KR20150062779A - Enhancement of cornering stability of direct-drive electric vehicle - Google Patents

Abstract

The present invention relates to a wheel torque control system and method for an in-wheel electric vehicle capable of accurately controlling wheel torque of each wheel to promote driving safety by using a longitudinal shaft control device to calculate a slip rate and a transverse shaft control device to calculate a yaw rate when cornering. When an in-wheel electric vehicle to which a rear wheel drive/front wheel steering system is applied turns, the wheel torque control system and method for an in-wheel electric vehicle according to the present invention receives information from the longitudinal shaft control device to calculate a slip rate and the transverse shaft control device to calculate a yaw rate and information about an accelerator pedal and a steering wheel angle by a driver as torque instruction values to compensate for the difference between real time values of the slip rate and the yaw rate which are representative control parameters for a longitudinal and a transverse shaft and reference values to accurately control the wheel torque of each wheel by using a wheel torque control device or the like to generate rear wheel torque required for optimal acceleration/deceleration and cornering to promote driving safety when abruptly accelerating and cornering.

Description

[0001] The present invention relates to a wheel torque control system for an in-wheel electric vehicle,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system and a method for controlling a wheel torque of an in-wheel electric vehicle, and more particularly, to a wheel torque control system and method for controlling an accurate wheel torque for each wheel by using a longitudinal axis controller for calculating a slip ratio at the time of turning and a transverse axis controller for calculating a yaw rate, And more particularly, to a system and method for controlling a wheel torque of an in-wheel electric vehicle.

BACKGROUND ART An electric vehicle is an environmentally friendly vehicle which has no discharge of exhaust gas. The electric vehicle includes a high voltage battery for supplying energy for driving, an inverter for converting direct current power (DC) output from a high voltage battery into alternating current (AC) And a driving motor for driving the vehicle by driving the vehicle by receiving the alternating electric power of the electric motor and the like. The rotational power of the motor is decelerated by the decelerator and then transmitted to the wheel through the driving shaft to drive the electric vehicle.

When the electric vehicle is divided into the driving types of the powertrain, the on-body electric vehicle (middle view in FIG. 2) in which the traveling motor is mounted on the lower part of the bonnet, and the in- And a homogeneous electric vehicle (the right drawing of Fig. 2).

1, an in-wheel motor including a stator, a wheel bearing, an inverter, a permanent magnet, and a rotor is disposed in a tire mounting wheel in a predetermined arrangement The power of the motor can be directly transmitted to the wheel.

Such an in-wheel electric vehicle can improve the power transmission efficiency and response speed compared to the conventional electric vehicle due to the elimination of the power transmission device such as the differential gear in addition to the environmental friendliness at the time of running, which is an advantage of a general electric vehicle, The space occupied by the room can be utilized as a space for storage and safety devices, and the degree of freedom in chassis design can be greatly increased.

On the other hand, in-wheel electric vehicles tend to have poor ride quality due to an increase in the ratio of the unsprung mass, which is the lower weight of the sprung mass, which means the upper weight based on the suspension, and the output per wheel Is limited to the output of the in-wheel motor, so that there is a disadvantage in that the output per wheel is smaller than the system of distributing the power using the differential gear.

Accordingly, there is a continuing research to improve the driving stability at the time of rapid acceleration, rapid braking, and turning of an in-wheel electric vehicle capable of controlling the direct wheel torque of each wheel.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide an electric vehicle having a rear wheel drive / front wheel steering system including a vertical axis controller for calculating a slip ratio at the time of turning of an in- , The accelerator pedal information and the steering angle information from the driver are input to the torque command value, and the error, which is the difference between the reference value and the real-time state value, of the slip ratio and the yaw rate, which are representative control parameters for the vertical and horizontal axes, Wheel vehicle of an in-wheel electric vehicle in which an accurate wheel torque is controlled for each wheel by using a wheel torque controller for generating rear wheel torque for acceleration / deceleration and turning, A control system and method are provided.

In order to achieve the above object, the present invention provides a method for controlling an in-wheel electric vehicle, comprising: calculating an optimum slip ratio according to a current turning state of an in-wheel electric vehicle; calculating a current slip ratio by receiving feedback of a front / A vertical axis controller for inputting an error value between the current slip rate to the wheel torque controller; A transverse axis controller for calculating an optimum yaw rate value from the steering angle and lateral speed information according to the driver's intention and inputting an error value between the calculated optimum yaw rate value and the actual yaw rate value to the wheel torque controller; A wheel torque controller for increasing or decreasing a slip ratio error value input from the vertical axis controller and a yaw rate error value input from the horizontal axis controller in proportion to the wheel torque command value according to the driver's chair to output the wheel torque of the rear wheel; And a wheel torque control system for an in-wheel electric vehicle.

According to another aspect of the present invention, there is provided a method of controlling a slip ratio of an automotive vehicle, the method comprising: calculating a slip ratio of an automobile based on an actual slip ratio and a slip ratio of the current vehicle, Inputting an error value to the wheel torque controller; Inputting to the wheel torque controller a yaw rate error value which is a difference between an ideal yaw rate value and an actual yaw rate value calculated from the steering angle information and the current vehicle speed information in the transverse axis controller; The wheel torque controller receives the wheel torque command value according to the driver's intention and calculates the rear wheel torque for optimum acceleration / deceleration and turning based on the slip ratio error value input from the vertical axis controller and the yaw rate error value input from the horizontal axis controller Calculating; The present invention provides a wheel torque control method for an in-wheel electric vehicle.

Through the above-mentioned means for solving the problems, the present invention provides the following effects.

According to the present invention, the wheel torque of an in-wheel electric vehicle to which a rear wheel drive / front wheel steering system is applied is controlled by using a wheel torque controller including a longitudinal axis controller and a transverse axis controller. The slip ratio and yaw rate It is possible to improve the driving stability at the time of rapid acceleration and turning of the in-wheel electric vehicle by controlling the rear wheel torque for optimum acceleration / deceleration and turning by compensating the error between the ideal value and the present value.

1 is a schematic view showing an in-wheel motor configuration of an in-wheel electric vehicle,
2 is a schematic view showing the kind of electric vehicle,
3 is a block diagram showing a wheel torque control system of an in-wheel electric vehicle according to the present invention,
FIGS. 4 to 7 are graphs showing simulation results of performance evaluation of a system and method for controlling the torque of an in-wheel electric vehicle according to the present invention.

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

In general, an internal combustion engine car has difficulties in accurately estimating the torque of each wheel without an additional wheel torque sensor due to the high nonlinearity of the power generation together with the complex power transmission system of the engine-torque converter-transmission-differential gear, The engine is equipped with a separate active safety system (ABS / TCS / VDC / ESP / ...) to control the slip of the vehicle, which is the ratio of the wheel speed to the vehicle speed.

However, since the in-wheel electric vehicle can estimate the wheel torque with high accuracy from the current information of the motor directly mounted on each wheel at relatively low cost, if the accurate wheel torque estimation and control of each wheel is possible, It is possible to realize a highly stable active safety system with a quick response characteristic without mounting the system.

In view of this, the present invention can control the accurate wheel torque for each wheel of an in-wheel electric vehicle and realize an active safety system such as TCS / ABS / VDC to improve driving stability at the time of rapid acceleration and turning And to provide a wheel torque control system and method.

3 is an overall block diagram showing a wheel torque control system of an in-wheel electric vehicle according to the present invention.

The wheel torque control system of the present invention is for controlling the wheel torque of an in-wheel electric vehicle to which a front wheel steering / rear wheel in-wheel driving system is applied. The wheel torque control system includes a longitudinal controller 10 and a lateral controller 20, And a torque controller 30 (Torque controller) for controlling the wheel torque.

The vertical axis controller 10 is a slip controller that calculates the optimal slip ratio according to the current turning situation and calculates the current slip ratio by receiving the feedback of the front and rear wheel speeds of the actual vehicle, (Difference value) between the slip ratio and the current slip ratio to the wheel torque controller 30. [

The yaw rate controller 20 is a yaw rate controller that calculates the steering angle according to the driver's will and the optimum value calculated from the lateral velocity information fed back from the IMU sensor (combined with the acceleration sensor and the gyro sensor) (Difference value) between the yaw rate value and the actual yaw rate value of the in-wheel electric vehicle is input to the wheel torque controller 30. [

The wheel torque controller 30 receives the wheel torque command value, i.e., the amount of depression of the accelerator pedal and the steering angle information according to the driver's intention. The wheel torque controller 30 receives the slip ratio error value input from the vertical axis controller 10 for vertical axis control, Wheel torque for optimum acceleration / deceleration and turning based on the yaw rate error value input from the yaw rate sensor 20.

Hereinafter, the wheel torque control system of the in-wheel electric vehicle according to the present invention will be described in detail as follows.

A vertical axis controller

Generally, the slip ratio of a vehicle which maximizes the running performance of the vehicle by maximizing the coefficient of friction between the tire and the road surface on the asphalt and concrete roads is about 0.15 to 0.2. Therefore, the conventional slip rate control algorithm The ABS and the TCS have set a slip ratio which is a constant between 0.15 and 0.2 and have performed a slip control so that the running slip of the vehicle can converge to the value. However, in addition to the slip ratio in the straight running environment, The slip rate control algorithm can not be changed according to the turning state but the constant.

In other words, the study on the existing vehicle slip ratio was set to a constant (generally 0.15 to 0.2) regardless of the state of the road surface or the current state of the vehicle. However, when the slip ratio of the longitudinal axis and the lateral axis is simultaneously considered, It depends on the condition of the road surface and the turning state of the vehicle.

Accordingly, the longitudinal axis controller according to the present invention estimates the ideal slip ratio according to the current turning environment on the basis of Equation (2) below, and calculates the slip ratio of the current vehicle from the wheel speeds of the front / And then the error between the estimated ideal slip ratio and the calculated slip ratio of the vehicle is inputted to the wheel torque controller so that the actual slip ratio of the vehicle is designed to follow the estimated ideal slip ratio.

In the above equation (1),? Represents the slip ratio of the vehicle, V _wheel represents the wheel speed in the linear direction of the _vehicle , and V _vehicle represents the vehicle speed.

는 차량의 선회시 요레이트 값을 나타낸다.In Equation (2),? _D denotes an ideal slip ratio according to the state of the vehicle, k denotes a yaw rate gain constant,

Represents the yaw rate value when the vehicle turns.

Transverse axis controller

In the past, vehicle body transverse slip control has been applied to control the slip angle of the vehicle rather than the yaw rate value. However, this requires an expensive sensor such as a slip angle sensor for direct measurement or a wheel lateral force sensor for indirect estimation .

Accordingly, in order to provide a transverse axis controller having an optimal yaw rate selection algorithm, a reference parameter on the vertical axis and a horizontal axis for the wheel torque control is required, a parameter on the horizontal axis for turning is selected as the yaw rate, For this purpose, the yaw rate of the vehicle is measured using a relatively inexpensive IMU sensor.

The transverse axis controller sets an ideal yaw rate value from the steering angle information based on the driver's will and the current vehicle speed information at the time of turning and inputs an error with the yaw rate value measured in the vehicle to the wheel torque controller, Is applied.

The ideal yaw rate value can be approximated as a function of the vehicle speed and the steering angle of the wheel, which can be expressed as Equation (3) below.

는 이상적인 요레이트 값,

는 차량의 종축으로의 속도,

는 전륜 휠의 조향 각도,

는 차량의 횡축으로의 속도,

는 차량의 무게 중심으로부터 전륜까지의 거리,

은 차량의 무게 중심으로부터 후륜까지의 거리를 나타낸다.In the above equation (3)

Is the ideal yaw rate value,

The speed to the longitudinal axis of the vehicle,

The steering angle of the front wheel,

The speed to the vehicle's horizontal axis,

The distance from the center of gravity of the vehicle to the front wheel,

Represents the distance from the center of gravity of the vehicle to the rear wheel.

Wheel torque controller

The wheel torque controller calculates the error between the ideal slip ratio and the calculated slip ratio of the vehicle and the error received from the transverse axis controller, that is, the ideal yaw rate and the measured yaw rate The left and right wheel torques of the rear wheels calculated based on the following equations (4) and (5) are output by proportionally increasing or decreasing the input torque command value according to the driver's intention and outputting the wheel torque, The function can be implemented without the active safety system such as TCS and VDC mounted by torque.

For reference, the Traction Control System (TCS) is a system that controls the slip rate to within a certain limit so that the maximum driving force can be obtained when the slip rate becomes too large to drive the vehicle. VDC (Vehicle Dynamics Control) This system controls the wheel torque based on the yaw rate so as to prevent oversteer or understeer and ensure stable turning.

은 후륜 좌측 휠토크를 나타내고,

은 후륜 우측 휠토크를 나타내며,

는 운전자 의지로부터 입력받은 휠토크 지령치를 나타내고,

와

는 각각 종축과 횡축으로의 휠토크 이득 상수를 나타낸다.In the above equations (4) and (5)

Represents the rear-left wheel torque,

Represents the rear-right wheel torque,

Represents a wheel torque command value input from the driver's will,

Wow

Represent the wheel torque gain constants on the vertical axis and the horizontal axis, respectively.

Hereinafter, the wheel torque control method of the present invention based on the above system configuration will be described.

The vertical axis controller 10 calculates the optimal slip ratio according to the current turning driving condition on the basis of Equation 2 and feedbacks the front and rear wheel speeds of the actual vehicle to the optimum slip ratio, The slip ratio error value (difference value) obtained by comparing the actual slip ratio calculated based on Equation (1) to the wheel torque controller (30).

In addition, the transverse axis controller 20 calculates an optimal yaw rate value based on the steering angle according to the driver's will and the lateral speed information fed back from the IMU sensor (combined with the acceleration sensor and the gyro sensor) (Difference value) obtained by comparing this optimum yaw rate value with the actual yaw rate value measured in the vehicle is input to the wheel torque controller 30. The yaw rate error value (difference value)

At this time, the wheel torque controller 30 receives the wheel torque command value (the amount of depression of the accelerator pedal and the steering angle information) according to the driver's will and receives the slip ratio error value inputted from the vertical axis controller 10 and the slip ratio error value inputted from the transverse axis controller 20 Based on the received yaw rate error value, the rear wheel torque for optimum acceleration / deceleration and turning is calculated based on Equations (5) and (6) above and applied to the in-wheel motor.

In this manner, the wheel torque controller increases or decreases the torque command value inputted in accordance with the driver's will on the basis of the slip ratio error value and the yaw rate error value, thereby outputting the wheel torque, The safety system function can be implemented, thereby improving the stability of the running of the in-wheel electric automobile at the time of acceleration / deceleration and turning.

Test Example

The simulation for the performance evaluation of the wheel torque control system of the in-wheel electric vehicle according to the present invention was performed based on the parameters shown in Table 1 below.

Simulation tool is performed by interlocking with known Carsim and Simulink. Simulation is performed by receiving feedback of each parameter value of the algorithm performed in the system of the present invention. In the case where the in wheel electric vehicle performs circle- , And the results are shown in the attached FIGS. 4 to 7.

FIG. 6 is a graph showing the vehicle speed and running locus (circle turn) in the case where there is a wheel torque controller including the vertical axis and the horizontal axis controller and in the absence of the wheel torque controller. In the absence of a controller at the same traveling speed, It was found that the vehicle showed a trajectory in which the vehicle left the circle trajectory while the vehicle was running, and the vehicle trajectory in which the vehicle kept the circle trajectory when the controller was present. This means that the wheel output from the wheel torque controller to the in- This is because the active safety system functions such as TCS and VDC are demonstrated by the torque.

As described above, the present invention compensates an error, which is a difference between a slip ratio and a yaw rate value, which are representative control parameters on the vertical and horizontal axes, and a real-time state value, By generating the torque, it is possible to improve the running stability at the time of rapid acceleration and turning.

10: vertical axis controller
20: transverse axis controller
30: Wheel torque controller

Claims (5)

Calculates an optimal slip ratio according to the current turning situation of the in-wheel electric vehicle, calculates the current slip ratio by receiving the feedback of the front and rear wheel speeds, and outputs the error value between the optimal slip ratio and the current slip ratio to the wheel torque controller Axis controller;
A transverse axis controller for calculating an optimum yaw rate value from the steering angle and lateral speed information according to the driver's intention and inputting an error value between the calculated optimum yaw rate value and the actual yaw rate value to the wheel torque controller;
A wheel torque controller for increasing or decreasing a slip ratio error value input from the vertical axis controller and a yaw rate error value input from the horizontal axis controller in proportion to the wheel torque command value according to the driver's chair to output the wheel torque of the rear wheel;
Wherein the wheel torque control system further comprises:
Inputting a slip ratio error value, which is a difference between an ideal slip ratio and an actual vehicle slip ratio, to the wheel torque controller by calculating an ideal slip ratio and a current vehicle slip ratio according to the current turning driving situation in the longitudinal axis controller;
Inputting to the wheel torque controller a yaw rate error value which is a difference between an ideal yaw rate value and an actual yaw rate value calculated from the steering angle information and the current vehicle speed information in the transverse axis controller;
The wheel torque controller receives the wheel torque command value according to the driver's intention and calculates the rear wheel torque for optimum acceleration / deceleration and turning based on the slip ratio error value input from the vertical axis controller and the yaw rate error value input from the horizontal axis controller Calculating;
Wherein the wheel torque control method comprises the steps of:
The method of claim 2,
The ideal slip rate

And the slip rate of the current vehicle is calculated by

And the wheel torque of the in-wheel electric vehicle is calculated.
In the above equation, λ is the slip ratio of the current vehicle, V _wheel is the wheel speed in the linear direction of the _vehicle , V _vehicle is the vehicle speed, λ _d is the ideal slip rate, k is the yaw rate gain constant,

Is the yaw rate value when the vehicle turns.
The method of claim 2,
The ideal yaw rate value

And the wheel torque of the in-wheel electric vehicle is calculated.
In the above equation,

Is the ideal yaw rate value,

The speed to the longitudinal axis of the vehicle,

The steering angle of the front wheel,

The speed to the vehicle's horizontal axis,

The distance from the center of gravity of the vehicle to the front wheel,

Is the distance from the center of gravity of the vehicle to the rear wheel.
The method of claim 2,
The rear wheel torque is:

The left rear wheel torque calculated by the rear left wheel torque calculating means,

And a rear right wheel torque calculated by the rear wheel torque estimating means.
In the above equation,

The rear wheel left wheel torque,

The rear right wheel torque,

A wheel torque command value input from the driver's will,

Wow

Is the wheel torque gain constant on the vertical and horizontal axes, respectively.

Images