JPH01187425A - Torque sensor for steering shaft - Google Patents

Abstract

PURPOSE:To enable accurate torque detection even if a horn driving current flows through the steering shaft axially by removing a noise signal component according to the difference between the frequency of the noise signal component generated with the horn driving signal and the frequency of a torque signal. CONSTITUTION:Amorphous magnetic metal zones 31 and 32 are fixed on the steering shaft, and coils 39 and 40 arranged nearby them without contacting the steering shaft output torque signals of the steering shaft based upon a turning force. At this time, the coils 39 and 40 vary in impedance with a magnetic field HI produced with the horn driving current I flowing through the steering shaft and the variation is the noise signal component which is harmful to the torque detection. This is extracted by a high-pass filter and a rectifying circuit and removed from an original signal by a subtracting circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a torque sensor for a steering shaft that detects the torque of a steering shaft using magnetostrictive effects.

(Prior Art) As is well known, there are various types of torque sensors that detect shaft torque. Among these are torque sensors that utilize the magnetostrictive effect of amorphous magnetic metal materials. A typical torque sensor that utilizes the magnetostrictive effect of an amorphous magnetic metal material is made of an amorphous magnetic metal with a large magnetostrictive effect on the outer peripheral surface of the shaft, as disclosed in Japanese Patent Publication No. 62-28413. In addition to fixing the band, a coil is arranged near the metal band without contacting the shaft, and the coil impedance changes and induction caused by the change in magnetic permeability of the amorphous magnetic metal band caused by the rotational force applied to the shaft. Shaft torque is detected from voltage changes. This type of torque sensor can detect torque without contacting the shaft, can be installed on existing shafts, and can easily detect the direction of torque by selecting an axis that is easy to magnetize with an amorphous magnetic metal strip. It does not require any processing that weakens the mechanical strength of the shaft.

It has features such as not restricting the shaft constituent materials and being less affected by temperature changes.

By the way, torque sensors that utilize the magnetostrictive effect of amorphous magnetic metal materials have various advantages over other torque sensors as described above, so they can be used not only for machine tools and robots, but also for applications such as machine tools and robots. It is conceivable that it could be used as a torque sensor for power steering devices that are mounted on automobiles and exposed to harsh conditions.

However, when trying to use a torque sensor that utilizes the magnetostrictive effect of an amorphous magnetic metal material as a torque sensor for a power steering device of an automobile or the like, the following problems arise. That is, the position where the torque sensor is provided is necessarily around the steering axis. Generally, a steering wheel is attached to the upper end of the steering shaft, and the steering wheel is provided with a manually operated horn switch. 1. Normally, the steering shaft is used as part of a conductive path constituting a horn drive circuit. Therefore, when the horn switch is operated, a horn drive current of about 5 A flows in the axial direction within the steering shaft. In this way, when a current flows in the axial direction of the steering shaft, a magnetic field is generated in the circumferential direction of the steering shaft.

This magnetic field changes the magnetization state of the amorphous magnetic metal material fixed to the steering shaft. Therefore, when the horn drive current is flowing through the steering shaft, there is a problem in that the shaft torque cannot be accurately detected.

Therefore, it is conceivable to configure the horn drive circuit so that the horn drive current does not flow through the steering shaft, but this would complicate the configuration of the horn drive circuit.

(Problems to be Solved by the Invention) As described above, when a torque sensor that utilizes the magnetostrictive effect of an amorphous magnetic metal material is used as a torque sensor for a power steering device, a problem occurs due to the horn drive current flowing through the steering shaft. There was a problem that accurate torque detection was not possible due to the influence of magnetic fields.

Therefore, the present invention provides a torque sensor for a steering shaft that can accurately detect torque even when a horn drive current flows through the steering shaft, and that can maximize the characteristics of utilizing the magnetostrictive effect of an amorphous magnetic metal material. is intended to provide.

[Structure of the Invention (Means for Solving the Problems) In order to achieve the above objects, 1. In the steering shaft torque sensor of the present invention, the frequency of the noise signal component generated by the horn drive current flowing in the axial direction of the steering shaft is A noise signal removing means is provided for removing the noise signal component based on the difference between the frequency of the torque signal and the frequency of the torque signal.

(Function) Generally, the frequency of the horn drive current flowing through the steering shaft is 30
The frequency is about 0 to 500Hz. On the other hand, the frequency of the torque signal to be detected is from DC to about several tens of Hz. A torque sensor for a steering shaft according to the present invention is a torque sensor for a steering shaft.

This method focuses on the difference in frequency, and removes high-frequency signal components, that is, noise signal components caused by the horn drive current, from the obtained original signal. Therefore, it is possible to output only the torque signal component unrelated to the horn drive current.

(Example) An embodiment will be described below with reference to one drawing.

FIG. 1 schematically shows an example in which a steering shaft torque sensor according to an embodiment is installed around the steering shaft of an automobile.

That is, 1 in FIG. 1 is a metal steering shaft arranged with its axis line obliquely. The steering shaft 1 is rotatably supported via bearings 2 and 3 on a support 4.5 provided in a part of the vehicle body. A steering wheel 6 is attached to the upper end of the steering shaft 1. A movable terminal 8 and a fixed terminal 9 forming a horn switch 7 are attached to the steering wheel 6. The movable terminal 8 is attached via an insulating support 10, and the fixed terminal 9 is attached to the steering shaft 1.
is electrically connected to the upper end of the The movable terminal 8 is connected to a slip ring 12 supported on the steering shaft 1 via an insulating support 11. slip ring 1
2, a sliding piece 14 supported by a support 4 via an insulating support 13 is in sliding liquid contact. And the sliding piece 14 is
It is electrically connected to the vehicle body via a horn 15 and a battery 16. Further, a support body 5 that supports the bearing 3 is also electrically connected to the vehicle body. Therefore, when the horn switch 7 is turned on, the battery 16 - the horn 15 -
A horn drive current flows through the path from the sliding piece 14 to the slip ring 12 to the movable terminal 8 to the fixed terminal 9 to the steering shaft 1 to the support 5 to the vehicle body to the battery 16, causing the horn 15 to sound.

On the other hand, a detection section 22 of a steering shaft torque sensor 21 is arranged around the steering shaft 1 between the bearings 2 and 3, and a signal processing section 23 connected to the detection section 22 is arranged near the detection section 22. It is provided.

The detection section 22 is configured as shown in FIG. That is, 1 in FIG. 1 is the above-mentioned steering shaft.

Amorphous magnetic metal bands 31 and 32 are fixed to the outer peripheral surface of the steering shaft 1 in the circumferential direction at two locations in the axial direction. As the amorphous magnetic metal band 31, one having uniaxial magnetic anisotropy with an axis of easy magnetization in the direction of an angle α with respect to the axial center line of the steering shaft 1 is used. Further, the amorphous magnetic metal band 32 also has uniaxial magnetic anisotropy with its axis of easy magnetization in a direction at an angle -α with respect to the axis of the steering shaft 1.

Around the steering shaft 1, around the part where the amorphous magnetic metal bands 31 and 32 are provided, and around the parts on both sides around the said part, a cylindrical cylinder made of non-magnetic material is arranged to surround the steering shaft 1. A housing 33 having a shape is fixed. Bearings 34 and 35 are inserted between the inner surfaces of both ends of the housing 33 and the steering shaft 1, respectively. In the portion located within the housing 33 between the bearings 34 and 35.

A cylindrical coil bobbin 36 made of non-magnetic material is attached. In the portion facing the amorphous magnetic metal strips 31 and 32 on the outer peripheral surface of the coil bobbin 36.

Grooves 37 and 38 are respectively formed in the circumferential direction.

Inside these grooves 37.38 are coils 39.4 with an equal number of turns.
0 is attached to each. These coils 39.40
The wire ends of the wires are led out of the housing 33.

It is connected to a signal processing section 23 which will be described next. In addition, in FIG. 2, 41 indicates a locking convex portion for holding the coil bobbin 36, 42 indicates a spacer ring, and 43 and 4
4 indicates a stop ring for fixing the inner races of the bearings 34, 35.

On the other hand, the signal processing section 23 is configured as shown in FIG. That is, the above-mentioned coil 39°40 and resistor 4
5.46 constitutes a bridge circuit, and the power input terminal of this bridge circuit is connected to a variable resistor 47.48 for balance adjustment.
It is connected to the output end of the AC oscillator 49 via. Then, the potential between the midpoints of the bridge circuit is input to a differential amplifier 50, and the output of this differential amplifier 50 is introduced to a synchronous detection circuit 51. The synchronous detection circuit 51 includes a reference wave phase setter 5
The output of the differential amplifier 50 is detected and rectified based on the second output phase. After the output of the synchronous detection circuit 51 is smoothed by a filter circuit 53, it is introduced into one input terminal of a subtraction circuit 54 on one side, and introduced into a bypass filter 55 on the other side. The bypass filter 55 has a cutoff frequency set to a value lower than the frequency of the horn current. The high frequency component signal that has passed through the bypass filter 55 is rectified by a rectifier circuit 56 and then introduced into the other input terminal of the subtractor circuit 54 . The subtraction circuit 54 outputs a signal obtained by subtracting the output of the rectifier circuit 56 from the output of the filter circuit 53. Then, the output of the subtraction circuit 54 is smoothed by a filter circuit 57,
It is output as a DC torque signal ■o. This torque signal Vo is given as a control signal to a power assist motor (not shown).

Next, the operation of the steering shaft torque sensor configured as described above will be explained.

First, the resistors 47 and 48 are adjusted in advance so that the output amplitude of the differential amplifier 50 is minimized.

As shown in FIG. 2, when a steering torque T is applied to the steering shaft 1, distortion occurs in the amorphous magnetic metal bands 31 and 32 on the steering shaft 1 due to the influence of this torque T. As a result, the magnetic permeability of the amorphous magnetic metal bands 31 and 32 changes due to the magnetostrictive effect.

As mentioned above, the amorphous magnetic metal strips 31 and 32 used have uniaxial magnetic anisotropy with easy magnetization axes in the directions at angles α and -α with respect to the axis of the steering shaft 1. ing.

When α is approximately 45 degrees, the axis of easy magnetization is in the same direction as the direction of surface stress generated on the steering shaft 1 by the steering torque T. Therefore, as shown in FIG. 2, when the steering torque T is applied, tensile stress is applied to the amorphous magnetic metal band 31, compressive stress is applied to the amorphous magnetic metal band 32, and magnetostrictive The effect occurs efficiently and the amorphous magnetic metal strip 3
1 increases, and the magnetic permeability of the amorphous magnetic metal strip 32 decreases. With this change in magnetic permeability, the coils 39, 40
impedance changes. Therefore, the output vo of the signal processing section 23 changes depending on the magnitude and direction of the steering torque T. This output V.

is used as a control signal for the power assist motor.

By the way, in such a state, the horn switch 7
When turned on, a horn drive current (2) flows in the axial direction of the steering shaft 1 as shown by the solid line arrow in FIG. As a result,
A magnetic field H is generated around the steering shaft 1, as shown by the solid line arrow in FIG. This magnetic field H1 is applied to the amorphous magnetic metal strip 31.
32, the magnetization state of the amorphous magnetic metal strips 31.32 changes, with the result that the coil 39. '40 impedance changes. In other words, the AC impedance of the coils 39 and 40 changes depending on the horn drive current. This relationship will be explained in detail as follows.

That is, FIG. 4 shows the structure of the magnetic field and magnetization acting on the amorphous magnetic metal strips 31 and 32.

The magnetic field H generated by the horn drive current I is applied to the amorphous magnetic metal strips 31 and 32 in the same direction. On the other hand, the magnetic field HP 1 + generated in the coil 39.40
HP 2 is applied to the amorphous magnetic metal strips 31, 32 in a perpendicular relationship to the magnetic field H1.

In the figure, the magnetic field HP1. HP2 is amorphous magnetic metal band 31.3
2 is applied in the same direction. Magnetic anisotropy constant Ku1. of amorphous magnetic metal strip 31.32. K
u2 is determined by the composition of the amorphous magnetic metal bands 31 and 32, and is equal if the materials have the same composition. The direction α of the axis of easy magnetization is 0<α ±π/2, but in the case of a torque sensor, it is generally set to π/4 in accordance with the stress direction of the axis.

Moreover, spontaneous magnetization Is1. Is2 is an amorphous magnetic metal band 31
．． This is a constant determined by the composition and processing of 32. Also,
The magnetic energy E1 of the amorphous magnetic metal band 31 is as follows.

El mKul sin” (π bar 01) Is
IHp 1eO8θ1 −I81HIsinθ1 − (1) Similarly, the magnetic energy E2 of the amorphous magnetic metal band 32
teeth.

E2 = Ku2 sin 2(θ2-πc)-Is2H
p2cosθ2 −IS2H1sinθ2 (2). Angle θ1°O2 of spontaneous magnetization IS1+ 182
is the condition 9 where each energy in equations (1) and (2) is minimum.
It is determined by El /a 01=0,9 E2 /aθ2=0.

Magnetic field generated in coil 39.40 HP 1 + HP 2
The magnitude of spontaneous magnetization in the direction of 11. I2 is.

I 1= I s 1eO8θ1 − (
3) I 2 ”” I s2 CO8O2...(
4). The impedance of the coils 39, 40 is proportional to 11+I2, respectively.

As can be seen from equations (1) to (4), 11. I2 is the magnetic field HI generated by the horn drive current flowing through the steering shaft 1.
is a function of Therefore, the impedance of the coils 39 and 40 changes depending on the horn drive current. This change in impedance due to the horn drive current I is harmful to torque detection.

However, in this embodiment, the output of the filter circuit 53 is used as the original signal in the signal processing section 23, and the signal bone, that is, the noise signal component accompanying the horn drive current included in this original signal is sent to the bypass filter 55 and the rectifier circuit. 56, and a subtraction circuit 54 removes noise signal components from the original signal. Therefore, the output vo corresponds only to the steering torque T, and as a result, the torque can be detected without being affected by the horn drive current I flowing through the steering shaft 1.

In addition, the magnetic field HP 1 generated by the coil 39.40
r If the directions of HP 2 are opposite to each other.

K u 1 - K u 2 + HP 1 = HP 2
In Case of.

θ1=02. Therefore, the configuration of the signal processing section 23 shown in FIG. 3 does not detect the noise signal component due to the horn drive current. However, the amorphous magnetic metal strip 31.
It is impossible to make the angles of the easy magnetization axes of coils 39 and 32 completely equal due to the anisotropy imparting process.
Since it is difficult to set 0 to the amorphous magnetic metal strips 31 and 32 under exactly the same conditions, that is, to set HP1=HP2, 1 is usually not θ1-02. Therefore, since there is always an impedance difference between the coils 39 and 40 and the noise signal component due to the horn drive current is detected, it is effective to remove the noise signal component.

Further, in the above-described embodiment, the horn drive current is a direct current, but in the case of an alternating current, the output of the bypass filter 55 may be directly introduced into the subtraction circuit 54 without providing the rectifier circuit 56. Further, although the steering shaft 1 is formed hollow and made of a ferromagnetic material, it may be formed solid or may be formed of a non-magnetic metal material. Furthermore, a separate coil for AC excitation may be provided, and the difference in voltages induced in the coils 39 and 40 may be extracted as an output. Also.

The amorphous magnetic metal strip does not have to be long enough to go around the steering shaft.

[Effects of the Invention] Since the steering shaft torque sensor according to the present invention is configured as described above, it has the following effects.

This is because a means is provided to remove noise signal components generated by the horn drive current flowing through the steering shaft.

Steering torque can be accurately detected regardless of horn drive current, contributing to the realization of a highly reliable power steering device.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of an example in which a torque sensor for a steering shaft according to an embodiment is provided around the steering shaft, Fig. 2 is a longitudinal cross-sectional view of a detection section of the torque sensor, and Fig. 3 is a longitudinal sectional view of the detection section of the same torque sensor. FIG. 4 is a diagram for explaining the influence of the horn drive current on the sensor. 1... Steering shaft, 6... Steering wheel, 7...
...Horn switch, 15...Horn, 16...Battery. 21... Steering shaft torque sensor, 22... Detection section. 23... Signal processing unit, 31.32... Amorphous magnetic metal strip, 33... Housing, 34.35... Bearing,
36...Coil bobbin, 39.40...Coil, 5
0... Differential amplifier, 51... Synchronous detection circuit, 52...
... Reference wave phase setter, 53.57 ... Filter circuit, 54 ... Subtraction circuit, 55 ... Bypass filter. Applicant's agent Patent attorney Takehiko Suzue Figure 1

Claims (1)

[Claims] An amorphous magnetic metal material having a magnetostrictive effect is fixed to the steering shaft, and a plurality of coils are disposed near the amorphous magnetic metal material without contacting the steering shaft, and the rotation applied to the steering shaft is For a steering shaft, the signal corresponding to the impedance or induced voltage of the plurality of coils that changes in accordance with the change in magnetic permeability of the amorphous magnetic metal material caused by force is output as a torque signal of the steering shaft. The torque sensor is characterized by comprising noise signal removing means for removing the noise component signal based on the difference between the frequency of the noise signal component generated by the current flowing in the axial direction of the steering shaft and the frequency of the torque signal. Torque sensor for steering shaft.