JP2014084081A - Steering angle control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steering angle control device capable of suppressing possibility that a vehicle spins when a steering angle of rear wheels is controlled to turn the vehicle.SOLUTION: A steering angle control device 10 includes: steering means for steering front wheels 22; a steering angle sensor 14 for detecting a steering angle of the front wheels 22; a steering actuator 32 for steering rear wheels 24; and an ECU 20 for, on the basis of vehicle speed and the steering angle of the front wheels 22, deriving a target steering angle of the rear wheels 24, and controlling the steering actuator 32 so as to obtain the target steering angle. When the vehicle speed is equal to or above predetermined vehicle speed, the ECU 20 derives a target steering angle of the rear wheels 24, by which cornering force of the front wheels 22 becomes the ground load of the front wheels 22 when lateral acceleration of a vehicle reaches a predetermined value, and controls the steering actuator 32 so as to obtain the target steering angle.

Description

  The present invention relates to a rudder angle control device, and more particularly to control of a rudder angle of a wheel in a rudder angle control device.

  In recent years, a technique for stabilizing the behavior of a running vehicle has been known. For example, Patent Document 1 includes a front wheel and a rear wheel, and a pair of intermediate wheels disposed between the front wheel and the rear wheel. A technique for stabilizing a vehicle by adjusting a grounding force distribution of each wheel by adjusting a braking force applied to each wheel in the vehicle having the vehicle is disclosed.

  In addition, in a vehicle having a pair of front wheels and a pair of rear wheels, a four-wheel steering technique is known in which the rudder angle of the front and rear wheels of the vehicle is controlled to improve the turning ability.

International Publication No. 2011-045854

  By the way, in the steering technology for controlling the steering angle of the wheels arranged in the front and rear, there is a technology for improving the turning ability of the vehicle by turning the rear wheels to the opposite side to the steering angle of the front wheels. If the vehicle speed is high when the rear wheels are steered to the opposite side to the rudder angle of the front wheels, a large lateral acceleration is applied to the turning vehicle, and the traveling state of the vehicle may become unstable.

  The present invention has been made in view of such circumstances, and an object of the present invention is to control the possibility that the traveling state of the vehicle becomes unstable when the steering angle of the rear wheel is controlled when the vehicle turns. It is to provide a control device.

  In order to solve the above-described problems, a steering angle control device according to an aspect of the present invention includes a steering unit that steers front wheels, a steering angle detection unit that detects a steering angle of the front wheels, and a steering actuator that steers the rear wheels. And a control means for deriving a target rudder angle of the rear wheel based on the vehicle speed and the rudder angle of the front wheel and controlling the steered actuator so as to be the target rudder angle. The control means derives the target rudder angle of the rear wheel at which the cornering force of the front wheel becomes the ground load of the front wheel when the lateral acceleration of the vehicle reaches a predetermined value when the vehicle speed is equal to or higher than a predetermined vehicle speed, and the target rudder The steered actuator is controlled to be a corner.

  According to this aspect, when the lateral acceleration at the time of turning of the vehicle reaches a predetermined value, the grip force of the wheels other than the front wheels is suppressed while the grip force of the front wheels is reduced, and the traveling state of the entire vehicle is in the spin state. Can be suppressed.

  According to the present invention, when the steering angle of the rear wheel is controlled when the vehicle is turning, the possibility that the traveling state of the vehicle becomes unstable can be suppressed.

It is a mimetic diagram showing a schematic structure of a rudder angle control device of an embodiment. It is a figure for demonstrating steering control of the rear wheel of a prior art. It is a figure for demonstrating steering control of the rear-wheel of embodiment. It is a figure for demonstrating other steering control of the rear wheel of a prior art.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate.

  Drawing 1 is a mimetic diagram showing a schematic structure of a rudder angle control device of an embodiment. The steering angle control device 10 includes a steering wheel 12, a steering angle sensor 14, a steering shaft 16, a front wheel gear 18, an ECU 20, a front wheel 22, a rear wheel 24, an intermediate wheel 26, a drive motor 28, a vehicle speed sensor 30, a steering actuator 32, and a rudder. An angle sensor 34 is provided.

  The handle 12 functions as a steering member that is rotated by the driver to input a steering amount. The handle 12 is connected to the front wheel 22 via the steering shaft 16. The steering angle sensor 14 detects the rotation angle of the handle 12 as the steering amount input by the driver, and outputs the detected value to the ECU 20.

  The steering angle sensor 14 functions as a detection unit that detects information according to the operation amount of the handle 12. Since the steering angle of the front wheels varies according to the steering angle (operation amount) of the handle 12, the steering angle sensor 14 also functions as a steering angle detection unit that detects the steering angle of the front wheels 22. The front wheel gear 18 converts the rotation operation of the steering shaft 16 into an operation for changing the turning angle of the front wheel 22. A sensor that directly detects the turning angle of the front wheel 22 may be provided as the steering angle detection means.

  A pair of intermediate wheels 26 are provided between the front wheels 22 and the rear wheels 24. The intermediate wheel 26 is provided with a drive motor 28 that rotates the intermediate wheel 26 and a vehicle speed sensor 30 that detects the amount of rotation of the intermediate wheel 26. The vehicle speed may be calculated by the average of the left and right vehicle speed sensors 30. The drive of the drive motor 28 is controlled by the ECU 20 according to the operation of an accelerator pedal (not shown), that is, the operation amount of the driver. Each drive motor 28 may be individually controllable. Note that the intermediate wheel 26 is set so as not to be steered but to travel in the straight direction of the vehicle.

  A steering actuator 32 and a steering angle sensor 34 are provided on the rear wheel 24. The steered actuator 32 operates under the control of the ECU 20 to steer the rear wheel 24. The steering angle sensor 34 detects the steering angle of the rear wheel 24 and sends it to the ECU 20.

  The ECU 20 controls the drive motor 28 and the steering actuator 32 based on information from various sensors. The ECU 20 is composed of, for example, a CPU, a ROM, a RAM, and a data bus that interconnects them, and is based on the detection result of the steering angle sensor 14 of the front wheels 22 and the detection result of the vehicle speed sensor 30 according to a program stored in the ROM. It functions as a control means for performing control for turning the rear wheel 24. Here, a technique for controlling the steering angle of the rear wheel based on the steering angle of the front wheel will be described with reference to FIG.

  FIG. 2 is a diagram for explaining steering control of the rear wheels of the prior art, and shows a state in which the rear wheels 24 are steered to the opposite side to the front wheels 22 when the steering angle of the front wheels 22 is large. As shown in FIG. 2, the steering to the opposite phase side means that when the front wheels 22 are steered leftward with respect to the straight traveling direction S of the vehicle, the rear wheels 24 are moved rightward, that is, the front wheels 22. And turning to the same phase side means that when the front wheels 22 are steered leftward, the rear wheels 24 are steered leftward, that is, on the same side as the front wheels 22. Say.

  In FIG. 2, the front wheel 22 is steered leftward, and the rear wheel 24 is steered to the opposite phase side of the front wheel 22. Although the turning of the rear wheel 24 can make a small turn, the yaw rate and the lateral acceleration with respect to the steering angle of the front wheel 22 increase during high-speed driving, making it difficult for the driver to steer, and when the lateral acceleration reaches the limit range, There is a risk of spinning.

  Therefore, the ECU 20 according to the embodiment sets the rear wheel 24 target so that the cornering force of the front wheel 22 becomes a predetermined ratio to the ground load of the front wheel 22 when the lateral acceleration acting on the vehicle is a predetermined limit value at a predetermined vehicle speed or higher. A steering angle is set, and the steering actuator 32 is controlled. The wheel cornering force is a force generated in a direction perpendicular to the traveling direction of the wheel, and increases in proportion to the slip angle of the wheel. The upper limit of the cornering force is obtained by multiplying the friction coefficient μ between the wheel and the road surface by the ground contact load of the wheel. When μ = 1, the cornering force and the ground load are equal. If the slip angle of the wheel is increased and the cornering force reaches the upper limit and then the slip angle of the wheel is increased beyond that angle, the cornering force is lowered and the so-called gripping force is reduced. That is, when the lateral acceleration acting on the vehicle reaches a predetermined limit value, the cornering force of the front wheel 22 becomes a predetermined ratio (upper limit determined by μ) by the steering angle control of the rear wheel 24, and the grip force is reduced. Car body slip angle is controlled so as to slide. If the front wheel 22 is slid before the other wheels in this way, the vehicle is in a drift-out state, and the behavior is more stable than in a spin state in which the other wheels slide first. Further, in the embodiment, a mode in which a predetermined ratio is fixed as the upper limit of the cornering force = the ground load according to μ = 1 will be described. However, since the upper limit of the cornering force changes according to the friction coefficient μ, the detected friction coefficient You may control according to (micro | micron | mu).

  Drawing 3 is a figure for explaining steering control of rear wheel 24 of an embodiment. FIGS. 3A to 3C are calculated so that the cornering force of the front wheel 22 is equal to the ground load of the front wheel 22 when the lateral acceleration of the vehicle is a predetermined limit value. ) Shows the relationship between the steering angle δf of the front wheel 22 and the vehicle speed, FIG. 3B shows the relationship between the steering angle δr of the rear wheel 24 and the vehicle speed, and FIG. 3C shows the relationship between the front wheel 22 and the rear wheel. The steering angle ratio k of the wheel 24 is shown. When the rudder angle is zero, it indicates that the vehicle is traveling straight, the left rudder angle is negative, and the right rudder angle is positive. In FIG. 3A, the steering angle to the right is shown, and the steering angle to the left is omitted. In this aspect, the steering angle of the steering wheel 12 is used as the steering angle δf of the front wheel 22, and the steering angle has an upper limit of ± π / 2 radians.

γ：ヨーレート、Ｖ：車速、Ｋｆ・Ｋｃ・Ｋｒ：コーナリングスティッフネス（またはコーナリングパワー）、ｌｆ・ｌｃ・ｌｒ：重心から車輪までの距離、ｍ：車両質量、β：車体のスリップ角、βｆ：前輪のスリップ角、Ｃｐ：単位荷重当りのコーナリングステッィフネス、ｅｆ：操舵系剛性によるコーナリングステッィフネスの低下率。 In the following formula (1), the limit value of the lateral acceleration Ay is set. The limit value of the lateral acceleration Ay is a value at which the possibility that the vehicle will spin or roll over increases if the lateral acceleration Ay becomes larger than the limit value, or the vehicle spins or rolls if the lateral acceleration Ay becomes smaller than the limit value. This value is determined in consideration of the position of the center of gravity, vehicle specifications such as tread, suspension characteristics, and the like.

γ: yaw rate, V: vehicle speed, Kf · Kc · Kr: cornering stiffness (or cornering power), lf · lc · lr: distance from the center of gravity to the wheel, m: vehicle mass, β: slip angle of the vehicle body, βf: Slip angle of front wheel, Cp: Cornering stiffness per unit load, ef: Decrease rate of cornering stiffness due to steering system rigidity.

In the following equation (2), the cornering force of the front wheel 22 and the ground load of the front wheel 22 are set to a predetermined ratio.

  Equations (1) and (2) are solved as simultaneous equations, and the steering angle ratio k at which the steering angles δf and δr = kδf of the front wheels 22 are calculated. The steering angle ratio k is stored in the ECU 20 in advance. The ECU 20 may store the steering angle ratio k as a mathematical expression or may store it in a table format.

  If the detection result of the vehicle speed sensor 30 is equal to or higher than the predetermined vehicle speed V1, the ECU 20 multiplies the steering angle δf of the front wheel 22 acquired from the steering angle sensor 14 by the steering angle ratio k shown in FIG. The target steering angle δr of 24 is derived, and the drive of the steering actuator 32 is controlled so that the derived target steering angle δr of the rear wheel 24 is obtained. The predetermined vehicle speed V1 is a speed below which δf at which the cornering force of the front wheels is equal to the ground load does not exist.

  3A to 3C show a steering angle and a steering angle ratio that are equal to or higher than a predetermined vehicle speed V1. FIG. 3A shows the relationship between the steering angle δf of the front wheel 22 and the vehicle speed at which the front wheel 22 starts to slip at the limit value. As the vehicle speed increases, the steering angle δf that starts to slide decreases. When the vehicle speed V2 is exceeded, the steering angle δf is substantially constant.

  FIG. 3B shows the steering angle δr of the rear wheel 24 when the front wheel 22 starts to slide. When the vehicle speed is low, the control is performed at the steering angle δr on the opposite phase side, the steering angle is almost the maximum on the opposite phase side at the vehicle speed V1, and the phase is switched from the opposite phase side to the in-phase side at the vehicle speed V2. In this example, the vehicle speed V2 is about 37 km / h.

  Since the steering angle ratio k shown in FIG. 3C has a relationship of δr = kδf, it switches from a negative value to a positive value at the vehicle speed V2 in the same manner as the steering angle δr of the rear wheel 24 shown in FIG. As shown in FIG. 3C, k = −1 at the vehicle speed V1, and the rear wheel 24 is always steered in the opposite phase at a low speed equal to or less than the vehicle speed V2, so that even if the steering angle δf of the front wheel 22 increases. The slip angle of the front wheels does not become too large, and the vehicle can turn without drifting out until a predetermined lateral acceleration is applied to the vehicle body. Further, at a vehicle speed of V2 or higher, the rear wheel 24 is controlled in phase with the front wheel 22 and understeering, while the slip angle of the front wheel 22 is increased so that the cornering force reaches the upper limit when a predetermined lateral acceleration is applied to the vehicle body. ing. As a result, the grip force of the front wheels 22 is reduced, and the vehicle can be controlled to drift out without spinning.

  FIG. 4 is a diagram for explaining another steering control of the rear wheel of the prior art, and shows a state in which the rear wheel 24 is steered to the same phase as the front wheel 22 when the steering angle of the front wheel 22 is small. .

  As shown in FIG. 4, when the steering angle of the front wheel 22 is small, the rear wheel 24 is steered smaller than the steering angle of the front wheel 22 on the same phase side as the front wheel 22. In this case, each wheel receives a cornering force (frictional force) in the direction of the arrow. Since the steering angle of the front wheel 22 is larger than the steering angle of the rear wheel 24, the cornering force Cf of the front wheel 22 is larger than the cornering force Cr of the rear wheel 24. Since the vehicle body slip angle β is provided, the cornering force Cc of the intermediate wheel 26 is in the direction opposite to the front wheel 22 and the rear wheel 24.

  At this time, the slip angle of the front wheel 22 becomes large, and the maximum value of the cornering force comes out first in each wheel. When such steering control of the rear wheel 24 is executed at a predetermined vehicle speed or less, the front wheel 22 may slip and cannot turn.

  Therefore, at a vehicle speed V1 or less (not shown in FIG. 3), control is performed so that δr = −δf. That is, when the vehicle speed is as low as several kilometers, the ECU 20 executes control for turning the rear wheel 24 with a simple reverse phase with respect to the front wheel 22. Further, when the vehicle speed is V1 or more and V2 or less, the control for turning in the opposite phase is executed based on the turning ratio k. As a result, the slip angle of the front wheel 22 does not become too large compared to the prior art of FIG. 4, and the front wheel 22 does not lose the grip until the predetermined lateral acceleration is generated at a low speed equal to or lower than the predetermined vehicle speed, and the vehicle can make a small turn. At a vehicle speed of V2 or higher, control is performed to steer the rear wheels 24 in phase based on the steering ratio k. As a result, the slip angle of the front wheel 22 is increased while the vehicle is understeered, and the cornering force of the front wheel 22 reaches the upper limit when a predetermined lateral acceleration that causes unstable behavior is applied to the vehicle body, resulting in a decrease in gripping force. The vehicle drifts out without spinning. As an execution condition for turning the rear wheel 24, it may be determined whether the front wheel 22 is steered by a predetermined angle or more. As a result, the response gain of the vehicle in the vicinity of the neutral position of steering can be lowered, which may facilitate driving.

  As described above, the present invention has been described with reference to the above-described embodiment. However, the present invention is not limited to the above-described embodiment, and the present invention can be appropriately combined or replaced with the configuration of the embodiment. It is included in the present invention. In addition, it is possible to appropriately change the combination and processing order in the embodiment based on the knowledge of those skilled in the art and to add various modifications such as various design changes to the embodiment. The described embodiments can also be included in the scope of the present invention.

  Although the embodiment has been described using a vehicle in which wheels are arranged at the apexes of the rhombus, the present invention is not limited to the vehicle. For example, the vehicle may be a normal vehicle having two front wheels and two rear wheels each having a steering mechanism on the front wheels and a steering actuator on the rear wheels.

  The steering angle ratio k may be corrected and used in accordance with the road surface condition during vehicle travel. For example, when the road surface is frozen or the road surface is wet, the friction coefficient μ decreases, and the upper limit value of the cornering force is lowered. What is necessary is just to change to the steering angle ratio k which correct | amended the value of Numerical formula 2 and solved the equation.

  DESCRIPTION OF SYMBOLS 10 Steering angle control apparatus, 12 Steering wheel, 14 Steering angle sensor, 16 Steering shaft, 18 Front wheel gear, 20 ECU, 22 Front wheel, 24 Rear wheel, 26 Intermediate wheel, 28 Drive motor, 30 Vehicle speed sensor, 32 Steering actuator, 34 Rudder angle sensor.

Claims (1)

Steering means for steering the front wheels;
Rudder angle detection means for detecting the rudder angle of the front wheels;
A steering actuator that steers the rear wheels;
A control means for deriving a target rudder angle of a rear wheel based on a vehicle speed and a rudder angle of a front wheel, and controlling the steering actuator so as to be the target rudder angle;
The control means derives the target rudder angle of the rear wheel at which the cornering force of the front wheel and the ground contact load of the front wheel become a predetermined ratio when the lateral acceleration of the vehicle reaches a predetermined value when the vehicle speed is equal to or higher than a predetermined vehicle speed. And a steering angle control device for controlling the steering actuator so as to achieve the target steering angle.

Images