KR102779114B1 - Sequential steering system for front and rear wheels for stable rotation of a four-wheel steering moving body and method therefor - Google Patents

Abstract

The present invention relates to a sequential steering system of front and rear wheels for stable rotation of a four-wheel steering vehicle, and is characterized by including: a vehicle; front wheels formed on both sides of the front lower portion of the vehicle and moving the vehicle through rotation and steering angle adjustment; rear wheels formed on both sides of the rear lower portion of the vehicle and moving the vehicle through rotation and steering angle adjustment; a driving unit formed on the vehicle and configured to provide driving force to the front wheel or the rear wheel and control the steering of the front wheel; and a control unit formed on the vehicle and configured to change the steering angle of the rear wheel in the opposite direction to the steering angle of the front wheel when the steering angle of the front wheel is steered to a maximum angle to adjust the rotation center point of the vehicle.

Description

Sequential steering system for front and rear wheels for stable rotation of a four-wheel steering moving body and method therefor

The present invention relates to a sequential steering system of front and rear wheels for stable rotation of a four-wheel steering vehicle and a method thereof, and more specifically, to a sequential steering system of front and rear wheels for stable rotation of a four-wheel steering vehicle and a method thereof, which automatically controls a turning radius and speed when a vehicle capable of moving using four wheels is turned to the left or right, thereby enabling stable rotation.

In general, a four-wheel steering vehicle is one that can drive and turn left and right using a pair of front wheels and a pair of rear wheels, and is used in vehicles that users ride in and unmanned robots that move by remote control.

These four-wheel steering vehicles are formed so that the left and right steering of the vehicle can be controlled using a steering wheel or joystick depending on the type. In the case of existing two-wheel steering vehicles, only the front wheels are operated to control the direction when steering left and right, whereas four-wheel steering vehicles are formed so that the front and rear wheels can move at the same rotation angle at the same time.

In this way, a four-wheel steering vehicle can change its turning radius more quickly than a two-wheel steering vehicle with only the front wheels steered, enabling it to turn left or right and move in narrow areas.

However, in the case of these four-wheel steering vehicles, there was a problem in that it was difficult for the driver driving the vehicle or the operator controlling the robot to predict the direction of travel of the vehicle because the turning radius changed rapidly.

In addition, as in the past, when the front and rear wheels are steered at the same angle at the same time, the stability of rotation is reduced due to slipping, etc. during high-speed driving. Therefore, when the vehicle is moving at high speed or is loaded with heavy cargo and is rapidly turned left and right, there was a problem that the turning radius also became rapid, which could lead to a tipping accident.

Korean Patent Publication No. 10-2022-0055947

The purpose of the present invention to solve the above problems is to provide a sequential steering system of front and rear wheels for stable rotation of a four-wheel steering vehicle, and a method therefor, which enables an operator to operate the four-wheel steering vehicle stably and precisely using a steering wheel or joystick.

In addition, another object of the present invention is to provide a sequential steering system and method for the front and rear wheels for stable rotation of a four-wheel steering vehicle, which enables the operator to steer the four-wheel steering vehicle based on the steering feel of a conventional two-wheel steering vehicle, thereby making it easy to predict and control the direction of travel.

In addition, another object of the present invention is to provide a sequential steering system of front and rear wheels and a method therefor for stable rotation of a four-wheel steering vehicle, which can induce a stable rotation by reducing the current speed without a separate operation of an operator when rotating at high speed.

In order to solve the above problem, the present invention provides a sequential steering system of front and rear wheels for stable rotation of a four-wheel steering vehicle, the system including: a vehicle; front wheels formed on both sides of the front lower portion of the vehicle and moving the vehicle through rotation and steering angle adjustment; rear wheels formed on both sides of the rear lower portion of the vehicle and moving the vehicle through rotation and steering angle adjustment; a driving unit formed on the vehicle and configured to provide driving force to the front wheel or the rear wheel and control the steering of the front wheel; and a control unit formed on the vehicle and configured to change the steering angle of the rear wheel in the opposite direction to the steering angle of the front wheel when the steering angle of the front wheel is steered to a maximum angle to adjust the rotation center point of the vehicle.

In addition, the control unit of the sequential steering system of the front and rear wheels for stable rotation of the four-wheel steering vehicle of the present invention is characterized in that, when the command speed input from the driving unit is higher than a set threshold speed, a speed compensation scaler is applied according to the steering angle of the rear wheels to output a compensated command speed lower than the input command speed, thereby reducing the driving speed of the vehicle.

In addition, the control unit of the sequential steering system of the front and rear wheels for stable rotation of the four-wheel steering mobile body of the present invention calculates the center of rotation of the mobile body based on the steering angles of the front and rear wheels located in the inner direction in which the mobile body rotates, and recalculates and adjusts the steering angles of the front and rear wheels located in the outer direction in which the mobile body rotates around the center of rotation.

In addition, the control unit of the sequential steering system of the front and rear wheels for stable rotation of the four-wheel steering mobile body of the present invention is characterized in that it drives in a two-wheel steering manner through the front wheels, and when the steering angle of the front wheels is converted to a maximum angle, it sequentially drives the rear wheels to convert to a four-wheel steering manner.

In addition, the control unit of the sequential steering system of the front and rear wheels for stable rotation of the four-wheel steering vehicle of the present invention is characterized in that when the steering angle of the rear wheels becomes 0 degrees while the vehicle is changed to a four-wheel steering mode, it switches to a two-wheel steering mode.

The present invention relates to a sequential steering method of front and rear wheels for stable rotation of a four-wheel steering vehicle, comprising: a steering operation step for inputting a steering signal for operating the steering of a pair of front wheels through a driving unit to control a driving direction of the vehicle; a front wheel steering step for controlling a steering angle of the front wheels based on the steering signal input through the steering operation step; a rear wheel steering step for changing the steering angle of the pair of rear wheels to the opposite direction to the steering angle of the front wheels when the steering angle of the front wheels is steered to a maximum angle through the front wheel steering step; a rotation center point calculation step for calculating a rotation center point of the vehicle based on the steering angles of the front wheels and the rear wheels located in an inner direction in which the vehicle rotates after the rear wheel steering step; and an outer steering angle calculation step for recalculating and adjusting the steering angles of the front wheels and the rear wheels located in an outer direction in which the vehicle rotates around the rotation center point calculated through the rotation center point calculation step. The present invention is characterized by including a driving speed compensation step for reducing the driving speed of the moving body by applying a speed compensation scaler to output a compensated command speed lower than the input command speed when the command speed input from the driving unit according to the steering angle of the rear wheel is higher than the set threshold speed after the calculating step and the outer steering angle calculating step.

In addition, in the rotation center point calculation step of the sequential steering method of the front and rear wheels for stable rotation of the four-wheel steering mobile body of the present invention, the rotation center point (P _x, P _y ) is calculated using the following mathematical expressions 1 and 2.

[Mathematical formula 1]

(P _x : x-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, L: length between the front and rear wheels, θ _Fi : steering angle of the front wheel located inward in the direction of rotation of the moving body, θ _Bi : steering angle of the rear wheel located inward in the direction of rotation of the moving body)

[Mathematical formula 2]

(P _y : y-axis coordinate of the center of rotation, θ _Fi : steering angle of the front wheel located inside the direction of rotation of the moving body, P _x : x-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, L: length between the front and rear wheels)

In addition, in the outer steering angle calculation step of the sequential steering method of the front and rear wheels for stable rotation of the four-wheel steering mobile body of the present invention, the steering angle is calculated using mathematical expressions 3 and 4.

[Mathematical Formula 3]

(θ _Fo : steering angle of the front wheel located outside the direction of rotation of the moving body, L: length between the front and rear wheels, P _y : y-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, P _x : x-axis coordinate of the center of rotation)

[Mathematical formula 4]

(θ _Bo : steering angle of the rear wheel located outside the direction of rotation of the moving body, L: length between the front and rear wheels, P _y : y-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, P _x : x-axis coordinate of the center of rotation)

In addition, in the driving speed correction step of the sequential steering method of the front and rear wheels for stable rotation of the four-wheel steering vehicle of the present invention, the steering angle of the rear wheel is characterized in that the driving speed is corrected based on the steering angle of the rear wheel located inside the rotation direction of the vehicle.

In addition, in the driving speed compensation step of the sequential steering method of the front and rear wheels for stable rotation of the four-wheel steering vehicle of the present invention, the speed compensation scaler is characterized by being determined by the following mathematical expression 5.

[Mathematical Formula 5]

(S: speed compensation scaler, S _min : minimum value of speed compensation scaler, θ _max : maximum mechanically steerable angle, θ _B : steering angle of the rear wheel located inside the rotation direction of the moving body, θ _BR : right rear wheel steering angle, θ _BL : left rear wheel steering angle, θ _J : target steering angle input to the driving unit)

In addition, the command speed corrected in the driving speed correction step of the sequential steering method of the front and rear wheels for stable rotation of the four-wheel steering vehicle of the present invention is characterized by being determined by the following mathematical expression 6.

[Mathematical Formula 6]

(V _C : compensated command speed, V _IN : command speed input from the drive unit, V _t ^bwd : critical speed when moving backward, V _t ^fwd : critical speed when moving forward, S: speed compensation scaler)

As described above, the sequential steering system and method of the front and rear wheels for stable rotation of a four-wheel steering vehicle according to the present invention have the effect of enabling an operator to operate a four-wheel steering vehicle stably and precisely using a steering wheel or joystick.

In addition, according to the sequential steering system and method of the front and rear wheels for stable rotation of a four-wheel steering vehicle according to the present invention, the operator can steer the four-wheel steering vehicle based on the steering feel of a conventional two-wheel steering vehicle, thereby facilitating prediction and control of the direction of travel.

In addition, according to the sequential steering system of the front and rear wheels and the method thereof for stable rotation of the four-wheel steering vehicle according to the present invention, there is an effect of inducing stable rotation by reducing the current speed without a separate operation of the operator when rotating at high speed.

Figure 1 is a configuration diagram showing the configuration of a sequential steering system of front and rear wheels for stable rotation of a four-wheel steering vehicle according to the present invention.
Figure 2 is a flowchart showing the steps of a sequential steering method of front and rear wheels for stable rotation of a four-wheel steering vehicle according to the present invention.
FIG. 3 is a drawing showing wheel positions in a two-dimensional coordinate system in a sequential steering system and method of front and rear wheels for stable rotation of a four-wheel steering vehicle according to the present invention.
FIG. 4 is a drawing showing a state in which the front wheels are steered for a right turn in a sequential steering system and method of the front and rear wheels for stable rotation of a four-wheel steering vehicle according to the present invention.
FIG. 5 is a drawing showing a state in which the sequential steering system of the front and rear wheels for stable rotation of a four-wheel steering vehicle according to the present invention steers the rear wheels for a right turn.
FIG. 6 is a drawing showing a state in which the front wheels are steered for a left turn in a sequential steering system and method of the front and rear wheels for stable rotation of a four-wheel steering vehicle according to the present invention.
FIG. 7 is a drawing showing a state in which the rear wheels are steered for a left turn in a sequential steering system and method of the front and rear wheels for stable rotation of a four-wheel steering vehicle according to the present invention.
FIG. 8 is a graph showing changes in speed compensation values according to rear wheel steering in a sequential steering system and method of front and rear wheels for stable rotation of a four-wheel steering vehicle according to the present invention.
FIG. 9 is a graph showing the appearance of speed being reduced according to rear wheel steering in a sequential steering system and method of front and rear wheels for stable rotation of a four-wheel steering vehicle according to the present invention.

The specific features and advantages of the present invention are described in detail below with reference to the attached drawings. If it is determined that a detailed description of the functions and configurations related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

The present invention relates to a sequential steering system of front and rear wheels for stable rotation of a four-wheel steering vehicle and a method thereof, and more specifically, to a sequential steering system of front and rear wheels for stable rotation of a four-wheel steering vehicle and a method thereof, which automatically controls a turning radius and speed when a vehicle capable of moving using four wheels is turned to the left or right, thereby enabling stable rotation.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

Figure 1 is a configuration diagram showing the configuration of a sequential steering system of the front wheels (100) and rear wheels (200) for stable rotation of a four-wheel steering mobile body (500) according to the present invention.

As shown in Fig. 1, the sequential steering system of the front wheels (100) and the rear wheels (200) for stable rotation of the four-wheel steering mobile body (500) according to the present invention comprises: a mobile body (500); front wheels (100) formed on both sides of the front lower portion of the mobile body (500) to move the mobile body (500) through rotation and steering angle adjustment; rear wheels (200) formed on both sides of the rear lower portion of the mobile body (500) to move the mobile body (500) through rotation and steering angle adjustment; a driving unit (300) formed on the mobile body (500) to provide driving force to the front wheels (100) or the rear wheels (200) and control the steering of the front wheels (100); and a driving unit (300) formed on the mobile body (500) to control the steering of the rear wheels (200) when the steering angle of the front wheels (100) is steered to the maximum angle. It is characterized by including a control unit (400) that adjusts the center of rotation of a moving body (500) by changing it in the opposite direction to the steering angle of the front wheel (100).

In addition, the control unit (400) is characterized in that it drives in a two-wheel steering mode through the front wheels (100) and then sequentially drives the rear wheels (200) when the steering angle of the front wheels (100) is switched to the maximum angle, thereby switching to a four-wheel steering mode.

In addition, the control unit (400) is characterized in that when the steering angle of the rear wheel (200) becomes 0 degrees while the moving body (500) is changed to a four-wheel steering mode, it switches to a two-wheel steering mode.

The mobile body (500) can be used as a passenger vehicle, personal mobility device, unmanned robot, automatic unmanned transport vehicle, heavy equipment vehicle, etc., and is formed so that various devices can be installed so that functions and purposes can be implemented according to the purpose.

At this time, it is desirable that the mobile body (500) be configured to be capable of driving using its own power through four wheels, and can be configured to be operated while riding in a vehicle or to be operated remotely as an unmanned robot.

The front wheels (100) are formed as a pair on both sides of the lower front of the moving body (500), with a left front wheel (110) provided on the left side and a right front wheel (120) provided on the right side.

The rear wheels (200) are formed as a pair on both sides of the lower rear of the moving body (500), with a left rear wheel (210) provided on the left side and a right rear wheel (220) provided on the right side.

At this time, both the front wheel (100) and the rear wheel (200) are formed so that the steering angle can be adjusted, and more preferably, the left front wheel (110), the right front wheel (120), the left rear wheel (210), and the right rear wheel (220) can individually adjust the steering angle, and this will be described later.

The driving unit (300) provides driving force to the front wheel (100) or the rear wheel (200) using an engine or a motor depending on the type of the moving body (500), and includes a driving unit (320) including an accelerator pedal, a deceleration pedal, an acceleration button, and a deceleration button.

The driving unit (320) of the driving unit (300) enables the moving body (500) to drive along the ground by rotating the front wheel (100) or the rear wheel (200), and the driving direction of the moving body (500) can also be controlled by adjusting the steering angle of the front wheel (100) using the steering unit (310) using a steering wheel or joystick.

In a general situation, when a moving body (500) is driven based on the steering unit (310) and the driving unit (320) of the driving unit (300), the driving unit (300) is configured to control the direction of the moving body (500) by two-wheel steering that adjusts the steering angle of the front wheels (100), and the four-wheel steering is configured to operate under specific conditions.

The control unit (400) is formed in the moving body (500) and is used to control the steering angle of the rear wheel (200). When the steering angle of the front wheel (100) is steered to the maximum angle in the left or right direction, the control unit (400) controls the steering angle of the rear wheel (200) to change to four-wheel steering and is used to control the driving of the moving body (500).

By using the steering unit (310) formed in the driving unit (300), the operator can drive with the same feeling as a normal vehicle based on two-wheel steering in normal situations. However, in this case, there was a problem that the turning radius increased when only the front wheels (100) were used when making a left turn, right turn, or U-turn.

In contrast, in the case of four-wheel steering, the steering angles of the front wheels (100) and rear wheels (200) change simultaneously, so the turning radius of the moving body (500) is reduced, which has the advantage of making it easy to turn even in narrow sections. However, there was a problem in that users accustomed to two-wheel steering were unable to estimate the turning radius, which resulted in accidents.

In the present invention, the control unit (400) can automatically change between two-wheel steering and four-wheel steering according to the usage environment, so that driving is possible in two-wheel steering mode in normal times and can be changed to four-wheel steering mode only in specific situations.

To this end, the control unit (400) can change the steering angle of the rear wheel (200) by steering the front wheel (100) to the maximum angle toward the left or right using the steering wheel or joystick of the steering unit (310) to switch to four-wheel steering.

At this time, the control unit (400) controls the front wheel (100) to be steered first to the maximum steering angle and then the rear wheel (200) to be steered, and the rear wheel (200) is steered to the maximum angle in the opposite direction of the front wheel (100) to reduce the turning radius of the moving body (500).

That is, the control unit (400) can reduce the turning radius of the moving body (500) by sequentially operating the rear wheels (200) after the front wheels (100) are first steered to the maximum angle, and can also control the steering angle of the rear wheels (200) through the steering unit (310) of the driving unit (300).

In addition, when the steering angle of the rear wheel (200) reaches 0 degrees, which is a left-right neutral state, the control unit (400) maintains the rear wheel (200) in a 0 degree state to switch to a two-wheel steering mode, and the steering unit (310) of the drive unit (300) can be controlled so that the rear wheel (200) cannot be steered.

That is, when the front wheel (100) is turned to the maximum angle, the rear wheel (200) is steered to the maximum angle, thereby switching to a four-wheel steering mode, and when the left turn, right turn, and U-turn are completed by the driving unit (300) and the steering angle of the front wheel (100) becomes 0 degrees, which is the neutral state, the rear wheel (200) also becomes 0 degrees and is maintained in a locked state by the control unit (400), thereby enabling switching to a two-wheel steering mode.

In addition, the control unit (400) calculates the center of rotation (10) of the moving body (500) based on the steering angles of the front wheels (100) and rear wheels (200) located in the inner direction in which the moving body (500) rotates, and recalculates and adjusts the steering angles of the front wheels (100) and rear wheels (200) located in the outer direction in which the moving body (500) rotates around the center of rotation (10).

The control unit (400) can calculate the center of rotation (10) using the angles of the front wheels (100) and rear wheels (200) located in the inner direction of the direction in which the moving body (500) is rotated in a four-wheel steering manner. When the moving body (500) turns right, the center of rotation (10) can be calculated based on the steering angles of the right front wheel (120) and the right rear wheel (220), and when the moving body (500) turns left, the center of rotation (10) can be calculated based on the steering angles of the left front wheel (110) and the left rear wheel (210).

Once the center of rotation (10) is calculated, the steering angles of the front wheels (100) and rear wheels (200) located on the outer side where the moving body (500) rotates are adjusted so that they match the center of rotation (10), so that all four wheels of the front wheels (100) and rear wheels (200) can rotate based on the center of rotation (10).

At this time, when the moving body (500) turns right, the steering angles of the left front wheel (110) and the left rear wheel (210) are controlled by the control unit (400) to coincide with the center of rotation (10), and when the moving body (500) turns left, the steering angles of the right front wheel (120) and the right rear wheel (220) are controlled to coincide with the center of rotation (10).

Through this process, all four wheels of the front wheel (100) and the rear wheel (200) are aligned with the center of rotation (10), allowing the moving body (500) to make stable left, right, and U-turns.

In addition, the control unit (400) is characterized in that, when the command speed input from the driving unit (300) is higher than the set threshold speed, the control unit (400) applies a speed compensation scaler according to the steering angle of the rear wheel (200) to output a compensated command speed that is lower than the input command speed, thereby reducing the driving speed of the moving body (500).

When a vehicle (500) turns left, right, or makes a U-turn using four-wheel steering, the turning radius is reduced compared to two-wheel steering, so if the rear wheels (200) turn sharply while driving at high speed, the possibility of overturning or slipping increases.

To prevent this, the control unit (400) is equipped with a speed compensation scaler to reduce the speed according to the steering angle of the rear wheel (200), and when the rear wheel (200) is steered and the moving body (500) rotates, if the command speed input by the driving unit (300) is higher than the critical speed set by the operator, the speed compensation scaler is applied to drive at a speed lower than the input command speed, thereby preventing overturning or slipping.

At this time, the operator can set the correction value of the speed compensation scaler, and it is desirable to control the speed compensation scaler so that the correction value is applied to the maximum when the steering angle of the rear wheel (200) is the maximum angle, and the command speed input from the driving unit (300) is output as is when the steering angle of the rear wheel (200) is 0 degrees, which is the neutral state.

In addition, it is preferable that the control unit (400) be equipped with a front wheel steering angle sensor (410) and a rear wheel steering angle sensor (420) for measuring the steering angles of the front wheel (100) and the rear wheel (200), thereby enabling comparison between the steering angle input through the steering unit (310) and the actual steering angles of the front wheel (100) and the rear wheel (200).

In addition, it is preferable that the front wheel steering angle sensors (410) are formed on each of the left front wheel (110) and the right front wheel (120) so as to individually measure the steering angles, and the rear wheel steering angle sensors (420) are formed on each of the left rear wheel (210) and the right rear wheel (220) so as to individually measure the steering angles.

The control unit (400) can detect the steering angle of each of the four wheels, the front wheel (100) and the rear wheel (200), and through this, the control unit (400) can individually control the steering angle of each wheel, thereby finely adjusting the steering angle so that it matches the center of rotation (10) when the moving body (500) turns left, right, or makes a U-turn.

In addition, the control unit (400) is provided with a driving speed sensor (430) so that the driving speed of the moving body (500) can be checked, and through this, it is possible to check whether the current driving speed of the moving body (500) matches the command speed input from the driving unit (300).

The detailed contents will be described later with the attached drawings.

Figure 2 is a flow chart showing the steps of a sequential steering method of the front wheels (100) and rear wheels (200) for stable rotation of a four-wheel steering mobile body (500) according to the present invention.

As shown in FIG. 2, the sequential steering method of the front wheels (100) and the rear wheels (200) for stable rotation of the four-wheel steering mobile body (500) according to the present invention comprises: a steering operation step (S10) for inputting a steering signal for operating the steering of a pair of front wheels (100) through a driving unit (300) to control the driving direction of the mobile body (500); a front wheel steering step (S20) for controlling the steering angle of the front wheels (100) based on the steering signal input through the steering operation step (S10); a rear wheel steering step (S30) for changing the steering angle of the pair of rear wheels (200) to the opposite direction to the steering angle of the front wheels (100) when the steering angle of the front wheels (100) is steered to the maximum angle through the front wheel steering step (S20); and after the rear wheel steering step (S30), The invention is characterized by including a rotation center point calculation step (S40) for calculating a rotation center point (10) of a moving body (500) based on the steering angles of the front wheels (100) and rear wheels (200) located in the inner direction in which the moving body (500) rotates, an outer steering angle calculation step (S50) for calculating and steering the steering angles of the front wheels (100) and rear wheels (200) located in the outer direction in which the moving body (500) rotates around the rotation center point (10) calculated through the rotation center point calculation step (S40), and a driving speed correction step (S60) for reducing the driving speed of the moving body (500) by applying a speed correction scaler to output a corrected command speed that is lower than the input command speed when the command speed input from the driving unit (300) according to the steering angle of the rear wheels (200) is higher than a set threshold speed after the outer steering angle calculation step (S50).

The steering operation step (S10) is a step for controlling the steering angle of the front wheel (100) by using the steering unit (310) formed in the driving unit (300), and the pair of front wheels (100) can control the driving direction of the moving body (500) while being steered at the same angle.

The front wheel steering stage (S20) is a stage in which the control unit (400) receives a steering signal input through the steering wheel or joystick of the steering unit (310) and controls the steering angle of the front wheel (100) to match the input steering signal.

At this time, if the steering angle of the front wheel (100) is not the maximum angle, the vehicle is driven in a two-wheel steering mode, and if the steering angle of the front wheel (100) is the maximum angle, the vehicle can be switched to a four-wheel steering mode.

The rear wheel steering stage (S30) is a stage in which, when the front wheel (100) is steered to the left or right at the maximum angle in the steering operation stage (S10), the control unit (400) changes the steering angle of the rear wheel (200) to the maximum angle in the opposite direction of the front wheel (100) to convert to a four-wheel steering mode.

When the control unit (400) is changed to a four-wheel steering mode, the steering angles of the front wheels (100) and rear wheels (200) can be controlled simultaneously by operating the steering unit (310) of the driving unit (300). When the steering angle of the rear wheels (200) reaches 0 degrees, which is a neutral state, it is preferable that the control unit (400) be changed to a two-wheel steering mode so that only the front wheels (100) are controlled by operating the steering unit (310).

The rotation center point calculation step (S40) is a step for calculating the rotation radius of the moving body (500) in a state where the steering angle of the rear wheel (200) is steered to the maximum angle in the opposite direction of the front wheel (100) when the front wheel (100) is steered to the maximum angle in the left or right direction.

Here, the center of rotation (10) means the area where vertically extended lines based on the steering angles of the front wheel (100) and the rear wheel (200) located in the inner direction in which the moving body (500) rotates overlap, and the center of rotation (10) around which the moving body (500) rotates can be identified as a coordinate point through the center of rotation (10).

At this time, when calculating the center of rotation (10), the control unit (400) uses the left front wheel (110) and the left rear wheel (210) when the moving body (500) turns left, and uses the right front wheel (120) and the right rear wheel (220) when turning right.

That is, the center of rotation (10) is calculated using the front wheel (100) and the rear wheel (200) located in the inner direction of the direction in which the moving body (500) rotates.

The outer steering angle calculation step (S50) is a step in which the control unit (400) recalculates the steering angles of the front wheels (100) and rear wheels (200) located in the outer direction in which the moving body (500) rotates, based on the center of rotation (10), and individually adjusts the steering angles. This enables precise control so that the four wheels can rotate simultaneously around the center of rotation (10).

When a moving body (500) is rotated in a four-wheel steering manner through the outer steering angle calculation step (S50), it can rotate stably with respect to the center of rotation (10), so it can rotate smoothly without any vibration or shaking occurring during driving.

The driving speed compensation step (S60) is a step used to prevent the moving body (500) from falling or slipping by reducing the command speed input from the driving unit (300) according to the steering angle of the rear wheel (200).

In order to compensate for the driving speed, the control unit (400) can set a critical speed that serves as a reference speed for reducing the speed according to the steering angle of the rear wheel (200), and if the command speed input through the driving unit (320) is high based on the critical speed, the control unit (400) can apply a speed compensation scaler to the input speed to reduce the output speed compared to the input command speed.

At this time, the speed compensation scaler can be set to output the input command speed as it is when the steering angle of the rear wheel (200) is 0 degrees, which is the neutral state, and when the steering angle changes, the compensation value of the speed compensation scaler can be gradually changed according to the steering angle of the rear wheel (200), so that the output speed decreases compared to the input command speed.

It is desirable for the operator to be able to directly set the minimum value at which the speed compensation scaler is applied when the steering angle of the rear wheel (200) is maximum and the critical speed at which the speed compensation scaler is applied through the control unit (400).

Below, the details of calculating the center of rotation (10) for each step, calculating the outer steering angle, and correcting the driving speed will be explained through the attached drawings.

FIG. 3 is a drawing showing wheel positions in a two-dimensional coordinate system in a sequential steering system and method of the front wheels (100) and rear wheels (200) for stable rotation of a four-wheel steering mobile body (500) according to the present invention.

As illustrated in FIG. 3, the sequential steering system and method of the front wheels (100) and rear wheels (200) for stable rotation of a four-wheel steering mobile body (500) according to the present invention converts the range of target steering values as in mathematical expression 1 when an operator steers using a steering unit (310) formed of a steering wheel or joystick.

(θ _max : mechanical maximum steering angle, θ _J : target steering angle input to the driving unit)

As shown in Fig. 3, by arranging the position of each wheel on a two-dimensional plane coordinate with the origin as the center by the width (W) between the rotation axes of the front wheel (100) or the rear wheel (200) formed on the moving body (500) and the length (L) between the front wheel (100) and the rear wheel (200), each wheel arranged on the two-dimensional plane coordinate can have its own unique coordinate.

At this time, the mechanical maximum steering angle refers to the maximum angle at which the wheels can be steered when the steering wheel or joystick is operated to the left or right, and is expressed as plus and minus to distinguish between the left and right of the input steering direction.

FIG. 4 is a drawing showing a state in which the front wheel (100) is steered for a right turn in a sequential steering system and method of the front wheel (100) and rear wheel (200) for stable rotation of a four-wheel steering mobile body (500) according to the present invention, and FIG. 5 is a drawing showing a state in which the rear wheel (200) is steered for a right turn in a sequential steering system and method of the front wheel (100) and rear wheel (200) for stable rotation of a four-wheel steering mobile body (500) according to the present invention.

As shown in FIGS. 4 and 5, in the rotation center point calculation step (S40) of the sequential steering system of the front wheels (100) and the rear wheels (200) for stable rotation of the four-wheel steering mobile body (500) according to the present invention and the method thereof, the rotation center point (10) (P _x, P _y ) is characterized by being calculated using the following mathematical expressions 3 and 4.

When the moving body (500) steers to the right, the steering angles of the right front wheel (120) and the right rear wheel (220) can be calculated using mathematical expression 2, and after the right front wheel (120) is steered to the maximum angle, the steering angle of the right rear wheel (220) is steered.

(θ _FR : right front wheel steering angle, θ _J : target steering angle input to the drive unit, θ _BR : right rear wheel steering angle, θ _max : mechanical maximum steering angle, θ _J : target steering angle input to the drive unit)

Using the rotation axis coordinate values of each wheel described in Fig. 3 and the steering angles of the right front wheel (120) and the right rear wheel (220), the common rotation center point coordinates (P _x, P _y ) of the four wheels are obtained using mathematical expressions 3 and 4.

(P _x : x-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, L: length between the front and rear wheels, θ _FR : right front wheel steering angle, θ _BR : right rear wheel steering angle)

(P _y : y-axis coordinate of the center of rotation, θ _FR : right front wheel steering angle, P _x : x-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, L: length between the front and rear wheels)

Here, the steering angle of the right front wheel (120) and the steering angle of the right rear wheel (220) are located on the inner side of the turning radius in which the moving body (500) turns right, and therefore, they can be named as the steering angle of the front wheel (100) or the rear wheel (200) located on the inner side of the turning direction of the moving body (500).

In addition, in the outer steering angle calculation step (S50), the steering angle is calculated using mathematical expressions 5 and 6.

The left front wheel (110) and the left rear wheel (210) use the coordinate values of each wheel and the coordinate values of the common center of rotation point (10) of the four wheels to obtain and output the angle at which each wheel rotates based on the common point.

(θ _FL : left front wheel steering angle, L: length between front and rear wheels, P _y : y-axis coordinate of rotation center point, W: width between rotation axes of front or rear wheels, P _x : x-axis coordinate of rotation center point)

(θ _BL : left rear wheel steering angle, L: length between front and rear wheels, P _y : y-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, P _x : x-axis coordinate of the center of rotation)

Here, the steering angle of the left front wheel (110) and the steering angle of the left rear wheel (210) are located outside the turning radius when the moving body (500) turns right, so it may be applied as the steering angle of the front wheel (100) or the rear wheel (200) located outside the turning direction of the moving body (500).

FIG. 6 is a drawing showing a state in which the front wheel (100) is steered for a left turn in a sequential steering system and method of the front wheel (100) and rear wheel (200) for stable rotation of a four-wheel steering mobile body (500) according to the present invention, and FIG. 7 is a drawing showing a state in which the rear wheel (200) is steered for a left turn in a sequential steering system and method of the front wheel (100) and rear wheel (200) for stable rotation of a four-wheel steering mobile body (500) according to the present invention.

As shown in FIGS. 6 and 7, in the sequential steering system and method of the front wheels (100) and rear wheels (200) for stable rotation of a four-wheel steering mobile body (500) according to the present invention, when the mobile body (500) steers to the left, the steering angles of the left front wheel (110) and the left rear wheel (210) can be calculated as in the following mathematical expression 7, and after the left front wheel (110) is steered to the maximum angle, the steering angle of the left rear wheel (210) is steered.

(θ _FL : left front wheel steering angle, θ _J : target steering angle input to the drive unit, θ _BL : left rear wheel steering angle, θ _max : mechanical maximum steering angle, θ _J : target steering angle input to the drive unit)

Using the rotation axis coordinate values of each wheel described in Fig. 3 and the steering angles of the right front wheel (120) and the right rear wheel (220), the common rotation center point coordinates (P _x, P _y ) of the four wheels are obtained using mathematical expressions 8 and 9.

(P _x : x-axis coordinate of the center of rotation (10), W: width between the rotation axes of the front or rear wheels, L: length between the front and rear wheels, θ _FL : left front wheel steering angle, θ _BL : left rear wheel steering angle)

(P _y : y-axis coordinate of the center of rotation, θ _FL : left front wheel steering angle, P _x : x-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, L: length between the front and rear wheels)

Here, the steering angle of the left front wheel (110) and the steering angle of the left rear wheel (210) are located on the inner side of the turning radius around which the moving body (500) turns when turning left, and therefore can be named as the steering angle of the front wheel (100) or the rear wheel (200) located on the inner side of the turning direction of the moving body (500).

The left front wheel (110) and the left rear wheel (210) use the coordinate values of each wheel and the coordinate values of the common center of rotation point (10) of the four wheels to output the angle at which each wheel rotates based on the common point using mathematical expressions 10 and 11.

(θ _FR : right front wheel steering angle, L: length between front and rear wheels, P _y : y-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, P _x : x-axis coordinate of the center of rotation)

(θ _BR : right rear wheel steering angle, L: length between front and rear wheels, P _y : y-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, P _x : x-axis coordinate of the center of rotation)

Here, the steering angle of the right front wheel (120) and the steering angle of the right rear wheel (220) are located outside the turning radius of the moving body (500) when turning left, so it may be applied as the steering angle of the front wheel (100) or the rear wheel (200) located outside the turning direction of the moving body (500).

FIG. 8 is a graph showing a change in a speed compensation value according to rear wheel (200) steering in a sequential steering system and method of front wheels (100) and rear wheels (200) for stable rotation of a four-wheel steering mobile body (500) according to the present invention, and FIG. 9 is a graph showing a speed reduction according to rear wheel (200) steering in a sequential steering system and method of front wheels (100) and rear wheels (200) for stable rotation of a four-wheel steering mobile body (500) according to the present invention.

As illustrated in FIGS. 8 and 9, in the driving speed correction step (S60) of the sequential steering system of the front wheels (100) and rear wheels (200) for stable rotation of the four-wheel steering mobile body (500) according to the present invention and the method thereof, the steering angle of the rear wheels (200) is characterized in that the driving speed is corrected based on the steering angle of the rear wheels (200) located inside the rotation direction of the mobile body (500).

In addition, in the driving speed compensation step (S60), the speed compensation scaler is characterized by being determined by the following mathematical expression 12.

When the rear wheel (200) of a four-wheel steering vehicle (500) moves at high speed and the rear wheel (200) rotates rapidly, the possibility of overturning or slipping increases, thereby reducing stability. Therefore, when the size of the command speed input by the driving unit (300) is higher than the critical speed, the speed compensation scaler is adjusted according to the size of the steering angle of the rear wheel (200) to compensate the command speed to a lower value.

At this time, the steering angle of the rear wheel (200) is used when turning right, the steering angle of the right rear wheel (220), and when turning left, the steering angle of the left rear wheel (210) is used.

That is, the steering angle of the rear wheel (200) located on the inner side of the rotation direction in which the moving body (500) rotates is used.

(S: speed compensation scaler, S _min : minimum value of speed compensation scaler, θ _max : maximum mechanically steerable angle, θ _B : steering angle of rear wheel located inside the rotation direction of the moving body, θ _BR : steering angle of right rear wheel, θ _BL : steering angle of left rear wheel (210), θ _J : target steering angle input to the driving unit)

At this time, the speed compensation scaler is configured to be able to set a minimum value through the control unit (400), and the minimum value means a compensation value for reducing the driving speed to the maximum when the rear wheel (200) is steered at the maximum angle.

In addition, the command speed corrected in the driving speed correction step (S60) is characterized by being determined by the following mathematical expression 13.

(V _C : compensated command speed, V _IN : command speed input from the drive unit, V _t ^bwd : critical speed when moving backward, V _t ^fwd : critical speed when moving forward, S: speed compensation scaler)

The moving body (500) can move forward or backward depending on the driving situation, and therefore, when switching to a four-wheel steering mode, it is necessary to set the critical speeds of the forward and rear wheels respectively.

At this time, V _t ^fwd is the critical speed value when moving forward, so it is a positive number greater than 0, and V _t ^bwd is the critical speed value when moving backward, so it is set to a negative number less than 0.

As in the first condition of mathematical expression 13, if the command speed input from the driving unit is less than the critical speed when moving forward and higher than the critical speed when moving backward, the driving unit is controlled so that the input command speed is output as is.

That is, the input command speed is used as the compensated command speed without using a speed compensation scaler.

As in the second condition of mathematical expression 13, when the input command speed is higher than the critical speed when the moving body (500) is moving forward, the size of the input command speed is considered to be high, so speed compensation scaling is applied to output a corrected command speed with the size of the input command speed lowered.

As in the third condition of mathematical expression 13, when the input command speed is lower than the critical speed when the moving body (500) is moving backwards, the size of the input command speed is considered to be high, so speed compensation scaling is applied to output a corrected command speed that reduces the size of the input command speed.

To summarize, this can be expressed as in Fig. 9. Assuming that the range of the input command speed is -1 to 1, the speed correction scaling (S) is set to 0.2, the critical speed when moving backward (V _t ^bwd ) is set to -0.3, and the critical speed when moving forward (V _t ^fwd ) is set to 0.5, as an example.

For the compensated command speed (V _C ), a positive value means forward movement and a negative value means backward movement based on 0. In the case of backward movement, an increase in the negative value means that the backward speed increases.

In section B of FIG. 9, the command speed (V _IN ) input from the driving unit (300) is greater than the critical speed (V _t ^bwd ) when moving backward and lower than the critical speed (V _t ^fwd ) when moving forward, so the control unit (400) outputs the corrected command speed (V _C ) without compensating the command speed (V _IN ) input from the driving unit (300).

Section A is a state in which the command speed (V _IN ) input when the moving body (500) moves backward is lower than or equal to the critical speed (V _t ^bwd ) when moving backward. At this time, since the critical speed (V _t ^bwd ) when moving backward is based on a negative number, the meaning that the command speed (V _IN ) input is lower than or equal to the critical speed (V _t ^bwd ) when moving backward means that the command speed (V _IN ) input when the moving body (500) moves backward exceeds the critical speed (V _t ^bwd ) when moving backward at high speed.

If the command speed (V _IN ) input in section A is lower than or equal to the critical speed (V _t ^bwd ) when moving backward, the vehicle is moving backward at high speed. Therefore, the control unit (400) applies a correction speed scaler to the command speed (V _IN ) input from the driving unit (300) so that the output corrected command speed (V _C ) has a low value, thereby reducing the backward speed of the moving body (500).

That is, even if the operator inputs the command speed (V _IN ), a compensated command speed (V _C ) in a reduced state with a lower value than the command speed (V _IN ) input through the compensation speed scaler can be output.

Section C is a state in which the moving body (500) is moving forward at a high speed forward at a command speed (V _IN ) exceeding the critical speed (V _t ^fwd ) when moving forward, and the control unit (400) applies a correction speed scaler to the command speed (V _IN ) input from the driving unit (300) so that the output corrected command speed (V _C ) has a low value, thereby reducing the forward speed of the moving body (500).

That is, even if the operator inputs the command speed (V _IN ), a compensated command speed (V _C ) in a reduced state with a lower value than the command speed (V _IN ) input through the compensation speed scaler can be output.

In addition, since the speed compensation scaler gradually changes as the steering angle of the rear wheel (200) increases, as the steering angle of the rear wheel (200) increases, the correction value of the speed compensation scaler also increases, so that the value of the command speed to be corrected can become lower than the input command speed.

Through this, when the moving body (500) moves at high speed and turns in a four-wheel steering manner, the command speed input according to the rear wheel (200) steering angle is scaled to a low value, so that the moving body (500) can turn stably.

As a result, after the front wheel (100) is steered to the maximum angle, the rear wheel (200) is steered, so that an operator who is familiar with steering the front wheel (100) can easily predict and control the direction of travel of the vehicle (500), and stable driving is possible because the rear wheel (200) is not steered abruptly.

In addition, since the front wheel (100) is used first, the rear wheel (200) steering device or tires can be changed to use less durable or cheaper products, and the vehicle speed of the moving body (500) is reduced in proportion to the rear wheel (200) steering angle, so that it can rotate stably without falling over even when moving at high speed or when loading heavy cargo.

As described above, according to the sequential steering system of the front and rear wheels for stable rotation of a four-wheel steering vehicle according to the present invention and the method therefor, an operator can operate a four-wheel steering vehicle stably and precisely using a steering wheel or a joystick, and the operator can steer the four-wheel steering vehicle based on the steering feel of a conventional two-wheel steering vehicle, making it easy to predict and control the direction of travel, and when rotating at high speed, the current speed can be reduced to induce stable rotation without a separate operation of the operator.

As described above, the present invention has been described with reference to preferred embodiments, but it will be apparent to those skilled in the art that various modifications or variations may be made to the present invention without departing from the technical idea and scope described in the claims of the present invention. Accordingly, the scope of the present invention should be interpreted by the claims, which are described to include such numerous examples of modifications.

10: Center of rotation 100: Front wheel
110: Left front wheel 120: Right front wheel
200 : Rear wheel 210 : Left rear wheel
220 : Right rear wheel 300 : Drive unit
310: Steering unit 320: Driving unit
400: Control unit 410: Front wheel steering angle sensor
420: Rear wheel steering angle sensor 430: Driving speed sensor
500 : Mobile
S10: Steering operation stage S20: Front wheel steering stage
S30: Rear wheel steering stage S40: Rotation center point calculation stage
S50: Outer steering angle calculation step S60: Driving speed correction step

Claims (11)

With moving objects;
Front wheels formed on each side of the front lower portion of the above-mentioned mobile body and configured to move the above-mentioned mobile body by adjusting rotation and steering angle;
A rear wheel formed on each side of the lower rear surface of the above-mentioned mobile body and configured to move the above-mentioned mobile body by adjusting rotation and steering angle;
A driving unit formed on the above-mentioned moving body to provide driving force to the front wheel or the rear wheel and control the steering of the front wheel;
A control unit formed on the above-mentioned moving body and configured to adjust the center of rotation of the moving body by changing the steering angle of the rear wheel in the opposite direction to the steering angle of the front wheel when the steering angle of the front wheel is steered to the maximum angle;
The above control unit
The center of rotation of the moving body is calculated based on the steering angles of the front and rear wheels located in the inner direction where the moving body rotates,
It is characterized by recalculating and adjusting the steering angles of the front wheels and the rear wheels located in the outer direction in which the moving body rotates around the center of rotation.
A sequential steering system for the front and rear wheels for stable rotation of a four-wheel steering vehicle.
In paragraph 1,
The above control unit
The driving speed of the moving body is characterized in that, when the command speed input from the driving unit is higher than the set threshold speed, a speed compensation scaler is applied according to the steering angle of the rear wheel to reduce the driving speed of the moving body in comparison with the input command speed.
A sequential steering system for the front and rear wheels for stable rotation of a four-wheel steering vehicle.
delete In paragraph 1,
The above control unit
It is characterized in that when driving in a two-wheel steering mode through the front wheels, when the steering angle of the front wheels is switched to the maximum angle, the rear wheels are sequentially driven to switch to a four-wheel steering mode.
A sequential steering system for the front and rear wheels for stable rotation of a four-wheel steering vehicle.
In paragraph 4,
The above control unit
The above-mentioned moving body is characterized in that when the steering angle of the rear wheel becomes 0 degrees while the four-wheel steering mode is changed, it is changed to the two-wheel steering mode.
A sequential steering system for the front and rear wheels for stable rotation of a four-wheel steering vehicle.
A steering operation step for inputting a steering signal to operate the steering of a pair of front wheels through a driving unit to control the driving direction of a moving body;
A front wheel steering step for controlling the steering angle of the front wheels based on the steering signal input through the above steering operation step;
A rear wheel steering step for changing the steering angle of a pair of rear wheels in the opposite direction to the steering angle of the front wheels when the steering angle of the front wheels is steered to the maximum angle through the front wheel steering step;
A rotation center point calculation step for calculating the rotation center point of the moving body based on the steering angles of the front and rear wheels located in the inner direction in which the moving body rotates after the rear wheel steering step;
An outer steering angle calculation step for recalculating and adjusting the steering angles of the front wheels and the rear wheels located in the outer direction around which the moving body rotates around the rotation center point calculated through the rotation center point calculation step;
It is characterized by including a driving speed compensation step, which reduces the driving speed of the moving body by applying a speed compensation scaler to output a compensated command speed lower than the input command speed when the command speed input from the driving unit is higher than the set threshold speed according to the steering angle of the rear wheel after the outer steering angle calculation step.
A sequential steering method of the front and rear wheels for stable rotation of a four-wheel steering vehicle.
In paragraph 6,
In the above rotation center point calculation step
The above rotation center point (P _x, P _y ) is characterized by being calculated using the mathematical expressions 1 and 2 below.
A sequential steering method of the front and rear wheels for stable rotation of a four-wheel steering vehicle.

[Mathematical formula 1]

(P _x : x-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, L: length between the front and rear wheels, θ _Fi : steering angle of the front wheel located inward in the direction of rotation of the moving body, θ _Bi : steering angle of the rear wheel located inward in the direction of rotation of the moving body)

[Mathematical formula 2]

(P _y : y-axis coordinate of the center of rotation, θ _Fi : steering angle of the front wheel located inside the direction of rotation of the moving body, P _x : x-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, L: length between the front and rear wheels)
In paragraph 6,
In the above outer steering angle calculation step
The above steering angle is characterized in that it is calculated using mathematical expressions 3 and 4.
A sequential steering method of the front and rear wheels for stable rotation of a four-wheel steering vehicle.

[Mathematical Formula 3]

(θ _Fo : steering angle of the front wheel located outside the direction of rotation of the moving body, L: length between the front and rear wheels, P _y : y-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, P _x : x-axis coordinate of the center of rotation)

[Mathematical formula 4]

(θ _Bo : steering angle of the rear wheel located outside the direction of rotation of the moving body, L: length between the front and rear wheels, P _y : y-axis coordinate of the center of rotation, W: width between the rotation axes of the front or rear wheels, P _x : x-axis coordinate of the center of rotation)
In paragraph 6,
In the above driving speed correction step
The steering angle of the rear wheel is characterized in that the driving speed is corrected based on the steering angle of the rear wheel located inside the rotation direction of the moving body.
A sequential steering method of the front and rear wheels for stable rotation of a four-wheel steering vehicle.
In paragraph 6,
In the above driving speed correction step
The above speed compensation scaler is characterized by being determined by the following mathematical expression 5.
A sequential steering method of the front and rear wheels for stable rotation of a four-wheel steering vehicle.

[Mathematical Formula 5]

(S: speed compensation scaler, S _min : minimum value of speed compensation scaler, θ _max : maximum mechanically steerable angle, θ _B : steering angle of the rear wheel located inside the rotation direction of the moving body, θ _BR : right rear wheel steering angle, θ _BL : left rear wheel steering angle, θ _J : target steering angle input to the driving unit)
In paragraph 6,
In the above driving speed correction step
The above-mentioned corrected command speed is characterized by being determined by the mathematical expression 6 below.
A sequential steering method of the front and rear wheels for stable rotation of a four-wheel steering vehicle.

[Mathematical Formula 6]

(V _C : compensated command speed, V _IN : command speed input from the drive unit, V _t ^bwd : critical speed when moving backward, V _t ^fwd : critical speed when moving forward, S: speed compensation scaler)