Regenerative braking control device for an electrically powered four-wheel drive vehicle

Abstract

The present invention relates to a regenerative braking control device for an electrified four-wheel drive vehicle. The regenerative braking control device can improve fuel efficiency by regenerative braking control optimized for an electrified four-wheel drive vehicle.

Description

TECHNICAL FIELD

[0001] The present application relates to a regenerative braking control device for an electrified four-wheel drive vehicle, and more particularly to a regenerative braking control device for an electrified four-wheel drive vehicle that optimizes regenerative braking to improve fuel efficiency. BACKGROUND

[0002] As is well known, hybrid electric vehicles, electric vehicles, hydrogen fuel cell vehicles, and the like are provided with electric motors as a travel drive source, and such vehicles are referred to as electrified vehicles.

[0003] As an example of a four-wheel drive powertrain of an electrified vehicle, a powertrain can be applied in which an engine and a front wheel motor are connected to front wheels, and a rear wheel motor smaller in size than the front wheel motor is connected to rear wheels.

[0004] In the case of a four-wheel drive powertrain having an engine and a front wheel motor connected to front wheels, both of which are main drive sources for vehicle travel, and a rear wheel motor connected to rear wheels, which is an auxiliary drive source, an optimized regenerative braking control technique for ensuring fuel efficiency has not been established, and regenerative braking control is performed in the same method as a two-wheel drive powertrain, which becomes a factor in reducing fuel efficiency.

[0005] Since the regenerative braking control technique is a technique that occupies the largest portion in ensuring fuel efficiency of an electrified vehicle, a regenerative braking control technique optimized for an electrified four-wheel drive vehicle, which is different from an electrified two-wheel drive vehicle, is required to maximize fuel efficiency of an electrified four-wheel drive vehicle.

[0006] The information included in the Background section of this application is intended only to enhance understanding of the general background of the present application, and should not be considered to constitute admission of prior art to a patentable application, nor should it constitute any representation by the patentees about the existence of a prior art. SUMMARY

[0007] Various aspects of the present application aim to provide a regenerative braking control device for an electrified four-wheel drive vehicle that can improve fuel efficiency through regenerative braking control optimized for an electrified four-wheel drive vehicle.

[0008] Accordingly, various aspects of the present application provide a regenerative braking control device for an electrically powered four-wheel drive vehicle, the regenerative braking control device including: a front-wheel powertrain including an engine, a front-wheel motor, an engine clutch installed between the engine and the front-wheel motor, a hybrid starter generator (HSG) connected to the engine to start the engine, and a transmission that steps up power of the engine and the front-wheel motor to output the stepped-up power to front wheels of the vehicle; a rear-wheel powertrain including a rear-wheel motor and a reducer that steps down power of the rear-wheel motor to output the stepped-down power to rear wheels of the vehicle; a battery connected to the front-wheel motor, the rear-wheel motor, and the hybrid starter generator to charge and discharge; and a control unit connected to the front-wheel powertrain and the rear-wheel powertrain and configured to: allocate an amount of rear-wheel regenerative braking required to the rear-wheel motor when braking is started; and allocate an amount of front-wheel regenerative braking required to the front-wheel motor when it is determined that the rear wheels will slip based on a speed difference between the front wheels and the rear wheels.

[0009] According to various exemplary embodiments of the present application, the regenerative braking control device has the following specific features.

[0010] The control unit is configured to allocate the amount of front-wheel regenerative braking required to the front-wheel motor if the maximum power of the rear-wheel motor is less than an amount of regenerative braking allowable based on an amount of braking required by a driver when it is determined that the rear wheels will not slip based on the speed difference between the front wheels and the rear wheels.

[0011] When it is determined that the rear wheels will slip, the control unit determines the amount of front-wheel regenerative braking required based on the speed difference between the front wheels and the rear wheels. When the speed difference between the front wheels and the rear wheels is less than a predetermined first reference value (α), the control unit determines that the rear wheels will not slip, and when the speed difference between the front wheels and the rear wheels is greater than or equal to the first reference value, the control unit determines that the rear wheels will slip, thereby performing front-wheel regenerative braking control.

[0012] Further, the control unit is configured to reduce the amount of rear-wheel regenerative braking required allocated to the rear-wheel motor from the amount of front-wheel regenerative braking required allocated to the front-wheel motor when it is determined that the rear wheels will slip.

[0013] Further, the control unit is configured to, when the amount of regenerative braking required for the front wheels is allocated to the front motor and then it is determined that the rear wheels are not slipping based on the speed difference between the front wheels and the rear wheels, maintain the amount of regenerative braking required for the front wheels and determine the value obtained by subtracting the amount of regenerative braking required for the front wheels from the regenerative braking allowance amount as the amount of regenerative braking required for the rear wheels. When the speed difference between the front wheels and the rear wheels becomes equal to or less than a second reference value (β), the control unit determines that the wheels are not slipping, and the second reference value (β) is determined as a value smaller than the first reference value (α).

[0014] Further, when it is determined that the rear wheels are not slipping based on the speed difference between the front wheels and the rear wheels, the control unit determines the value obtained by subtracting the amount of regenerative braking required for the rear wheels from the regenerative braking allowance amount as the amount of regenerative braking required for the front wheels.

[0015] Further, the control unit is configured to, when it is determined that the rear wheels are not slipping, if the regenerative braking allowance amount is greater than the sum of the amount of regenerative braking executed for the rear wheels and the amount of regenerative braking executed for the front wheels, allocate the amount of regenerative braking required for a hybrid starter generator (HSG) to the HSG. At this time, the value obtained by subtracting the amount of regenerative braking executed for the front wheels, the amount of regenerative braking executed for the rear wheels, and the amount of engine friction from the regenerative braking allowance amount is determined as the amount of regenerative braking required for the HSG.

[0016] The control unit executes regenerative braking control of a hybrid starter generator (HSG) using the HSG in a state where the engine clutch is locked and fuel supply to the engine is stopped.

[0017] According to the above configuration, when the vehicle starts braking, if the efficient regenerative braking of the rear wheels is preferentially executed and there is a problem of slipping due to the preferential execution of the regenerative braking of the rear wheels, the present application can execute the regenerative braking of the front wheels to eliminate the slipping, thereby ensuring braking stability while improving fuel efficiency.

[0018] Further, when the regenerative braking of the rear wheels is executed first, if the regenerative braking allowance amount is not satisfied, the present application can further execute the HSG regenerative braking in addition to the regenerative braking of the front wheels, thereby maximizing the effect of improving fuel efficiency by the regenerative braking.

[0019] It should be understood that the term "vehicle" or "vehicles" or other similar terms as used herein generally includes motor vehicles, such as passenger cars, including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, boats, ships, including various watercraft, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from non-fossil sources). As referred to herein, a hybrid vehicle is a vehicle having two or more sources of power, such as a vehicle having both gasoline power and electric power.

[0020] The above and other features of the present application are discussed in the following.

[0021] The method and apparatus of the present application has other features and advantages which will be apparent from or which will be elaborated upon in the accompanying drawings and the detailed description which follows, and which generally serve to provide a more complete understanding of the principles of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic diagram showing a power transmission system of an electrically powered four-wheel drive vehicle as an example.

[0023] Figure 2 is a schematic diagram showing a configuration for regenerative braking control of an electrically powered four-wheel drive vehicle according to various exemplary embodiments of the present application.

[0024] Figure 3 is a flowchart showing a regenerative braking control process of an electrically powered four-wheel drive vehicle according to various exemplary embodiments of the present application.

[0025] Figure 4 is a schematic diagram showing an energy transmission path at the time of rear wheel regenerative braking of an electrically powered four-wheel drive vehicle according to various exemplary embodiments of the present application.

[0026] Figure 5 is a schematic diagram showing an energy transmission path at the time of front wheel and rear wheel regenerative braking of an electrically powered four-wheel drive vehicle according to various exemplary embodiments of the present application.

[0027] Figure 6 is a schematic diagram showing an energy transmission path at the time of regenerative braking cooperative control of an electrically powered four-wheel drive vehicle according to various exemplary embodiments of the present application.

[0028] It should be appreciated that the appended drawings are not necessarily drawn to scale, but are merely intended to illustrate various features of the application in a simplified form. The specific design features of the application disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes, will be determined in part by the particular environment in which the application is used and applied.

[0029] In these drawings, like numerals of reference designate the same or equivalent parts throughout the several views of the drawings that implement the present application. DETAILED DESCRIPTION

[0030] Reference will now be made in detail to various embodiments of the application, examples of which are illustrated in the accompanying drawings and described below. While the application will be described in conjunction with the exemplary embodiments, it will be understood that the application is not limited to the exemplary embodiments. On the contrary, the application is intended to cover alternatives, modifications, equivalents, and other embodiments, which can be included within the spirit and scope of the application as defined by the appended claims.

[0031] Exemplary embodiments of the present application will be described below with reference to the accompanying drawings. In order to easily describe the exemplary embodiments of the present application, items expressed in the drawings can be different from forms actually implemented as a schematic diagram.

[0032] Figure 1 is a schematic view showing a power transmission system of an electrically-powered four-wheel drive (E-4WD) vehicle (i.e., an electrically-powered four-wheel drive vehicle) in which a front-wheel powertrain including a front-wheel motor and a rear-wheel powertrain including a rear-wheel motor are combined, Figure 2 is a schematic view showing a configuration for regenerative braking control of an electrically-powered four-wheel drive vehicle according to various exemplary embodiments of the present application.

[0033] As Figure 1 shown, the front-wheel powertrain 100 can be configured to include an engine 110, a front-wheel motor 120, a transmission 130, an engine clutch 140, and a hybrid starter generator (HSG) 170.

[0034] The engine 110 and the front-wheel motor 120 can be connected in series to each other and can output power for vehicle travel.

[0035] The transmission 130 is connected to a rear end (output end) of the front motor 120 to shift the power of the engine 110 and the front motor 120, thereby outputting the shifted power to the front wheels 150. The transmission 130 can shift the power generated by the engine 110 and the front motor 120 according to shift gear stages to transmit the shifted power to the front wheels 150. For example, the transmission 130 can employ an automatic transmission (AT) or a dual clutch transmission (DCT).

[0036] The engine clutch 140 can be installed between the engine 110 and the front motor 120 to be engaged or disengaged. The engine clutch 140 can connect the engine 110 with the front wheels 150 to enable power transmission between the engine 110 and the front wheels 150 or disconnection. When the engine clutch 140 is engaged, the engine power is transmitted to the front wheels 150 through the transmission 130, and when the engine clutch 140 is disengaged, the engine power is disconnected and not transmitted to the transmission 130.

[0037] The hybrid starter generator 170 is an electric machine connected to the engine 110 to start the engine 110 or generate electricity using residual power of the engine 110. The hybrid starter generator 170 is configured as a starter motor to start the engine 110, or functions as a generator to selectively recover rotational energy of the engine 110 after the engine 110 is started.

[0038] The front motor 120 and the hybrid starter generator 170 are electrically connected to the battery 160. That is, the battery 160 is connected to the front motor 120 and the hybrid starter generator 170 to perform charging and discharging. The battery 160 can discharge to the front motor 120 and the hybrid starter generator 170, or can be charged by the front motor 120 and the hybrid starter generator 170.

[0039] In addition, the rear powertrain 200 can be configured to include a rear motor 210 connected to the battery 160 to perform charging and discharging, and a reducer 220 to reduce power of the rear motor 210 to output the reduced power to the rear wheels 230. The rear motor 210 can be driven to output power for vehicle travel.

[0040] The present application can improve fuel efficiency through regenerative braking control optimized for an electrified four-wheel drive vehicle employing a powertrain configured as described above.

[0041] The control unit 10 serves as a control subject of the front motor 120, the rear motor 210, the hybrid starter generator 170, etc. at the time of regenerative braking of the electrified four-wheel drive vehicle, as Figure 2As shown, the superordinate controller 11, the motor controller 12, the battery controller 13, the brake controller 14, the transmission controller 15, the engine controller 16, and the like can be employed.

[0042] Here, the motor controller 12, the battery controller 13, the brake controller 14, the transmission controller 15, and the engine controller 16 can be referred to as subordinate controllers.

[0043] The subordinate controllers 12, 13, 14, 15, 16 can provide various information to the superordinate controller 11, or receive a command from the superordinate controller 11 to perform a control corresponding to the respective command. Further, the superordinate controller 11 can command any one of the subordinate controllers 12, 13, 14, 15, 16 based on information received from one or more of the subordinate controllers 12, 13, 14, 15, 16.

[0044] The motor controller 12 can receive a command from the superordinate controller 11 to control the overall operation of the motor 120, 210 and the hybrid starter generator 170. For example, the motor controller 12 can control the power generation operation of the motor 120, 210 and the hybrid starter generator 170 according to the command from the superordinate controller 11.

[0045] The battery controller 13 can receive a command from the superordinate controller 11 to control the charge and discharge of the battery 160. Further, the battery controller 13 can transmit the battery power information currently chargeable to the superordinate controller 11.

[0046] The brake controller 14 can receive a command from the superordinate controller 11 to distribute a brake force or control hydraulic braking of a brake system. For example, the brake controller 14 can command hydraulic braking of the brake system that ensures a brake force by hydraulic pressure, and control the amount of hydraulic braking. The brake system can employ an active hydraulic booster (AHB) or the like, which is an electrified hydraulic booster.

[0047] Further, the brake controller 14 can divide the amount of brake required by the driver into the amount of hydraulic braking and the amount of regenerative braking. The amount of hydraulic braking is the amount of braking ensured by hydraulic braking at the time of braking, and the amount of regenerative braking is the amount of braking ensured by regenerative braking at the time of braking. At this time, the amount of hydraulic braking can be referred to as the amount of hydraulic braking demand, and the amount of regenerative braking can also be referred to as the amount of regenerative braking allowance.

[0048] The engine controller 16 can transmit information such as the amount of engine friction to the superordinate controller 11.

[0049] The control unit 10 of the electric four-wheel drive vehicle can perform regenerative braking control optimized for the electric four-wheel drive vehicle through cooperative control of the upper controller 11 and the lower controllers 12, 13, 14, 15, and 16.

[0050] The control unit 10 can perform regenerative braking control different from conventional regenerative braking control not only with the front motor 120 but also with the rear motor 210 and the hybrid starter generator 170. That is, when the driver requests braking, the control unit 10 can perform regenerative braking control optimized by combining rear regenerative braking, front regenerative braking, and HSG regenerative braking.

[0051] As is well known, regenerative braking refers to the operation of the motor as a generator by the residual driving force of the wheels at the time of braking, thereby charging the battery. Regenerative braking can regenerate the battery by charging the residual energy of the wheels not required for running into the battery at the time of braking, thereby improving fuel efficiency.

[0052] Here, the rear regenerative braking is charging the residual driving force of the rear wheels 230 into the battery 160 by the rear motor 210 at the time of braking, and the front regenerative braking is charging the residual driving force of the front wheels 150 into the battery 160 by the front motor 120 at the time of braking. In addition, the HSG regenerative braking is charging the residual driving force of the front wheels 150 into the battery 160 by the hybrid starter generator 170 at the time of braking.

[0053] The rear powertrain 200 does not use a transmission, and thus has higher power transmission efficiency than the front powertrain 100. Therefore, the power transmission efficiency of the rear regenerative braking is higher than that of the front regenerative braking, and it is preferable to perform the rear regenerative braking in preference to the front regenerative braking.

[0054] Here, the regenerative braking control method of the electric four-wheel drive vehicle according to various exemplary embodiments of the present application will be further described with reference to Figure 3 , Figure 4 , Figure 5 and Figure 6

[0055] Figure 3 is a flowchart showing, as an example, the regenerative braking control process of the electric four-wheel drive vehicle according to various exemplary embodiments of the present application, Figure 4 is a schematic diagram showing the energy transmission path at the time of rear regenerative braking of the electric four-wheel drive vehicle according to various exemplary embodiments of the present application, Figure 5 is a schematic diagram showing the energy transmission path at the time of front and rear regenerative braking of the electric four-wheel drive vehicle according to various exemplary embodiments of the present application, Figure 6 ​is a schematic diagram showing an energy transmission path at the time of HSG regenerative braking of an electrically powered four-wheel drive vehicle according to various exemplary embodiments of the present application.

[0056] As shown in Figure 3 the regenerative braking control process first determines whether braking is started during vehicle travel (S100), and starts rear-wheel regenerative braking control at the time of starting braking (S110).

[0057] The control unit 10 can determine whether the brake pedal is operated to determine whether braking is started. In addition, the control unit 10 can determine the total braking amount (i.e., the amount of braking required by the driver) that changes according to the stroke of the brake pedal.

[0058] If the driver depresses the brake pedal, a signal of the pedal force generating device 18 operated according to the stroke of the brake pedal can be input to the brake controller 14. The brake controller 14 can determine the total braking amount that changes according to the stroke of the brake pedal based on the signal from the pedal force generating device 18.

[0059] For example, the pedal force generating device can be a pedal simulator that generates pedal force according to the stroke of the brake pedal.

[0060] When the brake pedal is operated, the control unit 10 can determine the torque configured to charge the battery 160 in real time using the motor 120, 210 and the hybrid starter generator 170 (i.e., the currently chargeable torque) and the power configured to charge the battery 160 in real time (i.e., the currently chargeable power). The control unit 10 can determine the possible regenerative braking amount based on the currently chargeable torque and the currently chargeable power.

[0061] The motor controller 12 can determine the currently chargeable torque based on information such as the real-time driving force of the wheels and the stroke of the brake pedal, and the battery controller 13 can determine the currently chargeable power based on information such as the state of charge (SOC) value of the battery 160. The upper controller 11 can determine the possible regenerative braking amount based on the currently chargeable torque information received from the motor controller 12 and the currently chargeable power information received from the battery controller 13.

[0062] At this time, the transmission controller 15 can request to stop regenerative braking during shifting according to the travel mode of the vehicle. For example, the transmission controller 15 can request the upper controller 11 to limit regenerative braking when shifting to a hill climb mode, a sport mode, etc. When a request to limit regenerative braking is received from the transmission controller 15, the upper controller 11 does not determine the possible regenerative braking amount or can determine it as "0".

[0063] When the current chargeable torque is determined, the motor controller 12 can transmit maximum torque information related to the front motor 120, the rear motor 210, and the hybrid starter generator 170 to the upper controller 11.

[0064] Further, when the upper controller 11 transmits the possible regenerative braking amount information to the brake controller 14, the brake controller 14 can divide the driver required braking amount into a regenerative braking allowable amount and a hydraulic braking demand amount. That is, the brake controller 14 can determine the regenerative braking allowable amount based on the driver required braking amount and the possible regenerative braking amount.

[0065] The possible regenerative braking amount refers to energy that can be recovered from the wheels using the front motor 120, the rear motor 210, and the hybrid starter generator 170 at the time of braking, and the regenerative braking allowable amount refers to energy recovered by regenerative braking of the driver required braking amount.

[0066] The upper controller 11 first determines the rear regenerative braking required amount based on the regenerative braking allowable amount information received from the brake controller 14. The rear regenerative braking required amount can be determined to be below the regenerative braking allowable amount, and can be determined to be a maximum braking amount (i.e., a maximum power of the rear motor) that can be allocated to the rear motor 210.

[0067] As described above, in S110, when the rear regenerative braking control is started, the upper controller 11 determines the rear regenerative braking required amount, determines the rear regenerative braking torque based on the rear regenerative braking required amount, and commands the torque output of the rear motor 210 based on the rear regenerative braking torque. The rear regenerative braking torque can be determined by converting the rear regenerative braking required amount into a torque value.

[0068] The upper controller 11 transmits the rear regenerative braking torque information to the motor controller 12, and the motor controller 12 controls the output of the rear motor 210 according to the command from the upper controller 11. At this time, the rear motor 210 outputs the rear regenerative braking torque, and the battery 160 is charged with power corresponding to the output of the rear motor 210. Thus, as shown in FIG. 2, the remaining driving force of the rear wheel 230 can be charged into the battery 160 through the rear motor 210. Figure 4

[0069] Since the rear motor 210 is connected to the speed reducer 220 without being connected to the transmission 130, the loss at the time of power transmission of the rear motor 210 is smaller than that of the front motor 120, and thus it is very advantageous in terms of power transmission efficiency if regenerative braking is performed using the rear motor 210. Therefore, it is also advantageous in terms of improving fuel efficiency to perform regenerative braking using the rear motor 210 before performing regenerative braking using the front motor 120.

[0070] ​However, if the rear wheel regenerative braking is first started only at the time of braking, there is a problem of wheel slip. Therefore, when the rear wheel regenerative braking is started, it is necessary to determine whether the rear wheel 230 has slipped according to a speed difference between the front wheel 150 and the rear wheel 230 (hereinafter referred to as "wheel speed difference") to secure braking stability. When the rear wheel 230 slips, it can cause a vehicle accident, and thus it is preferable to determine whether the slip has occurred using the wheel speed difference.

[0071] To determine whether the slip has occurred, the wheel speed difference can be compared with a predetermined first reference value (a) (S120), and when the wheel speed difference is the first reference value (a) or more, it can be determined that the rear wheel 230 has slipped or it can be predicted that the rear wheel 230 will slip.

[0072] The brake controller 14 can determine the difference between the front wheel speed and the rear wheel speed to transmit the determined result to the upper controller 11, and the upper controller 11 can predict and determine whether the rear wheel 230 has slipped based on the wheel speed difference information received from the brake controller 14.

[0073] Here, the first reference value (a) can be determined as a value obtained through previous experiments, evaluations, or the like, and is set as a value to predict or determine the occurrence of wheel slip. The first reference value (a) can be set as a value less than a slip determination reference value generally applied when only the front wheel regenerative braking is performed, for example, the first reference value (a) can be determined as a value less than 2.5 kph.

[0074] In addition, the first reference value (a) is preferably determined as a value configured to determine whether the wheel has slipped before a system such as an electronic stability control system (ESC) for vehicle attitude control needs to work due to wheel slip.

[0075] In S120, when it is determined that the speed difference between the front wheel 150 and the rear wheel 230 is the first reference value (a) or more, the front wheel regenerative braking control is started to reduce the wheel slip (S130). That is, when the rear wheel regenerative braking is started and the speed difference between the front wheel 150 and the rear wheel 230 is the first reference value (a) or more, the amount required for the front wheel regenerative braking is allocated to the front wheel motor 120, thereby starting the front wheel regenerative braking.

[0076] At this time, the amount required for the front wheel regenerative braking can be determined based on the speed difference between the front wheel 150 and the rear wheel 230 to release the slip of the rear wheel 230.

[0077] The upper controller 11 can determine the front wheel regenerative braking required amount based on the wheel speed difference information transmitted from the brake controller 14. The upper controller 11 can determine the front wheel regenerative braking torque based on the front wheel regenerative braking required amount, and command the torque output of the front wheel motor 120 based on the front wheel regenerative braking torque.

[0078] The upper controller 11 can transmit the front wheel regenerative braking torque information to the motor controller 12, and the motor controller 12 can control the output of the front wheel motor 120 according to the command of the upper controller 11. At this time, the front wheel motor 120 can output the front wheel regenerative braking torque, and the battery 160 can be charged with power corresponding to the output of the front wheel motor 120. Therefore, as shown in FIG. 1B, the remaining driving force of the front wheel 150 can be charged into the battery 160 through the front wheel motor 120. Figure 5

[0079] When the front wheel regenerative braking and the rear wheel regenerative braking are allocated, if a speed difference occurs between the front wheel 150 and the rear wheel 230, there is a problem that slippage occurs. Therefore, by determining the front wheel regenerative braking required amount based on the speed difference between the front wheel 150 and the rear wheel 230, it is possible to secure braking stability and improve fuel efficiency.

[0080] In addition, when the front wheel regenerative braking is started, it is preferable to reduce the regenerative braking torque of the rear wheel motor 210 allocated to the regenerative braking torque of the front wheel motor 120. That is, when the front wheel regenerative braking is started, it is preferable to subtract the determined front wheel regenerative braking required amount from the rear wheel regenerative braking required amount. The above is to make the sum of the front wheel regenerative braking required amount and the rear wheel regenerative braking required amount not exceed the regenerative braking allowable amount, because, if it is determined that slippage occurs based on the wheel speed difference, the front wheel regenerative braking is performed for braking stability, regardless of the regenerative braking allowable amount.

[0081] That is, by subtracting the increased front wheel regenerative braking required amount from the rear wheel regenerative braking required amount when the front wheel regenerative braking is started, it is possible to prevent the sum of the front wheel regenerative braking required amount and the rear wheel regenerative braking required amount from exceeding the regenerative braking allowable amount.

[0082] After the front wheel regenerative braking is started in S130, in order to determine whether the slippage of the rear wheel 230 is reduced and the braking is stable, the speed difference between the front wheel 150 and the rear wheel 230 is compared with a predetermined second reference value (β) (S140).

[0083] When the speed difference between the front wheel 150 and the rear wheel 230, that is, the wheel speed difference, is greater than the second reference value (β), it can be determined that the slippage of the rear wheel 230 has not been resolved, and when the wheel speed difference is the second reference value (β) or less, it can be determined that the slippage of the rear wheel 230 is resolved.

[0084] ​Therefore, when the wheel speed difference is greater than the second reference value (β), the amount required for the front wheel regenerative braking and the amount required for the rear wheel regenerative braking are maintained as they are, and when the wheel speed difference decreases and becomes below the second reference value (β), the amount required for the front wheel regenerative braking is maintained as it is, and the amount required for the rear wheel regenerative braking is determined and allocated based on the regenerative braking allowance and the amount required for the front wheel regenerative braking (S150).

[0085] For example, if the sum of the amount required for the front wheel regenerative braking and the amount required for the rear wheel regenerative braking is less than the regenerative braking allowance when the wheel speed difference becomes the second reference value (β), the amount required for the front wheel regenerative braking can be maintained, and the amount required for the rear wheel regenerative braking can be increased so that the sum of the amount required for the front wheel regenerative braking and the amount required for the rear wheel regenerative braking becomes the regenerative braking allowance. That is, when the wheel speed difference becomes below the second reference value (β), the value obtained by subtracting the amount required for the front wheel regenerative braking from the regenerative braking allowance can be determined as the amount required for the rear wheel regenerative braking.

[0086] Further, if the regenerative braking allowance decreases, the amount required for the front wheel regenerative braking and the amount required for the rear wheel regenerative braking decrease at the same time while the ratio of the amount required for the front wheel regenerative braking to the amount required for the rear wheel regenerative braking is maintained as it is. The ratio of the amount required for the front wheel regenerative braking to the amount required for the rear wheel regenerative braking is the ratio when the wheel speed difference becomes the second reference value (β).

[0087] Here, the second reference value (β) can be determined as a value obtained through previous experiments, evaluations, etc., and the second reference value (β) is determined as a value smaller than the first reference value (α). Further, in order to prevent the rear wheel 230 from slipping again during the current regenerative braking, the second reference value (β) is preferably set to a value greater than the first reference value (α) by a predetermined value or more. Further, the second reference value (β) is preferably set to a value greater than the speed measurement error of the front wheel 150 and the rear wheel 230, and the speed measurement error is about 0.5 kph. For example, when the second reference value (β) is set mainly for fuel efficiency, the speed measurement error can be set to 1 kph to 1.5 kph.

[0088] Meanwhile, as a result of comparing the speed difference between the front wheel 150 and the rear wheel 230 with the first reference value (α) in S120, when the speed difference between the front wheel 150 and the rear wheel 230 is less than the first reference value (α), that is, when it is determined that the rear wheel 230 does not slip, the maximum power of the rear motor is compared with the regenerative braking allowance (S160). At this time, the regenerative braking allowance can be converted into a power value and then compared with the maximum power of the rear motor. The maximum power of the rear motor is the maximum power that can be output from the rear motor 210 to charge the battery 160.

[0089] As a result of the comparison in S160, when the maximum power of the rear motor is greater than the regenerative braking allowance amount, the regenerative braking allowance amount can be satisfied by the rear wheel regenerative braking alone, and thus the rear wheel regenerative braking alone can be continued.

[0090] Further, as a result of the comparison in S160, if the maximum power of the rear motor is less than the regenerative braking allowance amount, the regenerative braking allowance amount cannot be satisfied by the rear wheel regenerative braking alone, and thus the front wheel regenerative braking is started. At this time, a value obtained by subtracting the amount of rear wheel regenerative braking required from the regenerative braking allowance amount (regenerative braking allowance amount - amount of rear wheel regenerative braking required) is determined as the amount of front wheel regenerative braking required (S170).

[0091] After the front wheel regenerative braking is started, a value obtained by adding the amount of front wheel regenerative braking executed to the amount of rear wheel regenerative braking executed (amount of front wheel regenerative braking executed + amount of rear wheel regenerative braking executed) is compared with the regenerative braking allowance amount (S180).

[0092] When the sum of the amount of front wheel regenerative braking executed and the amount of rear wheel regenerative braking executed is greater than the regenerative braking allowance amount, the amount of rear wheel regenerative braking required and the amount of front wheel regenerative braking required are redistributed. When the sum of the amount of front wheel regenerative braking executed and the amount of rear wheel regenerative braking executed is equal to or less than the regenerative braking allowance amount, that is, when the regenerative braking allowance amount is greater than the sum of the amount of front wheel regenerative braking executed and the amount of rear wheel regenerative braking executed, it is determined whether the engine clutch 140 can be closed to start the HSG regenerative braking.

[0093] In order for the engine clutch 140 to perform the closing operation, the rotational speed of the front motor 120 needs to be greater than the lowest controllable rotational speed of the engine 110 (hereinafter referred to as "lowest control rotational speed").

[0094] When the closing condition of the engine clutch 140 is satisfied, that is, when the rotational speed of the front motor 120 is greater than the lowest control rotational speed of the engine 110, the engine clutch 140 is closed to connect the hybrid starter generator 170 to the front wheel 150, and thus power transmission is achieved (S190). When the engine clutch 140 is closed, engine fuel supply is stopped (S200) to stop the drive of the engine 110.

[0095] That is, when the regenerative braking allowance amount is greater than the sum of the amount of front wheel regenerative braking executed and the amount of rear wheel regenerative braking executed, and the engine clutch 140 is closed, the fuel supply to the engine 110 is stopped and the HSG regenerative braking control is started.

[0096] Since the engine 110 is installed between the front wheels 150 and the HSG 170, and the engine 110 operates as a load when the HSG regenerative braking is performed, the amount of engine friction is considered to determine the amount required for the HSG regenerative braking. The value obtained by subtracting the amount of front wheel regenerative braking execution, the amount of rear wheel regenerative braking execution, and the amount of engine friction from the amount of regenerative braking allowance as expressed in Equation 1 below can be determined as the amount required for the HSG regenerative braking (S210).

[0097] Equation 1: Amount required for HSG regenerative braking = Amount of regenerative braking allowance - Amount of front wheel regenerative braking execution - Amount of rear wheel regenerative braking execution - Amount of engine friction.

[0098] Here, the value obtained by multiplying the engine friction (i.e., engine friction torque) by the engine rotational speed (engine friction x engine rotational speed) can be determined as the amount of engine friction. The engine rotational speed is the rotational speed applied to the engine 110 when the HSG outputs the HSG regenerative braking torque.

[0099] The upper controller 11 can determine the HSG output torque (i.e., HSG regenerative braking torque) for charging the battery 160 based on the amount required for the HSG regenerative braking determined as described above. The upper controller 11 can determine the HSG regenerative braking torque by converting the amount required for the HSG regenerative braking into a torque value, and command the motor controller 12 to perform the power generation operation of the HSG 170. At this time, the motor controller 12 can command the output of the torque (HSG regenerative braking torque) to the HSG 170 according to the command from the upper controller 11.

[0100] As shown in FIG. 2, if the HSG 170 performs the power generation operation, i.e., if the HSG 170 outputs the HSG regenerative braking torque, the remaining driving force of the front wheels 150 can be charged into the battery 160 through the HSG 170. Figure 6

[0101] After the amount required for the HSG regenerative braking is determined in S210, the total amount of regenerative braking execution is compared with the amount of regenerative braking allowance (S220).

[0102] The total amount of regenerative braking execution refers to the braking energy that basically acts on the wheels when the regenerative braking is performed using the front motor 120, the rear motor 210, and the HSG 170, and can be different from the amount of regenerative braking allowance. The value obtained by adding the amount of front wheel regenerative braking execution, the amount of rear wheel regenerative braking execution, the amount of HSG regenerative braking execution, and the amount of engine friction can be determined as the total amount of regenerative braking execution.

[0103] ​The front wheel regenerative braking execution amount refers to the braking energy actually transmitted to the front wheel 150 and acting on the front wheel 150 when the front wheel motor 120 outputs the front wheel regenerative braking torque, the rear wheel regenerative braking execution amount refers to the braking energy actually transmitted to the rear wheel 230 and acting on the rear wheel 230 when the rear wheel motor 210 outputs the rear wheel regenerative braking torque, and the HSG regenerative braking execution amount refers to the braking energy actually transmitted to the front wheel 150 and acting on the front wheel 150 when the hybrid starter generator 170 outputs the HSG regenerative braking torque.

[0104] Therefore, the front wheel regenerative braking execution amount can be different from the front wheel regenerative braking required amount, the rear wheel regenerative braking execution amount can be different from the rear wheel regenerative braking required amount, and the HSG regenerative braking execution amount can be different from the HSG regenerative braking required amount.

[0105] For example, according to the pre-determination, the upper controller 11 can determine the front wheel regenerative braking execution amount based on the front wheel regenerative braking torque, determine the rear wheel regenerative braking execution amount based on the rear wheel regenerative braking torque, and determine the HSG regenerative braking execution amount based on the HSG regenerative braking torque.

[0106] The upper controller 11 can determine the regenerative braking execution total amount to transmit the determined result to the brake controller 14, and the brake controller 14 can determine the hydraulic braking amount again based on the regenerative braking execution total amount information received from the upper controller 11.

[0107] As a result of comparing the regenerative braking execution total amount with the regenerative braking allowable amount in S220, when the regenerative braking execution total amount is less than the regenerative braking allowable amount, the hydraulic braking amount is determined and allocated again. At this time, a value obtained by subtracting the regenerative braking execution total amount from the driver required braking amount (driver required braking amount - regenerative braking execution total amount) can be determined as the hydraulic braking amount (S230).

[0108] The brake controller 14 can control the hydraulic braking of the brake system based on the determined hydraulic braking amount.

[0109] As described above, the present application can prioritize the rear wheel regenerative braking when the vehicle starts braking, and if there is a problem of slipping due to the prioritization of the rear wheel regenerative braking, the front wheel regenerative braking is performed to remove the slipping, thereby ensuring braking stability while improving fuel efficiency.

[0110] In addition, if the regenerative braking allowable amount is not satisfied when the rear wheel regenerative braking is first performed, the present application can further perform the HSG regenerative braking in addition to the front wheel regenerative braking, thereby maximizing the effect of improving fuel efficiency through regenerative braking.

[0111] Additionally, the terms "controller," "control unit," or "control device" refer to a hardware device including a memory and a processor configured to execute one or more steps interpreted as an algorithmic structure. The memory stores the algorithmic steps, and the processor executes the algorithmic steps to perform one or more processes of methods according to various exemplary embodiments of the invention. A controller according to an exemplary embodiment of the invention can be implemented using non-volatile memory and a processor configured to store algorithms for controlling the operation of various components of a vehicle or data regarding software commands for executing the algorithms, the processor being configured to perform the aforementioned operations using the data stored in the memory. The memory and processor can be separate chips. Alternatively, the memory and processor can be integrated into a single chip. The processor can be implemented as one or more processors.

[0112] The controller or control unit may be at least one microprocessor operated by a predetermined program, which may include a series of commands for performing the methods included in the various exemplary embodiments of the present invention described above.

[0113] The aforementioned invention can also be implemented as computer-readable code on a computer-readable recording medium. A computer-readable recording medium is any data storage device capable of storing data that can subsequently be read by a computer. Examples of computer-readable recording media include: hard disk drives (HDDs), solid-state drives (SSDs), silicon disk drives (SDDs), read-only memory (ROM), random access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, etc., and are implemented as carrier waves (e.g., transmitted via the Internet).

[0114] In various exemplary embodiments of the present invention, each of the above operations can be performed by a controller, and the controller can consist of multiple controllers or an integrated single controller.

[0115] For ease of interpretation and precise definition of the appended claims, the terms “upper,” “lower,” “inner,” “outer,” “above,” “below,” “upward,” “downward,” “front,” “back,” “behind,” “inner side,” “outer side,” “inward,” “outer,” “internal,” “external,” “inner,” “outer,” “internal,” “external,” “forward,” and “backward” are used to describe features of the exemplary embodiments with reference to the positions of these features shown in the accompanying drawings. It will be further understood that the term “connection” or its derivatives refer to both direct and indirect connections.

[0116] The foregoing description of specific exemplary embodiments of the application is presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the application to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain the principles of the application and its practical application to thereby enable others skilled in the art to best utilize the application and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the application be defined by the claims appended hereto and their equivalents.

Claims

1. A regenerative braking control device for a vehicle, the regenerative braking control device comprising: a front wheel powertrain including a first element including an engine, a front motor, an engine clutch, a hybrid starter generator, and a transmission, the engine clutch being installed between the engine and the front motor, the hybrid starter generator being connected to the engine to start the engine, the transmission varying the power of the engine and the front motor to output the varied power to front wheels of the vehicle; a rear wheel powertrain including a second element including a rear motor and a reducer, the reducer reducing the power of the rear motor to output the reduced power to rear wheels of the vehicle; a battery connected to the front motor, the rear motor, and the hybrid starter generator to charge and discharge; a control unit connected to the front wheel powertrain and the rear wheel powertrain and configured to: when braking is started, allocate an amount of rear wheel regenerative braking required to the rear motor by controlling at least one of the first element of the front wheel powertrain and the second element of the rear wheel powertrain; when it is determined that the rear wheels will slip based on a speed difference between the front wheels and the rear wheels, allocate an amount of front wheel regenerative braking required to the front motor by controlling at least one of the first element of the front wheel powertrain and the second element of the rear wheel powertrain, wherein the control unit is configured to: when it is determined that the speed difference between the front wheels and the rear wheels is less than a predetermined first reference value, determine that the rear wheels will not slip; and when it is determined that the speed difference between the front wheels and the rear wheels is greater than or equal to the first reference value, determine that the rear wheels will slip, thereby performing front wheel regenerative braking control.

2. The regenerative braking control device for a vehicle according to claim 1, the control unit is configured to: when it is determined that the rear wheels will not slip based on the speed difference between the front wheels and the rear wheels, allocate the amount of front wheel regenerative braking required to the front motor if a maximum power of the rear motor is less than a regenerative braking allowance amount determined based on an amount of braking required by a driver. wherein 3. The regenerative braking control device for a vehicle according to claim 1, the control unit is configured to: when it is determined that the rear wheels will slip, determine the amount of front wheel regenerative braking required based on the speed difference between the front wheels and the rear wheels. wherein, 4. The regenerative braking control device for a vehicle according to claim 1, the control unit is configured to: when it is determined that the rear wheels will slip, reduce the amount of rear wheel regenerative braking required allocated to the rear motor from the amount of front wheel regenerative braking required allocated to the front motor. wherein 5. The regenerative braking control device for a vehicle according to claim 1, the control unit is configured to: when the amount of front wheel regenerative braking required is allocated to the front motor, and then it is determined that the rear wheels are relieved from slipping based on the speed difference between the front wheels and the rear wheels, maintain the amount of front wheel regenerative braking required, and determine the amount of rear wheel regenerative braking required as a value obtained by subtracting the amount of front wheel regenerative braking required from a regenerative braking allowance amount. wherein 6. The regenerative braking control device for a vehicle according to claim 5, ​ wherein The control unit is configured to determine that the rear wheel is not slipping when the speed difference between the front wheel and the rear wheel is determined to be less than or equal to a second reference value, the second reference value being smaller than the first reference value.

7. The regenerative braking control device for a vehicle according to claim 2, wherein The control unit is configured to determine the amount of regenerative braking required for the front wheel as a value obtained by subtracting the amount of regenerative braking required for the rear wheel from the regenerative braking allowance amount when it is determined that the rear wheel is not slipping.

8. The regenerative braking control device for a vehicle according to claim 7, wherein The control unit is configured to distribute the amount of regenerative braking required for the hybrid starter generator to the hybrid starter generator if it is determined that the regenerative braking allowance amount is greater than the sum of the amount of regenerative braking executed for the rear wheel and the amount of regenerative braking executed for the front wheel when it is determined that the rear wheel is not slipping.

9. The regenerative braking control device for a vehicle according to claim 8, wherein The amount of regenerative braking required for the hybrid starter generator is determined as a value obtained by subtracting the amount of regenerative braking executed for the front wheel, the amount of regenerative braking executed for the rear wheel, and the amount of engine friction from the regenerative braking allowance amount.

10. The regenerative braking control device for a vehicle according to claim 8, wherein, The control unit is configured to execute the regenerative braking control of the hybrid starter generator using the hybrid starter generator in a state where the engine clutch is locked and the engine fuel supply is stopped.

11. A method of controlling a regenerative braking control device for a vehicle, the method comprising: distributing, by a controller, an amount of regenerative braking required for a rear wheel motor to a rear wheel when braking is started; distributing an amount of regenerative braking required for a front wheel to a front wheel motor when it is determined that the rear wheel of the vehicle will slip according to a speed difference between the front wheel and the rear wheel of the vehicle, wherein the regenerative braking control device includes: a front wheel powertrain including a first element including an engine, a front wheel motor, an engine clutch installed between the engine and the front wheel motor, a hybrid starter generator connected to the engine to start the engine, and a transmission that changes the power of the engine and the front wheel motor to output the changed power to a front wheel of the vehicle; a rear wheel powertrain including a second element including a rear wheel motor and a reducer that reduces the power of the rear wheel motor to output the reduced power to a rear wheel of the vehicle; and a control unit configured to control at least one of the first element of the front wheel powertrain and the second element of the rear wheel powertrain, wherein the control unit is configured to determine that the rear wheel will not slip when the speed difference between the front wheel and the rear wheel is determined to be less than a predetermined first reference value, and to determine that the rear wheel will slip when the speed difference between the front wheel and the rear wheel is determined to be greater than or equal to the first reference value, thereby executing a front wheel regenerative braking control.

12. The method according to claim 11, wherein The control unit is configured to, when it is determined from the speed difference between the front wheels and the rear wheels that the rear wheels are not slipping, allocate the amount of regenerative braking required for the front wheels to the front motor if the maximum power of the rear motor is less than the amount of regenerative braking allowed determined from the amount of braking required by the driver.

13. The method of claim 12, wherein, When the maximum power of the rear motor is less than the amount of regenerative braking allowed, the value obtained by subtracting the amount of regenerative braking required for the rear wheels from the amount of regenerative braking allowed is determined as the amount of regenerative braking required for the front wheels.

14. The method of claim 13, wherein, When the sum of the amount of regenerative braking executed for the front wheels and the amount of regenerative braking executed for the rear wheels is less than or equal to the amount of regenerative braking allowed and the rotational speed of the front motor is greater than the minimum control rotational speed of the engine, the control unit locks the engine clutch to connect the hybrid starter generator to the front wheels.

15. The method of claim 14, wherein, The value obtained by subtracting the amount of regenerative braking executed for the front wheels, the amount of regenerative braking executed for the rear wheels, and the amount of engine friction from the amount of regenerative braking allowed is determined as the amount of regenerative braking required for the hybrid starter generator.

16. The method according to claim 12, When the amount of regenerative braking required for the front wheels is allocated to the front motor and it is then determined from the speed difference between the front wheels and the rear wheels that the rear wheels are not slipping, the amount of regenerative braking required for the front wheels is maintained, and the amount of regenerative braking required for the rear wheels is determined as the value obtained by subtracting the amount of regenerative braking required for the front wheels from the amount of regenerative braking allowed.

17. The method according to claim 16, wherein The control unit is configured to determine that the rear wheels are not slipping when it is determined that the speed difference between the front wheels and the rear wheels is less than or equal to a reference value.

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