CN109850003B - Energy storage type steer-by-wire system and fault-tolerant control method - Google Patents
Energy storage type steer-by-wire system and fault-tolerant control method Download PDFInfo
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- CN109850003B CN109850003B CN201910136314.7A CN201910136314A CN109850003B CN 109850003 B CN109850003 B CN 109850003B CN 201910136314 A CN201910136314 A CN 201910136314A CN 109850003 B CN109850003 B CN 109850003B
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Abstract
The invention discloses an energy storage type steer-by-wire system and a fault-tolerant control method, which comprise a steering wheel, a steering column, an electronic control unit, a first angle sensor, a second angle sensor, a displacement sensor, a torsion spring, locking pliers at the position of the torsion spring, a first electromagnetic valve, a second electromagnetic valve, a gearwheel, a first hydraulic pipeline, a second hydraulic pipeline, a steering motor, a planetary gear train, locking pliers at the position of an output shaft, a rack-and-pinion steering gear, a steering tie rod and steering wheels, wherein the steering wheel is connected with the electronic control unit through the electronic control unit; the system stores energy for the torsion spring at the initial stage of starting the automobile; when the automobile normally runs, the torsion spring is locked, and the operation of the steer-by-wire system cannot be influenced; when the system breaks down, according to the different fault types, the steering motor or the torsion spring drives the steering wheel to return to the right, so that the vehicle is prevented from being out of control due to continuous steering. Compared with the existing redundant steer-by-wire system, the system can deal with common faults of the steer-by-wire system only by virtue of the torsion spring and the gear, and simultaneously simplifies the system structure.
Description
Technical Field
The invention belongs to the technical field of automobile steer-by-wire systems, and particularly relates to an energy storage type steer-by-wire system and a fault-tolerant control method.
Background
Various novel steering systems emerge in the field of automobile steering at present, including active steering, differential steering, steer-by-wire, four-wheel steering and the like, wherein the steer-by-wire is a key technology in an automobile intelligent process. Compared with the traditional steering system, the steer-by-wire eliminates part of mechanical connection, and the part is replaced by a circuit composed of an electronic control unit ECU, a sensor, a signal wire harness and the like. The steer-by-wire has the advantage of facilitating the control of the dynamics of the whole vehicle by adjusting the steering angle, because it comprises an ECU and a steering motor. But the disadvantage is also obvious, in order to maintain the road feel of the driver, the steer-by-wire system also needs a road feel motor to simulate the road feel of the driver; furthermore, steer-by-wire requires a very high reliability, so the system must be fault tolerant. The above causes the hardware and the circuit of the steer-by-wire system to have various types, complex connection and higher cost.
There have been many efforts in China to date on steer-by-wire. The invention has the Chinese patent application number of CN201610389410.9, is named as a double-chip redundancy and fault-tolerant control system for automobile steering-by-wire, adopts a double-chip technology, not only lightens the work load of the chip, but also has a self-checking function, so that when one chip reports errors, the other chip plays a full role, and the stability and the reliability of the system are greatly improved. The Chinese patent application No. CN201110171716.4 entitled redundant fault-tolerant control method applied to a dual-motor steer-by-wire system adopts a mode that a corner motor and an auxiliary motor work together to deal with the situation that one motor fails. The above designs related to the steer-by-wire fault-tolerant function essentially adopt double ECUs or double motors, which have the disadvantages that the cost and the quality of the system are increased, and the mechanism with the safety function still belongs to electronic equipment, and compared with a mechanical structure, the reliability is still lower.
In order to solve the above problem, it is necessary to recognize that the steered wheels have a certain tendency to return to the straight state during running. If the auxiliary power with a certain size can be additionally provided for the wheels when the linear control system breaks down, the wheels can be kept to be accurately steered or quickly aligned.
Disclosure of Invention
In view of the above-mentioned deficiencies of the prior art, an object of the present invention is to provide an energy-storing steer-by-wire system and a fault-tolerant control method, which can automatically take corresponding measures when the steer-by-wire system fails, so as to keep the wheels steering accurately or quickly, avoid the vehicle from being out of control, and effectively improve the driving safety of the steer-by-wire vehicle, so as to solve the existing technical problems.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the invention relates to an energy storage type steer-by-wire system, which comprises a steering wheel, a steering column, an electronic control unit, a first angle sensor, a second angle sensor, a displacement sensor, a torsion spring, a locking clamp at the position of the torsion spring, a first electromagnetic valve, a second electromagnetic valve, a gearwheel, a first hydraulic pipeline, a second hydraulic pipeline, a steering motor, a planetary gear train, a locking clamp at the position of an output shaft, a rack-and-pinion steering gear, a steering tie rod and steering wheels, wherein the steering wheel is arranged on the steering column;
the steering wheel is connected with a steering column, and the steering column is provided with a first angle sensor which is used for transmitting the angle information of the steering wheel to the electronic control unit through a CAN bus; the torsional spring and the locking pliers at the torsional spring are coaxially installed, the locking pliers at the torsional spring are connected with a first electromagnetic valve through a first hydraulic pipeline, and the first electromagnetic valve is also connected with an electronic control unit through a CAN bus; the large gear is linked with the torsion spring and is meshed with a gear ring of the planetary gear train; the steering motor is connected with the electronic control unit through a CAN bus, an output shaft of the steering motor is connected with a sun gear of the planetary gear train, and a second angle sensor is arranged on the output shaft of the steering motor and connected with the electronic control unit through the CAN bus; the lower row of gear rings of the planetary gear train is fixed, the output shaft of the planetary gear train is connected with a pinion of the rack and pinion steering gear, and the output shaft of the planetary gear train is provided with an output shaft locking clamp which is connected with a second electromagnetic valve through a second hydraulic pipeline, and the second electromagnetic valve is also connected with an electronic control unit through a CAN bus; the rack of the rack and pinion steering gear is provided with a displacement sensor which is connected with an electronic control unit through a CAN bus, the tail end of the rack is connected with one end of a tie rod, and the other end of the tie rod is connected with a steering wheel.
An Electronic Control Unit (ECU) acquires a steering wheel angle signal through a first angle sensor so as to identify the steering intention of a driver; collecting a steering motor corner signal through a second angle sensor to judge the working state of the motor; and a displacement sensor is used for acquiring a displacement signal of the gear type steering gear so as to obtain wheel steering feedback.
The invention discloses a fault-tolerant control method of an energy storage type steer-by-wire system, which is based on the system and comprises the following steps:
1) establishing a steer-by-wire system model;
2) designing a fault threshold judgment condition of the steer-by-wire system;
3) the state of the steer-by-wire system is divided, and countermeasures corresponding to the failure are provided.
Preferably, the steer-by-wire system model in step 1) is specifically:
in the initial starting stage of the automobile, the electronic control unit sends out an output shaft locking command e and an output shaft locking torque ToTo a set maximum value TomaxThe steering motor starts to store energy for the torsion spring, and the dynamic model of the torsion spring in the state is as follows:
θr2＝βθs
in the formula, JsIs torsional spring moment of inertia; thetasIs a torsion spring corner; alpha is the gear ratio of the planetary gear train gear ring and the planetary gear train sun gear; thetar2The rotation angle of an upper row gear ring of the planetary gear train; t iss1Is the torque of the sun gear of the planetary gear train; t issLocking the torque for the torsion spring; beta is the ratio of the torsional spring gear to the number of teeth on the upper row of the planetary gear train; ksThe elastic coefficient of the torsion spring; when the rotation angle of the torsion spring reaches the maximum value thetasmaxOn one hand, the electronic control unit sends out a torsional spring locking instruction to enable the torsional spring locking torque to reach a set maximum value TsmaxOn the other hand, the end of energy storage is indicated by cutting off the steering command of the steering motor.
Preferably, the faults of the steer-by-wire system in the step 2) are divided into a steering motor precision fault, a steering motor complete failure fault and an electronic control unit fault.
Preferably, the steering motor accuracy failure threshold determination condition in the step 2) is as follows,
in the formula (I), the compound is shown in the specification,
for rack displacement at time tMeasuring values; t is t1The time interval upper limit of the precision fault of the steering motor is set; t ish1Is a motor precision threshold.
The electronic control unit can send a steering instruction U according to a steering system model and the previous momenta(t-1) calculating a theoretical value x of rack displacement at the next momentr(t), therefore, when the calculation result satisfies the above condition, the electronic control unit determines that the motor accuracy failure has occurred.
Preferably, the steering motor complete failure threshold determination condition in the step 2) is as follows,
in the formula, λi(i ═ 1,2,3,4) is a weight coefficient; t is t2The time interval upper limit of the failure of the steering motor is set;
the measured value of the turning angle of the steering motor at the moment t;
the measured value of the turning angle of the steering motor at the moment t-1;
is the measured value of the rack displacement at the time t-1; t ish2Is the motor failure threshold.
T after the electronic control unit sends a steering instruction2And in time, when the two signals of the turning angle of the steering motor and the displacement of the rack meet the conditions, the electronic control unit judges that the steering motor completely fails.
Preferably, the electronic control unit in step 2) comprises a calculating module, a register module and a self-diagnosis module, wherein the calculating module is used for analyzing signals of each sensor, calculating a steering command at the current moment, and calculating a motor rotation angle and a corresponding motor steering command required for returning the rack to the correct state at the current state; the register module is used for storing a steering system model and two locking instructions and steering instructions from the calculation module, and the steering instruction at the previous moment is output to the steering motor and then covered by a new steering instruction; the self-diagnosis module is used for detecting and collecting internal program abnormity of the electronic control unit; when the program has an irresolvable abnormality, the electronic control unit generates a fault, the self-diagnosis module interrupts the operation of the calculation module at the moment, and two locking instructions in the register module are confirmed to be transmitted to the actuator.
Preferably, the steer-by-wire system state in step 3) comprises: the method comprises the following steps of initial starting, normal running, steering motor precision failure, steering motor complete failure and electronic control unit failure.
Preferably, the countermeasure for the fault in step 3) is as follows:
after the precision fault of the steering motor occurs, the steering precision is ensured by the intervention of the torsion spring within a certain time, specifically, an electronic control unit adjusts the locking instruction of the torsion spring to ensure that the locking pliers at the torsion spring are loosened or closed at high frequency so as to change the locking torque T of the torsion springsThe torsion spring is rotated and the rotation angle of the torsion spring is superposed to the movement of the rack through the planetary gear train, and finally the error of the rack displacement is reduced to be below a threshold value;
when the steering motor is completely out of work, the electronic control unit standsNamely, the steering command is cut off to prevent the steering motor from suddenly recovering to operate when the torsion spring is involved; and interrupting the torsional spring locking instruction, completely loosening the locking pliers at the torsional spring, and enabling the torsional spring to have the maximum torque TsmaxOutput to the planetary gear train and the rack; when the electronic control unit detects
When the steering motor is started, the electronic control unit is started to stop the steering motor, and the rack is indicated to return to the middle position, and then the electronic control unit immediately restores a torsional spring locking instruction to enable the locking pliers at the torsional spring to be completely closed, the torsional spring is instantly locked, the steering motor cannot run, and the rack and the steering wheel are guaranteed to return to the right state in the shortest time;
when the electronic control unit has a fault, a fault correcting instruction in the register module is continuously sent to the steering motor, and meanwhile, the self-diagnosis module triggers two locking instructions in the register module to enable the locking pliers at the torsion spring to be tightly closed and the locking pliers at the output shaft to be loosened; the steering motor can drive the steering wheel to quickly return to the right through the planetary gear train, the output shaft of the planetary gear train, the pinion, the rack and the steering tie rod under the condition of no interference of the torsion spring; and the failure return command is a continuous constant signal, and the steering wheel cannot rotate to another direction or swing back and forth beyond the middle position after returning to the middle position.
The invention has the beneficial effects that:
1. compared with the original steer-by-wire system, the invention only adds the torsion spring, the locking pliers, the hydraulic pipeline and the electromagnetic valve, thereby having simple structure, low cost and high reliability.
2. Compared with the existing redundant steer-by-wire device, the invention uses a mechanical mechanism to replace electronic equipment to process the condition that the steer-by-wire system has faults, thereby greatly improving the steering reliability and the driving safety.
3. According to the invention, by establishing a steer-by-wire system model and setting a fault threshold judgment condition, the state of the steering system can be rapidly and accurately monitored in the whole process of automobile driving, the fault of the steering system can be found in time, and corresponding emergency measures can be triggered.
4. The mechanical structure provided by the invention can be repeatedly used and does not need frequent maintenance; the device can automatically store energy for the torsion spring when the automobile is started, does not need manual operation, and is convenient to use.
5. Does not affect the steering intention of the driver: additional mechanisms such as torsion springs only play a role when the line control steering system breaks down, and steering operation of a driver is not disturbed in the normal driving process.
Drawings
FIG. 1 is a schematic structural diagram of an energy-storing steer-by-wire system;
FIG. 2 is a simplified model of a steering motor;
FIG. 3a is a schematic diagram of torsional spring energy storage at the initial stage of starting of the vehicle;
FIG. 3b is a schematic view of a normal driving steering of the vehicle;
FIG. 3c is a schematic diagram of motor accuracy fault tolerance;
FIG. 3d is a fault tolerant schematic diagram of a complete failure of the motor;
FIG. 3e is a schematic diagram of the fault tolerance of the ECU;
in the figure: 1-steering wheel, 2-steering column, 3-first angle sensor, 9-second angle sensor, 4-torsional spring locking clamp, 5-torsional spring, 6-first hydraulic pipeline, 18-second hydraulic pipeline, 7-first electromagnetic valve, 19-second electromagnetic valve, 8-steering motor, 10-big gear, 11-planetary gear train, 12-planetary gear train output shaft, 13-output shaft locking clamp, 14-small gear, 15-rack, 16-displacement sensor, 17-steering cross rod, 20-steering wheel, 21-electronic control unit, a-steering wheel rotation angle signal, b-torsional spring locking command, c-steering command, d-steering motor rotation angle signal, e-output shaft locking command, f-rack displacement, g-fault return-to-positive command.
Detailed Description
In order to facilitate understanding of those skilled in the art, the present invention will be further described with reference to the following examples and drawings, which are not intended to limit the present invention.
Referring to fig. 1, the energy storage type steer-by-wire system of the present invention comprises a steering wheel 1, a steering column 2, an Electronic Control Unit (ECU)21, a first angle sensor 3, a second angle sensor 9, a displacement sensor 16, a torsion spring 5, a locking clamp 4 at the torsion spring, a first electromagnetic valve 7, a second electromagnetic valve 19, a gearwheel 10, a first hydraulic pipeline 6, a second hydraulic pipeline 18, a steering motor 8, a planetary gear train 11, a locking clamp 13 at the output shaft, a rack and pinion steering gear, a steering tie rod 17 and a steering wheel 20;
the steering wheel 1 is connected with a steering column 2, and a first angle sensor 3 is arranged on the steering column 2 and used for transmitting the rotation angle information of the steering wheel 1 to an electronic control unit 21 through a CAN bus; the torsion spring 5 and the locking pliers 4 at the torsion spring are coaxially arranged, the locking pliers 4 at the torsion spring are connected with a first electromagnetic valve 7 through a first hydraulic pipeline 6, and the first electromagnetic valve 7 is also connected with an electronic control unit 21 through a CAN bus; the large gear 10 is linked with the torsion spring 5 and is meshed with a gear ring of the planetary gear train 11; the steering motor 8 is connected with the electronic control unit 21 through a CAN bus, the output shaft of the steering motor is connected with the sun gear of the planetary gear train 11, the output shaft of the steering motor is provided with a second angle sensor 9, and the second angle sensor 9 is connected with the electronic control unit 21 through the CAN bus; the lower row of gear rings of the planetary gear train 11 is fixed, the output shaft 12 of the planetary gear train is connected with a pinion 14 of the rack and pinion steering gear, an output shaft locking clamp 13 is assembled on the output shaft, the output shaft locking clamp 13 is connected with a second electromagnetic valve 19 through a second hydraulic pipeline 18, and the second electromagnetic valve 19 is also connected with an electronic control unit 21 through a CAN bus; the rack 15 of the rack and pinion steering gear is provided with a displacement sensor 16, the displacement sensor 16 is connected with an electronic control unit 21 through a CAN bus, the tail end of the rack 15 is connected with one end of a tie rod 17, and the other end of the tie rod 17 is connected with a steering wheel 20.
The electronic control unit comprises a calculation module, a register module and a self-diagnosis module; the calculation module is used for analyzing signals of each sensor and calculating a steering command at the current moment, a motor rotation angle required for returning the rack to the correct position under the current state and a corresponding motor steering command; the register module is provided with two storage areas, wherein one storage area is a constant area and is used for storing a steering system model, the other storage area is a variable area and is used for storing a locking instruction and a steering instruction of the calculation module, and the steering instruction at the previous moment is covered by a new steering instruction after being output to a steering motor; the self-diagnosis module is used for detecting and collecting the internal program abnormity of the electronic control unit.
When the program has an irresolvable abnormality, the electronic control unit is indicated to generate a fault, and at the moment, the self-diagnosis module interrupts the operation of the calculation module on one hand and confirms that two locking instructions in the register module are transmitted to the steering motor 8 on the other hand.
An Electronic Control Unit (ECU) collects a steering wheel turning angle signal a through a first angle sensor 3 to identify the steering intention of a driver; collecting a steering motor corner signal d through a second angle sensor 9 to judge the working state of the motor; and a displacement signal of the gear type steering gear is acquired through the displacement sensor 16 so as to obtain wheel steering feedback.
The invention discloses a fault-tolerant control method of an energy storage type steer-by-wire system, which is based on the system and comprises the following steps:
step 1: establishing a dynamic model of the steer-by-wire system;
11) a steering motor model:
the steering motor used on the steer-by-wire automobile has the characteristics of small volume, quick response, convenient maintenance, stable and reliable operation, accurate regulation and control and the like. The invention selects the permanent magnet brushless direct current motor as the steer-by-wire motor by comprehensively considering various performances and use cost of the motor.
The steering motor dynamics model can be simplified as shown in fig. 2, and the voltage balance equation is:
in the formula of UaIs the armature terminal voltage of the machine; l isaIs the armature inductance of the motor; i isaIs the motor armature current; raIs a motor armature resistance; kmIs the motor back electromotive force coefficient; thetamIs the motor rotation angle.
The dynamic analysis is carried out on the steering motor, and the following dynamic differential equation is shown:
Tm＝KaIa
in the formula, JmIs the rotational inertia of the motor; b ismDamping the motor; t ismIs the motor electromagnetic torque; t islIs the torque of the sun gear of the planetary gear train; kaIs the motor electromagnetic torque constant.
12) Planetary gear train model (zero initial condition):
θs2＝θs1-αθr2
Ts2＝Ts1＝Tl
in the formula, thetas2Is the rotation angle of the output shaft; thetas1Is the angle of rotation of the input shaft, and θs1＝θm(ii) a Alpha is the gear ratio of the gear ring to the sun gear of the input shaft, thetar2Is the angle of rotation of the upper row of toothed rings, Ts2For output shaft torque, Ts1Is the input shaft torque.
13) The dynamic model of the rack and pinion steering gear is as follows:
xr＝θp·rp
in the formula, MrThe mass of the rack; x is the number ofrIs the rack displacement; t is0For output shaft locking torque, which may be approximated by T0＝C0θp；C0Is the output shaft locking coefficient; r ispIs the pinion radius; b isrThe damping coefficient of rack motion is taken as the damping coefficient; t isRThe steering resistance moment applied to the two front wheels for the road surface can be approximated by TR＝CRxr；CRIs the moment of resistance coefficient; i.e. i0The standard transmission ratio from the small gear to the front wheel; thetapIs the angle of rotation of the pinion, and θp＝θs2；FδDisturbance transmitted to front wheel for road surfaceForce.
14) In the initial starting stage of the automobile, the ECU sends out an output shaft locking instruction and an output shaft locking torque ToTo a set maximum value TomaxThe steering motor starts to store energy for the torsion spring, and the dynamic model of the torsion spring in the state is as follows:
θr2＝βθs
in the formula, JsIs torsional spring moment of inertia; thetasIs a torsion spring corner; alpha is the gear ratio of the planetary gear train gear ring and the planetary gear train sun gear; thetar2The rotation angle of an upper row gear ring of the planetary gear train; t islIs the torque of the sun gear of the planetary gear train; t issLocking the torque for the torsion spring; beta is the ratio of the torsional spring gear to the number of teeth on the upper row of the planetary gear train; ksThe elastic coefficient of the torsion spring; when the rotation angle of the torsion spring reaches the maximum value thetasmaxOn one hand, the electronic control unit sends out a torsional spring locking instruction to enable the torsional spring locking torque to reach a set maximum value TsmaxOn the other hand, the end of energy storage is indicated by cutting off the steering command of the steering motor.
The above steer-by-wire system model is stored in the vehicle-mounted ECU, after the vehicle is started, the ECU continuously calculates and updates theoretical values of various state quantities in the steering system according to the model and various sensor signals, and the calculation result is used as a basis for judging the fault of the steering system in the following step 2.
Step 2: setting a fault threshold judgment condition;
in the normal driving process after the automobile is started, the common faults of the steer-by-wire system mainly include three types:
21) precision failure of a steering motor: the ECU can calculate the theoretical value x of rack displacement at the later moment according to a steering system model and a steering command sent out at the previous momentrTherefore, the ECU determines that the motor has an accuracy failure when the calculation result satisfies the following condition:
in the formula (I), the compound is shown in the specification,
is the measured value of rack displacement at the time t; t is t1The time interval upper limit of the precision fault of the steering motor is set; t ish1Is a motor precision threshold.
22) Complete failure of the steering motor: in a period of time after the ECU sends a steering instruction, when two signals, namely a steering motor rotation angle and a rack displacement, meet the following conditions, the ECU judges that the steering motor is completely invalid:
in the formula, λi(i ═ 1,2,3,4) is a weight coefficient; t is t2The time interval upper limit of the failure of the steering motor is set;
the measured value of the turning angle of the steering motor at the moment t;
for turning to time t-1Measuring the rotation angle of the motor;
is the measured value of the rack displacement at the time t-1; t ish2Is the motor failure threshold.
23) The ECU has a fault: the ECU internally comprises a calculation module, a register module and a self-diagnosis module, wherein the calculation module is used for analyzing signals of all sensors, calculating a normal steering command at the current moment, and calculating a motor rotation angle and a corresponding fault aligning command which are required for aligning the rack in the current state; the register module is provided with two storage areas, wherein one storage area is a constant area and stores a steering system model and two locking instructions, the other storage area is a variable area and stores a normal steering instruction and a fault correcting instruction from the calculation module, and the steering instruction at the previous moment is covered by a new steering instruction after being output to an actuator (a steering motor); the self-diagnosis module is used for detecting and collecting the abnormality of the internal program of the ECU. When the program has an irresolvable abnormality, the ECU generates a fault, and at the moment, the self-diagnosis module interrupts the operation of the calculation module on one hand and confirms that two locking instructions in the register module are transmitted to the actuator on the other hand.
And step 3: vehicle driving state classification and fault countermeasure;
as shown in fig. 3, according to the characteristics of the steer-by-wire system, the vehicle states can be classified into five types: the method comprises the following steps of initial starting, normal running, steering motor precision failure, complete failure of the steering motor and ECU calculation module failure. The operation modes of the steer-by-wire system are different when the automobile states are different, and the specific description is as follows:
31) at the initial starting stage of the automobile, the ECU 21 sends a planetary gear output shaft locking instruction e to the second electromagnetic valve 19, the second electromagnetic valve 19 is opened, the hydraulic pressure in the second hydraulic pipeline 18 is increased, the locking clamp 13 at the output shaft is locked, the output shaft 12 of the planetary gear train is locked, and the steering wheel 20 cannot steer; on the other hand, the ECU 21 interrupts a torsional spring locking instruction b for the first electromagnetic valve 7, the first electromagnetic valve 7 is closed, the hydraulic pressure in the first hydraulic pipeline 6 is reduced, and the locking pliers 4 at the torsional spring are released; then the ECU 21 sends a steering command c to the steering motor 8, and the steering motor 8 drives the torsion spring 5 to rotate a certain angle through the planetary gear train 11 and the large gear 10, so that the torsion spring 5 stores a certain potential energy.
32) When the automobile normally runs, the ECU 21 interrupts the output shaft locking command e to the second electromagnetic valve 19, the second electromagnetic valve 19 is closed, the hydraulic pressure in the second hydraulic pipeline 18 is reduced, the locking clamp 13 at the output shaft is released, the output shaft 12 of the planetary gear train and the pinion 14 can rotate, and the steering wheel 20 can steer. Meanwhile, the ECU 21 sends a torsion spring locking instruction b to the first electromagnetic valve 7, the first electromagnetic valve 7 is opened, and the hydraulic pressure in the first hydraulic pipeline 6 is increased, so that the locking pliers 4 at the torsion spring is locked, and the torsion spring 5 cannot rotate. Thus, when the steering wheel 1 rotates during the running of the automobile, the steering intention of the driver is detected by the first angle sensor 3 through the steering column 2, the first angle sensor 3 sends a steering wheel angle signal a to the ECU 21, the ECU 21 comprehensively analyzes the steering wheel angle signal a, the steering motor angle signal d and the rack displacement f and then sends a steering command c, and the steering motor 8 is controlled to drive the pinion 14, the rack 15, the steering tie rod 17 and the steering wheel 20 to move through the planetary gear train 11, so that the steer-by-wire function is completed.
33) After the precision of the steering motor 8 is failed, the steering precision can be ensured by the intervention of the torsion spring 5 within a certain time. Concretely, the ECU 21 adjusts a torsional spring locking instruction b to ensure that the locking pliers 4 at the torsional spring is loosened or closed at high frequency, so as to change the torsional spring locking torque TsThe torsion spring 5 is rotated and the torsion spring rotation angle is superimposed on the movement of the rack 15 by the planetary gear system 11 or the like, and finally the error in the rack displacement is reduced below the threshold value.
34) When the steering motor completely fails, the ECU 21 immediately cuts off the steering command c on one hand to prevent the steering motor 8 from suddenly recovering to operate when the torsion spring 4 intervenes, and on the other hand interrupts the torsion spring locking command b, the locking pliers 4 at the torsion spring is completely loosened, and the torsion spring 5 has the maximum torque TsmaxOutput to the planetary gear 11 and the rack 15. When the ECU detects
When the time comes, the rack 15 returns to the middle position, and the ECU immediately restores the torsion spring locking instruction b at the time to enable the torsion spring locking pliers 4 to be completely locked at the torsion springAnd the torsion spring 5 is locked instantly, and the steering motor cannot run, so that the rack 15 and the steering wheel 20 can be ensured to return to the right in the shortest time.
35) When the computing module of the ECU 21 is in fault, the fault aligning command c in the register module is continuously sent to the steering motor 8, and meanwhile, the self-diagnosis module triggers two locking commands in the register to enable the locking pliers 4 at the torsion spring to be tightly closed and the locking pliers 13 at the output shaft to be loosened, so that the steering motor 8 can drive the steering wheels 20 to be quickly aligned through the planetary gear system 11, the output shaft 12 of the planetary gear system, the pinion 14, the rack 15 and the steering tie rods 17 without interference of the torsion spring 5. In addition, since the fail-back command g is a constant signal that is continuous, the steerable wheels do not turn in the other direction or oscillate back and forth beyond the neutral position after returning to the neutral position quickly.
The method stores the established steer-by-wire system model in a constant area of a register module of the ECU; a calculation module of the ECU solves theoretical values of various state quantities of the system in real time according to the system model and signals of various sensors; a self-diagnosis module of the ECU determines whether the system is faulty and the type of the fault according to preset fault threshold determination conditions and theoretical and measured values of the state quantities.
While the invention has been described in terms of its preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
Claims (9)
1. An energy storage type steer-by-wire system is characterized by comprising a steering wheel, a steering column, an electronic control unit, a first angle sensor, a second angle sensor, a displacement sensor, a torsion spring, a locking clamp at the position of the torsion spring, a first electromagnetic valve, a second electromagnetic valve, a gearwheel, a first hydraulic pipeline, a second hydraulic pipeline, a steering motor, a planetary gear train, a locking clamp at the position of an output shaft, a rack-and-pinion steering gear, a steering tie rod and steering wheels;
the steering wheel is connected with a steering column, and the steering column is provided with a first angle sensor which is used for transmitting the angle information of the steering wheel to the electronic control unit through a CAN bus; the torsional spring and the locking pliers at the torsional spring are coaxially installed, the locking pliers at the torsional spring are connected with a first electromagnetic valve through a first hydraulic pipeline, and the first electromagnetic valve is also connected with an electronic control unit through a CAN bus; the large gear is linked with the torsion spring and is meshed with a gear ring of the planetary gear train; the steering motor is connected with the electronic control unit through a CAN bus, an output shaft of the steering motor is connected with a sun gear of the planetary gear train, and a second angle sensor is arranged on the output shaft of the steering motor and connected with the electronic control unit through the CAN bus; the lower row of gear rings of the planetary gear train is fixed, the output shaft of the planetary gear train is connected with a pinion of the rack and pinion steering gear, and the output shaft of the planetary gear train is provided with an output shaft locking clamp which is connected with a second electromagnetic valve through a second hydraulic pipeline, and the second electromagnetic valve is also connected with an electronic control unit through a CAN bus; the rack of the rack and pinion steering gear is provided with a displacement sensor which is connected with an electronic control unit through a CAN bus, the tail end of the rack is connected with one end of a tie rod, and the other end of the tie rod is connected with a steering wheel.
2. A fault-tolerant control method of an energy-storing steer-by-wire system based on the system of claim 1, comprising the steps of:
1) establishing a steer-by-wire system model;
2) designing a fault threshold judgment condition of the steer-by-wire system;
3) the state of the steer-by-wire system is divided, and countermeasures corresponding to the failure are provided.
3. The fault-tolerant control method of the energy-storing steer-by-wire system according to claim 2, wherein the steer-by-wire system model in the step 1) is specifically:
in the initial starting stage of the automobile, the electronic control unit sends out an output shaft locking command e and an output shaft locking torque ToTo a set maximum value TomaxThe steering motor starts to store energy for the torsion spring,the dynamic model of the torsion spring in this state is:
θr2＝βθs
in the formula, JsIs torsional spring moment of inertia; thetasIs a torsion spring corner; alpha is the gear ratio of the planetary gear train gear ring and the planetary gear train sun gear; thetar2The rotation angle of an upper row gear ring of the planetary gear train; t iss1Is the torque of the sun gear of the planetary gear train; t issLocking the torque for the torsion spring; beta is the ratio of the torsional spring gear to the number of teeth on the upper row of the planetary gear train; ksThe elastic coefficient of the torsion spring; when the rotation angle of the torsion spring reaches the maximum value thetasmaxOn one hand, the electronic control unit sends out a torsional spring locking instruction to enable the torsional spring locking torque to reach a set maximum value TsmaxOn the other hand, the end of energy storage is indicated by cutting off the steering command of the steering motor.
4. The fault-tolerant control method of the energy-storing steer-by-wire system according to claim 2, wherein the faults of the steer-by-wire system in the step 2) are classified into a steering motor precision fault, a steering motor complete failure fault and an electronic control unit fault.
5. The fault-tolerant control method of a storage-type steer-by-wire system according to claim 4, wherein the steering motor accuracy failure threshold determination condition in the step 2) is as follows,
in the formula (I), the compound is shown in the specification,
is the measured value of rack displacement at the time t; x is the number ofr(t) is a theoretical value of rack displacement at the moment t; t is t1The time interval upper limit of the precision fault of the steering motor is set; t ish1Is a motor precision threshold.
6. The fault-tolerant control method of a storage-by-wire steering system according to claim 5, wherein the steering motor complete failure threshold determination condition in step 2) is as follows,
in the formula, λi(i ═ 1,2,3,4) is a weight coefficient; t is t2The time interval upper limit of the failure of the steering motor is set;
the measured value of the turning angle of the steering motor at the moment t;
the measured value of the turning angle of the steering motor at the moment t-1;
is the measured value of the rack displacement at the time t-1; t ish2Is the motor failure threshold.
7. The fault-tolerant control method of an energy-storing steer-by-wire system according to claim 4, wherein the electronic control unit failure threshold determination condition in step 2) is as follows: the electronic control unit comprises a calculation module, a register module and a self-diagnosis module, wherein the calculation module is used for analyzing signals of all sensors, calculating a steering command at the current moment, and calculating a motor rotation angle and a corresponding motor steering command which are required for correcting the rack in the current state; the register module is used for storing a steering system model and two locking instructions and steering instructions from the calculation module, and the steering instruction at the previous moment is output to the steering motor and then covered by a new steering instruction; the self-diagnosis module is used for detecting and collecting internal program abnormity of the electronic control unit; when the program has an irresolvable abnormality, the electronic control unit generates a fault, the self-diagnosis module interrupts the operation of the calculation module at the moment, and two locking instructions in the register module are confirmed to be transmitted to the actuator.
8. The fault-tolerant control method of an energy-storing steer-by-wire system according to claim 2, wherein the steer-by-wire system state in step 3) comprises: the method comprises the following steps of initial starting, normal running, steering motor precision failure, steering motor complete failure and electronic control unit failure.
9. The fault-tolerant control method of the energy-storing steer-by-wire system according to claim 2, wherein the corresponding countermeasure against the fault in the step 3) is as follows:
after the precision fault of the steering motor occurs, the steering precision is ensured by the intervention of the torsion spring within a certain time, specifically, an electronic control unit adjusts the locking instruction of the torsion spring to ensure that the locking pliers at the torsion spring are loosened or closed at high frequency so as to change the locking torque T of the torsion springsThe torsion spring is rotated and the rotation angle of the torsion spring is superposed to the movement of the rack through the planetary gear train, and finally the error of the rack displacement is causedFalls below a threshold;
when the steering motor is completely out of work, the electronic control unit immediately cuts off the steering instruction to prevent the steering motor from suddenly recovering to operate when the torsion spring is involved; and interrupting the torsional spring locking instruction, completely loosening the locking pliers at the torsional spring, and enabling the torsional spring to have the maximum torque TsmaxOutput to the planetary gear train and the rack; when the electronic control unit detects the measured value of rack displacement
When the steering motor is started, the electronic control unit is started to stop the steering motor, and the rack is indicated to return to the middle position, and then the electronic control unit immediately restores a torsional spring locking instruction to enable the locking pliers at the torsional spring to be completely closed, the torsional spring is instantly locked, the steering motor cannot run, and the rack and the steering wheel are guaranteed to return to the right state in the shortest time;
when the electronic control unit has a fault, a fault correcting instruction in the register module is continuously sent to the steering motor, and meanwhile, the self-diagnosis module triggers two locking instructions in the register module to enable the locking pliers at the torsion spring to be tightly closed and the locking pliers at the output shaft to be loosened; the steering motor can drive the steering wheel to quickly return to the right through the planetary gear train, the output shaft of the planetary gear train, the pinion, the rack and the steering tie rod under the condition of no interference of the torsion spring; and the failure return command is a continuous constant signal, and the steering wheel cannot rotate to another direction or swing back and forth beyond the middle position after returning to the middle position.
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| CN111422247A (en) * | 2020-03-20 | 2020-07-17 | 合肥工业大学 | Fault diagnosis and fault tolerance compensation algorithm for steer-by-wire motor and sensor |
| CN112373559A (en) * | 2020-11-29 | 2021-02-19 | 同济大学 | Automobile rear steering axle system with failure correcting function and control method thereof |
| CN114347004B (en) * | 2022-02-21 | 2024-04-12 | 国能联合动力技术(连云港)有限公司 | Yaw robot supporting seat and rotating arm cooperation positioning control system |
| CN117068253A (en) * | 2022-05-10 | 2023-11-17 | 武汉路特斯汽车有限公司 | Method for controlling rear wheel steering of vehicle, controller and storage medium |
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