Drive anti-slip control methods and systems, independent four-wheel drive electric vehicles

Abstract

This invention discloses a drive anti-slip control method and system, and an independent four-wheel drive electric vehicle. The drive anti-slip control method includes: when the electric vehicle deviates from a preset steering trajectory and a wheel slips during steering, controlling the torque of the slipping wheel to be reduced until the electric vehicle returns to the preset steering trajectory. The drive anti-slip control method shown in this application also considers lateral control during vehicle steering. By recognizing the vehicle's steering state, when the electric vehicle deviates from the preset steering trajectory and a wheel slips, the torque of the slipping wheel is reduced until the electric vehicle returns to the preset steering trajectory, thus maintaining neutral steering during steering, enhancing the vehicle's steering tracking ability, and improving the drive anti-slip capability of the independent four-wheel drive electric vehicle.

Description

Technical Field

[0001] This application relates to the field of vehicles, and more specifically to a drive anti-slip control method and system thereof, and an independent four-wheel drive electric vehicle. Background Technology

[0002] In traditional gasoline-powered vehicles, the Traction Control System (TCS) reduces wheel speed by limiting wheel speed through brake calipers, lowering the vehicle's slip ratio on low-friction surfaces and keeping the wheels near the optimal slip ratio. This allows the vehicle to achieve the best acceleration performance on the current low-friction surface. If the engine output torque is high, and relying solely on brake calipers to reduce wheel speed is insufficient, the TCS will also actively control the engine throttle opening, thereby controlling the engine's output torque and reducing wheel slippage.

[0003] With the development of electric vehicles, they are gradually replacing traditional gasoline vehicles and becoming the trend in passenger car development. Because electric motors have a more sensitive response than engines, the advantages of TCS (Traction Control System) can be further realized, especially for independent four-wheel drive electric vehicles, where they will have better results. However, current TCS development for independent four-wheel drive electric vehicles only considers longitudinal slip control, resulting in poor steering tracking ability during cornering. Summary of the Invention

[0004] This application is made to address at least one of the aforementioned problems. According to a first aspect of this application, a drive anti-slip control method is provided, the drive anti-slip control method being applied to an independent four-wheel drive electric vehicle, the drive anti-slip control method comprising: when the electric vehicle deviates from a preset steering trajectory during steering and there are slipping wheels, controlling the slipping wheels to reduce torque until the electric vehicle returns to the preset steering trajectory.

[0005] In one embodiment of this application, the electric vehicle deviating from a preset steering trajectory during steering includes: the electric vehicle steering too much or too little relative to the preset steering trajectory during steering.

[0006] In one embodiment of this application, the electric vehicle over-steering or under-steering relative to the preset steering trajectory during steering includes: if the current actual yaw rate of the electric vehicle is greater than the steady-state yaw rate, then the electric vehicle over-steering; if the current actual yaw rate of the electric vehicle is less than the steady-state yaw rate, then the electric vehicle under-steering; wherein the steady-state yaw rate is determined based on the preset steering trajectory.

[0007] In one embodiment of this application, when the electric vehicle is understeering, if there is a slipping wheel, the slipping wheel is controlled to gradually reduce torque until the electric vehicle is no longer understeering.

[0008] In one embodiment of this application, controlling the slipping wheel to step down torque until the electric vehicle no longer understeers includes: determining a step gradient value for controlling the slipping wheel to step down torque based on the current speed of the electric vehicle and the difference between the actual yaw rate and the steady-state yaw rate.

[0009] In one embodiment of this application, determining the step gradient value for controlling the slipping wheel to reduce torque based on the current speed of the electric vehicle and the difference between the actual yaw rate and the steady-state yaw rate includes: the greater the current speed of the electric vehicle, the greater the step gradient value for controlling the slipping wheel to reduce torque; the greater the difference between the current actual yaw rate and the steady-state yaw rate of the electric vehicle, the greater the step gradient value for controlling the slipping wheel to reduce torque.

[0010] In one embodiment of this application, when the electric vehicle oversteers, if there is a slipping wheel, the target slip ratio of the slipping wheel is adjusted, and the torque of the slipping wheel is reduced until the electric vehicle no longer oversteers.

[0011] In one embodiment of this application, adjusting the target slip ratio of the slipping wheel and controlling the reduction of torque of the slipping wheel includes: adjusting the target slip ratio of the slipping wheel, and using a motion control algorithm based on the adjusted target slip ratio to control the reduction of torque of the slipping wheel.

[0012] In one embodiment of this application, adjusting the target slip ratio of the slipping wheel includes: calculating the current road surface adhesion coefficient, and determining the basic target slip ratio of the slipping wheel based on the current road surface adhesion coefficient; determining a gain coefficient based on the current speed of the electric vehicle and the difference between the actual yaw rate and the steady-state yaw rate; wherein the gain coefficient is greater than 1; and determining the adjusted target slip ratio of the slipping wheel based on the product of the basic target slip ratio and the gain coefficient.

[0013] In one embodiment of this application, determining the gain coefficient based on the current speed of the electric vehicle and the difference between the actual yaw rate and the steady-state yaw rate includes: the greater the current speed of the electric vehicle, the greater the gain coefficient; the greater the difference between the actual yaw rate and the steady-state yaw rate, the greater the gain coefficient.

[0014] In one embodiment of this application, the drive anti-slip control method further includes: when all wheels of the electric vehicle are the slipping wheels, using an acceleration integral algorithm to calculate the vehicle speed of the electric vehicle; and when some wheels of the electric vehicle are the slipping wheels, using a Kalman filter algorithm to calculate the vehicle speed of the electric vehicle.

[0015] In one embodiment of this application, the drive anti-skid control method further includes: calculating the current utilization coefficient of adhesion and the actual slip rate of each wheel of the electric vehicle; and using a fuzzy algorithm, estimating the current fuzzy road surface adhesion coefficient of each wheel as a fuzzy factor, and using it as the current road surface adhesion coefficient of each wheel.

[0016] In one embodiment of this application, calculating the current utilization coefficient of adhesion for each wheel includes: calculating the corrected torque currently input to each wheel based on the current motor input torque, motor speed, motor moment of inertia, motor-to-wheel transmission ratio, and mechanical efficiency of the motor corresponding to each wheel; calculating the current longitudinal driving force of each wheel based on the corrected torque and wheel radius; and calculating the current utilization coefficient of adhesion for each wheel based on the current longitudinal driving force, lateral driving force, and wheel end vertical load of each wheel.

[0017] According to a second aspect of this application, a drive anti-slip control system is also provided, which is applied to an independent four-wheel drive electric vehicle. The drive anti-slip control system includes a storage medium and a processor. The storage medium stores a computer program that is executed by the processor. When the computer program is executed by the processor, it causes the processor to perform any of the drive anti-slip control methods described above.

[0018] According to a third aspect of this application, a storage medium is also provided, on which a computer program is stored, wherein the computer program, when running, executes any of the aforementioned drive anti-slip control methods.

[0019] According to a fourth aspect of this application, an independent four-wheel drive electric vehicle is also provided, the independent four-wheel drive electric vehicle comprising: a vehicle body, and any one of the aforementioned drive anti-slip control systems disposed on the vehicle body.

[0020] According to the drive anti-slip control method and system and independent four-wheel drive electric vehicle provided in the embodiments of this application, when the electric vehicle deviates from the preset steering trajectory and there are slipping wheels during the steering process, the torque of the slipping wheels is reduced until the electric vehicle returns to the preset steering trajectory. Compared with the existing control strategies that only consider longitudinal slip, the drive anti-slip control method shown in this application also considers lateral control during the vehicle steering process. By recognizing the vehicle steering state, when the electric vehicle deviates from the preset steering trajectory and there are slipping wheels, the torque of the slipping wheels is reduced until the electric vehicle returns to the preset steering trajectory, so that the vehicle maintains neutral steering during the steering process, enhances the vehicle's steering tracking ability, and improves the drive anti-slip capability of the independent four-wheel drive electric vehicle. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a flowchart illustrating a drive anti-slip control method for an independent four-wheel drive electric vehicle according to an embodiment of the present invention;

[0023] Figure 2 A flowchart illustrating a drive anti-slip control method for an independent four-wheel drive electric vehicle according to another embodiment of the present invention;

[0024] Figure 3 This is a schematic flowchart illustrating the calculation process of a drive anti-slip control method for an independent four-wheel drive electric vehicle, as shown in another embodiment of the present invention.

[0025] Figure 4 A flowchart illustrating a drive anti-slip control method for an independent four-wheel drive electric vehicle according to another embodiment of the present invention;

[0026] Figure 5 This is a reference schematic diagram illustrating the calculation of the target slip ratio according to an embodiment of the present invention;

[0027] Figure 6 This is a schematic block diagram illustrating the structure of a drive anti-slip control system for an independent four-wheel drive electric vehicle according to an embodiment of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the present invention more apparent, exemplary embodiments according to the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are merely a part of the embodiments of the present invention, and not all of the embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein. Based on the embodiments of the present invention described herein, all other embodiments obtained by those skilled in the art without inventive effort should fall within the protection scope of the present invention.

[0029] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0030] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0032] To fully understand this invention, a detailed structure will be presented in the following description to illustrate the technical solution proposed by this invention. Optional embodiments of the invention are described in detail below; however, in addition to these detailed descriptions, the invention may have other embodiments.

[0033] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0034] First, it is necessary to introduce the application scenario of the drive anti-slip control method in this application. The drive anti-slip control method is applied to an independent four-wheel drive electric vehicle, in which the four wheels of the independent four-wheel drive electric vehicle are provided with drive torque by a motor.

[0035] refer to Figure 1This application provides a drive anti-slip control method, which includes: when an electric vehicle deviates from a preset steering trajectory during steering and there are slipping wheels, controlling the slipping wheels to reduce torque until the electric vehicle returns to the preset steering trajectory.

[0036] In the above-described scheme, when an electric vehicle deviates from the preset steering trajectory and a wheel slips during steering, the torque of the slipping wheel is reduced until the electric vehicle returns to the preset steering trajectory. Compared to existing control strategies that only consider longitudinal slippage, the drive anti-slip control method disclosed in this application also considers lateral control during vehicle steering. By recognizing the vehicle's steering state, when the electric vehicle deviates from the preset steering trajectory and a wheel slips, the torque of the slipping wheel is reduced until the electric vehicle returns to the preset steering trajectory, thus maintaining neutral steering during steering, enhancing the vehicle's steering tracking ability, and improving the drive anti-slip capability of independent four-wheel drive electric vehicles. The following is a detailed description of each step with reference to the accompanying drawings.

[0037] For example, refer to Figure 1 and Figure 2 Deviating from a preset steering trajectory during a turn can include oversteering or understeering relative to the preset trajectory. During the turn, the system monitors whether the electric vehicle is oversteering or understeering relative to the preset steering trajectory. Oversteering and understeering respectively reflect the difference between the electric vehicle and the preset steering trajectory during the turn. Oversteering refers to a turn that is faster than the preset steering trajectory, for example, it can be reflected in an excessively high yaw rate. Understeering refers to a turn that is slower than the preset steering trajectory, for example, it can be reflected in an excessively low yaw rate. Various methods can be used to determine whether an electric vehicle is oversteering or understeering. One such method is described below.

[0038] For example, an electric vehicle may oversteer or understeer relative to a preset steering trajectory during a steering process, including: if the current actual yaw rate of the electric vehicle is greater than the steady-state yaw rate, the electric vehicle oversteers; if the current actual yaw rate of the electric vehicle is less than the steady-state yaw rate, the electric vehicle understeers; wherein the steady-state yaw rate is determined based on the preset steering trajectory.

[0039] For example, when determining whether an electric vehicle is oversteering or understeering, a steady-state model of the vehicle can be established based on a preset steering trajectory, and the vehicle's current steady-state yaw rate can be output. Then, the difference between the electric vehicle's current actual yaw rate and its steady-state yaw rate is compared to determine whether it is oversteering or understeering. The actual yaw rate of the electric vehicle can be calculated from its lateral acceleration. For instance, if the current actual yaw rate is greater than the steady-state yaw rate, it indicates that the steering is faster than the preset steering trajectory, and the electric vehicle is oversteering. If the current actual yaw rate is less than the steady-state yaw rate, it indicates that the steering is slower than the preset steering trajectory, and the electric vehicle is understeering. The difference between the current actual yaw rate and the steady-state yaw rate is used to control the overall steering state of the electric vehicle. It should be understood that the above only illustrates one method for determining oversteering or understeering; other methods can also be used.

[0040] Additionally, in the embodiments of this application, during the turning process, reference is made to... Figure 1 and Figure 2 In addition to monitoring the degree of deviation of the electric vehicle from the preset steering trajectory, it also monitors whether there are slipping wheels. There are several ways to monitor whether there are slipping wheels. Several methods are illustrated below.

[0041] First, refer to Figure 2 This involves obtaining vehicle-related information for electric vehicles, including at least: motor torque information and vehicle driving status information. For example, refer to... Figure 3 Vehicle-related information may include vehicle driving status information such as wheel speed of the four wheels, vehicle acceleration, wheel end dynamic load, vehicle yaw rate, and acceleration pedal travel, and may also include motor torque information such as motor input torque.

[0042] Next, refer to Figure 2 Based on vehicle information, determine if any wheels of the electric vehicle are slipping. If the result shows no slipping wheels, the electric vehicle is operating well and no anti-slip control is needed. Continue acquiring vehicle information and monitoring for slipping wheels. If slipping wheels are detected, the electric vehicle is in a slipping state, its operation is unstable, and anti-slip control is required. Figure 2As shown, specifically, if the electric vehicle is neither oversteering nor understeering relative to the preset steering trajectory (i.e., the electric vehicle has not deviated from the preset steering trajectory), then the longitudinal slip control method in the prior art can be used to prevent the slipping wheels from slipping. If the electric vehicle is oversteering or understeering relative to the preset steering trajectory (i.e., the electric vehicle has deviated from the preset steering trajectory), then the slip control method shown in this application's embodiment needs to be used to reduce the torque of the slipping wheels until the electric vehicle returns to the preset steering trajectory. Compared to existing control strategies that only consider longitudinal slip, the drive anti-slip control method shown in this application also considers lateral control during vehicle steering. By recognizing the vehicle's steering state, when the electric vehicle deviates from the preset steering trajectory and there are slipping wheels, the torque of the slipping wheels is reduced until the electric vehicle returns to the preset steering trajectory, enabling the vehicle to maintain neutral steering during steering, enhancing the vehicle's steering tracking ability, and simultaneously improving the drive anti-slip capability of independent four-wheel drive electric vehicles.

[0043] There are several ways to reduce torque on the slipping wheels of an electric vehicle when it deviates from the preset steering trajectory until the vehicle returns to the preset steering trajectory. Several methods are illustrated below.

[0044] For example, refer to Figure 2 When an electric vehicle oversteers, if any wheels are slipping, the target slip ratio of the slipping wheels is adjusted, and torque is reduced on those wheels until the oversteer stops. In other words, when an electric vehicle is oversteer and wheels are slipping, the target slip ratio of the slipping wheels is adjusted, and based on the adjusted target slip ratio and the actual slip ratio of the slipping wheels, the torque output to those wheels is reduced until the oversteer stops. The difference between the actual yaw rate and the steady-state yaw rate of the electric vehicle is determined through a mapping relationship with the target slip ratio. That is, by changing the target slip ratio, the overall steering state of the electric vehicle is controlled, mitigating the oversteer tendency and thus reducing the oversteer state.

[0045] There are various methods for adjusting the target slip ratio of a slipping wheel and controlling the reduction of torque on the slipping wheel. Several implementation methods are illustrated below. For example, one method is to adjust the target slip ratio of the slipping wheel and, based on the adjusted target slip ratio, use a motion control algorithm to control the reduction of torque on the slipping wheel. That is, after adjusting the target slip ratio of the slipping wheel, a motion control algorithm such as, but not limited to, PI, PD, and PID is used to control the reduction of torque on the slipping wheel to improve the accuracy of torque reduction.

[0046] For example, various methods can be used to adjust the target slip ratio of a slipping wheel. One method is as follows: First, calculate the current road surface adhesion coefficient and determine the basic target slip ratio of the slipping wheel based on this coefficient. Then, determine a gain coefficient (greater than 1) based on the electric vehicle's current speed and the difference between the actual yaw rate and the steady-state yaw rate. Finally, determine the adjusted target slip ratio of the slipping wheel based on the product of the basic target slip ratio and the gain coefficient. Since the gain coefficient is greater than 1, the adjusted target slip ratio is larger than the basic target slip ratio; that is, the target slip ratio has been increased. When calculating the torque output to the slipping wheel using a motion control algorithm based on the increased target slip ratio and the actual slip ratio of the slipping wheel, the calculated torque output to the slipping wheel is often smaller than before the target slip ratio was increased, thus indirectly reducing the driving torque.

[0047] There are several ways to determine the gain coefficient. For example, when determining the gain coefficient based on the electric vehicle's current speed and the difference between the actual yaw rate and the steady-state yaw rate, the following rules can be used: the higher the current speed of the electric vehicle, the higher the gain coefficient; the higher the difference between the actual yaw rate and the steady-state yaw rate, the higher the gain coefficient. Conversely, the lower the current speed of the electric vehicle, the lower the gain coefficient; the lower the difference between the actual yaw rate and the steady-state yaw rate, the lower the gain coefficient. The higher the current speed of the electric vehicle, the shorter the control time needs to be; otherwise, control convergence will be difficult to achieve. The difference between the actual yaw rate of an electric vehicle and its steady-state yaw rate is often greatest during the initial adjustment, at which point the gain coefficient is also typically at its maximum. Subsequently, as the adjustment takes effect, the difference between the actual and steady-state yaw rates decreases, leading to a gradual decrease in the gain coefficient. Finally, as the difference between the actual and steady-state yaw rates gradually equals zero, the gain coefficient decreases to 1. In other words, multiple adjustment cycles are used during the adjustment of the target slip ratio. Each adjustment cycle redefines a target slip ratio based on the adjustment effect of the previous cycle, and the adjustment continues.

[0048] For example, refer to Figure 2When an electric vehicle is understeer, if a wheel is slipping, the torque to the slipping wheel is gradually reduced until the understeer is resolved. When both understeer and slipping wheels are present, the torque output to the slipping wheel is directly reduced using a step-down torque reduction method. Understeer indicates that the steering is slower than the preset steering trajectory. After the anti-slip control is activated for the slipping wheel, the torque output to the slipping wheel is first directly reduced using a step-down torque reduction method to alleviate the understeer tendency and reduce the understeer until the understeer is resolved, thus controlling the overall steering state of the electric vehicle. This adjustment method does not calculate the torque output to the slipping wheel based on the target slip ratio and the actual slip ratio of the slipping wheel.

[0049] When understeer occurs and one wheel is slipping, the slipping wheel is usually the front wheel of the electric vehicle. Therefore, the torque output to the axle corresponding to the front wheel is typically reduced. However, it should be noted that when understeer occurs and one wheel is slipping, the slipping wheel is not necessarily limited to the front wheel. Even when the rear wheels of the electric vehicle are slipping, the same method of torque reduction can still be used. Several step-down torque reduction methods can be used when reducing the torque output to the slipping wheel. Several step-down torque reduction methods are illustrated below.

[0050] For example, controlling the slipping wheels to gradually reduce torque until the electric vehicle no longer understeers can include: determining the step gradient value for controlling the slipping wheels to gradually reduce torque based on the current speed of the electric vehicle and the difference between the actual yaw rate and the steady-state yaw rate. That is, in the process of reducing the torque output to the slipping wheels, multiple adjustment cycles are used. In each adjustment cycle, the torque is reduced once based on the previous cycle, and the difference between the torques of two adjacent adjustment cycles is the step gradient. The step gradient can be an evenly spaced step gradient or an unequally spaced step gradient. After each torque reduction, the feedback on the electric vehicle's driving state after the reduction is also monitored. If the feedback is still that the electric vehicle is understeer, the next adjustment cycle is triggered, and the torque output to the slipping wheels is reduced again directly based on the previous adjustment until the electric vehicle exits the understeer state.

[0051] For example, when determining the step gradient value for reducing torque on slipping wheels based on the current speed of the electric vehicle and the difference between the actual yaw rate and the steady-state yaw rate, the step gradient can be related to the current speed of the electric vehicle, or it can be related to the degree of understeer. For instance, the higher the current speed of the electric vehicle, the larger the step gradient value for reducing torque on slipping wheels; the larger the difference between the current actual yaw rate and the steady-state yaw rate, the greater the degree of understeer, and the larger the step gradient value for reducing torque on slipping wheels. Conversely, the lower the current speed of the electric vehicle, the smaller the step gradient value for reducing torque on slipping wheels; the smaller the degree of understeer, i.e., the smaller the difference between the current actual yaw rate and the steady-state yaw rate, the smaller the step gradient value for reducing torque on slipping wheels. The higher the current speed of the electric vehicle, the shorter the control time needs to be, otherwise it will be difficult to achieve control convergence. The difference between the actual yaw rate of an electric vehicle and its steady-state yaw rate is often the largest during the initial adjustment, and the step gradient value is also often the largest at this time. Subsequently, as the adjustment effect gradually appears, the difference between the actual yaw rate of the electric vehicle and its steady-state yaw rate will become smaller and smaller, and the step gradient value will also gradually decrease. As the difference between the actual yaw rate of the electric vehicle and its steady-state yaw rate gradually equals zero, the step gradient value gradually decreases to zero, thereby improving the accuracy of step torque reduction.

[0052] For example, refer to Figure 2 The drive anti-slip control method can further include: when there is a slipping wheel and the electric vehicle is in a longitudinal drive slip state, calculating the torque output to the slipping wheel using a PID algorithm based on the target slip rate and the actual slip rate of the electric vehicle. The longitudinal drive slip state at this time refers to a drive slip state where the electric vehicle is neither in the aforementioned understeer state nor in the aforementioned oversteer state. At this time, the torque output to the slipping wheel can be calculated using a PID algorithm based on the target slip rate and the actual slip rate of the electric vehicle, causing the slipping wheel to gradually stop slipping. It can be seen that the drive anti-slip control method shown in this application prioritizes lateral yaw control; if lateral yaw control is detected as needed, the calculated yaw control torque is output first.

[0053] For example, when calculating the torque output to the wheel in a slipping state using a PID algorithm based on the target slip ratio and the actual slip ratio of the electric vehicle, various methods can be employed. For instance, it can be achieved using an anti-saturation PID control method, where the input is the error value between the actual slip ratio and the target slip ratio, and the output is the torque calculated by the PID, as shown in the following formula:

[0054]

[0055] The system's k-th cycle, where T represents the sampling duration of the discrete system. u(k) is the result of the anti-saturation PID calculation, and K... P K i Here are the product term gain coefficient and integral term gain coefficient of the PID controller, e(k) is the slip rate error value, and f(k) is the saturation control function.

[0056] It should be noted that, during the aforementioned process of adjusting the target slip ratio or directly reducing torque in steps for the electric vehicle, if it is detected that the adjusted electric vehicle has exited the oversteering or understeering state, but the slipping wheels are still slipping, the drive anti-slip control method for the electric vehicle in the aforementioned longitudinal drive slip state can be switched to. Based on the target slip ratio and the actual slip ratio of the electric vehicle, a PID algorithm is used to calculate the torque output to the slipping wheels. The target slip ratio is no longer increased or the torque is reduced in steps.

[0057] The aforementioned anti-skid control process requires the vehicle speed parameter multiple times. There are various methods to obtain the vehicle speed. One implementation method is described below as an example.

[0058] For example, different calculation methods can be selected based on the number of wheels of the electric vehicle that are slipping. For instance, when all wheels of the electric vehicle are slipping, an acceleration integral algorithm can be used to calculate the vehicle speed; that is, when all four wheels of the electric vehicle are slipping, the acceleration integral algorithm can be used to calculate the vehicle speed. When some, but not all, of the wheels of the electric vehicle are slipping, a Kalman filter algorithm can be used to calculate the vehicle speed; that is, when 1 to 3 wheels of the electric vehicle are slipping, the Kalman filter algorithm can be used to calculate the vehicle speed. In existing TCS technologies based on electric vehicles, most lack emphasis on and development of vehicle speed estimation, which is a prerequisite for achieving precise control. This application adopts the above-mentioned vehicle speed calculation method, which can improve the accuracy of the acquired vehicle speed, addressing vehicle speed estimation and road surface recognition under conditions of all wheels slipping, and enhancing the driving anti-skid capability.

[0059] When calculating the speed of an electric vehicle using the Kalman filter algorithm, various methods can be employed. For example, the Kalman filter includes two processes: prediction and update, and contains the following five formulas:

[0060] Prediction formula:

[0061]

[0062] p k - =AP k-1A T +Q

[0063] Updated formula:

[0064] K k =(p k - )H T {H(p k - )H T +R} -1

[0065]

[0066] p k =(EK) k H)p k -

[0067] in, This is the optimal estimate from the previous moment; p is the current predicted value. k - P represents the covariance of the predicted values. k-1 K represents the covariance of the filtered output value at the previous time step. k is the Kalman gain, whose value ∈ [0,1], where 0 indicates greater confidence in the predicted value and 1 indicates greater confidence in the measured value; This is the current optimal estimate.

[0068] For example, when calculating the speed of an electric vehicle using the acceleration integral algorithm described above, various methods can be employed. For instance, the acceleration integral formula shown below can be used:

[0069] v = v0 + at

[0070] Where v is the vehicle speed calculated at the current moment, v0 is the initial value during integration, a is the current vehicle acceleration, and t is the sampling time.

[0071] There are several ways to determine the target slip ratio for each wheel. One such method is described below.

[0072] For example, the drive anti-skid control method may further include: calculating the current utilized coefficient of adhesion and the actual slip rate of each wheel of the electric vehicle; then, using a fuzzy algorithm, estimating the current fuzzy road surface adhesion coefficient of each wheel as a fuzzy factor, using the current utilized coefficient of adhesion and the actual slip rate of each wheel as fuzzy factors, and using this as the current road surface adhesion coefficient of each wheel. Subsequently, the current target slip rate of each wheel can be determined based on the current road surface adhesion coefficient of each wheel.

[0073] For example, based on vehicle-related information, the current utilization coefficient of adhesion and actual slip rate of each wheel can be calculated first. Then, a fuzzy algorithm is used, with the current utilization coefficient of adhesion and actual slip rate of each wheel as fuzzy factors, to estimate the current fuzzy road surface adhesion coefficient of each wheel. Finally, based on the road surface material and fuzzy road surface adhesion coefficient of each wheel, the target slip rate of each wheel is determined. For example, the target slip rate of each wheel can be determined by looking up a table, and the specific basis for looking up the table can be as follows: Figure 5 The curve shown is for reference, estimating the mapping relationship between vehicle speed and target slip ratio. The target slip ratio increases with increasing vehicle speed.

[0074] It should be noted that the target slip ratio obtained by the above calculation method will change after changes in the wheel's coefficient of adhesion or the actual slip ratio, and the target slip ratio can be re-determined. The target slip ratio determined by the above method is the basic target slip ratio. As mentioned above, the basic target slip ratio in the slip control process when an electric vehicle is in oversteering is determined using the above method. Based on the basic target slip ratio in controlling oversteering, a gain coefficient greater than 1 can be multiplied to obtain the target slip ratio for correcting wheel slippage during oversteering.

[0075] There are several ways to calculate the actual slip ratio of a wheel under various slip conditions. For example, the following formula can be used:

[0076]

[0077] Where Sr is the actual slip ratio, V Wheel V is the wheel speed of the wheel. vehicle This indicates the speed of the electric vehicle.

[0078] The calculation method for the current adhesion coefficient of each wheel can be obtained using various methods. One such method is described below.

[0079] There are several ways to calculate the current coefficient of adhesion for each wheel. For example, one method is as follows: First, calculate the corrected torque input to each wheel based on the current motor input torque, motor speed, motor moment of inertia, motor-to-wheel transmission ratio, and mechanical efficiency of the motor corresponding to each wheel. Then, calculate the current longitudinal driving force of each wheel based on the corrected torque and wheel radius. Finally, calculate the current coefficient of adhesion for each wheel based on the current longitudinal driving force, lateral driving force, and wheel-end vertical load. It should be understood that the above is only an example of one way to calculate the current coefficient of adhesion for a wheel; other methods can also be used.

[0080] For example, when calculating the corrected torque input to each wheel based on the current motor input torque, motor speed, motor moment of inertia, motor-to-wheel transmission ratio, and mechanical efficiency of the motor corresponding to each wheel, various methods can be used. For instance, the following formula can be used for calculation:

[0081] M actual =(M vcu -J mot *α*i ratio )*η

[0082] Among them, M actual For the corrected torque, M VCU J is the motor torque input to the motor. mot Let i be the moment of inertia of the motor. raito Let η be the transmission ratio from the motor to the wheel, and η be the mechanical efficiency. It can be seen that correcting the input motor's drive torque mainly considers the torque consumed by the rotational inertia of the rotating components from the motor to the wheel, resulting in a more accurate drive torque input from the motor to the wheel, thus improving the accuracy of subsequent anti-slip control.

[0083] For example, when calculating the current coefficient of adhesion for each wheel based on its current longitudinal driving force, lateral driving force, and wheel-end vertical load, various methods can be used. For instance, it can be calculated using the following formula:

[0084]

[0085] Among them, F x F is the longitudinal driving force, Fy is the lateral force of the tire, and F z denoted as the vertical load at the wheel end, and μ as the current coefficient of adhesion of the wheel.

[0086] For example, the above-mentioned fuzzy algorithm uses the current utilization adhesion coefficient and actual slip rate of each wheel as fuzzy factors to estimate the current fuzzy road surface adhesion coefficient of each wheel. Various methods can be employed. For instance, the fuzzy algorithm can use triangular membership functions and trapezoidal membership functions to construct the membership relationship between the actual slip rate, the utilization adhesion coefficient, and the fuzzy road surface adhesion coefficient. Specifically, the following formula can be used:

[0087]

[0088]

[0089] In the definition of fuzzy algorithms, there is a concept of membership functions used to classify the input fuzzy factors. The first function formula for f is the triangular membership function, where a and c determine the "feet" of the triangle, and parameter b determines the "peak." x represents the input fuzzy factor, and f is the curve constructed by the current mapping relationship. The second function formula for f is the trapezoidal membership formula, where a and d determine the "feet" of the trapezoid, and b and c determine the "shoulders."

[0090] The following combination Figure 3 and Figure 4 An exemplary anti-slip control process is described.

[0091] Step 401: Obtain vehicle-related information. This can be achieved by collecting vehicle-related information required for the drive anti-slip control method through vehicle sensors. This information may include wheel speeds of the four wheels, vehicle acceleration, wheel-end dynamic load, motor input drive torque, vehicle yaw rate, accelerator pedal travel, and other information.

[0092] Step 402: Determine if all four wheels are slipping. If not all wheels are slipping, use Kalman filtering to calculate the vehicle speed; if all wheels are slipping, use acceleration integral to calculate the vehicle speed.

[0093] Step 403: Calculate the torque consumption of each rotating component of the motor during transmission, subtract the consumed torque from the input torque, and obtain the actual input drive torque at the corrected wheel end.

[0094] Step 404: Based on the wheel speed of the slipping wheel and the speed of the electric vehicle, calculate the actual slip ratio of each wheel.

[0095] Step 405: Using the longitudinal driving force at the wheel end, the lateral force of the tire, and the vertical load at the wheel end, calculate the adhesion coefficient of the four wheels according to the adhesion ellipse theory.

[0096] Step 406: Using the fuzzy inference system, the triangular membership function and the trapezoidal membership function are used to estimate the current fuzzy road surface adhesion coefficient based on the current actual slip rate and the adhesion coefficient.

[0097] Step 407: Determine the optimal target slip ratio under the current fuzzy adhesion coefficient based on the fuzzy road adhesion coefficient and vehicle speed.

[0098] Step 408: Calculate the vehicle's yaw rate based on the lateral acceleration, and determine the current driving state of the electric vehicle based on the vehicle's yaw rate and the actual sliding state.

[0099] Step 409: When the wheels are in a state of understeer and slipping, based on the degree of understeer and the current vehicle speed, obtain the step gradient value for reducing the slipping wheels in the current state, and use the step torque reduction method to reduce the driving torque of each wheel.

[0100] Step 410: When the wheels are in a state of oversteering and slippage, the target slip ratio is adjusted based on the current degree of oversteering and the current vehicle speed. The target slip ratio is then input into the motion control algorithm of the longitudinal slip control module. The motion control algorithm is used to determine the torque of each wheel, thereby reducing torque.

[0101] Step 411: When a wheel is in a longitudinal drive slip state, that is, neither understeering nor oversteering and is slipping, the torque of the wheel is calculated by using a PID control algorithm based on the principle of controlling the actual slip rate of each slipping wheel to near the optimal target slip rate.

[0102] refer to Figure 3 Dedicated calculation modules can be established for vehicle speed estimation, drive torque correction, road surface adhesion coefficient estimation, slip ratio calculation, understeer control, oversteer control, and longitudinal slip control. These modules are generated to implement their respective functions and are responsible for vehicle speed estimation, drive torque correction, road surface adhesion coefficient estimation, slip ratio calculation, understeer control, oversteer control, and longitudinal slip control, respectively. Specific calculation methods can be found in the descriptions of the corresponding sections above. Figure 3 The yaw control module can be divided into an understeer control module and an oversteer control module. The understeer control module determines whether the vehicle is understeer based on yaw and lateral acceleration requirements. If understeer is detected, a torque reduction strategy is implemented on the corresponding axle using a step-down torque reduction method. The oversteer module also determines whether the vehicle is oversteer based on yaw and lateral acceleration requirements. If oversteer is detected, the target slip ratio is changed to reduce the oversteer. Specifically, vehicle speed, slip ratio, and road adhesion coefficient can be input into the longitudinal slip control within the understeer and oversteer control modules. Output torque processing modules can also be established for understeer, oversteer, and longitudinal slip control to specifically calculate the torque for each wheel.

[0103] The output torque processing module may include a state arbitration module and a torque arbitration module. The state arbitration module monitors whether there are wheels in a slipping state and activates the aforementioned functional modules when a wheel is slipping. The torque arbitration judgment module arbitrates the state and torque output of understeer control, oversteer control, and longitudinal slip control, prioritizing torque output for lateral yaw control.

[0104] In the various embodiments shown above, when an electric vehicle deviates from a preset steering trajectory and a wheel slips during steering, the torque of the slipping wheel is reduced until the electric vehicle returns to the preset steering trajectory. Compared to existing control strategies that only consider longitudinal slip, the drive anti-slip control method shown in this application also considers lateral control during vehicle steering. By recognizing the vehicle's steering state, when the electric vehicle deviates from the preset steering trajectory and a wheel slips, the torque of the slipping wheel is reduced until the electric vehicle returns to the preset steering trajectory, thus maintaining neutral steering during steering, enhancing the vehicle's steering tracking ability, and improving the drive anti-slip capability of independent four-wheel drive electric vehicles.

[0105] In addition, this application embodiment also provides a drive anti-slip control system, which is applied to an independent four-wheel drive electric vehicle. The drive anti-slip control system includes a storage medium and a processor. The storage medium stores a computer program that is run by the processor. When the computer program is run by the processor, it causes the processor to execute any of the drive anti-slip control methods described above.

[0106] Figure 6 A schematic block diagram of a drive anti-slip control system 100 according to an embodiment of this application is shown. Figure 6 As shown, the drive anti-skid control system 100 according to an embodiment of this application may include a storage medium 110 and a processor 120. The storage medium 110 stores a computer program executed by the processor 120. When the computer program is executed by the processor 120, the processor 120 performs the drive anti-skid control method described above according to an embodiment of this application. Those skilled in the art can understand the specific operation of the drive anti-skid control system 100 deployment device according to the embodiments of this application in conjunction with the foregoing content; for the sake of brevity, it will not be described in detail here.

[0107] Furthermore, embodiments of this application also provide a storage medium storing a computer program that, when executed, performs any of the aforementioned drive anti-slip control methods. This storage medium may, for example, include a memory card of a smartphone, a storage component of a tablet computer, a hard disk of a personal computer, a read-only memory (ROM), an erasable programmable read-only memory (EPROM), a portable compact disc read-only memory (CD-ROM), a USB memory, or any combination of the aforementioned storage media. A computer-readable storage medium may be any combination of one or more computer-readable storage media.

[0108] Furthermore, this application embodiment also provides an independent four-wheel drive electric vehicle, which includes: a vehicle body and any of the aforementioned drive anti-slip control systems disposed on the vehicle body. The vehicle body may include structures such as a frame, wheels, transmission, and steering wheel. Any of the drive anti-slip control systems shown above is disposed on the vehicle body. This drive anti-slip control system can be a module with both computing and storage functions, disposed on the vehicle body's on-board terminal. Alternatively, the drive anti-slip control system can be an independent control module disposed in the vehicle body's domain control system.

[0109] The present invention has been described through the above embodiments. However, it should be understood that the above embodiments are for illustrative purposes only and are not intended to limit the invention to the scope of the described embodiments. Furthermore, those skilled in the art will understand that the present invention is not limited to the above embodiments, and many more variations and modifications can be made based on the teachings of the present invention, all of which fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A drive anti-slip control method, applied to an independent four-wheel drive electric vehicle, characterized in that, include: When the electric vehicle deviates from the preset steering trajectory during steering and there are slipping wheels, the torque of the slipping wheels is reduced until the electric vehicle returns to the preset steering trajectory. The electric vehicle deviating from the preset steering trajectory during the steering process includes: the electric vehicle turning too much or too little relative to the preset steering trajectory during the steering process; When the electric vehicle is understeering, if there are slipping wheels, the torque of the slipping wheels is controlled to decrease gradually until the electric vehicle is no longer understeering. Controlling the torque of the slipping wheels by decreasing gradually includes: determining a step gradient value for controlling the torque of the slipping wheels based on the current speed of the electric vehicle and the difference between the actual yaw rate and the steady-state yaw rate; wherein, the higher the current speed of the electric vehicle, the larger the step gradient value for controlling the torque of the slipping wheels; the larger the difference between the current actual yaw rate and the steady-state yaw rate, the larger the step gradient value for controlling the torque of the slipping wheels. When the electric vehicle oversteers, if there are slipping wheels, the target slip ratio of the slipping wheels is adjusted, and the torque of the slipping wheels is reduced until the electric vehicle no longer oversteers; adjusting the target slip ratio of the slipping wheels and reducing the torque of the slipping wheels includes: adjusting the target slip ratio of the slipping wheels, and using a motion control algorithm based on the adjusted target slip ratio to control the torque reduction of the slipping wheels; The adjustment of the target slip ratio of the slipping wheel includes: calculating the current road surface adhesion coefficient, and determining the basic target slip ratio of the slipping wheel based on the current road surface adhesion coefficient; determining a gain coefficient based on the current speed of the electric vehicle and the difference between the actual yaw rate and the steady-state yaw rate; wherein the gain coefficient is greater than 1, the higher the current speed of the electric vehicle, the higher the gain coefficient, and the higher the difference between the actual yaw rate and the steady-state yaw rate, the higher the gain coefficient; and determining the adjusted target slip ratio of the slipping wheel based on the product of the basic target slip ratio and the gain coefficient.

2. The drive anti-slip control method as described in claim 1, characterized in that, The electric vehicle over-steering or under-steering relative to the preset steering trajectory during steering includes: If the current actual yaw rate of the electric vehicle is greater than the steady-state yaw rate, then the electric vehicle is oversteering. If the current actual yaw rate of the electric vehicle is less than the steady-state yaw rate, then the electric vehicle is understeering. The steady-state yaw rate is determined based on the preset steering trajectory.

3. The drive anti-slip control method as described in claim 1, characterized in that, Also includes: When all wheels of the electric vehicle are the slipping wheels, the vehicle speed is calculated using an acceleration integral algorithm; When some of the wheels of the electric vehicle are the slipping wheels, the Kalman filter algorithm is used to calculate the speed of the electric vehicle.

4. The drive anti-slip control method as described in claim 1, characterized in that, Also includes: Calculate the current coefficient of adhesion and actual slip ratio of each wheel of the electric vehicle; A fuzzy algorithm is used to estimate the current fuzzy road surface adhesion coefficient of each wheel by using the current utilization adhesion coefficient and actual slip rate of each wheel as fuzzy factors, and then using this as the current road surface adhesion coefficient of each wheel.

5. The drive anti-slip control method as described in claim 4, characterized in that, The calculation of the current coefficient of adhesion for each wheel includes: Based on the current motor input torque, motor speed, motor moment of inertia, motor-to-wheel transmission ratio, and mechanical efficiency of the motor corresponding to each wheel, calculate the corrected torque currently input to each wheel; Calculate the current longitudinal driving force for each wheel based on the corrected torque and wheel radius of each wheel; Calculate the current coefficient of adhesion for each wheel based on its current longitudinal driving force, lateral driving force, and wheel-end vertical load.

6. A drive anti-slip control system, applied to an independent four-wheel drive electric vehicle, characterized in that, include: A storage medium and a processor, wherein the storage medium stores a computer program executed by the processor, the computer program, when executed by the processor, causes the processor to perform the drive anti-slip control method as described in any one of claims 1 to 5.

7. A storage medium, characterized in that, The storage medium stores a computer program, which, when running, executes the drive anti-slip control method as described in any one of claims 1 to 5.

8. An independent four-wheel drive electric vehicle, characterized in that, include: Vehicle body; The drive anti-skid control system as described in claim 6 is installed on the vehicle body.

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