Boarding and alighting auxiliary control method based on steer-by-wire system

Abstract

The invention relates to the technical field of steering systems, in particular to a getting-on and getting-off auxiliary control method based on a steer-by-wire system. The invention discloses a boarding and alighting auxiliary control method based on a steer-by-wire system. The boarding and alighting auxiliary control method is characterized by comprising the following specific procedures that whether a boarding and alighting auxiliary function is started or not is judged; a flow of PID control is carried out; a flow of steering wheel speed feed-forward control is carried out; a stability control process is carried out; getting-on and getting-off auxiliary request torque is obtained; judging whether the get-on and get-off auxiliary function is finished; and ending. Compared with the prior art, the getting-on and getting-off auxiliary control method based on the steer-by-wire system has the advantages that PID control, steering wheel speed feedforward control and stability control are superposed and output to obtain final motor output torque required by getting-on and getting-off auxiliary; after output force unloading is completed, whether the function is finished or not needs to be judged; and the purpose of boarding and alighting assistance is achieved through complete force output and unloading and starting and quitting judgment.

Description

Technical Field

[0001] The invention relates to the technical field of steering systems, and in particular to a vehicle getting on and off assisting control method based on a wire-controlled steering system. Background Art

[0002] The vehicle entry and exit assistance function means that the driver needs to hold the steering wheel when getting on or off the vehicle, so that the body can have an effective support point to complete the force action of getting on or off the vehicle. In traditional electric power-assisted vehicles, the vehicle has already been powered off and the steering gear has lost its power-assisting ability. The driver can complete the vehicle entry and exit actions by holding the steering wheel by relying on the mechanical connection of the steering gear itself, as well as the load and high friction. At the same time, the steering wheel remains fixed at the power-off angle or changes at a small angle. During this process, the driver's hand force can reach 20Nm or even more.

[0003] Due to the continuous iteration of chassis technology and the demand for more driving modes, the steer-by-wire system has eliminated the intermediate connecting shaft of the upper and lower columns of the electric power steering transmission, achieved the decoupling of the upper and lower steering gears, and communicated between the upper and lower steering gears through proprietary CAN signals to achieve follow-up. It is precisely because of the cancellation of the connection of the intermediate shaft that when the driver wants to complete the action of getting on and off the vehicle and seeks the steering wheel as a support point, the steering wheel cannot complete this function through mechanical connection and friction like the electric power steering. Therefore, it is necessary to develop an on-and-off assist function on the upper steering to simulate the electric power steering, and achieve it by outputting the same or greater reaction force from the motor. At the same time, it is also necessary to avoid the problem of excessive rebound and excessive rebound angle caused by excessive motor output, and avoid the phenomenon of the driver's hand hitting when he lets go. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a vehicle getting on and off assist control method based on a wire-controlled steer system, which utilizes PID control, steering wheel speed feedforward control, and stability control, and the three are superimposed to obtain the motor output torque required for the final vehicle getting on and off assist.

[0005] In order to achieve the above purpose, a vehicle getting on and off assist control method based on a wire-controlled steering system is designed, including PID control, steering wheel speed feedforward control, and stability control. The specific process of the vehicle getting on and off assist control method is as follows:

[0006] (1) Start;

[0007] (2) Determine whether the boarding and alighting assistance function is enabled. If yes, proceed to step (3); otherwise, jump to step (1);

[0008] (3) Perform PID control process and calculate the PID control torque u PID ;

[0009] (4) Perform the process of steering wheel speed feedforward control and calculate the feedforward control torque u fw ;

[0010] (5) Perform stability control and calculate the stability control torque u sta ;

[0011] (6) The PID control torque u calculated from steps (3) to (5) is PID , feedforward control torque u fw , stability control torque u sta The superposition is performed to obtain the vehicle boarding and exiting assistance request torque u, that is, u = u PID +u fw +u sta ;

[0012] (7) Determine whether the boarding and alighting assistance function has ended. If so, proceed to step (8); otherwise, continue to determine whether the boarding and alighting assistance function has ended.

[0013] (8)End.

[0014] The PID control is a closed-loop control. The specific process of PID control is as follows:

[0015] S31, when the vehicle entry and exit assistance function is turned on, the current steering wheel angle is recorded as the default zero angle q ref ;

[0016] S32, when the driver gets on or off the vehicle, after turning the steering wheel by hand, the current steering wheel angle is recorded as the angle after turning q act ;

[0017] S33, calculate the default zero angle q ref The angle q after rotation act The angle difference e, that is, e=q ref -q act ;

[0018] S34, output PID control torque u through PID control PID ;

[0019] The PID control output is obtained by adding proportional control, integral control, and differential control, that is, Among them, u PID is the PID control torque, K P is the proportional coefficient, e is the angle difference, K i is the integration coefficient, K d is the differential coefficient.

[0020] The specific process of the steering wheel speed feedforward control is as follows:

[0021] S41, when the driver pulls quickly, the steering wheel speed increases sharply, and the current steering wheel speed v is obtained. act ;

[0022] S42, current steering wheel speed v act After taking the absolute value, the feedforward torque is obtained by looking up the table (the table uses the absolute value of the steering wheel speed as the X-axis, and the values ​​are {0, 50, 100, 300, 500, 700, 1000}; the feedforward torque is the Y-axis, and the values ​​are {0, 0.2, 0.5, 3, 5, 7, 10});

[0023] S43, reversing the direction of the current steering wheel speed;

[0024] S44, combining step S42 and step S43, outputs the feedforward control torque u fw , that is u fw =-sign(v act )*f1(abs(v act )), where u fw is the feedforward control torque, sign is the sign function, which takes the positive or negative sign of the input; f1 is the steering wheel speed lookup function, which directly gets the corresponding output by looking up the table, and the changing trend is that the greater the steering wheel speed, the greater the output feedforward torque; abs is the absolute value function, which takes the absolute value of the input signal.

[0025] The specific process of the stability control is as follows:

[0026] S51, obtain the current rotor acceleration r acc ;

[0027] S52, the current rotor acceleration r acc Perform first-order low-pass filtering;

[0028] S53, the front rotor acceleration r processed by the first-order low-pass filter acc After taking the absolute value, the current stability torque is obtained by looking up the table (the table uses the absolute value of the rotor acceleration as the X-axis, with values ​​of {0, 200, 600, 1000, 1500, 2000}; and the stability torque as the Y-axis, with values ​​of {0, 0.05, 0.1, 0.15, 0.2, 0.25});

[0029] S54, reverse the direction of the current rotor acceleration;

[0030] S55, obtaining hand force signal t TBT ;

[0031] S56, hand force signal t TBT Perform first-order differential processing;

[0032] S57, the hand force signal t after first-order differential processing TBT After taking the absolute value, the table is looked up (the table uses the absolute value of the rotor acceleration as the X-axis, with values ​​of {0, 2, 4, 6, 8, 10}; the stability moment torque as the Y-axis, with values ​​of {0, 0.2, 0.4, 0.6, 0.8, 0.9}) to obtain the current hand force change factor;

[0033] S58, combining steps S53, S54 and S57, outputs the stability control torque u sta ,Right now Among them, u sta is the stability control torque, f PT1 is a first-order filter function, f2 is a rotor acceleration lookup function, and the output torque increases with the increase of rotor acceleration; f3 is a hand force lookup function, and the output increases with the increase of the hand force differential value.

[0034] The calculation formula of the first-order filter function is: is the state value at the previous moment.

[0035] In step (7), the process of determining whether the boarding and alighting assistance function is terminated also includes integrity determination. The specific process of integrity determination is as follows:

[0036] S71, the upper and lower bunk auxiliary torque u is obtained according to PID control, steering wheel speed feedforward control, and stability control; S72, the default zero angle q ref , the angle after rotation q act The resulting angle difference e;

[0037] S73, determining whether the vehicle boarding and exiting assistance request torque u is less than a torque threshold;

[0038] S74, determining whether the angle difference e is less than an angle threshold;

[0039] S75, combining step S73 and step S74, if both are satisfied, it is determined that the output of the boarding and alighting assistance function is terminated;

[0040] S76, combining the output of the boarding and getting-in assistance function in step S75 and whether the door is closed, if both conditions are met, it is determined that the boarding and getting-in assistance function is ended.

[0041] In the step (2), whether the boarding and alighting assistance function is turned on is determined based on actual vehicle signals.

[0042] Compared with the prior art, the present invention provides a vehicle getting on and off assist control method based on a wire-controlled steering system, which utilizes PID control, steering wheel speed feedforward control, and stability control, and the three are superimposed to output the motor output torque required for the final vehicle getting on and off assist; after the output unloading is completed, it is also necessary to judge whether the function itself has ended; the purpose of vehicle getting on and off assist is achieved through complete output unloading and start and exit judgment. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a flow chart of the present invention.

[0044] Figure 2 This is the PID control flow chart.

[0045] Figure 3 This is the steering wheel speed feedforward control flow chart.

[0046] Figure 4 This is the stability control flow chart.

[0047] Figure 5 This is a flowchart for completeness judgment.

[0048] Figure 6 This is a change curve diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0049] The present invention will be further described below with reference to the accompanying drawings.

[0050] like Figure 1 The control flow chart of the present invention is shown in FIG. The specific flow is as follows:

[0051] (1) Start;

[0052] (2) Determine whether the boarding and alighting assistance function is enabled. If yes, proceed to step (3); otherwise, jump to step (1);

[0053] (3) Perform PID control process and calculate the PID control torque u PID ;

[0054] (4) Perform the process of steering wheel speed feedforward control and calculate the feedforward control torque u fw ;

[0055] (5) Perform stability control and calculate the stability control torque u sta ;

[0056] (6) The PID control torque u calculated from steps (3) to (5) is PID , feedforward control torque u fw , stability control torque u staThe superposition is performed to obtain the vehicle boarding and exiting assistance request torque u, that is, u = u PID +u fw +u sta ;

[0057] (7) Determine whether the boarding and alighting assistance function has ended. If so, proceed to step (8); otherwise, continue to determine whether the boarding and alighting assistance function has ended.

[0058] (8)End.

[0059] The present invention is mainly to support the driver to complete the boarding and getting off the vehicle by outputting equal or greater reaction force by the motor. Because it is for the wire-controlled steering system, the premise of this function is that the motor is normally powered and provides assistance during the boarding and getting off the vehicle. The activation condition of the function can be determined according to the actual vehicle signal.

[0060] The first part, such as Figure 2 As shown in the figure, the flow chart of PID control belongs to closed-loop control. Since the on-board assist function needs to output force according to the angle difference when it is turned on, and return to the default zero position after the driver lets go, the PID control algorithm is selected. This output is also the main output, with an upper limit of 20Nm. When the function is turned on, the current steering wheel angle is recorded as the default zero positionq ref When the driver gets on or off the vehicle, he or she can use the current angle q to pull the steering wheel. act The error e is obtained by making a difference with the default zero position and the corresponding control is performed. The PID control output is obtained by adding the proportional, integral and differential control. The calculation formula of the angle difference e is e=q ref -q act ;PID control torque u PID The calculation formula is Among them, K P is the proportionality coefficient, K i is the integration coefficient, K d is the differential coefficient.

[0061] The second part, such as Figure 3 As shown in the figure, the flow chart of the steering wheel speed feedforward control. The PID control function has a large enough output due to the existence of the integral term, but it takes a certain amount of time for the integral term to build up force. Therefore, when the steering wheel is pulled quickly, the PID control cannot quickly build up force. This requires feedforward control to quickly respond to the driver's pull of the steering wheel. The most obvious change when pulling quickly is the steering wheel speed. When the driver pulls quickly, the steering wheel speed v actThere will be an obvious sharp rise process. The current steering wheel speed is obtained, and its absolute value is taken as a lookup table (the table uses the absolute value of the steering wheel speed as the X-axis, and the value is {0, 50, 100, 300, 500, 700, 1000}; the feedforward torque is the Y-axis, and the value is {0, 0.2, 0.5, 3, 5, 7, 10}). The faster the steering wheel speed, the greater the feedforward torque. At the same time, the direction of the output force is opposite to the steering wheel speed, and the upper limit is 10Nm. This feedforward control is not only applicable to the force building process, but also after the driver lets go, due to the large output force (more than 20Nm), the steering wheel will have a large rebound and the rebound speed is very fast. Therefore, after letting go, there will still be a reaction force to prevent the steering wheel from rebounding quickly, which avoids the phenomenon of hitting the hand due to rapid rebound. Feedforward control torque u fw The calculation formula is u fw =-sign(v act )*f1(abs(v act )), where sign is the sign function, which takes the positive or negative sign of the input; f1 is the steering wheel speed lookup function, which directly gets the corresponding output by looking up the table through the input, and the changing trend is that the greater the steering wheel speed, the greater the output feedforward torque; abs is the absolute value function, which takes the absolute value of the input signal.

[0062] The third part, such as Figure 4 The figure shows the flow chart of stability control. After the basic force PID control torque and the steering wheel speed feedforward torque are obtained, the stability of the center area will become unstable under the superposition of two large and fast-changing forces, and it is easy to shake when the driver pulls the steering wheel and changes direction quickly. In view of this situation, the stability control part is superimposed on the output force, which is essentially an acceleration term. By obtaining the current rotor acceleration and looking up the table r acc (The table uses the absolute value of the rotor acceleration as the X-axis, with values ​​of {0, 200, 600, 1000, 1500, 2000}; the stability torque as the Y-axis, with values ​​of {0, 0.05, 0.1, 0.15, 0.2, 0.25}). The rotor acceleration itself has certain fluctuations, and the rate of change is relatively fast. Therefore, the signal is processed by a first-order low-pass filter to make the signal smoother. The stability torque is obtained by looking up the table based on the processed rotor acceleration. The greater the rotor acceleration, the greater the stability torque. The direction of the stability torque is opposite to the direction of the rotor acceleration. In addition, instability is strongly related to hand strength. The hand force signal t is obtained. TBT , and then the hand force change rate is obtained by first-order differentiation. According to the hand force change rate, the hand force change rate factor is obtained by looking up the table (the table uses the absolute value of the rotor acceleration as the X-axis, and the values ​​are {0, 2, 4, 6, 8, 10}; the stability torque is the Y-axis, and the values ​​are {0, 0.2, 0.4, 0.6, 0.8, 0.9}). This factor is multiplied by the stability torque as the final output torque. Stability control torque usta The calculation formula is Among them, f PT1 is a first-order filtering function, and the calculation formula is is the state value at the previous moment; f2 is the rotor acceleration lookup function, and the output torque increases with the increase of the rotor acceleration; f3 is the hand force lookup function, and the output increases with the increase of the hand force differential value.

[0063] Finally, the three output forces are superimposed and limited to obtain the on-board assist request torque. The calculation formula of the on-board assist request torque u is u = u PID +u fw +u sta The vehicle entry and exit assist request torque u is used as the final output torque and is output through the motor.

[0064] In addition, if Figure 5 As shown in the figure, when the driver finishes getting on and off the car, the on and off assist function itself also needs to determine whether it has been completely completed. First, it is necessary to determine whether the function torque has been output. By reading whether the on and off assist force is less than a certain threshold for a period of time, this threshold can be calibrated; then determine whether the steering wheel angle has returned to the default zero position, that is, whether the difference between the current steering wheel angle and the default zero position is less than a certain threshold for a period of time. The threshold can also be calibrated. Through the judgment of torque and angle, if both are satisfied, the function output ends, and the function is turned off in combination with whether the door is opened or closed.

[0065] like Figure 6 As shown, it is a diagram of the change in the assisting angle for getting on and off the vehicle and the corresponding change in the motor force using an embodiment of the method of the present invention. It can be seen from the figure that the total output torque is continuously increasing to about 1.7N / m (converted to a hand force of about 19N / m) during the gradual increase in the angle difference, and as the motor output torque increases, the hand force also increases to the upper limit of 11N / m; after letting go of the hand at 10s, the angle difference is continuously reduced under control, and finally stabilized at 0. According to the embodiment, it can be seen that the present invention can effectively provide a reaction force support torque for the driver's getting on and off the vehicle, and quickly and stably returns to the initial zero position after letting go.

Claims

1. A vehicle boarding and disembarking assist control method based on a wire-controlled steering system, comprising PID control, steering wheel speed feedforward control, and stability control, characterized in that: The specific process of the vehicle getting on and off assisting control method is as follows: (1) Start; (2) Determine whether the boarding and alighting assistance function is enabled. If yes, proceed to step (3); otherwise, jump to step (1); (3) Perform PID control process and calculate the PID control torque u PID ; (4) Perform the process of steering wheel speed feedforward control and calculate the feedforward control torque u fw ; (5) Perform stability control and calculate the stability control torque u sta ; (6) The PID control torque u calculated from steps (3) to (5) is PID , feedforward control torque u fw , stability control torque u sta The superposition is performed to obtain the vehicle boarding and exiting assistance request torque u, that is, u = u PID +u fw +u sta ; (7) Determine whether the boarding and alighting assistance function has ended. If so, proceed to step (8); otherwise, continue to determine whether the boarding and alighting assistance function has ended. (8)End.

2. The vehicle boarding and exiting assist control method based on a steer-by-wire system according to claim 1, characterized in that: The PID control is a closed-loop control. The specific process of PID control is as follows: S31, when the vehicle entry and exit assistance function is turned on, the current steering wheel angle is recorded as the default zero angle q ref ; S32, when the driver gets on or off the vehicle, after turning the steering wheel by hand, the current steering wheel angle is recorded as the angle after turning q act ; S33, calculate the default zero angle q ref The angle q after rotation act The angle difference e, that is, e=q ref -q act ; S34, output PID control torque u through PID control PID ; The PID control output is obtained by adding proportional control, integral control, and differential control, that is, Among them, u PID is the PID control torque, K P is the proportional coefficient, e is the angle difference, K i is the integration coefficient, K d is the differential coefficient.

3. The vehicle boarding and exiting assist control method based on a steer-by-wire system according to claim 1, characterized in that: The specific process of the steering wheel speed feedforward control is as follows: S41, when the driver pulls quickly, the steering wheel speed increases sharply, and the current steering wheel speed v is obtained. act ; S42, current steering wheel speed v act After taking the absolute value, the feedforward torque is obtained by looking up the table; S43, reversing the direction of the current steering wheel speed; S44, combining step S42 and step S43, outputting the feedforward control torque u fw , that is u fw =-sign(v act )*f1(abs(v act )), where u fw is the feedforward control torque, sign is the sign function, which takes the positive or negative sign of the input; f1 is the steering wheel speed lookup function, which directly gets the corresponding output by looking up the table, and the changing trend is that the greater the steering wheel speed, the greater the output feedforward torque; abs is the absolute value function, which takes the absolute value of the input signal.

4. The vehicle boarding and exiting assist control method based on a steer-by-wire system according to claim 1, characterized in that: The specific process of the stability control is as follows: S51, obtain the current rotor acceleration r acc ; S52, the current rotor acceleration r acc Perform first-order low-pass filtering; S53, the front rotor acceleration r processed by the first-order low-pass filter acc After taking the absolute value, the current stability torque is obtained by looking up the table; S54, reverse the direction of the current rotor acceleration; S55, obtaining hand force signal t TBT ; S56, hand force signal t TBT Perform first-order differential processing; S57, the hand force signal t after first-order differential processing TBT After taking the absolute value, the current hand force change factor is obtained by looking up the table; S58, combining steps S53, S54 and S57, outputs the stability control torque u sta ,Right now Among them, u sta is the stability control torque, f PT1 is a first-order filter function, f2 is a rotor acceleration lookup function, and the output torque increases with the increase of rotor acceleration; f3 is a hand force lookup function, and the output increases with the increase of the hand force differential value.

5. The vehicle boarding and exiting assisting control method based on a steer-by-wire system according to claim 4, characterized in that: The calculation formula of the first-order filter function is: is the state value at the previous moment.

6. The vehicle boarding and exiting assisting control method based on a steer-by-wire system according to claim 1, characterized in that: In step (7), the process of determining whether the boarding and alighting assistance function is terminated also includes integrity determination. The specific process of integrity determination is as follows: S71, obtaining the upper and lower bunk auxiliary torque u according to PID control, steering wheel speed feedforward control and stability control; S72, according to the default zero angle q ref , the angle after rotation q act The resulting angle difference e; S73, determining whether the vehicle boarding and exiting assistance request torque u is less than a torque threshold; S74, determining whether the angle difference e is less than an angle threshold; S75, combining step S73 and step S74, if both are satisfied, it is determined that the output of the boarding and alighting assistance function is terminated; S76, combining the output of the boarding and getting-in assistance function in step S75 and whether the door is closed, if both conditions are met, it is determined that the boarding and getting-in assistance function is ended.

7. The vehicle boarding and exiting assist control method based on a steer-by-wire system according to claim 1, characterized in that: In the step (2), whether the boarding and alighting assistance function is turned on is determined based on actual vehicle signals.

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