JP2000241265A - Torque sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate machining and assembly and to obtain the torque sensor which has small variance in detection characteristics. SOLUTION: When a helm is applied with torque, and an input shaft 2 and an output shaft 3 rotate relatively, a coil spring 9 increases and decreases a twist. Consequently, the pitch of the coil spring 9 varies, so the quantity of the air gap between adjacent windings varies, so that the magnetic resistance of a magnetic circuit composed of detection coils 16 and 17 increases and decreases. The detection coils 16 and 17, therefore, vary in impedance. That is led out as the voltage across the detection coils 16 and 17 to obtain the output corresponding to the torque.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque sensor, and more particularly, to a torque sensor suitable for application to an electric power steering device of an automobile.

[0002]

2. Description of the Related Art An electric power steering device is being developed as a power steering device for assisting a force for operating a steering wheel of an automobile. This detects the torque applied to the steered wheels,
According to the detected torque, the motor provided in the steering mechanism is rotated. Incidentally, as this torque detecting means, for example, a torque sensor disclosed in Japanese Patent Application Laid-Open No. Sho 59-208431 is known.

In this torque sensor, a cylinder is provided which rotates integrally with an input shaft and an output shaft connected via a torsion bar, and tooth portions are provided on opposite end surfaces of these cylinders, respectively. A predetermined gap is provided between the input shaft in the axial direction and the rotation direction of the input shaft so as to oppose each other.

[0004]

However, since the teeth are machined into a plurality of cylindrical bodies, it is troublesome and the manufacturing cost is increased. In addition, the positions of the teeth of each cylinder overlap in both the axial direction and the rotational direction, and the setting of the gap between the teeth greatly affects the detection accuracy. Also,
When assembling the torque detecting device, it is necessary to position and assemble with high accuracy in a neutral state where no torque is applied, but this assembling work has been extremely difficult.

Further, it is practically impossible to perform accurate positioning between the teeth as described above in a state where the torque is zero. Therefore, there is a large variation in detection characteristics among the individual torque sensors. The present invention has been made in view of the above problems, and has as its object to provide a torque sensor that can eliminate troublesome processing and difficult assembling work, and that has less variation in detection characteristics.

[0006]

Means for Solving the Problems As means for solving the problems to achieve the above object, the aspect of the invention according to claim 1 is as follows.
In a torque sensor that detects a torque applied to an input shaft and an output shaft that are relatively rotatably connected via a torsion bar, each end portion is twisted with the relative rotation of the input shaft and the output shaft. Includes a helical coil spring made of a magnetic material that engages with a corresponding shaft, and a detection coil that surrounds the coil spring and detects torque based on a change in magnetic resistance accompanying a change in pitch of the coil spring. It is characterized by the following.

In this embodiment, when the input shaft and the output shaft rotate relative to each other, the coil spring increases or decreases the torsion,
The pitch between the turns of the coil spring changes. The torque is detected by the detection coil based on the change in the magnetic resistance accompanying the pitch change. Since a helical coil spring, which is a simple and standard mechanical element, is used, difficult processing and assembly are not required. Further, even if strict positioning is not performed, the pitch of the windings of the coil spring does not vary so much, and the torque is detected based on such a change in the pitch of the coil spring.

According to a second aspect of the present invention, in the first aspect, the coil spring is interposed between a pair of opposed end faces of an input shaft and an output shaft, and the pair of end faces are arranged in the axial direction. The spring length of the coil spring is changed by a phase shift between the inclined surfaces. In this aspect, when the input shaft and the output shaft rotate relative to each other, the end faces of both shafts formed of inclined surfaces change the spring length of the coil spring between each other. This allows
Compared to a case where the coil spring is simply twisted, the change in pitch of the coil spring can be made larger and the detection output can be made larger. As a result, detection sensitivity and detection accuracy can be improved.

According to a third aspect of the present invention, in the first or second aspect, the winding of the coil spring has a square cross section. In the case of a rectangular cross section, a minimum gap between adjacent windings can be obtained on the side closer to the detection coil as compared with the case of a round cross section. Therefore, the detection output can be improved by shortening the length of the magnetic circuit, and as a result, the detection sensitivity can be improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic sectional view of a main part of a steering device in which a torque sensor according to the present invention is incorporated. With reference to FIG. 1, the present steering apparatus 1 enables an input shaft 2 connected to a steering wheel (not shown), an output shaft 3 connected to a steering mechanism (not shown), and the input shaft 2 and the output shaft 3 to be relatively rotatable. And a torsion bar 4 to be connected. Input shaft 2
At the opposite end of the output shaft 3, first and second cylinders 5, 6 which rotate integrally with the respective shafts 2, 3 are attached. Opposite end surfaces 7, 8 of the two cylindrical bodies 5, 6 are inclined surfaces parallel to each other, and a helical coil spring 9 is interposed between the end surfaces 7, 8.

The coil spring 9 is made of a magnetic material such as iron, and has both ends 9a and 9b as winding ends of the coil spring 9.
Are fitted on the outer periphery of annular spring guides 10 and 11 protruding from the end surfaces 7 and 8 of the cylindrical bodies 5 and 6. 12
Is a fixing member comprising a pin or a rivet for fixing each end 9a, 9b of the coil spring 9 to the corresponding spring guide 10, 11. The cross section of the winding of the coil spring 9 is shown in FIG.
It is rectangular as shown in (a) and (b).

The periphery of the two cylindrical bodies 5, 6 and the coil spring 9 interposed therebetween are surrounded by a cylindrical housing 13 fixed to a predetermined portion of the vehicle. First cylinder 5
Is rotatably supported by the housing 13 via a needle roller bearing 14, and the second cylindrical body 6 is rotatably supported by the housing 13 via a ball bearing 15. Also,
First and second detection coils 16 and 17 surrounding the coil spring 9 are arranged adjacent to each other in the axial direction on the inner periphery of the housing 13. Each of the detection coils 16 and 17 is housed and held in a wound state in a circumferential groove of a cylindrical body 19 or 20 made of a magnetic material having a U-shaped cross section and held in a first annular recess 18 on the inner circumference of the housing 13. Have been. 21 is both cylinders 19,
It is a spacer that is interposed between and regulates the distance between the detection coils 16 and 17.

Reference numeral 22 denotes a retaining ring which is fitted into a peripheral groove at one end of a second annular concave portion 23 having a diameter larger than that of the first annular concave portion 18, and is provided between the retaining ring 22 and an end face of the cylindrical body 20. In
A disc spring 24 is interposed as urging means for urging the two cylindrical bodies 19 and 20 and the spacer 21 integrally in the axial direction.
The cylindrical body 19 urged by the disc spring 24 abuts the positioning step 25 at one end of the first annular concave portion 18,
Both detection coils 16, 17 are positioned and held in the axial direction.

The first and second cylinders 5 and 6, the coil spring 9, and the first and second detection coils 16 and 17 constitute a torque sensor T. Next, the operation of the torque sensor will be described. The magnetic flux generated in each of the detection coils 16 and 17 by the oscillating operation of an oscillator (not shown) is transmitted through the adjacent windings 9c and 9d of the spiral coil spring 9 as shown in FIGS. Although the circuits C1 and C2 are configured, the reluctance of the magnetic circuits C1 and C2 depends on the air gap amounts d1 and d2 between the adjacent windings 9c and 9d of the coil spring 9. On the other hand, the amount of the air gap changes when the coil spring 9 strengthens or weakens the torsion when the steering is performed and the relative rotation occurs between the input shaft 2 and the output shaft 3.

For example, when the steering wheel is turned right when the coil spring 9 is right-handed, the coil spring 9 increases torsion, so that the winding pitch of the coil spring 9 becomes narrower.
As a result, the air gap amount d1 becomes narrower as shown in FIG. 2A than when the steering device is at the neutral position. For this reason, the magnetic resistance of the magnetic circuit by each of the detection coils 16 and 17 decreases, and the impedance of each of the detection coils 16 and 17 increases.

On the other hand, when the steering wheel is turned to the left, the coil spring 9
Since the torsion is weakened, the pitch of the windings of the coil spring 9 is widened, and as a result, the air gap amount d2 becomes wider as shown in FIG. . For this reason, the magnetic resistance of the magnetic circuit of each detection coil 16 and 17 increases, and the impedance of each detection coil 16 and 17 decreases. These impedance changes are extracted as voltages across the detection coils 16 and 17 and amplified by an amplifier (not shown) to obtain an output corresponding to the torque.

In this embodiment, a coil spring 9 is mounted between the cylindrical bodies 5 and 6 fixed to the ends of the input shaft 2 and the output shaft 3, and the coil spring 9 is mounted in a housing 13 in which detection coils 16 and 17 are mounted. By inserting the torque sensor T, the torque sensor T can be easily assembled. In the conventional case where the teeth are opposed to each other, the teeth have to be positioned in both the axial direction and the rotation direction in a state where the torque is zero,
In the present embodiment in which the torque is detected based on a change in the pitch of the coil spring 9 which is a simple mechanical element, the positioning in the axial direction may be rough, and the assembly is also easy from this point. Further, even if strict positioning is not performed, the pitch of the windings of the coil spring 9 does not vary so much, and the torque is detected based on such a change in the pitch of the coil spring 9, so that the variation in detection characteristics is small.

In particular, since each of the detection coils 16 and 17 detects an air gap change over the entire circumference of the coil spring 9, variation in the set length of the coil spring 9 at the time of assembling hardly affects the detection characteristics. Absent. Also,
With the relative rotation of the input shaft 2 and the output shaft 3, the first and second
The end surfaces 7, 8 of the cylindrical bodies 5, 6 formed of inclined surfaces are shifted in phase from each other, whereby the entire length of the coil spring 9 partially changes in a part in the circumferential direction. On the other hand, detection coils 16 and 17
Is affected by a change in the air gap over the entire circumference of the coil spring 9, so that the above-described partial change in the pitch can be detected. That is, when relative rotation occurs between the input and output shafts 2 and 3, not only is the torsion of the coil spring 9 increased or decreased, but the entire length of the coil spring 9 is partially changed. Thereby, a relatively large pitch change can be obtained with respect to the amount of relative rotation of the input and output shafts 2 and 3.
As a result, the detection output of the detection coils 16 and 17 can be increased. As a result, the detection sensitivity can be improved.

Furthermore, since the cross section of the winding of the coil spring 9 is rectangular, the minimum gap amount (minimum air gap amount) between adjacent windings is compared with the case where the cross section is round.
Can be obtained on the side close to the detection coils 16 and 17. Therefore, the detection output of the detection coils 16 and 17 can be improved by shortening the length of the magnetic circuit, and as a result, the detection sensitivity can be improved.

Also, the first and second detection coils 16, 1
If the output characteristics of the output coils 7 are set to be opposite to each other (one output increases and the other output decreases), the differential output of the two detection coils 16 and 17 is obtained and reduced to 1/2. Accordingly, the temperature-influencing components included in the outputs of the respective detection coils 16 and 17 in the same amounts can be canceled to perform the temperature compensation.

The present invention is not limited to the above embodiment. For example, the end faces 7, 8 of the cylindrical bodies 5, 6 are
The surface may be orthogonal to the central axis of the input shaft 2 or the output shaft 3. Further, the cross-sectional shape of the winding of the coil spring 9 may be round. Further, the cylinders 5 and 6 may be formed integrally with the corresponding input shaft 2 and output shaft 3. Further, in the present embodiment, a pair of detection coils is provided for the purpose of temperature compensation, but a single detection coil may be used.
In addition, various changes can be made within the scope of the present invention.

[0022]

According to the first aspect of the present invention, since a helical coil spring, which is a simple and standard mechanical element, is used, difficult processing and assembly are unnecessary, and the manufacturing cost can be reduced. Also, without strict positioning,
The winding pitch of the coil spring does not vary much, and the torque is detected based on such a change in the pitch of the coil spring.

According to the second aspect of the present invention, the total length of the coil spring can be changed in accordance with the relative rotation of the input shaft and the output shaft. The change in the pitch of the spring can be made larger, and as a result, the detection output can be made larger and the detection sensitivity can be improved. According to the third aspect of the invention, the minimum gap between the adjacent windings can be obtained on the side close to the detection coil, so that the detection output can be improved by shortening the length of the magnetic circuit, thereby improving the detection sensitivity. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a main part of a steering device to which a torque sensor according to an embodiment of the present invention is applied.

FIGS. 2A and 2B are schematic cross-sectional views of a main part of a coil spring and a detection coil. FIG. The state of the magnetic circuit when the steering is weakened is shown.

[Explanation of symbols]

 T Torque sensor 1 Steering device 2 Input shaft 3 Output shaft 4 Torsion bar 5 First cylinder 6 Second cylinder 7, 8 End face 9 Coil spring 9a, 9b End 9c, 9d Winding 13 Housing 16 First Detection coil 17 Second detection coil

Claims (3)

[Claims] 1. A torque sensor for detecting a torque applied to an input shaft and an output shaft which are connected to each other via a torsion bar so as to be rotatable, wherein the torque sensor is twisted with the relative rotation of the input shaft and the output shaft. A helical coil spring made of a magnetic material, each end of which engages with a corresponding shaft; and a coil spring surrounding the coil spring and detecting torque based on a change in magnetic resistance caused by a change in pitch of the coil spring. A torque sensor comprising a detection coil. 2. The coil spring is interposed between a pair of opposed end surfaces of an input shaft and an output shaft, and the pair of end surfaces are inclined surfaces inclined with respect to an axial direction. 2. The torque sensor according to claim 1, wherein the spring length of the coil spring is changed by the phase shift. 3. The torque sensor according to claim 1, wherein the winding of the coil spring has a rectangular cross section.