JP2006064446A - Magnetostrictive type torque sensor, and motor-driven steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent troubles in a magnetostrictive type sensor from being misdetected. <P>SOLUTION: In this magnetostrictive type sensor 30 mounted on a vehicle to detect torque, based on the change in the magnetic characteristics caused by magnetostriction, an output from the magnetostrictive type sensor 30 is invalidated, when an operation of actuator for making a prescribed magnetic field change generated is detected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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.

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. The magnetostrictive torque sensor is used for detecting steering torque of a vehicle steering device (see Patent Document 1).
This type of magnetostrictive torque sensor includes two magnetostrictive films having different magnetic anisotropies provided on a rotating shaft and a detection coil arranged opposite to each magnetostrictive film ( Patent Document 2). The principle of the magnetostrictive torque sensor is that when the torque is applied to the rotating shaft, the magnetic permeability of the magnetostrictive film changes, and the inductance of the detection coil changes accordingly, and the torque is detected based on this change.

By the way, when this type of magnetostrictive torque sensor is used, it is necessary to detect a failure of the torque sensor when detecting the torque.
In the case of the magnetostrictive torque sensor having the two magnetostrictive films described above, when detecting torque, the detection output of one detection coil (hereinafter referred to as the first detection output VT1) and the detection output of the other detection coil ( Hereinafter, the torque detection output VT3 is calculated based on the difference between the second detection output VT2 and when detecting a failure, the failure detection output VTF is calculated based on the sum of the first detection output VT1 and the second detection output VT2. The failure is detected from the comparison with the threshold value.

3 is an output characteristic diagram when the torque detection output VT3 is calculated based on the equation (1), and FIG. 5 is an output characteristic diagram when the failure detection output VTF is calculated based on the equation (2). . In equations (1) and (2), k, V0, and C are constants.
VT3 = k · (VT1-VT2) + V0 (1) Formula VTF = | VT1 + VT2 | −C (2)
JP 2002-316658 A JP 59-164932 A

By the way, when the above-described magnetostrictive torque sensor is mounted on a vehicle and used, for example, when a magnet is installed on the road surface or when an actuator such as a starter motor is activated with a large current, When the magnetic field change occurs, the first detection output VT1 and the second detection output VT2 change, and the torque detection output VT3 may change.
Further, when the first detection output VT1 and the second detection output VT2 change as indicated by the dotted line in FIG. 3 due to the magnetic field change, the torque detection output VT3 is a differential between the first detection output VT1 and the second detection output VT2. Since it is an output, it is hardly affected by changes in the magnetic field. In such a case, the torque detection output VT3 becomes a correct value even if the magnetic field changes.

However, since the failure detection output VTF is a sum output of the first detection output VT1 and the second detection output VT2, the first detection output VT1 and the second detection output VT2 are indicated by dotted lines in FIG. When the change occurs, the failure detection output VTF is also affected by the change in the magnetic field. In some cases, as shown in FIGS. 4 and 5, the failure detection output VTF deviates from the failure detection threshold, and the torque sensor is normal. Nevertheless, it may be considered a failure.
Accordingly, the present invention provides a magnetostrictive torque sensor capable of preventing erroneous detection and an electric steering device capable of preventing deterioration of steering feeling.

In order to solve the above-described problem, the invention according to claim 1 is a magnetostrictive torque sensor (for example, a magnetostrictive type in an embodiment described later) that is mounted on a vehicle and detects torque based on a change in magnetic characteristics caused by magnetostriction. The magnetostrictive torque sensor 30) is characterized in that a part or all of its output is invalidated when detecting or estimating the operation of an actuator that generates a predetermined magnetic field change.
With this configuration, it is possible to prevent the magnetostrictive torque sensor from being erroneously detected due to a change in the magnetic field when the actuator is operated.

The invention according to claim 2 is a magnetostrictive torque sensor (for example, a magnetostrictive torque sensor 30 in an embodiment described later) that is mounted on a vehicle and detects torque based on a change in magnetic characteristics caused by magnetostriction. A magnetic field change detecting means for detecting or estimating the magnetic field change (for example, a magnetic field change detecting means 41 in the embodiment described later), and when the magnitude of the magnetic field change detected by the magnetic field change detecting means is a predetermined value or more, The magnetostrictive torque sensor is characterized in that part or all of the output is invalidated.
With this configuration, it is possible to prevent the magnetostrictive torque sensor from being erroneously detected due to a change in the magnetic field as well as when the actuator is operated.

The invention according to claim 3 is an electric steering device (for example, in an embodiment described later) that detects steering torque by a magnetostrictive torque sensor and drives the motor by a target current corresponding to the detected steering torque to steer the vehicle. In the electric power steering apparatus 100), the magnetostrictive torque sensor is a magnetostrictive torque sensor according to claim 1 or 2 (for example, a magnetostrictive torque sensor 30 in an embodiment described later).
With this configuration, even if the magnetostrictive torque sensor for detecting the steering torque of the electric steering device is normal but erroneously detected due to a change in the magnetic field, the adverse effect on steering is prevented. can do.

In the invention according to claim 4, the steering torque is detected by a magnetostrictive torque sensor (for example, a magnetostrictive torque sensor 30 in an embodiment described later), and the motor is driven by a target current corresponding to the detected steering torque. In an electric steering apparatus for turning (for example, an electric power steering apparatus 100 in an embodiment to be described later), the target current is reduced when an operation of an actuator that generates a predetermined magnetic field change is detected or estimated.
With such a configuration, the auxiliary steering force can be reduced when the steering torque detected by the magnetostrictive torque sensor is affected by the change in the magnetic field when the actuator is operated.

In the invention according to claim 5, the steering torque is detected by a magnetostrictive torque sensor (for example, a magnetostrictive torque sensor 30 in an embodiment to be described later), and the motor is driven by a target current corresponding to the detected steering torque. The electric steering apparatus to be steered (for example, the electric power steering apparatus 100 in the embodiment described later) includes magnetic field change detection means for detecting or estimating a magnetic field change, and the magnitude of the magnetic field change detected by the magnetic field change detection means. When the value is equal to or greater than a predetermined value, the target current is reduced.
With this configuration, the auxiliary steering force can be reduced when the steering torque detected by the magnetostrictive torque sensor is affected by the change in the magnetic field.

According to the sixth aspect of the present invention, the steering torque is detected by a magnetostrictive torque sensor (for example, a magnetostrictive torque sensor 30 in an embodiment described later), and the motor is driven by a target current corresponding to the detected steering torque. An electric steering apparatus for turning (for example, an electric power steering apparatus 100 in an embodiment described later) includes activation detection means for detecting or estimating the activation of the power of the vehicle, and the activation of the power is detected by the detection means. The target current is reduced or reduced to zero.
With this configuration, the auxiliary steering force can be reduced when the steering torque detected by the magnetostrictive torque sensor is affected by the change in the magnetic field.

According to the first aspect of the present invention, it is possible to prevent the magnetostrictive torque sensor from being erroneously detected due to a change in the magnetic field when the actuator is operated, and as a result, the reliability of the magnetostrictive torque sensor is improved.
According to the second aspect of the invention, it is possible to prevent the magnetostrictive torque sensor from erroneously detecting not only when the actuator is operated but also due to a change in the magnetic field. As a result, the reliability of the magnetostrictive torque sensor is improved. improves.

According to the third aspect of the invention, the magnetostrictive torque sensor for detecting the steering torque of the electric steering device can be prevented from being erroneously detected due to a change in the magnetic field even though it is normal. The reliability of the electric steering device is improved.
According to the fourth aspect of the invention, even when the steering torque detected by the magnetostrictive torque sensor is affected by the change in the magnetic field when the actuator is operated, the auxiliary steering force is reduced to steer the influence of the false detection. Fail-safe that is not given to the system can be realized, and deterioration of the steering feeling can be prevented.
According to the fifth aspect of the present invention, even when the steering torque detected by the magnetostrictive torque sensor is affected by the change in the magnetic field, the auxiliary steering force is reduced and the influence of erroneous detection is not given to the steering system. Fail safe can be realized, and deterioration of steering feeling can be prevented.

  According to the sixth aspect of the present invention, the auxiliary steering force is reduced even when the steering torque detected by the magnetostrictive torque sensor is affected by a magnetic field change by an actuator such as a starter motor when the vehicle power is started. Or since it does not act, the fail safe which does not give the influence of a misdetection to a steering system can be implement | achieved, and the deterioration of steering feeling can be prevented. Also, when the power of the vehicle is started, for example, in the case of an engine, a signal from a generator installed in itself can be used, and in the case of an electric motor (electric vehicle), a signal from the electric motor can be used. It is not necessary to use a new sensor.

Embodiments of a magnetostrictive torque sensor according to the present invention and an electric steering apparatus having the same will be described below with reference to the drawings of FIGS.
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 configured 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 a rack 8 a of a 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. ing. 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 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.
The magnetostrictive torque sensor 30 includes two magnetostrictive films 31 and 32 that are annularly provided on the outer peripheral surface of the pinion shaft 5 over the entire circumferential direction, and a first detection coil that is disposed opposite to the magnetostrictive films 31 and 32. 33, the second detection coil 34, and detection circuits 35 and 36 connected to the first detection coil 33 and the second detection coil 34, respectively, are the main components.
The magnetostrictive films 31 and 32 are metal films made of a material having a large change in magnetic permeability with respect to the change in strain. For example, the magnetostrictive films 31 and 32 are made of a Ni—Fe alloy film formed on the outer periphery of the pinion shaft 5 by a plating method.

One magnetostrictive film 31 is configured to have a magnetic anisotropy in a direction inclined by about 45 degrees with respect to the axis of the pinion shaft 5, and the other magnetostrictive film 32 is a magnetic anisotropy of the magnetostrictive film 31. The magnetic anisotropy is provided in a direction inclined by about 90 degrees with respect to the direction of. 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 is coaxially arranged around the magnetostrictive film 31 with a predetermined gap therebetween, and the second detection coil 34 has a predetermined gap around the magnetostrictive film 32. It is arranged coaxially in the state.

By setting the magnetic anisotropy of the magnetostrictive films 31 and 32 as described above, a compressive force is applied to one of the magnetostrictive films 31 and 32 in the principal stress direction even when no torque is applied to the pinion shaft 5. However, the magnetic permeability of the magnetostrictive films 31 and 32 is set to be approximately equal. In a state where torque is applied to the pinion shaft 5, the magnetic permeability of one magnetostrictive film increases and the magnetic permeability of the other magnetostrictive film decreases. In response to this, one inductance of the detection coils 33 and 34 increases and the other inductance decreases.
The first detection coil 33 is connected to a detection circuit 35 having a conversion circuit, and the second detection coil 34 is connected to a detection circuit 36 having a conversion circuit. The inductance change 34 is converted into a voltage change and output to an electronic control unit (ECU) 50.

As shown in FIG. 2, the ECU 50 detects the torque acting on the pinion shaft 5 and detects the failure of the magnetostrictive torque sensor 30 based on the output voltages from the detection circuits 35 and 36.
Here, the torque detection voltage VT3 and the failure detection voltage VTF are based on the equations (3) and (4) when the output voltage from the detection circuit 35 is VT1 and the output voltage from the detection circuit 36 is VT2. calculate. In equations (3) and (4), k, V0, and C are constants.
VT3 = k · (VT1−VT2) + V0 (3) Expression VTF = | VT1 + VT2 | −C (4) Then, the ECU 50 sets the target of the electric motor 11 according to the detected torque detection voltage VT3. The electric current is set, the electric motor 11 is driven by the target current to generate an auxiliary steering force, and the vehicle is steered. Further, the ECU 50 determines that the magnetostrictive torque sensor 30 is in failure when the failure detection output VTF exceeds a predetermined threshold A.

By the way, in general, vehicles equipped with the electric power steering device 100 are also equipped with actuators such as a starter motor, a power window device, a lighting device, a rear defroster device, a blower motor, and a wiper device (all not shown). When the magnetic field changes when these actuators are activated, the output voltages VT1 and VT2 of the detection circuits 35 and 36 change.
As described above, when the output voltages VT1 and VT2 change due to the magnetic field change, the torque detection voltage VT3 may be erroneously detected as described above. In addition, since the torque detection voltage VT3 is a differential output of the output voltages VT1 and VT2, the failure detection voltage VTF is output even when the torque detection voltage VT3 is almost correct without being affected by the change in the magnetic field. Since it is a combined output of the voltages VT1 and VT2, it is affected by a change in the magnetic field. In some cases, the failure detection voltage VTF deviates from the failure detection threshold as shown by the dotted line in FIG. Although it is normal, there is a risk of being determined as a failure.

  Therefore, in the first embodiment, as shown in FIG. 1, an actuator operation detecting means 40 for detecting or estimating the operation of an actuator that causes a magnetic field change such as a starter motor is provided, and the detection signal is output to the ECU 50. When the actuator operation detecting means 40 detects or estimates the operation of the actuator, the ECU 50 invalidates part or all of the output of the magnetostrictive torque sensor 30. As a result, it is possible to prevent the torque detection voltage VT3 from being erroneously detected due to a change in the magnetic field when the actuator is operated, or the magnetostrictive torque sensor 30 from being erroneously detected as a failure. The reliability of the torque sensor 30 is improved, and consequently the reliability of the electric power steering device is improved. The actuator operation detection means 40 detects an ON signal of a switch used for an operation command of an actuator such as a corresponding starter motor, power window device, illumination device, rear defroster device, blower motor, wiper device, or the like. However, for an automatic operation device such as an automatic wiper device, the operation is estimated from the operation command signal of the control device.

Here, “invalidate part or all of the output of the magnetostrictive torque sensor 30” means that the failure detection voltage VTF is invalidated but the torque detection voltage VT3 is not invalidated, or the torque detection voltage VT3 and the failure It means that the detection voltage VTF is invalidated and the detection voltages VT3 and VTF are not used as control signals.
More specifically, among the actuators, power window devices, lighting devices, rear defroster devices, blower motors, wiper devices, etc. that have a relatively small operating current (less than several tens of amperes) and a small magnetic effect are the failure detection voltage VTF. Although the torque detection voltage VT3 is not invalidated, the control continues as usual, and the torque detection voltage VT3 and the failure detection voltage VTF are invalidated for a large current (several hundred amps) such as a starter motor. Thus, the detection voltages VT3 and VTF are not used as control signals.
By setting in this way, it is possible to prevent the magnetostrictive torque sensor from being erroneously detected due to a change in the magnetic field when the actuator is operated, and as a result, the reliability of the magnetostrictive torque sensor is improved.

In the second embodiment, when the actuator operation detecting means 40 detects or estimates the operation of the actuator, the ECU 50 invalidates the failure detection voltage VTF, but sets the output voltages VT1 and VT2 of the detection circuits 35 and 36 to be invalid. Based on the calculation of the torque detection voltage VT3, the target current of the motor 11 is reduced below the target current value corresponding to the torque detection voltage VT3 while the actuator is detected to drive the motor 11. I tried to do it.
As a result, not only can the auxiliary steering force be reduced and the influence on the steering can be reduced when the torque detection voltage VT3 is affected by the change in the magnetic field due to the actuator operation of the auto cruise device that operates at high speed, but also the steering auxiliary force is reduced A firm feeling of steering force can be given. Further, it is possible to realize a fail safe that can reduce the influence on the steering even when affected by the change of the magnetic field, and it is possible to prevent the steering feeling from deteriorating.

Further, in the third embodiment, instead of providing the actuator operation detection means 40, as shown by a broken line in FIG. 1, a magnetic field change is detected in the vicinity of the electric power steering device 100 (preferably in the vicinity of the magnetostrictive torque sensor 30). The magnetic field change detecting means 41 is provided to output the detection signal to the ECU 50. When the detected value or the estimated value (that is, the magnitude of the magnetic field change) of the magnetic field change detecting means 41 is a predetermined value or more, the ECU 50 In this case, part or all of the output of the magnetostrictive torque sensor 30 is invalidated. Although this magnetic field change detecting means 41 is not shown, for example, a multiple winding coil is separately provided in the magnetostrictive torque sensor 30 to directly detect the magnetic field change, or an element such as a Hall element or multiple winding coil is magnetostrictive. A magnetic field change that is provided in the vicinity of the torque sensor 30 and that affects the magnetostrictive torque sensor 30 is indirectly estimated.
This prevents the torque detection voltage VT3 from being erroneously detected due to a change in the magnetic field on the road or outside, not only during the operation of the actuator, or from erroneously detecting that the magnetostrictive torque sensor 30 is faulty. As a result, the reliability of the magnetostrictive torque sensor 30 is improved, and as a result, the reliability of the electric power steering device is improved. The meaning of “invalidate part or all of the output of the magnetostrictive torque sensor 30” is the same as in the first embodiment.

  In the fourth embodiment, when the detected value or estimated value of the magnetic field change detecting means 41 (that is, the magnitude of the magnetic field change) is equal to or greater than a predetermined value, the ECU 50 invalidates the failure detection voltage VTF, but each detection circuit Calculation of the torque detection voltage VT3 is executed based on the output voltages VT1 and VT2 of 35 and 36, and the target current of the motor 11 is set to the target corresponding to the torque detection voltage VT3 while the magnitude of the magnetic field change is equal to or greater than a predetermined value. The electric motor 11 is driven by reducing the current value. As a result, even when the torque detection voltage VT3 is affected by a magnetic field change, not only can the auxiliary steering force be reduced to reduce the influence on the steering, but also a firm sense of steering force can be imparted by the reduction of the steering auxiliary force. . Further, it is possible to realize a fail safe that can reduce the influence on the steering even when affected by the change of the magnetic field, and it is possible to prevent the steering feeling from deteriorating.

Further, the fifth embodiment includes activation detection means for detecting or estimating the activation of the power of the vehicle based on the number of revolutions of the generator, and the target current is reduced or zero when detected by this detection means.
As a result, even if the starter motor or other actuator is affected by changes in the magnetic field when the vehicle power is started, the auxiliary steering force is not reduced or acted on, so a fail-safe operation that does not affect the steering system is realized. It is possible to prevent the steering feeling from deteriorating. Also, when the power of the vehicle is started, for example, in the case of an engine, a signal from a generator installed in itself can be used, and in the case of an electric motor (electric vehicle), a signal from the electric motor can be used. It is not necessary to use a new sensor.

[Other Examples]
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 steering apparatus for a vehicle 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 a schematic configuration diagram of a vehicular electric power steering apparatus including a magnetostrictive torque sensor according to the present invention. It is a figure explaining the torque detection and failure detection by a magnetostrictive torque sensor. It is an output characteristic view of a magnetostrictive torque sensor at the time of torque detection. It is a figure which shows an example of the output change of the magnetostrictive torque sensor at the time of a magnetic field change. It is an output characteristic figure of a magnetostriction type torque sensor at the time of failure detection.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Electric motor 30 Magnetostrictive torque sensor 41 Magnetic field change detection means 100 Electric power steering apparatus (electric steering apparatus)

Claims (6)

A magnetostrictive torque sensor that is mounted on a vehicle and detects torque based on a change in magnetic characteristics caused by magnetostriction,
A magnetostrictive torque sensor characterized by invalidating part or all of its output when detecting or estimating an operation of an actuator that generates a predetermined magnetic field change. A magnetostrictive torque sensor that is mounted on a vehicle and detects torque based on a change in magnetic characteristics caused by magnetostriction,
Magnetic field change detecting means for detecting or estimating the magnetic field change,
A magnetostrictive torque sensor, wherein a part or all of its output is invalidated when the magnitude of the magnetic field change detected by the magnetic field change detecting means is a predetermined value or more. In the electric steering device for detecting the steering torque by a magnetostrictive torque sensor and driving the electric motor with a target current corresponding 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. In the electric steering device for detecting the steering torque by a magnetostrictive torque sensor and driving the electric motor with a target current corresponding to the detected steering torque to steer the vehicle,
An electric steering apparatus characterized in that the target current is reduced when an operation of an actuator that generates a predetermined magnetic field change is detected or estimated. In the electric steering device for detecting the steering torque by a magnetostrictive torque sensor and driving the electric motor with a target current corresponding to the detected steering torque to steer the vehicle,
Magnetic field change detecting means for detecting or estimating the magnetic field change,
The electric steering apparatus according to claim 1, wherein the target current is reduced when the magnitude of the magnetic field change detected by the magnetic field change detection means is a predetermined value or more. In the electric steering device for detecting the steering torque by a magnetostrictive torque sensor and driving the electric motor with a target current corresponding to the detected steering torque to steer the vehicle,
An activation detection means for detecting or estimating the activation of the power of the vehicle;
The electric steering apparatus according to claim 1, wherein the target current is reduced or made zero when the detection means detects the activation of the power.

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