JP2010030431A - Control device for electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an electric power steering device capable of presuming a neutral position angle at high accuracy using an SAT detection value by calculating a relative steering angle and a motor angular speed of a steering wheel from a motor angle sensor mounted to a motor for generating steering auxiliary force and capable of simultaneously attaining calculation of an absolute angle. <P>SOLUTION: The control device for the electric power steering device for giving assist torque to a steering mechanism of the vehicle is provided with: a motor angle sensor for detecting the motor angle; an SAT detection means for detecting SAT of the vehicle; a relative steering angle detection part for detecting the relative steering angle of the steering from the motor angle; a steering angle speed detection part for determining a motor angular speed; and a vehicle speed detection part. The control device also includes: a neutral position operation part for performing determination of linear advancement traveling of the vehicle based on the steering angle speed, the SAT detection value and the vehicle speed and performing operation for making the relative steering angle when the linear advancement traveling is continued for a predetermined time or longer as the neutral position angle; and an absolute steering angle operation part for determining an absolute steering angle by difference of the neutral position angle obtained by the neutral position operation part and the relative steering angle. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an improvement in a control device for an electric power steering device that controls a steering assist amount based on a steering torque and a vehicle speed, and in particular, a rudder used for calculation and compensation of a steering assist current command value. The present invention relates to a control device for an electric power steering apparatus having an angle use function and an algorithm function for estimating an absolute steering angle.

  An electric power steering device for assisting a vehicle steering device with a rotational force of a motor is applied to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. The auxiliary load is energized. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist torque). In the feedback control, the motor applied voltage is adjusted so that the difference between the current command value and the detected motor current is small. Generally, the adjustment of the motor applied voltage is a duty of PWM (pulse width modulation) control. This is done by adjusting the tee ratio.

  Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. 8. A steering shaft (column shaft) 2 of the handle 1 is steered through a reduction gear 3, universal joints 4 A and 4 B and a pinion rack mechanism 5. It is connected to the tie rod 6 of the wheel. The steering shaft 2 is provided with a torque sensor 10 that detects the steering torque Th of the handle 1, and a motor 20 that assists the steering force of the handle 1 is connected to the steering shaft 2 via the reduction gear 3. ing. The vehicle speed V detected by the vehicle speed sensor 12 is input to the control unit 30 that controls the power steering device. Further, power is supplied from the battery 14 and an ignition key signal is input from the ignition key 11. . The motor 20 is provided with a motor angle sensor 110 for detecting a motor angle, and the motor angle θs from the motor angle sensor 110 is input to the control unit 30. The control unit 30 calculates an assist command steering assist command value I based on the steering torque Th detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12, and the calculated steering assist command value I is calculated. Is used to control the current supplied to the motor 20.

  The control unit 30 is mainly composed of a CPU (including an MPU (Micro Processor Unit), MCU (Micro Controller Unit), etc.). FIG. 9 shows general functions executed by a program inside the CPU. become. For example, the phase compensation unit 31 does not indicate a phase compensation unit as independent hardware, but indicates a phase compensation function executed by the CPU.

  The function and operation of the control unit 30 will be described with reference to FIG. 9. The steering torque Th detected and input by the torque sensor 10 is phase-compensated by the phase compensator 31 in order to improve the stability of the steering system. The compensated steering torque TA is input to the steering assist command value calculation unit 32. Further, the vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculation unit 32. Further, the motor angle θs output from the motor angle sensor 110 is input to the steering angle utilization function unit 100.

  The steering assist command value calculation unit 32 calculates a steering assist command value I that is a control target value of the current supplied to the motor 20 based on the input steering torque TA and vehicle speed V. The calculated steering assist command value I is input to the subtraction unit 30A and also input to the feedforward differential compensation unit 34 for increasing the response speed, and the deviation (I-i) of the subtraction unit 30A is a proportional calculation unit. 35 and also to an integral calculation unit 36 for improving the characteristics of the feedback system. Along with the output of the differential compensator 34, the outputs of the proportional calculator 35 and the integral calculator 36 and the output Iu of the steering angle utilization function unit 100 are also added and input to the adder 30B. E is input to the motor drive circuit 37 as a motor drive signal, and the motor 20 is driven by the motor drive circuit 37. The current i of the motor 20 is detected by the motor current detection circuit 38 and fed back to the subtraction unit 30A. A portion excluding the motor drive circuit 37 constitutes a torque control unit.

In such an electric power steering apparatus, in order to perform appropriate assist control, it is necessary to detect or estimate the absolute steering angle of the absolute value. Therefore, in Japanese Patent Application Laid-Open No. 2003-276635 (Patent Document 1), a relative steering angle is calculated using an angle signal of a motor, and determination of straight traveling is performed using each wheel speed and steering torque, so that straight traveling is determined. The relative steering angle of the steering wheel is estimated as a neutral point, and the absolute steering angle is calculated from the estimated neutral point. That is, in Patent Document 1, motor rotation angle detection means for detecting the rotation angle of the motor, neutral point position detection means for detecting the neutral position of the steering mechanism based on the rotation speed of the wheel of the vehicle, and this neutral point Absolute steering angle detection means for detecting the absolute steering angle of the steering mechanism based on the neutral point position detected by the position detection means and the rotation angle detected by the motor rotation angle detection means is provided.
JP 2003-276635 A JP 2007-106283 A

  However, since the electric power steering device disclosed in Patent Document 1 is provided with absolute steering angle detection means and uses a wheel speed difference for the determination of straight traveling, a wheel speed sensor is necessary. There is a problem that cannot be applied to vehicles not equipped with.

  As a control device for an electric power steering apparatus that solves such a problem, an apparatus disclosed in Japanese Patent Application Laid-Open No. 2007-106283 (Patent Document 2) has been proposed. However, the apparatus of Patent Document 2 has a problem that the information from the road surface to the tire cannot be accurately reflected because the vehicle is judged to travel straight using the steering torque. The straight-run determination is to estimate the state of the tire of the vehicle (the tire turning angle), but since the steering torque is the state of the steering, for example, let go and the friction of the steering mechanism and the SAT (self-aligning torque) balance. In this case, there is a problem that it is determined that the vehicle travels straight even when the steering torque is zero and the steering wheel is bent. In particular, the error becomes large on a low μ road surface. In such a case, if the tire slips, the difference between the left and right wheel speeds becomes almost zero, and there is a risk of erroneous determination even if the wheel speed is added to the straight traveling determination condition.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to calculate the steering wheel relative steering angle, steering angular speed or motor angular speed from the motor angle sensor, and to calculate the steering angular speed or motor angular speed, SAT and vehicle speed. It is an object of the present invention to provide a control device for an electric power steering apparatus that can estimate the neutral point angle (neutral position) of the steering angle with high accuracy and that can calculate the absolute angle using the relative steering angle.

The present invention relates to a control device for an electric power steering device that drives a motor via a current control unit with a current command value calculated by a torque control unit and applies assist torque to a steering mechanism of a vehicle by driving the motor. The object of the present invention is to provide a motor angle sensor for detecting a motor angle, a SAT detection means for detecting the SAT of the vehicle, a relative steering angle detection unit for detecting a relative steering angle θr of the steering based on the motor angle, A steering angular velocity detection unit for obtaining an angular velocity of the motor, and a vehicle speed detection unit for detecting a vehicle speed, and determining whether the vehicle travels straight based on the steering angular velocity, the SAT detection value, and the vehicle speed. A neutral point calculation unit that calculates the relative rudder angle θr as a neutral point angle when it continues for a predetermined time or more, and a difference between the neutral point angle and the relative rudder angle θr It is achieved by including the absolute steering angle calculating unit for obtaining the pair steering angle.

The object of the present invention is to provide a reliability coefficient that increases when the neutral point calculation unit increases the vehicle speed and the straight travel duration when the straight travel duration exceeds the first threshold under the condition that the straight travel is determined. The neutral point angle _obtained by previously correcting the value D (θr−θ _k−1 ) _obtained by multiplying the deviation between the neutral point angle θ _k−1 corrected last time and the relative steering angle θr by the reliability coefficient D (θr−θ _k−1 ). By adding θ _k−1 to a new neutral point angle θ _k , or by setting an estimated value reliability coefficient obtained by integrating the reliability coefficient D, the estimated value reliability coefficient is greater than or equal to a second threshold. when it becomes the by reliability reduces the coefficient D to reduce the correction displacement of the neutral point angle theta _k with, or by performing a determination of the straight running by adding wheel rotational speeds, more effectively Achieved.

  According to the control device for the electric power steering apparatus according to the present invention, the algorithm for calculating the absolute steering angle is used, the steering angular speed is used for the straight traveling determination, and further, by using the SAT detection means and the vehicle speed sensor, It is possible to estimate the neutral point angle with high accuracy. In addition, by adding the wheel rotation speed to the determination of the straight traveling, it is possible to perform a quick and reliable estimation.

  The SAT is information transmitted from the road surface to the tire, and the state of the tire can be accurately grasped. In the present invention, the SAT is used to determine whether the vehicle is going straight. Detection can be performed.

  In the present invention, the steering wheel relative rudder angle is calculated from the motor angle obtained from the motor angle sensor in consideration of the gear ratio of the speed reduction unit, and the neutral point angle of the rudder angle is estimated based on the obtained relative rudder angle. . Further, in the present invention, the vehicle speed, the SAT detection value, and the rudder angular speed are used for the determination of the straight traveling, and it is determined that the vehicle is traveling straight when the condition for determining the straight traveling is satisfied and the state continues for a predetermined time, The neutral point angle is estimated based on the relative steering angle. Furthermore, by setting a rectilinear reliability coefficient and estimating according to the reliability coefficient, it is possible to estimate the neutral point angle with higher accuracy and faster, and the relative steering angle is subtracted from the obtained neutral point angle. By doing so, the absolute rudder angle is calculated. A steering angle utilization function such as steering wheel return control is accurately operated from the obtained absolute steering angle and the estimated value reliability coefficient obtained from the reliability coefficient.

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

  FIG. 1 shows an embodiment of the present invention. An electric power steering apparatus includes a motor angle sensor 110 that detects a motor angle θs of a motor 20, a SAT detection means 111 that detects a SAT of a vehicle, and a vehicle speed of the vehicle. And a vehicle speed sensor 112 for detecting V. The motor angle θs from the motor angle sensor 110 is input to the relative steering angle detection unit 101 and the steering angular velocity detection unit 102, and the SAT detection value SATd from the SAT detection unit 111 and the vehicle speed V from the vehicle speed sensor 112 are input to the straight travel determination unit 200. Entered. Depending on the vehicle, an acceleration sensor is mounted, and an acceleration signal in the front-rear direction can be obtained. Therefore, it is also possible to obtain the speed V by acquiring and integrating the acceleration signal via a CAN (Controller Area Network) or the like. is there.

  The relative steering angle detection unit 101 detects the steering relative steering angle θr in consideration of the gear ratio based on the motor angle θs, and the steering angular velocity detection unit 102 differentiates the motor angle θs and considers the gear ratio to determine the steering angular velocity ω. Is detected. The steering angular velocity ω detected by the steering angular velocity detection unit 102 is input to the straight traveling determination unit 200, and the straight traveling determination signal Ni calculated by the straight traveling determination unit 200 is input to the absolute steering angle calculation unit 104. The steering angular velocity ω may be the motor angular velocity as it is.

  The relative rudder angle detection unit 101 integrates the motor angle θs after the ignition key is turned on and the output of the motor angle θs from the motor angle sensor 110 is started, and the relative rudder angle θr of the steering wheel is considered in consideration of the gear ratio. The steering angular velocity detector 102 detects the steering angular velocity ω based on the motor angle θs. The absolute steering angle calculation unit 104 detects the absolute steering angle θa and the estimated value reliability coefficient D based on the relative steering angle θr and the straight traveling determination signal Ni. The steering angle utilization function unit 100 that inputs the absolute steering angle θa and the estimated value reliability coefficient D performs a steering wheel return control using the steering angle and a steering angle adjustment function in accordance with the vehicle behavior, based on the output Iu.

  When the steering angular velocity ω and the SAT detection value SATd are equal to or less than the threshold at which the straight traveling determination unit 200 is neutral, and the vehicle speed V or more at which the SAT detection value SATd acts continues for a certain time (t) or longer, It has a function to judge straight running.

Here, the SAT detection unit 111 will be described. The state of the torque generated between the road surface and the steering is as shown in FIG. That is, the steering torque Th is generated when the driver steers the steering wheel, and the motor 20 generates the assist torque Tm according to the steering torque Th. As a result, the wheels are steered and SAT is generated as a reaction force. Further, at that time, torque serving as steering steering resistance is generated by the inertia J and friction (static friction) Fr of the motor 20. Considering the balance of these forces, the following equation of motion is obtained.
(Equation 1)
J ・ * ω + Fr ・ sign (ω) + SAT = Tm + Th

Here, when the above equation 1 is Laplace transformed with an initial value of zero and the SAT is solved, the following equation 2 is obtained.
(Equation 2)
SAT (s) = Tm (s) + Th (s) − J · * ω (s) − Fr · sign (ω (s))

As can be seen from the above equation 2, the motor rotation angular velocity ω, rotation angular acceleration * ω, assist torque Tm (steering assist force), and steering torque Th are obtained by obtaining the inertia J and static friction Fr of the motor 20 as constants in advance. Thus, SAT (SAT detection value SATd) can be obtained. It is also possible to directly obtain the SAT detection value SATd by disposing a known SAT sensor in the vehicle.

On the other hand, the absolute rudder angle calculation unit 104 calculates the absolute rudder angle θa by executing the estimation of the neutral point angle of the rudder angle and the calculation of Equation 3 below.
(Equation 3)
Absolute steering angle (θa) = Relative steering angle (θr) −Estimated neutral point angle (θk)

The absolute steering angle θa and the estimated value reliability coefficient D calculated by the absolute steering angle calculation unit 104 are used by the steering angle utilization function unit 100. The estimated value reliability coefficient D has the following significance. Yes. That is, since the absolute steering angle θa in the present invention is estimated from the vehicle information, the reliability for accuracy differs after the initial estimation stage and after the estimation is sufficiently performed. Depending on the function using the absolute steering angle θa, it may be safer to reduce the effect of the function before sufficient estimation is made. Because of such a function, the reliability coefficient D of the estimated value is given so that control according to the reliability coefficient D can be performed. For example, the steering wheel return control output is small when the estimated value reliability coefficient D is low, and is large when the estimated value reliability coefficient D is high.

Next, details of the straight-ahead determination unit 200 will be described with reference to FIGS. 3 and 4. In FIG. 3, the SAT detection value SATd from the SAT detection unit 111 and the vehicle speed V from the vehicle speed sensor 112 are low pass filters (LPFs), respectively. ) 201 and 203, the output of the low-pass filter 201 is input to the comparison unit 210, and the output of the low-pass filter 203 is input to the comparison unit 212 and the neutral point angle correction unit 240. The motor angle θs from the motor angle sensor 110 is input to the rudder angular velocity detection unit 102 and also to the neutral point angle correction unit 240 via the relative rudder angle detection unit 101 and the low pass filter 204. The output of the steering angular velocity detection unit 102 is input to the comparison unit 211 via the low-pass filter 202. Note that the low-pass filters 201 to 204 are not essential elements.

  The SAT detection value SATd from the low-pass filter 201, the motor angular velocity ω from the low-pass filter 202, and the vehicle speed V from the low-pass filter 203 are compared with the reference value SATth, the reference value ωth, and the reference value Vth by the comparison units 210, 211, and 212, respectively. The comparison results are input to the AND circuit 220. The AND circuit 220 performs straight-ahead determination based on the AND condition of each comparison result, and outputs a straight-ahead signal St in the case of a straight-ahead determination.

  The SAT detection value SATd that has passed through the low-pass filter 201 is input to the comparison unit 210, and the comparison unit 210 outputs a result of comparing the SAT with the reference value SATth set in the setting unit 213. That is, when the SAT detection value SATd is smaller than the reference value SATth, the vehicle often travels straight, and the comparison unit 210 outputs, for example, a logical value “1”. Further, the motor angular velocity ω is input to the comparison unit 211 via the low-pass filter 202, and the comparison unit 211 outputs a result of comparing the motor angular velocity ω with the reference value ωth set in the setting unit 214. That is, when the motor angular velocity ω is smaller than the reference value ωth, the vehicle is often traveling straight, and the comparison unit 211 outputs a logical value “1”, for example. Further, the vehicle speed V that has passed through the low-pass filter 203 is input to the comparison unit 212, and the comparison unit 212 outputs a result of comparing the vehicle speed V with the reference value Vth set in the setting unit 215. That is, when the vehicle speed V is faster than the reference value Vth, the vehicle is often traveling straight, and the comparison unit 212 outputs a logical value “1”, for example.

  Then, the AND condition of all outputs of the comparison units 210 to 212 is taken by the AND circuit 220, and a straight traveling signal St as a result of comprehensive judgment is output. That is, when all the outputs of the comparators 210 to 212 are logical values “1”, it is determined that the vehicle travels straight, and a straight signal St with a logical value “1” is output. A straight ahead signal St of “0” is output. The logical value may be the opposite of “1” and “0”.

  The straight signal St is input to the comparison unit 221, and the comparison unit 221 determines whether or not to continue straight when the logical value “1” of the straight signal St continues for the continuation determination time t0 set in the setting unit 222. , A straight running continuation signal Sc is output. The straight travel continuation signal Sc is input to the neutral angle correction means 240. When the straight traveling signal St is less than the continuation determination time t0, the straight traveling continuation signal Sc is not output.

  Next, the neutral point angle correction unit 240 will be described with reference to FIG. 4. The neutral point angle correction unit 240 includes a relative steering angle θr detected by the relative steering angle detection unit 101 and passed through the low-pass filter 204, and a vehicle speed sensor. The vehicle speed V detected at 112 and passed through the low-pass filter 203 and the straight travel continuation signal Sc from the comparison unit 221 are input. However, it is necessary to correct the neutral point angle under the condition that the vehicle is traveling straight. Therefore, the switch 241 for imposing the condition is disposed between the low-pass filter 204 that is an input path of the relative steering angle θr and the subtractor 244, and the low-pass filter that the switch 242 is an input path of the vehicle speed V 203 and the Dv table 243. The switches 241 and 242 are closed (ON) only while the straight travel continuation signal Sc is input.

The estimation of the neutral point angle θ _k is performed based on the following equation (4), and the neutral point angle correcting means 240 executes the following equation (4).
(Equation 4)
θ _k = D (θr−θ _k−1 ) + θ _k−1

Here, “θ _k−1 ” is the previously estimated neutral point angle, and “θk” is the new neutral point angle after the current estimation. Further, D is a reliability coefficient obtained by the absolute rudder angle calculation unit 104, and is basically a coefficient that increases as the vehicle speed V increases.

  The neutral point angle correction in the neutral point angle correcting means 240 will be described. The vehicle speed V input via the switch 242 is input to the Dv table 243. The Dv table 243 has a characteristic of outputting a reliability basic coefficient Dv that increases as the vehicle speed V increases. Basically, the reliability coefficient D increases as the reliability basic coefficient Dv increases. Here, FIG. 5 shows a characteristic example of the Dv table.

When the vehicle speed V is input to the Dv table 243, the reliability basic coefficient Dv is output according to the function of FIG. The output reliability basic coefficient Dv is input as one of the addition values of the addition unit 250. The output of the adding unit 250 is input to the limiter 251 and controlled so that the output of the limiter 251, that is, the reliability coefficient D is within the set value. The reliability coefficient D, which is the output of the limiter 251, is input to the delay unit 252 (Z ⁻¹ ), the output of the delay unit 252 is multiplied by the gain Dt by the gain unit 253, and the multiplication result is input to the adder unit 250. It is added to the reliability basic coefficient Dv from the table 243. Thus, the reliability basic coefficient Dv regarding the vehicle speed V is integrated, and the reliability coefficient D is calculated. The reliability coefficient D is also input to the multiplication unit 245.

On the other hand, the relative steering angle θr input to the neutral point angle correcting means 240 via the switch 241 is input to the subtracting unit 244, and the subtracting unit 244 receives the previously estimated neutral point angle θ _k−1 that is the output of the delay unit 247. Is entered. Therefore, the output of the subtraction unit 244 becomes a deviation (θr−θ _k−1 ). The multiplication unit 245 multiplies the deviation from the subtraction unit 244 and the reliability coefficient D from the limiter 251, and the multiplication unit 245 outputs the multiplication value D · (θr−θ _k−1 ). D · (θr−θ _k−1 ) output from the multiplication unit 245 is input to the addition unit 246 and added to the previously estimated neutral point angle θ _k−1 output from the delay unit 247, and the calculation result {D · (θr−θ _k−1 ) + θ _k−1 } is output as a new neutral point angle θ _k estimated as. That is, the neutral point angle θ _k output from the neutral point angle correcting means 240 is expressed by the following equation (5).
(Equation 5)
_{θ k = D · (θr-} θ k-1) + θ k-1

Integration by the calculation D · (θr−θ _k−1 ) is performed only when the straight travel continuation signal Sc is input from the comparison unit 221, that is, only during the straight travel. Further, when the straight running continuation signal Sc is no longer input from the comparison unit 221, the duration t is reset to “0”, the neutral point angle θ _k of the calculation result is stored in the storage means such as RAM, and the next straight running continuation signal again. Used as the offset initial value θ _k−1 when Sc is input and the neutral point angle correction means 240 starts the calculation.

As described above, the straight travel determination unit 200 performs a calculation assuming that the relative rudder angle at the time of the straight travel determination is regarded as a neutral point, but the neutral point angle θ _k− previously corrected as a method of calculating the neutral point angle θ _{k. 1} newly acquired relative steering angle [theta] r and the detected deviation _{(θr-θ k-1)} , the reliability coefficient D (V, t) the value D · multiplied by _{(θr-θ k-1)} calculate. Then, the previous neutral point angle θ _k−1 is added to calculate a new neutral point angle θ _k according to the above equation (5).

The reliability coefficient D (V, t) is calculated by integrating the reliability basic coefficient Dv depending on the vehicle speed V with the duration when the straight running duration (t) exceeds the threshold. Since the relative rudder angle when entering the condition at high speed is considered to be a reliable value, the reliability coefficient D increases by setting the reliability basic coefficient Dv high, and the longer the duration time is, reliability coefficient D is increased, the relative steering angle θr is immediately reflected to the neutral point angle theta _k.

  In addition, since the initial value at which the estimation is started may be erroneously estimated, the value of the reliability coefficient D is integrated so that the function using the steering angle does not function until the estimation is continued for a certain time or more. The estimated value reliability coefficient Dest is set as the reliability of the estimated value. When the estimated value reliability coefficient Dest becomes equal to or higher than the threshold, it is determined that the accuracy of the neutral point has been improved, and thereafter, the value of the reliability coefficient D is decreased at a constant rate so that the neutral point angle does not change suddenly. Further, the estimated value reliability coefficient Dest is output outside the module for operation conditions and gain of the function using the absolute steering angle.

  The above-described operation is executed according to the flowchart shown in FIG. That is, the relative steering angle θr, the steering angular speed ω, the SAT detection value SATd, and the vehicle speed V are acquired (step S1), it is determined whether the vehicle speed V is greater than the vehicle speed threshold Vth (step S2), and the vehicle speed V is the vehicle speed threshold. If Vth or less, the neutral point position and the estimated value reliability are determined, the previous value is held, and the straight traveling reliability is reset (step S8). If the vehicle speed V is greater than the vehicle speed threshold Vth in step S2, it is determined whether the absolute value | SATd | of the SAT detection value SATd is smaller than the threshold SATth (step S3), and the absolute value of the SAT detection value SATd. If | SATd | is equal to or greater than the threshold SATth, the process proceeds to step S8. If the absolute value | SATd | of the SAT detection value SATd is smaller than the threshold SATth, the absolute value | ω | of the steering angular speed ω is further equal to the threshold ωth. It is determined whether or not (step S4). If the absolute value | ω | of the steering angular velocity ω is equal to or greater than the threshold ωth, the process proceeds to step S8. If the absolute value | ω | of the steering angular velocity ω is smaller than the threshold ωth, the timer counts up (step S5), it is determined whether or not the count time t is equal to or greater than the threshold th (step S6). If the timer count time t is smaller than the threshold, the process proceeds to step S8. If the timer count time t is equal to or greater than the threshold th, the straight travel reliability integration, the neutral position and the estimated value reliability are updated. (Step S7). Then, the neutral point position and the estimated value reliability are output and the process ends (step S10).

  Next, another embodiment of the present invention will be described.

上記数６において、操舵角θと、左後輪車輪速Ψ_ｉ、右後輪車輪速Ψ_ｒとは、ｋ_１を定数として下記数７で表される。
（数７）
ｔａｎθ＝ｋ_１・（Ψ_ｉ−Ψ_ｒ）／（Ψ_ｉ＋Ψ_ｒ）

そして、操舵角θが小さいときは直進とみなせるので、上記数７の右辺がスレッショルド以下であるかを判定するが、三角関数のｔａｎや除算があるとＣＰＵやＭＰＵでの演算が困難になる。このため、本発明では、ｋ_２を定数として下記数８のように変形している。
（数８）
０ ≦ ｋ_２/ｋ_１・｜Ψ_ｉ＋Ψ_ｒ｜−｜Ψ_ｉ−Ψ_ｒ｜

上記数８より、右辺が０以上であれば直進と判定する。 When the wheel rotation speed can be used, it is possible to estimate with higher accuracy by adding the wheel rotation speed to the straight traveling determination condition in the above estimation method. Judgment conditions based on wheel rotation speed are as follows. The difference between the left and right wheel speeds is 0 in an ideal straight traveling state, so the same condition can be obtained. However, since the wheel speed difference greatly varies depending on the vehicle speed, the following relational expression based on the turning radius is used instead of providing a threshold for the wheel speed difference.

In the above formula 6, the steering angle θ, the left rear wheel speed ψ _i , and the right rear wheel speed ψ _r are expressed by the following formula 7, where k ₁ is a constant.
(Equation 7)
tan θ = k ₁ · (Ψ _i −Ψ _r ) / (Ψ _i + Ψ _r )

When the steering angle θ is small, it can be considered that the vehicle travels straight, so it is determined whether the right side of Equation 7 is equal to or less than the threshold. However, if there is a tan or division of a trigonometric function, calculation by the CPU or MPU becomes difficult. For this reason, in the present invention, k ₂ is a constant and the following equation 8 is modified.
(Equation 8)
0 ≦ k ₂ / k ₁ · | Ψ _i + Ψ _r | − | Ψ _i −Ψ _r |

From Equation 8, if the right side is 0 or more, it is determined that the vehicle is going straight.

  FIG. 7 shows an example of an apparatus in which left and right wheel rotational speeds are used, corresponding to FIG. In the present embodiment, the left and right wheel speed rotation sensor 120 is provided, and the output from the calculation unit 130 that processes the wheel speed rotation signal is input to the neutral point detection unit 200A, so that straight travel can be determined more accurately. That is, in the embodiment of FIG. 7, the arithmetic unit 130 for executing the condition of Equation 8 is added to the straight-ahead determination of the straight-ahead determination unit 200A, and the other configuration is exactly the same as that of FIG.

  In this way, when the left and right wheel rotation speeds are used, the absolute steering angle can be estimated with higher accuracy.

It is a block block diagram which shows an example of the control apparatus which concerns on this invention. It is a schematic diagram for demonstrating the detection of SAT. It is a block block diagram which shows the detailed structural example of a neutral point detection part. It is a block block diagram which shows the detailed structural example of a neutral point detection part. It is a figure which shows an example of Dv table. It is a flowchart which shows the operation example of this invention. It is a block block diagram which shows the other example of the control apparatus which concerns on this invention. 1 is a structural diagram showing an outline of a general electric power steering apparatus. It is a block block diagram which shows an example of a control unit.

Explanation of symbols

1 Handle 2 Steering shaft (column shaft)
3 Reduction gear 10 Torque sensor 11 Ignition key 12, 112 Vehicle speed sensor 14 Battery 20 Motor 30 Control unit 100 Steering angle utilization function unit 101 Relative steering angle detection unit 102 Steering angular velocity detection unit 104 Absolute steering angle calculation unit 110 Motor angle sensor 111 SAT Detection means 120 Left and right wheel rotation speed sensor 130 Arithmetic unit 200, 200A Straight travel determination unit 210-212 Comparison unit 220 AND circuit 240 Neutral point angle correction unit 243 Dv table 251 Limiter

Claims (5)

A motor angle is detected in a control device of an electric power steering apparatus that drives a motor through a current control unit with a current command value calculated by a torque control unit and applies assist torque to a steering mechanism of the vehicle by driving the motor. A motor angle sensor that detects the SAT of the vehicle, a relative steering angle detector that detects a relative steering angle θr of the steering based on the motor angle, and a steering angular velocity detector that determines the angular velocity of the motor And a vehicle speed detection unit that detects the vehicle speed, and determines whether the vehicle is traveling straight on the basis of the rudder angular velocity, the SAT detection value, and the vehicle speed, and the relative rudder when the straight traveling continues for a predetermined time or more. A neutral point calculation unit for calculating an angle θr as a neutral point angle, and an absolute steering angle calculation for obtaining an absolute steering angle by a difference between the neutral point angle and the relative steering angle θr. Control device for an electric power steering apparatus characterized by comprising a part. The neutral point calculation unit sets a reliability coefficient D that increases according to the vehicle speed and the straight travel duration when the straight travel duration exceeds the first threshold under the condition that the straight travel is determined. A value D (θr−θ _k−1 ) _obtained by multiplying the deviation between the neutral point angle θ _k−1 and the relative rudder angle θr by the reliability coefficient D is added to the previously corrected neutral point angle θ _k−1 . The control device for the electric power steering apparatus according to claim 1, wherein a new neutral point angle θ _k is set. An estimated value reliability coefficient obtained by integrating the reliability coefficient D is set, and when the estimated value reliability coefficient is equal to or higher than a second threshold, the reliability coefficient D is decreased to reduce the neutral point angle θ _k . The control device for the electric power steering apparatus according to claim 2, wherein the correction displacement is reduced. The control device for an electric power steering apparatus according to any one of claims 1 to 3, wherein the controller determines the straight traveling by adding a wheel rotation speed. A vehicle equipped with the control device for an electric power steering device according to any one of claims 1 to 4.

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