Electric all-wheel drive vehicle

Abstract

The invention provides an electric all-wheel drive vehicle capable of further improving electric efficiency, in which front wheels are driven by a front electric motor and rear wheels are driven by a rear electric motor. When a predetermined learning condition is satisfied, an EV-CU (60) of an electric all-wheel drive vehicle (1) learns a front-rear rotation difference in which the output torque of a motor generator (22) and the output torque of a front motor generator (21) are varied while satisfying a requested torque and the total power consumption or the total torque of the front motor generator (21) and a rear motor generator (22) is minimized. After the front-rear rotation difference is learned, the output torque of the front motor generator (21) and the output torque of the rear motor generator (22) are controlled so that the actual front-rear rotation difference matches the learned front-rear rotation difference.

Description

Technical Field

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

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

[0003] Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Publication No. 2018-93646 Summary of the Invention

[0004] Technical issues However, in electric all-wheel drive vehicles, it is desired to increase (improve) the electrical efficiency (km / kWh or kWh / km). However, in the electric all-wheel drive vehicle described in Patent Document 1, no consideration is given to increasing (improving) the electrical efficiency.

[0005] The present invention has been made to solve the above-mentioned problems, and its object is to provide an electric all-wheel drive vehicle capable of further improving electrical efficiency, wherein the electric all-wheel drive vehicle has front wheels driven by a front electric motor and rear wheels driven by a rear electric motor.

[0006] Technical Solution An electric all-wheel drive vehicle according to one embodiment of the present invention is characterized in that it comprises: a front electric motor for driving the front wheels, a rear electric motor for driving the rear wheels, an acceleration sensor for detecting the amount of accelerator operation, a front wheel speed sensor for detecting the rotation speed of the front wheels, a rear wheel speed sensor for detecting the rotation speed of the rear wheels, and a control unit for controlling the front electric motor and the rear electric motor respectively based on the amount of accelerator operation, the rotation speed of the front wheels, and the rotation speed of the rear wheels, wherein the control unit learns the front and rear rotation difference when a predetermined learning condition is satisfied, and after learning the front and rear rotation difference, controls the output torque of each of the front and rear electric motors in a manner such that the actual front and rear rotation difference is consistent with the learned front and rear rotation difference, wherein the front and rear rotation difference is the difference between the rotation speed of the front wheels and the rotation speed of the rear wheels so that the output torque of the rear electric motor and the output torque of the front electric motor are variable while satisfying the requested torque and the total power consumption or total torque of the front and rear electric motors is minimized.

[0007] Furthermore, the electrical efficiency of an electric all-wheel-drive vehicle is affected by driving resistance, which in turn is affected by the front-rear driving force distribution. According to one embodiment of the electric all-wheel-drive vehicle of the present invention, when predetermined learning conditions are met, a front-rear rotational difference (the difference between the front and rear wheel rotational speeds) is learned, allowing the output torque of the rear electric motor and the output torque of the front electric motor to be variable while satisfying the requested torque and minimizing the total power consumption or total torque of the front and rear electric motors. After learning this front-rear rotational difference, the output torques of the front and rear electric motors are controlled so that the actual front-rear rotational difference matches the learned front-rear rotational difference. Consequently, the front-rear driving force distribution can be controlled so that the total power consumption or total torque of the front and rear electric motors is minimized while satisfying the requested torque, further improving electrical efficiency. Furthermore, increasing the output of the rear electric motor and correspondingly decreasing the output of the front electric motor change the slip rates of the rear and front wheels, respectively, and thus the front-rear rotational difference.

[0008] Technical Effects According to the present invention, 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, the electric efficiency can be further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 1 is a diagram showing the overall structure of an electric all-wheel drive vehicle according to an embodiment.

[0010] Figure 2 1 is a diagram showing output characteristics (TN characteristics) of the front motor generator and the rear motor generator.

[0011] Figure 3 It is a diagram showing the characteristics (relationship) between driving force and tire slip (slip ratio).

[0012] Figure 4 1 is a diagram for explaining a method of learning a minimum value of total power consumption or total torque in the electric all-wheel drive vehicle according to the embodiment.

[0013] Figure 5 : is a diagram showing an example of a target front-back rotation difference map.

[0014] Figure 6 This is a flowchart showing the processing procedure of learning the front-rear rotation difference of the electric all-wheel drive vehicle according to the embodiment.

[0015] Figure 7 This is a flowchart showing the processing procedure of the front-rear rotation difference control of the electric all-wheel drive vehicle according to the embodiment.

[0016] Explanation of symbols 1: Electric all-wheel drive vehicle 10FL, 10FR: front wheel (wheel) 10RL, 10RR: rear wheel (wheel) 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 electric generator (front electric motor) 22: Rear electric 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: Longitudinal acceleration sensor 56: Lateral acceleration sensor 57: Yaw rate sensor 58: Brake switch 60:EV-CU 61: Acceleration sensor 62, 63: Rotary transformer 64, 65: Temperature sensor 66: Oil temperature sensor 70: PCU 71: High-voltage battery 100: CAN DETAILED DESCRIPTION

[0017] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in the drawings, the same reference numerals are used for the same or equivalent parts. In addition, in each figure, the same reference numerals are used for the same elements and repeated descriptions are omitted.

[0018] First, use Figure 1 The structure of an electric all-wheel drive vehicle (AWD BEV) 1 according to the embodiment will be described. Figure 1 1 is a diagram showing the overall structure of the electric all-wheel drive vehicle 1 .

[0019] The front motor generator 21 (corresponding to the front electric motor recited in the claims) is connected to the left front wheel drive shaft 45L and the right front wheel drive shaft 45R, for example, via a gear (front reduction gear), a front differential, and the like (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. That is, the front motor generator 21 is connected to the front wheels 10FL, 10FR in a manner capable of transmitting torque, and drives the front wheels 10FL, 10FR.

[0020] Likewise, the rear motor generator 22 (corresponding to the rear electric motor recited in the claims) is connected to the left rear wheel drive shaft 48L and the right rear wheel drive shaft 48R, for example, via a gear (rear reduction gear), a rear differential, and the like (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. That is, the rear motor generator 22 is connected to the rear wheels 10RL, 10RR in a manner capable of transmitting torque, and drives the rear wheels 10RL, 10RR.

[0021] The front motor generator 21 and the rear motor generator 22 are configured as synchronous motor generators that have both a function as a motor that converts supplied electric power into mechanical power and a function as a generator that converts input mechanical power into electric power. That is, the front motor generator 21 and the rear motor generator 22 each function as a motor that generates driving torque when driving the vehicle and as a generator when regenerating.

[0022] Here, in Figure 2 The output characteristics (T-N characteristics) of the front motor generator 21 and the rear motor generator 22 are shown. Figure 2 The horizontal axis is the motor speed (rpm), and the vertical axis is the driving force (Nm). As shown in Figure 2 The front motor generator 21 and the rear motor generator 22 have characteristics (T-N characteristics) in which the higher the motor speed, the lower the driving force (output torque) due to an increase in induced electromotive force (induced voltage) in a region above a base speed.

[0023] Returning to Figure 1, brakes 11FL to 11RR (hereinafter, all brakes 11FL to 11RR may also be collectively referred to as brakes 11) are mounted on each wheel 10FL to 10RR (hereinafter, all brakes 11FL to 11RR may also be collectively referred to as brakes 11) for braking the wheels 10FL to 10RR. Furthermore, wheel speed sensors 12FL to 12RR (hereinafter, all wheel speed sensors 12FL to 12RR may also be collectively referred to as wheel speed sensors 12) are mounted on each wheel 10FL to 10RR for detecting the wheel's rotational speed. Specifically, front wheel speed sensors 12FL and 12FR are mounted on the front wheels 10FL and 10FR to detect the rotational speed (rotational speed) of the front wheels 10FL and 10FR, and rear wheel speed sensors 12RL and 12RR are mounted on the rear wheels 10RL and 10RR to detect the rotational speed (rotational speed) of the rear wheels 10RL and 10RR.

[0024] The wheel speed sensor 12 is a non-contact sensor that detects changes in the magnetic field generated by a rotor (gear rotor or magnet rotor) that rotates along with the wheel 10. For example, a method for detecting rotor rotation using an electromagnetic pickup, a Hall effect element, an MR element, or the like is preferably used. The wheel speed sensor 12 is connected to the EV-CU 60, described later.

[0025] Due to this configuration, in the electric all-wheel-drive vehicle 1 (hereinafter also referred to as "vehicle 1"), 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, the balance between the driving force of the front motor generator 21 and the driving force of the rear motor generator 22 is controlled, allowing the driving force to be arbitrarily and variably distributed between the front and rear wheels 10. Furthermore, regeneration can be performed using the front motor generator 21 and the rear motor generator 22 during braking, for example.

[0026] The driving 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 communicatively connected to a vehicle dynamics control unit (hereinafter referred to as "VDCU") 50, etc., via a CAN (Controller Area Network) 100, which suppresses vehicle skidding and improves driving stability.

[0027] The EV-CU 60 and VDCU 50 are configured to include a microprocessor for performing calculations, an EEPROM storing programs for causing the microprocessor to execute various processes, a RAM storing various data such as calculation results, a backup RAM for holding the stored data, and input / output I / Fs.

[0028] 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 acceleration acting on the vehicle 1 in the longitudinal direction, while the lateral acceleration sensor 56 detects acceleration acting on the vehicle 1 in the lateral direction (vehicle width direction). Furthermore, the steering angle sensor 16 detects the steering angle of the front wheels 10FL and 10FR (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.

[0029] The VDCU 50 brakes the vehicle by driving the brake actuator based on the amount of brake pedal operation (depression amount). It also 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 uses automatic braking and motor torque control to suppress side slip and ensure vehicle stability during cornering. Specifically, the VDCU 50 prevents side slip when entering a corner at excessive speed or when the vehicle's posture (behavior) becomes disturbed due to sudden steering operation, thereby ensuring excellent driving stability. In addition to the aforementioned VDC (Vehicle Disturbance Control) function, the VDCU 50 also includes ABS (Anti-lock Braking System) and TCS (Traction Control System) functions.

[0030] The VDCU 50 transmits the detected steering angle, longitudinal acceleration, lateral acceleration, yaw rate, and braking information to the EV-CU 60 via the CAN 100 .

[0031] Various sensors are connected to the EV-CU 60. These sensors include, for example, an acceleration sensor 61 that detects the amount of accelerator pedal depression (operation amount), a resolver 62 that detects the rotational position (rotational speed) of the front motor generator 21, a resolver 63 that detects the rotational position (rotational 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. Furthermore, the EV-CU 60 is connected to temperature sensors 64 and 65 that detect the temperatures of the front motor generator 21 and rear motor generator 22, and an oil temperature sensor 66 that detects the temperature of the oil (oil temperature) that lubricates and cools the front reduction gears and front differential (front motor unit) and the rear reduction gears and rear differential (rear motor unit).

[0032] Furthermore, the EV-CU 60 receives various information such as steering angle, longitudinal acceleration, lateral acceleration, yaw rate, and braking information from the VDCU 50 via the CAN 100 .

[0033] Based on this acquired information, the EV-CU 60 comprehensively controls the driving of the front motor-generator 21 and the rear motor-generator 22. For example, the EV-CU 60 calculates and outputs torque command values ​​(requested power) for each of the front motor-generator 21 and the rear motor-generator 22 based on the accelerator operation amount, the front and rear wheel speeds, the vehicle speed (body speed) calculated from these front and rear wheel speeds (wheel speeds), and the state of charge (SOC) of the high-voltage battery 71. In other words, the EV-CU 60 functions as the control unit described in the claims.

[0034] At this time, the EV-CU 60 controls the output torque of the front motor-generator 21 and the rear motor-generator 22 (during normal control) in a manner that, for example, distributes the driving force front-to-rear in response to the friction (or slip rate) between the front wheels 10FL, 10FR and the rear wheels 10RL, 10RR and the road surface. The EV-CU 60 calculates the ground loads of the front wheels 10FL, 10FR and the rear wheels 10RL, 10RR based on the longitudinal and lateral accelerations of the vehicle, and estimates the friction between the front wheels 10FL, 10FR and the road surface based on these ground loads.

[0035] Based on the torque command value (requested power), the power control unit (hereinafter referred to as "PCU") 70 drives the front motor generator 21 and the rear motor generator 22 via the inverter 70a. The inverter 70a converts DC power from the high-voltage battery 71 into three-phase AC power, which is then supplied to the front motor generator 21 and the rear motor generator 22. During regeneration, the inverter 70a converts the 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.

[0036] The EV-CU 60 also has a cruise control function that maintains the vehicle speed at a set speed, independent of the driver's accelerator operation. More specifically, if the driver operates a cruise control switch to set a target vehicle speed (set speed), the EV-CU 60 controls the output torque of the front motor-generator 21 and the rear motor-generator 22, among other factors, to maintain the vehicle speed at the set target speed (set speed). The cruise control function includes a cruise control function with a preceding vehicle following function (Adaptive Cruise Control: ACC), which controls the vehicle to maintain a constant speed if no preceding vehicle is detected and to follow the preceding vehicle if a preceding vehicle is detected.

[0037] In particular, the EV-CU 60 has a function of further improving the electrical efficiency of the electric all-wheel drive vehicle 1. In the EV-CU 60, this function is realized by a microprocessor executing a program stored in an EEPROM or the like.

[0038] However, the electrical efficiency of an electric all-wheel-drive vehicle is affected by running resistance, which is influenced by the front-to-rear driving force distribution. Examples of how this front-to-rear driving force distribution affects running resistance (electrical efficiency) include the efficiency of the front and rear motor units and the effect of compliance steer (the change in actual steering angle caused by deflection of the suspension, steering gear, etc.) caused by driving the front and rear tires. These effects also vary depending on factors such as the temperature of the front and rear motor generators 21 and 22, the oil temperature of the motor units, and the wheel alignment.

[0039] Therefore, the EV-CU 60 first learns the front-rear rotational difference (the difference between the front wheel speed and the rear wheel speed) when predetermined learning conditions are met. This front-rear rotational difference is a front-rear rotational difference that allows the output torque of the rear motor generator 22 and the output torque of the front motor generator 21 to be variable (oscillate) while satisfying the requested torque (requested driving force) and minimizing the total power consumption or total torque of the front motor generator 21 and the rear motor generator 22 (taking a minimum value).

[0040] More specifically, to minimize the impact on handling stability, the EV-CU 60 determines that the aforementioned predetermined learning conditions are met and learns the front-rear rotation difference when the vehicle is in cruise control and the steering angle (steering angle or rudder angle) is less than a predetermined value (i.e., in a straight-ahead or substantially straight-ahead state).

[0041] Here, when cruise control is in effect, the requested torque (requested driving force) is obtained based on, for example, the deviation between the set vehicle speed (target vehicle speed) and the actual vehicle speed. Furthermore, when not in effect, the requested torque (requested driving force) is obtained based on, for example, the accelerator operation amount and the vehicle speed.

[0042] Furthermore, when learning the front-to-rear rotation difference, the EV-CU 60 preferably increases the output torque (rear torque) of the rear motor-generator 22 and decreases the output torque of the front motor-generator 21 (front torque = requested torque - rear torque) using FF (front-wheel drive) as a reference (base). It should be noted that increasing (raising) the output of the rear motor-generator 22 and correspondingly decreasing (reducing) the output of the front motor-generator 21 changes the slip rates of the rear wheels 10RL, 10RR and the front wheels 10FL, 10FR (details will be described later), thereby changing the front-to-rear rotation difference.

[0043] When learning the front and rear rotation differences, it is preferable that the EV-CU 60 keeps the slip rates of the front wheels 10FL, 10FR and the slip rates of the rear wheels 10RL, 10RR within a predetermined slip rate range (for example, approximately ±2%). Figure 3 The output torque of the rear motor generator 22 and the output torque of the front motor generator 21 are made variable (oscillate) in such a manner as to be within the range of MIN to MAX as shown, that is, a level at which grip is not lost).

[0044] Here, Figure 3 It is a diagram showing the characteristics (relationship) between driving force and tire slip (slip ratio). Figure 3 The vertical axis is the driving force (Nm), and the horizontal axis is the slip rate (%). Figure 3 In FIG, the characteristics (relationship) for the case of a low μ (friction coefficient) road and the case of a high μ road are shown. Figure 3 As shown, the higher the driving force, the higher the slip rate. Furthermore, the peak of the driving force is exceeded and the tire enters the slip zone (i.e., the tire reaches its limit, where it can no longer transmit driving force). Therefore, as described above, if the output of the rear motor generator 22 is increased and the output of the front motor generator 21 is correspondingly reduced, the slip rate of the rear wheels 10RL and 10RR increases, while the slip rate of the front wheels 10FL and 10FR decreases, and the front-to-rear rotation difference changes.

[0045] Furthermore, by making the slip rates of the front wheels 10FL, 10FR and the slip rates of the rear wheels 10RL, 10RR fall within a predetermined slip rate range (for example, approximately ±2%), Figure 3By making the output torque of the rear motor generator 22 and the output torque of the front motor generator 21 variable (in the range shown in the figure between MIN and MAX), the front and rear rotational differences can be stably learned while maintaining grip even on low-μ roads (regardless of the road surface's μ). Assuming the front and rear wheels 10 have the same diameter and axle weight, the front and rear rotational differences are considered to be "front and rear rotational differences ≈ slip rate differences." Therefore, by limiting the front and rear rotational differences, abnormal slip rates are prevented. In other words, if the front and rear driving force distribution is determined by torque control, there is a risk that the wheels 10 may unexpectedly slip (enter the slip zone) on low-μ roads (road surfaces with a large increase in slip rate per 1 Nm). Therefore, the learning search range is limited by the front and rear wheel 10 speed difference (≈ slip rate difference).

[0046] In addition, here, Figure 4 This is a diagram for explaining a method of learning the minimum value of the total power consumption or the total torque. Figure 4 The horizontal axis is the front-rear rotation difference (rpm), and the vertical axis is the total power consumption (kWh) or total torque (Nm). It should be noted that a known method (algorithm) can be used to search for the front-rear rotation difference that minimizes the total power consumption or total torque.

[0047] If it returns Figure 1 Continuing with the explanation, after learning the front-rear rotation difference, the EV-CU 60 controls the output torque of each of the rear motor generator 22 and the front motor generator 21 (F / B control) in such a way that the actual front-rear rotation difference (actual front-rear rotation difference) is consistent with the learned front-rear rotation difference (target front-rear rotation difference).

[0048] More specifically, after learning the front-rear rotational difference, the EV-CU 60 controls the output torque (rear torque) of the rear motor generator 22 and the output torque of the front motor generator 21 (front torque = requested torque - rear torque) in such a way that the actual front-rear rotational difference is consistent with the learned front-rear rotational difference (target front-rear rotational difference) when the vehicle is in cruise control and the steering angle (steering angle or rudder angle) is less than a predetermined value (F / B control).

[0049] It should be noted that here, the learning of the front-rear rotation difference can be repeatedly performed to update the learning value in sequence, and the latest learning value can be used (controlled) as the target value (target front-rear rotation difference), or the acquired learning data can be mapped and used.

[0050] When performing mapping, it is preferable that the EV-CU 60 learns the front-rear rotation difference for each vehicle speed and for each requested torque.

[0051] Furthermore, the EV-CU 60 generates a target front-rear rotation difference map that defines the relationship between the vehicle speed, the requested driving force, and the learned front-rear rotation difference.

[0052] After generating the target front-rear rotation difference map, the EV-CU 60 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 when the vehicle is in cruise control and the steering angle (steering angle or rudder angle) is less than a predetermined value (i.e., in a straight-ahead state or a substantially straight-ahead state).

[0053] Specifically, the EV-CU 60 stores a map (target front-to-back rotation difference map) that defines the relationship between vehicle speed, requested torque, and the learned front-to-back rotation difference (target front-to-back rotation difference) in an EEPROM or the like. The EV-CU 60 retrieves the target front-to-back rotation difference map based on the vehicle speed and requested torque to determine the target front-to-back rotation difference. Furthermore, the output torque of each of the front motor-generator 21 and the rear motor-generator 22 is controlled based on the target front-to-back rotation difference.

[0054] Here, in Figure 5 An example of target front-back rotation difference mapping is shown in . Figure 5 In the target front-rear rotation difference map, the horizontal axis represents vehicle speed (km / h) and the vertical axis represents requested torque (Nm). The learned front-rear rotation difference (target front-rear rotation difference) is stored for each combination of vehicle speed and requested torque (grid point).

[0055] The EV-CU 60 can also learn the front-rear rotational difference based on the respective temperatures of the front motor-generator 21 and the rear motor-generator 22 and / or the respective temperatures of the oil (oil temperature) that lubricates and cools the front and rear motor units. Furthermore, these parameters can be added to the axes of the target front-rear rotational difference map.

[0056] Next, refer to Figure 6 and Figure 7 , the operation of the electric all-wheel drive vehicle 1 will be described. Figure 6 1 is a flowchart showing the processing procedure of learning the front-back rotation difference. Figure 7 This is a flowchart showing the processing procedure of the front-rear rotation difference control. This processing is mainly repeatedly executed in the EV-CU 60 at predetermined timings.

[0057] First, use Figure 6 The following describes the process sequence for learning the front-rear rotation difference. In step S100, a determination is made as to whether cruise control is in effect. If cruise control is not in effect, this process is temporarily terminated. On the other hand, if cruise control is in effect, the process proceeds to step S102.

[0058] In step S102, a determination is made as to whether the steering angle (steering angle or rudder angle) is below a predetermined value (i.e., the vehicle is traveling straight or substantially straight). If the steering angle is greater than the predetermined value, the process is temporarily terminated. On the other hand, if the steering angle is below the predetermined value, the process proceeds to step S104.

[0059] In step S104, the output torque of the rear motor generator 22 and the output torque of the front motor generator 21 are made variable while satisfying the requested torque. For example, the output torque of the rear motor generator 22 (rear torque) is increased, and the output torque of the front motor generator 21 is correspondingly decreased (front torque = requested torque - rear torque).

[0060] Next, in step S106, a determination is made as to whether the total power consumption or total torque of the front and rear motor generators 21, 22 is minimized (or has reached a minimum value). If the total power consumption or total torque has not yet reached a minimum, the process of steps S104 through S106 is repeated until the total power consumption or total torque reaches a minimum. More specifically, in step S104, after the output torque (rear torque) of the rear motor generator 22 is further increased and the output torque of the front motor generator 21 is correspondingly decreased (front torque = requested torque - rear torque), a determination is again made in step S106 as to whether the total power consumption or total torque of the front and rear motor generators 21, 22 is minimized (or has reached a minimum value). If the total power consumption or total torque of the front and rear motor generators 21, 22 is minimized, the process shifts to step S108.

[0061] In step S108 , the front-rear rotational difference (the difference between the front wheel speed and the rear wheel speed) at which the total power consumption or total torque of the front motor generator 21 and the rear motor generator 22 is minimized is learned and stored.

[0062] Next, use Figure 7 The processing sequence for front-to-rear rotation difference control will be described. In step S200, a determination is made as to whether cruise control is in effect. If cruise control is not in effect, this process is temporarily terminated. On the other hand, if cruise control is in effect, the process proceeds to step S202.

[0063] In step S202, a determination is made as to whether the steering angle (steering angle or rudder angle) is below a predetermined value (i.e., the vehicle is traveling straight or substantially straight). If the steering angle is greater than the predetermined value, the process is temporarily terminated. On the other hand, if the steering angle is below the predetermined value, the process proceeds to step S204.

[0064] 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.

[0065] Next, in step S206 , the latest learned front-rear rotation difference (target front-rear rotation difference) is read, or a target front-rear rotation difference map is retrieved based on the vehicle speed and the requested torque to determine the target front-rear rotation difference.

[0066] Next, in step S208, the output torque (rear torque) of the rear motor generator 22 and the output torque (front torque = requested torque - rear torque) of the front motor generator 21 are controlled (F / B control) so that the target front-rear rotational difference matches the actual front-rear rotational difference. This process is then temporarily exited.

[0067] As described in detail above, according to this embodiment, when predetermined learning conditions are met, a front-rear rotational difference (the difference between the front and rear wheel speeds) is learned that allows the output torque of the rear motor generator 22 and the output torque of the front motor generator 21 to be variable while satisfying the requested torque and minimizing the total power consumption or total torque of the front and rear motor generators 21, 22. After learning this front-rear rotational difference, the output torques of the front and rear motor generators 21, 22 are controlled so that the actual front-rear rotational difference matches the learned front-rear rotational difference. Consequently, the front-rear driving force distribution can be controlled so that the total power consumption or total torque of the front and rear motor generators 21, 22 is minimized while satisfying the requested torque, further improving electrical efficiency. Consequently, electrical efficiency can be further improved in the electric all-wheel-drive vehicle 1, in which the front motor generator 21 drives the front wheels 10FL, 10FR and the rear motor generator 22 drives the rear wheels 10RL, 10RR. Furthermore, learning can also accommodate individual differences and changes (degradation) over time.

[0068] Furthermore, according to this embodiment, when cruise control is in progress and the steering angle is below a predetermined value, a predetermined learning condition is determined to be satisfied, and a front-rear rotation difference is learned. After learning this front-rear rotation difference, when cruise control is in progress and the steering angle is below 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 difference matches the learned front-rear rotation difference (target front-rear rotation difference). This minimizes the impact on steering stability.

[0069] According to this embodiment, the output torque of the rear motor generator 22 and the output torque of the front motor generator 21 are made variable so that the slip rates of the front wheels 10FL and 10FR and the slip rates of the rear wheels 10RL and 10RR fall within predetermined slip rate ranges. Therefore, it is possible to prevent the wheels 10 from slipping abnormally (excessively).

[0070] According to the present embodiment, the front-rear rotation difference is learned for each vehicle speed and each requested torque. Therefore, it is possible to create a map taking into account changes in the running resistance corresponding to changes in the vehicle speed and requested torque.

[0071] Furthermore, according to this embodiment, the front-rear rotational 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 map the changes in running resistance that correspond to changes in the temperatures of the front and rear motor generators 21 and 22, and the oil temperature.

[0072] While the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and various modifications are possible. For example, in the above-described embodiment, the present invention is applied to 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. However, the present invention can also be applied to an electric all-wheel drive vehicle in which in-wheel motors are installed in each of the four wheels.

[0073] In the above embodiment, when the vehicle is in cruise control and the steering angle is less than a predetermined value, the EV-CU 60 determines that the predetermined learning condition is met and learns the front-rear rotation difference. However, the present invention is not limited to this. Alternatively, when the vehicle is in cruise control and the steering angle is less than a predetermined value, the EV-CU 60 determines that the predetermined learning condition is met and learns the front-rear rotation difference.

[0074] In the above embodiment, after learning the front-to-rear rotational difference, while the vehicle is in cruise control and the steering angle is below a predetermined value, the EV-CU 60 controls the output torques of the front and rear electric motors so that the actual front-to-rear rotational difference matches the learned front-to-rear rotational difference. However, the present invention is not limited to this embodiment. Alternatively, after learning the front-to-rear rotational difference, while the vehicle is in cruise control and the steering angle is below a predetermined value, the EV-CU 60 controls the output torques of the front and rear electric motors so that the actual front-to-rear rotational difference matches the learned front-to-rear rotational difference.

[0075] Furthermore, the system configuration of controllers such as the EV-CU 60 and VDCU 50, as well as the functional assignments of each controller, are not limited to those in the above-described embodiment. For example, in the above-described embodiment, the wheel speed sensor 12 is connected to the EV-CU 60. However, the wheel speed sensor 12 may also be connected to the VDCU 50 and transmit information to the EV-CU 60 via the CAN 100. Furthermore, in the above-described embodiment, the EV-CU 60, PCU 70, and VDCU 50 are interconnected via the CAN 100 to enable communication with each other. However, the system configuration is not limited to this configuration and, for example, can be arbitrarily modified (e.g., combined) to take into account functional requirements and cost.

Claims

1. An electric all-wheel drive vehicle, characterized in that: have: a front electric motor, which drives the front wheels; a rear electric motor, which drives the rear wheels; an acceleration sensor that detects an amount of operation of the accelerator; a front wheel speed sensor, which detects the rotation speed of the front wheel; a rear wheel speed sensor, which detects the rotation speed of the rear wheel; as well as a control unit that controls the front electric motor and the rear electric motor based on the amount of operation of the accelerator, the rotation speed of the front wheels, and the rotation speed of the rear wheels, respectively; The control unit learns a front-rear rotation difference when a predetermined learning condition is satisfied, the front-rear rotation difference being a difference between the rotation speeds of the front wheels and the rotation speeds of the rear wheels such that the output torque of the rear electric motor and the output torque of the front electric motor are variable while satisfying a requested torque and the total power consumption or total torque of the front and rear electric motors is minimized. After learning the front-rear rotation difference, the control unit controls the output torque of each of the front electric motor and the rear electric motor so that the actual front-rear rotation difference matches the learned front-rear rotation difference.

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

3. The electric all-wheel drive vehicle according to claim 2, wherein: When the vehicle is in cruise control and the steering angle is less than a predetermined value, the control unit determines that the predetermined learning condition is satisfied and learns the front-rear rotation difference. After learning the front-rear rotation difference, when the vehicle is in cruise control and the steering angle is lower than a predetermined value, the control unit controls the output torque of each of the front and rear electric motors so that the actual front-rear rotation difference matches the learned front-rear rotation difference.

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 for each requested torque.

5. The electric all-wheel drive vehicle according to claim 4, characterized in that: The control unit learns the front-rear rotation difference with respect to each temperature of the front electric motor and the rear electric motor and each temperature of oil.

6. The electric all-wheel drive vehicle according to claim 4, characterized in that: The control unit learns the front-rear rotation difference for each temperature of the front electric motor and the rear electric motor.

7. The electric all-wheel drive vehicle according to claim 4, wherein: The control unit learns the front-rear rotation difference for each oil temperature.

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