KR102615533B1 - Control method of electronic limited slip differential for electric vehicle - Google Patents

Abstract

The present invention includes the steps of a controller determining the start of handling and driving of an electric vehicle; When it is determined that handling driving has started, the controller determines whether the electric vehicle driving motor is in single mode or dual mode; The controller determining whether the electric vehicle is in an acceleration state or a regenerative braking state; The controller receiving the current motion state value of the electric vehicle and comparing and calculating an error with the intended motion state value; and controlling, by the controller, the electronic limited-slip differential with a torque value and torque change rate optimized for the single mode or the dual mode.

Description

Control method of electronic limited slip differential for electric vehicles {CONTROL METHOD OF ELECTRONIC LIMITED SLIP DIFFERENTIAL FOR ELECTRIC VEHICLE}

The present invention relates to a control method of an electronic limited-slip differential for an electric vehicle, and more specifically, to a control method of an electronic limited-slip differential for an electric vehicle that can improve handling and driving stability.

Recently, vehicles are equipped with an electronic limited slip differential (e-LSD) to improve handling performance and rough terrain escape performance by controlling torque distribution between left and right drive wheels.

When driving on a curved road instead of driving straight, the left and right drive wheels must rotate at different rotation speeds, so the differential function is essential. However, the unrestricted differential function has problems such as making it difficult to escape from rough roads, so a limited-slip differential device that appropriately limits the differential function is used. And the electronically controlled e-LSD can actively control torque distribution between the left and right driving wheels using electrical signals. Therefore, in a vehicle equipped with an e-LSD, if understeer or oversteer occurs during handling (cornering), the vehicle body can be corrected by controlling the e-LSD.

However, the e-LSD control method used in conventional internal combustion engine vehicles cannot be directly applied to electric vehicles driven by drive motors. In particular, electric vehicles driven by dual motors have several characteristics that distinguish them from internal combustion engine vehicles, such as the front and rear wheels being driven independently by separate motors, the accelerator pedal being more responsive than that of an internal combustion engine, and deceleration using regenerative braking. Because.

Therefore, a control method for an electronic limited-slip differential for electric vehicles that suits the characteristics of electric vehicles is needed.

The purpose of the present invention is to provide a control method of an electronic limited-slip differential for electric vehicles that suits the characteristics of electric vehicles.

In order to achieve the above-mentioned object, the present invention includes the steps of a controller determining the start of handling and driving of an electric vehicle; When it is determined that handling driving has started, the controller determines whether the electric vehicle driving motor is in single mode or dual mode; The controller determining whether the electric vehicle is in an acceleration state or a regenerative braking state; The controller receiving the current motion state value of the electric vehicle and comparing and calculating an error with the intended motion state value; and controlling, by the controller, the electronic limited-slip differential with a torque value and torque change rate optimized for the single mode or the dual mode.

In addition, according to an embodiment of the present invention, the step of the controller determining the start of handling driving of the electric vehicle is to determine the start of handling driving when the speed, steering angle, steering angle speed, lateral acceleration, and yaw rate of the electric vehicle all exceed the set values. You can.

In addition, according to an embodiment of the present invention, the step of determining whether the electric vehicle driving motor is single mode or dual mode by the controller includes determining whether the electric vehicle is a vehicle model equipped with an electronic limited-slip differential; Determining whether the electric vehicle is equipped with a single motor or an electric vehicle with a dual motor; and determining that an electric vehicle equipped with a single motor and an electric vehicle in which the motor torque of one of the dual motors is 0 or less is in single mode, and an electric vehicle in which the motor torques of both dual motors are greater than 0 is determined in a dual mode; may include.

In addition, according to an embodiment of the present invention, in the step of the controller determining whether the electric vehicle is in an acceleration state or a regenerative braking state, the controller determines the acceleration state if the accelerator pedal opening amount is a positive value, and if the accelerator pedal opening amount is 0 and the regenerative braking state is performed, the controller determines the electric vehicle to be in an acceleration state. If the braking torque is a positive value, it can be determined to be in a regenerative braking state.

In addition, according to an embodiment of the present invention, when the electric vehicle is determined to be in an acceleration state, the controller receives the steering angle, lateral acceleration, and yaw rate values of the electric vehicle, and determines the driver's intended yaw rate value and the actual received yaw rate value. By comparing, the error can be calculated, and the torque value and torque change rate of the electronic limited-slip differential device can be controlled according to the error and the lateral acceleration value.

In addition, according to an embodiment of the present invention, when the electric vehicle is determined to be in a regenerative braking state, the controller receives the current regenerative braking torque value and adjusts the torque value and torque change rate of the electronic limited-slip differential according to the regenerative braking torque value. You can control it.

The control method of the electronic limited-slip differential for electric vehicles according to the present invention can control the electronic limited-slip differential for electric vehicles according to the characteristics of the electric vehicle.

As a result, the handling and driving performance of the electric vehicle is greatly improved.

1 is a flowchart showing a control method of an electronic limited-slip differential for an electric vehicle according to an embodiment of the present invention;
FIG. 2 is a diagram illustrating in detail the handling driving start determination of FIG. 1;
Figure 3 is a detailed diagram showing the single/dual mode determination of Figure 1;
Figure 4 is a diagram showing in detail the acceleration state determination of Figure 1;
Figure 5 is a detailed view showing the e-LSD agile driving performance control of Figure 1;
Figure 6 is a diagram showing the regenerative braking judgment of Figure 1 in detail;
Figure 7 is a diagram showing the e-LSD regenerative braking linkage control of Figure 1 in detail;
Figure 8 is a diagram comparing an electric vehicle equipped with an e-LSD and an electric vehicle not equipped with an e-LSD controlled according to an embodiment of the present invention in single mode;
Figure 9 is a diagram comparing an electric vehicle equipped with an e-LSD and an electric vehicle not equipped with an e-LSD controlled according to an embodiment of the present invention in dual mode.

Hereinafter, a method of controlling an electronic limited slip differential for an electric vehicle according to an embodiment of the present invention will be described in detail with reference to the attached drawings.

FIG. 1 is a flowchart showing a control method of an electronic limited-slip differential for an electric vehicle according to an embodiment of the present invention, FIG. 2 is a detailed diagram showing the handling start determination of FIG. 1, and FIG. 3 is a single/dual mode determination of FIG. 1. A drawing showing in detail, FIG. 4 is a drawing showing in detail the acceleration state determination in FIG. 1, FIG. 5 is a drawing showing in detail the e-LSD agile driving performance control in FIG. 1, and FIG. 6 is a drawing showing in detail the regenerative braking determination in FIG. 1. , FIG. 7 is a diagram showing the e-LSD regenerative braking linkage control of FIG. 1 in detail.

Unlike internal combustion engine vehicles that are driven by engines, electric vehicles (EVs) are driven by motors. The power source of the motor may be various, such as a battery or fuel cell. The drive motor may be provided singly or may be provided in plural numbers. A typical passenger electric vehicle has two drive axles, one on the front wheel and one on the rear wheel, but a dual-motor electric car with two drive motors is equipped with a front-wheel drive motor that provides driving force to the front wheels and a rear-wheel drive motor that provides driving force to the rear wheels. Two drive motors transmit torque to the front and rear wheels, respectively, enabling four-wheel drive. In other words, front-wheel torque and rear-wheel torque come from independent drive motors, which distinguishes them from internal combustion engine vehicles that transmit power to all drive wheels with a single engine.

In a dual-motor electric vehicle, the front-wheel drive motor and rear-wheel drive motor can have different maximum torques, and can produce different torques while driving. The torque distribution of this dual motor can be appropriately controlled according to various conditions, such as the weight distribution (center of gravity) or acceleration of the electric vehicle.

Cornering or turning through sharp curves is called handling driving. During the handling drive, the vehicle moves in a yawing manner. However, in the above handling driving conditions, such as excessive entry speed or sharp steering angle, rear wheel grip may be lost and slip may occur, causing an oversteer phenomenon in which the vehicle turns larger than the intended yaw rate. Conversely, if the front wheel, which is responsible for steering, loses grip, an understeer phenomenon may occur where the vehicle cannot turn at the intended yaw rate.

At this time, the electronic limited slip differential (e-LSD) controls the torque distribution of the left and right wheels in real time to maintain the vehicle body stably in oversteer and understeer situations. As a specific example, when understeer occurs, greater torque is transmitted to the outer wheels than to the inner wheels, and when oversteer occurs, greater torque is transmitted to the inner wheels than the outer wheels. This torque distribution must be done very quickly and accurately.

The electric vehicle is equipped with a controller that electronically controls the e-LSD. The controller is connected to various sensors of the electric vehicle and can receive various information about the movement of the vehicle body.

Referring to FIG. 1, a method of controlling an electronic limited slip differential for an electric vehicle according to an embodiment of the present invention includes the steps of the controller determining the start of handling of the electric vehicle (S100); When it is determined that handling driving has started, the controller determines whether the electric vehicle driving motor is in single mode or dual mode (S200); A step of the controller determining whether the electric vehicle is in an acceleration state or a regenerative braking state (S300); The controller receiving the current motion state value of the electric vehicle and comparing and calculating an error with the intended motion state value; and the controller controlling the electronic limited-slip differential with a torque value and torque change rate optimized for the single mode or the dual mode.

In this embodiment, the controller determines whether handling has started. In order to determine handling driving, the vehicle's speed, steering angle, steering angular velocity, lateral acceleration, and yaw rate are compared to determine whether they exceed the set values, and if they all exceed the set values, it is judged as handling driving.

If it is determined that handling and driving have started, the controller goes through a step of determining whether the electric vehicle is equipped with an e-LSD (S210) and, if it is a model equipped with an e-LSD, goes through a step of determining whether it has a single motor specification (S220).

If it is a single motor specification, it is judged to be in single mode operation. In this embodiment, single mode means a state in which only the rear wheel side drive motor is operated.

If it is a dual motor specification, a step (S230) is made to determine whether the motor torque of one of the dual motors is 0 Nm or less. Even if an electric vehicle has dual motor specifications, if the torque of any one motor is less than 0 Nm, it is judged as single mode, and if the torque of both dual motors exceeds 0 Nm, it is judged as dual mode.

Single mode is rear-wheel drive (two-wheel drive) with torque transmitted only to the rear wheels, and dual mode is front-wheel drive (four-wheel drive) with power transmitted to both front and rear wheels.

What to note here is that even if the vehicle is equipped with a dual motor, if the current output torque of one of the two motors is 0 Nm or less, it has substantially the same characteristics as a single motor electric vehicle, so it is important to check whether the torque of one of the two motors is 0 Nm or less. A further step is taken to determine whether or not it is possible.

Next, determine whether the electric vehicle is in acceleration state. Here, the acceleration state refers to the state in which the driver is pressing the accelerator pedal. Therefore, the accelerator pedal opening amount is measured, and if the opening amount (%) is a positive number, the acceleration state is determined.

The controller is connected to various sensors that measure motion information of the vehicle body through CAN communication. Examples of information received by the controller include steering angle, lateral acceleration, and yaw rate values.

The controller calculates an error by comparing the actual yaw rate value with the driver's intended yaw rate value. If the actual yaw rate is greater than the intended yaw rate by more than the set value, it is judged as oversteer. If it is less than the set value, it is judged as understeer. Steering angle information is added to determine countersteer.

Each oversteer, understeer, and countersteer state is controlled using the e-LSD torque value and torque change rate optimized according to the previously determined single mode or dual mode. For example, even in the same oversteer state, the left and right torque distribution values and torque change rates in the e-LSD may be set differently depending on the single mode and dual mode. In this way, the e-LSD actively intervenes and changes the left and right torque, thereby controlling the unstable vehicle body and achieving stable driving.

If none of the oversteer, understeer, and countersteer conditions apply, the vehicle is operating normally and enters the e-LSD control standby state. In the e-LSD control standby state, active intervention of the e-LSD does not occur.

If the electric vehicle is not accelerating, determine whether it is in regenerative braking. Unlike internal combustion engine vehicles, electric vehicles are equipped with a regenerative braking system to improve driving range. The regenerative braking system is known as a system that converts kinetic energy when a vehicle decelerates into electrical energy and stores it in the battery.

When the driver presses the brake pedal, regenerative braking does not operate and the vehicle decelerates due to the friction force of the brake. Therefore, if the driver steps on the brake pedal, it is determined that the vehicle is in a deceleration state.

If the driver does not press the brake pedal and the regenerative braking torque value is positive, it is judged to be in a regenerative braking state.

If the electric vehicle is determined to be in regenerative braking, the e-LSD is controlled in conjunction with regenerative braking. Regenerative braking can be set to several levels by the driver, and the regenerative braking torque value is determined according to the regenerative braking level. If set to a large level, the deceleration will be more rapid, and if set to a small level, the deceleration will be more gradual.

The controller receives the set regenerative braking level or current regenerative braking torque value and determines whether it is single mode or dual mode. In addition, the e-LSD is controlled with the e-LSD torque value and torque change rate optimized for single mode and dual mode, respectively. The e-LSD torque value when not in the regenerative braking state may be different from the e-LSD torque value in the regenerative braking state. In regenerative braking, the vehicle decelerates quickly, and the larger the regenerative braking torque value, the greater the acceleration. Therefore, the degree of deceleration is calculated and the torque distribution in the e-LSD is optimized for regenerative braking.

Hereinafter, the effects of the electronic limited-slip differential for electric vehicles according to this embodiment will be described.

Figure 8 is a diagram comparing an electric vehicle equipped with an e-LSD and an electric vehicle not equipped with an e-LSD controlled according to an embodiment of the present invention in single mode. (a) is an electric vehicle without an e-LSD, and (b) is an electric vehicle with an e-LSD.

In an electric vehicle without an e-LSD, as shown in (a), the torque applied to the inner and outer rear wheels is evenly distributed when turning.

However, when a driving force greater than the contact force between the rear wheels and the road surface is transmitted during an acceleration turn of an electric vehicle, slip may occur on the inner rear wheel, resulting in loss of driving torque, and the vehicle may not be able to maintain a stable posture.

On the other hand, as shown in (b), an electric vehicle equipped with an e-LSD controlled according to this embodiment can actively distribute greater torque to the outer rear wheels based on the turning direction by the e-LSD. Accordingly, the possibility of slip of the inner rear wheel can be reduced and driving torque loss can also be reduced. As a result, the limit handling performance of electric vehicles increases, making sharp turning movements at higher speeds possible.

Figure 9 is a diagram comparing an electric vehicle equipped with an e-LSD and an electric vehicle not equipped with an e-LSD controlled according to an embodiment of the present invention in dual mode. (a) is an electric vehicle without an e-LSD, and (b) is an electric vehicle with an e-LSD.

In an electric vehicle without an e-LSD, as shown in (a), the torque applied to the inner and outer rear wheels is evenly distributed when turning.

However, when a driving force greater than the contact force between the rear wheels and the road surface is transmitted during an acceleration turn of an electric vehicle, slip may occur on the inner rear wheel, resulting in loss of driving torque, and the vehicle may not be able to maintain a stable posture.

On the other hand, as shown in (b), an electric vehicle equipped with an e-LSD controlled according to this embodiment can actively distribute greater torque to the outer rear wheels based on the turning direction by the e-LSD. Accordingly, the possibility of slip of the inner rear wheel can be reduced and driving torque loss can also be reduced.

However, the increased torque due to such e-LSD control may cause slip in both the inner and outer rear wheels. In other words, an example is a case where the increased torque at the outer rear wheel is greater than the grip force, and the torque is reduced at the inner rear wheel, but it is still greater than the grip force.

In this case, the road grip of the rear wheels can be secured by reducing the rear-wheel side motor torque itself, which drives the rear wheels, or, conversely, by increasing the front-wheel side motor torque.

Therefore, in the case of dual mode, oversteering can be reduced by increasing the longitudinal acceleration of the vehicle body in the electric vehicle steering direction through control such as increasing the motor torque on the front wheel side when necessary. As a result, the limit handling performance of electric vehicles increases, making sharp turning movements at higher speeds possible.

Claims (6)

A controller determining the start of handling and driving of an electric vehicle;
When it is determined that handling driving has started, the controller determines whether the electric vehicle driving motor is in single mode or dual mode;
The controller determining whether the electric vehicle is in an acceleration state or a regenerative braking state;
The controller receiving the current motion state value of the electric vehicle and comparing and calculating an error with the intended motion state value; and
Comprising the step of the controller controlling the electronic limited-slip differential with a torque value and torque change rate optimized for the single mode or the dual mode,
The step of the controller determining whether the electric vehicle driving motor is single mode or dual mode includes determining whether the electric vehicle is a vehicle model equipped with an electronic limited-slip differential; Determining whether the electric vehicle is equipped with a single motor or an electric vehicle with a dual motor; And judging an electric vehicle equipped with a single motor and an electric vehicle in which the motor torque of one of the dual motors is 0 or less as single mode, and determining an electric vehicle in which the motor torques of both dual motors are greater than 0 as a dual mode. Control method of electronic limited-slip differential. According to paragraph 1,
The step where the controller determines the start of handling and driving of the electric vehicle is:
A control method for an electronic limited-slip differential for an electric vehicle that determines the start of handling when the speed, steering angle, steering angle speed, lateral acceleration, and yaw rate of the electric vehicle all exceed the set values. delete According to paragraph 1,
The step of the controller determining whether the electric vehicle is in an acceleration state or a regenerative braking state,
The controller determines the acceleration state when the accelerator pedal opening amount is a positive value, and determines the regenerative braking state when the accelerator pedal opening amount is 0 and the regenerative braking torque is a positive value. According to paragraph 4,
When the electric vehicle is judged to be accelerating,
The controller receives the steering angle, lateral acceleration, and yaw rate values of the electric vehicle, calculates an error by comparing the yaw rate value intended by the driver and the actual received yaw rate value, and calculates the error according to the error and the lateral acceleration value. A control method of an electronic limited-slip differential for electric vehicles that controls the torque value and torque change rate of the limited-slip differential. According to paragraph 4,
If the electric vehicle is determined to be in regenerative braking,
A method of controlling an electronic limited-slip differential for an electric vehicle, wherein the controller receives a current regenerative braking torque value and controls the torque value and torque change rate of the electronic limited-slip differential according to the regenerative braking torque value.