CN112172788A - Distributed three-motor driving force distribution strategy for improving vehicle steering stability - Google Patents

Distributed three-motor driving force distribution strategy for improving vehicle steering stability Download PDF

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CN112172788A
CN112172788A CN202011065439.4A CN202011065439A CN112172788A CN 112172788 A CN112172788 A CN 112172788A CN 202011065439 A CN202011065439 A CN 202011065439A CN 112172788 A CN112172788 A CN 112172788A
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torque
motor
axle
distributed
driving
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王念
史建鹏
赵春来
秦博
张泽阳
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Dongfeng Motor Corp
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Dongfeng Motor Corp
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
    • B60W30/02—Control of vehicle driving stability
    • 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
    • B60L15/00—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles
    • B60L15/32—Control or regulation of multiple-unit electrically-propelled vehicles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W50/00—Details of control systems for road vehicle drive control not related to the control of a particular sub-unit, e.g. process diagnostic or vehicle driver interfaces
    • 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
    • B60L2240/40—Drive Train control parameters
    • B60L2240/42—Drive Train control parameters related to electric machines
    • B60L2240/423—Torque
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W50/00—Details of control systems for road vehicle drive control not related to the control of a particular sub-unit, e.g. process diagnostic or vehicle driver interfaces
    • B60W2050/0001—Details of the control system
    • B60W2050/0019—Control system elements or transfer functions
    • 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
    • Y02T10/64—Electric machine technologies in electromobility

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  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Automation & Control Theory (AREA)
  • Human Computer Interaction (AREA)
  • Power Engineering (AREA)
  • Electric Propulsion And Braking For Vehicles (AREA)
  • Arrangement And Driving Of Transmission Devices (AREA)

Abstract

The invention discloses a distributed three-motor driving force distribution strategy for improving the vehicle operation stability, which comprises the following steps: obtaining a total target torque expected by a driver according to the input of an accelerator pedal of the driver; distributing front and rear axle driving torques to the total target torque by adopting a distribution mode in direct proportion to axle load; taking the steering wheel angle and the total driving moment of a rear shaft as input, taking the difference between the ideal yaw rate and the actual yaw rate of the automobile as a control quantity, and obtaining the actual control quantity deviation through a controller; the yaw moment is controlled through decision of the controller, and the distribution of the driving force of the hub motors on the left side and the right side of the rear axle is realized through the differential torque distribution module; and after passing through the torque limiting module, the torque is finally distributed to the two hub motors of the rear shaft. The invention causes the turning radius to be slightly influenced by longitudinal acceleration and has better maneuverability; even under the limit working condition, certain lateral stability can be considered, and the steady-state steering characteristic of the automobile is ensured.

Description

Distributed three-motor driving force distribution strategy for improving vehicle steering stability
Technical Field
The invention relates to the technical field of electric automobile driving, in particular to a distributed three-motor driving force distribution strategy for improving vehicle operation stability.
Background
The hub motor drive is to install driving motor directly in the drive wheel, is a novel drive arrangement form of automobile solution power and power efficiency, and it has outstanding advantages such as drive transmission chain is short, the transmission is high-efficient, compact structure, response are fast, is an important direction of future electric motor car development. The hub motor drives the driving actuator of the vehicle, namely the hub motor is arranged in the independent wheel, and the control freedom degree and the accuracy are greatly improved. In the four-wheel drive vehicle based on the hub motor, because the high-low voltage wire harnesses and the cooling pipelines of the motor are arranged at the wheel ends, when the wire harnesses and the pipelines are arranged at front wheels, steering and jumping are considered, and new challenges are provided for the originally tense wheel end arrangement space.
The steering performance of the automobile is a main aspect reflecting the steering stability of the automobile. The steering performance determines the execution capacity of a vehicle for the driver path following intention, and is the most manipulation characteristic which can bring the driver to intuitively feel the driving feeling. The reason for changing the yaw movement of the vehicle is, among other things, the yaw moment exerted at the center of mass of the vehicle.
The distributed three-motor drive is that the front shaft is driven by a central motor, the rear shaft is driven by a two-hub motor, the arrangement mode can effectively avoid the arrangement problem of the front wheels of the hub motors, the size of the assembly is reduced, two-drive and four-drive modes can be switched according to road conditions, the energy consumption of the whole automobile is reduced, the endurance mileage of the electric automobile is increased, but the yaw rate response steady-state process and the yaw rate transient response process of the automobile can be seriously influenced due to the unmatched problem of power distribution of the front and rear shafts and left and right distribution of the rear wheels under the four-drive mode of the automobile, and the operation stability of the automobile is poor. How to provide a driving force distribution strategy in a distributed three-motor four-wheel drive mode to improve the vehicle operation stability has become a technical problem which needs to be solved urgently by those skilled in the art.
CN201810184598.2
Distributed three-motor driving power system
The wheel-hub motor comprises a front wheel centralized drive and a rear wheel distributed drive, but the adopted wheel-hub motor is different from the wheel-hub motor in nature, and no specific driving force distribution strategy is adopted
Disclosure of Invention
The technical problem to be solved by the invention is to provide a distributed three-motor driving force distribution strategy for improving the vehicle operation stability aiming at the defects in the prior art, carry out differential torque distribution of left and right hub motors of a rear wheel, realize yaw moment control, have small influence on turning radius by longitudinal acceleration and have better operability; even under the limit working condition, certain lateral stability can be considered, and the steady-state steering characteristic of the automobile is ensured.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a distributed three-motor driving force distribution strategy for improving vehicle operation stability is disclosed, wherein a distributed three-motor driving system comprises a power battery system, a vehicle control unit, a front axle driving system and a rear axle driving system, and the vehicle control unit and the power battery system are connected with the front axle driving system and the rear axle driving system;
the front axle driving system comprises an alternating current motor, a speed reducer and front wheel half axles, the power battery system and the vehicle control unit are connected with the alternating current motor, and the alternating current motor is respectively connected with the two front wheel half axles through the speed reducer;
the rear axle driving system comprises hub motors which are arranged in the two rims and integrated with motor controllers, the power battery system is connected with the hub motors, and the whole vehicle controller is connected with the two hub motors through low-voltage lines;
the distributed three-motor driving force distribution strategy for improving the vehicle steering stability comprises the following steps:
1) obtaining a total target torque expected by a driver according to the input of an accelerator pedal of the driver;
2) the total target torque T is divided by a distribution mode proportional to the axle loadtotDistributing front and rear shaft driving torque;
3) taking the steering wheel angle and the total driving moment of a rear shaft as input, taking the difference between the ideal yaw rate and the actual yaw rate of the automobile as a control quantity, and obtaining the actual control quantity deviation through a sensitivity controller;
4) controlling the yaw moment through a PID controller decision, and realizing the distribution of the driving force of the hub motors at the left side and the right side of the rear axle through a differential torque distribution module;
5) and after passing through the torque limiting module, the torque is finally distributed to the two hub motors of the rear shaft.
According to the technical scheme, in the step 2), the specific process of the front and rear shaft driving force distribution comprises the following steps:
1) calculating the axle load of a front axle and the axle load of a rear axle during acceleration;
the axle load of the front axle during acceleration is as follows: fzj1＝Fz1-△Fz
Wherein, Fzj1For front axle load during acceleration, Fz1For front axle static axle load,. DELTA.FzIs the amount of axial load transfer;
the rear axle load during acceleration is: fzj2＝Fz2+△Fz
Wherein, Fzj2For rear axle load during acceleration, Fz2For the rear axle static axle load,. DELTA.FzIs the amount of axial load transfer;
2) the axle load of the front axle and the axle load of the rear axle during acceleration are respectively converted into:
Figure BDA0002713626720000031
Figure BDA0002713626720000032
wherein M is the total mass of the automobile, a is the distance from the center of mass to the front axle, b is the distance from the center of mass to the rear axle, L is the axle distance, h is the height of the center of mass, axIs the vehicle acceleration, g is the gravitational acceleration;
3) the front and rear shaft driving torque distribution ratio is as follows:
Figure BDA0002713626720000033
4) and calculating driving torques Tf and Tr distributed by the front shaft and the rear shaft respectively through the total target torque by the driving torque distribution ratio of the front shaft and the rear shaft.
According to the above technical solution, in the step 3), the ideal yaw rate is:
Figure BDA0002713626720000034
in the formula, ωdIn order to "design" the ideal yaw rate,
Figure BDA0002713626720000035
the final ideal yaw velocity after the road surface attachment is considered;
according to the technical scheme, in the step 4), the yaw moment distribution needs to meet the following constraints:
1) the longitudinal torque requirement is unchanged;
2) motor torque output capability.
According to the technical scheme, in the step 4), the differential torque moment of the hub motors on the left side and the right side of the rear axle wheel is distributed according to the following formula:
Figure BDA0002713626720000036
TRR＝TRR_ref+ΔFr·RRR
TRL＝TRL_ref-ΔFr·RRL
wherein, TRR_refTorque demand for the right rear motor, TRL_refFor left rear motor demand torque, TRRIs a right rear motorInter torque, TRLActual torque of the left rear motor, d2For rear track, Δ FrThe driving force is added to the rear axle wheels, and if the total required torque is required to be constant, the increase and decrease of the total torque on the left side and the right side of the rear axle wheels of the automobile are the same when differential torque distribution is carried out, so that the requirement of the total torque is guaranteed to be constant;
the torque is dynamically adjusted after the torque output capacity of the motor is considered, and the delta MzFor rear axle differential torque yaw moment distribution, Δ MrmaxFor the corresponding maximum achievable yaw moment value of the differential torque, when Δ Mz≥ΔMrmaxWhen, Δ Mr＝ΔMrma；ΔMz＜ΔMrmaxWhen, Δ Mr＝ΔMz。
According to the technical scheme, the decision of taking the difference torque yaw moment as the maximum difference torque moment value in the positive time is calculated as follows:
Figure BDA0002713626720000041
wherein, TRR_maxThe external characteristic moment of the right rear motor;
the maximum differential torque value when the differential torque yaw moment is negative is calculated as follows:
Figure BDA0002713626720000042
wherein, TRL_maxThe external characteristic torque of the left rear motor.
According to the technical scheme, the front axle driving system further comprises a central motor controller/inverter, and the central motor controller/inverter is respectively connected with the alternating current motor, the power battery system and the whole vehicle controller; the high voltage of the power battery transmits power to the alternating current motor through the motor controller/inverter to enable the alternating current motor to work, and the alternating current motor transmits torque to the half shaft through the speed reducer so as to drive wheels.
According to the technical scheme, in the step 3), the ideal yaw angular velocity is output by the corresponding two-degree-of-freedom model.
The invention has the following beneficial effects:
1. the vehicle control unit identifies the intention of a driver, decides the current total driving torque demand according to the current vehicle state, firstly distributes the driving force of front and rear shafts according to a torque distribution method in proportion to the shaft load, and then distributes the differential torque of left and right hub motors of rear wheels under the condition of keeping the total output torque of the rear shafts unchanged, thereby realizing the control of the yaw moment; the invention adopts a distribution mode which is in direct proportion to the axle load as a front and rear axle moment distribution mode of the driving force, so that the longitudinal acceleration change is small, the turning radius is slightly influenced by the longitudinal acceleration, and the maneuverability is good; even under the limit working condition, certain lateral stability can be considered, and the steady-state steering characteristic of the automobile is ensured; the steering yaw movement is controlled through different wheel moment distribution modes, tire abrasion is avoided, meanwhile, as the interference to the longitudinal driving requirement of a driver is basically avoided, control can be exerted under the normal running working condition, the possibility that an automobile enters a limit area is reduced, and the operation stability of the automobile is improved.
2. The direct yaw moment control of an ideal yaw rate control target is determined by adjusting the response characteristic parameters of a second-order system through the differential torque distribution mode of the two-degree-of-freedom model to the left and right hub motors of the rear wheels, and the transient response of the yaw rate of the automobile is improved.
Drawings
FIG. 1 is a schematic structural diagram of a distributed three-motor drive system according to an embodiment of the present invention;
FIG. 2 is a schematic illustration of a distributed three motor drive force distribution strategy for improved vehicle handling stability in an embodiment of the present invention;
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and examples.
Referring to fig. 1 to 2, in an embodiment of the present invention, a distributed three-motor driving force distribution strategy for improving vehicle operation stability is provided, where the distributed three-motor driving system includes a power battery system, a vehicle control unit, a front axle driving system and a rear axle driving system, the vehicle control unit and the power battery system are respectively connected to the front axle driving system and the rear axle driving system through CAN buses, and a power battery provides power to drive motors for the front and rear motors;
the front axle driving system is driven by a centralized motor and comprises an alternating current motor, a speed reducer and front wheel half axles, a power battery system and a vehicle control unit are connected with the alternating current motor, and the alternating current motor is respectively connected with the two front wheel half axles through the speed reducer;
the rear axle driving system is driven by a hub motor and comprises the hub motor which is arranged in two rims and integrated with a motor controller, a power battery system is connected with the hub motor and provides power for driving the hub motor, and the whole vehicle controller is connected with the two hub motors through low-voltage wires; the tail end of the low-voltage wire is provided with a connector; the whole vehicle controller sends a torque instruction to the two hub motor controllers through the CAN to drive the hub motors to move;
the power battery system comprises a power battery and a management system thereof;
the distributed three-motor driving force distribution strategy for improving the vehicle steering stability comprises the following steps:
1) obtaining a total target torque expected by a driver according to the input of an accelerator pedal of the driver;
2) the total target torque T is divided by a distribution mode proportional to the axle loadtotDistributing front and rear shaft driving torque;
3) taking the steering wheel angle and the total driving moment of a rear shaft as input, taking the difference between the ideal yaw rate output by the two-degree-of-freedom model and the actual yaw rate of the automobile as a control quantity, and obtaining the actual control quantity deviation through a sensitivity controller;
4) controlling the yaw moment through a PID controller decision, and realizing the distribution of the driving force of the hub motors at the left side and the right side of the rear axle through a differential torque distribution module;
5) and after passing through the torque limiting module, the torque is finally distributed to the two hub motors of the rear shaft.
Further, in the step 2), the specific process of the front-rear axle driving force distribution comprises the following steps:
1) calculating the axle load of a front axle and the axle load of a rear axle during acceleration;
the axle load of the front axle during acceleration is as follows: fzj1＝Fz1-△Fz
Wherein, Fzj1For front axle load during acceleration, Fz1For front axle static axle load,. DELTA.FzIs the amount of axial load transfer;
the rear axle load during acceleration is: fzj2＝Fz2+△Fz
Wherein, Fzj2For rear axle load during acceleration, Fz2For the rear axle static axle load,. DELTA.FzIs the amount of axial load transfer;
2) the axle load of the front axle and the axle load of the rear axle during acceleration are respectively converted into:
Figure BDA0002713626720000061
Figure BDA0002713626720000062
wherein M is the total mass of the automobile, a is the distance from the center of mass to the front axle, b is the distance from the center of mass to the rear axle, L is the axle distance, h is the height of the center of mass, axIs the vehicle acceleration, g is the gravitational acceleration;
3) the front and rear shaft driving torque distribution ratio is as follows:
Figure BDA0002713626720000063
4) and calculating driving torques Tf and Tr distributed by the front shaft and the rear shaft respectively through the total target torque by the driving torque distribution ratio of the front shaft and the rear shaft.
Further, in the step 3), the two-degree-of-freedom model decides the ideal yaw rate to include a steady-state part and a transient part, the steady-state part keeps the original vehicle gain unchanged, and the transient part adjusts omega in a second-order characteristic linknThe ideal yaw rate dynamic response characteristic is 'designed' with the zeta value; the final determined yaw moment ensures the actual yaw velocity transientThe state response characteristic follows this design value;
yaw rate response procedure:
Figure BDA0002713626720000064
in the formula, ωr(s) vehicle yaw rate, GrSteady state gain for yaw rate versus front wheel angle input, stability factor, omeganZeta is damping ratio, τ, for the system natural circular frequencyrAnd s is a Laplace change constant which is a response time constant and is a front wheel rotating angle of the vehicle.
Further, in the step 3), the ideal yaw rate is:
Figure BDA0002713626720000071
in the formula, ωdIn order to "design" the ideal yaw rate,
Figure BDA0002713626720000072
the final ideal yaw velocity after the road surface attachment is considered;
further, in said step 4), the yaw moment distribution needs to satisfy the following constraints:
1) the longitudinal torque requirement is unchanged;
2) motor torque output capability.
Further, in the step 4), the differential torque moment of the hub motors at the left and right sides of the rear axle wheel is distributed according to the following formula:
Figure BDA0002713626720000073
TRR＝TRR_ref+ΔFr·RRR
TRL＝TRL_ref-ΔFr·RRL
wherein, TRR_refTorque demand for the right rear motor, TRL_refFor left rear motor demand torque, TRRIs the actual torque of the right rear motor, TRLActual torque of the left rear motor, d2For rear track, Δ FrThe driving force is added to the rear axle wheels, and if the total required torque is required to be constant, the increase and decrease of the total torque on the left side and the right side of the rear axle wheels of the automobile are the same when differential torque distribution is carried out, so that the requirement of the total torque is guaranteed to be constant;
the torque is dynamically adjusted after the torque output capacity of the motor is considered, and the delta MzFor rear axle differential torque yaw moment distribution, Δ MrmaxFor the corresponding maximum achievable yaw moment value of the differential torque, when Δ Mz≥ΔMrmaxWhen, Δ Mr＝ΔMrma；ΔMz＜ΔMrmaxWhen, Δ Mr＝ΔMz(ii) a Therefore, the limitation of the torque output capacity of the motor at the current rotating speed is considered, and the yaw moment value applied to the mass center is guaranteed to meet the decision value to the maximum extent.
Further, the decision of the maximum difference torque moment value when the difference torque yaw moment is positive is calculated as follows:
Figure BDA0002713626720000081
wherein, TRR_maxThe external characteristic moment of the right rear motor;
the maximum differential torque value when the differential torque yaw moment is negative is calculated as follows:
Figure BDA0002713626720000082
wherein, TRL_maxThe external characteristic torque of the left rear motor.
Furthermore, the front axle driving system also comprises a central motor controller/inverter, and the central motor controller/inverter is respectively connected with the alternating current motor, the power battery system and the whole vehicle controller; the high voltage of the power battery transmits power to the alternating current motor through the motor controller/inverter to enable the alternating current motor to work, and the alternating current motor transmits torque to the half shaft through the speed reducer so as to drive wheels.
The working principle of the invention is as follows: the invention provides a distributed three-motor driving system, as shown in the attached figure 1: the system comprises a power battery and a management system thereof, a vehicle control unit, a front axle driving system and a rear axle driving system. The power battery provides power for the front motor and the rear motor to drive the motors, and the vehicle control unit and the battery management system are respectively connected with the front axle driving system and the rear axle driving system through the CAN bus.
In this example, the front axle drive system is a centralized motor drive, including a central motor controller/inverter, an AC motor, a speed reducer, half-axles, and wheels disposed at the ends of the half-axles. The central motor controller/inverter is connected with the alternating current motor and the power battery respectively, and the speed reducer is arranged between the power battery and the half shaft. The high voltage of the power battery transmits power to the alternating current motor through the motor controller/inverter, so that the alternating current motor works. The ac motor transmits torque to the half-shafts through a speed reducer, thereby driving the wheels.
In the example, the rear axle driving system is driven by a hub motor and comprises the hub motor which is arranged in two wheel rims and integrated with a motor controller, and a power battery is connected with the hub motor and provides power for the driving of the hub motor; the whole vehicle controller is connected with the two hub motors through a low-voltage wire, and a connector is arranged at the tail end of the low-voltage wire; the vehicle control unit sends a torque instruction to the two hub motor controllers through the CAN to drive the hub motors to move.
A distributed three-motor driving force distribution strategy for improving the vehicle steering stability comprises the following specific embodiments:
as shown in fig. 2, in the four-wheel drive mode, during driving, the vehicle controller performs table lookup (accelerator percentage-drive torque table) according to the obtained input of the accelerator pedal of the driver to obtain the total target torque T expected by the drivertot. After obtaining the total target torque T expected by the drivertotThen, the total target torque T is firstly distributed in a manner proportional to the axle loadtotThe driving force distribution of the front and rear shafts is carried out, then the steering wheel angle and the total driving torque of the rear shaft are used as input, and a two-degree-of-freedom model is adopted for outputThe difference between the ideal yaw velocity and the actual yaw velocity of the automobile is used as a control quantity, the actual control deviation is obtained through a sensitivity controller, the yaw moment is controlled through a PID controller decision, and the yaw moment is controlled to realize the distribution of the driving force of the hub motors on the left side and the right side of the rear axle through a differential torque distribution module. And after passing through the torque limiting module, the torque is finally distributed to the two hub motors of the rear shaft.
(1) Front and rear axle drive force distribution
In the total driving force distribution of the automobile, the driving force distribution of the front and rear axles mainly influences the steady-state steering characteristic. The main characteristics of the tire are realized by changing the cornering characteristics of the front and rear tires, and the characteristics are mainly reflected in the aspects of load transfer, friction ellipse cornering angle change, low-adhesion front and rear axle sliding and the like. The distribution mode of the load moment is in direct proportion to the change of the longitudinal acceleration, the turning radius is slightly influenced by the longitudinal acceleration, and the maneuverability is better; even under the limit working condition, certain lateral stability can be considered, so that a distribution mode in proportion to the axle load is selected as an ideal distribution mode of the front and rear axle moments of the driving force. The method comprises the following specific steps:
the mass center position of the automobile is not at the geometric center under the influence of uneven mass distribution, and load transfer can also occur during acceleration and deceleration running. The two reasons cause the load of the front axle and the rear axle to change, and further cause the size of the attachment ellipse of the front wheel and the rear wheel to change, namely the attachment capability of the front axle and the rear axle on the road surface with the same attachment coefficient is influenced by the acceleration of the automobile. The influence of axle load transfer on the adhesion capability is considered during the distribution of the driving force of the front and rear axles, and the influence is converted into a linear relation by combining the driving force and the relationship between the adhesion coefficient and the vertical load of the road surface, so that a distribution torque method in direct proportion to the axle load is obtained.
The axle load of the automobile during acceleration driving can be expressed as follows:
Fzj＝Fz±△Fz
wherein, FzjFor axial load during acceleration, FzStatic axle load,. DELTA.FzIs the amount of axial load transfer.
The front and rear axle loads at acceleration can be expressed as:
Fzj1＝Fz1-△Fz
Fzj2＝Fz2+△Fz
the front and rear axle loads when the formula is brought into available acceleration are respectively:
Figure BDA0002713626720000091
Figure BDA0002713626720000092
wherein M is the total mass of the automobile, a is the distance from the center of mass to the front axle, b is the distance from the center of mass to the rear axle, L is the axle distance, h is the height of the center of mass, axIs the vehicle acceleration.
Therefore, the torque distribution ratio of the front shaft to the rear shaft is as follows:
Figure BDA0002713626720000101
further, driving torques Tf and Tr distributed to the front and rear shafts, respectively, can be calculated.
(2) Rear axle left and right side drive force distribution
The yaw rate response process can be fully expressed as:
Figure BDA0002713626720000102
based on the assumption of a two-degree-of-freedom linear model, direct yaw moment control for determining an ideal yaw rate control target by adjusting a second-order system response characteristic parameter is provided, and the transient response of the yaw rate of the automobile is improved.
The direct yaw moment control process adopts the difference between the ideal yaw velocity output by the two-degree-of-freedom model and the actual yaw velocity of the automobile as a control quantity, obtains an actual control deviation through a sensitivity controller, controls the yaw moment through a PID controller decision, controls the yaw moment through a left motor and a right motor differential torque mode, and finally distributes the yaw moment to a left wheel and a right wheel of a rear axle through a distribution link.
The two-degree-of-freedom model decision-making ideal yaw rate comprises a steady-state part and a transient-state part, wherein the steady-state part keeps the original vehicle gain unchanged, and the transient-state part adjusts omega in a second-order characteristic linknThe desired yaw rate dynamic response characteristic is "designed" with the zeta value. The finally decided yaw moment ensures that the transient response characteristic of the actual yaw velocity follows the design value.
The adjustment of the dynamic performance parameters of the second-order system of the yaw angular velocity and the realized constraint conditions are comprehensively considered, and the ideal yaw angular velocity is obtained as follows:
Figure BDA0002713626720000103
in the formula, ωdIn order to "design" the ideal yaw rate,
Figure BDA0002713626720000104
in order to consider the final ideal yaw rate after the road surface is attached.
The differential torque control torque obtained through PID decision needs to be distributed to two rear wheels. The yaw moment distribution needs to satisfy the following constraints:
(1) constant longitudinal torque demand
The whole control process faces the driving process under the conventional working condition, the control aim is to improve the automobile maneuverability during steering, and the control is not the stability control under the limit working condition, so the total torque requirement is required to be unchanged in the whole control process, and the speed control process of a driver is not interfered.
(2) Torque output capability of motor
The motor can only send out fixed maximum torque under a certain rotating speed limited by external characteristics. Therefore, during differential torque distribution, the differential torque distribution needs to be dynamically adjusted according to the working point of the motor.
Considering the constraint condition (1), the differential torque moment is distributed according to the following formula:
Figure BDA0002713626720000111
TRR＝TRR_ref+ΔFr·RRR
TRL＝TRL_ref-ΔFr·RRL
in the formula TRR_ref、TRL_refRight rear and left rear motors demand torque. T isRR、TRLThe actual torque of the right rear motor and the actual torque of the left rear motor. d2Is the rear track width. Δ FrIncreased driving force for the rear axle wheels. If the total torque requirement is not changed, the increase and decrease of the total torque on the left side and the right side of the rear wheel of the automobile are the same when differential torque distribution is carried out, so that the requirement of the total torque is not changed.
The torque is dynamically adjusted after the torque output capacity of the motor is considered, and the delta Mz、ΔMrmaxRespectively allocating the value of the rear axle differential torsion yaw moment and the corresponding value of the maximum differential torsion yaw moment which can be realized. When Δ Mz≥ΔMrmaxWhen, Δ Mr＝ΔMrmax；ΔMz＜ΔMrmaxWhen, Δ Mr＝ΔMz. Therefore, the limitation of the torque output capacity of the motor at the current rotating speed is considered, and the yaw moment value applied to the mass center is guaranteed to meet the decision value to the maximum extent.
The maximum torque difference value when the torque difference yaw moment is determined as the positive is calculated as follows:
Figure BDA0002713626720000112
wherein, TRR_maxIs the external characteristic moment of the right rear motor. And when the differential torque yaw moment is negative, calculating according to the moment characteristic of the motor on the left side.
The above is only a preferred embodiment of the present invention, and certainly, the scope of the present invention should not be limited thereby, and therefore, the present invention is not limited by the scope of the claims.

Claims (8)

1. A distributed three motor drive force distribution strategy for improving vehicle handling stability,
the distributed three-motor driving system comprises a power battery system, a vehicle control unit, a front axle driving system and a rear axle driving system, wherein the vehicle control unit and the power battery system are connected with the front axle driving system and the rear axle driving system;
the front axle driving system comprises an alternating current motor, a speed reducer and front wheel half axles, the power battery system and the vehicle control unit are connected with the alternating current motor, and the alternating current motor is respectively connected with the two front wheel half axles through the speed reducer;
the rear axle driving system comprises hub motors which are arranged in the two rims and integrated with motor controllers, the power battery system is connected with the hub motors, and the whole vehicle controller is connected with the two hub motors through low-voltage lines;
the distributed three-motor driving force distribution strategy for improving the vehicle steering stability comprises the following steps:
1) obtaining a total target torque expected by a driver according to the input of an accelerator pedal of the driver;
2) the total target torque T is divided by a distribution mode proportional to the axle loadtotDistributing front and rear shaft driving torque;
3) taking the steering wheel angle and the total driving moment of a rear shaft as input, taking the difference between the ideal yaw rate and the actual yaw rate of the automobile as a control quantity, and obtaining the actual control quantity deviation through a controller;
4) the yaw moment is controlled through decision of the controller, and the distribution of the driving force of the hub motors on the left side and the right side of the rear axle is realized through the differential torque distribution module;
5) and after passing through the torque limiting module, the torque is finally distributed to the two hub motors of the rear shaft.
2. The distributed three motor drive power distribution strategy for improving vehicle handling stability according to claim 1, wherein at said step 2), the detailed process of front and rear axle drive power distribution comprises the steps of:
1) calculating the axle load of a front axle and the axle load of a rear axle during acceleration;
the axle load of the front axle during acceleration is as follows: fzj1＝Fz1-△Fz
Wherein, Fzj1For front axle load during acceleration, Fz1For front axle static axle load,. DELTA.FzIs the amount of axial load transfer;
the rear axle load during acceleration is: fzj2＝Fz2+△Fz
Wherein, Fzj2For rear axle load during acceleration, Fz2For the rear axle static axle load,. DELTA.FzIs the amount of axial load transfer;
2) the axle load of the front axle and the axle load of the rear axle during acceleration are respectively converted into:
Figure FDA0002713626710000011
Figure FDA0002713626710000012
wherein M is the total mass of the automobile, a is the distance from the center of mass to the front axle, b is the distance from the center of mass to the rear axle, L is the axle distance, h is the height of the center of mass, axIs the vehicle acceleration, g is the gravitational acceleration;
3) the front and rear shaft driving torque distribution ratio is as follows:
Figure FDA0002713626710000021
4) and calculating driving torques Tf and Tr distributed by the front shaft and the rear shaft respectively through the total target torque by the driving torque distribution ratio of the front shaft and the rear shaft.
3. The distributed three motor drive power distribution strategy for improving vehicle handling stability according to claim 1, wherein in said step 3), the desired yaw rate is:
Figure FDA0002713626710000022
in the formula, ωdIn order to "design" the ideal yaw rate,
Figure FDA0002713626710000023
in order to consider the final ideal yaw angular velocity after the road surface is attached, u is the road surface attachment coefficient, omegarFor the actual yaw rate of the vehicle, VxIs the vehicle longitudinal speed.
4. The distributed three-motor drive force distribution strategy for improving vehicle handling stability according to claim 1, wherein in said step 4), the yaw moment distribution is required to satisfy the following constraints:
1) the longitudinal torque requirement is unchanged;
2) motor torque output capability.
5. The distributed three-motor driving force distribution strategy for improving the vehicle steering stability according to claim 1, wherein in the step 4), the differential torque moment of the hub motors at the left and right sides of the rear axle wheel is distributed according to the following formula:
Figure FDA0002713626710000024
TRR＝TRR_ref+ΔFr·RRR
TRL＝TRL_ref-ΔFr·RRL
wherein, TRR_refTorque demand for the right rear motor, TRL_refFor left rear motor demand torque, TRRIs the actual torque of the right rear motor, TRLActual torque of the left rear motor, d2For rear track, Δ FrIncreased driving force for rear axle wheels, RRL、RRRThe radius of the left wheel and the right wheel of the rear wheel are respectively, if the total required torque is not changed, the differential torque force is carried outWhen the torque is distributed, the increase and decrease of the total torque at the left side and the right side of the rear wheel of the automobile are the same, so that the requirement of the total torque is unchanged;
the torque is dynamically adjusted after the torque output capacity of the motor is considered, and the delta MzFor rear axle differential torque yaw moment distribution, Δ MrmaxFor the corresponding maximum achievable yaw moment value of the differential torque, when Δ Mz≥ΔMrmaxWhen, Δ Mr＝ΔMrma；ΔMz＜ΔMrmaxWhen, Δ Mr＝ΔMz。
6. The distributed three motor drive power distribution strategy for improving vehicle handling stability according to claim 5, wherein deciding the difference yaw moment as a positive maximum difference moment value is calculated as follows:
Figure FDA0002713626710000031
wherein, TRR_maxThe external characteristic moment of the right rear motor;
the maximum differential torque value when the differential torque yaw moment is negative is calculated as follows:
Figure FDA0002713626710000032
wherein, TRL_maxThe external characteristic torque of the left rear motor.
7. The distributed three-motor drive power distribution strategy for improving vehicle handling stability according to claim 1, wherein the front axle drive system further comprises a central motor controller/inverter, the central motor controller/inverter being connected to the ac motor and the power battery system and the vehicle control unit, respectively; the high voltage of the power battery transmits power to the alternating current motor through the motor controller/inverter to enable the alternating current motor to work, and the alternating current motor transmits torque to the half shaft through the speed reducer so as to drive wheels.
8. The distributed three motor drive power distribution strategy for improving vehicle handling stability according to claim 1, wherein in step 3), the ideal yaw rate is output by a corresponding two-degree-of-freedom model.
CN202011065439.4A 2020-09-30 2020-09-30 Distributed three-motor driving force distribution strategy for improving vehicle steering stability Pending CN112172788A (en)

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