A creep control method based on PI

Abstract

The present invention discloses a creep control method based on PI, comprising the following steps: detecting the current state of the vehicle, determining the driving intention of the driver, judging whether the vehicle meets the creep condition and activating the creep function; calculating the initial creep torque of the vehicle after activating the creep function according to the calibration map and PI control. The present invention judges whether the vehicle can be driven if the creep condition is met. If the vehicle cannot be driven, the creep torque is cancelled to protect the hardware; if the vehicle can be driven, the creep function is entered, and the vehicle start and climbing are separated. The basic map calibration is used when starting, and after reaching a certain vehicle speed, PI control is used to ensure the smoothness of the start and the function of creeping on the slope, thereby improving the drivability; the creep torque is corrected by the brake pedal opening and the steering wheel torsion angle, and the control logic is simple and in line with the driver's driving habits.

Description

Technical Field

[0001] The invention belongs to the field of vehicle control, and in particular relates to a creep control method based on PI. Background Art

[0002] Cars generally drive at low speeds when parking or following other vehicles on congested roads. In traditional cars, this is usually achieved by the automatic transmission controller through the clutch. That is, the transmission hardware applies some torque to the wheels that is not controlled by the software, allowing the car to crawl at low speed on a flat road.

[0003] The creep function of electric vehicles is generally achieved through software control, using the motor to generate the required real-time creep torque to help drivers control the vehicle more easily in traffic jams, starting and on slopes, playing an important role in vehicle assisted driving.

[0004] In the existing automobile creep control strategy, on flat ground, the basic creep torque is set according to the vehicle speed and gear position, and adjusted according to external influencing factors such as brake pressure and temperature. On slopes, most of the time, the basic creep torque is preset based on the slope coefficient, and then attenuation filtering is performed based on the resistance. The motor is controlled based on the torque output from the filter as the required torque. Although this method can achieve the purpose of controlling the creep torque, the control method is not accurate enough and is very dependent on the slope coefficient on slopes. Summary of the invention

[0005] The purpose of the present invention is to provide a PI-based creep control method. When the creep conditions are met, it is determined whether the vehicle can be driven. If the vehicle cannot be driven, the creep torque is canceled to protect the hardware. If the vehicle can be driven, the creep function is entered, and the vehicle start and climbing are separated, ensuring the smoothness of the start and the function of slope creeping, and improving the drivability. The creep torque is corrected by the brake pedal opening and the steering wheel torsion angle, and the control logic is simple and conforms to the driver's driving habits.

[0006] To solve the above technical problems, the technical solution of the present invention is: a creep control method based on PI, comprising the following steps:

[0007] Detect the current state of the vehicle, determine the driver's driving intention, judge whether the vehicle meets the creeping conditions and activate the creeping function;

[0008] According to the calibrated map and PI control, the initial creep torque of the vehicle after the creep function is activated is calculated.

[0009] The following steps are also included:

[0010] When the vehicle turns, the initial creep torque is corrected according to the brake pedal opening or brake fluid pressure and the steering wheel torsion angle. The correction method is:

[0011] T=T 初始 *K p *K θ

[0012] Where, T is the corrected creep torque, T 初始 is the initial creep torque, K p is the torque attenuation coefficient calculated based on the brake fluid pressure, K θ is the torque adjustment coefficient calculated according to the steering wheel twist angle.

[0013] The method for calculating the torque reduction coefficient based on the brake fluid pressure is:

[0014]

[0015] Where, 0≤K p ≤1,p calibration It represents the calibratable brake fluid pressure, and p represents the brake fluid pressure when the driver steps on the brake pedal.

[0016] The method for calculating the torque adjustment coefficient based on the steering wheel twist angle is:

[0017]

[0018] In the formula, θ, θ calibration and θ calibration are steering angles, θ calibration2 and θ calibration are the second calibration value of the steering angle and the first calibration value of the steering angle, respectively, and |θ calibration2 |>|θ calibration1 |, θ is the real-time steering angle. When the vehicle turns left, θ is a positive value; when the vehicle turns right, θ is a negative value;

[0019] When |θ min |≤|θ|≤|θ calibration1 |, indicating that the road curvature is small at this time, and the creep torque is not adjusted, θ min is the minimum calibrable steering angle;

[0020] When |θ calibration1 |≤|θ|≤|θ calibration2 |, indicating that the road curvature is moderate at this time, and the above formula is applicable to adjust the creep torque;

[0021] When |θ calibration |≤|θ|≤|θ max|, indicating that the road is very curved at this time, and turning with a higher torque is dangerous, so the creep torque is assigned a smaller preset fixed torque T calibration ,θ max is the maximum calibrable steering angle.

[0022] The current driver's driving intention is determined based on the position of the gear lever; when the gear is in D or R, the brake pedal, accelerator pedal and handbrake are released, and the vehicle speed is lower than the creeping speed threshold v calibration When , it is judged that the vehicle meets the creep condition.

[0023] When the creep condition is met, if the vehicle speed v is within the preset time T calibration If the level of v0<v<v1 is continuously maintained within the range, it is determined that the vehicle cannot start creeping and the creeping function cannot be activated; otherwise, the creeping function is activated; wherein v0 is the first creeping activation threshold, v1 is the second creeping activation threshold, and v1<v calibration .

[0024] The initial creep torque is calculated as:

[0025] T PI =k p ×Δv+k i ×Δv

[0026] T 初始 =max{C1,min(C2,T PI )}

[0027] Where, T PI is the current vehicle creep torque, k p is the proportionality coefficient, k i is the integral coefficient, Δv=v Target -v 实际 is the difference between the target speed and the actual speed, C1 is the minimum torque, and C2 is the maximum torque.

[0028] To avoid a rough start, a basic torque T is set. 基础 , when the vehicle starts, the initial creep torque is T 基础 .

[0029] A computer device is also provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of any of the above methods when executing the computer program.

[0030] A computer-readable storage medium is also provided, on which a computer program is stored, and when the computer program is executed by a processor, the steps of any of the above methods are implemented.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention determines whether the vehicle can be driven when the creeping conditions are met. If the vehicle cannot be driven, the creeping torque is canceled to protect the hardware. If the vehicle can be driven, the creeping function is entered, and the vehicle start and climbing are separated, thereby ensuring the smoothness of the start and the function of creeping on the slope, and improving the drivability. The creeping torque is corrected by the brake pedal opening and the steering wheel torsion angle, and the control logic is simple and conforms to the driver's driving habits. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of a process for determining creeping conditions in an embodiment of the present invention;

[0034] Figure 2 A schematic diagram of a process for determining a creep activation condition in an embodiment of the present invention;

[0035] Figure 3 Schematic diagram of the process of the creep adjustment method during turning in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] The present invention provides a creep control method based on PI, and the specific control steps are as follows:

[0038] (1) Determine whether the vehicle's creep function has been activated based on the vehicle's current state and the driver's intention;

[0039] (2) Creep control method and initial creep torque calculation;

[0040] (3) Correct the creep torque to obtain the final creep torque.

[0041] 1. The method to determine whether the creep function is activated is as follows:

[0042] Detect the current state of the vehicle and the driver's intention. The driver's operation of the gear is sent to the VCU through the CAN signal. The VCU determines the current driver's intention based on the position of the gear lever. When the vehicle is in D gear or R gear, the brake pedal and accelerator pedal are released, the handbrake is released, and the vehicle speed is lower than V calibration (can be calibrated), then the creeping condition is satisfied, if v 车速 In a period of time T calibrationIf the torque is continuously within v0<v<v1 (where v0 and v1 are calibrable) within a certain period of time, it can be determined that the vehicle cannot start by creeping normally. After an adjustable period of time, the creep torque is reduced and the creep function is cancelled. If the vehicle can be driven, the creep function is activated normally. The specific judgment method is as follows: Figure 1 and Figure 2 shown.

[0043] 2. Creep control method and initial creep torque calculation

[0044] If the PI control is used alone, it is impossible to take into account both the flat ground starting and the smoothness and the creeping function on the slope. Because the invention presets the basic torque, after the vehicle starts smoothly, the PI control is intervened to ensure the stability of the creeping. The specific control method is as follows:

[0045] In order to avoid a rough start, when the creeping conditions are met, a smaller basic torque T is preset according to the vehicle speed and gear position when starting. 基础 , when the vehicle starts, T 初始 Equal to T 基础 ; In order to ensure the creeping function of the vehicle on the slope, when the vehicle starts smoothly and the speed reaches v (which can be calibrated), PI control is turned on. At this time, the creeping torque is T PI =k p ×Δv+k i ×Δv,T 初始 =max{C1,min(C2,T PI )},

[0046] where k p is the proportionality coefficient, k i is the integral coefficient, Δv=v Target -v 实际 is the difference between the target speed and the actual speed, C1 is the minimum torque of PI control, and C2 is the maximum torque of PI control;

[0047] The strategy for converting basic torque control to PI control is to filter according to the current vehicle speed, operating cycle, and the difference between the two. When the difference between the two is less than T c (calibrable), PI control takes effect;

[0048] 3. Correct the creep torque to get the final creep torque

[0049] The creep torque obtained in the second step is corrected according to the brake pedal opening or brake fluid pressure and steering wheel torsion angle

[0050] The corrected torque is: T = T 初始 *K p *K θ

[0051] in:

[0052] K p Indicates the torque attenuation coefficient calculated based on the brake fluid pressure.

[0053] 0≤K p ≤1;

[0054] K θ Indicates the torque adjustment coefficient calculated based on the steering wheel twist angle.

[0055] The calculation process of the steering wheel twist angle torque adjustment coefficient is as follows:

[0056] The turning angle signal θ sent by the EPS sensor has directionality, so the present invention stipulates that when the turning angle signal θ is positive, it indicates that the vehicle is turning left, when the turning angle signal θ is negative, it indicates that the vehicle is turning right, and when the turning angle signal θ is 0, it indicates that the vehicle is traveling on a straight road.

[0057] Take left turn as an example, the turning angle signal θ is positive at this time, K θ The torque adjustment coefficient is divided into the following three cases;

[0058] When |θ min |≤|θ|≤|θ calibration1 |, indicating that the road curvature is small at this time, and the creep torque is not adjusted, θ min is the minimum calibrable steering angle;

[0059] When |θ calibration1 |≤|θ|≤|θ calibration2 |, indicating that the road curvature is moderate at this time, and the above formula is applicable to adjust the creep torque;

[0060] When |θ calibration2 |≤|θ|≤|θ max |, indicating that the road is very curved at this time, and turning with a higher torque is dangerous, so the creep torque is assigned a smaller preset fixed torque T calibration ,θ max is the maximum calibrable steering angle.

[0061] According to the above analysis, K θ The formula is as follows:

[0062]

[0063] The creep torque is calculated according to formula 1 and sent to the motor controller to control the creep function of the vehicle when turning. The implementation process is as follows: Figure 3 shown.

[0064] In particular, when the driver wants to take over and operate the vehicle according to his own will at low speeds, he can use the creep function switch button to turn the creep on and off, which can meet the driver's needs more conveniently and quickly on turns or straight roads.

[0065] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A creep control method based on PI, characterized in that: The following steps are involved: Detect the current state of the vehicle, determine the driver's driving intention, judge whether the vehicle meets the creeping conditions and activate the creeping function; According to the calibration map and PI control, the initial creep torque of the vehicle after the creep function is activated is calculated; The following steps are also included: When the vehicle turns, the initial creep torque is corrected according to the brake pedal opening or brake fluid pressure and the steering wheel torsion angle. The correction method is: T=T 初始 *K p *K θ Where, T is the corrected creep torque, T 初始 is the initial creep torque, K p is the torque attenuation coefficient calculated based on the brake fluid pressure, K θ is the torque adjustment coefficient calculated according to the steering wheel twist angle; The method for calculating the torque reduction coefficient based on the brake fluid pressure is: Where, 0≤K p ≤1,p calibration It represents the calibratable brake fluid pressure, and p represents the brake fluid pressure when the driver steps on the brake pedal.

2. A creep control method based on PI according to claim 1, characterized in that: The method for calculating the torque adjustment coefficient based on the steering wheel twist angle is: In the formula, θ calibration1 is the first calibration value of the steering angle, θ calibration2 is the second calibration value of the steering angle, and |θ calibration2 |>|θ calibration1 |; θ is the real-time steering angle. When the vehicle turns left, θ is a positive value; when the vehicle turns right, θ is a negative value; When |θ min |≤|θ|≤|θ calibration1 |, indicating that the road curvature is small at this time, and the creep torque is not adjusted, θ min is the minimum calibrable steering angle; When |θ calibration1 |≤|θ|≤|θ calibration2 |, indicating that the road curvature is moderate at this time, and the above formula is applicable to adjust the creep torque; When |θ calibration2 |≤|θ|≤|θ max |, indicating that the road is very curved at this time, and turning with a higher torque is dangerous, so the creep torque is assigned a smaller preset fixed torque T calibration ,θ max is the maximum calibrable steering angle.

3. The creep control method based on PI according to claim 1, characterized in that: Determine the current driver's driving intention based on the position of the gear lever; When the gear is in D or R, the brake pedal, accelerator pedal and parking brake are released, and the vehicle speed is lower than the creeping speed threshold v calibration When , it is judged that the vehicle meets the creep condition.

4. The creep control method based on PI according to claim 3, characterized in that: When the creep condition is met, if the vehicle speed v is within the preset time T calibration If the value of v0<v<v1 is maintained, the vehicle is judged to be unable to creep start and the creep function cannot be activated; otherwise, the creep function is activated; Wherein, v0 is the first threshold of peristalsis activation, v1 is the second threshold of peristalsis activation, and v1<v calibration .

5. The creep control method based on PI according to claim 1, characterized in that: The initial creep torque is calculated as: T PI =k p ×Δv+k i ×Δv T 初始 =max{C1,min(C2,T PI )} Where, T PI is the current vehicle creep torque, k p is the proportionality coefficient, k i is the integral coefficient, Δv=v Target -v 实际 is the difference between the target speed and the actual speed, C1 is the minimum torque, and C2 is the maximum torque.

6. The creep control method based on PI according to claim 1, characterized in that: To avoid a rough start, a basic torque T is set. 基础 , when the vehicle starts, the initial creep torque is T 基础 .

7. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 6 are implemented.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

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