CN108275200B - Composite energy-saving power-assisted steering device of electric wheel driven automobile and control method thereof - Google Patents

Composite energy-saving power-assisted steering device of electric wheel driven automobile and control method thereof Download PDF

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CN108275200B
CN108275200B CN201810217474.XA CN201810217474A CN108275200B CN 108275200 B CN108275200 B CN 108275200B CN 201810217474 A CN201810217474 A CN 201810217474A CN 108275200 B CN108275200 B CN 108275200B
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steering
wheel
power
torque
motor
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CN108275200A (en
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王军年
罗正
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Jilin University
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Jilin University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D5/00—Power-assisted or power-driven steering
    • B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
    • B62D5/0418—Electric motor acting on road wheel carriers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L15/00—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles
    • B60L15/20—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles for control of the vehicle or its driving motor to achieve a desired performance, e.g. speed, torque, programmed variation of speed
    • B60L15/2036—Electric differentials, e.g. for supporting steering vehicles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D5/00—Power-assisted or power-driven steering
    • B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
    • B62D5/0457—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear characterised by control features of the drive means as such
    • B62D5/046—Controlling the motor
    • B62D5/0463—Controlling the motor calculating assisting torque from the motor based on driver input
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L2220/00—Electrical machine types; Structures or applications thereof
    • B60L2220/40—Electrical machine applications
    • B60L2220/44—Wheel Hub motors, i.e. integrated in the wheel hub
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/72—Electric energy management in electromobility

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  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Power Engineering (AREA)
  • Steering Control In Accordance With Driving Conditions (AREA)
  • Power Steering Mechanism (AREA)

Abstract

The invention discloses a composite energy-saving power steering device of an electric wheel driven automobile, which comprises: the steering system comprises a steering wheel, a steering shaft, a steering wheel torque sensor, a steering wheel corner sensor, a power-assisted motor, a worm gear speed reducing mechanism, a gear rack steering device, a left steering tie rod, a right steering tie rod, a left front wheel, a left hub motor, a right front wheel, a right hub motor, a main coordination control module, a differential power-assisted steering control module, a slip rate control module and an electric power-assisted steering control module. The invention also discloses a control method of the electric wheel drive automobile composite energy-saving power steering device, which comprises the following steps: and collecting data, and entering an energy-saving steering mode, a safe steering mode and a failure protection mode according to the monitoring data.

Description

Composite energy-saving power-assisted steering device of electric wheel driven automobile and control method thereof
Technical Field
The invention relates to the technical field of automobiles, in particular to a composite energy-saving power-assisted steering device of an electric wheel driven automobile and a control method thereof.
Background
The electric wheel independent driving automobile omits a transmission system of the traditional automobile, and the power is directly provided by a hub motor or a wheel side motor arranged in the wheel or at the wheel side to drive the wheel. The electric wheel driving automobile has simple structure, saves space and is easier to realize advanced chassis dynamics integrated control.
An Electric Power Steering (EPS) system utilizes a power-assisted motor to realize power assistance, can realize speed-dependent adjustable power assistance, and is the most widely applied power-assisted system of a traditional automobile or an electric automobile at present. However, the electric power steering system also has the self disadvantages that the moment of inertia of the accelerator and decelerator of the power-assisted motor can reduce the dynamic response quality when the large torque is required for assistance, and the problems of hysteresis and overshoot are solved. In addition, energy conservation is an important research focus for electric vehicles at the present stage. In addition, when the steering motor fails, the steering system cannot provide reliable power assistance, and particularly for large vehicles, the steering system has great potential safety hazards.
Differential power steering (Differential Drive Assist Steering, DDAS) technology is a new technology for steering power based on an electric wheel independent driving automobile platform. The differential power-assisted steering fully utilizes the characteristic that the torque of each wheel of the electric wheel driven automobile can be independently controlled, and utilizes the torque difference generated by different torques of the left and right front wheels to realize the power-assisted steering. The differential power-assisted steering system omits a power-assisted output part of the traditional power-assisted steering system, and only needs to be integrated in the original whole vehicle driving controller in a software mode, so that the structure is compact, the occupied space is small, the cost and the vehicle quality are reduced, the differential power-assisted steering can reduce the turning resistance while assisting the power, and meanwhile, the driving motors of the two front wheels work at the working point with higher efficiency, so that the energy consumption can be saved to a certain extent, and the driving mileage of the electric vehicle is improved. However, when the differential power steering is used as an indirect power steering mode and needs large power torque, the performance and quality of working condition power assistance such as in-situ steering are poor, in addition, the noise mechanism caused by uneven road surface also can influence the stability of the power torque output of the DDAS system, and compared with the EPS system, the DDAS system can increase the tire abrasion to a certain extent during working.
Patent application 2016111665807 proposes a multimode steering system and a control method of an electric wheel driven automobile, wherein the system fixedly connects a rotor of an electric power-assisted motor with a steering shaft coaxially, increases steering inertia of the steering shaft, reduces dynamic response quality when a large torque power-assisted requirement, and has response problems of hysteresis and overshoot. Meanwhile, a speed reducing mechanism is not arranged, the size of a needed power-assisted motor is increased, and in addition, the system does not consider the problem of energy consumption of a steering system.
Disclosure of Invention
The invention designs and develops a composite energy-saving power steering device of an electric wheel driven automobile, and the aims of reducing the turning resistance and optimizing the working point of a motor and reducing the energy consumption of the whole system are fulfilled by combining differential power steering and an electric power steering system.
The invention designs and develops a control method of a composite energy-saving power steering device of an electric wheel driven automobile, and the control method is used for realizing coordination control of differential power steering and electric power steering, thereby effectively reducing the total energy consumption of the automobile during steering and achieving the aim of solid line energy saving.
The technical scheme provided by the invention is as follows:
an electric wheel drive automotive composite energy-saving power steering device comprising:
a steering wheel;
a steering shaft connected to the center of the steering wheel, and on which a steering angle sensor and a torque sensor are mounted;
the output end of the speed reducing mechanism is connected with the steering shaft;
the power-assisted motor is connected with the input end of the speed reducing mechanism;
a steering gear connected to the lower end of the steering shaft, and connected to wheels at both ends of the steering gear through tie rods, respectively;
the electronic control device is electrically connected with the rotation angle sensor, the torque sensor and the whole vehicle CAN bus;
the electronic control device comprises a main coordination control device, an electric power steering control device, a differential power steering control device and a slip ratio control device;
the electric power steering control is electrically connected with the power motor;
the slip ratio control device is electrically connected with an in-wheel motor in the wheel.
Preferably, the speed reducing mechanism is provided in a worm and gear structure.
Preferably, the steering gear is a rack-and-pinion steering gear;
wherein the steering gear of the rack-and-pinion steering gear is connected with the lower end of the steering shaft; and
the rack of the rack-and-pinion steering gear is in meshed transmission with the steering gear, and the rack is connected with the tie rod.
Preferably, the tie rod is connected to the knuckle of the wheel by a ball stud.
The control method of the composite energy-saving power-assisted steering device of the electric wheel drive automobile, which uses the steering device, is characterized by comprising the following steps:
step one, judging a power-assisted motor, and if the power-assisted motor fails, enabling the electronic control device to enter a failure protection control mode; if the power-assisted motor operates normally, data acquisition is carried outSet comprising yaw rate omega r Vehicle speed v, centroid slip angle beta, centroid slip angular velocityAnd road adhesion coefficient μ;
step two, determining a stable domain boundary parameter value B according to the road adhesion coefficient mu 1 、B 2 And according to the stable domain boundary parameter value B 1 、B 2 Phase plane stability domain calculations are performed ifIf yes, the electronic control device enters into energy-saving steering mode, if +.>When the electronic control device enters a safe steering mode;
wherein the energy-saving steering mode includes:
monitoring steering wheel torque T sw Vehicle speed v, steering wheel angle delta sw Total driving demand torque T g The method comprises the steps of carrying out a first treatment on the surface of the According to the steering wheel angle delta sw And different initial values of the differential power steering working weight coefficient value k are obtained through a first optimization objective function, and the optimized initial value k is obtained through data arrangement c The method comprises the steps of carrying out a first treatment on the surface of the Wherein the optimization process minimizes the value of the first optimization objective function;
the first optimization objective function is
Wherein T is 1 The torque is output for the motor of the left front wheel; n is n 1 The output rotating speed of the left front wheel; t (T) 2 The torque is output for the motor of the right front wheel; n is n 2 The output rotating speed of the right front wheel; a, a 1 、a 2 、a 3 Respectively the weight coefficients; t (T) t The output torque of the power-assisted motor is; n is n t The output rotating speed of the power-assisted motor; a, a 1 、a 2 、a 3 Respectively the weight coefficients; lambda (lambda) 1 ，λ 2 ，λ t The efficiency of the left front wheel motor, the right front wheel motor and the power-assisted motor are respectively;
according to the initial value k c Optimizing the working weight coefficient value k through a second optimization objective function; wherein the optimizing process minimizes the value of the second optimizing objective function;
the second optimization objective function is
The constraint equation of the working weight coefficient value k is c 1 k c ≤k≤c 2 k c ；
Wherein T is g The main coordination control module calculates the total driving moment T according to the difference value of the vehicle speed and the target vehicle speed z Front wheel differential torque, b, required for assistance determined by the differential power steering control module 1 ，b 2 ，b t Respectively corresponding optimized weight coefficients, c 1 And c 2 Respectively optimizing boundary coefficients;
determining front wheel differential moment T z And a control voltage signal required by the booster motor, and determining the final output front wheel booster demand differential moment delta T according to the working weight coefficient k z Total driving torque T g The differential power-assisted steering controller outputs the required yaw moment to be distributed to the two front wheels, and the yaw moment is corrected through the wheel slip rate control device, and the power-assisted motor outputs the power-assisted moment to act on the steering wheel through the steering system transmission mechanism.
Preferably, the safe steering mode includes:
monitoring steering wheel torque T sw Vehicle speed v, steering wheel angle delta sw According to the steering wheel angle delta sw Obtaining ideal steering wheel torque T from vehicle speed v swd ；
Setting the steering wheel torque T sw And the ideal steering wheel torque T swd Is input into electric powerThe steering control device calculates a control voltage signal of the booster motor through fuzzy PID, and transmits the voltage signal to the booster motor to output booster torque.
Preferably, the fail-safe steering mode includes:
monitoring steering wheel torque T sw Vehicle speed v, steering wheel angle delta sw And a total driving demand torque T g According to the steering wheel angle delta sw Obtaining ideal steering wheel torque T from vehicle speed v swd ；
Setting the steering wheel torque T sw And the ideal steering wheel torque T swd The difference value of the (a) is input into a differential power steering control device, and the differential moment value T of the required front wheel is calculated through PID z Calculating moment values required by the left and right front wheels;
and respectively inputting the calculated required torque values of the left front wheel and the right front wheel into a slip ratio control device of each wheel for correction, and outputting the corrected required torque values of the front wheels to an in-wheel motor for control.
It is preferred that the composition of the present invention,
determining front wheel differential moment T z Outputting through a differential power-assisted steering control device, wherein the differential power-assisted steering control device adopts a PID controller; and
the control voltage signal required by the power-assisted motor is determined and output through an electric power-assisted steering control device, and the electric power-assisted steering control device adopts a fuzzy PID controller.
Preferably, the front wheel differential moment DeltaT z The calculation is performed by the following formula:
wherein T is i (i=1, 2) is the left front wheel and the right front wheel output torque, respectively.
Preferably, the correction process of the wheel slip rate control device includes:
calculating the slip rate of each wheel in real time, simultaneously estimating the optimal slip rate of the wheel at each moment in real time, and when the actual slip rate of the wheel is larger than the optimal slip rate of the wheel at the moment, starting the slip rate control device to work, and calculating the output slip rate control correction moment T through a PID control algorithm xi (i=1, 2), the corrected wheel demand torque T si (i=1, 2) the calculation formula is T si ＝T i +T xi 。
Compared with the prior art, the invention has the following beneficial effects:
1. the energy consumption is low; the composite energy-saving power-assisted steering system of the electric wheel driven automobile can generate steering power through the left and right driving torque difference of the front wheels, reduces turning resistance while assisting the power, and enables the front wheels to work at a high-efficiency point of a motor, so that compared with a pure electric power-assisted steering technology, the energy consumption of the whole automobile steering system and a driving system is effectively reduced; in addition, compared with a simple differential power steering technology, the tire abrasion can be reduced as much as possible, the quick response of a steering system is improved, and the road feel of a driver is improved;
2. the reliability is high; the electric power steering system and the differential power steering system contained in the electric wheel drive automobile composite energy-saving power steering system can work independently and normally, and when any one of the systems fails, the other power steering system can realize power assistance normally, so that the reliability of the whole automobile is ensured;
3. the safety is good; the composite energy-saving power-assisted steering system of the electric wheel driven automobile disclosed by the invention adopts differential power-assisted steering and electric power-assisted steering to work together in the stable region of a phase plane so as to realize energy saving. When the vehicle state is in the phase plane unstable region, the differential power steering is turned off, the attached tires are all reserved for the stability control system of the whole vehicle, and meanwhile the instability of the whole vehicle caused by positive additional yaw moment generated by the differential power steering power is avoided.
Drawings
Fig. 1 is a schematic diagram of a composite energy-saving power steering system for an electric wheel drive vehicle according to the present invention.
Fig. 2 is a main flow chart of a control method of the electric wheel drive automobile composite energy-saving power steering system.
Fig. 3 is a sub-flowchart of an energy-saving steering mode of a control method of an electric wheel drive vehicle composite energy-saving power steering system according to the present invention.
Fig. 4 is an ideal steering wheel torque diagram of a control method of an electric wheel drive vehicle composite energy-saving power steering system according to the present invention.
Fig. 5 is a sub-flowchart of a safe steering mode of a control method of a composite energy-saving power steering system of an electric wheel drive vehicle according to the present invention.
Fig. 6 is a sub-flowchart of a fail-safe steering mode of a control method of a hybrid power steering system for an electric wheel drive vehicle according to the present invention.
Detailed Description
The present invention is described in further detail below with reference to the drawings to enable those skilled in the art to practice the invention by referring to the description.
It will be understood that terms, such as "having," "including," and "comprising," as used herein, do not preclude the presence or addition of one or more other elements or groups thereof.
As shown in fig. 1, the composite energy-saving power steering device for the electric wheel driven automobile disclosed by the invention can realize the purpose of reducing the energy consumption of the whole system by reducing the turning resistance and optimizing the working point of a motor through the combination of the differential power steering and the electric power steering system, simultaneously reduces the steering inertia of the electric power steering system, improves the dynamic response quality, and simultaneously can respectively serve as redundant backup of the other parts of the differential power steering and the electric power steering, thereby improving the reliability of the whole automobile; the steering apparatus main body includes a steering wheel 100, a steering shaft 150, a steering wheel torque sensor 200, a steering wheel angle sensor 250, a power-assisted motor 400, a worm reduction mechanism 300, a rack-and-pinion steering gear 630, a left tie rod 610, a right tie rod 620, a left front wheel 600, a left hub motor 500, a right front wheel 650, a right hub motor 550, a main coordination control module 710, a differential power-assisted steering control module 900, a slip ratio control module 950, and an electric power-assisted steering control module 800.
The steering wheel 100 is centrally connected to a steering shaft 150, a steering wheel rotation angle sensor 200 and a steering wheel torque sensor 250 are mounted on the steering shaft 150, and at the same time, the steering shaft 150 is connected to an output end of a worm gear reduction mechanism 300, and an output end of a booster motor 400 is connected to an input end of the worm gear reduction mechanism 300. The steering shaft 150 has a lower end connected to a steering gear of the rack-and-pinion steering gear 630, the steering gear of the rack-and-pinion steering gear 630 is engaged with a rack of the rack-and-pinion steering gear 630, both left and right ends of the rack-and-pinion steering gear 630 are respectively connected to a left tie rod 610 and a right tie rod 620, the other end of the left tie rod 610 is connected to a knuckle of the left front wheel 600 through a ball stud, and the other end of the right tie rod 620 is connected to a knuckle of the right front wheel 650 through a ball stud. The left front wheel 600 has the left hub motor 500 mounted thereon, and the right front wheel 650 has the right hub motor 550 mounted thereon.
The main coordination control module 710, the differential power steering control module 900, the electric power steering control module 800 and the slip ratio control module 950 form a control unit (ECU) 700 of the composite energy-saving power steering system, the control unit 700 is connected with a CAN bus of the whole vehicle, and the vehicle speed v, the centroid slip angle beta, the road surface adhesion coefficient mu and the total required driving torque T in the CAN bus CAN be read g . Simultaneously, the steering wheel torque T measured by the steering wheel angle sensor 200 and the steering wheel torque sensor 250 can be read sw Rotation angle delta sw . Meanwhile, the electric power steering control module 800 in the control unit 700 may output a control command to the power-assisted motor 400, the differential power steering control module 900 in the control unit 700 may output a control command to the slip ratio control module 950, and the slip ratio control module 950 may output a motor control command to the left and right front wheel hub motors 500 and 550.
In another embodiment, the main coordination control module 710, the electric power steering control module 800, the differential power steering control module 900, and the slip ratio control module 950 in the control unit (ECU) 700 may be separately provided as physical controllers, may be integrated into one physical controller, and may even be integrated into the vehicle driving controller.
As shown in fig. 2, the invention further provides a control method of a composite energy-saving power steering system of an electric wheel driven automobile, the control method is used for realizing coordination control of differential power steering and electric power steering, effectively reducing total energy consumption of the automobile during steering, achieving the aim of solid line energy saving, improving dynamic response quality during power steering, realizing failure protection when one of the systems fails, and improving the safety of the whole automobile, and the method comprises the following steps:
step 1: self-checking the system; the main coordination control module 710 reads a self-checking signal of the power-assisted motor 400, if the power-assisted motor 400 fails, step 5 is performed, and if not, step 2 is performed;
step 2: obtaining the yaw rate omega of the whole vehicle by a yaw rate sensor r The signal, get the vehicle speed signal v of the whole car by the vehicle speed sensor or vehicle speed observer, get the centroid cornering angle beta and centroid cornering angular velocity by the centroid cornering angle observerThe signal, observe by the adhesion coefficient observer of the road surface and get the adhesion coefficient μ of road surface in real time;
step 3: obtaining a stable domain boundary parameter value B according to the road adhesion coefficient mu table 1 、B 2 ；
Stability domain boundary parameter value B 1 、B 2 Derived fromThe phase plane stability domain is divided, and the boundary is divided by adopting a double-line method, namely, the stability domain boundary is divided by adopting two parallel straight lines. Namely said->The phase plane stability domain may be represented by the following formula:
wherein B is 1 And B 2 The stability domain boundary parameters are mainly related to road surface adhesion coefficients, different road surface adhesion coefficients are given, and the values of the boundary coefficients under the adhesion coefficients are obtained through a computer simulation or real vehicle calibration method; in actual use, will B 1 、B 2 The data table is prepared and stored in the ECU in advance, and the data table is directly checked when in use; as shown in Table 1B 1 、B 2 And a parameter table.
TABLE 1B 1 、B 2 Parameter meter
Road adhesion coefficient B 1 B 2
0.8≤μ≤1 0.283 0.175
0.6≤μ＜0.8 0.343 0.167
0.4≤μ＜0.6 0.378 0.152
0.3≤μ＜0.4 0.454 0.150
0.2≤μ＜0.3 0.624 0.138
μ＜0.2 0.938 0.03
Step 4. CalculatedAnd judge +.>Whether or not it is: if yes, the system enters an energy-saving steering mode and jumps to the step 6; if not, the system enters a safe steering mode and jumps to step 6.
Step 5: the system enters fail-safe steering mode.
Step 6: the steering mode decision is completed.
As shown in fig. 3, in another embodiment, the energy saving steering mode includes the steps of:
step 1: reading steering wheel torque T sw Vehicle speed v, steering wheel angle delta sw Total driving demand torque T g ；
Step 2: according to steering angle delta sw The vehicle speed v is checked in real time to obtain the initial value k of the differential power steering working weight coefficient value k c ；
In another embodiment, the initial value k c The working weight coefficient k of the differential power-assisted steering is obtained by off-line simulation optimization, the working conditions of the vehicle respectively running at a fixed speed and a fixed steering wheel angle are calculated in a simulation manner in the whole vehicle dynamics simulation software such as Simulink, carsim and the like c Performing the whole processLocal optimization; in the present embodiment, k c The optimizing range is 0.ltoreq.k c And (3) the objective function of offline optimization is as follows:
wherein T is 1 The torque is output for the motor of the left front wheel; n is n 1 The output rotating speed of the left front wheel; t (T) 2 The torque is output for the motor of the right front wheel; n is n 2 The output rotating speed of the right front wheel; a, a 1 、a 2 、a 3 Respectively the weight coefficients; t (T) t The output torque of the power-assisted motor is; n is n t The output rotating speed of the power-assisted motor; a, a 1 、a 2 、a 3 Respectively the weight coefficients; lambda (lambda) 1 ，λ 2 ，λ t The efficiency of the left front wheel motor, the right front wheel motor and the booster motor are respectively.
The smaller the objective function value J is, the better the energy-saving effect is, the purpose of the initial value obtained by offline optimization is to provide an optimizing initial value for the next online optimization, so that the online optimization speed can be obviously improved, the method has obvious engineering significance, and the offline optimized differential power steering working weight coefficient k of the working conditions of each vehicle speed and fixed steering wheel angle is made into a data table, stored in an ECU and directly called when in use; as shown in table 2, when the actual steering wheel angle and the specific vehicle speed value are not in the table, the interpolation method is adopted for value taking.
TABLE 2k c Value table
Step 3: initial value k of differential power steering operation weight coefficient value k based on table lookup c Performing online optimization, k c The working weight coefficient of the differential power steering is obtained by real-time on-line optimizing for optimizing the starting point;
the purpose of on-line optimizing is to calculate the rotation of the current instant moment on line through an optimizing algorithmThe differential power-assisted steering operation weight coefficient value obtained in the last step is added to the differential power-assisted steering operation weight coefficient value when the system power is minimum c As a starting point of optimizing an optimization algorithm, the optimizing speed can be greatly improved, and the requirement of control instantaneity is met.
The objective function of online optimization is as follows:
wherein T is g The main coordination control module calculates the total driving moment T according to the difference value of the vehicle speed and the target vehicle speed z Front wheel differential torque, b, required for assistance determined by the differential power steering control module 1 ，b 2 ，b t Respectively corresponding optimized weight coefficients. The smaller the objective function value, the better the explanatory effect. The constraint equation for the optimization variable k is as follows: c 1 k c ≤k≤c 2 k c The method comprises the steps of carrying out a first treatment on the surface of the Wherein, c 1 And c 2 The specific value of the optimized boundary coefficient is determined according to the power and torque characteristics of the booster motor and the hub or wheel side motor of the front wheel, and the specific calibration is carried out by a real vehicle experiment; in the present embodiment, c 1 Typically, the value of c is 0.8 2 Typically a value of 1.2 is available.
In another embodiment, a sequence least squares method is selected as the optimization algorithm for the online optimization.
It should be noted that, the torque optimizing and distributing method selected by the present invention is a sequence quadratic programming method, but the torque optimizing and distributing method is not limited to this method, and other optimizing and solving methods can be selected as required, which does not limit the scope of protection of the claims of the present invention.
Step 4: front wheel differential moment T required by power output of differential power steering control module z The method comprises the steps of carrying out a first treatment on the surface of the The electric power steering control module outputs a control voltage signal required by the power motor 400;
in another embodiment, the differential power steering control module employs steeringA disc torque direct control strategy; the control strategy is specifically to measure the actual steering wheel torque T by means of a steering wheel torque sensor 200 sw At the same time, the vehicle speed v and the steering wheel angle delta on the CAN bus are obtained sw Reading the signal and the MAP of ideal steering wheel torque stored in the controller to obtain the ideal steering wheel torque T at the moment swd According to the actual steering wheel torque T sw With ideal steering wheel torque T swd The difference between the left wheel torque and the right wheel torque is calculated so as to enable the actual steering wheel torque to track the ideal steering wheel torque, thereby achieving the purpose of reducing the steering hand force.
As shown in fig. 4, the ideal steering wheel torque MAP determines a driver-preference steering wheel torque, that is, an ideal steering wheel torque T, in accordance with the results of numerous companies and research institutions that have conducted extensive experiments before, in combination with the vehicle speed and the steering wheel angle swd The ideal steering wheel torque MAP data is stored in the ECU in advance, and the ideal steering wheel torque MAP data can be directly checked in use.
In another embodiment, the differential power steering controller is selected as a PID controller, and the controller input is the actual steering wheel torque T sw And ideal steering wheel torque T swd Is output as the differential moment T of the front wheel required by assistance z The method comprises the steps of carrying out a first treatment on the surface of the Output differential moment T z I.e. calculated from the following formula:
in the formula, e (T) =t sw -T swd ，k p 、k i 、k d Parameters are controlled for the PID controller.
In another embodiment, the differential power steering controller of the control method of the electric wheel drive automobile composite energy-saving power steering system is not limited to the PID controller, and other types of controllers can be designed according to requirements, which does not limit the protection scope of the claims of the invention.
In another embodiment, the electric power steering controller also employs a steeringA direct torque control strategy to disk; the control strategy is in particular the measurement of the actual steering wheel torque T by means of a steering wheel torque sensor sw At the same time, the vehicle speed v and the steering wheel angle delta on the CAN bus are obtained sw Signal, and ideal steering wheel torque MAP is read to obtain ideal steering wheel torque T at that time swd Outputting a voltage signal of the booster motor 400 through the controller so that the actual steering wheel torque tracks the ideal steering wheel torque in real time; in the present embodiment, the ideal steering wheel torque MAP here coincides with the ideal steering wheel torque MAP employed by the differential power steering controller.
In another embodiment, the electric power steering controller also employs a fuzzy PID controller; the fuzzy PID is composed of a PID controller and a fuzzy controller, and the fuzzy controller corrects three parameters K of the PID controller in real time p 、K i 、K d The method comprises the steps of carrying out a first treatment on the surface of the The input of the fuzzy controller is the actual steering wheel torque T sw And ideal steering wheel torque T swd The difference e and the difference change rate de/dt of (2) are output as K p 、K i 、K d And inputting the correction value to the PID controller; the argument of the difference e is { -5,5}, the ambiguity set is { Negative Big (NB), negative Medium (NM), negative Small (NS), zero (ZO), positive Small (PS), median (PM), positive Big (PB) }, the argument of the difference change rate de/dt is { -10,10}, the ambiguity set is { Negative Big (NB), negative Medium (NM), negative Small (NS), zero (ZO), positive Small (PS), median (PM), positive Big (PB) }. Output control parameter K p 、K i 、K d The arguments of (a) are {0,3}, and the ambiguity sets are { Zero (ZO), small (PS), medium (PM), large (PB) }; the fuzzy control rules are shown in table 3.
Table 3 fuzzy control rule table of fuzzy PID controller
The input of the fuzzy PID controller is the actual steering wheel torque T sw And ideal steering wheel torque T swd The output is a control voltage signal of the booster motor 400, and the output control voltage is calculated by the following formula:
in the formula, e (T) =t sw -T swd ，K p 、K i 、K d The value of (2) is output in real time by the fuzzy controller.
Step 5: according to the working weight coefficient k of the differential power-assisted steering obtained by on-line optimization, determining and outputting the final output front wheel power-assisted demand differential moment delta T z Total driving torque T g The differential power steering controller outputs the required yaw moment to be distributed to the two front wheels.
Front wheel differential torque Δt of assistance actually output to torque distribution controller z The obtained differential power steering operation weight coefficient k, namely delta T is combined z Calculated from the following formula:
ΔT z ＝kT z ；
total driving torque T g The differential power steering controller outputs the required yaw moment to be distributed to the two front wheels;
the following formula is shown:
wherein T is i (i=1, 2) is the left front wheel and the right front wheel output torque, respectively.
Step 6: the demand torque of the 2 wheels is corrected by the wheel slip rate control module 950, and the corrected demand torque T of the wheels is corrected si (i=1, 2) control commands are sent to the controllers of the in-wheel motors in the respective wheels.
In another embodiment, the specific correction method is as follows: based on measurements or estimations to obtain vehicle correlationThe state parameter calculates the slip rate of each wheel in real time, simultaneously estimates the optimal slip rate of the wheel at each moment in real time, inputs the difference between the slip rate and the optimal slip rate into a PID control algorithm, and when the actual slip rate of the wheel is larger than the optimal slip rate of the wheel at the moment, the slip rate control module 950 starts to work, and the PID control algorithm calculates the output slip rate control correction moment T xi (i=1, 2), the correction torque is directly related to the initial wheel demand torque T i Superimposed, i.e. corrected, wheel demand torque T si (i=1, 2) the calculation formula is as follows: t (T) si ＝T i +T xi The method comprises the steps of carrying out a first treatment on the surface of the In this embodiment, the optimal slip ratio control selected by the slip ratio control method according to the present invention is not limited to the application of such a slip ratio control method, but other slip ratio control methods may be selected as required, which does not limit the scope of protection of the claims of the present invention.
Step 7: the assist motor 400 outputs an assist torque to act on the steering wheel 100 via a steering system transmission mechanism.
In another embodiment, as shown in fig. 5, the safe steering mode includes the steps of:
step 1: reading steering wheel torque T sw Vehicle speed v, steering wheel angle delta sw A signal;
step 2: according to steering wheel angle delta sw Ideal steering wheel torque T for reading vehicle speed v table swd ；
Step 3: steering wheel torque T sw And ideal steering wheel torque T swd The difference value of the first and second signals is input into an electric power steering control module;
step 4: the electric power steering control module calculates a control voltage signal of the power motor 400 by adopting a fuzzy PID control algorithm and transmits the voltage signal to the power motor;
step 5: the assist motor 400 outputs an assist torque;
in another embodiment, as shown in fig. 6, the fail-safe steering mode includes the steps of:
step 1: reading steering wheel torque T sw Vehicle speed v, steering wheel angle delta sw Total driving demand torque T g A signal;
step 2: according to steering wheel angle delta sw Ideal steering wheel torque T for reading vehicle speed v table swd ；
Step 3: steering wheel torque T sw And ideal steering wheel torque T swd The difference value of the first and second signals is input into a differential power steering control module;
the differential power steering control module in this step adopts a PID control algorithm, and the PID control algorithm of the differential power steering control module in the same-steering energy-saving mode is not described in detail herein.
Step 4: the differential power steering control module calculates a differential torque value T of the required front wheels z And calculating moment values required by the left and right front wheels according to the following formula;
step 5: the calculated required torque values of the left front wheel and the right front wheel are respectively input into a slip ratio control module 950 of each wheel for correction;
step 6: the corrected demand torque values of the left and right front wheels 600 and 650 are output to the motor controllers of the hub motors 500 and 550 of the left and right front wheels.
Although embodiments of the present invention have been disclosed above, it is not limited to the details and embodiments shown and described, it is well suited to various fields of use for which the invention would be readily apparent to those skilled in the art, and accordingly, the invention is not limited to the specific details and illustrations shown and described herein, without departing from the general concepts defined in the claims and their equivalents.

Claims (9)

1. The control method of the composite energy-saving power-assisted steering device of the electric wheel drive automobile is characterized in that the steering device comprises the following steps:
a steering wheel;
a steering shaft connected to the center of the steering wheel, and on which a steering angle sensor and a torque sensor are mounted;
the output end of the speed reducing mechanism is connected with the steering shaft;
the power-assisted motor is connected with the input end of the speed reducing mechanism;
a steering gear connected to the lower end of the steering shaft, and connected to wheels at both ends of the steering gear through tie rods, respectively;
the electronic control device is electrically connected with the rotation angle sensor, the torque sensor and the whole vehicle CAN bus;
the electronic control device comprises a main coordination control device, an electric power steering control device, a differential power steering control device and a slip ratio control device;
the electric power steering control device is electrically connected with the power motor;
the slip rate control device is electrically connected with a hub motor in the wheel;
the control method comprises the following steps:
step one, judging a power-assisted motor, and if the power-assisted motor fails, enabling the electronic control device to enter a failure protection control mode; if the booster motor is operating normally, data acquisition is performed, including yaw rate ω r Vehicle speed v, centroid slip angle beta, centroid slip angular velocityAnd road adhesion coefficient μ;
step two, determining a stable domain boundary parameter value B according to the road adhesion coefficient mu 1 、B 2 And according to the stable domain boundary parameter value B 1 、B 2 Phase plane stability domain calculations are performed ifIf yes, the electronic control device enters into energy-saving steering mode, if +.>When the electronic control device enters a safe steering mode;
wherein the energy-saving steering mode includes:
monitoring steering wheel torque T sw Vehicle speed v, steering wheel angle delta sw Total driving demand torque T g The method comprises the steps of carrying out a first treatment on the surface of the According to the steering wheel angle delta sw And different initial values of the differential power steering working weight coefficient value k are obtained through a first optimization objective function, and the optimized initial value k is obtained through data arrangement c The method comprises the steps of carrying out a first treatment on the surface of the Wherein the optimization process minimizes the value of the first optimization objective function;
the first optimization objective function is
Wherein T is 1 The torque is output for the motor of the left front wheel; n is n 1 The output rotating speed of the left front wheel; t (T) 2 The torque is output for the motor of the right front wheel; n is n 2 The output rotating speed of the right front wheel; t (T) t The output torque of the power-assisted motor is; n is n t The output rotating speed of the power-assisted motor; a, a 1 、a 2 、a 3 Respectively the weight coefficients; lambda (lambda) 1 ，λ 2 ，λ t The efficiency of the left front wheel motor, the right front wheel motor and the power-assisted motor are respectively;
according to the initial value k c Optimizing the working weight coefficient value k through a second optimization objective function; wherein the optimizing process minimizes the value of the second optimizing objective function;
the second optimization objective function is
The constraint equation of the working weight coefficient value k is c 1 k c ≤k≤c 2 k c ；
Wherein T is g The main coordination control module calculates the total driving moment T according to the difference value of the vehicle speed and the target vehicle speed z Front wheel differential torque, b, required for assistance determined by the differential power steering control module 1 ，b 2 ，b t Respectively corresponding optimized weight coefficients, c 1 And c 2 Respectively optimizing boundary coefficients;
determining front wheel differential moment T z And a control voltage signal required by the booster motor, and determining the final output front wheel booster demand differential moment delta T according to the working weight coefficient k z Total driving torque T g The differential power-assisted steering controller outputs the required yaw moment to be distributed to the two front wheels, and the yaw moment is corrected through the slip rate control device, and the power-assisted motor outputs the power-assisted moment to act on the steering wheel through the steering system transmission mechanism.
2. The control method of an electric wheel drive vehicle composite energy-saving power steering apparatus according to claim 1, wherein the speed reducing mechanism is provided as a worm gear structure.
3. The control method of a composite energy-saving power steering apparatus for an electric wheel drive vehicle according to claim 1 or 2, wherein the steering gear is a rack-and-pinion steering gear;
wherein the steering gear of the rack-and-pinion steering gear is connected with the lower end of the steering shaft; and
the rack of the rack-and-pinion steering gear is in meshed transmission with the steering gear, and the rack is connected with the tie rod.
4. A control method of an electric wheel drive vehicle composite energy saving power steering apparatus according to claim 3, wherein the tie rod is connected to the knuckle of the wheel via a ball stud.
5. The control method of an electric wheel drive vehicle composite energy saving power steering apparatus according to claim 4, wherein the safe steering mode includes:
monitoring steering wheel torque T sw Vehicle speed v, steering wheel angle delta sw According to the steering wheel angle delta sw Obtaining ideal steering wheel torque T from vehicle speed v swd ；
Setting the steering wheel torque T sw And the ideal steering wheel torque T swd The difference value of the voltage signal is input into an electric power steering control device, a control voltage signal of a power motor is calculated through fuzzy PID, the voltage signal is transmitted to the power motor, and the power torque is output.
6. The control method of an electric wheel drive vehicle composite energy saving power steering apparatus according to claim 1, wherein the fail-safe control mode includes:
monitoring steering wheel torque T sw Vehicle speed v, steering wheel angle delta sw And a total driving demand torque T g According to the steering wheel angle delta sw Obtaining ideal steering wheel torque T from vehicle speed v swd ；
Setting the steering wheel torque T sw And the ideal steering wheel torque T swd The difference value of the (a) is input into a differential power steering control device, and the differential moment value T of the required front wheel is calculated through PID z Calculating moment values required by the left and right front wheels;
and respectively inputting the calculated required torque values of the left front wheel and the right front wheel into a slip ratio control device of each wheel for correction, and outputting the corrected required torque values of the front wheels to an in-wheel motor for control.
7. The control method of an electric wheel drive vehicle composite energy saving power steering apparatus according to claim 1, wherein,
determining front wheel differential moment T z Outputting through a differential power-assisted steering control device, wherein the differential power-assisted steering control device adopts a PID controller; and
the control voltage signal required by the power-assisted motor is determined and output through an electric power-assisted steering control device, and the electric power-assisted steering control device adopts a fuzzy PID controller.
8. The control method of an electric wheel drive vehicle composite energy saving power steering apparatus according to claim 7, wherein the front wheel differential torque Δt z The calculation is performed by the following formula:
wherein T is i (i=1, 2) is the left front wheel and the right front wheel output torque, respectively.
9. The control method of an electric wheel drive vehicle composite energy saving power steering apparatus according to claim 8, wherein the correcting process of the slip ratio control apparatus includes:
calculating the slip rate of each wheel in real time, simultaneously estimating the optimal slip rate of the wheel at each moment in real time, and when the actual slip rate of the wheel is larger than the optimal slip rate of the wheel at the moment, starting the slip rate control device to work, and calculating the output slip rate control correction moment T through a PID control algorithm xi (i=1, 2), the corrected wheel demand torque T si (i=1, 2) the calculation formula is T si ＝T i +T xi 。
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