CN113771635B - Energy recovery control method based on brake-by-wire - Google Patents
Energy recovery control method based on brake-by-wire Download PDFInfo
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- CN113771635B CN113771635B CN202111091358.6A CN202111091358A CN113771635B CN 113771635 B CN113771635 B CN 113771635B CN 202111091358 A CN202111091358 A CN 202111091358A CN 113771635 B CN113771635 B CN 113771635B
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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
- B60L7/10—Dynamic electric regenerative braking
- B60L7/12—Dynamic electric regenerative braking for vehicles propelled by dc motors
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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
- B60L7/24—Electrodynamic brake systems for vehicles in general with additional mechanical or electromagnetic braking
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/72—Electric energy management in electromobility
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Abstract
The invention relates to an energy recovery control method based on linear control, which comprises the following steps: acquiring real-time data and parameters of the distributed electric drive whole vehicle; establishing an EMB electromechanical brake system model; judging whether to start braking energy recovery; acquiring braking strength Z; according to the braking intensity Z, obtaining the front axle braking moment T according to the set front and rear axle braking force curve bf And rear axle braking moment T br The method comprises the steps of carrying out a first treatment on the surface of the The current brake pedal signal Brk, the real-time longitudinal vehicle speed V and the SOC value of the battery are used as inputs, and the motor brake moment duty ratio coefficient K is obtained by fuzzy control; and obtaining braking energy feedback moment on each shaft, and braking the motor according to the braking energy recovery moment given by the whole vehicle controller VCU. The invention calculates the braking strength through real-time conditions, distributes the braking force on each shaft, and then obtains the recovered energy through fuzzy control of the calculated duty ratio of the regenerative braking force on each shaft.
Description
Technical Field
The invention relates to the technical field of energy recovery of electric automobiles, in particular to an energy recovery control method based on brake-by-wire.
Background
The occupancy ratio of the pure electric vehicles in the number of the global vehicles is increased, and the position is more and more important. The pure electric vehicle has the characteristics of zero emission, zero pollution, high efficiency and energy conservation, so that the pure electric vehicle becomes the trend of vehicle development. Some of the energy conservation of the electric automobile is realized through the conversion of braking force, and the braking energy is converted into electric energy to be stored in a battery through the recovery of braking energy.
However, if braking energy recovery is achieved by using conventional hydraulic braking in combination with a motor, great difficulty is generated because braking force cannot be precisely controlled. If brake-by-wire is used, dynamic and accurate control of the braking force can be achieved. Based on the brake-by-wire, the accurate control of the braking force can be realized. In order to increase the efficiency of braking energy recovery, an efficient braking force distribution and control system is required to perform regenerative braking and mechanical friction braking of the reasonably distributed motor.
In China, the electronic mechanical braking system, the hub motor, the storage battery and the like are combined to study, so that the braking energy recovery efficiency of the automobile is rarely improved, and most of the electronic mechanical braking system, the hub motor, the storage battery and the like are independently studied.
Disclosure of Invention
The invention aims to provide an energy recovery control method based on brake-by-wire, which realizes recovery of more brake energy by real-time distribution control of braking force on the premise of ensuring brake stability.
In order to achieve the above purpose, the present invention adopts the following technical scheme: an energy recovery control method based on brake-by-wire, the method comprising the following sequential steps:
(1) Acquiring real-time data and parameters of a distributed electric drive whole vehicle: acquiring real-time longitudinal vehicle speed V, current brake pedal signal Brk and SOC value of a battery of the distributed electrically-driven whole vehicle under different working conditions; acquiring parameters of the distributed electric drive whole vehicle, wherein the parameters comprise a distance a from a mass center to a front shaft, a distance b from the mass center to a rear shaft, a mass center height hg, a mass m of the whole vehicle, a wheel base L, an effective friction radius r of a brake disc, a braking area A of a brake piston of the brake, a friction coefficient mu of the brake, a braking efficiency eta of the brake and a specific factor c of the brake;
(2) Establishing an EMB electromechanical brake system model;
(3) Judging whether to start braking energy recovery or not according to the current braking pedal signal Brk, the real-time longitudinal vehicle speed V and the SOC value of the battery;
(4) Acquiring a braking intensity Z according to the current whole vehicle parameter and a current braking pedal signal Brk; according to the braking intensity Z, obtaining the front axle braking moment T according to the set front and rear axle braking force curve bf And rear axle braking moment T br ；
(5) The current brake pedal signal Brk, the real-time longitudinal vehicle speed V and the SOC value of the battery are used as inputs, and the motor brake moment duty ratio coefficient K is obtained by fuzzy control; and obtaining braking energy feedback moment on each shaft, and braking the motor according to the braking energy recovery moment given by the whole vehicle controller VCU.
The step (2) specifically comprises the following steps:
(2a) Establishing a mathematical model of the brushless direct current motor:
T m (t)＝C m ·i(t)
E＝C E ·N
wherein U is the armature voltage; i (t) is the armature current; l (L) m Is the armature inductance; r is R m Is the whole loop resistance; e is the armature back EMF; tm (t) is the torque produced by the motor; cm is the torque coefficient; c (C) E Is the electromotive force coefficient induced by the motor; n is the rotor speed;
(2b) Establishing a planetary gear reduction mechanism mathematical model:
T x ＝T a ·i x ·η x
wherein T is x Is the output torque of the planet carrier; t (T) a ＝T m Is the input torque of the sun gear; i.e x Is a transmission ratio; η (eta) x Is the transmission efficiency of the planetary gear;
(2c) Establishing a ball screw pair mathematical model:
T g ＝F·P h /(2π)
T g ＝T x ·η g
wherein T is g Is the driving torque of the ball screw; f is the thrust of the screw rod; p (P) h Is the lead of the screw rod; η (eta) g Is the transmission efficiency of the ball screw;
(2d) Establishing an EMB electromechanical brake system model:
F＝2π·C m ·i(t)·i x ·η x ·η g /P h 。
the step (3) specifically comprises the following steps: judging whether to start braking energy recovery or not according to the current braking pedal signal Brk, the real-time longitudinal vehicle speed V and the SOC value of the battery: when the SOC of the battery is more than 90%, closing the braking energy recovery; when the real-time longitudinal vehicle speed V is less than 5km/h, closing the braking energy recovery; if the current brake pedal has signal input and the real-time longitudinal vehicle speed V is greater than 5km/h and the SOC value of the battery is not greater than 90%, starting braking energy recovery.
The step (4) specifically refers to: according to AVL Cruise theory manual, the formula between the braking torque and the braking pressure is found as follows:
T＝2pAημrc
wherein T is the braking torque required by the current automobile; p is the braking pressure required by converting into the current mechanical brake of the automobile; a is the braking area of a brake piston of a brake; η is the brake efficiency of the brake; μ is the brake coefficient of friction; r is the effective friction radius of the brake disc; c is a brake specific factor;
according to the formula of the braking intensity:
wherein m is the mass of the whole vehicle; r is the radius of the wheel, and the braking strength Z is obtained;
according to the braking intensity Z, combining the designed front and rear axle braking force curves to obtain a front axle braking force Fx1 and a rear axle braking force Fx2;
the point A is the intersection point of the ECE rule curve and the abscissa axis, corresponds to the first braking intensity Z1, and corresponds to the first front axle braking force Fx1A; the curve I is an ideal braking force distribution curve;
when the braking intensity Z is smaller than the first braking intensity Z1, front and rear axle braking forces are distributed according to the OA line segments, namely all braking forces are provided by the front axle, and the rear axle does not participate in braking;
the point B corresponds to the second braking intensity Z2, and the point B is the coordinate point position obtained when the braking intensity Z is equal to 0.2, namely Z2=0.2; the corresponding second front axle braking force is Fx2A, the second rear axle braking force is Fx2B, and when the braking intensity Z is between Z1 and Z2, the braking force of the front axle and the rear axle is distributed according to the AB line;
the point C corresponds to the third braking intensity Z3, and the point C is a coordinate point position obtained by increasing the front axle braking force when the braking intensity Z is equal to 0.4, namely Z3=0.4, and the rear axle braking force is kept unchanged;
the corresponding third front axle braking force is Fx1C, the third rear axle braking force is Fx2C, when the braking intensity is between Z2 and Z3, the second rear axle braking force is Fx2B, and the front axle braking force is increased, namely BC segment;
the point D corresponds to the fourth braking intensity Z4, and the point D is the coordinate point position obtained when the braking intensity Z is equal to 0.6, namely Z4=0.6; the fourth front axle braking force is Fx1D, the fourth rear axle braking force is Fx2D, and when the braking strength is between Z3 and Z4, the braking force of the front axle and the rear axle is distributed according to a CD line;
the corresponding braking strength of the E point is Z5, the E point is a coordinate point position obtained when the braking strength Z is equal to 0.75, Z5=0.75, and emergency braking is performed after the Z point is larger than the E point;
when the braking strength is between Z4 and Z5, the braking force of the front and rear axles is distributed according to the DE line;
when the braking strength is greater than Z5, the front and rear axle braking force is distributed according to the I curve, and the motor exits from the braking link; the front-rear axle braking force must be distributed between the ECE regulation curve and the I curve;
knowing the braking intensity Z, the allocation strategy is as follows:
when Z < Z1, the front-rear axis braking force distribution line segment is OA:
g is gravity, fx1 is front axle braking force, fx2 is rear axle braking force;
when Z1< Z2, the front-rear axis braking force distribution line segment is AB:
when Z2< Z3, the front-rear axis braking force distribution line segment is BC:
when Z3< Z4, the front-rear axis braking force distribution line segment is CD:
when Z4< Z5, the front-rear axle braking force distribution line segment is DE:
when Z > Z5, the front and rear axis braking force distribution line segment is an I curve;
wherein: k (K) AB 、K CD 、K DE Slopes of line segments AB, CD, DE, respectively;
obtaining front axle braking force Fx1 and rear axle braking force Fx2 to obtain front axle braking moment T bf And rear axle braking moment T br 。
The step (5) specifically refers to: the braking energy feedback moment on each shaft is obtained by using the following formula, and the motor brakes according to the braking energy recovery moment given by the whole vehicle controller VCU:
T regn ＝T brk *K
wherein T is regn Is regenerative braking torque; t (T) brk Is the total braking torque; k is the motor braking torque duty cycle.
According to the technical scheme, the beneficial effects of the invention are as follows: firstly, the invention relates to a distributed electric drive brake-by-wire-based energy recovery control strategy, which is characterized in that the brake strength is calculated through real-time conditions, the magnitude of braking force on each shaft is distributed, and then the duty ratio of regenerative braking force on each shaft calculated through fuzzy control is utilized, so that the recovered energy is obtained; secondly, compared with the prior art, the hydraulic braking of the traditional automobile is abandoned, the brake-by-wire is adopted, the braking force is distributed by utilizing the designed braking force distribution curve, the energy recovery efficiency is further improved, and the braking force distribution is easier to realize; thirdly, the invention can build a control strategy by combining the distribution of braking force and fuzzy control, thereby realizing the effects of improving the braking force accuracy and the driving mileage on the premise of ensuring the braking stability and the braking safety.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a front-rear axle brake force distribution diagram;
FIG. 3 is a graph of SOC membership functions;
FIG. 4 is a graph of vehicle speed membership function;
FIG. 5 is a graph of brake pedal displacement membership function;
FIG. 6 is a chart of a motor brake duty cycle K membership function;
FIG. 7 is a graph comparing battery pack SOC under NEDC cycle conditions;
FIG. 8 is a graph comparing energy recovered from a battery pack during NEDC cycle conditions;
FIG. 9 is a graph comparing battery pack SOC under CLTC-P cycling conditions;
FIG. 10 is a graph comparing the energy recovered from a battery pack during CLTC-P cycling.
Detailed Description
As shown in fig. 1, a brake-by-wire based energy recovery control method includes the following sequential steps:
(1) Acquiring real-time data and parameters of a distributed electric drive whole vehicle: acquiring real-time longitudinal vehicle speed V, current brake pedal signal Brk and SOC value of a battery of the distributed electrically-driven whole vehicle under different working conditions; acquiring parameters of the distributed electric drive whole vehicle, wherein the parameters comprise a distance a from a mass center to a front shaft, a distance b from the mass center to a rear shaft, a mass center height hg, a mass m of the whole vehicle, a wheel base L, an effective friction radius r of a brake disc, a braking area A of a brake piston of the brake, a friction coefficient mu of the brake, a braking efficiency eta of the brake and a specific factor c of the brake;
(2) Establishing an EMB electromechanical brake system model;
(3) Judging whether to start braking energy recovery or not according to the current braking pedal signal Brk, the real-time longitudinal vehicle speed V and the SOC value of the battery;
(4) Acquiring a braking intensity Z according to the current whole vehicle parameter and a current braking pedal signal Brk; according to the braking intensity Z, obtaining the front axle braking moment T according to the set front and rear axle braking force curve bf And rear axle braking moment T br ；
(5) The current brake pedal signal Brk, the real-time longitudinal vehicle speed V and the SOC value of the battery are used as inputs, and the motor brake moment duty ratio coefficient K is obtained by fuzzy control; and obtaining braking energy feedback moment on each shaft, and braking the motor according to the braking energy recovery moment given by the whole vehicle controller VCU.
The step (2) specifically comprises the following steps:
(2a) Establishing a mathematical model of the brushless direct current motor:
T m (t)＝C m ·i(t)
E＝C E ·N
wherein U is the armature voltage; i (t) is the armature current; l (L) m Is the armature inductance; r is R m Is the whole loop resistance; e is the armature back EMF; tm (t) is the torque produced by the motor; cm is the torque coefficient; c (C) E Is the electromotive force coefficient induced by the motor; n is the rotor speed;
(2b) Establishing a planetary gear reduction mechanism mathematical model:
T x ＝T a ·i x ·η x
wherein T is x Is the output torque of the planet carrier; t (T) a ＝T m Is the input torque of the sun gear; i.e x Is a transmission ratio; η (eta) x Is the transmission efficiency of the planetary gear;
(2c) Establishing a ball screw pair mathematical model:
T g ＝F·P h /(2π)
T g ＝T x ·η g
wherein T is g Is the driving torque of the ball screw; f is the thrust of the screw rod; p (P) h Is the lead of the screw rod; η (eta) g Is the transmission efficiency of the ball screw;
(2d) Establishing an EMB electromechanical brake system model:
F＝2π·C m ·i(t)·i x ·η x ·η g /P h 。
the step (3) specifically comprises the following steps: judging whether to start braking energy recovery or not according to the current braking pedal signal Brk, the real-time longitudinal vehicle speed V and the SOC value of the battery: when the SOC of the battery is more than 90%, closing the braking energy recovery; when the real-time longitudinal vehicle speed V is less than 5km/h, closing the braking energy recovery; if the current brake pedal has signal input and the real-time longitudinal vehicle speed V is greater than 5km/h and the SOC value of the battery is not greater than 90%, starting braking energy recovery.
The step (4) specifically refers to: according to AVL Cruise theory manual, the formula between the braking torque and the braking pressure is found as follows:
T＝2pAημrc
wherein T is the braking torque required by the current automobile; p is the braking pressure required by converting into the current mechanical brake of the automobile; a is the braking area of a brake piston of a brake; η is the brake efficiency of the brake; μ is the brake coefficient of friction; r is the effective friction radius of the brake; c is a brake specific factor;
according to the formula of the braking intensity:
wherein m is the mass of the whole vehicle; r is the radius of the wheel, and the braking strength Z is obtained;
according to the braking intensity Z, combining the designed front and rear axle braking force curves to obtain a front axle braking force Fx1 and a rear axle braking force Fx2;
as shown in fig. 2, point a is the intersection point of the ECE regulation curve and the abscissa axis, and corresponds to the braking intensity Z1, and the corresponding first front axle braking force is Fx1A; the curve I is an ideal braking force distribution curve;
when the braking strength is smaller than Z1, front and rear axle braking forces are distributed according to the OA line segments, namely all braking forces are provided by the front axle, and the rear axle does not participate in braking;
the point A is the intersection point of the ECE rule curve and the abscissa axis, corresponds to the first braking intensity Z1, and corresponds to the first front axle braking force Fx1A; the curve I is an ideal braking force distribution curve;
when the braking intensity Z is smaller than the first braking intensity Z1, front and rear axle braking forces are distributed according to the OA line segments, namely all braking forces are provided by the front axle, and the rear axle does not participate in braking;
the point B corresponds to the second braking intensity Z2, and the point B is the coordinate point position obtained when the braking intensity Z is equal to 0.2, namely Z2=0.2; the corresponding second front axle braking force is Fx2A, the second rear axle braking force is Fx2B, and when the braking intensity Z is between Z1 and Z2, the braking force of the front axle and the rear axle is distributed according to the AB line;
the point C corresponds to the third braking intensity Z3, and the point C is a coordinate point position obtained by increasing the front axle braking force when the braking intensity Z is equal to 0.4, namely Z3=0.4, and the rear axle braking force is kept unchanged;
the corresponding third front axle braking force is Fx1C, the third rear axle braking force is Fx2C, when the braking intensity is between Z2 and Z3, the second rear axle braking force is Fx2B, and the front axle braking force is increased, namely BC segment;
the point D corresponds to the fourth braking intensity Z4, and the point D is the coordinate point position obtained when the braking intensity Z is equal to 0.6, namely Z4=0.6; the fourth front axle braking force is Fx1D, the fourth rear axle braking force is Fx2D, and when the braking strength is between Z3 and Z4, the braking force of the front axle and the rear axle is distributed according to a CD line;
the corresponding braking strength of the E point is Z5, the E point is a coordinate point position obtained when the braking strength Z is equal to 0.75, Z5=0.75, and emergency braking is performed after the Z point is larger than the E point;
when the braking strength is between Z4 and Z5, the braking force of the front and rear axles is distributed according to the DE line;
when the braking strength is greater than Z5, the front and rear axle braking force is distributed according to the I curve, and the motor exits from the braking link; the front-rear axle braking force must be distributed between the ECE regulation curve and the I curve;
knowing the braking intensity Z, the allocation strategy is as follows:
when Z < Z1, the front-rear axis braking force distribution line segment is OA:
g is gravity, fx1 is front axle braking force, fx2 is rear axle braking force;
when Z1< Z2, the front-rear axis braking force distribution line segment is AB:
when Z2< Z3, the front-rear axis braking force distribution line segment is BC:
when Z3< Z4, the front-rear axis braking force distribution line segment is CD:
when Z4< Z5, the front-rear axle braking force distribution line segment is DE:
when Z > Z5, the front and rear axis braking force distribution line segment is an I curve;
wherein: k (K) AB 、K CD 、K DE Slopes of line segments AB, CD, DE, respectively;
obtaining front axle braking force Fx1 and rear axle braking force Fx2 to obtain front axle braking moment T bf And rear axle braking moment T br 。
The step (5) specifically refers to: the braking energy feedback moment on each shaft is obtained by using the following formula, and the motor brakes according to the braking energy recovery moment given by the whole vehicle controller VCU:
T regn ＝T brk *K
wherein T is regn Is regeneration ofBraking torque; t (T) brk Is the total braking torque; k is the motor braking torque duty cycle.
After the front and rear axle torque is distributed, the torque on each axle is distributed. And (3) using a fuzzy control method, and performing fuzzy control input: the input comprises a real-time longitudinal vehicle speed V; acquiring a brake pedal signal Brk; acquiring an SOC value of a battery;
(1) The battery SOC was set as follows:
when the battery of the electric automobile is charged and discharged, the SOC needs to be monitored in real time, and damage can be caused by the fact that the SOC value is too high or too low, so that the braking energy can be recovered within a certain range by taking the safety of the battery into consideration, and the SOC value is set to three different levels, { high (G), medium (Z) and low (D) }, as shown in figure 3;
(2) The vehicle speed V is set as follows:
when the vehicle speed is lower than a certain value, the regenerative braking is turned off, and when the vehicle speed is higher than the certain value, the regenerative braking duty ratio is properly increased. The vehicle speed is divided into 4 different levels, { high (G), medium (Z), low (D), very low (HD) }, as shown in fig. 4;
(3) The brake pedal travel Brk is set as follows:
the brake pedal is a brake demand of the driver, and is used for limiting the output torque according to the demand of the driver. The brake pedal travel is divided into three different levels, { high (G), medium (Z), low (D) }, as shown in fig. 5;
(4) The output motor braking duty ratio K is set as follows:
the braking force ratio k range for setting the regenerative braking is [0,1]. The fuzzy subset is set to 5, { very High (HG), high (G), medium (Z), low (D), very low (HD) }, as shown in FIG. 6;
formulating fuzzy rules as shown in table 1; and obtaining a motor braking moment duty ratio coefficient K. When the braking torque provided by the motor is insufficient, the electromechanical braking system provides the rest of the mechanical braking force to supplement.
TABLE 1
In order to better compare the technical effects adopted in the invention for verification and explanation, the embodiment selects a braking energy recovery strategy with a fixed proportion to carry out comparison test with the method of the invention, and uses scientific and strict means to compare experimental results to verify the authenticity of the method of the invention.
The following is a comparison of NEDC and CLTC-P conditions, respectively.
First, NEDC operation is shown in FIGS. 7 and 8.
Table 1: NEDC working condition
| SOC | SOC reduction | Energy recovery | |
| The control strategy of the |
85％—82.0407％ | 2.9593％ | 792.453KJ |
| Fixed |
85％—81.4037％ | 3.5963％ | 463.56KJ |
The next is the CLTC-P operating mode, as shown in FIGS. 9 and 10.
Table 2: CLTC-P operating mode
| SOC | SOC reduction | Energy recovery | |
| The control strategy of the |
85％—80.4734％ | 4.5266％ | 1193.59KJ |
| Fixed |
85％—80.1305％ | 4.8695％ | 738.622KJ |
Therefore, in the two typical working conditions, compared with the prior fixed proportion recovery control strategy, the recovery efficiency is effectively improved, and the consumption of battery energy is reduced.
In summary, the invention relates to a distributed electric drive brake-by-wire-based energy recovery control strategy, which calculates the brake strength through real-time conditions, distributes the magnitude of the braking force on each shaft, and then obtains the recovered energy through fuzzy control of the calculated duty ratio of the regenerative braking force on each shaft; compared with the prior art, the hydraulic braking of the traditional automobile is abandoned, the brake-by-wire is adopted, the designed braking force distribution curve is utilized for braking force distribution, the energy recovery efficiency is further improved, and the braking force distribution is easier to realize; the invention can build a control strategy by combining the distribution of braking force and fuzzy control, thereby realizing the effects of improving the braking force accuracy and the driving mileage on the premise of ensuring the braking stability and the safety.
Claims (5)
1. The energy recovery control method based on brake-by-wire is characterized by comprising the following steps of: the method comprises the following steps in sequence:
(1) Acquiring real-time data and parameters of a distributed electric drive whole vehicle: acquiring real-time longitudinal vehicle speed V, current brake pedal signal Brk and SOC value of a battery of the distributed electrically-driven whole vehicle under different working conditions; acquiring parameters of the distributed electric drive whole vehicle, wherein the parameters comprise a distance a from a mass center to a front shaft, a distance b from the mass center to a rear shaft, a mass center height hg, a mass m of the whole vehicle, a wheel base L, an effective friction radius r of a brake disc, a braking area A of a brake piston of the brake, a friction coefficient mu of the brake, a braking efficiency eta of the brake and a specific factor c of the brake;
(2) Establishing an EMB electromechanical brake system model;
(3) Judging whether to start braking energy recovery or not according to the current braking pedal signal Brk, the real-time longitudinal vehicle speed V and the SOC value of the battery;
(4) Acquiring a braking intensity Z according to the current whole vehicle parameter and a current braking pedal signal Brk; according to the braking intensity Z, obtaining the front axle braking moment T according to the set front and rear axle braking force curve bf And rear axle braking moment T br ；
(5) The current brake pedal signal Brk, the real-time longitudinal vehicle speed V and the SOC value of the battery are used as inputs, and the motor brake moment duty ratio coefficient K is obtained by fuzzy control; and obtaining braking energy feedback moment on each shaft, and braking the motor according to the braking energy recovery moment given by the whole vehicle controller VCU.
2. The brake-by-wire based energy recovery control method according to claim 1, characterized in that: the step (2) specifically comprises the following steps:
(2a) Establishing a mathematical model of the brushless direct current motor:
T m (t)＝C m ·i(t)
E＝C E ·N
wherein U is the armature voltage; i (t) is the armature current; l (L) m Is the armature inductance; r is R m Is the whole loop resistance; e is the armature back EMF; tm (t) is the torque produced by the motor; cm is the torque coefficient; c (C) E Is the electromotive force coefficient induced by the motor; n is the rotor speed;
(2b) Establishing a planetary gear reduction mechanism mathematical model:
T x ＝T a ·i x ·η x
wherein T is x Is the output torque of the planet carrier; t (T) a ＝T m Is the input torque of the sun gear; i.e x Is a transmission ratio; η (eta) x Is the transmission efficiency of the planetary gear;
(2c) Establishing a ball screw pair mathematical model:
T g ＝F·P h /(2π)
T g ＝T x ·η g
wherein T is g Is the driving torque of the ball screw; f is the thrust of the screw rod; p (P) h Is the lead of the screw rod; η (eta) g Is the transmission efficiency of the ball screw;
(2d) Establishing an EMB electromechanical brake system model:
F＝2π·C m ·i(t)·i x ·η x ·η g /P h 。
3. the brake-by-wire based energy recovery control method according to claim 1, characterized in that: the step (3) specifically comprises the following steps: judging whether to start braking energy recovery or not according to the current braking pedal signal Brk, the real-time longitudinal vehicle speed V and the SOC value of the battery: when the SOC of the battery is more than 90%, closing the braking energy recovery; when the real-time longitudinal vehicle speed V is less than 5km/h, closing the braking energy recovery; if the current brake pedal has signal input and the real-time longitudinal vehicle speed V is greater than 5km/h and the SOC value of the battery is not greater than 90%, starting braking energy recovery.
4. The brake-by-wire based energy recovery control method according to claim 1, characterized in that: the step (4) specifically refers to: according to AVL Cruise theory manual, the formula between the braking torque and the braking pressure is found as follows:
T＝2pAημrc
wherein T is the braking torque required by the current automobile; p is the braking pressure required by converting into the current mechanical brake of the automobile; a is the braking area of a brake piston of a brake; η is the brake efficiency of the brake; μ is the brake coefficient of friction; r is the effective friction radius of the brake disc; c is a brake specific factor;
according to the formula of the braking intensity:
wherein m is the mass of the whole vehicle; r is the radius of the wheel, and the braking strength Z is obtained;
according to the braking intensity Z, combining the designed front and rear axle braking force curves to obtain a front axle braking force Fx1 and a rear axle braking force Fx2;
the point A is the intersection point of the ECE rule curve and the abscissa axis, corresponds to the first braking intensity Z1, and corresponds to the first front axle braking force Fx1A; the curve I is an ideal braking force distribution curve;
when the braking intensity Z is smaller than the first braking intensity Z1, front and rear axle braking forces are distributed according to the OA line segments, namely all braking forces are provided by the front axle, and the rear axle does not participate in braking;
the point B corresponds to the second braking intensity Z2, and the point B is the coordinate point position obtained when the braking intensity Z is equal to 0.2, namely Z2=0.2; the corresponding second front axle braking force is Fx2A, the second rear axle braking force is Fx2B, and when the braking intensity Z is between Z1 and Z2, the braking force of the front axle and the rear axle is distributed according to the AB line;
the point C corresponds to the third braking intensity Z3, and the point C is a coordinate point position obtained by increasing the front axle braking force when the braking intensity Z is equal to 0.4, namely Z3=0.4, and the rear axle braking force is kept unchanged;
the corresponding third front axle braking force is Fx1C, the third rear axle braking force is Fx2C, when the braking intensity is between Z2 and Z3, the second rear axle braking force is Fx2B, and the front axle braking force is increased, namely BC segment;
the point D corresponds to the fourth braking intensity Z4, and the point D is the coordinate point position obtained when the braking intensity Z is equal to 0.6, namely Z4=0.6; the fourth front axle braking force is Fx1D, the fourth rear axle braking force is Fx2D, and when the braking strength is between Z3 and Z4, the braking force of the front axle and the rear axle is distributed according to a CD line;
the corresponding braking strength of the E point is Z5, the E point is a coordinate point position obtained when the braking strength Z is equal to 0.75, Z5=0.75, and emergency braking is performed after the Z point is larger than the E point;
when the braking strength is between Z4 and Z5, the braking force of the front and rear axles is distributed according to the DE line;
when the braking strength is greater than Z5, the front and rear axle braking force is distributed according to the I curve, and the motor exits from the braking link; the front-rear axle braking force must be distributed between the ECE regulation curve and the I curve;
knowing the braking intensity Z, the allocation strategy is as follows:
when Z < Z1, the front-rear axis braking force distribution line segment is OA:
g is gravity, fx1 is front axle braking force, fx2 is rear axle braking force;
when Z1< Z2, the front-rear axis braking force distribution line segment is AB:
when Z2< Z3, the front-rear axis braking force distribution line segment is BC:
when Z3< Z4, the front-rear axis braking force distribution line segment is CD:
when Z4< Z5, the front-rear axle braking force distribution line segment is DE:
when Z > Z5, the front and rear axis braking force distribution line segment is an I curve;
wherein: k (K) AB 、K CD 、K DE Slopes of line segments AB, CD, DE, respectively;
fx1 is the front axle braking force, fx2 is the rear axle braking force, and the front axle braking moment T is obtained bf And rear axle braking moment T br 。
5. The brake-by-wire based energy recovery control method according to claim 1, characterized in that: the step (5) specifically refers to: the braking energy feedback moment on each shaft is obtained by using the following formula, and the motor brakes according to the braking energy recovery moment given by the whole vehicle controller VCU:
T regn ＝T brk *K
wherein T is regn Is regenerative braking torque; t (T) brk Is the total braking torque; k is the motor braking torque duty cycle.
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| DE102015211560A1 (en) * | 2015-06-23 | 2016-12-29 | Volkswagen Aktiengesellschaft | Motor vehicle with recuperation and friction-dependent brake control |
| CN110254239A (en) * | 2019-06-28 | 2019-09-20 | 福州大学 | A kind of Torque distribution method during electric car regenerative braking transient response |
| CN113147412A (en) * | 2021-04-25 | 2021-07-23 | 南京依维柯汽车有限公司 | Brake energy recovery strategy for rear-drive pure electric commercial vehicle |
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| DE102015211560A1 (en) * | 2015-06-23 | 2016-12-29 | Volkswagen Aktiengesellschaft | Motor vehicle with recuperation and friction-dependent brake control |
| CN110254239A (en) * | 2019-06-28 | 2019-09-20 | 福州大学 | A kind of Torque distribution method during electric car regenerative braking transient response |
| CN113147412A (en) * | 2021-04-25 | 2021-07-23 | 南京依维柯汽车有限公司 | Brake energy recovery strategy for rear-drive pure electric commercial vehicle |
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