CN109878347A - A kind of multiaxis drives the wheel torque distribution method of distributed vehicle - Google Patents

A kind of multiaxis drives the wheel torque distribution method of distributed vehicle Download PDF

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CN109878347A
CN109878347A CN201910237861.4A CN201910237861A CN109878347A CN 109878347 A CN109878347 A CN 109878347A CN 201910237861 A CN201910237861 A CN 201910237861A CN 109878347 A CN109878347 A CN 109878347A
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torque
wheel
wheels
distribution
vehicle
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CN109878347B (en
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连小珉
杜鹏
徐达
陈浩
江燕华
王源
袁良信
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Tsinghua University
Beijing Automotive Research Institute Co Ltd
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Tsinghua University
Beijing Automotive Research Institute Co Ltd
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Abstract

The invention proposes the wheel torque distribution methods that a kind of multiaxis drives distributed vehicle, the torque of wheel is divided into left and right distribution and front and back two stages of distribution by for wheel parsing longitudinal torque and to parse steering torque with wheel poor for the longitudinal direction of car power of upper controller and vehicle yaw moment are instruction morphing by the present invention;Single wheel is considered as an entirety when distribution of left and right, using steering preferential principle;Front and back is distributed by the way of considering the mean allocation under different wheel limit value, keeps ipsilateral wheel torque burden close, torque mutually compensates between ipsilateral wheel, accurately realizes the distribution of ipsilateral wheel torque sum.Complicated multiaxis wheel torque assignment problem is decomposed into the torque assignment problem of less wheel by the present invention, reduce the complexity of wheel torque distribution, guarantee the dynamic property and steering stability of vehicle, and the maximum of upper controller requirement command is realized, especially suitable for the wheel torque distribution under wheel energy power limit or the operating condition of damage.

Description

Wheel torque distribution method of multi-axis driving distributed vehicle
Technical Field
The invention belongs to the field of vehicle dynamics control, and particularly relates to a wheel torque distribution method of a multi-axis driving distributed vehicle.
Background
The distributed vehicle is a vehicle with a motor directly arranged in a wheel (namely, a hub motor) or nearby (namely, a wheel-side motor) and realizes the control of the vehicle through the torque of the motor. The distributed vehicle has the outstanding advantages of short driving transmission chain, high transmission efficiency, compact structure and the like, and is widely concerned by automobile industry research personnel year by year.
At present, the whole vehicle control of the distributed vehicle can be realized by an upper layer controller and a lower layer controller, wherein the upper layer controller obtains an upper layer demand instruction of the vehicle according to the operation of a driver, the vehicle state and the like, and the upper layer demand instruction comprises the longitudinal force and the yaw moment of the vehicle; and the bottom controller distributes wheel torque according to the demand instruction of the upper controller, so that the control of the whole vehicle is realized.
The multi-shaft driving distributed vehicle generally has a plurality of power sources, increases the combination mode and complexity of vehicle power distribution, and can combine various optimization targets, such as dynamic property, economy, stability and the like, to distribute wheel torque.
The wheel torque distribution method generally adopted by the conventional bottom controller is to establish a wheel torque distribution optimization function and solve the wheel torque distribution optimization function so as to improve the economy, stability and the like of the whole vehicle, but the optimization solving problem is not only constrained by an equation realized by the longitudinal force and the yaw moment of the vehicle, but also constrained by an inequality of a torque capacity limit value of a single wheel, and the calculation cost is high in the conventional solving method, so that the optimal solution is difficult to solve in control time under various complex working conditions of the vehicle, such as the torque distribution in a limp-home mode; secondly, the parameters of the optimization function need to be calibrated according to different working conditions, and the research and development cost of the torque distribution algorithm is increased, so that the optimization function is difficult to apply to actual vehicles. In addition, a rule-based wheel torque distribution method is also provided, at present, two-axis vehicles are mostly distributed, wheel torques of front and rear axes are firstly determined, and then torque commands of left and right wheels of each axis are determined, at this time, when the wheel torque of one axis cannot be realized due to a torque capacity limit value, the wheel torque of the other axis cannot be compensated, and the torque commands of an upper layer controller are lost due to improper torque distribution.
In the wheel torque distribution, when the wheels cannot meet the requirement of an upper controller due to torque limit values, some current schemes select a longitudinal force priority principle, so that although the longitudinal requirement of the vehicle is ensured, the yaw moment of the vehicle is influenced, and particularly the stability control of the vehicle is not facilitated at high speed or on a low-attachment road surface. In some cases, the longitudinal force priority or the steering priority is selected by determining a condition. However, the priority determination condition is complicated, and is associated with ground adhesion, driver operation, and the like, which increases the complexity of vehicle torque distribution. If the steering yaw moment is selected to be preferred all the time, the steering stability of the vehicle is always preferred, the steering radius of the vehicle can be reduced at low speed, good stability can be obtained at high speed, torque distribution is simplified, and the steering safety of the vehicle is improved.
In summary, for the multi-axis driving distributed vehicle torque distribution problem, if the existing torque distribution mode for solving the optimization function is adopted, the problem is constrained by a plurality of equalities and inequalities, the solving and calculating cost is high, and the optimization function parameters need to be determined by experiments, so that the research and development cost is increased. However, the current rule-based torque distribution mode cannot fully exert all torque capacities of the wheels to realize the demand instruction of the upper controller, and when the wheel torque limit cannot meet the demand instruction of the upper controller, the current algorithm cannot well solve the balance coordination between the steering stability and the dynamic property, is not favorable for the stability control of the vehicle at high speed or low load, and influences the steering safety of the vehicle.
Disclosure of Invention
The invention aims to solve the problems that calculation and solving costs are high, optimization parameters are difficult to determine, wheel torques cannot be mutually compensated to realize a requirement instruction of an upper-layer controller to the maximum extent, and the like in the conventional multi-shaft driving vehicle torque distribution. A multi-axis drive distributed vehicle wheel torque distribution method is provided.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a wheel torque distribution method of a multi-shaft driving distributed vehicle, wherein the multi-shaft driving distributed vehicle comprises 2N wheels which are symmetrically arranged left and right, each wheel is driven by a corresponding motor, each motor is controlled by a motor controller, and the motor is a hub motor or a wheel-side motor; characterized in that the wheel torque distribution method comprises the steps of:
1) establishing a vehicle coordinate system
Defining a vehicle coordinate system OXYZ according to international standards, wherein an origin O of the coordinate system is a mass center of the vehicle, a coordinate axis X is a forward direction of the vehicle, a coordinate axis Y is a left direction of the forward direction of the vehicle, and a coordinate axis Z is outward perpendicular to a straight surface;
the torque coordinate direction of the wheels is specified to be positive when consistent with the Y direction, otherwise, the torque coordinate direction is negative; when the longitudinal force direction of the vehicle is consistent with the X direction, the longitudinal force direction is positive, otherwise, the longitudinal force direction is negative; when the direction of the vehicle yaw moment is consistent with the Z direction, the vehicle yaw moment is positive, otherwise, the vehicle yaw moment is negative;
2) analyzing longitudinal force and transverse moment of vehicle
Acquiring upper layer controller demand instructions including vehicle longitudinal force FxYaw moment M with vehiclez(ii) a The wheel is regulated not to slip, and the longitudinal force F of the vehicle is obtainedxConverted to the sum of the torque of the left and right wheels and defined as the wheel resolved longitudinal torque sum TaaYaw moment M of the vehicle to be acquiredzConverted into torque difference of left and right wheels and defined as wheel analysis steering torque difference TsaThe calculation formulas are respectively shown in formulas (1) and (2):
Taa=Fxr (1)
in the formulas (1) and (2), r is the rolling radius of the wheel, and B is the wheel track of the vehicle;
3) distribution of wheel torque according to steering priority
When the multi-axis driving distributed vehicle wheel torque distribution is carried out, the influence of the steering angle of the front wheel on the ground acting force direction of the front wheel is ignored, and one side wheel is regarded as oneIntegrally, the left and right distribution of the upper layer control required torque is firstly carried out to obtain the left and right wheel torque and TL、TRThen, the torque sum of the left wheel and the right wheel is distributed front and back, so that the torque of each wheel is obtained; the method specifically comprises the following steps:
3.1) left-right distribution of wheel torque demand
3.1.1) limiting the wheel resolved longitudinal torque and the wheel resolved steering torque difference
Analyzing the longitudinal torque and the T of the wheels according to the positive and negative maximum torque limit values of the left and right wheelsaaAnd resolving the wheel steering torque difference TsaLimiting to obtain the limited longitudinal torque and T of the wheelaDifference of steering torque T with wheels(ii) a Wherein,
for wheel longitudinal torque sum TaAccording to the principle of steering priority, the yaw moment to the vehicle cannot be formed when left-right distribution is performed, and the longitudinal torque and T are analyzed by equation (3)aaAnd (4) limiting:
in the formula (3), TaIn order to limit the rear wheel longitudinal torque sum,the sum of the forward maximum torques of the left wheels,the negative maximum torque sum of the left wheel is shown,the sum of the maximum torque in the forward direction of the right wheel,the calculation formulas of the negative maximum torque sum of the wheels on the right side are respectively shown as the formulas (4), (b), (c) and (d)5) Shown in the figure:
in the formulas (4) and (5),positive and negative torque capacity limits for the ith left wheel,the positive and negative maximum torque limit values of the jth wheel on the right side are respectively obtained by the feedback of a corresponding motor controller for controlling each wheel;
steering torque difference T for wheelsThe steering torque difference T is analyzed by the equation (6) according to the steering priority rulesaAnd (4) limiting:
in the formula (6), TsThe other variables have the same physical meanings as the wheel steering torque difference after limitation;
3.1.2) calculating the characteristic torque difference
The left and right wheel torques are respectively composed of a straight-going torque and a yaw torque, and the straight-going torque is composed of a wheel longitudinal torque and a wheel TaCalculating to obtain; yaw torque steering torque difference T by wheelssCalculating to obtain; resolving the steering torque difference T according to the wheels determined in the step 2)saThe characteristic torque difference is calculated and used for judging whether the sum of the straight-moving torque and the yaw torque of the left wheel and the right wheel exceeds the torque limit values of the left wheel and the right wheel, and the expression is shown as the formula (7):
in the formula (7), the reaction mixture is,
Tsaresolving a steering torque difference for the wheels determined according to step 2);
the negative limit steering torque difference of the left wheels represents the steering torque difference when the sum of the straight-going torque and the yaw torque of the left wheels is equal to the negative maximum torque limit value when the vehicle turns anticlockwise;
the steering torque difference is the positive limit steering torque difference of the right wheels, and represents the steering torque difference when the sum of the straight-going torque and the yaw torque of the right wheels is equal to the positive maximum torque limit value when the vehicle turns anticlockwise;
the steering torque difference is the positive limit steering torque difference of the left wheel, and represents the steering torque difference when the sum of the straight-going torque and the yaw torque of the left wheel is equal to the positive maximum torque limit value when the vehicle turns clockwise;
the negative limit steering torque difference of the right wheel represents the steering torque difference when the sum of the straight-going torque and the yaw torque of the right wheel is equal to the negative maximum torque limit value when the vehicle turns clockwise;
3.1.3) matching the torque sum of the left wheel and the right wheel according to the characteristic torque difference, wherein the specific distribution mode is as follows:
3.1.3.1) judgmentWheel steering torque difference TsPositive or negative of (1), if TsIf not less than 0, entering step 3.1.3.2), otherwise entering step 3.1.3.6);
3.1.3.2) determining the steering torque difference T of the wheelssRight positive limit steering torque differenceLeft negative limit steering torque differenceThe minimum value of the three is the steering torque difference T of the wheelssThen go to step 3.1.3.3); if the minimum value is the steering torque difference of the positive limit on the right sideStep 3.1.3.4 is entered); if the minimum value is the left negative limit steering torque differenceStep 3.1.3.5 is entered);
3.1.3.3) calculating the left and right side wheel torques and T according to equation (8)L、TR
The torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.1.3.4) calculate the left and right side wheel torques and according to equation (9):
the torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.1.3.5) calculate the left and right side wheel torques and according to equation (10):
the torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.1.3.6) determining the wheel steering torque difference TsRight negative limit steering torque differenceLeft positive limit steering torque differenceThe maximum value of the three is the steering torque difference T of the wheelssThen go to step 3.1.3.3); if the maximum value is the steering torque difference of the negative limit on the right sideStep 3.1.3.7 is entered); if the maximum value is the left positive limit steering torque differenceStep 3.1.3.8);
3.1.3.7) calculate the left and right side wheel torques and according to equation (11):
the torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.1.3.8) calculate the left and right side wheel torques and according to equation (12):
the torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.2) front and back distribution of same-side wheel torque and
the front and back distribution of the torque sum of the wheels on the same side adopts an average distribution mode, the distribution methods of the torque sum of the wheels on the left side and the torque sum of the wheels on the right side are consistent, and the front and back distribution of the torque sum of the wheels on the left side is executed according to the following steps:
3.2.1) left wheel Torque and TLIf left side wheel torque and TLIf not less than 0, entering the step 3.2.2); if left wheel torque and TLIf less than 0, entering step 3.2.7);
3.2.2) Forward maximum Torque Limit in left N wheelsSequencing from small to large to obtain a new sequencek represents the t-thiThe positive torque capacity limit of each wheel is arranged at the k-th position in the positive torque limit sequence of the left wheel; let the number of dispensing times be s, the initial value of s is 1, ifStep 3.2.3) is entered; otherwise, s is 2, go to step 3.2.4);
3.2.3) calculate the left wheel torques according to equation (13):
the torque distribution of the left wheel is completed;
3.2.4) ifStep 3.2.5) is entered, otherwise step 3.2.6) is entered;
3.2.5) calculates the left hand wheel torques according to equation (14):
the torque distribution of the left wheel is completed;
3.2.6) let s be s +1, if s is N +1, then the left wheel torque distribution is completed, otherwise return to step 3.2.4);
3.2.7) negative maximum Torque Limit in left N wheelsSequencing from big to small to obtain a new sequencek represents the r-thiThe negative direction maximum torque limit value of each wheel is arranged at the kth position in the negative direction torque limit value sequence of the left wheels; let the number of dispensing times be s, the initial value of s is 1, ifStep 3.2.8 is entered); otherwise, s is 2, go to step 3.2.9);
3.2.8) calculates the left-hand wheel torques according to equation (15):
the torque distribution of the left wheel is completed;
3.2.9) ifStep 3.2.10) is entered, otherwise step 3.2.11) is entered;
3.2.10) calculates the left-hand wheel torques according to equation (16):
the torque distribution of the left wheel is completed;
3.2.11) let s be s +1, if s is N +1, then the left wheel torque distribution is completed, otherwise return to step 3.2.9);
and performing front-back distribution of the right wheel torque sum by referring to the left side to complete wheel torque distribution.
The invention has the characteristics and beneficial effects that:
the invention provides a wheel torque distribution method of a multi-axis driving distributed vehicle, which converts a longitudinal force and a yaw moment instruction of an upper layer controller into a wheel analysis longitudinal torque and a wheel analysis steering torque difference, and divides the wheel torque distribution into a left-right distribution stage and a front-back distribution stage. When left and right distribution is carried out, the wheels on one side are regarded as a whole, and the steering stability control of the vehicle is ensured by adopting the principle of steering priority; the front and back distribution adopts a mode of average distribution under consideration of different wheel limit values, so that the torque loads of wheels on the same side are close, the torques of the wheels on the same side can be mutually compensated, and the torque sum of the wheels on the same side can be accurately realized. The wheel torque limit value is fed back in real time and can reflect the working state of a wheel motor in the running process.
According to the wheel torque distribution method, based on vehicle dynamics, the complex multi-axis wheel torque distribution problem is decomposed into the torque distribution problem of fewer wheels, the complexity of wheel torque distribution is reduced, and the dynamic property and steering stability of a vehicle and the maximum realization of the demand instruction of an upper controller are ensured; in the wheel torque distribution process, the influence of different wheel torque limit values on torque distribution is considered, wheels on the same side are mutually compensated, and the multi-axle distributed type vehicle torque distribution method is particularly suitable for multi-axle distributed vehicle torque distribution under the working condition that the capacity of certain wheels is limited or damaged. The concrete embodiment is as follows:
1. according to the wheel torque distribution method of the multi-axis driving distributed vehicle, the torque distribution of the multi-axis driving vehicle is divided into left-right distribution and front-back distribution, the distribution problem of the torque of one multi-wheel is simplified into the torque distribution problem of two fewer wheels, and the wheel torque distribution method can be simplified. The adopted wheel torque distribution method is particularly suitable for wheel torque distribution of a multi-shaft driving distributed vehicle without a mechanical steering system.
2. According to the wheel torque distribution method of the multi-axis driving distributed vehicle, when the wheel torque capacity meets the requirement of an upper controller, the intention of an upper control instruction can be accurately realized, so that the vehicle has good dynamic property and stability.
3. According to the wheel torque distribution method of the multi-axis driving distributed vehicle, when the wheel torque capacity cannot meet the requirement of an upper controller, the requirement instruction of the upper controller is realized to the maximum extent according to the principle of steering priority (steering yaw moment priority). The steering radius of the vehicle can be reduced at low speed so as to improve the steering performance of the vehicle, and meanwhile, the stability control of the vehicle at high speed can be ensured, and the device is particularly suitable for torque distribution under the working conditions that the capacity of certain wheels is limited or damaged.
4. According to the wheel torque distribution method for the multi-shaft driving distributed vehicle, when one wheel on one side cannot meet the torque requirement on the same side, the other wheels on the same side can compensate, and the torque sum of the wheels on the same side is accurately achieved.
5. The wheel torque distribution method of the multi-axis driving distributed vehicle can be popularized to the multi-axis driving distributed vehicle with the same structure and a plurality of driving wheels on one side.
6. According to the wheel torque distribution method of the multi-shaft driving distributed vehicle, the distribution parameters are real-time feedback parameters of the wheel motor, the method is suitable for various working conditions of the vehicle, the states of the wheel motor can be fed back through different wheel torque responses under the same input, and the motor states can be monitored.
Drawings
FIG. 1 is a schematic view of a vehicle coordinate system defined by an embodiment of the present invention.
Detailed Description
The invention provides a wheel torque distribution method of a multi-shaft driving distributed vehicle, which is further described by combining specific examples and drawings as follows:
the invention provides a multi-axis driving distributed vehicle wheel torque distribution method, which is used for a distributed vehicle driven by 2N (in the embodiment, N is 3) in-wheel motors, wherein each motor is controlled by a motor controller, and the motor is an in-wheel motor or a wheel-side motor, and the method specifically comprises the following steps:
1) establishing a vehicle coordinate system
A vehicle coordinate system xyz is defined, and the positive and negative of each parameter in the vehicle coordinate system are defined.
A vehicle coordinate system oyx is defined according to international standards, and an origin O of the coordinate system is a center of mass of the vehicle, a coordinate axis X is a forward direction of the vehicle, a coordinate axis Y is a left direction of the forward direction of the vehicle, and a coordinate axis Z is outward perpendicular to a straight plane, as shown in fig. 1.
The method comprises the steps that when the direction of a T coordinate of wheel torque is consistent with the Y direction, the direction is positive, otherwise, the direction is negative; when the longitudinal force direction of the vehicle is consistent with the X direction, the longitudinal force direction is positive, otherwise, the longitudinal force direction is negative; when the vehicle yaw moment direction is consistent with the Z direction, the vehicle yaw moment direction is positive, and otherwise, the vehicle yaw moment direction is negative.
The hub motors of the left and right wheels of the vehicle are sequentially sequenced from front to back, in the embodiment, the left wheel of the vehicle is sequenced into (1, 2, 3) from front to back, and the right wheel is sequenced into (1, 2, 3) from front to back; and corresponding the feedback information of the motor controller to the sequencing of each hub motor one by one.
2) Analyzing longitudinal force and transverse moment of vehicle
Acquiring upper layer controller demand instructions including vehicle longitudinal force FxYaw moment M with vehiclez(ii) a The wheel is regulated not to slip, and the longitudinal force F of the vehicle is obtainedxConverted to the sum of the torque of the left and right wheels and defined as the wheel resolved longitudinal torque sum TaaYaw moment M of the vehicle to be acquiredzConverted into torque difference of left and right wheels and defined as wheel analysis steering torque difference TsaThe calculation formulas are respectively shown in formulas (1) and (2):
Taa=Fxr (1)
in the formulas (1) and (2), r is the rolling radius of the wheel, B is the wheel track of the vehicle, and the rolling radius is determined by the design of the whole vehicle and is a known quantity;
3) distribution of wheel torque according to steering priority
When multi-axis driving distributed vehicle wheel torque distribution is carried out, the influence of the steering angle of the front wheels on the ground acting force direction of the front wheels is ignored. The influence of the torque of the wheels on the same side on the motion of the vehicle is consistent, so that the wheels on one side can be regarded as a whole, the upper-layer control required torque is firstly distributed leftwards and rightwards to obtain the torque of the wheels on the left side and the right side and the torque T of the wheels on the right sideL、TRAnd then the torque sum of the left and right wheels is distributed back and forth, so that the torque of each wheel is obtained. The specific implementation process is as follows:
3.1) left-right distribution of wheel torque demand
3.1.1) limiting the wheel resolved longitudinal torque and the wheel resolved steering torque difference
Calculation of vehicle longitudinal force F by upper layer controllerxYaw moment M with vehiclezWithout taking into account the torque capacity limit of each wheel. Therefore, the longitudinal torque and T of the wheel need to be analyzed according to the positive and negative maximum torque limit values of the left and right wheelsaaAnd resolving the wheel steering torque difference TsaLimiting to obtain the limited longitudinal torque and T of the wheelaDifference of steering torque T with wheels
For wheel longitudinal torque sum TaSince the yaw moment to the vehicle cannot be formed when left-right distribution is performed according to the principle of steering priority, the longitudinal torque and T are analyzedaaThe limiting expression is represented by formula (3):
in the formula (3), TaIn order to limit the rear wheel longitudinal torque sum,the sum of the forward maximum torques of the left wheels,the negative maximum torque sum of the left wheel is shown,the sum of the maximum torque in the forward direction of the right wheel,the calculation formula is shown in formulas (4) and (5) respectively as the negative maximum torque sum of the wheels on the right side:
in the formulas (4) and (5),positive and negative torque capacity limits for the ith left wheel,the positive and negative maximum torque limit values of the jth wheel on the right side are respectively obtained by the feedback of a corresponding motor controller for controlling each wheel;
steering torque difference T for wheelsAnalyzing the steering torque difference T according to the steering priority principlesaWhen limiting, the steering torque difference T is analyzed only by considering whether the steering torque difference is within the wheel torque limit value rangesaThe limiting expression is represented by formula (6):
in the formula (6), TsThe other variables have the same physical meanings as the wheel steering torque difference after limitation;
3.1.2) calculating the characteristic torque difference
The left and right wheel torques are respectively composed of a straight-going torque and a yaw torque, and the straight-going torque is composed of a wheel longitudinal torque and a wheel TaCalculating to obtain; yaw torque steering torque difference T by wheelssAnd (4) calculating. From step 3.1.1) the straight-moving torque and yaw torque of the wheels, which are within the torque limits of the left and right wheels, respectively, can be obtained, but the sum of the straight-moving torque and yaw torque may exceed the torque limits of the wheels, so further determination is required.
Resolving the steering torque difference T according to the wheels determined in the step 2)saThe characteristic torque difference is calculated and used for judging whether the sum of the straight-moving torque and the yaw torque of the left wheel and the right wheel exceeds the torque limit values of the left wheel and the right wheel, and the expression is shown as the formula (7):
in the formula (7), the reaction mixture is,
Tsaresolving a steering torque difference for the wheels determined according to step 2);
the negative limit steering torque difference of the left wheels represents the steering torque difference when the sum of the straight-going torque and the yaw torque of the left wheels is equal to the negative maximum torque limit value when the vehicle turns anticlockwise;
the steering torque difference is the positive limit steering torque difference of the right wheels, and represents the steering torque difference when the sum of the straight-going torque and the yaw torque of the right wheels is equal to the positive maximum torque limit value when the vehicle turns anticlockwise;
the steering torque difference is the positive limit steering torque difference of the left wheel, and represents the steering torque difference when the sum of the straight-going torque and the yaw torque of the left wheel is equal to the positive maximum torque limit value when the vehicle turns clockwise;
the negative limit steering torque difference of the right wheel represents the steering torque difference when the sum of the straight-going torque and the yaw torque of the right wheel is equal to the negative maximum torque limit value when the vehicle turns clockwise;
when the sum of the straight-ahead torque and the yaw torque in the sum of the right and left side wheel torques has not exceeded the right and left side wheel torque limit value, the wheel steering torque TsAnd wheel longitudinal torque sum TaAre independent of each other, i.e. the wheel steering torque TsThe distribution of (A) does not affect the longitudinal torsion of the wheelSum of moments Ta(ii) a When the sum of the straight-moving torque and the yaw torque in the torque sum of the left and right wheels exceeds the torque limit value of the left and right wheels, the steering torque difference T needs to be ensured according to the steering priority principlesIs realized by the actual distributed longitudinal torque sum TaIs affected.
3.1.3) matching the torque sum of the left wheel and the right wheel according to the characteristic torque difference, wherein the specific distribution mode is as follows:
3.1.3.1) determining the steering torque difference T of the wheelssPositive or negative of (1), if TsIf not less than 0, entering step 3.1.3.2), otherwise entering step mapoly 3.1.3.6);
3.1.3.2) determining the steering torque difference T of the wheelssRight positive limit steering torque differenceLeft negative limit steering torque differenceThe minimum value of the three is the steering torque difference T of the wheelssThen go to step 3.1.3.3); if the minimum value is the steering torque difference of the positive limit on the right sideStep 3.1.3.4 is entered); if the minimum value is the left negative limit steering torque differenceStep 3.1.3.5 is entered);
3.1.3.3) calculating the left and right side wheel torques and T according to equation (8)L、TR
The torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.1.3.4) calculate the left and right side wheel torques and according to equation (9):
the torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.1.3.5) calculate the left and right side wheel torques and according to equation (10):
the torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.1.3.6) determining the wheel steering torque difference TsRight negative limit steering torque differenceLeft positive limit steering torque differenceThe maximum value of the three is the steering torque difference T of the wheelssThen go to step 3.1.3.3); if the maximum value is the steering torque difference of the negative limit on the right sideStep 3.1.3.7 is entered); if the maximum value is the left positive limit steering torque differenceStep 3.1.3.8);
3.1.3.7) calculate the left and right side wheel torques and according to equation (11):
the torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.1.3.8) calculate the left and right side wheel torques and according to equation (12):
left and right wheel torque and split are complete, step 3.2).
3.2) front and back distribution of same-side wheel torque and
the influence of the torque of the wheels on the same side on the vehicle is consistent, in order to reduce the load of individual wheels and ensure that the torque commands finally distributed to the wheels on the same side are similar, the torque of the wheels on the same side is uniformly distributed; due to the difference in wheel torque capacity limits, it is necessary to accommodate different torque capacity limits of the wheels. The left and right wheel torque sums are distributed in the same manner, and the left side is taken as an example for explanation.
The torque sum of the left wheels is distributed forwards and backwards in the following specific distribution mode:
3.2.1) left wheel Torque and TLIf left side wheel torque and TLIf not less than 0, entering the step 3.2.2); if left wheel torque and TLIf less than 0, entering step 3.2.7);
3.2.2) Forward maximum Torque Limit in left N wheelsSequencing from small to large to obtain a new sequencek represents the t-thiThe positive torque capacity limit for an individual wheel is at the kth position in the sequence of left wheel positive torque limits. Let the number of dispensing times be s, the initial value of s is 1, ifStep 3.2.3) is entered; otherwise, s is 2, go to step 3.2.4);
3.2.3) calculate the left wheel torques according to equation (13):
the torque distribution of the left wheel is completed;
3.2.4) ifStep 3.2.5) is entered, otherwise step 3.2.6) is entered;
3.2.5) calculates the left hand wheel torques according to equation (14):
the torque distribution of the left wheel is completed;
3.2.6) let s be s +1, if s is N +1, then the left wheel torque distribution is completed, otherwise return to step 3.2.4);
3.2.7) negative maximum Torque Limit in left N wheelsSequencing from big to small to obtain a new sequencek represents the r-thiThe negative direction maximum torque limit value of each wheel is arranged at the kth position in the negative direction torque limit value sequence of the left wheels; let the number of dispensing times be s, the initial value of s is 1, ifThen enter intoStep 3.2.8); otherwise, s is 2, go to step 3.2.9);
3.2.8) calculates the left-hand wheel torques according to equation (15):
the torque distribution of the left wheel is completed;
3.2.9) ifStep 3.2.10) is entered, otherwise step 3.2.11) is entered;
3.2.10) calculates the left-hand wheel torques according to equation (16):
the torque distribution of the left wheel is completed;
3.2.11) let s be s +1, if s is N +1, then the left wheel torque distribution is complete, otherwise return to step 3.2.9).
The front-back distribution of the right wheel torque sum is carried out by referring to the left side, and the description is omitted, so that the wheel torque distribution is finally completed.
The wheel torque command can be obtained by the above steps.
The invention provides a multi-axis driving distributed vehicle wheel torque distribution method. Belonging to the field of vehicle dynamics control. The invention converts the longitudinal force and the yaw moment instruction of the upper layer controller into wheel analysis longitudinal torque and wheel analysis steering torque difference, limits the analysis longitudinal torque and the wheel analysis steering torque difference according to the torque capacity limit value of the wheels to obtain the longitudinal torque and the steering torque difference, and divides the torque distribution of the wheels into a left-right distribution stage and a front-back distribution stage. When left and right distribution is carried out, the wheels on one side are regarded as a whole, the principle of steering priority is adopted, the maximum realization of the demand instruction of an upper layer controller is realized, and the steering stability control of the vehicle is ensured; the front and back distribution adopts a mode of average distribution under consideration of different wheel limit values, so that the torque loads of wheels on the same side are close, the torques of the wheels on the same side can be mutually compensated, and the torque sum of the wheels on the same side can be accurately realized. The multi-axle distributed vehicle torque distribution device is particularly suitable for multi-axle distributed vehicle torque distribution under the working condition that the capacity of certain wheels is limited or damaged. Meanwhile, the wheel torque limit value is fed back in real time, and the working state of a wheel motor can be monitored.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (1)

1. A wheel torque distribution method of a multi-shaft driving distributed vehicle comprises 2N wheels which are symmetrically arranged left and right, wherein each wheel is driven by a corresponding motor, each motor is controlled by a motor controller, and the motors are hub motors or wheel-side motors; characterized in that the wheel torque distribution method comprises the steps of:
1) establishing a vehicle coordinate system
Defining a vehicle coordinate system OXYZ according to international standards, wherein an origin O of the coordinate system is a mass center of the vehicle, a coordinate axis X is a forward direction of the vehicle, a coordinate axis Y is a left direction of the forward direction of the vehicle, and a coordinate axis Z is outward perpendicular to a straight surface;
the torque coordinate direction of the wheels is specified to be positive when consistent with the Y direction, otherwise, the torque coordinate direction is negative; when the longitudinal force direction of the vehicle is consistent with the X direction, the longitudinal force direction is positive, otherwise, the longitudinal force direction is negative; when the direction of the vehicle yaw moment is consistent with the Z direction, the vehicle yaw moment is positive, otherwise, the vehicle yaw moment is negative;
2) analyzing longitudinal force and transverse moment of vehicle
Acquiring upper layer controller demand instructions including vehicle longitudinal force FxYaw moment M with vehiclez(ii) a The wheel is regulated not to slip, and the longitudinal force F of the vehicle is obtainedxConverted to the sum of the torque of the left and right wheels and defined as the wheel resolved longitudinal torque sum TaaYaw moment M of the vehicle to be acquiredzConverted into torque difference of left and right wheels and defined as wheel analysis steering torque difference TsaThe calculation formulas are respectively shown in formulas (1) and (2):
Taa=Fxr (1)
in the formulas (1) and (2), r is the rolling radius of the wheel, and B is the wheel track of the vehicle;
3) distribution of wheel torque according to steering priority
When multi-axis driving distributed vehicle wheel torque distribution is carried out, influence of a front wheel steering angle on the ground acting force direction of a front wheel is ignored, one side wheel is regarded as a whole, upper-layer control required torque is distributed left and right, and left and right wheel torques and T are obtainedL、TRThen, the torque sum of the left wheel and the right wheel is distributed front and back, so that the torque of each wheel is obtained; the method specifically comprises the following steps:
3.1) left-right distribution of wheel torque demand
3.1.1) limiting the wheel resolved longitudinal torque and the wheel resolved steering torque difference
Analyzing the longitudinal torque and the T of the wheels according to the positive and negative maximum torque limit values of the left and right wheelsaaAnd analysis ofWheel steering torque difference TsaLimiting to obtain the limited longitudinal torque and T of the wheelaDifference of steering torque T with wheels(ii) a Wherein,
for wheel longitudinal torque sum TaAccording to the principle of steering priority, the yaw moment to the vehicle cannot be formed when left-right distribution is performed, and the longitudinal torque and T are analyzed by equation (3)aaAnd (4) limiting:
in the formula (3), TaIn order to limit the rear wheel longitudinal torque sum,the sum of the forward maximum torques of the left wheels,the negative maximum torque sum of the left wheel is shown,the sum of the maximum torque in the forward direction of the right wheel,the calculation formula is shown in formulas (4) and (5) respectively as the negative maximum torque sum of the wheels on the right side:
in the formulas (4) and (5),positive and negative torque capacity limits for the ith left wheel,the positive and negative maximum torque limit values of the jth wheel on the right side are respectively obtained by the feedback of a corresponding motor controller for controlling each wheel;
steering torque difference T for wheelsThe steering torque difference T is analyzed by the equation (6) according to the steering priority rulesaAnd (4) limiting:
in the formula (6), TsThe other variables have the same physical meanings as the wheel steering torque difference after limitation;
3.1.2) calculating the characteristic torque difference
The left and right wheel torques are respectively composed of a straight-going torque and a yaw torque, and the straight-going torque is composed of a wheel longitudinal torque and a wheel TaCalculating to obtain; yaw torque steering torque difference T by wheelssCalculating to obtain; resolving the steering torque difference T according to the wheels determined in the step 2)saThe characteristic torque difference is calculated and used for judging whether the sum of the straight-moving torque and the yaw torque of the left wheel and the right wheel exceeds the torque limit values of the left wheel and the right wheel, and the expression is shown as the formula (7):
in the formula (7), the reaction mixture is,
Tsaresolving a steering torque difference for the wheels determined according to step 2);
the negative limit steering torque difference of the left wheels represents the steering torque difference when the sum of the straight-going torque and the yaw torque of the left wheels is equal to the negative maximum torque limit value when the vehicle turns anticlockwise;
the steering torque difference is the positive limit steering torque difference of the right wheels, and represents the steering torque difference when the sum of the straight-going torque and the yaw torque of the right wheels is equal to the positive maximum torque limit value when the vehicle turns anticlockwise;
the steering torque difference is the positive limit steering torque difference of the left wheel, and represents the steering torque difference when the sum of the straight-going torque and the yaw torque of the left wheel is equal to the positive maximum torque limit value when the vehicle turns clockwise;
the negative limit steering torque difference of the right wheel represents the steering torque difference when the sum of the straight-going torque and the yaw torque of the right wheel is equal to the negative maximum torque limit value when the vehicle turns clockwise;
3.1.3) matching the torque sum of the left wheel and the right wheel according to the characteristic torque difference, wherein the specific distribution mode is as follows:
3.1.3.1) determining the steering torque difference T of the wheelssPositive or negative of (1), if TsIf not less than 0, entering step 3.1.3.2), otherwise entering step 3.1.3.6);
3.1.3.2) determining the steering torque difference T of the wheelssRight positive limit steering torque differenceLeft negative limit steering torque differenceThe minimum value of the three is the steering torque difference T of the wheelssThen go to step 3.1.3.3); if the minimum value is the steering torque difference of the positive limit on the right sideStep 3.1.3.4 is entered); if the minimum value is the left negative limit steering torque differenceStep 3.1.3.5 is entered);
3.1.3.3) calculating the left and right side wheel torques and T according to equation (8)L、TR
The torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.1.3.4) calculate the left and right side wheel torques and according to equation (9):
the torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.1.3.5) calculate the left and right side wheel torques and according to equation (10):
the torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.1.3.6) determining the wheel steering torque difference TsRight negative limit steering torque differenceLeft positive limit steering torque differenceThe maximum value of the three is the steering torque difference T of the wheelssThen go to step 3.1.3.3); if the maximum value is the steering torque difference of the negative limit on the right sideStep 3.1.3.7 is entered); if the maximum value is the left positive limit steering torqueMoment differenceStep 3.1.3.8);
3.1.3.7) calculate the left and right side wheel torques and according to equation (11):
the torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.1.3.8) calculate the left and right side wheel torques and according to equation (12):
the torque and distribution of the left and right wheels are finished, and the step 3.2) is carried out;
3.2) front and back distribution of same-side wheel torque and
the front and back distribution of the torque sum of the wheels on the same side adopts an average distribution mode, the distribution methods of the torque sum of the wheels on the left side and the torque sum of the wheels on the right side are consistent, and the front and back distribution of the torque sum of the wheels on the left side is executed according to the following steps:
3.2.1) left wheel Torque and TLIf left side wheel torque and TLIf not less than 0, entering the step 3.2.2); if left wheel torque and TLIf less than 0, entering step 3.2.7);
3.2.2) Forward maximum Torque Limit in left N wheelsSequencing from small to large to obtain a new sequencek represents the t-thiThe positive torque capacity limit of each wheel is arranged at the k-th position in the positive torque limit sequence of the left wheel; let the number of dispensing times be s, the initial value of s is 1, ifStep 3.2.3) is entered; otherwise, s is 2, go to step 3.2.4);
3.2.3) calculate the left wheel torques according to equation (13):
the torque distribution of the left wheel is completed;
3.2.4) ifStep 3.2.5) is entered, otherwise step 3.2.6) is entered;
3.2.5) calculates the left hand wheel torques according to equation (14):
the torque distribution of the left wheel is completed;
3.2.6) let s be s +1, if s is N +1, then the left wheel torque distribution is completed, otherwise return to step 3.2.4);
3.2.7) negative maximum Torque Limit in left N wheelsSequencing from big to small to obtain a new sequencek represents the r-thiThe negative direction maximum torque limit value of each wheel is arranged at the kth position in the negative direction torque limit value sequence of the left wheels; let the number of dispensing times be s, the initial value of s is 1, ifStep 3.2.8 is entered); otherwise, s is 2, go to step 3.2.9);
3.2.8) calculates the left-hand wheel torques according to equation (15):
the torque distribution of the left wheel is completed;
3.2.9) ifStep 3.2.10) is entered, otherwise step 3.2.11) is entered;
3.2.10) calculates the left-hand wheel torques according to equation (16):
the torque distribution of the left wheel is completed;
3.2.11) let s be s +1, if s is N +1, then the left wheel torque distribution is completed, otherwise return to step 3.2.9);
and performing front-back distribution of the right wheel torque sum by referring to the left side to complete wheel torque distribution.
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