Energy recovery control method and system for improving stability of rear-drive vehicle

Abstract

The invention provides an energy recovery control method and system for improving the stability of a rear-wheel-driven vehicle, and the method and system are suitable for a new energy vehicle with a rear-wheel-driven belt for recovering sliding energy and braking energy, and the method comprises the following steps: under the working conditions that the driving torque is smaller than 0 and the turning angle of a vehicle steering wheel or the change rate of the turning angle of the steering wheel is larger than a preset threshold value, the steering wheel is started; the real-time rear axle load of the vehicle is obtained; when the rear axle load is lower than a first preset threshold value, braking energy recovery is quitted, and sliding energy recovery is reserved; and when the rear axle load is lower than a second preset threshold value, sliding energy recovery is quitted. The method is suitable for the working condition that the lateral acceleration of a vehicle is large during large-angle steering or rapid steering in the high-speed deceleration process of a rear-drive vehicle, and the method is used for solving the problem of excessive steering drifting caused by insufficient energy recovery rear axle adhesion of a new energy vehicle.

Description

Technical Field

[0001] The present invention belongs to the technical field of automotive braking, and particularly relates to an energy recovery control method and system for improving the stability of rear-wheel drive vehicles. Background Art

[0002] When the vehicle is in coasting energy recovery or braking deceleration, the axle load transfers forward to the front axle. Especially in the downhill driving condition, the influence of the road gradient further causes a significant reduction in the axle load of the rear axle, resulting in a decrease in the vertical force of the rear wheels. Under the same road adhesion coefficient, the lateral and longitudinal adhesion forces of the rear wheels decrease accordingly. For rear-wheel drive vehicles, when the longitudinal adhesion force of the rear wheels is insufficient, if coasting energy recovery and braking energy recovery are carried out simultaneously, a large braking torque will be generated, causing the rear wheels to tend to lock, the slip ratio to increase, and further reducing the adhesion force of the rear wheels, deteriorating the vehicle stability. Especially when making a large-angle or rapid turn at a high vehicle speed, since the vehicle's demand for lateral adhesion force increases significantly, once the adhesion force of the rear wheels is insufficient, an oversteering and fishtailing phenomenon is extremely likely to occur. In such working conditions, it is extremely difficult for the driver to correct the steering wheel to restore the vehicle stability. Most drivers are difficult to effectively respond, and may even exacerbate the fishtailing trend due to misoperation, leading to vehicle out of control, causing driver panic and even serious traffic accidents.

[0003] The prior art CN114670648A provides an energy recovery control method for electric vehicles, which determines the exit of energy recovery by identifying the current driving road surface type (high-adhesion or low-adhesion road surface) to avoid wheel locking. However, this solution is only applicable to the targeted exit control after identifying the road surface type, and fails to effectively solve the oversteering problem caused by insufficient lateral adhesion force of the rear wheels of rear-wheel drive vehicles under the conditions of high-adhesion road surface, high-speed braking, and simultaneous large-angle or rapid turning, and cannot quickly respond to exit energy recovery when an obvious locking trend appears.

[0004] Another prior art CN118665192A provides a method for controlling coasting energy recovery based on the wheel locking state and pedal state. This method is to gradually exit the braking energy recovery when the wheel locking trend is obvious and maintain partial coasting energy recovery to dynamically adjust the wheel braking torque and keep the wheels in a critical locking and intermittent rolling state. However, the exit timing of this solution is after the locking trend is significant, and the dynamic adjustment of the braking torque is limited by the torque response speed, and cannot effectively avoid the fishtailing risk caused by insufficient adhesion force due to the reduction of the rear axle load under the transient working conditions of high vehicle speed and rapid turning.

[0005] Therefore, there is an urgent need to provide a more accurate and responsive energy recovery exit control method, which can avoid the occurrence of oversteering and fishtailing phenomena for rear-wheel drive vehicles under special working conditions of high vehicle speed and high dynamic turning, and significantly improve the safety and stability of vehicle driving. Summary of the Invention

[0006] The purpose of the present invention is to solve the deficiencies existing in the above-mentioned background technology, and provide an energy recovery control method and system for improving the stability of rear-wheel drive vehicles, which is applicable to the working conditions where the lateral acceleration of the vehicle is large during high-speed deceleration, large-angle steering or rapid steering of rear-wheel drive models, and is used to solve the problem of oversteering and tail-swing of the vehicle due to insufficient adhesion of the rear axle during energy recovery of new energy vehicles.

[0007] The technical solution adopted by the present invention is: an energy recovery control method for improving the stability of rear-wheel drive vehicles, which is applicable to new energy vehicles with rear-wheel drive and coasting energy recovery and braking energy recovery, and includes the following steps:

[0008] Under the working condition that the driving torque is less than 0 and the steering wheel angle or the change rate of the steering wheel angle of the vehicle is greater than a preset threshold, obtain the real-time rear axle load of the vehicle;

[0009] When the rear axle load is lower than the first preset threshold, exit the braking energy recovery and retain the coasting energy recovery;

[0010] When the rear axle load is lower than the second preset threshold, exit the coasting energy recovery.

[0011] In the above technical solution, the following steps are also included: obtain the real-time longitudinal deceleration and slope of the vehicle, and calculate the real-time rear axle load according to the curb weight of the vehicle, the height of the center of mass, the distance from the center of mass to the front axle, and the wheelbase.

[0012] In the above technical solution, the rear axle load F Z2 is calculated by the following formula:

[0013]

[0014] where, m is the curb weight of the whole vehicle, L1 is the distance from the center of mass to the front axle, L is the wheelbase, h is the height of the unloaded center of mass, θ is the current slope angle of the vehicle, α is the longitudinal deceleration of the vehicle, and g is the acceleration due to gravity.

[0015] In the above technical solution, the longitudinal deceleration of the vehicle is obtained by the brake controller acquiring the wheel speeds of the four wheels of the vehicle and calculating according to the change of the wheel speeds.

[0016] In the above technical solution, the slope of the vehicle calculates the current slope angle of the vehicle according to the inertial sensor of the whole vehicle, and corrects the slope angle according to vehicle dynamics.

[0017] In the above technical solution, after the braking energy recovery is exited, the hydraulic braking is compensated to make the total braking torque meet the braking deceleration requirement.

[0018] In the above technical solution, the first preset threshold is two-thirds of the rear axle load when the vehicle is unloaded and traveling at a constant speed on a horizontal road surface.

[0019] In the above technical solution, the second preset threshold is one-third of the rear axle load when the vehicle is unloaded and traveling at a constant speed on a horizontal road surface.

[0020] In the above technical solution, before executing any energy recovery step exit, it is determined whether the recovery mode exists; if not, the exit step is skipped.

[0021] In the above technical solution, it is determined whether the driving torque is less than 0; if it is greater than or equal to 0, this method ends.

[0022] Optionally, if the load information of the vehicle can be obtained through sensors and other information, the actual load of the rear axle can be corrected according to the load information.

[0023] The present invention also provides an energy recovery control system for improving the stability of a rear-wheel drive vehicle, which is applicable to new energy vehicles with rear-wheel drive, coasting energy recovery, and braking energy recovery, and includes:

[0024] A rear axle load calculation module, configured to obtain the real-time rear axle load of the vehicle under the condition that the driving torque is less than 0 and the steering wheel angle or the change rate of the steering wheel angle of the vehicle is greater than a preset threshold;

[0025] A braking energy recovery exit module, configured to exit the braking energy recovery and retain the coasting energy recovery when the rear axle load is lower than the first preset threshold;

[0026] A coasting energy recovery exit module, configured to exit the coasting energy recovery when the rear axle load is lower than the second preset threshold.

[0027] The beneficial effects of the present invention are as follows: By judging the rear axle load based on the rear axle load before the vehicle slip ratio rises in two stages to exit the braking and coasting energy recovery when the driving torque is less than 0 and during high-dynamic steering, the "pre-stabilization" control is realized. It can cut off the recovery torque in time before the insufficient adhesion of the rear wheels caused by the decrease of the rear axle load of the vehicle, significantly reduce the risk of fishtailing, improve the driving safety of the vehicle under the condition of sudden deceleration + large steering, and make full use of the existing control system to optimize the control strategy to improve the driving safety of users.

[0028] Furthermore, the present invention introduces the acquisition of real-time longitudinal deceleration and slope, and combines the vehicle parameters to calculate the rear axle load, which ensures the accuracy of the load judgment, makes the threshold trigger more in line with the actual working conditions, and improves the robustness and repeatable calibration of the control strategy.

[0029] Furthermore, the present invention defines a calculation formula for the rear axle load, quantitatively evaluates the load change based on the vehicle dynamics model, making the withdrawal timing well-founded, avoiding the uncertainty brought by empirical settings, and improving the engineering feasibility of the method.

[0030] Furthermore, the present invention calculates the deceleration by obtaining the wheel speed change through the vehicle brake controller, without the need for additional sensors, simplifies the system deployment, and ensures the real-time and reliability of the deceleration data.

[0031] Furthermore, the present invention determines the slope by using in-vehicle inertial sensors and combining with dynamic correction, enhancing the accuracy of load calculation under uphill and downhill conditions and reducing the interference of slope changes on the judgment logic.

[0032] Furthermore, after the present invention exits the regenerative braking energy recovery, it automatically compensates the hydraulic braking to ensure that the braking deceleration required by the driver can still be satisfied after the recovery is exited, with a smooth connection, avoiding a sudden braking feeling, and improving the riding comfort and safety.

[0033] Furthermore, the present invention takes two-thirds of the rear axle of the static unloaded vehicle as an example of the first-level threshold, providing an engineering-feasible and easily calibrated starting value, and greatly shortening the real vehicle tuning cycle.

[0034] Furthermore, the present invention takes one-third of the rear axle of the static unloaded vehicle as an example of the second-level threshold to ensure that the regenerative torque is completely cut off when the load drops to a low level, leaving the maximum friction margin for the rear wheels, and further ensuring the stability under extreme conditions.

[0035] Furthermore, before exiting any recovery step, the present invention first determines whether the recovery mode exists, which can avoid executing useless logic under invalid conditions, reduce the burden on the controller, and improve the system execution efficiency and reliability.

[0036] Furthermore, the present invention adds the determination of "ending the method when the driving torque is greater than or equal to 0", ensuring that the control logic only takes effect in the deceleration recovery stage, avoiding the mis-triggering of the recovery exit strategy in the acceleration or cruise stage, and improving the accuracy of the strategy and the user experience.

[0037] Furthermore, the present invention modularizes the method functions into three sub-modules: "load calculation", "braking recovery exit", and "coasting recovery exit", which is convenient for software / hardware hierarchical implementation and extended deployment, and improves the system integration, maintainability, and flexibility of engineering implementation. Description of the Drawings

[0038] Figure 1 It is a schematic diagram of the method flow of the present invention.

[0039] Figure 2 It is a schematic diagram of the principle of the present invention;

[0040] Figure 3 Schematic diagram of the application scenario of the present invention;

[0041] Figure 4 Schematic diagram of the method flow of the embodiment. Specific implementation manner

[0042] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, which is convenient for clearly understanding the present invention, but they do not limit the present invention.

[0043] Embodiment 1

[0044] As Figure 1 shown, an energy recovery control method for improving the stability of a rear-wheel drive vehicle according to the present invention is applicable to new energy vehicles with rear-wheel drive, coasting energy recovery and braking energy recovery, and includes the following steps:

[0045] Under the condition that the driving torque is less than 0 and the steering wheel angle or the change rate of the steering wheel angle of the vehicle is greater than a preset threshold, obtain the real-time rear axle load of the vehicle;

[0046] When the rear axle load is lower than the first preset threshold, exit the braking energy recovery and retain the coasting energy recovery;

[0047] When the rear axle load is lower than the second preset threshold, exit the coasting energy recovery.

[0048] Specifically, in daily driving, when a rear-wheel drive new energy vehicle enters a large-angle or rapid steering condition (such as the steering wheel angle > 180° or the angle change rate > 300° / s) at a high speed (> 30 kph), the lateral acceleration of the vehicle suddenly increases. At this time, the wheels not only have to bear the longitudinal braking force during braking or recovery, but also provide sufficient lateral adhesion to complete stable turning.

[0049] In working conditions such as large-angle turning or emergency obstacle avoidance in mountainous areas, the lateral acceleration of the vehicle is large, and the required lateral adhesion of the wheels is large. The rear-wheel drive vehicle needs to bear both the longitudinal deceleration and the lateral steering force at the same time, and these two are shared in the wheel friction resources: it is required that the rear wheels do not show a tendency of locking, resulting in insufficient lateral adhesion and oversteering. When the lateral acceleration reaches 0.5g (typical sharp turn in mountainous areas) or higher, the required lateral force has occupied most of the friction ellipse. When a large longitudinal recovery torque (such as a deceleration of 0.3g) is continued to be retained at this time, the resultant force will break through the limit, resulting in rear-wheel slip and further oversteering.

[0050] The maximum resultant force of the wheel is limited by the normal load. When the recovery torque increases, the lateral adhesion force is squeezed, and instability will occur when the margin of the lateral adhesion force is insufficient. During braking or coasting energy recovery, the vehicle body decelerates, the center of gravity moves forward, and the load on the rear axle decreases; driving downhill further reduces the load on the rear axle. The real-time change of the rear axle load directly affects the friction limit of the rear wheels. Therefore, it must be used as a quantitative index of "available adhesion force".

[0051] The rear axle load is proportional to the available frictional force, and can more accurately reflect the margin of the wheel adhesion force than the simple slip ratio or pedal signal. The load judgment takes into account both the current deceleration (longitudinal) and the steering intensity (lateral) to achieve a dynamic assessment of the resultant force demand. The present invention uses the physical quantity of the rear axle load to achieve refined dynamic control of the energy recovery mode, effectively solving the risk of fishtailing under high vehicle speed and large steering conditions, and significantly improving the driving safety of the vehicle.

[0052] In the continuous intervention-exit process of coasting and braking energy recovery of the present invention, two levels of rear axle load thresholds are introduced to achieve "pre-stabilization" control. The following combines Figure 2 with the embodiments to describe its principle and advantages.

[0053] As Figure 2 shown, the horizontal axis is time in both figures. The vertical axis in the upper figure is the energy recovery torque, and the vertical axis in the lower figure is the rear axle load (schematically shown as a linear decrease). The present invention sets two load thresholds on this curve, and dynamically matches the available friction resources by segmentally truncating the recovery torque. The principle and advantages are as follows.

[0054] 1. Initial recovery stage (load > the first-level threshold)

[0055] When the throttle pedal opening of the vehicle is 0, the coasting energy recovery is started, and a gradually increasing negative torque is generated on the driving wheels; subsequently, the driver steps on the brake pedal, and the brake controller distributes the torque between hydraulic braking and braking energy recovery, and the negative torque continues to rise. As the vehicle braking force increases, the deceleration increases, and the vehicle is driving under a downhill condition. In the condition where the driving torque is less than 0 and the vehicle steering wheel angle or the change rate of the steering wheel angle is greater than the preset threshold, the rear axle load is calculated in real time in this embodiment.

[0056] When going downhill + braking, the rear axle load gradually decreases, but is still greater than the first-level threshold; at this time, both braking energy recovery ( Figure 2 the solid line in the figure gradually descends from the maximum torque to the threshold) and coasting energy recovery ( Figure 2 the horizontal dotted line in the upper figure in the figure) are allowed to work simultaneously to maximize the recovery efficiency.

[0057] 2. Triggering of the first-level threshold (load = the first-level threshold)

[0058] When the rear axle load drops to the first - stage threshold, which corresponds to the lowest load level at which the rear - wheel adhesion can still meet the friction limit when braking energy recovery and lateral force coexist, the braking controller immediately issues an instruction to exit the braking energy recovery and only retain the coasting recovery torque, so as to avoid prematurely occupying the lateral adhesion resources due to the superposition of the braking recovery torque and the hydraulic braking force.

[0059] That is, once Figure 2 the solid line (rear axle load) in the lower - middle figure drops to the first horizontal line, immediately set the braking energy recovery torque of the solid line in the upper - middle figure to zero (vertically drop to the coasting recovery level) and only retain the relatively small coasting recovery torque. At this rear axle load level, if the braking recovery torque + hydraulic braking is superimposed again, it will break through the friction ellipse limit and cause the rear wheels to slip. Figure 2

[0060] 3. Coasting recovery stage (first - stage threshold > load > second - stage threshold)

[0061] Retain Figure 2 the torque marked as "coasting energy recovery" (orange or red horizontal segment) in the upper - middle figure, which not only continues to recover energy but also ensures that the recovery torque will not cause lateral or longitudinal out - of - control.

[0062] 4. Triggering of the second - stage threshold (load = second - stage threshold)

[0063] When the driver continues to deeply depress the brake pedal or the downhill slope increases, resulting in a continuous increase in the deceleration demand and the rear axle load further drops to the second - stage threshold, which corresponds to the lowest load level at which the rear - wheel adhesion just meets the lateral demand under only the coasting recovery torque, the braking controller issues another instruction to exit the coasting energy recovery and completely cut off the motor drag torque, ensuring that all the friction force of the rear wheels is used for lateral stability control, thus avoiding the risk of an increase in the slip ratio and resulting in over - steering (fishtailing).

[0064] That is, when Figure 2 the solid line in the lower - middle figure drops below the second horizontal line, also set the coasting recovery torque in the upper figure to zero (vertically drop to zero again). At this time, the rear axle load is no longer sufficient to bear any form of recovery torque and must be completely cut off to ensure that all the friction force is used for vehicle stability.

[0065] ​In this embodiment, within the safe range, both braking recovery and coasting recovery are used in the initial stage, making use of all recoverable torque. By means of two-level thresholds, "physical load" and "recovery torque" are tightly coupled to ensure that the recovery torque ≤ μ·Fz at any time, thus avoiding the risk of rear-wheel lock-up or skidding at the source. Each time when exiting, only a part of the torque is truncated (braking first and then coasting), and it can be smoothly switched within milliseconds, reducing the sense of jerk. The two-level thresholds can be quickly calibrated according to the empirical values of 2 / 3 and 1 / 3 of the static unloaded rear axle load, and can also be fine-tuned through vehicle tests. Whether it is a long downhill, large-angle steering or emergency obstacle avoidance, it will automatically respond according to the same logic without the need to write multiple sets of rules for each scenario.

[0066] Among them, the first-level threshold is located at the critical point of the friction resources of "braking recovery + lateral adhesion". After determining the corresponding relationship between the rear axle load and the slip rate inflection point through experimental calibration, a safety margin is added. The second-level threshold is located at the limit point of the friction resources of "coasting recovery + lateral adhesion" to ensure that all lateral friction margins can be retained under the most severe working conditions.

[0067] By setting two levels to orderly exit the recovery in two steps before the slip rate significantly rises, the lateral adhesion is released in advance. First, the braking recovery with large torque is exited, and then the coasting recovery is exited. The recovery switching process is smooth, avoiding the sudden braking feeling. Maximize the energy recovery efficiency within the safe range; when the demand for steering safety, quickly cut off the recovery to ensure stability. At the same time, the two-level thresholds can be calibrated according to different vehicle models and are applicable to various high-lateral acceleration scenarios such as downhill, large turning, and emergency obstacle avoidance.

[0068] Through the above two-level threshold control, this embodiment can balance energy recovery and vehicle stability in real time under extreme working conditions such as large-angle turning or emergency obstacle avoidance in mountainous areas, and significantly improve the driving safety and handling experience of rear-wheel drive vehicles under high vehicle speed + large dynamic steering conditions.

[0069] Specifically, it further includes the following steps: obtaining the real-time longitudinal deceleration and slope of the vehicle, and calculating the real-time rear axle load according to the vehicle curb weight, center of mass height, distance from the center of mass to the front axle, and wheelbase based on the unloaded weight.

[0070] When the vehicle is braking / recovering and decelerating, the resultant force acting on the center of mass includes the gravity component G (decomposed into the component perpendicular to the road surface and the component along the slope), the inertial force ma (along the longitudinal direction of the vehicle), and the road surface reaction force.

[0071] As Figure 3 shown, taking the side view of the vehicle as an example, let: m: vehicle unloaded mass + 110 kg; L: wheelbase, L1, L2: distances from the center of mass to the front and rear axles; h: unloaded center of mass height; θ: current slope angle (downhill is positive); a: longitudinal deceleration (braking or recovery); g represents the acceleration due to gravity. By performing moment balance on the rear axle, we get:

[0072] Rear axle load F Z2 It is calculated using the following formula:

[0073]

[0074] This formula comprehensively considers the center of gravity position, slope influence, and deceleration effect, and can reflect the dynamic changes of the rear axle normal load in real time. As the deceleration a increases, the inertial force ma generates a "load reduction" effect on the rear axle through the center of gravity height h; when going downhill, the component of gravity along the slope direction mgsinθ further reduces the rear axle load; the aforementioned formula couples the two to accurately depict the rear axle load under different slope and deceleration combinations.

[0075] The rear axle load calculation method adopted in this embodiment converts the abstract "deceleration + slope influence" into measurable load values, which is more intuitive and accurate than using only the slip rate or pedal signal. The formula only requires vehicle parameters and common quantities (deceleration, slope) as input, and the calculation process is continuous, and the calculation results of the rear axle load can be output in real time throughout the deceleration process. Based on the parameter combination of the unloaded mass, center of gravity height, and wheelbase, accurate data can be obtained through calibration for different vehicle models; there is no need to deeply rely on empirical values. By comparing with thresholds, this physical quantity is directly mapped to the energy recovery exit decision - the first threshold controls the braking recovery, and the second threshold controls the coasting recovery - realizing the integration of "physical quantity → control quantity". Whether it is on a flat road, downhill, or at different deceleration levels, the same model can cover them, and there is no need to design multiple sets of logics for each scenario additionally.

[0076] Specifically, the longitudinal deceleration of the vehicle is obtained by the brake controller acquiring the four-wheel speeds of the vehicle and calculating based on the changes in the wheel speeds.

[0077] In this embodiment, high-resolution wheel speed sensors are arranged at the ends of the four wheel axles, and the sampling frequency is not less than 100Hz; the arithmetic mean or weighted mean (excluding the sudden change in the wheel speed of the slipping wheel) is taken for the four-wheel speeds v i (t) to obtain the vehicle longitudinal speed v(t):

[0078]

[0079] Furthermore, the finite difference method is used to calculate the longitudinal deceleration:

[0080]

[0081] A first-order low-pass filter (or Kalman filter) is introduced to suppress the measurement noise:

[0082]

[0083] For mutation or "slipping" jump points, the value of the previous moment can be temporarily locked in combination with the slip rate to avoid false deceleration interfering with the rear axle load. When ABS intervenes and ESC stability control works, abnormal jump data can be assisted in elimination to ensure that the deceleration signal only reflects the actual braking conditions of driving / regeneration.

[0084] Specifically, the slope of the vehicle calculates the current slope angle of the vehicle according to the inertial sensor of the whole vehicle, and corrects the slope angle according to vehicle dynamics.

[0085] In this embodiment, a 6-axis IMU (3-axis accelerometer + 3-axis gyroscope) is installed at the front end of the vehicle body center or the front and rear parts of the chassis. The acceleration component represents gravity + inertia, and the integral of the gyroscope can provide the tilt rate of change.

[0086] Complementary filtering or extended Kalman filtering (EKF) is used to fuse the gyroscope and accelerometer data:

[0087] Short-term dependence on the gyro signal ω y (angular velocity about the transverse axis) is integrated to obtain the temporary pitch angle θ gyro ;

[0088] Long-term dependence on the accelerometer components (a x , a z ) is used to calculate the pitch in the gravity direction:

[0089]

[0090] Furthermore, complementary filtering:

[0091]

[0092] What the accelerometer itself measures is the superposition of gravity and inertial force, and the inertial component caused by the longitudinal deceleration needs to be eliminated:

[0093]

[0094] Or directly use the deceleration as the known input in the EKF state equation to filter out the dynamic components.

[0095] The zero bias and scale factor of the IMU will drift with temperature, and online zero recalibration can be performed during vehicle startup or constant-speed cruising; second-order low-pass filtering (cutoff 5Hz) is performed on the high-frequency vibration components to further improve the stability of the slope angle.

[0096] This embodiment is for sampling and filtering above 100 Hz, ensuring that during sudden deceleration / rapid turning, the deceleration and slope angle can be output within a delay of <10 ms. Through differential + low-pass, complementary / EKF fusion, and cross-verification of ABS / ESC information, multiple means are used to suppress errors. The filter coefficients and zero-bias update strategy can both be calibrated on a real vehicle to match the vehicle's dynamic characteristics. This embodiment can stably output high-precision physical quantities using only common wheel speed and IMU modules, and is easy to deploy on existing electronic control units (ECUs). The system can obtain the vehicle deceleration and slope in real time and accurately, providing solid and reliable data support for the calculation of rear axle load and the judgment of energy recovery withdrawal.

[0097] Specifically, after the braking energy recovery is exited, hydraulic braking is compensated to make the total braking torque meet the braking deceleration requirement.

[0098] When the driver steps on the brake pedal or the vehicle control unit (brake controller) receives a deceleration demand signal, the brake controller first determines the required total braking deceleration a according to the driver's brake pedal opening and high-level logics such as ACC / ESP. req . Subsequently, the brake controller distributes the braking torque according to the following steps:

[0099] Determine the available braking energy recovery torque T according to the maximum recoverable power of the motor and the current charging power limit of the battery. regen,max ;

[0100] Calculate the deceleration component a that the electric motor braking can bear under the corresponding braking deceleration. regen =T regen / (mr) (r is the driving wheel radius);

[0101] If a regen ≤a req , then set the electric motor braking torque T regen =mra regen , and the remaining deceleration demand a hyd =a req -a regen is borne by hydraulic braking;

[0102] If a regen >a req , then limit T regen =mra req , and hydraulic braking does not intervene temporarily.

[0103] When the rear axle load drops below the first preset threshold, the braking energy recovery logic is triggered to exit: the brake controller immediately reduces the electric motor braking torque T regen to zero;

[0104] To ensure that the total braking deceleration still meets a req , the hydraulic braking torque Thyd Cooperatively increase to compensate for the deceleration loss after the withdrawal of recuperation:

[0105] mra hyd,new = mra req -0 i.e., T hyd,new = mra req .

[0106] Since the hydraulic braking system has the capabilities of fast response and large torque reserve, it can complete the torque compensation switching within 10–20 ms, ensuring a smooth transition of the vehicle deceleration and no obvious deceleration loss.

[0107] When the intensity of the coasting energy recuperation setting is relatively high, for example, if 0.15g is all generated by the rear axle of a rear-wheel drive vehicle, the braking force of the rear axle is still relatively large. At the same time, if the hydraulic braking force of the rear axle is further superimposed, there is still a risk of locking when the deviation of the rear-wheel braking force is more significant when the rear axle load decreases. To fully ensure the stability and safety of the vehicle, when the rear axle load drops below the second preset threshold, the coasting energy recuperation is triggered to exit: the brake controller only closes the electric motor braking torque without additional hydraulic braking compensation.

[0108] Since the driver does not step on the accelerator at this time and may not step deeply on the brake either, the system defaults that the deceleration demand decreases or the vehicle speed is maintained by the road resistance, and does not actively increase the hydraulic braking; therefore, there will be a certain decrease in the vehicle deceleration after the coasting recuperation exits, and the driver's feeling is relatively smooth.

[0109] When exiting the braking recuperation, due to the quick switch to hydraulic braking and sufficient compensation, the passengers cannot feel the deceleration decrease and the ride comfort is high.

[0110] When exiting the coasting recuperation, without compensation, the coasting braking force suddenly decreases, and the passengers can feel a slight sense of acceleration. However, at this time, it is mostly a low deceleration condition, which has little impact on the vehicle stability.

[0111] In this embodiment, the brake controller needs to monitor the motor recuperation ability and the hydraulic braking state in real time, and update the torque distribution at the millisecond level; at the moment of exiting the braking recuperation, a linear or exponential transition function can be introduced (such as ramping down the electric motor braking torque and ramping up the hydraulic braking torque within 50 ms) to further smooth the driving experience; after the coasting recuperation exits, the brake light logic or HMI can be used to prompt the driver of the change in the braking state to enhance the driver's confidence.

[0112] Through the above embodiments, while taking into account the efficient energy recuperation, the present invention utilizes the fast compensation ability of hydraulic braking to eliminate the deceleration loss caused by the exit of braking recuperation, ensuring that the required deceleration is still maintained when the rear axle load drops to a low level, and maximizing the driving stability and riding comfort.

[0113] Specifically, the first preset threshold and the second preset threshold can be determined through on-vehicle calibration according to different vehicles.

[0114] In the specific implementation manner, the "first preset threshold" and the "second preset threshold" are not fixed constants, but optimal parameters obtained through on-vehicle calibration for different vehicle models, different curb weights, and centroid arrangements. The calibration process and examples of preferred values are as follows:

[0115] In the specific implementation manner, in order to adapt to the mass distribution, suspension characteristics, and regenerative braking capabilities of different vehicles, on-vehicle calibration of the first-stage threshold and the second-stage threshold is required, and the process can be carried out according to the following steps:

[0116] 1. Static parameter measurement

[0117] Park the test vehicle on a horizontal test bench and define the unloaded state (the driver and removable parts are removed);

[0118] Use a force measuring platform or four-wheel force sensors to measure the static normal loads on the front / rear axles respectively;

[0119] Use a pitch test stand or a three-dimensional measuring device to measure the unloaded vehicle's centroid height, the distance between the front and rear axles, and the horizontal distance from the front axle to the centroid.

[0120] 2. Dynamic condition preparation

[0121] Select a traffic-free, straight downhill test runway (gradient 3% - 10%);

[0122] Arrange a steering test area and a braking test area at the end of the runway.

[0123] Adjust the vehicle to the normal operating state (fully charged, unloaded or semi-loaded);

[0124] Turn off ESC / ABS and only enable the regenerative braking control algorithm to observe the pure regenerative effect.

[0125] 3. Calibration of Threshold 1 (before braking regeneration exits)

[0126] In the state of throttle release (0%), let the coasting regeneration stably intervene in a slow downhill or constant-speed driving manner, and record the torque level at this time.

[0127] The driver or the automatic controller gradually increases the opening of the brake pedal to make the electric motor braking torque increase from small to large; record the corresponding dynamic load on the rear axle and the slip ratio at each electric motor braking torque level.

[0128] Find the rear axle load F corresponding to the first time the slip ratio exceeds the set upper limit (such as 20%) when the electric motor braking torque is equal to the typical braking regeneration torque o ;

[0129] Take the first level threshold as F1=F o *(1+δ1)

[0130] Where δ1 is a safety margin (e.g. 5%–10%).

[0131] 4. Calibration of threshold 2 (before exiting coasting recovery)

[0132] At a constant speed, gradually increase the coasting recovery torque to the maximum available;

[0133] Maintain the maximum available sliding recovery torque wei and find the rear axle load F corresponding to the first excessive slip rate t ;

[0134] Take the secondary threshold as F2 = F t *(1+δ2)

[0135] The safety margin of δ2 can be appropriately smaller than δ1.

[0136] 5. Parameter setting and verification

[0137] Write the obtained F1 and F2 into the energy recovery control ECU parameter table;

[0138] Repeat the test at different slopes, different speeds (20–80 kph) and different tire / road conditions to verify that the slip rate remains within the safe range;

[0139] Fine-tune δ1, δ2 or typical torque levels based on retest results to ensure smooth transition and error-free operation.

[0140] This embodiment is calibrated based on real vehicle data and accurately reflects the real dynamic load transfer characteristics of the vehicle. Thresholds can be set for different vehicle models, different loads, and different road conditions, and has good scalability. By introducing a margin, a protection space is left above the test inflection point to further improve safety. It can fully feed back energy under high recovery torque and smoothly and promptly exit recovery when the load is insufficient, taking into account both endurance and driving stability.

[0141] Preferably, the first preset threshold is two-thirds of the rear axle load when the vehicle is unloaded and driving at a constant speed on a horizontal road. In actual vehicle tests, it was found that when the rear axle load drops below ≈66% of the static reference, if the braking recovery torque is added, the rear wheel slip rate is likely to rise to more than 20%, and signs of insufficient adhesion begin to appear.

[0142] The second preset threshold is one third of the rear axle load when the vehicle is unladen and driving at a constant speed on a level surface. When the load drops below ≈33% of the static reference, even light sliding regeneration will quickly cause the rear wheels to enter the low adhesion zone, and all regeneration torque must be completely cut off.

[0143] Specifically, before exiting any energy recovery step, it is determined whether the recovery mode exists; if not, the exit step is skipped.

[0144] Preferably, in order to ensure the efficiency and reliability of the control process, it is necessary to detect the operating state of the corresponding recovery mode before each execution of "exiting braking energy recovery" or "exiting coasting energy recovery": the system determines whether braking energy recovery or coasting energy recovery is currently being executed by reading the status flag inside the energy recovery controller; if it is detected that the braking energy recovery has not been started, the "exiting braking recovery" step is directly skipped to avoid sending invalid instructions; similarly, if the coasting energy recovery is already in the closed state, the "exiting coasting recovery" operation is not executed, but directly proceeds to the subsequent judgment.

[0145] Specifically, it is determined whether the driving torque is less than 0; if it is greater than or equal to 0, this method ends.

[0146] Preferably, after each recovery exit judgment in the control process, the driving torque signal should be immediately read: if the driving torque is greater than or equal to zero, it indicates that the driver requests acceleration again, and at this time, the current energy recovery exit logic should be immediately aborted and restored to the initial monitoring state; only when the driving torque continues to be less than zero, the subsequent rear axle load judgment and energy recovery exit steps are continued.

[0147] As Figure 4 shown, this embodiment specifically includes the following steps:

[0148] S1: Determine whether the driving torque is less than 0, and whether the steering wheel angle is greater than the preset steering wheel angle threshold or the steering wheel angle change rate is greater than the preset steering wheel angle change rate threshold. If so, proceed to S2; if not, return to S1.

[0149] S2: Obtain the current deceleration and slope of the vehicle, calculate the load of the current rear axle of the vehicle based on the vehicle parameters according to the unloaded weight, and determine whether the load of the rear axle is less than the first preset threshold. If so, proceed to S3; if not, return to S1.

[0150] S3: If there is braking energy recovery, request the motor to exit the braking energy recovery, and establish the energy recovery for the braking hydraulic compensation to exit. If the brake is not depressed or limited by the motor charging power and no braking energy recovery is generated, skip S3.

[0151] S4: Determine whether the driving torque is greater than or equal to 0. If the driving torque is greater than or equal to 0, such as when the driver depresses the accelerator pedal or the ACC requests acceleration, the program ends and returns to S1; if the throttle opening is still 0, proceed to S5.

[0152] S5: Determine whether the current load on the rear axle is less than the second preset threshold. If so, and there is coasting energy recovery, request the motor to exit coasting energy recovery to avoid oversteering caused by coasting energy recovery. If coasting energy recovery is turned off, skip S5.

[0153] S6: Determine whether the driving torque is greater than or equal to 0. If so, the program ends and returns to S1. If not, return to S6.

[0154] Embodiment 2

[0155] The present invention also provides an energy recovery control system for improving the stability of a rear-wheel drive vehicle, which is applicable to new energy vehicles with rear-wheel drive, coasting energy recovery, and braking energy recovery, and includes:

[0156] A rear axle load calculation module, configured to obtain the real-time rear axle load of the vehicle under the condition that the driving torque is less than 0 and the steering wheel angle or the change rate of the steering wheel angle of the vehicle is greater than a preset threshold.

[0157] A braking energy recovery exit module, configured to exit braking energy recovery and retain coasting energy recovery when the rear axle load is lower than the first preset threshold.

[0158] A coasting energy recovery exit module, configured to exit coasting energy recovery when the rear axle load is lower than the second preset threshold.

[0159] Embodiment 3

[0160] The present invention provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it implements the energy recovery control method for improving the stability of a rear-wheel drive vehicle described in the above technical solution.

[0161] Embodiment 4

[0162] The present invention provides an electric vehicle, including: a memory and a processor, which are communicatively connected to each other. The memory stores computer instructions, and the processor executes the computer instructions to execute the energy recovery control method for improving the stability of a rear-wheel drive vehicle described in the above technical solution.

[0163] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can be implemented in the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can be implemented in the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes.

[0164] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing device generate a means for implementing the functions specified in one flow Figure 1 one flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0165] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including an instruction means that implements the functions specified in one flow Figure 1 one flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0166] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one flow Figure 1 one flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0167] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit and scope protected by the present invention and the claims. All of these fall within the protection scope of the present invention.

[0168] The content not described in detail in this specification belongs to the prior art well-known to those of ordinary skill in the art.

Claims

1. An energy recovery control method for improving the stability of a rear-wheel drive vehicle, characterized in that: Applicable to rear-wheel drive new energy vehicles with coasting energy recovery and braking energy recovery, including the following steps: Under the condition that the driving torque is less than 0 and the vehicle steering wheel angle or the steering wheel angle change rate is greater than a preset threshold, obtaining the real-time rear axle load of the vehicle; When the rear axle load is lower than a first preset threshold, braking energy recovery is terminated while coasting energy recovery is retained; When the rear axle load is lower than a second preset threshold, coasting energy recovery is exited.

2. The method according to claim 1, characterized in that: The following steps are also included: The real-time longitudinal deceleration and slope of the vehicle are obtained, and the real-time rear axle load is calculated according to the vehicle's curb weight, center of mass height, distance from the center of mass to the front axle and wheelbase, based on the empty weight.

3. The method according to claim 2, characterized in that: The rear axle load F Z2 The calculation is done using the following formula: Among them, m is the unladen mass of the vehicle, L1 is the distance from the center of mass to the front axle, L is the wheelbase, h is the height of the unladen center of mass, θ is the current slope angle of the vehicle, α is the longitudinal deceleration of the vehicle, and g represents the acceleration due to gravity.

4. The method according to claim 2, characterized in that: The longitudinal deceleration of the vehicle is calculated by the brake controller based on the change in wheel speed by obtaining the four-wheel speed of the vehicle.

5. The method according to claim 2, characterized in that: The slope of the vehicle is calculated based on the inertial sensor of the vehicle and the slope angle is corrected according to the vehicle dynamics.

6. The method according to claim 1, characterized in that: After the brake energy recovery is exited, the hydraulic brake is compensated so that the total braking torque meets the braking deceleration requirements.

7. The method according to claim 1, characterized in that: The first preset threshold is two-thirds of the rear axle load when the vehicle is unloaded and traveling at a constant speed on a level road.

8. The method according to claim 1, characterized in that: The second preset threshold is one third of the rear axle load when the vehicle is unloaded and traveling at a constant speed on a level road.

9. The method according to claim 1, characterized in that: Before executing exiting any energy recovery step, determine whether the recovery mode exists; if not, skip the exit step.

10. The method according to claim 1, characterized in that Determine whether the driving torque is less than 0; if it is greater than or equal to 0, end this method.

11. An energy recovery control system for a rear-wheel drive vehicle with improved stability, characterized in that: Applicable to rear-wheel drive new energy vehicles with coasting energy recovery and braking energy recovery, including: A rear axle load calculation module is used to obtain the real-time rear axle load of the vehicle under the condition that the driving torque is less than 0 and the vehicle steering wheel angle or the steering wheel angle change rate is greater than a preset threshold; A braking energy recovery exit module, used to exit braking energy recovery and retain coasting energy recovery when the rear axle load is lower than a first preset threshold; The coasting energy recovery exit module is used to exit the coasting energy recovery when the rear axle load is lower than a second preset threshold.

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