A method for assisting drift control of electric vehicles

Abstract

The present invention is applicable to the field of drift control technology and provides an assisted drift control method for electric vehicles, comprising the following steps: calculating the ideal drift balance point and related parameters under any working conditions based on vehicle dynamics and tire models. When the vehicle is in a specific driving mode, it is determined whether the assisted drift intervention threshold is reached based on the driver's operation and the vehicle status. If it is met, the assisted drift control is started. This control uses a feedforward plus feedback method to enable the front and rear wheel torques to work together to achieve drift. At the same time, the weight coefficient is used to adjust the torque from different sources to adjust the assisted drift intervention intensity. When it is detected that the driver's accelerator pedal is less than the threshold, the assisted drift exit threshold is reached and the control is immediately exited. The present invention can intervene in assisted drift in a timely manner when the driver is not operating the steering wheel, lowering the driving threshold, reducing dependence on the steering wheel, and optimizing the driving experience; it can achieve personalized adjustment and improve drift safety, allowing the driver to enjoy the fun of drifting with peace of mind.

Description

Technical Field

[0001] The present invention belongs to the technical field of drift control, and in particular relates to an auxiliary drift control method for an electric vehicle. Background Art

[0002] In professional racing, "drifting" is a common driving strategy used by professional drivers. It aims to reduce lap times or evade obstacles by intentionally controlling wheel locking or slipping. Drifting behavior has the following key characteristics: First, the vehicle experiences a significant slip angle, causing severe sideways sliding. The slip angle here refers to the angle between the vehicle's actual direction of motion and its longitudinal axis. Second, there is a "counter-steering" phenomenon, where the steering wheel angle is turned in the opposite direction of the yaw rate. Third, rear wheel adhesion reaches saturation. When the rear wheels experience significant longitudinal force, the maximum available lateral force is reduced due to the limited adhesion circle, making the vehicle highly susceptible to tailspin.

[0003] These characteristics clearly demonstrate that drifting is a highly demanding and challenging driving technique. The vehicle can easily spin out of control, creating a high degree of risk. Only highly skilled professionals can master it, making it difficult for the average driver. Currently, mainstream drift control methods typically use the steering wheel to adjust the vehicle's posture. This means the driver must release the steering wheel during drifting, or frequently experience hand-slapping. This reduces the average driver's ability to experience the joy of drifting and diminishes their sense of participation.

[0004] Given the aforementioned drawbacks of existing drift control technology, how to achieve drift assistance at any steering wheel angle without actively interfering with the steering wheel, and how to flexibly adjust the drift assistance intensity according to the needs of different drivers, has become an urgent problem to be solved. To this end, the present invention proposes an assisted drift control method for electric vehicles. Summary of the Invention

[0005] The purpose of the present invention is to provide an electric vehicle assisted drift control method, aiming to solve the problems raised in the above background technology.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] An electric vehicle assisted drift control method comprises the following steps:

[0008] Step 1: Calculate the vehicle drift balance point;

[0009] Based on the vehicle dynamics model and the tire model considering nonlinear regions, the ideal drift equilibrium point is calculated for any adhesion coefficient, steering wheel angle, and vehicle speed. The relevant parameters of the ideal drift equilibrium point include the yaw rate, sideslip angle, front wheel lateral force, rear wheel lateral force, rear wheel longitudinal force, and rear wheel speed under the ideal drift condition.

[0010] Step 2: Auxiliary drift intervention threshold judgment;

[0011] When the vehicle is in a specific driving mode, assisted drift control decides whether to intervene based on the detected driver's steering wheel operation, throttle depth, and whether the vehicle is currently unstable;

[0012] Step 3: Assisted drift control;

[0013] Auxiliary drift control is achieved through feedforward plus feedback control, with the sum of feedforward torque and feedback torque used as rear wheel drive torque, and the rear wheel drive torque cooperates with the front wheel differential torque or the differential braking of the front wheel brakes to control vehicle drift;

[0014] Step 4: Auxiliary drift intervention intensity adjustment;

[0015] The weight coefficient is used to adjust the torque calculated by the auxiliary drift control and the driving torque obtained by the driver pressing the accelerator pedal and analyzed by the vehicle controller, and the final vehicle output motor torque is calculated to adjust the auxiliary drift control strength;

[0016] Step 5: Auxiliary drift exit threshold judgment;

[0017] When it is detected that the driver's accelerator pedal is less than a threshold during the assisted drift control, the assisted drift control is exited.

[0018] Furthermore, in step 1, the vehicle dynamics model adopts a three-degree-of-freedom single-track model that takes into account the vehicle longitudinal velocity, yaw rate, and center-of-mass sideslip angle derivative. The specific formula is as follows:

[0019] ;

[0020] ;

[0021] ;

[0022] Where: is the center of mass sideslip angle derivative; is the yaw rate derivative; is the vehicle longitudinal velocity derivative; is the vehicle longitudinal speed; and are the tire lateral forces of the front and rear wheels respectively; is the vehicle's front wheel turning angle; is the yaw angular velocity; is the longitudinal force of the rear tire; and The vehicle mass and The moment of inertia of the shaft; and are the distances from the front and rear axles to the vehicle's center of mass, respectively; is the sideslip angle of the center of mass;

[0023] The tire model considers the coupling relationship between lateral force and longitudinal force when the wheel is in a highly saturated or near-saturated state, and introduces an adhesion circle constraint. The formula is as follows:

[0024] ;

[0025] Where: is the longitudinal force of the tire; is the tire lateral force; is the vertical force of the tire; is the adhesion coefficient between the tire and the ground.

[0026] Furthermore, in step 1, the drift equilibrium point includes a positive rudder drift equilibrium point, i.e., the yaw angular velocity is in the same direction as the steering wheel angle, and a negative rudder drift equilibrium point, i.e., the yaw angular velocity is in the opposite direction to the steering wheel angle. The negative rudder drift equilibrium point always exists.

[0027] Furthermore, in step 2, when the vehicle is in a specific driving mode and meets the ground adhesion conditions, vehicle speed, the steering wheel operated by the driver is greater than a threshold, the throttle is greater than a threshold, and the vehicle is critically unstable, the auxiliary drift control intervenes and performs assisted drift.

[0028] Furthermore, the judgment criterion for critical instability of the vehicle is: the actual yaw rate of the vehicle reaches or exceeds the yaw rate of the ideal drift equilibrium point, and the difference between the actual center of mass sideslip angle of the vehicle and the center of mass sideslip angle of the ideal drift equilibrium point is less than a threshold.

[0029] Furthermore, in step 3, the feedforward torque is obtained by dividing the longitudinal force of the rear wheel at the ideal drift balance point by the tire rolling radius, and then dividing it by the transmission ratio of the relevant transmission system; the feedback torque is obtained by negative feedback control based on the three sets of parameters of ideal yaw angular velocity, center of mass sideslip angle, and rear wheel speed and the actual error.

[0030] Furthermore, in step 3, for a distributed drive electric vehicle, differential driving of the motors on both sides of the front wheels is adopted; for a front-rear drive or pure rear drive electric vehicle, differential braking of the brakes on both sides of the front wheels is adopted to achieve the additional yaw request.

[0031] Furthermore, in step 4, the weight coefficient is between 100% and 0%. For a general pure rear-wheel drive vehicle, the throttle-analyzed front-wheel drive torque is 0 Nm. The final calculation formulas for the vehicle's rear wheel torque, front wheel torque, and front wheel brake are as follows:

[0032] ;

[0033] ;

[0034] ;

[0035] Where: They are the final vehicle rear wheel torque, front wheel torque, and front wheel brake respectively; They are rear wheel torque, front wheel torque, and front wheel brake calculated for auxiliary drift control; The rear wheel torque is obtained by the vehicle controller VCU when the driver steps on the accelerator pedal; is the weight coefficient of the auxiliary drift intervention intensity.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] Lowering the barrier to entry: Traditional drifting requires advanced driving skills, making it difficult for ordinary drivers to achieve. This invention uses a scientific model to calculate the ideal drift equilibrium point. Even without steering control, assisted drift control can intervene at the right time, enabling drifting at any steering wheel angle. This allows ordinary drivers to easily achieve drifting without complex steering wheel operation skills, significantly broadening the audience for drift driving.

[0038] Improved driving experience: Previous mainstream drift control methods can cause drivers to struggle with steering wheel operation during drifting, impacting the driving experience. This invention, through a specific control strategy, reduces reliance on the steering wheel during drifting, allowing drivers to focus more on overall control, improving driving smoothness and comfort.

[0039] Achieve personalized adjustment: Different drivers have different requirements for drift assistance intensity. The present invention utilizes a manually adjustable weight coefficient to enable the driver to freely adjust the intensity of the assisted drift according to his or her own driving habits and skills to meet personalized driving needs.

[0040] Improve drifting safety: During drifting, there is a high risk of the vehicle spinning out of control. This invention effectively reduces this risk through real-time monitoring and precise control, creating a safer drifting environment for the driver, allowing the driver to enjoy the fun of drifting more safely. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1Flow chart of the method of the present invention.

[0042] Figure 2 Examples of images of some ideal drift equilibrium points at different steering wheel angles with a 0.85 adhesion coefficient and a speed of 40 kph; (a) is the ideal center of mass sideslip angle Follow the ideal steering wheel angle The curve of the change, (b) is the ideal yaw rate Follow the ideal steering wheel angle The changing curve, (c) is the ideal rear wheel longitudinal force Follow the ideal steering wheel angle The changing curve.

[0043] Figure 3 This is an experimental diagram of the auxiliary drift control method using the Dongfeng S73 chassis model eπ007 experimental vehicle as an example.

[0044] Figure 4 The drift target following data curve of assisted drift control in a real vehicle; (a) is the drift yaw rate following curve, (b) is the ideal center of mass sideslip angle following curve, (c) is the driver's steering wheel angle curve, and (d) is the assisted drift control trigger flag curve. DETAILED DESCRIPTION

[0045] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0046] The present invention provides an electric vehicle assisted drift control method, the flow chart of which is as follows: Figure 1 As shown, the method includes the following steps:

[0047] Step 1: Calculate the vehicle drift balance point;

[0048] Based on the vehicle dynamics model and the tire model considering the nonlinear region, the ideal drift balance point is calculated under any adhesion coefficient, steering wheel angle, and vehicle speed; the relevant parameters of the ideal drift balance point include the yaw rate, sideslip angle of the center of mass, front wheel lateral force, rear wheel lateral force, rear wheel longitudinal force, and rear wheel speed (rear wheel slip rate) under the ideal drift condition.

[0049] In step 1, the vehicle dynamics model adopts a three-degree-of-freedom single-track model that takes into account the vehicle longitudinal velocity, yaw rate, and center-of-mass sideslip angle derivative. The specific formula is as follows:

[0050] ;

[0051] ;

[0052] ;

[0053] Where: is the center of mass sideslip angle derivative; is the yaw rate derivative; is the vehicle longitudinal velocity derivative; is the vehicle longitudinal speed; and are the tire lateral forces of the front and rear wheels respectively; is the vehicle's front wheel turning angle; is the yaw angular velocity; is the longitudinal force of the rear tire; and The vehicle mass and The moment of inertia of the shaft; and are the distances from the front and rear axles to the vehicle's center of mass, respectively; is the sideslip angle of the center of mass;

[0054] The tire model considers the coupling relationship between lateral force and longitudinal force when the wheel is in a highly saturated or near-saturated state, and introduces an adhesion circle constraint. The formula is as follows:

[0055] ;

[0056] Where: is the longitudinal force of the tire; is the tire lateral force; is the vertical force of the tire; is the adhesion coefficient between the tire and the ground.

[0057] By coupling a qualified vehicle dynamics model with a tire model, the ideal drift equilibrium point can be obtained under arbitrary adhesion coefficients, steering wheel angles, and vehicle speeds. The drift equilibrium points include the forward-steering drift equilibrium point (where the yaw velocity and the steering wheel angle are in the same direction) and the reverse-steering drift equilibrium point (where the yaw velocity and the steering wheel angle are in opposite directions). The forward-steering drift equilibrium point may not exist under some operating conditions, but the reverse-steering drift equilibrium point always exists.

[0058] Step 2: Auxiliary drift intervention threshold judgment;

[0059] Under normal driving conditions, the vehicle's motor torque response is determined by the driver's accelerator pedal depth. However, when the vehicle is in a specific driving mode (Track Drift), Assisted Drift Control determines whether to intervene based on the driver's steering wheel operation, accelerator pedal depth, and whether the vehicle is currently unstable.

[0060] In step 2, assisted drift control intervenes to perform assisted drift only when the vehicle is in a specific driving mode and meets the following conditions: ground adhesion conditions, vehicle speed, driver steering wheel pressure greater than a threshold, throttle pressure greater than a threshold, or critical vehicle instability. The steering wheel and throttle pressure thresholds are directly related to the current ground adhesion conditions and vehicle speed.

[0061] The judgment standard for critical vehicle instability is: the actual yaw rate of the vehicle reaches or exceeds the yaw rate at the ideal drift equilibrium point, and the difference between the actual center of mass sideslip angle of the vehicle and the center of mass sideslip angle at the ideal drift equilibrium point is less than a threshold.

[0062] Step 3: Assisted drift control;

[0063] Assisted drift control is achieved through feedforward and feedback control. The rear wheel longitudinal force at the ideal drift equilibrium point serves as the feedforward control variable, acting on the rear wheel drive torque (i.e., the drive torque of the rear-wheel motor). This portion of the rear wheel drive torque generated by the rear wheel longitudinal force is called the feedforward torque. Simultaneously, the yaw rate, sideslip angle at the ideal drift equilibrium point, and rear wheel speed are combined with the vehicle's actual true values ​​to form the feedback control variable, generating the feedback rear wheel drive torque. This portion of the rear wheel drive torque generated by feedback control is called the feedback torque. Finally, the feedforward torque and the feedback torque are added to obtain the rear wheel drive torque. The rear wheel drive torque and the front wheel differential torque (i.e., the differential torque of the front wheel motor) work together to control vehicle drift. If the front wheels lack differential torque, the front wheel brakes can perform differential braking to achieve the equivalent effect.

[0064] In step 3, the feedforward torque is calculated by dividing the rear wheel longitudinal force at the ideal drift equilibrium point by the tire rolling radius, and then by the transmission ratio of the relevant drivetrain. The feedback torque is obtained by performing negative feedback (PID) control based on the actual error between the ideal yaw rate, center of mass sideslip angle, and rear wheel speed.

[0065] For electric vehicles with different drive forms, distributed drive uses differential drive of the motors on both sides of the front wheels, while front and rear drive or pure rear drive uses differential braking of the brakes on both sides of the front wheels to achieve additional yaw request.

[0066] Step 4: Auxiliary drift intervention intensity adjustment;

[0067] Based on the driving torque and differential torque calculated by assisted drift control, combined with the driving torque analyzed by the vehicle control unit (VCU) when the driver presses the accelerator pedal, the two torques are adjusted using a weighting coefficient. The final vehicle output motor torque is calculated using a formula, allowing for free adjustment of the assisted drift control intensity.

[0068] In step 4, the weight coefficient is between 100% and 0% and can be manually adjusted by the driver. 100% means the vehicle is completely controlled by the auxiliary drift torque, and 0% means the vehicle is completely controlled by the accelerator pedal torque. Most people drift in a pure rear-wheel drive vehicle, so the accelerator-analyzed front-wheel torque is 0 Nm. The final calculation formulas for the vehicle's rear wheel torque, front wheel torque, and front wheel brake are as follows:

[0069] ;

[0070] ;

[0071] ;

[0072] Where: They are the final vehicle rear wheel torque, front wheel torque, and front wheel brake respectively; are respectively the rear wheel torque (i.e., the rear wheel drive torque in step 3), the front wheel torque (i.e., the front wheel differential torque in step 3), and the front wheel brake (generated when the front wheel brake performs differential braking in step 3) calculated by the auxiliary drift control; The rear wheel torque is obtained by the vehicle controller VCU when the driver steps on the accelerator pedal; is the weight coefficient of the auxiliary drift intervention intensity.

[0073] Step 5: Auxiliary drift exit threshold judgment;

[0074] When it is detected that the driver's accelerator pedal is less than a threshold during the assisted drift control process, it is regarded that the driver wants to exit drifting, and the assisted drift control is exited at this time.

[0075] In step 5, a professional driver typically exits drift by reducing rear wheel torque to stop the rear wheels from slipping and return the vehicle to a steady state. Therefore, if the driver's accelerator pedal pressure is detected to be less than a threshold, it can be considered that the driver wants to exit drift. At this time, assisted drift control is terminated, the accelerator pedal torque applied is output, and the vehicle returns to a steady state.

[0076] The specific implementation of the present invention is described in detail below with reference to specific embodiments.

[0077] Example 1: Figure 3 As shown, using the Dongfeng S73 chassis model eπ007 test vehicle as an example, a domain controller based on the TC297 chip was added to the original VCU vehicle controller as an auxiliary drift controller. The vehicle was equipped with Dunlop 235 / 50R20 tires on all four wheels and the auxiliary drift control method was tested at the Wuhan Longlingshan Intelligent Connected Vehicle Test Field. The specific test conditions were set as follows:

[0078] 1) Since this model is a front- and rear-wheel drive electric vehicle, the torque difference algorithm is executed by differential braking of the front wheel brake calipers.

[0079] 2) Through steady-state circular working condition testing, the maximum lateral acceleration was measured and the estimated field adhesion coefficient reached 0.95.

[0080] 3) During assisted drift control, basic vehicle signals such as yaw rate, vehicle speed, and wheel speed are acquired by the chassis Can, while the sideslip angle of the center of mass is obtained by the installed RT3000 inertial navigation system.

[0081] Referring to step 1 of the present invention, the 0.85 adhesion coefficient is calculated based on the relevant parameters of the Dongfeng S73 chassis model eπ007 experimental vehicle. At a speed of 40kph, the curve of the drift balance point of some vehicles changing with the front wheel angle is as follows: Figure 2 As shown in (a) through (c), the triangles represent different ideal equilibrium points when drifting left or right. The curves show that, within a certain range, changes in the front wheel steering angle will cause corresponding changes in the ideal center of mass slip angle, yaw rate, and rear wheel longitudinal force. These parameter changes provide a key theoretical basis for assisted drift control.

[0082] like Figure 4 As shown in Figures (a) through (d), at time t1, the assisted drift control trigger flag is set from 0 to 1, indicating that the assisted drift intervention threshold has been reached. The assisted drift control calculated torque takes over the original vehicle controller torque. During the time period t1 to t2, the assisted drift control trigger flag remains at 1, and assisted drift control is in effect. According to the control strategy in step 3 of the present invention, the actual vehicle yaw rate and center of mass slip angle continuously track the ideal yaw rate and center of mass slip angle calculated from the drift equilibrium point. Simultaneously, the final vehicle output motor torque is calculated according to step 4 of the present invention, combining the driving torque analyzed by the vehicle controller (VCU) when the driver presses the accelerator pedal. This allows for flexible adjustment of the assisted drift control intensity. As the driver turns the steering wheel, the drift equilibrium point is continuously updated and tracked. Around 389 seconds, the steering wheel angle approaches 0°, and the vehicle remains in a drifting state. During the time period t1 to 389 seconds, the vehicle is in a positive rudder drift state, with the steering wheel angle and yaw rate both in the same negative direction. From 389 seconds to t2, the vehicle is in a counter-steering drift state, with the steering wheel angle and yaw rate in opposite directions. Simultaneously, as the steering wheel counter-steering angle increases, the ideal center of mass slip angle at the drift equilibrium point increases, and the vehicle's actual drifting posture becomes more pronounced. At t2, the assisted drift control trigger flag changes from 1 to 0, indicating that the assisted drift exit threshold has been reached, and assisted drift control is now exited.

[0083] The above are only preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, several variations and improvements can be made without departing from the concept of the present invention. These should also be regarded as the scope of protection of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. An electric vehicle assisted drift control method, characterized in that: The following steps are involved: Step 1: Calculate the vehicle drift balance point; Based on the vehicle dynamics model and the tire model considering nonlinear regions, the ideal drift equilibrium point is calculated for any adhesion coefficient, steering wheel angle, and vehicle speed. The relevant parameters of the ideal drift equilibrium point include the yaw rate, sideslip angle, front wheel lateral force, rear wheel lateral force, rear wheel longitudinal force, and rear wheel speed under the ideal drift condition. Step 2: Auxiliary drift intervention threshold judgment; When the vehicle is in a specific driving mode, assisted drift control decides whether to intervene based on the detected driver's steering wheel operation, throttle depth, and whether the vehicle is currently unstable; Step 3: Assisted drift control; Auxiliary drift control is achieved through feedforward plus feedback control. The sum of the feedforward torque and the feedback torque is used as the rear-wheel drive torque. The rear-wheel drive torque cooperates with the front-wheel differential torque or the differential braking of the front wheel brakes to control vehicle drift. For distributed drive electric vehicles, the front-wheel motors are differentially driven. For front-wheel drive or pure rear-wheel drive electric vehicles, the front-wheel brakes are differentially braked to achieve additional yaw request. Step 4: Auxiliary drift intervention intensity adjustment; The weight coefficient is used to adjust the torque calculated by the auxiliary drift control and the driving torque obtained by the driver pressing the accelerator pedal and analyzed by the vehicle controller, and the final vehicle output motor torque is calculated to adjust the auxiliary drift control strength; Step 5: Auxiliary drift exit threshold judgment; When it is detected that the driver's accelerator pedal pressure is less than a threshold during the assisted drift control process, the assisted drift control is exited; In step 1, the vehicle dynamics model adopts a three-degree-of-freedom single-track model that takes into account the vehicle longitudinal velocity, yaw rate, and center-of-mass sideslip angle derivative. The specific formula is as follows: ； ； ； Where: is the center of mass sideslip angle derivative; is the yaw rate derivative; is the vehicle longitudinal velocity derivative; is the vehicle longitudinal speed; and are the tire lateral forces of the front and rear wheels respectively; is the vehicle's front wheel turning angle; is the yaw angular velocity; is the longitudinal force of the rear tire; and The vehicle mass and The moment of inertia of the shaft; and are the distances from the front and rear axles to the vehicle's center of mass, respectively; is the sideslip angle of the center of mass; The tire model considers the coupling relationship between lateral force and longitudinal force when the wheel is in a highly saturated or near-saturated state, and introduces an adhesion circle constraint. The formula is as follows: ； Where: is the longitudinal force of the tire; is the tire lateral force; is the vertical force of the tire; is the adhesion coefficient between the tire and the ground; In step 1, the drift equilibrium points include a positive rudder drift equilibrium point, i.e., a yaw angular velocity and a steering wheel angle are in the same direction, and a negative rudder drift equilibrium point, i.e., a yaw angular velocity and a steering wheel angle are in opposite directions. The negative rudder drift equilibrium point always exists; In step 2, when the vehicle is in a specific driving mode and meets the following conditions: ground adhesion determination, vehicle speed determination, driver-operated steering wheel pressure greater than a threshold, throttle pressure greater than a threshold, and critical vehicle instability, the assisted drift control intervenes to perform assisted drifting. Criteria for determining critical vehicle instability are: the vehicle's actual yaw rate reaches or exceeds the yaw rate at the ideal drift equilibrium point, and the difference between the vehicle's actual center of mass slip angle and the ideal center of mass slip angle at the drift equilibrium point is less than a threshold. In step 3, the feedforward torque is obtained by dividing the rear wheel longitudinal force at the ideal drift balance point by the tire rolling radius, and then by the transmission ratio of the relevant transmission system; The feedback torque is obtained by negative feedback control based on the actual error between the three sets of parameters: ideal yaw rate, center of mass sideslip angle, and rear wheel speed; In step 4, the weight coefficient is between 100% and 0%. For a general pure rear-wheel drive vehicle, the throttle-analyzed front-wheel drive torque is 0 Nm. The final calculation formulas for the vehicle's rear wheel torque, front wheel torque, and front wheel brake are as follows: ； ； ； Where: They are the final vehicle rear wheel torque, front wheel torque, and front wheel brake respectively; They are rear wheel torque, front wheel torque, and front wheel brake calculated for auxiliary drift control; The rear wheel torque is obtained by the vehicle controller VCU when the driver steps on the accelerator pedal; is the weight coefficient of the auxiliary drift intervention intensity.

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