CN110014851B - Method for distributing torque between front and rear double-motor four-wheel drive vehicle axles - Google Patents

Method for distributing torque between front and rear double-motor four-wheel drive vehicle axles Download PDF

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CN110014851B
CN110014851B CN201910282643.2A CN201910282643A CN110014851B CN 110014851 B CN110014851 B CN 110014851B CN 201910282643 A CN201910282643 A CN 201910282643A CN 110014851 B CN110014851 B CN 110014851B
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torque
motor
vehicle
driving
mode
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CN110014851A (en
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李超
吴爱彬
赵永强
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FAW Group Corp
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FAW Group Corp
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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
    • B60L15/00—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles
    • B60L15/20—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles for control of the vehicle or its driving motor to achieve a desired performance, e.g. speed, torque, programmed variation of speed
    • 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
    • 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
    • B60L2240/10—Vehicle control parameters
    • B60L2240/14—Acceleration
    • B60L2240/16—Acceleration longitudinal
    • 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
    • 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
    • B60L2240/60—Navigation input
    • B60L2240/64—Road conditions
    • B60L2240/642—Slope of road
    • 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
    • B60L2260/00—Operating Modes
    • B60L2260/20—Drive modes; Transition between modes
    • B60L2260/28—Four wheel or all wheel drive
    • 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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  • Transportation (AREA)
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Abstract

The invention discloses a method for distributing torque between front and rear double-motor four-wheel drive vehicle axles, which is used for acquiring current parameters of a vehicle, automatically selecting a distribution mode of driving torque of front and rear axle motors of the vehicle according to a driving mode of a driver and an actual driving working condition of the vehicle, and distributing an inter-axle torque distribution coefficient i according to the efficiency or longitudinal driving performance of the front and rear axle motors. When the required torque is detected to be larger than zero, automatically selecting an inter-axle torque distribution mode according to the difference between the driving mode and the vehicle mode, wherein the inter-axle torque distribution mode comprises the step of distributing the inter-axle driving torque according to a motor driving performance mode or the step of distributing the inter-axle driving torque according to a motor efficiency mode; when a deceleration request of a driver is detected, the driving torque between the front axle and the rear axle is distributed according to the motor driving performance mode. The inter-axle torque can be automatically distributed according to the driving mode of the vehicle and the running condition of the vehicle, and the inter-axle torque can be distributed according to the economy and the driving performance, so that the economy and the driving performance requirements of a driver can be met through the inter-axle torque distribution.

Description

Method for distributing torque between front and rear double-motor four-wheel drive vehicle axles
Technical Field
The invention relates to the technical field of electric control of electric automobiles, in particular to a method for distributing torque between front and rear double-motor four-wheel drive vehicle axles.
Background
Under the large background that global energy and environmental problems are increasingly severe, the development of electric vehicles is faster and faster. Compared with the traditional automobile, the electric automobile, particularly the front-rear axle four-wheel drive automobile, has a plurality of power sources, so that the torque control is more complicated. In the existing electric four-wheel drive electric vehicle in mass production, the torque distribution of the front motor and the rear motor is basically fixed proportion or several adjustable fixed proportions during normal running. Patent (CN105584382A) and patent (CN107097686A) disclose a motor torque distribution control method that distributes inter-shaft torque mainly based on motor efficiency, and this type of patent only focuses on economy and does not consider acceleration performance of the vehicle. Patent (CN106379197A) and patent (CN107640062A) disclose a method for distributing driving torque based on acceleration, but this kind of patent only focuses on acceleration factor in the aspect of axle load transfer, does not fully consider axle load transfer caused by gradient and vehicle longitudinal acceleration, and cannot fully exert the adhesion capability of front and rear wheels, so that the vehicle obtains the maximum lateral force potential. In the actual driving process, the driving torque of the front and rear axle motors is distributed by adopting a single index or a fixed proportion, so that the driving requirement of the economical efficiency or the dynamic efficiency of a driver cannot be met, and therefore, a control method of the driving torque of the front and rear axle motors is urgently needed.
Disclosure of Invention
The invention provides a control method capable of automatically distributing torque between axles, aiming at the problem that the torque distribution of the existing electric four-wheel drive vehicle only aims at single indexes (economy and acceleration performance).
The invention adopts the following technical scheme:
a method for distributing torque between front and rear double-motor four-wheel drive vehicle axles comprises the following steps:
the method comprises the steps of firstly, obtaining current parameters of a vehicle, including longitudinal acceleration of the vehicle, road gradient, required torque and driving mode of the vehicle;
step two, automatically selecting a distribution mode of the driving torque of the front and rear axle motors of the vehicle according to the driving mode of a driver and the actual running condition of the vehicle, and distributing an inter-axle torque distribution coefficient i according to the efficiency or longitudinal driving performance of the front and rear axle motors:
the driver's required torque is detected first,
1) when the required torque is detected to be larger than zero, automatically selecting an inter-axle torque distribution mode according to different driving modes and vehicle modes:
1.1) when the driver has a driving demand, firstly judging the influence of the gradient, and when the gradient is larger than a certain threshold value thetapAutomatically selecting a mode of distributing the driving torque between the shafts according to the driving performance of the motor;
1.2) otherwise, judging the influence of the driving mode of the vehicle:
when the driver selects the Sport mode, the driver selects to distribute the driving torque between the shafts according to the motor driving performance mode;
when the driver selects the Eco mode, the inter-axle driving torque is automatically distributed according to the motor efficiency mode;
when the driver selects the Normal mode, the relationship between the actual acceleration of the vehicle and the maximum acceleration is combined to determine the torque distribution mode if the actual acceleration a of the vehicle isactWith maximum acceleration amaxWhen the proportion exceeds a certain threshold k, the inter-shaft driving torque is distributed according to a motor driving performance mode; otherwise, the driving torque between the shafts is distributed according to the motor efficiency mode;
2) when a deceleration request of a driver is detected, the driving torque between the front axle and the rear axle is distributed according to the motor driving performance mode.
Further, the inter-axle torque distribution coefficient i refers to the proportion of the output torque of the rear axle motor to the total output torque of the front and rear motors, and is combined with the torque T required by the driverreqAnd obtaining the driving torque of the front and rear axle motors by the inter-axle torque distribution coefficient i:
Figure GDA0002985878890000021
in the formula, TrRepresenting the output torque, T, of the rear axle motorfIndicating the output torque of the front and rear motors.
Further, the vehicle maximum acceleration amaxThe calculating method of (2):
the longitudinal acceleration a of the vehicle is acquired at any timexWith lateral acceleration ayAnd calculating the actual total acceleration a of the vehicleact:
Figure GDA0002985878890000022
When an ESP intervenes in the running process of the vehicle, the acceleration calculated at the intervened time is taken as the maximum acceleration a of the vehiclemaxAnd storing; when the ESP is not intervened, the total acceleration a is calculatedactCompared with the maximum acceleration stored at the previous moment, if the total acceleration aactIf the acceleration is larger than the maximum acceleration at the previous moment, the acceleration of the vehicle at the moment is taken as the maximum acceleration a of the vehiclemaxOtherwise, the maximum acceleration a stored at the previous moment is maintainedmax。
Further, the inter-shaft driving torque is distributed according to the motor efficiency mode, and an efficiency MAP method for calculating an inter-shaft torque distribution coefficient according to the motor efficiency is adopted:
the principle of motor efficiency distribution is as follows:
Figure GDA0002985878890000031
in the formula, TfRepresents the front axle motor output torque, Nm; t isreqRepresents the total driver demand torque, Nm; t isrRepresents the rear axle motor output torque, Nm; i represents an interaxial torque distribution coefficient; n represents the rotating speed of the motor, r/min; pf，PrRespectively representing the output power, kw, of the front and rear shaft motors; etaf，ηrRespectively showing the working efficiency of the front and rear shaft motors; preqRepresenting the total output power, kw, of the front and rear axle motors;
the constraints of tolerance are introduced and defined as follows:
Figure GDA0002985878890000032
wherein tolerance represents a tolerance threshold in an off-line calibration process, Preq_bestThe total output power corresponding to the optimal distribution coefficient under a certain working point is represented; preq_TThe total output power under the constraint condition of meeting a certain tolerance is represented, namely the distribution coefficient is considered to be optimal under the condition that the total output power of the front motor and the rear motor meets a certain tolerance;
selecting a certain fixed tolerance threshold, and obtaining the efficiency MAP by giving different vehicle speeds and required torques;
and if the calculated torque of a certain shaft motor exceeds the capacity limit of the shaft motor, the exceeded torque is transferred to the other shaft in order to meet the driving requirement of a driver, and finally the torques distributed to the two shafts do not exceed the capacity limits of the respective motors.
Further, the inter-shaft driving torque is distributed according to the motor driving performance mode, and a performance MAP method for calculating an inter-shaft torque distribution coefficient according to the motor driving performance is adopted:
considering the problem of axle load transfer caused by the longitudinal acceleration of the vehicle and the gradient of the road, ensuring that the torque distribution coefficient is distributed according to the axle load, and obtaining the performance MAP through off-line calculation;
and finally, limiting the output torque of each motor, ensuring that the output torque of each shaft is in a capacity range, automatically transferring to another shaft when the motor of one shaft cannot respond to the torque due to capacity limitation, and ensuring that the motor can respond to the required torque of the driver to the maximum extent in the capacity range of the output torque of the motor.
The invention has the following beneficial effects:
the method for distributing the torque between the shafts of the electric four-wheel drive vehicle can automatically distribute the torque between the shafts according to the economical efficiency and the driving performance according to the driving mode and the driving working condition of the vehicle, so that the technical effect of improving the energy consumption is achieved by optimizing the algorithm of the motor driving torque distribution coefficient under the condition of not changing the original power system structure and not increasing the cost, and the method can meet the economical efficiency of a driver and the driving performance requirement. When a motor of one shaft cannot respond to the torque due to capacity limitation, in order to preferentially ensure the driving requirement of a driver, the motor of the other shaft is automatically transferred to ensure that the motor can maximally respond to the required torque of the driver within the capacity range of the output torque of the motor.
The invention firstly detects the torque required by driving, when the driver is detected to have a driving demand, namely the torque required is larger than zero, the efficiency mode and the performance mode are automatically selected according to the difference between the driving mode and the vehicle mode to distribute the torque of the front and rear shafts, and when the driver is detected to have a deceleration request, the torque of the front and rear shaft motors is distributed according to the performance mode.
The invention can automatically learn the road adhesion coefficient without adding an additional sensor, thereby obtaining the maximum acceleration of the vehicle.
The invention provides a distribution method for distributing inter-axle torque according to motor efficiency, which comprises the steps of firstly establishing an efficiency MAP off-line method for distributing inter-axle torque according to motor efficiency, and providing a tolerance concept in the method to prevent the influence on the economy of a vehicle due to the back-and-forth shaking of the output torque of front and rear motors caused by the back-and-forth jumping of a distribution coefficient when the inter-axle torque is distributed according to the motor efficiency.
The invention provides a performance MAP off-line formulation method for distributing torque between shafts according to the driving performance of a motor, which considers the axle load transfer caused by the longitudinal acceleration and the gradient of a vehicle, can give full play to the driving performance of front and rear motors, enables the vehicle to obtain the maximum lateral force potential and gives full play to the adhesion capability of front and rear wheels.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 flow chart of an interaxial torque distribution method
FIG. 2 maximum acceleration calculation
FIG. 3 distribution of inter-axle torque according to motor efficiency
FIG. 4 apportioning interaxial torque according to driveability modes
FIG. 5 economic MAP
FIG. 6 Performance MAP
Detailed Description
The technical scheme of the invention is described in detail in the following with reference to the attached drawings:
a method for distributing torque between front and rear double-motor four-wheel drive vehicle axles comprises the following steps:
obtaining current parameters of a vehicle, wherein the current parameters comprise: vehicle longitudinal acceleration, road grade, torque demand, vehicle driving mode (Normal, Sport, Eco);
according to the driving mode of a driver and the actual running condition of the vehicle, the distribution mode of the driving torque of the front and rear axle motors of the vehicle is automatically selected, and the inter-axle torque distribution coefficient i is distributed according to the efficiency or the longitudinal driving performance of the front and rear axle motors. The inter-axle torque distribution coefficient i of the invention refers to the proportion of the output torque of the rear axle motor to the total output torque of the front and rear motors (similar to the total torque of the front axle motor), and combines the torque T required by the driverreqAnd obtaining the respective driving torque of the front and rear axle motors by the inter-axle torque distribution coefficient i.
Figure GDA0002985878890000051
In the formula, TrRepresenting the output torque, T, of the rear axle motorfRepresenting the output torque of the front axle motor. If the calculated torque of the motor of one shaft exceeds the capacity limit of the motor of the shaft, in order to meet the driving requirement of a driver, the exceeded torque is transferred to the other shaft, and finally, the torques distributed to the two shafts do not exceed the capacity limits of the motors of the two shafts.
The torque distribution mode of the front and rear axle motors is automatically selected according to the driving mode and the road gradient information and the longitudinal acceleration information of the vehicle. The distribution mode of the torque between the shafts is shown in fig. 1, the invention firstly detects the required torque of a driver, and when the driver is detected to have a driving requirement, namely the required torque is larger than zero, the efficiency mode and the performance mode are automatically selected according to the difference of the driving mode and the vehicle mode to distribute the torque of the front shaft and the rear shaft; when a deceleration request is detected by the driver, the front and rear axle motor torques are distributed according to the performance mode. When the driver is detected to have a driving demand, the influence of the gradient is judged firstly, and when the gradient is larger than a certain threshold thetap(for example, the invention is a 6 degree slope), automatically selecting a mode of distributing the driving torque between the axles according to the driving performance, otherwise, judging the influence of the driving mode of the vehicle, when the driver selects the Sport mode, distributing the driving torque between the axles according to the driving performance mode, when the driver selects the Eco mode, automatically selecting the mode of distributing the driving torque between the axles according to the motor efficiency, when the driver selects the Normal mode, determining the distribution mode of the torque by combining the relation between the actual acceleration of the vehicle and the maximum acceleration, at this time, if the actual acceleration a of the vehicle isactWith maximum acceleration amaxWhen the proportion exceeds a certain threshold k (0.5 in the invention), the torque between the shafts is distributed according to the motor performance mode, otherwise, the torque between the shafts is distributed according to the motor efficiency mode.
Can automatically learn the road adhesion coefficient and further obtain the maximum acceleration a of the vehiclemax. The invention acquires the longitudinal acceleration a of the vehicle at any momentxWith lateral acceleration ayAnd calculating the actual total acceleration a of the vehicleact. When the vehicle has an ESP intervention during driving, the acceleration calculated at the time of the intervention is stored as the maximum acceleration of the vehicle. When the ESP is not intervened, the total acceleration a to be calculatedactAnd comparing the acceleration with the maximum acceleration stored at the last moment, if the acceleration is greater than the maximum acceleration at the last moment, taking the acceleration of the vehicle at the moment as the maximum acceleration of the vehicle, and otherwise, maintaining the maximum acceleration stored at the last moment.
Figure GDA0002985878890000061
And (3) an efficiency MAP (MAP) making method for calculating an inter-shaft torque distribution coefficient according to the motor efficiency. Since the operating efficiency of the electric machine directly affects the economy of the vehicle, the operating efficiency of the electric machine is different at different torques and rotational speeds. The principle of front and rear axle torque distribution according to motor efficiency is that under the condition of ensuring that the required torque is met, the output torque of the front and rear axle motors is adjusted, so that the working points of the front and rear axle motors fall in the efficient working area of the motors as far as possible, the sum of the total working efficiency of the two motors is optimal, and the economical efficiency of the vehicle is ensured. The principle of the motor efficiency distribution is shown in the following formula 3.
Figure GDA0002985878890000062
In the formula TfRepresenting front axle motor output torque, Nm. T isreqRepresenting the total driver demanded torque, Nm. T isrRepresenting rear axle motor output torque, Nm. i represents an interaxial torque distribution coefficient. N represents the motor speed, r/min. Pf，PrRespectively, the output power, kw, of the front and rear axis motors. Etaf，ηrRespectively showing the working efficiency of the front and rear shaft motors. PreqRepresenting the total output power, kw, of the front and rear axle motors.
In the off-line calibration process of the efficiency MAP, in order to avoid the back-and-forth jumping of the distribution coefficients of the front and rear shaft motors, the invention introduces the constraint condition of tolerance. The tolerance constraint is defined as follows:
Figure GDA0002985878890000063
wherein tolerance represents a tolerance threshold value in an off-line calibration process, Preq_bestWhich represents the total output power corresponding to the optimal distribution coefficient at a certain operating point. Preq_TRepresenting the total output power with certain tolerance constraints. That is, the distribution coefficient is considered to be optimal when the total output power of the front and rear motors meets a certain tolerance.
As can be seen from equation 3, the motor efficiency is closely related to the required torque and the motor speed (vehicle speed). In the process of distributing the torque between the shafts according to the motor efficiency, if the tolerance is selected too low in the process of optimizing the distribution coefficient, the distribution coefficient can jump back and forth, the economy of the vehicle is affected, the optimization effect can be unobvious due to too high tolerance, and the economy of the vehicle cannot be improved. By selecting a fixed tolerance threshold (as exemplified by 5 in the present invention), the efficiency MAP can be obtained by giving different vehicle speeds and torque demands. A flow chart for distributing inter-shaft torque in terms of motor efficiency is shown in fig. 3. And if the calculated torque of a certain shaft motor exceeds the capacity limit of the shaft motor, the exceeded torque is transferred to the other shaft in order to meet the driving requirement of a driver, and finally the torques distributed to the two shafts do not exceed the capacity limits of the respective motors.
A method for establishing a performance MAP for calculating an inter-shaft torque distribution coefficient according to a motor driving performance. Performance MAP formulation is closely related to front and rear axis loading. The longitudinal drive performance mode is primarily to distribute the inter-axle torque based on the front and rear axle loads. Since the vehicle under acceleration causes a transfer of vertical axle load of the front and rear axles, the acceleration directly determines the magnitude of the axle load transfer. The acceleration is different, the axle load transfer is also different, and the axle load calculation of the front and rear axles is shown as 3.
Figure GDA0002985878890000071
Wherein m represents the mass of the whole vehicle in kg. L represents the wheelbase, m. b represents the distance of the centroid to the rear axis, m. a represents the distance of the centroid to the front axis, m. g represents the acceleration of gravity, m/s2And H represents a tread, m. Theta denotes the gradient, axRepresenting the longitudinal acceleration m/s of the vehicle2，FfzhIndicating front axle load, FrzhIndicating the rear axle load. From equation 5, it can be seen that the acceleration and gradient of the vehicle directly affect the axle load of the front and rear axles of the vehicle, and further affect the longitudinal driving performance mode. The front motor and the rear motor preferably slip at the same time, so that the driving performance of the motors can be fully exerted, therefore, the driving torque of the front motor and the driving torque of the rear motor are distributed according to the axle load proportion of the front shaft and the rear shaft, and the performance MAP can be obtained through off-line calculation. A flow chart for distributing inter-shaft torque according to motor performance is shown in fig. 4. It can be seen from the figure that the distribution coefficient obtained by table lookup filtering needs to be subjected to filtering limitation to obtain the distribution coefficient of the front and rear shaft motors, and the distribution coefficient obtained by table lookup filtering needs to be subjected to filtering limitationAnd if the calculated torque of a certain shaft motor exceeds the capacity limit of the shaft motor to the distribution coefficient of the front shaft motor and the rear shaft motor, in order to meet the driving requirement of a driver, the exceeded torque is transferred to the other shaft, and finally, the torques distributed to the two shafts do not exceed the capacity limits of the respective motors.

Claims (4)

1. A method for distributing torque between front and rear double-motor four-wheel drive vehicle axles is characterized by comprising the following steps:
the method comprises the steps of firstly, obtaining current parameters of a vehicle, including longitudinal acceleration of the vehicle, road gradient, required torque and driving mode of the vehicle;
step two, automatically selecting a distribution mode of the driving torque of the front and rear axle motors of the vehicle according to the driving mode of a driver and the actual running condition of the vehicle, and distributing an inter-axle torque distribution coefficient i according to the efficiency or longitudinal driving performance of the front and rear axle motors:
the driver's required torque is detected first,
1) when the required torque is detected to be larger than zero, automatically selecting an inter-axle torque distribution mode according to different driving modes and vehicle modes:
1.1) when the driver has a driving demand, firstly judging the influence of the gradient, and when the gradient is larger than a certain threshold value thetapAutomatically selecting a mode of distributing the driving torque between the shafts according to the driving performance of the motor;
1.2) otherwise, judging the influence of the driving mode of the vehicle:
when the driver selects the Sport mode, the driver selects to distribute the driving torque between the shafts according to the motor driving performance mode;
when the driver selects the Eco mode, the inter-axle driving torque is automatically distributed according to the motor efficiency mode;
when the driver selects Normal mode, the torque split mode is determined in combination with the actual acceleration of the vehicle versus the maximum acceleration: if the actual acceleration a of the vehicle isactWith maximum acceleration amaxWhen the proportion exceeds a certain threshold k, the inter-shaft driving torque is distributed according to a motor driving performance mode; otherwise, the shaft is distributed according to the motor efficiency modeAn intermediate drive torque;
maximum acceleration a of the vehiclemaxThe calculation method comprises the following steps:
the longitudinal acceleration a of the vehicle is acquired at any timexWith lateral acceleration ayAnd calculating the actual total acceleration a of the vehicleact:
Figure FDA0002985878880000011
When an ESP intervenes in the running process of the vehicle, the acceleration calculated at the intervened time is taken as the maximum acceleration a of the vehiclemaxAnd storing; when the ESP is not intervened, the total acceleration a is calculatedactCompared with the maximum acceleration stored at the previous moment, if the total acceleration aactIf the acceleration is larger than the maximum acceleration at the previous moment, the acceleration of the vehicle at the moment is taken as the maximum acceleration a of the vehiclemaxOtherwise, the maximum acceleration a stored at the previous moment is maintainedmax；
2) When a deceleration request of a driver is detected, the driving torque between the front axle and the rear axle is distributed according to the motor driving performance mode.
2. The method for distributing the torque between the front and rear double-motor four-wheel drive vehicle axles as claimed in claim 1, wherein the torque distribution coefficient i between the axles refers to the ratio of the output torque of the rear axle motor to the total output torque of the front and rear motors, and combines the torque T required by the driverreqAnd obtaining the driving torque of the front and rear axle motors by the inter-axle torque distribution coefficient i:
Figure FDA0002985878880000021
in the formula, TrRepresenting the output torque, T, of the rear axle motorfIndicating the output torque of the front and rear motors.
3. The method for distributing the torque between the axles of the front and rear dual-motor four-wheel drive vehicle as claimed in claim 1, wherein the method for distributing the driving torque between the axles according to the motor efficiency is characterized in that an efficiency MAP method for calculating the torque distribution coefficient between the axles according to the motor efficiency is adopted:
the principle of motor efficiency distribution is as follows:
Figure FDA0002985878880000022
in the formula, TfRepresents the front axle motor output torque, Nm; t isreqRepresents the total driver demand torque, Nm; t isrRepresents the rear axle motor output torque, Nm; i represents an interaxial torque distribution coefficient; n represents the rotating speed of the motor, r/min; pf，PrRespectively representing the output power, kw, of the front and rear shaft motors; etaf，ηrRespectively showing the working efficiency of the front and rear shaft motors; preqRepresenting the total output power, kw, of the front and rear axle motors;
the constraints of tolerance are introduced and defined as follows:
Figure FDA0002985878880000023
wherein tolerance represents a tolerance threshold in an off-line calibration process, Preq_bestThe total output power corresponding to the optimal distribution coefficient under a certain working point is represented; preq_TThe total output power under the constraint condition of meeting a certain tolerance is represented, namely the distribution coefficient is considered to be optimal under the condition that the total output power of the front motor and the rear motor meets a certain tolerance;
selecting a certain fixed tolerance threshold, and obtaining the efficiency MAP by giving different vehicle speeds and required torques;
and if the calculated torque of a certain shaft motor exceeds the capacity limit of the shaft motor, the exceeded torque is transferred to the other shaft in order to meet the driving requirement of a driver, and finally the torques distributed to the two shafts do not exceed the capacity limits of the respective motors.
4. The method for distributing the torque between the axles of the front and rear dual-motor four-wheel drive vehicle as claimed in claim 1, wherein the method for distributing the driving torque between the axles according to the driving performance of the motors adopts a performance MAP method for calculating the distribution coefficient of the torque between the axles according to the driving performance of the motors:
considering the problem of axle load transfer caused by the longitudinal acceleration of the vehicle and the gradient of the road, ensuring that the torque distribution coefficient is distributed according to the axle load, and obtaining the performance MAP through off-line calculation;
and finally, limiting the output torque of each motor, ensuring that the output torque of each shaft is in a capacity range, automatically transferring to another shaft when the motor of one shaft cannot respond to the torque due to capacity limitation, and ensuring that the motor can respond to the required torque of the driver to the maximum extent in the capacity range of the output torque of the motor.
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