Braking force distribution control method and system for low-speed composite braking system

Abstract

The invention relates to a braking force distribution control method and system for a low-speed composite braking system, and the method comprises the steps: obtaining a vehicle speed threshold value and a control reset threshold value in a starting state of a holding stage based on the maximum electric braking torque of a motor system and the expected braking force of current ACC cruise; judging whether a brake distribution switch is turned on or not; if yes, state machine state conversion is executed based on the current vehicle speed, the vehicle speed threshold value in the keeping stage starting state, the control reset threshold value and the state machine state, a transition mode is entered, and in the transition mode, the electric braking parameters are gradually reduced; otherwise, the state position of the state machine is initialized, the compound braking system is controlled to be switched into pure hydraulic braking, and electric braking is closed. When the braking distribution switch is in the on state, the electric braking parameters are gradually reduced in a gradual mode instead of sudden change switching, and therefore braking force fluctuation caused by capacity boundary change of the electric braking system in a low-speed area is effectively eliminated.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of braking systems, in particular to a low-speed composite braking system braking force distribution control method and system. BACKGROUND

[0002] In the existing braking system of electric vehicles and hybrid electric vehicles, electric braking energy recovery technology is widely used to improve energy utilization efficiency. However, this technology has significant defects in low-speed driving conditions: on the one hand, when the vehicle is driving at low speed, the electric braking energy recovery efficiency is low, resulting in insufficient energy recovery utilization rate; on the other hand, when the vehicle is braking at low speed, the system is easily affected by environmental factors (such as uneven road surface, braking request fluctuation or slight change of vehicle speed), and enters the zero-crossing condition (i.e. vehicle speed zero-crossing, torque zero-crossing state). In this state, the electric braking system needs to switch from working mode to electric driving mode, but this switching process will cause obvious power interruption and jerk, seriously affecting driving comfort and braking smoothness. In the prior art, there is no effective solution to optimize the braking mode switching under low-speed zero-crossing condition, resulting in frequent jerk problems when the vehicle is braking at low speed, and the balance between electric braking efficiency and driving experience cannot be considered. SUMMARY

[0003] The present application provides a low-speed composite braking system braking force distribution control method and system, which can solve the problem of jerk caused by switching from electric braking to electric driving mode under low-speed zero-crossing condition in the prior art.

[0004] In a first aspect, the embodiments of the present application provide a low-speed composite braking system braking force distribution control method, which comprises: obtaining a vehicle speed threshold and a control reset threshold in the starting state of the maintaining stage based on the maximum electric braking torque of the motor system and the expected braking force of the current ACC cruise; determining whether the braking distribution switch is on; if yes, performing state machine state conversion based on the current vehicle speed, the vehicle speed threshold and the control reset threshold in the starting state of the maintaining stage, and the state machine state, and entering a transition mode, wherein in the transition mode, the electric braking parameter is gradually reduced; otherwise, initializing the state machine state bit, and controlling the composite braking system to switch to pure hydraulic braking and electric braking to be closed.

[0005] In combination with the first aspect, in an implementation manner, the vehicle speed threshold and the control reset threshold in the starting state of the maintaining stage are obtained based on the maximum electric braking torque of the motor system and the expected braking force of the current ACC cruise, and specifically comprising: obtaining a low-speed composite braking system distribution control threshold based on the maximum electric braking torque of the motor system and the expected braking force of the current ACC cruise; obtaining a vehicle speed threshold in the keep stage starting state based on the low-speed composite braking system distribution control threshold and the braking deceleration; obtaining a control reset threshold based on the low-speed composite braking system distribution control threshold, the calibration parameter and the low-speed hydraulic system pre-charge vehicle speed.

[0006] In combination with the first aspect, in an implementation, the transition mode includes a pre-charge mode, a keep mode and an exit mode, wherein: In the pre-charge mode, the electric braking parameter is gradually reduced from an initial value, and the pre-charge mode includes: when the vehicle speed is less than or equal to the vehicle speed threshold in the keep stage starting state or the keep stage starting flag bit is set, switching to the keep mode; In the keep mode, the electric braking parameter remains constant, and the keep mode includes: when the low-speed transition mode in the keep mode is entered and the exit mode starting flag bit is not set, or the exit mode starting flag bit is set, switching to the exit mode; The exit mode includes: when the electric braking exit initial value is greater than the electric braking exit vehicle speed threshold, gradually reducing the electric braking braking force through a polynomial algorithm.

[0007] In combination with the first aspect, in an implementation, the pre-charge mode further includes: activating the pre-charge module when the vehicle speed is greater than or equal to the low-speed composite braking system distribution control threshold, less than or equal to the sum of the low-speed composite braking system distribution control threshold and the low-speed hydraulic system pre-charge vehicle speed, and the slope end starting flag bit is not set and the pre-charge starting flag bit is set; initializing the state machine state bit when the vehicle speed is greater than the control reset threshold and the braking distribution switch is not set.

[0008] In combination with the first aspect, in an implementation, the condition for entering the low-speed transition mode includes: the vehicle speed is less than the low-speed composite braking system distribution control threshold, and the slope end starting flag bit is not set; After entering the low-speed transition mode, the method further includes: locking the electric braking exit initial value as the current value of the low-speed braking distribution control threshold, and setting the electric braking force reduction amount cumulative value to 0; obtaining a single-cycle electric braking reduction fixed amount based on the initial electric braking force of the electric braking distribution control strategy.

[0009] In combination with the first aspect, in an implementation, the keep mode further includes: initializing the state machine state bit when the vehicle speed is greater than the low-speed composite braking system distribution control threshold and the braking activation flag bit is not set; and returning to the pre-charge mode when the vehicle speed is greater than or equal to the vehicle speed threshold in the keep stage starting state and the keep stage starting flag bit is not set. In the maintaining mode, the maximum output braking force of the electric braking force and the starting electric braking force of the electric braking distribution control strategy are the minimum value of the maximum electric braking torque of the motor system and the expected braking force of the current ACC cruise.

[0010] In combination with the first aspect, in an implementation, the exiting mode further includes: When the electric braking exiting initial value is less than or equal to the electric braking exiting vehicle speed threshold, the control switches the compound braking system to pure hydraulic braking, and the maximum output braking force of the electric braking force is 0.

[0011] In combination with the first aspect, in an implementation, when the electric braking exiting initial value is greater than the electric braking exiting vehicle speed threshold, the electric braking braking force is gradually reduced by a polynomial algorithm, specifically including: Based on the maximum output braking force of the electric braking force at the previous moment, the single-period electric braking reduction change amount in the exiting mode is obtained. Based on the single-period electric braking reduction change amount in the exiting mode, the maximum value of the single-period electric braking reduction fixed amount in the maintaining mode, and the starting electric braking force of the electric braking distribution control strategy, the remaining electric braking proportion is obtained. Based on the remaining electric braking proportion and the polynomial algorithm, the electric braking coefficient is obtained. Based on the electric braking coefficient and the starting electric braking force of the electric braking distribution control strategy, the maximum electric braking force at the current moment is obtained. After obtaining the maximum electric braking force at the current moment, the method further includes the step of judging whether hydraulic braking supplement is needed: Based on the maximum electric braking force at the current moment and the wheel radius, the electric braking torque is obtained. Based on the minimum value of the electric braking torque and the safety threshold, the actual electric braking torque is determined. When the electric braking torque is greater than the safety threshold, the hydraulic braking supplement mechanism is started. When the electric braking torque is less than the safety threshold, the hydraulic braking supplement mechanism is not started.

[0012] In combination with the first aspect, in an implementation, the condition for opening the braking distribution switch includes that there is a requested braking torque output, the electric braking function is opened, and it is not in the AEB, parking, or other non-ACC cruise state. When the state bit of the state machine is initialized, the maintaining stage start flag bit is not set, the slope end start flag bit is not set, and the pre-charge start flag bit is not set.

[0013] In a second aspect, the embodiments of the present application provide a low-speed composite braking system, which comprises: a first module and a second module, the first module is configured to obtain a vehicle speed threshold in a keep stage starting state and a control reset threshold based on a maximum electric braking torque of a motor system and a desired braking force of a current ACC cruise; the second module is configured to determine whether a brake distribution switch is opened; if yes, perform state machine state conversion based on a current vehicle speed, the vehicle speed threshold in the keep stage starting state, the control reset threshold and a state machine state, and enter a transition mode, wherein in the transition mode, electric braking parameters are gradually reduced; otherwise, initialize a state machine state bit, and control the composite braking system to switch to pure hydraulic braking, and electric braking is closed.

[0014] The technical scheme provided by the embodiments of the present application has the following beneficial effects: The embodiments of the present application provide a low-speed composite braking system braking force distribution control method and system, which dynamically obtains a vehicle speed threshold in a keep stage starting state and a control reset threshold based on a maximum electric braking torque of a motor system and a desired braking force of a current ACC cruise, so that the system can adapt to changes in real-time braking demand and avoid braking timing mismatch caused by fixed thresholds; in an opened state of a brake distribution switch, the system triggers a state machine to convert into a transition mode according to a current vehicle speed and the dynamically generated threshold, in which mode electric braking parameters are gradually reduced in a progressive manner instead of being switched suddenly, thereby effectively eliminating braking force fluctuations caused by changes in the ability boundary of the electric braking system in the low-speed area; when the brake distribution switch is closed, the system actively initializes a state machine state bit and switches to a pure hydraulic braking mode, ensuring that the electric braking system completely exits and the state is cleared, providing an initial condition without residual for the next braking request; this control logic based on dynamic threshold generation and parameter progressive adjustment matches braking demand and system ability boundary, so that the electric braking exit process and the hydraulic braking takeover realize seamless connection, avoiding instantaneous torque mutation in braking switching and improving the smoothness and driving comfort of the braking process. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 It is a flowchart of the low-speed composite braking system braking force distribution control method of the present application; Figure 2 It is a specific flowchart of step 101 of the low-speed composite braking system braking force distribution control method of the present application. DETAILED DESCRIPTION

[0016] In order to make the person skilled in the art better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0017] The present application provides a low-speed composite braking system braking force distribution control method and system, which can solve the problem of jerk feeling caused by the switching of electric braking to electric driving mode in the low-speed braking zero-crossing working condition in the prior art.

[0018] In order to make the purpose, technical solutions and advantages of the present application more clear, the embodiments of the present application will be described in further detail in conjunction with the drawings.

[0019] In a first aspect, the embodiments of the present application provide a low-speed composite braking system braking force distribution control method, which comprises: 101: obtaining a vehicle speed threshold in the starting state of the maintaining stage and a control reset threshold based on the maximum electric braking torque of the motor system and the expected braking force of the current ACC cruise; 102: judging whether the brake distribution switch is opened; 103: if yes, performing state machine state conversion based on the current vehicle speed, the vehicle speed threshold in the starting state of the maintaining stage, the control reset threshold and the state machine state, and entering a transition mode, wherein in the transition mode, the electric braking parameter is gradually reduced; 104: otherwise, initializing the state machine state bit, and controlling the composite braking system to switch to pure hydraulic braking and the electric braking to be closed.

[0020] In the present application, the vehicle speed threshold in the starting state of the maintaining stage and the control reset threshold are dynamically obtained based on the maximum electric braking torque of the motor system and the expected braking force of the current ACC cruise, so that the system can adapt to the change of real-time braking demand and avoid the mismatch of braking opportunity caused by fixed threshold; in the opened state of the brake distribution switch, the system triggers the state machine to enter the transition mode according to the current vehicle speed and the dynamically generated threshold, and in this mode, the electric braking parameter is gradually reduced in a progressive manner instead of sudden switching, thereby effectively eliminating the braking force fluctuation caused by the change of ability boundary of the electric braking system in the low-speed area. When the brake distribution switch is closed, the system initiates the state machine state bit and switches to the pure hydraulic braking mode, ensuring that the electric braking system is completely withdrawn and the state is cleared, providing an initial condition without residual for the next brake request; This control logic based on dynamic threshold generation and parameter progressive adjustment matches the braking demand and system capability boundary, making the electric braking exit process and hydraulic braking takeover seamless, avoiding instantaneous torque mutation in brake switching, and improving the smoothness and driving comfort of the braking process.

[0021] On the basis of the above-mentioned embodiments, in this embodiment, based on the maximum electric braking torque of the motor system and the expected braking force of the current ACC cruise, the vehicle speed threshold in the hold phase start state and the control reset threshold are obtained, specifically including steps 1011-1013: In the parameter extraction and initialization phase, first, based on the maximum electric braking torque of the motor system, the absolute value FbRegenMax and the expected braking force FbTagetMax of the current ACC cruise are obtained, and the low-speed composite braking system distribution control threshold V_start is obtained; Then, based on the low-speed composite braking system distribution control threshold V_start and the brake deceleration , the vehicle speed threshold V_Hold in the hold phase start state (HoldPhaseStarted state) is obtained; Then, based on the low-speed composite braking system distribution control threshold V_start, the calibration parameter C and the low-speed hydraulic system pre-charge vehicle speed V_Prefill, the control reset threshold V_reset is obtained.

[0022] Specifically, in the parameter extraction and initialization phase, the system first directly collects the maximum electric braking torque of the system and takes its absolute value as FbRegenMax, which represents the upper limit of the electric braking capability of the motor system under the current working condition; At the same time, the absolute value of the expected braking force of the current ACC cruise is taken as FbTagetMax, which reflects the dynamic request of the intelligent driving system to the total braking force. Based on this, the system calculates the low-speed composite braking system distribution control threshold V_start, which is determined by the smaller value of FbRegenMax and FbTagetMax divided by the calibrated slope (the maximum reduction value of the moment torque per unit time). Specifically, , wherein, is the electric braking exit vehicle speed threshold; is the brake deceleration; is the smaller value of FbRegenMax and FbTagetMax divided by the calibrated slope, which ensures that the system starts the transition phase in advance when the vehicle speed approaches V_start, avoiding sudden exit due to insufficient electric braking capability, thereby reserving sufficient response time for subsequent brake mode switching.

[0023] The low-speed hydraulic system pre-charging vehicle speed V_Prefill is dynamically generated by multiplying the absolute value of the acceleration (the current absolute value of the acceleration) by a calibrated quantity (with respect to time), and the core is that when the vehicle is suddenly braked (high acceleration), V_Prefill is automatically increased to activate the hydraulic system in advance, significantly shorten the response delay, and improve the low-speed braking smoothness.

[0024] The vehicle speed threshold V_Hold in the hold phase start state (HoldPhaseStarted state) is calculated by the low-speed composite brake system distribution control threshold and the brake deceleration, and is further expanded to In the high brake deceleration working condition, V_Hold is correspondingly reduced to ensure that the electric brake can be earlier exited and seamlessly switched to the hydraulic brake.

[0025] The control reset threshold V_reset is determined by the low-speed composite brake system distribution control threshold V_start, the calibrated parameter C, and the low-speed hydraulic system pre-charging vehicle speed V_Prefill, The calibrated parameter C is used to adjust the system switching sensitivity, and when the value of C increases, V_reset is more conservative, effectively inhibiting frequent mode switching caused by vehicle speed fluctuations, thereby maintaining the stability of the brake control in complex low-speed scenarios.

[0026] The coordinated design of these thresholds systematically solves the two core problems of insufficient electric brake capacity and hydraulic response lag through the constraint mechanism of FbRegenMax, the dynamic pre-charging characteristics of V_Prefill, and the sensitivity adjustment of the C parameter, and provides a safe and smooth control basis for the subsequent brake distribution strategy.

[0027] It needs to be pointed out in advance that in the present application, the conditions for opening the braking distribution switch BrakingActive_B include: there is a request for brake torque output, the electric brake function is opened, and it is not in the AEB, parking, and other non-ACC cruise states; When initializing the state bit of the state machine, the hold phase start flag bit is not set HoldPhaseStarted_B=0, the end ramp start flag bit is not set EndRampStarted_B=0, and the pre-charging start flag bit is not set PrefillStart_B=0.

[0028] In the implementation of the brake distribution logic, the opening condition of the brake distribution switch BrakingActive_B is defined as: there is a brake torque request, the electric brake function is in the active state, and the system is not currently in the AEB (automatic emergency brake), parking and other non-ACC cruise modes. This design ensures that the brake distribution is only enabled in the normal braking scenario of ACC cruise, avoiding response delay or strategy conflict caused by the intervention of electric brake in high-priority brake states such as AEB, thereby ensuring driving safety and system coordination. For example, in the AEB working condition, the system preferentially uses hydraulic brake to ensure maximum braking force, and the electric brake function is temporarily disabled to prevent the brake distribution logic from interfering with the emergency braking strategy.

[0029] At the same time, the state machine initialization phase explicitly sets the hold phase start flag HoldPhaseStarted_B, the end ramp start flag EndRampStarted_B and the prefill start flag PrefillStart_B to 0, indicating that the system is in the initial state after startup or reset, and all phases are not activated. This initialization method effectively avoids the risk of false triggering caused by residual states, such as avoiding false entry into the hold phase due to historical state residues when the vehicle restarts, providing a reliable starting point for subsequent brake mode switching, ensuring that low-speed compound brake control can be dynamically adjusted based on real-time vehicle speed, achieving smooth transition of electric brake and hydraulic brake, and completely eliminating the jerk feeling.

[0030] In addition, it should be noted that when the brake distribution switch BrakingActive_B is 0, the system automatically performs the state machine initialization process, resets the hold phase start flag HoldPhaseStarted_B, the end ramp start flag EndRampStarted_B and the prefill start flag PrefillStart_B to 0, and forcibly closes the electric brake function. At this time, the compound brake system immediately switches to a pure hydraulic control mode, and the hydraulic brake system independently bears all brake force output.

[0031] This design is crucial in non-ACC cruise scenarios (such as AEB automatic emergency braking or parking state): when the system detects that the vehicle is in AEB mode (requires instantaneous maximum braking force) or parking state (braking demand conflicts with dynamic cruise logic), BrakingActive_B is automatically closed; in the parking scene, pure hydraulic control ensures the direct correspondence between brake pedal force and braking effect, eliminating the virtual position of the brake pedal that may be caused by electric brake.

[0032] On the basis of the above embodiment, in the present embodiment, the transition mode includes a prefill mode, a hold mode and an exit mode, wherein: When the braking distribution switch BrakingActive_B is set from 0 to 1, the system state machine immediately enters the pass through state, which serves as an initial stage of braking distribution, the core of which lies in safely and smoothly establishing the electric braking output reference. In the pass through state, the electric braking force maximum output FbRegenMax and the electric braking distribution control strategy starting electric braking force FbRegenMaxStart are both synchronously set to the minimum value of FbRegenMax and FbTagetMax (i.e. min(FbRegenMax, FbTagetMax)). When the vehicle enters a low-speed working condition, the system can smoothly start the step-by-step release of electric braking capability based on this reference value (EndRamp mode), rather than directly outputting full power, effectively inhibiting the jerkiness of the brake pedal.

[0033] In the implementation of the pass through mode, it is ensured that the electric braking parameters are gradually reduced from the initial value to achieve a smooth transition, wherein the gradual reduction of the electric braking parameters refers to the gradual reduction of the electric braking braking force output value. Specifically, the pass through mode includes: when the vehicle speed v is less than or equal to the vehicle speed threshold V_Hold in the hold phase started state (HoldPhaseStarted state) or the hold phase started flag bit is set (HoldPhaseStarted_B is 1), switching to the hold mode, that is, entering the HoldPhaseStarted state bit; this condition effectively avoids the braking jerk caused by the sudden shortage of electric braking capability when the vehicle speed approaches V_Hold - for example, when the vehicle decelerates to V_Hold, the system actively triggers the hold phase to reserve a buffer time for the hydraulic brake to take over, rather than relying on the natural decline of the vehicle speed, thereby significantly improving the driving smoothness of low-speed braking.

[0034] In addition, the activation mechanism of the pre-charge mode is defined as follows: when the vehicle speed v is greater than or equal to the low-speed composite braking system distribution control threshold V_start and less than or equal to the sum of the low-speed composite braking system distribution control threshold and the low-speed hydraulic system pre-charge vehicle speed (V_start+V_Prefill), that is, (V_start)≤vehicle speed v≤(V_start+V_Prefill), and the ramp end start flag EndRampStarted_B is not set to 1 and the pre-charge start flag PrefillStart_B is set to 1, the pre-charge module is activated. The condition chain covers the transition interval of the electric brake exit through the dynamic range of V_start+V_Prefill, and the constraint that EndRampStarted_B is not set prevents the pre-charge module from being repeatedly triggered during the ramp phase, avoiding parameter oscillation and ensuring that the electric brake parameters are smoothly attenuated according to the preset slope. After the pre-charge module is activated, the VLC outputs a lower brake torque to the hydraulic system until the ACC request acceleration is positive, and the module is exited.

[0035] In addition, when the vehicle speed v is greater than the control reset threshold V_reset and the braking distribution switch is not set (BrakingActive_B is 0), that is, vehicle speed v>(V_reset) and BrakingActive_B is 0, the system automatically initializes the state machine state bits: HoldPhaseStarted_B=0, EndRampStarted_B=0, PrefillStart_B=0. This mechanism completely clears the residual state when the braking request ends or the vehicle speed rises, prevents the system from entering the holding or pre-charge phase prematurely due to historical state misjudgment, and thus realizes seamless connection between electric braking and hydraulic braking in low-speed working conditions, completely eliminates the jerk problem caused by mode switching, and improves the robustness of the system to vehicle speed fluctuations.

[0036] When HoldPhaseStarted_B is set to 1 (i.e. the system enters the HoldPhaseStarted state), the brake distribution strategy enters the stable holding phase, the function of which is to maintain the dynamic balance of the electric brake output, ensuring the smoothness and safety of the low-speed cruise braking process. In this state, the maximum electric brake force FbRegenMaxF and the starting electric brake force FbRegenMaxStart of the electric brake distribution control strategy are both maintained at the minimum value of FbRegenMax and FbTagetMax (i.e. min(FbRegenMax, FbTagetMax)). This stable output strategy of the holding phase not only eliminates the pedal jitter caused by the mismatch between the electric brake capacity and the request value, but also provides a deterministic reference for the smooth transition of subsequent low-speed composite braking (such as the gradual transition from HoldPhase to EndRamp), significantly improving the braking comfort and system reliability in complex low-speed working conditions.

[0037] In the holding mode (Hold mode), the electric brake parameters are kept constant to ensure the stability and driving smoothness of the braking process. The holding mode includes: when entering the low-speed transition mode (Hold1 mode) in the holding mode (Hold mode) and the exit mode start flag bit is not set (EndRampStarted_B is not 1), or the exit mode start flag bit is set (EndRampStarted_B is 1), switch to the exit mode (EndRamp mode); this design effectively avoids the response delay when the electric brake capacity is insufficient or the external conditions change suddenly (such as the vehicle speed rising), for example, when the vehicle speed rapidly decreases below V_start to trigger the low-speed transition, the system can immediately respond to the exit flag to prevent braking mode switching conflicts.

[0038] The conditions for entering the low-speed transition mode include: the vehicle speed v is less than the low-speed composite brake system distribution control threshold V_start, and the ramp end start flag bit is not set (EndRampStarted_B is not 1); this condition chain avoids repeated entry into the transition in the ramp decay phase through the constraint of EndRampStarted_B, ensuring that the system only starts smooth transition when the electric brake capacity is about to be exhausted, thereby eliminating the braking fluctuations caused by parameter oscillation.

[0039] After entering the low-speed transition mode, the system performs an operation to ensure the accuracy of the transition, and the method further comprises: first, locking the initial value V_startFreeze of the electric brake out as the current value of the low-speed brake distribution control threshold V_start, as the reference point of the subsequent electric brake reduction amount, to avoid calculation deviation caused by dynamic changes of V_start, and setting the electric brake force reduction amount cumulative value Factor_FbStepSum to 0 to provide a zero starting point for the single-cycle electric brake attenuation, and to ensure that the reduction amount is strictly accumulated according to the calibrated slope; Finally, based on the starting electric brake force FbRegenMaxStart of the electric brake distribution control strategy, a single-cycle electric brake reduction fixed amount Const_Dec_FbStep is obtained: in this step, the electric brake reduction fixed step Const_Dec_Step is first determined: ; in the formula, is the system period, and is set to 0.01s.

[0040] Single-cycle electric brake reduction fixed amount Const_Dec_FbStep: ; When entering the Hold1 mode and EndRampStarted_B is not 1, or when EndRampStarted_B is 1, the EndRamp mode is entered.

[0041] In the boundary processing of the Hold mode, the system also monitors the following conditions to improve robustness, specifically, the Hold mode further comprises: when the vehicle speed v is greater than the low-speed compound brake system distribution control threshold V_reset, and the brake activation flag bit is not set (BrakingActive_B is 0), the state machine state bit is initialized (HoldPhaseStarted_B=0, EndRampStarted_B=0, PrefillStart_B=0), this mechanism prevents false triggering caused by residual states after the brake request ends or the vehicle speed rises, for example, after the ACC cruise exits, the system is quickly reset to avoid false maintenance of the Hold phase; when the vehicle speed v is greater than or equal to the vehicle speed threshold V_Hold in the Hold phase start state, and the Hold phase start flag bit is not set (HoldPhaseStarted_B is not 1), the prefill mode is returned, that is, the pass through state bit is returned; this design is suitable for vehicle speed rising scenarios (such as vehicle acceleration), to ensure that the system can timely re-enter the prefill phase to prepare for the next brake switching, rather than being stranded in the low-speed transition strategy, thereby maintaining the adaptive ability of the brake mode in dynamic working conditions.

[0042] In the holding mode, the maximum output braking force FbRegenMaxF and the starting electric braking force FbRegenMaxStart of the electric braking distribution control strategy are both the minimum value of the maximum electric braking torque FbRegenMax of the motor system and the expected braking force FbTagetMax of the current ACC cruise. This not only matches the upper limit of the braking force demand of the ACC cruise, but also avoids system overload caused by over-limit of the electric braking capacity, provides a unified input reference for the entire low-speed composite braking control chain (V_start→V_Hold→V_reset), and finally realizes seamless connection of electric braking and hydraulic braking, and completely eliminates the low-speed jerk problem.

[0043] In the exit mode (EndRamp mode), the system realizes smooth decay of the electric braking braking force through a polynomial algorithm, ensuring that the braking process is free of jerk.

[0044] The exit mode (EndRamp mode) includes: when the electric braking exit initial value V_startFreeze is greater than the electric braking exit vehicle speed threshold , the ramp2 mode is entered, and the electric braking braking force is gradually reduced through a polynomial algorithm; and when the electric braking exit initial value V_startFreeze is less than or equal to the electric braking exit vehicle speed threshold , it is judged that the vehicle speed is too low, at which time the electric braking recovery efficiency is low, the composite braking system is switched to pure hydraulic braking, and the maximum output braking force FbRegenMaxF of the electric braking force is 0, avoiding brake deficiency or system overload caused by invalid energy recovery.

[0045] In the scenario where the electric braking exit initial value V_startFreeze is greater than the electric braking exit vehicle speed threshold , the execution logic of the exit mode is further refined: That is, when the electric braking exit initial value is greater than the electric braking exit vehicle speed threshold, the electric braking braking force is gradually reduced through a polynomial algorithm, which specifically includes: First, based on the maximum output braking force of the electric braking force at the previous moment (i.e., the current electric braking actual output value), the single-period electric braking reduction change Var_Dec_FbStep in the exit mode is obtained: ; In the formula, is the at the previous moment.

[0046] Then based on the maximum value of the single-cycle electric braking reduction amount Var_Dec_FbStep in the exit mode and the single-cycle electric braking reduction fixed amount Const_Dec_FbStep in the holding mode, the value is continuously accumulated with the cycle and divided by the starting electric braking force FbRegenMaxStart of the electric braking distribution control strategy to obtain the reduced electric braking proportion, and 1 minus the value obtains the remaining electric braking proportion Factor_Step.

[0047] And based on the remaining electric braking proportion and the polynomial algorithm, the electric braking coefficient is obtained: that is, the remaining electric braking proportion is put into the polynomial algorithm: ; In the formula is the cubic equation coefficient, is the quadratic equation coefficient. The characteristics of the slope of the polynomial in the [0, 1] interval from slow to fast to slow control the smooth exit of the electric braking, and the electric braking coefficient Factor_FbRegenMax that decreases with time is obtained; Finally, based on the electric braking coefficient Factor_FbRegenMax and the starting electric braking force FbRegenMaxStart of the electric braking distribution control strategy, the current time electric braking maximum braking force FbRegenMaxF is obtained: the electric braking coefficient Factor_FbRegenMax multiplied by FbRegenMaxStart obtains the current time electric braking maximum braking force FbRegenMaxF.

[0048] After obtaining the current time electric braking maximum braking force FbRegenMaxF, the system automatically executes the hydraulic braking supplement judgment, that is, the method further comprises the step of judging whether the hydraulic braking supplement is needed: Firstly, based on the current time electric braking maximum braking force FbRegenMaxF and the wheel radius, the electric braking torque TrqRegenMaxF is obtained; then based on the minimum value of the electric braking torque TrqRegenMaxF and the safety threshold (Trq_0.3g), the actual electric braking torque is determined; when the electric braking torque is greater than the safety threshold, the hydraulic braking supplement mechanism is started; when the electric braking torque is less than the safety threshold, the hydraulic braking supplement mechanism is not started.

[0049] In this step, after the output FbRegenMaxF is obtained, it is multiplied by the wheel radius to obtain the electric braking torque TrqRegenMaxF; then, TrqRegenMaxF is compared with the maximum electric braking torque corresponding to 0.3g (Trq_0.3g) and the smaller value is taken to ensure that the electric braking torque is always within the safety boundary. If the value of TrqRegenMaxF is greater than the braking torque of 0.3g, the actual electric braking torque is limited to Trq_0.3g, and the remaining braking force is obtained by subtracting the actual electric braking force FbRegenMaxF from the total requested braking force FbTagetMax, i.e., the remaining braking force = FbTagetMax-FbRegenMaxF, and this part of the demand is supplemented by the hydraulic braking system, and the corresponding hydraulic braking torque is (FbTagetMax-FbRegenMaxF) x wheel radius. This mechanism not only eliminates the risk of electric braking overload (because TrqRegenMaxF is always ≤ Trq_0.3g), but also ensures the accuracy of brake distribution through force level calculation, avoids the confusion of torque and force units, and thus realizes smooth and safe electric-hydraulic collaborative control in low-speed composite braking.

[0050] In summary, the present application effectively solves the problem of motor jerk in the zero-crossing working condition of low-speed braking by systematically designing the low-speed composite braking control logic, while ensuring the continuity and accuracy of real vehicle braking torque control. Based on the maximum electric braking torque (FbRegenMax) of the motor system and the expected braking force (FbTagetMax) of the ACC cruise, a threshold chain is dynamically constructed: the low-speed composite braking system distribution control threshold (V_start) is used as the starting point for the electric braking exit, the holding stage starting speed threshold (V_Hold) is used to trigger the transition stage in advance, and the control reset threshold (V_reset) is used to reset the state machine. The system starts the pre-charging mode when the vehicle speed approaches V_start, so that the electric braking force is smoothly reduced; when the vehicle speed drops to V_Hold, the system enters the holding mode to maintain the constant output of the electric braking to avoid sudden changes; finally, in the exit mode, the system uses a polynomial algorithm to realize the nonlinear decay of the electric braking force, ensuring the continuous and stepless output of the braking torque. This mechanism not only completely eliminates the jerk, but also ensures the safety boundary of braking through real-time torque monitoring, ensuring that the electric braking efficiency and driving smoothness are optimized without affecting the accuracy of real vehicle braking torque control.

[0051] In a second aspect, a low-speed composite braking system includes a first module configured to obtain a vehicle speed threshold in a keep stage start state and a control reset threshold based on a maximum electric braking torque of a motor system and a desired braking force of a current ACC cruise; and a second module configured to determine whether a brake distribution switch is on. If the brake distribution switch is on, a state machine state is switched based on a current vehicle speed, the vehicle speed threshold in the keep stage start state, the control reset threshold, and a state machine state, and a transition mode is entered, in which an electric braking parameter is gradually reduced. If the brake distribution switch is not on, a state machine state bit is initialized, and the composite braking system is switched to pure hydraulic braking, and the electric braking is turned off.

[0052] In the present application, the vehicle speed threshold in the keep stage start state and the control reset threshold are dynamically obtained based on the maximum electric braking torque of the motor system and the desired braking force of the current ACC cruise, so that the system can adapt to changes in real-time braking demand and avoid mismatch of braking timing caused by fixed thresholds. In the on state of the brake distribution switch, the system triggers the state machine to switch to the transition mode according to the current vehicle speed and the dynamically generated threshold, and the electric braking parameter is gradually reduced in the transition mode instead of being suddenly switched, thereby effectively eliminating the braking force fluctuation caused by the change of the electric braking system capability boundary in the low-speed area. When the brake distribution switch is off, the system actively initializes the state machine state bit and switches to the pure hydraulic braking mode, so as to ensure that the electric braking system completely exits and the state is cleared, and to provide an initial condition without residual for the next braking request. The control logic based on dynamic threshold generation and gradual parameter adjustment matches the braking demand and the system capability boundary, so that the electric braking exit process and the hydraulic braking takeover are seamlessly connected, the instantaneous torque mutation in the braking switching is avoided, and the smoothness and driving comfort of the braking process are improved.

[0053] The functions of the modules in the low-speed composite braking system braking force distribution control system correspond to the steps in the low-speed composite braking system braking force distribution control method, and the functions and implementation processes are not repeated here.

[0054] In a third aspect, the embodiments of the present application provide a low-speed composite braking system braking force distribution control device. The low-speed composite braking system braking force distribution control device can be a personal computer (PC), a notebook computer, a server, or other devices with data processing functions.

[0055] In the embodiments of the present application, the low-speed composite braking system braking force distribution control device can include a processor, a memory, a communication interface, and a communication bus.

[0056] The communication bus can be any type, which is used to interconnect the processor, the memory, and the communication interface.

[0057] The communication interface includes an input / output (I / O) interface, a physical interface, and a logical interface, and the like, which are used to realize the interconnection of devices inside the low-speed composite braking system brake force distribution control device, and the interconnection of the low-speed composite braking system brake force distribution control device and other devices (such as other computing devices or user devices). The physical interface can be an Ethernet interface, a fiber interface, an ATM interface, and the like; and the user device can be a display (Display), a keyboard (Keyboard), and the like.

[0058] The memory can be various types of storage media, such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), flash memory, optical storage, hard disk, programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), and the like.

[0059] The processor can be a general-purpose processor, which can invoke the low-speed composite braking system brake force distribution control program stored in the memory and execute the low-speed composite braking system brake force distribution control method provided by the embodiments of the present application. For example, the general-purpose processor can be a central processing unit (CPU). The method executed by the low-speed composite braking system brake force distribution control program when invoked can refer to each embodiment of the low-speed composite braking system brake force distribution control method of the present application, which will not be described here.

[0060] In a fourth aspect, the embodiments of the present application further provide a computer readable storage medium.

[0061] The computer readable storage medium of the present application stores a low-speed composite braking system brake force distribution control program, wherein the low-speed composite braking system brake force distribution control program is executed by the processor to realize the steps of the low-speed composite braking system brake force distribution control method as described above.

[0062] The method realized by the low-speed composite braking system brake force distribution control program when executed can refer to each embodiment of the low-speed composite braking system brake force distribution control method of the present application, which will not be described here.

[0063] It should be noted that the above-mentioned sequence numbers of the embodiments of the present application are only for description, and do not represent the advantages and disadvantages of the embodiments.

[0064] The terms "include", "has" and "has" in the description and claims of the present application and the above-mentioned drawings are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units is not limited to the listed steps or units, but can optionally include steps or units not listed, or can optionally include other steps or units inherent to these processes, methods, products or devices. The terms "first", "second" and "third" and the like descriptions are used to distinguish different objects, etc., and do not represent the order or limit the "first", "second" and "third" to be different types.

[0065] In the description of the embodiments of the present application, "exemplary", "for example" or "for example" is used to represent an example, illustration or description. Any embodiment or design scheme described as "exemplary", "for example" or "for example" in the embodiments of the present application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. In fact, the words "exemplary", "for example" or "for example" are intended to present the relevant concept in a specific way.

[0066] In the description of the embodiments of the present application, unless otherwise specified, " / " means or, for example, A / B can mean A or B; "and / or" in the text only describes the relationship between the associated objects, which means that there can be three relationships, for example, A and / or B, which means that there are three cases of A alone, A and B together, and B alone. In addition, in the description of the embodiments of the present application, "multiple" means two or more than two.

[0067] In some of the processes described in the embodiments of the present application, a plurality of operations or steps are included in a specific order, but it should be understood that these operations or steps can be executed or executed in parallel without the order in which they appear in the embodiments of the present application. The serial number of the operation is only used to distinguish each different operation, and the serial number itself does not represent any execution order. In addition, these processes can include more or fewer operations, and these operations or steps can be executed in sequence or in parallel, and these operations or steps can be combined.

[0068] Those skilled in the art can clearly understand the above-mentioned embodiment method can be realized by means of software and the necessary general hardware platform, of course, can also be realized by hardware, but in many cases, the former is a better embodiment. Based on such understanding, the technical solutions of the present application can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) as described above, and includes a plurality of instructions for making a terminal device execute the method described in each embodiment of the present application.

[0069] The above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation using the content of the specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A brake force distribution control method for a low-speed compound brake system, characterized by, It comprises: Based on the maximum electric braking torque of the motor system and the expected braking force of the current ACC cruise, the vehicle speed threshold in the keep stage starting state and the control reset threshold are obtained; Determine whether the brake distribution switch is on; If so, based on the current vehicle speed, the vehicle speed threshold in the keep stage starting state, the control reset threshold and the state machine state, the state machine state transition is executed to enter the transition mode, wherein in the transition mode, the electric braking parameter is gradually reduced; Otherwise, initialize the state machine state bit, and control the composite brake system to switch to pure hydraulic braking, and the electric braking is closed.

2. The brake force distribution control method for a low-speed compound brake system according to claim 1, characterized by, Based on the maximum electric braking torque of the motor system and the expected braking force of the current ACC cruise, the vehicle speed threshold in the keep stage starting state and the control reset threshold are obtained, specifically comprising: Based on the maximum electric braking torque of the motor system and the expected braking force of the current ACC cruise, the low-speed composite brake system distribution control threshold is obtained; Based on the low-speed composite brake system distribution control threshold and the braking deceleration, the vehicle speed threshold in the keep stage starting state is obtained; Based on the low-speed composite brake system distribution control threshold, the calibration parameter and the low-speed hydraulic system pre-charge vehicle speed, the control reset threshold is obtained.

3. The brake force distribution control method for a low-speed compound brake system according to claim 1, characterized by, The transition mode comprises a pre-charge mode, a keep mode and an exit mode, wherein: In the pre-charge mode, the electric braking parameter is gradually reduced from the initial value, and the pre-charge mode comprises: when the vehicle speed is less than or equal to the vehicle speed threshold in the keep stage starting state or the keep stage starting flag bit is set, switching to the keep mode; In the keep mode, the electric braking parameter remains constant, and the keep mode comprises: when entering the low-speed transition mode in the keep mode and the exit mode starting flag bit is not set, or the exit mode starting flag bit is set, switching to the exit mode; The exit mode comprises: when the electric braking exit initial value is greater than the electric braking exit vehicle speed threshold, gradually reducing the electric braking braking force by a polynomial algorithm.

4. The brake force distribution control method for a low-speed compound brake system according to claim 3, characterized by, The pre-charge mode further comprises: When the vehicle speed is greater than or equal to the low-speed composite brake system distribution control threshold, less than or equal to the sum of the low-speed composite brake system distribution control threshold and the low-speed hydraulic system pre-charge vehicle speed, and the slope end starting flag bit is not set, the pre-charge starting flag bit is set, the pre-charge module is activated; When the vehicle speed is greater than the control reset threshold and the brake distribution switch is not set, initialize the state machine state bit.

5. The brake force distribution control method for a low-speed compound brake system according to claim 3, characterized by, The conditions for entering the low-speed transition mode include: the vehicle speed is less than the low-speed composite brake system distribution control threshold, and the slope end starting flag bit is not set; After entering the low-speed transition mode, the method further comprises: Lock the electric braking exit initial value as the current value of the low-speed brake distribution control threshold, and set the electric braking force reduction amount cumulative value to 0; Based on the starting electric braking force of the electric braking distribution control strategy, the single-cycle electric braking reduction fixed amount is obtained.

6. The brake force distribution control method for a low-speed compound brake system according to claim 3, characterized by, The keep mode further comprises: when the vehicle speed is greater than the low-speed composite brake system distribution control threshold, and the brake activation flag bit is not set, initialize the state machine state bit; when the vehicle speed is greater than or equal to the vehicle speed threshold in the keep stage starting state, and the keep stage starting flag bit is not set, return to the pre-charge mode; In the maintaining mode, the maximum output braking force of the electric braking force and the starting electric braking force of the electric braking distribution control strategy are the minimum value of the maximum electric braking torque of the motor system and the expected braking force of the current ACC cruise.

7. The brake force distribution control method for a low-speed compound brake system according to claim 3, characterized by, The exiting mode further comprises: When the initial value of the electric braking exit is less than or equal to the electric braking exit vehicle speed threshold, the control switches the composite braking system to pure hydraulic braking, and the maximum output braking force of the electric braking force is 0.

8. The brake force distribution control method for a low-speed compound brake system according to claim 3, characterized by, When the initial value of the electric braking exit is greater than the electric braking exit vehicle speed threshold, the electric braking force is gradually reduced by a polynomial algorithm, specifically comprising: Based on the maximum output braking force of the electric braking force at the previous moment, the single-period electric braking reduction change amount in the exiting mode is obtained; Based on the maximum value of the single-period electric braking reduction fixed amount in the maintaining mode and the single-period electric braking reduction change amount in the exiting mode, and the starting electric braking force of the electric braking distribution control strategy, the remaining electric braking proportion is obtained; Based on the remaining electric braking proportion and the polynomial algorithm, the electric braking coefficient is obtained; Based on the electric braking coefficient and the starting electric braking force of the electric braking distribution control strategy, the maximum braking force of the electric braking at the current moment is obtained; After obtaining the maximum braking force of the electric braking at the current moment, the method further comprises the step of judging whether hydraulic braking supplement is needed: Based on the maximum braking force of the electric braking at the current moment and the wheel radius, the electric braking torque is obtained; Based on the minimum value of the electric braking torque and the safety threshold, the actual electric braking torque is determined; When the electric braking torque is greater than the safety threshold, the hydraulic braking supplement mechanism is started; When the electric braking torque is less than the safety threshold, the hydraulic braking supplement mechanism is not started.

9. The braking force distribution control method of the low-speed composite braking system according to claim 1, characterized in that: The condition for opening the braking distribution switch comprises: there is a requested braking torque output, the electric braking function is opened, and it is not in the AEB, parking or other non-ACC cruise state; When initializing the state bit of the state machine, the maintaining stage starting flag bit is not set, the slope end starting flag bit is not set, and the pre-charge starting flag bit is not set.

10. A low speed composite braking system characterized by, It comprises: The first module is configured to obtain a vehicle speed threshold and a control reset threshold in the maintaining stage starting state based on the maximum electric braking torque of the motor system and the expected braking force of the current ACC cruise; The second module is configured to judge whether the braking distribution switch is opened; if yes, based on the current vehicle speed, the vehicle speed threshold and the control reset threshold in the maintaining stage starting state, and the state machine state, the state machine state conversion is performed, and the transition mode is entered, wherein in the transition mode, the electric braking parameter is gradually reduced; Otherwise, the state bit of the state machine is initialized, and the composite braking system is switched to pure hydraulic braking, and the electric braking is closed.

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