A rear-drive vehicle stability improvement energy recovery control method and system

Abstract

The application provides a rear-drive vehicle stability improvement energy recovery control method and system, which is suitable for new energy vehicles with rear-wheel drive and sliding energy recovery and brake energy recovery. The method comprises the following steps: in the working 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, the real-time rear axle load of the vehicle is obtained; when the rear axle load is lower than a first preset threshold, the brake energy recovery is exited while the sliding energy recovery is retained; and when the rear axle load is lower than a second preset threshold, the sliding energy recovery is exited. The application is suitable for the working condition that the lateral acceleration of the vehicle is large during the deceleration process of the rear-drive vehicle at a high speed and during large-angle steering or rapid steering, and is used for solving the problem that the new energy vehicle produces excessive steering and fishtailing due to the insufficient rear axle adhesion after energy recovery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of automobile braking, and particularly relates to an energy recovery control method and system for improving the stability of rear-drive vehicles. BACKGROUND

[0002] When the vehicle is in energy recovery or braking deceleration, the axle load is transferred to the front axle, especially in downhill driving conditions, the influence of road slope further causes the axle load of the rear axle to be significantly reduced, which reduces the vertical force of the rear wheels, and under the same road surface adhesion coefficient, the lateral and longitudinal adhesion of the rear wheels is reduced. For rear-drive vehicles, when the longitudinal adhesion of the rear wheels is insufficient, if energy recovery and braking energy recovery are performed at the same time, a large braking torque will be generated, causing the rear wheels to tend to lock, and the slip ratio to rise, thereby further reducing the adhesion of the rear wheels and worsening the stability of the vehicle. Especially when high-speed steering or rapid steering is performed at high speed, the demand for lateral adhesion of the vehicle increases significantly, and once the adhesion of the rear wheels is insufficient, the over-steering fishtailing phenomenon is prone to occur. Under such conditions, it is extremely difficult for the driver to recover the stability of the vehicle through steering correction, and most drivers cannot effectively respond, and even a misoperation may exacerbate the fishtailing trend, causing the vehicle to lose control and causing the driver to panic or 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 or low adhesion road surface) to avoid wheel lock. However, this solution only applies to targeted exit control after identifying the road surface type, and cannot effectively solve the problem of over-steering caused by insufficient lateral adhesion of the rear wheels under the condition of high adhesion road surface and high-speed braking with large-angle steering or rapid steering for rear-drive vehicles, and cannot quickly respond to exit energy recovery when the lock tendency is obvious.

[0004] Another prior art CN118665192A provides a method for controlling energy recovery by gradually exiting braking energy recovery and maintaining partial energy recovery when the wheel lock tendency is obvious. However, the exit timing of this solution is after the lock tendency is obvious, and the dynamic adjustment of braking torque is limited by the response speed of the torque, which cannot effectively avoid the risk of fishtailing caused by insufficient adhesion due to reduced load on the rear axle under high-speed and rapid steering transient conditions.

[0005] Therefore, there is an urgent need to provide a more accurate and rapid energy recovery exit control method that can avoid the occurrence of over-steering fishtailing phenomenon under the special conditions of high-speed and high-dynamic steering for rear-drive vehicles, and significantly improve the safety and stability of vehicle driving. SUMMARY

[0006] The present application aims to solve the above problems in the background art, and provides an energy recovery control method and system for improving the stability of a rear-drive vehicle.

[0007] The technical scheme adopted by the present application is as follows: an energy recovery control method for improving the stability of a rear-drive vehicle, which is suitable for a new energy vehicle with rear-wheel drive and energy recovery, and comprises the following steps:

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

[0009] When the rear axle load is lower than a first preset threshold, the brake energy recovery is exited while the coasting energy recovery is retained;

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

[0011] The above technical scheme further comprises 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 curb weight, the center of mass height, the center of mass to front axle distance and the wheelbase.

[0012] In the above technical scheme, the rear axle load F Z2 The following formula is used for calculation:

[0013]

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

[0015] In the above technical scheme, the longitudinal deceleration of the vehicle is obtained by the brake controller according to the change of the wheel speed.

[0016] In the above technical scheme, the slope of the vehicle is calculated according to the current slope angle of the vehicle by the inertia sensor of the vehicle, and the slope angle is corrected according to the vehicle dynamics.

[0017] In the above technical scheme, the brake energy recovery is exited to compensate for the hydraulic brake, so that the total brake torque meets the brake deceleration requirement.

[0018] In the technical solution, the first preset threshold is two-thirds of the axle load of the rear axle when the vehicle is evenly driven on a horizontal road and is empty.

[0019] In the technical solution, the second preset threshold is one-third of the axle load of the rear axle when the vehicle is evenly driven on a horizontal road and is empty.

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

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

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

[0023] The application also provides an energy recovery control system for improving the stability of a rear-wheel drive vehicle, which is suitable for a new energy vehicle with rear-wheel drive and energy recovery through coasting and braking, and comprises:

[0024] A rear axle load calculation module is 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 steering wheel angle change rate of the vehicle is greater than a preset threshold.

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

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

[0027] The application has the following beneficial effects: the application judges the two-stage exit of the braking and coasting energy recovery before the vehicle slip rate rises based on the rear axle load when the driving torque is less than 0 and the high dynamic steering is performed, realizes the "pre-stabilization" control, cuts off the recovery torque in time before the rear wheel adhesion is insufficient due to the decrease of the rear axle load, significantly reduces the risk of spinout, improves the driving safety of the vehicle under the condition of rapid deceleration + large steering, fully utilizes the existing control system to optimize the control strategy and improve the safety of the user driving.

[0028] Further, the application introduces the acquisition of the real-time longitudinal deceleration and slope, and calculates the rear axle load in combination with the vehicle parameters, guarantees the accuracy of the load judgment, makes the threshold triggering more suitable for the actual working condition, and improves the robustness and repeatability of the control strategy.

[0029] Further, the application specifies the calculation formula of the rear axle load, quantitatively evaluates the load change based on the vehicle dynamics model, makes the exit timing reasonable and avoids the uncertainty caused by the experience type setting, and improves the engineering implementation of the method.

[0030] Further, the application calculates the deceleration by obtaining the wheel speed change through the vehicle brake controller, without additional sensors, simplifying the system deployment, and ensuring the real-time and reliability of the deceleration data.

[0031] Further, the application uses the on-board inertial sensor and combines dynamics correction to determine the slope, enhances the accuracy of load calculation in uphill and downhill working conditions, and reduces the interference of slope changes on the judgment logic.

[0032] Further, the application automatically compensates for hydraulic braking after exiting the brake energy recovery, ensures that the required brake deceleration of the driver is still met after exiting the recovery, smoothly connects, avoids abrupt braking, and improves ride comfort and safety.

[0033] Further, the application takes two-thirds of the static empty rear axle as the first level threshold example, provides an engineering feasible and easy to calibrate starting value, and greatly shortens the real vehicle tuning period.

[0034] Further, the application takes one-third of the static empty rear axle as the second level threshold example, ensures that the recovery torque is completely cut off when the load is reduced to a low level, leaves the largest friction margin for the rear wheels, and further guarantees the stability in extreme working conditions.

[0035] Further, the application first determines whether the recovery mode exists before exiting any recovery step, which can avoid executing useless logic in invalid working conditions, reduce the burden of the controller, and improve the execution efficiency and reliability of the system.

[0036] Further, the application adds the determination that "the driving torque is greater than or equal to 0, and the method is ended", which ensures that the control logic only takes effect in the deceleration recovery phase, avoids the mis-triggering of the recovery exit strategy in the acceleration or cruising phase, and improves the precision of the strategy and user experience.

[0037] Further, the application modularizes the method into three sub-modules of "load calculation", "brake recovery exit" and "coasting recovery exit", which facilitates software / hardware layered implementation and extended deployment, improves the system integration, maintainability and flexibility of engineering landing. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The method flowchart of the application.

[0039] Figure 2 The principle diagram of the application;

[0040] Figure 3 An application scenario of the present application is shown in the figure;

[0041] Figure 4 An application scenario of the present application is shown in the figure; DETAILED DESCRIPTION

[0042] The present application will be further described in conjunction with the accompanying drawings and specific embodiments, so as to make the present application clear.

[0043] Embodiment 1

[0044] As shown in the figure, the energy recovery control method for improving the stability of a rear-wheel drive vehicle is suitable for a new energy vehicle with rear-wheel drive and with both coasting energy recovery and braking energy recovery, and includes the following steps: Figure 1 In the working condition where 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, the real-time rear axle load of the vehicle is obtained;

[0045] When the rear axle load is lower than a first preset threshold, the braking energy recovery is exited while the coasting energy recovery is retained;

[0046] When the rear axle load is lower than a second preset threshold, the coasting energy recovery is exited.

[0047] Specifically, in daily driving, when the rear-wheel drive new energy vehicle enters a large-angle or rapid steering working condition (such as a steering wheel angle > 180° or an angle change rate > 300° / s) at a high vehicle speed (> 30kph), the lateral acceleration of the vehicle increases sharply. At this time, the wheels not only have to bear the longitudinal braking force during braking or recovery, but also have to provide sufficient lateral adhesion to complete stable turning.

[0048] In the working condition of large-angle turning in mountainous areas or emergency obstacle avoidance, the lateral acceleration of the vehicle is large, and the required wheel lateral adhesion is large. The rear-wheel drive vehicle needs to bear both longitudinal deceleration and lateral steering force, which are shared in the wheel friction resources: it is required that the rear wheels cannot be locked to cause insufficient lateral adhesion and produce excessive steering. When the lateral acceleration reaches 0.5g (typical mountainous sharp turn) or higher, the required lateral force has occupied more than half of the friction ellipse. When a large longitudinal recovery torque (such as a deceleration of 0.3g) is continued at this time, the resultant force will break through the limit, causing the rear wheels to slip and further produce excessive steering.

[0049]

[0050] ​The maximum resultant force of the wheels is limited by the normal load, and when the recovery torque increases, the lateral adhesion force is occupied, and the vehicle will lose stability when the lateral adhesion force margin is insufficient. When braking or coasting recovery, the vehicle body decelerates, the center of gravity moves forward, and the rear axle load decreases; downhill driving further reduces the load of the rear axle. The real-time change of the rear axle load directly affects the friction limit of the rear wheel, so it must be quantified as an index of "available adhesion force".

[0051] The rear axle load is proportional to the available friction force, and is more accurate than the slip rate or pedal signal in reflecting the adhesion margin of the wheels. The load judgment takes into account the current deceleration (longitudinal) and steering strength (lateral) at the same time, and realizes the dynamic evaluation of the resultant force demand. The present application uses the physical quantity of the rear axle load to realize fine dynamic control of the energy recovery mode, effectively solves the risk of spinning at high vehicle speed and large steering working conditions, and significantly improves the driving safety of the vehicle.

[0052] The present application introduces two levels of rear axle load thresholds in the continuous intervention-exit process of coasting and braking energy recovery to realize "pre-stabilization" control. The principles and advantages thereof are described below in combination with Figure 2 and examples.

[0053] As shown in Figure 2 , the horizontal axis is time, the upper vertical axis is energy recovery torque, and the lower vertical axis is rear axle load (linearly decreasing). The present application sets two load thresholds on this curve, and dynamically matches the available friction resources by segmenting and cutting the recovery torque, and the principles and advantages thereof are as follows.

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

[0055] When the vehicle accelerator pedal opening is 0, the coasting energy recovery is started, and the driving wheels generate gradually increasing negative torque; then the driver steps on the brake pedal, and the brake controller distributes 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 drives on a downhill, in the working condition that the driving torque is less than 0 and the steering wheel angle or the steering wheel angle change rate is greater than the preset threshold, the present embodiment calculates the rear axle load in real time.

[0056] When driving downhill and braking, the rear axle load gradually decreases, but is still greater than the first level threshold; at this time, the braking energy recovery ( Figure 2 The solid line in the middle gradually decreases from the maximum torque to the threshold) and the coasting energy recovery ( Figure 2 Indicated by the upper horizontal dashed line in the middle) work at the same time to maximize the recovery efficiency.

[0057] 2. First level threshold triggering (load = first level threshold)

[0058] When the rear axle load drops to the first threshold value - which corresponds to the lowest load level at which the rear wheel adhesion can still meet the friction limit in the presence of lateral force and brake recovery - the brake controller immediately issues an order to exit brake energy recovery, leaving only the coasting recovery torque, to avoid premature encroachment on lateral adhesion resources due to the superposition of brake recovery torque and hydraulic braking force.

[0059] That is, as soon as Figure 2 The middle lower graph solid line (rear axle load) drops to the first horizontal line, the brake energy recovery torque of the upper middle graph solid line is zeroed (vertically dropped to the coasting recovery level), leaving only the smaller coasting recovery torque. At this rear axle load level, if the brake recovery torque + hydraulic braking is superimposed, it will break through the friction ellipse limit, causing the rear wheel to slip. Figure 2

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

[0061] The remaining Figure 2 The torque marked as "coasting energy recovery" in the upper middle graph (orange or red horizontal segment) continues to recover energy while ensuring that the recovery torque does not cause lateral or longitudinal instability.

[0062] 4. Second threshold trigger (load = second threshold)

[0063] When the driver continues to press the brake pedal deeply or the downhill slope increases, causing the deceleration demand to continue to rise, the rear axle load further decreases to the second threshold value - which corresponds to the lowest load level at which the rear wheel adhesion just meets the lateral demand under the sole coasting recovery torque - the brake controller issues an order to exit coasting energy recovery, completely cutting off the motor counter-drag torque, ensuring that all friction of the rear wheel is used for lateral stability control, thereby avoiding the risk of slip rate rising and causing excessive steering (spin).

[0064] That is, when Figure 2 The upper graph coasting recovery torque is also zeroed (again vertically dropped to zero) when the middle lower graph solid line drops below the second horizontal line. At this point, the rear axle load is insufficient to withstand any form of recovery torque and must be completely cut off to ensure that all friction is used for vehicle stability.

[0065] ​Within a safe range, this embodiment utilizes both braking and coasting recovery in the initial stage, taking full advantage of the available regenerative torque. By tightly coupling "physical load" and "regenerative torque" through two-level thresholds, it ensures that the regenerative torque is ≤μ·Fz at any given time, preventing rear wheel lock-up or sideslip from the outset. Each withdrawal only cuts off a portion of the torque (braking first, then coasting), allowing for a smooth switch within milliseconds and reducing jerking. The two thresholds can be quickly calibrated based on empirical values ​​of 2 / 3 and 1 / 3 of the static unloaded rear axle load, and can also be fine-tuned through real-vehicle testing. Regardless of long downhill slopes, sharp cornering, or emergency obstacle avoidance, the system automatically responds according to the same logic, eliminating the need to write multiple sets of rules for each scenario.

[0066] The first threshold is set at the critical point of friction resources of "brake recovery + lateral adhesion". The corresponding relationship between rear axle load and slip ratio inflection point is determined by experimental calibration, and a safety margin is added. The second threshold is set at the limit point of friction resources of "coasting recovery + lateral adhesion" to ensure that all lateral friction margin is retained even under the most severe operating conditions.

[0067] By setting two levels, regeneration is discontinued in two orderly steps before the slip ratio increases significantly, releasing lateral adhesion in advance. First, high-torque braking regeneration discontinues, followed by coasting regeneration, resulting in a smooth transition and avoiding abrupt braking. Energy recovery efficiency is maximized within safe limits; when the need shifts to safety, regeneration is quickly cut off to ensure stability. Furthermore, the two threshold levels can be calibrated for different vehicle models, making it suitable for various high lateral acceleration scenarios such as downhill driving, sharp turns, 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 conditions such as sharp turns in mountainous areas or emergency obstacle avoidance, significantly improving the driving safety and handling experience of rear-wheel drive vehicles under high speed and large dynamic steering conditions.

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

[0070] When a vehicle decelerates by braking / regenerative braking, the resultant force acting on its center of mass includes the gravitational component G (decomposed into components perpendicular to the road surface and along the slope), the inertial force ma (along the longitudinal direction of the vehicle), and the road reaction force.

[0071] like Figure 3 As shown, taking a vehicle side view as an example, let: m: vehicle unloaded mass + 110kg; L: wheelbase; L1, L2: distance from the center of gravity to the front and rear axles, respectively; h: height of the unloaded center of gravity; θ: current slope angle (positive for downhill); a: longitudinal deceleration (braking or regenerative braking); g: gravitational acceleration. Performing torque balancing on the rear axle yields:

[0072] Rear axle load F Z2 The following formula is used for calculation:

[0073]

[0074] The formula comprehensively considers the gravity center position, slope influence and deceleration effect, and can reflect the dynamic change of the rear axle normal load in real time. With the increase of the deceleration a, the inertial force ma through the gravity center height h has a "load reduction" effect on the rear axle; when descending a slope, the gravity component along the slope mgsinθ further reduces the load on the rear axle; the foregoing formula couples the two to accurately depict the rear axle load under different combinations of slope and deceleration.

[0075] The rear axle load calculation method used in this embodiment converts the abstract "deceleration + slope influence" into a measurable load value, which is more intuitive and accurate than using only slip rate or pedal signal. The formula only needs to input vehicle parameters and common quantities (deceleration, slope), and the calculation process is uninterrupted, so the calculation result of the rear axle load can be output in real time throughout the deceleration process. Based on the parameter combination of empty mass, gravity center height and wheelbase, accurate data can be obtained through calibration for different vehicle models; it does not need to rely on experience values. This physical quantity is directly mapped to the energy recovery exit decision through threshold comparison - the primary threshold controls the braking recovery, and the secondary threshold controls the coasting recovery - realizing the integration of "physical quantity → control quantity". Whether it is on a flat road, descending a slope, or different deceleration levels, the same model can be covered, and there is no need to design multiple sets of logic for each scenario.

[0076] Specifically, the longitudinal deceleration of the vehicle is obtained by the brake controller acquiring the wheel speeds of the four wheels of the vehicle, and is calculated according to the change of the wheel speeds.

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

[0078]

[0079] The finite difference method is further used to calculate the longitudinal deceleration:

[0080]

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

[0082]

[0083] For the mutation or "slip" jump point, the slip rate can be combined to determine the temporary locking of the last time value, avoiding false deceleration interference to the rear axle load. When ABS intervention and ESC stable control work, abnormal jump data can be removed to ensure that the deceleration signal only reflects the actual braking condition of driving / recovery.

[0084] Specifically, the slope of the vehicle is calculated according to the inertial sensor of the whole vehicle to obtain the current slope angle of the vehicle, and the slope angle is corrected according to the vehicle dynamics.

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

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

[0087] Short-time dependent gyroscope signal ω y (angular velocity around the transverse axis) is integrated to obtain the temporary pitch angle θ gyro ;

[0088] Long-time dependent accelerometer components (a x , a z ) are used to calculate the gravity direction pitch:

[0089]

[0090] Further complementary filtering:

[0091]

[0092] The accelerometer itself measures the superposition of gravity and inertial force, and needs to remove the inertial component caused by the longitudinal deceleration:

[0093]

[0094] Or directly take the deceleration as a known input in the EKF state equation to filter out the dynamic component.

[0095] The IMU zero offset and scale factor will drift with temperature, and the online zero point can be recalibrated during vehicle startup or constant speed cruising. The high-frequency vibration component is subjected to second-order low-pass filtering (cutoff 5Hz), which further improves the stability of the slope angle.

[0096] This embodiment targets sampling and filtering at frequencies above 100Hz, ensuring that deceleration and gradient angle are output within a delay of <10ms during rapid deceleration / sharp cornering. Multiple methods are employed to suppress errors, including differential + low-pass filtering, complementary / EKF fusion, and cross-validation using ABS / ESC information. The filter coefficients and zero-bias update strategy can be calibrated on a real vehicle to match its dynamic characteristics. This embodiment uses only common wheel speed and IMU modules to stably output high-precision physical quantities, making it easy to deploy on existing electronic control units (ECUs). The system can acquire vehicle deceleration and gradient in real time and accurately, providing robust and reliable data support for calculating rear axle load and determining energy recovery exit.

[0097] Specifically, after the regenerative braking system is deactivated, hydraulic braking is compensated to ensure that the total braking torque meets the braking deceleration requirements.

[0098] When the driver presses 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' based on the driver's brake pedal opening and higher-level logic such as ACC / ESP. req Subsequently, the brake controller distributes the braking torque according to the following steps:

[0099] Based on the motor's maximum recyclable power and the battery's current charging power limit, determine the available regenerative braking torque T. regen,max ;

[0100] Calculate the deceleration component 'a' that the motor braking can handle under the corresponding braking deceleration. regen =T regen / (mr)(r is the radius of the drive wheel);

[0101] If a regen ≤a req Then let the motor braking torque T regen =mra regen The remaining deceleration requirement a hyd =a req -a regen Hydraulic braking is used to handle this;

[0102] If a regen >a req Then the amplitude limit T regen =mra req Hydraulic braking will not be engaged at this time.

[0103] When the rear axle load drops below the first preset threshold, the regenerative braking logic is triggered: the brake controller will reduce the motor braking torque T. regen Immediately drop to zero;

[0104] To ensure that the total braking deceleration still meets the a standard req Hydraulic braking torque Thyd Cooperative increase, compensation for the loss of deceleration after exiting recovery:

[0105] mra hyd,new = mra req -0, that is, T hyd,new = mra req .

[0106] Since the hydraulic braking system has fast response capability and large torque reserve, torque compensation switching can be completed within 10-20 ms, ensuring smooth transition of vehicle deceleration and no significant loss of deceleration.

[0107] When the coasting energy recovery setting strength is large, such as 0.15g generated by the rear axle of a rear-drive vehicle after passing through, the braking force of the rear axle is still large, and if the hydraulic braking force of the rear axle is further superimposed, the rear wheel braking force deviation is more when the rear axle load decreases, and there is still a risk of locking. In order to fully ensure the stability and safety of the vehicle, when the rear axle load decreases to below the second preset threshold, the brake controller only closes the 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 on the brake deeply, the system defaults to reduce the deceleration demand or maintain the vehicle speed by road resistance, and does not actively increase the hydraulic braking; therefore, after the coasting recovery is exited, the vehicle deceleration will decrease to a certain extent, and the driver feels relatively smooth.

[0109] When exiting the brake recovery, the passenger does not feel the deceleration decrease due to the fast switching to hydraulic braking and sufficient compensation, and the smoothness is high.

[0110] When exiting the coasting recovery, the coasting braking force decreases suddenly without compensation, and the passenger can feel a slight acceleration, but at this time it is mostly low deceleration conditions, which has little effect on vehicle stability.

[0111] In this embodiment, the brake controller needs to monitor the motor recovery capability and hydraulic braking state in real time, and update the torque distribution at a millisecond level; at the moment of exiting the brake recovery, a linear or exponential transition function (such as a ramp-down motor braking torque and a ramp-up hydraulic braking torque within 50 ms) can be introduced to further smooth the driving experience; after the coasting recovery is exited, the driver can be prompted about the change in braking state through brake light logic or HMI, enhancing the driver's confidence.

[0112] Through the above embodiments, while taking into account efficient energy recovery, the present application uses the fast compensation capability of hydraulic braking to eliminate the deceleration loss caused by the exit of brake recovery, ensures that the required deceleration is maintained when the rear axle load decreases to a low level, and maximizes the guarantee of driving stability and ride comfort.

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

[0114] In the specific embodiment, the "first preset threshold" and the "second preset threshold" are not fixed constants, but optimal parameters obtained through real vehicle calibration for different vehicle models, different curb weights and center of mass arrangements. The calibration process and preferred values are as follows:

[0115] In the specific embodiment, in order to adapt to the mass distribution, suspension characteristics and power recovery capability of different vehicles, real vehicle calibration is required for the first threshold and the second threshold, and the process can be performed according to the following steps:

[0116] 1. Static parameter measurement

[0117] Park the test vehicle on a horizontal test bench and frame the empty state (remove the driver and unloadable parts);

[0118] Use a force platform or four-wheel force sensor to measure the static normal load of the front / rear axle respectively;

[0119] Use a pitch test stand or a three-dimensional measuring device to measure the empty center of mass height of the vehicle, the front-rear axle distance and the horizontal distance from the front axle to the center of mass.

[0120] 2. Dynamic condition preparation

[0121] Select a traffic-free, straight downhill test track (slope 3%–10%);

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

[0123] Adjust the vehicle to a normal operating state (full load, empty or half load);

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

[0125] 3. Threshold 1 (braking recovery exit before) calibration

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

[0127] The driver or automatic controller gradually increases the brake pedal opening, so that the motor brake torque increases from small to large; record the corresponding rear axle dynamic load and slip rate at each motor brake torque level.

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

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

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

[0131] 4. Threshold 2 (before glide recovery exit) calibration

[0132] In the uniform state, gradually increase the glide recovery torque to the maximum available;

[0133] Maintain the glide recovery torque wei the maximum available, find the rear axle load F corresponding to the first overrun of the slip ratio t ;

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

[0135] Where δ2 is the safety margin, which 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] Under different slopes, different speeds (20-80 kph) and different tire / pavement conditions, retest to verify whether the slip ratio always remains in the safety interval;

[0139] According to the retest results, fine-tune δ1, δ2 or typical torque level to ensure smooth transition and no false action.

[0140] The embodiment is based on real vehicle data calibration, accurately reflecting the real dynamic load transfer characteristics of the vehicle; different thresholds can be set for different vehicle models, different loads and different road conditions, with good scalability; by introducing a margin, a protection space is left above the test inflection point, further improving safety; it can fully feedback energy under high recovery torque, and smoothly and timely exit recovery when the load is insufficient, balancing range and driving stability.

[0141] Preferably, the first preset threshold is two-thirds of the rear axle load when the vehicle is empty and uniformly driven on a horizontal road. It is found in real vehicle tests that when the rear axle load drops below ≈66% of the static reference, if brake recovery torque is superimposed, the rear wheel slip ratio is easy to rise above 20%, showing signs of insufficient adhesion

[0142] The second preset threshold is one-third of the rear axle load when the vehicle is empty and uniformly driven on a horizontal road. When the load drops below ≈33% of the static reference, even light glide recovery will quickly put the rear wheel into the low adhesion zone, at which point all recovery torque must be completely cut off.

[0143] Specifically, before executing the exit step of 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, the running state of the corresponding recovery mode needs to be detected before each execution of the "exit brake energy recovery" or "exit coasting energy recovery": the system determines whether the brake energy recovery or the coasting energy recovery is currently being executed by reading the state flag inside the energy recovery controller; if it is detected that the brake energy recovery has not started, the "exit brake recovery" step is directly skipped to avoid sending invalid instructions; similarly, if the coasting energy recovery is already in the off state, the "exit coasting recovery" operation is not performed, but directly proceeds to the subsequent determination.

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

[0146] Preferably, after each recovery exit determination of the control process is completed, the driving torque signal should be immediately read: if the driving torque is greater than or equal to zero, it indicates that the driver has re-requested acceleration, at which time the current energy recovery exit logic should be immediately suspended and returned to the initial monitoring state; only when the driving torque continues to be less than zero, the subsequent rear axle load determination and energy recovery exit steps are continued.

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

[0148] S1: it is determined whether the driving torque is less than 0 and the steering wheel angle is greater than a preset steering angle threshold or the steering wheel angle change rate is greater than a preset steering angle change rate threshold, if yes, proceed to S2, if not, return to S1;

[0149] S2: the current deceleration and slope of the vehicle are obtained, the load of the rear axle of the vehicle is calculated based on the vehicle parameters according to the empty weight, and it is determined whether the load of the rear axle is less than a first preset threshold, if yes, proceed to S3, if not, return to S1;

[0150] S3: if there is brake energy recovery, the motor is requested to exit the brake energy recovery, and the energy recovery is compensated by establishing brake hydraulic pressure. If the brake is not stepped on or is limited by the motor charging power, and the brake energy recovery is not requested to be generated, S3 is skipped;

[0151] S4: it is determined whether the driving torque is greater than or equal to 0, if the driving torque is greater than or equal to 0, such as the driver stepping on the accelerator pedal or the ACC requesting acceleration, the program ends and returns to S1; if the throttle opening is still 0, proceed to S5;

[0152] S5: determining whether the current rear axle load is less than a second preset threshold value, if yes, and there is coasting energy recovery, requesting the motor to exit the coasting energy recovery, avoiding the coasting energy recovery leading to the vehicle appearing to be over-steering. If the coasting energy recovery is closed, S5 is skipped.

[0153] S6: determining whether the driving torque is greater than or equal to 0, if yes, the program ends, returning to S1, if not, returning to S6.

[0154] Embodiment 2

[0155] The application also provides an energy recovery control system for improving the stability of a rear-wheel drive vehicle, which is suitable for a new energy vehicle with coasting energy recovery and braking energy recovery, and comprises:

[0156] a rear axle load calculation module, configured to obtain a 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 value;

[0157] a braking energy recovery exit module, configured to exit the braking energy recovery while retaining the coasting energy recovery when the rear axle load is lower than a first preset threshold value;

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

[0159] Embodiment 3

[0160] The application provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the energy recovery control method for improving the stability of a rear-wheel drive vehicle.

[0161] Embodiment 4

[0162] The application provides an electric vehicle, which comprises a memory and a processor, the memory and the processor are in communication connection with each other, the memory stores computer instructions, and the processor executes the computer instructions to perform the energy recovery control method for improving the stability of a rear-wheel drive vehicle.

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

[0164] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flowcharts and / or blocks Figure 1 means for functionally implementing the steps listed in the flowchart block or 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 apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the function specified in the flowchart block or blocks. Figure 1 one or more flowcharts and / or blocks Figure 1 means for functionally implementing the steps listed in the flowchart block or blocks.

[0166] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flowcharts and / or blocks Figure 1 means for functionally implementing the steps listed in the flowchart block or blocks.

[0167] The embodiments of the present application described above are merely intended to illustrate the present application, but are not intended to limit the present application. The above-described embodiments are merely illustrative, and are not intended to limit the present application, and any person skilled in the art can make many modifications without departing from the spirit and scope of the present application, and these are intended to be included in the scope of the present application.

[0168] The contents not described in detail in the specification are the prior art known to those skilled in the art.

Claims

1. A method for energy recovery control for improving stability of a rear-drive vehicle, characterized by: The application relates to a new energy vehicle suitable for rear-wheel driving with slip energy recovery and brake energy recovery, and comprises the following steps. In a working 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, the real-time rear axle load of the vehicle is obtained; When the rear axle load is lower than a first preset threshold, brake energy recovery is exited while slip energy recovery is retained; When the rear axle load is lower than a second preset threshold, slip energy recovery is exited; The first preset threshold is two-thirds of the rear axle load when the vehicle is empty and uniformly travels on a horizontal road, and the second preset threshold is one-third of the rear axle load when the vehicle is empty and uniformly travels on a horizontal road.

2. The method of claim 1, wherein: The application further comprises the following steps: The real-time longitudinal deceleration and slope of the vehicle are obtained, and the real-time rear axle load is calculated according to the empty weight based on the vehicle kerb mass, the mass center height, the mass center to front axle distance and the wheelbase.

3. The method of claim 2, wherein: The rear axle load F Z2 The following formula is used: ； Wherein, m represents the vehicle kerb mass, L1 represents the mass center to front axle distance, L represents the wheelbase, h represents the empty mass center height, theta represents the current slope angle of the vehicle, alpha represents the longitudinal deceleration of the vehicle, and g represents the gravity acceleration.

4. The method of claim 2, wherein: The longitudinal deceleration of the vehicle is obtained by a brake controller acquiring the four-wheel wheel speeds of the vehicle and calculating the wheel speed change.

5. The method of claim 2, wherein: The slope of the vehicle is calculated according to the inertia sensor of the vehicle to obtain the current slope angle of the vehicle, and the slope angle is corrected according to the vehicle dynamics.

6. The method of claim 1, wherein: After the brake energy recovery is exited, the hydraulic brake is compensated, so that the total brake torque meets the brake deceleration requirement.

7. The method of claim 1, wherein, Before the exit step of any energy recovery is executed, it is judged whether the recovery mode exists; if not, the exit step is skipped.

8. The method of claim 1, wherein, It is judged whether the driving torque is less than 0; if greater than or equal to 0, the method is ended.

9. An energy recovery control system for improving stability of a rear-drive vehicle, characterized by: The application relates to a new energy vehicle suitable for rear-wheel driving with slip energy recovery and brake energy recovery, and comprises the following steps. A rear axle load calculation module is used for obtaining the real-time rear axle load of the vehicle in a working 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 brake energy recovery exit module is used for exiting brake energy recovery while retaining slip energy recovery when the rear axle load is lower than a first preset threshold; A slip energy recovery exit module is used for exiting slip energy recovery when the rear axle load is lower than a second preset threshold; The first preset threshold is two-thirds of the rear axle load when the vehicle is empty and uniformly travels on a horizontal road, and the second preset threshold is one-third of the rear axle load when the vehicle is empty and uniformly travels on a horizontal road.

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