Wheel hub motor driving and braking integrated system with built-in speed reducer and control method

Abstract

The invention relates to a hub motor driving and braking integrated system with a built-in speed reducer and a control method, and belongs to the technical field of electric vehicle braking, the system comprises a motor, a planetary gear speed reducer and a brake, the planetary gear speed reducer comprises a sun gear, a gear, a planet carrier plate and a planet shaft, the sun gear and the gear are integrally formed, the sun gear is of a hollow structure, the sun gear is connected to the motor through a spline, the planet shaft and a wheel bolt are arranged in a staggered mode, and the planet carrier plate is fixedly connected to a wheel bolt fixing plate. The technical problems that in the prior art, a hub motor with a built-in speed reducer is low in internal space utilization rate, poor in heat dissipation effect and large in noise due to insufficient structures and strategies are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of electric vehicle braking, and in particular to a hub motor drive and brake integrated system with a built-in reducer and a control method. Background Art

[0002] Compared with other drive schemes, wheel hub motor drive can not only simplify the structural layout of the vehicle, but also improve the driving and braking control performance of the vehicle, which is the development direction of new energy vehicles. Wheel hub motors can currently be divided into direct drive and reduction type. Direct drive wheel hub motors are difficult to provide large torque while controlling volume and weight. In contrast, reduction wheel hub motors can enable the car to obtain stable and large torque, and the existence of the reducer reduces the burden on the motor. Most of the current reduction wheel hub motors are equipped with planetary gear reducers, and the brakes are disc brakes. Without considering the installation space, some reduction wheel hub motors use a two-stage planetary gear reducer and realize two-speed wheel hub motor speed change through a shifting mechanism. At present, there are still some defects in the reduction wheel hub motor. Their mass is relatively large, which will increase the unsprung mass, thereby affecting the vehicle's handling stability and smoothness. Secondly, because the internal space is not fully utilized, the axial size is large, which makes the installation process more difficult. In addition, the inadequacy of the structure and control strategy may cause a large noise when running at high speed. At the same time, the integrated installation of the motor, reducer and brake and the small internal clearance limit the heat dissipation performance, and heat accumulation may reduce the performance and life of the wheel hub motor. Finally, the heat generated by the brake during braking will cause the assembly temperature to rise rapidly, which may cause thermal decay of the brake. These problems need to be solved through technological innovation and design optimization to improve the performance and reliability of the reduction wheel hub motor. Summary of the invention

[0003] In view of this, it is necessary to provide a hub motor drive and braking integrated system and control method with an internal reducer to solve the technical problems in the prior art of low internal space utilization, poor heat dissipation, and high noise caused by insufficient structure and strategy of the hub motor with an internal reducer.

[0004] In order to solve the above problems, the present invention provides a hub motor drive and brake integrated system with a built-in reducer, comprising a motor and a planetary gear reducer, including: The planetary gear reducer comprises a sun gear, a gear, a planet carrier plate and a planet shaft, the sun gear and the gear are integrally formed, and the sun gear is a hollow structure, the sun gear is connected to the motor through a spline, and the planet shaft is staggered with the wheel bolts; The planetary gear reducer comprises a planet carrier plate, and the planet carrier plate is fixedly connected to a wheel bolt fixing plate.

[0005] In a possible implementation, the gears of the planetary gear reducer are all designed as helical gears.

[0006] In a possible implementation, the planet shafts of the planet carrier plate and the wheel bolts of the wheel bolt fixing plate are arranged alternately.

[0007] In a possible implementation, the thickness of the planet carrier plate is 14 mm.

[0008] In a possible implementation, the housing of the planetary gear reducer is a lightweight housing designed by topology optimization, including: The following topology optimization model is used to perform topology optimization on the planetary gear reducer housing:

[0009] in, Represents the relative density of the reducer housing, m Represents the mass of the reducer housing, Represents the original volume of the reducer housing, represents the volume to be removed, To modify the upper limit of the volume, X Represents the displacement of the reducer housing, represents the yield limit of the material, Indicates the relative volume of the reducer housing. i Indicates i data points, n Indicates the total amount.

[0010] In a possible implementation, the planetary gear reducer includes a locking nut, and an outer circumferential surface of the locking nut is in contact with an oil seal.

[0011] In a second aspect, the present invention further provides a control method for a hub motor drive and brake integrated system with a reducer built in, which is applied to the hub motor drive and brake integrated system with a reducer built in as described in any one of the above items, comprising: According to the opening change rate of the brake pedal pressed by the driver, the driver's expected braking deceleration and braking torque are obtained; Determining a regenerative braking torque according to the braking deceleration based on a regenerative braking capability and a battery charge; According to the vertical load ratio and regenerative braking torque of each wheel, the actual distribution regenerative braking torque of each wheel is determined; According to the braking torque and the actual distribution of regenerative braking torque to each wheel, the actual expected main actuation pressure is determined based on the PID controller.

[0012] In some embodiments, determining the regenerative braking torque according to the braking deceleration, based on the regenerative braking capability and the battery power, includes: Based on the braking force distribution principle of the front and rear axles of the vehicle, ECE braking regulations, vehicle regenerative braking constraints and braking impact degree limits, the motor-hydraulic compound braking force distribution strategy is determined for the purpose of safety and comfort; The relationship between the battery SOC value and the threshold, the working state of the ABS and the fault state of the hub motor system are used as the opening and closing conditions of the regenerative braking system.

[0013] In some embodiments, the motor-hydraulic compound braking force distribution strategy includes: According to the difference between the braking torque of the whole vehicle and the actual distributed regenerative braking torque of each wheel, the mechanical braking torque required for the whole vehicle braking is obtained; According to the mechanical braking torque required by the vehicle braking, based on the corresponding relationship between the preset braking torque and the main driving force, the required main driving pressure is determined; Based on the PID controller, the compensated main actuating pressure is obtained; According to the required main drive pressure and the compensated main actuation pressure, the actual desired main actuation pressure is obtained.

[0014] In some embodiments, it also includes: A preset fuzzy C-means clustering algorithm is used to classify the driving styles, and a driving style classification result is obtained, and a support vector machine model is trained according to the driving style classification result; A driving style category is determined based on the support vector machine model, and based on the driving style category, an actual desired main actuator pressure is determined.

[0015] The beneficial effects of the present invention are: by integrating the reducer sun gear shaft and the gear, it is beneficial to increase the strength of the sun gear and realize the lightweight of the reducer, and the sun gear shaft is designed as a hollow structure, which allows more effective thermal management, dissipates heat through internal channels, reduces the heat accumulation of parts during operation, and reduces the mass of parts to effectively reduce the inertia of rotating parts, thereby improving their rotational flexibility and dynamic response. At the same time, by fixing the planet carrier plate to the wheel bolt fixing plate, the mass of the planet carrier plate and the wheel bolt fixing plate can be reduced, reducing the overall mass of the vehicle.

[0016] Furthermore, the driver's braking demand is analyzed, and then the required regenerative braking torque is limited by the regenerative braking deceleration limiting module, and initially distributed according to the vertical load ratio of each wheel. In addition, multiple factors such as driving speed, braking deceleration, battery power state, battery charging state, ABS system status, and potential fault signals are comprehensively considered to accurately calculate the expected electric braking torque for each wheel. This approach not only improves braking performance, but also helps to optimize energy recovery and extend the service life of the braking system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a general structural diagram of the electric wheel in the hub motor drive and brake integrated system with a built-in reducer provided by the present invention; Figure 2 A structure diagram of a reducer in the hub motor drive and brake integrated system with a built-in reducer provided by the present invention; Figure 3 In the hub motor drive and brake integrated system with a built-in reducer provided by the present invention, the power transmission route of the reducer; Figure 4 An exploded diagram of an electric wheel in the integrated wheel hub motor drive and brake system with a built-in reducer provided by the present invention; Figure 5 A schematic flow chart of an embodiment of a control method for a hub motor drive-brake integrated system with a reducer built-in provided by the present invention; Figure 6 A logic diagram of an electro-hydraulic composite brake system in a control method of a hub motor drive brake integrated system with a reducer built in the present invention; Figure 7 A schematic diagram of the PID control flow of the mechanical hydraulic brake system in the control method of the hub motor drive brake integrated system with a reducer built in the present invention; Figure 8 A longitudinal force analysis diagram of a vehicle during braking in a control method of a hub motor drive and brake integrated system with a reducer built in the present invention; in, Figure 1 In: 1. Bolts for reducer end cover; 2. Internal gear ring; 3. Tapered roller bearing; 4. Planetary gear bearing; 5. Planetary gear; 6. Sun gear; 7. Wheel bolts; 8. Cassette oil seal; 9. Motor rotor; 10. Motor magnet; 11. Motor stator; 12. Motor rotary transformer; 13. Brake wheel cylinder; 14. Motor rotor bracket; 15. Planet carrier; 16. Brake shoe; 17. Brake spring; 18. Brake drum; 19. Motor end cover; 20. Motor housing; Figure 2 In: 1. Reducer housing; 2. Rotary oil seal; 3. Lock nut; 4. Rotary oil seal; 5. Sun gear; 6. Planet carrier; 7. Tapered roller bearing; 8. Planet gear shaft; 9. Wheel bolts; 10. Planet gear bearing; 11. Planet gear; 12. Planet carrier plate; 13. Internal gear ring; 14. Cassette oil seal; 15. Reducer end cover bolts; Figure 4 In: 1. Drum brake; 2. Motor stator and rotor assembly; 3. Planetary gear reducer; 4. Motor rotor bracket; 5. Motor housing. DETAILED DESCRIPTION

[0018] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0019] A specific embodiment of the present invention discloses a hub motor drive brake integrated system with a built-in reducer, including a motor and a planetary gear reducer, see Figure 1-Figure 4 ,include: The planetary gear reducer comprises a sun gear, a gear, a planet carrier plate and a planet shaft, the sun gear and the gear are integrally formed, and the sun gear is a hollow structure, the sun gear is connected to the motor through a spline, and the planet shaft is staggered with the wheel bolts; The planetary gear reducer comprises a planet carrier plate, and the planet carrier plate is fixedly connected to a wheel bolt fixing plate.

[0020] In this embodiment, the sun gear shaft of the reducer is integrated with the gear, which is conducive to increasing the strength of the sun gear and achieving lightweight of the reducer. The sun gear shaft is designed as a hollow structure, which allows more effective thermal management, dissipates heat through internal channels, and reduces the heat accumulation of parts during operation. At the same time, reducing the mass of parts can effectively reduce the inertia of rotating parts, thereby improving their rotational flexibility and dynamic response. At the same time, by fixing the planet carrier plate to the wheel bolt fixing plate, the mass of the planet carrier plate and the wheel bolt fixing plate can be reduced, reducing the overall mass of the vehicle.

[0021] It should be noted that the motor, planetary gear reducer and brake involved in the present invention are highly integrated structures. In terms of brakes, the problem of heating during braking is solved by electro-hydraulic composite braking. During braking, electric braking is given priority, and mechanical braking is considered when electric braking is insufficient, which minimizes the working time of the brake, greatly reduces the heat dissipation of the assembly during braking, and also reduces noise, solving the problem of high temperature and noise during braking.

[0022] Furthermore, the braking system brakes the input end of the reducer instead of the traditional braking on the output end of the reducer, which can effectively utilize the torque-increasing effect of the reducer to amplify the braking torque, not only to obtain the minimum braking torque, but also to make the braking system structure more compact, meeting the miniaturization and lightweight design of the brake.

[0023] Furthermore, the reducer sun gear is connected to the motor through a spline hub, and the motor and reducer share a common end cover. The motor power is directly transmitted to the reducer, avoiding power efficiency loss; at the same time, the motor rotor bracket drives the brake drum to rotate, and the motor is indirectly stopped by the brake drum during braking to achieve braking. Figure 1 and Figure 2As shown, the function of providing power for the permanent magnet inner rotor motor is mainly realized by the rotor 8, the magnet 9, the stator 10, and the rotary transformer 19. The outer side of the stator is close to the inner wall of the motor housing for positioning. The magnet is fixed at the opening on the side of the stator. The rotor is installed on the rotor bracket with an air gap between it and the stator. The drum brake is powered by the hydraulic cylinder 18, and the brake spring 14, the brake drum 13, and the brake shoe 15 are used as actuators to achieve braking.

[0024] The structure of single-stage NGW planetary gear reducer is as follows: Figure 3 The main reduction mechanism is composed of a sun gear 5, a planetary gear 11, and an inner gear ring 13. The sun gear 5 is connected to the Figure 1 The motor rotor bracket 17 is connected to receive the power from the motor. The sun gear power is transmitted to the planetary gear 11, and the planetary gear 11 transmits the decelerated power to the planetary carrier through the planetary gear bearing 10 and the planetary gear shaft, and outputs it to the wheel through the wheel bolt. The power transmission route is as follows Figure 4 .

[0025] The reducer is oil-immersed and lubricated inside, and a rotary oil seal is used for sealing. A box oil seal 14 is used at the connection with the outside to prevent leakage caused by harsh working conditions. The relative rotation between the housing and the planetary carrier is guaranteed by a tapered roller bearing 3. The reducer end cover and the housing are connected by the reducer end cover bolts 1. The reducer is embedded in the motor and shares the housing, which can not only reduce the axial size and assembly weight, but also reduce the number of connectors and improve the structural strength of the hub motor assembly.

[0026] During normal driving, Figure 1 As shown, the magnet 10 is energized to rotate the rotor 9, and there is a certain gap between the rotor 9 and the stator 11, which is called the air gap. The rotor 9 drives the rotor bracket 14 to rotate, and the shaft in the middle of the rotor bracket 14 drives the brake to rotate synchronously. At the same time, the shaft is connected to the sun gear 6 through a spline, and the sun gear 6 transmits power to the planetary gear 5. The planetary gear 5 meshes with the inner gear ring 2 to achieve a deceleration effect. The relative rotation of the planetary gear 5 and the gear shaft is ensured by the planetary gear bearing 4. The revolution of the planetary gear 5 transmits power to the planetary carrier plate through the gear shaft. The planetary carrier plate is connected to the wheel bolts through a spline, driving the wheel bolts 7 to rotate, and the wheel bolts 7 output power as an output mechanism. Among them, the relative rotation between the planetary carrier and the housing is ensured by the tapered roller bearing 3. The gap between the planetary carrier plate and the housing is sealed by a cassette oil seal 8. The gaps between the central axis of the rotor bracket 14 and the locking nut, and between the locking nut and the housing are sealed by ordinary oil seals.

[0027] During braking, the motor receives the command from the motor controller and implements electric braking. The speed of the rotor bracket 19 starts to decrease. The VCU determines whether the braking force is sufficient. If it is insufficient, the drum brake makes up for the shortfall. At this time, the drum brake provides a clamping force to the brake shoe 15 through the brake hydraulic cylinder 18. The friction between the brake shoe 15 and the brake drum 13 decelerates the rotor bracket 19, thereby reducing the speed of the sun gear and the output speed of the assembly, thus achieving braking.

[0028] In some embodiments, the gears of the planetary gear reducer are all designed as helical gears.

[0029] In this embodiment, in order to make the reducer have the characteristics of low noise, the reducer adopts a helical gear design, which effectively reduces the noise generated by meshing by increasing the overlap. And after heat treatment, the gear grinding and tooth top chamfering are performed to effectively reduce the noise of the reducer. The gear shaping is firstly to use bilateral symmetrical shaping for the gear tooth profile, then to use drum shaping for the gear tooth direction, and finally to use drum shaping for the spline tooth direction. Through this shaping scheme design, the impact and vibration generated when the gear meshes can be reduced, thereby reducing noise. At the same time, it can improve the contact stress distribution of the tooth surface, reduce stress concentration, improve the bearing capacity of the gear, help to extend the service life of the gear, and improve the transmission stability.

[0030] The load balancing problem of planetary gears will cause excessive noise in the reducer and unstable transmission. In order to solve the load balancing problem during the operation of planetary gears, the reducer adopts a sun gear floating mechanism design. A spline is used at one end of the sun gear shaft to achieve sun gear floating. The structure is simple and the cost is low. Through this design, the sun gear floating allows it to displace and deflect in the radial direction to automatically find the equilibrium position, realize the uniform distribution of loads between planetary gears, and prevent the planetary gear system from resonating and deforming in actual work, affecting the stability and accuracy of the transmission, and even causing damage to the entire transmission system. At the same time, it effectively reduces the vibration and noise generated by the gears during the transmission process.

[0031] In some embodiments, the planet shafts of the planet carrier plate and the wheel bolts of the wheel bolt fixing plate are arranged alternately.

[0032] In this embodiment, the reducer integrates the two functional components, the planet carrier plate and the wheel bolt fixing plate, on a 14mm planet carrier plate under the condition that the strength is qualified. As the output end of the reducer, the planet carrier needs to effectively transmit the torque output by the motor to the wheel. The thickness of the planet carrier plate with a reasonable design has an important influence on its torque transmission capacity. The 14mm thickness of the planet carrier plate can effectively reduce the weight and improve the transmission efficiency while maintaining the strength. To prevent interference, the 5 wheel bolts and 3 planetary shafts are designed to be staggered and distributed in the same plane. This structure makes the axial structure of the reducer compact.

[0033] In some embodiments, the housing of the planetary gear reducer is a lightweight housing designed by topology optimization, including: The following topology optimization model is used to perform topology optimization on the planetary gear reducer housing:

[0034] in, Represents the relative density of the reducer housing, m Represents the mass of the reducer housing, Represents the original volume of the reducer housing, represents the volume to be removed, To modify the upper limit of the volume, X Represents the displacement of the reducer housing, represents the yield limit of the material, Indicates the relative volume of the reducer housing. i Indicates i data points, n Indicates the total amount.

[0035] Furthermore, the axial dimension compression of the reducer can not only achieve the goal of easy installation, but also reduce weight by reducing the volume. To achieve the axial dimension compression, the reducer has three special designs.

[0036] In some embodiments, the planetary gear reducer includes a locking nut, and the outer circumferential surface of the locking nut is in contact with the oil seal.

[0037] In this embodiment, the locking nut is optimized and designed so that the axial dimension is shortened by 10 mm compared with the traditional structure. The locking washer is eliminated in the embodiment of the present invention, and the outer circle of the locking nut is directly designed as the contact surface of the oil seal lip, thereby eliminating the part of the rear shaft originally used for the oil seal lip contact. This modification not only simplifies the structure, but also utilizes the originally unused space inside, effectively saving the external dimensions. At the same time, the design converts the threaded connection position of the locking nut to the hole of the planetary carrier, inverting the traditional structural layout, further saving the external dimensions, and making the design more compact. The locking nut is positioned by cooperating with the end of the planetary carrier through its external thread to ensure that the end face of the 32915 bearing is pressed and aligned while leaving a suitable clearance, and then the locking bolt is locked through the 5 threaded holes on the locking bolt and the 8 bolt holes at the end of the planetary carrier to limit the axial movement of the locking bolt, thereby achieving axial fixation of the 32915 bearing.

[0038] Furthermore, under the condition of meeting the strength test, the planetary gear transmission mechanism inside the reducer is optimized, and the tooth thickness is reduced by increasing the center distance, so as to realize the flattening of the planetary gear transmission mechanism. The axial dimension of the gear with the same strength and thickness is reduced by 7mm, which effectively compresses the axial dimension. In order to make the reducer obtain high strength, the sun gear and planetary gear as vulnerable parts are made of 20CrMnTi material, and the inner ring gear is made of 42CrMo material. 20CrMnTi needs to go through normalizing, carburizing, quenching, tempering and other heat treatment processes. After carburizing at 910-940℃, quenching at 870℃, and tempering at 180-200℃, the mechanical properties of tensile strength ≥1100Mpa, yield strength ≥850Mpa, elongation ≥10%, section shrinkage ≥45%, impact toughness ≥680, and hardness of 58-62HRC surface layer obtains high strength, hardness and wear resistance. 42CrMo adopts a heat treatment process of quenching and tempering, which is quenching and high-temperature tempering. After quenching and tempering, 42CrMo has high fatigue strength, is suitable for bearing cyclic loads, and has good wear resistance.

[0039] Based on the above-mentioned in-wheel hub motor drive brake integrated system with built-in reducer, the embodiment of the present invention also provides a control method of the in-wheel hub motor drive brake integrated system with built-in reducer, please refer to Figure 5 ,include: S501, obtaining a braking deceleration and a braking torque expected by the driver according to a rate of change of the opening of the brake pedal when the driver steps on it; S502, determining a regenerative braking torque according to the braking deceleration, based on a regenerative braking capability and a battery power; S503, determining the actual distribution of the regenerative braking torque to each wheel according to the vertical load ratio and the regenerative braking torque of each wheel; S504 : Determine the actual expected main actuation pressure based on the PID controller according to the braking torque and the actual distributed regenerative braking torque of each wheel.

[0040] In this embodiment, the driver's braking demand is first analyzed, and then the required regenerative braking torque is limited by the regenerative braking deceleration limiting module, and initially distributed according to the vertical load ratio of each wheel. In addition, the strategy also takes into account multiple factors such as driving speed, braking deceleration, battery power state, battery charging state, ABS system status, and potential fault signals to accurately calculate the expected electric braking torque for each wheel. This approach not only improves braking performance, but also helps optimize energy recovery and extend the service life of the braking system.

[0041] In some embodiments, determining the regenerative braking torque according to the braking deceleration, based on the regenerative braking capability and the battery power, includes: Based on the braking force distribution principle of the front and rear axles of the vehicle, ECE braking regulations, vehicle regenerative braking constraints and braking impact degree limits, the motor-hydraulic compound braking force distribution strategy is determined for the purpose of safety and comfort; The relationship between the battery SOC value and the threshold, the working state of the ABS and the fault state of the hub motor system are used as the opening and closing conditions of the regenerative braking system.

[0042] In this embodiment, the total braking torque of the vehicle is subtracted from the expected motor regenerative braking torque of each wheel to obtain the required mechanical braking torque of the vehicle, and then the currently required main drive pressure is calculated through the table lookup module. In addition, the actual expected main actuation pressure can be obtained by combining the compensated main actuation pressure output by the PID controller.

[0043] The ABS controller monitors the vehicle's wheel speed throughout the entire process. When an emergency occurs, the ABS intervenes to stop the vehicle. At the same time, during the vehicle braking process, a regenerative braking strategy is used to step on the brakes and use the excess energy to charge the battery. Figure 6 , 7 shown.

[0044] After obtaining the driver's braking deceleration based on the brake pedal opening rate, the front and rear axle braking force distribution of the vehicle, ECE braking regulations, vehicle regenerative braking constraints, and braking impact degree limits are considered from multiple angles, with high safety and high comfort as the goal, to design a motor-hydraulic composite braking force distribution strategy that meets the regulations, ensures safety, and adapts to the driver's driving habits. Under most working conditions, electric braking plays the main braking role. When the battery SOC is too high, the ABS is working, or the wheel hub motor system fails, regenerative braking exits and mechanical braking enters. According to power calculations and battery motor constraints, when the electric braking capacity cannot meet the vehicle's braking capacity, the mechanical brake fluid pressure is used to make up for the missing torque. The constraints are:

[0045] In the formula is the motor regenerative braking current; is the maximum charging current of the power battery, is the motor regenerative braking power, It is the maximum charging power of the power battery.

[0046] Furthermore, the motor-hydraulic compound braking force distribution strategy includes: According to the difference between the braking torque of the whole vehicle and the actual distributed regenerative braking torque of each wheel, the mechanical braking torque required for the whole vehicle braking is obtained; According to the mechanical braking torque required by the vehicle braking, based on the corresponding relationship between the preset braking torque and the main driving force, the required main driving pressure is determined; Based on the PID controller, the compensated main actuating pressure is obtained; According to the required main drive pressure and the compensated main actuation pressure, the actual desired main actuation pressure is obtained.

[0047] The braking force is distributed to the front and rear axles. When a car is driving on a straight road, when encountering an emergency, the driver takes the brake operation, the car starts to brake to slow down, ignoring the air resistance when the car brakes and slows down. At this time, the longitudinal force of the whole vehicle is as follows Figure 8 As shown. Among them, , are the normal reaction forces on the front and rear axles, , are the ground braking forces of the front and rear axles, a and b represent the distances from the center of mass of the vehicle to the front and rear axles, L represents the wheelbase of the vehicle, represents the height from the center of mass to the road surface, and m represents the vehicle mass.

[0048] By analyzing the force on the vehicle and taking the torque at the ground contact points of the front and rear wheels of the vehicle, we can obtain:

[0049] If the ground braking force on the loader wheel is the maximum road adhesion, and the braking intensity z is equal to the road adhesion coefficient φ, then equation (3) can be rewritten as:

[0050] When a vehicle begins to brake on the road, without considering the effect of the ABS system, three situations may occur: (1) the front and rear wheels lock and skid at the same time; (2) the front wheels lock and skid first; (3) the rear wheels lock and skid first. The degree of danger of the three situations is also different.

[0051] (1) The front and rear wheels are locked and skidding at the same time. The braking force of the front and rear wheels is

[0052] (2) The front wheel locks and slides first, and then the rear wheel locks and slides. The braking force of the front and rear wheels is

[0053] (3) The rear wheel locks and slides first, then the front wheel locks and slides. The braking forces of the front and rear wheels are

[0054] When the vehicle is in working condition (1), the road adhesion coefficient is utilized at the highest rate. The vehicle avoids dangerous situations such as skidding and tail swinging while also having a certain degree of directional stability. Therefore, locking the front and rear axles at the same time is the most ideal braking condition.

[0055] The torque distribution of the front and rear axles is based on the I curve and ECE regulations. The system monitors the speed of the motor in real time and calculates the maximum allowable braking torque that the motor can provide in the current state. The vehicle control unit (VCU) evaluates whether the maximum allowable braking torque of the single hub motor of the rear axle is less than half of the required braking torque of the front axle. If this condition is met, the electric braking torque command of the left rear wheel (or right rear wheel) will be set to the maximum allowable braking torque of the hub motor; at the same time, the hydraulic brake braking torque command of the left rear wheel (or right rear wheel) will be set to half of the required braking torque of the rear axle minus the maximum allowable braking torque of the hub motor. If this condition is not met, the electric braking torque command of the left rear wheel (or right rear wheel) will be directly set to half of the required braking torque of the rear axle, and the hydraulic brake braking torque command of the left rear wheel (or right rear wheel) will be zero. Finally, the system sends the electric braking torque command and the mechanical braking torque command to the corresponding actuator.

[0056] The braking impact degree is used to limit the braking smoothness. Generally, the smaller the braking impact degree during braking, the better the braking smoothness, the smaller the rate of change of the vehicle pitch angle, and the better the driver's comfort. The expression of the vehicle's braking impact degree is:

[0057] Where: is the vehicle braking impact ); is the vehicle braking deceleration ( ); v is the longitudinal velocity of the vehicle ( ).

[0058] In order to adapt to the braking needs under different driving habits and ensure the smoothness of the electro-hydraulic hybrid brake system during operation, the driving behavior of the driver is first analyzed through the driving style recognition module. This module can determine the driver's driving style and calculate the time required for the braking force to reach the peak value. Then, the system will limit the change speed of the braking torque generated by the motor and the wheel cylinder hydraulic pressure according to the current braking mode and the driver's expected braking impact to ensure smoothness when switching between different braking modes. In addition, by controlling the motor torque and wheel cylinder hydraulic pressure, the impact feeling during braking can be effectively controlled.

[0059] In the process of implementing this strategy, a data set containing various braking situations is used to classify driving styles using the fuzzy C-means clustering algorithm, and the driver's driving style is roughly divided into three types: aggressive, standard, and conservative. Then, based on these historical braking data and classification results, a support vector machine (SVM) algorithm model is trained, which can be used as a driving style recognition module to accurately identify the driver's driving style. The training set data classified by the FCM algorithm is input into the driving style recognition model based on SVM to obtain an accurate driving style.

[0060] By designing an inverse model, the main actuation force is obtained from the required braking torque. Generally speaking, the calculation formula of the vehicle hydraulic braking torque T is shown in (9):

[0061] In the formula, is the proportional coefficient of the hydraulic brake system, is the wheel cylinder pressure.

[0062] The braking torque required by the current vehicle can be calculated by formula (10):

[0063] In the formula is the hydraulic piston diameter, is the effective radius of the brake disc, is the friction coefficient, For mechanical efficiency.

[0064] Combining equations (9) and (10) yields the proportionality coefficient for:

[0065] After determining the mechanical braking torque required by the vehicle, the reverse lookup table technology is used to calculate the main actuation pressure that the vehicle is expected to achieve. Considering that the braking system of the vehicle may have a delay during actual driving, a 0.06s hysteresis response time is set. In order to ensure the safety of the vehicle during braking, the upper limit of the main actuation pressure and its increase rate are restricted: the maximum value of the pressure shall not exceed 15MPa, and the pressure rise rate shall not exceed 125MPa / s. Such measures help to ensure the stability and safety of the vehicle during braking.

[0066] According to the above structure and control strategy, in a specific embodiment, the vehicle starts to brake to a stop at an initial speed of 160km / h with a braking deceleration of 5.76m / s2. Under the joint constraints of the motor and battery, the braking torque of the whole vehicle is 5272N / m to 5520N / m. The wheel end braking torque can be obtained from the whole vehicle torque. The braking torque at the input end of the wheel reducer can be calculated according to the reduction ratio, wheel radius and other coefficients. Under the condition that the electric braking force is fully exerted, it can be known that the mechanical braking torque that needs to be involved can fully exert the electric braking capacity. The battery constraint is performed according to the battery map and the motor constraint is considered. At high speed, the electric braking torque is small. As the braking speed decreases, the electric braking torque gradually increases. When the speed is decelerated to 50km / h, the electric braking torque basically remains stable, and the mechanical braking sharing braking torque is reduced to 0 , the work can be completed by electric braking. The electric braking deceleration increases from 2.52m / s2 to 5.76m / s2 as the vehicle speed and electric braking torque increase, and the mechanical braking deceleration decreases from 3.23m / s2 to 0m / s2. Compared with the motor constraint, under the high-speed braking with joint constraint of the motor and battery, the mechanical braking shares a larger torque, and requires the joint participation of electric braking and mechanical braking.

[0067] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A hub motor drive and brake integrated system with a built-in reducer, characterized in that: include: Motor, planetary gear reducer and brake; The planetary gear reducer comprises a sun gear, a gear, a planet carrier plate and a planet shaft, the sun gear and the gear are integrally formed, and the sun gear is a hollow structure, the sun gear is connected to the motor through a spline, and the planet shaft is staggered with the wheel bolts; The planet carrier plate is fixedly connected to the wheel bolt fixing plate.

2. The wheel hub motor drive and brake integrated system with built-in reducer according to claim 1, characterized in that: The gears of the planetary gear reducer are all helical gears.

3. The wheel hub motor drive and brake integrated system with built-in reducer according to claim 1, characterized in that: The planet shafts of the planet carrier plate and the wheel bolts of the wheel bolt fixing plate are arranged alternately.

4. The wheel hub motor drive and brake integrated system with built-in reducer according to claim 3, characterized in that: The thickness of the planet carrier plate is 14 mm.

5. The wheel hub motor drive and brake integrated system with built-in reducer according to claim 1, characterized in that: The housing of the planetary gear reducer is a lightweight housing designed through topology optimization; The following topology optimization model is used to perform topology optimization on the planetary gear reducer housing: in, Represents the relative density of the reducer housing, m Represents the mass of the reducer housing, Represents the original volume of the reducer housing, represents the volume to be removed, To modify the upper limit of the volume, X Represents the displacement of the reducer housing, represents the yield limit of the material, Indicates the relative volume of the reducer housing. i Indicates i data points, n Indicates the total amount.

6. The wheel hub motor drive and brake integrated system with built-in reducer according to claim 1, characterized in that: The planetary gear reducer comprises a locking nut, and the outer cylindrical surface of the locking nut is in contact with the oil seal.

7. A control method for a wheel hub motor drive brake integrated system with a built-in reducer, applied to the wheel hub motor drive brake integrated system with a built-in reducer as claimed in any one of claims 1 to 6, characterized in that: include: According to the opening change rate of the brake pedal pressed by the driver, the driver's expected braking deceleration and braking torque are obtained; Determining a regenerative braking torque according to the braking deceleration based on a regenerative braking capability and a battery charge; Determine the actual distribution of regenerative braking torque to each wheel according to the vertical load ratio and regenerative braking torque of each wheel; According to the braking torque and the actual distribution of regenerative braking torque to each wheel, the actual expected main actuation pressure is determined based on the PID controller.

8. The control method of the wheel hub motor drive and brake integrated system with a built-in reducer according to claim 7, characterized in that: The step of determining the regenerative braking torque according to the braking deceleration, based on the regenerative braking capability and the battery power includes: Based on the braking force distribution principle of the front and rear axles of the vehicle, ECE braking regulations, vehicle regenerative braking constraints and braking impact degree limits, the motor-hydraulic compound braking force distribution strategy is determined for the purpose of safety and comfort; The relationship between the battery SOC value and the threshold, the working state of the ABS and the fault state of the hub motor system are used as the opening and closing conditions of the regenerative braking system.

9. The control method of the wheel hub motor drive and brake integrated system with a built-in reducer according to claim 8, characterized in that: The motor-hydraulic compound braking force distribution strategy includes: According to the difference between the braking torque of the whole vehicle and the actual distributed regenerative braking torque of each wheel, the mechanical braking torque required for the whole vehicle braking is obtained; According to the mechanical braking torque required by the vehicle braking, based on the corresponding relationship between the preset braking torque and the main driving force, the required main driving pressure is determined; Based on the PID controller, the compensated main actuating pressure is obtained; According to the required main drive pressure and the compensated main actuation pressure, the actual desired main actuation pressure is obtained.

10. The control method of the wheel hub motor drive and brake integrated system with a built-in reducer according to claim 8, characterized in that: Also includes: A preset fuzzy C-means clustering algorithm is used to classify the driving styles, and a driving style classification result is obtained, and a support vector machine model is trained according to the driving style classification result; A driving style category is determined based on the support vector machine model, and based on the driving style category, an actual desired main actuator pressure is determined.

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