Brake control method for four-wheel independent steering vehicle

Abstract

To provide a brake control method for a four-wheel independent steering vehicle capable of reducing a shock when stopping the vehicle so as to safely secure braking force.SOLUTION: There is disclosed a brake control method for a four-wheel independent steering vehicle. The method comprises the steps of: when the vehicle is decelerating in response to a braking operation by the driver of the vehicle, determining, by an ECU 10, whether or not a vehicle speed measured by a vehicle speed sensor 20 has become equal to or less than a predetermined value, for example; and when determining that the vehicle speed has become equal to or less than the predetermined value, reducing, by a brake system 30, braking force of each of four wheels of the vehicle; and causing, by the ECU 10, front wheels of four wheels to toe in or toe out by a predetermined angle with respect to respective tire angles of the respective four wheels during deceleration, of the vehicle, and rear wheels to toe out or toe in by a predetermined angle. These steps can reduce shock at a time of stopping the vehicle, as well as, safely secure the braking force by controlling the tire angles of the respective wheels.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a brake control method for a vehicle with four-wheel independent steering.

Background Art

[0002] There is known a vehicle control device that suppresses a brake shock during stopping regardless of the driver's skill (see, for example, Patent Document 1). The control device described in Patent Document 1 employs a method of mechanically increasing or decreasing the toe angle of a wheel to control the braking force.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the control device described in Patent Document 1, during braking of the vehicle, the actual frictional braking force (hydraulic brake) of the braking device is not reduced. With such a control method, the shock reduction effect is almost non-existent or limited even if there is any. Also, when the toe angle is controlled for the purpose of increasing the deceleration while the vehicle is moving at a certain speed, excessive force may be applied around the suspension.

[0005] The present disclosure has been made to solve such problems, and an object thereof is to provide a brake control method for a vehicle with four-wheel independent steering that can reduce the shock during vehicle stopping and can securely ensure the braking force by controlling the tire angle of each wheel.

Means for Solving the Problems

[0006] The brake control method for a vehicle with four-wheel independent steering according to the present disclosure is A braking control method for a vehicle with four-wheel independent steering, when the vehicle is decelerating in response to a braking operation by the driver of the vehicle, determining whether the vehicle speed of the vehicle has become equal to or lower than a predetermined value, when it is determined that the vehicle speed has become equal to or lower than the predetermined value, reducing the braking force of each of the four wheels of the vehicle, for each of the tire angles of the four wheels during deceleration of the vehicle, among the four wheels, turning the front wheels in toe-in or toe-out by a predetermined angle and turning the rear wheels in toe-out or toe-in by the predetermined angle.

Advantages of the Invention

[0007] According to the present disclosure, it is possible to provide a braking control method for a vehicle with four-wheel independent steering that can reduce the shock at the time of vehicle stop and can securely ensure braking force by controlling the tire angles of each wheel.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, the invention according to the claims is not limited to the following embodiments. Also, not all of the configurations described in the embodiments are necessarily essential as means for solving the problems. For the sake of clarity of explanation, the following description and drawings have been appropriately omitted and simplified. In each drawing, the same elements are denoted by the same reference numerals, and duplicate explanations are omitted as necessary.

[0010] (Problems related to vehicle braking control) First, regarding the braking control of a vehicle, the problems found by the present inventor will be described. This problem is included in the technical idea of this embodiment.

[0011] Shock reduction control when the vehicle stops (hereinafter referred to as "SS control (Smooth Stop control)") is control that measures the vehicle speed and reduces the shock by reducing the braking force until just before stopping according to the vehicle speed.

[0012] In order to reduce the shock when the vehicle stops, it is important how much the braking force can be reduced when the vehicle speed is near 0. As with the control device described in Patent Document 1, by toeing in both the front wheels and the rear wheels, the vehicle can be decelerated, but the deceleration of the vehicle cannot be controlled overall unless it cooperates with the control of the frictional braking force. Thus, with the control of the control device described in Patent Document 1, it is difficult to obtain a shock reduction effect because the deceleration cannot be made infinitely small just before stopping.

[0013] Therefore, the present inventor came up with a braking control method that cooperates the SS control of the frictional braking force and the toe-in / toe-out control of the tire angle to more reliably reduce the shock when the vehicle stops.

[0014] (Embodiment) Next, a schematic configuration of a control device that executes a braking control method for a four-wheel independently steered vehicle according to the present embodiment (hereinafter, may be abbreviated as "braking control method") will be described.

[0015] <Configuration of Control Device for Four-Wheel Independently Steered Vehicle> Before the braking control method, the configuration of a control device related to the brakes of the vehicle will be described. FIG. 1 is a block diagram showing an example of a schematic configuration of a control device 1 that executes a braking control method for a four-wheel independently steered vehicle according to the present embodiment. Note that in FIG. 1, only the components related to the braking control method of the present embodiment are shown, not the components related to the control of the entire vehicle.

[0016] As shown in FIG. 1, the control device 1 of the present embodiment includes an ECU (Electronic Control Unit) 10, a vehicle speed sensor 20, and a brake system 30. The brake system 30 includes a brake actuator 31, a stroke sensor 32, and a hydraulic pressure sensor 33.

[0017] The ECU 10 controls the entire vehicle. In this example, as will be described later, the ECU 10 controls the brake actuator 31. The vehicle speed sensor 20 detects the vehicle speed of the vehicle and outputs the detected vehicle speed to the ECU 10. Note that instead of the vehicle speed sensor 20, the ECU 10 may be configured to aggregate the wheel speeds of each wheel and calculate a representative value as the vehicle speed.

[0018] The brake system 30 is a system that performs braking control of the vehicle. The brake system 30 controls the brake actuator 31 based on the detection values detected by various sensors under the control of the ECU 10.

[0019] The brake actuator 31 increases or decreases the braking force independently of the movement of the brake pedal (not shown) of the driver of the vehicle according to the instruction of the ECU 10 via the brake system 30. The stroke sensor 32 detects the stroke amount of the brake pedal due to the depression by the driver of the vehicle and outputs the detected stroke amount to the ECU 10. The hydraulic pressure sensor 33 detects the pressure of the hydraulic pressure of the hydraulic brake and outputs the detected pressure to the ECU 10.

[0020] As described above, the brake system 30 of the present embodiment is premised on a by-wire brake, but a brake system using an electric brake may be adopted as long as such characteristics can be realized.

[0021] The ECU 10 can independently control the four wheels of the vehicle according to the movement of the steering (not shown) operated by the driver, the vehicle state, the vehicle speed, the control method determined by the driver, and the like. In particular, the ECU 10 controls the respective tire angles of the four wheels during brake control in the brake control method described later.

[0022] <Brake Control Method> Next, the operation of the control device 1 of the four-wheel independent steering vehicle according to the present embodiment will be described. In the braking control method of the present embodiment, in cooperation with the braking force reduction control during the execution of the SS control, the tire angle of each wheel is added with an angular difference to the left and right based on the angle before the start of control, thereby performing control of the steering in a direction in which the vehicle does not move as a whole. For example, when the vehicle is going straight, the ECU 10 controls the braking system 30 so that the front wheels are on the toe-in side and the rear wheels are on the toe-out side. Thereby, the same effect as stepping on (applying the brakes) the brake pedal by the driver can be obtained. At this time, the braking force of each wheel during the SS control is kept reduced. The angle of the tire can ensure a braking force corresponding to the stroke amount of the brake pedal by giving a differential angle corresponding to the braking amount (stepping force, pedal stroke amount). Hereinafter, the braking control method of the four-wheel independent steering vehicle will be described in detail based on the timing chart shown in FIG. 2.

[0023] FIG. 2 is a timing chart of physical quantities in the braking control method of the four-wheel independent steering vehicle according to the present embodiment. As shown in FIG. 2, in the braking control method of this example, braking control is performed according to the vehicle speed V of the vehicle, the braking force of the braking system 30, and the timing of the tire angle.

[0024] First, when the vehicle is cruising at a constant speed, at a predetermined timing, the driver of the vehicle steps on the brake pedal. Then, as shown in the middle of FIG. 2, the braking force increases according to the amount of depression of the brake pedal. At this time, the stroke sensor 32 detects the stroke amount of the brake pedal and outputs the detected stroke amount of the brake pedal to the ECU 10. Also, the vehicle speed sensor 20 detects the vehicle speed V of the vehicle and outputs the detected vehicle speed V to the ECU 10. Thereafter, as shown in the upper part of FIG. 2, the vehicle speed V gradually decreases according to the detected stroke amount of the brake pedal.

[0025] Next, the ECU 10 determines whether the vehicle speed V received from the vehicle speed sensor 20 is equal to or lower than a predetermined value V1. When it is determined at time point T1 that the vehicle speed V is equal to or lower than the predetermined value V1, the ECU 10 starts SS control according to the detection values of various sensors, and the brake actuator 31 of the brake system 30 gradually reduces the braking force of each of the four wheels of the vehicle. The braking force reduction process by the brake actuator 31 may be controlled, for example, to reduce the braking force at a constant rate.

[0026] Next, the ECU 10 determines whether the vehicle speed V received from the vehicle speed sensor 20 is equal to or lower than a predetermined value V2. When it is determined at time point T2 that the vehicle speed V is equal to or lower than the predetermined value V2, it can be determined that the influence on vehicle body vibration and the like due to steering change is negligible, and the ECU 10 controls the front wheels among the four wheels to toe-in or toe-out by a predetermined angle θ with respect to the tire angles of each of the four wheels during deceleration of the vehicle, and conversely, controls the rear wheels to toe-out or toe-in by a predetermined angle θ. In the example shown in FIG. 2, as shown in the lower part of FIG. 2, the toe-in / toe-out control is performed such that the left front wheel and the right rear wheel change the tire angle by +θ, and the left rear wheel and the right front wheel change the tire angle by -θ. As will be described later, the tire angle becomes a positive number in the left-to-right direction of the vehicle (see FIG. 3).

[0027] After time point T1, in a state where the brake pedal is depressed, if the stroke amount and the depression force of the brake pedal do not change, in normal control, the braking force does not change as shown by A in the middle part of FIG. 2. On the other hand, in SS control, at time point T1, since the vehicle speed V falls below the predetermined value V1, as shown by the solid line in the middle part of FIG. 2, the brake system 30 reduces the braking force.

[0028] Also, in the conventional SS control, as shown by B in the middle part of FIG. 2, the braking force is restored when the vehicle completely stops or is almost stopped, but in the brake control method of this example, since the toe-in / toe-out control is performed on the four wheels, it is not necessary to restore the braking force.

[0029] Next, based on the detected value of the stroke sensor 32, the ECU 10 determines whether the brake pedal has been turned off, that is, whether the driver has stopped depressing the brake pedal. At time T3, it indicates that the brake pedal has been turned off, and as shown at C in the middle row of FIG. 2, the virtual braking force returns to 0. Then, the ECU 10 controls so as to return the tire angle of each of the four wheels to the original angle of 0°. As a result, at time T4, the tire angle of each of the four wheels returns to its original state.

[0030] The states of the four wheels FR, FL, RR, and RL of the vehicle 100 at this time are shown in FIG. 3. FIG. 3 is a conceptual diagram showing an example in which the toe angles of the respective wheels FR, FL, RR, and RL are controlled by the braking control method of the four-wheel independent steering vehicle 100 shown in FIG. 2. As can also be seen from the position of the steering S of the vehicle 100, the vehicle 100 is traveling (decelerating) in the direction from bottom to top on the plane of FIG. 3.

[0031] First, until time T2, as shown in the lower row of FIG. 2 and FIG. 3(a), the tire angles of the respective wheels FR, FL, RR, and RL of the vehicle 100 are 0°. At time T2, as shown in the lower row of FIG. 2 and FIG. 3(b), the ECU 10 performs toe-in control on the front wheels FR and FL and toe-out control on the rear wheels RR and RL among the respective wheels FR, FL, RR, and RL. Then, from time T2 to time T4, the four wheels FR, FL, RR, and RL of the vehicle 100 maintain this state. After that, after time T4, as shown in the lower row of FIG. 2, the ECU 10 returns the tire angle of each of the four wheels FR, FL, RR, and RL to the original tire angle and ends this control.

[0032] Note that, different from the present example shown in FIG. 3, the ECU 10 may perform toe-out control on the front wheels FR and FL and toe-in control on the rear wheels RR and RL. Also, similar to the conventional SS control, after it is confirmed that the vehicle 100 has stopped, for example, at time T3, the ECU 10 may restore the braking force together with the operation of returning the tire angle of each of the four wheels FR, FL, RR, and RL to the original tire angle.

[0033] Also, in the SS control of this example, the timing of implementing the SS control for the front and rear wheels may be shifted to create a time difference. In this case, the ECU 10, depending on whether the engine, fuel cell, etc. are mounted at the front or rear of the vehicle 100, that is, depending on the vehicle weight load, first reduces the braking force of the front wheels (so-called FR vehicle) or rear wheels (so-called FF vehicle) with a lighter vehicle weight load, and may also shift the tire angle by θ first.

[0034] Here, as the predetermined value V1 of the vehicle speed V, for example, a speed of about 2.0 to 2.5 km / h is assumed, and as the predetermined value V2 of the vehicle speed V, for example, a speed of about 1.5 to 2.0 km / h is assumed. Thus, in the braking control method of this example, the predetermined value V1 and the predetermined value V2 may be substantially the same speed. That is, the predetermined value in this example only needs to satisfy the relationship V1≧V2.

[0035] Also, the angle θ of the tire in the toe-in / toe-out control may be, for example, about 5°. In the braking control method of this example, since the predetermined value V2 of the vehicle speed V is sufficiently small as described above, excessive force is not applied around the suspension of the vehicle 100.

[0036] As described above, in the braking control method for the four-wheel independent steering vehicle 100 according to the present embodiment, when the vehicle 100 is decelerating in response to a braking operation by the driver of the vehicle 100, it is determined whether the vehicle speed V of the vehicle 100 has become equal to or less than a predetermined value V1. When it is determined that the vehicle speed V has become equal to or less than the predetermined value V1, the braking force of each of the four wheels FR, FL, RR, and RL of the vehicle 100 is reduced, and for each of the tire angles of the four wheels FR, FL, RR, and RL during deceleration of the vehicle 100, among the four wheels, the front wheels FR and FL are toe-in or toe-out by a predetermined angle θ, and conversely, the rear wheels RR and RL are toe-out or toe-in by a predetermined angle θ. By configuring the braking control method for the four-wheel independent steering vehicle 100 in this way, after sufficiently reducing the vehicle speed V by the braking operation by the driver of the vehicle 100, while reducing the braking force by the SS control, the toe angles of the four wheels are controlled, and finally the vehicle 100 will stop. Thereby, according to the braking control method for the four-wheel independent steering vehicle 100, it is possible to reduce the shock at the time of vehicle stop, and by controlling the tire angles of each wheel FR, FL, RR, and RL, the braking force of the vehicle 100 can be safely ensured.

[0037] Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments, and can be appropriately changed without departing from the gist.

Explanation of Reference Numerals

[0038] 1 Control device 10 ECU (Electronic Control Unit) 20 Vehicle speed sensor 30 Brake system 31 Brake actuator 32 Stroke sensor 33 Hydraulic pressure sensor 100 Vehicle

Claims

【Claim 1】 A braking control method for a vehicle with four-wheel independent steering, comprising: when the vehicle is decelerating in response to a braking operation by the driver of the vehicle, determining whether the vehicle speed of the vehicle has become equal to or less than a predetermined value; when it is determined that the vehicle speed has become equal to or less than the predetermined value, reducing the braking force of each of the four wheels of the vehicle; with respect to the tire angle of each of the four wheels during deceleration of the vehicle, toeing in or toeing out the front wheels by a predetermined angle and toeing out or toeing in the rear wheels by the predetermined angle among the four wheels; A braking control method for a vehicle with four-wheel independent steering.

Images