CN108984860B - Power parameter optimization method for composite power source EPS - Google Patents
Power parameter optimization method for composite power source EPS Download PDFInfo
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Abstract
The invention discloses a power parameter optimization method of a composite power source EPS, which comprises the following steps: collecting the electric load, the steering wheel turning angle and the vehicle speed of the whole vehicle electric appliance of the heavy commercial vehicle in a certain operation period; simulating and calculating the steering resisting moment of the commercial vehicle, fitting an analytic expression of the steering resisting moment on the vehicle speed and the steering wheel rotation angle, and determining the critical vehicle speed of extremely-low-speed steering; counting the maximum power load of the electric appliance of the whole vehicle, the minimum interval time of two times of extremely low speed steering and the maximum time of single time of extremely low speed steering; establishing a multi-objective optimization function by taking the charging and discharging current of the super capacitor as an optimization variable and the minimum capacitance value of the super capacitor and the minimum rated output current of a finished automobile power supply as optimization targets, and setting optimization constraint conditions; and solving the Pareto optimal solution by adopting an MOPSO algorithm to obtain the optimal rated output current of the whole vehicle power supply and the capacitance value of the super capacitor. The method is beneficial to reducing the rated output current of the whole vehicle power supply in the composite power supply and the capacitance value of the super capacitor, and improves the utilization rate of the composite power supply.
Description
Technical Field
The invention relates to the field of automobile steering systems, in particular to a power supply parameter optimization method of a hybrid power supply EPS.
Background
At present, a heavy commercial vehicle generally adopts a hydraulic power steering system (HPS) with single power-assisted characteristic, and after the power-assisted characteristic design of the HPS is finished, the power-assisted size of the vehicle cannot change along with the change of the vehicle speed, so that the high-speed steering road feel is poor, and the high-speed 'floating' is easily caused; in addition, no matter the automobile is in a straight-driving state or a turning state, the steering pump of the HPS is driven by the engine to run at a high speed all the time, and the data show that about 80 percent of the running mileage of the automobile is in a straight-driving state, which shows that most of energy consumed by the HPS is reactive loss.
In recent years, electric power steering systems (EPS) have been widely used in passenger vehicles and light commercial vehicles due to their safety, energy saving, and environmental protection advantages. The EPS provides steering power through a motor, the power is controlled by a software program, the variable power-assisted characteristic along with the speed can be conveniently realized, and the control stability of the vehicle is improved; under the non-steering working condition, the power-assisted motor does not work, and the EPS almost does not consume electric energy, so that the EPS is an 'on-demand' power-assisted steering system in the real sense. However, the front axle load of the heavy commercial vehicle is large, the required steering power is large, the power supply system of the whole vehicle cannot provide the steering power required by the EPS, the steering power required by the front axle load of the heavy commercial vehicle of 6000kg is about 4kW during low-speed steering, the working current of the motor is about 160A, the instantaneous current reaches 200A and exceeds the bearing capacity of the power supply system of the whole vehicle, and therefore the existing EPS scheme is not suitable for the heavy commercial vehicle.
Although the steering power required by the heavy commercial vehicle in low-speed steering is very large, the heavy commercial vehicle is in a medium-speed or high-speed running state in most of the running time, the corresponding steering resistance moment is small, the required steering power is also small, and the power supply system of the whole vehicle can completely meet the requirement of the steering power. The super capacitor has the advantages of high power density, short charging time, strong discharging capacity and the like, researchers integrate the super capacitor at the power end of the whole vehicle to construct an electric power steering system (SC-EPS) based on a hybrid power supply, the super capacitor in the hybrid power supply obtains energy from the power supply of the whole vehicle under the working condition of non-low-speed steering, releases the energy in a high-power mode under the working condition of low-speed steering, and provides steering power for the heavy commercial vehicle together with the power supply of the whole vehicle. The patent (JP 2003-320942) discloses an EPS system based on a hybrid power supply, which provides a power supply mode of the hybrid power supply, and controls a selector switch according to the detected steering wheel torque, so that a storage battery and a super capacitor are in a parallel or series connection state. A patent (JP 2007-223510) discloses an EPS system using a super capacitor as an auxiliary power supply, and gives a condition that the auxiliary power supply intervenes in the work. The patent (CN 201180034669.7) discloses a fault detection circuit of an EPS system based on a hybrid power supply, and provides a fault detection and processing method. The patent (CN 201410080799) discloses a power supply circuit and a power supply method of an automobile EPS system based on a super capacitor. The above patent refers to a hybrid power supply consisting of a battery and a super capacitor, and actually supplies power to the EPS system not the battery but the generator, and in addition the above patent does not mention a parameter optimization method of the hybrid power supply.
Disclosure of Invention
The invention provides a power parameter optimization method of a hybrid power source (EPS) in order to reduce the rated output current of a vehicle power source (generator) and the rated capacitance value of a super capacitor in the EPS system of the hybrid power source and improve the utilization rate of the hybrid power source.
The technical purpose is realized by the following technical scheme:
a power parameter optimization method of a composite power source EPS comprises the following steps:
step 1, selecting a plurality of heavy commercial vehicles as test objects, and collecting power loads i of whole vehicle electrical appliances of each heavy commercial vehicle in a certain operation period e Angle of rotation theta of steering wheel h And vehicle speed v;
Step 4, discharging current i by using super capacitor sc amplifier And a charging current i Sc charger For optimizing the variables, the rated capacitance value C of the super capacitor is used sc Minimum and rated output current i of vehicle power supply g amount Establishing a multi-objective optimization function and setting optimization constraint conditions, wherein the minimum is an optimization target;
and 5, solving a Pareto optimal solution by adopting a multi-target particle swarm optimization algorithm to obtain the optimal rated output current of the vehicle power supply and the optimal capacitance value of the super capacitor.
In the scheme, the electric load i of the electric appliance of the whole motor coach is e The rotation angle theta of a steering wheel is measured by installing a current sensor at the output end of the original vehicle power supply h The vehicle speed v is measured by a vehicle speed sensor, which is mounted below the steering wheel.
In the above scheme, the critical vehicle speed v of the extremely low speed steering 0 Obtained by the following steps:
1) The method comprises the following steps of establishing a finite element model of the friction force between automobile tires and the ground by taking a certain type of small automobile as a research object, carrying out simulation analysis on the change relation of the friction force along with the rolling speed of the tires, the deflection angle of the tires, the vertical load and the road surface friction coefficient, and fitting to obtain a relation formula of the friction force: f f ＝0.7121F z ·e -0.048v In which F is z Front axle load, v vehicle speed;
2) Calculating the steering resisting moment caused by the inward inclination of the automobile main pin, synthesizing the steering resisting moment caused by the inward inclination of the main pin and the steering resisting moment caused by the friction force between the tire and the ground to obtain a small automobile low-speed steering resisting moment model, and simultaneously verifying and correcting through a real automobile test;
the calculation formula of the steering resistance moment caused by the inclination of the main pin is
Wherein delta is a front wheel corner, c is a kingpin offset moment, and beta is a kingpin inclination angle;
3) Building a corresponding model of the heavy commercial vehicle based on a model of the small-sized vehicle low-speed steering resistance moment verified by a test, carrying out simulation analysis on the change rule of the heavy commercial vehicle low-speed steering resistance moment along with the vehicle speed and the steering wheel corner, and fitting by adopting a least square method to obtain an analytic expression of the heavy commercial vehicle low-speed steering resistance moment on the vehicle speed and the steering wheel corner;
the low-speed steering resistance torque model of the small automobile is as follows:
wherein L is the diameter of the tire footprint circle; the analytic formula of the heavy commercial vehicle low-speed steering resistance torque about the vehicle speed and the steering wheel angle is as follows: />
In the formula [ theta ] h To the steering wheel angle, G s Is the gear ratio of the steering system;
4) Converting the steering resistance torque of the heavy commercial vehicle into the current required by an EPS power-assisted motor, making a change curve of the current along with the vehicle speed and the steering wheel angle, and taking the intersection point of the change curve of the current along with the vehicle speed and a straight line formed by the rated output current of a power supply of the whole vehicle as the critical vehicle speed v of extremely low-speed steering 0 。
In the above scheme, the multi-objective optimization function is as follows:
f(x)＝[min f 1 (x),min f 2 (x)]，x＝(i sc amplifier ，i sc charger )
Wherein the content of the first and second substances,
f 2 (x)＝i g forehead ＝i epsmax +i emax -i sc discharge (ii) a In the formula i eps For the vehicle speed to be greater than the critical vehicle speed v 0 The current required by the time EPS power-assisted motor can be obtained by conversion of steering resistance torque, i epsmax The vehicle speed is less than or equal toVehicle speed v 0 The current required by the time EPS power-assisted motor can be obtained by conversion of extremely low speed steering resistance torque u 0 Is the maximum terminal voltage of the super capacitor, u min Is the minimum terminal voltage, i, of the supercapacitor emax The maximum power load of the electric appliance of the whole vehicle is obtained by statistics of collected power load data of the electric appliance of the whole vehicle.
In the scheme, the process of optimizing the rated output current of the whole vehicle power supply and the capacitance value of the super capacitor by the multi-objective particle swarm optimization algorithm is as follows:
1) Initializing a particle swarm: given a population size N, randomly generating a position x for each particle i Velocity v i Setting iteration times;
2) By an objective function f 1 (x)、f 2 (x) Calculating the Fitness value Fitness of each particle respectively 1 [i]、Fitness 2 [i]；
3) Calculating individual extrema pBest of each particle with respect to two objective functions 1 [i]、pBest 2 [i]；
4) Respectively calculating global extreme values gBest of two objective functions 1 、gBest 2 ；
5) Calculating the mean gBest and distance dgBest of the two global extrema:
gBest＝Average(gBest 1 ，gBest 2 )
dgBest＝Distance(gBest 1 ，gBest 2 )
6) Calculating the extreme value pBest of each particle individual 1 [i]、pBest 2 [i]Distance dpBest [ i ] between]；
For i＝1 to N
dgBest[i]＝Distance(pBest 1 [i]，pBest 2 [i])
Next i
7) Calculating an individual extreme value pBest [ i ] used when the position and the speed of each particle pair are updated:
8) Updating the position x of each particle i And velocity v i ：
v i ＝ωv i +c 1 rand()(pBest[i]-x i )+c 2 rand()(gBest-x i )
x i ＝x i +v i
Wherein: omega is the inertial weight, c 1 、c 2 Is a learning factor;
9) Exit if the number of iterations is reached, otherwise return to 2).
The beneficial effects of the invention are:
1. the problem that the power of the power supply system is insufficient limits the application of the EPS in the heavy commercial vehicle, the composite power supply system constructed by the invention is beneficial to improving the power of the power supply system, and the composite power supply EPS is beneficial to improving the operation stability of the heavy commercial vehicle and greatly reducing the energy consumption of a steering system;
2. according to the invention, the rated output current of the vehicle power supply and the capacitance value of the super capacitor are minimized by a particle swarm multi-objective optimization method, and energy exchange is generated between the vehicle power supply and the super capacitor in the composite power supply, so that the utilization rate of the composite power supply is improved on the basis of meeting the performance;
3. the MOPSO algorithm adopted by the invention is beneficial to converging the rated output current of the power supply of the whole vehicle and the capacitance value of the super capacitor in a non-inferior optimal solution area.
Drawings
FIG. 1 is a schematic diagram of an EPS system based on a hybrid power supply;
fig. 2 is a classification diagram of a power supply mode of an EPS system based on a hybrid power supply, where (a) in fig. 2 is a power supply mode diagram of the hybrid power supply, fig. 2 (b) is a power supply mode diagram of a vehicle power supply, and fig. 2 (c) is a power supply mode diagram of a super capacitor;
FIG. 3 is a diagram of a finite element simulation model of the steering friction between a tire and the ground;
fig. 4 is a power parameter optimization flowchart of the hybrid power source EPS.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings, but the scope of the invention is not limited thereto.
FIG. 1 is a schematic diagram of an EPS composition of an automobile based on a hybrid power supply, and an EPS system of the automobile based on the hybrid power supply comprises a steering wheel, an input shaft, a torque/corner sensor, an intermediate shaft, a power-assisted motor, a recirculating ball steering gear (comprising a worm and gear speed reducing mechanism), a steering gear output shaft, a steering gear rocker arm, a steering transmission mechanism, steering wheels, an EPS controller and the hybrid power supply, wherein the steering wheel, the intermediate shaft, the torque/corner sensor, the input shaft, the recirculating ball steering gear (comprising a worm and gear speed reducing mechanism), the steering gear output shaft, the steering gear rocker arm, the steering transmission mechanism and the steering wheels are mechanically connected in sequence, the output shaft of the power-assisted motor is connected with the worm and gear speed reducing mechanism, the EPS controller is connected with the power-assisted motor through an electric wire, the EPS controller is powered by the hybrid power supply, and the EPS controller receives a torque/corner signal, a vehicle speed signal, an electric quantity signal of the hybrid power supply and a current signal of the power-assisted motor. The hybrid power supply comprises a vehicle power supply, a super capacitor, a discharge circuit and a charging circuit, wherein the super capacitor is connected with the discharge circuit in series and then connected with the vehicle power supply in parallel, and the vehicle power supply is connected with the charging circuit in series and then connected with the super capacitor in series.
Fig. 2 is a power supply mode classification diagram of an automobile EPS based on a hybrid power supply having three power supply modes: a hybrid power supply mode (fig. 2 (a)), a vehicle power supply mode (fig. 2 (b)), and a super capacitor power supply mode (fig. 2 (c)); the controller determines the power supply mode of the composite power supply, and the mode and proportion of the steering power provided by the whole vehicle power supply system and the super capacitor according to the signals of the vehicle speed, the steering wheel angle and the like. When the speed is low, the system is in a composite power supply mode, and a whole vehicle power supply system and the super capacitor provide steering power for the motor together; when the speed is high, the system is in a finished automobile power supply mode, the finished automobile power supply system independently provides steering power for the motor, meanwhile, the super capacitor is used as a load of the finished automobile power supply system and is in a charging state, and stored energy is used for low-speed steering; when the power supply of the whole vehicle breaks down, the system is in a super capacitor power supply mode, and the super capacitor independently provides steering power for the motor to maintain short-time steering assistance.
Fig. 4 is a power parameter optimization process of the hybrid power source EPS, where the heavy-duty commercial vehicle of this embodiment takes an XMQ6118Y2 type bus as an example, and specifically includes the following steps:
step 1, selecting a plurality of buses as test objects, and collecting the power loads i of the whole bus electrical appliances of each bus in a certain operation period e Angle of rotation theta of steering wheel h And vehicle speed v; the operation cycle of the real-time test of the motor bus comprises the daytime and the night, the sunny day and the rainy day, the winter and the summer, and comprises a normal driving working condition, a starting and turning working condition, a turning working condition and a backing working condition; current sensor is arranged at the output end of the original whole bus power supply to measure the electrical load i of the whole bus electrical appliance of the motor bus e Measuring the angle of rotation theta of the steering wheel by means of a rotation angle sensor mounted under the steering wheel h The vehicle speed v is measured by a vehicle speed sensor.
Critical vehicle speed v of very low speed steering 0 Obtained by the following steps:
1) A finite element model (figure 3) of friction between automobile tires and the ground is established by using an ABAQUS software with an S-shaped car of a developer as a research object, the change relation of the friction along with the rolling speed of the tires, the deflection angle of the tires, the vertical load and the road surface friction coefficient is simulated and analyzed, and the relation formula of the friction is obtained by fitting:
F f ＝0.7121F z ·e -0.048v (1)
in the formula, F z Front axle load, v vehicle speed;
steering resistance moment due to friction (integrated):
wherein L is the diameter of the tire grounding seal circle; theta and r are intermediate variables of polar coordinate integration;
2) Calculating the steering resisting moment caused by the inward inclination of the main pin, synthesizing the steering resisting moment caused by the inward inclination of the main pin and the steering resisting moment caused by the friction force between the tire and the ground to obtain a car low-speed steering resisting moment model, and simultaneously verifying and correcting through a real vehicle test;
the calculation formula of the steering resistance moment caused by the kingpin inclination is as follows:
in the formula, delta is a front wheel corner, c is a kingpin offset, and beta is a kingpin inclination angle;
the low-speed steering resistance torque model is as follows:
3) Building a corresponding model of the motor bus based on the model of the low-speed steering resistance torque of the car verified by the test (the parameters in the model of the low-speed steering resistance torque of the car are converted into the corresponding parameters of the motor bus, and then the low-speed steering resistance of the motor bus is obtainedA moment model), simulating to obtain low-speed steering resistance moment, and analyzing the vehicle-mounted speed v and the steering wheel rotation angle theta of the low-speed steering resistance moment h The change rule of the steering wheel is obtained by fitting the least square method to obtain the low-speed steering resistance torque of the heavy commercial vehicle relative to the vehicle speed v and the steering wheel rotation angle theta h The analytical formula (2);
and also
The analytic expression of the obtained low-speed steering resistance torque of the motor bus about the speed and the steering wheel angle is as follows:
in the formula, theta h For steering wheel angle, G s Is the gear ratio of the steering system;
4) Converting the steering resistance torque of the bus into the current required by the electric power steering system, and making the current according to the speed v and the steering wheel rotation angle theta h The intersection point of the variation curve of the current along with the vehicle speed v and a straight line formed by the rated output current of the power supply of the whole vehicle is taken as the critical vehicle speed v of extremely low-speed steering 0 ；
When the EPS system runs, the torque output by the power-assisted motor is transmitted to wheels after being decelerated and torque-increased by a two-stage speed reducing mechanism of a turbine-worm and a recirculating ball steering gear, and the wheels are deflected by overcoming steering resistance torque, so that the steering resistance torque is divided by the transmission ratio of the steering gear and the transmission ratio of the turbine-worm to obtain the output torque of the power-assisted motor, and then the output torque is divided by the torque coefficient of the motor to obtain the current of the power-assisted motor, wherein the current is shown as the following formula:
in the formula, G m In worm-gear-worm drive ratio, k i Is the current coefficient.
Step 4, discharging current i by using super capacitor sc amplifier And a charging current i Sc charger For optimizing the variables, the capacitance value C of the super capacitor is used sc Minimum and rated output current i of vehicle power supply g amount Establishing a multi-objective optimization function and setting optimization constraint conditions for the minimum optimization target;
the optimization function is as follows:
f(x)＝[min f 1 (x),min f 2 (x)]，x＝(i sc discharge ，i Sc charger ) (7)
Wherein the content of the first and second substances,
f 2 (x)＝i g amount ＝i epsmax +i emax -i sc amplifier ；
In the formula i eps For the vehicle speed to be greater than the critical vehicle speed v 0 The current required by the EPS power-assisted motor can be obtained by conversion of steering resistance torque (formula (5)), and the maximum power load i of the electric appliance of the whole vehicle emax Is obtained by statistics of collected power load data of electric appliances of the whole vehicle i epsmax The vehicle speed is less than or equal to the critical vehicle speed v 0 The current required by the EPS motor can be obtained by conversion of extremely low speed steering resistance torque (formula (5)), and u 0 Is the maximum terminal voltage of the super capacitor, u min Is the minimum terminal voltage of the super capacitor.
Step 5, solving a Pareto optimal solution by adopting a multi-objective particle swarm optimization (MOPSO) algorithm to obtain the optimal rated output current of the vehicle power supply and the optimal capacitance value of the super capacitor;
the process for optimizing the rated output current of the vehicle power supply and the capacitance value of the super capacitor by adopting the MOPSO algorithm comprises the following steps:
1) Initializing a particle swarm: given population size N, randomGenerating the position x of each particle i Velocity v i Setting iteration times T;
2) By an objective function f 1 (x)、f 2 (x) Calculating the Fitness value Fitness of each particle respectively 1 [i]、Fitness 2 [i]；
3) Calculating individual extrema pBest of each particle about two objective functions 1 [i]、pBest 2 [i]；
4) Respectively calculating global extreme values gBest of two objective functions 1 、gBest 2 ；
5) Calculating the mean gBest and distance dgBest of the two global extrema:
gBest＝Average(gBest 1 ，gBest 2 )
dgBest＝Distance(gBest 1 ，gBest 2 )
6) Calculating the extreme value pBest of each particle individual 1 [i]、pBest 2 [i]The distance dpBest [ i ] between]；
For i＝1 to N
dgBest[i]＝Distance(pBest 1 [i]，pBest 2 [i])
Next i
7) Calculating an individual extreme value pBest [ i ] used when the position and the speed of each particle pair are updated:
8) Updating the position x of each particle i And velocity v i ：
v i ＝ωv i +c 1 rand()(pBest[i]-x i )+c 2 rand()(gBest-x i )
x i ＝x i +v i
Wherein: omega is the inertial weight, c 1 、c 2 Is a learning factor;
9) Exit if the number of iterations is reached, otherwise return to 2).
The above embodiments are only used for illustrating the design idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and the protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications based on the principles and design concepts disclosed herein are intended to be included within the scope of the present invention.
Claims (7)
1. A power parameter optimization method of a hybrid power source EPS is characterized by comprising the following steps:
step 1, selecting a plurality of heavy commercial vehicles as test objects, and collecting power loads i of whole vehicle electrical appliances of each heavy commercial vehicle in a certain operation period e Angle of rotation theta of steering wheel h And vehicle speed v;
step 2, simulating and calculating the steering resistance moment of the heavy commercial vehicle, analyzing the change rule of the steering resistance moment along with the vehicle speed and the steering wheel angle, fitting an analytic expression of the steering resistance moment about the vehicle speed and the steering wheel angle, and determining the critical vehicle speed v of extremely-low-speed steering 0 ；
Step 3, combining the critical speed v of the extremely low speed steering according to the steering wheel angle and the automobile speed data 0 Counting the minimum interval time t of two times of extremely low speed steering jmin And maximum time t of single extremely low speed steering smax ；
Step (ii) of4, discharge current i with super capacitor sc amplifier And a charging current i Sc charger For optimizing the variables, the capacitance value C of the super capacitor is used sc Minimum and rated output current i of vehicle power supply g amount Establishing a multi-objective optimization function and setting optimization constraint conditions, wherein the minimum is an optimization target;
the multi-objective optimization function is as follows:
f(x)＝[minf 1 (x),minf 2 (x)]，x＝(i sc amplifier ，i Sc charger )
Wherein the content of the first and second substances,
f 2 (x)＝i g amount ＝i epsmax +i emax -i sc discharge (ii) a In the formula i eps For the vehicle speed to be greater than the critical vehicle speed v 0 The current required by the EPS power-assisted motor is obtained by conversion of steering resistance torque, i epsmax For vehicle speed less than or equal to the critical vehicle speed v 0 The current required by the time EPS power-assisted motor is obtained by conversion of extremely low speed steering resistance moment u 0 Is the maximum terminal voltage of the super capacitor, u min Is the minimum terminal voltage, i, of the super capacitor emax The maximum power load of the electric appliance of the whole vehicle is obtained by counting the collected power load data of the electric appliance of the whole vehicle;
and 5, solving a Pareto optimal solution by adopting a multi-target particle swarm optimization algorithm to obtain the optimal rated output current of the whole vehicle power supply and the optimal capacitance value of the super capacitor.
2. The method for optimizing the power supply parameters of the hybrid power supply EPS of claim 1, wherein the electrical load i of the entire electrical appliance of the heavy-duty commercial vehicle is e The rotation angle theta of a steering wheel is measured by installing a current sensor at the output end of the original vehicle power supply h Measured by a steering angle sensor mounted below the steering wheel,the vehicle speed v is measured by a vehicle speed sensor.
3. The method as claimed in claim 1, wherein the critical vehicle speed v of the very low speed steering is a critical vehicle speed v 0 Obtained by the following steps:
1) Establishing a finite element model of friction between automobile tires and the ground by taking a certain type of small automobile as a research object, carrying out simulation analysis on the change relation of the friction along with the rolling speed of the tires, the deflection angle of the tires, the vertical load and the road surface friction coefficient, and fitting to obtain a friction relation;
2) Calculating the steering resisting moment caused by the inward inclination of the automobile main pin, synthesizing the steering resisting moment caused by the inward inclination of the main pin and the steering resisting moment caused by the friction force between the tire and the ground to obtain a low-speed steering resisting moment model of the small automobile, and simultaneously verifying and correcting through a real automobile test;
3) Building a corresponding model of the heavy commercial vehicle based on a model of the small-sized vehicle low-speed steering resistance moment verified by a test, carrying out simulation analysis on the change rule of the heavy commercial vehicle low-speed steering resistance moment along with the vehicle speed and the steering wheel corner, and fitting by adopting a least square method to obtain an analytic expression of the heavy commercial vehicle low-speed steering resistance moment on the vehicle speed and the steering wheel corner;
4) The current required by the EPS power-assisted motor is converted from the steering resistance torque of the heavy commercial vehicle, a change curve of the current along with the vehicle speed and the steering wheel angle is made, and the intersection point of the change curve of the current along with the vehicle speed and a straight line formed by the rated output current of a power supply of the whole vehicle is used as the critical vehicle speed v of the extremely-low-speed steering 0 。
4. The method as claimed in claim 3, wherein the relationship of the friction force is F f ＝0.7121F z ·e -0.048v In which F z Is the front axle load.
5. The method for optimizing the power supply parameters of the hybrid power supply EPS according to claim 4, wherein the method comprisesThe calculation formula of the steering resistance moment caused by the inclination of the main pin is
Wherein delta is the front wheel corner, c is the kingpin offset moment, and beta is the kingpin inclination angle.
6. The method for optimizing power supply parameters of a hybrid power supply EPS according to claim 5, wherein the low-speed steering resistance torque model of the small car is:
wherein L is the diameter of the tire footprint circle; the analytic formula of the heavy commercial vehicle low-speed steering resistance torque about the vehicle speed and the steering wheel angle is as follows:
in the formula G s Is the gear ratio of the steering system.
7. The method for optimizing the power supply parameters of the hybrid power supply EPS of claim 1, wherein the process of optimizing the rated output current of the entire vehicle power supply and the capacitance value of the super capacitor by the multi-objective particle swarm optimization algorithm is as follows:
1) Initializing a particle swarm: given a population size N, randomly generating a position x for each particle i Velocity v i Setting iteration times;
2) By an objective function f 1 (x)、f 2 (x) Calculating the Fitness value Fitness of each particle respectively 1 [i]、Fitness 2 [i]；
3) Calculating individual extrema pBest of each particle about two objective functions 1 [i]、pBest 2 [i]；
4) Respectively calculating global extreme values gBest of two objective functions 1 、gBest 2 ；
5) Calculating the mean gBest and distance dgBest of the two global extrema:
gBest＝Average(gBest 1 ，gBest 2 )
dgBest＝Distance(gBest 1 ，gBest 2 )
6) Calculating the extreme value pBest of each particle individual 1 [i]、pBest 2 [i]The distance dpBest [ i ] between]；
For i＝1 to N
dgBest[i]＝Distance(pBest 1 [i]，pBest 2 [i])
Next i
7) Calculating an individual extreme value pBest [ i ] used when each particle pair updates the position and the speed:
8) Updating the position x of each particle i And velocity v i ：
v i ＝ωv i +c 1 rand()(pBest[i]-x i )+c 2 rand()(gBest-x i )
x i ＝x i +v i
Wherein: omega is the inertial weight, c 1 、c 2 Is a learning factor;
9) If the iteration number is reached, exiting, otherwise returning to 2).
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