CN112109734B - Automatic driving switching method and device based on C-EPS system - Google Patents

Automatic driving switching method and device based on C-EPS system Download PDF

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Publication number
CN112109734B
CN112109734B CN202011010112.7A CN202011010112A CN112109734B CN 112109734 B CN112109734 B CN 112109734B CN 202011010112 A CN202011010112 A CN 202011010112A CN 112109734 B CN112109734 B CN 112109734B
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steering
steering wheel
motor
automatic driving
mode
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CN112109734A (en
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虞忠潮
***
王燮辉
朱兴旺
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Hangzhou Shibao Auto Steering Gear Co ltd
Zhejiang Lover Health Science and Technology Development Co Ltd
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Hangzhou Shibao Auto Steering Gear Co ltd
Zhejiang Lover Health Science and Technology Development Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W60/00—Drive control systems specially adapted for autonomous road vehicles
    • B60W60/005—Handover processes
    • B60W60/0059—Estimation of the risk associated with autonomous or manual driving, e.g. situation too complex, sensor failure or driver incapacity
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W60/00—Drive control systems specially adapted for autonomous road vehicles
    • B60W60/001—Planning or execution of driving tasks
    • B60W60/0015—Planning or execution of driving tasks specially adapted for safety
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W60/00—Drive control systems specially adapted for autonomous road vehicles
    • B60W60/005—Handover processes
    • 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
    • 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
    • B62D6/08—Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits responsive only to driver input torque
    • B62D6/10—Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits responsive only to driver input torque characterised by means for sensing or determining torque

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  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Automation & Control Theory (AREA)
  • Human Computer Interaction (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Steering Control In Accordance With Driving Conditions (AREA)

Abstract

The invention discloses an automatic driving switching method based on a C-EPS system, when the input torque of a steering wheel is smaller than a lower threshold value, a vehicle is switched to an automatic driving mode, when the input torque of the steering wheel is larger than the lower threshold value, the vehicle is switched to an artificial driving mode, after the artificial driving mode is switched, when the angular acceleration of the steering wheel is larger than the angular acceleration threshold value of the steering wheel and the input torque of the steering wheel exceeds an upper threshold value of the input torque of the steering wheel, the driving system judges that the vehicle is in an emergency state, if the steering wheel turning angle controlled by a driver is in the same direction as the target turning angle of the steering wheel of the C-EPS system and the steering wheel turning angle approaches to the target turning angle of the steering wheel, the driving system is switched to the emergency steering mode to assist the artificial driving mode to complete the avoidance of the emergency situation. The invention can effectively switch the driving modes according to the driving conditions of the driver, thereby reducing the harm brought by driving.

Description

Automatic driving switching method and device based on C-EPS system
Technical Field
The invention relates to the technical field of automatic driving of automobiles, in particular to an automatic driving switching method and device based on a C-EPS system.
Background
In the process of driving a vehicle generally, a driver can be tired in time after driving for a period of time due to time or physical reasons, and fatigue driving can be realized if the driver continues to drive the vehicle. Therefore, the degree of intellectualization of the current vehicle is higher and higher, and the automatic driving vehicle gradually appears. The automatic driving automobile becomes the focus of the modern automobile development, various advanced technologies are fused in the automatic driving automobile, so that the automobile can be safely driven in a non-driver state, the road safety is improved, the road efficiency is improved, and the traffic accident rate of the driver in dangerous behaviors is reduced. However, the advanced technology relates to a safety problem, and therefore, how to effectively avoid a traffic accident caused by driving behaviors by switching an automatic driving mode according to the driving condition of a driver and reduce the harm caused by driving becomes a technical problem which needs to be solved by the applicant.
Disclosure of Invention
The invention aims to provide an automatic driving switching method and device based on a C-EPS system. The invention can effectively switch the driving modes according to the driving conditions of the driver, thereby reducing the harm brought by driving. In addition, the invention can also realize the perception of the road surface quality and the adhesion coefficient of the road surface so as to improve the accuracy and the safety of the automatic driving system to the vehicle control.
The technical scheme of the invention is as follows: an automatic driving switching method based on a C-EPS system comprises a driving system, wherein an automatic driving mode, an emergency steering mode and a manual driving mode are arranged in the driving system; in the manual driving mode, the C-EPS system is in a power-assisted mode; in the automatic driving mode, the C-EPS system is in an active steering mode; in the emergency steering mode, the C-EPS system is in an emergency power-assisted active steering mode; the C-EPS system calculates a lower threshold and an upper threshold of the steering wheel input torque according to the rotating speed and the rotating inertia of the steering wheel; when the steering wheel input torque is smaller than a lower threshold value, the vehicle is switched to an automatic driving mode, and when the steering wheel input torque is larger than the lower threshold value, the vehicle is switched to an artificial driving mode; after the manual driving mode is switched, when the angular acceleration of the steering wheel is larger than the angular acceleration threshold of the steering wheel, and the input torque of the steering wheel exceeds the upper threshold of the input torque of the steering wheel, the driving system judges that the vehicle is in an emergency state, if the steering wheel angle controlled by the driver is in the same direction as the target steering wheel angle of the C-EPS system and the steering wheel angle approaches to the target steering wheel angle, the driving system is switched to the emergency steering mode, and the manual driving mode is assisted to complete the avoidance of the emergency.
In the automatic driving switching method based on the C-EPS system, the lower threshold of the steering wheel input torque is as follows:
Figure GDA0003175311500000021
in the formula: i iscIs the steering wheel moment of inertia;
Figure GDA0003175311500000022
is the angular acceleration of the steering wheel, i.e. the second derivative of the steering wheel angle;
in the foregoing automatic driving switching method based on the C-EPS system, the calculation process of the steering wheel angular acceleration threshold and the upper threshold of the steering wheel input torque is as follows: establishing a model of a C-EPS system:
Figure GDA0003175311500000023
in the formula: a is a system state space matrix, represented as:
Figure GDA0003175311500000031
Kcthe steering column mandrel stiffness; b iscDamping the steering column; j. the design is a squarecIs the rotational inertia of the steering column; j is the reduction ratio of the steering motor reducer; j. the design is a squareeqEquivalent rotational inertia of a steering transmission mechanism and a steering gear; keqThe equivalent rigidity of a steering transmission mechanism and a steering gear is provided; b iseqThe damping is equivalent to a steering transmission mechanism and a steering gear; kbIs the steering motor electromagnetic torque constant; keIs the counter electromotive force coefficient of the steering motor; rmIs the armature inductance of the steering motor; l ismArmature resistance of steering motor;
Figure GDA0003175311500000032
θcis the steering wheel angle;
Figure GDA0003175311500000033
steering wheel speed, the first derivative of steering wheel angle; thetamIs the motor corner;
Figure GDA0003175311500000034
is the rotating speed of the steering motor, namely the first derivative of the rotating angle of the steering motor; i ismIs the current of the steering motor; b is1To control the matrix, it is expressed as:
Figure GDA0003175311500000035
u＝udis the driving voltage; b is2Is an interference input matrix, expressed as:
Figure GDA0003175311500000036
w is the interference input, w ═ ThTR]T，ThFor steering input torque, when in the automatic driving mode, Th＝0；TRIs the steering drag torque;
Figure GDA0003175311500000041
Tmoutputting torque for a steering motor; c is the output matrix, expressed as:
Figure GDA0003175311500000042
according to a mathematical model of vehicle dynamics and a steering input torque ThVehicle speed v and current I of steering motormCalculated power-assisted torque TcCalculating the yaw angular velocity beta and the lateral acceleration a under the current vehicle speed in real timey(ii) a When yaw rate beta and lateral acceleration ayAre all larger than the upper threshold value of the yaw rate under the current vehicle speed
Figure GDA0003175311500000043
And an upper threshold for lateral acceleration
Figure GDA0003175311500000044
Current steering input torque ThAnd angular acceleration of steering wheel
Figure GDA0003175311500000045
I.e. the upper threshold value of the steering wheel input torque at the current vehicle speed
Figure GDA0003175311500000046
And steering wheel angular acceleration threshold
Figure GDA0003175311500000047
The yaw rate upper threshold value
Figure GDA0003175311500000048
And an upper threshold for lateral acceleration
Figure GDA0003175311500000049
Respectively as follows:
β(v)＝βmax(v)·k2；
Figure GDA00031753115000000410
aymax(v) maximum lateral acceleration at the current vehicle speed, betamax(v) Is the maximum yaw rate, k, at the current vehicle speed1And k2The safety factors are respectively, and the value is 0.5-0.7.
In the automatic driving switching method based on the C-EPS system, in an automatic driving mode, an automatic driving decision layer is used for releasing a steering control law that a steering system target corner gives to the C-EPS system, the steering control law controls a driving voltage to drive a steering motor to complete steering of the steering system, and in the steering process of the steering system, the steering resistance reference value, the steering resistance estimation value and the current estimation value of the steering motor are used for judging the road surface quality and the road surface adhesion coefficient, so that the road surface quality and the road surface adhesion coefficient are sensed.
According to the automatic driving switching method based on the C-EPS system, the steering resistance reference value is calculated according to the steering wheel angle and the automobile speed, and the steering resistance estimation value is calculated according to the steering wheel angle, the current of a steering motor and the driving voltage; calculating the current estimation value of the steering motor according to the steering resistance estimation value and the target rotation angle of the steering system; the method specifically comprises the following steps:
when in the automatic driving mode, D ═ B2 B1]TAnd constructing an unknown input observer:
Figure GDA0003175311500000051
in the formula, DTIs a transpose of matrix D; e is the base number of the natural logarithm; i is an identity matrix having the same dimension as matrix A;
obtaining the interference input w of the C-EPS system at the time k according to each parameter value in the x matrix of the C-EPS system at the time k +1, thereby obtaining the estimated value of the steering resistance at the time k
Figure GDA0003175311500000052
Calculating a steering resistance reference value T according to the automobile mathematical model and the automobile driving and steering working conditionsR0：
Figure GDA0003175311500000053
In the formula: f is TR0Refers to a calculation function; v is vehicle speed; mu.s0Taking 0.7 by reference to the adhesion coefficient;
steering the system by a target angle thetarefAngle of rotation theta of steering wheelcThe subtracted value is input into a PID controller and output to obtain a driving voltage ud(ii) a According to the rotation speed of the steering motor
Figure GDA0003175311500000054
And steering motor back electromotive force coefficient KeCalculating to obtain induced electromotive force epsilon, and driving voltage udSubtracting the induced electromotive force epsilon and inputting the subtracted result into a motor circuit transfer function, wherein the output of the motor circuit function is a current estimated value of the steering motor
Figure GDA0003175311500000055
Finally, the steering resistance reference value T is calculatedR0Steering resistance estimation value
Figure GDA0003175311500000061
And current estimation value of steering motor
Figure GDA0003175311500000062
Inputting the road surface quality and adhesion coefficient into a judging module for judging, wherein the judging result
Figure GDA0003175311500000063
Therefore, the average value of S is more than 0 in a period of time, the road adhesion coefficient is more than 0.7, and the road quality is good; and if the average value of S is less than 0 in a period of time, the road adhesion coefficient is less than 0.7, and the road quality is poor.
The device of the automatic driving switching method based on the C-EPS system comprises a steering column assembly with a C-EPC system and a steering wheel; the lower end of the steering column assembly is connected with a planetary gear reducer through a coupler, and the lower end of the planetary gear reducer is connected with a steering motor; the upper end of the steering column assembly is provided with a steering mandrel gear and a steering column gear idler wheel which are meshed with each other; the lower end of the steering wheel is provided with a steering wheel gear; the steering wheel gear is meshed with the steering column gear idler wheel.
According to the device for the automatic driving switching method based on the C-EPS system, a steering wheel center piece is arranged in the middle of the steering wheel; the lower end of the steering wheel central piece is provided with a fixed shaft, and the fixed shaft is fixedly connected with the upper end of the steering column assembly through a nut.
Compared with the prior art, the C-EPC system calculates the lower threshold of the steering wheel input torque according to the steering wheel rotating speed and the steering wheel rotating inertia; when the input torque of the steering wheel is smaller than the lower threshold value, the vehicle is switched to an automatic driving mode, and when the input torque of the steering wheel is larger than the lower threshold value, the vehicle is switched to an artificial driving mode. Furthermore, the invention can judge the vehicle condition according to the angular acceleration of the steering wheel and the input torque condition of the steering wheel; if the steering wheel angle controlled by the driver is in the same direction as the target steering wheel angle of the C-EPS system and the steering wheel angle approaches to the target steering wheel angle, the driving system is switched into an emergency steering mode to assist the manual driving mode to complete the avoidance of the emergency situation. In the automatic driving mode, the automatic driving decision layer is utilized to release a steering control law of a steering system target corner to a C-EPS system, the steering control law controls driving voltage to drive a steering motor to complete steering of the steering system, and in the steering process of the steering system, the steering resistance reference value, the steering resistance estimation value and the current estimation value of the steering motor are utilized to judge the road surface quality and the road surface adhesion coefficient, so that the road surface quality and the road surface adhesion coefficient are sensed, and the accuracy and the safety of the automatic driving system on vehicle control are improved.
Drawings
FIG. 1 is a schematic flow diagram of the present invention;
fig. 2 is a schematic flow chart of setting of the steering wheel angular acceleration threshold value and the upper threshold value;
FIG. 3 is a schematic flow diagram of the present invention automated driving perception augmentation;
FIG. 4 is a schematic flow chart of the calculation of the current estimation value of the steering motor;
fig. 5 is a schematic configuration diagram of the steering system.
Reference numerals:
1. a steering column assembly; 2. a steering wheel; 3. a coupling; 4. a planetary gear reducer; 5. a steering motor; 6. a steering spindle gear; 7. a steering column gear idler; 8. a steering wheel gear; 9. a steering wheel center; 10. and fixing the shaft.
Detailed Description
The invention is further illustrated by the following figures and examples, which are not to be construed as limiting the invention.
Example 1: an automatic driving switching method based on a C-EPS system comprises a driving system, wherein an automatic driving mode, an emergency steering mode and a manual driving mode are arranged in the driving system; in the manual driving mode, the C-EPS system is in a power-assisted mode; in the automatic driving mode, the C-EPS system is in an active steering mode; in the emergency steering mode, the C-EPS system is in an emergency power-assisted active steering mode; the C-EPS system calculates a lower threshold value of the steering wheel input torque according to the rotating speed of the steering wheel and the rotating inertia of the steering wheel; when the steering wheel input torque is smaller than a lower threshold value, the vehicle is switched to an automatic driving mode, and when the steering wheel input torque is larger than the lower threshold value, the vehicle is switched to an artificial driving mode; after the manual driving mode is switched, when the angular acceleration of the steering wheel is larger than the angular acceleration threshold of the steering wheel, and the input torque of the steering wheel exceeds the upper threshold of the input torque of the steering wheel, the driving system judges that the vehicle is in an emergency state, if the steering wheel angle controlled by the driver is in the same direction as the target steering wheel angle of the C-EPS system and the steering wheel angle approaches to the target steering wheel angle, the driving system is switched to the emergency steering mode, and the manual driving mode is assisted to complete the avoidance of the emergency.
Example 2: an automatic driving switching method based on a C-EPS system comprises a driving system, wherein an automatic driving mode, an emergency steering mode and a manual driving mode are arranged in the driving system; as shown in fig. 1, after the vehicle starts, in the manual driving mode, the C-EPS system (abbreviated EPC in fig. 1) is in the assist mode (torque mode); only after the driving system receives an automatic driving request, the driving system starts an automatic driving mode and takes over the vehicle, in the automatic driving mode, the C-EPC system is in an active steering mode (angle mode), due to the existence of the rotational inertia of a steering wheel, the rotation of the steering wheel can cause a torque sensor to output a steering wheel torque signal (the rotating speed of the steering wheel and the rotational inertia of the steering wheel) during automatic driving, and in the emergency steering mode, the C-EPS system is in an emergency power-assisted active steering mode; thus, the C-EPC system calculates a lower threshold for steering wheel input torque based on steering wheel speed and steering wheel moment of inertiaT h(ii) a When steering wheel inputs torque ThLess than a lower thresholdT hWhen the vehicle is switched to or maintained in the automatic driving mode, the steering wheel inputs torque ThGreater than a lower thresholdT hWhen the vehicle is switched into a manual driving mode, the vehicle is taken over by a driver, but the automatic driving mode is in a standby state (all modules in the automatic driving mode keep working states, but do not participate in vehicle control); when angular acceleration of steering wheel
Figure GDA0003175311500000081
Greater than the angular acceleration threshold of the steering wheel
Figure GDA0003175311500000082
And steering wheel input torque ThExceeding an upper threshold value for steering wheel input torque
Figure GDA0003175311500000083
At the moment, the driving system judges that the vehicle is in an emergency state, and if the steering wheel angle theta controlled by the driver at the momentcAnd a target steering wheel angle theta of the C-EPS systemrefIn the same direction, i.e. thetac′θrefIs greater than 0, and the steering wheel rotating angle approaches to the target steering wheel rotating angle, namely
Figure GDA0003175311500000084
And the driving system is switched into an emergency steering mode to assist the manual driving mode to complete the avoidance of emergency situations.
In order to avoid misjudgment of automatic driving switching caused by input torque interference caused by the moment of inertia of a steering wheel and the angular velocity of the steering wheel in an automatic driving mode, the lower threshold value of the input torque of the steering wheel is as follows:
Figure GDA0003175311500000091
in the formula: i iscIs the steering wheel moment of inertia; thetacIs the angular acceleration of the steering wheel, i.e. the second derivative of the steering wheel angle;
in order to judge whether the vehicle is in an emergency state, the calculation mode of the steering wheel angular acceleration threshold value and the upper threshold value is as follows; as shown in fig. 2, a model of the C-EPS system is established:
Figure GDA0003175311500000092
in the formula: a is a system state space matrix, represented as:
Figure GDA0003175311500000093
Kcthe steering column mandrel stiffness; b iscDamping the steering column; j. the design is a squarecIs the rotational inertia of the steering column; j is the reduction ratio of the steering motor reducer; j. the design is a squareeqEquivalent rotational inertia of a steering transmission mechanism and a steering gear; keqThe equivalent rigidity of a steering transmission mechanism and a steering gear is provided; b iseqThe damping is equivalent to a steering transmission mechanism and a steering gear; kbIs the steering motor electromagnetic torque constant; keIs the counter electromotive force coefficient of the steering motor; rmIs the armature inductance of the steering motor; l ismArmature resistance of steering motor;
Figure GDA0003175311500000094
θcis the steering wheel angle;
Figure GDA0003175311500000095
steering wheel speed, the first derivative of steering wheel angle; thetamIs the motor corner;
Figure GDA0003175311500000101
is the rotating speed of the steering motor, namely the first derivative of the rotating angle of the steering motor; i ismIs the current of the steering motor; b is1To control the matrix, it is expressed as:
Figure GDA0003175311500000102
u＝udis the driving voltage; b is2Is an interference input matrix, expressed as:
Figure GDA0003175311500000103
w is the interference input, w ═ Th TR]T，ThFor steering input torque, when in the automatic driving mode, Th＝0；TRIs the steering drag torque;
Figure GDA0003175311500000104
Tmoutputting torque for a steering motor; c is the output matrix, expressed as:
Figure GDA0003175311500000105
according to a mathematical model of vehicle dynamics and a steering input torque ThVehicle speed v and current I of steering motormCalculated power-assisted torque Tc(Tc＝Im×Kb) Calculating the yaw angular velocity beta and the lateral acceleration a under the current vehicle speed in real timey(ii) a When yaw rate beta and lateral acceleration ayAre all larger than the upper threshold value of the yaw rate under the current vehicle speed
Figure GDA0003175311500000106
And an upper threshold for lateral acceleration
Figure GDA0003175311500000107
Current steering input torque ThAnd angular acceleration of steering wheel
Figure GDA0003175311500000108
I.e. the upper threshold value of the steering wheel input torque at the current vehicle speed
Figure GDA0003175311500000115
And steering wheel angular acceleration threshold
Figure GDA0003175311500000111
The yaw rate upper thresholdValue of
Figure GDA0003175311500000112
And an upper threshold for lateral acceleration
Figure GDA0003175311500000113
Respectively as follows:
β(v)＝βmax(v)·k2；
Figure GDA0003175311500000114
aymax(v) maximum lateral acceleration at the current vehicle speed, betamax(v) Is the maximum yaw rate, k, at the current vehicle speed1And k2The safety factors are respectively, and the value is 0.5-0.7.
Example 3: an automatic driving switching method based on a C-EPS system comprises a driving system, wherein an automatic driving mode, an emergency steering mode and a manual driving mode are arranged in the driving system; in the manual driving mode, the C-EPS system is in a power-assisted mode; in the automatic driving mode, the C-EPS system is in an active steering mode; in the emergency steering mode, the C-EPS system is in an emergency power-assisted active steering mode; the C-EPS system calculates a lower threshold value of the steering wheel input torque according to the rotating speed of the steering wheel and the rotating inertia of the steering wheel; when the steering wheel input torque is smaller than a lower threshold value, the vehicle is switched to an automatic driving mode, and when the steering wheel input torque is larger than the lower threshold value, the vehicle is switched to an artificial driving mode; after the manual driving mode is switched, when the angular acceleration of the steering wheel is larger than the angular acceleration threshold of the steering wheel, and the input torque of the steering wheel exceeds the upper threshold of the input torque of the steering wheel, the driving system judges that the vehicle is in an emergency state, if the steering wheel angle controlled by the driver is in the same direction as the target steering wheel angle of the C-EPS system and the steering wheel angle approaches to the target steering wheel angle, the driving system is switched to the emergency steering mode, and the manual driving mode is assisted to complete the avoidance of the emergency.
In the autonomous driving mode, as shown in FIG. 3, an autonomous driving decision layer (i.e., an autonomous driving decision layer) is utilizedThe automatic-drive upper controller in fig. 3) issues a steering system target steering angle θrefGiving a steering control law of the C-EPS system, and controlling a driving voltage to drive a steering motor to complete steering of the steering system by the steering control law; however, the existing small passenger cars mostly adopt a rack and pinion steering gear, which has high reverse efficiency, and the steering wheel is deflected by wheel vibration and deflection caused by the road surface, commonly called as the driver. When the C-EPS is in an automatic driving mode, the working mode is an angle mode, when the wheel deflects due to uneven road surface, the steering motor needs extra current to maintain the wheel rotating angle to follow the target rotating angle, and therefore, the current I of the steering motor in a period of time is countedmAnd current estimation value of steering motor
Figure GDA0003175311500000121
Variance σ of the differenceIThe current road condition can be judged. If the variance of the difference between the current of the steering motor and the current estimation value of the steering motor is large, the steering motor needs extra current to overcome wheel deflection caused by uneven road, so that the actual turning angle of the steering system can better follow the target turning angle; thus, the steering resistance reference value T is used during steering of the steering systemR0Steering resistance estimation value
Figure GDA0003175311500000122
And current estimation value I of steering motormAnd judging the road surface quality and the road surface adhesion coefficient to realize the perception of the road surface quality and the road surface adhesion coefficient.
As shown in fig. 3, the steering resistance reference value TR0According to steering wheel rotation angle theta in the steering resistance modelcAnd calculating the speed v of the vehicle, and the estimated value of the steering resistance
Figure GDA0003175311500000123
According to steering wheel angle theta in unknown input observercCurrent I of steering motormAnd a driving voltage udCalculating; current estimation value I of the steering motormAccording to rotation in a mathematical model of a steering systemEstimation of the directional resistance
Figure GDA0003175311500000124
And a target steering angle theta of the steering systemrefCalculating; the method specifically comprises the following steps:
establishing a model of a C-EPS system:
Figure GDA0003175311500000125
in the formula: a is a system state space matrix, represented as:
Figure GDA0003175311500000126
Kcthe steering column mandrel stiffness; b iscDamping the steering column; j. the design is a squarecIs the rotational inertia of the steering column; j is the reduction ratio of the steering motor reducer; j. the design is a squareeqEquivalent rotational inertia of a steering transmission mechanism and a steering gear; keqThe equivalent rigidity of a steering transmission mechanism and a steering gear is provided; b iseqThe damping is equivalent to a steering transmission mechanism and a steering gear; kbIs the steering motor electromagnetic torque constant; keIs the counter electromotive force coefficient of the steering motor; rmIs the armature inductance of the steering motor; l ismArmature resistance of steering motor;
Figure GDA0003175311500000131
θcis the steering wheel angle;
Figure GDA0003175311500000132
steering wheel speed, the first derivative of steering wheel angle; thetamIs the motor corner;
Figure GDA0003175311500000133
is the rotating speed of the steering motor, namely the first derivative of the rotating angle of the steering motor; i ismIs the current of the steering motor; b is1To control the matrix, it is expressed as:
Figure GDA0003175311500000134
u＝udis the driving voltage; b is2Is an interference input matrix, expressed as:
Figure GDA0003175311500000135
w is the interference input, w ═ Th TR]T，ThFor steering input torque, when in the automatic driving mode, Th＝0；TRIs the steering drag torque;
Figure GDA0003175311500000136
Tmoutputting torque for a steering motor; c is the output matrix, expressed as:
Figure GDA0003175311500000141
when in the automatic driving mode, D ═ B2 B1]TAnd constructing an unknown input observer:
Figure GDA0003175311500000142
in the formula, DTIs a transpose of matrix D; e is the base number of the natural logarithm; i is an identity matrix having the same dimension as matrix A;
obtaining the interference input w of the C-EPS system at the time k according to each parameter value in the x matrix of the C-EPS system at the time k +1, thereby obtaining the estimated value of the steering resistance at the time k
Figure GDA0003175311500000143
Calculating a steering resistance reference value T according to the automobile mathematical model and the automobile driving and steering working conditionsR0：
Figure GDA0003175311500000144
In the formula: f is TR0Refers to a calculation function; v is vehicle speed; mu.s0Taking 0.7 by reference to the adhesion coefficient;
turning the steering system to the target steering angle theta as shown in FIG. 4refAngle of rotation theta of steering wheelcThe subtracted value is input into a PID controller and output to obtain a driving voltage ud(ii) a According to the rotation speed of the steering motor
Figure GDA0003175311500000145
And steering motor back electromotive force coefficient KeCalculating to obtain induced electromotive force epsilon, and driving voltage udSubtracting the induced electromotive force epsilon and inputting the subtracted result into a motor circuit transfer function, wherein the output of the motor circuit function is a current estimated value of the steering motor
Figure GDA0003175311500000151
Finally, the steering resistance reference value T is calculatedR0Steering resistance estimation value
Figure GDA0003175311500000152
And current estimation value of steering motor
Figure GDA0003175311500000153
Inputting the road surface quality and adhesion coefficient into a judging module for judging, wherein the judging result
Figure GDA0003175311500000154
Therefore, the average value of S is more than 0 in a period of time, the road adhesion coefficient is more than 0.7, and the road quality is good; if the average value of S is less than 0 in a period of time, the road surface adhesion coefficient is less than 0.7, and the road surface quality is poor; the accuracy and the safety of the automatic driving mode for vehicle control are improved through the feedback of the road adhesion coefficient and the road quality.
Embodiment 4 an apparatus of an automatic driving switching method based on a C-EPS system, as shown in fig. 5, includes a steering column assembly 1 having a C-EPC system, a steering wheel 2 being provided at an upper end of the steering column assembly 1; the lower end of the steering column assembly 1 is connected with a planetary gear reducer 4 through a coupler 3, and the lower end of the planetary gear reducer 4 is connected with a steering motor 5; the upper end of the steering column assembly 1 is provided with a steering mandrel gear 6 and a steering column gear idler gear 7 which are meshed with each other; the lower end of the steering wheel 2 is provided with a steering wheel gear 8; the steering wheel gear 8 is meshed with the steering column gear idler gear 7; the middle part of the steering wheel 2 is provided with a steering wheel center piece 9; a system control element, a display screen and the like are arranged in the steering wheel center piece 9; the lower end of the steering wheel center piece 9 is provided with a fixed shaft 10, and the fixed shaft 10 is fixedly connected with the upper end of the steering column assembly 1 through a nut.
In conclusion, the invention can effectively switch the driving modes according to the driving conditions of the driver, thereby reducing the harm brought by driving. In addition, the invention can also realize the perception of the road surface quality and the adhesion coefficient of the road surface so as to improve the accuracy and the safety of the automatic driving system to the vehicle control.

Claims (6)

1. An automatic driving switching method based on a C-EPS system comprises a driving system, wherein an automatic driving mode, an emergency steering mode and a manual driving mode are arranged in the driving system; in the manual driving mode, the C-EPS system is in a power-assisted mode; in the automatic driving mode, the C-EPS system is in an active steering mode; in the emergency steering mode, the C-EPS system is in an emergency power-assisted active steering mode; the method is characterized in that: the C-EPS system calculates a lower threshold value of the steering wheel input torque according to the rotating speed of the steering wheel and the rotating inertia of the steering wheel; when the steering wheel input torque is smaller than a lower threshold value, the vehicle is switched to an automatic driving mode, and when the steering wheel input torque is larger than the lower threshold value, the vehicle is switched to an artificial driving mode; after the manual driving mode is switched, when the angular acceleration of the steering wheel is larger than the angular acceleration threshold value of the steering wheel and the input torque of the steering wheel exceeds the upper threshold value of the input torque of the steering wheel, the driving system judges that the vehicle is in an emergency state, if the steering wheel turning angle controlled by the driver is in the same direction as the target turning angle of the steering wheel of the C-EPS system at the moment and the steering wheel turning angle approaches to the target turning angle of the steering wheel, the driving system is switched into the emergency steering mode to assist the manual driving mode to complete the avoidance of the emergency;
the calculation process of the steering wheel angular acceleration threshold and the steering wheel input torque upper threshold is as follows: establishing a model of a C-EPS system:
Figure FDA0003175311490000011
in the formula: a is a system state space matrix, represented as:
Figure FDA0003175311490000021
Kcthe steering column mandrel stiffness; b iscDamping the steering column; j. the design is a squarecIs the rotational inertia of the steering column; j is the reduction ratio of the steering motor reducer; j. the design is a squareeqEquivalent rotational inertia of a steering transmission mechanism and a steering gear; keqThe equivalent rigidity of a steering transmission mechanism and a steering gear is provided; b iseqThe damping is equivalent to a steering transmission mechanism and a steering gear; kbIs the steering motor electromagnetic torque constant; keIs the counter electromotive force coefficient of the steering motor; rmIs the armature inductance of the steering motor; l ismArmature resistance of steering motor;
Figure FDA0003175311490000022
θcis the steering wheel angle;
Figure FDA0003175311490000023
steering wheel speed, the first derivative of steering wheel angle; thetamIs the motor corner;
Figure FDA0003175311490000024
is the rotating speed of the steering motor, namely the first derivative of the rotating angle of the steering motor; i ismIs the electricity of a steering motorA stream; b is1To control the matrix, it is expressed as:
Figure FDA0003175311490000025
u＝udis the driving voltage; b is2Is an interference input matrix, expressed as:
Figure FDA0003175311490000026
w is the interference input, w ═ Th TR]T，ThFor steering input torque, when in the automatic driving mode, Th＝0；TRIs the steering drag torque;
Figure FDA0003175311490000031
Tmoutputting torque for a steering motor; c is the output matrix, expressed as:
Figure FDA0003175311490000032
according to a mathematical model of vehicle dynamics and a steering input torque ThVehicle speed v and current I of steering motormCalculated power-assisted torque TcCalculating the yaw angular velocity beta and the lateral acceleration a under the current vehicle speed in real timey(ii) a When yaw rate beta and lateral acceleration ayAre all larger than the upper threshold value of the yaw rate under the current vehicle speed
Figure FDA0003175311490000038
And an upper threshold for lateral acceleration
Figure FDA0003175311490000039
Current steering input torque ThAnd angular acceleration of steering wheel
Figure FDA0003175311490000033
I.e. the upper threshold value of the steering wheel input torque at the current vehicle speed
Figure FDA0003175311490000034
And steering wheel angular acceleration threshold
Figure FDA0003175311490000035
The yaw rate upper threshold value
Figure FDA00031753114900000310
And an upper threshold for lateral acceleration
Figure FDA00031753114900000311
Respectively as follows:
β(v)＝βmax(v)·k2；
Figure FDA00031753114900000312
aymax(v) maximum lateral acceleration at the current vehicle speed, betamax(v) Is the maximum yaw rate, k, at the current vehicle speed1And k2The safety factors are respectively, and the value is 0.5-0.7.
2. The automatic driving switching method based on the C-EPS system according to claim 1, wherein: the lower threshold value of the steering wheel input torque is as follows:
Figure FDA0003175311490000036
in the formula: i iscIs the steering wheel moment of inertia;
Figure FDA0003175311490000037
is the angular acceleration of the steering wheel, i.e. the second derivative of the steering wheel angle.
3. The automatic driving switching method based on the C-EPS system according to claim 1, wherein: in an automatic driving mode, an automatic driving decision layer is used for releasing a steering control law of a steering system target corner to a C-EPS system, the steering control law controls a driving voltage to drive a steering motor to complete steering of the steering system, and in the steering process of the steering system, the steering resistance reference value, the steering resistance estimated value and the current estimated value of the steering motor are used for judging the road surface quality and the road surface adhesion coefficient, so that the road surface quality and the road surface adhesion coefficient are sensed.
4. The automatic driving switching method based on the C-EPS system according to claim 1, wherein: the steering resistance reference value is calculated according to the steering wheel angle and the automobile speed, and the steering resistance estimation value is calculated according to the steering wheel angle, the current of a steering motor and the driving voltage; calculating the current estimation value of the steering motor according to the steering resistance estimation value and the target rotation angle of the steering system; the method specifically comprises the following steps:
when in the automatic driving mode, D ═ B2 B1]TAnd constructing an unknown input observer:
Figure FDA0003175311490000041
in the formula, DTIs a transpose of matrix D; e is the base number of the natural logarithm; i is an identity matrix having the same dimension as matrix A;
obtaining the interference input w of the C-EPS system at the time k according to each parameter value in the x matrix of the C-EPS system at the time k +1, thereby obtaining the estimated value of the steering resistance at the time k
Figure FDA0003175311490000042
Calculating a steering resistance reference value T according to the automobile mathematical model and the automobile driving and steering working conditionsR0：
Figure FDA0003175311490000043
In the formula: f is TR0Refers to a calculation function; v is vehicle speed; mu.s0Taking 0.7 by reference to the adhesion coefficient;
steering the system by a target angle thetarefAngle of rotation theta of steering wheelcThe subtracted value is input into a PID controller and output to obtain a driving voltage ud(ii) a According to the rotation speed of the steering motor
Figure FDA0003175311490000051
And steering motor back electromotive force coefficient KeCalculating to obtain induced electromotive force epsilon, and driving voltage udSubtracting the induced electromotive force epsilon and inputting the subtracted result into a motor circuit transfer function, wherein the output of the motor circuit function is a current estimated value of the steering motor
Figure FDA0003175311490000052
Finally, the steering resistance reference value T is calculatedR0Steering resistance estimation value
Figure FDA0003175311490000053
And current estimation value of steering motor
Figure FDA0003175311490000054
Inputting the road surface quality and adhesion coefficient into a judging module for judging, wherein the judging result
Figure FDA0003175311490000055
Therefore, the average value of S is more than 0 in a period of time, the road adhesion coefficient is more than 0.7, and the road quality is good; and if the average value of S is less than 0 in a period of time, the road adhesion coefficient is less than 0.7, and the road quality is poor.
5. The apparatus of the automatic driving switching method based on the C-EPS system according to any one of claims 1-4, wherein: the steering column assembly (1) comprises a C-EPC system, and a steering wheel (2) is arranged at the upper end of the steering column assembly (1); the lower end of the steering column assembly (1) is connected with a planetary gear reducer (4) through a coupler (3), and the lower end of the planetary gear reducer (4) is connected with a steering motor (5); the upper end of the steering column assembly (1) is provided with a steering mandrel gear (6) and a steering column gear idler gear (7) which are meshed with each other; the lower end of the steering wheel (2) is provided with a steering wheel gear (8); the steering wheel gear (8) is meshed with the steering column gear idler wheel (7).
6. The apparatus of the automatic driving switching method based on the C-EPS system according to claim 5, wherein: a steering wheel center piece (9) is arranged in the middle of the steering wheel (2);
the lower end of the steering wheel central piece (9) is provided with a fixed shaft (10), and the fixed shaft (10) is fixedly connected with the upper end of the steering column assembly (1) through a nut.
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