WO2020134622A1 - Magneto-rheological fluid-based recirculating ball electro-hydraulic steering system and optimization method therefor - Google Patents

Abstract

A magneto-rheological fluid-based recirculating ball electro-hydraulic steering system and an optimization method therefor. Said system comprises: a mechanical transmission module, an electric power assist module, a magneto-rheological fluid power assist module, and a power assist control module (ECU); magneto-rheological fluid materials (25) are provided in magneto-rheological fluid cavities (24) in a recirculating ball steering gear (7); excitation coils (8) are provided outside a recirculating ball steering gear housing (18); and the direction of the magnetic field generated by energizing the excitation coils (8) is perpendicular to the direction of the electric field formed by energizing electrode plates (12). By establishing an electro-hydraulic steering system optimization model and performing optimization using a niche multi-target particle swarm optimization algorithm, the structure of said system is simplified and the controllability of steering feel is improved.

Description

Circulating ball type electro-hydraulic steering system based on magnetorheological fluid and its optimization method Technical field

The invention belongs to the technical field of automobile steering systems, and in particular relates to a circulating ball type electro-hydraulic steering system based on magnetorheological fluid and a multi-objective optimization method.

Background technique

Magnetorheological fluid is a new type of liquid material. When the magnetic field attached to the magnetorheological fluid changes, its apparent viscosity will change with the change of the magnetic field, so that the magnetorheological fluid can be used in fluids and solids. There is a reversible transformation between them, and it also has the advantages of good controllability, high magnetic permeability, no pollution, low energy consumption and so on. Because magnetorheological fluid can generate strong damping force in a short time according to the additional magnetic field, it can realize the function of transmitting torque and changing damping. It is currently widely used in automobile suspension systems, transmission systems, and braking systems. In the field of automobile steering systems, magnetorheological fluids are currently used in a small number of applications, for example, the Chinese patent application number is CN201610913543.1, the patent name is "a vehicle steering control system", and an automobile steering control system uses magnetorheological fluids. Designing a new type of clutch to improve the safety and reliability when switching the driving mode of the car; the Chinese patent application number is CN201110185746.0, and the patent name is "Wire-controlled steering vehicle road sensor simulation execution device". The magneto-rheological fluid damper is used as the main The road sensor simulates the actuator and controls the return speed through the magnetorheological fluid damper to ensure the stability of the steering wheel; the Chinese patent application number is CN201420522322.8, and the patent name is "a composite steering tie rod". The steering tie rod uses the physical characteristics of the magnetorheological fluid to control the viscosity of the magnetorheological fluid when the car punctures, thereby locking the tie rod and reducing the damage caused by the tyre puncture.

According to a series of excellent characteristics of magnetorheological fluid, it also has a large application space and value in automotive steering systems. The electro-hydraulic power steering system is a relatively new type of power steering system. It combines the advantages of the electric power steering system and the electronically controlled hydraulic power steering system. It has low energy consumption, good economy, fast response, large assist torque, and high-speed road. Feel better and other advantages. However, the existing electro-hydraulic steering system still uses the traditional hydraulic power assist mechanism. The entire system has high energy consumption and a complicated structure, which is not easy to install and maintain, and the manufacturing and maintenance costs have increased accordingly. The sense of road and sensitivity are not enough coordination.

Summary of the invention

In view of the above shortcomings of the prior art, the object of the present invention is to provide a circulating ball type electro-hydraulic steering system based on magnetorheological fluid and its optimization method, which solves the problem of large energy waste in the traditional steering system, The invention utilizes the physical properties of the magnetorheological fluid to realize the boosting function, greatly simplifies the structure of the system, and at the same time improves the controllability of the steering feel at high speed.

To achieve the above objectives, the technical solutions adopted by the present invention are as follows:

A circulating ball type electro-hydraulic steering system based on magnetorheological fluid of the present invention includes: a mechanical transmission module, an electric booster module, a magnetorheological fluid booster module and a booster control module;

The mechanical transmission module includes steering wheel, steering shaft, recirculating ball steering gear, steering rocker arm, steering straight tie rod, steering tie rod, left knuckle arm, left trapezoidal arm, left knuckle and left wheel, right knuckle arm , Right trapezoidal arm, right knuckle, right wheel;

The upper end of the steering shaft is connected to the steering wheel, and the lower end is connected to the input end of the recirculating ball diverter; the recirculating ball diverter includes a steering screw, a steering nut rack, a recirculating ball diverter housing, a gear fan, and a recirculating steel ball, wherein The recirculating steel ball is placed in the closed pipeline between the steering nut rack and the steering screw; the output end of the recirculating ball diverter is connected to one end of the steering rocker arm through the gear fan, and the other end of the steering rocker arm is passed through the steering straight rod and left The knuckle arm is connected to drive the left knuckle and the left wheel to deflect; the left knuckle arm is connected to one end of the steering tie rod via the left trapezoidal arm; the other end of the steering tie rod is connected to the right trapezoidal arm, and the right trapezoidal arm is via the right knuckle The arm is connected to the right knuckle, and the right knuckle drives the right wheel to steer;

The electric booster module includes a booster motor and a booster motor deceleration mechanism, the input end of the booster motor deceleration mechanism is connected to the booster motor, and the output end of the booster motor deceleration mechanism is connected to the steering shaft;

The magnetorheological fluid boosting module includes a magnetorheological fluid cavity, a magnetorheological fluid material, an excitation coil, and an electrode plate;

The magnetorheological fluid material is placed in the magnetorheological fluid cavity in the circulating ball diverter; the exciting coil is placed outside the casing of the circulating ball diverter, and the direction of the magnetic field generated when the exciting coil is energized is energized with the electrode plate The directions of the formed electric fields are perpendicular to each other;

The input end of the assist control module is connected to a torque sensor, a vehicle speed sensor, a steering wheel angular displacement sensor, and a displacement sensor, and the output end is connected to an assist motor, an excitation coil, and an electrode plate, respectively.

Further, the torque sensor is installed on the steering shaft, and the torque input by the driver is acquired through the steering shaft and the torque signal is transmitted to the power assist control module; the vehicle speed sensor is installed on the vehicle for Obtain the vehicle speed signal; the steering wheel angular displacement sensor is installed on the steering wheel to obtain the steering wheel angle signal input by the driver when the car is turning; the displacement sensor is installed on the steering tie rod to obtain the output of the steering tie rod Displacement signal.

Further, the recirculating ball diverter is a rectangular parallelepiped; wherein, two ends of the steering nut rack are provided with a sealed and insulated magnetorheological fluid cavity, and the two magnetorheological fluid cavity are filled with magnetorheological fluid material , And communicate with each other through the catheter.

Further, the number of the electrode plates is two, which are respectively placed at the front and back ends of the recirculating ball diverter housing in the radial direction, and the outside of the electrode plates is provided with an insulating layer, which is generated between the two electrode plates when energized electric field.

Further, the excitation coils are rectangular in cross-section and are two identical pairs. The two pairs of excitation coils are installed symmetrically on both sides of the exterior of the recirculating ball diverter housing in the axial direction. Each pair of excitation coils is placed radially At the upper and lower ends of the outer part of the recirculating ball steering gear housing, the current direction in the excitation coil is consistent and the excitation coil installation plane is perpendicular to the electrode plate installation plane. The upper and lower excitation coils on the same side are separated by an insulating material.

According to the system of the present invention, the torque input by the driver sequentially turns the steering wheel and the steering shaft during steering; the power assist control module (ECU) outputs a power assist motor control signal to control the power assist motor according to the signals collected by the sensors, and the power assist motor outputs The electromagnetic torque acts on the steering shaft through the assist motor deceleration mechanism to achieve the first level of steering assistance; the steering shaft drives the steering screw of the recirculating ball steering gear. The steering screw pushes the steering nut rack along the axial direction, and the steering nut rack The steering rocker arm is driven to reciprocate and shake; the power control module changes the current in the excitation coil by adjusting the excitation coil output signal, adjusts the size of the generated magnetic field, and then controls the characteristics of the magnetorheological fluid material, changing its excitation coil and electrode plate The magnitude of the Lorentz force received in the mutually perpendicular electric fields is formed, and the Lorentz force is exerted on the steering nut rack to achieve the second-stage assist effect.

The present invention also proposes an optimization method for a circulating ball type electro-hydraulic steering system based on magnetorheological fluid. Based on the above system, it includes the following steps:

(1) Establish electro-hydraulic steering system model, vehicle dynamics model and tire model;

(2) Select the steering feel, steering sensitivity and energy consumption of the steering system of the vehicle's electro-hydraulic steering system as performance evaluation indicators;

(3) Select the steering screw center distance r _a, sector gear pitch radius r _p, the steering column stiffness K, motor inertia J _m, excitation coil turns N, the steering nut effective area A, a toothed segment moment of inertia J _c as an optimization Variables, taking the steering feel and energy consumption of the steering system as the optimization objectives, under the constraints of steering sensitivity and steering assist range, establish a multi-objective optimization model of the electro-hydraulic steering system;

(4) The niche multi-objective particle swarm optimization algorithm is used to optimize the optimization variables of the electro-hydraulic steering system, and the optimal solution is obtained according to the optimization algorithm.

Further, the electro-hydraulic steering system model includes a steering wheel model, a recirculating ball steering gear model, an electric power assist module model, and a magnetorheological fluid assist power module model.

Further, the specific steps of the niche multi-objective particle swarm optimization algorithm in step (4) are as follows:

4.1 Initialize the particle population m, randomly generate the initial position X ₀ and initial velocity V ₀ , the initial individual optimal position of the particle P _best = X ₀ , the external set N _s is empty, and the number of iterations t = 0;

4.2 Calculate the objective function of each particle and store the non-dominated solution in an external set;

4.3 Calculate the fitness of each particle in the external set, and randomly select the particles in the external set as the historical global optimal position G _best according to the league selection method;

4.4 Update the position and velocity of particles according to formula (1) and formula (2), and update the external set N _s with the non-dominated solution in the current particle swarm;

V _i (t+1)=V _i (t)+c ₁ *r ₁ *(P _best (t)-X _i (t))+c ₂ *r ₂ *(G _best (t)-X _i ( t)) (1)

X _i (t+1)=X _i (t)+V _i (t+1) (2)

In the formula, V _i (t) and V _i (t+1) are the velocity of particles at time t and t+1 respectively, and X _i (t) and X _i (t+1) are respectively time t and t The position of the particle at +1, c ₁ and c ₂ are learning factors, r ₁ and r ₂ are random numbers between 0 and 1;

4.5 Determine whether the number of particles in the external collection exceeds the given maximum capacity, if it exceeds, delete the particles with the smallest fitness value, otherwise proceed to the next step 4.6;

4.6 Perform mutation operations in the external set according to the mutation probability, and search for newly generated non-dominated solutions;

4.7 If the termination condition is met, the search is stopped, and the Pareto optimal solution set is output from the external set, otherwise go to step 4.3 for recycling until the output of the Pareto optimal solution set is ended.

Further, the calculation in the step 4.3 uses the following formula:

Where: F _i is the fitness of the individual X _i in the external set; N _s is the number of individuals in the niche; S _i is the sharing degree of the individual X _i ; f _sh (d _ij ) is the relationship between the individual X _i and the individual X _j Sharing function; α is the parameter that controls the shape of the sharing function; σ _share is the initially specified sharing distance; d _ij represents the Euclidean distance between the individual X _i and the individual X _j .

Further, the step (3) comprises: selecting a steering screw center distance r _a, sector gear pitch radius r _p, the steering column stiffness K, motor inertia J _m, excitation coil turns N, the effective area A steering nut , The fan inertia J _c as an optimization variable, then the vector space in the niche multi-objective particle swarm optimization algorithm is a seven-dimensional vector space, and in the initial m particle position vector and velocity vector group, the first i particle position X _'i and the speed vector V' _i is expressed as follows:

Further, the vector space corresponding to the optimization variable of the individual optimal position represented by P _{best in} steps 4.1 and 4.4 is:

Further, the vector global space corresponding to the optimization variable of the historical global optimal position of the particle represented by G _{best in} steps 4.3 and 4.4 is:

The beneficial effects of the invention:

Compared with the existing electro-hydraulic compound steering system, the present invention uses a magnetorheological fluid power assist module, which greatly simplifies the system structure, solves the road feel and sensitivity problems in the traditional hydraulic power assist module, and uses magnetorheological fluid The physical characteristics effectively improve the controllability of the road feel.

The invention replaces the complicated hydraulic mechanism by using the combination of magnetorheological fluid, excitation coil and electrode plate, produces similar boosting effect and improves the reliability and controllability of the system.

The optimization method of the present invention considers the multi-object coupling of the electro-hydraulic steering system, adopts the niche multi-object particle swarm optimization algorithm, and optimizes the steering feel, steering sensitivity and energy consumption of the electro-hydraulic steering system at the same time, and can obtain better overall performance Optimization results.

BRIEF DESCRIPTION

1 is a block diagram of the principle structure of the system of the present invention;

2 is an A-A sectional view of the recirculating ball diverter of the present invention;

3 is a flowchart of the optimization method of the present invention;

4 is a flowchart of the algorithm used in the present invention;

In the picture: 1-steering wheel, 2-angle sensor, 3-steering shaft, 4-torque sensor, 5-assisted motor deceleration mechanism, 6-assisted motor, 7-circulating ball steering gear, 8-excitation coil, 9-guide Liquid tube, 10-steering screw, 11-steering nut rack, 12-electrode plate, 13-left wheel, 14-left steering knuckle, 15-left steering knuckle arm, 16-left trapezoidal arm, 17-steering tie rod , 18-circulating ball steering gear housing, 19-steering straight rod, 20-steering rocker arm, 21-tooth fan, 22-displacement sensor, 23-circulating steel ball, 24-magnetorheological fluid cavity, 25-magnetic Rheological fluid material, 26-displacement signal, 27-excitation coil control signal, 28-assisted motor control signal, 29-torque signal, 30-steering wheel angle signal, 31-vehicle speed signal, 32-right wheel, 33-right Knuckle, 34-right trapezoidal arm, 35 right knuckle arm.

detailed description

In order to facilitate the understanding of those skilled in the art, the present invention will be further described below in conjunction with the embodiments and drawings, and the content mentioned in the embodiments does not limit the present invention.

Referring to FIG. 1 and FIG. 2, a circulating ball type electro-hydraulic steering system based on magnetorheological fluid of the present invention includes: a mechanical transmission module, an electric power assist module, a magnetorheological fluid power assist module and a power assist control module (ECU ).

The mechanical transmission module includes a steering wheel 1, a steering shaft 3, a recirculating ball steering device 7, a steering rocker arm 20, a steering straight tie rod 19, a steering tie rod 17, a left knuckle arm 15, a left trapezoid arm 16, and a left knuckle 14 And left wheel 13, right knuckle arm 35, right trapezoid arm 34, right knuckle 33, right wheel 32;

The upper end of the steering shaft 3 is connected to the steering wheel 1 and the lower end is connected to the input end of the recirculating ball diverter 7; the recirculating ball diverter 7 includes a steering screw 10, a steering nut rack 11, a recirculating ball diverter housing 18, and teeth Fan 21 and circulating steel ball 23, wherein the circulating steel ball 23 is placed in a closed pipe between the steering nut rack 11 and the steering screw 10; the output end of the circulating ball diverter 7 passes through the gear fan 21 and the steering rocker 20 One end is connected, and the other end of the steering rocker arm 20 is connected to the left knuckle arm 15 through the steering straight rod 19 and drives the left knuckle 14 and the left wheel 13 to deflect; the left knuckle arm 15 passes through the left trapezoidal arm 16 and the steering tie rod 17 The other end of the tie rod 17 is connected to the right trapezoidal arm 34. The right trapezoidal arm 34 is connected to the right knuckle 33 via the right knuckle arm 35. The right knuckle 33 drives the right wheel 32 to steer;

Wherein, the recirculating ball diverter is a rectangular parallelepiped; wherein, two ends of the steering nut rack 11 are respectively provided with a sealed and insulated magnetorheological fluid cavity, and the two magnetorheological fluid cavity are filled with magnetorheological fluid material , And communicate with each other through the catheter 9.

In addition, the recirculating ball diverter housing 18 surrounds the steering screw 10, the steering nut rack 11, the circulating steel ball 23 and the gear fan 21.

The electric booster module includes a booster motor 6 and a booster motor reduction mechanism 5, the input end of the booster motor reduction mechanism 5 is connected to the booster motor 6, and the output end of the booster motor reduction mechanism 5 is connected to the steering shaft 3;

The magnetorheological fluid boosting module includes a magnetorheological fluid cavity 24, a magnetorheological fluid material 25, an excitation coil 8, and an electrode plate 12;

The magnetorheological fluid material 25 is placed in the magnetorheological fluid cavity 24 in the circulating ball diverter 7; the exciting coil 8 is placed outside the casing 18 of the circulating ball diverter. The direction of the magnetic field is perpendicular to the direction of the electric field formed when the electrode plate 12 is energized;

The input end of the assisted control module (ECU) is connected to the torque sensor 4, the vehicle speed sensor, the steering wheel angular displacement sensor 2, and the displacement sensor 22, and the output end is connected to the assisted motor 6, the excitation coil 8, and the electrode plate 12, respectively.

Wherein, the torque sensor 4 is installed on the steering shaft 3, and the torque input by the driver is obtained through the steering shaft 3 and the torque signal 29 is transmitted to the assist control module; the vehicle speed sensor is installed on the vehicle , Used to obtain the vehicle speed signal 31; the steering wheel angular displacement sensor 2 is installed on the steering wheel 1 to obtain the steering wheel angle signal 30 input by the driver when the vehicle is turning; the displacement sensor 22 is installed on the steering tie rod 17 , Used to obtain the displacement signal 26 output from the tie rod.

Wherein, the number of the electrode plates is two, which are respectively placed in the radial direction at the front and rear ends of the recirculating ball diverter housing, and the outside of the electrode plates is provided with an insulating layer, and an electric field is generated between the two electrode plates when energized .

Wherein, the cross section of the exciting coil is rectangular and is exactly the same two pairs, the two pairs of exciting coils are installed symmetrically along the axial direction on both sides of the exterior of the recirculating ball steering gear housing, and each pair of exciting coils is placed in the circulation in the radial direction At the upper and lower ends of the ball steering gear housing, the current direction in the excitation coil is consistent and the excitation coil installation plane is perpendicular to the electrode plate installation plane. The upper and lower excitation coils on the same side are separated by an insulating material.

In the system of the present invention, the torque input by the driver sequentially turns the steering wheel and the steering shaft during steering; the assist control module outputs the assist motor control signal 28 according to the signals collected by the sensors to control the assist motor to assist, and the electromagnetic output by the assist motor The torque acts on the steering shaft through the assist motor deceleration mechanism to achieve the first-stage steering assist; the steering shaft drives the steering screw of the recirculating ball steering gear. The steering screw pushes the steering nut rack along the axial direction, and the steering nut rack passes through the teeth The fan-driven steering rocker reciprocates; the assist control module changes the current in the excitation coil by adjusting the excitation coil control signal 27, adjusts the size of the generated magnetic field, and then controls the characteristics of the magnetorheological fluid material to change its formation in the excitation coil and electrode plate The magnitude of the Lorentz force received in the mutually perpendicular electric field, the Lorentz force is exerted on the steering nut rack to achieve the second level of boosting effect.

Referring to FIG. 3, the present invention also proposes an optimization method for a circulating ball type electro-hydraulic steering system based on magnetorheological fluid. Based on the above system, it includes the following steps:

(1) Establish electro-hydraulic steering system model, vehicle dynamics model and tire model;

The electro-hydraulic steering system model includes a steering wheel model, a circulating ball steering gear model, an electric power assist module model, and a magnetorheological fluid power assist module model;

Among them, the electro-hydraulic steering system model is:

In the formula, θ _m , J _m , B _m and T _m are the rotation angle, rotational inertia, damping coefficient and output assist torque of the assisted motor, respectively, L _A1 U _A1 , I _A1 and R _A1 are the inductance of the assisted motor armature factor, voltage, current, _{resistance, K T1, K a, ω} 1 were induced voltage coefficient assist motor, scale factor, the angular velocity, J _lg is the moment of inertia of the steering screw, θ _lg steering screw angle, B _lg steering screw viscous damping coefficient, T _S is the measured torque of the torque sensor value, F _b is the axial screw turning work load, r _a is the center distance of the screw force, m _lm steering nut mass, x _m is The displacement of the steering nut rack, B _lm is the viscosity resistance coefficient of the steering nut rack, F _lm is the axial force of the nut rack, T _cs is the rack fan torque, r _w is the pitch circle radius of the rack, B _cs is the tooth The viscous damping coefficient of the fan, θ _cs is the rotation angle of the tooth fan, T _p is the equivalent steering resistance torque, J _c is the rotational inertia of the tooth fan, and F _MRF is the assistance provided by the magnetorheological fluid module;

The vehicle dynamics model is:

The tire model is:

In the formula, I _z is the moment of inertia of the mass of the car on the z-axis, ω _r is the yaw rate, φ is the body roll angle, and N _r , N _β , N _φ , and N _δ are the unit yaw rate and the center of mass side deviation, respectively Angle, unit roll angle speed, unit front wheel angle to the z-axis moment, u is the longitudinal speed, m is the mass of the vehicle, I _x is the inertia of the suspension mass to the x-axis, β is the lateral angle of the center of mass, α is the front wheel slip angle, δ is the front wheel steering angle, I _xz for the sprung mass of inertia of x, z-axis, d is the tread, G _P is a screw gear ratio to the front wheels, h is the centroid of the suspension to the roll axis The distance, L _p and L _φ are the unit roll angular velocity and the external moment of the unit roll angle to the x-axis respectively, Y _r , Y _β , Y _φ and Y _δ are the unit yaw rate, the unit vehicle slip angle, and the unit respectively The lateral reaction force on the ground caused by the roll angle and the unit front wheel rotation angle, k ₁ is the front wheel deflection stiffness, and E ₁ is the radian factor.

(2) Select the steering feel, steering sensitivity and energy consumption of the steering system of the vehicle's electro-hydraulic steering system as performance evaluation indicators;

(3) Select the steering screw center distance r _a, sector gear pitch radius r _p, the steering column stiffness K, motor inertia J _m, excitation coil turns N, the steering nut effective area A, a toothed segment moment of inertia J _c as an optimization Variables, taking the steering feel and energy consumption of the steering system as the optimization objectives, under the constraints of steering sensitivity and steering assist range, establish a multi-objective optimization model of the electro-hydraulic steering system;

The multi-objective optimization model of the electro-hydraulic steering system is:

In the formula, f ₁ (X) is the energy consumption of the steering system, f ₂ (X) is the steering feel, g ₁ (X) is the steering assist range, and g ₂ (X) is the steering sensitivity.

(4) The niche multi-objective particle swarm optimization algorithm is used to optimize the optimization variables of the electro-hydraulic steering system, and the optimal solution is obtained according to the optimization algorithm;

Referring to Figure 4, the specific steps of the niche multi-objective particle swarm optimization algorithm are as follows:

4.1 Initialize the particle population m, randomly generate the initial position X ₀ and initial velocity V ₀ , the initial individual optimal position of the particle P _best = X ₀ , the external set N _s is empty, and the number of iterations t = 0;

4.2 Calculate the objective function of each particle and store the non-dominated solution in an external set;

4.3 Calculate the fitness of each particle in the external set, and randomly select the particles in the external set as the historical global optimal position G _best according to the league selection method;

4.4 Update the position and velocity of particles according to formula (1) and formula (2), and update the external set N _s with the non-dominated solution in the current particle swarm;

V _i (t+1)=V _i (t)+c ₁ *r ₁ *(P _best (t)-X _i (t))+c ₂ *r ₂ *(G _best (t)-X _i ( t)) (1)

X _i (t+1)=X _i (t)+V _i (t+1) (2)

In the formula, V _i (t) and V _i (t+1) are the velocity of particles at time t and t+1 respectively, and X _i (t) and X _i (t+1) are respectively time t and t The position of the particle at +1, c ₁ and c ₂ are learning factors, r ₁ and r ₂ are random numbers between 0 and 1;

4.5 Determine whether the number of particles in the external collection exceeds the given maximum capacity, if it exceeds, delete the particles with the smallest fitness value, otherwise proceed to the next step 4.6;

4.6 Perform mutation operations in the external set according to the mutation probability, and search for newly generated non-dominated solutions;

4.7 If the termination condition is met, the search is stopped, and the Pareto optimal solution set is output from the external set, otherwise go to step 4.3 for recycling until the output of the Pareto optimal solution set is ended.

The calculation in step 4.3 uses the following formula:

Where: F _i is the fitness of the individual X _i in the external set; N _s is the number of individuals in the niche; S _i is the sharing degree of the individual X _i ; f _sh (d _ij ) is the relationship between the individual X _i and the individual X _j Sharing function; α is the parameter that controls the shape of the sharing function; σ _share is the initially specified sharing distance; d _ij represents the Euclidean distance between the individual X _i and the individual X _j .

Wherein said step (3) comprises: selecting a steering screw center distance r _a, sector gear pitch radius r _p, the steering column stiffness K, motor inertia J _m, excitation coil turns N, the steering nut effective area A, With the tooth fan rotational inertia J _c as the optimization variable, the vector space in the niche multi-objective particle swarm optimization algorithm is a seven-dimensional vector space, and in the initial m particle position vector and velocity vector group, the i particles positions X _'i and the speed vector V' _i is expressed as follows:

Wherein, the vector space corresponding to the optimization variable of the individual optimal position represented by P _{best in} steps 4.1 and 4.4 is:

The vector global space corresponding to the optimization variable of the historical global optimal position of the particle represented by G _{best in} steps 4.3 and 4.4 is:

There are many specific application ways of the present invention, and the above are only preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, several improvements can be made without departing from the principles of the present invention. Improvements should also be regarded as the scope of protection of the present invention.

Claims (10)

1. A circulating ball type electro-hydraulic steering system based on magnetorheological fluid is characterized by comprising: a mechanical transmission module, an electric power assist module, a magnetorheological fluid power assist module and a power assist control module;

   The mechanical transmission module includes steering wheel, steering shaft, recirculating ball steering gear, steering rocker arm, steering straight tie rod, steering tie rod, left knuckle arm, left trapezoidal arm, left knuckle, left wheel, right knuckle arm , Right trapezoidal arm, right knuckle, right wheel;

   The upper end of the steering shaft is connected to the steering wheel, and the lower end is connected to the input end of the recirculating ball diverter; the recirculating ball diverter includes a steering screw, a steering nut rack, a recirculating ball diverter housing, a gear fan, and a recirculating steel ball, wherein The recirculating steel ball is placed in the closed pipeline between the steering nut rack and the steering screw; the output end of the recirculating ball diverter is connected to one end of the steering rocker arm through the gear fan, and the other end of the steering rocker arm is passed through the steering straight rod and left The knuckle arm is connected to drive the left knuckle and the left wheel to deflect; the left knuckle arm is connected to one end of the steering tie rod via the left trapezoidal arm; the other end of the steering tie rod is connected to the right trapezoidal arm, and the right trapezoidal arm is via the right knuckle The arm is connected to the right knuckle, and the right knuckle drives the right wheel to steer;

   The electric booster module includes a booster motor and a booster motor deceleration mechanism, the input end of the booster motor deceleration mechanism is connected to the booster motor, and the output end of the booster motor deceleration mechanism is connected to the steering shaft;

   The magnetorheological fluid boosting module includes a magnetorheological fluid cavity, a magnetorheological fluid material, an excitation coil, and an electrode plate;

   The magnetorheological fluid material is placed in the magnetorheological fluid cavity in the circulating ball diverter; the exciting coil is placed outside the casing of the circulating ball diverter, and the direction of the magnetic field generated when the exciting coil is energized is energized with the electrode plate The directions of the formed electric fields are perpendicular to each other;

   The input end of the assist control module is connected to a torque sensor, a vehicle speed sensor, a steering wheel angular displacement sensor, and a displacement sensor, and the output end is connected to an assist motor, an excitation coil, and an electrode plate, respectively.
2. The recirculating ball type electro-hydraulic steering system based on magnetorheological fluid according to claim 1, wherein the torque sensor is installed on the steering shaft, and the torque input by the driver is acquired through the steering shaft The torque signal is transmitted to the assist control module; the vehicle speed sensor is installed on the vehicle; the steering wheel angular displacement sensor is installed on the steering wheel; and the displacement sensor is installed on the steering tie rod.
3. The recirculating ball type electro-hydraulic steering system based on magnetorheological fluid according to claim 1, characterized in that, the recirculating ball diverter is a rectangular parallelepiped; The magnetorheological fluid cavity is filled with magnetorheological fluid material, and communicates with each other through the catheter.
4. The circulating ball type electro-hydraulic steering system based on magnetorheological fluid according to claim 1, characterized in that the number of the electrode plates is two, which are respectively placed in the housing of the circulating ball diverter in the radial direction At both ends, the outside of the electrode plate is provided with an insulating layer, and an electric field is generated between the two electrode plates when energized.
5. The recirculating ball type electro-hydraulic steering system based on magnetorheological fluid according to claim 1, characterized in that the cross section of the exciting coil is rectangular and is exactly two pairs, and the two pairs of exciting coils are installed symmetrically along the axis On both sides of the outside of the recirculating ball diverter housing, each pair of excitation coils are placed radially on the upper and lower ends of the outside of the recirculating ball diverter housing. The current direction in the excitation coil remains the same and the installation plane of the excitation coil is perpendicular to the electrode plate In the installation plane, the two excitation coils on the same side are separated by an insulating material.
6. An optimization method of a circulating ball type electro-hydraulic steering system based on magnetorheological fluid, based on the system according to any one of claims 1 to 5, characterized in that it includes the following steps:

   (1) Establish electro-hydraulic steering system model, vehicle dynamics model and tire model;

   (2) Select the steering feel, steering sensitivity and energy consumption of the steering system of the vehicle's electro-hydraulic steering system as performance evaluation indicators;

   (3) Select the steering screw center distance r _a, sector gear pitch radius r _p, the steering column stiffness K, motor inertia J _m, excitation coil turns N, the steering nut effective area A, a toothed segment moment of inertia J _c as an optimization Variables, taking the steering feel and energy consumption of the steering system as the optimization objectives, under the constraints of steering sensitivity and steering assist range, establish a multi-objective optimization model of the electro-hydraulic steering system;

   (4) The niche multi-objective particle swarm optimization algorithm is used to optimize the optimization variables of the electro-hydraulic steering system, and the optimal solution is obtained according to the optimization algorithm.
7. The method for optimizing a circulating ball electro-hydraulic steering system based on magnetorheological fluid according to claim 6, wherein the electro-hydraulic steering system model includes a steering wheel model, a circulating ball steering gear model, and an electric power assist module Model, magnetorheological fluid power module model.
8. The method for optimizing a recirculating ball electro-hydraulic steering system based on magnetorheological fluid according to claim 6, wherein the specific steps of the niche multi-objective particle swarm optimization algorithm in the step (4) are as follows:

   4.1 Initialize the particle population m, randomly generate the initial position X ₀ and initial velocity V ₀ , the initial individual optimal position of the particle P _best = X ₀ , the external set N _s is empty, and the number of iterations t = 0;

   4.2 Calculate the objective function of each particle and store the non-dominated solution in an external set;

   4.3 Calculate the fitness of each particle in the external set, and randomly select the particles in the external set as the historical global optimal position G _best according to the league selection method;

   4.4 Update the position and velocity of particles according to formula (1) and formula (2), and update the external set N _s with the non-dominated solution in the current particle swarm;

   V _i (t+1)=V _i (t)+c ₁ *r ₁ *(P _best (t)-X _i (t))+c ₂ *r ₂ *(G _best (t)-X _i ( t)) (1)

   X _i (t+1)=X _i (t)+V _i (t+1) (2)

   In the formula, V _i (t) and V _i (t+1) are the velocity of particles at time t and t+1 respectively, and X _i (t) and X _i (t+1) are respectively time t and t The position of the particle at +1, c ₁ and c ₂ are learning factors, r ₁ and r ₂ are random numbers between 0 and 1;

   4.5 Determine whether the number of particles in the external collection exceeds the given maximum capacity, if it exceeds, delete the particles with the smallest fitness value, otherwise proceed to the next step 4.6;

   4.6 Perform mutation operation in the external set according to mutation probability to search for newly generated non-dominated solutions;

   4.7 If the termination condition is satisfied, the search is stopped and the Pareto optimal solution set is output from the external set, otherwise go to step 4.3 to recycle until the output of the Pareto optimal solution set is ended.
9. The method for optimizing a circulating ball type electro-hydraulic steering system based on magnetorheological fluid according to claim 8, characterized in that the calculation in step 4.3 uses the following formula:

   

   Where: F _i is the fitness of the individual X _i in the external set; N _s is the number of individuals in the niche; S _i is the sharing degree of the individual X _i ; f _sh (d _ij ) is the relationship between the individual X _i and the individual X _j Sharing function; α is the parameter that controls the shape of the sharing function; σ _share is the initially specified sharing distance; d _ij represents the Euclidean distance between the individual X _i and the individual X _j .
10. The optimization method based on the recirculating ball MRF electro-hydraulic steering system according to claim 6, wherein said step (3) comprises: selecting a steering screw center distance r _a, sector gear pitch radius r _p , steering column stiffness K, motor rotational inertia J _m , excitation coil turns N, steering nut effective area A, tooth fan rotational inertia J _c as optimization variables, then the niche multi-objective particle swarm optimization algorithm described in The vector space is a seven-dimensional vector space, and in the position group and velocity vector group of the initial m particles, the position X′ _i and velocity vector V′ _{i of} the i-th particle are expressed as follows:

    

    

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