JP2019171906A - Steering system and vehicle provided with same - Google Patents

Abstract

To provide a steering system and a vehicle provided with same which can achieve improvement in both stability and safeness for running of the vehicle by a simple structure without causing a driver to feel strangeness.SOLUTION: This steering system 101 is a vehicular steering system that includes a steering device 150 which individually turns right and left wheels by driven steering actuators provided in a tire housing. The steering device 150 includes a control unit 150b that individually controls the steering actuators for right and left wheels 9 and 9. The control unit 150b includes: toe-angle control means 38 for controlling the right and left steering actuators so as to cause the right and left wheels to symmetrically perform toe-in or toe-out turning; and friction coefficient estimating means 39 for individually estimating the friction coefficient of the right and left wheels and the friction coefficient of a road surface in accordance with a predetermined rule when the toe-angle control means 38 controls the right and left steering actuators.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a steering system and a vehicle including the steering system, and relates to a technique capable of improving steering stability and safety during turning of the vehicle.

Various techniques for estimating a friction coefficient between a wheel and a road surface have been proposed (Patent Documents 1 to 3).
(1). Patent Document 1
In Patent Document 1, a detection means for detecting a repulsive force with respect to a steering wheel operation and a steering angle detection means for detecting a steering angle are provided. The steering angle information detected by the steering angle detection means and the detection means detected by the steering angle detection means. The coefficient of friction is estimated from the repulsive force information.

(2). Patent Document 2
In Patent Document 2, a torque detection unit that detects a repulsive force for a handle operation disposed between a handle and a tire, and a weight detection unit that detects a vehicle weight, the vehicle weight detected by the weight detection unit, The friction coefficient is estimated according to the repulsive force information detected by the torque detecting means.

(3). Patent Document 3
In Patent Document 3, a steering angle detection unit that detects a steering angle, a vehicle speed detection unit that detects a vehicle speed, and a detection unit that detects a repulsive force with respect to a steering operation disposed between the steering wheel and a tire. The friction coefficient is estimated according to the repulsive force information detected by the detecting means and the vehicle speed detected by the vehicle speed detecting means.

(4). Patent Document 4
By the way, not only the driver's intention is reflected in the behavior of the vehicle, but also the behavior of the vehicle in which the front wheels are steered is controlled in order to control the behavior of the vehicle so as to further improve the stability and riding comfort of the vehicle posture. A vehicle behavior control device has been proposed (Patent Document 4). This device is a steering device that transmits rotation of a steering wheel to a front wheel, and includes a steering wheel side mechanism and a wheel side mechanism that steers the front wheel with a steering wheel mechanically separated from the steering wheel side mechanism. Device, a first steering angle sensor that is provided in the steering wheel side mechanism and detects the rotational steering angle of the steering wheel, and a second steering angle sensor that is provided in the wheel side mechanism and detects the steering angle corresponding to the steering of the front wheels And comprising. In this vehicle behavior control device, the steering speed is calculated from the output of the first steering angle sensor and the output of the second steering angle sensor, and the steering generated in the vehicle corresponds to the steering operation that the driver intentionally performed. Is determined based on the output of the first and second steering angle sensors, and the steering speed is determined based on the determination result.

(5). Patent Document 5
In Patent Document 5, two motors are used in one wheel, the wheel angle is freely changed, and the toe angle and the camber angle are adjusted.

Japanese Unexamined Patent Publication No. 63-64879 JP-A 63-64880 JP-A-63-64881 Japanese Patent No. 6270251 German Patent Application Publication No. 10201206337

  In a vehicle in which wheels and a steering device are mechanically connected, both the left and right wheels move simultaneously in the same direction. Therefore, when the friction coefficient is estimated by operating the steering wheel as in Patent Documents 1 to 3, for example, a snowy road Even if the road surface on one wheel side is frozen, it is impossible to separately grasp the friction coefficient for each of the left and right wheels, and further, it is not possible to steer each wheel according to the friction coefficient at different angles.

  It is also conceivable that the wheel is automatically steered using an electric power steering motor or the like to similarly estimate the friction coefficient. However, since the left and right wheels are simultaneously steered in the same direction by the steering device mechanically connected to the wheels, torque may be transmitted to the steering wheel on the driver side, and the driver may feel uncomfortable.

Further, when the steer-by-wire system is used as in Patent Document 4, the reaction force of the wheel is not transmitted to the steering wheel, but there is a problem in safety when an abnormality occurs in the power source.
A conventional mechanism having an auxiliary steering function has a complicated structure because it aims to freely change a toe angle or a camber angle of a wheel in a vehicle.

  In Patent Document 5, since two motors are used, not only the cost increases due to the increase in the number of motors, but also a complicated and large structure is required to control both the toe angle and the camber angle within one wheel. Become.

  An object of the present invention is to provide a steering system and a vehicle equipped with the steering system that can improve the stability and safety of traveling of the vehicle with a simple structure and without giving the driver a sense of incongruity. .

A steering system 101 of the present invention is a vehicle steering system including a steering device 150 that individually steers left and right wheels 9 by driving a steering actuator 5 provided in a tire housing 105 of the vehicle 100.
The steering device 150 includes a control unit 150b that controls the steering actuators 5 and 5 of the left and right wheels 9 and 9 individually, and the control unit 150b is configured such that the left and right wheels 9 and 9 are symmetrical. Alternatively, the toe angle control means 38 for controlling the left and right steering actuators 5 and 5 to steer to toe-out, and the left and right steering actuators 5 and 5 are controlled by the toe angle control means 38 are determined. Friction coefficient estimation means 39 for individually estimating the friction coefficients of the left and right wheels 9 and 9 and the road surface according to a rule.
The predetermined rule is a rule arbitrarily determined by design or the like, and is determined by seeking an appropriate rule by, for example, one or both of testing and simulation.

  According to this configuration, the control unit 150 b of the steering device 150 individually controls the left and right steering actuators 5 and 5 provided in the tire housing 105 to individually steer the left and right wheels 9 and 9. . The toe angle control means 38 of the control unit 150b controls the left and right steering actuators 5 and 5 so that the left and right wheels 9 and 9 are steered symmetrically to toe-in and toe-out while the vehicle 100 is running or stopped. To do.

  When the left and right steering actuators 5 and 5 are controlled by the toe angle control means 38, the friction coefficient estimation means 39 in the control unit 150b performs the respective steering operations when the left and right wheel angles are slightly changed to the toe-in or toe-out state. The friction coefficients between the left and right wheels 9 and 9 and the road surface can be estimated individually based on, for example, a current value applied to the actuators 5 and 5. The relationship between the current value and the friction coefficient is stored in advance in a relationship setting unit such as a map by a test or the like, and the friction coefficient estimation unit 39 collates each detected current value with the relationship setting unit, thereby The friction coefficients of the wheels 9, 9 and the road surface can be estimated individually.

  At this time, instead of steering the left and right wheels 9 and 9 in the same direction to the left and right, steering to toe-in or toe-out, which is a direction that automatically cancels the reaction force, affects the traveling direction of the vehicle 100. Therefore, the friction coefficient with the road surface can be estimated separately for each of the left and right wheels 9 and 9 without causing the driver to feel uncomfortable. For example, the control unit 150b can determine the steering angle of each of the wheels 9 and 9 based on information such as the friction coefficient of the road surface, the vehicle speed, and the steering angle (steering angle), and adjust it to an appropriate angle. With this configuration, the toe angle of each wheel 9 can be freely adjusted with a simple structure without changing the basic structure of an existing vehicle.

  The controller 150b may control the steering actuator 5 so as to correct the steering angle of one or both of the left and right wheels 9, 9 based on the estimated friction coefficient. In this case, the left and right wheels 9 and 9 can travel safely and stably even on frozen roads having different friction coefficients.

A first steering device 11 for steering the front wheels 9, 9 of the vehicle 100;
A second steering device 150 which is the steering device including the steering actuator 5 and the control unit 150b;
A vehicle information detection unit 110 that detects vehicle information including a vehicle speed and a steering angle,
The controller 150b may control the steering actuators 5 and 5 of the left and right wheels 9 and 9 individually on the left and right sides based on the vehicle information.

According to this configuration, for example, the first steering device 11 steers the wheel in accordance with a steering amount command output by the steering command devices 200 and 200A. As the steering command devices 200 and 200A, for example, a driver's steering wheel or an automatic steering command device can be applied. Adjustment of the direction of the vehicle 100 by such a steering command device or the like can be performed similarly to a conventional vehicle.
The second steering device 150 drives the steering actuator 5 provided in the tire housing 105 to steer the left and right wheels 9 and 9 individually. The control unit 150b of the second steering device 150 controls the steering actuators 5 of the left and right wheels 9 and 9 separately from the left and right from the vehicle speed and the steering angle obtained from the vehicle information detection unit 110, for example, The running stability when the vehicle 100 is traveling straight at a high speed can be improved, and the small turning performance of the vehicle 100 can be improved when the vehicle 100 is turning at a low speed.

The second steering device 150 includes:
A hub unit body 2 having a hub bearing 15 for supporting the wheel 9;
A unit support member 3 provided on the undercarriage frame component 6 of the suspension device 12 and rotatably supporting the hub unit body 2 about a turning axis A extending in the vertical direction;
The steering unit 5 may be provided to rotate the hub unit body 2 about the turning axis A.

According to this configuration, the hub unit body 2 including the hub bearing 15 that supports the wheel 9 can be freely rotated around the turning axis A within a certain range by driving the steering actuator 5. For this reason, steering can be performed independently for each wheel, and the toe angle of the wheel 9 can be arbitrarily changed according to the traveling state of the vehicle 100.
Further, during turning, the difference in steering angle between the left and right wheels 9, 9 can be changed according to the traveling speed. For example, the steering geometry can be changed during traveling, such as parallel geometry for turning in a high speed region and Ackermann geometry for turning in a low speed region. Thus, since the wheel angle can be arbitrarily changed during traveling, it is possible to improve the motion performance of the vehicle 100 and travel stably and safely. Furthermore, by appropriately changing the steering angle of the left and right steered wheels, the turning radius of the vehicle 100 in turning traveling can be reduced and the turning performance can be improved.

The control unit 150b of the second steering device 150 outputs an auxiliary steering control unit 151 that outputs a current command signal according to a given steering angle command signal, and a current command signal input from the auxiliary steering control unit 151. The actuator drive control units 31R and 31L that drive and control the steering actuator 5 by outputting a current corresponding to the above may be provided.
According to this configuration, the auxiliary steering control unit 151 outputs a current command signal corresponding to the given steering angle command signal. The actuator drive control units 31R and 31L drive and control the steering actuator 5 by outputting a current corresponding to the current command signal input from the auxiliary steering control unit 151. Therefore, it is possible to arbitrarily change the wheel angle in addition to steering by a driver's steering wheel operation or the like.

  The steering actuator 5 may include a reverse input prevention mechanism 25 b that prevents reverse input from the wheels 9. In this case, it is possible to suppress the wobbling of the hub bearing 15 that supports each wheel 9.

  A vehicle 100 according to the present invention includes the steering system 101 having the above-described configuration according to the present invention. Therefore, each effect mentioned above about the steering system 101 of this invention is acquired.

  The steering system according to the present invention is a vehicle steering system including a steering device for individually steering left and right wheels by driving a steering actuator provided in a tire housing of the vehicle, wherein the steering device includes the left and right wheels. And a toe angle control means for controlling the left and right steering actuators such that the left and right wheels are steered symmetrically to toe-in or toe-out. In addition, when the left and right steering actuators are controlled by the toe angle control means, there are provided friction coefficient estimation means for individually estimating the friction coefficients of the left and right wheels and the road surface according to a predetermined rule. For this reason, it is possible to improve the stability and safety of traveling of the vehicle with a simple structure without causing the driver to feel uncomfortable.

  Since the vehicle according to the present invention includes the steering system having the above-described configuration according to the present invention, it is possible to improve the running stability and safety of the vehicle with a simple structure without causing the driver to feel uncomfortable. it can.

1 is a diagram schematically illustrating a conceptual configuration of a steering system according to a first embodiment of the present invention. It is a longitudinal cross-sectional view which shows the structure of the mechanism part of the 2nd steering apparatus in the steering system, and its periphery. It is a horizontal sectional view showing composition of a mechanism part etc. of the 2nd steering device. It is a perspective view which shows the external appearance of the mechanism part of the 2nd steering apparatus. It is a disassembled front view of the mechanism part of the 2nd steering device. It is a side view of the mechanism part of the 2nd steering device. It is a top view of the mechanism part of the 2nd steering device. It is the VIII-VIII sectional view taken on the line of FIG. It is a block diagram which shows the conceptual structure of the steering system. It is a flowchart which shows the process which estimates a friction coefficient in steps. It is a block diagram which shows the structure of the auxiliary steering control part of the 2nd steering apparatus. It is a graph which shows the example of a relationship between an actual lateral acceleration / standard lateral acceleration, a tire angle, and a friction coefficient. It is a figure which shows schematically the conceptual structure of the steering system which concerns on 2nd Embodiment of this invention. It is a figure which shows schematically the conceptual structure of the steering system which concerns on 3rd Embodiment of this invention.

[First Embodiment]
A first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a diagram schematically showing a conceptual configuration of a vehicle 100 such as an automobile equipped with a steering system 101 according to this embodiment. The vehicle 100 is a four-wheel vehicle having left and right wheels 9 and 9 as front wheels and left and right wheels 9 and 9 as rear wheels, and the driving method is any of front wheel drive, rear wheel drive, and four wheel drive. It may be.

The steering system 101 is a system for steering the vehicle 100, and includes a first steering device 11, a second steering device 150 that is a steering device that individually steers left and right wheels 9, 9, and a vehicle. And an information detection unit 110.
The first steering device 11 is a device that steers the left and right wheels 9 and 9 that are the steering wheels of the vehicle 100 by a driver's operation with respect to a steering command device such as the handle 200. In this embodiment, the first steering device 11 is a front wheel steering type. ing.

  The second steering device 150 is a device that performs auxiliary steering by control according to the state of the vehicle 100, and includes a mechanism unit 150a and a control unit 150b. The mechanism part 150a is a mechanism provided for each of the wheels 9 and 9 that are targets of auxiliary steering. The mechanism 150a is provided in the tire housing 105 of the vehicle 100, and individually steers the wheels 9 by driving the steering actuator 5 (FIG. 2). The control unit 150b performs control based on vehicle information representing the state of the vehicle 100 detected by the vehicle information detection unit 110.

In other words, the steering system 101
The left and right wheels 9 and 9 serving as the front wheels of the vehicle 100 are mechanically interlocked, and the left and right wheels 9 and 9 serving as the front wheels of the vehicle 100 according to the steering amount command output from the steering command device are The first steering device 11 that is steered by changing the angles of the knuckles 6 and 6 that are left and right underbody frame parts of the suspension device 12 on which the suspension device 12 is installed,
By driving auxiliary steering actuators (steering actuators 5 (FIG. 2)) provided for the left and right wheels 9, 9, the wheels 9, 9 with respect to the knuckles 6, 6 as the underbody frame parts are driven. A second steering device 150 for steering the left and right wheels 9, 9 individually by changing the angle;
A vehicle information detection unit 110 to be described later.

The vehicle information detection unit 110 is a means for detecting the state of the vehicle 100 and refers to a group of various sensors. The vehicle information detected by the vehicle information detection unit 110 is transferred to the control unit 150b of the second steering device 150 via the main ECU 130.
The ECU 130 is a control device that performs cooperative control or overall control of the vehicle 100, and is also referred to as a VCU.

<Configuration of first steering device 11>
The first steering device 11 is a system for steering the left and right wheels 9 and 9 that are the front wheels of the vehicle 100 in conjunction with each other in response to an input to the steering wheel 200 by the driver, and includes a steering shaft 32, a rack and pinion (see FIG. (Not shown) and a tie rod 14 or the like, which has a known mechanical configuration. When the driver inputs rotation to the handle 200, the steering shaft 32 also rotates in conjunction with it. When the steering shaft 32 rotates, the tie rod 14 connected to the steering shaft 32 is moved in the vehicle width direction by the rack and pinion, so that the direction of the wheel 9 is changed, and the left and right wheels 9, 9 are steered in conjunction with each other. It is possible.

<Schematic configuration of second steering device 150>
As shown in FIGS. 1 and 9, the second steering device 150 can steer the left and right wheels 9 and 9 independently. A right wheel hub unit 1R and a left wheel hub unit 1L are provided as a mechanism portion 150a of the second steering device 150. The right wheel hub unit 1 </ b> R and the left wheel hub unit 1 </ b> L steer the wheels 9 and 9 by a steering actuator 5 (FIG. 2) provided in the tire housing 105.

<Specific Configuration Example of Mechanism 150a of Second Steering Device 150>
The mechanism portion 150a of the second steering device 150 includes the right wheel hub unit 1R and the left wheel hub unit 1L as described above, and both the right wheel hub unit 1R and the left wheel hub unit 1L are shown in FIG. It is configured as a functional hub unit 1.
As shown in FIG. 2, the hub unit 1 includes a hub unit main body 2, a unit support member 3, a rotation allowable support component 4, and a steering actuator 5. The unit support member 3 is provided integrally with a knuckle 6 that is a suspension frame part.

As shown in FIG. 5, the actuator main body 7 of the steering actuator 5 is provided on the inboard side of the unit support member 3, and the hub unit main body 2 is provided on the outboard side of the unit support member 3. With the hub unit 1 (FIG. 2) mounted on the vehicle, the vehicle width direction outer side of the vehicle is referred to as an outboard side, and the vehicle width direction center side of the vehicle is referred to as an inboard side.
As shown in FIGS. 3 and 4, the hub unit main body 2 and the actuator main body 7 are connected by a joint portion 8. Usually, the joint portion 8 is provided with a boot (not shown) for waterproofing and dustproofing.

  As shown in FIG. 2, the hub unit body 2 is supported by the unit support member 3 via the rotation-allowing support parts 4 and 4 at two upper and lower positions so as to be rotatable around the turning axis A extending in the vertical direction. Has been. The turning axis A is an axis different from the rotation axis O of the wheel 9, and is different from the kingpin axis that performs main steering. In a normal vehicle, the kingpin angle is set to 10 to 20 degrees for the purpose of improving the straight running stability of the vehicle traveling. However, the hub unit 1 of this embodiment has an angle (axis) different from the kingpin angle. It has a steering shaft. The wheel 9 includes a wheel 9a and a tire 9b.

  As shown in FIG. 1, the hub unit 1 (FIG. 2) of this embodiment is added to the steering of the left and right wheels 9, 9 as front wheels by the first steering device 11, and has a small angle ( As a mechanism for steering about ± 5 deg), the knuckle 6 of the suspension device 12 is integrally provided. The first steering device 11 is of a rack and pinion type, but any type of steering device may be used. For example, although the strut suspension mechanism that directly fixes the shock absorber to the knuckle 6 is applied to the suspension device 12, a multi-link suspension mechanism or other suspension mechanisms may be applied.

<About hub unit body 2>
As shown in FIG. 2, the hub unit main body 2 includes a hub bearing 15 for supporting the wheels 9, an outer ring 16, and an arm portion 17 (FIG. 4) that is a steering force receiving portion described later.
As shown in FIG. 8, the hub bearing 15 includes an inner ring 18, an outer ring 19, and rolling elements 20 such as balls interposed between the inner and outer rings 18, 19. 2).

  In the illustrated example, the hub bearing 15 is an angular ball bearing in which the outer ring 19 is a fixed ring, the inner ring 18 is a rotating ring, and the rolling elements 20 are in a double row. The inner ring 18 includes a hub ring portion 18a having a hub flange 18aa and constituting a race surface on the outboard side, and an inner ring portion 18b constituting a race surface on the inboard side. As shown in FIG. 2, the wheel 9a of the wheel 9 is bolted to the hub flange 18aa so as to overlap the brake rotor 21a. The inner ring 18 rotates around the rotation axis O.

As shown in FIG. 8, the outer ring 16 includes an annular portion 16a fitted to the outer peripheral surface of the outer ring 19, and a trunnion shaft-shaped mounting shaft portion that protrudes upward and downward from the outer periphery of the annular portion 16a. 16b, 16b. Each attachment shaft portion 16 b is provided coaxially with the turning shaft center A.
As shown in FIG. 3, the brake 21 has a brake rotor 21a and a brake caliper 21b. The brake caliper 21b is mounted on two upper and lower brake caliper mounting portions 22 (FIG. 6) formed integrally with the outer ring 19 so as to project into an arm shape.

<About rotation-supporting support parts and unit support members>
As shown in FIG. 8, each rotation-allowing support component 4 is formed of a rolling bearing. In this example, a tapered roller bearing is applied as the rolling bearing. The rolling bearing has an inner ring 4a fitted to the outer periphery of the mounting shaft portion 16b, an outer ring 4b fitted to the unit support member 3, and a plurality of rolling elements 4c interposed between the inner and outer rings 4a and 4b.

  The unit support member 3 includes a unit support member main body 3A and a unit support member combined body 3B. A substantially ring-shaped unit support member assembly 3B is detachably fixed to the end of the unit support member main body 3A on the outboard side. Partial concave spherical fitting hole forming portions 3a are respectively formed on the upper and lower portions of the side surface of the inboard side of the unit support member assembly 3B.

  As shown in FIGS. 7 and 8, partial concave spherical fitting hole forming portions 3Aa are formed in the upper and lower portions of the outboard side end of the unit support member main body 3A. As shown in FIG. 4, the unit support member combined body 3B is fixed to the outboard side end of the unit support member main body 3A, and the fitting hole forming portions 3a and 3Aa (FIG. 7) are combined with each other for each upper and lower portion. As a result, a fitting hole is formed continuously around the entire circumference. The outer ring 4b (FIG. 8) is fitted into this fitting hole. In FIG. 4, the unit support member 3 is indicated by a one-dot chain line.

  As shown in FIG. 8, each mounting shaft portion 16b in the outer ring 16 is formed with a female screw portion extending in the radial direction, and is provided with a bolt 23 that is screwed into the female screw portion. A disc-like pressing member 24 is interposed on the end surface of the inner ring 4a, and a preload is applied to each rotation-allowing support component 4 by applying a pressing force to the end surface of the inner ring 4a by a bolt 23 that is screwed into the female screw portion. Giving. Thereby, the rigidity of each rotation permission support component 4 can be improved. Even when the weight of the vehicle acts on the hub unit, the initial preload is set so as not to be released. Note that the rolling bearing of the rotation-allowing support component 4 is not limited to the tapered roller bearing, and an angular ball bearing can be used depending on use conditions such as a maximum load. In such a case as well, a preload can be applied in the same manner as described above.

  As shown in FIG. 3, the arm portion 17 is a portion serving as an action point for applying a steering force to the outer ring 19 of the hub bearing 15, and is integrated with a part of the outer periphery of the annular portion 16 a or a part of the outer periphery of the outer ring 19. Protrusively. The arm portion 17 is rotatably connected to the linear motion output portion 25 a of the steering actuator 5 via the joint portion 8. As a result, when the linear motion output portion 25a of the steering actuator 5 advances and retreats, the hub unit body 2 rotates around the turning axis A (FIG. 2), that is, is steered.

<About the steering actuator 5>
As shown in FIG. 4, the steering actuator 5 includes an actuator body 7 that rotates the hub unit body 2 about the turning axis A (FIG. 2).
As shown in FIG. 3, the actuator body 7 converts a motor 26, a speed reducer 27 that decelerates the rotation of the motor 26, and a forward / reverse rotation output of the speed reducer 27 into a reciprocating linear motion of the linear motion output unit 25a. And a linear motion mechanism 25. The motor 26 is, for example, a permanent magnet type synchronous motor, but may be a DC motor or an induction motor.

  As the speed reducer 27, a wrapping type transmission mechanism such as a belt transmission mechanism or a gear train can be used. In the example of FIG. 3, a belt transmission mechanism is used. The reducer 27 includes a drive pulley 27a, a driven pulley 27b, and a belt 27c. A drive pulley 27 a is coupled to the motor shaft of the motor 26, and a driven pulley 27 b is provided in the linear motion mechanism 25. The driven pulley 27b is disposed in parallel to the motor shaft. The driving force of the motor 26 is transmitted from the drive pulley 27a to the driven pulley 27b via the belt 27c. The drive pulley 27a, the driven pulley 27b, and the belt 27c constitute a winding-type speed reducer 27.

  As the linear motion mechanism 25, a feed screw mechanism such as a slide screw or a ball screw, a rack and pinion mechanism, or the like can be used. In this example, a feed screw mechanism (reverse input prevention mechanism) 25b using a trapezoidal screw slide screw is used. Is used. Since the linear motion mechanism 25 includes the feed screw mechanism 25b using the slide screw of the trapezoidal screw, the effect of preventing reverse input from the tire 9b can be enhanced. A reverse input prevention mechanism such as a worm gear may be employed instead of the feed screw mechanism 25b using the trapezoidal screw sliding screw. Also in this case, the effect of preventing reverse input from the tire 9b can be enhanced. The actuator body 7 including the motor 26, the speed reducer 27, and the linear motion mechanism 25 is assembled as a semi-assembly and is detachably attached to the case 6b with bolts or the like. A mechanism that directly transmits the driving force of the motor 26 to the linear motion mechanism 25 without using a reduction gear is also possible.

  The case 6 b is integrally formed with the unit support member main body 3 </ b> A as a part of the unit support member 3. The case 6 b is formed in a bottomed cylindrical shape, and is provided with a motor housing portion that supports the motor 26 and a linear motion mechanism housing portion that supports the linear motion mechanism 25. A fitting hole for supporting the motor 26 at a predetermined position in the case is formed in the motor housing portion. The linear motion mechanism accommodating portion is formed with a fitting hole for supporting the linear motion mechanism 25 at a predetermined position in the case, a through hole for allowing the linear motion output portion 25a to advance and retreat.

  As shown in FIG. 4, the unit support member main body 3A includes the case 6b, a shock absorber mounting portion 6c serving as a shock absorber mounting portion, and a steering device coupling serving as a coupling portion of the first steering device 11 (FIG. 3). Part 6d. The shock absorber mounting portion 6c and the steering device coupling portion 6d are also integrally formed with the unit support member main body 3A. A shock absorber mounting portion 6c is formed on the upper portion of the outer surface portion of the unit support member main body 3A so as to protrude. A steering device coupling portion 6d is formed on the side surface portion of the outer surface portion of the unit support member main body 3A so as to protrude.

<Configuration of Vehicle Information Detection Unit 110>
As shown in FIG. 9, vehicle information detection section 110 detects vehicle information and outputs it to ECU 130. The vehicle information detection unit 110 includes a vehicle speed detection unit 111, a steering angle detection unit 112, a vehicle height detection unit 113, an actual yaw rate detection unit 114, an actual lateral acceleration detection unit 115, an accelerator pedal sensor 116, and a brake pedal sensor 117.

The vehicle speed detection unit 111 detects the speed of the vehicle (vehicle speed) based on the output of a sensor (not shown) such as a speed sensor attached to the inside of a transmission provided in the vehicle, and sends vehicle speed information (simply “ It is also called "vehicle speed".
The steering angle detection unit 112 detects the steering angle based on the output of a sensor (not shown) such as a resolver attached to the motor unit included in the first steering device 11, for example, and sends the steering angle information (simply “ Steering angle ").

  The vehicle height detection unit 113 measures the distance between the chassis of the vehicle 100 (FIG. 1) and the ground using a laser displacement meter, or the angle of the upper arm or lower arm (not shown) in the suspension device 12 (FIG. 1) of the vehicle 100. The vehicle height of each wheel 9 (FIG. 1) to be steered by the second steering device 150 is detected by a method of detecting the angle with an angle sensor. Then, the vehicle height detection unit 113 outputs the detected vehicle height to the ECU 130 as vehicle height information.

The actual yaw rate detection unit 114 detects the actual yaw rate based on the output of a sensor such as a gyro sensor attached to the vehicle 100 (FIG. 1), for example, and outputs the actual yaw rate information to the ECU 130.
The actual lateral acceleration detection unit 115 detects the actual lateral acceleration based on the output of a sensor such as a gyro sensor attached to the vehicle 100 (FIG. 1), for example, and outputs the actual lateral acceleration information to the ECU 130. The accelerator pedal sensor 116 detects an input to the accelerator pedal 210 by the driver, and outputs the detected value to the ECU 130 as an accelerator command value. The brake pedal sensor 117 detects an input to the brake pedal 220 by the driver, and outputs the detected value to the ECU 130 as a brake command value. The ECU 130 outputs vehicle information including the steering angle command signal to the control unit 150b of the second steering device 150.

<Control Unit 150b of Second Steering Device 150>
The control unit 150b of the second steering device 150 acquires vehicle information including vehicle speed information, steering angle information, vehicle height information, actual yaw rate information, actual lateral acceleration information, an accelerator command value, and a brake command value from the ECU 130. Based on the acquired vehicle information, the auxiliary steering control unit 151 controls the actuator drive control unit 31R for the right wheel and the actuator drive control unit 31L for the left wheel, so that the right wheel hub unit 1R and the left wheel hub unit 1L are controlled. The left and right wheels can be steered independently by driving the motor 26 provided in the vehicle.

In the control unit 150b, the relationship between each information such as the steering angle information as the vehicle information and the command value for driving the motor 26 is determined as a control rule using, for example, a map or an arithmetic expression. Control using rules.
The control unit 150b is provided as a dedicated ECU, for example, but may be provided as a part of the main ECU 130.

  The auxiliary steering control unit 151 in the control unit 150 b includes a toe angle control unit 38 and a friction coefficient estimation unit 39. The toe angle control means 38 controls the respective steering actuators 5 (FIG. 2) so that the left and right wheels 9, 9 (FIG. 1) as front wheels are steered symmetrically to toe-in or toe-out. When the toe angle control means 38 controls the left and right steering actuators 5 and 5 (FIG. 2), the friction coefficient estimating means 39 follows the predetermined rule and the friction coefficient between the left and right wheels 9 and 9 (FIG. 1) and the road surface. Are estimated individually. In this embodiment, when the vehicle speed exceeds a predetermined vehicle speed while the vehicle is running, the toe angle control by the toe angle control means 38 and the friction coefficient by the friction coefficient estimation means 39 are estimated. During the stop, for example, the toe angle control and the friction coefficient may be estimated every predetermined time.

  When the left and right steering actuators are controlled by the toe angle control means 38, the friction coefficient estimation means 39 is loaded on each steering actuator when the left and right wheel angles are slightly changed in the toe-in or toe-out state, for example. Depending on the current value, the left and right wheels 9, 9 (FIG. 1), which are front wheels, and the friction coefficient of the road surface can be estimated individually. For example, when the current value is high, the road surface friction coefficient is high, and conversely, when the current value is low, the road surface friction coefficient is low. The relationship between the current value and the friction coefficient is stored in advance in a relationship setting unit such as a map by a test or the like, and the friction coefficient estimation unit 39 collates each detected current value with the relationship setting unit, thereby The coefficient of friction between the wheel and the road surface can be estimated separately. Each current value can be detected by a current sensor (not shown) that detects the motor current flowing in the motors 26 and 26, respectively.

FIG. 10 is a flowchart showing the process of estimating the friction coefficient step by step. The description will be made with reference to FIGS. 1, 2 and 9 as appropriate.
When the vehicle speed V becomes equal to or higher than the predetermined vehicle speed V0 while the vehicle 100 is traveling (step S1: YES), the friction coefficient estimating operation is started by the hub unit 1 with a steering function (step S2). When the vehicle speed V is less than the predetermined vehicle speed V0 (step S1: NO), the process returns to step S1. The vehicle speed V0 is a vehicle speed arbitrarily determined by design or the like, and is determined by obtaining an appropriate vehicle speed by, for example, one or both of a test and a simulation.

  Next, the toe angle control means 38 toe-in or toe-out the left and right wheels 9, 9 as front wheels symmetrically by a minute angle by the steering function-equipped hub units 1, 1 (the wheels 9, 9 represented by dotted lines in FIG. 1). Represents a toe-in state) (step S3). Next, when it is confirmed that the toe angle control means 38 has steered to the specified steering angle (step S4: YES), the process proceeds to step S5. For example, the toe angle control means 38 determines that the vehicle has been steered to a designated steering angle when the detected sensor values are each equal to or greater than a threshold value. When the vehicle is not steered to the specified steering angle (step S4: NO), the process returns to step S1.

  The friction coefficient estimating means 39 calculates the maximum value of the motor current at the time of steering operation on the left and right sides (step S5), and estimates the friction coefficient between the left and right wheels and the road surface individually according to the magnitude of this current value ( Step S6). The controller 150b determines the gain G of the steering function-equipped hub units 1 and 1 to be corrected by the magnitude of the friction coefficient (step S7). The relationship between the magnitude of the friction coefficient and the gain G is determined on a map or the like by testing or the like. The steering operation of the minute angle toe-in or toe-out at the left and right wheels 9 and 9 described above is because the reaction forces from the wheels 9 and 9 cancel each other and are operations of a minute angle. It can be carried out automatically without giving a sense of incongruity.

  Thereafter, when there is an operation confirmation from the steering wheel 200, that is, during turning traveling in which the steering wheel angle is output from the steering angle detection unit 112 to the control unit 150b via the ECU 130 (step S8: YES), the control unit 150b After calculating the corrected steering amount (that is, the current flowing through each motor 26) θA of the actuator (step S9), the product of the corrected steering amount θA and the gain G (step S10) Each steering actuator is driven (step S11). Thereafter, this process is terminated. If there is no operation confirmation from the handle 200 (step s8: NO), the process returns to step S1.

In addition to the control shown in FIG. 10 and the like, the auxiliary steering control unit 151 performs control for independently steering the left and right wheels as shown in FIG. The control shown in FIG. 11 and the control shown in FIG. 10 and the like may be switched according to the operation of the driver or the vehicle situation, or may be executed in parallel.
As shown in FIG. 11, the auxiliary steering control unit 151 includes a reference lateral acceleration calculation unit 152, a right wheel tire angle calculation unit 153, a left wheel tire angle calculation unit 154, a right wheel road surface friction coefficient calculation unit 155, and a target yaw rate calculation unit 156. A left wheel road surface friction coefficient calculation unit 157, a target yaw rate correction unit 158, a target left and right wheel tire angle calculation unit 159, a right wheel command value calculation unit 160, and a left wheel command value calculation unit 161.

  The right wheel tire angle calculation unit 153 and the left wheel tire angle calculation unit 154 acquire steering angle information and vehicle height information from the ECU 130 at a predetermined cycle. The right wheel tire angle calculation unit 153 and the left wheel tire angle calculation unit 154 calculate the current angle of the tire that the second steering device 150 (FIG. 9) steers based on the acquired steering angle information and vehicle height information. Then, the calculated tire angle information is output to the reference lateral acceleration calculation unit 152.

  The reference lateral acceleration calculation unit 152 calculates the reference lateral acceleration based on the vehicle speed information acquired from the ECU 130 and the tire angle information. The reference lateral acceleration calculation unit 152 outputs the calculated reference lateral acceleration as reference lateral acceleration information to the right wheel road surface friction coefficient calculation unit 155 and the left wheel road surface friction coefficient calculation unit 157.

FIG. 12 is a diagram showing a map for calculating the road surface friction coefficient, and this map is stored in the right wheel road surface friction coefficient calculation unit 155 and the left wheel road surface friction coefficient calculation unit 157 shown in FIG.
The right wheel road surface friction coefficient calculation unit 155 and the left wheel road surface friction coefficient calculation unit 157 calculate road surface friction coefficients based on the actual lateral acceleration information acquired from the ECU 130 and the reference lateral acceleration information input from the reference lateral acceleration calculation unit 152. I do. Specifically, when the reference lateral acceleration information is input from the reference lateral acceleration calculation unit 152, the right wheel road surface friction coefficient calculation unit 155 and the left wheel road surface friction coefficient calculation unit 157 receive the right wheel tire angle calculation unit 153 and the left wheel tire. Tire angle information is acquired from the angle calculation unit 154. The right wheel road surface friction coefficient calculation unit 155 and the left wheel road surface friction coefficient calculation unit 157 calculate the road surface friction coefficient from the actual lateral acceleration / reference lateral acceleration and the tire angle based on the map (FIG. 12). The right wheel road surface friction coefficient calculating unit 155 and the left wheel road surface friction coefficient calculating unit 157 include right wheel road surface friction coefficient information that is the calculated road surface friction coefficient of the right wheel and left wheel road surface friction coefficient information that is the road surface friction coefficient of the left wheel. And output to the target yaw rate correction unit 158.

The target yaw rate calculation unit 156 calculates a target yaw rate based on vehicle speed information and steering angle information acquired from the ECU 130 at a predetermined cycle, and outputs the calculated target yaw rate to the target yaw rate correction unit 158 as target yaw rate information.
When the right wheel road surface friction coefficient information and the left wheel road surface friction coefficient information are input from the right wheel road surface friction coefficient calculation unit 155 and the left wheel road surface friction coefficient calculation unit 157, the target yaw rate correction unit 158 receives the target yaw rate calculation unit 156 from the target yaw rate calculation unit 156. The yaw rate information is acquired, and the target yaw rate is corrected according to the road surface friction coefficient represented by the right wheel road surface friction coefficient information and the left wheel road surface friction coefficient information. The target yaw rate correction unit 158 outputs the corrected target yaw rate to the target left and right wheel tire angle calculation unit 159 as corrected yaw rate information.

  When the corrected left and right wheel tire angle calculation unit 159 receives the corrected yaw rate information, the target left and right wheel tire angle calculation unit 159 acquires the actual yaw rate information, the accelerator command value, and the brake command value from the ECU 130, and the right wheel road surface friction coefficient information and the left wheel road surface friction coefficient information. And the target left and right wheel tire angle, which is the target value of the tire angle of the left and right wheels, is calculated. Specifically, the target left and right wheel tire angle calculation unit 159 calculates the target angle of each of the left and right tires based on the following formula (1).

In equation (1), θ _y is the actual vehicle yaw rate amount represented by the actual yaw rate information, X _A is the accelerator command value, X _B is the brake command value, μ _R is the right wheel road surface friction coefficient, and μ _L is the left wheel. the road surface friction coefficient, θ _tR1 the target tire angle of the right wheel, θ _tL1 is the target tire angle of the left wheel.
The target left and right wheel tire angle calculation unit 159 outputs the calculated target tire angles of the left and right wheels to the right wheel command value calculation unit 160 and the left wheel command value calculation unit 161 as target tire angle information.

  When the target wheel angle information is input, the right wheel command value calculation unit 160 and the left wheel command value calculation unit 161 represent the current tire angle from the right wheel tire angle calculation unit 153 and the left wheel tire angle calculation unit 154. Tire angle information is acquired, and the target tire angle represented by the target tire angle information is compared with the current tire angle. If there is a deviation as a result of comparing the target tire angle with the current tire angle, right wheel steering indicating the amount by which each of the right wheel hub unit 1R (FIG. 9) and the left wheel hub unit 1L (FIG. 9) is steered. Amount information and left wheel steering amount information are generated. The right wheel command value calculation unit 160 outputs the generated right wheel steering amount information (current command signal) to the right wheel actuator drive control unit 31R, and the left wheel command value calculation unit 161 generates the generated left wheel steering amount information ( Current command signal) is output to the left wheel actuator drive control section 31L.

Each actuator drive control unit 31R, 31L includes an inverter. Each actuator drive control unit 31R, 31L controls the current to the motor 26 (FIG. 9) of each steering actuator based on the right wheel steering amount information and the left wheel steering amount information.
Specifically, as shown in FIGS. 9 and 11, each actuator drive control unit 31R, 31L receives the right wheel steering amount information and the left wheel steering amount information from the right wheel command value calculation unit 160 and the left wheel command value calculation unit 161, respectively. When input, position information of each motor 26 indicating the steering angle of the current right wheel hub unit 1R and left wheel hub unit 1L is acquired, and the target of the motor 26 is obtained based on the right wheel steering amount information and the left wheel steering amount information. The position is determined, and the current supplied to each motor 26 is controlled.

  That is, as shown in FIG. 4, each actuator drive control unit 31R, 31L outputs a current corresponding to the current command signal input from the auxiliary steering control unit 151 to drive and control the steering actuator 5. The actuator drive controllers 31R and 31L control the power supplied to the coil of the motor 26. The actuator drive control units 31R and 31L constitute, for example, a half bridge circuit using a switch element (not shown), and perform PWM control for determining a motor applied voltage based on an ON-OFF duty ratio of the switch element. Thereby, in addition to steering by the driver's steering wheel operation, the angle of the wheel can be minutely changed. Even during straight running, the amount of toe angle can be adjusted according to the vehicle speed.

<Effect>
According to the steering system 101 described above, when the left and right steering actuators 5, 5 are controlled by the toe angle control means 38, the friction coefficient estimation means 39 in the control unit 150 b minutely moves the left and right wheels in the toe-in or toe-out state. The coefficient of friction between the left and right wheels 9 and 9 and the road surface can be estimated individually based on, for example, the current value applied to each steering actuator 5 when the angle is changed. At this time, instead of steering both left and right wheels in the same direction left and right, steering to toe-in or toe-out, which automatically cancels the reaction force, has no effect on the traveling direction of the vehicle. The friction coefficient with the road surface can be estimated separately for each of the left and right wheels without giving the person a sense of discomfort. For example, the control unit can determine the steering angle of each wheel based on information such as the friction coefficient of the road surface, the vehicle speed, and the steering angle (steering angle), and adjust the steering angle to an appropriate angle. With this configuration, the toe angle of each wheel can be freely adjusted with a simple structure without changing the basic structure of an existing vehicle.

  Since the control unit 150b controls the steering actuator 5 so as to correct the steering angle of one or both of the left and right wheels 9, 9 based on the estimated friction coefficient, the freezing coefficient is different between the left and right wheels. It enables safe and stable driving on the road.

Further, the steering actuator 5 includes a feed screw mechanism 25b using a trapezoidal screw sliding screw that prevents reverse input from the wheel 9, and the maximum steering angle of the hub unit 1 is a minute angle necessary for the correction operation. (Approx. ± 5 deg), when an abnormality occurs in the power supply of one actuator drive control unit 31R (31L), by stopping the control of the other actuator drive control unit 31L (31R), The steering angle of the hub units 1 and 1 is fixed, and the driver can safely move the vehicle 100 to a safe place such as a road shoulder using the handle 200. Therefore, a mechanism for safety measures when the steering system is abnormal can be omitted or simplified.
This steering system enables simple and safe driving on frozen roads and the like with different friction coefficients between the left and right wheels.

<About other embodiments>
In the following description, the same reference numerals are given to portions corresponding to the matters described in advance in the respective embodiments, and overlapping descriptions are omitted. When only a part of the configuration is described, the other parts of the configuration are the same as those described in advance unless otherwise specified. The same effect is obtained from the same configuration. Not only the combination of the parts specifically described in each embodiment, but also the embodiments can be partially combined as long as the combination does not hinder.

[Second Embodiment]
As shown in FIG. 13, the steering system 101 according to the second embodiment is the first embodiment in that the first steering device 11 and the second steering device 150 steer different wheels 9 from each other. Is different. That is, in the steering system 101, the first steering device 11 steers the left and right front wheels 9 and 9 of the vehicle 100, and the second steering device 150 steers the left and right rear wheels 9 and 9 of the vehicle 100. . The mechanism portion 150 b of the second steering device 150 is installed in the rear wheel tire housing 105.

[Third Embodiment]
As shown in FIG. 14, the steering system 101 according to the third embodiment is different from the first embodiment in that it includes _{two second} steering devices 150 ₁ and 150 ₂ .
One second steering device 150 ₁ performs steering of the same wheels 9,9 in the first steering device 11, the second steering device 150 ₂ on the other, the wheel different from the second steering device 150 9 , 9 is steered. That is, the second steering device 150 ₂ on one performs the same operation as the second steering device 150 according to the first embodiment, the second steering device 150 ₂ on the other, to a second embodiment The same operation as that of the second steering device 150 is performed.

According to this steering system 101, by providing a plurality of (two in this example) second steering devices 150 ₁ and 150 ₂ , it becomes possible to more independently independently steer four wheels, It is possible to improve the running stability of the vehicle 100 and reduce the fuel consumption.

  Further, as a vehicle including a steering system according to another embodiment, the left and right wheels are each provided with a second steering device that can be steered independently, and each wheel is independently driven by a steering actuator. These steering devices may be, for example, steer-by-wire types that are not mechanically coupled to the steering command device. In each of the embodiments described above, the steering command device is the handle 200. However, a manual steering command device other than the handle 200, for example, a joystick may be used. The steering command device 200A may be used. This automatic steering command device 200A is a device that recognizes a vehicle surrounding situation from the vehicle surrounding situation detection means 230 and automatically generates a steering command. The vehicle surrounding state detection means 230 is, for example, a sensor such as a camera or a millimeter wave radar.

  The automatic steering command device 200A recognizes white lines and obstacles on the road, for example, and generates and outputs a steering command. The automatic steering command device 200A may be a part of a device that performs automatic driving of a vehicle or a device that supports steering by manual driving. Even in a vehicle equipped with such a steering command device 200A that automatically generates a steering command, by providing the second steering device 150, operations that cannot be performed by the first steering device 11, such as toe angle control, can be performed. It is also possible to perform main steering in the traveling direction of the vehicle with the first steering device 11 and to correct it with the second steering device 150, and to correct the vehicle direction with respect to the steering amount command. Thus, it is possible to maintain the running stability of the vehicle.

  As mentioned above, although the form for implementing this invention based on embodiment was demonstrated, embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 2 ... Hub unit main body, 3 ... Unit support member, 5 ... Steering actuator, 6 ... Knuckle (suspension frame part), 9 ... Wheel, 11 ... First steering device, 12 ... Suspension device, 25b ... Feed screw mechanism (Reverse input prevention mechanism), 31R, 31L ... Actuator drive control unit, 38 ... Toe angle control means, 39 ... Friction coefficient estimation means, 100 ... Vehicle, 101 ... Steering system, 105 ... Tire housing, 110 ... Vehicle information detection unit 150 ... second steering device, 150b ... control unit, 151 ... auxiliary steering control unit,

Claims (7)

In a vehicle steering system including a steering device that individually steers left and right wheels by driving a steering actuator provided in a tire housing of the vehicle,
The steering device includes a control unit that individually controls the left and right steering actuators for the left and right wheels, and the control unit controls the left and right steering units so that the left and right wheels are steered symmetrically in toe-in or toe-out. Toe angle control means for controlling the actuator, and friction coefficient estimation for individually estimating the friction coefficients of the left and right wheels and the road surface according to a predetermined rule when the left and right steering actuators are controlled by the toe angle control means And a steering system.   The steering system according to claim 1, wherein the control unit controls the steering actuator so as to correct a steering angle of one or both of the left and right wheels based on the estimated friction coefficient. system. The steering system according to claim 1 or 2,
A first steering device for steering the front wheels of the vehicle;
A second steering device which is the steering device including the steering actuator and the control unit;
A vehicle information detection unit that detects vehicle information including a vehicle speed and a steering angle,
The control unit is a steering system that individually controls the left and right steering actuators of the left and right wheels based on the vehicle information. The steering system according to claim 3, wherein the second steering device is
A hub unit body having a hub bearing for supporting the wheel;
A unit support member provided on a suspension frame part of the suspension device and rotatably supporting the hub unit body about a turning axis extending in the vertical direction;
A steering system comprising: the steering actuator that rotates the hub unit body about the turning axis.   5. The steering system according to claim 3, wherein the control unit of the second steering device includes an auxiliary steering control unit that outputs a current command signal according to a given steering angle command signal, and the auxiliary steering control unit. A steering system comprising: an actuator drive control unit that drives and controls the steering actuator by outputting a current corresponding to a current command signal input from the steering control unit.   6. The steering system according to claim 1, wherein the steering actuator includes a reverse input prevention mechanism that prevents a reverse input from the wheel. 7.   A vehicle comprising the steering system according to any one of claims 1 to 6.

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