JP2009210325A - Magnetostrictive torque sensor and vehicle steering apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve detection accuracy by suppressing an eddy current generated in a back-yoke, in a magnetostrictive torque sensor wherein the back-yoke is arranged on the outer periphery of a coil. <P>SOLUTION: A cylindrical back yoke 43 is arranged on the outer periphery of coils 41A, 41B; 42A, 42B arranged on the outer periphery of magnetostrictive films 39A, 39B formed on the surface of a pinion shaft 17 of an electric power steering apparatus, to thereby constitute a magnetic circuit passing the back-yoke 43 and the magnetostrictive films 39A, 39B, and to increase an output gain of the coils, and also to improve sensitivity of the magnetostrictive torque sensor St, and a slit 43a extending in the axial direction of the back-yoke 43 is formed, and the eddy current generated in the back yoke 43 is suppressed by the slit 43a, to thereby improve detection accuracy. A rectangular metal plate made of a magnetic body is bent cylindrically to form the back-yoke 43, and the slit 43a is constituted between two opposite sides, and a structure of the back-yoke 43 is extremely simplified, to thereby realize inexpensive manufacture. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  In the present invention, a coil wound around a bobbin is disposed on the outer periphery of a magnetostrictive film formed on the surface of a rotating shaft, a cylindrical back yoke is disposed on the outer periphery of the coil, and the change in magnetic characteristics of the magnetostrictive film The present invention relates to a magnetostrictive torque sensor that detects torque applied to the rotating shaft by detecting the torque with a coil, and a vehicle steering apparatus that uses the magnetostrictive torque sensor as a steering torque sensor.

A magnetostrictive torque sensor for detecting torque applied to the shaft includes a pair of magnetostrictive films formed on the outer periphery of the shaft so as to have mutually opposite magnetic anisotropies, an excitation coil surrounding the outer periphery of each magnetostrictive film, and And detecting a change in permeability of a pair of magnetostrictive films that change according to torsional deformation of the shaft based on a change in AC resistance of the excitation coil and the detection coil, and input to the shaft. A device for detecting torque is known from Patent Document 1 below.
JP 11-132877 A

  By the way, such a magnetostrictive torque sensor includes a back yoke that surrounds the excitation coil and the detection coil to form a magnetic path. However, the back yoke of the magnetostrictive torque sensor described in Patent Document 1 is described below. Since the excitation coil and the detection coil are surrounded by 360 °, eddy currents are likely to be generated, which may adversely affect the detection accuracy.

  Also, since magnetic flux is likely to be concentrated on the edge of the back yoke, if the back yoke has an irregular edge shape or variations in the edge shape, the AC resistance of the coil may vary. there were.

  The present invention has been made in view of the above circumstances, and when a back yoke is arranged on the outer periphery of a coil of a magnetostrictive torque sensor, the generation of eddy current in the back yoke is suppressed and the AC resistance of the coil is reduced. The purpose is to stabilize and increase the detection accuracy.

  To achieve the above object, according to the first aspect of the present invention, a coil wound around a bobbin is disposed on the outer periphery of a magnetostrictive film formed on the surface of the rotating shaft, and a cylinder is disposed on the outer periphery of the coil. In a magnetostrictive torque sensor that detects a torque applied to the rotating shaft by detecting a change in magnetic characteristics of the magnetostrictive film with the coil, the back yoke is fixed in the radial direction. A magnetostrictive torque sensor is proposed that includes a slit sandwiched between a pair of flat end faces having a width and extending in the axial direction.

  According to the second aspect of the present invention, in addition to the configuration of the first aspect, the back yoke is formed by curving a rectangular magnetic metal plate into a cylindrical shape, and the pair of the opposing pairs A magnetostrictive torque sensor is proposed in which the slit is formed between end faces.

  According to a third aspect of the present invention, in addition to the configuration of the first aspect, a pair of yoke rings that cover both ends in the axial direction of the back yoke are provided, and the back yoke and the yoke ring are not in contact with each other. A magnetostrictive torque sensor characterized by being arranged is proposed.

  According to a fourth aspect of the present invention, in addition to the configuration of the third aspect, the bobbin includes an annular extending portion extending radially outward, and the extending portion includes the back yoke and the back yoke. A magnetostrictive torque sensor characterized by being sandwiched between yoke rings is proposed.

  According to the invention described in claim 5, the vehicle steering apparatus using the magnetostrictive torque sensor according to any one of claims 1 to 4, wherein the magnetostrictive torque sensor is A vehicular steering apparatus that is used as a steering torque sensor that detects a steering torque input to a steering shaft, and that controls the operation of an actuator of an electric power steering apparatus based on the steering torque detected by the steering torque sensor. Is proposed.

  The upper steering shaft 12 and the lower steering shaft 14 of the embodiment correspond to the steering shaft of the present invention, and the pinion shaft 17 of the embodiment corresponds to the rotating shaft of the present invention. The two magnetostrictive films 39A and 39B correspond to the magnetostrictive film of the present invention, and the first and second excitation coils 41A and 41B and the first and second detection coils 42A and 42B of the embodiment correspond to the coils of the present invention. The steering torque sensor St of the embodiment corresponds to the magnetostrictive torque sensor of the present invention, and the electric motor M of the embodiment corresponds to the actuator of the present invention.

  According to the configuration of the first aspect, since the cylindrical back yoke is further disposed on the outer periphery of the coil disposed on the outer periphery of the magnetostrictive film formed on the surface of the rotating shaft, the magnetic circuit passing through the back yoke and the magnetostrictive film is provided. It can be configured to increase the output gain of the coil and increase the sensitivity of the magnetostrictive torque sensor. In addition, since the slit is formed between the pair of flat end surfaces having a constant width in the radial direction and extending in the axial direction in the back yoke, the eddy current generated in the back yoke is blocked and suppressed by the slit. The AC resistance of the coil can be stabilized and the detection accuracy of the magnetostrictive torque sensor can be increased.

  According to the second aspect of the present invention, a rectangular magnetic metal plate is curved into a cylindrical shape to form a back yoke, and a slit is formed between a pair of opposing end faces. It becomes very simple and can be manufactured inexpensively.

  According to the third aspect of the present invention, since the pair of yoke rings that cover both axial ends of the back yoke are provided, not only the output gain of the coil can be further increased, but also the back yoke and the yoke ring are not contacted. Therefore, the variation in magnetic permeability due to the contact state between the back yoke and the yoke ring can be reduced to further improve the detection accuracy of the magnetostrictive torque sensor.

  According to the fourth aspect of the present invention, since the annular extending portion provided on the bobbin so as to extend radially outward is sandwiched between the back yoke and the yoke ring, the distance between the back yoke and the yoke ring is uniform. Thus, variation in magnetic permeability can be prevented, and detection accuracy can be further enhanced while increasing the sensitivity of the magnetostrictive torque sensor.

  According to the fifth aspect of the present invention, since the magnetostrictive torque sensor is used as the steering torque sensor of the vehicle steering apparatus, the steering torque input to the steering shaft is detected with high accuracy to operate the actuator of the power steering apparatus. By controlling the above, it is possible to improve the steering feeling.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  1 to 6 show a first embodiment of the present invention. FIG. 1 is an overall perspective view of an electric power steering apparatus, FIG. 2 is an enlarged sectional view taken along line 2-2 of FIG. 1, and FIG. 4 is a sectional view taken along line 3-3, FIG. 4 is an enlarged view of a portion 4 in FIG. 2, FIG. 5 is a perspective view of the back yoke, and FIG. 6 is a diagram showing a change characteristic of the torque detection signal with respect to the steering torque.

  As shown in FIG. 1, the upper steering shaft 12 that rotates integrally with the steering wheel 11 includes a pinion shaft 17 that protrudes upward from the speed reducer 16 via an upper universal joint 13, a lower steering shaft 14, and a lower universal joint 15. Connected to. Tie rods 19 and 19 projecting from the left and right ends of the steering gear box 18 connected to the lower end of the speed reducer 16 are connected to knuckles (not shown) of the left and right wheels WL and WR. A motor M is supported on the speed reducer 16, and the operation of the motor M is controlled by an electronic control unit U to which a signal from a steering torque sensor St housed in the speed reducer 16 is input.

  As shown in FIGS. 2 and 3, the speed reducer 16 includes a lower case 21 integrated with the steering gear box 18 and an upper case 23 coupled to the upper surface thereof with bolts 22. The pinion shaft 17 is rotatably supported by ball bearings 26 and 27 on the upper case 23. A pinion 28 provided at the lower end of the pinion shaft 17 meshes with a rack 30 provided on a rack bar 29 supported inside the steering gear box 18 so as to be movable left and right. A pressing member 31 is slidably accommodated in a through hole 18 a formed in the steering gear box 18, and the pressing member 31 is attached to the rack bar 29 by a spring 33 disposed between the nut member 32 closing the through hole 18 a. By biasing toward the back surface, the rack 30 can be properly meshed with the pinion 28 while suppressing the deflection of the rack bar 29.

  A rotation shaft 34 of the motor M extending inside the reduction gear 16 is rotatably supported by the lower case 21 by a pair of ball bearings 35 and 36. A worm 37 provided on the rotating shaft 34 of the motor M meshes with a worm wheel 38 fixed to the pinion shaft 17.

  As shown in FIGS. 2 and 4, the steering torque sensor St that detects the steering torque input to the steering wheel 11 is formed to cover the surface of the pinion shaft 17 with a predetermined width, for example, from Ni—Fe plating. First and second magnetostrictive films 39A and 39B, and a first excitation coil 41A and a first detection coil 42A wound around an upper portion of a synthetic resin bobbin 40 so as to surround the first magnetostrictive film 39A. The second exciting coil 41B and the second detecting coil 42B wound around the lower portion of the bobbin 40 so as to surround the second magnetostrictive film 39B, the first exciting coil 41A, the first detecting coil 42A, the second A substantially cylindrical back yoke 43 made of a magnetic material surrounding the excitation coil 41B and the second detection coil 42B is provided.

  As is apparent from FIG. 5, the back yoke 43 is a rectangular plate made of a magnetic material and is curved into a substantially cylindrical shape, and a slit 43a is formed between two opposing end surfaces. The two end faces sandwiching the slit 43a of the back yoke 43 are formed as flat and elongated rectangles.

  The bobbin 40 includes first to sixth flanges 40b to 40g that project radially outward from a cylindrical bobbin main body 40a, and the first detection coil 42A is wound between the first and second flanges 40b and 40c. The first exciting coil 41A is wound between the second and third flanges 40c and 40d, and the second exciting coil 41B is wound between the fourth and fifth flanges 40e and 40f. The second detection coil 40B is wound between the flanges 40f and 40g.

  An excitation circuit 44 is connected to the first and second excitation coils 41A and 41B, and first and second conversion circuits 45A and 45B are connected to the first and second detection coils 42A and 42B, respectively. An amplifier 46 is connected to the two conversion circuits 45A and 45B.

  When the torque acts on the pinion shaft 17 and torsionally deforms, the magnetic permeability of the first and second magnetostrictive films 39A and 39B changes. Therefore, a high-frequency AC voltage is applied to the first and second excitation coils 41A and 41B from the excitation circuit 44. By applying, the change in the magnetic permeability of the first and second magnetostrictive films 39A and 39B can be detected as the change in the impedance of the first and second detection coils 42A and 42B.

  As shown in FIG. 2, the back yoke 43 and the bobbin 40 are supported by the upper case 23 via the stay 47.

  As shown in FIG. 6, the first and second conversion circuits 45A and 45B convert the impedance changes of the first and second detection coils 42A and 42B to voltage signals VT1 and VT2, respectively. A difference between the signals VT1 and VT2 is amplified by an amplification factor k, and a torque detection signal VT3 obtained by adding a predetermined bias voltage Vb (for example, 2.5 V) thereto is output. This torque detection signal VT3 changes according to the torque input to the pinion shaft 17.

VT3 = k (VT1-VT2) + Vb
In this way, when the pinion shaft 17 is twisted and deformed together with the first and second magnetostrictive films 39A and 39B by the steering torque input to the steering wheel 11, the first and second magnetostrictive films 39A and 39B and the back yoke 43 are formed. By changing the magnetic flux density along the two magnetic paths, the steering torque can be detected based on the change in the magnetic flux density.

  The output voltages of the first and second exciting coils 41A and 41B are VT12 (low impedance) and VT21 (low impedance), respectively, and the output voltages of the first and second detection coils 42A and 42B are VT11 (high impedance) and When VT22 (impedance is large), the main torque detection value: V31 = VT12 / (VT12 + VT22) is compared with the redundant torque detection value: V32 = VT21 / (VT11 + VT21). By performing the failure determination, it is possible to increase the detection accuracy by eliminating variations in the neutral point of the steering torque sensor St.

  As described above, since the slit 43a extending in the axial direction is formed in the back yoke 43 surrounding the first and second exciting coils 41A and 41B and the first and second detecting coils 42A and 42B, the first and second exciting coils are formed. Generation of eddy current in the back yoke 43 when 41A and 41B are excited can be suppressed by the slit 43a, and the detection accuracy of the steering torque sensor St can be improved. In addition, since the back yoke 43 is formed by bending a single rectangular plate member into a cylindrical shape, the slit 43a is automatically formed between two opposing end surfaces of the back yoke 43 during bending. The structure can be greatly simplified and the manufacturing cost can be reduced. Further, since the end face of the back yoke 43 is flat, it is difficult to be affected by the edge, and the AC resistances of the first and second exciting coils 41A and 41B and the first and second detecting coils 42A and 42B are stabilized and detected. The accuracy can be further increased.

  Next, a second embodiment of the present invention will be described with reference to FIG.

  In the second embodiment, yoke rings 48 and 48 made of annular plates are added to both axial ends of the back yoke 43 of the first embodiment, thereby forming a more effective magnetic path. The aim is to further increase the output gain of the first and second detection coils 42A, 42B. At this time, if the inner surfaces of the yoke rings 48 and 48 are brought into direct contact with the axial end surface of the back yoke 43, the permeability becomes unstable due to variations in surface roughness and parallelism of the contact portions. There is a possibility that the detection accuracy of the steering torque sensor St is lowered.

  However, in the second embodiment, the flanges 40b and 40g at both ends in the axial direction of the bobbin 40 are extended in the radial direction to form plate-like extension portions 40h and 40h having a constant thickness, and these extension portions By sandwiching 40h and 40h between the back yoke 43 and the yoke rings 48 and 48, the back yoke 43 and the yoke rings 48 and 48 are not in contact with each other. For this reason, the magnetic permeability between the back yoke 43 and the yoke rings 48, 48 is slightly reduced, but the variation in the magnetic permeability due to the state of the contact portion is eliminated, and the distance between the two is kept constant, thereby reducing the magnetic permeability. As a result, the detection accuracy of the steering torque sensor St can be improved.

  Therefore, if the steering torque sensor St described in the first and second embodiments is used in the vehicle steering device, the steering torque input to the steering wheel 11 is detected with high accuracy, and the power steering device is electrically driven. By controlling the motor M, the steering feeling can be improved.

  The embodiments of the present invention have been described above, but various design changes can be made without departing from the scope of the present invention.

  For example, in the embodiment, the magnetostrictive torque sensor is applied to the steering torque sensor St, but the magnetostrictive torque sensor of the present invention is applied to a torque sensor for any application that detects torque input to the rotating shaft. Can do.

1 is an overall perspective view of an electric power steering apparatus according to a first embodiment. 2-2 line enlarged sectional view of FIG. 3-3 sectional view of FIG. 4 enlarged view of FIG. Perspective view of back yoke The figure which shows the change characteristic of the torque detection signal with respect to steering torque The figure corresponding to the said FIG. 4 based on 2nd Embodiment

Explanation of symbols

12 Upper steering shaft (steering shaft)
14 Lower steering shaft (steering shaft)
17 Pinion shaft (rotating shaft)
39A First magnetostrictive film (magnetostrictive film)
39B Second magnetostrictive film (magnetostrictive film)
40 Bobbin 40h Extension part 41A First exciting coil (coil)
41B Second excitation coil (coil)
42A First detection coil (coil)
42B Second detection coil (coil)
43 Back yoke 43a Slit 48 Yoke ring M Electric motor (actuator)
St Steering torque sensor (magnetostrictive torque sensor)

Claims (5)

Coils (41A, 41B; 42A, 42B) wound around a bobbin (40) are arranged on the outer periphery of a magnetostrictive film (39A, 39B) formed on the surface of the rotating shaft (17), and the coils (41A, 41B) are arranged. A cylindrical back yoke (43) is arranged on the outer periphery of 42A, 42B), and changes in the magnetic properties of the magnetostrictive films (39A, 39B) are detected by the coils (41A, 41B; 42A, 42B). In the magnetostrictive torque sensor for detecting the torque applied to the rotating shaft (17),
The back yoke (43) includes a slit (43a) sandwiched between a pair of flat end surfaces having a constant width in the radial direction and extending in the axial direction.   A rectangular magnetic metal plate is curved into a cylindrical shape to form the back yoke (43), and the slit (43a) is formed between the pair of opposed end faces. Item 2. The magnetostrictive torque sensor according to Item 1.   A pair of yoke rings (48) covering both axial ends of the back yoke (43) are provided, and the back yoke (43) and the yoke ring (48) are disposed in a non-contact manner. Item 2. The magnetostrictive torque sensor according to Item 1.   The bobbin (40) includes an annular extension (40h) extending radially outward, and the extension (40h) is sandwiched between the back yoke (43) and the yoke ring (48). The magnetostrictive torque sensor according to claim 3, wherein: A vehicle steering apparatus using the magnetostrictive torque sensor according to any one of claims 1 to 4,
The magnetostrictive torque sensor is used as a steering torque sensor (St) for detecting the steering torque input to the steering shaft (12, 14), and the electric power is based on the steering torque detected by the steering torque sensor (St). A vehicle steering apparatus that controls an operation of an actuator (M) of the steering apparatus.

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