JP2003200842A - Electric power steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate steering operations such as a steering operation during stopping in case a vehicle stops due to failure of a torque sensor, in an electric power steering system. <P>SOLUTION: In case failure occurs in the torque sensor, when a vehicular speed V is 0 or below a predetermined value in proximity to 0 (namely, threshold value V0), based on a steering angle θ and a steering angle velocity ωwhich is a differential value thereof, in the case of ω=0 or |θ|≤α, a current target value It is set to 0 (S134), in the case of ω>0 and θ>α, to k(θ-α) (S142), in the case of ω>0 and θ<-α to -k(θ+α) (S144), in the case of ω<0 and θ>α, to -k(θ-α) (S152), and in the case of ω<0 and θ<-α, to k(θ+α) (S154). In a case where the vehicular speed V exceeds the threshold value V0, the current target value It is set in such a way that the current target value It is reduced at a predetermined descent rate to finally become 0 (S128). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for applying a steering assist force to a steering mechanism of a vehicle by an electric motor, and more particularly to steering when a torque sensor fails in such an electric power steering apparatus. Regarding assistance.

[0002]

2. Description of the Related Art Conventionally, there has been used an electric power steering apparatus which applies a steering assist force to a steering mechanism by driving an electric motor according to a steering torque applied to a steering wheel (steering wheel) by a driver.
This electric power steering device is provided with a torque sensor that detects a steering torque applied to a steering wheel that is an operating means for steering, and the electric current that should be supplied to the electric motor based on the steering torque detected by the torque sensor is provided. The target value is set. Then, a command value to be given to the drive means of the electric motor is generated based on the deviation between the target value and the detected value of the current actually flowing in the electric motor.
The drive means of the electric motor is a PW that generates a pulse width modulation signal (PWM signal) having a duty ratio according to the command value.
An M signal generation circuit and a motor drive circuit configured by using a power transistor that turns on / off according to the duty ratio of the PWM signal, and drives a voltage according to the duty ratio, that is, a voltage according to a command value. Apply to the motor. The current flowing in the electric motor due to this voltage application is detected by the current detection circuit, and the difference between the detected value and the target value is used as the deviation for generating the command value. In the electric power steering device, feedback control is thus performed so that the electric current of the target value set based on the steering torque flows through the electric motor.

In such an electric power steering apparatus, when a torque sensor fails due to some abnormality, conventionally, steering assist by an electric motor is stopped to prevent malfunction of the steering apparatus and avoid dangerous behavior. It was However, in this case, the steering torque that the driver should apply to the steering wheel becomes large. In particular, when the steering wheel operation (hereinafter referred to as "stationary steering operation") is performed when the vehicle speed is 0 or close to 0, the steering torque that the driver should apply to the steering wheel becomes very large. As a result, when the vehicle is stopped because the torque sensor has failed,
Next, it becomes difficult to perform a steering operation for starting the vehicle. For example, if a torque sensor fails,
In order to move the vehicle from the stop point to the repair shop, we often stop the vehicle once on the road shoulder, etc.
It is necessary to start the stopped vehicle. But,
Due to the start, there is a problem that it is virtually impossible to perform the stationary steering operation while the vehicle is stopped.

On the other hand, a structure in which steering assist is performed based on the vehicle speed and the rotation angle of the steering wheel when a failure occurs in the torque sensor has been proposed, for example, in Japanese Patent Laid-Open No. 9-58505. However, this is intended to eliminate the driver's anxiety caused by the sudden stop of the steering assist due to the failure of the torque sensor, and the steering assist due to the steering angle and the like at that point causes the steering assist force to be zero. It is temporary until. Therefore, it is not easy to perform the steering operation of starting the vehicle by performing the stationary steering operation from the stop point after the vehicle stops and the steering assist force becomes zero.

[0005]

Therefore, according to the present invention, even when the vehicle is once stopped due to a failure of the torque sensor, the steering operation for starting the vehicle to, for example, a repair shop can be easily performed. As described above, it is an object of the present invention to provide an electric power steering device that improves the operability of steering when the vehicle is stopped when the torque sensor fails.

[0006]

SUMMARY OF THE INVENTION A first aspect of the present invention is directed to a steering mechanism of a vehicle by driving an electric motor according to a steering torque applied by an operating means for steering the vehicle. An electric power steering apparatus for providing a steering torque, a torque sensor for detecting the steering torque, a steering angle sensor for detecting a steering angle indicating an operation amount of the operating means, and a vehicle speed sensor for detecting a vehicle speed that is the speed of the vehicle. A target value setting means for setting a target value of a current to be supplied to the electric motor, a current detecting means for detecting a current flowing through the electric motor and outputting a detected value of the current, and the current target value. Control means for generating a command value for feedback control for driving the electric motor based on a deviation from the detected current value, and in accordance with the command value It is provided with a drive means for driving the electric motor and a failure determination means for determining whether or not a failure has occurred in the torque sensor, wherein the target value setting means is that the failure determination means has not failed. If it is determined, the current target value is set according to the steering torque detected by the torque sensor, and the failure determination unit determines that a failure has occurred, and the vehicle speed sensor detects the failure. When the vehicle speed is equal to or less than a predetermined value near 0, the electric motor generates a larger steering assist force as the absolute value of the steering angle detected by the steering angle sensor increases.
The current target value is set.

According to the first aspect of the invention, as the steering wheel is farther away from the neutral position (the absolute value of the steering angle θ is greater), a larger steering assist force is generated in the same direction as the steering wheel rotating direction. The electric motor is driven to. This improves steering operability such as stationary steering operation when the vehicle is temporarily stopped due to a failure of the torque sensor, so that the vehicle can be sent to a repair shop etc. without causing any difficulty in steering operation. It can be launched to move.

In a second aspect based on the first aspect, the target value setting means determines that a failure has occurred by the failure determining means, and the vehicle speed detected by the vehicle speed sensor is 0. Alternatively, when it is equal to or less than a predetermined value near 0, the current target value It is set as follows based on the steering angle θ and a steering angular velocity ω that is a differential value of the steering angle: ω = 0 or | θ | ≦ α, It = 0, ω> 0 and θ> α, It = k (θ−α), ω> 0 and θ <−α, It = −k (θ + α), ω It = −k (θ−α) when <0 and θ> α, It = k (θ + α) when ω <0 and θ <−α, where k is a positive coefficient and α is the operation described above. In the means, the dead band angle is left and right from the neutral position where θ = 0, and when the electric motor is It> 0, ω 0 becomes rotated in the direction, shall rotate omega <0 becomes direction when It <0.

According to the second aspect of the invention, the current target value It is set in consideration of the vehicle speed, the steering angle θ, the steering angular velocity ω, and the dead zone angle α, so that the stationary steering operation or the like is stopped. The steering operation can be further facilitated.

In a third aspect based on the first aspect, when the target value setting means determines that a failure has occurred by the failure determination means, the vehicle speed detected by the vehicle speed sensor is 0. Alternatively, when it exceeds a predetermined value near 0, the current target value is reduced at a predetermined drop rate and set to 0.

According to the third aspect of the invention as described above, the current target value It is set when the vehicle speed is restarted and the vehicle speed exceeds 0 or a predetermined value in the vicinity of 0, particularly after a failure occurs in the torque sensor and the vehicle is stopped. The steering assist force does not suddenly decrease because it gradually decreases to 0. Therefore, the driver can perform the steering operation without feeling uncomfortable.

[0012]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. <1. Overall Configuration> FIG. 1 is a schematic diagram showing a configuration of an electric power steering apparatus according to an embodiment of the present invention together with a vehicle configuration related thereto. In this electric power steering apparatus, a steering shaft 102 having one end fixed to a steering wheel (steering wheel) 100 as an operating means for steering, and a rack and pinion mechanism 104 connected to the other end of the steering shaft 102.
And a steering angle sensor 2 for detecting the steering angle of the steering wheel 100.
A torque sensor 3 for detecting a steering torque applied to the steering shaft 102 by operating the steering wheel 100; and an electric motor 6 for generating a steering assist force for reducing a driver's load due to steering operation (steering operation).
And a reduction gear 7 for transmitting the steering assist force to the steering shaft 102 and a power supply from an on-vehicle battery 8 via an ignition switch 9, and a steering angle sensor 2,
An electronic control unit (ECU) 5 that controls driving of the motor 6 based on the sensor signals from the torque sensor 3 and the vehicle speed sensor 4 is provided. When the driver operates the steering wheel 100 in a vehicle equipped with such an electric power steering device, the steering torque caused by the operation is detected by the torque sensor 3. The ECU 5 drives the motor 6 based on either the detected steering torque or the steering angle detected by the steering angle sensor 2 and the vehicle speed detected by the vehicle speed sensor 4. As a result, the motor 6 generates a steering assist force, and the steering assist force is applied to the steering shaft 102 via the reduction gear 7, whereby the load on the driver due to the steering operation is reduced. That is, the sum of the steering torque applied by the steering wheel operation and the torque due to the steering assist force generated by the motor 6 is output torque, and the steering shaft 10
2 to the rack and pinion mechanism 104. As a result, when the pinion shaft rotates, the rotation is converted into a reciprocating motion of the rack shaft by the rack and pinion mechanism 104. Both ends of the rack shaft are connected to a wheel 108 via a connecting member 106 including a tie rod and a knuckle arm, and the direction of the wheel 108 changes according to the reciprocating motion of the rack shaft.

<2. Configuration of Control Device> FIG. 2 is an ECU which is a control device in the electric power steering device.
5 is a block diagram showing the functional configuration of FIG. This ECU 5
Is a microcomputer (hereinafter abbreviated as “microcomputer”) 10 that functions as a motor control unit, and a PWM that generates a pulse width modulation signal (PWM signal) having a duty ratio according to a command value Dfb output from the microcomputer 10. The signal generation circuit 18 includes a motor drive circuit 20 that applies a voltage according to the duty ratio of the PWM signal to the motor 6, and a current detector 19 that detects a current flowing through the motor 6.

The microcomputer 10 executes a predetermined program stored in its internal memory to execute the target current setting unit 12, the subtractor 14, the feedback control calculation unit (hereinafter abbreviated as "FB control calculation unit"). And 16 function as a motor control unit. In this motor control unit, the detected value of the steering torque output from the torque sensor 3 (hereinafter referred to as "steering torque detected value") Ts or the detected value of the steering angle output from the steering angle sensor 2 (hereinafter referred to simply as "steering"). Angle θ ”) and a vehicle speed detection value V output from the vehicle speed sensor 4 (hereinafter simply referred to as“ vehicle speed V ”), a target value It of a current to be passed through the motor 6
To decide. The subtractor 14 calculates a deviation It-Is between the current target value It and the detected value Is of the motor current output from the current detector 19. The FB control calculation unit 16 calculates the proportional-plus-integral control based on the deviation It-Is.
The command value Dfb for feedback control to be given to the PWM signal generation circuit 18 is generated.

The PWM signal generation circuit 18 uses the command value D
A pulse signal having a duty ratio corresponding to fb, that is, a PWM signal whose pulse width changes according to the command value Dfb is generated. The motor drive circuit 20 applies a voltage according to the pulse width (duty ratio) of the PWM signal to the motor 6.
The motor 6 generates a torque having a magnitude and direction according to the current flowing by the voltage application.

FIG. 3 is a circuit diagram showing one structural example of the motor drive circuit 20. In this example, four electric field effect transistors (hereinafter referred to as “FET”) 21 to
A bridge circuit is constituted by 24, and this bridge circuit is connected between the power supply line and the ground line of the battery 8. Then, when the right steering is to be assisted, the PWM signal is input from the PWM signal generation circuit 18 to the gates of the FETs 21 and 24, and the FETs 22 and 23 are input.
A signal for turning them off is input to the gate of. As a result, the motor 6 is applied with a voltage according to the duty ratio of the PWM signal by the motor drive circuit 20,
Generates torque that assists steering to the right. On the other hand, when the left steering should be assisted, the PWM signal is input from the PWM signal generation circuit 18 to the gates of the FETs 22 and 23, and a signal for turning them off is input to the gates of the FETs 21 and 24. As a result, the motor 6 is applied with a voltage according to the duty ratio of the PWM signal in the opposite direction to the above by the motor drive circuit 20, and generates a torque for assisting the leftward steering.

<3. Operation> FIG. 4 is a flowchart showing a process for motor control by the microcomputer 10 in the present embodiment. In the present embodiment, when the ignition switch 9 is turned on and the ECU 5 is powered on, the microcomputer 10 operates as follows, whereby the motor control unit having the configuration shown in FIG. 2 is realized.

That is, the microcomputer 10 firstly outputs the steering angle θ from the steering angle sensor 2, the steering torque detection value Ts from the torque sensor 3, the vehicle speed V from the vehicle speed sensor 4, and the current detector 1.
The detected current value Is is inputted from 9 respectively (step S
12-S18). Here, it is assumed that the position where the steering angle θ = 0 is the neutral position, the steering from the neutral position to θ> 0 corresponds to the rightward steering, and the steering to θ <0 corresponds to the leftward steering. Further, the motor 6 generates torque in a direction that assists the steering to the right when the current flowing therethrough is positive (when Is> 0), and when the current is negative (when Is <0). It is assumed that torque is generated in the direction that assists the steering to the left.

When the steering angle θ, the steering torque detection value Ts, the vehicle speed V, and the current detection value Is are input as described above, it is then determined whether or not a failure has occurred in the torque sensor 3. Failure determination processing is executed (step S2
0). Various known methods can be adopted as the failure determination method in this failure determination processing. For example, the method disclosed in Japanese Patent No. 2597167, that is, a plurality of sensors are provided as the torque sensor 3 for detecting the steering torque, and the maximum value and the minimum value of the steering torque detected by these sensors are set. It is possible to employ a method of determining that the torque sensor 3 has failed when the difference becomes equal to or larger than a predetermined value. Also, instead of this,
The method disclosed in JP 2001-106099 A, that is, when the motor current detection value Is is equal to or more than a predetermined current value and the steering torque detection value Ts is equal to or more than a predetermined torque value, the torque A method of determining that the sensor 3 has an abnormality (failure) may be adopted.

Next, the target current setting process is executed to determine the target value It of the current to be passed through the motor 6 based on the result of the above-described failure determination process (step S2).
2). FIG. 5 is a flowchart showing the procedure of this target current setting process.

In this target current setting process, when no fault is detected in the torque sensor 3 in the fault determination process, that is, when it is determined No in step S122, a table (hereinafter " Referred to as a "normal assist table"), the current target value It corresponding to the steering torque detection value Ts and the vehicle speed V is determined (step S124). The normal assist table is a table showing the relationship between the steering torque and the absolute value of the target current value to be passed through the motor 6 with the vehicle speed as a parameter, and is stored in advance in the memory of the microcomputer 10.
Further, instead of such a normal assist table, the current target value It may be determined by a functional expression that uniquely calculates the current target value It from the steering torque detection value Ts and the vehicle speed V.

On the other hand, when it is determined in the failure determination process that the torque sensor 3 has failed, that is, when it is determined Yes in step S122, the vehicle speed V is 0 or a predetermined value near 0 ( For example, a few km /
It is determined whether or not the threshold V0 which is h) is exceeded (step S126). When the vehicle speed V is 0 or exceeds a predetermined value near 0 (V> V0), that is, Yes in step S126.
If s is determined, the target current value I
The current target value It is set so that t is reduced and finally becomes 0 (step S128). The current target value It is thus set to 0 in order to prevent the steering device from malfunctioning by stopping the steering assist by the electric motor and avoid the dangerous behavior. Further, it is preferable that the descent rate is selected from a value that gently lowers the target current value It to such an extent that the driver does not feel uncomfortable due to the sudden decrease in the steering assist force. By reducing the current target value It at such a drop rate, for example,
Not only when the torque sensor 3 fails during running, but also when the vehicle speed V exceeds 0 or a predetermined value near 0 because the torque sensor 3 fails, the steering assist force is suddenly increased. Since it does not decrease, the driver does not feel uncomfortable. Further, when the vehicle speed V is 0 or less than or equal to a predetermined value near 0 (V ≦ V0), that is, when it is determined as No in step S126, appropriate steering assistance should be performed without using the steering torque detection value Ts. The target current value It is determined as follows.

That is, first, the steering angular velocity ω = dθ / dt is calculated by differentiating the steering angle θ detected by the steering angle sensor 2 with time (step S130). Next, the steering angular velocity ω is 0 or | θ | ≦ α, and the steering angular velocity ω is
> 0 and | θ |> α, steering angular velocity ω <0 and | θ |> α
It is determined which of the two is (step S132). However, in practice, a relatively small positive value ε is preset and −
It is preferable to consider ω = 0 if ε ≦ ω ≦ ε, ω <0 if ω <−ε, and ω> 0 if ω> ε.

As a result of the determination in step S132, if the steering angular velocity ω = 0 or | θ | ≦ α, the steering wheel 100
Is not operated or is within the range of the dead zone angle, it is determined that the steering assist is not necessary, and the current target value It is set to 0 (step S134). Here, α is a dead zone angle, and the handle 100 is an angle ± α from the neutral position to the left and right.
When operated within the range, the angle means that steering assistance is unnecessary. In addition, as described in detail below,
When θ |> α, the steering assist force is generated in the direction in which the steering should be assisted, that is, in the same direction as the rotation direction of the steering wheel 100.

If the result of determination in step S132 is that steering angular velocity ω> 0 and | θ |> α, further steering angle θ
Is greater than the dead zone angle α (step S
140). As a result of this determination, if θ> α, the steering wheel 100 is turned to the right on the right side beyond the dead zone angle from the neutral position, so a constant value k (θ−α) determined almost in proportion to the steering angle θ. ) Is set as the current target value It (step S142). Here, k is a positive proportional constant, and the same shall apply hereinafter. In order to realize such an operation of the microcomputer 10, for example, in a memory inside the microcomputer 10, a table as shown in FIG. 7 showing a relationship between the absolute value of the current target value It and the steering angle θ (hereinafter referred to as “failure”). "Assistance table") is stored in advance and the absolute value of the current target value It corresponding to the input steering angle θ is set by referring to this failure assistance table. As described above, if the absolute value of the current target value It is set to be larger as the absolute value of the steering angle θ is larger, the steering assist force becomes larger as the steering angle θ becomes larger at the time of stationary steering, which facilitates the steering operation. Become. The sign of the current target value It may be set to be the same as the sign of the steering angular velocity ω because the steering assist force is generated in the same direction as the rotation direction of the steering wheel 100. Further, as a result of the determination in step S140, if θ> α (that is, θ <−α), the steering wheel 100 is turned to the right on the left side beyond the dead zone angle from the neutral position. A constant value −k (θ + α), which is determined substantially in proportion to the angle θ, is set as the current target value It (step S144). Here, the minus sign added to the proportional constant k is for making the current target value It a positive value, and the steering assist force is always the steering wheel 1
It occurs in the same direction as the rotation direction of 00.

If the result of determination in step S132 is that steering angular velocity ω <0 and | θ |> α, further steering angle θ
Is greater than the dead zone angle α (step S
150). As a result of this determination, if θ> α, the steering wheel 100 is turned leftward beyond the dead zone angle from the neutral position, so a constant value −k (θ− α) is set as the current target value It (step S152). Further, as a result of the determination in step S140, if θ> α (that is, θ <−α), the steering wheel 100 is turned leftward beyond the dead zone angle from the neutral position. A constant value k (θ + α), which is determined substantially in proportion to the angle θ, is set as the current target value It (step S154). Here, also in order to obtain the current target value It corresponding to the steering angle θ, the failure assist table shown in FIG. 7 may be referred to as in the above. However, the sign needs to be inverted.

When the current target value It is set as described above, the target current setting process is ended and the process returns to the main routine shown in FIG.

When the target current setting process is completed, the PWM signal generating circuit is operated by the proportional-plus-integral control calculation based on the deviation It-Is between the set current target value It and the detected current value Is input from the current detector 19. A command value Dfb for feedback control to be given to 18 is generated (step S24). Then, this command value Dfb is output from the microcomputer 10 as the motor control unit (step S2).
6). Then, the process returns to step S12, and thereafter, steps S12 to S12 are performed until the ignition switch 9 is turned off.
26 is repeatedly executed.

The command value Dfb output from the microcomputer 10 as the motor control section is input to the PWM signal generation circuit 18, where a PWM signal having a pulse width varying according to the command value Dfb is generated. This PWM signal is supplied to the motor drive circuit 20, and the motor drive circuit 20
A voltage according to the pulse width (duty ratio) of the PWM signal is applied to the motor 6.

In this way, the PWM signal generation circuit 18
A voltage corresponding to the command value Dfb given to the motor 6 is applied to the motor 6, and a torque having a magnitude and a direction corresponding to the current flowing through the motor 6 is generated from the motor 6 by the voltage application. The current detector 19 detects the current flowing through the motor 6 at this time and outputs the current detection value Is. The detected current value Is is input to the subtractor 14 and used to calculate the deviation It-Is as described above.

The torque generated by the motor 6 driven as described above is transmitted to the steering shaft 102 via the reduction gear 7 as steering assist torque.

<4. Effect> According to the above-described embodiment, when the torque sensor 3 has a failure and the vehicle speed V detected by the vehicle speed sensor 4 is 0 or a predetermined value near 0 or less, the current target value It is It is set as follows based on the steering angle θ and the steering angular velocity ω that is the differential value thereof. That is, the current target value It is (1) set to 0 when the steering wheel 100 is not operated or within the dead zone angle (ω = 0 or | θ | ≦ α), and (2) When the handle 100 is turned to the right from the neutral position over the dead zone angle (ω> 0 and θ>
(when α), k (θ−α) is set, and (3) when the steering wheel 100 is turned to the right on the left side beyond the dead zone angle from the neutral position (ω> 0 and θ <−α) (4) is set to −k (θ + α), and (4) when the steering wheel 100 is turned leftward from the neutral position beyond the dead zone angle (when ω <0 and θ> α). -K (θ-α)
(5) When the steering wheel 100 is turned leftward beyond the dead zone angle from the neutral position (ω <0
When θ <−α), k (θ + α) is set.

As a result, the motor 6 is driven so as to generate a large steering assist force in the same direction as the steering direction as the steering wheel 100 moves farther from the neutral position (the absolute value of the steering angle θ increases). In this way, when the torque sensor 3 fails and is temporarily stopped, the operability of steering such as stationary steering operation is improved as compared with the conventional case, so that the vehicle can be repaired without causing a great difficulty in the steering operation. You can start to move to etc.

When the torque sensor 3 fails and stops, and then the vehicle restarts and the vehicle speed exceeds 0 or a predetermined value near 0, the current target value It has the above-described predetermined drop rate. The steering assist force does not suddenly decrease because it gradually decreases to 0. Therefore, the driver can perform the steering operation without feeling uncomfortable.

<5. Modification> In the above-described embodiment, the current target value It that is set when the torque sensor 3 fails and the vehicle speed is equal to or less than a predetermined value near 0 or 0 depends on the steering angle θ. Determined, but further, vehicle speed V
The current target value It may be changed according to the above. That is, the proportional constant k may be a function of the vehicle speed V. Similarly, the drop rate of the current target value It that is set when the vehicle speed exceeds 0 or a predetermined value near 0 when the torque sensor 3 fails may also be a function of the vehicle speed V.

Further, in the above embodiment, when the torque sensor 3 fails during traveling, the target current value It is gradually decreased at a predetermined drop rate to zero.
The current target value It may be lowered in any manner, such as being set according to one or both of the steering angle θ and the vehicle speed V.

Further, in the above embodiment, when the torque sensor 3 fails, the current target value It is determined by the steering angle θ.
Is set based on the steering angular velocity ω and the vehicle speed V, and in addition to these, the current target value is also considered in consideration of the steering angular acceleration γ = dω / dt = d ² θ / dt ² which is the time derivative of the steering angular velocity ω. It may be set.

The functional structure of the motor control unit shown in FIG. 2 is a simplified one in which parts that are not directly related to the present invention are omitted. In an actual electric power steering device, steering stability is improved. Phase compensation for improving, feedforward control for improving control response, and the like are also performed.

Although the above embodiment has been described focusing only on the failure in the torque sensor 3, in the actual electric power steering apparatus, other failures such as the failure of the current detector 19 are also detected and the safety is improved. In order to secure the vehicle or secure the self-propelled vehicle at a predetermined distance as described above, a failure process or a temporary motor control process corresponding to the failure is performed.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an electric power steering apparatus according to an embodiment of the present invention together with a vehicle configuration related thereto.

FIG. 2 is a block diagram showing a functional configuration of an ECU that is a control device in the electric power steering device according to the above embodiment.

FIG. 3 is a circuit diagram showing a configuration example of a motor drive circuit in the embodiment.

FIG. 4 is a flowchart showing a procedure of control processing for controlling a motor in the above embodiment.

FIG. 5 is a flowchart showing a procedure of a target current setting process for determining a target value of a current to be passed through the motor in the above embodiment.

FIG. 6 is a diagram showing a normal assist table for setting a target value of a current to be supplied to a motor in the above embodiment.

FIG. 7 is a diagram showing a failure assist table for setting a target value of a current to be supplied to the motor when the torque sensor fails in the above embodiment.

[Explanation of symbols]

2 ... Rudder angle sensor 3 ... Torque sensor 4 ... Vehicle speed sensor 5 ... Electronic control unit (ECU) 6 ... Motor 8 ... Battery 10 ... Microcomputer (motor control unit) 12 ... Target current setting section 14 ... Subtractor 16 ... Feedback control calculation unit (FB control calculation unit) 18 ... PWM signal generation circuit 19 ... Current detector 20 ... Motor drive circuit It ... Target current value Is ... Current detection value Ts ... Steering torque detection value V ... Vehicle speed θ… Steering angle ω ... Steering angular velocity α: dead zone angle

Claims (3)

[Claims] 1. An electric power steering apparatus for applying a steering assist force to a steering mechanism of a vehicle by driving an electric motor according to a steering torque applied by an operating means for steering a vehicle, wherein the steering torque is A torque sensor for detecting, a steering angle sensor for detecting a steering angle indicating an operation amount of the operating means, a vehicle speed sensor for detecting a vehicle speed that is the speed of the vehicle, and a target value of a current to be supplied to the electric motor. Target value setting means for setting, current detection means for detecting a current flowing through the electric motor and outputting a detection value of the current, and based on a deviation between the current target value and the current detection value, the electric motor Control means for generating a command value for feedback control for driving; drive means for driving the electric motor according to the command value; A failure determination unit that determines whether or not a failure has occurred in the Luk sensor, and the target value setting unit detects the torque sensor when the failure determination unit determines that no failure has occurred. The current target value is set according to the steering torque, and the vehicle speed detected by the vehicle speed sensor is 0 or less than or equal to a predetermined value when the failure determination unit determines that a failure has occurred. The electric power steering is characterized in that the electric current target value is set so that the electric motor generates a larger steering assist force as the absolute value of the steering angle detected by the steering angle sensor increases. apparatus. 2. The target value setting means is a case where the failure determination means determines that a failure has occurred, and when the vehicle speed detected by the vehicle speed sensor is 0 or a predetermined value near 0 or less. The electric power steering device according to claim 1, wherein the current target value It is set as follows based on the steering angle θ and a steering angular velocity ω that is a differential value of the steering angle: ω = 0 or | θ | ≦ α, It = 0, ω> 0 and θ> α, It = k (θ−α), and ω> 0 and θ <−α, It = −k (θ + α), It = −k (θ−α) when ω <0 and θ> α, It = k (θ + α) when ω <0 and θ <−α, where k is a positive coefficient and α is the above In the operating means, the dead band angle is left and right from the neutral position where θ = 0, and the electric motor has It> When 0, it rotates in the direction of ω> 0, and when It <0, it rotates in the direction of ω <0. 3. The target value setting means, when the failure determination means determines that a failure has occurred and the vehicle speed detected by the vehicle speed sensor exceeds 0 or a predetermined value near 0, The electric power steering system according to claim 1, wherein the current target value is reduced to a predetermined drop rate and set to zero.