JP2012237591A - Torque sensor and electric power steering device equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a torque sensor and an electric power steering device that can reduce the processing cost while improving the sensitivity of the torque sensor as well as securing the strength of a stopper.SOLUTION: In a torque sensor: coaxially disposed first and second rotational shafts 1, 2 are connected via a torsion bar 3; a cylindrical member 12 surrounding the outer circumferential surface of the first rotational shaft 1 is integrally formed in the rotational direction with the second rotational shaft; grooves 11b forming a plurality of projections 11a extending in the shaft direction as opposing the inner circumferential surface of the cylindrical member are formed on the first rotational shaft 1; windows 12a, 12b whose overlapping degree with the projections 11a changes are formed on the cylindrical member 12; and torque is detected based on the overlapping degree of the windows and the projections. Stopper grooves 11c regulating the relative rotation angle formed between the first and second rotational shafts are formed on the first rotational shaft 1 so that each set of a plurality of grooves 11b forming the projections 11a is grouped.

Description

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

  As a conventional torque sensor applied to, for example, an electric power steering apparatus, a torque sensor described in Patent Document 1 is known. This torque sensor is formed by, for example, forming four V-shaped grooves in the axial direction in the large diameter portion of the input shaft to form four ridges, and a cylinder integrated with the output shaft so as to cover these ridges. A member is arranged, and a window partially facing the ridge is formed on the cylindrical member, and torque is detected based on a magnetic change caused by relative rotation of the window and the ridge. Then, the position restriction of the relative rotation between the input shaft and the output shaft is similarly formed on the tip side from the large-diameter portion of the input shaft, and this is inserted into the recess formed in the output shaft. The relative position is regulated by engaging the convex portion with the circumferential side wall.

Japanese Patent No. 3336978

  By the way, in the torque sensor described in Patent Document 1, an axial groove formed on the input shaft forms a ridge facing the window of the cylindrical member and a convex portion serving as a stopper. Compared to the case where the number of grooves, width, and circumferential position of the shaft are matched with the number of grooves, width, and circumferential position of the stopper, the number of grooves of the sensor shaft is 8, and the number of stopper grooves is 4. Cost can be reduced.

However, it is preferable from the viewpoint of sensor sensitivity that the number of grooves on the sensor shaft, that is, the number of protrusions, is preferable. If the number of grooves on the sensor shaft is increased and the number of grooves on the stopper is the same as that on the sensor shaft, the stopper Thus, there is an unsolved problem that the width of the convex portion becomes thin, the required stopper strength cannot be obtained, and both the improvement of the sensor sensitivity and the securing of the stopper strength cannot be satisfied.
Therefore, the present invention has been made paying attention to the above-mentioned unsolved problems of the conventional example, and a torque sensor capable of reducing machining costs while improving the sensor sensitivity of the torque sensor and ensuring the stopper strength. An object of the present invention is to provide an electric power steering apparatus provided with this.

  In order to solve the above-described object, a torque sensor according to an aspect of the present invention connects first and second rotating shafts disposed coaxially via a torsion bar, and the first rotation. A cylindrical member surrounding the outer peripheral surface of the shaft is formed integrally with the second rotation shaft in the rotation direction, and extends in the axial direction on the first rotation shaft so as to face the inner peripheral surface of the cylindrical member. Grooves that form a plurality of ridges are formed, a window in which the degree of overlap with the ridges is formed in the cylindrical member, and torque is detected based on the degree of overlap between the windows and the ridges. And a stopper groove for restricting a relative rotation angle of the first and second rotating shafts so as to group a plurality of grooves forming the protruding strips on the first rotating shaft. It is characterized by the formation.

In the torque sensor according to another aspect of the present invention, A = nB (n is a positive integer of 2 or more), where A is the number of grooves forming the ridges and B is the number of stopper grooves. It is characterized by setting.
Furthermore, the torque sensor according to another embodiment of the present invention is characterized in that the groove width of the stopper groove is set larger than the groove width of the groove forming the ridge.
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.

According to the present invention, the stopper groove for restricting the relative rotation angle of the first and second rotating shafts is formed on the first rotating shaft so as to group a plurality of grooves for forming the ridges. Therefore, one of the grooves forming the ridges becomes a stopper groove, so that the width of the protrusion formed by the stopper groove is increased while increasing the number of ridges and improving the sensor sensitivity. The stopper strength can be ensured. Moreover, if the ridge is formed, the stopper groove can be processed at the same time, so that the processing cost can be reduced.
In addition, since the electric power steering apparatus is configured by using the torque sensor having the above-described effect, the steering assist control can be performed with higher steering torque detection accuracy and higher reliability, and the overall manufacturing cost can be reduced. can do.

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 structure of the torque sensor applicable to the said electric power steering apparatus. It is a perspective view explaining the formation method of a sensor shaft, Comprising: (a) is a perspective view which shows a cold forging product, (b) is a perspective view which shows the finished product which cut the stopper part. It is a figure explaining the protrusion of the surface of a sensor shaft part, 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 a torque calculation circuit. It is a figure which shows the 1st comparative example of a torque sensor, Comprising: (a) is a perspective view, (b) is sectional drawing. It is a figure which shows the 2nd comparative example of a torque sensor, Comprising: (a) is a perspective view, (b) is sectional drawing.

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, reference numeral 5 denotes a housing constituting an electric power steering apparatus, and the housing 5 has a structure 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 2 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 or serrated. Yes. In FIG. 1, a steering wheel (not shown) is integrally attached to the protruding end of the input shaft 1. 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 2 will be described with reference to FIGS. 1 and 2. The torque detector 10 includes a sensor shaft 11 formed on the input shaft 1, a pair of detection coils 13 and 14 disposed inside the input shaft side housing 5 a, and the sensor shaft 11 and the detection coils 13 and 14. And a cylindrical member 12 disposed between the two.
A sensor shaft portion 11 made of a magnetic material is formed on the input shaft 1, and a stopper portion 16 having a diameter smaller than the outer diameter of the sensor shaft portion 11 is formed at the tip of the sensor shaft portion 11.

As shown in FIGS. 2 and 3, a plurality of A (A = 12 in the example of FIG. 2) protruding strips 11 a extending in the axial direction are formed on the surface of the sensor shaft portion 11 along the circumferential direction. Thus, a plurality of B stopper grooves 11c (B = 4 in the example of FIG. 2) are formed so as to group these axial grooves 11b into a plurality of groups. That is, the number of grooves A of the axial grooves 11b is formed such that A = nB when n is a positive integer.
The protrusions 11a and the axial grooves 11b are unequally arranged when viewed in the circumferential direction, and the stopper grooves 11c are equally arranged in the circumferential direction. The axial grooves 11b grouped by the stopper grooves 11c are formed in a V shape having a substantially flat bottom, and similarly, the stopper grooves 11c are also formed in a V shape having a substantially flat bottom.

  Further, the width of the open end of the stopper groove 11c is wider than the width of the open end of the axial groove 11b, and the depth of the stopper groove 11c is deeper than the depth of the axial groove 11b. In other words, the distance from the central axis of the sensor shaft 11 is set larger in the groove bottom of the axial groove 11b than in the groove bottom of the stopper groove 11c. That is, the depth of the axial groove 11 b is set to a depth at which the bottom reaches the outer peripheral surface of the stopper portion 16, and the depth of the stopper groove 11 c is set so that the bottom is inside the outer peripheral surface of the stopper portion 16. Yes. For this reason, in the stopper part 16, wide stopper ridges 16a are formed between the stopper grooves 11c.

  In order to form the sensor shaft portion 11, first, a cylindrical blank is cold-forged to form an axial groove 11b and a stopper groove 11c for forming the ridge 11a as shown in FIG. 3 (a). A forged shape 11 'is formed, and then, as shown in FIG. 3B, a portion corresponding to the tip of the sensor shaft portion 11 of the cold forged shape 11' is formed on the bottom of the axial groove 11b with a lathe or the like. By cutting to a corresponding position or inside (outside the stopper groove), a small-diameter stopper portion 16 is formed and a finished product is obtained.

  Thus, since the axial groove 11b and the stopper groove 11c are formed at different positions in the circumferential direction without overlapping in the axial direction, the axial groove 11b and the stopper groove 11c are simultaneously formed by cold forging. Can do. Incidentally, when the axial groove 11b and the stopper groove 11c overlap in the axial direction, it is not possible to form all by one cold forging, but after forming one groove by the first forging. In the second forging, the other groove is formed, which increases the machining process and the machining time.

Further, an end portion 2e of the output shaft 2 is inserted into a stopper groove 11c in the stopper portion 16 of the sensor shaft portion 11 and engages with a side surface of the stopper protrusion 16a to restrict a rotation position (not shown). Is formed.
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 has a plurality of (12 in FIG. 2) rectangles arranged at intervals corresponding to the protrusions 11a in the circumferential direction at positions facing the protrusions 11a on the surface of the sensor shaft portion 11 described above. A plurality of windows having the same shape as the window 12a and having different phases in the circumferential direction at positions shifted axially from the first window row (12 in FIG. 2). ) Rectangular window 12b and a second window row.

  The outer periphery of the cylindrical member 12 is surrounded by yokes 15a and 15b around which detection coils 13 and 14 of the same standard are wound. That is, the detection coils 13 and 14 are arranged coaxially with the cylindrical member 12, the detection coil 13 surrounds the first window row portion made of the window 12a, and the detection coil 14 has the second window row portion made of the window 12b. Siege. The yokes 15a and 15b are fixed inside the input shaft side housing portion 5a, and the output lines of the detection coils 13 and 14 are connected to a circuit board 19 arranged inside the input shaft side housing portion 5a.

  4 (a) and 4 (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. 4 (a) shows the reference position (torsion bar 3). FIG. 4B shows the positional relationship between the protrusion 11a on the surface of the sensor shaft portion 11 and the window 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, twelve windows 12a and 12b are provided, but the protrusions 11a are unequally arranged, so the windows 12a of the first window row and 12b of the second window row are respectively Unequally distributed in the circumferential direction.
The angle a of the windows 12a and 12b is set to be smaller (a <b) than the angle b of the portion that faces the axial groove 11b and does not have the windows 12a and 12b, and the angle c of the tip of the ridge 11a is equal to that of the axial groove 11b. It is set smaller than the angle d of the open end (c <d). This is to make the change in impedance of the detection coil steep.

As is apparent from FIGS. 4A and 4B, when the torsion bar 3 is not twisted, that is, when the steering torque is zero (0), the convex of the sensor shaft portion 11 protrudes from the clockwise end portion of the window 12a. The circumferential width of the windows 12a and 12b so that the counterclockwise end of the strip 11a is positioned in the counterclockwise direction and the clockwise end of the convex strip 11a is positioned at the counterclockwise end of the window 12b; The width of the ridge 11a and the relative positional relationship in the circumferential direction with 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, the friction force such as the frictional force between the steered wheel and the road surface or the meshing of the gear of the steering mechanism coupled to the output shaft 2 acts on the output shaft 2. For this reason, the torsion bar 3 connecting the input shaft 1 and the output shaft 2 is twisted, and is located on the convex shaft 11a on the surface of the sensor shaft portion 11 on the input shaft 1 side and on the output shaft 2 side. Relative rotation occurs with the cylindrical member 12.

Since the cylindrical member 12 is made of a conductive and non-magnetic material at a portion where the cylindrical member 12 has no window, when an alternating current is generated through the detection coils 13 and 14 to generate an alternating magnetic field, the cylindrical member 12 An eddy current in the direction opposite to the coil current is generated on the outer peripheral surface of the coil. 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.
In the part where the window is formed in the cylindrical member 12, since 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, 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 and the center of the ridge 11a of the sensor shaft portion 11 coincide with each other, and the inductances of the detection coils 13 and 14 according to the increase and decrease of the magnetic flux. Increase / decrease and change to a substantially sine wave.

  In a state where torque does not act, the position is set at a phase where the inductance is minimized (a phase where the windows 12a and 12b and the ridge 11a do not overlap), so the torque acts and the torsion bar 3 is twisted, and the sensor When a phase difference occurs between the shaft portion 11 and the cylindrical member 12, one of the inductances of the two detection coils 13 and 14 increases and the other decreases.

FIG. 5 is a characteristic diagram showing the relationship between the steering torque T and the change in inductance of the detection coil 13 (or 14). The horizontal axis shows the steering torque T, and the vertical axis shows the inductance L.
When the right steering torque is generated, the sensor shaft portion 11 rotates clockwise in FIGS. 4A and 4B. Therefore, as shown in FIG. 5, the inductance L13 of the detection coil 13 increases as the steering torque T increases. It decreases, and the inductance L14 of the detection coil 14 increases.

When the left steering torque is generated, the sensor shaft portion 11 rotates counterclockwise in FIGS. 4A and 4B, so that the inductance of the detection coil 13 increases as the steering torque T increases as shown in FIG. L13 increases and the inductance of the inductance L14 of the detection coil 14 decreases.
The characteristics of the inductances L13 and L14 in FIG. 5 can be directly replaced with voltages output in proportion.
FIG. 6 is a block diagram of the torque calculation circuit 20 mounted on the circuit board 19.
A torque calculation unit 21 having a torque detection system that detects steering torque using the pair of detection coils 13 and 14 of the torque detection unit 10 is provided.

The circuit board 19 includes an AC signal source 200 that outputs an AC signal having a predetermined frequency to the torque calculator 21, and a noise filter 202 and a noise filter 202 that receive main torque and sub torque output from the torque calculator 21, respectively. A connector 203 is provided for outputting the output filter output to the control unit 30 for steering assist control of the steering assist electric motor 31. 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 unit 21 as the power source voltage V and the reference voltage Vref.
The AC signal source 200 includes an oscillating unit 201 that generates an AC signal having a predetermined frequency, and a current amplifying unit 211 that amplifies the AC signal output from the oscillating unit 201 and supplies the amplified AC signal to the torque calculating unit 21. ing.

The torque calculation unit 21 has a configuration in which one ends of the pair of detection coils 13 and 14 are connected to each other and grounded, resistors R1a and R1b are connected in series to the other end, and the other ends of these resistors R1a and R1b are connected to each other. It has a bridge circuit 210.
In this bridge circuit 210, in a state where no torque is applied to the input shaft 1, the resistors R1a and R1b are preliminarily set so that the voltages appearing at both ends of the detection coils 13 and 14 become equal, that is, the differential voltage becomes zero. The resistance value is adjusted.
Then, the connection point between the resistors R1a and R1b of the bridge circuit 210 is connected to the current amplifier 211 of the AC signal source 200, and the AC voltage signal Vosc is input.

  The torque calculation unit 21 receives a voltage signal appearing at both ends of the detection coils 13 and 14 of the bridge circuit 210 and a main amplification / full wave rectification unit 212 to which an AC voltage signal Vosc is input, and the main amplification. A main smoothing / neutral adjustment unit 213 to which a rectified signal output from the full-wave rectifying unit 212 is input. Here, the main amplification / full-wave rectification unit 212 calculates a differential signal Vdef of the voltage signal appearing at both ends of the detection coils 13 and 14, amplifies the differential signal Vdef, and rectifies the rectified signal into a main smoothing signal. Output to the neutral adjustment unit 213. The main smoothing / neutral adjustment unit 213 smoothes the rectified signal input from the main amplification / full-wave rectification unit 212 and adjusts the neutral voltage to output it to the noise filter 202 as a torque detection signal. Then, the torque detection signal filtered by the noise filter 202 is output via the connector 203 to the control unit 30 that performs steering assist control as the main torque detection signal Tm.

  The torque calculation unit 21 receives a voltage signal appearing at both ends of the detection coils 13 and 14 of the bridge circuit 210 and a sub-amplification / full-wave rectification unit 214 to which an AC voltage signal Vosc is input, and the sub-amplification. A sub-smoothing / neutral adjustment unit 215 to which a rectified signal output from the full-wave rectifying unit 214 is input. Here, the sub-amplification / full-wave rectification unit 214 calculates a differential signal Vdef of the voltage signal appearing at both ends of the detection coils 13 and 14, amplifies the differential signal Vdef, and rectifies the rectified signal to sub-smooth / Output to the neutral adjustment unit 215. The sub-smoothing / neutral adjustment unit 215 smoothes the rectified signal input from the sub-amplification / full-wave rectification unit 214, 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 Ts.

  Further, the torque calculation unit 21 is based on the AC voltage signal Vosc and the difference signal Vdef of the bridge circuit 210 output from the sub-amplification / full-wave rectification unit 214 as described in, for example, Japanese Patent Application Laid-Open No. 2006-267045. And detecting a contact failure between the detection coil 13 or 14 and the resistor R1a or R1b by a change in the differential voltage Vdef of the bridge circuit 210, and detecting an abnormality in the circuit system based on a phase shift with respect to the reference voltage Vref. When detected, an abnormal signal AB is output. That is, the monitoring unit 216 detects the phase difference between the waveform of the applied AC signal and the waveform of the differential voltage Vdef of the bridge circuit 210, and when the phase difference exceeds a predetermined value, the detection coils 13 and 14 and the resistor R1a , R1b or the circuit 210 is abnormal and outputs an abnormal signal AB.

  The abnormal signal AB output from the monitoring unit 216 is supplied to the sub-smoothing / neutral adjustment unit 215. When the abnormal signal AB is input to the sub-smoothing / neutral adjustment unit 215, the output torque detection signal is set to 0V. Set. As a result, the control unit 30 can detect a failure because the balance of the voltage cross characteristics shown in FIG. 5 with the main torque signal is lost. For this reason, the abnormal signal AB is not input to the main-side main smoothing / neutral adjustment unit 213 used by the control unit 30 to drive the steering assist electric motor 31.

  As shown in FIG. 6, the control unit 30 receives the main torque detection signal Tm and the sub torque detection signal Ts from the torque sensor TS. The control unit 30 includes an abnormality determination unit 32 that performs signal monitoring based on the input main torque detection signal Tm and the sub torque detection signal Ts, and performs steering assist control based on the main torque detection signal Tm to perform steering assist electric motor. A steering assist control unit 33 that drives and controls the motor 31 is provided.

  The abnormality determination unit 32 detects a disconnection or a ground fault depending on whether or not the main torque detection signal Tm is a predetermined value (for example, 0.3 V) or less, and detects a power fault depending on whether or not the main torque detection signal Tm is a predetermined value (for example, 4.7 V) or more. To do. In addition, a disconnection or a ground fault is detected based on whether or not the sub torque detection signal Ts is a predetermined value (for example, 0.3 V) or less, and a self-diagnosis of the torque calculation circuit 20 is performed to determine whether or not the predetermined value (for example, 4.7 V) or more. Detect the skyline. Further, an abnormality that deviates from the voltage cross characteristic shown in FIG. 5 depending on whether or not the added value of the main torque detection signal Tm and the sub torque detection signal Ts is a predetermined value (for example, 5.3 V) or more or a predetermined value (for example, 4.7 V) or less. Is detected.

The steering assist control unit 33 calculates a steering assist current command value using the main torque detection signal Tm in a normal state in which no abnormality is detected by the abnormality determination unit 32, the calculated steering assist 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-torque detection signal Ts is only used for monitoring the abnormality of the torque sensor and is not used for driving the steering assist electric motor 31.

  When the abnormality determination unit 32 determines that the torque detection system (the torque calculation unit 21 and the bridge circuit 210) of the torque sensor TS is abnormal, the steering assist control unit 33 uses the normal past torque value to assist steering. The electric motor 31 is driven, a torque gradual reduction process for gradually decreasing 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.

Next, the operation of the above embodiment will be described.
Now, it is assumed that a steering wheel (not shown) connected to the input shaft 1 is not steered, and the input shaft 1 and the output shaft 2 are in the same rotational phase without relative rotation.
In this state, the torsion bar 3 inserted between the input shaft 1 and the output shaft 2 is not twisted. For this reason, as shown in FIGS. 4 (a) and 4 (b), the protrusion 11a of the sensor shaft portion 11 formed on the input shaft 1 has the counterclockwise end at the tip thereof in the clockwise end of the window 12a. And located at the counterclockwise end of the window 12b.

  In this state, the impedances detected by the exciting coils 13 and 14 are equally median, and the two AC output voltages output from the bridge circuit 210 are equal. For this reason, when the main amplification / full-wave rectification unit 212 calculates the difference signal Vdef of the voltage signal appearing at both ends of the detection coils 13 and 14, the difference signal Vdef becomes substantially zero. The differential signal Vdef is amplified and rectified to output a rectified signal to the main smoothing / neutral adjustment unit 213. The main smoothing / neutral adjustment unit 213 smoothes the rectified signal input from the main amplification / full wave rectification unit 212 and adjusts the neutral voltage to output it to the noise filter 202 as a torque detection signal. Then, the torque detection signal filtered by the noise filter 202 is output to the controller 30 via the connector 203 as the main torque detection signal Tm.

  Therefore, in the controller 30, the steering assist control unit 34 calculates, for example, a steering assist control command based on the main torque detection signal Tm, and a deviation between the steering assist control current command and the motor current detected by the electric motor 34. Based on the steering assist control voltage, and outputs a gate drive current to be supplied to the motor drive circuit 34 based on the steering assist control voltage. At this time, since the main torque detection signal Tm is zero, the gate drive current is also zero, and the output of the motor current from the motor drive circuit 34 is stopped. For this reason, the electric motor 31 continues the stopped state.

Thereafter, when a steering wheel (not shown) is steered to the left, for example, the convex strip 11a of the sensor shaft portion 11a of the torque sensor TM rotates counterclockwise, whereby the outer peripheral surface of the convex strip 11a facing the window 12a of the cylindrical member 12 However, the ridge 11a facing the window 12b moves away from the window 12b.
For this reason, since the inductance L of the detection coil 13 increases, the inductance L of the detection coil 14 decreases, and the impedance of the detection coil 13 changes, the difference signal Vdef calculated by the main amplification / full-wave rectification unit 212 is For example, it increases in the negative direction and is amplified, and the full-wave rectified torque detection value Tm is output to the main smoothing / neutral adjustment unit. The main smoothing / neutral adjustment unit 213 adjusts the smoothing and neutral positions, and outputs a torque detection value Tm to the controller 30.

Therefore, the steering assist control unit 33 calculates the steering assist current command value based on the detected torque detection value Tm, and performs PI control or the like based on the deviation between the steering assist current command value and the motor current detection value. Then, a voltage command value is calculated, and a drive current is supplied from the motor drive circuit 34 to the electric motor 31 based on the voltage command value. For this reason, a steering assist force is generated from the electric motor 31, and this steering assist force is transmitted to the output shaft 2 via the worm 8 and the worm wheel 7, whereby the output shaft 2 is rotationally driven in the counter direction. It can be steered with a light steering force.
Similarly, when the steering wheel is steered to the right, the input shaft 1 is rotated in the clockwise direction as viewed in FIG. 4, so that the differential signal Vdef calculated by the main amplification / full wave rectification unit 212 increases, for example, in the positive direction. The electric motor 31 generates a steering assisting force in the opposite direction to the above, and the output shaft 2 is driven to rotate in the clockwise direction and can be steered with a light steering force.

  By the way, in embodiment mentioned above, the stopper groove | channel 11c with a large width | variety and depth is formed compared with the axial direction groove | channel 11b so that the plurality of axial direction groove | channels 11b which form the protruding item | line 11a, for example, two, may be grouped. As a result, the relationship between the number A of the axial grooves 11b forming the ridge 11a and the number B of the stopper grooves 11c can be set to A = nB when n is an integer of 2 or more. In addition, the number B of the stopper grooves 11c can be reduced while increasing the number of ridges 11a to improve the sensor sensitivity. For this reason, the width | variety of the stopper protruding item | line 16a of the stopper part 16 formed of the stopper groove | channel 11c can be enlarged, and stopper strength can be ensured. And since the axial direction groove | channel 11b and the stopper groove | channel 11c which form the protruding item | line 11c can be processed simultaneously, a processing cost can be reduced and processing time can also be shortened.

Incidentally, when the axial groove 11b and the stopper groove 11c are formed with the same groove, as shown in FIGS. 7 (a) and (b), the number of ridges 11a of the sensor shaft portion 11 is eight. In addition, there are eight stopper ridges 16a. When the number of ridges 11a of the sensor shaft portion 11 is 12 as in this embodiment, the sensor sensitivity can be improved, but as shown in FIGS. 8A and 8B, the stopper There are also 12 ridges 16a, and the width of each stopper ridge 16a cannot be secured. And, due to manufacturing variations, the portion receiving the load on each stopper ridge 16a is not dispersed, and the load may concentrate on any one of the stopper ridges 16a, resulting in a decrease in the limit strength of the stopper. become.
However, in the present embodiment, as described above, the number of the stopper grooves 11c can be reduced while increasing the number of the protrusions 11a of the sensor shaft portion 11, and the strength of the stopper protrusions 16a is sufficiently ensured. can do.

  Then, the steering torque input to the steering system is detected using the torque sensor TS having the above effect, the steering assist current command value is calculated based on the detected steering torque, the calculated steering assist current command value, Since the voltage command value for driving the motor drive circuit 34 is calculated based on the deviation from the motor current detection value of the electric motor, the sensor sensitivity of the steering torque can be improved and accurate steering assist control can be performed. At the same time, the overall manufacturing cost can be reduced. Since the strength of the stopper portion 16 can be improved, the reliability of the electric power steering device can be improved.

In the first embodiment, the case where the connectors 16 are provided on the yokes 15a and 15b has been described. However, the present invention is not limited to this. You may make it form the slit which penetrates a connection pin in the open end part side of the housing part 5a.
In the above embodiment, the case where the detection coils 13 and 14 are respectively installed in the two yokes 15a and 15b of the torque detection unit 10 of the torque sensor TS has been described. However, the present invention is not limited to this. Three or more pairs of detection coils can be provided by incorporating the above detection coils. In this case, what is necessary is just to increase the number of the torque calculation parts of the torque calculation circuit 20 according to the logarithm of a detection coil, and a more reliable torque sensor can be provided.

Moreover, in the said embodiment, although the case where the groove number B of the stopper groove | channel 11c was set to 4 was demonstrated, it is not limited to this, The groove number B of the stopper 11c is the convex strip 11a of the sensor shaft part 11. It may be set to a divisor of the number of.
Further, in the above-described embodiment, the case where one detection coil 13 and 14 is wound in each of the yokes 15a and 15b has been described. However, the present invention is not limited to this, and a pair of each in the yokes 15a and 15b is provided. The detection coils 13a, 13b and 14a, 14b may be wound. In this case, one bridge circuit is formed by the detection coils 13a and 14a, another bridge circuit is formed by the detection coils 13b and 14b, and the above-described torque calculation unit 21 is individually provided for each bridge circuit. Two sets of main and sub detection torques Tm and Ts can be detected, and a more reliable torque sensor can be provided.

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 part, 11a ... Projection, 11b ... Axial groove, 11c ... Stopper groove, 12 ... Cylindrical member, 13, 14 ... Detection coil, 15a, 15b ... Yoke, 16 ... Stopper part, 16a ... stopper projection, 19 ... circuit board, 20 ... torque calculation circuit, 21 ... torque calculation unit, 30 ... control unit, 31 ... electric motor for steering assist, 32 ... abnormality determination unit, 33 ... steering assist control unit, 34 DESCRIPTION OF SYMBOLS Motor drive circuit 200 ... AC signal source 201 ... Oscillating unit 202 ... Noise filter 203 ... Connector 210 ... Bridge circuit 211 ... Current amplification , 212 ... main amplifier, full-wave rectifier, 213 ... main smoothing and neutral adjuster, 214 ... sub amplification and full-wave rectifier, 215 ...... sub smooth-neutral adjuster, 216 ... monitor

Claims (4)

The first and second rotating shafts arranged coaxially are connected via a torsion bar, and a cylindrical member surrounding the outer peripheral surface of the first rotating shaft is connected to the second rotating shaft in the rotation direction. The groove is formed integrally with the first rotating shaft to form a plurality of ridges extending in the axial direction so as to face the inner peripheral surface of the cylindrical member, and the ridges are formed on the cylindrical member. A torque sensor that forms a window with a varying degree of overlap and detects torque based on the degree of overlap between the window and the ridge,
A stopper groove for restricting a relative rotation angle of the first and second rotating shafts is formed on the first rotating shaft so as to group a plurality of grooves forming the convex stripes. Torque sensor.   2. The torque according to claim 1, wherein A = nB (n is a positive integer of 2 or more), where A is the number of grooves forming the ridges and B is the number of stopper grooves. Sensor.   3. The torque sensor according to claim 1, wherein a groove width of the stopper groove is set to be larger than a groove width of the groove forming the ridge. 4.   A torque sensor according to any one of claims 1 to 3 is provided, and a steering assist control is performed by 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. An electric power steering apparatus comprising a steering assist control unit.

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