CN113085576B - Four-wheel drive torque limiting method and device based on fuzzy PID - Google Patents
Four-wheel drive torque limiting method and device based on fuzzy PID Download PDFInfo
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- CN113085576B CN113085576B CN202110455039.2A CN202110455039A CN113085576B CN 113085576 B CN113085576 B CN 113085576B CN 202110455039 A CN202110455039 A CN 202110455039A CN 113085576 B CN113085576 B CN 113085576B
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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
- 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
- B60L2240/00—Control parameters of input or output; Target parameters
- B60L2240/10—Vehicle control parameters
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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
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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
- B60L2260/00—Operating Modes
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- B60L2260/48—Control modes by fuzzy logic
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Abstract
The invention provides a four-wheel drive torque limiting method and device based on fuzzy PID, and belongs to the technical field of automobiles. The method solves the problems that the prediction torque reduction protection cannot be realized and the safety is not enough in the prior art. The four-wheel drive torque limiting method based on fuzzy PID comprises the following steps: carrying out open-loop control according to the road surface adhesion coefficient of the front axle to obtain a torque limit value of the front axle, and carrying out open-loop control according to the road surface adhesion coefficient of the rear axle to obtain a torque limit value of the rear axle; carrying out fuzzy PID control according to a front axle speed difference value obtained by the front axle speed and the vehicle speed to obtain a front axle maximum torque value; carrying out fuzzy PID control on a rear axle difference value obtained according to the rear axle speed and the vehicle speed to obtain a maximum torque value of a rear axle; and respectively and correspondingly comparing the front axle torque limit value and the rear axle torque limit value with the front axle torque maximum value and the rear axle torque maximum value, and selecting a value with a small value to limit the front axle torque and the rear axle torque. The invention can carry out predictive control on the vehicle instability state and improve the safety of the vehicle.
Description
Technical Field
The invention belongs to the technical field of automobiles, and relates to a four-wheel drive torque limiting method and device based on fuzzy PID.
Background
The electric four-wheel drive automobile is usually provided with an independent front axle electric drive system and a rear axle electric drive system, the front and rear electric drive systems can distribute the torque required by a driver in a (0-1) proportion range, so that independent front drive, independent rear drive or four-wheel drive can be easily realized, and the torque distribution of the front and rear drive systems of the electric four-wheel drive automobile is greatly flexible. However, the torque distribution of the front axle and the rear axle is basically a fixed proportion or a plurality of adjustable fixed proportions during normal running at present, but in the actual running process, the wheels are easy to slip due to different road adhesion conditions by adopting the fixed proportion, so that the safety of the vehicle is affected.
In order to solve the problems, the conventional vehicle enterprises mainly utilize a Traction Control System (TCS) to control the traction of the vehicle, wherein the TCS is an active control system which can inhibit the driving wheels from slipping to enable the vehicle to generate the optimal driving force according to the driving behavior of the vehicle, and can improve the acceleration performance and the climbing capability of the vehicle, so that the vehicle can be smoothly started and driven on a road surface with poor adhesion condition, and the vehicle is prevented from moving transversely or drifting due to the slipping of the driving wheels. Although the traction control system can intervene in the braking torque after the driving state of the vehicle is abnormal, and the driving posture is adjusted through the change of the driving torque, so that the safety and the stability of the vehicle are ensured. However, the intervention of the traction control system has communication delay and the like, and feedback control can be performed only under the condition that the vehicle is unstable to correct the vehicle posture and control stability, so that predictive control cannot be performed in a targeted manner, the predicted torque reduction protection is realized, and the safety is not sufficient.
Disclosure of Invention
The invention aims to provide a four-wheel drive torque limiting method and a four-wheel drive torque limiting device based on fuzzy PID (proportion integration differentiation), aiming at solving the technical problems that: how to carry out predictive control on the vehicle instability state and improve the safety of the vehicle.
The purpose of the invention can be realized by the following technical scheme: a fuzzy PID based four-wheel drive torque limiting method comprises the following steps:
acquiring a front axle speed, a rear axle speed, a vehicle speed, a front axle road surface adhesion coefficient and a rear axle road surface adhesion coefficient;
the whole vehicle controller performs open-loop control according to the front axle road surface adhesion coefficient to obtain a front axle torque limit value, and performs open-loop control according to the rear axle road surface adhesion coefficient to obtain a rear axle torque limit value;
the vehicle control unit performs fuzzy PID control on a front axle difference value obtained according to the front axle speed and the vehicle speed so as to obtain a front axle maximum torque value; carrying out fuzzy PID control on a rear axle difference value obtained according to the rear axle speed and the vehicle speed so as to obtain a maximum torque value of the rear axle;
the vehicle control unit compares the front axle torque limit value with the maximum front axle torque value, selects a small value as a front axle torque control value and limits the front axle torque; and the vehicle control unit also compares the rear axle torque limit value with the maximum rear axle torque value respectively, selects a small value as a rear axle torque control value and limits the rear axle torque.
When the fuzzy PID-based four-wheel drive torque limiting method is used for controlling, firstly, a front axle torque limiting value and a rear axle torque limiting value are obtained by calculation according to a front axle pavement adhesion coefficient and a rear axle pavement adhesion coefficient; the invention adopts two modes to obtain the torque value required by torque reduction and carries out torque reduction of the front and rear axle torques of the vehicle by comparing and selecting the small value, thereby improving the reliability and the accuracy of the torque reduction control of the vehicle, being capable of quickly and reliably adjusting the posture of the vehicle and avoiding the condition of skidding after torque reduction. The vehicle attitude can be adjusted before the vehicle is unstable through the scheme of the invention, thereby realizing the predictive control of the vehicle unstable state and improving the stability and the safety of the vehicle.
In the four-wheel drive torque limiting method based on fuzzy PID, the method further comprises:
presetting an activation condition and a quit condition for the whole vehicle controller to carry out front and rear axle torque limit control;
comparing the acquired vehicle speed with the front axle speed and the rear axle speed respectively, judging that the activation condition is met when the front axle speed and/or the rear axle speed is/are greater than the vehicle speed, and enabling the whole vehicle controller to enter front and rear axle torque limitation;
and monitoring whether the traction control system intervenes in a signal for controlling the driving torque in real time, judging that the quit condition is met when the traction control system intervenes, and quitting the torque limitation of the front axle and the rear axle of the whole vehicle controller.
The torque limiting method has the advantages that the torque limiting device is provided with the torque limiting activation condition and the torque limiting exit condition of the vehicle control unit, the vehicle instability condition can be predicted through the activation condition, the torque reduction processing is timely carried out when the instability risk exists, the stability and the safety of the vehicle are improved, in addition, the traction control system is used as an active control system for restraining the driving wheels from skidding, the torque limiting exit of the vehicle control unit is carried out when the traction control system enters the control, and the economic efficiency of the vehicle can be improved.
In the four-wheel drive torque limiting method based on fuzzy PID, the whole vehicle controller performs open-loop control according to the road surface adhesion coefficient of the front axle to obtain a torque limiting value of the front axle, and the operation of performing open-loop control according to the road surface adhesion coefficient of the rear axle to obtain the torque limiting value of the rear axle comprises:
acquiring longitudinal acceleration and lateral acceleration of the vehicle by using an accelerometer sensor;
estimating and obtaining the vertical load of each wheel of the vehicle according to the longitudinal acceleration and the lateral acceleration and the physical structure parameters of the vehicle;
calculating according to the lateral acceleration and the front axle road surface adhesion coefficient to obtain the maximum longitudinal acceleration of the front axle; calculating according to the lateral acceleration and the road surface adhesion coefficient of the rear axle to obtain the maximum longitudinal acceleration of the rear axle;
comparing the obtained vertical load of the left front wheel with the vertical load of the right front wheel, selecting the vertical load of the front wheel with a small value, and calculating the vertical load and the maximum longitudinal acceleration of the front axle according to a front axle torque calculation formula to obtain a front axle torque limit value;
and comparing the obtained vertical load of the left rear wheel with the vertical load of the right rear wheel, selecting the vertical load of the rear wheel with a small value, and calculating the vertical load and the maximum longitudinal acceleration of the rear axle according to a rear axle torque calculation formula to obtain a rear axle torque limit value.
In the scheme, the vertical load of each wheel of the vehicle is calculated according to the longitudinal acceleration and the lateral acceleration, the real-time motion state of the vehicle is reflected, the estimation accuracy of the vertical load is improved, the calculation accuracy of the torque limiting values of the front axle and the rear axle is further improved, and the safe driving of the vehicle is guaranteed.
In the fuzzy PID-based four-wheel drive torque limiting method, the front axle torque calculation formula is:
wherein, T q front For front axle torque limit, F fl Vertical load of the left front wheel; f fr Is the right front wheel vertical load; l is the rolling radius; g is the acceleration of gravity; a is Before x For the front axle maximum longitudinal acceleration, the front axle maximum longitudinal acceleration is calculated as follows:
wherein, a y Is the lateral acceleration; mu.s Front side The front axle road surface adhesion coefficient.
In the fuzzy PID-based four-wheel drive torque limiting method, the rear axle torque calculation formula is:
wherein, T q after For rear axle torque limit, F rl Vertical load for the left rear wheel; f rr Is the vertical load of the right rear wheel; l is the rolling radius, g is the acceleration of gravity; a is x after For the maximum longitudinal acceleration of the rear axle, the formula is calculated as follows:
wherein, a y Is the lateral acceleration; mu.s Rear end For rear axle road surfaceThe coefficient of adhesion.
In the fuzzy PID-based four-wheel drive torque limiting method, the operation of obtaining the front axle maximum torque value comprises the following steps:
and performing difference calculation on the obtained front axle speed and the obtained vehicle speed to obtain a front axle difference, performing difference calculation on the front axle difference and the front axle difference at the previous moment to obtain a front axle difference change rate, and performing fuzzy PID control on the front axle difference and the front axle difference change rate to obtain a front axle maximum torque value.
In the fuzzy PID-based four-wheel drive torque limiting method, the operation of obtaining the rear axle maximum torque value comprises the following steps:
and performing difference calculation on the obtained rear axle speed and the obtained vehicle speed to obtain a speed difference value of the rear axle, performing difference calculation on the rear axle difference value and the rear axle difference value at the previous moment to obtain a rear axle difference value change rate, and performing fuzzy PID control on the rear axle difference value and the rear axle difference value change rate to obtain a maximum rear axle torque value.
The utility model provides a four wheel drive moment of torsion limiting device based on fuzzy PID, includes vehicle control unit and is used for acquireing the signal acquisition module of front axle speed, rear axle speed and speed of a motor vehicle, vehicle control unit includes:
the road surface adhesion coefficient acquisition module is used for acquiring a front axle road surface adhesion coefficient and a rear axle road surface adhesion coefficient;
the open-loop torque control module is used for calculating a front axle torque limit value and a rear axle torque limit value according to the front axle road surface adhesion coefficient and the rear axle road surface adhesion coefficient;
the closed-loop torque control module is used for carrying out fuzzy PID control on a front axle difference value between the axle speed of a front axle and the vehicle speed so as to obtain a maximum torque value of the front axle and carrying out fuzzy PID control on a difference value between the axle speed of a rear axle and the vehicle speed so as to obtain a maximum torque value of the rear axle;
the torque value comparison module is used for comparing the front axle torque limit value with the front axle maximum torque value to select a front axle torque control value with a small value, and comparing the rear axle torque limit value with the rear axle maximum torque value to select a rear axle torque control value with a small value;
and the torque limiting control module is used for limiting the torque of the front axle and the torque of the rear axle according to the torque control value of the front axle and the torque control value of the rear axle selected by the torque value comparison module.
When the four-wheel-drive torque limiting device based on the fuzzy PID is controlled, an open-loop torque control module calculates according to a front axle road surface adhesion coefficient and a rear axle road surface adhesion coefficient to obtain a front axle torque limiting value and a rear axle torque limiting value; the invention adopts two modes to obtain the torque value required by torque reduction, carries out torque reduction of the front and rear axle torques of the vehicle by comparing and selecting the small value, and can improve the reliability of the torque reduction control of the vehicle, the situation that the sliding still exists after the torque is reduced is avoided. The invention realizes the predictive control of the vehicle instability state, can quickly and reliably adjust the vehicle posture, and improves the stability and the safety of the vehicle.
In the fuzzy PID-based four-wheel drive torque limiting apparatus, the vehicle controller further includes:
the activation condition judgment module is used for comparing the acquired vehicle speed with the front axle speed and the rear axle speed respectively, and the whole vehicle controller enters front and rear axle torque limitation when the front axle speed and/or the rear axle speed are/is greater than the vehicle speed;
and the exit condition judgment module is used for monitoring whether the traction control system intervenes in a signal for controlling the driving torque in real time and exiting the torque limitation of the front axle and the rear axle of the whole vehicle controller when the traction control system intervenes.
The arrangement of the activation condition judgment module can predict the instability condition of the vehicle and timely make a torque condition when the instability risk exists, so that the stability and the safety of the vehicle are improved. The exit condition judgment module is arranged, so that the torque limit of the whole vehicle controller can be timely exited when the traction control system enters control, and the economic efficiency of the vehicle is improved.
In the fuzzy PID-based four-wheel drive torque limiting apparatus described above, the closed-loop torque control module comprises:
the first fuzzy PID controller is used for calculating the difference between the obtained front axle speed and the vehicle speed to obtain a speed difference value of the front axle, calculating the difference between the speed difference value of the front axle and the speed difference value at the previous moment to obtain a front axle difference value change rate, and further performing fuzzy PID control on the speed difference value of the front axle and the front axle difference value change rate to obtain a maximum torque value of the front axle;
and the second fuzzy PID controller calculates the difference between the acquired rear axle speed and the vehicle speed to obtain a rear axle speed difference, calculates the difference between the rear axle speed difference and the last-moment speed difference to obtain a rear axle difference change rate, and performs fuzzy PID control on the rear axle speed difference and the rear axle difference change rate to obtain a rear axle maximum torque value.
Compared with the prior art, the four-wheel drive torque limiting method and device based on fuzzy PID have the following advantages:
1. the invention integrates the integrated strategy design of open-loop torque limiting and fuzzy PID closed-loop torque limiting in the vehicle controller, can quickly adjust the vehicle posture when the vehicle is unstable, adopts two modes to obtain the torque limiting value, and compares the torque limiting value to select the optimal torque limiting value for torque limiting, has reliable operation, and improves the stability and the safety of the vehicle.
2. The invention also sets an activation condition and a quit condition for torque limitation of the vehicle controller, can predict the instability condition of the vehicle through the activation condition, and timely reduces the torque when the instability risk exists, thereby improving the stability and the safety of the vehicle.
Drawings
Fig. 1 is a control flow chart according to a first embodiment of the present invention.
Fig. 2 is a control flow chart of the second embodiment of the present invention.
Fig. 3 is a schematic structural diagram of a first embodiment of the present invention.
Fig. 4 is a schematic structural diagram of a second embodiment of the present invention.
In the figure, 1, a signal acquisition module; 2. a vehicle control unit; 21. a road adhesion coefficient acquisition module; 22. an open loop torque control module; 23. a closed loop torque control module; 23a, a fuzzy PID controller I; 23b, a fuzzy PID controller II; 24. a torque value comparison module; 25. a torque limit control module; 26. an activation condition judgment module; 27. and an exit condition judgment module.
Detailed Description
The following are specific embodiments of the present invention and are further described with reference to the accompanying drawings, but the present invention is not limited to these embodiments.
The first embodiment is as follows:
as shown in fig. 3, the four-wheel-drive torque limiting device based on the fuzzy PID comprises a vehicle control unit 2 and a signal acquisition module 1 for acquiring a front axle speed, a rear axle speed and a vehicle speed, wherein the signal acquisition module 1 is connected with the vehicle control unit 2, the vehicle control unit 2 comprises a road adhesion coefficient acquisition module 21, an open-loop torque control module 22, a closed-loop torque control module 23, a torque value comparison module 24 and a torque limit control module 25, the road adhesion coefficient module is respectively connected with the signal acquisition module 1 and the open-loop torque control module 22, the signal acquisition module 1 is further connected with the closed-loop torque control module 23 and the open-loop torque control module 22, the closed-loop torque control module 23 comprises a fuzzy PID controller one 23a and a fuzzy PID controller two 23b, the fuzzy PID controller one 23a and the fuzzy PID controller two 23b are respectively connected with the signal acquisition module 1, the fuzzy PID controller I23 a and the fuzzy PID controller II 23b in the closed-loop torque control module 23 are also respectively connected with a torque value comparison module 2424, the open-loop torque control module 22 is connected with a torque value comparison module 24, and the torque value comparison module 24 is connected with a torque limit control module 25.
The signal acquisition module 1 comprises a CAN bus and an accelerometer sensor, and in a vehicle network, the CAN bus establishes vehicle-mounted network connection, so that signals sent by a front axle speed sensor, a rear axle speed sensor and a vehicle speed sensor CAN be acquired through the CAN bus, and the accelerometer sensor acquires longitudinal acceleration and lateral acceleration of the vehicle.
The four-wheel-drive torque limiting device based on the fuzzy PID is a four-wheel-drive torque limiting method based on the fuzzy PID, which is realized by arranging various functional components to respectively correspond to each other. The operation principle of the fuzzy PID based four-wheel drive torque limiting device is explained by the fuzzy PID based four-wheel drive torque limiting method.
As shown in fig. 1, the fuzzy PID-based four-wheel drive torque limiting method is a control method of a fuzzy PID-based four-wheel drive torque limiting device, when the four-wheel drive electric automobile runs, the CAN bus in the signal acquisition module 1 acquires the speed, the front axle speed and the rear axle speed in real time and sends the speeds to the closed-loop torque control module 23, the fuzzy PID controller I23 a in the closed-loop torque control module 23 receives the front axle speed and the speed, and the difference value of the front axle speed and the vehicle speed is calculated to obtain a front axle difference value, the change rate of the front axle difference value and the front axle difference value obtained at the last moment is calculated to obtain a front axle difference value change rate, the front axle difference value and the front axle difference value change rate are subjected to fuzzy control, and finding out output quantity according to the fuzzy rule table to optimize three parameters of Kp, Ki and Kd in real time, performing PID control on the front axle difference value and the three parameters of Kp, Ki and Kd to obtain a front axle maximum torque value, and transmitting the front axle maximum torque value to the torque value comparison module 24.
Meanwhile, a second fuzzy PID controller 23b in the closed-loop torque control module 23 receives the rear axle speed and the vehicle speed, calculates a difference between the rear axle speed and the vehicle speed to obtain a rear axle difference, calculates a change rate of the rear axle difference and the rear axle difference obtained at the previous moment to obtain a rear axle difference change rate, performs fuzzy control on the rear axle difference and the rear axle difference change rate, finds out an output quantity according to a fuzzy rule table to optimize in real time to obtain three parameters of Kp, Ki and Kd, performs PID control on the rear axle difference and the three parameters of Kp, Ki and Kd to obtain a maximum rear axle torque value, and transmits the maximum rear axle torque value to the torque value comparison module 24.
Meanwhile, the accelerometer sensor in the signal acquisition module 1 acquires lateral acceleration and longitudinal acceleration in real time and sends the lateral acceleration and the longitudinal acceleration to the road adhesion coefficient acquisition module 21, and the road adhesion coefficient acquisition module 21 estimates the vertical load of each wheel according to the lateral acceleration and the longitudinal acceleration in combination with the physical structure parameters of the vehicle, wherein the physical structure parameters of the vehicle are fixed parameters including a rear wheel base, a front wheel base, a rear wheel base, a front wheel base and a center of mass height after the vehicle is manufactured. The vertical load of each wheel is calculated by the following formula:
wherein, F fl Vertical load of the left front wheel; f fr Is the right front wheel vertical load; f rl Vertical load for the left rear wheel; f rr Is the vertical load of the right rear wheel; l is r Is the rear wheelbase; l is f Is the front wheelbase; l is the wheelbase; a is a rear axle wheel base; b is the front axle wheel track; h is the height of the centroid; m is the mass of the whole vehicle; a is x Is the longitudinal acceleration; a is y Is the lateral acceleration.
After the vertical load of each wheel is obtained by calculation according to the formula, the vertical load of the front axle is equal to the vertical load of the left front wheel plus the vertical load of the right front wheel, namely the vertical load F of the front axle f ＝F fl +F fr (ii) a The vertical load of the rear axle is equal to the sum of the vertical load of the left rear wheel and the vertical load of the right rear wheel, namely the vertical load F of the rear axle r ＝F rl +F rr 。
Then the road adhesion coefficient obtaining module 21 calculates according to the vertical load of the front axle and the driving force of the front axle to obtain the road adhesion coefficient mu of the front axle Front side The calculation formula is as follows:
wherein, F Before X Is a front axle driving force; mu.s Front part The front axle road surface adhesion coefficient.
The road surface adhesion coefficient acquisition module 21 calculates according to the vertical load of the rear axle and the driving force of the rear axle to obtain the road surface adhesion coefficient mu of the rear axle Rear end Finally, it is calculated by the following formula:
wherein, F After X Is a rear axle driving force; mu.s Rear end The road surface adhesion coefficient of the rear axle is. The front and rear axle driving force is the ability of the front axle to drive the vehicle and the ability of the rear axle to drive the vehicle. When the CAN bus is used, signals of rear axle driving force and front axle driving force CAN be directly acquired through the CAN bus. In the invention, in the calculation of the front and rear axle road surface adhesion coefficients, the dynamic motion state of the vehicle is combined for calculation, the problems that the vertical loads of the front and rear axles are half of the weight of the whole vehicle and the dynamic motion state of the vehicle is not combined at present are solved, the precision of vertical load estimation is improved through the scheme of the invention, and the front axle road surface adhesion coefficient mu is further improved Front side Road surface adhesion coefficient mu of rear axle Rear end Accuracy of acquisition such that the front axle torque limit value T is subsequently obtained q front And rear axle torque limit value T q after More accurate, provide the guarantee for the security and the stability of vehicle.
The road adhesion coefficient acquisition module 21 acquires the road adhesion coefficient mu of the front axle Front side Road surface adhesion coefficient mu of rear axle Rear end Is transmitted to an open-loop torque control module 22, and is controlled by the open-loop torque control module 22 according to the road surface adhesion coefficient mu of the front axle Front side And lateral acceleration a y Calculating according to the following formula I to obtain the maximum longitudinal acceleration a of the front axle x front The first formula is:
wherein g is the acceleration of gravity, a y Is the lateral acceleration.
The open-loop torque control module 22 controls the torque according to the road surface adhesion coefficient mu of the rear axle Rear end And lateral acceleration a y Calculating according to the following formula II to obtain the maximum longitudinal acceleration a of the rear axle x after The second formula is:
wherein g is the acceleration of gravity, a y Is the lateral acceleration.
The open-loop torque control module 22 calculates a maximum front axle longitudinal acceleration a Before x And maximum acceleration a of rear axle x after Thereafter, the open loop torque control module 22 obtains the maximum longitudinal acceleration a of the front axle Before x Left front wheel vertical load F fl And right front wheel vertical load F fe Calculating the parameters according to a front axle torque calculation formula to obtain a front axle torque limit value T q front Before calculating the front axle torque limit value T q front Firstly, the vertical load F of the left front wheel obtained by calculation is calculated fl And right front wheel vertical load F fr Making a comparison, e.g. vertical load F of the left front wheel fl Is less than rightVertical front wheel load F fr Selecting the vertical load F of the left front wheel fl Substituting into the front axle torque calculation formula to obtain the front axle torque limit value T q front ；
Front axle torque calculation formula:
wherein l is the rolling radius.
If the vertical load F of the left front wheel fl Greater than the vertical load F of the right front wheel fr Then, the right front wheel vertical load F is selected fr Substituting into the front axle torque calculation formula to calculate to obtain the front axle torque limit value T q front ；
The front axle torque calculation formula is as follows:
wherein l is the rolling radius.
Open-loop torque control module 22 to obtain maximum rear axle longitudinal acceleration a x after Left rear wheel vertical load F rl And right rear wheel vertical load F rr Calculating a rear axle torque limit value T for the parameter according to a rear axle torque calculation formula q after At calculation of the rear axle torque limit value T q after Firstly, the vertical load F of the left rear wheel obtained by calculation is calculated rl And right rear wheel vertical load F rr Making comparisons, e.g. left rear wheel vertical load F rl Is smaller than the vertical load F of the right rear wheel rr Selecting the vertical load F of the left rear wheel rl Substituting the torque into a rear axle torque calculation formula to obtain a front axle torque limit value T q after ；
The rear axle torque calculation formula is:
wherein l is the rolling radius.
If the left rear wheel vertical load F rl Greater than the vertical load F of the right rear wheel rr Then the right rear wheel vertical load F is selected rr Substituting the torque into a rear axle torque calculation formula to obtain a front axle torque limit value T q after ；
Rear axle torque calculation formula:
wherein l is the rolling radius.
Then, the open-loop torque control module 22 sends the obtained front axle torque limit value and rear axle torque limit value to the torque value comparison module 24, the torque value comparison module 24 compares and compares the received front axle torque limit value, rear axle torque limit value, front axle maximum torque value and rear axle maximum torque value, comparing the front axle torque limit value with the front axle maximum torque value, selecting a value with a small value as a front axle torque control value, if the front axle torque limit value is smaller than the front axle maximum torque value, the torque value comparison module 24 transmits the front axle torque limit value as a front axle torque control value to the torque limit control module 25, the torque limit control module 25 limits the front axle torque according to the front axle torque limit value, otherwise, the torque value comparison module 24 outputs the front axle maximum torque value as the front axle torque control value to the torque limit control module 25, and the torque limit control module 25 limits the front axle torque according to the front axle maximum torque value; meanwhile, the rear axle torque limit value and the rear axle maximum torque value are compared to select a value with a small value as a rear axle torque control value, if the rear axle torque limit value is smaller than the rear axle maximum torque value, the torque value comparison module 24 outputs the rear axle torque limit value as a rear axle torque control value to the torque limit control module 25, the torque limit control module 25 limits the rear axle torque according to the rear axle torque limit value, otherwise, the torque value comparison module 24 outputs the rear axle maximum torque value as a rear axle torque control value to the torque limit control module 25, the torque limit control module 25 limits the rear axle torque according to the rear axle maximum torque value, the scheme of the invention can adjust the front axle initial torque value and the rear axle initial torque value of the vehicle, ensure that the front axle torque value output by the current vehicle is smaller than the front axle torque limit value or the front axle maximum torque value, ensure that the rear axle torque value output by the current vehicle is smaller than the rear axle torque limit value or the rear axle maximum torque value, the safety and the stability of the vehicle running are ensured.
The second embodiment:
the technical solution in this embodiment is basically the same as that in the first embodiment, except that, as shown in fig. 4, in the four-wheel drive torque limiting device based on the fuzzy PID, the vehicle controller 2 further includes:
the activation condition judgment module 26 is configured to compare the acquired vehicle speed with a front axle speed and a rear axle speed, respectively, and when the front axle speed and/or the rear axle speed is greater than the vehicle speed, the vehicle control unit 2 enters front and rear axle torque limitation;
and the exit condition judgment module 27 is used for monitoring whether the traction control system intervenes in a signal for controlling the driving torque in real time and exiting the torque limitation of the front axle and the rear axle of the vehicle control unit 2 when the traction control system intervenes.
As shown in fig. 2, the fuzzy PID-based four-wheel drive torque limiting method further includes:
presetting an activation condition and a quitting condition for the whole vehicle controller 2 to carry out front and rear axle torque limit control;
and comparing the acquired vehicle speed with the front axle speed and the rear axle speed respectively, judging that the activation condition is met when the front axle speed and/or the rear axle speed is/are greater than the vehicle speed, and entering front and rear axle torque limitation by the vehicle control unit 2, otherwise, returning to the comparison of the front axle speed and the rear axle speed with the vehicle speed when the front axle speed and the rear axle speed are both less than the vehicle speed.
Whether the traction control system intervenes in a signal for controlling the driving torque or not is monitored in real time, and when the traction control system intervenes, the vehicle controller 2 judges that the quit condition is met, and quits the torque limitation of the front axle and the rear axle, otherwise, when the traction control system does not intervene, the vehicle controller 2 continues the torque limitation of the front axle and the rear axle, so that the vehicle posture can be adjusted quickly when the vehicle is unstable, and the stability and the safety of the vehicle are improved.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments, or alternatives may be employed, by those skilled in the art, without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (9)
1. A four-wheel drive torque limiting method based on fuzzy PID is characterized by comprising the following steps:
acquiring a front axle speed, a rear axle speed, a vehicle speed, a front axle road surface adhesion coefficient and a rear axle road surface adhesion coefficient;
the whole vehicle controller (2) performs open-loop control according to the front axle road surface adhesion coefficient to obtain a front axle torque limit value, and performs open-loop control according to the rear axle road surface adhesion coefficient to obtain a rear axle torque limit value;
the vehicle control unit (2) calculates the difference between the front axle speed and the vehicle speed to obtain a front axle difference, calculates the change rate of the front axle difference from the front axle difference obtained at the last moment to obtain a front axle difference change rate, performs fuzzy control on the front axle difference and the front axle difference change rate, finds out the output quantity according to a fuzzy rule table to optimize in real time to obtain three parameters Kp, Ki and Kd, and performs PID control on the front axle difference and the three parameters Kp, Ki and Kd to obtain a front axle maximum torque value;
the vehicle control unit (2) calculates the difference between the rear axle speed and the vehicle speed to obtain a rear axle difference, calculates the change rate of the rear axle difference from the rear axle difference obtained at the previous moment to obtain a rear axle difference change rate, performs fuzzy control on the rear axle difference and the rear axle difference change rate, finds out the output quantity according to a fuzzy rule table to optimize in real time to obtain three parameters Kp, Ki and Kd, and performs PID control on the rear axle difference and the three parameters Kp, Ki and Kd to obtain a maximum rear axle torque value;
the vehicle control unit (2) compares the front axle torque limit value with the maximum front axle torque value, selects the small value as the front axle torque control value and limits the front axle torque; and the vehicle control unit (2) also compares the rear axle torque limit value with the maximum rear axle torque value, selects a small value as a rear axle torque control value and limits the rear axle torque.
2. The fuzzy PID based four-wheel drive torque limiting method according to claim 1, further comprising:
presetting an activation condition and a quit condition for the whole vehicle controller (2) to carry out front and rear axle torque limit control;
comparing the acquired vehicle speed with the front axle speed and the rear axle speed respectively, judging that the activation condition is met when the front axle speed and/or the rear axle speed is/are greater than the vehicle speed, and enabling the vehicle control unit (2) to enter front and rear axle torque limit;
and monitoring whether the traction control system intervenes in a signal for controlling the driving torque in real time, judging that the quit condition is met when the traction control system intervenes, and quitting the torque limitation of the front axle and the rear axle by the vehicle control unit (2).
3. The fuzzy PID based four-wheel drive torque limiting method according to claim 1 or 2, wherein the operation of obtaining the front axle torque limiting value by the vehicle control unit (2) through open loop control according to the front axle road surface adhesion coefficient, and obtaining the rear axle torque limiting value through open loop control according to the rear axle road surface adhesion coefficient comprises:
acquiring longitudinal acceleration and lateral acceleration of the vehicle by using an accelerometer sensor;
estimating and obtaining the vertical load of each wheel of the vehicle according to the longitudinal acceleration and the lateral acceleration and the physical structure parameters of the vehicle;
calculating according to the lateral acceleration and the front axle road surface adhesion coefficient to obtain the maximum longitudinal acceleration of the front axle; calculating according to the lateral acceleration and the road surface adhesion coefficient of the rear axle to obtain the maximum longitudinal acceleration of the rear axle;
comparing the obtained vertical load of the left front wheel with the vertical load of the right front wheel, selecting the vertical load of the front wheel with a small value, and calculating the vertical load and the maximum longitudinal acceleration of the front axle according to a front axle torque calculation formula to obtain a front axle torque limit value;
and comparing the obtained vertical load of the left rear wheel with the vertical load of the right rear wheel, selecting the vertical load of the rear wheel with a small value, and calculating the vertical load and the maximum longitudinal acceleration of the rear axle according to a rear axle torque calculation formula to obtain a rear axle torque limit value.
4. The fuzzy PID based four-wheel drive torque limiting method according to claim 3, wherein the front axle torque calculation formula is:
wherein, T q front For front axle torque limit, F fl Vertical load of the left front wheel; f fr Is the right front wheel vertical load; l is the rolling radius; g is the acceleration of gravity; a is Before x For the front axle maximum longitudinal acceleration, the front axle maximum longitudinal acceleration is calculated as follows:
wherein, a y Is the lateral acceleration; mu.s Front side The front axle road surface adhesion coefficient.
5. The fuzzy PID based four-wheel drive torque limiting method according to claim 3, wherein the rear axle torque calculation formula is:
wherein, T q after For rear axle torque limit, F rl Vertical load for the left rear wheel; f rr Is the vertical load of the right rear wheel; l is the rolling radius, g is the acceleration of gravity; a is x after For the maximum longitudinal acceleration of the rear axle, the formula is calculated as follows:
wherein, a y Is the lateral acceleration; mu.s Rear end The road surface adhesion coefficient of the rear axle is.
6. The fuzzy PID based four-wheel drive torque limiting method according to claim 1 or 2, wherein the operation of obtaining a front axle maximum torque value comprises:
and calculating the difference between the obtained front axle speed and the vehicle speed to obtain a front axle difference, calculating the change rate of the front axle difference and the front axle difference at the previous moment to obtain the front axle difference change rate, and performing fuzzy PID control on the front axle difference and the front axle difference change rate to obtain the maximum torque value of the front axle.
7. The fuzzy PID based four-wheel drive torque limiting method according to claim 1 or 2, characterized in that the operation of obtaining the rear axle maximum torque value comprises:
and calculating the difference between the obtained rear axle speed and the vehicle speed to obtain a speed difference of the rear axle, calculating the change rate of the rear axle difference and the rear axle difference at the last moment to obtain the change rate of the rear axle difference, and performing fuzzy PID control on the rear axle difference and the change rate of the rear axle difference to obtain the maximum torque value of the rear axle.
8. The utility model provides a four wheel drive torque limiting device based on fuzzy PID, includes vehicle control unit (2) and is used for acquireing signal acquisition module (1) of front axle speed, rear axle speed and speed of a motor vehicle, its characterized in that, vehicle control unit (2) include:
the road surface adhesion coefficient acquisition module (21) is used for acquiring a front axle road surface adhesion coefficient and a rear axle road surface adhesion coefficient;
the open-loop torque control module (22) is used for calculating a front axle torque limit value and a rear axle torque limit value according to the front axle road adhesion coefficient and the rear axle road adhesion coefficient;
the closed loop torque control module (23) includes:
the fuzzy PID controller I (23a) is used for calculating the difference value of the front axle speed and the vehicle speed to obtain a front axle difference value, calculating the change rate of the front axle difference value and the front axle difference value obtained at the previous moment to obtain a front axle difference value change rate, carrying out fuzzy control on the front axle difference value and the front axle difference value change rate, finding out output quantity according to a fuzzy rule table to optimize in real time to obtain three parameters of Kp, Ki and Kd, carrying out PID control on the front axle difference value and the three parameters of Kp, Ki and Kd to obtain a maximum torque value of the front axle, and transmitting the maximum torque value of the front axle to the torque value comparison module (24);
the second fuzzy PID controller (23b) is used for calculating the difference between the rear axle speed and the vehicle speed to obtain a rear axle difference, calculating the change rate of the rear axle difference and the rear axle difference obtained at the last moment to obtain a rear axle difference change rate, performing fuzzy control on the rear axle difference and the rear axle difference change rate, finding out output quantity according to a fuzzy rule table to optimize in real time to obtain three parameters of Kp, Ki and Kd, and performing PID control on the rear axle difference and the three parameters of Kp, Ki and Kd to obtain a maximum rear axle torque value and transmitting the maximum rear axle torque value to the torque value comparison module (24);
the torque value comparison module (24) is used for comparing the front axle torque limit value with the front axle maximum torque value to select a small value as a front axle torque control value, and comparing the rear axle torque limit value with the rear axle maximum torque value to select a small value as a rear axle torque control value;
and the torque limiting control module (25) is used for limiting the torque of the front axle and the torque of the rear axle according to the torque control value of the front axle and the torque control value of the rear axle selected by the torque value comparison module (24).
9. The fuzzy PID based four-wheel drive torque limiting device according to claim 8, characterized in that the vehicle controller (2) further comprises:
the activation condition judgment module (26) is used for comparing the acquired vehicle speed with the front axle speed and the rear axle speed respectively, and the vehicle control unit (2) enters front and rear axle torque limitation when the front axle speed and/or the rear axle speed are/is greater than the vehicle speed;
and the exit condition judgment module (27) is used for monitoring whether the traction control system intervenes in a signal for controlling the driving torque in real time and exiting the torque limitation of the front axle and the rear axle of the vehicle control unit (2) when the traction control system intervenes.
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