JP7596682B2 - Magnetostrictive torque sensor - Google Patents

Description

The present invention relates to a magnetostrictive torque sensor that uses the inverse magnetostrictive effect that occurs in a rotating body to measure the torque transmitted by the rotating body.

For example, in the field of automotive technology, it has been common to measure the torque transmitted by the rotating shaft that constitutes an automatic transmission, and use the measurement results to control the gear shifting of the transmission and the output of the engine.

As another example of a technique for measuring the torque transmitted by a rotating shaft, JP 2017-96826 A (Patent Document 1) describes a technique for measuring the torque using a magnetostrictive torque sensor arranged around the rotating shaft.

JP 2017-96826 A

The magnetostrictive torque sensor described in JP 2017-96826 A has room for further improvement in terms of improving the torque measurement accuracy. That is, in order to improve the torque measurement accuracy of the magnetostrictive torque sensor, it is effective to precisely regulate the distance between the detection unit of the magnetostrictive torque sensor and the detection surface of the rotating shaft. In contrast, in the structure described in JP 2017-96826 A, the detection member is the drive plate that connects the engine crankshaft and the torque converter case so that torque can be transmitted, and the detection unit of the magnetostrictive torque sensor supported and fixed to the cylinder block of the engine is opposed to the drive plate. Therefore, in order to regulate the distance between the detection unit of the magnetostrictive torque sensor and the detection surface of the rotating shaft, it is necessary to sufficiently ensure the shape accuracy and assembly accuracy of each part that constitutes the engine and the torque converter, which may increase the manufacturing cost of the automobile.

In view of the above, the present invention aims to realize a magnetostrictive torque sensor structure that can improve the torque measurement accuracy.

The magnetostrictive torque sensor of the present invention is attached to a part that does not rotate even when in use, and is positioned opposite the detection surface of a rotating body having magnetostrictive properties, and measures the torque transmitted by the rotating body by utilizing the inverse magnetostriction effect generated in the rotating body.
The magnetostrictive torque sensor of the present invention comprises a holder made of synthetic resin and a detection portion embedded in the holder.
The detection portion is disposed around the entire circumference of the detection surface.
The holder has a main body portion that holds the detection portion, and at least one positioning protrusion having a tip portion that is in sliding contact with or closely facing the detection surface of the rotating body.
The at least one positioning protrusion is arranged so as to protrude radially inward from three or more circumferential locations on the inner surface of the main body portion, or is arranged so as to protrude radially inward from the inner surface of the main body portion around the entire circumference.

The magnetostrictive torque sensor of the present invention can improve the torque measurement accuracy.

FIG. 1 is an end view of a magnetostrictive torque sensor according to an embodiment of the present invention, as viewed from the axial direction. FIG. 2 is a cross-sectional view taken along line XX of FIG. 3A and 3B are schematic diagrams showing the detection unit of a magnetostrictive torque sensor according to one example of an embodiment in an expanded state, in which FIG. 3A shows the first detection coil and the fourth detection coil, and FIG. 3B shows the second detection coil and the third detection coil. FIG. 4 is a circuit diagram showing a measurement section of a magnetostrictive torque sensor according to an embodiment of the present invention. FIG. 5 is a view corresponding to FIG. 2 and showing a modified example of the magnetostrictive torque sensor according to the embodiment.

An example of an embodiment of the present invention will be described with reference to Figures 1 to 5. The magnetostrictive torque sensor 1 of this example is attached to a non-rotating member such as a casing that does not rotate even when in use, and is arranged around a rotating shaft 2 that has magnetostrictive properties to measure the torque transmitted by the rotating shaft 2. That is, the magnetostrictive torque sensor 1 has a detection unit 3 facing a detection surface 4 provided on the outer circumferential surface of the rotating shaft 2. The magnetostrictive torque sensor 1 uses the detection unit 3 to detect changes in the magnetic permeability of the rotating shaft 2 that occur when the rotating shaft 2 transmits torque, based on the inverse magnetostrictive effect, and measures the torque transmitted by the rotating shaft 2.

The magnetostrictive torque sensor 1 comprises a detection unit 3, a holder 5, and a measurement circuit 6.

The detection unit 3 includes a bobbin 7, multiple detection coils 8a to 8d each made of an insulated wire wound around the bobbin 7, and a back yoke 9.

The bobbin 7 has a cylindrical shape and is made of a resin material, which is a non-magnetic material. On the outer circumferential surface of the bobbin 7, there are a plurality of first inclined grooves 10a inclined at a predetermined angle (+45 degrees in the illustrated example) with respect to the axial direction of the bobbin 7, and a plurality of second inclined grooves 10b inclined at a predetermined angle (-45 degrees in the illustrated example) in the opposite direction to the first inclined grooves 10a with respect to the axial direction of the bobbin 7. The inclination angles of the first inclined grooves 10a and the second inclined grooves 10b can be set arbitrarily.

Of the multiple detection coils 8a to 8d, the first detection coil 8a and the fourth detection coil 8d are each formed by winding an insulated electric wire along the first inclined groove 10a of the bobbin 7. In contrast, of the multiple detection coils 8a to 8d, the second detection coil 8b and the third detection coil 8c are each formed by winding an insulated electric wire along the second inclined groove 10b of the bobbin 7.

That is, the multiple detection coils 8a to 8d are stacked in the radial direction. The first detection coils 8a are arranged at equal intervals in the circumferential direction, and adjacent first detection coils 8a in the circumferential direction are connected in series. The second detection coils 8b are arranged at equal intervals in the circumferential direction, and adjacent second detection coils 8b in the circumferential direction are connected in series. The third detection coils 8c are arranged at equal intervals in the circumferential direction, and adjacent third detection coils 8c in the circumferential direction are connected in series. The fourth detection coils 8d are arranged at equal intervals in the circumferential direction, and adjacent fourth detection coils 8d in the circumferential direction are connected in series.

The first detection coil 8a and the fourth detection coil 8d detect the change in magnetic permeability of the rotating shaft 2 in a first direction inclined at a predetermined angle (+45 degrees in the illustrated example) with respect to the axial direction of the rotating shaft 2. The second detection coil 8b and the third detection coil 8c detect the change in magnetic permeability of the rotating shaft 2 in a second direction inclined at a predetermined angle (-45 degrees in the illustrated example) on the opposite side to the first direction with respect to the axial direction of the rotating shaft 2. The insulated electric wires that make up the detection coils 8a to 8d are electrically connected to the measurement circuit 6.

The back yoke 9 has a cylindrical shape and is made of a magnetic material (ferromagnetic material) such as iron, and is fitted and fixed to the outside of the bobbin 7. The back yoke 9 has the function of suppressing leakage of magnetic flux generated by the detection coils 8a to 8d arranged around the bobbin 7 to the outside.

The holder 5 comprises a main body 11, a number of positioning protrusions 12 (three in the illustrated example), and a connector portion 13.

The main body 11 has a cylindrical shape. The main body 11 is disposed around the rotating shaft 2 and holds the detection unit 3 inside. In other words, the detection unit 3 is embedded (molded) inside the main body 11.

Each of the positioning protrusions 12 protrudes radially inward from each of multiple circumferential locations (three locations equally spaced circumferentially in the illustrated example) on the inner peripheral surface of the main body 11. The tip portion (the radially inner end portion) of each of the positioning protrusions 12 is in sliding contact with or closely opposed to, preferably in sliding contact with, the detection surface 4 of the rotating shaft 2. In this example, each of the positioning protrusions 12 has, at its tip portion, a concave curved portion 14 in the shape of a partial cylindrical surface centered on the central axis of the main body 11.

In this example, as shown in FIG. 2, each of the positioning protrusions 12 protrudes radially inward from an end of the inner peripheral surface of the main body 11 on one axial side (the left side in FIG. 2). However, as shown in FIG. 5, for example, each of the positioning protrusions 12 can also protrude over the entire axial length from the inner peripheral surface of the main body 11. Alternatively, each of the positioning protrusions can protrude radially inward from an axial middle portion or an end on the other axial side of the inner peripheral surface of the main body.

The connector portion 13 protrudes radially outward from one circumferential point on the outer circumferential surface of the main body portion 11. A harness 15 is connected to the connector portion 13. The harness 15 electrically connects the insulated wires that make up the detection coils 8a to 8d to the measurement circuit 6. Alternatively, a substrate portion on which the measurement circuit 6 is mounted can be embedded inside the holder 5, and the torque signal output by the torque calculation portion 16 of the measurement circuit 6 can be extracted by the harness 15.

The holder 5 in this example can be made by injection molding a thermoplastic resin such as epoxy resin, polyphenylene sulfide (PPS), PA (polyamide), or PPA (polyphthalamide). That is, a mold is placed around the detection unit 3, molten resin is pumped into the cavity defined between the detection unit 3 and the mold, and the molten resin is cooled and solidified. This forms the holder 5, and the detection unit 3 is embedded inside the main body 11 of the holder 5.

The measurement circuit 6 measures the torque transmitted by the rotating shaft 2 by detecting the change in inductance of each of the detection coils 8a to 8d. The measurement circuit 6 includes a bridge circuit 17, an oscillator 18, a voltage measurement device (lock-in amplifier) 19, and a torque calculation unit 16.

The bridge circuit 17 is formed by connecting the first detection coil 8a, the second detection coil 8b, the third detection coil 8c, and the fourth detection coil 8d in a ring shape. The oscillator 18 applies an AC voltage between a contact A between the first detection coil 8a and the second detection coil 8b, and a contact B between the third detection coil 8c and the fourth detection coil 8d. The voltage measuring device 19 detects the voltage between a contact C between the first detection coil 8a and the third detection coil 8c, and a contact D between the second detection coil 8b and the fourth detection coil 8d. The torque calculation unit 16 calculates the torque transmitted by the rotating shaft 2 based on the output signal of the voltage measuring device 19.

To measure the torque transmitted by the rotating shaft 2 using the magnetostrictive torque sensor 1 of this example, an AC voltage is applied between points A and B by the oscillator 18, and an AC current is passed through each of the detection coils 8a to 8d. Then, in each of the detection coils 8a to 8d, currents in the opposite directions flow between pairs of detection coils adjacent in the circumferential direction. As a result, an AC magnetic field is generated around the detection coils 8a to 8d, and part of the magnetic flux of the AC magnetic field passes through the surface layer of the rotating shaft 2. In this state, when torque is applied to the rotating shaft 2, the magnetic permeability of the rotating shaft 2 increases (or decreases) in the +45 degree direction relative to the axial direction due to the inverse magnetostriction effect, and the magnetic permeability of the rotating shaft 2 decreases (or increases) in the -45 degree direction relative to the axial direction. Therefore, the inductance decreases (or increases) in the first detection coil 8a and the fourth detection coil 8d, and the inductance increases (or decreases) in the second detection coil 8b and the third detection coil 8c. As a result, the voltage value detected by the voltage measuring device 19 changes, and the torque calculation unit 16 calculates the torque transmitted by the rotating shaft 2 based on this voltage value.

On the other hand, when the rotating shaft 2 is not transmitting torque, the inductances of the detection coils 8a to 8d are equal to each other. Therefore, the voltage detected by the voltage measuring device 19 is zero.

In the magnetostrictive torque sensor 1 of this example, the main body 11 of the holder 5 is disposed around the detection surface 4 of the rotating shaft 2, and the concave curved surface 14 of the positioning protrusion 12 is in sliding contact with or close to the detection surface 4 of the rotating shaft 2. As a result, the magnetostrictive torque sensor 1 has the detection unit 3 disposed around the detection surface 4 and facing the detection surface 4. At least the part of the rotating shaft 2 that includes the detection surface 4 is made of a material having magnetostrictive properties, such as steel (iron alloy) such as SCr420 (chrome steel), SCM420 (chrome molybdenum steel), and SNCM420 (nickel chrome molybdenum steel). Specifically, the entire rotating shaft 2 can be made of a material having magnetostrictive properties. Alternatively, the part including the detection surface 4 can be made of a material having magnetostrictive properties and can be fixed to the parts that make up the remaining part.

In addition, a modified layer with improved magnetostrictive properties can be formed on the detection surface 4 by performing a shot peening process. By forming such a modified layer, it is possible to improve the sensitivity and hysteresis of torque measurement by the magnetostrictive torque sensor 1.

In the magnetostrictive torque sensor 1 of this example, the concave curved surface portion 14 provided at the tip of each of the positioning protrusions 12 of the holder 5 is in sliding contact with or close to the detection surface 4 of the rotating shaft 2, preferably in sliding contact with it. Therefore, the distance between the detection unit 3 embedded inside the main body portion 11 of the holder 5 and the detection surface 4 of the rotating shaft 2 can be precisely regulated without excessively increasing the shape precision and assembly precision of the parts of the mechanical device including the magnetostrictive torque sensor 1 and the rotating shaft 2. In other words, the radial positioning of the detection unit 3 relative to the detection surface 4 of the rotating shaft 2 can be precisely performed. Therefore, the torque measurement precision of the magnetostrictive torque sensor 1 can be improved without excessively increasing the manufacturing cost of the mechanical device.

The above describes an embodiment of the present invention, but the present invention is not limited to this and can be modified as appropriate without departing from the technical concept of the invention.

In this example, the positioning protrusion 12 is formed on the holder 5 in which the detection unit 3 is embedded . Although it is outside the technical scope of the present invention , it is also possible to form a positioning protrusion on a bobbin around which a detection coil is wound, and to place the tip of the positioning protrusion in sliding contact with or adjacent to the detection surface of the rotating body. In this case, the radial outside of the bobbin can be covered with a holder made of synthetic resin.

In this example, the positioning protrusions 12 are arranged at multiple locations in the circumferential direction, but the positioning protrusions can also be formed in an annular shape around the entire circumference. However, when the tip of the positioning protrusion comes into sliding contact with the detected surface of the rotating body, it is preferable to arrange the positioning protrusions intermittently at multiple locations in the circumferential direction, preferably at three or more locations, in order to reduce the sliding contact resistance by reducing the sliding contact area between the tip of the positioning protrusion and the detected surface of the rotating body.

In this example, the bridge circuit 17 is made up of four detection coils 8a to 8d, but two of the four detection coils that make up the bridge circuit can be replaced with resistors. Alternatively, instead of the coil member made up of multiple detection coils and a bobbin, a magnetic sensor equipped with a magnetic detection element such as a Hall element, a Hall IC, an MR element, a GMR element, an AMR element, a TMR element, or an MI element can be used.

In this example, the detection unit 3 of the magnetostrictive torque sensor 1 is disposed around the detection surface 4 provided on the outer circumferential surface of the rotating shaft 2, but the detection unit may be arranged to face the detection surface provided on the axial side surface of the rotating body, although this is outside the technical scope of the present invention. In this case, the positioning protrusion is formed to protrude in the axial direction toward the detection surface.

The magnetostrictive torque sensor of the present invention can be incorporated into, for example, an automobile powertrain for use. In this case, the device into which it is incorporated is not particularly limited, and can be a transmission that changes gears under vehicle control, such as an automatic transmission (AT), a belt-type continuously variable transmission, a toroidal-type continuously variable transmission, an automatic manual transmission (AMT), or a double clutch transmission (DCT), or a transfer case. In addition, the drive system (FF, FR) of the target vehicle is also not particularly important.

Furthermore, the magnetostrictive torque sensor of the present invention can be incorporated and used not only in automobile powertrains, but also in various types of machinery and equipment such as bicycles, including electrically assisted bicycles, windmills, railway vehicles, rolling mills, machine tools, construction machinery, agricultural machinery, and household electrical appliances.

REFERENCE SIGNS LIST 1 magnetostrictive torque sensor 2 rotating shaft 3 detection section 4 detected surface 5 holder 6 measurement circuit 7 bobbin 8a first detection coil 8b second detection coil 8c third detection coil 8d fourth detection coil 9 back yoke 10a first inclined groove 10b second inclined groove 11 main body 12 positioning protrusion 13 connector 14 concave curved surface 15 harness 16 torque calculation section 17 bridge circuit 18 oscillator 19 voltage measurement device

Claims (1)

A magnetostrictive torque sensor that is attached to a part that does not rotate even when in use, is disposed opposite to a detection surface of a rotating body having magnetostrictive properties, and measures a torque transmitted by the rotating body by utilizing an inverse magnetostrictive effect generated in the rotating body,
A holder made of synthetic resin;
A detection unit embedded in the holder;
Equipped with
The detection portion is disposed around the entire circumference of the detection surface,
the holder has a main body portion that holds the detection portion , and at least one positioning protrusion having a tip portion that is in sliding contact with or closely opposed to the detection surface of the rotating body ,
The at least one positioning protrusion is provided so as to protrude radially inward from three or more circumferential positions on the inner circumferential surface of the main body, or is provided so as to protrude radially inward from the inner circumferential surface of the main body over the entire circumference.
Magnetostrictive torque sensor.

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