JP2004114711A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device not impairing good steering feeling of a driver by setting an inertia compensation current value to an appropriate value. <P>SOLUTION: The inertia compensation part is provided with a differentiator receiving a steering torque value T and outputting a differential value (dT/dt) thereof; an inertia compensation current setting part 40 for calculating the inertia compensation current value Ii based on this differential value; and an inertia compensation current correction part 50 for multiplying a gain set by a predetermined method to this inertia compensation current value Ii and outputting the corrected inertia compensation current value Ii'. The inertia compensation current correction part 50 includes a first gain determination part 51 for outputting a first gain Gj1 based on a steering angular velocity ω; a second gain determination part 52 for outputting a second gain Gj2 based on the steering torque value T; and a gain multiplication part 53 for outputting the inertia compensation current value Ii' corrected based on the first and second gains Gj1, Gj2. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric power steering device that applies a steering assist force to a steering mechanism of a vehicle by an electric motor.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electric power steering device that 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 has been used. This electric power steering device is provided with a torque sensor that detects a steering torque applied to a steering wheel, which is an operating means for steering, and outputs a torque detection signal indicating the steering torque. A target value of a current to be passed to the electric motor is set based on the detection signal. Then, a command value to be given to the driving means of the electric motor is generated based on the deviation between the target value and the detected value of the current actually flowing through the electric motor. The driving means of the electric motor uses a PWM signal generation circuit that generates a pulse width modulation signal (PWM signal) having a duty ratio according to the command value, and a power transistor that turns on / off according to the duty ratio of the PWM signal. And a voltage corresponding to the duty ratio, that is, a voltage corresponding to the command value, is applied to the electric motor. The current flowing through the electric motor by the application of the voltage is detected by a current detection circuit, and the difference between the detected value and the target value is used as a deviation for generating the command value. In the electric power steering apparatus, the feedback control is performed such that the current of the target value set based on the steering torque indicated by the torque detection signal from the torque sensor flows to the electric motor.
[0003]
As described above, the target value of the current to be passed to the electric motor is determined according to the steering torque. More specifically, the influence of the moment of inertia of the electric motor on the current value determined according to the steering torque is determined. The target value of the current to be supplied to the electric motor is determined by adding an inertia compensation current value or the like for suppressing the electric current. Here, the inertia compensation current value is determined according to the differential value of the steering torque. With this inertia compensation current value, a response delay due to inertia of the electric motor or the like is compensated, and the steering feeling of the driver is improved.
[0004]
[Patent Document 1]
JP-A-6-344940
[Problems to be solved by the invention]
However, the electric power steering device has a configuration in which the inertia compensation current value is determined based only on the differential value of the steering torque. According to this configuration, even when the differential value of the steering torque is the same value, it is not considered that the steering feeling may be different under different driving conditions. As a result, there is a possibility that a favorable steering feeling of the driver may be impaired in some cases. For example, if the steering angular velocity is large at the time of the driving operation for returning the steering wheel, the steering torque becomes large, so that the steering feeling may be deteriorated.
[0006]
Therefore, an object of the present invention is to provide an electric power steering device that does not impair a good steering feeling of a driver by setting an inertia compensation current value to an appropriate value.
[0007]
Means for Solving the Problems and Effects of the Invention
A first invention is an electric power steering device that applies a steering assist force to a steering mechanism of a vehicle by driving an electric motor in accordance with a steering torque applied by operating means for steering the vehicle,
A torque sensor for detecting the steering torque,
Steering angular velocity detecting means for detecting a steering angular velocity which is a speed of a steering angle change by operation of the operation means,
Target value setting means for setting a value of a current to be supplied to the electric motor as a target value,
Current detection means for detecting a current flowing in the electric motor and outputting a detection value of the current,
Control means for generating a command value for feedback control on driving of the electric motor based on a current deviation between the current target value and the current detection value,
Driving means for driving the electric motor according to the command value,
The target value setting means,
Inertia compensation current value setting means for setting an inertia compensation current value for inertia compensation of the electric motor based on a differential value of the steering torque,
When the operating means is operated so as to return to the neutral position direction after being operated leftward or rightward from the predetermined neutral position, the inertia compensation current value increases as the absolute value of the steering angular velocity increases. Inertia compensation current correction means for generating an inertia compensation current value corrected to be large,
Calculating a target value of the current to be supplied to the electric motor based on the steering torque, and adding the corrected inertia compensation current value to the calculated target value to calculate the current target value Value calculation means.
[0008]
According to the first aspect of the invention, the corrected inertia compensation current value increases as the steering angular velocity increases during the driving operation of returning the operating means (for example, the steering wheel). With this configuration, even when the steering angular velocity is high, the steering torque is prevented from increasing when the driving operation is performed to return the operating means, so that a good steering feeling can be maintained.
[0009]
In a second aspect, in the first aspect,
The inertia compensation current correction unit is configured to set a first gain set based on the steering angular velocity and a second gain set based on the steering torque with respect to the inertia compensation current value set by the inertia compensation current value setting unit. A corrected inertia compensation current value is generated by multiplying the calculated inertia compensation current value.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
<1. Overall Configuration>
FIG. 1 is a schematic diagram showing a configuration of an electric power steering device according to a first embodiment of the present invention, together with a vehicle configuration related thereto. This electric power steering apparatus includes a steering shaft 102 having one end fixed to a steering wheel (steering wheel) 100 as an operating means for steering, a rack and pinion mechanism 104 connected to the other end of the steering shaft 102, A steering angular velocity sensor 2 that detects a steering angular velocity that is a rotation angular velocity of 100, a torque sensor 3 that detects a steering torque applied to a steering shaft 102 by operating the steering wheel 100, and a vehicle speed of a vehicle equipped with the electric power steering device Speed sensor 4, an electric motor 6 for generating a steering assist force for reducing a driver's load due to steering operation (steering operation), and a steering assist force generated by the motor 6 transmitted to the steering shaft 102. Reduction gear 7 and the vehicle Powered by the Terri 8 through the ignition switch 9, and an electronic control unit (ECU) 5 for controlling the driving of the motor 6 based on sensor signals from the torque sensor 3 and the vehicle speed sensor 4.
[0011]
Here, in the steering shaft 102, a torsion bar is interposed between a portion on the handle 100 side and a portion to which the steering assist torque is applied via the reduction gear 7. The torque sensor 3 detects the steering torque by detecting the torsion of the torsion bar. The detected value T of the steering torque thus detected is output from the torque sensor 3 as a steering torque detection signal, and is input to the ECU 5. The steering angular velocity sensor 2 outputs a signal indicating a detected value ω of the steering angular velocity, which is the rotational angular velocity of the steering wheel 100, as a steering angular velocity signal. Further, the vehicle speed sensor 4 outputs a signal indicating a detected value V of the vehicle speed of the vehicle as a vehicle speed signal. These steering angular speed signal and vehicle speed signal are also input to the ECU 5. In addition, instead of the steering angular velocity sensor 2, there is provided a steering angle sensor that outputs a signal indicating a detected value θ of the steering angle, which is the rotation angle of the steering wheel 100, as a steering angle signal, and differentiates the detected value θ of the steering angle. May be used to calculate the detected value ω of the steering angular velocity.
[0012]
When the driver operates the steering wheel 100 in a vehicle equipped with such an electric power steering device, a steering torque resulting from the operation is detected by the torque sensor 3, and the detected value T of the steering torque and the vehicle speed detected by the vehicle speed sensor 4 are detected. The motor 6 is driven by the ECU 5 based on the detected value V. 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 operating the steering wheel and the torque generated by the steering assist force generated by the motor 6 is provided to the rack and pinion mechanism 104 via the steering shaft 102 as the output torque. As a result, when the pinion shaft rotates, the rotation is converted by the rack and pinion mechanism 104 into a reciprocating motion of the rack shaft. Both ends of the rack shaft are connected to wheels 108 via a connecting member 106 including a tie rod and a knuckle arm, and the direction of the wheels 108 changes according to the reciprocating motion of the rack shaft.
[0013]
<2. Configuration and operation of control device>
FIG. 2 is a block diagram showing a functional configuration of the ECU 5 which is a control device in the electric power steering device. The ECU 5 generates a microcomputer (hereinafter abbreviated as “microcomputer”) 10 functioning as a motor control unit and a pulse width modulation signal (PWM signal) having a duty ratio corresponding to a command value D output from the microcomputer 10. A motor drive circuit 20 for applying a voltage corresponding to the duty ratio of the PWM signal to the motor 6, and a current detector 19 for detecting a current flowing through the motor 6.
[0014]
The microcomputer 10 executes a predetermined program stored in an internal memory of the microcomputer 10 so that the target current setting unit 12, the subtracter 14, and the feedback control calculation unit (hereinafter abbreviated as “FB control calculation unit”) 16 Function as a motor control unit. In this motor control unit, the target current setting unit 12 calculates a detected value ω of the steering angular velocity output from the steering angular velocity sensor 2 (hereinafter, simply referred to as “steering angular velocity ω”) and the steering torque output from the torque sensor 3. Based on the detected value T (hereinafter, simply referred to as “steering torque T”) and the detected value V of the vehicle speed outputted from the vehicle speed sensor 4 (hereinafter, simply referred to as “vehicle speed V”), the target of the current to be passed to the motor 6 Determine the value It. The detailed configuration and operation of the target current setting section 12 will be described later. The subtractor 14 calculates a deviation It−Is between the current target value It output from the target current setting unit 12 and the detection value Is of the motor current output from the current detector 19. The FB control calculation unit 16 generates the above-described command value D for feedback control to be given to the PWM signal generation circuit 18 by proportional integration control calculation based on the difference It-Is.
[0015]
The PWM signal generation circuit 18 generates a pulse signal having a duty ratio according to the command value D, that is, a PWM signal whose pulse width changes according to the command value D. The motor drive circuit 20 is typically a bridge circuit composed of four power field effect transistors connected between the power supply line and the ground line of the battery 8, and has a pulse width (duty duty) of a PWM signal. A voltage corresponding to the (ratio) is applied to the motor 6. The motor 6 generates a torque having a magnitude and a direction corresponding to a current flowing by applying the voltage.
[0016]
<3. Detailed configuration and operation of target current setting section>
FIG. 3 is a block diagram illustrating a configuration of the target current setting unit 12 according to the embodiment of the present invention. The target current setting unit 12 receives a steering torque value T, and performs a phase lead compensation. The phase compensation unit 121 performs the phase advance compensation. The steering torque value T (hereinafter, phase compensation is performed by the phase compensation unit 121). The target value calculator 122 receives the steering torque value T (hereinafter simply referred to as “steering torque value T”) and outputs the current target value, and the (phase-compensated) steering torque value T is input to the motor. 6, an inertia compensating unit 123 that outputs an inertia compensating current value for suppressing the influence of the inertia moment, and an output value from the inertia compensating unit 123 and an output value from the target value calculating unit 122 are added to obtain a final value. And an adder 124 that outputs a desired current value. Hereinafter, the operation of these components will be described in detail.
[0017]
The phase compensating unit 121 compensates for the delay of the transfer characteristic in the control system, and in order to stabilize the control system, the steering torque value T provided from the torque sensor 3 is passed through a phase lead / phase lag filter. The phase compensation is performed, and the phase-compensated steering torque value T is output. Here, specifically, the phase compensating unit 121 performs the phase compensation such that the phase advance increases as the frequency of the steering torque increases.
[0018]
The target value calculator 122 calculates a current target value based on the steering torque value T and the vehicle speed V. Specifically, a table (referred to as an “assist table”) indicating the relationship between the target current value It to be supplied to the motor 6 and the steering torque value T to generate an appropriate steering assist force with the vehicle speed V as a parameter is provided. The target value calculation section 122 is stored in advance in the target value calculation section 122, and sets the current target value It with reference to the assist table. This assist table is set so that the target current value It increases as the vehicle speed V decreases and the steering torque T increases. Then, the heavier the steering wheel, the greater the steering assist force, and the easier the steering operation.
[0019]
The inertia compensation unit 123 outputs an inertia compensation current value based on a value obtained by differentiating the steering torque value T. Hereinafter, the configuration and operation will be described in detail. FIG. 4 is a block diagram illustrating a configuration of the inertial compensation unit 123. The inertia compensation unit 123 includes a differentiator 30, an inertia compensation current setting unit 40, and an inertia compensation current correction unit 50. The differentiator 30 receives the steering torque value T and outputs a differential value (dT / dt) of the steering torque value T. The inertia compensation current setting unit 40 calculates an inertia compensation current value Ii based on a differential value (dT / dt) of the steering torque value T. Specifically, a table indicating the relationship between the inertia compensation current value Ii for performing appropriate inertia compensation and the differential value (dT / dt) of the steering torque value T is stored in the inertia compensation current setting unit 40 in advance. The inertia compensation current setting unit 40 sets the inertia compensation current value Ii with reference to this table. FIG. 5 is a diagram showing a table stored in the inertia compensation current setting unit 40 in advance. As shown in the figure, this table is set such that the larger the differential value (dT / dt) of the steering torque T, the larger the inertia compensation current value Ii. Then, since the influence of the moment of inertia of the motor 6 can be suppressed, the steering operation is facilitated. This table may be a table indicating the relationship between the inertia compensation current value Ii and the differential value (dT / dt) of the steering torque value T using the vehicle speed V as a parameter, similarly to the assist table. The inertia compensation current correction unit 50 multiplies the inertia compensation current value Ii from the inertia compensation current setting unit 40 by a gain set by a predetermined method, and outputs a corrected inertia compensation current value Ii ′. Hereinafter, the configuration and operation of the inertial compensation current correction unit 50 will be described in detail.
[0020]
The inertia compensation current correction unit 50 outputs a first gain determination unit 51 that outputs a first gain Gj1 determined based on the steering angular velocity ω, and outputs a second gain Gj2 determined based on the steering torque value T. It includes a second gain determining section 52 and a gain multiplying section 53 that outputs an inertia compensation current value Ii ′ corrected based on the first gain Gj1 and the second gain Gj2.
[0021]
The first gain determination unit 51 receives the steering angular velocity ω, and calculates a first gain Gj1 based on the steering angular velocity ω. Specifically, a table indicating the relationship between the steering angular velocity ω and the first gain Gj1 is stored in the first gain determination unit 51 in advance, and the first gain determination unit 51 refers to this table. First gain Gj1 is determined. FIG. 6 is a diagram showing a table stored in the first gain determination unit 51 in advance. The steering angular velocity ω is a positive value when the steering wheel 100 is rotated rightward, and is a negative value when the steering wheel 100 is rotated leftward. As shown in the drawing, this table is set so that the first gain Gj1 increases as the absolute value of the steering angular velocity ω increases.
[0022]
The second gain determining unit 52 receives the steering torque value T, and calculates a second gain Gj2 based on the steering torque value T. Specifically, a table indicating the relationship between the steering torque value T and the second gain Gj2 is stored in the second gain determination unit 52 in advance, and the second gain determination unit 52 refers to this table. To determine the second gain Gj2. FIG. 7 is a diagram showing a table held in advance by the second gain determination unit 52. FIG. 7A shows a case where the steering angular velocity ω is positive, and FIG. , The case where the steering angular velocity ω is negative is shown. Note that the steering torque value T is a positive value when the steering wheel 100 is rotated rightward, and is a negative value when the steering wheel 100 is rotated leftward. The table shown in FIG. 7A has a maximum value at a predetermined steering torque value Tk (for example, a steering torque value that is normally applied when returning the steering wheel), and the second value is such that the peak value indicates a mountain-shaped characteristic. The gain Gj2 is set, and in the table shown in FIG. 7B, the second gain Gj2 is set so that the maximum value is obtained at a predetermined steering torque value −Tk and the value is the peak and the mountain shape characteristic is exhibited. I have. The tables shown in FIGS. 6 and 7 may be tables showing the vehicle speed V as a parameter, similarly to the assist table. Here, when the steering wheel is turned to the left from the neutral position and then returned to the neutral position, the steering angular velocity ω becomes positive, so the second gain determining unit 52 shown in FIG. The second gain Gj2 is calculated based on the steering torque value T by referring to the table. Further, when the steering wheel is turned rightward from the neutral position and then returned to the neutral position, the steering angular velocity ω becomes negative. Therefore, the second gain determining unit 52 sets the table shown in FIG. , The second gain Gj2 is calculated based on the steering torque value T.
[0023]
The gain multiplier 53 multiplies the inertia compensation current value Ii by the first gain Gj1 and the second gain Gj2 set as described above to output a corrected inertia compensation current value Ii ′. . Therefore, these relations are expressed as the following equation (1).
Ii ′ = Gj1 × Gj2 × Ii (1)
The corrected inertia compensation current value Ii 'is added by the adder 124 to the current target value output from the target value calculation unit 122, and the final current target value It is obtained. According to the above configuration, the corrected inertia compensation current value Ii ′ increases as the steering angular velocity increases during the driving operation of returning the steering wheel 100, so that it is possible to suppress an increase in the steering torque. Therefore, the steering feeling is improved.
[0024]
<4. Effect>
According to the above-described embodiment, the first gain Gj1 increases as the absolute value of the steering angular velocity ω increases, and the second gain Gj1 increases at a predetermined steering torque value | Tk | The inertia compensation current value Ii is multiplied by a gain Gj2. With this configuration, the corrected inertia compensation current value Ii ′ increases as the steering angular velocity increases during the driving operation of returning the steering wheel 100. Therefore, even when the steering angular velocity is high, an increase in the steering torque during the driving operation of returning the steering wheel 100 is suppressed, so that a good steering feeling can be maintained. Furthermore, since the second gain Gj2 is increased in the range from the steering torque value (substantially zero) corresponding to the turning back in the steering direction to a predetermined range, good inertia compensation can be performed even during the turning back steering. .
[0025]
<5. Modification>
In the above-described embodiment, the first gain Gj1 and the second gain Gj2 are calculated based on the table. However, the first gain Gj1 and the second gain Gj2 are calculated using a predetermined calculation formula or a conditional formula based on the steering angular velocity and the steering torque. There may be.
[0026]
In the above-described embodiment, the inertia compensation current value Ii ′ is calculated by multiplying the inertia compensation current value Ii by the first gain Gj1 and the second gain Gj2. At the time of the driving operation for returning the steering wheel 100 based on the steering angular velocity ω and the steering torque value T, a correction amount that is set to increase as the steering angular velocity increases is calculated, and the correction amount for the inertia compensation current value Ii is calculated. May be added to calculate a corrected inertia compensation current value Ii ′.
[0027]
Further, in the above embodiment, the assist table may be set with the vehicle speed V as a parameter, and other tables may be set with the vehicle speed V as a parameter. However, the table does not necessarily need to be set with the vehicle speed V as a parameter, and the table is not limited to the vehicle speed, and other running conditions of the vehicle may be set as a parameter.
[0028]
Furthermore, in the above-described embodiment, the microcomputer 10 executes a predetermined program so that various components in the target current setting unit 12 are realized as software. However, some or all of these components are implemented. May be realized in hardware by a dedicated electronic circuit or the like.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of an electric power steering device 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 which is a control device in the electric power steering device according to the embodiment.
FIG. 3 is a block diagram illustrating a configuration of a target current setting unit in the embodiment.
FIG. 4 is a block diagram illustrating a configuration of an inertial compensation unit in the embodiment.
FIG. 5 is a diagram showing a table held in advance by an inertia compensation current setting unit in the embodiment.
FIG. 6 is a diagram showing a table held in advance by a first gain determination unit in the embodiment.
FIG. 7 is a diagram showing a table held in advance by a second gain determination unit in the embodiment.
[Explanation of symbols]
1 ... steering angular velocity sensor 4 ... vehicle speed sensor 5 ... electronic control unit (ECU)
6 Motor 10 Microcomputer (motor control unit)
12 ... target current setting unit (target value setting means)
14 ... subtractor 16 ... feedback control calculation unit (FB control calculation unit)
18 PWM signal generation circuit 19 Current detector 20 Motor drive circuit 30 Differentiator 40 Inertial compensation current setting unit 50 Inertial compensation current correction unit 51 First gain determination unit 52 Second gain determination unit 53 gain multiplying unit 121 phase compensating unit 122 target value calculating unit 123 inertia compensating unit 124 adder It current target value Is current detection value Ii inertia compensating current value V vehicle speed D command value T Steering torque ω ... Steering angular velocity

Claims (2)

An electric power steering device that applies a steering assist force to a steering mechanism of the vehicle by driving an electric motor in accordance with a steering torque applied by an operation unit for steering the vehicle,
A torque sensor for detecting the steering torque,
Steering angular velocity detecting means for detecting a steering angular velocity which is a speed of a steering angle change by operation of the operation means,
Target value setting means for setting a value of a current to be supplied to the electric motor as a target value,
Current detection means for detecting a current flowing in the electric motor and outputting a detection value of the current,
A control unit that generates a command value for feedback control on driving of the electric motor based on a current deviation between the current target value and the current detection value,
Driving means for driving the electric motor according to the command value,
The target value setting means,
Inertia compensation current value setting means for setting an inertia compensation current value for inertia compensation of the electric motor based on a differential value of the steering torque,
When the operating means is operated so as to return to the neutral position direction after being operated leftward or rightward from the predetermined neutral position, the inertia compensation current value increases as the absolute value of the steering angular velocity increases. Inertia compensation current correction means for generating an inertia compensation current value corrected to be large,
Calculating a target value of the current to be supplied to the electric motor based on the steering torque, and adding the corrected inertia compensation current value to the calculated target value to calculate the current target value An electric power steering apparatus, comprising: a value calculating unit. The inertia compensation current correction unit is configured to set a first gain set based on the steering angular velocity and a second gain set based on the steering torque with respect to the inertia compensation current value set by the inertia compensation current value setting unit. The electric power steering apparatus according to claim 1, wherein a corrected inertial compensation current value is generated by multiplying the inertia compensation current value by a gain of (i).

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