JP2001219863A - Electric power steering device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To enable a driver to smoothly turn back a steering wheel without feeling uncomfortable even while receiving resistance mainly having a static friction coefficient immediately after the start of turning of the steering wheel. . A control unit 12, the steering torque signal T, sets the target current signal I _MS by the vehicle speed signal V. Friction compensation means 21, the steering torque signal T, vehicle speed signal V, to obtain a correction current signal I _t alpha by speed signal MV. By adding the correction current signal I _t alpha to the target current signal I _MS applying vibration to the target current signal I _MS. In this way, control for giving vibration to the auxiliary steering torque generated by the electric motor 8 is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for reducing the steering force of a driver by directly applying electric motor power to a steering system.

[0002]

2. Description of the Related Art An electric power steering apparatus assists a driver's steering force by directly using the driving force of an electric motor. 2. Description of the Related Art Vehicles equipped with an electric power steering device are widely and widely used. With this electric power steering device, the movement of the steering is reduced, and the driver does not need to operate the steering with a strong force.

An example of such an electric power steering apparatus is disclosed in Japanese Patent Application Laid-Open No. 8-40294.

When the vehicle turns, the driver turns the steering wheel. Here, immediately after the turning of the steering wheel, the static friction coefficient mainly acts on a contact portion of each mechanism such as a rack & pinion and a bearing in the electric power steering device. Then, after a short period of time after the steering starts to be turned over, the dynamic friction coefficient mainly comes into play.

[0005]

However, in the conventional electric power steering apparatus disclosed in the above publication, when the static friction coefficient mainly works immediately after the turning of the steering wheel,
When the dynamic friction coefficient mainly works after the turning of the steering wheel, the driver assists the steering force by the same auxiliary steering torque. For this reason, immediately after the turning of the steering wheel, the driver receives a relatively large resistance with a static friction coefficient, so that the driver feels strange when turning the steering wheel.

Accordingly, an object of the present invention is to enable a driver to smoothly turn back a steering wheel without feeling uncomfortable even during a period of time immediately after the start of turning back of the steering wheel while receiving a resistance mainly having a static friction coefficient. It is to make.

[0007]

According to the present invention, there is provided an electric motor for applying an auxiliary steering torque to a steering system of a vehicle; a steering torque sensor for detecting a manual steering torque of the steering system; Control means for outputting a control signal for controlling the electric motor based on a signal from the torque sensor, wherein the control means is configured to control the motor based on at least a signal from the steering torque sensor. An electric power steering apparatus characterized in that an auxiliary steering torque is determined, and control is performed such that the auxiliary steering torque oscillates at a predetermined amplitude and frequency around the center auxiliary steering torque.

According to the first aspect of the present invention, when determining the auxiliary steering torque generated by the electric motor, so-called dither control is performed, in which correction is performed to add a predetermined amplitude and frequency to the center auxiliary steering torque. . For this reason, by giving a torque whose amplitude apex exceeds the resistance value with the static friction coefficient applied thereto, even when receiving a resistance mainly with the static friction coefficient such as at the start of turning of the steering wheel,
The driver can smoothly turn the steering wheel without feeling uncomfortable. In addition, by performing control to apply vibration even when returning the turned-back steering, it is possible to similarly apply a torque exceeding the resistance to which the static friction coefficient is applied, so that the steering can be returned well.

According to a second aspect of the present invention, the control means includes:
2. The control device according to claim 1, wherein when the speed of the electric motor is equal to or less than a predetermined rotation speed, the center auxiliary steering torque is controlled to oscillate at a predetermined amplitude and a predetermined frequency around the center auxiliary steering torque. It is an electric power steering device.

Generally, the resistance to which the coefficient of static friction is applied is received when the speed of the motor is equal to or lower than a predetermined rotation speed. Therefore, in order to prevent the control from being wasted, in the invention according to claim 2, when the speed of the electric motor is equal to or less than the predetermined number of revolutions, the control for applying vibration to the torque generated by the electric motor is performed. At this time, the predetermined rotation speed is
Although the numerical value is not particularly limited, for example, it can be set to the speed of the electric motor at which the rotational speed of the steering becomes 0.1 rev / sec.

[0011]

Embodiments of the present invention will be specifically described below with reference to the drawings. The electric power steering apparatus according to the present embodiment generates an auxiliary steering torque (auxiliary steering force) by the driving force of the electric motor in order to assist the driver's manual steering torque. For this purpose, the electric power steering apparatus includes a steering torque sensor for detecting a driver's manual steering torque (steering force) and a control unit for outputting a control signal (motor control signal) for controlling the electric motor.

Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. First, the overall configuration of the electric power steering device 1 will be described with reference to FIGS. Here, FIG. 1 is an overall configuration diagram of the electric power steering device, FIG. 2 is a block diagram of an electric system of the electric power steering device, and FIG. 3 is a circuit diagram of an electric motor driving means of the control means.

As shown in FIG. 1, an electric power steering apparatus 1 is configured such that when a driver steers a steering wheel 3, a manual steering force generating means (steering system) 2 causes front wheels W, W to be rolled by manual steering so that the vehicle is driven. Change direction. Furthermore, the electric power steering apparatus 1, the motor voltage V _M generated by the motor drive unit 13 based on the motor control signal V _O from the control unit 12, the auxiliary steering torque by driving the motor 8 in this motor voltage V _M (Auxiliary steering force) to reduce the manual steering force by the manual steering force generation means 2.

The manual steering force generating means 2 is connected to a steering shaft 4 provided integrally with the steering wheel 3 via a connecting shaft 5 to a pinion 7a of a rack & pinion mechanism 7 provided in a steering gear box 6. You. The connecting shaft 5 has universal joints 5a and 5b at both ends. The rack and pinion mechanism 7 has a rack shaft 9 formed with rack teeth 7b meshing with the pinion 7a.
The rotation of the pinion 7a is defined as the reciprocating movement of the rack shaft 9 in the lateral direction due to the engagement between the rack shaft 7 and the rack teeth 7b. Further, left and right front wheels W, W as rolling wheels are connected to both ends of the rack shaft 9 via tie rods 10, 10, respectively.

In the electric power steering apparatus 1, an electric motor 8 is driven by a rack shaft 9 to generate an auxiliary steering torque.
And coaxially arranged. Then, the rotation of the electric motor 8 is converted into thrust through a ball screw mechanism 11 provided coaxially with the rack shaft 9, and this thrust acts on the rack shaft 9 (ball screw shaft 11a).

The control means 12 includes a steering torque sensor T
S, a vehicle speed sensor VS, the detection signal T of the rotational speed sensor MVS and the motor current detector 14, V, MV, I _MO is entered. The control means 12 outputs the detection signals T, V, MV,
The magnitude of the motor current I _M flowing through the motor 8 is determined based on I _MO , and the motor control means 13
Outputs _O (control signal). The control unit 12 includes an arithmetic unit that performs various calculations and processes, an input signal conversion unit, a signal generation unit, a storage unit, and the like. Details of these points will be described later.

The steering torque sensor TS includes a steering torque sensor TS.
It is arranged in the gearbox 6 and detects the magnitude and direction of the manual steering torque (steering force) by the driver. And
The steering torque sensor TS transmits a manual steering torque signal T corresponding to the detected manual steering torque to the control means 12.

The vehicle speed sensor VS is provided on the rotation shaft of the wheel W and detects a vehicle speed corresponding to the magnitude of the rotation speed of the wheel W. Then, the vehicle speed sensor VS transmits a vehicle speed signal V corresponding to the detected vehicle speed to the control means 12.

The motor drive unit 13, the motor voltage V _M based on the motor control signal V _O which control unit 12 has output supplied to the electric motor 8 to drive the motor 8. The motor driving means 13 includes, for example, four field-effect transistors (hereinafter referred to as “power FETs”) 13a ₁ , as shown in FIG.
It comprises a bridge circuit 13a composed of switching elements 13a ₂ , 13a ₃ and 13a ₄ and a gate drive circuit 13b. The power FETs 13a ₁ , 13a ₂ , 13a ₃ ,
When each gate G1, G2, G3, G4 in the motor control signal V _O of 13a ₄ is input, the motor voltage V _M is supplied to the electric motor 8 based on the motor control signal V _O. Then, the electric motor 8 flows the motor current I _M, the electric motor 8 generates assist steering torque proportional to the motor current I _M, to assist the steering operation of the driver.

The motor current detecting means 14 includes a resistor or a Hall element connected in series to the motor 8,
Actually flowing through the motor 8 to detect the magnitude and direction of the motor current I _M. Then, the motor current detecting means 14, controlling the motor current signal I _MO corresponding to the motor current I _M means 1
Feedback to 2 (negative feedback).

Next, the configuration of the control means 12 will be further described with reference to FIG. The control unit 12 includes a target current setting unit 20, a friction correction unit 21, an addition unit 22, a deviation calculation unit 23, and a drive control unit 24.

The target current setting means 20 is for determining the center assist steering torque of the present invention, and is provided with a ROM (Read).
(E.g., only memory). ROM in stores the corresponding data in the manual steering torque signal T and the vehicle speed signal V and the target current signal I _MS which is set based on the experimentally predetermined value or design value. Then, the target current setting unit 20 uses the steering torque signal T and the vehicle speed signal V as addresses to correspond to the target current signal I
_MS is read out and the target current signal _IMS is output to the adding means 22. Note that the target current signal _IMS is set to be equal to or less than the maximum target current because the maximum current that can flow through the motor 8 is defined.

The friction correction means 21 performs correction for performing control for giving vibration to the auxiliary steering torque mainly when a resistance having a static friction coefficient is applied.
The friction correction means 21 includes a storage means such as a ROM, and stores a reference correction formula having a vibration waveform shown in FIG. 4A as a reference when performing a correction for applying vibration to the target current. . Further, the friction correction means 21 generates maps 1 to 3 shown in FIGS. 4 (b) to 4 (d) for correcting the target current set in advance based on experimental values or design values. It is remembered. Using these reference correction formulas and maps 1 to 3, a correction current for performing a correction for giving a vibration to the target current is obtained.

The reference correction formula having the waveform shown in FIG. 4A is used as a reference for obtaining a correction current by correcting the target current to give a vibration, and is represented by the following formula (1). . _{I t α = Ksin2πft ··· (1} ) where, I _t alpha: correction current K: amplitude f: frequency t: time

[0025] The amplitude K of the reference correction expression shown in equation (1), by calculating on the basis of the map 1 to map 3, the correction current I _t alpha is obtained. The reason why the rotation speed signal MV, the vehicle speed signal V, and the manual steering torque signal T are used to determine the amplitude K is that if the amplitude is too small, the resistance with the static friction coefficient cannot be easily exceeded. If it is too long, the driver's feeling deteriorates. Although the frequency f in the reference correction formula is set in advance to, for example, 100 Hz, it is desirable that the frequency f be set between 100 and 200 Hz. Frequency f is too small, 100H
If it is less than z, the driver will feel a swelling feeling, and it will take time to exceed the resistance with the static friction coefficient. Also, when setting the frequency, it is preferable to set the frequency by removing the resonance point of each mechanism. Furthermore, it is also desirable to set in consideration of the current responsiveness determined by the reactance of the electric motor 8.

Map 1 shown in FIG. 4B is a function K ₀ indicating a first correction coefficient corresponding to the rotation speed of the electric motor 8.
The rotation speed of the electric motor 8 is measured by a rotation speed sensor MVS shown in FIG. From this rotation speed sensor MVS, a rotation speed signal MV representing the rotation speed of the electric motor 8 is output from the friction correction means 2.
1 is output. In the friction correction means 21, the first correction coefficient K ₀ is obtained by referring to the map 1 based on the rotation speed signal MV output from the rotation speed sensor MVS.
In map 1, the first correction coefficient K ₀ is large when the rotation speed signal MV is 0, and decreases in proportion to the rotation speed signal MV until the rotation speed signal MV reaches a predetermined size. Then, when the rotation speed signal MV reaches a predetermined magnitude, for example, the speed of the electric motor 8 at which the steering rotation speed becomes 0.1 rev / sec, the first correction coefficient K ₀ becomes zero. in this way,
The reason why the first correction coefficient K ₀ is multiplied only when the speed of the motor 8 is low and is equal to or lower than the predetermined rotation speed is that when the speed of the motor 8 is high, the resistance already having the static friction coefficient is not applied, and the dynamic friction is not applied. This is because it is not necessary to apply vibration since the resistance having the coefficient is applied. Instead of providing the rotation speed sensor MVS, a motor current detection unit 14 and a motor voltage detection unit for detecting a voltage between terminals of the motor 8 are provided, and the control unit 12 calculates the rotation speed based on signals from both detection units. May be obtained.

Map 2 shown in FIG. 4 (c) shows the vehicle speed signal V
It is a function of a second correction coefficient K ₁ corresponding to, based on the vehicle speed signal V outputted from the vehicle speed sensor VS, with reference to the map 2, obtaining a second correction coefficient K _1. In map 2, when the vehicle speed signal V is near 0, the second correction coefficient K ₁
Is also 0, and thereafter the second correction coefficient K ₁ increases in proportion to the vehicle speed signal V. Then, when the vehicle speed signal V is equal to or greater than a certain value is to keep the second correction coefficient K ₁ constant. The vehicle speed signal V has a second correction coefficient K ₁ and 0 when the near 0, given the large vibrations when the vehicle speed is slow state, so if there is a sound generated during stationary steering the sound and noise This is to avoid this noise.

A map 3 shown in FIG. 4D is a function indicating a third correction coefficient K ₂ corresponding to the manual steering torque signal T, and is based on the manual steering torque signal T output from the manual steering torque sensor TS. Te, by referring to the map 3, obtaining a third correction factor K _2. In Map 3, when the manual steering torque signal T is near 0, the third correction coefficient K ₂ is also 0, and thereafter, the third correction coefficient K ₂ increases in proportion to the manual steering torque signal T. Then, the manual steering torque signal T
There when it becomes a predetermined value or more is to keep the third correction factor K ₂ constant. In the manual of steering torque signal is a third correction factor K ₂ 0 when close to zero, when manual steering torque T is near 0, so little to generate steering assist torque, since there is no need to provide a vibration is there.

The amplitude K in the reference correction formula shown in the above (1) can be calculated from the following formula (2). K = K ₀ · K ₁ · K ₂ (2) The amplitude K thus obtained is a correction reference formula (1)
By substituting the equation, the correction current I _t alpha is obtained. Thus corresponding to the correction current I _t alpha obtained by the correction current signal I _t alpha is outputted to the addition unit 22.

The addition unit 22, an adder or an addition function of the software control, the correction current signal I _t from the target current signal I _MS and friction correcting unit 21 from the target current setting unit 20
is input, and a correction target current signal It is obtained. The auxiliary steering torque is oscillated by the corrected target current signal It. The calculated correction target current signal It
Is output to the deviation calculating means 23. The addition means 22
Adds the target current signal I _MS correction current signal I _t alpha, calculates a corrected target current signal _{It (= I MS + I t} α).

The deviation calculating means 23 is a subtractor or a software.
A control subtraction function is provided, and the correction target power from the adding means 22 is provided.
Current signal It and the motor current from the motor current detecting means 14.
Signal I_MOIs input to the drive control means 24.
_MIs output. The deviation calculating means 23 calculates the corrected target current signal
Motor current signal I from It_MOIs subtracted, and the deviation signal ΔI _M
(= It-I_MO) Is calculated.

The drive control means 24, and the like PID controller, PWM signal generating means and the logic circuit, the deviation signal [Delta] I _M from the deviation calculating means 23, and outputs the motor control signal V _O to the motor driving unit 13 . Drive control means 24 first deviation signal [Delta] I _M to P (proportional), I
(Integration) and D PWM shown in FIG. 3 corresponding to the magnitude and polarity of the (differential) performs control, further deviation signal [Delta] I _M
A signal V _PWM , an ON signal V _ON , and an OFF signal V _OFF are generated and output to the motor driving means 13 as a motor control signal V _O. The motor voltage V _M output by the motor drive unit 13 is supplied to the electric motor 8, the motor 8 is driven.

Incidentally, in the motor driving means 13,
PWM signal V _PWM is the gate G1 or power FET1 power FETs 13a ₁ constituting the bridge circuit 13a
Is input to the 3a ₂ gate G2, the power according to the magnitude of the deviation signal [Delta] I _M FETs 13a ₁ or the power FET13
The a ₂ acting as a signal for PWM driving. In addition, PW
M or signal V _PWM is input to both gates of the gate G1 or the gate G2 is determined by the polarity of the difference signal [Delta] I _M. In addition, PWM of the gate G1 or the gate G2
The gate signal V _PWM is not input is input off signal V _OFF, power FETs 13a ₁ or power FET13
a ₂ is OFF. When the PWM signal V _PWM to the gate G1 is input, the on signal V _ON is input to the gate G4 of power FETs 13a _4, power FET13
a ₄ is driven ON. On the other hand, when the PWM signal V _PWM to the gate G2 is input, the on signal V _ON to the gate G3 of power FETs 13a ₃ is inputted, the power FET13
a ₃ is driven ON.

Next, the operation and operation of the electric power steering apparatus according to this embodiment will be described. When the driver starts turning the steering wheel 3 shown in FIG.
In the control means 12 shown in FIG. 2, the manual steering torque signal T from the steering torque sensor TS and the vehicle speed sensor V
The vehicle speed signal V from S is read by the target current setting means 20 and the friction correction means 21.

[0035] In the target current setting means 20, the target current signal from the manual steering torque signal T and the vehicle speed signal V I _MS
Is read. The read target current signal _IMS is output from the target current setting means 20 to the adding means 22. on the other hand,
The friction correction unit 21, the correction current signal I _t alpha for the correction for vibrating the target current signal I _MS is determined.
When obtaining the correction current signal I _t alpha, the friction correction means 21
Then, the first correction coefficient K ₀ is obtained by referring to the map 1 using the rotation speed signal MV from the rotation speed sensor MVS. The second obtains a correction coefficient K ₁ with reference to the manual steering torque signal T from the steering torque sensor TS to map 2, a vehicle speed sensor VS
The third correction coefficient K is obtained by referring to the map 3
Ask for ₂ . The first correction coefficient K ₀ thus obtained
The amplitude K is calculated by substituting the third correction coefficient K ₂ into the equation (2). By substituting this amplitude K in equation (1), to obtain a correction current signal I _t alpha. Correction current signal I _t alpha thus obtained is output to the adding means 22 from the friction correcting unit 21.

[0036] In addition means 22 calculates the corrected target current signal adds the target current setting means 20 target current signal I _MS and the correction current signal outputted from the friction compensation unit 21 I _t alpha output from . The calculated correction target current signal It is output from the adding means 22 to the deviation calculating means 23. Further, the motor current signal _IMO is output from the motor current detecting means 14 to the deviation calculating means 23.

In the deviation calculating means 23, the adding means 2
The difference signal ΔI _M is calculated by subtracting the motor current signal I _MO output from the motor current detection means 14 from the correction target current signal It output from 2. Then, it outputs the deviation signal [Delta] I _M to the drive control unit 24. In the drive control unit 24, based on the output deviation signal [Delta] I _M, and outputs the motor control signal V _O to the motor drive unit 13.

[0038] Then, the electric motor driving unit 13 outputs a motor voltage V _M to the motor 8. Thereby, the electric motor 8
Generates assist steering torque as usual to assist the driver in steering operation. At this time, the magnitude of the auxiliary steering torque generated by the electric motor 8 substantially depends on the correction target current signal It. In the present embodiment, the corrected target current signal It is vibrating under the influence of the correction current signal I _t alpha by friction correcting unit 21. For this reason,
The magnitude of the auxiliary steering torque generated by the electric motor 8 also vibrates.

FIG. 5 shows an example of the auxiliary steering torque generated at this time. FIG. 5 is a graph in which the vertical axis represents the auxiliary steering torque generated by the electric motor 8 and the horizontal axis represents the turning angle of the steering wheel 3. As can be seen from FIG.
When starting to turn the steering wheel 3 to the right or left from the neutral (N) position, and when starting to return to the neutral direction from the position to which the steering wheel 3 is turned fully to the right or left, respectively, Vibration is occurring. In the waveform having a large amplitude in the waveform indicating the large vibration, the resistance over the static friction coefficient generated in each mechanism is overcome. For this reason, at the time of starting the turning of the steering wheel 3 and the time of starting the returning, the driver does not feel uncomfortable,
The steering wheel 3 can be operated with a smooth feeling.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, a reference correction formula having a sine wave is used, but a reference correction formula having a pulse wave can be used, for example. Further, when the amplitude is obtained, the rotation speed of the electric motor, the manual steering torque, and the vehicle speed are used. However, it is not essential to use these, and a mode in which some of these are used may be adopted. Further, the amplitude may be kept constant.

[0041]

As described above, claim 1 of the present invention
According to the invention according to the present invention, by applying a torque at which the peak of the amplitude exceeds the resistance value at which the static friction coefficient is applied,
The driver can smoothly turn back the steering wheel without feeling uncomfortable even when the vehicle is subjected to resistance mainly due to the coefficient of static friction, such as at the start of turning back of the steering wheel. Also, by performing control to apply vibration when returning the steering wheel that has been turned back, a torque exceeding the resistance to which the static friction coefficient is applied can be similarly applied, so that the steering can be returned well. Can be.

According to the second aspect of the present invention, the control according to the first aspect can be performed only when a resistance having a static friction coefficient is mainly applied, and there is no need to perform useless control. .

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an electric power steering device according to the present embodiment.

FIG. 2 is a block diagram of an electric system of the electric power steering device of FIG. 1;

FIG. 3 is a circuit diagram of a motor driving means in the control means of FIG. 2;

FIG. 4A is a graph showing a reference correction formula serving as a reference when performing a correction for applying vibration to a target current, and FIG. 4B shows a first correction coefficient K ₀ corresponding to a rotation speed signal MV. Map 1, (c) shows a second correction coefficient K ₁ corresponding to the vehicle speed signal V.
And (d) are maps 3 showing the third correction coefficient K ₂ corresponding to the manual steering torque signal T.

FIG. 5 is a graph in which the vertical axis represents auxiliary steering torque generated by the generator, and the horizontal axis represents the turning angle of the steering wheel.

[Explanation of symbols]

1 an electric power steering device 2 Steering system (manual steering force generating means) 8 motor 12 control unit 13 electric motor drive means 20 the target current setting unit 21 friction correcting means I _MS target current signal I _t alpha correction current signal (correction current) It correction Target current signal TS Steering torque sensor T Manual steering torque signal (manual steering torque) VS Vehicle speed sensor V Vehicle speed signal (vehicle speed) V _O Motor control signal (control signal)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3D032 CC08 CC50 DA15 DA23 DA63 DA64 DA65 DB11 DC01 DC02 DC03 DC34 DD01 DD10 DD17 DE01 EA01 EB11 EC23 GG01 3D033 CA13 CA16 CA20 CA21

Claims (2)

[Claims] An electric motor for applying an auxiliary steering torque to a steering system of a vehicle, a steering torque sensor for detecting a manual steering torque of the steering system, and control for controlling the electric motor based on at least a signal from the steering torque sensor. Control means for outputting a signal, wherein the control means determines a center assist steering torque based on at least a signal from the steering torque sensor, and determines the center assist steering torque. An electric power steering apparatus, wherein the auxiliary steering torque is controlled so as to oscillate with a predetermined amplitude and a predetermined frequency as a center. 2. The control means controls the center assist steering torque so that the center assist steering torque oscillates at a predetermined amplitude and a predetermined frequency around the center assist steering torque when the speed of the electric motor is equal to or lower than a predetermined number of revolutions. The electric power steering device according to claim 1, wherein: