JP2013199256A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce burden of steering operation even when a fault of a torque sensor is detected.SOLUTION: An electric power steering device is mounted on a vehicle and includes a steering shaft, a pinion shaft, a torsion bar, a rack shaft, a motor 51, a torque sensor 61, a steering angle sensor 62, a fault determination part 112 determining whether the torque sensor 61 is normal or not, a torque target current calculation part 121 that calculates a torque target current on the basis of the steering torque, a steering angle target current calculation part 131 that calculates a steering angle target current on the basis of a steering angle, and an output control part 141 that controls a target current to be output to the motor 51. The output control part 141 executes a torque control mode for controlling the target current according to the torque target current when the torque sensor 61 is determined to be normal, and executes a steering angle control mode for controlling the target current according to the steering angle target current when the torque sensor 61 is determined to be faulty.

Description

  The present invention relates to an electric power steering apparatus.

  An electric power steering device is known as a device for assisting (assisting) a driver's steering in a vehicle (see, for example, Patent Documents 1 and 2). In the electric power steering apparatus, the steering torque is detected by a torque sensor, and the motor is driven based on the steering torque.

JP-A 61-169366 Japanese Patent No. 3274377

  Here, in the conventional electric power steering apparatus, when a failure of the torque sensor is detected and confirmed, the assist by the motor is stopped to prevent self-steering. If it does so, since it will be in the state where a driver | operator requires big steering force, the burden of the steering operation to a driver | operator will become large.

  Therefore, an object of the present invention is to provide an electric power steering device that reduces the burden of steering operation even when a torque sensor failure is detected.

  As means for solving the problems, the present invention provides a steering shaft that rotates integrally with a steering wheel, an intermediate shaft, a torsion bar that connects the steering shaft and the intermediate shaft, and is twistable, and a steering wheel. A vehicle width direction axis that is connected to and reciprocating in the vehicle width direction, a conversion mechanism that converts the rotational movement of the intermediate shaft into a linear movement of the vehicle width direction axis, and an assist force that assists the steering force are generated A motor for detecting the steering torque generated by the torsion bar, a horn angle sensor for detecting the horn angle of the steering shaft, a failure determination means for determining normality / failure of the torque sensor, and the torque Torque target current calculation that calculates the torque target current based on the steering torque detected by the sensor A steering angle target current calculation means for calculating a steering angle target current based on the steering angle detected by the steering angle sensor, and a target current output to the motor according to the torque target current or the steering angle target current. Output control means, and an electric power steering device mounted on a vehicle, wherein the output control means determines that the target current according to the torque target current when the failure determination means determines that the torque sensor is normal. A torque control mode for controlling the target current, and when the failure determination means determines that the torque sensor has failed, a steering angle control mode for controlling the target current according to the steering angle target current is executed. This is an electric power steering device.

  According to such a configuration, when the output control unit determines that the torque sensor has failed, the output control unit executes the steering angle control mode in which the target current is controlled according to the steering angle target current. Thereby, even when a failure of the torque sensor is detected, the burden of the steering operation can be reduced.

  In the electric power steering device, the steering angle target current limit value setting means for setting a steering angle target current limit value that is a limit value of the steering angle target current is provided, and the steering angle target current limit value setting means includes: When the failure determination means detects a failure signal from the torque sensor, the steering angle target current limit value is gradually increased. When the failure determination means detects a failure signal from the torque sensor, the torque sensor has failed. It is preferable that the torque sensor failure be determined when the gradually increasing steering angle target current limit value reaches a predetermined steering angle target current limit value.

  According to such a configuration, the failure determination means determines that the torque sensor has failed when a failure signal is detected from the torque sensor, and the steering angle target current limit value that gradually increases is a predetermined steering angle target current limit value. Is reached, the torque sensor failure is determined. Thereby, a predetermined time can be formed between the failure detection of the torque sensor and the failure confirmation of the torque sensor.

  Thus, by gradually increasing the rudder angle target current limit value, when shifting from the torque control mode to the rudder angle control mode, the steering angle target current (target current) increases rapidly or excessively. (Target current) output can be prevented. In addition, by forming a predetermined time between the failure detection of the torque sensor and the failure determination (failure determination) of the torque sensor, an error in the failure of the torque sensor with respect to an instantaneous torque signal (steering torque) abnormality due to noise or the like. Confirmation can be prevented.

  Further, in the electric power steering apparatus, the steering angle target current limit value setting means may calculate a rate at which the steering angle target current limit value gradually increases based on a steering angle detected by the steering angle sensor. Increasing the height is preferable.

According to such a configuration, the steering angle target current limit value setting means increases the rate at which the steering angle target current limit value gradually increases as the steering angular speed increases. It is possible to vary the predetermined time between failure confirmation).
That is, when the steering angular velocity is high, the predetermined time is shortened, and the torque control mode is shifted to the steering angle control mode at an early stage. On the other hand, when the rudder angular velocity is low, the predetermined time becomes longer and the rudder angle target current limit value rises gently, so that the rudder angle target current easily rises gently.

  The electric power steering apparatus further includes torque target current limit value setting means for setting a torque target current limit value that is a limit value of the torque target current, wherein the torque target current limit value setting means is the failure determination means. When a failure signal is detected from the torque sensor, the torque target current limit value is preferably set to zero.

  According to such a configuration, the torque target current limit value setting means sets the torque target current limit value to 0 when the failure determination means detects a failure signal from the torque sensor. As a result, the torque target current is also zero and self-steering is prevented.

  Further, in the electric power steering apparatus, the steering angle target current calculation means is configured to increase the steering angle speed calculated based on the steering angle detected by the steering angle sensor during execution of the steering angle control mode. It is preferable to correct the angle target current so as to increase.

  According to such a configuration, the steering angle target current calculation unit corrects the steering angle target current to increase as the steering angular speed increases during execution of the steering angle control mode. Thereby, the steering angle target current becomes an appropriate magnitude.

  The electric power steering apparatus may further include a vehicle speed sensor that detects the speed of the vehicle, and the steering angle target current calculation unit may detect the vehicle speed detected by the vehicle speed sensor during execution of the steering angle control mode. It is preferable to correct so that the steering angle target current becomes smaller as it becomes higher.

  According to such a configuration, the steering angle target current calculation means corrects the steering angle target current so that it decreases as the vehicle speed increases during execution of the steering angle control mode. Thereby, the steering angle target current becomes an appropriate magnitude.

  ADVANTAGE OF THE INVENTION According to this invention, even when the failure of a torque sensor is detected, the electric power steering apparatus which reduces the burden of steering operation can be provided.

It is a lineblock diagram of the electric power steering device concerning this embodiment. It is a block diagram which shows the structure of ECU which concerns on this embodiment. It is a flowchart which shows operation | movement of the electric power steering apparatus which concerns on this embodiment. 4 is a diagram illustrating a relationship between torque generated by a torsion bar and a voltage (torque signal) output from a torque sensor. It is a map which shows the relationship between a torque, a target electric current, and a vehicle speed. It is a map which shows the relationship between a steering angle, a target electric current, and a vehicle speed. It is a map which shows the relationship between the steering angular velocity and the correction coefficient of target current. It is a time chart which shows one operation example of the electric power steering device concerning this embodiment.

  An embodiment of the present invention will be described with reference to FIGS.

≪Configuration of electric power steering device≫
The electric power steering apparatus 1 according to the present embodiment is an apparatus that is mounted on a vehicle and steers a front wheel W that is a steered wheel.

The electric power steering apparatus 1 is configured as a rack assist type that applies an assist force to the rack shaft 41.
The electric power steering apparatus 1 includes a steering shaft 11, a pinion shaft 21 (intermediate shaft), a torsion bar 31, a rack shaft 41 (vehicle width direction axis), a motor 51, a torque sensor 61, and a steering angle sensor 62. And a resolver 63 and an ECU 100 (Electronic Control Unit) that controls the entire system.

<Steering shaft>
The steering shaft 11 is rotatably supported with respect to the vehicle body, and a steering wheel 12 operated by a driver is fixed to an upper end portion of the steering shaft 11. The steering shaft 11 rotates together with the steering wheel 12.
The steering shaft 11 may be divided into a plurality of parts, and a plurality of divided steering shafts may be connected by a universal joint (a cross joint). The same applies to the pinion shaft 21.

<Pinion shaft>
The pinion shaft 21 is rotatably supported with respect to the vehicle body, and a pinion 22 is formed at a lower end portion thereof. The pinion 22 meshes with a rack 42 described later, and a rack and pinion mechanism (a conversion mechanism) that converts the rotational motion of the pinion shaft 21 into the reciprocating motion (linear motion) of the rack shaft 41 in the vehicle width direction. ). However, the conversion mechanism may be a ball and nut mechanism in addition to the rack and pinion mechanism.

<Torsion bar>
The torsion bar 31 connects the lower end portion of the steering shaft 11 and the upper end portion of the pinion shaft 21. The torsion bar 31 is configured to be twistable in accordance with the driver's steering force and steering speed (steering angular speed) input from the steering wheel 12, and generates a steering torque (Nm) corresponding to the amount of twist. It is like that. The torsion bar 31 is configured to be twisted by appropriately changing the thickness, length, material, and the like.

<Rack shaft>
The rack shaft 41 extends in the vehicle width direction and is reciprocally movable in the vehicle width direction with respect to the vehicle body. Both ends of the rack shaft 41 are connected to a front wheel W which is a steering wheel via a tie rod and a knuckle arm (not shown). It is connected. A rack 42 is formed on the rack shaft 41, and the pinion 22 is engaged with the rack 42. The rack shaft 41 reciprocates in accordance with the rotation direction and rotation angle (rotation amount) of the pinion 22, The rudder angle (front wheel rudder angle) of the front wheels W is variable.

<Motor>
The motor 51 is an electric motor that generates an assist force that assists the steering force input to the steering wheel 12 in order for the driver to steer the front wheels W. The assist force generated by the motor 51 is input (applied) to the rack shaft 41 in this embodiment. When the assist force is input in this way, the steering force input by the driver to the steering wheel 12 is reduced, and the burden of the steering operation is reduced.

  More specifically, the motor 51 is constituted by, for example, a brushless motor, and is constituted by a hollow mold having a hollow portion through which the rack shaft 41 is inserted on the central axis thereof, and is disposed on the radially inner side. A cylindrical rotor having a hollow portion, a stator arranged concentrically on the outer side in the radial direction of the rotor, and a coil that is attached to the teeth of the stator and distributed to the U-phase, V-phase, and W-phase And. When a three-phase alternating current is supplied from the ECU 100 to the coil, the rotor rotates according to the magnitude and direction of the current, and an assist force is generated by the motor 51. The assist force is transmitted via the ball screw mechanism. Thus, it is input to the rack shaft 41.

The ball screw mechanism is integrated with the rack screw 41 and the ball screw shaft that rotates when power (assist force) is input from the rotor, and the ball screw shaft is integrated with the rack shaft 41. And a ball screw nut that reciprocates in the vehicle width direction.
However, the motor 51 is not limited to the hollow type, and is not limited to the ball screw mechanism, and the assist force generated by the motor 51 may be transmitted to the rack shaft 41 by another mechanism.

<Torque sensor>
The torque sensor 61 is a sensor that detects the steering torque generated in the torsion bar 31 and outputs it to the ECU 100.
Such a torque sensor 61 includes, for example, a sensor that detects rotational displacement (relative position) in the circumferential direction between the steering shaft 11 and the pinion shaft 21 and calculates steering torque based on the rotational displacement. The rotational displacement varies according to the amount of twist of the torsion bar 31.

  Specifically, the torque sensor 61 is configured by, for example, a non-contact magnetic detection type, and is fixed to the steering shaft 11 and an annular magnet integrated with the steering shaft 11, and the pinion shaft 21 is fixed to the pinion shaft 21. The magnetism detection element (magnetoresistive element) that detects the change in the circumferential direction of the magnetic flux density generated by the magnet and the steering torque is calculated based on the detection signal of the magnetism detection element and corresponds to the steering torque. And a microcomputer (see FIG. 4, arrow A1) that converts the torque signal (voltage, electric signal). 4 is obtained by a preliminary test or the like and stored in the torque sensor 61 in advance. Further, in the X axis of FIG. 4, “0” indicates a neutral position, “(+)” corresponds to the right steering side, and “(−)” corresponds to the left steering side. The same applies to the other FIG.

<Rudder angle sensor>
The rudder angle sensor 62 detects the rudder angle (position) of the steering shaft 11 when steered with reference to the neutral position (steering angle 0 (deg)) where the steering wheel 12 is not steered, and the ECU 100 It is a sensor which outputs to. Such a steering angle sensor 62 is configured similarly to the torque sensor 61.

<Resolver>
The resolver 63 is a sensor that detects the rotational position (rotational angle θ) of the rotor of the motor 51 and outputs it to the ECU 100. Specifically, the resolver 63 generates a sine wave signal and a cosine wave signal corresponding to the rotational position of the rotor, and outputs them to an output control unit 141 described later on the ECU 100 (see FIG. 2). . The output control unit 141 detects the position of the rotor based on the input sine wave signal and cosine wave signal, and feedback-controls the current output to the motor 51 while detecting the position of the rotor. .

<Other equipment>
IG64 is a start switch of the electric power steering apparatus 1 (vehicle), and is provided around the driver's seat. And IG64 outputs the ON / OFF signal to ECU100.

  The engine rotation speed sensor 65 is a sensor that detects the rotation speed (rpm) of an engine (not shown) that generates power for running the vehicle, that is, the rotation speed of the crankshaft. The engine rotation speed sensor 65 outputs the detected engine rotation speed to the ECU 100. The engine rotation speed sensor 65 includes a crankshaft angle (crank angle) detected by the crank angle sensor, and calculation means for calculating the rotation speed of the crankshaft (engine rotation speed) based on the crank angle. It can also be configured.

  The vehicle speed sensor 66 is a sensor that detects the vehicle speed (the speed of the vehicle) and is attached at an appropriate position. The vehicle speed sensor 66 outputs the detected vehicle speed to the ECU 100.

  The warning lamp 67 is an informing means for notifying the driver that the torque sensor 61 is out of order by being lit (operated) when the failure of the torque sensor 61 is confirmed.

  The battery 71 is a power source of the ECU 100, and is constituted by, for example, a 12V battery.

<ECU>
The ECU 100 is a control device that electronically controls the electric power steering apparatus 1 and includes a CPU, a ROM, a RAM, various interfaces, an electronic circuit, and the like. Various devices are installed according to programs stored therein. Control and execute various processes.

ECU 100 includes a three-phase AC generation circuit 211 and a relay 212.
The three-phase alternating current generating circuit 211 is an inverter circuit that converts direct current from the battery 71 into three-phase alternating current in accordance with a command from the output control unit 141 described later. The three-phase AC generation circuit 211 supplies three-phase AC to the motor 51.

  Relay 212 is provided between three-phase AC generation circuit 211 and battery 71, and turns on / off electrical connection between three-phase AC generation circuit 211 and battery 71 in accordance with a command from relay control unit 111 described later. Switch.

  The ECU 100 also includes a relay control unit 111, a failure determination unit 112 (failure determination unit), a torque target current calculation unit 121 (torque target current calculation unit), and a torque target current limit value setting unit 122 (torque target current limit). Value setting means), rudder angle target current calculation unit 131 (steering angle target current calculation means), rudder angle target current limit value setting unit 132 (steering angle target current limit value setting means), and output control unit 141 (output) A control unit) and a current detection unit 142.

  The relay control unit 111 has a function of performing ON / OFF control of the relay 212 based on the ON / OFF signal of the IG 64 and the engine speed.

  The failure determination unit 112 has a function of determining normality / failure of the torque sensor 61 based on a torque signal (voltage) from the torque sensor 61.

  The torque target current calculation unit 121 calculates a steering torque based on a torque signal (voltage) from the torque sensor 61 (see arrow A2 in FIG. 4), and outputs a torque target current (to be output to the motor 51 based on the steering torque). Arms) is provided (see FIG. 5). The torque target current is an effective value. The steering angle target current (Arms) described later is also an effective value.

  The torque target current limit value setting unit 122 has a function of setting a torque target current limit value that is a limit value of the torque target current. The limit value of the torque target current is an absolute value of the limit value (upper limit side) of the torque target current and the limit value (lower limit side) of the torque target current (see FIG. 5).

  The steering angle target current calculation unit 131 has a function of calculating a steering angle target current (Arms) to be output to the motor 51 based on the steering angle from the steering angle sensor 62 (see FIG. 6).

  The steering angle target current limit value setting unit 132 has a function of setting a steering angle target current limit value that is a limit value of the steering angle target current. The limit value of the steering angle target current is an absolute value of the limit value (upper limit side) of the steering angle target current and the limit value (lower limit side) of the steering angle target current (see FIG. 6).

  The output control unit 141 has a function of controlling the target current output to the motor 51 according to the torque target current or the target steering angle current. That is, the output control unit 141 has a function of executing the torque feedback control mode or the steering angle feedback control mode.

  The torque feedback control mode is a mode that is executed when the torque sensor 61 is normal. The output control unit 141 adopts the torque target current as the target current so that the torque target current is supplied to the motor 51. This is a mode for controlling the three-phase AC generating circuit 211.

  The steering angle feedback control mode is a mode that is executed when the torque sensor 61 is out of order. The output control unit 141 adopts the steering angle target current as the target current, and this steering angle target current is applied to the motor 51. In this mode, the three-phase AC generation circuit 211 is controlled to be supplied.

  The current detection unit 142 has a function of detecting a current that is currently generated by the three-phase AC generation circuit 211 and is output to the motor 51.

≪Operation of electric power steering system≫
The operation of the electric power steering device 1 will be described with reference to FIG.

  In step S101, the relay control unit 111 determines whether to start assist control for assisting the steering force. Here, in the state where the ON signal of IG64 is detected, it is determined that the assist control is started when the engine speed is equal to or higher than a predetermined speed. The predetermined rotation speed is obtained by a preliminary test or the like and stored in advance in the relay control unit 111.

  When it determines with starting assist control (S101 * Yes), the process of ECU100 progresses to step S102. On the other hand, when it determines with not starting assist control (S101 * No), ECU100 repeats determination of step S101.

  In step S102, the relay control unit 111 turns on the relay 212.

  In step S103, the failure determination unit 112 determines whether or not the torque sensor 61 is normal. Here, when the torque signal (voltage) input from the torque sensor 61 is not less than the lower threshold and not more than the upper threshold, it is determined that the torque sensor 61 is normal, and the torque signal is smaller than the lower threshold or lower than the upper threshold. Is larger, it is determined that a failure of the torque sensor 61 has been detected (see FIG. 4). The lower limit threshold value and the upper limit threshold value that serve as determination criteria are obtained by a preliminary test or the like and are stored in the failure determination unit 112 in advance.

  When it is determined that the torque sensor 61 is normal (S103 / Yes), the processing of the ECU 100 proceeds to step S104. On the other hand, when it is determined that the torque sensor 61 is not normal (S103, No), that is, when the torque sensor 61 detects that there is a possibility of failure, the process of the ECU 100 proceeds to step S109.

In step S104, the torque target current limit value setting unit 122 determines whether or not the torque target current limit value is equal to or greater than a predetermined torque target current limit value (predetermined value).
The initial value of the torque target current limit value is zero. The predetermined torque target current limit value is obtained by a preliminary test or the like, and is stored in advance in the torque target current limit value setting unit 122. Further, the predetermined torque target current limit value has a relationship that increases as the rated output of the motor 51 increases.

  When it is determined that the torque target current limit value is equal to or greater than the predetermined torque target current limit value (S104 / Yes), the process of the ECU 100 proceeds to step S105. On the other hand, when it is determined that the torque target current limit value is not equal to or greater than the predetermined torque target current limit value (S104, No), the process of the ECU 100 proceeds to step S106.

  In step S106, the torque target current limit value setting unit 122 gradually increases the torque target current limit value. The rate of gradually increasing the torque target current limit value (Arms / s) is obtained by a preliminary test or the like and stored in advance in the torque target current limit value setting unit 122.

In step S105, the ECU 100 (output control unit 141) executes the torque feedback control mode.
That is, the torque target current calculation unit 121 calculates the steering torque based on the torque signal (voltage) from the torque sensor 61 and the map of FIG. 4 (see arrow A2). The map of FIG. 4 is obtained by a preliminary test or the like, and is stored in advance in the torque target current calculation unit 121.

Next, the torque target current calculation unit 121 calculates a torque target current based on the calculated steering torque, the vehicle speed input from the vehicle speed sensor 66, and the map of FIG. In this case, the torque target current is in a range not less than the torque target current limit value (lower limit) and not more than the torque target current limit value (upper limit). Further, the process passes through step S106, and during the gradual increase of the torque target current limit value, a range of the torque target current limit value (lower limit) being gradually increased and not more than the torque target current limit value (upper limit) being gradually increased, To do.
Note that, as shown in FIG. 5, the absolute value of the torque target current increases as the absolute value of the steering torque increases and as the vehicle speed decreases. 5 is obtained by a preliminary test or the like, and is stored in advance in the torque target current calculation unit 121.

  Next, the output control unit 141 controls the three-phase AC generation circuit 211 so that the target current according to the torque target current calculated by the torque target current calculation unit 121 is output to the motor 51.

  In this case, the output control unit 141 detects a current actually output from the three-phase AC generation circuit 211 to the motor 51 via the current detection unit 142, and the detected current is a torque target current (target current). Give feedback so that The output control unit 141 detects the position of the rotor of the motor 51 via the resolver 63 and feeds back the detected position to a position corresponding to the torque target current (target current). The relationship between the torque target current (target current) and the rotor position of the motor 51 is obtained by a preliminary test or the like and stored in advance in the output control unit 141.

  In step S107, the relay control unit 111 determines whether to stop the assist control for assisting the steering force. Here, when the OFF signal of IG64 is detected, or when the rotational speed of the engine is not equal to or higher than the predetermined rotational speed, it is determined to stop the assist control.

  When it is determined that the assist control is to be stopped (S107 / Yes), the process of the ECU 100 proceeds to step S108. On the other hand, when it determines with not stopping assist control (S107 * No), the process of ECU100 progresses to step S103.

  In step S108, the relay control unit 111 turns off the relay 212.

  Thereafter, the processing of the ECU 100 proceeds to step S101.

  In step S109, the torque target current limit value setting unit 122 sets the torque target current limit value to zero. As a result, the torque target current calculated by the torque target current calculation unit 121 is also zero (see FIG. 8). Accordingly, self-steering is prevented.

In step S110, the steering angle target current limit value setting unit 132 determines whether the steering angle target current limit value is equal to or greater than a predetermined steering angle target current limit value (predetermined value).
The initial value of the steering angle target current limit value is zero. The predetermined rudder angle target current limit value is obtained by a preliminary test or the like, and is stored in advance in the rudder angle target current limit value setting unit 132. Further, the predetermined steering angle target current limit value has a relationship that increases as the rated output of the motor 51 increases.

  When it is determined that the steering angle target current limit value is equal to or greater than the predetermined steering angle target current limit value (S110 / Yes), the process of the ECU 100 proceeds to step S111. On the other hand, when it is determined that the steering angle target current limit value is not equal to or greater than the predetermined steering angle target current limit value (S110 · No), the process of the ECU 100 proceeds to step S112.

In step S111, the ECU 100 (output control unit 141) executes the steering angle feedback control mode.
That is, the steering angle target current calculation unit 131 is based on the steering angle (steering angle signal) input from the steering angle sensor 62, the vehicle speed input from the vehicle speed sensor 66, and the map of FIG. Calculate the current. In this case, the steering angle target current is set to a range not less than the steering angle target current limit value (lower limit) and not more than the steering angle target current limit value (upper limit).
As shown in FIG. 6, the absolute value of the steering angle target current increases as the absolute value of the steering angle increases and as the vehicle speed decreases. Further, the map of FIG. 6 is obtained by a preliminary test or the like, and is stored in the steering angle target current calculation unit 131 in advance.

In addition to this, the steering angle target current may be corrected so as to increase as the steering angular speed increases. That is, a steering angle target current correction coefficient is calculated based on the steering angular speed and the map of FIG. 7, and the corrected steering angle target current is obtained by multiplying the correction coefficient by the steering angle target current. .
Note that, as shown in FIG. 7, the correction coefficient increases as the absolute value of the steering angular velocity increases. Further, the map of FIG. 7 is obtained by a preliminary test or the like, and is stored in the steering angle target current calculation unit 131 in advance.

  Next, the output control unit 141 controls the three-phase AC generation circuit 211 so that the target current according to the steering angle target current calculated by the steering angle target current calculation unit 131 is output to the motor 51.

  In this case, the output control unit 141 detects the current actually output from the three-phase AC generation circuit 211 to the motor 51 via the current detection unit 142, and the detected current is the steering angle target current (target current). ) Is fed back. Further, the output control unit 141 detects the position of the rotor of the motor 51 via the resolver 63 and feeds back the detected position to a position corresponding to the steering angle target current (target current). Note that the relationship between the steering angle target current (target current) and the position of the rotor of the motor 51 is obtained by a preliminary test or the like and stored in advance in the output control unit 141.

  Thereafter, the processing of the ECU 100 proceeds to step S107.

In step S112, the ECU 100 (output control unit 141) executes the steering angle feedback control mode as in step S111.
However, since the steering angle target current limit value is equal to or less than the predetermined value until Step S114 · Yes described later, the steering angle target current calculated by the steering angle target current calculation unit 131 is limited by the steering angle target current limit value. Is done.

In step S113, the steering angle target current limit value setting unit 132 gradually increases the steering angle target current limit value.
In this case, the steering angle target current limit value setting unit 132 varies the rate of gradually increasing the steering angle target current limit value based on the steering angular speed (deg / s). That is, as the rudder angular velocity increases, the rate of gradually increasing the rudder angle target current limit value is increased (see FIG. 8). Note that the rudder angular velocity is calculated based on the rudder angle from the rudder angle sensor 62.

  In step S114, the steering angle target current limit value setting unit 132 determines whether or not the steering angle target current limit value is equal to or greater than a predetermined steering angle target current limit value (predetermined value).

  When it is determined that the steering angle target current limit value is equal to or greater than the predetermined steering angle target current limit value (S114 / Yes), that is, when it is determined that the steering angle target current limit value has reached the predetermined steering angle target current limit value The process of the ECU 100 proceeds to step S115. On the other hand, when it is determined that the steering angle target current limit value is not equal to or greater than the predetermined steering angle target current limit value (S114, No), the ECU 100 repeats the determination in step S114.

  In step S115, the failure determination unit 112 determines (determines) that the torque sensor 61 has failed. That is, the failure determination unit 112 determines a failure of the torque sensor 61 and outputs a signal corresponding to the failure to the output control unit 141.

  In step S116, failure determination unit 112 turns on (turns on) warning lamp 67.

  Thereafter, the processing of the ECU 100 proceeds to step S107.

≪Effect of electric power steering system≫
The effects of the electric power steering apparatus 1 will be described with reference to FIG.
If a failure of the torque sensor 61 is detected during execution of the torque feedback control mode (S105) (Yes in S104), the torque target current limit value is set to 0 (S109), the torque target current is also set to 0, and the self-steer is Is prevented.

  Next, when shifting from the torque feedback control mode (S105) to the steering angle feedback control mode (S112), the steering angle target current is limited by the gradually increasing steering angle target current limit value. While reducing / relaxing, it is possible to prevent a sudden increase in the steering angle target current (target current) or an output of an excessive steering angle target current (target current).

Further, since the rate at which the steering angle target current limit value gradually increases is varied by the steering angular speed (S113), smooth mode transition can be realized.
That is, when the rudder angular velocity is high, the rate at which the rudder angle target current limit value gradually increases is increased, so that the rudder angle target current limit value reaches the predetermined rudder angle target current limit value early, and mode transition (switching) is fast. Therefore, the non-assist time is shortened, and the burden on the steering operation of the driver is reduced.
On the other hand, when the rudder angular velocity is low, the rate at which the rudder angle target current limit value gradually increases is reduced. Therefore, the rudder angle target current limit value gradually increases toward the predetermined rudder angle target current limit value, and the rudder angle target current also increases. It will rise gradually, and mode transition will be gradual.

  When the steering angle target current limit value reaches the predetermined steering angle target current limit value (S114, Yes), the failure of the torque sensor 61 is determined (S115), that is, the failure detection and the failure determination of the torque sensor 61 are performed. Since a predetermined time is formed between the torque sensor and the torque sensor, it is possible to prevent erroneous determination of a failure of the torque sensor with respect to an instantaneous torque signal (steering torque) abnormality due to noise or the like.

≪Modification≫
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to this, For example, you may change as follows.

  In the above-described embodiment, the case where the rack shaft 41 is configured by a rack assist type that applies an assist force is illustrated, but, for example, a column assist type and a pinion assist type may be configured.

1 Electric Power Steering Device 11 Steering Shaft 12 Steering Wheel 21 Pinion Shaft (Intermediate Shaft)
22 pinion (conversion mechanism)
31 Torsion bar 41 Rack axis (vehicle width direction axis)
42 racks (conversion mechanism)
51 Motor 61 Torque sensor 62 Steering angle sensor 66 Vehicle speed sensor 112 Failure determination unit (failure determination means)
121 Torque target current calculation unit (torque target current calculation unit)
122 Torque target current limit value setting unit (torque target current limit value setting means)
131 Rudder angle target current calculation part (steering angle target current calculation means)
132 Steering angle target current limit value setting unit (steering angle target current limit value setting means)
141 Output control unit (output control means)

Claims (6)

A steering shaft that rotates integrally with the steering wheel;
An intermediate shaft,
A torsion bar connecting the steering shaft and the intermediate shaft and being twistable;
A vehicle width direction axis connected to the steering wheel and reciprocating in the vehicle width direction;
A conversion mechanism for converting the rotational movement of the intermediate shaft into a linear movement of the vehicle width direction axis;
A motor that generates an assist force for assisting the steering force;
A torque sensor for detecting a steering torque generated in the torsion bar;
A snake angle sensor for detecting the snake angle of the steering shaft;
Failure determination means for determining normality / failure of the torque sensor;
Torque target current calculation means for calculating a torque target current based on the steering torque detected by the torque sensor;
Rudder angle target current calculating means for calculating a rudder angle target current based on the rudder angle detected by the snake angle sensor;
Output control means for controlling a target current output to the motor according to a torque target current or a steering angle target current;
Comprising an electric power steering device mounted on a vehicle,
The output control means includes
When the failure determination means determines that the torque sensor is normal, it executes a torque control mode for controlling the target current according to the torque target current,
When the failure determination means determines that the torque sensor has failed, a steering angle control mode for controlling a target current according to a steering angle target current is executed. A steering angle target current limit value setting means for setting a steering angle target current limit value which is a limit value of the steering angle target current,
The steering angle target current limit value setting means, when the failure determination means detects a failure signal from the torque sensor, gradually increases the steering angle target current limit value,
The failure determination means determines that the torque sensor has failed when a failure signal is detected from the torque sensor, and when the gradually increasing steering angle target current limit value reaches a predetermined steering angle target current limit value. The electric power steering apparatus according to claim 1, wherein a failure of the torque sensor is determined. The rudder angle target current limit value setting means increases the rate at which the rudder angle target current limit value gradually increases as the rudder angular velocity calculated based on the rudder angle detected by the rudder angle sensor increases. The electric power steering apparatus according to claim 2. A torque target current limit value setting means for setting a torque target current limit value which is a limit value of the torque target current;
4. The torque target current limit value setting unit sets the torque target current limit value to 0 when the failure determination unit detects a failure signal from the torque sensor. 5. The electric power steering apparatus according to Item 1. The steering angle target current calculation means corrects the steering angle target current to increase as the steering angular speed calculated based on the steering angle detected by the steering angle sensor increases during execution of the steering angle control mode. The electric power steering apparatus according to any one of claims 1 to 4, wherein: A vehicle speed sensor for detecting the speed of the vehicle;
The steering angle target current calculation means corrects the steering angle target current so that it decreases as the speed of the vehicle detected by the vehicle speed sensor increases during execution of the steering angle control mode. The electric power steering apparatus according to any one of claims 1 to 5.

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