JP2004025912A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize excellent steering wheel return control that hardly produces excess and deficiency in output value of steering wheel return torque T<SB>R</SB>by a motor. <P>SOLUTION: Only in case a decision condition indicated at a stop 401 is detected in succession, it is decided that it is during steering wheel return steering, and only in this case, the value of a decision flag S for whether it is needed or not is set to ON. For example, when a means to decide whether return torque is needed is constituted like this, even before a value of a steering angular speed ω reaches 0 or the direction of the steering angular speed ω is reversed, even if the value of steering torque γ reached 0 or the direction of the steering torque γ is reversed, the value of the decision flag S for whether it is needed is varied from ON to OFF. This timing is interpreted as a timing at which the will of a driver for steering wheel return operation (namely, necessity of steering wheel return torque T<SB>R</SB>) is quenched. Thus, this constitution effectively prevents the occurrence of a trouble such as overshooting. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
According to the present invention, when the driver attempts to return the steering wheel (steering wheel) to a predetermined neutral position, the steering wheel return torque T is expected to be output. _R The present invention relates to an electric power steering apparatus having steering wheel return control means for calculating the value of the steering wheel.
[0002]
[Prior art]
As the electric power steering device of the type described above, for example, those described in Japanese Patent Laid-Open Publication No. 2000-289639 (electric power steering device) (hereinafter referred to as well-known example 1) are generally widely known. ing. These prior arts are useful for an electric power steering device controlled by a motor control device having no rotation angle sensor.
[0003]
FIG. 15 illustrates a control block diagram of the handle return control means based on these conventional techniques. For example, in such a steering wheel return control means based on the prior art, the steering torque τ and the steering angular velocity ω (estimated value) are input and the steering wheel return torque T _R A return torque necessity determining means for outputting a necessity determination flag S (= ON / OFF) relating to the necessity of output of the vehicle, and inputting each value of the vehicle speed u and the steering angular velocity ω to obtain an intermediate result T of the steering wheel return torque. _R ', Which outputs a steering wheel return torque calculating unit for outputting the output values (S, T _R ′), The steering wheel return torque T _R Is controlling the value of.
[0004]
For example, in the return control canceling means of FIG. _R = T _R 'And output T when S = OFF _R = 0 is output.
The end determination unit of the return torque necessity determination means determines the steering wheel return torque T based on the steering angular velocity ω (estimated value) of the steering wheel. _R Is determined at which timing the output should end.
[0005]
[Problems to be solved by the invention]
FIGS. 16, 17 and 18 show various steering conditions (steering torque τ, steering wheel return torque T) relating to the steering system based on the above-described conventional technology. _R , Absolute steering angle).
Hereinafter, the neutral point is defined as a zero point (reference point), a rightward direction (clockwise) is defined as a negative direction, and a leftward direction (counterclockwise) is defined as a positive direction.
[0006]
For example, when steering as illustrated in FIGS. 16 and 18 is performed, in the related art such as the above-described known example 1, the steering wheel return torque is determined based only on the steering angular velocity ω (estimated value). T _R Since the end time of the output shown in FIG. 17 is determined, as shown in FIGS. _R The determination of the timing at which the output should be terminated tends to be delayed, and sometimes this output period is unduly extended, so that the steering wheel may overshoot by about 30 ° as illustrated in FIG.
[0007]
SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a power steering apparatus having a motor, in which a steering wheel return torque T _R The object of the present invention is to realize better steering wheel return control in which the output value of the steering wheel does not easily become excessive or insufficient.
[0008]
Means for Solving the Problems, Functions and Effects of the Invention
In order to solve the above-mentioned problems, the following means are effective.
That is, a first means of the present invention includes a motor for applying an auxiliary torque to a steering mechanism of a vehicle, a motor control device for controlling the driving of the motor, and a method in which a driver sets a steering wheel (steering wheel) at a predetermined neutral position. Handle return torque T expected to be output by the motor when returning _R Of the steering wheel return torque T based on the variation of both the steering wheel angular velocity ω and the steering torque τ applied by the driver to the steering wheel. _R A return torque necessity determining means for determining the required period of output of the steering wheel, and a steering wheel return torque T based on a predetermined determination result (no) output by the return torque necessity determination means. _R And a return control suspending means for suspending the output of the steering torque τ, and using the value or the sign of the steering torque τ in the end determination of the required period in the return torque necessity determining means.
[0009]
That is, both the conventional steering angular velocity ω and the steering torque τ applied to the steering wheel by the driver are used to determine the end of the required period.
The steering torque τ is a physical quantity that represents the driver's steering intention most directly, simply and faithfully. Therefore, the steering torque-related value such as the steering torque τ or its differential value (dτ / dt) is determined as the end determination. , It is easy or possible to perform more accurate end determination.
[0010]
Therefore, according to the first means of the present invention, it is possible to effectively prevent the delay of the end determination as described above, and to effectively prevent, eliminate, or alleviate a problem such as overshoot. , Easy or possible, and the steering wheel return torque T required for the steering system _R Can be given moderately.
Hereinafter, a more specific description will be given.
[0011]
That is, the second means of the present invention is to provide a reversal event detection means for detecting a reversal event in the steering direction of the steering torque τ in the return torque necessity determination means of the first means.
When the driver intends to return the steering wheel to disappear or to prevent overshooting, the driver usually reverses the steering direction.
Therefore, according to the first means of the present invention, the steering wheel return torque T is earlier than before. _R , It is possible to judge the required period of output, and thus it is possible to effectively prevent or mitigate problems such as overshoot.
[0012]
Further, a third means is that the return torque necessity determining means of the first or second means is provided with a fluctuation gradient determining means for determining a value of a time derivative of an absolute value of the steering torque τ.
[0013]
For example, when the absolute value of the steering torque τ has a value equal to or greater than a certain value during the steering operation of returning the steering wheel, it is determined that there is a relatively strong steering intention, but the absolute value of the τ decreases rapidly. At some point, the handle return torque T _R It can be estimated that the need for the output of the power supply also rapidly decreases.
Therefore, according to the third means of the present invention, it is possible to estimate or predict the required period of the steering wheel return control with relatively high accuracy, and thus to effectively prevent or mitigate problems such as overshoot. Becomes possible.
[0014]
Further, the fourth means is the return torque necessity determining means of any one of the first to third means, wherein the product value τω of the steering torque τ and the steering wheel angular velocity ω falls within a predetermined appropriate range. A product value appropriateness determining means for determining whether the product value falls within a proper range is provided. _R Is determined to be a necessary period. That is, the determination is made based on the driver's power.
[0015]
The above-mentioned known example 1 discloses an embodiment in which the steering wheel return control is realized by an extremely complicated control procedure. The main causes of the complicated control processing procedure are as follows.
(Cause 1) Control is executed separately for left and right.
(Cause 2) Therefore, the "returning determination timer" is also provided separately for the left and right.
(Cause 3) Therefore, the process of updating the “returning determination timer” is complicated.
[0016]
However, according to the fourth means of the present invention, these control processes can be more unifiedly configured by the superordinate concept of the power of the driver τω without dividing the control processes into left and right separately. As a result, the number of program development steps and the number of dynamic steps during execution can be significantly reduced.
Therefore, according to the fourth aspect of the present invention, the productivity and the performance of the electric power steering device can be effectively improved.
This embodiment will be illustrated in more detail in a second embodiment of the present invention.
[0017]
The fifth means is the steering wheel return control means of any one of the first to fourth means described above, wherein a function F (ω, u) having the steering wheel angular velocity ω and the vehicle speed u as independent variables is used. Handle return torque T _R Is calculated, and this function F (ω, u) is represented by the product of the function f (ω) and the function g (u). Further, the function f (ω) is expressed by f (−ω) = − f (ω) Is satisfied and the maximum value is obtained, the monotonic increasing function in a broad sense is defined as −ω1 ≦ ω ≦ ω1, and the monotone decreasing function in a broad sense is defined as ω1 ≦ | ω |.
[0018]
Here, the monotone increasing function in a broad sense refers to a function that satisfies “a <b⇒f (a) ≦ f (b)” in a predetermined domain. Similarly, the monotone decreasing function in a broad sense refers to a function that satisfies “a <b⇒f (a) ≧ f (b)” in a predetermined domain.
[0019]
Although such a setting form of the function f can be seen in the above-mentioned known example 1, the combination of such a setting form of the function f and each of the above-described means (fifth means of the present invention) makes it possible to increase the function f. Effectively handle return torque T _R Can be prevented from becoming excessive. Therefore, according to the fifth aspect of the present invention, overshoot can be more effectively prevented or mitigated than before.
[0020]
Further, the sixth means is that in any one of the first to fifth means described above, the handle return angle θ (≧ 0), which is the absolute value of the angle at which the handle is returned by the handle return control means, A return angle calculating means for calculating using a time integration operation on the angular velocity ω, and a steering wheel return torque T calculated by the steering wheel return control means _R In addition, a scale adjusting means for multiplying by an adjustment coefficient (gain G2) is provided, and the scale adjustment means converts the adjustment coefficient (gain G2) using a function h (θ) having the handlebar return angle θ as an independent variable. It is to calculate.
The start time of the time integration is determined by the return torque T by the steering wheel return control. _R The time when the output of ($ 0) is started may be sufficient.
[0021]
For example, when the amount of inertia (inertia or the like) of the steering system is relatively large, or when the friction acting on the steering system (such as internal friction of the mechanical system or external friction with the road surface) is relatively small, the steering wheel return torque T _R In many cases, a relatively large value between the start of returning the handle and the return angle of the handle reaching the vicinity of the initial 10 ° to 30 ° is often sufficient.
According to the sixth aspect of the present invention, the steering wheel return torque T depends on the steering wheel return angle θ in accordance with the specific characteristics of various steering systems depending on the vehicle type and the like. _R Can be optimized. As a result, the steering wheel returning torque T _R Can be calculated.
[0022]
For example, when the amount of inertia (inertia) of the steering system is relatively large, or when the friction acting on the steering system (internal friction of the mechanical system, external friction with the road surface, etc.) is relatively small, etc. Means are effective.
That is, a seventh means of the present invention is that in the sixth means, the function h (θ) is a monotone decreasing function in a broad sense.
For example, by such means, the handle return torque T _R Can be effectively prevented from being excessively reduced.
By the means of the present invention described above, the above problems can be effectively or rationally solved.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on specific examples. However, the present invention is not limited to the embodiments described below.
[First embodiment]
FIG. 1 is a system configuration diagram of an electric power steering apparatus 100 according to each embodiment of the present invention.
[0024]
A steering wheel (steering wheel) 11 is attached to one end of the steering shaft 10 in FIG. 1, and a pinion shaft 13 supported on a gear box 12 is connected to the other end. The pinion shaft 13 is meshed with a rack shaft 14 fitted in the gear box 12, and both ends of the rack shaft 14 are connected to unillustrated steering wheels via ball joints or the like, though not shown. I have. A motor M for applying assist torque is connected to the steering shaft 10 via two gears 17 having a reduction ratio Gi.
[0025]
The motor control device 110 includes a CPU 111, a ROM 112b, a RAM 112a, a drive circuit 113, an input interface (IF) 114 having an A / D converter, a measurement signal saving register, and the like, a current detector 115 for detecting a motor current I, and a motor. It comprises a voltage detector 116 for detecting the voltage V and the like. Further, the current detector 115 and the voltage detector 116 include a low-pass filter circuit (not shown) that removes high-frequency noise generated by chopper control or driving (rotation) of the motor M.
[0026]
The drive circuit 113 includes a battery, a PWM converter (113a), a PMOS drive circuit, and the like (see FIG. 2), and supplies a motor current I to the motor M by a known chopper control. That is, the command voltage V is applied to the motor M. _n , The motor current I is supplied from the drive circuit 113 of the motor control device 110 via the current detector 115 and the voltage detector 116.
[0027]
Further, the steering shaft 10 is provided with a torque detector 15 for detecting the magnitude and direction (steering torque τ) of the manual steering force applied to the steering wheel (handle) 11 by the driver.
[0028]
The CPU 111 of the motor control device 110 includes output signals (real-time measured values) from the torque sensor 15 used for detecting the steering torque τ of the steering wheel, the vehicle speedometer 50 used for calculating the vehicle speed u, and the like. Are input via the input interface (IF) 114. The CPU 111 determines a torque value (command torque T) to be output by the motor M based on a predetermined torque calculation from these input values, and further determines a command current I based on the command torque T. _n Is determined.
[0029]
FIG. 2 is a control block diagram of the motor control device 110 included in the electric power steering device 100. The torque current converter 280 of FIG. _n Is determined based on the above-mentioned command torque T. _n -T map (table data) and the like. This I _n -T map indicates the command current I _n At the same time also serves as a "current command limiter" that defines the upper limit value and the lower limit value.
[0030]
PI control section 290 performs current deviation ΔI (ＩI) by well-known proportional integral control (or proportional control, proportional integral differential control). _n -I), the command value V of the voltage to be applied to the motor M _n Is calculated.
Further, the rotation speed calculation section 190 calculates the rotation speed Ω of the motor M based on the current I, the voltage V, and the impedance Z of the motor M.
[0031]
The command torque calculator 200 calculates the steering torque τ of the steering wheel calculated by the steering torque calculator 170, the vehicle speed u calculated by the vehicle speed calculator 160, and the rotation speed Ω of the motor M calculated by the rotation speed calculator 190. Based on the above, a desired torque command value (command torque T) to be output is calculated.
[0032]
The command torque calculator 200 mainly includes the assist torque T _A And an inertia compensation torque T _K Compensation torque calculating section 220 for calculating the damper torque T _D And a steering wheel return torque T _R Is calculated. The command torque calculator 200 calculates the command torque T according to the following equation (1).
(Equation 1)
T = T _A + T _K + T _D + T _R … (1)
[0033]
FIG. 3 is a control block diagram of the handle return control means 240 included in the command torque calculator 200. Although FIG. 3 has a configuration similar to that of FIG. 15 described above, the known example 1 also shows that the driver inputs (sees) the steering torque τ applied to the steering wheel 11 in the end determination unit 243 as well. 15 is essentially different from the prior art (FIG. 15).
[0034]
That is, in the end determination unit 243 that forms a part of the return torque necessity determination unit 241 in FIG. _R The end determination is also performed using the value of the steering torque τ as the end determination condition of the necessary period of the output.
A more specific description of the torque necessity determination unit 241 and the termination determination unit 243 will be exemplarily described later with reference to FIG. Further, a more specific description of the return control suspending means 248 will be exemplarily described later with reference to FIG.
[0035]
In the steering wheel return torque calculating section 246 (FIGS. 3 and 4), the steering wheel return torque T is calculated based on the steering angular velocity ω and the vehicle speed u by a known or arbitrary appropriate procedure. _R '(T _R Is obtained as a suitable value of the intermediate result) when calculating.
FIG. 4 illustrates a control block diagram of the steering wheel return torque calculator 246.
[0036]
In a low speed region of the vehicle speed u or when the friction coefficient μ between the road surface and the tire is small, the road surface reaction force (self-aligning torque) is relatively small compared to the frictional resistance generated in the steering system including the motor M. It tends to be smaller. Therefore, the steering wheel return torque T _R ′ Is set so as to act in the rotation direction of the motor M in a low-speed region where it is difficult to obtain a road surface reaction force as shown in FIG. 4, for example. Of course, setting according to the friction coefficient μ may be performed.
[0037]
FIG. 5 is a flowchart showing a processing procedure (algorithm) for realizing the return torque necessity determining means 241 in the first embodiment.
(symbol)
S: Necessity determination flag (S = ON period is T _R Required period of output)
τ ... steering torque
τ0… S = retraction area of steering torque τ when ON is set
ω… steering angular velocity
ω0… S = retraction area for the value of steering angular velocity ω when ON is set
[0038]
However, the above-mentioned steering angular velocity ω uses an estimated value calculated based on the following equations (2) to (4).
(Equation 2)
ω = Ω / Gi (2)
[Equation 3]
Ω = (V−ZI) / K _e … (3)
(Equation 4)
Z = ρ + λS (4)
(Symbol definition)
Gi: reduction ratio (gear ratio between motor and pinion shaft)
K _e : Motor back EMF constant
V: Motor voltage (measured value in real time)
I: Motor current (measured value in real time)
Z: Motor impedance
ρ: Motor armature resistance
λ: Motor inductance
[0039]
The initial value of the flag S is OFF, and the initial value of the counter n is 0. These are initialized when the system (electric power steering device 100) is started (when the power is turned on). The value of the constant N is determined based on the execution cycle of this routine and the measurement accuracy and reliability of each sensor such as τ and ω. In a system where the measurement accuracy of τ and ω is high and the measurement error due to noise or the like is small, the value of N can be set relatively small for a predetermined execution cycle. ε1, ε2, and ε3 are predetermined constants equal to or less than 0, and the optimum value can be empirically obtained similarly to the value of N. For example, when the dead zone of the torque sensor 15 is wide, the absolute value of ε2 may be increased accordingly. The same applies to ε1 and ε3.
[0040]
Also, for example, when this routine is called and executed at a cycle of 20 milliseconds, a slight noise may be assumed under a system configuration using various sensors such as a steering torque which is widely used. Also, the value of N can be set to, for example, about 3. That is, according to this setting, it is determined that the steering wheel is being returned by steering only when the determination condition shown in step 410 is continuously detected for 60 msec or more, and only in this case, the value of the necessity determination flag S is turned ON. Is set to
When the return torque necessity determination means 241 is realized by the configuration shown in FIG. 5 and the like, the following operation can be obtained.
[0041]
(Function 1) When S = OFF, the necessity determination is made when it is recognized that the power τω of the driver has definitely become a negative value by the operation of steps 410 to 460 that embody the start determination unit 242. The flag S is changed to ON.
(Function 2) When S = ON, if it is recognized that the driver's power τω has definitely returned to a positive value by the operation of steps 470 to 490 embodying the end determination unit 243, it is unnecessary. The determination flag S is changed to OFF.
[0042]
(Function 3) Therefore, even before the value of the steering angular velocity ω reaches 0 or the direction of the steering angular velocity ω is reversed, the value of the steering torque τ reaches 0 or the direction of the steering torque τ becomes If it is inverted, the value of the necessity determination flag S can be changed from ON to OFF. This timing is determined by the intention of the driver to return the steering wheel (ie, the steering wheel return torque T). _R Need) can be interpreted as the timing at which the extinction has disappeared.
[0043]
Therefore, according to the above configuration, it is possible to effectively prevent delay in end determination and the like, thereby effectively preventing or alleviating problems such as overshoot and the like, and to reduce steering wheel return torque required for the steering system. T _R Can be given moderately.
[0044]
FIG. 6 is a flowchart showing a processing procedure (algorithm) for realizing the return control stopping means 248 of the handle return control means 240 in the first embodiment (and the third embodiment) of the present invention. Steps 510 to 530 correspond to the array T _R '(K) is a process for cyclically using the save area represented by (1 ≦ k ≦ K) by wrap-around operation. The initial value of the counter k is set in the same manner as the above-mentioned initial value of the counter n.
[0045]
The subroutine of step 550 is realized by the steering wheel return torque calculator 246 of FIG. Also, as a result of the operation of steps 540 and 560, the steering wheel return torque T _R 'Is stopped.
[0046]
In step 570, a smoothing process of the output value is realized. This processing is performed to alleviate the sense of discomfort caused by a sudden change in the steering feeling. That is, the recent K handle return torques T _R '(Intermediate result), the steering wheel return torque T to be finally output _R Value. Of course, any other known or arbitrary processing may be used as the output value smoothing processing. The above integer K is a parameter indicating the smoothness of the smoothing process. The effect of this annealing process can be read from, for example, FIG.
[0047]
FIGS. 7, 8, and 9 show the steering conditions (steering torque τ, steering wheel return torque T) related to the steering system of the vehicle having the electric power steering device 100 according to the first embodiment of the present invention. _R 3 is a graph illustrating measurement data of absolute steering angle).
As can be easily understood from these graphs, according to the present invention, the steering wheel return torque T _R Since the period during which the output of the motor M is required can be accurately determined, the output torque of the motor M (T _R ) Can be effectively prevented or mitigated, such as excessive return of the steering wheel (overshoot), and the steering wheel return torque T required for the steering system. _R Can be given moderately.
[0048]
Note that such an embodiment of the present invention includes a torque sensor and a brushless DC motor, such as an electric power steering device described in Japanese Patent Laid-Open Publication No. 2002-136182: Motor Control Device. Also, the present invention can be applied to any other electric power steering device.
[0049]
For example, the first embodiment described above may be modified as follows.
That is, in the first embodiment described above, the above equation (2) is used in step 410 (FIG. 4) of the subroutine SBR1 as the equation for calculating the steering angular velocity ω. The following equation (5) may be used instead of equation (2).
(Equation 5)
ω = Ω / Gi + αdτ / dt (5)
[0050]
Here, dτ / dt is the time derivative of the steering torque τ, and α is the reciprocal of the unillustrated torsion bar spring constant of the torque sensor 15.
That is, the steering speed ω is obtained by calculating the rotation angular velocity (αdτ / dt) of the torsion bar with respect to the pinion shaft 13 calculated from the amount of change in the steering torque τ, and the rotation of the pinion shaft 13 calculated by the above equation (2). It is calculated as the sum of the angular velocities (Ω / Gi).
[0051]
According to such a correction means, the steering angular velocity ω can be calculated more accurately than in the first embodiment without ignoring the influence of the deformation amount of the unillustrated torsion bar of the torque sensor 15. It becomes possible. Therefore, if the above equation (5) is used in step 410, the operation and effect of the present invention can be more reliably obtained.
Such correction is particularly effective when the value of the constant α is large, that is, when the spring constant of the torsion bar is relatively small.
[0052]
[Second embodiment]
FIG. 10 is a flowchart showing a processing procedure (algorithm) for realizing the handle return control means 240 in the second embodiment of the present invention. Step 630 performs the same determination as step 410 (FIG. 5) of the first embodiment. Further, the integer N may be substantially the same as the integer N in FIG. The counters m and n are initialized to 0 when the system is started (immediately after the power is turned on).
[0053]
For example, according to such a configuration (algorithm), step 650 has substantially the same operation as step 490 (FIG. 5) of the first embodiment, and step 660 is step 540 (FIG. 5) of the first embodiment. Since the operation substantially the same as that of 6) is achieved, the handle return control means 240 having the operation and effect approximately equivalent to that of the first embodiment can be realized by such a processing procedure (algorithm).
Further, according to this processing procedure, it is possible to configure an electric power steering apparatus in which overshoot is much less likely to occur than in the related art, with a much smaller number of development steps than in the related art.
[0054]
However, in the processing procedure of the second embodiment illustrated in FIG. _R The annealing process is omitted. Also in the processing procedure of the second embodiment, T _R When the smoothing process is also performed at the same time, steps 680 and 690 in FIG. 10 are replaced with steps 550 to 570 in FIG. 6, and at the beginning of the subroutine (algorithm) in FIG. In the same manner as in (Steps 600 to 620), the update processing of the argument k of the array (for example, Steps 510 to 530) may be performed simultaneously.
[0055]
[Third embodiment]
In the present embodiment, the same hardware (the electric power steering apparatus 100 in FIG. 1) as in the above-described first and second embodiments is used, and the steering wheel returning torque T is calculated based on the steering torque τ and the time displacement of the steering torque τ. _R An example is shown in which the necessity / unnecessity determination is made.
That is, for example, when returning the steering wheel from the left to the neutral position, the steering wheel return torque T _R Are defined by the following equations (6) and (7).
[0056]
(Equation 6)
τ> τ1 (τ1 ≧ 0) (6)
(Equation 7)
dτ <−dτ1 (dτ1 ≧ 0) (7)
Here, dτ is a time displacement (difference value) of the current steering torque τ based on the previous steering torque, and τ1 and dτ1 are appropriate constants individually determined. This determination condition indicates that the relatively large steering torque τ is relatively rapidly attenuating, and matches the condition observed when returning the steering wheel from the left to the neutral position.
[0057]
Similarly, when returning the steering wheel from the right to the neutral position, the steering wheel return torque T _R Can be expressed by the following equations (8) and (9).
[0058]
(Equation 8)
τ <−τ1 (8)
(Equation 9)
dτ> dτ1 (9)
[0059]
FIG. 11 shows a processing procedure (algorithm) for realizing the return torque necessity determination means 241 in the third embodiment.
(symbol)
R: Necessity judgment flag (for judging the necessity of return torque from the left to the neutral point)
i… Counter (same as above)
L: Necessity judgment flag (for judging the necessity of return torque from right to neutral point)
j… Counter (same as above)
The counters i and j are initialized to 0 when the system is started. Further, since the integer N has the same effect as that of the first or second embodiment, it may be the same constant as the integer N of the first or second embodiment.
For example, according to such a processing procedure, when returning the steering wheel from the left to the neutral position, the steering wheel returning torque T _R Is required, R = ON is set, and when returning the steering wheel from the right to the neutral position, the steering wheel return torque T is set. _R Is required, L = ON is set.
[0060]
FIG. 12 is a flowchart illustrating a processing procedure (algorithm) for realizing the end determination unit 243 according to the third embodiment of the present invention. Also in this end determination unit 243, the steering wheel returning torque T is determined based on the steering torque τ and the time displacement of the steering torque τ. _R Is determined.
That is, for example, when returning the steering wheel from the left to the neutral position, the steering wheel return torque T _R Is determined to be unnecessary when any of the following equations (10), (11) and (12) is satisfied.
[0061]
(Equation 10)
τ <−τ2 (τ2 ≧ 0) (10)
[Equation 11]
τ ≦ τ0−TF, (TF ≧ 0)
dτ <−dτ2 (dτ2 ≧ 0) (11)
(Equation 12)
dτ> dτ3 (dτ3 ≧ 0) (12)
Here, τ2, dτ2 (return direction threshold) and dτ3 (cutting direction threshold) are appropriate constants individually determined. Further, τ0 is the value of the steering torque τ at the start of the steering wheel return control stored in step 775, and the constant TF is a predetermined torque value for taking into account friction in the steering system.
[0062]
The physical meaning of each condition is as follows.
(A) Equation (10) indicates that steering is performed in the steering wheel return direction (ie, rightward when returning from the left) with a steering force greater than a certain value (= dτ2 ≧ 0), or the hand is released from the steering wheel. Overshoot and start to cut to the right.
(B) Equation (11) means the case where the reverse steering is started before returning.
(C) Equation (12) means a case where steering is performed to the left again during turning back, or a case where steering is started to the left after returning is completed. This steering indicates the driver's will to prevent overshoot.
[0063]
Therefore, in the third embodiment, in any of the above cases (a), (b) and (c), the steering wheel return torque T _R Since the subsequent output is stopped (suppressed), overshoot can be effectively prevented, and for example, when it is necessary to turn the steering wheel to the left again during the returning operation from the left side, etc. Excessive handle return torque T _R A good steering feeling based on the above-described suppression control can be obtained.
[0064]
Note that the subroutine Lfine called and executed in step 730 of FIG. 11 also sets the neutral point to the zero point (reference point), the right direction (clockwise) to the negative direction, and the left direction (counterclockwise) to the negative point. Recalling the premise of “positive orientation” and paying attention to the left-right symmetry, the configuration can be made exactly the same as the above-described subroutine Rfine.
[0065]
By using the values of the necessity determination flags R and L set according to the above-described processing procedures in the same manner as the necessity determination flag S described above, substantially the same operation and effect as in the first embodiment can be obtained. Obtainable. For example, the handle return torque T _R When the subroutine of FIG. 6 is used to output the calculation result of (1), a logical operation process of S = OR (L, R) is added (inserted) at the beginning of this subroutine (FIG. 6) or immediately before step 540. What is necessary is just to execute a lever subroutine.
[0066]
[Other Modifications 1]
FIG. 13 illustrates a modified example of the steering wheel return torque calculation unit 246. This graph is a modified form of the function f that represents the ω dependence of the function F of the following equation (13) realized by the steering wheel return torque calculation unit 246 of FIG.
(Equation 13)
T _R '= F (ω, u) = G1 · T _R ″,
G1 = g (u),
T _R ″ = F (ω) (13)
However, also in the first modification, it is assumed that the symmetry of f (−ω) = − f (ω) is satisfied. With such a setting form of the function f, when the steering angular velocity ω is large, it is possible to prevent the steering wheel return torque from being output more than necessary against the driver's steering intention, so that the steering wheel can be more effectively operated than before. Return torque T _R Can be prevented from becoming excessive.
[0067]
Alternatively, S = OFF may be set when the absolute value of the steering angular velocity ω reaches an appropriate predetermined value ω2 satisfying ω1 ≦ ω2. As such a value of ω2, for example, the value of ω2 illustrated in FIG. 13 or a steering observed near the inflection point of the steering angle (absolute steering angle) in the period when S = ON in FIG. The absolute value of the angular velocity ω or the like can be used.
It can be easily inferred from the comparison between the graphs of FIG. 9 and FIG. 18 that such a configuration may provide an operation and an effect substantially equal to or greater than those of the above-described embodiment.
[0068]
Also, at the above-mentioned timing of setting S = OFF when the absolute value of ω reaches ω2, or at the timing when the sign of dω / dt is inverted during the period when S = ON, etc. Instead of setting S = OFF as described above, for example, the steering wheel return torque T as shown in the following equation (14) _R ', The value of another new gain (adjustment coefficient G3) may be reset to a smaller value (constant) (0 ≦ G3 <1).
[0069]
[Equation 14]
T _R = G3 · T _R ′
= G3 · (G1 · T _R ″)… (14)
[0070]
However, this initial value is set to G3 = 1 at the beginning of the steering wheel return control. If G3 is reset to 0 at the above timing, this method results in the above-described method in which S = OFF is set when the absolute value of ω reaches ω2. Of course, an appropriate positive constant such as 0 <G3 <1 may be set. The optimum value of this value depends on the amount of inertia (inertia) of the steering system, mechanical internal friction, and the like, but the optimum value can be empirically determined. It may be a constant.
[0071]
By interposing such an adjustment coefficient (gain G3), the gain G3 can be changed at a good timing, and as a result, the steering wheel return torque T _R According to the above-mentioned method, overshoot can be effectively prevented or reduced, and the steering wheel return torque T suitable for the steering system can be effectively reduced. _R Can be given.
[0072]
If a new opportunity (a change in situation) such as the sign of dω / dt being inverted again is observed during the period in which S = ON, the value of G3 is returned to 1 again. In some cases, various applications such as changing the value to another appropriate constant (0 <G3 <1) or the like may be effective.
[0073]
Note that with the reversal of the sign of dω / dt, the value of the gain G3 (therefore, T _R ”Or T _R Changing this value corresponds to giving a hysteresis characteristic to the graph of FIG. For example, if G3 is reset to 0 when the value of ω reaches ω2, the hysteresis loop at that time matches the loop with the horizontal axis as the return path. In other words, it can be said that the gain G3 is a parameter for determining such a hysteresis characteristic.
[0074]
For example, if G3 is set to 1/2, and the steering angular velocity ω reaches the value of ω1 in FIG. 13 and the sign of dω / dt is inverted only there, the hysteresis loop at this time becomes the origin. On the way back to, discontinuity occurs only at ω = ω1. However, even in such a case, the steering wheel return torque T that is actually finally output due to the operation of the smoothing process illustrated in FIG. _R Is generally continuous. Therefore, in effect, when the sign of dω / dt is inverted (or, for example, when ω = ω3 (ω1 ≦ ω3 ≦ ω2) is satisfied, etc.), only one control parameter (gain G3) is changed. A hysteresis loop can be formed.
[0075]
[Other Modification 2]
FIG. 14 is a graph illustrating an embodiment of the seventh means of the present invention. For example, in the electric power steering apparatus 100 shown in the first embodiment, the steering wheel return angle θ (> 0) can be obtained as in the following equation (15).
[Equation 15]
θ = | ∫ωdt | (integration start time is S = ON set time) (15)
[0076]
Therefore, according to FIG. 4 at step 550 in FIG. _R '(K) = F (ω, u) instead of setting T ( _R The value of '(k) is determined according to the following equation (16). (Scale adjustment means for further multiplying by an adjustment coefficient (gain G2))
(Equation 16)
T _R '(K) = G2F (ω, u),
G2 = h (θ) = κ1 (1 + exp (−θ / θ1)) (16)
[0077]
However, instead of the function h of the above equation (16), the function h of the following equation (17) or (18) may be used. κ1, κ2, κ3, κ4 and θ1 are appropriate constants.
[Equation 17]
G2 = h (θ) = κ2 · exp (−θ / θ1) (17)
(Equation 18)
G2 = h (θ) = κ3 (1 / (1 + κ4 · θ)) (18)
[0078]
For example, it is often convenient to set the function h as a monotonically decreasing function. In particular, on a low μ road, it is difficult to obtain a self-aligning torque when starting to return. _R Is required. However, once the vehicle returns smoothly, the kinetic friction between the road surface and the tires is small. _R Is sufficient. Therefore, on a low μ road, it is more effective to set the fluctuation of the gain G2 to a relatively large value. Further, this tendency increases as the amount of inertia (inertia or the like) of the steering system increases or the friction of the steering system (mechanical internal friction or external friction between road tires) decreases.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of an electric power steering device 100 according to each embodiment of the present invention.
FIG. 2 is a control block diagram of a motor control device 110 included in the electric power steering device 100.
FIG. 3 is a control block diagram of handle return control means 240 included in command torque calculation unit 200.
FIG. 4 is a control block diagram of a handle return torque calculation unit 246 of the handle return control means 240.
FIG. 5 is a flowchart illustrating a processing procedure (algorithm) for realizing the return torque necessity determination unit 241 according to the first embodiment of the present invention.
FIG. 6 is a flowchart illustrating a processing procedure (algorithm) for realizing a return control canceling unit 248 included in the handle return control unit 240 according to the first and third embodiments of the present invention.
FIG. 7 is a graph illustrating measurement data of a steering condition (steering torque τ) relating to a steering system having the electric power steering device 100 according to the first embodiment of the present invention.
FIG. 8 shows a steering condition (a steering wheel return torque T) related to a steering system having the electric power steering device 100 according to the first embodiment of the present invention. _R 6) is a graph illustrating the measurement data of FIG.
FIG. 9 is a graph illustrating measurement data of a steering condition (absolute steering angle) regarding a steering system having the electric power steering device 100 according to the first embodiment of the present invention.
FIG. 10 is a flowchart showing a processing procedure (algorithm) for realizing the handle return control means 240 according to the second embodiment of the present invention.
FIG. 11 is a flowchart showing a processing procedure (algorithm) for realizing the return torque necessity determining means 241 according to the third embodiment of the present invention.
FIG. 12 is a flowchart illustrating a processing procedure (algorithm) for realizing an end determination unit according to a third embodiment of the present invention.
FIG. 13 is a graph illustrating a modified example of the steering wheel return torque calculation unit 246.
FIG. 14 is a graph illustrating an embodiment of the seventh means of the present invention.
FIG. 15 is a control block diagram of a handle return control means based on the prior art.
FIG. 16 is a graph exemplifying measurement data of a steering condition (steering torque τ) relating to a steering system based on the prior art.
FIG. 17 shows a steering condition (steering wheel return torque T) related to a steering system based on the prior art. _R 6) is a graph illustrating the measurement data of FIG.
FIG. 18 is a graph exemplifying measurement data of a steering condition (absolute steering angle) relating to a steering system based on a conventional technique.
[Explanation of symbols]
100… Power steering device
110… Motor control device
200… command torque calculator
240… handle return control means
241 ... return torque necessity determination means
242 start start determination unit
243… end determination unit
246… steering wheel return torque calculator
248… Return control suspension means
M ... motor
S: Necessity flag
R: Necessity flag (return from the left to the neutral point)
L: Necessity flag (return from right to neutral point)
τ ... steering torque
ω… steering angular velocity
u ... vehicle speed
Ω: Rotational angular velocity of motor M
T _R … Steering wheel return torque (output value)
T _R ´… steering wheel return torque (intermediate result)
T _R ″… Steering wheel return torque (intermediate result)
x (n): array storing variable x (1 ≦ n ≦ N)
y (k) ... array storing variable y (1 ≦ k ≦ K)
F… function (T _R '= F (ω, u))
f ... function (T _R ″ = F (ω))
g ... function (G1 = g (u))
h ... Function (G2 = h (θ))
θ: Handle return angle (= | ∫ωdt |)

Claims (7)

A motor for applying an auxiliary torque to a steering mechanism of the vehicle, a motor control device for driving and controlling the motor, and an output from the motor when a driver attempts to return a steering wheel (steering wheel) to a predetermined neutral position. An electric power steering apparatus having a steering wheel return control means for calculating an expected value of the steering wheel return torque TR _;
Based on the variation form of both variables of the steering torque τ that the driver and the angular velocity ω of the steering wheel is imparted to the handle, a torque necessity determination means returns determining required period of the output of said steering wheel return torque T _R,
Based on a predetermined determination results (not) output by said return torque necessity determination unit, and a control stop unit returns to stop an output of said steering wheel return torque T _R,
The electric power steering apparatus according to claim 1, wherein the return torque necessity determination unit uses the value or the sign of the steering torque τ to determine the end of the required period. The return torque necessity determination means,
2. The electric power steering apparatus according to claim 1, further comprising a reversal event detecting unit that detects a reversal event of the steering direction of the steering torque τ. The return torque necessity determination means,
3. The electric power steering apparatus according to claim 1, further comprising a fluctuation gradient determination unit configured to determine a value of a time derivative of an absolute value of the steering torque τ. The return torque necessity determination means,
A product value appropriate determination unit for determining whether a product value τω of the steering torque τ and the angular velocity ω of the steering wheel falls within a predetermined appropriate range,
Electric power according to any one of claims 1 to 3, characterized in that the product value τω is determined that at least a portion back the handle required period of the torque T _R period remain in the proper range Steering device. Said handle return control means, the function F (omega, u) of an independent variable angular velocity omega and the vehicle speed u of the vehicle of the handle by calculating the steering wheel return torque T _R,
The function F (ω, u) is represented by the product of a function f (ω) and a function g (u),
The function f (ω) is
f (−ω) = − f (ω), and
2. The angular velocity ω1 (> 0) that gives the maximum value is a monotonically increasing function in a broad sense when −ω1 ≦ ω ≦ ω1, and a monotone decreasing function in a broad sense when ω1 ≦ | ω |. The electric power steering device according to claim 4. Return angle calculation means for calculating a handle return angle θ (≧ 0), which is an absolute value of an angle at which the handle is returned by the handle return control means, using a time integration operation related to the angular velocity ω of the handle;
Relative to the handle return the steering wheel return torque T _R calculated by the control means further comprises a scale adjustment unit multiplying an adjustment factor (gain G2),
The said scale adjustment means calculates the said adjustment coefficient using the function h ((theta)) which makes the said steering wheel return angle (theta) an independent variable, The Claims 1 thru | or 5 characterized by the above-mentioned. Electric power steering device. The electric power steering device according to claim 6, wherein the function h (θ) is a monotone decreasing function in a broad sense.

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