Electric all-wheel drive vehicle

Abstract

To provide an electrically-operated all-wheel drive vehicle that is configured so that front wheels are driven directly by a front electric motor and rear wheels are driven directly by a rear electric motor, which can give a driver a feeling of acceleration which is above vehicle acceleration which is actually generated, when an accelerator pedal is stepped on, in a high-vehicle speed area where output torque of the front electric motor and of the rear electric motor decrease.SOLUTION: An electrically-operated all-wheel drive vehicle 1 comprises: a front motor generator 21 that directly drives front wheels 10FL and 10FR; a rear motor generator 22 that directly drives rear wheels 10RL and 10RR; and an EV-CU 60 that controls driving of the front motor generator 21 and the rear motor generator 22 on the basis of operation amounts of an accelerator and a vehicle speed. In a state where the vehicle speed is above a predetermined speed, the EV-CU 60 changes front and rear distributions of driving force so that weight of the driving force is imposed on the rear wheels, when the operation amounts of the accelerator increase to a predetermined speed or higher.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electric all-wheel drive vehicle. [Background technology]

[0002] In recent years, electric vehicles (EVs) that use electric motors as a driving force source and do not emit exhaust gases have been put into practical use. For example, Patent Document 1 discloses an electric all-wheel drive vehicle in which the front wheels are driven by a front motor and the rear wheels are driven by a rear motor.

[0003] In such electric vehicles, for example, small, highly efficient interior permanent magnet (IPM) motors, which incorporate magnets inside the iron core of the rotor, are suitable for use. Since IPM motors have permanent magnets embedded inside the rotor, they are suitable for high-speed rotation, and because they can utilize the reluctance torque that attracts and repels part of the yoke (protrusion) in the magnetic circuit, they can obtain large output torque from the combined torque of the magnet torque resulting from the attractive / repulsive forces of the coil and the permanent magnet. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-105482 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, electric motors such as IPM motors have an output characteristic (TN characteristic) in which the output torque decreases as the rotation speed increases above the base rotation speed. Therefore, in the case of a vehicle in which the electric motor is directly connected to the wheels, in the high vehicle speed range where the rotation speed of the electric motor increases, it becomes difficult to accelerate the vehicle even if the accelerator pedal is depressed hard, and the driver does not get a sense of acceleration.

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide an electric all-wheel drive vehicle in which the front wheels are directly driven by a front electric motor and the rear wheels are directly driven by a rear electric motor, and which is capable of giving the driver a sense of acceleration that is greater than the actual vehicle acceleration (longitudinal acceleration) when the accelerator pedal is depressed at high vehicle speeds where the output torque of the front electric motor and rear electric motor decreases. [Means for solving the problem]

[0007] The electric all-wheel drive vehicle of the present invention comprises a front electric motor that directly drives the front wheels, a rear electric motor that directly drives the rear wheels, an accelerator sensor that detects the amount of accelerator operation, a vehicle speed sensor that detects the vehicle speed, and a control unit that controls the drive of the front electric motor and the rear electric motor based on the amount of accelerator operation and the vehicle speed, and is characterized in that when the vehicle speed is above a predetermined speed and the amount of accelerator operation is increased above the predetermined speed, the control unit changes the front / rear distribution of driving force to be biased towards the rear wheels.

[0008] In the electric all-wheel drive vehicle according to the present invention, when the vehicle speed is above a predetermined speed and the accelerator pedal depression amount is increased at a speed above the predetermined speed, the front / rear drive force distribution is shifted to a rear-wheel bias. For example, the drive force of the front electric motor is reduced and the drive force of the rear electric motor is increased. This causes the rear of the vehicle to pitch, as if squatting. As a result, the driver can feel an acceleration greater than the actual vehicle acceleration (longitudinal acceleration). [Effects of the Invention]

[0009] According to the present invention, in an electric all-wheel drive vehicle in which the front wheels are directly driven by a front electric motor and the rear wheels are directly driven by a rear electric motor, when the accelerator pedal is depressed at high vehicle speeds where the output torque of the front electric motor and the rear electric motor decreases, it is possible to give the driver a sense of acceleration that is greater than the actual vehicle acceleration (longitudinal acceleration). [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing the overall configuration of an electric all-wheel drive vehicle according to an embodiment; [Figure 2] FIG. 4 is a diagram showing the output characteristics (TN characteristics) of the front motor generator and the rear motor generator. [Figure 3] 4 is a flowchart showing a processing procedure for rear-wheel bias control (acceleration sensation production control) performed by an electric all-wheel drive vehicle according to an embodiment. [Figure 4] 1 is a timing chart showing changes in accelerator opening, front motor generator driving force, rear motor generator driving force, pitching direction G jerk, etc. during rear wheel bias control (acceleration feeling production control) by an electric all-wheel drive vehicle according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts will be designated by the same reference numerals. In addition, the same elements will be designated by the same reference numerals in each drawing, and redundant explanations will be omitted.

[0012] First, the configuration of an electric all-wheel drive vehicle (AWD EV) 1 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram showing the overall configuration of the electric all-wheel drive vehicle 1.

[0013] The front motor generator 21 (corresponding to the front electric motor described in the claims) is connected to the left front wheel 10FL via the left front wheel drive shaft 45L so as to be able to transmit torque, and is also connected to the right front wheel 10FR via the right front wheel drive shaft 45R so as to be able to transmit torque. In other words, the front motor generator 21 is directly connected to the front wheels 10FL, 10FR and directly drives the front wheels 10FL, 10FR.

[0014] The term "directly" means that the rotation speed (vehicle speed) of the front wheels 10FL, 10FR is determined uniquely (one-to-one) by the rotation speed of the front motor generator 21, without the intervention of a transmission or clutch. Therefore, in addition to the configuration (this embodiment) in which the front motor generator 21 directly drives the left front wheel drive shaft 45L and the right front wheel drive shaft 45R, it also includes a configuration in which the left front wheel drive shaft 45L and the right front wheel drive shaft 45R are driven via a pair of gears (reduction gears) with a fixed gear ratio, and a configuration in which the left front wheel drive shaft 45L and the right front wheel drive shaft 45R are driven via gears (reduction gears) and a front differential.

[0015] Similarly, the rear motor generator 22 (corresponding to the rear electric motor described in the claims) is connected to the left rear wheel 10RL via the left rear wheel drive shaft 48L so as to be able to transmit torque, and is also connected to the right rear wheel 10RR via the right rear wheel drive shaft 48R so as to be able to transmit torque. In other words, the rear motor generator 22 is directly connected to the rear wheels 10RL and 10RR, and directly drives the rear wheels 10RL and 10RR. The meaning of the word "directly" is the same as in the case of the front motor generator 21 described above.

[0016] The front motor generator 21 and the rear motor generator 22 are configured as synchronous generator motors that combine the function of a motor that converts supplied electric power into mechanical power and the function of a generator that converts input mechanical power into electric power. That is, the front motor generator 21 and the rear motor generator 22 each operate as a motor that generates drive torque when driving the vehicle, and as a generator when regenerating.

[0017] The output characteristics (TN characteristics) of the front motor generator 21 and the rear motor generator 22 are shown in Figure 2. The horizontal axis of Figure 2 represents vehicle speed (km / h), i.e., motor rotation speed (rpm), and the vertical axis represents driving force (Nm). As shown in Figure 2, the front motor generator 21 and the rear motor generator 22 have a characteristic (TN characteristic) in which, in the range above the base rotation speed, the higher the vehicle speed (motor rotation speed), the lower the driving force (output torque) due to an increase in induced electromotive force (induced voltage).

[0018] Returning to Fig. 1, each of the wheels 10FL-10RR (hereinafter, all of the wheels 10FL-10RR may be collectively referred to as wheels 10) is fitted with a brake 11FL-11RR (hereinafter, all of the brakes 11FL-11RR may be collectively referred to as brake 11) that brakes the wheels 10FL-10RR. Also, each of the wheels 10FL-10RR is fitted with a wheel speed sensor 12FL-12RR (hereinafter, all of the wheel speed sensors 12FL-12RR may be collectively referred to as wheel speed sensor 12) that detects the wheel rotation speed.

[0019] The wheel speed sensor 12 is a non-contact sensor that detects changes in the magnetic field caused by a rotor (gear rotor or magnetic rotor) that rotates together with the wheel 10. For example, a method of detecting rotor rotation using a magnetic pickup, a Hall element, an MR element, or the like is preferably used. The wheel speed sensor 12 is connected to the EV-CU 60, which will be described later.

[0020] As a result of this configuration, in the electric all-wheel drive vehicle 1 (hereinafter also referred to simply as "vehicle 1"), the front wheels 10FL, 10FR are directly driven by the front motor generator 21, and the rear wheels 10RL, 10RR are directly driven by the rear motor generator 22. The balance between the driving force of the front motor generator 21 and the driving force of the rear motor generator 22 is controlled, and the driving force of the front and rear wheels 10 is variably distributed as desired. Furthermore, regeneration can also be performed by the front motor generator 21 and the rear motor generator 22 during braking, etc.

[0021] The drive of the front motor generator 21 and the rear motor generator 22 is comprehensively controlled by the EV-CU 60. The EV-CU 60 is connected via a CAN (Controller Area Network) 100 to be able to communicate with a vehicle dynamics control unit (hereinafter referred to as "VDCU") 50 and other components that improve driving stability by suppressing skidding of the vehicle.

[0022] The EV-CU60 and VDCU50 are configured with a microprocessor that performs calculations, an EEPROM that stores programs and the like for causing the microprocessor to execute each process, a RAM that stores various data such as calculation results, a backup RAM in which the stored contents are retained, and an input / output I / F, etc.

[0023] Connected to the VDCU 50 are, for example, a steering angle sensor 16, a longitudinal acceleration (longitudinal G) sensor 55, a lateral acceleration (lateral G) sensor 56, a yaw rate sensor 57, and a brake switch 58. The longitudinal acceleration sensor 55 detects longitudinal acceleration acting on the vehicle 1, and the lateral acceleration sensor 56 detects lateral acceleration acting on the vehicle 1. The steering angle sensor 16 detects the turning angle of the front wheels 10FL, 10FR, which are steered wheels (i.e., the steering angle of the steering wheel 15), by detecting the rotation angle of the pinion shaft. The yaw rate sensor 57 detects the yaw rate of the vehicle 1.

[0024] The VDCU 50 drives the brake actuator to brake the vehicle according to the amount of brake pedal operation (amount of depression), and detects vehicle behavior using various sensors (e.g., wheel speed sensor 12, steering angle sensor 16, longitudinal acceleration sensor 55, lateral acceleration sensor 56, yaw rate sensor 57, etc.), and suppresses skidding and ensures vehicle stability during cornering through brake control by automatic pressure application and motor torque control. In other words, the VDCU 50 prevents skidding and ensures excellent driving stability when, for example, the vehicle enters a corner at an excessive speed or when the vehicle posture (behavior) becomes unstable due to abrupt steering.

[0025] The VDCU 50 transmits the detected steering angle, longitudinal acceleration, lateral acceleration, yaw rate, braking information, and the like to the EV-CU 60 via the CAN 100.

[0026] Various sensors are connected to the EV-CU 60, including, for example, an accelerator opening sensor 61 (corresponding to the accelerator sensor described in the claims) that detects the amount of depression of the accelerator pedal (accelerator opening), a resolver 62 that detects the rotational position (rotation speed) of the front motor generator 21, a resolver 63 that detects the rotational position (rotation speed) of the rear motor generator 22, and a wheel speed sensor 12 (corresponding to the vehicle speed sensor described in the claims) that detects the speed of the wheels 10 described above.

[0027] Furthermore, the EV-CU 60 receives various information from the VDCU 50 via the CAN 100, such as the steering angle, longitudinal acceleration, lateral acceleration, yaw rate, and braking information.

[0028] Based on the various types of information acquired, EV-CU 60 comprehensively controls the drive of front motor generator 21 and rear motor generator 22. EV-CU 60 calculates and outputs torque command values (required power) for front motor generator 21 and rear motor generator 22 based on, for example, accelerator pedal opening (driver's required driving force), vehicle operating conditions (vehicle speed, etc.), and the state of charge (SOC) of high-voltage battery 71. In other words, EV-CU 60 functions as a control unit as recited in the claims.

[0029] At this time, EV-CU 60 adjusts (controls) the output torque of front motor generator 21 and rear motor generator 22 so that the front and rear driving force distribution is in accordance with the frictional force between the front wheels 10FL, 10FR and the rear wheels 10RL, 10RR and the road surface. EV-CU 60 calculates the ground contact loads of front wheels 10FL, 10FR and rear wheels 10RL, 10RR from the longitudinal acceleration and lateral acceleration of the vehicle, and estimates the frictional force between the front wheels 10FL, 10FR and the rear wheels 10RL, 10RR and the road surface based on the ground contact loads.

[0030] A power control unit (hereinafter referred to as "PCU") 70 drives the front motor generator 21 and the rear motor generator 22 via an inverter 70a based on the torque command value (required power). Here, the inverter 70a converts DC power from the high-voltage battery 71 into three-phase AC power and supplies it to the front motor generator 21 and the rear motor generator 22. Meanwhile, during regeneration, the inverter 70a converts AC voltage generated by the front motor generator 21 and / or the rear motor generator 22 into DC voltage to charge the high-voltage battery 71.

[0031] In particular, the EV-CU 60 has a function that gives the driver a feeling of acceleration greater than the actual vehicle acceleration (longitudinal acceleration) when the accelerator pedal is depressed at high vehicle speeds where the output torque of the front motor generator 21 and the rear motor generator 22 decreases. The EV-CU 60 realizes this function by having a microprocessor execute a program stored in an EEPROM or the like.

[0032] Therefore, when the accelerator operation amount is increased at or above a predetermined speed while the vehicle 1 is traveling at a speed above the predetermined speed, the EV-CU 60 changes the front / rear distribution of the target driving force to be rear-wheel biased.

[0033] More specifically, for example, when the speed of vehicle 1 is above a predetermined speed and the accelerator operation amount is increased above the predetermined speed, EV-CU60 reduces the driving force of front motor generator 21 and increases the driving force of rear motor generator 22.

[0034] As the driving force of the front motor generator 21 is reduced and the driving force of the rear motor generator 22 is increased, pitching occurs, causing the rear end (rear side) of the vehicle 1 to squat (squat). That is, during acceleration, the rear end (rear side) of the vehicle squats (squats) due to the shift in load, and this state is simulated. Note that pitching is a rotational moment about an axis (Y axis) that passes through the center of gravity of the vehicle 1 and penetrates the vehicle body in the vehicle width direction.

[0035] At this time, it is preferable that EV-CU 60 increase the degree of rear wheel bias (that is, increase the amount of increase in the driving force of rear motor generator 22) as the rate of increase in the accelerator operation amount (Δ accelerator opening) increases.

[0036] Furthermore, it is preferable that EV-CU 60 increase the degree of rear wheel bias (that is, increase the amount of increase in the driving force of rear motor generator 22) as the speed (vehicle speed) of vehicle 1 increases.

[0037] On the other hand, EV-CU 60 returns the front / rear distribution of the target driving force to a normal value (e.g., 50:50) when, for example, a predetermined time or more has passed since changing the front / rear distribution of the target driving force to be rear-wheel biased, or when a state in which the target driving force of rear motor generator 22 is equal to or greater than a predetermined value has passed for a predetermined time or more. In other words, rear-wheel bias control is terminated, and the front / rear driving force distribution is restored to a value that corresponds to factors such as the frictional force between the front wheels 10FL, 10FR and the rear wheels 10RL, 10RR and the road surface. Therefore, EV-CU 60 controls the drive of front motor generator 21 and rear motor generator 22 (front / rear distribution ratio) according to factors such as the frictional force between the front and rear wheels 10 and the road surface.

[0038] Next, the operation of the electric all-wheel drive vehicle 1 will be described with reference to Figures 3 and 4. Figure 3 is a flowchart showing the processing procedure for rear-wheel bias control (acceleration sensation creation control) by the electric all-wheel drive vehicle 1. This processing is executed repeatedly at predetermined timings, mainly by the EV-CU 60. Figure 4 is a timing chart showing changes in the accelerator opening, front motor generator driving force, rear motor generator driving force, G-jerk in the pitching direction, etc., during rear-wheel bias control (acceleration sensation creation control) by the electric all-wheel drive vehicle 1.

[0039] In step S100, a determination is made as to whether the speed of the vehicle 1 (vehicle speed) is equal to or greater than a predetermined speed (i.e., whether the driving force of the front motor generator 21 and the driving force of the rear motor generator 22 have dropped below a predetermined value). If the vehicle speed is below the predetermined speed, the process temporarily ends. On the other hand, if the vehicle speed is equal to or greater than the predetermined speed, the process proceeds to step S102.

[0040] In step S102, a determination is made as to whether the increase in accelerator opening over a predetermined time period (Δaccelerator opening) is equal to or greater than a predetermined value (i.e., whether the accelerator opening is increased at a rate equal to or greater than a predetermined speed). If the increase in accelerator opening is less than the predetermined value, the process temporarily terminates. On the other hand, if the increase in accelerator opening is equal to or greater than the predetermined value, the process proceeds to step S104 (see time t1 in FIG. 4).

[0041] In step S104, a rear-wheel bias flag is set (1), indicating that rear-wheel bias control is being executed to shift the front-rear distribution of the target driving force toward the rear-wheel bias side, and the transition of the front-rear distribution of the target driving force toward the rear-wheel bias side is initiated (see time t1 in Figure 4).

[0042] In the next step S106, the target drive force of the front motor generator 21 and the target drive force of the rear motor generator 22 are calculated based on, for example, the speed of the vehicle 1 and the rate of increase in the accelerator opening (Δ accelerator opening). More specifically, the target drive force of the front motor generator 21 is reduced, and the target drive force of the rear motor generator 22 is increased (see times t1 to t2 in FIG. 4).

[0043] Next, in step S108, the required power of the front motor generator 21 and the required power of the rear motor generator 22 are calculated based on the target driving force of the front motor generator 21 and the target driving force of the rear motor generator 22 calculated in step S106. Then, the required power is supplied to the front motor generator 21 and the rear motor generator 22, and the front motor generator 21 and the rear motor generator 22 are driven (see times t1 to t2 in FIG. 4). As the driving force of the front motor generator 21 is reduced and the driving force of the rear motor generator 22 is increased, pitching (G jerk in the pitching direction) occurs such that the rear side of the vehicle 1 sinks (squats) (see times t1 to t2 in FIG. 4).

[0044] Next, in step S110, a determination is made as to whether or not the conditions for terminating rear-wheel-biased control, which shifts the front-rear distribution of the target driving force toward a rear-wheel bias, are met. More specifically, the following determinations are made: whether or not a predetermined time has elapsed since the front-rear distribution of the target driving force was changed toward a rear-wheel bias; whether or not a predetermined time has elapsed since the target driving force of the rear motor generator 22 was at or above a predetermined value; whether or not skidding of the vehicle 1 has been detected; and whether or not an abnormality (failure) of a sensor or the like has been detected. If all of the conditions are not met, the process temporarily exits. On the other hand, if at least one of the conditions is met, the process proceeds to step S112.

[0045] In step S112, the rear wheel bias flag indicating that rear wheel bias control is being executed is reset (0), and the transition of the front / rear target drive force distribution to the rear wheel bias side (rear wheel bias control) is ended (see time t2 in FIG. 4).

[0046] Next, in step S114, a determination is made as to whether or not the return from rear-wheel biased control to normal control has been completed (i.e., whether or not the front / rear distribution of the target driving force has returned to the value during normal control (e.g., 50:50)). If the return to normal control has been completed, the process ends (see time t3 onward in FIG. 4). On the other hand, if the return to normal control has not yet been completed, the process proceeds to step S116.

[0047] In step S116, the target drive force of the front motor generator 21 and the target drive force of the rear motor generator 22 are calculated so that the front / rear distribution of the target drive force is gradually returned to the value during normal control (i.e., so that the distribution gradually approaches the front / rear distribution according to the frictional force between the front wheels 10FL, 10FR and the rear wheels 10RL, 10RR and the road surface, etc.) More specifically, the target drive force of the front motor generator 21 is gradually increased, and the target drive force of the rear motor generator 22 is gradually decreased (see times t2 to t3 in FIG. 4).

[0048] Next, in step S118, the required power of the front motor generator 21 and the required power of the rear motor generator 22 are calculated based on the target driving force of the front motor generator 21 and the target driving force of the rear motor generator 22 calculated in step S116. Then, the required power is supplied to the front motor generator 21 and the rear motor generator 22, and the front motor generator 21 and the rear motor generator 22 are driven (see times t2 to t3 in FIG. 4). Thereafter, the process returns to step S114, and the processes from step S114 onwards are repeatedly executed until the return to normal control is completed.

[0049] As described above in detail, according to this embodiment, when the vehicle speed is above a predetermined speed and the accelerator operation amount is increased at a speed above the predetermined speed, the front / rear distribution of the target driving force is changed to be rear-wheel biased. For example, the driving force of the front motor generator 21 is reduced and the driving force of the rear motor generator 22 is increased. This causes the rear end (rear side) of the vehicle 1 to pitch, as if squatting. As a result, according to this embodiment, when the accelerator pedal is depressed at a high vehicle speed where the output torque of the front motor generator 21 and the rear motor generator 22 is reduced, the driver can be given a feeling of acceleration that is greater than the actual vehicle acceleration (longitudinal acceleration).

[0050] Furthermore, according to this embodiment, the greater the rate of increase in the accelerator operation amount (Δaccelerator opening), the greater the degree of rear wheel bias (i.e., the greater the increase in the driving force of the rear motor generator 22), so the greater the accelerator operation amount (the greater the driver's acceleration request), the greater the feeling of acceleration (squat).

[0051] According to this embodiment, the higher the vehicle speed, the greater the degree of rear wheel bias (i.e., the greater the increase in driving force of the rear motor generator 22), so that the driver can feel an acceleration even when the vehicle speed is higher (i.e., when the output torque of the front motor generator 21 and the rear motor generator 22 is lower).

[0052] Although the present invention has been described above as being an embodiment, it is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, the present invention is applied to an electric all-wheel drive vehicle 1 configured such that the left and right front wheels 10FL, 10FR are driven by a front motor generator 21 and the left and right rear wheels 10RL, 10RR are driven by a rear motor generator 22. However, the present invention can also be applied to an electric all-wheel drive vehicle in which an in-wheel motor is attached to each of the four wheels, for example.

[0053] Furthermore, the system configuration of the controllers such as the EV-CU 60 and the VDCU 50, and the allocation of functions among the controllers, are not limited to the above-described embodiments. For example, in the above-described embodiments, the wheel speed sensor 12 is connected to the EV-CU 60, but it may be connected to the VDCU 50 and transmit the information to the EV-CU 60 via the CAN 100. Furthermore, in the above-described embodiments, the EV-CU 60, the PCU 70, and the VDCU 50 are connected to each other via the CAN 100 so that they can communicate with each other, but the system configuration is not limited to this, and can be arbitrarily changed (integrated, etc.) in consideration of, for example, functional requirements, costs, etc. [Explanation of symbols]

[0054] 1 Electric all-wheel drive vehicle 10FL,10FR,10RL,10RR wheels 11FL, 11FR, 11RL, 11RR Brake 12FL, 12FR, 12RL, 12RR wheel speed sensor 16 Steering angle sensor 21 Front motor generator (front electric motor) 22 Rear motor generator (rear electric motor) 45L left front wheel drive shaft 45R right front wheel drive shaft 48L Left rear wheel drive shaft 48R right rear wheel drive shaft 50 VDCU 55 Front and rear acceleration sensor 56 Lateral acceleration sensor 57 Yaw rate sensor 58 Brake switch 60 EV-CU 61 Accelerator opening sensor 62, 63 Resolver 70 PCU 71 High Voltage Battery 100 CAN

Claims

1. A front electric motor that directly drives the front wheels; a rear electric motor that directly drives the rear wheels; an accelerator sensor that detects an accelerator operation amount; a vehicle speed sensor that detects the speed of the vehicle; a control unit that controls the driving of the front electric motor and the rear electric motor based on the operation amount of the accelerator and the speed of the vehicle, the control unit changes the front / rear distribution of driving force to a rear-wheel bias side when the operation amount of the accelerator is increased at a speed equal to or greater than a predetermined speed while the vehicle speed is equal to or greater than a predetermined speed, The control unit increases the degree of rear wheel bias as the rate of increase in the accelerator operation amount increases.

2. 2. The electric all-wheel drive vehicle according to claim 1, wherein the control unit reduces the driving force of the front electric motor and increases the driving force of the rear electric motor when the operation amount of the accelerator is increased at a speed equal to or greater than a predetermined speed while the vehicle speed is equal to or greater than a predetermined speed.

3. 3. The electric all-wheel drive vehicle according to claim 1, wherein the control unit increases the degree of rear wheel bias as the speed of the vehicle increases.

4. The electric all-wheel drive vehicle according to any one of claims 1 to 3, characterized in that the control unit returns the front / rear distribution of driving force to a normal value when a predetermined time or more has passed since the front / rear distribution of driving force was changed to be rear-wheel biased, or when a predetermined time or more has passed since the driving force of the rear electric motor has been at or above a predetermined value.

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