Steering system and vehicle

Abstract

To provide a steering system capable of improving reliability while suppressing the cost of the system.SOLUTION: A steering system according to the invention includes: a steering actuator 5 including a motor 26 for rotationally driving a wheel 9 around a steering shaft center A extending in a vertical direction; and a control device 29 for controlling the steering actuator 5 by using a motor current. The control device 29 includes: a steering control unit 30 that outputs a current command signal corresponding to a given steering angle command signal; and an actuator drive control unit 31 that outputs a current corresponding to the current command signal which is input from the steering control unit 30 to drive-control the steering actuator 5. The control device 29 includes abnormality determination means 30a for determining that the steering actuator 5 is abnormal when the motor current deviates from a predetermined range.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a steering system and a vehicle, and to a technique for improving fuel efficiency and improving the stability and reliability of driving performance by controlling the steering angles of left and right wheels to appropriate angles according to driving conditions. [Background technology]

[0002] In general automobiles and other vehicles, the steering wheel and steering device are mechanically connected, and both ends of the steering device are connected to the left and right wheels by tie rods. Therefore, the turning angle of the left and right wheels in response to the movement of the steering wheel is determined by the initial setting. There are two types of vehicle geometries known: (1) "parallel geometry," in which the turning angle of the left and right wheels is the same, and (2) "Ackermann geometry," in which the angle of the inside wheel is turned larger than the angle of the outside wheel in order to have a single turning center.

[0003] In Ackermann geometry, the steering angle difference between the left and right wheels is set so that each wheel turns around a common point in order to allow the vehicle to turn smoothly when cornering at low speeds where the centrifugal force acting on the vehicle can be ignored. However, in high speed cornering where centrifugal force cannot be ignored, it is desirable for the wheels to generate a cornering force in a direction that balances the centrifugal force, so parallel geometry is preferable to Ackermann geometry.

[0004] As mentioned above, the steering device of a typical vehicle is mechanically connected to the wheels, so that it can only have a single fixed steering geometry, and is often set to an intermediate geometry between the Ackermann geometry and the parallel geometry. However, in this case, the steering angle difference between the left and right wheels is insufficient at low speeds, resulting in an excessive steering angle of the outer wheel, and at high speeds, the steering angle of the inner wheel is excessive. If there is an unnecessary imbalance in the wheel lateral force distribution between the inner and outer wheels in this way, it can cause a deterioration in fuel efficiency and early tire wear due to an increase in running resistance, and also cause problems such as a loss of smooth cornering because the inner and outer wheels cannot be used efficiently. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3477889 [Patent Document 2] JP 2009-227122 A Summary of the Invention [Problem to be solved by the invention]

[0006] The rear wheel steering device of Patent Document 1 is equipped with an abnormality determination means for determining steering abnormality based on the detection value of a rear wheel steering angle sensor that detects the target steering angle and the actual steering angle of the rear wheels. In this case, since the rear wheel steering angle sensor is used as the abnormality detection means, it may take time to detect an abnormality depending on the behavior of the entire system or the sensor, making it difficult to improve reliability. In Patent Document 2, the control of the rear wheel steering device and the abnormality monitoring are performed by separate arithmetic processing means. In this case, a high-cost CPU device is used for each arithmetic processing means, which increases the cost of the entire system.

[0007] An object of the present invention is to provide a steering system that can reduce system costs while improving reliability. [Means for solving the problem]

[0008] The steering system of the present invention is a steering system including a steering actuator 5 including a motor 26 that rotates and drives a wheel 9 around a steering axis A extending in a vertical direction, and a control device 29 that controls the steering actuator 5 using a motor current, The control device 29 has an abnormality determination means 30a that determines that an abnormality has occurred in the steering actuator 5 when the motor current falls outside a predetermined range. The "predetermined range" is a range that is arbitrarily determined by design or the like, and is determined by obtaining an appropriate range through, for example, either one or both of a test and a simulation.

[0009] According to this configuration, the control device 29 can control the angle of the wheels 9 around the steering axis A by controlling the steering actuator 5 using the motor current. The abnormality determination means 30a of the control device 29 can determine the presence or absence of an abnormality in the steering actuator 5 using the above-mentioned motor current used in existing control without using an external sensor or the like. Therefore, costs can be reduced compared to the conventional technology that determines steering abnormality using an external sensor or the like. When the abnormality determination means 30a determines that the steering actuator 5 is abnormal, for example, the steering system can be stopped instantly. In this case, the time required for abnormality detection can be shortened compared to the conventional technology that uses a rear wheel steering angle sensor or the like, and the reliability of the steering system can be improved.

[0010] The steering actuator 5 may comprise a hub unit body 2 having a hub bearing 15 that supports the rotation of the wheel 9, and a unit support member 3 that is provided on a suspension frame component of the suspension system 12 (12R) and supports the hub unit body 2 rotatably about the steering axis A, and the steering actuator 5 may drive the hub unit body 2 to rotate about the steering axis A. In this case, when the abnormality determination means 30a determines that there is an abnormality in the steering actuator 5, it may be possible to stop the rotational drive of the hub unit body 2, for example. This makes it possible to ensure redundancy.

[0011] The control device 29 has a function of independently controlling the steering of each of the left and right wheels 9 by the pair of steering actuators 5, 5. The control device 29 may be provided in a plurality of units corresponding to the steering actuators 5, or may be a single control device capable of controlling all the steering actuators 5. When a plurality of control devices 29 are provided corresponding to the steering actuators 5, it is possible to simplify the control system. When a single control device 29 capable of controlling all the steering actuators 5 is provided, it is possible to reduce the number of parts and the manufacturing costs compared to a structure including a plurality of control devices.

[0012] The control device 29 may have a steering control unit 30 that outputs a current command signal corresponding to a given steering angle command signal, and an actuator drive control unit 31 that outputs a current corresponding to the current command signal input from the steering control unit 30 to drive and control the steering actuator 5. With this configuration, the steering actuator 5 of the steering system can be controlled with a simple configuration.

[0013] The control device 29 may perform current feedback control by obtaining the motor current in response to the current command signal and making the motor current follow the current command signal. By performing current feedback control in this manner, the angle of the wheels 9 can be appropriately and accurately managed.

[0014] In the vehicle of the present invention, either or both of the front wheels 9F and the rear wheels 9R are supported using the hub unit body 2 in the steering system of any of the above configurations of the present invention. Therefore, the above-mentioned effects of the steering system of the present invention can be obtained. The front wheels 9F are generally considered to be steered wheels, and when the hub unit body 2 is applied to the steered wheels, it is effective for adjusting the toe angle while traveling. In addition, the rear wheels 9R are generally considered to be non-steered wheels, and when applied to the non-steered wheels, it is possible to reduce the minimum turning radius during low-speed traveling by slightly steering the non-steered wheels.

[0015] The steering actuator may have a linear motion mechanism that converts the rotation output of the motor into linear motion, and the linear motion mechanism may have a function of preventing reverse input from the tires. In this case, it is possible to simply evaluate whether the motor current is outside the specified range. On the other hand, if reverse input from the tires is possible and a load is applied to the linear motion mechanism from the opposite side, the load for steering will change undesirably, and the motor current may not be accurately evaluated. The "opposite side" refers to the direction of the force acting on the output part (output rod) of the linear motion mechanism from the tire via the connecting part. Effect of the Invention

[0016] The steering system of the present invention determines that the steering actuator is abnormal when the motor current for controlling the steering actuator falls outside a specified range, thereby making it possible to reduce system costs and improve reliability. [Brief description of the drawings]

[0017] [Figure 1] 1 is a vertical cross-sectional view showing a configuration of a steering function-equipped hub unit and its surroundings in a steering system according to a first embodiment of the present invention. FIG. [Diagram 2] 2 is a horizontal cross-sectional view of the steering function-equipped hub unit and a block diagram of a control system thereof. FIG. [Diagram 3] FIG. 2 is a perspective view showing the external appearance of the steering function-equipped hub unit. [Figure 4] FIG. 2 is a side view of the steering function-equipped hub unit. [Diagram 5] FIG. 2 is a plan view of the steering function-equipped hub unit. [Figure 6] 6 is a cross-sectional view taken along line VI-VI in FIG. 4. [Figure 7] FIG. 4 is a side view of the linear motion mechanism of the steering function-equipped hub unit. [Figure 8] FIG. 11 is a diagram illustrating a motor load when an abnormality is detected. [Figure 9A] FIG. 2 is a schematic plan view of an example of a vehicle equipped with the steering system. [Figure 9B]FIG. 13 is a schematic plan view showing a modified example of the steering system in which the control system is changed. [Figure 10] FIG. 11 is a schematic plan view of another example of a vehicle equipped with any one of the steering systems. [Figure 11] FIG. 11 is a schematic plan view of another example of a vehicle equipped with any one of the steering systems. [Figure 12] FIG. 11 is a schematic plan view of another example of a vehicle equipped with any one of the steering systems. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] [First embodiment] A steering system according to an embodiment of the present invention will be described with reference to FIGS. 1 to 9A. The steering system includes a hub unit with a steering function and a control device (to be described later) that controls a steering actuator of the hub unit with a steering function. The steering system is mounted on a vehicle.

[0019] <Outline of the structure of the hub unit with steering function> As shown in FIG. 1, this hub unit with steering function 1 includes a hub unit body 2, a unit support member 3, a rotation-permitting support part 4, and a steering actuator 5. The unit support member 3 is provided integrally with a knuckle 6, which is a suspension frame part. The steering actuator 5 is provided on the inboard side of this unit support member 3, and the hub unit body 2 is provided on the outboard side of the unit support member 3. With the hub unit with steering function 1 mounted on a vehicle, the outer side in the vehicle width direction is referred to as the outboard side, and the center side in the vehicle width direction is referred to as the inboard side. Note that the hub unit with steering function 1 may be simply referred to as the hub unit 1.

[0020] As shown in Fig. 2, the hub unit body 2 and the steering actuator 5 are connected by a joint portion 8. Usually, this joint portion 8 is fitted with a boot (not shown) for waterproofing and dustproofing.

[0021] As shown in Fig. 1, the hub unit body 2 is supported by a unit support member 3 at two upper and lower points via rotation-permitting support parts 4, 4 so as to be rotatable around a steering axis A extending in the vertical direction. The steering axis A is an axis different from the rotation axis O of the wheel 9, and is also different from the kingpin axis that performs the main steering. In a normal vehicle, the kingpin angle is set at 10 to 20 degrees for the purpose of improving the straight-line stability of the vehicle when traveling, but the hub unit 1 with steering function of this embodiment has a steering axis with an angle (axis) different from the kingpin angle. The wheel 9 includes a wheel 9a and a tire 9b.

[0022] <Installation location of steering hub unit> In this embodiment, the steering function equipped hub unit 1 is provided integrally with the knuckle 6 of the suspension device 12 as a mechanism for steering the left and right wheels individually at a small angle (approximately ±5 degrees) in addition to the steering by the steering device 11 of the steering wheels, specifically, the front wheels 9F of the vehicle 10 as shown in FIG. 9A. However, in the steering function equipped hub unit 1 for the steering wheels, depending on the vehicle control requirements, the left and right wheels may each take a relatively large angle, for example, 10° to 20°, instead of the small angle. The same applies to the steering function equipped hub units 1 shown in FIGS. 10, 11, and 12 described later.

[0023] As shown in Fig. 9A, the steering device 11 is attached to the vehicle body and is operated by the operation of a steering wheel 11a by the driver or by commands from an automatic driving device or a driving support device (not shown), and its advancing and retreating tie rod 14 is connected to a steering coupling portion 6d (described later) of the unit support member 3 in Fig. 2. The steering device 11 is of a rack and pinion type or the like, but any type of steering device may be used. The suspension device 12 in Fig. 9A employs, for example, a strut-type suspension mechanism in which a shock absorber is directly fixed to the knuckle 6, but a double wishbone suspension mechanism, a multi-link suspension mechanism, or other suspension mechanisms may also be employed.

[0024] <About the hub unit> As shown in FIG. 1, the hub unit body 2 includes a hub bearing 15 for supporting the wheel 9, an outer ring 16 which is a circular portion with a steering shaft, and an arm portion 17 (FIG. 3) which is a steering force receiving portion. As shown in Figure 6, hub bearing 15 has an inner ring 18, an outer ring 19, and rolling elements 20 such as balls interposed between the inner and outer rings 18, 19, and serves to connect components on the vehicle body side to the wheel 9 (Figure 1).

[0025] In the example of Fig. 1, this hub bearing 15 is an angular contact 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 double-row. As shown in Fig. 6, the inner ring 18 has a hub flange 18aa and a hub ring portion 18a that forms an outboard side raceway surface, and an inner ring portion 18b that forms an inboard side raceway surface. As shown in Fig. 1, the wheel 9a of the wheel 9 is bolted to the hub flange 18aa in a state where it overlaps with the brake rotor 21a. The inner ring 18 rotates around the rotation axis O.

[0026] As shown in Fig. 6, outer ring (annular portion with steering shaft portions) 16 has annular portion 16a fitted to the outer peripheral surface of outer ring 19, and trunnion-shape steering shaft portions 16b, 16b provided so as to protrude upward and downward from the outer periphery of this annular portion 16a.

[0027] 2, the brake 21 has a brake rotor 21a and a brake caliper 21b. The brake caliper 21b is attached to upper and lower brake caliper attachment portions 22 (FIG. 4) that are integrally formed with the outer ring 19 and protrude like arms.

[0028] <About rotation-allowing support parts and unit support members> As shown in Fig. 6, each rotation-permitting support part 4 is made of a rolling bearing. In this example, a tapered roller bearing is used as the rolling bearing. The rolling bearing has an inner ring 4a fitted to the outer periphery of the steered shaft portion 16b, an outer ring 4b fitted to the unit support member 3, and multiple rolling elements 4c interposed between the inner and outer rings 4a and 4b.

[0029] The unit support member 3 has a unit support member main body 3A and a unit support member combination 3B. The generally ring-shaped unit support member combination 3B is detachably fixed to the outboard end of the unit support member main body 3A. Partial cylindrical fitting hole formation portions 3Ba are formed on the upper and lower portions of the inboard side surface of the unit support member combination 3B.

[0030] As shown in Figures 5 and 6, a partially cylindrical fitting hole forming portion 3Aa is formed in each of the upper and lower portions of the outboard end of the unit support member main body 3A. The unit support member combined body 3B is fixed to the outboard end of the unit support member main body 3A, and the fitting hole forming portions 3Aa, 3Ba of the upper and lower portions are combined with each other to form a fitting hole that continues around the entire circumference. An outer ring 4b is fitted into this fitting hole. In Figure 3, the unit support member 3 is represented by a dashed line.

[0031] As shown in FIG. 6, each steered shaft 16b is a hollow shaft, and a female thread is formed in the inner peripheral hole so as to extend radially, and a bolt 23 is provided to screw into the female thread. A disk-shaped pressing member 24 is interposed on the end face of the inner ring 4a, and a pressing force is applied to the end face of the inner ring 4a by the bolt 23 screwed into the female thread, thereby applying a preload to each rotation-allowing support part 4. In other words, an initial preload is set so that the preload does not disappear even when an external force such as the weight of the vehicle acts on the hub unit. This can increase the rigidity of each rotation-allowing support part 4. Note that the rolling bearing of the rotation-allowing support part 4 may be an angular ball bearing or a four-point contact ball bearing instead of a tapered roller bearing. In this case, the preload can be applied in the same manner as described above.

[0032] 1, the upper and lower steered shaft portions 16b, 16b are supported by the unit support member 3 via rotation-permitting support parts 4, 4, respectively, and each rotation-permitting support part 4 is located inside the wheel 9a of the wheel 9. In this example, each rotation-permitting support part 4 is disposed inside the wheel 9a near the middle of the wheel 9a in the width direction.

[0033] 2, the arm portion 17 is a point of action that applies auxiliary steering force to the outer ring 19 of the hub bearing 15, and protrudes integrally with a part of the outer circumference of the outer ring 16 or the outer ring 19. The arm portion 17 is rotatably connected to an output rod 25a that serves as a linear output portion of the steering actuator 5 via a joint portion 8. As a result, when the output rod 25a of the steering actuator 5 moves forward and backward (linear motion), the hub unit body 2 rotates about the steering axis A, that is, auxiliary steering is performed.

[0034] <Steering actuator> The vehicle 10 in Fig. 9A is equipped with a pair of steering actuators 5, 5 shown in Fig. 2 for independently steering each of the left and right front wheels 9F. The pair of left and right steering actuators 5, 5 have the same structure, and each actuator will be described below as a steering actuator 5. The steering actuator 5 is equipped with a motor 26 as a rotational drive source that rotates the hub unit body 2 around the steering axis A, a reduction gear 27 that reduces the rotation of the motor 26, and a linear motion mechanism 25 that converts the forward and reverse rotational output of the reduction gear 27 into a reciprocating linear motion (linear motion) of an output rod 25a. The motor 26 is, for example, a permanent magnet type synchronous motor, but may be a DC motor or an induction motor.

[0035] <Reducer> The reducer 27 may be a wrap-around transmission mechanism such as a belt transmission mechanism or a gear train, and in the example of FIG. 2, a belt transmission mechanism is used. The reducer 27 has a drive pulley 27a, a driven pulley 27b, and a belt 27c. The drive pulley 27a is coupled to the rotor shaft 26b of the motor 26, and the driven pulley 27b is provided on the rotatable nut portion 35 of the linear motion mechanism 25. The driven pulley 27b is disposed parallel to the rotor shaft 26b. 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 the wrap-around reducer 27.

[0036] <About the linear motion mechanism> The linear motion mechanism 25 can use a feed screw mechanism of a sliding screw type such as a trapezoidal screw or a triangle screw, and in this example, a feed screw mechanism using a sliding screw of a trapezoidal screw is used. The linear motion mechanism 25 has a feed screw mechanism using a sliding screw of a trapezoidal screw, and therefore has a function of preventing reverse input from the tire 9b. Grease is sealed inside the sliding screw. This linear motion mechanism 25 has the feed screw mechanism, a rotation support bearing 28, a rotation prevention part 43, and an actuator case 34 that covers these components.

[0037] The feed screw mechanism has a nut portion 35, the output rod 25a which is a screw shaft, and a sliding bearing. The output rod 25a is prevented from rotating relative to the unit support member 3 by a rotation prevention part 43. The nut portion 35 is provided with a driven pulley 27b at the axially intermediate portion of its outer periphery, and is rotatably supported on the unit support member 3 by rotation support bearings 28, 28 on both axial sides. A female thread is provided on the inner periphery of the nut portion 35. A male thread that meshes with the female thread of the nut portion 35 is provided on the outer periphery of the output rod 25a.

[0038] A plain bearing through which the output rod 25a slidably passes is provided on both axial ends of the nut portion 35. Each plain bearing guides the axial movement of the output rod 25a and prevents a radial force from being applied to the output rod 25a when an external force from the tire side is input to the output rod 25a.

[0039] In this example, two tapered roller bearings are combined face-to-face via the driven pulley 27b as the rotation support bearing 28. The rotation support bearings 28, 28 may be arranged either back-to-back or face-to-face, but a face-to-face arrangement is preferable in terms of ease of assembly and preload adjustment using shims or the like. The rotation support bearing 28 may also be an angular ball bearing. In this case, the rotation support bearings 28, 28 may also be arranged either back-to-back or face-to-face.

[0040] The anti-rotation component 43 is a shaft-shaped member provided at the inboard end, which is the rear end, of the output rod 25a. The anti-rotation component 43 is fitted and fixed to the inboard end of the output rod 25a in a penetrating manner so as to extend, for example, in directions perpendicular to the up-down direction and the axial direction of the output rod 25a. As shown in Fig. 7, annular plain bearings 49a, 49b are fitted to both axial ends of the outer periphery of the anti-rotation component 43.

[0041] A flat surface (a so-called D-cut surface) 50 parallel to one end face of the plain bearing 49b is formed on the inboard end of the output rod 25a at a portion facing one plain bearing 49b. One end face of the plain bearing 49b abuts against the flat surface 50 of the output rod 25a, and a bolt 51 that presses the other end face of the plain bearing 49b is screwed into the anti-rotation part 43. This restricts the positions of the anti-rotation part 43, the bolt 51, and the plain bearings 49a, 49b to desired positions relative to the actuator case 34 (the positions in the vertical direction in FIG. 2).

[0042] A guide groove 52 having a substantially rectangular parallelepiped shape and including guide surfaces 52a, 52b that respectively guide the outer circumferential surfaces of the plain bearings 49a, 49b is formed in the actuator case 34. In other words, the anti-rotation component 43 slidably contacts the guide surfaces 52a, 52b of the actuator case 34, which is a fixed part of the linear motion mechanism 25, via the plain bearings 49a, 49b. Thus, by sliding the anti-rotation component 43 along the guide groove 52 of the actuator case 34 via the plain bearings 49a, 49b, the output rod 25a can be reciprocated in the axial direction.

[0043] As shown in FIG. 2, the linear motion mechanism 25 includes a feed screw mechanism using a sliding screw of the trapezoidal screw, and therefore can enhance the effect of preventing reverse input from the tire 9b. The steering actuator 5 including the motor 26, the reducer 27, and the linear motion mechanism 25 is assembled as a subassembly and detachably attached to the case 6b with bolts or the like. The steering actuator 5 of this embodiment includes the motor 26, the reducer 27, and the linear motion mechanism 25, but the reducer may be omitted. In other words, a mechanism that transmits the driving force of the motor 26 directly to the linear motion mechanism 25 without the reducer is also possible. In addition, the linear motion mechanism 25 may be a mechanism that can convert rotational motion into linear motion, such as a ball screw or a rack and pinion mechanism, in addition to the trapezoidal screw shown in this embodiment.

[0044] <Other mechanical configurations> The case 6b is formed integrally with the unit support member main body 3A as a part of the unit support member 3. The case 6b is formed in a bottomed cylindrical shape and is provided with a motor accommodating section that supports the motor 26 and a linear motion mechanism accommodating section that supports the linear motion mechanism 25. The motor accommodating section has a fitting hole that supports the motor 26 at a predetermined position in the case. The linear motion mechanism accommodating section has a fitting hole that supports the linear motion mechanism 25 at a predetermined position in the case, and a through hole that allows the output rod 25a to advance and retreat.

[0045] As shown in Fig. 3, the unit support member main body 3A has the case 6b, a shock absorber mounting portion 6c which serves as a mounting portion for a shock absorber, and a steering device coupling portion 6d which serves as a coupling portion for a steering device 11 (Fig. 2). The shock absorber mounting portion 6c and the steering device coupling portion 6d are also formed integrally with the unit support member main body 3A. The shock absorber mounting portion 6c is formed so as to protrude from the upper portion of the outer surface portion of the unit support member main body 3A. The steering device coupling portion 6d is formed so as to protrude from the side portion of the outer surface portion of the unit support member main body 3A.

[0046] <About the control system> As shown in Fig. 2, the control device 29 has a steering control section 30 and an actuator drive control section 31. The control device 29 has a function of independently controlling the steering of the left and right wheels. In this example, one control device 29 shown in Fig. 9A is applied, which is capable of controlling a pair of actuators 5, 5 for the left and right wheels, that is, all of the actuators 5. However, as shown in Fig. 9B, a plurality of control devices 29 may be provided corresponding to the respective actuators 5.

[0047] As shown in FIG. 2, the steering control unit 30 calculates and outputs a current command signal corresponding to an auxiliary steering angle command signal (steering angle command signal) given from a higher-level control unit 32. At this time, the control device 29 performs current feedback control, as a basic configuration of this control system, to obtain a motor current from a current detection means Sa and make it follow the calculated current command signal. This current feedback control can appropriately and accurately manage the angle of the wheels 9. As the current detection means Sa, for example, a current sensor made of an amplifier that detects a voltage across a shunt resistor, or a non-contact sensor that detects a magnetic flux or the like around the current path of the phase current of the motor 26 can be used. The current detection means Sa may be configured to detect, for example, a terminal voltage or the like of a switch element or the like that constitutes an actuator drive control unit 31 described later.

[0048] The upper control unit 32 is a higher-level control means of the steering control unit 30, and an electric control unit (Vehicle Control Unit, abbreviated as VCU) that controls the entire vehicle is applied as the upper control unit 32. The actuator drive control unit 31 outputs a current according to a current command signal input from the steering control unit 30 to drive and control the steering actuator 5. The actuator drive control unit 31 controls the power supplied to the coil of the motor 26.

[0049] The actuator drive control unit 31, for example, configures a half-bridge circuit using a switching element (not shown) and performs PWM control to determine the voltage applied to the motor by the ON-OFF duty ratio of the switching element. This allows the wheel 9 to be slightly changed in angle in addition to the steering by the driver's steering wheel operation. Even when driving in a straight line, the amount of toe angle can be adjusted according to each situation. Note that the steering system may operate the steering actuators 5, 5 by commands from an automatic driving device or a driving assistance device (not shown) instead of the driver's steering wheel operation.

[0050] The steering control section 30 of the control device 29 has an abnormality determination means 30a that determines that an abnormality has occurred in the steering actuator 5 when the motor current falls outside a predetermined range. <Normal and abnormal operation> Fig. 8 is a diagram showing the motor load during abnormal operation, etc. The figure shows an example of steering to a certain angle, and the vertical axis shows the motor load (current value). The explanation will be given with reference to Fig. 2 as well.

[0051] <Normal operation> As shown in Fig. 8(a), during normal operation, when a signal is received and a current is passed through the motor 26 to operate the steering actuator 5, in section t1 where the motor operates at a steady speed after acceleration, a current flows within a dotted range (predetermined range) δa in Fig. 8(a) according to the load of the mechanical parts connected after the motor. In this case, the abnormality determination means 30a determines that there is no abnormality in the steering actuator 5. Note that current feedback control is performed in all sections where the steering actuator 5 is operated.

[0052] If an abnormality occurs in the steering actuator 5 for either the left or right wheel, or in the steering actuators 5,5 for both the left and right wheels while the vehicle is traveling, the control device 29 outputs an abnormality signal to the higher-level control unit 32 on the vehicle side to indicate that the abnormality has occurred, and stops control of both steering actuators 5,5.

[0053] <Load (low) during abnormal operation> For example, if the belt (timing belt) of the reducer 27 breaks, the load of the mechanical parts connected after the motor will be lost, as shown in Fig. 8(b). Therefore, in section t1 in which the motor 26 operates at a steady speed, the load (current value) driving the motor 26 will be lower than the dotted range δa during normal operation. If this state continues for a certain period of time, the abnormality determination means 30a will determine that the connection after the motor has been lost (abnormality determination), and the control device 29 will stop controlling both steering actuators 5,5 in response to the abnormality determination.

[0054] <Load (large) during abnormal operation> For example, if a foreign object or the like gets into the moving parts, the load (current value) driving the motor 26 becomes higher than the dotted line range δa during normal operation in section t1 when the motor 26 is operating at a steady speed, as shown in Fig. 8(c). If this state continues for a certain period of time, the abnormality determination means 30a determines that a foreign object or the like has got into the moving parts (abnormality determination), and the control device 29 receives the abnormality determination and stops control of both steering actuators 5,5.

[0055] <Action and effect> According to the steering system described above, the hub unit body 2 including the hub bearing 15 supporting the wheel 9 in Fig. 2 can be freely rotated around the steering axis A by driving the steering actuator 5. This rotation is added to the steering by the driver's handlebar operation, i.e., added to the rotation of the knuckle around the kingpin shaft by the steering device 11, and is performed as auxiliary steering, and also allows independent steering of one wheel. By making the auxiliary steering angle of the left and right wheels 9, 9 different, the toe angle between the left and right wheels 9, 9 can be changed as desired.

[0056] Therefore, the hub unit 1 with steering function may be used for either steered wheels such as front wheels or non-steered wheels such as rear wheels. When used for steered wheels, it is installed on a member whose direction can be changed by the steering device 11, and becomes a mechanism that performs minute angle changes of the wheels 9 individually for the left and right wheels, or in conjunction with the left and right wheels, in addition to the steering by the driver's steering wheel operation. A small angle is sufficient for the angle of auxiliary steering to improve the maneuverability and driving stability of the vehicle, and it is sufficient even if the angle of auxiliary steering is within ±5 degrees. The angle of auxiliary steering is controlled by the steering actuator 5.

[0057] In addition, when turning, the steering angle difference between the left and right wheels can be changed according to the driving speed. For example, the steering geometry can be changed while driving, such as using parallel geometry when turning at high speeds and Ackermann geometry when turning at low speeds. In this way, the wheel angle can be changed freely while driving, improving the vehicle's maneuverability and enabling stable driving. By appropriately changing the steering angle of the left and right steering wheels when turning, the vehicle's turning radius can be reduced and its maneuverability can be improved. Furthermore, by adjusting the toe angle to suit each situation, even when driving in a straight line, it is possible to adjust the tires so that they are oriented straight in the direction of travel at low speeds, thereby reducing rolling resistance and preventing a deterioration in fuel efficiency, and at high speeds the tire angle is toe-in to ensure driving stability.

[0058] When the steering function equipped hub unit 1 is applied to the non-steered rear wheel 9R (Fig. 10), if the steering angle is set to the same phase as the front wheel 9F (Fig. 10) during cornering, the yaw that occurs during steering can be suppressed and the stability of the vehicle can be improved. By adjusting the toe angle independently for the left and right, driving stability can be ensured even during straight driving. In order to control the behavior of the vehicle in this way, it is necessary to accurately control the steering angle of the wheels 9, and in the event of an abnormality, it is necessary to quickly stop the control of the steering actuator 5.

[0059] In this embodiment, the control device 29, as a basic configuration of the control system, performs current feedback control by obtaining a motor current from the current detection means Sa and making the motor current follow the calculated current command signal, thereby appropriately and accurately managing the angle of the wheels 9. The abnormality determination means 30a of the control device 29 can determine the presence or absence of an abnormality in the steering actuator 5 using the above-mentioned motor current used in the existing control without using an external sensor or the like. Therefore, the cost can be reduced compared to the conventional technology that determines the steering abnormality using an external sensor or the like. When the abnormality determination means 30a determines that the steering actuator 5 is abnormal, the control device 29 receives the abnormality determination and instantly stops the control of both steering actuators 5,5. In this case, the time required for abnormality detection can be shortened compared to the conventional technology that uses a rear wheel steering angle sensor or the like, and the reliability of the steering system can be improved.

[0060] The steering actuator 5 has a linear motion mechanism 25 that converts the rotation output of the motor 26 into linear motion, and the linear motion mechanism 25 has a function of preventing reverse input from the tire 9b. In this case, it is possible to simply evaluate whether the motor current is outside a specified range (normal, abnormal). Conversely, if reverse input from the tire 9b is possible and a load is applied to the linear motion mechanism 25 from the opposite side, the load for steering will change undesirably, and it may not be possible to accurately evaluate the motor current. The "opposite side" refers to the direction of the force acting on the output rod 25a of the linear motion mechanism 25 from the tire 9b via the connecting part.

[0061] When one control device 29 capable of controlling all of the actuators 5 is applied as in FIG. 9A, it is possible to reduce the number of parts and manufacturing costs compared to a structure including a plurality of control devices. As shown in FIG. 9B, when a plurality of control devices 29 are provided corresponding to the steering actuators 5, the control system can be simplified.

[0062] <Other embodiments> In the following description, parts corresponding to matters previously described in each embodiment are given the same reference numerals, and duplicated description is omitted. When only a part of the configuration is described, the other parts of the configuration are the same as the previously described embodiment unless otherwise specified. The same configuration has the same action and effect. It is possible to combine not only the parts specifically described in each embodiment, but also partially combine embodiments together, provided that there is no particular problem with the combination.

[0063] The hub unit 1 with steering function may be used for non-steered wheels. For example, as shown in Fig. 10, in a front-wheel-steered vehicle, it may be set in a suspension frame part 6R that serves as a wheel bearing installation part of a suspension device 12R that supports a rear wheel 9R, and used for rear-wheel steering. In the hub unit 1 with steering function for non-steered wheels, depending on the requirements for vehicle control, the steering angle is not limited to the small steering angle described above, and a relatively large angle of, for example, 10° to 20° may be taken for each of the left and right wheels. As shown in FIG. 11, the steering function-equipped hub unit 1 may be used for each of left and right front wheels 9F, 9F which are steered wheels and left and right rear wheels 9R, 9R which are non-steered wheels.

[0064] As shown in Fig. 12, the left and right rear wheels 9R, 9R may be steered by one steering actuator 5. This steering actuator 5 is disposed near the center of the vehicle width direction so that the actuator body extends in the left-right direction of the vehicle. Left and right output rods 25a, 25a are disposed so as to face outboard from the one actuator body. When the left and right rear wheels 9R, 9R are steered by one steering actuator 5, the number of parts can be reduced and the structure can be simplified compared to a configuration in which the left and right rear wheels are steered by two steering actuators. However, in this case, the steering angles of the left and right rear wheels 9R, 9R are controlled in the same phase.

[0065] 2 may be electrically connected to an alarm means for generating an alarm in response to an abnormality signal output from the control device 29. Examples of the alarm include an alarm sound, an alarm lamp, and an alarm display. The alarm generated by the alarm means alerts the driver of the vehicle that an abnormality has occurred in the steering actuator 5, and measures can be taken such as promptly moving the vehicle to a repair shop, etc.

[0066] Furthermore, the steering function-equipped hub unit of the present invention can be applied to both driving wheels and driven wheels.

[0067] Although the embodiment for carrying out the present invention has been described above, the embodiment disclosed herein is illustrative in all respects and is not restrictive. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0068] 1...Hub unit with steering function 1, 2...Hub unit main body, 3...Unit support member, 5...Steering actuator, 6...Knuckle (suspension frame part), 6R...Suspension frame part, 9...Wheel, 9F...Front wheel, 9R...Rear wheel, 9b...Tire, 12, 12R...Suspension device, 15...Hub bearing, 25...Linear motion mechanism, 26...Motor, 29...Control device, 30...Steering control unit, 30a...Abnormality determination means, 31...Actuator drive control unit

Claims

1. A steering system including a steering actuator including a motor that rotates a wheel around a steering axis extending in a vertical direction, and a control device that controls the steering actuator using a motor current, The control device has an abnormality determination means for determining that an abnormality has occurred in the steering actuator when the motor current falls outside a predetermined range.

2. 2. The steering system according to claim 1, further comprising: a hub unit body having a hub bearing that supports the wheel; and a unit support member that is provided on a suspension frame component of a suspension system and supports the hub unit body rotatably about the steering axis, The steering actuator rotates the hub unit body about the steering axis.

3. In the steering system according to claim 1 or 2, the control device has a function of independently controlling the steering of each of the left and right wheels by the pair of steering actuators, The steering system may include a plurality of the control devices provided in correspondence with the steering actuators, or may include a single control device capable of controlling all of the steering actuators.

4. 3. The steering system according to claim 1 or 2, wherein the control device has a steering control unit that outputs a current command signal in response to a given steering angle command signal, and an actuator drive control unit that outputs a current in response to the current command signal input from the steering control unit to drive and control the steering actuator.

5. 5. The steering system according to claim 4, wherein the control device performs current feedback control by obtaining the motor current in response to the current command signal and making the motor current follow the current command signal.

6. A vehicle in which either or both of a front wheel and a rear wheel are supported by using the hub unit body in the steering system according to claim 2.

7. 3. The steering system according to claim 1, wherein the steering actuator has a linear motion mechanism that converts the rotational output of the motor into linear motion, and the linear motion mechanism has a function of preventing reverse input from tires.

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