A vehicle roll-over prevention control system based on a drive-by-wire chassis

Abstract

The application discloses a vehicle anti-rollover control system based on a drive-by-wire chassis, which comprises a vehicle running information detection unit, a vehicle rollover danger index calculation unit, a vehicle anti-rollover judgment unit and a vehicle anti-rollover execution unit. The vehicle running information detection unit is used for acquiring real-time vehicle speed, vehicle body roll angle, lateral acceleration, wheel vertical load and tire side force; the vehicle rollover danger index calculation unit is used for calculating a lateral load transfer rate, a lateral load offset coefficient and a lateral load excitation index, so as to obtain a rollover danger index; the vehicle anti-rollover judgment unit is used for judging whether the anti-rollover system is executed to control work or not, wherein the control mode comprises a single control work mode and a joint control mode; and the vehicle anti-rollover execution unit comprises a drive-by-wire steering system, a drive-by-wire braking system and an active suspension system, and different control systems are controlled according to different control modes.

Description

TECHNICAL FIELD

[0001] The present application relates to a vehicle anti-rollover control system based on a drive-by-wire chassis. BACKGROUND

[0002] At present, vehicle anti-rollover control is applied more and more widely. In driving scenarios such as high-speed cornering, obstacle avoidance, and sudden lane changing, vehicle rollover is a common traffic accident that can cause serious injuries to drivers, passengers, and pedestrians. However, existing anti-rollover systems often cannot meet the needs of complex road conditions and cannot jointly control the dangers. The control method is relatively single, the evaluation factors are relatively single, and it is difficult to perform decoupling control of vehicle anti-rollover in different directions, which leads to the inability to take timely measures in the above-mentioned situations and insufficient safety. Therefore, how to effectively ensure the realization of joint control mode of vehicle anti-rollover control when the vehicle is driving in different complex working conditions and improve the smoothness and comfort of the vehicle has become a technical problem to be solved by the applicant. In order to improve these problems, the present application proposes a vehicle anti-rollover control system based on a drive-by-wire chassis. SUMMARY

[0003] The purpose of the present application is to provide a vehicle anti-rollover control system based on a drive-by-wire chassis to solve the problems faced in the background art.

[0004] To achieve the above-mentioned purpose, the present application provides the following technical solution: a vehicle anti-rollover control system based on a drive-by-wire chassis, which comprises a vehicle driving information detection unit, a vehicle rollover danger index calculation unit, a vehicle anti-rollover judgment unit, and a vehicle anti-rollover execution unit.

[0005] The vehicle driving information detection unit is used to obtain real-time vehicle speed, body roll angle, lateral acceleration, wheel vertical load, and tire side force, establish a three-degree-of-freedom vehicle model, and list the roll motion moment balance equation, the yaw motion moment balance equation, and the lateral motion force balance equation.

[0006] The vehicle rollover danger index calculation unit is used to calculate the lateral load transfer rate LTR, the lateral load offset coefficient LTP, and the lateral load excitation index LTQ, thereby obtaining the rollover danger index RRI.

[0007] The vehicle anti-rollover judging unit is used to judge whether the anti-rollover system executes control work, if the rollover risk index |RRI|≤0.3, the anti-rollover control system does not execute control work, if the rollover risk index 0.3

[0008] The vehicle anti-rollover executing unit includes a steer-by-wire system, a brake-by-wire system and an active suspension system, different systems are controlled according to the different control modes, the single control mode only corrects the angle of the wheel rotation through the steer-by-wire system in the main steer-by-wire chassis, the control method is proportional-integral-derivative, the joint control mode adopts the steer-by-wire system, the brake-by-wire system and the active suspension system for joint control, the wheel correction angle controlled by the steer-by-wire system and the wheel braking force controlled by the brake-by-wire system can change the vehicle yaw motion moment, the average value of the absolute value of the tire braking force of each wheel of the vehicle The average value of the absolute value of the wheel rotation angle The control adjustment is made, the control method adopts fuzzy control, the active suspension control system changes the vehicle roll motion moment by controlling the roll-resisting moment and the damper damping force, the damper damping force difference coefficient λ is introduced to represent the size of the left and right damper damping force difference factor ζ, and the effect of the active suspension on the vehicle anti-rollover is evaluated according to the size of the left and right damper damping force difference factor ζ.

[0009] Specifically includes the following contents:

[0010] S1, a three-degree-of-freedom vehicle model is established,

[0011] The roll motion moment balance equation around the X-axis is:

[0012]

[0013] The yaw motion moment balance equation around the Z-axis is:

[0014]

[0015] Lateral motion force balance equation around Y axis:

[0016]

[0017] where, l x is roll moment of inertia, l z is yaw moment of inertia, is roll angle acceleration, is roll angle velocity, is vehicle body roll angle, m is vehicle mass, m s is sprung mass, h s is the distance from roll center to ground, is yaw angle acceleration, a is the distance from mass center to front axle, b is the distance from mass center to rear axle, a y is lateral acceleration, K is equivalent roll stiffness of suspension, C is equivalent roll damping of suspension, F yf is front wheel aligning force, F yr is rear wheel aligning force;

[0018] S2, the vehicle rollover risk index calculation unit, can calculate lateral load transfer rate according to the following formula:

[0019]

[0020] where, F zl is left wheel vertical load, F zr is right wheel vertical load;

[0021] S3, the vehicle rollover risk index calculation unit, obtains lateral load shift coefficient according to vehicle body roll angle, roll angle velocity and lateral acceleration:

[0022]

[0023] where, l is wheel track, k1, k2 are weighting coefficients, and k1+k2=1, h r is the height of sprung mass center of mass to roll center;

[0024] S4, the vehicle rollover risk index calculation unit, obtains lateral load excitation index according to vehicle speed, critical speed and different types of vehicles:

[0025]

[0026] where, v is vehicle speed, v cr is critical speed, K H is vehicle height weighting coefficient, its value depends on the type of vehicle, when the vehicle is A-class vehicle, K H =0.85, when the vehicle is B-class vehicle, K H= 0.90, when the vehicle is a C-class vehicle, K H = 0.95, when the vehicle is a D-class vehicle, K H = 1.0, is a vehicle body roll angle coefficient, the value of which depends on the vehicle body roll angle, when the vehicle body roll angle satisfies , when the vehicle body roll angle satisfies , when the vehicle body roll angle satisfies , K S is a vehicle loss coefficient, the value of which depends on a vehicle purchase time coefficient K T , a vehicle total mileage coefficient K x , a weekly driving time coefficient K t , and a number of accidents in the past three years coefficient K a , and its expression is:

[0027]

[0028] wherein β1, β2, β3, and β4 are weight coefficients, and β1+β2+β3+β4=1, when the vehicle purchase time is less than 1 year, K T = 0.1, when the vehicle purchase time is more than 1 year but not more than 3 years, K T = 0.25, when the vehicle purchase time is more than 3 years, K T = 0.4, when the vehicle total mileage is less than 15,000 km, K x = 0.15, when the vehicle total mileage is more than 15,000 km but not more than 35,000 km, K x = 0.3, when the vehicle total mileage is more than 35,000 km, K x = 0.45, when the weekly driving time is less than 10 hours, K t = 0.2, when the weekly driving time is more than 10 hours but not more than 15 hours, K t = 0.3, when the weekly driving time is more than 15 hours, K t = 0.4, when the number of accidents in the past three years is less than 3, K a = 0.1, when the number of accidents in the past three years is more than 3 but not more than 5, K a = 0.35, when the number of accidents in the past three years is more than 5, K a = 0.6.

[0029] The vehicle rollover risk index calculation unit determines a rollover risk index RRI according to the lateral load transfer rate LTR, the lateral load shift coefficient LTP, and the lateral load excitation index LTQ, and its expression is:

[0030] RRI = a1LTR + a2LTP + a3LTQ, -1≤RRI≤1,

[0031] Simultaneous expression of the said S1, S2, S3, S4, can be obtained:

[0032]

[0033] Convert it into matrix form as follows:

[0034]

[0035] Wherein, Q e is a parameter weight matrix, a1, a2, a3 are weight factors, wherein a1 + a2 + a3 = 1.

[0036] The vehicle anti-rollover judging unit judges the execution control mode of the anti-rollover control system according to the size of the rollover risk index, if the rollover risk index |RRI|≤0.3, the anti-rollover control system does not execute the control work, if the rollover risk index 0.3<|RRI|≤0.65, the anti-rollover control system executes a single control mode, if the rollover risk index 0.65<|RRI|≤1, the anti-rollover control system executes a joint control mode;

[0037] The single control mode is to use the steer-by-wire system control, the brake-by-wire system and the active suspension system are not started to work, through proportional-integral-derivative control, the angle of the wheel angle is controlled moderately to prevent violating the driver's intention, the specific content is as follows:

[0038] The steer-by-wire system control is to reduce the steering angle to reduce the yaw angular velocity and the lateral acceleration, thereby reducing the lateral load transfer rate;

[0039] In the steady state steering condition, the yaw angular velocity gain can be expressed as:

[0040]

[0041] Wherein, L is the wheelbase, δ is the front wheel angle, K z is the understeering coefficient, the size is:

[0042]

[0043] Wherein, when K z =0, the vehicle behaves as neutral steering, when K z <0, the vehicle behaves as oversteering, when K z >0, the vehicle behaves as understeering, k1 is the front wheel cornering stiffness, k2 is the rear wheel cornering stiffness,

[0044] The steady-state response of yaw rate ω to front wheel angle δ input can be expressed as:

[0045]

[0046] The angle δ of the wheel angle corrected by the steer-by-wire system c The change in yaw rate caused by the angle δ is:

[0047]

[0048] The combined control mode adopts the steer-by-wire system, the brake-by-wire system and the active suspension system for combined control, and the wheel correction angle controlled by the steer-by-wire system and the wheel braking force controlled by the brake-by-wire system can change the vehicle yaw motion moment, and the average value of the absolute values of the braking forces of the vehicle wheels The average value of the absolute values of the wheel angles and the vehicle speed v The control adjustment is made, the control method adopts fuzzy control, the active suspension control system changes the vehicle roll motion moment by controlling the roll-resisting moment and the size of the damper damping force, the difference coefficient λ of the damping force is introduced to represent the size of the left and right side damper damping force difference factor ζ, and the effect of the active suspension on the vehicle rollover prevention is evaluated according to the size of the left and right side damper damping force difference factor ζ, and the specific content is as follows:

[0049] The steer-by-wire system control in the combined control mode is the same as the steer-by-wire system control in the single control mode;

[0050] The brake-by-wire system control refers to applying different braking forces to different wheels to increase an anti-yaw moment for the vehicle, according to the attachment ellipse characteristics of the tire, increasing the braking force of the vehicle can reduce the cornering force of the vehicle, and the formula for the mutual influence of the cornering force and the braking force is:

[0051]

[0052] Among them, F xmax is the maximum braking force of the tire, F ymax is the maximum cornering force of the tire, F x is the braking force of the tire, and F y is the cornering force of the tire;

[0053] The maximum cornering force can be considered as the cornering force of the tire at a certain cornering angle without braking force, and the maximum braking force is determined by the vertical force of the tire and the road adhesion coefficient, and the formula is as follows:

[0054] F xmax = φF z ,

[0055] Among them, φ is the road adhesion coefficient, F zThe vertical force on the tire;

[0056] The yaw moment balance equation of the vehicle after adopting steer-by-wire and brake-by-wire control systems is changed to:

[0057]

[0058] Among them, M b The anti-yaw moment generated by the linear braking is:

[0059]

[0060] Where l is the wheel track, F xrf For the braking force of the right wheel tire on the front axle, F xrr For braking force on the right rear wheel tire, F xlf For the braking force of the left wheel tire on the front axle, F xlr Braking force for the left rear wheel tire;

[0061] Based on the average absolute value of the braking force of each wheel tire of the vehicle The magnitude and speed v of the vehicle, and the average absolute value of the turning angle of each wheel Make adjustments, The expression is as follows:

[0062]

[0063] The expression is as follows:

[0064]

[0065] Where, δ fl The left front wheel steering angle, δ fr The steering angle of the right front wheel is δ. rl The left rear wheel steering angle is δ. rr The steering angle of the right rear wheel;

[0066] The adjustment method used is fuzzy control. The inputs to this fuzzy control method are the vehicle speed and the average of the absolute values ​​of the wheel angles. The fuzzy set of vehicle speeds is defined as ZX, X, Z, D, ZD, with the following fuzzy rules: ZX is a vehicle speed v satisfying 0 ≤ v ≤ 35 km / h, X is a vehicle speed v satisfying 35 < v ≤ 50 km / h, Z is a vehicle speed v satisfying 50 < v ≤ 70 km / h, D is a vehicle speed v satisfying 70 < v ≤ 90 km / h, and ZD is a vehicle speed v satisfying v > 90 km / h. The fuzzy set of the average of the absolute values ​​of the wheel angles is defined as ZX, X, Z, D, ZD, with the following fuzzy rules: ZX is the average of the absolute values ​​of the wheel angles. satisfy X is the average of the absolute values ​​of the steering angles of each wheel. satisfy Z is the average of absolute values of each wheel rotation angle satisfies D is the average of absolute values of each wheel rotation angle satisfies ZD is the average of absolute values of each wheel rotation angle satisfies

[0067] The fuzzy control method outputs the average of absolute values of each wheel tire braking force of the vehicle The fuzzy set is defined as ZX, X, Z, D, ZD, and the fuzzy rules are defined as follows: ZX is the average of absolute values of each wheel tire braking force of the vehicle satisfies X is the average of absolute values of each wheel tire braking force of the vehicle satisfies Z is the average of absolute values of each wheel tire braking force of the vehicle satisfies D is the average of absolute values of each wheel tire braking force of the vehicle satisfies ZD is the average of absolute values of each wheel tire braking force of the vehicle satisfies

[0068] The active suspension system control refers to applying different damping forces to the shock absorbers in the active suspension to increase an anti-roll moment for the vehicle, and the roll motion moment balance equation of the vehicle after the active suspension control changes to:

[0069]

[0070] wherein, M d is the anti-roll moment generated by the active suspension system, and the size is:

[0071]

[0072] wherein, F zrf is the right front suspension shock absorber damping force, F zrr is the right rear suspension shock absorber damping force, F zlf is the left front suspension shock absorber damping force, F zlr is the right front suspension shock absorber damping force;

[0073] A left-right side shock absorber damping force difference degree factor ζ is introduced to evaluate the degree of vehicle rollover prevention control by the active suspension, and the expression is as follows:

[0074]

[0075] Wherein, lambda is a damping force difference coefficient, which size depends on wheelbase l, when wheelbase l is not more than 1.6m, lambda=0.5, when wheelbase l is more than 1.6m but not more than 1.8m, lambda=0.65, when wheelbase l is more than 1.8m, lambda=0.8;

[0076] According to the size of left and right side shock absorber damping force difference degree factor zeta, the vehicle is adjusted correspondingly, and the adjustment rule is as follows:

[0077] When left and right side shock absorber damping force difference degree factor zeta is less than or equal to 8%, it is judged that the active suspension system control rollover effect is good, the active suspension control is still normally executed, and the shock absorber damping force is still normally output; when left and right side shock absorber damping force difference degree factor zeta is greater than 8%, it is judged that the active suspension system control rollover effect is poor, the active suspension control is temporarily normally executed, and the control system continues to judge whether zeta is greater than 8% after 5s, if zeta is greater than 8% again, the active suspension system control is still normally executed, and the shock absorber damping force is still normally output, if zeta is less than or equal to 8% again, the control and shock absorber damping force of the active suspension system need to be adjusted again.

[0078] Compared with the prior art, the present application has the following beneficial effects:

[0079] 1. A vehicle anti-rollover control system based on a drive-by-wire chassis calculates a rollover risk index according to a lateral load transfer rate, a lateral load offset coefficient and a lateral load excitation index, which is used to judge the risk of rollover.

[0080] 2. The control mode of the present application is a single control mode and a combined control mode, wherein the single control mode only corrects the angle of the wheel through the drive-by-wire steering system in the drive-by-wire chassis, and the combined control mode uses the drive-by-wire steering system, the drive-by-wire braking system and the active suspension system for combined control, the wheel correction angle controlled by the drive-by-wire steering system and the wheel braking force controlled by the drive-by-wire braking system can change the lateral motion moment of the vehicle, and the active suspension control system changes the lateral motion moment of the vehicle by controlling the size of the anti-roll moment and the shock absorber damping force.

[0081] 3. Fuzzy control is used to control the wheel correction angle controlled by the drive-by-wire steering system and the wheel braking force controlled by the drive-by-wire braking system, and for the active suspension control system, a damping force difference coefficient is introduced to represent the size of the left and right side shock absorber damping force difference degree factor, and the effect of the active suspension on vehicle anti-rollover is evaluated according to the size of the left and right side shock absorber damping force difference degree factor. BRIEF DESCRIPTION OF DRAWINGS

[0082] The present application will be further described below in conjunction with the drawings:

[0083] Figure 1A control framework diagram of a vehicle anti-rollover control system based on a drive-by-wire chassis is provided. DETAILED DESCRIPTION

[0084] The application is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0085] As shown in the drawings, Figure 1 The application is a vehicle anti-rollover control system based on a drive-by-wire chassis, which comprises a vehicle running information detection unit, a vehicle rollover risk index calculation unit, a vehicle anti-rollover judgment unit, and a vehicle anti-rollover execution unit.

[0086] The vehicle running information detection unit is used to obtain real-time vehicle speed, body roll angle, lateral acceleration, wheel vertical load, and tire cornering force, establish a three-degree-of-freedom vehicle model, and list roll motion moment balance equation, yaw motion moment balance equation, and lateral motion force balance equation.

[0087] The vehicle rollover risk index calculation unit is used to calculate lateral load transfer ratio LTR, lateral load transfer coefficient LTP, and lateral load transfer index LTQ, thereby obtaining rollover risk index RRI.

[0088] The vehicle anti-rollover judgment unit is used to judge whether the anti-rollover system performs control work, and if |RRI|≤0.3, the anti-rollover control system does not perform control work, if 0.3<|RRI|≤0.65, the anti-rollover control system performs a single control mode, and if 0.65<|RRI|≤1, the anti-rollover control system performs a joint control mode, wherein the single control mode only corrects the angle of the wheel angle through the drive-by-wire steering system in the drive-by-wire chassis, the joint control mode adopts the drive-by-wire steering system, the drive-by-wire braking system, and the active suspension system for joint control, the wheel correction angle controlled by the drive-by-wire steering system and the wheel braking force controlled by the drive-by-wire braking system can change the vehicle yaw motion moment, the control method adopts fuzzy control, the active suspension control system changes the vehicle roll motion moment by controlling the size of the roll moment and the damper damping force, and the effect of the active suspension on vehicle anti-rollover is evaluated according to the size of the left and right damper damping force difference degree factor ζ.

[0089] The vehicle anti-rollover execution unit includes a steer-by-wire system, a brake-by-wire system and an active suspension system, different systems are controlled according to the different control modes, a single control mode only corrects the angle of the wheel angle through the steer-by-wire system in the main steer-by-wire chassis, the control method is proportional-integral-derivative, and the joint control mode adopts the steer-by-wire system, the brake-by-wire system and the active suspension system for joint control, the wheel correction angle controlled by the steer-by-wire system and the wheel braking force controlled by the brake-by-wire system can change the vehicle yaw motion moment, the average value of the absolute values of the braking forces of the tires of each wheel of the vehicle The average value of the absolute values of the wheel angles of each wheel The control adjustment is made, the control method adopts fuzzy control, the active suspension control system changes the vehicle roll motion moment by controlling the size of the anti-roll moment and the damper damping force, the damper force difference coefficient λ is introduced to represent the size of the left-right side damper damping force difference degree factor ζ, and the effect of the active suspension on the vehicle anti-rollover is evaluated according to the size of the left-right side damper damping force difference degree factor ζ.

[0090] Specifically includes the following contents:

[0091] S1, a three-degree-of-freedom vehicle model is established,

[0092] The roll motion moment balance equation around the X axis is:

[0093]

[0094] The yaw motion moment balance equation around the Z axis is:

[0095]

[0096] The lateral motion force balance equation around the Y axis is:

[0097]

[0098] Wherein, l x is the roll moment of inertia, l z is the yaw moment of inertia, is the roll angular acceleration, is the roll angular velocity, is the roll angle of the vehicle body, m is the mass of the vehicle, m s is the sprung mass, h s is the distance from the roll center to the ground, is the yaw angular acceleration, a is the distance from the mass center to the front axle, b is the distance from the mass center to the rear axle, a y is the lateral acceleration, K is the equivalent roll stiffness of the suspension, C is the equivalent roll damping of the suspension, F yf is the front wheel cornering force, F yr is the rear wheel cornering force;

[0099] S2, the vehicle rollover risk index calculation unit, the lateral load transfer rate can be calculated according to the following formula:

[0100]

[0101] Wherein, F zl is the left side wheel vertical load, F zr is the right side wheel vertical load;

[0102] S3, the vehicle rollover risk index calculation unit, according to the body roll angle, roll angle velocity, lateral acceleration to obtain lateral load offset coefficient:

[0103]

[0104] Wherein, l is the wheel track, k1, k2 is the weighting coefficient, and k1+k2=1, h r is the height of the sprung mass center to the roll center;

[0105] S4, the vehicle rollover risk index calculation unit, according to the vehicle speed, critical speed, different types of vehicles to obtain lateral load excitation index:

[0106]

[0107] Wherein, v is the vehicle speed, v cr is the critical speed, K H is the vehicle height weighting coefficient, its value depends on the type of vehicle, when the vehicle is A class vehicle, K H =0.85, when the vehicle is B class vehicle, K H =0.90, when the vehicle is C class vehicle, K H =0.95, when the vehicle is D class vehicle, K H =1.0, is the body roll angle coefficient, its value depends on the body roll angle, when the body roll angle satisfies , when the body roll angle satisfies , when the body roll angle satisfies , K S is the vehicle loss coefficient, its value depends on the vehicle purchase time coefficient K T , the total mileage coefficient K x , the weekly driving time coefficient K t and the number of accidents in the past three years coefficient K a , its expression is:

[0108]

[0109] wherein β1, β2, β3, β4 are weight coefficients, and β1+β2+β3+β4=1, when the vehicle purchase time is less than 1 year, K T =0.1, when the vehicle purchase time is more than 1 year but not more than 3 years, K T =0.25, when the vehicle purchase time is more than 3 years, K T =0.4, when the total mileage of the vehicle is less than 15000km, K x =0.15, when the total mileage of the vehicle is more than 15000km but not more than 35000km, K x =0.3, when the total mileage of the vehicle is more than 35000km, K x =0.45, when the driving time per week is less than 10 hours, K t =0.2, when the driving time per week is more than 10 hours but not more than 15 hours, K t =0.3, when the driving time per week is more than 15 hours, K t =0.4, when the number of accidents in the past three years is less than 3, K a =0.1, when the number of accidents in the past three years is more than 3 but not more than 5, K a =0.35, when the number of accidents in the past three years is more than 5, K a =0.6.

[0110] The vehicle rollover risk index calculation unit determines the rollover risk index RRI according to the lateral load transfer rate LTR, the lateral load shift coefficient LTP and the lateral load excitation index LTQ, and the expression is:

[0111] RRI=α1LTR+α2LTP+α3LTQ,-1≤RRI≤1,

[0112] By combining the expressions in S1, S2, S3, S4, we can get:

[0113]

[0114] Convert it to matrix form as follows:

[0115]

[0116] wherein Q e is a parameter weight matrix, and α1, α2, α3 are weight factors, wherein α1+α2+α3=1.

[0117] The vehicle roll-over prevention judging unit judges the execution control mode of the roll-over prevention control system according to the size of the roll-over risk index, if the roll-over risk index |RRI|≤0.3, the roll-over prevention control system does not execute control work, if the roll-over risk index 0.3<|RRI|≤0.65, the roll-over prevention control system executes single control mode, if the roll-over risk index 0.65<|RRI|≤1, the roll-over prevention control system executes joint control mode;

[0118] The single control mode is to control by using the steer-by-wire system, the brake-by-wire system and the active suspension system are not started to work, through proportional-integral-derivative control, the angle of the wheel angle is moderately controlled to prevent against the driver's intention, the specific content is as follows:

[0119] The steer-by-wire system control is to reduce the steering angle to reduce the yaw rate and lateral acceleration, thereby reducing the lateral load transfer rate;

[0120] In the steady state steering working condition, the yaw rate gain can be expressed as:

[0121]

[0122] Wherein, L is the wheelbase, δ is the front wheel angle, K z is the understeer coefficient, the size is:

[0123]

[0124] Wherein, when K z =0, the vehicle behaves as neutral steering, when K z <0, the vehicle behaves as oversteering, when K z >0, the vehicle behaves as understeering, k1 is the front wheel cornering stiffness, k2 is the rear wheel cornering stiffness,

[0125] The steady state response of the yaw rate ω to the front wheel angle δ input can be expressed as:

[0126]

[0127] The yaw rate change amount caused by the wheel angle angle δ c corrected by the steer-by-wire system is:

[0128]

[0129] The joint control mode adopts the steer-by-wire system, the brake-by-wire system and the active suspension system for joint control, the wheel correction angle controlled by the steer-by-wire system and the wheel braking force controlled by the brake-by-wire system can change the vehicle yaw motion moment, the average value of the absolute value of the vehicle tire braking force Vehicle speed v, average value of absolute value of each wheel angle The control adjustment is made, the control method adopts fuzzy control, the active suspension control system changes the vehicle roll movement moment by controlling the size of the anti-roll moment and the damper damping force, the damper force difference coefficient λ is introduced to represent the size of the left and right side damper damping force difference degree factor ζ, the effect of the active suspension on the vehicle roll prevention is evaluated according to the size of the left and right side damper damping force difference degree factor ζ, and the specific content is as follows:

[0130] The steer-by-wire system control is the same as the steer-by-wire system control scheme in the single control mode;

[0131] The brake-by-wire system control means that different braking forces are applied to different wheels to increase an anti-yaw moment for the vehicle, according to the attachment ellipse characteristics of the tire, increasing the braking force of the vehicle can reduce the side slip force of the vehicle, and the formula for the mutual influence of the side slip force and the braking force is:

[0132]

[0133] Among them, F xmax is the maximum braking force of the tire, F ymax is the maximum side slip force of the tire, F x is the tire braking force, and F y is the tire side slip force;

[0134] The maximum side slip force can be considered as the side slip force of the tire at a certain side slip angle without braking force, and the maximum braking force is determined by the tire vertical force and the tire and road attachment coefficient, and the formula is as follows:

[0135] F xmax =φF z ,

[0136] Among them, φ is the road attachment coefficient, and F z is the tire vertical force;

[0137] The vehicle yaw movement moment balance equation after adopting the steer-by-wire system control and the brake-by-wire system control is changed to:

[0138]

[0139] Among them, M b is the anti-yaw moment generated by the brake-by-wire, and the size is:

[0140]

[0141] Among them, l is the wheel track, F xrf is the front axle right wheel tire braking force, F xrr is the rear axle right wheel tire braking force, and F xlfFor the braking force of the left wheel tire on the front axle, F xlr Braking force for the left rear wheel tire;

[0142] Based on the average absolute value of the braking force of each wheel tire of the vehicle The magnitude and speed v of the vehicle, and the average absolute value of the turning angle of each wheel Make adjustments, The expression is as follows:

[0143]

[0144] The expression is as follows:

[0145]

[0146] Where, δ fl The left front wheel steering angle is δ. fr The steering angle of the right front wheel is δ. rl The left rear wheel steering angle is δ. rr The steering angle of the right rear wheel;

[0147] The adjustment method used is fuzzy control. The inputs to this fuzzy control method are the vehicle speed and the average of the absolute values ​​of the wheel angles. The fuzzy set of vehicle speeds is defined as ZX, X, Z, D, ZD, with the following fuzzy rules: ZX is a vehicle speed v satisfying 0 ≤ v ≤ 35 km / h, X is a vehicle speed v satisfying 35 < v ≤ 50 km / h, Z is a vehicle speed v satisfying 50 < v ≤ 70 km / h, D is a vehicle speed v satisfying 70 < v ≤ 90 km / h, and ZD is a vehicle speed v satisfying v > 90 km / h. The fuzzy set of the average of the absolute values ​​of the wheel angles is defined as ZX, X, Z, D, ZD, with the following fuzzy rules: ZX is the average of the absolute values ​​of the wheel angles. satisfy X is the average of the absolute values ​​of the steering angles of each wheel. satisfy Z is the average of the absolute values ​​of the steering angles of all wheels. satisfy D is the average of the absolute values ​​of the steering angles of all wheels. satisfy ZD is the average of the absolute values ​​of the steering angles of all wheels. satisfy

[0148] The output of this fuzzy control method is the average of the absolute values ​​of the braking forces of each wheel tire of the vehicle. The fuzzy set is defined as ZX, X, Z, D, ZD, and the fuzzy rule is defined as follows: ZX is the average absolute value of the braking force of each wheel of the vehicle. satisfy X is the average absolute value of the braking force of each wheel tire of the vehicle. satisfies Z is the average of the absolute values of the tire braking forces of each wheel of the vehicle satisfies D is the average of the absolute values of the tire braking forces of each wheel of the vehicle satisfies ZD is the average of the absolute values of the tire braking forces of each wheel of the vehicle satisfies

[0149] The active suspension system control refers to applying different damping forces to the shock absorbers in the active suspension to increase an anti-roll moment for the vehicle, and the roll motion moment balance equation of the vehicle after the active suspension control changes to:

[0150]

[0151] wherein M d is the anti-roll moment generated by the active suspension system, and the size is:

[0152]

[0153] wherein F zrf is the right front suspension shock absorber damping force, F zrr is the right rear suspension shock absorber damping force, F zlf is the left front suspension shock absorber damping force, and F zlr is the right front suspension shock absorber damping force;

[0154] A left and right side shock absorber damping force difference degree factor ζ is introduced to evaluate the degree of vehicle roll-over prevention control by the active suspension, and the expression is as follows:

[0155]

[0156] wherein λ is a damping force difference coefficient, and the size depends on the wheelbase l, when the wheelbase l does not exceed 1.6 m, λ = 0.5, when the wheelbase l exceeds 1.6 m but does not exceed 1.8 m, λ = 0.65, and when the wheelbase l exceeds 1.8 m, λ = 0.8;

[0157] According to the size of the left and right side shock absorber damping force difference degree factor ζ, the vehicle is adjusted accordingly, and the adjustment rules are as follows:

[0158] When the difference degree factor ζ of the left and right side shock absorber damping forces is less than or equal to 8%, it is judged that the active suspension system control rollover effect is good, the active suspension control is still normally executed, and the shock absorber damping force is still normally output; when the difference degree factor ζ of the left and right side shock absorber damping forces is greater than 8%, it is judged that the active suspension system control rollover effect is poor, the active suspension control is temporarily normally executed, the control system continues to judge whether ζ is greater than 8% after 5s, if it is judged again that ζ is greater than 8%, the active suspension system control is still normally executed, and the shock absorber damping force is still normally output, if it is judged again that ζ is less than or equal to 8%, the active suspension system control and the shock absorber damping force need to be adjusted again.

Claims

1. A roll-over prevention control system for a vehicle based on a drive-by-wire chassis, characterized by, The vehicle driving information detection unit, the vehicle rollover danger index calculation unit, the vehicle anti-rollover judgment unit and the vehicle anti-rollover execution unit are included. The vehicle driving information detection unit is used for acquiring real-time vehicle speed, body roll angle, lateral acceleration, wheel vertical load and tire side force, establishing a three-degree-of-freedom vehicle model, listing roll motion moment balance equation, yaw motion moment balance equation and lateral motion force balance equation. The vehicle rollover danger index calculation unit is configured to calculate a lateral load transfer rate , a lateral load offset coefficient , and a lateral load excitation index , thereby obtaining a rollover danger index ; and the expression is: ， wherein , , is a weight factor, wherein ; The vehicle anti-rollover judging unit is configured to judge whether the anti-rollover system performs a control operation, if the rollover risk index , the anti-rollover control system does not perform a control operation, if the rollover risk index , the anti-rollover control system performs a single control operation mode, if the rollover risk index , the anti-rollover control system performs a joint control operation mode, wherein the single control mode only corrects the angle of the wheel rotation through the steer-by-wire system in the chassis-by-wire system, the joint control mode adopts the steer-by-wire system, the brake-by-wire system and the active suspension system for joint control, the wheel correction angle controlled by the steer-by-wire system and the wheel braking force controlled by the brake-by-wire system can change the lateral motion moment of the vehicle, the control method adopts fuzzy control, the active suspension control system changes the roll motion moment of the vehicle by controlling the size of the anti-roll torque and the damper damping force, and the effect of the active suspension on the vehicle anti-rollover is evaluated according to the size of the left and right damper damping force difference degree factor . The vehicle anti-rollover execution unit includes a steer-by-wire system, a brake-by-wire system, and an active suspension system, different systems are controlled according to different control modes, a single control mode only corrects the angle of the wheel angle through the steer-by-wire system in the main steer-by-wire chassis, the control method is proportional-integral-derivative, the combined control mode adopts the steer-by-wire system, the brake-by-wire system and the active suspension system for combined control, the wheel correction angle controlled by the steer-by-wire system and the wheel braking force controlled by the brake-by-wire system can change the vehicle yaw motion moment, the average value of the absolute value of the tire braking force of each wheel of the vehicle , vehicle speed , average value of absolute value of each wheel angle Control adjustment is made, the control method adopts fuzzy control, the active suspension control system changes the vehicle roll motion moment by controlling the roll resistance moment and the size of the damper damping force, and introduces a damping force difference coefficient to represent the size of the left and right side damper damping force difference degree factor , and the effect of the active suspension on the vehicle anti-rollover is evaluated according to the size of the left and right side damper damping force difference degree factor .

2. The vehicle roll-over control system based on the drive-by-wire chassis according to claim 1, characterized in that: Specifically, the following contents are included: S1, a three-degree-of-freedom vehicle model is established, The roll motion moment balance equation around the X-axis is: ， The yaw motion moment balance equation around the Z-axis is: ， The lateral motion force balance equation around the Y-axis is: ， wherein, is the roll rotational inertia, is the yaw rotational inertia, is the roll angular acceleration, is the roll angular velocity, is the roll angle of the vehicle body, is the total vehicle mass, is the sprung mass, is the distance from the roll center to the ground, is the yaw angular acceleration, is the distance from the center of mass to the front axle, is the distance from the center of mass to the rear axle, is the lateral acceleration, is the suspension equivalent roll stiffness, is the suspension equivalent roll damping, is the front wheel cornering power, is the rear wheel cornering power; S2, the vehicle rollover danger index calculation unit can calculate the lateral load transfer ratio according to the following formula: ， wherein, is the left side wheel vertical load, is the right side wheel vertical load; S3, the vehicle rollover danger index calculation unit obtains the lateral load offset coefficient according to the body roll angle, roll angular velocity and lateral acceleration: ， wherein, is the wheel track, is a weighting factor, and , is the height of the sprung mass center to the roll center; S4, the vehicle rollover danger index calculation unit obtains the lateral load excitation index according to the vehicle speed, critical vehicle speed and different types of vehicles: ， wherein, is the vehicle speed, is the critical vehicle speed, is the vehicle height weighting coefficient, whose value depends on the type of vehicle, when the vehicle is a class A vehicle, when the vehicle is a class B vehicle, when the vehicle is a class C vehicle, when the vehicle is a class D vehicle, , is the vehicle body roll angle coefficient, whose value depends on the vehicle body roll angle, when the vehicle body roll angle satisfies , when the vehicle body roll angle satisfies , when the vehicle body roll angle satisfies , , is the vehicle wear coefficient, whose value depends on the vehicle purchase time coefficient , the total mileage coefficient of the vehicle , the weekly driving time coefficient and the number of accidents in the past three years coefficient , and its expression is: ， wherein, , , , is a weight coefficient, and when the vehicle purchase time is less than 1 year, when the vehicle purchase time is more than 1 year but not more than 3 years, when the vehicle purchase time is more than 3 years, when the total vehicle mileage is less than 15000 km, when the total vehicle mileage is more than 15000 km but not more than 35000 km, when the total vehicle mileage is more than 35000 km, when the weekly driving time is less than 10 hours, when the weekly driving time is more than 10 hours but not more than 15 hours, when the weekly driving time is more than 15 hours, when the number of accidents in the past three years is less than 3, when the number of accidents in the past three years is more than 3 but not more than 5, when the number of accidents in the past three years is more than 5, .

3. The vehicle anti-rollover control system based on the drive-by-wire chassis according to claim 2, characterized in that: The expressions in steps S1, S2, S3 and S4 are solved simultaneously to obtain: ， The matrix form is as follows: ， ， where Q e is a parameter weight matrix.

4. The vehicle roll-over control system based on a drive-by-wire chassis according to claim 1, wherein: Specifically, the following contents are included: The vehicle anti-rollover judging unit judges the execution control working mode of the anti-rollover control system according to the magnitude of the rollover danger index, if the rollover danger index , the anti-rollover control system does not execute control working, if the rollover danger index , the anti-rollover control system executes single control working mode, if the rollover danger index , the anti-rollover control system executes joint control working mode; The single control mode is to control by using the drive-by-wire steering system, and the drive-by-wire braking system and the active suspension system are not started to work, and the angle of the wheel angle is controlled moderately by using proportional-integral-derivative control to prevent the violation of the intention of the driver, and the specific content is as follows: The drive-by-wire steering system control is to reduce the steering angle to reduce the yaw angular velocity and the lateral acceleration, thereby reducing the lateral load transfer ratio; In the steady-state steering working condition, the yaw angular velocity gain can be expressed as: ， wherein, is the wheelbase, is the front wheel steering angle, is the understeer coefficient, which is given by: ， wherein the vehicle exhibits neutral steering when the vehicle exhibits under-steer when the vehicle exhibits over-steer when the vehicle exhibits a vehicle performance as understeer, Kf is a front cornering stiffness, Kf is a front cornering stiffness, yaw angular velocity to front wheel steering angle The steady state response of the input can be expressed as: ， The angle of the wheel angle corrected by the steer-by-wire system The amount of change in yaw angular velocity caused by the steering angle is: ； The combined control mode adopts a steer-by-wire system, a brake-by-wire system and an active suspension system for combined control, the wheel correction angle controlled by the steer-by-wire system and the wheel braking force controlled by the brake-by-wire system can change the vehicle yaw motion moment, the average value of the absolute values of the braking forces of the vehicle wheels , the vehicle speed , the average value of the absolute values of the wheel angles The control adjustment is made, the control method adopts fuzzy control, the active suspension control system changes the vehicle roll motion moment by controlling the roll-resisting moment and the size of the damper damping force, and a damping force difference coefficient is introduced to represent the size of the left and right side damper damping force difference degree factor , the effect of the active suspension on the vehicle roll-over prevention is evaluated according to the size of the left and right side damper damping force difference degree factor , and the specific content is as follows: The drive-by-wire steering system control in the single control mode is the same as the drive-by-wire steering system control scheme; The drive-by-wire braking system control means that different braking forces are applied to different wheels to increase an anti-yaw moment for the vehicle, according to the attachment ellipse characteristics of the tire, increasing the braking force of the vehicle can reduce the side force of the vehicle, and the formula for the mutual influence of the side force and the braking force is: ， wherein, is the maximum braking force of the tire, is the maximum cornering force of the tire, is the braking force of the tire, is the cornering force of the tire; The maximum side force can be considered as the side force of the tire at a certain side angle without braking force, and the maximum braking force is determined by the vertical force of the tire and the attachment coefficient of the tire and the road, and the formula is as follows: ， wherein, is the road adhesion coefficient, is the tire vertical force; After the drive-by-wire steering system control and the drive-by-wire braking system control are adopted, the yaw motion moment balance equation of the vehicle changes to: ， wherein is the anti-yaw moment generated by the brake-by-wire, and has the magnitude ， wherein, is the wheel base, is the right front wheel tire braking force, is the right rear wheel tire braking force, is the left front wheel tire braking force, is the left rear wheel tire braking force; According to the average value of the absolute values of the tire braking forces of the wheels of the vehicle of the size and the vehicle speed of the average values of the absolute values of the wheel turning angles Adjustment is made, The expression is as follows: ， The expression is as follows: ， wherein, is a left front wheel steering angle, is a right front wheel steering angle, is a left rear wheel steering angle, is a right rear wheel steering angle; The adjusting method used adopts a fuzzy control method, the input of which is the average value of the vehicle speed and the absolute value of each wheel angle, the fuzzy set of the vehicle speed is defined as ZX, X, Z, D, ZD, the fuzzy rule is defined as follows: ZX is the vehicle speed satisfies km / h, X is the vehicle speed satisfies km / h, Z is the vehicle speed satisfies km / h, D is the vehicle speed satisfies km / h, ZD is the vehicle speed satisfies km / h; the fuzzy set of the average value of the absolute value of each wheel angle is defined as ZX, X, Z, D, ZD, the fuzzy rule is defined as follows: ZX is the average value of the absolute value of each wheel angle satisfies , X is the average value of the absolute value of each wheel angle satisfies , Z is the average value of the absolute value of each wheel angle satisfies , D is the average value of the absolute value of each wheel angle satisfies , ZD is the average value of the absolute value of each wheel angle satisfies ; The fuzzy control method outputs the average of the absolute values of the braking forces of the tires of each wheel of the vehicle , the fuzzy sets are defined as ZX, X, Z, D, ZD, and the fuzzy rules are defined as follows: ZX is the average of the absolute values of the braking forces of the tires of each wheel of the vehicle satisfies N, X is the average of the absolute values of the braking forces of the tires of each wheel of the vehicle satisfies N, Z is the average of the absolute values of the braking forces of the tires of each wheel of the vehicle satisfies N, D is the average of the absolute values of the braking forces of the tires of each wheel of the vehicle satisfies N, ZD is the average of the absolute values of the braking forces of the tires of each wheel of the vehicle satisfies N; The active suspension system control means that different damping forces are applied to the shock absorber in the active suspension to increase an anti-roll moment for the vehicle, and the roll motion moment balance equation of the vehicle after the active suspension control changes to: ， wherein is the anti-roll moment generated by the active suspension system, which is given by: ， wherein, is a front suspension right shock absorber damping force, is a rear suspension right shock absorber damping force, is a front suspension left shock absorber damping force, is a front suspension right shock absorber damping force; Introducing a left and right shock absorber damping force difference degree factor For evaluating the degree of active suspension to vehicle roll-over prevention control, the expression is as follows: ， wherein is the damping force difference coefficient, which depends on the wheelbase = 0.5 when the wheelbase does not exceed 1.6 m, = 0.5 when the wheelbase exceeds 1.6 m but does not exceed 1.8 m, = 0.65 when the wheelbase exceeds 1.8 m, = 0.

8. According to the size of the left and right side shock absorber damping force difference degree factor , the vehicle is adjusted accordingly, and the adjustment rules are as follows: Factors related to the difference in damping forces between the left and right shock absorbers At that time, it was determined that the active suspension system effectively controlled the rollover, the active suspension control was still executing normally, and the damper damping force was still outputting normally; when the difference in damping force between the left and right dampers was factored in... If the system determines that the rollover control effect of the active suspension system is poor, the active suspension control will temporarily operate normally, and the control system will reassess the situation after 5 seconds. Is it greater than If judged again If the active suspension system control is still functioning normally, and the shock absorber damping force is still outputting normally, then if the judgment is made again... If so, the control of the active suspension system and the damping force of the shock absorbers need to be readjusted.

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