Method of manufacturing coil for torque sensor

A method of manufacturing a coil for a torque sensor includes: holding a bobbin with a jig, the bobbin being formed in a cylindrical shape and provided with first inclined grooves and second inclined grooves on a cylindrical outer peripheral surface of the bobbin, the first inclined grooves being inclined at a preset specified angle with respect to an axial direction of the cylindrical shape, and the second inclined grooves being inclined at the specified angle with respect to the axial direction in a direction opposite to the first inclined grooves; and rotating the bobbin while simultaneously supplying insulated wires from nozzles arranged to surround the bobbin, and driving the nozzles in a direction orthogonal to a rotation direction of the bobbin so as to wind the insulated wires around the bobbin along the first inclined grooves or the second inclined grooves.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No. 2019-024397 filed on Feb. 14, 2019 with the Japan Patent Office, the entire disclosure of which is incorporated herein by reference.

BACKGROUND

The present disclosure relates to a method of manufacturing a coil for a torque sensor.

There is widely known a torque sensor that measures a torque applied to a rotation shaft having magnetostrictive properties. For example, Japanese Unexamined Patent Application Publication No. 2016-200552 proposes a technique of winding an insulated wire forming a coil around a bobbin when manufacturing a coil for a magnetostrictive torque sensor used in a torque sensor by alternately repeating (i) winding the insulated wire around the bobbin while rotating the bobbin one turn in a forward direction, and then (ii) winding the insulated wire around the bobbin while rotating the bobbin one turn in a reverse direction.

SUMMARY

In the aforementioned torque sensor, however, an amount of movement to rotate the bobbin in the reverse direction is large when manufacturing the coil for the magnetostrictive torque sensor. Therefore, if it is attempted to simultaneously wind multiple insulated wires around the bobbin, the insulated wires tend to be entangled with each other relatively easily.

One aspect of the present disclosure relates to improvement of workability of manufacturing a coil for a torque sensor.

One aspect of the present disclosure provides a method of manufacturing a coil for a torque sensor. The method comprises: holding a bobbin with a jig; rotating the bobbin while simultaneously supplying insulated wires from nozzles arranged to surround the bobbin; and driving the nozzles in a direction orthogonal to a rotation direction of the bobbin so as to wind the insulated wires around the bobbin along first inclined grooves or second inclined grooves. The bobbin is formed in a cylindrical shape and provided with the first inclined grooves and the second inclined grooves on its cylindrical outer peripheral surface. The first inclined grooves are inclined at a preset specified angle with respect to an axial direction of the cylindrical shape, and the second inclined grooves are inclined at the specified angle with respect to the axial direction in a direction opposite to the first inclined groove.

According to the method as above, the insulated wires are continuously wound around the bobbin along the first inclined grooves or the second inclined grooves. Therefore, it is only necessary to drive the nozzles in a direction orthogonal to the rotation direction of the bobbin, and there is no need to drive the nozzles in the rotation direction of the bobbin. As a result, the nozzles can be less likely to hit each other, and therefore it is possible to simultaneously wind multiple insulated wires around the bobbin. Thus, a speed of winding the insulated wires around the bobbin can be improved, or workability of manufacturing a coil for a magnetostrictive torque sensor can be improved.

Another aspect of the present disclosure may provide a coil for a magnetostrictive torque sensor used as a torque sensor for measuring a torque applied to a rotation shaft having magnetostrictive properties. The coil may comprise a bobbin, a first detection coil, and a second detection coil.

The bobbin is non-metallic, and is provided coaxially with and apart from the rotation shaft having magnetostrictive properties. The bobbin is formed into a hollow cylindrical shape and is provided with first inclined grooves and second inclined grooves on an outer peripheral surface of the bobbin. The first inclined grooves are inclined at a preset specified angle with respect to an axial direction of the cylindrical shape, and the second inclined grooves are inclined at the specified angle with respect to the axial direction in a direction opposite to the first inclined grooves.

The first detection coil is configured with a first wire, which is an insulated wire wound around the bobbin and is arranged along the first inclined grooves in the order of one rotation direction of the bobbin. The second detection coil is configured with a second wire, which is another insulated wire wound around the bobbin and is arranged along the second inclined grooves in the order of the one rotation direction of the bobbin. The first wire is arranged to run through the first inclined grooves longitudinally and transversely, and the second wire is arranged to run through the second inclined grooves longitudinally and transversely.

The configuration as above can be obtained by winding the first wire and the second wire around the bobbin while continuously rotating the bobbin generally in one direction without largely reversing the bobbin when manufacturing the first detection coil and the second detection coil. Therefore, the configuration as such allows simultaneously winding multiple insulated wires around the bobbin while suppressing entanglement of the multiple insulated wires. As a result, workability of manufacturing a coil for a magnetostrictive torque sensor can be improved.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[1-1. Overall Configuration of Torque Sensor]

FIG.1is an exploded perspective view of a torque sensor1in one aspect of the present disclosure.FIG.2is a sectional view of the torque sensor1attached to a rotation shaft2.

As shown inFIGS.1and2, the torque sensor1is a magnetostrictive sensor attached around the rotation shaft2having magnetostrictive properties for measuring a rotation torque applied to the rotation shaft2mounted on a vehicle.

The torque sensor1comprises a magnetostrictive torque sensor coil5, shields6,7, and a magnetic ring8. The magnetostrictive torque sensor coil5comprises a bobbin20made of a resin, and a first detection coil30and a second detection coil35(hereinafter, also referred to as “detection coils30,35”) configured by winding insulated wires31,32,33,34(hereinafter, also referred to as “insulated wires31to34”) around the bobbin20.

The rotation shaft2is made of a material having magnetostrictive properties, and is formed in a columnar shape, or a rod-like shape. Examples of the material having magnetostrictive properties include nickel, an iron-aluminum alloy, an iron-cobalt alloy and the like.

The material used for the rotation shaft2may be either a positive magnetostrictive material, of which magnetic permeability decreases under compression and increases under tension, or a negative magnetostrictive material, of which magnetic permeability increases under compression and decreases under tension. As the rotation shaft2, for example, a shaft for use in powertrain torque transmission, a shaft for use in torque transmission of a vehicle engine and the like may be employed.

The magnetic ring8comprises a magnetic body, for example, a ferromagnetic body, and is formed into a hollow cylindrical shape. The bobbin20provided with the detection coils30,35is inserted to a hollow part of the magnetic ring8, and the magnetic ring8is arranged to cover an outer peripheral surface of the bobbin20.

An internal diameter of the magnetic ring8is generally the same as an external diameter of the bobbin20, and is made slightly larger than the external diameter of the bobbin20. The magnetic ring8serves to suppress decrease in sensitivity due to leakage of magnetic flux generated in the detection coils30,35to an exterior.

The shields6,7have a function of fixing the bobbin20to the magnetic ring8, and a function to protect the detection coils30,35from external electromagnetic noises (or to block electromagnetic noises). The shields6,7are each formed in a ring shape having an external diameter generally consistent with an external diameter of the magnetic ring8, and with an internal diameter generally consistent with an internal diameter of the bobbin20.

The bobbin20is inserted to the hollow part of the magnetic ring8. The shields6,7are arranged on both sides of the bobbin20in an axial direction L of the rotation shaft2. In other words, the bobbin20is interposed between the shields6,7and is fixed to the magnetic ring8.

The torque sensor1has a gap between an inner wall of the bobbin20and the rotation shaft2. The gap avoids contact between the torque sensor1and the rotation shaft2. Further, the torque sensor1is fixed to a fixing member such as a housing. This prevents the torque sensor1from rotating with rotation of the rotation shaft2.

As shown inFIGS.1to3, the bobbin20is made of a resin and is formed into a hollow cylindrical shape as a whole. The bobbin20is provided apart from the rotation shaft2by a specified distance Δd, and is coaxial with the rotation shaft2.

First inclined grooves10and second inclined grooves11are formed on an outer peripheral surface of the bobbin20. The first inclined grooves10are inclined at a preset specified angle with respect to the axial direction L of the rotation shaft2. The second inclined grooves11are inclined at the specified angle with respect to the axial direction L in a direction opposite to the first inclined grooves10. The angle of the first inclined grooves10with respect to the axial direction L is set to be the same as the angle of the second inclined grooves11with respect to the axial direction L.

In the present embodiment, as shown inFIG.3, the first inclined grooves10are formed to be inclined at +45 degrees with respect to the axial direction L, and the second inclined grooves11are formed to be inclined at −45 degrees with respect to the axial direction L.FIG.3shows that the first inclined grooves10and the second inclined grooves11are inclined by 45 degrees with respect to a straight line Lp that is parallel to the axial direction L.

In the torque sensor1, the detection coils30,35are formed by winding the insulated wires31to34along the first inclined grooves10and the second inclined grooves11(hereinafter, also referred to as “inclined grooves10,11”). Change in magnetic permeability when a torque is applied to the rotation shaft2is largest in directions of ±45 degrees with respect to the axial direction L. Therefore, detection sensitivity of the torque sensor1can be improved by setting the inclinations of the inclined grooves10,11with respect to the axial direction L to ±45 degrees respectively.

The inclinations of the inclined grooves10,11are not limited to ±45 degrees. Too small or too large inclinations of the inclined grooves10,11, however, can decrease sensitivity. Therefore, it is desirable that inclinations of the inclined grooves10,11are within ranges of ±30 to 60 degrees.

On the outer peripheral surface of the bobbin20of the present embodiment, an even number of the first inclined grooves10and an even number of the second inclined grooves11are alternately formed at equal intervals in a circumferential direction of the rotation shaft2orthogonal to the axial direction L. In the present embodiment, six first inclined grooves10and six second inclined grooves11are formed for every 60 degrees respectively in the circumferential direction of the rotation shaft2.

Further, on the outer peripheral surface of the bobbin20, side passages13are formed along both opposite sides of the bobbin20. The sides of the bobbin20indicate side surfaces in the axial direction L, in other words, side surfaces adjacent to the shields6,7.

On the outer peripheral surface of the bobbin20, there are diamond projections14having a diamond-shape, triangular projections15having an isosceles triangular shape, the inclined grooves10,11that serve as valleys between the diamond projections14and the triangular projections15(hereinafter, also referred to as “projections14,15”), and the side passages13, as a whole. The number of each of the inclined grooves10,11is not limited to six as described in the present embodiment, and can be changed as appropriate depending on the external diameter of the bobbin20, the external diameter of the rotation shaft2and the like.

In the present embodiment, the detection coils30,35are formed on the outer peripheral surface of the bobbin20. Therefore, it is preferable to use the bobbin20made of a material such as a resin which has a less effect on a magnetic flux generated in the detection coils30,35than a metallic material. The material of the bobbin20is not limited to the resin, and may be a non-metal that has a less effect on a magnetic flux than a metal.

When the torque sensor1is used in an environment where oil such as a lubricant may contact the torque sensor1, it is preferable to make the bobbin20from a material having an oil resistance. When the torque sensor1is used in a high temperature environment, it is preferable to make the bobbin20from a material having a heat resistance.

Further, it is desirable to make the bobbin20from a material having a linear expansion coefficient similar to that of copper or a copper alloy which is generally employed as a material for the insulated wires31to34. More specifically, as the resin for use in forming the bobbin20, it is preferable to use a material of which linear expansion coefficient is within ±25% of the linear expansion coefficient of copper or a copper alloy. This reduces a difference between a deformation amount of the bobbin20and a deformation amount of the insulated wires31to34due to temperature change, and suppresses breakage of the insulated wires31to34.

In the present embodiment, the detection coils30,35are configured by stacking four layers, each of which is formed from each one of the insulated wires31to34. The first detection coil30comprises the insulated wire31which forms a first layer of the four layers, and the insulated wire33which forms a third layer of the four layers. The second detection coil35comprises the insulated wire32which forms a second layer of the four layers, and the insulated wire34which forms a fourth layer of the four layers.

The first detection coil30is configured by winding the insulated wires (first wires)31,33around the bobbin20along the first inclined grooves10, a one-side passage13A, and an other-side passage13B.FIGS.4to6and8are developed views of the bobbin20.

As shown inFIG.4, in forming the first layer of the first detection coil30, the insulated wire31is first arranged along the first inclined groove10from a winding start position1atoward the other-side passage13B. The winding start position1ais a position in the one-side passage13A that corresponds to an end of the specified first inclined groove10. Then, the insulated wire31is arranged along the side passage13B toward the adjacent first inclined groove10(first inclined groove10on the right inFIG.4). Then, the insulated wire31is arranged along the adjacent first inclined groove10from the other-side passage13B to the one-side passage13A. Then, the insulated wire31is arranged along the side passage13A toward the further adjacent first inclined groove10(first inclined groove10further on the right inFIG.4). Hereinafter, the insulated wire31is repeatedly arranged along the first inclined grooves10, the one-side passage13A, and the other-side passage13B. The insulated wire31is wound on an outer periphery of the bobbin20by a specified number of turns. A winding end position1bof the insulated wire31can be exemplified as the same position as the winding start position1a. The insulated wire31is wired substantially in a crank-shape, that is, a zigzag, in which the insulated wire31goes back and forth between the one-side passage13A and the other-side passage13B through the first inclined grooves10.

The third layer of the first detection coil30, like the first layer, is formed by moving the insulated wire33back and forth between the one-side passage13A and the other-side passage13B through the first inclined grooves10. Specifically, the insulated wire33is first arranged along the first inclined groove10from a winding start position4atoward the other-side passage13B. A procedure of arranging the insulated wire33hereinafter is the same as that in the first layer. A winding end position4bof the insulated wire33can be exemplified as the same position as the winding start position4a. The winding start position4ais a position in the one-side passage13A that corresponds to an end of the first inclined groove10adjacent to the winding start position1a(specified first inclined groove10).

In the first layer of the first detection coil30, as shown by a solid line inFIG.5, the insulated wire31is arranged on three sides (adjacent first inclined grooves10, and one of the side passage13A and the side passage13B) out of four sides that form a parallelogram surrounded by the adjacent first inclined grooves10, the one-side passage13A, and the other-side passage13B. In the third layer of the first detection coil30, as shown by a broken line inFIG.5, the insulated wire33is arranged on three sides (adjacent first inclined grooves10, and the other of the side passage13A and the side passage13B) out of four sides that form the parallelogram (the same parallelogram as that in the first layer) surrounded by the adjacent first inclined grooves10and the one-side passage13A and the other-side passage13B.

That is, one or both of the insulated wire31of the first layer and the insulated wire33of the third layer are arranged on the four sides (adjacent first inclined grooves10, the one-side passage13A, and the other-side passage13B) forming the aforementioned parallelogram. In other words, the aforementioned parallelogram is formed by a combination of the insulated wire31of the first layer and the insulated wire33of the third layer.

The second detection coil35is configured by winding the insulated wires (second wires)32,34around the bobbin20along the second inclined grooves11, the one-side passage13A, and the other-side passage13B. As shown inFIG.4, in forming the second layer of the second detection coil35, the insulated wire32is first arranged along the one-side passage13A from a winding start position2atoward the adjacent second inclined groove11(second inclined groove11on the right inFIG.4). The winding start position2ais a position in the one-side passage13A that corresponds to an end of the specified second inclined groove11.

Then, the insulated wire32is arranged along the adjacent second inclined groove11from the one-side passage13A toward the other-side passage13B. Then, the insulated wire32is arranged along the other-side passage13B from the adjacent second inclined groove11toward the further adjacent second inclined groove11. Then, the insulated wire32is arranged along the further adjacent second inclined groove11from the other-side passage13B toward the one-side passage13A.

Hereinafter, the insulated wire32is repeatedly arranged along the second inclined grooves11, the one-side passage13A, and the other-side passage13B. The insulated wire32is wound on the outer periphery of the bobbin20by a specified number of turns. A winding end position2bof the insulated wire32can be exemplified as the same position as the winding start position2a. The insulated wire32is wired substantially in a crank-shape, that is, a zigzag, in which the insulated wire32goes back and forth between the one-side passage13A and the other-side passage13B through the second inclined grooves11.

The fourth layer of the second detection coil35, like the second layer, is formed by moving the insulated wire34back and forth between the one-side passage13A and the other-side passage13B through the second inclined grooves11. Specifically, the insulated wire34is first arranged along the second inclined groove11from a winding start position3atoward the other-side passage13B. A procedure of arranging the insulated wire34hereinafter is the same as that in the second layer. A winding end position3bof the insulated wire34can be exemplified as the same position as the winding start position3a.

The winding start position3ais the same position as the winding start position2a. Similar to the insulated wire31of the first layer and the insulated wire33of the third layer, one or both of the insulated wire32of the second layer and the insulated wire34of the fourth layer are arranged on four sides of a parallelogram configured by the adjacent second inclined grooves11, the one-side passage13A, and the other-side passage13B. In other words, the aforementioned parallelogram is formed by a combination of the insulated wire32of the second layer and the insulated wire34of the fourth layer.

The detection coils30,35of the present embodiment can be formed generally by rotating the bobbin20in one direction along an X-axis direction inFIGS.5and6and moving later-described nozzles54, which supply the insulated wires31to34, in a Y-axis direction. In other words, it is not necessary to move the nozzles54in the X-axis direction. The X-axis direction is a circumferential direction of the bobbin20, and the Y-axis direction is the axial direction L.

In a reference example method as shownFIG.6, one insulated wire is arranged to pass through all the sides of the aforementioned parallelogram. When the insulated wire is arranged as such, it is necessary to largely rotate the bobbin20not only in one direction but also in the other direction which means a reverse rotation. Alternatively, it is necessary to move the nozzles not only in the Y-axis direction but also in the X-axis direction.

In the method of the present embodiment, the insulated wires31to34are wound around the bobbin20using, for example, a coil manufacturing device50as shown inFIG.7.

As shown inFIG.7, the coil manufacturing device50comprises supply bobbins51, tensioners52, movable holders53and the nozzles54. The coil manufacturing device50comprises a rotation jig55. Four supply bobbins51, four tensioners52, four movable holders53, and four nozzles54are provided, and two of each of them are shown inFIG.7.

The insulated wires31to34supplied to the bobbin20to become the detection coils30,35are wound around the supply bobbins51. The insulated wires31to34are continuously sent to the tensioners52.

The tensioners52supply the insulated wires31to34toward the bobbin20while holding the insulated wires31to34such that tension of the insulated wires31to34to be wound around the bobbin20is generally constant. The movable holders53comprise the nozzles54, and are configured to be movable in the Y-axis direction together with the nozzles54. The Y-axis direction inFIG.7is an up and down direction of the sheet of the drawing. The movable holder53may be movable in the X-axis direction.

The nozzles54supply the insulated wires31to34, which are sent from the tensioners52, to the bobbin20through ends of the nozzles54.

The rotation jig55is arranged to penetrate through an inside of the bobbin20and holds the bobbin20from the inside of the bobbin20. The rotation jig55is rotated by an actuator such as a motor, and also the bobbin20rotates with the rotation of the rotation jig55. When the rotation jig55rotates in a state where leading ends of the insulated wires31to34are held by the bobbin20, tension is applied to the insulated wires31to34, and the insulated wires31to34are supplied from the tensioners52to the bobbin20.

In order to optimize positions of the nozzles54in the Y-axis direction as positions to wind the insulated wires31to34, positions of the movable holders53in the Y-axis direction are controlled in synchronization with rotation of the rotation jig55.

In the reference example method, in simultaneously winding multiple insulated wires, nozzles (not shown) that supply the insulated wires move not only in the Y-axis direction but also in the X-axis direction. Therefore, the nozzles may come into contact with each other. As a result, the number of insulated wires that can be simultaneously wound is limited. In the method of the present embodiment, there is no need to move the nozzles54in the X-axis direction. Therefore, simultaneously winding multiple insulated wires around the bobbin20is facilitated as compared to the reference example method.

In the method of the present embodiment, there is no need to reverse the bobbin20when winding the insulated wires along the side passages13. In other words, a rotation amount to reverse the bobbin20can be reduced to the minimum (amount to wind the insulated wires along the inclined grooves10,11). Therefore, as compared to the reference example method, the method of the present embodiment allows simultaneously winding multiple insulated wires around the bobbin20. In addition, a speed of winding the insulated wires31to34around the bobbin20can be improved.

When the insulated wires31to34are wound around the bobbin20according to the method of the present embodiment, the insulated wires31,33are arranged to diagonally traverse all of the first inclined grooves10, as shown inFIG.8. Also, the insulated wires32,34are arranged to diagonally traverse all of the second inclined grooves11.

That is, the insulated wire31is wound around a corner15A arranged on the one-side passage13A side and around a corner15B arranged on the other-side passage13B in the first inclined groove10, whereby the insulated wire31changes directions and is arranged. In other words, the insulated wire31is arranged to run through an area of the first inclined grooves10longitudinally and transversely, from the corner15A toward the corner15B, or from the corner15B toward the corner15A.

The corner15A is a corner on the X-axis positive side of the triangular projection15facing the one-side passage13A where the insulated wire31is arranged. The corner15B is a corner on the X-axis negative side of the triangular projection15facing the other-side passage13B where the insulated wire31is arranged.

The insulated wire33is wound around a corner15D arranged on the one-side passage13A side and around a corner15C arranged on the other-side passage13B side in the first inclined groove10, whereby the insulated wire33changes directions and is arranged. In other words, the insulated wire33is arranged to run through the area of the first inclined grooves10longitudinally and transversely, from the corner15C toward the corner15D, or from the corner15D toward the corner15C.

The corner15C is a corner on the X-axis positive side of the triangular projection15facing the other-side passage13B where the insulated wire33is arranged. The corner15D is a corner on the X-axis negative side of the triangular projection15facing the one-side passage13A where the insulated wire33is arranged.

The insulated wire32is wound around a corner15E arranged on the one-side passage13A side and around a corner15F arranged on the other-side passage13B side in the second inclined groove11, whereby the insulated wire32changes directions and is arranged. In other words, the insulated wire32is arranged to run through an area of the second inclined grooves11longitudinally and transversely, from the corner15E toward the corner15F, or from the corner15F toward the corner15E.

The insulated wire34is wound around a corner15H arranged on the one-side passage13A side and around a corner15G arranged on the other-side passage13B side in the second inclined groove11, whereby the insulated wire34changes directions and is arranged. In other words, the insulated wire34is arranged to run through the area of the second inclined grooves11longitudinally and transversely, from the corner15G toward the corner15H, or from the corner15H toward the corner15G. The insulated wires31to34are arranged to intersect at intersections23where the first inclined grooves10and the second inclined grooves11intersect.

As shown inFIG.9, in a section of the intersection23, all the insulated wires31to34that pass through the intersection23are stacked. Also, at the intersection23, the insulated wires31,33of the first detection coil30and the insulated wires32,34of the second detection coil35are alternately stacked. All the insulated wires31to34may be stacked at the same position, or the insulated wires31to34may be stacked at positions generally close to each other.

The number of the insulated wires31to34stacked at the intersection23is a number obtained by multiplying the number of layers forming the detection coils30,35by the number of turns in each layer. For example, when the number of turns of each of layers (four layers in total) configured by the insulated wires31to34is 30 turns, a product of the above multiplication, that is,120insulated wires, are stacked at the intersection23. The same number of insulated wires may be stacked at all the intersections23or at positions generally close to the respective intersections23.

The bobbin20is fixed to a jig when winding the insulated wires31to34around the bobbin20. At that time, an end of the bobbin20in the axial direction L is locked to the jig to prevent rotation of the bobbin20due to the tension of the insulated wires31to34.

The four nozzles54are arranged at every 90 degrees to surround the bobbin20. While the insulated wires31to34are simultaneously supplied from the four nozzles54, the bobbin20is rotated generally in one direction, and the nozzles54are driven in a direction orthogonal to the rotation direction of the bobbin20. At that time, the nozzles54are repeatedly driven so that the insulated wires31,33follow the first inclined grooves10in sequence and the insulated wires32,34follow the second inclined grooves11in sequence. Thus, the four-layer detection coils30,35are manufactured as described above.

The insulated wires31to34that form the respective layers (first layer to fourth layer) of the detection coils30,35have generally the same length and are configured so that the layers have generally the same resistance value.

[1-3. Configuration of Measurement Section]

As shown inFIG.10, the torque sensor1includes a measurement section41. The measurement section41detects change in inductances of the first detection coil30and the second detection coil35thereby to measure a torque applied to the rotation shaft2. Hereinafter, an inductance of the first detection coil30in the first layer is indicated by L1, an inductance of the second detection coil35in the second layer is indicated by L2, an inductance of the first detection coil30in the third layer is indicated by L4, and an inductance of the second detection coil35in the fourth layer is indicated by L3.

The measurement section41comprises a bridge circuit42, an oscillator43, a voltage measurement circuit44, and a torque calculator45. The bridge circuit42is configured by sequentially coupling the detection coils30,35of the first layer, the fourth layer, the third layer, and the second layer in series in a ring-shape.

The oscillator43applies an alternating current voltage between a contact a between the detection coils30,35of the first layer and the second layer, and a contact b between the detection coils30,35of the third layer and the fourth layer. The voltage measurement circuit44detects voltage between a contact c between the detection coils30,35of the first layer and the fourth layer, and a contact d between the detection coils30,35of the third layer and the second layer.

The torque calculator45calculates a torque applied to the rotation shaft2based on the voltage detected in the voltage measurement circuit44. In the measurement section41, the inductances L1to L4of the detection coils30,35of the respective layers are the same and the voltage detected by the voltage measurement circuit44is almost zero when no torque is applied to the rotation shaft2.

When a torque is applied to the rotation shaft2, magnetic permeability in a direction of +45 with respect to the axial direction L decreases or increases, and magnetic permeability in a direction of −45 degrees with respect to the axial direction L increases or decreases. Accordingly, when a torque is applied to the rotation shaft2in a state where an alternating current voltage is applied by the oscillator43, the inductance decreases or increases in the first detection coil30of the first and third layers, and the inductance increases or decreases in the second detection coil35of the second and fourth layers. As a result, the voltage detected by the voltage measurement circuit44changes, and the torque calculator45calculates the torque applied to the rotation shaft2based on the change in the voltage.

The detection coils30,35of the respective layers have totally the same configuration except for the difference in the winding directions. Therefore, use of the bridge circuit42as shown inFIG.10can cancel an effect on the inductances of the detection coils30,35due to temperature, and allows accurate detection of the torque applied to the rotation shaft2. In the torque sensor1, when the inductance increases or decreases in the first detection coil30, the inductance inevitably decreases or increases in the second detection coil35. Thus, use of the bridge circuit42as shown inFIG.10can improve detection sensitivity.

The embodiment detailed in the above produces following effects.

(1a) One aspect of the present disclosure provides a method of manufacturing the magnetostrictive torque sensor coil5, the method comprising: holding the bobbin20with the jig; rotating the bobbin20while simultaneously supplying the insulated wires31to34from the nozzles54arranged to surround the bobbin20, and driving the nozzles54in the direction orthogonal to the rotation direction of the bobbin20so as to wind the insulated wires31to34around the bobbin20along the first inclined grooves10or the second inclined grooves11. The bobbin20is formed in a cylindrical shape. The bobbin20has the first inclined grooves10and the second inclined grooves11on the cylindrical outer peripheral surface. The first inclined grooves10are inclined at a preset specified angle with respect to the axial direction, and the second inclined grooves11are inclined at the preset specified angle with respect to the axial direction in the direction opposite to the first inclined grooves10.

According to the method as above, the insulated wires are continuously wound around the bobbin along the first inclined grooves10or the second inclined grooves11. Therefore, it is only necessary to drive the nozzles54in the direction orthogonal to the rotation direction of the bobbin20, and there is no need to drive the nozzles54in the rotation direction of the bobbin20. As a result, the nozzles54are less likely to hit each other, and thus, it is possible to simultaneously wind multiple insulated wires around the bobbin20. Therefore, the speed of winding the insulated wires around the bobbin20can be improved. In other words, workability of manufacturing the magnetostrictive torque sensor coil5can be improved.

(1b) In the method of manufacturing the magnetostrictive torque sensor coil5of the present disclosure, the insulated wires31to34are simultaneously supplied from the four nozzles54arranged at every 90 degrees around the bobbin20to surround the bobbin20so that the four insulated wires31to34are simultaneously wound around the bobbin20.

According to the method as above, since it is only necessary to drive the four nozzles54in the direction orthogonal to the rotation direction of the bobbin20, the four nozzles54are less likely to hit each other. Accordingly, the four insulated wires31to34can be simultaneously wound around the bobbin20.

(1c) One aspect of the present disclosure provides the magnetostrictive torque sensor coil5for use in the torque sensor1that measures a torque applied to the rotation shaft2having magnetostrictive properties. The magnetostrictive torque sensor coil5comprises the bobbin20, the first detection coil30, and the second detection coil35.

The bobbin20is non-metallic and is provided coaxially with and apart from the rotation shaft2having magnetostrictive properties. The bobbin20is formed into a hollow cylindrical shape. On the outer peripheral surface of the bobbin20, there are the first inclined grooves10inclined at the preset specified angle with respect to the axial direction L, and the second inclined grooves11inclined at the specified angle with respect to the axial direction L in the direction opposite to the first inclined grooves10.

The first detection coil30is formed by winding the insulated wires31,33around the bobbin20along the first inclined grooves10. The second detection coil35is formed by winding the insulated wires32,34around the bobbin20along the second inclined grooves11. The insulated wires31,33are wound around the bobbin20while diagonally traversing all the first inclined grooves10, and the insulated wires32,34are wound around the bobbin20while diagonally traversing all the second inclined grooves11.

With the configuration as above, the first detection coil30and the second detection coil35can be obtained by winding the insulated wires31,33and the insulated wires32,34around the bobbin20while continuously rotating the bobbin20generally in one direction. In other words, the first detection coil30and the second detection coil35can be produced without rotating the bobbin20largely in the direction opposite to the aforementioned one direction. Accordingly, this configuration can inhibit entanglement of the insulated wires31to34when manufacturing the first detection coil30and the second detection coil35, and allows simultaneously winding the insulated wires31to34around the bobbin20. As a result, improvement of workability of manufacturing the magnetostrictive torque sensor coil5is facilitated.

(1d) Description is now made on a relationship between torque and sensor output in a detection coil (detection coil having an equivalent configuration to the first detection coil30and the second detection coil35) obtained by winding a polyamideimide copper wire, which has a wire diameter of 0.1 mm, by 30 turns around the aforementioned bobbin20. The relationship between torque and sensor output of the detection coil was measured by an experiment, and a relationship as shown inFIG.11was obtained. The sensor output was generally proportional to increase and decrease in torque. Sensor sensitivity was 4.54 mV/Nm, and a hysteresis error was 1.07% FS.

The hysteresis error indicates a relative reversibility error, or a difference between characteristic curves obtained when a load is increased and decreased respectively. It is preferable that the hysteresis error has a small value.

As a result of the above measurement, the detection coil of the present embodiment is considered to have almost the same good properties as the detection coil wound with insulated wires by the conventional method shown inFIG.6. A relationship between torque and sensor output in the conventional detection coil was generally consistent with the result by the detection coil of the present embodiment shown inFIG.11, and thus description thereof is omitted.

(1e) In one aspect of the present disclosure, the bobbin20may have the intersections23for the first inclined grooves10and the second inclined grooves11. The intersections23indicate portions where the first inclined grooves10and the second inclined grooves11intersect at substantially center in the axial direction L of the rotation shaft2. In the intersections23, the insulated wires31,33and the insulated wires32,34may be sequentially stacked by the number of turns.

(1f) In one aspect of the present disclosure, the same numbers of the insulated wires31,33and the insulated wires32,34may be stacked in each of all the intersections23.

With such configuration, it is possible to simultaneously wind the insulated wires31,33and the insulated wire32,34around the bobbin20while continuously rotating the bobbin20generally in one direction. Such configuration facilitates improvement of workability of manufacturing the magnetostrictive torque sensor coil5.

(1g) In one aspect of the present disclosure, the first inclined grooves10may be formed to be inclined at +45 degrees with respect to the axial direction L. The second inclined grooves11may be formed to be inclined at −45 degrees with respect to the axial direction L.

With the configuration as above, the first detection coil30and the second detection coil35can easily detect stress generated by the twisting of the rotation shaft2, as compared to a case in which the inclination angles are different from ±45 degrees.

2. Other Embodiments

The embodiments of present disclosure have been described in the above. The present disclosure is not limited to the aforementioned embodiments and can be implemented in various forms without departing from the gist of the present disclosure.

(2a) In the aforementioned embodiments, the magnetostrictive torque sensor coil5having the four layers of the coils is described, but the present disclosure is not limited to this. For example, a magnetostrictive torque sensor coil comprising multiple two layers of coils or having a multi-layer structure other than the four-layer structure may be manufactured.

(2b) Functions of one component in the aforementioned embodiments may be achieved by two or more components, and a function of one component may be achieved by two or more components. Functions of two or more components may be achieved by one component, and a function achieved by two or more components may be achieved by one component. A part of the aforementioned embodiments may be omitted. At least a part of the configuration of the aforementioned embodiment may be added to or may replace the configuration of the other embodiment. It should be noted that any and all modes that are encompassed in the technical ideas defined by the languages in the scope of the claims are embodiments of the present disclosure.

(2c) The present disclosure may be implemented in various modes in addition to the above-described method of manufacturing a magnetostrictive torque sensor coil. Such modes include a magnetostrictive torque sensor coil, a torque sensor comprising the magnetostrictive torque sensor coil, a system provided with the magnetostrictive torque sensor coil, and the like.