JP4524641B2 - Vehicle steering device - Google Patents

Description

  The present invention relates to a vehicle steering apparatus for steering a pair of steering wheels included in a vehicle.

2. Description of the Related Art Conventionally, as a vehicle steering device for turning a steering wheel of a vehicle, a vehicle steering device that has a steering actuator for each steering wheel and can independently steer left and right steering wheels is known. (For example, refer to Patent Document 1). As a vehicle steering device capable of adjusting the steering angle of the left and right steering wheels, a vehicle steering device having a steering angle variable device that changes the distance between the rack of the steering gear box and one of the left and right steering wheels is known. (For example, refer to Patent Document 2).
JP 2003-112650 A Japanese Patent Laid-Open No. 10-324253

  As described above, if steering actuators are provided for the left and right steering wheels, the steering angle of each steering wheel can be adjusted independently. However, in order to make the steering gear ratio variable or increase the turning angle, it is necessary to use a high output and a large stroke as each steering actuator. For this reason, in the above conventional example, it is difficult to make the vehicle steering device compact and reduce the energy consumption.

  Accordingly, an object of the present invention is to provide a vehicle steering apparatus that has a variable transmission ratio function and that can easily achieve downsizing of the apparatus and reduction of energy consumption.

  A vehicle steering apparatus according to the present invention is a vehicle steering apparatus for steering a pair of steering wheels included in a vehicle, a steering shaft coupled to a steering handle, a steering rod for turning each steering wheel, and a steering Provided between the steering angle transmission mechanism that converts the rotational movement of the shaft into the left and right linear movement of the steering rod, and the steering handle and the steering angle transmission mechanism, and the steering angle of the steering wheel and the turning angle of the steering wheel A transmission ratio variable means for changing a transmission ratio between the steering angle transmission mechanism and one of the steering wheels, an actuator for changing the effective length of the steering rod, a transmission ratio variable means and an actuator And a control means for controlling.

  In this vehicle steering apparatus, basically, the turning angle of the pair of steered wheels is set by the transmission ratio variable means, and the actuator is operated when setting the steered angle of the pair of steered wheels independently. As a result, a variable transmission function can be realized without using a plurality of large actuators, and a relatively low output actuator can be adopted as an actuator for independently setting the turning angles of a pair of steered wheels. . Therefore, in this vehicle steering device, the variable transmission ratio function can be realized, the entire device can be made compact, and the energy consumption can be reduced.

  The vehicle steering apparatus according to the present invention preferably further includes an electric assist unit that is provided between the transmission ratio variable means and the actuator and includes a motor for assisting the linear motion of the steering rod.

  Under such a configuration, the transmission ratio variable means changes the transmission ratio between the steering angle of the steering wheel and the turning angle of the steering wheel with the assistance of the electric assist unit. It is possible to adopt a low output and compact one.

  Furthermore, it is preferable that the control means permits the operation of the actuator during the operation of the electric assist unit.

  As described above, if the independent steering of the pair of steered wheels by the actuator is executed at the time of assist by the electric assist unit, the load on the actuator can be reduced. It becomes possible to achieve energy consumption.

  The control means includes an assist amount setting means for setting an assist amount by the electric assist unit, a target steering reaction force acquisition means for acquiring a target steering reaction force according to a steering input of the driver, and an actuator that operates the steering rod. The actual steering reaction force acquisition means for acquiring the actual steering reaction force when the effective length of the vehicle is changed, and when the actuator is operated, the motor is electrically driven based on the deviation between the target steering reaction force and the actual steering reaction force. It is preferable to include correction means for correcting the assist amount by the assist unit.

  When the pair of steered wheels are independently steered by the actuator described above, the road surface reaction forces on the steered wheels are different from each other because the steered angles of the steered wheels are different. For this reason, the steering reaction force differs depending on whether or not the pair of steered wheels are independently steered by the actuator. Therefore, in order to obtain a desired turning angle, the steering wheel should be input. The steering force will also fluctuate. In view of such points, in this vehicle steering apparatus, the target steering reaction force according to the driver's steering input and the actual steering reaction force when the actuator is operated to change the effective length of the steering rod The assist amount by the electric assist unit is corrected based on the deviation. Accordingly, it is possible to suppress the fluctuation of the steering force satisfactorily by suppressing the influence of the fluctuation of the steering reaction force caused by the independent steering of the steered wheels by the electric assist unit.

  Further, the vehicle steering apparatus according to the present invention may further include a steering angle detection means for detecting a steering angle of the steering handle and a vehicle speed detection means for detecting the vehicle speed of the vehicle, and the control means is detected by the steering angle detection means. The first target turning angle obtaining means for obtaining the first target turning angle so that the Ackermann angle becomes a predetermined value based on the steering angle, and the steering angle detecting means using a vehicle motion model created in advance. Second target turning angle acquisition means for acquiring a second target turning angle according to the detected steering angle, and first target turning angle and second target turning angle according to the vehicle speed detected by the vehicle speed detection means. It is preferable to include a target turning angle setting means for setting any one of the steering angles as a target turning angle.

  By adopting such a configuration, it is possible to set the optimum target turning angle according to the vehicle speed and the steering angle, and to improve the running performance and handling performance of the vehicle.

  In this case, the target turning angle setting means sets the first target turning angle as the target turning angle when the vehicle speed detected by the vehicle speed detection means is below a predetermined value, and is detected by the vehicle speed detection means. It is preferable that the second target turning angle is set as the target turning angle when the vehicle speed is equal to or higher than a predetermined value.

  ADVANTAGE OF THE INVENTION According to this invention, while having a variable transmission ratio function, the vehicle steering apparatus which can achieve the compactness of an apparatus and reduction of energy consumption easily is attained.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing a main part of a vehicle equipped with a vehicle steering apparatus according to the present invention. As shown in the figure, the vehicle 1 is a hybrid power that drives a pair of left and right steering wheels 2L, 2R, which are front wheels in this embodiment, or a rear wheel (not shown), an electric motor, or a combination thereof. The vehicle includes a drive source (not shown) such as a unit, and includes a vehicle steering device 10 for steering the left steering wheel 2L and the right steering wheel 2R. The steered wheels 2L and 2R each include a wheel and a tire, and the wheels of the steered wheels 2L and 2R are supported by a knuckle 4 via a disk rotor 3 constituting a brake unit. A knuckle arm 5 is integrated with or connected to the knuckle 4, and the knuckle 4 is supported to the vehicle body via a strut bar, a lower arm, or the like that constitutes a suspension device of the vehicle 1. A brake caliper 6 for applying a braking force to the steering wheels 2L and 2R via the disc rotor 3 is disposed inside the wheels of the steering wheels 2L and 2R.

  On the other hand, the vehicle steering device 10 of the vehicle 1 includes a steering handle 11 operated by a driver. The steering handle 11 is fixed to one end of a steering shaft 12, and the other end of the steering shaft 12 is connected to a steering gear box 14. The steering gear box 14 includes a pinion gear (not shown) fixed to the end of the steering shaft 12 and a rack 15 as a steering rod that meshes with the pinion gear. It functions as a steering angle transmission mechanism that converts to. Further, a transmission ratio variable mechanism 16 is incorporated in the steering shaft 12 so as to be positioned between the steering handle 11 and the steering gear box 14. The transmission ratio variable mechanism 16 has a function of changing a transmission ratio that is a ratio of the steering angle of the steered wheels 2L and 2R to the steering angle of the steering handle 11, and a drive source for changing the transmission ratio. The actuator 16a which uses the DC motor as a main component, and the reduction gear (differential device) 16b are included.

  The vehicle steering apparatus 10 is configured as a so-called electric power steering unit, and includes an electric assist unit 17 that applies torque to the rack 15 (steering rod) to assist the linear motion. In the present embodiment, the electric assist unit 17 is provided between the transmission ratio variable mechanism 16 and an actuator 20 described later, more specifically, between the steering gear box 14 and the actuator 20. The electric assist unit 17 includes a motor 18 including a stator and a rotor, and is configured as a so-called ball screw type assist unit, for example. In this embodiment, a ball screw nut (not shown) is fixed to the rotor of the motor 18, and this ball screw nut and a ball (not shown) and one end side of the rack 15 (in this embodiment, the steered wheel 2 </ b> L side). Torque is transmitted from the motor 18 to the rack 15 through the formed thread groove.

  Further, the vehicle steering apparatus 10 includes an actuator 20 disposed between the steering gear box 14, that is, the electric assist unit 17 and one of the steering wheels 2 </ b> L. The actuator 20 is connected to a rack 15 extending from the steering gear box 14 via the electric assist unit 17, and changes the effective length of the rack 15 as a steering rod. As shown in FIG. 2, the actuator 20 includes a housing 21, and the end portion of the rack 15 is accommodated in the housing 21. An enlarged cylindrical portion 15a is formed at the end of the rack 15 accommodated in the housing 21, and the stator 22 constituting the electric motor is fixed to the inner peripheral surface of the cylindrical portion 15a. Has been. A screw shaft 24 is rotatably supported inside the cylindrical portion 15 a of the rack 15 via a bearing 23. The screw shaft 24 has a thread groove on the outer periphery and functions as a rotor of a motor including the stator 22.

  A cylindrical portion 25 a formed at one end of an actuator rod 25 that constitutes a steering rod together with the rack 15 is inserted into the cylindrical portion 15 a of the rack 15. A ball screw nut 26 is fixed to the inner peripheral surface of the cylindrical portion 25a of the actuator rod 25, and the ball screw nut 26 engages with a screw groove of the screw shaft 24 via a ball (not shown). Thereby, if electric power is supplied to the motor comprised by the stator 22 and the screw shaft 24 as a rotor, the screw shaft 24 will rotate. As the screw shaft 24 rotates, the ball screw nut 26 and the cylindrical portion 25a rotate, whereby the actuator rod 25 moves forward and backward in the axial direction of the rack 15. In this way, by operating the actuator 20 to expand and contract the actuator rod 25, the effective length of the steering rod constituted by the rack 15 and the actuator rod 25 can be changed. The stator 22 is supplied with electric power from an external power source (not shown) via a spiral cable 27.

  A nut stopper 28 that can come into contact with the cylindrical portion 25 a of the actuator rod 25 is attached to the end portion of the cylindrical portion 15 a of the rack 15. In this case, the inner peripheral portion of the nut stopper 28 and the outer peripheral portion of the cylindrical portion 25a may be spline-engaged so that the nut stopper 28 has a detent function for preventing the actuator rod 25 from rotating. Further, two planes parallel to each other may be formed on the inner periphery of the nut stopper 28, and two planes engaged with the two inner planes of the nut stopper 28 may be formed on the outer periphery of the cylindrical portion 25a. Even if such a configuration is adopted, the nut stopper 28 can have a function of preventing the rotation of the actuator rod 25.

  The end of the actuator rod 25 extending from the housing 21 is connected to the knuckle arm 5 of the left steering wheel 2L via the tie rod 19. A boot 29 that covers the periphery of the connecting portion between the actuator rod 25 and the tie rod 19 is attached to the end of the housing 21 of the actuator 20. Further, the end of the rack 15 extending from the steering gear box 14 toward the steering wheel 2R is connected to the knuckle arm 5 of the right steering wheel 2R via a tie rod 19.

  As shown in FIG. 1, the vehicle steering apparatus 10 configured as described above is controlled by a steering electronic control unit (hereinafter referred to as “steering ECU”) 30 as control means. That is, the transmission ratio variable mechanism 16, the electric assist unit 17, and the actuator 20 included in the vehicle steering apparatus 10 are each controlled by the steering ECU 30. The steering ECU 30 includes a CPU that executes various arithmetic processes, a ROM that stores various control programs, a RAM that is used as a work area for data storage and program execution, an input / output interface, a memory, and the like.

  A steering angle sensor 31, a steering torque sensor 32, an actuator operating angle sensor 33, an EPS torque sensor 34, a stroke sensor 35, an ammeter 36, a wheel speed sensor 37, and a yaw rate sensor 38 are connected to the input / output interface of the steering ECU 30. Has been. The steering angle sensor 31 detects the steering angle of the steering handle 11, and gives a signal indicating the detected value to the steering ECU 30. The steering torque sensor 32 detects the steering torque given from the driver to the steering handle 11, and gives a signal indicating the detected value to the steering ECU 30. The actuator operating angle sensor 33 detects a change (increase) in the steering angle due to the operation of the transmission ratio variable mechanism 16 and gives a signal indicating the detected value to the steering ECU 30.

  The EPS torque sensor 34 detects the assist torque from the electric assist unit 17 and gives a signal indicating the detected value to the steering ECU 30. The stroke sensor 35 detects the displacement of the actuator rod 25 included in the actuator 20 and gives a signal indicating the detected value to the steering ECU 30. The ammeter 36 detects the value of the current supplied to the stator 22 constituting the motor of the actuator 20, and gives a signal indicating the detected value to the steering ECU 30. The wheel speed sensor 37 is provided on all the wheels including the steered wheels 2L and 2R. Each wheel speed sensor 37 detects the rotational speed of the corresponding wheel, and gives a signal indicating the detected value to the steering ECU 30. The yaw rate sensor 38 detects a rotational angular velocity (yaw rate) around the vertical axis of the vehicle 1 and gives a signal indicating the detected value to the steering ECU 30. The steering ECU 30 controls the transmission ratio variable mechanism 16, the electric assist unit 17, and the actuator 20 based on signals from the sensors 31 to 38 and the like.

  In the vehicle 1 including the vehicle steering device 10 described above, the steering ECU 30 determines a transmission ratio between the steering angle and the turning angle corresponding to the vehicle speed of the vehicle 1 obtained from the detection values of the wheel speed sensors 37, for example. The transmission ratio variable mechanism 16 is controlled so that the transmission ratio is realized. Thereby, the turning angle of the pair of steered wheels 2L and 2R is set by the transmission ratio variable mechanism 16. Further, when the turning angles of the pair of steering wheels 2L and 2R are set independently, the actuator 20 is operated by the steering ECU 30, and the effective length of the steering rod constituted by the rack 15 and the actuator rod 25 changes. Be made. As a result, the vehicle steering apparatus 10 realizes a variable transmission function without using a plurality of large actuators, and has a high output as the actuator 20 for independently setting the turning angles of the pair of steering wheels 2L and 2R. Need not be adopted. Therefore, in the vehicle steering apparatus 10, it is possible to make the entire apparatus compact and reduce the energy consumption.

  Further, in the vehicle steering apparatus 10, since the electric assist unit 17 that assists the linear motion of the rack 15 is provided between the transmission ratio variable mechanism 16 and the actuator 20, the transmission ratio variable mechanism 16 is an electric assist unit 17. With this support, the transmission ratio between the steering angle of the steering wheel 11 and the turning angles of the steering wheels 2L and 2R can be changed. Therefore, in the vehicle steering device 10, it is possible to adopt a low output and compact one as the transmission ratio variable mechanism 16. The electric assist unit 17 is not limited to the rack assist type as described above, and may be of a pinion assist type or a column assist type as long as it is provided between the transmission ratio variable mechanism 16 and the actuator 20. May be.

  In the vehicle steering apparatus 10, basically, the operation of the actuator 20 is permitted by the steering ECU 30 during the operation of the electric assist unit 17. As described above, the independent steering of the pair of steered wheels 2L and 2R by the actuator 20 is generally limited and allowed at the time of assist by the electric assist unit 17, so that the load on the actuator 20 can be reduced. Thus, the entire apparatus can be made compact and energy consumption can be reduced.

  Further, in the vehicle steering device 10, since the operation of the actuator 20 is allowed during the operation of the electric assist unit 17 as described above, the electric assist unit 17 is further transmitted from the viewpoint of reliably reducing the driver's steering burden. The priority of control is determined in the order of the variable ratio mechanism 16 and the actuator 20. That is, even if independent control of the pair of steered wheels 2L and 2R is not executed, there is basically no hindrance to normal traveling of the vehicle 1. Further, even if the transmission ratio variable mechanism 16 is not operated, a desired turning angle can be obtained by increasing the driver's handle operation amount. Therefore, if the electric assist unit 17, the transmission ratio variable mechanism 16, and the actuator 20 are controlled in accordance with the above-mentioned priority order with priority given to reducing the driver's steering burden and the like, the steered state of the left and right steered wheels 2L and 2R is controlled. Can be stabilized, and the control loss can be reduced.

  In the vehicle steering device 10, control according to the vehicle speed and the steering angle is executed in accordance with the procedure shown in FIG. 3 in order to stabilize the steering performance of the vehicle 1 and further reduce the control loss. . FIG. 3 is a flowchart for explaining a procedure for switching the control of the vehicle steering device 10 in accordance with the vehicle speed and the steering angle of the vehicle 1. The routine shown in the figure is repeatedly executed by the steering ECU 30 every predetermined time. In this case, the steering ECU 30 first acquires the vehicle speed of the vehicle 1 based on the signals from the wheel speed sensors 37 and acquires the steering angle set by the driver based on the signals from the steering angle sensor 31 ( S10). Further, the steering ECU 30 determines whether or not the vehicle speed acquired in S10 is below a predetermined threshold value (S12). The threshold value used in S12 is determined from a range of, for example, about 5 to 10 km, and when it is determined that the vehicle speed of the vehicle 1 is lower than the threshold value (Yes in S12), the steering ECU 30 causes the left and right steering wheels 2L and 2R. A process of optimizing the Ackermann angle, which is the difference in the steering angle between the two, is executed (S14).

  In S14, the steering ECU 30 first obtains the target turning radius of the vehicle 1 based on the steering angle acquired in S10. Furthermore, the steering ECU 30 uses a predetermined map or the like to turn the target wheels 2L and 2R so that the Ackermann angle is optimal from the calculated target turning radius and the wheel base and tread of the vehicle 1. An angle (first target turning angle) is calculated. When the target turning angle of each steered wheel 2L, 2R is calculated, the steering ECU 30 obtains the turning angle of the steered wheel 2R on the side where the actuator 20 for left and right independent steering is not provided. Calculate the operating amount. Next, the steering ECU 30 calculates the turning angle set by the transmission ratio variable mechanism 16 for the steering wheel 2L on the side where the actuator 20 for left and right independent steering is provided, and the obtained steering wheel 2L Based on the deviation between the turning angle and the target turning angle of the steered wheel 2L, the operation amount of the actuator 20, that is, the displacement of the actuator rod 25 is calculated.

  When the operation amount of the transmission ratio variable mechanism 16 and the operation amount of the actuator 20 are calculated in this way, the steering ECU 30 operates the transmission ratio variable mechanism 16 and the actuator 20 by the determined operation amounts. Gives a control signal for. As a result, each of the steering wheels 2L and 2R is steered by the transmission ratio variable mechanism 16 and the actuator 20 so that the turning angle of the inner wheel is larger than the turning angle of the outer wheel by a predetermined amount. The turning angles of the wheels 2L and 2R are set. Thus, in the vehicle steering apparatus 10, when the vehicle speed is lower than the predetermined threshold, the transmission ratio variable mechanism 16 and the actuator 20 are controlled so that the Ackermann angle is optimized. As a result, since the lateral force applied to the wheels becomes extremely small by optimizing the Ackermann angle, the vehicle 1 can be smoothly turned in a desired direction.

  When the processing of S14 is executed, the steering ECU 30 determines the operation amount of the actuator 20 so as to suppress the actuator 20 from operating excessively and the steering angle difference between the left and right steering wheels 2L and 2R from becoming larger than necessary. After setting the guard value so as not to exceed the predetermined threshold (S16), the processes after S10 are repeated.

  On the other hand, when it is determined in S12 that the vehicle speed of the vehicle 1 is not lower than the threshold value (No in S12), the steering ECU 30 determines whether or not the steering angle acquired in S10 is lower than a predetermined threshold value. (S18). The threshold value used in S18 is set to a value that allows the vehicle 1 to be regarded as traveling substantially straight. When it is determined that the steering angle is below the threshold value and the driver intends to drive the vehicle 1 straight (Yes in S18), the steering ECU 30 executes a process for stabilizing the vehicle 1 traveling straight ahead. (S20).

  In S20, the steering ECU 30 controls the transmission ratio variable mechanism 16 and the actuator 20 so that the left and right steering wheels 2L and 2R are steered to the toe-in side by a predetermined angle, respectively. That is, the steering ECU 30 calculates the operation amount of the transmission ratio variable mechanism 16 for obtaining the toe-in angle of the steering wheel 2R on the side where the actuator 20 for left and right independent steering is not provided. Next, the steering ECU 30 calculates the turning angle set by the transmission ratio variable mechanism 16 for the steering wheel 2L on the side where the actuator 20 for left and right independent steering is provided, and the obtained steering wheel 2L Based on the deviation between the steered angle and the toe-in angle of the steered wheel 2L, the operation amount of the actuator 20, that is, the displacement of the actuator rod 25 is calculated.

  When the operation amount of the transmission ratio variable mechanism 16 and the operation amount of the actuator 20 are calculated, the steering ECU 30 generates a control signal for operating the transmission ratio variable mechanism 16 and the actuator 20 by the determined operation amounts. give. Accordingly, the left and right steered wheels 2L and 2R are steered to the toe-in side by a predetermined angle by the transmission ratio variable mechanism 16 and the actuator 20. Thereby, in the vehicle steering device 10, when the driver's steering input is less than a predetermined amount, it is possible to ensure the straight running stability of the vehicle 1 satisfactorily. When the process of S20 is executed, the steering ECU 30 sets the guard value so that the operation amount of the actuator 20 does not exceed a predetermined threshold (S16), and repeatedly executes the processes after S10 again.

  On the other hand, if it is determined in S18 that the steering angle is not below a predetermined threshold (No in S18), the steering ECU 30 executes control for turning the vehicle 1 (S22). In S22, the steering ECU 30 determines a target turning radius of the vehicle 1 based on the steering angle acquired in S10. Further, the steering ECU 30 calculates a target turning angle (second target turning angle) of each of the steered wheels 2L and 2R according to the obtained target turning radius using a vehicle motion model created in advance. The vehicle motion model used here takes into account the wheel base and tread of the vehicle 1, the centrifugal force applied to the wheels during the turning of the vehicle 1, etc., and the optimum steering wheels 2 </ b> L and 2 </ b> R according to the target turning radius. It is created based on experiment and analysis so as to define the target turning angle.

  When the target turning angle of each steered wheel 2L, 2R is calculated, the steering ECU 30 obtains the turning angle of the steered wheel 2R on the side where the actuator 20 for left and right independent steering is not provided. Calculate the operating amount. Next, the steering ECU 30 calculates the turning angle set by the transmission ratio variable mechanism 16 for the steering wheel 2L on the side where the actuator 20 for left and right independent steering is provided, and the obtained steering wheel 2L Based on the deviation between the turning angle and the target turning angle of the steered wheel 2L, the operation amount of the actuator 20, that is, the displacement of the actuator rod 25 is calculated. When the operation amount of the transmission ratio variable mechanism 16 and the operation amount of the actuator 20 are calculated in this way, the steering ECU 30 operates the transmission ratio variable mechanism 16 and the actuator 20 by the determined operation amounts. Gives a control signal for. Thereby, the transmission angle variable mechanism 16 and the actuator 20 set the steered angles of the steered wheels 2L and 2R to appropriate values that can generate a lateral force corresponding to the centrifugal force applied to the wheels.

  As described above, in the vehicle steering device 10, when the vehicle speed of the vehicle 1 is lower than the predetermined value, the target turning angle (first target turning angle) is set so that the Ackermann angle becomes a predetermined value based on the steering angle. Is obtained and set as the target turning angle of the steered wheels 2L and 2R. Further, when the vehicle speed of the vehicle 1 is equal to or higher than a predetermined value, a target turning angle (second target turning angle) corresponding to the steering angle is acquired using a vehicle motion model created in advance, and the steered wheels 2L and 2R are acquired. Is set as the target turning angle. Thus, by setting the optimal target turning angle according to the vehicle speed and the steering angle, it becomes possible to improve the running performance and handling performance of the vehicle 1.

  By the way, in the vehicle 1 described above, as shown in FIG. 4, the steering wheels 2L and 2R are approximately in accordance with the road surface reaction forces applied to the steering wheels 2L and 2R during straight traveling where the steering wheels 2L and 2R are respectively slightly steered to the toe-in side. Wheel reaction forces RL and RR having the same magnitude and opposite directions are applied to the steering rod constituted by the rack 15 and the actuator rod 25. For this reason, in the actuator 20, as shown in FIG. 4, an internal force Fi is generated for maintaining the turning angle of each steered wheel 2L, 2R. Further, when the steering wheels 2L and 2R are steered, for example, in the right direction in the drawing in a state where the steering wheels 2L and 2R are not independently steered by the actuator 20, the steering rod constituted by the rack 15 and the actuator rod 25 is used. As shown in FIG. 5, wheel reaction forces RL and RR having substantially the same size and the same direction (leftward in the figure) are applied. As described above, when the steered wheels 2L and 2R are steered in a state where the steered wheels 2L and 2R are not independently steered by the actuator 20, the internal force Fi generated in the actuator 20 is almost the same as that during straight travel, The steering reaction force is a steering reaction force necessary to maintain the turning angle of each steered wheel 2L, 2R.

  On the other hand, as shown in FIG. 6, the steered wheels 2L and 2R are steered to the right in the figure, for example, and the actuator 20 is operated so that the steer angle of the left steered wheel 2L is steered to the right. When it is larger than the turning angle of the wheel 2R, wheel reaction forces RL and RR having directions as shown in FIG. 6 are applied to the steering rod constituted by the rack 15 and the actuator rod 25 according to the road surface reaction force. It is done. In the example of FIG. 6, the wheel reaction force RL from the left steering wheel 2L is larger than the wheel reaction force RR from the right steering wheel 2R. In this case, the internal force Fi of the actuator 20 for maintaining the steered angles of the steered wheels 2L and 2R is greater than when the steered wheels 2L and 2R are not independently steered.

  Therefore, depending on the difference in the magnitude of the internal force Fi generated in the actuator 20 between the case where the independent steering of the pair of steered wheels 2L and 2R by the actuator 20 is not performed and the case where it is performed, FIG. As shown in FIG. 6, the magnitude of the axial force Fs applied to the steering rod constituted by the rack 15 and the actuator rod 25 changes. As a result, the steering reaction force against the driver differs between when the steering wheels 2L and 2R are not independently steered and when they are performed. The steering force to be input also varies.

  That is, when the independent steering of the pair of steered wheels 2L and 2R is not performed by the actuator 20, the correlation between the driver's steering force (steering torque) and the steering reaction force as shown by a solid line in FIG. In contrast, when the independent steering of the pair of steered wheels 2L and 2R is performed by the actuator 20, the internal force Fi generated by the actuator 20 increases, and the correlation between the two is In FIG. 7, it is as shown by a two-dot chain line. As can be seen from FIG. 7, when the steering wheel 2L, 2R is independently steered and the internal force Fi generated by the actuator 20 becomes large, in order to obtain a desired turning angle, according to the increase in the internal force Fi. Therefore, the steering force to be applied to the steering handle 11 must be increased.

  In view of these points, in the vehicle 1 described above, a routine for suppressing fluctuations in the steering force of the driver is executed by the steering ECU 30 when the steering wheels 2L and 2R are steered. FIG. 8 is a flowchart showing a routine for suppressing the fluctuation of the steering force of the driver when the vehicle 1 is steered. The routine shown in the figure is executed when the vehicle 1 is steered by the steering ECU 30. As shown in FIG. 8, the steering ECU 30 determines the presence or absence of a steering command from the driver (S30). If it is determined that a steering command has been made (Yes in S30), the steering ECU 30 is based on the signal from each wheel speed sensor 37. The vehicle speed of the vehicle 1 is acquired, the steering angle set by the driver based on the signal from the steering angle sensor 31 is acquired, and the steering input by the driver to the steering wheel based on the signal from the steering torque sensor 32 is acquired. Torque is acquired (S32). Further, the steering ECU 30 obtains the vehicle speed, the steering obtained in S10 from a map prepared in advance so as to define the correlation between the vehicle speed, the steering angle, the steering force (steering torque) by the driver, and the target steering reaction force accordingly. A target steering reaction force corresponding to the angle and the steering torque is acquired (S34).

  After the process of S34, the steering ECU 30 determines whether the left and right steered wheels 2L and 2R are independently steered by the actuator 20 based on the vehicle speed, the steering angle, etc. acquired in S32 (S36). When the steering ECU 30 determines that the steering wheels 2L and 2R are independently steered (Yes in S36), the steering ECU 30 determines the actual current value at that time based on the detection value of the ammeter 36 that detects the supply current value to the actuator 20. A steering reaction force (actual steering reaction force) is acquired (S38). As described above, the steering reaction force depends on the magnitude of the internal force Fi generated by the actuator 20. Further, the internal force Fi generated by the actuator 20 is approximately proportional to the value of the current supplied to the actuator 20 in order to maintain the turning angle of each steered wheel 2L, 2R. Therefore, the actual steering reaction force can be estimated from the supply current value for the actuator 20 detected by the ammeter 36. Therefore, in S38, the steering ECU 30 uses a map created in advance so as to define the correlation between the supply current value for the actuator 20 and the actual steering reaction force, and the actual steering reaction according to the supply current value for the actuator 20. Get power.

  Next, the steering ECU 30 obtains a deviation between the target steering reaction force obtained in S34 and the actual steering reaction force obtained in S38 (S40), and further, the electric assist unit 17 calculates the deviation so that the deviation becomes zero. The correction amount of the assist amount is calculated (S42). When the correction amount of the assist amount is calculated, the steering ECU 30 sets the assist amount by the electric assist unit 17 using the correction amount (S44). As described above, in the vehicle 1 including the vehicle steering device 10, the target steering reaction force according to the driver's steering input and the effective length of the steering rod including the rack 15 and the actuator rod 25 are changed by operating the actuator 20. The assist amount by the electric assist unit 17 is corrected based on the deviation from the actual steering reaction force at the time. As a result, the electric assist unit 17 can suppress the fluctuation of the steering reaction force caused by the independent steering of the steered wheels 2L and 2R and can satisfactorily suppress the fluctuation of the steering force.

  When it is determined in S36 that the steered wheels 2L and 2R are not independently steered (No in S36), the assist amount correction amount by the electric assist unit 17 is set to zero (S46), and in S44. The assist amount by the electric assist unit 17 is set. If it is determined that the steering command has not been issued by the driver (No in S30), the process of shifting to S32 is skipped, and the presence or absence of the steering command by the driver is determined again.

It is a schematic block diagram which shows the principal part of the vehicle provided with the vehicle steering device by this invention. It is a fragmentary sectional view which shows the actuator contained in the vehicle steering apparatus of FIG. 2 is a flowchart for explaining a procedure for switching control of a vehicle steering device in accordance with a vehicle speed and a steering angle of the vehicle in FIG. 1. FIG. 2 is a schematic diagram for explaining a force acting on a vehicle steering device during travel of the vehicle of FIG. FIG. 2 is a schematic diagram for explaining a force acting on a vehicle steering device during travel of the vehicle of FIG. 1. FIG. 2 is a schematic diagram for explaining a force acting on a vehicle steering device during travel of the vehicle of FIG. It is a graph which shows the correlation of the steering force and steering reaction force in the case where independent steering of a steered wheel is not performed, and when it is performed. 3 is a flowchart showing a routine for suppressing fluctuations in a driver's steering force during steering of a vehicle.

Explanation of symbols

1 vehicle, 2L, 2R steering wheel, 3 disc rotor, 4 knuckle, 5 knuckle arm, 6 brake caliper, 10 vehicle steering device, 11 steering handle, 12 steering shaft, 14 steering gear box, 15 rack, 16 transmission ratio variable mechanism , 17 Electric assist unit, 18 Motor, 19 Tie rod, 20 Actuator, 21 Housing, 22 Stator, 23 Bearing, 24 Screw shaft, 25 Actuator rod, 26 Ball screw nut, 27 Spiral cable, 28 Nut stopper, 29 Boot, 30 Steering ECU, 31 steering angle sensor, 32 steering torque sensor, 33 actuator operating angle sensor, 34 EPS torque sensor, 35 stroke sensor, 36 ammeter, 37 wheel speed sensor, 38 yaw rate sensor.

Claims (5)

In a vehicle steering apparatus for steering a pair of steering wheels included in a vehicle,
A steering shaft coupled to the steering handle;
A steering rod for turning each steering wheel;
A steering angle transmission mechanism for converting the rotational movement of the steering shaft into the left and right linear movement of the steering rod;
A transmission ratio variable means that is provided between the steering handle and the steering angle transmission mechanism, and changes a transmission ratio between a steering angle of the steering handle and a turning angle of the steering wheel;
The steering angle transmission mechanism and is provided between at least one of the steering wheel, when setting the steering angle of the pair of steerable wheels independently, by changing the effective length of the steering rod rolling An actuator for setting the rudder angle ;
The operating amount of the transmission ratio variable means and the operating amount of the actuator are calculated so that the turning angle of the wheel located inside of the pair of steered wheels is larger than the turning angle of the wheel located outside. A vehicle steering apparatus comprising: a control means for supplying a control signal corresponding to an operation amount to the transmission ratio variable means and the actuator .   2. The vehicle steering according to claim 1, further comprising an electric assist unit that is provided between the transmission ratio variable means and the actuator and includes a motor for assisting a linear motion of the steering rod. apparatus.   The vehicle steering apparatus according to claim 2, wherein the control unit allows the actuator to be operated during the operation of the electric assist unit. The control means includes
An assist amount setting means for setting an assist amount by the electric assist unit;
Target steering reaction force acquisition means for acquiring a target steering reaction force according to a driver's steering input;
An actual steering reaction force acquisition means for acquiring an actual steering reaction force when the actuator is operated to change the effective length of the steering rod;
The correction means which correct | amends the assist amount by the said electric assist unit based on the deviation of the said target steering reaction force and the said actual steering reaction force when the said actuator is act | operated is characterized by the above-mentioned. Or the vehicle steering device of 3. Steering angle detection means for detecting the steering angle of the steering wheel; and vehicle speed detection means for detecting the vehicle speed of the vehicle;
The control means includes
First target turning angle acquisition means for acquiring a first target turning angle so that the Ackermann angle becomes a predetermined value based on the steering angle detected by the steering angle detection means;
Second target turning angle acquisition means for acquiring a second target turning angle corresponding to the steering angle detected by the steering angle detection means using a vehicle motion model created in advance;
When the vehicle speed detected by the vehicle speed detection means is below a predetermined value, the first target turning angle is set as a target turning angle, while the vehicle speed detected by the vehicle speed detection means is greater than or equal to the predetermined value. The vehicle steering apparatus according to any one of claims 1 to 4, further comprising target turning angle setting means for setting the second target turning angle as a target turning angle in some cases .

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