CN110606078B - Multi-shaft distributed electrically-driven vehicle steering control method - Google Patents

Multi-shaft distributed electrically-driven vehicle steering control method Download PDF

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CN110606078B
CN110606078B CN201910885566.XA CN201910885566A CN110606078B CN 110606078 B CN110606078 B CN 110606078B CN 201910885566 A CN201910885566 A CN 201910885566A CN 110606078 B CN110606078 B CN 110606078B
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axle
steering
ith
differential
value
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CN110606078A (en
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李军求
王启贤
孙逢春
孙超
杨森
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Beijing Institute of Technology BIT
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Beijing Institute of Technology BIT
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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, or advanced driver assistance systems for ensuring comfort, stability and safety or drive control systems for propelling or retarding the vehicle
    • B60W30/02—Control of vehicle driving stability
    • 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, or advanced driver assistance systems for ensuring comfort, stability and safety or drive control systems for propelling or retarding the vehicle
    • B60W30/02—Control of vehicle driving stability
    • B60W30/045—Improving turning performance
    • 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
    • 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
    • B60W2050/0002—Automatic control, details of type of controller or control system architecture
    • B60W2050/0008—Feedback, closed loop systems or details of feedback error signal
    • B60W2050/0011—Proportional Integral Differential [PID] controller
    • 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
    • B60W2710/00—Output or target parameters relating to a particular sub-units
    • B60W2710/20—Steering systems

Abstract

The invention discloses a multi-axis distributed electrically-driven vehicle steering control method, which comprises the steps of firstly inputting a steering angle according to a driver11Reference centroid slip angle betarefAnd actual centroid slip angle betaactCalculating a longitudinal reference distance D 'of the mechanical-differential steering axle in the current state by a fuzzy controller, and then inputting a corner by a driver according to the longitudinal reference distance D' and the geometric relation of the vehicle steering axle11Resolving to obtain the reference corner of the differential steering bridgeijrefThen, the lower layer corner tracking controller tracks the reference corner based on the fuzzy PID algorithmijrefAnd calculating to obtain a proper differential torque to drive the differential steering axle to complete steering. The invention fully utilizes the self characteristics of the multi-axle steering vehicle using the steering trapezoid mechanism, determines more reasonable rear axle differential steering corner relation and realizes the operation stability of the multi-axle distributed vehicle front axle machinery and rear axle differential combined steering.

Description

Multi-shaft distributed electrically-driven vehicle steering control method
Technical Field
The invention relates to the technical field of steering system control, in particular to a steering control method of a multi-shaft distributed electrically-driven vehicle.
Technical Field
In-wheel motor drive is one of the solutions for realizing distributed drive of electrically driven armored vehicles. The advantages of the distributed driving form of the hub motor are as follows: the mechanical mechanism of the chassis is greatly simplified, transmission parts such as a transmission, a differential mechanism, a speed reducer, a half shaft, a universal joint and the like in the traditional driving system are omitted, the space is saved, and the transmission efficiency is improved; the driving torque of each wheel can be controlled independently, which provides more freedom for the dynamic control of the vehicle and also makes differential steering possible.
The hub motor distributed driving mode can realize the differential steering function by utilizing the trapezoidal structure on the premise of not increasing a steering power assisting device, obviously improves the maneuverability of a large-scale multi-axle vehicle, and has wide application prospect on a multi-axle large-scale material transportation wheel type armored vehicle.
In addition, simulation research shows that the rear axle differential steering system adopting an ideal Ackerman steering angle relationship can keep the vehicle in the operation stability at low speed, the yaw rate and the mass center side deviation angle can be quickly stabilized at a steady state value, and the lateral acceleration is also in a reasonable range; however, when the vehicle speed is high, the mass center slip angle and the lateral acceleration of the vehicle under the set working condition both exceed a reasonable range, the yaw rate cannot be rapidly stabilized at a steady value, and the vehicle cannot keep good operation stability.
In order to fully utilize the advantages of distributed driving, improve the steering performance of a multi-axle vehicle and reduce the tire abrasion of a non-steering axle, the original non-steering axle can be changed into a differential steering axle by combining a steering trapezoid structure and electric wheel driving torque control on two sides,
aiming at the problems, the invention redesigns and calculates the reference corner, and provides a method for adjusting each steering axle PiCalculating the reference angle of the rear differential steering axle at the relative position of the points, wherein PiThe point is the intersection of the left and right wheel axes of the ith axle.
In general, in order to ensure the reliability of a steering system, a set of traditional mechanical steering system needs to be reserved; therefore, the problem of the combined control of the front axle machinery and the rear axle differential steering of the multi-axle distributed electrically-driven vehicle becomes a technical difficulty.
In order to solve the problems, the invention designs a double-layer controller, and an upper-layer controller calculates a reference rotation angle. Based on adjustment of each steering axle PiControl method of rear differential steering axle reference angle of point relative position, wherein PiThe point is the intersection of the left and right wheel axes of the ith axle. The lower layer controller is a fuzzy PID controller, each differential steering axle uses an independent fuzzy PID corner tracking control module to realize corner tracking, and the driving torque difference value delta T of the left and right steering wheel driving motors of the ith axle is calculatedi；
In particular, the invention makes a detailed concrete implementation description for the combined control of the front axle machinery and the differential steering of the rear axle, and the lower layer controller tracks the reference rotation angle to complete the combined steering control of the front axle machinery and the differential steering of the rear axle.
Disclosure of Invention
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a steering control method of a multi-shaft distributed electrically-driven vehicle,
the vehicle is provided with multiple shafts, and comprises at least one ith steering axle in a first region, at least one ith steering axle in a second region and at least one non-steering axle, wherein the ith steering axles in the first and second regions adopt trapezoid mechanisms which are independent from each other; the ith axle steering axle of the second area is a differential steering axle; driver input corner11An ith axle steer bridge to the at least one first zone;
the ith axle steering axle is an axle which is positioned on the ith axle and is a steering axle, and i is [1, N ];
step 1) obtaining the input corner of the driver11And the actual centroid slip angle betaactAnd calculating the centroid slip angle deviation value eβAnd the rate of change e of the deviation value of the centroid slip anglecβ；
Step 2) calculating a longitudinal reference distance value D 'by an upper layer controller'
By driver input of steering angle11Centroid slip angle deviation value eβRate of change e of deviation value of centroid slip anglecβAs an input variable of the fuzzy controller, outputting a variable longitudinal reference distance value D' through a fuzzy algorithm;
kappa is the average transverse centerline of the non-steer axle;
the intersection points of the left and right wheel axes of one or more ith axle steering axles in the first region are overlapped and are recorded as a first region steering intersection point PmAnd the intersection points of the left and right wheel axes of one or more ith axle steering axles positioned in the second region are overlapped at one point and are recorded as a second region steering intersection point PdFirst region turning intersection point PmAnd a second region turning intersection point PdLocated on the line κ;
the longitudinal reference distance D' is: the left steering wheel axis and P of the Nth axle steering axlemThe distance value from the intersection point of the longitudinal line where the point is located to the straight line kappa;
and 3) calculating the reference rotation angles of the left wheel and the right wheel of the ith axle steering axle by the upper layer controller according to the geometric relation of the steering axle and by using the longitudinal reference distance Dijref。
Step 4), the lower layer controller is a fuzzy PID controller, and each differential steering bridge uses an independent fuzzy PID corner tracking control module to realize corner tracking;
using the deviation e and the change rate e of the deviationcAs input variables of the lower layer controller, outputting variables through a fuzzy algorithm, wherein the output variables comprise a proportion parameter fine adjustment value kpIntegral parameter fine adjustment value kiAnd a differential parameter fine adjustment value kd；
Step 5) utilizing the initial proportional coefficient parameter K of the initial PID controllerp0Initial integral coefficient Ki0Initial differential coefficient Kd0And the fine adjustment value k of the proportional parameterpIntegral parameter fine adjustment value kiAnd a differential parameter fine adjustment value kdCalculating the proportional coefficient K in the PID controller parameterpIntegral coefficient KiDifferential coefficient Kd；
Step 6) the PID controller uses the proportional coefficient K obtained by the calculationpIntegral coefficient KiDifferential coefficient KdAnd calculating the driving torque difference value delta T of the left and right steering wheel driving motors of the ith axle steering axle of the second regioni；
Step 7) driving torque difference Delta T of ith axle steering bridge of the second areaiThe torque integration module input into the whole vehicle model carries out torque integration of corresponding electric wheels, and the driving torque T generated by the left electric wheel and the right electric wheel of the axle for tracking the reference rotation angle at the current moment can be obtainedij。
Preferably, the ith axle steering axle of the first region is mechanically steered, the ith axle steering axle of the second region is differentially steered, and the ith axle steering axle of the second region calculated in the step 3) isReference corner for left and right wheels of bridgeijref。
Preferably, the ith steering axle of the first region comprises a 1 st steering axle and a 2 nd steering axle, and the steering axle ladder mechanisms of the 1 st steering axle and the 2 nd steering axle are mutually coupled; the ith steering axle of the second region comprises a 7 th steering axle and an 8 th steering axle, the steering axle ladder-shaped mechanisms of the 7 th steering axle and the 8 th steering axle are independent of each other, and the reference rotation angles of the left wheel and the right wheel of the 7 th steering axle and the 8 th steering axle are calculated in the step 3)ijref。
Preferably, the method further comprises the step 8) of judging whether anti-integral saturation processing is needed according to the capacity of the driving motor.
Preferably, in the step 4), the turning angle deviation e and the turning angle deviation change rate ecThe calculation process of (2) is as follows:
e＝ijref-ij
ec＝de/dt
in the formula (I), the compound is shown in the specification,ijis the actual turning angle of the ith axle steer axle,ijrefthe reference rotation angle calculated in the step 3);
further, in the step 4), the fuzzy PID controller inputs the variable corner deviation e and the change rate of the corner deviation ecWhose domain of discourse is taken to normalized [ -7,7 [ ]]The linguistic value sets are all { NB, NM, NS, ZO, PS, PM, PB }; system output kp、ki、kdAll are [0,1 ]]The linguistic value sets are { MIN, MIB, MIM, MIS, DEF, MAS, MAM, MAB, MAX }, the membership function of the input variable and the output variable mainly adopts a triangular membership function, and a gravity center method is adopted for defuzzification operation.
Preferably, in the step 5), a final proportionality coefficient K is calculatedpIntegral coefficient KiDifferential coefficient KdThe calculation process of (2) is as follows:
Kp＝Kpmin+kp·(Kpmax-Kpmin)
Ki＝Kimin+ki·(Kimax-Kimin)
Kd＝Kdmin+kd·(Kdmax-Kdmin)
in the formula, Kp∈[Kpmin,Kpmax]、Ki∈[Kimin,Kimax]、Kd∈[Kdmin,Kdmax]；
Wherein the values of the interval endpoints are respectively selected from an initial parameter value Kp0、Ki0、Kd0The value range of 60% to 140% is obtained;
initial default value Kp0、Ki0、Kd0The method is obtained by primarily setting by a Ziegler-Nichols method and combining trial and error adjustment.
Preferably, the anti-integral saturation treatment in the step 8) comprises the following steps:
substep 8.1) of calculating the drive torque T of the left wheel of the ith shaft at the (k-1) th sampling instanti1And right wheel driving torque Ti2；
Substep 8.2) of applying the left wheel drive torque Ti1And right wheel driving torque Ti2Maximum value of the two and maximum driving torque T of the in-wheel motormmaxComparing; if less than the maximum driving torque TmmaxIf yes, connecting an integration link, otherwise, entering a substep 8.3);
substep 8.3) comparing whether e (k) and e (k-1) are both positive or both negative; if the difference is not the same, connecting an integration link, otherwise, entering a substep 8.4);
substep 8.4), the integration element is disconnected.
The invention also relates to a vehicle, characterized in that: the multi-axis distributed vehicle reference corner control method as described above is used.
Preferably, the ladder mechanisms of a plurality of i-th axle steering bridges are all independent from each other, or the ladder mechanisms of a plurality of i-th axle steering bridges are partially coupled to each other and partially independent from each other.
According to the technical scheme, the technical scheme of the invention has the following beneficial effects:
1. the upper controller of the invention adjusts the P of each steering axleiPhase of dotsThe position is designed by fuzzy control to design the reference corner of the rear axle differential steering axle, the self characteristics of the multi-axle steering vehicle using the steering trapezoidal mechanism are fully utilized, the corner relation between the front-drive steering axle and the rear-drive steering axle can be adjusted by adjusting the longitudinal reference distance D ', and the advantages that D' is introduced without directly using D as a control variable are as follows: when the difference between the reference rotation angles of the front and rear bridges is large, the absolute value change range of the D value is [0, + ∞), and the change of the absolute value of the D value in [0, + ∞) can be mapped only in the range of [0, | Ls8|), so that the representation and the processing are convenient.
2. The lower layer controller tracks the reference rotation angle calculated by the upper layer controller, the maneuverability of the multi-axle vehicle can be improved under the low-speed steering working condition, the operation stability of the vehicle can be ensured under the medium-high speed steering working condition, and the reasonable matching of the differential steering of the rear axle and the front axle is ensured according to the actual working condition.
Drawings
FIG. 1 is a multi-axle distributed drive vehicle front axle mechanical and rear axle differential combined steering system of the present invention;
FIG. 2 is a flow chart of a steering control method of the present invention;
FIG. 3 shows a front axle mechanical and rear axle differential combined steering P of the present inventionm、PdA schematic diagram of relative position relationship;
FIG. 4 is a basic block diagram of the lower level controller of the present invention;
FIG. 5 is a logic diagram of the anti-integral saturation processing of the lower level controller of the present invention;
FIG. 6 is another steering configuration to which the present invention is applicable;
Detailed Description
In order to understand the technical content of the present invention, the following detailed description is made with reference to the accompanying drawings:
distributed vehicles in the art mean individual wheel hub motor drives.
The embodiment 1 provides a multi-axle distributed drive vehicle front axle mechanical and rear axle differential combined steering system, as shown in fig. 1, wherein the steering system comprises a traditional mechanical hydraulic power-assisted steering system, a differential steering system, a wheel rotation angle sensor and a vehicle body mass center slip angle sensor.
The 1 st and 2 nd axle steering axles are mechanical steering axles, and the two steering trapezoidal mechanisms are linked, and a steering oil pump drives a hydraulic steering power-assisted system to complete steering according to the torque and corner information input by a driver through a steering wheel;
the Nth axle and the (N-1) th axle which are adjacent to the tail of the vehicle are differential steering axles, preferably N is 8, the differential steering system is applied to the 7 th and 8 th axles, the Nth axle and the (N-1) th axle are subjected to differential steering by the hub motor, and the differential steering adopts a steering trapezoid mechanism; the Nth axle steering axle and the (N-1) th axle steering axle are independent from each other and are not directly and mechanically connected with a steering wheel and steering mechanisms of the front two axles;
the wheel rotation angle sensor is arranged on the left or right wheel of the 1 st axle steering axle and used for measuring the current input angle of the driver11(ii) a Preferably, a left wheel mounted on said 1 st axle.
The vehicle body mass center slip angle sensor is used for measuring the current vehicle body mass center slip angle;
fig. 2 shows a flow schematic of a combined steering control method for the front axle machinery and rear axle differential motion of a multi-axle distributed drive vehicle.
The invention adopts a layered control structure to carry out steering control on the differential steering of a rear axle: upper level control based on adjustment of individual steering axles PiA rear differential steering axle reference angle control method of point relative position; the lower layer control is realized by a lower layer corner tracking controller, and the tracking control of the differential steering axle on the reference corner of the rear differential steering axle is realized based on a fuzzy PID algorithm;
the steps 1) to 3) of the upper layer control are as follows:
step 1), acquiring the input corner of the driver through a sensor11Actual centroid slip angle βactAnd calculating the centroid slip angle deviation value eβAnd the rate of change e of the deviation value of the centroid slip anglecβ；
Further, in the step 1), the centroid slip angle deviation value eβAnd the side of the center of mass thereofRate of change e of deflection angle deviationcβThe calculation process of (a) is as follows;
eβ＝βact-βref
ecβ＝deβ/dt
in the formula, betarefIs a reference centroid slip angle.
Step 2) inputting the turning angle by the driver11Centroid slip angle deviation value eβRate of change e of deviation value of centroid slip anglecβAs an input variable of the fuzzy controller, outputting a variable longitudinal reference distance value D' through a fuzzy algorithm;
further, in the step 2), the definition of the longitudinal reference distance value D' is explained with reference to fig. 3, which is specifically as follows:
the intersection point of the left and right wheel axes of the ith axle steering axle is recorded as Pi；
Kappa is the average transverse centerline of the non-steer axle;
point P of 1 st axle steer axle of the present invention1And point P of 2 nd axle steering bridge2The point where the two points coincide is denoted as a mechanical steering intersection point PmAnd the point is on the straight line κ, the absolute position of which is determined by the input steering angle given by the driver.
In order to minimize the unevenness of the wear of the tires, P of the N-1 st axle is assumedN-1P of Nth axle steering bridgeNThe points also coincide at one point and are denoted as a differential steering intersection point PdWhen N is 8, P of 7 th axle steering bridge78 th axle steering bridge P8Point coincident with PdThe angle of rotation between the differential steering axle and the mechanical steering axle can be represented by P, as shown in FIG. 3d、PmThe relative positions of the two points are determined and Pd、PmBoth points lie on a straight line κ defining a mechanical steering intersection point PdAnd differential steering intersection point PmThe distance between the two points is D:
D＝LPd-LPm
the x axis of the vehicle coordinate system is the coordinate system origin and coincides with the vehicle mass center, and when the vehicle is in a static state on a horizontal road surface, the x axis is parallel to the coordinate axis of the ground pointing to the front of the vehicle;
in the formula LpmIs the mechanical steering intersection point PmDistance from the x-axis of the vehicle coordinate system, LpdIs a differential steering intersection point PdDistance from the x-axis of the vehicle coordinate system.
The longitudinal reference distance D' is defined as: the Nth axle, preferably the 8 th axle, the left steering wheel axis and PmThe distance value from the intersection point of the longitudinal line where the point is located to the straight line kappa;
the advantages of introducing D' without directly using D as a control variable are: when the difference between the reference rotation angles of the front and rear bridges is large, the absolute value change range of the D value is [0, + ∞), and the change of the absolute value of the D value in [0, + ∞) can be mapped only in the range of [0, | Ls8|), so that the representation and the processing are convenient.
Further, in the step 2), the input variable mass center slip angle deviation value e in the fuzzy controllerβThe variation rate ec of the deviation value of the centroid slip angleβAll are [ -7,7 [ ]]Input variable driver input steering angle11Is 0,7 and the domain of discourse of the longitudinal reference distance D' output by the fuzzy system](ii) a Deviation value e of centroid slip angleβAnd rate of change ec of centroid slip angle deviationβThe language value set of (1) is (NB, NM, NS, ZO, PS, PM, PB), and represents (minus big, minus middle, minus small, zero, plus small, plus middle, plus big) in natural language, and the driver inputs the turning angle11And the linguistic value sets of the longitudinal reference distance D' are all { ZO, PS, PM, PB }, and represent { zero, small, middle, large } in the natural language; the input variable and the output variable membership function in the fuzzy controller mainly adopt a form of combining a triangular membership function and a trapezoidal membership function, and a gravity center method is adopted for defuzzification operation.
Step 3), calculating and obtaining the reference rotation angles of the left and right wheels of the Nth steering axle and the (N-1) th steering axle according to the geometric relationship of the steering axlesijref；
Further, in the step 3), the ith axle steer axle left wheel or right wheel reference steering angleijrefThe calculation process is as follows:
Figure GDA0002536626720000061
wherein j-1 represents the ith left wheel, j-2 represents the ith right wheel,
Ltis the wheel track;
Lsiis the distance from the ith axle steering bridge axis to the kappa line;
Lpdis a differential steering intersection point PdDistance from the x-axis of the vehicle coordinate system;
the calculation process is as follows:
Figure GDA0002536626720000062
wherein L ispmIs the mechanical steering intersection point PmDistance from the x-axis of the vehicle coordinate system. The value of which can be inputted by the driver11The following equation is obtained:
Figure GDA0002536626720000063
as shown in fig. 4, the lower layer control step includes steps 4) to 7), specifically as follows:
step 4), the lower layer controller is a fuzzy PID controller, each differential steering bridge uses an independent fuzzy PID corner tracking control module to realize corner tracking, and the corner deviation e and the change rate of the corner deviation e are usedcAs input variables of the lower layer controller, outputting variables through a fuzzy algorithm, wherein the output variables comprise a proportion parameter fine adjustment value kpIntegral parameter fine adjustment value kiAnd a differential parameter fine adjustment value kd；
Further, in the step 4), the turning angle deviation e and the turning angle deviation change rate ecThe calculation process of (2) is as follows:
e＝ijref-ij
ec＝de/dt
in the formula (I), the compound is shown in the specification,ijis the actual turning angle of the ith bridge,ijrefin step 3) ofA calculated reference rotation angle;
further, in the step 4), the fuzzy PID controller inputs the variable corner deviation e and the change rate of the corner deviation ecWhose domain of discourse is taken to normalized [ -7,7 [ ]]The linguistic value sets are all { NB, NM, NS, ZO, PS, PM, PB }; system output kp、ki、kdAll are [0,1 ]]The linguistic value sets are { MIN, MIB, MIM, MIS, DEF, MAS, MAM, MAB, MAX }, the membership function of the input variable and the output variable mainly adopts a triangular membership function, and a gravity center method is adopted for defuzzification operation.
Step 5), utilizing the initial proportional coefficient parameter K of the initial PID controllerp0Initial integral coefficient Ki0Initial differential coefficient Kd0And the fine adjustment value k of the proportional parameterpIntegral parameter fine adjustment value kiAnd a differential parameter fine adjustment value kdCalculating the proportional coefficient K in the PID controller parameterpIntegral coefficient KiDifferential coefficient Kd；
In a further step 5), a final scaling factor K is calculatedpIntegral coefficient KiDifferential coefficient KdThe calculation process of (2) is as follows:
Kp＝Kpmin+kp·(Kpmax-Kpmin)
Ki＝Kimin+ki·(Kimax-Kimin)
Kd＝Kdmin+kd·(Kdmax-Kdmin)
in the formula, Kp∈[Kpmin,Kpmax]、Ki∈[Kimin,Kimax]、Kd∈[Kdmin,Kdmax]；
Wherein the values of the interval endpoints are respectively selected from an initial parameter value Kp0、Ki0、Kd0The value range of 60% to 140% is obtained;
initial default value Kp0、Ki0、Kd0The method is obtained by primarily setting by a Ziegler-Nichols method and combining trial and error adjustment.
Step 6), the PID controller uses the proportional coefficient K obtained by the calculationpIntegral coefficient KiDifferential coefficient KdCalculating the driving torque difference Delta T of the left and right steering wheel driving motors of the ith axleiI.e. the differential torque value;
step 7) differential torque value DeltaT of ith bridgeiThe torque integration module input into the whole vehicle model carries out torque integration of corresponding electric wheels, and the driving torque T generated by the left electric wheel and the right electric wheel of the axle for tracking the reference rotation angle at the current moment can be obtainedij。
And 8) judging whether integral saturation resisting treatment is needed or not according to the capacity of the driving motor.
The integral saturation phenomenon of the PID controller is as follows: when the controller outputs a control quantity in one direction to enable the actuator to reach the limit capacity and enter a saturation region, if the control quantity continues to increase in the direction due to the accumulated deviation quantity of the integral element, the actuator cannot provide larger capacity in the direction; when the deviation value changes the direction, the control value is continuously increased in the original direction due to the effect of the integral link and cannot rapidly exit from the saturation area, so that the actuating mechanism still stays at the limit position in the original direction and cannot rapidly follow the reverse deviation, and the system has a transient out-of-control phenomenon, namely the integral saturation phenomenon. The longer the time to enter the saturation region and the deeper the depth, the longer the time to exit the integral saturation. To avoid this, the PID controller needs to be subjected to anti-integral saturation processing.
As shown in fig. 5, the anti-integral saturation process of the fuzzy PID control module comprises the following steps:
substep 8.1) of calculating the drive torque T of the left wheel of the ith shaft at the (k-1) th sampling instanti1And right wheel driving torque Ti2；
Substep 8.2) of applying the left wheel drive torque Ti1And right wheel driving torque Ti2Maximum value of the two and maximum driving torque T of the in-wheel motormmaxComparing; if less than the maximum driving torque TmmaxIf yes, connecting an integration link, otherwise, entering a substep 8.3);
substep 8.3) comparing whether e (k) and e (k-1) are both positive or both negative; if the difference is not the same, connecting an integration link, otherwise, entering a substep 8.4);
substep 8.4), the integration element is disconnected.
Fig. 6 is a further steering configuration to which the invention is applicable, fig. 6 not being exhaustive, in summary the invention is applicable to steering angle control for a vehicle having the following structure:
the vehicle has multiple axles, including at least one steering axle located at the front axle and at least one steering axle located at the rear axle, the steering axle located at the rear axle being differentially steered; the steering axle adopts a trapezoidal mechanism, and the trapezoidal mechanisms are mutually independent. The trapezoidal mechanisms are independent from each other, namely the steering motions between the two axles do not interfere with each other.
The steering axle ladder mechanism is suitable for wheels of which all the steering axle ladder mechanisms are independent from each other, such as the wheels shown in figures 6(a) - (d), and is also suitable for a structure in which a part of the steering axle ladder mechanisms are mutually connected, such as the structure shown in figure 1(a), and the structure in which the other part of the steering axle ladder mechanisms are independent from each other, such as the structure shown in figure 1 (b).
In which the 1 st and 2 nd axle ladder mechanisms of the embodiment of fig. 1 of the present invention are coupled to each other and may be considered a steer axle.
The multi-axle distributed vehicle steering control method can fully utilize the self characteristics of a multi-axle steering vehicle using a steering trapezoid mechanism to calculate an ideal reference corner, and a lower layer controller tracks the reference corner to complete the combined control of differential steering of a front axle steering axle and a rear axle, so as to realize the differential steering control of the rear axle.

Claims (9)

1. A multi-shaft distributed electric drive vehicle steering control method is characterized in that:
the vehicle has multiple axles, including at least one i-th axle steering axle in the first region and at least one i-th axle rotation in the second regionThe steering axle of the ith shaft in the first area and the ith shaft in the second area adopt trapezoidal mechanisms which are mutually independent; the ith axle steering axle of the second area is a differential steering axle; driver input corner11An ith axle steer bridge to the at least one first zone;
the ith axle steering axle is an axle which is positioned on the ith axle and is a steering axle, and i is [1, N ], and N represents an Nth axle;
step 1) obtaining the input corner of the driver11And the actual centroid slip angle betaactAnd calculating the centroid slip angle deviation value eβAnd the rate of change e of the deviation value of the centroid slip anglecβ；
Step 2), the upper controller calculates a longitudinal reference distance value D';
by driver input of steering angle11Centroid slip angle deviation value eβRate of change e of deviation value of centroid slip anglecβAs an input variable of the fuzzy controller, outputting a variable longitudinal reference distance value D' through a fuzzy algorithm;
kappa is the average transverse centerline of the non-steer axle;
the intersection points of the left and right wheel axes of one or more ith axle steering axles in the first region are overlapped and are recorded as a first region steering intersection point PmAnd the intersection points of the left and right wheel axes of one or more ith axle steering axles positioned in the second region are overlapped at one point and are recorded as a second region steering intersection point PdFirst region turning intersection point PmAnd a second region turning intersection point PdLocated on the line κ;
the longitudinal reference distance D' is: the left steering wheel axis and P of the Nth axle steering axlemThe distance value from the intersection point of the longitudinal line where the point is located to the straight line kappa;
and 3) calculating the reference rotation angles of the left wheel and the right wheel of the ith axle steering axle by the upper layer controller according to the geometric relation of the steering axle and by using the longitudinal reference distance Dijref；
Step 4), the lower layer controller is a fuzzy PID controller, and each differential steering bridge uses an independent fuzzy PID corner tracking control module to realize corner tracking;
using the deviation e and the change rate e of the deviationcAs input variables of the lower layer controller, outputting variables through a fuzzy algorithm, wherein the output variables comprise a proportion parameter fine adjustment value kpIntegral parameter fine adjustment value kiAnd a differential parameter fine adjustment value kd；
Step 5) utilizing the initial proportional coefficient parameter K of the initial PID controllerp0Initial integral coefficient Ki0Initial differential coefficient Kd0And the fine adjustment value k of the proportional parameterpIntegral parameter fine adjustment value kiAnd a differential parameter fine adjustment value kdCalculating the proportional coefficient K in the PID controller parameterpIntegral coefficient KiDifferential coefficient Kd；
Step 6) the PID controller uses the proportional coefficient K obtained by the calculationpIntegral coefficient KiDifferential coefficient KdAnd calculating the driving torque difference value delta T of the left and right steering wheel driving motors of the ith axle steering axle of the second regioni；
Step 7) driving torque difference Delta T of ith axle steering bridge of the second areaiThe torque integration module input into the whole vehicle model carries out torque integration of corresponding electric wheels, and the driving torque T generated by the left electric wheel and the right electric wheel of the axle for tracking the reference rotation angle at the current moment can be obtainedij。
2. The method of claim 1, wherein:
the ith axle steering axle of the first region is in mechanical steering, the ith axle steering axle of the second region is in differential steering, and the left and right wheel reference rotation angles of the ith axle steering axle of the second region are calculated in the step 3)ijref。
3. The method of claim 1, wherein:
the ith axle steering bridge of the first region comprises a 1 st axle steering bridge and a 2 nd axle steering bridge, and the axle steering ladder mechanisms of the 1 st axle steering bridge and the 2 nd axle steering bridge are mutually coupled; the ith axle steering bridge of the second region comprises a 7 th axle steering bridge andthe 8 th steering axle, the 7 th steering axle and the 8 th steering axle have the steering axle ladder-shaped mechanisms which are independent from each other, and the reference rotation angles of the left wheel and the right wheel of the 7 th steering axle and the 8 th steering axle are calculated in the step 3)ijref。
4. A method according to any of claims 1 to 3, characterized by:
and 8) judging whether anti-integral saturation processing is needed according to the capacity of the driving motor.
5. A method according to any of claims 1 to 3, characterized by:
in the step 4), the corner deviation e and the corner deviation change rate ecThe calculation process of (2) is as follows:
e＝ijref-ij
ec＝de/dt
in the formula (I), the compound is shown in the specification,ijis the actual turning angle of the ith axle steer axle,ijrefthe reference rotation angle calculated in the step 3);
further, in the step 4), the fuzzy PID controller inputs the variable corner deviation e and the change rate of the corner deviation ecWhose domain of discourse is taken to normalized [ -7,7 [ ]]The linguistic value sets are all { NB, NM, NS, ZO, PS, PM, PB }; system output kp、ki、kdAll are [0,1 ]]The linguistic value sets are { MIN, MIB, MIM, MIS, DEF, MAS, MAM, MAB, MAX }, the membership function of the input variable and the output variable mainly adopts a triangular membership function, and a gravity center method is adopted for defuzzification operation.
6. A method according to any of claims 1 to 3, characterized by:
in the step 5), the final proportionality coefficient K is calculatedpIntegral coefficient KiDifferential coefficient KdThe calculation process of (2) is as follows:
Kp＝Kpmin+kp·(Kpmax-Kpmin)
Ki＝Kimin+ki·(Kimax-Kimin)
Kd＝Kdmin+kd·(Kdmax-Kdmin)
in the formula, Kp∈[Kpmin,Kpmax]、Ki∈[Kimin,Kimax]、Kd∈[Kdmin,Kdmax]；
Wherein the values of the interval endpoints are respectively selected from an initial parameter value Kp0、Ki0、Kd0The value range of 60% to 140% is obtained;
initial default value Kp0、Ki0、Kd0The method is obtained by primarily setting by a Ziegler-Nichols method and combining trial and error adjustment.
7. The method of claim 4, wherein:
the anti-integral saturation treatment in the step 8) comprises the following steps:
substep 8.1) of calculating the drive torque T of the left wheel of the ith shaft at the (k-1) th sampling instanti1And right wheel driving torque Ti2；
Substep 8.2) of applying the left wheel drive torque Ti1And right wheel driving torque Ti2Maximum value of the two and maximum driving torque T of the in-wheel motormmaxComparing; if less than the maximum driving torque TmmaxIf yes, connecting an integration link, otherwise, entering a substep 8.3);
substep 8.3) comparing whether e (k) and e (k-1) are both positive or both negative; if the difference is not the same, connecting an integration link, otherwise, entering a substep 8.4);
substep 8.4), the integration element is disconnected.
8. A vehicle, characterized in that: use of a method according to any one of claims 1 to 7.
9. The vehicle of claim 8, characterized in that: the trapezoid mechanisms of the ith axle steering bridges are all independent from each other, or the trapezoid mechanisms of the ith axle steering bridges are partially connected with each other and partially independent from each other.
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