Device and method for controlling the drive of an electrically driven four-wheel drive vehicle

Abstract

An apparatus for controlling an electric four-wheel drive (E-4WD) of a vehicle includes a first power train for front wheels, wherein the first power train includes an engine and a front motor, and a second power train for rear wheels, wherein the second power train includes a rear motor. The apparatus provides a rear motor drive mode, a front motor drive mode, a combined drive mode in which the front motor and the rear motor are driven, and an engine-on mode according to a driver demand power of the vehicle, thereby improving fuel efficiency of the vehicle.

Description

TECHNICAL FIELD

[0001] The present invention relates to an apparatus and method for controlling an electric four-wheel drive (E-4WD) vehicle. More particularly, the present invention relates to an apparatus and method for controlling driving of an E-4WD vehicle in which an engine and a front motor are connected to front wheels, and a rear motor is connected to rear wheels. BACKGROUND

[0002] The statements in this section merely provide background information related to the present invention and can not constitute prior art.

[0003] As is well known, in hybrid vehicles, electric vehicles, hydrogen fuel cell vehicles, and the like, an electric motor is provided as a running drive source, and these vehicles are referred to as electric vehicles.

[0004] As an example of a four-wheel drive (4WD) powertrain of an electric vehicle, an electric vehicle applies a powertrain in which an engine and / or a front motor are connected to front wheels, and a rear motor, which is smaller than the front motor, is connected to rear wheels.

[0005] In one form, the 4WD powertrain can provide a main drive source of the vehicle by the engine and the front motor connected to the front wheels, and provide an auxiliary drive source by the rear motor connected to the rear wheels. Since an optimized drive control method for running of the vehicle has not been established, and the rear motor maintains a limited drive level in terms of drive assistance, it is desirable to apply a more effective drive control method.

[0006] In another form, when a drive force loss occurs due to operation of the engine during shifting of the transmission while running, the 4WD powertrain uses the engine connected to the front wheels as a main drive source of running of the vehicle, and the rear motor connected to the rear wheels as a secondary drive source. The rear motor operates to compensate for the loss of drive force. SUMMARY

[0007] In one aspect, the present invention provides an apparatus and method for controlling driving of an electric four-wheel drive (E-4WD) vehicle, which drives controls a 4WD powertrain in which an engine and a front motor are connected to front wheels, and a rear motor is connected to rear wheels, by respectively applying a rear motor drive control mode, a front motor drive control mode, a four motor drive control mode, and an engine-on control mode, thereby achieving improvement in fuel efficiency.

[0008] The objectives of the present application are not limited to the above-mentioned objectives, and other objectives of the present application not mentioned can be understood from the following description, and will also be obvious to those skilled in the art from the form of the present application. In addition, the objectives of the present application can be achieved by the means described in the appended claims and combinations thereof.

[0009] In an exemplary form, the present application provides an apparatus for controlling driving of an E-4WD vehicle, comprising: a first powertrain for front wheels, including: an engine, a front wheel motor, an engine clutch arranged between the engine and the front wheel motor and configured to selectively transmit power of the engine, and a transmission configured to shift power of the engine and power of the front wheel motor and output the shifted power to the front wheels; a second powertrain for rear wheels, including: a rear wheel motor, and a reducer configured to reduce power of the rear wheel motor and output the reduced power to the rear wheels; a battery connected to the front wheel motor and the rear wheel motor for chargeable and dischargeable; and a controller configured to: when a driver demand power is less than a sum of available power of the front wheel motor and available power of the rear wheel motor, perform control to selectively drive the front wheel motor and the rear wheel motor according to power transmission efficiency of the front wheel motor and the rear wheel motor, during driving of the front wheel motor or the rear wheel motor, when the driver demand power is greater than the available power of the front wheel motor or the available power of the rear wheel motor, the controller drives the front wheel motor and the rear wheel motor together, and when the driver demand power is greater than the total available power, control to drive the engine according to engine-on.

[0010] In another exemplary form, the present application provides a method of controlling driving of an electric four-wheel drive (E-4WD) vehicle, the vehicle including: a powertrain for front wheels including: an engine, a front motor, an engine clutch disposed between the engine and the front motor and configured to transmit or interrupt power of the engine, and a transmission configured to step up power of the engine and power of the front motor to output the stepped-up power to the front wheels; and a powertrain for rear wheels including: a rear motor and a reducer configured to step down power of the rear wheels and output the stepped-down power to the rear wheels, and a battery connected to the front motor and the rear motor for chargeable and dischargeable, the method including: when a driver demand power is less than total available power, selectively driving the front motor or the rear motor based on power transmission efficiency of the front motor and the rear motor; during driving of the front motor or the rear motor, when the driver demand power is greater than available power of the front motor or available power of the rear motor, driving the front motor and the rear motor together; and when the driver demand power is greater than the total available power, driving the engine.

[0011] Other aspects and exemplary forms of the present application are discussed below.

[0012] It should be understood that the term "vehicle" or "vehicular" or other similar term used herein generally includes a typical motor vehicle such as a passenger automobile, a passenger bus, a truck, a passenger vehicle including a sport utility vehicle (SUV), a passenger vehicle including various commercial vehicles, a watercraft including various boats and ships, an aircraft, and the like, and includes a hybrid vehicle, an electric vehicle, a plug-in hybrid electric vehicle, a hydrogen-powered vehicle, and other alternative fuel vehicles (e.g., a vehicle that obtains fuel from a resource other than petroleum). As referred to herein, a hybrid vehicle is a vehicle having two or more power sources, for example, a vehicle having both a gasoline power source and an electric power source.

[0013] Other applicable fields will become apparent from the description provided herein. It should be understood that the description and specific examples are merely illustrative and are not intended to limit the scope of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order that the present application can be better understood, various forms thereof will now be described, by way of example only, with reference to the accompanying drawings in which:

[0015] FIG. 1 is a block diagram illustrating power transmission of an electric four-wheel drive (E-4WD) vehicle;

[0016] FIG. 2 is a control configuration diagram illustrating a driving control method of an E-4WD vehicle according to a form of the present application.

[0017] FIG. 3 and FIG. 4 is a flowchart showing a drive control method of an E-4WD vehicle according to one form of the present application;

[0018] FIG. 5 is a power transmission block diagram showing a power transmission process in a rear wheel motor drive control mode in the drive control method of the E-4WD vehicle according to one form of the present application;

[0019] FIG. 6 is a power transmission block diagram showing a power transmission process in a front wheel motor drive control mode in the drive control method of the E-4WD vehicle according to one form of the present application;

[0020] FIG. 7 is a power transmission block diagram showing a power transmission process in a front wheel motor and rear wheel motor drive control mode in the drive control method of the E-4WD vehicle according to one form of the present application; and

[0021] FIGS. 8 to 10 is a power transmission block diagram showing a power transmission process in an engine-on control mode in the drive control method of the E-4WD vehicle according to the present application.

[0022] The accompanying drawings described herein are for purposes of illustration only and are not intended to limit the scope of the application in any way. DETAILED DESCRIPTION

[0023] The following description is merely exemplary in nature and is not intended to limit the present application, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0024] Hereinafter, forms of the present application will be described in detail with reference to the accompanying drawings.

[0025] It is to be understood that the drawings are not necessarily to scale, and that the various features are shown in slightly simplified form to illustrate the basic principles of the application. Particular design features of the application as invented herein, including for example particular dimensions, orientations, locations, and shapes, will be determined in part by the particular design application and use environment.

[0026] FIG. 1 is a block diagram showing power transmission of an electric four-wheel drive (E-4WD) vehicle in which a powertrain for front wheels having an engine and a front wheel motor is combined with a powertrain for rear wheels having a rear wheel motor, and FIG. 2 is a control configuration diagram showing a drive control method of an E-4WD vehicle according to one form of the present application. is a block diagram showing power transmission of an electric four-wheel drive (E-4WD) vehicle in which a powertrain for front wheels having an engine and a front wheel motor is combined with a powertrain for rear wheels having a rear wheel motor, and is a control configuration diagram showing a drive control method of an E-4WD vehicle according to one form of the present application.

[0027] As FIG. 1 shown, the powertrain for the front wheels includes an engine 100, a front motor 120, an engine clutch 110 disposed between the engine 100 and the front motor 120 and configured to transmit or interrupt the power of the engine 100, a transmission 130 configured to shift the power from the engine 100 and the front motor 120 and output the shifted power to front wheels 140, a hybrid starter generator (HSG) 150 connected to a crank pulley of the engine 100 and configured to perform starting of the engine 100 and generate electric power, and a battery 160 connected to the front motor 120 and the HSG 150 for chargeable and dischargeable.

[0028] The transmission 130 can employ an automatic transmission (AT) or a dual clutch transmission (DCT).

[0029] The powertrain for the rear wheels includes a rear motor 170 connected to the battery 160 for chargeable and dischargeable, and a reducer 180 configured to reduce the power of the rear motor 170 and output the reduced power to rear wheels 190.

[0030] As described above, the present contents focus on performing drive control of running of an E-4WD vehicle (in which the powertrain for the front wheels is combined with the powertrain for the rear wheels) in a rear motor drive control mode, a front motor drive control mode, a front and rear motor (four-motor) drive control mode, and an engine-on control mode, respectively, according to a required power of a driver, so that improvement of fuel efficiency can be achieved, and the marketability of the E-4WD vehicle can be improved.

[0031] As FIG. 2 shown, the control device (a control subject during drive control of running of the E-4WD vehicle) can include a high-level controller 10, an engine controller 20 configured to receive an instruction of the high-level controller 10 and control overall drive and an operating point of the engine 100, and a motor controller 30 configured to receive a torque command from the high-level controller 10 and control overall drive of the front motor 120 and the rear motor 170.

[0032] Hereinafter, a drive control method of the E-4WD vehicle according to the present application will be described with respect to various control modes.

[0033] FIG. 3 and FIG. 4 are flowcharts showing a drive control method of the E-4WD vehicle according to the present application.

[0034] Rear wheel motor drive control mode

[0035] When the driver demand power is less than the sum of the available power of the front motor 120 and the available power of the rear motor 170 (available power of the front motor 120 + available power of the rear motor 170), control for selectively driving the front motor 120 and the rear motor 170 is performed in advance according to the power transmission efficiency of the front motor 120 and the rear motor 170.

[0036] That is, the driver demand power which varies according to the amount by which the driver depresses the accelerator pedal is compared with the total available power (the sum of the available power of the front motor 120 and the available power of the rear motor 170). As a result of the comparison, when the driver demand power is less than the total available power (the sum of the available power of the front motor 120 and the available power of the rear motor 170), the front motor 120 and the rear motor 170 can be selectively driven to travel in the electric vehicle (EV) mode.

[0037] In this case, when the level of the state of charge (SOC) of the battery 160 decreases to be equal to or less than a predetermined level, since the discharge of the battery 160 should be reduced or minimized, it is desirable to limit travel in the EV mode. Therefore, it is desirable to use the factor of the respective SOC of the battery 160 to determine the front motor 120 drive only or the rear motor 170 drive only, or the engine-on time.

[0038] For reference, it is noted that the factor of the respective SOC of the battery 160 is a mappable variable item.

[0039] Therefore, the driver demand power is compared with the difference between the total available power and the factor of the respective SOC of the battery 160 ((available power of the front motor 120 + available power of the rear motor 170) - factor of the respective SOC of the battery 160) (S101). As a result of the comparison, when the driver demand power is less than the difference between the total available power and the factor of the respective SOC of the battery 160, the front motor 120 only or the rear motor 170 only can be driven to travel in the EV mode.

[0040] Otherwise, when the driver demand power is greater than the difference between the total available power and the factor of the respective SOC of the battery 160 ((available power of the front motor 120 + available power of the rear motor 170) - factor of the respective SOC of the battery 160), in order to reduce or minimize the discharge of the battery 160, it is desirable to limit travel in the EV mode, and therefore, the engine 100 is driven according to the engine-on control mode in which the battery 160 is chargeable, as described below.

[0041] In one form, the control that selectively drives the front motor 120 and the rear motor 170 includes determining whether to drive the front motor 120 or the rear motor 170 based on power transmission efficiency of the front motor 120 and the rear motor 170.

[0042] To this end, as a result of the comparison in S101, when the driver demand power is less than the difference between the total available power and the factor of each SOC of the battery 160 ((available power of the front motor 120 + available power of the rear motor 170) - factor of each SOC of the battery 160), it is desired to perform the determination of whether to drive the front motor 120 or the rear motor 170 for the travel in the EV mode. The reason for using the front motor 120 or the rear motor 170 is that which motor has better power transmission efficiency with respect to each wheel.

[0043] In this case, the power transmission efficiency of the front motor 120 is the power transmission efficiency when the power of the front motor 120 is output to the front wheel 140 through the transmission 130, and can be determined by the operating efficiency of the transmission 130, and the power transmission efficiency of the rear motor 170 is the power transmission efficiency when the power of the rear motor 170 is output to the rear wheel 190 through the reduction gear 180, and can be determined by the operating efficiency of the reduction gear 180.

[0044] Therefore, in order to determine whether to drive the front motor 120 or the rear motor 170 for the travel in the EV mode, the product of the available power of the front motor 120 and the operating efficiency of the transmission 130 (available power of the front motor 120 x operating efficiency of the transmission 130) is compared with the product of the available power of the rear motor 170 and the operating efficiency of the reduction gear 180 (available power of the rear motor 170 x operating efficiency of the reduction gear 180) (S102). As a result of the comparison, when the product of the available power of the rear motor 170 and the operating efficiency of the reduction gear 180 (available power of the rear motor 170 x operating efficiency of the reduction gear 180) is greater, only the rear motor 170 is driven to travel in the EV mode (S103).

[0045] For example, the high-level controller 10 compares the product of the available power of the front-wheel motor 120 and the work efficiency of the transmission 130 (available power of the front-wheel motor 120 x work efficiency of the transmission 130) with the product of the available power of the rear-wheel motor 170 and the work efficiency of the reduction gear 180 (available power of the rear-wheel motor 170 x work efficiency of the reduction gear 180). When the product of the available power of the rear-wheel motor 170 and the work efficiency of the reduction gear 180 (available power of the rear-wheel motor 170 x work efficiency of the reduction gear 180) is determined to be larger, the high-level controller 10 commands the motor controller 30 to execute the EV mode so that only the rear-wheel motor 170 can be driven due to the current control of the motor controller 30.

[0046] Therefore, as FIG. 5 shown, when the rear-wheel motor 170 is driven only using the power of the battery 160, the rotational force of the rear-wheel motor 170 is transmitted to the rear wheels 190 through the reduction gear 180 so that initial acceleration travel of the vehicle can be executed and the driver demand power can be satisfied by the available power of the rear-wheel motor 170.

[0047] Meanwhile, during the driving of the rear wheels 190 using the power of the rear-wheel motor 170, when the travel surface is a low-friction surface, the rear wheels 190 slip and the speed of the rear wheels 190 is abruptly increased compared to the speed of the front wheels 140 so that acceleration travel of the vehicle can not be smoothly executed and thus the travel stability of the vehicle can be reduced.

[0048] To solve the above problem, the difference between the speed of the rear wheels 190 and the speed of the front wheels 140 (speed of the rear wheels 190 - speed of the front wheels 140) is compared with the maximum reference value a (S104). As a result of the comparison, when the difference between the speed of the rear wheels 190 and the speed of the front wheels 140 is greater than the maximum reference value a, the front-wheel motor 120 is driven by increasing the drive ratio of the front-wheel motor 120 and the rear-wheel motor 170 up to a unit of 1% for a predetermined period of time (for example, 10 ms) (S105).

[0049] For example, when the high-level controller 10 compares the speed of the rear wheels 190 and the speed of the front wheels 140 and determines that the difference between the speed of the rear wheels 190 and the speed of the front wheels 140 (speed of the rear wheels 190 - speed of the front wheels 140) is greater than the maximum reference value a, the high-level controller 10 commands the motor controller 30 to drive the front-wheel motor 120 so that the front-wheel motor 120 can be driven according to the current control of the motor controller 30 to increase the drive ratio up to a unit of 1% for a predetermined period of time.

[0050] In one form, the driving of the front wheel motor 120 is performed by increasing the driving ratio of the front wheel motor 120 by a unit of up to 1% for a predetermined period (S105) until the difference between the speed of the rear wheel 190 and the speed of the front wheel 140 (speed of the rear wheel 190 - speed of the front wheel 140) is reduced to be less than the minimum reference value β.

[0051] In this case, the difference between the speed of the rear wheel 190 and the speed of the front wheel 140 (speed of the rear wheel 190 - speed of the front wheel 140) is compared with the minimum reference value β (S106). As a result of the comparison, when the difference between the speed of the rear wheel 190 and the speed of the front wheel 140 is determined to be less than the minimum reference value β, the driving ratios of the rear wheel motor 170 and the front wheel motor 120 are oppositely increased by a predetermined unit for a predetermined period for the stability of the acceleration travel of the vehicle (S107).

[0052] As described above, while satisfying the driver demand power, since only the rear wheel motor 170 is driven, the acceleration travel of the vehicle can be performed. In particular, since the rear wheel motor 170 is driven on a low friction road, the driving ratios of the front wheel motor 120 and the rear wheel motor 170 are changed so that stable vehicle acceleration can be performed.

[0053] In addition, the small rear wheel motor 170 having a capacity smaller than that of the front wheel motor 120 is used to perform travel in the EV mode for initial acceleration of the vehicle. Accordingly, improvement in fuel efficiency can be achieved.

[0054] Front wheel motor drive control mode

[0055] As described above, the driver demand power varying according to the amount by which the driver depresses the accelerator pedal is compared with the total available power (the sum of the available power of the front wheel motor 120 and the available power of the rear wheel motor 170). As a result of the comparison, when the driver demand power is less than the total available power (the sum of the available power of the front wheel motor 120 and the available power of the rear wheel motor 170), the front wheel motor 120 and the rear wheel motor 170 can be selectively driven to travel in the EV mode.

[0056] In this case, when the SOC level of the battery 160 is reduced to be equal to or less than a predetermined level, since the discharge of the battery 160 should be reduced or minimized, it is desirable to limit travel in the EV mode. Accordingly, it is desirable to determine the rear wheel motor 170 driving only or the front wheel motor 120 driving only, or the engine-on time using a factor of each SOC of the battery 160.

[0057] Therefore, the difference between the total available power and the factor of the SOC of the battery 160 ((available power of the front wheel motor 120 + available power of the rear wheel motor 170) - factor of the SOC of the battery 160) is compared with the driver demand power (S101). As a result of the comparison, when the driver demand power is smaller than the difference between the total available power and the factor of the SOC of the battery 160, only the rear wheel motor 170 or only the front wheel motor 120 can be driven to travel in the EV mode.

[0058] Subsequently, as a result of the comparison in S101, when the driver demand power is smaller than the difference between the total available power and the factor of the SOC of the battery 160 ((available power of the front wheel motor 120 + available power of the rear wheel motor 170) - factor of the SOC of the battery 160), the determination of whether to drive the front wheel motor 120 or the rear wheel motor 170 for the travel in the EV mode as described above is desired to be performed. The reason for using the front wheel motor 120 or the rear wheel motor 170 is that which motor has a better power transmission efficiency with respect to each wheel.

[0059] Therefore, in order to determine whether to drive the front wheel motor 120 or the rear wheel motor 170 for the travel in the EV mode, the product of the available power of the front wheel motor 120 and the operating efficiency of the transmission 130 (available power of the front wheel motor 120 x operating efficiency of the transmission 130) is compared with the product of the available power of the rear wheel motor 170 and the operating efficiency of the reduction gear 180 (available power of the rear wheel motor 170 x operating efficiency of the reduction gear 180) (S102). As a result of the comparison, when the product of the available power of the rear wheel motor 170 and the operating efficiency of the reduction gear 180 (available power of the rear wheel motor 170 x operating efficiency of the reduction gear 180) is small, i.e., the product of the available power of the front wheel motor 120 and the operating efficiency of the transmission 130 (available power of the front wheel motor 120 x operating efficiency of the transmission 130) is large, only the front wheel motor 120 is driven to travel in the EV mode (S108).

[0060] For example, the high-level controller 10 compares the product of the available power of the front wheel motor 120 and the operating efficiency of the transmission 130 (available power of the front wheel motor 120 x operating efficiency of the transmission 130) with the product of the available power of the rear wheel motor 170 and the operating efficiency of the reduction gear 180 (available power of the rear wheel motor 170 x operating efficiency of the reduction gear 180). When the product of the available power of the front wheel motor 120 and the operating efficiency of the transmission 130 (available power of the front wheel motor 120 x operating efficiency of the transmission 130) is determined to be large, the high-level controller 10 commands the motor controller 30 to perform the EV mode so that only the front wheel motor 120 can be driven due to the current control of the motor controller 30.

[0061] Thus, as FIG. 6 indicated, when the front wheel motor 120 is driven using only the power of the battery 160, the rotational force of the front wheel motor 120 is transmitted to the front wheel 140 through the transmission 130, so that initial acceleration running of the vehicle can be performed, and the driver demand power can be satisfied by the available power of the front wheel motor 120.

[0062] Front wheel motor and rear wheel motor drive control mode

[0063] The front wheel motor and rear wheel motor driving control mode refers to a mode in which the front wheel motor 120 and the rear wheel motor 170 are driven together when the available power of the front wheel motor 120 or the available power of the rear wheel motor 170 cannot satisfy the driver demand power.

[0064] In other words, the front wheel motor and rear wheel motor driving control mode refers to a mode in which the front wheel motor 120 is driven together while the rear wheel motor 170 is driven, and the rear wheel motor 170 is driven together while the front wheel motor 120 is driven, when the available power of the front wheel motor 120 or the available power of the rear wheel motor 170 cannot satisfy the driver demand power.

[0065] When stable vehicle acceleration is performed due to driving only the rear wheel motor 170, that is, when the difference between the speed of the rear wheel 190 and the speed of the front wheel 140 (speed of the rear wheel 190 - speed of the front wheel 140) is compared with the maximum reference value a (S104), and as a result of the comparison, when the difference between the speed of the rear wheel 190 and the speed of the front wheel 140 (speed of the rear wheel 190 - speed of the front wheel 140) remains less than the maximum reference value a, the front wheel motor 120 can be driven together with the rear wheel motor 170 according to the driver demand power.

[0066] Thus, in a state in which the difference between the speed of the rear wheel 190 and the speed of the front wheel 140 (speed of the rear wheel 190 - speed of the front wheel 140) remains less than the maximum reference value a due to driving only the rear wheel motor 170, the driver demand power is compared with the available power of the rear wheel motor 170 (S112), and as a result of the comparison, when the driver demand power is large, since the driver demand power cannot be satisfied only by the available power of the rear wheel motor 170, the front wheel motor 120 is driven together with the rear wheel motor 170 (S113).

[0067] For example, in a state where the difference between the speed of the rear wheel 190 and the speed of the front wheel 140 (speed of the rear wheel 190 - speed of the front wheel 140) is kept to be less than the maximum reference value a, as a result of the comparison of the driver demand power with the available power of the rear wheel motor 170, when the driver demand power is large, the high-level controller 10 commands the motor controller 30 to execute the EV mode so that the drive of the front wheel motor 120 can be further executed due to the current control of the motor controller 30 (S113).

[0068] In this case, when the front wheel motor 120 is driven together with the drive of the rear wheel motor 170, the power output of the rear wheel motor 170 is the maximum available power, and the power of the front wheel motor 120 is output at a level where the driver demand power is subtracted by the power of the rear wheel motor 170 (driver demand power - power of the rear wheel motor 170).

[0069] On the contrary, when stable vehicle acceleration is executed due to the drive of the front wheel motor 120 only, the rear wheel motor 170 can be driven together according to the driver demand power.

[0070] Therefore, the driver demand power is compared with the available power of the front wheel motor 120 (S109), and, as a result of the comparison, when the driver demand power is large, the rear wheel motor 170 is driven together with the front wheel motor 120 because the driver demand power cannot be satisfied by the available power of the front wheel motor 120 only (S110).

[0071] For example, as a result of the comparison of the driver demand power with the available power of the front wheel motor 120, when the driver demand power is large, the high-level controller 10 commands the motor controller 30 to execute the EV mode so that the drive of the rear wheel motor 170 can be further executed due to the current control of the motor controller 30 (S110).

[0072] In this case, when the rear wheel motor 170 is driven together with the drive of the front wheel motor 120, the power output of the front wheel motor 120 is the maximum available power, and the power of the rear wheel motor 170 is output at a level where the driver demand power is subtracted by the power of the front wheel motor 120 (driver demand power - power of the front wheel motor 120).

[0073] As described above, when the driver demand power cannot be satisfied by the available power of the front wheel motor 120 only or by the available power of the rear wheel motor 170 only, the front wheel motor 120 is driven together with the drive of the rear wheel motor 170, and the rear wheel motor 170 is driven together with the drive of the front wheel motor 120, so that the driver demand power can be satisfied. As FIG. 7As shown, the 4WD running in which the power output of the front motor 120 to the front wheels 140 and the power output of the rear motor 170 to the rear wheels 190 are performed at the same time can be executed.

[0074] Engine-on control mode

[0075] When the driver demand power is greater than the total available power and the factor of the SOC of the battery 160 ((available power of the front motor 120 + available power of the rear motor 170) - factor of the SOC of the battery 160), the engine-on control mode refers to a mode in which the running in the EV mode is limited to reduce or minimize the discharge of the battery 160, and at the same time, the engine 100 is turned on to satisfy the driver demand power.

[0076] As described above, during the driving of the front motor 120 and / or the rear motor 170, when the level of the SOC of the battery 160 is reduced to be equal to or less than a predetermined level, it is desirable to limit the running in the EV mode to reduce or minimize the discharge of the battery 160, and thus the factor of the SOC of the battery 160 can be used to determine the engine-on time.

[0077] Therefore, as a result of the comparison between the driver demand power and the difference between the total available power and the factor of the SOC of the battery 160 ((available power of the front motor 120 + available power of the rear motor 170) - factor of the SOC of the battery 160) in S101, when the driver demand power is greater than the difference between the total available power and the factor of the SOC of the battery 160 ((available power of the front motor 120 + available power of the rear motor 170) - factor of the SOC of the battery 160), the engine 100 is turned on (S201).

[0078] In addition, after S110 (driving the rear motor 170 together with the front motor 120), or after S113 (driving the front motor 120 together with the rear motor 170), when the driver demand power is determined to be greater than the difference between the total available power and the factor of the SOC of the battery 160 ((available power of the front motor 120 + available power of the rear motor 170) - factor of the SOC of the battery 160), the engine 100 is turned on (S201).

[0079] For example, when the high-level controller 10 determines that the driver demand power is greater than the difference between the total available power and the factor of the SOC of the battery 160 ((available power of the front motor 120 + available power of the rear motor 170) - factor of the SOC of the battery 160), the engine controller 20 controls the engine to be turned on according to the command of the high-level controller 10.

[0080] In one form, the engine controller 20 controls the engine 100 to be driven at the preset optimal engine operating point for improving fuel efficiency (S202) according to the command of the high-level controller 10.

[0081] Therefore, in the state of driving the engine 100, a hybrid electric vehicle (HEV) travel mode can be realized in which the front wheel motor 120 or the rear wheel motor 170 is driven together, or the front wheel motor 120 and the rear wheel motor 170 are driven simultaneously.

[0082] In this case, when the engine 100 is driven at the preset optimal engine operating point, the driver demand power is compared with the optimal engine power at the preset optimal engine operating point (S203). As a result of the comparison, when the driver demand power is less than the optimal engine power, i.e., the optimal engine power is greater than the driver demand power, the front wheel motor 120 performs power generation for charging the battery 160 (S204).

[0083] In other words, when the optimal engine power is greater than the driver demand power, it indicates that the driver demand power can be satisfied by the optimal engine power. Therefore, as shown in FIG. 2B, the power of the engine 100 is output to the front wheels 140, and at the same time, the front wheel motor 120 is driven as a generator so that the battery 160 can be charged. FIG. 8

[0084] Otherwise, as a result of the comparison of the driver demand power with the optimal engine power at the preset optimal engine operating point in S203, when the driver demand power is greater than the optimal engine power, i.e., the optimal engine power is less than the driver demand power, because it indicates that the optimal engine power cannot satisfy the driver demand power, the rear wheel motor 170 can be used as an auxiliary drive source to satisfy the driver demand power.

[0085] To this end, as a result of the comparison of the driver demand power with the optimal engine power, when the engine 100 is driven at the preset optimal engine operating point in S203 and the driver demand power is greater than the optimal engine power, i.e., the optimal engine power is less than the driver demand power, the rear wheel motor 170 can be used as an auxiliary drive source under the control of the motor controller 30 according to the command of the high-level controller 10 (S205).

[0086] In another form, the auxiliary driving force of the rear wheel motor 170 can be determined as a value obtained by subtracting the optimal engine power from the driver demand power (driver demand power - optimal engine power).

[0087] ​In this case, the reason why the rear wheel motor 170 is driven as an auxiliary power source is that the power transmission path for transmitting power from the rear wheel motor 170 to the rear wheel 190 through the reduction gear 180 is shorter and more efficient than the power transmission path for transmitting power from the front wheel motor 120 to the front wheel 140 through the transmission 130.

[0088] Therefore, as shown in FIG. 2, the power of the engine 100 is output to the front wheel 140, and at the same time, the power of the rear wheel motor 170 is output to the rear wheel 190, so that the HEV mode in which the vehicle travels using both the power of the engine 100 and the power of the rear wheel motor 170 can be implemented while 4WD travel can be performed. FIG. 9

[0089] Next, the driver demand power is compared with the sum of the optimum engine power and the available power of the rear wheel motor 170 (optimum engine power + available power of rear wheel motor 170) (S206). As a result of the comparison, when the driver demand power is large, it is indicated that the driver demand power cannot be satisfied by the sum of the optimum engine power and the available power of the rear wheel motor 170. Therefore, in order to satisfy the driver's demand power, the front wheel motor 120 is further driven to be used as a travel power source under the control of the motor controller 30 according to the command of the high-level controller 10 in addition to the rear wheel motor 170 (S207).

[0090] In some forms of the present application, the drive power of the front wheel motor 120 can be determined as a value obtained by subtracting the sum of the optimum engine power and the available power of the rear wheel motor 170 from the driver demand power (driver demand power - (optimum engine power + available power of rear wheel motor 170)).

[0091] Therefore, as shown in FIG. 3, the power of the engine 100 and the power of the front wheel motor 120 are output to the front wheel 140, and at the same time, the power of the rear wheel motor 170 is output to the rear wheel 190, so that the HEV mode in which both the power of the engine 100 and the power of the front wheel motor 120 can be used in addition to the power of the engine 100 to implement the HEV mode of high load travel can be implemented while 4WD travel can be performed. FIG. 10

[0092] The present application provides the following effects through the above-described problem solving means.

[0093] ​​First, according to the present application, the running drive control of the E-4WD vehicle in which the power train for the front wheels including the engine and the front motor is combined with the power train for the rear wheels including the rear motor can be individually executed in the rear motor drive control mode, the front motor drive control mode, the front and rear motor drive control mode, and the engine-on control mode in accordance with the driver demand power, so that improvement of fuel efficiency can be achieved, and the marketability of the E-4WD vehicle can be improved.

[0094] Second, the vehicle running satisfying the driver demand power can be achieved in the entire load region of the E-4WD vehicle.

[0095] Third, the drive ratio of the front motor and the rear motor is adjusted so that stable vehicle acceleration can be executed on a low friction road surface.

[0096] While the forms of the present application have been described in detail, the scope of the present application is not limited to these forms, and various modifications and improvements designed by those skilled in the art using the basic concept of the present application defined by the appended claims can further fall within the scope of the present application.

Claims

1. A device for controlling an electric four-wheel drive system of a vehicle, the device comprising: The first power transmission system for the front wheels. The first power transmission system includes: An engine, a front wheel electric motor, and an engine clutch, the engine clutch being disposed between the engine and the front wheel electric motor and configured to selectively transmit power from the engine, and The transmission is configured to change the power of the engine and the power of the front wheel electric motor, and to output the changed power to the front wheels; Second power drive system for the rear wheels The second power transmission system includes: Rear wheel motor, and A speed reducer is configured to reduce the power of the rear wheel motor and output the reduced power to the rear wheel; The battery is connected to the front wheel motor and the rear wheel motor; and The controller is configured as follows: When the driver's power demand is less than the sum of the available power from the front wheel motor and the available power from the rear wheel motor, the front wheel motor or the rear wheel motor is selectively driven. During the operation of the front wheel motor or the rear wheel motor, when the driver's power demand exceeds the available power of the front wheel motor or the available power of the rear wheel motor, the rear wheel motor or the front wheel motor is additionally operated. The engine is activated when the driver's power demand exceeds the sum of the available power from the front wheel motor and the rear wheel motor; Specifically, when the driver's power demand is less than the difference between the sum of the available power and the factors of each state of charge of the battery, the controller is configured to drive only the rear wheel motor or only the front wheel motor to operate the vehicle in electric vehicle mode.

2. The apparatus according to claim 1, wherein, The controller is configured to determine whether to operate the front wheel motor or the rear wheel motor based on the power transmission efficiency of the front wheel motor and the rear wheel motor when selectively driving the front wheel motor or the rear wheel motor. The power transmission efficiency of the front wheel electric motor is the power transmission efficiency when the power of the front wheel electric motor is output to the front wheels through the transmission, and is determined by the operating efficiency of the transmission; and The power transmission efficiency of the rear wheel motor is the power transmission efficiency when the power of the rear wheel motor is output to the rear wheel through the reducer, and is determined by the working efficiency of the reducer.

3. The apparatus according to claim 2, wherein: When determining whether to operate the front wheel motor or the rear wheel motor, the available power of the front wheel motor, multiplied by the operating efficiency of the transmission, is compared with the available power of the rear wheel motor, multiplied by the operating efficiency of the reducer; and When the available power of the rear wheel motor multiplied by the operating efficiency of the reducer is greater than the available power of the front wheel motor multiplied by the operating efficiency of the transmission, the controller is configured to operate only the rear wheel motor to enable the vehicle to operate in electric vehicle mode.

4. The apparatus according to claim 2, wherein, When determining whether to operate the front wheel motor or the rear wheel motor, the available power of the front wheel motor, multiplied by the operating efficiency of the transmission, is compared with the available power of the rear wheel motor, multiplied by the operating efficiency of the reducer; and When the available power of the front wheel motor multiplied by the operating efficiency of the transmission is greater than the available power of the rear wheel motor multiplied by the operating efficiency of the reducer, the controller is configured to operate only the front wheel motor to enable the vehicle to operate in electric vehicle mode.

5. The apparatus according to claim 1, wherein, When the initial acceleration of the vehicle is performed solely by the rear wheel electric motor, the controller is configured to: When the difference between the speed of the rear wheel and the speed of the front wheel is greater than the maximum reference value α, the front wheel motor is driven, and Within a predetermined interval, the drive ratio of the front wheel motor to the rear wheel motor is increased by a predetermined unit value until the difference between the speed of the rear wheel and the speed of the front wheel decreases to less than a minimum reference value β. When the difference between the speed of the rear wheel and the speed of the front wheel is determined to be less than the minimum reference value β, the controller is configured to increase the drive ratio of the rear wheel motor to the front wheel motor by a predetermined unit value within a predetermined interval.

6. The apparatus according to claim 1, wherein: When the difference between the speed of the rear wheel, driven solely by the rear wheel motor, and the speed of the front wheel is less than a maximum reference value α, and the driver's power demand is greater than the available power of the rear wheel motor, the controller is further configured to operate the front wheel motor in conjunction with the rear wheel motor; and While only the front wheel motor is being driven, the controller is also configured to operate the rear wheel motor in conjunction with the front wheel motor when the driver's power demand exceeds the available power of the front wheel motor.

7. The apparatus according to claim 1, wherein, When the driver's power demand of the vehicle is greater than the difference between the sum of the available power and the factors of the various states of charge of the battery, the controller is configured to operate the engine and to operate the vehicle in hybrid electric vehicle mode.

8. The apparatus according to claim 7, wherein, The controller is configured to compare the driver’s power demand with the optimal engine power when the engine is driven at the optimal engine operating point. When the driver's power requirement is less than the optimal engine power, the front wheel electric motor is configured to generate power to charge the battery; The controller is configured to compare the driver's power demand with the optimal engine power when the engine is driven at the optimal engine operating point; and When the driver's power demand exceeds the optimal engine power, the rear wheel electric motor is driven as an auxiliary power source.

9. The apparatus according to claim 8, wherein, When the driver’s power demand is greater than the sum of the optimal engine power and the available power of the rear wheel motor, the controller is configured to drive the front wheel motor such that the front wheel motor is used as a driving power source in addition to the rear wheel motor.

10. A method for controlling the electric four-wheel drive of a vehicle, the vehicle having a first power drive system for the front wheels, a second power drive system for the rear wheels, and a battery, wherein, The first powertrain includes: an engine, a front wheel electric motor, an engine clutch disposed between the engine and the front wheel electric motor, and a transmission that changes the speed of the power from the engine and the power from the front wheel electric motor and outputs the changed power to the front wheels; and the second powertrain includes: a rear wheel electric motor and a reducer that reduces the speed of the power from the rear wheel electric motor and outputs the reduced power to the rear wheels; the method includes: When the driver's power demand of the vehicle is less than the sum of the available power from the front wheel motor and the available power from the rear wheel motor, the controller selectively drives the front wheel motor or the rear wheel motor based on the power transmission efficiency of the front wheel motor and the rear wheel motor. During the operation of either the front wheel motor or the rear wheel motor, when the driver's power demand exceeds the available power of either the front wheel motor or the rear wheel motor, the controller jointly drives both the front wheel motor and the rear wheel motor; and When the driver's power demand exceeds the sum of the available power, the engine is driven by the controller; Specifically, when selectively driving the front wheel motor or the rear wheel motor, if the driver's power demand is less than the difference between the sum of the available power and the factors of each state of charge of the battery, only the rear wheel motor or only the front wheel motor is driven, so that the vehicle can operate in electric vehicle mode.

11. The method according to claim 10, wherein, The power transmission efficiency of the front wheel electric motor is the power transmission efficiency when the power of the front wheel electric motor is output to the front wheels through the transmission, and is determined by the operating efficiency of the transmission; and The power transmission efficiency of the rear wheel motor is the power transmission efficiency when the power of the rear wheel motor is output to the rear wheel through the reducer, and is determined by the working efficiency of the reducer.

12. The method according to claim 11, wherein, When determining whether to operate the front wheel motor or the rear wheel motor, the available power of the front wheel motor, multiplied by the operating efficiency of the transmission, is compared with the available power of the rear wheel motor, multiplied by the operating efficiency of the reducer; and Specifically, when the available power of the rear wheel motor multiplied by the working efficiency of the reducer is greater than the available power of the front wheel motor multiplied by the working efficiency of the transmission, only the rear wheel motor is driven so that the vehicle operates in electric vehicle mode.

13. The method according to claim 11, wherein, When determining whether to operate the front wheel motor or the rear wheel motor, the available power of the front wheel motor, multiplied by the operating efficiency of the transmission, is compared with the available power of the rear wheel motor, multiplied by the operating efficiency of the reducer; and Specifically, when the available power of the front wheel motor multiplied by the working efficiency of the transmission is greater than the available power of the rear wheel motor multiplied by the working efficiency of the reducer, only the front wheel motor is driven so that the vehicle operates in electric vehicle mode.

14. The method of claim 10, wherein: When the initial acceleration of the vehicle is performed solely by the rear wheel motor, if the difference between the speed of the rear wheel and the speed of the front wheel is greater than a maximum reference value α, the front wheel motor is driven, and the drive ratio of the front wheel motor to the rear wheel motor is increased by a predetermined unit value at predetermined intervals until the difference between the speed of the rear wheel and the speed of the front wheel decreases to less than a minimum reference value β; and When the difference between the speed of the rear wheel and the speed of the front wheel is less than the minimum reference value β, the drive ratio of the rear wheel motor to the front wheel motor is increased by a predetermined unit value within a predetermined interval.

15. The method according to claim 10, wherein, When the difference between the speed of the rear wheel driven solely by the rear wheel motor and the speed of the front wheel is less than the maximum reference value α, and when the driver's power demand is greater than the available power of the rear wheel motor, the front wheel motor is driven together with the rear wheel motor; and While only the front wheel motor is being driven, the rear wheel motor is driven in conjunction with the front wheel motor when the driver's power demand exceeds the available power of the front wheel motor.

16. The method of claim 10, wherein, When the driver's power demand for the vehicle is greater than the difference between the sum of the available power and the factors of the various states of charge of the battery, the engine is driven to enable the vehicle to operate in hybrid electric vehicle mode.

17. The method according to claim 16, wherein, When driving the engine, the driver's power requirement is compared with the optimal engine power when driving the engine at its optimal operating point. When the driver's power requirement is less than the optimal engine power, the front wheel electric motor generates power to charge the battery; The driver's power requirement is compared with the optimal engine power when the engine is driven at its optimal operating point, and When the driver's power demand exceeds the optimal engine power, the rear wheel electric motor is driven as an auxiliary power source.

18. The method according to claim 17, wherein, When the engine is driven, if the driver's power demand is greater than the sum of the optimal engine power and the available power of the rear wheel motor, the front wheel motor is driven as a driving power source in addition to the rear wheel motor.

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