JP2012025262A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of stably continuing steering torque detection and power assist control even after there is one remaining normal sensor signal.SOLUTION: A microcomputer 21 detects steering torque τ' based on the other remaining sensor signal when the normal sensor signal remains even after abnormality is caused in either of respective sensor signals Sa, Sb that a torque sensor outputs. The microcomputer 21 includes an abnormality determination during continuation part 30 that carries out the abnormality determination of the remaining sensor signal when carrying out continuous control with the steering torque τ' as a base. The abnormality determination during continuation part 30 carries out abnormality determination by comparing a sign of a differential value Δθ between a steering angle θs (θs') as a first rotation angle closer to a steering side than to a torsion bar and a second rotation angle θp closer to a steered wheel side than to the torsion bar with the sign of the steering torque τ'.

Description

  The present invention relates to an electric power steering apparatus.

  Usually, an electric power steering device (EPS) executes its power assist control by detecting a steering torque transmitted to a steering system based on torsion of a torsion bar provided in the middle of the steering shaft. Conventionally, in a torque sensor constituting the torque detection means, a magnetic detection element such as a Hall IC is used as a sensor element, so that the output level (output voltage) of the sensor signal according to the torsion bar twisting. Is configured to change (see, for example, Patent Document 1).

  In other words, such a magnetic torque sensor has an advantage that the configuration is simple and small in comparison with a so-called twin resolver torque sensor in which a pair of wound resolvers are arranged at both ends of a torsion bar. In addition, since it is possible to easily increase the number of sensor elements, high detection accuracy can be ensured by multiplexing the sensor signals. Further, even after an abnormality occurs in any sensor signal, as long as a normal sensor signal remains, the steering torque can be detected stably based on the remaining sensor signal. Note that the abnormality determination for a specific sensor signal can be performed, for example, based on whether or not the output level clearly exceeds the appropriate range. Thus, even after an abnormality occurs in the steering torque detection process (torque sensor, signal wiring thereof, etc.), the power assist control can be continued to improve the convenience for the driver.

JP 2003-149062 A JP 2009-255645 A

  However, the number of sensor elements provided in an actual torque sensor is “two” in many cases due to the balance between its performance and economic rationality. In order to ensure the required determination accuracy in the abnormality determination in the steering torque detection process, at least two systems of sensor signals are required except for the case of showing a complete abnormal value (for example, patents) Reference 2). For this reason, conventionally, the detection of the steering torque using the remaining sensor signal as described above and the continuation of the power assist control are also tentative until the assist application to the steering system is stopped. However, there was still room for improvement in this respect.

  The present invention has been made to solve the above problems, and its purpose is to stably detect the steering torque and perform power assist control even after the remaining normal sensor signal becomes one. An object of the present invention is to provide an electric power steering device that can continue the operation.

  In order to solve the above-described problems, the invention according to claim 1 is directed to a steering force assisting device that applies an assisting force to a steering system using a motor as a drive source, and torsion of a torsion bar provided in the middle of the steering shaft. A torque sensor that outputs a plurality of sensor signals whose output levels change in response, a torque detector that detects a steering torque based on the sensor signal, and a control that controls the operation of the steering force assisting device based on the steering torque. And an abnormality determining means for determining an abnormality of each sensor signal, wherein the torque detecting means has a normal sensor signal remaining even after an abnormality occurs in any of the sensor signals. In the electric power steering apparatus for detecting the steering torque based on the remaining sensor signal, the steering shaft First rotation angle detection means for detecting a first rotation angle on the steering side of the torsion bar; and second rotation angle detection means for detecting a second rotation angle of the steered wheel side of the steering shaft with respect to the torsion bar. When the remaining sensor signal becomes one, by comparing the sign of the steering torque detected based on the sensor signal with the sign of the difference value between the first rotation angle and the second rotation angle, The gist of the present invention is to include second abnormality determination means for determining abnormality of the remaining sensor signal.

  That is, the difference value between the first rotation angle on the steering side with respect to the torsion bar and the second rotation angle on the steered wheel side with respect to the torsion bar corresponds to the twist (angle) of the torsion bar that is the basis for detecting the steering torque. . Therefore, according to the above configuration, it is possible to accurately determine abnormality of the remaining sensor signal even after the remaining sensor signal becomes one. As a result, steering torque detection and power assist control based on the remaining sensor signal can be stably continued.

  According to a second aspect of the present invention, the second rotation angle detection means detects the second rotation angle by converting a motor rotation angle detected by a motor resolver, and the first rotation angle detection means The first rotation angle is detected by a steering sensor having a detection accuracy rougher than that of a motor resolver, and the second abnormality determination means executes a steering state switching determination based on a change in the first rotation angle. The gist is to correct the first rotation angle so as to coincide with the second rotation angle at the switching timing.

  That is, by using a steering sensor with a rough detection accuracy as the first rotation angle detection means, a difference between the first rotation angle and the second rotation angle due to a delay in the detection of the first rotation angle due to the rough detection accuracy. There is a possibility that an error occurs in the value, that is, the value corresponding to the twist angle of the torsion bar. However, according to the above configuration, it is possible to accurately determine the abnormality of the remaining sensor signal by correcting the delay in the rise of the first rotation angle detection due to the roughness of the detection accuracy.

  According to the present invention, there is provided an electric power steering apparatus capable of stably continuing the steering torque detection and the power assist control even after the remaining normal sensor signal becomes one. .

The schematic block diagram of an electric power steering device (EPS). The control block diagram of EPS. The flowchart which shows the process sequence of the abnormality determination about the said remaining sensor signal after the remaining sensor signal becomes one.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
As shown in FIG. 1, in the electric power steering apparatus (EPS) 1 of the present embodiment, a steering shaft 3 to which a steering 2 is fixed is connected to a rack shaft 5 via a rack and pinion mechanism 4, and the steering The rotation of the steering shaft 3 accompanying the operation is converted into a reciprocating linear motion of the rack shaft 5 by the rack and pinion mechanism 4. The steering shaft 3 of this embodiment is formed by connecting a column shaft 3a, an intermediate shaft 3b, and a pinion shaft 3c. Then, the reciprocating linear motion of the rack shaft 5 accompanying the rotation of the steering shaft 3 is transmitted to a knuckle (not shown) via tie rods 6 connected to both ends of the rack shaft 5, whereby the steering angle of the steered wheels 7. That is, the traveling direction of the vehicle is changed.

  Further, the EPS 1 includes an EPS actuator 10 as a steering force assisting device that applies an assist force for assisting a steering operation to the steering system, and an ECU 11 as a control unit that controls the operation of the EPS actuator 10. .

  The EPS actuator 10 of the present embodiment is configured as a so-called column-type EPS actuator in which a motor 12 that is a drive source is drivingly connected to a column shaft 3 a via a speed reduction mechanism 13. In the present embodiment, the motor 12 employs a brushless motor that rotates by supplying three-phase (U, V, W) driving power. The EPS actuator 10 is configured to apply the motor torque as an assist force to the steering system by decelerating the rotation of the motor 12 and transmitting it to the column shaft 3a.

  On the other hand, a torque sensor 14, a vehicle speed sensor 15, and a steering sensor (steering angle sensor) 16 are connected to the ECU 11. The ECU 11 detects the steering torque τ, the vehicle speed V, and the steering angle θs as the first rotation angle based on the output signals of these sensors.

  More specifically, in the present embodiment, the torsion bar 17 is provided in the middle of the column shaft 3a, more specifically, on the steering 2 side with respect to the speed reduction mechanism 13 constituting the EPS actuator 10. The torque sensor 14 of the present embodiment outputs sensor signals Sa and Sb that can detect the steering torque τ transmitted through the steering shaft 3 based on the twist of the torsion bar 17. It is configured with.

  Such a torque sensor includes, for example, two magnetic detection elements (this embodiment) on the outer periphery of a sensor core (not shown) that generates a magnetic flux change based on torsion of the torsion bar 17, as shown in the above-mentioned conventional document 1. Then, the Hall IC) can be formed by arranging the sensor elements 14a and 14b.

  That is, when the torsion bar 17 is twisted by torque input to the steering shaft 3 that is the rotating shaft, the magnetic flux passing through the sensor elements 14a and 14b changes. The torque sensor 14 according to the present embodiment is configured to output the output levels (voltages) of the sensor elements 14a and 14b, which fluctuate with changes in the magnetic flux, to the ECU 11 as sensor signals Sa and Sb, respectively.

  The steering sensor 16 according to the present embodiment includes a rotor 18 fixed to the column shaft 3a on the steering 2 side of the torque sensor 14, and a sensor element (Hall IC) that detects a change in magnetic flux accompanying the rotation of the rotor 18. ) 19 and a magnetic rotation angle sensor.

  Then, the ECU 11 calculates a target assist force based on each detected state quantity, and through the supply of drive power to the motor 12 that is the drive source in order to cause the EPS actuator 10 to generate the target assist force. The operation of the EPS actuator 10, that is, the assist force applied to the steering system is controlled.

Next, an aspect of assist control in the EPS of the present embodiment will be described.
As shown in FIG. 2, the ECU 11 includes a microcomputer 21 that outputs a motor control signal, and a drive circuit 22 that supplies drive power to a motor 12 that is a drive source of the EPS actuator 10 based on the motor control signal. Yes.

  In the present embodiment, the ECU 11 includes a current sensor 23 for detecting the actual current value I supplied to the motor 12 and a motor resolver 24 (motor rotation angle sensor, see FIG. 1) for detecting the motor rotation angle θm. ) Is connected. The microcomputer 21 outputs a motor control signal to the drive circuit 22 based on the vehicle state quantities and the actual current value I of the motor 12 and the motor rotation angle θm detected by the current sensor 23 and the motor resolver 24. Is generated.

  Each control block shown below is realized by a computer program executed by the microcomputer 21. Then, the microcomputer 21 detects each state quantity at a predetermined sampling period, and generates a motor control signal by executing each arithmetic processing shown in the following control blocks every predetermined period.

  More specifically, the microcomputer 21 of the present embodiment includes a steering torque detector 25 serving as torque detection means for detecting the steering torque τ based on the sensor signals Sa and Sb output from the torque sensor 14, and the steering torque τ. Based on the current command value I * corresponding to the target assist force, and a motor control signal output unit 27 that outputs a motor control signal based on the current command value I *. ing.

  A vehicle speed V detected by the vehicle speed sensor 15 is input to the current command value calculation unit 26 of the present embodiment together with the steering torque τ detected by the steering torque detection unit 25. The current command value calculation unit 26 calculates a current command value I * corresponding to a larger target assist force as the steering torque τ (absolute value) is larger and the vehicle speed V is smaller. ing.

  The motor control signal output unit 27 includes the current command value I * output from the current command value calculation unit 26, the actual current value I detected by the current sensor 23, and the motor rotation detected by the motor resolver 24. The angle θm is input. The motor control signal output unit 27 calculates a motor control signal by executing feedback control so that the actual current value I follows the current command value I *.

  Specifically, the current sensor 23 of the present embodiment detects each phase current value Iu, Iv, Iw as the actual current value I. The motor control signal output unit 27 converts the phase current values Iu, Iv, and Iw into d and q axis current values in the d / q coordinate system (d / q conversion), thereby performing the current feedback control. Execute.

  That is, the current command value calculation unit 26 calculates the q-axis current command value as the current command value I * (d-axis current command value is “0”), and the motor control signal output unit 27 calculates the d / q coordinate. Current feedback control is executed so that the shaft current value follows each shaft current command value of the system. The motor control signal output unit 27 maps each phase voltage command value (Vu) obtained by mapping (d / q reverse conversion) each axis voltage command value obtained by the current feedback control to a three-phase AC coordinate system. *, Vv *, Vw *) to generate a motor control signal.

  In the present embodiment, the motor control signal generated in this way is output from the microcomputer 21 to the drive circuit 22, so that three-phase drive power is supplied to the motor 12. As a result, an assist force corresponding to the steering torque τ is applied to the steering system.

(Continuous control after sensor signal abnormality detection and judgment of residual sensor signal abnormality)
Next, a description will be given of the continuation control after the detection of the sensor signal abnormality in the present embodiment and the manner of abnormality determination of the remaining sensor signal at the time of the continuation control.

  As described above, the torque sensor 14 of the present embodiment employs a magnetic torque sensor using a magnetic detection element (Hall IC) as the sensor element (14a, 14b). The steering torque detector 25 of the present embodiment performs correction processing (temperature characteristics, temperature characteristics, distortion of spatial magnetic flux density distribution, etc.) using the two sensor signals Sa and Sb output from the torque sensor 14. Thus, the steering torque τ can be detected with high accuracy.

In addition, the steering torque detector 25 of the present embodiment is provided with a function as an abnormality determining means for determining an abnormality of the sensor signals Sa and Sb input from the torque sensor 14.
Specifically, the steering torque detector 25 of the present embodiment determines whether or not the values of the sensor signals Sa and Sb input from the torque sensor 14 deviate from the values that can be taken at normal times. And the comparison of both values and the amount of change in unit time are performed to determine whether the sensor signals Sa and Sb are abnormal (see, for example, Patent Document 2).

  Here, when a normal sensor signal remains even after an abnormality has occurred in any one of these sensor signals Sa and Sb, the steering torque detection unit 25 of the present embodiment, the other remaining sensor. A steering torque τ ′ is detected based on the signal. As such a case, there is a case where one of the sensor signals Sa and Sb shows an obvious abnormal value, while the other value is within a normal range. In the present embodiment, the power assist control is continued on the basis of the steering torque τ ′ detected based on the remaining sensor signal (continuous control).

  Moreover, the microcomputer 21 of this embodiment is provided with the continuation abnormality determination part 30 as a 2nd abnormality determination part which performs abnormality determination of the remaining sensor signal at the time of execution of such continuation control.

  Specifically, the continuation abnormality determination unit 30 receives the steering angle θs as the first rotation angle on the steering 2 side with respect to the torsion bar 17 detected by the steering sensor 16. Further, the abnormality determination unit 30 at the time of continuous input receives the abnormality determination signal Str1 indicating the result of the abnormality determination performed by the steering torque detection unit 25 and the steering torque τ ′ detected based on the remaining sensor signal. The In addition, the motor abnormality angle θm detected by the motor resolver 24 is input to the continuation abnormality determination unit 30. The continuation abnormality determination unit 30 converts the motor rotation angle θm. Thus, the second rotation angle θp closer to the steered wheel 7 than the torsion bar 17 is detected. In the continuation abnormality determination unit 30 of the present embodiment, the motor rotation angle θm is input to the conversion calculation unit 31, and the conversion calculation unit 31 operates the EPS actuator 10 together with the motor 12 with respect to the motor rotation angle θm. The motor rotation angle θm is converted into the second rotation angle θp by multiplying the gear ratio of the speed reduction mechanism 13 (see FIG. 1). Then, the continuation abnormality determination unit 30 of the present embodiment performs an abnormality determination on the remaining sensor signal based on each of these state quantities (and control signals) (second abnormality determination).

  More specifically, in the continuation abnormality determination unit 30, a steering angle θs (corrected steering angle θs ′ described later) input as the first rotation angle, and the second rotation angle detected by the conversion calculation unit 31. θp is input to the subtractor 32. Then, the continuation abnormality determination unit 30 of the present embodiment uses the difference value (Δθ = θs′−θp) calculated by the subtractor 32 and the steering torque τ ′ detected based on the remaining sensor signal. Based on this, an abnormality determining unit 33 is provided for determining an abnormality of the remaining sensor signal.

  Specifically, the abnormality determination unit 33 of the present embodiment compares the sign of the difference value Δθ with the sign of the steering torque τ ′ detected based on the remaining sensor signal. And when both code | symbols differ, it is comprised so that it may determine with the remaining sensor signal being abnormal.

  That is, the difference value Δθ between the steering angle θs (θs ′) detected as the first rotation angle on the steering 2 side of the torsion bar 17 and the second rotation angle θp on the steered wheel 7 side of the torsion bar 17 is This corresponds to the twist (corner) of the torsion bar 17 which is the basis for detecting the steering torque. In the present embodiment, the sign of the difference value Δθ and the sign of the steering torque τ (τ ′) coincide with each other in the normal state. Therefore, it can be determined that the remaining sensor signal is abnormal when the signs of both are not the same.

  The continuation abnormality determination unit 30 of the present embodiment outputs the result of the abnormality determination by the abnormality determination unit 33 to the current command value calculation unit 26 as the abnormality determination signal Str2. In the present embodiment, when the abnormality determination signal Str2 indicates an abnormality of the remaining sensor signal, the current assist value I * output from the current instruction value calculation unit 26 is gradually decreased to reduce the power assist. The control is stopped.

  Here, normally, the detection accuracy required for the steering sensor 16 is considerably lower (coarse) than the detection accuracy of the motor resolver 24. For this reason, for example, there is a gap between the rotor 18 (see FIG. 1) and the steering shaft 3 (column shaft 3a).

  However, when the steering sensor 16 is used as the first rotation angle detection means as described above, the difference value between the steering angle θs detected as the first rotation angle and the second rotation angle θp due to the effect of the rotation play. There is a possibility that an error occurs in Δθ, that is, a value corresponding to the twist angle of the torsion bar 17.

  That is, by configuring the second rotation angle detection means using the motor resolver 24 having high detection accuracy, the second rotation angle θp on the steered wheel 7 side with respect to the torsion bar 17 substantially simultaneously with the rotation of the steering shaft 3. Can be detected. However, since the above-mentioned rotation play exists in the steering sensor 16, even if the steering shaft 3 rotates, the rotor 18 does not rotate until the rotation play is clogged. For this reason, with respect to the steering angle θs detected by the steering sensor 16, the rise of the change is delayed from the second rotation angle θp based on the motor rotation angle θm detected by the motor resolver 24. As a result, a value larger than the actual value may be calculated as the difference value Δθ between the two corresponding to the twist angle of the torsion bar 17.

  Therefore, as shown in FIG. 2, the continuation abnormality determination unit 30 of the present embodiment includes a correction calculation unit 34 that corrects the steering angle θs so as to eliminate the influence of the rotation play existing in the steering sensor 16. Is provided. Then, based on the steering angle θs ′ corrected by the correction calculation unit 34, the difference value Δθ with respect to the second rotation angle θp is calculated, and an abnormality determination based on the difference value Δθ is performed. The configuration ensures the accuracy of determination.

  More specifically, the continuation abnormality determination unit 30 of the present embodiment is provided with a switching determination unit 35 that performs switching determination of the steering operation state (steering state). The correction calculation unit 34 includes the switching determination unit 35. The determination result by the switching determination unit 35 is input as the switching signal S_cn. Then, the correction calculator 34 of the present embodiment corrects the steering angle θs, which is the first rotation angle, to coincide with the second rotation angle θp at the switching timing of the steering state.

  That is, in steering operation, “cutting” in which the steering 2 is operated in the direction to increase the steering angle (absolute value thereof), “turnback” in which the steering angle is decreased in the opposite direction, and the steering angle is maintained. There are three main states of "Holding". The influence of the rotation play becomes apparent when the steering state is switched to “cut” or “turn back”.

  That is, when the “cutting” or “cutback” is in a continuous state, the rotation play is already clogged in the steering direction. However, when the steering direction is reversed or switched from “steering” to “cutting” or “turning back”, the above-described rotation play exists in the new steering direction.

  Based on this point, the switching determination unit 35 of the present embodiment determines whether the steering state is switched to “cut” or “switch back”. Specifically, the steering angle θs as the first rotation angle is input to the switching determination unit 35 of the present embodiment, and the switching determination unit 35 determines the steering angle θs input in the previous calculation cycle. The value is held in the storage area 35a as the previous value θs_b. Then, based on the steering angle θs and the previous value θs_b input in each calculation cycle, the change (increase / decrease) in the steering angle θs is monitored, and the switching determination of the steering state is executed. It outputs to the correction | amendment calculating part 34 as switching signal S_cn.

  On the other hand, the correction rotation unit 34 receives the second rotation angle θp detected by the conversion calculation unit 31 together with the steering angle θs as the first rotation angle and the switching signal S_cn. And the correction | amendment calculating part 34 of this embodiment uses the difference of steering angle (theta) s as a 1st rotation angle and 2nd rotation angle (theta) p which exist in the switching timing of the steering state shown by the switching signal S_cn to the switching timing. Is calculated as an offset value θ0 that matches the steering angle θs and the second rotation angle θp (θ0 = θs−θp).

  In other words, the switching timing of the steering state detected by the switching determination based on the steering angle θs (change) is the moment when the rotation 18 existing in the steering sensor 16 is clogged and the rotor 18 rotates. Therefore, the difference between the steering angle θs as the first rotation angle and the second rotation angle θp at this switching timing is the delay in the detection of the steering angle due to the presence of the rotation play, and this difference is used as the offset value θ0 to determine the steering angle. By subtracting from θs, it is possible to make the corrected steering angle θs ′ coincide with the second rotation angle θp at the switching timing of the steering state. In the present embodiment, this makes it possible to accurately determine the abnormality by eliminating the influence of the rotation play.

  The correction calculation unit 34 of the present embodiment holds the offset value θ0 calculated in this manner in the storage area 34a and reads the offset value θ0 every calculation cycle, thereby correcting the steering angle θs. Execute. Then, every time the input switching signal S_cn indicates the switching timing of the steering state, the correction calculation unit 34 calculates a new offset value θ0 and holds it in the storage area 34a with the new offset value θ0. Value to be updated.

Next, a description will be given of an abnormality determination process of the remaining sensor signal by the continuous abnormality determination unit of the present embodiment configured as described above.
As shown in the flowchart of FIG. 3, when the continuation abnormality determination unit 30 of the present embodiment acquires each state quantity (step 101), first, based on the abnormality determination signal Str1 output from the steering torque detection unit 25, It is determined whether or not the continuous control is being executed after an abnormality has occurred in any of the sensor signals Sa and Sb output from the torque sensor 14 (step 102). If it is determined that the continuous control after the occurrence of an abnormality is being executed (step 102: YES), the motor rotation angle θm detected by the motor resolver 24 is subsequently converted, so that the steering shaft 3 A second rotation angle θp closer to the steered wheel 7 than the torsion bar 17 is detected (step 103). If it is determined in step 102 that the continuous control after the occurrence of abnormality is not being executed (step 102: NO), the processing after step 103 is not executed.

  Next, the continuation abnormality determination unit 30 performs the steering state switching determination based on the change (increase / decrease) in the steering angle θs as the first rotation angle detected by the steering sensor 16 (step 104), and the steering It is determined whether or not it is a state switching timing (step 105). If it is determined that it is the switching timing of the steering state (step 105: YES), a new offset value θ0 is calculated by subtracting the second rotation angle θp from the steering angle θs, and the new offset value is calculated. The held value is updated by θ0 (θ0 = θs−θp, step 106). Then, the continuation abnormality determination unit 30 corrects the steering angle θs by subtracting the offset value θ0 from the steering angle θs as the first rotation angle (θs ′ = θs−θ0, step 107).

  When it is determined in step 105 that it is not the switching timing (step 105: NO), the calculation and update of the new offset value θ0 in step 106 are not executed. Then, the continuation abnormality determination unit 30 executes the correction calculation in step 107 using the offset value θ0 held therein.

  Next, the continuation abnormality determination unit 30 calculates a difference value Δθ between the corrected steering angle θs ′ and the second rotation angle θp (Δθ = θs′−θp, step 108), and further calculates the difference value Δθ. It is determined whether or not the sign and the sign of the steering torque τ ′ detected based on the remaining sensor signal, that is, the sign of the steering torque τ ′ that is the basis of the continuous control are the same (step 109). If the sign of the difference value Δθ and the sign of the steering torque τ ′ are the same, it is determined that the “residual sensor signal” based on the detection of the steering torque τ ′ is normal. (Step 110) If the two codes are not the same, it is determined that the “remaining sensor signal” is abnormal (Step 111).

  Then, the continuation abnormality determination unit 30 of the present embodiment outputs the determination result in step 110 or step 111 to the current command value calculation unit 26 as the abnormality determination signal Str2 (step 112).

As described above, according to the present embodiment, the following operations and effects can be obtained.
(1) The microcomputer 21 (steering torque detector 25) determines that if a normal sensor signal remains even after an abnormality has occurred in any of the sensor signals Sa and Sb output from the torque sensor 14, The steering torque τ ′ is detected based on the other remaining sensor signal. In addition, the microcomputer 21 includes a continuation abnormality determination unit 30 that performs abnormality determination of the remaining sensor signal when executing the continuous control based on the steering torque τ ′ detected based on the remaining sensor signal. . Then, the continuation abnormality determination unit 30 calculates the steering angle θs (θs) ′ as the first rotation angle on the steering 2 side with respect to the torsion bar 17 and the second rotation angle θp on the steered wheel 7 side with respect to the torsion bar 17. The abnormality determination is performed by comparing the sign of the difference value Δθ with the sign of the steering torque τ ′.

  That is, the difference value Δθ between the steering angle θs (θs ′) detected as the first rotation angle on the steering 2 side of the torsion bar 17 and the second rotation angle θp on the steered wheel 7 side of the torsion bar 17 is This corresponds to the twist (corner) of the torsion bar 17 which is the basis for detecting the steering torque. Therefore, according to the above configuration, it is possible to accurately determine abnormality of the remaining sensor signal even after the remaining sensor signal becomes one. As a result, steering torque detection and power assist control based on the remaining sensor signal can be stably continued.

  (2) The continuation abnormality determination unit 30 executes the steering state switching determination based on the change (increase / decrease) in the steering angle θs as the first rotation angle detected by the steering sensor 16. Then, at the switching timing of the steering state (timing to switch to “cutting” or “switching back”), the steering angle θs that is the first rotation angle is corrected so as to coincide with the second rotation angle θp.

  That is, normally, the detection accuracy required for the steering sensor 16 is considerably lower (coarse) than the detection accuracy of the motor resolver 24. Therefore, many steering sensors 16 have rotational play. When the steering sensor 16 is used as the first rotation angle detection means as described above, the steering angle θs detected as the first rotation angle and the second rotation due to the delay of the steering angle detection due to the effect of the rotation play. There is a possibility that an error occurs in the difference value Δθ from the angle θp, that is, the value corresponding to the twist angle of the torsion bar 17.

  However, as described above, the steering state switching timing determined based on the steering angle θs, that is, the timing at which the change in the steering angle θs detected by the steering sensor 16 having a rough detection accuracy rises, the value is detected more accurately. By making it coincide with a high second rotation angle value, it is possible to eliminate the influence of the rotation play and accurately determine the abnormality.

  (3) If the microcomputer 21 determines that the remaining sensor signal is abnormal, the microcomputer 21 performs control to stop the power assist control. Thereby, fail safe can be achieved promptly.

In addition, you may change the said embodiment as follows.
In the above embodiment, the present invention is embodied in a so-called column type EPS 1, but the present invention may be applied to a so-called pinion type or rack assist type EPS.

  In the above embodiment, the torque sensor 14 outputs two sensor signals Sa and Sb. However, the present invention is not limited to this, and the present invention is applied to a case where a torque sensor that outputs three or more independent sensor signals is provided and the normal sensor signal remains even after the failure of the torque sensor. Also good.

  In the above embodiment, the sign of the difference value Δθ between the steering angle θs (θs) ′ as the first rotation angle and the second rotation angle θp closer to the steered wheel 7 than the torsion bar 17 and the steering torque τ ′ The abnormality determination is performed by comparing the sign. However, the present invention is not limited to this, and it is also possible to monitor the change in the steering torque τ ′ and execute the abnormality determination based on the comparison between the sign of the amount of change in the steering torque τ ′ and the sign of the difference value Δθ. Good.

  In the above embodiment, the second rotation angle θp closer to the steered wheel 7 than the torsion bar 17 is detected by converting the motor rotation angle θm detected by the motor resolver 24. However, the present invention is not limited to this. For example, when a DC motor with a brush is used as a drive source, it may be estimated from the wheel speed (rear wheel speed).

In addition, about the rudder angle estimation based on a wheel speed, it is good to use following Formula.
θt = (2 × WB × (W1−Wr)) / (RW × (W1 + Wr)) × (180 / π)
However, in the above equation, “θt” is the steering angle of the steered wheels, “WB” is the wheelbase length of the vehicle, “RW” is the tread length of the vehicle, and “Wl” and “Wr” are the left and right wheel speeds ( Rear wheel speed).

  In the above embodiment, it is assumed that the steering sensor 16 constituting the first rotation angle detection means has a rotation backlash, and the steering angle θs detected as the first rotation angle is corrected to eliminate the influence. . However, the present invention is not limited to this, and even when the steering sensor 16 does not have a noticeable rotational play, the detection accuracy of the steering sensor 16 is higher than the detection accuracy of the motor resolver 24 constituting the second rotation angle detection means. For rough ones, the same correction is performed. That is, the steering state switching determination is executed based on the steering angle θs, and at the switching timing, the steering angle θs that is the first rotation angle may be corrected so as to coincide with the second rotation angle θp. As a result, it is possible to accurately determine the abnormality of the remaining sensor signal by correcting the delay in the rise of the first rotation angle detection due to the roughness of the detection accuracy.

If the steering sensor 16 has detection accuracy equivalent to that of the motor resolver 24, the steering angle θs as the first rotation angle as described above need not be corrected.
Next, technical ideas that can be grasped from the above embodiments will be described together with effects.

  (A) The electric power steering apparatus characterized in that the control means controls to stop the application of the assist force when it is determined that the remaining one sensor signal is abnormal. Thereby, fail safe can be achieved promptly.

  (B) In the electric power steering apparatus, the control means gradually reduces the assist force in the stop control of the assist force. Thereby, a favorable steering feeling can be realized while suppressing torque fluctuation.

  (C) The electric power steering device, wherein the torque sensor outputs two systems of the sensor signals. By applying to such a configuration, a more remarkable effect can be obtained.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus (EPS), 2 ... Steering, 3 ... Steering shaft, 3a ... Column shaft, 7 ... Steering wheel, 10 ... EPS actuator, 11 ... ECU, 12 ... Motor, 14 ... Torque sensor, 14a, 14b DESCRIPTION OF SYMBOLS ... Sensor element, 16 ... Steering sensor, 17 ... Torsion bar, 18 ... Rotor, 21 ... Microcomputer, 22 ... Drive circuit, 24 ... Motor resolver, 25 ... Steering torque detection part, 26 ... Current command value calculation part, 27 ... Motor control signal output unit, 30 ... continuous abnormality determination unit, 31 ... conversion calculation unit, 32 ... subtractor, 33 ... abnormality determination unit, 34 ... correction calculation unit, 34a ... storage area, 35 ... switch determination unit, 35a ... Storage area, I *: current command value, I: actual current value, τ, τ ′: steering torque, Sa, Sb: sensor signal, θs, θs ′: steering angle (first rotation angle), θ s_b: previous value, θp: second rotation angle, θm: motor rotation angle, Δθ: difference value, S_cn: switching signal, θ0: offset value, Str1, Str2 ... abnormality determination signal.

Claims (2)

A steering force assisting device that applies assist force to the steering system using a motor as a drive source, a torque sensor that outputs a plurality of sensor signals whose output levels change according to torsion of a torsion bar provided in the middle of the steering shaft, Torque detection means for detecting steering torque based on the sensor signal, control means for controlling the operation of the steering force assisting device based on the steering torque, and abnormality determination means for determining abnormality of each sensor signal. The torque detecting means detects the steering torque based on the remaining sensor signal when the normal sensor signal remains even after an abnormality occurs in any of the sensor signals. In the power steering device,
First rotation angle detection means for detecting a first rotation angle on the steering side of the steering shaft relative to the torsion bar;
Second rotation angle detection means for detecting a second rotation angle on the steered wheel side of the torsion bar in the steering shaft;
When the number of the remaining sensor signals becomes one, the sign of the steering torque detected based on the sensor signal is compared with the sign of the difference value between the first rotation angle and the second rotation angle, so that the remaining Second abnormality determination means for determining abnormality of the sensor signal to be performed,
An electric power steering device. The electric power steering apparatus according to claim 1, wherein
The second rotation angle detection means detects the second rotation angle by converting a motor rotation angle detected by a motor resolver, and the first rotation angle detection means has a steering with coarser detection accuracy than the motor resolver. A first rotation angle is detected by a sensor;
The second abnormality determination means performs a steering state switching determination based on a change in the first rotation angle, and corrects the first rotation angle to coincide with the second rotation angle at the switching timing; An electric power steering device.

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