JP4883972B2 - Torque sensor and electric power steering device - Google Patents

Description

  The present invention relates to a torque sensor and an electric power steering apparatus.

  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.

  As described in Patent Document 1, the conventional torque sensor has a cylindrical shape fixed to the input shaft, a first core having a magnetic path forming portion formed on the end surface, and a cylindrical shape fixed to the output shaft. A second core in which a magnetic path forming portion facing the magnetic path forming portion of the first core is formed on an end surface, and a cylindrical body that houses a detection coil that constitutes a magnetic circuit together with the first and second cores. And detecting a torque acting on a torsion bar connecting the input shaft and the output shaft.

The first and second cores are provided with teeth at a plurality of positions in the circumferential direction of the end surface of the lower end portion of the cylinder made of a magnetic material such as iron, and stainless steel, aluminum, resin, etc. at the valleys between adjacent teeth A non-shielding portion on the side of the portion shielded by the shielding portion of the shielding material in the circumferential direction of the end surface of the cylinder is fitted as the magnetic path forming portion on the end surface of the cylinder. Yes.
JP2005-3461

The torque sensor disclosed in Patent Document 1 has the following problems.
(1) Each core has a shielding material fitted to a cylinder made of a magnetic material, and an air gap is generated due to variations in the fitting dimensions of both parts, reducing the detection sensitivity of the torque sensor.

  (2) In order to improve the detection sensitivity of the torque sensor, it is necessary to strictly manage the dimensional tolerance between the cylinder made of the magnetic material described in (1) above and the shielding material, and it is difficult to assemble both parts with small dimensional tolerance. Accompany.

  (3) A cylinder made of a magnetic material requires sintering, sizing, and annealing processes, resulting in high costs.

  An object of the present invention is to improve the workability and assembling property of parts constituting the torque sensor and improve the detection sensitivity of the torque sensor.

  Another object of the present invention is to improve detection sensitivity of steering torque applied to a steering wheel and improve assist accuracy by an electric motor in an electric power steering apparatus.

The invention of claim 1 has a cylindrical shape fixed to the input shaft, a magnetic core forming portion formed on the end face, and a cylindrical shape fixed to the output shaft. A second core having an end surface with a magnetic path forming portion facing the path forming portion; and a cylindrical body that houses a detection coil that constitutes a magnetic circuit together with the first and second cores. In the torque sensor for detecting the torque acting on the torsion bar connected to the shaft, each of the first and second cores is inserted with a shielding material made of a nonmagnetic material with a magnetic material in which a magnetic material metal powder is mixed with a resin. molded becomes, the non-shielding portion of the magnetic material on the side near the portion where the shield portion of the shield member in the circumferential direction of the end face of the core shields, it was with the magnetic path forming portion of the end face of the core, wherein Press-fit the first core shielding material into the input shaft, and press-fit the second core shielding material into the output shaft Is obtained in such a manner that Te.

According to a second aspect of the present invention, in the first aspect of the present invention, the shielding material is cylindrical, and teeth are provided at a plurality of circumferential positions at one end, and the magnetic material is disposed at valleys between adjacent teeth. It is made by molding .

According to a third aspect of the present invention, in the second aspect of the present invention, the shielding member further includes teeth projecting radially outward at a plurality of positions in the circumferential direction of one end portion of the cylindrical main body, and the phase of the one end portion of the cylindrical main body. A trough is formed between adjacent teeth, and the magnetic material is molded into the outer periphery and trough of the cylindrical main body of the shielding material .

According to a fourth aspect of the present invention, in the third aspect of the present invention, the magnetic material is molded on the outer periphery of the cylindrical body of the shielding material at one end to the outer periphery, and not molded on the outer periphery of the intermediate to the other end. It is a thing.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the first and second cores have the same shape .

The invention of claim 6 has an input shaft to which the steering wheel is coupled and an output shaft interlocked with the electric motor, and drives the electric motor by the torque detected by the torque sensor according to any one of claims 1 to 5. This is an electric power steering device .

(Claim 1)
(a) A shielding material made of a non-magnetic material is provided on the end surfaces of the first and second cores, and the non-shielding portion of the magnetic material near the shielding portion of the shielding material is used as a magnetic path forming portion. The path of the magnetic flux generated between the magnetic path forming part of the first core and the magnetic path forming part of the second core is a shield adjacent to each other in the first core as shown by the solid line arrow in FIG. 3B is limited to the shield part of the material and the magnetic path forming part in the range sandwiched by the shield part, and the shield part of the shield material adjacent to the second core and the magnetic path forming part in the range sandwiched by the shield part. ) Around the side of the shielding portion as indicated by the broken-line arrows. For this reason, only the change in the overlapping area (magnetic flux passage area) of the magnetic path forming part of the first core and the magnetic path forming part of the second core accompanying torsion of the torsion bar between the input shaft and the output shaft. Therefore, the amount of change in magnetic permeability according to the above can be increased, the detection output width of the torque detection coil can be increased, and the detection accuracy and sensitivity can be improved.

  (b) Each core is formed by insert-molding a shielding material made of a non-magnetic material with a magnetic material in which a magnetic metal powder is mixed with a resin, thereby eliminating an air gap between the magnetic material and the shielding material. Detection sensitivity can be improved.

  (c) Each core eliminates the need for dimensional tolerance management for assembling both the magnetic material and the shielding material, and improves assemblability.

  (d) The magnetic material is integrally formed simply by molding a mixture of a magnetic material metal powder and a resin around the shielding material set in the mold, thereby reducing the cost.

(e) The first core shielding material is press-fitted into the input shaft, and the second core shielding material is press-fitted into the output shaft, so that the assembly of each core can be simplified.

(Claim 2 )
(f) Each core can improve assemblability by molding a magnetic material in a valley between adjacent teeth of a shielding material set in a mold.

(Claim 3 )
(g) Since each core is formed by molding a magnetic material in the outer periphery and valley of the cylindrical main body of the shielding material, the bond strength between the magnetic material and the shielding material can be enhanced in the axial direction and the circumferential direction.

(Claim 4 )
(h) Since each core molds the magnetic material on the outer periphery of the cylindrical body of the shielding material from one end portion to the outer periphery and does not mold the outer periphery from the intermediate portion to the other end portion, the shielding material insert set in the mold The heat dissipation at the time of molding is improved at the middle part to the other end part. As a result, the thermal strain at this part of the shielding material is minimized, and the accuracy of press fit to the input shaft or output shaft is improved. Improve assembly.

(Claim 5 )
(i) Since each core has the same shape, each core can be made into a common part.

(Claim 6 )
(j) In the torque sensor of the electric power steering apparatus, the above (a) to (i) 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.

  FIG. 1 is a cross-sectional view showing a main part of the electric power steering apparatus, FIG. 2 is an enlarged cross-sectional view showing a torque sensor, and FIG. 3 is a schematic view of the torque sensor.

  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 an input bearing 17, and the output shaft 15 is an output. The first housing 11 is supported via a bearing 18.

  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.

  The electric power steering device 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.

  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.

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. A cylindrical portion 14A is attached to the outer periphery of the first core 40, and a cylindrical first core 40 is press-fitted and fixed to the small-diameter portion B. The lower end face of the first core 40 is provided with a large number of magnetic path forming portions 40 </ b> A having a rectangular shape in plan view and formed at an equal pitch in the circumferential direction.

  The output shaft 15 has a cylindrical second core 50 attached to the outer periphery of a portion located inside the housing 12 and coaxially coupled to the input shaft 14 in a press-fit manner. On the end surface of the upper end portion of the second core 50, a large number of magnetic path forming portions 50 </ b> A having a rectangular shape in plan view and formed at an equal pitch in the circumferential direction facing the magnetic path forming portions 40 </ b> A of the first core 40 are provided.

  A first cylinder 60 and a second cylinder 70 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.

  The first cylindrical body 60 is fitted in the housing 12 so as to straddle the opposing portions of the first core 40 and the second core 50 and accommodates the torque detection coil 61. Reference numeral 62 denotes a detection connection line connected to the torque detection coil 61. The first cylinder 60 constitutes the first core 40 and the second core 50 and the magnetic circuit a. The magnetic circuit a is an air gap between the first cylinder 60 and the surface of the first core 40. a1, an air gap a2 with the surface of the second core 50, and an air gap a3 between the opposed surfaces of the first core 40 and the second core 50 are formed. The torque detection coil 61 is electromagnetically coupled to the first core 40 and the second core 50 and attracts a voltage corresponding to the electromagnetic coupling state.

  The second cylindrical body 70 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 71. Reference numeral 72 denotes a detection connection line connected to the temperature compensation coil 71. The second cylindrical body 70 constitutes a cylindrical portion 14A and a magnetic circuit b. The magnetic circuit b is formed so as to pass through air gaps b1 and b2 between the second cylindrical body 70 and the surface of the cylindrical portion 14A. . The temperature compensation coil 71 is electromagnetically coupled to the cylindrical portion 14A and induces a voltage corresponding to the electromagnetic coupling state for temperature compensation.

  When no torque acts on the torsion bar 16, the first core 40, the second core 50, and the cylindrical portion 14A are electromagnetically coupled so that the induced voltages of the torque detection coil 61 and the temperature compensation coil 71 are equal. The state is obtained, and the first core 40 and the second core 50 are respectively 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 corresponds to the air gaps a1, a2, and a3 in the magnetic circuit a. Are set to be equal to the influence of the magnetic resistances on the magnetic field, that is, the sum of the respective magnetic resistances ga1, ga2, and ga3.

  Therefore, in the torque sensor 30, the difference between the induced voltages of the torque detection coil 61 and the temperature compensation coil 71 is obtained to cancel the induced voltage due to the ambient temperature change, and the first core 40 and the second core 50. The electromagnetic coupling state corresponding to the relative rotation amount is detected, and only the torque acting on the torsion bar 16, in other words, the steering torque applied to the steering wheel can be detected.

Hereinafter, configurations of the first core 40 and the second core 50 will be described.
The first core 40 has a shielding material 42 made of a non-magnetic material such as stainless steel, aluminum, copper, resin, etc. set in a mold, and a magnetic metal powder such as iron powder or the like around the shielding material 42. The magnetic material 41 mixed with is cast and insert molded. Specifically, the shielding material 42 has a cylindrical shape (cylindrical body 42A), teeth 42B are provided at a plurality of positions in the circumferential direction of the lower end, and the magnetic material 41 is molded in a valley 42C between adjacent teeth 42B. . More specifically, the shielding member 42 forms teeth 42B projecting radially outward from a plurality of circumferential positions at the lower end of the cylindrical main body 42A, and is formed on the downward end surface of the crest of the teeth 42B. A rectangular end surface in plan view is formed in a plane orthogonal to the central axis of the input shaft 14, and a valley portion 42 </ b> C is formed between adjacent teeth 42 </ b> B at the lower end portion of the cylindrical main body 42 </ b> A. The cylindrical body 42A is molded into the outer periphery and the valley portion 42C. The magnetic material 41 includes a cylindrical main body 41A molded on the outer periphery of the cylindrical main body 42A of the shielding material 42, and a loading portion 41B protruding inward in the radial direction in an L shape from a plurality of circumferential positions at the lower end of the cylindrical main body 41A. And the rectangular end surface in plan view, which is the downward end surface of the loading portion 41B, is formed in a plane perpendicular to the central axis of the input shaft 14 by matching the downward end surface itself of the crest of the tooth 42B.

  The first core 40 uses the teeth 42 </ b> B of the shielding material 42 as a magnetic shielding part 40 </ b> B for the magnetic material 41. The first core 40 is magnetized on the side of the portion shielded by the shielding portion 40B (teeth 42B) of the shielding material 42 in the circumferential direction of the lower end surface (rectangular portion in plan view sandwiched between the adjacent shielding portions 40B and 40B). The non-shielding portion (loading portion 41B) of the material 41 is matched with the downward end surface of the crest of the tooth 42B, and this non-shielding portion is used as the above-described magnetic path forming portion 40A.

  At this time, the first core 40 molds the magnetic material 41 on the outer periphery of the cylindrical body 42 </ b> A of the shielding material 42 on the outer periphery of the lower end part to the intermediate part, and does not mold on the outer periphery of the intermediate part to the upper end part. The first core 40 press-fits the cylindrical body 42 </ b> A of the shielding material 42 into the small diameter portion B of the input shaft 14.

  In the second core 50, a shielding material 52 made of a nonmagnetic material such as stainless steel, aluminum, copper, or resin is set in a mold. Around the shielding material 52, a magnetic material metal powder such as iron powder is applied to the resin. The magnetic material 51 mixed with is cast and insert molded. Specifically, the shielding material 52 has a cylindrical shape (cylindrical main body 52A), teeth 52B are provided at a plurality of positions in the circumferential direction of the upper end portion, and the magnetic material 51 is molded in the valley portions 52C between the adjacent teeth 52B. . More specifically, the shielding material 52 forms teeth 52B projecting radially outward from a plurality of circumferential positions at the upper end of the cylindrical main body 52A, and the upward end surface of the crest of the teeth 52B. A rectangular end surface in a plan view is formed on a plane orthogonal to the central axis of the output shaft 15, and a valley portion 52 </ b> C is formed between adjacent teeth 52 </ b> B at the upper end portion of the cylindrical main body 52 </ b> A. The cylindrical body 52A is molded into the outer periphery and the valley 52C. The magnetic material 51 includes a cylindrical main body 51A molded on the outer periphery of the cylindrical main body 52A of the shielding material 52, and a loading portion 51B that protrudes inward in the radial direction in an L shape from a plurality of circumferential positions at the upper end of the cylindrical main body 51A. And the rectangular end surface in plan view, which is the upward end surface of the loading portion 51B, is formed in a plane perpendicular to the central axis of the output shaft 15 by matching the upward end surface of the tooth 52B.

  The second core 50 uses the teeth 52 </ b> B of the shielding material 52 as a magnetic shielding part 50 </ b> B for the magnetic material 51. The second core 50 is magnetic on the side of the portion shielded by the shielding portion 50B (teeth 52B) of the shielding material 52 in the circumferential direction of the upper end surface (rectangular portion in plan view sandwiched between adjacent shielding portions 50B and 50B). The non-shielding part (loading part 51B) of the material 51 is matched with the upward end surface itself of the crest of the tooth 52B, and this non-shielding part is used as the magnetic path forming part 50A.

  At this time, the second core 50 molds the magnetic material 51 on the outer periphery of the cylindrical body 52 </ b> A of the shielding material 52, and does not mold the outer periphery of the intermediate portion to the lower end. The second core 50 press-fits the cylindrical body 52 </ b> A of the shielding material 52 into the output shaft 15.

  The magnetic path forming part 40A of the first core 40 and the magnetic path forming part 50A of the second core 50 have a facing relationship that is appropriately spaced apart. In the present embodiment, the first core 40 (magnetic material 41, shielding material 42) and the second core 50 (magnetic material 51, shielding material 52) have the same shape with the same inner and outer diameter dimensions and axial length dimensions. ing.

According to the present embodiment, the following operational effects can be obtained.
(a) The shielding members 42 and 52 made of a non-magnetic material are provided on the end surfaces of the first and second cores 40 and 50, and the non-shielding portion of the magnetic material beside the shielding portions 40B and 50B of the shielding materials 42 and 52. Were defined as magnetic path forming portions 40A and 50A. The path of the magnetic flux generated between the magnetic path forming portion 40A of the first core 40 and the magnetic path forming portion 50A of the second core 50 is the first core 40 as shown by the solid line arrow in FIG. The adjacent shield member 42 has a shield part 40B and a magnetic path forming part 40A in the range sandwiched between the shield parts 40B, and the second core 50 has a shield part 52B and the shield part 50B and the shield part 50B. This is limited to the magnetic path forming portion 50A, and is prevented from wrapping around the shielding portions 40B and 50B as indicated by broken line arrows in FIG. For this reason, the overlapping area of the magnetic path forming portion 40A of the first core 40 and the magnetic path forming portion 50A of the second core 50 accompanying the twist 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 passage area) can be increased, so that the detection output width of the torque detection coil 61 can be increased, thereby improving the detection accuracy and sensitivity.

  (b) The cores 40 and 50 are formed by insert-molding the shielding materials 42 and 52 made of a non-magnetic material with the magnetic materials 41 and 51 in which the magnetic material metal powder is mixed with the resin. The air gap between the shielding members 42 and 52 can be eliminated, and the detection sensitivity of the torque sensor 30 can be improved.

  (c) The cores 40 and 50 do not require management of dimensional tolerances for assembling both the magnetic members 41 and 51 and the shielding members 42 and 52, and improve the assemblability.

  (d) The magnetic materials 41 and 51 are formed simply by molding a mixture of magnetic material metal powder in a resin around the shielding materials 42 and 52 set in a mold, thereby reducing the cost.

  (e) The shielding material 42 of the first core 40 is press-fitted into the input shaft, and the shielding material 52 of the second core 50 is press-fitted into the output shaft. Can be.

  (f) The cores 40 and 50 are assembled by molding the magnetic materials 41 and 51 in the valley portions 42C and 52C between the adjacent teeth 42B and 52B of the shielding materials 42 and 52 set in the mold. Can be improved.

  (g) Since each of the cores 40 and 50 is formed by molding the magnetic materials 41 and 51 into the outer periphery of the cylindrical main bodies 42A and 52A and the valley portions 42C and 52C of the shielding materials 42 and 52, the magnetic materials 41 and 51 The coupling strength of the shielding materials 42 and 52 can be enhanced in the axial direction and the circumferential direction.

  (h) Since the cores 40 and 50 mold the magnetic materials 41 and 51 only on the outer periphery of the cylindrical body of the shielding materials 42 and 52 only on the outer periphery of the intermediate portion and the other end, The heat dissipation during the insert molding of the shielding materials 42 and 52 set in the mold is improved at the intermediate portion to the other end portion, and as a result, the thermal strain at this portion of the shielding materials 42 and 52 is minimized and input is performed. The press-fitting dimension accuracy to the shaft or the output shaft is improved, and the assemblability of the cores 40 and 50 is improved.

  (i) Since the cores 40 and 50 have the same shape, the cores 40 and 50 can be made into common parts.

  (j) In the torque sensor 30 of the electric power steering apparatus 10, the above (a) to (i) 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.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and even if there is a design change or the like without departing from the gist of the present invention. It is included in the present invention. For example, in the cores 40 and 50 of the present invention, the shielding materials 42 and 52 may be made of a metal (aluminum, copper, etc.) having a lower electrical resistivity than the magnetic materials 41, 51 (iron, etc.).

FIG. 1 is a cross-sectional view showing a main part of the electric power steering apparatus. FIG. 2 is an enlarged sectional view showing the torque sensor. FIG. 3 is a schematic diagram of the 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 40 1st core 40A Magnetic path formation part 40B Shielding part 41 Magnetic material 42 Shielding material 42A Cylindrical main body 42B Teeth 42C Valley 50 Second core 50A Magnetic path forming part 50B Shielding part 51 Magnetic material 52 Shielding material 52A Cylindrical main body 52B Teeth 52C Valley part 60 Cylindrical body 61 Detection coil

Claims (6)

A first core having a cylindrical shape fixed to the input shaft and having a magnetic path forming portion formed on an end face;
A second core having a cylindrical shape fixed to the output shaft and having a magnetic path forming portion opposite to the magnetic path forming portion of the first core formed on the end face;
A cylindrical body that houses a detection coil that constitutes a magnetic circuit together with the first and second cores;
In the torque sensor for detecting the torque acting on the torsion bar connecting the input shaft and the output shaft,
Each of the first and second cores is formed by insert-molding a shielding material made of a non-magnetic material with a magnetic material in which a magnetic material metal powder is mixed with a resin, and the shielding portion of the shielding material in the circumferential direction of the end surface of the core There the unshielded portion of the magnetic material on the side near the part to be shielded, it was with the magnetic path forming portion of the end face of the core,
A torque sensor, wherein the first core shielding material is press-fitted into an input shaft, and the second core shielding material is press-fitted into an output shaft . The torque sensor according to claim 1 , wherein the shielding material has a cylindrical shape, teeth are provided at a plurality of positions in the circumferential direction of one end, and the magnetic material is molded in a valley portion between adjacent teeth. The shield material is provided with teeth projecting radially outward at a plurality of circumferential positions at one end of the cylindrical body, and a valley is formed between adjacent teeth at one end of the cylindrical body,
The torque sensor according to claim 2 , wherein the magnetic material is molded in an outer periphery and a valley portion of a cylindrical main body of a shielding material. 4. The torque sensor according to claim 3 , wherein the magnetic material is molded on one outer periphery to the outer periphery of the cylindrical body of the shielding material and is not molded on the outer periphery of the intermediate portion to the other end. The torque sensor according to any one of claims 1 to 4 , wherein the first and second cores have the same shape. An electric motor having an input shaft to which a steering wheel is coupled and an output shaft interlocked with the electric motor, and driving the electric motor with the torque detected by the torque sensor according to any one of claims 1 to 5. Power steering device.

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