Electric vehicle sliding energy recovery control method and system

Abstract

The invention discloses an electric automobile sliding energy recovery control method and system, and belongs to the technical field of electric automobiles. The method comprises the steps that the accelerator pedal opening degree at the current moment, the accelerator pedal opening degree at the previous moment, the target automobile speed and the actual automobile speed are obtained; calculating a vehicle speed difference and a pedal opening degree variable quantity; based on the vehicle speed difference, the pedal opening degree variable quantity, a vehicle speed difference threshold value where regenerative braking torque intervenes and a vehicle speed difference threshold value where the regenerative braking torque exits, the braking intention is judged; and based on the braking intention and the rear axle wheel slip rate, the RBCS state switching unit is controlled to be switched among a driving mode, a regenerative braking torque increasing mode, a regenerative braking torque keeping mode and a regenerative braking emergency exit mode. The driving intention can be adaptively recognized, the control parameters are dynamically adjusted, and the safety of complex road conditions is considered.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric vehicles, and in particular relates to a method and system for controlling the coasting energy recovery of an electric vehicle. Background Art

[0002] In the field of new energy vehicles, the coasting energy recovery control strategy based on the accelerator pedal is one of the key technologies to improve vehicle endurance. Its core lies in achieving efficient control of the regenerative braking system (RBCS) by accurately identifying driving intentions.

[0003] Existing driving intention recognition methods often rely on a constant accelerator pedal zero-position threshold, distinguishing between acceleration and deceleration intentions by presetting a fixed angle point at the accelerator pedal position. This control strategy has significant limitations: First, it simply links the accelerator pedal to the motor brake pedal, resulting in a constant and relatively small braking stroke. This fails to fully utilize the pedal stroke to improve energy recovery, especially at high speeds and with deep pedal positions, where braking delays can easily lead to safety hazards. Second, during actual coasting braking, drivers typically need to steadily reduce vehicle speed from a higher value to the target speed. Existing strategies require drivers to frequently adjust the accelerator pedal position to maintain a stable speed, significantly increasing the driver's workload.

[0004] Furthermore, existing regenerative braking control strategies lack adaptability to driving styles. The thresholds for regenerative braking engagement and disengagement are often fixed, resulting in frequent switching between positive and negative motor torque or delayed braking response, impacting ride smoothness and motor life. Furthermore, under complex driving conditions, such as low-adhesion roads, existing strategies fail to fully account for the impact of wheel slip on regenerative braking, making it difficult to balance energy recovery efficiency and driving safety, posing a risk of vehicle skidding.

[0005] Therefore, there is an urgent need for a regenerative braking control technology that can adaptively identify driving intentions, dynamically adjust control parameters, and take into account safety in complex road conditions, so as to address the shortcomings of existing strategies in energy recovery efficiency, driving comfort and safety.

[0006] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the Invention

[0007] The purpose of the present invention is to provide a method and system for controlling coasting energy recovery in electric vehicles, which can adaptively identify driving intentions, dynamically adjust control parameters, and take into account safety in complex road conditions.

[0008] To achieve the above object, the present invention provides a method for controlling coasting energy recovery in an electric vehicle, comprising the following steps:

[0009] Get the current accelerator pedal opening APP t 、Previous moment accelerator pedal opening APP t-1 , target vehicle speed v t and actual vehicle speed v r ;

[0010] Calculate the speed difference Δ=v t -v r and pedal opening change d APP =APP t -APP t-1 ;

[0011] Based on the vehicle speed difference Δ and the pedal opening change d APP , the speed difference threshold α for regenerative braking torque intervention, and the speed difference threshold for regenerative braking torque exit , determine the braking intention;

[0012] Based on the braking intention and the rear axle wheel slip rate, the RBCS state switching unit is controlled to switch between the driving mode, the regenerative braking torque increasing mode, the regenerative braking torque maintaining mode and the regenerative braking emergency exit mode.

[0013] Optionally, the vehicle speed difference threshold α for regenerative braking torque intervention is calculated by a fuzzy control algorithm, specifically including:

[0014] APR=d APP / d t ,α=fuzzy(APR,v r );

[0015] Among them, APP t is the current accelerator pedal opening, APP t-1 is the accelerator pedal opening at the previous moment; APR is the accelerator pedal change rate, d APP is the change in accelerator pedal opening; d t is the time difference between the two moments; fuzzy is the fuzzy control algorithm, the input of which is the accelerator pedal change rate APR and the actual vehicle speed v r The output is the speed difference threshold α for regenerative braking intervention, where the APR membership function is differentiated according to the driving style, and the membership function of the speed difference threshold α for regenerative braking intervention adopts a trapezoidal distribution.

[0016] Optionally, based on the vehicle speed difference Δ, the pedal opening change d APP , the speed difference threshold α for regenerative braking torque intervention, and the speed difference threshold for regenerative braking torque exit , determine the braking intention, including:

[0017] when When it is less than α for the first time, it is determined that the braking intensity is increasing, and the motor queries the current vehicle speed v from the pre-stored regenerative braking torque MAP. r The corresponding target torque value T_target increases toward the target torque value T_target, wherein the first time it is less than α refers to the moment when Δ changes from ≥α to <α;

[0018] when and >d1, indicating that the driver lightly presses the pedal during braking, which is determined as the intention to maintain the braking intensity, and the motor maintains the current torque unchanged, where d1=5km / h is the positive threshold of the pedal change;

[0019] when , < d2, indicating that the driver pulls back on the pedal during braking, which is considered an intention to increase the braking intensity. The motor continues to increase the torque toward the target. d2 = -5 km / h is the negative threshold of the pedal change.

[0020] when When the driver's braking intention is determined to be released, the regenerative braking torque is withdrawn, the motor torque gradually decreases from a negative value to 0, and the driving mode is entered again;

[0021] in, , d1, d2 are constants.

[0022] Optionally, the mode switch also includes: when the regenerative braking torque exits, the motor torque gradually drops from a negative value to 0, and then increases to a balance with the vehicle's inherent resistance to maintain the target speed. The vehicle's inherent resistance balance means that when the motor torque drops to 0, the vehicle relies solely on rolling resistance to maintain the target speed.

[0023] Optionally, the domain of the accelerator pedal change rate APR is [-50, 0], and the fuzzy set is {F (fast), M (medium), S (slow)}; the actual vehicle speed v r The domain of discourse is [0,220] km / h, and the fuzzy set is {S (small), M (medium), B (large)}.

[0024] Optionally, the vehicle speed difference threshold for the regenerative braking torque intervention is The domain of discourse is set according to the driving style:

[0025] Aggressive driving style: ∈[-10,-5] km / h;

[0026] Standard driving style: ∈[-15,-5] km / h;

[0027] Conservative driving style: ∈[-20,-5] km / h.

[0028] Optionally, the activation condition of the regenerative braking emergency exit mode of the RBCS state switching unit is: the rear axle left wheel slip ratio RLS or the right wheel slip ratio RRS is greater than 4%, and fault counting is performed when activated.

[0029] Optionally, the exit condition of the regenerative braking emergency exit mode of the RBCS state switching unit is: the rear axle left wheel slip ratio RLS and the right wheel slip ratio RRS are both less than 1% and the fault count is ≤5 times; when the fault count is greater than 5 times, the emergency exit mode is maintained.

[0030] Optionally, in the regenerative braking torque increase mode, the motor increases toward the target torque according to the regenerative braking torque MAP; in the regenerative braking torque hold mode, the electric vehicle coasting energy recovery control system motor maintains the current torque unchanged.

[0031] Another aspect of the present invention provides an electric vehicle coasting energy recovery control system, comprising:

[0032] Data acquisition unit, used to obtain the current accelerator pedal opening APP t 、Previous moment accelerator pedal opening APP t-1 , target vehicle speed v t and actual vehicle speed v r ;

[0033] Calculation unit, used to calculate the vehicle speed difference Δ=v t -v r and pedal opening change d APP =APP t -APP t-1 ;

[0034] The driving intention recognition unit is used to identify the driving intention based on the vehicle speed difference Δ and the pedal opening change d APP , speed difference threshold for regenerative braking torque intervention , and the speed difference threshold for regenerative braking torque exit , determine the braking intention;

[0035] The RBCS state switching unit is used to control the RBCS state switching unit to switch between driving mode, regenerative braking torque increase mode, regenerative braking torque holding mode and regenerative braking emergency exit mode based on braking intention and rear axle wheel slip rate.

[0036] Compared with the prior art, the electric vehicle coasting energy recovery control method and system according to the present invention have the following beneficial effects:

[0037] By collecting the accelerator pedal opening, target vehicle speed, actual vehicle speed and rear axle slip rate in real time, combining the dual-parameter analysis of vehicle speed difference and pedal change, and dynamically calculating the regenerative braking intervention threshold α with the fuzzy control algorithm, a multi-dimensional judgment of the driver's braking intention is achieved, so that the regenerative braking intervention threshold α is dynamically adjusted according to driving habits, avoiding the "misjudgment" problem of traditional fixed threshold solutions for drivers with different driving styles.

[0038] By “first less than α”, “d APP >5km / h”, “d APP The system can combine conditions such as "speed < -5km / h" and subdivide the braking intention into three levels: "increase", "maintain" and "weaken", solving the defect of the traditional single-threshold solution that cannot distinguish between "light braking" and "strong braking", avoiding unnecessary torque fluctuations and ensuring maximum energy recovery efficiency.

[0039] By switching between the "regenerative braking torque growth mode", "regenerative braking torque holding mode" and "regenerative braking torque exit mode", combined with the zero-crossing zone torque slope control, a smooth transition of the motor torque is achieved, significantly reducing the impact on the transmission system, ensuring a strong correlation between the energy recovery process and the vehicle speed, avoiding high-frequency vibration of the motor caused by frequent torque adjustments, and improving driving smoothness.

[0040] Through real-time monitoring of the rear axle wheel slip rate (RLS / RRS) and a fault counting mechanism, a dual safety protection system is built to ensure driving safety under extreme working conditions.

[0041] By comparing the accelerator pedal change rate (APR) with the actual vehicle speed (v r ) is incorporated into the fuzzy control input and the membership function is designed based on driving style differentiation, which significantly improves the robustness of the threshold calculation. Among them, the trapezoidal / triangular / Gaussian membership functions ensure that the output of α has no jumps, avoiding the control command mutation problem caused by the traditional step function and improving the smoothness of the motor torque regulation.

[0042] The regenerative braking intervention threshold α is relaxed according to the driving style. For example, the conservative α domain is [-20,-5] km / h, which extends the activation time of regenerative braking and increases the energy recovery opportunity. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a flow chart of a coasting energy recovery control method for an electric vehicle according to an embodiment of the present invention;

[0044] Figure 2 Schematic diagram of the relationship between the accelerator pedal opening and the target vehicle speed MAP according to one embodiment of the present invention;

[0045] Figure 3Schematic diagram of the principle of a fuzzy controller according to one embodiment of the present invention;

[0046] Figure 4 is a graph showing an actual vehicle speed membership function curve according to an embodiment of the present invention;

[0047] Figure 5 is a graph showing a membership function curve of an accelerator pedal change rate according to an embodiment of the present invention;

[0048] Figure 6 A graph showing a membership function curve of a vehicle speed difference threshold value for regenerative braking torque intervention according to an embodiment of the present invention;

[0049] Figure 7 This is a schematic diagram of the output results of the fuzzy controller according to one embodiment of the present invention;

[0050] Figure 8 Schematic diagram of the RBCS state switching process according to one embodiment of the present invention. DETAILED DESCRIPTION

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0052] The terms "first," "second," "third," "fourth," and so forth (if any) in the description and claims of the present invention and in the accompanying drawings are used to distinguish similar items and are not necessarily used to describe a particular order or sequential sequence. It should be understood that the terms used in this manner are interchangeable where appropriate, such that the embodiments of the present invention described herein can be practiced in sequences other than those illustrated or described herein.

[0053] It should be understood that in various embodiments of the present invention, the size of the sequence number of each process does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0054] It should be understood that in the present invention, "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0055] It should be understood that in the present invention, "multiple" refers to two or more. "And / or" is only a description of the association relationship of associated objects, indicating that three relationships can exist. For example, and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. "Contains A, B and C", "Contains A, B, C" means that A, B, and C are all included, "Contains A, B or C" means that one of A, B, and C is included, and "Contains A, B and / or C" means that any one, any two, or any three of A, B, and C are included.

[0056] In accelerator-pedal-based coasting energy recovery control strategies, previous driving intention recognition methods have often been designed with a constant pedal zero position, using a preset threshold value of the accelerator pedal position as a constant angle point to identify acceleration and deceleration intentions within a pedal stroke. On the one hand, control strategies with this constant switching point only achieve a simple assembly between the accelerator pedal and the motor brake pedal, resulting in a constant and small braking stroke. This fails to fully utilize the pedal stroke to improve energy recovery, especially when driving at high speeds with a deep pedal position. Braking delay is significant, which can easily lead to safety issues. On the other hand, during actual coasting braking, drivers typically do not reduce the vehicle speed to zero, but rather prefer to smoothly descend from a higher speed to a new target speed. Previous control strategies require drivers to frequently adjust the accelerator pedal position to maintain a stable target speed, which undoubtedly increases the driver's burden. To address these issues, the present invention discloses a coasting energy recovery control method for electric vehicles that adaptively adjusts the control variable based on the difference between the target speed and the actual speed to improve driving performance. This method formulates driving intention recognition rules, considers driving style, and determines the regenerative braking system activation threshold based on a fuzzy controller. It optimizes the RBCS state switching logic based on driving intention and wheel slip rate to improve the safety and adaptability of the system.

[0057] The following specific embodiments are used to describe the technical solution of the present invention in detail. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0058] like Figure 1 As shown, the electric vehicle coasting energy recovery control method according to the preferred embodiment of the present invention includes the following steps:

[0059] Get the current accelerator pedal opening APP t 、Previous moment accelerator pedal opening APP t-1 , target vehicle speed v t and actual vehicle speed v r ; Among them, the target speed v t and actual vehicle speed vr Used to calculate the speed difference Δ=v t -v r , represents the vehicle coasting state, Δ>0 indicates coasting acceleration, and Δ<0 indicates deceleration;

[0060] Calculate the speed difference Δ=v t -v r and pedal opening change d APP =APP t -APP t-1 ;

[0061] Based on the vehicle speed difference Δ and the pedal opening change d APP , speed difference threshold for regenerative braking torque intervention , and the speed difference threshold for regenerative braking torque exit , determine the braking intention, where Can be set to a fixed value of -3km / h. When the vehicle is ≤-3km / h, the coasting speed is significantly higher than the target speed. Exiting regenerative braking at this time can avoid excessive deceleration and improve driving comfort. The speed difference threshold for regenerative braking torque intervention is Dynamically generated through fuzzy control algorithms;

[0062] Based on braking intent and rear axle wheel slip, the RBCS state switching unit switches between drive mode, regenerative braking torque boost mode, regenerative braking torque hold mode, and regenerative braking emergency exit mode. In drive mode (state 0), the motor outputs positive torque, accelerating or driving at a constant speed. In regenerative braking torque boost mode (state 1), the motor gradually increases torque from zero to the target regenerative torque. In regenerative braking torque hold mode (state 2), the current regenerative torque is maintained to avoid frequent fluctuations. In regenerative braking emergency exit mode (state 3), regenerative braking is forcibly exited when the slip ratio exceeds the limit to ensure safety. Emergency exit is activated when the rear axle left / right wheel slip ratio (RLS / RRS) exceeds 4% to prevent wheel lock.

[0063] In the embodiment of the present invention, the regenerative braking torque intervention threshold Setting it too small (absolute value) will cause frequent switching of the motor's positive and negative torque, affecting driving smoothness and motor life; threshold Setting the threshold too high (in absolute value) can cause a delay in the regenerative braking response, so the maximum range of the threshold is set to -20 km / h to -5 km / h. Taking into account the actual vehicle speed, the driver's real-time operating intensity, and driving style, this embodiment of the present invention proposes a dynamic threshold adjustment method based on a fuzzy controller to improve the control system's adaptability to the driver. Specifically, the speed difference threshold α for regenerative braking torque intervention is calculated using a fuzzy control algorithm, specifically including: APR=d APP / d t ,α=fuzzy(APR,v r ), Among them, APP t is the current accelerator pedal opening, APP t-1 is the accelerator pedal opening at the previous moment; APR is the accelerator pedal change rate, d APP is the change in accelerator pedal opening; d t is the time difference between the two moments; fuzzy is the fuzzy control algorithm, the input of which is the accelerator pedal change rate APR and the actual vehicle speed v r , the output is the speed difference threshold α for regenerative braking intervention, as shown in the following example: Figure 3 The fuzzy controller principle diagram is shown in Figure 1. The APR membership function is designed differently according to the driving style.

[0064] Furthermore, the input and output variables in fuzzy logic need to be fuzzified. Considering the driving preference accelerator pedal opening rate APR domain is [-50,0], its fuzzy language description is: fast, medium, slow, the corresponding fuzzy set is {F,M,S}; the actual vehicle speed v r The domain is [0,220], and its fuzzy language description is: small, medium, large, and the corresponding fuzzy set is {S,M,B}; the speed difference threshold for regenerative braking torque intervention The domain is set to suit different driving styles: the aggressive threshold is [-10, -5], allowing earlier regenerative braking; the standard threshold is [-15, -5]; and the conservative threshold is [-20, -5], delaying triggering to prioritize power response. Fuzzy language describes the thresholds as high, medium, and low, corresponding to the fuzzy set {H, M, L}. Compared to fixed thresholds, dynamic thresholds can adapt to different driving habits and improve energy recovery efficiency.

[0065] Membership function is used to describe the fuzzy set of input and output variables. Common membership functions include triangle, trapezoidal, Gaussian, S-type, etc. In order to balance the calculation efficiency and accuracy, the embodiment of the present invention adopts a combination of triangle and trapezoidal membership functions to calculate APR, v r and The following two formulas are the expressions of triangular and trapezoidal membership functions respectively: , ,

[0066] It should be noted that the triangular function is used in non-platform areas where variables change rapidly (such as the start / stop stage), and its linear characteristics are used to reduce the amount of calculation; the trapezoidal function is used in platform areas where variables need to be stably controlled (such as the target value tracking stage), and the platform segment is used to reduce the impact of small disturbances on the membership degree, avoiding the loss of accuracy caused by slope changes in traditional triangular functions.

[0067] Parameters a, b, c, d can be flexibly adjusted according to the physical characteristics of the variable (such as range, threshold), for example: for APR variable, you can set a=0 (no acceleration), b=v min (minimum effective acceleration), c=v max (maximum effective acceleration), d=+∞ (theoretical upper limit), forming a "left triangle-right triangle" structure.

[0068] Because different driving styles have different habits of operating the pedals, for the accelerator pedal change rate APR, a medium-speed change for a conservative driving style may only be equivalent to a low-speed change for an aggressive driving style. Therefore, when designing the accelerator pedal change rate membership function, it is necessary to distinguish between driving styles. The membership functions of the accelerator pedal change rate APR for the three driving styles are as follows: Figure 4 As shown; the membership functions of the actual vehicle speed vr of the three driving styles are the same, as shown in Figure 5 As shown; the speed difference threshold for regenerative braking torque intervention in three driving styles The membership function curves of have the same shape, only the domains are different, that is, the horizontal coordinates of the curves are different. Figure 6 Taking the standard driving style as an example, the membership function of this variable is shown.

[0069] In the embodiment of the present invention, based on the vehicle speed difference Δ, the pedal opening change d APP , speed difference threshold for regenerative braking torque intervention , and the speed difference threshold for regenerative braking torque exit , determine the braking intention, including:

[0070] when When it is greater than 0, it is determined that the driver currently intends to accelerate, and the motor calculates the driving torque based on the driving torque MAP to accelerate the vehicle.

[0071] when When the vehicle is judged to have the intention to glide or to drive at a constant speed, the regenerative braking torque does not intervene, and the motor still outputs positive torque according to the drive torque MAP. During the glide phase, the vehicle only relies on inherent resistance such as air resistance and vehicle rolling friction to decelerate.

[0072] when First time less than When the braking intensity is determined to increase, the motor queries the current vehicle speed v from the pre-stored regenerative braking torque MAP. r The corresponding target torque value T_target is as follows: Figure 2 As shown in the accelerator pedal opening-target vehicle speed MAP diagram, and increases toward the target torque value T_target, wherein the first time being less than α refers to the moment when Δ changes from ≥α to <α;

[0073] Further, when , it is determined that the driver has the intention to brake, at which time the regenerative braking torque intervenes, Gradually In this process, the braking intention is further divided into the intention to increase braking intensity, the intention to maintain braking intensity, and the intention to reduce braking intensity.

[0074] when and >d1, indicating that the driver lightly presses the pedal during braking, which is determined as an intention to maintain the braking intensity, and the motor maintains the current torque unchanged. d1 = 5 km / h is the positive threshold of the pedal change (light pedal press);

[0075] when , < d2, indicating that the driver pulls back on the pedal during braking, which is considered an intention to increase braking intensity. The motor continues to increase the torque toward the target. d2 = -5 km / h is the negative threshold of the pedal change (pulling back the pedal).

[0076] when When the driver's braking intention is determined to be released, the regenerative braking torque is exited, and the motor torque gradually decreases from a negative value to 0, and the driving mode is entered again. The torque increases to a balance with the inherent resistance of the vehicle's driving process, so that the vehicle finally maintains the target speed.

[0077] in, , d1, d2 are constants. According to actual calibration experience, Calibrated to -3km / h, d1 calibrated to 5, d2 calibrated to -5; It is a dynamic quantity.

[0078] Based on actual driving experience, the fuzzy control rule language in this study is: the greater the vehicle speed, the slower the accelerator pedal change rate, and the higher the regenerative braking torque intervention threshold to ensure driving smoothness; the lower the vehicle speed, the faster the accelerator pedal change rate, and the lower the regenerative braking torque intervention threshold to ensure braking response speed. The control rules are shown in the following table: , As shown in the table above, vehicle speed (v r): reflects the vehicle's operating status and is divided into three levels: S (low speed), M (medium speed), and B (high speed); APR: accelerator pedal change rate (F fast change, M medium speed change, S slow change); α: regenerative braking torque intervention threshold (L low, M medium, H high). At high speed (v r =B), in order to avoid the shock caused by frequent energy recovery, the regenerative braking torque intervention threshold needs to be increased, corresponding to the output bias M / H in the table, that is, "the higher the speed, the higher the threshold." At the same time, the driver's sensitivity to pedal changes is reduced at high speeds, allowing the accelerator pedal change rate to be slowed down. At low speeds (v r =S), in order to ensure the response speed during emergency braking, the regenerative braking torque intervention threshold needs to be lowered. At low speeds, the driver's accelerator pedal will not be stepped on very deeply, and the accelerator pedal change will not be large, so the threshold is lowered to ensure that the driver can trigger the energy recovery mode normally. The output bias in the corresponding table is L / M, that is, low speed corresponds to a low threshold. At low speeds, the driver is more sensitive to the braking response and needs to speed up the accelerator pedal change rate. The embodiment of the present invention combines the driver's operating intention (accelerator pedal change rate) with the vehicle state (vehicle speed) through fuzzy control rules to dynamically adjust the intervention strategy of the regenerative braking system: at high speeds, it focuses on smoothness (high threshold), and at low speeds, it focuses on response speed (low threshold), to achieve coordinated optimization of comfort and safety.

[0079] According to the rule, a fuzzy controller is established in Matlab. The center of gravity method is used for defuzzification. Taking the standard driving style as an example, the output results are as follows: Figure 7 As shown in the accompanying 3D curve, it's clear that under a standard driving style, the fuzzy controller's output of the "vehicle speed difference threshold for regenerative braking torque intervention" exhibits significant regularity. When the actual vehicle speed is low (e.g., below 50 km / h), the system is relatively insensitive to the rate of change in accelerator pedal opening, and the output threshold (Z-axis value) generally fluctuates between -7 and -9. Inputs between -7 and -9 indicate a relatively easy entry point for regenerative braking, as throttle opening doesn't fluctuate significantly at low speeds. Therefore, lowering the entry threshold appropriately is more consistent with driving habits. At higher speeds, inputs between -12 and -13 increase the entry threshold, as throttle opening and closing are more frequent at higher speeds. Raising the entry threshold appropriately prevents inadvertent entry into regenerative mode, which could lead to torque fluctuations during aggressive high-speed driving and frequent switching in and out of regenerative mode.

[0080] In the area where the actual vehicle speed is close to 0, the output threshold is at a medium to low level. When the vehicle speed is lower than 5km / h, the speed of the drive motor is low, the actual recovery torque is unstable, and the vehicle is prone to shaking. Therefore, when the actual vehicle speed is lower than 5km / h, the energy recovery mode will be exited and no negative torque request will be made. The threshold value below 5km / h is also meaningless. The threshold value is lowered when the vehicle speed is greater than 25km / h (low speed range) so that the driver can easily enter the energy recovery mode at a lower speed by using a higher rate of change of releasing the accelerator pedal rather than a large actual release of the accelerator opening, which is more in line with real driving habits.

[0081] In the range where the accelerator pedal opening rate is close to 0 (i.e., during steady or constant driving), the output threshold is generally higher. This indicates that in steady driving conditions without a clear deceleration intention, the system tends to set the regenerative braking intervention threshold too late and too low, thereby reducing unnecessary braking force intervention, improving ride smoothness, and reducing mechanical component fatigue.

[0082] The control strategy of this fuzzy controller model can dynamically adjust the intervention strategy of the regenerative braking system according to the vehicle's real-time operating status (vehicle speed) and the driver's operating intention (accelerator pedal opening rate), thereby maximizing the energy recovery efficiency while ensuring driving safety and driving comfort.

[0083] In this embodiment of the present invention, the mode switch also includes: when regenerative braking torque is discontinued, the motor torque gradually decreases from a negative value to zero, then increases until it balances with the vehicle's inherent resistance to maintain the target speed. Inherent resistance balance refers to the situation where, when the motor torque drops to zero, the vehicle relies solely on rolling resistance to maintain the target speed. This dual-stage control strategy of "torque gradient attenuation + resistance balance compensation" optimizes the smoothness of the regenerative braking disengagement process, maintains vehicle speed stability, and securely engages the energy recovery system, addressing the impact, speed fluctuation, and control blind spots that can occur during traditional regenerative braking disengagement.

[0084] In this embodiment of the present invention, the RBCS state switching unit activates the regenerative braking emergency exit mode when the left rear axle slip ratio (RLS) or the right rear axle slip ratio (RRS) exceeds 4%, and fault counting is performed during activation. The RBCS state switching unit exits the regenerative braking emergency exit mode when both the left rear axle slip ratio (RLS) and the right rear axle slip ratio (RRS) are less than 1% and the fault count is ≤5. If the fault count exceeds 5, the emergency exit mode remains in effect. The slip ratio is linked to the mode during activation, and the slip ratio is linked to the fault count during exit, forming a closed-loop management system of "state monitoring-fault recording-tiered response." This differs from the simple "failure-locks" logic. This system not only rapidly responds to dynamic wheel slip risks but also allows for recovery from occasional faults. This allows the regenerative braking system to operate more flexibly and reliably under complex operating conditions, enhancing user confidence in the stability of the new energy vehicle's braking system.

[0085] In an embodiment of the present invention, in the regenerative braking torque increasing mode, the motor increases toward the target torque according to the regenerative braking torque MAP; in the regenerative braking torque maintaining mode, the motor maintains the current torque unchanged.

[0086] It should be noted that three RBCS states are set to match the driving intent determined above: 0 - Driving Mode, 1 - Regenerative Braking Torque Increase Mode, and 2 - Regenerative Braking Torque Maintain Mode. When the driving intent is determined to be driving, coasting, or constant speed driving, the motor is required to output positive torque, and the RBCS state is set to 0. When the driving intent is determined to be increasing braking intensity, the motor is required to reduce the driving torque to 0 and then gradually increase it toward the target regenerative braking torque, and the RBCS state is set to 1. When the driving intent is determined to be maintaining braking intensity, the regenerative braking torque output by the motor is required to remain unchanged, and the RBCS state is set to 2.

[0087] Considering the impact of wheel slip on regenerative braking, the RBCS state is set to 3 - Regenerative Braking Emergency Exit Mode when the vehicle is about to slip. In the target vehicle model of this embodiment, the rear axle is the drive axle. During regenerative braking, the rear wheels may slip on low-adhesion surfaces. The RBCS must enter Regenerative Braking Emergency Exit Mode before the rear wheels slip to avoid safety accidents.

[0088] It should be noted that there are four RBCS states, as follows: Figure 8 As shown, where α is the regenerative braking torque intervention threshold, Δ is the vehicle speed difference, δ is the accelerator pedal opening difference, and v r is the actual vehicle speed, RLS is the rear axle left wheel slip rate, and RRS is the rear axle right wheel slip rate, specifically including:

[0089] RBCS state 0 (driving mode): the driving intention is driving intention, coasting intention or constant speed driving intention, and the motor outputs positive torque; when the driving intention is determined to be driving, coasting or constant speed driving, it directly enters state 0. When Δ<α, RLS<1%, RRS<1%, and v r When the speed difference reaches the intervention threshold, the wheels are not slipping, and the driver has a deceleration requirement, the system begins to gradually increase the regenerative braking torque and enters state 1.

[0090] RBCS State 1 (Regenerative Braking Torque Growth Mode): In regenerative braking torque growth mode, under safe conditions (slip ratio <1%), the regenerative braking torque is gradually increased according to the trend of the accelerator pedal opening to achieve smooth energy recovery. State 1 has three branches:

[0091] Branch ①: RLS or RRS>4%, that is, slip occurs, then turn to state 3;

[0092] Branch ②: Actual vehicle speed v r Less than 5 or Δ>-3, that is, no intention to decelerate, the steering state is 0;

[0093] Branch ③: If the accelerator pedal opening difference δ is greater than 5 within a certain period, that is, the intention to decelerate is reduced by lightly pressing the accelerator or there is a possibility of acceleration, the vehicle enters the torque holding state 2 to ensure stable braking torque;

[0094] RBCS State 2 (Regenerative Braking Torque Hold Mode): When the driver releases the accelerator pedal and the deceleration intention weakens (the driver changes from releasing the accelerator pedal to slightly pressing it), the current regenerative braking torque is maintained to meet the driver's braking intention. This prevents a continuous increase in regenerative torque that could exceed the driver's braking expectations or cause physical discomfort. The system then waits in State 2 for subsequent judgment conditions to maintain the current deceleration (State 2), switch to acceleration (State 0), or continue to increase acceleration (State 1).

[0095] RBCS state 3 (regenerative braking emergency exit mode): When the rear axle left wheel slip ratio RLS> 4% or the right wheel slip ratio RRS> 4%, enter state 3. When RLS < 1% and RRS < 1%, or v r When <5, it returns to state 0. The wheel slip ratios RLS and RRS are provided by the vehicle's anti-lock braking system (ABS).

[0096] Furthermore, after RBCS state 3 is triggered, the regenerative braking torque quickly returns to zero and the fault count is +1. When the fault count reaches 5 times, it indicates that the current road conditions are not suitable for energy recovery mode. Considering driving safety, the vehicle will no longer enter state 0 mode. After the vehicle is parked and powered off or enters P gear, the current fault count is reset to 0 to ensure that the vehicle can enter energy recovery mode normally after entering a normal road section.

[0097] All state transitions are based on a slip ratio (RLS / RRS < 1%) to prevent wheel slippage from causing energy recovery failure or vehicle instability.

[0098] The present invention also provides an embodiment of an electric vehicle coasting energy recovery control system, comprising:

[0099] Data acquisition unit, used to obtain the current accelerator pedal opening APP t 、Previous moment accelerator pedal opening APP t-1 , target vehicle speed v t and actual vehicle speed v r ;

[0100] Calculation unit, used to calculate the vehicle speed difference Δ=v t -v r and pedal opening change d APP =APP t -APP t-1 ;

[0101] The driving intention recognition unit is used to identify the driving intention based on the vehicle speed difference Δ and the pedal opening change d APP , speed difference threshold for regenerative braking torque intervention , and the speed difference threshold for regenerative braking torque exit (fixed value = -3km / h), determine braking intention;

[0102] The RBCS state switching unit is used to control the RBCS state switching unit to switch between driving mode, regenerative braking torque increase mode, regenerative braking torque holding mode and regenerative braking emergency exit mode based on braking intention and rear axle wheel slip rate.

[0103] It should be noted that the information interaction, execution process, etc. between the above-mentioned units are based on the same concept as the method embodiment of the present application, and are a system corresponding to the above-mentioned electric vehicle coasting energy recovery control method. All implementation methods in the above-mentioned method embodiment are applicable to the embodiments of the system. Its specific functions and the technical effects brought about can be found in the method embodiment part, which will not be repeated here.

[0104] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for controlling coasting energy recovery of an electric vehicle, characterized in that: The following steps are involved: Get the current accelerator pedal opening APP t 、Previous moment accelerator pedal opening APP t-1 , target vehicle speed v t and actual vehicle speed v r ; Calculate the speed difference Δ=v t -v r and pedal opening change d APP =APP t -APP t-1 ; Based on the vehicle speed difference Δ and the pedal opening change d APP , speed difference threshold for regenerative braking torque intervention , and the speed difference threshold for regenerative braking torque exit , determine the braking intention; Based on the braking intention and the rear axle wheel slip rate, the RBCS state switching unit is controlled to switch between the driving mode, the regenerative braking torque increasing mode, the regenerative braking torque maintaining mode and the regenerative braking emergency exit mode.

2. The electric vehicle coasting energy recovery control method according to claim 1, characterized in that: The vehicle speed difference threshold α for regenerative braking torque intervention is calculated by a fuzzy control algorithm, specifically including: APR=d APP / d t ,α=fuzzy(APR,v r ); Among them, APP t is the current accelerator pedal opening, APP t-1 is the accelerator pedal opening at the previous moment; APR is the accelerator pedal change rate, d APP is the change in accelerator pedal opening; d t is the time difference between the two moments; fuzzy is the fuzzy control algorithm, the input of which is the accelerator pedal change rate APR and the actual vehicle speed v r , the output is the speed difference threshold α for regenerative braking intervention, where the APR membership function is designed differently according to the driving style.

3. The electric vehicle coasting energy recovery control method according to claim 2, characterized in that: Based on the vehicle speed difference Δ and the pedal opening change d APP , speed difference threshold for regenerative braking torque intervention , and the speed difference threshold for regenerative braking torque exit , determine the braking intention, including: when First time less than When α is less than α, it is determined that there is an intention to increase the braking intensity. The motor queries the target torque value T_target corresponding to the current vehicle speed vr from the pre-stored regenerative braking torque MAP and increases toward the target torque value T_target. The first time Δ is less than α refers to the moment when Δ changes from ≥α to <α. when and >d1, it is determined as the intention to maintain the braking intensity, and the motor maintains the current torque unchanged, where d1=5km / h is the positive threshold of the pedal change; when , < d2, it is determined as an intention to increase the braking intensity, and the motor continues to increase toward the target torque, where d2 = -5 km / h is the negative threshold of the pedal change; when When the driver's braking intention is determined to be released, the regenerative braking torque is withdrawn, the motor torque gradually decreases from a negative value to 0, and the driving mode is entered again; in, , d1, and d2 are constants.

4. The electric vehicle coasting energy recovery control method according to claim 3, characterized in that: Mode switching also includes: when the regenerative braking torque exits, the motor torque gradually drops from a negative value to 0, and then increases to balance with the vehicle's inherent resistance to maintain the target speed. The vehicle's inherent resistance balance means that when the motor torque drops to 0, the vehicle relies solely on rolling resistance to maintain the target speed.

5. The electric vehicle coasting energy recovery control method according to claim 2, characterized in that: The domain of the accelerator pedal change rate APR is [-50,0], and the fuzzy set is {F (fast), M (medium), S (slow)}; the actual vehicle speed v r The domain of discourse is [0,220] km / h, and the fuzzy set is {S (small), M (medium), B (large)}.

6. The electric vehicle coasting energy recovery control method according to claim 2, characterized in that: The vehicle speed difference threshold for the regenerative braking torque intervention The domain of discourse is set according to the driving style: Aggressive driving style: ∈[-10,-5] km / h; Standard driving style: ∈[-15,-5] km / h; Conservative driving style: ∈[-20,-5] km / h.

7. The electric vehicle coasting energy recovery control method according to claim 1, characterized in that: The activation condition of the regenerative braking emergency exit mode of the RBCS state switching unit is: the rear axle left wheel slip ratio RLS or the right wheel slip ratio RRS is greater than 4%, and fault counting is performed when activated.

8. The electric vehicle coasting energy recovery control method according to claim 7, characterized in that: The exit conditions of the regenerative braking emergency exit mode of the RBCS state switching unit are: the rear axle left wheel slip ratio RLS and the right wheel slip ratio RRS are both less than 1% and the fault count is ≤5 times; when the fault count is greater than 5 times, the emergency exit mode is maintained.

9. The electric vehicle coasting energy recovery control method according to claim 1, characterized in that: In the regenerative braking torque increase mode, the motor increases toward the target torque according to the regenerative braking torque MAP; in the regenerative braking torque hold mode, the motor maintains the current torque unchanged.

10. An electric vehicle coasting energy recovery control system, characterized in that: include: Data acquisition unit, used to obtain the current accelerator pedal opening APP t 、Previous moment accelerator pedal opening APP t-1 , target vehicle speed v t and actual vehicle speed v r ; Calculation unit, used to calculate the vehicle speed difference Δ=v t -v r and pedal opening change d APP =APP t -APP t-1 ; The driving intention recognition unit is used to identify the driving intention based on the vehicle speed difference Δ and the pedal opening change d APP , speed difference threshold for regenerative braking torque intervention , and the speed difference threshold for regenerative braking torque exit , determine the braking intention; The RBCS state switching unit is used to control the RBCS state switching unit to switch between driving mode, regenerative braking torque increase mode, regenerative braking torque holding mode and regenerative braking emergency exit mode based on braking intention and rear axle wheel slip rate.

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