JP2021146977A - Vehicle steering apparatus - Google Patents

Abstract

To provide a vehicle steering apparatus, restraining the adverse effect of a road surface state such as cant and reducing the estimated errors of a road surface friction coefficient in an independent steering vehicle.SOLUTION: In a vehicle steering apparatus 20, one or more lines of tires 91 to 94 among two or more pairs of left/right tires in a vehicle longitudinal direction are mounted to an independently steering vehicle 100 independently steerable by the left and right wheels. Plural steering actuators 31 to 34 drive each of tires 91 to 94 in a steering direction. A toe angle control part 25 outputs a driving signal to the actuators 31 to 34 to carry out "periodic steering" changing periodically the toe angle by the prescribed steering frequency and angle amplitude. A tire external force detection part 29 detects a tire external force (SAT) imposed to the tires 91 to 94 steered by the steering actuators 31 to 34. Besides, a road surface friction coefficient estimation part 26 carries out the frequency analysis of the tire external force and estimates the road surface friction coefficient based on the relation of the tire external force with the road surface friction coefficient.SELECTED DRAWING: Figure 1

Description

The present invention relates to a steering device for automobiles.

The angle set so that the front ends of the left and right pairs of tires face inward or outward with respect to the traveling direction of the vehicle is called a toe angle. When the toe angle is positive, the front end of the tire faces inward, resulting in a "toe-in", which enhances straight-line stability. When the toe angle is negative, the front end of the tire faces outward, resulting in "toe-out", which improves turning performance. In sports cars, it may be set to toe-out, but in general, one or both of the front wheels and rear wheels are often set to toe-in in order to improve straight-line stability.

For example, Patent Document 1 discloses a steering system provided with toe angle control means in an independently steering vehicle capable of independently steering the left and right tires. In this steering system, when the vehicle speed is equal to or higher than a predetermined value, the road surface friction coefficient is estimated based on the current value of the steering actuator.

International release WO2019 / 189096

The prior art of Patent Document 1 estimates the tire external force (for example, self-aligning torque) generated when the toe angle is controlled in an independent steering vehicle from the current generated in the steering actuator, and further from the characteristics with respect to the tire external force. It can be understood that the road friction coefficient is estimated.

However, this conventional technique does not consider the influence of road gradients such as cants. When there is a cant on the road surface, in addition to the force related to the road surface friction coefficient, the lateral force due to the cant also acts on the tire, so the detected value of the tire external force to be detected may vary, and an estimation error of the road surface friction coefficient may occur. ..

The present invention has been created in view of the above points, and an object of the present invention is to suppress the influence of road surface conditions such as cants in an independently steering vehicle and reduce the estimation error of the road surface friction coefficient. Is to provide.

In the steering device for automobiles according to the present invention, among two or more rows of left and right tires in the front-rear direction of the vehicle, one or more rows of tires (91-94) can be independently steered by the left wheel and the right wheel. It is mounted on the steering vehicle (100). This automobile steering device includes a plurality of steering actuators (31-34) for driving each tire to be driven in the steering direction, a toe angle control unit (25), a tire external force detection unit (29), and the tire external force detection unit (29). A road surface friction coefficient estimation unit (26) is provided.

The angle at which the front ends of the left and right pairs of tires face inward with respect to the traveling direction of the vehicle is defined as positive, the angle facing outward is negative, and the angle deflected symmetrically by the steering actuator is defined as the "toe angle". The toe angle control unit outputs a drive signal to the steering actuator so as to execute "periodic steering" in which the toe angle is periodically changed at a predetermined steering frequency and angle amplitude.

The tire external force detecting unit detects the tire external force applied to the tire steered by the steering actuator. The road surface friction coefficient estimation unit frequency-analyzes the tire external force and estimates the road surface friction coefficient based on the relationship between the tire external force and the road surface friction coefficient at the steering frequency.

For example, when a certain cant is provided on the road, the external force generated by the cant on the tire is a direct current component. Therefore, by frequency-analyzing the tire external force due to periodic steering and estimating the road surface friction coefficient using only the steering frequency component, it is possible to suppress an error due to the road surface condition.

The block diagram of the steering device for automobiles according to one embodiment. The figure which shows the state of (a) toe angle 0, (b) toe-in. The figure which shows the lateral force acting on a tire and SAT (tire external force). The figure which shows the estimation (comparative example) of the road surface friction coefficient based on SAT at a constant toe angle. The figure which shows the tire external force by a cant. The figure which shows the time change of SAT at the time of running with a constant toe angle. A flowchart of road surface friction coefficient estimation according to an embodiment. Waveform diagram of toe angle and SAT in periodic steering. The figure explaining the influence on SAT by acceleration / deceleration during periodic steering. SAT waveform diagram in periodic steering with a road friction coefficient μ = 0.4. The figure which shows the frequency analysis result of SAT in the periodic steering. The figure which shows the estimation (the present embodiment) of the road surface friction coefficient based on the SAT maximum value at the steering frequency extracted by the frequency analysis.

Hereinafter, an automobile steering device according to an embodiment of the present invention will be described with reference to the drawings. The steering device for automobiles of the present embodiment is mounted on an independent steering vehicle in which one or more rows of tires can be independently steered by the left wheel and the right wheel among two or more rows of left and right tires in the front-rear direction of the vehicle. Will be done.

Conventionally, in a general vehicle, a pair of left and right tires are mechanically connected via a link, and the tires are steered by steering. In the future, it is expected to develop into a steer-by-wire system in which the steering wheel and the left-right pair of tire links are mechanically separated, and an independent steering vehicle in which the left-right pair of tires can be steered independently. In steer-by-wire, the left and right pairs of tires work together and move only in the same phase, whereas in an independent steering vehicle, the left and right wheels can be freely steered.

An example of the merits of the independent steering vehicle will be described. In a conventional vehicle, the steering angle of the tire when turning is always the same on the left and right. However, geometrically, if the steering angle on the inside of the turn is not larger than the steering angle on the outside of the turn, the tire will skid. On the other hand, in the case of an independent steering vehicle, the left and right steering angles can be freely set according to the turning radius, so that the running resistance due to the side slip of the tire can be reduced as compared with the conventional case.

(One Embodiment)
With reference to FIG. 1, the configuration of the steering device 20 for automobiles according to one embodiment will be described. The independent steering vehicle 100 shown in FIG. 1 is a four-wheeled vehicle having two rows of left and right tires in the front-rear direction of the vehicle, and the front row tires 91 and 92 and the rear row tires 93 and 94 can all be independently steered. be. The automobile steering device 20 includes a plurality of (for example, four) steering actuators 31-34, a toe angle control unit 25, a road surface friction coefficient estimation unit 26, an acceleration / deceleration detection unit 27, a vehicle state detection unit 28, and a tire external force. A detection unit 29 is provided.

The plurality of steering actuators 31-34 drive each tire 91-94 in the steering direction. In the four-wheel independent steering vehicle 100, the steering actuator FL31 and the steering actuator FR32 for driving the front row left and right tires 91 and 92, and the steering actuator RL33 and the steering actuator for driving the rear row left and right tires 93 and 94. RR34 is provided.

The toe angle control unit 25 outputs a drive signal to the steering actuators 31-34 so as to execute "periodic steering" in which the toe angle is periodically changed at a predetermined steering frequency f and an angle amplitude θamp. .. In the present specification, the "toe angle" is symmetrical with respect to the traveling direction of the vehicle by the steering actuators 31-34, where the angle at which the front ends of the left and right pairs of tires face inward is positive and the angle at which the front ends of the left and right tires face outward is negative. It is defined as "the angle to be deflected".

That is, in the conventional general vehicle, the toe angle is initially set in the alignment adjustment when the vehicle is stopped, whereas in the independent steering vehicle 100, the steering actuators 31-34 are driven while the vehicle is running. It is possible to change the toe angle and perform periodic steering. Further, in the present embodiment, the toe angle control unit 25 can individually set the steering frequency f and the angle amplitude θamp of each row. However, it is not assumed that the left and right pairs of tires in each row will be asymmetrically periodically steered. The front row tires 91 and 92 are periodically steered by the symmetrical drive signals output from the front row left and right steering actuators 31 and 32. The tires 93 and 92 in the rear row are periodically steered by the symmetrical drive signals output from the steering actuators 33 and 34 on the left and right in the rear row.

Further, the toe angle is defined as positive when the front end of the left and right pair of tires faces inward, and the toe angle is defined as negative when the front end of the left and right pair of tires faces inward. At toe-in, straight-line stability is high but turning performance is low, and at toe-out, straight-line stability is high but straight-line stability is low. As shown in FIG. 2, in order to improve the straight running stability, the vehicle is usually adjusted to a "toe-in" in which the front ends of the left and right pairs of tires face slightly inward (1 [deg] or less) in the straight running state.

As a trade-off for stabilizing the vehicle, as shown in FIG. 3, the direction of the tire deviates from the traveling direction, so that a tire lateral force depending on the road surface friction coefficient μ is generated. The road surface friction coefficient μ is a coefficient representing the friction between the road surface and the tire. Since the running resistance increases due to this tire lateral force, it is basically desirable to set the toe angle to 0 [deg].

Next, the tire external force detecting unit 29 detects the tire external force applied to the tires 91-94 steered by the steering actuator 31-34. The tire external force means a self-aligning torque (hereinafter referred to as “SAT”) or a tire lateral force that tries to return the tire in the direction opposite to the steering direction. Hereinafter, the tire external force will be described as SAT. The description of "SAT" is interpreted as "external tire force" as appropriate. As shown in FIG. 3, SAT is a function of the wheel load F, the road surface friction coefficient μ, and the toe angle θ. The tire external force detection unit 29 can detect the SAT by the load current of the steering actuators 31-34 and the force sensor or torque sensor provided in the steering mechanism.

By the way, since the SAT and the road surface friction coefficient μ have a correlation, the road surface friction coefficient μ can be estimated by detecting the SAT. When traveling with the toe angle set to a constant value (for example, 2 [deg]), SAT corresponding to the road surface friction coefficient μ is generated as shown by the solid line in FIG. 4 (that is, when the cant is 0%). When traveling on an ideally flat road, a constant SAT is detected, and the road surface friction coefficient μ can be estimated accurately from the detected SAT. In addition, the specific numerical value of SAT is not described in each figure. However, in order to clearly indicate that it is a torque dimension quantity, "SAT [Nm]" is written on the axis of each figure.

Patent Document 1 (International Publication WO2019 / 189096) discloses a technique for estimating the road surface friction coefficient in an independently steered vehicle. In this conventional technique, it can be understood that the tire external force (for example, SAT) generated when the toe angle is controlled is estimated from the current generated in the steering actuator, and the road surface friction coefficient is estimated from the characteristics with respect to the tire external force.

However, the actual road cannot be flat because it has a cant that is a cross slope for improving drainage and has ruts. Kant is set at ± 2% by the Road Structure Ordinance. As shown in FIG. 5, when the cant is provided, a tire external force is always applied to the tire in either direction. Due to the influence of the cant, the SAT in FIG. 4 changes in the range from the broken line (cant-2%) to the alternate long and short dash line (cant + 2%), and the road surface friction coefficient μ estimated from the same SAT value has an error of up to 19%. Occurs. Therefore, the estimation of the road surface friction coefficient based on the SAT at a constant toe angle will be treated as a comparative example with respect to the present embodiment.

FIG. 6 shows the time change of the SAT during running at a constant toe angle. The SAT at cant-2% is slightly larger than the SAT at cant 0%, and the SAT at cant + 2% is slightly smaller. This difference becomes the SAT detection error due to the cant. However, after the vehicle starts, the SAT generated in the tire maintains a constant value while the cant is traveling on a constant road, and can be regarded as a low-frequency constant component. Therefore, it is considered that the SAT by the cant and the SAT according to the road surface friction coefficient μ by the periodic steering can be distinguished by periodically changing the toe angle at a predetermined steering frequency f.

In the present embodiment, based on this point of view, the toe angle control unit 25 outputs a drive signal to the steering actuators 31-34 so as to execute periodic steering as described above. Then, the road surface friction coefficient estimation unit 26 frequency-analyzes the SAT detected by the tire external force detection unit 29, and estimates the road surface friction coefficient μ based on the relationship between the SAT and the road surface friction coefficient μ at the steering frequency f.

Returning to FIG. 1, the automobile steering device 20 of the present embodiment further includes an acceleration / deceleration detection unit 27 and a vehicle state detection unit 28. The acceleration / deceleration detection unit 27 detects the rate of change in speed per hour during acceleration or deceleration of the vehicle, and notifies the road surface friction coefficient estimation unit 26. The rate of change in speed during acceleration corresponds to positive acceleration, and the rate of change in speed during deceleration corresponds to negative acceleration.

The vehicle condition detection unit 28 detects the vehicle condition due to the vehicle behavior or an external force, and notifies the road surface friction coefficient estimation unit 26. Vehicle behavior means the active behavior of the vehicle, and external force means the force of disturbance acting on the tires due to ruts, swells, crosswinds, etc. on the road surface. For example, the vehicle state detection unit 28 detects roll, yaw, lateral acceleration, vehicle height change amount, and the like by using a yaw rate sensor, a lateral acceleration sensor, a height sensor, and the like.

The road surface friction coefficient estimation unit 26 determines whether or not the road surface friction coefficient μ can be estimated based on the information from the acceleration / deceleration detection unit 27 and the vehicle state detection unit 28. The road surface friction coefficient estimation unit 26 estimates the road surface friction coefficient μ only when the absolute value of the speed change rate is equal to or less than a predetermined rate of change threshold and the vehicle state satisfies a predetermined stability condition.

Next, with reference to the flowchart of FIG. 7 and FIGS. 8 to 12, the estimation of the road surface friction coefficient according to the present embodiment will be described. In the description of the flowchart, the symbol "S" means a step. In S51, the acceleration / deceleration detection unit 27 detects acceleration or deceleration of the vehicle. In S52, it is determined whether the absolute value of the rate of change is equal to or less than the rate of change threshold. If NO in S52, the process does not proceed to the next step and returns to the start.

If YES in S52, the vehicle state detection unit 28 detects the vehicle state such as roll, yaw, and lateral acceleration in S53. In S54, it is determined whether or not the stability condition, which is a criterion for determining that the vehicle state is stable, is satisfied. For example, when the detection value of the yaw rate sensor or the lateral acceleration sensor mounted on the vehicle is equal to or less than a predetermined threshold value, it is determined that the stability condition is satisfied. Other parameters that reflect the vehicle condition are not limited to the parameters that are judged to be "the lower the value, the more stable the vehicle condition". If NO in S54, the process does not proceed to the next step and returns to the start. If YES in S54, the process proceeds to S55.

In S55, the toe angle control unit 25 sets the steering frequency f and the angle amplitude θamp of the periodic steering. In S56, the toe angle control unit 25 drives the steering actuators 31-34 with the set steering frequency f and the angle amplitude θamp. In S57, the tire external force detection unit 29 detects SAT as the tire external force.

FIG. 8 shows changes in the toe angle and SAT during periodic steering. The steering conditions are vehicle speed V = 80 [km / Hr], road friction coefficient μ = 1.0, steering frequency f = 0.5Hz, central toe angle θc = 2 [deg], and angle amplitude θamp = 2 [ deg]. From 1 second, the toe angle θ changes periodically in the range of 2 ± 2 [deg], and the SAT also changes periodically accordingly. Here, the toe angle θ in the periodic steering is set so as to always be 0 or more, in other words, not to be negative even at the minimum value. Further, the amplitude SATp on the positive side of the SAT and the amplitude SATn on the negative side do not match, and in this example, the amplitude SATn on the negative side is slightly larger than the amplitude SATp on the positive side. This is thought to be the effect of Kant.

Further, as shown in FIG. 9, when the vehicle accelerates or decelerates during the periodic steering, an extra external force different from the SAT due to the toe angle of the periodic steering and the road surface friction coefficient μ is generated in the tire. Similarly, when the vehicle condition is unstable and the vehicle is swung from side to side, extra external force is generated on the tires. Therefore, in S52 and S54 described above, when the vehicle is accelerating or decelerating or when the vehicle condition is not stable, the estimation of the road surface friction coefficient μ is not performed.

In S58, the road surface friction coefficient estimation unit 26 confirms the maximum value of SAT and the distortion of the waveform. FIG. 10 shows changes in the toe angle and SAT during periodic steering when the road friction coefficient μ is relatively small. The steering conditions are vehicle speed V = 80 [km / Hr], road friction coefficient μ = 0.4, steering frequency f = 0.5Hz, angle amplitude θamp = 0.5, 1, 2 [deg]. .. From 1 second later, the SAT changes periodically as the toe angle θ changes.

In FIG. 10, when the angular amplitude θamp = 0.5 [deg], the maximum SAT value is smaller than the lower limit value appropriate for detection. In that case, if the angle amplitude θamp = 1 [deg] is increased, the maximum SAT value becomes large and detection becomes easy. On the other hand, if the angle amplitude is made too large to θamp = 2 [deg], the tire slips and the SAT waveform is distorted.

In S59, it is determined whether the maximum value of SAT and the distortion are within an appropriate range. Specifically, it is determined whether the maximum value of SAT is equal to or higher than the lower limit value, and the number of inflection points and the width of distortion are within a predetermined value for distortion. When NO in S59, the toe angle control unit 25 resets the steering frequency f and the angle amplitude θamp of the periodic steering in S60. After that, the steps S56 to S59 are repeated until YES is determined in S59. In this way, the toe angle control unit 25 changes the steering frequency f or the angle amplitude θamp of the periodic steering according to the detected SAT.

If YES is determined in S59, the road surface friction coefficient estimation unit 26 performs frequency analysis of the SAT in S61 and extracts the maximum value of the SAT at the steering frequency f. The result of frequency analysis of SAT data by FFT is shown in FIG. A peak appears at the steering frequency f of 0.5 Hz. The difference in cant (0 ± 2%) affects only the DC component near 0 Hz, and has almost no effect on the peak value (that is, the maximum value).

In S62, the road surface friction coefficient estimation unit 26 estimates the road surface friction coefficient μ based on the relationship between the maximum SAT value at the steering frequency f and the road surface friction coefficient μ. As shown in FIG. 12, the road surface friction coefficient μ is estimated based on the maximum SAT value at 0.5 Hz obtained in FIG. The maximum error due to the difference in cant (0 ± 2%) in this embodiment is about 6%, which is less than one-third of the maximum error of 19% in the comparative example shown in FIG.

(Effect of this embodiment)
(1) The toe angle control unit 25 of the automobile steering device 20 outputs a drive signal to the steering actuators 31-34 so as to execute periodic steering. The road surface friction coefficient estimation unit 26 frequency-analyzes the SAT detected by the tire external force detection unit 29, and estimates the road surface friction coefficient μ based on the relationship between the SAT and the road surface friction coefficient μ at the steering frequency f. For example, when a certain cant is provided on the road, the external force generated by the cant on the tire is a direct current component. Therefore, by frequency-analyzing the SAT due to periodic steering and estimating the road surface friction coefficient μ using only the steering frequency component, it is possible to suppress an error due to the road surface condition.

(2) The toe angle control unit 25 changes the steering frequency f or the angle amplitude θamp of the periodic steering according to the SAT. When the road friction coefficient μ is relatively small, the SAT generated by periodic steering is small and slippery. Therefore, the toe angle control unit 25 slowly steers by increasing the angle amplitude θamp or reducing the steering frequency f (in other words, extending the steering period). In this way, by setting the steering frequency f or the angular amplitude θamp of the periodic steering to an appropriate value, the detected SAT can be increased and the estimation accuracy of the road surface friction coefficient μ can be improved.

(3) The automobile steering device 20 includes an acceleration / deceleration detection unit 27 that detects the speed change rate during acceleration or deceleration of the vehicle, and the road surface friction coefficient estimation unit 26 has a predetermined absolute value of the speed change rate. The road surface friction coefficient μ is estimated when the rate of change is equal to or less than the threshold. When the vehicle accelerates or decelerates, an extra external force is generated on the tires. Therefore, the road surface friction coefficient estimation unit 26 can reduce the error by estimating the road surface friction coefficient μ only in a stable state where the absolute value of the velocity change rate is equal to or less than a predetermined change rate threshold.

(4) The steering device 20 for automobiles includes a vehicle condition detection unit 17 that detects a vehicle condition due to vehicle behavior or an external force, and a road surface friction coefficient estimation unit 26 provides road surface friction when the vehicle condition satisfies a predetermined stability condition. Estimate the coefficient μ. When the vehicle condition is unstable and the vehicle is swung from side to side, extra external force is generated on the tires. Therefore, the road surface friction coefficient estimation unit 26 can reduce the error by estimating the road surface friction coefficient μ only when the vehicle state is stable.

(5) The toe angle in periodic steering is set to be always zero or more. The vehicle has high straight-line stability when it is toe-in. Therefore, straight-line stability can be improved by setting the fluctuation range of the toe angle so that it is always toe-in. In other words, it prevents the vehicle from becoming unstable due to a temporary toe-out.

(6) In the automobile steering device 20 mounted on the vehicle 100 in which the tires in the front row and the rear row can be independently steered, the toe angle control unit 25 determines the steering frequency f or the angular amplitude of the periodic steering in each row. θamp can be set individually. For example, the toe angle control unit 25 does not change the toe angle of the front row and the back row in the same phase, but shifts the phase by 180 [deg] so that the toe angle of either row is always large, and the straight running stability is improved. Can be secured.

(Other embodiments)
(A) In the independent steering vehicle 100 shown in FIG. 1, the front row tires 91 and 92 and the rear row tires 93 and 94 can be independently steered, but only the front row or rear row tires can be independently steered. It may be. Further, the steering device for automobiles of the present invention may be mounted on a trailer or the like having six or more wheels capable of independently steering three or more rows of tires in the front-rear direction of the vehicle.

In that case, the toe angle control unit 25 can individually set the steering frequency f or the angle amplitude θamp of the periodic steering of each row according to the priority of vehicle stability and reduction of running resistance. Is preferable. For example, in a vehicle having a large front-rear weight difference such as a trailer, the angle amplitude θamp in the front row, which is heavy, may be relatively small, and the angle amplitude θamp in the rear row, which is light in weight, may be relatively large.

(B) The waveform of periodic steering is not limited to a sine wave, and may be a triangular wave, a rectangular wave, a square wave, or the like as long as it is a periodic waveform. Further, only the waveform on the positive side with respect to the center of amplitude may be used by half-wave rectification or full-wave rectification. By using the rectified waveform only on the positive side, it becomes easy to set the toe angle in the periodic steering to be always 0 or more.

(C) In the above embodiment, the road surface friction coefficient estimation unit 26 estimates the road surface friction coefficient μ based on the maximum value of SAT at the steering frequency f after frequency analysis. However, the road surface friction coefficient μ may be estimated based on a value of a predetermined ratio to the maximum value, for example, 80% of the maximum value, not limited to the maximum value of SAT.

As described above, the present invention is not limited to such embodiments, and can be implemented in various embodiments without departing from the spirit of the present invention.

The controls and methods thereof described in the present disclosure are realized by a dedicated computer provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. May be done. Alternatively, the controls and methods thereof described in the present disclosure may be implemented by a dedicated computer provided by configuring the processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and method thereof described in the present disclosure may be a combination of a processor and memory programmed to perform one or more functions and a processor composed of one or more hardware logic circuits. It may be realized by one or more dedicated computers configured. Further, the computer program may be stored in a computer-readable non-transitional tangible recording medium as an instruction executed by the computer.

20 ... Automotive steering device,
25 ... Toe angle control unit,
26 ... Road friction coefficient estimation unit, 27 ... Acceleration / deceleration detection unit,
28 ... Vehicle condition detection unit, 29 ... Tire external force detection unit,
31-34 ... Steering actuator,
91-94 ... Tires, 100 ... Independent steering vehicle.

Claims (6)

Of the two or more rows of left and right tires in the front-rear direction of the vehicle, one or more rows of tires (91-94) are mounted on an independent steering vehicle (100) that can be independently steered by the left and right wheels.
A plurality of steering actuators (31-34) that drive each tire to be driven in the steering direction, and
The toe angle is defined as the angle at which the front side of the pair of left and right tires faces inward with respect to the traveling direction of the vehicle is positive, the angle toward the outside is negative, and the angle deflected symmetrically by the steering actuator is defined as the toe angle. A toe angle control unit (25) that outputs a drive signal to the steering actuator so as to execute periodic steering that periodically changes the angle at a predetermined steering frequency and angular amplitude.
A tire external force detecting unit (29) that detects a tire external force applied to a tire that has been steered by the steering actuator, and a tire external force detecting unit (29).
A road surface friction coefficient estimation unit (26) that performs frequency analysis of the tire external force and estimates the road surface friction coefficient based on the relationship between the tire external force and the road surface friction coefficient at the steering frequency.
A steering device for automobiles. The automobile steering device according to claim 1, wherein the toe angle control unit changes the steering frequency or the angular amplitude of the periodic steering according to the tire external force. It is equipped with an acceleration / deceleration detection unit (27) that detects the rate of change in speed per hour when the vehicle is accelerating or decelerating.
The steering device for automobiles according to claim 1 or 2, wherein the road surface friction coefficient estimation unit estimates the road surface friction coefficient when the absolute value of the speed change rate is equal to or less than a predetermined rate of change threshold. It is equipped with a vehicle condition detection unit (28) that detects the vehicle condition due to vehicle behavior or external force.
The steering device for an automobile according to any one of claims 1 to 3, wherein the road surface friction coefficient estimation unit estimates the road surface friction coefficient when the vehicle state satisfies a predetermined stability condition. The vehicle steering device according to any one of claims 1 to 4, wherein the toe angle in the periodic steering is always set to 0 or more. Two or more rows of tires are mounted on a vehicle that can be independently steered in the front-rear direction of the vehicle.
The automobile steering device according to any one of claims 1 to 5, wherein the toe angle control unit can individually set the steering frequency or the angular amplitude of the periodic steering in each row.

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