JP2008256432A - Torque sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance detection precision for a torque sensor without reducing an outside diameter of a torque shaft. <P>SOLUTION: This torque sensor 50 is provided with a magnetostrictive membrane 55 provided on a surface of the torque shaft 30, and an electromagnetic coil 51 provided around the magnetostrictive membrane 55, and detects a torque input into the torque shaft 30, based on a change of inductance in the electromagnetic coil 51, the torque shaft 30 has a sensor shaft part 48 provided with the magnetostrictive membrane 55, and a torque transmission shaft part 49 for transmitting a torque, and the torque shaft 30 is heat-treated to make a hardness of the sensor shaft part 48 lower than that of the torque transmission shaft part 49. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an improvement in a torque sensor that detects torque using the stress magnetic effect of a magnetostrictive film.

  Conventionally, for example, a torque sensor disclosed in Patent Document 1 includes a magnetostrictive film provided on the surface of a torque shaft and an electromagnetic coil provided around the magnetostrictive film.

  In this case, when a torque is applied to the torque shaft and a torsional distortion occurs in the torque shaft and the magnetostrictive film, the inductance of the electromagnetic coil changes as the magnetic permeability of the magnetostrictive film changes. Based on the torque, the torque acting on the torque shaft is detected.

The torque sensor disclosed in Patent Document 2 includes a magnetostrictive film on which a magnetostrictive film is formed, and the magnetostrictive film is attached to the surface of the torque shaft by adhesion.
JP 2003-291830 A JP-A-5-5660

  In order to increase the detection accuracy of such a torque sensor, it is conceivable to reduce the outer diameter of the torque shaft and increase the torsional distortion generated in the torque shaft.

  However, when the outer diameter of the torque shaft is reduced, there arises a problem that the magnetostrictive film attached to the outer peripheral surface of the torque shaft is easily peeled off.

  The present invention has been made in view of the above problems, and an object thereof is to increase the detection accuracy of a torque sensor without reducing the outer diameter of the torque shaft.

  The present invention includes a torque shaft for transmitting torque, a magnetostrictive film provided on the surface of the torque shaft, and an electromagnetic coil provided around the magnetostrictive film, and the torque shaft is provided based on an inductance change of the electromagnetic coil. A torque sensor for detecting input torque, wherein the torque shaft has a sensor shaft portion provided with a magnetostrictive film and a torque transmission shaft portion for transmitting torque, and the hardness of the sensor shaft portion is lower than that of the torque transmission shaft portion. It was characterized by doing.

  According to the present invention, the torque of the torque shaft caused by transmitting torque is reduced by making the hardness of the sensor shaft of the torque shaft lower than that of the torque transmission shaft and partially lowering the rigidity of the sensor shaft. Since the torsional distortion concentrated on the shaft portion and generated in the sensor shaft portion increases, the inductance change of the electromagnetic coil also increases, and the detection accuracy of the torque sensor can be improved.

  Even if the outer diameter of the sensor shaft portion is increased, by reducing the rigidity of the sensor shaft portion, the amount of torsional distortion generated in the sensor shaft portion is ensured, and the accuracy with which the torque sensor detects the input torque can be increased. By increasing the outer diameter of the sensor shaft portion, it is possible to prevent the magnetostrictive film bonded to the sensor shaft portion from peeling off from the sensor shaft portion.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows an example of a vehicle power steering apparatus to which the present invention is applied. The power steering apparatus 1 is linked to a torque shaft (steering system) 30 linked to a steering handle (not shown) and wheels (not shown) as a power transmission mechanism for transmitting a driver's steering torque to a steering system. The rack shaft (output system) 3 is provided, and the wheels are steered when the rack shaft 3 moves in the axial direction by the rotation of the torque shaft 30.

  The torque shaft 30 is supported by the casings 5 and 6 through the first and second bearings 7 and 8 so as to be rotatable about the center line O, and the first and second bearings 7 and 8 are used for the radial load of the torque shaft 30. Thrust weight can be received. The first and second bearings 7 and 8 are ball bearings in which a plurality of balls are interposed between the inner race and the outer race.

  Each casing 5, 6 is fastened via a plurality of bolts 19, and an outer race of the second bearing 8 is sandwiched between each casing 5, 6.

  A serration shaft portion 32 with serrations is formed at the upper end portion of the torque shaft 30, and a joint (not shown) linked to the steering handle is connected to the serration shaft portion 32 so that the driver operates the steering handle. Torque is input to the serration shaft portion 32.

  The steering gear mechanism 4 includes a pinion 42 engraved on the torque shaft 30 and a rack 3a engraved on the rack shaft 3, and the pinion 42 meshes with the rack 3a. When the torque shaft 30 rotates, the rack shaft 3 moves in the axial direction by the rotation of the pinion 42, and the left and right wheels are steered via tie rods (not shown) linked to the rack shaft 3.

  The rack shaft 3 is slidably supported with respect to the casing 6 so as to move in the lateral direction of the vehicle. A guide 11 slidably contacting the outer peripheral surface of the rack shaft 3 and a spring 12 for biasing the guide 11 are interposed in the casing 6, and the rack 3 a is pressed against the pinion 42 by the biasing force of the spring 12. The biasing force of the spring 12 is adjusted by an adjustment bolt 13 screwed into the casing 6.

  The steering gear mechanism 4 is not limited to a mechanism including the rack 3a and the pinion 42, and other mechanisms may be used.

  A lower end shaft portion 43 is formed at the lower end of the torque shaft 30, and the lower end shaft portion 43 is rotatably supported by the casing 6 via the needle bearing 9. As a result, the radial load acting on the portion of the torque shaft 30 where the pinion 42 is engraved is supported at both ends via the needle bearing 9 and the second bearing 8.

  The power steering device 1 includes a torque sensor 50 that detects a steering torque acting on the torque shaft 30 and an electric motor (not shown) that drives the rack shaft 3 as an assist mechanism that assists in applying a steering torque. An electric motor applies a steering assist torque to the rack shaft 3 in accordance with a steering torque detected by a torque sensor 50 by a controller (not shown).

  In addition, you may use not only the mechanism in which an electric motor drives the rack shaft 3, but another mechanism.

  The torque sensor 50 is a magnetostrictive detection device that electrically detects magnetostriction characteristics that change in accordance with the amount of torsional distortion of the torque shaft 30. The torque sensor 50 is provided with two magnetostrictive films 55 arranged in the longitudinal direction on the surface of the torque shaft 30, and electrically detects a change in magnetostrictive characteristics generated in each magnetostrictive film 55 around each magnetostrictive film 55. A pair of electromagnetic coils 51 is provided. Each magnetostrictive film 55 and each electromagnetic coil 51 are arranged concentrically with the rotation center line O of the torque shaft 30.

  The magnetostrictive film 55 is, for example, a Ni—Fe or Fe—B alloy film. When the torque is input to the torque shaft 30 and the torque shaft 30 is twisted, distortion occurs, and the permeability changes due to the stress magnetic effect. It is a thin film. When distortion occurs in the magnetostrictive film 55 and the magnetic permeability of the magnetostrictive film 55 changes, the inductance of each electromagnetic coil 51 changes.

  When torsional distortion occurs in the torque shaft 30 and each magnetostrictive film 55 by applying a steering torque to the torque shaft 30, the inductance of the electromagnetic coil 51 that confronts this increases as the permeability of one of the magnetostrictive films 55 increases. As the magnetic permeability of the other magnetostrictive film 55 becomes smaller, the inductance of the electromagnetic coil 51 facing this becomes larger. The controller inputs the inductance change of each electromagnetic coil 51 through a detection circuit (not shown), and detects the magnitude and direction of the steering torque applied to the torque shaft 30.

  The magnetostrictive film 55 is formed on a thin plate-like magnetostrictive film 56, and this magnetostrictive film 56 is attached to the outer peripheral surface of the metal torque shaft 30 by adhesion.

  However, since the magnetostrictive film 56 is affixed in a state of being bent along the outer peripheral surface of the cylindrical torque shaft 30, the magnetostrictive film 56 is torqued by an elastic restoring force that tries to return to a flat original shape. There exists a problem that it is easy to peel from the outer peripheral surface of the shaft 30.

  As a countermeasure against this, the present invention increases the outer diameter of the sensor shaft 48 to which the magnetostrictive film 56 of the torque shaft 30 is attached, and increases the hardness of the sensor shaft 48 to which the magnetostrictive film 55 is provided by heat-treating the torque shaft 30. The torque transmission shaft portion 49 (the serration shaft portion 32, the pinion 42) that transmits at least torque is set lower.

  The sensor shaft portion 48 is a portion where the torque shaft 30 is hatched in FIG. 1, and faces the electromagnetic coils 51. A magnetostrictive film 56 is attached to the outer peripheral surface of the cylindrical sensor shaft portion 48 by adhesion.

  The first and second shafts 31 and 41 obtained by dividing the torque shaft 30 in the axial direction are provided, and the first and second shafts 31 and 41 have a cylindrical hollow cylindrical portion 38 centered on the rotation center line O, and a sensor shaft. A portion 48 is formed, and the hollow cylinder portions 38 and the end portions of the sensor shaft portion 48 are fixed to each other by welding. The first and second shafts 31 and 41 are made of steel.

  The torque shaft 30 is divided into first and second shafts 31 and 41 at a portion located between the first and second bearings 7 and 8, and the first shaft 31 rotates on the casing 5 via the first bearing 7. The second shaft 41 is rotatably supported by the casings 5 and 6 via the second bearings 8.

  The first shaft 31 has the serration shaft portion 32 formed at the upper end portion thereof, the hollow cylinder portion 38 formed at the lower end portion thereof, and the inner portion of the first bearing 7 between the serration shaft portion 32 and the hollow cylinder portion 38. A bearing portion 37 into which the race is fitted is formed.

  The first shaft 31 is subjected to, for example, induction hardening treatment on the entire area thereof, and the hardness thereof is uniformly increased. Thereby, the hardness of the serration shaft portion 32, the bearing portion 37, and the hollow cylinder portion 38 provided on the first shaft 31 is higher than the hardness of the sensor shaft portion 48 of the second shaft 41.

  The second shaft 41 has a hollow cylindrical sensor shaft portion 48 formed at the upper end thereof, a pinion 42 and a lower end shaft portion 43 formed at the lower end thereof, and a second bearing between the sensor shaft portion 48 and the pinion 42. The bearing portion 45 into which the inner race 7 is fitted is formed. A radial load acting on a portion of the second shaft 41 where the pinion 42 is engraved is supported at both ends via the needle bearing 9 and the second bearing 8.

  The second shaft 41 performs, for example, a high-frequency quenching process on other portions except for the sensor shaft portion 48 hatched in FIG. As a result, the hardness of the portion of the second shaft 41 where the pinion 42, the lower end shaft portion 43, and the bearing portion 45 are formed is higher than the hardness of the sensor shaft portion 48.

  The torque of the sensor shaft 48 provided with the magnetostrictive film 55 by heat-treating the torque shaft 30 is made lower than that of the serration shaft 32 and the pinion 42 for transmitting torque, and the rigidity of the sensor shaft 48 is partially increased. By lowering, the torsional stress of the torque shaft 30 caused by the input of the steering torque concentrates on the sensor shaft portion 48, and the torsional distortion generated in the sensor shaft portion 48 increases, so that the inductance change of each electromagnetic coil 51 also changes. This increases the accuracy with which the torque sensor 50 detects the steering torque.

  By increasing the outer diameter of the sensor shaft portion 48, it is possible to prevent the magnetostrictive film 56 adhered to the sensor shaft portion 48 from being peeled off from the sensor shaft portion 48. However, even if the outer diameter of the sensor shaft portion 48 is increased, the sensor By reducing the rigidity of the shaft portion 48, the amount of torsional distortion generated in the sensor shaft portion 48 can be secured, and the accuracy with which the torque sensor 50 detects the steering input torque can be increased.

  The torque shaft 30 has a serration shaft portion 32 and a pinion 42 as the torque transmission shaft portion 49. Since the serration shaft portion 32 and the pinion 42 are quenched, the durability of the serration shaft portion 32 and the pinion 42 is improved. It is possible to improve both the detection accuracy of the torque sensor 50.

  Since the sensor shaft portion 48 of the torque shaft 30 is formed in a hollow cylindrical shape, even if the outer diameter of the sensor shaft portion 48 is increased, the amount of torsional distortion generated in the sensor shaft portion 48 by reducing the thickness of the sensor shaft portion 48 is reduced. And the accuracy with which the torque sensor 50 detects the steering input torque according to the torsional distortion generated in the torque shaft 30 can be improved. As a result, the outer diameter of the sensor shaft portion 48 is increased, and the magnetostrictive film 56 bonded to the sensor shaft portion 48 can be prevented from peeling from the sensor shaft portion 48.

  The torque shaft 30 may be a solid integrated structure. In this case, the number of processing steps can be greatly reduced as compared with the conventional structure in which the first and second shafts 31 and 41 are divided.

  The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

It is sectional drawing of the power steering apparatus which shows embodiment of this invention.

Explanation of symbols

30 Torque shaft 32 Serration shaft portion 42 Pinion 48 Sensor shaft portion 49 Torque transmission shaft portion 50 Torque sensor 51 Electromagnetic coil 55 Magnetostrictive film 56 Resin film

Claims (3)

A torque shaft for transmitting torque, a magnetostrictive film provided on the surface of the torque shaft, and an electromagnetic coil provided around the magnetostrictive film are provided and input to the torque shaft based on an inductance change of the electromagnetic coil. A torque sensor for detecting torque,
The torque shaft has a sensor shaft portion on which the magnetostrictive film is provided and a torque transmission shaft portion for transmitting torque, and the hardness of the sensor shaft portion is lower than that of the torque transmission shaft portion.   The torque sensor according to claim 1, wherein the torque shaft is subjected to quenching processing on the torque transmission shaft portion.   The torque sensor according to claim 1, wherein the sensor shaft portion is formed in a hollow cylindrical shape.

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