CN106114287B - A kind of electric automobile antiskid control system and control method - Google Patents

Abstract

The invention provides an anti-skid control system for an electric vehicle, comprising a vehicle control unit, a PID controller, a drive motor, a TA _max memory and a TA value detection module, the vehicle control unit is connected to the PID controller and the drive motor, the TA value detection module and the drive The motor is connected to the PID controller, the TA _max memory is connected to the PID controller, the vehicle control unit is used to excite the driving motor, the TA value detection module is used to detect the TA value signal output by the driving motor, and the PID controller compares the TA _max value and the TA value And send instructions to the vehicle control unit so that the TA value is always smaller than the TA _max value. The TA _max memory is used to store the TA _max value. The TA value is equal to the ratio of the driving wheel angular acceleration to the motor torque. The electric vehicle anti-skid control system disclosed in the present invention uses the parameter TA instead of the traditional slip rate, avoids the measurement of the vehicle speed signal, does not need the equipment for measuring the vehicle speed, and does not need to rely on the assistance of the traditional hydraulic braking system at the same time, reducing the production costs and improved system stability.

Description

An electric vehicle anti-skid control system and control method

technical field

The invention relates to the field of electric vehicles, in particular to an electric vehicle anti-skid control system and control method based on the ratio of wheel angular acceleration and motor torque.

Background technique

From a control point of view, the main advantage of an electric motor over an internal combustion engine is that it can be used both as a drive and as an actuator. As a driving device, its small size and high power output allow it to have a variety of vehicle drive configurations. As an actuator, the fast response characteristics and torque information feedback realize more accurate and effective dynamic real-time control. Therefore, electric vehicles are not only green and environmentally friendly, but also a driving experience with higher active safety, handling stability and better ride comfort can be realized through advanced electrification control technology.

In the safety anti-skid control of vehicles, anti-lock braking system (ABS) and traction control system (TCS) are used in traditional internal combustion engine vehicles to realize relevant functions. It usually adopts a two-parameter control method to evaluate the wheel slip condition when the vehicle is running. The two-parameter control method needs to measure the necessary information of vehicle speed and wheel speed, and then use it to calculate the slip ratio. Slip rate is one of the widely used parameters to indicate the state of wheel locking or slipping. In the two-parameter control method, it is necessary to limit the slip rate to prevent the wheel from slipping. Traditional anti-skid controllers use slip ratio to represent the locked or slipped state of the wheels. When the vehicle accelerates, assuming ωr>v, the slip rate is defined as:

where v is the longitudinal velocity of the vehicle, ω is the angular velocity of the wheel, and r is the equivalent radius of the wheel. When the vehicle decelerates, since ωr<v, the slip rate expression can be written as:

The relationship between the slip ratio and the friction coefficient of the road surface is more complicated. The friction coefficient of the road surface is a scalar quantity used to express the ratio between the friction force and the vertical normal pressure, which is defined as follows:

where F _f is the friction force and F _n is the vertical normal pressure.

As shown in Figure 1, before the road surface friction coefficient reaches its maximum value (the slip rate corresponding to the maximum value is usually between 0.1 and 0.3), the road surface friction coefficient is an increasing function of the slip rate, and this region is called Linear region, in the linear region, the running state of the wheel is stable and controllable, so it is also a stable region. After this region, as the slip ratio becomes larger, not only the road surface friction coefficient starts to decrease, but also enters an unstable region. In the unstable region, the running state of the wheel is unstable and severe skidding may occur. Therefore, the slip rate is usually limited by the vehicle's anti-skid controller to a corresponding safe area.

The traditional two-parameter control method of limiting the slip rate has been widely used in the controllers of the anti-lock braking system and traction control system in the industry. However, on the one hand, this method relies on the hydraulic brake mechanism to complete the action execution, which increases the cost of the brake; on the other hand, this method requires the necessary sensing equipment to complete the accurate measurement of the vehicle speed, such as accelerometers, optical sensors, GPS, etc. These devices will lead to an increase in cost; the increase in the devices also makes it prone to failure or signal failure under certain specific conditions, such as the difficulty in obtaining GPS signals in tunnels. For motor-driven electric vehicles, the advantages of fast response of the motor body can be fully utilized, and the corresponding anti-skid control system can be designed by taking advantage of its characteristics as both an actuator and a sensor.

Different from the traditional two-parameter anti-skid control, the present invention makes full use of the unique advantage of the electric vehicle that the motor torque can be obtained quickly and accurately, and designs a new parameter TA to replace the traditional slip rate method to carry out vehicle anti-skid control. Skid control. In the new parameter TA, the torque value of the motor and the acceleration value of the wheel are used for calculation, both of which are very easy to obtain on electric vehicles, without additional sensors; at the same time, no hydraulic brakes are required. With the cooperation of the moving system, the motor body is directly used as the actuator. Therefore, the present invention is a low-cost efficient anti-skid control method suitable for electric vehicles.

Contents of the invention

The technical problem to be solved by the present invention is to use a new parameter TA to replace the traditional slip rate method. In order to solve the above problems, the present invention provides an electric vehicle anti-skid control system, including a vehicle control unit, a PID controller, a drive motor, The TA _max memory is connected to the TA value detection module, the vehicle control unit is connected to the PID controller and the drive motor, the TA value detection module is connected to the drive motor and the PID controller, the TA _max memory is connected to the PID controller, and the vehicle control unit is used to drive the drive The motor, the TA value detection module is used to detect the TA value signal output by the driving motor, the PID controller compares the TA _max value and the TA value and sends an instruction to the vehicle control unit so that the TA value is always smaller than the TA _max value, and the TA _max memory is used for storage TA _max value, TA value is equal to the ratio of driving wheel angular acceleration and motor torque.

Further, the PID controller includes a PI controller.

Further, the anti-slip control system also includes a low-pass filter, which is used to remove high-frequency noise generated during the calculation of the angular acceleration of the driving wheels.

The present invention also discloses a control method of an electric vehicle anti-skid control system, which includes the following steps:

Step 1: The TA value detection module detects the TA value during the operation of the drive motor and transmits it to the PID controller;

Step 2: The PID controller compares the TA value and the TA _max value, and when the TA value is greater than the TA _max value, the PID controller transmits an instruction to reduce the torque to the vehicle control unit;

Step 3: The vehicle control unit applies the torque to be output to the driving motor, and the angular acceleration of the driving wheel is reduced, so that the TA value is smaller than the TA _max value.

Further, in step 2, the TA value is calculated by the following formula (4):

where T is the motor torque; ω is the angular velocity of the drive wheel, is the angular acceleration of the driving wheel.

Further, TA _max is calculated by the following formula (7):

Among them, α is the ratio of the vehicle running acceleration to the equivalent linear acceleration of the wheel, M is the mass of the vehicle, J is the moment of inertia of the wheel, and r is the radius of the wheel.

The present invention has following beneficial effect:

1. A kind of anti-skid control method for electric vehicles based on the wheel angular acceleration and motor torque ratio of the present invention uses the parameter TA to replace the traditional slip rate, and does not require equipment for accurate measurement of vehicle speed, which reduces production costs and improves System stability.

2. In the electric vehicle anti-skid control system based on the wheel angular acceleration and motor torque ratio of the present invention, the motor body is used as the actuator to adjust the driving torque in real time and quickly, without the cooperation of the hydraulic brake of the traditional anti-skid system, which further reduces the Device dependent.

3. The TA single parameter control used in the electric vehicle anti-skid control method based on the wheel angular acceleration and motor torque ratio of the present invention fully utilizes the unique advantage that the motor torque can be obtained quickly and accurately, and the algorithm is concise and easy to implement.

Description of drawings

Figure 1 is a schematic diagram of the relationship between friction coefficient and slip rate.

Figure 2 is a schematic diagram of the wheel dynamics of an electric vehicle.

FIG. 3 is a structural schematic diagram of an electric vehicle anti-skid control system based on the ratio of wheel angular acceleration and motor torque according to the present invention.

Fig. 4 is a graph of the corresponding relationship between the single parameter TA and the ratio of the vehicle running acceleration and the equivalent linear acceleration of the wheel in the anti-skid control system.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and with reference to the data. It should be understood that the embodiments are only for illustrating the present invention and not limiting the scope of the present invention in any way.

As shown in Figure 3, a kind of antiskid control system and method of electric vehicle of the present invention, comprise vehicle control unit, PID controller, drive motor and TA value detection module, vehicle control unit is connected with PID controller and drive motor, TA value The detection module is connected to the drive motor and the PID controller. The vehicle control unit is used to excite the drive motor. The TA value detection module is used to detect the TA value signal output by the drive motor. The PID controller compares the TA _max value and the TA value and sends instructions to the vehicle The control unit makes the TA value always smaller than the TA _max value, and the TA _max memory is used to store the TA _max value, and the TA value is equal to the ratio of the drive wheel angular acceleration to the motor torque. When the driver of the vehicle depresses the accelerator pedal, a torque command is sent to the vehicle control unit. The PID controller applies the required output torque to the drive motor through a typical proportional-integral-derivative (PID) control, and the PID controller is used to limit the monitoring parameter TA of wheel slip, keeping it stable within its own safe area, so as to Prevent wheel slipping; in one embodiment the PID controller is a PI controller.

The definition of TA among the present invention is represented by formula (4):

where T is the motor torque; ω is the angular velocity of the drive wheel, is the driving wheel angular acceleration;

As shown in Figure 2, the dynamic expression of a car tire running is as follows:

Where M is the mass of the vehicle, v is the vehicle speed, f is the road resistance, ω is the angular velocity of the driving wheel, J is the moment of inertia of the tire, T is the motor torque, and r is the wheel radius.

If α is defined as the ratio of the vehicle's driving acceleration to the equivalent linear acceleration of the wheel, the following formula:

Further, combined with formula (4)(5)(6) derivation, it can be derived that TA is calculated by the following formula (7):

The value of TA _max can be obtained according to the value range of α.

The invention also discloses an anti-skid control method for electric vehicles based on the ratio of wheel angular acceleration and motor torque, comprising the following steps:

Step 1: The TA value detection module detects the TA value during the operation of the drive motor and transmits it to the PID controller;

Step 2: The PID controller compares the TA value and the TA _max value, and when the TA value is greater than the TA _max value, the PID controller transmits an instruction to reduce the torque to the vehicle control unit;

Step 3: The vehicle control unit applies the torque to be output to the driving motor, and the angular acceleration of the driving wheel is reduced, so that the TA value is smaller than the TA _max value.

In the embodiment shown in FIG. 3 , the first step needs to evaluate the value of TA while the vehicle is running. Use the motor torque T fed back by the drive motor itself in real time and the drive wheel angular acceleration delivered by the drive motor Input to the TA value detection module to obtain the corresponding evaluation value in real time. Since vehicle dynamics control (including antiskid control) is usually required to be performed in a relatively low frequency range (100-1000 Hz), a low-pass filter can be used to remove possible high frequencies in the calculation of drive wheel angular acceleration noise.

The second step of implementation requires evaluating the allowable range of TA values for maintaining safe slip while the vehicle is in motion. In the design process of the anti-skid controller, the TA value will be limited in its safe area, and this limit value is represented by TA _max in Fig. 3.

According to the standard definition of slip ratio, it is calculated from the ratio of the vehicle speed v to the tire line speed, and one of its expressions is as follows (8):

Definition α is the ratio of the vehicle running acceleration to the equivalent linear acceleration of the wheel, as shown in the following formula (9):

Combining the above two formulas, the slip rate λ can be deduced as the following formula (10):

The control limit of α is related to slip rate λ, assuming that the value of α is bounded, its upper limit is α _H , and the lower limit is α _L , then the range of slip rate λ in the above formula can be expressed by the following formula:

According to the empirical range of the allowable slip rate of the tire during vehicle running, it can be known that the slip rate λ is generally between 0.1-0.3 to achieve safe driving. According to the above formula, it can be deduced that the safe range of α is between 0.7 and 0.9. From formula (7), the maximum value limit of TA can be obtained as follows:

In the third step of implementation, in Fig. 3, when the measured TA value exceeds TA _max , the controller considers that the wheels are slipping. At this time, the PID controller calculates the torque value that needs to be output, and the torque value that needs to be output makes the TA value smaller than the TA _max value, and reduces the angular acceleration of the driving wheel by reducing the torque control command. It is easy for those skilled in the art to know that when the motor torque T decreases, the drive wheel angular acceleration will also decrease accordingly, due to the angular acceleration of the driving wheel in the slipping state The magnitude of the reduction is larger, so that the TA value is controlled to decrease so as not to exceed the TA _max value. During this control process, TA will be kept within a reasonable range in order to ensure that the driving wheels do not enter a slipping state.

The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make many modifications and changes according to the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art shall be within the scope of protection defined by the claims.

Claims (5)

1. Electric steamThe vehicle antiskid control system is characterized by comprising a vehicle control unit, a PID controller, a driving motor and a TA _max The vehicle control unit is connected with the PID controller and the driving motor, the TA value detection module is connected with the driving motor and the PID controller, and the TA value detection module is connected with the driving motor and the PID controller _max The storage is connected with the PID controller, the vehicle control unit is used for exciting the driving motor, the TA value detection module is used for detecting a TA value signal output by the driving motor, and the PID controller compares the TA value signal _max Value and TA value and sending a command to the vehicle control unit to cause the TA value to be less than the TA at all times _max Value, said TA _max A memory for storing the TA _max A value, said TA value being equal to the ratio of the drive wheel angular acceleration and the motor torque.

2. The anti-skid control system for electric vehicle of claim 1, wherein said PID controller comprises a PI controller.

3. An electric vehicle antiskid control system according to claim 1, wherein said antiskid control system further comprises a low-pass filter for removing high-frequency noise generated in calculation of angular acceleration of said driving wheel.

4. A control method of an electric automobile antiskid control system is characterized by comprising the following steps:

the method comprises the following steps: the TA value detection module detects a TA value in the running process of the driving motor and transmits the TA value to the PID controller, wherein the TA value is obtained by calculating according to the following formula (4):

wherein T is motor torque; omega is the angular velocity of the drive wheel,is the drive wheel angular acceleration;

step two: the PID controller compares the TA value with the TA _max Value when TA is greater than TA _max When the value is positive, the PID controller transmits a command to reduce the torque to the vehicle control unit;

step three: the vehicle control unit applies the torque required to be output to the driving motor, the angular acceleration of the driving wheel is reduced, and therefore the TA value is smaller than TA _max The value is obtained.

5. The control method of claim 4, wherein the TA _max Calculated by the following equation (7):

wherein alpha is the ratio of the vehicle running acceleration to the wheel equivalent linear acceleration, the value of alpha is assumed to be bounded, and the lower limit is alpha _L M is the vehicle mass, J is the wheel moment of inertia, and r is the wheel radius.