JP5708572B2 - Electric power steering device for vehicle - Google Patents

Description

  The present invention relates to an electric power steering device for a vehicle that generates a steering assist torque by driving a motor based on a steering operation of a driver.

  2. Description of the Related Art Conventionally, an electric power steering apparatus detects a steering torque input by a driver to a steering wheel using a torque sensor, and calculates a target assist torque based on the detected steering torque. Then, the steering operation of the driver is assisted by controlling the current flowing through the motor so as to obtain the target assist torque. Such energization control of the motor is called assist control.

  If the torque sensor fails, the target assist torque cannot be calculated and assist control cannot be performed. On the other hand, Patent Document 1 proposes an electric power steering device that performs steering assist even when a torque sensor fails. In the electric power steering apparatus proposed in Patent Document 1, when a failure of the torque sensor is detected, a detection signal is detected from the steering angle sensor that detects the steering angle of the steering wheel and the tire angle sensor that detects the tire angle. The steering torque is estimated from the detected steering angle and tire angle. Specifically, the steering torque is calculated by multiplying the deviation (torsion angle of the torsion bar) between the steering angle and the tire angle by the spring constant of the torsion bar of the torque sensor.

JP 2006-143151 A

  However, the electric power steering device proposed in Patent Document 1 requires a new sensor called a tire angle sensor, and the configuration becomes large. Patent Document 1 also describes that a detected value of a motor rotation angle used for a brushless motor is used instead of the tire angle sensor. However, the motor rotation angle sensor detects the relative angle between the stator and the rotor of the motor, and the origin at the steering angle does not coincide with the origin at the motor rotation angle. In this case, for example, if the relationship between the origin at the motor rotation angle and the origin at the steering angle is calculated, then the torsion angle of the torsion bar can be detected using the motor rotation angle and the steering wheel steering angle. However, since the motor rotation angle sensor is reset when the vehicle is started (when the ignition switch is turned on), the relationship cannot be used. Therefore, the steering assist cannot be started after the vehicle is started.

  The present invention has been made to cope with the above-described problem, and an object of the present invention is to enable steering assist to be started from the start of a vehicle when a torque sensor failure is detected.

In order to achieve the above object, a feature of the present invention is based on the degree of twist of the torsion bar (12t) interposed in the steering mechanism (10) that connects the steering handle (11) and the wheels (Wfl, Wfr). A torque sensor (21) for detecting a steering torque input from the steering handle to the steering mechanism, and a motor (20) connected to the steering mechanism closer to the wheel than the torsion bar to give a steering assist force ), A motor rotation angle sensor (23) that detects a motor rotation angle that is a relative angle between the stator and rotor of the motor, an abnormality detection means (72) that detects an abnormality of the torque sensor, If no abnormality is detected, the target steering assist control amount (Ta) is based on the steering torque detected by the torque sensor. 0) and the target steering assist control amount (Ta1) is set based on information different from the steering torque when an abnormality is detected in the normal control amount setting means (71) and the torque sensor. The motor is driven and controlled based on the target steering assist control amount and the motor rotation angle set by the abnormal control amount setting means (80) and the normal control amount setting means or the abnormal control amount setting means. In an electric power steering device for a vehicle provided with motor control means (60, 40),
The abnormal time control amount setting means increases with increasing first steering angle obtaining means (22) for obtaining a first steering angle (θ1) representing the absolute steering angle of the steering wheel. A first abnormality control amount calculating means (81) for calculating a target steering assist control amount (Ta11), and when it is determined that the vehicle is traveling straight ahead, the first steering angle and the motor rotation angle; Offset value acquisition means (84, 841, 842) for acquiring an offset value (θofs) corresponding to a deviation from the second steering angle (θ2) representing the steering angle corresponding to the motor rotation angle (θm) detected by the sensor. And a second abnormality that calculates a target steering assist control amount (Ta12) that increases as the torsion angle of the torsion bar estimated from the first steering angle, the second steering angle, and the offset value increases. In that a control amount calculation means (86).

  In the present invention, when an abnormality of the torque sensor is detected, the abnormal time control amount setting means sets the target steering assist control amount based on information different from the steering torque, and the motor control means The motor is driven and controlled based on the steering assist control amount and the motor rotation angle. The abnormal time control amount setting means includes first steering angle acquisition means, first abnormal time control amount calculation means, offset value acquisition means, and second abnormal time control amount calculation means. The first steering angle acquisition means acquires a first steering angle representing the absolute steering angle of the steering wheel. The first abnormality control amount calculation means calculates a target steering assist control amount that increases as the first steering angle increases. Since the first steering angle is an absolute steering angle capable of specifying the rotational position of the steering handle relative to the vehicle body in the entire range in which the steering handle can be rotated, the first abnormality control amount calculation means is used when the vehicle is started (electric power steering The target steering assist control amount can be calculated from the time of startup of the device. Therefore, even when the torque sensor breaks down, the steering assist based on the first steering angle can be performed from the start of the vehicle.

  When performing steering assist based on the first steering angle, the steering torque input by the driver is not estimated, so that over-assist does not occur even when driving on a road surface with a low friction coefficient (low μ road surface) It is necessary to set the target steering assist control amount small. For this reason, when driving on a normal friction road surface, steering assist is insufficient and the burden on the driver increases. Therefore, in the present invention, an offset value acquisition unit and a second abnormality control amount calculation unit are provided.

  The offset value acquisition means includes a first steering angle and a second steering angle representing a steering angle corresponding to the motor rotation angle detected by the motor rotation angle sensor when it is determined that the vehicle is traveling straight ahead. An offset value corresponding to the deviation is obtained. For example, the offset value acquisition unit includes a straight traveling determination unit that acquires information representing the behavior of the vehicle (for example, yaw rate, lateral acceleration, left and right wheel speed difference, etc.) and determines whether the vehicle is traveling straight ahead. Get it.

  The second steering angle may be obtained by converting the rotation angle from the origin to the steering angle with the arbitrarily set rotation angle (rotation position) of the motor as the origin. Since the motor is connected to the steering mechanism on the wheel side of the torsion bar, the second steering angle corresponds to the rotation angle on the wheel side of the torsion bar.

  Since the offset value corresponds to the deviation between the first steering angle and the second steering angle when it is determined that the vehicle is traveling straight ahead, it is assumed that the torsion bar is not twisted. This corresponds to the deviation between the first steering angle and the second steering angle. Therefore, after obtaining the offset value, for example, the torsion angle of the torsion bar can be estimated by subtracting the offset value from the deviation between the first steering angle and the second steering angle.

  The second abnormal control amount calculation means calculates a target steering assist control amount that increases as the torsion bar twist angle estimated from the first steering angle, the second steering angle, and the offset value increases. It can be estimated that the greater the estimated torsion angle of the torsion bar, the greater the steering torque input by the driver to the steering wheel. Therefore, the second abnormal control amount calculation means calculates a target steering assist control amount that increases as the steering torque estimated to be input by the driver increases. Therefore, a larger steering assist torque can be applied as compared with the first abnormal time control amount calculation means, and a good steering assist performance can be obtained.

  Thus, according to the present invention, even when the torque sensor is out of order, the steering assist can be started from the start of the vehicle, and good steering assist can be performed. In this specification, when discussing the magnitude of the angle, the control amount, etc., an absolute value that does not specify the left and right steering directions is described.

Another feature of the present invention is that the abnormal control amount setting means uses the calculation result of the first abnormal control amount calculation means while the offset value acquisition means cannot acquire the offset value. After the steering assist control amount is set and the offset value acquisition unit can acquire the offset value, the target steering assist control amount is switched using the calculation result of the second abnormal time control amount calculation unit. The switching means (87, 872) is provided.

In the present invention, the switching means first sets the target steering assist control amount using the calculation result of the first abnormality control amount calculation means, and after obtaining the offset value, the second abnormality control amount calculation means. Switch to set the target steering assist control amount using the calculation result. For this reason, steering assist is performed from the start of the vehicle using the calculation result of the first abnormal control amount calculation means, and good steering assist using the calculation result of the second abnormality control amount calculation means at an appropriate timing. You can switch to

  Another feature of the present invention is that the abnormal time control amount setting means corrects the offset value so that the target steering assist control amount calculated when it is determined that the vehicle is traveling straight ahead is reduced. The offset value correcting means (841, 842) is provided.

  For example, if the first steering angle of the steering wheel includes an error, the first steering angle does not indicate a neutral point even when it is determined that the vehicle is traveling straight ahead. For this reason, the target steering assist control amount calculated by the first abnormality control amount calculation means does not become zero, and the motor generates an inappropriate torque. In such a case, the driver applies a force to the steering handle so as to cancel the torque generated by the motor in order to keep the vehicle traveling straight, so the torsion bar is twisted. Therefore, if the offset value is set in this state, the offset value becomes inappropriate.

  When it is determined that the vehicle is traveling straight ahead, it is ideal that the motor originally does not generate steering torque, that is, the target steering assist control amount is zero. Therefore, in the present invention, the offset value correction means corrects the offset value so that the target steering assist control amount calculated when it is determined that the vehicle is traveling straight ahead is reduced. In this case, the offset value may be corrected with a larger correction amount as the target steering assist control amount is larger. For example, a value obtained by dividing the output torque of the motor represented by the target steering assist control amount calculated when it is determined that the vehicle is traveling straight ahead by the rigidity of the torsion bar (corresponding to the estimated torsion angle of the torsion bar) Is used as a correction amount for correcting the offset value.

  Therefore, according to the present invention, an appropriate offset value can be acquired, so that a better steering assist can be performed.

Another feature of the present invention is that the switching unit (872) is configured to weight the calculation result (Ta11) of the first abnormal time control amount calculation unit after the offset value acquisition unit has acquired the offset value. 1−λ) is decreased, and the target steering assist control amount is set to the first abnormality control amount calculation unit so that the weight (λ) of the calculation result (Ta12) of the second abnormality control amount calculation unit is increased. The calculation result is gradually switched to the calculation result of the second abnormal control amount calculation means.

Immediately after the offset value acquisition means can acquire the offset value, when the motor is controlled by switching from the calculation result of the first abnormal control amount calculation means to the calculation result of the second abnormal control amount calculation means, the offset value is If it is set to an inappropriate value, the influence on the driving operation may be increased. Therefore, in the present invention, after the offset value can be acquired, the weight of the calculation result of the first abnormality control amount calculation unit is decreased, and the weight of the calculation result of the second abnormality control amount calculation unit is increased. Then, the target steering assist control amount is gradually switched from the calculation result of the first abnormal control amount calculation means to the calculation result of the second abnormal control amount calculation means. Therefore, it is possible to reduce the influence on the driving operation when the calculation method is switched.

Another feature of the present invention is that the switching means is configured to control the target steering assist control when the target steering assist control amount calculated when it is determined that the vehicle is traveling straight ahead is larger than when the target steering assist control amount is small. It is to increase the switching speed for switching the amount from the calculation result of the first abnormal control amount calculation means to the calculation result of the second abnormal control amount calculation means (S28 to S29).

The reliability of the offset value can be estimated to be higher as the target steering assist control amount calculated when it is determined that the vehicle is traveling straight ahead is smaller. Further, when the offset value is highly reliable, even if the target steering assist control amount is quickly switched from the calculation result of the first abnormality control amount calculation unit to the calculation result of the second abnormality control amount calculation unit, There is little impact on. Also, better to drive and control the motor with the calculation result of the second abnormality control amount calculating section than the first abnormality control amount calculation means, good steering assist performance. For this reason, in the present invention, the target steering assist control amount is set to the first abnormality when the target steering assist control amount calculated when it is determined that the vehicle is traveling straight ahead is smaller than when the target steering assist control amount is large. The switching speed for switching from the calculation result of the hourly control amount calculation means to the calculation result of the second abnormal time control amount calculation means is increased. Thus, according to the present invention, good steering assist performance can be obtained at an early timing while reducing the influence on the driving operation due to the switching of the calculation method.

For example, whenever it is determined that the vehicle is traveling straight ahead, the offset correction means corrects the offset value so that the target steering assist control amount at that time is reduced, and the switching means performs the first abnormality control. You may make it change the weight of the calculation result of a quantity calculation means, and the calculation result of the 2nd abnormal time control amount calculation means.

  In the above description, in order to help the understanding of the invention, the reference numerals used in the embodiments are attached to the configuration of the invention corresponding to the embodiments in parentheses, but each constituent element of the invention is represented by the reference numerals. It is not limited to the embodiments specified.

1 is a schematic configuration diagram of an electric power steering device for a vehicle according to an embodiment of the present invention. It is a functional block diagram of assist ECU. It is a graph showing a normal time assist map. It is a functional block diagram of the control amount calculation part at the time of abnormality. It is a graph showing the 1st abnormality time assist map. It is a graph showing the 2nd abnormality time assist map. It is a flowchart showing an assist control routine. It is a functional block diagram of the abnormal time control amount calculation part concerning the modification 2. 10 is a flowchart showing an offset value / calculated value ratio setting routine according to Modification 2; 10 is a graph showing a ratio increase amount map according to Modification 2; 10 is a graph showing another ratio increase amount map according to Modification 2. 10 is a flowchart showing a calculation value ratio adjustment routine according to Modification 2.

  Hereinafter, an electric power steering device for a vehicle according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an electric power steering apparatus 1 for a vehicle according to the embodiment.

  The electric power steering apparatus 1 is configured according to a steering mechanism 10 that steers steered wheels by a steering operation of a steering handle 11, a motor 20 that is assembled to the steering mechanism 10 and generates steering assist torque, and an operating state of the steering handle 11. The electronic control unit 100 that controls the operation of the motor 20 is provided as a main part. Hereinafter, the electronic control unit 100 is referred to as an assist ECU 100.

  The steering mechanism 10 converts the rotation around the axis of the steering shaft 12 in conjunction with the turning operation of the steering handle 11 into the left and right stroke motion of the rack bar 14 by the rack and pinion mechanism 13. The left front wheel Wfl and the right front wheel Wfr are steered by movement. The steering shaft 12 connects the main shaft 12a, which is connected to the upper end of the steering handle 11, the pinion shaft 12c, which is connected to the rack and pinion mechanism 13, and the main shaft 12a and the pinion shaft 12c via universal joints 12d and 12e. And an intermediate shaft 12b.

  The rack bar 14 has a gear portion 14 a housed in the rack housing 15, and both left and right ends thereof are exposed from the rack housing 15 and connected to the tie rod 16. The other ends of the left and right tie rods 16 are connected to knuckles (not shown) provided on the left and right front wheels Wfl and Wfr. Hereinafter, the left front wheel Wfl and the right front wheel Wfr are simply referred to as steered wheels W.

  A motor 20 is assembled to the steering shaft 12 (main shaft 12a) via a speed reducer 25. For example, a three-phase brushless motor is used as the motor 20. The motor 20 rotationally drives the steering shaft 12 around its central axis via the speed reducer 25 by the rotation of the rotor, and applies assist torque to the turning operation of the steering handle 11.

  The motor 20 is provided with a motor rotation angle sensor 23. The motor rotation angle sensor 23 outputs a detection signal representing a motor rotation angle θm that is a relative angle of the rotor with respect to the stator. The motor rotation angle sensor 23 is constituted by, for example, a resolver. The motor rotation angle θm is used for detecting an electrical angle necessary for controlling the phase of the motor 20.

  A torque sensor 21 is provided between the steering handle 11 and the speed reducer 25 on the steering shaft 12 (main shaft 12a). The torque sensor 21 detects the torsional force acting on the torsion bar 12t interposed in the steering shaft 12 (main shaft 12a) as the steering torque Tr applied to the steering handle 11. Therefore, the torque sensor 21 detects the steering torque Tr according to the degree of twist of the torsion bar 12t. For example, the torque sensor 21 transmits the magnetic flux proportional to the twist angle of the torsion bar 12t to the Hall IC to thereby reduce the steering torque Tr. Various devices such as a Hall IC torque sensor to detect, a twin resolver torque sensor that provides a resolver at both ends of the torsion bar 12t, and detects the steering torque Tr based on the difference in rotational angle detected by the two resolvers. Can be used.

  The steering torque Tr identifies the direction in which the torque works by the sign, and the torque acting in the clockwise direction on the steering shaft 12 (in a torsional state where the upper part of the torsion bar 12t is in the right-rotating position relative to the lower part). (Torque) is represented by a positive value, and torque acting in the counterclockwise direction (torque in a torsional state where the upper portion of the torsion bar 12t is in the left rotational position relative to the lower portion) is represented by a negative value. Further, when discussing the magnitude of the steering torque Tr, the absolute value thereof is used.

  A steering angle sensor 22 is provided on the steering shaft 12 (main shaft 12a) between the steering handle 11 and the torsion bar 12t. The steering angle sensor 22 detects the steering angle θ1 of the steering handle 11, and generates a detection signal indicating an absolute steering angle with the neutral position (rotation position where the vehicle goes straight) determined in advance as the origin. Output. The steering angle sensor 22 only needs to output a signal that can specify the rotational position (absolute steering angle) of the steering handle 11 relative to the vehicle body in the entire range in which the steering handle 11 can be rotated. A rotation angle sensor can be used. The steering angle θ1 specifies the direction in which the steering handle 11 is turned by a sign, with the neutral position as the zero point, and the angle when the steering handle 11 is turned to the right is a positive value, and the left direction The angle when the steering wheel 11 is turned is represented by a negative value. When discussing the magnitude of the steering angle θ1, the absolute value is used.

  Hereinafter, the steering handle 11 side of the torsion bar 12t is referred to as an input side, and the speed reducer 25 side of the torsion bar 12t is referred to as an output side. The steering angle sensor 22 detects the rotation angle (absolute angle) on the input side of the torsion bar 12t.

  Since the output side of the torsion bar 12t is connected to the motor 20 via the speed reducer 25, the rotation angle on the output side of the torsion bar 12t corresponds to the rotation angle of the rotor of the motor 20. The motor rotation angle sensor detects the relative rotation angle of the rotor with respect to the stator in order to detect the electrical angle of the motor 20, but when the wheel is directed to the neutral position (straight direction) (the steering angle of the wheel). If the relative angle of the rotor with respect to the stator (at the zero point) is specified, it can be used to detect the steering angle, which is the rotation angle with respect to the neutral position on the output side of the torsion bar 12t. In this case, the rotation angle of the motor from the zero point is integrated (right rotation is positive and left rotation is negative), and the integrated value is converted into the rotation angle of the torsion bar 12t using the reduction gear ratio.

  Next, the assist ECU 100 will be described. As shown in FIG. 2, the assist ECU 100 calculates a target control amount of the motor 20 and outputs a switch drive signal corresponding to the calculated target control amount, and is output from the electronic control circuit 50. And a motor drive circuit 40 that energizes the motor 20 in accordance with the switch drive signal.

  The electronic control circuit 50 includes a microcomputer including a CPU, ROM, RAM, and the like, various input / output interfaces, a switch drive circuit that supplies a switch drive signal to the motor drive circuit 40, and the like.

  When the electronic control circuit 50 pays attention to its function, the motor control amount calculation unit 70 that calculates the target assist torque, which is the control amount of the motor 20, and the switch drive signal so that the target assist torque flows to the motor 20. And a motor control unit 60 that outputs to 40. The processing in each functional unit is repeatedly executed at a predetermined short period by the microcomputer.

  The motor control amount calculation unit 70 includes a normal control amount calculation unit 71, an abnormal control amount calculation unit 80, an abnormality detection unit 72, and a control switching unit 73. The normal control amount calculation unit 71 receives the abnormality determination flag Ffail output from the abnormality detection unit 72, calculates the target assist torque Ta0 when the abnormality determination flag Ffail is “0”, and calculates the abnormality determination flag Ffail. Is “1”, the calculation block stops the calculation process. The abnormal time control amount calculation unit 80 receives the abnormality determination flag Ffail output from the abnormality detection unit 72, and calculates the target assist torque Ta1 when the abnormality determination flag Ffail is “1”, and the abnormality determination flag Ffail. Is “0”, the calculation block stops the calculation process.

  The abnormality detection unit 72 determines whether there is an abnormality in the torque sensor 21. If it is determined that there is no abnormality, the abnormality detection flag Ffail is set to “0”, and if it is determined that there is an abnormality, Then, the abnormality determination flag Ffail is set to “1”, and the set abnormality determination flag Ffail is output to the normal control amount calculation unit 71, the abnormal control amount calculation unit 80, and the control switching unit 73.

  The control switching unit 73 inputs the target assist torque Ta0 calculated by the normal control amount calculation unit 71 and the target assist torque Ta1 calculated by the abnormal control amount calculation unit 80, and the abnormality determination flag Ffail is “0”. ", The target assist torque Ta0 is selected, and when the abnormality determination flag Ffail is" 1 ", the target assist torque Ta1 is selected. Then, the selected target assist torque Ta0 (or Ta1) is set as the target assist torque Ta *, and the target assist torque Ta * is output to the motor control unit 60.

  Details of each functional unit of the motor control amount calculation unit 70 will be described later.

  The motor control unit 60 includes a current feedback control unit 61 and a PWM signal generation unit 62. The current feedback control unit 61 receives the target assist torque Ta * output from the control switching unit 73, and generates the target assist torque Ta * by dividing the target assist torque Ta * by the torque constant of the motor 20. The target current i * required for the calculation is calculated. Then, a motor current im (referred to as an actual current im) detected by a current sensor 41 provided in the motor drive circuit 40 is read, a deviation between the target current i * and the actual current im is calculated, and this deviation is used. The target voltage v * is calculated so that the actual current im follows the target current i * by proportional-integral control. Then, a PWM control signal (switch drive signal) corresponding to the target voltage v * is output to the switching element of the motor drive circuit (inverter) 40. As a result, the motor 20 is driven and an assist torque that follows the target assist torque Ta * is applied to the steering mechanism 10.

  The current feedback control unit 61 inputs the motor rotation angle θm detected by the motor rotation angle sensor 23 provided in the motor 20, converts the motor rotation angle θm into an electrical angle, and sets the target based on the electrical angle. Controls the phase angle of the current. In this case, if the motor rotation angle θm detected by the motor rotation angle sensor 23 represents an electrical angle, the detected value may be used.

  For example, the current feedback control unit 61, based on the electrical angle detected by the motor rotation angle sensor 23, a d-axis that is a direction through which the magnetic field of the permanent magnet of the three-phase brushless motor 20 penetrates, and a direction orthogonal to the d-axis ( The motor 20 is driven and controlled by current vector control using dq coordinates that define a q axis that is a direction in which the electrical angle is advanced by π / 2 from the d axis.

  Next, each functional unit of the motor control amount calculation unit 70 will be described in detail. The normal control amount calculation unit 71 inputs the vehicle speed V detected by the vehicle speed sensor 24 and the steering torque Tr detected by the torque sensor 21, and refers to the normal assist map shown in FIG. Torque Ta0 is calculated. The normal assist map is stored in the normal control amount calculation unit 71, and is association data in which the relationship between the steering torque Tr and the target assist torque Ta0 is set for each of a plurality of representative vehicle speeds V. The target assist torque Ta0 is set such that it increases as the magnitude (absolute value) of the torque Tr increases and decreases as the vehicle speed V increases.

  In calculating the target assist torque Ta0, various compensation torques may be added to the target assist torque Ta0. For example, a friction compensation torque that compensates for the frictional force in the steering mechanism 10 may be added. Moreover, you may make it add the friction viscosity compensation torque which compensates a viscosity component in addition to a friction component. Further, the target assist torque Ta0 may not be varied according to the vehicle speed V.

  When the abnormality determination flag Ffail output from the abnormality detection unit 72 is “0”, the normal control amount calculation unit 71 repeatedly executes such calculation processing at a predetermined short cycle, and the target assist torque as a calculation result is obtained. Ta0 is output to the control switching unit 73.

  The abnormality detection unit 72 determines whether the torque sensor 21 is abnormal. For example, when the torque sensor 21 has an abnormality detection function, an abnormality detection signal output from the torque sensor 21 may be input to determine whether there is an abnormality. Further, based on the detection signal output from the torque sensor 21, when the value (voltage value or the like) indicated by the detection signal is out of the normal range, it is determined that an abnormality has occurred in the torque sensor 21. Also good. Further, for example, in the case of the torque sensor 21 using a rotation angle sensor whose output voltage periodically changes in a sine wave shape like a resolver, when the output voltage is fixed at a constant value, disconnection or short circuit It may be determined that such an abnormality has occurred.

  The abnormality detection unit 72 determines whether the torque sensor 21 is abnormal as described above, and sets the abnormality determination flag Ffail to “1” (abnormal) or “0” (abnormal) according to the abnormality determination result. .

  Next, the abnormal time control amount calculation unit 80 will be described. The normal control amount calculation unit 71 described above calculates the target assist torque Ta0 based on the steering torque Tr, but cannot calculate the target assist torque Ta0 if the torque sensor 21 fails. Therefore, the abnormal control amount calculation unit 80 calculates the target assist torque Ta1 instead of the normal control amount calculation unit 71 when an abnormality of the torque sensor 21 is detected.

  As shown in FIG. 4, the abnormal time control amount calculation unit 80 includes a first assist torque calculation unit 81, a steering angle conversion unit 82, a difference calculation unit 83, an offset value calculation unit 84, and a twist angle calculation unit 85. And a second assist torque calculating unit 86 and a switching unit 87. The processing in each functional unit is repeatedly executed at a predetermined short period by the microcomputer.

  The first assist torque calculator 81 receives the steering angle θ1 detected by the steering angle sensor 22, and calculates a first target assist torque Ta11 based on the steering angle θ1. The abnormal time control amount calculation unit 80 calculates the target assist torque Ta1 using the angle on the input side and the angle on the output side of the torsion bar 12t, and hereinafter, the steering that is the angle on the input side of the torsion bar 12t. The angle θ1 is referred to as a first steering angle θ1, and the angle on the output side of the torsion bar 12t is referred to as a second steering angle θ2.

  The first assist torque calculator 81 calculates the first target assist torque Ta11 based on the first steering angle θ1 with reference to the first abnormality assist map shown in FIG. The first abnormality assist map is stored in the first assist torque calculator 81 and is association data in which the relationship between the first steering angle θ1 and the first target assist torque Ta11 is set. The first target assist torque Ta11 is set to increase as the magnitude (absolute value) increases. The first assist torque calculation unit 81 outputs the calculated first target assist torque Ta11 to the switching unit 87. Note that the first abnormality assist map may have a vehicle speed sensitivity characteristic such that the first target assist torque Ta11 decreases as the vehicle speed V increases, considering the vehicle speed V, as in the normal assist map. Good.

  The steering angle conversion unit 82 receives the motor rotation angle θm detected by the motor rotation angle sensor 23, and converts the motor rotation angle θm into a second steering angle θ2 that is an angle (rotational position) on the output side of the torsion bar 12t. To do. When the ignition switch of the vehicle is turned on, the motor rotation angle sensor 23 is reset. Therefore, the rudder angle conversion unit 82 calculates the second steering angle θ2 with the motor rotation angle θm at the time of reset as the zero point. In this case, at the time of resetting, the steered wheel W does not always face the neutral position. Therefore, the second steering angle θ2 does not represent an angle from the neutral position, and is only when the vehicle is started (ignition). This represents the steering angle with the rotational position on the output side of the torsion bar 12t at the time of turning on the switch being zero. Since the motor 20 is connected to the output side of the torsion bar 12t via the speed reducer 25, the motor 20 rotates N (> 1) with respect to one rotation of the torsion bar 12t. Therefore, in calculating the second steering angle θ2, the rotation angle of the motor 20 from the zero point is accumulated (plus for right rotation and minus for left rotation), and the accumulated value is multiplied by a conversion factor (1 / N). Thus, the rotation angle of the torsion bar 12t may be calculated. The rudder angle conversion unit 82 outputs the calculated second steering angle θ2 to the difference calculation unit 83. In the present embodiment, the second steering angle θ2 is calculated with the motor rotation angle θm at the time of reset as the zero point, but the zero point of the motor rotation angle θm can be arbitrarily set.

  The difference calculation unit 83 calculates a difference value (θ1−θ2) between the first steering angle θ1 that is an angle on the input side of the torsion bar 12t and the second steering angle θ2 calculated by the steering angle conversion unit 82, The calculation result is output to the offset value calculation unit 84 and the twist angle calculation unit 85.

  The offset value calculation unit 84 determines whether or not the vehicle is traveling straight ahead, and sets a difference value (θ1−θ2) when it is determined that the vehicle is traveling straight ahead to the offset value θofs. For example, the offset value calculation unit 84 reads the left front wheel speed Vfl, right front wheel speed Vfr, left rear wheel speed Vrl, and right rear wheel speed Vrr detected by the wheel speed sensor 26, and the difference between the left and right wheel speeds is read. It is determined that the vehicle is traveling straight when the state where the value is equal to or less than the threshold value for determining whether the vehicle travels straight travels for a certain period of time. As the wheel speed difference between the left and right, the wheel speed difference of only the front wheels may be used, the wheel speed difference of only the rear wheels may be used, or the average wheel speed difference of the front and rear wheels may be used. It can be calculated by this method. Further, as a straight traveling determination means for determining whether the vehicle is traveling straight, instead of the wheel speed sensor 26, a detection signal of a yaw rate sensor or a lateral acceleration sensor is input, and the vehicle turns represented by the yaw rate or the lateral acceleration of the vehicle. It may be determined that the vehicle is traveling straight when the state where the amount is equal to or less than the straight traveling determination threshold value continues for a certain period of time. When the accuracy of the steering angle (absolute steering angle) detected by the steering angle sensor 22 is sufficiently high, it is determined that the vehicle is traveling straight when the first steering angle θ1 is zero (substantially zero). You may do it.

When it is determined that the vehicle is traveling straight ahead, the offset value calculation unit 84 uses the difference value (θ1−θ2) output from the difference calculation unit 83 as an offset value as shown in the following equation (1). Set to θofs.
θofs = θ1-θ2 (1)
In this case, for example, an average value of difference values (θ1−θ2) during a certain period in which it is determined that the vehicle is traveling straight ahead may be calculated, and the average value may be set as the offset value θofs. When the offset value calculator 84 stores the set offset value θofs, the offset value calculator 84 outputs the offset value θofs to the twist angle calculator 85. Further, the offset value calculation unit 84 outputs the offset value valid flag Fofs to the switching unit 87, and when the setting of the offset value θofs is completed, the offset value valid flag Fofs is switched from “0” to “1”. The offset value valid flag Fofs indicates that the offset value θofs is not set (invalid) by “0”, and that the offset value θofs has been set (valid) by “1”.

  When the vehicle travels straight, the torsion bar 12t is not twisted because the driver does not apply steering turning power to the steering handle 11. Therefore, the value obtained by adding the offset value θofs to the second steering angle θ2 represents the steering angle (the steering angle on the output side of the torsion bar 12t) with the vehicle traveling straight ahead as the zero point.

  The torsion angle calculation unit 85 calculates the estimated torsion angle (θ1−θ2−θofs) of the torsion bar 12t by subtracting the offset value θofs from the difference value (θ1−θ2) output from the difference calculation unit 83, The calculation result is output to the second assist torque calculator 86.

As shown in the following equation (2), the second assist torque calculator 86 multiplies the estimated torsion angle (θ1−θ2−θofs) by the rigidity Ktb of the torsion bar 12t, so that the driver inputs the steering wheel 11 An estimated value of steering torque (referred to as estimated steering torque Tr ′) is calculated.
Tr ′ = Ktb · (θ1-θ2-θofs) (2)
Then, the second assist torque calculator 86 calculates the second target assist torque Ta12 with reference to the second abnormality assist map shown in FIG. The second abnormality assist map is stored in the second assist torque calculator 86 and is association data in which the relationship between the estimated steering torque Tr ′ and the second target assist torque Ta12 is set. The second target assist torque Ta12 is set to increase as the magnitude (absolute value) increases. The second assist torque calculation unit 86 outputs the calculated second target assist torque Ta12 to the switching unit 87. The second abnormality assist map may have a vehicle speed sensitivity characteristic such that the second target assist torque Ta12 decreases as the vehicle speed V increases, taking into account the vehicle speed V, as in the normal assist map. Good.

  The switching unit 87 inputs the first target assist torque Ta11 calculated by the first assist torque calculation unit 81 and the second target assist torque Ta12 calculated by the second assist torque calculation unit 86, and the offset value valid flag. When Fofs is “0”, the first target assist torque Ta11 is selected, and when the offset value valid flag Fofs is “1”, the second target assist torque Ta12 is selected. Then, the selected target assist torque Ta11 (or Ta12) is set to the target assist torque Ta1, and the target assist torque Ta1 is output to the control switching unit 73.

  Hereinafter, the control mode in which the first assist torque calculating unit 81 calculates the first target assist torque Ta11 using the first steering angle θ1 is referred to as a first mode, and the second assist torque calculating unit 86 is the estimated torsion of the torsion bar 12t. A control mode for calculating the second target assist torque Ta12 using the angle (θ1-θ2-θofs) is referred to as a second mode.

  Next, the overall processing flow of the assist ECU 100 will be described. FIG. 7 shows an assist control routine executed by the assist ECU 100. This routine is started when the ignition switch is turned on and a predetermined initial diagnosis is completed. When this routine is started, the assist ECU 100 determines whether or not the torque sensor 21 is normal in step S11. If normal, the assist ECU 100 starts normal-time assist control in step S12. That is, steering assist based on the target assist torque Ta0 calculated by the normal control amount calculation unit 71 is started. In this case, in step S13, the assist ECU 100 determines whether or not the ignition switch is turned off, and continues the normal assist control until it is detected that the ignition switch is turned off.

  On the other hand, when it is determined that the torque sensor 21 is abnormal (S11: No), it is determined in step S14 whether the steering angle sensor 22 is normal. Information representing the steering angle θ1 is transmitted to a CAN (Controller Area Network) communication line and used in various vehicle ECUs. Since abnormality determination data of various sensors including the steering angle sensor 22 is also transmitted to the CAN communication line, determination is made by reading the abnormality determination data of the steering angle sensor 22 in step S14. If the steering angle sensor 22 is abnormal, the first steering angle θ1 does not show an appropriate value, and therefore the target assist torque Ta1 cannot be calculated by the abnormal time control amount calculation unit 80. For this reason, assist ECU100 advances the process to step S13. Therefore, steering assist is not performed.

  When the steering angle sensor 22 is normal (S14: Yes), the assist ECU 100 starts steering assist in accordance with the first target assist torque Ta11 calculated by the first assist torque calculator 81 in step S15. That is, in the first mode, steering assist having a magnitude proportional to the magnitude of the first steering angle θ1 (absolute steering angle) detected by the steering angle sensor 22 is started.

  Subsequently, in step S16, the assist ECU 100 determines whether or not the motor rotation angle sensor 23 is normal. For example, the value of the detection signal of the motor rotation angle sensor 23 is out of the normal range, the periodic fluctuation signal that should be generated is not obtained, the detection signal is fixed to a constant value, etc. Judge by detecting. When the motor rotation angle sensor 23 is abnormal, the drive of the motor 20 cannot be controlled. For this reason, assist ECU100 advances the process to step S13. Therefore, steering assist is not performed.

  When the motor rotation angle sensor 23 is normal (S16: Yes), the assist ECU 100 starts calculating the offset value θofs in step S17. In this case, the offset value calculation unit 84 starts determining whether the vehicle is traveling straight ahead, waits until straight traveling is detected, and then sets the difference value (θ1-θ2) at that time to the offset value θofs.

  Next, in step S18, the assist ECU 100 waits until the calculation of the offset value θofs is completed. When the calculation of the offset value θofs is completed, the second target assist calculated by the second assist torque calculation unit 86 in step S19. Steering assist is started according to the torque Ta12. That is, in the second mode, steering assist having a magnitude corresponding to the steering torque Tr 'set from the estimated torsion angle (θ1-θ2-θofs) of the torsion bar 12t is started. When the assist ECU 100 starts the steering assist in the second mode, the assist ECU 100 advances the process to step S13. Accordingly, the steering assist in the second mode is continued until the ignition switch is turned off.

  Here, the reason for switching between the first mode and the second mode when the abnormal-time control amount calculation unit 80 calculates the target assist torque Ta1 will be described. Since the first mode calculates the target assist torque Ta11 having a magnitude proportional to the first steering angle θ1, which is an absolute steering angle, the first mode can be implemented when the vehicle is started (when the ignition switch is turned on). . However, since the steering torque input by the driver is not estimated, the steering assist amount (target assist torque Ta11) needs to be set small in advance so that the tire does not slip on the low friction road surface. For this reason, on a normal friction road surface, the steering assist is reduced and the burden on the driver is increased.

  On the other hand, in the second mode, since the estimated steering torque Tr ′ is calculated from the estimated torsion angle (θ1−θ2−θofs) of the torsion bar 12t, it is possible to apply a larger steering assist torque than in the first mode. The assist performance is superior to the first mode. However, in the second mode, it is necessary to calculate the estimated twist angle (θ1-θ2-θofs) of the torsion bar 12t, but the estimated twist angle (θ1-θ2-θofs) can be calculated from when the vehicle is started. Can not. As described above, the motor rotation angle sensor 23 is reset when the vehicle is started. For this reason, the angle on the output side of the torsion bar 12t when the vehicle is activated (when the assist ECU 100 is activated) is reset as the zero point of the second steering angle θ2. For this reason, when the vehicle is started with the wheels W being steered, the zero points of the first steering angle θ1 representing the absolute steering angle of the steering handle 11 and the second steering angle θ2 do not match. Even if the second steering angle θ2 at the time of starting the vehicle is considered to be equal to the first steering angle θ2 and is reset, the vehicle is in a state in which the driver applies a force to the steering handle 11 (a state in which a turning operation force is input). Is activated, the zero point is shifted by the amount of twist of the torsion bar 12t.

  For this reason, in the present embodiment, when the vehicle is traveling straight, it is considered that no torsion torque is generated in the torsion bar 12t, and the first steering angle θ1 and the second steering angle θ2 during the straight traveling are considered. Is set to the offset value θofs, and the estimated torsion angle (θ1-θ2-θofs) of the torsion bar 12t is calculated using the offset value θofs.

  Therefore, the abnormal time control amount calculation unit 80 performs steering assist in the first mode when the vehicle is started, and after switching to the steering assist in the second mode after calculating the offset value θofs.

  According to the electric power steering apparatus of the present embodiment described above, the steering assist can be started from the start of the vehicle (at the start of the assist ECU 100) when the abnormality of the torque sensor 21 is detected. In addition, since the steering assist in the first mode is started and the offset value θofs is calculated, the steering assist is switched to the steering assist in the second mode.

<Modification 1>
Next, a modification of the above embodiment will be described. In the embodiment described above, the first steering angle θ1 detected by the steering angle sensor 22 is assumed to be accurate. However, if there is an error in the first steering angle θ1 detected by the steering angle sensor 22, in the first mode, a steering assist proportional to the first steering angle θ is output. Incorrect torque is generated from the motor 20 on either the left or right side by the error of the first steering angle θ1. At this time, in order to keep the vehicle traveling straight, the driver is applying force to the steering wheel 11 so as to cancel out the unauthorized torque. For this reason, the offset value calculation unit 84 calculates and stores the offset value θofs while the torsion bar 12t is twisted. When the offset value θofs is stored, the mode shifts from the first mode to the second mode. However, in the second mode, a larger steering assist torque is output than in the first mode, so that the influence on the driving operation is increased.

  For example, when the incorrect torque in the first mode is 3 Nm, a canceling torque of 3 Nm manually input by the driver is required to travel straight ahead. When the offset value θofs is stored in this state, an error occurs in the offset value θofs by 3 Nm in terms of the twist angle of the torsion bar 12t. Therefore, when the mode is shifted from the first mode to the second mode as it is, an illegal torque of “3 Nm × assist magnification” is output even in the state of letting go.

In practice, there is a limit to reducing the error of the first steering angle θ1 detected by the steering angle sensor 22, and it is difficult to completely reduce the error to zero. Therefore, in the first modification, when the straight traveling condition of the vehicle is satisfied in the state where the incorrect torque is generated due to the error of the first steering angle θ1, the torsion angle of the torsion bar 12t is corrected by the incorrect torque and offset. Calculate the value θofs. The offset value θofs can be calculated by the following equation (3), where Tx is the incorrect torque during straight traveling of the vehicle, and Ktb is the rigidity of the torsion bar 12t.
θofs = θ1−θ2 + (Tx / Ktb) (3)
Therefore, (Tx / Ktb) is the offset correction amount.

  The abnormal-time control amount calculation unit 80 in Modification 1 includes an offset value calculation unit 841 (indicated by reference numerals in parentheses in FIG. 4) instead of the offset value calculation unit 84 of the previous embodiment, and this offset value calculation unit 841. Calculates the offset value θofs using the above equation (3). About another structure, it is the same as that of the above-mentioned embodiment. In this case, the offset value calculation unit 841 inputs the target assist torque Ta1 as indicated by the broken line arrow in FIG. 4, and sets the target assist torque Ta1 (= Ta11) when the straight traveling condition of the vehicle is satisfied as the incorrect torque Tx. Is used to calculate the corrected offset value θofs.

  For example, consider a case where the midpoint (zero point) of the first steering angle θ1 is shifted to the right (plus) from the original position. In this case, since the first assist torque calculation unit 81 recognizes that the left operation is being performed even when the vehicle is traveling straight ahead, the first assist torque calculation unit 81 generates an incorrect torque (for example, −3 Nm) in the left direction. When the driver slightly turns the steering handle 11 in the right direction so as to cancel out this illegal torque, straight running is maintained. Therefore, the offset value calculation unit 841 determines that the straight traveling condition of the vehicle is satisfied in a state where the input side of the torsion bar 12t is twisted by 3 Nm. In this case, if the rigidity Ktb of the torsion bar 12t is 1.5 Nm / deg (known), the twisted angle of the torsion bar 12t is 2 deg. At this time, if the difference value (θ1−θ2) between the first steering angle θ1 and the second steering angle θ2 calculated by the difference calculation unit 83 is +15 deg, the offset value θofs set by the offset value calculation unit 841. Becomes +13 deg.

  In the first modification described above, even if there is an error in the first steering angle θ1 detected by the steering angle sensor 22, the incorrect torque Tx (target steering assist control amount) when the vehicle is traveling straight ahead is reduced. Since the offset value θofs is corrected with a larger correction amount (Tx / Ktb) as the unauthorized torque Tx is larger, an appropriate offset value θofs can be set. Thereby, the estimation accuracy of the torsion angle of the torsion bar 12t is increased, and the left / right unbalance feeling given to the driving operation can be reduced. As a result, good steering assist can be performed, and the burden on the driver can be reduced. In the above modification, the corrected offset value θofs is calculated before shifting from the first mode to the second mode. Instead, for example, after shifting to the second mode, the vehicle The offset value θofs may be corrected based on the incorrect torque Tx (Ta12 in this case) during straight traveling.

<Modification 2>
Even if the offset value θofs is corrected, the accurate offset value θofs may not always be acquired due to external factors such as friction inherent in the steering mechanism 10 and unevenness of the road surface. For this reason, if the first mode is switched to the second mode immediately after obtaining the offset value θofs, there is a concern about the influence on the driving operation due to the error of the offset value θofs. Therefore, it is better to gradually switch from the first mode to the second mode.

  For example, immediately after obtaining the offset value θofs, A% of the second target assist torque Ta12 calculated by the second assist torque calculator 86 and the first target assist torque calculated by the first assist torque calculator 81. If the sum of Ta11 and (100-A)% is set to the target assist torque Ta1, and then the ratio A is increased from the initial value (<100%) to 100%, the first mode is changed to the first mode. Switching to the 2 mode can be performed gradually. In this case, the mode can be shifted more smoothly as the ratio A is changed more finely.

  Even in that case, the influence on the driving operation at the time of the mode switching can be reduced. However, in the second modification, the switching from the first mode to the second mode is further performed according to the reliability of the offset value θofs. Variable speed. As described above, the steering assist in the second mode is superior in performance from the steering assist in the first mode. Therefore, if the switching from the first mode to the second mode is performed slowly, even if an accurate offset value θofs is set, the shift to the second mode will be delayed. The period during which the steering burden is large will become longer. Therefore, in the second modification, the higher the reliability of the offset value θofs, the faster the mode switching speed, and the lower the reliability of the offset value θofs, the slower the mode switching speed. Further, during the mode switching (transition period), the reliability of the offset value θofs is improved by recalculating and updating the offset value θofs.

  The reliability of the offset value θofs can be estimated by the magnitude (absolute value) of the incorrect torque Tx when the offset value θofs is acquired, that is, when the vehicle straight running condition is satisfied, and the magnitude of the incorrect torque Tx. The smaller the value, the higher the reliability.

  FIG. 8 is a functional block diagram illustrating a configuration of the abnormal time control amount calculation unit 80 according to the second modification. The abnormal control amount calculation unit 80 includes an offset value calculation unit 842 and a switching unit 872 instead of the offset value calculation unit 84 and the switching unit 87 of the abnormal control amount calculation unit 80 of the above-described embodiment. Other configurations are the same as those in the embodiment. Hereinafter, the offset value calculation unit 842 and the switching unit 872 will be described.

  FIG. 9 shows an offset value / calculated value ratio setting routine executed by the offset value calculator 842. This offset value / calculated value ratio setting routine is activated when the abnormality determination flag Ffail becomes “1”. When this routine is started, the offset value calculation unit 842 determines whether the vehicle is traveling straight in step S21. As described above, this determination is made based on the difference between the left and right wheel speeds detected by the wheel speed sensor 26 or the amount of turning of the vehicle expressed by the yaw rate or the lateral acceleration. The straight-running determination condition may be satisfied.

  Subsequently, in step S22, the offset value calculation unit 842 determines whether or not the straight traveling determination condition is satisfied. The straight-running determination condition is determined as “No” immediately after the start of this routine because it is necessary to detect straight-running that has continued for a certain period of time. In this case, the offset value calculation unit 842 sets the straight travel determination flag Fs to zero (Fs = 0) in step S23. The straight traveling determination flag Fs is set to “1” when it is determined that the vehicle is traveling straight, and is set to “0” when it is not determined that the vehicle is traveling straight. is there.

  The offset value calculation unit 842 repeats such processing until the straight traveling determination condition is satisfied. If it is determined that the vehicle is traveling straight (S22: Yes), it is determined in step S24 whether the straight traveling determination flag Fs is zero (Fs = 0). In this case, since the straight travel determination flag Fs is set to zero, that is, since it has been determined that the vehicle has not traveled straight ahead, it is determined as “Yes” in step S24, and the offset value calculation unit 842 The process proceeds to step S25.

  In step S25, the offset value calculation unit 842 sets the straight travel determination flag Fs to “1”. Subsequently, in step S26, the incorrect torque Tx is detected. The unauthorized torque Tx is the target assist torque Ta1 at the present time (when the straight traveling determination condition is satisfied). Accordingly, in step S25, the target assist torque Ta1 output from the switching unit 872 is read. Subsequently, in step S27, the offset value calculation unit 842 calculates the offset value θofs using the above equation (3), and outputs the calculated offset value θofs to the twist angle calculation unit 85.

  Subsequently, in step S28, the offset value calculation unit 842 calculates the ratio increase amount Δλ based on the unauthorized torque Tx. The offset value calculation unit 842 stores a ratio increase amount map as shown in FIG. The ratio increase amount map has a characteristic of setting a ratio increase amount Δλ that decreases as the absolute value | Tx | of the illegal torque Tx increases. The offset value calculation unit 842 refers to the ratio increase amount map to calculate the ratio increase amount Δλ corresponding to the unauthorized torque Tx. Note that the ratio increase amount map only needs to have a characteristic in which the ratio increase amount Δλ decreases with an increase in the illegal torque | Tx |. Also good. Further, the ratio increase amount Δλ is set to a positive value whose maximum value is smaller than 1.

  Subsequently, in step S29, the offset value calculation unit 842 calculates a calculated value ratio λ obtained by integrating the ratio increase amount Δλ. The calculated value ratio λ sets the ratio (weight) between the first target assist torque Ta11 and the second target assist torque Ta12 when the switching unit 872 calculates the target assist torque Ta1. 2 represents the usage ratio of the target assist torque Ta12. The initial value of the calculated value ratio λ is set to zero (λ = 0). Therefore, when the process of step S29 is first performed, the calculated value ratio λ is equal to the ratio increase amount Δλ.

  In step S30, the offset value calculation unit 842 determines whether or not the calculated value ratio λ is equal to or greater than 1. At this stage, since the calculated value ratio λ has not yet become 1 or more, the offset value calculating unit 842 determines “No” and outputs the calculated value ratio λ to the switching unit 872 in step S31. The switching unit 872 calculates the target assist torque Ta1 using the calculated value ratio λ. This calculation process will be described later.

  When the offset value calculation unit 842 outputs the calculated value ratio λ, the process returns to step S21. In this case, since the straight traveling determination flag Fs is set to “1”, the determination in step S24 becomes “No” while the vehicle is traveling straight ahead, and the process returns to step S21. If it is determined that the vehicle is not turning straight due to turning or the like, the straight travel determination flag Fs is set to “0” in step S23. As a result, when a straight traveling of the vehicle is detected thereafter, the processes after step S25 are performed.

  By repeating such processing, the offset value calculation unit 842 performs calculation of the offset value θofs (S26 to S27) and calculation of the calculated value ratio λ (S28 to S29) each time a straight traveling of the vehicle is detected. Then, the offset value θofs is output to the twist angle calculation unit 85, and the calculated value ratio λ is output to the switching unit 872. As a result, the offset value θofs is updated each time a straight traveling of the vehicle is detected. Also, the calculated value ratio λ increases by a ratio increase amount Δλ.

  When the calculated value ratio λ increases to 1 or more (S30: Yes), the offset value calculation unit 842 sets the calculated value ratio λ to 1 (λ = 1) in step S32, and in step S33, the calculated value The ratio λ (= 1) is output to the switching unit 872, and this routine ends.

Next, processing of the switching unit 872 will be described. FIG. 12 shows a calculation value ratio adjustment routine executed by the switching unit 872. This calculated value ratio adjustment routine starts when the abnormality determination flag Ffail becomes “1”. When this routine is started, the switching unit 872 sets the calculated value ratio λ to the initial value of zero in step S41 (λ = 0). Subsequently, in step S42, the target assist torque Ta1 is calculated according to the following equation (4). This target assist torque Ta1 is the final output value of the control amount calculation unit 80 at the time of abnormality.
Ta1 = (1-λ) Ta11 + λ · Ta12 (4)

  As can be seen from this equation (4), the target assist torque Ta1 is calculated by the first target assist torque Ta11 calculated by the first assist torque calculator 81 and the second target assist torque calculated by the second assist torque calculator 86. The torque Ta12 is calculated by adding the distribution set by the calculated value ratio λ. Therefore, (1-λ) is a weighting coefficient for the first target assist torque Ta11, and λ is a weighting coefficient for the second target assist torque Ta12. At the start of this routine, since the initial value of the calculated value ratio λ is zero, the target assist torque Ta1 is set to the first target assist torque Ta11 (Ta1 = Ta11).

  Subsequently, in step S43, the switching unit 872 determines whether or not the calculated value ratio λ has been input. When the calculation value ratio λ output from the offset value calculation unit 842 is input (S43: Yes), in step S44, the current calculation value ratio λ is updated to the input calculation value ratio λ. If the calculated value ratio λ is not input, the process of step S44 is skipped.

  In step S45, the switching unit 872 determines whether or not the ignition switch is turned off. If the ignition switch is not turned off, the process returns to step S42. Therefore, each time the calculated value ratio λ is output from the offset value calculating unit 842, the updated calculated value ratio λ is updated.

  The calculated value ratio λ gradually increases from 0 and finally reaches 1. Therefore, at the start of this routine, the target assist torque Ta1 (= Ta11) calculated in the first mode is output. Then, the ratio of the second target assist torque Ta12 in the target assist torque Ta1 increases and finally becomes 100%, and conversely, the ratio of the first target assist torque Ta11 decreases and finally becomes 0%. It becomes. Thus, in the second modification, the first mode can be gradually shifted to the second mode.

  The calculated value ratio λ is an integrated value of the ratio increase amount Δλ, and the ratio increase amount Δλ is set to a larger value as the magnitude of the unauthorized torque Tx is smaller. Further, the reliability of the offset value θofs is higher as the magnitude of the incorrect torque Tx is smaller. Therefore, the speed at which the first mode is switched to the second mode is higher as the reliability of the offset value θofs is higher. In addition, every time when the vehicle travels straight, the offset value θofs is updated based on the magnitude of the unauthorized torque Tx. Therefore, the unauthorized torque Tx converges toward zero, and the reliability of the offset value θofs is also improved. It gets higher gradually.

  According to the modified example 2 described above, switching from the first mode to the second mode can be performed at an appropriate speed according to the reliability of the offset value θofs. Accordingly, if the reliability of the offset value θofs is high from the beginning, it is possible to quickly shift to the second mode, and the driver's steering operation burden can be reduced quickly. In addition, when the reliability of the offset value θofs is low, the mode switching speed is slowed down, and the offset value θofs is updated to a highly reliable value during the mode switching period (transient period). The steering assist in the second mode can be appropriately performed. As a result, it is possible to quickly shift to the second mode while reducing the influence on the driving operation due to the mode switching. In addition, since the offset value θofs is appropriately corrected, it is possible to reduce the left / right unbalance feeling given to the driving operation.

  The electric power steering device for a vehicle according to the present embodiment and the modification has been described above, but the present invention is not limited to the above-described embodiment and the modification, and various modifications can be made without departing from the object of the present invention. Is possible.

  For example, in the present embodiment, the column assist type electric power steering apparatus that applies the torque generated by the motor 20 to the steering shaft 12 has been described. However, the rack assist type that applies the torque generated by the motor to the rack bar 14 is described. An electric power steering device may be used.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 10 ... Steering mechanism, 11 ... Steering handle, 12 ... Steering shaft, 12t ... Torsion bar, 20 ... Motor, 21 ... Torque sensor, 22 ... Steering angle sensor, 23 ... Motor rotation angle sensor, 24 DESCRIPTION OF SYMBOLS ... Vehicle speed sensor, 25 ... Reduction gear, 26 ... Wheel speed sensor, 40 ... Motor drive circuit, 50 ... Electronic control circuit, 60 ... Motor control part, 70 ... Motor control amount calculation part, 71 ... Normal-time control amount calculation part, 72: Abnormality detection unit, 73 ... Control switching unit, 80 ... Control amount calculation unit during abnormality, 81 ... First assist torque calculation unit, 82 ... Steering angle conversion unit, 83 ... Difference calculation unit, 84, 841, 842 ... Offset Value calculation unit, 85 ... Torsion angle calculation unit, 86 ... Second assist torque calculation unit, 87, 872 ... Switching unit, 100 ... Assist ECU, Wfl ... Left front wheel, Wfr ... Right front wheel.

Claims (5)

A torque sensor for detecting a steering torque input from the steering handle to the steering mechanism based on a torsional degree of a torsion bar interposed in a steering mechanism connecting the steering handle and the wheels;
A motor that is connected to the steering mechanism on the wheel side of the torsion bar and applies a steering assist force;
A motor rotation angle sensor that detects a motor rotation angle that is a relative angle between a stator and a rotor of the motor;
An abnormality detecting means for detecting an abnormality of the torque sensor;
A normal control amount setting means for setting a target steering assist control amount based on the steering torque detected by the torque sensor when no abnormality is detected in the torque sensor;
An abnormality control amount setting means for setting a target steering assist control amount based on information different from the steering torque when an abnormality of the torque sensor is detected;
Electric power of a vehicle comprising: the target steering assist control amount set by the normal control amount setting means or the abnormal control amount setting means; and motor control means for driving and controlling the motor based on the motor rotation angle In the steering device,
The abnormal time control amount setting means includes:
First steering angle acquisition means for acquiring a first steering angle representing an absolute steering angle of the steering handle;
First abnormal control amount calculation means for calculating a target steering assist control amount that increases as the first steering angle increases;
Corresponding to a deviation between the first steering angle and a second steering angle representing a steering angle corresponding to the motor rotation angle detected by the motor rotation angle sensor when it is determined that the vehicle is traveling straight ahead. Offset value acquisition means for acquiring an offset value to be performed;
Second abnormal-time control amount calculation means for calculating a target steering assist control amount that increases as the torsion angle of the torsion bar estimated from the first steering angle, the second steering angle, and the offset value increases; An electric power steering device for a vehicle, comprising: The abnormal time control amount setting means includes:
While the offset value acquisition unit is not able to acquire the offset value, a target steering assist control amount is set using the calculation result of the first abnormal time control amount calculation unit, and the offset value acquisition unit sets the offset value. 2. The vehicle according to claim 1, further comprising a switching unit that switches to set the target steering assist control amount using the calculation result of the second abnormal time control amount calculation unit after obtaining the Electric power steering device. The abnormal time control amount setting means includes:
The offset value correcting means for correcting the offset value so as to reduce the target steering assist control amount calculated when it is determined that the vehicle is traveling straight ahead. An electric power steering device for a vehicle. After the offset value acquisition means can acquire the offset value, the switching means reduces the weight of the calculation result of the first abnormal control amount calculation means, and the calculation result of the second abnormal control amount calculation means The target steering assist control amount is gradually switched from the calculation result of the first abnormality control amount calculation means to the calculation result of the second abnormality control amount calculation means so as to increase the weight of The electric power steering device for a vehicle according to claim 2 or 3. The switching means controls the target steering assist control amount when the target steering assist control amount calculated when it is determined that the vehicle is traveling straight ahead is smaller than when the target steering assist control amount is small. 5. The electric power steering apparatus for a vehicle according to claim 4, wherein the switching speed for switching from the calculation result of the amount calculation means to the calculation result of the second abnormal time control amount calculation means is increased.

Images