JP2018043730A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which can perform handle return control for making a driver hardly feel an incongruity by imposing restrictions on the control so that a difference between a target steering angle speed and a steering angle speed does not become excessively large, in the handle return control for performing a smooth handle return without causing the incongruity even in the intervention of the steering of the driver in a linear traveling state by a correction based on steering torque and a vehicle speed taking into consideration a vehicle characteristic.SOLUTION: In an electric power steering device which drives a motor on the basis of a current command value, and assist-controls a steering system by the drive control of the motor, the electric power steering device comprises a handle return control part which calculates a target steering angle speed by using a steering angle, a vehicle speed, steering torque and the current command value, calculates a handle return control current by using a limit target steering angle speed which is acquired by imposing restrictions on the target steering angle speed according to a steering angle speed, and drives the motor by using a compensation current command value which is obtained by adding the handle return control current to the current command value.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an electric power steering apparatus that applies an assist torque to a steering system by PWM control of a motor by an inverter based on a current command value, and in particular, calculates a target rudder angular speed based on a virtual vehicle model, and controls a steering wheel return control current. The function of the steering wheel return control is improved by correcting the current command value at the same time, and an excessive output is suppressed by limiting the target steering angular speed in the steering wheel return control, thereby reducing the uncomfortable feeling of steering. The present invention relates to a power steering device.

  An electric power steering device that applies an assist torque to a steering mechanism of a vehicle by a rotational force of a motor transmits a driving force of the motor to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a reduction mechanism. It is supposed to be granted as Such a conventional electric power steering device (EPS) 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 steering assist command value (current command value) and the motor current detection value is small. The adjustment of the motor applied voltage is generally performed by PWM (pulse width). This is done by adjusting the duty of modulation) control.

  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 for detecting the steering torque Td of the steering wheel 1 and a steering angle sensor 14 for detecting the steering angle θ, and a motor 20 for assisting the steering force of the steering wheel 1 is a reduction gear. 3 is connected to the column shaft 2 through 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. The control unit 30 calculates a current command value of an assist (steering assist) command based on the steering torque Td detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12, and compensates the current command value. The current supplied to the motor 20 is controlled by the voltage control command value Vref subjected to. The steering angle sensor 14 is not essential and may not be provided.

  The control unit 30 is connected to a CAN (Controller Area Network) 40 that transmits and receives various types of vehicle information, and the vehicle speed V 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.

  The control unit 30 is mainly composed of a CPU (including MCU, MPU, etc.). FIG. 2 shows general functions executed by a program inside the CPU.

  The function and operation of the control unit 30 will be described with reference to FIG. 2. The steering torque Td detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12 (or from the CAN 40) are represented by the current command value Iref 1. The current command value calculation unit 31 to be calculated is input. The current command value calculation unit 31 calculates a current command value Iref1, which is a control target value of the current supplied to the motor 20, using an assist map or the like based on the input steering torque Td and the vehicle speed V. The current command value Iref1 is input to the current limiter 33 through the adder 32A, and the current command value Irefm whose maximum current is limited is input to the subtractor 32B, and the deviation I (Irefm) from the fed back motor current value Im. -Im) is calculated, and the deviation I is input to the PI control unit 35 for improving the characteristics of the steering operation. The voltage control command value Vref whose characteristics are improved by the PI control unit 35 is input to the PWM control unit 36, and the motor 20 is PWM driven via an inverter 37 as a drive unit. The current value Im of the motor 20 is detected by the motor current detector 38 and fed back to the subtraction unit 32B. The inverter 37 uses a FET as a drive element, and is configured by a bridge circuit of the FET.

  A compensation signal CM from the compensation signal generator 34 is added to the adder 32A, and the compensation of the steering system system is performed by adding the compensation signal CM to improve the convergence and inertia characteristics. . The compensation signal generation unit 34 adds the self-aligning torque (SAT) 343 and the inertia 342 by the addition unit 344, and further adds the convergence 341 to the addition result by the addition unit 345, and compensates the addition result of the addition unit 345. The signal CM is used.

  In such an electric power steering device, the friction is large due to the reduction gear and the rack and pinion, and the equivalent inertia moment around the steering shaft is large due to the motor for generating the assist torque. Therefore, in a low vehicle speed range where the self-aligning torque (SAT) is small, the steering wheel returns poorly due to large friction. This is because the steering angle does not return to the neutral point only by SAT in the straight traveling state, and it is necessary to return to the neutral point by the driver's steering intervention, which is a burden on the driver.

  On the other hand, in the high vehicle speed range where SAT is large, since the SAT is large, the steering angular speed tends to be faster than in the low vehicle speed range, but the inertia torque due to the moment of inertia is also large, and the steering wheel converges at the neutral point of the steering angle. Therefore, the vehicle characteristics may be felt unstable because of overshooting.

  As described above, compensation of characteristics different depending on the vehicle speed or the steering state is necessary, and various control methods for providing appropriate assistance when returning the steering wheel have been proposed in order to achieve them. Among these steering wheel return controls, there is an electric power steering device disclosed in Japanese Patent No. 4658557 (Patent Document 1) as a prior art for the purpose of performing a smooth steering wheel return control even during steering intervention by a driver. .

  In the device of Patent Document 1, a controller configured to follow the target rudder angular velocity corrects the base correction rudder angular velocity by multiplication and addition by the vehicle speed and the steering torque, and calculates the target rudder angular velocity. At the time of steering intervention by the driver, the target steering angular speed is corrected in the direction in which the steering torque is applied, thereby reducing the uncomfortable feeling when the driver steers.

  In order to realize a smooth steering wheel return in the released state, it is preferable that the rudder angular velocity is zero at the rudder angle neutral point without largely varying the rudder angular acceleration. However, in the apparatus described in Patent Document 1, correction is performed using the steering torque when setting the target rudder angular velocity, but correction using the assist torque is not performed. Since the assist torque is generally set so as to decrease as the vehicle speed increases, it takes time to calculate a preferable correction amount in the correction based on the steering torque and the vehicle speed.

  In order to solve such a problem, in the electric power steering apparatus disclosed in Japanese Patent No. 5896091 (Patent Document 2), the target return torque is defined according to the steering angle and the vehicle speed, and the steering torque and the assist torque are defined as the target return torque. The target rudder angular velocity is calculated by multiplying the result obtained by adding the transfer characteristic corresponding to the virtual steering system characteristic. Then, by performing at least one of P (proportional) control, I (integral) control, and D (differential) control on the deviation between the target rudder angular speed and the actual rudder angular speed, even during steering intervention by the driver Realization of a handle return control with a natural feeling.

Japanese Patent No. 4658557 Japanese Patent No. 5896091

  However, in the device described in Patent Document 2, depending on the steering state, the deviation between the target rudder angular speed and the actual rudder angular speed may be excessive in the steering wheel return control, which causes the steering wheel return control to work excessively, which makes the driver feel uncomfortable. There is a risk of becoming.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to provide a smooth steering wheel without a sense of incongruity even when a driver intervenes in a straight traveling state by a correction based on a steering torque and a vehicle speed in consideration of vehicle characteristics. To provide an electric power steering device capable of providing a steering wheel return control that is less uncomfortable for the driver by restricting the deviation between the target steering angular velocity and the steering angular velocity so as not to become excessive in the steering wheel return control for realizing the return. is there.

  The present invention relates to an electric power steering device that calculates a current command value based on a steering torque and a vehicle speed, drives a motor based on the current command value, and assists a steering system by driving control of the motor. The above-mentioned object is to calculate a target rudder angular speed using the rudder angle, the vehicle speed, the steering torque, and the current command value, and to obtain a limited target rudder obtained by limiting the target rudder angular speed according to the rudder angular speed. This is achieved by providing a handle return control unit that calculates a handle return control current using an angular velocity and drives the motor with a compensation current command value obtained by adding the handle return control current to the current command value.

  Further, the object of the present invention is that the steering wheel return control unit is integrated using the steering torque and the current command value, a steering angle angular velocity calculation unit that calculates a steering angular velocity using the steering angle and the vehicle speed. An integrated torque calculation unit for calculating torque, a steering system characteristic unit for calculating the target steering angular velocity based on a virtual vehicle model using the return steering angular velocity and the integrated torque, and the target according to the steering angular velocity A target rudder angular speed limiter that limits the target rudder angular speed by setting a limit value with respect to the rudder angular speed and the deviation before restriction that is a deviation of the rudder angular speed, and the deviation of the limited target rudder angular speed and the rudder angular speed A steering wheel return control deviation calculating unit for obtaining a steering wheel return control deviation by multiplying the post-limit deviation by a vehicle speed gain and a steering torque gain, and for the steering wheel return control deviation A steering wheel return control current calculation unit that performs at least one of the P control calculation, the I control subtraction, and the D control calculation, and obtains the steering wheel return control current by limiting the output by the vehicle speed gain and the steering torque gain. Alternatively, the target rudder angular velocity limiting unit may be configured such that the pre-limit deviation is larger than the limit value when the pre-limit deviation is a return deviation that acts to return the handle to neutral. By setting the limit value so that the magnitude of the limit value in the case of a damping deviation that acts so as to converge the movement becomes larger, or the target rudder angular velocity limit unit further reduces the value before the limit. The limit value is set so that the magnitude of the limit value when the deviation is the damping deviation is smaller when it is increased than when it is switched back. By setting, or the target rudder angular velocity limiting unit further, the magnitude of the limit value when the deviation before restriction is the damping deviation, so that the magnitude of the limit value increases as the rudder angular speed increases. By setting a limit value or in the situation of switchback, the value before the limit is negative when the rudder angle is positive or positive when the rudder angle is negative. In a situation where the steering angular speed is fast, the value before the limit is positive when the steering angle is positive, or the value before the limit is negative when the steering angle is negative, is the damping deviation. The limit value is changed by the vehicle speed, the limit value is changed by the steering angle, or the limit value is changed by the steering angular speed. Is achieved more effectively.

  According to the electric power steering device according to the present invention, the target rudder angular speed is calculated using the rudder angle, vehicle speed, steering torque and current command value, and the target rudder angular speed is limited according to the rudder angular speed, In the steering wheel return control, it is possible to suppress the deviation between the target steering angular speed and the steering angular speed from being excessive, and to provide the steering wheel return control with less uncomfortable feeling.

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 (1st Embodiment) of this invention. It is a characteristic view which shows the example of an output of a return rudder angular velocity calculating part. It is a characteristic view which shows the output example of a viscosity coefficient output part. It is a characteristic view which shows the example of an output of a steering torque gain part. It is a characteristic view which shows the example of an output of a vehicle speed gain part. It is a characteristic figure which shows the example of a setting of a limit value. It is a block diagram which shows the structural example (1st Embodiment) of a restriction | limiting part. It is a figure which shows the time change example of a steering angle, a steering angular velocity, a target steering angular velocity, and a deviation. It is a flowchart which shows the operation example (1st Embodiment) of this invention. It is a flowchart which shows the operation example (1st Embodiment) of a restriction | limiting process. It is a block diagram which shows the structural example (2nd Embodiment) of this invention. It is a characteristic view which shows the example of a setting of the limit value changed with a vehicle speed. It is a characteristic view which shows the example of an output of a steering angle gain part. It is a characteristic view which shows the example of an output of a steering angular velocity gain part. It is a flowchart which shows the operation example (2nd Embodiment) of a restriction | limiting process.

  In the steering wheel return control according to the present invention, the operation is hindered by the friction of the reduction gear and the rack and pinion for transmitting the auxiliary force in the electric power steering device, and the steering wheel is neutral in spite of the traveling state where it is desired to return to the straight traveling state. Since the vehicle may not be able to go straight ahead without returning to the point, the steering wheel can be used in the running state where the current command value is corrected (compensated) with the steering wheel return control current according to the steering angle, vehicle speed, etc. To positively return to neutral. The steering wheel return control is executed by calculating a target rudder angular velocity based on a simple virtual vehicle model and performing PID (proportional integral derivative) control on a deviation between the target rudder angular velocity and the rudder angular velocity (actual rudder angular velocity). The In the steering wheel return control, by limiting the target steering angular speed by following the steering angular speed, the generated deviation is suppressed to a certain level or less, the steering wheel return control is prevented from working excessively, and the steering discomfort is felt. Decrease.

A simple virtual vehicle model according to the present invention has a steering system virtual moment of inertia J and steering torque Td and assist torque Ta with respect to a return steering angular speed (target value) ωt, a steering torque Td and an assist torque Ta obtained from the steering angle θ and the vehicle speed V. This is a model for calculating the target rudder angular velocity ω ₀ by applying vehicle characteristics (vehicle transmission characteristics) corresponding to the viscosity coefficient C.

  By using the virtual vehicle model (steering system characteristic unit), the virtual inertia moment J and the viscosity coefficient C of the steering system can be set, so that the vehicle characteristics can be arbitrarily determined. Further, since the virtual vehicle model takes into account the driver's steering intervention in consideration of the assist torque Ta, smooth steering wheel return control can be provided even when the driver is steering.

  Here, when it is assumed that the steering system has no static friction, Coulomb friction, and elasticity terms, the balance equation of the forces of the self-aligning torque (SAT) Sat, the steering torque Td, and the assist torque Ta is expressed by the following equation (1).

そして、舵角速度ωは舵角θの時間微分であるので、下記数２が成立する。

Since the steering angular velocity ω is a time derivative of the steering angle θ, the following formula 2 is established.

よって、ω＝ω_０とすると、下記数３が成立する。

Therefore, when ω = ω ₀ , the following formula 3 is established.

更に、上記数３をラプラス変換すると下記数４となり（ｓはラプラス演算子）、数４を目標舵角速度ω_０について解くと、下記数５となる。

Further, when the above formula 3 is Laplace transformed, the following formula 4 is obtained (s is a Laplace operator), and when the formula 4 is solved for the target steering angular velocity ω ₀ , the following formula 5 is obtained.

上記数５より、目標舵角速度ω_０を求める。数５において、Ｓａｔ／ＣはＳＡＴによって発生する舵角速度として、車両特性に応じて設定する戻り舵角速度ωｔとして考えることができる。１／｛（Ｊ／Ｃ）ｓ＋１｝は仮想車両モデルから求められる伝達特性（以下、「仮想特性」とする）であり、（Ｔｄ＋Ｔａ）／Ｃは操舵トルクＴｄ及びアシストトルクＴａによって発生する舵角速度である。

From the above _equation 5, the target rudder angular velocity ω ₀ is obtained. In Equation 5, Sat / C can be considered as a steering angular velocity ωt set according to vehicle characteristics as a steering angular velocity generated by SAT. 1 / {(J / C) s + 1} is a transfer characteristic obtained from the virtual vehicle model (hereinafter referred to as “virtual characteristic”), and (Td + Ta) / C is a steering angular velocity generated by the steering torque Td and the assist torque Ta. It is.

Since SAT Sat is generally determined by the vehicle speed V and the steering angle θ, the return steering angular speed ωt is also set according to the vehicle speed V and the steering angle θ. The steering torque Td is detected by a torque sensor, and the assist torque Ta can be calculated from the current command value Iref in consideration of the motor torque constant Kt. Therefore, by dividing the torque (integrated torque) Tc obtained by adding the steering torque Td and the assist torque Ta by the virtual viscosity coefficient C of the steering system, the steering angular speed generated by the integrated torque Tc (hereinafter referred to as “integrated steering angular speed”). Ωc is calculated, the return steering angular velocity ωt and the integrated steering angular velocity ωc are added together, and converted by the virtual characteristic to obtain the target steering angular velocity ω ₀ .

In the present invention, the target rudder angular velocity ω ₀ obtained in this way is limited so that the deviation (pre-limit deviation) between the target rudder angular velocity ω ₀ and the rudder angular velocity ω does not become excessive. In other words, a limit value is set for the deviation so that the deviation does not exceed the limit value. At this time, compared with the magnitude (absolute value) of the limit value (hereinafter referred to as “return limit value”) that is set when the deviation is a deviation (return deviation) that returns the handle to neutral (neutral point), The limit value is set so that the limit value (hereinafter referred to as “dumping limit value”) set when the deviation is a deviation that causes the movement of the steering wheel to converge (dumping deviation) is larger. Further, since the amount of compensation necessary for the convergence of the steering wheel increases as the steering angular speed ω increases, the damping limit value increases as the steering angular speed ω increases. In addition, the magnitude of the damping limit value at the time of the increase is made smaller than the magnitude of the damping limit value at the time of the return so that the driver's steering is not hindered at the time of the increase.

  Since the return performance of the steering wheel and the convergence of the vehicle differ depending on the vehicle speed V, the output of the steering wheel return control is made variable by multiplying the vehicle speed gain according to the vehicle speed V, for example. Further, the steering wheel return control is mainly required when the ratio of the friction torque to the steering torque Td applied to the column shaft is relatively large. Therefore, when the steering torque Td is large, the steering wheel return control is required. Return control does not require large output. Therefore, for example, the output of the steering wheel return control is made variable by multiplying the steering torque gain Th that becomes smaller according to the steering torque Td.

Thus, by performing control according to the deviation between the target rudder angular velocity ω ₀ and the rudder angular velocity ω, it is possible to realize a smooth steering wheel return and to provide a steering wheel return control that does not feel strange even when the driver steers. .

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

  FIG. 3 shows a configuration example (first embodiment) of the handle return control unit 100 according to the present invention. The steering torque Td input to the steering wheel return control unit 100 is supplied to the steering torque gain unit 151 and the addition unit 122, the current command value Iref is supplied to the motor torque constant unit 121 and the addition unit 171, and the steering angular speed ω is determined to be increased / returned. The steering angle θ is returned to the steering angle speed calculation unit 111, the increase / return determination unit 141 and the limitation unit 142, the vehicle speed V is returned to the steering angular velocity calculation unit 111, and the viscosity coefficient is output to the unit 141, the limitation unit 142, and the subtraction unit 154. Are input to the unit 131 and the vehicle speed gain unit 152, respectively.

  The return steering angular velocity calculation unit 111 calculates the return steering angular velocity ωt according to the vehicle speed V and the steering angle θ. For example, the steering angular speed ωt is determined from the input vehicle speed V and the steering angle θ based on the characteristics shown in FIG. In the characteristics shown in FIG. 4, since the SAT increases with the steering angle θ, the return steering angular velocity ωt also gradually increases as the steering angle θ increases. Further, the vehicle speed V increases and decreases as the vehicle speed V increases. As described above, since Sat / C can be regarded as the return steering angular velocity ωt, the return steering angular velocity ωt can be calculated by estimating or measuring SAT Sat and dividing by the viscosity coefficient C. good.

  The current command value Iref input to the motor torque constant unit 121 is multiplied by the motor torque constant Kt and output as the assist torque Ta. Then, the assist torque Ta and the steering torque Td are added by the adding unit 122 to become an integrated torque Tc.

  The viscosity coefficient output unit 131 determines the viscosity coefficient C according to the vehicle speed V. For example, the viscosity coefficient C has a characteristic as shown in FIG. 5 and is constant at a small viscosity coefficient C1 at least up to the vehicle speed V1, gradually increases from the vehicle speed V1 to the vehicle speed V2 (> V1), and increases to the vehicle speed V2 or more. Then, it becomes constant with a large viscosity coefficient C2. The characteristic of the viscosity coefficient C is not limited to such a characteristic. The viscosity coefficient C is input to the viscosity characteristic unit 132 and the virtual characteristic unit 133.

The viscosity characteristic unit 132 calculates the integrated steering angular velocity ωc by dividing the integrated torque Tc by the viscosity coefficient C. The integrated rudder angular velocity ωc is added to the return rudder angular velocity −ωt whose sign is reversed by the reversing unit 112 and added by the adding unit 134 and is input to the virtual characteristic unit 133, and the virtual characteristic unit 133 receives the moment of inertia J from the input. Then, using the virtual characteristic defined by the viscosity coefficient C, the target rudder angular velocity ω ₀ is obtained. That is, the adding unit 122, the viscosity characteristic unit 132, the inverting unit 112, the adding unit 134, and the virtual characteristic unit 133 execute Expression 5. Note that if the return steering angular velocity calculation unit 111 calculates the return steering angular velocity ωt so as to be in the direction opposite to the integrated steering angular velocity ωc, the reversing unit 112 is unnecessary.

  The increase / return determination unit 141 determines whether the steering wheel is steered in the increasing direction, steered in the return direction, or in the steered state based on the steering angular speed ω and the steering angle θ. The determination results Js are output as “increase”, “return”, or “maintain”, respectively. That is, if the rudder angle θ or the rudder angular speed ω is substantially 0, “steering”, otherwise (not “steering”), if the signs of the rudder angle θ and the rudder angular speed ω match, If it does not match, it is determined as “turnback”.

The limiting unit 142 limits the target rudder angular velocity ω ₀ based on the determination result Js, the rudder angular velocity ω, and the rudder angle θ from the increase / return determination unit 141, and sets the limited target rudder angular velocity ω ₀ ′. Output, and the deviation (post-limit deviation) SG1 (= ω ₀ ′ −ω) between the limited target steering angular speed ω ₀ ′ and the steering angular speed ω is obtained by the subtraction unit 154. Details of the restriction unit 142 will be described later.

  The steering torque gain unit 151 outputs a steering torque gain Th according to the steering torque Td. For example, the steering torque gain Th has a characteristic as shown in FIG. 6 and is a constant value gain Th1 until the steering torque Td exceeds T1, and gradually decreases when it exceeds T1, and becomes a gain 0 when T2 or more. Yes.

  The vehicle speed gain unit 152 outputs a vehicle speed gain KP according to the vehicle speed V. For example, the vehicle speed gain KP has a characteristic as shown in FIG. 7 and is constant at a small gain KP1 at least up to the vehicle speed V3, gradually increases above the vehicle speed V3, and constant at a large gain KP2 above the vehicle speed V4. It is not limited to such characteristics.

  Both the steering torque gain Th and the vehicle speed gain KP are input to the multiplier 153 and the limiter 163.

  The steering wheel return control deviation SG2 from the multiplication unit 153 obtained by multiplying the deviation SG1 by the steering torque gain Th and the vehicle speed gain KP is input to the addition unit 164 and also input to the integration control unit 161 for improving characteristics. The signal SG4 that is input to the limiter 163 via the unit 162 and whose output is limited according to the steering torque gain Th and the vehicle speed gain KP by the limiter 163 is added to the steering wheel return control deviation SG2 by the adding unit 164, and the steering wheel return control current Output as HR. The integration compensates for the low steering torque range that is easily affected by friction, and makes use of the integration especially in the region where it loses friction by hand. An adder 171 adds and corrects (compensates) the handle return control current HR to the current command value Iref, and the corrected compensation current command value Irefn is input to the motor drive system. In order to remove noise, the handle return control current HR may be input to the adder 171 after passing through, for example, a low-pass filter.

  In the configuration example shown in FIG. 3, the motor torque constant unit 121 and the addition unit 122 constitute an integrated torque calculation unit, and the viscosity coefficient output unit 131, the viscosity characteristic unit 132, the virtual characteristic unit 133, and the addition unit 134 serve as steering system characteristics. The steering angle gain limiting unit is configured by the increase / return determination unit 141 and the limiting unit 142, and the steering wheel gain control unit 151, the vehicle speed gain unit 152, the multiplying unit 153, and the subtracting unit 154 handle the steering wheel return control deviation. The calculation unit is configured, and the integral control unit 161, the integral gain unit 162, the limiter 163, and the addition unit 164 form a handle return control current calculation unit.

  Here, details of the restricting unit 142 will be described.

Limiting section 142, the target steering angular velocity omega _0, so that the target steering angular velocity omega ₀ and the steering angular velocity omega deviation (pre-limitation deviation) does not become excessively large, by setting a limit value for the deviation, limit multiply. The limit value is such that the magnitude of the damping limit value is larger than the magnitude of the return limit value (hereinafter referred to as “condition 1”), and the magnitude of the damping limit value is determined by the steering angular speed ω. In order to increase as the speed increases (hereinafter referred to as “Condition 2”), and further, the magnitude of the damping limit value at the time of increase is smaller than the magnitude of the damping limit value at the time of return (hereinafter referred to as “Condition 2”). 3 ”). In the situation of switchback, when the steering angle θ is positive, the value is negative or when the steering angle θ is negative, the limit value for the deviation that is positive is set as the return limit value, and the steering angular speed ω is In a fast situation, when the steering angle θ is positive, the value is positive, or when the steering angle θ is negative, the limit value for the deviation is negative as the damping limit value. Prepare another damping limit value to satisfy the above three conditions. For example, when the steering angle θ is positive, the limit value is a characteristic as shown in FIG. FIG. 8 is a characteristic diagram in which the vertical axis is the limit value and the horizontal axis is the absolute value | ω | of the rudder angular velocity ω. The solid line is the return limit value, and the broken line is the damping limit value at the time of return ”Is the damping limit value when the one-dot chain line is increased (hereinafter referred to as“ additional damping limit value ”). Note that the damping limit value is a name when the steering angular speed ω is high (when the absolute value of the steering angular speed | ω | is large), but hereinafter, it will be referred to as a damping limit value even when the steering angular speed ω is low. . As shown in FIG. 8A, the return limit value is a constant value, and the damping limit value is a constant value (may be zero) until | ω | is a predetermined value | ω1 | It increases in proportion to ω |. The cutoff damping limit value is smaller than the return damping limit value. When the steering angle θ is negative, the sign of the limit value is reversed, and the limit value has characteristics as shown in FIG. The characteristic of the limit value is not limited to the characteristic as shown in FIG. 8, and may be a characteristic including a curve or the like as long as the above three conditions are satisfied, and may be a characteristic satisfying at least condition 1. In the case of characteristics satisfying at least condition 1, the damping limit value may be a constant value.

The limiting unit 142 limits the target rudder angular velocity ω ₀ by using the characteristics shown in FIG. A configuration example of the limiting unit 142 is shown in FIG. The limiting unit 142 first obtains a deviation Δω between the target rudder angular velocity ω ₀ and the rudder angular velocity ω by the subtracting unit 149. Then, the sign of the steering angle θ and the sign of the deviation Δω are obtained by the sign parts 145 and 146, respectively, and the limit value to be used is determined based on the sign and the determination result Js from the increase / return determination part 141. The limit execution unit 148 limits the deviation Δω using the determined limit value Lt. That is, when the determination result Js is “switchback”, if the steering angle θ is positive and the deviation Δω is positive, the switchback damping limit value in FIG. 8A (hereinafter referred to as “switchback damping limit value 1”). If the steering angle θ is positive and the deviation Δω is negative, the return limit value shown in FIG. 8A is used. If the steering angle θ is negative and the deviation Δω is positive, the same return limit value is used. If θ is negative and deviation Δω is negative, the switchback damping limit value (hereinafter referred to as “switchback damping limit value 2”) in FIG. 8B is used. When the determination result Js is “additional increase”, if the steering angle θ is positive and the deviation Δω is positive, the additional damping limit value (hereinafter referred to as “additional damping limit value 1”) in FIG. 8A is used. If the steering angle θ is positive and the deviation Δω is negative or the steering angle θ is negative and the deviation Δω is positive, the return limit value is used. If the steering angle θ is negative and the deviation Δω is negative, the return value shown in FIG. The additional damping limit value (hereinafter referred to as “additional damping limit value 2”) is used. When the determination result Js is “steering”, the return limit value is used. Then, the limited deviation Δω is added to the target steering angular velocity ω ₀ by the adding unit 150 to calculate the limited target steering angular velocity ω ₀ ′. The limiting unit 142 may be realized as a program inside the CPU, instead of the configuration shown in FIG.

The reason for limiting the target steering angular velocity ω ₀ by the limiting unit 142 in this way will be described by taking a case where the steering angle θ is positive as an example.

FIGS. 10A, 10B, and 10C are diagrams showing temporal changes in the steering angle θ, the steering angular speed ω, and the target steering angular speed ω ₀ , where the solid line is the steering angle θ, the broken line is the steering angular speed ω, A one-dot chain line is the target rudder angular velocity ω ₀ . FIG. 10D is a diagram showing a change over time in the deviation Δω between the target steering angular velocity ω ₀ and the steering angular velocity ω in FIGS. 10A and 10B, and FIG. It is a figure showing the time change of deviation (DELTA) omega in C).

FIG. 10A shows a case where the restriction by the restriction unit 142 is not applied, and the deviation Δω is large in the vicinity of the time point t1, thereby increasing the amount of compensation in the steering wheel return control, which may cause a sense of incongruity. There is. Therefore, if the magnitude of the steering speed omega is less than the magnitude of the target steering angular velocity omega _0, so that the deviation Δω is not increased, the target steering angular velocity omega _0, as the two-dot chain line in FIG. 10 (B) restriction To do. That is, in this case, as shown in FIG. 10D, since the steering angle θ is positive and the deviation Δω is negative and the compensation amount is output in the direction to return the steering wheel to neutral, the compensation amount does not become too large. As shown by the dotted line, the deviation Δω is limited.

As in the vicinity of the time point t2 in FIG. 10C, the deviation Δω also increases when the rudder angular velocity ω is larger than the target rudder angular velocity ω _{0. In} this case, however, the sudden return is suppressed. In order to keep the deviation Δω large, the restriction on the target rudder angular velocity ω ₀ is released (it is difficult to apply the restriction). That is, in this case, as shown in FIG. 10E, the steering angle θ is positive and the deviation Δω is also positive, and the compensation amount is output in the direction in which the movement of the steering wheel is converged (the direction in which the return is suppressed). Therefore, the deviation Δω is not limited. As described above, since the control is based on the deviation Δω, the larger the deviation Δω, the larger the output of the compensation amount, and the output in the direction to converge the movement of the steering wheel is larger than the output in the direction to return the steering wheel to neutral. It becomes possible to do.

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

  First, the steering torque Td, the current command value Iref, the vehicle speed V, the steering angle θ, and the steering angular speed ω are input (read) (step S1), and the steering torque gain unit 151 outputs the steering torque gain Th (step S2). The motor torque constant unit 121 calculates the assist torque Ta by multiplying the current command value Iref by the motor torque constant Kt (step S3), and the addition unit 122 adds the steering torque Td to calculate the integrated torque Tc (step S4). ) And output to the viscosity characteristic section 132.

Further, the return steering angular speed calculation unit 111 obtains the return steering angular speed ωt based on the input steering angle θ and the vehicle speed V (step S5), and the reversing unit 112 inverts the sign of the return steering angular speed ωt (step S6). , Input to the adder 134. The vehicle speed gain unit 152 outputs the vehicle speed gain KP according to the vehicle speed V (step S7), and the viscosity coefficient output unit 131 outputs the viscosity coefficient C according to the vehicle speed V (step S8). The viscosity coefficient C is input to the viscosity characteristic unit 132 and the virtual characteristic unit 133. The viscosity characteristic unit 132 divides the input integrated torque Tc by the viscosity coefficient C to calculate the integrated steering angular velocity ωc (step S9) and adds Output to the unit 134. The return rudder angular velocity -ωt and the integrated rudder angular velocity ωc whose signs are reversed are added by the adding unit 134 (step S10), and the virtual characteristic unit 133 obtains the target rudder angular velocity ω ₀ using the virtual characteristic (step S11). The target rudder angular velocity ω ₀ is input to the limiting unit 142.

  The increase / return determination unit 141 inputs the steering angular velocity ω and the steering angle θ, determines the steering direction of the steering wheel based on them (step S12), and outputs the determination result Js.

The restriction unit 142 inputs the steering angular speed ω, the steering angle θ, the target steering angular speed ω _0, and the determination result Js, and performs a restriction process (step S13). The restriction process will be described with reference to the flowchart of FIG.

The limiting unit 142 obtains a deviation Δω between the target rudder angular velocity ω ₀ and the rudder angular velocity ω by the subtracting unit 149 (step S101). Then, the sign 145 and 146 obtain the sign of the steering angle θ and the sign of the deviation Δω, respectively, and the limit value determination part 147 confirms the determination result Js (step S102). When the determination result Js is “switchback” If the steering angle θ is positive (step S103) and the deviation Δω is positive (step S104), the limit execution unit 148 limits the deviation Δω using the return damping limit value 1 (step S105). If Δω is negative (step S104), the deviation Δω is limited using the return limit value (step S106). If the steering angle θ is negative (step S103) and the deviation Δω is positive (step S107), the deviation Δω is limited using the return limit value (step S108), and if the deviation Δω is negative (step S107). Then, the deviation Δω is limited using the cut-back damping limit value 2 (step S109). When the determination result Js is “increase”, if the steering angle θ is positive (step S110) and the deviation Δω is positive (step S111), the deviation Δω is limited using the increase damping limit value 1 ( If the deviation Δω is negative (step S111), the deviation Δω is limited using the return limit value (step S113). If the steering angle θ is negative (step S110) and the deviation Δω is positive (step S114), the deviation Δω is limited using the return limit value (step S115), and if the deviation Δω is negative (step S114). Then, the deviation Δω is limited using the additional damping limit value 2 (step S116). When the determination result Js is “steering”, the deviation Δω is limited using the return limit value (step S117). The limit execution unit 148 applies a limit to the deviation Δω when the deviation Δω exceeds the limit value (when the absolute value of the deviation Δω is greater than the absolute value of the limit value), and the limit value is set to the deviation Δω. Otherwise, the deviation Δω is left as it is. The limited deviation Δω is added to the target rudder angular velocity ω ₀ by the adding unit 150 to calculate the restricted target rudder angular velocity ω ₀ ′ (step S118).

The limited target rudder angular velocity ω ₀ ′ is added to the subtractor 154, and a deviation SG1 from the subtracted rudder angular velocity ω is obtained (step S14), and the deviation SG1 is input to the multiplier 153. A steering torque gain Th and a vehicle speed gain KP are input to the multiplication unit 153, and a steering wheel return control deviation SG2 is obtained by multiplying them (step S15). The handle return control deviation SG2 is integrated by the integration controller 161 (step S16), further multiplied by the integration gain KI (step S17), and limited by the limiter 163 (step S18).

  The signal SG4 subjected to the limit processing by the limiter 163 is input to the adding unit 164, added to the handle return control deviation SG2 (step S19), and the handle return control current HR is output (step S20). The adding unit 171 corrects the steering wheel return control current HR by adding it to the current command value Iref, and outputs a compensation current command value Irefn (step S21).

  Note that the order of data input, calculation, and processing in FIGS. 11 and 12 can be changed as appropriate.

  It is also possible to change the limit value for the deviation between the target rudder angular speed and the rudder angular speed depending on the vehicle speed, the rudder angle, and / or the rudder angular speed.

  The SAT changes depending on the vehicle speed, and the assist torque also changes in a general vehicle speed-sensitive electric power steering apparatus. Therefore, the steering wheel return also changes due to these changes, and by changing the limit value according to the vehicle speed, a smooth steering wheel return can be realized in a wide vehicle speed range.

  By changing the limit value according to the rudder angle, in the off-center area where the vehicle characteristics greatly appear, even when the handle is returned to neutral or when the movement of the handle is converged, a further control effect can be obtained. . Further, even in the on-center region where the influence of friction becomes large, a further control effect can be expected.

  As shown in FIG. 8, the limit value is changed to some extent according to the steering angular speed. However, in order to create a reaction feeling when shifting from increasing to switching back, the limit value is further set to the steering angular speed. Change accordingly. There is a time range when shifting from increasing to returning to steering, but there is a steering area where the steering angular speed is always zero.Therefore, by changing the limit value according to the steering angular speed, It becomes possible to create a reaction force. This also provides the effect of compensating for static friction.

  FIG. 13 shows a configuration example (second embodiment) of the steering wheel return control unit 200 when the limit value is changed depending on the vehicle speed, the steering angle, and the steering angular speed. Compared to the configuration example of the first embodiment shown in FIG. 3, the limiting unit 142 is replaced with the limiting unit 242, and the vehicle speed V is also input to the limiting unit 242. Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  The limit unit 242 has a limit value set for each arbitrary vehicle speed in order to change the limit value depending on the vehicle speed, and in order to change the limit value according to the steering angle and the steering angular speed, the steering angle gain unit 243 and the steering angular speed A gain unit 244 is provided.

  As the limit value set for each arbitrary vehicle speed, for example, as shown in FIG. 14, a plurality of damping limit values and return limit values are prepared for each of the return time and the increase time that are changed according to the vehicle speed. . When there is no limit value corresponding to the input vehicle speed V, this is dealt with by using the limit value of the nearest vehicle speed, using the limit value interpolated from the prepared limit value, or the like.

  The steering angle gain unit 243 determines the steering angle gain Ga according to the steering angle θ. For example, it has characteristics as shown by the solid line in FIG. 15, and the steering angle gain Ga increases as the steering angle θ increases. Note that the characteristic of the steering angle gain Ga is not limited to such a characteristic. For example, as shown by the broken line in FIG. 15, when the steering angle θ is small, the characteristic decreases as the steering angle θ increases. Thereafter, the characteristics may be increased.

  The steering angular speed gain unit 244 determines the steering angular speed gain Gv according to the steering angular speed ω. For example, it has characteristics as shown in FIG. 16, and as the steering angular speed ω increases, the steering angular speed gain Gv decreases and becomes constant after a predetermined steering angular speed. Note that the characteristic of the steering angular speed gain Gv is not limited to such a characteristic.

  The limiter 242 limits the deviation Δω using a limit value obtained by multiplying the limit value set according to the vehicle speed V by the steering angle gain Ga and the steering angle speed gain Gv.

  The operation of the second embodiment differs from the operation of the first embodiment in the operation of the restriction process in the restriction unit.

  FIG. 17 shows an operation example of the restriction process in the second embodiment. Compared with the limiting process in the first embodiment shown in FIG. 12, in the operation of limiting the deviation Δω using the limiting value (steps S105, S106, S108, S109, S112, S113, S115, S116, S117). There is a change in the operation of determining the limit value to be executed (steps S121, S123, S125, S127, S129, S131, S133, S135, S137), and gain multiplication between the limit value determination and the limit execution (step S122, The operations of S124, S126, S128, S130, S132, S134, S136, and S138) are added. In the limit value determination, a limit value to be used is determined according to the input vehicle speed V. For example, in step S121, the switchback damping limit value 1 corresponding to the vehicle speed V is used. In the gain multiplication, the limit value determined by the limit value determination is multiplied by the steering angle gain Ga corresponding to the steering angle θ and the steering angular speed gain Gv corresponding to the steering angular speed ω. The deviation Δω is limited using the limit values obtained by these operations.

  Note that the change in the limit value depending on the vehicle speed may be performed by gain multiplication, similarly to the change in the limit value depending on the steering angle and the steering angular speed. In this case, the gain for the damping limit value and the return limit value may be the same or different. The change of the limit value depending on the steering angle and the steering angle speed may be performed by a method of setting the limit value for each arbitrary steering angle or steering angle speed, similarly to the change of the limit value depending on the vehicle speed. The limit value may be changed not by gain multiplication but by offset addition / subtraction. In the above description, the limit value is changed using all of the vehicle speed, the steering angle, and the steering angular speed. However, the limit value may be changed using at least one.

  In the above-described embodiments (the first embodiment and the second embodiment), the steering angular speed can be obtained by the motor angular speed × the gear ratio, and the virtual characteristics are the vehicle speed, the steering angle, the increase / return / remaining state. It may be made variable according to. Further, a virtual friction characteristic may be added to the virtual vehicle model. Furthermore, although I (integral) control calculation is performed on the steering wheel return control deviation, all of P (proportional) control calculation, I control calculation, and D (differentiation) control calculation can be performed. What is necessary is just to perform at least 1 control calculation of PID.

1 Handle 2 Column shaft (steering shaft, handle shaft)
10 Torque sensor 12 Vehicle speed sensor 14 Rudder angle sensor 20 Motor 30 Control unit (ECU)
31 Current command value calculating unit 33 Current limiting unit 34 Compensation signal generating unit 35 PI control unit 36 PWM control unit 37 Inverter 40 CAN
100, 200 Steering wheel return control unit 111 Return steering angular velocity calculation unit 112 Inversion unit 121 Motor torque constant unit 131 Viscosity coefficient output unit 132 Viscosity characteristic unit 133 Virtual characteristic unit 141 Increase / return determination unit 142, 242 Limiting units 145, 146 Sign unit 147 Limit value determination unit 148 Limit execution unit 151 Steering torque gain unit 152 Vehicle speed gain unit 161 Integral control unit 163 Limiter 243 Steering angle gain unit 244 Steering angular velocity gain unit

Claims (9)

In an electric power steering device that calculates a current command value based on a steering torque and a vehicle speed, drives a motor based on the current command value, and assists and controls a steering system by driving control of the motor.
A target steering angular speed is calculated using the steering angle, the vehicle speed, the steering torque, and the current command value, and the steering is performed using the limited target steering angular speed obtained by limiting the target steering angular speed according to the steering angular speed. An electric power steering apparatus comprising: a handle return control unit that calculates a return control current and drives the motor with a compensation current command value obtained by adding the handle return control current to the current command value. The handle return control unit includes:
A return rudder angular velocity calculation unit for calculating a return rudder angular velocity using the rudder angle and the vehicle speed;
An integrated torque calculator that calculates an integrated torque using the steering torque and the current command value;
A steering system characteristic unit that calculates the target rudder angular velocity based on a virtual vehicle model using the return rudder angular velocity and the integrated torque;
A target rudder angular speed limiter that limits the target rudder angular speed by setting a limit value for a deviation before restriction that is a deviation of the target rudder angular speed and the rudder angular speed according to the rudder angular speed;
A steering wheel return control deviation calculating unit that obtains a steering wheel return control deviation by multiplying a post-restriction deviation that is a deviation between the restriction target steering angular speed and the steering angular speed by a vehicle speed gain and a steering torque gain;
Handle return for obtaining the handle return control current by performing at least one control calculation of P control calculation, I control subtraction, and D control calculation for the steering wheel return control deviation and limiting output by the vehicle speed gain and the steering torque gain. The electric power steering apparatus according to claim 1, further comprising a control current calculation unit. The target rudder angular velocity limiter is
When the pre-limit deviation is a return deviation that acts to return the steering wheel to neutral, and the pre-limit deviation is a damping deviation that acts to converge the handle movement compared to the magnitude of the limit value. The electric power steering apparatus according to claim 2, wherein the limit value is set so that a size of the limit value increases. The target rudder angular velocity limiter is
The limit value is set so that the magnitude of the limit value when the pre-limit deviation is the dumping deviation is smaller when the deviation is increased than when the switchback is performed. Electric power steering device. The target rudder angular velocity limiter is
5. The electric power according to claim 3, wherein the limit value is set so that a magnitude of the limit value when the pre-limit deviation is the damping deviation increases as the rudder angular speed increases. Steering device. In the situation of switchback, when the steering angle is positive, the value is negative, or when the steering angle is negative, the value before the limit is positive, the return deviation,
4. The deviation before limit, which is positive when the rudder angle is positive or negative when the rudder angle is negative in the situation where the rudder angular speed is high, is defined as the damping deviation. The electric power steering apparatus according to any one of claims 5 to 6.   The electric power steering apparatus according to claim 2, wherein the limit value is changed according to the vehicle speed.   The electric power steering apparatus according to claim 2, wherein the limit value is changed according to the steering angle. The electric power steering apparatus according to claim 2, wherein the limit value is changed according to the steering angular speed.

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