CN112319602B - 6X4 electric automobile chassis system capable of realizing all-wheel steering and steering control method - Google Patents

6X4 electric automobile chassis system capable of realizing all-wheel steering and steering control method Download PDF

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Publication number
CN112319602B
CN112319602B CN202011277273.2A CN202011277273A CN112319602B CN 112319602 B CN112319602 B CN 112319602B CN 202011277273 A CN202011277273 A CN 202011277273A CN 112319602 B CN112319602 B CN 112319602B
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China
Prior art keywords
steering
shaft
wheel
driving
rotation angle
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CN112319602A (en
Inventor
靳立强
田梦杰
王凯
张奇祥
许杰
崔明萱
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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
    • B62D5/0403—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 constructional features, e.g. common housing for motor and gear box
    • 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
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D6/00—Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits
    • B62D6/001—Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits the torque NOT being among the input parameters
    • 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)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Steering Control In Accordance With Driving Conditions (AREA)

Abstract

The invention discloses a 6X4 electric automobile chassis system capable of realizing all-wheel steering, which comprises: a frame including a first shaft, a second shaft, and a third shaft disposed in parallel in a lateral direction; a steering wheel; a steering wheel angle sensor connected to the steering wheel; the driving devices are symmetrically arranged on the first shaft and the third shaft respectively and are used for driving the vehicle to run; the driving wheels are respectively connected with the driving device and are symmetrically arranged at two ends of the first shaft and the third shaft; the two driven wheels are symmetrically arranged at two ends of the second shaft; the mechanical steering device is connected with the steering wheel and connected with the first shaft; the plurality of steering-by-wire devices are symmetrically arranged on the second shaft and the third shaft respectively, and are connected with the steering wheel angle sensor. The invention also discloses a control method of the chassis system of the 6 multiplied by 4 electric automobile capable of realizing all-wheel steering, and the steering performance of the automobile is improved by coordinating two steering modes.

Description

6X4 electric automobile chassis system capable of realizing all-wheel steering and steering control method
Technical Field
The invention relates to the technical field of automobile chassis design, in particular to a 6 multiplied by 4 electric automobile chassis system capable of realizing all-wheel steering and a steering control method.
Background
Compared with the traditional fuel oil automobile, the electric automobile has higher environmental protection and dynamic property, and is the development direction of the current automobile. Because of the output characteristic of the motor, namely the low speed and the large torque, the electric automobile can obtain larger driving moment when starting, so the dynamic property is better. Besides, the electric automobile has small noise, simpler overall structure and great development prospect.
Passenger cars are typically two-axle vehicles, while commercial vehicles typically have three or more axles because of the cargo carried by them. 6x4 means that the automobile has three axles and six wheels, wherein four wheels are driving wheels, and the other two wheels are driven wheels, mainly play a bearing role, and are suitable for light trucks and transporting goods.
The steering-by-wire system of the automobile detects the angle of a steering wheel by using a sensor, transmits the angle to an ECU through a bus, and outputs a control instruction to a steering control mechanism through a corresponding control algorithm to realize steering. Meanwhile, the information of the steering mechanism is transmitted to the whole vehicle controller through a bus and then fed back to the steering wheel, so that a driver obtains road feel.
Since the three-axle automobile has a longer body, the steering radius required for steering is larger, and the domestic partial road cannot meet the requirement, the requirement for the road width should be actively reduced from the viewpoint of the automobile itself. At present, most automobiles adopt an all-wheel steering scheme, namely front wheels and rear wheels are steering wheels, so that the steering radius of the automobiles can be greatly reduced. All-wheel steering can provide a plurality of steering modes, in-situ steering and crab steering can be realized, so that the lateral parking of the automobile is more convenient, and the trafficability of the automobile is greatly improved. However, most of the schemes are aimed at two-axle automobiles, the structure is complex, and the schemes are in a theoretical stage and have less practical application. Meanwhile, fewer solutions are available for three-axis electric cargo vehicles.
Disclosure of Invention
The invention aims to design and develop a 6 multiplied by 4 electric automobile chassis system capable of realizing all-wheel steering, and four wheels are driven by symmetrically arranged driving motors respectively on a first shaft and a third shaft; by combining the mechanical steering system and the steer-by-wire system, the steering structure is optimized, the all-wheel steering of the 6X4 electric automobile is realized, and the trafficability of the automobile and the safety of the all-wheel steering are improved.
Another object of the present invention is to design and develop a control method of a chassis system of a 6×4 electric vehicle capable of realizing all-wheel steering, which precisely controls the wheel turning angle according to the output torque of a steering motor, realizes all-wheel steering, reduces the steering radius of the vehicle during low-speed running, and improves the steering stability during high-speed running.
The technical scheme provided by the invention is as follows:
a 6x4 electric vehicle chassis system capable of achieving all-wheel steering, comprising:
a frame including a first axis, a second axis and a third axis spaced apart in parallel in a transverse direction; and
a steering wheel disposed on the frame;
a steering wheel angle sensor connected to the steering wheel for measuring an angle of the steering wheel;
the driving devices are symmetrically arranged on the first shaft and the third shaft respectively and are used for driving the vehicle to run;
the driving wheels are respectively connected with the driving device in a one-to-one correspondence manner and are respectively and symmetrically arranged at two ends of the first shaft and the third shaft;
two driven wheels symmetrically arranged at two ends of the second shaft;
a mechanical steering device connected to the steering wheel, the mechanical steering device being connected to the first shaft;
the steering-by-wire devices are symmetrically arranged on the second shaft and the third shaft respectively, and are connected with the steering wheel angle sensor.
Preferably, the driving device includes:
a driving motor;
the input end of the speed reducer is connected with the output end of the driving motor;
and one end of the half shaft is connected with the output end of the speed reducer, and the other end of the half shaft is connected with the driving wheels.
Preferably, the mechanical steering device includes:
a steering column tube connected to the steering wheel;
a steering gear connected to the steering column tube;
the steering shaft is connected with the output end of the steering gear;
a tie rod engaged with an output end of the steering shaft, the tie rod being movable in a lateral direction of the frame;
one end of each steering knuckle arm is connected with two ends of the transverse pull rod in a one-to-one correspondence manner;
and one ends of the two steering knuckles are respectively connected with the other ends of the two steering knuckle arms in one-to-one correspondence, and the other ends of the two steering knuckles are respectively fixedly connected with the driving wheels.
Preferably, the steer-by-wire apparatus includes:
a steering motor connected to the driving wheel or the driven wheel;
one end of the motor rocker arm is connected with the output end of the steering motor;
one end of the pull rod is connected with the other end of the motor rocker arm;
and one end of the steering knuckle arm is connected with the other end of the pull rod, and the other end of the steering knuckle arm is connected with the wheel.
Preferably, the method further comprises:
the wheel rotation angle sensors are respectively arranged on the driving wheels and the driven wheels in a one-to-one correspondence manner and are used for measuring rotation angles of the driving wheels and the driven wheels;
the wheel speed sensors are respectively arranged on the driving wheels and the driven wheels in a one-to-one correspondence manner and are used for measuring the speed of the vehicle;
the whole vehicle controller is connected with the steering wheel angle sensor, the plurality of wheel angle sensors and the plurality of wheel speed sensors and is used for providing signal transmission and controlling steering;
and the instrument panel is connected with the whole vehicle controller and is used for displaying the driving mode.
A control method of a 6X4 electric automobile chassis system capable of realizing all-wheel steering, which uses the 6X4 electric automobile chassis system capable of realizing all-wheel steering, comprises the following steps:
step one, acquiring a driving mode, an actual wheel rotation angle and a vehicle speed;
step two, if the driving mode is a lateral driving mode, the steering directions and the steering angles of the first shaft, the second shaft and the third shaft are the same;
if the driving mode is a driving mode, and the vehicle speed is lower than the critical speed, the steering directions of the wheels of the first shaft, the second shaft and the third shaft are opposite, the extension lines of the first shaft, the second shaft and the third shaft intersect at one point, and meanwhile, the torque of the outer steering motor is larger than the torque of the inner steering motor, so that differential power-assisted steering is formed;
if the driving mode is a driving mode, and the vehicle speed is higher than the critical speed, the steering directions of the wheels of the first shaft, the second shaft and the third shaft are the same, the rotation angles of the wheels of the second shaft and the third shaft are smaller than those of the first shaft, and meanwhile, the torque of the outer steering motor is larger than that of the inner steering motor, so that differential power-assisted steering is formed;
if the actual rotation angle of the wheel and the theoretical rotation angle of the wheel meet the following conditions:
Δθ×Δα > 0, and
the whole vehicle controller judges that the steering device fails, only the mechanical steering of the first shaft is reserved at the moment, and the steering motors of the second shaft and the third shaft are closed;
wherein θ is the actual rotation angle, θ 0 For a theoretical rotation angle, Δθ is the rotation angle deviation, and Δθ=θ - θ 0 Delta alpha is the deviation change rate, alpha is the safety coefficient, M is the sprung mass of the single wheel, g is the gravitational acceleration, F is the longitudinal force of the wheel, and n is the rotational speed of the wheel.
Preferably, the critical speed is 55km/h.
Preferably, when the driving mode is the lateral running mode, the theoretical rotation angle satisfies:
δ 1 ＝δ 2 ＝δ 3 ；
in delta 1 Is the theoretical rotation angle delta of the driving wheel of the first shaft 2 Is the theoretical rotation angle delta of the driven wheel of the second shaft 3 A theoretical rotation angle of the driving wheel of the third shaft;
when the driving mode is a running mode and the vehicle speed is lower than a critical speed, the theoretical rotation angle satisfies:
δ 3 ＝α 1 δ 1 +α 2 μ c γ；
wherein alpha is 1 As a first scale factor, alpha 2 Mu, as the second proportionality coefficient c The vehicle speed is the yaw rate of the whole vehicle, gamma is the wheelbase from the second shaft to the third shaft, L is the wheelbase of the whole vehicle, and a is the wheelbase from the first shaft to the second shaft;
when the driving mode is a running mode and the vehicle speed is higher than a critical speed, the theoretical rotation angle satisfies:
δ 3 ＝α 1 δ 1 +α 2 μ c γ；
δ 2 ＝δ 3 ；
wherein the theoretical rotation angle of the driving wheel of the first shaft is obtained through a mechanical steering transmission ratio.
Preferably, the torque of the steering motor is obtained by a PID fuzzy controller:
deviation e and deviation change rate e of input wheel rotation angle c The proportional coefficient, the proportional integral coefficient and the differential coefficient of the output PID are input into a PID controller to carry out error compensation control on the output torque of the steering motor.
Preferably, the method further comprises:
the fuzzy domain of deviation e of the wheel rotation angle is [ -1.5,1.5]The quantization factor is 20; the deviation change rate e c The fuzzy discourse domain of [ -3,3]The quantization factor is 1;
the fuzzy domain of the proportionality coefficient of the output PID is [ -6,0], and the quantization factor is 0.1; the fuzzy domain of the proportional integral coefficient is [ -1.5,1.5], and the quantization factor is 0.1; the fuzzy argument of the differential coefficient is [ -6,6], its quantization factor is 0.0001;
the deviation e and the deviation change rate e c Dividing into 7 grades; the proportional coefficient, the proportional integral coefficient and the differential coefficient of the output PID are divided into 7 grades;
the fuzzy sets of the input and output of the fuzzy PID controller are { NB, NM, NS, Z0, PS, PM, PB }.
The beneficial effects of the invention are as follows:
the invention provides a 6X4 electric automobile chassis system capable of realizing all-wheel steering, which is characterized in that two driving motors are respectively arranged on a first shaft and a third shaft for driving four wheels of a driving system. For the steering system, the mechanical steering system and the steer-by-wire system are combined, the steering structure is optimized, the all-wheel steering of the 6X4 electric automobile is realized, the abrasion of tires is reduced, the steering radius of the automobile is reduced, and the passing performance of the automobile and the safety of all-wheel steering are improved.
According to the control method of the 6X4 electric automobile chassis system capable of realizing all-wheel steering, which is provided by the invention, the torque of the steering motor is controlled through the ECU according to various state parameters in the running process of the automobile, the wheel turning angle is precisely controlled, the all-wheel steering is realized, the steering radius of the automobile in low-speed running is reduced, the steering stability in high-speed running is improved, and meanwhile, the fault tolerance of the steering system is improved through fault diagnosis, so that the system is safer.
Drawings
Fig. 1 is a schematic diagram of the overall structure of a chassis system of a 6×4 electric vehicle capable of realizing all-wheel steering according to the present invention.
Fig. 2 is a program flow chart of a steering control method of a chassis system of a 6×4 electric vehicle capable of realizing all-wheel steering according to the present invention.
FIG. 3 is a membership function chart of the input bias e of the fuzzy PID controller according to the invention.
FIG. 4 shows the input deviation change rate e of the fuzzy PID controller according to the invention c Membership function of (a)And (5) a digital graph.
FIG. 5 shows the output scaling factor K of the fuzzy PID controller according to the invention p Membership function graph of (a).
FIG. 6 shows the output proportional-integral coefficient K of the fuzzy PID controller according to the invention i Membership function graph of (a).
FIG. 7 shows the differential coefficient K of the output of the fuzzy PID controller according to the invention d Membership function graph of (a).
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.
As shown in fig. 1, the chassis system of a 6×4 electric vehicle capable of implementing all-wheel steering according to the present invention specifically includes: a frame 110, a steering device, 4 driving devices, a signal control system and a steering wheel 130, wherein the driving devices are arranged on the frame 110 and used for driving wheels; for the steering device, combining the mechanical steering device with the 4 steering devices by wire, optimizing the steering structure, and realizing the all-wheel steering of the 6X4 electric automobile; the signal control system is used for controlling the transmission and steering of signals; the steering wheel 130 is disposed at the upper portion of the frame 110, and the steering wheel 130 provides a steering signal as a starting end of the steering device.
The type of the frame 110 is not limited to a specific one, and the 6×4 electric vehicle chassis system designed by the invention and capable of realizing all-wheel steering is applicable to any frame type, and the frame 110 in this embodiment is a side beam frame with relatively wide application, and the related structural arrangement form is described by the side beam frame in the embodiment.
The frame 110 comprises three shafts, namely a first shaft 111, a second shaft 112 and a third shaft 113, which are transversely and parallelly arranged at intervals in sequence; 2 first-axis driving wheels 171 are symmetrically disposed at both ends of the first axis 111, and 2 third-axis driving wheels 172 are symmetrically disposed at both ends of the third axis 113; the 2 second axle driven wheels 173 are symmetrically disposed at both ends of the second axle 112.
The 4 driving devices are symmetrically arranged on the first shaft 111 and the third shaft 113 respectively, and the 4 driving devices are all arranged below the frame 110 and are used for driving the vehicle to run; on the first shaft 111, the driving device comprises a first shaft driving motor 121, a first shaft speed reducer 122 and a first shaft half shaft 123, wherein the input end of the first shaft speed reducer 122 is connected with the output end of the first shaft driving motor 121; one end of a first axle half shaft 123 is connected with the output end of the first axle reducer 122, and the other end is connected with the first axle driving wheel 171; on the third shaft 113, the driving device includes a third shaft driving motor 124, a third shaft reducer 125, and a third shaft half shaft 126, where an input end of the third shaft reducer 125 is connected to an output end of the third shaft driving motor 124; one end of the third axle shaft 126 is connected to the output end of the third axle reducer 125, and the other end is connected to the third axle driving wheel 172.
With respect to the steering device, the first shaft 111 is a conventional mechanical steering device, and the second shaft 112 and the third shaft 113 are steer-by-wire devices, so that it is ensured that the conventional mechanical steering device of the first shaft 111 is still functional when the steer-by-wire device fails.
The mechanical steering device includes: steering column tube 151, steering gear 152, steering shaft 153, tie rod 154, two knuckle arms 155 and knuckle 156, wherein said steering column tube 151 is connected with said steering wheel 130, transmitting steering wheel torque and angle information; the steering gear 152 is connected with the steering column tube 151 and is used for decelerating and increasing torque of power transmitted from the steering column tube 151; a steering shaft 153 is connected to the output end of the steering gear 152; a tie rod 154 is engaged with an output end of the steering shaft 153, and the tie rod 154 is movable in a lateral direction of the frame 110; one end of each of the two knuckle arms 155 is connected with two ends of the tie rod 154 in a one-to-one correspondence manner; one end of each of the two knuckles 156 is connected to the other end of each of the two knuckle arms 155 in a one-to-one correspondence, and the other end is fixedly connected to the first axle driving wheel 171.
The steering-by-wire device of the second shaft and the steering-by-wire device of the third shaft have the same structure, and the steering-by-wire device of the third shaft specifically comprises: a steering motor 161, a motor rocker 162, a tie rod 163, a knuckle arm 164 and a third axle knuckle 165, wherein the steering motor 161 is connected to the third axle drive wheel 172 for powering steering of the third axle drive wheel 172; one end of a motor rocker 162 is connected with the output end of the steering motor 161 and used for transmitting torque; one end of a pull rod 163 is connected to the other end of the motor rocker 162, one end of a knuckle arm 164 is connected to the other end of the pull rod 163, and the other end is connected to the third axle driving wheel 172 through the knuckle, so as to drive the third axle driving wheel 172 to steer.
The signal control system includes: a steering wheel angle sensor 141, 6 wheel speed sensors 142, 6 wheel angle sensors 143, an instrument panel 144, a bus 145, and a vehicle control unit (ECU) 146, wherein the steering wheel angle sensor 141 is connected with the steering wheel 130 for measuring the angle of the steering wheel 130, and the steering wheel angle sensor 141 is connected with the steer-by-wire device for providing steering signals to the steer-by-wire device; the 6 wheel rotation angle sensors 143 are respectively arranged on the first axle driving wheel 171, the third axle driving wheel 172 and the second axle driven wheel 173 in a one-to-one correspondence manner, and are used for measuring rotation angles of the first axle driving wheel 171, the third axle driving wheel 172 and the second axle driven wheel 173; the 6 wheel speed sensors 142 are respectively arranged on the first axle driving wheel 171, the third axle driving wheel 172 and the second axle driven wheel 173 in a one-to-one correspondence manner and are used for measuring the speed of the vehicle; the whole vehicle controller 146 is connected with the steering wheel angle sensor 141, the 6 wheel speed sensors 142 and the 6 wheel angle sensors 143 through a bus 145 and is used for providing signal transmission and controlling steering; the instrument panel 144 is connected with the vehicle controller 146 and is used for displaying driving modes; bus 145 is distributed throughout the chassis, providing for information transfer.
The invention provides a 6X4 electric automobile chassis system capable of realizing all-wheel steering, which is characterized in that two driving motors are respectively arranged on a first shaft and a third shaft for driving four wheels of a driving device; for the steering device, the mechanical steering device and the steer-by-wire device are combined, the steering structure is optimized, the all-wheel steering of the 6×4 electric automobile is realized, the abrasion of tires is reduced, the steering radius of the automobile is reduced, and the passing performance of the automobile and the safety of all-wheel steering are improved.
As shown in fig. 2, the present invention provides a steering control method for a 6×4 electric vehicle chassis system capable of implementing all-wheel steering, and the method for implementing all-wheel steering by using the 6×4 electric vehicle chassis system comprises the following steps:
step one, acquiring a driving mode, an actual wheel rotation angle and a vehicle speed;
wherein, the driver selects a driving mode through the instrument panel 144, obtains the actual wheel rotation angle through the 6 wheel rotation angle sensors 143, and obtains the vehicle speed through the 6 wheel speed sensors 142;
step two, if the driving mode is a lateral driving mode, indicating that a driver wants to park laterally, the steering directions and steering angles of the first shaft, the second shaft and the third shaft are the same, and oblique movement is formed;
if the driving mode is a driving mode, the speed of the vehicle is lower than the critical speed, and the vehicle runs at a low speed, the steering directions of the wheels of the first shaft, the second shaft and the third shaft are opposite, the extension lines of the first shaft, the second shaft and the third shaft intersect at one point, the turning radius is reduced, and meanwhile, the torque of the outer steering motor is larger than that of the inner steering motor, so that differential power-assisted steering is formed;
if the driving mode is a driving mode, the speed of the vehicle is higher than the critical speed, and the vehicle runs at a high speed, the steering directions of the wheels of the first shaft, the second shaft and the third shaft are the same, the rotation angles of the wheels of the second shaft and the third shaft are smaller than those of the first shaft, the wheels belong to follow-up steering, the stability of the high-speed steering of the automobile is improved, and meanwhile, the torque of the outer steering motor is larger than that of the inner steering motor, so that differential power-assisted steering is formed;
wherein the critical speed is 55km/h;
then PID fuzzy controller control is carried out through the whole vehicle controller 146 through the difference value between the actual rotation angle of the wheels and the theoretical rotation angle of the vehicle, and the whole vehicle controller 146 outputs a command to the steering motor 161 to reduce the rotation angle error;
if the actual rotation angle of the wheel and the theoretical rotation angle of the wheel meet the following conditions:
Δθ×Δα > 0, and
the whole vehicle controller judges that the steering device fails, only the mechanical steering of the first shaft is reserved at the moment, and the steering motors of the second shaft and the third shaft are closed;
wherein θ is the actual rotation angle, θ 0 For a theoretical rotation angle, Δθ is the rotation angle deviation, and Δθ=θ - θ 0 Delta alpha is the deviation change rate, alpha is a safety coefficient, M is the sprung mass of the single wheel, g is the gravitational acceleration, F is the longitudinal force of the wheel, and n is the rotational speed of the wheel;
the vehicle controller 146 determines that the steering system is faulty, and only the mechanical steering of the first axle 111 is maintained, and the steering motors 161 of the second axle 112 and the third axle 113 are turned off;
wherein, when the driving mode is a lateral driving mode, the theoretical rotation angle satisfies:
δ 1 ＝δ 2 ＝δ 3 ；
in delta 1 Is the theoretical rotation angle delta of the driving wheel of the first shaft 2 Is the theoretical rotation angle delta of the driven wheel of the second shaft 3 A theoretical rotation angle of the driving wheel of the third shaft;
when the driving mode is a running mode and the vehicle speed is lower than a critical speed, the theoretical rotation angle satisfies:
δ 3 ＝α 1 δ 1 +α 2 μ c γ；
wherein alpha is 1 For the first scale factor, alpha is preferably 1 Has a value of 0 to 1, alpha 2 Is a second proportionality coefficient，α 2 The value of (a) is 0-1 mu c The vehicle speed is the yaw rate of the whole vehicle, gamma is the wheelbase from the second shaft to the third shaft, L is the wheelbase of the whole vehicle, and a is the wheelbase from the first shaft to the second shaft;
when the driving mode is a running mode and the vehicle speed is higher than a critical speed, the theoretical rotation angle satisfies:
δ 3 ＝α 1 δ 1 +α 2 μ c γ；
δ 2 ＝δ 3 ；
wherein the theoretical rotation angle of the driving wheel of the first shaft is obtained through a mechanical steering transmission ratio.
The setting of the PID fuzzy controller comprises the following steps:
deviation e and deviation change rate e of wheel rotation angle c The proportional coefficient, the proportional integral coefficient and the differential coefficient of the output PID are subjected to fuzzy processing, and when the control is not performed, the fuzzy argument of the deviation e is [ -1.5,1.5]The quantization factor is 20; rate of change of deviation e c The fuzzy discourse domain of [ -3,3]The quantization factor is 1; proportional coefficient K of PID p The ambiguity domain of (2) is [ -6,0]The quantization factor is 0.1; proportional integral coefficient K i The ambiguity domain of (2) is [ -1.5,1.5]The quantization factor is 0.1; differential coefficient K d The ambiguity domain of (2) is [ -6,6]The quantification factor is 0.0001.
In order to ensure the control precision, realize better control, repeatedly perform experiments to determine the optimal input and output levels, wherein the deviation e and the deviation change rate e in the fuzzy controller c Dividing into 7 grades; the proportional coefficient, the proportional integral coefficient and the differential coefficient of the output PID are divided into 7 grades; the fuzzy sets of input and output are { NB, NM, NS, Z0, PS, PM, PB }, and the membership functions of input and output are triangle membership functions, as shown in FIGS. 3-7. The fuzzy control rule is as follows:
1. when the deviation |e| is large, K is increased p Thereby the deviation is reduced rapidly, but a larger deviation change rate is generated at the same time, a smaller K is adopted d K is usually taken i ＝0；
2. When |e c Values of i and i e are at medium time, K is suitably reduced to avoid overshoot p To take the value of K i Smaller, select K of appropriate size d ；
3. When the deviation |e| is small, K is increased p 、K i To avoid unstable oscillations around the steady state value of the system, the value of (i) is usually calculated as c When I is larger, take smaller K d The method comprises the steps of carrying out a first treatment on the surface of the When |e c When I is smaller, take larger K d The method comprises the steps of carrying out a first treatment on the surface of the Specific fuzzy control rules are shown in tables I, II and III.
Table one PID scaling factor K p Fuzzy control table of (a)
Table II PID proportional integral coefficient K i Fuzzy control table of (a)
Differential coefficient K of Table three PID d Fuzzy control table of (a)
Deviation e and deviation change rate e of input wheel rotation angle c The proportional coefficient, the proportional integral coefficient and the differential coefficient of the output PID are defuzzified by a height method, and are input into a PID controller for error compensation control of the output torque of the steering motor, wherein the control formula is as follows:
through simulation analysis, the output torque of the steering motor is regulated by a fuzzy PID controller, so that the wheel rotation angle is accurately controlled, and the deviation is less than 0.1%.
According to the control method of the chassis system of the 6X4 electric automobile capable of realizing all-wheel steering, which is provided by the invention, the ECU controls the torque of the steering motor, precisely controls the wheel rotation angle, realizes all-wheel steering, reduces the steering radius of the automobile during low-speed running, improves the steering stability during high-speed running, and simultaneously improves the fault tolerance of the steering system through fault diagnosis, so that the system is safer.
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. A steering control method of a 6x4 electric vehicle chassis system capable of realizing all-wheel steering, characterized by using the 6x4 electric vehicle chassis system capable of realizing all-wheel steering, comprising the following steps:
step one, acquiring a driving mode, an actual wheel rotation angle and a vehicle speed;
step two, if the driving mode is a lateral driving mode, the steering directions and steering angles of the first shaft, the second shaft and the third shaft are the same;
if the driving mode is a driving mode, and the vehicle speed is lower than the critical speed, the steering directions of the wheels of the first shaft, the second shaft and the third shaft are opposite, the extension lines of the first shaft, the second shaft and the third shaft intersect at one point, and meanwhile, the torque of the outer steering motor is larger than the torque of the inner steering motor, so that differential power-assisted steering is formed;
if the driving mode is a driving mode, and the vehicle speed is higher than the critical speed, the steering directions of the wheels of the first shaft, the second shaft and the third shaft are the same, the rotation angles of the wheels of the second shaft and the third shaft are smaller than those of the first shaft, and meanwhile, the torque of the outer steering motor is larger than that of the inner steering motor, so that differential power-assisted steering is formed;
if the actual rotation angle of the wheel and the theoretical rotation angle of the wheel meet the following conditions:
the whole vehicle controller judges that the steering device fails, only the mechanical steering of the first shaft is reserved at the moment, and the steering motors of the second shaft and the third shaft are closed;
wherein θ is the actual rotation angle, θ 0 For a theoretical rotation angle, Δθ is the rotation angle deviation, and Δθ=θ - θ 0 Delta alpha is the deviation change rate, A is the safety coefficient, M is the sprung mass of the single wheel, g is the gravitational acceleration, F is the longitudinal force of the wheel, and n is the rotational speed of the wheel;
the 6×4 electric vehicle chassis system capable of realizing all-wheel steering comprises:
the vehicle frame comprises a first shaft, a second shaft and a third shaft which are transversely arranged at intervals in parallel; and
a steering wheel disposed on the frame;
a steering wheel angle sensor connected to the steering wheel for measuring an angle of the steering wheel;
the driving devices are symmetrically arranged on the first shaft and the third shaft respectively and are used for driving the vehicle to run;
the driving wheels are respectively connected with the driving device in a one-to-one correspondence manner and are respectively and symmetrically arranged at two ends of the first shaft and the third shaft;
two driven wheels symmetrically arranged at two ends of the second shaft;
a mechanical steering device connected to the steering wheel, the mechanical steering device being connected to the first shaft;
the steering-by-wire devices are symmetrically arranged on the second shaft and the third shaft respectively, and are connected with the steering wheel angle sensor.
2. The steering control method of a 6x4 electric vehicle chassis system capable of realizing all-wheel steering according to claim 1, wherein the driving device includes:
a driving motor;
the input end of the speed reducer is connected with the output end of the driving motor;
and one end of the half shaft is connected with the output end of the speed reducer, and the other end of the half shaft is connected with the driving wheels.
3. The steering control method of a 6x4 electric vehicle chassis system capable of realizing all-wheel steering according to claim 2, wherein the mechanical steering device comprises:
a steering column tube connected to the steering wheel;
a steering gear connected to the steering column tube;
the steering shaft is connected with the output end of the steering gear;
a tie rod engaged with an output end of the steering shaft, the tie rod being movable in a lateral direction of the frame;
one end of each steering knuckle arm is connected with two ends of the transverse pull rod in a one-to-one correspondence manner;
and one ends of the two steering knuckles are respectively connected with the other ends of the two steering knuckle arms in one-to-one correspondence, and the other ends of the two steering knuckles are respectively fixedly connected with the driving wheels.
4. The steering control method of a 6x4 electric vehicle chassis system capable of realizing all-wheel steering according to claim 3, wherein the steer-by-wire apparatus comprises:
a steering motor connected to the driving wheel or the driven wheel;
one end of the motor rocker arm is connected with the output end of the steering motor;
one end of the pull rod is connected with the other end of the motor rocker arm;
and one end of the steering knuckle arm is connected with the other end of the pull rod, and the other end of the steering knuckle arm is connected with the wheel.
5. The steering control method of a 6x4 electric vehicle chassis system capable of realizing all-wheel steering according to claim 4, wherein the 6x4 electric vehicle chassis system capable of realizing all-wheel steering further comprises:
the wheel rotation angle sensors are respectively arranged on the driving wheels and the driven wheels in a one-to-one correspondence manner and are used for measuring rotation angles of the driving wheels and the driven wheels;
the wheel speed sensors are respectively arranged on the driving wheels and the driven wheels in a one-to-one correspondence manner and are used for measuring the speed of the vehicle;
the whole vehicle controller is connected with the steering wheel angle sensor, the plurality of wheel angle sensors and the plurality of wheel speed sensors and is used for providing signal transmission and controlling steering;
and the instrument panel is connected with the whole vehicle controller and is used for displaying the driving mode.
6. The steering control method of a 6x4 electric vehicle chassis system capable of realizing all-wheel steering according to claim 1, wherein the critical speed is 55km/h.
7. The steering control method of a 6x4 electric vehicle chassis system capable of realizing all-wheel steering according to claim 1, wherein when the driving mode is a lateral driving mode, the theoretical steering angle satisfies:
δ 1 ＝δ 2 ＝δ 3 ；
in delta 1 Is the theoretical rotation angle delta of the driving wheel of the first shaft 2 Is the theoretical rotation angle delta of the driven wheel of the second shaft 3 Driving vehicle with third shaftTheoretical rotation angle of the wheel;
when the driving mode is a running mode and the vehicle speed is lower than a critical speed, the theoretical rotation angle satisfies:
δ 3 ＝α 1 δ 1 +α 2 μ c γ；
wherein alpha is 1 As a first scale factor, alpha 2 Mu, as the second proportionality coefficient c The vehicle speed is the yaw rate of the whole vehicle, gamma is the wheelbase from the second shaft to the third shaft, L is the wheelbase of the whole vehicle, and a is the wheelbase from the first shaft to the second shaft;
when the driving mode is a running mode and the vehicle speed is higher than a critical speed, the theoretical rotation angle satisfies:
δ 3 ＝α 1 δ 1 +α 2 μ c γ；
δ 2 ＝δ 3 ；
wherein the theoretical rotation angle of the driving wheel of the first shaft is obtained through a mechanical steering transmission ratio.
8. The steering control method of a 6x4 electric vehicle chassis system capable of realizing all-wheel steering according to claim 7, wherein the torque of the steering motor is obtained by a PID fuzzy controller:
deviation e and deviation change rate e of input wheel rotation angle c The proportional coefficient, the proportional integral coefficient and the differential coefficient of the output PID fuzzy controller are input into the PID fuzzy controller to carry out error compensation control on the output torque of the steering motor.
9. The steering control method of a 6x4 electric vehicle chassis system capable of realizing all-wheel steering according to claim 8, further comprising:
deviation e of the wheel angleThe ambiguity domain is [ -1.5,1.5]The quantization factor is 20; the deviation change rate e c The fuzzy discourse domain of [ -3,3]The quantization factor is 1;
the fuzzy domain of the proportional coefficient of the output PID fuzzy controller is [ -6,0], and the quantization factor is 0.1; the fuzzy domain of the proportional integral coefficient is [ -1.5,1.5], and the quantization factor is 0.1; the fuzzy argument of the differential coefficient is [ -6,6], its quantization factor is 0.0001;
the deviation e and the deviation change rate e c Dividing into 7 grades; the proportional coefficient, the proportional integral coefficient and the differential coefficient of the output PID fuzzy controller are divided into 7 grades;
the fuzzy set of the input and output of the PID fuzzy controller is { NB, NM, NS, Z0, PS, PM, PB }.
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