JP2014172476A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of providing a good operation feeling even if tooth skipping occurs.SOLUTION: An electric power steering device includes a motor 19 which generates assisting force which is supplied to a rack shaft, an input pulley, an output pulley, a belt which engages with the input pulley and the output pulley so that rotation of the motor 19 is transmitted to the output pulley, a motor rotational angle sensor 23 which calculates rotational angle of the motor 19, and an ECU22 which estimates a steering angle of a steering wheel of a vehicle based on the detection result and controls motor 19 based on the estimated steering angle. The ECU22, if a motor angular acceleration which is obtained by differentiating the detection result of the motor rotation angle sensor 23 with time twice, is larger than a set value, calculates again so that the detection result of the motor rotation angle sensor 23 corresponds to the steering angle.

Description

  The present invention relates to an electric power steering device that assists a driver's steering operation.

  2. Description of the Related Art There is known an electric power steering device that assists a driver's steering operation by applying motor power to a vehicle steering mechanism. The electric power steering apparatus of Patent Document 1 includes a speed reduction mechanism having a pair of pulleys and a belt stretched between the pair of pulleys. Each of the pair of pulleys and belt has teeth and meshes with each other. One of the pair of pulleys is connected to the motor shaft, and the other is connected to the steering mechanism. The speed reduction mechanism applies the power of the motor to the steering mechanism via a pair of pulleys and a belt. The electric power steering apparatus includes a torque sensor that detects a steering torque based on a torsion amount of a torsion bar provided at an intermediate portion of the steering shaft, and a vehicle speed sensor that detects a vehicle speed. The control unit of the electric power steering apparatus calculates an assist torque to be applied to the steering mechanism based on the detection result of the torque sensor and the detection result of the vehicle speed sensor, and adjusts the current supplied to the motor based on the assist torque. The electric power steering apparatus also includes a steering angle sensor that detects the steering angle of the steering wheel, and a rotation speed sensor that detects the rotation speed of the motor shaft. Based on the comparison between the detection result of the steering angle sensor and the detection result of the rotational speed sensor, the control unit detects slippage between the pair of pulleys and the belt, more precisely, how much the tooth surfaces engaged with each other are displaced. Then, the current supplied to the motor is adjusted by the deviation.

JP 2008-105604 A

  By the way, the control part of the electric power steering device of Patent Document 1 detects slipping between the pair of pulleys and the belt, and adjusts the current supplied to the motor by that amount, but the previous slipping is greatly engaged with the teeth. Even if a so-called tooth skip occurs, the portion cannot be recognized. Therefore, the control unit does not adjust the current supplied to the motor even if tooth skipping occurs. For this reason, the timing at which the power of the motor is applied to the steering mechanism and the magnitude of the power to be applied are shifted, and there is a possibility that the steering of the steering may feel uncomfortable.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide an electric power steering apparatus that can obtain a good operation feeling even if tooth skipping occurs.

  In order to solve the above problems, an electric power steering apparatus includes a motor that generates a steering assist force applied to a steering mechanism of a vehicle, a driving vehicle that is attached to an output shaft of the motor, and a driven vehicle that is attached to the steering mechanism. A transmission member that meshes with the driving vehicle and the driven vehicle and transmits the rotation of the driving vehicle to the driven vehicle, a motor rotation angle sensor that calculates a rotation angle of the motor, and a detection result of the motor rotation angle sensor. And a control device that controls the motor based on the estimated turning angle and the steering operation of the vehicle, the control device including the motor rotation angle. If the sensor detection result twice differentiated by time is greater than the first set value, between the driving vehicle and the transmission member, and between the driven vehicle and the transmission member Since the tooth skipping at least one is likely to occur, and be required to re-computed so that the detection result of the motor rotational angle sensor and the turning angle corresponds.

  When tooth skipping occurs between at least one of the driving vehicle and the transmission member and between the driven vehicle and the transmission member, the detection result of the motor rotation angle sensor and the steered wheel of the vehicle that corresponded before the tooth skipping occurred. The steering angle becomes incompatible. Since the control device controls the motor based on the turning angle, if the detection result of the motor rotation angle sensor does not match the turning angle, the motor cannot be controlled to generate an appropriate steering assist force. As a result, the user may feel uncomfortable with the operation of the steering wheel.

  In that respect, according to the same configuration, when there is a possibility of tooth skipping, the control device recalculates so that the detection result of the motor rotation angle sensor and the turning angle correspond to each other. The motor can be controlled to generate a steering assist force. Thereby, even if tooth skipping occurs, the user can obtain a good operation feeling.

  Note that the condition for generating tooth skipping is limited to the case where the steering assist force applied by the motor is large. The steering assist force corresponds to the so-called rotational acceleration of the motor obtained by differentiating the detection result of the motor rotation angle sensor twice with respect to time. That is, it is possible to determine whether or not there is a possibility of tooth skipping through the rotational acceleration of the motor.

  In the above configuration, the steering mechanism includes a rack and pinion mechanism that converts the rotation of the steering wheel into the axial movement of the rack shaft accommodated in the rack housing, and the control device uses the detection result of the motor rotation angle sensor. When the one-time derivative is larger than the second set value, it is preferable to compare the first-set value with the two-time differentiated detection result of the motor rotation angle sensor.

  The situation where tooth jump occurs in a vehicle having a rack and pinion mechanism is limited to a so-called rack end collision in which the rack end of the rack shaft abuts against the inner wall of the rack housing at high speed. According to this configuration, the control device, when the detection result of the motor rotation angle sensor correlated with the movement speed of the rack shaft is differentiated once by time (motor rotation speed) is greater than the second set value In addition, since there is a possibility that a rack end collision may occur, the first set value is compared with a result obtained by differentiating the detection result of the motor rotation angle sensor twice with respect to time (rotational acceleration of the motor). Therefore, the control device wastefully rotates the motor as compared with an electric power steering device that does not detect the possibility of a rack end collision, that is, only compares the rotational acceleration of the motor with the first set value. Recalculation is reduced so that the detection result of the angle sensor corresponds to the turning angle. Since the control device when recalculating so that the detection result of the motor rotation angle sensor and the turning angle correspond, the motor cannot be controlled, and hence the steering assist force cannot be applied to the steering mechanism. The user may feel uncomfortable with the operation of the steering wheel.

  In that respect, according to the same configuration, the number of times of recalculation is reduced so that the detection result of the motor rotation angle sensor corresponds to the turning angle, compared with the case where the presence or absence of a rack end collision is not detected. That is, since the number of times the application of the steering assist force is interrupted is reduced, the user can obtain a good operation feeling.

In the above configuration, it is preferable that the steering mechanism includes a ball screw mechanism that connects the driven vehicle and the rack shaft.
According to this configuration, the rotation of the driven vehicle is smoothly converted into the axial movement of the rack shaft by the ball screw mechanism.

  According to the electric power steering device of the present invention, a good operation feeling can be obtained even if tooth skipping occurs.

The block diagram which shows schematic structure of an electric power steering apparatus. The side view including the partial cross section which shows a ball screw mechanism and a deceleration mechanism. The block diagram which shows schematic structure of ECU. The flowchart which shows the process of a tooth jump occurrence possibility judgment part.

Hereinafter, an embodiment of the electric power steering apparatus will be described.
<Outline of electric power steering device>
As shown in FIG. 1, an electric power steering device (EPS) 1 includes a steering mechanism 2 that steers steered wheels based on a steering operation of a driver, a steering assist mechanism 3 that assists the steering operation of the driver, and An ECU (electronic control unit) 22 that controls the operation of the steering assist mechanism 3 is provided.

The steering mechanism 2 includes a steering wheel 4 operated by a driver, and a steering shaft 5 that rotates integrally with the steering wheel 4. The steering shaft 5 includes a column shaft 6 connected to the center of the steering wheel 4, an intermediate shaft 7 connected to the lower end portion of the column shaft 6, and a pinion shaft 8 connected to the lower end portion of the intermediate shaft 7. . The pinion shaft 8 is divided into an input shaft 15 and an output shaft 16. The input shaft 15 and the output shaft 16 are provided on the same axis and are connected via a torsion bar 17. The lower end portion of the pinion shaft 8, more precisely the lower end portion of the output shaft 16, meshes with the rack shaft 12 (more precisely, the portion 11 on which the rack teeth are formed) extending in the direction intersecting the output shaft 16. Therefore, the rotational motion of the steering shaft 5 is converted into the reciprocating linear motion of the rack shaft 12 by the rack and pinion mechanism 10 including the pinion shaft 8 and the rack shaft 12. The reciprocating linear motion is transmitted to the left and right steered wheels 14 and 14 via tie rods 13 respectively connected to both ends (rack ends) of the rack shaft 12. Thereby, the turning angle θ _ta of the steered wheels 14 and 14 is changed. The traveling direction of the vehicle is changed by changing the turning angle θ _ta of the turning wheels 14 and 14. The rack shaft 12 is accommodated in a rack housing 9 supported by the vehicle body. For this reason, the turning of the steered wheels 14 and 14 is restricted by the rack end of the rack shaft 12 coming into contact with the rack housing 9 (rack end collision).

  The steering assist mechanism 3 includes a motor 19 that is a generation source of the steering assist force. As the motor 19, a three-phase AC motor such as a brushless motor is employed. The motor 19 is connected to the rack shaft 12 via a speed reduction mechanism 21 and a ball screw mechanism 20. The reduction mechanism 21 reduces the rotation of the motor 19. The speed reduction mechanism 21 will be described in detail later. The ball screw mechanism 20 transmits the rotation of the motor 19 decelerated by the decelerating mechanism 21 to the rack shaft 12. That is, the motor torque is applied to the rack shaft 12 as a steering assist force (assist force), thereby assisting the driver's steering operation.

As shown in FIG. 2, the speed reduction mechanism 21 includes an input pulley 35, an output pulley 36, and a belt 37.
The input pulley 35 is a toothed pulley. The input pulley 35 is connected to an input shaft 32 connected to the motor shaft 18 of the motor 19 via a joint, and rotates integrally with the input shaft 32 and the motor shaft 18.

  The output pulley 36 is a toothed pulley similar to the input pulley 35, and has a larger diameter than the input pulley 35. The output pulley 36 is connected to the ball screw mechanism 20.

  The belt 37 is a toothed belt and is stretched between the input pulley 35 and the output pulley 36. Thereby, the power of the motor 19, that is, the rotation of the motor shaft 18 is transmitted to the ball screw mechanism 20 through the input pulley 35, the belt 37, and the output pulley 36. Since the output pulley 36 has a larger diameter than the input pulley 35, the output pulley 36 rotates at a lower speed than the input pulley 35. Further, the input pulley 35 corresponds to the driving vehicle, the output pulley 36 corresponds to the driven vehicle, and the belt 37 corresponds to the transmission member.

  The ball screw mechanism 20 includes a ball nut 38, a ball screw groove 39 formed on the outer periphery of the rack shaft 12, and a large number of balls 40. The ball nut 38 rotates integrally with the output pulley 36. The ball nut 38 is fitted in the output pulley 36 and is screwed into the ball screw groove 39 via the ball 40. The rotation of the ball nut 38 is smoothly converted into the axial movement of the rack shaft 12 by the ball 40 and the ball screw groove 39.

As shown in FIG. 1, the ECU 22 acquires the detection results of various sensors provided in the vehicle as information indicating a driver's request or driving state, and controls the motor 19 in accordance with the acquired various information. To do. Examples of the various sensors include a vehicle speed sensor 26, a torque sensor 25, and a motor rotation angle sensor 23. The vehicle speed sensor 26 detects a vehicle speed (vehicle traveling speed) V. The torque sensor 25 detects the steering torque T _h by a relative rotational displacement amount between the input shaft 15 of the pinion shaft 8 through the torsion bar 17 and the output shaft 16. The motor rotation angle sensor 23 detects the rotation angle θ _m of the motor 19. ECU22 the vehicle speed V is acquired through these sensors, the steering torque _{T h,} and on the basis of the motor rotational angle theta _m, controls the motor 19.

<ECU>
Next, the ECU 22 will be described.
As shown in FIG. 3, the ECU 22 includes an assist torque calculation unit 51, a torque correction unit 52, a target current calculation unit 53, an output current control unit 54, a motor drive circuit 55, a motor current detection circuit 56, It has.

Assist torque calculation unit 51 calculates the assist torque T _{the as} based on the steering torque T _h and the vehicle speed V is acquired by the torque sensor 25 and a vehicle speed sensor 26.
The torque correction unit 52 determines the turning angle θ of the steered wheels 14 and 14 based on the motor rotation angle θ _m and the midpoint motor rotation angle θ _{m0 at} which the turning angle θ _ta of the steered wheels 14 and 14 becomes 0 (zero). _ta is calculated, and a corrected assist torque T _asr obtained by correcting the assist torque T _as based on the turning angle θ _ta is calculated. The midpoint motor rotation angle θ _m0 is calculated by a midpoint calculation unit 64 described later and stored in the memory 52a of the torque correction unit 52. The torque correction unit 52 rewrites the data stored in the memory 52a every time the midpoint motor rotation angle θ _m0 is calculated by the midpoint calculation unit 64.

The target current calculation unit 53 calculates a current command value I ^* to be supplied to the motor 19 based on the correction assist torque T _asr . The current command value I ^* is a command value indicating a current to be supplied to the motor 19.

The output current control unit 54 takes in the current command value I ^* and the current I actually supplied to the motor 19, and performs feedback control so that the actual current I follows the current command value I ^* based on the taken-in information. To output a corrected current command value I ^* _r .

The motor drive circuit 55 controls the current I supplied to the motor 19 by performing PMW (Plus Width Modulation) control based on the correction current command value I ^* _r .

The motor current detection circuit 56 detects the current I actually supplied to the motor 19 and sends the detected current I to the output current control unit 54.
Further, the ECU 22 includes a motor angular velocity calculation unit 61, a motor angular acceleration calculation unit 62, a determination unit 63, and a midpoint calculation unit 64.

Motor angular velocity calculation unit 61 calculates the motor angular velocity ω a (a differentiated once with motor rotation angle theta _m time) based on the motor rotation angle theta _m.
The motor angular acceleration calculation unit 62 calculates a motor angular acceleration α (a value obtained by differentiating the motor rotation angle θ _m twice with respect to time) based on the rotation angle θ _m of the motor 19 detected by the motor rotation angle sensor 23.

  Based on the motor angular velocity ω and motor angular acceleration α, the determination unit 63 determines whether or not there is a possibility of tooth skipping between the input pulley 35 and the belt 37 and between the belt 37 and the output pulley 36. Judge about. The tooth jump occurs under the condition that the rack shaft 12 moves in the axial direction at a high speed by the user's operation of the steering wheel 4 and the end of the rack collides with the movement. It is known that it is limited to when strongly assisting the axial movement of. In other words, whether or not there is a possibility of tooth skipping can be determined by whether or not there is a possibility of rack end collision.

  The memory 63a of the determination unit 63 stores various data for determining the presence or absence of a rack end collision. Specifically, a set value ω1 to be compared with the absolute value of the motor angular velocity ω and a set value α1 to be compared with the absolute value of the motor angular acceleration α are stored. The set values ω 1 and α 1 are values determined by the degree of engagement between the teeth between the input pulley 35 and the belt 37 and between the belt 37 and the output pulley 36. The determination unit 63 determines whether or not the rack shaft 12 is moving in the axial direction at a speed higher than the set value by comparing the absolute value of the motor angular velocity ω with the set value ω1, and determines the absolute value of the motor angular acceleration α. Through comparison with the set value α1, it is determined whether or not the assist force of the motor 19 is greater than the set value. The set value α1 corresponds to the first set value, and the set value ω1 corresponds to the second set value.

  Further, the determination unit 63 sets or defeats a flag F indicating that high-speed steering is being performed, which is used to determine whether or not a rack-end collision may occur, in the memory 63a. The flag F is set when there is a possibility that the rack shaft 12 is moving in the axial direction at a high speed. Further, the determination unit 63 includes a counter 63b used for determining a rack end collision. The counter 63b counts the number of times that processing for determining the presence or absence of a rack end collision in the state where the flag F is set is performed.

The memory 63a stores a set value T _d 1 for determining whether or not the rack shaft 12 is moving in the axial direction at a high speed. The set value T _d 1 is a value to be compared with the count data T _d counted by the counter 63b, and the rack shaft 12 is at a high speed, that is, at a speed at which tooth skipping may occur. The number is set to the number of times the determination unit 63 performs the process of determining whether or not there is a rack end collision before the inner wall comes into contact with the other inner wall (rack end collision). The determination unit 63 determines whether or not the rack shaft 12 has just moved in the axial direction at a high speed through a comparison between the count data T _d and the set value T _d 1. Even if the motor angular velocity ω is equal to or less than the set value ω1, if the rack shaft 12 is immediately moved in the axial direction at a high speed, the tooth skipping is caused by receiving external force such as the turning wheels 14 and 14 hitting the curb. This is because there is a possibility of occurrence. The set value T _d 1 is determined based on the difference between the length of the rack shaft 12 and the length between the inner walls of the rack housing 9 and the moving speed of the rack shaft 12 that may cause tooth skipping.

The determination unit 63 determines whether or not a rack end collision may occur based on the motor angular velocity ω, the motor angular acceleration α, and the count data _Td . When there is a possibility that a rack end collision will occur, it is determined that there is a possibility that tooth jump will occur, and a midpoint calculation command signal is output. The processing in the determination unit 63 will be described in detail later.

Midpoint computing section 64, the midpoint computing instruction signal is input, the vehicle speed V, the motor angular velocity omega, based on the motor rotation angle theta _m, turning angle theta _ta of the steered wheels 14, 14 are zero (0) The midpoint motor rotation angle θ _m0 is calculated as follows. In addition, since the process _concerning calculation of the midpoint motor rotation angle θ _m0 is known, a detailed description thereof will be omitted.
<Processing by tooth skipping possibility determination unit>
Next, processing for determining whether or not there is a possibility of a rack end collision in the determination unit 63 will be described with reference to the flowchart of FIG. This process is executed at a predetermined control cycle. The determination unit 63 acquires the motor angular velocity ω and the motor angular acceleration α every 5 msec, for example.

As shown in FIG. 4, when the determination unit 63 acquires the motor angular velocity ω and the motor angular acceleration α, it first determines whether or not the absolute value of the motor angular velocity ω is larger than the set value ω1 (step S1). If YES in step S1, that is, if the absolute value of the motor angular velocity ω is larger than the set value ω1, it is determined that the rack shaft 12 is moving in the axial direction at a high speed. In this case, the determination unit 63 resets the count data _Td to 0 (zero) (step S2) and sets a flag F (step S3).

  Next, the determination unit 63 determines whether or not the absolute value of the motor angular acceleration α is larger than the set value α1 (step S4). If YES in step S4, that is, if the absolute value of the motor angular acceleration α is larger than the set value α1, the assisting force of the motor 19 is large, so that the tooth jump may occur when the rack shaft 12 collides with the rack end. There is. In this case, the determination unit 63 outputs a midpoint calculation command signal to the midpoint calculation unit 64 (step S5), and ends a series of processes.

If NO in step S1, that is, if the absolute value of the motor angular velocity ω is equal to or less than the set value ω1, it is determined whether or not the flag F is set (step S6). If YES in step S6, that is, if the flag F is set, there is a possibility that the axial movement of the rack shaft 12 is continued at a high speed. In this case, determination unit 63, the count data _{T d} is incremented (1 is added to the previous count data _{T d)} (step S7), and count data _{T d} is determined greater or not than the set value _{T d} 1 (Step S8). If YES in step S8, that is, if the count data _Td is larger than the set value _Td1 , it is determined that the rack shaft 12 is not moving at a speed at which tooth skipping occurs. In this case, the determination unit 63 defeats the flag F (step S9) and ends a series of processes.

Note that, in step S8 NO, i.e., when the count data T _d is equal to or smaller than the set value T _{d 1} is the rack shaft 12 if it is immediately after the axial movement at a high speed, the steering wheel 14, 14 curb or the like When an external force such as a collision is applied, there is a possibility that tooth skipping may occur, so the determination unit 63 proceeds to step S4.

If NO in step S6, that is, if the flag F is not set, it is determined that the rack shaft 12 is not moving at a speed at which tooth skipping occurs. In this case, the determination unit 63 resets the count data _Td to 0 (zero) (step S10), and ends the series of processes.

As described above in detail, according to the present embodiment, the following effects can be obtained.
(1) When the absolute value of the motor angular acceleration α obtained by differentiating the motor rotation angle θ _m twice with respect to time is larger than the set value α1, the ECU 22 determines that tooth skipping may occur. The point calculation unit 64 includes a determination unit 63 that outputs a midpoint calculation command signal. Midpoint computing section 64, the midpoint computing instruction signal is input, the vehicle speed V, the motor angular velocity omega, based on the motor rotation angle theta _m, turning angle theta _ta of the steered wheels 14, 14 are zero (0) The midpoint motor rotation angle θ _m0 is calculated as follows. Then, the ECU 22 controls the motor 19 based on the calculated midpoint motor rotation angle θ _m0 . Thereby, even if tooth skipping occurs, the midpoint motor rotation angle θ _m0 is corrected each time, so that an appropriate turning angle θ _ta can be obtained from the motor rotation angle θ. As a result, the appropriate assist torque T _as and the current command value I ^* can be obtained, so that the user can obtain a good operation feeling.

(2) The determination unit 63 assumes that a rack end collision may occur when the absolute value of the motor angular velocity ω obtained by differentiating the motor rotation angle θ _m once with respect to time is larger than the set value ω1. The absolute value of the motor angular acceleration α is compared with the set value α1. It has been found that the occurrence of tooth skipping in a vehicle having a rack and pinion mechanism is limited to a so-called rack end collision in which the rack end of the rack shaft abuts against the inner wall of the rack housing at high speed. Thus, unlike the case where the determination unit 63 outputs a midpoint calculation command signal regardless of whether or not there is a possibility of a rack end collision, it is less likely to output a useless midpoint calculation command signal. Therefore, the chance that the midpoint calculation unit 64 calculates the midpoint motor rotation angle θ _m0 is reduced. Since the ECU 22 that is recalculating the midpoint motor rotation angle θ _m0 cannot appropriately control the motor 19, the user may feel uncomfortable with the operation of the steering wheel. In that respect, since the ECU 22 has few opportunities to calculate the midpoint motor rotation angle θ _m0 , the user can obtain a good operation feeling.

  (3) The steering mechanism 2 is provided with the ball screw mechanism 20 that connects the output pulley 36 and the rack shaft 12. The ball screw mechanism 20 includes a ball nut 38, a ball screw groove 39 formed on the outer periphery of the rack shaft 12, and a ball 40. The ball nut 38 is rotated integrally with the output pulley 36. Further, the ball nut 38 is screwed into the ball screw groove 39 via the ball 40. Thereby, the rotation of the ball nut 38 is smoothly converted into the axial movement of the rack shaft 12 by the ball 40 and the ball screw groove 39, rather than being converted into the axial movement by the normal screw pair. Therefore, the user can obtain a good operation feeling.

  (4) The steering mechanism 2 includes a belt 37 spanned between the input pulley 35 and the output pulley 36. Since the belt 37 can be deformed in shape, the degree of freedom in the positional relationship between the input pulley 35 and the output pulley 36 is increased.

(5) The determination unit 63 determines whether or not the rack shaft 12 has just moved in the axial direction at a high speed through a comparison between the count data T _d and the set value T _d 1. When the rack shaft 12 is immediately after moving in the axial direction at high speed, the absolute value of the motor angular acceleration α is compared with the set value α1. Immediately after the rack shaft 12 moves in the axial direction at a high speed, if the steered wheels 14 and 14 are subjected to an external force such as hitting a curb or the like, tooth skipping may occur, so the absolute value of the motor angular acceleration α And the set value α1 are compared to determine whether or not there is a possibility of tooth skipping. Then, the determination unit 63 generates a midpoint calculation command signal when there is a possibility of tooth skipping. Thus, since the midpoint motor rotation angle θ _m0 is corrected, the user can obtain a good operation feeling even if tooth skipping occurs.

In addition, you may change the said embodiment as follows.
In the above embodiment, the determination unit 63 does not have to compare the absolute value of the motor angular velocity ω with the set value ω1. That is, in FIG. 4, you may abbreviate | omit the process of step S1-S3 and step S6-S10. In this case, the determination unit 63 outputs a midpoint calculation command signal when the absolute value of the motor angular acceleration α is larger than the set value α1. Even in such a configuration, the same effect as the effect (1) of the above embodiment can be obtained.

  In the above embodiment, the steering mechanism 2 may not include the ball screw mechanism 20. In this case, for example, the output pulley 36 and the rack shaft 12 are connected by a screw pair. Even if comprised in this way, the effect similar to the effect of (1) and (2) of the said embodiment can be acquired.

  In the above embodiment, the belt 37 corresponding to the transmission member may be a gear that meshes with the input pulley 35 and the output pulley 36. Even if comprised in this way, the effect similar to the effect of (1)-(3) of the said embodiment can be acquired.

In the above embodiment, the determination unit 63 may not compare the count data T _d with the set value T _d 1. That is, in FIG. 4, the processing of steps S6 to S10 may be omitted. Even if comprised in this way, the effect similar to the effect of (1)-(4) of the said embodiment can be acquired.

In the above embodiment, the power of the motor 19 is used to assist the axial displacement of the rack shaft 12, but it may be used to assist the rotation of the steering shaft 5.
In the above embodiment, the amount of change in the steering torque T, the steering angle of the steering wheel 4 and the like may be combined with the determination of the presence or absence of the tooth skipping state.

Next, a technical idea conceived from the embodiment and the other examples will be additionally described.
(A) In the above configuration, the prime mover and the follower have teeth on outer peripheral surfaces, and the transmission member is a toothed belt that is stretched over the prime mover and the follower.

Since the belt can be deformed in shape, the degree of freedom in the positional relationship between the driving vehicle and the driven vehicle is increased.
(B) In the above configuration, the control device immediately after the rack shaft has moved at a high speed when the result obtained by differentiating the detection result of the motor rotation angle sensor once in time is equal to or less than a second set value. If it is immediately after, the result obtained by differentiating the detection result of the motor rotation angle sensor twice with time is compared with the first set value.

  If the rack shaft has just moved at a high speed, tooth skipping may occur due to external forces such as the turning wheels of the vehicle hitting the curb. In this regard, in this configuration, when the rack shaft has just moved at high speed, the first set value is compared with the result obtained by differentiating the detection result of the motor rotation angle sensor twice with respect to time. Therefore, the control device recalculates the turning angle when there is a possibility of tooth skipping, so that the motor can be controlled to generate an appropriate steering assist force. Thereby, even if tooth skipping occurs, the user can obtain a good operation feeling.

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering mechanism, 3 ... Steering assist mechanism, 4 ... Steering wheel, 9 ... Rack housing, 10 ... Rack and pinion mechanism, 12 ... Rack shaft, 14 ... Steering wheel, 19 ... Motor, 20 ... Ball screw mechanism, 21 ... Deceleration mechanism, 22 ... ECU,
DESCRIPTION OF SYMBOLS 23 ... Motor rotation angle sensor, 25 ... Torque sensor, 26 ... Vehicle speed sensor, 35 ... Input pulley (driven vehicle), 36 ... Output pulley (driven vehicle), 37 ... Belt, 38 ... Ball nut, 39 ... Ball screw groove, DESCRIPTION OF SYMBOLS 40 ... Ball, 51 ... Assist torque calculation part, 52 ... Torque correction part, 53 ... Target current calculation part, 54 ... Output current control part, 55 ... Motor drive circuit, 56 ... Motor current detection circuit, 61 ... Motor angular velocity calculation part 62 ... Motor angular acceleration calculation unit, 63 ... Determination unit, 64 ... Midpoint calculation unit.

Claims (3)

A motor that generates a steering assist force to be applied to a steering mechanism of the vehicle, a prime mover that is attached to an output shaft of the motor, a follower that is attached to the steering mechanism, and the prime mover and the follower that mesh with the prime mover; A transmission member that transmits the rotation of the vehicle to the driven vehicle, a motor rotation angle sensor that calculates the rotation angle of the motor, and a steered angle of a steered wheel of the vehicle based on a detection result of the motor rotation angle sensor A control device for controlling the motor based on the estimated turning angle and a steering operation of the vehicle,
The control device, when a result obtained by differentiating the detection result of the motor rotation angle sensor twice with respect to time is larger than a first set value, between the driving vehicle and the transmission member and between the driven vehicle and the transmission. An electric power steering apparatus that recalculates the detection result of the motor rotation angle sensor and the turning angle to correspond to each other because tooth skipping may occur in at least one of the members. The electric power steering apparatus according to claim 1, wherein
The steering mechanism includes a rack and pinion mechanism that converts rotation of a steering wheel into an axial movement of a rack shaft housed in a rack housing,
The control device is configured to differentiate the detection result of the motor rotation angle sensor twice in time when the detection result of the motor rotation angle sensor differentiated once in time is larger than a second set value. An electric power steering device for comparing with a first set value. The electric power steering apparatus according to claim 2,
The steering mechanism is an electric power steering apparatus including a ball screw mechanism that connects the driven vehicle and the rack shaft.