Method and system for controlling vehicle braking

Abstract

The invention provides a method and system for controlling braking of a vehicle. When the isolator is disconnected and the auxiliary drive wheel is separated from the drive system, the vehicle braking is performed by regenerative braking of the main drive wheel motor during braking. Subsequently, the isolator is connected according to the vehicle stability state, and then braking is performed simultaneously on the auxiliary drive wheel and the main drive wheel.

Description

Technical Field

[0001] The present invention relates to a method and system for controlling vehicle braking, and more specifically, to a method and system for controlling vehicle braking in a vehicle equipped with an isolator for reducing drive wheel side resistance loss and a drive unit with regenerative control function. Background Technology

[0002] In recent years, four-wheel drive (4WD) electric vehicles have been developed. 4WD electric vehicles are equipped with independent drive units for the front and rear wheels. The drive units in a four-wheel drive electric vehicle can be driven individually or together depending on driving conditions. All drive units for the front and rear wheels can be battery-powered motors. Specifically, a four-wheel drive electric vehicle is an electric vehicle equipped with independent drive motors for the front and rear wheels, i.e., front-wheel drive motors and rear-wheel drive motors.

[0003] Typical four-wheel drive electric vehicles use a two-wheel drive (2WD) mode (where torque is supplied to one axle of the two front wheels or the two rear wheels) as the basic drive mode, and switch to a four-wheel drive (4WD) mode (where torque is supplied to two axles of the two front wheels and the two rear wheels) when the driving force is insufficient. Figure 1A and Figure 1B These are schematic diagrams of existing technology, each showing a four-wheel drive (4WD) system equipped with a front-wheel drive motor, a rear-wheel drive motor, and an isolator. Figure 2 This is a schematic diagram of the prior art, which is shown in more detail in... Figure 1A and Figure 1B The diagram shows the configuration and arrangement of the power transmission system on the auxiliary drive wheel side and the state of the drive system components in the four-wheel drive electric vehicle shown.

[0004] Figure 1A and Figure 1B The diagram shows a four-wheel drive electric vehicle equipped with a front-wheel drive motor (“front wheel motor”) 2 for driving the front wheels 1 and a rear-wheel drive motor (“rear wheel motor”) 8 for driving the rear wheels 7. As described above, the four-wheel drive electric vehicle can operate in either four-wheel drive (4WD) mode or two-wheel drive (2WD) mode. When operating in two-wheel drive mode, the unused drive motor and drive wheels are predetermined.

[0005] In a four-wheel drive electric vehicle equipped with a separate front-wheel drive motor 2 and a rear-wheel drive motor 8, if the drive wheel not used during two-wheel drive mode is defined as an auxiliary drive wheel, then when the auxiliary drive wheel is not used during driving (e.g., when driving in 2WD mode), reverse driving force is transmitted from the auxiliary drive wheel 1 to the reducer 3, which may result in drag loss. Therefore, when driving in two-wheel drive mode, it is necessary to prevent the transmission of reverse driving force from the auxiliary drive wheel 1 to prevent drag loss.

[0006] Therefore, isolator 6 can be installed on drive shaft 5 of auxiliary drive wheel 1. In a vehicle equipped with isolator 6, isolator 6 is connected to drive shaft 5 when driving in four-wheel drive mode to enable power transmission, and disconnected (e.g., disengaged) from drive shaft 5 when driving in two-wheel drive mode to deactivate power transmission.

[0007] Figure 1A and Figure 1B Electric vehicles equipped with a front wheel isolator 6 are shown. In the illustrated vehicles, the front wheels are auxiliary drive wheels. The front wheel isolator 6, which connects or disconnects the power transmission, is located between the front wheel 1, which is the auxiliary drive wheel, and the front wheel drive system components, more specifically, between the front wheel 1 and the differential 4.

[0008] When the isolator 6 is engaged in a vehicle equipped with a front wheel isolator 6, the vehicle can drive in four-wheel drive mode. When the front wheel isolator 6 is disengaged, the vehicle can drive in rear-wheel drive mode. Therefore, the isolator 6 selectively engages or disengages, thereby enabling or disengaging the power transmission on the drive axle 5. In this case, the isolator 6 connects or disconnects the auxiliary drive wheel 1 and the power transmission drive system components (e.g., reducer 5). Here, the drive system components refer to the components that generate or transmit driving force for the vehicle; the isolator 6 can be implemented as a claw clutch.

[0009] Figure 1A This shows the state in which the front wheel isolator (claw clutch) 6 is disconnected when driving in two-wheel drive (rear-wheel drive) mode. Figure 1B This shows the state in which the front wheel isolator (claw clutch) 6 is engaged when driving in four-wheel drive mode. According to... Figure 2 This illustrates the connection and arrangement of drive system components (e.g., drive motor 2, reducer 3 and differential 4, isolator (claw clutch) 6) and wheels 1. Here, wheels 1 are auxiliary drive wheels. Figure 1A and Figure 1B The middle wheel can be the front wheel of a vehicle.

[0010] In an electric vehicle, the drive motor 2 operates at high speed while the vehicle is in motion. A reducer 3 connected to the drive motor 2 reduces its speed to a suitable level for vehicle operation. The rotational force generated by the reducer 3 is transmitted to the drive shaft 5 via a differential 4, thereby driving the vehicle. On the other hand, optimal control technology for regenerative braking in four-wheel-drive electric vehicles equipped with independent front-wheel drive motors, independent rear-wheel drive motors, and isolators is necessary; however, the optimal control technology for regenerative braking (which reflects the characteristics of four-wheel-drive electric vehicles equipped with isolators) is currently unclear.

[0011] For four-wheel drive electric vehicles equipped with independent front-wheel drive motors, independent rear-wheel drive motors, and isolators, a regenerative mode can also be implemented. In regenerative mode, when the vehicle brakes (e.g., decelerates) or coasts using inertial forces, the kinetic energy of the vehicle is recovered through each drive motor, and the generated energy is used to charge the battery. In regenerative mode, when the vehicle's kinetic energy is transferred to the drive motors through the drive wheels, the drive motors act as generators, thus charging the vehicle's battery with energy generated by the inverter.

[0012] However, in four-wheel drive electric vehicles, when the isolator disconnects during vehicle acceleration and coasting, it can prevent damage from auxiliary drive wheels (such as...) Figure 1A and Figure 1B The drag loss caused by the front wheels (in the example) helps improve vehicle fuel efficiency. Furthermore, when the driver engages the brake pedal to apply brakes in this situation, regenerative braking via the auxiliary drive wheels is impossible. In other words, when the isolator disconnects while the vehicle is coasting, drag loss is prevented, thus increasing the vehicle's travel distance. However, when the brake pedal is engaged while the isolator is disconnected, only the main drive wheels (e.g., the front wheels) are utilized. Figure 1A and Figure 1B In the example shown, regenerative braking can be performed on the rear wheels, but not on the auxiliary drive wheels. Therefore, the total amount of regenerative braking in the vehicle is reduced, thus decreasing fuel efficiency. Summary of the Invention

[0013] The purpose of this invention is to provide a method for controlling vehicle braking, wherein the vehicle is equipped with an independent drive unit configured to drive the front wheels, an independent drive unit configured to drive the rear wheels, and an isolator. This method can ensure vehicle stability and braking performance during braking, and increase regenerative braking, thereby helping to improve vehicle fuel efficiency.

[0014] According to one aspect of the invention, a method for controlling vehicle braking is provided. The vehicle includes independent drive units configured to drive the front wheels, independent drive units configured to drive the rear wheels, and an isolator mounted in a drive axle and configured to engage and disengage power transmission. The control method may include: determining a current vehicle stability index based on information fragments collected within the vehicle; engaging or disengaging the isolator according to the determined vehicle stability index; and performing regenerative braking on the front or rear wheels of the vehicle, or on all front and rear wheels, based on the control state of the isolator. In this method, the vehicle may be a four-wheel drive electric vehicle with front and rear wheel motors as drive units and an isolator mounted on its front drive axle.

[0015] According to another aspect of the invention, a method for controlling vehicle braking may include: determining whether a brake pedal is operated when the vehicle is traveling in a state where an isolator is disconnected to disengage the power transmission connection; in response to determining that the brake pedal is operated, determining a current vehicle stability index based on information fragments collected within the vehicle, and comparing the determined vehicle stability index with a preset reference value; when the determined vehicle stability index is less than the preset reference value, comparing the braking torque required by the driver with a feasible torque for regenerative braking of the rear wheel motor corresponding to the current vehicle speed; and when the braking torque required by the driver is equal to or less than the feasible torque for regenerative braking of the rear wheel motor, performing regenerative braking of the rear wheel motor and achieving the braking torque required by the driver by generating only the rear wheel regenerative braking torque.

[0016] In addition, based on the vehicle deceleration, rear wheel slip, and the distribution ratio of front and rear braking forces, the vehicle stability index is calculated using Equation 1:

[0017] Vehicle stability index = vehicle deceleration × rear wheel slip × front wheel braking force to rear wheel braking force distribution ratio

[0018] Among them, vehicle deceleration is the current actual vehicle deceleration measured by sensors, and the distribution ratio between front wheel braking force and rear wheel braking force is the value of the ratio of front wheel braking force to rear wheel braking force.

[0019] The feasible torque for regenerative braking of the rear wheel motor can be based on the current vehicle speed and can be determined according to a curve representing the feasible torque for regenerative braking of the rear wheel motor. The method may further include: engaging the isolator when a determined vehicle stability index is equal to or greater than the reference value; and, while the isolator is engaged, simultaneously applying front and rear wheel braking to achieve the braking torque required by the driver.

[0020] Control of front and rear wheel braking may include: comparing the braking torque required by the driver with the regenerative braking torque feasible for the front and rear wheel motors corresponding to the current vehicle speed; when the braking torque required by the driver is equal to or less than the regenerative braking torque feasible for the front and rear wheel motors, performing regenerative braking for the front and rear wheel motors, and achieving the braking torque required by the driver by generating only the regenerative braking torque for the front and rear wheels.

[0021] Furthermore, the feasible regenerative braking torque for both the front and rear wheel motors can be the sum of the feasible regenerative braking torques for the front and rear wheel motors. The feasible regenerative braking torque for the front wheel motor can be determined based on the current vehicle speed and a curve representing the feasible regenerative braking torque for the front wheel motor. Similarly, the feasible regenerative braking torque for the rear wheel motor can be determined based on the current vehicle speed and a curve representing the feasible regenerative braking torque for the rear wheel motor.

[0022] The control of the front and rear wheel braking may further include: when the braking torque required by the driver is greater than the regenerative braking torque feasible by the front and rear wheel motors, comparing the hydraulic braking torque of the front and rear wheels with a predetermined combined limit torque of regenerative braking and hydraulic braking; and in response to determining that the hydraulic braking torque of the front and rear wheels is less than the combined limit torque of regenerative braking and hydraulic braking, performing regenerative braking of the front and rear wheel motors and hydraulic braking of the front and rear wheels, and achieving the braking torque required by the driver, wherein the hydraulic braking torque of the front and rear wheels can be obtained by subtracting the regenerative braking torque feasible by the front and rear wheel motors from the braking torque required by the driver.

[0023] Furthermore, the control of front wheel braking and rear wheel braking may include: when the hydraulic braking torque of the front wheels and rear wheels is equal to or greater than the combined limit torque of regenerative braking and hydraulic braking, limiting and maintaining the regenerative braking torque of the front wheels to the combined limit torque of regenerative braking and hydraulic braking, while simultaneously achieving the braking torque required by the driver by executing regenerative braking of the front wheel motor and rear wheel motor and hydraulic braking of the front wheels and rear wheels.

[0024] In this method, when the driver's required braking torque is achieved by generating only the rear wheel regenerative braking torque, the isolator can be engaged when the vehicle stability index increases with the increase of brake pedal operation and reaches the reference value. When the front wheel regenerative braking torque is limited and maintained as a combined limit torque of regenerative and hydraulic braking, the rear wheel regenerative braking torque can be maintained at the rear wheel regenerative braking torque at the point when the vehicle stability index reaches the reference value.

[0025] Furthermore, when the driver's required braking torque is achieved by generating only the rear wheel regenerative braking torque, the isolator can be engaged when the vehicle stability index increases with the increase in brake pedal operation and reaches the reference value. When performing regenerative braking of the front and rear wheel motors, as well as hydraulic braking of the front and rear wheels, to achieve the driver's required braking torque, the rear wheel regenerative braking torque can be maintained at the level at which the vehicle stability index reaches the reference value.

[0026] When the isolator is engaged and, based on information fragments collected within the vehicle, a state where regenerative braking into the motors is feasible is determined, the braking torque required by the driver can be compared with the feasible regenerative braking torques of the front and rear wheel motors. When the isolator is engaged and, based on information fragments collected within the vehicle, a state where regenerative braking into the motors is not feasible is determined, hydraulic braking control can be executed to achieve the braking torque required by the driver by generating hydraulic braking torque only for the front and rear wheels.

[0027] When the driver's required braking torque is achieved by generating only the rear wheel regenerative braking torque, the isolator can be engaged when the vehicle stability index increases with the increase of brake pedal operation and reaches the reference value. When the driver's required braking torque is achieved by generating only the front and rear wheel regenerative braking torques, the rear wheel regenerative braking torque can be maintained at the rear wheel regenerative braking torque at the time point when the vehicle stability index reaches the reference value. The method may further include: when the driver's required braking torque is greater than the feasible torque of the rear wheel motor's regenerative braking, performing regenerative braking of the rear wheel motor and hydraulic braking of the front and rear wheels, and achieving the driver's required braking torque.

[0028] Using the vehicle braking control method according to the invention, in a 2WD state where the isolator is disconnected and the auxiliary drive wheels are thus separated from the drive system, vehicle braking can be performed using only regenerative braking from the main drive wheel motor during braking. Subsequently, the isolator can be reconnected based on the vehicle's stability status, and a switch to a 4WD state can be performed. Braking can then be performed simultaneously on both the auxiliary and main drive wheels. Therefore, this method ensures vehicle stability and braking performance, and can contribute to improved vehicle fuel efficiency by maximizing the amount of regenerative braking. Attached Figure Description

[0029] The above and other features of the invention will now be described in detail with reference to certain exemplary embodiments of the invention shown in the accompanying drawings, which are given by way of illustration only below, and thus the invention is not limiting, wherein:

[0030] Figure 1A and Figure 1BThese are schematic diagrams showing a vehicle equipped with a front-wheel drive motor, a rear-wheel drive motor, and an isolator according to the prior art;

[0031] Figure 2 It is to show more specifically the prior art Figure 1A and Figure 1B The diagram shows the structure of the powertrain on the auxiliary drive wheel side and the arrangement of the drive system components in the vehicle.

[0032] Figure 3 This is a diagram illustrating the structure of an isolator in a vehicle according to an exemplary embodiment of the present invention;

[0033] Figure 4 This is a block diagram illustrating the structure of a system for performing braking control in a vehicle according to an exemplary embodiment of the present invention;

[0034] Figure 5 This is a flowchart illustrating a braking control process according to an exemplary embodiment of the present invention;

[0035] Figure 6 It is a graph showing the curves representing the TN (torque-speed) characteristics of a motor according to an exemplary embodiment of the present invention, wherein the TN characteristics define the feasible torque values ​​for regenerative braking of the motor according to the vehicle speed;

[0036] Figure 7 This is a schematic diagram illustrating when the vehicle stability index reaches reference value A, the isolator is connected, and where front wheel regenerative braking and rear wheel regenerative braking are performed simultaneously according to an exemplary embodiment of the present invention.

[0037] Figure 8 This is a diagram illustrating the segmented braking torque states during the braking control process according to an exemplary embodiment of the present invention;

[0038] Figures 9 to 12 These are schematic diagrams that clearly illustrate the changes in vehicle deceleration and the state of each braking control phase when a driver operates the brake pedal according to an exemplary embodiment of the present invention; and

[0039] Figure 13 This is a reference diagram illustrating the behavior of a vehicle when the rear wheels lock up due to excessive braking force, according to an exemplary embodiment of the present invention. Detailed Implementation

[0040] It should be understood that the term "vehicle" or "of a vehicle" or other similar terms as used herein generally include motor vehicles, such as passenger vehicles including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, vessels including various boats and ships, aircraft, etc., and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., vehicles derived from non-gasoline energy sources). As mentioned herein, a hybrid vehicle is a vehicle with two or more power sources, such as both gasoline power and electric power.

[0041] Although the exemplary embodiments are described as utilizing multiple units to perform the exemplary processes, it should be understood that the exemplary processes can also be performed by one or more modules. Furthermore, it should be understood that the term controller / control unit refers to a hardware device including a memory and a processor. The memory is configured to store modules, and the processor is specifically configured to execute said modules to perform one or more processes further described below.

[0042] Furthermore, the control logic of the present invention can be implemented with respect to a non-volatile computer-readable medium containing executable program instructions that are executed by a processor, controller / control unit, etc. Examples of computer-readable media include (but are not limited to) ROM, RAM, optical disc (CD)-ROM, magnetic tape, floppy disk, flash drive, smart card, and optical data storage device. The computer-readable recording medium can also be distributed across a network-connected computer system, such that the computer-readable medium is stored and executed in a distributed manner, for example, via a telematics server or a controller area network (CAN).

[0043] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “an,” and “this” as used herein are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should be further understood that when the terms “comprises” and / or “comprising” are used in this specification, they specify the presence of the stated features, values, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or groups thereof. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0044] Unless specifically stated or obvious from the context, as used herein, the term "approximately" is understood to mean within the normal tolerance range in the field, such as within 2 standard deviations of the mean. "Approximately" can be understood to mean within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless it is clear from the context otherwise, all numerical values ​​provided herein are modified by the term "approximately".

[0045] The invention will now be described in detail with reference to the accompanying drawings in a manner that allows those skilled in the art to practice it without excessive experimentation. However, the invention is not limited to the exemplary embodiments described herein, and may be implemented in other exemplary embodiments.

[0046] Unless otherwise stated, when the phrase "includes a component" is used throughout the specification, the expression means "further includes any other component" rather than "excludes any other component".

[0047] This invention relates to a method for controlling vehicle braking. Specifically, this invention relates to a method for controlling vehicle braking, the vehicle including a separate drive unit configured to drive the front wheels, a separate drive unit configured to drive the rear wheels, and a connector mounted in the drive shaft for connecting and disconnecting power transmission.

[0048] More specifically, according to the present invention, a method for controlling the braking of a vehicle equipped with an independent drive unit (the drive unit being configured to have regenerative braking function) is provided, as well as a control method for controlling the braking of a four-wheel drive electric vehicle equipped with an isolator and a front-wheel drive motor and a rear-wheel drive motor, which is used to reduce the resistance loss on the auxiliary drive wheel side.

[0049] Furthermore, according to the present invention, a method for controlling the braking of a four-wheel drive electric vehicle equipped with a motor drive unit for the front wheels, a motor drive unit for the rear wheels, and an isolator is provided. This method ensures vehicle stability and braking performance during braking and increases the amount of regenerative braking, thereby contributing to improved vehicle fuel efficiency. According to the present invention, when the isolator is disconnected and the auxiliary drive wheels are thus separated from the drive system, vehicle braking can only be performed regeneratively by the main drive wheel motor during braking. Subsequently, the isolator can be connected according to the vehicle's stable state, and then regenerative braking can be performed simultaneously on the auxiliary drive wheels and the main drive wheels.

[0050] In the following description of exemplary embodiments, the vehicle to which the controlled braking method according to an exemplary embodiment of the present invention is applied is a well-known four-wheel drive electric vehicle, each vehicle being equipped with a front-wheel drive motor, a rear-wheel drive motor, and an isolator. Reference will now be made to the prior art. Figure 1A , Figure 1B and Figure 2 This describes the structure of the e-4WD system and powertrain of a four-wheel drive electric vehicle.

[0051] For reference only. Figure 3 This is a schematic diagram showing the structure of the isolator. The isolator 6 can be mounted on the drive shaft 5 between the reducer 3 and the wheel (e.g., the auxiliary drive wheel) 1, more precisely, between the differential 4 and the wheel 1. The isolator 6 may include components that allow for the connection and disconnection of power transmission between the input and output shafts. The input shaft of the isolator 6 can be connected to the output shaft of the differential 4, and the output shaft of the isolator 6 can be connected to the auxiliary drive shaft 1 side.

[0052] In the following description, the main drive wheel and auxiliary drive wheel are defined as described above, and the purpose, location, operation, function, and role of the isolator are the same as those in the well-known four-wheel drive electric vehicles described above. During four-wheel drive, the rotational force of the drive motor 2 can be transmitted to the input shaft of the isolator 6 through the reducer 3 and the differential 4. With the isolator 6 engaged, the output shaft of the isolator 6 can transmit the rotational force transmitted to its input shaft to the drive wheel 1 (e.g., in the example below, the front wheel as the auxiliary drive wheel).

[0053] Without driving the auxiliary drive wheel motor (e.g., Figure 1A , Figure 1B During two-wheel drive (e.g., the front wheel motor in the drive system), reverse driving force is transmitted from the auxiliary drive wheel 1 to the reducer 3, resulting in drag loss. To prevent this, the isolator 6 can be disconnected to prevent power transmission between the drive system components (e.g., reducer 3 and differential 4) and the auxiliary drive wheel 1. Furthermore, in the auxiliary drive wheel motor (e.g., Figure 1A , Figure 1B During regenerative braking of the front wheel motor (in the middle), isolator 6 can be connected to assist the drive wheels (e.g., Figure 1A , Figure 1B The rotational force of the front wheel can be transmitted to the motor.

[0054] According to the present invention, such as Figure 3 As shown, the isolator 6 can have the same structure as a well-known claw clutch. (Refer to...) Figure 3The isolator 6, which is implemented as a claw clutch, may include: a shaft gear 11 disposed on the input shaft to rotate with the input shaft, a hub 12 disposed on the output shaft to rotate with the output shaft, and a sleeve 13 combined with the hub 12 to slide in the axial direction and rotate with the hub 12.

[0055] The shaft gear 11 can be a splined gear with teeth formed longitudinally along the axial direction on its circumferential surface. The hub 12 can also be a splined gear with teeth formed longitudinally along the axial direction on its circumferential surface. Specifically, the sleeve 13 can be combined with the shaft gear 11 and the hub 12, which each have teeth formed longitudinally along the axial direction on their circumferential surfaces, and these teeth are respectively arranged inwards. The sleeve 13 can be mounted to rotate continuously and engage with the hub 12. The sleeve 13 can slide slidably from the hub 12 in the axial direction, and therefore can selectively engage or disengage with the shaft gear 11 based on the direction and position of the sleeve 13's movement.

[0056] In addition, isolator 6 may include a drive mechanism 14, such as Figure 3 As shown, the drive mechanism 14 can be configured to slide the sleeve 13 from the hub 12 in the axial direction to engage or disengage with the shaft gear 11. The structure of the drive mechanism 14 is well known to those skilled in the art and is therefore not shown in detail in the drawings. However, by way of example, the drive mechanism 14 can be configured to convert the rotational force of the disconnect motor 15 into a radial moving force via a screw (not shown) and a reciprocating element into which the screw is screwed (e.g., engaged), to move the shift fork 16 back and forth, thereby causing the sleeve 13, combined with the shift fork 16, to slide in the axial direction.

[0057] On the other hand, in four-wheel drive electric vehicles, regenerative braking can also be performed during braking. In regenerative braking, the vehicle's kinetic energy is recovered as electrical energy through the generation of electricity by the drive motor, and the generated electrical energy is used to charge the battery. In addition to regenerative braking, hydraulic braking (e.g., friction braking) can be performed by hydraulic braking devices (e.g., friction braking devices) installed on each wheel. The regenerative braking of the drive motor and the hydraulic braking of the hydraulic braking devices can be performed individually or together on the front and rear wheels.

[0058] In electric vehicles employing regenerative braking and hydraulic braking, the required deceleration D and the driver's desired braking torque (e.g., target braking force or total braking force) are first determined based on a braking signal corresponding to the driver's braking operation (e.g., driver's brake input or brake pedal engagement), such as a brake pedal sensor (BPS) signal based on brake pedal operation. Subsequently, the regenerative braking torque and hydraulic braking torque (e.g., friction braking torque) can be allocated, and the regenerative braking torque and hydraulic braking torque are summed to obtain the driver's desired braking torque. Furthermore, when the regenerative braking torque (e.g., regenerative braking force) and hydraulic braking torque (e.g., hydraulic braking force) are determined through allocation, motor regenerative braking control and hydraulic braking control can be executed to generate the braking torque produced by the allocation.

[0059] According to the present invention, regenerative braking as described above can be performed when specific regenerative braking conditions are met and regenerative braking of the motor is feasible. Furthermore, the distribution of regenerative braking torque and hydraulic braking torque can be performed, and both regenerative braking and hydraulic braking can be performed on all front and rear wheels. Therefore, the distribution of braking torque between the front wheels and the rear wheels can also be performed.

[0060] Furthermore, the driving and braking control of a four-wheel drive electric vehicle can be performed under the coordinated control of multiple controllers. These controllers may include: a vehicle control unit (VCU), which is an advanced controller configured to perform overall vehicle operation; a brake control unit (BCU), configured to perform vehicle braking control and operate the hydraulic braking system; a motor control unit (MCU), configured to perform motor operation; and a battery management system (BMS), configured to collect information about the battery status and manage the battery.

[0061] The controller can be configured to exchange information for vehicle braking and perform cooperative control via a vehicle network (e.g., a controller area network). This is also true when performing braking control according to the invention. For example, the vehicle controller can be configured to determine and output a regenerative braking torque command, and perform regenerative operation of the drive motor using an inverter based on the regenerative braking torque command received from the vehicle controller. Furthermore, the vehicle controller can be configured to perform operations to connect and disconnect isolator 6.

[0062] In other words, when the vehicle controller outputs a control signal to connect or disconnect the isolator 6, the drive mechanism (specifically, the isolator motor 15, which acts as an actuator in the drive mechanism) can be operated based on the control signal. According to the control of the operation of the isolator motor 15, the sleeve 13 can slide axially between the shaft gear 11 and the hub 12, thereby connecting or disconnecting the isolator 6.

[0063] The method of controlling braking according to the present invention will now be described in more detail. Figure 4 This is a block diagram illustrating the structure of a system for performing braking control within a vehicle according to the present invention. In the following description, the front-wheel drive motor 2 and the rear-wheel drive motor 8 are referred to as the "front wheel motor" and the "rear wheel motor," respectively. The plurality of controllers involved in the braking control process according to the present invention are collectively referred to as controller 120, such as... Figure 4 As shown. Controller 120 may include a vehicle controller, a brake controller, a motor controller, and a battery controller (configured to provide information about the battery's state of charge (SOC), etc.) configured to perform brake coordination control.

[0064] also, Figure 5 This is a flowchart illustrating the braking control process according to the present invention. Firstly, in a four-wheel drive (4WD) electric vehicle equipped with a front wheel motor 2, a rear wheel motor 8, and a front wheel isolator 6, when the driver releases the accelerator pedal (when the accelerator pedal is disengaged or released), the vehicle control unit (VCU) (which in...) Figure 4 The figure in the diagram (labeled "120") can be configured to disconnect (disconnect) the front wheel isolator 6. Therefore, as Figure 1A As shown, the vehicle can glide in 2WD mode (and also in rear-wheel drive mode).

[0065] Because the front wheel isolator 6 is disconnected, the reverse driving force is transmitted from the front wheel 1, which acts as an auxiliary drive wheel, to the reducer 3, preventing drag loss and improving vehicle fuel efficiency. Since the front wheel 1 is separated from the drive system components (e.g., the front wheel motor 2, the reducer 3, and the differential 4), the vehicle's travel distance can be maximized when coasting by inertia.

[0066] Subsequently, when the vehicle is traveling with the accelerator pedal disengaged and the front wheel isolator 6 disconnected, the brake controller can be configured to determine whether the brake pedal is in the ON state (e.g., engaged) (S11). In other words, when the vehicle is coasting, when the driver depresses or engages the brake pedal (e.g., when the brake pedal is ON), the brake controller (BPS) determines whether the brake pedal is ON based on the signal from the brake pedal sensor (BPS) 111. Figure 4 The attached diagram (labeled "120") can be configured to determine whether braking or deceleration is in progress. Subsequently, based on information collected in the vehicle, the brake controller can be configured to determine whether the current vehicle state meets specific regenerative braking operation conditions (S12).

[0067] Regenerative braking operating conditions can be well-known conditions. For example, regenerative braking operating conditions can be determined to be met when one or more of the following conditions are met: the shift lever is in the drive (D) position; the vehicle speed (obtained from the wheel speed sensor) is equal to or greater than a set value; the required deceleration (determined by the brake pedal sensor (BPS) signal value) is equal to or less than a set value; the amount of brake pedal operation (BPS signal value) is equal to or greater than a set value; the slip of each wheel is equal to or less than a set value; the anti-lock braking system (ABS) and electronic stability control system (ESC) are not operating; and the wheel speed sensor 113 and the hydraulic sensor (not shown) are operating normally (e.g., without malfunction or failure).

[0068] Subsequently, based on the information collected in the vehicle, the vehicle controller can be configured to determine whether the vehicle has entered a state where regenerative braking of the motors is feasible (S13). Here, the motors can be the rear wheel motor 8 acting as the main drive wheel motor, or it can refer to the rear wheel motor 8 and the front wheel motor 2 acting as auxiliary drive wheel motors. Specifically, based on information such as curves showing motor torque revolutions per minute (RPM), system efficiency, and battery state of charge (SOC), the vehicle controller can be configured to calculate the amount of feasible regenerative braking, and then, based on the calculated amount of feasible regenerative braking, determine whether to enter a state where regenerative braking of the front wheel motor 2 and the rear wheel motor 8 is feasible.

[0069] The process of determining whether regenerative braking is feasible is a well-known process performed in any regenerative braking vehicle; therefore, a detailed description of the method or process for determining whether regenerative braking is feasible is omitted. Furthermore, the vehicle controller may be configured to send the result of determining whether regenerative braking is feasible to the brake controller. In response to determining that regenerative braking is feasible for the motor, and in response to receiving the result from the vehicle controller, the brake may be configured to determine a vehicle stability index based on information collected within the vehicle.

[0070] When the brake controller does not receive information from the vehicle controller indicating that regenerative braking of the front wheel motor 2 is feasible, the brake controller can be configured to determine that the front wheel isolator 6 is in a disconnected state (2WD state). Furthermore, the brake controller can be configured to determine a vehicle stability index (S14), then compare the calculated vehicle stability index with a preset reference value A (S15), and send the determination result to the vehicle controller. Specifically, the brake controller can be configured to calculate the vehicle stability index using Equation 1 based on vehicle deceleration, rear wheel slip, and the distribution ratio between front and rear wheel braking forces.

[0071] Vehicle stability index = Vehicle deceleration × Rear wheel slip × Distribution ratio of front and rear braking force (Equation 1)

[0072] The vehicle deceleration is the actual vehicle deceleration measured in real time by sensors in the vehicle and obtained based on the signal from the longitudinal acceleration sensor 112 installed in the vehicle.

[0073] Furthermore, known calculation methods can be used to obtain the rear wheel slip in a vehicle, and methods for calculating wheel slip are well known to those skilled in the art. Therefore, this specification omits a detailed description of the methods for calculating wheel slip. The distribution ratio between the front wheel braking force and the rear wheel braking force can be determined as the ratio of the front wheel braking force to the rear wheel braking force (or the ratio of the front wheel braking torque to the rear wheel braking torque), and the front wheel braking force and the rear wheel braking force can be calculated using Equations 2 and 3, respectively.

[0074]

[0075]

[0076] Equations 2 and 3 are equations for ideal braking distribution, where B f Indicates the front wheel braking force, B r W represents the rear wheel braking force, μ represents the road surface friction coefficient, and W represents the braking force. f W represents the weight of the front wheel. r Let represent the weight of the rear wheel, 'a' represent the vehicle deceleration, 'g' represent the acceleration due to gravity, 'h' represent the vertical height of the vehicle's center of gravity above the ground, and 'L' represent the wheelbase. In Equations 2 and 3, the coefficient of friction μ can be a predetermined constant, and the distribution ratio between the front and rear braking forces is defined as the ratio of the front braking force to the rear braking force.

[0077] In addition, the vehicle deceleration 'a' is the actual vehicle deceleration measured in real time by the longitudinal acceleration sensor 112, and the front wheel weight W... f Rear wheel weight W r The vehicle's center of gravity height h and wheelbase L (which are data segments specific to the corresponding vehicle) are input as predetermined values ​​into the brake controller for storage and later use. According to the present invention, the higher the value of the vehicle stability index, the lower the vehicle's stability. Conversely, the lower the value of the vehicle stability index, the more stable the vehicle's state.

[0078] Reference value A is a value determined through a process of prior testing and evaluation of vehicles of the same type. Specifically, reference value A is a value that can be determined and adjusted after checking vehicle deceleration, slippage, vehicle condition (e.g., oversteer or understeer), stability, etc., under various conditions (e.g., low-friction roads, downhill roads, and curved roads). The maximum stability index that ensures vehicle stability can be set as reference value A.

[0079] In response to determining in step S15 that the vehicle stability index is less than a reference value A, the brake controller can be configured to compare the braking torque required by the driver with the feasible regenerative braking torque of the rear wheel motor corresponding to the current vehicle speed (S16). In response to determining that the braking torque required by the driver is equal to or less than the feasible regenerative braking torque of the rear wheel motor corresponding to the current vehicle speed, the brake controller can be configured to perform regenerative braking (e.g., rear wheel regenerative braking) only through the rear wheel motor 8 (S17). In other words, only a single control can be performed on the rear wheel regenerative braking. The braking torque required by the driver (e.g., total braking torque) can be achieved by generating only the rear wheel regenerative braking torque without performing hydraulic braking on the front and rear wheels.

[0080] According to the present invention, vehicle speed can be obtained in real time based on the signal from wheel speed sensor 113. When determining the braking torque required by the driver based on the signal value of brake pedal sensor 111 (which represents the degree of brake pedal engagement in a normal vehicle), the required braking torque must be achieved by adding the "front wheel braking torque" and the "rear wheel braking torque" or by adding the "regenerative braking torque" and the "hydraulic braking torque". The braking torque required by the driver can be divided into front wheel braking torque and rear wheel braking torque, and the sum of the two is the braking torque required by the driver.

[0081] Specifically, the front wheel braking torque can be obtained by adding the "front wheel regenerative braking torque" and the "front wheel hydraulic braking torque," and the rear wheel braking torque can be obtained by adding the "rear wheel regenerative braking torque" and the "rear wheel hydraulic braking torque." Similarly, the regenerative braking torque can be obtained by adding the "front wheel regenerative braking torque" and the "rear wheel regenerative braking torque," and the hydraulic braking torque can be obtained by adding the "front wheel hydraulic braking torque" and the "rear wheel hydraulic braking torque."

[0082] Equations 2 and 3 above represent ideal braking distribution. The braking torque required by the driver can be divided into front wheel braking torque and rear wheel braking torque using Equations 2 and 3. Alternatively, regenerative braking torque can be divided into front wheel regenerative braking torque and rear wheel regenerative braking torque, and hydraulic braking torque can be divided into front wheel and rear wheel hydraulic braking torque.

[0083] In summary, when in Figure 5In step S15 of the flowchart shown, the vehicle enters a stable state where the vehicle stability index is less than the reference value A. And when the braking torque required by the driver in step S16 is equal to or less than the regenerative braking torque feasible by the rear wheel motor corresponding to the current vehicle speed, in step S17, regenerative braking can be performed by the rear wheel motor 8 alone, while maintaining 2WD without connecting the front wheel isolator 6.

[0084] In other words, the braking torque required by the driver is achieved by generating only the regenerative braking torque of the rear wheels, while the values ​​of the front wheel braking torque (e.g., front wheel regenerative braking torque + front wheel hydraulic braking torque) and the rear wheel hydraulic braking torque are both "0". Then, although... Figure 5 It is not shown in the figure, but after executing step S17, the control process can return to step S11.

[0085] Figure 6 This is a schematic diagram showing an example curve representing the TN (torque-speed) characteristic of a motor, which defines the feasible torque value for regenerative braking. The feasible torque for regenerative braking corresponding to the current vehicle speed can be determined from the curve representing the TN characteristic of the motor.

[0086] The curve representing the TN characteristic of the motor can be defined by the feasible amount of regenerative braking torque generated by the motor according to the vehicle speed. The feasible amount of regenerative braking torque at the current vehicle speed (e.g., the torque value at which regenerative braking can be performed) is limited by the curve showing the TN characteristic of the motor.

[0087] Figure 6 The diagram illustrates how a feasible torque value for regenerative braking (as a value based on vehicle speed) is determined using curves representing the TN characteristics of the motor. These curves can be used to determine feasible torque values ​​for regenerative braking of both the front and rear wheel motors.

[0088] In other words, according to the present invention, a curve representing the TN characteristics of the rear wheel motor (used in step S16) (defining the feasible torque value for regenerative braking of the rear wheel motor according to the vehicle speed) and a curve showing the TN characteristics of the front wheel motor (used in step S21) (defining the feasible torque value for regenerative braking of the front wheel motor according to the vehicle speed) are provided and can be used.

[0089] Reference Figure 6When the braking torque required by the driver is equal to or less than the regenerative braking torque feasible for the motor based on the current vehicle speed and determined based on a curve representing the TN characteristics of the motor, the required braking torque can be achieved solely by the motor generating regenerative braking torque. However, when the braking torque required by the driver is greater than the regenerative braking torque feasible for the motor based on the current vehicle speed and determined based on a curve representing the TN characteristics of the motor, the regenerative braking torque can be limited to the regenerative braking torque feasible for the motor, as indicated by the curve representing the TN characteristics of the motor.

[0090] Specifically, hydraulic braking torque must be generated to obtain a braking torque exceeding that feasible for regenerative braking. To achieve the braking torque required by the driver, hydraulic braking must be performed in conjunction with regenerative braking from the electric motor. Figure 6 In the example, when the vehicle speed is approximately 150 km / h and the driver requires approximately 2000 Nm of braking torque, in the initial stage, a hydraulic braking torque much greater than the regenerative braking torque must be generated to achieve the driver's required braking torque. Subsequently, as the vehicle speed decreases, more hydraulic braking torque can be reduced, while more regenerative braking torque can be increased.

[0091] In addition, Figure 6 In the example, when the vehicle speed is equal to or less than approximately 50 km / h, the braking torque required by the driver can be achieved solely through regenerative braking generated by the electric motor. Therefore, hydraulic braking is unnecessary. According to the present invention, as... Figure 6 As shown, the curve representing the TN characteristic of the motor, specifically the curve representing the TN characteristic of the rear wheel motor (the TN characteristic of the rear wheel motor is defined based on the feasible torque value for regenerative braking of the rear wheel motor according to the vehicle speed), can also be pre-input into the brake controller for storage, and can be... Figure 5 It is used in step S16.

[0092] At the same time, with Figure 6 In a similar manner to the example in the example, the curve representing the TN characteristic of the front wheel motor (the TN characteristic of the front wheel motor is defined as the feasible torque value for regenerative braking of the front wheel motor based on vehicle speed) can be pre-input into the brake controller for storage, and can be... Figure 5 Used in step S21. If in Figure 5 In step S16, if the braking torque required by the driver is greater than the regenerative braking torque feasible by the rear wheel motor corresponding to the current vehicle speed, then in step S18, in addition to the regenerative braking of the rear wheel motor 8, the front wheel hydraulic braking and rear wheel hydraulic braking of the hydraulic braking devices 131 and 132 are also executed. Therefore, by adding the regenerative braking torque of the rear wheel motor 8 to the front wheel and rear wheel hydraulic braking torques, the braking torque required by the driver can be achieved.

[0093] Specifically, the distribution of hydraulic braking torque between the front and rear wheels can be performed according to the distribution ratio between the front and rear wheel braking forces, which is obtained according to Equations 2 and 3. Furthermore, according to the invention, this can also be applied to the distribution of braking torque between the front and rear wheels. Moreover, according to the invention, regenerative braking and hydraulic braking can be performed under the coordinated control of the vehicle controller, the brake controller, and the motor controller. Hydraulic braking can be performed by a brake controller configured to drive hydraulic braking devices 131 and 132. When the vehicle controller generates and outputs a regenerative braking torque command, regenerative braking can be performed by a motor controller configured to perform regenerative operations of the corresponding motors 2 and 8 according to the regenerative braking torque command received from the vehicle controller.

[0094] On the other hand, when Figure 5 In step S15, when the brake controller can be configured to determine that the vehicle stability index is equal to or greater than the reference value A, and can send the determination result to the vehicle controller based on the determination result received from the brake controller, the vehicle controller can connect the front wheel isolator 6, thereby switching to 4WD (S19).

[0095] In the following description, "4WD state" refers to the state in which an isolator (e.g., front wheel isolator 6) installed on the auxiliary drive wheel side (e.g., front wheel side) for vehicle braking is connected to the vehicle drive system for vehicle braking, while "2WD state" refers to the state in which isolator 6 is disconnected (e.g., disengaged) from the vehicle drive system for braking. When switched to 4WD state, in order to achieve the braking torque required by the driver, both front and rear wheel braking can be controlled simultaneously, thereby generating braking force on all front and rear wheels.

[0096] Therefore, firstly, in step S20, in the same manner as in step S12, the vehicle controller can be configured to determine whether regenerative braking of the front wheel motor 2 and the rear wheel motor 8 is feasible, and send the determination result to the brake controller. Subsequently, when the brake controller receives the determination result from the vehicle controller that regenerative braking of the front wheel motor 2 and the rear wheel motor 8 is feasible, Figure 5 In step S21, the brake controller can be configured to compare the braking torque required by the driver with the regenerative braking torque feasible for the front wheel motor and the rear wheel motor corresponding to the current vehicle speed.

[0097] At this point, the feasible regenerative braking torque for both the front and rear wheel motors can be the sum of the regenerative braking torque of the front wheel motor corresponding to the current vehicle speed and the regenerative braking torque of the rear wheel motor corresponding to the current vehicle speed. Specifically, the feasible regenerative braking torque of the front wheel motor can be determined as a value corresponding to the current vehicle speed based on the curve representing the TN characteristic of the front wheel motor, and the feasible regenerative braking torque of the rear wheel motor can be determined as a value corresponding to the current vehicle speed based on the curve representing the TN characteristic of the rear wheel motor.

[0098] When in Figure 5 In step S21, when the brake controller determines that the braking torque required by the driver is equal to or less than the feasible torque for regenerative braking of the front wheel motor and the rear wheel motor, the brake controller can be configured to send the determined result, and accordingly, the vehicle controller and the motor controller can be configured to perform coordinated control, thereby performing regenerative braking of the front wheel motor 2 and the rear wheel motor 8 (S22). In particular, only the regenerative braking control of the front wheel motor 2 and the rear wheel motor 8 can be performed, and the front wheel hydraulic braking and rear wheel hydraulic braking performed by the hydraulic braking devices 131 and 132 are not performed.

[0099] although Figure 5 It is not shown in the figure, but when the brake pedal is held in the ON state (e.g., engaged state) during the execution of step S22, the method can return to step S20 and then switch from step S20 to step S26 or from step S21 to step S23.

[0100] Figure 7 This is a schematic diagram showing the state in which isolator 6 is connected when the vehicle stability index reaches the reference value A, and regenerative braking of the front wheels and regenerative braking of the rear wheels are performed simultaneously in step S22. Figure 7 It is shown that when the driver keeps the brake pedal engaged (“Brake indicator”) and the vehicle stability index reaches reference value A, isolator 6 can be engaged (“Isolator indicator”), in which case regenerative braking of the front wheel motor 2 and regenerative braking of the rear wheel motor 8 can be performed simultaneously.

[0101] exist Figure 7 In this context, "front wheel regenerative braking torque" indicates the state of regenerative braking by the front wheel motor, and "rear wheel regenerative braking torque" indicates the state of regenerative braking by the rear wheel motor. For example... Figure 7 As shown, the maximum amount of regenerative braking torque of the rear wheels can be limited and maintained as the value of the regenerative braking torque of the rear wheels at the time point when the vehicle stability index reaches the reference value A. According to the present invention, through actual vehicle evaluation tests, when braking is performed using only the regenerative braking of the rear wheel motor 8, the reference value A can be determined as the maximum value of the vehicle stability index that ensures vehicle stability.

[0102] In addition, such as Figure 7 As shown, when the vehicle stability index reaches reference value A, the front wheel isolator 6 can be engaged, and a switch to 4WD mode can be performed. Then, regenerative braking (e.g., front wheel regenerative braking torque) of the front wheel motor 2 can be generated separately. At this time, the braking torque required by the driver can be achieved by adding the regenerative braking torque of the rear wheel motor 8 (e.g., rear wheel regenerative braking torque) and the regenerative braking torque of the front wheel motor 2 (e.g., front wheel regenerative braking torque). In other words, the rear wheel regenerative braking torque can be limited and maintained to its value at the point when the vehicle stability index reaches reference value A, while simultaneously, the same amount of front wheel regenerative braking torque as is required to achieve the driver's desired braking torque can be generated separately. Therefore, the braking torque required by the driver can be achieved.

[0103] If entering 4WD mode that connects the front wheel isolator 6 and meets the requirements Figure 5 If the conditions in steps S20 and S21 are met, the driver can further engage the brake pedal, thereby increasing the braking torque required by the driver. At this time, if... Figure 7 As shown, the regenerative braking torque of the rear wheels can remain constant, but the regenerative braking torque of the front wheels can gradually increase to achieve the braking torque required by the driver. Furthermore, after the front wheel isolator 6 can be engaged and the vehicle drive system state can be switched to 4WD in step S19, the vehicle controller will no longer perform vehicle braking within the corresponding braking cycle and will maintain 4WD state until the vehicle stops. This is done to increase the smoothness of the start-up feel when the vehicle accelerates again after braking has ceased or after the vehicle has come to a stop.

[0104] In addition, refer to Figure 7 When braking occurs and the conditions in step S15 are met but the front wheel isolator 6 is not immediately engaged (i.e., when the vehicle stability index reaches the reference value A), the front wheel isolator 6 can be engaged. The reason for not immediately engaging the front wheel isolator 6 during braking is that, in terms of fuel efficiency, when the vehicle stability index is less than the reference value A (e.g., in areas where the vehicle deceleration is low), it is more advantageous to brake the vehicle using only the regenerative braking of the rear wheel motor 8. This is especially true for e-4WD systems where the rear wheel motor 8 has a higher inverter efficiency than the front wheel motor 2. In this case, it is more advantageous to generate as much regenerative braking as possible using the rear wheel motor 8 in terms of vehicle fuel efficiency.

[0105] On the other hand, when Figure 5In step S21, the brake controller can be configured to determine that the braking torque required by the driver is greater than the regenerative braking torque feasible for the front and rear wheel motors corresponding to the current vehicle speed. In step S23, the brake controller can be configured to compare the front and rear wheel hydraulic braking torques with a predetermined combined limit torque for regenerative and hydraulic braking. Specifically, the front and rear wheel hydraulic braking torques refer to the sum of the front and rear wheel hydraulic braking torques, and can be obtained as a value obtained by subtracting the regenerative braking torque feasible for the front and rear wheel motors corresponding to the current vehicle speed from the braking torque required by the driver.

[0106] In response to the determination in step S23 that the hydraulic braking torque of the front and rear wheels is less than the combined limit torque of regenerative braking and hydraulic braking, the brake controller can be configured to send the determined result to the vehicle controller. In step S24, correspondingly, the vehicle controller and the motor controller can be configured to perform coordinated control, thereby performing regenerative braking via the front wheel motor 2 and the rear wheel motor 8 (e.g., performing front wheel regenerative braking and rear wheel regenerative braking). Specifically, to achieve the braking torque required by the driver, regenerative braking torque corresponding to the current vehicle speed can be generated by the regenerative braking of the front wheel motor and the regenerative braking of the rear wheel motor, as much as the feasible regenerative braking torque of the front wheel motor and the rear wheel motor.

[0107] Furthermore, in step S24, the brake controller can be configured to operate hydraulic braking devices 131 and 132 to jointly perform front wheel hydraulic braking and rear wheel hydraulic braking. Specifically, the hydraulic braking torque can be generated by hydraulic braking devices 131 and 132 and can be applied to the front wheel 1 and the rear wheel 7, wherein the hydraulic braking torque is equal to the braking torque obtained by subtracting the regenerative braking torque of the front wheel motor 2 and the rear wheel motor 8 (e.g., the sum of the front wheel regenerative braking torque and the rear wheel regenerative braking torque) from the braking torque required by the driver.

[0108] On the other hand, when the hydraulic braking torque of the front and rear wheels is greater than the combined limit torque of regenerative braking and hydraulic braking in step S23, the regenerative braking torque of the front wheels can be limited and maintained at the combined limit torque in step S25, while the hydraulic braking torque can be increased. Therefore, a hydraulic braking torque can be generated that is as much as the braking torque required to achieve the driver's desired braking torque, which cannot be generated solely as regenerative braking torque.

[0109] Specifically, the rear-wheel regenerative braking torque can be limited and maintained to its value at the time point when the vehicle stability index reaches reference value A. The hybrid limit torque can be set to the maximum value of the front-wheel regenerative braking torque. In summary, in step S25, the rear-wheel regenerative braking torque can be limited and maintained to its value at the time point when the vehicle stability index reaches reference value A, and the front-wheel regenerative braking torque can be limited and maintained to the hybrid limit torque.

[0110] Furthermore, the value obtained by subtracting the regenerative braking torque of the front and rear wheels from the braking torque required by the driver can be divided into front and rear wheel hydraulic braking torques. In this case, both the front and rear wheel regenerative braking torques can remain constant. Therefore, the front and rear wheel hydraulic braking torques change in a manner corresponding to the increase and decrease of the braking torque required by the driver. In other words, as the braking torque required by the driver gradually increases, the regenerative braking torque can remain constant without any change. Therefore, the hydraulic braking torque can also be gradually increased.

[0111] although Figure 5 Not shown, but when performing step S25, if the brake pedal remains in the ON state, the method can return to step S20, and then step S20 and subsequent steps can be repeated continuously. According to the invention, the combination of regenerative braking and hydraulic braking can include situations where the regenerative braking torque increases as the hydraulic braking torque decreases, or decreases as the hydraulic braking torque increases, in such a way that the sum of the regenerative braking torque and the hydraulic braking torque equals the braking torque required by the driver.

[0112] Furthermore, the combined limit torque of regenerative braking and hydraulic braking refers to the maximum amount of regenerative braking torque at a level where, when the hydraulic braking torque is adjusted accordingly and variably based on the degree of change in regenerative braking torque, responsiveness, following performance, linearity, etc., are satisfactory without any loss of deceleration or comfort. For example, when a vehicle is moving (e.g., without error), it rolls on a low-friction road surface (e.g., while driving), causing wheel slippage to increase rapidly. ABS hydraulic control must be activated to prevent wheel lock-up. However, for ABS operation and hydraulic control to occur, the regenerative braking torque generated by the motor must first be rapidly replaced with hydraulic braking torque.

[0113] As described above, in order to perform ABS operation and hydraulic control, when the regenerative braking torque is rapidly replaced by the hydraulic braking torque, the maximum amount of the motor regenerative braking torque (i.e., the combined limit torque of regenerative braking and hydraulic braking) can be set to a level where the responsiveness and linearity of the hydraulic braking torque can be guaranteed.

[0114] On the other hand, in response to Figure 5If step S11 determines that the regenerative braking operation conditions are not met, or in response to the determination in steps S12 and S20 that regenerative braking of the front wheel motor 2 and regenerative braking of the rear wheel motor 8 are not feasible, in step S26, the vehicle controller no longer performs regenerative braking of the front wheel motor and regenerative braking of the rear wheel motor.

[0115] Furthermore, the vehicle controller can be configured to send the determined results to the brake controller, and correspondingly, the brake controller can be configured to perform front wheel hydraulic braking control and rear wheel hydraulic braking control. Therefore, the braking torque required by the driver can be achieved by generating only the hydraulic braking torque of the front and rear wheels, rather than by generating regenerative braking torque from the motor.

[0116] The aforementioned state where regenerative braking of the front and rear wheel motors is infeasible can be a state where the braking torque required by the driver exceeds the range under which regenerative braking is feasible. Therefore, in response to determining that this state has been entered, regenerative braking of any motor is no longer performed; instead of regenerative braking, only front and rear wheel hydraulic braking can be performed.

[0117] Figure 8 This is a diagram illustrating the segmented braking torque states during the braking control process according to the present invention. First, Figure 8 Part ① is the following: Before connecting isolator 6, in the area where low vehicle deceleration is performed, such as in Figure 5 In step S17, the regenerative braking of the rear wheels is controlled individually.

[0118] Next, Figure 8 Part ② is as follows: In the low deceleration region of the vehicle, only the regenerative braking control of the front wheel motor 2 and the regenerative braking control of the rear wheel motor 8 in step S22 are performed, and hydraulic braking is not performed after the isolator 6 is connected.

[0119] exist Figure 8 In Part ②, as the amount of brake pedal operation and the braking torque required by the driver gradually increase, the regenerative braking torque of the front wheels can increase, but the regenerative braking torque of the rear wheels will be limited and maintained at its value at the time point when the vehicle stability index reaches the reference value A (see reference). Figure 7 (Description of the process).

[0120] Figure 8 Part ③ in the text refers to the following: In the connected state of isolator 6, such as in... Figure 5 In step S24, coordinated control of regenerative braking of the front wheel motor 2 and regenerative braking of the rear wheel motor 8, as well as coordinated control of hydraulic braking of the front wheels and hydraulic braking of the rear wheels, can be performed.

[0121] Figure 8Part ④ is the cooperative control section, which occurs when isolator 6 is in the connected state and the vehicle is in a medium-to-high deceleration state, such as in Figure 5 In step S25, the regenerative braking torque of the front wheels can be limited and maintained as a hybrid limit torque, while the front wheel hydraulic braking and the rear wheel hydraulic braking can be performed to achieve the braking torque required by the driver.

[0122] exist Figure 8 In section ④, the regenerative braking torque of the rear wheels can be limited and maintained at its value at the time point when the vehicle stability index reaches the reference value A. Therefore, the individual values ​​of the regenerative braking torque of the front wheels and the regenerative braking torque of the rear wheels can remain constant. Thus, when the braking torque required by the driver increases, the hydraulic braking torque also increases.

[0123] Figure 8 Part ⑤ is as follows: In the connected state of isolator 6 and the high deceleration state of the vehicle, such as in Figure 5 In step S26, regenerative braking is no longer performed, and only front wheel hydraulic braking and rear wheel hydraulic braking control are performed.

[0124] Figure 8 As shown in section ⑤, before ABS operation begins, the regenerative braking torque is entirely replaced by hydraulic braking torque. After ABS operation to prevent wheel lock-up, only hydraulic braking control is performed, and regenerative braking is not activated. Furthermore, Figure 8 Shown in Figure 8 In part ④, when the ABS is activated, the hydraulic braking torque is rapidly replaced by the regenerative braking torque. The regenerative braking torque of the front wheels can be limited to and maintained as the mixed limit torque, and the regenerative braking torque of the rear wheels can be limited to and maintained as its value at the time point when the vehicle stability index reaches the reference value A.

[0125] also, Figures 9 to 12 It is a schematic diagram that clearly shows the changes in vehicle deceleration and the state of each braking control phase as the driver slowly depresses or engages the brake pedal to a specific position and gradually increases the amount of pedal operation (e.g., gradually increasing the amount of engagement). Figure 9 Corresponding to braking using only the rear wheel motor 8 Figure 8 Part ① of the diagram shows the following: In the initial stage of brake pedal operation, the vehicle is in a low deceleration state, and only regenerative braking of the rear wheel motor 8 is performed before isolator 6 is engaged. Figure 5 Step S17 in the process.

[0126] exist Figure 9In this state, the front wheel isolator 6 is in a disconnected state. Therefore, regenerative braking of the front wheel motor 2 cannot be performed, and neither can the hydraulic braking of the front wheel hydraulic braking device 131 nor the rear wheel hydraulic braking device 132. Furthermore, the regenerative braking torque of the rear wheel motor 8 gradually increases with the increase of pedal operation. In this way, only rear wheel regenerative braking torque is generated until the vehicle stability index reaches the reference value A.

[0127] Figure 9 The lower right portion shows the curve representing ideal brake distribution. The X-axis represents the front wheel braking force and deceleration, and the Y-axis represents the rear wheel braking force and deceleration. (Example:) Figure 9 As shown in the lower part, the rear wheel braking deceleration is generated by the rear wheel braking force until the vehicle stability index reaches the reference value A. The rear wheel braking deceleration is higher than the curve representing ideal brake distribution. This indicates that the rear wheel braking deceleration is in the unstable region.

[0128] Since the rear wheel braking deceleration is in an unstable region, the reference value A of the vehicle stability index is set to a level that can ensure vehicle stability on low-friction roads, inclined roads, and curved roads through actual vehicle evaluation tests, based on vehicle deceleration, rear wheel slip, and the distribution ratio of front wheel braking force to rear wheel braking force.

[0129] Figure 10 Corresponding to Figure 8 Part ② in the text indicates that it is temporarily following. Figure 9 The state of the state in the middle. Figure 10 The following section is shown: When the vehicle is in a low to medium deceleration state, after the isolator 6 is connected, regenerative braking of the front wheels and regenerative braking of the rear wheels are performed together, while hydraulic braking is not performed. Figure 5 Step S22). Figure 10 Under these conditions, as shown above, the regenerative braking torque of the rear wheels is limited and maintained at its value at the time point when the vehicle stability index reaches the reference value A.

[0130] The isolator 6 can be engaged at the point when the vehicle stability index reaches reference value A, and regenerative braking can be performed by each of the front wheel motor 2 and the rear wheel motor 8. At this time, hydraulic braking is not applied. (Refer to...) Figure 10 In the upper right section, deceleration is generated solely by regenerative braking force from the rear wheels, and regenerative braking is performed only on the rear wheels until the deceleration reaches X at the time point when the vehicle stability index reaches the reference value A.

[0131] Subsequently, regenerative braking force is generated in the front wheels, and a deceleration Y (deceleration = X + Y) is generated at the point when the regenerative braking torque of the front wheels reaches the combined limit torque. Furthermore, in Figure 10The lower right portion generates deceleration X through regenerative braking force from the rear wheels, and then additional deceleration Y is generated solely through regenerative braking force from the front wheels. At this point, only the front wheel braking deceleration increases. This is due to... Figure 10 The horizontal curve in the lower right part represents this.

[0132] Figure 10 The state described in the figure refers to the situation where the front wheel braking force is increased. Therefore, as the vehicle approaches the curve representing the ideal brake distribution, it can gradually stabilize. Braking stability increases with the increase of regenerative braking force on the front wheels. Figure 11 The state in corresponds to Figure 8 Part ④ of the text, and shows a temporary follow. Figure 10 The state of the state in the middle. Figure 11 This is shown to be performed in the connected state of isolator 6 and in the medium-to-high deceleration state of the vehicle. Figure 5 Step S25 in the process.

[0133] exist Figure 11 In the state of isolator 6 connection and vehicle medium-high deceleration, such as in Figure 5 In step S25, the regenerative braking torque of the front wheels can be limited and maintained at a mixed limit torque, while the hydraulic braking of the front and rear wheels can be performed in a manner that achieves the braking torque required by the driver. At this time, the regenerative braking torque of the rear wheels can be maintained at its value at the time point when the vehicle stability index reaches the reference value A.

[0134] Reference Figure 11 The upper right part can perform regenerative braking only on the rear wheels until deceleration X occurs, or it can perform regenerative braking on both the front and rear wheels until deceleration X+Y occurs. After deceleration X+Y is reached, hydraulic braking can be performed in addition to regenerative braking (for example, hydraulic braking on the front wheels and hydraulic braking on the rear wheels are performed simultaneously) to obtain additional deceleration.

[0135] In addition, such as in Figure 11 In the upper right section, after deceleration X+Y occurs, front and rear wheel hydraulic braking can be applied simultaneously. This is represented by a curve inclined in a direction other than the horizontal and vertical directions. At this point, since the brake distribution state is similar to that represented by the curve indicating ideal brake distribution, vehicle braking stability can be ensured.

[0136] Then, Figure 12 Show temporary follow Figure 11 The state in the context is shown below: Figure 8 In part ⑤, when the vehicle is in a high deceleration state and isolator 6 is engaged, regenerative braking is no longer performed, and only front wheel hydraulic braking and rear wheel hydraulic braking control are performed (e.g., Figure 5(The control phase in step S26). After deceleration Z (e.g., the condition of maximum deceleration), regenerative braking of the front wheels and regenerative braking of the rear wheels can be terminated, and hydraulic braking of the front wheels and hydraulic braking of the rear wheels can be performed.

[0137] Figure 12 The lower right portion shows that regenerative braking force from any motor disappears, generating only hydraulic braking force for the front and rear wheels. Therefore, the brake distribution state is similar to that represented by the graph indicating the actual brake distribution, which points to a more stable region than the curve representing the ideal brake distribution. Consequently, regenerative braking force disappears, and the brake distribution state enters a more stable region.

[0138] Figure 13 This is a reference diagram used to describe the behavior of a vehicle when wheel lock-up occurs in the rear wheels due to excessive braking force. When the rear wheel braking force is too great, because the rear wheels lock up, lateral forces do not act on the rear wheels; therefore, only the braking force F is affected. xr The braking force F acts on the rear wheels. xf and lateral force F yf It acts on the front wheels.

[0139] In particular, the inertial force F x and lateral force F y The repulsive forces, acting as braking force and lateral force respectively, act on the vehicle's longitudinal and lateral centers of gravity. The resultant longitudinal force acting on the vehicle has parallel force and moment, but the longitudinal force F... y The torque "F" is generated relative to the vehicle's center of gravity. y ×b”. When the vehicle turns longitudinally due to this torque, the angle α between the inertial force and the resultant force acting on the center of gravity increases. Therefore, the magnitude of the yaw phenomenon increases, and the vehicle's braking stability decreases.

[0140] Exemplary embodiments of the present invention have been described in detail above, but this does not limit the scope of the claims. Various modifications and improvements made by those skilled in the art using the basic concepts of the invention as defined in the appended claims are also included within the scope of the claims.

Claims

1. A method of controlling braking of a vehicle having a first independent drive unit configured to drive front wheels, a second independent drive unit configured to drive rear wheels, and an isolator installed in a drive shaft and connecting and disconnecting power transmission, the method comprising: determining, by a controller, a current vehicle stability index based on information collected in the vehicle; connecting or disconnecting, by the controller, the isolator based on the determined vehicle stability index; performing, by the controller, regenerative braking of the front wheels or the rear wheels of the vehicle, or of all the front and rear wheels, based on a controlled state of the isolator, wherein the vehicle is a four-wheel drive electric vehicle having front and rear motor as drive units and an isolator installed on a front wheel drive shaft of the vehicle, determining, by the controller, whether a brake pedal is operated when the vehicle is driven in a state in which the isolator is disconnected to release power transmission; in response to determining that the brake pedal is operated, determining, by the controller, a current vehicle stability index based on information collected in the vehicle and comparing the determined vehicle stability index with a preset reference value; when the determined vehicle stability index is less than the preset reference value, comparing, by the controller, a driver required braking torque with a regenerative braking feasible torque of the rear motor corresponding to a current vehicle speed; when the driver required braking torque is equal to or less than the regenerative braking feasible torque of the rear motor, performing, by the controller, regenerative braking of the rear motor and implementing the driver required braking torque by generating only a rear regenerative braking torque, when the determined vehicle stability index is equal to or greater than the reference value, connecting, by the controller, the isolator; in a state in which the isolator is connected, simultaneously operating, by the controller, front and rear brakes to implement the driver required braking torque, wherein operating the front and rear brakes includes: comparing, by the controller, the driver required braking torque with regenerative braking feasible torques of the front and rear motors corresponding to the current vehicle speed; when the driver required braking torque is equal to or less than the regenerative braking feasible torques of the front and rear motors, performing, by the controller, regenerative braking of the front and rear motors and implementing the driver required braking torque by generating front and rear regenerative braking torques.

2. The method of controlling the brakes of a vehicle of claim 1 wherein, The vehicle stability index is calculated using Equation 1 according to a vehicle deceleration, a rear wheel slip amount, and a distribution ratio between front and rear braking forces: Equation 1: Vehicle stability index = vehicle deceleration × rear wheel slip amount × distribution ratio between front and rear braking forces wherein the vehicle deceleration is a current actual vehicle deceleration measured using a sensor, and the distribution ratio between the front and rear braking forces is a value of a ratio between the front and rear braking forces.

3. The method of controlling vehicle braking of claim 1, wherein, The regenerative braking feasible torque of the rear motor is determined according to a value of the current vehicle speed and according to a curve representing the regenerative braking feasible torque of the rear motor. 4.The method of controlling braking of a vehicle according to claim 1, wherein: The regenerative-braking feasible torque of the front motor and the regenerative-braking feasible torque of the rear motor are summed up, The regenerative-braking feasible torque of the front motor is determined according to the value of the current vehicle speed and according to a curve representing the regenerative-braking feasible torque of the front motor, and The regenerative-braking feasible torque of the rear motor is determined according to the value of the current vehicle speed and according to a curve representing the regenerative-braking feasible torque of the rear motor.

5. The method of controlling vehicle braking of claim 1, wherein, The operation of the front and rear brakes further includes: When the driver's required braking torque is greater than the regenerative-braking feasible torque of the front motor and the regenerative-braking feasible torque of the rear motor, the controller compares the front and rear hydraulic braking torques with the predetermined regenerative-braking and hydraulic-braking mixed limit torque; When the front and rear hydraulic braking torques are less than the regenerative-braking and hydraulic-braking mixed limit torque, the controller executes the regenerative braking of the front motor and the regenerative braking of the rear motor and the front hydraulic braking and the rear hydraulic braking, and realizes the driver's required braking torque, wherein the front and rear hydraulic braking torques are obtained by subtracting the regenerative-braking feasible torque of the front motor and the regenerative-braking feasible torque of the rear motor from the driver's required braking torque.

6. The method of controlling the brakes of a vehicle of claim 5 wherein, The operation of the front and rear brakes further includes: When the front and rear hydraulic braking torques are equal to or greater than the regenerative-braking and hydraulic-braking mixed limit torque, the controller limits and maintains the front regenerative braking torque to the regenerative-braking and hydraulic-braking mixed limit torque, while realizing the driver's required braking torque by executing the regenerative braking of the front motor and the rear motor and the front and rear hydraulic braking.

7. The method of controlling the brakes of a vehicle of claim 6 wherein, In the case where the driver's required braking torque is realized by generating only the rear regenerative braking torque, when the vehicle stability index increases as the brake pedal operation amount increases and reaches the reference value, the isolator is connected, and, while the front regenerative braking torque is limited and maintained to the regenerative-braking and hydraulic-braking mixed limit torque, the rear regenerative braking torque is maintained to the rear regenerative braking torque at the point in time when the vehicle stability index reaches the reference value.

8. The method of controlling vehicle braking of claim 5, wherein, In the case where the driver's required braking torque is realized by generating only the rear regenerative braking torque, when the vehicle stability index increases as the brake pedal operation amount increases and reaches the reference value, the isolator is connected, and, while the front and rear hydraulic braking torques are realized by executing the regenerative braking of the front motor and the rear motor and the front and rear hydraulic braking, the rear regenerative braking torque is maintained to the rear regenerative braking torque at the point in time when the vehicle stability index reaches the reference value.

9. The method of controlling vehicle braking of claim 1, wherein, In the state where the isolator is connected and based on the information collected in the vehicle, the controller determines that the state where the regenerative braking of the motors is feasible is entered, and compares the driver's required braking torque with the regenerative-braking feasible torque of the front motor and the regenerative-braking feasible torque of the rear motor.

10. The method of controlling the brakes of a vehicle of claim 9, wherein, In the state where the isolator is connected and based on the information collected in the vehicle, the controller determines that the state where the regenerative braking of the motors is not feasible is entered, and executes the hydraulic braking control for realizing the driver's required braking torque by generating only the front and rear hydraulic braking torques.

11. The method of controlling vehicle braking of claim 1, wherein, In a case where the driver required braking torque is realized by generating only the rear wheel regenerative braking torque, when the vehicle stability index increases as the brake pedal operation amount increases and reaches the reference value, the isolator is connected, and, in a case where the driver required braking torque is realized by generating only the front wheel regenerative braking torque and the rear wheel regenerative braking torque, the rear wheel regenerative braking torque is maintained as the rear wheel regenerative braking torque at the point in time when the vehicle stability index reaches the reference value.

12. The method of controlling vehicle braking of claim 1, further comprising: when the driver required braking torque is greater than the regenerative braking feasible torque of the rear wheel motor, performing regenerative braking of the rear wheel motor and hydraulic braking of the front and rear wheels by the controller, and realizing the driver required braking torque.

13. A system for controlling braking of a vehicle having a first independent drive unit configured to drive front wheels, a second independent drive unit configured to drive rear wheels, and an isolator mounted in a drive shaft and connecting and releasing a power transmission connection, wherein, The vehicle is a four-wheel drive electric vehicle having front and rear wheel motors as drive units and an isolator installed on a front wheel drive shaft of the vehicle, and the system includes: a memory configured to store program instructions; and a processor configured to execute the program instructions, which when executed are configured to: determine a current vehicle stability index based on information collected within the vehicle, operate the vehicle controller to connect or disconnect the isolator based on the determined vehicle stability index, operate the brake controller to perform regenerative braking on the front or rear wheels of the vehicle, or on all of the front and rear wheels based on the controlled state of the isolator, determine whether the brake pedal is operated when the vehicle is driven in a state where the isolator is disconnected to release the power transmission connection; in response to determining that the brake pedal is operated, determine a current vehicle stability index based on information collected within the vehicle, and compare the determined vehicle stability index with a preset reference value; when the determined vehicle stability index is less than the preset reference value, compare the driver required braking torque with a regenerative braking feasible torque of the rear wheel motor corresponding to the current vehicle speed; when the driver required braking torque is equal to or less than the regenerative braking feasible torque of the rear wheel motor, perform regenerative braking of the rear wheel motor, and realize the driver required braking torque by generating only the rear wheel regenerative braking torque, when the determined vehicle stability index is equal to or greater than the reference value, connect the isolator; in a state where the isolator is connected, simultaneously operate the front and rear brakes to realize the driver required braking torque, wherein operating the front and rear brakes includes: comparing the driver required braking torque with regenerative braking feasible torques of the front and rear wheel motors corresponding to the current vehicle speed; when the driver required braking torque is equal to or less than the regenerative braking feasible torques of the front and rear wheel motors, performing regenerative braking of the front and rear wheel motors, and realizing the driver required braking torque by generating the front and rear wheel regenerative braking torques.

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