to the detected steering torque to steer the vehicle,
The electric steering apparatus according to claim 1, wherein the magnetostrictive torque sensor is the magnetostrictive torque sensor according to claim 1 .

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