JP2006062406A - Vehicular steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the generation of noise due to a speed reducer connected to an electric motor, in a vehicular steering device. <P>SOLUTION: The vehicular steering device is provided with the electric motor 31 for assisting steering. Rotation output of the electric motor 15 is reduced and converted into a linear motion by a ball screw mechanism 16 to be transmitted to a rack bar 14. An electronic control unit 24 adds control torque related to the rotation speed of the electric motor 15 to target steering assist torque, thereby controlling the rotation torque of the electric motor 15. The control torque is calculated on the basis of anglular speed ω calculated by using a motor rotation angle θm detected by a rotation angle sensor 22, and is a feedback control signal showing a differential value between a target value and detected speed for suppressing changes in the angular speed ω. The target value is renewed according to changes in the angular speed of the electric motor 15. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a vehicle steering apparatus that steers steered wheels according to a steering operation of a steering handle.

Conventionally, as shown in, for example, Patent Document 1 below, in order to assist steering of a steered wheel according to a steering operation of the steering handle, to transmit a steering force applied to the steered wheel to the steered wheel. 2. Description of the Related Art A vehicle steering apparatus is known in which a rotational driving force of an electric motor is transmitted to a transmission mechanism via a ball screw mechanism that is a speed reducer.
JP 2003-314654 A

  Generally, in this type of conventional device, it is necessary to increase the clearance in the ball screw mechanism (decelerator) to some extent in order to reduce the frictional force. In particular, since this clearance changes according to the temperature, it is necessary to consider the decrease due to the temperature change. However, if the ball screw mechanism (speed reducer) is given clearance, an abnormal noise is generated when the ball screw mechanism collides with the ball screw mechanism when driving on a Belgian road (stone path) or turning the steering wheel. In the case of using a reduction gear as a speed reducer, abnormal noise is generated due to the collision of meshed teeth. In particular, when the fluctuation cycle of the rotational speed of the electric motor coincides with the natural vibration cycle of the control system, the generation of abnormal noise becomes significant.

  The present inventor has noticed that the occurrence of abnormal noise due to this collision is caused by a change in the angular velocity of the output shaft of the electric motor. The present invention has been made based on this viewpoint, and an object of the present invention is to provide a vehicle steering apparatus that suppresses the generation of the abnormal noise.

  In order to achieve the above object, a feature of the present invention is that a vehicle steering apparatus includes an electric motor and a speed reducer, and transmits the rotation of the electric motor to the steered wheels via the speed reducer. And a suppression control signal for suppressing fluctuations in the angular velocity of the electric motor using the detected angular velocity, and adding the generated suppression control signal to the rotation control signal of the electric motor. And a fluctuation suppression control means for providing the same.

  In this case, for example, the fluctuation suppression control unit includes a difference value calculation unit that repeatedly calculates a difference value between a target angular velocity representing a target angular velocity of the electric motor and an angular velocity detected by the angular velocity detection, and a difference value. Each time a difference value is calculated by the calculation means, a difference value limiting means for limiting an upper limit and a lower limit of values that can be taken by the calculated difference value, and a difference value limiting means from the target angular velocity used in the calculation by the difference value calculation means The target angular velocity updating means for subtracting the upper and lower limit limited difference values and updating the target angular velocity to make the subtraction result the target angular velocity used for the next difference value calculation by the difference value calculating means. The calculated difference value may be used as a suppression control signal.

  In the present invention, for example, the rotation control signal of the electric motor is a steering assist control signal for assisting the steering operation of the steering wheel, and the fluctuation suppression control means adds the suppression control signal to the steering assist control signal. It is good to. The rotation control signal of the electric motor is a steering control signal for turning the steered wheels according to the steering operation of the steering handle, and the fluctuation suppression control means adds the suppression control signal to the steering control signal. May be.

  According to this, since the fluctuation suppression control means generates a suppression control signal for suppressing fluctuations in the angular velocity of the electric motor and adds it to the rotation control signal of the electric motor, the rotation of the electric motor input to the speed reducer The fluctuation of the angular velocity at is suppressed. As a result, even if a clearance is provided in the speed reducer, it is possible to prevent abnormal noise due to the clearance. In particular, if the fluctuation suppression control means is composed of a difference value calculation means, a difference value restriction means, and a target angular velocity update means, it is possible to suppress fluctuations in angular velocity during rotation of the electric motor by setting an upper limit and a lower limit in the difference value restriction means. The degree of follow-up of the rotation of the electric motor with respect to the rotation control signal can be varied, and it is possible to easily adjust the rotation follow-up of the electric motor while suppressing the occurrence of abnormal noise. .

a. DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 relates to the first embodiment, and is an overall vehicle steering apparatus having an assist function with respect to a steering operation by a driver. FIG.

  The vehicle steering apparatus includes a steering shaft 12 connected to a steering handle 11 so that an upper end thereof is integrally rotated. A pinion gear 13 is connected to a lower end of the shaft 12 so as to be integrally rotated. The pinion gear 13 meshes with rack teeth formed on the rack bar 14 to constitute a rack and pinion mechanism. Left and right front wheels FW1 and FW2 are steerably connected to both ends of the rack bar 14, and the left and right front wheels FW1 and FW2 are left and right according to the axial displacement of the rack bar 14 as the steering shaft 12 rotates about the axis. Steered to. An electric motor 15 for steering assist is assembled to the rack bar 14. The rotation of the electric motor 15 is decelerated by the ball screw mechanism 16 constituting the speed reducer and converted into a linear motion of the rack bar 14.

  Next, the electric control device 20 that controls the operation of the electric motor 15 will be described. The electric control device 20 includes a steering torque sensor 21, a rotation angle sensor 22, and a vehicle speed sensor 23. The steering torque sensor 21 is assembled to the upper part of the steering shaft 12 and detects the steering torque Tr acting on the steering shaft 12 by the turning operation of the steering handle 11. The steering torque Tr represents the steering torque Tr when the steering handle 11 is steered in the right direction and the left direction by positive and negative values. The rotation angle sensor 22 is assembled to the electric motor 15 and detects the motor rotation angle θm from the neutral position of the electric motor 15. The motor rotation angle θm represents a rotation angle when the electric motor 15 rotates forward and backward by a positive / negative value. The vehicle speed sensor 23 detects and outputs the vehicle speed V.

  The electric control device 20 includes an electronic control unit 24 connected to the steering torque sensor 21, the rotation angle sensor 22, and the vehicle speed sensor 23. The electronic control unit 24 controls the electric motor 15 via the drive circuit 25 by executing the assist control program shown in FIG. The drive circuit 25 causes the drive current specified by the electronic control unit 24 to flow through the electric motor 15.

  Next, the operation of the first embodiment configured as described above will be described. The electronic control unit 24 starts to repeatedly execute the assist control program every predetermined short time by turning on the ignition switch. The execution of the assist control program is started in step S10 of FIG. 2, and the steering torque Tr, the motor rotation angle θm, and the vehicle speed V are input from the steering torque sensor 21, the rotation angle sensor 22, and the vehicle speed sensor 23 in step S11, respectively. .

  Next, in step S12, the electronic control unit 24 refers to an assist command value table provided in the ROM, and calculates a target assist torque Tas that changes according to the steering torque Tr and the vehicle speed V. As shown in FIG. 3, the assist command value table stores a plurality of target assist torques Tas that increase nonlinearly as the steering torque Tr increases for each of a plurality of representative vehicle speed values. The target assist torque Tas is larger as the vehicle speed V is lower than the same steering torque Tr. Instead of using this assist command value table, the target assist torque Tr that changes according to the steering torque Tr and the vehicle speed V is defined in advance by a function, and the target assist torque Tr is calculated by using the function. You may make it calculate.

  After the process of step S12, the electronic control unit 24 performs a differentiation operation in step S13 using both motor rotation angles θm input by the process of step S11 during execution of the current and previous assist control program. Then, the angular velocity ω (= dθm / dt) of the electric motor 15 is calculated. In step S14, the angular velocity difference value Δω (= ω * −ω) is calculated by subtracting the calculated current angular velocity ω from the current target angular velocity ω *. The target angular velocity ω * is a variable that represents the target angular velocity of the electric motor 15 and is a value calculated when the previous assist control program is executed.

  After calculating the difference value Δω, the electronic control unit 24 calculates the control torque Tc based on the difference value Δω in step S15. In calculating the control torque Tc, for example, a PID control method can be used. That is, a proportional term k1 · Δω obtained by multiplying the difference value Δω by the coefficient k1, a differential term k2 · d (Δω) / dt obtained by multiplying the differential value d (Δω) / dt obtained by differentiating the difference value Δω, and The value obtained by adding the integral term k3 · ∫ (Δω) dt obtained by integrating the difference value Δω and the integral value ∫ (Δω) dt to the coefficient k3 is the control torque Tc (= k1 · Δω + k2 · d (Δω) / dt + k3 · ∫ (Δω) dt). In the differential calculation and integration calculation of the difference value Δω, the difference value Δω previously calculated when the assist control program is executed is used in addition to the difference value Δω calculated when the assist control program is executed this time. The coefficients k1, k2, and k3 are predetermined values. Further, in the calculation of the control torque Tc, any one of the proportional term k1 · Δω, the differential term k2 · d (Δω) / dt and the integral term k3 · ∫ (Δω) dt is used without using the PID control method. May be the control torque Tc, or any two added values may be the control torque Tc.

  Next, in step S16, the electronic control unit 24 controls the electric motor 15 via the drive circuit 25, and a torque Tas + Tc having a magnitude obtained by adding the control torque Tc to the calculated target assist torque Tas is generated. Thus, the electric motor 15 is operated. Specifically, the electronic control unit 24 outputs a current command value representing a current having a magnitude proportional to the torque Tas + Tc to the drive circuit 25, and the drive circuit 25 electrically drives a current having a magnitude specified by the current command value. Flow to motor 15.

  Thereby, the electric motor 15 outputs a rotational torque equal to the torque Tas + Tc to its output shaft. This rotational torque is transmitted to the ball screw mechanism 16, which decelerates the rotation of the electric motor 15 and converts it into linear motion to drive the rack bar 14 in the axial direction. As a result, the turning operation of the steering handle 11 by the driver is assisted by the electric motor 15, and the left and right front wheels FW 1 and FW 2 are steered by the steering force by the driver and the assist force by the electric motor 15.

  After the control of the electric motor 15 in step S16, the target angular velocity ω * is updated for the next assist control program by the processing in steps S17 and S18, and the execution of the assist control program is temporarily terminated in step S19. In step S17, limiter processing is performed to limit the upper and lower limits of values that can be taken by the difference value Δω calculated by the processing in step S14. In this limiter processing, a target difference value Δω corresponding to the difference value Δω is calculated with reference to a difference value table provided in the ROM. As shown in FIG. 4, the difference value table changes linearly within a predetermined range of a predetermined difference value Δω (within a range from a negative predetermined value −Δω1 to a positive predetermined value Δω1) and out of the predetermined range. A target difference value Δω * which is a constant value (within a range below the negative predetermined value −Δω1 and beyond the positive predetermined value Δω1) is stored. In the first embodiment, the proportional coefficient of the target difference value Δω * that linearly changes with respect to the difference value Δω in the predetermined range of the predetermined difference value Δω is “1”, but other than “1”. The value of may be adopted. Further, the target difference value Δω * may be nonlinearly changed with respect to the difference value Δω within a predetermined range of the predetermined difference value Δω. Further, instead of using this difference value table, a target difference value Δω * that changes in the characteristics according to the difference value Δω is defined in advance by a function, and the target difference value Δω * is obtained by using the function. May be calculated.

  In step S18, the limiter process in step S17 is performed from the target angular speed ω * used in the calculation process in step S14 (that is, the target angular speed ω * calculated in step S18 when the assist control program is executed last time). The target angular velocity ω * is updated by subtracting the target difference value Δω * obtained by the above and setting the subtraction result ω * −Δω * as a new target angular velocity ω * (= ω * −Δω *). The updated target angular velocity ω * is used when the assist control program is executed next time. The initial value of the target angular velocity ω * is set to “0”, for example, by an initial setting process (not shown).

  In the first embodiment that operates as described above, the rotational torque of the electric motor 15 is made closer to the target angular velocity ω * by the control torque Tc added to the target assist torque Tas by the processing of steps S13 to S16. Be controlled. The target angular velocity ω * is changed so as to approach the actual angular velocity ω of the electric motor 15 by the process of step S18, but the range of change of the target difference value Δω * is limited by the limiter process of step S17. . That is, control is performed so that the change in the target angular velocity ω * is suppressed by the processing in steps S17 and S18. As a result, the control term based on the control torque Tc for the rotation control of the electric motor 15 acts so as to suppress the fluctuation of the angular velocity of the electric motor 15. Therefore, fluctuations in angular velocity due to rotation of the electric motor 15 input to the ball screw mechanism 16 that is a speed reducer are suppressed, and even if a clearance is provided in the ball screw mechanism 16, it is possible to prevent the generation of noise due to the clearance.

  In the limiter process in step S17, by setting the absolute value | Δω1 | of the predetermined value Δω1 small, the change in the target angular velocity ω * is more greatly restricted, and the variation in the angular velocity of the electric motor 15 is further suppressed, that is, the target. The followability of the rotation of the electric motor 15 with respect to the assist torque Tas is deteriorated. On the other hand, by setting the absolute value | Δω1 | of the predetermined value Δω1 large, the restriction on the change in the target angular velocity ω * is relaxed, and a large variation in the angular velocity of the electric motor 15 is allowed, that is, the electric motor 15 with respect to the target assist torque Tas. The follow-up performance of the rotation becomes good. Accordingly, the degree of suppression of fluctuations in the angular velocity during the rotation of the electric motor 15, that is, the followability of the rotation of the electric motor 15 with respect to the target assist torque Tas can be varied only by appropriately setting the limiting characteristic of the limiter process. In addition, it is possible to easily adjust the rotation of the electric motor 15 so as to ensure the follow-up of the rotation of the electric motor 15 while suppressing the generation of abnormal noise.

  In the first embodiment, the steering operation of the steering handle 11 is assisted by driving the rack bar 14 with the electric motor 15. However, instead of this, the steering operation of the steering handle 11 may be assisted by driving the steering shaft 12 around the axis. In this case, as shown by a broken line in FIG. 1, the electric motor 31 is assembled to the steering shaft 12, and the rotation of the electric motor 31 is transmitted to the steering shaft 12 via the speed reducer 32 to drive the shaft 12 about the axis. You can do that. As the speed reducer 32 in this case, a reduction gear mechanism such as a combination of a small gear and a large gear or a planetary gear mechanism may be used. Also in this case, the rotation angle sensor 33 is assembled to the electric motor 31 to detect the rotation angle θm of the electric motor 31.

  In the modified example configured as described above, an abnormal noise caused by the collision of meshed teeth in the gear mechanism constituting the speed reducer 32 becomes a problem. However, as in the case of the first embodiment, the electronic control unit 24 controls the rotation of the electric motor 31 in the same manner as in the first embodiment by executing the assist control program of FIG. Therefore, also in this modification, as in the case of the first embodiment, the generation of abnormal noise due to the collision of the meshed teeth can be satisfactorily suppressed.

b. Second Embodiment Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 5 is an overall schematic diagram of a steer-by-wire vehicle steering apparatus according to the second embodiment.

  This vehicle steering apparatus also includes a steering shaft 42 that is connected to the steering handle 41 so as to rotate integrally at its upper end, and an electric motor 43 for steering reaction force is assembled to the lower end of the shaft 42. The electric motor 43 applies a steering reaction force to the turning operation of the steering handle 41 by its rotation.

  Further, the vehicle steering apparatus includes a steered shaft 44 that is separated from the steering shaft 42 and extends in the left-right direction. Left and right front wheels FW1 and FW2 are steerably connected to both ends of the steered shaft 44, and the left and right front wheels FW1 and FW2 are steered to the left and right according to the axial displacement of the steered shaft 44. An electric motor 45 for turning is assembled on the turning shaft 44. The rotation of the electric motor 45 is decelerated by a ball screw mechanism 46 constituting a speed reducer and converted into a linear motion of the steered shaft 44.

  Next, the electric control device 50 that controls the operation of the electric motors 43 and 45 will be described. The electric control device 50 includes a steering angle sensor 51 and a rotation angle sensor 52. The steering angle sensor 51 is assembled to the steering shaft 42 and detects the steering angle θh by detecting the rotation angle around the axis of the steering shaft 42. The steering wheel steering angle θh represents the steering angle of the steering wheel 11 in the right direction and the left direction by positive and negative values. The rotation angle sensor 52 is assembled to the electric motor 45 and detects the motor rotation angle θm from the neutral position of the electric motor 45. The motor rotation angle θm represents a rotation angle when the electric motor 15 rotates forward and backward by a positive / negative value.

  Further, the electric control device 50 includes an electronic control unit 53 connected to the steering angle sensor 51 and the rotation angle sensor 52. The electronic control unit 53 also has a microcomputer composed of a CPU, ROM, RAM, etc. as main components, and controls the drive of the electric motors 43 and 45 via the drive circuits 54 and 55 by executing the steering control program shown in FIG. To do. The drive circuits 54 and 55 flow drive currents designated by the electronic control unit 53 to the electric motors 43 and 45, respectively.

  Next, the operation of the second embodiment configured as described above will be described. The electronic control unit 24 starts to repeatedly execute the steering control program every predetermined short time by turning on the ignition switch. The execution of the steering control program is started in step S20 in FIG. 6, and the steering wheel steering angle θh and the motor rotation angle θm are input from the steering angle sensor 51 and the rotation angle sensor 52 in step S21, respectively. Next, in step S22, the actual turning angle δ of the left and right front wheels FW1, FW2 is calculated based on the input motor rotation angle θm by proportional conversion in consideration of the ball screw mechanism 46 and the like.

  Next, in step S23, the electronic control unit 53 refers to a target turning angle table prepared in advance in the ROM, and calculates a target turning angle δ * corresponding to the input steering wheel steering angle θh. . As shown in FIG. 7, the target turning angle table stores a target turning angle δ * that increases as the steering wheel steering angle θh increases. Instead of using the target turning angle table, a function in which the relationship between the steering wheel steering angle θh and the target turning angle δ * is defined in advance is defined, and the input steering angle using the same function is defined. A target turning angle δ * corresponding to θ may be calculated. In addition, a vehicle speed sensor, a yaw rate sensor, a lateral acceleration sensor, and the like may be provided to correct the calculated target turning angle δ * according to the vehicle speed, yaw rate, lateral acceleration, and the like detected by the sensors. .

  Next, in step S24, the electronic control unit 53 refers to the target steering reaction force table and calculates the target steering reaction force Th corresponding to the input steering angle θh. As shown in FIG. 8, the target steering reaction force table stores a target steering reaction force Th that increases as the steering wheel steering angle θh increases. Instead of using the target steering reaction force table, a function that defines the relationship between the steering angle θh and the target steering reaction force Th is defined in advance, and the input steering angle is input using the same function. The target steering reaction force Th corresponding to θh may be calculated. In this case, the target steering reaction force Th may be corrected according to the vehicle speed, the yaw rate, the lateral acceleration, and the like.

  After calculating the target turning angle δ * and the target steering reaction force Th, the electronic control unit 53 performs the difference value by the processing of steps S25 to S27 similar to steps S13 to S15 of FIG. 2 of the first embodiment. Δω and control torque Tc are calculated. Then, in step S28, the electronic control unit 24 multiplies the subtraction value δ * -δ obtained by subtracting the actual turning angle δ from the calculated target turning angle δ * by a predetermined coefficient k to obtain the multiplication value k. The operation of the electric motor 45 is controlled via the drive circuit 55 according to the control signal k · (δ * −δ) + Tc obtained by adding the control torque Tc to (δ * −δ). Specifically, the electronic control unit 53 outputs a current command value representing a current having a magnitude proportional to the control signal k · (δ * −δ) + Tc to the drive circuit 55, and the drive circuit 55 uses the current command value. A current having a designated magnitude is supplied to the electric motor 45.

  As a result, the electric motor 45 outputs a rotational torque equal to the control signal k · (δ * −δ) + Tc to the output shaft. This rotational torque is transmitted to the ball screw mechanism 46, which decelerates the rotation of the electric motor 45 and converts it into a linear motion to drive the steered shaft 44 in the axial direction. As a result, the left and right front wheels FW1, FW2 are basically steered to the target turning angle δ *.

  After the control of the electric motor 45 for turning, the electronic control unit 53 controls the electric motor 43 for steering reaction force via the drive circuit 54 in step S29 to calculate the calculated target steering reaction force Th. Is generated in the electric motor 45. Specifically, the electronic control unit 53 outputs a current command value representing a current having a magnitude proportional to the steering reaction force Th to the drive circuit 54, and the drive circuit 55 outputs a current having a magnitude specified by the current command value. The electric motor 43 flows. As a result, an appropriate steering reaction force Th is applied to the steering operation of the steering handle 11 by the driver.

  After the control of the electric motors 43 and 45 in steps S28 and S29, in steps S30 and S31, the same processing as in steps S17 and S18 in FIG. 2 of the first embodiment is performed for the next assist control program. The angular velocity ω * is updated, and the execution of the assist control program is temporarily terminated in step S32.

  In the second embodiment that operates as described above, as in the case of the first embodiment, the rotational torque of the electric motor 45 is changed to the target turning angle δ * and the actual turning by the processing in steps S25 to S28. It is controlled by the control torque Tc added to the difference value δ * -δ of the angle δ. Also in this case, as in the case of the first embodiment, the control term by the control torque Tc for the rotation control of the electric motor 45 suppresses the fluctuation of the angular velocity of the electric motor 45 by the processing of the steps S30 and S31. Acts like As a result, fluctuations in angular velocity due to rotation of the electric motor 45 input to the ball screw mechanism 46 that is a speed reducer are suppressed, and even if a clearance is provided in the ball screw mechanism 46, it is possible to prevent the generation of noise due to the clearance. Further, as in the case of the first embodiment, the degree of suppression of fluctuations in the angular velocity during the rotation of the electric motor 45, that is, the left and right front wheels FW1, FW2 can be set only by appropriately setting the limiting characteristics of the limiter process in step S30. The followability of the rotation of the electric motor 45 with respect to the control signal δ * -δ for turning to the target turning angle δ * can be varied, and the occurrence of abnormal noise can be suppressed and the rotation of the electric motor 45 can be controlled. It can be easily adjusted to ensure follow-up performance.

  In the second embodiment, the steered shaft 44 is linearly driven by the electric motor 45 and the ball screw mechanism 46 to steer the left and right front wheels FW1, FW2. However, instead of this, as shown in FIG. 9, the rotational torque of the electric motor 61 may be transmitted to the pinion gear 63 via the speed reducer 62 and the pinion gear 63 may be rotationally driven. In this case, the reduction gear 62 may be a reduction gear mechanism such as a combination of a small gear and a large gear or a planetary gear mechanism. The pinion gear 63 meshes with the rack teeth formed on the rack bar 64, and the rack bar 64 is displaced in the axial direction by rotation thereof. The left and right front wheels FW1 and FW2 are steerably connected to both ends of the rack bar 64, and are steered to the left and right according to the axial displacement of the rack bar 64 as the electric motor 61 rotates. Also in this case, the rotation angle sensor 65 is assembled to the electric motor 61 so that the rotation angle θm of the electric motor 31 is detected.

  In the modified example configured as described above, an abnormal noise caused by collision of meshed teeth in the gear mechanism constituting the speed reducer becomes a problem. However, as in the case of the second embodiment, the electronic control unit 53 controls the rotation of the electric motor 61 in the same manner as in the second embodiment by executing the steering control program of FIG. Therefore, according to this modification, as in the case of the second embodiment, the generation of abnormal noise due to the collision of the meshed teeth can be satisfactorily suppressed.

c. Other Modifications Further, the present invention is not limited to the first and second embodiments and the modifications, and various modifications can be adopted within the scope of the present invention.

  In the first embodiment and the modification thereof, the target angular velocity ω * is calculated by the calculation processing of steps S17 and S18. In the second embodiment and the modification thereof, the target angular velocity ω * is calculated by the calculation processing of steps S30 and S31. Was calculated. However, in addition to these calculation processes, a calculation process for executing a low-pass filter process may be performed on the calculated target angular velocity ω * to further suppress a change in the target angular velocity ω *.

  Furthermore, in the said 1st and 2nd embodiment and those modifications, what was rotated as the steering handles 11 and 41 was employ | adopted. However, the present invention is also applicable to a vehicle steering apparatus using a steering handle for steering the left and right front wheels FW1 and FW2 by a linear operation such as a joystick instead of the steering handles 11 and 41.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall schematic diagram of a vehicle steering apparatus according to a first embodiment and having an assist function with respect to a steering operation by a driver. It is a flowchart of the assist control program performed by the electronic control unit of FIG. It is a graph which shows the relationship between steering torque, a vehicle speed, and target assist torque. It is a graph which shows the limiter characteristic of a difference value. It is a whole schematic diagram of the steering device of vehicles concerning a 2nd embodiment and adopting a steer-by-wire system. It is a flowchart of the steering control program performed by the electronic control unit of FIG. It is a graph which shows the relationship between a steering wheel steering angle and a target turning angle. It is a graph which shows the relationship between a steering wheel steering angle and a target steering reaction force. FIG. 10 is an overall schematic diagram of a vehicle steering apparatus that employs a steer-by-wire system according to a modification of the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11,41 ... Steering handle, 12, 42 ... Steering shaft, 13 ... Pinion gear, 14 ... Rack bar, 15, 31, 43, 45, 61 ... Electric motor, 16, 46 ... Ball screw mechanism, 21 ... Steering torque sensor, 22, 33, 52, 65 ... rotational angle sensor, 23 ... vehicle speed sensor, 24, 53 ... electronic control unit, 32, 62 ... speed reducer, 44 ... steered shaft, 51 ... steering angle sensor.

Claims (4)

In a vehicle steering apparatus comprising an electric motor and a speed reducer, wherein the rotation of the electric motor is transmitted to the steered wheels via the speed reducer.
Angular velocity detection means for detecting the angular velocity of the electric motor;
Fluctuation suppression control means for generating a suppression control signal for suppressing the fluctuation of the angular velocity of the electric motor using the detected angular velocity and adding the generated suppression control signal to the rotation control signal of the electric motor is provided. A vehicle steering system characterized by that. 2. The vehicle steering apparatus according to claim 1, wherein the fluctuation suppression control means is
Difference value calculation means for repeatedly calculating a difference value between a target angular velocity representing a target angular velocity of the electric motor and the angular velocity detected by the angular velocity detection every predetermined time;
Difference value limiting means for limiting the upper and lower limits of the values that can be taken by the difference value calculated each time the difference value is calculated by the difference value calculating means;
The difference value limited by the difference value limiting unit is subtracted from the target angular velocity used in the calculation by the difference value calculating unit, and the subtraction result is used to calculate the next difference value by the difference value calculating unit. A vehicle steering apparatus comprising target angular velocity update means for updating a target angular velocity to obtain a target angular velocity to be used, and using the calculated difference value as the suppression control signal.   The rotation control signal of the electric motor is a steering assist control signal for assisting a steering operation of a steering wheel, and the fluctuation suppression control means adds the suppression control signal to the steering assist control signal. Or the vehicle steering apparatus described in 2 The rotation control signal of the electric motor is a steering control signal for turning the steered wheels in accordance with a steering operation of the steering handle, and the fluctuation suppression control means adds the suppression control signal to the steering control signal. The vehicle steering apparatus according to claim 1 or 2, wherein

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