JP2005003459A - Torque sensor and electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the detection output width of a detection coil in a torque sensor, and to improve detection accuracy and sensitivity. <P>SOLUTION: This torque sensor has the first cylinder 31 fixed on an input shaft 14 and having a magnetic path formation part 31A formed on the end face, the second cylinder fixed on an output shaft 15 and having a magnetic path formation part 32A facing to the magnetic path formation part 31A of the first cylinder 31 and formed on the end face, and a cylinder body 33 for storing the detection coil 35 constituting a magnetic circuit together with the first and second cylinders 31, 32. In the sensor, the magnetic path formation parts 31A, 32A formed on the end faces of the first and second cylinders 31, 32 comprise ridged parts of teeth 41, 42 formed on the end faces of the cylinders 31, 32, and shielding materials 51, 52 comprising a non-magnetic material are filled in grooved parts of the teeth 41, 42. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a torque sensor and an electric power steering apparatus.
[0002]
[Prior art]
In the electric power steering apparatus, an input shaft to which a steering wheel is coupled and an output shaft are connected via a torsion bar, and a steering torque applied to the steering wheel is detected by a torque sensor, and the electric motor is driven by the detected torque. The generated torque of the electric motor is transmitted to the output shaft, and as a result, the generated torque of the electric motor is used as an assist force for the steering force applied by the driver to the steering wheel.
[0003]
As described in Patent Document 1, the conventional torque sensor is fixed to the input shaft 1 and fixed to the first cylinder 2 made of a magnetic material having a magnetic path forming portion (tooth) 2A formed on the end face and to the output shaft 3. The second cylinder 4 made of a magnetic material having a magnetic path forming portion (tooth) 4A facing the magnetic path forming portion 2A of the first cylinder 2 formed on the end face, and the first and second cylinders 2, 4 In addition, it has a cylindrical body 5 that houses a torque detection coil 5A constituting a magnetic circuit, and detects a torque that acts on a torsion bar that connects the input shaft 1 and the output shaft 3 (FIG. 4).
[0004]
[Patent Document 1]
Real registration 2583974 (3 pages, Fig. 2)
[0005]
[Problems to be solved by the invention]
In the torque sensor disclosed in Patent Document 1, as shown in FIG. 4A, the magnetic path forming portion 2A of the first cylinder 2 and the magnetic path forming portion 4A of the second cylinder 4 are arranged in the circumferential direction of their axial end surfaces. It is composed of tooth crests that are processed so as to repeat unevenness at equal intervals. The overlapping area of the magnetic path forming portion 2A (peak portion) of the first cylinder 2 and the magnetic path forming portion 4A (peak portion) of the second cylinder 4 is determined by the first cylinder 2 and the second cylinder 4 as follows. It is set as the magnetic flux path area of the magnetic circuit to comprise. Then, due to torsion of the torsion bar between the input shaft 1 and the output shaft 3, the magnetic path forming portion 2A (peak portion) of the first cylinder 2 and the magnetic path forming portion 4A (peak portion) of the second cylinder 4 are The overlapping area, in other words, the magnetic flux path area is changed as shown in FIGS. 4B and 4C, and the change in permeability according to the change in area is detected by the torque detection coil 5A. Torque acting on the torsion bar is detected from the detection result.
[0006]
However, in the torque sensor of Patent Document 1, the path of the magnetic flux generated between the magnetic path forming portion 2A of the first cylinder 2 and the magnetic path forming portion 4A of the second cylinder 4 is as shown in FIG. The magnetic path forming portions 2A and 4A go not only to the top surfaces of the crests but also to the side surfaces to reduce the amount of change in the magnetic permeability due to the torsion bar torsion between the input shaft 1 and the output shaft 3. The detection output of the torque detection coil 5A is reduced.
[0007]
An object of the present invention is to increase a detection output width of a detection coil in a torque sensor and improve detection accuracy and sensitivity.
[0008]
Another object of the present invention is to improve detection accuracy of steering torque applied to a steering wheel and improve assist accuracy by an electric motor in an electric power steering apparatus.
[0009]
[Means for Solving the Problems]
According to the first aspect of the present invention, a first cylinder made of a magnetic material fixed to the input shaft and having a magnetic path forming portion formed on the end face, and fixed to the output shaft and facing the magnetic path forming portion of the first cylinder. A second cylinder made of a magnetic material having a magnetic path forming portion formed on the end face; and a cylindrical body that houses a detection coil that constitutes a magnetic circuit together with the first and second cylinders. In the torque sensor for detecting the torque acting on the torsion bar connected to the shaft, the magnetic path forming portion formed on the end surfaces of the first and second cylinders is formed from the peak portion of the teeth formed on the end surfaces of the cylinders. Thus, the valleys of the teeth are filled with a shielding material made of a nonmagnetic material.
[0010]
According to a second aspect of the present invention, in the first aspect of the present invention, the first cylinder and the second cylinder have the same shape.
[0011]
According to a third aspect of the present invention, there is provided an electric power having an input shaft to which the steering wheel is coupled and an output shaft interlocked with the electric motor, and driving the electric motor by the torque detected by the torque sensor according to the first or second aspect. It is a steering device.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
1 is a cross-sectional view showing a main part of an electric power steering apparatus, FIG. 2 is an enlarged cross-sectional view showing a torque sensor, FIG. 3 is a schematic view showing a torque sensor, and FIG. 4 is a schematic view showing a conventional torque sensor. is there.
[0013]
First Embodiment (FIGS. 1 to 3)
As shown in FIG. 1, the electric power steering apparatus 10 bolts a second housing 12 to a first housing 11 fixed to a vehicle body frame or the like. The input shaft 14 to which the steering wheel is coupled and the output shaft 15 are coaxially coupled via a torsion bar 16. The input shaft 14 is supported by the second housing 12 via a bearing 17, and the output shaft 15 is supported by a bearing 18. It supports to the 1st housing 11 via.
[0014]
The electric power steering device 10 connects a pinion shaft to the output shaft 15 and supports a rack shaft including a rack that meshes with the pinion of the pinion shaft so that the rack shaft can move left and right. The rotary motion of the output shaft 15 is converted into the linear motion of the rack shaft via the pinion shaft, and the wheels are steered.
[0015]
The electric power steering apparatus 10 supports an electric motor (not shown) on a first housing 11, a worm gear 21 is coupled to an output shaft of the electric motor, and a worm wheel 22 meshing with the worm gear 21 is connected to the first housing 11 and the second housing 11. The housing 12 is fixed to the output shaft 15.
[0016]
The electric power steering apparatus 10 is provided with a torque sensor 30 between the input shaft 14 and the output shaft 15. The steering torque applied to the steering wheel is detected by the torque sensor 30, the electric motor is driven by the detected torque, and the generated torque of the electric motor is transmitted to the output shaft 15 via the worm gear 21 and the worm wheel 22. Thereby, the torque generated by the electric motor is used as an assist force for the steering force applied by the driver to the steering wheel.
[0017]
However, the torque sensor 30 is configured as follows (FIG. 2).
The input shaft 14 is made of a magnetic material, and includes a large diameter portion A and a small diameter portion B on the side of a portion located inside the housing 12 and coaxially coupled to the output shaft 15. The outer periphery of the first cylinder 31 is a cylindrical portion 14A, and a first cylinder 31 made of a magnetic material is attached to the small-diameter portion B in a press-fit manner. The lower end surface of the first cylinder 31 is provided with a large number of magnetic path forming portions 31 </ b> A having a rectangular shape in plan view and formed at an equal pitch in the circumferential direction.
[0018]
Here, in the first cylinder 31, a large number of rectangular teeth 41 are formed in the circumferential direction of the lower end surface, and the top surface of the peak portion of the mountain portion of the teeth 41 is orthogonal to the central axis of the input shaft 14. To form a flat surface. The valleys of the teeth 41, which are part of the lower end surface of the first cylinder 31, are filled with a shielding material 51 made of a nonmagnetic material such as stainless steel, aluminum, or resin (FIG. 3). The first cylinder 31 is set in the mold, and after filling the molten shielding material 51 into the valleys of the teeth 41 (molding), it is cooled and solidified. The shielding material 51 is filled in the valleys of the teeth 41 without any gap, and the upper surface of the shielding material 51 is flush with the top surface of the crests of the teeth 41. In the circumferential direction of the end surface of the first cylinder 31, the non-shielding part on the side of the part shielded by the shielding material 51 (the rectangular part in a plan view sandwiched between the neighboring shielding materials 51, 51) is the peak part of the teeth 41. This non-shielding portion becomes the above-described magnetic path forming portion 31A.
[0019]
The output shaft 15 has a second cylinder 32 made of a magnetic material press fitted and fixed to the outer periphery of a portion located inside the housing 12 and coaxially coupled to the input shaft 14. The first cylinder 31 and the second cylinder 32 are juxtaposed in the axial direction of the input shaft 14 and the output 15. The upper end surface of the second cylinder 32 is provided with a large number of magnetic path forming portions 32 </ b> A having a rectangular shape in plan view and formed at an equal pitch in the circumferential direction.
[0020]
Here, in the second cylinder 32, a large number of rectangular teeth 42 are formed in the circumferential direction of the upper end surface, and the top surface of the rectangular portion of the peak portion of the teeth 42 is orthogonal to the central axis of the output shaft 15. To form a flat surface. The valleys of the teeth 42 that are part of the upper end surface of the second cylinder 32 are filled with a shielding material 52 made of a nonmagnetic material such as stainless steel, aluminum, or resin (FIG. 3). The second cylinder 32 is set in a mold and filled with a shielding material 52 in a molten state in the valleys of the teeth 42 (mold), and then cooled and solidified. The shielding material 52 is filled in the valleys of the teeth 42 without a gap, and the upper surface of the shielding material 52 is flush with the top surface of the crests of the teeth 42. In the circumferential direction of the end surface of the second cylinder 32, the non-shielding portion on the side of the portion shielded by the shielding material 52 (the rectangular portion in a plan view sandwiched between the neighboring shielding materials 52, 52) is the peak portion of the tooth 42. This non-shielding portion is the magnetic path forming portion 32A described above.
[0021]
When the shielding materials 51 and 52 are molded, an annular cavity is formed from the end surfaces of the cylinders 31 and 32 to the inner surface, and the cooled and solidified shielding materials 51 and 52 are polymerized in the radial direction on the inner surfaces of the cylinders 31 and 32. By adopting the shape, more reliable coupling can be maintained.
[0022]
The magnetic path forming portion 31A of the first cylinder 31 and the magnetic path forming portion 32A of the second cylinder 32 have a facing relationship that is appropriately separated by a long distance. In the present embodiment, the first cylinder 31 and the second cylinder 32 have the same shape with the same inner and outer diameter dimensions and axial length dimensions.
[0023]
A first cylinder 33 and a second cylinder 34 having a U-shaped cross section made of a sintered alloy, which is a magnetic material, or a press, are inserted into the inner periphery of the housing 12.
[0024]
The first cylinder 33 is fitted into the housing 12 so as to straddle the opposing portions of the first cylinder 31 and the second cylinder 32 and accommodates the torque detection coil 35. Reference numeral 35A denotes a measurement cord connected to the torque detection coil 35. The first cylinder 33 constitutes a first cylinder 31 and a second cylinder 32 and a magnetic circuit a. The magnetic circuit a is an air gap between the first cylinder 33 and the surface of the first cylinder 31. a1, an air gap a2 with the surface of the second cylinder 32, and an air gap a3 between the opposing end faces of the first cylinder 31 and the second cylinder 32. The torque detection coil 35 is electromagnetically coupled to the first cylinder 31 and the second cylinder 32 and attracts a voltage corresponding to the electromagnetic coupling state.
[0025]
The second cylinder 34 is fitted in the housing 12 so as to surround the cylindrical portion 14 </ b> A of the input shaft 14 and accommodates the temperature compensation coil 36. Reference numeral 36A denotes a measurement cord connected to the temperature compensation coil 36. The second cylindrical body 34 constitutes a cylindrical portion 14A and a magnetic circuit b, and the magnetic circuit b is formed so as to pass through air gaps b1 and b2 between the second cylindrical body 34 and the surface of the cylindrical portion 14A. . The temperature compensation coil 36 is electromagnetically coupled to the cylindrical portion 14A and induces a voltage corresponding to the electromagnetic coupling state.
[0026]
When no torque is applied to the torsion bar 16, the first cylinder 31, the second cylinder 32, and the cylindrical portion 14A are electromagnetically coupled so that the induced voltages of the torque detection coil 35 and the temperature compensation coil 36 are equal. A state is calculated | required and the 1st cylinder 31 and the 2nd cylinder 32 are each positioned. The outer diameter of the cylindrical portion 14A depends on the influence of the air gaps b1 and b2 in the magnetic circuit b on the magnetic field, that is, the sum of the respective magnetic resistances gb1 and gb2 is the air gaps a1, a2, and a3 in the magnetic circuit a. Are set to be equal to the influence of each of the magnetic resistances on the magnetic field, that is, the sum of the respective magnetic resistances ga1, ga2, and ga3.
[0027]
Therefore, in the torque sensor 30, the difference between the induced voltages of the torque detection coil 35 and the temperature compensation coil 32 is obtained to cancel the induced voltage due to the ambient temperature change, and the first cylinder 31 and the second cylinder 32. The electromagnetic coupling state corresponding to the relative rotation amount is detected, and the torque applied to the torsion bar 16, that is, the steering torque applied to the steering wheel can be detected.
[0028]
According to this embodiment, there exist the following effects.
(1) Magnetic path forming portions 31A and 32A are formed at the crests of the teeth 41 and 42 formed on the end surfaces of the first and second cylinders 31 and 32, and the nonmagnetic material is formed at the troughs of the teeth 41 and 42. The shielding materials 51 and 52 made of are filled by casting. The path of the magnetic flux generated between the magnetic path forming part 31A of the first cylinder 31 and the magnetic path forming part 32A of the second cylinder 32, as shown by the solid line arrow in FIG. The top surface of the peak portion of the tooth 41 sandwiched between the materials 51 and the top surface of the top portion of the peak portion of the tooth 42 sandwiched between the shielding material 52 and the shielding material 52 are shielded as shown by the broken line arrows in FIG. It is suppressed that it goes around to the side surface of the peak part shielded by the materials 51 and 52. For this reason, the overlapping area of the magnetic path forming portion 31A of the first cylinder 31 and the magnetic path forming portion 32A of the second cylinder 32 due to the torsion of the torsion bar 16 between the input shaft 14 and the output shaft 15 ( The amount of change in the magnetic permeability according to only the change in the magnetic flux path area) can be increased, and the detection output width of the torque detection coil 35 can be increased.
[0029]
(2) The first and second cylinders 31 and 32 have the same shape and can be made into a common part. (3) In the torque sensor 30 of the electric power steering apparatus 10, the above (1) and (2) can be realized. Thereby, the detection accuracy of the steering torque applied to the steering wheel can be improved, and the assist accuracy by the electric motor can be improved.
[0030]
Although the embodiment of the present invention has been described with reference to the drawings, the specific configuration of the present invention is not limited to this embodiment, and there are design changes and the like without departing from the scope of the present invention. Are also included in the present invention. For example, a cylindrical body that houses a temperature compensation coil is provided so as to straddle the opposing portions of two cylinders fixed to the input shaft, and a magnetic circuit for the temperature compensation coil is formed by the cylinder and the two cylinders. May be formed. And at this time, you may comprise the magnetic path formation part formed in each of the opposing end surface of two cylinders by the fitting structure of the shielding material of this invention.
[0031]
【The invention's effect】
According to the present invention, the detection output width of the detection coil in the torque sensor can be increased, and the detection accuracy and sensitivity can be improved.
[0032]
Further, according to the present invention, in the electric power steering apparatus, the detection accuracy of the steering torque applied to the steering wheel can be improved, and the assist accuracy by the electric motor can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a main part of an electric power steering apparatus.
FIG. 2 is an enlarged cross-sectional view of a torque sensor.
FIG. 3 is a schematic diagram showing a torque sensor.
FIG. 4 is a schematic diagram showing a conventional torque sensor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 14 Input shaft 15 Output shaft 16 Torsion bar 30 Torque sensor 31 1st cylinder 31A Magnetic path formation part 32 2nd cylinder 32A Magnetic path formation part 33, 34 Cylindrical bodies 35, 36 Detection coils 41, 42 Teeth 51, 52 Shielding material

Claims (3)

A first cylinder made of a magnetic material fixed to the input shaft and having a magnetic path forming portion formed on the end face;
A second cylinder made of a magnetic material fixed to the output shaft and having a magnetic path forming portion opposed to the magnetic path forming portion of the first cylinder formed on an end surface;
A cylindrical body that houses a detection coil that forms a magnetic circuit together with the first and second cylinders;
In the torque sensor for detecting the torque acting on the torsion bar connecting the input shaft and the output shaft,
The magnetic path forming portions formed on the end surfaces of the first and second cylinders are formed by tooth crests formed on the end surfaces of the cylinders, and the tooth valley portions are filled with a shielding material made of a nonmagnetic material. A torque sensor characterized by comprising: The torque sensor according to claim 1, wherein the first cylinder and the second cylinder have the same shape. 3. An electric power steering apparatus comprising: an input shaft to which a steering wheel is coupled; and an output shaft interlocked with the electric motor, wherein the electric motor is driven by torque detected by a torque sensor according to claim 1 or 2. .

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