JP7153239B2 - vehicle steering system - Google Patents

Description

The present invention relates to a high-performance vehicle steering system that achieves a desired steering torque based on the torsion angle of a torsion bar or the like, is unaffected by road conditions, and is unaffected by changes in mechanical system characteristics over time.

An electric power steering system (EPS), which is one type of vehicle steering system, applies an assist force (steering assist force) to the steering system of a vehicle using the rotational force of a motor. The driving force of the controlled motor is applied as an assist force to the steering shaft or the rack shaft by a transmission mechanism including a speed reduction mechanism. Such a conventional electric power steering device performs feedback control of the motor current in order to generate an assist force accurately. Feedback control adjusts the voltage applied to the motor so that the difference between the steering assist command value (current command value) and the motor current detection value is reduced. modulation) control duty adjustment.

A general configuration of an electric power steering apparatus is shown in FIG. 6b and further through hub units 7a, 7b to steerable wheels 8L, 8R. The column shaft 2 having the torsion bar is provided with a torque sensor 10 for detecting the steering torque Ts of the steering wheel 1 and a steering angle sensor 14 for detecting the steering angle θh. 20 is connected to the column shaft 2 via the speed reduction mechanism 3 . A control unit (ECU) 30 that controls the electric power steering apparatus is supplied with power from a battery 13 and receives an ignition key signal via an ignition key 11 . The control unit 30 calculates the current command value of the assist (steering assistance) command based on the steering torque Ts detected by the torque sensor 10 and the vehicle speed Vs detected by the vehicle speed sensor 12, and compensates the current command value. is applied, the current supplied to the EPS motor 20 is controlled by the voltage control command value Vref.

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

The control unit 30 is mainly composed of a CPU (including MCU, MPU, etc.), and general functions executed by programs inside the CPU are shown in FIG.

The functions and operations of the control unit 30 will be described with reference to FIG. 31. 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 Ts and vehicle speed Vs. The current command value Iref1 is input to the current limiter 33 via the adder 32A, the current command value Irefm whose maximum current is limited is input to the subtractor 32B, and the deviation I (= Irefm-Im) is calculated, and the deviation I is input to a PI (proportional integral) control unit 35 for improving steering operation characteristics. A voltage control command value Vref whose characteristics have been 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 driving unit. A current value Im of the motor 20 is detected by the motor current detector 38 and fed back to the subtractor 32B.

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

Thus, in the assist control of the conventional electric power steering device, the steering torque applied by the driver's manual input is detected by the torque sensor as the torsion torque of the torsion bar, and the assist current mainly corresponding to the torque is detected. to control the motor current. However, when the control is performed by this method, the steering torque may vary depending on the steering angle due to the difference in road surface conditions (for example, inclination). Steering torque may also be affected by variations in motor output characteristics due to long-term use.

In order to solve this problem, an electric power steering system as disclosed in Japanese Patent No. 5208894 (Patent Document 1) has been proposed. In the electric power steering apparatus of Patent Document 1, in order to provide an appropriate steering torque based on the tactile characteristics of the driver, the ratio between the steering angle and the steering torque is determined based on the relationship between the steering angle or the steering torque and the amount of response. The target value of the steering torque is set based on the relationship (steering reaction force characteristic map).

Japanese Patent No. 5208894

However, in the electric power steering apparatus of Patent Document 1, the steering reaction force characteristic map must be obtained in advance, and control is performed based on the deviation between the target value of the steering torque and the detected steering torque. Therefore, there is a possibility that the influence on the steering torque remains. In addition, the assist command cannot sufficiently suppress fluctuations in the transmission efficiency of the deceleration mechanism and pinion rack mechanism in the steering system, and fluctuations in the contact resistance (friction) between the tires and the road surface. A driver may perceive this as a variation in steering torque (torque ripple).

The present invention has been made in view of the circumstances described above, and an object of the present invention is to provide a steering wheel that is not affected by road conditions, is not affected by changes in the mechanical characteristics of the steering system due to aging, and is capable of adjusting the steering angle and the like. An object of the present invention is to provide a vehicle steering system capable of easily realizing equivalent steering torque. Furthermore, the torque ripple is intended to be reduced.

The present invention relates to a steering system for a vehicle, which includes at least a torsion bar having an arbitrary spring constant and a sensor for detecting the torsion angle of the torsion bar, and assists and controls a steering system by driving and controlling a motor. is provided with a torsion angle control unit that calculates a motor current command value that causes the torsion angle to follow a target torsion angle, and the torsion angle control unit calculates the deviation between the target torsion angle and the torsion angle a torsion angle feedback compensator for calculating a target torsion angular velocity, a torsion angular velocity calculator for calculating a torsion angular velocity from the torsion angle, and a speed control for calculating a basic motor current command value based on the target torsion angular velocity and the torsion angular velocity. and a torque ripple countermeasure compensator for calculating a first compensated motor current command value by performing filtering on the torsion angle using a filter designed to cope with torque ripple, which is a variation in steering torque. and calculating the motor current command value by subtracting the first compensating motor current command value from the basic motor current command value, and driving and controlling the motor based on the motor current command value. achieved by

The torsion angle control unit further includes a stabilization compensation unit for calculating a second compensation motor current command value by setting a transfer function with respect to the motor angular velocity, and the basic motor current By calculating the motor current command value by compensating the command value with the first compensating motor current command value and the second compensating motor current command value, or by calculating the motor current command value by the torsion angle control section. By further including an output limiter that limits the upper and lower limits, or a target steering torque generator that generates a target steering torque, and the target steering torque that is used by the torsion angle controller, the target twist angle Alternatively, the target steering torque generation unit uses a basic map unit that obtains the first torque signal from the steering angle using a basic map and a damper gain map that is responsive to vehicle speed. a damper calculation section for obtaining a second torque signal based on angular velocity information; and a hysteresis correction section for obtaining a third torque signal having a hysteresis characteristic using the steering state and the steering angle, wherein the first torque signal, By calculating the target steering torque from at least one signal of the second torque signal and the third torque signal, or by the characteristics of the basic map and the hysteresis correction unit being vehicle speed sensitive, or , the target steering torque generation unit further includes a phase compensation unit that performs phase compensation before or after the basic map unit; This can be achieved more effectively by obtaining the first torque signal more effectively.

According to the vehicle steering system of the present invention, speed control is performed on the target torsion angular velocity calculated based on the target torsion angle, so that the torsion angle follows the target torsion angle. A steering torque can be realized, and an appropriate steering torque based on the steering feeling of the driver can be applied.

Further, the torque ripple countermeasure compensator can reduce the torque ripple generated during steering.

1 is a configuration diagram showing an outline of an electric power steering device; FIG. FIG. 2 is a block diagram showing a configuration example inside a control unit (ECU) of the electric power steering device; FIG. 3 is a structural diagram showing an installation example of an EPS steering system and various sensors; It is a block diagram which shows the structural example (1st Embodiment) of this invention. FIG. 3 is a block diagram showing a configuration example of a target steering torque generator; FIG. 5 is a diagram showing an example of characteristics of a basic map; FIG. 5 is a diagram showing an example of characteristics of a damper gain map; FIG. 5 is a diagram showing an example of characteristics of a hysteresis corrector; 4 is a block diagram showing a configuration example of a twist angle control unit; FIG. 4 is a diagram showing an example of setting upper and lower limit values in an output limiter; FIG. It is a flowchart which shows the operation example (1st Embodiment) of this invention. 4 is a flowchart showing an operation example of a target steering torque generator; 4 is a flow chart showing an operation example of a twist angle control unit; FIG. 4 is a Bode diagram showing frequency characteristics of a filter used in a simulation showing the effect of the torque ripple countermeasure compensator. 7 is a graph showing an example of torque input as disturbance torque in a simulation showing the effect of the torque ripple countermeasure compensator. 10 is a graph showing an example of steering torque generated with and without compensation by the torque ripple countermeasure compensator in a simulation showing the effect of the torque ripple countermeasure compensator. It is a block diagram which shows the structural example (2nd Embodiment) of this invention. FIG. 4 is a block diagram showing an example of insertion of a phase compensator; 1 is a configuration diagram showing an outline of an SBW system; FIG. It is a block diagram which shows the structural example (3rd Embodiment) of this invention. It is a block diagram which shows the structural example of a target steering angle production|generation part. It is a block diagram which shows the structural example of a steering angle control part. It is a flowchart which shows the operation example (3rd Embodiment) of this invention.

The present invention is a steering system for a vehicle, which is not affected by road surface conditions and which achieves steering torque equivalent to a steering angle or the like. A desired steering torque is realized by performing control so as to follow .

BEST MODE FOR CARRYING OUT THE INVENTION Below, embodiments of the present invention will be described with reference to the drawings.

First, an installation example of various sensors for detecting information related to an electric power steering device, which is one of the vehicle steering devices according to the present invention, will be described. FIG. 3 is a diagram showing an installation example of the EPS steering system and various sensors, and the column shaft 2 is provided with a torsion bar 2A. A road surface reaction force Fr and road surface information μ act on the steered wheels 8L and 8R. An upper angle sensor is provided on the handle side of the column shaft 2 with the torsion bar 2A interposed therebetween, and a lower angle sensor is provided on the steering wheel side of the column shaft 2 with the torsion bar 2A interposed therebetween. detects the steering wheel angle _θ1 and the _lower angle sensor detects the column angle θ2. The steering angle θh is detected by a steering angle sensor provided above the column shaft ₂ , and from the deviation of the steering wheel angle θ1 and the column angle θ2, the twist angle Δθ of the torsion bar and the torsion bar torque are obtained by the following equations 1 and ₂ . Tt can be obtained. Kt is the spring constant of the torsion bar 2A.

トーションバートルクＴｔは、例えば特開２００８－２１６１７２号公報で示されるトルクセンサを用いて検出することも可能である。なお、本実施形態では、トーションバートルクＴｔを操舵トルクＴｓとしても扱うこととする。

The torsion bar torque Tt can also be detected using a torque sensor disclosed in Japanese Patent Application Laid-Open No. 2008-216172, for example. In this embodiment, the torsion bar torque Tt is treated as the steering torque Ts.

Next, a configuration example of the present invention will be described.

FIG. 4 is a block diagram showing a configuration example (first embodiment) of the present invention. Steering by the driver is assist-controlled by a motor in the EPS steering system/vehicle system 100 . In addition to the steering angle θh, the target steering torque generator 120 that outputs the target steering torque Tref receives the vehicle speed Vs and the right-turn or left-turn steering state STs output from the right-turn/left-turn determination unit 110 . be. The target steering torque Tref is converted into a target torsion angle Δθref by the conversion unit 130, and the target torsion angle Δθref is input to the torsion angle control unit 140 together with the torsion angle Δθ of the torsion bar 2A and the motor angular velocity ωm. The torsion angle control unit 140 calculates a motor current command value Imc such that the torsion angle Δθ becomes the target torsion angle Δθref, and the EPS motor is driven by the motor current command value Imc.

The right-turn/left-turn determination unit 110 determines whether the steering is right-turn or left-turn based on the motor angular velocity ωm, and outputs the determination result as the steering state STs. That is, when the motor angular velocity ωm has a positive value, it is determined as "right turning", and when it has a negative value, it is determined as "left turning". Instead of the motor angular velocity ωm, an angular velocity calculated by performing _a velocity calculation _on the steering angle θh, the steering wheel angle θ1, or the column angle θ2 may be used.

FIG. 5 shows a configuration example of the target steering torque generation section 120. The target steering torque generation section 120 includes a basic map section 121, a differentiation section 122, a damper gain section 123, a hysteresis correction section 124, a multiplication section 125 and an addition section 126. and 127, the steering angle θh is input to the basic map portion 121, the differentiation portion 122, and the hysteresis correction portion 124, and the steering state STs output from the right turn/left turn determination portion 110 is input to the hysteresis correction portion 124. .

The basic map unit 121 has a basic map, and uses the basic map to output a torque signal (first torque signal) Tref_a having the vehicle speed Vs as a parameter as shown in FIG. That is, the magnitude of the torque signal Tref_a increases as the magnitude (absolute value) |θh| of the steering angle θh increases, and also increases as the vehicle speed Vs increases. The magnitude of the torque signal Tref_a is multiplied by the sign from the sign section 121A for calculating the sign (+1, -1) of the steering angle θh in the multiplication section 121B, and the torque signal Tref_a is output. In FIG. 6, the map is configured by the magnitude |θh| of the steering angle θh, but the map may be configured according to the positive or negative steering angle θh. You may change the aspect of a change with a negative case. Further, although the basic map shown in FIG. 6 is vehicle speed sensitive, it does not have to be vehicle speed sensitive.

The differentiation unit 122 differentiates the steering angle θh to calculate a steering angular velocity ωh, which is angular velocity information, and the steering angular velocity ωh is input to the multiplication unit 125 .

A damper gain section 123 outputs a damper gain DG to be multiplied by the steering angular velocity _ωh . The steering angular velocity _ωh multiplied by the damper gain DG in the multiplier 125 is input to the adder 127 as a torque signal (second torque signal) Tref_b. The damper gain _DG is obtained according to the vehicle speed Vs using the vehicle speed sensitive damper gain map of the damper gain section 123 . The damper gain map has a characteristic of gradually increasing as the vehicle speed Vs increases, as shown in FIG. 7, for example. The damper gain map may be variable according to the steering angle θh. The damper gain section 123 and the multiplication section 125 constitute a damper calculation section.

The hysteresis correction unit 124 calculates a torque signal (third torque signal) Tref_c according to Equation 3 below based on the steering angle θh and the steering state STs. In Equation 3 below, x=θh, y=Tref_c, a>1, c>0, and _Ahys is the hysteresis width.

右切り操舵から左切り操舵、左切り操舵から右切り操舵へ切り替える際に、最終座標（ｘ１，ｙ１）の値に基づき、切り替え後の数３の“ｂ”に以下の数４を代入する。これにより、切り替え前後の連続性が保たれる。

When switching from right-turn steering to left-turn steering and from left-turn steering to right-turn steering, the following equation 4 is substituted for "b" in equation 3 after switching based on the values of the final coordinates (x1, y1). This maintains continuity before and after switching.

上記数４は、上記数３中のｘにｘ１を、ｙ_Ｒ及びｙ_Ｌにｙ１を代入することにより導出することができる。

Equation 4 above can be derived by substituting x1 for x and y1 for _yR and _yL in Equation 3 above.

Any positive number greater than 1 can be used as "a". For example, when Napier's number "e" is used, Equations 3 and 4 become Equations 5 and 6 below.

数５及び数６においてＡ_ｈｙｓ＝１［Ｎｍ］、ｃ＝０．３と設定し、０［ｄｅｇ］から開始し、＋５０［ｄｅｇ］、－５０［ｄｅｇ］の操舵をした場合の、ヒステリシス補正されたトルク信号Ｔｒｅｆ＿ｃの線図例を図８に示す。即ち、ヒステリシス補正部１２４からのトルク信号Ｔｒｅｆ＿ｃは、０の原点→Ｌ１（細線）→Ｌ２（破線）→Ｌ３（太線）のようなヒステリシス特性である。

Set A _hys = 1 [Nm] and c = 0.3 in Equations 5 and 6, start from 0 [deg], and hysteresis correction when steering +50 [deg], -50 [deg] FIG. 8 shows an example diagram of the torque signal Tref_c. That is, the torque signal Tref_c from the hysteresis correction unit 124 has hysteresis characteristics such as the origin of 0→L1 (thin line)→L2 (dashed line)→L3 (thick line).

The coefficient A _hys representing the output width of the hysteresis characteristic and the coefficient c representing the roundness may be variable according to the vehicle speed Vs and/or the steering angle θh.

Adders 126 and 127 add the torque signals Tref_a, Tref_b, and Tref_c, and the addition result is output as the target steering torque Tref.

Although the steering angular velocity ωh is obtained by differential calculation with respect to the steering angle θh, it is appropriately subjected to low-pass filter (LPF) processing in order to reduce the influence of high-frequency noise. Alternatively, the differential operation and LPF processing may be performed using a high-pass filter (HPF) and gain. Further, the steering angular velocity ωh is not calculated from the steering angle θh, but is calculated by performing differentiation and LPF processing on the steering wheel angle θ1 detected by the _upper angle sensor or the column angle θ2 detected by the _lower angle sensor. Also good. The motor angular velocity ωm may be used as the angular velocity information instead of the steering angular velocity ωh, in which case the differentiating section 122 becomes unnecessary.

Conversion unit 130 has a characteristic of -1/Kt, which is the reciprocal of the spring constant Kt of torsion bar 2A, and converts target steering torque Tref into target twist angle Δθref.

The torsion angle control unit 140 calculates a motor current command value Imc based on the target torsion angle Δθref, the torsion angle Δθ, and the motor angular velocity ωm. FIG. 9 is a block diagram showing a configuration example of the torsion angle control unit 140. The torsion angle control unit 140 includes a torsion angle feedback (FB) compensation unit 141, a torsion angular velocity calculation unit 142, a speed control unit 150, and a torque ripple countermeasure compensation unit. 143, a stabilization compensator 144, an output limiter 145, subtractors 146 and 147, and an adder 148. Δθ is subtracted and input to the subtractor 146 , is input to the torsional angular velocity calculator 142 and the torque ripple countermeasure compensator 143 , and the motor angular velocity ωm is input to the stabilization compensator 144 .

The torsion angle FB compensation unit 141 multiplies the deviation Δθ ₀ between the target torsion angle Δθref and the torsion angle Δθ calculated by the subtraction unit 146 by a compensation value C _FB (transfer function) to obtain the torsion angle Δθ outputs a target torsional angular velocity ωref that follows. The compensation value CFB may be a simple gain _Kpp or a generally used compensation value such as a PI control compensation value. The target torsional angular velocity ωref is input to the velocity controller 150 . The torsion angle FB compensation section 141 and the speed control section 150 allow the torsion angle Δθ to follow the target torsion angle Δθref, thereby realizing a desired steering torque.

The torsion angular velocity calculator 142 calculates a torsion angular velocity ωt by differential calculation with respect to the torsion angle Δθ, and the torsion angular velocity ωt is input to the velocity controller 150 . Pseudo-differentiation using HPF and gain may be performed as the differential operation. Alternatively, the torsion angular velocity ωt may be calculated by another means or other than the torsion angle Δθ and input to the velocity control section 150 .

The speed control unit 150 calculates a motor current command value (basic motor current command value) Imca0 such that the torsional angular velocity ωt follows the target torsional angular velocity ωref by IP control (proportional leading PI control). The difference (ωref-ωt) between the target twist angular velocity ωref and the twist angular velocity ωt is calculated by the subtraction unit 153, the difference is integrated by the integration unit 151 having the gain Kvi, and the integration result is added to the subtraction unit 154. be. The torsional angular velocity ωt is also input to the proportional section 152 , subjected to proportional processing by the gain Kvp, and subtracted and input to the subtracting section 154 . The result of subtraction by subtraction unit 154 is output as motor current command value Imca0. Note that the speed control unit 150 performs PI control, P (proportional) control, PID (proportional-integral-derivative) control, PI-D control (differential-preceding PID control), model matching control, and model reference control, instead of IP control. The motor current command value Imca0 may be calculated by a commonly used control method such as control.

The torque ripple compensation unit 143 performs filtering on the torsion angle Δθ and calculates a motor current command value (first compensation motor current command value) Imca1. By subtracting the motor current command value Imca1 from the motor current command value Imca0 in the subtraction unit 147, the motor current command value is compensated and the torque ripple is reduced. Variations in steering torque (torque ripple) due to variations in the transmission efficiency of the steering mechanism and variations in the contact resistance between the tire and the road surface appear in the torsion angle Δθ. Therefore, the torque ripple can be reduced by appropriately filtering the torsion angle Δθ and compensating the motor current command value in the direction in which the torsion angle Δθ becomes smaller. As a filter, we use a first-order filter with a transfer function C _trq expressed by Equation 7 below.

ここで、Ｋ_ｔｒｑはゲイン、Ｔｎ及びＴｄは時定数であり、これらは予め設定されている。ｓはラプラス演算子である。なお、フィルタの次数は２次以上でも良い。

Here, _Ktrq is a gain, Tn and Td are time constants, which are set in advance. s is the Laplacian operator. Note that the order of the filter may be second or higher.

The stabilization compensator 144 has a compensation value Cs (transfer function) and calculates a motor current command value (second compensation motor current command value) Imca2 from the motor angular velocity ωm. If the gains of the torsion angle FB compensator 141 and the speed controller 150 are increased in order to improve followability and disturbance characteristics, a controllable high-frequency oscillation phenomenon occurs. As a countermeasure, a transfer function (Cs) necessary for stabilizing the motor angular velocity ωm is set in the stabilization compensator 144 . This makes it possible to stabilize the entire EPS control system. As the transfer function (Cs) of the stabilization compensator 144, for example, a first-order filter represented by Equation 8 below, which is set by pseudo-differentiation using a first-order HPF structure and gain, is used.

ここで、Ｋ_ｓｔａはゲインで、ｆｃは遮断周波数であり、ｆｃとして例えば１５０［Ｈｚ］を設定する。なお、伝達関数として、２次フィルタ、４次フィルタ等を使用しても良い。

Here, _Ksta is a gain, fc is a cutoff frequency, and fc is set to 150 [Hz], for example. A second-order filter, a fourth-order filter, or the like may be used as the transfer function.

The motor current command value Imca calculated by subtracting the motor current command value Imca1 from the motor current command value Imca0 in the subtraction unit 147 and the motor current command value Imca2 are added in the addition unit 148 and output as the motor current command value Imcb. be.

Output limiter 145 limits the upper and lower limits of motor current command value Imcb and outputs motor current command value Imc. As shown in FIG. 10, an upper limit value and a lower limit value for the motor current command value are set in advance. otherwise, the motor current command value Imcb is output as the motor current command value Imc.

In such a configuration, an operation example of this embodiment will be described with reference to the flow charts of FIGS. 11 to 13. FIG.

When the operation is started, the right-turn/left-turn determination unit 110 receives the motor angular velocity ωm, determines whether the steering is right-turned or left-turned based on the sign of the motor angular velocity ωm, and uses the determination result as the steering state STs. Output to the target steering torque generator 120 (step S10).

The target steering torque generator 120 receives the steering angle θh and the vehicle speed Vs along with the steering state STs, and generates a target steering torque Tref (step S20). An example of the operation of the target steering torque generator 120 will be described with reference to the flowchart of FIG.

The steering angle θh inputted to the target steering torque generating section 120 is inputted to the basic map section 121, the differentiation section 122 and the hysteresis correction section 124, the steering state STs is inputted to the hysteresis correction section 124, and the vehicle speed Vs is inputted to the basic map section 121 and the damper gain section 123. , respectively (step S21).

The basic map unit 121 uses the basic map shown in FIG. 6 to generate a torque signal Tref_a corresponding to the steering angle θh and the vehicle speed Vs, and outputs it to the addition unit 126 (step S22).

The differentiating unit 122 differentiates the steering angle θh to output the steering angular velocity _ωh (step S23), and the damper gain unit 123 outputs the damper gain DG according to the vehicle speed Vs using the damper gain map shown in FIG. S24), the multiplication unit 125 multiplies the steering angular velocity _ωh and the damper gain DG to calculate the torque signal Tref_b, and outputs it to the addition unit 127 (step S25).

The hysteresis correction unit 124 performs hysteresis correction on the steering angle θh by switching between calculations based on Equations 5 and 6 according to the steering state STs (step S26), generates a torque signal Tref_c, and sends the torque signal Tref_c to the addition unit 127. Output (step S27). Although the hysteresis widths A _hys , c, x1 and y1 in Equations 5 and 6 are set and held in advance, b and b′ are calculated in advance from Equation 6, and b and b′ are calculated instead of x1 and y1. may be held.

The addition unit 127 adds the torque signals Tref_b and Tref_c, and the addition unit 126 adds the torque signal Tref_a to the addition result to calculate the target steering torque Tref (step S28).

The target steering torque Tref generated by the target steering torque generation unit 120 is input to the conversion unit 130, where it is converted into the target torsion angle Δθref (step S30). The target twist angle Δθref is input to the twist angle control section 140 .

The torsion angle control unit 140 inputs the torsion angle Δθ and the motor angular velocity ωm along with the target torsion angle Δθref, and calculates the motor current command value Imc (step S40). An operation example of the twist angle control section 140 will be described with reference to the flowchart of FIG. 13 .

The target torsion angle Δθref input to the torsion angle control unit 140 is supplied to the subtraction unit 146, the torsion angle Δθ is supplied to the subtraction unit 146, the torsion angular velocity calculation unit 142 and the torque ripple countermeasure compensation unit 143, and the motor angular velocity ωm is supplied to the stabilization compensation unit 144. Each is input (step S41).

The subtraction unit 146 calculates the deviation Δθ ₀ by subtracting the torsion angle Δθ from the target torsion angle Δθref (step S42). The deviation Δθ ₀ is input to the torsion angle FB compensator 141, and the torsion angle FB compensator 141 multiplies the deviation Δθ ₀ by the compensation value C _FB to compensate for the deviation Δθ ₀ (step S43), and the target torsion angular velocity ωref is output to the speed control unit 150 .

The torsion angular velocity calculation unit 142 having received the torsion angle Δθ calculates a torsion angular velocity ωt by differential calculation with respect to the torsion angle Δθ (step S 44 ), and outputs it to the speed control unit 150 .

In the speed control unit 150, the difference between the target torsional angular velocity ωref and the torsional angular velocity ωt is calculated by the subtracting unit 153, the difference is integrated (Kvi/s) by the integrating unit 151, and added to the subtracting unit 154 (step S45). ). Furthermore, the torsional angular velocity ωt is proportionally processed (Kvp) by the proportional unit 152, the proportional result is subtracted and input to the subtracting unit 154 (step S45), and the motor current command value Imca0, which is the subtraction result of the subtracting unit 154, is supplied to the subtracting unit 147. Added input.

The torque ripple countermeasure compensation unit 143 performs filtering on the input torsion angle Δθ using a filter having a transfer function C _trq expressed by Equation 7 to calculate a motor current command value Imca1 (step S46). The command value Imca1 is subtracted and input to the subtractor 147 .

The subtraction unit 147 subtracts the motor current command value Imca1 from the motor current command value Imca0 (step S47), and the motor current command value Imca, which is the subtraction result, is input to the addition unit 148 .

The stabilization compensator 144 performs stabilization compensation on the input motor angular velocity ωm using the transfer function Cs represented by Equation 8 (step S48), and the motor current command value Imca2 from the stabilization compensator 144 is is input to the addition unit 148 .

The adder 148 adds the motor current command values Imca and Imca2 (step S49), and the motor current command value Imcb, which is the addition result, is input to the output limiter 145 . The output limiter 145 limits the upper and lower limits of the motor current command value Imcb by preset upper and lower limits (step S50), and outputs the motor current command value Imc (step S51).

The motor is driven based on the motor current command value Imc output from the torsion angle control unit 140, and current control is performed (step S60).

Note that the order of data input and calculation in FIGS. 11 to 13 can be changed as appropriate.

The effect of the torque ripple countermeasure compensator in this embodiment will be described based on simulation results.

In the simulation, a transfer function having frequency characteristics as shown in FIG. 14 was used as the transfer function C _trq of the filter of the torque ripple countermeasure compensator 143 . In FIG. 14, the horizontal axis is frequency [Hz], the vertical axis is gain [dB] in FIG. 14(A), phase [deg] in FIG. 14(B), and amplitude (gain) in FIG. FIG. 14B is the phase characteristic. Further, in order to confirm the effect of the compensation by the torque ripple countermeasure compensator 143, a torque having an amplitude of 3 Nm and a frequency of 20 Hz as shown in FIG. The generation of steering torque (torsion bar torque) was investigated with and without compensation. In FIG. 15, the horizontal axis is time [sec] and the vertical axis is torque [Nm].

FIG. 16(A) shows a simulation result of the steering torque generated when there is no compensation by the torque ripple countermeasure compensator, and FIG. 16(B) shows a simulation of the steering torque generated when there is compensation by the torque ripple countermeasure compensator. shows the results. As in FIG. 15, in FIG. 16, the horizontal axis is time [sec] and the vertical axis is torque [Nm]. Comparing FIGS. 16A and 16B, it can be seen that the amplitude of the steering torque is smaller in FIG. 16B, and the steering torque can be reduced. Therefore, it can be seen that the pulsation (torque ripple) of the steering torque generated when the disturbance is applied can be reduced by performing the compensation by the torque ripple countermeasure compensator.

Another configuration example of the present invention will be described.

A current command value (hereinafter referred to as "assist current command value") calculated based on the steering torque in the conventional EPS is added to the motor current command value Imc output from the torsion angle control unit in the first embodiment. For example, the current command value Iref1 output from the current command value calculation unit 31 shown in FIG. 2 or the current command value Iref2 obtained by adding the compensation signal CM to the current command value Iref1 may be added.

FIG. 17 shows a configuration example (second embodiment) in which the above contents are applied to the first embodiment. The assist control unit 200 includes a current command value calculation unit 31, or a current command value calculation unit 31, a compensation signal generation unit 34, and an addition unit 32A. Assist current command value Iac output from assist control unit 200 (corresponding to current command value Iref1 or Iref2 in FIG. 2) and motor current command value Imc output from torsion angle control unit 140 are added by adding unit 260. , the current command value Ic, which is the result of the addition, is input to the current limiter 270, and the motor is driven based on the current command value Icm with the maximum current limited, and current control is performed.

Instead of the assist current command value Iac, or together with the assist current command value Iac, a current command value for steering wheel vibration suppression may be added to the motor current command value Imc.

In the target steering torque generation section 120 in the first and second embodiments, at least one of the basic map section 121, the damper calculation section, and the hysteresis correction section 124 is left in the case where cost and processing time are emphasized. , and others may be omitted. When the basic map unit 121 is omitted, the addition unit 126 can also be omitted. When the damper calculation unit is omitted, the differentiation unit 122 and the addition unit 127 can also be omitted. The cut determination unit 110 and the addition unit 127 can also be omitted. Also, a phase compensator 128 that performs phase compensation may be inserted before or after the basic map unit 121 . That is, the configuration of the region R surrounded by the dashed line in FIG. 5 may be changed to the configuration shown in FIG. 18(A) or (B). In the phase compensator 128, when phase lead compensation is set as phase compensation and, for example, phase lead compensation is performed with a primary filter having a numerator cutoff frequency of 1.0 Hz and a denominator cutoff frequency of 1.3 Hz, A clean feel can be achieved. The target steering torque generator is not limited to the above configuration as long as it is based on the steering angle.

Also, if the EPS control system is stable, the stabilization compensator may be omitted. The output limiter can also be omitted.

Although the present invention is applied to a column-type EPS in FIGS. 1 and 3, the present invention is not limited to an upstream-type EPS such as a column-type EPS, and can also be applied to a downstream-type EPS such as a rack and pinion. Furthermore, in terms of performing feedback control based on the target torsion angle, it is also applicable to a steer-by-wire (SBW) reaction force device or the like that includes at least a torsion bar (arbitrary spring constant) and a torsion angle detection sensor. An embodiment (third embodiment) in which the present invention is applied to an SBW reaction force device having a torsion bar will be described.

First, the entire SBW system including the SBW reaction force device will be described. FIG. 19 is a diagram showing a configuration example of the SBW system in correspondence with the general configuration of the electric power steering apparatus shown in FIG. In addition, the same code|symbol is attached|subjected to the same structure, and detailed description is abbreviate|omitted.

The SBW system does not have an intermediate shaft that is mechanically connected to the column shaft 2 at the universal joint 4a, and is a system that transmits the operation of the steering wheel 1 to the steering mechanism consisting of the steerable wheels 8L, 8R, etc. by electrical signals. . As shown in FIG. 19, the SBW system includes a reaction device 60 and a drive device 70, and a control unit (ECU) 50 controls both devices. The reaction force device 60 detects the steering angle θh with the steering angle sensor 14, and at the same time, transmits the motion state of the vehicle transmitted from the steered wheels 8L, 8R to the driver as reaction torque. The reaction torque is generated by the reaction force motor 61 . Some SBW systems do not have a torsion bar in the reaction force device, but the SBW system to which the present invention is applied has a torsion bar, and the torque sensor 10 detects the steering torque Ts. do. Also, the angle sensor 74 detects the motor angle θm of the reaction force motor 61 . The driving device 70 drives a driving motor 71 in accordance with the steering of the steering wheel 1 by the driver, applies the driving force to the pinion rack mechanism 5 via the gear 72, and passes through the tie rods 6a and 6b to drive the driving motor 71. The direction wheels 8L and 8R are steered. An angle sensor 73 is arranged near the pinion rack mechanism 5 to detect the turning angle θt of the steered wheels 8L, 8R. In order to cooperatively control the reaction force device 60 and the drive device 70, the ECU 50 controls the vehicle speed Vs and the like from the vehicle speed sensor 12 in addition to information such as the steering angle θh and the turning angle θt output from both devices. A voltage control command value Vref1 for driving and controlling the reaction force motor 61 and a voltage control command value Vref2 for driving and controlling the drive motor 71 are generated.

A configuration of a third embodiment in which the present invention is applied to such an SBW system will be described.

FIG. 20 is a block diagram showing the configuration of the third embodiment. In the third embodiment, control of the torsion angle Δθ (hereinafter referred to as “torsion angle control”) and control of the turning angle θt (hereinafter referred to as “turning angle control”) are performed to control the reaction force device. It is controlled by angle control, and the driving device is controlled by steering angle control. Note that the driving device may be controlled by other control methods.

In the torsion angle control, the torsion angle Δθ follows the target torsion angle Δθref calculated through the target steering torque generation unit 120 and the conversion unit 130 using the steering angle θh and the like by the same configuration and operation as in the first embodiment. control such as The motor angle θm is detected by the angle sensor 74 , and the motor angular velocity ωm is calculated by differentiating the motor angle θm by the angular velocity calculator 951 . A steering angle θt is detected by an angle sensor 73 . Further, in the first embodiment, the processing in the EPS steering system/vehicle system 100 is not described in detail, but the current control unit 160 includes the subtraction unit 32B, the PI control unit 35, and the PWM control shown in FIG. With the same configuration and operation as the unit 36 and the inverter 37, based on the motor current command value Imc output from the torsion angle control unit 140 and the current value Imr of the reaction force motor 61 detected by the motor current detector 170, Current control is performed by driving the reaction force motor 61 .

In the steering angle control, the target steering angle θtref is generated based on the steering angle θh in the target steering angle generation section 910, and the target steering angle θtref is input to the steering angle control section 920 together with the steering angle θt. , the steering angle control unit 920 calculates a motor current command value Imct that causes the steering angle θt to become the target steering angle θtref. Then, based on the motor current command value Imct and the current value Imd of the drive motor 71 detected by the motor current detector 940, the current control unit 930 controls the drive motor 71 with the same configuration and operation as the current control unit 160. 71 is driven to perform current control.

FIG. 21 shows a configuration example of the target steering angle generation section 910. As shown in FIG. The target steering angle generator 910 includes a limiter 931 , a rate limiter 932 and a corrector 933 .

A limiting unit 931 limits the upper and lower limits of the steering angle θh and outputs the steering angle θh1. Similar to the output limiter 145 in the torsion angle controller 140, the upper limit and lower limit of the steering angle θh are preset and limited.

A rate limiter 932 limits the amount of change in the steering angle θh1 by setting a limit value to avoid a sudden change in the steering angle, and outputs a steering angle θh2. For example, if the amount of change is the difference from the steering angle θh1 one sample before, and the absolute value of the amount of change is greater than a predetermined value (limit value), the steering angle The steering angle .theta.h2 is output by adding or subtracting .theta.h1. If the steering angle .theta.h2 is equal to or less than the limit value, the steering angle .theta.h1 is directly output as the steering angle .theta.h2. Instead of setting a limit value for the absolute value of the amount of change, an upper limit value and a lower limit value may be set for the amount of change to limit the amount of change. You may make it restrict|limit with respect to a rate.

A correction unit 933 corrects the steering angle θh2 and outputs a target steering angle θtref. For example, using a map such as the basic map section 121 in the target steering torque generation section 120 that defines the characteristics of the target steering angle θtref with respect to the magnitude |θh2| of the steering angle θh2, the target steering angle Find the angle θtref. Alternatively, the target steering angle θtref may be obtained simply by multiplying the steering angle θh2 by a predetermined gain.

A configuration example of the turning angle control section 920 is shown in FIG. The steering angle control section 920 has the same configuration as the configuration example of the torsion angle control section 140 shown in FIG. A target steering angle θtref and a steering angle θt are input instead of the target torsion angle Δθref and the torsion angle Δθ, and a steering angle feedback (FB) compensator 921, a steering angular velocity calculator 922, and a speed controller 923, an output limiting unit 926 and a subtracting unit 927 have the same configurations as the torsion angle FB compensating unit 141, the torsion angular velocity calculating unit 142, the speed control unit 150, the output limiting unit 145 and the subtracting unit 146 and perform the same operations.

With such a configuration, an operation example of the third embodiment will be described with reference to the flowchart of FIG.

When the operation starts, the angle sensor 73 detects the steering angle θt, the angle sensor 74 detects the motor angle θm (step S110), the steering angle θt is sent to the steering angle control unit 920, and the motor angle θm is the angular velocity. They are input to the calculation unit 951 respectively.

The angular velocity calculation unit 951 differentiates the motor angle θm to calculate the motor angular velocity ωm, and outputs it to the right-turn/left-turn determination unit 110 and the twist angle control unit 140 (step S120).

Thereafter, the target steering torque generator 120 performs the same operations as steps S10 to S60 shown in FIG. 11 to drive the reaction force motor 61 and perform current control (steps S130 to S170).

On the other hand, in steering angle control, the target steering angle generator 910 inputs the steering angle θh, and the steering angle θh is input to the limiter 931 . The limiting unit 931 limits the upper and lower limits of the steering angle θh with preset upper and lower limits (step S180), and outputs the result to the rate limiting unit 932 as the steering angle θh1. The rate limiter 932 limits the amount of change in the steering angle θh1 by a preset limit value (step S190), and outputs it to the correction unit 933 as the steering angle θh2. The correction unit 933 corrects the steering angle θh2 to obtain the target turning angle θtref (step S200), and outputs the target turning angle θtref to the turning angle control unit 920 .

The turning angle control unit 920, which receives the turning angle θt and the target turning angle θtref, calculates the deviation Δθt ₀ by subtracting the turning angle θt from the target turning angle θtref in the subtraction unit 927 (step S210). The deviation Δθt ₀ is input to the turning angle FB compensator 921, and the turning angle FB compensator 921 multiplies the deviation Δθt ₀ by a compensation value to compensate for the deviation Δθt ₀ (step S220), and obtains the target turning angular velocity. ωtref is output to the speed controller 923 . The steering angular velocity calculator 922 inputs the steering angle θt, calculates the steering angular velocity ωtt by differential calculation with respect to the steering angle θt (step S 230 ), and outputs it to the speed controller 923 . Speed control unit 923 calculates motor current command value Imcta by IP control in the same manner as speed control unit 150 (step S 240 ), and outputs it to output limiting unit 926 . The output limiter 926 limits the upper and lower limits of the motor current command value Imcta by preset upper and lower limits (step S250), and outputs the motor current command value Imct (step S260).

The motor current command value Imct is input to the current control unit 930 , and the current control unit 930 controls the drive motor 71 based on the motor current command value Imct and the current value Imd of the drive motor 71 detected by the motor current detector 940 . 71 is driven to perform current control (step S270).

Note that the order of data input and calculation in FIG. 23 can be changed as appropriate. Further, like the speed control unit 150 in the torsion angle control unit 140, the speed control unit 923 in the turning angle control unit 920 is not IP control, but PI control, P control, PID control, PI control, P control, PID control, and PI control. control, etc., can be realized, and any one of P, I, and D control may be used, and follow-up control by the steering angle control unit 920 and the twist angle control unit 140 is generally used. You can do it with a control structure that has

In the third embodiment, as shown in FIG. 19, one ECU 50 controls the reaction device 60 and the driving device 70. You can set it. In this case, the ECUs transmit and receive data through communication. The SBW system shown in FIG. 19 does not have a mechanical connection between the reaction force device 60 and the drive device 70. However, when an abnormality occurs in the system, the column shaft 2 and the steering mechanism are connected by a clutch or the like. The present invention can also be applied to an SBW system that has a mechanical torque transmission mechanism that mechanically couples at . In such an SBW system, when the system is normal, the clutch is turned off to disengage mechanical torque transmission, and when the system is abnormal, the clutch is turned on to enable mechanical torque transmission.

The torsion angle control unit 140 in the first to third embodiments and the assist control unit 200 in the second embodiment directly calculate the motor current command value Imc and the assist current command value Iac. Before calculating them, the motor torque to be output (target torque) may be calculated first, and then the motor current command value and the assist current command value may be calculated. In this case, in order to obtain the motor current command value and the assist current command value from the motor torque, the generally used relationship between the motor current and the motor torque is used.

1 steering wheel 2 column axis (steering shaft, steering wheel axis)
2A torsion bar 3 speed reduction mechanism 10 torque sensor 12 vehicle speed sensor 14 steering angle sensor 20 motors 30, 50 control unit (ECU)
31 current command value calculators 33, 270 current limiter 34 compensation signal generators 38, 160, 940 motor current detector 60 reaction force device 61 reaction force motor 70 drive device 71 drive motor 72 gears 73, 74 angle sensor 100 EPS steering system/vehicle system 110 right-turn/left-turn determination unit 120 target steering torque generation unit 121 basic map unit 123 damper gain unit 124 hysteresis correction unit 128 phase compensation unit 130 conversion unit 140 torsion angle control unit 141 torsion angle feedback (FB) Compensator 142 Torsional angular velocity calculator 143 Torque ripple countermeasure compensator 144 Stabilization compensator 145, 926 Output limiter 150, 923 Speed controller 160, 930 Current controller 200 Assist controller 910 Target turning angle generator 920 Turning angle Control unit 921 Steering angle feedback (FB) compensator 922 Steering angular velocity calculator 931 Limiter 932 Rate limiter 933 Corrector 951 Angular velocity calculator

Claims (7)

A steering system for a vehicle, which includes at least a torsion bar having an arbitrary spring constant and a sensor for detecting the torsion angle of the torsion bar, and assists and controls a steering system by driving and controlling a motor,
a torsion angle control unit that calculates a motor current command value that causes the torsion angle to follow a target torsion angle;
The torsion angle control unit
a torsion angle feedback compensation unit that calculates a target torsion angular velocity from the target torsion angle and a deviation of the torsion angle;
a torsion angular velocity calculator that calculates a torsion angular velocity from the torsion angle;
a speed control unit that calculates a basic motor current command value based on the target torsional angular velocity and the torsional angular velocity;
Filter processing using a filter designed to deal with torque ripple, which is fluctuations in steering torque. for the torsion anglerowa torque ripple countermeasure compensator for calculating a first compensated motor current command value,
Basic motor current command valuefromThe first compensating motor current command valueto subtractBybeforeCalculate the motor current command value,
A steering system for a vehicle, wherein the driving of the motor is controlled based on the motor current command value. The torsion angle control unit
further comprising a stabilization compensator for setting a transfer function with respect to the motor angular velocity and calculating a second compensating motor current command value;
2. The vehicle steering system according to claim 1, wherein the motor current command value is calculated by compensating the basic motor current command value with the first compensating motor current command value and the second compensating motor current command value. The torsion angle control unit
3. The steering system for a vehicle according to claim 1, further comprising an output limiter for limiting upper and lower limits of said motor current command value. a target steering torque generator that generates a target steering torque;
4. The vehicle steering system according to any one of claims 1 to 3, further comprising a conversion section that converts the target steering torque into the target twist angle used by the twist angle control section. The target steering torque generation unit
a basic map unit that obtains a first torque signal from a steering angle using the basic map;
a damper calculation unit that obtains a second torque signal based on angular velocity information using a damper gain map sensitive to vehicle speed;
a hysteresis correction unit that obtains a third torque signal having a hysteresis characteristic using the steering state and the steering angle;
5. A vehicle steering system according to claim 4, wherein said target steering torque is calculated from at least one of said first torque signal, said second torque signal and said third torque signal. 6. The vehicle steering system according to claim 5, wherein the characteristics of the basic map and the hysteresis correction unit are vehicle speed sensitive. The target steering torque generation unit
further comprising a phase compensation unit that performs phase compensation before or after the basic map unit;
7. The vehicle steering system according to claim 5, wherein the first torque signal is obtained from the steering angle and the vehicle speed via the basic map section and the phase compensation section.

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