JP5588414B2 - Power steering device - Google Patents

Description

  The present invention relates to a power steering device that applies a steering assist force to steered wheels of an automobile.

  2. Description of the Related Art Conventionally, there is known a power steering device that improves steering feeling by suppressing vibration of a steering mechanism that occurs due to reverse input from a road surface. For example, the power steering device disclosed in Patent Document 1 extracts a specific frequency component corresponding to the vibration of the steering mechanism generated by the reverse input from the road surface from the pinion angle as a signal indicating the state of the steering mechanism. Thus, the vibration of the steering mechanism is detected, and the steering assist force is corrected based on the detection result.

JP 2009-90953 A

  However, since the frequency components of vibrations generated by the steering operation are wide and the frequency components of vibrations generated by reverse input from the road surface are also wide, it is difficult to extract the specific frequency components with the conventional power steering device. There was a problem. An object of the present invention is to provide a power steering device that can detect vibrations of a steering mechanism caused by reverse input from a road surface with higher accuracy.

  In order to achieve the above object, the power steering apparatus of the present invention preferably includes a first strain sensor that detects strain vibration generated in the input shaft, and a second strain sensor that detects strain vibration generated in the output shaft. When the phase of the second strain vibration that is the output signal of the second strain sensor is ahead of the first strain vibration that is the output signal of the first strain sensor, reverse input torque acts on the steering mechanism from the road surface. It was decided that it was.

  Therefore, it is possible to detect the vibration of the steering mechanism caused by the reverse input from the road surface with higher accuracy.

1 is a system configuration diagram of a power steering apparatus according to Embodiment 1. FIG. FIG. 3 is an axial sectional view of the steering mechanism according to the first embodiment. 1 is a schematic view of an assembly of a strain sensor according to Embodiment 1. FIG. FIG. 3 is a circuit diagram illustrating a Wheatstone bridge circuit of the strain sensor according to the first embodiment. It is a figure which shows the relationship between the resistance of the strain sensor of Example 1, the shape of dummy resistance, and the crystal orientation of a silicon substrate. 1 is a block diagram illustrating a configuration of an ECU according to a first embodiment. The example of the waveform of the 1st distortion vibration V1 of Example 1 and the 2nd distortion vibration V2 is shown (at the time of positive input). The example of the waveform of the 1st distortion vibration V1 of Example 1 and the 2nd distortion vibration V2 is shown (at the time of reverse input). 3 is a flowchart illustrating an outline of control processing performed in the ECU according to the first embodiment. It is a system block diagram of the power steering apparatus of Example 2. FIG. 6 is a block diagram illustrating a configuration of an ECU according to a third embodiment. FIG. 6 is a system configuration diagram of a power steering apparatus according to a fourth embodiment. It is a figure which shows the shearing stress which generate | occur | produces when a torque arises in a rotating shaft.

  Hereinafter, embodiments for realizing a power steering apparatus of the present invention will be described with reference to the drawings.

[Example 1]
FIG. 1 is a system configuration diagram of the power steering apparatus EPS according to the first embodiment. A steering mechanism (steering system) of a vehicle provided with the power steering device EPS includes an operation mechanism, a gear mechanism 3 and a link mechanism. The operating mechanism includes a steering wheel (steering wheel) 1 as a steering force input means to which a driver's steering force is input as a rotational force, and a steering shaft (steering shaft 2) connected to the steering wheel (steering shaft 2). With. The gear mechanism 3 is connected to the steering shaft 2 to convert and increase the rotational force. The link mechanism transmits the power from the gear mechanism 3 to the steered wheels 5 (for example, left and right front wheels) as a steered force. The steering shaft 2 includes a first column shaft 20 connected to the steering wheel 1, a second column shaft (intermediate shaft) 21 connected to the first column shaft 20 via a joint, and a joint to the second column shaft 21. The third column shaft (input shaft) 22 is connected to the third column shaft 22 via a torsion bar 23 and is rotated by the steering operation of the steering wheel 1. A pinion shaft (output shaft) 24 to be transmitted is included. The second column shaft 21 includes a coupling 25 preferably formed of rubber or resin as an elastic body that generates a damping force for suppressing rotational fluctuation and vibration. The gear mechanism 3 is a conversion mechanism that converts the rotation of the pinion shaft 24 into the turning operation of the steered wheels 5. The gear mechanism 3 is a so-called rack and pinion type, and includes a pinion 300 formed at the tip of the pinion shaft 24 and a rack 310 formed on the rack shaft 31 so as to mesh with the pinion 300. The steered wheels 5 are coupled to both ends of the rack shaft 31 in the axial direction via tie rods 4 as link mechanisms. When the driver steers the steering wheel 1, the steering shaft 2 (pinion shaft 24) is rotationally driven, the rack shaft 31 is moved in the axial direction by the gear mechanism 3, and the steered wheels 5 are steered via the tie rod 4.

  The power steering device EPS (hereinafter referred to as device EPS) includes an EPS actuator 6 as a steering force assisting device that applies a steering assist force that assists the steering force of the driver to the steering mechanism, and detection that detects the state of the steering mechanism. A steering state sensor 7 as means, and an ECU (electronic control unit) 8 as steering assist force control means for drivingly controlling the EPS actuator 6 based on a signal indicating the state of the steering mechanism output from the steering state sensor 7. . The EPS actuator 6 includes an electric motor (hereinafter referred to as a motor 60) and a speed reduction mechanism 61. That is, the device EPS is an electric power steering device. The motor 60 is driven by electric power supplied from a power source (battery) mounted on the vehicle, and for example, a three-phase brushless DC motor can be used. The motor 60 is provided with a rotation angle sensor 601 such as a resolver for detecting the rotation angle or rotation position of the output shaft. The reduction mechanism 61 is a gear mechanism that reduces the rotation of the motor 60 and transmits it to the steering shaft 2. In the first embodiment, a worm gear mechanism is used. The speed reduction mechanism 61 includes a worm 610 provided on the output shaft of the motor 60 and a worm wheel 611 provided on the pinion shaft 24 of the steering shaft 2 and meshing with the worm 610. The motor 60 provides auxiliary power to the rotation of the pinion shaft 24 via the speed reduction mechanism 61 and applies steering assist force to the steered wheels 5. That is, the device EPS is a so-called electric direct connection type (pinion assist type) in which the motor 60 directly drives a gear to generate a steering assist force.

  FIG. 2 is a sectional view in the axial direction of a part of the steering mechanism (a section taken along a plane passing through the axis O of the steering shaft 2). As shown in FIG. 2, each part of the steering mechanism and the device EPS is accommodated in a housing 9. The housing 9 includes a sensor housing 90, a gear housing 91, a motor housing, and an ECU housing. A torque sensor 70 is accommodated in the sensor housing 90. The gear mechanism 3 is accommodated in the gear housing 91. The motor 60 is accommodated in the motor housing. An ECU 8 is accommodated in the ECU housing. The sensor housing 90 and the gear housing 91 are combined with each other to constitute one EPS unit. The motor housing is also assembled integrally with the gear housing 91. Furthermore, the ECU housing may be provided integrally with the motor housing, and a so-called electromechanical integrated unit may be provided. Hereinafter, the x-axis is provided in the direction in which the third column shaft 22 and the pinion shaft 24 extend, and the steering wheel 1 side (upstream side) is the positive direction, and the gear mechanism 3 side (downstream side) is the negative direction. The third column shaft 22 and the pinion shaft 24 are rotatably accommodated in the housing 9. The third column shaft 22 is accommodated in the sensor housing 90. The pinion shaft 24 is connected to the third column shaft 22 via the torsion bar 23 and is accommodated in the gear housing 91.

  The third column shaft 22 has a bottomed cylindrical shape and has an axial hole 220 that opens to the x-axis negative direction side. An x-axis positive end portion of the torsion bar 23 is installed on the inner periphery of the axial hole 220 on the x-axis positive direction side, and this end portion is formed by a neutral pin 25 extending in the radial direction of the third column shaft 22 in the third column. It is fixed to the shaft 22. The x-axis negative direction end portion of the third column shaft 22 is rotatably accommodated in a recess 240 provided at the x-axis positive direction end portion of the pinion shaft 24. The x-axis negative direction end portion of the torsion bar 23 is fixed to a fitting hole 241 provided in the bottom portion of the concave portion 240 of the pinion shaft 24 by press-fitting or the like. An inner ring holding portion 221 is formed on the outer periphery of the third column shaft 22 on the negative side in the x-axis direction, and an inner ring 701 is installed and held on the inner ring holding portion 221. A sensor coil 700 is installed on the inner periphery of the sensor housing 90 at a portion facing the inner ring 701 in the radial direction. The third column shaft 22 is supported by the sensor housing 90 via the bearing BRG1 so as to be rotatable at a portion on the x-axis positive direction side with respect to the inner ring holding portion 221 and is more negative than the inner ring holding portion 221 on the x axis. At the end on the direction side, it is rotatably supported by a needle bearing installed and held in the recess 240 of the pinion shaft 24. The x-axis positive direction side of the third column shaft 22 protrudes from the opening at the x-axis positive direction end of the x sensor housing 90. The opening of the sensor housing 90 at the positive end in the x-axis direction is covered and closed with a waterproof boot 92.

  On the outer periphery of the pinion shaft 24, an outer ring holding part 242, a worm wheel installation part 243, a first supported part 244, a pinion 300, in order from the x-axis positive direction side to the x-axis negative direction side, A second supported portion 245 is provided. The pinion shaft 24 is rotatably supported by the gear housing 91 via the bearings BRG2, 3 at the first and second supported portions 244, 245, respectively. The outer ring holding portion 242 is installed and held at the negative end in the x-axis direction of the outer ring 702, and the outer ring 702 is interposed between the sensor coil 700 and the inner ring 701. A worm wheel 611 is installed and fixed on the worm wheel installation section 243, and the worm wheel 611 meshes with a worm 610 provided on the output shaft of the motor 60 and accommodated in the gear housing 91. A pinion 300 is formed on the outer periphery of the pinion shaft 24 on the x-axis negative direction side. The pinion 300 meshes with the teeth (rack 310) of the rack shaft 31 housed in the gear housing 91 to constitute a rack and pinion mechanism. On the back side of the teeth of the rack shaft 31, a retainer 33 that presses the rack shaft 31 against the pinion shaft 24 by the elastic force of the spring 32 is installed.

  The steering state sensor 7 includes a torque sensor 70, a first strain sensor 71, and a second strain sensor 72. The torque sensor 70 is a so-called magnetostrictive type, and includes a sensor coil 700, an inner ring 701 and an outer ring 702 as magnetic path resistance variable members, and a sensor substrate 703. The torque sensor 70 detects the rotation state (rotation amount) of the steering shaft 2 and outputs it to the ECU 8. Specifically, the relative rotation amount between the third column shaft 22 and the pinion shaft 24 (that is, the twist amount of the torsion bar 23) is detected as a steering torque generated in the steering shaft 2 by the steering operation of the driver.

  The first strain sensor 71 is provided on the third column shaft 22 and detects strain generated in the third column shaft 22. The first strain sensor 71 is attached (applied) to the outer periphery of the third column shaft 22 projecting into the waterproof boot 92 (on the x-axis positive direction side with respect to the neutral pin 25). The first strain sensor 71 is installed in the waterproof boot 92 so that it can cope with the external use environment. The first strain sensor 71 is provided so as to be able to communicate with the ECU 8 via the reception-side antenna unit 73. The reception-side antenna unit 73 has a substantially annular shape, and is installed at a position facing the first strain sensor 71 in the radial direction so as to surround the third column shaft 22. An antenna is installed on the receiving side antenna unit 73 so as to surround the third column shaft 22. The antenna is connected to the ECU 8 via a connection line, and functions as a receiving antenna that receives a signal transmitted from the first strain sensor 71 and sends the signal to the ECU 8, and receives power from the ECU 8 and receives the signal. Functions as a power feeding coil that sends to the first strain sensor 71. The second strain sensor 72 is provided on the pinion shaft 24 and detects strain generated in the pinion shaft 24. The second strain sensor 72 is attached to the outer periphery of the pinion shaft 24 housed in the gear housing 91 (at the x-axis positive direction end of the pinion 300). The second strain sensor 72 is installed in the gear housing 91 so that it can cope with an external use environment. A reception-side antenna unit 74 similar to the reception-side antenna unit 73 is installed at a position facing the second strain sensor 72 in the radial direction.

[Configuration of strain sensor]
Hereinafter, details of the strain sensor will be described using the first strain sensor 71 as an example. FIG. 3 is a schematic diagram illustrating the configuration of the assembly 710 of the strain sensor 71. This assembly 710 includes a Wheatstone bridge circuit 712 having a resistor 712a and a dummy resistor 712b on the same silicon substrate 711, a strain sensor amplifier group 713, an analog / digital converter 714, a rectification / detection / modulation / demodulation circuit unit 715, a communication A control unit 716, an antenna 718, and an adhesive unit 717 are provided. The silicon substrate 711 is formed of a silicon single crystal. Hereinafter, the silicon substrate 711 and the thin film group formed on the silicon substrate 711 are collectively referred to as a chip. The assembly 710 is bonded to the third column shaft 22 by the bonding portion 717. That is, the back surface of the silicon substrate is used as an adhesive surface with the third column shaft 22. The assembly 710 smoothes the power high-frequency signal sent from the receiving-side antenna unit 73 via the antenna 718 by the rectification / detection / modulation / demodulation circuit unit 715, and converts the DC power to a constant voltage to supply power to each circuit in the chip. Supply as. A predetermined current is supplied to the Wheatstone bridge circuit 712 (the resistor 712a and the dummy resistor 712b).

  FIG. 4 is a circuit diagram showing the Wheatstone bridge circuit 712, and FIG. 5 is a diagram showing the relationship between the shape of the resistor 712a and the dummy resistor 712b and the crystal orientation of the silicon substrate 711. The Wheatstone bridge circuit 712 includes a set of resistors 712a provided on two opposite sides and a set of dummy resistors 712b provided on the other two sides on the (001) plane of the single crystal silicon substrate 711. Become. The resistor 712a is composed of a silicon crystal including a diffused resistor in which impurities are diffused, and the silicon crystal is a single crystal. That is, the resistor 712a is an element for measuring the amount of strain, which is formed by locally diffusing a P-type impurity layer in the silicon substrate 711. The longitudinal direction (a straight line connecting both terminals of the resistor 712a) is formed so as to substantially coincide with the <−110> direction of the silicon substrate 711. Similar to the resistor 712a, the dummy resistor 712b is formed in a V shape by locally diffusing a P-type impurity layer in the silicon substrate 711. The lengths of the two linear portions forming the V-shape are equal, the longitudinal direction of one linear portion is the <100> direction, and the other longitudinal direction is a direction rotated by 90 ° with respect to the <100> direction. To. The dummy resistor 712b is formed in a V shape in this way, and while gaining a resistance value, as a whole, the dummy resistor 712b is rotated by 90 ° with respect to the <−110> direction which is the longitudinal direction of the resistor 712a <110>. It is formed so as to substantially coincide with the direction. In addition, the internal resistance values of the resistor 712a and the dummy resistor 712b are formed to be substantially the same value.

  When strain is applied to the third column shaft 22 (stress is applied), strain is transmitted from the third column shaft 22 to the entire silicon substrate 711. That is, in the assembly 710, since the bonding portion 717 is disposed on the back surface of the silicon substrate 711 facing the element formation surface, distortion of the third column shaft 22 applies distortion to the entire silicon substrate 711 through the bonding portion 717. The strain sensor 71 measures this strain. Specifically, a voltage is applied to the Wheatstone bridge circuit 712 (longitudinal direction of the resistor 712a and the dummy resistor 712b) in the silicon substrate 711 to supply a predetermined current. When strain is applied to the silicon substrate 711 (stress is applied), the internal resistance value of the Wheatstone bridge circuit 712 changes based on the piezoresistance effect. The strain sensor 71 detects the distortion of the third column shaft 22 by detecting the amount of voltage drop accompanying the change in the internal resistance value with respect to the predetermined current supplied. The detected voltage drop amount (corresponding to the distortion amount of the third column shaft 22) is converted into a digital signal through the distortion sensor amplifier group 713 and the analog / digital converter 714, and is transmitted from the antenna 718 to the receiving antenna unit 73 (ECU8). Sent. Actually, the strain applied to the third column shaft 22 by external vibration is generated as vibration having a predetermined frequency, amplitude and waveform. Hereinafter, this is referred to as strain vibration. The first strain sensor 71 detects and outputs strain vibration generated in the third column shaft 22 (hereinafter referred to as first strain vibration V1).

  Since the resistance value of the impurity diffusion layer is strongly influenced by temperature fluctuations, the temperature compensation circuit includes a resistor 712a as an active resistor that is sensitive to strain and a dummy resistor 712b that is not sensitive to strain. A Wheatstone bridge circuit 712 is formed. That is, in the case of a silicon single crystal, the piezoresistive effect has orthogonal anisotropy depending on the crystal orientation. Therefore, when strain is applied to the third column shaft 22 (silicon substrate 711), the internal resistance value of only the resistor 712a constituting the Wheatstone bridge circuit 712 changes based on the piezoresistance effect, and the internal resistance value of the dummy resistor 712b. Adjust the chip arrangement (the crystal orientation of silicon and the arrangement of resistors 712a and 712b) with respect to the coordinate system (distortion direction of the third column shaft 22) as a reference for distortion so as not to change based on the piezoresistance effect. As a result, the difference between the outputs of the resistor 712a and the dummy resistor 712b with respect to the strain applied to the silicon substrate 711 is increased, and the sensitivity of the output of the bridge circuit 712 is increased. As described above, since the processing circuit of the strain sensor 71 is highly integrated in the same silicon substrate 711, the configuration is compact. It is desirable that the thickness of the silicon substrate 711 be 100 μm or less. In this case, the strain value of the third column shaft 22 and the strain value at the position of the strain sensor 71 (resistor 712a) should be substantially matched. Can do. That is, the measurement accuracy can be improved.

  The second strain sensor 72 is configured similarly to the first strain sensor 71. That is, the second strain sensor 72 is constituted by a silicon crystal including a diffused resistor in which impurities are diffused, and the silicon crystal is a single crystal. The second strain sensor 72 detects strain vibration generated in the pinion shaft 24 due to vibration from the outside, and outputs this (hereinafter referred to as second strain vibration V2). The internal resistance value of the second strain sensor 72 changes based on the piezoresistance effect due to external vibration acting on the pinion shaft 24. The second strain sensor 72 is supplied with a predetermined current, and detects a second strain vibration V2 by detecting a voltage drop amount accompanying a change in internal resistance value with respect to this current. The detected second distortion vibration V2 is transmitted to the ECU 8 via the reception-side antenna unit 74.

  When the steering wheel 1 is steered by the driver, the steering torque input to the pinion shaft 24 via the first to third column shafts 20 to 22 is detected by the torque sensor 70. The detected steering torque signal is input to the ECU 8. Further, the ECU 8 receives a vehicle speed signal from a vehicle speed sensor (not shown) and a steering angle signal from a steering angle sensor. In addition, strain vibration signals V1, V2 from the first and second strain sensors 71, 72 are input to the ECU 8. The ECU 8 calculates a basic steering assist amount (target steering assist force) on the basis of information such as the input steering torque, and sends the target steering assist force to the motor 60 on the basis of signals such as the input motor rotation position. A drive current is output and the operation of the motor 60 is controlled. By controlling the current (drive current) flowing through the motor 60 by the ECU 8, an appropriate auxiliary power is given to the rotation of the pinion shaft 24, and the driver's steering force is assisted. Further, the ECU 8 determines the presence or absence of reverse input torque acting on the steering mechanism from the road surface based on the input strain vibrations V1 and V2 information. 60 drive current is corrected.

  FIG. 6 is a block diagram showing the configuration of the ECU 8. The ECU 8 includes a microcomputer 80 that outputs a motor control signal and a drive circuit 81 that supplies drive power to the motor 60 based on the motor control signal. The ECU 8 is connected to a current sensor 600 for detecting an actual current value I energized to the motor 60 and a rotation angle sensor 601 for detecting the motor rotation angle θm. The microcomputer 80 generates a motor control signal to be output to the drive circuit 81 based on the signal indicating the state of the steering mechanism, the actual current value I of the motor 60 and the motor rotation angle θm.

  More specifically, the microcomputer 80 includes a target value of assist force applied to the steering mechanism, that is, a current command value calculation circuit (target assist force calculation circuit) 82 that calculates a current command value Iq * corresponding to the target assist force, A motor control signal output circuit 83 that outputs a motor control signal based on the current command value Iq * calculated by the command value calculation circuit 82 is provided. The current command value calculation circuit 82 includes a basic assist amount calculation circuit 820 that calculates a basic assist control amount Ias *, which is a basic control component of the target assist force, and a differential value (steering torque differential) of the steering torque τ as its compensation component. A torque inertia compensation amount calculation circuit 821 for calculating a torque inertia compensation amount Iti * based on the value dτ). The basic assist amount calculation circuit 820 receives the steering torque τ and the vehicle speed V. Based on the steering torque τ and the vehicle speed V, the basic assist amount calculation circuit 820 calculates a larger basic assist control amount Ias * as the steering torque τ increases and the vehicle speed V decreases.

  On the other hand, the torque inertia compensation amount calculation circuit 821 receives the vehicle speed V in addition to the steering torque differential value dτ. Then, the torque inertia compensation amount calculation circuit 821 calculates the torque inertia compensation amount Iti * based on each of these state amounts in order to execute the torque inertia compensation control. The “torque inertia compensation control” is a control that compensates for the influence of the inertia of the device EPS such as the motor 60, the actuator, etc., that is, “feeling of catching (following delay)” at the time of “start of cutting” and “end of cutting” in steering operation. This is a control for suppressing the “flow feeling (overshoot)”. The torque inertia compensation control has an effect of suppressing vibrations generated in the steering mechanism due to application of reverse input stress to the steered wheels 5. The basic assist control amount Ias * and the torque inertia compensation amount Iti * (Iti **) are input to the adder 822. The current command value calculation circuit 82 calculates the current command value Iq * as the target assist force by superimposing the torque inertia compensation amount Iti * on the basic assist control amount Ias * in the adder 822. The current command value Iq * output from the current command value calculation circuit 82 is supplied to the motor control signal output circuit 83 together with the actual current value I detected by the current sensor 600 and the motor rotation angle θm detected by the rotation angle sensor 601. Entered. The motor control signal output circuit 83 calculates a motor control signal by executing feedback control so that the actual current value I follows the current command value Iq * corresponding to the target assist force. Then, the ECU 8 outputs the motor control signal generated as described above to the drive circuit 81 by the microcomputer 80, and the drive circuit 81 supplies the drive power based on the motor control signal to the motor 60. Control the operation.

  The microcomputer 80 is provided with a phase determination circuit 84. The phase determination circuit 84 includes a first strain vibration V1 that is an output signal of the first strain sensor 71 and a second strain vibration V2 that is an output signal of the second strain sensor 72 as signals indicating the state of the steering mechanism. Entered. The first strain vibration V1 indicates the vibration state of the third column shaft 22 constituting the steering mechanism, and the second strain vibration V2 indicates the vibration state of the pinion shaft 24 constituting the steering mechanism. The phase determination circuit 84 detects a predetermined peak value Peak1 of the first strain vibration V1 and a predetermined peak value Peak2 (corresponding to the peak value Peak1) of the second strain vibration V2 detected within a predetermined time, By comparing the phases (time shifts), it is determined whether or not the phase of the second strain vibration V2 is ahead of the first strain vibration V1. The microcomputer 80 determines the generation source of the vibration generated in the steering mechanism based on the phase difference between the first and second strain vibrations V1 and V2 determined by the phase determination circuit 84. That is, these vibrations are caused by the positive input stress applied to the steering wheel 1 by the driver's steering operation, or the reverse input stress applied to the steered wheels 5 from the road surface. Judge whether or not. 7 and 8 show examples of waveforms of the first strain vibration V1 and the second strain vibration V2 detected within a predetermined time. As shown in FIG. 7, if the phase of the peak value Peak2 of the second strain vibration V2 is delayed from the phase of the peak value Peak1 of the first strain vibration V1, it is determined as a positive input. As shown in FIG. 8, if the phase of the peak value Peak2 of the second strain vibration V2 is ahead of the phase of the peak value Peak1 of the first strain vibration V1, it is determined that the input is reverse.

  When the microcomputer 80 determines that the input is reverse, the torque inertia compensation control is strengthened, that is, a compensation component based on the steering torque differential value dτ in order to suppress the vibration of the steering mechanism due to the application of the reverse input stress. Increase the torque inertia compensation amount Iti *. As described above, the torque inertia compensation control has an effect of suppressing the vibration generated in the steering mechanism. By strengthening the torque inertia compensation control, the vibration of the steering mechanism due to the application of the reverse input stress is suppressed. It can be effectively suppressed. However, such enhancement of torque inertia compensation control (increase in torque inertia compensation amount Iti *) has a feature that the rise of assist torque tends to be excessive, and its abuse is a deterioration of steering feeling in normal times ( There is a risk of causing problems such as a so-called “disengagement feeling” at the beginning of cutting or instability of control (vibration). Based on this point, the apparatus EPS detects the occurrence of vibration due to the application of reverse input stress promptly by determining the phase difference between the first and second strain vibrations V1 and V2 as described above. Then, based on the detection of the vibration, the torque inertia compensation control is strengthened, thereby avoiding the adverse effects associated with the strengthening of the torque inertia compensation control and promptly reducing the vibration caused by the application of the reverse input stress. Try to control.

  More specifically, the current command value calculation circuit 82 of the microcomputer 80 is provided with an enhanced gain setting circuit 824 that sets the enhanced gain K for enhancing the torque inertia compensation control, that is, increasing the torque inertia compensation amount Iti *. The determination result output from the phase determination circuit 84 is input to the enhancement gain setting circuit 824. When the determination result that the phase of the second distortion vibration V2 is advanced (not delayed) from the first distortion vibration V1 is input to the enhancement gain setting circuit 824, the enhancement gain K is increased from “0” to “ On the other hand, when the determination result that the phase of the second strain vibration V2 is delayed from the first strain vibration V1 is input while being set to a predetermined value smaller than “1”, the reinforcement gain K is set to “0”. The enhancement gain K set by the enhancement gain setting circuit 824 is input to the adder 825. The adder 825 adds “1” to the enhancement gain K to obtain the gain K ′. Further, the gain K ′ is input to the multiplier 826, and is multiplied by the torque inertia compensation amount Iti * in the multiplier 826. When the phase of the second strain vibration V2 is ahead of the first strain vibration V1, the gain K ′ having a value at least greater than “1” is added by adding “1” to the enhancement gain K. Become. By multiplying the torque inertia compensation amount Iti * by this gain K ′, the torque inertia compensation amount Iti * is increased and corrected, and the torque inertia compensation amount Iti ** after this increase correction is used, so that torque inertia compensation control is performed. Strengthening is performed. Thus, when the torque inertia compensation control is strengthened, the current command value Iq * (motor drive current) is corrected in a direction in which the reverse input torque is reduced. As described above, when the phase determination circuit 84 determines that the phase of the second distorted vibration V2 is ahead of the phase of the first distorted vibration V1, the strengthening gain setting circuit 824 makes the steering mechanism from the road surface. A drive current correction circuit that determines that the reverse input torque to be applied is operating and corrects the drive current (motor assist control amount) of the motor 60 in a direction that reduces the reverse input torque is configured.

  FIG. 9 is a flowchart showing an outline of vibration generation detection processing by reverse input and vibration suppression processing based on the detection result performed in the ECU 8. In step S1, output signals (steering torque τ and vehicle speed V) of the torque sensor 70 and the vehicle speed sensor are read, and a current command value Iq * (motor drive current) is calculated based on these signals. Thereafter, the process proceeds to step S2. In step S2, the output signals (first and second strain vibrations V1 and V2) of the first and second strain sensors 71 and 72 are read, and the process proceeds to step S3. In step S3, it is determined whether or not the second strain vibration V2 is delayed from the first strain vibration V1, and if it is determined to be delayed, the process proceeds to step S4, and if it is determined that it is not delayed (advanced). The process proceeds to step S5. In step S4, the current command value Iq * (motor drive current) is not corrected (the enhancement gain K is set to “0”), and the process proceeds to step S6. In step S5, the current command value Iq * (motor drive current) is corrected in the direction in which the reverse input torque is reduced (the enhancement gain K is set to a value larger than “0”), and the process proceeds to step S6. In step S6, drive control of the motor 60 is performed based on the current command value Iq * (motor drive current).

[Operation of Example 1]
Next, the operation of the apparatus EPS according to the first embodiment will be described.
The phase determination circuit 84 determines whether or not the phase of the second strain vibration V1 is ahead of the first strain vibration V1, and the phase determination circuit 84 has a phase of the second strain vibration V1 of the first strain vibration V1. If it is determined that the phase is ahead of the phase, it is determined that reverse input torque is acting on the steering mechanism from the road surface. Thus, by detecting the vibration source (whether the input is a positive input from the steering operation or the reverse input from the road surface) based on the phase difference between the output signals of the pair of strain sensors 71 and 72, the reverse input from the road surface is detected. Detection accuracy can be increased. That is, for example, a specific frequency component corresponding to the vibration of the steering mechanism generated by reverse input from the road surface is estimated in advance by experiments or the like, and the specific frequency component is calculated from a signal (steering angle or the like) indicating the state of the steering mechanism. A method of determining the presence or absence of reverse input from the road surface by extracting is also conceivable. However, in reality, the frequency component of vibration generated by the steering operation is wide, and the frequency component of vibration generated by reverse input from the road surface is also wide. Therefore, the reverse input from the road surface using only the specific frequency component is used. It is difficult to judge the presence or absence. On the other hand, in the apparatus EPS according to the first embodiment, since the presence or absence of reverse input from the road surface is detected based on the phase difference between the output signals of the pair of strain sensors 71 and 72, the steering mechanism generated by reverse input from the road surface is used. Vibration can be detected with high accuracy regardless of the frequency. By accurately detecting vibration due to reverse input, it is possible to reduce the influence of reverse input on the detected value of steering torque τ used to calculate the basic assist control amount Ias * and to create an appropriate current command value Iq * is there. Therefore, generation | occurrence | production of the steering assist force which inhibits a driver | operator's steering operation can be suppressed. In addition, the accuracy of reverse input damping control (torque inertia compensation control) from the road surface can be improved. Therefore, the steering feeling can be further improved.

  In the first embodiment, the strain sensors 71 and 72 are provided on the upstream side (third column shaft 22) and the downstream side (pinion shaft 24) of the torsion bar 23, respectively. It is sufficient that the pair of strain sensors 71 and 72 are separated by a distance such that a detectable phase difference is generated between the output signals. Therefore, the sensors 71 and 72 may be arranged at arbitrary positions on the power transmission path (the steering shaft 2 and the rack shaft 31) between the steering wheel 1 and the steered wheels 5.

  The phase determination circuit 84 compares the phase of the peak value Peak1 of the first strain vibration V1 and the peak value Peak2 of the second strain vibration V2 detected within a predetermined time, so that the phase of the second strain vibration V2 is the first. It is determined whether or not the phase of the strain vibration 1 is advanced. Therefore, the calculation load of the calculation circuit can be reduced while ensuring the phase comparison accuracy of the strain vibrations V1 and V2.

  The strain sensors 71 and 72 detect strain vibrations V1 and V2, respectively, based on changes in internal resistance values that change based on the piezoresistance effect due to external vibrations acting on the third column shaft 22 and the pinion shaft 24, respectively. To do. That is, silicon has a piezoresistive effect in which the resistance value changes when stress is applied. As described above, when the strain sensors 71 and 72 using the piezoresistive effect are used, a strain sensor (for example, a resistance wire using a thin metal thin wire) that uses a change in resistance caused by a change in the cross-sectional area of the resistance. Since the change in resistance value due to strain is significantly greater than when using a strain gauge), strain amount detection with high detection accuracy can be performed. Therefore, it is possible to improve the detection accuracy of the vibration of the steering mechanism generated by the reverse input from the road surface. Each of the strain sensors 71 and 72 is supplied with a predetermined current, and detects strain vibrations V1 and V2, respectively, by detecting a voltage drop amount associated with a change in the internal resistance value with respect to the current. Therefore, distortion vibration can be detected with a simple configuration.

  Each of the strain sensors 71 and 72 is composed of a silicon crystal including a diffused resistor in which impurities are diffused. Therefore, a highly accurate and reliable strain sensor can be obtained as compared with the case where a resistance wire strain gauge that easily causes high cycle fatigue is used. In other words, a semiconductor crystal with a high yield strength is used for applications involving high-cycle deformation such as measurement of rotational shaft distortion, or for applications that require high reliability such as automobile steering shafts. There is no fatigue even with cycle loads. Also, when a Wheatstone bridge circuit is configured using a plurality of resistors for temperature correction, there is no concern about resistance peeling or damage. Therefore, long-term reliability can be ensured. The silicon crystal is a single crystal. Therefore, it is a single crystal and has no grain boundaries compared to resistance wire strain gauges that are easily corroded by using metal thin films and semiconductor gauges that use polycrystalline silicon that can cause environmental corrosion at multiple crystal grain boundaries. Therefore, it is possible to obtain a strain sensor with high reliability and high detection accuracy that does not corrode even in a corrosive environment or in an environment with moisture. In addition, there are advantages such as good consistency with other electric circuits, high breaking strength, and low cost.

[Effect of Example 1]
The effects achieved by the power steering device EPS according to the first embodiment will be listed below.
(1) An input shaft (third column shaft 22) that rotates in accordance with a steering operation of the steering wheel 1 and an output shaft (pinion shaft 24) that is connected to the input shaft via a torsion bar 23 and transmits the rotation of the input shaft. ), A conversion mechanism (gear mechanism 3) that converts the rotation of the output shaft into a turning operation of the steered wheels 5, an electric motor 60 that applies a steering force to the steering mechanism, and an input shaft The first strain sensor 71 for detecting the strain vibration generated on the input shaft, the second strain sensor 72 for detecting the strain vibration generated on the output shaft, and the output signal of the second strain sensor 72 The phase determination circuit 84 for determining whether or not the phase of the second distortion vibration V2 is higher than the first distortion vibration V1 that is the output signal of the first strain sensor 71, and the phase determination circuit 84 are the second distortion. The phase of vibration V2 is the position of the first strain vibration V1 Drive current for correcting the drive current of the electric motor 60 in a direction in which the reverse input torque is reduced by determining that the reverse input torque acting on the steering mechanism is acting from the road surface. A correction circuit (enhanced gain setting circuit 824).
Therefore, it is possible to detect the vibration of the steering mechanism caused by the reverse input from the road surface with higher accuracy.

(2) The phase determination circuit 84 compares the phase of the peak value Peak1 of the first strain vibration V1 and the peak value Peak2 of the second strain vibration V2 detected within a predetermined time, thereby determining the phase of the second strain vibration V2. It is determined whether or not it is ahead of the phase of the first strain vibration V1.
With such a simple configuration, it is possible to reduce the calculation load of the calculation circuit (phase determination circuit 84).

(3) The first strain sensor 71 and the second strain sensor 72 change based on the piezoresistance effect due to external vibrations acting on the input shaft (third column shaft 22) and the output shaft (pinion shaft 24). Based on the change in the internal resistance value, the first strain vibration V1 and the second strain vibration V2 are detected.
Therefore, detection accuracy can be improved by using a strain sensor using a piezoresistance effect.

(4) The first strain sensor 71 and the second strain sensor 72 are supplied with a predetermined current, and the first strain vibration V1 and the second strain are detected by detecting a voltage drop amount associated with a change in the internal resistance value with respect to the current. Detects vibration V2.
Therefore, the configuration can be simplified.

(5) The first strain sensor 71 and the second strain sensor 72 are made of a silicon crystal including a diffused resistor in which impurities are diffused.
Therefore, it is possible to improve detection accuracy while improving reliability.

(6) The silicon crystal is a single crystal.
Therefore, it is possible to improve detection accuracy while improving reliability.

[Example 2]
The second embodiment shows an example in which the first and second strain sensors 71 and 72 are arranged on the upstream side and the downstream side of the coupling 25, respectively.

  FIG. 10 is a system configuration diagram of the apparatus EPS according to the second embodiment. The first strain sensor 71 is arranged on the upstream side of the coupling 25, that is, on the column shaft between the coupling 25 and the steering wheel 1, specifically on the first column shaft 20. Note that the first strain sensor 71 may be disposed upstream of the coupling 25 in the second column shaft 21. The second strain sensor 72 is disposed on the downstream side of the coupling 25, that is, on the power transmission path between the coupling 25 and the steered wheels 5. Specifically, it is arranged on the rack shaft 31. The second column shaft 21 may be disposed at any position as long as it is downstream of the coupling 25. For example, the third column shaft 22, the pinion shaft 24, or the tie rod 4 ( The second strain sensor 72 may be disposed in the fourth embodiment). Other configurations, for example, the configurations of the first and second strain sensors 71 and 72 and the configuration of the ECU 8 (phase determination circuit 84 and drive current correction circuit) are the same as those in the first embodiment.

  That is, strain sensors 71 and 72 are provided on the input shaft (first column shaft 20) and the output shaft (third column shaft 22 and pinion shaft 24) or rack shaft 31 connected via the coupling 25, respectively. Based on the phase difference between the strain vibrations V1 and V2 detected by the sensors 71 and 72, the presence or absence of reverse input is determined. Therefore, if the distance between the strain sensors 71 and 72 is made larger than that of the first embodiment, the phase difference between the output signals (distortion vibrations) of the strain sensors 71 and 72 will be larger than that of the first embodiment. Thereby, the vibration of the steering mechanism generated by the reverse input from the road surface can be detected with higher accuracy. Further, the output signals (distortion vibrations) of the strain sensors 71 and 72 not only generate a phase difference by the distance between the strain sensors 71 and 72 but also pass through a coupling 25 having a predetermined damping characteristic. As a result, the phase difference further increases. Specifically, the vibration transmitted from the rack shaft 31 on the downstream (steered wheel 5) side to the upstream (steering wheel 1) side is attenuated and the phase is delayed after passing the coupling 25 as a delay element. Similarly, vibration transmitted from the first column shaft 20 on the upstream side to the downstream (rack shaft 31) side is attenuated and delayed in phase after passing through the coupling 25. Therefore, the phase difference between the strain vibrations V1 and V2 detected by the respective strain sensors 71 and 72 increases, and the phase difference (time difference caused by the input direction) between the peak values Peak1 and Peak2 for determining reverse input is also large. Therefore, the accuracy of determination can be improved. Other functions and effects are the same as those of the first embodiment.

(Effect of Example 2)
Hereinafter, the effects grasped from Example 2 are listed.
(1) An input shaft (first column shaft 20) that rotates in accordance with the steering operation of the steering wheel 1 is connected to the input shaft via a coupling 25 formed of rubber or resin, and the rotation of the input shaft is transmitted. A steering mechanism comprising: an output shaft (third column shaft 22 and pinion shaft 24) and a conversion mechanism (gear mechanism 3) for converting the rotation of the output shaft into a turning operation of the steered wheels 5. An electric motor 60 for applying a steering force to the input shaft, a first strain sensor 71 provided on the input shaft for detecting strain vibration generated on the input shaft, and a second strain sensor provided on the output shaft for detecting strain vibration generated on the output shaft. Phase determination for determining whether the phase of the strain sensor 72 and the second strain vibration V2 that is the output signal of the second strain sensor 72 is ahead of the first strain vibration V1 that is the output signal of the first strain sensor 71 Circuit 84, and When the phase determination circuit 84 determines that the phase of the second strain vibration V2 is ahead of the phase of the first strain vibration V1, it is determined that reverse input torque acting on the steering mechanism from the road surface is acting. And a drive current correction circuit (enhanced gain setting circuit 824) for correcting the drive current of the electric motor 60 in the direction in which the reverse input torque is reduced.
Therefore, it is possible to detect the vibration of the steering mechanism caused by the reverse input from the road surface with higher accuracy.

(2) The conversion mechanism (gear mechanism 3) is a rack and pinion mechanism, and the second strain sensor 72 is provided on the rack shaft 31 and detects strain vibration generated in the rack shaft 31.
Therefore, the detection accuracy can be improved by increasing the distance between the strain sensors 71 and 72.

[Example 3]
In the third embodiment, as in the second embodiment, the first and second strain sensors 71 and 72 are arranged on the upstream side and the downstream side of the coupling 25, respectively. An example in which a filter 85 for extracting a predetermined frequency component is provided in the ECU 8 is shown.

  FIG. 11 is a block diagram illustrating the configuration of the ECU 8 according to the third embodiment. The microcomputer 80 includes a filter 85 as a specific frequency extraction circuit in addition to the configuration of the first embodiment. The filter 85 sets a specific frequency component corresponding to the vibration of the steering mechanism generated by the reverse input torque from the road surface in advance by experiments or the like, and specifies the above-mentioned specific one of the input first strain vibration V1 or second strain vibration V2. The frequency component of is extracted. Then, the extracted frequency component is output to the enhancement gain setting circuit 824. When the enhancement gain setting circuit 824 extracts the specific frequency component by the filter 85 and the phase determination circuit 84 determines that the phase of the second distortion vibration V2 is ahead of the phase of the first distortion vibration V1, The torque inertia compensation control is strengthened by increasing the torque inertia compensation amount Iti *. That is, the current command value Iq * (motor drive current) is corrected so that the input frequency component is reduced. The filter 85 outputs the effective value of the extracted frequency component as a power spectrum Sp to the enhanced gain setting circuit 824, and the enhanced gain setting circuit 824 outputs the torque inertia compensation amount Iti * when the power spectrum Sp is equal to or greater than a predetermined threshold. May be increased.

  In the apparatus EPS according to the second embodiment configured as described above, the frequency of the strain vibration transmitted from one to the other changes through the coupling 25 between the first strain sensor 71 and the second strain sensor 72. (Delay). This change improves the accuracy of extracting the reverse input torque component as the specific frequency component. That is, even when a positive input torque component is mixed in the extracted frequency component, it is possible to suppress erroneous determination of the mixed component as the reverse input torque through the determination result of the phase determination circuit 84. . Therefore, the control accuracy of the correction control of the current command value Iq * (motor driving current) can be improved. Other functions and effects are the same as those of the second embodiment. As in the first embodiment, the coupling 25 may not be interposed between the first strain sensor 71 and the second strain sensor 72.

(Effect of Example 3)
Hereafter, the effects grasped from Example 3 are listed.
(1) A filter 85 that extracts a predetermined frequency component corresponding to the reverse input torque from the first strain vibration V1 or the second strain vibration V2 is provided, and the drive current correction circuit (enhanced gain setting circuit 824) is a phase determination circuit. When 84 determines that the phase of the second strain vibration V2 is ahead of the phase of the first strain vibration V1, the drive current of the electric motor 60 is corrected so that the predetermined frequency component is reduced.
Therefore, it is possible to detect the vibration of the steering mechanism caused by the reverse input from the road surface with higher accuracy.

[Example 4]
In the fourth embodiment, similarly to the second embodiment, the first strain sensor 71 detects the steering torque τ in the configuration in which the first and second strain sensors 71 and 72 are arranged on the upstream side and the downstream side of the coupling 25, respectively. An example of this is shown.

  FIG. 12 is a system configuration diagram of the apparatus EPS according to the fourth embodiment. The first strain sensor 71 is disposed on the first column shaft 20 as in the second embodiment. Note that the first strain sensor 71 may be disposed upstream of the coupling 25 in the second column shaft 21. Unlike the second embodiment, the second strain sensor 72 is disposed on the tie rod 4. In addition, you may arrange | position in arbitrary positions if it is a downstream from the coupling 25. FIG. Further, the magnetostrictive torque sensor 70 for detecting the twist amount of the torsion bar 23 is omitted, and instead, the first strain sensor 71 detects the steering torque τ based on the strain amount of the first column shaft 20. As shown in FIG. 13, when torque is generated in the steering shaft 2 (first column shaft 20), a difference in rotational amount occurs between both ends of the shaft, and shear stress τxy is generated in the shaft. When the first strain sensor 71 detects the shear stress τxy as a strain amount, the amount of torque (steering torque τ) generated in the steering shaft 2 (first column shaft 20) can be measured. Specifically, the distortion reference is made so that the internal resistance value of only the resistor 712a constituting the Wheatstone bridge circuit 712 of the first strain sensor 71 changes based on the piezoresistance effect and the internal resistance value of the dummy resistor 712b does not change. The arrangement of the chip (the crystal orientation of silicon and the arrangement of resistors 712a and 712b) is adjusted with respect to the coordinate system (xy coordinates in FIG. 13). In addition, it is good also as measuring steering torque (tau) based on the combination of both detected values using two chips | tips. Further, the chip constituting the torque sensor and the chip constituting the detection sensor for the first strain vibration V1 may be shared or provided separately. Other configurations are the same as those of the second embodiment.

  In the apparatus EPS of the fourth embodiment, the torque sensor 70 is omitted, and the steering torque τ is detected by the first strain sensor 71. Therefore, the configuration of the apparatus EPS can be simplified. Other functions and effects are the same as those of the second embodiment.

[Other embodiments]
As mentioned above, although the form for implement | achieving this invention has been demonstrated based on Examples 1-4, the concrete structure of this invention is not limited to an Example, The range which does not deviate from the summary of invention. Such design changes are included in the present invention.
For example, the gear mechanism 3 of the apparatus EPS is not limited to the rack and pinion type, and may be a variable gear ratio type, for example. The apparatus EPS is a pinion assist type in which the motor 60 provides auxiliary power to the rotation of the pinion shaft PS. However, the apparatus EPS is not limited to this, and for example, the motor 60 is attached to the rack shaft 31 to drive the rack shaft. A rack assist type that gives auxiliary power to the movement of 31 may be used.
In the embodiment, in order to suppress vibration generated in the steering mechanism due to application of reverse input stress, torque inertia compensation amount calculation circuit 821 is provided in ECU 8 to perform torque inertia compensation control, and torque inertia compensation is performed when it is determined that reverse input is present. Although the control is strengthened, it is possible to provide a drive current correction circuit that directly corrects the basic assist amount Ias * based on the phase determination result without performing the torque inertia compensation control as in the embodiment. Further, for example, damping control of reverse input torque may be performed using an inverse filter.
In the embodiment, the antennas of the strain sensors 71 and 72 are built in the chip in order to improve reliability by eliminating the need for electrode pads for external connection. However, in order to increase the power (output), the antennas outside the chip are used. It is good also as forming an antenna in this. In addition, power is supplied to the strain sensors 71 and 72 from the outside of the chip, but a power source (storage battery) may be provided in the chip. The energy supply and communication method with the ECU 8 includes not only electromagnetic induction that forms an induction electromagnetic field in the antenna, but also microwave reception and demodulation, and energy supply and communication using light. It may be done. Moreover, not only a wireless format but a wired format using a slip ring or a fixed harness may be used.
The crystal orientation of silicon and the arrangement of the resistors 712a and 712b are not limited to those of the embodiment, and can be arbitrarily adjusted. For example, any of the following combinations may be used.
1) The resistor 712a is an N-type impurity diffusion layer and the <100> direction is long, the dummy resistor 712b is a P-type impurity diffusion layer and the <100> direction is long, and two resistors 712a and two dummy resistors 712b are arranged in parallel. 2) The resistor 712a is an N-type impurity diffusion layer with the <100> direction as the length, the dummy resistor 712b is formed of an N-type impurity diffusion layer, and the dummy resistor 712b is a V-shaped straight line that forms a V-shape. 3) The resistor 712a is formed of a P-type impurity diffusion layer, the dummy resistor 712b is formed of an N-type impurity diffusion layer, and both the resistor 712a and the dummy resistor 712b are <110>. It is formed so that the direction is long, and two resistors 712a and two dummy resistors 712b are arranged in parallel.

1 Steering wheel 22 Third column shaft (input shaft)
23 Torsion bar 24 Pinion shaft (output shaft)
3 Gear mechanism (conversion mechanism)
5 Steering wheel 60 Electric motor 71 First strain sensor 72 Second strain sensor 84 Phase determination circuit 824 Strengthening gain setting circuit (drive current correction circuit)

Claims (3)

An input shaft that rotates in accordance with a steering operation of the steering wheel, an output shaft that is connected to the input shaft via the torsion bar, and that transmits the rotation of the input shaft, and the turning operation of the steered wheels that rotates the output shaft A steering mechanism composed of a conversion mechanism for converting into
An electric motor for applying a steering force to the steering mechanism;
A first strain sensor that is provided on the input shaft and detects strain vibration generated in the input shaft;
A second strain sensor that is provided on the output shaft and detects strain vibration generated on the output shaft;
A phase determination circuit that determines whether the phase of the second strain vibration that is the output signal of the second strain sensor is ahead of the first strain vibration that is the output signal of the first strain sensor;
When the phase determination circuit determines that the phase of the second strain vibration is ahead of the phase of the first strain vibration, a reverse input torque acting on the steering mechanism is acting from the road surface. judges, have a, a drive current correction circuit for correcting the driving current of the electric motor in a direction in which the reverse input torque is reduced,
The phase determination circuit compares the phase of the peak value of the first strain vibration and the peak value of the second strain vibration detected within a predetermined time, thereby determining the phase of the second strain vibration to the first strain vibration. It is judged whether it is ahead of the phase of the power steering device characterized by things. An input shaft that rotates in response to a steering operation of the steering wheel, an output shaft that is connected to the input shaft through a coupling formed of rubber or resin, and that transmits the rotation of the input shaft, and the rotation of the output shaft A steering mechanism composed of a conversion mechanism that converts the steering wheel into a turning operation of the steered wheels,
An electric motor for applying a steering force to the steering mechanism;
A first strain sensor that is provided on the input shaft and detects strain vibration generated in the input shaft;
A second strain sensor that is provided on the output shaft and detects strain vibration generated on the output shaft;
A phase determination circuit that determines whether the phase of the second strain vibration that is the output signal of the second strain sensor is ahead of the first strain vibration that is the output signal of the first strain sensor;
When the phase determination circuit determines that the phase of the second strain vibration is ahead of the phase of the first strain vibration, a reverse input torque acting on the steering mechanism is acting from the road surface. judges, have a, a drive current correction circuit for correcting the driving current of the electric motor in a direction in which the reverse input torque is reduced,
The phase determination circuit compares the phase of the peak value of the first strain vibration and the peak value of the second strain vibration detected within a predetermined time, thereby determining the phase of the second strain vibration to the first strain vibration. Whether it is ahead of the phase of
A power steering device characterized by that. An input shaft that rotates in response to a steering operation of the steering wheel, an output shaft that is connected to the input shaft through a coupling formed of rubber or resin, and that transmits the rotation of the input shaft, and the rotation of the output shaft A steering mechanism composed of a conversion mechanism that converts the steering wheel into a turning operation of the steered wheels,
An electric motor for applying a steering force to the steering mechanism;
A first strain sensor that is provided on the input shaft and detects strain vibration generated in the input shaft;
A second strain sensor that is provided on the output shaft and detects strain vibration generated on the output shaft;
A phase determination circuit that determines whether the phase of the second strain vibration that is the output signal of the second strain sensor is ahead of the first strain vibration that is the output signal of the first strain sensor;
When the phase determination circuit determines that the phase of the second strain vibration is ahead of the phase of the first strain vibration, a reverse input torque acting on the steering mechanism is acting from the road surface. A drive current correction circuit that determines and corrects the drive current of the electric motor in a direction in which the reverse input torque is reduced;
A filter that extracts a predetermined frequency component corresponding to the reverse input torque from the first strain vibration or the second strain vibration, and
The drive current correction circuit is configured to reduce the predetermined frequency component when the phase determination circuit determines that the phase of the second distortion vibration is ahead of the phase of the first distortion vibration. A power steering device that corrects the drive current of the motor .

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