JP5452957B2 - Magnetostrictive torque sensor and electric power steering device - Google Patents

Description

  The present invention relates to a magnetostrictive torque sensor and an electric power steering apparatus that detect torque acting on a rotating shaft based on a change in magnetic characteristics caused by magnetostriction.

  As a non-contact type torque sensor, a magnetostrictive torque sensor that detects torque based on a change in magnetic characteristics caused by magnetostriction is known. This magnetostrictive torque sensor is used for detecting steering torque of an electric steering device, for example. (For example, Patent Document 1 (FIG. 3)).

Patent document 1 is demonstrated based on the following figure.
As shown in FIG. 4, in the conventional electric power steering apparatus 100, one end portion 102 a of the rotating shaft 102 is connected to the universal shaft joint 101, and the other end portion 102 b of the rotating shaft 102 is connected via a rack and pinion mechanism 103. Thus, the rack shaft 104 is connected.

  The rotating shaft 102 is supported on the housing 107 by two bearings 105 and 106 except for one end 102a. The rotating shaft 102 supports only both ends of the pinion 108 of the rack and pinion mechanism 103 with two bearings 105 and 106.

  The electric power steering apparatus 100 includes a magnetostrictive torque sensor 110. The magnetostrictive torque sensor 110 detects the steering torque of the steering system applied to the steering handle. The magnetostrictive films 111 and 112 provided on the surface of the portion 102a, and the detection coils 113 and 114 disposed in the vicinity of the magnetostrictive films 111 and 112, respectively. Since the magnetostrictive characteristics of the magnetostrictive films 111 and 112 change according to the torque acting on the rotating shaft 102, the torque can be detected magnetically by detecting this with the detection wires 113 and 114.

  In order to prevent erroneous detection of the failure of the magnetostrictive torque sensor 110 described above, the first detection coil and the second detection coil are arranged in opposition to the first magnetic film, and the third detection is performed on the second magnetic film. A magnetostrictive torque sensor based on the outputs of the first detection circuit, the output of the second detection coil, the output of the third detection coil, and the output of the fourth detection coil. A technique for detecting 110 failures is also known (for example, Patent Document 2 (FIG. 1)).

  By the way, the universal shaft joint 101 is disposed above the rotating shaft 102, and the universal shaft joint 101 serves as a load source, and a downward force or a bending force due to the angle θ2 is applied to the rotating shaft 102. As a result, asymmetric stresses act on the magnetostrictive films 111 and 112 provided on the rotating shaft 102, respectively, and there may be a difference in inductance change between the magnetostrictive film 111 and the magnetostrictive film 112.

  In addition, even if the environmental change is made up of a temperature change or a magnetic field fluctuation in the steering shaft, the asymmetrical environmental change may cause a similar difference in the change in inductance of each of the magnetostrictive films 111 and 112. As described above, when the magnetostrictive films 111 and 112 are subjected to an asymmetrical load or an environmental change and a difference occurs in the amount of inductance, the torque midpoint voltage fluctuates and the detection accuracy is lowered.

JP 2007-101422 A JP 2006-64445 A

  It is an object of the present invention to provide a magnetostrictive torque sensor and an electric power steering device that can suppress a change in inductance even when an influence of a universal shaft joint or an environmental change acts.

The invention according to claim 1, a steering operator operated by a driver for steering a universal coupling for transmitting the rotation action of the steering operator, one end of the rotary shaft The universal joint coupling is connected, A magnetostrictive torque sensor that detects torsion of the rotating shaft by a magnetic action and calculates a torque applied to the rotating shaft, and an auxiliary steering force is applied to the rotating shaft according to the torque calculated by the magnetostrictive torque sensor. An electric power steering device comprising a magnetostrictive torque sensor comprising: a motor to be added; and an electronic control device that controls driving of the motor based on a signal related to the torque calculated by the magnetostrictive torque sensor. The magnetostrictive torque sensor is disposed on the outer peripheral surface of the rotating shaft and has different magnetic anisotropy between adjacent ones in a state where torque is applied. 1 magnetic film, a second magnetic layer, and the third magnetostrictive film, the first magnetic film are opposed with a predetermined gap therebetween, detecting a change in inductance in accordance with a change in the permeability of the first magnetic layer a first detection coil, the second magnetic film to be opposed with a predetermined gap therebetween, the first consisting of two detection coils for detecting a change in inductance in accordance with a change in magnetic permeability of said second magnetic layer Two detection coils, a third detection coil that is disposed opposite to the third magnetic film with a predetermined gap therebetween, and detects a change in inductance according to a change in permeability of the third magnetic film, and the first detection Therefore the sum of the coil and the output signal of one of the detection coil of the second detection coil, by dividing the output signal of the smaller of the output signals of one of the detection coil of the first detection coil and the second detection coil Generate the first signal, before By the sum of the other detecting coil and an output signal of the third detection coil of the second detection coil, dividing the output signal of the smaller of the output signal of the second said the other of the detection coil of the detection coil the third detection coil And an arithmetic circuit for generating a second signal and calculating a torque acting on the rotating shaft from a difference between the first signal and the second signal.

According to a second aspect of the present invention, in the electric power steering apparatus including the magnetostrictive torque sensor according to the first aspect, the arithmetic circuit has a denominator of one of the detection coils of the first detection coil and the second detection coil. A first output signal is generated by assigning a sum of output signals and assigning and dividing a smaller output signal of the output signals of one of the first detection coil and the second detection coil to the numerator. A sum of output signals of the other detection coil of the second detection coil and the third detection coil is assigned to the denominator, and the other detection coil of the second detection coil is assigned to the numerator. And a second half bridge that generates and outputs the second signal by assigning and dividing the smaller one of the output signals of the three detection coils.

The invention of claim 3 is the electric power steering apparatus having a magnetostrictive torque sensor according to claim 1, wherein said third magnetic film and the first magnetic film has the same first anisotropic characterized by disposing said third magnetic film having a different second anisotropy and the first anisotropy between said first magnetic film and the third magnetic film .

According to a fourth aspect of the present invention, in the magnetostrictive torque sensor for detecting the twist of the rotating shaft by a magnetic action and calculating the torque applied to the rotating shaft, the magnetostrictive torque sensor is arranged on the outer peripheral surface of the rotating shaft and the torque is applied. At least the first magnetic film , the second magnetic film , and the third magnetostrictive film, which have different magnetic anisotropy between adjacent ones of the first magnetic film and the first magnetic film with a predetermined gap therebetween, 1 a first detection coil for detecting a change in inductance in accordance with a change in the magnetic permeability of the magnetic film, are opposed with a predetermined gap in the second magnetic film, a change in magnetic permeability of said second magnetic layer A second detection coil comprising two detection coils for detecting a change in inductance according to
A third detection coil disposed opposite to the third magnetic film with a predetermined gap to detect a change in inductance in accordance with a change in magnetic permeability of the third magnetic film; the first detection coil; and the second detection coil. The first signal is generated by dividing the smaller one of the output signals of the first detection coil and the second detection coil by the sum of the output signals of one of the detection coils of the detection coil. and, wherein the sum of the output signals of the second said the other of the detection coil of the detection coil the third detection coil, the smaller the output of the other detection coil and output signal of the third detection coil of the second detection coil An arithmetic circuit that divides the signal to generate a second signal and calculates a torque acting on the rotating shaft from a difference between the first signal and the second signal; .

According to the present invention, at least the first magnetic film , the second magnetic film , and the third magnetostrictive film, and the first magnetic film , the second magnetic film , and the third magnetostrictive film , which have different magnetic anisotropy between adjacent ones. detecting a change in inductance in accordance with a change in the permeability of the membrane, the first detection coil, the second detection coil, and a third detection coil provided, of which the second detection coil one and the other of the two detection It consists of a coil. Then, the arithmetic circuit, the sum of the first detection coil and the output signal of one of the detection coil of the second detection coil, the output of the smaller of the first detection coil and the output signal of one of the detection coil of the second detection coil The signal is divided to generate the first signal, and the output of the other detection coil of the second detection coil and the output of the third detection coil is obtained by the sum of the output signals of the other detection coil of the second detection coil and the third detection coil. By dividing the smaller output signal of the signals to generate the second signal and calculating the torque acting on the rotating shaft from the difference between the first signal and the second signal, the rotating shaft The variation of the torque midpoint voltage when a load other than the torque is applied to one end of the sensor can be reduced, and the variation of the sensor medium voltage can be suppressed even when an environmental change occurs.

It is a figure which shows schematic structure of the electric power steering apparatus provided with the magnetostrictive torque sensor which concerns on this invention. It is the figure which showed the basic structure of the magnetostrictive torque sensor which concerns on this invention. It is a torque detection output characteristic figure of the magnetostriction type torque sensor concerning the present invention. It is a figure which shows the outline | summary of the electric steering apparatus which has the conventional magnetostrictive torque sensor.

  Hereinafter, embodiments of the present invention will be described in detail.

  As shown in FIG. 1, in the electric power steering apparatus 10, a universal shaft joint 13 is connected to a steering shaft 12 extending from a handle 11 as a steering operator, and an intermediate shaft 14 is extended from the universal shaft joint 13. A universal shaft joint 15 is connected to the lower end of the intermediate shaft 14, and a rotary shaft 16 is connected to the universal shaft joint 15.

  The rotary shaft 16 is supported by three bearings 17, 18, 19, a worm wheel 21 and a pinion 22 are provided at the lower part, and a magnetostrictive torque sensor 30 is disposed between the two bearings 17, 18. .

The worm wheel 21 meshes with a worm gear 24 provided on the motor shaft of the motor 23 and is driven by the motor 22.
The pinion 22 meshes with the rack 28 of the rack shaft 27 passed to the left and right front wheels 25 and 26, and moves the rack shaft 27 in the vehicle width direction.

  The magnetostrictive torque sensor 30 is provided in an annular shape over the entire circumference of the outer peripheral surface of the rotary shaft 16, and has at least a first magnetostrictive film 31 that is adjacent to each other in a state where torque is applied and has a different permeability. The second magnetostrictive film 32 (32a, 32b), the third magnetostrictive film 33, the first magnetostrictive film 31, the second magnetostrictive film 32 (32a, 32b), and the third magnetostrictive film 33 are spaced apart from each other. A first detection coil 34, a second detection coil 35b, and a third detection that are arranged opposite to each other and detect a change in inductance in accordance with a change in magnetic permeability of each of the magnetostrictive films 31, 32 (32a, 32b), 33. A coil 35a and a fourth detection coil 36 are provided.

The change in inductance of each detection coil 34, 35b, 35a, 36 is converted into a voltage change and output to the electronic control unit (ECU 40).
The ECU 40 compares the difference between the first signal obtained by comparing the output signals of the first detection coil 34 and the third detection coil 35a and the second signal obtained by comparing the output signals of the second detection coil 3b and the fourth detection coil 36. Functions as an arithmetic circuit for calculating torque acting on the rotary shaft 16 from the rotation.

  In addition, the direction of the magnetic anisotropy of each of the first magnetostrictive film 31, the second magnetostrictive film 32 (32a, 32b), and the third magnetostrictive film 33 described above, the first detection coil 34, the second detection coil 35b, the third The inductance change in each of the detection coil 35a and the fourth detection coil 36 and the principle of torque calculation by the ECU 40 will be described in detail with reference to FIG.

In the following description, (CC), (BB), (AA), and (DD) indicate inductances for the magnetostrictive films 31, 32b, 32a, and 33, respectively.
As shown in FIG. 2, the magnetostrictive torque sensor 30 according to the embodiment of the present invention includes a rotating shaft 16 and four magnetostrictive films 31 (CC), 32b (BB), 32a (AA), 333 (DD ) And the respective magnetostrictive films 31 (CC), 32b (BB), 32a (AA), and 333 (DD) with a predetermined gap therebetween, and the magnetostrictive films 31 (CC), 32b (BB), The first detection coil 34, the second detection coil 35b, the third detection coil 35a, and the fourth detection coil 36 detect changes in inductance according to changes in the magnetic permeability of 32a (AA) and 333 (DD). Is done.

Here, the magnetic anisotropy adding directions of the four magnetostrictive films 31 (CC), 32b (BB), 32a (AA), and 333 (DD) are axial directions, for example, right, left, left, and right, respectively. And It may be left, right, right, left.
Each of the magnetostrictive films 31 (CC), 32b (BB), 32a (AA), and 333 (DD) is a metal film made of a material having a large change in magnetic permeability with respect to strain, and Ni—Fe formed by a plating method. Any of an alloy film, a sputtered film and a chevron structure may be used.

  The detection bridge that detects the change in inductance in accordance with the change in the magnetic permeability of each of the magnetostrictive films 31 (CC), 32b (BB), 32a (AA), and 333 (DD) is one (first) half bridge. VT1 = CC / (AA + CC) and the other (second) half bridge is VT2 = BB / (BB + DD), and the differential output by the two half-bridge differential amplifiers 41 (VT3 = VT2-VT1). Full bridge configuration. Here, VT1 and VT2 are half-bridge output voltages, and VT3 is a torque detection voltage.

  However, due to the influence of the load from the universal shaft joint 15, the inductance change is a distance from the universal shaft joint 15 to the center position of each of the magnetostrictive films 31 (CC), 32b (BB), 32a (AA), and 333 (DD). It changes according to. Here, BB> DD and CC> AA.

Using this, the ECU 40 uses the sum of the output signals of the first detection coil 34 and the third detection coil 35b as the denominator constituting the first half bridge, and uses the first detection coil 34 and the third detection coil 35b as the numerator. The half-bridge output voltage VT1, which is the first detection signal, is generated by assigning and dividing the smaller one of the output signals (here, the first detection coil 34) (VT1 = CC / (AA + CC)).
The sum of the output signals of the second detection coil 35b and the fourth detection coil 34 is used for the denominator constituting the second half bridge, and the smaller one of the output signals of the second detection coil 35b and the fourth detection coil 34 is used for the numerator. (Here, the second detection coil 35b) is assigned and divided to generate the half-bridge output voltage VT2 that is the second detection signal (VT2 = BB / (BB + DD)).

  The failure detection output VTF is a sum output (VTF = VT1 + VT2) of the first detection signal VT1 and the second detection signal VT2 by the adder 42 as in the conventional case.

  The torque detection output characteristics of the magnetostrictive torque sensor 30 will be described with reference to FIG. In FIG. 3, the horizontal axis represents the torque applied to the rotating shaft 16 (rotating shaft), and the vertical axis represents the voltage (inductance change).

As shown in FIG. 3, VT1 = CC / (AA + CC) and VT2 = BB / (BB + DD) have magnetic anisotropies in which the adjacent magnetostrictive films are in opposite directions, so that VT1 and VT2 intersect. The vertical axis including the intersection B is substantially line symmetric.
VT3 indicates a torque output characteristic created by using VT1 and VT2 and taking the difference between the two characteristics. By monitoring this VT3, the torque applied to the rotating shaft 16 can be calculated. Actually, the point B of VT3 is set to the origin position (torque midpoint), and the right part is treated as a positive area and the left part as a negative area. Information on the rotational direction and magnitude of the torque can be obtained by this VT3.

  According to the magnetostrictive torque sensor 30 according to the embodiment of the present invention, by allocating a magnetostrictive film having a small magnetic change to the molecules constituting the detection bridge described above, fluctuation cancellation at the time of torque calculation by the differential of VT1 and VT2 is performed. The effect can be increased, and fluctuations in the torque midpoint voltage when a load other than torque is applied to the rotating shaft 16 can be reduced.

  Evaluation data of the magnetostrictive torque sensor 30 according to the embodiment of the present invention is shown below.

  Table 1 shows the state of impedance change of the magnetostrictive torque sensor 30 when a load of 250 Nm is applied to the universal joint 15, and the universal joint 15 for each of the four magnetostrictive films (DD, AA, BB, CC). The distance (position) from the origin position to the center position of each magnetostrictive film, the initial impedance (initial Z), the impedance when a load is applied (Z when loaded), and the impedance change (Δ) It is shown in the form.

  In Table 1, for example, for the magnetostrictive film (DD), the position is 83.5 mm, the initial Z is 250Ω, the loaded Z is 248.2414Ω, and Δ is 11.75859Ω. Hereinafter, similarly, the position, initial Z, loading Z, and Δ for each of the magnetostrictive films (AA), (BB), and (CC) are shown. According to Table 1, it can be understood that the magnetostrictive film located near the universal shaft joint 15 has a smaller characteristic change (DD <AA <BB <CC).

Table 2 shows the state of voltage changes of VT1, VT2, and VT3 at this time in a table format.
In Table 2, A is a conventional method for detecting a pair of magnetostrictive films disclosed in Patent Document 2, for example, and a torque midpoint voltage value when a disturbance is applied. B is an application of the present invention. Thus, it can be understood that the fluctuation of the torque midpoint voltage generated by about 9% (9.331104) can be reduced to 1% or less (0.8127638).

  As described above, according to the magnetostrictive torque sensor 30 according to the embodiment of the present invention, at least three magnetostrictive films are provided on the rotating shaft 16 and, for example, right, left, and right from the upper end in the axial direction. By adding a different magnetic anisotropy to each other and disposing a magnetostrictive film with small magnetic change on the molecules constituting the detection bridge, the torque midpoint voltage when a load other than the input torque is applied to the upper end of the shaft Fluctuations can be reduced. Similarly, when the magnetic field change occurs from the upper end to the lower end of the shaft due to a temperature change or a running environment, the fluctuation of the torque midpoint voltage can be greatly reduced. As a result, the reliability of the magnetostrictive torque sensor 30 can be greatly increased, and the application fields including the electric power steering apparatus 10 can be expanded.

  In addition, according to the electric power steering apparatus 10 including the magnetostrictive torque sensor 30 according to the embodiment of the present invention, the drive of the motor 23 is controlled based on the signal related to the torque calculated by the magnetostrictive torque sensor 30. Thus, even when a load other than torque is applied to one end of the rotary shaft 16 due to the fulcrum position of the universal shaft joint 15 or the like, fluctuations in the torque midpoint voltage can be reduced, and temperature and magnetic field changes can be reduced. Even when it occurs, the fluctuation of the torque midpoint voltage can be suppressed, and the electric power steering apparatus 10 with high reliability can be provided.

  The present invention is particularly effective when applied to the magnetostrictive torque sensor 30 used for detecting the steering torque of the electric power steering apparatus 10.

  DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 13, 15 ... Universal shaft coupling, 16 ... Rotary shaft, 30 ... Magnetostrictive torque sensor, 31 ... 1st magnetostrictive film, 32a, 32b ... 2nd magnetostrictive film, 33 ... 3rd magnetostrictive film, 34 ... 1st detection coil, 35 ... 2nd detection coil, 36 ... 3rd detection coil, 40 ... ECU, 41 ... Differential amplifier, 42 ... Adder

Claims (4)

A steering operator operated by the driver for steering;
A universal shaft coupling that transmits the rotational action of the steering operator;
One end of the rotating shaft to the universal joint coupling is connected, the magnetostrictive torque sensor to calculate the torque applied to the rotating shaft is detected by the magnetic action of twisting of said rotary shaft,
A motor for adding an auxiliary steering force to the rotating shaft according to the torque calculated by the magnetostrictive torque sensor;
An electronic control device that controls driving of the motor based on a signal related to the torque calculated by the magnetostrictive torque sensor, and an electric power steering device comprising a magnetostrictive torque sensor,
The magnetostrictive torque sensor is
At least a first magnetic film , a second magnetic film , and a third magnetostrictive film that are disposed on the outer peripheral surface of the rotating shaft and have different magnetic anisotropy between adjacent ones in a state where torque is applied;
A first detection coil disposed opposite to the first magnetic film with a predetermined gap and detecting a change in inductance according to a change in permeability of the first magnetic film;
Said second magnetic film to be opposed with a predetermined gap therebetween, the second detection coil composed of two detection coils for detecting a change in inductance in accordance with a change in magnetic permeability of said second magnetic layer,
A third detection coil disposed opposite to the third magnetic film with a predetermined gap and detecting a change in inductance according to a change in permeability of the third magnetic film;
Wherein the sum of the first detection coil and the output signal of one of the detection coil of the second detection coil Therefore, the smaller of the output signals of the output signals of one of the detection coil of the first detection coil and the second detection coil To generate the first signal, and the other detection coil of the second detection coil and the third detection by the sum of the output signals of the other detection coil of the second detection coil and the third detection coil An arithmetic circuit that generates a second signal by dividing the smaller one of the output signals of the coil, and calculates a torque acting on the rotating shaft from a difference between the first signal and the second signal When,
An electric power steering apparatus comprising a magnetostrictive torque sensor. The arithmetic circuit is:
The sum of the output signals of one detection coil of the first detection coil and the second detection coil is assigned to the denominator, and the smaller one of the output signals of the detection coils of the first detection coil and the second detection coil is assigned to the numerator. A first half bridge that assigns and divides one output signal to generate the first signal;
The sum of the output signals of the other detection coil of the second detection coil and the third detection coil is assigned to the denominator, and the output of the other detection coil of the second detection coil and the third detection coil is assigned to the numerator. A second half bridge that assigns and divides the smaller output signal of the signals to generate the second signal;
An electric power steering apparatus comprising the magnetostrictive torque sensor according to claim 1. Wherein the first magnetic film third magnetic film has the same first anisotropic, and the first anisotropic between said third magnetic film and the first magnetic film an electric power steering apparatus having a magnetostrictive torque sensor according to claim 1, wherein placing the third magnetic film having a different second anisotropy. In a magnetostrictive torque sensor that detects torsion of a rotating shaft by a magnetic action and calculates torque applied to the rotating shaft,
At least a first magnetic film , a second magnetic film , and a third magnetostrictive film that are disposed on the outer peripheral surface of the rotating shaft and have different magnetic anisotropy between adjacent ones in a state where torque is applied;
A first detection coil disposed opposite to the first magnetic film with a predetermined gap and detecting a change in inductance according to a change in permeability of the first magnetic film;
Said second magnetic film to be opposed with a predetermined gap therebetween, the second detection coil composed of two detection coils for detecting a change in inductance in accordance with a change in magnetic permeability of said second magnetic layer,
A third detection coil disposed opposite to the third magnetic film with a predetermined gap and detecting a change in inductance according to a change in permeability of the third magnetic film;
By the sum of the output signal of one of the detection coil of the second detection coil and the first detection coil, the output signal of the smaller of the output signals of one of the detection coil of the first detection coil and the second detection coil The first detection signal is generated by division, and the other detection coil of the second detection coil and the third detection coil are obtained by the sum of the output signals of the other detection coil of the second detection coil and the third detection coil. An arithmetic circuit that generates a second signal by dividing a smaller one of the output signals of the output signal, and calculates a torque acting on the rotating shaft from a difference between the first signal and the second signal; ,
A magnetostrictive torque sensor comprising:

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