JP2004291687A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device which attains stable steering feeling without making excess current flow to a motor, even if a steering angle becomes a maximum value in steering and the number of revolution of the motor is rapidly reduced. <P>SOLUTION: This power steering device generates assist torque by the electric motor. An electric motor control means is provided with: a maximum steering position estimating means for deciding a time when a target current value is a target current maximum value to be a maximum value of a target value set in advance and detected actual current value is more than an allowable current value larger than at least the current maximum value as a maximum steering position; and a driving voltage command value correction means to adjust a driving voltage command value so that an actual current value may be the target current maximum value when the maximum steering position is decided by the maximum steering position estimating means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power steering device that assists steering by driving an electric motor.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an electric power steering apparatus, a technique disclosed in Patent Literature 1 discloses a technique in which an electric motor is driven based on an output of a torque sensor that detects a steering torque to assist steering. In this publication, feedback control is performed so that the motor current of the electric power steering becomes a target motor current value.
[0003]
[Patent Document 1]
JP-A-11-81776 (see FIG. 1).
[0004]
[Problems to be solved by the invention]
However, the electric power steering device described in Patent Literature 1 has the following problems. That is, in the electric power steering, at the time of turning, a back electromotive force that generates an electromotive force in the opposite direction as in a generator is generated in a direction in which torque assist is hindered. Therefore, the voltage command value is set so as to overcome this back electromotive force and to obtain a necessary driving force (current value). At this time, when the steering angle reaches the maximum value and hits the stopper, the rotational speed of the motor becomes zero at a stretch, and the back electromotive force becomes zero. Then, there is a problem that all the voltage supplied to the electric motor becomes a drive voltage, and an overcurrent flows. Further, since the weighting of the control amount for the integration in the feedback control changes over time, there is a problem that the motor current becomes excessive and the steering feeling is deteriorated.
[0005]
The present invention has been made in view of the above-described problems, and is stable without overcurrent flowing through the motor even when the turning angle reaches a maximum value during turning and the rotational speed of the motor suddenly decreases. It is an object of the present invention to provide an electric power steering device capable of achieving the improved steering feeling.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, the maximum turning position can be estimated by detecting the actual current flowing through the electric motor by the maximum turning position estimating means. When it is determined that the vehicle is in the maximum steering position, the drive voltage command value is adjusted so that the actual current value becomes the target current maximum value. As a result, it is possible to prevent an excessive supply of the motor current at the time of hitting the stopper at the time of turning, so that it is possible to save power and improve the steering feeling. Further, since the maximum steering position is detected by the actual current flowing through the motor, no separate sensor or the like is required. In addition, it is possible to prevent erroneous determination that the motor is overcurrent.
[0007]
Further, in the invention according to claim 2, when the drive voltage command value is corrected, when it is determined that the steering position is the maximum steering position, the drive voltage command value lower than the drive voltage command value corresponding to the target current maximum value is set. By outputting, it is possible to speed up the convergence to the target current value, and it is possible to realize stable steering control while preventing overcurrent.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
FIG. 1 is a system diagram illustrating an overall configuration of a power steering device according to Embodiment 1 of the present invention. First, the configuration will be described. 1 is a steering wheel, 2 is a steering shaft, 3 is a rack and pinion type gear mechanism, 5 is a power steering mechanism that assists a driver's steering force, 6 is an electric motor, 7 is a steering wheel 10 Is a control unit for controlling the power steering mechanism.
[0009]
The power steering mechanism 5 transmits the rotation of the electric motor 6 to a speed reduction mechanism provided on the steering shaft 2. When the driver operates the steering wheel 1, the rotation direction of the electric motor 6 is switched according to the operation direction, and assists the driver's steering force.
[0010]
Further, the steering shaft 2 is provided with a torque sensor 12 for detecting a driver's steering torque.
[0011]
The steering torque signal from the torque sensor 12 is input to the control unit 10. A command signal is output to the electric motor 6 based on the input signal.
[0012]
FIG. 2 is a block diagram illustrating a configuration inside the control unit 10. Reference numeral 101 denotes a steering control unit that calculates a target current i ^* of the electric motor 6 based on the input torque signal. Reference numeral 102 denotes a motor control unit that outputs a command voltage based on a deviation between the actual motor current i and the target current i ^* . A drive circuit 103 outputs a commanded voltage to the electric motor 6.
[0013]
FIG. 3 is a block diagram illustrating a configuration of the motor control unit 102. A target motor current value i ^* output from the steering control unit 101, an input current of the motor current value i outputted from the driving circuit 103, and outputs the motor command voltage V _0. In the present embodiment, the motor command voltage V ₀ is determined by PI control, and is determined by the following equation.
Δi = i ^* −i
_{V 0 (n) = {(} Δi (n) -Δi (n-1)) Kp + (Δi (n) + Δi (n-1)) Ki} + V 0 (n-1)
Kp: proportional gain Ki: integral gain (n) represents the current control cycle, and (n-1) represents the previous control cycle.
[0014]
FIG. 4 is a control model diagram showing a motor model of the electric motor 6. When a voltage V ₀ (n) is applied to the electric motor 6, a current i (n) is generated, and the current i (n) generates a motor torque M ₀ . The electric motor 6, the motor internal friction M ₂ due to the load M ₁ and the motor rotational speed ω from the steering shaft 2 is applied. Therefore, the motor torque T is determined by the following equation.
T = M ₀ −M ₁ −M ₂
[0015]
The motor is rotated by the motor torque T. At this time, the rotation of the electric motor 6 generates a back electromotive voltage V ′ (ω) proportional to the motor rotation speed ω. Therefore, the driving voltage V (n) related to driving the electric motor 6 is determined by the following equation.
_{V (n) = V 0 (} n) -V '(ω)
[0016]
Here, the setting of the motor command voltage V ₀ (n) will be described. The command voltage V ₀ (n) to the electric motor 6 is determined according to the deviation between the target motor current i ^* determined by the steering torque of the driver and the actual motor current i. At this time, even if the back electromotive voltage V ′ (ω) generated in the electric motor 6 occurs, the motor command voltage V ₀ (n) is set to be higher so as to reach the target motor current i ^*. .
[0017]
FIG. 5 is a flowchart showing the overcurrent prevention control at the time of hitting the stopper according to the present invention.
[0018]
In step 201, the motor current value i (n) and the motor command voltage previous value _V 0 read (n-1).
[0019]
In step 202, it is determined whether or not the motor current value i (n) has exceeded a preset abutting determination current value. If the current value has exceeded, the process proceeds to step 203, otherwise the control ends. Corresponding to the maximum turning position estimating means described in the range).
[0020]
In step 203, it is determined whether or not the previous motor command voltage value V ₀ (n−1) has exceeded the maximum current output equivalent voltage V ₁ at the motor rotation speed 0, and if so, the process proceeds to step 204; This control ends.
[0021]
In step 204, a preset contact determination voltage V ₂ is set as the previous motor command voltage value V ₀ (n−1).
[0022]
The above control contents will be described based on the time chart of FIG. At time t1, the driver starts steering. At this time, the driver starts sudden turning.
[0023]
At time t2, a large steering torque of the driver, it with (corresponding to the power supply voltage) Maximum value Vmax also motor command voltage _{V 0} becomes, at time t21, the target motor current ^{i *} is also set to the maximum value imax. However, the driver is turning sharply, and exceeds the maximum assist torque Amax of the electric motor 6.
[0024]
After the time t2, rotation of the electric motor 6 starts to be input from the steering shaft 2 side by the driver's steering. At this time, the back electromotive voltage V ′ (ω) becomes larger than the motor command voltage V ₀ (time t22), and the motor current value i gradually decreases even if the motor command voltage V ₀ is set to Vmax (the target current value is also imax). I will do it.
[0025]
At time t3, when the steering angle δ reaches the maximum value and hits the stopper, the rotation of the steering shaft 2 also stops, and the number of revolutions input to the electric motor 6 also becomes zero. Then, the back electromotive voltage V ′ (ω) becomes 0 at a stretch, and the motor command voltage maximum value Vmax is set as the drive voltage of the electric motor 6 as it is. Along with this, the motor current value i starts to increase rapidly.
[0026]
After the time t3 elapses, the steering torque of the driver begins to decrease, the motor command voltage V ₀ with it also starts to decrease. At this time, as described in the configuration of the motor controller of FIG. 3, when determining the motor command voltage V ₀ in accordance with the deviation between the target current value i ^* and the actual current value i, the control amount of the integrated amount is accumulated (Accumulated from time t2 to t31, the maximum value is Vmax). Therefore, the motor command voltage V ₀ is only gradually not reduced. As a result, a high voltage is applied in a state where the rotation speed of the electric motor 6 is 0, that is, in a state where the back electromotive voltage V ′ (ω) is not generated. There is a fear.
[0027]
Therefore, at time t4, when it exceeds abutment determination current value i _T is a predetermined tolerance value greater than the current maximum value imax, it is determined that there is a possibility that overcurrent flows to the electric motor 6. In step 203 specifically, the motor command voltage previous value V _{0 (n-1)} to determine whether it exceeds the maximum current output corresponding voltage V _1.
[0028]
Here, the maximum current output corresponding voltage V _1, while the motor speed is 0, an output voltage capable of motor current maximum value imax. When it exceeds the maximum current output corresponding voltage V _1, since the resulting overcurrent flows, the flow proceeds to step 204, as the motor command voltage previous value V _{0 (n-1),} the maximum current output corresponding value V ₁ also low, to set the voltage V ₂ when the judgment abutment. As a result, the current motor command voltage V (n) is also set to a low value, and it is possible to prevent an overcurrent from flowing through the electric motor 6. Furthermore, the motor command voltage V ₀ also, it is possible to quickly converge to the maximum current output value corresponding V _1, it is possible to quickly converge to the current maximum value imax. Therefore, supply of an excessive motor current can be prevented, and power saving and steering feeling can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an overall configuration of a power steering device according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a control circuit according to the first embodiment.
FIG. 3 is a diagram illustrating a control configuration of a motor control unit according to the first embodiment.
FIG. 4 is a diagram illustrating a motor model of the electric motor according to the first embodiment.
FIG. 5 is a flowchart illustrating overcurrent prevention control at the time of stopper abutting determination according to the first embodiment.
FIG. 6 is a time chart illustrating overcurrent prevention control at the time of stopper abutting determination according to the first embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Gear mechanism 5 Power steering mechanism 6 Electric motor 7 Steering wheel 10 Control unit (SBWCU)
12 Torque sensor

Claims (2)

Electric power steering means for assisting the driver's steering with the driving force of the electric motor;
Torque detection means for detecting the driver's steering torque;
Target torque calculating means for calculating a target assist torque based on the detected torque and vehicle speed,
Target current value calculating means for calculating a target current value of the electric motor according to the calculated target assist torque;
An actual current value detecting means for detecting an actual current value of the electric motor;
An electric motor control unit that outputs a drive voltage command value to the electric motor based on the calculated target current value and a deviation of the detected actual current value;
In a power steering device provided with
In the electric motor control means, the target current value is a target current maximum value which is a maximum value of a preset target value, and the detected actual current value is at least an allowable current larger than the current maximum value. When the value exceeds the value, a maximum turning position estimating means for determining the maximum turning position,
When the maximum turning position estimating means determines the maximum turning position, the driving voltage command value correcting means for adjusting the driving voltage command value so that the actual current value becomes the target current maximum value is provided. Characteristic power steering device. The power steering device according to claim 1,
The drive voltage command value correction means outputs a drive voltage command value lower than a drive voltage command value corresponding to the target current maximum value when the maximum steered position estimating means determines that the vehicle is at the maximum turning position. A power steering device, comprising:

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