JP4718955B2 - 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 is a first type in which each of the input shaft and the output shaft is supported on the housing via the input bearing and the output bearing, and is fixed to each of the input shaft and the output shaft. A torque detection coil that constitutes a magnetic circuit together with the second core is provided in the housing, and a torque acting on a torsion bar connecting the input shaft and the output shaft is detected.

Moreover, in the torque sensor of patent document 1, the temperature compensation coil which comprises a magnetic circuit with the outer peripheral cylindrical part of the input shaft which consists of magnetic materials is provided in a housing, and the difference of the induced voltage of a torque detection coil and a temperature compensation coil is calculated | required. This cancels the induced voltage due to ambient temperature changes and improves the detection accuracy of the torque sensor.
JP2005-3462

  In the torque sensor of Patent Document 1, an input bearing is provided near the temperature compensation coil in the housing axial direction, and the temperature compensation coil is electromagnetically coupled to the outer peripheral cylindrical portion of the input shaft, and has the following problems.

  (1) An input bearing is provided directly above the temperature compensation coil, and it is necessary to consider magnetic shielding so that the input bearing does not interfere magnetically with the magnetic circuit of the temperature compensation coil to deteriorate the magnetic characteristics. .

  (2) Since the input bearing is positioned on the opposite side of the output bearing across the temperature compensation coil in the axial direction of the input shaft and the output shaft, the support span of the input bearing and the output bearing is large. For this reason, there is a difficulty in improving the coaxiality of the input shaft and the output shaft, and there is a possibility that the torque detection accuracy may be impaired due to the rotational eccentricity of both.

  An object of the present invention is to stabilize the magnetic characteristics of a temperature compensation coil and improve the detection accuracy of a torque sensor.

  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.

  According to the first aspect of the present invention, the input shaft and the output shaft are supported by the housing via the input bearing and the output bearing, respectively, and the first and second cores fixed to the input shaft and the output shaft are magnetized together. In a torque sensor that detects torque acting on a torsion bar that connects an input shaft and an output shaft, a torque detection coil that constitutes a circuit is provided in the housing, and the temperature compensation coil is connected to the input shaft. The input bearing is provided between them, and the temperature compensation coil is electromagnetically coupled to the input bearing.

  According to a second aspect of the present invention, in the first aspect of the present invention, the input bearing is provided between a coil bobbin of the temperature compensation coil and the input shaft.

  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.

(Claim 1)
(a) Since an input bearing is provided between the temperature compensation coil provided in the housing and the input shaft, and the temperature compensation coil is directly electromagnetically coupled to the input bearing, the input bearing constitutes the magnetic circuit of the temperature compensation coil. There is no need to consider interference of the input bearing with the magnetic circuit. Accordingly, the magnetic characteristics of the temperature compensation coil can be easily stabilized.

  (b) Since the input bearing is not located on the opposite side of the output bearing across the temperature compensation coil in the axial direction of the input shaft and the output shaft, it is located at the same position as the temperature compensation coil. Support span between bearings can be reduced. For this reason, the coaxiality of the input shaft and the output shaft is improved, and the torque eccentricity can be suppressed by suppressing the rotational eccentricity of both.

(Claim 2)
(c) The input bearing can be held on the coil bobbin of the temperature compensation coil to stably support the input shaft.

(Claim 3)
(d) In the torque sensor of the electric power steering device, the above (a) to (c) 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 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.

  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 has a diameter portion A and a diameter portion B on the side of a portion located inside the housing 12 and coaxially coupled to the output shaft 15. Is a cylindrical portion 14A, and a cylindrical first core 40 is press-fitted and fixed to the 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 are provided opposite to the magnetic path forming portions 40 </ b> A of the first core 40.

  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 surrounds the diameter portion A of the input shaft 14 and is fitted into the housing 12 to accommodate the temperature compensation coil 71. Reference numeral 72 denotes a detection connection line connected to the temperature compensation coil 71.

  Here, the torque sensor 30 is provided with the aforementioned input bearing 17 made of a magnetic material between the temperature compensation coil 71 and the diameter portion A of the input shaft 14. The input bearing 17 fits and holds the outer ring 17 </ b> A on the inner circumferential step surface of the resin coil bobbin 71 </ b> A of the temperature compensation coil 71, and the inner ring 17 </ b> B is fitted on the outer circumferential step surface of the diameter portion A of the input shaft 14. Is supported rotatably. The second cylindrical body 70 constitutes an input bearing 17 (outer ring 17A) and a magnetic circuit b. The magnetic circuit b is an air gap b1 between the second cylindrical body 70 and the surface of the input bearing 17 (outer ring 17A), It is formed so as to pass through b2. The temperature compensation coil 71 and the second cylindrical body 70 are electromagnetically coupled to the input bearing 17 (outer ring 17A) and induce a voltage corresponding to the electromagnetic coupling state.

  When no torque acts on the torsion bar 16, the first core 40, the second core 50, and the input bearing 17 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 size of the input bearing 17 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 Each is set to be equal to the influence of 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.

According to the present embodiment, the following operational effects can be obtained.
(a) Since the input bearing 17 is provided between the temperature compensation coil 71 provided in the housing 12 and the input shaft 14 and the temperature compensation coil 71 is directly electromagnetically coupled to the input bearing 17, the input bearing 17 is magnetically coupled to the temperature compensation coil 71. It forms part of the circuit and does not interfere with the magnetic circuit. Therefore, the magnetic characteristics of the temperature compensation coil 71 can be easily stabilized.

  (b) Since the input bearing 17 is not located on the opposite side of the output bearing across the temperature compensation coil 71 in the axial direction of the input shaft 14 and the output shaft 15, it is located at the same position as the temperature compensation coil 71. The support span between the input bearing 17 and the output bearing 18 can be reduced. For this reason, the coaxiality of the input shaft 14 and the output shaft 15 is improved, and the rotational eccentricity of both is suppressed and the torque detection accuracy can be improved.

  (c) The input bearing 17 is held on the coil bobbin 71A of the temperature compensation coil 71 and can be disposed close to the temperature compensation coil 71, so that the input shaft 14 can be stably supported.

  (d) In the torque sensor 30 of the electric power steering apparatus 10, the above-described (a) to (c) 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.

  In the torque sensor 30, the first core 40 and the second core 50 are configured as follows.

  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 orthogonal to the central axis of the input shaft 14 by matching the downward end surface of the crest of the tooth 42B itself.

  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 42A of the shielding material 42 on the outer periphery of the lower end portion to the intermediate portion, and does not mold on the outer periphery of the intermediate portion to the upper end portion. 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.

Therefore, in this embodiment, the following operational effects are also achieved.
(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 one end to the outer periphery of the cylindrical body of the shielding materials 42 and 52 and do not mold on the outer periphery of the intermediate and other ends, The heat dissipation at the time of insert molding of the shielding materials 42 and 52 set in the mold is improved from the middle 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 the input shaft Or the press-fit dimension precision to an output shaft is improved, and the assembly | attachment property of each core 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 11, 12 Housing 14 Input shaft 15 Output shaft 16 Torsion bar 17 Input bearing 18 Output bearing 30 Torque sensor 40 1st core 50 2nd core 61 Torque detection coil 71 Temperature compensation coil 71A Coil bobbin

Claims (3)

Support the input shaft and output shaft to the housing via the input bearing and output bearing,
A torque detection coil that constitutes a magnetic circuit together with the first and second cores fixed to the input shaft and the output shaft is provided in the housing,
In the torque sensor for detecting the torque acting on the torsion bar connecting the input shaft and the output shaft,
A torque sensor comprising: a temperature compensation coil provided in a housing; the input bearing provided between the temperature compensation coil and an input shaft; and the temperature compensation coil being electromagnetically coupled to the input bearing.   The torque sensor according to claim 1, wherein the input bearing is provided between a coil bobbin of a temperature compensation coil and an input shaft.   3. An electric power steering apparatus comprising: an input shaft to which a steering wheel is coupled; and an output shaft linked to 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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