JP2004042697A - Steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress offset fluctuation due to fluctuation of positional relation between a target and a magnetic sensor in the direction of tangential line of a target plate. <P>SOLUTION: A steering device is provided with a steering member 30, a steering shaft 3 extending substantially laterally from the steering member 30, the target 20 generating periodic change of magnetic field due to rotation of the steering shaft 3 in a peripheral part, and the magnetic sensors 1A, 1B, 2A, 2B provided at positions at a predetermined interval for the target 20 to generate output corresponding to change of the magnetic field. The magnetic sensors are arranged above or below the steering shaft 3. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a steering device.
[0002]
[Prior art]
2. Description of the Related Art An electric power steering device, which is a kind of a steering device of an automobile, includes a steering member (steering wheel) and a steering shaft extending slightly laterally downward from the steering member, and detects a steering torque applied to the steering member. Then, a steering assist motor is driven based on the detection result, and the rotational power of the motor is transmitted to a steering mechanism to assist the steering.
In this electric power steering device, a torque detecting device is required for detecting the steering torque. The steering torque is a relative angular displacement between the input shaft and the output shaft caused by torsion of the torsion bar when the steering torque is applied to a steering shaft composed of an input shaft and an output shaft connected by a torsion bar (connection shaft). This is done by detecting.
In addition, it is necessary to detect the rotation angle (steering angle) of the input shaft in order to use it for driving control of a steering assist motor, and a rotation angle detecting device is used for such steering angle detection. Sometimes it is done.
[0003]
The applicant has provided a target plate provided with a magnetic target on the steering shaft for torque detection and rotation angle detection, so that the rotation of the steering shaft causes a periodic magnetic field change to occur in the peripheral portion. Conventionally, a technique has been proposed in which a change in the magnetic field is detected in a non-contact manner by a magnetic sensor such as a magnetoresistive element (MR element).
That is, the rotation angle can be detected by detecting a change in the magnetic field as a wave-shaped output by a magnetic sensor, and by providing a magnetic sensor corresponding to a target plate provided on each of the input shaft and the output shaft of the steering shaft. The torque can be detected based on the difference between the rotation angles of the two shafts given as the output difference between the two magnetic sensors.
[0004]
[Problems to be solved by the invention]
When a magnetic sensor detects a magnetic field that changes with the rotation of the steering shaft, the distance (air gap) between the magnetic sensor and the target to be detected must be kept constant to improve the detection accuracy. It is.
That is, the strength of the magnetic field varies depending on the distance from the magnetic pole. If the air gap fluctuates, the sensor gain of the magnetic sensor fluctuates, and the detection accuracy decreases. For example, when the air gap increases, the magnetic field weakens and the output decreases. Conversely, when the air gap decreases, the magnetic field increases and the output increases.
[0005]
However, as shown in FIG. 5, if the positional relationship between the target 100 and the magnetic sensor 101 only changes in the radial direction of the target plate 102 (the direction A in FIG. 5), the change in the sensor output due to the change will not occur. It is only the gain fluctuation, and if it is only the gain fluctuation, it can be reduced by calculation.
On the other hand, when the positional relationship between the target and the magnetic sensor fluctuates in the tangential direction of the target plate (B direction in FIG. 5), not only gain fluctuation but also offset fluctuation (middle point fluctuation) of the output waveform is accompanied. Even if the calculation for reducing the gain variation as described above is performed, it is not possible to reduce the offset variation.
[0006]
The present invention has been made in view of such a problem, and an object thereof is to suppress an offset fluctuation due to a change in a positional relationship between a target and a magnetic sensor in a tangential direction of a target plate.
[0007]
[Means for Solving the Problems]
The present invention provides a steering member, a steering shaft extending substantially laterally from the steering member,
A target that generates a periodic magnetic field change in the peripheral portion by the rotation of the steering shaft; and a magnetic sensor that is provided at a predetermined distance from the target and generates an output according to the magnetic field change. , The magnetic sensor is arranged above or below a steering shaft.
The position fluctuation between the target and the magnetic sensor is often caused by the fluctuation of the steering axis in the steering device, and the main factor of the fluctuation of the steering axis is the leaning of the driver on the steering member. The present invention has been made by paying attention to the fact that the main factor of the steering axis fluctuation is the leaning of the driver. That is, when the driver leans on the steering member, the steering shaft fluctuates from top to bottom. If the magnetic sensor is arranged above or below the steering shaft as in the present invention, the positional relationship between the target and the magnetic sensor only changes in the radial direction, and hardly changes in the tangential direction.
[0008]
Further, it is preferable that the target is formed of gear-shaped projections projecting at substantially equal intervals in the circumferential direction of the steering shaft, and the magnetic sensor is preferably a magnetoresistive element.
Further, it is preferable that a means for detecting the rotation angle of the steering shaft based on the output of the magnetic sensor is provided.
The steering shaft includes an input shaft and an output shaft connected by a connecting shaft, and the target is provided on each of the input shaft and the output shaft, and each of the magnetic sensors provided corresponding to each target. Preferably, there is provided means for detecting the torque applied to the steering shaft based on the output.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing a part of a steering device 1 according to the present invention. As shown in the figure, an input shaft 31 having an upper end connected to a steering member 30 (steering wheel) and an output shaft 32 having a lower end connected to a pinion 33 forming a part of a steering mechanism are connected to a small-diameter torsion bar 34 ( A steering shaft 3 is connected coaxially via a connection shaft) and communicates the steering member 30 with a steering mechanism.
A rotation angle detection device and a torque detection device are provided near the connection between the input shaft 31 and the output shaft 32. The rotation angle detection device and the torque detection device are configured as follows.
[0010]
A disk-shaped target plate 2 made of a magnetic material is externally coaxially fixed to the input shaft 31 near the end on the connection side with the output shaft 32. As shown, the target plate 2 is formed in a gear shape in which the distance between the outer periphery 20 of the target plate 2 and the input shaft 31 changes as the target plate 2 rotates.
The similar target plate 2 is also fitted and fixed near an end of the output shaft 32 connected to the input shaft 31. The target plate 2 is connected to the outer periphery 20 and the output shaft 32 as the target plate 2 rotates. Are formed in a gear shape in which the distance varies. The positions of the teeth of the target plate 2 of the output shaft 32 and the target plate 2 of the input shaft 31 are aligned in the circumferential direction. Hereinafter, the portion of the outer periphery 20 where the teeth of the target plate 2 are formed is referred to as a target.
[0011]
The sensor box 1 is disposed at the fixed position outside the target plates 2 and 2 as described above so as to face the targets 20 and 20.
The sensor box 1 is fixedly supported by a housing H (partially shown) that supports an input shaft 31 and an output shaft 32. Inside the sensor box 1, two magnetic sensors facing the targets 20, 20,. 1A, 1B and two magnetic sensors 2A, 2B opposed to the targets 20, 20,... On the output shaft 32 side are accommodated, and input is performed by the magnetic sensors 1A, 1B and the targets 20, 20,. A sensor unit for detecting the rotation angle of the shaft 31 and a sensor unit for detecting the rotation angle of the output shaft 32 by the magnetic sensors 2A, 2B and the targets 20, 20,.
[0012]
Since the target plate 20 is gear-shaped, the magnetic field around the target periodically changes with the rotation of the targets 20, 20,..., And the magnetic sensors 1A, 1B, 2A, 2B detect such a change and , 32 are detected.
The magnetic sensors 1A and 1B face the target 20 on the input shaft 31 side, and are arranged such that the phases of their output voltages are shifted by 90 electrical degrees.
The magnetic sensors 2A and 2B face the target 20 on the output shaft 32 side, and are arranged such that the phases of the respective output voltages are shifted by 90 ° in electrical angle.
The magnetic sensor 1A and the magnetic sensor 2A are housed in the sensor box 1 with their circumferential positions correctly aligned, and the magnetic sensors 1B and 2B are housed in the sensor box 1 with their circumferential positions correctly aligned. I have.
[0013]
Each of the magnetic sensors 1A, 1B, 2A, and 2B uses an element such as a magnetoresistive element (MR element) having a characteristic in which an electrical specification (resistance) changes by the action of a magnetic field, and an output voltage according to a change in a peripheral magnetic field. Is configured to change. The outputs of the magnetic sensors 1A, 1B, 2A, 2B are given to an arithmetic processing unit 4 using a microprocessor.
[0014]
As shown in FIG. 2, the sensor box 1 is disposed above a steering shaft 3 which extends obliquely downward from the steering member 30 and extends substantially horizontally. Therefore, when the driver leans on the steering member 30, the steering shaft 3 moves downward. Therefore, the radial distance (air gap) between the targets 20, 20,... And the magnetic sensors 1A, 1B, 2A, 2B increases, and the sensor gain fluctuates. However, the offset fluctuation is small.
[0015]
Further, as shown in FIG. 3, the sensor box 1 may be arranged below the steering shaft 3. In this case, when the steering shaft 3 moves downward due to leaning of the driver, the radial distance (air gap) between the targets 20, 20,... And the magnetic sensors 1A, 1B, 2A, 2B decreases, and the sensor gain fluctuates. . However, the offset fluctuation is small.
[0016]
FIG. 4 shows an example in which the magnetic sensor 1A is configured by an MR element. In this magnetic sensor 1A, two MR elements 22, 22 are arranged side by side in the tangential direction of the axes 31, 32 (target plate 2) and are half-bridge connected. That is, the voltage Vcc is applied to the MR elements 22, 22 connected to each other, and the voltage between the two MR elements 22, 22 is used as the sensor output. When the resistance of each MR element changes due to the rotation of the targets 20, 20,..., The voltage value between the two MR elements 22, 22 changes periodically, and a sinusoidal output is obtained.
[0017]
Further, since the magnetic sensors 1A, 1B are arranged so as to face portions different from each other by an electrical angle of 90 ° in the circumferential direction of the targets 20, 20,..., The magnetic field is calculated from sin (θ ± (π / 2)) = ± cos θ. When the sensor 1B rotates in the direction of the magnetic sensor 1A, the angular outputs V1A and V1B of the magnetic sensors 1A and 1B can be regarded as V1A = sin θ1 and V1B = cos θ1. Similarly, the outputs V2A and V2B of the magnetic sensors 2A and 2B can be regarded as V2A = sin θ2 and V2B = cos θ2.
Then, from tan θ = sin θ / cos θ, tan θ1 can be obtained based on V1A and V1B, and tan θ2 can be obtained based on V2A and V2B. Even if there is a gain variation in V1A, V1B (V2A, V2B), when calculating tan θ1 or tan θ2, the influence of the gain variation is eliminated by the calculation of sin θ / cos θ. Note that the calculation for reducing the gain variation is not limited to this.
[0018]
The rotation angle θ1 of the input shaft 31 and the rotation angle θ2 of the output shaft 32 can be obtained from inverse functions of tan θ. The arithmetic processing unit 4 includes a data table that refers to the value of tan θ and the angle θ corresponding thereto, and can obtain the θ1 value and the θ2 value using the data table.
Further, the arithmetic processing unit 4 calculates a steering torque value from the angle difference between the angle θ1 and the angle θ2. The torque is based on the relative angular displacement between the input shaft 31 and the output shaft 32 caused by torsion of the torsion bar 34 = (θ1−θ2), and refer to a conversion table between (θ1−θ2) and the steering torque value. Can be obtained by Note that the conversion table is provided in the arithmetic processing unit.
[0019]
According to the present embodiment, even if the position of the target 2 and the magnetic sensor fluctuates due to the fluctuation of the steering shaft 3, the offset fluctuation hardly occurs in the sensor output, and the gain fluctuation is reduced by the calculation. The rotation angle and the torque can be detected almost without being affected by the disturbance such as the fluctuation of the shaft 3.
[0020]
【The invention's effect】
According to the present invention, since the magnetic sensor is arranged above or below the steering shaft, the positional relationship between the target and the magnetic sensor hardly fluctuates in the tangential direction, and offset fluctuation can be prevented.
[Brief description of the drawings]
FIG. 1 is a partial schematic diagram of a steering device.
FIG. 2 is a side view showing an example of the steering device.
FIG. 3 is a side view showing another example of the steering device.
FIG. 4 is a configuration diagram of a magnetic sensor including an MR element.
FIG. 5 is a diagram showing a positional relationship between a target plate and a magnetic sensor.
[Explanation of symbols]
3 Steering shaft 2 Target plate 20 Target 30 Steering member 31 Input shaft 32 Output shaft 34 Torsion bar (connection shaft)
1A Magnetic sensor 1B Magnetic sensor 2A Magnetic sensor 2B Magnetic sensor

Claims (4)

A steering member;
A steering shaft extending substantially sideways from the steering member;
A target that generates a periodic magnetic field change in the periphery by rotation of the steering shaft,
A magnetic sensor that is provided at a predetermined distance from the target and generates an output in accordance with a change in the magnetic field;
The steering device according to claim 1, wherein the magnetic sensor is disposed above or below a steering shaft. The target is composed of gear-shaped projections projecting at substantially equal intervals in the circumferential direction of the steering shaft,
The steering device according to claim 1, wherein the magnetic sensor is a magnetoresistive element. The steering apparatus according to claim 1, further comprising a unit configured to detect a rotation angle of a steering shaft based on an output of the magnetic sensor. The steering shaft includes an input shaft and an output shaft connected by a connection shaft,
The target is provided on each of the input shaft and the output shaft,
The steering device according to any one of claims 1 to 3, further comprising a unit configured to detect a torque applied to the steering shaft based on each output of a magnetic sensor provided for each target. .

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