CN110466602A - The timesharing four-wheel steering system and its control method of hub motor driven electric vehicle - Google Patents
The timesharing four-wheel steering system and its control method of hub motor driven electric vehicle Download PDFInfo
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- CN110466602A CN110466602A CN201910820810.4A CN201910820810A CN110466602A CN 110466602 A CN110466602 A CN 110466602A CN 201910820810 A CN201910820810 A CN 201910820810A CN 110466602 A CN110466602 A CN 110466602A
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L15/00—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles
- B60L15/20—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles for control of the vehicle or its driving motor to achieve a desired performance, e.g. speed, torque, programmed variation of speed
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D11/00—Steering non-deflectable wheels; Steering endless tracks or the like
- B62D11/02—Steering non-deflectable wheels; Steering endless tracks or the like by differentially driving ground-engaging elements on opposite vehicle sides
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- 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
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/72—Electric energy management in electromobility
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- Transportation (AREA)
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- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
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- Steering-Linkage Mechanisms And Four-Wheel Steering (AREA)
- Steering Control In Accordance With Driving Conditions (AREA)
Abstract
The invention discloses a kind of steering of hub motor driven electric vehicle Differential Driving and the control methods of stability, whether exceed the judgement of stable region by the phase path to operation vehicle, vehicle in stable region is considered as linear model, the Differential Driving course changing control of linear model is carried out to it；By the vehicle outside stable region, pro-active intervention is carried out to Vehicular turn using the direct yaw moment of generation, it is made to return to stable state from unstable state.The present invention, which uses, to be jointly controlled, make the non-linear vehicle turned to by Differential Driving in the angle range that deflecting roller allows, on different attachment coefficient road surfaces can track reference model well side slip angle and yaw velocity, the stability for effectively improving vehicle guarantees the safety of driving.
Description
Technical Field
The invention relates to a steering control system and a method, in particular to a time-sharing four-wheel steering system of an electric automobile driven by a hub motor and a control method thereof, belonging to the technical field of electric automobiles.
Background
The independent wheel driving and steering is usually realized by adopting a distributed driving mode, and the independent wheel driving and steering can be divided into wheel edge motor driving and wheel hub motor driving according to a motor driving mode. The wheel side motor drive is characterized in that a motor system is arranged near a wheel, and the wheel is driven through a wheel side speed reducer; the hub motor drive is to install the hub motor in the wheel hub to directly drive the wheel. The hub motor driven automobile integrates driving and transmission in the hub, mechanical parts such as a clutch, a transmission shaft, a differential mechanism and the like required by the traditional automobile are omitted, the mechanical structure of the automobile is greatly simplified, and the space utilization rate of the automobile is improved. Meanwhile, the control of the hub motor drive only needs the motor and the controller, so that the delay influence of mechanical structures such as an electromagnetic valve and a hydraulic pipeline is avoided, the real-time performance and the precision are good, and various control schemes can be fully applied.
The Active Four-Wheel Steering (4 WS) system can effectively improve the maneuvering flexibility of the vehicle at low speed, the Steering stability at high speed and the path tracking problem of the intelligent vehicle by actively controlling the rotating angles of the front Wheel and the rear Wheel. However, since the rear wheels are involved in steering and a common control concept is to make the centroid slip angle of the vehicle zero, it is inevitable that the driver's feeling is different from driving a conventional front-wheel steering vehicle. Therefore, how to give full play to the advantages of the active four-wheel steering system and feed back good road feel is beneficial to the drivers when driving the electric wheel automobile; furthermore, uncertainty such as mass, centroid position, tire cornering stiffness and the like which vary with the working conditions can occur in the process of driving of an actual vehicle, so that the problem to be solved is to design a reasonable control strategy to improve the robustness of system response.
Disclosure of Invention
The invention mainly aims to overcome the defects in the prior art and provide a time-sharing four-wheel steering system of an electric vehicle driven by a hub motor and a control method thereof, which can not only switch front wheel steering and four-wheel steering according to the requirements of a driver and provide a proper road feel for the driver, but also have the advantages of simple structure, accurate steering and the like and good robustness.
In order to achieve the purpose, the invention adopts the technical scheme that:
a time-sharing four-wheel steering system of an in-wheel motor driven electric automobile comprises:
the detection module is used for detecting the driving parameters of the electric automobile and inputting the driving parameters to the whole automobile controller; the driving parameters comprise a steering wheel angle signal, a pedal position signal of an accelerator pedal, a driving vehicle speed signal, a front wheel steering angle signal and a rear wheel steering angle signal;
the steering mode selection switch is used for manually selecting a steering mode by a driver, wherein the steering mode comprises front wheel steering and four-wheel steering, and the selected steering mode is input to the whole vehicle controller;
the vehicle speed tracking module is used for calculating the running speed of the electric vehicle and the required front wheel driving torque according to the pedal position signal of the accelerator pedal, controlling the in-wheel motor to execute a running vehicle speed signal of a driver and inputting the running speed to the vehicle control unit;
the vehicle control unit is used for receiving the driving speed, transmitting a steering wheel turning angle signal to the front wheel linear control steering control module when the selected steering module is front wheel steering, and outputting a rear wheel locking signal to the rear wheel steering locking module; when the selected steering mode is four-wheel steering, calculating to obtain an ideal front and rear wheel steering angle required by the four-wheel steering and outputting a rear wheel unlocking signal to a rear wheel steering locking module, wherein the ideal front and rear wheel steering angle comprises an ideal front wheel steering angle and an ideal rear wheel steering angle, and transmitting the ideal front wheel steering angle to a front wheel linear control steering control module and the ideal rear wheel steering angle to a rear wheel differential steering control module;
the front wheel linear control steering control module is used for driving a front wheel steering execution motor to steer the front wheels according to the steering wheel angle signal and the front wheel steering angle signal or the ideal front wheel steering angle, providing corresponding steering road feel for a driver and feeding the steering road feel back to the whole vehicle controller;
the rear wheel differential steering control module is used for calculating to obtain a rear wheel differential torque according to an ideal rear wheel steering angle and driving a rear wheel hub motor to steer the rear wheel according to the rear wheel differential torque;
and the rear wheel steering locking module is used for driving the steering locking mechanism to rotate the rear wheels in a right direction according to the rear wheel locking signal and the rear wheel steering angle signal, forbidding the rear wheels to steer, and driving the steering locking mechanism to release the steering locking according to the rear wheel unlocking signal.
The system of the invention is further configured as follows: the steering locking mechanism comprises a return motor and two groups of steering mechanisms which are symmetrically arranged on the frame and have the same structure, the return motor is connected with the rear wheel steering locking module, and the two groups of steering mechanisms are connected with the return motor and respectively act on the left rear wheel and the right rear wheel;
the steering mechanism comprises an electromagnetic clutch, a return spur gear, a locking pull rod, a front binding rod, a first steering knuckle arm and a second steering knuckle arm which are sequentially connected, an electromagnet which is lapped on the surface of the locking pull rod and is arranged on the frame, steering main pins which are connected with one end of the first steering knuckle arm and one end of the second steering knuckle arm, an upper cross arm and a lower cross arm which are arranged on the frame, and a locking pull rod displacement sensor which is used for detecting the angle of a rear wheel and is arranged on the locking pull rod; the electromagnetic clutch is connected with the positive electricity return machine and connected with the rear wheel steering locking module, the locking pull rod is connected with the positive electricity return machine through a rod face rack, the locking pull rod and the toe rod as well as the toe rod and the first steering knuckle arm are connected through spherical hinges, two ends of the steering main pin are respectively connected with the upper cross arm and the lower cross arm through the spherical hinges, the electromagnet is used for generating suction after being electrified and attracting the locking pull rod to enable the locking pull rod to be locked on the frame, and the locking pull rod displacement sensor is used for detecting displacement parameters between the locking pull rod and the vehicle body in real time and feeding the displacement parameters back to the vehicle controller to determine the rear wheel steering angle.
The system of the invention is further configured as follows: the front wheel steering actuating motor makes the front wheel turn to through drive front wheel steering driving medium, drive front wheel steering driving medium is including consecutive left front wheel knuckle arm, left front wheel steering tie rod, rack, steering gear, right front wheel steering tie rod and right front wheel knuckle arm, left front wheel steering knuckle arm acts on left front wheel, right front wheel steering knuckle arm acts on right front wheel, steering gear links to each other with front wheel steering actuating motor.
The system of the invention is further configured as follows: the detection module comprises a torque sensor and a steering wheel angle sensor for detecting a steering wheel, a pedal position sensor for detecting an accelerator pedal, and a rack displacement sensor for detecting the angle of rotation of a front wheel and located on a rack.
The invention also provides a control method of the time-sharing four-wheel steering system of the hub motor driven electric automobile, which is operated in the time-sharing four-wheel steering system of the hub motor driven electric automobile and comprises the following steps:
1) the vehicle control unit acquires driving parameters acquired by the detection module and a steering mode selected by a driver and input by a steering mode selection switch, wherein the driving parameters comprise a steering wheel angle signal, a pedal position signal of an accelerator pedal, a driving vehicle speed signal, a front wheel steering angle signal and a rear wheel steering angle signal;
2) the vehicle speed tracking module calculates the running speed of the electric vehicle and the required front wheel driving torque according to the pedal position signal of an accelerator pedal, controls the hub motor to execute a running vehicle speed signal of a driver and inputs the running speed to the vehicle control unit;
3) when the vehicle runs, the vehicle control unit judges whether the steering mode selected by the driver is front wheel steering or four-wheel steering;
if the steering mode is front wheel steering, adopting a front wheel linear control steering and rear wheel steering locking mode, executing the steps 4) to 5), and then returning to the step 1);
if the steering mode is four-wheel steering, adopting a front wheel linear control steering mode and a rear wheel differential steering mode, executing the steps 6) -8), and then returning to the step 1);
4) when the selected steering module is used for steering the front wheel, the vehicle control unit transmits a steering wheel turning angle signal to the front wheel linear control steering control module and outputs a rear wheel aligning signal to the rear wheel steering locking module so that the rear wheel is aligned and then the rear wheel steering is locked;
5) the front wheel linear control steering control module drives a front wheel steering execution motor to perform front wheel steering according to the steering wheel angle signal and the front wheel steering angle signal, provides corresponding steering road feel for a driver and feeds the steering road feel back to the whole vehicle controller; meanwhile, the rear wheel steering locking module drives the rotary locking mechanism to correct the rear wheel and forbid the rear wheel to steer according to the rear wheel locking signal and the rear wheel steering signal;
6) when the selected steering mode is four-wheel steering, the vehicle control unit calculates to obtain ideal front and rear wheel turning angles required by the four-wheel steering and outputs a rear wheel unlocking signal to the rear wheel steering locking module, wherein the ideal front and rear wheel turning angles comprise the ideal front wheel turning angle and the ideal rear wheel turning angle, the ideal front wheel turning angle is transmitted to the front wheel linear control steering control module, and the ideal rear wheel turning angle is transmitted to the rear wheel differential steering control module;
7) the front wheel linear control steering control module drives a front wheel steering execution motor to steer the front wheel according to an ideal front wheel steering angle, provides corresponding steering road feel for a driver and feeds the steering road feel back to the whole vehicle controller; meanwhile, the rear wheel steering locking module drives the rotary locking mechanism to release steering locking according to the rear wheel unlocking signal;
8) and the rear wheel differential steering control module calculates to obtain a rear wheel differential torque according to the ideal rear wheel steering angle, and drives a rear wheel hub motor to steer the rear wheel according to the rear wheel differential torque.
The method of the invention is further provided with the following steps: the vehicle speed tracking controller searches a relationship curve of the longitudinal speed and the position of the accelerator pedal which is predetermined in the system according to a signal acquired by a pedal position sensor of the accelerator pedal, so that the running speed of the electric vehicle is obtained.
The method of the invention is further provided with the following steps: the vehicle control unit calculates and obtains ideal front and rear wheel rotation angles required by four-wheel steering, specifically,
the vehicle control unit inputs the collected steering wheel angles to a reference model to obtain ideal yaw rate and centroid yaw angle, and the ideal yaw rate and centroid yaw angle of the decoupled linear four-wheel steering model are controlled by an asymptotic tracking controller to track the ideal yaw rate and centroid yaw angle, so that ideal front and rear wheel angles of the four-wheel steering vehicle are obtained; the reference model is a linear two-degree-of-freedom vehicle model with neutral steering characteristics after the centroid slip angle amplitude reduction filtering.
The method of the invention is further provided with the following steps: the equation of state of the reference model is,
let xd＝[γdβd]T，ud＝[δf]，
The reference model is expressed as
In the formula,
wherein, γdIs the yaw rate, beta, of the reference modeldIs the centroid slip angle of the reference model, m is the vehicle mass, uxIs the longitudinal speed, delta, at the centre of mass of the vehiclefFor the angle of rotation of the front wheel, /)fdIs the distance of the center of mass to the front axis,/rdIs the distance of the center of mass to the rear axis, kfYaw stiffness, k, of the front wheelrFor cornering stiffness of the rear wheels, IzThe moment of inertia of the vehicle to the Z axis;
the centroid side drift angle is processed by an amplitude reduction filter, the transfer function of the amplitude reduction filter is adopted as,
wherein eta is a gain coefficient, xi is a damping coefficient, and omeganIs the circular frequency;
by adjusting the frequency omega of the circlenThe magnitude of the centroid slip angle is adjusted.
The method of the invention is further provided with the following steps: the linear dynamic model adopted by the linear four-wheel steering model is
In the equation, the ratio of the total of the components,
wherein lfDistance of front axle to center of mass,/rIs the distance from the rear axle to the center of mass;
the input and output of the linear four-wheel steering model are decoupled,
the transfer function adopted is
Wherein,
introduction of parameter u1、u2To realize the decoupling of the yaw velocity gamma and the centroid side slip angle beta, and the yaw velocity gamma obtained after the decoupling is relative to u1And centroid slip angle β with respect to u2Respectively is G11(s) and G22(s)；
Then there is
If and only ifWhile the yaw rate and the centroid slip angle are controlled by variables u1And u2And thus, the method can obtain the product,
wherein, a0＝(a12b21-a22b11)(a21b12-a11b22+a11b12-a12b22)，a1＝a21b12b11-a11b22b11+a11b12b21-a12b21b12，a2＝b11b22-b21b12，b0＝(a21b12-a11b22)(a12b21-a22b11)，b1＝a21b12b11-a11b22b11+a12b21b22-a22b11b22，b2＝b22b11，b3＝(a11b12-a12b22)(a21b12-a11b22)，b4＝-a21b2 12+a11b22b12+a11b12b22-a12b2 22，b5＝-b12b22，b6＝(-a12b21+a22b11)(a21b11-a11b21)，b7＝-a12b2 21+a22b11b21-a21b2 11+a11b11b21，b8＝-b11b21，b9＝(a21b12-a11b22)(a12b21-a22b11)，b10＝a21b12b11-a11b22b11+a12b21b22-a22b11b22，b11＝b22b11；
Let the transfer function of the asymptotic tracking controller be GC1(s) the asymptotic tracking controller is a P, PI, PD or PID controller;
for control equation e (t) ═ γd(t)-γ(t)＝γd(t)-GC1(t)G11(t) e (t) pull transform,
to obtain
Is provided with
Then
Characteristic polynomial d of 2-order systemg(s)dc(s)+ng(s)ncReduction of(s) to (0) to (d)2s2+d1s+d0＝0；
Wherein d is2＝1+b11kd，d1＝b11kp+(-a22b11+a12b21)kd-(a11+a22)，
d0＝a11a22-a21a12+kp(-a22b11+a12b21)；
Determining parameters of an asymptotic tracking controller for controlling yaw velocity and centroid yaw angle according to a Route decision table and a Route-Hurwitz stability criterion;
wherein the route judgment table isIn the formula
The Router-Hurwitz stability criterion is that the coefficients of the characteristic polynomials of the 2-order system are all positive or all negative.
The method of the invention is further provided with the following steps: the rear wheel differential steering control module calculates to obtain the rear wheel differential torque according to the ideal rear wheel steering angle, specifically,
establishing a dynamic model, taking a two-degree-of-freedom four-wheel steering vehicle with ideal front and rear wheel corners as input as a reference model, and designing a sliding mode variable structure controller to obtain a rear wheel differential torque for driving the rear wheel to steer;
the method comprises the following steps:
a) the equation of state of the front wheel linear control steering and the rear wheel differential steering is as follows, except the following turning angle of the wheels,
wherein beta is the vehicle mass center slip angle, gamma is the vehicle yaw rate,as the yaw angular acceleration of the vehicle,is the vehicle mass center slip angle velocity, m is the vehicle mass, uxIs the longitudinal speed at the centre of mass of the car,/fFrom front axis to centre of massA distance of lrIs the distance of the rear axle to the center of mass, δfIs the angle of rotation of the front wheel, kfYaw stiffness, k, of the front wheelrFor cornering stiffness of the rear wheels, IzIs the moment of inertia of the vehicle about the Z axis, drIs the rear wheel track, R is the effective radius of the tire;
b) let state space variable x (t) be [ β γ [ ]]TThe driving torque difference u (T) of the front and rear wheels is input as Δ T, and the state equations of the front wheel linear steering and the rear wheel differential steering are converted into
Wherein,
c) definition of slip form surface s ═ gamma-gammad+ξ(β-βd)，
Where ξ is the weight coefficient, γdYaw rate, beta, for reference modeldIs the centroid slip angle of the reference model;
the derivation is carried out to obtain the result,
in the formula,
wherein,in order to refer to the yaw angular acceleration of the model,is the centroid yaw angular velocity of the reference model;
due to the fact thatIs bounded, thenThereinIs a constant;
using an approach law with a saturation function, the controller is
Compared with the prior art, the invention has the beneficial effects that:
the time-sharing four-wheel steering system of the hub motor driven electric automobile and the control method thereof provided by the invention not only can switch the front wheel steering and the four-wheel steering according to the requirements of a driver and provide a proper road feel for the driver, but also have the advantages of simple structure, accurate steering and the like and have good robustness. When the selected steering mode is that the front wheels are steered, the front wheels are controlled by the front wheel linear control steering control module to perform traditional front wheel steering, and the rear wheels are locked in a return-to-normal mode. When the selected steering mode is four-wheel steering, the rear wheels are unlocked, the front wheels are independently steered by adopting the traditional steering mode and the rear wheel differential steering mode, the rear wheels are independently driven and are combined with the differential steering technology, the maneuverability of the vehicle can be effectively improved under the low-speed working condition, and the tail flicking and sideslip during the turning of the vehicle can be effectively reduced at high speed; and meanwhile, the active safety and the operation stability of the automobile can be improved.
The foregoing is only an overview of the technical solutions of the present invention, and in order to more clearly understand the technical solutions of the present invention, the present invention is further described below with reference to the accompanying drawings.
Drawings
FIG. 1 is a schematic structural diagram of a time-sharing four-wheel steering system of an electric vehicle driven by a hub motor according to the present invention;
FIG. 2 is a diagram illustrating a simulated yaw rate at a low speed according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating a centroid slip angle at low speed simulated by an embodiment of the method of the present invention;
FIG. 4 illustrates the x and y positions at low speed simulated by an embodiment of the method of the present invention;
FIG. 5 is a diagram illustrating the low speed torque simulated by an embodiment of the method of the present invention;
fig. 6 shows the simulated yaw rate at medium speed according to the embodiment of the present invention;
fig. 7 shows the simulated yaw rate at medium speed according to the embodiment of the present invention;
FIG. 8 shows simulated x and y positions at medium speed in accordance with an embodiment of the present invention;
FIG. 9 shows the medium speed torque simulated by the embodiment of the method of the present invention;
FIG. 10 is a diagram illustrating a simulated yaw rate at high speed according to an embodiment of the method of the present invention;
FIG. 11 is a diagram illustrating the centroid slip angle at high speed simulated by an embodiment of the method of the present invention;
FIG. 12 illustrates the x and y positions at high speed simulated by an embodiment of the method of the present invention;
FIG. 13 shows the torque at high speed simulated by the embodiment of the method of the present invention.
In the figure: 1-a left front wheel steering knuckle arm; 2-left front wheel steering tie rod; 3-a rack; 4-a steering gear; 5-steering actuating motor and reducer; 6-rack displacement sensor; 7-rear wheel hub motor; 8-steering wheel angle sensor; 9-road feel simulation motor and reducer; 10-a torque sensor; 11-a steering wheel; 12-a front wheel steer-by-wire module; 13-vehicle control unit; 14-a rear wheel differential steering control module; 15-left rear wheel; 16-a toe rod; 17-upper cross arm; 18-kingpin; 19-spherical hinge; 20-a lower cross arm; 21-locking pull rod displacement sensor; 22-return spur gear; 23-an electromagnetic clutch; 24-a return motor; 25-locking pull rod; 26-first knuckle arm end, 27-electromagnet, 28-frame, 29-second knuckle arm.
Detailed Description
The invention is further described with reference to the accompanying drawings.
The present invention provides a time-sharing four-wheel steering system of an electric vehicle driven by a hub motor, as shown in fig. 1, comprising:
the detection module is used for detecting the driving parameters of the electric automobile and inputting the driving parameters to the vehicle control unit 13; the driving parameters comprise a steering wheel angle signal, a pedal position signal of an accelerator pedal, a driving vehicle speed signal, a front wheel steering angle signal and a rear wheel steering angle signal;
a steering mode selection switch for a driver to manually select a steering mode including front wheel steering and four wheel steering, and to input the selected steering mode to the vehicle control unit 13;
the vehicle speed tracking module is used for calculating the running speed of the electric vehicle and the required front wheel driving torque according to the pedal position signal of the accelerator pedal, controlling the in-wheel motor to execute a running vehicle speed signal of a driver and inputting the running speed to the vehicle control unit 13;
the vehicle control unit 13 is configured to receive a driving speed, transmit a steering wheel angle signal to the front wheel steer-by-wire control module 12 when the selected steer module is front wheel steer, and output a rear wheel lock signal to the rear wheel steer lock module; when the selected steering mode is four-wheel steering, calculating to obtain an ideal front and rear wheel steering angle required by the four-wheel steering and outputting a rear wheel unlocking signal to a rear wheel steering locking module, wherein the ideal front and rear wheel steering angle comprises an ideal front wheel steering angle and an ideal rear wheel steering angle, and transmitting the ideal front wheel steering angle to a front wheel linear control steering control module and the ideal rear wheel steering angle to a rear wheel differential steering control module;
the front wheel linear control steering control module 12 is used for driving the front wheel steering execution motor 5 to steer the front wheels according to the steering wheel angle signal and the front wheel steering angle signal or the ideal front wheel steering angle, providing corresponding steering road feel for a driver through the road feel simulation motor and the speed reducer 9, and feeding the steering road feel back to the vehicle control unit 13;
the rear wheel differential steering control module 14 is used for calculating to obtain a rear wheel differential torque according to an ideal rear wheel steering angle and driving the rear wheel hub motor 7 to steer the rear wheel according to the rear wheel differential torque;
and the rear wheel steering locking module is used for driving the steering locking mechanism to rotate the rear wheels in a right direction according to the rear wheel locking signal and the rear wheel steering angle signal, forbidding the rear wheels to steer, and driving the steering locking mechanism to release the steering locking according to the rear wheel unlocking signal.
As shown in fig. 1, the steering locking mechanism includes a return positive motor 24 and two sets of steering mechanisms that are symmetrically installed on the frame 18 and have the same structure, the return positive motor 24 is connected to the rear wheel steering locking module, and both sets of steering mechanisms are connected to the return positive motor 24 and respectively act on the left rear wheel 15 and the right rear wheel.
The steering mechanism comprises an electromagnetic clutch 23, a return spur gear 22, a locking pull rod 25, a toe-in rod 16, a first knuckle arm 26 and a second knuckle arm 29 which are connected in sequence, an electromagnet 27 which is lapped on the surface of the locking pull rod 25 and is arranged on a vehicle frame 28, a steering main pin 18 which is connected with one end of the first knuckle arm 26 and one end of the second knuckle arm 29, an upper cross arm 17 and a lower cross arm 20 which are arranged on the vehicle frame 28, and a locking pull rod displacement sensor 21 which is used for detecting the angle of a rear wheel and is arranged on the locking pull rod 25; the electromagnetic clutch 23 is connected with a back positive motor 24 and connected with a rear wheel steering locking module, the locking pull rod 25 is connected with a back spur gear 22 through a face rack, the locking pull rod 25 is connected with the toe rod 16, the toe rod 16 is connected with the first steering knuckle arm 26 through a ball hinge 19, two ends of the steering main pin 18 are respectively connected with the upper cross arm 17 and the lower cross arm 20 through the ball hinge 19, the electromagnet 27 is used for generating suction after being electrified and attracting the locking pull rod 25 to lock the locking pull rod 25 on the frame 28, and the locking pull rod displacement sensor 21 is used for detecting displacement parameters between the locking pull rod 25 and the frame in real time and feeding the displacement parameters back to the vehicle controller 13 to determine the rear wheel steering angle.
As shown in fig. 1, the front wheel steering actuator motor 5 steers the front wheel by driving a front wheel steering transmission including a left front wheel knuckle arm 1, a left front wheel steering tie rod 2, a rack 3, a steering gear 4, a right front wheel knuckle arm and a right front wheel knuckle arm connected in sequence, the left front wheel knuckle arm 1 acting on the left front wheel, the right front wheel knuckle arm acting on the right front wheel, and the steering gear 4 connected to the front wheel steering actuator motor 5.
As shown in fig. 1, the detection module includes a torque sensor 10 and a steering wheel angle sensor 8 for detecting a steering wheel 11, a pedal position sensor for detecting an accelerator pedal, and a rack displacement sensor 6 for detecting a front wheel steering angle and located on a rack 3.
The invention also provides a control method of the time-sharing four-wheel steering system of the hub motor driven electric automobile, which is operated in the time-sharing four-wheel steering system of the hub motor driven electric automobile shown in figure 1 and comprises the following steps:
1) the vehicle control unit acquires driving parameters acquired by the detection module and a steering mode selected by a driver and input by a steering mode selection switch, wherein the driving parameters comprise a steering wheel angle signal, a pedal position signal of an accelerator pedal, a driving vehicle speed signal, a front wheel steering angle signal and a rear wheel steering angle signal;
2) the vehicle speed tracking module calculates the running speed of the electric vehicle and the required front wheel driving torque according to the pedal position signal of an accelerator pedal, controls the hub motor to execute a running vehicle speed signal of a driver and inputs the running speed to the vehicle control unit;
3) when the vehicle runs, the vehicle control unit judges whether the steering mode selected by the driver is front wheel steering or four-wheel steering;
if the steering mode is front wheel steering, adopting a front wheel linear control steering and rear wheel steering locking mode, executing the steps 4) to 5), and then returning to the step 1);
if the steering mode is four-wheel steering, adopting a front wheel linear control steering mode and a rear wheel differential steering mode, executing the steps 6) -8), and then returning to the step 1);
4) when the selected steering module is used for steering the front wheel, the vehicle control unit transmits a steering wheel turning angle signal to the front wheel linear control steering control module and outputs a rear wheel aligning signal to the rear wheel steering locking module so that the rear wheel is aligned and then the rear wheel steering is locked;
5) the front wheel linear control steering control module drives a front wheel steering execution motor to perform front wheel steering according to the steering wheel angle signal and the front wheel steering angle signal, provides corresponding steering road feel for a driver and feeds the steering road feel back to the whole vehicle controller; meanwhile, the rear wheel steering locking module drives the rotary locking mechanism to correct the rear wheel and forbid the rear wheel to steer according to the rear wheel locking signal and the rear wheel steering signal;
6) when the selected steering mode is four-wheel steering, the vehicle control unit calculates to obtain ideal front and rear wheel turning angles required by the four-wheel steering and outputs a rear wheel unlocking signal to the rear wheel steering locking module, wherein the ideal front and rear wheel turning angles comprise the ideal front wheel turning angle and the ideal rear wheel turning angle, the ideal front wheel turning angle is transmitted to the front wheel linear control steering control module, and the ideal rear wheel turning angle is transmitted to the rear wheel differential steering control module;
7) the front wheel linear control steering control module drives a front wheel steering execution motor to steer the front wheel according to an ideal front wheel steering angle, provides corresponding steering road feel for a driver and feeds the steering road feel back to the whole vehicle controller; meanwhile, the rear wheel steering locking module drives the rotary locking mechanism to release steering locking according to the rear wheel unlocking signal;
8) and the rear wheel differential steering control module calculates to obtain a rear wheel differential torque according to the ideal rear wheel steering angle, and drives a rear wheel hub motor to steer the rear wheel according to the rear wheel differential torque.
In the method, the vehicle speed tracking controller searches a relationship curve of the longitudinal speed and the position of the accelerator pedal which is predetermined in a system according to a signal acquired by a pedal position sensor of the accelerator pedal, so that the running speed of the electric vehicle is obtained.
In the method, the vehicle controller calculates and obtains ideal front and rear wheel corners required by four-wheel steering, specifically, the vehicle controller inputs the collected steering wheel corners to a reference model to obtain ideal yaw velocity and centroid yaw angle, and the yaw velocity and centroid yaw angle of the decoupled linear four-wheel steering model are controlled by adopting an asymptotic tracking controller to track the ideal yaw velocity and centroid yaw angle, so as to obtain the ideal front and rear wheel corners of the four-wheel steering vehicle; the reference model is a linear two-degree-of-freedom vehicle model with neutral steering characteristics after the centroid slip angle amplitude reduction filtering.
In the method of the invention, the state equation of the reference model is,
let xd＝[γd βd]T，ud＝[δf]，
The reference model is expressed as
In the formula,
wherein, γdIs the yaw rate, beta, of the reference modeldIs the centroid slip angle of the reference model, m is the vehicle mass, uxIs the longitudinal speed, delta, at the centre of mass of the vehiclefFor the angle of rotation of the front wheel, /)fdIs the distance of the center of mass to the front axis,/rdIs the distance of the center of mass to the rear axis, kfYaw stiffness, k, of the front wheelrFor cornering stiffness of the rear wheels, IzThe moment of inertia of the vehicle to the Z axis;
the centroid side drift angle is processed by an amplitude reduction filter, the transfer function of the amplitude reduction filter is adopted as,
wherein eta is a gain coefficient, xi is a damping coefficient, and omeganIs the circular frequency;
by adjusting the frequency of the circleωnThe magnitude of the centroid slip angle is adjusted.
In the method, the linear dynamic model adopted by the linear four-wheel steering model is
In the equation, the ratio of the total of the components,
wherein lfDistance of front axle to center of mass,/rIs the distance from the rear axle to the center of mass;
the input and output of the linear four-wheel steering model are decoupled,
the transfer function adopted is
Wherein,
introduction of parameter u1、u2To realize the decoupling of the yaw velocity gamma and the centroid side slip angle beta, and the yaw velocity gamma obtained after the decoupling is relative to u1And centroid slip angle β with respect to u2Respectively is G11(s) and G22(s)；
Then there is
If and only ifWhile the yaw rate and the centroid slip angle are controlled by variables u1And u2And thus, the method can obtain the product,
wherein, a0＝(a12b21-a22b11)(a21b12-a11b22+a11b12-a12b22)，a1＝a21b12b11-a11b22b11+a11b12b21-a12b21b12，a2＝b11b22-b21b12，b0＝(a21b12-a11b22)(a12b21-a22b11)，b1＝a21b12b11-a11b22b11+a12b21b22-a22b11b22，b2＝b22b11，b3＝(a11b12-a12b22)(a21b12-a11b22)，b4＝-a21b2 12+a11b22b12+a11b12b22-a12b2 22，b5＝-b12b22，b6＝(-a12b21+a22b11)(a21b11-a11b21)，b7＝-a12b2 21+a22b11b21-a21b2 11+a11b11b21，b8＝-b11b21，b9＝(a21b12-a11b22)(a12b21-a22b11)，b10＝a21b12b11-a11b22b11+a12b21b22-a22b11b22，b11＝b22b11；
Let the transfer function of the asymptotic tracking controller be GC1(s) the asymptotic tracking controller is a P, PI, PD or PID controller;
for control equation e (t) ═ γd(t)-γ(t)＝γd(t)-GC1(t)G11(t) e (t) pull transform,
to obtain
Is provided with
Then
Characteristic polynomial d of 2-order systemg(s)dc(s)+ng(s)ncReduction of(s) to (0) to (d)2s2+d1s+d0＝0；
Wherein d is2＝1+b11kd，d1＝b11kp+(-a22b11+a12b21)kd-(a11+a22)，
d0＝a11a22-a21a12+kp(-a22b11+a12b21)；
Determining parameters of an asymptotic tracking controller for controlling yaw velocity and centroid yaw angle according to a Route decision table and a Route-Hurwitz stability criterion;
wherein the route judgment table isIn the formula
The Router-Hurwitz stability criterion is that the coefficients of the characteristic polynomials of the 2-order system are all positive or all negative.
In the method of the invention, the rear wheel differential steering control module calculates the rear wheel differential torque according to the ideal rear wheel steering angle, specifically,
establishing a dynamic model, taking a two-degree-of-freedom four-wheel steering vehicle with ideal front and rear wheel corners as input as a reference model, and designing a sliding mode variable structure controller to obtain a rear wheel differential torque for driving the rear wheel to steer;
the method comprises the following steps:
a) the equation of state of the front wheel linear control steering and the rear wheel differential steering is as follows, except the following turning angle of the wheels,
wherein beta is the vehicle mass center slip angle, gamma is the vehicle yaw rate,as the yaw angular acceleration of the vehicle,is the vehicle mass center slip angle velocity, m is the vehicle mass, uxIs the longitudinal speed at the centre of mass of the car,/fDistance of front axle to center of mass,/rIs the distance of the rear axle to the center of mass, δfIs the angle of rotation of the front wheel, kfYaw stiffness, k, of the front wheelrFor cornering stiffness of the rear wheels, IzIs the moment of inertia of the vehicle about the Z axis, drIs the rear wheel track, R is the effective radius of the tire;
b) let state space variable x (t) be [ β γ [ ]]TThe input is the difference between the driving torque of the front and rear wheels, i.e., u (T) ═ Δ TTransforming the state equation of the front wheel linear control steering and the rear wheel differential steering into
Wherein,
c) definition of slip form surface s ═ gamma-gammad+ξ(β-βd)，
Where ξ is the weight coefficient, γdYaw rate, beta, for reference modeldIs the centroid slip angle of the reference model;
the derivation is carried out to obtain the result,
in the formula,
wherein,in order to refer to the yaw angular acceleration of the model,is the centroid yaw angular velocity of the reference model;
due to the fact thatIs bounded, thenThereinIs a constant;
using an approach law with a saturation function, the controller is
Simulation analysis:
when the steering mode is four-wheel steering, the four-wheel steering is taken as a reference model, the front wheels finish independent steering in the traditional steering and rear wheel differential steering modes, and simulation analysis is carried out.
Different vehicle speeds and front wheel turning angles are used as input, front wheel turning angles and rear wheel turning angles are used as output, parameter curves such as yaw velocity, mass center slip angle and the like are simulated after decoupling calculation is carried out.
At low speed, u is 5m/s, v is 5m/s, and front wheel turning angle delta is selectedf＝0.2094rad，
After decoupling, get deltaf1＝0.2092rad，δr1＝-0.0005454rad。
At medium speed, u is 15m/s, v is 15m/s, and front wheel turning angle delta is selectedf＝0.0721rad，
After decoupling, get deltaf1＝0.07194rad，δr1＝-2.505e-06rad。
At high speed, u is 25m/s, v is 25m/s, and front wheel turning angle delta is selectedf＝0.0454rad，
After decoupling, get deltaf1＝0.04512rad，δr1＝-0.0001544rad。
Corresponding vehicle speed and decoupled front and rear wheel turning angles are used as input, and graphs such as yaw rate, centroid slip angle and the like are obtained through simulation, as shown in fig. 1 to 12.
As can be seen from fig. 1 to 12, the curve of the conventional steering model of the front wheels and the curve of the differential steering model of the rear wheels are substantially consistent with the curve of the four-wheel steering model, which shows that the method can well realize the four-wheel steering.
As can be seen from fig. 1, 5, and 9, the yaw-rate stable value increases with an increase in vehicle speed, and is stabilized between 3.3rad/s and 3.8 rad/s. Meanwhile, as can be seen from fig. 1, the conventional steering of the front wheels and the differential steering of the rear wheels at low speed are more stable than the stable value of the yaw rate of the four-wheel steering model.
As can be seen from fig. 2, 6, and 10, the centroid slip angle stabilization value decreases as the vehicle speed increases. The stable value of the centroid slip angle at low speed is 0.058 rad; the stable value of the mass center side slip angle is-0.03 rad at medium speed; the stable value of the centroid slip angle at high speed is-0.078 rad. Meanwhile, as can be seen from fig. 2, the traditional steering of the front wheels and the differential steering of the rear wheels are more stable in the low-speed state than the stable value of the centroid slip angle of the four-wheel steering model.
As can be seen from fig. 3, 7 and 11, the x and y position curves of the front wheel conventional steering and rear wheel differential steering model are identical to the x and y position curves of the four wheel steering model, and the maximum values of the x and y positions increase with increasing vehicle speed.
As can be seen from fig. 4, 8, and 12, the torque value decreases and stabilizes within a certain range as the vehicle speed increases.
Simulation results show that the steering characteristics of the front wheels in a traditional steering mode and a rear wheel differential steering mode are ideal, so that the rear wheels are independently driven and combined with a differential steering technology, the maneuverability of the vehicle can be effectively improved under a low-speed working condition, and the tail flicking and sideslip during the turning of the vehicle can be effectively reduced at high speed; and meanwhile, the active safety and the operation stability of the automobile can be improved.
The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (10)
1. The utility model provides an in-wheel motor drive electric automobile's timesharing four-wheel steering system which characterized in that includes:
the detection module is used for detecting the driving parameters of the electric automobile and inputting the driving parameters to the whole automobile controller; the driving parameters comprise a steering wheel angle signal, a pedal position signal of an accelerator pedal, a driving vehicle speed signal, a front wheel steering angle signal and a rear wheel steering angle signal;
the steering mode selection switch is used for manually selecting a steering mode by a driver, wherein the steering mode comprises front wheel steering and four-wheel steering, and the selected steering mode is input to the whole vehicle controller;
the vehicle speed tracking module is used for calculating the running speed of the electric vehicle and the required front wheel driving torque according to the pedal position signal of the accelerator pedal, controlling the in-wheel motor to execute a running vehicle speed signal of a driver and inputting the running speed to the vehicle control unit;
the vehicle control unit is used for receiving the driving speed, transmitting a steering wheel turning angle signal to the front wheel linear control steering control module when the selected steering module is front wheel steering, and outputting a rear wheel locking signal to the rear wheel steering locking module; when the selected steering mode is four-wheel steering, calculating to obtain an ideal front and rear wheel steering angle required by the four-wheel steering and outputting a rear wheel unlocking signal to a rear wheel steering locking module, wherein the ideal front and rear wheel steering angle comprises an ideal front wheel steering angle and an ideal rear wheel steering angle, and transmitting the ideal front wheel steering angle to a front wheel linear control steering control module and the ideal rear wheel steering angle to a rear wheel differential steering control module;
the front wheel linear control steering control module is used for driving a front wheel steering execution motor to steer the front wheels according to the steering wheel angle signal and the front wheel steering angle signal or the ideal front wheel steering angle, providing corresponding steering road feel for a driver and feeding the steering road feel back to the whole vehicle controller;
the rear wheel differential steering control module is used for calculating to obtain a rear wheel differential torque according to an ideal rear wheel steering angle and driving a rear wheel hub motor to steer the rear wheel according to the rear wheel differential torque;
and the rear wheel steering locking module is used for driving the steering locking mechanism to rotate the rear wheels in a right direction according to the rear wheel locking signal and the rear wheel steering angle signal, forbidding the rear wheels to steer, and driving the steering locking mechanism to release the steering locking according to the rear wheel unlocking signal.
2. The time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 1, characterized in that: the steering locking mechanism comprises a return motor and two groups of steering mechanisms which are symmetrically arranged on the frame and have the same structure, the return motor is connected with the rear wheel steering locking module, and the two groups of steering mechanisms are connected with the return motor and respectively act on the left rear wheel and the right rear wheel;
the steering mechanism comprises an electromagnetic clutch, a return spur gear, a locking pull rod, a front binding rod, a first steering knuckle arm and a second steering knuckle arm which are sequentially connected, an electromagnet which is lapped on the surface of the locking pull rod and is arranged on the frame, steering main pins which are connected with one end of the first steering knuckle arm and one end of the second steering knuckle arm, an upper cross arm and a lower cross arm which are arranged on the frame, and a locking pull rod displacement sensor which is used for detecting the angle of a rear wheel and is arranged on the locking pull rod; the electromagnetic clutch is connected with the positive electricity return machine and connected with the rear wheel steering locking module, the locking pull rod is connected with the positive electricity return machine through a rod face rack, the locking pull rod and the toe rod as well as the toe rod and the first steering knuckle arm are connected through spherical hinges, two ends of the steering main pin are respectively connected with the upper cross arm and the lower cross arm through the spherical hinges, the electromagnet is used for generating suction after being electrified and attracting the locking pull rod to enable the locking pull rod to be locked on the frame, and the locking pull rod displacement sensor is used for detecting displacement parameters between the locking pull rod and the vehicle body in real time and feeding the displacement parameters back to the vehicle controller to determine the rear wheel steering angle.
3. The time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 1, characterized in that: the front wheel steering actuating motor makes the front wheel turn to through drive front wheel steering driving medium, drive front wheel steering driving medium is including consecutive left front wheel knuckle arm, left front wheel steering tie rod, rack, steering gear, right front wheel steering tie rod and right front wheel knuckle arm, left front wheel steering knuckle arm acts on left front wheel, right front wheel steering knuckle arm acts on right front wheel, steering gear links to each other with front wheel steering actuating motor.
4. The time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 3, characterized in that: the detection module comprises a torque sensor and a steering wheel angle sensor for detecting a steering wheel, a pedal position sensor for detecting an accelerator pedal, and a rack displacement sensor for detecting the angle of rotation of a front wheel and located on a rack.
5. A control method of a time-sharing four-wheel steering system of an in-wheel motor driven electric vehicle, which is operated in the time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle of any one of claims 1 to 4, comprising the steps of:
1) the vehicle control unit acquires driving parameters acquired by the detection module and a steering mode selected by a driver and input by a steering mode selection switch, wherein the driving parameters comprise a steering wheel angle signal, a pedal position signal of an accelerator pedal, a driving vehicle speed signal, a front wheel steering angle signal and a rear wheel steering angle signal;
2) the vehicle speed tracking module calculates the running speed of the electric vehicle and the required front wheel driving torque according to the pedal position signal of an accelerator pedal, controls the hub motor to execute a running vehicle speed signal of a driver and inputs the running speed to the vehicle control unit;
3) when the vehicle runs, the vehicle control unit judges whether the steering mode selected by the driver is front wheel steering or four-wheel steering;
if the steering mode is front wheel steering, adopting a front wheel linear control steering and rear wheel steering locking mode, executing the steps 4) to 5), and then returning to the step 1);
if the steering mode is four-wheel steering, adopting a front wheel linear control steering mode and a rear wheel differential steering mode, executing the steps 6) -8), and then returning to the step 1);
4) when the selected steering module is used for steering the front wheel, the vehicle control unit transmits a steering wheel turning angle signal to the front wheel linear control steering control module and outputs a rear wheel aligning signal to the rear wheel steering locking module so that the rear wheel is aligned and then the rear wheel steering is locked;
5) the front wheel linear control steering control module drives a front wheel steering execution motor to perform front wheel steering according to the steering wheel angle signal and the front wheel steering angle signal, provides corresponding steering road feel for a driver and feeds the steering road feel back to the whole vehicle controller; meanwhile, the rear wheel steering locking module drives the rotary locking mechanism to correct the rear wheel and forbid the rear wheel to steer according to the rear wheel locking signal and the rear wheel steering signal;
6) when the selected steering mode is four-wheel steering, the vehicle control unit calculates to obtain ideal front and rear wheel turning angles required by the four-wheel steering and outputs a rear wheel unlocking signal to the rear wheel steering locking module, wherein the ideal front and rear wheel turning angles comprise the ideal front wheel turning angle and the ideal rear wheel turning angle, the ideal front wheel turning angle is transmitted to the front wheel linear control steering control module, and the ideal rear wheel turning angle is transmitted to the rear wheel differential steering control module;
7) the front wheel linear control steering control module drives a front wheel steering execution motor to steer the front wheel according to an ideal front wheel steering angle, provides corresponding steering road feel for a driver and feeds the steering road feel back to the whole vehicle controller; meanwhile, the rear wheel steering locking module drives the rotary locking mechanism to release steering locking according to the rear wheel unlocking signal;
8) and the rear wheel differential steering control module calculates to obtain a rear wheel differential torque according to the ideal rear wheel steering angle, and drives a rear wheel hub motor to steer the rear wheel according to the rear wheel differential torque.
6. The control method of the time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 5, characterized in that: the vehicle speed tracking controller searches a relationship curve of the longitudinal speed and the position of the accelerator pedal which is predetermined in the system according to a signal acquired by a pedal position sensor of the accelerator pedal, so that the running speed of the electric vehicle is obtained.
7. The control method of the time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 5, characterized in that: the vehicle control unit calculates and obtains ideal front and rear wheel rotation angles required by four-wheel steering, specifically,
the vehicle control unit inputs the collected steering wheel angles to a reference model to obtain ideal yaw rate and centroid yaw angle, and the ideal yaw rate and centroid yaw angle of the decoupled linear four-wheel steering model are controlled by an asymptotic tracking controller to track the ideal yaw rate and centroid yaw angle, so that ideal front and rear wheel angles of the four-wheel steering vehicle are obtained; the reference model is a linear two-degree-of-freedom vehicle model with neutral steering characteristics after the centroid slip angle amplitude reduction filtering.
8. The control method of the time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 7, characterized in that: the equation of state of the reference model is,
let xd＝[γd βd]T，ud＝[δf]，
The reference model is expressed as
in the formula,
wherein ,γdIs the yaw rate, beta, of the reference modeldIs the centroid slip angle of the reference model, m is the vehicle mass, uxIs the longitudinal speed, delta, at the centre of mass of the vehiclefFor the angle of rotation of the front wheel, /)fdIs the distance of the center of mass to the front axis,/rdIs the distance of the center of mass to the rear axis, kfYaw stiffness, k, of the front wheelrFor the side-bias of the rear wheelsRigidity, IzThe moment of inertia of the vehicle to the Z axis;
the centroid side drift angle is processed by an amplitude reduction filter, the transfer function of the amplitude reduction filter is adopted as,
wherein eta is a gain coefficient, xi is a damping coefficient, and omeganIs the circular frequency;
by adjusting the frequency omega of the circlenThe magnitude of the centroid slip angle is adjusted.
9. The control method of the time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 8, characterized in that: the linear dynamic model adopted by the linear four-wheel steering model is
In the equation, the ratio of the total of the components,
wherein ,lfDistance of front axle to center of mass,/rIs the distance from the rear axle to the center of mass;
the input and output of the linear four-wheel steering model are decoupled,
the transfer function adopted is
wherein ,
introduction of parameter u1、u2To realize transverselyDecoupling the yaw angular velocity gamma and the centroid slip angle beta, and obtaining the yaw angular velocity gamma relative to u after decoupling1And centroid slip angle β with respect to u2Respectively is G11(s) and G22(s)；
Then there is
If and only ifWhile the yaw rate and the centroid slip angle are controlled by variables u1 and u2And thus, the method can obtain the product,
wherein ,a0＝(a12b21-a22b11)(a21b12-a11b22+a11b12-a12b22)，a1＝a21b12b11-a11b22b11+a11b12b21-a12b21b12，a2＝b11b22-b21b12，b0＝(a21b12-a11b22)(a12b21-a22b11)，b1＝a21b12b11-a11b22b11+a12b21b22-a22b11b22，b2＝b22b11，b3＝(a11b12-a12b22)(a21b12-a11b22)，b4＝-a21b2 12+a11b22b12+a11b12b22-a12b2 22，b5＝-b12b22，b6＝(-a12b21+a22b11)(a21b11-a11b21)，b7＝-a12b2 21+a22b11b21-a21b2 11+a11b11b21，b8＝-b11b21，b9＝(a21b12-a11b22)(a12b21-a22b11)，b10＝a21b12b11-a11b22b11+a12b21b22-a22b11b22，b11＝b22b11；
Let the transfer function of the asymptotic tracking controller be GC1(s) the asymptotic tracking controller is a P, PI, PD or PID controller;
for control equation e (t) ═ γd(t)-γ(t)＝γd(t)-GC1(t)G11(t) e (t) pull transform,
to obtain
Is provided with
Then
Characteristic polynomial d of 2-order systemg(s)dc(s)+ng(s)ncReduction of(s) to (0) to (d)2s2+d1s+d0＝0；
wherein ,d2＝1+b11kd，d1＝b11kp+(-a22b11+a12b21)kd-(a11+a22)，
d0＝a11a22-a21a12+kp(-a22b11+a12b21)；
Determining parameters of an asymptotic tracking controller for controlling yaw velocity and centroid yaw angle according to a Route decision table and a Route-Hurwitz stability criterion;
wherein the route judgment table is in the formula
The Router-Hurwitz stability criterion is that the coefficients of the characteristic polynomials of the 2-order system are all positive or all negative.
10. The control method of the time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 5, characterized in that: the rear wheel differential steering control module calculates to obtain the rear wheel differential torque according to the ideal rear wheel steering angle, specifically,
establishing a dynamic model, taking a two-degree-of-freedom four-wheel steering vehicle with ideal front and rear wheel corners as input as a reference model, and designing a sliding mode variable structure controller to obtain a rear wheel differential torque for driving the rear wheel to steer;
the method comprises the following steps:
a) the equation of state of the front wheel linear control steering and the rear wheel differential steering is as follows, except the following turning angle of the wheels,
whereinBeta is the vehicle mass center slip angle, gamma is the vehicle yaw rate,as the yaw angular acceleration of the vehicle,is the vehicle mass center slip angle velocity, m is the vehicle mass, uxIs the longitudinal speed at the centre of mass of the car,/fDistance of front axle to center of mass,/rIs the distance of the rear axle to the center of mass, δfIs the angle of rotation of the front wheel, kfYaw stiffness, k, of the front wheelrFor cornering stiffness of the rear wheels, IzIs the moment of inertia of the vehicle about the Z axis, drIs the rear wheel track, R is the effective radius of the tire;
b) let state space variable x (t) be [ β γ [ ]]TThe driving torque difference u (T) of the front and rear wheels is input as Δ T, and the state equations of the front wheel linear steering and the rear wheel differential steering are converted into
wherein ,
c) definition of slip form surface s ═ gamma-gammad+ξ(β-βd)，
Where ξ is the weight coefficient, γdYaw rate, beta, for reference modeldIs the centroid slip angle of the reference model;
the derivation is carried out to obtain the result,
in the formula,
wherein ,in order to refer to the yaw angular acceleration of the model,is the centroid yaw angular velocity of the reference model;
due to the fact thatIs bounded, thenThereinIs a constant;
using an approach law with a saturation function, the controller is
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| CN111232052A (en) * | 2020-02-25 | 2020-06-05 | 东南大学 | Four-wheel steering mode for four-wheel independent drive electric automobile |
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| CN112278070A (en) * | 2020-08-08 | 2021-01-29 | 清华大学 | Independent steering device and front wheel steering system using same |
| CN112248794A (en) * | 2020-10-30 | 2021-01-22 | 厦门理工学院 | Structure and method for cooperative control of driving and steering of electric forklift |
| CN113022551A (en) * | 2021-03-26 | 2021-06-25 | 华南理工大学 | Control rod steer-by-wire control method |
| CN113022551B (en) * | 2021-03-26 | 2022-03-29 | 华南理工大学 | Control rod steer-by-wire control method |
| CN113401222A (en) * | 2021-08-05 | 2021-09-17 | 沈阳德恒装备股份有限公司 | Four-wheel steering chassis for electric road sweeper |
| CN114801701A (en) * | 2022-04-29 | 2022-07-29 | 北京理工大学 | Wheel hub motor driven articulated vehicle marshallable configuration structure |
| CN114801701B (en) * | 2022-04-29 | 2024-05-24 | 北京理工大学 | In-wheel motor driven articulated vehicle marshalling configuration structure |
| CN114735076A (en) * | 2022-05-19 | 2022-07-12 | 吉林大学 | Fault-tolerant control method for differential cooperative steer-by-wire |
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