JP5668504B2 - Torque sensor and electric power steering apparatus provided with the same - Google Patents

Description

  The present invention relates to a torque sensor that detects a torque generated on a rotating shaft in a non-contact manner and an electric power steering apparatus including the torque sensor.

  As a torque sensor applied to a conventional electric power steering apparatus, a torque sensor described in Patent Document 1 is known. This torque sensor is provided with two systems of bridge circuits each consisting of a pair of detection coils and resistors whose impedances change in opposite directions according to the torque generated on the rotating shaft, and these bridge circuits are connected redundantly. Thus, the above can be easily detected, and even if an abnormality occurs in one of the detection circuits, the steering assist can be continued by the torque signal from the other detection circuit.

JP 2006-267045 A

By the way, in the torque sensor described in the above-mentioned Patent Document 1, four coils each arranged in a coil yoke are arranged along the axial direction, and a bridge circuit is configured by these coils and resistors, Torque is detected by a differential circuit.
However, although the effect of drift due to coil temperature change can be eliminated to some extent by the differential circuit, there is an unsolved problem that the effect of drift due to temperature change or the like cannot be completely eliminated.
Accordingly, the present invention has been made paying attention to the unsolved problems of the above-described conventional example, and a torque sensor capable of completely removing the influence of drift due to a temperature change or the like, and an electric power steering apparatus including the torque sensor The purpose is to provide.

In order to achieve the above object, a torque sensor according to an embodiment of the present invention has a pair of yokes arranged in parallel in the axial direction, and two detection coils are provided in each of the pair of yokes. a belt torque detecting unit to change the impedance in opposite directions in response to torque generated in the rotary shaft, and two detection coils among axial direction of both ends of the pair of detection coils of two pairs that are equipped with the yoke thereof A first bridge circuit composed of resistors connected in series to each other, two axially central detection coils of the two pairs of detection coils, and resistors connected in series to these. A second bridge circuit, and a torque calculator that calculates at least two sets of detected torque signals based on a difference signal when an AC signal is individually applied to the first bridge circuit and the second bridge circuit. with The torque detector is individually opposed to the pair of yokes disposed on the inner peripheral side of the pair of yokes, and extends in the axial direction at predetermined intervals in the circumferential direction and at different intervals in the circumferential direction. A conductive and non-magnetic cylindrical body formed with a pair of windows and an axial ridge which is relatively rotated according to torque with the cylindrical body disposed on the inner peripheral side of the cylindrical body at a predetermined interval The sensor shaft portion formed in step ( 1) is provided , and magnetic symmetry is taken between the two detection coils constituting the first bridge circuit and the second bridge circuit so as to eliminate the influence of the magnetic path configuration. It is characterized in that the.

In the torque sensor according to another aspect of the present invention, the torque calculation unit calculates a main detection torque signal and a sub detection torque signal based on a difference signal when an AC signal is applied to the first bridge circuit. Two sets of torque calculation units including a torque calculation unit that calculates a main detection torque signal and a sub detection torque signal based on a difference signal when an AC signal is applied to the second bridge circuit. It is characterized by having.
Furthermore, in the torque sensor according to another aspect of the present invention, the torque calculation unit receives two sets of main detection torque signals and sub detection torque signals calculated by the two sets of torque calculation units, and the two sets And an abnormality determination unit that determines abnormality of the two torque calculation units based on the main detection torque signal and the sub detection torque signal .
In the torque sensor according to another aspect of the present invention, the abnormality determination unit detects a disconnection, a ground fault, and a power fault abnormality for each of the two sets of the main detection torque signal and the sub detection torque signal. The present invention is characterized in that an abnormality deviating from the cross characteristic is detected based on the added values of the two sets of main detection torque signals and sub detection torque signals.

An electric power steering apparatus according to an embodiment of the present invention includes a torque sensor having any one of the above-described configurations, and generates an auxiliary steering torque that is transmitted to a steering mechanism based on a torque detected by the torque sensor. A steering assist control unit that performs steering assist control by driving a motor is provided.
An electric power steering apparatus according to an embodiment of the present invention includes a torque sensor having any one of the above-described configurations, and generates an auxiliary steering torque that is transmitted to a steering mechanism based on a torque detected by the torque sensor. An abnormality determination for determining abnormality of the torque detection unit of the torque sensor based on a plurality of detected torques output from a plurality of torque calculation units of the torque sensor and a steering assist control unit that drives the motor to perform steering assist control Part.

  According to the present invention, magnetic symmetry can be obtained between the two coils constituting the bridge circuit, and the influence of the magnetic path configuration can be eliminated. Thereby, it is hard to be influenced by temperature etc., and stable torque can be detected compared with the conventional example.

It is sectional drawing which shows the principal part of the electric power steering apparatus which shows one Embodiment of this invention. It is a perspective view which shows the torque sensor which can be applied to embodiment of FIG. It is a figure explaining the protrusion on the surface of the sensor shaft part of a torque sensor, and the window arrangement | positioning of a cylindrical member. It is a characteristic diagram which shows the relationship between a torque and the inductance of a detection coil. It is a block diagram which shows the torque calculating circuit which can be applied to embodiment of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view showing a main part of an electric power steering apparatus according to the present invention, and FIG. 2 is a perspective view showing a configuration of a torque sensor according to the present invention.
In FIG. 1, the housing 5 has a structure that is divided into an input shaft side housing portion 5a and an output shaft side housing portion 5b. Inside the input shaft side housing portion 5a, the input shaft 1 is rotatably supported by a bearing 6a. The output shaft 2 is rotatably supported by bearings 6b and 6c in the output shaft side housing portion 5b.

The input shaft 1 and the output shaft 3 are connected via a torsion bar 3 disposed inside the input shaft 1.
The input shaft 1, the torsion bar 3, and the output shaft 2 are arranged coaxially, the input shaft 1 and the torsion bar 3 are pin-coupled, and the torsion bar 3 and the output shaft 2 are spline-coupled. In FIG. 1, a steering wheel (not shown) is integrally attached to the opposite side of the input shaft 1 from the output shaft 2. Further, a pinion shaft 2a is integrally formed on the output shaft 2 on the side opposite to the input shaft 1, and the pinion shaft 2a meshes with the rack 4 to constitute a known rack and pinion type steering mechanism. .

  A worm wheel 7 that is coaxial with the output shaft 2 and rotates integrally with the output shaft 2 is fixed to the output shaft 2 and meshes with a worm 8 that is driven by an electric motor (not shown) in the output shaft side housing portion 5b. Yes. In the worm wheel 7, a synthetic resin tooth portion 7b is integrally fixed to a metal hub 7a. The rotational force of the electric motor is transmitted to the output shaft 2 through the worm 8 and the worm wheel 7, and a steering assist torque in an arbitrary direction is applied to the output shaft 2 by appropriately switching the rotation direction of the electric motor.

  Next, the configuration of the torque detector 10 that constitutes the torque sensor TS that detects the torque between the input shaft 1 and the output shaft 3 will be described with reference to FIGS. 1 and 2. The torque detection unit 10 includes a sensor shaft portion 11 formed on the input shaft 1 on the output shaft 3 side in FIG. 1 and two pairs of detection coils 13a, 13b and 14a disposed inside the input shaft side housing portion 5a. 14b and a cylindrical member 12 disposed between the two.

  FIG. 2 is a perspective view showing the configuration of the torque detector. A sensor shaft portion 11 made of a magnetic material is formed on the outer side of the input shaft 1 near the right end in FIG. 1, and a plurality of (in the illustrated example, axially extending) surfaces are formed on the surface of the sensor shaft portion 11. Nine) ridges 11a are formed at equal intervals along the circumferential direction, and groove portions 11b wider than the width t1 of the ridges 11a are formed between the ridges 11a.

Further, on the outside of the sensor shaft portion 11, a cylindrical member 12 made of a conductive and non-magnetic material, for example, aluminum, which is close to the sensor shaft portion 11, is arranged coaxially with the sensor shaft portion 11, The extension 12 e of the cylindrical member 12 is fixed to the outside of the end 2 e of the output shaft 2.
The cylindrical member 12 includes a plurality (9 in FIG. 2) of rectangular windows 12a arranged at equal intervals in the circumferential direction at positions facing the protrusions 11a on the surface of the sensor shaft portion 11 described above. A plurality of (9 in FIG. 2) rectangular windows having the same shape as the window 12a but having different phases in the circumferential direction at positions shifted in the axial direction from the first window row. And a second window row made of 12b.

  The outer periphery of the cylindrical member 12 is surrounded by yokes 15a and 15b around which detection coils 13a, 13b and 13c and 13d of the same standard are wound. That is, the detection coils 13a, 13b, 13c, and 13d are arranged coaxially with the cylindrical member 12, the detection coils 13a and 13b surround the first window row portion including the window 12a, and the detection coils 13c and 13d are connected to the window 12b. The second window row portion is surrounded. The yokes 15a and 15b are fixed inside the input shaft side housing part 5a, and the output lines 16 of the detection coils 13a, 13b and 13c, 13d are connected to a circuit board 17 arranged inside the input shaft side housing part 5a. Yes.

  3 (a) and 3 (b) are diagrams for explaining the protrusions on the surface of the sensor shaft portion and the window of the cylindrical member as viewed from the output shaft 2 side, and FIG. 3 (a) is a reference position (torsion bar 3). FIG. 3B shows the positional relationship between the projections 11a on the surface of the sensor shaft portion 11 and the windows 12a of the first window row in the cylindrical member 12 in a state where the torsion bar 3 is not twisted. FIG. 6 is a diagram showing a positional relationship between the protrusions 11a on the surface of the sensor shaft portion 11 and the windows 12b of the second window row in the cylindrical member 12 in an untwisted state.

In this embodiment, since nine windows 12a and 12b are provided, the window 12a of the first window row and the window 12b of the second window row each have an angle θ = 360/9 = 40 in the circumferential direction. It will be shifted by degrees.
The angle a of the windows 12a and 12b is set smaller than the angle b of the portion without the windows 12a and 12b (a <b), and the angle c of the ridge 11a is set smaller than the angle d of the groove 11b (c <d). Is done. This is to make the change in impedance of the detection coil steep.

As apparent from FIGS. 3A and 3B, when the torsion bar 3 is not twisted, that is, when the steering torque is zero (0), the sensor shaft is located at the center of the circumferential width of the window 12a. So that one end in the circumferential direction of the ridge 11a of the portion 11 is located and the other end in the circumferential direction of the ridge 11a is located in the center of the circumferential width of the window 12b. The circumferential width of 12a and 12b, the width of the ridge 11a, and the relative positional relationship in the circumferential direction between the windows 12a and 12b are set. That is, the positional relationship in the circumferential direction between the windows 12a and 12b with respect to the ridge 11a is opposite to each other.
When the steering system is in a straight traveling state and the steering torque is zero, the torsion bar 3 is not twisted and the input shaft 1 and the output shaft 2 do not rotate relative to each other. Therefore, relative rotation does not occur between the protrusion 11a on the surface of the sensor shaft portion 11 on the input shaft 1 side and the cylindrical member 12 on the output shaft 2 side.

  On the other hand, when a rotational force is applied to the input shaft 1 by operating the steering wheel, the rotational force is transmitted to the output shaft 2 via the torsion bar 3. At this time, a frictional force such as a frictional force between the steered wheel and the road surface or a meshing gear of a steering mechanism coupled to the output shaft 2 acts on the output shaft 2. Torsion is generated in the torsion bar that joins between them, and relative rotation occurs between the protrusion 11a on the surface of the sensor shaft portion 11 on the input shaft 1 side and the cylindrical member 12 on the output shaft 2 side.

When the cylindrical member 12 has no window, the cylindrical member 12 is made of a conductive and non-magnetic material. Therefore, when an alternating current is generated in the detection coil 13 to generate an alternating magnetic field, the outer periphery of the cylindrical member 12 is An eddy current in the direction opposite to the coil current is generated on the surface. When the magnetic field due to the eddy current and the magnetic field due to the coil current are superimposed, the magnetic field inside the cylindrical member 12 is canceled out.
When a window is formed in the cylindrical member 12, the eddy current generated on the outer peripheral surface of the cylindrical member 12 cannot circulate around the outer peripheral surface by the windows 12a and 12b. Therefore, the cylindrical member 12 is formed along the end surfaces of the windows 12a and 12b. Around the inner peripheral surface, flows in the same direction as the coil current, and returns to the outer peripheral surface along the end surfaces of the adjacent windows 12a and 12b to form a loop. That is, a state occurs in which eddy current loops are periodically arranged in the circumferential direction inside the detection coil. The magnetic field generated by the coil current and the magnetic field generated by the eddy current are superimposed, and a magnetic field that periodically changes in strength in the circumferential direction and a magnetic field having a gradient in the radial direction that decreases toward the center are formed inside and outside the cylindrical member 12. It is formed. The strength of the periodic magnetic field in the circumferential direction is strong at the center of the windows 12a and 12b affected by the adjacent eddy currents, and becomes weaker as it deviates from the center.

  A sensor shaft portion 11 made of a magnetic material is coaxially arranged inside the cylindrical member 12, and the ridges 11a are arranged at the same cycle as the windows 12a and 12b. A magnetic material placed in a magnetic field is magnetized to generate a magnetic flux, but the amount of magnetic flux increases according to the strength of the magnetic field until it is saturated. For this reason, the magnetic flux generated in the sensor shaft portion 11 by the cylindrical member 12 due to the strength of the periodic magnetic field in the circumferential direction and the magnetic field having a gradient in the radial direction that decreases toward the center is generated between the cylindrical member 12 and the sensor. It increases or decreases depending on the relative phase with the shaft portion 11. The phase at which the magnetic flux is maximum is such that the centers of the windows 12a and 12b of the cylindrical member 12 coincide with the centers of the ridges 11a of the sensor shaft portion 11, and the detection coils 13a, 13b and 13c, The inductance of 13d also increases or decreases and changes to a substantially sine wave shape.

  In the state where torque does not act, the center of the ridge 11a of the sensor shaft portion 11 is the ridge 11a with respect to the phase where the inductance is maximum (the phase where the windows 12a and 12b coincide with the center of the ridge 11a). Since the torque acts to twist the torsion bar 3 and a phase difference occurs between the sensor shaft portion 11 and the cylindrical member 12, One of the inductances of the detection coils 13a, 13b and 13c, 13d increases and the other decreases.

  FIG. 4 is a characteristic diagram showing the relationship between the torque T and the change in inductance of the detection coils 13a (or 13b) and 13c (or 13d). The horizontal axis represents the torque T and the vertical axis represents the inductance L. When the right steering torque is generated, the sensor shaft 11 rotates counterclockwise in FIGS. 3 (a) and 3 (b). Therefore, as shown in FIG. 4, the detection coil 13a (or 13b) increases as the torque increases. The inductance L13 increases and the inductance L14 of the detection coil 13c (or 13d) decreases.

Also, when the left steering torque is generated, the sensor shaft portion 11 rotates clockwise in FIGS. 3A and 3B, so that the detection coil 13a (or 13b) increases as the torque increases as shown in FIG. The inductance L13 decreases and the inductance L14 of the detection coil 13c (or 13d) increases.
The characteristics of the inductances L13 and L14 in FIG. 4 can be directly replaced with voltages that are output in proportion, and when the characteristics of the inductances L13 and L14 are replaced with voltages, the detection torque voltage of the detection coil 13a (or 13b), the detection coil The detected torque voltage of 13c (or 13d) is related to the steering torque T, and the neutral voltage that is the intersection of the detected torque voltages is adjusted to 2.5 V in this embodiment. From this voltage cross characteristic, the total value of the detected torque voltage of the detection coil 13a (or 13b) and the detected torque voltage of the detection coil 13c (or 13d) is 2.5 + 2.5 = 5.0V.

FIG. 5 is a block diagram of the torque calculation circuit 20 mounted on the circuit board 17.
A first torque detection system that detects a first torque using a pair of detection coils 13a and 13d on both ends in the axial direction of the torque detector 10, and a pair of detection coils 13b and 13c on the center side in the axial direction are used. And two sets of torque calculation units 21A and 21B having the same configuration so as to constitute a second torque detection system for detecting the second torque.

  From the AC signal source 200 that outputs an AC signal having a predetermined frequency to the torque calculators 21A and 21B, the noise filter 202 and the noise filter 202 that receive the main torque and the sub-torque output from the torque calculators 21A and 21B, respectively. A connector 203 that outputs the output filter output to an external control unit 30 that assists steering control of an electric motor (not shown) is provided in common to the torque calculation units 21A and 21B. Further, the power source and the reference power source input to the connector 203 are filtered by a noise filter and supplied to the AC signal source 200 and the torque calculation units 21A and 21B as the power source voltage V and the reference voltage Vref.

Here, the AC signal source 200 includes an oscillating unit 201 that generates an AC signal having a predetermined frequency, and a current amplifying unit 211A that amplifies the AC signal output from the oscillating unit 201 and supplies it to the torque calculation units 21A and 21B. And 211B.
The torque calculation unit 21A has a configuration in which one ends of the pair of detection coils 13a and 13d are connected to each other and grounded, resistors R1a and R1b are connected in series to the other ends, and the other ends of these resistors R1a and R1b are connected to each other. A bridge circuit 210A is provided.

Similarly, in the torque calculation unit 21B, one ends of the pair of detection coils 13b and 13c are connected to each other and grounded, and the other ends of the resistors R2a and R2b are connected in series, and the other ends of these resistors R2a and R2b are connected to each other. The bridge circuit 210B having the above-described configuration is provided.
In these bridge circuits 210A and 210B, when no torque is applied to the input shaft 1, the voltages appearing at both ends of the detection coils 13a, 13d and 13b, 13c are equal to each other, that is, the differential voltage is zero. The resistance values of the resistors R1a, R1b and R2a, R2b are adjusted in advance.

Then, the connection points of the resistors R1a and R1b and the connection points of the resistors R2a and R2b of the bridge circuits 210A and 210B are individually connected to the current amplifiers 211A and 211B of the AC signal source 200, respectively, and the AC voltage signals Vosc1 and Vosc2c are Entered.
The torque calculation unit 21A receives a main amplification / full wave rectification unit 212A to which voltage signals appearing at both ends of the detection coils 13a and 13d of the bridge circuit 210A and an AC signal Vosc1 are input, and the main amplification / It has a main smoothing / neutral adjustment unit 213A to which a rectified signal output from the full-wave rectification unit 212A is input. Here, the main amplification / full-wave rectification unit 212A calculates a differential signal Vdef of the voltage signal appearing at both ends of the detection coils 13a and 13d, amplifies the differential signal Vdef, and rectifies the rectified signal as a main smoothing signal. Output to the neutral adjustment unit 213A.

  Further, the main smoothing / neutral adjustment unit 213A smoothes the rectified signal input from the main amplification / full wave rectification unit 212A, adjusts the neutral voltage, and outputs it as a torque detection signal to the noise filter 202. Then, the torque detection signal filtered by the noise filter 202 is output as a main torque detection signal Tm1 to the control unit 30 that performs steering assist control via the connector 203.

  The torque calculation unit 21A receives a voltage signal appearing at both ends of the detection coils 13a and 13d of the bridge circuit 210A and a sub-amplification / full-wave rectification unit 214A to which an AC signal Vosc1 is input, and this sub-amplification / A sub-smoothing / neutral adjustment unit 215A to which a rectification signal output from the full-wave rectification unit 214A is input. Here, the sub-amplification / full-wave rectification unit 214A calculates a differential signal Vdef of the voltage signal appearing at both ends of the detection coils 13a and 13b, amplifies the differential signal Vdef, and rectifies the rectified signal to a sub-smooth / Output to the neutral adjustment unit 215A. The sub-smoothing / neutral adjustment unit 215A smoothes the rectified signal input from the sub-amplification / full-wave rectification unit 214A, adjusts the neutral voltage, and outputs it as a torque detection signal to the noise filter 202. Then, the torque detection signal filtered by the noise filter 202 is output via the connector 203 to the control unit 30 that performs the steering assist control as the sub torque detection signal Ts1.

  Further, as described in Patent Document 1 described above, the torque calculation unit 21A detects the detection coil based on the AC voltage signal Vosc1 and the difference signal Vdef of the bridge circuit 210A output from the sub-amplification / full-wave rectification unit 214A. A contact failure between the resistor 13a or 13d and the resistor R1a or R1b is detected by a change in the differential voltage of the bridge circuit, an abnormality of the circuit system is detected based on a phase shift with respect to the reference voltage, and an abnormality signal is detected when the abnormality is detected. AB1 is output. That is, the monitoring unit 216A detects the phase difference between the waveform of the applied AC signal and the waveform of the differential voltage Vdef of the bridge circuit, and the detection coil, resistor, or circuit is abnormal when the phase difference exceeds a predetermined value. It is determined that there is an error, and an abnormal signal AB1 is output.

  The abnormal signal AB1 output from the monitoring unit 216A is supplied to the sub-smoothing / neutral adjustment unit 215A. When the abnormal signal AB1 is input to the sub-smoothing / neutral adjustment unit 215A, the output torque detection signal is set to 0V. Set. Thereby, the balance of the cross torque characteristic shown in FIG. 4 with the main torque signal is lost, so that the control unit 30 can detect a failure. For this reason, the abnormality signal AB1 is not input to the main smoothing / neutral adjustment unit 213A on the main side used for driving the steering assist electric motor 31 by the control unit 30.

Similarly, in the torque calculation unit 21B, the main amplification / full wave rectification unit 212B, the main smoothing / neutral adjustment unit 213B, the sub amplification / full wave rectification unit 214B, and the sub smoothing / neutral adjustment having the same configuration as the torque conversion unit 21A. Unit 215B and monitoring unit 216B.
As shown in FIG. 5, the control unit 30 receives main detection torque signals Tm1, Tm2 and sub detection torque signals Ts1, Ts2 from the torque sensor TS. The control unit 30 includes an abnormality determination unit 32 that performs signal monitoring based on the input main detection torque signals Tm1, Tm2 and sub detection torque signals Ts1, Ts2, and steering assist control based on the main detection torque signals Tm1, Tm2. And a steering assist control unit 33 that controls the drive of the steering assist electric motor 31.

The abnormality determination unit 32 detects a disconnection or a ground fault depending on whether or not the main detection torque signals Tm1 and Tm2 are equal to or lower than a predetermined value (for example, 0.3V), and determines whether the main detection torque signals Tm1 and Tm2 are equal to or higher than a predetermined value (for example, 4.7V). Detects a fault. In addition, a disconnection or a ground fault is detected based on whether or not the sub detection torque signals Ts1 and Ts2 are equal to or lower than a predetermined value (for example, 0.3 V), and a self-diagnosis of the torque calculation circuit is performed to determine a predetermined value (for example, 4.7 V) or higher. Whether or not the sky is detected. Further, FIG. 4 shows whether or not each added value of the main detection torque signals Tm1 and Tm2 and the sub detection torque signals Ts1 and Ts2 is a predetermined value (for example, 5.3 V) or more or a predetermined value (for example, 4.7 V) or less. Anomalies that deviate from the cross characteristics are detected.

In the normal state where no abnormality is detected by the abnormality determination unit 32, the steering auxiliary control unit 33 calculates the steering auxiliary current command value using the main detection torque signal Tm1, and calculates the steering auxiliary current command value and the steering A drive for controlling the motor drive circuit 34 based on the calculated steering assist voltage command value by calculating a steering assist voltage command value by, for example, PD control processing of the deviation from the detected value of the motor current supplied to the auxiliary electric motor 31. A signal is formed, and this drive signal is output to the motor drive circuit 34.
Here, the sub detection torque signals Ts1, Ts2 are only used for monitoring abnormality of the torque sensor, and are not used for driving the steering assist electric motor.

When the abnormality determination unit 32 determines that the abnormality of the first torque detection system of the torque sensor TS is normal and the second torque detection system is normal, the abnormality detection unit 32 replaces the main detection torque signal Tm1 of the first torque detection system. The steering assist control is continued by the steering assist control unit 33 using the main detection torque signal Tm2 of the two torque detection system.
Further, when the abnormality determination unit 32 determines that both the first torque detection system and the second torque detection system are abnormal, the steering assist control unit 33 uses the normal past torque value for steering assist. The electric motor is driven, a torque gradual decrease process for gradually decreasing the steering assist torque is performed, and the process shifts to a fail safe mode in which the steering assist control is safely stopped.

Next, the operation of the above embodiment will be described.
First, in a state where a steering wheel (not shown) is not steered, torque is not transmitted to the input shaft 1, so the torsion bar 3 is not twisted, and the ridge 11 a of the sensor shaft portion 11, the window 12 a of the cylindrical body 12, and 3b is maintained in the relationship of FIGS. 3A and 3B, and the inductances of the detection coils 13a and 13b and the inductances of the detection coils 13c and 13d cross the characteristic curves L13 and L14 of FIG. The values are equal to each other.

For this reason, in the bridge circuit 210A, the voltages between the terminals of the detection coils 13a and 13d become equal, the detection torques output from the main amplification / full wave rectification unit 212A and the sub amplification full wave rectification unit 21A are both zero, and the connector 203 Main detection torque Tm1 and sub detection torque Ts1 are output to the control unit 30.
Similarly, in the bridge circuit 210B, the voltages between the terminals of the detection coils 13b and 13c become equal, and the detection torques output from the main amplification / full wave rectification unit 212B and the sub amplification full wave rectification unit 21B are both zero. From 203, the main detection torque Tm2 and the sub detection torque Ts2 are output to the control unit 30.

In this state, the abnormality determination unit 32 of the control unit 30 determines that the torque calculation units 21A and 21B are normal, and the steering assist control unit 33 performs the steering assist control process based on the main detected torque Tm1. However, since the main detection torque Tm1 is zero, the driving of the steering assist electric motor 31 by the motor drive circuit 34 is stopped.
When the steering wheel is steered right (or left) from the non-steering state of the steering wheel, as described above, the inductances of the detection coils 13a and 13b increase (or decrease), and the inductances of the detection coils 13c and 13d decrease ( Or increase). In accordance with this change in inductance, the differential voltage output from the bridge circuits 210A and 210B becomes positive (or negative). Therefore, the detection torque output from the main amplification / full wave rectification units 212A and 212B and the sub amplification / full wave rectification units 214A and 214B increases in the positive direction (or negative direction), and the main detection torque signal Tm1 corresponding to this increases. And Tm2 and the sub detection torque signals Ts1 and Ts2 are output to the control unit 30 via the connector 203.

For this reason, the steering assist control unit 33 performs a steering assist control process based on the main detected torque signal Tm1, calculates a steering assist voltage command value, and outputs it to the motor drive circuit 34, thereby steering. The auxiliary electric motor 31 is driven forward (or reverse) to generate a steering assist torque corresponding to the steering torque input from the steering wheel.
When the abnormality determination unit 32 determines that the first torque detection system is abnormal from this normal state, in the state where the second torque detection system is normal, the steering assist control unit 33 uses the torque calculation unit 21B. Steering assist control is continued based on the main detection torque signal Tm2 calculated by the main amplification / full wave rectification unit 212B and the main smoothing / neutral adjustment unit 213B, and the motor drive circuit 33 is controlled. The steering assist electric motor 31 is driven by the motor current thus generated, and a steering assist torque corresponding to the steering torque is generated.

Further, when the abnormality determination unit 32 determines that both the first torque detection system and the second torque detection system are abnormal, the steering assist control unit 33 uses the normal past torque value to assist the steering assist. The electric motor is driven, a torque gradual reduction process for gradually reducing the steering assist torque is performed, and a transition is made to a fail safe mode in which the steering assist control is safely stopped.
Thus, since the two torque detection systems are provided in the torque sensor TS, the steering assist control can be normally continued even if an abnormality occurs in one of the torque detection systems.

  As described above, in the above-described embodiment, the detection coils 13a, 13b, 13c, and 13d mounted in the yokes 15a and 15b face the windows 12a and 12b, respectively, so that the inductance characteristics with respect to the torque of the detection coils in the yoke are the same. Thus, the yoke can be shared, and the axial length can be shortened as compared with the case where the yoke is formed for every four detection coils.

  In addition, among the detection coils 13a to 13d arranged in the axial direction, a bridge circuit 210A is configured by combining the detection coils 13a and 13d on both ends in the axial direction and a resistor, and the detection coils 13b and 13c on the central side in the axial direction. Since the bridge circuit 210B is configured by combining the resistor and the resistor, magnetic symmetry can be obtained between the two coils constituting the bridge circuit, and the influence of the magnetic path configuration can be eliminated. Thereby, it is hard to be influenced by temperature etc., and stable torque can be detected compared with the conventional example.

In addition, since the torque calculation circuit 20 of the torque sensor TS has the above-described configuration, the abnormality of the torque calculation unit is determined based on the four detection torque signals of the main detection torque signals Tm1 and Tm2 and the sub detection torque signals Ts1 and Ts2. Therefore, it is possible to provide a highly reliable electric power steering apparatus.
In the above embodiment, the case where the abnormality determination unit 32 is provided on the control unit 30 side has been described. However, the present invention is not limited to this, and the abnormality determination unit 32 is provided on the torque calculation circuit 20 side. You may make it notify the control unit 30 of the abnormality determination result of the determination part 32. FIG.

  In the above embodiment, the case where the torque sensor TS according to the present invention is applied to the electric power steering apparatus has been described. However, the present invention is not limited to this, and the torque of the rotating shaft is detected in addition to the electric power steering apparatus. In this case, the torque sensor TS according to the present invention can be applied.

  DESCRIPTION OF SYMBOLS 1 ... Input shaft, 2 ... Output shaft, 3 ... Torsion bar, 5 ... Housing, 5a ... Input shaft side housing part, 5b ... Output shaft side housing part, 7 ... Worm wheel, 8 ... Worm, TS ... Torque sensor, 10 DESCRIPTION OF SYMBOLS ... Torque detection part, 11 ... Sensor shaft, 12 ... Cylindrical member, 13a-13d ... Detection coil, 15a, 15b ... Yoke, 16 ... Output line, 17 ... Circuit board, 20 ... Torque calculation circuit, 21A, 21B ... Torque calculation , 30 ... control unit, 31 ... steering assist electric motor, 32 ... abnormality determination unit, 33 ... steering assist control unit, 34 ... motor drive circuit, 200 ... AC signal source, 201 ... oscillation unit, 202 ... noise filter , 203 ... Connector, 210A and 210B ... Bridge circuit, 211A and 211B ... Current amplification unit, 212A and 212B ... Main amplification and full wave adjustment Part, 213A, 213B ... the main smooth and neutral adjustment unit, 214A, 214B ... sub-amplification and full-wave rectifier, 215A, 215B ...... sub smooth and neutral adjustment unit, 216A, 216B ... monitoring unit

Claims (6)

A pair of yokes arranged side by side in the axial direction, belt torque detection to change the impedance in opposite directions in response to torque generated in the rotation axis is provided by two detection coils each interior of said pair of yokes And
A first bridge circuit composed of two detection coils on both ends in the axial direction of the two pairs of detection coils provided in the pair of yokes and a resistor connected in series with the two detection coils;
A second bridge circuit composed of two detection coils on the central side in the axial direction of the two pairs of detection coils and a resistor connected in series to the two detection coils;
A torque calculator that calculates at least two sets of detected torque signals based on differential signals when an AC signal is individually applied to the first bridge circuit and the second bridge circuit ;
The torque detector is individually opposed to the pair of yokes disposed on the inner peripheral side of the pair of yokes, and extends in the axial direction at predetermined intervals in the circumferential direction and at different intervals in the circumferential direction. A conductive and non-magnetic cylindrical body formed with a pair of windows and an axial ridge which is relatively rotated according to torque with the cylindrical body disposed on the inner peripheral side of the cylindrical body at a predetermined interval in comprising a <br/> and forming the sensor shaft portion,
A torque sensor characterized in that magnetic symmetry is taken between two detection coils constituting the first bridge circuit and the second bridge circuit to remove the influence of the magnetic path configuration . The torque calculation unit is configured to calculate a main detection torque signal and a sub detection torque signal based on a difference signal when an AC signal is applied to the first bridge circuit, and an AC to the second bridge circuit. 2. The torque according to claim 1, further comprising two sets of torque calculation units including a torque calculation unit that calculates a main detection torque signal and a sub detection torque signal based on a difference signal when the signal is applied. Sensor. The torque calculation unit receives two sets of main detection torque signals and sub detection torque signals calculated by the two sets of torque calculation units, and 2 based on the two sets of main detection torque signals and sub detection torque signals. The torque sensor according to claim 2 , further comprising an abnormality determination unit that determines abnormality of the set of torque calculation units. The abnormality determination unit detects disconnection, ground fault and power fault abnormality for each of the two sets of main detection torque signal and sub detection torque signal, and each of the two sets of main detection torque signal and sub detection torque signal. torque sensor according to claim 3, characterized that you have been configured to detect an abnormality deviating from the cross characteristics based on the added value.   5. A steering system comprising the torque sensor according to claim 1 and driving an electric motor that generates a steering assist torque that is transmitted to a steering mechanism based on a torque detected by the torque sensor to perform steering assist control. An electric power steering apparatus comprising an auxiliary control unit. Comprising a torque sensor according to claim 1 or 2, and steering assisting control unit that performs steering assist control by driving an electric motor for generating a steering assist torque transmitted to the steering mechanism on the basis of the detected torque of the torque sensor, An electric power steering apparatus comprising: an abnormality determination unit that determines abnormality of the torque detection unit of the torque sensor based on a plurality of detected torques output from a plurality of torque calculation units of the torque sensor.

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