JP4683210B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering device that applies a steering assist force by a motor.

In an electric power steering apparatus including a motor for generating a steering assist force, the steering characteristics are improved by correcting the output of the motor according to an output correction value obtained based on the steering angle. In this case, if a sensor for detecting a value corresponding to the mechanical movement of the wheel is used to obtain the rudder angle, the cost increases. Therefore, the counter electromotive force is obtained from the detection result of the motor driving current, applied voltage, temperature corresponding to the internal resistance, etc., the relative steering angle is obtained based on the back electromotive force, and whether the vehicle is in a straight traveling state or not. It has been proposed to determine the rudder angle with the average value of the cumulative relative rudder angles determined when the vehicle is in a straight traveling state as the rudder angle midpoint (see Patent Document 1).
Japanese Patent No. 2781854

  In the above-described prior art, since it is difficult to accurately determine whether or not the vehicle is in a straight traveling state, the cumulative average value of the relative steering angles obtained when it is determined that the vehicle is in a straight traveling state is the steering angle. The midpoint. However, if the number of determinations is reduced, the accuracy is lowered and accurate control cannot be performed, and if it is increased, the start of control is delayed. Such a problem occurs due to deterioration of sensor accuracy with time even when the steering angle is obtained by a sensor that detects a value corresponding to the mechanical movement of the wheel. An object of the present invention is to provide an electric power steering apparatus that can solve such a problem.

The electric power steering device of the present invention includes a motor that generates a steering assist force, a relative rudder angle determination unit, a determination unit that determines whether or not the vehicle is in a straight traveling state, and a vehicle that is in a straight traveling state. The average reference rudder angle determination unit obtained by dividing the total of the relative rudder angles at the time of determination by the number of determinations that the vehicle is traveling straight, and the average reference rudder angle as the rudder angle midpoint, A rudder angle determination unit that obtains a rudder angle by subtracting a point from a relative rudder angle, a correction unit that corrects the output of the motor according to an output correction value obtained based on the obtained rudder angle, and the output correction value And a changing unit that changes so as to be positively correlated with the number of determinations that the vehicle is traveling straight.
According to the present invention, the accuracy of the average reference rudder angle used as the rudder angle midpoint increases as the number of determinations that the vehicle is in the straight traveling state increases. Therefore, the output correction value obtained based on the rudder angle obtained using the average reference rudder angle as the midpoint of the rudder angle is obtained with higher accuracy as the number of determinations increases. By changing the output correction value so that it correlates positively with the number of determinations, when the number of determinations is small and the accuracy of the output correction value is low, the motor output correction amount is reduced so as not to affect the accuracy and the control is quickly performed. When the number of determinations increases and the accuracy of the output correction value increases, the motor output correction amount can be increased and the control can be performed with high accuracy.

  In the present invention, a sensor for obtaining a steering torque, a controller for controlling the motor so that a steering assist force corresponding to the obtained steering torque is generated, and whether or not the vehicle is steered back to the straight steering position. The output correction value is preferably inversely correlated with the obtained steering angle when a return steering is performed. Thus, the influence of the steering reaction force acting from the road surface via the wheel can be reduced by increasing the magnitude of the output correction value as the steering angle is larger when the return steering is being performed.

  According to the electric power steering apparatus of the present invention, the output correction of the steering assist force generating motor for improving the steering characteristics can be started quickly and accurately.

  The vehicle electric power steering apparatus 1 according to the embodiment of the present invention shown in FIG. 1 includes a mechanism for transmitting the rotation of the steering wheel 2 by steering to the wheels 3 so that the steering angle changes. In the present embodiment, the rotation of the steering wheel 2 is transmitted to the pinion 5 via the steering shaft 4, so that the rack 6 meshing with the pinion 5 moves, and the movement of the rack 6 moves via the tie rod 7 and the knuckle arm 8. The steering angle is changed by being transmitted to the wheel 3.

  A motor 10 is provided that generates a steering assist force that acts on a path for transmitting the rotation of the steering wheel 2 to the wheel 3. In the present embodiment, the steering assist force is applied by transmitting the rotation of the output shaft of the motor 10 to the steering shaft 4 via the reduction gear mechanism 11.

  The motor 10 is connected to a control device 20 configured by a computer via a drive circuit 21. The drive circuit 21 controls the power supplied from the battery 27 to the motor 10 by the PWM control signal from the control device 20. The control device 20 includes a torque sensor 22 for determining the steering torque T of the steering wheel 2, a yaw rate sensor 23 for determining the vehicle yaw rate γ, a vehicle speed sensor 24 for determining the vehicle speed V, a current sensor 26 for determining the drive current i of the motor 10, and the motor 10 A voltage detection unit 28 for obtaining the applied voltage E to the motor and a temperature detection unit 29 for obtaining the temperature ta of the motor 10 are connected. The signs of the steering torque T, the yaw rate γ, the drive current i, and the applied voltage E are positive when the vehicle is turned left and right and negative when the vehicle is turned in the opposite direction. The voltage detection unit 28 can be configured by obtaining an applied voltage E to the motor 10 from the voltage between the terminals of the battery 27 and the PWM duty, and the temperature detection unit 29 includes a temperature detection sensor of a power transistor that constitutes the drive circuit 21; It can be configured by determining the temperature of the motor 10 from the correspondence between the temperature of the power transistor and the temperature of the motor 10.

  The control device 20 controls the motor 10 to generate a steering assist force corresponding to the basic assist torque corresponding to the obtained steering torque T, changes the steering assist force according to the detected vehicle speed V, and Correct according to the rudder angle.

  FIG. 2 shows a control block diagram of the motor 10 by the control device 20. The output signal of the torque sensor 22 is input to the calculation unit 41 via the low-pass filter 61 and used to determine the basic assist current io. In the calculation unit 41, the correspondence relationship between the steering torque T and the basic assist current io is stored as, for example, a table or an arithmetic expression, and the basic assist current io corresponding to the detected steering torque T is calculated. The correspondence relationship between the steering torque T and the basic assist current io is such that, for example, as shown in the calculation unit 41, the magnitude of the basic assist current io increases as the magnitude of the steering torque T increases.

  In the calculation unit 42, the correspondence relationship between the vehicle speed V and the basic vehicle speed gain Gv is stored as, for example, a table or an arithmetic expression, and the basic vehicle speed gain Gv corresponding to the calculated vehicle speed V is calculated. As for the correspondence relationship between the vehicle speed V and the basic vehicle speed gain Gv, for example, as shown in the calculation unit 42, the basic vehicle speed gain Gv is larger when the vehicle speed V is small than when it is large. The product of the basic assist current io and the basic vehicle speed gain Gv corresponds to the basic assist torque. As shown in FIG. 3, if the vehicle speed V is constant, the magnitude of the basic assist torque To increases to the set upper limit as the magnitude of the steering torque T increases, and if the steering torque T is constant. The magnitude of the basic assist torque To increases as the vehicle speed V decreases. By storing the correspondence between the steering torque T and the basic assist current io and the correspondence between the vehicle speed V and the basic vehicle speed gain Gv, the correspondence between the steering torque T and the basic assist torque To is stored. become.

In the calculation unit 43, the steering angle δ is calculated. The steering angle δ is positive when the vehicle goes to the left or right, and negative when the vehicle goes in the opposite direction. In this embodiment, first, the internal resistance R of the motor 10 is obtained from the relationship of R = Ro + α · (ta−to) · Ro. Here, ta is a detected temperature of the motor 10 by the temperature detection unit 29, to is a preset reference temperature, Ro is an internal resistance of the motor 10 at the reference temperature to, and α is a resistance temperature coefficient at the reference temperature. Next, the counter electromotive force Ea of the motor 10 is obtained from the relationship of Ea = E−R · i. Since the steering angle change speed ω is obtained from the relationship ω = Ea / K, where K is a proportional constant, the calculation period of the control device 20 is t1, and the steering angle change speed ω and the relative steering angle δ that are obtained in the nth calculation period. _Assuming that _r is ω _n and δ _rn , the relative steering angle δ _r is obtained for each calculation cycle from the relationship of δ _rn = δ _rn-1 + ω _n · t1. Next, it is determined whether or not the vehicle is traveling straight. In this embodiment, the magnitude of the steering torque T is equal to or less than the set value T ′ and steering is not substantially performed, the magnitude of the yaw rate γ is equal to or less than the set value γ ′, and the vehicle traveling direction is substantially equal. When the vehicle speed V is equal to or higher than the set value V ′ and the vehicle is not stopped continues for the set time t ′ or longer, it is determined that the vehicle is traveling straight. The relative rudder angle δ _r at the time when it is determined that the vehicle is traveling straight ahead is set as the reference rudder angle, and an average reference rudder angle is obtained by dividing the total of the reference rudder angles by the number of determinations. The reference steering angle when it is determined that the vehicle is traveling straight ahead is δ _rm , where δ _m = {(m−1) · δ _m−1 + δ _rm } / m. An average reference rudder angle δ _m when it is determined that the vehicle is running is m-th time. Thereafter, the latest mean reference steering angle as the steering angle midpoint .delta.o, determined from the relative steering angle [delta] _r is a relationship δ = δ _r -δo steering angle [delta] at every calculation cycle from the steering angle midpoint .delta.o.

  The determination unit 44 determines whether or not the vehicle is steered back toward the straight-ahead steering position. If the steering is returned, the calculated steering angle δ is input to the calculation unit 45. If the return steering is not performed, the calculation unit 45 is operated. The steering angle δ input to is set to zero. The determination as to whether or not the vehicle is returning steer is made, for example, when the sign of the steering speed does not coincide with the sign of the detected steering torque T.

  In the calculation unit 45, the set correspondence relationship between the steering angle δ and the correction current i1 that is the output correction value of the motor 10 is stored as, for example, a table or an arithmetic expression, and the stored correspondence relationship and the calculated steering angle δ are calculated. Based on the above, the correction current i1 is calculated. When not in the return steering state, the steering angle δ input to the calculation unit 45 is zero, so the correction current i1 is zero. When the return steering is performed, the correspondence between the steering angle δ and the correction current i1 is such that the correction current i1 is inversely correlated with the steering angle δ, as shown in the calculation unit 45 of FIG.

  In the calculation unit 46, a correspondence relationship between the determination number m that the vehicle is in a straight traveling state and the midpoint determination gain Gm is stored as, for example, a table or an arithmetic expression, and the midpoint determination gain Gm corresponding to the determination number m is calculated. Calculated. The midpoint determination gain Gm has a positive correlation with the number of determinations m, and is zero until the number of determinations m reaches the first set value m1 as shown in the calculation unit 46, for example, and thereafter is proportional to the number of determinations m. And reaches a second set value m2 to be a constant value.

The controller 20 adds the sum of the value obtained by multiplying the correction current i1 by the midpoint determination gain Gm in the multiplier 47 and the value obtained by multiplying the basic assist current io and the basic vehicle speed gain Gv by the multiplier 49 in the adder 48. As the target drive current i ^* . A steering assist force is applied by feedback-controlling the motor 10 so as to reduce the deviation between the target drive current i ^* and the calculated drive current i. As a result, the output of the motor 10 is corrected according to the correction current i1 obtained based on the obtained steering angle δ, the correction current i1 is changed so as to be positively correlated with the number of determinations m, and return steering is performed. The correction current i1 is inversely correlated with the steering angle δ.

A control procedure of the motor 10 by the control device 20 will be described with reference to the flowcharts of FIGS. 4 and 5. First, the detection value by each sensor is read (step S1), and the steering angle midpoint δo is calculated (step S2). Calculation of the steering angle midpoint δo obtains the internal resistance R of the motor 10 (step S101), obtains the counter electromotive force Ea of the motor 10 (step S102), obtains the relative steering angle [delta] _r (step S103). Note that initial setting values may be used for the relative rudder angle and the rudder angle midpoint at the beginning of control, for example, zero. Next, it is determined whether or not the magnitude of the steering torque T is equal to or smaller than the set value T ′ (step S104). If the magnitude is equal to or smaller than the set value T ′ (S104: YES), the magnitude of the yaw rate γ is equal to or smaller than the set value γ ′. (S105: YES), it is determined whether the vehicle speed V is equal to or higher than the set value V '(step S106), and if it is equal to or higher than the set value (step S106). S106: YES) The timer is turned on (step S107), and it is determined whether or not the set time t 'or more has passed (step S108). If the set time t' or more has passed (S108: YES), the vehicle is in a straight traveling state. Is increased by one (step S109), and then the steering angle midpoint δo is obtained (step S110) and the process returns. If the determination is negative in steps S104, S105, and S106, the timer is reset (step S111), and the process returns. If the determination in step S108 is negative (S108: NO), the process returns without resetting the timer. After calculating the steering angle midpoint δo, the steering angle δ is calculated (step S3). Next, it is determined whether or not return steering is performed (step S4). If return steering is performed (S4: YES), a correction current i1 corresponding to the obtained steering angle δ is calculated (step S5). A midpoint determination gain Gm corresponding to the number of determinations m that the vehicle is traveling straight is calculated (step S6). If the return steering is not performed (S4: NO), the correction current i1 is set to zero (step S7). ). Next, a basic assist current io corresponding to the detected steering torque T is calculated (step S8), a target drive current i ^* = Gv · io + Gm · i1 is obtained (step S9), and the target drive current i ^* and the detected drive current i are calculated. The motor 10 is feedback-controlled so as to reduce the deviation from (step S10). After that, whether or not to end the control is determined based on, for example, whether the ignition switch is on or off (step S11). If the control is not ended (S11: NO), the process returns to step S1.

  According to the embodiment, the accuracy of the average reference rudder angle used as the rudder angle midpoint δo increases as the number m of determinations that the vehicle is traveling straight ahead increases. Therefore, the correction current i1 obtained based on the steering angle δ obtained using the average reference steering angle as the steering angle midpoint δo is obtained with higher accuracy as the number of determinations m increases. By changing the correction current i1 so as to be positively correlated with the number of determinations m, when the number of determinations m is small and the accuracy of the correction current i1 is low, the output correction amount of the motor 10 is reduced and controlled so as not to affect the accuracy. When the determination number m increases and the accuracy of the correction current i1 increases, the output correction amount of the motor 10 can be increased and the control can be performed with high accuracy. Further, by increasing the magnitude of the correction current i1 as the steering angle δ increases when the return steering is being performed, it is possible to reduce the influence of the steering reaction force acting via the wheels 3 from the road surface.

  The present invention is not limited to the above embodiment. For example, the method for determining whether or not the vehicle is traveling straight is not particularly limited. For example, the steering angle change speed is equal to or less than a set value, and steering is not substantially performed. Is below the set value, the vehicle traveling direction has not changed substantially, the vehicle speed is at or above the set value, and the vehicle has not stopped for more than the set time, the vehicle is running straight It may be determined that Further, instead of obtaining the relative rudder angle by calculation, it may be obtained by an angle sensor, so that the rudder angle from the rudder angle midpoint can be accurately obtained even if the accuracy of the angle sensor decreases due to deterioration over time or the like. be able to. Further, the motor output correction value is not limited to that obtained based on the rudder angle alone. For example, the motor output correction value changes according to the rudder angle change speed, the rudder angle change acceleration, or the like so as to compensate for the influence of the motor inertia or disturbance. You may do. The mechanism for transmitting the rotation of the steering wheel to the wheel so that the steering angle changes is not limited to the embodiment, and the rotation of the steering wheel may be transmitted from the steering shaft to the wheel via a link mechanism other than the rack and pinion. Furthermore, the mechanism for transmitting the output of the motor for generating the steering assist force to the steering system is not limited to the embodiment as long as the steering assist force can be applied. For example, a ball nut screwed to a ball screw integrated with the rack is attached to the motor. A steering assist force may be applied by driving with an output.

Configuration explanatory diagram of an electric power steering apparatus according to an embodiment of the present invention Control block diagram of electric power steering apparatus according to an embodiment of the present invention The figure which shows the relationship between the steering torque in the electric power steering device of embodiment of this invention, a basic assist torque, and a vehicle speed. The flowchart which shows the control procedure in the electric power steering apparatus of embodiment of this invention. The flowchart for calculating | requiring the steering angle midpoint in the electric power steering apparatus of embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 10 Motor 20 Control apparatus 22 Torque sensor 23 Yaw rate sensor 24 Vehicle speed sensor 26 Current sensor 28 Voltage detection part 29 Temperature detection part

Claims (2)

A motor that generates steering assist force;
A relative rudder angle determination unit;
A determination unit for determining whether or not the vehicle is traveling straight;
An average reference rudder angle determination unit obtained by dividing the total of the relative rudder angles at the time of determination that the vehicle is in a straight traveling state by the number of determinations that the vehicle is in a straight traveling state;
The average reference rudder angle as the rudder angle midpoint, and a rudder angle determination unit for obtaining the rudder angle by subtracting the rudder angle midpoint from the relative rudder angle;
A correction unit for correcting the output of the motor according to the output correction value obtained based on the obtained steering angle;
An electric power steering apparatus comprising: a changing unit that changes the output correction value so as to be positively correlated with the number of determinations that the vehicle is traveling straight. A sensor for determining steering torque;
A controller for controlling the motor so that a steering assist force corresponding to the obtained steering torque is generated;
A determination unit for determining whether or not the vehicle is steered back to the straight steering position,
The electric power steering apparatus according to claim 1, wherein when the return steering is performed, the output correction value is inversely correlated with the obtained steering angle.

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