JP2011068213A - Four-wheel steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the traveling resistance of rear wheels during steering traveling, in an automobile equipped with a four-wheel steering device. <P>SOLUTION: A rear wheel steering angle is obtained from a vehicle speed and a front wheel steering angle using a map 42a which is set as a two-wheel model. A turning radius formed of the front wheel steering angle and the rear wheel steering angle is obtained. A rear wheel steering angle determination section 42 determining a steered wheel angle of the each rear wheel so that the right and left rear wheels roll on circumferences centering on the turning center of the turning radius. A rear wheel control section 41 wheel-steer controls the right and left wheels by the use of corresponding actuators 11R, 11L for steering the rear wheels so that the steered wheel angle of each rear wheel reaches a determined steered angle. When the rear wheels are steered during the steering traveling, the right and left rear wheels (inner and outer wheels) are steered so as to make the same turning center, eliminating a difference between amounts of traveling resistance generated by the displacement of the turning center, thus reducing a wear difference between the right and left wheels and the deterioration of fuel economy. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a four-wheel steering apparatus capable of steering four wheels of an automobile.

  Conventionally, in a four-wheel steering system for an automobile, the steering system of the front wheels and the steering system of the rear wheels are connected by a link, and the steering direction and the steering angle of the rear wheels are changed according to the steering angle of the front wheels. was there. Further, there is a system in which the steering system and the steering angle of the rear wheel are controlled based on the steering angle (steering angle) and the vehicle speed by driving the rear wheel steering system with an independent actuator ( For example, see Patent Document 1).

JP-A-9-290767

  In a four-wheel steering device for an automobile, the turning radius can be reduced with respect to the one without the rear wheel steering mechanism by steering the rear wheels in the reverse direction with respect to the front wheel steering direction. In addition, when changing the oblique line during high speed traveling, the front wheel and the rear wheel can be steered in the same direction, so that the lane change can be performed quickly and stably.

  On the other hand, in an automobile without a rear wheel steering mechanism, the rear wheels rotate in a parallel state with respect to the vehicle longitudinal axis, and the extension lines of the axles of the left and right rear wheels overlap on one straight line. It is known. Further, the front wheel steering device uses an Ackermann type steering mechanism in which the turning centers of the left and right front wheels coincide with each other on the extension line of the rear wheel axle.

  In some conventional four-wheel steering devices, the front and rear steering systems are connected by links, and in that case, the steering angle of the rear wheels is the same for the left and right wheels with respect to the steering angle of the front wheels. It is. However, when the turning angles of the left and right rear wheels are the same, the extension lines of the left and right rear wheel axles are parallel, so that the turning center of the inner and outer wheels of the rear wheels is shifted and the steering is performed in the opposite direction. In this case, the rear wheels will pass the inner tracks, the rear wheels will have higher running resistance and the inner wheels will have higher running resistance than the outer wheels, and there will be a difference in tire wear on the rear wheels between the left and right wheels. There was a possibility that the problem of going out or causing deterioration of fuel consumption might occur.

  Also, even in the case where the steering angle is not the same on the left and right of the rear wheel, as described above, the left and right rear wheels are steered in a predetermined relationship based on the input conditions of the front wheel steering angle and the vehicle speed. The turning center of the rear wheel deviates from the turning center of the front wheel, and there is a problem similar to the above. Even when steering in the same direction, the turning center of the rear wheel shifts to the side where the turning radius becomes larger than the turning center of the front wheel. There is a problem that the difference occurs.

  In order to solve such a problem and reduce the running resistance of the rear wheels during steering in a vehicle equipped with a four-wheel steering device, in the present invention, a steering angle sensor for detecting the front wheel steering angle is used. (14), a vehicle speed sensor (13) for detecting the vehicle speed, the rear wheel steering actuators (11L, 11R) for independently steering the left and right rear wheels (5L, 5R), the front wheel steering angle, Rear wheel steering angle determining means (42) for determining a rear wheel steering angle set in advance according to the vehicle speed, and the left and right rear wheels (5L, 5R) based on the front wheel steering angle and the rear wheel steering angle. And the left and right rear wheels (5L, 5R) by the rear wheel steering actuators (11L, 11R) so as to match the respective turning centers of the left and right rear wheels (5L, 5R) with the turning center. ) Rear wheel to control steering It was assumed to have a steering control unit (41).

  According to this, in a four-wheel steering device, for example, the rear wheels are steered in the reverse direction to improve the turning ability at low speeds, or the rear wheels are improved in order to improve responsiveness when changing lanes at high speeds. When turning in the same direction, the rear wheel steering angle with respect to the front wheel steering angle set in advance according to vehicle characteristics, etc. is obtained, and the left and right turning angles of the rear wheels are set with the turning center of the rear wheel steering angle as the turning center. Thus, the left and right rear wheels are steered at different turning angles, so that a difference in running resistance between the left and right wheels (inner and outer wheels) at the time of rear wheel steering is suppressed.

  In particular, the rear wheel steering angle determining means (42) may have a map (42a) for determining a rear wheel steering angle from a front wheel steering angle by a two-wheel model in which a four-wheel vehicle is replaced with a two-wheel vehicle. According to this, the calculation of the rear wheel steering angle with respect to the front wheel steering angle can be easily performed, and the cost reduction of the device can be promoted.

  Thus, according to the present invention, when the rear wheels are steered during steering traveling, the left and right wheels (inner and outer wheels) of the rear wheels are steered so that they have the same turning center. A difference in the magnitude of running resistance does not occur, and the difference in wear between the left and right wheels and the deterioration of fuel consumption can be reduced.

It is a schematic block diagram of the motor vehicle which applied the rear-wheel steering apparatus with which this invention was applied. It is a perspective view which shows a left rear suspension. It is the figure seen from the arrow III line of FIG. It is a schematic block diagram of a rear-wheel steering control means. It is a flowchart which shows the control point based on this invention. It is explanatory drawing using a two-wheel model. It is explanatory drawing which shows the state which steered the rear wheel to the reverse direction.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an automobile V to which a rear wheel steering device 10 to which the present invention is applied is applied. In the description, for the wheels and members arranged for them, that is, tires, electric actuators, etc., subscripts L or R indicating left and right are attached to the numerals, respectively, for example, rear wheel 5L (left), For example, the rear wheel 5R (right) is referred to as the rear wheel 5. The vehicle body 1 is used as a reference for front and rear, left and right, and top and bottom.

  As shown in FIG. 1, the vehicle V includes left and right front wheels 3L and 3R to which tires 2L and 2R are attached, and left and right rear wheels 5L and 5R to which tires 4L and 4R are attached. Front wheels 3L, 3R and rear wheels 5L, 5R are suspended from the vehicle body 1 by left and right front suspensions 6L, 6R and rear suspensions 7L, 7R, respectively.

  In addition, the vehicle V corresponds to the front wheel steering device 9 that directly steers the left and right front wheels 3L and 3R via the rack and pinion mechanism and the left and right rear suspensions 7L and 7R by steering the steering wheel 8. Left and right electric actuators 11L and 11R are provided as rear wheel steering actuators that are respectively attached to appropriate positions. The left and right electric actuators 11L and 11R can be driven to change (control) the turning angles of the rear wheels 5L and 5R independently, and thus the rear wheel steering device 10 is provided.

  Next, a specific example of a structure for making the turning angles of the rear wheels 5L and 5R variable will be described with reference to FIGS. 2 and 3 showing the left rear suspension. FIG. 2 is a perspective view of the left rear suspension 7L, and FIG. 3 is a rear view of the left rear suspension 7L. Since the right rear suspension may have the same structure only in the left and right sides, the left suspension is omitted from FIGS.

  The rear suspension 7 may be of a double wishbone type, and includes a knuckle 21 that rotatably supports the rear wheel 5, an upper arm 22 and a lower arm 23 that connect the knuckle 21 to the vehicle body 1 so as to move up and down, and a rear wheel 5. An electric actuator 11 connected between the knuckle 21 and the vehicle body 1 to change the turning angle, a damper 24 with a suspension spring that cushions the vertical movement of the rear wheel 5L, and the like.

  The base end portions of the upper arm 22 and the lower arm 23 are connected to the vehicle body 1 through rubber bush joints 25 and 26 so as to be pivotable in the vertical direction, and the tip portions of the upper arm 22 and the lower arm 23 are respectively connected to ball joints 27 and 28. It is connected with the upper and lower parts of the knuckle 21 via the via. The damper 24 with suspension spring has an upper end coupled to the vehicle body 1 and a lower end coupled to the upper portion of the knuckle 21 via a rubber bush joint 31.

  Thus, the left rear suspension is configured, and the left rear wheel 5L can follow the road surface change independently of the other wheels, as in the known four-wheel independent suspension. The same applies to the right rear wheel 5R.

  One end of the electric actuator 11 is connected to the vehicle body 1 via a rubber bush joint 29, and the other end is connected to the rear part of the knuckle 21 via a rubber bush joint 30. By adopting such a configuration, when the output rod of the electric actuator 11 is driven to extend, the rear portion of the knuckle 21 rotates outward in the vehicle width direction, so that the turning angle of the rear wheel 5 is in the vehicle traveling direction. On the other hand, it changes inward (toe-in side). Conversely, when the output rod of the electric actuator 11 is driven to contract, the rear part of the knuckle 21 rotates inward in the vehicle width direction, so that the turning angle of the rear wheel 5 is outward (toe-out) with respect to the vehicle traveling direction. Side).

  Thus, the suspension according to the present invention can change the turning angle (toe angle) by driving the electric actuator 11. The electric actuator 11 is assembled in the same geometry as a known independent suspension that passively controls the toe angle with the neutral position.

  As shown in FIG. 1, the vehicle V is provided with an ECU (Electronic Control Unit) 12 as a rear wheel steering control means as well as overall control of various systems, and a vehicle speed sensor 13 that detects the vehicle speed. The steering angle sensor 14 for detecting the steering direction and the steering angle by the steering wheel 8 that steers the front wheels 3L and 3R, the yaw rate sensor 15, the lateral acceleration sensor 16, and various other sensors (not shown) are arranged at appropriate positions. Has been. Detection signals from the sensors are input to the ECU 12 and used for vehicle control. The ECU 12 includes a microcomputer, a ROM, a RAM, a peripheral circuit, an input / output interface, various drivers, and the like. The sensors 13 to 16 and the like, the electric actuators 11L and 11R, and the actuator displacement sensor 17L, via a communication line. 17R is connected.

  As shown in FIG. 4, the ECU 12 includes a rear wheel control unit 41 that controls the electric actuators 11 </ b> L and 11 </ b> R, and left and right rear wheels according to detection results of the vehicle speed by the vehicle speed sensor 13 and the steering angle by the steering angle sensor 14. A rear wheel turning angle determining unit 42 is provided as a rear wheel turning angle determining means for determining the 5L and 5R turning angles. The rear wheel turning angle determination unit 42 has a map 42a for obtaining the rear wheel steering angle based on the two-wheel model according to the vehicle speed and the steering angle. Then, the rear wheel control unit 41 calculates the turning angles of the left and right rear wheels 5L and 5R based on the rear wheel steering angles obtained using the map 42a, and determines the displacement amounts of the electric actuators 11L and 11R. Then, each turning angle control of the left and right rear wheels 5L, 5R is performed.

  The electric actuators 11L and 11R are provided with actuator displacement sensors 17L and 17R (steering angle sensors) for detecting the positions of output rods connected to the rear suspensions 7L and 7R, respectively. The signals of the actuator displacement sensors 17L and 17R are input to the ECU 12 (rear wheel control unit 41), and the ECU 12 performs feedback control of the electric actuators 11L and 11R. Thus, the electric actuators 11L and 11R extend and contract the output rod by a predetermined amount determined by the ECU 12, and if one of the left and right electric actuators 11L and 11R is extended and the other is contracted, both rear wheels 5L and 5R Can be steered right and left, and the steered angles of the rear wheels 5L and 5R can be accurately changed. Note that the toe-in / to-out of the rear wheels 5L and 5R can be freely controlled under appropriate conditions by simultaneously symmetrically displacing the left and right electric actuators 11L and 11R.

  Next, the control point of the rear wheel turning angle based on the present invention will be described with reference to the schematic flowchart shown in FIG. Note that the control subject is the ECU 12, and unless otherwise specified, the ECU 12 performs processing. First, at step ST1, the steering angle detected by the steering angle sensor 14 by the steering wheel 8 is input, and at the next step ST2, the vehicle speed detected by the vehicle speed sensor 13 is input.

  In the next step ST3, the rear wheel steering angle θr corresponding to the vehicle speed and the steering wheel steering angle read in the processing in steps ST1 and ST2 is obtained from the map 42a. In the map 42a, the rear wheel steering angle θr according to the vehicle speed and the steering angle of the steering wheel designed as a two-wheel model in advance according to the characteristics of the vehicle to be controlled is written. The steering wheel steering angle may be used as it is to create the map 42a. However, a processing unit for converting the steering wheel angle into the average steering angle of both the front wheels 3L and 3R is provided, and the average steering angle is used. The map 42a may be created. In any case, the steering wheel steering angle and the average front wheel steering angle are the same.

  With respect to the relationship between the steering wheel angle and the vehicle speed and the rear wheel steering angle θr in the map 42a, for example, the rear wheel is steered in the reverse direction at a low vehicle speed at which a small turning performance is desired, and the rear wheel steering angle is proportional to the steering wheel steering angle. At higher vehicle speeds, which increase θr and reach the maximum rear wheel steering angle at the maximum steering angle and improve stability by lane changes, etc., the rear wheels are steered in the same direction, and the rear is proportional to the steering angle. The wheel steering angle θr is increased, but its maximum value is made smaller than the maximum rear wheel steering angle at low vehicle speeds.

  When the rear wheel steering angle θr is obtained from the map 42a in step ST3, in the next step ST4, a turning radius R based on the front wheel steering angle θf and the rear wheel steering angle θr is calculated. As shown in FIG. 6, which is a two-wheel model, the turning radius R is defined as a turning center Ct, which is an intersection of the extension lines of the axles of the front wheel 3 and the rear wheel 5, and the center Cv of the vehicle body. Good as a distance.

  In the next step ST5, the turning angles θrl, θrr of the left and right rear wheels 5L, 5R are calculated from the turning radius R obtained in step ST4. The left rear wheel 5L rotates so that the left and right rear wheels 5L and 5R turn around the turning center Ct and on the respective circumferences from the turning center cT to the ground contact center portions of the rear wheels 5L and 5R. The steering angle θrl and the turning angle θrr of the right rear wheel 5R are respectively calculated.

  In step ST6, the electric actuators 11L and 11R are driven and controlled so as to have the turning angles θrl and θrr calculated in step ST5, so that the left and right rear wheels 5L and 5R have the turning angles θrl and θrr. (FIG. 7). As shown in the figure, the turning angle θrl of the left rear wheel 5L serving as the inner wheel is larger than the turning angle θrr of the right rear wheel 5R serving as the outer wheel.

  As a result, the left and right rear wheels 5L and 5R roll on the circumferences with large and small radii having different lengths from the turning center Ct to the rear wheels 5L and 5R, respectively, with the turning center Ct as the center. . In the left and right rear wheels 5L and 5R, the inner ring side is steered so as to face the tangential direction of the circle with a small radius (Rs in FIG. 7), and the outer ring side faces in the tangential direction of the circle with a large radius (Rb in FIG. 7). By turning in this way, a difference in running resistance does not occur between the left and right tires 4L, 4R. Therefore, there is no difference in wear between the left and right tires 4L, 4R, and deterioration of fuel consumption is suppressed.

  In the above description, the turning radius R is the distance from the turning center Ct to the center Cv of the vehicle body 1 in the two-wheel model, but the distance to the midpoint between the left and right front wheels 3L and 3R and the distance between the left and right rear wheels 5L and 5R. It may be calculated as the distance to the middle point.

  Moreover, although the case where the rear wheels 5L and 5R are steered in the reverse direction in order to realize the small turning performance has been described, the same applies to the case where the rear wheels 5L and 5R are steered in the same direction at a high vehicle speed. When turning in the same direction, the turning center is located farther from the rear wheels 5L and 5R than when turning in the opposite direction, so the turning radius is increased and the turning between the left and right rear wheels 5L and 5R is increased. Although the difference in the steering angle is small, the same effect as described above can be achieved by providing a difference in the left and right steering angles in consideration of the turning radius.

5L, 5R Rear wheels 11L, 11R Rear wheel steering actuator 13 Vehicle speed sensor 14 Steering angle sensor 41 Rear wheel steering control unit (rear wheel steering control means)
42 Rear wheel steering angle determination unit (rear wheel steering angle determination means)
42a map

Claims (2)

A steering angle sensor for detecting the front wheel steering angle;
A vehicle speed sensor for detecting the vehicle speed;
Each rear wheel steering actuator that independently steers the left and right rear wheels,
Rear wheel steering angle determining means for determining a rear wheel steering angle set in advance according to the front wheel steering angle and the vehicle speed;
The left and right rear wheel turning centers are determined by the front wheel steering angle and the rear wheel steering angle, and the left and right rear wheel actuators are arranged so that the turning centers of the left and right rear wheels coincide with the turning center. A four-wheel steering device comprising rear-wheel steering control means for controlling the steering of the rear wheels.   The four-wheel steering apparatus according to claim 1, wherein the rear-wheel steering angle determining means includes a map for obtaining a rear-wheel steering angle from a front-wheel steering angle based on a two-wheel model in which a four-wheel vehicle is replaced with a two-wheel vehicle.

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