Speed limit method, system and vehicle

Abstract

The application discloses a kind of vehicle speed limiting method and system, the method comprises the following steps: step S1: when the current speed of vehicle reaches the preset activation threshold, activate speed limiting control logic;Wherein, activation threshold is lower than the maximum speed of vehicle;Step S2: calculate the approaching speed, and the approaching speed is calculated according to the maximum speed of vehicle and current speed, and always between current speed and maximum speed;Step S3: the difference between the approaching speed and current speed is calculated as the deviation feedback, and it is input into PID controller;Step S4: according to the size of deviation feedback, dynamically adjust the proportional parameter and integral parameter of PID controller, and calculate torque control quantity according to the adjusted parameter to control the speed of vehicle.The speed limiting method of the application, by introducing the concept of approaching speed, and with variable parameter PID control strategy and anti-integral saturation algorithm, realizes the control effect of fast, stable and no overshoot of vehicle under speed limiting condition.

Description

Technical Field

[0001] This invention belongs to the field of automotive technology. Specifically, this invention relates to a method, system, and vehicle for limiting vehicle speed. Background Technology

[0002] With the development of electric vehicle technology, digital dashboards have become a mainstream feature. Vehicle speed is usually displayed precisely in digital form, which means that any fluctuations in speed control, especially overshooting beyond the set speed limit, will be directly and clearly shown to the driver, affecting the driving experience and the perceived quality of the vehicle.

[0003] In vehicle speed limit control, the PID (Proportional-Integral-Derivative) control algorithm is widely used due to its simple structure and good stability. However, traditional PID control methods have significant limitations when applied to vehicle speed limiting. In pursuit of a fast response, it often leads to overshoot; adjusting parameters to avoid overshoot may result in a slower response or difficulty in accurately reaching the target speed within the specified time. Although the control effect can be optimized through extensive calibration, this significantly increases development costs and time.

[0004] An improved method for limiting vehicle speed is provided, particularly regarding how to achieve fast response, high stability, no overshoot, and precise speed control. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a vehicle speed limiting method, which aims to achieve fast response, high stability, no overshoot, and precise vehicle speed control.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a vehicle speed limiting method, comprising: Step S1: When the vehicle's current speed reaches a preset activation threshold, the speed limit control logic is activated; wherein, the activation threshold is lower than the vehicle's maximum speed. Step S2: Calculate the approximation speed. The approximation speed is calculated based on the vehicle's maximum speed and current speed, and it always lies between the current speed and the maximum speed. Step S3: Calculate the difference between the approaching vehicle speed and the current vehicle speed as the deviation feedback quantity, and input it into the PID controller; Step S4: Based on the magnitude of the deviation feedback, dynamically adjust the proportional and integral parameters of the PID controller, and calculate the torque control quantity based on the adjusted parameters to perform speed limiting control on the vehicle.

[0007] In step S2, the formula for calculating the approximate vehicle speed is: V _appr = V _max+ k × (V _max - V _act ) Among them, V _appr For the approximate vehicle speed, V _max V is the maximum vehicle speed. _act The current vehicle speed is given, and k is a variable parameter with a value between 0 and 1.

[0008] The variable parameter k changes exponentially based on the difference ∆V between the maximum vehicle speed and the current vehicle speed, and the calculation formula is as follows: k = ΔV / (1 + ΔV) Where, △V=V _max - V _act .

[0009] The activation threshold is 90% of the maximum vehicle speed; when the difference between the maximum vehicle speed and the current vehicle speed is greater than 10% of the maximum vehicle speed, the speed limit control logic is exited.

[0010] In step S4, dynamically adjusting the proportional parameter and the integral parameter specifically includes: When the deviation feedback amount is greater than the first preset threshold, the proportional parameter and the integral parameter are set to the first parameter combination for rapid response; When the deviation feedback amount is less than the first preset threshold and greater than the second preset threshold, the proportional parameter and the integral parameter are gradually reduced to reduce the risk of overshoot. When the deviation feedback amount is less than the second preset threshold, the proportional parameter and the integral parameter are set to the second parameter combination to stabilize the vehicle speed.

[0011] The PID controller employs an anti-integral saturation algorithm, which includes: Set the vehicle speed deviation threshold E0; When the deviation feedback amount is less than or equal to the vehicle speed deviation threshold E0, the integral term calculation is disabled. When the deviation feedback amount is greater than the vehicle speed deviation threshold E0, the integral term calculation is enabled.

[0012] The anti-integral saturation algorithm also includes: The calculation result of the integral term is subjected to a limiting process, restricting the value of the integral term to between an upper limit value and a lower limit value; When the accelerator pedal signal is detected to be zero, the calculation result of the integral term is cleared to zero.

[0013] The process following step S4 also includes: The torque control quantity is compared and arbitrated with the torque required by the driver, and the arbitrated torque is used as the final output torque.

[0014] The present invention also provides a vehicle speed limiting system, comprising: An activation module is used to activate the speed limit control logic when the current speed of the vehicle reaches a preset activation threshold; wherein the activation threshold is lower than the maximum speed of the vehicle. The calculation module is used to calculate the approximate vehicle speed, which is calculated based on the maximum vehicle speed and the current vehicle speed, and is always located between the current vehicle speed and the maximum vehicle speed. The PID control module is used to calculate the difference between the approach speed and the current speed as a deviation feedback quantity, and dynamically adjust the proportional and integral parameters according to the magnitude of the deviation feedback quantity, thereby calculating the torque control quantity to limit the speed of the vehicle.

[0015] The present invention also provides a vehicle including the aforementioned vehicle speed limiting system.

[0016] The vehicle speed limiting method of the present invention, by introducing the concept of approximating vehicle speed and combining it with a variable parameter PID control strategy and an anti-integral saturation algorithm, achieves a fast, stable and overshoot-free control effect for vehicles under speed-limited conditions. Attached Figure Description

[0017] This manual includes the following figures, which illustrate the following: Figure 1 This is a flowchart illustrating the vehicle speed limiting method of the present invention; Figure 2 This diagram illustrates the relationship between the maximum speed, the approximate speed, and the actual speed. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0019] It should be noted that in the following embodiments, the terms "first," "second," and "third" do not represent an absolute distinction in structure and / or function, nor do they represent the order of execution; they are merely for the convenience of description.

[0020] Firstly, such as Figure 1As shown, this invention provides a vehicle speed limiting method to address the problems of overshoot, slow response, and insufficient control accuracy at the target speed in traditional PID control methods during vehicle speed limiting. Especially for electric vehicles using digital speedometers, speed overshoot is directly perceived by the driver, affecting the driving experience. This invention introduces the concept of approximating vehicle speed and combines it with a variable parameter PID control strategy and an anti-integral saturation algorithm to achieve fast, stable, and overshoot-free control of the vehicle under speed-limited conditions. The vehicle speed limiting method includes the following steps: Step S1: When the vehicle's current speed reaches a preset activation threshold, the speed limit control logic is activated; wherein, the activation threshold is lower than the vehicle's maximum speed. Step S2: Calculate the approximation speed. The approximation speed is calculated based on the vehicle's maximum speed and current speed, and it always lies between the current speed and the maximum speed. Step S3: Calculate the difference between the approaching vehicle speed and the current vehicle speed as the deviation feedback quantity, and input it into the PID controller; Step S4: Based on the magnitude of the deviation feedback, dynamically adjust the proportional and integral parameters of the PID controller, and calculate the torque control quantity based on the adjusted parameters to perform speed limiting control on the vehicle.

[0021] Specifically, in step S1 above, the vehicle's maximum speed is the design limit of the vehicle, typically determined by the powertrain's power limitations or safety strategies. To avoid driving roughness caused by control lag or sudden intervention when the vehicle approaches its maximum speed, this embodiment of the invention provides an early activation strategy. A preset activation threshold below the maximum speed is established; for example, this threshold is set to 90% of the maximum speed. When the difference between the maximum speed and the current speed exceeds 10% of the maximum speed, the speed limit control logic exits. Of course, those skilled in the art can set this threshold to 85% or 95% of the maximum speed, etc., based on the actual vehicle's power response characteristics; this invention does not strictly limit this setting.

[0022] When the vehicle's current speed V _act Below this activation threshold, for example, below 0.9 × V _max When the speed limit control logic is inactive, the vehicle is driven normally according to the driver's required torque, and neither the PID control module nor the approximation speed calculation module participates. As the vehicle speed continues to increase, and the current vehicle speed V... _act When the activation threshold is reached or exceeded, the vehicle control unit (VCU) immediately activates the speed limit control logic, including the subsequent approximation speed calculation module and PID calculation module, thereby intervening in the vehicle speed control in advance and reserving control margin for the final smooth arrival at the maximum vehicle speed.

[0023] Traditional PID control directly uses the maximum vehicle speed as the target value. Due to control inertia, the vehicle speed can easily exceed the maximum speed, causing overshoot. This invention introduces a dynamically changing internal target value, namely, an approximation of the vehicle speed V. _appr In step S2 above, the approximate vehicle speed V is calculated. _appr The formula is: V _appr = V _max +k× (V _max - V _act ) Among them, V _appr To approach the vehicle's speed, V _max V is the maximum speed. _act The current vehicle speed is given by k, which is a variable parameter with a value between 0 and 1.

[0024] In this formula, the variable parameter k plays a crucial adjusting role. The value of k is not fixed but dynamically changes with the difference between the vehicle's actual speed and its maximum speed. Specifically, the variable parameter k varies exponentially based on the difference ∆V between the maximum speed and the current speed, calculated using the following formula: k = ΔV / (1 + ΔV) Where, △V=V _max - V _act .

[0025] like Figure 2 As shown, the characteristics of approximating vehicle speed are analyzed: When the vehicle is near the activation threshold, i.e., the current vehicle speed V _act Distance from maximum speed V _max When the distance is greater, ΔV is larger. According to the formula k = ΔV / (1 + ΔV), when ΔV is larger, the value of k approaches 1. At this time, the approximate vehicle speed V... _appr ≈V _max +1×(V _max -V _act ) = 2 V _max - V_act. This is the approximate vehicle speed V. _appr Higher than the maximum speed V _max In this state, the internal target value calculated by the system is much higher than the current vehicle speed. The deviation feedback of the PID controller is large, which can output a large torque to ensure that the vehicle can still maintain a relatively fast acceleration in the initial stage of speed limit, avoiding the driver feeling that the vehicle suddenly "floats" or the power is interrupted, and ensuring the continuity of acceleration.

[0026] As the vehicle accelerates, its current speed V _act Gradually approaching the top speed V _max As ∆V gradually decreases and approaches 0, the value of k approaches 0 exponentially, approximating the vehicle speed V._appr It then descends smoothly, approaching its maximum speed V. _max During this process, the vehicle speed V approaches. _appr The target value serves as the dynamic input to the PID controller. This value varies with the current vehicle speed V. _act With the highest vehicle speed V _max As the difference between them gradually decreases, the variable parameter k also decays, making the approximate vehicle speed V... _appr The value is directed towards the maximum vehicle speed V _max Smooth transition. This mechanism achieves smooth adjustment of the vehicle's drive torque control intensity by dynamically adjusting the deviation feedback of the PID controller, ensuring that the vehicle speed smoothly reaches the maximum speed.

[0027] When V _act Approaching top speed V _max When ΔV is minimal, k≈0, V _appr ≈V _max At this point, the internal target value coincides with the maximum vehicle speed, and the system enters the precise control phase.

[0028] Through the above mechanism, the vehicle speed V is approximated. _appr Always at the current vehicle speed V _act and maximum speed V _max The system dynamically adjusts within or near the speed limit range, achieving a fast yet stable speed-limiting effect. It maintains a sense of acceleration in the initial stage of speed limiting and smoothly transitions when approaching the limit, eliminating the possibility of overshoot.

[0029] In step S3 above, after calculating the approximate vehicle speed V... _appr After that, the maximum speed V is not directly set. _max With current vehicle speed V _act The difference is used as the input to the PID controller, instead of approximating the vehicle speed V. _appr With current vehicle speed V _act The difference is used as the deviation feedback quantity.

[0030] Due to approaching vehicle speed V _appr It is based on the current vehicle speed V _act The deviation feedback is dynamically adjusted, therefore exhibiting nonlinear and adaptive characteristics. At lower vehicle speeds, the deviation is larger, driving the PID controller to output a stronger control action; as the vehicle speed approaches the limit, the deviation decreases with the approaching vehicle speed V. _appr The drop in torque naturally decreases, allowing the output torque of the PID controller to decrease smoothly, thus achieving precise control over the speed limiting process.

[0031] The PID controller used in this embodiment employs a variable parameter strategy. Traditional PID controllers have fixed parameters, making it difficult to simultaneously meet the requirements of fast response and no overshoot. This embodiment uses a variable parameter strategy based on the deviation feedback quantity V. _deltaThe size of V is adjusted by segmenting the proportional parameter p and the integral parameter i. _delta =V _max -V _act In step S4 above, dynamically adjusting the proportional and integral parameters specifically includes: Rapid Response Phase: When the deviation feedback exceeds the first preset threshold, it indicates that the current vehicle speed is far from the target. At this point, the proportional parameter p and integral parameter i are set to the first parameter combination for rapid response. A larger p value can improve the system response speed, and a larger i value can quickly eliminate steady-state error, allowing the vehicle speed to rapidly approach the target.

[0032] Overshoot prevention transition phase: When the deviation feedback is less than the first preset threshold and greater than the second preset threshold, it indicates that the vehicle speed is approaching the target area. At this time, the proportional parameter p and the integral parameter i are gradually reduced. During this process, the values ​​of the proportional parameter p and the integral parameter i transition from the value level of the first parameter combination to the value level of the second parameter combination as the deviation feedback decreases. Reducing the parameter values ​​can reduce the system gain, slow down the vehicle speed approach speed, thereby effectively reducing the risk of overshoot and preparing for a smooth arrival at the vehicle speed limit.

[0033] Stable Maintenance Phase: When the deviation feedback is less than the second preset threshold, it indicates that the vehicle speed is very close to the maximum speed. At this point, the proportional parameter p and integral parameter i are set to a smaller combination of the second parameters. Smaller parameter values ​​ensure the stability of the system near the target speed, resist external disturbances (such as changes in wind resistance and gradient), and avoid oscillations caused by overly sensitive control.

[0034] The proportional parameter p and integral parameter i in the first parameter combination are both numerically greater than the corresponding parameters in the second parameter combination used during the steady-state phase. Through the above-described piecewise variable parameter control based on deviation, the PID controller can adopt the most suitable control strategy in different vehicle speed ranges, balancing response speed and control stability.

[0035] Furthermore, to further prevent overshoot caused by the accumulation of integral terms, in this embodiment of the invention, the PID controller employs an anti-integral saturation algorithm, which includes: Set the vehicle speed deviation threshold E0; When the deviation feedback is less than or equal to the vehicle speed deviation threshold E0, integral term calculation is disabled, and only proportional control is used. This is because when the deviation is small, the continuous accumulation of the integral term can easily lead to excessive control input, thereby causing overshoot. Disabling the integral term can eliminate this potential risk.

[0036] When the deviation feedback is greater than the vehicle speed deviation threshold E0, the integral term calculation is enabled.

[0037] In this embodiment of the invention, the anti-integral saturation algorithm further includes: Limit the calculation result of the integral term, restricting the value of the integral term to between the upper and lower limits; When the accelerator pedal signal is detected to be zero, the calculation result of the integral term is cleared to zero.

[0038] When the accelerator pedal signal is detected to be zero, it means the driver has released the accelerator. At this point, the calculation result of the integral term is cleared to zero. This logic ensures that the system state can be quickly reset after the driver releases the accelerator. The next time the accelerator is pressed, the integral term is calculated from zero, avoiding the residual influence of historical integral values ​​and improving the reusability and safety of the system.

[0039] When the maximum vehicle speed V _max With current vehicle speed V _act When the difference is greater than 10% of the maximum vehicle speed (i.e., the current vehicle speed is lower than the activation threshold), the system determines that the vehicle has left the speed limit zone, exits the PID calculation module and the approximation speed calculation module, and restores the driver's normal torque request.

[0040] Following step S4 above, the vehicle speed limiting method of this embodiment of the invention further includes: The torque control quantity is compared and arbitrated with the torque demanded by the driver, and the arbitrated torque is used as the final output torque.

[0041] After the PID controller calculates the torque control value, torque arbitration is required. The specific process is as follows: the sum of the torque calculated by the PID controller and the actual wheel-end torque is compared with the calculated torque demanded by the driver. If the driver's torque demand is less than the speed limit torque demand, the torque output is based on the driver's demand to ensure the driver's control of the vehicle; if the driver's torque demand is greater than the speed limit torque demand, the torque output is based on the speed limit torque demand to ensure the vehicle speed does not exceed the maximum speed. Finally, the arbitration-adjusted torque is sent to the vehicle's power system as the final torque demand.

[0042] Secondly, embodiments of the present invention also provide a vehicle speed limiting system, comprising: The activation module is used to activate the speed limit control logic when the vehicle's current speed reaches a preset activation threshold; wherein the activation threshold is lower than the vehicle's maximum speed. The calculation module is used to calculate the approximate speed, which is calculated based on the maximum speed and the current speed, and always lies between the current speed and the maximum speed. The PID control module is used to calculate the difference between the approximate vehicle speed and the current vehicle speed as the deviation feedback quantity, and dynamically adjusts the proportional and integral parameters according to the magnitude of the deviation feedback quantity, thereby calculating the torque control quantity to limit the vehicle speed.

[0043] In this embodiment of the invention, the output terminal of the activation module is connected to the control terminals of the calculation module and the PID control module; the output terminal of the calculation module is connected to the input terminal of the PID control module; and the output terminal of the PID control module is used to output the torque control quantity.

[0044] The activation module monitors the vehicle's current speed in real time and compares it with a preset activation threshold. When the current speed reaches the threshold, the activation module generates and outputs an activation signal. This activation signal is transmitted to the calculation module and the PID control module to control their operating states.

[0045] After being activated, the calculation module acquires the vehicle's maximum speed and current speed, and calculates an approximate speed according to a preset algorithm. The calculation module outputs this approximate speed to the PID control module as the target input value for the PID control module.

[0046] The PID control module receives the approximate vehicle speed output from the calculation module and simultaneously acquires the vehicle's actual current speed as a feedback signal. The PID control module calculates the difference between the approximate vehicle speed and the current vehicle speed to obtain the deviation feedback value, and performs variable parameter PID calculations based on this deviation feedback value, ultimately generating a torque control value to be output to the vehicle's power system to limit the vehicle speed.

[0047] Thirdly, embodiments of the present invention also provide a vehicle including the vehicle speed limiting system described above. Since the vehicle of the present invention includes the vehicle speed limiting system described in the above embodiments, it possesses all the advantages of the aforementioned vehicle speed limiting system. That is, when the vehicle performs the speed limiting function, it can achieve the control requirements of fast response, strong stability, no overshoot, and reaching the control target at the specified speed, effectively solving the problems of easy overshoot and slow response in traditional vehicles when limiting speed, thus improving the driving experience and safety.

[0048] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution; or the direct application of the inventive concept and technical solution to other situations without modification, are all within the protection scope of the present invention.

Claims

1. A method for limiting vehicle speed, characterized in that, include: Step S1: When the vehicle's current speed reaches the preset activation threshold, the speed limit control logic is activated; Step S2: Calculate the approximation speed. The approximation speed is calculated based on the vehicle's maximum speed and current speed, and it always lies between the current speed and the maximum speed. Step S3: Calculate the difference between the approaching vehicle speed and the current vehicle speed as the deviation feedback quantity, and input it into the PID controller; Step S4: Based on the magnitude of the deviation feedback, dynamically adjust the proportional and integral parameters of the PID controller, and calculate the torque control quantity based on the adjusted parameters to perform speed limiting control on the vehicle.

2. The vehicle speed limiting method according to claim 1, characterized in that, In step S2, the formula for calculating the approximate vehicle speed is: V _appr = V _max + k × (V _max - V _act ) Among them, V _appr For the approximate vehicle speed, V _max V represents the maximum vehicle speed. _act The current vehicle speed is given, and k is a variable parameter with a value between 0 and 1.

3. The vehicle speed limiting method according to claim 2, characterized in that, The variable parameter k changes exponentially based on the difference ∆V between the maximum vehicle speed and the current vehicle speed, and the calculation formula is as follows: k = ΔV / (1 + ΔV) Where, △V=V _max - V _act .

4. The vehicle speed limiting method according to claim 1, characterized in that, The activation threshold is 90% of the maximum vehicle speed; when the difference between the maximum vehicle speed and the current vehicle speed is greater than 10% of the maximum vehicle speed, the speed limit control logic is exited.

5. The vehicle speed limiting method according to claim 1, characterized in that, In step S4, dynamically adjusting the proportional parameter and the integral parameter specifically includes: When the deviation feedback amount is greater than the first preset threshold, the proportional parameter and the integral parameter are set to the first parameter combination for rapid response; When the deviation feedback amount is less than the first preset threshold and greater than the second preset threshold, the proportional parameter and the integral parameter are gradually reduced to reduce the risk of overshoot. When the deviation feedback amount is less than the second preset threshold, the proportional parameter and the integral parameter are set to the second parameter combination to stabilize the vehicle speed.

6. The vehicle speed limiting method according to claim 1, characterized in that, The PID controller employs an anti-integral saturation algorithm, which includes: Set the vehicle speed deviation threshold E0; When the deviation feedback amount is less than or equal to the vehicle speed deviation threshold E0, the integral term calculation is disabled. When the deviation feedback amount is greater than the vehicle speed deviation threshold E0, the integral term calculation is enabled.

7. The vehicle speed limiting method according to claim 6, characterized in that, The anti-integral saturation algorithm also includes: The calculation result of the integral term is subjected to a limiting process, restricting the value of the integral term to between an upper limit value and a lower limit value; When the accelerator pedal signal is detected to be zero, the calculation result of the integral term is cleared to zero.

8. The vehicle speed limiting method according to claim 1, characterized in that, The process following step S4 also includes: The torque control quantity is compared and arbitrated with the torque required by the driver, and the arbitrated torque is used as the final output torque.

9. A vehicle speed limiting system, characterized in that, include: An activation module is used to activate the speed limit control logic when the current speed of the vehicle reaches a preset activation threshold; wherein the activation threshold is lower than the maximum speed of the vehicle. The calculation module is used to calculate the approximate vehicle speed, which is calculated based on the maximum vehicle speed and the current vehicle speed, and is always located between the current vehicle speed and the maximum vehicle speed. The PID control module is used to calculate the difference between the approach speed and the current speed as a deviation feedback quantity, and dynamically adjust the proportional and integral parameters according to the magnitude of the deviation feedback quantity, thereby calculating the torque control quantity to limit the speed of the vehicle.

10. A vehicle, characterized in that, Includes the vehicle speed limiting system as described in claim 9.

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