JP2017171057A - 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 overheat of a motor which may occur when a steering wheel holding state is continued before the rack end.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 offsets an input to or an output from the viscoelastic model to prevent overheating 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 ECU and the motor, which may occur when the rudder state is continued before the rack end, are prevented.

  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 based on the viscoelastic model as a reference model within a predetermined angle range before the rack end, and an offset is given to the input or output to the viscoelastic model to prevent overheating. This is achieved by preventing.

  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 The vehicle state information includes a second converter that converts the motor shaft torque 2 into the current command value 2, and an offset that is subtracted from the rack shaft force or the column shaft torque 1 or the viscoelastic model output of the viscoelastic model following control unit. An overheat protection control unit that calculates based on the current command value 2, and performs the assist control based on the current command value 3 obtained by adding the current command value 2 to the current command value 1, thereby preventing rack end end contact 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.

  Further, since an offset is given to the input or output to the viscoelastic model, the current flowing through the motor can be reduced, and overheating of the ECU and the motor can be prevented.

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 of this invention. It is a block diagram which shows the structural example (Example 1) of a viscoelastic model follow-up control part. It is a block diagram which shows the structural example (Example 2) 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 flowchart which shows the operation example of an overheat protection control part. It is a block diagram which shows the detailed structural example (Example 2) of a viscoelastic model follow-up control part. It is a flowchart which shows the operation example (Example 2) of a viscoelastic model follow-up control part. It is an image figure which shows the example of a change of the data by offset provision. It is a flowchart which shows the other operation example (Example 3) of an overheat protection control part. It is a block diagram which shows the other detailed structural example (Example 4) of a viscoelastic model follow-up control part. It is a block diagram which shows the other structural example (Example 5) of this invention. It is a flowchart which shows the other operation example (whole) (Example 5) 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. 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 feedback control unit or a feedforward control unit and a feedback control unit, and normal assist control outside a predetermined angle before the rack end. The model following control is performed within a predetermined angle in front of the rack end to prevent it from hitting the rack end.

  Also, by giving an offset to the input or output of the viscoelastic model in the viscoelastic model following control unit, the motor current can be reduced, and an ECU that may occur when the steering state is maintained before the rack end Prevent motor overheating. Specifically, the offset is subtracted from the rack axial force or column shaft torque input to the viscoelastic model follow-up control unit, or the target rack displacement (target steering angle) output from the viscoelastic model. Thereby, the rack axial force or column shaft torque output from the viscoelastic model follow-up control unit is suppressed, and the suppression is fed back to the current command value, and the motor current is reduced. The offset is calculated by the overheat protection control unit. The overheat protection control unit has a large motor current flowing in the steered state based on the current command value, the steering torque, the motor rotation speed, the rack displacement speed, etc., which are vehicle state information, within a predetermined angle before the rack end. (Hereinafter, a condition used for this determination is referred to as an “offset calculation condition”), and if the state continues, an offset is calculated. And by gradually increasing the offset value, the motor current is intermittently reduced. However, if part of the conditions for determining the steered state is not satisfied, the increase in the offset value is interrupted, and the rack When the angle is outside the predetermined angle before the end, the offset is reset to zero so that no offset is given. Also, by setting an upper limit value for the offset, the motor current is prevented from becoming excessively small. The lower limit value of the current command value is set instead of the upper limit value of the offset, and the offset value when the current command value reaches the lower limit value is stored as the upper limit offset. The value may remain at the upper limit offset so that the motor current does not become excessively small.

  By integrating and executing model following control and offset application to the input and output of the viscoelastic model within a predetermined angle before the rack end, it is possible to perform overheat protection while preventing damage to the torque and thrust transmission mechanism By activating both functions individually, the current value causes hunting (fluctuation), and the possibility that the driver feels uncomfortable can be reduced.

  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. The feedback element (N / F) 141 is a reference model as described above, corresponds to a viscoelastic model, and the output from the feedback element (N / F) 141 becomes the target rack displacement.

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. Furthermore, in Embodiment 3 in FIG. 14 and Embodiment 4 in FIG. 15, control calculations of both the feedforward control unit 130 and the feedback control unit 140 are executed, but the configuration of only the feedback control unit 140 may be used.

  Next, examples of the present invention will be described.

  FIG. 18 shows an embodiment of the present invention corresponding to FIG. 3, and a rack displacement speed calculation unit 150 and an overheat protection control unit 160 are added to the embodiment shown in FIG. The rack displacement x and the switching signal SWS output from the rack end approach determination unit 110 include the rack displacement x in the rack displacement speed calculation unit 150 and the switching signal in the overheat protection control unit 160, in addition to the viscoelastic model following control unit 220. Each SWS is input. The rack displacement speed calculation unit 150 calculates the rack displacement speed Rv from the rack displacement x and outputs the rack displacement speed Rv to the overheat protection control unit 160. In addition to the switching signal SWS and the rack displacement speed Rv, the overheat protection control unit 160 inputs a steering torque Th, a vehicle speed Vel, and a current command value Iref3 described later, and calculates an offset of. The offset of is input to the viscoelastic model follow-up control unit 220 together with the rack axial force f, the switching signal SWS, and the rack displacement x, and the rack axial force ff controlled and calculated by the viscoelastic model follow-up control unit 220 is converted into a current by the conversion unit 102. It is converted into a command value Iref2. Other configurations are the same as those of the embodiment shown in FIG.

  Details of the viscoelastic model follow-up control unit 220 are shown in FIG. 19 (Embodiment 1) corresponding to FIG. 5 and in FIG. 20 (Embodiment 2) corresponding to FIG.

  The offset of output from the overheat protection control unit 160 is input to the feedback control unit 240. The other configuration is the same as that of the first embodiment in FIG. 5 or the second embodiment in FIG.

  In such a configuration, an example of the entire operation and an example of the viscoelastic model follow-up control will be described with reference to the flowcharts of FIGS. 21, 22, and 23.

  FIG. 21 is a flowchart showing an overall operation example. Compared with the flowchart of FIG. 7, step S12A is added, and the operation of the viscoelastic model following control is changed as described later (step S20A). ). Other operations are the same as those in the first or second embodiment.

  In step S12A, when the rack end approach determination unit 110 determines whether or not the rack end approach is based on the determination rack position Rx, the result of the rack end approach is not the rack end approach, and the value of the offset of in the overheat protection control unit 160 is set to zero. The resetting operation is executed.

  When the rack end approach determination unit 110 determines the rack end approach, viscoelastic model follow-up control is performed by the overheat protection control unit 160 and the viscoelastic model follow-up control unit 220 (step S20A).

  FIG. 22 is a flowchart showing an operation example of the viscoelastic model following control. Compared with the flowchart of FIG. 8, steps S203A and S203B are added, and the operation of the feedback control is changed (from steps S205 to S205A). Other changes are the same as those in the first or second embodiment. The feedback control in step S205A is executed by the feedback control unit 240. The operation will be described in the detailed description of the viscoelastic model follow-up control unit 220 described later.

  In step S203A, the rack displacement speed calculation unit 150 inputs the rack displacement x output from the rack end approach determination unit 110, and the operation of calculating the rack displacement speed Rv from the rack displacement x is executed. In step S203B, the overheat protection control unit 160 detects the rack end approach based on the switching signal SWS, and calculates the offset of based on the steering torque Th, the vehicle speed Vel, the rack displacement speed Rv, and the current command value Iref3.

  The calculation of the offset of in the overheat protection control unit 160 is executed in the procedure as shown in FIG.

  The offset of is updated when the offset calculation condition is satisfied only for a predetermined time, and a flag (hereinafter referred to as “predetermined time elapse flag”) indicating whether or not the offset calculation condition is satisfied is provided. It is OFF at the start stage. The value of the offset of is zero at the start stage.

  When the overheat protection control unit 160 detects the approach of the rack end based on the output of the switching signal SWS, the overheat protection control unit 160 reads the current command value Iref3, the steering torque Th, the rack displacement speed Rv, and the vehicle speed Vel, which are vehicle state information (step S301), for a predetermined time. The progress flag is confirmed (step S302).

  If the predetermined time elapsed flag is OFF, it is confirmed whether the offset calculation condition is satisfied for a predetermined time (step S303). The offset calculation conditions are “the vehicle speed Vel is smaller than the predetermined vehicle speed value”, “the steering torque Th is larger than the predetermined steering torque value”, “the rack displacement speed Rv is smaller than the predetermined speed value”, and “the current command value Iref3. Is larger than a predetermined current command value ”, and the time when the offset calculation condition is satisfied is measured using a time counter. If the offset calculation condition is satisfied for a predetermined time, the predetermined time elapse flag is turned on (step S304), and the offset of is output (step S305). If the offset calculation condition is not satisfied for a predetermined time, the predetermined time elapsed flag is left as it is, and the offset of is output (step S305).

  If the predetermined time elapse flag is ON, it is confirmed whether a part of the condition for determining the steered state is not satisfied (step S306). That is, at least one of the three conditions “the vehicle speed Vel is smaller than the predetermined vehicle speed value”, “the steering torque Th is larger than the predetermined steering torque value”, or “the rack displacement speed Rv is smaller than the predetermined speed value”. Check whether the two conditions are not satisfied. If all three conditions are satisfied, the offset of is updated by adding a predetermined value to the offset of (step S307). Then, it is confirmed whether or not the updated offset of exceeds a predetermined upper limit value (step S308). If the offset is exceeded, the predetermined upper limit value is set as the value of the offset of (step S309). The value of is not changed and the offset of is output (step S305). If at least one of the above three conditions is not satisfied, the predetermined time elapsed flag is turned off (step S310), and the offset of is output without being updated (step S305). When turning off the predetermined time elapsed flag, the time counter used in step S303 is cleared to zero.

  If the angle is outside the predetermined angle before the rack end and it is determined that the rack end is not approaching, as described above, the value of the offset of is reset to zero (step S12A).

  The offset of calculated as described above is input to the feedback control unit 240 of the viscoelastic model follow-up control unit 220.

  In the offset calculation condition, there may be no condition regarding the vehicle speed Vel, and other conditions may be added. Alternatively, the motor rotational speed may be used instead of the rack displacement speed Rv, and the condition that “the motor rotational speed is smaller than a predetermined rotational speed” may be used. In this case, the motor rotation speed is calculated from the rotation angle θ output from the rotation angle sensor 21. Furthermore, the offset of is updated by adding a predetermined value. However, if the offset of is updated so as to gradually increase, other methods such as exponential increase are used. It may be updated.

  Here, the viscoelastic model follow-up control unit 220 will be described in further detail with reference to FIGS. 24 and 25. FIG.

  FIG. 24 shows a specific configuration example of the viscoelastic model follow-up control unit 220 in the second embodiment of FIG. This corresponds to the fourth embodiment shown in FIG. 15, and the feedback control unit 140 is replaced with the feedback control unit 240. Since other configurations are the same as those of the fourth embodiment, description thereof is omitted.

  The feedback control unit 240 includes a feedback element (N / F) 141, a control element unit 143, a subtraction unit 142, and a subtraction unit 145, and the offset of from the overheat protection control unit 160 is subtracted and input to the subtraction unit 145.

  The rack axial force f input to the feedback control unit 240 is added to the subtraction unit 145, and the offset of the subtraction input to the subtraction unit 145 is subtracted, and the rack axial force f ′ is input to the feedback element (N / F) 141. Entered.

  An example of the operation in such a configuration is shown in the flowchart of FIG.

First, similarly to the operation in the fourth embodiment shown in FIG. 17, the switching signal SWS and the rack displacement x are output from the rack end approach determination unit 110 (steps S21 and S22), and the rack displacement x is a spring constant term 131, The viscous friction coefficient term 132, the parameter setting unit 124, and the subtraction unit 142 are input. The parameter setting unit 124 sets the spring constant k ₀ and the viscous friction coefficient μ to the spring constant term 131, the viscous friction coefficient term 132, and the feedback element (N / F) 141 (step S23), and the conversion unit 101 sets the current command value. Iref1 is converted into a rack axial force f (step S23A). The rack axial force f is added and input to the subtracting unit 145. The rack displacement speed calculation unit 150 calculates the rack displacement speed Rv from the rack displacement x (step S23B), and the rack displacement speed Rv together with the switching signal SWS, the steering torque Th, the vehicle speed Vel, and the current command value Iref3, the overheat protection control unit 160. And the offset of is calculated by the overheat protection control unit 160 (step S23C). The offset of is subtracted and input to the subtracting unit 145, and the rack axial force f ′ obtained by subtracting the offset of is input to the feedback element (N / F) 141, and N / F calculation is performed (step S24).

  Thereafter, the same operations as those in steps S24A to S27 in the fourth embodiment are performed, and the process leads to step S14.

  Note that the configuration in which the feedback control unit 140 in the third embodiment shown in FIG. 14 is replaced with the feedback control unit 240 in the second example in FIG. 24 is replaced by the viscoelastic model follow-up control unit 220 in the first example in FIG. A specific configuration example can be obtained. The operation of the configuration example is the same as the operation in the second embodiment, except that the portion (element) to which the rack axial force f and the rack displacement x are input is different.

  Here, FIG. 26 shows an image of changes in each data (signal) due to the offset. In FIG. 26, the horizontal axis is time, and the vertical axis is the size of each data. However, since the purpose here is to show the state of change, the size of each data is different from the actual size. In addition, the timing at which each data changes may actually cause a deviation, but there is no deviation, and the rack axial force f and the rack displacement x input to the viscoelastic model following control unit 220 are constant. .

If the offset calculation condition is satisfied for a predetermined time at a time t ₁ within a predetermined angle before the rack end, the value of the offset of gradually increases, and the rack axial force f ′ decreases accordingly. As a result, the N / F calculation value, which is the output from the viscoelastic model, also decreases, the deviation from the rack displacement x calculated by the subtraction unit 142 increases, and the control element unit (Cd) 143 that receives the deviation as input. The rack axial force FB, which is the output of, decreases. In response to the decrease in the rack axial force FB, the current command value also decreases.

  When there is no function for providing an offset, each data remains constant as shown by a dotted line in FIG. 26. As a result, the motor current is not reduced, and the ECU and the motor may be overheated. Can be seen to work effectively.

When at time t ₂ and the offset of reaching the upper limit value, the time t ₂ later, the offset of becomes constant at the upper limit value, becomes constant at the value of the other data at the time t _2. Thereby, it can prevent that an electric current command value falls too much.

  As described above, in the above-described embodiments (Examples 1 and 2), the upper limit value is set for the offset so that the motor current does not become excessively small, but instead of the upper limit value of the offset. Set the lower limit value of the current command value, store the offset value when the current command value reaches the lower limit value as the upper limit offset, and keep the offset value as the upper limit offset while the current command value is less than the lower limit value. By doing so, it is possible to prevent the motor current from becoming excessively small.

  The configuration of the embodiment (embodiment 3) in this case is the same as that of the above embodiment, but there is a difference in the operation of calculating the offset of in the overheat protection control unit 160.

  FIG. 27 is a flowchart showing an operation example of calculation of the offset of in the overheat protection control unit 160 in the third embodiment. Compared with the flowchart shown in FIG. 23, the current command value Iref3, which is vehicle state information, the steering Steps S301A to S301D are added after the reading of the torque Th, the rack displacement speed Rv and the vehicle speed Vel (step S301), and the processing after the update of the offset of (step S307) is changed from step S308 and S309 to steps S308A and S309A. It is changing. In the present embodiment, a flag (hereinafter referred to as “limit flag”) indicating whether or not the current command value has reached the lower limit value is provided, and is OFF at the start stage.

  The overheat protection control unit 160 checks whether or not the read current command value Iref3 is smaller than a predetermined lower limit value (step S301A). If smaller, the value of the offset of at that time is stored as an upper limit offset (step S301B), and a limit flag Is turned ON (step S301C). If the current command value Iref3 is not smaller than the lower limit value, the limit flag is turned OFF (step S301D).

  After the offset of is updated (step S307), the limit flag is confirmed (step S308A). When the limit flag is ON, the upper limit offset is set to the value of the offset of (step S309A), and when it is OFF, the value of the offset of. Does not change.

  Thus, since the offset is limited by the magnitude of the current command value directly related to the overheating of the ECU and the motor, the overheating can be effectively prevented.

  The subtraction of the offset is not performed on the rack axial force f input to the feedback element (N / F) 141, which is a viscoelastic model, but to the N / F calculation value output from the feedback element (N / F) 141. It is also possible to do this.

  FIG. 28 shows the N / F calculation value output from the feedback element (N / F) 141 by subtracting the offset of from the configuration example of the viscoelastic model follow-up control unit in the second embodiment shown in FIG. A configuration example (embodiment 4) in the case where it is performed for this is shown.

  The configuration other than the feedback control unit 250 is the same as the configuration of the second embodiment shown in FIG. 24. The components of the feedback control unit 250 are the same, but the connection of the components is different. The rack axial force f is input to the feedback element (N / F) 141 instead of the subtraction unit 145, and the N / F calculation value output from the feedback element (N / F) 141 is not the subtraction unit 142 but the subtraction unit 145. Is added and input. In the subtracting unit 145, the offset of is subtracted from the N / F calculation value, the subtracted value is added to the subtracting unit 142, the rack displacement x is subtracted, and input to the control element unit 143.

  The flow of the rack axial force in the feedback control unit is the same in the fourth embodiment and the other embodiments described above, and since an offset is given in the same flow, the fourth embodiment is also equivalent to the other embodiments. The effect of can be obtained.

  Note that the subtraction of the offset of is also performed on the N / F calculation value output from the feedback element (N / F) 141 in the configuration example of the viscoelastic model follow-up control unit in the first embodiment. It is possible.

  The processing executed using the rack displacement x in the above-described embodiments (embodiments 1 to 4) is the displacement of the rotation angle θ of the motor (hereinafter referred to as “rotation angle displacement”) instead of the rack displacement x. ) Execution is possible even using θd. The rack position and the rotation angle are interlocked so that the rotation angle θ is converted to the determination rack position Rx in the rack position conversion unit 100 in the above embodiment, so that the predetermined position or angle before the rack end is set. Substitution is possible between the rack displacement and the rotation angle displacement as the base point.

  Corresponding to FIG. 18, FIG. 29 shows an example (Example 5) in which the rotational angular displacement θd is used instead of the rack displacement x.

In the fifth embodiment, since it is not necessary to obtain the rack position, the rack position conversion unit 100 is unnecessary, and the rack end approach determination unit 110 replaces the rack end approach determination unit 210 and replaces the rack displacement speed calculation unit 150. Is provided with a motor rotation number calculation unit 250, the overheat protection control unit 160 is replaced with the overheat protection control unit 260, and the viscoelastic model follow-up control unit 220 is replaced with the viscoelastic model follow-up control unit 320. The rotation angle θ from the rotation sensor 21 is input to the rack end approach determination unit 210. The rack end approach determination unit 210 has a rotation angle corresponding to the rack end and a rotation angle corresponding to a predetermined position before the rack end. When it is determined that it is between θ ₀ , the suppression control function is activated to output a rotation angle displacement θd that is a deviation between the rotation angle θ and the rotation angle θ _{0 and} a switching signal SWS. The rotational angular displacement θd is input to the viscoelastic model follow-up control unit 320 and the motor rotation number calculation unit 250, and the switching signal SWS is input to the viscoelastic model follow-up control unit 320 and the overheat protection control unit 260. The motor rotational speed calculation unit 250 calculates the motor rotational speed ω from the rotational angular displacement θd and outputs it to the overheat protection control unit 260. The overheat protection control unit 260 calculates the offset of using the motor rotation speed ω instead of the rack displacement speed Rv. The viscoelastic model follow-up control unit 320 calculates the rack axial force ff using the rotational angular displacement θd instead of the rack displacement x.

  The overall operation example of the fifth embodiment is as shown in FIG. 30, and compared with the operation example shown in FIG. 21, the rack position conversion process (step S11) for converting the rotation angle θ into the determination rack position Rx is unnecessary. It has become. In other processes, the rotation angle displacement θd is calculated and used instead of the rack displacement x, and the operation is the same except that the motor rotational speed ω is calculated and used instead of the rack displacement speed Rv. .

  By using the rotation angle displacement θd instead of the rack displacement x, the rotation angle can be used directly, so that the processing amount and the calculation error can be reduced.

  In the above-described embodiment, the control calculation of both the feedforward control unit and the feedback control unit is executed, but the configuration of only the feedback control unit may be used.

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, 210 Rack end approach determination unit 120, 220, 320 Viscoelastic model following control unit 121, 122 Switching unit 124 Parameter setting unit 130 Feedforward control unit 140, 240 Feedback control unit 150 Rack displacement speed calculation unit 160, 260 Overheat protection control unit 250 Motor rotation number calculation unit

Claims (15)

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,
In order to prevent overheating, an electric power steering device is characterized in that an offset is given to an input or output to the viscoelastic model to suppress damage to the torque and thrust transmission mechanism.   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 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 second converter for converting the rack shaft force or column shaft torque 2 into a current command value 2;
An overheat protection control unit that calculates an offset to be subtracted from the output of the viscoelastic model of the rack axial force or the column shaft torque 1 or the viscoelastic model following control unit based on vehicle state information;
An electric power steering apparatus characterized in that the assist control is performed based on a current command value 3 obtained by adding the current command value 2 to the current command value 1 to prevent 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 5, 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 5, 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 6 or 7, wherein parameters of the feedback control unit and the feedforward control unit are changed according to the rack displacement. The overheat protection control unit is
The electric power steering apparatus according to claim 5, wherein the offset is calculated when it is determined by the vehicle state information that the steered state is continued within a range of a predetermined angle before the rack end. The vehicle state information comprises at least the current command value 3, the steering torque and the motor rotation speed or the rack displacement speed;
If at least the current command value 3 is larger than a predetermined current command value, the steering torque is larger than a predetermined steering torque value, and the motor rotation speed or rack displacement speed is smaller than a predetermined value, the offset The electric power steering device according to claim 9, wherein   The electric power steering apparatus according to claim 9 or 10, wherein the offset value is updated so as to gradually increase from a calculation start time.   The electric power steering apparatus according to claim 11, wherein when the offset value exceeds a predetermined upper limit value, the predetermined upper limit value is set as the offset value.   The offset value at the time when the current command value 3 becomes less than a predetermined lower limit value is stored as an upper limit offset, and the upper limit offset is set to the offset value while the current command value 3 is less than the predetermined lower limit value. The electric power steering apparatus according to claim 11.   14. The offset update is interrupted when the steering torque becomes equal to or less than the predetermined steering torque value, or when the motor rotation speed or rack displacement speed becomes equal to or higher than the predetermined value. The electric power steering device according to claim 1. The electric power steering apparatus according to any one of claims 9 to 14, wherein the offset value is reset to zero when the angle is out of a predetermined angle range before the rack end.

Images