JP2017171059A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which constitutes a control system based on a physical model, and also constitutes a model-following-control in which an output of an object to be control (a distance to a rack end) follows a normative model to suppress damage of a torque and thrust transmission mechanism, as well as to prevent incompatible sense to a driver, by changing assist forces before and after the model-following-control.SOLUTION: An electric power steering device performs assist-control of a steering system by: calculating a current command value at least on the basis of a steering torque; and driving a motor on the basis of the current command value. The electric power steering device constitutes a model-following-control defining a viscoelastic model as a normative model in a predetermined angle range before a rack end, and changes a control amount in the model-following-control so that a change amount of the control amount will not exceed a predetermined value, so as to prevent a rack end abutment.SELECTED DRAWING: Figure 18

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. As a reference model, the assist torque is reduced by narrowing the current command value near the rack end, the momentum at the time of end contact is attenuated, impact energy is lowered, damage to the torque and thrust transmission mechanism is suppressed, and steering feeling The present invention relates to an electric power steering apparatus with improved performance.

  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 by a driving force of the motor. 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.

  Moreover, 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. It is an object of the present invention to provide an electric power steering device that constitutes simple model following control and suppresses breakage of a torque and thrust transmission mechanism. Furthermore, the driver does not feel uncomfortable due to the change in assist force before and after the model following control.

  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. The model following control is configured with a viscoelastic model as a reference model within a predetermined angle range in front of the rack end so that the control amount in the model following control is within a predetermined value. This is accomplished by changing and preventing rack end end padding.

  In addition, the present invention relates to an electric power steering apparatus that calculates a current command value 1 based on at least a steering torque and drives the motor based on the current command value 1 to assist control the steering system. Based on the first conversion unit that converts the current command value 1 into rack axial force or column shaft torque 1, the rack position conversion unit that converts the rotation angle of the motor into the determination rack position, and the determination rack position. A viscoelasticity model based on the rack end force determining unit that determines that the rack end is approached and outputs a rack displacement and switching signal, the rack axial force or column shaft torque 1, the rack displacement and the switching signal. A viscoelastic model follow-up control unit for generating rack axial force or column axial torque 2 with reference to A change amount limiting unit that changes the rack axial force or the column shaft torque 2 so that the change amount becomes the predetermined value when the change amount of the main shaft torque 2 exceeds a predetermined value; A second converter for converting the column shaft torque 2 into the current command value 2, and adding the current command value 2 to the current command value 1 to perform the assist control to prevent rack end end contact. Is achieved.

  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.

  In addition, since the amount of change in the control amount is limited so that the assist force does not change suddenly due to model following control, it is possible to suppress the driver from feeling fluctuations in the steering torque.

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 block diagram which shows the detailed structural example (Embodiment 4) 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 flowchart which shows the operation example of a viscoelastic model follow-up control part. It is a block diagram which shows the structural example (Example 1) of this invention. It is a figure which shows the example of a characteristic of the predetermined value with respect to a rack displacement. It is a flowchart which shows the operation example (whole) (Example 1) of this invention. It is a flowchart which shows the operation example (Example 1) of a viscoelastic model follow-up control part. It is a block diagram which shows the structural example (Example 2) of this invention. It is a figure which shows the example of a characteristic of the predetermined value with respect to a rotation angle. It is a figure which shows the example of a characteristic of the predetermined value changed with the code | symbol of the difference of a rack axial force.

  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. This is an electric power steering device that constitutes model following control that follows and 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.

  Also, in order to prevent the driver from suddenly changing the steering torque at the start of model following control or when returning to normal assist control, etc. The amount of change in the control amount that changes due to the control is suppressed. Specifically, the change amount limiting unit traces the output from the viscoelastic model following control unit corresponding to the control amount, and when the output change amount becomes larger than a predetermined value, the change amount becomes the predetermined value. The output has been changed. It is possible to suppress sudden changes in assist force by adjusting the parameter for calculating the current command value, but finding the optimal parameter among various factors such as steering speed, tires and road surface conditions, Since the degree of freedom of adjustment is small and the adjustment may take time, in the present invention, the degree of freedom of adjustment is increased and the adjustment time is shortened by limiting the control amount directly linked to the assist force. .

  The predetermined value used in the variation limiter is set so that the size changes near the predetermined angle before and after the rack end where model following control starts or ends, and increases near the rack end. Is done. In the vicinity of the rack end, the predetermined value is increased so as not to suppress the amount of change in the output from the viscoelastic model follow-up control unit in order to prevent the generation of abnormal noise during end contact, which is the first purpose. In the vicinity of a predetermined angle before the rack end, the predetermined value is reduced as much as possible in order to suppress a sudden change in assist force. In order to realize this, the predetermined value is changed based on steering information such as rack displacement, motor rotation angle, and steering angle, which will be described later. That is, as the value of the steering information increases, the closer to the rack end, the greater the predetermined value is set. In addition, the direction of change (±) of the output from the viscoelastic model following control unit is usually opposite between when entering and leaving the range of a predetermined angle in front of the rack end. By changing the value, it is possible to use a predetermined value having different characteristics for entering and exiting, and to make more flexible adjustment.

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

  FIG. 3 shows an example of an embodiment of the present invention corresponding to FIG. 2. 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 converted into the viscoelastic model following control unit 120. Is input. 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. In addition, the same code | symbol is attached | subjected to the structure same as the structure shown by FIG. 2, and description is abbreviate | omitted.

  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。

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. Further, although the rotation angle θ is obtained from the rotation angle sensor 21 connected to the motor, it may be obtained from the steering angle sensor.

  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の詳細を、図５又は図６に示す。

Details of the viscoelastic model follow-up 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, an entire operation example of the present invention will be described with reference to the flowchart of FIG. .

  In the start stage, the switching units 121 and 122 are turned off by the switching signal SWS. 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 F ₀ and F ₁ 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τ_ｅ→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 = ∞, τ _e → 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) represents a control element part. (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の項を左辺に、ｆの項を右辺に揃えると、数２４が導かれる。

By arranging Equation 23 and aligning the term of the output x with the left side and the term of f with the right side, 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, a specific configuration example of the present invention will be described below with reference to FIGS. The third embodiment of FIG. 14 corresponds to the first embodiment of FIG. 5, and the rack axial force f is input to the feedforward element 144 (D / F expressed by Equation 21) and the feedback control unit 140 in the feedforward control unit 130. Then, the rack displacement x is input to the feedback control unit 140. 15 corresponds to the second embodiment of FIG. 6, and the rack displacement x is input to the spring constant term 131 and the viscous friction coefficient term 132 in the feedforward control unit 130, and the rack axial force f is fed back. Input to the control unit 140.

  In Embodiment 3 of FIG. 14, the rack axial force FF from the feedforward element 144 is input to the b1 contact of the switching unit 121. In Embodiment 4 of FIG. 15, the subtraction unit 133 subtracts the outputs of the spring constant term 131 and the viscous friction coefficient term 132 in the feedforward control unit 130, and the rack axial force FF that is the subtraction result of the subtraction unit 133 is obtained. The signal is input to the b1 contact of the switching unit 121. A fixed value “0” is input from the fixing unit 125 to the a1 contact of the switching unit 121.

  In both Embodiment 3 of FIG. 14 and Embodiment 4 of FIG. 15, the feedback control unit 140 includes a feedback element (N / F) 141, a subtraction unit 142, and a control element unit 143. 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.

In the third embodiment of FIG. 14, the rack axial force f is input to the feedforward element 144 in the feedforward control unit 130 and also to the feedback element (N / F) 141 of the feedback control unit 140. The rack displacement x is subtracted and input to the subtraction unit 142 of the feedback control unit 140 and is also input to the parameter setting unit 124. The parameter setting unit 124 outputs, for example, a spring constant k ₀ and a viscous friction coefficient μ having characteristics as shown in FIG. 16 with respect to the rack displacement x. The spring constant k ₀ and the viscous friction coefficient μ are supplied to the feedforward control unit 130. The feed forward element 144 and the feedback element (N / F) 141 in the feedback control unit 140 are input.

In the fourth embodiment shown in FIG. 15, the rack displacement x is input to the spring constant term 131 and the viscous friction coefficient term 132 in the feedforward control unit 130 and to the subtraction unit 142 of the feedback control unit 140, and further parameter setting is performed. Is input to the unit 124. The rack axial force f is input to the feedback element (N / F) 141 of the feedback control unit 140. The parameter setting unit 124 outputs a spring constant k ₀ and a viscous friction coefficient μ similar to those described above for the rack displacement x, and the spring constant k ₀ is input to the spring constant term 131 and the feedback element (N / F) 141. The viscous friction coefficient μ is input to the viscous friction coefficient term 132 and the feedback element (N / F) 141.

  The switching signal SWS is input to the switching units 121 and 122 in the third and fourth embodiments, and the contacts of the switching units 121 and 122 are normally connected to the contacts a1 and a2, respectively. Each of the contacts b1 and b2 is switched.

  In such a configuration, an operation example of the fourth embodiment in FIG. 15 will be described with reference to a flowchart in FIG.

A switching signal SWS is output from the rack end approach determination unit 110 (step S21), and a rack displacement x is output (step S22). The rack displacement x is input to the spring constant term 131, the viscous friction coefficient term 132, the parameter setting unit 124, and the subtraction unit 142. The parameter setting unit 124 calculates the spring constant k ₀ and the viscous friction coefficient μ obtained according to the characteristics of FIG. 16 according to the rack displacement x, the spring constant term 131, the viscous friction coefficient term 132, and the feedback element (N / F) 141. (Step S23). Further, the converter 101 converts the current command value Iref1 into the rack axial force f (step S23A), and the rack axial force f is input to the feedback element (N / F) 141 and is subjected to N / F calculation (step S24). . The N / F calculation value is added to the subtraction unit 142, the rack displacement x is subtracted (step S24A), and the subtraction value is Cd calculated by the control element unit 143 (step S24B). The calculated rack axial force FB is output from the control element unit 143 and input to the contact point b2 of the switching unit 122.

Viscous friction coefficient term 132 in the feed-forward control unit 130, based on the viscous friction coefficient μ "(μ-η) · s" performs the operation of (step S25), and setting the spring constant _{k 0} to the spring constant term 131 (step S25A), performs subtraction of the spring constant _{k 0} and the subtraction unit "(μ-η) · s " ( step S25B), and outputs the rack shaft force FF as the operation result. The rack axial force FF is input to the contact b1 of the switching unit 121. Note that the calculation order of the feedforward control unit 130 and the feedback control unit 140 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 contacts of the switching units 121 and 122 are switched from a1 to b1 and from a2 to b2, and the racks from the switching units 121 and 122 are switched. The axial forces u ₁ and u ₂ are added by the adding unit 123 (step S26), and the rack axial force ff as the addition result is converted into the current command value Iref2 by the converting unit 102 (step S26A). The current command value Iref2 is input to the adding unit 103, added to the current command value Iref1 (step S27), steering control is executed, and the process goes to step S14.

  Note that the control element unit 143 (Cd) may have any configuration of PID (proportional integral derivative) control, PI control, and PD control. Further, the operation of the third embodiment shown in FIG. 14 is the same except that the portion (element) to which the rack axial force f and the rack displacement x are input is different. Further, in the third embodiment of FIG. 14 and the fourth embodiment of FIG. 15, the control calculation of both the feedforward control unit 130 and the feedback control unit 140 is executed, but the configuration of only the feedforward control unit 130 may be used. Only the feedback control unit 140 may be configured.

  Next, examples of the present invention will be described.

  FIG. 18 shows an embodiment of the present invention corresponding to FIG. 3, and a change amount limiting unit 150 is added to the embodiment shown in FIG. 3. The rack displacement x output from the rack end approach determination unit 110 and the rack axial force ff output from the viscoelastic model following control unit 120 are input to the change amount limiting unit 150 and output from the change amount limiting unit 150. The force ffm is input to the conversion unit 102.

  In the change amount limiting unit 150, the rack axial force ff (t) at time t and the rack axial force ffm (t−T) at time t−T before T time (one sample time before, T is sampling time). When the absolute value | Δffm (t) | (change amount) of the difference Δffm (t) = ff (t) −ffm (t−T) is larger than the predetermined value THf, the change amount becomes the same as the predetermined value THf. The rack axial force ff (t) is changed by the following equation 33 and output as the rack axial force ffm.

ここで、ｓｉｇｎ（Ｘ）は符号関数で、実数Ｘの符号（−１，０，１）を返す。変化量が所定値ＴＨｆ以下の場合は、ラック軸力ｆｆ（ｔ）がそのままラック軸力ｆｆｍとして出力される。ラック軸力ｆｆｍ（ｔ）は、次の時刻での変化量算出で使用されるので、変化量制限部１５０に保持される。

Here, sign (X) is a sign function, and returns the sign (-1, 0, 1) of the real number X. When the change amount is equal to or less than the predetermined value THf, the rack axial force ff (t) is output as it is as the rack axial force ffm. Since the rack axial force ffm (t) is used in the change amount calculation at the next time, it is held in the change amount limiting unit 150.

  As the predetermined value THf, for example, a value proportional to the rack displacement x as shown in FIG. 19 is used. That is, the change amount limiting unit 150 determines the predetermined value THf from the input rack displacement x, limits the rack axial force ff using the determined predetermined value THf, and outputs the rack axial force ffm. In FIG. 19, what is actually used as the predetermined value THf is a range where the rack displacement x is from zero to a value corresponding to the rack end, corresponding to a range of a predetermined angle before the rack end.

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

  FIG. 20 is a flowchart showing an example of the entire operation. Compared with the flowchart of FIG. 7, processing in the variation limiter 150 is added to normal steering (step S13) and viscoelastic model following control (step S20). A change has occurred (steps S13A, S20A).

  In normal steering (step S13A), first, the rack displacement x is output from the rack end approach determination unit 110. The viscoelastic model follow-up control unit 120 outputs a rack axial force ff having a value of zero. The variation limiter 150 receives the rack displacement x and the rack axial force ff, and determines a predetermined value THf from the rack displacement x according to FIG. Then, the rack axial force ffm is calculated from the comparison between the rack axial force ff value (zero) and the amount of change in the rack axial force ffm before time T and the predetermined value THf, and is output. The rack axial force ffm is converted into the current command value Iref2 by the conversion unit 102, and is added to the current command value Iref1 by the addition unit 103. Immediately after changing from viscoelastic model following control to normal steering, the rack axial force ffm before time T is likely to be a value other than zero, and as a result, the current command value Iref2 may be a value other than zero. However, as the time elapses, the rack shaft force ffm approaches zero, and as a result, the current command value Iref2 also becomes zero, so that the steering control is performed based on the current command value Iref1.

  The operation in the viscoelastic model follow-up control (step S20A) is shown in the flowchart of FIG. Compared with the flowchart of FIG. 8, step S207A is added. In step S207A, an operation similar to the operation of the change amount limiting unit 150 in the normal steering is performed. That is, the predetermined value THf is determined from the rack displacement x according to FIG. 19, and the rack axial force ffm is calculated from the comparison between the rack axial force ff value and the amount of change in the rack axial force ffm before time T and the predetermined value THf. ,Output. The rack axial force ffm is converted into the current command value Iref2 by the conversion unit 102 (step S208A), and is added to the current command value Iref1 by the addition unit 103.

  Another embodiment (embodiment 2) of the present invention will be described.

  In the first embodiment, the predetermined value used in the change amount limiting unit is changed based on the rack displacement, but in the present embodiment, the predetermined value is changed based on the rotation angle of the motor. Since the rack position and the rotation angle are linked so that the rotation angle θ is converted into the determination rack position Rx in the rack position conversion unit 100, the embodiment can be implemented even if the predetermined value is changed based on the rotation angle. An effect equivalent to 1 can be obtained.

  FIG. 22 shows a configuration example of the second embodiment. Compared with the configuration example of the first embodiment shown in FIG. 18, the rotation angle θ is input to the change amount limiting unit instead of the rack displacement x.

  In the variation limiting unit 250, as in the case of the first embodiment, the amount of change in the rack axial force ff (t) at time t and the rack axial force ffm (t−T) at time t−T before time T. The rack axial force ffm is calculated from a comparison between the predetermined value THf and a value proportional to the rotation angle θ is used as the predetermined value THf as shown in FIG. That is, the change amount limiting unit 250 determines the predetermined value THf from the input rotation angle θ, limits the rack axial force ff using the determined predetermined value THf, and outputs the rack axial force ffm. In FIG. 23, what is actually used as the predetermined value THf is a range between the rotation angle corresponding to the predetermined position in front of the rack end and the rotation angle corresponding to the rack end.

  The operation of the second embodiment is different from that of the first embodiment except that the determination of the predetermined value THf by the change amount limiting unit 250 is executed based on the rotation angle θ output from the rotation angle center 21. It is the same.

  In the change amount limiting unit in the first and second embodiments, the absolute value of the difference Δffm (t) between the rack axial force ff (t) at time t and the rack axial force ffm (t−T) at time t−T. Since the value is compared with the predetermined value THf as the amount of change, if the absolute value is the same even if the sign of Δffm (t) is different, the same predetermined value THf is used, but it is used depending on the sign of Δffm (t). It is also possible to change the predetermined value THf. That is, when the absolute value of Δffm (t) is the same but the sign is different, a different predetermined value THf is used. Usually, the sign of Δffm (t) is opposite between when entering and leaving the range of a predetermined angle before the rack end, so that by changing the predetermined value THf according to the sign of Δffm (t), more flexible adjustment is possible. become able to.

  FIG. 24 shows an example of the characteristic of the predetermined value used in the change amount limiting unit in the example (Example 3) in such a case. As shown in FIG. 24, when Δffm (t) is positive, a characteristic indicated by a solid line is used, and when Δffm (t) is negative, a characteristic indicated by a dotted line is used.

  In the above embodiments (Examples 1 to 3), the absolute value of the difference Δffm (t) between the rack axial force ff (t) at time t and the rack axial force ffm (t−T) at time t−T is calculated. Although the amount of change is used, the ratio may be the amount of change. For example, the ratio of the absolute value of Δffm (t) to the rack axial force ffm (t−T) is set as a change amount, and a predetermined value is set for the change amount. In addition, the predetermined value is a characteristic proportional to the steering information (rack displacement, rotation angle), but if the characteristic increases as the steering information increases, a characteristic that changes in a curve, a characteristic such as a step function, etc. But it ’s okay. Further, the switching signal SWS output from the rack end approach determining unit is also input to the change amount limiting unit, so that it is determined whether the switching signal SWS enters or leaves a predetermined angle range in front of the rack end by ON / OFF of the switching signal SWS. It is also possible to limit the amount of change only within a predetermined angle range before the rack end and until the next timing out of the range. Thereby, the amount of processing in normal steering can be reduced. In addition, the above-described determination may be performed, and the predetermined value THf may be changed as in the third embodiment depending on whether the predetermined angle is in the range of the predetermined angle before the rack end. Thereby, the same effect as Example 3 can be acquired.

  In the above-described embodiment, the viscoelastic model follow-up control unit may be configured with only the feedforward control unit or only the feedback control unit.

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 21 Rotation angle sensor 30 Control unit (ECU)
31 Torque control unit 35 Current control unit 36 PWM control unit 100 Rack position conversion unit 110 Rack end approach determination unit 120 Viscoelastic model following control unit 121, 122 Switching unit 124 Parameter setting unit 130 Feedforward control unit 140 Feedback control unit 150, 250 variation limiter

Claims (14)

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,
A model following control with a viscoelastic model as a reference model within a predetermined angle range before the rack end,
An electric power steering apparatus characterized in that a control amount in the model following control is changed so that a change amount of the control amount is within a predetermined value, and damage to the torque and the thrust transmission mechanism is suppressed.   The electric power steering apparatus according to claim 1, wherein the configuration of the model following control is a feedback control unit.   The electric power steering apparatus according to claim 1, wherein the configuration of the model following control is a feedforward control unit.   The electric power steering apparatus according to claim 1, wherein the model following control includes a feedback control unit and a feedforward control unit.   The electric power steering apparatus according to claim 1, wherein a parameter of the reference model is varied based on rack displacement. In the electric power steering apparatus that calculates the current command value 1 based on at least the steering torque and drives the motor based on the current command value 1, thereby assisting the steering system.
A first converter that converts the current command value 1 into rack axial force or column axial torque 1;
A rack position conversion unit for converting the rotation angle of the motor into a determination rack position;
A rack end approach determination unit that determines that the rack end is approached based on the determination rack position and outputs a rack displacement and a switching signal;
A viscoelastic model follow-up control unit that generates a rack axial force or a column shaft torque 2 using a viscoelastic model as a reference model based on the rack axial force or the column shaft torque 1, the rack displacement, and the switching signal;
A change amount limiting unit that changes the rack shaft force or the column shaft torque 2 so that the change amount becomes the predetermined value when the change amount of the rack shaft force or the column shaft torque 2 exceeds a predetermined value;
A second converter for converting the rack shaft force or column shaft torque 2 into a current command value 2;
The electric power steering apparatus is characterized in that the assist command control is performed by adding the current command value 2 to the current command value 1 to suppress damage to the torque and thrust transmission mechanism. The viscoelastic model following control unit is
A feedforward control unit that outputs a rack axial force or a column shaft torque 3 by performing a feedforward control based on the rack axial force or the column shaft torque 1;
A feedback control unit that performs a feedback control based on the rack displacement and the rack axial force or the column shaft torque 1 to output a rack axial force or a column shaft torque 4;
A first switching unit for turning on / off the output of the rack shaft force or the column shaft torque 3 by the switching signal;
A second switching unit for turning on / off the output of the rack shaft force or the column shaft torque 4 by the switching signal;
The electric power steering apparatus according to claim 6, further comprising: an adding unit that adds the outputs of the first and second switching units to output the rack axial force or the column shaft torque 2. The viscoelastic model following control unit is
A feedforward control unit that performs feedforward control based on the rack displacement and outputs a rack axial force or a column axial torque 3.
A feedback control unit that performs a feedback control based on the rack displacement and the rack axial force or the column shaft torque 1 to output a rack axial force or a column shaft torque 4;
A first switching unit for turning on / off the output of the rack shaft force or the column shaft torque 3 by the switching signal;
A second switching unit for turning on / off the output of the rack shaft force or the column shaft torque 4 by the switching signal;
The electric power steering apparatus according to claim 6, further comprising: an adding unit that adds the outputs of the first and second switching units to output the rack axial force or the column shaft torque 2.   The electric power steering apparatus according to claim 7 or 8, wherein parameters of the feedback control unit and the feedforward control unit are changed according to the rack displacement.   The electric power steering apparatus according to any one of claims 6 to 9, wherein the predetermined value is changed according to a sign of a change amount of the rack shaft force or the column shaft torque 2.   The electric power steering apparatus according to any one of claims 6 to 9, wherein the predetermined value is changed by ON / OFF of rack end approach determination.   The electric power steering apparatus according to any one of claims 6 to 11, wherein the predetermined value of the change amount limiting unit is changed based on steering information.   The electric power steering apparatus according to claim 12, wherein the predetermined value is changed so as to increase near the rack end. The electric power steering apparatus according to claim 12 or 13, wherein the steering information is the rack displacement or the rotation angle of the motor.

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