JP2017165268A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device comprising a control system based on a physical model, having a configuration of model following control in which a control target output follows a normative model, suppressing damage to a torque and thrust transmission mechanism, varying a model parameter and a control parameter, and suppressing damage by limiting input.SOLUTION: An electric power steering device having a configuration of model following control including an FB control part, specifying a viscoelastic model as a normative model in a predetermined angle range in front of a rack end, comprises: a correction part composed of an FB element where the FB control part calculates a target rack displacement based on an input side rack axial force and a control element part that outputs an output side rack axial force based on a position deviation of the target rack displacement and a rack displacement, and variably sets at least one parameter of the FB element and the control element part; an axial force calculation part that calculates a rack axial force based on a steering torque and a current command value; and a limiter that limits the maximum limit value of the rack axial force by a limit value and outputs it.SELECTED DRAWING: Figure 17

Description

  The present invention relates to an electric power steering apparatus that calculates a current command value based on at least a steering torque, drives a motor based on the current command value, and applies an assist force to a steering system of a vehicle. The reference model is reduced by reducing the assist torque by reducing the current command value in the vicinity of the rack end, the momentum at the end is reduced, and the model parameters and control system of the reference model based on the rack axial force (SAT) and rack displacement High-performance electric power steering system that can control the torque and thrust transmission mechanism by limiting the input control parameters, improve the safety, improve the safety, and handle all road conditions About.

  An electric power steering device (EPS) that applies an assist force to a vehicle steering system by a rotational force of a motor assists a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a reduction gear. It is designed to give power. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque. In feedback control, the motor applied voltage is adjusted so that the difference between the current command value and the motor current detection value becomes small. In general, the adjustment of the motor applied voltage is performed by the duty of PWM (pulse width modulation) control. It is done by adjustment.

  The general configuration of the electric power steering apparatus will be described with reference to FIG. 1. A column shaft (steering shaft, handle shaft) 2 of a handle 1 is a reduction gear 3, universal joints 4a and 4b, a pinion rack mechanism 5, a tie rod 6a, 6b is further connected to the steering wheels 8L and 8R via hub units 7a and 7b. The column shaft 2 is provided with a torque sensor 10 that detects the steering torque of the handle 1, and a motor 20 that assists the steering force of the handle 1 is connected to the column shaft 2 via the reduction gear 3. . The control unit (ECU) 30 that controls the electric power steering apparatus is supplied with electric power from the battery 13 and also receives an ignition key signal via the ignition key 11. Based on the steering torque Th detected by the torque sensor 10 and the vehicle speed Vel detected by the vehicle speed sensor 12, the control unit 30 calculates the current command value of the assist command using the assist map, and calculates the calculated current. The current supplied to the motor 20 is controlled by a voltage control value Vref obtained by compensating the command value.

  The control unit 30 is connected to a CAN (Controller Area Network) 40 that exchanges various types of vehicle information, and the vehicle speed Vel can also be received from the CAN 40. The control unit 30 can be connected to a non-CAN 41 that exchanges communications, analog / digital signals, radio waves, and the like other than the CAN 40.

  In such an electric power steering apparatus, the control unit 30 is mainly composed of a CPU (including an MPU and MCU). General functions executed by a program inside the CPU are shown in FIG. The structure is

  The function and operation of the control unit 30 will be described with reference to FIG. 2. The steering torque Th from the torque sensor 10 and the vehicle speed Vel from the vehicle speed sensor 12 are input to and calculated by the torque control unit 31 that calculates the current command value. The current command value Iref1 is input to the subtraction unit 32B and is subtracted from the motor current detection value Im. Deviation I (= Iref1-Im) as a subtraction result in subtraction unit 32B is controlled by current control unit 35 such as PI control, and current-controlled voltage control value Vref is input to PWM control unit 36 to calculate the duty. Then, the motor 20 is PWM driven via the inverter 37 with the PWM signal. The motor current value Im of the motor 20 is detected by the motor current detector 38, and is input to the subtraction unit 32B and fed back. A rotation angle sensor 21 such as a resolver is connected to the motor 20, and the rotation angle θ is detected and output.

  In such an electric power steering device, when a large assist torque is applied by the motor in the vicinity of the maximum steering angle (rack end) of the steering system, a large impact occurs when the steering system reaches the maximum steering angle, and the torque In addition, an excessive load is applied to the thrust transmission mechanism, which may deteriorate durability.

  Therefore, Japanese Patent Publication No. 6-4417 (Patent Document 1) includes steering angle determination means for determining that the steering angle of the steering system is a predetermined value before the maximum steering angle, and the steering angle is maximum steering. There has been disclosed an electric power steering apparatus provided with a correction means for reducing the assist torque by reducing the electric power supplied to the motor when the angle is a predetermined value before the angle.

  Japanese Patent No. 4115156 (Patent Document 2) determines whether or not the adjusting mechanism is approaching the end position, and if it is found that the adjusting mechanism is approaching the end position, the steering assist is reduced. An electric power steering device is shown in which the adjustment speed determined by the position sensor is evaluated in order to control the drive means and determine the speed at which the adjustment mechanism approaches the end position.

Japanese Patent Publication No. 6-4417 Japanese Patent No. 4115156

  However, in the electric power steering apparatus disclosed in Patent Document 1, the power is reduced because the steering angle is a predetermined value before the maximum steering angle, and the steering speed is not considered at all. Current reduction control is not possible. Moreover, the characteristic which reduces the assist torque of a motor is not shown at all, and it is not a concrete structure.

  Further, in the electric power steering device disclosed in Patent Document 2, the assist amount decreases as it approaches the end, but the assist amount reduction speed is adjusted according to the speed approaching the end, and the speed at the end is increased. I try to drop it enough. However, Patent Document 2 shows only changing the characteristics to be reduced according to the speed, and is not based on a physical model. In addition, since feedback control is not performed, characteristics or results may change depending on road surface conditions (load conditions).

  The present invention has been made under the circumstances described above, and an object of the present invention is to configure a control system based on a physical model so that the output of the control target (distance to the rack end) follows the reference model. The model following control is configured to prevent damage to the torque and thrust transmission mechanism, further improving safety, making the model parameters and control parameters of the feedback (FB) control unit variable, and torque and thrust by limiting the input. An object of the present invention is to provide a high-performance electric power steering device that suppresses breakage of a transmission mechanism.

The present invention relates to an electric power steering apparatus that calculates a current command value based on at least a steering torque and drives a motor based on the current command value to assist control the steering system. viscoelastic models within a predetermined angle x ₀ of the rack end before was the norm model, a configuration model following control made by the feedback controller, the feedback controller based on the input-side rack axial force f target A feedback element that calculates a rack displacement, and a control element unit that outputs an output-side rack axial force ff based on a positional deviation between the target rack displacement and the rack displacement x, and at least of the feedback element and the control element unit A correction unit that variably sets one of the parameters, and the steering torque and the current command value. Therefore, this is achieved by including an axial force calculation unit that calculates the rack axial force f4 and a limiter that limits the maximum value of the rack axial force f4 by a limit value and outputs the input side rack axial force f.

The above-described object of the present invention, by the limit value is set to the variable, or is a variable of the limit value, as performed in accordance with the initial rack axial force Fz when reaches a predetermined angle x ₀ The limit value increases linearly or nonlinearly according to the initial rack axial force Fz, or the limit value decreases linearly or nonlinearly according to the initial rack axial force Fz. This is achieved more effectively by removing the inertia component and the friction component in the calculation of the rack axial force.

  According to the electric power steering apparatus of the present invention, since the control system based on the physical model is configured, it is easy to make a constant design perspective, and the output of the control target (distance to the rack end) follows the reference model. Therefore, there is an advantage that it is possible to protect the torque and the thrust transmission mechanism that are robust against the load state (disturbance) and the fluctuation of the control target.

  Furthermore, according to the electric power steering apparatus of the present invention, the model parameter of the reference model and the parameter of the control element are variable based on the rack axial force and the rack displacement, so that the controllability is further improved, and the rack axial force Since the input is limited, the impact can be suppressed, and there is an advantage that it is possible to cope with any road surface condition.

It is a lineblock diagram showing an outline of an electric power steering device. It is a block diagram which shows the structural example of the control system of an electric power steering apparatus. It is a block diagram which shows the structural example of this invention. It is a figure which shows the example of a characteristic of a rack position conversion part. It is a block diagram which shows the structural example (Embodiment 1) of a viscoelastic model follow-up control part. It is a block diagram which shows the structural example (2nd Embodiment) of a viscoelastic model follow-up control part. It is a flowchart which shows the operation example (whole) of this invention. It is a flowchart which shows the operation example of a viscoelastic model follow-up control part. It is a schematic diagram of a viscoelastic model. It is a block diagram for demonstrating the detailed principle of a viscoelastic model follow-up control part. It is a block diagram for demonstrating the detailed principle of a viscoelastic model follow-up control part. It is a block diagram for demonstrating the detailed principle of a viscoelastic model follow-up control part. It is a block diagram for demonstrating the detailed principle of a viscoelastic model follow-up control part. It is a block diagram which shows the detailed structural example (Embodiment 3) of a viscoelastic model follow-up control part. It is a figure which shows the example which changes the parameter of a reference | standard model according to a rack position. It is a characteristic view which shows the example of a characteristic of the reaction force (rack axial force) by a driving state. It is a block block diagram which shows 1st Example of this invention. It is a characteristic view which shows the example of a characteristic of a limiter. It is a characteristic view which shows the example of a characteristic of a control parameter setting part. It is a flowchart which shows the operation example of 1st Example of this invention. It is a flowchart which shows the operation example of feedback control. It is a characteristic view explaining the effect of the present invention. It is a block block diagram which shows 2nd Example of this invention. It is a characteristic view which shows the example of a change (increase) of a limit value. It is a characteristic view which shows the example of a change (decrease) of a limit value. It is a block block diagram which shows 3rd Example of this invention.

  The present invention constitutes a control system based on a physical model in the vicinity of the rack end, uses a viscoelastic model (spring constant, viscous friction coefficient) as a reference model, and outputs the control target (distance to the rack end) to the reference model. The model following control is configured to follow the torque, the damage of the torque and thrust transmission mechanism is suppressed, the safety is further improved, and the model parameters and control parameters of the feedback (FB) control unit are made variable to limit the input. This is a high-performance electric power steering device that suppresses damage to the torque and thrust transmission mechanism.

  Model following control is composed of a viscoelastic model following control unit, and the viscoelastic model following control unit is composed of a feedforward control unit and / or a feedback control unit, and normal assist control is performed outside a predetermined angle before the rack end. The model following control is performed within a predetermined angle before the rack end to prevent it from hitting the rack end.

  Further, in the present invention, the model parameters of the model following control viscoelastic model and the control parameters for the control elements (control gain of the feedback control unit) are varied within a predetermined angle, and the maximum input of the rack axial force is limited. For example, in the vicinity of the start steering angle, the spring term of the viscoelastic model is decreased, the control gain is decreased, and is increased as the rack end is approached. Further, the spring term is increased and the control gain is set larger as the rack axial force when entering the predetermined angle range is smaller. By doing so, the control amount in the vicinity of the start steering angle is small, and the change amount of the assist amount within and outside the predetermined range is small. This prevents the driver from feeling uncomfortable reaction force due to the change in the assist amount. Further, since the control gain can be set large in the region close to the rack end and the control amount can be increased, it is possible to prevent reaching the rack end.

  Further, the rack axial force within a predetermined angle range varies depending on the road surface condition (asphalt, wet road surface, ice, snow, etc.). When the road surface friction coefficient is small (on ice or snow), the rack axial force is small, and asphalt has a large road surface friction coefficient and a large rack axial force. If model parameters and control parameters (gains) are set appropriately on asphalt, they may not be appropriate on ice or snow. When the friction coefficient is small, there is a large margin for generating a large assist force toward the rack end, the steering angle advances greatly, and the possibility of reaching the rack end increases. As the rack axial force when entering the predetermined angle range is smaller, it is desired to increase the spring constant of the viscoelastic model and increase the control gain to reduce the steering angle advance angle. Therefore, in the present invention, as the rack axial force becomes smaller, a correction unit that can increase the control gain with a larger spring constant is provided, and the maximum input of the rack axial force is limited by the limit value to suppress the impact. ing.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, model following control which is a premise of the present invention will be described with reference to FIG. 3 corresponding to FIG.

  In the model following control shown in FIG. 3, the current command value Iref1 is converted into the rack axial force f by the conversion unit 101, and the rack axial force f is input to the viscoelastic model follow-up control unit 120. The rack axial force f is equivalent to the column axial torque, but in the following description, it will be described as a rack axial force for convenience.

  The conversion from the current command value Iref1 to the rack axial force f is performed according to the following equation (1).

ここで、Ｋｔをトルク定数［Ｎｍ／Ａ］、Ｇｒを減速比、Ｃｆを比ストローク［ｍ／ｒｅｖ．］として、Ｇ１＝Ｋｔ×Ｇｒ×（２π／Ｃｆ）である。

回転角センサ２１からの回転角θはラック位置変換部１００に入力され、判定用ラック位置Ｒｘに変換される。判定用ラック位置Ｒｘはラックエンド接近判定部１１０に入力され、ラックエンド接近判定部１１０は図４に示すように、判定用ラック位置Ｒｘがラックエンド手前の所定位置ｘ_０以内にあると判定したときに端当て抑制制御機能を働かせ、ラック変位ｘを出力すると共に切替信号ＳＷＳを出力する。切替信号ＳＷＳ及びラック変位ｘは、ラック軸力ｆと共に粘弾性モデル追従制御部１２０へ入力され、粘弾性モデル追従制御部１２０で制御演算されたラック軸力ｆｆは変換部１０２で電流指令値Ｉｒｅｆ２に変換され、電流指令値Ｉｒｅｆ２は加算部１０３で電流指令値Ｉｒｅｆ１と加算されて電流指令値Ｉｒｅｆ３となる。電流指令値Ｉｒｅｆ３に基づいて、上述したアシスト制御が行われる。

Here, Kt is a torque constant [Nm / A], Gr is a reduction ratio, and Cf is a specific stroke [m / rev. ], G1 = Kt × Gr × (2π / Cf).

The rotation angle θ from the rotation angle sensor 21 is input to the rack position conversion unit 100 and converted to the determination rack position Rx. Determination rack position Rx is input to the rack end approach determination unit 110, the rack end approach determination unit 110 as shown in FIG. 4, the determination rack position Rx is determined that there is within a predetermined position x ₀ of the front rack end Sometimes the end contact suppression control function is activated to output the rack displacement x and the switching signal SWS. The switching signal SWS and the rack displacement x are input to the viscoelastic model follow-up control unit 120 together with the rack axial force f, and the rack axial force ff controlled and calculated by the viscoelastic model follow-up control unit 120 is converted into a current command value Iref2 by the conversion unit 102. The current command value Iref2 is added to the current command value Iref1 by the adding unit 103 to become the current command value Iref3. The assist control described above is performed based on the current command value Iref3.

The predetermined position x ₀ to set the rack end proximal region shown in FIG. 4 can be set at an appropriate position.

  The conversion from the rack axial force ff to the current command value Iref2 in the conversion unit 102 is performed according to the following formula 2.

粘弾性モデル追従制御部１２０の詳細は、図５又は図６に示される。

Details of the viscoelastic model following control unit 120 are shown in FIG. 5 or FIG.

In Embodiment 1 of FIG. 5, the rack axial force f is input to the feedforward control unit 130 and the feedback control unit 140, and the rack displacement x is input to the feedback control unit 140. The rack axial force FF from the feedforward control unit 130 is input to the switching unit 121, and the rack axial force FB from the feedback control unit 140 is input to the switching unit 122. The switching units 121 and 122 are turned on / off by the switching signal SWS, and when the switching units 121 and 122 are turned off by the switching signal SWS, the outputs u ₁ and u ₂ are zero. When the switching unit 121 and 122 are ON by the switching signal SWS, the rack shaft force FF from the switching unit 121 is output as the rack shaft force _{u 1,} the rack shaft force FB from the switching unit 122 as a rack axial force _{u 2} Is output. The rack axial forces u ₁ and u ₂ from the switching units 121 and 122 are added by the adding unit 123, and the added rack axial force ff is output from the viscoelastic model following control unit 120. The rack axial force ff is converted into a current command value Iref2 by the converter 102.

In the second embodiment of FIG. 6, the rack displacement x is input to the feedforward control unit 130 and the feedback control unit 140, and the rack axial force f is input to the feedback control unit 140. In the following, the rack axial force FF from the feedforward control unit 130 is input to the switching unit 121 and the rack axial force FB from the feedback control unit 140 is input to the switching unit 122 as in the first embodiment of FIG. The switching units 121 and 122 are turned on / off by the switching signal SWS, and when the switching units 121 and 122 are turned off by the switching signal SWS, the outputs u ₁ and u ₂ are zero. When the switching unit 121 and 122 are ON by the switching signal SWS, the rack shaft force FF from the switching unit 121 is output as the rack shaft force _{u 1,} the rack shaft force FB from the switching unit 122 as a rack axial force _{u 2} Is output. The rack axial forces u ₁ and u ₂ from the switching units 121 and 122 are added by the adding unit 123, and the added rack axial force ff is output from the viscoelastic model following control unit 120. The rack axial force ff is converted into a current command value Iref2 by the converter 102.

  In such a configuration, first, the entire operation example will be described with reference to the flowchart of FIG. 7, and then the operation example of the viscoelastic model following control (Embodiments 1 and 2) will be described with reference to the flowchart of FIG.

  In the start stage, both the switching units 121 and 122 of the first and second embodiments are turned off by the switching signal SWS from the rack end approach determination unit 110. When the operation starts, first, the torque control unit 31 calculates the current command value Iref1 based on the steering torque Th and the vehicle speed Vel (step S10), and the rack position conversion unit 100 calculates the rotation angle θ from the rotation angle sensor 21. Conversion to the determination rack position Rx (step S11). The rack end approach determination unit 110 determines whether the rack end is approaching based on the determination rack position Rx (step S12). If the rack end approach is not approaching, the rack axial force ff is obtained from the viscoelastic model following control unit 120. The normal steering control based on the current command value Iref1 is executed without being output (step S13), and is continued until the end (step S14).

  On the other hand, when the rack end approach determination unit 110 determines the rack end approach, the viscoelastic model follow-up control by the viscoelastic model follow-up control unit 120 is executed (step S20). That is, as shown in FIG. 8, the switching signal SWS is output from the rack end approach determination unit 110 (step S201), and the rack displacement x is output (step S202). Further, the conversion unit 101 converts the current command value Iref1 into the rack axial force f according to the equation 1 (step S203). In Embodiment 1 of FIG. 5, the feedforward control unit 130 performs feedforward control based on the rack axial force f (step S204), and the feedback control unit 140 performs feedback control based on the rack displacement x and the rack axial force f. This is performed (step S205). In Embodiment 2 of FIG. 6, the feedforward control unit 130 performs feedforward control based on the rack displacement x (step S204), and the feedback control unit 140 performs feedback control based on the rack displacement x and the rack axial force f. Is performed (step S205). In any case, the order of the feedforward control and the feedback control may be reversed.

The switching signal SWS from the rack end approach determination unit 110 is input to the switching units 121 and 122, and the switching units 121 and 122 are turned on (step S206). When the switching unit 121 and 122 is turned ON, the output rack shaft force FF from the feedforward controller 130 is a rack axial force _{u 1,} the output rack shaft force from the feedback control unit 140 FB is a rack axial force _{u 2} Is done. The rack axial forces u ₁ and u ₂ are added by the adding unit 123 (step S207), and the rack axial force ff as an addition result is converted by the converting unit 102 into the current command value Iref2 according to the equation 2 (step S208). .

Here, the viscoelastic model follow-up control unit 120 of the present invention is a control system based on a physical model in the vicinity of the rack end, and the viscoelastic model (spring constant k ₀ [N / m], viscous friction coefficient μ [N / (m / s)]) as a model model (input: force, output: physical model described by displacement), and is configured to hit the rack end. It is preventing.

  FIG. 9 shows a schematic diagram in the vicinity of the rack end, and the relationship between the mass m and the forces Fo and F1 is Equation 3. The calculation of the viscoelastic model equation is described in, for example, Journal of Science and Engineering of Kansai University “Science and Technology” Vol. 17 (2010), “Basics of Elastic Films and Viscoelastic Mechanics” (Kenkichi Ohba).

そして、ラック変位ｘ_１、ｘ_２に対して、ｋ_０、ｋ_１をバネ定数とすると、数４〜数６が成立する。

When k ₀ and k ₁ are spring constants with respect to the rack displacements x ₁ and x ₂ , Equations 4 to 6 are established.

従って、上記数３に上記数４〜数６を代入して数７となる。

Accordingly, Equation 7 is obtained by substituting Equation 4 to Equation 6 into Equation 3.

上記数７を微分すると、下記数８となり、μ_１／ｋ_１を両辺に乗算すると数９となる。

When the above formula 7 is differentiated, the following formula 8 is obtained. When μ ₁ / k ₁ is multiplied on both sides, the formula 9 is obtained.

そして、数７と数９を加算すると、数１０となる。

Then, when Expression 7 and Expression 9 are added, Expression 10 is obtained.

数１０に上記数４及び数６を代入すると、下記数１１となる。

Substituting Equation 4 and Equation 6 into Equation 10 yields Equation 11 below.

ここで、μ_１／ｋ_１＝τ_ｅ，ｋ_０＝Ｅ_ｒ，μ_１（１／ｋ_０＋１／ｋ_１）＝τ_δとすると、上記数１１は数１２となり、ラプラス変換すると数１３が成立する。

Here, when μ ₁ / k ₁ = τ _e , k ₀ = E _r , μ ₁ (1 / k ₀ + 1 / k ₁ ) = τ _δ , the above equation 11 becomes the equation 12, and the Laplace transform yields the equation 13 To establish.

上記数１３をＸ（ｓ）／Ｆ（ｓ）で整理すると、下記数１４となる。

When the above equation 13 is arranged by X (s) / F (s), the following equation 14 is obtained.

数１４は入力力ｆから出力変位ｘまでの特性を示す３次の物理モデル（伝達関数）となり、バネ定数ｋ_１＝∞のバネとするとτｅ→０であり、τ_δ＝μ_１・１／ｋ_０であるので、２次関数の下記数１５が導かれる。

Equation 14 is a third-order physical model (transfer function) indicating the characteristics from the input force f to the output displacement x. When a spring having a spring constant k ₁ = ∞, τe → 0, and τ _δ = μ ₁ · 1 / Since k ₀ , the following equation 15 of the quadratic function is derived.

本発明では、数１５で表される２次関数を規範モデルＧｍとして説明する。即ち、数１６を規範モデルＧｍとしている。ここで、μ_１＝μとしている。

In the present invention, the quadratic function expressed by Equation 15 will be described as the reference model Gm. That is, Equation 16 is used as the reference model Gm. Here, μ ₁ = μ.

次に、電動パワーステアリング装置の実プラント１４６を下記数１７で表わされるＰとし、本発明の規範モデル追従型制御を２自由度制御系で設計すると、Ｐｎ及びＰｄを実際のモデルとして図１０の構成となる。ブロック１４３（Ｃｄ）は、ＰＩＤ，ＰＩ，ＰＤ等の制御要素部を示している。（例えば朝倉書店発行の前田肇、杉江俊治著「アドバンスト制御のためのシステム制御理論」参照）

Next, when the actual plant 146 of the electric power steering apparatus is set to P represented by the following Expression 17, and the reference model following control of the present invention is designed with a two-degree-of-freedom control system, Pn and Pd are set as actual models in FIG. It becomes composition. A block 143 (Cd) indicates a control element unit such as PID, PI, and PD. (For example, see “System Control Theory for Advanced Control” by Satoshi Maeda and Shunji Sugie, published by Asakura Shoten.)

実プラントＰを安定な有理関数の比で表わすために、Ｎ及びＤを下記数１８で表わす。Ｎの分子はＰの分子、Ｄの分子はＰの分母となる。ただし、αは（ｓ＋α）＝０の極が任意に選択できる。

In order to express the actual plant P by the ratio of a stable rational function, N and D are expressed by the following equation (18). The numerator of N is the numerator of P and the numerator of D is the denominator of P. However, the pole of (s + α) = 0 can be arbitrarily selected as α.

図１０の構成を規範モデルＧｍに適用すると、ｘ／ｆ＝Ｇｍとなるためには、１／Ｆを下記数１９のように設定する必要がある。なお、数１９は、数１６及び数１８より導かれる。

When the configuration of FIG. 10 is applied to the reference model Gm, 1 / F needs to be set as in the following equation 19 in order to satisfy x / f = Gm. Equation 19 is derived from Equations 16 and 18.

フィードバック制御部のブロックＮ／Ｆは下記数２０である。

The block N / F of the feedback control unit is the following equation (20).

フィードフォワード制御部のブロックＤ／Ｆは下記数２１である。

The block D / F of the feedforward control unit is the following equation (21).

２自由度制御系の一例を示す図１０において、実プラントＰへの入力（ラック軸力若しくはコラム軸トルクに対応する電流指令値）ｕは、下記数２２で表される。

In FIG. 10 showing an example of the two-degree-of-freedom control system, the input (current command value corresponding to the rack axial force or the column shaft torque) u to the actual plant P is expressed by the following equation (22).

また、実プラントＰの出力（ラック変位）ｘは下記数２３である。

Further, the output (rack displacement) x of the actual plant P is the following Expression 23.

数２３を整理し、出力ｘの項と左辺ｆの項を右辺に揃えると、数２４が導かれる。

By arranging the equation 23 and aligning the term of the output x and the term of the left side f with the right side, the equation 24 is derived.

数２４を入力ｆに対する出力ｘの伝達関数として表わすと、数２５となる。ここで、３項目以降ではＰ＝Ｐｎ／Ｐｄとして表現している。

When Expression 24 is expressed as a transfer function of the output x with respect to the input f, Expression 25 is obtained. Here, P = Pn / Pd is expressed from the third item onward.

実プラントＰを正確に表現できたとすれば、Ｐｎ＝Ｎ、Ｐｄ＝Ｄとすることができ、入力ｆに対する出力ｘの特性は、Ｐｎ／Ｆ（＝Ｎ／Ｆ）として表わされるので、数２６が成立する。

If the actual plant P can be expressed accurately, Pn = N and Pd = D can be obtained, and the characteristic of the output x with respect to the input f is expressed as Pn / F (= N / F). Is established.

入力ｆに対して出力ｘの特性（規範モデル（伝達関数））を、下記数２７のようにすると考えるとき、

When considering that the characteristic of the output x with respect to the input f (reference model (transfer function)) is

１／Ｆを下記数２８のようにすることで達成できる。

This can be achieved by setting 1 / F to the following formula 28.

図１０において、フィードフォワード制御系をブロック１４４→実プラントＰの経路で考えると、図１１となる。ここで、Ｐ＝Ｎ／Ｄとすると、図１１（Ａ）は図１１（Ｂ）となり、数２０より図１１（Ｃ）が得られる。図１１（Ｃ）より、ｆ＝（ｍ・ｓ^２＋μ・ｓ＋ｋ０）ｘとなるので、これを逆ラプラス変換すると、下記数２９が得られる。

In FIG. 10, when the feedforward control system is considered by the route of block 144 → actual plant P, FIG. 11 is obtained. Here, if P = N / D, FIG. 11A becomes FIG. 11B, and FIG. From FIG. 11C, f = (m · s ² + μ · s + k0) x. Therefore, when this is inverse Laplace transformed, the following equation 29 is obtained.

一方、図１２に示すようなフィードフォワード制御系の伝達関数ブロックを考えると、下記数３０が入力ｆ及び出力ｘにおいて成立する。

On the other hand, when a transfer function block of the feedforward control system as shown in FIG. 12 is considered, the following equation 30 is established at the input f and the output x.

数３０を整理すると下記３１となり、数３１を入力ｆについて整理すると、数３２が得られる。

When the number 30 is arranged, the following 31 is obtained. When the number 31 is arranged for the input f, the number 32 is obtained.

数３２を逆ラプラス変換すると上記数２９となり、結果的に図１３に示すように２つのフィードフォワード制御部Ａ及びＢは等価である。

When the inverse Laplace transform is performed on the equation 32, the above equation 29 is obtained. As a result, the two feedforward control units A and B are equivalent as shown in FIG.

Based on the above assumption, there is no problem in operation without the feedforward control unit 130, and the configuration of the viscosity model following control unit 120 in this case is shown in FIG. 14 (Embodiment 3). That is, the feedback control unit 140 includes a feedback element (N / F) 141 that calculates a target rack displacement (target steering angle) based on the rack axial force f using the spring constant k ₀ and the viscous friction coefficient μ as parameters, and a target A subtracting unit 142 for obtaining the rack displacement and the positional deviation of the rack displacement x, and a control element unit 143 composed of PID, PI and the like for controlling the rack axial force FB based on the positional deviation. The rack axial force FB, that is, the output of the control element unit 143 is input to the b2 contact of the switching unit 122. A fixed value “0” is input from the fixing unit 126 to the a2 contact of the switching unit 122. The rack axial force f is input to the feedback element 141, and the rack displacement x is input to the parameter setting unit 124 while being subtracted from the subtraction unit 142 in the feedback control unit 140. The parameter setting unit 124 outputs the spring constant k ₀ and the viscous friction coefficient μ with the characteristics shown in FIG. 15 with respect to the rack displacement x, and the spring constant k ₀ and the viscous friction coefficient μ are input to the feedback element 141. . The contact of the switching unit 122 can be switched between the contact a <b> 2 and the contact b <b> 2 by a switching signal SWS from the rack end approach determination unit 120.

  In the present invention, the model parameter (feedback element 141) of the reference model, the control parameter of the control element unit, or both parameters are varied based on the rack axial force (SAT) f and the rack displacement x and input. The input of the side rack axial force f to the feedback element 141 is limited by setting a limit value (variable).

  In other words, within the range of a predetermined angle in front of the rack end, the model following control is configured using the viscoelastic model as a reference model, and the model parameters and control parameters (control gain) of the viscoelastic model are variable within the predetermined angle. And In addition, the model parameter and the control parameter are made variable according to the rack axial force when entering the predetermined angle range. For example, in the vicinity of the start steering angle, the spring term of the viscoelastic model is decreased, the control gain is decreased, and is increased as the rack end is approached. Further, the smaller the rack axial force when entering the predetermined angle range, the larger the spring term is set and the control gain is set larger. By doing so, the control amount in the vicinity of the start steering angle is small, and the change amount of the assist amount within and outside the predetermined range is small. As a result, the driver can be prevented from feeling uncomfortable reaction force due to the change in the assist amount. Further, since the control gain can be set large in the region close to the rack end and the control amount can be increased, it is possible to prevent reaching the rack end.

  Furthermore, the rack axial force within a predetermined angle range varies depending on the road surface condition (asphalt, wet road surface, on ice, on snow). When the road surface friction coefficient is small (on ice or snow), the rack axial force is small, and asphalt has a large road surface friction coefficient and a large rack axial force. Also, as shown in FIG. 16, when the vehicle is stopped or traveling at creeping speed, the reaction force from the tires is different and the rack axial force is changed. Also, the load characteristics vary depending on the degree of tire twist. It is desired to control the rudder angle at a substantially constant value regardless of the road surface condition or the traveling condition. In order to achieve this, the present invention limits the positive and negative maximum values of the rack axial force input to the reference model. If the input is restricted by setting a limit value, the reference model output (target rudder angle) becomes constant, and variations in control effects can be suppressed. Further, by making it possible to adjust the limit value according to the rack axial force, it is possible to adjust the reference model output (target rudder angle) and further reduce the variation in effect.

  FIG. 17 shows a first embodiment of the present invention corresponding to FIG. 3 and FIG. 14. From the conversion unit 200 for converting the steering torque Th to the rack axial force f1, the rack axial force f1 and the conversion unit 101 Of the rack axial force f2, the axial force calculating unit 201 for calculating the rack axial force f4 from the rack axial force f3 (= f1 + f2) obtained by the adding unit 202, and the axial force calculating unit 201 A limiter 204 that limits the maximum value of the rack axial force f4 and outputs the input side rack axial force f, a control parameter setting unit 211 that sets control parameters of the control system, and a model parameter setting that sets model parameters of the model system Part 221 is provided.

  The axial force calculation unit 201 that inputs the rack axial force f3 (= f1 + f2) sets and stores the rack axial force f3 when the rack displacement x falls within a predetermined angle range as the initial rack axial force Fz and stores the setting storage unit 201−. 1 and the subtracting unit 201-2 that subtracts the initial rack axial force Fz from the rack axial force f3 and outputs the axial force f4. The initial rack axial force Fz is a rack axial force when the rack displacement x falls within a predetermined angle range, and the axial force calculation unit 201 determines that the rack axis according to the following equation 33 after the rack displacement x falls within the predetermined angle range. The force f4 is calculated. This is because the reference model output is set to “0” at a predetermined angle, and the rack axial force FB output from the control element unit 143 is set to “0”. This is because steering near the predetermined angle eliminates the step of the command value and facilitates steering.

リミッタ２０４は、例えば図１８に示すような特性で正負最大値を制限し、最大値を制限された入力側ラック軸力ｆがフィードバック制御部１４０内のフィードバック要素１４１に入力される。なお、図１８において、ｘＯＲ及びｘＯＬは、所定角度範囲を設定する角度である。

For example, the limiter 204 limits the positive and negative maximum values with the characteristics shown in FIG. 18, and the input side rack axial force f with the maximum value limited is input to the feedback element 141 in the feedback control unit 140. In FIG. 18, xOR and xOL are angles for setting a predetermined angle range.

  Further, the control parameter setting unit 211 of the control system inputs the rack displacement x and outputs the control parameters kd and kp in a non-linear relationship in which the increase rate increases as the rack displacement x increases, for example, as shown in FIG. To do. The control parameters kd and kp are set in the control element unit 143 in the feedback control unit 140 as shown in the following Expression 34.

モデル系の制御パラメータ設定部２１１はラック変位ｘを入力し、例えば図１５に示すような特性でモデルパラメータμ（粘性摩擦係数）、ｋ_０（バネ定数）を出力する。モデルパラメータμ、ｋ_０は、フィードバック制御部１４０内のフィードバック要素（Ｎ／Ｆ）１４１に設定される。

The control parameter setting unit 211 of the model system inputs the rack displacement x, and outputs model parameters μ (viscous friction coefficient) and k ₀ (spring constant) with characteristics as shown in FIG. 15, for example. The model parameters μ and k ₀ are set in the feedback element (N / F) 141 in the feedback control unit 140.

  In such a configuration, an operation example of the first embodiment of FIG. 17 will be described with reference to the flowcharts of FIGS.

  The switching signal SWS is output from the rack end approach determination unit 110, the contact of the switching unit 122 is switched from a2 to the contact b2 (step S201), and the steering torque Th is converted into the rack axial force f1 by the conversion unit 200 ( Step S202). The current command value Iref1 is calculated by the torque control unit 31, and the current command value Iref1 is converted into the rack axial force f2 by the conversion unit 101 (step S203). At the moment when the switching unit 122 is switched to the contact b2, the rack shaft at that time The force f3 = f1 + f2 is set in the setting storage unit 201-1 as the initial rack axial force Fz (step S204), and thereafter, the stored initial rack axial force Fz is subtracted from the rack axial force f3 by the subtracting unit 201-2. The rack axial force f4 is calculated (step S205), the limiter 204 performs the limiting process (step S206), and the limited rack axial force is input to the feedback element 141 in the feedback control unit 140 as the input side rack axial force f. input.

Further, the rack displacement x is output from the rack end approach determination unit 110 (step S210), and the rack displacement x is subtracted and input to the subtraction unit 142 in the feedback control unit 140, and the control parameter setting unit 211 and model parameter setting unit. 221 is input. The control parameter setting unit 211 calculates control parameters kp and kd based on the rack displacement x (step S211), and the control parameters kp and kd are set in the control element unit 143 in the feedback control unit 140. The model parameter setting unit 221 calculates model parameters μ and k ₀ based on the rack displacement x (step S213), and the model parameters μ and k ₀ are set in the feedback element 141 in the feedback control unit 140.

Feedback control unit 140, the rack shaft force f, rack displacement x and set control parameters kp, kd, model parameters mu, performs processing of the feedback control by _{k 0} (step S220), outputs an output-side rack shaft force ff (Step S230). The rack axial force ff is converted into a current command value Iref2 by the converter 102 (step S231), and the above operation is repeated until the end (step S232).

  When the process ends in step S232, the contact of the switching unit 122 is switched from the contact b2 to the contact a2 by the output of the switching signal SWS (step S233), and then the process proceeds to step S14 in FIG.

  The feedback control process in the feedback control unit 140 is performed as shown in FIG.

First, the model parameters μ and k ₀ calculated by the model parameter setting unit 221 are set in the feedback element 141 (step S221), N / F processing is performed in the feedback element 141, and the target rack displacement (target steering angle) is calculated. (Step S222). The target rack displacement is added and input to the subtractor 142, the position deviation from the subtracted rack displacement x is calculated (step S223), and the obtained position deviation is input to the control element unit 143. Further, the control parameters kp and kd calculated by the control parameter setting unit 211 are set in the control element unit 143 (step S224), the control calculation is performed (step S225), and the rack axial force FB obtained by the control calculation. Is output (step S226). The order of setting the control parameters kp and kd can be changed as appropriate.

  In the present invention, since the input of the input side rack axial force f is limited by the limiter 204, the reference model output is saturated as shown by the solid line in FIG. If it is not limited, it continues to change without saturation as shown by the broken line.

  Next, a second embodiment of the present invention will be described with reference to FIG.

  In the second embodiment, the initial rack axial force Fz set and stored in the setting storage unit 201-1 is input to the limiter 204 as a parameter. The limit value fth for limiting the maximum value is made variable according to the initial rack axial force Fz. For example, as shown by the characteristic A in FIG. 24, the limit value fth is changed so that the initial rack axial force Fz is small when the initial rack axial force Fz is small and increases linearly as the initial rack axial force Fz increases. Thus, the limit value fth is increased non-linearly. Alternatively, the limit value fth is changed so that the initial rack axial force Fz is small and linearly decreases as the initial rack axial force Fz increases as shown in the characteristic A of FIG. As described above, the limit value fth is reduced non-linearly. As a result, the adjustment can be made according to how the rack axial force of the vehicle rises (the ratio of the rack shaft increasing when the rudder angle increases).

  FIG. 26 shows a third embodiment of the present invention, which is a value obtained by removing the inertia component and the friction component in the setting of the initial rack axial force Fz. Thereby, the stored initial rack axial force Fz is stored as the rack axial force when the steering is held at a predetermined angle.

  That is, in the third embodiment, the axial force calculation unit 201 is further provided with an inertia / friction unit 201-3 and a subtraction unit 201-4. Then, the rack speed and the rack acceleration are input to the inertia / friction unit 201-3, and the calculated inertia component and friction component are subtracted and input to the subtraction unit 201-4. Also, the rack axial force f3 (= f1 + f2) is subtracted and input to the subtraction unit 201-4, and the rack axial force f5 subtracted by the subtraction unit 201-4 is input to the setting storage unit 201-1. . Therefore, when the rack displacement x reaches a predetermined angle, the rack axial force obtained by subtracting the inertia component and the friction component is set and stored as the initial rack axial force Fz.

  Note that the control element unit 143 (Cd) may have any configuration of PID (proportional integral derivative) control, PI control, and PD control. In the above description, the position correction unit and the parameter setting unit are individually displayed. However, an integrated configuration may be used. Furthermore, although the rotation angle θ is obtained from the rotation angle sensor connected to the motor in the above description, it may be obtained from the steering angle sensor.

1 Handle 2 Column shaft (steering shaft, handle shaft)
DESCRIPTION OF SYMBOLS 10 Torque sensor 12 Vehicle speed sensor 13 Battery 14 Steering angle sensor 20 Motor 23 Motor drive part 30 Control unit (ECU)
31 Torque control unit 35 Current control unit 36 PWM control unit 100 Rack position conversion unit 101, 200 Conversion unit 110 Rack end approach determination unit 120 Viscoelastic model follow-up control unit 121, 122 Switching unit 130 Feedforward control unit 140 Feedback control unit 141 Feedback element 143 Control element unit 201 Axial force calculation unit 201-1 Setting storage unit 201-3 Inertia / friction unit 203 Angular velocity calculation unit 211 Control parameter setting unit 221 Model parameter setting unit

Claims (6)

In the electric power steering device for calculating the current command value based on at least the steering torque and driving the motor based on the current command value to assist the steering system,
It is a configuration of model following control composed of a feedback control unit using a viscoelastic model as a reference model within a range of a predetermined angle x ₀ before the rack end.
The feedback control unit calculates a target rack displacement based on the input rack axial force f, and a control element unit outputs the output rack axial force ff based on the target rack displacement and the positional deviation of the rack displacement x. And consists of
A correction unit that variably sets at least one parameter of the feedback element and the control element unit;
An axial force calculator that calculates a rack axial force f4 based on the steering torque and the current command value;
A limiter for limiting the maximum value of the rack axial force f4 by a limit value and outputting the input side rack axial force f;
An electric power steering apparatus characterized in that the torque and thrust transmission mechanism are prevented from being damaged. The electric power steering apparatus according to claim 1, wherein the limit value is variable. The variable limit, the electric power steering apparatus according to in which claim 2 adapted to perform in accordance with the initial rack axial force Fz when reaches a predetermined angle x _0. The electric power steering apparatus according to claim 3, wherein the limit value has a characteristic that increases linearly or nonlinearly according to the initial rack axial force Fz. The electric power steering apparatus according to claim 3, wherein the limit value has a characteristic that decreases linearly or nonlinearly according to the initial rack axial force Fz. The electric power steering apparatus according to any one of claims 1 to 5, wherein an inertia component and a friction component are removed in the calculation of the rack axial force.

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