JP2012254649A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which can perform continuous and stable steering operation even at an abnormality of a torque sensor.SOLUTION: When the abnormality of the steering torque sensor is detected, motor torque equivalent to an assist force target value based on an axial force operated from lateral G and a yaw rate in place of the steering torque sensor is generated, and assist control is continued by executing the supply of drive power. As a result, since the assist force target value based on the axial force operated from the lateral G and the yaw rate is generated, a change or the like of a road face status can sufficiently be transmitted to a driver, and steering feeling can be improved.

Description

  The present invention relates to an electric power steering apparatus.

  2. Description of the Related Art Conventionally, power steering apparatuses for vehicles include an electric power steering apparatus (EPS) using a motor as a drive source. Normally, in such EPS, a steering torque input to the steering system is detected by a torque sensor, and an assist force target value to be applied to the steering system is calculated based on the steering torque. The operation is controlled through supply of drive power to the motor so as to generate motor torque corresponding to the assist force target value.

  However, in such a configuration, when an abnormality occurs in the torque sensor, the power assist control based on the steering torque cannot be executed. Therefore, conventionally, a method for calculating the alternative assist force target value based on the steering angle detected by the steering sensor has been proposed.

  For example, Patent Document 1 discloses a method of giving hysteresis characteristics to the calculation of the assist force target value based on the determination result of the steering angle and steering direction. Patent Document 2 discloses a method for calculating the assist force target value by multiplying the steering speed by a coefficient corresponding to the steering angle. As a result, the assist force can be suitably applied even when the torque sensor is abnormal.

JP 2004-338562 A JP 2004-114755 A

  However, all of these conventional methods are positioned to calculate an alternative target value for the assist force target value based on the steering torque, and the actual torque cannot be detected by the torque sensor. There has been a problem that changes and the like are not properly reflected in the assist force, and in this respect, there is still room for improvement.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an electric power steering device capable of continuously performing a stable steering operation even when a torque sensor is abnormal. It is in.

  In order to solve the above problems, the invention according to claim 1 is directed to a steering force assisting device (10) that applies an assist force to a steering system using a motor (12) as a drive source, and a drive for the motor (12). Control means (11) for controlling the operation of the steering force assisting device (10) through supply of electric power, a lateral G sensor (18) for detecting the lateral G of the vehicle, and a yaw rate sensor (19 for detecting the yaw rate of the vehicle) ), A steering torque sensor (14) for detecting a steering torque input to the steering system, and an abnormality detection means (21) for detecting an abnormality of the steering torque sensor (14), the control means ( 11) In order to generate a motor torque corresponding to an assist force target value based on the steering torque, the drive power is supplied and an abnormality of the steering torque sensor (14) is detected. In the case where it is determined, instead of the steering torque sensor (14), supply of the driving power is performed so as to generate a motor torque corresponding to an assist force target value based on the axial force calculated from the lateral G and the yaw rate. The gist is to execute.

According to the electric power steering device of the first aspect, when an abnormality of the steering torque sensor is detected, it corresponds to the assist force target value based on the axial force calculated from the lateral G and the yaw rate instead of the steering torque sensor. The assist control can be continued by generating the motor torque to be executed and supplying the drive power.
In addition, since the assist force target value based on the axial force calculated from the lateral G and the yaw rate is generated, a change in road surface condition and the like can be appropriately reflected in the assist, and the excess or deficiency of the assist can be prevented.

Thus, the electric power steering apparatus according to the first aspect of the present invention provides the assist force target value based on the axial force calculated from the lateral G and the yaw rate, instead of the steering torque sensor, when an abnormality of the steering torque sensor is detected. Since it is generated, a change in the road surface condition or the like can be appropriately reflected in the assist, and an excessive or insufficient assist can be prevented.
As a result, it is possible to continue providing the assist force more stably.

  According to the present invention, it is possible to provide an electric power steering apparatus capable of continuously performing a stable steering operation even when the torque sensor is abnormal.

The schematic block diagram of an electric power steering device (EPS). The control block diagram of EPS. The block diagram of an alternative assist control part. The flowchart figure of an axial force calculating part. The map figure of axial force / alternative assist control amount generation.

Hereinafter, an embodiment in which the present invention is embodied in a column-type electric power steering apparatus will be described with reference to the drawings.
As shown in FIG. 1, in the electric power steering apparatus (EPS) 1 of the present embodiment, a steering shaft 3 to which a steering 2 is fixed is connected to a rack shaft 5 via a rack and pinion mechanism 4, and the steering The rotation of the steering shaft 3 accompanying the operation is converted into a reciprocating linear motion of the rack shaft 5 by the rack and pinion mechanism 4.

  The steering shaft 3 of this embodiment is formed by connecting a column shaft 3a, an intermediate shaft 3b, and a pinion shaft 3c. Then, the reciprocating linear motion of the rack shaft 5 accompanying the rotation of the steering shaft 3 is transmitted to a knuckle (not shown) via tie rods 6 connected to both ends of the rack shaft 5, whereby the steering angle of the steered wheels 7. That is, the traveling direction of the vehicle is changed.

  Further, the EPS 1 includes an EPS actuator 10 as a steering force assisting device that applies an assist force for assisting a steering operation to the steering system, and an ECU 11 as a control unit that controls the operation of the EPS actuator 10. .

  The EPS actuator 10 of the present embodiment is configured as a so-called column-type EPS actuator in which a motor 12 that is a driving source is drivingly connected to a column shaft 3 a via a speed reduction mechanism 13. In the present embodiment, a brushless DC motor is adopted as the motor 12. However, the motor 12 may of course employ a brushed DC motor. The EPS actuator 10 is configured to apply the motor torque as an assist force to the steering system by decelerating the rotation of the motor 12 and transmitting it to the column shaft 3a.

  On the other hand, the ECU 11 is connected with a torque sensor 14, a vehicle speed sensor 15, a lateral G sensor 18 and a yaw rate sensor 19. The ECU 11 detects the steering torque τ, the vehicle speed V, the lateral G, and the yaw rate γ based on the output signals of these sensors.

  The torque sensor 14 of the present embodiment is a magnetic torque sensor using a magnetic detection element (Hall IC) as the sensor element (14a, 14b). In the present embodiment, a torsion bar 16 is provided in the middle of the column shaft 3a, more specifically, on the steering 2 side with respect to the speed reduction mechanism 13 constituting the EPS actuator 10. The torque sensor 14 of the present embodiment outputs sensor signals Sa and Sb that can detect the steering torque τ transmitted through the steering shaft 3 based on the twist of the torsion bar 16. It is configured with.

  Such a torque sensor includes, for example, two magnetic detection elements (in this embodiment, a Hall IC) on the outer periphery of a sensor core (not shown) in which magnetic flux changes due to torsion of the torsion bar 16, and each of the sensor elements 14a. , 14b can be formed.

  That is, when the torsion bar 16 is twisted by the torque input of the steering shaft 3 that is the rotating shaft, the magnetic flux passing through the sensor elements 14a and 14b changes. The torque sensor 14 according to the present embodiment is configured to output the output voltages of the sensor elements 14a and 14b, which fluctuate with the change in magnetic flux, to the ECU 11 as sensor signals Sa and Sb, respectively.

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

Next, an aspect of assist control in the EPS of the present embodiment will be described.
FIG. 2 is a control block diagram of the EPS of this embodiment. As shown in the figure, the ECU 11 includes a microcomputer 21 that outputs a motor control signal, and a drive circuit 22 that supplies drive power to a motor 12 that is a drive source of the EPS actuator 10 based on the motor control signal. ing.

In the present embodiment, the ECU 11 is connected to a current sensor 27 for detecting an actual current value I supplied to the motor 12 and a rotation angle sensor 17 for detecting the rotation angle θm of the motor 12. Then, the microcomputer 21 controls the drive circuit 22 based on the detected actual current value I and the rotation angle θm of the motor 12 based on the vehicle state quantities and the output signals of the current sensor 27 and the rotation angle sensor 17. A motor control signal to be output is generated.

  Each control block shown below is realized by a computer program executed by the microcomputer 21. Then, the microcomputer 21 detects each state quantity at a predetermined sampling period, and generates a motor control signal by executing each arithmetic processing shown in the following control blocks at every predetermined period.

  More specifically, the microcomputer 21 calculates a current command value calculation unit 23 that calculates a current command value I *, which is a target value for power supply to the motor 12, and a current command value I * calculated by the current command value calculation unit 23. And a motor control signal output unit 24 for outputting a motor control signal.

  The current command value calculation unit 23 is provided with a basic assist control unit 26 for calculating a basic assist control amount Ias * as a basic component of the assist force target value. In this embodiment, the basic assist control unit 26 is provided. Is input with a vehicle speed V and a steering torque τ.

  Here, in the present embodiment, the output signals Sa and Sb of the torque sensor 14 are input to a steering torque detection unit 25 provided in the microcomputer 21, and the basic assist control unit 26 receives the same steering. A steering torque τ detected on the basis of the output signals Sa and Sb in the torque detector 25 is input. The basic assist control unit 26 is configured to calculate a basic assist control amount Ias * indicating that a larger assist force should be applied as the absolute value of the steering torque τ is larger and the vehicle speed V is smaller. ing.

  Further, in the present embodiment, the steering torque detector 25 is provided with a function as an abnormality detection means for detecting an abnormality of the torque sensor 14 based on the output signals Sa and Sb of the torque sensor 14. The current command value calculation unit 23 calculates a value based on the basic assist control amount Ias * when the abnormality detection function determines that the current state is the normal state, that is, when the torque sensor 14 is operating normally. The current command value I * is output to the motor control signal output unit 24.

  The motor control signal output unit 24 includes the current command value I * output from the current command value calculation unit 23, the actual current value I detected by the current sensor 27, and the motor 12 detected by the rotation angle sensor 17. The rotation angle θm is input. The motor control signal output unit 24 calculates a motor control signal by executing feedback control so that the actual current value I follows the current command value I *.

  Specifically, in the present embodiment, a brushless motor that rotates by supplying three-phase (U, V, W) driving power is used as the motor 12. The motor control signal output unit 24 converts the phase current value (Iu, Iv, Iw) of the motor 12 detected as the actual current value I into d and q axis current values in the d / q coordinate system (d / q The current feedback control is performed by performing conversion.

  That is, the current command value I * is input to the motor control signal output unit 24 as a q-axis current command value, and the motor control signal output unit 24 is based on the rotation angle θm detected by the rotation angle sensor 17. The current values (Iu, Iv, Iw) are d / q converted. The motor control signal output unit 24 calculates the d and q-axis voltage command values based on the d and q-axis current values and the q-axis current command value. Then, the d and q axis voltage command values are inversely converted by d / q to calculate the phase voltage command values (Vu *, Vv *, Vw *), and the motor control signal is calculated based on the phase voltage command values. Is generated.

  The motor control signal generated in this way is output from the microcomputer 21 to the drive circuit 22, and the drive circuit 22 supplies three-phase drive power to the motor 12 based on the motor control signal. And, by generating a motor torque corresponding to the current command value I * as the assist force target value based on the steering torque τ, an assist force corresponding to the assist force target value is applied to the steering system. It has become.

(Assist continuation control when torque sensor is abnormal)
Next, assist continuation control when the torque sensor is abnormal in the EPS of the present embodiment will be described.
As shown in FIG. 2, the current command value calculation unit 23 of the present embodiment is provided with an alternative assist control unit 28 that performs assist continuation control when the torque sensor is abnormal, in addition to the basic assist control unit 26.

  Specifically, the alternative assist control unit 28 inputs the lateral G detected by the lateral G sensor and the yaw rate γ detected by the yaw rate sensor. The alternative assist control unit 28 calculates an axial force (F, which will be described later) from the lateral G and the yaw rate, and outputs an alternative assist control amount Ibs * corresponding to the axial force.

More specifically, the alternative assist control unit 28 includes the axial force (F) calculation unit 30 and the axial force / alternative assist control amount generation map 31 shown in FIG.
First, details of the axial force (F) calculation unit 30 will be described with reference to FIG. In step S101, the microcomputer 21 reads the distance l between the front and rear wheels of the vehicle, that is, the wheel base, from the temporary storage device (ROM in microcomputer, not shown). Next, in step S102, the microcomputer 21 reads the distance lr from the center of gravity of the vehicle to the rear wheel from the ROM in the microcomputer.

  Next, in step S103, the microcomputer 21 reads the vehicle weight m from the microcomputer ROM. Next, in step S104, the microcomputer 21 reads the inertia I in the rotational direction around the center of gravity of the vehicle from the ROM in the microcomputer. Next, in step S105, the microcomputer 21 reads the axial force gain K from the microcomputer ROM. The conversion gain K to axial force is a value determined by the amount of trail ξ and the knuckle arm length ln, and is usually set to a relationship of K = ξ / ln.

  Next, in step S106, the microcomputer 21 captures the lateral G detected by the lateral G sensor. Next, in step S107, the microcomputer 21 takes in the yaw rate γ detected by the yaw rate sensor.

In step S108, the microcomputer 21 calculates the axial force F using equation (1).
F = K / l × (lr × m × lateral G + I × γ) Formula (1)
Next, in step S109, the microcomputer 21 outputs the axial force F to the axial force / alternative assist control amount generation map 31 and ends the process.

Next, the axial force / alternative assist control amount generation map 31 will be described with reference to FIG.
The axial force / alternative assist control amount generation map 31 represents the axial force (F) on the horizontal axis and the alternative assist control amount Ibs * on the vertical axis. The axial force / alternative assist control amount generation map 31 is configured such that as the axial force (F) increases in the + direction, the alternative assist control amount Ibs * also increases linearly in the + direction. Then, the substitute assist control amount Ibs * output from the axial force / substitute assist control amount generation map 31 is input to the switching control unit 29 (described later).

  Here, the current command value calculation unit 23 of the present embodiment is calculated by the basic assist control unit 26 when an abnormality of the torque sensor 14 is detected by the steering torque detection unit 25 as the abnormality detection means. The calculation of the current command value I * using the basic assist control amount Ias * as a basic component is stopped. The basic component of the current command value calculation is switched to the alternative assist control amount Ibs * calculated by the alternative assist control unit 28, and the current command value I * is calculated.

  More specifically, the current command value calculation unit 23 of the present embodiment is provided with a switching control unit 29, and the basic assist control amount Ias * calculated by the basic assist control unit 26 and the alternative assist. The substitute assist control amount Ibs * calculated by the control unit 28 is input to the switching control unit 29.

  The switching control unit 29 is input with an abnormality detection signal Str output from the steering torque detection unit 25 as the abnormality detection means. When the input abnormality detection signal Str indicates that the torque sensor 14 is abnormal, the switching control unit 29 changes the output control signal from the basic assist control amount Ias * to the alternative assist control amount Ibs. Switch to *. Then, the current command value calculation unit 23 calculates a current command value I * as a target value for current control in the motor control signal output unit 24 based on the control signal output from the switching control unit 29.

  That is, when the torque sensor 14 is abnormal, the ECU 11 according to the present embodiment stops power supply for generating a motor torque corresponding to the assist force target value in a normal state. Then, the driving power supply form for the motor 12 is switched to power supply based on the assist force obtained from the axial force / alternate assist control amount generation map corresponding to the axial force by calculating the axial force from the lateral G and the yaw rate. .

  With such a configuration, even when the steering torque cannot be detected due to an abnormality of the torque sensor 14, the steering system can be motor-driven according to the steering operation. In this embodiment, since the assist control amount is generated according to the axial force obtained from the lateral G and the yaw rate, changes in road surface conditions and the like can be reflected in the assist force, preventing excessive or insufficient assist. can do. As a result, the assist force can be stably applied even when the torque sensor 14 is abnormal.

As described above, according to the present embodiment, the following operations and effects can be obtained.
When an abnormality of the steering torque sensor 14 is detected, the microcomputer 21 generates a motor torque corresponding to the assist force target value based on the axial force obtained from the lateral G and the yaw rate, instead of the steering torque sensor 14. The assist control is continued by executing the drive power supply (assist continuation control).

  According to the above configuration, since the assist force target value based on the axial force obtained from the lateral G and the yaw rate is generated, changes in road surface conditions and the like can be reflected in the assist force, preventing excessive or insufficient assist. can do. As a result, it is possible to continue providing the assist force more stably.

In addition, you may change each said embodiment as follows.
In the above embodiment, the axial force / alternative assist control amount generation map is configured so that the alternative assist control amount increases linearly in the + direction as the axial force increases in the + direction. You may comprise so that it may become.

In the above embodiment, the normal axial force gain K is set to K = ξ / ln, but may be variable according to the road surface condition or the vehicle speed.

In each of the above embodiments, the present invention is embodied in a so-called column type EPS 1, but the present invention may be applied to a so-called pinion type or rack assist type EPS.

1: Electric power steering device (EPS), 2: Steering,
3: Steering shaft, 3a: Column shaft,
3b: Intermediate shaft, 3c: Pinion shaft,
4: rack and pinion mechanism, 5: rack shaft, 6: tie rod, 7: steered wheel,
10: EPS actuator, 11: ECU, 12: motor, 13: deceleration mechanism,
14: torque sensor, 14a, 14b: sensor element, 15: vehicle speed sensor,
16: Torsion bar, 17: Rotation angle sensor, 18: Lateral G sensor,
19: Yaw rate sensor
21: Microcomputer, 22: Drive circuit, 23: Current command value calculation unit,
24: motor control signal output unit, 25: steering torque detection unit, 26: basic assist control unit,
27: current sensor (current detector), 28: alternative assist control unit, 29: switching control unit,
30: Axial force (F) calculation unit, 31: Axial force / alternative assist control amount generation map,
τ: steering torque, Sa, Sb: sensor signal, V: vehicle speed, G: lateral G, θm: rotation angle,
γ: yaw rate, F: axial force,
I *: current command value, I: actual current value, Ias *: basic assist control amount,
Ibs *: alternative assist control amount, Iu, Iv, Iw: phase current value,
Vu *, Vv *, Vw *: Phase voltage command value, Str: Abnormality detection signal,
L: Distance between wheelbases, lr: Distance from vehicle center of gravity to rear wheel,
m: vehicle weight, I: inertia in rotational direction around the center of gravity of the vehicle, K: axial force gain,
ξ: Trail amount, ln: Knuckle arm length

Claims (1)

A steering force assist device that applies assist force to the steering system using a motor as a drive source;
Control means for controlling the operation of the steering force assisting device through supply of driving power to the motor;
A lateral G sensor for detecting the lateral G of the vehicle;
A yaw rate sensor for detecting the yaw rate of the vehicle;
A steering torque sensor for detecting a steering torque input to the steering system;
An abnormality detecting means for detecting an abnormality of the steering torque sensor,
The control means executes the supply of the driving power so as to generate a motor torque corresponding to an assist force target value based on the steering torque,
When abnormality of the steering torque sensor is detected, instead of the steering torque sensor, to generate a motor torque corresponding to an assist force target value based on an axial force calculated from the lateral G and the yaw rate,
Performing the drive power supply;
An electric power steering device.

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