JP2012046094A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of continuing more stable assist force application when steering torque based on one sensor signal is detected.SOLUTION: When assist continuation control using a sensor signal (residual sensor signal) output from a sensor element in which a failure is not detected is executed, an ECU controls the operation of an EPS actuator so that periodical and instantaneous motor torque may be applied to a steering system in relation to a changed direction of an assist force. An abnormality of the residual sensor signal is detected on the basis of whether the application of the instantaneous motor torque is reflected on the residual sensor signal being a base of the assist continuation control.

Description

  The present invention relates to an electric power steering apparatus.

  Usually, an electric power steering apparatus (EPS) using a motor as a drive source includes a torque sensor that outputs a sensor signal based on torsion of a torsion bar provided in the middle of the steering shaft. Then, the motor torque is controlled so that an assist force corresponding to the steering torque detected based on the sensor signal is applied to the steering system. For this reason, conventionally, in EPS, stable and accurate detection of the steering torque has become one of the most important issues.

  For example, Patent Document 1 discloses a configuration in which a non-contact type magnetic detection element is used as a sensor element, thereby eliminating an electrical contact portion from the torque sensor and improving its reliability. Further, by adopting such a configuration, it is possible to easily increase the number of sensor elements without increasing the size of the torque sensor. By multiplexing the sensor signals, it is possible to improve the detection accuracy of the steering torque, detect the steering torque based on the remaining sensor signals, and continue to apply the assist force.

  Furthermore, for example, Patent Document 2 discloses a method of specifying a sensor element on the failed side with higher accuracy when any sensor signal becomes abnormal. As a result, the situation in which the assist continuation control is possible can be expanded.

JP 2003-149062 A JP 2000-185657 A

  However, in order to enjoy the benefits of such multiplexing of sensor signals, of course, at least two sensor signals are required. In particular, since magnetic sensor elements have variations in temperature characteristics, correction processing using a plurality of sensor signals is indispensable for highly accurate torque detection. For this reason, conventionally, the assist continuation control after the remaining sensor signal becomes one has been limited to gradually reducing the assist force using the remaining sensor signal in order to quickly stop the application of the assist force. However, there was still room for improvement in this respect.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide an electric power capable of continuing assist force application more stably when detecting a steering torque based on one sensor signal. The object is to provide a steering device.

  In order to solve the above 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 sensor signal based on the sensor signal, a torque detection unit that detects a steering torque based on the sensor signal, and a control unit that controls the operation of the steering force assisting device to generate the assist force corresponding to the steering torque. And an abnormality detection means for detecting an abnormality of the sensor signal, wherein the control means operates the steering force assisting device to apply an instantaneous motor torque to the steering system in the same direction as the assist force. The abnormality detecting means detects an abnormality of the sensor signal when the instantaneous application of the motor torque is not reflected in the sensor signal. It, and the gist.

  According to the electric power steering apparatus of the first aspect, the torsion bar provided on the steering shaft can be twisted by applying the instantaneous motor torque in the same direction as the assist force. Thus, the electric power steering apparatus according to claim 1 creates a situation where the timing and direction of change of the sensor signal can be naturally predicted, and monitors the change of the sensor signal of the torque sensor under such a situation. Thus, the abnormality can be detected at an early stage. In addition, the electric power steering apparatus according to the first aspect can continue to provide the assist force more stably even when the steering torque is detected using one sensor signal.

  According to a second aspect of the present invention, in the first aspect of the present invention, the torque sensor includes a plurality of output elements that output the sensor signal. Abnormality detection based on reflection in the sensor signal is a case where the application of the assist force is continued using the sensor signal output by the remaining output element after the remaining output element in which no failure is detected becomes one. The gist of this is

  The sensor signal abnormality detection based on the instantaneous application and reflection of the motor torque has a more remarkable effect in the case where the sensor signal includes a plurality of output elements that output the sensor signal. For example, even when any of the plurality of output elements fails, it is possible to continue to apply the assist force using the remaining sensor output by the remaining output elements in which the failure is not detected. As a result, the electric power steering apparatus according to claim 2 can further improve the reliability.

  According to a third aspect of the present invention, in the invention according to the first or second aspect, the control unit periodically applies the instantaneous motor torque and the abnormality detection unit. The gist is to determine that an output element corresponding to a sensor signal has failed when an abnormality of the sensor signal is detected a predetermined number of times. According to the said structure, the failure of an output element can be determined more correctly. As a result, it is possible to suppress the occurrence of erroneous determination and continue the assist force application more stably.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, when the abnormality of the sensor signal is detected, the control means shortens the period of applying the instantaneous motor torque. Is the gist.

  According to a fifth aspect of the present invention, in the invention according to the third or fourth aspect of the present invention, the control means includes the instantaneous motor until a failure is detected after the abnormality of the sensor signal is detected. The gist is to shorten the period in which the torque is applied.

  According to a sixth aspect of the present invention, in the invention according to the fourth or fifth aspect, the control means detects a normal sensor signal after shortening a cycle in which the instantaneous motor torque is applied. In this case, the gist is to lengthen the period to recover.

  That is, from the viewpoint of determining a failure quickly and with high accuracy, it is preferable that the instantaneous application period of the motor torque is shorter. However, the shortening of the application cycle acts in the direction of worsening the steering feeling. In this regard, according to each of the above-described configurations, it is possible to quickly and accurately determine the failure of the output element corresponding to the sensor signal while ensuring a good steering feeling when executing the assist continuation control.

  The invention according to claim 7 is the invention according to any one of claims 1 to 6, wherein the control means is configured so that the magnitude of the assist force is within a range from a predetermined upper limit value to a lower limit value. If so, the instantaneous motor torque is applied, and if the assist force is out of a range from a predetermined upper limit value to a lower limit value, the instantaneous motor torque to be applied is reduced. Or the application of the instantaneous motor torque is stopped.

  The electric power steering apparatus according to claim 7 limits the application of instantaneous motor torque when the magnitude of the assist force is within a predetermined range, and reduces the instantaneous motor torque to be applied in other ranges. Alternatively, by stopping the instantaneous application of the motor torque, the energization amount can be reduced and the heat generation in the motor or the like can be suppressed. In addition, when the magnitude of the assist force is out of the predetermined range for the application of instantaneous motor torque, the driver continuously diagnoses the failure of the torque sensor by continuously applying a small instantaneous motor torque. Can be recognized.

  The invention according to claim 8 is the invention according to any one of claims 1 to 7, further comprising a steering sensor for detecting a steering angle generated in the steering, wherein the control means is in the vicinity of the neutral position. When a predetermined steering angle range is set, and the steering angle detected by the steering sensor falls within the steering angle range and a predetermined time has elapsed, the magnitude of the instantaneous motor torque to be applied is reduced. Or the application of the instantaneous motor torque is stopped.

  In the electric power steering device according to the eighth aspect, when the steering angle shifts to a predetermined steering angle range set in the vicinity of the neutral position and does not reach the predetermined time, instantaneous motor torque is applied while When the time has elapsed, the magnitude of the instantaneous motor torque to be applied is reduced or the application of the instantaneous motor torque is stopped. Thus, the electric power steering device according to claim 8 prevents the abnormality detection from being interrupted every time the steering angle reaches the vicinity of the neutral position, and suppresses the energization amount after a predetermined time has passed, thereby preventing the motor or the like from being detected. Heat generation can be suppressed. In addition, after the steering angle reaches near the neutral position, the torque sensor is continuously diagnosed for failure by reducing the size and continuing to apply the instantaneous motor torque after a predetermined time has elapsed. Can be recognized.

  The invention according to claim 9 is the invention according to any one of claims 1 to 8, further comprising a steering sensor for detecting a steering angle generated in the steering within a predetermined detection range, and the control means. When the steering angle detected by the steering sensor exceeds the detection range of the steering sensor, the magnitude of the instantaneous motor torque to be applied is reduced or the application of the instantaneous motor torque is stopped. The gist is to do.

  That is, when the steering angle detected by the steering sensor exceeds the detection range of the steering sensor, the torsion bar provided on the steering shaft has already been greatly twisted. Therefore, even when instantaneous motor torque is applied in such a situation, it is difficult to detect the timing and direction of change of the sensor signal, and there is a risk of erroneous detection. Therefore, when the steering angle detected by the steering sensor exceeds the detection range of the steering sensor, the electric power steering device according to claim 9 stops the instantaneous application of the motor torque to reduce the energization amount. Heat generation can be suppressed. As a result, occurrence of erroneous detection can be eliminated.

  The invention described in claim 10 is the invention described in any one of claims 1 to 7, further comprising a current detector for detecting a current value flowing through the motor, wherein the control means is in the vicinity of the neutral position. A predetermined current value range is set, and when the current value detected by the current detector enters the current value range and a predetermined time has elapsed, the magnitude of the instantaneous motor torque to be applied is set. The gist is to reduce or stop the application of the instantaneous motor torque.

  The electric power steering device according to claim 10 applies an instantaneous motor torque when the actual current shifts to a predetermined current value range set in the vicinity of the neutral position and does not reach a predetermined time. When the time has elapsed, the magnitude of the instantaneous motor torque to be applied is reduced, or the application of the instantaneous motor torque is stopped. Thus, the electric power steering apparatus according to claim 10 prevents the abnormality detection from being interrupted every time the current value reaches the vicinity of the neutral position, and suppresses the energization amount after a predetermined period of time, thereby preventing the motor etc. Heat generation can be suppressed. In addition, after the actual current reaches near the neutral position, the torque sensor is continuously diagnosed for failure by reducing the magnitude and continuing to apply instantaneous motor torque even after a lapse of a predetermined time. Can be recognized.

  According to an eleventh aspect of the present invention, in the invention according to any one of the first to tenth aspects, the control means is configured to generate a current command value to generate the assist force corresponding to the steering torque. Feedback control means based on the deviation from the actual current flowing through the motor, and the feedback gain of the feedback control means is selected by the feedback gain determination means determined by the flag during the assist continuation control output from the abnormality detector. The feedback gain determining means, when the output element in which the failure is not detected becomes one remaining, and when the application of the assist force is continued using the sensor signal output by the remaining output element, Compared to the case where two or more remaining output elements in which the failure is not detected remain, the feed Kkugein be a large a, and the gist.

  In the electric power steering device according to claim 11, when the remaining output element is not detected and the remaining output element is continuously applied with the assist force using the sensor signal output, The feedback gain of the feedback control means is increased compared with the case where two or more output elements in which no failure is detected remain. Thus, the electric power steering apparatus according to claim 11 continues the application of the assist force using the sensor signal output by the remaining output element after the remaining one of the output elements in which no failure is detected remains. When an instantaneous application of motor torque occurs in order to improve the reliability of the torque sensor, the sensor signal output by the remaining output element can be output with good response.

  According to the present invention, it is possible to provide an electric power steering apparatus capable of continuing the application of assist force more stably when detecting a steering torque based on one sensor signal.

The schematic block diagram of an electric power steering device (EPS). The control block diagram of EPS. The control block diagram of the motor control signal output part of EPS. The flowchart which shows the aspect of the power assist control according to the abnormality generation mode of a torque sensor. The flowchart which shows the process sequence of abnormality detection of a residual sensor signal. A), B) The schematic block diagram of a gain map. FIG. 4 is an output diagram of basic assist control amounts and steering angles in a virtual steering state 1 with a vehicle. The output diagram of the basic assist control amount and the steering angle in a virtual steering state 2 where the vehicle is present. The output figure of the basic assist control amount and steering angle in the virtual steering state 3 with a vehicle. The flowchart which shows the process sequence of the state determination of a basic assist control amount. The flowchart which shows the process sequence of test torque control amount calculation. The output figure of the electric current command value and steering angle in the virtual steering state 1 with a vehicle. The output figure of the electric current command value and steering angle in the virtual steering state 2 with a vehicle. The output figure of the electric current command value and steering angle in the virtual steering state 3 with a vehicle. The output figure of a torque sensor at the time of application of instantaneous motor torque. The output figure of a torque sensor at the time of application of the instantaneous motor torque in the virtual steering state 1 with a vehicle. The flowchart which shows the process sequence of failure determination of the sensor element corresponding to a residual sensor signal. The flowchart which shows the process sequence regarding the change of the application period of instantaneous motor torque. Explanatory drawing which shows the application mode of the instantaneous motor torque at the time of assist continuation control.

Hereinafter, an embodiment in which the present invention is embodied in a column-type electric power steering apparatus 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 driving source is drivingly connected to a column shaft 3 a via a speed reduction mechanism 13. In the present embodiment, the motor 12 is a DC motor with a brush. 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, the ECU 11 is connected with a torque sensor 14, a vehicle speed sensor 15, and a steering sensor (steering angle sensor) 16 as a steering angle detection means. The ECU 11 detects the steering torque τ, the vehicle speed V, and the steering angle θs based on the output signals of these sensors.

  The torque sensor 14 of the present embodiment is a magnetic torque sensor using a magnetic detection element (Hall IC) as the sensor element (14a, 14b). 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 via 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) in which a magnetic flux change occurs due to torsion of the torsion bar 17, as described in Patent Document 1 above. 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 the torque input of 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 voltages of the sensor elements 14a and 14b, which fluctuate with the change in magnetic flux, to the ECU 11 as sensor signals Sa and Sb, respectively.

  Further, the steering sensor 16 of the present embodiment includes a rotor 18 fixed to the column shaft 3a and a sensor element (hole) for detecting a change in magnetic flux accompanying the rotation of the rotor 18 on the steering 2 side of the torque sensor 14. IC) 19 is a magnetic rotation angle sensor. The steering sensor 16 outputs the output voltage of the sensor element 19 that fluctuates with a change in magnetic flux to the ECU 11 as a sensor signal θs.

  In the present embodiment, the ECU 11 as torque detecting means detects the steering torque τ based on the sensor signals Sa and Sb output from the torque sensor 14, more specifically, the sensor elements 14a and 14b as output elements. The ECU 11 calculates a target assist force based on the steering torque τ and the vehicle speed V detected by the vehicle speed sensor 15, and drives the motor 12 as a drive source to generate the target assist force in the EPS actuator 10. By supplying power, 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.
FIG. 2 is a control block diagram of the EPS of this embodiment. As shown in the figure, 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. ing.

More specifically, the microcomputer 21 of the present embodiment is calculated by a current command value calculation unit 23 that calculates a current command value I * corresponding to a target assist force to be generated by the EPS actuator 10, and a current command value calculation unit 23. A motor control signal output unit 24 that outputs a motor control signal based on the current command value I *, a steering torque detection unit 25 that detects the steering torque τ based on the sensor signals Sa and Sb output from the torque sensor 14, and It is equipped with.
The current command value calculation unit 23 calculates Ias * as a basic component of the target assist force using the steering torque τ detected by the steering torque detection unit 25 and the vehicle speed V detected by the vehicle speed sensor 15. The steering torque detection unit 25 detects the steering torque τ with high accuracy by performing correction processing (temperature characteristics and the like) using the two systems of sensor signals Sa and Sb output from the torque sensor 14.

  As shown in FIG. 2, the current command value calculation unit 23 includes an assist control unit 26 that receives the steering torque τ and the vehicle speed V and generates a basic assist control amount Ias *. The assist control unit 26 sets a larger value (absolute value) so that the larger the steering torque τ (absolute value) is, or the smaller the vehicle speed V is, the greater assist force is applied to the steering system. A basic assist control amount Ias * is calculated. In the present embodiment, the calculation of the basic assist control amount Ias * as the basic component is performed using a vehicle speed sensitive three-dimensional map.

  In this way, the current command value calculation unit 23 uses the basic assist control amount Ias * calculated by the assist control unit 26 as the basic component of the target assist force in the power assist control to be supplied to the motor control signal output unit 24. Command value I * is calculated. The motor control signal output unit 24 receives the current command value I * calculated by the current command value calculation unit 23 and the actual current value I of the motor 12 detected by the current sensor (current detector) 27. Is done. Then, the motor control signal output unit 24 of the present embodiment generates a motor control signal by executing current feedback control so that the actual current value I follows the current command value I *.

  In the ECU 11 of this embodiment, the microcomputer 21 outputs the motor control signal generated in this way to the drive circuit 22. The drive circuit 22 controls the operation of the EPS actuator 10 by supplying drive power based on the motor control signal to the motor 12. Thereby, ECU11 performs the power assist control.

(Assist continuation control when torque sensor is abnormal)
Next, assist continuation control when the torque sensor is abnormal in the EPS of the present embodiment will be described.
As shown in FIG. 2, the current command value calculation unit 23 generates a FLG signal (in this embodiment, 0, 1, or 2) indicating the steering state of the vehicle from the basic assist control amount Ias * and the steering angle θs. An assist control amount determination unit 28 to be generated, a test torque control unit 31 that outputs a test torque control amount Itt * as a basic component of instantaneous motor torque based on the FLG signal input from the assist control unit 28, and an assist current The switching unit 29 and a timer 34 that measures an elapsed time Th after the vehicle shifts to the straight traveling state.

  Each time the test torque control unit 31 outputs the test torque control amount Itt *, the test torque control unit 31 outputs an application signal Sim indicating that an instantaneous motor torque based on the test torque control amount Itt * is applied to the abnormality detection unit 30. . Further, the test torque control unit 31 outputs the assist current switching signal Sich to the assist current switching unit 29 based on the FLG signal input from the assist control amount determination unit 28, and generates the instantaneous motor torque. The component test torque control amount Itt * is output to the adder 33. The test torque control amount Itt * output from the test torque control unit 31 is once such that the steering 2 hardly moves due to its inertia when an instantaneous motor torque is applied based on the test torque control amount Itt *. The hit output time (1 ms in this embodiment) is set.

  The assist current switching unit 29 switches the basic assist control amount Ias * by switching the contact P to either the contact Q or the contact R based on the assist current switching signal Sich output from the test torque control unit 31. That is, when the assist current switching signal Sich is “1”, the assist current switching unit 29 connects the contacts P and Q, and outputs the basic assist control amount Ias * input from the assist control unit 26 as it is. When the assist current switching signal Sich is “0”, the assist current switching unit 29 connects the contacts P and R and replaces the basic assist control amount Ias * input from the assist control unit 26 with “0 value”. Is output as the basic assist control amount Ias *.

  As shown in FIG. 2, the microcomputer 21 is provided with an abnormality detection unit 30 that detects an abnormality in each of the sensor signals Sa and Sb output from the torque sensor 14. The ECU 11 (microcomputer 21) determines the abnormality of the torque sensor 14 based on the abnormality detection of the abnormality detection unit 30. Then, the ECU 11 as the control unit and the abnormality detection unit executes the power assist control according to the abnormality generation mode of the torque sensor 14 detected by the abnormality detection unit 30.

  More specifically, as shown in the flowchart of FIG. 4, when the microcomputer 21 detects an abnormality of each sensor signal Sa, Sb in the abnormality detection unit 30 (step 101: YES), the flag ASFLG (indicating that the assist continuation control is being performed) 0 is written in the flag indicating the state quantity (memory) (step 102). Next, based on the result of abnormality detection detected in step 101, failure determination (detection) of each sensor element 14a, 14b, which is an output element of each sensor signal Sa, Sb, is executed (step 103). When it is determined that both of the sensor elements 14a and 14b have both failed (step 104: YES), the assist force is gradually reduced in order to quickly stop the power assist control and achieve failsafe. Control is executed (assist stop control, step 106). Further, the test torque control unit 31 stops outputting the test torque control amount Itt * based on the abnormality detection signal Str input from the abnormality detection unit 30.

  In the present embodiment, the abnormality detection for each of the sensor signals Sa and Sb in the above step 101 determines whether or not the values of the sensor signals Sa and Sb deviate from values that can be taken when normal, and The determination is made based on comparison and determination of each value and the amount of change in unit time (for example, see Patent Document 2). When normal sensor signals Sa and Sb are detected in step 101 (step 101: NO), the microcomputer 21 writes 0 in the flag ASFLG indicating that the assist continuation control is being performed (step 109). Assist control is executed (step 110).

  Further, the microcomputer 21 of the present embodiment determines that only one of the sensor elements 14a and 14b corresponding to the sensor signals Sa and Sb has failed in step 104 (step 104: NO). Detects the steering torque τ based on the sensor signal (residual sensor signal) output by the remaining sensor element. Then, 1 is written in the flag ASFLG indicating that the assist continuation control is in progress (step 107), and the power assist control using the remaining sensor signal is continued (assist continuation control, step 108).

  As shown in FIG. 2, the abnormality detection result of the sensor signals Sa and Sb executed by the abnormality detection unit 30 and the failure detection result of the corresponding sensor elements 14a and 14b are calculated as an abnormality detection signal Str. Is input to the unit 23 and the steering torque detection unit 25. Further, a flag ASFLG indicating that the assist continuation control is being performed is also input from the abnormality detection unit 30 to the motor control signal output unit 24. When the abnormality detection signal Str indicating that both of the sensor elements 14a and 14b corresponding to the sensor signals Sa and Sb have both failed is input to the current command value calculation unit 23, the current command value Stop the output of I *.

  When the abnormality detection signal Str indicates that only one of the sensor elements 14a and 14b has failed, the steering torque detection unit 25 uses the remaining sensor signal output by the sensor element that has not failed. The steering torque τ is detected. The EPS 1 of the present embodiment continues the calculation and output of the current command value I * using the steering torque τ detected from the remaining sensor signal, and performs the assist continuation control. In this case, the complementary processing using the two sensor signals Sa and Sb as described above is not executed.

  Next, the motor control signal output unit 24 will be described with reference to FIG. The motor control signal output unit 24 receives the current command value I *, the actual current value I, and the flag ASFLG indicating that the assist continuation control is being performed, and the motor control signal is output to the drive circuit 22. The motor control signal output unit 24 includes a subtractor 40 that calculates the difference between the current command value I * and the actual current value I, and a PI control calculation unit 41 that amplifies the current deviation value ΔI that is the output of the subtractor 40. . The voltage command value V * that is output from the PI control calculation unit 41 is input to the PWM calculation unit 42, and after the duty ratio is calculated, it is output from the PWM output unit 43 to the subsequent drive circuit 22 as a motor control signal.

  Further, the flag ASFLG indicating that the assist continuation control is being input, which is input to the motor control signal output unit 24, is input to the feedback gain determination unit 44 that determines the values of the proportional gain Kp and the integral gain Ki of the PI control calculation unit 41. The feedback gain determination unit 44 has two types of gain maps shown in A) and B) of FIG. That is, it is a gain map of ASFLG = 0 indicating normal control and ASFLG = 1 indicating assist continuation control. The ASFLG = 0 gain map indicating the normal control is a proportional gain Kp1 and an integral gain Ki1 (A in FIG. 6). A gain map of ASFLG = 1 indicating that the assist continuation control is in progress is a proportional gain Kp2 and an integral gain Ki2 (B in FIG. 6). Here, Kp1 <Kp2 and Ki1 <Ki2 are set. In this way, when an instantaneous application of motor torque occurs during the assist continuation control, the sensor signal output by the remaining output element can be output with good response.

  Here, when any one of the sensor elements 14a and 14b fails, it is natural that the abnormality determination (detection) based on the comparison with the other sensor signals as described above cannot be performed on the remaining sensor signal. Therefore, in the assist continuation control, the ECU 11 according to the present embodiment periodically applies instantaneous motor torque to the steering system in association with the application of the assist force, which is an essential function of the EPS, and corrects the remaining sensor signal abnormality. To detect. Specifically, when instantaneous motor torque is applied to the steering system, torsion bars 16 that constitute the steering system are caused by torsion caused by the instantaneous motor torque. The ECU 11 of the present embodiment detects an abnormality in the remaining sensor signal based on whether or not the twist caused by the instantaneous motor torque is reflected in the remaining sensor signal.

  That is, the EPS 1 of the present embodiment can detect the abnormality at an early stage before the residual sensor signal clearly shows an abnormal value by monitoring the change of the residual sensor signal. It has become. For example, as shown in FIG. 16, the EPS 1 of the present embodiment uses a test torque control amount Itt * as a control component for applying an instantaneous motor torque for a predetermined time tr (in this embodiment) from the time t (l). 1 ms), and instantaneous motor torque is applied to the steering system. When instantaneous motor torque is applied to the steering system, it is caused by instantaneous motor torque after a predetermined time trr (10 ms in this embodiment) from the time t (l) when the test torque control amount Itt * is output. Twisting occurs in the torsion bar. The EPS 1 measures the change amount Δτ of the steering torque τ at a predetermined time trr from the time when the test torque control amount Itt * is output, and the change amount Δτ is equal to or less than a predetermined value (in this embodiment, 0.5 Nm). As a condition, it is determined that the sensor element corresponding to the remaining sensor signal is abnormal.

  In the present embodiment, the instantaneous application of motor torque to the steering system is sized and the direction of application changes according to the steering state of the vehicle. A method for applying instantaneous motor torque will be described below assuming a specific vehicle steering state.

  7 to 9 are output diagrams of the basic assist control amount and the steering angle when a certain steering state of the vehicle is assumed. 7 to 9, the left vertical axis represents the basic assist control amount Ias *, the right vertical axis represents the steering angle θs, and the horizontal axis represents the time axis. Here, on the left vertical axis of FIGS. 7 to 9, a first predetermined current value Ia1 which is a + side test torque control amount and a second predetermined current value −Ia1 which is a − side test torque control amount are set. The first predetermined current value Ia1 and the second predetermined current value -Ia1 are values of the test torque control amount Itt *, which is a basic component for generating instantaneous motor torque, and are appropriately set according to the vehicle system and environment. The Further, the first predetermined current value Ia1 and the second predetermined current value -Ia1 indicate that the driver notices that one of the sensor elements 14a and 14b of the torque sensor 14 has failed, and the momentary inertia of the motor torque. Thus, the size is set such that the steering 2 hardly moves (60A in this embodiment).

  On the right vertical axis, the first predetermined steering angle θsl in the vicinity of the + side neutral position, the second predetermined steering angle θsmax that is the + side maximum steering angle, the third predetermined steering angle −θsl in the vicinity of the − side neutral position, and − A fourth predetermined steering angle −θsmax, which is the side maximum steering angle, is set. The first predetermined steering angle θsl and the third predetermined steering angle −θsl are reference values for determining whether the vehicle is traveling straight ahead. The second predetermined steering angle θsmax is the right end angle of the steering 2, and the fourth predetermined steering angle −θsmax is the left end angle of the steering 2.

  7 to 9 are divided into a plurality of zones (in this embodiment, six types of zones A to F) according to the steering state of the vehicle. Zone A is the cutting state when the steering wheel is steered to the right, Zone B is the switching back state when the steering wheel is steered to the right, Zone C is the straight running state with the steering wheel returned to neutral, and Zone D is the steering state When the steering wheel is steered to the left, zone E corresponds to a so-called end contact state in which the steering wheel is turned to the full left end, and zone F corresponds to a reversing state when the steering wheel is steered to the left. is doing.

  The steering state 1 in FIG. 7 is divided into four zones (zones A, B, D, and F). In the steering state 1, the steering angle θs is equal to or smaller than the second predetermined steering angle θsmax and equal to or larger than the fourth predetermined steering angle −θsmax in the entire steering region. Further, in the entire steering region, the basic assist control amount Ias * is not more than the first predetermined current value Ia1 and not less than the second predetermined current value -Ia1.

  Steering state 2 in FIG. 8 is divided into five zones (zones A, B, D, E, and F). In the steering state 2, the steering angle θs reaches the fourth predetermined steering angle −θsmax in the steering region of the zone E. Further, the basic assist control amount Ias * is a numerical value smaller than the second predetermined current value −Ia1 in the zone E steering region. That is, the steering state 2 is characterized in that the steering angle θs is larger than that in the steering state 1 and the end contact state is provided.

  The steering state 3 in FIG. 9 is divided into four zones (zones A, B, C, and D). In the steering state 3, in the steering region of the zone C, the steering angle θs is equal to or smaller than the first predetermined steering angle θsl and equal to or larger than the third predetermined steering angle −θsl. Further, the basic assist control amount Ias * is equal to or smaller than the first predetermined current value Ia1 and equal to or larger than the second predetermined current value −Ia1 in the entire steering region. That is, the steering state 3 has a straight traveling state.

  Next, a processing procedure in which the assist control amount determination unit 28 determines the steering state of the vehicle and generates the FLG signal from the vehicle steering state of FIGS. 7 to 9 will be described according to the flowchart of FIG.

  As shown in the flowchart of FIG. 10, the assist control amount determination unit 28 first determines whether or not the steering angle θs is equal to or smaller than the second predetermined steering angle θsmax (step 801). When the steering angle θs is equal to or smaller than the second predetermined steering angle θsmax (step 801: YES), the assist control amount determination unit 28 determines whether the steering angle θs is equal to or larger than the first predetermined steering angle θsl (step 802). When the steering angle θs is equal to or greater than the first predetermined steering angle θsl (step 802: YES), the assist control amount determination unit 28 determines whether or not the basic assist control amount Ias * (n) is equal to or less than the first predetermined current value Ia1. (Step 803).

  Here, n in parentheses indicates the nth sampling value. When the basic assist control amount Ias * (n) is equal to or smaller than the first predetermined current value Ia1 (step 803: YES), the assist control amount determination unit 28 assists because the steering angle θs is equal to or larger than the first predetermined steering angle θsl. Is in the positive region (in this embodiment, the vehicle is in the right cut-in state or the right switch-back state, that is, the vehicle is in the zone A or zone B steering state), and FLG (flag indicating state quantity: memory) ) Is written to 1 (step 804), and this process ends.

  In step 803, when the basic assist control amount Ias * (n) is larger than the first predetermined current value Ia1 (step 803: NO), the assist control amount determination unit 28 has already reached the upper limit value. It is determined that the value is 0, 0 is written in the FLG (step 805), and this process is terminated.

  In step 802, when the steering angle θs is less than the first predetermined steering angle θsl (step 802: NO), the assist control amount determination unit 28 determines whether the steering angle θs is equal to or smaller than a third predetermined steering angle −θsl. (Step 806). When the steering angle θs is equal to or smaller than the third predetermined steering angle −θsl (step 806: YES), the assist control amount determination unit 28 determines whether the steering angle θs is equal to or larger than the fourth predetermined steering angle −θsmax (step 807). ). When the steering angle θs is equal to or greater than the fourth predetermined steering angle −θsmax (step 807: YES), the assist control amount determination unit 28 determines whether the basic assist control amount Ias * (n) is equal to or greater than the second predetermined current value −Ia1. Is determined (step 808).

  When the basic assist control amount Ias * (n) is equal to or larger than the second predetermined current value −Ia1 (step 808: YES), the assist control amount determination unit 28 determines that the steering angle θs is equal to or smaller than the third predetermined steering angle −θsl. From this, it is determined that the magnitude of the assist force is in a negative region (in this embodiment, the left cut-in state or the left turn-back state, that is, the vehicle is in the steering state of zone D or zone F), and 2 is written in FLG ( Step 809), the process ends.

  In step 808, when the basic assist control amount Ias * (n) is less than the second predetermined current value −Ia1 (step 808: NO), the assist control amount determination unit 28 has already obtained the basic assist control amount Ias * (n). It is determined that the lower limit has been reached, 0 is written in the FLG (step 810), and this process ends.

  In step 807, when the steering angle θs is less than the fourth predetermined steering angle −θsmax (step 807: NO), the assist control amount determination unit 28 determines that the vehicle is in the end contact or in the vicinity thereof. , 0 is written in FLG (step 811), and this process is finished.

  In step 806, when the steering angle θs is larger than the third predetermined steering angle −θsl (step 806: NO), the assist control amount determination unit 28 determines that the vehicle is in a straight traveling state. Here, as shown in FIG. 2, the current command value calculation unit 23 is provided with a timer 34, and the assist control amount determination unit 28 sends a reset signal Sk to the timer 34 when the vehicle moves straight. Is output, and an elapsed time Th after the vehicle shifts to the straight traveling state is measured.

  In the flowchart of FIG. 10, the assist control amount determination unit 28 determines whether or not the elapsed time Th is equal to or shorter than the straight traveling state determination predetermined time th (1 s in the present embodiment) (step 812). When the straight traveling state determination time Th is less than or equal to the straight traveling state determination predetermined time th (step 812: YES), the assist control amount determination unit 28 determines whether or not the basic assist control amount Ias * (n) is 0 or more (step) 813).

  When the basic assist control amount Ias * (n) is 0 or more (step 813: YES), the assist control amount determination unit 28 determines that the magnitude of the assist force is in the positive region in the zone C, and sets 1 to FLG. Write (step 814), the process is terminated. In Step 813, when the basic assist control amount Ias * (n) is less than 0 (Step 813: NO), the assist control amount determination unit 28 determines that the magnitude of the assist force is in the negative region in the zone C. Then, 2 is written in the FLG (step 815), and this process is finished.

  In step 812, when the elapsed time Th is greater than the straight traveling state determination predetermined time th (step 812: NO), the assist control amount determination unit 28 determines that the vehicle has shifted to the straight traveling state of the zone C and has passed a predetermined time. Determination is made and 0 is written in the FLG (step 816), and this processing is terminated.

  In step 801, when the steering angle θs is equal to or larger than the second predetermined steering angle θsmax (step 801: NO), the assist control amount determination unit 28 determines that the vehicle is in the end contact or in the vicinity thereof, and sets the FLG. 0 is written (step 817), and this processing is terminated.

  Next, the function of the test torque control unit 31 will be described. As shown in FIGS. 12 to 14, the test torque control unit 31 determines the test torque control amount Itt * (instantaneous occurrence) at the timings t1 to t13 on the time axis based on the FLG signal received from the assist control amount determination unit 28. Output of typical motor torque). It should be noted that the intervals between the time points t1, t2, t3,... At which the test torque control amount Itt * is output are longer than the test torque control amount output time tr at which the test torque control amount Itt * is output. Is set.

  Hereinafter, the test torque control amount calculation method executed by the test torque control unit 31 will be described in detail using the flowchart of FIG. First, the test torque control unit 31 determines whether or not the FLG input from the assist control amount determination unit 28 is 0 (step 901). When FLG is 0 (step 901: YES), the test torque control unit 31 writes 0 in the test torque control amount Itt * (m) (memory) (step 906), and the process is terminated. Here, m in parentheses indicates that the current value is the mth sampling value. The sampling number of the basic assist control amount Ias * is n and the sampling number of the test torque control amount Itt * is m. In this embodiment, the sampling of the basic assist control amount Ias * and the test torque control amount Itt * is performed. This is because the period is different.

In the present embodiment, the following three cases are assumed as a case where 0 is written in the test torque control amount Itt * (m), that is, a case where FLG is 0.
In the first case, the basic assist control amount Ias * has reached the first predetermined current value Ia1 (upper limit value) or the second predetermined current value −Ia1 (lower limit value), and the basic assist control amount Ias * Even if the test torque control amount Itt * is applied, the torque change is small and it is difficult to detect an abnormality of the torque sensor (step 805: NO, step 810: NO in FIG. 10). Therefore, when the test torque control amount Itt * is larger than the upper limit value or smaller than the lower limit value, the test torque control unit 31 of the present embodiment stops the instantaneous application of the motor torque.

  The second case is a zone E in FIG. In this case, since the steering is hitting the mechanical end, no torque change occurs even if the test torque control amount Itt * is applied to the basic assist control amount Ias *. Therefore, the test torque control unit 31 stops application of instantaneous motor torque.

  The third case is a case where a predetermined time Th has elapsed after the vehicle has shifted to zone C in FIG. The straight traveling state is a state in which the steering angle θs is in a very narrow range between the first predetermined steering angle θsl and the third predetermined steering angle −θsl, and the basic assist control amount Ias * is almost a value of 0. It is. Therefore, the test torque control unit 31 is configured to stop the application of instantaneous motor torque even in this case. Thereby, the EPS 1 can reduce the amount of energization and suppress the heat generation of the motor and the ECU 11.

  In step 901 of the flowchart of FIG. 11, when FLG is not 0 (step 901: NO), the test torque control unit 31 determines whether FLG is 1 (step 902). When FLG is 1 (step 902: YES), the test torque control unit 31 writes 0 to Ias * (n) and also writes the first predetermined current value Ia1 to Itt * (m) (step 905). End processing.

  When FLG is 1, the basic assist control amount Ias * is a positive value and is equal to or less than the first predetermined current value Ia1 (the vehicle is in the right cut state or the right turn back state: zone A or zone B), or the vehicle is traveling straight ahead. Transition to the state (zone C) is within a predetermined time th and the basic assist control amount Ias * is a positive value. When FLG is 1, the test torque control unit 31 performs setting such that the test torque control amount Itt * becomes the first predetermined current value Ia1.

  When FLG is not 1 (step 902: NO), the test torque control unit 31 determines whether FLG is 2 (step 903). When FLG is 2 (step 903: YES), the test torque control unit 31 writes 0 to Ias * (n) and writes the second predetermined current value −Ia1 to Itt * (m) (step 904). This process ends.

  When FLG is 2, this means that the basic assist control amount Ias * is a negative value and is equal to or greater than the second predetermined current value −Ia1 (the vehicle is in the left cut-in state or the left turn-back state: zone D or zone F), Transition to the running state (zone C) is within a predetermined time th and the basic assist control amount Ias * is in a negative value state. When FLG is 2, the test torque control unit 31 performs setting such that the test torque control amount Itt * becomes the second predetermined current value −Ia1. If FLG is not 2 in step 903 (step 903: NO), the test torque control unit 31 ends this process without doing anything.

  In each of FIGS. 12 to 14, the algorithm shown in FIGS. 10 and 11 is applied to the vehicles in the respective steering states of FIGS. 7 to 9, and the test torque control amount is added to the basic assist control amount Ias *. It is a waveform of the current command value I * and the steering angle θs on which Itt * is superimposed. In the EPS 1 of the present embodiment, as shown in FIGS. 12 to 14, the magnitude of the test torque control amount Itt * is set so that the steering angle θs is hardly affected by the instantaneous application of the motor torque. ing.

  Here, the characteristics of the waveform in FIG. 13 are at time points t10 and t11. At time points t10 and t11 in FIG. 13, the vehicle steering 2 is in the mechanical end contact state (zone E). In this case, as described above, since the steering torque does not change even when the test torque control amount Itt * is applied, the test torque control unit 31 stops applying the test torque control amount Itt *. Thereby, it is possible to suppress the energization amount to the ECU 11 and suppress the heat generation of the motor and the ECU 11.

  The characteristic of the waveform in FIG. 14 is in the interval from time t6 to t11. The section from time t6 to t11 is a so-called straight traveling state (zone C) in which steering is performed near the neutral position of the steering wheel. As can be seen from FIG. 14, in a section where the vehicle shifts to the steering state of zone C and the elapsed time Th is less than the straight traveling state determination predetermined time th, the test torque control amount Itt * is set according to the algorithm of FIGS. Output. On the other hand, the output of the test torque control amount Itt * is stopped in a section (t9 to t11) in which the elapsed time Th has passed the straight traveling state determination predetermined time th. Thereby, it is possible to suppress the energization amount to the ECU 11 and suppress the heat generation of the motor and the ECU 11.

Next, the abnormality determination method for the torque sensor 14 will be specifically described with reference to FIGS. 15 and 16.
FIG. 15 is a graph showing the current command value I * and the steering torque τ when the algorithm shown in FIGS. 10 and 11 is applied to the vehicle in the steering state of FIG. FIG. 16 is an enlarged graph of a part of FIG. 15 and 16, the left vertical axis represents the current command value I * in which the test torque control amount Itt * is superimposed on the basic assist control amount Ias *. The right vertical axis represents the steering torque τ detected by the torque sensor 14, and the horizontal axis represents the time axis.

  FIG. 15 and FIG. 16 show how the steering torque τ detected by the torque sensor fluctuates when an instantaneous motor torque is applied to the steering system. The steering state of the vehicle in FIG. 16 represents a cutting state when the steering wheel is steered to the right (for example, zone A in FIG. 7), and at time t (l) when the basic assist control amount Ias * increases. The test torque control amount Itt * is output for a predetermined time tr (for example, 1 ms in this embodiment).

  As a result, instantaneous motor torque is applied to the steering system, and after a predetermined time trr (10 ms in the present embodiment) from the time t (l) when the test torque control amount Itt * is output, Torsion caused by instantaneous motor torque occurs. The abnormality detection unit 30 remains when the change amount Δτ of the steering torque τ is equal to or less than a predetermined value (in this embodiment, for example, 0.5 Nm) at a predetermined time trr from the time when the test torque control amount Itt * is output. The sensor element corresponding to the sensor signal is determined to be abnormal.

  Further, as shown in FIG. 2, every time the test torque control unit Itt * outputs the test torque control amount Itt *, the test torque control unit 31 of the present embodiment applies instantaneous motor torque based on the test torque control amount Itt *. Is output to the abnormality detection unit 30. The abnormality detection unit 30 of the present embodiment performs abnormality detection of the remaining sensor signal during the assist continuation control based on the applied signal Sim.

  That is, as shown in the flowchart of FIG. 5, the abnormality detection unit 30 determines whether or not the flag ASFLG indicating that the assist continuation control is being performed is 1 (step 201). If ASFLG is 1 (step 201: YES), the assist continuation control gain map (FIG. 6, B)) is selected (step 202), and the application signal Sim is input (step 203: YES). In step 204, it is determined whether or not the instantaneous application of the motor torque indicated by the application signal Sim is reflected in the input residual sensor signal. As shown in FIG. 16, in this embodiment, whether or not the instantaneous application of the motor torque is reflected in the residual sensor signal is determined according to the appropriate application of the instantaneous motor torque. This is performed based on whether the residual sensor signal changes at the timing (within a predetermined time trr) and whether the direction and magnitude of the change are appropriate values.

  When the instantaneous sensor torque is reflected in the residual sensor signal (step 204: YES), the abnormality detection unit 30 determines that the residual sensor signal is normal (step 205) and is not reflected. If so (step 204: NO), it is determined that the remaining sensor signal is abnormal (step 206). If ASFLG is not 1 (step 201: NO), the normal control gain map (FIG. 6, A)) is selected (step 207), and this process ends.

  As shown in FIG. 2, the microcomputer 21 of the present embodiment is provided with a timer 32, and the abnormality detection unit 30 detects the abnormality of the remaining sensor signal as described above (FIG. 5). Reference, step 206), the timer 32 is used to measure the elapsed time Td from the first abnormality detection. Then, the abnormality detection unit 30 according to the present embodiment detects the sensor corresponding to the remaining sensor signal when the abnormality detection is performed a predetermined number of times (N0) before the elapsed time Td exceeds the failure detection predetermined time td. It is determined that the element has failed.

  Specifically, as shown in the flowchart of FIG. 17, when the abnormality detection unit 30 detects an abnormality in the remaining sensor signal (step 301: YES), the failure determination for the sensor element corresponding to the remaining sensor signal has already been performed. It is determined whether it is in the middle (step 302). If failure determination has not yet been performed (step 302: NO), that is, if the abnormality detection in step 301 is the first abnormality detection that is the starting point of failure determination, a failure determination flag is set. (Step 303).

  That is, the determination of whether or not the failure is being determined in step 302 is made based on whether or not the failure determination flag shown in step 303 is set. After the failure determination flag is set, the abnormality detection unit 30 outputs a reset signal Sre to the timer 32 (step 304), and starts measuring the failure detection elapsed time Td, whereby the remaining sensor in which the abnormality is detected. A failure determination process is executed for the sensor element corresponding to the signal.

  As described above, when the failure determination process is started by executing Step 303 and Step 304, or when it is determined in Step 302 that the failure determination has already been performed (Step 302: YES), the abnormality detection unit 30 continues. Then, the counter for counting the number N of abnormal detections is incremented (N = N + 1, step 305). When it is determined that the abnormality detection number N is equal to or greater than the predetermined number N0 (N ≧ N0, step 306: YES), it is determined that the sensor element corresponding to the remaining sensor signal has failed (step 307). ).

  On the other hand, when it is determined in step 306 that the abnormality detection number N is less than the predetermined number N0 (N <N0, step 306: NO), the abnormality detection unit 30 continues to detect failure detection from the timer 32. Time Td is acquired (step 308). Then, it is determined whether or not the failure detection elapsed time Td is equal to or greater than the failure detection predetermined time td (step 309). When it is determined that the failure detection elapsed time Td is equal to or greater than the failure detection predetermined time td (Td ≧ td, step 309: YES). Determines that the sensor element corresponding to the remaining sensor signal is normal when the failure detection predetermined time td is exceeded (time over) (step 310).

  Thereafter, the abnormality detection unit 30 resets the failure determination flag (step 311), resets the counter (N = 0, step 312), and ends the series of failure determination processing. When it is determined in step 309 that the failure detection elapsed time Td is less than the failure detection predetermined time td (Td <td, step 309: NO), the processing of steps 310 to 312 is not executed.

  Further, as shown in FIG. 19, the test torque control unit 31 of the present embodiment performs the pre-abnormality detection after the time when the abnormality of the remaining sensor signal is detected during the assist continuation control (time t21 in the figure). The output cycle of the test torque control amount Itt * is shortened so that the output cycle f2 after the abnormality detection is shorter than the output cycle f1 (f1> f2). Thereby, while the failure determination of the sensor element corresponding to the remaining sensor signal is being executed, the period for applying the instantaneous motor torque is shortened.

  In addition, after the abnormality of the remaining sensor signal is detected and the output cycle of the test torque control amount Itt * is shortened, the remaining sensor signal may return to normal again (after time t22 in the figure). In this case, the test torque control unit 31 of the present embodiment is configured to return the output period of the test torque control amount Itt * from f2 to f1 again.

  That is, from the viewpoint of determining a failure quickly and with high accuracy, it is preferable that the instantaneous application period of the motor torque is short. However, such shortening of the application cycle acts in the direction of worsening the steering feeling. In consideration of this point, the EPS 1 of the present embodiment shortens the instantaneous motor torque application cycle only during the execution of the residual sensor signal failure determination, and when the residual sensor signal returns to a normal value, Immediately set the original motor cycle to the original cycle. Thereby, EPS1 of this embodiment can perform failure determination of the sensor element corresponding to the remaining sensor signal quickly and with high accuracy while ensuring a good steering feeling during execution of the assist continuation control. is there.

  More specifically, as shown in the flowchart of FIG. 18, the test torque control unit 31 determines whether or not the flag ASFLG indicating that the assist continuation control is being performed is 1 (step 401). Then, when the flag ASFLG indicating that the assist continuation control is being performed is 1 (step 401: YES), it is determined whether or not the sensor element failure determination by the abnormality detection unit 30 is performed (step 402). Note that the test torque control unit 31 of the present embodiment is configured to acquire the result of the failure determination performed by the abnormality detection unit 30 based on the abnormality detection signal Str output from the abnormality detection unit 30. If it is determined that the failure determination is not being executed (step 402: NO), the test torque control amount Itt * is output in the basic cycle (see FIG. 19, output cycle f1) (step 402). 403).

  On the other hand, when it is determined in step 402 that the failure determination is being performed (step 402: YES), the test torque control unit 31 first determines whether or not the failure of the sensor element corresponding to the remaining sensor signal is confirmed. Is determined (step 404). If the failure of the sensor element corresponding to the remaining sensor signal has not been determined (step 404: NO), the test torque control unit 31 determines whether or not the sensor element corresponding to the remaining sensor signal is normal. Determination is made (step 405). As a result, when the normality of the sensor element corresponding to the remaining sensor element is not determined, that is, when the abnormality of the sensor element continues (step 405: NO), the test torque control unit 31 performs the basic cycle ( The test torque control amount Itt * is output in a short cycle shorter than f1) (see FIG. 19, output cycle f2) (step 406).

  Conversely, when the normality of the sensor element corresponding to the remaining sensor signal is determined in step 405, that is, when the sensor element returns to normal (step 405: YES), in step 403, the basic cycle is determined. The output of the test torque control amount Itt * in (f1) is executed. Note that the test torque control amount Itt * is not output when the flag ASFLG indicating that the assist continuation control is in progress is not 1 (step 401: NO) and when a failure of the sensor element is confirmed (step 404: YES). .

As described above, according to the present embodiment, the following operations and effects can be obtained.
(1) When a failure of any one of the sensor elements 14a and 14b constituting the torque sensor 14 is detected, the ECU 11 outputs a sensor signal (residual sensor signal) output from the sensor element that has not detected the failure. ) Is used to continue the power assist control (assist continuation control). Further, when the assist continuation control is executed, the ECU 11 controls the operation of the EPS actuator 10 so as to apply a momentary motor torque periodically to the steering system in the same direction as the assist force. Then, the abnormality of the residual sensor signal is detected based on whether or not the instantaneous application of the motor torque is reflected in the residual sensor signal that is the basis of the assist continuation control.

  According to the above configuration, when the instantaneous motor torque is applied, the torsion bar 16 provided on the steering shaft 3 constituting the steering system is largely twisted, whereby the timing and change of the remaining sensor signal change. You can create a situation where you can naturally predict the direction. Under such circumstances, by monitoring the change in the residual sensor signal, the abnormality can be detected at an early stage before the residual sensor signal clearly shows an abnormal value. As a result, even when assist control using the remaining sensor signal is executed, it is possible to continue providing the assist more stably.

  (2) The ECU 11 periodically applies instantaneous motor torque to the steering system. Then, the ECU 11 determines that the sensor element corresponding to the remaining sensor signal has failed when the abnormality is detected for the remaining sensor signal for a predetermined number of times (N0) within the predetermined failure detection time (td). . According to the above configuration, the failure of the sensor element can be determined more accurately. As a result, it is possible to suppress the occurrence of erroneous determination and continue the assist force application more stably.

  (3) The ECU 11 shortens the period of applying the instantaneous motor torque while executing the failure determination for the sensor element corresponding to the remaining sensor signal. That is, from the viewpoint of determining a failure quickly and with high accuracy, it is preferable that the instantaneous application period of the motor torque is shorter. However, such shortening of the application cycle acts in the direction of worsening the steering feeling. In this regard, according to the above-described configuration, it is possible to quickly and accurately determine the failure of the sensor element corresponding to the remaining sensor signal while ensuring a good steering feeling during execution of the assist continuation control. As a result, it is possible to continue providing the assist force more stably.

  (4) The ECU 11 shifts to a so-called straight traveling state in which steering is performed near the neutral position of the steering wheel, and in a section where the elapsed time Th is less than the predetermined time th for determining the straight traveling state, the test torque control amount is determined according to the algorithm of FIGS. Outputs Itt *. On the other hand, output of the test torque control amount Itt * is stopped in a section where the elapsed time Th has passed the straight traveling state determination predetermined time th. Thereby, it is possible to suppress the energization amount to the ECU 11 and suppress the heat generation of the motor and the ECU 11.

  (5) The control means includes feedback control means based on a deviation between the current command value and the actual current flowing through the motor so as to generate an assist force corresponding to the steering torque, and the feedback gain of the feedback control means is an abnormality detector. Selected by the feedback gain determining means determined by the flag during the assist continuation control output from the feedback gain determining means, after the output element in which no failure is detected becomes one remaining, the remaining output element outputs When the assist force is continuously applied using the sensor signal, the feedback gain is increased as compared with the case where two or more output elements in which no failure is detected remain. In order to improve the reliability of the remaining torque sensor by continuously applying the assist force using the sensor signal output by the remaining output element after the remaining one output element has no failure detected. When a momentary application of motor torque occurs, the sensor signal output by the remaining output elements can be output with good response.

In addition, you may change each said embodiment as follows.
In the embodiment described above, the present invention is embodied in detecting an abnormality of the torque sensor 14 that outputs the two sensor signals Sa and Sb. However, the present invention is not limited to this, and the invention may be applied to abnormality detection of a torque sensor that outputs three or more sensor signals. That is, in the case of having three or more sensor signal output elements, the assist force is applied using the sensor signal output by the remaining output element after the remaining output element in which no failure is detected becomes one. It may be applied when continuing.

The present invention may also be applied to abnormality detection for an EPS torque sensor that detects steering torque using a single sensor signal. That is, the abnormality detection based on the instantaneous application of the motor torque and the reflection to the sensor signal is not necessarily limited to the temporary control (at the time of assist continuation control) after the abnormality of the torque sensor is detected. You may perform also at the time of control. Thereby, higher reliability can be ensured.

In the above embodiment, the calculation cycle is the same in the steering torque calculation cycle during normal control when both torque sensors are normal and during assist continuation control when one torque sensor is abnormal, but assist continuation control when one torque sensor is abnormal Sometimes, in order to reflect the instantaneous application of motor torque in the sensor signal, the steering torque calculation period during the assist continuation control when one torque sensor is abnormal is longer than the steering torque calculation period during normal control when both torque sensors are normal. Of course.

In the above embodiment, during the assist continuation control when one torque sensor is abnormal, instantaneous application of motor torque is reflected in the sensor signal to determine the abnormality of the one torque sensor, but when the reflected sensor signal suddenly changes Of course, the assist continuation control may be stopped.

-Although it did not mention in particular in the said embodiment, what kind of thing may be sufficient about the magnetic detection element which comprises the sensor element which uses a sensor signal as an output element. Further, the present invention may be applied to abnormality detection other than a magnetic torque sensor.

In the above embodiment, a predetermined steering angle range is set in the vicinity of the neutral position of the steering sensor 16 and it is determined whether or not the vehicle is traveling straight, but the present invention is not limited to such a configuration. Absent. Instead of the steering sensor 16, a current sensor 27 may be used, and a predetermined current value range near the neutral position may be set in the current sensor detection range to determine whether or not the vehicle is in a straight traveling state.

In the above embodiment, the application of the instantaneous motor torque is stopped when the FLG generated by the assist control amount determination unit 28 is 0. However, the present invention is not limited to such a configuration. Absent. For example, when the FLG generated by the assist control amount determination unit 28 is 0, the value of the test torque control amount Itt *, which is a basic component for generating instantaneous motor torque, is set to the first predetermined current value Ia1 or the first The current value may be changed to a current value smaller than the predetermined current value -Ia1 (for example, about 1/3), and an instantaneous motor torque may be applied. By doing so, it is possible to make the driver recognize that the fault diagnosis of the torque sensor is constantly performed.

In the above embodiment, instantaneous motor torque is periodically applied to the steering system. However, the present invention is not limited to this, and a configuration may be employed in which instantaneous motor torque is randomly applied and abnormality of the residual sensor signal is detected based on whether or not the residual sensor signal is reflected.

  In the above-described embodiment, when an abnormality is detected a predetermined number (N0) or more within the failure detection predetermined time (td), the failure of the sensor element as the output element corresponding to the remaining sensor signal is determined. did. However, the present invention is not limited to this, and the time may not be over when the predetermined time T0 is exceeded, and a configuration in which a failure of the corresponding sensor element is determined by one abnormality detection may be employed. Needless to say, a configuration in which a failure is determined by detecting an abnormality a plurality of times and a time limit is set for the failure determination, as in the above-described embodiment, is more preferable.

In the above embodiment, the period for applying the instantaneous motor torque is shortened while the failure determination is performed on the sensor element corresponding to the remaining sensor signal. However, the present invention is not limited to this, and the application cycle may be changed according to the number N of abnormal detections of the remaining sensor signal. With such a configuration, it is possible to perform failure determination of the sensor element corresponding to the remaining sensor signal more quickly and with high accuracy while ensuring a good steering feeling during execution of the assist continuation control. .
In this case, whether or not the application period is restored to the basic period (see FIG. 17, output period f1) after the sensor element is determined to be normal by the failure determination, or is kept shortened. May be arbitrarily selected depending on the point of emphasis, that is, whether the emphasis is on ensuring good steering feeling or the importance of early failure detection.

In each of the above embodiments, a brushed DC motor is used as the motor 12 that is the drive source of the EPS actuator 10. However, the present invention is not limited to this, and the invention may be embodied to use a brushless motor or an induction motor. In particular, when the instantaneous motor torque application period is changed in accordance with the steering speed as described above, a rotation angle sensor of a brushless motor may be used to detect the steering speed.

In each of the above embodiments, 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.

1: electric power steering device (EPS), 2: steering, 3: steering shaft, 3a: column shaft, 10: EPS actuator, 11: ECU,
12: motor, 14: torque sensor, 14a, 14b: sensor element, 15: vehicle speed sensor, 16: steering sensor, 17: torsion bar, 21: microcomputer, 22: drive circuit, 23: current command value calculation unit, 24: Motor control signal output unit, 25: steering torque detection unit, 26: assist control unit, 27: current sensor, 28: assist control amount determination unit, 29: assist current switching unit, 30: abnormality detection unit, 31: test torque control Unit, 32: timer, 33: adder, 40: subtractor, 41: PI control calculation unit, 42: PWM calculation unit,
43: PWM output unit, 44: Feedback gain determination unit,
θs: steering angle, τ: steering torque, Sa, Sb: sensor signal, V: vehicle speed, I *: current command value, Ias *: basic assist control amount, Itt *: test torque control amount,
Sim: Test torque application signal, Str: Abnormality detection signal,
FLG: vehicle steering state determination flag,
ASFLG: Assist continuous control flag, Sre: Timer reset signal,
Kp1, Kp2: proportional gain, Ki1, Ki2: integral gain,
Sich: Assist current switching signal, θsl: First predetermined steering angle near the + side neutral position,
θsmax: a second predetermined steering angle which is the + side maximum steering angle, −θsl: a third predetermined steering angle in the vicinity of the −side neutral position, −θsmax: a fourth predetermined steering angle which is the −side maximum steering angle, Ia1: + First predetermined current value that is the side test torque control amount, -Ia1: second predetermined current value that is the-side test torque control amount, Ias * (n): current value of the basic assist control amount, Itt * (m): test Torque control amount this value,
N: number of times of abnormality detection, N0: predetermined number of times, Td: failure detection elapsed time, td: failure detection predetermined time, Th: straight-ahead state determination time, th: straight-ahead state determination predetermined time, tr: test torque control amount output time, trr : Steering torque change measurement time, t (l): Test torque control amount application time, Δτ: Steering torque change amount, f1, f2: Test torque control amount output cycle

Claims (11)

A steering force assist device that applies assist force to the steering system using a motor as a drive source;
A torque sensor that outputs a sensor signal based on torsion of a torsion bar provided in the middle of the steering shaft;
Torque detecting means for detecting a steering torque based on the sensor signal;
Control means for controlling the operation of the steering force assisting device to generate the assist force corresponding to the steering torque;
An abnormality detecting means for detecting an abnormality of the sensor signal,
The control means controls the operation of the steering force assisting device to apply instantaneous motor torque to the steering system in the same direction as the assist force;
The abnormality detecting means detects an abnormality of the sensor signal when the instantaneous application of the motor torque is not reflected in the sensor signal;
An electric power steering device. The torque sensor has a plurality of output elements that output the sensor signal,
The instantaneous application of the motor torque by the control unit and the abnormality detection by the abnormality detection unit are performed using sensor signals output from the remaining output elements after the remaining one of the output elements in which no failure is detected. To be performed when the assist force is continuously applied;
The electric power steering apparatus according to claim 1. The control means periodically applies the instantaneous motor torque,
When the abnormality detection means detects an abnormality of the sensor signal a predetermined number of times,
Determining that the output element corresponding to the sensor signal has failed;
The electric power steering apparatus according to claim 1 or 2, wherein The control means shortens the period of applying the instantaneous motor torque when an abnormality of the sensor signal is detected,
The electric power steering apparatus according to claim 3. The control means shortens a cycle of applying the instantaneous motor torque until an abnormality of the sensor signal is detected and it is determined as a failure.
The electric power steering apparatus according to claim 3 or 4, characterized in that: The control means, after shortening the period of applying the instantaneous motor torque, if a normal sensor signal is detected, increasing the period to recover the period,
6. The electric power steering apparatus according to claim 4 or 5, wherein: If the magnitude of the assist force is within a range from a predetermined upper limit value to a lower limit value, the control means applies the instantaneous motor torque,
If the magnitude of the assist force is outside the range from a predetermined upper limit value to a lower limit value, the magnitude of the instantaneous motor torque to be applied is reduced, or the application of the instantaneous motor torque is stopped. thing,
The electric power steering apparatus according to any one of claims 1 to 6, wherein A steering sensor for detecting a steering angle generated in the steering;
The control means sets a predetermined steering angle range near the neutral position,
When the steering angle detected by the steering sensor falls within the steering angle range and a predetermined time has elapsed, the magnitude of the instantaneous motor torque to be applied is reduced, or the instantaneous motor torque Stopping the application of
The electric power steering apparatus according to any one of claims 1 to 7, wherein A steering sensor that detects a steering angle generated in the steering in a predetermined detection range;
When the steering angle detected by the steering sensor exceeds the detection range of the steering sensor, the control means reduces the magnitude of the instantaneous motor torque to be applied, or reduces the instantaneous motor torque. Stop applying,
The electric power steering apparatus according to any one of claims 1 to 8, wherein A current detector for detecting a current value flowing through the motor;
The control means sets a predetermined current value range near the neutral position,
When the current value detected by the current detector falls within the current value range and a predetermined time has elapsed, the magnitude of the instantaneous motor torque to be applied is reduced, or the instantaneous motor Stop applying torque,
The electric power steering apparatus according to any one of claims 1 to 7, wherein The control means includes feedback control means based on a deviation between a current command value and an actual current flowing through the motor to generate the assist force corresponding to the steering torque,
The feedback gain of the feedback control means is selected by a feedback gain determination means determined by a flag during assist continuation control output from the abnormality detector,
When the feedback gain determination means continues to provide the assist force using the sensor signal output by the remaining output element after the remaining output element in which the failure is not detected becomes one, Compared to the case where two or more remaining output elements in which no failure is detected remain, the feedback gain is increased,
The electric power steering device according to any one of claims 1 to 10, wherein

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