Drive control device for four-wheel drive electric vehicle

Abstract

To provide a drive control device of a four-wheel drive electric vehicle which minimizes energy loss generated on a power transmission path at the time of shift gears, and can improve fuel consumption.SOLUTION: A drive control device of a four-wheel drive electric vehicle includes: a power train for front wheels including an engine, a front wheel motor and a transmission for changing power of the engine and the front motor and outputting the changed power to front wheels; a power train for rear wheels including a rear wheel motor and a speed reducer for reducing the power of the rear wheel motor and outputting the reduced power to rear wheels; and a control part for instructing the rear wheel motor to output power capable of outputting by the rear wheel motor among driver request power when shift gear starts by the transmission during travel by driving the engine, and for instructing the front wheel motor to output power left after subtracting output power which the rear wheel motor is instructed to output and the engine output power from the drive request power (driver request power-rear wheel motor output power-engine output power).SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a drive control device for a four-wheel drive electric vehicle, and more particularly to a drive control device for a four-wheel drive electric vehicle that can improve fuel efficiency by minimizing energy loss that occurs in a power transmission path during gear changes. [Background technology]

[0002] As is well known, hybrid vehicles, electric vehicles, hydrogen fuel cell vehicles, and the like are equipped with electric motors as a driving source, and such vehicles are called electrified vehicles. An example of a four-wheel drive powertrain for an electrified vehicle is a powertrain in which an engine and / or a front-wheel motor are connected to the front wheels and a rear-wheel motor, which is smaller than the front-wheel motor, is connected to the rear wheels. In a four-wheel drive powertrain in which an engine and a front-wheel motor, which serve as the main driving source for vehicle propulsion, are connected to the front wheels and a rear-wheel motor, which serves as an auxiliary driving source, is connected to the rear wheels, a transmission is connected to the front-wheel motor, and a reduction gear is connected to the rear-wheel motor without a transmission. Since such a four-wheel drive powertrain is equipped with a transmission, gear shifting is unavoidable. When gear shifting is performed while driving using the front-wheel motor and / or the engine connected to the transmission, gear shifting loss occurs depending on the gear ratio of the gear. Gear shifting loss acts as a factor that reduces fuel efficiency, resulting in a decrease in fuel efficiency. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2012-043683 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made in consideration of the above-mentioned points, and an object of the present invention is to provide a drive control device for a four-wheel drive electric vehicle that can minimize energy loss that occurs in a power transmission path during gear changes, thereby improving fuel efficiency. [Means for solving the problem]

[0005] The drive control device for a four-wheel drive electric vehicle according to the present invention includes a front wheel powertrain including an engine, a front wheel motor, and a transmission that changes the speed of power from the engine and the front wheel motor and outputs it to the front wheels; a rear wheel powertrain including a rear wheel motor and a speed reducer that reduces the speed of power from the rear wheel motor and outputs it to the rear wheels; and a control unit that, when a gear change begins in the transmission while driving the engine, commands the rear wheel motor to output a power that the rear wheel motor can output from the driver's requested power, and commands the front wheel motor to output the remaining power after subtracting the output power commanded to the rear wheel motor and the output power of the engine from the driver's requested power.

[0006] In addition, when the combined power of the maximum power that the front wheel motor and the maximum power that the rear wheel motor can output during driving is smaller than the driver's requested power, the control unit drives the engine and commands the engine to output a power determined by a driving point map.

[0007] The control unit commands the rear wheel motor to output maximum power if the driver's requested power during gear shifting is greater than the maximum power that the rear wheel motor can output, and the engine output power output by the engine is output to the front wheel by a power equal to the driver's requested power minus the rear wheel motor maximum power.

[0008] The vehicle also includes a battery connected to the front wheel motor and the rear wheel motor so as to be capable of being charged and discharged, and the control unit commands the front wheel motor to generate power to charge the battery if the sum of the rear wheel motor maximum power and the engine output power is greater than the driver's requested power during gear shifting, and the front wheel motor generates power to charge the battery using the remaining power obtained by subtracting the rear wheel motor maximum power and the engine output power from the driver's requested power.

[0009] The control unit commands the rear wheel motor to output the driver requested power when the driver requested power is equal to or less than the maximum power of the rear wheel motor during gear shifting, and commands the front wheel motor to generate power to charge the battery, and the front wheel motor generates power to charge the battery using engine output power.

[0010] The control unit is characterized in that, when the transmission does not perform a gear change while the engine is driven and the vehicle is running, it subtracts the engine output power from the driver's requested power and commands the remaining power to be output to the front wheel motor.

[0011] The control unit commands the front wheel motor to generate power for charging the battery if the driver requested power is less than the engine output power, and the front wheel motor generates power for charging the battery using the remaining power obtained by subtracting the engine output power from the driver requested power.

[0012] When the driver's requested power exceeds the engine output power, the control unit subtracts the engine output power from the driver's requested power and commands the front wheel motor to output the remaining power.

[0013] When a gear shift begins in the transmission while the vehicle is traveling using only the power of the front wheel motor, the control unit commands the rear wheel motor to output the power that the rear wheel motor can output from the driver's requested power, and commands the front wheel motor to output the remaining power after subtracting the rear wheel motor output power from the driver's requested power.

[0014] The control unit is characterized in that, when a maximum power of the rear wheel motor is equal to or greater than a power required by a driver during a gear shift, the control unit commands the rear wheel motor to output the power required by the driver.

[0015] The control unit commands the front wheel motor to output '0' power if the maximum power of the rear wheel motor is equal to or greater than the power required by the driver during gear shifting.

[0016] The control unit is characterized in that, if the rear wheel motor maximum power is less than the driver-requested power during gear shifting, it commands the rear wheel motor to output the maximum power it can output, and commands the front wheel motor to output power obtained by subtracting the rear wheel motor maximum power from the driver-requested power.

[0017] The control unit is characterized in that, if the sum of the front wheel motor maximum power and the rear wheel motor maximum power is equal to or greater than the driver's requested power, and the product of the rear wheel motor maximum power and the operating efficiency of the reducer is smaller than the product of the front wheel motor maximum power and the operating efficiency of the transmission, the control unit drives only the front wheel motor alone during driving.

[0018] Another drive control device for a four-wheel drive electric vehicle according to the present invention is characterized in that it includes a front wheel powertrain including an engine and a transmission that changes the speed of the engine's power and outputs it to the front wheels; a rear wheel powertrain including a rear wheel motor and a reducer that reduces the speed of the rear wheel motor's power and outputs it to the rear wheels; and a control unit that, when a gear change begins in the transmission while driving the engine, commands the rear wheel motor to output power that the rear wheel motor can output from the driver's requested power, and commands the engine to output power that is the driver's requested power minus the rear wheel motor output power.

[0019] The control unit is characterized in that, if the maximum power that the rear wheel motor can output during gear shifting is equal to or greater than the driver's requested power, it commands the rear wheel motor to output the driver's requested power and stops the engine.

[0020] The control unit is characterized in that, if the rear wheel motor maximum power is less than the driver's requested power during gear shifting, it commands the rear wheel motor to output maximum power, and commands the engine to output the remaining power obtained by subtracting the rear wheel motor maximum power from the driver's requested power. [Effects of the Invention]

[0021] According to the present invention, it is possible to minimize the energy loss that occurs in the power transmission path during gear shifting, thereby improving fuel efficiency, and it is also possible to eliminate most of the gear shift shock caused by torque intervention during gear shifting, thereby improving marketability. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing an example of a power transmission system of a four-wheel drive electric vehicle. [Figure 2] 1 is a diagram showing a configuration for drive control of a four-wheel drive electric vehicle according to the present invention; [Figure 3]1 is a diagram showing a power transmission path when the front wheels of a four-wheel drive electric vehicle according to the present invention are driven by a motor. FIG. [Figure 4] 1 is a diagram showing a power transmission path during a gear change while the front wheel motor is driven in a four-wheel drive electric vehicle according to the present invention; [Figure 5] FIG. 2 is a diagram showing a power transmission path when the four-wheel drive electric vehicle according to the present invention is running in engine-on mode. [Figure 6] FIG. 2 is a diagram showing a power transmission path when shifting gears while traveling in engine-on mode in a four-wheel drive electric vehicle according to the present invention. [Figure 7a] 4 is a flowchart showing a drive control process during gear shifting in a four-wheel drive electric vehicle according to the present invention. [Figure 7b] 4 is a flowchart showing a drive control process during gear shifting in a four-wheel drive electric vehicle according to the present invention. [Figure 8] FIG. 10 is a diagram showing another example of a power transmission system for a four-wheel drive electric vehicle. [Figure 9] FIG. 10 is a diagram showing another example of a power transmission system for a four-wheel drive electric vehicle. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will now be described with reference to the accompanying drawings. The details shown in the accompanying drawings are schematic diagrams for easily explaining embodiments of the present invention. In the accompanying drawings, FIG. 1 illustrates a power transmission system of an electronic four-wheel drive (E-4WD) electric vehicle that combines a front-wheel powertrain including an engine and a front-wheel motor with a rear-wheel powertrain including a rear-wheel motor. FIG. 2 illustrates a configuration for drive control during gear shifting in an electric four-wheel drive vehicle according to the present invention. As shown in FIG. 1, a front-wheel powertrain 100 includes an engine 110, a front-wheel motor 120, a transmission 130, and an engine clutch 140. The engine 110 and the front-wheel motor 120 output power for driving the vehicle. The transmission 130 is connected to the rear end (output end) of the front-wheel motor 120 and can change the speed of the power from the engine 110 and the front-wheel motor 120 and output it to front wheels 150. The engine clutch 140 is disposed between the engine 110 and the front wheel motor 120 and is operable to be engaged or disengaged. More specifically, when the engine clutch 140 is engaged, engine power is transmitted to the transmission 130, and when the engine clutch 140 is released, engine power is cut off and not transmitted to the transmission 130.

[0024] The transmission 130 can change the speed of power generated by the engine 110 and the front wheel motor 120 through a transmission gear and transmit the power to the front wheels 150. For example, an automatic transmission (AT) or a dual clutch transmission (DCT) can be adopted as the transmission 130. Reference numeral 170 denotes a hybrid starter generator (HSG) 170 that is connected to a crank pulley of the engine 110 to start the engine and generate electricity. The front wheel motor 120 and the starter generator 170 are electrically connected to a battery 160. The battery 160 is connected to the front wheel motor 120 and the starter generator 170 so that it can be charged and discharged. More specifically, the battery 160 can be discharged to the front wheel motor 120 and the starter generator 170 or can be charged by the front wheel motor 120 and the starter generator 170. The rear wheel powertrain 200 includes a rear wheel motor 210 connected to the battery 160 so as to be capable of being charged and discharged, and a reducer 220 that reduces the power of the rear wheel motor 210 and outputs the reduced power to rear wheels 230. The rear wheel motor 210 is driven to output power for driving the vehicle.

[0025] In the present invention, when a gear change is performed in the transmission 130 while a four-wheel drive electric vehicle combining a front-wheel powertrain 100 and a rear-wheel powertrain 200 is running, the output power of the engine 110 and the motors 120 and 210 that drive the vehicle can be controlled to minimize gear change losses. Specifically, when a gear change begins while the vehicle is running using the front-wheel motor 120 and / or the engine 110 to which the transmission 130 is connected, the power of the rear-wheel motor 210 to which the transmission 130 is not connected is maximized, thereby minimizing energy loss that occurs in the power transmission system during gear change and improving fuel efficiency. As shown in FIG. 2, the control unit 10, which is the main controller of the engine 110 and the motors 120 and 210 when shifting gears in a four-wheel drive electric vehicle, may include a host controller 11, an engine controller 12 that receives commands from the host controller 11 to control the overall operation of the engine 110, and a motor controller 13 that receives commands from the host controller 11 to control the overall operation of the front wheel motor 120 and the rear wheel motor 210.

[0026] In addition, the upper controller 11 can issue commands to the transmission controller 14 or receive information such as a gear shift phase from the transmission controller 14. The transmission controller 14 can control the operation of the transmission 130 by receiving commands from the upper controller 11. The four-wheel drive electric vehicle can provide driving modes such as an EV (electric vehicle) mode in which the vehicle runs using only the power of the front wheel motor 120 and / or the rear wheel motor 210, and an engine-on mode in which the vehicle runs using the power of the engine 110. Here, the EV mode includes a front wheel motor drive mode in which the vehicle runs using only the power of the front wheel motor 120. The engine-on mode includes an engine-only drive mode in which the vehicle runs using only the power of the engine 110, and an HEV (hybrid electric vehicle) mode in which the vehicle uses the engine 110 as a main power source and the front wheel motor 120 and / or the rear wheel motor 210 as an auxiliary power source. In the present invention, when a gear shift begins while driving using the power of the front wheel powertrain 100 equipped with the transmission 130 in the above-described driving modes, it is possible to reduce energy loss occurring in the power transmission path. In other words, when a gear shift begins while driving in the front wheel motor drive mode or the engine-on mode, it is possible to maximize the use of the power of the rear wheel motor 210, thereby minimizing gear shift loss.

[0027] 3 and 4 are diagrams illustrating power transmission paths when driving in front-wheel motor drive mode. Specifically, FIG. 3 illustrates the power transmission paths before a gear shift in a four-wheel drive electric vehicle according to the present invention, and FIG. 4 illustrates the power transmission paths when a gear shift in a four-wheel drive electric vehicle according to the present invention is performed. When driving using the front-wheel motor 120, as shown in FIG. 3, power from the front-wheel motor 120 is transmitted to the front wheels 150 via the transmission 130, and the front-wheel motor 120 is driven by power from the battery 160. If the driver's requested power, which varies depending on the driver's accelerator pedal depression amount (i.e., accelerator pedal stroke), is less than the sum of the front-wheel motor maximum power and the rear-wheel motor maximum power, the front-wheel motor 120 and / or the rear-wheel motor 210 may be driven to drive in EV mode. The front-wheel motor maximum power is the maximum power that the front-wheel motor 120 can output, and the rear-wheel motor maximum power is the maximum power that the rear-wheel motor 210 can output. When traveling in EV mode, whether to drive the front wheel motor 120 or the rear wheel motor 210 independently can be determined based on power transmission efficiency. That is, based on the power transmission efficiency of the front wheel motor 120 and the rear wheel motor 210, one of the front wheel motor 120 and the rear wheel motor 210 can be selected and driven independently.

[0028] The power transmission efficiency of the front wheel motor 120 is the power transmission efficiency when the power of the front wheel motor 120 is output to the front wheel 150 via the transmission 130, and may be determined by the operational efficiency of the transmission 130. The power transmission efficiency of the rear wheel motor 210 is the power transmission efficiency when the power of the rear wheel motor 210 is output to the rear wheel 230 via the speed reducer 220, and is determined by the operational efficiency of the speed reducer 220. Therefore, a first value (A) calculated by multiplying the maximum power of the front wheel motor 120 by the operational efficiency of the transmission 130 is compared with a second value (B) calculated by multiplying the maximum power of the rear wheel motor 210 by the operational efficiency of the speed reducer 220. If the first value (A) is greater than the second value (B), it is preferable in terms of power transmission efficiency to drive the front wheel motor 120 alone when traveling in EV mode. Furthermore, when the first value (A) is greater than the second value (B), the power transmission efficiency of the front wheel powertrain 100 increases, and the driver's requested power can be satisfied by driving the front wheel motor 120 alone. That is, when the first value (A) is greater than the second value (B), the front wheel motor maximum power value can be equal to or greater than the driver's requested power. Therefore, the control unit 10 drives the front wheel motor 120 alone among the vehicle drive sources if "front wheel motor maximum power + rear wheel motor maximum power ≥ driver's requested power" and "rear wheel motor maximum power × speed reducer operating efficiency < front wheel motor maximum power × transmission operating efficiency."

[0029] For example, if the upper controller 11 determines that the combined power value of the front wheel motor maximum power and the rear wheel motor maximum power (front wheel motor maximum power + rear wheel motor maximum power) is equal to or greater than the driver's requested power, and if the value obtained by multiplying the front wheel motor maximum power by the transmission operating efficiency (front wheel motor maximum power × transmission operating efficiency) is greater than the value obtained by multiplying the rear wheel motor maximum power by the reducer operating efficiency (rear wheel motor maximum power × reducer operating efficiency), the upper controller 11 can request the motor controller 13 to drive the front wheel motor 120 alone, and the motor controller 13 can drive the front wheel motor 120 alone. If the transmission 130 starts shifting while the vehicle is running using only the front wheel motor 120 among the engine 110, front wheel motor 120, and rear wheel motor 210, the control unit 10 commands the rear wheel motor 210 to output as much power as the rear wheel motor 210 can output from the driver's requested power. Here, the rear wheel motor 210 is requested to output power equal to or less than the rear wheel motor maximum power. Whether or not shifting of the transmission 130 can be started can be determined based on the shifting phase. The control unit 10 can determine that shifting of the transmission 130 has started if the shifting phase of the transmission 130 is equal to or greater than a predetermined first phase (α) while the vehicle is traveling driven solely by the front wheel motor 120.

[0030] For example, if the shift phase value received from the transmission controller 14 is equal to or greater than the first phase (α), the upper controller 11 may determine that a shift has started in the transmission 130. The first phase (α) may be set to the commonly used value '1', but may also be set to a value other than '1' depending on the torque reduction speed of the front wheel motor 120 during a shift. For example, if the torque of the front wheel motor 120 can be reduced relatively quickly during a shift, the first phase (α) may be set to a value other than '1'. If the control unit 10 determines that a shift has started based on the shift phase information of the transmission 130, it compares the rear wheel motor maximum power with the driver's requested power. If the rear wheel motor maximum power is equal to or greater than the driver's requested power, the rear wheel motor 210 can output power that satisfies the driver's requested power, and therefore the rear wheel motor 210 is controlled to output the driver's requested power. In other words, if the rear wheel motor maximum power is greater than or equal to the driver's requested power, a command is transmitted to the rear wheel motor 210 requesting it to output power equal to the driver's requested power, and a command is transmitted to the front wheel motor 120 requesting it to output '0' power.

[0031] If the rear wheel motor maximum power is less than the driver-requested power, rear wheel motor 210 cannot output the entire driver-requested power, so rear wheel motor 210 is controlled to output maximum power, and front wheel motor 120 is controlled to output power obtained by subtracting the rear wheel motor maximum power from the driver-requested power (driver-requested power - rear wheel motor maximum power). In other words, if the rear wheel motor maximum power is less than the driver-requested power, control unit 10 controls rear wheel motor 210 to output rear wheel motor maximum power, and front wheel motor 120 to output power obtained by subtracting the rear wheel motor maximum power from the driver-requested power. As a result, as shown in FIG. 4, rear wheel motor maximum power is output to rear wheel 230 via speed reducer 220, and front wheel motor output power is output to front wheel 150 via transmission 130. In this way, when shifting gears, the front wheel motor output power is controlled to '0' or the front wheel motor output power is controlled to a power value that is reduced from that before the shifting gears, thereby minimizing the shifting loss.

[0032] 5 and 6 are diagrams illustrating power transmission paths during driving in engine-on mode. Specifically, FIG. 5 illustrates the power transmission paths before a gear shift in a four-wheel drive electric vehicle according to the present invention, and FIG. 6 illustrates the power transmission paths during a gear shift in a four-wheel drive electric vehicle according to the present invention. If the driver's requested power is greater than the combined power value of the front wheel motor maximum power and the rear wheel motor maximum power (front wheel motor maximum power + rear wheel motor maximum power), the control unit 10 drives the engine 110 to satisfy the driver's requested power. For example, if the driver's requested power is greater than the sum of the front wheel motor maximum power and the rear wheel motor maximum power, the upper controller 11 requests the engine controller 12 to drive the engine 110, and the engine controller 12 drives the engine 110 according to a predetermined optimal operating line (OOL) condition. The engine 110 outputs power determined by the conditions of the optimal operating point according to a command, and the front wheel motor 120 is requested to output the remaining power (driver requested power - engine output power) obtained by subtracting the power output by the engine 110 (i.e., engine output power) from the driver requested power. Here, if the power requested of the front wheel motor 120 is a positive (+) value, the front wheel motor 120 is driven while discharging the battery 160 to output power to the front wheels 150, and if the power requested of the front wheel motor 120 is a negative (-) value, the front wheel motor 120 operates in a power generation mode to charge the battery 160.

[0033] The optimal operating point may be preset as a value for improving fuel efficiency and stored in the engine controller 12. For example, a operating point map configured to determine an optimal engine torque that maximizes engine efficiency according to the engine rotation speed (RPM) may be stored in the engine controller 12. The engine controller 12 may control the driving of the engine 110 at the optimal operating point (i.e., optimal torque value) determined via the operating point map in accordance with a command from the upper controller 11. As shown in FIG. 5, when traveling in an engine-on mode using the power of the engine 110, the power of the engine 110 is transmitted to the front wheels 150 via the transmission 130. When the transmission 130 starts shifting gears while the vehicle is traveling in the engine-on mode using the power of the engine 110 or the power of the engine 110 and the front wheel motor 120, or when the transmission 130 starts shifting gears while the vehicle is traveling in the engine-on mode using the power of the engine 110, the front wheel motor 120, and the rear wheel motor 210 as shown in FIG. 5, the control unit 10 commands the rear wheel motor 210 to output as much power as the rear wheel motor 210 can output from the driver's requested power, charges the battery 160 with the engine power, and minimizes the torque input to the transmission 130. As described above, whether the transmission 130 starts shifting gears may be determined based on the shifting phase. The control unit 10 may determine that the transmission 130 has started shifting gears if the shifting phase of the transmission 130 is equal to or greater than the predetermined second phase (β) while the vehicle is traveling in the engine-on mode.

[0034] For example, if the shift phase value received from the transmission controller 14 is equal to or greater than the second phase (β), the upper controller 11 can determine that a shift has started in the transmission 130. The second phase (β) can be set to the commonly used value '1', but can also be set to a value other than '1' depending on the torque reduction speed of the engine 110 during a shift. For example, if the torque of the engine 110 can be reduced relatively quickly during a shift, a value other than '1' can be applied to the second phase (β). If a shift in the transmission 130 starts while the vehicle is running in the engine-on mode, the control unit 10 requests the rear wheel motor 210 to output a predetermined power based on the result of comparing the maximum power of the rear wheel motor with the power requested by the driver. Specifically, if the rear wheel motor maximum power is equal to or greater than the driver-requested power, the control unit 10 requests the rear wheel motor 210 to provide the driver-requested power and controls the rear wheel motor 210 to output power equal to the driver-requested power, and if the rear wheel motor maximum power is less than the driver-requested power, the control unit 10 requests the rear wheel motor 210 to provide maximum power and controls the rear wheel motor 210 to output maximum power. When the driver-requested power is requested from the rear wheel motor 210, the engine 110 is instructed to output optimal power determined according to the conditions of the optimal operating point, and the front wheel motor 120 is instructed to output power obtained by subtracting the rear wheel motor output power and the engine output power from the driver-requested power (driver-requested power - rear wheel motor output power - engine output power).

[0035] Here, since the rear wheel motor output power is the same as the driver's requested power (rear wheel motor output power = driver's requested power), the front wheel motor 120 is requested to output power equal to the minus (-) value of the engine output power, and therefore the front wheel motor 120 charges the battery 160 using the engine output power. In other words, the front wheel motor 120 operates as a generator using the engine output power to charge the battery 160. For example, if the rear wheel motor maximum power is equal to or greater than the driver's requested power, the upper controller 11 commands the motor controller 13 to request the rear wheel motor 210 to output the driver's requested power and to request the front wheel motor 120 to output the minus (-) value of the engine output power. Then, the motor controller 13 commands the rear wheel motor 210 to output the driver's requested power and commands the front wheel motor 120 to generate power to charge the battery 160 using the engine output power. As a result, when the rear wheel motor 210 outputs all the power requested by the driver, the power output by the engine 110 (i.e., engine output power) is not output to the front wheels 150 but is applied to the front wheel motor 120, and the front wheel motor 120 charges the battery 160 using the engine output power. In addition, the rear wheel motor output power is transmitted to the rear wheels 230 via the reducer 220.

[0036] In addition, when a shift starts and the rear wheel motor 210 is requested to provide maximum power, the engine 110 is requested to provide output power determined by the operating point map, and the front wheel motor 120 is requested to provide power obtained by subtracting the rear wheel motor maximum power and the engine output power from the driver's requested power (driver's requested power - rear wheel motor maximum power - engine output power). If the rear wheel motor 210 cannot output all of the driver's requested power during a shift, the power that the rear wheel motor 210 cannot output (i.e., the shortfall between the rear wheel motor maximum power and the driver's requested power) is met with the engine output power. In other words, if the rear wheel motor maximum power is lower than the driver's requested power, at least a portion of the engine output power is transmitted to the front wheel 150 via the transmission 130. Here, the power transmitted to the front wheel 150 is determined to be power obtained by subtracting the rear wheel motor maximum power from the driver's requested power (driver's requested power - rear wheel motor maximum power). As a result, power (front wheel transmission power - engine output power) obtained by subtracting the engine output power from the power transmitted to the front wheels 150 (hereinafter referred to as 'front wheel transmission power') is requested from the front wheel motor 120. If the power obtained by subtracting the engine output power from the front wheel transmission power is a negative (-) value, i.e., if the sum of the rear wheel motor maximum power and the engine output power is greater than the driver-requested power, the front wheel motor 120 charges the battery 160 using the power obtained by subtracting the front wheel transmission power from the engine output power (engine output power - front wheel transmission power).

[0037] More specifically, when the transmission 130 performs a gear change, if the sum of the powers requested from the rear wheel motor 210 and the engine 110 (rear wheel motor maximum power + engine output power) is greater than the driver's requested power, the control unit 10 commands the front wheel motor 120 to generate power to charge the battery 160. Here, the front wheel motor 120 performs a power generation operation to charge the battery 160 using the power obtained by subtracting the rear wheel motor maximum power and the engine output power from the driver's requested power (driver's requested power - rear wheel motor maximum power - engine output power). For example, if the rear wheel motor maximum power is less than the driver-requested power, the upper controller 11 instructs the motor controller 13 to request the rear wheel motor 210 to output maximum power and to request the front wheel motor 120 to output power obtained by subtracting the engine output power from the front wheel transmission power (front wheel transmission power - engine output power), and the motor controller 13 instructs the rear wheel motor 210 to output maximum power and instructs the front wheel motor 120 to charge the battery 160 by the power obtained by subtracting the front wheel transmission power from the engine output power (engine output power - front wheel transmission power). 6, when the rear wheel motor 210 outputs maximum power, a portion of the power output by the engine 110 (i.e., front wheel transmission power) is transmitted to the front wheel 150, and the remaining power (engine output power - front wheel transmission power) is used by the front wheel motor 120 to charge the battery 160. Here, the rear wheel motor maximum power is output to the rear wheel 230 via the reducer 220.

[0038] In this way, when the transmission 130 starts shifting gears while the vehicle is running in the engine-on mode, the rear wheel motor 210 outputs as much driving power as possible, so that the rear wheel motor 210 can output more driving power than the engine 110. Hereinafter, a drive control method for shifting gears in a four-wheel drive electric vehicle according to the present invention will be described with reference to FIGS. 7a and 7b. FIGS. 7a and 7b are flowcharts illustrating a drive control method for shifting gears in a four-wheel drive electric vehicle according to the present invention, but the drive control method for shifting gears in the present invention is not necessarily limited to the steps shown in FIGS. 7a and 7b. Referring to FIG. 7a, first, the driver's requested power is compared with the combined power of the front wheel motor maximum power and the rear wheel motor maximum power (front wheel motor maximum power + rear wheel motor maximum power) (S100). If the driver's requested power is greater than the combined power of the front wheel motor maximum power and the rear wheel motor maximum power, the engine 110 is driven (S210). If the driver-requested power is equal to or less than the combined power of the front wheel motor maximum power and the rear wheel motor maximum power, a first value (front wheel motor maximum power × transmission operation efficiency) obtained by multiplying the front wheel motor maximum power and the transmission operation efficiency is compared with a second value (rear wheel motor maximum power × speed reducer operation efficiency) obtained by multiplying the rear wheel motor maximum power and the speed reducer operation efficiency (S110).

[0039] If the first value is greater than the second value, the front wheel motor 120 is driven independently from among the vehicle's driving sources to travel in EV mode (S120). While the front wheel motor 120 is driven independently, it is determined whether the transmission 130 begins shifting gears (S130). If the transmission 130 begins shifting gears, the rear wheel motor maximum power is compared with the driver's requested power (S140). If the rear wheel motor maximum power is equal to or greater than the driver's requested power, the rear wheel motor 210 is commanded to output power equal to the driver's requested power until the shifting is complete (S150), and the front wheel motor 120 is commanded to output '0' power to minimize shifting losses. If the rear wheel motor maximum power is less than the driver's requested power, the rear wheel motor 210 is commanded to output maximum power until the gear shift is complete, and the front wheel motor 120 is commanded to output power obtained by subtracting the rear wheel motor maximum power from the driver's requested power (driver's requested power - rear wheel motor maximum power) (S160), thereby reducing energy loss occurring in the transmission 130. Once the gear shift in the transmission 130 is complete, the vehicle drive mode is switched back to the front wheel motor drive mode (S170), and the driver's requested power is compared with the front wheel motor maximum power (S180). If the driver's requested power is less than the front wheel motor maximum power, the front wheel motor drive mode is maintained, and if the driver's requested power is greater than the front wheel motor maximum power, the rear wheel motor 210 is driven (S190).

[0040] Once the rear wheel motor 210 begins to operate, the driver's requested power is compared with the combined power of the front wheel motor maximum power and the rear wheel motor maximum power (S200). If the driver's requested power is greater than the sum of the front wheel motor maximum power and the rear wheel motor maximum power, the driver's requested power cannot be satisfied by driving the motors 120 and 210 alone, and the engine 110 is driven (S210). Referring to FIG. 7b, the engine 110 is driven to output power that maximizes engine efficiency through optimal operating point control (S220). Once the engine 110 is driven, the transmission 130 determines whether a gear shift is about to begin (S230). If a gear shift is not about to begin, the driver's requested power is compared with the engine output power according to optimal operating point control (S240). If a gear shift is not about to begin, the front wheel motor 120 is commanded to output power equal to the driver's requested power minus the engine output power. Therefore, if the driver's requested power is smaller than the engine output power, the front wheel motor 120 charges the battery 160 electrically connected to the front wheel motor 120 in accordance with a command from the control unit 10 (S250). Here, the front wheel motor 120 generates electricity using power obtained by subtracting the driver's requested power from the engine output power. If the driver's requested power is larger than the engine output power, the front wheel motor 120 outputs power obtained by subtracting the engine output power from the driver's requested power in accordance with a command from the control unit 10. Here, the front wheel motor 120 is driven using the power of the battery 160, and the front wheel motor output power is transmitted to the front wheels 150 via the transmission 130.

[0041] If it is determined from the comparison result in step S230 that a gear shift has begun in the transmission 130, the rear wheel motor maximum power is compared with the driver's requested power (S260). If the rear wheel motor maximum power is equal to or greater than the driver's requested power, the rear wheel motor 210 can output the driver's requested power, so the rear wheel motor 210 is commanded to output the driver's requested power, and the front wheel motor 120 is commanded to output power obtained by subtracting the rear wheel motor output power and the engine output power from the driver's requested power (S270). Here, since the rear wheel motor output power has the same power value as the driver's requested power, the front wheel motor 120 charges the battery 160 using the engine output power. Until the gear shift is completed in the transmission 130, the rear wheel motor 210 outputs the driver's requested power, and the front wheel motor 120 charges the battery 160 using the engine output power. If the rear wheel motor maximum power is less than the driver requested power, the rear wheel motor 210 cannot fully output the driver requested power, so the rear wheel motor 210 is requested to output maximum power and at least a portion of the engine output power is sent to the front wheel 150 (S280). Here, the engine power transmitted to the front wheel 150 (i.e., front wheel transmitted power) is determined as the power obtained by subtracting the rear wheel motor maximum power from the driver requested power (driver requested power - rear wheel motor maximum power).

[0042] Then, the controller 13 requests the front wheel motor 120 to output power (driver requested power - rear wheel motor maximum power - engine output power) obtained by subtracting the rear wheel motor maximum power and the engine output power from the driver requested power (S280). Thus, the front wheel motor 120 uses the power (engine output power - front wheel transmitted power) obtained by subtracting the front wheel transmitted power transmitted to the front wheels 150 from the engine output power for battery charging. For example, the motor controller 13 can control the battery charging operation of the front wheel motor 120 according to a command from the upper controller 11. Here, the motor controller 13 can control the engine power used by the front wheel motor 120 to transmit at least a portion of the engine output power to the front wheels 150. Until the gear shift is completed in the transmission 130, the rear wheel motor 210 outputs maximum power, and the front wheel motor 120 charges the battery 160 using the power (engine output power - front wheel transmitted power) obtained by subtracting the front wheel transmitted power from the engine output power. 8 and 9 are diagrams showing other examples of a power transmission system for a four-wheel drive electric vehicle. The arrows in Fig. 8 indicate the power transmission path before a gear shift begins while driving in engine-on mode, and the arrows in Fig. 9 indicate the power transmission path during a gear shift. Referring to Fig. 8, the four-wheel drive electric vehicle may have a power transmission system that combines a front-wheel powertrain 101 including an engine 111 and a rear-wheel powertrain 201 including a rear-wheel motor 211.

[0043] Specifically, the front-wheel powertrain 101 includes an engine 111 and a transmission 131 that changes the speed of the engine 111 and outputs the power to front wheels 151, but does not include a front-wheel motor. The rear-wheel powertrain 201 includes a rear-wheel motor 211 and a speed reducer 221 that reduces the speed of the rear-wheel motor 211 and outputs the power to rear wheels 231. Even in a vehicle equipped with the front-wheel powertrain 101 and the rear-wheel powertrain 201, when a gear change occurs while driving, the rear-wheel motor 211 can be instructed to output maximum power, thereby minimizing gear change loss. That is, when a gear change occurs while driving using the engine 111 connected to the transmission 131, the driving force for driving can be maximized through the rear-wheel motor 211 not connected to the transmission 131, thereby reducing energy loss occurring in the power transmission system during the gear change and improving fuel efficiency. 8, if the front wheel powertrain 101 does not include a front wheel motor, battery charging using the front wheel motor is not possible, but gear shifting loss can be reduced by reducing engine power transmitted to the front wheels 151 via the transmission 131. When gear shifting is not performed by the transmission 131, the vehicle may request the engine 111 to provide driver requested power based on the driver requested power that varies depending on the accelerator pedal depression amount of the driver, or may request the engine 111 to provide power determined by the engine's optimal operating point.

[0044] Here, if the engine 111 cannot output the full power requested by the driver, the rear wheel motor 211 can be requested to output power equal to the driver's requested power minus the engine output power (driver's requested power - engine output power). As such, if a gear shift begins in the transmission 131 while the vehicle is running using the power of the engine 111 or the power of the engine 111 and the rear wheel motor 211, i.e., while the vehicle is running in the engine-on mode, the control unit 10 compares the rear wheel motor maximum power with the driver's requested power and requests the rear wheel motor 211 to output the power that it can output based on the comparison result. If the rear wheel motor maximum power is equal to or greater than the driver's requested power, the rear wheel motor 211 can output the full power of the driver's requested power, so the control unit 10 commands the rear wheel motor 211 to output the driver's requested power and requests the engine 111 to output 0 power, thereby stopping the engine 111, as shown in FIG. 9. If the rear wheel motor maximum power is less than the driver's requested power, the rear wheel motor 211 cannot output all of the driver's requested power, so the control unit 10 commands the rear wheel motor 211 to output maximum power and commands the engine 111 to output power obtained by subtracting the rear wheel motor maximum power from the driver's requested power (driver's requested power - rear wheel motor maximum power). In this way, by minimizing the power transmitted to the front wheels 151 via the transmission 131 during gear shifting, it is possible to reduce energy loss occurring in the power transmission system during gear shifting.

[0045] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and includes all modifications within the scope of the present invention. [Explanation of symbols]

[0046] 10 Control Unit 11 Upper controller 12 Engine controller 13 Motor Controller 14 Transmission controller 100, 101 Front wheel powertrain 110, 111 engines 120 front wheel motor 130, 131 Transmission 140 Engine clutch 150, 151 front wheels 160, 161 Battery 170, 171 Starter generator 200, 201 rear wheel powertrain 210, 211 rear wheel motor 220, 221 reducer 230, 231 rear wheels

Claims

1. a front-wheel powertrain including an engine, a front-wheel motor, and a transmission that changes the speed of power from the engine and the front-wheel motor and outputs the power to the front wheels; a rear wheel power train including a rear wheel motor and a reducer that reduces the power of the rear wheel motor and outputs it to the rear wheel; a control unit that, when a gear shift is started in the transmission while the engine is being driven and the vehicle is running, compares a driver's requested power with a maximum power that the rear wheel motor can output, and if the driver's requested power is greater than the maximum power that the rear wheel motor can output, commands the rear wheel motor to output the maximum power, and commands the front wheel motor to output the remaining power by subtracting the output power commanded to the rear wheel motor and the output power of the engine from the driver's requested power; A drive control device for a four-wheel drive electric vehicle, comprising:

2. 2. The drive control device for a four-wheel drive electric vehicle according to claim 1, wherein the control unit drives the engine and commands the engine to output a power determined by a driving point map when a combined power of a maximum power that the front wheel motor and the rear wheel motor can output is smaller than a driver-requested power.

3. A drive control device for a four-wheel drive electrified vehicle as described in Claim 2, characterized in that the engine output power output by the engine is output to the front wheels by the power obtained by subtracting the maximum power of the rear wheel motor from the driver's requested power.

4. a battery connected to the front wheel motor and the rear wheel motor in a chargeable and dischargeable manner; the control unit commands the front wheel motor to generate power for charging the battery if the sum of the rear wheel motor maximum power and the engine output power is greater than the driver's requested power during gear shifting; 4. The drive control device for a four-wheel drive electric vehicle according to claim 3, wherein the front wheel motor generates power for charging the battery using the remaining power obtained by subtracting the rear wheel motor maximum power and the engine output power from the driver's requested power.

5. the control unit commands the rear wheel motor to output the driver requested power and commands the front wheel motor to generate power for charging the battery when the driver requested power is equal to or less than the rear wheel motor maximum power during gear shifting; 5. The drive control device for a four-wheel drive electric vehicle according to claim 4, wherein the front wheel motor generates power for charging the battery using engine output power.

6. 5. The drive control device for a four-wheel drive electric vehicle according to claim 4, wherein the control unit, when the transmission does not perform a gear change while the engine is running, commands the front wheel motor to output the remaining power by subtracting the engine output power from the driver's requested power.

7. 7. The drive control device for a four-wheel drive electric vehicle of claim 6, wherein the control unit commands the front wheel motor to generate power to charge the battery if the driver's requested power is less than the engine output power, and the front wheel motor generates power to charge the battery using the power remaining after subtracting the engine output power from the driver's requested power.

8. 7. The drive control device for a four-wheel drive electric vehicle according to claim 6, wherein, when the driver requested power exceeds the engine output power, the control unit subtracts the engine output power from the driver requested power and commands the front wheel motor to output the remaining power.

9. 2. The drive control device for a four-wheel drive electric vehicle according to claim 1, wherein, when a gear shift begins in the transmission while the vehicle is running using only the power of the front wheel motor, the control unit commands the rear wheel motor to output a power that the rear wheel motor can output from the driver's requested power, and commands the front wheel motor to output a power that is the driver's requested power minus the rear wheel motor output power.

10. 10. The drive control device for a four-wheel drive electric vehicle according to claim 9, wherein the control unit commands the rear wheel motor to output the driver's requested power if the rear wheel motor maximum power is equal to or greater than the driver's requested power during gear shifting.

11. 11. The drive control device for a four-wheel drive electric vehicle of claim 10, wherein the control unit commands the front wheel motor to output '0' power if the rear wheel motor maximum power is equal to or greater than the driver's requested power during gear shifting.

12. 11. The drive control device for a four-wheel drive electric vehicle according to claim 10, wherein the control unit, when shifting gears, if the rear wheel motor maximum power is less than the driver-requested power, commands the rear wheel motor to output the maximum power it can output, and commands the front wheel motor to output power obtained by subtracting the rear wheel motor maximum power from the driver-requested power.

13. 10. The drive control device for a four-wheel drive electric vehicle of claim 9, wherein the control unit drives only the front wheel motor alone during driving if the sum of the front wheel motor maximum power and the rear wheel motor maximum power is equal to or greater than the driver's requested power, and if the product of the rear wheel motor maximum power and the operating efficiency of the reducer is smaller than the product of the front wheel motor maximum power and the operating efficiency of the transmission.

14. a front-wheel power train including an engine and a transmission that changes the speed of the engine power and outputs it to the front wheels; a rear wheel power train including a rear wheel motor and a reducer that reduces the power of the rear wheel motor and outputs it to the rear wheel; a control unit that, when a gear shift is started in the transmission while the vehicle is running by driving the engine, commands the rear wheel motor to output a power that the rear wheel motor can output from among a driver's requested power, and commands the rear wheel motor to output the maximum power if the driver's requested power is greater than the maximum power that the rear wheel motor can output; A drive control device for a four-wheel drive electric vehicle, comprising:

15. 15. The drive control device for a four-wheel drive electric vehicle of claim 14, wherein the control unit commands the rear wheel motor to output maximum power if the rear wheel motor maximum power is less than the driver's requested power during gear shifting, and commands the engine to output the remaining power obtained by subtracting the rear wheel motor maximum power from the driver's requested power.

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