JP4445219B2 - Torque sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a torque sensor that detects an input torque of a vehicle steering, and more particularly to a torque sensor that detects an input torque as a change in impedance of a coil.
[0002]
[Prior art]
An example of a conventional torque sensor is disclosed in Patent Document 1. This torque sensor converts the input torque into a relative rotational displacement of both shafts by connecting the input shaft and the output shaft via a torsion bar, and further converts the rotational displacement into a change in the impedance of the coil. The input torque is obtained based on the impedance value detected by the detection circuit. The coil is held by a yoke having an annular shape with a substantially U-shaped cross section with an inner peripheral side opened.
[0003]
A cylindrical non-magnetic body that rotates with the output shaft is disposed on the inner peripheral side of the coil, and a plurality of windows are disposed on the non-magnetic body in two rows in the axial direction and at equal intervals in the circumferential direction. Has been. A magnetic body that rotates together with the input shaft is disposed further on the inner peripheral side of the non-magnetic body. The magnetic body has, for example, a gear shape in which a plurality of axial grooves are formed at equal intervals in the circumferential direction so that the strength of the magnetic force appears alternately in the circumferential direction. Therefore, the amount of magnetic flux passing through the window changes due to the relative rotational displacement of both shafts, and the impedance of the coil changes.
[0004]
In Patent Document 1, the axial length of each window is made longer than the axial length of the coil and shorter than the axial length of the yoke, so that the accuracy of parts in the axial direction, assembly errors, etc. can be detected. effect can be reduced to give the, that have been described as.
[0005]
[Patent Document 1]
JP-A-9-61264 [0006]
[Problems to be solved by the invention]
However, since the yoke has a function of inducing the magnetic flux of the coil, if the axial length of the window is limited to be shorter than the axial length of the yoke as in Patent Document 1, the amount of magnetic flux passing through the window is limited. As a result, the detected value of the coil impedance is suppressed to a low level, leading to a decrease in detection accuracy. The present invention has been made in view of such problems, and its main purpose is to effectively increase the amount of magnetic flux passing through the window, that is, the detected value of the impedance of the coil, and to improve the torque detection accuracy. Yes.
[0007]
[Means for Solving the Problems]
A torque sensor according to the present invention includes a torsion bar that can be twisted and deformed around an axis, a first shaft and a second shaft that are coaxially connected by the torsion bar, and the first shaft, which rotates together with the strength of the magnetic force. And a non-magnetic body having a substantially cylindrical shape made of a non-magnetic material that is concentrically provided on the outer peripheral side of the magnetic body, rotates together with the second shaft, and is made of a conductive non-magnetic material. A plurality of windows formed in the circumferential direction of the non-magnetic material and having at least an axial length substantially constant, and concentrically on the outer peripheral side of the non-magnetic material corresponding to the axial position of the window. Corresponding to the axial position of the first coil (9A) and the window, the first coil (9A) is concentrically arranged on the outer peripheral side of the non-magnetic material and is offset from the first coil in the axial direction. Second coil (9B) and a small number of the first coil The first coil is held so as to surround at least both sides in the axial direction, and the second yoke is held so as to surround at least both sides in the axial direction of the first yoke made of a magnetic material and the second coil. And a second yoke (16B) made of a magnetic material and an inner peripheral surface provided between the first yoke and the second yoke so as to be opposed to the nonmagnetic body, and nonmagnetic And a torque detection means for detecting the input torque of the first shaft or the second shaft based on the impedance of the coil that changes depending on the degree of overlap between the magnetic body and the window,
The magnetic body (13) includes a magnetic member (13a) formed in a cylindrical shape with a magnetic material, and a nonmagnetic member (13b) provided on the outer periphery of the magnetic member and formed of a nonmagnetic material. The nonmagnetic member is provided at an axially intermediate portion of the nonmagnetic member and has a plurality of axial holes (13c) formed in the circumferential direction, and the window corresponds to the first coil. A first window (21A) formed at a position, and a second window (21B) formed axially spaced from the first window so as to correspond to the second coil. The axial length of the first window is longer than the axial length of the first yoke, and both the pair of axial inner edges of the first window are axially outer surfaces of the first yoke. compared to, the first located farther from the axial center of the yoke, the axial length of the second window is the second yaw Longer than the axial length of, and the both of the pair of axial inner edge of the second window, compared to the axial outer side of the second yoke, the side away from the axial center of the second yoke It is characterized by being located in .
[0008]
According to the present invention, it is possible to reduce or eliminate the fact that the amount of magnetic flux passing through each window is limited in the axial direction on both axial sides of each window. Therefore, the detection value of the coil impedance can be secured sufficiently high, and the torque detection accuracy can be improved.
[0012]
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. First, with reference to FIGS. 3 to 6, the basic configuration of the torque sensor 1 common to a later-described first embodiment and a reference example and the operation and effects thereof will be described.
[0013]
The torque sensor 1 is applied to a steering torque detector of a vehicle power steering device. As shown in FIG. 3, a housing 2 supported and fixed on the vehicle body side has an input shaft (first shaft) 3 on the steering wheel side, and an output shaft (second shaft) 4 linked to a wheel steering rack. However, each is supported rotatably via a bearing 5 (the bearing of the output shaft 4 is not shown). The shafts 3 and 4 are connected coaxially via a torsion bar 6 that can be twisted around an axis, and torque acting between them is converted into a torsion amount of the torsion bar 6. An assist gear 7 is attached to the outer periphery of the intermediate position of the output shaft 4 in the axial direction, and an output gear (not shown) of an electric motor 8 for applying an assist force corresponding to the input torque meshes with the gear 7. Has been.
[0014]
The torque sensor 1 converts the relative rotational amount and rotational displacement of the shafts 3 and 4 due to the torsion bar 6 torsion into the amount of change in the impedance of the coil 9 according to the input torque, and electrically detects the detection signal based on the impedance. It outputs to the control part of the motor 8. That is, the torque sensor 1 has a substantially cylindrical magnetic body 13 concentrically disposed on the outer periphery of the input shaft 3 and a substantially cylindrical shape concentrically disposed in a non-contact state on the outer peripheral side of the magnetic body 13. A non-magnetic body 14 and a pair of first coil units 11A that are concentrically disposed in a non-contact state on the outer peripheral side of the non-magnetic body 14 and are fixed to the housing 2 and include the coil 9 described above. And a second coil unit 11B and a detection circuit unit 12 for detecting the impedance of the coil 9 of each coil unit 11A, 11B.
[0015]
The first coil unit 11A and the second coil unit 11B are juxtaposed in the axial direction and have substantially the same configuration. In the following description, a component corresponding to the first coil unit is given an A after the reference symbol as necessary, and a component corresponding to the second coil unit is appended after the reference symbol as necessary. B is attached.
[0016]
The magnetic body 13 has a function of alternately generating magnetic strength in the circumferential direction. For example, in this example, it has the cylindrical magnetic member 13a (refer FIG. 4) which has magnetism, and the nonmagnetic member 13b which consists of an electroconductive nonmagnetic material surrounding the outer periphery of this magnetic member 13a. As shown in FIG. 5, a predetermined number (eight in this example) of axial holes 13c exposing the magnetic member 13a are formed in the nonmagnetic member 13b at equal intervals in the circumferential direction. The magnetic force is strong in the circumferential portion of the axial hole 13c, and the magnetic force is weak in the circumferential portion other than the axial hole 13c.
[0017]
The nonmagnetic body 14 is formed of a conductive and nonmagnetic material such as aluminum, is fixed to the input shaft 3, and rotates together with the input shaft 3. As shown in FIG. 6, the non-magnetic body 14 includes a plurality of first windows in two upper and lower rows in the axial direction corresponding to the axial positions of the first and second coil units 11A and 11B. 21A and a second window 21B are formed. In each row, the same number (eight in this example) of windows as the axial holes 13c are formed at equal intervals in the circumferential direction. However, the first window 21A and the second window 21B are arranged offset in the circumferential direction. Each window 21 has a rectangular shape that has a constant axial length and a circumferential length and is long in the axial direction. The axial hole 13c is formed to extend in the axial length beyond the first window 21A and the second window 21B so that the amount of magnetic flux passing through the window 21 is not limited (see FIG. 3).
[0018]
At the neutral position where the torsion bar 6 has a twist of 0, the degree of overlap (area) between the first window 21A and the axial hole 13c is equal to the degree of overlap between the second window 21B and the axial hole 13c, The impedance detection values of the first coil 9A of the first coil unit 11A and the second coil 9B of the second coil unit 11B are set to be equal. When the input shaft 3 and the output shaft 4 are relatively rotated from this neutral position, the impedances of the coils 9A and 9B are always changed in the opposite directions by the same amount. For example, when the shafts 3 and 4 rotate relative to one from the neutral position, the degree of overlap between the first window 21A and the axial hole 13c increases and the degree of overlap between the second window 21B and the axial hole 13c decreases. To do. Conversely, when the shafts 3 and 4 rotate relative to each other, the degree of overlap between the first window 21A and the axial hole 13c decreases and the degree of overlap between the second window 21B and the axial hole 13c increases. The difference in impedance between the two coils 9A and 9B is obtained, and the input torque is obtained based on the difference. Therefore, in the case of this torque sensor 1, the impedance change due to factors other than the input torque such as the temperature change is canceled, and as a result, stable torque detection is possible.
[0019]
1 and 2 are cross-sectional views showing the coil unit 11 and the non-magnetic material 14. FIG. 1 corresponds to the first embodiment, and FIG. 2 corresponds to a reference example . In FIGS. 1 and 2, the first window 21 </ b> A and the second window 21 </ b> B are drawn at the same circumferential position for clarity of explanation, but in reality, the windows 21 </ b> A and 21 </ b> B are circumferential in the direction as described above. Are offset from each other.
[0020]
Each coil unit 11 has a substantially annular shape with a substantially U-shaped cross section so as to surround a resin-made coil bobbin 15 around which the coil 9 is wound and three sides of the coil bobbin 15 on both sides in the axial direction and on the outer peripheral side. 9 and a coil yoke 16 for holding the coil bobbin 15. The coil bobbin 15 has a substantially U-shaped cross section that is open on the outer peripheral side, and has a substantially annular shape as a whole. The coil yoke 16 includes a main yoke block 17 having a substantially L-shaped cross section that surrounds one axial side and the outer peripheral side of the coil bobbin 15, and an annular plate-shaped sub yoke block 18 that covers the other axial side of the coil bobbin 15. It is comprised and is formed of the magnetic material which has magnetism. At the time of assembly, the sub yoke block 18 is fixed to the main yoke block 17 by press fitting or the like with the coil 9 and the coil bobbin 15 housed inside the main yoke block 17.
[0021]
The two coil units 11 </ b> A and 11 </ b> B are supported by the housing 2 in a state where the sub yoke block 18 side is abutted against each other in the axial direction by an urging force such as a disc spring (not shown). However, in the first embodiment of FIG. 1, a spacer 30 is interposed between the two coil units 11A and 11B.
[0022]
Next, with reference to FIG. 1, the characteristic configuration and operational effects of the first embodiment will be described.
[0023]
The axial length L1 of the window 21 is set to be longer than the axial length L2 of the yoke 16, and the pair of axial inner edges 22 and 23 of the window 21 are axially outer surfaces of the corresponding yoke 16. It is located on the side farther from the axial center of the yoke 16 than 24 and 25. That is, the window 21 extends in the axial direction beyond the yoke 16. Therefore, the yoke 16 having a function of guiding the magnetic flux of the coil can be exposed from the window 21 over the entire length in the axial direction. For this reason, the magnetic flux passing through the window 21 is not restricted in the axial direction, and the detection value (gain) of the coil impedance can be secured sufficiently high, so that the torque detection accuracy can be sufficiently increased.
[0024]
In particular, even when the first window 21A and the second window 21B are close to each other in the axial direction, the axial inner edge 23 of the window 21 is located on the side farther from the axial center of the yoke 16 than the axial outer surface 25 of the yoke 16. As described above, a spacer 30 having a predetermined axial dimension is interposed between the first yoke 16A and the second yoke 16B. The spacer 30 is made of, for example, an inexpensive resin material that is nonconductive and nonmagnetic. Therefore, by preventing the magnetic fluxes from affecting each other in the first coil unit 11A and the second coil unit 11B adjacent in the axial direction by the spacer 30, the window 21 is extended from the yoke 16 as described above. An effect of improving detection accuracy can be obtained.
[0025]
Predetermined axial gaps L3 and L4 are set between the inner edges 22 and 23 of the window 21 and the outer faces 24 and 25 of the yoke 16, and the two axial gaps L3 and L4 are equal to each other. Is set to Therefore, even if the non-magnetic body 14 and the coil unit 11 are displaced in the axial direction due to an axial dimensional error or an assembly error, the impedance of the coil between the first coil unit 11A and the second coil unit 11B. Increase or decrease almost equally and their influence is canceled out, so that the influence on the torque detection accuracy is minimized.
[0026]
Next, with reference to FIG. 2, the characteristic configuration and effects of the reference example will be listed.
[0027]
In this reference example , the spacer 30 is omitted, and the sub yoke blocks 18 of the first yoke 16A and the second yoke 16B are in direct surface contact with each other. Therefore, the axial dimension is shortened compared to the first embodiment, and the size and simplification can be achieved.
[0028]
In addition, the axial inner edge 23 of the first window 21A and the second window 21B on the side close to each other is located closer to the axial center of the yoke 16 than the corresponding axial outer surface 25 of the yoke 16. ing. That is, the window 21 is formed shorter than the yoke 16 on the side where the windows 21A and 21B are close to each other. On the other hand, the axially inner edges 22 of the first window 21A and the second window 21B on the far side are located on the side farther from the axial center of the yoke 16 than the corresponding axially outer surface 24 of the yoke 16. Yes. That is, the window 21 extends beyond the yoke 16 on the side where the windows 21A and 21B are separated from each other.
[0029]
As described above, in the reference example , while the axial direction is shortened by omitting the spacer, a wall having a predetermined dimension is formed between the axial inner edges 23 on the side where the first window 21A and the second window 21B are close to each other. 31, the magnetic fluxes of the yokes 16A and 16B adjacent in the axial direction mutually affect the detection accuracy effectively, and the first window 21A and the second window 21B are separated from each other. On the side to be detected, the detection accuracy can be improved by extending the window 21 in the axial direction from the corresponding yoke 16. That is, axial shortening and detection accuracy can be improved in a balanced manner.
[0030]
As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes without departing from the spirit of the present invention. . For example, as in the above-mentioned JP-A-9-61264, the above magnetic body is made into a gear shape in which a plurality of axial grooves are formed at equal intervals in the circumferential direction, and the strength of the magnetic force is alternately varied in the circumferential direction. You may make it appear.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a coil unit and a nonmagnetic material according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a coil unit and a nonmagnetic material according to a reference example of the present invention.
FIG. 3 is a cross-sectional view showing a torque sensor to which the first embodiment and the reference example are applied.
4 is a cross-sectional view showing a magnetic member of a magnetic body of the torque sensor of FIG. 3 alone.
5A and 5B are a cross-sectional view taken along a line 5A-5A and a cross-sectional view taken along a line 5B-5B showing a nonmagnetic member of the magnetic body of the torque sensor shown in FIG. 3 alone.
6 is a partially cutaway view (A) showing a nonmagnetic material of the torque sensor of FIG. 3 alone and a cross-sectional view (B) along the line 6B-6B.

Claims (1)

A torsion bar that can be twisted and deformed around an axis;
A first shaft and a second shaft connected coaxially by the torsion bar;
A magnetic body that rotates with the first shaft and in which the strength of the magnetic force is alternately generated in the circumferential direction;
A substantially cylindrical non-magnetic body that is concentrically provided on the outer peripheral side of the magnetic body, rotates together with the second shaft, and is made of a non-magnetic material having conductivity;
A plurality of windows formed in the circumferential direction of the non-magnetic material, and at least the axial length is substantially constant;
A first coil (9A) disposed concentrically on the outer peripheral side of the non-magnetic material, corresponding to the axial position of the window;
Corresponding to the axial position of the window, a second coil (9B) that is concentric on the outer peripheral side of the non-magnetic material and is offset from the first coil in the axial direction;
Holding the first coil so as to surround at least both axial sides of the first coil, and a first yoke (16A) made of a magnetic material;
Holding the second coil so as to surround at least both axial sides of the second coil, and a second yoke (16B) made of a magnetic material;
A spacer formed between the first yoke and the second yoke so that an inner peripheral surface is exposed so as to face the nonmagnetic material; and a spacer formed of a nonmagnetic material;
Torque detecting means for detecting the input torque of the first shaft or the second shaft based on the impedance of the coil that changes depending on the degree of overlap between the magnetic body and the window,
The magnetic body (13) includes a magnetic member (13a) formed in a cylindrical shape with a magnetic material, and a nonmagnetic member (13b) provided on the outer periphery of the magnetic member and formed of a nonmagnetic material. And
The nonmagnetic member has an axial hole (13c) provided in the axially intermediate portion of the nonmagnetic member and formed in the circumferential direction.
The window includes a first window (21A) formed at a position corresponding to the first coil and a first window formed axially spaced from the first window so as to correspond to the second coil. 2 windows (21B),
The axial length of the first window is longer than the axial length of the first yoke, and both of the pair of axial inner edges of the first window are on the axially outer surface of the first yoke. In comparison, located on the far side from the axial center of the first yoke,
The axial length of the second window is longer than the axial length of the second yoke, and both the pair of axial inner edges of the second window are on the axially outer surface of the second yoke. In comparison, the torque sensor is located on the far side from the axial center of the second yoke.

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