CN111469670A - Electric automobile regenerative braking control strategy based on road surface identification - Google Patents
Electric automobile regenerative braking control strategy based on road surface identification Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
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- B60L7/10—Dynamic electric regenerative braking
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L7/00—Electrodynamic brake systems for vehicles in general
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- B60L7/18—Controlling the braking effect
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
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- B60L2240/00—Control parameters of input or output; Target parameters
- B60L2240/40—Drive Train control parameters
- B60L2240/42—Drive Train control parameters related to electric machines
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L2240/00—Control parameters of input or output; Target parameters
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Abstract
The invention discloses an electric automobile regenerative braking control strategy based on road surface identification, which comprises the following steps: 1) collecting vehicle operation parameters in real time; calculating the slip rate and utilizing the adhesion coefficient in real time; 2) judging the vehicle state, and if the vehicle is in the braking state, implementing regenerative braking control strategy processing; otherwise, executing the step 1); the implementing a regenerative braking control strategy process for the vehicle includes: identifying the type of the road on which the vehicle runs currently, and calculating the currently expected total braking force and braking strength; obtaining a front wheel braking force optimal distribution rule and a rear wheel braking force optimal distribution rule and a regenerative braking force distribution rule based on the road surface type and the braking strength; obtaining the braking force required by the front wheels according to the braking force optimal distribution rule of the front wheels and the rear wheels; and performing secondary distribution on the braking force required by the front wheels according to the regenerative braking force distribution rule, and determining the friction braking force and the regenerative braking force of the front wheels. The invention can realize the maximization of the efficiency of regenerative braking energy recovery on the premise of ensuring the braking stability and the braking safety.
Description
Technical Field
The invention relates to a regenerative braking control technology, in particular to an electric vehicle regenerative braking control strategy based on road surface identification.
Background
Environmental pollution, global warming, and foreseeable resource exhaustion have become serious problems affecting the survival of the present human society and are also common challenges facing the global automobile industry. New energy automobiles have become a development hotspot of the automobile industry in the 21 st century. The electric automobile is an important representative of new energy automobiles and has regenerative braking performance, which is one of the biggest differences from the traditional fuel oil automobiles. Kinetic energy of the automobile is converted into heat energy through friction in the braking process and is lost, and a large amount of energy is wasted. The electric vehicle recovers and stores kinetic energy of the vehicle during braking, and the stored energy is called regenerative energy. The automobile has low speed and large fluctuation of load rate change in urban areas, and needs to be started and braked ceaselessly, and related research data shows that the energy consumed in the air in a heat energy mode in the automobile braking process accounts for about 50% of the total driving energy, and if the energy lost in the braking process can be stored and reused, the driving range of the automobile can be greatly improved.
The following technical scheme is given in the document 'regenerative braking control strategy of four-wheel independent drive electric vehicle with hub motor' (mechanical science and technology, 2017,36(11), 1778-: 1) when the braking strength z is less than or equal to 0.1, the braking force is provided by the front axle, mainly the braking force of the motor; 2) when the braking strength is more than 0.1 and less than or equal to 0.8, the friction braking and the motor braking form composite braking; 3) when the braking strength z is larger than 0.8, in order to ensure the braking safety, the motor is braked and quit, and the friction braking provides all braking force. However, the applicant believes that the difference in road surface conditions during braking affects the requirements for braking stability and safety; braking under the condition of different braking strengths also influences the requirements of braking stability and safety, thereby influencing the distribution coefficient of braking force of front and rear wheels of a vehicle and finally influencing the recovery total amount of regenerative braking energy. It can be seen that this method does not take into account the influence of road conditions and brake intensity on the regenerative braking control strategy.
The invention patent with publication number CN109204260A discloses a method for distributing control force of an electric vehicle, which comprises the following steps: (1) dividing the braking strength z into three ranges of z not less than 0 and not more than 0.2, z not less than 0.2 and not more than 0.7 and z not more than 0.7, and dividing the braking force of the front wheel and the braking force of the rear wheel into specific curves according to the specific ranges; (2) and the output is the proportion of reducing the regenerative braking force to the front wheel braking force by taking the slip ratio as the input through a slip film controller. The influence of the braking strength z on the braking force distribution coefficient of the front wheel and the rear wheel is considered, so that when the vehicle distributes the braking force according to the distribution mode provided by the invention, the vehicle has better braking stability and safety in the braking process, but the influence of the adhesion condition of the road surface on the braking process of the vehicle is not considered.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a regenerative braking control strategy of an electric vehicle based on road surface identification, aiming at the defects in the prior art, the strategy can select the optimal regenerative braking strategy according to the current braking conditions, so that the regenerative braking energy recovery efficiency is maximized on the premise of ensuring the braking stability and the braking safety, and the driving range of the vehicle is further prolonged.
In order to solve the technical problems, the invention adopts the following technical scheme:
an electric vehicle regenerative braking control strategy based on road surface identification comprises the following steps:
1) collecting vehicle operation parameters in real time; calculating the slip rate and utilizing the adhesion coefficient in real time;
2) judging whether the vehicle is in a braking state, if so, carrying out regenerative braking control strategy processing on the vehicle until the vehicle returns to a normal driving state or stops; otherwise, executing step 1); wherein the implementing a regenerative braking control strategy process for the vehicle comprises:
identifying the type of a road surface on which the vehicle runs currently, and calculating the currently expected total braking force and braking strength;
obtaining a front wheel braking force optimal distribution rule and a rear wheel braking force optimal distribution rule and a regenerative braking force distribution rule based on the road surface type and the braking strength;
obtaining the braking force required by the front wheels according to the braking force optimal distribution rule of the front wheels and the rear wheels;
and secondly, performing secondary distribution on the braking force required by the front wheel according to a regenerative braking force distribution rule, determining the friction braking force and the regenerative braking force of the front wheel, then performing energy recovery by using the regenerative braking force, and recovering and storing the energy lost in the braking process into an energy storage element.
In step 1) of the technical scheme of the invention, the vehicle operation parameters comprise wheel radius R, longitudinal speed u, wheel angular speed omega and wheel angular deceleration
Braking torque TbAnd rolling resistance torque Tf. The acquisition may be performed using conventional techniques.
In step 1) of the technical scheme of the invention, the wheel radius R is combined with the wheel longitudinal speed u and the wheel angular speed omega through a formula
And obtaining the real-time slip rate s. Reuse formula
Calculating to obtain a corresponding real-time utilization adhesion coefficient; wherein μ is the coefficient of adhesion, JωIs the moment of inertia, R is the wheel radius,
for angular deceleration of the wheel, TbFor braking torque, TfIs rolling moment of resistance, FZfIs the normal acting force applied to the front wheel.
In step 2) of the technical scheme of the present invention, the conventional method may be adopted to determine whether the vehicle is in the braking state, preferably, the method for determining whether the vehicle is in the braking state according to the rate of change of the vehicle speed includes: rate of change of speed in longitudinal direction
Judging that the vehicle is in a normal driving state; rate of change of speed in longitudinal direction
It is judged that the vehicle is in a braking state.
In step 2) of the technical scheme of the invention, the method for identifying the type of the road surface on which the vehicle runs currently comprises the following steps: calculating the slip ratio of different road surface types according to the slip ratio by using the theoretical value mu of the adhesion coefficientn(s) and then the theoretical value of μnAnd(s) calculating the difference value between the current slip rate and the real-time calculated value mu of the adhesion coefficient, and selecting the road surface type corresponding to the minimum difference value as the identified road surface type. Wherein the real-time slip rate s is determined by the formula mun(s)＝a[1-exp(-bs)]Cs finding the theoretical value μ of the coefficient of adhesion for the slip ratio for different road surface typesn(s), wherein s is the current slip ratio; mu.sn(s) is the utilization adhesion coefficient corresponding to different road surface types under the current slip rate; a. b and c are road surface parameters which are fixed values in a Burckhardt model, wherein the parameters of three typical road surfaces are shown in the following table.
| Road surface | a | b | c |
| Dry asphalt | 1.280 | 23.99 | 0.52 |
| Wet asphalt | 0.857 | 33.82 | 0.35 |
| Ice | 0.050 | 306.39 | 0.001 |
In step 2) of the technical scheme of the invention, the currently expected total braking force is calculated according to the prior art, specifically, the following formula is adopted for calculation:
wherein, FXbAs the total braking force, m is the total mass of the vehicle,
is the vehicle running acceleration. The braking strength is calculated according to the following formula:
wherein z is the braking intensity,
the acceleration of the vehicle is, and g is the acceleration of gravity.
In step 2) of the technical scheme of the invention, the target of the front and rear wheel braking force optimal distribution rule based on the road surface type and the braking strength is as follows: 1. controlling the rear wheel slip ratio to be always smaller than the front wheel slip ratio; 2. minimizing slippage of the front and rear wheels; 3. the ground adhesion coefficient is fully utilized. In the present application, the following data model is used:
s.t.sr＜sf
FXb1+FXb2＝mzg
0≤sf≤1
0≤sr≤1
FXb1＝μf(sf)Fzf
FXb2＝μr(sr)Fzr；
wherein the content of the first and second substances,
FZf、FZrthe normal acting force from the ground on the front wheel and the rear wheel respectively; m is the total mass of the vehicle; g is the acceleration of gravity;
is the running acceleration of the vehicle, L is the distance between the front and rear axles of the vehicle, a and b are the distances between the center of mass and the front and rear axles, hgIs the vehicle centroid height; z is the braking intensity; sfIs the slip ratio of the front wheels of the vehicle; srIs the slip ratio of the rear wheel of the vehicle; mu.sfThe utilization adhesion coefficient for the front wheels of the vehicle; mu.srThe utilization adhesion coefficient for the rear wheels of the vehicle; fXb1Ground braking force for the front wheels of the vehicle; fXb2Ground braking force for the rear wheels of the vehicle;
front and rear wheel braking force distribution coefficient β ═ FXb1/FXb。
In step 2) of the technical scheme of the invention, the regenerative braking force distribution rule is determined by the maximum regenerative braking force which can be provided by the vehicle motor, wherein the maximum regenerative braking force which can be provided by the motor is calculated by comprehensively considering the mechanical characteristics, the battery characteristics and relevant factors of the motor.
In step 2) of the technical solution of the present invention, the energy storage element is usually a battery.
The technical scheme of the invention firstly calculates the total braking force required during braking, and then selects the front and rear wheel braking force distribution rule corresponding to the road surface type according to the road surface type obtained by identification, thereby obtaining the braking force required by the front wheel; and secondly, distributing the obtained braking force required by the front wheels for the second time according to the determined regenerative braking force distribution rule. Compared with the prior art, the invention is characterized in that:
1. collecting vehicle operation parameters, calculating the slip rate and the utilization adhesion coefficient in real time, and calculating the theoretical values of the utilization adhesion coefficient of different road surface types under the current slip rate by combining a tire Burckhardt model; according to the calculated value and the theoretical value of the adhesion coefficient, the road type is identified, and the effect of identifying the road type in real time without adding an additional sensor is achieved.
2. According to the requirements of ECE regulations (United nations European economic Commission automobile regulations), constraint conditions of the braking force variable ratio optimization distribution algorithm are determined, the influence of braking strength and road surface adhesion conditions is considered, the rear wheel slip ratio is expected to be controlled to be always smaller than the front wheel slip ratio and the slip of each wheel is expected to be minimum, an objective function of the algorithm is established, and finally the braking force variable ratio optimization distribution coefficients of different road surface types are obtained through solving. On the premise of ensuring safety, the influence of the current motion state and the road adhesion condition is considered at the same time, and a new brake force ratio optimizing distribution coefficient is obtained.
3. According to the motor characteristics of the electric automobile, a regenerative braking control strategy is formulated, so that energy recovery is carried out as much as possible on the premise of meeting the requirements of direction stability and braking efficiency in the automobile braking process.
Drawings
FIG. 1 is a flow chart of an electric vehicle regenerative braking control strategy based on road identification according to the present invention;
FIG. 2 is a force analysis diagram of an automobile according to an embodiment of the present invention;
fig. 3 is a model of a single front-wheel vehicle of an automobile in an embodiment of the present invention.
Detailed Description
The invention will be better understood from the following detailed description of the invention with reference to the drawings and specific examples, which should not be construed as limiting the invention.
In the prior art, a driving assistance system is mounted on a vehicle, so that energy recovery can be performed automatically during braking, and a recoverable part of energy consumed during braking can be stored in an on-board energy storage element (such as a battery). The auxiliary driving system comprises an information acquisition subsystem, an information processing subsystem and an execution subsystem. The information acquisition subsystem includes: corresponding vehicle-mounted sensors are installed for detecting parameters such as real-time longitudinal speed, real-time wheel angular speed, real-time rolling resistance torque, real-time braking torque and the like. The information processing subsystem mainly comprises a main controller which processes the acquired data, implements a corresponding control strategy and sends an instruction for applying a corresponding braking force to the execution subsystem. The execution subsystem mainly comprises an electric control hydraulic brake module and applies braking force to each wheel according to data provided by the information processing subsystem.
The invention discloses an electric vehicle regenerative braking control strategy based on road surface identification, and a flow chart is shown in figure 1. And acquiring the running parameters of the vehicle by using the vehicle-mounted sensor, judging the braking state, and if the vehicle is in the normal running state, continuously acquiring the running parameters of the vehicle by using the vehicle sensor. If the vehicle is in the braking state, firstly identifying the type of the road surface on which the vehicle runs currently, and estimating the total braking force and the braking strength expected currently; then, performing braking force distribution processing according to a front and rear wheel braking force optimal distribution rule based on the road surface type and the braking strength to obtain the braking force required by the front wheels; finally, the maximum regenerative braking force which can be provided by the motor (the regenerative braking force F provided by the motor in the power generation mode) is obtained according to the characteristics of the motorregCan be expressed as:
in the formula TregFor regenerative braking of electric machinesMoment, ioThe transmission ratio of the main speed reducer is set; i.e. igη for speed variator ratioTFor transmission system mechanical efficiency; the motor regenerative braking torque may be expressed as:
wherein p isnFor rated power of the motor, nnThe rated rotating speed of the motor, and n is the rotating speed of the motor), the braking force required by the front wheels is secondarily distributed, the friction braking force and the regenerative braking force of the front wheels are determined, then the regenerative braking force is utilized to recover energy, and the energy lost in the braking process is recovered and stored in an energy storage element (such as a battery). The method specifically comprises the following steps:
1) collecting vehicle operation parameters in real time; calculating the slip rate and utilizing the adhesion coefficient in real time;
2) judging whether the vehicle is in a braking state, if so, carrying out regenerative braking control strategy processing on the vehicle until the vehicle returns to a normal driving state or stops; otherwise, executing step 1); wherein the implementing a regenerative braking control strategy process for the vehicle comprises:
identifying the type of a road surface on which the vehicle runs currently, and calculating the currently expected total braking force and braking strength;
obtaining a front wheel braking force optimal distribution rule and a rear wheel braking force optimal distribution rule and a regenerative braking force distribution rule based on the road surface type and the braking strength;
obtaining the braking force required by the front wheels according to the braking force optimal distribution rule of the front wheels and the rear wheels;
and secondly, performing secondary distribution on the braking force required by the front wheel according to a regenerative braking force distribution rule, determining the friction braking force and the regenerative braking force of the front wheel, then performing energy recovery by using the regenerative braking force, and recovering and storing the energy lost in the braking process into an energy storage element.
Firstly, extracting real-time longitudinal speed u, real-time wheel rotating speed omega and real-time braking torque T from vehicle running parametersbAnd real time rolling resistance torque Tf. The input of the real-time slip rate calculating system is real-time longitudinal speed v, real-time wheel rotating speed omega and wheel radius R, and the output is real-time slip rate s; at the same timeConverting the obtained real-time slip rate s through a Burckhardt model to obtain a theoretical value mu corresponding to the slip rate by using an adhesion coefficient under different typical road surface typesn(s). The real-time longitudinal speed u, the real-time wheel rotation speed omega and the real-time braking torque T are input by utilizing the real-time calculation system of the adhesion coefficientbAnd real time rolling resistance torque TfThe output is a real-time calculated value mu(s) by using the adhesion coefficient; according to the obtained theoretical value mu utilizing the adhesion coefficientnThe method comprises the steps of(s) calculating a value mu(s) by utilizing an adhesion coefficient in real time, obtaining a current running road type through road identification, selecting corresponding front and rear wheel braking force distribution coefficients β according to the road type obtained through real-time identification and braking intensity z required by braking according to a front and rear wheel braking force optimal distribution rule, thus obtaining the braking force required by front wheel braking under the current braking condition, comprehensively determining the maximum regenerative braking force of a motor according to the mechanical characteristics, battery characteristics and other influence factors of the motor of a running vehicle, further formulating a regenerative braking force distribution rule according to the maximum regenerative braking force of the motor, and further determining a part distributed as the regenerative braking force and a part distributed as friction braking force in the braking force required by the front wheel.
In the step 1), the vehicle operation parameters comprise real-time wheel rotating speed omega and real-time braking torque T of the vehiclebAnd real time rolling resistance torque Tf. The slip ratio is calculated by the formula:
the formula of calculation using the adhesion coefficient is:
in the above two formulas, s is the slip ratio, R is the wheel radius, u is the wheel longitudinal velocity, ω is the wheel angular velocity, JωIn order to be the moment of inertia,
for angular deceleration of the wheel, TbFor braking torque, TfIs rolling moment of resistance, FZfThe calculation formula of the normal acting force applied to the front wheel is as follows:
can be deduced according to the automobile stress analysis chart (shown in figure 2). Wherein m is the total mass of the vehicle; g is the gravity borne by the vehicle, and G is m.g, wherein G is the gravity acceleration;
is the running acceleration of the vehicle, L is the distance between the front and rear axles, a and b are the distances between the center of mass and the front and rear axles, hgIs the vehicle centroid height; fXb1Ground braking force for front wheels, FXb2The ground braking force of the rear wheel.
The Burckhardt model is an empirical model obtained by fitting various typical road test data, and the expression of the model is as follows: mu.sn(s)＝a[1-exp(-bs)]-cs. Wherein a, b and c are road surface parameters (fixed values in a Burckhardt model, specifically as described above); s is the current slip rate; mu.snAnd(s) is a theoretical value of the utilization adhesion coefficient corresponding to different road surface types under the current slip ratio.
The formula for the adhesion coefficient is derived from the wheel moment balance equation, and the single wheel model is shown in fig. 3. The wheel moment balance equation can be obtained:
the formula for calculating the adhesion coefficient is obtained by sorting:
moment analysis is carried out on the contact point of the front wheel of the electric automobile and the ground, and the normal acting force F of the ground to the front wheel can be obtainedZfExpression (c):
wherein z is the braking strength and the ratio of the braking deceleration to the gravity acceleration. Assuming a braking deceleration of the vehicle of
Then for the braking intensity z there is
The formula is arranged, and then a calculation formula of the normal acting force applied to the front wheel can be obtained.
In step 2), judging whether the vehicle is in a braking state according to the change rate of the vehicle speed, wherein the specific judgment method comprises the following steps:
rate of change of speed in longitudinal direction
Judging that the vehicle is in a normal running state, and continuously monitoring the longitudinal speed change rate
Slip ratio, using parameters such as adhesion coefficient;
rate of change of speed in longitudinal direction
It is judged that the vehicle is in a braking state.
Calculating a value mu(s) of the current utilization adhesion coefficient obtained in the step 1) in real time, and calculating a theoretical value mu of the utilization adhesion coefficient of different road surface types corresponding to the current slip rationAnd(s) respectively making differences between the road types, and taking the road type corresponding to the theoretical value of the adhesion coefficient with the minimum difference as the identified road type.
According to the formula
Calculating the currently desired total braking force, wherein FXbAs the total braking force, m is the total mass of the vehicle,
is the vehicle running acceleration.
According to the formula
Calculating the braking intensity, wherein z is the braking intensity,
the acceleration of the vehicle is, and g is the acceleration of gravity.
The target of the front and rear wheel braking force optimal distribution rule based on the road surface type and the braking strength is as follows: 1. controlling the rear wheel slip ratio to be always smaller than the front wheel slip ratio; 2. minimizing slippage of the front and rear wheels; 3. the ground adhesion coefficient is fully utilized. According to this objective, the following mathematical model is established, resulting in an optimized allocation rule:
s.t.sr＜sf
FXb1+FXb2＝mzg
0≤sf≤1
0≤sr≤1
FXb1＝μf(sf)Fzf
FXb2＝μr(sr)Fzr
wherein the content of the first and second substances,
FZf、FZrthe normal acting force from the ground on the front wheel and the rear wheel respectively; m is the total mass of the vehicle; g is the acceleration of gravity;
is the running acceleration of the vehicle, L is the distance between the front and rear axles of the vehicle, a and b are the distances between the center of mass and the front and rear axles, hgIs the vehicle centroid height; z is the braking intensity; sfIs the slip ratio of the front wheels of the vehicle; srIs the slip ratio of the rear wheel of the vehicle; mu.sfThe utilization adhesion coefficient for the front wheels of the vehicle; mu.srThe utilization adhesion coefficient for the rear wheels of the vehicle; fXb1Is the front of a vehicleGround braking force of the wheel; fXb2The ground braking force of the rear wheels of the vehicle.
Through calculation, the corresponding front and rear wheel braking force distribution coefficient β is F when the vehicle is braked under the conditions of different braking strengths under different road surface typesXb1/FXb。
Regenerative braking force F provided by motor in power generation moderegCan be expressed as:
in the formula TregFor regenerative braking torque of the machine ioThe transmission ratio of the main speed reducer is set; i.e. igη for speed variator ratioTFor transmission system mechanical efficiency; the motor regenerative braking torque may be expressed as:
wherein p isnFor rated power of the motor, nnThe rated rotating speed of the motor is shown, and n is the rotating speed of the motor.
When the vehicle enters a regenerative braking mode, judging whether a front wheel brake needs additionally provided mechanical friction braking force according to the maximum regenerative braking capacity of the motor, if the regenerative braking force provided by the motor is larger than the braking force distributed by the front wheel of the vehicle, the braking force is completely provided by the regenerative braking of the motor, and the regenerative braking force is equal to the braking force required by the front wheel; if the motor can provide a regenerative braking force that is less than the braking force distributed to the front wheels of the vehicle, a portion of that braking force is provided by regenerative braking of the motor, where the regenerative braking force is equal to the maximum regenerative braking force that the motor can provide, thereby enabling recovery of the regenerative braking energy.
Claims (10)
1. An electric vehicle regenerative braking control strategy based on road surface identification comprises the following steps:
1) collecting vehicle operation parameters in real time; calculating the slip rate and utilizing the adhesion coefficient in real time;
2) judging whether the vehicle is in a braking state, if so, carrying out regenerative braking control strategy processing on the vehicle until the vehicle returns to a normal driving state or stops; otherwise, executing step 1); wherein the implementing a regenerative braking control strategy process for the vehicle comprises:
identifying the type of a road surface on which the vehicle runs currently, and calculating the currently expected total braking force and braking strength;
obtaining a front wheel braking force optimal distribution rule and a rear wheel braking force optimal distribution rule and a regenerative braking force distribution rule based on the road surface type and the braking strength;
obtaining the braking force required by the front wheels according to the braking force optimal distribution rule of the front wheels and the rear wheels;
and secondly, performing secondary distribution on the braking force required by the front wheel according to a regenerative braking force distribution rule, determining the friction braking force and the regenerative braking force of the front wheel, then performing energy recovery by using the regenerative braking force, and recovering and storing the energy lost in the braking process into an energy storage element.
2. The regenerative braking control strategy for electric vehicles based on road surface identification as claimed in claim 1, wherein in step 1), the vehicle operation parameters comprise wheel radius R, longitudinal speed u, wheel angular speed ω, wheel angular deceleration
Braking torque TbAnd rolling resistance torque Tf。
3. The regenerative braking control strategy for the electric vehicle based on the road surface identification according to claim 1, wherein in step 1), the slip ratio is calculated according to the following formula:
where s is the slip ratio, R is the wheel radius, u is the wheel longitudinal velocity, and ω is the wheel angular velocity.
4. The regenerative braking control strategy for the electric vehicle based on the road surface recognition according to claim 1, wherein in step 1), the adhesion coefficient is calculated according to the following formula:
wherein μ is the coefficient of adhesion, JωIs the moment of inertia, R is the wheel radius,
for angular deceleration of the wheel, TbFor braking torque, TfIs rolling moment of resistance, FZfIs the normal acting force applied to the front wheel.
5. The regenerative braking control strategy for the electric vehicle based on the road surface identification as claimed in claim 1, wherein in the step 2), whether the vehicle is in the braking state is judged according to the change rate of the vehicle speed, and the specific judgment method is as follows:
rate of change of speed in longitudinal direction
Judging that the vehicle is in a normal driving state;
rate of change of speed in longitudinal direction
It is judged that the vehicle is in a braking state.
6. The regenerative braking control strategy for the electric vehicle based on the road surface identification according to any one of claims 1-5, wherein in the step 2), the method for identifying the type of the road surface on which the vehicle is currently running is as follows:
calculating the slip ratio of different road surface types according to the slip ratio by using the theoretical value mu of the adhesion coefficientn(s) and then the theoretical value of μnAnd(s) calculating the difference value between the current slip rate and the real-time calculated value mu of the adhesion coefficient, and selecting the road surface type corresponding to the minimum difference value as the identified road surface type.
7. The regenerative braking control strategy for the electric vehicle based on the road surface identification according to any one of claims 1-5, wherein in step 2), the currently desired total braking force is calculated according to the following formula:
wherein, FXbAs the total braking force, m is the total mass of the vehicle,
is the vehicle running acceleration.
8. The regenerative braking control strategy for the electric vehicle based on the road surface identification according to any one of claims 1-5, wherein in step 2), the braking intensity is calculated according to the following formula:
wherein z is the braking intensity,
the acceleration of the vehicle is, and g is the acceleration of gravity.
9. The regenerative braking control strategy for the electric vehicle based on the road surface identification according to any one of claims 1-5, characterized in that in step 2), the following data model is adopted to obtain the optimal distribution rule of the braking force of the front and rear wheels based on the road surface type and the braking intensity:
s.t.sr＜sf
FXb1+FXb2＝mzg
0≤sf≤1
0≤sr≤1
FXb1＝μf(sf)Fzf
FXb2＝μr(sr)Fzr；
wherein the content of the first and second substances,
FZf、FZrthe normal acting force from the ground on the front wheel and the rear wheel respectively; m is the total mass of the vehicle; g is the acceleration of gravity;
is the running acceleration of the vehicle, L is the distance between the front and rear axles of the vehicle, a and b are the distances between the center of mass and the front and rear axles, hgIs the vehicle centroid height; z is the braking intensity; sfIs the slip ratio of the front wheels of the vehicle; srIs the slip ratio of the rear wheel of the vehicle; mu.sfThe utilization adhesion coefficient for the front wheels of the vehicle; mu.srThe utilization adhesion coefficient for the rear wheels of the vehicle; fXb1Ground braking force for the front wheels of the vehicle; fXb2Ground braking force for the rear wheels of the vehicle;
front and rear wheel braking force distribution coefficient β ═ FXb1/FXb。
10. The road surface identification-based electric vehicle regenerative braking control strategy according to any one of claims 1-5, wherein in step 2), the regenerative braking force distribution rule is determined by the maximum regenerative braking force that can be provided by the vehicle motor, wherein the maximum regenerative braking force that can be provided by the motor is calculated by comprehensively considering the mechanical characteristics, the battery characteristics and the related factors of the motor.
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