Driving anti-skid control method and system and independent four-wheel-drive electric automobile

Abstract

The invention discloses a driving anti-skid control method and system and an independent four-wheel-drive electric automobile, and the driving anti-skid control method comprises the steps that when the electric automobile deviates from a preset steering track in the steering process and has slipping wheels, the slipping wheels are controlled to reduce the torque until the electric automobile recovers to the preset steering track. According to the driving anti-skid control method, lateral control in the vehicle steering process is further considered, through recognition of the vehicle steering state, when the electric vehicle deviates from the preset steering track and the slipping wheels exist, torque reduction is conducted on the slipping wheels till the electric vehicle recovers to the preset steering track, and therefore the driving anti-skid control method is suitable for the electric vehicle. Neutral steering of the vehicle is maintained in the steering process, the steering tracking capacity of the vehicle is enhanced, and meanwhile the driving anti-skid capacity of the independent four-wheel-drive electric vehicle is improved.

Description

Technical Field

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

[0002] In the Traction Control System (TCS) based on traditional fuel vehicles, the vehicle's slip rate on low-adhesion roads is reduced by limiting the wheel speed through the brake caliper, so that the wheel is kept near the optimal slip rate, thereby enabling the vehicle to achieve the best acceleration effect on the current low-adhesion road. If the engine output torque is large and the wheel speed is reduced by the brake caliper alone, the drive anti-skid control system will also actively control the engine's throttle opening to control the engine's output torque and reduce the degree of wheel slip.

[0003] With the development of electric vehicles, electric vehicles are gradually replacing traditional fuel vehicles and becoming the development trend of passenger vehicles. Since the motor has a more sensitive response characteristic than the engine, the functional advantages of TCS can be further exerted, especially for independent four-wheel drive electric vehicles. However, the current TCS development of independent four-wheel drive electric vehicles only considers the control of longitudinal slip, resulting in poor steering tracking ability of the vehicle during steering. Summary of the invention

[0004] The present application is proposed to solve at least one of the above problems. According to a first aspect of the present application, a driving anti-skid control method is provided, and the driving anti-skid control method is applied to an independent four-wheel drive electric vehicle, and the driving anti-skid control method comprises: when the electric vehicle deviates from a preset steering trajectory during steering and there is a slipping wheel, controlling the slipping wheel to reduce torque until the electric vehicle restores the preset steering trajectory.

[0005] In one embodiment of the present application, the electric vehicle deviates from a preset steering trajectory during the steering process, including: the electric vehicle oversteers or understeers relative to the preset steering trajectory during the steering process.

[0006] In one embodiment of the present application, the electric vehicle oversteers or understeers relative to the preset steering trajectory during the steering process, including: if the current actual yaw velocity of the electric vehicle is greater than the yaw velocity in a steady state, the electric vehicle oversteers; if the current actual yaw velocity of the electric vehicle is less than the yaw velocity in a steady state, the electric vehicle understeers; wherein the yaw velocity in a steady state is determined based on the preset steering trajectory.

[0007] In one embodiment of the present application, when the electric vehicle understeers, if there is a slipping wheel, the slipping wheel is controlled to step-down torque until the electric vehicle no longer understeers.

[0008] In one embodiment of the present application, the step-by-step torque reduction of the slipping wheel is controlled until the electric vehicle no longer understeers, comprising: determining a step gradient value for controlling the step-by-step torque reduction of the slipping wheel according to a current speed of the electric vehicle and a difference between an actual yaw angular velocity and a yaw angular velocity in a steady state.

[0009] In one embodiment of the present application, the step gradient value for controlling the step torque reduction of the slipping wheel is determined based on the current vehicle speed of the electric vehicle and the difference between the actual yaw angular velocity and the yaw angular velocity in a steady state, including: the greater the current vehicle speed of the electric vehicle, the greater the step gradient value for controlling the step torque reduction of the slipping wheel; the greater the difference between the current actual yaw angular velocity of the electric vehicle and the yaw angular velocity in a steady state, the greater the step gradient value for controlling the step torque reduction of the slipping wheel.

[0010] In one embodiment of the present application, when the electric vehicle oversteers, if there is a slipping wheel, the target slip rate of the slipping wheel is adjusted, and the slipping wheel is controlled to reduce torque until the electric vehicle no longer oversteers.

[0011] In one embodiment of the present application, adjusting the target slip rate of the slipping wheel and controlling the slipping wheel to reduce torque include: adjusting the target slip rate of the slipping wheel, and based on the adjusted target slip rate, using a motion control algorithm to control the slipping wheel to reduce torque.

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

[0013] In one embodiment of the present application, the gain coefficient is determined based on the current vehicle speed of the electric vehicle and the difference between the actual yaw angular velocity and the yaw angular velocity in a steady state, including: the greater the current vehicle speed of the electric vehicle, the greater the gain coefficient; the greater the difference between the actual yaw angular velocity and the yaw angular velocity in a steady state, the greater the gain coefficient.

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

[0015] In one embodiment of the present application, the drive anti-skid control method also includes: calculating the currently utilized adhesion coefficient and the actual slip rate of each wheel of the electric vehicle; using a fuzzy algorithm, taking the currently utilized adhesion coefficient and the actual slip rate of each wheel as fuzzy factors, and estimating the current fuzzy road adhesion coefficient of each wheel as the current road adhesion coefficient of each wheel.

[0016] In one embodiment of the present application, the calculation of the current utilization adhesion coefficient of each wheel includes: calculating the corrected torque currently input to each wheel based on the current motor input torque, motor speed, motor rotational 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 of each wheel; calculating the current utilization adhesion coefficient of each wheel based on the current longitudinal driving force, lateral driving force, and wheel-end vertical load of each wheel.

[0017] According to the second aspect of the present application, a drive anti-skid control system is also provided, which is applied to an independent four-wheel drive electric vehicle. The drive anti-skid control system includes: a storage medium and a processor, wherein a computer program executed by the processor is stored on the storage medium, and when the computer program is executed by the processor, the processor executes any one of the above-mentioned drive anti-skid control methods.

[0018] According to a third aspect of the present application, a storage medium is further provided, on which a computer program is stored. When the computer program is run, it executes any one of the above-mentioned drive anti-skid control methods.

[0019] According to a fourth aspect of the present application, an independent four-wheel drive electric vehicle is also provided, comprising: a vehicle body, and any one of the above-mentioned drive anti-skid control systems arranged on the vehicle body.

[0020] According to the drive anti-skid control method and system thereof, and the independent four-wheel drive electric vehicle provided by the embodiments of the present application, when the electric vehicle deviates from the preset steering trajectory and there is a slipping wheel during the steering process, the slipping wheel is controlled to reduce torque until the electric vehicle restores the preset steering trajectory. Compared with the existing control strategy that only considers longitudinal slip, the drive anti-skid control method shown in the present application also considers lateral control during the vehicle steering process. By identifying the vehicle steering state, when the electric vehicle deviates from the preset steering trajectory and there is a slipping wheel, the slipping wheel is reduced in torque until the electric vehicle restores to the preset steering trajectory, so that the vehicle maintains neutral steering during the steering process, enhances the vehicle's steering tracking ability, and at the same time improves the drive anti-skid ability of the independent four-wheel drive electric vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

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

[0023] Figure 2 This is a flow chart of a driving anti-skid control method for an independent four-wheel drive electric vehicle according to another embodiment of the present invention;

[0024] Figure 3 A schematic block diagram of the calculation process of a driving anti-skid control method for an independent four-wheel drive electric vehicle according to another embodiment of the present invention;

[0025] Figure 4 This is a flow chart of a driving anti-skid control method for an independent four-wheel drive electric vehicle according to another embodiment of the present invention;

[0026] Figure 5 A reference schematic diagram for calculating a target slip rate according to an embodiment of the present invention;

[0027] Figure 6 The present invention is a schematic structural block diagram of a driving anti-skid control system for an independent four-wheel drive electric vehicle according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present invention more obvious, the exemplary embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments of the present invention, and 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 in the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the protection scope of the present invention.

[0029] In the following description, a large number of specific details are provided to provide a more thorough understanding of the present invention. However, it is apparent to those skilled in the art that the present invention can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present invention, some technical features well known in the art are not described.

[0030] It should be understood that the present invention can be implemented in different forms and should not be interpreted as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make the disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0031] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present invention. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "consisting of" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0032] In order to fully understand the present invention, a detailed structure will be proposed in the following description to illustrate the technical solution proposed by the present invention. The optional embodiments of the present invention are described in detail as follows, but in addition to these detailed descriptions, the present invention may also have other implementations.

[0033] Some embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

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

[0035] refer to Figure 1An embodiment of the present application provides a drive anti-skid control method, which includes: when an electric vehicle deviates from a preset steering trajectory during steering and there is a slipping wheel, controlling the slipping wheel to reduce torque until the electric vehicle restores the preset steering trajectory.

[0036] In the above scheme, when the electric vehicle deviates from the preset steering trajectory and there are slipping wheels during the steering process, the slipping wheels are controlled to reduce torque until the electric vehicle restores the preset steering trajectory. Compared with the existing control strategy that only considers longitudinal slip, the drive anti-skid control method shown in the present application also considers lateral control during the vehicle steering process. By identifying the vehicle steering state, when the electric vehicle deviates from the preset steering trajectory and there are slipping wheels, the slipping wheels are reduced in torque until the electric vehicle restores to the preset steering trajectory, so that the vehicle maintains neutral steering during the steering process, enhances the vehicle's steering tracking ability, and at the same time improves the drive anti-skid ability of the independent four-wheel drive electric vehicle. The above steps are described in detail below in conjunction with the accompanying drawings.

[0037] Exemplary, reference Figure 1 and Figure 2 , the deviation of the electric vehicle from the preset steering trajectory during the steering process may include: the electric vehicle oversteers or understeers relative to the preset steering trajectory during the steering process. During the steering process of the electric vehicle, monitor whether the electric vehicle oversteers or understeers relative to the preset steering trajectory. Among them, oversteer and understeer respectively reflect the difference between the electric vehicle and the preset steering trajectory during the steering process. Oversteer refers to a steering degree that is faster than the steering degree of the preset steering trajectory, for example, it can be reflected in a yaw angular velocity that is too large. Understeer refers to a steering degree that is slower than the steering degree of the preset steering trajectory, for example, it can be reflected in a yaw angular velocity that is too small. When judging whether the electric vehicle is in an oversteer state or an understeer state, a variety of methods can be used to judge. The following is an exemplary introduction to a judgment method.

[0038] Exemplarily, the electric vehicle oversteers or understeers relative to a preset steering trajectory during the steering process, including: if the current actual yaw angular velocity of the electric vehicle is greater than the yaw angular velocity in a steady state, the electric vehicle oversteers; if the current actual yaw angular velocity of the electric vehicle is less than the yaw angular velocity in a steady state, the electric vehicle understeers; wherein the yaw angular velocity in a steady state is determined based on the preset steering trajectory.

[0039] Exemplarily, when judging whether the electric vehicle is in an oversteering state or an understeering state, a steady-state model of the vehicle can be established according to a preset steering trajectory, and the current steady-state yaw rate of the vehicle can be output. Afterwards, the size between the current actual yaw rate of the electric vehicle and the steady-state yaw rate is judged to judge whether it is in an oversteering state or an understeering state. Among them, the actual yaw angle of the electric vehicle can be calculated by the lateral acceleration of the electric vehicle. For example, if the current actual yaw rate of the electric vehicle is greater than the steady-state yaw rate, it means that the steering degree is faster than the preset steering trajectory, and the electric vehicle is in an oversteering state. If the current actual yaw rate of the electric vehicle is less than the steady-state yaw rate, it means that the steering degree is slower than the preset steering trajectory, and the electric vehicle is in an understeering state. The steering state of the entire electric vehicle is controlled by the difference between the current actual yaw rate of the electric vehicle and the steady-state yaw rate. It should be understood that the above only shows one way to judge the oversteering state or the understeering state, and other judgment methods can also be used in addition.

[0040] In addition, in the steering process of the embodiment of the present application, 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 many ways to monitor whether there are slipping wheels. Several methods are introduced as examples below.

[0041] First, refer to Figure 2 , obtain vehicle-related information of the electric vehicle, the vehicle-related information at least includes: motor torque information and vehicle driving state information. For example, refer to Figure 3 The vehicle-related information may include vehicle driving status information such as the wheel speed of the four wheels, vehicle acceleration, wheel-end dynamic load, vehicle yaw angular velocity, accelerator pedal travel, etc., and may also include motor torque information such as motor input torque.

[0042] Next, refer to Figure 2 , based on the vehicle-related information, determine whether the electric vehicle has a slipping wheel. If the result of the judgment is that the electric vehicle does not have a slipping wheel, it means that the current operation state of the electric vehicle is good, and there is no need to perform drive anti-skid control on the electric vehicle. You can continue to obtain vehicle-related information of the electric vehicle and continue to monitor whether the electric vehicle has a slipping wheel. If it is detected that the electric vehicle has a slipping wheel, it means that the current electric vehicle is in a slipping state, the operation state of the electric vehicle is unstable, and drive anti-skid control is required for the electric vehicle. Figure 2As shown, specifically, if the electric vehicle has neither oversteering nor understeering relative to the preset steering trajectory at this time, that is, the electric vehicle has not deviated from the preset steering trajectory, the longitudinal slip control in the prior art can be used to prevent the slipping wheels from slipping. If the electric vehicle has oversteering or understeering relative to the preset steering trajectory at this time, that is, the electric vehicle has deviated from the preset steering trajectory, it is necessary to adopt the slip control method shown in the embodiment of the present application to reduce the torque of the slipping wheels until the electric vehicle restores the preset steering trajectory. Compared with the existing control strategy that only considers longitudinal slip, the drive anti-skid control method shown in the present application also considers the lateral control during the vehicle steering process. By identifying the vehicle steering state, when the electric vehicle deviates from the preset steering trajectory and there is a slipping wheel, the slipping wheel is reduced in torque 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-skid ability of the independent four-wheel drive electric vehicle.

[0043] When the electric vehicle deviates from the preset turning track and there is a slipping wheel, there may be multiple ways to reduce the torque of the slipping wheel until the electric vehicle returns to the preset turning track. Several ways are exemplarily introduced below.

[0044] Exemplary, reference Figure 2 , when the electric vehicle oversteers, if there is a slipping wheel, the target slip rate of the slipping wheel is adjusted, and the slipping wheel is controlled to reduce torque until the electric vehicle no longer oversteers. That is, when the electric vehicle is in an oversteer state and there is a slipping wheel, the target slip rate of the slipping wheel is adjusted, and based on the adjusted target slip rate and the actual slip rate of the slipping wheel, the torque output to the slipping wheel is reduced until the electric vehicle no longer oversteers. The difference between the actual yaw rate of the electric vehicle and the yaw rate in the steady state is determined by a mapping relationship with the target slip rate of the electric vehicle. That is, by changing the target slip rate, the steering state of the entire electric vehicle is controlled, the oversteer tendency is alleviated, and the oversteer state of the vehicle is reduced.

[0045] When adjusting the target slip rate of the slipping wheel and controlling the slipping wheel to reduce torque, multiple methods can be used. Several implementation methods are introduced as examples below. For example, the following method can be used: adjusting the target slip rate of the slipping wheel, and based on the adjusted target slip rate, using a motion control algorithm to control the slipping wheel to reduce torque. That is, after adjusting the target slip rate of the slipping wheel, a motion control algorithm such as but not limited to PI, PD, PID, etc. is used to control the slipping wheel to reduce torque, so as to improve the accuracy of torque reduction.

[0046] Exemplarily, when adjusting the target slip rate of the slipping wheel, a variety of methods can be used. For example, the following method can be used: first, calculate the current road adhesion coefficient, and determine the basic target slip rate of the slipping wheel according to the current road adhesion coefficient; then, determine the gain coefficient according to the current speed of the electric vehicle and the difference between the actual yaw rate and the yaw rate in the steady state, wherein the gain coefficient is greater than 1; and then determine the adjusted target slip rate of the slipping wheel according to the product of the basic target slip rate and the gain coefficient. Since the gain coefficient is greater than 1, the adjusted target slip rate is larger than the basic target slip rate, that is, the target slip rate is increased. When the torque output to the slipping wheel is calculated based on the increased target slip rate and the actual slip rate of the slipping wheel using the motion control algorithm, the calculated torque value output to the slipping wheel is often smaller than that before the target slip rate is increased, thereby achieving the purpose of indirectly reducing the driving torque.

[0047] When determining the gain coefficient, a variety of methods can be used. For example, when determining the gain coefficient based on the current speed of the electric vehicle and the difference between the actual yaw rate and the yaw rate in a steady state, the following rule can be used: 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 yaw rate in a steady state, the greater the gain coefficient. Conversely, the smaller the current speed of the electric vehicle, the smaller the gain coefficient can be; the smaller the difference between the actual yaw rate and the yaw rate in a steady state, the smaller the gain coefficient. The greater the current speed of the electric vehicle, the shorter the control time needs to be, otherwise it is difficult to achieve control convergence. The difference between the actual yaw rate of the electric vehicle and the yaw rate in the steady state is often the largest during the initial adjustment, and the gain coefficient is often the largest at this time; afterwards, as the effect of the adjustment gradually appears, the difference between the actual yaw rate of the electric vehicle and the yaw rate in the steady state will become smaller and smaller, so the gain coefficient will gradually decrease, and as the difference between the actual yaw rate of the electric vehicle and the yaw rate in the steady state gradually equals zero, the gain coefficient will gradually decrease to 1. That is, multiple adjustment cycles are used in the process of adjusting the target slip rate, and each adjustment cycle re-determines a target slip rate based on the adjustment effect of the previous adjustment cycle, and continues to adjust.

[0048] Exemplary, reference Figure 2When the electric vehicle is understeering, if there is a slipping wheel, the slipping wheel is controlled to step down the torque until the electric vehicle no longer understeers. When the electric vehicle is in understeering and there is a slipping wheel, the torque output to the slipping wheel is directly reduced by stepping the torque reduction method. The understeering state indicates that the steering degree is slower than the preset steering trajectory. After the electric vehicle starts the anti-skid control when the slipping wheel appears, the stepping torque reduction method is first directly used to reduce the torque output to the slipping wheel to alleviate the understeering trend, thereby reducing the understeering state of the vehicle until the electric vehicle no longer understeers, and the steering state of the entire electric vehicle is controlled. At this time, the adjustment method does not calculate the torque output to the slipping wheel through the target slip rate and the actual slip rate of the slipping wheel.

[0049] When an understeer state occurs and a wheel is in a slipping state, the slipping wheel is often located at the front wheel of the electric vehicle, so at this time, the torque output to the shaft corresponding to the front wheel of the electric vehicle is often reduced. However, it should be noted that when an understeer state occurs and a wheel is in a slipping state, the slipping wheel is not absolutely limited to the front wheel of the electric vehicle. When the rear wheel of the electric vehicle slips, the above-mentioned method can still be used for reduction. When reducing the torque output to the slipping wheel, a variety of step-by-step torque reduction methods can be used for reduction. The following is an illustrative introduction to several step-by-step torque reduction methods.

[0050] Exemplarily, controlling the slipping wheel to step down the torque until the electric vehicle no longer understeers may include: determining the step gradient value when controlling the slipping wheel to step down the torque according to the current speed of the electric vehicle and the difference between the actual yaw rate and the yaw rate in the steady state. That is, in the process of reducing the torque output to the slipping wheel, multiple adjustment cycles are used, each adjustment cycle reduces the torque once on the basis of the previous cycle, and the difference between the torques of two adjacent adjustment cycles is the step gradient. The step gradient may adopt a step gradient of equal interval size or a step gradient of unequal interval size. Each time the torque is reduced, the feedback of the driving state of the electric vehicle after the reduction is also monitored. If the feedback is still that the electric vehicle is understeering, the next adjustment cycle is triggered, and the torque output to the slipping wheel is further reduced directly on the basis of the previous adjustment until the electric vehicle exits the understeering state.

[0051] Exemplarily, when determining the step gradient value for stepping down the torque of the wheel that is slipping according to the current speed of the electric vehicle and the difference between the actual yaw rate and the yaw rate in a steady state, the step gradient can be related to the current speed of the electric vehicle and can also be related to the degree of understeering. For example, the greater the current speed of the electric vehicle, the greater the step gradient value for stepping down the torque of the wheel that is slipping; the greater the difference between the current actual yaw rate of the electric vehicle and the yaw rate in a steady state, the greater the degree of understeering, and the greater the step gradient value for stepping down the torque of the wheel that is slipping. Conversely, the smaller the current speed of the electric vehicle, the smaller the step gradient value for reducing the torque output to the slipping wheel; the smaller the degree of understeering of the electric vehicle, that is, the smaller the difference between the current actual yaw rate of the electric vehicle and the yaw rate in a steady state, the smaller the step gradient value for reducing the torque output to the slipping wheel. The greater the current speed of the electric vehicle, the shorter the control time needs to be, otherwise it is difficult to achieve control convergence. The difference between the actual yaw rate of the electric vehicle and the yaw rate in the steady state is often the largest during the initial adjustment, and the step gradient value at this time is often also the largest; afterwards, as the effect of the adjustment gradually appears, the difference between the actual yaw rate of the electric vehicle and the yaw rate in the steady state will become smaller and smaller, so that the step gradient value will gradually decrease, and as the difference between the actual yaw rate of the electric vehicle and the yaw rate in the steady state gradually becomes equal to zero, the step gradient value gradually decreases to zero, thereby improving the accuracy of the step torque reduction.

[0052] Exemplary, reference Figure 2 , the drive anti-skid control method may further include: when there is a slipping wheel and the electric vehicle is in a longitudinal drive slip state, based on the target slip rate and the actual slip rate of the electric vehicle, a PID algorithm is used to calculate the torque output to the slipping wheel. The longitudinal drive slip state at this time refers to a drive slip state in which the electric vehicle is neither in the above-mentioned understeering state nor in the above-mentioned oversteering state. At this time, the PID algorithm can be used to calculate the torque output to the slipping wheel based on the target slip rate and the actual slip rate of the electric vehicle, so that the slipping wheel gradually stops slipping. It can be seen that the drive anti-skid control method shown in the embodiment of the present application gives priority to lateral yaw control. If it is recognized that lateral yaw control is currently required, the yaw control calculated torque is output first.

[0053] For example, when the PID algorithm is used to calculate the torque output to the wheel in the slipping state based on the target slip rate and the actual slip rate of the electric vehicle, multiple methods can be used. For example, it can be implemented by an anti-saturation PID control method, where the input is the error value between the actual slip rate and the target slip rate, and the output is the torque calculated by PID, and the formula is as shown below:

[0054]

[0055] The kth cycle of the system, T represents the sampling time of the discrete system. u(k) is the calculation result of the anti-saturation PID, K P , K i are the product term gain coefficient and integral term gain coefficient of PID, e(k) is the slip rate error value, and f(k) is the saturation control function.

[0056] It should be noted that, during the process of adjusting the target slip rate or directly reducing the torque in steps, if it is detected that the adjusted electric vehicle exits the oversteering state or understeering state, but the slipping wheel is still slipping, the drive anti-skid control method when the electric vehicle is in the longitudinal drive slip state can be switched to calculate the torque output to the slipping wheel based on the target slip rate and the actual slip rate of the electric vehicle using the PID algorithm. The target slip rate is no longer increased or the torque is no longer reduced by stepping the torque down.

[0057] In the above anti-skid control process, the speed parameter of the electric vehicle is needed many times. There are many ways to obtain the speed of the electric vehicle. An implementation method is introduced as follows.

[0058] Exemplarily, different calculation methods can be selected according to the number of wheels in the slipping state of the electric vehicle. For example, when all wheels of the electric vehicle are in a slipping state, the acceleration integral algorithm can be used to calculate the speed of the electric vehicle, that is, when all four wheels of the electric vehicle are in a slipping state, the acceleration integral algorithm can be used to calculate the speed of the electric vehicle. When some but not all wheels of the electric vehicle are in a slipping state, the Kalman filter algorithm is used to calculate the speed of the electric vehicle, that is, when 1 to 3 wheels of the electric vehicle are in a slipping state, the Kalman filter algorithm can be used to calculate the speed of the electric vehicle. In the existing TCS technology based on electric vehicles, most of them lack the attention and development of vehicle speed estimation, and vehicle speed estimation is the premise for achieving precise control. The present application adopts the above-mentioned vehicle speed calculation method, which can improve the accuracy of the acquired vehicle speed, so as to cope with the vehicle speed estimation and road surface recognition under the slipping of all wheels, and improve the driving anti-skid capability.

[0059] Among them, when the Kalman filter algorithm is used to calculate the speed of the electric vehicle, multiple methods can be used. For example, the Kalman filter includes two processes: prediction and update. There are five formulas as follows:

[0060] Prediction formula:

[0061]

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

[0063] Update 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, is the optimal estimate at the previous moment; is the current predicted value; p k - is the covariance of the predicted value; P k-1 is the covariance of the filter output value at the previous moment; K k is the Kalman gain, whose value ∈[0,1], 0 means more confidence in the predicted value, and 1 means more confidence in the measured value; is the current best estimate.

[0068] Exemplarily, when the acceleration integral algorithm is used to calculate the speed of the electric vehicle, multiple methods may be used. For example, the acceleration integral formula shown below may be used:

[0069] v=v0+at

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

[0071] When determining the target slip rate of each wheel, multiple methods may be used, and one determination method is exemplarily introduced below.

[0072] Exemplarily, the driving anti-skid control method may further include: calculating the current utilization adhesion coefficient and actual slip rate of each wheel of the electric vehicle; then, using a fuzzy algorithm, taking the current utilization adhesion coefficient and actual slip rate of each wheel as fuzzy factors, estimating the current fuzzy road adhesion coefficient of each wheel as the current road adhesion coefficient of each wheel. Then, the current target slip rate of each wheel may be determined according to the current road adhesion coefficient of each wheel.

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

[0074] It should be noted that the target slip rate obtained by the above calculation method will also change after the utilization adhesion coefficient or actual slip rate of the wheel changes, and the target slip rate can be re-determined. The target slip rate determined by the above method is the basic target slip rate. As mentioned above, the basic target slip rate in the slip control process when the electric vehicle is in oversteering is determined by the above method, and based on the basic target slip rate in controlling oversteering, a gain coefficient greater than 1 can be multiplied as the target slip rate of the wheel that slips during the oversteering process.

[0075] When calculating the actual slip rate of each wheel in a slipping state, multiple methods can be used. For example, the following formula can be used for calculation:

[0076]

[0077] Among them, Sr is the actual slip rate, V Wheel is the wheel speed, V vehicle Indicates the speed of the electric car.

[0078] The above-mentioned calculation method for the current utilization adhesion coefficient of each wheel can be obtained by using a variety of calculation methods. An exemplary calculation method is introduced as follows.

[0079] When calculating the current utilization adhesion coefficient of each wheel, a variety of methods can be used. Exemplarily, the following method can be used: first, according to 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, the corrected torque currently input to each wheel is calculated; then, according to the corrected torque of each wheel and the wheel radius, the current longitudinal driving force of each wheel is calculated; then, according to the current longitudinal driving force, lateral driving force, and wheel-end vertical load of each wheel, the current utilization adhesion coefficient of each wheel is calculated. It should be understood that the above only exemplifies one method of calculating the current utilization adhesion coefficient of the wheel, and other methods can also be used in addition to this.

[0080] Exemplarily, when calculating the corrected torque currently input to each wheel according to the current motor input torque, motor speed, motor rotational inertia, motor-to-wheel transmission ratio, and mechanical efficiency of the motor corresponding to each wheel, multiple methods may be used. For example, the following formula may be used for calculation:

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

[0082] Among them, M actual is the corrected torque, M VCU is the motor torque input to the motor, J mot is the motor moment of inertia, i raito is the transmission ratio from the motor to the wheel end, and η is the mechanical efficiency. It can be seen that the correction of the driving torque input to the motor mainly considers the torque consumed by the rotational inertia of the rotating parts from the motor to the wheel end, so as to obtain a more accurate driving torque input from the motor to the wheel and improve the accuracy of the subsequent driving anti-skid control.

[0083] For example, when calculating the current utilization adhesion coefficient of each wheel according to the current longitudinal driving force, lateral driving force and wheel end vertical load of each wheel, multiple methods may be used. For example, the following formula may be used for calculation:

[0084]

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

[0086] Exemplarily, the above-mentioned fuzzy algorithm is used to use the current utilization adhesion coefficient and actual slip rate of each wheel as fuzzy factors to estimate the current fuzzy road adhesion coefficient of each wheel. For example, the fuzzy algorithm can use a triangular membership function and a trapezoidal membership function to construct the membership relationship between the actual slip rate, the utilization adhesion coefficient and the fuzzy road adhesion coefficient. Specifically, the following formula can be used:

[0087]

[0088]

[0089] Among them, in the definition of fuzzy algorithm, there is the concept of membership function, which is used to classify the input fuzzy factors. The first function formula of the f function is the triangle membership function, a and c determine the "foot" of the triangle, and parameter b determines the "peak" of the triangle. x is the input fuzzy factor. f is the curve constructed by the current mapping relationship. In the second function formula of the f function, the formula is the trapezoid membership formula, a and d are used to determine the "foot" of the trapezoid, and b and c are used to determine the "shoulder" of the trapezoid.

[0090] Combine as follows Figure 3 and Figure 4 An exemplary drive anti-skid control process is introduced.

[0091] Step 401: Obtain vehicle-related information. Vehicle-related information required for the drive anti-skid control method may be collected through vehicle sensors, which may include four wheel speeds, vehicle acceleration, wheel-end dynamic load, motor input drive torque, vehicle yaw angular velocity, accelerator pedal travel and other information.

[0092] Step 402: Determine whether all four wheels are in a slipping state. If not, the speed of the electric vehicle is calculated using Kalman filtering; if all four wheels are in a slipping state, the speed of the electric vehicle is calculated using acceleration integration.

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

[0094] Step 404: Calculate the actual slip rate of each wheel according to the wheel speed of the wheel in the slipping state and the speed of the electric vehicle.

[0095] Step 405: Calculate the utilization adhesion coefficients of the four wheels according to the adhesion ellipse theory using the longitudinal driving force of the wheel end, the tire lateral force and the wheel end vertical load.

[0096] Step 406: By using the fuzzy inference system, using the triangle membership function and the trapezoidal membership function, the current fuzzy road adhesion coefficient is estimated according to the current actual slip rate and the adhesion coefficient.

[0097] Step 407: Determine the optimal target slip rate under the current fuzzy adhesion coefficient according to the fuzzy road adhesion coefficient and the vehicle speed.

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

[0099] Step 409: When the wheel is understeering and slipping, the step gradient value for reducing the slipping wheel in the current state is obtained according to the degree of understeering and the current vehicle speed, and the step torque reduction method is adopted to reduce the driving torque of each wheel.

[0100] Step 410: When the wheel is in an oversteer and slipping state, the current increased target slip rate is obtained according to the current degree of oversteer and the current vehicle speed, and the increased target slip rate is 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 achieving torque reduction.

[0101] Step 411: When the vehicle is in a longitudinal drive slip state, that is, it is neither in an understeer state nor in an oversteer state and there is a slipping wheel, the wheel torque is calculated through 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 , a special calculation module can be established for vehicle speed estimation, driving torque correction, road adhesion coefficient estimation, slip rate calculation, understeer control, oversteer control, and longitudinal slip control. The calculation module is generated to realize the corresponding functions, and is responsible for vehicle speed estimation, driving torque correction, road adhesion coefficient estimation, slip rate calculation, understeer control, oversteer control, and longitudinal slip control. The specific calculation method can refer to the description of the corresponding part above. Reference Figure 3 The lateral yaw control module can be divided into an understeering control module and an oversteering control module. The understeering control module determines whether the current vehicle is in an understeering state through the yaw and lateral acceleration requirements. If it is in an understeering state, the torque reduction strategy is implemented on the corresponding axis through a step-by-step torque reduction method. The oversteering module also determines whether the current vehicle is in an oversteering state through the yaw and lateral acceleration requirements. If it is in an oversteering state, the oversteering state of the vehicle is reduced by changing the target slip rate. During the specific calculation, the vehicle speed, slip rate and road adhesion coefficient can be input into the longitudinal slip control in the understeering control and oversteering control. It is also possible to establish an output torque processing module for understeering control, oversteering control 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, wherein the state arbitration module is used to monitor whether there are wheels in a slipping state, and when there are wheels in a slipping state, the above-mentioned functional modules are activated. The torque arbitration judgment module arbitrates the states and torque output of understeering control, oversteering control, and longitudinal slip control, and prioritizes the torque output with lateral yaw control.

[0104] In the various embodiments shown above, when the electric vehicle deviates from the preset steering trajectory and there are slipping wheels during the steering process, the slipping wheels are controlled to reduce torque until the electric vehicle resumes the preset steering trajectory. Compared with the existing control strategy that only considers longitudinal slip, the drive anti-skid control method shown in the present application also considers lateral control during the vehicle steering process. By identifying the vehicle steering state, when the electric vehicle deviates from the preset steering trajectory and there are slipping wheels, the slipping wheels are reduced in torque until the electric vehicle resumes the preset steering trajectory, so that the vehicle maintains neutral steering during the steering process, enhances the vehicle's steering tracking ability, and at the same time improves the drive anti-skid ability of the independent four-wheel drive electric vehicle.

[0105] In addition, an embodiment of the present application also provides a drive anti-skid control system, which is applied to an independent four-wheel drive electric vehicle. The drive anti-skid control system includes: a storage medium and a processor, and the storage medium stores a computer program run by the processor. When the computer program is run by the processor, the processor executes any one of the above-mentioned drive anti-skid control methods.

[0106] Figure 6 FIG. 1 shows a schematic block diagram of a driving anti-skid control system 100 according to an embodiment of the present application. Figure 6 As shown, the driving anti-skid control system 100 according to the embodiment of the present 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 executes the driving anti-skid control method according to the embodiment of the present application described above. Those skilled in the art can understand the specific operation of the deployment device of the driving anti-skid control system 100 according to the embodiment of the present application in combination with the above content, and for the sake of brevity, it will not be repeated here.

[0107] Furthermore, an embodiment of the present application further provides a storage medium, on which a computer program is stored, and when the computer program is run, any of the above-mentioned drive anti-skid control methods is executed. The storage medium may include, for example, a memory card of a smart phone, 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 disk read-only memory (CD-ROM), a USB memory, or any combination of the above-mentioned storage media. The computer-readable storage medium may be any combination of one or more computer-readable storage media.

[0108] In addition, the embodiment of the present application also provides an independent four-wheel drive electric vehicle, which includes: a vehicle body, and any one of the above-mentioned drive anti-skid control systems arranged on the vehicle body. The above-mentioned vehicle body may include structures such as a frame, wheels, a gearbox, and a steering wheel. Any one of the above-mentioned drive anti-skid control systems is arranged on the vehicle body. The drive anti-skid control system can be used as a module with both computing and storage functions and arranged on the vehicle terminal of the vehicle body. Of course, the drive anti-skid control system can also be used as an independent control module and arranged in the domain control system of the vehicle body.

[0109] The present invention has been described by the above embodiments, but it should be understood that the above embodiments are only for the purpose of example and description, and are not intended to limit the present invention to the scope of the described embodiments. In addition, it can be understood by those skilled in the art that the present invention is not limited to the above embodiments, and more variations and modifications can be made according to the teachings of the present invention, and these variations and modifications all fall within the scope of the protection claimed by the present invention. The protection scope of the present invention is defined by the attached claims and their equivalents.

Claims

1. A drive anti-skid control method, applied to an independent four-wheel drive electric vehicle, characterized in that: include: When the electric vehicle deviates from a preset steering trajectory and has a slipping wheel during steering, the slipping wheel is controlled to reduce torque until the electric vehicle recovers the preset steering trajectory.

2. The driving anti-skid control method according to claim 1, characterized in that: The electric vehicle deviates from the preset steering trajectory during the steering process, including: The electric vehicle oversteers or understeers relative to the preset steering trajectory during the steering process.

3. The driving anti-skid control method according to claim 2, characterized in that: The electric vehicle oversteers or understeers relative to the preset steering trajectory during the steering process, including: If the current actual yaw rate of the electric vehicle is greater than the yaw rate in the steady state, the electric vehicle is oversteering; If the current actual yaw rate of the electric vehicle is less than the steady-state yaw rate, the electric vehicle is understeering; Wherein, the steady-state yaw angular velocity is determined based on the preset steering trajectory.

4. The driving anti-skid control method according to claim 2, characterized in that: When the electric vehicle understeers, if there is a slipping wheel, the slipping wheel is controlled to step-down torque until the electric vehicle no longer understeers.

5. The driving anti-skid control method according to claim 4, characterized in that: The step of controlling the slipping wheel to reduce torque in a stepwise manner until the electric vehicle no longer understeers comprises: The step gradient value for controlling the step torque reduction of the slipping wheel is determined according to the current vehicle speed of the electric vehicle and the difference between the actual yaw angular velocity and the yaw angular velocity in a steady state.

6. The driving anti-skid control method according to claim 5, characterized in that: The stepping gradient value for controlling the stepping torque reduction of the slipping wheel according to the current speed of the electric vehicle and the difference between the actual yaw angular velocity and the yaw angular velocity in a steady state comprises: The greater the current speed of the electric vehicle, the greater the step gradient value for controlling the step torque reduction of the slipping wheel; The greater the difference between the actual yaw rate of the electric vehicle and the yaw rate in the steady state, the greater the step gradient value for controlling the step torque reduction of the slipping wheel.

7. The driving anti-skid control method according to claim 2, characterized in that: When the electric vehicle oversteers, if there is a slipping wheel, the target slip rate of the slipping wheel is adjusted, and the slipping wheel is controlled to reduce torque until the electric vehicle no longer oversteers.

8. The driving anti-skid control method according to claim 7, characterized in that: The step of adjusting the target slip rate of the slipping wheel and controlling the slipping wheel to reduce torque comprises: The target slip rate of the slipping wheel is adjusted, and based on the adjusted target slip rate, a motion control algorithm is used to control the slipping wheel to reduce torque.

9. The driving anti-skid control method according to claim 8, characterized in that: The step of adjusting the target slip rate of the slipping wheel comprises: Calculating a current road surface adhesion coefficient, and determining a basic target slip rate of the slipping wheel according to the current road surface adhesion coefficient; Determine a gain coefficient according to the current speed of the electric vehicle and the difference between the actual yaw rate and the yaw rate in a steady state; wherein the gain coefficient is greater than 1; The adjusted target slip rate of the slipping wheel is determined according to the product of the basic target slip rate and the gain coefficient.

10. The driving anti-skid control method according to claim 9, characterized in that: Determining the gain coefficient according to the current speed of the electric vehicle and the difference between the actual yaw rate and the yaw rate in a steady state 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 yaw rate in the steady state, the greater the gain coefficient.

11. The driving anti-skid control method according to claim 1, characterized in that: Also includes: When all wheels of the electric vehicle are the slipping wheels, an acceleration integration algorithm is used to calculate the speed of the electric vehicle; When some of the wheels of the electric vehicle are the slipping wheels, a Kalman filter algorithm is used to calculate the speed of the electric vehicle.

12. The driving anti-skid control method according to claim 1, characterized in that: Also includes: Calculating the current utilized adhesion coefficient and actual slip rate of each wheel of the electric vehicle; A fuzzy algorithm is used to take the current utilized adhesion coefficient and actual slip rate of each wheel as fuzzy factors to estimate the current fuzzy road adhesion coefficient of each wheel as the current road adhesion coefficient of each wheel.

13. The driving anti-skid control method according to claim 12, characterized in that: The calculating the current utilized adhesion coefficient of each wheel comprises: Calculate the corrected torque currently input to each wheel based on the current motor input torque, motor speed, motor rotational 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 according to the corrected torque and wheel radius of each wheel; The current utilization adhesion coefficient of each wheel is calculated based on the current longitudinal driving force, lateral driving force and wheel end vertical load of each wheel.

14. A drive anti-skid 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 to be executed by the processor, and when the computer program is executed by the processor, the processor executes the drive anti-skid control method according to any one of claims 1 to 13.

15. A storage medium, characterized in that: The storage medium stores a computer program, and when the computer program is run, the drive anti-skid control method according to any one of claims 1 to 13 is executed.

16. An independent four-wheel drive electric vehicle, characterized in that: include: Vehicle body; The driving anti-skid control system according to claim 14 is provided on the vehicle body.

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