A vehicle stability control method based on drift balance

Abstract

The present invention relates to a vehicle stability control method based on drift balance. A stability control method based on drift balance is added to a traditional vehicle stability control method to improve the stability control effect of the vehicle under extreme conditions. Specifically, a conventional stability control mode, an active drift stability control mode, and a passive drift stability control mode are set. In the conventional stability control mode, a reference value is established by a linear two-degree-of-freedom model. In the two drift stability control modes, a nonlinear two-degree-of-freedom model is used to calculate the reference value. Different reference value calculation methods and different state parameter selection methods are used in different modes. The triggering and switching methods of each mode are determined by establishing a drift condition coefficient, a driver operation coefficient, an environmental threat coefficient, and a lateral state coefficient.

Description

Technical Field

[0001] The present invention belongs to the field of vehicle stability control, and in particular relates to a vehicle stability control method based on drift balance. Background Art

[0002] Electronic stability control is an active vehicle safety feature that provides yaw torque through driving and braking to suppress understeering or oversteering tendencies of the vehicle, preventing the vehicle from losing steering ability and stability.

[0003] Traditional vehicle stability control typically uses a linear two-degree-of-freedom vehicle model as a reference model to implement feedback control. This approach fails to account for the nonlinear characteristics of tires, making it difficult to obtain accurate tire forces. Furthermore, the reference value is limited based on road conditions, making it incapable of describing the vehicle's driving behavior under extreme conditions such as large slip angles and rear tire force saturation. Furthermore, control effectiveness is limited when the vehicle is unstable.

[0004] Drifting is an unconventional driving technique that uses a combination of the brake pedal, accelerator pedal, parking brake, and steering wheel to push the rear wheels to their limit of adhesion, causing them to skid. This method can quickly adjust the vehicle's posture and improve its maneuverability.

[0005] The vehicle can be actively brought into a drifting equilibrium state through active steering, direct yaw moment control, and other methods. The stability control method that brings the vehicle into drifting equilibrium can achieve stability control beyond the vehicle's stability limit. Since the rear wheels of the vehicle skid when drifting occurs, the vehicle is already in an unstable state. Therefore, changes in vehicle speed and road adhesion have relatively little impact on this control method. Summary of the Invention

[0006] The present invention provides a vehicle stability control method based on drift balance. On the basis of the traditional vehicle stability control method, a stability control method based on drift balance is added to improve the stability control effect of the vehicle under extreme conditions. The two methods respectively use different reference values for control. Specifically, three modes are set: conventional stability control mode, active drift stability control mode, and passive drift stability control. Different modes use different reference value calculation methods. The triggering and switching methods of each mode are determined by establishing a drift condition coefficient, a driver operation coefficient, an environmental threat coefficient, and a lateral state coefficient.

[0007] The technical solutions of the present invention are as follows:

[0008] A vehicle stability control method based on drift balance specifically comprises the following steps:

[0009] 1) Obtain vehicle driving parameters, including vehicle longitudinal speed vx , Lateral acceleration a y , Center of mass sideslip angle β, yaw angular velocity wr, yaw angular acceleration dwr, steering wheel angle st, accelerator pedal opening l a , Accelerator pedal opening l b Plate opening rate dl a , Brake pedal opening l b , Brake pedal opening rate dl b , Parking brake signal c, distance d between the vehicle and the obstacle in front f , Longitudinal distance d between the vehicle and the vehicle behind rx , Longitudinal distance change rate dd between the vehicle and the vehicle behind rx , Lateral distance d between the vehicle and the vehicle behind ry , Distance d between the vehicle and the road edge s ;

[0010] 2) Calculate the instability degree H according to the yaw angular velocity - center of mass sideslip angle phase plane diagram and vehicle driving parameters. When the instability degree H > H1, enter step 3); otherwise, return to step 1);

[0011] 3) Calculate the drift condition coefficient E, driver operation coefficient E d , Environmental threat coefficient E e , Lateral state coefficient E v , When the drift condition coefficient E < E1, enter step 4); otherwise, enter step 5);

[0012] 4) Enter the conventional stability control mode;

[0013] 5) When E d > E2 and E e < E3, enter step 6); otherwise, enter step 7);

[0014] 6) Enter the active drift stability control mode;

[0015] 7) Enter the passive drift stability control mode;

[0016] Furthermore, the instability degree H is determined by the yaw angular velocity - center of mass sideslip angle phase plane diagram and the vehicle's current center of mass sideslip angle, yaw angular velocity, road adhesion coefficient, vehicle front wheel angle, and longitudinal vehicle speed;

[0017] Furthermore, the calculation formula for the drift condition coefficient is as follows:

[0018]

[0019] In the formula, E d1 is the driver operation coefficient threshold; E v1is the vehicle state coefficient threshold; k1 is the driver operation coefficient E d and environmental threat coefficient E e The weight coefficient of the product part; k2 is the lateral state coefficient E v Partial weight coefficient;

[0020] Furthermore, the driver operation coefficient E d The calculation is as follows:

[0021]

[0022] Where st is the steering wheel angle; v x is the longitudinal speed; μ is the road adhesion coefficient; k d1 、k d2 is a constant coefficient, that is, it has a fixed value; Ped is the pedal operation factor, which is determined according to different vehicle drive forms. When the vehicle drive form is rear-wheel drive or four-wheel drive, the pedal operation factor Ped is calculated as follows:

[0023] Ped=[1-sgn(c+l b )]k p1 (l a +k p2 |dl a |)+k p3 [(1-c)(l b +k p4 dl b )+c]

[0024] When the vehicle is driven by front wheels, the pedal control factor Ped is calculated as follows:

[0025]

[0026] Where l a is the accelerator pedal opening; dl a is the rate of change of accelerator pedal opening; l b is the brake pedal opening; dl b is the rate of change of the brake pedal opening; c is the parking brake signal. When the parking brake is on, the value of c is 1, and when the parking brake is off, the value of c is 0; k p1 、k p2 、k p3 、k p4 、k p5 、k p6 、k p7 、k p8 、k p9 、k p10 is a constant coefficient, i.e. it has a fixed value;

[0027] Furthermore, the environmental threat coefficient E e The calculation formula is as follows:

[0028]

[0029] Medium f is the distance between the vehicle and the obstacle in front; d f1 The minimum longitudinal distance between the vehicle and the obstacle in front when the vehicle can avoid the obstacle by turning, d f1 It is about the longitudinal speed v x and the road adhesion coefficient μ; d s is the distance between the vehicle and the edge of the road, d s1 is the reference distance between the vehicle and the road edge; d rx is the longitudinal distance between the vehicle and the rear vehicle; d rx1 The reference longitudinal distance between the vehicle and the vehicle behind it; d ry is the lateral distance between the vehicle and the rear vehicle; dd rx k is the rate of change of the longitudinal distance between the vehicle and the vehicle behind it; e1 、k e2 、k e3 、k e4 、k e5 is a constant coefficient, i.e., has a fixed value; further, the lateral state coefficient E v The calculation formula is as follows:

[0030]

[0031] Where a y is the lateral acceleration; a y1 is the reference value of lateral acceleration; d wr is the yaw angular acceleration; d wr1 is the yaw angular acceleration reference value; k v1 、k v2 is a constant coefficient, i.e. it has a fixed value;

[0032] Furthermore, the conventional stability control mode adopts a linear reference value, which includes a linear reference value β of the sideslip angle of the center of mass dc and the yaw rate linear reference value wr dc , calculated directly from the linear two-degree-of-freedom vehicle model;

[0033] The drift stability control mode adopts nonlinear reference values, which include a nonlinear reference value β of the sideslip angle of the center of mass. de and the yaw rate nonlinear reference value wr de , obtained through the nonlinear two-degree-of-freedom vehicle model under unilateral drift conditions, the nonlinear reference value calculation formula is as follows:

[0034] β de =f1(β,-|δ r |)sgn(a y )

[0035] wr de =f2(β,-|δ r |)sgn(a y )

[0036] Where f1 is the nonlinear reference value β for calculating the sideslip angle of the center of mass de The linearization function; f2 is the nonlinear reference value wr of the yaw angular velocity de Linearization function of a y is the lateral acceleration; β is the sideslip angle of the center of mass; δ r The reference front wheel angle is selected according to the drift stability control mode at this time. When the vehicle is in the passive drift stability control mode, the reference front wheel angle δ r The calculation formula is as follows:

[0037] δ r =k δ1 sgn(-a y )-k δ2 (β-β de )-k δ3 (wr-wr de )

[0038] Where a y is the lateral acceleration; β is the sideslip angle of the center of mass; β de is the nonlinear reference value of the sideslip angle of the center of mass; wr is the yaw rate; wr de is the nonlinear reference value of yaw rate; k δ1 、k δ2 、k δ3 is a constant coefficient, i.e. it has a fixed value;

[0039] When the vehicle is in active drift stability control mode, the reference front wheel angle δ r The calculation formula is as follows:

[0040] δ r =k δ2 δ

[0041] Where δ is the front wheel turning angle; k δ2 is a constant coefficient, i.e. it has a fixed value;

[0042] In active drift stability control mode, only braking and driving are used to apply yaw torque without triggering active front wheel steering. In passive drift stability control mode, braking, driving and front wheel steering are controlled simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions implemented in this application, the following is a brief introduction to the drawings required for use in the embodiments of this application. The following drawings only show a certain embodiment of the present application and therefore should not be regarded as limiting the scope. For those skilled in the art in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 is a flow chart of a vehicle stability control method based on drift balance;

[0045] Figure 2 Schematic diagram for calculating the instability H;

[0046] Figure 3 It is the two-degree-of-freedom model diagram of the vehicle; DETAILED DESCRIPTION

[0047] In this embodiment, a vehicle stability control method based on drift balance is provided, and the present invention is further described below with reference to the accompanying drawings and embodiments.

[0048] Figure 1 Flowchart of a vehicle stability control method based on drift balance provided by an embodiment of the present invention. The specific steps are as follows:

[0049] 1) Obtain vehicle driving parameters, including vehicle longitudinal speed v x , lateral acceleration a y , sideslip angle β, yaw rate wr, yaw rate change rate dwr, steering wheel angle st, accelerator pedal opening l a , accelerate b Plate opening change rate dl a , brake pedal opening l b , brake pedal opening rate of change dl b , parking brake signal c, distance between the vehicle and the obstacle in front d f , the longitudinal distance d between the vehicle and the rear vehicle rx , the longitudinal distance change rate between the vehicle and the rear vehicle dd rx , the lateral distance d between the vehicle and the rear vehicle ry , the distance d between the vehicle and the road edge s ;

[0050] 2) Calculate the instability H based on the yaw rate-center of mass sideslip angle phase plane diagram and vehicle driving parameters. When the instability H>H1, proceed to step 3). Otherwise, return to step 1).

[0051] 3) Calculate the drift condition coefficient E and driver operation coefficient E according to the vehicle driving parameters d, Environmental threat coefficient E e , Lateral state coefficient E v , When the drift condition coefficient E < E1, enter step 4); in other cases, enter step 5).

[0052] 4) Enter the conventional stability control mode;

[0053] 5) When E d > E2 and E e < E3, enter step 6); in other cases, enter step 7).

[0054] 6) Enter the active drift stability control mode;

[0055] 7) Enter the passive drift stability control mode;

[0056] Figure 2 is a schematic diagram for calculating the instability degree H. In this embodiment, the instability degree H is determined by the vehicle yaw rate - sideslip angle phase plane diagram. Figure 2 The specific phase trajectory is not drawn in. The parallelogram frame represents the stable region in the phase plane diagram. The triangular symbol marks the vehicle's stable equilibrium point. Point A represents the position of the vehicle's state at a certain moment corresponding to the phase plane diagram. The specific calculation method of the instability degree H is: H = h1 + h2 + h3 + h4. The farther point A is from the equilibrium point, the larger H is, and the more unstable the vehicle is. The instability degree H can characterize the current stability of the vehicle, thereby judging whether the stability control system needs to intervene. When H is greater than the instability degree threshold H1, it is judged that the stability control system needs to intervene.

[0057] The present invention establishes a specific mathematical expression for the drift condition coefficient E. When the instability degree H is greater than the instability degree threshold H1, the drift condition coefficient E is used to judge whether the system enters the conventional stability control mode or the drift stability control mode.

[0058] The conventional stability control mode calculates the reference value using the linear vehicle two - degree - of - freedom model, and the obtained result is the linear reference value, including the linear reference value of the sideslip angle of the center of mass β dc and the linear reference value of the yaw rate wr dc , and the specific calculation formula is as follows:

[0059]

[0060]

[0061] In the formula, K is the stability factor; a is the distance from the vehicle's center of mass to the front axle; b is the distance from the vehicle's center of mass to the rear axle; v x is the longitudinal vehicle speed; μ is the road surface adhesion coefficient; g is the universal gravitational constant; m is the vehicle's total mass; k2 is the rear - wheel sideslip stiffness; δ is the front - wheel steering angle.

[0062] In the normal stability control mode, the system uses linear reference values to calculate the yaw torque applied by control and the front wheel angle applied by control. The yaw torque applied by control is achieved through the vehicle's braking and drive systems, and the front wheel angle applied by control is achieved through the vehicle's active steering.

[0063] The drift condition coefficient E can indicate whether the conditions for entering the drift stability control mode are met at this time. The larger the value of E, the more likely the system is to enter the drift stability control mode. When E is greater than the first drift condition threshold E1, the system enters the drift stability control mode. The specific calculation formula of E is as follows:

[0064]

[0065] Where E d1 is the driver operation coefficient threshold; E v1 is the vehicle state coefficient threshold; k1 is the driver operation coefficient E d and environmental threat coefficient E e The weight coefficient of the product part; k2 is the lateral state coefficient E v Partial weight coefficient.

[0066] E d It can evaluate the extreme degree of the driver’s driving behavior at a certain moment, E d The larger the value, the more aggressive the driver's operation, and the more likely the vehicle will become unstable and drift. d Greater than the driver operation coefficient threshold E d1 When the system thinks the driver's operation is too extreme, it can be controlled by E d To determine whether the vehicle enters the drift stability control mode, the drift condition coefficient E is equal to the driver operation coefficient E d , driver control coefficient E d The calculation formula is as follows:

[0067]

[0068] Where st is the steering wheel angle; v x is the longitudinal speed; μ is the road adhesion coefficient; k d1 、k d2 is a constant coefficient, that is, it has a fixed value; Ped is the pedal operation factor, which is determined according to different vehicle driving forms, and the driver operation factor E d It is determined by four parts: steering, pedal, road adhesion coefficient and longitudinal speed. The steering wheel angle represents the steering amplitude of the vehicle, and Ped represents the operation of the brake, accelerator pedal and handbrake. The higher the longitudinal speed, the larger the steering wheel angle, and the larger the Ped value, which means that the driver's operation is closer to the limit. dThe larger the value, the lower the road adhesion coefficient, which means the worse the road conditions are, and the lower the vehicle's ability to meet the extreme operation requirements. d The bigger it is.

[0069] For any type of driving vehicle, when the parking brake or service brake is applied during driving, the vehicle weight will be transferred to the front axle under the influence of inertia, the rear axle load will be reduced, and the maximum adhesion force transmitted to the rear wheels by the road surface will be reduced accordingly. When the driving force transmitted to the rear wheels by the drive unit is greater than the maximum adhesion force, the rear tire force will be saturated, and sideways drift may occur. The present invention adjusts the brake pedal opening to l b , brake pedal opening rate of change dl b , the parking brake signal c is a component of the pedal operation factor Ped. Since the service brake and parking brake execution end components are the same, the influence of the service brake is not considered when the parking brake exists.

[0070] For rear-wheel drive or four-wheel drive vehicles, under rapid acceleration conditions, the rear wheels need to generate a large driving force instantly, which can easily lead to tire force saturation and rear axle skidding. Therefore, when the vehicle is driven by front-wheel drive or four-wheel drive, the present invention sets the accelerator pedal opening to l a and accelerator pedal opening rate dl a As a component of the pedal operation factor Ped.

[0071] For any type of driving vehicle, when the accelerator pedal is quickly released during driving, since the vehicle body and tires are not rigidly connected, the wheels in contact with the ground will decelerate faster than the vehicle body. The forward movement of the vehicle body relative to the wheels will cause the vehicle mass to be transferred to the front axle, reducing the rear axle load and the maximum adhesion of the rear wheels. This may lead to saturation of the rear tire force and rear axle skidding. The present invention uses the accelerator pedal opening change rate dl a As a component of the pedal operation factor, for rear-wheel drive or four-wheel drive vehicles, the accelerator pedal opening rate dl a Whether positive or negative, the value of Ped will increase, using the accelerator pedal opening rate dl a The absolute value of the accelerator pedal opening rate dl is used as a parameter. For front-wheel drive vehicles, only when the accelerator pedal opening rate dl a When dl is negative a It will affect the value of Ped, so the Ped of the front-wheel drive vehicle adopts the form of a piecewise function.

[0072] When the driver brakes and accelerates simultaneously, only the braking operation is considered because the braking system is more likely to cause the rear axle to skid.

[0073] When the vehicle is rear-wheel drive or four-wheel drive, the Ped calculation formula is as follows:

[0074] Ped=[1-sgn(c+lb )]k p1 (l a +k p2 |dl a |)+k p3 [(1-c)(l b +k p4 dl b )+c]

[0075] When the vehicle is driven by front wheels, the Ped calculation formula is as follows:

[0076]

[0077] Where l a is the accelerator pedal opening; dl a is the rate of change of accelerator pedal opening; l b is the brake pedal opening; dl b is the rate of change of the brake pedal opening; c is the parking brake signal. When the parking brake is on, the value of c is 1, and when the parking brake is off, the value of c is 0; k p1 、k p2 、k p3 、k p4 、k p5 、k p6 、k p7 、k p8 、k p9 、k p10 is a constant coefficient, that is, it has a fixed value.

[0078] Establish environmental threat factor E e The mathematical expression of E e It can evaluate the dangerousness of the vehicle driving environment, E e The larger the value of E, the more dangerous the vehicle driving environment is and the greater the possibility of vehicle collision. e The specific calculation method is as follows:

[0079]

[0080] Where d f is the distance between the vehicle and the obstacle in front; d f1 The minimum longitudinal distance between the vehicle and the obstacle in front when the vehicle can avoid the obstacle by turning, d f1 It is about the longitudinal speed v x and the road adhesion coefficient μ; d s is the distance between the vehicle and the edge of the road, d s1 is the reference distance between the vehicle and the road edge; d rx is the longitudinal distance between the vehicle and the rear vehicle; d rx1The reference longitudinal distance between the vehicle and the vehicle behind it; d ry is the lateral distance between the vehicle and the rear vehicle; dd rx k is the rate of change of the longitudinal distance between the vehicle and the vehicle behind it; e1 、k e2 、k e3 、k e4 、k e5 is a constant coefficient, that is, it has a fixed value.

[0081] Environmental threat coefficient E e The first item represents the threat level of the obstacle in front to the vehicle, the second item represents the degree of restriction on driving by the road edge, and the third item represents the threat level of the rear vehicle. When quantifying the threat level of the rear vehicle, the longitudinal distance and lateral distance between the two vehicles are considered at the same time. This is because when there is a certain lateral distance between the two vehicles, once a collision occurs, the controlled vehicle will directly generate yaw torque and yaw angular velocity, which is likely to cause the vehicle to skid on the rear axle, which is the most dangerous.

[0082] Establish the lateral state coefficient E v The mathematical expression of E v The lateral motion state of the vehicle at this time can be evaluated, E v The larger the value, the worse the vehicle stability. v Greater than E v1 When the system considers that the vehicle is too unstable, it does not need to consider the influence of the driver's operation and the environment. At this time, the drift condition coefficient E is equal to E v , E v The specific calculation formula is as follows:

[0083]

[0084] Where a y is the lateral acceleration; a y1 is the lateral acceleration reference value; dwr is the yaw angular acceleration; dwr1 is the yaw angular acceleration reference value; k v1 、k v2 is a constant coefficient, that is, it has a fixed value.

[0085] When the driver's operating coefficient E d Less than E d1 And the lateral state coefficient E v Less than E v1 When the drift condition coefficient E is considered comprehensively, d 、E v 、E e .

[0086] When E>E1, the vehicle enters the drift stability control mode, and the system will further determine whether to enter the passive drift control mode or the active drift control mode.

[0087] The drift stability control mode uses a nonlinear vehicle two-degree-of-freedom model to calculate the friction reference value. The result is a nonlinear reference value, including the nonlinear reference value of the center of mass side slip angle β de and the yaw rate nonlinear reference value wr de The nonlinear two-degree-of-freedom model is different from the linear two-degree-of-freedom model. It uses a tire model to calculate tire forces. In this embodiment, the magic formula tire model is used. The specific formula is as follows:

[0088]

[0089]

[0090]

[0091] In the above formula, F yf is the lateral force of the front wheel; F yr is the rear wheel lateral force; v x is the longitudinal speed; wr is the yaw rate; m is the vehicle mass; δ r is the reference front wheel angle, I z is the vertical moment of inertia of the vehicle; a is the distance from the center of mass of the vehicle to the front axle; b is the distance from the center of mass of the vehicle to the rear axle; α f is the front wheel slip angle; α r is the rear wheel slip angle; β is the center of mass slip angle; Y represents the wheel lateral force, X is the longitudinal slip rate or tanα; α is the slip angle; B is the stiffness factor; C is the shape factor; D is the peak factor; E is the curvature factor; S H is the lateral offset; S V is the longitudinal offset.

[0092] According to the established nonlinear two-degree-of-freedom model, the vehicle's center of mass slip angle and yaw rate in the equilibrium state can be calculated for the vehicle's driving state (longitudinal speed, reference front wheel turning angle) at a certain moment. For any vehicle driving state, there are three equilibrium states, namely left-hand drift state, right-hand drift state, and stable state. Therefore, there are three groups of calculated vehicle center of mass slip angles and yaw rates. Since the left-hand drift state and the right-hand drift state are completely symmetrical, in this embodiment, the vehicle center of mass slip angle and yaw rate calculated in the left-hand drift state are taken as the reference, and the nonlinear equation group is linearized and then the nonlinear reference value β of the center of mass slip angle is calculated by the linearized equation. de and the yaw rate nonlinear reference value wr de , the calculated parameter is the nonlinear reference value, and the specific calculation formula is as follows;

[0093] β de =f1(β,-|δ r|)sgn(a y )

[0094] wr de =f2(β,-|δ r |)sgn(a y )

[0095] Where f1 is the nonlinear reference value β for calculating the sideslip angle of the center of mass de The linearization function; f2 is the nonlinear reference value wr of the yaw angular velocity de Linearization function of a y is the lateral acceleration; β is the sideslip angle of the center of mass; δ r The reference front wheel angle is selected according to the drift stability control mode at this time. Since the linearization function only considers the unilateral drift state, the correction coefficient sgn (a y ) makes it applicable to drift states in any direction.

[0096] When the vehicle is in passive stability control mode, the reference front wheel angle δ r The calculation formula is as follows:

[0097] δ r =k δ1 sgn(-a y )-k δ2 (β-β de )-k δ3 (wr-wr de )

[0098] Where a y is the lateral acceleration; β is the sideslip angle of the center of mass; β de is the nonlinear reference value of the sideslip angle of the center of mass; wr is the yaw rate; wr de is the nonlinear reference value of yaw rate; k δ1 、k δ2 、k δ3 is a constant coefficient, that is, it has a fixed value. In the passive stability control mode, the reference front wheel angle δ r It is also used for active front wheel steering control, that is, the reference front wheel angle δ r Used as a reference value to correct the actual vehicle front wheel angle;

[0099] When the vehicle is in active drift stability control mode, the reference front wheel angle δ r The calculation formula is as follows:

[0100] δ r =k δ2 δ

[0101] Where δ is the front wheel turning angle; k δ2is a constant coefficient, that is, it has a fixed value, and is used as the reference for the front wheel turning angle δ in the active drift stability control mode. r Only used to calculate the linear reference value β of the center of mass sideslip angle dc and the yaw rate linear reference value wr dc , does not actively control the wheel angle;

[0102] After the vehicle enters the drift stability control mode according to the drift condition coefficient E, the system will further determine whether to enter the passive drift stability control mode or the active drift stability control mode. d Greater than the second drift condition threshold E2 and the environmental threat coefficient E e When the vehicle is lower than the third drift condition threshold E3, the vehicle enters the active drift stability control mode. d With a larger value and E e Very small, which means that the driver has made extreme driving operations in an environment where there is almost no safety crisis. It is judged that the driver has made extreme operations subjectively and deliberately, so the system enters the active drift stability control mode. In the active drift stability control mode, the system does not affect the driver's steering operation, but only generates a certain control yaw torque through the braking and drive systems according to the nonlinear reference value to assist the driver's operation. The reference front wheel angle δ at this time is r The direction of the corner is consistent with the driver's desired direction.

[0103] After the vehicle enters the drift stability control mode, if the system determines that the vehicle does not meet the requirements of the active drift stability control mode, it will enter the passive drift stability control mode. At this time, the driver has not made any extreme maneuvers subjectively or has been forced to make extreme maneuvers due to dangerous conditions. Since the vehicle is in an extreme state at this time, it is difficult for non-professional drivers to make effective control. Therefore, the control system will have a stronger degree of intervention. In the passive drift stability control mode, the driving, braking, and steering systems work simultaneously and are controlled according to the nonlinear reference value. The reference front wheel angle δ at this time is r No longer considering the driver's input, only the vehicle state (lateral acceleration a y , sideslip angle β, yaw rate wr) and nonlinear reference value.

Claims

1. A vehicle stability control method based on drift balance, characterized in that: The vehicle stability control method based on drift balance includes two stability control modes, namely, a conventional stability control mode and a drift stability control mode; The drift stability control mode includes an active drift stability control mode and a passive drift stability control mode; The drift condition coefficient E and the driver operation coefficient E were established. d , Environmental threat coefficient E e , lateral state coefficient E v The mathematical expression of vehicle instability H and drift condition coefficient E are used to determine the triggering and switching of conventional stability control mode and drift stability control mode. The drift condition coefficient is determined by the driver operation coefficient E. d , Environmental threat coefficient E e , lateral state coefficient E v To calculate the driver's operating coefficient E d , Environmental threat coefficient E e Used to determine the triggering and switching methods of the active drift stability control mode and the passive drift stability control mode. The vehicle instability H is calculated using the phase plane diagram and the vehicle's center of mass sideslip angle β and yaw rate wr. The drift condition coefficient E is calculated as follows: ， Where E d1 is the driver operation coefficient threshold; E v1 is the vehicle state coefficient threshold; k1 is the driver operation coefficient E d and environmental threat coefficient E e The weight coefficient of the product part; k2 is the lateral state coefficient E v Partial weight coefficient; The driver operation coefficient E d The calculation formula is as follows: ， Where st is the steering wheel angle; v x is the longitudinal speed; μ is the road adhesion coefficient; k d1 、k d2 is a constant coefficient, that is, it has a fixed value; Ped is the pedal operation factor, which is determined according to different vehicle drive forms. When the vehicle drive form is rear-wheel drive or four-wheel drive, the pedal operation factor Ped is calculated as follows: ， When the vehicle drive form is front-wheel drive, the pedal operation factor Ped calculation formula is as follows: ， Where l a is the accelerator pedal opening; dl a is the rate of change of accelerator pedal opening; l b is the brake pedal opening; dl b is the rate of change of the brake pedal opening; c is the parking brake signal. When the parking brake is on, the value of c is 1, and when the parking brake is off, the value of c is 0; k p1 、k p2 、k p3 、k p4 、k p5 、k p6 、k p7 、k p8 、k p9 、k p10 is a constant coefficient, i.e. it has a fixed value; The environmental threat coefficient E e The calculation formula is as follows: ， Where d f is the distance between the vehicle and the obstacle in front; d f1 The minimum longitudinal distance between the vehicle and the obstacle in front when the vehicle can avoid the obstacle by turning, d f1 It is about the longitudinal speed v x and the function of the road adhesion coefficient μ; d s is the distance between the vehicle and the edge of the road, d s1 is the reference distance between the vehicle and the road edge; d rx is the longitudinal distance between the vehicle and the rear vehicle; d rx1 The reference longitudinal distance between the vehicle and the vehicle behind it; d ry is the lateral distance between the vehicle and the rear vehicle; dd rx k is the rate of change of the longitudinal distance between the vehicle and the vehicle behind it; e1 、k e2 、k e3 、k e4 、k e5 is a constant coefficient, i.e. it has a fixed value; The lateral state coefficient E v The calculation formula is as follows: ， Where a y is the lateral acceleration; a y1 is the lateral acceleration reference value; wr is the yaw angular velocity; wr1 is the yaw angular velocity reference value; k v1 、k v2 is a constant coefficient, i.e. it has a fixed value; The triggering and switching methods of the conventional stability control mode and the drift stability control mode include the following steps: 1) Obtain vehicle driving parameters, including vehicle longitudinal speed v x , lateral acceleration a y , sideslip angle β, yaw rate wr, steering wheel angle st, accelerator pedal opening l a , accelerator pedal opening rate dl a , brake pedal opening l b , brake pedal opening rate of change dl b , parking brake signal c, distance between the vehicle and the obstacle in front d f , the longitudinal distance d between the vehicle and the rear vehicle rx , the longitudinal distance change rate between the vehicle and the rear vehicle dd rx , the lateral distance d between the vehicle and the rear vehicle ry , the distance d between the vehicle and the road edge s ; 2) Calculate the instability degree H. When H < H1, return to step 1). In other cases, enter step 3). H1 is the instability degree threshold; 3) Calculate the drift condition coefficient E. When E < E1, enter step 4). When E > E1, enter step 5). E1 is the first drift condition threshold; 4) Trigger the conventional stability control mode; 5) E d > E2 and E e When it is > E3, go to step 6), and in other cases, go to step 7). E2 is the second drift condition threshold, and E3 is the third drift condition threshold; 6) Trigger the active drift stability control mode; 7) Trigger the passive drift stability control mode.

2. The vehicle stability control method based on drift balance according to claim 1, characterized in that: The conventional stability control mode adopts a linear reference value, which includes a linear reference value β of the sideslip angle of the center of mass. dc and the yaw rate linear reference value wr dc , calculated directly from the linear two-degree-of-freedom vehicle model; The drift stability control mode adopts nonlinear reference values, which include a nonlinear reference value β of the sideslip angle of the center of mass. de and the yaw rate nonlinear reference value wr de , obtained through the nonlinear two-degree-of-freedom vehicle model under unilateral drift conditions, the nonlinear reference value calculation formula is as follows: ， Where f1 is the nonlinear reference value β for calculating the sideslip angle of the center of mass de The linearization function; f2 is the nonlinear reference value wr of the yaw angular velocity de Linearization function of a y is the lateral acceleration; β is the sideslip angle of the center of mass; δ r The reference front wheel angle is selected according to the drift stability control mode at this time. When the vehicle is in the passive drift stability control mode, the reference front wheel angle δ r The calculation formula is as follows: ， Where a y is the lateral acceleration; β is the sideslip angle of the center of mass; β de is the nonlinear reference value of the sideslip angle at the center of mass; wr is the yaw angular velocity; wr de is the nonlinear reference value of yaw rate; k δ1 、k δ2 、k δ3 is a constant coefficient, i.e. it has a fixed value; When the vehicle is in active drift stability control mode, the reference front wheel angle δ r The calculation formula is as follows: ， Where δ is the front wheel turning angle; k δ2 is a constant coefficient, i.e. it has a fixed value; In the active drift stability control mode, only the braking and drive systems are used to apply the yaw moment without triggering the active front-wheel steering; In the passive drift stability control mode, the braking, drive, and active front-wheel steering are controlled simultaneously.

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