An EMB cooperative control method for not reducing driving power of a whole vehicle under a low adhesion condition

Abstract

The application discloses an EMB cooperative control method for not reducing the driving power of a whole vehicle under low adhesion conditions, which realizes the accurate start and stop of a control system by collecting the longitudinal vehicle speed, four-wheel wheel speed, wheel load and throttle pedal opening degree signals of a vehicle body in real time, calculating the real-time slip rate of each wheel and relying on two slip rate threshold values of 0.13 and 0.15; the PID closed-loop regulation and control of the four-wheel independent EMB brake is used to inhibit the excessive wheel slip, and the constant power torque cooperative compensation strategy is innovatively adopted to brake and consume the excess torque of the slipping wheel, and an equal amount of torque is compensated to the non-slip driving wheel with sufficient adhesion margin, so that the total driving torque of the whole vehicle is kept constant and the driving power of the whole vehicle is not reduced. The application can stably control the wheel slip rate to be less than 0.15 under low adhesion conditions, has fast control response speed and high stability, and effectively improves the starting acceleration stability and the escape ability of a vehicle under adverse conditions such as wet and slippery roads and being trapped.

Description

Technical Field

[0001] This invention belongs to the field of brake-by-wire technology for new energy vehicles, and specifically relates to an EMB collaborative control method that does not reduce the overall vehicle drive power under low adhesion conditions. Background Technology

[0002] The market penetration rate of new energy vehicles is increasing year by year, and the intelligent and refined control capabilities of chassis electronic control systems have become the core key to vehicle driving stability. Traditional vehicles rely on hydraulic braking systems for braking and anti-slip control, with ABS used for anti-lock braking during braking conditions and TCS achieving traction anti-slip by reducing drive wheel torque or braking slipping wheels.

[0003] The core mechanism of vehicle wheel slippage follows Coulomb's law of friction, and the maximum adhesion force on the ground satisfies the formula... ,in For maximum adhesion to the ground, For wheel load, This refers to the coefficient of friction with the ground. When the driving force of the wheels exceeds the maximum adhesion of the ground, the driving wheels will slip excessively, causing problems such as vehicle deviation, weak acceleration, and inability to get out of trouble.

[0004] The existing TCS anti-skid control strategy has obvious technical defects: when one wheel of the vehicle is stuck and driving on a low-traction surface, the control system will passively reduce the driving torque of the whole vehicle to suppress wheel slippage, which directly leads to the loss of driving power of the whole vehicle, a significant decrease in vehicle power and a poorer ability to get out of trouble; at the same time, conventional models do not have a mechanical differential lock structure, and cannot achieve differentiated torque distribution between the left and right wheels. Only high-end special vehicles can get out of trouble by adding a differential lock, which has poor adaptability and high cost.

[0005] With the industry trend of EMB drive-by-wire systems becoming increasingly widespread, how to leverage the high precision and fast response of EMB to achieve precise control of wheel slip ratio without reducing the total driving power of the vehicle, and replace the function of mechanical differential lock, has become a technical challenge that the industry urgently needs to solve. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies, such as loss of overall vehicle driving power, poor stability under low adhesion conditions, and weak ability to get out of trouble. It provides an EMB collaborative control method that does not reduce the overall vehicle driving power under low adhesion conditions. Through the coordinated regulation of braking and driving torque, it achieves precise control of slip ratio while maximizing the preservation of overall vehicle power performance.

[0007] To address the aforementioned technical problems, this invention provides an EMB cooperative control method that does not reduce the overall vehicle drive power under low adhesion conditions, characterized by the following steps:

[0008] Step A: Vehicle Start-up and Multi-Source Status Signal Acquisition: After the vehicle starts, the system enters the working state and collects the vehicle's operating status signals in real time, including the vehicle's longitudinal speed Vx, four-wheel speed ω, four-wheel wheel load Fz, and accelerator pedal opening Th; comprehensively acquiring the vehicle's real-time operating conditions and the driver's power requirements.

[0009] Step B: Four-wheel independent slip ratio calculation: Based on the collected longitudinal vehicle speed and wheel speed of each wheel, the real-time slip ratio of each of the four wheels is calculated using a preset slip ratio calculation formula. The slip ratio calculation formula is as follows:

[0010] (i = 1, 2, 3, 4)

[0011] in, Let be the real-time slip ratio of the i-th wheel. Let be the angular velocity of the i-th wheel, and R be the effective rolling radius of the wheel. Let i be the vehicle speed, and i = 1, 2, 3, 4 correspond to the four wheels of the vehicle.

[0012] Step C: Slip ratio threshold determination and system start-stop control: Preset two levels of slip ratio thresholds to construct a control dead zone to avoid frequent system start-stop interference; when the real-time wheel slip ratio λ < 0.13, it is determined that the vehicle is in normal driving state, and the slip ratio cooperative control system is turned off; when the real-time wheel slip ratio λ ≥ 0.15, it is determined that the wheel is severely slipping, the slip ratio cooperative control system is activated, and the closed-loop control process is entered.

[0013] Step D: Four-wheel independent EMB braking closed-loop control: The real-time slip ratio of each wheel is low-pass filtered to remove signal noise and obtain a stable filtered slip ratio; the slip ratio error is calculated. and the rate of change of error, of which A preset target slip ratio is used. When the filtered slip ratio exceeds the sum of the target slip ratio and the preset dead zone threshold, PID closed-loop control is initiated, and the braking torque command for each wheel is calculated using the PID formula.

[0014]

[0015] in For the braking torque of the i-th wheel, For proportionality coefficient, For integral coefficients, The differential coefficients are... The slip ratio error change rate is used to limit the upper and lower limits of the output braking torque command to avoid braking force overload. When the filtered slip ratio is not greater than the sum of the target slip ratio and the preset dead zone threshold, the braking force closed-loop control is turned off, the braking torque command of each wheel gradually decays and is released, and the integral term of PID control slowly returns to zero according to the preset time constant to ensure control smoothness.

[0016] Step E: Constant power drive torque collaborative compensation: Synchronously execute dynamic torque adjustment of the drive system, apply braking force to the slipping wheel to consume its excess drive torque, and at the same time compensate the excess torque equally to the coaxial or non-slipping drive wheel with sufficient adhesion margin of the whole vehicle, keep the total drive torque of the whole vehicle constant throughout the process, and completely avoid the power loss problem of traditional strategies.

[0017] For vehicles with a coaxial dual-drive wheel arrangement: when the slip ratio of any drive wheel on the coaxial side exceeds the limit for automatic intervention, the drive system outputs an equal amount of compensation torque to the non-slipping wheel on the other side of the coaxial side to ensure that the total torque of the coaxial side remains unchanged and the net driving force of a single wheel does not exceed the road surface adhesion limit.

[0018] For vehicles with independent multi-drive wheel layouts: when any independent drive wheel slips and brakes, the corresponding motor reduces torque by an equal amount, and the reduced torque is fully transferred to the drive motor with the largest adhesion margin of the whole vehicle, so that the total drive torque of the whole vehicle remains constant.

[0019] Step F: The vehicle dynamic closed-loop control integrates the four-wheel braking commands and the motor drive commands to form an integrated braking-drive closed-loop control, which converges and stabilizes the slip ratio of each wheel within the target range of 0.15, thereby achieving stable vehicle driving and rapid extrication under low adhesion and wheel stuck conditions.

[0020] Preferably, the present invention is pre-tested by The maximum ground adhesion of each wheel is calculated, and the maximum net driving torque of a single wheel is obtained. This provides a precise threshold basis for braking force regulation and torque compensation, avoiding over-limit regulation.

[0021] In summary, the beneficial effects of the above-described technical solutions conceived by this invention compared with the prior art include:

[0022] 1. This invention abandons the traditional TCS torque reduction and anti-slip control logic. Through a coordinated strategy of dissipating excess torque during braking and compensating for equal torque, it maintains a constant total driving torque of the vehicle throughout the entire process without sacrificing any driving power of the vehicle. It maximizes the preservation of the driver's power needs and significantly improves the acceleration performance and off-road capability of vehicles under low-adhesion conditions.

[0023] 2. This invention leverages the high precision and fast response of EMB brake-by-wire technology to achieve differentiated torque distribution between the left and right wheels and anti-slip and obstacle-avoidance functions through software algorithms. It eliminates the need for a mechanical differential lock, significantly reducing the overall vehicle hardware cost and structural complexity, and making it compatible with a wider range of vehicle models.

[0024] 3. This invention adopts four-wheel independent PID closed-loop braking control, combined with 0.13 and 0.15 dual threshold anti-shake start-stop logic. The system response time is ≤0.2s and the stabilization time is ≤0.5s. It can accurately lock the wheel slip ratio in the optimal range, effectively suppress wheel slippage, and ensure vehicle driving stability and steering controllability. Attached Figure Description

[0025] Figure 1 A flowchart of the EMB cooperative control method for not reducing the overall vehicle drive power under adhesion conditions provided by the present invention;

[0026] Figure 2 The diagram showing the change in wheel slip ratio under zero slip ratio cooperative control provided by this invention;

[0027] Figure 3 The diagram shows the change in wheel slip ratio under the intervention of the slip ratio cooperative control system provided by the present invention. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer from the following description and claims. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0029] Example

[0030] This invention provides an EMB cooperative control method that does not reduce the overall vehicle drive power under low adhesion conditions. Please refer to [link / reference]. Figure 1 .

[0031] Slip rate control when starting a vehicle driven by dual motors on the front and rear axles on a slippery surface.

[0032] 1. Operating conditions and parameter settings

[0033] The simulation of vehicle starting on a low-adhesion wet and slippery road surface was performed, with a road surface adhesion coefficient μ≈0.3. The vehicle's basic parameters were: total vehicle mass m=2000kg, effective wheel rolling radius R=0.393m, reducer transmission ratio I=10, and preset target slip ratio λ_target=0.15. The accelerator pedal was gradually increased to 30% opening within 2 seconds to simulate the power demand for normal starting.

[0034] 2. Slip Ratio Calculation

[0035] The left front wheel... The engine speed is 453.5 rpm, right front wheel The rotational speed is 459.6 rpm, which can be converted from the angular velocity formula. The angular velocity of the front wheel can be calculated using the angular velocity formula. rad / s; rad / s.

[0036] At this time, the vehicle speed =0.92m / s, substitute into the slip ratio calculation formula The slip ratios of both front wheels were approximately 0.95, far exceeding the target threshold of 0.15, indicating that the wheels were in a state of severe slippage.

[0037] 3. Slip ratio collaborative control decision-making and execution

[0038] The controller calculates the wheel adhesion limit based on the estimated road surface adhesion coefficient and the load on each wheel:

[0039] Front left wheel:

[0040] Maximum permissible net drive torque

[0041] Right front wheel:

[0042]

[0043] The calculated maximum net driving torque provides an important basis for our subsequent coordinated control.

[0044] Analyze the driver's driving intentions:

[0045] The driver's driving intention is strongly correlated with changes in the accelerator pedal signal; based on these changes, commands for the motor's drive torque can be obtained. At the first second, the driver's accelerator pedal opening is 15%, and the drive torque commands received by the motor at this time are as follows: , At this point, the driving torque command has far exceeded the maximum driving torque allowed by the ground.

[0046] Braking force control:

[0047] With the currently calculated wheel slip ratio as input, and the target slip ratio being less than 0.15, the system uses PID control and converts it into braking force commands. At 1 second, a braking force of 840.5N is applied to the left front wheel and a braking force of 844N is applied to the right front wheel.

[0048] Drive force control:

[0049] Using the maximum driving force allowed on the ground as the target and the current driving intention of the driver as the input, the input driving torque of the vehicle is controlled through PI regulation. At the same time, in coordination with the braking force control system, the output of braking force is reduced while ineffective driving torque is reduced, so as to achieve stable driving or getting out of trouble.

[0050] 4. Control effect

[0051] Figure 2 The diagram shows the changes in wheel slip ratio under zero slip ratio coordinated control. It is clear from the diagram that when starting on an icy or snowy road, the drive wheels are in a state of severe slippage.

[0052] Figure 3 The diagram shows the change in wheel slip ratio under the intervention of the slip ratio cooperative control system. The current cooperative control system intervenes in vehicle control at approximately 0.2 seconds and brings the vehicle to a balanced state after 0.5 seconds, meaning the wheel slip ratio is within 0.15. By increasing the speed to 1.6 km / h, compared to vehicles without a control system, the vehicle maintains stable posture while increasing speed. This invention fully retains the total power of the vehicle's drive system, while completely solving the problem of slippage when starting on low-traction surfaces, significantly improving the vehicle's ability to get out of trouble and its driving stability.

[0053] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An EMB cooperative control method that does not reduce the overall vehicle drive power under low adhesion conditions, characterized in that, Includes the following steps: Step A: Vehicle Start-up and Multi-Source Status Signal Acquisition: After the vehicle starts, the system enters the working state and collects the vehicle's operating status signals in real time, including the vehicle's longitudinal speed Vx, four-wheel speed ω, four-wheel wheel load Fz, and accelerator pedal opening Th; Step B: Four-wheel independent slip ratio calculation: Based on the collected longitudinal vehicle speed and wheel speed of each wheel, the real-time slip ratio of each of the four wheels is calculated using a preset slip ratio calculation formula. Step C: Slip ratio threshold determination and system start-stop control: Two levels of slip ratio thresholds are preset. When the real-time wheel slip ratio λ < 0.13, the slip ratio cooperative control system is turned off; when the real-time wheel slip ratio λ ≥ 0.15, the slip ratio cooperative control system is started and the closed-loop control process is entered. Step D: Four-wheel independent EMB braking closed-loop control: The real-time slip rate of each wheel is low-pass filtered, the slip rate error and error change rate are calculated, the basic braking torque command of each wheel is generated through the PID closed-loop algorithm, and the upper and lower limits of the braking torque command are set to achieve precise suppression of the slip rate of slipping wheels. Step E: Constant power drive torque collaborative compensation: Synchronously execute dynamic torque adjustment of the drive system, apply braking force to the slipping wheel to consume its excess drive torque, and at the same time compensate the excess torque to the coaxial or non-slipping drive wheel with sufficient adhesion margin of the whole vehicle, keep the total drive torque of the whole vehicle constant throughout the process, and do not reduce the total drive power of the whole vehicle. Step F: Vehicle dynamic closed-loop control: Integrate the four-wheel braking commands and motor drive commands to complete the dynamic closed-loop control of the whole vehicle, converge and stabilize the slip ratio of each wheel within the target slip ratio range, and achieve stable driving and extrication of the vehicle under low adhesion and wheel stuck conditions.

2. The EMB cooperative control method for low-adhesion conditions without reducing the overall vehicle drive power according to claim 1, characterized in that, The formula for calculating the real-time wheel slip ratio in step B is as follows: （i= 1、2、3、4） in, Let be the real-time slip ratio of the i-th wheel. Let be the angular velocity of the i-th wheel, and R be the effective rolling radius of the wheel. Let i be the vehicle speed, and i = 1, 2, 3, 4 correspond to the four wheels of the vehicle.

3. The EMB cooperative control method for low-adhesion conditions without reducing the overall vehicle drive power according to claim 1, characterized in that, The specific control logic for step D includes: Step D1: Perform low-pass filtering on the real-time slip ratio of each wheel to obtain the filtered slip ratio; Step D2: Calculate the slip ratio error and the rate of change of slip error ;in The preset target slip ratio; Step D3: When the filtered slip ratio is greater than the sum of the target slip ratio and the preset dead zone threshold, PID closed-loop control is initiated, using the formula... Calculate the braking torque command for each wheel, where For the braking torque of the i-th wheel, For proportionality coefficient, For integral coefficients, These are the differential coefficients. This represents the rate of change of slip ratio error; Step D4: When the filtered slip ratio is not greater than the sum of the target slip ratio and the preset dead zone threshold, the closed-loop control of braking force is turned off, the braking torque command of each wheel is gradually attenuated and released, and the integral term of PID control slowly returns to zero according to the preset time constant.

4. The EMB cooperative control method for low-adhesion conditions without reducing the overall vehicle drive power according to claim 3, characterized in that, The response intervention time of the PID closed-loop control is ≤0.2s, the control stabilization time is ≤0.5s, and the slip ratio of each wheel is stably controlled within 0.15 after regulation.

5. The EMB cooperative control method for low-adhesion conditions without reducing the overall vehicle drive power according to claim 1, characterized in that, For vehicles with a coaxial dual-drive wheel arrangement, the specific method for dynamic compensation of drive torque in step E is as follows: When a braking torque is applied to either drive wheel on the coaxial side due to excessive slip ratio, the drive system generates a torque compensation command with an amplitude equal to that braking torque, and distributes the compensation torque equally to the non-slipping drive wheel on the other side of the coaxial side, so that the total driving torque of the drive wheels on both sides of the coaxial side remains constant, and the net driving force of each wheel does not exceed the current road surface adhesion bearing limit.

6. The EMB cooperative control method for low-adhesion conditions without reducing the overall vehicle drive power according to claim 1, characterized in that, For vehicles with independent multi-drive wheel arrangements, the specific method for dynamic compensation of drive torque in step E is as follows: When the slip ratio of any independent drive wheel exceeds the limit and triggers braking intervention, the corresponding drive motor synchronously reduces the output torque. The torque reduction is equal to the wheel-side driving force corresponding to the braking torque applied to that wheel. The reduced torque is then fully transferred to the drive motor corresponding to the drive wheel with the largest current road surface adhesion margin, so that the total output torque of all drive motors in the vehicle remains unchanged.

7. The EMB cooperative control method for low-adhesion conditions without reducing the overall vehicle drive power according to claim 1, characterized in that, It also includes the calculation step of the maximum adhesion limit of the wheels: based on the real-time collected vertical load of each wheel and the road friction coefficient, using the formula The maximum ground adhesion of each wheel is calculated, and then the maximum net driving torque of each wheel is obtained by conversion, providing a threshold basis for braking torque control and driving torque compensation; among which... For maximum adhesion to the ground, For wheel load, is the coefficient of friction of the ground.

8. The EMB cooperative control method for low-adhesion conditions without reducing the overall vehicle drive power according to claim 1, characterized in that, The preset target slip ratio is set to 0.

15. The control method is applicable to low adhesion conditions with a road surface friction coefficient μ≤0.3, wheel slumping on one side, and slippery road surface starting and acceleration slipping conditions.

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