JP4680114B2 - Magnetostrictive torque sensor for vehicles - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetostrictive torque sensor having high trouble detecting accuracy even if temperature gradient arises in a steering shaft. <P>SOLUTION: The magnetostrictive torque sensor 30 for a vehicle has a first magnetostrictive film 31 and second magnetostrictive film 32 disposed in a steering shaft 1 whose upper part is connected with a steering wheel 2 and lower part is connected with a gear mechanism in a steering gear box 20, and detects torque input into the steering shaft 1 based on the variation of the magnetic characteristic of the magnetostrictive films 31 and 32. The torque sensor has first detecting coil 33 and second detecting coil 34 facing the first magnetostrictive film 31, and third detecting coil 35 and fourth detecting coil 36 facing the second magnetostrictive film 32. The first detecting coil 33, second detecting coil 34, third detecting coil 35, and fourth detecting coil 36 are arranged in the closing order to the steering wheel 2, and a sensor abnormality is detected, based on the added value of an intermediate output of the first detecting coil 33 and the third detecting coil 35 to an intermediate output of the second detecting coil 34 and the fourth detecting coil 36. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a magnetostrictive torque sensor that detects torque input to a steering shaft based on a change in magnetic characteristics caused by magnetostriction.

  In the magnetostrictive torque sensor, as shown in FIG. 3, two magnetostrictive films 91 and 92 having different magnetic anisotropies are provided on the rotating shaft 99, and the detection coils are respectively opposed to the magnetostrictive films 91 and 92. There is one configured by arranging 93 and 94 (see Patent Document 1). The principle of the magnetostrictive torque sensor 90 is that when the torque is applied to the rotary shaft 99, the magnetic permeability of the magnetostrictive films 91, 92 changes, and the inductance of the detection coils 93, 94 changes accordingly. Torque is detected based on this.

Further, as an improved type in which the detection accuracy of the magnetostrictive torque sensor is improved, as shown in FIG. 4, a pair of detection coils 93a and 93b are shifted in the axial direction so as to face one of the magnetostrictive films 91. A pair of detection coils 94a and 94b are arranged so as to be opposed to the other magnetostrictive film 92 and shifted in the axial direction, and two detection coils 93a and 94b are arranged on both outer sides (the highest and the lowest). The intermediate voltage VT1 ′ is detected, the intermediate voltage VT2 ′ of the two detection coils 93b and 94a disposed in the middle is detected, the torque is detected based on the intermediate voltage VT1 ′ or VT2 ′, and the intermediate voltage VT1 is detected. It is considered that a failure detection output VTF 'is calculated from the sum of' and VT2 'and a failure (sensor abnormality) of the magnetostrictive torque sensor is detected based on this VTF' (patent text) See 2).
JP 59-164932 A JP 2006-64445 A

  By the way, when this magnetostrictive torque sensor is used as a steering torque sensor for detecting the steering torque of the vehicle, the steering torque sensor is installed on the steering shaft and is arranged between the steering wheel and the steering gear box. When this vehicle is stopped after traveling at a high speed, the steering gear box is heated by the heat of the engine and the steering shaft is heated, but the temperature distribution of the steering shaft is not uniform, and the lower side closer to the engine is lower. The temperature is higher than the upper side far from the engine. Therefore, the temperature of the portion where the lowest detection coil 94b is arranged becomes high, the temperature of the portion where the highest detection coil 93a is arranged becomes lower, and the detection coils 93b and 94a are arranged. The temperatures of the portions are substantially the same at an intermediate temperature (hereinafter referred to as intermediate temperature).

Since the magnetic permeability μ of the magnetostrictive film has a temperature characteristic that increases as the temperature increases, when the temperature difference (temperature gradient) is generated in the steering shaft in this way, the intermediate voltage VT1 ′ is detected by the detection coil in the low temperature portion. Since the intermediate voltage VT2 'is an intermediate voltage between the detection coils 93b and 94a in the intermediate temperature portion, the intermediate voltage that should be essentially equal in the no-load state. The absolute values of VT1 ′ and VT2 ′ are different. As a result, the failure detection output VTF ′ drifts, and there is a possibility that it is determined as a failure although it is not a failure. For this reason, it is necessary to provide a large margin for the failure detection range, leading to a decrease in failure detection accuracy.
Accordingly, the present invention provides a magnetostrictive torque sensor having high failure detection accuracy even when a temperature gradient is generated in a steering shaft.

The vehicular magnetostrictive torque sensor according to the present invention employs the following means in order to solve the above problems.
According to the first aspect of the present invention, the upper part is connected to an operating element (for example, a handle 2 in an embodiment described later) and the lower part is accommodated in a steering gear box (for example, a steering gear box 20 in an embodiment described later) in the engine room. The first magnetostrictive film (for example, in the embodiments described later) is connected to the steering shaft (for example, the steering shaft 1 in the embodiments described later) connected to the gear mechanism (for example, the pinion 7 and rack teeth 8a in the embodiments described later). A first magnetostrictive film 31) and a second magnetostrictive film (for example, a second magnetostrictive film 32 in an embodiment to be described later) are provided, and torque input to the steering shaft is detected based on a change in magnetic characteristics of these magnetostrictive films. A magnetostrictive torque sensor for a vehicle (for example, a magnetostrictive torque sensor 30 in an embodiment described later). Thus, the first detection coil (for example, the first detection coil 33 in the embodiment described later) and the second detection coil (for example, the second detection coil 34 in the embodiment described later) disposed opposite to the first magnetostrictive film. A third detection coil (for example, a third detection coil 35 in an embodiment described later) and a fourth detection coil (for example, a fourth detection coil 36 in an embodiment described later) opposed to the second magnetostrictive film. , wherein the the order of proximity to the said operator first detection coil, the second detection coil, a third detection coil, the fourth detection coil is arranged, the intermediate output of the previous SL first detection coil and the third detection coil (For example, an intermediate voltage VT1 in an embodiment described later) and an added value of an intermediate output (for example, an intermediate voltage VT2 in an embodiment described later) of the second detection coil and the fourth detection coil For example, a magnetostrictive torque sensor for a vehicle for detecting one end of the one end and the third detection coil of said first detection coil is connected to the sensor abnormality based on failure detection output VTF) in Examples described later Thus, the first detection coil and the third detection coil are connected in series, and one end of the second detection coil and one end of the fourth detection coil are connected, whereby the second detection coil and the fourth detection coil are connected. A detection coil is connected in series, and the first detection coil and the third detection coil connected in series are connected in parallel to the second detection coil and the fourth detection coil connected in series, The other end of the first detection coil and the other end of the fourth detection coil are connected, and the other end of the second detection coil and the other end of the third detection coil are connected. The second detection coil, the third detection coil, and the fourth detection coil are excited by a rectangular wave voltage, and are a magnetostrictive torque sensor for a vehicle.

  When a temperature gradient is generated in the steering shaft, and a temperature gradient is generated in which the temperature increases in the first magnetostrictive film and the second magnetostrictive film in the downward direction, the temperature of the portion where the first detection coil is disposed is low, 2, the temperature of the part where the third detection coil is arranged is medium temperature, and the temperature of the part where the fourth detection coil is arranged is high. In this magnetostrictive torque sensor, the magnetostrictive torque sensor is based on the sum of the intermediate output of the low temperature first detection coil and the intermediate temperature third detection coil and the intermediate output of the intermediate temperature second detection coil and the high temperature fourth detection coil. An abnormality (failure) of the torque sensor is detected. In this case, the output of the added value of the intermediate output of the first detection coil and the third detection coil and the intermediate output of the second detection coil and the fourth detection coil is set to a specified value. (For example, 5 V), and drift of the failure detection signal can be prevented.

  According to the first aspect of the present invention, the added value of the intermediate output of the first detection coil and the third detection coil and the intermediate output of the second detection coil and the fourth detection coil can be made substantially equal. Even when a temperature gradient is generated on the shaft, it is possible to prevent a drift of a failure detection signal that is an added value of each intermediate output. As a result, the failure detection range can be set narrower than in the prior art, and erroneous detection of failure detection can be reduced as compared with the prior art, and failure detection accuracy can be increased.

Embodiments of a magnetostrictive torque sensor for a vehicle according to the present invention will be described below with reference to the drawings of FIGS.
As shown in FIG. 1, the electric power steering device 100 for a vehicle includes a steering shaft 1 connected to a handle (operator) 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 rods 9 and 9 constitute a turning mechanism, and the pinion 7 and the rack teeth 8a constitute a gear 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.
The pinion shaft 5, the rack 8, the worm gear 12, the worm wheel gear 13, and the magnetostrictive torque sensor 30 are accommodated in a steering gear box 20 in the engine room.

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 circumferential direction, and a first magnetostrictive film 31 that is disposed opposite to the first magnetostrictive film 31. 1 detection coil 33 and 2nd detection coil 34, 3rd detection coil 35 and 4th detection coil 36 which are arranged opposite to the 2nd magnetostriction film 32, 1st, 2nd, 3rd, 4th detection coil 33, Detection circuits 37, 38, 39, and 40 connected to 34, 35, and 36, respectively, are the main components.
The first and second magnetostrictive films 31 and 32 are metal films made of a material having a large change in magnetic permeability with respect to strain. For example, a Ni—Fe alloy film formed by plating on the outer periphery of the pinion shaft 5. Consists of. The first magnetostrictive film 31 is disposed closer to the handle 2 than the second magnetostrictive film 32 (that is, the upper side in FIG. 1).

The first magnetostrictive film 31 is configured to have magnetic anisotropy in a direction inclined by about 45 degrees with respect to the axis of the pinion shaft 5, and the second magnetostrictive film 32 is magnetically different from the first magnetostrictive film 31. The magnetic anisotropy is provided in a direction inclined by about 90 degrees with respect to the direction of the isotropic property. That is, the magnetic anisotropy of the two magnetostrictive films 31 and 32 are approximately 90 degrees out of phase with each other.
The first detection coil 33 and the second detection coil 34 are arranged coaxially around the first magnetostrictive film 31 with a predetermined gap therebetween, and the first detection coil 33 is the second detection coil 34. It is arranged on the side closer to the handle 2 (that is, the upper side in FIG. 1).
The third detection coil 35 and the fourth detection coil 36 are arranged coaxially around the second magnetostrictive film 32 with a predetermined gap therebetween, and the third detection coil 35 is the fourth detection coil 36. It is arranged on the side closer to the handle 2 (that is, the upper side in FIG. 1).
Therefore, the first detection coil 33, the second detection coil 34, the third detection coil 35, and the fourth detection coil 36 are arranged in order from the side closer to the handle 2.

By setting the magnetic anisotropy of the first and second magnetostrictive films 31 and 32 as described above, a compressive force acts on one of the magnetostrictive films 31 and 32 in a state where torque acts on the pinion shaft 5, A tensile force acts on the other, and as a result, the magnetic permeability of one magnetostrictive film increases and the magnetic permeability of the other magnetostrictive film decreases. Accordingly, the inductances of the two detection coils arranged around one magnetostrictive film are increased, and the inductances of the two detection coils arranged around the other magnetostrictive film are reduced.
The first, second, third, and fourth detection coils 33, 34, 35, and 36 are connected to detection circuits 37, 38, 39, and 40 each having a conversion circuit, and in these detection circuits 37 to 40, respectively. An inductance change of each of the detection coils 33 to 36 is converted into a voltage change and output to an electronic control unit (ECU) 50.

  The ECU 50 calculates a torque detection voltage based on output voltages from the detection circuits 37 to 40, and detects a steering torque acting on the pinion shaft 5 based on the torque detection voltage. Then, the ECU 50 sets a target current of the electric motor 11 according to the torque detection voltage, drives the electric motor 11 with the target current to generate an auxiliary steering force, and steers the vehicle. The method for calculating the torque detection voltage is the same as that of the prior art and is not the gist of the present invention, so that the description thereof is omitted.

Next, sensor abnormality detection (failure detection), which is a feature of the present invention, will be described.
Now, the output voltage of the detection circuit 37 is VT11, the output voltage of the detection circuit 38 is VT12, the output voltage of the detection circuit 39 is VT21, and the output voltage of the detection circuit 40 is VT22.
First, intermediate voltages VT1 and VT2 are calculated by the following equations (1) and (2). Here, k11, k12, k21, and k22 are proportional constants, V0 is a fixed number, and T is steering torque.
VT1 = VT11−VT21 + V0 = k11 · T − (− k21 · T) = (k11 + k21) T (1) Expression VT2 = VT12−VT22 + V0 = k12 · T − (− k22 · T) = (k12 + k22) T (2) In other words, the intermediate voltage VT1 is located at the third position from the top, arranged opposite to the first magnetostrictive film 31 and located at the uppermost position of the first detection coil 33 and the second magnetostrictive film 32. This is an intermediate voltage (intermediate output) of the third detection coil 35. Further, the intermediate voltage VT2 is generated between the second detection coil 34 that is disposed opposite to the first magnetostrictive film 31 and located second from the top, and the fourth detection coil 36 that is disposed opposite to the second magnetostrictive film 32 and located at the lowest position. Intermediate voltage (intermediate output).

Next, an added value of the intermediate voltage VT1 and the intermediate voltage VT2 is obtained and used as a failure detection voltage VTF (see equation (3)).
VTF = VT1 + VT2 (3) Equation (3) In this way, by adding the intermediate voltage VT1 and VT2 to the failure detection voltage VTF, accurate failure detection is performed even when the temperature of the entire steering shaft 1 changes uniformly. be able to.

  By the way, since the steering gear box 20 is disposed in the engine room, the temperature of the steering gear box 20 may increase due to heat from the engine depending on the driving state of the vehicle. For example, when the vehicle is stopped after traveling at a high speed, the steering gear box 20 is heated by the heat of the engine and the steering shaft 1 is heated. However, the temperature distribution of the steering shaft 1 is not uniform and is close to the engine. The temperature on the side is higher than the temperature on the upper side far from the engine. Therefore, also in the part where the magnetostrictive torque sensor 30 is installed, the temperature of the part where the lowermost fourth detection coil 36 is arranged becomes high, and the part where the uppermost first detection coil 33 is arranged. And the temperature of the portion where the second and third detection coils 34 and 35 are arranged is substantially the same at an intermediate temperature (that is, an intermediate temperature).

When the temperature difference (temperature gradient) is generated in the steering shaft 1 as described above, the failure detection signal drifts due to the temperature difference (temperature gradient) as described above. There was a risk of false detection.
On the other hand, in the magnetostrictive torque sensor 30 of this embodiment, even when a temperature difference (temperature gradient) occurs in the steering shaft 1, it is possible to prevent a failure detection signal from drifting. Detection accuracy can be increased. This will be described below with reference to the detection principle diagram of FIG.

  The magnetostrictive film has a temperature characteristic that the permeability μ increases as the temperature increases. Therefore, as described above, the portion where the uppermost first detection coil 33 is disposed is low temperature, the portion where the intermediate second and third detection coils 34 and 35 are disposed is medium temperature, and the lowermost first detection coil 33 is disposed. When the portion where the four detection coils 36 are disposed is at a high temperature, the permeability μ1 of the portion facing the first detection coil 33 in the first magnetostrictive film 31 is small, and the fourth magnetostrictive film 32 is the fourth in the second magnetostrictive film 32. The portion of the first magnetostrictive film 31 facing the second detection coil 34 and the portion of the first magnetostrictive film 31 facing the second detection coil 34 and the portion of the second magnetostrictive film 32 facing the third detection coil 35 are large. The magnetic permeability μ3 is approximately larger than μ1 and smaller than μ4 (μ1 <μ2 (μ3) <μ4).

  Further, it is known that the magnetic permeability μ of the magnetostrictive film and the impedance Z of the detection coil are in a substantially proportional relationship (μ∝Z). Therefore, when there is a temperature gradient as described above, the impedance Z1 of the first detection coil 33 is small, the impedance Z4 of the fourth detection coil 36 is large, and the impedances Z2 and Z3 of the second detection coil 34 and the third detection coil 35 are between them. (Z1 <Z2 (Z3) <Z4).

When the excitation voltage applied to the detection coils 33 to 36 is Vcc, the voltage VS1 at the midpoint between the first detection coil 33 and the third detection coil 35, and the midpoint between the second detection coil 34 and the fourth detection coil 36, respectively. The voltage VS2 is a divided voltage value between the coils, and is expressed by the following equations (4) and (5).
VS1 = Vcc × {(Z3 / (Z1 + Z3)} = Vcc × [1 / {(Z1 / Z3) +1}] (4) Formula VS2 = Vcc × {(Z2 / (Z2 + Z4)} = Vcc × [ 1 / {(Z4 / Z2) +1}] (5)

As a result, the sum of the midpoint voltage VS1 of the first detection coil 33 and the third detection coil 35 and the midpoint voltage VS2 of the second detection coil 34 and the fourth detection coil 36 is made substantially constant (for example, 5 V). Therefore, as described above, the drift of the failure detection signal due to the temperature gradient can be eliminated.
As a result, a constant failure detection signal can be obtained even when a temperature gradient occurs in the steering shaft 1, so that the failure detection range can be set narrower than before, and failure detection accuracy is improved. Can be made.

Next, a specific numerical value is given and the difference with a prior art is verified.
Now, when the detection coils 33 to 36 are excited with a rectangular wave voltage of 30 kHz, a temperature gradient is generated in the steering shaft 1, and the impedances Z1 to Z4 of the detection coils 33 to 36 are Z1 = 900Ω, Z2 = 950Ω, Assume that Z3 = 1000Ω and Z4 = 1050Ω.
In the above-described conventional magnetostrictive torque sensor, the sum of the intermediate voltage VT1 ′ between the first detection coil 33 and the fourth detection coil 36 and the intermediate voltage VT2 ′ between the second detection coil 34 and the third detection coil 35 fails. Since the detection signal VTF ′ is used (VTF ′ = VT1 ′ + VT2 ′) and failure detection is performed based on the failure detection signal VTF ′, the midpoint voltage VS1 ′ of the first detection coil 33 and the fourth detection coil 36, second The midpoint voltage VS2 ′ of the detection coil 34 and the third detection coil 35 affects the failure detection signal VTF ′.

Here, when the excitation voltage applied to the detection coils 33 to 36 is Vcc, VS1 ′ and VS2 ′ are expressed by the following equations (6) and (7).
VS1 ′ = Vcc × {(Z4 / (Z1 + Z4)} = Vcc × [1 / {(Z1 / Z4) +1}] (6) Expression VS2 ′ = Vcc × {(Z3 / (Z2 + Z3)} = Vcc × [1 / {(Z2 / Z3) +1}] (7) Equation VS1 ′ and VS2 ′ are calculated by substituting the impedances Z1 to Z4 of the detection coils 33 to 36 with the excitation voltage Vcc being 5 V. The failure detection signal VTF ′ is calculated as follows.
VS1 ′ = 2.692308 (V),
VS2 ′ = 2.564102 (V),
VTF ′ = VS1 ′ + VS2 ′ = 5.225641 (V).

  On the other hand, in the magnetostrictive torque sensor 30 in this embodiment, the intermediate voltage VT1 between the first detection coil 33 and the third detection coil 35 and the intermediate voltage VT2 between the second detection coil 34 and the fourth detection coil 36 are obtained. The added value is set as a failure detection signal VTF (VTF = VT1 + VT2), and failure detection is performed based on this failure detection signal VTF. The midpoint voltage VS2 of the fourth detection coil 36 affects the failure detection signal VTF.

Under the same conditions, the midpoint voltages VS1 and VS2 are calculated from the equations (4) and (5), and the failure detection signal VTF is calculated as follows.
VS1 = 2.631579 (V),
VS2 = 2.375000 (V),
VTF = VS1 + VS2 = 5.5006579 (V).
Therefore, if the normal detection range of the failure detection signal is 5V ± α, the failure detection signal VTF of the magnetostrictive torque sensor 30 of the embodiment is much more α than the failure detection signal VTF ′ of the conventional magnetostrictive torque sensor. The value of can be reduced. Thereby, even if the margin of the failure detection range is reduced, there is no possibility of erroneous detection, and the failure detection accuracy can be improved.

[Other Examples]
The present invention is not limited to the embodiment described above.
For example, the first magnetostrictive film 31 is divided into two in the axial direction of the pinion shaft 5, one of which is a magnetostrictive film dedicated to the first detection coil 33 and the other is a magnetostrictive film dedicated to the second detection coil 34. The magnetostrictive film 32 is divided into two in the axial direction of the pinion shaft 5, one of which is a magnetostrictive film dedicated to the third detection coil 35 and the other is a magnetostrictive film dedicated to the second detection coil 36. It is also possible to do.

1 is a schematic configuration diagram of a vehicular electric power steering apparatus including a magnetostrictive torque sensor according to the present invention. It is the schematic of the detection circuit of the said magnetostrictive torque sensor. It is a figure explaining the detection principle of the conventional magnetostrictive torque sensor. It is the schematic of the detection circuit of the conventional magnetostrictive torque sensor.

Explanation of symbols

1 Steering shaft 2 Handle (operator)
7 Pinion (gear mechanism)
8a Rack teeth (gear mechanism)
20 steering gear box 30 magnetostrictive torque sensor 31 first magnetostrictive film 32 second magnetostrictive film 33 first detection coil 34 second detection coil 35 third detection coil 36 fourth detection coil

Claims (1)

A first magnetostrictive film and a second magnetostrictive film are provided on a steering shaft connected to a gear mechanism housed in a steering gear box in an engine room and connected to an operating element on the upper side, to change the magnetic characteristics of these magnetostrictive films. A magnetostrictive torque sensor for a vehicle that detects torque input to the steering shaft based on the torque,
A first detection coil and a second detection coil disposed opposite to the first magnetostrictive film, and a third detection coil and a fourth detection coil disposed opposite to the second magnetostrictive film,
The first detection coil, the second detection coil, the third detection coil, and the fourth detection coil are arranged in order from the operator .
A magnetostrictive torque sensor for a vehicle that detects a sensor abnormality based on an added value of an intermediate output between the first detection coil and the third detection coil and an intermediate output between the second detection coil and the fourth detection coil. There,
By connecting one end of the first detection coil and one end of the third detection coil, the first detection coil and the third detection coil are connected in series,
By connecting one end of the second detection coil and one end of the fourth detection coil, the second detection coil and the fourth detection coil are connected in series,
The first detection coil and the third detection coil connected in series are connected in parallel with the second detection coil and the fourth detection coil connected in series,
The other end of the first detection coil and the other end of the fourth detection coil are connected;
The other end of the second detection coil and the other end of the third detection coil are connected,
A magnetostrictive torque sensor for a vehicle , wherein the first detection coil, the second detection coil, the third detection coil, and the fourth detection coil are excited by a rectangular wave voltage.

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