JP2014000930A - Electric power steering apparatus for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform steering assist capable of performing a steering operation when a failure of a torque sensor is detected.SOLUTION: An assist electric control unit (ECU) drives a motor in a steering operation direction when it detects a steering operation (at time t2), and drives the motor in an opposite steering operation direction when an angle at which the motor has rotated reaches a first threshold value A1 (at time t3). When the angle at which the motor has rotated is reduced to a second threshold value A2 (at time t4), the motor is stopped. When the steering operation is detected from this state (at time t5), the motor is driven again by the first threshold value A1 in the steering operation direction. The assist ECU repeats such processing, to continue a steering assist while confirming a driver's steering operation.

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.

  Conventionally, an electric power steering apparatus detects a steering torque applied to a steering wheel by a driver by 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. The electric power steering device proposed in Patent Document 1 is based on the steering angle of the steering wheel detected by the steering angle sensor when a torque sensor failure is detected and the vehicle speed is zero or near zero. The steering assist amount that increases as the absolute value of the steering angle increases is calculated, and the electric motor is driven and controlled so as to generate the calculated steering assist amount.

Japanese Patent Laid-Open No. 2003-200842

  However, in the electric power steering device proposed in Patent Document 1, if the steering assist amount with respect to the steering angle is set so that a stationary operation can be performed on a road surface with a normal friction coefficient, a road surface with a low friction coefficient (low On the μ road surface, the steering assist amount becomes too large. For this reason, the steering assist amount must be set small from the beginning so as not to over-assist. As a result, it is difficult to perform a stationary operation on a road surface having a normal friction coefficient.

  The present invention has been made to cope with the above-described problem, and an object of the present invention is to perform a steering assist capable of performing a stationary operation when a torque sensor failure is detected.

In order to achieve the above object, the present invention is characterized in that a steering torque sensor (21) for detecting a steering torque input from a steering handle to a steering shaft, and a motor for generating a steering assist torque provided in a steering mechanism ( 20), an abnormality detection means (72) for detecting an abnormality of the steering torque sensor, and the motor based on the steering torque detected by the steering torque sensor when no abnormality of the steering torque sensor is detected. A normal motor control means (71) for controlling the driving of the motor, and an abnormal motor control means for controlling the driving of the motor based on information different from the steering torque when an abnormality of the steering torque sensor is detected. 80), an electric power steering device for a vehicle,
The abnormal-time motor control means includes a steering operation detecting means (S12) for detecting a steering operation of the steering handle, and when the steering operation of the steering handle is detected, the motor is moved in the steering operation direction of the steering handle. Steering operation direction driving means (S14) for driving, and anti-steering operation direction driving means (S16) for driving the motor in a direction opposite to the steering operation direction after the motor is driven by the steering operation direction driving means. That is.

  In the present invention, when an abnormality of the steering torque sensor is detected, the motor control means at the time of abnormality drives and controls the motor based on information different from the steering torque. The abnormal motor control means includes a steering operation detection means, a steering operation direction drive means, and an anti-steer operation direction drive means. When a steering operation of the steering handle is detected, the steering operation direction drive means Drive in the steering operation direction of the steering wheel. As a result, steering assist torque is generated.

  Since there is an elastic element in the steering mechanism from the steering handle to the ground contact surface of the tire, the elastic element is deformed when the driver starts the steering operation. By detecting the physical quantity that changes due to the deformation of the elastic element, it is possible to detect the steering operation of the steering wheel, but after the motor generates the steering assist torque and steers the wheel, the elastic element changes. Since it is difficult to detect, it cannot be determined whether or not the driver continues the steering operation of the steering wheel. Therefore, after the motor is driven in the steering operation direction, the anti-steering operation direction driving means drives the motor in the direction opposite to the steering operation direction. Thereby, the deformation | transformation of an elastic element can be returned. If the driver continues the steering operation, the elastic element is deformed again, so that the steering operation can be detected. Thus, the steering operation direction driving means drives the motor again in the steering operation direction. Therefore, while the driver continues the steering operation, the steering operation direction driving means and the anti-steering operation direction driving means are alternately operated, so that the steering assist can be performed while detecting the steering operation of the driver.

  Another feature of the present invention is that the steering operation direction drive means (S14, S15) moves the motor in the steering operation direction by a first set amount (A1) when a steering operation of the steering wheel is detected. The anti-steering operation direction driving means (S16, S17) drives the motor by a second setting amount (A1-A2) smaller than the first setting amount after the motor is driven by the steering operation direction driving means. Is driven in the direction opposite to the steering operation direction.

  According to the present invention, the steering operation direction driving means and the anti-steering operation direction driving means can be alternately operated at an appropriate timing.

  The first set amount is for setting the angle at which the motor is rotated from the start of driving in the steering operation direction of the motor, for setting the elapsed time from the start of driving in the steering operation direction of the motor, or For example, a motor that sets the time until the rotational speed (angular speed) of the motor reaches a preset speed can be employed. Further, the second set amount is for setting the angle at which the motor is rotated from the start of driving in the counter-steering direction of the motor, or for setting the elapsed time from the start of driving in the counter-steering direction of the motor, Or what sets time until the rotational speed (angular speed) to the counter steering operation direction of a motor reaches the preset setting speed etc. is employable.

  Another feature of the present invention is that the second set amount is an amount corresponding to a torsion of a tire that occurs as the motor is driven by the steering operation direction driving means.

  According to the present invention, the motor is driven in the anti-steering operation direction by an amount corresponding to the amount of twisting of the tire caused by the driving of the motor in the steering operation direction, that is, an amount necessary for returning the tire torsion. Therefore, the steering operation can be detected more easily.

  Another feature of the present invention is that a first setting amount changing means for changing the first setting amount (A1) to be larger when the steering operation speed of the steering wheel is fast than when the steering operation speed is slow is provided. is there.

  According to the present invention, when the driver performs a fast steering operation, the amount of one-time steering assist increases, so that smoother steering assist can be performed.

  Another feature of the present invention is that the steering operation direction drive means changes the target current (i2) energized to the motor to be higher when the steering operation speed of the steering handle is higher than when the steering operation speed is low. The current changing means is provided.

  According to the present invention, when the driver performs a fast steering operation, the steering assist torque increases, so that smoother steering assist can be performed.

  In the above description, in order to help the understanding of the invention, the reference numerals used in the embodiments are attached in parentheses to the configurations of the invention corresponding to the embodiments. It is not limited to the embodiment defined by the reference numerals.

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 flowchart showing a motor control amount calculation routine at the time of abnormality. It is operation | movement explanatory drawing at the time of abnormality of a steering torque sensor. It is a graph showing a threshold value map. It is a graph showing a target current map.

  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 includes a main shaft 12a connected to the upper end of the steering handle 11, a pinion shaft 12c connected to the rack and pinion mechanism 13, and a main shaft 12a and a pinion shaft 12c connected 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 the steering wheel 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 is constituted by, for example, a resolver, and outputs a detection signal indicating the rotation angle θm of the rotor of the motor 20. The motor rotation angle θm is used for calculating the electrical angle of the motor 20.

  Since the motor 20 and the steering shaft 12 are connected via the speed reducer 25, when the driver steers the steering handle 11, the rotor of the motor 20 is turned and the detection angle of the motor rotation angle sensor 23 is increased. Change. Therefore, the motor rotation angle sensor 23 is used not only for detecting the electrical angle of the motor 20 but also as a steering operation sensor for detecting the driver's steering operation. In this case, the steering operation direction of the steering handle 11 can be detected from the rotation direction of the motor 20 detected by the motor rotation angle sensor 23, and the amount of change of the rotation angle θm detected by the motor rotation angle sensor 23 is further increased. The steering operation amount of the steering handle 11 (the angle at which the steering handle 11 is rotated) can be detected based on the above. Further, the motor rotation speed (angular speed) can be detected by calculating the degree of change (time differential value) per unit time of the rotation angle θm detected by the motor rotation angle sensor 23, and based on this motor rotation speed. Thus, the steering speed of the steering handle 11 can be detected.

  A steering torque sensor 21 is provided between the steering handle 11 and the speed reducer 25 on the steering shaft 12 (main shaft 12a). The steering 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. For example, resolvers are provided at both ends of the torsion bar 12t, and the steering torque Tr is detected based on the difference between the rotation angles detected by the two resolvers.

  The steering torque Tr is a counterclockwise rotation with a positive value for a torque acting in the clockwise direction on the steering shaft 12 (torque in a torsional state where the upper portion of the torsion bar 12t is in the right rotation position relative to the lower portion). The torque acting in the direction (torque in a torsional state where the upper part of the torsion bar 12t is in the left rotation position relative to the lower part) is represented by a negative value. Further, when discussing the magnitude of the steering torque Tr, the absolute value thereof is used. In the present embodiment, the torsion angle of the torsion bar 12t is detected by a resolver, but may be detected by another rotational angle sensor such as an MR sensor.

  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.

  Various motors 20 can be employed. For example, when a three-phase DC brushless motor is used, a three-phase inverter may be used as the motor drive circuit 40. When a brushed motor is used, an H-bridge circuit is used as the motor drive circuit 40. Good. In the present embodiment, description will be made assuming that a three-phase DC brushless motor is used.

  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 current that is the control amount of the motor 20 and the switch drive signal to the motor drive circuit 40 so that the target current flows to the motor 20. And a motor control unit 60 for outputting. 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 72, an abnormality detection unit 73, and a control switching unit 74. The normal control amount calculation unit 71 receives the abnormality determination flag Ffail output from the abnormality detection unit 73, and calculates the target current i1 corresponding to the target assist torque when the abnormality determination flag Ffail is “0”. When the abnormality determination flag Ffail is “1”, the calculation block stops the calculation process. When the abnormality determination flag Ffail output from the abnormality detection unit 73 is input and the abnormality determination flag Ffail is “1”, the abnormality control amount calculation unit 72 executes an abnormality motor control amount calculation routine described later. Then, the target current i2 is calculated, and when the abnormality determination flag Ffail is “0”, the calculation block stops the calculation process.

  The abnormality detection unit 73 determines whether or not the steering torque sensor 21 is abnormal. When it is determined that there is no abnormality, the abnormality determination flag Ffail is set to “0”, and when it is determined that there is an abnormality. Sets the abnormality determination flag Ffail to “1”, and outputs the set abnormality determination flag Ffail to the normal control amount calculation unit 71, the abnormal control amount calculation unit 72, and the control switching unit 74.

  The control switching unit 74 inputs the target current i1 calculated by the normal control amount calculation unit 71 and the target current i2 calculated by the abnormal control amount calculation unit 72, and the abnormality determination flag Ffail is “0”. In this case, the target current i1 is selected, and when the abnormality determination flag Ffail is “1”, the target current i2 is selected. Then, the selected target current i 1 (or i 2) is set to the target current i *, and the target current i * 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 inputs the target current i * output from the control switching unit 74 and reads the motor current im (referred to as the actual current im) detected by the current sensor 41 provided in the motor drive circuit 40. Then, the deviation between the target current i * and the actual current im is calculated, and the target voltage v * is calculated so that the actual current im follows the target current i * by proportional-integral control using this deviation. 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 assist torque corresponding to the target current i * is applied to the steering mechanism 10.

  In this embodiment, since a three-phase DC brushless motor is used, the current feedback control unit 61 inputs the rotation angle θm detected by the motor rotation angle sensor 23 provided in the motor 20 and rotates the rotation. The angle θm is converted into an electrical angle, and the phase of the target current is controlled based on the electrical angle.

  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 steering torque sensor 21, and refers to the normal assist map shown in FIG. The assist torque Ta 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 Ta is set for each of a plurality of representative vehicle speeds V. The target assist torque Ta has a characteristic that increases as the magnitude (absolute value) of the torque Tr increases and decreases as the vehicle speed V increases. The target assist torque Ta is calculated so as to work in the direction of the steering torque Tr.

  In calculating the target assist torque Ta, various compensation torques may be added to the target assist torque Ta. 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.

  When the abnormality determination flag Ffail output from the abnormality detection unit 73 is “0”, the normal control amount calculation unit 71 repeatedly executes such calculation processing at a predetermined short cycle, and the target assist torque that is the calculation result The target current i1 obtained by dividing Ta by the torque constant is output to the control switching unit 74.

  The abnormality detection unit 73 determines whether the steering torque sensor 21 is abnormal. The steering torque sensor 21 can calculate the steering torque by detecting the torsion angle of the torsion bar 12t provided in the middle of the steering shaft 12 (main shaft 12a), and the rotation angle of one end of the torsion bar 12t. The torsion angle is detected from the angle difference between the rotation angle at the other end and the rotation angle at the other end. The steering torque sensor 21 includes a rotation angle sensor such as a resolver or an MR sensor in order to detect the rotation angle. In addition to the calculated value of the torsion angle corresponding to the steering torque Tr, the detection signal of the rotation angle sensor is also sent to the assist ECU 100. Output. Note that only the detection signal of the rotation angle sensor may be output to the assist ECU 100 and the assist ECU 100 may calculate the steering torque.

  The rotation angle sensor provided in the steering torque sensor 21 outputs a voltage signal corresponding to the rotation angle. Therefore, when the voltage value of the output signal is out of the proper range, it is considered that a disconnection or a short circuit has occurred in the rotation angle sensor. Also, for example, when using a rotation angle sensor whose output voltage periodically changes in a sine wave shape, such as a resolver, even when the output voltage is fixed to a constant value, disconnection or short-circuiting may occur. It is thought that it occurred.

  The abnormality detection unit 73 detects an abnormality of the steering torque sensor 21 as described above based on the output voltage of the rotation angle sensor (determines whether there is an abnormality). Then, according to the abnormality determination result of the steering torque sensor 21, the abnormality determination flag Ffail is set to “1” (abnormal) or “0” (abnormal).

  Next, the abnormal time control amount calculation unit 72 will be described. The normal control amount calculation unit 71 described above calculates the target current i1 based on the steering torque Tr, but cannot calculate the target current i1 when the steering torque sensor 21 fails. Therefore, the abnormal control amount calculation unit 72 calculates the target current i2 instead of the normal control amount calculation unit 71 when an abnormality of the steering torque sensor 21 is detected.

  When the abnormal-time control amount calculation unit 72 detects a stationary operation by the driver, the motor 20 is rotated by a certain amount in the steering operation direction to assist the steering, and after the motor 20 is stopped, the motor 20 is tired. When the steering operation is detected thereafter, the target current i2 is calculated so as to further rotate the motor 20 in the steering operation direction by a certain amount. When performing a steering operation when the vehicle speed is zero or near zero, that is, a stationary operation, the steering operation becomes difficult without steering assist. If the steering assist is performed with a size proportional to the steering angle as in the prior art, once the steering handle 11 is turned on the low μ road surface, the steering assist is activated and the steering operation is stopped even if the steering operation is stopped. The handle 11 turns. This is because the driver's steering operation cannot be properly detected after the steering operation is started.

  Therefore, in this embodiment, the steering assist is divided in time series, and it is determined whether or not the steering operation is performed every time the steering assist is performed by a certain amount. Again, a certain amount of steering assist is resumed. Hereinafter, the principle of detecting the steering operation will be described.

  An elastic element exists between the steering handle 11 and the ground contact surface of the tire. For example, a torsion bar 12t exists as an elastic element between the steering handle 11 and the speed reducer 25. Further, between the speed reducer 25 and the ground contact surface of the tire, elasticity due to the rubber portion of the tire, elasticity of the downstream portion of the steering shaft 12, mounting bushes of the rack housing 15 and the like exist as elastic elements.

  When the driver inputs a turning operation force to the steering handle 11, the elastic element is deformed, so that the steering handle 11 can be turned even if the direction of the ground contact surface of the tire does not change. Therefore, at the start of the steering operation, the rotor of the motor 20 connected to the speed reducer 25 is rotated. Therefore, the steering operation can be detected by capturing the change in the rotation angle θm detected by the motor rotation angle sensor 23. After the elastic element is deformed by the steering operation, when there is no steering assist, it becomes difficult to further rotate the steering handle 11 and the speed reducer 25 does not rotate. For this reason, the rotation angle θm detected by the motor rotation angle sensor 23 does not change. Therefore, although the driver inputs the turning operation of the steering handle 11, the operation cannot be detected. On the other hand, if the steering assist is performed with a torque proportional to the steering angle as in the conventional device, the steering wheel may turn even if the steering operation is stopped on a low μ road surface.

  Therefore, in the present embodiment, it is detected that the driver has started the steering operation by detecting the change in the rotation angle θm, and the motor 20 is rotated by a certain amount in the steering operation direction to assist the steering. Then, after the motor 20 is stopped, the motor 20 is rotated in the anti-steering operation direction by the amount of deformation of the elastic element (the amount of twist of the tire in this embodiment). As a result, the deformation of the elastic element (twist of the rubber portion of the tire) is restored, and the elastic element becomes elastically deformable in the steering operation direction. Therefore, if the driver continues the steering operation, the elastic force is deformed by the operation force, the speed reducer 25 rotates in the steering operation direction, and the steering operation can be detected by the change in the rotation angle θm associated therewith. it can. When the steering operation is detected, the motor 20 is rotated again in the steering operation direction to assist the steering. In this way, by dividing the steering assist by a certain amount and repeatedly performing the process of detecting the steering operation after reversing the deformation of the elastic element by reversing the motor 20 at the end of each steering assist, Steering assist is possible.

  Hereinafter, specific processing of the abnormal time control amount calculation unit 72 will be described. FIG. 4 shows an abnormal motor control amount calculation routine performed by the abnormal control amount calculator 72. The abnormal-time motor control amount calculation routine is repeatedly executed at a predetermined calculation cycle when the input abnormality determination flag Ffail is “1”.

  When the abnormal-time motor control amount calculation routine starts, first, the abnormal-time control amount calculation unit 72 reads the vehicle speed V and determines whether or not the vehicle speed V is equal to or less than a threshold value Vref in step S11. This threshold value Vref is a vehicle speed for determining whether or not the vehicle speed corresponds to a stationary operation that requires a large force for turning the wheel W. Accordingly, the threshold value Vref is set to zero or a value near zero (for example, 0 to 2 km / hour per hour). If the vehicle speed V is not less than or equal to the threshold value Vref, this routine is once ended. In this case, the target current i2 is zero (i2 = 0). In this embodiment, since there is a feature in the steering assist control at the time of the stationary operation when the torque sensor is abnormal, the setting of the target current i2 at the time of the stationary operation will be described here. When there is no steering assist, the configuration may be such that steering assist is not performed, or various conventionally known steering assists may be performed.

  On the other hand, when the vehicle speed V is equal to or less than the threshold value Vref (S11: Yes), the control amount calculation unit 72 at the time of abnormality reads the rotation angle θm detected by the motor rotation angle sensor 23 in step S12, and moves rightward or It is determined whether the steering operation has been performed in the left direction. For example, it is determined whether or not the rotation angle θm has changed to the right or left by a steering determination threshold value or more within a certain time. When the steering operation is not detected (S12: No), this routine is once ended.

  The abnormal time motor control amount calculation routine is repeated at a predetermined short calculation cycle. When it is determined “Yes” in step S12, that is, when a stationary operation is detected, the abnormal time control amount calculation unit 72 advances the process to step S13 and sets the value Σθ of the steering amount counter. Reset (Σθ = 0). Subsequently, the abnormal time control amount calculation unit 72 sets a target current i2 for rotating the motor 20 in the steering direction in step S14, and outputs the target current i2 to the control switching unit 74. In this embodiment, the target current i2 is set to a constant value in advance. Accordingly, a constant target current i2 specifying the rotation direction of the motor 20 is output. Note that outputting the target current i2 means outputting information representing the target current i2.

  As a result, the motor control unit 60 drives and controls the motor 20 according to the target current i2, and the motor 20 generates a constant steering assist torque. In the following step S15, the abnormal time control amount calculation unit 72 determines whether or not the steering amount Σθ, which is the value of the steering amount counter, is equal to or greater than a first threshold value A1 set in advance. The value of the steering amount counter represents the angle at which the motor 20 rotates after the motor 20 is driven, that is, the steering amount for which the steering assist is performed by the motor 20. Since the steering amount Σθ is zero at the start of the steering assist, the abnormal time control amount calculation unit 72 returns the process to step S14. Thus, the target current i2 for driving the motor 20 in the steering operation direction is output until the steering amount Σθ measured by the steering amount counter reaches the first threshold value A1.

  When the steering amount Σθ reaches the first threshold value A1 (S15: Yes), the abnormal time control amount calculation unit 72 sets a target current i2 for rotating the motor 20 in a direction opposite to the steering operation direction in step S16. The target current i2 is output to the control switching unit 74. This target current i2 is set to a constant value in advance. In the present embodiment, the target current i2 is set to have an absolute value smaller than the target current i2 set in step S14, but it is not always necessary to do so. As a result, the motor control unit 60 drives and controls the motor 20 in the anti-steering operation direction according to the target current i2. Thereby, the deformation of the elastic element in the steering mechanism 10 starts to be returned.

  In step S17, the abnormal time control amount calculation unit 72 determines whether or not the steering amount Σθ measured by the steering amount counter is equal to or less than the second threshold value A2 (<A1). When the motor 20 is rotated in the reverse direction, the steering amount Σθ measured by the steering amount counter is decremented. Immediately after the motor 20 is rotated in the reverse direction, the steering amount Σθ has not yet decreased to the second threshold value A2 or less, so the abnormal time control amount calculation unit 72 returns the process to step S16. Accordingly, the target current i2 for driving the motor 20 in the counter-steering operation direction is output until the steering amount Σθ measured by the steering amount counter reaches the second threshold value A2.

  The second threshold value A2 is a timing at which the tire twist returns. That is, the value (A1-A2) obtained by subtracting the second threshold value A2 from the first threshold value A1 is the steering amount in the counter-steering operation direction necessary for returning the tire twist. Accordingly, by repeatedly executing the processing of steps S16 and S17, the amount of twist of the tire is returned. Thus, when the steering amount Σθ decreases to the second threshold value A2 or less, the abnormal time control amount calculation unit 72 sets the target current i2 to zero in step S18 (i2 = 0). As a result, the driving of the motor 20 in the counter steering operation direction is stopped. In this case, the torsion of the tire is returned to the original without turning the wheel W in the counter-steering operation direction.

  When the process of step S18 is completed, the abnormal time control amount calculation unit 72 once ends this routine. Then, similar processing is executed at a predetermined short calculation cycle. When this routine is started after one calculation cycle, the twist of the tire has been restored, so if the driver inputs the steering operation force to the steering handle 11, the force causes the tire to be elastic in the steering operation direction. Deformation changes the rotation angle θm detected by the motor rotation angle sensor 23. Therefore, the driver's steering operation can be detected in step S12. For this reason, the steering assist can be restarted by the processing after step S13.

  Thus, according to this routine, during a stationary operation, after performing a certain amount of steering assist, the motor 20 is reversely rotated to return the deformation of the elastic element in the steering mechanism 10 including the tire. Then, a state in which the driver's steering operation can be detected is made, and the steering assist is resumed when the steering operation is detected from the state. That is, a process of detecting a steering operation → steering assist → deformation return of an elastic element → detecting a steering operation → steering assist is repeated cyclically. Therefore, even when the stationary operation is performed, the steering assist can be performed while the driver is performing the steering operation.

  Here, the operation when the abnormal motor control amount calculation routine is executed will be described with reference to FIG. In the description, three angles θ1, θ2, and θ3 are defined. As shown in FIG. 1, the angle (rotational position) of the steering handle 11 is θ1, the angle of the speed reducer 25 (rotational position on the input side) downstream of the steering torque sensor 21 is θ2, and the cutting angle of the ground contact surface of the tire Is a value obtained by multiplying the gear ratio, that is, an angle obtained by converting the turning angle of the tire contact surface to the angle of the steering wheel 11 is θ3. θ2 has a one-to-one correspondence with the motor rotation angle θm.

  As shown in FIG. 5, when the steering handle 11 is turned by the driver at time t1, the speed reducer 25 starts rotating with a delay. The rotation of the speed reducer 25 rotates the rotor of the motor 20. Then, at the time t2 when the change amount of the rotation angle θm detected by the motor rotation angle sensor 23 reaches the steering determination threshold value, the abnormal time control amount calculation unit 72 detects that the steering operation has been performed (S12). : Yes). As a result, the target current i * flows through the motor 20 and the motor 20 generates a constant assist torque in the steering operation direction. Thus, the cutting angle of the ground contact surface of the tire increases.

  The reduction gear 25 is rotated by driving the motor 20, and the motor 20 is driven until the angle θ2 reaches the first threshold value A1 '. Note that the first threshold value A <b> 1 ′ represents an angle obtained by converting the first threshold value A <b> 1 that is the threshold value of the motor rotation angle θm into the rotation angle of the reduction gear 25. Similarly, the second threshold value A <b> 2 ′ in the drawing represents an angle obtained by converting the second threshold value A <b> 2 that is the threshold value of the motor rotation angle θm into the rotation angle of the speed reducer 25. In this example, the steering torque direction of the driver is reversed because the angle θ2 of the reduction gear 25 exceeds the angle θ1 of the steering handle 11 during the steering assist. At time t3 when the angle θ2 of the speed reducer 25 reaches the first threshold value A1 ′ (S15: Yes), the target current i * that is the anti-steering operation direction flows to the motor 20, and the motor 20 is in the anti-steering operation direction. Torque is generated. Thereby, the angle θ2 of the speed reducer 25 decreases. At this time, the twisted portion of the tire is returned. When the angle θ2 of the speed reducer 25 decreases to the second threshold value A2 ′, that is, when the speed reducer 25 rotates in the anti-steering operation direction by the angle (A1′−A2 ′), the energization to the motor 20 is stopped. (Time t4: S18). At this time, since the twisted portion of the tire has been restored, the steering handle 11 can be turned by the driver.

  When the steering operation force of the driver is continuously input to the steering handle 11, the steering handle 11 rotates in the steering operation direction, and the speed reducer 25 rotates in the steering operation direction. Then, at time t5 when the rotation angle of the speed reducer 25 exceeds the threshold value from time t4, the abnormal time control amount calculation unit 72 detects that the steering operation has been performed (S12: Yes). As a result, the target current i * flows through the motor 20 and the motor 20 generates a constant assist torque in the steering operation direction.

  As described above, in this embodiment, every time when a steering assist is performed by a certain amount, it is possible to determine whether or not the steering operation is performed by returning to the original amount corresponding to the twist of the tire, and the steering operation is performed in that state. Is detected, the process of performing a certain amount of steering assist is repeated again. Therefore, even if an abnormality occurs in the steering torque sensor 21, an appropriate stationary operation can be performed.

<Modification 1>
In the above-described embodiment, the steering operation (operation direction, steering operation amount) input by the driver to the steering handle 11 is detected based on the rotation angle θm detected by the motor rotation angle sensor 23. Thus, for example, a steering angle sensor that detects the rotation angle of the steering shaft 12 (main shaft 12a) may be provided to directly detect the steering operation of the steering handle 11. In this case, the steering angle sensor is not limited to the one provided on the steering handle 11 side relative to the steering torque sensor 21, and may be provided on the speed reducer 25 side.

<Modification 2>
In the above-described embodiment, the driver's steering operation is detected by determining whether or not the amount of change in the motor rotation angle θm within a certain time is equal to or greater than a threshold value. When the operation speed becomes equal to or higher than the threshold value, it may be determined that the driver's steering operation has been performed. In this case, the steering operation speed is not limited to the motor rotation angular speed (time differential value of the motor rotation angle θm), and when a steering angle sensor is provided, the steering angular speed (time differential value of the steering angle) may be used. it can.

<Modification 3>
In the embodiment described above, the one-time steering amount for rotating the motor 20 in the steering operation direction is set to a constant value (first threshold value A1 at the motor rotation angle θm), but the one-time steering amount is variable. You may make it do. For example, when it is desired for the driver to steer quickly, the one-time steering amount (A1) may be increased. In this case, when a steering operation is detected in step S12, the steering speed (motor rotational angular speed or steering angular speed of the steering handle 11) is calculated, and the first threshold value A1 that increases as the steering speed increases is set. What is necessary is just to incorporate the process to set between step S12 and step S13. For example, a threshold map as shown in FIG. 6 may be stored in the abnormal time control amount calculator 72, and the first threshold A1 for the steering speed may be set with reference to this threshold map. According to this, a smoother steering assist can be performed.

<Modification 4>
In the embodiment described above, the target current i2 set in step S14 is a constant value, but the target current i2 may be variable. For example, when the driver wants to steer quickly, the target current i2 may be increased. In this case, when a steering operation is detected in step S12, a steering speed (motor rotation angular speed or steering angular speed of the steering handle 11) is calculated, and a target current i2 that becomes larger as the steering speed is higher is set. What is necessary is just to incorporate a process between step S12 and step S13. For example, a target current map as shown in FIG. 7 may be stored in the abnormal time control amount calculator 72, and the target current i2 with respect to the steering speed may be set with reference to the target current map. According to this, a smoother steering assist can be performed.

<Modification 5>
In the above-described embodiment, the one-time steering amount for rotating the motor 20 in the steering operation direction is set by the rotation angle (the integrated value of the angle: A1), but the one-time steering amount is the rotation angle. It is not limited to what is set. For example, the amount of steering once may be set according to the elapsed time from the start of driving of the motor 20. That is, the motor 20 may be stopped when the motor 20 is activated in the steering operation direction and a set time has elapsed. This also makes it possible to set a single steering amount. Further, for example, the amount of steering once may be set by the time from the start of driving the motor 20 until the motor rotation speed reaches a preset set speed. That is, the motor 20 may be stopped when the motor 20 is started in the steering operation direction and the motor rotation speed reaches a preset set speed. This also makes it possible to set a single steering amount.

  Similarly, the one-time steering amount for rotating the motor 20 in the counter-steering operation direction is not limited to the one set by the rotation angle (the integrated value of angles: A1-A2). For example, a single steering amount may be set based on the elapsed time from the start of driving of the motor 20, or depending on the time from the start of driving of the motor 20 until the motor rotational speed reaches a preset set speed. It may be set.

<Modification 6>
In the above-described embodiment, since a three-phase brushless motor is used as the motor 20, the motor rotation angle sensor 23 is provided. For example, when a motor with a brush is used, the motor rotation angle sensor 23 is provided. It is often not equipped. In this case, with regard to detection of the steering operation in step S12, for example, the motor rotation speed and the rotation direction can be estimated by measuring a counter electromotive voltage generated between the motor terminals. Therefore, it may be determined that the steering operation has been performed when the rotational speed exceeds a preset threshold value. The motor rotation speed can be detected by dividing the back electromotive voltage by the reverse voltage constant.

  As for the timing of stopping the motor 20 determined in step S15 or step S17, as described in the fifth modification, the elapse of the set time or the arrival timing to the set speed may be used. The motor rotation speed is obtained by calculating the counter electromotive voltage. According to the sixth modification, even when a brush motor without the motor rotation angle sensor 23 is used, the abnormal motor control amount calculation routine can be executed without providing the steering angle sensor. Therefore, it can be carried out at a low cost.

<Modification 7>
When the steering operation is performed from the vicinity of the stroke end (near the maximum steering angle), there may be a case where the motor 20 cannot be rotated to the first threshold A1 due to the stroke end in steps S14 to S15. Therefore, for example, when the motor 20 is driven in the steering operation direction in step S14, an upper limit time is provided, and the steering amount counter value Σθ is equal to the first threshold value even if the upper limit time has elapsed since the start of driving the motor 20. If A1 is not reached, the motor 20 may be forcibly driven in reverse or stopped. According to this, overheating of the motor 20 can be prevented.

  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.

  In the present embodiment, vehicle speed detecting means (step S11) for detecting the vehicle speed is provided, and the steering assist is performed when the vehicle speed is zero or near zero and the steering operation of the steering handle 11 is detected. However, a configuration in which the process of step S11 is not provided is also possible.

  Moreover, it can also comprise so that the said modifications 1-7 may be combined arbitrarily.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 10 ... Steering mechanism, 11 ... Steering handle, 12 ... Steering shaft, 12t ... Torsion bar, 20 ... Motor, 21 ... Steering torque sensor, 23 ... Motor rotation angle sensor, 24 ... Vehicle speed sensor, 25 DESCRIPTION OF SYMBOLS ... Reducer, 40 ... Motor drive circuit, 50 ... Electronic control circuit, 60 ... Motor control part, 70 ... Motor control amount calculation part, 71 ... Control amount calculation part at normal time, 72 ... Control amount calculation part at abnormal time, 73 ... Abnormality detection unit, 74: control switching unit, 100: assist ECU, Wfl: left front wheel, Wfr: right front wheel

Claims (5)

A steering torque sensor for detecting a steering torque input from the steering handle to the steering shaft;
A motor provided in the steering mechanism for generating steering assist torque;
An abnormality detecting means for detecting an abnormality of the steering torque sensor;
A normal-time motor control means for driving and controlling the motor based on the steering torque detected by the steering torque sensor when no abnormality is detected in the steering torque sensor;
In an electric power steering apparatus for a vehicle, comprising: an abnormal motor control means for driving and controlling the motor based on information different from the steering torque when an abnormality of the steering torque sensor is detected.
The abnormal-time motor control means includes:
Steering operation detecting means for detecting a steering operation of the steering handle;
Steering operation direction drive means for driving the motor in the steering operation direction of the steering handle when a steering operation of the steering handle is detected;
An electric power steering apparatus for a vehicle, comprising: an anti-steering operation direction driving unit that drives the motor in a direction opposite to the steering operation direction after the motor is driven by the steering operation direction driving unit. The steering operation direction driving means drives the motor by a first set amount in the steering operation direction when a steering operation of the steering handle is detected,
The anti-steering direction driving means drives the motor in a direction opposite to the steering operating direction by a second set amount smaller than the first set amount after the motor is driven by the steering operation direction driving means. 2. The electric power steering apparatus according to claim 1, wherein   3. The electric power steering apparatus for a vehicle according to claim 2, wherein the second set amount is an amount corresponding to a torsion of a tire generated when the motor is driven by the steering operation direction driving unit.   4. The first setting amount changing means for changing the first setting amount to be larger when the steering operation speed of the steering handle is faster than when the steering operation speed is slow. Electric power steering device for vehicles.   When the steering operation speed of the steering wheel is high, the steering operation direction drive means includes target current changing means for changing the target current to be supplied to the motor to be higher than that when the steering operation speed is low. The electric power steering device for a vehicle according to any one of claims 1 to 4.

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