Electric all-wheel-drive vehicle

Abstract

To provide an electric all-wheel-drive vehicle in which front wheels are driven by a front electric motor and rear wheels are driven by a rear electric motor, and which makes it possible to improve electricity consumption.SOLUTION: An EV-CU 60 of a motor-driven all-wheel drive vehicle 1 is configured to: when a predetermined learning condition is satisfied, vary output torque of a rear electric motor generator 22 and output torque of a front electric motor generator 21 while satisfying requested torque, to learn longitudinal differential rotation at which total power consumption or total torque of the front electric motor generator 21 and the rear electric motor generator 22 is minimized; and after learning the longitudinal differential rotation, control the output torque of the front electric motor generator 21 and the output torque of the rear electric motor generator 22 to allow actual longitudinal differential rotation to match with the learned longitudinal differential rotation.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, battery electric vehicles (BEVs) that use electric motors as a driving force source and do not emit exhaust gases have been put to practical use. For example, Patent Document 1 discloses an electrically powered all-wheel drive vehicle (all-wheel drive electric vehicle) in which the front wheels are driven by a front motor and the rear wheels are driven by a rear motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-93646 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in electric all-wheel drive vehicles, improvement in electricity consumption (km / kWh or kWh / km) is desired. However, the electric all-wheel drive vehicle described in Patent Document 1 does not take into consideration improvement in electricity consumption.

[0005] 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 driven by a front electric motor and the rear wheels are driven by a rear electric motor, and which can further improve electricity consumption. [Means for solving the problem]

[0006] An electric all-wheel drive vehicle according to one aspect of the present invention comprises a front electric motor that drives the front wheels, a rear electric motor that drives the rear wheels, an accelerator sensor that detects the amount of accelerator operation, a front wheel speed sensor that detects the number of revolutions of the front wheels, a rear wheel speed sensor that detects the number of revolutions of the rear wheels, and a control unit that controls each of the front electric motor and the rear electric motor based on the amount of accelerator operation, the number of revolutions of the front wheels, and the number of revolutions of the rear wheels.When predetermined learning conditions are met, the control unit varies the output torque of the rear electric motor and the output torque of the front electric motor while satisfying the required torque, to learn a front-rear differential rotation, which is the difference between the number of revolutions of the front wheels and the number of revolutions of the rear wheels, that minimizes the total power consumption or total torque of the front electric motor and the rear electric motor, and after learning this front-rear differential rotation, controls the output torque of each of the front electric motor and the rear electric motor so that the actual front-rear differential rotation matches the learned front-rear differential rotation.

[0007] The electric fuel economy of an electric all-wheel drive vehicle is affected by running resistance, which in turn is affected by front and rear driving force distribution. In an electric all-wheel drive vehicle according to one aspect of the present invention, when a predetermined learning condition is met, the output torque of the rear electric motor and the output torque of the front electric motor are varied while satisfying the required torque, and a front-rear rotation speed differential (the difference between the rotation speeds of the front and rear wheels) that minimizes the total power consumption or total torque of the front electric motor and the rear electric motor is learned. After learning the front-rear rotation speed differential, the output torque of each of the front electric motor and the rear electric motor is controlled so that the actual front-rear rotation speed differential matches the learned front-rear rotation speed differential. This allows the front-rear driving force distribution to be controlled so as to minimize the total power consumption or total torque of the front electric motor and the rear electric motor while satisfying the required torque, thereby further improving electric economy. Increasing the output of the rear electric motor and decreasing the output of the front electric motor accordingly changes the slip ratios of the rear and front wheels, thereby changing the front-rear rotation speed differential. [Effects of the Invention]

[0008] According to the present invention, it is possible to further improve the electricity consumption in an electric all-wheel drive vehicle in which the front wheels are driven by a front electric motor and the rear wheels are driven by a rear electric motor. [Brief explanation of the drawings]

[0009] [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] FIG. 3 is a diagram showing the characteristics (relationship) between driving force and tire slip (slip ratio). [Figure 4] 10A and 10B are diagrams for explaining a method for learning the minimum value of total power consumption or total torque by an electric all-wheel drive vehicle according to an embodiment. [Figure 5] FIG. 10 is a diagram illustrating an example of a target front-rear rotation difference map. [Figure 6] 10 is a flowchart showing the processing procedure for learning a front-rear rotation difference in an electric all-wheel drive vehicle according to an embodiment. [Figure 7] 4 is a flowchart showing a processing procedure for front and rear rotation difference control performed by an electric all-wheel drive vehicle according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] First, the configuration of an electric all-wheel drive vehicle (AWD BEV) 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.

[0012] The front motor generator 21 (corresponding to the front electric motor described in the claims) is connected to a left front wheel drive shaft 45L and a right front wheel drive shaft 45R via, for example, a gear (front reduction gear) or a front differential (front motor unit). The left front wheel drive shaft 45L is connected to the left front wheel 10FL, and the right front wheel drive shaft 45R is connected to the right front wheel 10FR. In other words, the front motor generator 21 is connected to the front wheels 10FL, 10FR so as to be able to transmit torque thereto, and drives the front wheels 10FL, 10FR.

[0013] Similarly, the rear motor generator 22 (corresponding to the rear electric motor described in the claims) is connected to a left rear wheel drive shaft 48L and a right rear wheel drive shaft 48R via, for example, a gear (rear reduction gear) or a rear differential (rear motor unit). The left rear wheel drive shaft 48L is connected to the left rear wheel 10RL, and the right rear wheel drive shaft 48R is connected to the right rear wheel 10RR. In other words, the rear motor generator 22 is connected to the rear wheels 10RL and 10RR so as to be able to transmit torque to drive the rear wheels 10RL and 10RR.

[0014] 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.

[0015] 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 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 motor rotation speed, the greater the induced electromotive force (induced voltage), resulting in a decrease in driving force (output torque).

[0016] Returning to FIG. 1, brakes 11FL-11RR (hereinafter, all the brakes 11FL-11RR may be collectively referred to as wheels 10) that brake the wheels 10FL-10RR are attached to the wheels 10FL-10RR, respectively. Wheel speed sensors 12FL-12RR (hereinafter, all the wheel speed sensors 12FL-12RR may be collectively referred to as wheel speed sensors 12) that detect the wheel rotation speed are attached to the wheels 10FL-10RR. That is, front wheel speed sensors 12FL, 12FR that detect the rotation speed (rotation speed) of the front wheels 10FL, 10FR are attached to the front wheels 10FL, 10FR, and rear wheel speed sensors 12RL, 12RR that detect the rotation speed (rotation speed) of the rear wheels 10RL, 10RR are attached to the rear wheels 10RL, 10RR.

[0017] 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.

[0018] 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 driven by the front motor generator 21, and the rear wheels 10RL, 10RR are 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.

[0019] 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.

[0020] 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.

[0021] 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 (vehicle width) 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.

[0022] The VDCU 50 brakes the vehicle by driving the brake actuator in accordance with the amount of brake pedal operation (depression amount), 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 through brake control by automatic pressure application and motor torque control, thereby ensuring vehicle stability during cornering. 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's posture (behavior) becomes unstable due to abrupt steering operation. In addition to the above-mentioned VDC (Vehicle Dynamic Control) function, the VDCU 50 also has an ABS (Anti-lock Brake System) function and a TCS (Traction Control System) function.

[0023] 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.

[0024] Various sensors are connected to the EV-CU 60, including, for example, an accelerator sensor 61 that detects the amount of depression (operation amount) of the accelerator pedal, 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 wheel speed sensors 12 (front wheel speed sensors 12FL, 12FR, rear wheel speed sensors 12RL, 12RR) that detect the speed of the wheels 10 mentioned above. In addition, EV-CU 60 is also connected to temperature sensors 64, 65 that detect the temperatures of the front motor generator 21 and the rear motor generator 22, and an oil temperature sensor 66 that detects the temperature (oil temperature) of the oil that lubricates and cools the front reduction gear, front differential (front motor unit), and rear reduction gear, and rear differential (rear motor unit).

[0025] 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.

[0026] 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 operation amount, front wheel rotation speed, rear wheel rotation speed, vehicle speed (vehicle speed) calculated from the front wheel rotation speed and rear wheel rotation speed (wheel speed), 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.

[0027] At this time, EV-CU 60 controls the output torque of front motor generator 21 and rear motor generator 22 so as to achieve a front / rear driving force distribution according to the frictional force (or slip ratio) between the front wheels 10FL, 10FR and the rear wheels 10RL, 10RR and the road surface (under normal control). Note that EV-CU 60 calculates the ground contact loads of the front wheels 10FL, 10FR and the 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.

[0028] 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.

[0029] Additionally, EV-CU 60 has a cruise control function that executes cruise control to maintain the vehicle speed at a set speed regardless of the driver's accelerator operation. More specifically, when the driver operates a cruise control execution switch to set a target vehicle speed (set vehicle speed), EV-CU 60 controls the output torque of front motor generator 21 and rear motor generator 22, etc., to maintain the vehicle speed at the set target vehicle speed (set vehicle speed). Note that the cruise control function includes an adaptive cruise control (ACC) function that causes the host vehicle to travel at a constant speed if no leading vehicle is detected, and controls the host vehicle to follow the leading vehicle if a leading vehicle is detected.

[0030] In particular, the EV-CU 60 has a function to further improve the electricity consumption of the electric all-wheel drive vehicle 1. In the EV-CU 60, the function is realized by a microprocessor executing a program stored in an EEPROM or the like.

[0031] The electric fuel economy of an electric all-wheel drive vehicle is affected by running resistance, which in turn is affected by the front / rear driving force distribution. Examples of the influence of the front / rear driving force distribution on running resistance (electric fuel economy) include the influence of the efficiency of the front and rear motor units and the influence of compliance steer (changes in actual steering angle caused by deflection of the suspension, steering, etc.) caused by driving the front and rear tires. Furthermore, these influences change depending on the temperatures of the front and rear motor generators 21, 22, the oil temperature of the motor units, the state of alignment, etc.

[0032] Therefore, when a predetermined learning condition is met, EV-CU60 first varies (oscillates) the output torque of the rear motor generator 22 and the output torque of the front motor generator 21 while satisfying the required torque (required driving force), and learns the front / rear differential rotation (the difference between the front wheel rotation speed and the rear wheel rotation speed) at which the total power consumption or total torque of the front motor generator 21 and the rear motor generator 22 is minimized (takes a minimum value).

[0033] More specifically, in order to minimize the impact on driving stability, when cruise control is in progress and the steering angle (steering angle or turning angle) is equal to or less than a predetermined value (i.e., when the vehicle is traveling straight or approximately straight), EV-CU60 determines that the above-mentioned predetermined learning condition is met and learns the front / rear rotation difference.

[0034] Here, the required torque (required driving force) is obtained, for example, based on the deviation between the set vehicle speed (target vehicle speed) and the actual vehicle speed when cruise control is being executed, and is obtained, for example, based on the accelerator operation amount and the vehicle speed when cruise control is not being executed.

[0035] Furthermore, when learning the front-rear rotation difference, it is preferable that EV-CU 60 uses FF as a reference (base) and increases the output torque (rear torque) of rear motor generator 22 and decreases the output torque (front torque = required torque - rear torque) of front motor generator 21. Note that if the output of rear motor generator 22 is increased (up) and the output of front motor generator 21 is decreased (down) by that amount, the slip ratios of rear wheels 10RL, 10RR and front wheels 10FL, 10FR change (details will be described later), and the front-rear rotation difference changes.

[0036] Furthermore, when learning the front / rear rotation difference, it is preferable that EV-CU60 varies (oscillates) the output torque of the rear motor generator 22 and the output torque of the front motor generator 21 so that the slip ratio of the front wheels 10FL, 10FR and the slip ratio of the rear wheels 10RL, 10RR each fall within a predetermined slip ratio range (for example, approximately ±2%, between MIN and MAX shown in Figure 3, i.e., a level at which grip is not lost).

[0037] FIG. 3 is a diagram showing the relationship between driving force and tire slip (slip ratio). The vertical axis of FIG. 3 represents driving force (Nm), and the horizontal axis represents slip ratio (%). FIG. 3 also shows the relationship between driving force on a low μ road and a high μ road. As shown in FIG. 3, as the driving force increases, the slip ratio also increases. Then, the driving force peaks and the tire enters the slip region (i.e., the tire reaches its limit at which it can no longer transmit driving force). Therefore, as described above, if the output of rear motor generator 22 is increased and the output of front motor generator 21 is reduced by that amount, the slip ratio of rear wheels 10RL, 10RR increases and the slip ratio of front wheels 10FL, 10FR decreases, resulting in a change in the front / rear differential rotation.

[0038] Furthermore, by varying the output torque of the rear motor generator 22 and the output torque of the front motor generator 21 so that the slip ratios of the front wheels 10FL and 10FR and the rear wheels 10RL and 10RR are each within a predetermined slip ratio range (for example, approximately ±2%, between MIN and MAX as shown in FIG. 3), the front-rear differential rotation can be stably learned while maintaining grip even on low-μ roads (regardless of the road surface's μ). Assuming that the front and rear wheels 10 have the same diameter and axle load, the front-rear differential rotation can be considered to be approximately equal to the slip ratio difference, so regulating the front-rear differential rotation prevents abnormal slip ratios. In other words, if torque control is used to determine the front-rear driving force distribution, there is a risk that the wheels 10 will unintentionally slip (enter the slip region) on low-μ roads (road surfaces with a large increase in slip ratio per 1 Nm). Therefore, the search range for learning is limited by the difference in rotation speeds between the front and rear wheels 10 (≒ slip ratio difference).

[0039] 4 is a diagram for explaining a method for learning the minimum value of the total power consumption or total torque. The horizontal axis of FIG. 4 represents the front-rear rotation difference (rpm), and the vertical axis represents the total power consumption (kWh) or the total torque (Nm). A known method (algorithm) can be used to search for the front-rear rotation difference at which the total power consumption or total torque takes the minimum value.

[0040] Returning to Figure 1 to continue the explanation, after learning the front-rear differential rotation, EV-CU 60 controls (F / B control) the output torque of each of the rear motor generator 22 and the front motor generator 21 so that the actual front-rear differential rotation (actual front-rear differential rotation) matches the learned front-rear differential rotation (target front-rear differential rotation).

[0041] More specifically, after learning the front-rear differential rotation, when cruise control is in progress and the steering angle (steering angle or turning angle) is equal to or less than a predetermined value, EV-CU60 controls (F / B control) the output torque (rear torque) of rear motor generator 22 and the output torque (front torque = required torque - rear torque) of front motor generator 21 so that the actual front-rear differential rotation matches the learned front-rear differential rotation (target front-rear differential rotation).

[0042] Here, the learning of the front-rear rotation difference may be repeatedly executed to successively update the learning value, and the latest learning value may be used (controlled) as the target value (target front-rear rotation difference), or the acquired learning data may be mapped and used.

[0043] When creating the map, it is preferable that EV-CU 60 learns the front / rear rotation difference for each vehicle speed and each required torque.

[0044] Then, EV-CU 60 generates a target front-rear rotation difference map that defines the relationship between the vehicle speed, the required driving force, and the learned front-rear rotation difference.

[0045] After generating the target front-rear rotation difference map, when cruise control is in progress and the steering angle (steering angle or turning angle) is equal to or less than a predetermined value (i.e., when the vehicle is traveling straight or approximately straight), EV-CU60 uses the target front-rear rotation difference map to control the output torque of each of the front motor generator 21 and the rear motor generator 22.

[0046] That is, EV-CU 60 stores a map (target front-rear rotation difference map) that defines the relationship between vehicle speed, required torque, and learned front-rear rotation difference (target front-rear rotation difference) in an EEPROM or the like, and determines the target front-rear rotation difference by searching this target front-rear rotation difference map based on the vehicle speed and required torque. Then, EV-CU 60 controls the output torque of each of front motor generator 21 and rear motor generator 22 based on the target front-rear rotation difference.

[0047] An example of the target front-rear rotation difference map is shown in Fig. 5. In Fig. 5, the horizontal axis represents vehicle speed (km / h) and the vertical axis represents required torque (Nm). In the target front-rear rotation difference map, a learned front-rear rotation difference (target front-rear rotation difference) is stored for each combination (grid point) of vehicle speed and required torque.

[0048] Additionally, EV-CU 60 may learn the front / rear rotation difference for each temperature of front motor generator 21 and rear motor generator 22, and / or for each temperature of the oil that lubricates and cools the front and rear motor units (oil temperature).These parameters may then be added to the axes of the target front / rear rotation difference map described above.

[0049] Next, the operation of the electric all-wheel drive vehicle 1 will be described with reference to Figures 6 and 7. Figure 6 is a flowchart showing the procedure for learning the front / rear rotation difference. Figure 7 is a flowchart showing the procedure for controlling the front / rear rotation difference. This process is executed repeatedly at predetermined intervals, mainly by EV-CU 60.

[0050] First, the procedure for learning the front / rear rotation difference will be described with reference to Figure 6. In step S100, it is determined whether or not cruise control is in progress. If cruise control is not in progress, the process temporarily ends. On the other hand, if cruise control is in progress, the process proceeds to step S102.

[0051] In step S102, it is determined whether the steering angle (steering angle or turning angle) is equal to or less than a predetermined value (i.e., the vehicle is traveling straight or approximately straight). If the steering angle is greater than the predetermined value, the process temporarily ends. On the other hand, if the steering angle is equal to or less than the predetermined value, the process proceeds to step S104.

[0052] In step S104, the output torque of the rear motor generator 22 and the output torque of the front motor generator 21 are varied while satisfying the required torque. For example, the output torque (rear torque) of the rear motor generator 22 is increased, and the output torque of the front motor generator 21 (front torque = required torque - rear torque) is reduced accordingly.

[0053] Next, in step S106, it is determined whether the total power consumption or total torque of the front motor generator 21 and the rear motor generator 22 has reached a minimum (taken a local minimum value). If the total power consumption or total torque has not reached a minimum, the processes of steps S104 to S106 described above are repeated until the total power consumption or total torque reaches a minimum. More specifically, in step S104, the output torque (rear torque) of the rear motor generator 22 is further increased, and the output torque of the front motor generator 21 (front torque = required torque - rear torque) is further reduced by that amount. Then, in step S106, it is determined again whether the total power consumption or total torque of the front motor generator 21 and the rear motor generator 22 has reached a minimum (taken a local minimum value). On the other hand, if the total power consumption or total torque of the front motor generator 21 and the rear motor generator 22 has reached a minimum, the process proceeds to step S108.

[0054] In step S108, the front / rear rotation difference (the difference between the front wheel rotation speed and the rear wheel rotation speed) when the total power consumption or total torque of the front motor generator 21 and the rear motor generator 22 becomes minimum is learned and stored. After that, the process temporarily exits.

[0055] Next, the processing procedure of the front / rear rotation difference control will be explained using Figure 7. In step S200, it is determined whether or not cruise control is in progress. If cruise control is not in progress, the process is temporarily terminated. On the other hand, if cruise control is in progress, the process proceeds to step S202.

[0056] In step S202, it is determined whether the steering angle (steering angle or turning angle) is equal to or less than a predetermined value (i.e., the vehicle is traveling straight or approximately straight). If the steering angle is greater than the predetermined value, the process temporarily ends. On the other hand, if the steering angle is equal to or less than the predetermined value, the process proceeds to step S204.

[0057] In step S204, the rotation speeds of the front wheels 10FL, 10FR and the rear wheels 10RL, 10RR are read, and the actual front / rear rotation difference (front wheel rotation speed - rear wheel rotation speed) is calculated.

[0058] Next, in step S206, the latest learned front-rear rotation difference (target front-rear rotation difference) is read in. Alternatively, a target front-rear rotation difference map is searched based on the vehicle speed and required torque to determine the target front-rear rotation difference.

[0059] Next, in step S208, the output torque (rear torque) of the rear motor generator 22 and the output torque (front torque = required torque - rear torque) of the front motor generator 21 are controlled (F / B control) so that the target front-rear rotation difference and the actual front-rear rotation difference coincide with each other. After that, the process temporarily exits.

[0060] As described above in detail, according to this embodiment, when a predetermined learning condition is met, the output torque of the rear motor generator 22 and the output torque of the front motor generator 21 are varied while satisfying the required torque. This learns the front-rear rotation speed difference (the difference between the front wheel rotation speed and the rear wheel rotation speed) that minimizes the total power consumption or total torque of the front motor generator 21 and the rear motor generator 22. After learning this front-rear rotation speed difference, the output torques of the front motor generator 21 and the rear motor generator 22 are controlled so that the actual front-rear rotation speed difference matches the learned front-rear rotation speed difference. This allows the front-rear driving force distribution to be controlled so as to minimize the total power consumption or total torque of the front motor generator 21 and the rear motor generator 22 while satisfying the required torque, thereby further improving electricity efficiency. As a result, electricity efficiency can be further improved in an electric all-wheel drive vehicle 1 in which the front wheels 10FL and 10FR are driven by the front motor generator 21 and the rear wheels 10RL and 10RR are driven by the rear motor generator 22. Furthermore, learning can also absorb individual differences and changes over time (deterioration).

[0061] Furthermore, according to this embodiment, when cruise control is in progress and the steering angle is equal to or less than a predetermined value, it is determined that a predetermined learning condition is met and the front / rear rotation differential is learned, and after learning the front / rear rotation differential, when cruise control is in progress and the steering angle is equal to or less than the predetermined value, the output torques of the front motor generator 21 and the rear motor generator 22 are controlled so that the actual front / rear rotation differential and the learned front / rear rotation differential (target front / rear rotation differential) match. This makes it possible to minimize the impact on driving stability.

[0062] According to this embodiment, the output torque of the rear motor generator 22 and the output torque of the front motor generator 21 are varied so that the slip ratios of the front wheels 10FL, 10FR and the rear wheels 10RL, 10RR fall within a predetermined slip ratio range, thereby preventing the wheels 10 from slipping abnormally (excessively).

[0063] According to this embodiment, the front / rear rotation difference is learned for each vehicle speed and each required torque, so that the map can be created taking into account changes in running resistance in response to changes in vehicle speed and required torque.

[0064] Furthermore, according to this embodiment, the front and rear rotation difference is learned for each temperature of the front motor generator 21 and the rear motor generator 22 and / or for each oil temperature (oil temperature). Therefore, it is possible to create a map taking into consideration changes in running resistance according to changes in the temperatures of the front and rear motor generators 21, 22 and oil temperature.

[0065] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and various modifications are possible. For example, in the above embodiments, the present invention is applied to an electric all-wheel drive vehicle 1 configured such that the front wheels 10FL, 10FR are driven by a front motor generator 21 and the 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.

[0066] 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]

[0067] 1 Electric all-wheel drive vehicle 10FL,10FR Front wheel (wheel) 10RL, 10RR rear wheels 11FL, 11FR, 11RL, 11RR Brake 12FL, 12FR Front wheel speed sensor (wheel speed sensor) 12RL, 12RR Rear wheel speed sensor (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 sensor 62, 63 Resolver 64, 65 Temperature sensor 66 Oil temperature sensor 70 PCU 71 High Voltage Battery 100 CAN

Claims

1. A front electric motor that drives the front wheels; A rear electric motor that drives the rear wheels; an accelerator sensor that detects an accelerator operation amount; a front wheel speed sensor that detects the number of revolutions of the front wheels; a rear wheel speed sensor that detects the rotation speed of the rear wheel; a control unit that controls each of the front electric motor and the rear electric motor based on an operation amount of the accelerator, a rotation speed of the front wheels, and a rotation speed of the rear wheels, The control unit when a predetermined learning condition is established, the output torque of the rear electric motor and the output torque of the front electric motor are varied while satisfying a required torque, and a front-rear rotation difference, which is the difference between the rotation speed of the front wheels and the rotation speed of the rear wheels, is learned so that the total power consumption or total torque of the front electric motor and the rear electric motor is minimized; After learning the front-rear differential rotation, the output torque of each of the front electric motor and the rear electric motor is controlled so that the actual front-rear differential rotation coincides with the learned front-rear differential rotation. An electric all-wheel drive vehicle.

2. 2. The electric all-wheel drive vehicle according to claim 1, wherein, when the predetermined learning condition is met, the control unit varies the output torque of the rear electric motor and the output torque of the front electric motor while satisfying a required torque so that the slip ratio of the front wheels and the slip ratio of the rear wheels each fall within a predetermined slip ratio range.

3. The control unit When cruise control is in progress and the steering angle is equal to or less than a predetermined value, it is determined that the predetermined learning condition is met, and the front / rear rotation difference is learned; After learning the front-rear differential rotation, when cruise control is in progress and the steering angle is equal to or less than a predetermined value, the output torque of each of the front electric motor and the rear electric motor is controlled so that the actual front-rear differential rotation coincides with the learned front-rear differential rotation.

3. The electric all-wheel drive vehicle according to claim 2.

4. 4. The electric all-wheel drive vehicle according to claim 3, wherein the control unit learns the front-rear rotation difference for each vehicle speed and each required torque.

5. 5. The electric all-wheel drive vehicle according to claim 4, wherein the control unit learns the front and rear differential rotation for each temperature of the front electric motor and each temperature of the rear electric motor and / or for each temperature of oil.

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