Method for determining wheel speed of vehicle

Abstract

The invention relates to the technical field of vehicle data processing, and provides a vehicle wheel speed determination method. The method for determining the wheel speed of the vehicle comprises the steps that the current dynamic vertical load of each wheel in the vehicle is obtained, and the current vertical force of each wheel is determined according to the current dynamic vertical load of each wheel; obtaining the current slip rate of each wheel, and determining the current friction coefficient between each wheel and the ground based on a preset tire friction characteristic model; according to the current friction coefficient and the vertical force of each wheel, the current friction force between each wheel and the ground is determined; the current driving force of the vehicle is obtained according to the current friction force between each wheel and the ground, and the current vehicle speed of the vehicle is calculated according to the current driving force of the vehicle and the vehicle speed of the vehicle at the previous moment; and the current vehicle speed of the vehicle is equivalent to each wheel, and the wheel speed of each wheel is determined. According to the vehicle wheel speed determination method, the calculation error of the vehicle wheel speed can be reduced, and the accuracy of the vehicle wheel speed is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vehicle data processing, in particular to a vehicle wheel speed determination method. BACKGROUND

[0002] For a four-wheel independent wheel speed control vehicle, the wheel speeds of the four wheels need to be calculated in real time so as to facilitate accurate control. In the related art, a wheel speed calculation method based on Ackermann Steering Geometry is widely used.

[0003] Ackermann Steering Geometry is a classic vehicle steering model. The method for calculating wheel speed based on the Ackermann Steering Geometry model is to derive the wheel speed of each wheel by geometric relationship on the basis of assuming that the vehicle is in a specific state, such as no slip, etc., and ignoring the dynamics effect, thereby obtaining the wheel speed of each wheel.

[0004] However, in the actual driving process of the vehicle, the motion environment of the vehicle is variable. For example, the tires of the vehicle will inevitably slip, especially in the case of low adhesion coefficient road surface or high speed driving, etc., so that the way of calculating the wheel speed in the actual motion process of the vehicle by deriving the wheel speed through geometric relationship under the condition that the vehicle is in a specific state will have a large error, and the error will continuously accumulate as the vehicle continuously drives, thereby possibly seriously affecting the control of the wheel speed of the vehicle. SUMMARY

[0005] In view of this, the present application aims to provide a vehicle wheel speed determination method to reduce the calculation error of the vehicle wheel speed and improve the accuracy of the determined vehicle wheel speed.

[0006] To achieve the above-mentioned purpose, the technical solution of the present application is as follows:

[0007] A vehicle wheel speed determination method, the determination method comprising:

[0008] obtaining the current dynamic vertical load of each wheel in the vehicle, and determining the current vertical force of each wheel according to the current dynamic vertical load of each wheel;

[0009] obtaining the current slip rate of each wheel, and determining the friction coefficient between each wheel and the ground based on a preset tire friction characteristic model;

[0010] determining the friction force between each wheel and the ground according to the current friction coefficient and the vertical force of each wheel, respectively;

[0011] According to the friction force between each wheel and the ground, the current driving force of the vehicle is obtained, and according to the current driving force of the vehicle and the vehicle speed at the previous moment, the current vehicle speed of the vehicle is calculated;

[0012] The current vehicle speed of the vehicle is equivalent to each wheel, and the wheel speed of each wheel is determined.

[0013] Further, the tire friction characteristic model adopts a tire dynamics magic formula, the current slip ratio of each wheel is obtained, and based on a preset tire friction characteristic model, the friction coefficient between each wheel and the ground is determined, which comprises:

[0014] According to the geometric structure of the vehicle, the real-time wheel speed of each wheel is respectively converted to the center of mass of the vehicle, and the equivalent center of mass speed corresponding to each wheel is determined;

[0015] According to the equivalent center of mass speed corresponding to each wheel and the vehicle speed at the previous moment, the current slip ratio of each wheel is determined respectively;

[0016] The slip ratio corresponding to each wheel is substituted into the tire friction characteristic model, and the friction coefficient between each wheel and the ground is calculated.

[0017] Further, the real-time wheel speed of each wheel is respectively converted to the center of mass of the vehicle, and the equivalent center of mass speed corresponding to each wheel is determined, which comprises:

[0018] According to the difference between the real-time wheel speeds of each wheel, the speed adjustment factor of each wheel is calculated respectively;

[0019] According to the calculated speed adjustment factor of each wheel, the real-time wheel speed of each wheel is corrected to obtain the equivalent wheel speed of each wheel;

[0020] According to the geometric structure of the vehicle, the equivalent wheel speed of each wheel is converted to the center of mass of the vehicle, and the equivalent center of mass speed corresponding to each wheel is determined.

[0021] Further, the difference between the real-time wheel speeds of each wheel is calculated, and the speed adjustment factor of each wheel is calculated respectively, which comprises:

[0022] The difference between the real-time wheel speeds of each two wheels is calculated, and the wheel speed difference value corresponding to each wheel is obtained respectively, the wheel speed difference value corresponding to each wheel includes the difference between the real-time wheel speeds of the wheel and other three wheels;

[0023] determining wheel speed gains of the wheels based on wheel speed difference values corresponding to the wheels and a preset gain constant;

[0024] calculating target adjustment factors of the wheels based on the wheel speed gains of the wheels, the target adjustment factors representing target values expected to be adjusted under a current working condition of the vehicle;

[0025] determining speed adjustment factors of the wheels based on the target adjustment factors of the wheels by a preset closed-loop control algorithm.

[0026] Further, the determining of current slip rates of the wheels based on the equivalent center-of-mass speeds corresponding to the wheels and a vehicle speed at a previous time of the vehicle respectively comprises:

[0027] determining tire slip amounts corresponding to the wheels based on the equivalent center-of-mass speeds corresponding to the wheels and the vehicle speed at the previous time of the vehicle respectively;

[0028] calculating a ratio of the tire slip amounts to the vehicle speed at the previous time of the vehicle to obtain the current slip rates of the wheels.

[0029] Further, the obtaining of a current driving force of the vehicle based on frictional forces between the wheels and the ground respectively comprises:

[0030] calculating a motion resistance of the vehicle based on the vehicle speed at the previous time of the vehicle and static parameters of the vehicle;

[0031] summing the frictional forces between the wheels and the ground and subtracting the motion resistance to obtain the current driving force of the vehicle;

[0032] The static parameters are parameters describing static characteristics of the vehicle.

[0033] Further, the motion resistance comprises an air resistance and a rolling resistance, and the static parameters of the vehicle comprise a mass of the vehicle and a windward area of the vehicle.

[0034] The calculating of the motion resistance of the vehicle based on the vehicle speed at the previous time of the vehicle and the static parameters of the vehicle comprises:

[0035] calculating a rolling resistance of the vehicle based on the mass of the vehicle and a preset rolling resistance coefficient;

[0036] obtaining an air density, and calculating an air resistance of the vehicle based on the windward area of the vehicle, the air density and the vehicle speed at the previous time of the vehicle;

[0037] The sum of the air resistance and the rolling resistance is calculated to determine the motion resistance.

[0038] Further, the current dynamic vertical load of each of the wheels includes an inertial vertical load and a roll vertical load.

[0039] The current dynamic vertical load of each of the wheels in the vehicle is obtained by:

[0040] The mass, the height of the center of gravity, the wheelbase, and the average wheel track of the vehicle are obtained, wherein the average wheel track is the average of the wheel tracks of the wheels.

[0041] The current longitudinal acceleration and the current lateral acceleration of the vehicle are obtained.

[0042] The inertial vertical load is calculated based on the mass, the height of the center of gravity, the current longitudinal acceleration, and the wheelbase of the vehicle.

[0043] The roll vertical load is calculated based on the mass, the height of the center of gravity, the current lateral acceleration, and the average wheel track of the vehicle.

[0044] The current dynamic vertical load of each of the wheels is determined based on the inertial vertical load and the roll vertical load.

[0045] Further, the current speed of the vehicle is equivalently converted to each of the wheels to determine the wheel speed of each of the wheels, including:

[0046] The first distance between the instantaneous turning center of the vehicle and the center of the vehicle, and the second distance between the instantaneous turning center of the vehicle and each of the wheels are respectively calculated according to the front axle steering angle of the vehicle and the wheelbase of the vehicle.

[0047] The relative proportion between the second distance and the first distance is calculated to obtain the equivalent conversion proportion corresponding to each of the wheels.

[0048] The current speed of the vehicle is divided according to the equivalent conversion proportion to obtain the wheel speed of each of the wheels.

[0049] Further, the first distance between the instantaneous turning center of the vehicle and the center of the vehicle, and the second distance between the instantaneous turning center of the vehicle and each of the wheels are respectively calculated, including:

[0050] The current instantaneous turning center of the vehicle is determined based on the front axle steering angle, the wheelbase of the vehicle, and a preset Ackerman steering geometry model.

[0051] determining distances between the wheels and the current instantaneous turning center of the vehicle, to obtain the second distances;

[0052] determining the first distance based on a positional relationship between the current instantaneous turning center of the vehicle and the center of the vehicle.

[0053] Compared with the related art, the present application has the following advantages:

[0054] (1) The vehicle wheel speed determination method described in the present application calculates the friction coefficient according to the slip ratio of each wheel of the vehicle, and calculates the vertical force of the vehicle according to the dynamic vertical load of each wheel, so as to calculate the driving force according to the friction coefficient and the vertical force, and then convert the vehicle speed to the wheel speed to obtain the wheel speed of each wheel. In such a wheel speed determination method, the slip ratio of each wheel is considered when calculating the vehicle speed, that is, the slip condition of the wheel is considered, so that the wheel speed calculated by the vehicle speed is closer to the real wheel speed, which is beneficial to reduce the calculation error of the wheel speed and further improve the stability control of the vehicle.

[0055] (2) In the vehicle wheel speed determination method of the present application, not only the slip ratio of each wheel of the vehicle is considered, but also the real-time vehicle speed is calculated according to the dynamic vertical load in the real-time motion process of each wheel. Therefore, the calculated vehicle speed is more suitable for the actual motion condition, rather than being calculated according to a certain assumed condition in the related art, so as to further reduce the calculation error of the wheel speed. BRIEF DESCRIPTION OF DRAWINGS

[0056] The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application. The accompanying drawings should not be construed as an inappropriate limitation on the present application. In the drawings:

[0057] Figure 1 A flowchart of the vehicle wheel speed determination method described in the embodiments of the present application;

[0058] Figure 2 A flowchart of the step of calculating the slip ratio and the friction coefficient in the vehicle wheel speed determination method described in the embodiments of the present application;

[0059] Figure 3 A flowchart of the step of calculating the equivalent center of mass speed in the vehicle wheel speed determination method described in the embodiments of the present application;

[0060] Figure 4 A flowchart of the step of calculating the current driving force of the vehicle in the vehicle wheel speed determination method described in the embodiments of the present application;

[0061] Figure 5 A flowchart of a step of equivalent vehicle speed to wheel speed in the vehicle wheel speed determination method described in the embodiments of the present application;

[0062] Figure 6 An example schematic diagram of the positional relationship between the instantaneous turning center, the vehicle center and each wheel in the vehicle wheel speed determination method described in the embodiments of the present application;

[0063] Figure 7 A schematic diagram of the overall flow of the vehicle wheel speed determination method described in the embodiments of the present application. DETAILED DESCRIPTION

[0064] In order to make the technical solutions of the present application and their advantages clearer and more apparent, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application.

[0065] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0066] In addition, in the description of the present application, it should be noted that if terms indicating orientation or positional relationship such as "upper", "lower", "inner", "outer" and the like appear, they are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, if the terms "first", "second" and the like appear, they are also only for the purpose of description and cannot be understood as indicating or implying relative importance.

[0067] In addition, in the description of the present application, unless otherwise explicitly limited, the terms "mount", "connect", "connection", "connector" should be understood broadly. For example, it can be a fixed connection, or a detachable connection, or an integral connection; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or a communication between two elements inside. For those skilled in the art, the specific meaning of the above terms in the present application can be understood in conjunction with the specific circumstances.

[0068] In this application, the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" mean that a particular feature, structure, material, or characteristic is included in at least one embodiment or example of the present application. Exemplary expressions of the above terms in the specification do not necessarily refer to the same embodiment or example. Moreover, the described particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0069] In the following, the present application will be described in detail through exemplary embodiments. However, it should be understood that the elements, structures and features in one embodiment can be beneficially combined into other embodiments without further description.

[0070] The embodiment of the present application provides a vehicle wheel speed determination method, which calculates the vertical force of the vehicle in real time, combines the slip rate of the wheel, uses a preset tire friction characteristic model to calculate and determine the driving force of the wheel, calculates the vehicle speed, and converts the vehicle speed into the wheel speed. In the process of determining the vehicle wheel speed, the slip rate of the wheel is considered, the calculation error of the vehicle wheel speed is effectively reduced, and the accuracy of the wheel speed calculation is improved.

[0071] In the related art, the wheel speed calculation method based on the Ackerman steering geometry kinematic model is to obtain the vehicle speed on the basis of some basic assumptions, and then derive the wheel speed from the vehicle speed by using the geometric relationship. Specifically, the basic assumptions of the Ackerman steering geometry include assuming that the tire has no side slip and no slip. The vehicle speed is often obtained by calculating the average of the non-driving wheel speed on the basis of the basic assumption.

[0072] However, in the wheel speed calculation method using the Ackerman steering geometry kinematic model, at least the following problems exist:

[0073] (1) Insufficient static model assumption: Since the related art assumes that the tire has no side slip and ignores the dynamic effect (such as tire side slip angle), but in the process of vehicle driving, the tire will inevitably have side slip and tire side slip, etc. When these situations occur, the vehicle speed converted from the non-driving wheel speed will no longer represent the true vehicle speed, thus causing the wheel speed derived from the vehicle speed to deviate from the actual wheel speed, i.e., causing an error in the wheel speed calculation. If the wheel speed calculation error accumulates continuously with the vehicle driving in high-speed driving conditions, it will seriously affect the stability control of the vehicle

[0074] (2) Sensor fusion missing: in the related art, a single vehicle speed and / or steering angle signal is relied on, and wheel speed is derived through geometric relationship based on the single vehicle speed and / or steering angle signal. In a dynamic environment, for example, in the case of emergency braking of the vehicle, or in the case of driving on a low adhesion road surface (for example, an icy road surface), this way of calculating wheel speed completely through a single vehicle speed and / or steering angle signal is difficult to adapt to the dynamic environment, and errors are prone to occur.

[0075] (3) Insufficient adaptability to dynamic conditions: the Ackermann steering geometry model relies on the assumption of steady-state steering (such as fixed steering angle of the vehicle, uniform speed driving), and cannot cope with transient sudden conditions, such as emergency lane changing, braking intervention when ABS (Anti-lock Braking System) is triggered.

[0076] In view of this, in order to overcome the deficiencies in the related art, the embodiments provide a vehicle wheel speed determination method, which is executed by an electronic device. The electronic device can be a vehicle terminal device, or a server in communication with the vehicle terminal device. The server is used to process related data of the vehicle and feed back to the vehicle terminal device, which is not limited herein.

[0077] In the vehicle wheel speed determination method of the embodiments, the dynamic vertical load of each wheel of the vehicle is obtained, and the vertical force of each wheel is determined based on the dynamic vertical load of each wheel. Figure 1 As shown in the figure, the vehicle wheel speed determination method includes the following steps.

[0078] In step S110, the dynamic vertical load of each wheel of the vehicle is obtained, and the vertical force of each wheel is determined based on the dynamic vertical load of each wheel.

[0079] Specifically, in step S110, the vehicle includes four wheels, which are the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel. With reference to the direction of the tail of the vehicle pointing to the head of the vehicle, i.e., the forward direction of the vehicle, the left front wheel can be the wheel located at the left front end of the forward direction of the vehicle, the right front wheel can be the wheel located at the right front end of the forward direction of the vehicle, the left rear wheel can be the wheel located at the left rear end of the forward direction of the vehicle, and the right rear wheel can be the wheel located at the right rear end of the forward direction of the vehicle.

[0080] In step S110, the dynamic vertical load of each wheel is calculated, and the current vertical force of each wheel is determined.

[0081] Taking one of the wheels as an example, the vertical force of the wheel includes a static vertical load of the wheel and a dynamic vertical load of the wheel, the static vertical load refers to a vertical force borne by the wheel when the vehicle is static on a horizontal road surface, and the dynamic vertical load refers to a load variation amount caused by inertia or a roll moment when the wheel is in motion. The vertical force of the wheel can be equal to a sum of the static vertical load and the dynamic vertical load, that is, on the basis of the static vertical load, the load variation amount caused by the motion of the vehicle is added to obtain the vertical force of the wheel.

[0082] In the calculation of the vertical force of the wheel, the vehicle static parameters and the vehicle dynamic parameters of the vehicle can be obtained respectively to calculate the vertical force of each wheel by using the vehicle static parameters and the vehicle dynamic parameters.

[0083] The vehicle static parameters include basic parameters of the vehicle and parameters of the vehicle in a static state. The vehicle dynamic parameters include various parameters of the vehicle in a dynamic motion process.

[0084] For example, the vehicle static parameters include a total mass m of the vehicle, a gravity center height h, an axle distance L, a wheel track W of each wheel, and a static vertical load Fz of each wheel.

[0085] The gravity center height h is a vertical distance from the center of the vehicle to the ground, the axle distance L is a horizontal distance from the front axle gravity center to the rear axle gravity center of the vehicle, and the wheel track W is a lateral distance between the left and right wheel grounding center points of the same axle (front axle or rear axle).

[0086] For example, the vehicle dynamic parameters include a lateral acceleration ax of the vehicle and a longitudinal acceleration ay of the vehicle. The vehicle dynamic parameters can also include a real-time rotating speed of each wheel, a rotation angular velocity (vehicle yaw angular velocity) of the vehicle around a vertical axis, and a steering wheel angle.

[0087] The real-time rotating speed of each wheel can be measured by using a wheel speed sensor installed on each wheel, and the lateral acceleration ax, the longitudinal acceleration ay, the vehicle yaw angular velocity, and the steering wheel angle can be measured by using an inertial measurement unit (IMU) installed on the vehicle.

[0088] It is worth noting that in some embodiments, after the data is measured by using the sensors, the data is preprocessed by unit conversion and the like, and then the vehicle static parameters and the vehicle dynamic parameters with standard units are obtained. For example, after the mass of the vehicle is measured, the unit of the mass is converted to a standard unit, such as kg. The angle unit is converted to a radian unit (and the angular velocity unit is converted to rad / s for the same reason), and the speed unit is uniformly converted to m / s. Then the vehicle static parameters and the vehicle dynamic parameters in the standard units are used for calculation.

[0089] In step S110, the static vertical load of each wheel can be determined by the vehicle static parameters, the dynamic vertical load of each wheel is calculated according to the vehicle dynamic parameters and the vehicle static parameters, and the vertical force of each wheel is further calculated, so as to calculate the dynamic vertical load and the vertical force of the current left front wheel, the dynamic vertical load and the vertical force of the current right front wheel, the dynamic vertical load and the vertical force of the current left rear wheel, and the dynamic vertical load and the vertical force of the current right rear wheel.

[0090] In step S120, the current slip ratio of each wheel is obtained, and the friction coefficient between each wheel and the ground at present is determined based on the preset tire friction characteristic model.

[0091] Specifically, in step S120, the slip ratio of each wheel is calculated respectively, and then the corresponding friction coefficient of each wheel is obtained based on the preset tire friction characteristic model.

[0092] For example, one of the wheels is taken as an example (for example, the left front wheel), and the preset tire friction characteristic model can be a tire dynamics magic formula. The magic formula can specifically include:

[0093] F=D*sin(C*arctan(B*x-E*(arctan(B*x)-B*x)))

[0094] Wherein, B is a stiffness factor, C is a shape factor, D is a peak factor, and E is a curvature factor. Among them, B, C, D, and E are fitting coefficients, which depend on the specific type of tire, road conditions and other factors, and are calibrated by experimental data. The staff can calibrate each wheel in advance, and the experience value can be obtained by testing under various conditions to complete the calibration. For example, the left front wheel is experimentally calibrated, and the magic formula of the left front wheel can be obtained after calibration.

[0095] Wherein, F in the magic formula is the output quantity, and x is the input variable. The slip ratio of the left front wheel is taken as x and brought into the magic formula of the left front wheel, and the output F is the friction coefficient between the left front wheel and the ground at present.

[0096] In step S130, the friction force between each wheel and the ground at present is determined according to the friction coefficient and the vertical force of each wheel.

[0097] Specifically, in step S130, after the vertical force of each wheel at present and the friction coefficient of each wheel at present are calculated, the product of the friction coefficient and the vertical force of each wheel is calculated to obtain the friction force between each wheel and the ground.

[0098] For example, the vertical force of the left front wheel is multiplied by the friction coefficient of the left front wheel to obtain the friction force of the left front wheel; the vertical force of the right front wheel is multiplied by the friction coefficient of the right front wheel to obtain the friction force of the right front wheel; the vertical force of the left rear wheel is multiplied by the friction coefficient of the left rear wheel to obtain the friction force of the left rear wheel; and the vertical force of the right rear wheel is multiplied by the friction coefficient of the right rear wheel to obtain the friction force of the right rear wheel.

[0099] In step S140, the current driving force of the vehicle is obtained according to the friction force between each wheel and the ground at present, and the current speed of the vehicle is calculated according to the current driving force of the vehicle and the speed of the vehicle at the last moment.

[0100] Specifically, after obtaining the friction force of each wheel, since the friction force is the interaction force between the tire and the ground, the friction force is equivalent to the driving force applied by the ground to the tire, and thus in step S140, the sum of the friction force of each wheel is calculated, i.e., the total driving force applied by the ground to the vehicle is calculated, and then the current driving force of the vehicle is obtained.

[0101] For example, in the case of ignoring air resistance, the sum of the friction force of each wheel is equivalent to the current driving force of the vehicle; in the case of considering air resistance, the current driving force of the vehicle is equivalent to the sum of the friction force of each wheel minus the air resistance.

[0102] In step S140, after the current driving force of the vehicle is calculated, the current acceleration of the vehicle is calculated by dividing the mass m of the vehicle according to Newton's second law. Then, the current speed of the vehicle is calculated by using an integrator according to the speed of the vehicle at the last moment and the current acceleration.

[0103] In step S150, the current speed of the vehicle is equivalent to each wheel, and the wheel speed of each wheel is determined.

[0104] Specifically, in step S150, after the current speed of the vehicle is calculated, the current speed of the vehicle is equivalent to each wheel according to the static parameters of the vehicle, and the wheel speed of each wheel is obtained by using the geometric structure of the vehicle, so as to complete the wheel speed calculation.

[0105] It is worth noting that the above step S110 can be executed before step S120, simultaneously with step S120, or after step S120, which is not limited here.

[0106] Therefore, by the above steps S110-S140, the friction coefficient is calculated according to the slip ratio of each wheel of the vehicle, the vertical force of the vehicle is calculated according to the dynamic vertical load of each wheel, the driving force is calculated according to the friction coefficient and the vertical force, and then the wheel speed of each wheel is obtained by converting the speed of the vehicle to the wheel in step S150.

[0107] In this way, the slip ratio of each wheel is considered when calculating the vehicle speed, i.e., the slip condition of the wheel is considered, so that the wheel speed calculated by the vehicle speed is closer to the actual wheel speed, which is beneficial to reduce the calculation error of the wheel speed caused by the insufficient assumption of the static model in the related art, and further improve the stability control of the vehicle.

[0108] Continuing to combine Figure 1 As shown in the above step S110, in some exemplary embodiments, the current dynamic vertical load of each wheel is calculated and obtained according to the vehicle dynamic parameter and the vehicle static parameter of the vehicle, which can be calculated by the following way.

[0109] The current dynamic vertical load of each wheel can include an inertial vertical load and a roll vertical load. The inertial vertical load refers to the load change caused by the inertial moment of the vehicle, and the roll vertical load refers to the load change caused by the roll moment of the vehicle. The vehicle dynamic parameter includes the current longitudinal acceleration and the lateral acceleration of the vehicle. The vehicle static parameter includes the mass, the center of gravity height, the wheelbase and the average track of the vehicle.

[0110] In step S110, the way of calculating the dynamic vertical load includes:

[0111] The mass, the center of gravity height, the wheelbase and the average track of the vehicle are obtained, wherein the average track is the average of the tracks of the wheels. The current longitudinal acceleration and the lateral acceleration of the vehicle are obtained.

[0112] Then, the inertial vertical load is calculated based on the mass, the center of gravity height, the current longitudinal acceleration and the wheelbase of the vehicle.

[0113] Then, the roll vertical load is calculated based on the mass, the center of gravity height, the current lateral acceleration of the vehicle and the average track.

[0114] Then, the current dynamic vertical load of each wheel is determined based on the inertial vertical load and the roll vertical load. Specifically, the sum of the inertial vertical load and the roll vertical load can be calculated to obtain the dynamic vertical load.

[0115] The calculation formula of the inertial vertical load ΔF1 can include the following formula one.

[0116] ΔF1 = (m x a x x h) ÷ L (Formula One).

[0117] The calculation formula of the roll vertical load ΔF2 can include the following formula two.

[0118] ΔF2 = (m x a y x h) ÷ T (Formula Two).

[0119] wherein m is the total mass of the vehicle, h is the height of the center of gravity of the vehicle; L is the wheelbase of the vehicle; a x is the current longitudinal acceleration of the vehicle; a y is the current lateral acceleration of the vehicle; T is the average wheel track of the vehicle, specifically the average of the wheel track of the left front wheel, the wheel track of the left rear wheel, the wheel track of the right front wheel and the wheel track of the right rear wheel.

[0120] Taking one of the wheels as an example, the calculation method of the inertial vertical load and the roll vertical load of the wheel (for example, the left front wheel) is described, and the dynamic vertical load of the left front wheel is calculated.

[0121] The inertial vertical load AF1 of the left front wheel and the roll vertical load AF2 of the left front wheel are calculated by using the formula one and the formula two respectively, and then the sum of the inertial vertical load AF1 and the roll vertical load AF2 of the left front wheel is calculated to calculate the dynamic vertical load of the left front wheel.

[0122] For other wheels, the corresponding dynamic vertical loads are calculated according to the calculation method of the left front wheel, which will not be described here.

[0123] After the dynamic vertical load is calculated, the sum of the dynamic vertical load and the static vertical load Fx can be calculated, so that the vertical force of the left front wheel can be calculated.

[0124] In this embodiment, the vertical force is calculated by using the body geometry parameters (such as wheelbase, wheel track, static load) and motion parameters (such as lateral acceleration, longitudinal acceleration), on the one hand, such a vertical force calculation method fully considers the inertial and roll moment changes caused by motion, so that the accuracy of the calculated vertical force is higher, on the other hand, the application uses the vertical force calculated in this way to calculate the vehicle speed and the wheel speed, so that the calculated vehicle speed considers the influence of vehicle roll or inertia, thereby improving the problem that the vehicle speed and the wheel speed are calculated with large deviation due to the insufficient assumption of the static model in the related art, which is beneficial to reduce the calculation error of the vehicle speed and the wheel speed.

[0125] Continuing from Figure 1 , and in combination with Figure 2 , in some exemplary embodiments, in the step S120, the current slip rates of the wheels are obtained, and the friction coefficients between the wheels and the ground are determined based on a preset tire friction characteristic model, which can be achieved by the following steps S121-S123.

[0126] In step S121, the real-time wheel speeds of the wheels are respectively converted to the center of mass of the vehicle according to the geometry of the vehicle, and the equivalent center of mass speeds of the wheels are determined.

[0127] Specifically, in step S121, the real-time wheel speed of the wheel can be converted to the center of mass according to the geometry of the vehicle, the vehicle yaw rate and the steering wheel angle. Wherein, the vehicle yaw rate, the steering wheel angle and the real-time wheel speed can be obtained according to the above-mentioned vehicle dynamic parameters in step S121. Wherein, the real-time wheel speed of the wheel can be the real-time speed of the wheel collected by the above-mentioned wheel speed sensor. The vehicle yaw rate can be the rotation angular velocity of the vehicle around the vertical axis measured by the yaw rate sensor in the inertial measurement unit of the vehicle. The steering wheel angle can be the steering wheel angle measured by the steering wheel angle sensor in the inertial measurement unit of the vehicle.

[0128] Step S122, according to the equivalent center of mass speed corresponding to each wheel, and the vehicle speed at the last time, respectively determine the current slip ratio of each wheel.

[0129] Specifically, in step S122, the slip ratio refers to the parameter of the relative sliding degree between the single tire and the ground, which is used to quantify the longitudinal sliding degree between the tire and the ground. The slip ratios of different wheels are different, for example, the unilateral slip ratio may increase suddenly on low adhesion road surface. Therefore, in step S122, the current slip ratio of each wheel is calculated respectively. That is, the slip ratio of each of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel is calculated respectively.

[0130] Specifically, in step S122, when calculating the slip ratio of a single wheel, the relative difference between the speed of the tire and the actual vehicle speed can be analyzed to analyze the slip amount of the tire according to the relative difference, to determine the relative sliding degree of the tire, so as to calculate the slip ratio.

[0131] In step S122, the equivalent center of mass speed of the wheel is used as the speed of the tire, and the vehicle speed at the last time is used as the reference actual vehicle speed, so as to calculate the slip ratio between the wheel and the ground.

[0132] Specifically, in some exemplary embodiments, in step S122, the way of determining the current slip ratio of each wheel according to the equivalent center of mass speed corresponding to each wheel and the vehicle speed at the last time can specifically include:

[0133] According to the equivalent center of mass speed corresponding to each wheel and the vehicle speed at the last time, respectively determine the tire slip amount corresponding to each wheel; calculate the ratio of the tire slip amount to the vehicle speed at the last time, to calculate the current slip ratio of each wheel.

[0134] More specifically, for each wheel, the calculation formula of the current slip ratio of the wheel includes:

[0135] Slip rate = (vehicle speed at last time - equivalent mass center speed of wheel) / vehicle speed at last time. Wherein, (vehicle speed at last time - equivalent mass center speed of wheel) is the tire slip amount of wheel.

[0136] The current slip rate of the left front wheel, the current slip rate of the right front wheel, the current slip rate of the left rear wheel and the current slip rate of the right rear wheel are calculated by the slip rate calculation formula respectively, so as to provide a calculation method for calculating the slip rate, thereby facilitating the calculation of the vehicle speed and the wheel speed, and further facilitating the improvement of the calculation accuracy of the wheel speed.

[0137] In step S123, the slip rate corresponding to each wheel is substituted into the tire friction characteristic model to calculate the friction coefficient between each wheel and the ground at present.

[0138] Specifically, in step S121, the equivalent mass center speed of each wheel of the vehicle is calculated according to the geometric structure of the vehicle, the vehicle yaw rate, the steering wheel angle and the real-time wheel speed of the wheel respectively, and then in step S122, the slip rate of each wheel is calculated according to the equivalent mass center speed of each wheel. Then in step S123, each slip rate can be brought into the magic formula of the tire of each wheel to calculate the friction coefficient between each wheel and the ground at present, thereby providing a calculation method for calculating the slip rate and the calculated friction coefficient.

[0139] Moreover, in the steps S121-S123, when calculating the equivalent mass center speed of the wheel, the real-time wheel speed, the real-time yaw rate, the real-time steering wheel angle and other signals of the vehicle can also be combined to calculate, so that the accuracy of the calculated vehicle speed by the friction coefficient calculated by the equivalent mass center speed is higher. Moreover, the signals such as real-time wheel speed, real-time yaw rate and real-time steering wheel angle are fused in the embodiment, and in the dynamic working condition of the vehicle (including high-speed driving condition), the current vehicle speed in the actual working condition can be determined by following the real-time speed, real-time yaw rate and real-time steering wheel angle in the actual working condition, thereby solving the problems of insufficient static model assumption, missing sensor fusion and insufficient dynamic working condition adaptability in the related art.

[0140] Continue from Figure 1 and Figure 2 and combine Figure 3In some example embodiments, as shown, in the case where the vehicle is in a relatively stable driving state, for example, the steering wheel angle, yaw rate, wheel acceleration and other signals are small, the step S121 is to convert the real-time wheel speed of each wheel to the center of mass of the vehicle according to the geometry of the vehicle, and determine the equivalent center of mass speed of each wheel, which can be achieved by the following steps S1211-S1213.

[0141] In step S1211, the speed adjustment factor of each wheel is calculated according to the difference between the real-time wheel speeds of each wheel.

[0142] Specifically, in the case where the vehicle is in a relatively stable driving state, for example, the steering wheel angle, yaw rate, wheel acceleration and other signals are small, the speed of the four wheels can be aligned to calculate the equivalent wheel speed of each wheel, and then the equivalent wheel speed of each wheel is converted to the center of mass to obtain the equivalent center of mass speed of each wheel. In this way, in the stable driving state, for example, in the case of uniform speed, the wheel speed of the vehicle is aligned first, which reduces the probability of adverse effects on subsequent calculations due to the inconsistency of the speed of a wheel with other wheels.

[0143] Specifically, in step S1211, the speed adjustment factor of each wheel is calculated according to the difference between the real-time wheel speeds of each wheel, to align the speed of each wheel.

[0144] In some example embodiments, the calculation process of the speed adjustment factor in step S1211 can include:

[0145] The difference between the real-time wheel speeds of each two wheels is calculated to obtain the wheel speed difference value ΔV corresponding to each wheel. Then, based on the wheel speed difference value ΔV corresponding to each wheel and a preset gain constant, the wheel speed gain gain(n) of each wheel is determined. Then, based on the wheel speed gain gain(n) of each wheel, the target adjustment factor SecLevelGain(n) of each wheel is calculated. Then, according to the target adjustment factor SecLevelGain(n) of each wheel, the speed adjustment factor final_gain(n) of each wheel is determined by a preset closed-loop control algorithm.

[0146] The wheel speed difference value ΔV corresponding to the wheel includes the difference between the real-time wheel speeds of the wheel and the other three wheels. The target adjustment factor SecLevelGain(n) represents the target value expected to be adjusted under the current vehicle working condition.

[0147] Specifically, the calculation formula of the speed adjustment factor final_gain(n) can include:

[0148] final_gain(n) = Integrator((SecLevelGain(n) - delayedfinal_gain(n)) * factor).

[0149] SecLevelGain(n) = ((gain1 * V1 + gain2 * V2 + gain3 * V3 + gain4 * V4) / (gain1

[0150] + gain2 + gain3 + gain4) / Vn).

[0151]

[0152] Wherein, final_gain(n) is the speed adjustment factor of the nth wheel, SecLevelGain(n) is the target adjustment factor of the nth wheel, delayedfinal_gain(n) is the speed adjustment factor of the nth wheel calculated last time, factor is the speed adjustment rate factor, which is an empirical value, and can be a table value of signals such as vehicle acceleration and steering wheel angle or an empirical value of staff, etc.; Vn is the wheel speed of the nth wheel, and ΔV1-ΔV3 are the differences between the wheel speed of the nth wheel and the wheel speeds of other wheels, respectively. The gain constant is a calibration value, which represents the degree of speed alignment.

[0153] For example, assuming that the left front wheel is the first wheel, the right front wheel is the second wheel, the left rear wheel is the third wheel, and the right rear wheel is the fourth wheel, the calculation process of the speed adjustment factor of the left front wheel is described. The rotational speeds of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel are VFL, VFR, VRL, and VRR, respectively.

[0154] First, the wheel speed differences corresponding to each wheel are calculated, specifically:

[0155] The wheel speed differences corresponding to the left front wheel include the rotational speed difference between the left front wheel and the right front wheel (VFL-VFR), the wheel speed difference between the left front wheel and the left rear wheel (VFL-VRL), and the wheel speed difference between the left front wheel and the right rear wheel (VFL-VRR).

[0156] The wheel speed differences corresponding to the right front wheel include the rotational speed difference between the right front wheel and the left front wheel (VFR-VFL), the wheel speed difference between the right front wheel and the left rear wheel (VFR-VRL), and the wheel speed difference between the right front wheel and the right rear wheel (VFR-VRR).

[0157] The wheel speed differences corresponding to the left rear wheel include the rotational speed difference between the left rear wheel and the left front wheel (VRL-VFL), the wheel speed difference between the left rear wheel and the right front wheel (VRL-VFR), and the wheel speed difference between the left rear wheel and the right rear wheel (VRL-VRR).

[0158] The wheel speed difference corresponding to the right rear wheel includes: the wheel speed difference between the right rear wheel and the left front wheel (VRR-VFL), the wheel speed difference between the right rear wheel and the right front wheel (VRR-VFR), and the wheel speed difference between the right rear wheel and the left rear wheel (VRR-VRL).

[0159] Then, according to the wheel speed difference corresponding to each wheel, the wheel speed gain of each wheel is calculated, i.e., the wheel speed gain gain1 of the left front wheel, the wheel speed gain gain2 of the right front wheel, the wheel speed gain gain3 of the left rear wheel, and the wheel speed gain gain4 of the right rear wheel.

[0160]

[0161]

[0162]

[0163]

[0164] Then, taking the calculation of the target adjustment factor and the speed adjustment factor of the left front wheel as an example, the determination process of the target adjustment factor and the speed adjustment factor of each wheel is described.

[0165] The target adjustment factor of the left front wheel, i.e., SecLevelGain(1), is calculated, wherein:

[0166] SecLevelGain(1) = ((gain1*VFL+gain2*VFR+gain3*VRL+gain4*VRR) / (gain1+gain2+gain3+gain4) / VFL)

[0167] Then, the speed adjustment factor of the left front wheel, i.e., final_gain1, is calculated.

[0168] final_gain1 = Integrator((SecLevelGain1-delayedfinal_gain1)*

[0169] factor)

[0170] Wherein, Integrator is an integrator, which accumulates the difference in the subsequent parentheses, so that the speed adjustment factor gradually approaches the calculated target adjustment factor, and through gradually eliminating the deviation between the current speed adjustment factor and the target adjustment factor, the static error control is realized.

[0171] Wherein, factor is a dynamic adjustment coefficient, which is a lookup table value or a calibration value, and the value of the factor can be determined according to the vehicle acceleration, steering wheel angle, and yaw rate, etc. The value of the factor determines the change rate of the speed adjustment factor. For example, when driving gently, the factor is small, so that the speed adjustment factor gradually and slowly changes to the second level gain factor, so as to reduce the probability of the occurrence of jitter due to the rapid change of vehicle speed and the fierce response.

[0172] The calculation of the speed adjustment factor of other wheels can refer to the calculation method of the speed adjustment factor of the left front wheel, which will not be repeated here.

[0173] In step S1212, the real-time wheel speed of each wheel is corrected according to the calculated speed adjustment factor of each wheel to obtain the equivalent wheel speed of each wheel.

[0174] Specifically, in step S1212, the speed adjustment factor of each wheel is superimposed on the basis of the original real-time wheel speed to obtain the equivalent wheel speed of each wheel. For example, the equivalent wheel speed of the left front wheel = the real-time wheel speed of the left front wheel + final_gain1.

[0175] In step S1213, the equivalent wheel speed of each wheel is converted to the center of mass of the vehicle according to the geometric structure of the vehicle to determine the equivalent center of mass speed corresponding to each wheel.

[0176] Specifically, in step S1213, after obtaining the equivalent wheel speed, the equivalent wheel speed of each wheel can be converted to the center of mass of the vehicle according to the geometric structure of the vehicle to obtain the equivalent center of mass speed of each wheel, and then the slip rate of the vehicle can be calculated, and then the friction coefficient, the vehicle speed and the calculated wheel speed can be obtained.

[0177] For example, due to the different driving modes and steering systems of different vehicles, such as rear-wheel drive vehicles or front-wheel drive vehicles, etc. Here, the simplest rear-wheel drive vehicle without rear-wheel steering is taken as an example to illustrate the calculation process of converting the equivalent wheel speed to the center of mass to obtain the equivalent center of mass speed.

[0178] VCOG1 = VEquivalent1 + Yr*0.5*W;

[0179] VCOG2 = VEquivalent2 - Yr*0.5*W;

[0180] VCOG3 = VEquivalent3 + Yr*0.5*W;

[0181] VCOG4 = VEquivalent4 - Yr*0.5*W.

[0182] Wherein, VCOG1 is the equivalent mass center speed of the left front wheel, VCOG2 is the equivalent mass center speed of the right front wheel, VCOG3 is the equivalent mass center speed of the left rear wheel, VCOG4 is the equivalent mass center speed of the right rear wheel, Vequivalent1 is the equivalent wheel speed of the left front wheel calculated in step S1212, Vequivalent2 is the equivalent wheel speed of the right front wheel, Vequivalent3 is the equivalent wheel speed of the left rear wheel, Vequivalent4 is the equivalent wheel speed of the right rear wheel, Yr is the yaw rate of the vehicle, i.e. the yaw rate measured by the yaw rate sensor in the inertial measurement unit, and W is the wheel base.

[0183] In addition, it is worth mentioning that, in the case where the vehicle is not in a relatively stable driving state, the real-time speed of the wheel can be directly used to replace the equivalent wheel speed in step S1213 to directly calculate the equivalent mass center speed of the wheel when calculating the equivalent mass center speed.

[0184] Continuing from Figure 1 and in combination with Figure 4 In some exemplary embodiments, in step S140, the current driving force of the vehicle is obtained according to the friction between the wheels and the ground, which can include the following steps.

[0185] In step S141, the motion resistance of the vehicle is calculated according to the vehicle speed at the last moment and the static parameters of the vehicle.

[0186] The static parameters are parameters describing the static characteristics of the vehicle, i.e. the static parameters of the vehicle described in the above embodiments.

[0187] In step S142, the friction between the wheels and the ground is summed up and the motion resistance is subtracted to obtain the current driving force of the vehicle.

[0188] In step S142, for each wheel, the friction between each wheel and the ground is equivalent to the driving force provided by the ground to the wheel, and the sum of the friction of the four wheels is equivalent to the total driving force provided by the ground to the vehicle, but only part of the total driving force of the vehicle is used to offset the motion resistance during the motion of the vehicle, and the other part is used as the actual driving force to drive the vehicle. Therefore, in steps S141-S142, the motion resistance is calculated first, and then the sum of the friction of the wheels is calculated and subtracted from the motion resistance to obtain the real driving force of the vehicle. It can be seen that, in the calculation of the driving force of the vehicle, the influence of the motion resistance is considered, so that the calculated driving force is closer to the real driving force of the vehicle, and the accuracy of the calculated vehicle speed and wheel speed is improved.

[0189] Continuing from Figure 1 and in combination with Figure 4As shown in some of the exemplary embodiments, the motion resistance of the vehicle calculated in step S141 can specifically include air resistance and rolling resistance.

[0190] In step S141, the motion resistance of the vehicle is calculated according to the vehicle speed at the previous moment and the static parameters of the vehicle, which can specifically include calculating the rolling resistance of the vehicle according to the mass of the vehicle and a preset rolling resistance coefficient. Then, the air density is obtained, and the air resistance of the vehicle is calculated according to the frontal area of the vehicle, the air density, and the vehicle speed at the previous moment. The sum of the air resistance and the rolling resistance is calculated to determine the motion resistance.

[0191] The static parameters of the vehicle include the mass of the vehicle and the frontal area of the vehicle, so the mass of the vehicle and the frontal area of the vehicle can be directly obtained from the static parameters of the vehicle.

[0192] More specifically, the calculation formula of the rolling resistance includes: roll = C r × m × g.

[0193] The calculation formula of the air resistance includes: air = 0.5 × p × C d × A × v 2 .

[0194] Where Cr is the rolling resistance coefficient; m is the mass of the vehicle; g is the acceleration of gravity; unit m / s 2 ; p is the air density; Cd is the air resistance coefficient; A is the frontal area of the vehicle; v is the vehicle speed at the previous moment, which can be the vehicle speed calculated according to the above steps S110-S140 at the previous moment.

[0195] After calculating the rolling resistance and the air resistance, the sum of the rolling resistance and the air resistance is calculated, i.e., the motion resistance of the vehicle is calculated.

[0196] By calculating the air resistance and the rolling resistance to calculate the motion resistance, various resistances generated during the movement of the vehicle body are fully considered, so that the calculated driving force is closer to the real driving force of the vehicle, and the calculation accuracy of the vehicle speed and the wheel speed is improved.

[0197] Continuing from Figure 1 , and combining Figure 5 As shown in some of the exemplary embodiments, in the above step S150, the current vehicle speed of the vehicle is equivalent to each wheel, and the wheel speed of each wheel is determined respectively, which can be realized through the following steps S151-S153.

[0198] Step S151, according to the front axle steering angle of the vehicle and the wheelbase of the vehicle, respectively calculating a first distance between the instantaneous turning center of the vehicle and the center of the vehicle, and a second distance between the instantaneous turning center of the vehicle and each wheel.

[0199] In some exemplary embodiments, in step S151, the process of calculating the first distance and the second distance specifically includes: based on the front axle steering angle, the wheelbase of the vehicle, applying a preset Ackerman steering geometry model to determine the current instantaneous turning center of the vehicle. Based on the positional relationship between the current instantaneous turning center of the vehicle and each wheel, the distance between each wheel and the current instantaneous turning center of the vehicle is determined to obtain each second distance. Based on the positional relationship between the current instantaneous turning center of the vehicle and the center of the vehicle, the first distance is determined.

[0200] Specifically, the front axle steering angle δ is the steering angle of the front wheel after the steering wheel input is mechanically transmitted, which indicates the deflection angle of the front wheel relative to the longitudinal axis of the vehicle (i.e., the center of symmetry in the front-rear direction of the vehicle). It determines the position of the instantaneous turning center and the turning radius of the vehicle during turning.

[0201] Wherein, the instantaneous turning center refers to a virtual center point of the rotational motion of the vehicle at a certain moment during turning. For a rigid body (assuming no suspension deformation), the instantaneous turning center is located on the extension line of the rear axle. Specifically, in the preset Ackerman steering geometry model, assuming that the front wheel steering angle is δ and the rear wheel is not steered, the instantaneous turning center is located on the extension line of the rear axle of the vehicle, and the distance between the instantaneous turning center and the midpoint of the rear axle is

[0202] The center of the vehicle is the geometric center of the vehicle, which refers to the intersection of the center line of the front-rear axle and the center line of the left-right wheel.

[0203] After the instantaneous turning center is determined, the first distance and the second distance can be calculated. The first distance is the distance between the instantaneous turning center and the center of the vehicle, and the second distance is the distance between the instantaneous turning center and the wheel, more specifically, the distance between the wheel and the connecting point of the front-rear axle. Wherein, the wheels of the vehicle include the front left wheel, the front right wheel, the rear left wheel and the rear right wheel.

[0204] Exemplarily, reference can be made to Figure 6 , Figure 6 An example of the positional relationship between the instantaneous turning center, the center of the vehicle and each wheel in the vehicle is shown.

[0205] If the center of the rear axle is taken as the coordinate origin (0, 0) and the direction from the tail of the vehicle to the head of the vehicle is taken as the positive direction of the x-axis and the direction perpendicular to the right of the vehicle is taken as the positive direction of the y-axis, then the coordinates of each position are respectively:

[0206] Vehicle center (L / 2, 0); left front wheel (L, -W / 2); right front wheel (L, W / 2); left rear wheel (0, -W / 2); right rear wheel (0, W / 2); instantaneous turning center Wherein, δ is the front axle steering angle of the vehicle, right turn (i.e. clockwise steering) is positive, left turn is negative, L is the wheelbase of the vehicle, and W is the wheel track of the vehicle.

[0207] Then, the first distance and the second distance of each wheel can be calculated according to the coordinates of each position point.

[0208] More specifically, the first distance R, i.e. the calculation formula of the distance from the vehicle center to the instantaneous turning center, can include the following formula three.

[0209]

[0210] The calculation formula of each second distance Rwheelmay include the following formula four.

[0211]

[0212] Through the calculation formula of the first distance and the second distance in the step S151, the distances from the instantaneous turning center to the vehicle center, to the left front wheel, to the right front wheel, to the left rear wheel and to the right rear wheel can be calculated respectively, so as to facilitate the conversion of the vehicle speed by using the first distance and the second distance of each wheel subsequently.

[0213] In the step S152, the relative proportion between each second distance and the first distance is calculated respectively to obtain the equivalent conversion proportion corresponding to each wheel.

[0214] Specifically, the equivalent conversion proportion of each wheel can be R wheel For example, the equivalent conversion proportion of the left front wheel can be obtained by dividing the second distance of the left front wheel calculated in the step S151 by the first distance.

[0215] In the step S153, the current vehicle speed is divided according to the equivalent conversion proportions to obtain the wheel speeds of each wheel.

[0216] Specifically, in the step S153, after the equivalent conversion proportions are calculated, the wheel speed of each wheel can be obtained by multiplying the vehicle speed calculated in the step S140 by the equivalent conversion proportion corresponding to the wheel. For example, the wheel speed of the left front wheel can be obtained by multiplying the vehicle speed by the equivalent conversion proportion of the left front wheel.

[0217] Through the steps S151-S153, the calculated vehicle speed is equivalently distributed to the four wheels by using the instantaneous turning radius and the basic parameters of the vehicle, so as to obtain the wheel speed of each wheel. The algorithm of this wheel speed equivalent conversion can better distribute the speed of each wheel during turning, so as to improve the steering flexibility and stability of the vehicle, and is especially suitable for the demand for precise control in automatic driving technology.

[0218] It is worth noting that, based on the above exemplary embodiments, as a preferred exemplary embodiment, the vehicle wheel speed determination method according to the present embodiment specifically includes Figure 7 , and the overall process of the vehicle wheel speed determination method specifically includes:

[0219] Referring to Figure 7 , first, input the sensor data and the static parameters of the vehicle.

[0220] For example: the real-time rotational speed of the four wheels collected by the wheel speed sensor (unit: rad / s), the lateral acceleration of the vehicle measured by the lateral acceleration sensor in the inertial measurement unit (IMU) (unit: m / s 2 ), the longitudinal acceleration of the vehicle measured by the longitudinal acceleration sensor (unit: m / s 2 ), the rotational angular velocity of the vehicle around the vertical axis measured by the yaw rate sensor (unit: rad / s), and the steering wheel angle measured by the steering wheel angle sensor (unit: radian).

[0221] For example: the mass m of the vehicle, the wheelbase L, the track W, and the static load Fz of the four wheels. For example, the tire magic formula parameters (such as cornering stiffness, aligning torque coefficient, etc.) and the friction coefficient model parameters calibrated through experiments.

[0222] Then, the input parameters and data are preprocessed and fused. Specifically, the units of the data are converted to standard units, and the data are filtered to remove noise and improve data quality.

[0223] Then, based on the static parameters and the motion parameters of the vehicle, the dynamic load changes of each wheel caused by the inertia moment and the roll moment during the dynamic process of the vehicle are calculated, and the static load changes of each wheel of the vehicle are combined to calculate the dynamic vertical load of each wheel, so as to obtain the vertical force of each wheel.

[0224] Meanwhile, the rotational speed of the wheels after the preprocessing can be combined with signals such as the yaw rate, the lateral speed, and the steering wheel angle of the vehicle to calculate the equivalent wheel speed of each of the four wheels.

[0225] The slip ratio is then calculated in combination with the equivalent center-of-mass speed of each wheel, and the current friction coefficient of each wheel is calculated in combination with the magic formula. The driving force of each wheel is then calculated using the friction coefficient of each wheel and the vertical force of each wheel, and the driving force of the four wheels is summed and subtracted by the air resistance and the rolling resistance to calculate the driving force of the vehicle.

[0226] The corresponding acceleration of the vehicle can then be calculated using the processed data and the calculated driving force, so that the speed of the vehicle, i.e., the vehicle speed, can be calculated using an integrator.

[0227] After the vehicle speed is calculated, the calculated vehicle speed can be converted to the wheel speed of each of the four wheels in combination with the calculation method of the instantaneous turning radius and the parameters of the vehicle body.

[0228] The determination method of the vehicle wheel speed in this embodiment is designed as above, the slip ratio of each wheel of the vehicle is calculated, the preset magic formula of the tire is combined, and the real-time vertical force during the movement of the vehicle is calculated to calculate the driving force of the vehicle, and then the vehicle speed is obtained, and then the vehicle speed is converted to the wheel speed of each wheel according to the geometric relationship of the vehicle.

[0229] In this wheel speed calculation method, the slip ratio is combined to consider the situation of wheel slip of the vehicle, and the vertical force of each wheel during the movement of the wheel can be calculated in real time without being limited by the state of the vehicle. Compared with the wheel speed calculation method in the related art which assumes that the vehicle is in a specific driving state and does not consider the slip, the determination method of this embodiment overcomes the problem of insufficient static model assumption, does not ignore the side slip and slip of the wheel, and calculates in real time according to the actual situation, thereby improving the accuracy of the calculation of the wheel speed of the wheel and reducing the error.

[0230] In another aspect, in the vehicle wheel speed determination method of the present embodiment, the calculation error can be reduced, and signals such as the steering angle are combined, and multi-source data such as the wheel speed sensor and the inertial measurement unit of the vehicle are fused. The wheel speed of the vehicle is calculated by combining the lateral acceleration, the longitudinal acceleration, the yaw rate of the vehicle, the steering wheel angle, and the real-time speed of the wheel. In this way, the wheel speed of the vehicle is calculated based on the real-time motion data of the vehicle. Compared with the related art based on Ackerman steering geometry, more factors are considered, which is suitable for various complex working conditions during vehicle motion, has strong adaptability, and still has good calculation ability of vehicle wheel speed during vehicle motion.

[0231] Furthermore, in the wheel speed determination method of the present embodiment, the driving conditions of the vehicle are not assumed, but the wheel speed is calculated based on the actual motion data during vehicle driving. Unlike the related art based on Ackerman steering geometry, which assumes uniform vehicle speed or a fixed steering angle, the dynamic condition adaptability in calculating the wheel speed of the vehicle is improved.

[0232] Furthermore, in the wheel speed determination method of the present embodiment, when calculating the vertical force of the wheel, the wheel body geometric parameters (wheelbase, track, static load) and motion parameters (lateral acceleration, longitudinal acceleration) are used for calculation. Not only the static load of the wheel is considered, but also the change of the load caused by the motion process is considered, thereby improving the calculation accuracy of the vertical force of the wheel, and further improving the accuracy of the wheel speed of the vehicle, to further improve the handling stability of the vehicle, and on the basis of more accurate control, it is also beneficial to improve fuel efficiency and reduce tire wear.

[0233] Furthermore, in the wheel speed determination method of the present embodiment, when calculating the real driving force of the vehicle, the magic formula and the friction coefficient model are combined, and the effects of wind resistance, rolling resistance and other factors on the real driving force of the vehicle are considered. It can be seen that the present embodiment provides a calculation method for determining the real driving force of the vehicle with high accuracy. Further, it is beneficial to more accurately predict the power demand of the vehicle, thereby optimizing engine output and energy management, and improving the overall performance of the vehicle.

[0234] Furthermore, in the wheel speed determination method of the present embodiment, the calculated vehicle speed is distributed to each wheel to obtain the wheel speed of each wheel, which is calculated based on the instantaneous turning radius and the basic parameters of the vehicle body. This method can adjust the four-wheel speed in real time to adapt to the turning characteristics according to the size and direction of the steering angle of the vehicle, and can better distribute the speed of each wheel during turning, thereby improving the steering flexibility and stability of the vehicle.

[0235] The above merely provide some embodiments of the present application, but are not intended to limit the present application, and the technical features or structures in the different embodiments above can be combined as needed to form other specific technical solutions. Various modifications and changes can be made by those skilled in the art based on the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A method for determining a vehicle wheel speed, characterized in that: The determination method includes: Obtaining a current dynamic vertical load on each wheel of the vehicle, and determining a current vertical force on each wheel based on the current dynamic vertical load on each wheel; Obtaining a current slip rate of each wheel, and determining a current friction coefficient between each wheel and the ground based on a preset tire friction characteristic model; determining the current friction force between each wheel and the ground according to the current friction coefficient of each wheel and the vertical force; Obtaining a current driving force of the vehicle based on the current friction between each wheel and the ground, and calculating a current speed of the vehicle based on the current driving force of the vehicle and the speed of the vehicle at a previous moment; The current speed of the vehicle is equated to each of the wheels, and the wheel speed of each of the wheels is determined respectively.

2. The method for determining the vehicle wheel speed according to claim 1, characterized in that: The tire friction characteristic model adopts the magic formula of tire dynamics, and the current slip rate of each wheel is obtained, and the friction coefficient between each wheel and the ground is determined based on the preset tire friction characteristic model, including: According to the geometric structure of the vehicle, the acquired real-time wheel speed of each wheel is converted to the center of mass of the vehicle, and the equivalent center of mass speed corresponding to each wheel is determined; Determining the current slip rate of each wheel according to the equivalent center of mass velocity corresponding to each wheel and the vehicle speed at a previous moment; The slip rate corresponding to each wheel is substituted into the tire friction characteristic model to calculate the friction coefficient between each wheel and the ground.

3. The method for determining the vehicle wheel speed according to claim 2, wherein: The step of converting the acquired real-time wheel speed of each wheel to the center of mass of the vehicle to determine the equivalent center of mass speed of each wheel includes: Calculating a speed adjustment factor for each wheel according to a difference between the real-time wheel speeds of each wheel; Correcting the real-time wheel speed of each wheel according to the calculated speed adjustment factor of each wheel to obtain an equivalent wheel speed of each wheel; According to the geometric structure of the vehicle, the equivalent wheel speed of each wheel is converted to the center of mass of the vehicle to determine the equivalent center of mass speed corresponding to each wheel.

4. The method for determining the vehicle wheel speed according to claim 3, wherein: Calculating the speed adjustment factor of each wheel based on the difference between the real-time wheel speeds of each wheel includes: Calculating the difference in real-time wheel speed between every two wheels to obtain the wheel speed difference corresponding to each wheel, wherein the wheel speed difference corresponding to the wheel includes the difference in real-time wheel speed between the wheel and the other three wheels; determining a wheel speed gain of each wheel based on the wheel speed difference corresponding to each wheel and a preset gain constant; Calculating a target adjustment factor for each wheel based on a wheel speed gain of each wheel, wherein the target adjustment factor represents a target value expected to be adjusted under a current vehicle operating condition; According to the target adjustment factor of each wheel, a speed adjustment factor of each wheel is determined by a preset closed-loop control algorithm.

5. The method for determining the vehicle wheel speed according to claim 2, wherein: Determining the current slip rate of each wheel according to the equivalent center of mass velocity corresponding to each wheel and the vehicle speed at a previous moment includes: Determining the tire slip amount corresponding to each wheel based on the equivalent center of mass velocity corresponding to each wheel and the vehicle speed at a previous moment; The ratio of the tire slip amount to the vehicle speed at the last moment is calculated to obtain the current slip rate of each wheel.

6. The method for determining the vehicle wheel speed according to claim 1, wherein: Obtaining the current driving force of the vehicle according to the current friction between each wheel and the ground includes: Calculating the motion resistance of the vehicle based on the vehicle speed at a previous moment and the static parameters of the vehicle; Sum the friction forces between the wheels and the ground, and subtract the motion resistance to obtain the current driving force of the vehicle; The static parameters are parameters that describe the static characteristics of the vehicle.

7. The method for determining the vehicle wheel speed according to claim 6, wherein: The motion resistance includes air resistance and rolling resistance; the static parameters of the vehicle include the mass of the vehicle and the frontal area of ​​the vehicle; Calculating the motion resistance of the vehicle based on the vehicle's last speed and the vehicle's static parameters includes: Calculating the rolling resistance of the vehicle according to the mass of the vehicle and a preset rolling resistance coefficient; Obtaining air density, and calculating the air resistance of the vehicle based on the frontal area of ​​the vehicle, the air density, and the vehicle speed at a previous moment; The sum of the air resistance and the rolling resistance is calculated to determine the motion resistance.

8. The method for determining vehicle wheel speed according to claim 1, wherein: The current dynamic vertical load of each wheel includes an inertia vertical load and a roll vertical load; The obtaining of the current dynamic vertical load of each wheel in the vehicle includes: Obtaining the mass, center of gravity height, wheelbase, and average wheelbase of the vehicle, wherein the average wheelbase is the average of the wheelbases of the wheels; Obtaining the current longitudinal acceleration and lateral acceleration of the vehicle; Calculating an inertial vertical load based on the mass, center of gravity height, current longitudinal acceleration, and wheelbase of the vehicle; Calculating a roll vertical load based on the mass, center of gravity height, current lateral acceleration of the vehicle, and the average wheelbase; Based on the inertia vertical load and the roll vertical load, a current dynamic vertical load of each wheel is determined.

9. The method for determining the vehicle wheel speed according to claim 1, characterized in that: The step of equating the current speed of the vehicle to each wheel and determining the wheel speed of each wheel includes: Calculating, based on the front axle steering angle of the vehicle and the wheelbase of the vehicle, a first distance between the instantaneous turning center of the vehicle and the center of the vehicle, and a second distance between the instantaneous turning center of the vehicle and each of the wheels; respectively calculating a relative ratio between each of the second distances and the first distance to obtain an equivalent conversion ratio corresponding to each of the wheels; The current speed of the vehicle is divided according to each of the equivalent conversion ratios to obtain the wheel speed of each of the wheels.

10. The method for determining the vehicle wheel speed according to claim 9, characterized in that: The respectively calculating a first distance between the instantaneous turning center of the vehicle and the center of the vehicle, and a second distance between the instantaneous turning center of the vehicle and each of the wheels, comprises: Based on the front axle steering angle and the wheelbase of the vehicle, a preset Ackermann steering geometry model is applied to determine the current instantaneous turning center of the vehicle; determining, based on a positional relationship between a current instantaneous turning center of the vehicle and each of the wheels, a distance between each of the wheels and the current instantaneous turning center of the vehicle, to obtain each of the second distances; The first distance is determined based on a positional relationship between a current instantaneous turning center of the vehicle and a center of the vehicle.

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