CN106585709B - A kind of automobile chassis integrated system and its optimization method - Google Patents

Abstract

The invention discloses an automobile chassis integrated system and an optimization method thereof. The automobile chassis integrated system includes a differential power steering module, a motor braking module and a semi-active suspension module. During optimization, some structural parameters of the differential power steering module, motor braking module and semi-active suspension module are taken as the roots, and the differential power steering module, the motor braking module and the semi-active suspension module are taken as the roots, and the The comprehensive performance index of the car is the trunk, the steering performance, braking efficiency and suspension smoothness are the branches, and the steering road feel, steering sensitivity, braking deceleration, body acceleration, suspension dynamic deflection and relative dynamic load of the wheels are established as the leaves. A tree-structured vehicle chassis integrated system optimization model, and based on the optimization model, the Evol algorithm is used to optimize the design of the chassis integrated system.

Description

An automotive chassis integration system and its optimization method

technical field

The invention relates to a steering system, a braking system and a suspension system, in particular to an automobile chassis integrated system and an optimization method thereof.

Background technique

As a complex system, the automobile chassis mainly includes subsystems such as braking, steering and suspension. The steering system deflects the steering wheel according to the driver's input command to obtain the control of the driving direction of the car. The performance of the steering system determines the steering sensitivity, lightness and handling stability of the car; the function of the braking system is to make the driving The car decelerates or stops, the speed of the car driving downhill remains stable, and the car that has been parked remains stationary. The braking efficiency of the braking system and the directional stability during braking directly affect the driving safety of the car; The frame is used as a bridge connecting the body and the wheels. Its function is to transmit the vertical reaction force, longitudinal reaction force and lateral reaction force of the road surface on the wheels, as well as the torque generated by these reaction forces to the body, so as to ensure the safety of the car. In normal driving, the performance of the suspension system directly affects the ride comfort of the car.

In fact, under different driving conditions, the movements of various subsystems in the vehicle chassis system influence and interact with each other. Viewed longitudinally, the movement of individual subsystems must have an impact on many aspects of the car. From a horizontal perspective, when multiple subsystems coexist, there must be a problem of mutual influence between them. In the optimization process, due to the diversity of optimization objectives of the integrated system, it is necessary to design an appropriate optimization method to optimize the integrated system.

When the parameters of multiple subsystems are optimized according to different performance indicators, the improvement of the performance indicators of one subsystem must have a certain impact on other systems. The simple superposition of these subsystem optimizations cannot obtain the optimal chassis system synthesis. Therefore, it is particularly important to establish a suitable optimization model to optimize the chassis integrated system.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide an automobile chassis integrated system and an optimization method thereof in view of the defects involved in the background technology.

The present invention adopts the following technical solutions for solving the above-mentioned technical problems:

An automobile chassis integration system, comprising a differential power steering module, a motor braking module and a semi-active suspension module;

The differential power steering module includes a steering wheel torque angle sensor, a rack and pinion steering gear, two in-wheel motors, a vehicle speed sensor, two wheel speed sensors, a yaw rate sensor and a differential power steering control ECU;

The steering wheel assembly of the car is connected with the rack and pinion steering gear through the steering column, and the rack and pinion steering gear is connected with the axle of the front wheel of the car through the steering tie rod;

The steering wheel torque and angle sensor is arranged on the steering column and is used to obtain the torque and rotation angle of the steering wheel of the automobile;

The two in-wheel motors are respectively used for driving and braking the two front wheels;

The vehicle speed sensor is used to obtain the vehicle speed of the vehicle;

The two wheel speed sensors are respectively arranged on the two front wheels, and are respectively used to obtain the angular speed of the two front wheels;

The yaw rate sensor is used to obtain the yaw rate of the vehicle;

The differential power steering control ECU is electrically connected to the steering wheel torque and angle sensor, two in-wheel motors, vehicle speed sensor, two wheel speed sensors, and yaw rate sensor. The vehicle speed and the angular velocity of the two front wheels send current signals to the left and right wheel hub motors, so that the left and right wheel hub motors output different driving torques to achieve differential power steering;

The motor braking module includes a brake pedal position sensor and a motor braking control ECU;

The brake pedal position sensor is used to obtain vehicle brake pedal position information;

The motor braking control ECU is respectively electrically connected with the brake pedal position sensor, two wheel hub motors, vehicle speed sensor, two wheel speed sensors, and yaw rate sensor, and is used for according to the position of the brake pedal, the vehicle speed, the two front wheels The angular velocity and yaw angular velocity are adjusted to adjust the braking torque of the in-wheel motor to realize motor braking;

The semi-active suspension module includes an elastic element and a continuously adjustable shock absorber;

The elastic element and the continuously adjustable shock absorber are arranged side by side to connect the body of the automobile with the frame.

The invention also discloses an optimization method based on the vehicle chassis integrated system, comprising the following steps:

Step 1), establish a vehicle three-degree-of-freedom model;

Step 2), establishing the dynamic model of the differential power steering module, the motor braking module and the semi-active suspension module;

Step 3), deriving the quantitative formula of steering performance, braking efficiency and suspension ride comfort performance index;

Step 4), select optimization variables, establish an optimization model objective function, set constraints, and establish a tree-structured chassis integrated system optimization model;

Step 4.1), take the moment of inertia of the steering output shaft and pinion, the equivalent damping coefficient of the steering output shaft and pinion, the mass of the rack, the equivalent damping coefficient of the rack, the displacement of the rack, and the value of the tire including the hub motor. Equivalent moment of inertia, equivalent damping coefficient of tires including in-wheel motors, equivalent stiffness of front suspension, equivalent stiffness of rear suspension, equivalent damping coefficient of front suspension, equivalent damping coefficient of rear suspension as optimization variables ;

Step 4.2), the optimization model objective function is obtained from the quantitative formula of steering performance, braking efficiency and suspension smoothness performance index;

Step 4.3), set the constraints that the objective function of the optimization model needs to meet;

Step 4.4), take the optimization variable as the root, take the differential power steering module, the motor braking module and the semi-active suspension module as the root, take the comprehensive performance of the vehicle as the trunk, and take the steering performance, braking efficiency and suspension module as the root. The frame ride comfort is the branches, and the steering road feel, steering sensitivity, braking deceleration, body acceleration, suspension dynamic deflection and relative dynamic load of the wheels are used as the leaves to establish a tree-structured vehicle chassis integrated system optimization model;

Step 5), based on the optimization model of the vehicle chassis integrated system, using the Evol algorithm for optimization to obtain the optimal value of the optimization variable.

As a further optimization scheme of the optimization method of the vehicle chassis integrated system, the three-degree-of-freedom model of the vehicle described in step 1) is:

Wherein, Y ₁ =-k _f -k _r ; Y ₂ =-(ak _f -bk _r )/V; Y ₃ =-E ₁ k _f -E ₂ k _r -k _cf -k _cr ; Y ₄ =k _f ;

L ₁ =-ak _f +bk _r ; L ₂ =(2μ _r hmV ² -a ² k _f -b ² k _r )/V; L ₃ =-aE ₁ k _f +bE ₂ k _r -ak _cf +bk _cr ;

L ₄ =ak _f ; L ₅ =2μ _r hmV;

N ₁ =(k _f +k _r )h; N ₂ =(ak _f -bk _r )h/V;

N ₃ =mgh+2d(dK _2f -dK _2r 2-K _a1 -K _a2 )+h(E ₁ k _f +E ₂ k _r +k _cf +k _cr );

N ₄ =-k _f h; N ₅ =2d(dK _2f -dK _2r -K _a1 -K _a2 );

m is the mass of the vehicle; V is the speed of the vehicle; g is the acceleration of gravity; h is the height of the vehicle body; ω _r is the yaw rate; is the roll angle; δ is the rotation angle of the front wheel; I _x is the moment of inertia of the car mass to the x-axis; I _z is the moment of inertia of the car mass to the z-axis; I _xz is the inertia product of the car mass to the x and z-axes; a, b is the distance from the center of mass of the car to the front and rear wheelbases; k _f and k _r are the front and rear cornering stiffnesses respectively; E ₁ and E ₂ are the front and rear roll steering coefficients respectively; k _cf and k _cr are the front and rear lateral thrust coefficients respectively; K _a1 and K _a2 are the roll angle stiffness of the front and rear suspensions respectively; μ _r is the ground friction coefficient; d is half of the wheelbase; K _2f and K _2r are the stiffness of the front and rear suspensions, respectively.

As a further optimization scheme of the optimization method of the vehicle chassis integrated system, the quantification formula of the steering performance index described in step 3) includes the quantification formula of the steering road feel and the quantification formula of the steering sensitivity, and the quantification formula of the steering road feel is: :

The quantification formula of the steering sensitivity is:

in,

P ₃ =XA ₃ ; P ₂ =XA ₂ ; P ₁ =XA ₁ ;P ₀ =XA ₀ ;

Q ₆ =X ₂ B ₄ ; Q ₅ =X ₁ B ₄ +X ₂ B ₃ ; Q ₄ =X ₀ B ₄ +X ₁ B ₃ +X ₂ B ₂ ; Q ₃ =X ₀ B ₃ +X ₁ B ₂ + X ₂ B ₁ ;

Q ₂ =X ₀ B ₂ +X ₁ B ₁ +X ₂ B ₀ ; Q ₁ =X ₀ B ₁ +X ₁ B ₀ ; Q ₀ =X ₀ B ₀ ;

_{A3 = L4Vh2m2 - IxL5Y4} ^- _IxL4Vm ^- _{IxzN4Vm - L5N4hm - IxzVY4hm ; _}

A ₂ =I _x L ₄ Y ₁ -I _x L ₁ Y ₄ -I _xz N ₁ Y ₄ +I _xz N ₄ Y ₁ +L ₅ N ₅ Y ₄ +L ₄ N ₅ Vm-L ₁ N ₄ hm+ L ₄ N ₁ hm;

A ₁ =L ₁ N ₅ Y ₄ -L ₄ N ₅ Y ₁ +L ₅ N ₃ Y ₄ -L ₅ N ₄ Y ₃ -L ₃ N ₄ Vm+L ₄ N ₃ Vm-L ₃ VY ₄ hm+L ₄ VY ₃ hm;

A ₀ =L ₁ N ₃ Y ₄ -L ₁ N ₄ Y ₃ -L ₃ N ₁ Y ₄ +L ₃ N ₄ Y ₁ +L ₄ N ₁ Y ₃ -L ₄ N ₃ Y ₁ ;

B ₄ =I _z Vh ² m ² -I _x I _z Vm;

It is the transfer function of the torque transmitted from the wheel to the hand through the steering gear for the road excitation to the equivalent torque of the driver acting on the steering wheel; is the transfer function from the steering wheel angle to the yaw rate, s is the signal in the frequency domain, T _h ( _s ) is the equivalent torque of the driver acting on the steering wheel in the frequency domain; The torque transmitted by the steering gear to the hand; ω _r (s), θ _s (s) and δ (s) represent the yaw rate, steering wheel angle and front wheel angle in the frequency domain, respectively, K _s is the equivalent of the steering wheel torque and angle sensor Rigidity; n ₂ is the transmission ratio from the steering screw to the front wheel; J _e and _Be are the equivalent moment of inertia and equivalent damping coefficient of the steering output shaft and the gear structure of the rack and pinion steering gear, respectively; m _r is the equalization of the rack effective mass; b _r is the equivalent damping coefficient of the rack; k _r is the equivalent stiffness of the rack; x _r is the displacement of the rack; r _δ is the lateral offset distance of the kingpin of the left and right front steering wheels; r _p is the radius of the pinion; r is the radius of the wheel; N _l is the distance between the steering tie rod and the axle; G is the reduction ratio of the in-wheel motor reduction mechanism; J _eq and B _eq are the tires (including the in-wheel motor), etc. is the effective moment of inertia and equivalent damping coefficient; Ka is the torque coefficient of the in-wheel motor; K _m1 and K _m2 are the booster gains of the left and right in-wheel _motors , respectively.

As a further optimization scheme of the optimization method of the vehicle chassis integrated system, the quantitative formula of braking efficiency described in step 3) includes the quantitative formula of braking deceleration, which is specifically expressed as:

where: is the transfer function from the steering wheel angle to the braking deceleration, a(s) is the braking deceleration in the frequency domain,

As a further optimization scheme of the optimization method of the vehicle chassis integrated system, the quantification formula of the indicators of the suspension ride comfort performance described in step 3) includes the quantification formula of the vibration acceleration of the front and rear bodies, the quantification formula of the dynamic deflection of the front and rear suspensions, and the relative relationship between the front and rear wheels. The quantification formulas of dynamic load are:

where: and respectively represent the front and rear body vibration acceleration transfer functions; and respectively represent the dynamic deflection transfer function of the front and rear suspensions; and Respectively represent the relative dynamic load transfer function of the front and rear wheels; q represents the road excitation; Z _2f and Z _2r represent the front and rear body displacement, respectively; Z _1f and Z _1r represent the front and rear wheel displacement, respectively; f _df and f _dr represent the front and rear suspension dynamic deflection; and respectively represent the front and rear relative dynamic loads, in the formula, G _f =(m _1f +m _2f )g, G _r =(m _1r +m _2r )g; m _1f and m _1r respectively represent the front and rear unsprung masses; m _2f and m _2r represents the front and rear sprung mass respectively; K _t is the equivalent stiffness of the tire; K _2f and K _2r represent the front and rear suspension stiffness respectively; C _2f and C _2r represent the front and rear suspension damping respectively; g is the gravitational acceleration.

As a further optimization scheme of the optimization method of the vehicle chassis integrated system, the objective function f(X) of the optimization model described in step 4.2) is:

f(X)=W ₁ f ₁ (X)+W ₂ f ₂ (X)+W ₃ f ₃ (X)

where:

In the formula, f is the frequency of the road excitation input; is the pavement power spectral density; _wi is the weight coefficient; Wi is the weight coefficient of the sub-objective function _.

As a further optimization scheme of the optimization method of the vehicle chassis integrated system, the constraints that the objective function of the optimization model described in step 4.3) needs to satisfy are:

The denominator of the steering sensitivity quantification formula satisfies the Rolls criterion, the braking deceleration satisfies a≤g, the suspension dynamic deflection satisfies f _cr =(0.6～0.8)f _cf , the relative damping coefficient satisfies ξ _f ∈[0.2,0.4], ξ _r ∈ [0.2, 0.4];

Wherein, f _cf =(m _1f +m _2f )g/k _2f ; f _cr =(m _1r +m _2r )g/k _2r ;

Compared with the prior art, the present invention adopts the above technical scheme, and has the following technical effects:

The optimization model established by the present invention also takes into account the influence of the differential power steering module, the motor braking module and the semi-active suspension module on the comprehensive performance of the vehicle, can effectively coordinate the problem of the diversity of objectives in the optimization of the three subsystems, and integrates the three subsystems. Each subsystem is optimized as different branches, which can effectively improve the computing efficiency.

Description of drawings

1 is a schematic diagram of the arrangement of electric power steering and motor braking modules of the present invention;

2 is a schematic diagram of the arrangement of the semi-active suspension module of the present invention;

Fig. 3 is the optimization model structure schematic diagram of the present invention;

FIG. 4 is a flow chart of the optimization method of the present invention.

In the figure, 1- steering output shaft and pinion rotational inertia, 2- steering output shaft and pinion equivalent damping coefficient, 3- rack mass, 4- rack equivalent damping coefficient, 5- rack displacement, 6- Equivalent moment of inertia of tire including in-wheel motor, 7- Equivalent damping coefficient of tire including in-wheel motor, 8- Equivalent stiffness of front suspension, 9- Equivalent stiffness of rear suspension, 10- Front suspension, etc. Effective damping coefficient, 11 - equivalent damping coefficient of rear suspension, 12 - steering wheel torque angle sensor, 13 - rack and pinion steering gear, 14 - wheel hub motor.

Detailed ways

Below in conjunction with accompanying drawing, the technical scheme of the present invention is described in further detail:

The invention discloses an automobile chassis integrated system and an optimization method thereof. As shown in FIG. 1 , the present invention discloses an automobile chassis integrated system, which includes a differential power steering module, a motor braking module and a semi-active suspension module.

The differential power steering module includes a steering wheel torque angle sensor, a rack and pinion steering gear, two in-wheel motors, a vehicle speed sensor, two wheel speed sensors, a yaw rate sensor and a differential power steering control ECU; The steering column is connected with the rack and pinion steering gear through the steering column, and the rack and pinion steering gear is connected with the axle of the front wheel of the automobile through the steering tie rod; the steering wheel torque angle sensor is arranged on the steering column and is used to obtain the torque of the steering wheel of the automobile. and the turning angle; the two in-wheel motors are used for driving and braking the two front wheels respectively; the vehicle speed sensor is used to obtain the vehicle speed; the two wheel speed sensors are respectively arranged on the two front wheels, respectively Used to obtain the angular velocity of the two front wheels; the yaw angular velocity sensor is used for the yaw angular velocity of the car; the differential power steering control ECU is respectively connected with the steering wheel torque and angle sensor, two in-wheel motors, vehicle speed sensor, two The wheel speed sensor and the yaw rate sensor are electrically connected, and send current signals to the left and right hub motors according to the torque and angle of the steering wheel, the yaw rate, the vehicle speed and the angular velocity of the two front wheels, so that the left and right hub motors output different driving torques. for differential power steering.

The motor brake module includes a brake pedal position sensor and a motor brake control ECU; the brake pedal position sensor is used to obtain vehicle brake pedal position information; the motor brake control ECU and the brake pedal position sensor are respectively , Two in-wheel motors, vehicle speed sensor, two wheel speed sensors, and yaw angular velocity sensor are electrically connected, and are used to adjust the braking torque of the in-wheel motor according to the position of the brake pedal, the vehicle speed, the angular velocity of the two front wheels, and the yaw angular velocity. Adjust to achieve motor braking.

As shown in FIG. 2 , the semi-active suspension module includes an elastic element and a continuously adjustable shock absorber; the elastic element and the continuously adjustable shock absorber are arranged in parallel to connect the vehicle body and the frame.

As shown in Figure 3, some structural parameters of the differential power steering module, the motor braking module and the semi-active suspension module are taken as the roots, and the differential power steering module, the motor braking module and the semi-active suspension module are taken as the tree The root, taking the comprehensive performance index of the car as the trunk, taking the steering performance, braking efficiency and suspension smoothness as the branch, taking the steering road feel, steering sensitivity, braking deceleration, body acceleration, suspension dynamic deflection and wheel relative dynamic load A tree-structured vehicle chassis integrated system optimization model is established for leaves.

As shown in FIG. 4 , the present invention discloses an optimization method based on the integrated system of the automobile chassis, including the following steps:

Step 1), establish a three-degree-of-freedom model of the vehicle:

Wherein, Y ₁ =-k _f -k _r ; Y ₂ =-(ak _f -bk _r )/V; Y ₃ =-E ₁ k _f -E ₂ k _r -k _cf -k _cr ; Y ₄ =k _f ;

L ₁ =-ak _f +bk _r ; L ₂ =(2μ _r hmV ² -a ² k _f -b ² k _r )/V; L ₃ =-aE ₁ k _f +bE ₂ k _r -ak _cf +bk _cr ;

L ₄ =ak _f ; L ₅ =2μ _r hmV;

N ₁ =(k _f +k _r )h; N ₂ =(ak _f -bk _r )h/V;

N ₃ =mgh+2d(dK _2f -dK _2r 2-K _a1 -K _a2 )+h(E ₁ k _f +E ₂ k _r +k _cf +k _cr );

N ₄ =-k _f h; N ₅ =2d(dK _2f -dK _2r -K _a1 -K _a2 );

m is the mass of the vehicle; V is the speed of the vehicle; g is the acceleration of gravity; h is the height of the vehicle body; ω _r is the yaw rate; is the roll angle; δ is the rotation angle of the front wheel; I _x is the moment of inertia of the car mass to the x axis; I _z is the moment of inertia of the car mass to the z axis; I _xz is the inertia product of the car mass to the x and z axes; a, b is the distance from the center of mass of the car to the front and rear wheelbases; k _f and k _r are the front and rear cornering stiffnesses respectively; E ₁ and E ₂ are the front and rear roll steering coefficients respectively; k _cf and k _cr are the front and rear lateral thrust coefficients respectively; K _a1 and K _a2 are the roll angle stiffness of the front and rear suspensions respectively; μ _r is the ground friction coefficient; d is half of the wheelbase; K _2f and K _2r are the stiffness of the front and rear suspensions, respectively.

Step 2), establish the dynamic models of the differential power steering module, the motor braking module and the semi-active suspension module.

Step 3), in turn derive the quantification formulas of the steering performance, braking efficiency and suspension ride comfort performance index.

First, the steering performance indicators are derived, including steering road feel and steering sensitivity. The quantification formula is as follows:

The quantification formula of steering road feeling is:

where:

In order to derive the quantification formula of steering sensitivity, first derive the relationship between the yaw rate and the front wheel angle:

In the formula: A ₃ =L ₄ Vh ² m ² -I _x L ₅ Y ₄ -I _x L ₄ Vm-I _xz N ₄ Vm-L ₅ N ₄ hm-I _xz VY ₄ hm;

A ₂ =I _x L ₄ Y ₁ -I _x L ₁ Y ₄ -I _xz N ₁ Y ₄ +I _xz N ₄ Y ₁ +L ₅ N ₅ Y ₄ +L ₄ N ₅ Vm-L ₁ N ₄ hm+ L ₄ N ₁ hm;

A ₁ =L ₁ N ₅ Y ₄ -L ₄ N ₅ Y ₁ +L ₅ N ₃ Y ₄ -L ₅ N ₄ Y ₃ -L ₃ N ₄ Vm+L ₄ N ₃ Vm-L ₃ VY ₄ hm+L ₄ VY ₃ hm;

A ₀ =L ₁ N ₃ Y ₄ -L ₁ N ₄ Y ₃ -L ₃ N ₁ Y ₄ +L ₃ N ₄ Y ₁ +L ₄ N ₁ Y ₃ -L ₄ N ₃ Y ₁ ;

B ₄ =I _z Vh ² m ² -I _x I _z Vm;

Then derive the relationship between the front wheel angle and the pinion angle:

where:

The quantification formula of steering sensitivity is finally derived as:

In the formula: P ₃ =XA ₃ ; P ₂ =XA ₂ ; P ₁ =XA ₁ ; P ₀ =XA ₀ ;

Q ₆ =X ₂ B ₄ ; Q ₅ =X ₁ B ₄ +X ₂ B ₃ ; Q ₄ =X ₀ B ₄ +X ₁ B ₃ +X ₂ B ₂ ; Q ₃ =X ₀ B ₃ +X ₁ B ₂ + X ₂ B ₁ ;

Q ₂ =X ₀ B ₂ +X ₁ B ₁ +X ₂ B ₀ ; Q ₁ =X ₀ B ₁ +X ₁ B ₀ ; Q ₀ =X ₀ B ₀ ;

It is the transfer function of the torque transmitted from the wheel to the hand through the steering gear for the road excitation to the equivalent torque of the driver acting on the steering wheel; is the transfer function from the steering wheel angle to the yaw rate, s is the signal in the frequency domain, T _h ( _s ) is the equivalent torque of the driver acting on the steering wheel in the frequency domain; The torque transmitted by the steering gear to the hand; ω _r (s), θ _s (s) and δ (s) represent the yaw rate, steering wheel angle and front wheel angle in the frequency domain, respectively, K _s is the equivalent of the steering wheel torque and angle sensor Rigidity; n ₂ is the transmission ratio from the steering screw to the front wheel; J _e and _Be are the equivalent moment of inertia and equivalent damping coefficient of the steering output shaft and the gear structure of the rack and pinion steering gear, respectively; m _r is the equalization of the rack effective mass; b _r is the equivalent damping coefficient of the rack; k _r is the equivalent stiffness of the rack; x _r is the displacement of the rack; rδ is the lateral offset distance of the kingpin of the left and right front steering wheels; r _p is the radius of the pinion; r is the radius of the wheel; N _l is the distance between the tie rod and the axle; G is the reduction ratio of the in-wheel motor reduction mechanism; J _eq and B _eq are the equivalent of the tire (including the in-wheel motor) respectively Moment of inertia and equivalent damping coefficient; Ka is the torque coefficient of the in-wheel motor; K _m1 and K _m2 are the booster gains of the left and right in-wheel _motors , respectively.

Secondly, the braking efficiency index, including braking deceleration, is derived. Its quantitative formula is:

In the formula, is the transfer function from the steering wheel angle to the braking deceleration, a(s) is the braking deceleration in the frequency domain,

Finally, the suspension comfort index is derived, including the vibration acceleration of the front and rear body, the dynamic deflection of the front and rear suspension, and the relative dynamic load of the front and rear wheels. The quantitative formulas are:

where: and respectively represent the front and rear body vibration acceleration transfer functions; and respectively represent the dynamic deflection transfer function of the front and rear suspensions; and Respectively represent the relative dynamic load transfer function of the front and rear wheels; q represents the road excitation; Z _2f and Z _2r represent the front and rear body displacement, respectively; Z _1f and Z _1r represent the front and rear wheel displacement, respectively; f _df and f _dr represent the front and rear suspension dynamic deflection; and respectively represent the front and rear relative dynamic loads, in the formula, G _f =(m _1f +m _2f )g, G _r =(m _1r +m _2r )g; m _1f and m _1r respectively represent the front and rear unsprung masses; m _2f and m _2r represents the front and rear sprung mass respectively; K _t is the equivalent stiffness of the tire; K _2f and K _2r represent the front and rear suspension stiffness respectively; C _2f and C _2r represent the front and rear suspension damping respectively; g is the gravitational acceleration.

Step 4), select the optimization model optimization variables, establish the optimization model objective function, set the constraints, and establish the chassis integrated system optimization model of the tree structure;

(1) Select differential power steering module, motor braking module and semi-active suspension module steering output shaft and pinion rotational inertia, steering output shaft and pinion equivalent damping coefficient, rack mass, rack equivalent damping coefficient Rack displacement, equivalent moment of inertia of tire including in-wheel motor, equivalent damping coefficient of tire including in-wheel motor, equivalent stiffness of front suspension, equivalent stiffness of rear suspension, equivalent damping coefficient of front suspension, The equivalent damping coefficient of the rear suspension is used as an optimization variable;

(2) The objective function of the optimization model is obtained from the quantification formula of the steering performance, braking efficiency and suspension smoothness performance index;

Turning to the performance objective function:

Braking efficiency objective function:

Suspension smoothness objective function:

In the formula: f is the frequency when the road roughness is input; is the power spectral density of the road surface; w _i is the weight coefficient.

Combining the above three subsystem performance index objective functions, the optimization model objective objective function is obtained:

f(X)=W ₁ f ₁ (X)+W ₂ f ₂ (X)+W ₃ f ₃ (X)

In the formula: Wi is the weight _coefficient of the sub-objective function.

(3) In the optimization process, set the following constraints: the denominator of the steering sensitivity quantification formula should satisfy the Rolls criterion, the braking deceleration should satisfy _a≤g , and the suspension dynamic deflection should satisfy fcr=(0.6～0.8)f _cf and the relative damping coefficients satisfy ξ _f ∈ [0.2, 0.4], ξ _r ∈ [0.2, 0.4].

In the formula: f _cf =(m _1f +m _2f )g/k _2f ; f _cr =(m _1r +m _2r )g/k _2r ;

(4) According to the tree structure, some structural parameters of the differential power steering module, the motor braking module and the semi-active suspension module are used as roots, and the differential power steering module, the motor braking module and the semi-active suspension module are used as the roots. It is the root of the tree, the comprehensive performance index of the car is the trunk, the steering performance, braking efficiency and suspension smoothness are the branches, and the steering road feel, steering sensitivity, braking deceleration, body acceleration, suspension dynamic deflection and wheel relative Dynamic load builds a tree-structured vehicle chassis integrated system optimization model for leaves;

Step 5), based on the optimization model of the vehicle chassis integrated system, using the Evol algorithm for optimization to obtain the optimal value of the optimization variable.

The specific Evol algorithm implementation process is as follows:

Step1: Determine the optimization variable set and code it;

Step2: Determine the control parameters of the Evol algorithm and the specific strategy used. The control parameters of the Evol algorithm include: population size, mutation operator, crossover operator, maximum evolutionary algebra, termination conditions, etc.;

Step3: Randomly generate the initial population, evolution algebra t=1;

Step4: Evaluate the initial population, that is, calculate the fitness value of each individual in the initial population;

Step5: Determine whether the termination condition is reached or the evolutionary algebra reaches the minimum, if so, the evolution is terminated, and the best individual at this time is used as the solution output; if not, continue;

Step6: Perform mutation and crossover operations, process boundary conditions, and obtain temporary populations;

Step7: Evaluate the temporary population and calculate the fitness value of each individual in the temporary population;

Step8: Perform a selection operation to obtain a new population;

Step9: Evolutionary algebra t=t+1, go to step 4.

In the actual optimization process, just like the growth of a big tree, when the roots absorb nutrients from the land, they enter the roots to transport nutrients to the trunk, branches and leaves; when the leaves are photosynthesizing, the photosynthesis products are transmitted. Give branches and trunks. In the tree-structured vehicle chassis integration system optimization model, by changing the value of each optimization variable of the root, each subsystem of the tree root is affected. Each system performance index of the branch and each sub-indicator of the leaf change; when the sub-objective of the leaf changes, the system performance index of the branch and the comprehensive performance index of the car as the trunk will change.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as herein, are not to be taken in an idealized or overly formal sense. explain.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in further detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (7)

1. An optimization method of an automobile chassis integrated system comprises a differential power-assisted steering module, a motor braking module and a semi-active suspension module;

the differential power-assisted steering module comprises a steering wheel torque angle sensor, a rack and pinion steering gear, two hub motors, a vehicle speed sensor, two wheel speed sensors, a yaw rate sensor and a differential power-assisted steering control ECU;

the steering wheel assembly of the automobile is connected with a rack and pinion steering gear through a steering column, and the rack and pinion steering gear is connected with an axle of a front wheel of the automobile through a steering tie rod;

the steering wheel torque and corner sensor is arranged on the steering column and used for acquiring the torque and the corner of the automobile steering wheel;

the two hub motors are respectively used for driving and braking two front wheels;

the vehicle speed sensor is used for acquiring the vehicle speed of the automobile;

the two wheel speed sensors are respectively arranged on the two front wheels and are respectively used for obtaining the angular speeds of the two front wheels;

the yaw velocity sensor is used for acquiring the yaw velocity of the automobile;

the differential power-assisted steering control ECU is respectively electrically connected with a steering wheel torque corner sensor, two hub motors, a vehicle speed sensor, two wheel speed sensors and a yaw angular velocity sensor, and sends current signals to the left and right hub motors according to the torque and corner of the steering wheel of the automobile, the yaw angular velocity, the vehicle speed and the angular velocities of two front wheels, so that the left and right hub motors output different driving torques to realize differential power-assisted steering;

the motor braking module comprises a brake pedal position sensor and a motor braking control ECU;

the brake pedal position sensor is used for acquiring the position information of the automobile brake pedal;

the motor braking control ECU is respectively and electrically connected with a brake pedal position sensor, two hub motors, a vehicle speed sensor, two wheel speed sensors and a yaw rate sensor, and is used for adjusting the braking torque of the hub motors according to the position of the brake pedal, the vehicle speed, the angular speeds of two front wheels and the yaw rate to realize motor braking;

the semi-active suspension module comprises an elastic element and a continuously adjustable shock absorber;

the elastic element and the continuous adjustable shock absorber are arranged in parallel to connect the body of the automobile with the frame;

the optimization method of the automobile chassis integrated system is characterized by comprising the following steps of:

step 1), establishing a three-degree-of-freedom model of the whole vehicle;

step 2), establishing a dynamic model of a differential power-assisted steering module, a motor braking module and a semi-active suspension module;

step 3), deriving a quantitative formula of steering performance, braking efficiency and suspension ride comfort performance indexes;

step 4), selecting optimization variables, establishing an optimization model objective function, setting constraint conditions, and establishing a chassis integrated system optimization model with a tree structure;

step 4.1), taking the rotational inertia of the steering output shaft and the pinion, the equivalent damping coefficient of the steering output shaft and the pinion, the rack mass, the rack equivalent damping coefficient, the rack displacement, the equivalent rotational inertia of a tire comprising a hub motor, the equivalent damping coefficient of the tire comprising the hub motor, the front suspension equivalent stiffness, the rear suspension equivalent stiffness, the front suspension equivalent damping coefficient and the rear suspension equivalent damping coefficient as optimization variables;

step 4.2), obtaining an optimized model objective function according to a quantitative formula of steering performance, braking efficiency and suspension smoothness performance indexes;

step 4.3), setting constraint conditions which need to be met by an optimization model objective function;

step 4.4), establishing an automobile chassis integrated system optimization model with a tree structure by taking the optimized variable as a root, taking the differential power-assisted steering module, the motor braking module and the semi-active suspension module as tree roots, taking the comprehensive performance of the automobile as a trunk, taking the steering performance, the braking efficiency and the suspension smoothness as branches, and taking the steering road feel, the steering sensitivity, the braking deceleration, the automobile body acceleration, the suspension dynamic deflection and the relative dynamic load of wheels as leaves;

and 5) optimizing by adopting an Evol algorithm based on the automobile chassis integrated system optimization model to obtain the optimal value of the optimized variable.

2. The optimization method of the automobile chassis integrated system according to claim 1, wherein the three-degree-of-freedom model of the whole automobile in the step 1) is as follows:

wherein, Y₁＝-k_f-k_r；Y₂＝-(ak_f-bk_r)/V；Y₃＝-E₁k_f-E₂k_r-k_cf-k_cr；Y₄＝k_f；

L₁＝-ak_f+bk_r；L₂＝(2μ_rhmV²-a²k_f-b²k_r)/V；L₃＝-aE₁k_f+bE₂k_r-ak_cf+bk_cr；

L₄＝ak_f；L₅＝2μ_rhmV；

N₁＝(k_f+k_r)h；N₂＝(ak_f-bk_r)h/V；

N₃＝mgh+2d(dK_2f-dK_2r2-K_a1-K_a2)+h(E₁k_f+E₂k_r+k_cf+k_cr)；

N₄＝-k_fh；N₅＝2d(dK_2f-dK_2r-K_a1-K_a2)；

m is the mass of the whole vehicle; v is the vehicle speed; g is the acceleration of gravity; h is the height of the vehicle body; omega_rβ is the centroid slip angle;is a side inclination angle; delta is a front wheel corner; i is_xThe moment of inertia of the mass of the vehicle to the x-axis; i is_zThe moment of inertia of the mass of the automobile to the z axis; i is_xzThe inertia product of the automobile mass to the x and z axes; a. b is the distance from the center of mass of the automobile to the front-rear wheelbase respectively; k is a radical of_f、k_rFront and rear cornering stiffness, respectively; e₁、E₂Respectively the front and rear side-tipping steering coefficients; k is a radical of_cf、k_crFront and rear lateral thrust coefficients respectively; k_a1、K_a2Are respectively front and backSuspension roll stiffness; mu.s_rIs the ground friction coefficient; d is half of the wheel track; k_2f、K_2rFront and rear suspension stiffness, respectively.

3. The method for optimizing the vehicle chassis integration system according to claim 2, wherein the index quantization formula of the steering performance index in step 3) includes a quantization formula of steering road feel and a quantization formula of steering sensitivity, and the quantization formula of steering road feel is:

the quantization formula of the steering sensitivity is as follows:

wherein,

P₃＝XA₃；P₂＝XA₂；P₁＝XA₁；P₀＝XA₀；

Q₆＝X₂B₄；Q₅＝X₁B₄+X₂B₃；Q₄＝X₀B₄+X₁B₃+X₂B₂；Q₃＝X₀B₃+X₁B₂+X₂B₁；

Q₂＝X₀B₂+X₁B₁+X₂B₀；Q₁＝X₀B₁+X₁B₀；Q₀＝X₀B₀；

A₃＝L₄Vh²m²-I_xL₅Y₄-I_xL₄Vm-I_xzN₄Vm-L₅N₄hm-I_xzVY₄hm；

A₂＝I_xL₄Y₁-I_xL₁Y₄-I_xzN₁Y₄+I_xzN₄Y₁+L₅N₅Y₄+L₄N₅Vm-L₁N₄hm+L₄N₁hm；

A₁＝L₁N₅Y₄-L₄N₅Y₁+L₅N₃Y₄-L₅N₄Y₃-L₃N₄Vm+L₄N₃Vm-L₃VY₄hm+L₄VY₃hm；

A₀＝L₁N₃Y₄-L₁N₄Y₃-L₃N₁Y₄+L₃N₄Y₁+L₄N₁Y₃-L₄N₃Y₁；

B₄＝I_zVh²m²-I_xI_zVm；

a transfer function for road excitation from the torque transmitted by the wheels through the steering gear into the hand to the equivalent torque of the driver acting on the steering wheel;is a transfer function from the steering wheel angle to the yaw rate, s is a frequency domain signal, T_h(s) the equivalent moment of the driver acting on the steering wheel in the frequency domain; t is_s'(s) is the torque transmitted by the wheel to the hand through the steering gear under the frequency domain; omega_r(s)、θ_s(s) and δ(s) represent yaw rate, steering wheel angle and front wheel angle, respectively, in the frequency domain, K_sEquivalent stiffness of a steering wheel torque corner sensor; n is₂The transmission ratio from the steering screw to the front wheel; j. the design is a square_e、B_eRespectively the equivalent moment of inertia and the equivalent damping coefficient of the steering output shaft and the gear structure of the rack-and-pinion steering gear; m is_rIs the equivalent mass of the rack; b_rThe equivalent damping coefficient of the rack; k is a radical of_rIs the equivalent stiffness of the rack; x is the number of_rIs the displacement of the rack; r is_δThe transverse offset distance of the main pin of the left front steering wheel and the main pin of the right front steering wheel; r is_pIs the pinion radius; r is the wheel radius; n is a radical of_lThe distance between the tie rod and the axle; g is the reduction ratio of the hub motor reduction mechanism; j. the design is a square_eq、B_eqRespectively representing equivalent moment of inertia and equivalent damping coefficient of a tire including a hub motor; k_aIs the torque coefficient of the hub motor; k_m1And K_m2The left hub motor and the right hub motor respectively have boosting gain.

4. The optimization method of the vehicle chassis integrated system according to claim 3, wherein the quantitative formula of the braking effectiveness in step 3) comprises a quantitative formula of braking deceleration, which is specifically expressed as:

in the formula:is a transfer function of steering wheel angle to braking deceleration, a(s) is braking deceleration in the frequency domain,

5. the method for optimizing an integrated system of an automobile chassis according to claim 4, wherein the quantified formula of the suspension ride comfort performance in step 3) comprises a quantified formula of front and rear body vibration acceleration, a quantified formula of front and rear suspension dynamic deflection and a quantified formula of front and rear wheel relative dynamic load, which are respectively:

in the formula:andrespectively representing the vibration acceleration transfer functions of the front and the rear vehicle bodies;andrespectively representing dynamic deflection transfer functions of front and rear suspensions;andrespectively representing the relative dynamic load transfer functions of the front wheel and the rear wheel; q represents the road excitation; z_2fAnd Z_2rRespectively representing front and rear vehicle body displacements; z_1fAnd Z_1rRespectively representing the displacement of the front wheel and the rear wheel; f. of_dfAnd f_drRespectively representing the dynamic deflection of the front suspension and the rear suspension;andrespectively representing front and rear relative dynamic loads, wherein G_f＝(m_1f+m_2f)g，G_r＝(m_1r+m_2r)g；m_1fAnd m_1rRespectively representing front and rear unsprung masses; m is_2fAnd m_2rRespectively representing front and rear sprung masses; k_tIs the tire equivalent stiffness; k_2fAnd K_2rRespectively representing front and rear suspension stiffness; c_2fAnd C_2rRespectively representing front and rear suspension damping; g is the acceleration of gravity.

6. The method for optimizing an integrated system for automotive chassis according to claim 5, wherein the optimization model objective function f (X) in step 4.2) is:

f(X)＝W₁f₁(X)+W₂f₂(X)+W₃f₃(X)

in the formula:

in the formula, f is the frequency when the road surface excitation is input;is the road surface power spectral density; w is a_iIs a weight coefficient; w_iThe weight coefficients are sub-target function weights.

7. The method for optimizing the vehicle chassis integration system according to claim 6, wherein the constraint conditions to be satisfied by the optimization model objective function in the step 4.3) are as follows:

the denominator of the quantized formula of the steering sensitivity meets the Laus criterion, the braking deceleration meets a and g, and the dynamic deflection of the suspension is fullFoot f_cr＝(0.6～0.8)f_cfRelative damping coefficient satisfying ξ_f∈[0.2,0.4]、ξ_r∈[0.2,0.4]；

Wherein f is_cf＝(m_1f+m_2f)g/K_2f；f_cr＝(m_1r+m_2r)g/K_2r；