JPH0628673U - Magnetostrictive torque sensor - Google Patents

Abstract

(57) [Summary] [Purpose] To increase the ratio of the magnetoresistance of the magnetostrictive shaft to the total magnetoresistance and improve the torque detection sensitivity. [Structure] Each core member 21 is provided with a plurality of grooves 2 that are located at intervals of about 30 ° in the circumferential direction and have a depth dimension h that is equal to or greater than the skin depth S from the outer surface side to the inner surface side.
3, 23, ... Are provided. By the grooves 23, the core members 21 are substantially divided into a plurality of U-shaped cores 24, 24, ... Which are spaced apart in the circumferential direction, and the flow of the magnetic flux entering each core member 21 is regulated. As a result, the flow of the magnetic flux in each core member 21 becomes a straight line which is the shortest distance, and the magnetic path length is shortened.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a magnetostrictive torque sensor suitable for use in detecting a torque generated in an output shaft of an automobile engine, for example.

[0002]

[Prior art]

 FIGS. 3 to 6 show examples of a magnetostrictive torque sensor according to the prior art in which a two-coil magnetostrictive torque sensor is used for detecting torque in an automobile engine.

In the figure, 1 is a cylindrical casing fixed to a vehicle body (not shown) of an automobile, 2 is rotatably disposed in the casing 1 through bearings 3 and 3, and is, for example, a propeller shaft, Magnetostrictive shafts that form an output shaft, a drive shaft, and the like are shown. The magnetostrictive shaft 2 is formed of a positive magnetostrictive material such as chrome-molybdenum steel in a cylindrical shape, and a sensor portion 2A is integrally formed in the axial middle thereof. . Further, on the outer peripheral surface of the sensor portion 2A, a large number of one-side slit grooves 4, 4, ... Engraved at an angle of 45 ° downward and located facing the respective one-side slit grooves 4, A large number of other side slit grooves 5, 5, ... Engraved at an angle of 45 ° upward are provided.

Reference numerals 6 and 6 are axially spaced from each other, and cylindrical core members 7 and 7 are provided on the inner peripheral surface of the casing 1 so as to surround the outer peripheral side of the sensor portion 2A of the magnetostrictive shaft 2. A pair of core pieces constituting each core member 6 are shown. Each core piece 7 is formed of a high magnetic permeability soft magnetic material such as permalloy into a bottomed cylindrical shape as shown in FIGS. A shaft insertion hole 7A through which the magnetostrictive shaft 2 is inserted is axially formed in the central portion thereof, and its end portion is opposed to the sensor portion 2A of the magnetostrictive shaft 2 via a small air gap δ. The legs 7B and 7B are formed.

Reference numerals 8 and 8 denote coil bobbins provided on the inner peripheral side of each core member 6, and reference numerals 9 and 9 denote coils wound around the coil bobbins 8 as exciting and detecting coils, respectively. Is formed in a bridge circuit together with the adjusting resistor, and is connected to a detection circuit (not shown) including an oscillator and a differential amplifier. Here, each of the coils 9 serves as both an exciting coil which is excited by a high frequency voltage from an oscillator to generate a magnetic flux and a detecting coil which detects a magnetic flux flowing in the magnetic circuit shown in FIG. .

Reference numerals 10 and 10 denote outer spacers provided at the ends of the core members 6, and 11 denote inner spacers disposed between the core members 6, respectively. The spacers 10 and 11 are core members. 6 is sandwiched and fixed from both sides, and the core members 6 and the like integrated by the spacers 10 and 11 are fixed to the inner peripheral surface of the casing 1 by the C rings 12 and 12.

The magnetostrictive torque sensor according to the prior art has the above-mentioned configuration, and when an AC voltage is applied to each coil 9 from the oscillator of the detection circuit, for example, as shown by a chain double-dashed line in FIG. A magnetic circuit is formed from each core member 6 to the magnetostrictive shaft 2 by the magnetic flux generated from the coil 9.

Here, as shown in FIG. 5, the magnetic circuit includes a magnetic resistance R1 of the magnetostrictive shaft 2 that changes according to the torque T, magnetic resistances R2 and R2 of the air gap δ, and core materials 6 of each. And a magnetic resistance R4 by a magnetic flux that bypasses between the annular leg portions 7B of the core pieces 7 is formed in each coil bobbin 8, and the magnetic resistances R1, R2, R3, The value of R4 is

[0009]

## EQU1 ## R = A / μS where A: average magnetic path length (magnetic path length) S: magnetic path cross-sectional area μ: magnetic permeability

Therefore, the total magnetic resistance Rt, which is a combination of the main magnetic resistances R1, R2, and R3, is the magnetic path length of the magnetic flux flowing between the slit grooves 4 and 5, and the magnetic path of the magnetic flux flowing between the air gaps δ. If the length is A2, the magnetic path length of the magnetic flux flowing in the core member 6 is A3, and the magnetic path cross-sectional area and permeability in each magnetic path are S1, S2, S3, μ1, μ2, μ3, respectively,

[0011]

[Equation 2] Is required as.

On the other hand, if the number of coil turns is N, the self-inductance L of each coil 9 is

[0013]

## EQU3 ## It can be obtained as L = N ² / Rt.

When a counterclockwise torque T is applied to one end side of the magnetostrictive shaft 2 as shown in FIG. 3, a tensile stress + σ is generated along the one side slit groove 4 and the other side slit groove 5 is generated. A compressive stress −σ is generated along with. As a result, the magnetic permeability μ1 of the magnetostrictive shaft 2 on the one side slit 4 side increases due to the tensile stress + σ, and the magnetic resistance R1 of the magnetostrictive shaft 2 decreases, while the permeability μ1 of the magnetostrictive shaft 2 on the other side slit 5 side decreases. The magnetic susceptibility .mu.1 decreases due to the compressive stress-.sigma., And the magnetic resistance R1 increases.

As a result, the total magnetic resistance Rt of the coil 9 on one side decreases and the self-inductance L increases, whereas the total magnetic resistance Rt of the coil 9 on the other side increases and the self-inductance L increases. Since the voltage decreases, the balance of the bridge circuit is lost and an output voltage corresponding to the torque T appears in the differential amplifier.

On the contrary, when a clockwise torque is applied to the one end side of the magnetostrictive shaft 2, the magnetic permeability μ 1 becomes smaller due to the compressive stress −σ generated along the one side slit groove 4. Since the magnetic permeability μ1 increases due to the tensile stress + σ generated along the other side slit groove 5, the self-inductance L of the coil 9 on the one side decreases and the self-inductance L of the coil 9 on the other side increases, resulting in The voltage corresponding to this reverse torque is output from the dynamic amplifier.

[0017]

[Problems to be solved by the device]

 By the way, in the above-described conventional magnetostrictive torque sensor, an alternating voltage is applied to each coil 9 to generate a magnetic flux, and a magnetic circuit is formed across each core member 6, the air gap δ, and the magnetostrictive shaft 2. As a result, the torque applied to the magnetostrictive shaft 2 is detected by utilizing the magnetic resistance R1 of the magnetostrictive shaft 2 which changes according to the torque.

However, the total magnetic resistance Rt that determines the self-inductance L of each coil 9 as shown in the equation 3 is not only the magnetic resistance R1 of the magnetostrictive shaft 2 but also the other magnetic resistances R2 and R3. Since the value is a value, the change ΔR1 in which the magnetic resistance R1 of the magnetostrictive shaft 2 changes due to the stress σ has little influence on the total magnetic resistance Rt. The percentage is low.

Therefore, according to the above-described conventional technique, the magnetostrictive shaft that changes according to the torque due to the magnetic resistance R2 of each air gap δ and the magnetic resistance R3 of each core member 6 unrelated to the torque detection. There is a problem that the effect of the second magnetic resistance R1 on the total magnetic resistance Rt is reduced, the torque detection sensitivity is significantly reduced, and the detection accuracy and reliability are low.

In particular, as indicated by the chain double-dashed line in FIG. 6, since the flow of magnetic flux is forced in the oblique direction by the slit grooves 4 and 5 having low magnetic permeability on the surface of the magnetostrictive shaft 2, the magnetostrictive shaft 2 The magnetic flux that has entered into the core member 6 through the annular leg portions 7B of each core piece 7 easily flows diagonally on the surface of the core member 6 due to this influence. Therefore, since the magnetic path length A3 in the core member 6 tends to unnecessarily increase, the magnetic resistance R3 of the core member 6 becomes larger than the above-mentioned equation 1, and the magnetic resistance R1 of the magnetostrictive shaft 2 becomes relatively large. There is a problem that the ratio of the magnetic resistance Rt is reduced and the torque detection sensitivity is significantly reduced.

The present invention has been made in view of the above-described problems of the prior art. The magnetostrictive type that improves the torque detection sensitivity by increasing the ratio of the magnetoresistance of the magnetostrictive shaft to the total magnetoresistance. An object is to provide a torque sensor.

[0022]

[Means for Solving the Problems]

 In order to solve the above-mentioned problems, a feature of the structure adopted by the present invention is that the core member is provided with a plurality of grooves extending from the outer surface side to the inner surface side at predetermined intervals in the circumferential direction.

[0023]

[Action]

 Since the plurality of grooves provided from the outer surface side to the inner surface side of the core member have magnetic permeability substantially equal to that of air and smaller than that of the core member, the core members are separated by a predetermined distance in the circumferential direction by each groove. Then, the magnetic flux is divided into a plurality of parts, and the magnetic flux is restricted to the shortest distance by the grooves.

[0024]

【Example】

 An embodiment of the present invention will be described below with reference to FIGS. In the embodiment, the same components as those of the conventional technique shown in FIGS. 3 to 6 are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, reference numerals 21 and 21 denote cylindrical core members applied to this embodiment in place of the core member 6 described in the related art, and each core member 21 is each core described in the related art. Almost the same as the member 6, it is provided on the inner peripheral surface of the casing 1 so as to surround the outer peripheral side of the sensor portion 2A of the magnetostrictive shaft 2 so as to be spaced apart in the axial direction, and to collate core pieces 22, 22 described later. Is formed into a tubular shape. However, each core member 21 according to this embodiment is different in that a plurality of grooves 23, 23, which will be described later, are provided from the outer surface side to the inner surface side.

22 and 22 are formed of a high magnetic permeability soft magnetic material such as permalloy in a cylindrical shape with a bottom, and the shaft insertion hole 22A and the annular leg portion 22B are almost the same as each core piece 7 described in the prior art. The provided core pieces 23, 23, ... Denote 12 grooves provided from the outer surface side to the inner surface side of each core piece 22, respectively, and each groove 23 is formed as shown in FIG. For example, they are located at intervals of about 30 ° in the circumferential direction with respect to the center of the piece 22 and are connected to the other grooves 23 facing each other at the abutting surface of each core piece 22. Further, each groove 23 is formed in a U-shaped or semi-circular cross-section, and its depth dimension h is equal to or greater than the skin depth S calculated by the following equation 4 (h ≧ S).

[0027]

[Equation 4]

Since the magnetic permeability of each groove 23 is substantially equal to the magnetic permeability of the air inside, and the magnetic resistance is larger than the magnetic resistance R3 of each core member 21, each slit groove 4, As in the case of No. 5, the flow of magnetic flux in each core member 21 is regulated.

That is, since the magnetic flux concentrates and flows within the predetermined skin depth S shown in Formula 4 due to the skin effect, the magnetic flux is generated by the respective grooves 23 provided with the depth dimension h equal to or larger than the skin depth S. For the bundle, each core member 21 is equal to a state in which each core member 21 is divided into 12 U-shaped cores 24, 24, ... Positioned at intervals of about 30 degrees in the circumferential direction. As indicated by the dotted chain line, the magnetic flux that has entered each core member 21 is regulated by each groove 23 so that the flow direction is the shortest distance within the core member 21, that is, the straight line that is the shortest distance between the annular leg portions 22B. And flows in each U-shaped core 24.

The magnetostrictive torque sensor according to the present embodiment has the above-mentioned configuration, and its basic operation is not significantly different from that according to the prior art.

However, in the present embodiment, each core member 21 is located at intervals of about 30 ° in the circumferential direction and has a depth dimension h equal to or greater than the skin depth S from the outer surface side to the inner surface side. .. are provided, the core members 21 can be substantially divided by the grooves 23 into a plurality of U-shaped cores 24 that are spaced apart in the circumferential direction. It is possible to effectively regulate the flow of the magnetic flux that has entered the core member 21.

As a result, as shown in FIG. 2, the magnetic flux in each core member 21 can be made to flow in a straight line which is the shortest distance between the annular leg portions 22B, and the magnetic path length A3 of each core member 21 can be significantly increased. Since the length can be shortened, the ratio of the magnetic resistance R1 of the magnetostrictive shaft 2 to the total magnetic resistance Rt can be relatively increased, and the change in the magnetic permeability μ1 of the magnetostrictive shaft 2 can be effectively reflected to detect the torque. The sensitivity can be greatly increased.

Further, since each groove 23 is formed in a plurality in the circumferential direction from the outer surface side to the inner surface side of each core member 21, the surface area of each core member 21 should be increased by the amount of each groove 23. It is possible to effectively cool the core members 21 by the air flowing in the grooves 23 in the axial direction, and it is possible to prevent the core members 21 from being deformed by heat from the engine. it can.

It should be noted that, in the above-described embodiment, it has been described that twelve grooves 23, 23, ... Are provided at intervals of about 30 ° in the circumferential direction, but instead of this, 30 ° or less or 30 ° or less. They may be provided at intervals of 30 ° or more in the circumferential direction.

Further, in the above embodiment, the two-coil type magnetostrictive torque sensor has been described as an example, but the present invention is not limited to this, and may be used, for example, in a four-coil type magnetostrictive torque sensor. .

Further, in the above-described embodiment, the case where it is used to detect the torque of the automobile engine has been described as an example, but it can also be used to detect other torques such as the torque of the rotating shaft of the electric motor.

[0037]

[Effect of device]

 As described above in detail, according to the present invention, the core member is provided with a plurality of grooves that are spaced from each other in the circumferential direction by a predetermined distance from the outer surface side to the inner surface side. By the equal grooves, it is possible to substantially divide the core member into a plurality of U-shaped cores that are separated from each other by a predetermined distance in the circumferential direction for the magnetic flux affected by the skin effect. As a result, the flow of magnetic flux in the core member is regulated by each groove to a straight line with the shortest distance in the core member, and the magnetic path length of the magnetic flux flowing in the core member can be shortened to reduce the magnetic resistance. By reducing the magnetic resistance of the core member in the total magnetic resistance of the magnetic circuit, the ratio of the magnetic resistance of the magnetostrictive shaft can be made relatively large, and the change in the magnetic permeability of the magnetostrictive shaft can be effectively reflected to reduce the torque. The detection sensitivity can be improved.

[Brief description of drawings]

FIG. 1 is an enlarged vertical cross-sectional view showing an essential part of a magnetostrictive torque sensor according to an embodiment of the present invention.

FIG. 2 is a partially cutaway perspective view showing an enlarged core member in FIG.

FIG. 3 is a vertical sectional view showing a magnetostrictive torque sensor according to a conventional technique.

FIG. 4 is a vertical sectional view showing an enlarged main part in FIG.

FIG. 5 is a circuit diagram showing a magnetic circuit formed on a core member, a magnetostrictive shaft and the like.

FIG. 6 is a partially cutaway perspective view showing the core member in FIG. 3 in an enlarged manner.

[Explanation of symbols]

 1 Casing 2 Magnetostrictive shaft 9 Coil (excitation and detection coil) 21 Core member 23 Groove

Claims (1)

[Scope of utility model registration request] 1. A tubular casing, a magnetostrictive shaft rotatably arranged in the casing, and a tubular core member provided in the casing so as to surround an outer peripheral side of the magnetostrictive shaft. In order to detect the torque acting on the magnetostrictive shaft as an electric signal, in a magnetostrictive torque sensor consisting of at least a pair of excitation and detection coils provided on the inner peripheral side of the core member, the core member is circumferentially arranged. A magnetostrictive torque sensor characterized in that a plurality of grooves extending from the outer surface side to the inner surface side are provided at predetermined intervals.