JP2014139039A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of suppressing cost increase by a simple method, and having excellent steering feeling.SOLUTION: An electric power steering device comprises: motor rotation angular acceleration calculation means for calculating a motor rotation angular acceleration by differentiating twice a motor rotation angle detected from motor rotation angle detection means; and acceleration/current value conversion means for converting the motor rotation angular acceleration calculated from the motor rotation angular acceleration calculation means into a current value. The electric power steering device has a constitution having q-axis command voltage calculation means for calculating a q-axis command voltage from a difference with a q-axis command current after determining the q-axis command current by the acceleration/current value conversion means from the motor rotation angular acceleration calculated from the motor rotation angular acceleration calculation means.

Description

  The present invention relates to an electric power steering apparatus.

  Conventionally, in an electric power steering apparatus that assists steering by an electric motor, a target current is generated from a vehicle speed and a steering torque, and an actual current flowing through the electric motor is detected by a current detector. A comfortable steering feeling is obtained by calculating the difference between the target current and the actual current and generating the optimum assist force by performing the known PID control (proportional control, integral control, differential control). The motor is controlled so that

  However, when the temperature of the electric motor rises, the magnetic flux of the magnet constituting the rotor of the electric motor decreases. As a result, the torque generated by the electric motor is reduced, and the steering feeling may be deteriorated. Therefore, for example, in the electric power steering apparatus described in Patent Document 1, a temperature sensor is provided in the vicinity of the electric motor, and the target current is corrected according to an increase in temperature to prevent a decrease in torque generated by the electric motor. Was.

JP 10-67335 A

  However, the method as described above requires a separate temperature sensor, which raises a problem of an increase in cost. Moreover, if the temperature rise and the correction of the target current do not correspond accurately, there are cases where sufficient steering feeling cannot be obtained.

  An object of the present invention is to provide an electric power steering apparatus that suppresses an increase in cost and has a good steering feeling by a simple method.

  In order to solve the above-described problems, the invention according to claim 1 is directed to a steering force assisting device provided to apply an assist force for assisting a steering operation to a steering system by a motor, and a steering torque detection for detecting a steering torque. Means, vehicle speed detecting means for detecting the vehicle speed, actual current detecting means for detecting the actual current flowing through the motor, motor rotation angle detecting means for detecting the rotation angle of the motor, and steering torque detecting means. Based on the steering torque, the assist force generating means for generating the assist force from the vehicle speed detected from the vehicle speed detecting means, and the assist force command value generated by the assist force generating means, the drive source of the steering force assisting device An electric power steering system comprising: control means for controlling operation of the steering force assisting device by supplying driving power to a motor; The control means calculates the motor rotation angular acceleration by secondarily differentiating the motor rotation angle detected from the motor rotation angle detection means and calculates the motor rotation angular acceleration, and calculates from the motor rotation angular acceleration calculation means. Acceleration / current value conversion means for converting the motor rotation angular acceleration into a current value, and the control means converts the actual current detected from the actual current detection means to d-axis current by d / q-axis conversion. D-axis command voltage calculating means for calculating a d-axis command voltage from a difference from the d-axis command current, and the motor rotation angular acceleration calculated from the motor rotation angular acceleration calculation means as the acceleration / current value conversion means. Q-axis command voltage calculating means for calculating the q-axis command voltage from the difference from the q-axis command current, and obtaining the q-axis command voltage and the q-axis command voltage calculating means. The obtained d-axis, from the command voltage of the q-axis, to determine the voltage command of the three-phase phase, and the gist.

  In the electric power steering apparatus according to the present invention, the motor rotation angular acceleration calculating means for calculating the motor rotation angular acceleration by secondarily differentiating the motor rotation angle detected by the motor rotation angle detecting means, and the motor rotation angular acceleration calculating means. Acceleration / current value conversion means for converting the motor rotation angular acceleration into a current value is provided. Then, the q-axis command voltage is obtained by calculating the q-axis command voltage from the difference from the q-axis command current by obtaining the q-axis current from the motor rotation angular acceleration calculated by the motor rotation angular acceleration calculation unit by the acceleration / current value conversion unit. It was set as the structure which has a calculating means.

  That is, since the motor rotation angular acceleration includes all states that change due to disturbances such as the motor temperature, the values are converted into q-axis actual current values and fed back to the current control loop to change the disturbances. The response of the actual current with respect to can be improved, and torque fluctuation can be suppressed.

  As a result, a detection sensor such as a temperature sensor that causes an increase in cost is not required, and the cost can be reduced, and an electric power steering apparatus with good steering feeling can be provided.

  According to the present invention, it is possible to provide an electric power steering apparatus that suppresses an increase in cost and has a good steering feeling by a simple method.

The schematic block diagram of an electric power steering device (EPS). The control block diagram of EPS. The flowchart figure which shows the process sequence of acceleration / current value conversion.

Hereinafter, an embodiment of the present invention embodied in a column-type electric power steering apparatus (hereinafter referred to as EPS) will be described with reference to the drawings.
As shown in FIG. 1, in the 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. The rotation of the steering shaft 3 accompanying the steering 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 8, an intermediate shaft 9, and a pinion shaft 10. 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 11 connected to both ends of the rack shaft 5, so that the steering angle of the steered wheels 12 is increased. Has been changed.

  The EPS 1 controls the EPS actuator 24 (steering force assisting device) as a steering force assisting device that applies assisting force for assisting the steering operation to the steering system using the motor 21 as a driving source, and the operation of the EPS actuator 24. ECU27 which performs.

  The EPS actuator 24 of the present embodiment is a column type EPS actuator, and the motor 21 that is a drive source thereof is drivingly connected to the column shaft 8 via a speed reduction mechanism 23. The rotation of the motor 21 is decelerated by the speed reduction mechanism 23 and transmitted to the column shaft 8 so that the motor torque is applied to the steering system as an assist force.

  On the other hand, a vehicle speed sensor 25 (vehicle speed detection means), a torque sensor 26 (steering torque detection means), and a motor rotation angle sensor 22 (motor rotation angle detection means) are connected to the ECU 27. The vehicle speed V, the steering torque τ, and the motor rotation angle θm are detected based on the output signal.

Next, an electrical configuration in the EPS 1 of the present embodiment will be described.
FIG. 2 is a control block diagram of the EPS 1 of the present embodiment. As shown in the figure, the ECU 27 supplies three-phase drive power to a motor 21 that is a drive source of the EPS actuator 24 based on a microcomputer 29 (control means) that outputs a motor control signal and the motor control signal. Current sensors (actual current detection means) 30u, 30v, and 30w for detecting the U-phase current value Iu, the V-phase current value Iv, and the W-phase current value Iw that are supplied to the motor 40 and the motor 21; It has.

  The drive circuit 40 is a known PWM inverter (not shown) formed by connecting three arms corresponding to each phase in parallel with a pair of switching elements connected in series as a basic unit (arm). Further, the motor control signal output from the microcomputer 29 defines the on-duty ratio of each switching element constituting the motor drive circuit 40. A motor control signal is applied to the gate terminal of each switching element, and in response to the motor control signal, each switching element is turned on / off to generate three-phase motor driving power based on the power supply voltage of the battery 28. The motor 21 is configured to output.

  A motor rotation angle sensor 22 for detecting the motor rotation angle θm of the motor 21 is connected to the ECU 27. The microcomputer 29 detects each phase current value Iu, Iv, Iw of the motor 21 detected based on the output signal of each sensor, the motor rotation angle θm, the motor rotation angular velocity ωm obtained by differentiating the motor rotation angle θm, and the motor. Based on the motor rotational angular acceleration αm obtained by further differentiating the rotational angular velocity ωm, the steering torque τ, and the vehicle speed V, a motor control signal is output to the drive circuit 40.

  Each control block shown below is realized by a computer program executed by the microcomputer 29. The microcomputer 29 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 every predetermined period.

  As shown in FIG. 2, the microcomputer 29 includes a current command value calculation unit 31 that calculates a current command value for controlling the motor 21, and a motor control signal generation unit 44 that generates a motor control signal for controlling the drive circuit 40. It is equipped with.

The steering torque τ detected by the torque sensor 26 and the vehicle speed V detected by the vehicle speed sensor 25 are input to the current command value calculation unit 31. Based on the steering torque τ and the vehicle speed V, the current command value calculation unit 31 determines the q-axis current command value Iq *, which is a control target for the assist torque, from the steering torque / q-axis current command value map.
The steering torque / q-axis current command value map is configured to determine a larger q-axis current command value Iq * as the vehicle speed V is smaller for the same steering torque.

  The motor control signal generation unit 44 includes a d / q conversion calculation unit 34, a q-axis PID control unit 35, a d-axis PID control unit 36, a d / q reverse conversion calculation unit 37, a PWM output unit 38, and an acceleration / current value conversion unit. 32, differentiators 55 and 56, and subtractors 53 and 54.

  In the motor control signal generation unit 44, the microcomputer 29 maps the phase actual current values Iu, Iv, and Iw detected by the actual current value detection sensors 30u, 30v, and 30w to the d / q coordinate system ( d / q conversion), a d-axis actual current value is obtained, a deviation between this value and the d-axis command value (Id * = 0) is obtained, and the d-axis voltage command value Vd is obtained via the d-axis PID control unit 36. Calculate *. On the other hand, the microcomputer 29 obtains the motor rotation angular acceleration αm by using the primary differentiator 55 and the secondary differentiator 56 for the motor rotation angle θm. The obtained motor rotation angular acceleration αm is obtained by the acceleration / current value conversion unit 32 to obtain a q-axis actual current value, a deviation between this value and the q-axis command value is obtained, and the q-axis PID control unit 35 is passed through. The q-axis voltage command value Vq * is calculated.

  Then, the microcomputer 29 sends the calculated d-axis voltage command value Vd * and q-axis voltage command value Vq * to the U-phase voltage command value Vu * and V-phase voltage command via the d / q inverse conversion calculation unit 37. It is converted into a value Vv * and a W-phase voltage command value Vw * and input to the PWM output unit 38. Next, the PWM output unit 38 generates a DUTY command value that determines the on / off timing of the FET constituting the drive circuit 40, and outputs a gate on / off signal based on the DUTY command value.

Next, an acceleration / current value conversion processing procedure by the microcomputer 29 of this embodiment will be described with reference to FIG.
First, the microcomputer 29 reads the motor rotation angle θm (step S101). Then, the microcomputer 29 calculates the motor rotation angular velocity ωm by differentiating the read motor rotation angle θm (step S102). Further, the microcomputer 29 calculates the motor rotation angular acceleration αm by differentiating the calculated motor rotation angular velocity ωm (step S103).

  Next, the microcomputer 29 multiplies the calculated motor rotational angular acceleration αm by a motor inertial nominal value (Jmn) 57 and then divides by a motor torque constant nominal value (Ktn) 58 to obtain a q-axis current value Iq. Is obtained (step S104). Then, the microcomputer 29 outputs the obtained q-axis current value Iq to the subtractor 53 (step S105) and ends the process.

Next, the operation and effect of the EPS 1 of the present embodiment configured as described above will be described.
In this embodiment, the motor rotation angle acceleration calculating means for calculating the motor rotation angle acceleration by second-order differentiation of the motor rotation angle detected by the motor rotation angle detection means, and the motor rotation angle acceleration calculated by the motor rotation angle acceleration calculation means. Is provided with acceleration / current value conversion means for converting the current value into a current value. Then, the q-axis command voltage is obtained by calculating the q-axis command voltage from the difference from the q-axis command current by obtaining the q-axis current from the motor rotation angular acceleration calculated by the motor rotation angular acceleration calculation unit by the acceleration / current value conversion unit. It was set as the structure which has a calculating means.

  That is, since the motor rotation angular acceleration includes all states that change due to disturbances such as the motor temperature, the values are converted into q-axis actual current values and fed back to the current control loop to change the disturbances. The response of the actual current with respect to can be improved, and torque fluctuation can be suppressed.

  As a result, a detection sensor such as a temperature sensor that causes an increase in cost is not required, and the cost can be reduced, and an electric power steering apparatus with good steering feeling can be provided.

In addition, you may change this embodiment as follows.
In the present embodiment, the present invention is embodied in an electric power steering device, but the present invention may be applied to a transmission ratio variable device and a driving force distribution device.

In the present embodiment, the present invention is embodied in the column assist EPS, but the present invention may be applied to a rack assist EPS or a pinion assist EPS.

In this embodiment, the motor rotation angular acceleration calculated from the motor rotation angular acceleration calculation means according to the present invention is obtained by calculating the q-axis current by the acceleration / current value conversion means, and the value is directly fed back to the q-axis subtractor. The q-axis current may be multiplied by a gain that can be changed depending on the magnitude of the steering torque, and fed back to the q-axis subtractor.

1: Electric power steering device (EPS), 2: Steering,
3: Steering shaft, 4: Rack and pinion mechanism, 5: Rack shaft,
8: column shaft, 9: intermediate shaft, 10: pinion shaft, 11: tie rod, 12: steered wheel, 21: motor,
22: Motor rotation angle sensor (motor rotation angle detection means), 23: Deceleration mechanism,
24: EPS actuator (steering force assist device),
25: vehicle speed sensor (vehicle speed detection means), 26: torque sensor (steering torque detection means), 27: ECU, 28: battery, 29: microcomputer (control means),
30u, 30v, 30w: current sensor (actual current detecting means),
31: Current command value calculation unit (assist force generation means),
32: Acceleration / current value conversion unit (acceleration / current value conversion means),
34: d / q conversion calculation unit, 35: q-axis PID control unit, 36: d-axis PID control unit,
37: d / q inverse conversion calculation unit, 38: PWM output unit, 40: drive circuit,
44: Motor control signal generator, 53, 54: Subtractor,
55: primary differentiator, 56: secondary differentiator,
57: Motor inertia nominal value (Jmn),
58: Motor torque constant nominal value (Ktn),
V: vehicle speed, τ: steering torque, θm: motor rotation angle,
ωm: motor rotation angular velocity, αm: motor rotation angular acceleration,
Iu, Iv, Iw: current value of each phase,
Iq *: q-axis current command value, Iq: q-axis current value, ΔIq: q-axis deviation current value,
Id *: d-axis current command value, Id: d-axis current value, ΔId: d-axis deviation current value,
Vq *: q-axis voltage command value, Vd *: d-axis voltage command value,
Vu *, Vv *, Vw *: Voltage command value for each phase

Claims (1)

A steering force assisting device provided to apply an assisting force to assist the steering operation to the steering system by the motor;
Steering torque detection means for detecting steering torque;
Vehicle speed detection means for detecting the vehicle speed;
An actual current detecting means for detecting an actual current flowing through the motor;
Motor rotation angle detecting means for detecting the rotation angle of the motor;
An assist force generating means for generating an assist force from the steering torque detected from the steering torque detecting means and the vehicle speed detected from the vehicle speed detecting means;
Control means for controlling the operation of the steering force assisting device by supplying drive power to a motor that is a drive source of the steering force assisting device based on the assist force command value generated by the assist force generating device. When,
In the electric power steering apparatus with
The control means includes motor rotation angular acceleration calculation means for calculating a motor rotation angular acceleration by secondarily differentiating the motor rotation angle detected from the motor rotation angle detection means;
Acceleration / current value conversion means for converting the motor rotation angular acceleration calculated from the motor rotation angular acceleration calculation means into a current value;
The control means converts the actual current detected from the actual current detection means by d / q axis conversion,
d-axis command voltage calculating means for obtaining a d-axis current and calculating a d-axis command voltage from a difference from the d-axis command current;
Q-axis command voltage for calculating the q-axis command voltage from the difference from the q-axis command current by obtaining the q-axis current from the motor rotation angular acceleration calculated by the motor rotation angular acceleration calculation unit by the acceleration / current value conversion unit. Computing means,
Obtaining a voltage command for each of the three phases from the d-axis and q-axis command voltages obtained from the d-axis command voltage computing means and the q-axis command voltage computing means;
An electric power steering device.

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