JP2010066043A - Torque sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly-reliable, low-cost torque sensor, which reliably obtains torque acting on a rotating shaft even when a magnetic sensor is not in contact with a magnet ring, and which detects accurate torque even when a circumferentially multipolarly magnetized magnet is used. <P>SOLUTION: The torque sensor includes a shaft 2 which rotates together with the rotating shaft, a rotor 3 which is arranged in the vicinity of both ends of the shaft 2, a case 5 for covering the shaft 2, and a stator 4 which is arranged facing the rotor 3. The rotor 3 is made of the magnet 8 which is multipolarly magnetized in the rotation direction of the rotating shaft. The stator 4, which is of the claw pole type which includes sidewalls 4a on axially both sides and is formed with pole teeth 4b intermittently in the inner peripheral direction, includes a stator inner space surrounded by the inner periphery of the case 5, the sidewalls 4a, and the surface of the pole teeth 4b. A magnetic sensor 13 includes in the stator inner space for measuring the direction and amount of a magnetic field from the rotor 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a torque sensor that can detect a torsional torque of a rotating shaft, and in particular, can detect a pedaling force of an electric bicycle.

  In an electric bicycle, the pedaling force when the user depresses the pedal is detected, and auxiliary power corresponding to this torque is applied. Patent Document 1 is disclosed as an apparatus for detecting this torque. The pedaling force detection device for a battery-assisted bicycle described in Patent Document 1 detects torsional torque applied to a hollow shaft as means for detecting pedaling force applied to a pedal as information for controlling the assisting force of a bicycle with electric assist or the like. In this type of pedaling force detection device, magnet rings are provided on both outer sides of the hollow shaft, and MR sensors are arranged in contact with each other using springs facing each other. In the output waveform obtained by rotating the hollow shaft, the pedaling force is calculated from the phase difference of the output waveform generated in proportion to the twist amount of the hollow shaft.

  However, the detection of the treading force in the invention described in Patent Document 1 has a problem in durability because the MR sensor is in contact with the magnet ring and wear of parts occurs. In addition, the output tends to become unstable due to the roundness of the magnet ring and the balance of magnetization, which adversely affects the accuracy of treading force detection.

  Further, the magnet ring described in Patent Document 1 is multipolarly magnetized along the circumferential direction. When magnetizing such a ring-shaped multipole magnet, there is a clearance between the magnetized yoke inner diameter and the magnet outer diameter, and therefore the magnet is magnetized with the center shifted by the clearance. As a result, unevenness occurs in the magnetized pitch of the magnet and unevenness in the magnetic flux density for each magnetic pole. This unevenness also occurs when the roundness of the magnet is poor. Even if the magnet is magnetized without error, if the magnet is decentered or misaligned, a pitch shift or magnetic flux density unevenness occurs in the waveform detected by the magnetic sensor. Thus, if unevenness or deviation occurs, accurate torque detection becomes difficult as a result.

  The main type of torque sensor that detects the torque applied to the rotating shaft in a non-contact manner is the magnetostrictive type. However, this magnetostrictive type compensates for the difficulty in manufacturing the sensor shaft and the temperature correction to cope with the output change with respect to the temperature change. There are many problems such as the need for control and cost increase due to them.

JP 2003-335291 A

  The present invention takes the above-described conventional technology into consideration, and even when the magnetic sensor is not in contact with the magnet ring, it is possible to reliably obtain torque applied to the rotating shaft, and further to multipolar in the circumferential direction. An object of the present invention is to provide a highly reliable and low-cost torque sensor that can detect an accurate torque even when a magnetized magnet is used.

  In order to achieve the above object, according to the first aspect of the present invention, the shaft is fixed to the rotating shaft, rotates together with the rotating shaft, is fixed along the outer periphery of the shaft, and is disposed near both ends of the shaft. A rotor, a case that covers the shaft, and a stator that is fixed along the inner periphery of the case and is disposed so as to face the rotor; and the rotor is multipolar in the rotation direction of the rotating shaft. The stator is magnetized, and the stator has a side wall on both sides in the axial direction, and is a claw pole type in which pole teeth are intermittently formed in the inner circumferential direction, the inner circumferential surface of the case, There is provided a torque sensor comprising a stator inner space surrounded by a side wall and the pole tooth surface, wherein the stator inner space is provided with a magnetic sensor for measuring the direction and amount of a magnetic field from the rotor.

  The invention according to claim 2 is characterized in that the rotating shaft is a crankshaft connected to a pedal via a crank, and is applied to an electric bicycle.

  According to the first aspect of the present invention, since the magnetic sensor is disposed in the stator inner space surrounded by the stator and the case, the magnetic sensor is not in contact with the rotor (magnet). For this reason, the sensor is not worn by the rotation of the magnet and can be used for a long time. Therefore, for a long period of time, using this magnetic sensor, the direction and amount of the magnetic field from the magnet can be measured, the amount of twist generated at both ends of the shaft can be calculated, and the torque can be obtained. In addition, the magnetic characteristics of coils such as magnetostrictive type are used to pick up the amount of magnetic flux with magnetic sensors located at both ends of the shaft and calculate the torque based on the phase difference (time difference) of the output waveform detected by each magnetic sensor. This eliminates the influence of output changes caused by temperature, etc., enables stable torque detection even when temperature changes occur, improves reliability against environmental changes, and inputs temperature correction values during manufacturing, etc. As a result, a low-cost torque sensor can be provided. Furthermore, since the stator is a claw pole type and has pole teeth on the inner surface, even if the magnet has uneven magnetic pole pitch or magnetic flux density, or even if the magnet has eccentricity or misalignment, multiple polar teeth Since the magnetic flux collected is transmitted to the magnetic sensor and the magnetic flux is transmitted to the magnetic sensor, the effects of these irregularities and deviations are cancelled, and an accurate output waveform can be obtained, which is reliable, stable and highly accurate. Torque detection can be performed.

  According to the second aspect of the present invention, when applied to an electric bicycle, it is possible to reliably detect the user's pedaling force (torque) and to give more accurate auxiliary power to the user.

  Hereinafter, a torque sensor according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic sectional view of a torque sensor according to the present invention, and FIG. 2 is a schematic sectional view showing a rotor and a stator. FIG. 3 is an exploded view showing the torque sensor according to the present invention for each part, and FIG. 4 is a schematic cross-sectional view when the torque sensor according to the present invention is applied to a battery-assisted bicycle.

  As shown, the torque sensor 1 according to the present invention includes a cylindrical shaft 2, a rotor (magnet) 3, a stator 4, and a case 5. The shaft 2 is fixed to the outer periphery of a crankshaft 6 (see FIG. 4) that serves as a rotating shaft. Specifically, the uneven portion (not shown) formed on the outer peripheral surface of the crankshaft 6 and the uneven portion 7 formed on the inner peripheral surface of the shaft 2 are fixed by spline fitting. As a result, the shaft 2 rotates together with the crankshaft 6. An annular member 17 through which the crankshaft 6 can be inserted is disposed at the end of the shaft 2 opposite to the concave and convex portion 7. The shaft 2 is made of spring steel, stainless steel, titanium alloy, or the like.

  The rotor 3 includes an annular magnet 8. The magnet 8 is multipolarly magnetized in the radial direction (radial direction). The rotor 3 (magnet 8) is fixed along the outer periphery of the shaft 2, and is disposed near both ends of the shaft 2, respectively. The magnet 8 is formed of, for example, a plastic magnet, ferrite, or neodymium.

  The stator 4 is formed in an annular shape and is made of a magnetic material. The stator 4 has side walls 4a on both sides in the axial direction. A claw pole 4b rises in a comb shape from the side walls 4a, and the claw pole 4b is bent in the direction of the opposite side wall 4a. The stator 4 is formed such that the claw poles 4b from the side walls 4a on both sides mesh with each other. That is, the stator 4 is a claw pole type stator. The stator 4 is provided to face the rotor 3 along the inner periphery of the case 5 that covers the shaft 2. The stator 4 is formed of an electromagnetic steel plate, a galvanized steel plate, a sintered alloy, or the like.

  An annular member 21 made of PCB is disposed in a space formed between the stator 4 and the case 5 (between the side walls 4 a), and an MR (magnetic resistance) sensor 13 is fixed to the annular member 21. The MR sensor 13 may be any magnetic (magnetic field) sensor as long as it can detect the amount and direction of the magnetic flux or magnetic field. With such a configuration, the MR sensor 13 is not in contact with the rotor 3, so the sensor 13 is not worn by the rotation of the rotor 3, and the sensor 13 can be used for a long time. Therefore, for a long period of time, the MR sensor 13 is used to measure the direction and amount of the magnetic field from the magnet 8, calculate the amount of twist generated at both ends of the shaft 2 by a method as described later, and obtain the torque. it can.

  Since the above-described claw pole 4b is intermittently formed in the inner circumferential direction of the stator 4, this becomes a pole tooth. The pole teeth are alternately formed with S poles and N poles. The MR sensor 13 picks up the direction and amount (magnetic flux) of the magnetic field from the rotor 3 through the pole teeth. A plurality of MR sensors 13 may be provided in the stator 4 and the obtained results may be averaged and output. That is, the magnetic field of the magnet 8 is transmitted from the claw pole 4b to the side wall 4a along with the rotation of the shaft 2, and this is transmitted to the other side wall 4a opposite to it. At this time, the MR sensor 13 provided between the side walls 4a picks up this magnetic flux. From this amount of magnetic flux, output waveforms at both ends of the shaft 2 are calculated. Thereby, as will be described later, the torque can be calculated based on the phase difference (time difference) of the output waveform detected by the MR sensor 13. For this reason, the influence of output change due to temperature mainly due to temperature characteristics of coils such as magnetostrictive type is eliminated, stable torque detection is possible even if temperature change occurs, and reliability against environmental change is improved In addition, as a result, the low-cost torque sensor 1 can be provided without performing an operation such as inputting a temperature correction value at the time of manufacture. In addition, by using a claw pole type stator, the accuracy of the output waveform can be stabilized, and stable and highly accurate torque detection becomes possible.

  An annular bearing 18 is provided between the shaft 2 and the case 5 outside the rotor 3 and the stator 4 in the axial direction. The case 5 is formed of aluminum or other nonmagnetic material. The bearing 18 is formed of a ball bearing, a sintered alloy, a resin, or the like.

  As shown in FIG. 4, pedal-equipped cranks 14 are attached to both ends of the crankshaft 6. A pedaling force (torque) when a user who operates an electric bicycle depresses a pedal is transmitted from the crankshaft 6 to the torque sensor 1 and is transmitted to the sprocket 16 via the one-way clutch 15. Reference numeral 19 denotes a housing. Thus, by applying the torque sensor 1 to an electric bicycle, it is possible to reliably detect the pedaling force (torque) of the user and to give more accurate auxiliary power to the user. As another application, for example, it can be used for assisting the rotational torque of the power steering of an automobile.

  FIG. 5 is a graph showing the output waveform of the result obtained by the MR sensor.

  As shown in the figure, the amount of magnetic flux obtained by the MR sensor can be output as a voltage waveform as it is. The solid line A is the result of the MR sensor 13 on the side close to the concavo-convex portion 7 of the shaft 2, and the dotted line B is the result of the MR sensor 13 on the far side (refer to FIGS. 1 to 4 for symbols). Originally, when the shaft 2 rotates together with the crankshaft 6, the output waveforms of the MR sensors 13 at both ends of the shaft 2 should overlap each other. However, since only one end of the shaft 2 is spline-fitted to the crankshaft 6 by the concavo-convex portion 7, when the crankshaft 6 rotates, twisting occurs at both ends of the shaft 2. Therefore, the rotations at both ends of the shaft 2 are not synchronized, and a phase difference (time difference Δt) occurs in the output waveform. That is, the dotted line B on the side farther from the concavo-convex portion 7 results in rotation with a delay from the solid line A. Measuring this time difference Δt is the same as measuring the amount of twist of the shaft 2. Therefore, the torque can be calculated from this twist amount.

The torque can be obtained after calculating the twist angle θ. At that time, the initial error Tref resulting from the sensor assembly accuracy is used as a correction value. The period t indicates the time until the pole tooth reaches the position of the adjacent pole tooth. Since the torque and the torsion angle are in a proportional relationship, this proportionality constant is obtained in advance. The “number of sensor poles” is the number of N poles and S poles per rotor 3 (magnet 8). That is, it is the total number of N poles and S poles of the magnet 8 magnetized with multiple poles.
The twist angle θ can be obtained as follows.
Twist angle θ = time difference Δt × (360 / (number of sensor poles / 2)) / period t
The torque (T) can be obtained as follows.
Torque (T) = proportional constant × twist angle θ−initial error Tref

Further, the rotational speed of the crankshaft 6 is calculated from the period t of the output waveform and the number of decompositions of the rotor 3 (number of sensor poles), and the power (W) can be calculated by adding the torque obtained above. Thus, even if a speed sensor is not provided separately from the torque sensor, the force applied by the user's pedal can be obtained as power (W), and the assist amount control for instructing the motor proportional to the pedaling force is facilitated. . In addition, the system configuration is cheaper than the speed sensor.
The rotation speed (N) can be obtained as follows.
Rotational speed (N) = 1 / (cycle t × (number of sensor poles / 2))
The power (W) can be obtained as follows.
Power (W) = 1.047 × 10 ⁻¹ × Rotational speed (N) × Torque (T)

  FIG. 6 is an explanatory diagram when the magnetic flux is detected using a claw pole type stator.

  The stator 4 shown in the figure is formed by bending the claw pole 4b only in one direction (the front end of the claw faces the front side in the figure). As described above, when the ring-shaped magnet 8 is magnetized in the radial direction, the magnetization pitch may be uneven. In the figure, the right side of the figure shows a case where the pitch interval is small and the left side is large. In such a case, pitch deviation and magnetic flux density unevenness occur in the waveform detected by the magnetic sensor, and as a result, accurate torque detection may not be possible. However, by using the claw pole type stator, the magnetic flux collected by the protruding pole teeth is synthesized (arrow P) and transmitted to the magnetic sensor 13.

  For this reason, even if magnetic pole pitch unevenness or magnetic flux density unevenness occurs in the magnet 8, or even if the magnet 8 is eccentric or misaligned, the magnetic flux collected by the plurality of pole teeth (claw pole 4b) is synthesized. Since the magnetic flux is transmitted to the magnetic sensor 13, the influence of these unevenness and deviation can be canceled, an accurate output waveform can be obtained, and highly reliable, stable and highly accurate torque detection can be performed. it can. Therefore, the detection accuracy can be improved as compared with the case where the magnetic flux of the magnet is directly detected by the Hall element.

It is a schematic sectional drawing of the torque sensor which concerns on this invention. It is a schematic sectional drawing which shows a rotor and a stator. It is the exploded view which showed the torque sensor which concerns on this invention for every component. It is a schematic sectional drawing when the torque sensor which concerns on this invention is applied to a battery-assisted bicycle. It is a graph which shows the output waveform of the result obtained by MR sensor. It is explanatory drawing when detecting a magnetic flux using a claw pole type stator.

Explanation of symbols

1: Torque sensor, 2: Shaft, 3: Rotor, 4: Stator, 4a: Side wall, 4b: Claw pole, 5: Case, 6: Crankshaft, 7: Concavity and convexity, 8: Magnet, 13: MR sensor, 14 : Crank with pedal, 15: one-way clutch, 16: sprocket, 17: annular member, 18: bearing, 19: housing

Claims (2)

A shaft fixed to the rotating shaft and rotating together with the rotating shaft;
A rotor fixed along the outer periphery of the shaft and disposed near both ends of the shaft;
A case covering the shaft;
A stator fixed along the inner periphery of the case, and disposed opposite the rotor,
The rotor is composed of a magnet that is multipolarly magnetized in the rotation direction of the rotating shaft,
The stator is a claw pole type having side walls on both sides in the axial direction, and pole teeth are intermittently formed in an inner circumferential direction, the case inner circumferential surface, the side walls, and the pole tooth surfaces. With an enclosed stator space,
A torque sensor characterized in that a magnetic sensor for measuring the direction and amount of a magnetic field from the rotor is provided in the stator internal space.   The torque sensor according to claim 1, wherein the rotation shaft is a crankshaft connected to a pedal via a crank, and is applied to an electric bicycle.

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