Vehicle drive apparatus

Abstract

To provide a vehicle drive apparatus which can prevent vibration of a vehicle body when a vehicle is caused to travel with an engine being operated, and in addition, which can improve power performance when the vehicle is in a predetermined traveling state.SOLUTION: According to a vehicle drive apparatus 10, a differential mechanism 32 includes three rotary elements. An engine 20 and a first electric motor MG1 are connected to a first rotary element RE1, a second electric motor MG2 is connected to a second rotary element RE2, and a front drive shaft 38 is connected to a third rotary element RE3. Further, a third electric motor MG3 is connected to a rear drive shaft 58. When a vehicle 8 is in a predetermined traveling state, an electronic controller 70 causes the first electric motor MG1 to generate positive torque, causes the second electric motor MG2 to generate reaction torque, and causes the third electric motor MG3 to generate positive torque.SELECTED DRAWING: Figure 18

Description

[Technical Field]

[0001] The present invention relates to a vehicle drive system that includes an engine, three electric motors, a differential mechanism, drive shafts that drive front and rear wheels, and a control device. [Background technology]

[0002] A well-known vehicle drive system includes an engine, a first electric motor, a second electric motor, a third electric motor, a differential mechanism, a first drive shaft that drives one of the front and rear wheels, a second drive shaft that drives the other of the front and rear wheels, and a control device. For example, Patent Document 1 discloses such a vehicle drive system. Patent Document 1 discloses that the differential mechanism has four rotating elements: a first rotating element, a second rotating element, a third rotating element, and a fourth rotating element. Patent Document 1 also discloses that the engine is connected to the first rotating element, the first electric motor is connected to the second rotating element, the second electric motor is connected to the third rotating element, and the first drive shaft is connected to the fourth rotating element. Patent Document 1 also discloses that the third electric motor is connected to the second drive shaft. The vehicle drive device of Patent Document 1 also discloses that, in order to improve power performance when the vehicle starts or at medium to low vehicle speeds and to eliminate insufficient driving force, the first electric motor, the second electric motor, and the third electric motor are controlled so that the first electric motor and the second electric motor output torque in the same acting direction as the engine torque that drives the vehicle forward, and the third electric motor outputs torque that drives the vehicle forward together with the engine torque. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-118549 Summary of the Invention [Problem to be solved by the invention]

[0004] The vehicle drive system described in Patent Document 1 realizes a compound split mode in which, while the engine is running, one of the first and second electric motors is operated as a generator and the other is operated as a prime mover to drive the first drive shaft. The vehicle drive system described in Patent Document 1 also realizes an input split mode in which, while the engine is running, one of the first and second electric motors is operated as a generator and the third electric motor is operated as a prime mover to drive the second drive shaft. However, when the vehicle is running with the engine running, the first or second electric motor generates a reaction torque against the engine torque, and the torque vibration of the engine is transmitted to the first drive shaft, which may cause the vehicle body to vibrate.

[0005] The present invention has been made against the background of the above circumstances, and its purpose is to provide a vehicle drive device that is configured to make it difficult for the vehicle body to vibrate when the vehicle is driven with the engine running, and that can improve the power performance when the vehicle is in a specified driving state. [Means for solving the problem]

[0006] The gist of a first invention is a vehicle drive device including an engine, a first electric motor, a second electric motor, a third electric motor, a differential mechanism, a first drive shaft that drives one of the front wheels and the rear wheels, a second drive shaft that drives the other of the front wheels and the rear wheels, and a control device, wherein (a) the differential mechanism has three rotating elements: a first rotating element, a second rotating element, and a third rotating element, (b) the engine and the first electric motor are connected to the first rotating element, the second electric motor is connected to the second rotating element, and the first drive shaft is connected to the third rotating element, (c) the third electric motor is connected to the second drive shaft, and (d) the control device is configured to control the first electric motor, the second electric motor, and the third electric motor when the vehicle is in a predetermined running state, to generate a positive torque in the first electric motor, a reaction torque in the second electric motor, and a positive torque in the third electric motor.

[0007] The gist of the second invention is that in the first invention, the control device is configured to generate a reaction torque in the second electric motor and to increase the reaction torque of the second electric motor in a stepwise manner.

[0008] The gist of the third invention is that in the second invention, the control device is configured to increase the reaction torque of the second electric motor in a stepwise manner in response to an operation by the driver to increase the driving force. [Effects of the Invention]

[0009] According to a first aspect of the present invention, the differential mechanism includes three rotating elements: a first rotating element, a second rotating element, and a third rotating element. The first rotating element is connected to the engine and the first electric motor, the second rotating element is connected to the second electric motor, and the third rotating element is connected to the first drive shaft. The third electric motor is also connected to the second drive shaft. This allows for so-called series running, in which the first electric motor, which is connected to the same rotating element as the engine, operates as a generator, and the third electric motor operates as a prime mover to drive the second drive shaft with the generated electric power. In series running, torque vibrations of the engine are prevented from being transmitted to the first drive shaft, thereby reducing the likelihood of vibration of the vehicle body when the vehicle is running with the engine. Furthermore, when the vehicle is in a predetermined driving state, the control device controls the first electric motor, the second electric motor, and the third electric motor to generate positive torque in the first electric motor, generate reaction torque in the second electric motor, and generate positive torque in the third electric motor. As a result, even in a predetermined driving state, such as when the vehicle is starting or at an extremely low vehicle speed, the first electric motor and the second electric motor can transmit positive torque to the first drive shaft while suppressing a continuous large current flow biased to a specific phase of the inverter. In addition, since the third electric motor can transmit positive torque to the second drive shaft, power performance can be improved when the vehicle is in a predetermined driving state.

[0010] According to a second aspect of the invention, in the vehicle drive device of the first aspect, the control device is configured to generate a reaction torque in the second electric motor and to increase the reaction torque of the second electric motor in a stepwise manner. By increasing the reaction torque of the second electric motor in a stepwise manner, inertia torque is maintained in the first rotating element, and the torque transmitted to the first drive shaft can be temporarily increased. For example, even when the engine or the first electric motor is fully generating torque, the drive force can be temporarily increased.

[0011] According to a third aspect of the present invention, the vehicle drive device of the second aspect is configured such that the control device increases the reaction torque of the second electric motor in a stepwise manner in response to an operation by the driver to increase the drive force, thereby enabling the drive force to be increased in accordance with the driver's intention and improving drivability in situations where drive force is required. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram illustrating a schematic configuration of a vehicle equipped with a vehicle drive device (single pinion U / D type) to which the present invention is applied. [Figure 2] FIG. 2 is a nomographic diagram illustrating the configuration of the vehicle drive device. [Figure 3] FIG. 2 is a diagram illustrating a main part of a control system for various controls in the vehicle drive device. [Figure 4] FIG. 4 is a collinear diagram illustrating a BEV mode in which torque is generated in the first electric motor and the second electric motor. [Figure 5] FIG. 10 is a collinear diagram illustrating a BEV mode in which torque is generated by the second electric motor with the brake engaged. [Figure 6] FIG. 10 is a collinear diagram illustrating a BEV mode in which torque is generated by the third electric motor with the brakes engaged. [Figure 7] 1A and 1B are nomographic diagrams illustrating a first HEV mode (series mode) in which the engine is driven to rotate and power is exchanged between the first electric motor and the third electric motor. (a) is a nomographic diagram illustrating a case in which torque is generated in the third electric motor by the electric power generated by the first electric motor. (b) is a nomographic diagram illustrating a case in which the electric power generated by the third electric motor is consumed by the power running of the first electric motor to apply engine braking. [Figure 8] 10A and 10B are nomographic diagrams illustrating a second HEV mode (input split mode) in which the engine is operated and power is exchanged between the second electric motor and the third electric motor. (a) is a nomographic diagram illustrating a case in which torque is generated in the third electric motor by the electric power generated by the second electric motor. (b) is a nomographic diagram illustrating a case in which torque is generated in the second electric motor by the electric power generated by the third electric motor. [Figure 9] 10A and 10B are nomographic diagrams illustrating a third HEV mode (output split mode) in which the engine is operated and power is exchanged between the first and second electric motors. (a) is a nomographic diagram illustrating a case in which torque is generated in the second electric motor by the power generated by the first electric motor. (b) is a nomographic diagram illustrating a case in which torque is generated in the first electric motor by the power generated by the second electric motor. [Figure 10] FIG. 10 is a diagram showing an example of a drive mode switching map used for drive mode switching control, which is used in charge consumption running. [Figure 11] FIG. 10 is a diagram showing an example of a drive mode switching map used for drive mode switching control, which is used in charge-maintenance running. [Figure 12] 11 is a diagram showing an example of a drive mode switching map used for drive mode switching control, which is used in charge consumption running, and in which the drive force in FIG. 10 is replaced with the accelerator opening. [Figure 13] FIG. 12 is a diagram showing an example of a drive mode switching map used for drive mode switching control, which is used in charge-maintenance running, and in which the drive force in FIG. 11 is replaced with the accelerator opening. [Figure 14] This is a flowchart explaining the main control operations of the electronic control device, and is a flowchart explaining the control operations for realizing various driving modes when the vehicle is driven with the engine running. [Figure 15] 15 is a diagram showing an example of a time chart when the control operation shown in the flowchart of FIG. 14 is executed. FIG. [Figure 16] FIG. 6 is a diagram illustrating an example of the relationship between the rotation speed of the second electric motor and the maximum possible torque of the second electric motor. [Figure 17] FIG. 10 is a nomographic diagram illustrating a fourth HEV mode in which the engine is rotationally driven to generate positive torque in the first electric motor and the third electric motor, and generate reaction torque in the second electric motor. [Figure 18] 4 is a flowchart illustrating a main part of the control operation of the electronic control device when the vehicle is in a predetermined running state. [Figure 19] 19 is a diagram showing an example of a time chart when the control operation shown in the flowchart of FIG. 18 is executed. FIG. [Figure 20] 1 is a diagram illustrating a schematic configuration of a vehicle equipped with a vehicle drive device (single pinion O / D type) to which the present invention is applied, and is a diagram illustrating a vehicle different from the vehicle of FIG. [Figure 21] 21 is a nomographic diagram showing the configuration of the vehicle drive device of FIG. 20. FIG. [Figure 22] FIG. 10 is a nomographic diagram illustrating a fourth HEV mode in which the engine is rotationally driven to generate positive torque in the first electric motor and the third electric motor, and generate reaction torque in the second electric motor. [Figure 23] 4 is a flowchart illustrating a main part of the control operation of the electronic control device when the vehicle is in a predetermined running state. [Figure 24] 24 is a diagram showing an example of a time chart when the control operation shown in the flowchart of FIG. 23 is executed. FIG. [Figure 25] 1 is a diagram illustrating a schematic configuration of a vehicle equipped with a vehicle drive device (double pinion U / D type) to which the present invention is applied, the diagram illustrating a vehicle different from the vehicle of FIG. [Figure 26] FIG. 26 is a nomographic diagram illustrating the configuration of the vehicle drive device of FIG. 25. [Figure 27] FIG. 10 is a nomographic diagram illustrating a fourth HEV mode in which the engine is rotationally driven to generate positive torque in the first electric motor and the third electric motor, and generate reaction torque in the second electric motor. [Figure 28] 1 is a diagram illustrating a schematic configuration of a vehicle equipped with a vehicle drive device (double pinion O / D type) to which the present invention is applied, the diagram illustrating a vehicle different from the vehicle of FIG. [Figure 29] FIG. 29 is a nomographic diagram illustrating the configuration of the vehicle drive device of FIG. 28. [Figure 30] FIG. 10 is a nomographic diagram illustrating a fourth HEV mode in which the engine is rotationally driven to generate positive torque in the first electric motor and the third electric motor, and generate reaction torque in the second electric motor. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Example]

[0014] FIG. 1 is a diagram illustrating the schematic configuration of a vehicle 8 equipped with a vehicle drive system 10 to which the present invention is applied. In FIG. 1, the vehicle 8 is equipped with drive wheels 12 and a vehicle drive system 10 that drives the drive wheels 12. The drive wheels 12 include left and right front wheels 12f and left and right rear wheels 12r. The vehicle drive system 10 includes a front drive unit 10f that drives the front wheels 12f and a rear drive unit 10r that drives the rear wheels 12r. Note that the above "left and right" refer to left and right relative to the forward direction of the vehicle 8.

[0015] The front drive unit 10f includes an engine 20, a first electric motor MG1, a second electric motor MG2, and a front power transmission device 30. The rear drive unit 10r includes a third electric motor MG3 and a rear power transmission device 50. The vehicle 8 is a hybrid vehicle (HEV (Hybrid Electric Vehicle)) or a plug-in hybrid vehicle (PHEV (Plug-in Hybrid Electric Vehicle)). The vehicle 8 is also an all-wheel drive vehicle capable of independently driving the front wheels 12f and the rear wheels 12r. All-wheel drive (AWD) and four-wheel drive (4WD) are synonymous. The vehicle drive system 10 is capable of front-wheel drive, in which torque is transmitted only to the front wheels 12f, and rear-wheel drive, in which torque is transmitted only to the rear wheels 12r.

[0016] The engine 20 is, for example, a known internal combustion engine. An electronic control unit 70 (described later) controls an engine control device 60, thereby controlling the engine torque Te of the engine 20. The engine control device 60 is provided in the front drive unit 10f and includes a throttle actuator, a fuel injection device, an ignition device, etc.

[0017] The first electric motor MG1, the second electric motor MG2, and the third electric motor MG3 are rotating electric machines, so-called motor generators, that function as both a prime mover that generates mechanical power from electric power and a generator that generates electric power from mechanical power. For example, the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3 are synchronous motors in which a rotor is rotated by a rotating magnetic field generated by a stator. The rotating magnetic field is generated by passing multiple alternating currents of different phases through a stator coil provided in the stator. The first electric motor MG1, the second electric motor MG2, and the third electric motor MG3 are each connected to a battery 64 provided in the vehicle drive system 10 via an inverter 62 provided in the vehicle drive system 10. The torque of the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3 is controlled by controlling the inverter 62 by an electronic control device 70 (described later). The torque of the first electric motor MG1 is first electric motor torque Tmg1, the torque of the second electric motor MG2 is second electric motor torque Tmg2, and the torque of the third electric motor MG3 is third electric motor torque Tmg3. For example, the first electric motor torque Tmg1, the second electric motor torque Tmg2, and the third electric motor torque Tmg3 are generated by the inverter 62 controlling the magnitudes of the first electric motor current Img1, the second electric motor current Img2, and the third electric motor current Img3, respectively, as described below. The torque of the electric motors becomes power running torque when the electric motors function as prime movers, and becomes regenerative torque when the electric motors function as generators. The battery 64 is an electricity storage device that supplies and receives electric power to and from each of the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3. Unless otherwise specified, the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3 are controlled via the inverter 62 so as to supply and receive electric power simultaneously. "Simultaneously" means, for example, that the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3 are each capable of power running or regenerating independently at the same time, and the power balance between the power generated by any one of the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3 and the power consumed by the generated power being supplied to drive the other electric motors is balanced.

[0018] The front power transmission device 30 is provided in a power transmission path between the engine 20, the first electric motor MG1, and the second electric motor MG2, and the front wheels 12f. The front power transmission device 30 includes a differential mechanism 32, a front counter gear 34, a front differential gear 36, and left and right front drive shafts 38. The differential mechanism 32 and the front differential gear 36 are connected via the front counter gear 34. The front drive shaft 38 is connected to the front differential gear 36. The front power transmission device 30 transmits power from the engine 20, the second electric motor MG2, and the like to the front wheels 12f. The front drive shaft 38 is a first drive shaft that drives the front wheels 12f, which are one of the front wheels 12f and the rear wheels 12r.

[0019] The differential mechanism 32 is a single-pinion planetary gear device having a sun gear S, a pinion P, a carrier C that supports the pinion P so that it can rotate and revolve, and a ring gear R that meshes with the sun gear S via the pinion P. A second electric motor MG2 is connected to the sun gear S. The engine 20 and a first electric motor MG1 are connected to the ring gear R. The carrier C meshes with a front counter gear 34. A front drive shaft 38 is connected to the carrier C.

[0020] The engine 20 and the second electric motor MG2 are each disposed on a first axis CS1, which is the rotation axis of the differential mechanism 32. The first electric motor MG1 is disposed on a second axis CS2. The second axis CS2 is a rotation axis different from the first axis CS1 and is parallel to the first axis CS1. Therefore, the front power transmission device 30 further includes a power transmission member 40. The first electric motor MG1 is connected to a ring gear R of the differential mechanism 32 via the power transmission member 40. The power transmission member 40 includes, for example, an intermediate gear 40a fixed to the rotor shaft MG1rs of the first electric motor MG1 so as not to rotate relative to it, and a belt 40b connecting the intermediate gear 40a and the ring gear R. The intermediate gear 40a has a smaller diameter than the ring gear R, and the power transmission member 40 functions as, for example, a reduction mechanism. By arranging the first electric motor MG1 on the second axis CS2, the size of the front drive unit 10f in the direction of the first axis CS1 is reduced compared to when the first electric motor MG1 is arranged on the first axis CS1.

[0021] The front power transmission device 30 further includes a brake BR. One end of the brake BR is connected to the ring gear R of the differential mechanism 32, and the other end is connected to a non-rotating member (not shown). The non-rotating member to which the brake BR is connected is, for example, a case that houses the front power transmission device 30, etc. The brake BR is an engagement device that is operated by, for example, an electric or hydraulic actuator to selectively connect members at both ends. The brake BR functions as a brake mechanism that selectively stops rotation of the ring gear R of the differential mechanism 32. The ring gear R is selectively made rotatable or non-rotatable by the brake BR.

[0022] The rear power transmission device 50 is provided in a power transmission path between the third electric motor MG3 and the rear wheels 12r. The rear power transmission device 50 includes an output gear 52, a rear counter gear 54, a rear differential gear 56, and left and right rear drive shafts 58. The output gear 52 is fixed to the rotor shaft MG3rs of the third electric motor MG3 so as not to rotate relative to the rotor shaft MG3rs, and is in mesh with the rear counter gear 54. The output gear 52 and the rear differential gear 56 are connected via the rear counter gear 54. The rear drive shaft 58 is connected to the rear differential gear 56. The output gear 52 has a smaller diameter than the rear counter gear 54, and the output gear 52 and the rear counter gear 54 function as, for example, a reduction mechanism. The rear power transmission device 50 transmits power from the third electric motor MG3 to the rear wheels 12r. The rear drive shaft 58 is a second drive shaft that drives the other of the front wheels 12f and the rear wheels 12r, 12r. A third electric motor MG3 is connected to the rear drive shaft 58.

[0023] The rear power transmission device 50 further includes a parking mechanism PLC. One end of the parking mechanism PLC is connected to a non-rotating member (not shown). The parking mechanism PLC is operated by, for example, an electric actuator or a manually operated mechanical actuator, and the other end of the parking mechanism PLC is engaged with or disengaged from the output gear 52. The non-rotating member to which the parking mechanism PLC is connected is, for example, a case that houses the rear power transmission device 50. The parking mechanism PLC is a known parking lock device that switches between a parking lock state in which the output gear 52 is mechanically fixed so as to be non-rotatable, and a non-parking lock state in which the output gear 52 is rotatable. The output gear 52 is a rotating member that rotates together with the rear drive shaft 58. The output gear 52 and the rear drive shaft 58 are selectively non-rotatable or rotatable by the parking mechanism PLC.

[0024] FIG. 2 is a nomographic diagram showing the configuration of the vehicle drive system 10. In FIG. 2, the rear drive unit 10r is a main unit that is used for driving with priority over, for example, the front drive unit 10f. In this case, the front drive unit 10f is considered an auxiliary unit. "FrOUT" in FIG. 2 indicates the front wheels 12f, and "RrOUT" in FIG. 2 indicates the rear wheels 12r.

[0025] The differential mechanism 32 of the front drive unit 10f has three rotating elements: a first rotating element RE1, a second rotating element RE2, and a third rotating element RE3. An actuator is connected to each of the rotating elements RE1-RE3 of the differential mechanism 32. The nomographic diagram of FIG. 2 illustrates the three rotating elements of the differential mechanism 32 arranged in a straight line. Expressed using the nomographic diagram, the first rotating element RE1 is a ring gear R. The engine 20 and the first electric motor MG1 are connected to the first rotating element RE1. The second rotating element RE2 is a sun gear S. The second electric motor MG2 is connected to the second rotating element RE2. The third rotating element RE3 is a carrier C. The front drive shaft 38, i.e., the front wheels 12f, are connected to the third rotating element RE3. The brake BR is a brake mechanism that stops rotation of the first rotating element RE1 when engaged.

[0026] The third electric motor MG3 of the rear drive unit 10r is connected to the rear wheels 12r, and can therefore be considered to be connected to the front wheels 12f via the ground (see dashed lines). By controlling the first electric motor MG1, second electric motor MG2, and third electric motor MG3 so that electric power is exchanged simultaneously, it is possible to travel as if the third electric motor MG3 were connected to the front wheels 12f.

[0027] FIG. 3 is a diagram illustrating essential parts of a control system for various controls in the vehicle drive system 10. In FIGS. 1 and 3, the vehicle drive system 10 further includes an electronic control unit 70 as a controller including control devices related to the control of the vehicle drive system 10 and the like. The electronic control unit 70 includes, for example, a so-called microcomputer equipped with a CPU, RAM, ROM, an input / output interface, and the like. The CPU performs various controls of the vehicle 8 by, for example, performing signal processing according to a program pre-stored in the ROM. For example, the electronic control unit 70 controls the outputs of the engine 20, the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3, and performs drive mode switching control, which will be described later. The electronic control unit 70 is divided into a hybrid control ECU 72 (see "PHEV-ECU" in FIG. 3), an engine control ECU 74 (see "ENG-ECU" in FIG. 3), an electric motor control ECU 76 (see "MG-ECU" in FIG. 3), and the like, as needed.

[0028] The hybrid control ECU 72 receives various signals based on detection signals from various sensors provided in the vehicle 8. The various sensors include, for example, an accelerator pedal position sensor 80, a vehicle speed sensor 81, a battery sensor 82, a BEV switch 83, and a shift position sensor 84. The various sensors also include, for example, a first electric motor rotation sensor 85, a second electric motor rotation sensor 86, and a third electric motor rotation sensor 87, each of which may be a resolver. The various sensors also include, for example, an engine rotation speed sensor 88, a brake switch 89, a brake operation amount sensor 90, a crawl switch 91, a traction switch 92, and a kickdown switch 24. The various signals also include, for example, an accelerator pedal position θacc, a vehicle speed V, a signal for calculating a charge state of charge (SOC), a BEV-on signal BEVon, and a shift position POSop. The various signals also include, for example, a first electric motor rotation speed Nmg1, a second electric motor rotation speed Nmg2, and a third electric motor rotation speed Nmg3. The various signals include, for example, an engine rotation speed Ne, a brake-on signal BPon, a brake operation amount θbp, a crawl-on signal CRon, a traction-on signal TRon, a kick-down-on signal KDon, and the like.

[0029] The BEV switch 83 is a switch operated by the driver when BEV (Battery Electric Vehicle) driving is required. When the BEV switch 83 is operated, the engine 20 is not started, and the vehicle is driven in BEV mode using only the power of the battery 64. The crawl switch 91 is a switch operated by the driver when, for example, a scene is anticipated in which the vehicle will be driven at an extremely low speed and high load on a rocky road or the like. The towing switch 92 is a switch operated by the driver when the vehicle 8 is driven with a towed vehicle coupled to the rear of the vehicle. The kickdown switch 24 is a switch that detects, for example, when the driver's depression of the accelerator pedal 22 is at its maximum.

[0030] The accelerator opening θacc is the amount of accelerator operation by the driver, which indicates the magnitude of the driver's acceleration operation. The vehicle speed V is the speed of the vehicle 8. The signals for calculating the state of charge SOC are the battery charge / discharge current and battery voltage detected by the battery sensor 82. The state of charge SOC is the remaining charge of the battery 64 and is calculated by the electronic control unit 70 based on the battery charge / discharge current and battery voltage. The battery sensor 82 also detects the battery temperature. The BEV-on signal BEVon is a signal indicating that the BEV switch 83 has been operated by the driver. The shift operation position POSop is the lever position of the shift operation device, such as "P," "R," "N," or "D." The first electric motor rotation speed Nmg1 is the rotation speed of the first electric motor MG1. The second electric motor rotation speed Nmg2 is the rotation speed of the second electric motor MG2. The third electric motor rotation speed Nmg3 is the rotation speed of the third electric motor MG3. The engine rotation speed Ne is the rotation speed of the engine 20. The brake-on signal BPon is a signal indicating a state in which the brake pedal for operating the wheel brakes is being operated by the driver. The brake operation amount θbp is a signal indicating the magnitude of the brake pedal depression operation by the driver, i.e., the magnitude of the brake operation, and is synonymous with the brake pedal depression force. The crawl-on signal CRon is a signal indicating that the crawl switch 91 has been operated by the driver. The tow-on signal TRon is a signal indicating that the tow switch 92 has been operated by the driver. The kick-down on signal KDon is a signal indicating whether the magnitude of the accelerator pedal 22 depression operation by the driver is at or near the maximum value. When the driver strongly depresses the accelerator pedal 22, the kick-down switch 24 is turned on, and the kick-down on signal KDon is turned on. The driver's depression of the accelerator pedal 22, which turns the kick-down on signal KDon on, corresponds to the "operation by the driver to increase driving force" in this invention.

[0031] The engine control ECU 74 receives input of an air-fuel ratio A / F and the like based on detection signals from an air-fuel ratio sensor 93 and the like provided on the vehicle 8. The motor control ECU 76 receives input of a first electric motor rotation angle θmg1, a second electric motor rotation angle θmg2, a third electric motor rotation angle θmg3 and the like based on detection signals from a first electric motor rotation sensor 85, a second electric motor rotation sensor 86, a third electric motor rotation sensor 87, and the like.

[0032] The air-fuel ratio A / F is a signal that represents the state of the air-fuel ratio in the exhaust gas. The first electric motor rotation angle θmg1 is a signal that represents the rotational position, which is the rotational angle of the rotor of the first electric motor MG1 from a predetermined reference position. The second electric motor rotation angle θmg2 is a signal that represents the rotational position, which is the rotational angle of the rotor of the second electric motor MG2 from a predetermined reference position. The third electric motor rotation angle θmg3 is a signal that represents the rotational position, which is the rotational angle of the rotor of the third electric motor MG3 from a predetermined reference position.

[0033] The hybrid control ECU 72 outputs various command signals to the engine control ECU 74. The various command signals to the engine control ECU 74 include, for example, a command signal for a target engine torque Tetgt, a fuel cut request signal FCreq for requesting a fuel cut operation, etc. The hybrid control ECU 72 also outputs various command signals to the electric motor control ECU 76. The various command signals to the electric motor control ECU 76 include, for example, a command signal for a target first electric motor torque Tmg1tgt, a command signal for a target second electric motor torque Tmg2tgt, and a command signal for a target third electric motor torque Tmg3tgt, etc. The hybrid control ECU 72 also outputs a brake control command signal Sbr to the brake BR, etc.

[0034] The target engine torque Tetgt is a target value of the engine torque Te. The fuel cut operation is a control operation that cuts off the supply of fuel to the engine 20. The target first electric motor torque Tmg1tgt is a target value of the first electric motor torque Tmg1. The target second electric motor torque Tmg2tgt is a target value of the second electric motor torque Tmg2. The target third electric motor torque Tmg3tgt is a target value of the third electric motor torque Tmg3. The brake control command signal Sbr is a request signal for controlling the brake BR to an on state or an off state. Note that in an engagement device, the on state is synonymous with an engaged state (= connected state), and the off state is synonymous with a released state (= disconnected state).

[0035] The engine control ECU 74 outputs engine control command signals Se and the like to the engine control device 60 and the like. The engine control command signals Se are command signals for controlling the engine 20, and include command signals for the intake air amount Qair, the ignition timing TMig, the fuel injection amount Qfi, and the like.

[0036] The motor control ECU 76 outputs a first motor control command signal Smg1, a second motor control command signal Smg2, a third motor control command signal Smg3, etc. to the inverter 62, etc. The first motor control command signal Smg1 is a command signal for controlling the first motor MG1 and includes command signals such as a first motor current Img1. The second motor control command signal Smg2 is a command signal for controlling the second motor MG2 and includes command signals such as a second motor current Img2. The third motor control command signal Smg3 is a command signal for controlling the third motor MG3 and includes command signals such as a third motor current Img3. The first motor current Img1 is a drive current for the first motor MG1. The second motor current Img2 is a drive current for the second motor MG2. The third motor current Img3 is a drive current for the third motor MG3.

[0037] The hybrid control ECU 72 determines various command signals based on the driver's intentions, such as the accelerator opening θacc and the brake operation amount θbp, the first electric motor rotation speed Nmg1, the second electric motor rotation speed Nmg2, the third electric motor rotation speed Nmg3, and the engine rotation speed Ne. For example, the hybrid control ECU 72 determines a brake control command signal Sbr to control the engagement and release states of the brake BR. The engine control ECU 74 determines an engine control command signal Se based on a command signal for a target engine torque Tetgt, a fuel cut request signal FCreq requesting a fuel cut operation, and the like. The engine control ECU 74 outputs the engine control command signal Se to control the engine 20. The electric motor control ECU 76 determines electric motor control command signals Smg1, Smg2, and Smg3 based on a target first electric motor torque Tmg1tgt, a target second electric motor torque Tmg2tgt, and a target third electric motor torque Tmg3tgt, etc. The electric motor control ECU 76 outputs electric motor control command signals Smg1, Smg2, Smg3 to control the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3.

[0038] As a result, the electronic control unit 70 is configured to control the engine 20, the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3, and to switch the drive mode to one of a plurality of modes. Furthermore, when switching the drive mode, the electronic control unit 70 controls the brake BR to be engaged as necessary.

[0039] Here, the multiple modes into which the drive mode of the vehicle 8 can be switched will be described with reference to FIGS. 4 to 9. FIGS. 4 to 9 each show the relative rotational speeds of the rotational elements RE1-RE3 of the differential mechanism 32 in the alignment chart of FIG. 2. In this alignment chart, vertical lines Y1-Y3 are arranged in the order of Y1, Y2, and Y3 from the left side of the drawing. The vertical line Y1 represents the rotational speed of the sun gear S, which is the second rotational element RE2 connected to the second electric motor MG2. The vertical line Y2 represents the rotational speed of the carrier C, which is the third rotational element RE3 connected to the front wheels 12f (see "FrOUT" in the drawing). The vertical line Y3 represents the rotational speed of the ring gear R, which is the first rotational element RE1 connected to the engine 20 (see "ENG" in the drawing) and the first electric motor MG1. Furthermore, this indicates that the third electric motor MG3 connected to the rear wheels 12r (see "RrOUT" in the drawing) is connected to the front wheels 12f via the ground. Each arrow indicates the magnitude and direction of torque converted onto the axis of each rotating element RE1-RE3. The solid arrow indicates the torque output from each actuator, and the dashed arrow indicates the mechanically transmitted torque.

[0040] FIG. 4 is a nomographic diagram illustrating Mode1_MG2, a BEV mode in which torque is generated in the first electric motor MG1 and the second electric motor MG2, which is one of Mode1 modes that enables BEV driving. In FIG. 4, Mode1_MG2 is included in multiple modes that allow switching of the drive mode. Mode1_MG2 is a mode in which the engine 20 is stopped and torque is generated in the first electric motor MG1 and the second electric motor MG2 to perform BEV driving. In Mode1_MG2, the first electric motor MG1 and the second electric motor MG2 exchange power with the battery 64 and generate mutual torque so that the moment around the third rotating element RE3 becomes zero, thereby enabling BEV driving. At this time, the first electric motor torque Tmg1 is controlled, for example, so as not to cause drag of the engine 20, i.e., so that the rotational speed of the first rotating element RE1 becomes zero. In Mode1_MG2, the differential mechanism 32 is in a differential state, and torque is generated in the first electric motor MG1 and the second electric motor MG2, and the torque is mechanically transmitted to the third rotating element RE3, which is the output element. Note that in Mode1_MG2, it is also possible to increase the drive torque by generating torque in the third electric motor MG3.

[0041] FIG. 5 is a nomographic diagram illustrating Mode1_MG2_BRon, a BEV mode in which torque is generated by the second electric motor MG2 with the brake BR engaged, which is another mode of Mode1 that enables BEV driving. In FIG. 5, Mode1_MG2_BRon is included in multiple modes that allow switching of the drive mode. Mode1_MG2_BRon is a mode in which BEV driving is performed by stopping the engine 20 and causing the second electric motor MG2 to generate torque with the brake BR engaged. In Mode1_MG2_BRon, the brake BR is engaged and the rotational speed of the first rotating element RE1 is fixed to zero. Therefore, forward and reverse BEV driving is possible with the second electric motor MG2 using power from the battery 64 without generating torque in the first electric motor MG1. In this case, BEV driving is possible with maximum torque from the second electric motor MG2. In Mode1_MG2_BRon, the differential mechanism 32 is in a non-differential state, and torque is generated in the second electric motor MG2, which mechanically transmits the torque to the third rotating element RE3, which is the output element. Note that in Mode1_MG2_BRon, it is also possible to increase the drive torque by generating torque in the third electric motor MG3.

[0042] FIG. 6 is a nomographic diagram illustrating Mode1_MG3, a BEV mode in which the third electric motor MG3 generates torque with the brake BR engaged, which is yet another mode within Mode1 that enables BEV driving. In FIG. 6, Mode1_MG3 is included in multiple modes that allow switching of the drive mode. Mode1_MG3 is a mode in which the engine 20 is stopped and the third electric motor MG3 generates torque with the brake BR engaged, thereby achieving BEV driving. In Mode1_MG3, the brake BR is engaged and the rotational speed of the first rotating element RE1 is fixed to zero. This prevents drag from occurring in the engine 20 or the first electric motor MG1, and enables forward and reverse BEV driving by the third electric motor MG3 using the power of the battery 64.

[0043] In Mode1_MG3, it is also possible to increase the drive torque by causing the second electric motor MG2 to generate torque. Also, in Mode1_MG3, it is possible to perform BEV running by causing the third electric motor MG3 to generate torque even if the brake BR is not engaged. In other words, Mode1_MG3 may be a mode in which the engine 20 is stopped and the third electric motor MG3 is caused to generate torque to perform BEV running.

[0044] FIG. 7 is a nomographic diagram illustrating a first HEV mode, or Mode 2, in which the engine 20 is rotationally driven and power is exchanged between the first electric motor MG1 and the third electric motor MG3. FIG. 7(a) is a nomographic diagram when torque is generated in the third electric motor MG3 by the electric power generated by the first electric motor MG1. FIG. 7(b) is a nomographic diagram when engine braking is applied by consuming the electric power generated by the third electric motor MG3 through the power running of the first electric motor MG1. In FIG. 7, Mode 2 is included in multiple modes that allow switching of the drive mode. Mode 2 is a mode in which hybrid driving, or HEV driving, is possible, and is a series mode in which series driving using the engine 20 as a power source is possible.

[0045] In FIG. 7A, Mode 2 includes a mode in which the engine 20 is running to operate the first electric motor MG1 as a generator while the third electric motor MG3 is operated as a prime mover using the generated power of the first electric motor MG1. Mode 2 is a mode in which, with the brake BR disengaged, an electric continuously variable transmission function can be realized, with the input from the engine 20 and the output from the rear wheels 12r, performing series mode operation. In Mode 2, power is converted between the engine 20 and the first electric motor MG1, and between the first electric motor MG1 and the third electric motor MG3. The power conversion is between mechanical and electrical power. In Mode 2, explosive vibration torque of the engine 20 is not transmitted to the front drive shaft 38, which is advantageous for suppressing NV. "NV" is a general term for noise and vibration, such as booming noise, generated in the vehicle 8, and represents at least one of the noise and vibration in the vehicle 8. Therefore, Mode 2 is useful when used, for example, at low vehicle speeds and low loads where quietness is required. Furthermore, in Mode 2, for example, the setting of the operating point of the engine 20 is less subject to restrictions such as muffled noise, so the engine 20 can be operated at an operating point that provides good fuel efficiency.

[0046] In FIG. 7(b), Mode 2 includes a mode in which the third electric motor MG3 is operated as a generator, and the first electric motor MG1 is powered by the electric power generated by the third electric motor MG3 to rotate and drive the engine 20. In Mode 2, the electric power consumed by the power running of the first electric motor MG1 is covered by the regenerative electric power of the third electric motor MG3 generated by the kinetic energy of the vehicle 8, and the engine rotation speed Ne is increased by the power running of the first electric motor MG1. The rotation speed of the engine 20 is increased by the first electric motor torque Tmg1 in a fuel-cut state, and the torque converted onto the shaft of the first rotating element RE1 is negative torque. Note that even when the engine 20 is operated by injecting fuel, if the engine rotation speed Ne is increased by the first electric motor torque Tmg1 to a speed higher than that in the autonomous operation state, the torque converted onto the shaft of the first rotating element RE1 is negative torque. The positive direction of torque is the direction of torque when the engine 20 is operating. The case where the engine 20 is operating is synonymous with the case where the engine 20 alone generates positive torque. In Mode 2 of FIG. 7(b), power is converted between the kinetic energy of the vehicle 8 and the third electric motor MG3, and power is converted between the third electric motor MG3 and the first electric motor MG1. In this way, engine braking can be applied in Mode 2. Even when engine braking is applied in Mode 2, the explosive vibration torque of the engine 20 is not transmitted to the front drive shaft 38, which is advantageous for suppressing NV.

[0047] FIG. 8 is a nomographic diagram illustrating a second HEV mode, i.e., Mode 3, in which the engine 20 is operated and power is exchanged between the second electric motor MG2 and the third electric motor MG3. (a) of FIG. 8 is a nomographic diagram illustrating a case in which torque is generated in the third electric motor MG3 by the electric power generated by the second electric motor MG2. (b) of FIG. 8 is a nomographic diagram illustrating a case in which torque is generated in the second electric motor MG2 by the electric power generated by the third electric motor MG3. In FIG. 8, Mode 3 is included in a plurality of modes that enable switching of the drive mode. Mode 3 is a mode that enables hybrid driving, i.e., HEV driving, and is an input split mode that enables input split driving using the engine 20 as a power source. In Mode 3, the differential mechanism 32 is in a differential state, and the second electric motor MG2 takes up the reaction force of the engine torque Te, thereby mechanically transmitting torque to the third rotating element RE3. Mode 3 is a mode in which, with the brake BR released, an electric continuously variable transmission function can be realized, performing input split mode operation with the engine 20 as input and the front wheels 12f and rear wheels 12r as output. In Mode 3, engine braking can be applied. Expressed using a nomographic diagram, input split refers to a type in which two electric motors (MG2, MG3) and one engine are connected to three rotating elements of a differential mechanism, and the electric motor (MG3) is located as the output element (RE3).

[0048] The two-dot chain line A in FIG. 8(a) indicates a state in which a mechanical point is formed in the differential mechanism 32 where no electrical work is performed by setting the rotational speed of the second rotating element RE2 (second electric motor rotational speed Nmg2) to zero and the power of the second electric motor MG2 to zero. At this mechanical point in the differential mechanism 32, the rotational speed of the third rotating element RE3, which is the output element, is on the deceleration side, i.e., the underdrive (U / D) side, relative to the engine rotational speed Ne. In other words, the mechanical point of the differential mechanism 32 is set by the reduction ratio. In FIG. 8, Mode 3 is the U / D input split mode.

[0049] In (a) of Figure 8, Mode 3 includes at least a mode in which the engine 20 is operated to operate the second electric motor MG2 as a generator, while the third electric motor MG3 is operated as a prime mover by the electric power generated by the second electric motor MG2. In Mode 3, torque is mechanically transmitted to the third rotating element RE3, and the electric power generated by the second electric motor MG2 is supplied to the third electric motor MG3, causing the third electric motor MG3 to generate torque. In Mode 3, power is converted between the engine 20 and the second electric motor MG2, and between the second electric motor MG2 and the third electric motor MG3. Mode 3 has high transmission efficiency in the low vehicle speed and high load range, and is therefore useful for use in the low vehicle speed and high load range, for example.

[0050] In (b) of Fig. 8, Mode 3 may include a mode in which the second electric motor MG2 is operated as a prime mover by electric power generated by the third electric motor MG3 while the engine 20 is running. In Mode 3, the second electric motor MG2 is rotated in the forward direction when torque is mechanically transmitted to the third rotating element RE3, and therefore the electric power consumed in the power running of the second electric motor MG2 is covered by regenerative electric power of the third electric motor MG3 that is generated by the kinetic energy of the vehicle 8. In Mode 3 of (b) of Fig. 8, power conversion is performed between the kinetic energy of the vehicle 8 and the third electric motor MG3, and power conversion is performed between the third electric motor MG3 and the second electric motor MG2.

[0051] The vehicle drive device 10 is controlled to perform Mode 3 shown in (a) of Fig. 8 during normal driving where the drive mode is switched with emphasis on energy efficiency, for example. On the other hand, when the drive mode is switched with emphasis on power performance, for example, and Mode 3 shown in (a) of Fig. 8 is not executed, the vehicle drive device 10 is controlled to perform Mode 3 shown in (b) of Fig. 8.

[0052] FIG. 9 is a nomographic diagram illustrating a third HEV mode, i.e., Mode 4, in which the engine 20 is operated and power is exchanged between the first electric motor MG1 and the second electric motor MG2. (a) of FIG. 9 is a nomographic diagram illustrating a case in which torque is generated in the second electric motor MG2 by the electric power generated by the first electric motor MG1. (b) of FIG. 9 is a nomographic diagram illustrating a case in which torque is generated in the first electric motor MG1 by the electric power generated by the second electric motor MG2. In FIG. 9, Mode 4 is included in a plurality of modes that allow switching of the drive mode. Mode 4 is a mode that allows hybrid driving, i.e., HEV driving, and is an output split mode that allows output split driving using the engine 20 as a power source. In Mode 4, the differential mechanism 32 is in a differential state, and the second electric motor MG2 takes up the reaction force of the engine torque Te, thereby mechanically transmitting torque to the third rotating element RE3. Mode 4 is a mode in which, with the brake BR released, an electric continuously variable transmission function can be realized, in which the input is the engine 20 and the output is the front wheels 12f, performing output split mode operation. In Mode 4, engine braking can be applied. Since the mechanical point of the differential mechanism 32 is set by the reduction ratio, Mode 4 in FIG. 9 is U / D output split mode. Expressed using a collinear diagram, output split refers to a type in which, when two electric motors (MG1, MG2) and one engine are connected to three rotating elements of the differential mechanism, the electric motor (MG1) is located at the input element (RE1) to which the engine is connected.

[0053] In (a) of Fig. 9, Mode 4 includes at least a mode in which the engine 20 is operated to operate the first electric motor MG1 as a generator, while the second electric motor MG2 is operated as a prime mover by the electric power generated by the first electric motor MG1. In Mode 4, when torque is mechanically transmitted to the third rotating element RE3, the second electric motor MG2 is rotated in the forward direction. Therefore, the electric power consumed by the power running of the second electric motor MG2 is covered by the electric power generated by the first electric motor MG1 using the power of the engine 20. In Mode 4, power conversion is performed between the engine 20 and the first electric motor MG1, and power conversion is performed between the first electric motor MG1 and the second electric motor MG2. Mode 4 has high transmission efficiency at high vehicle speeds, and is therefore useful for use at high vehicle speeds, for example.

[0054] 9(b), Mode 4 may include a mode in which the first electric motor MG1 is operated as a prime mover by the electric power generated by the second electric motor MG2 while the engine 20 is running. In Mode 4, the second electric motor MG2 is rotated in the negative direction when torque is mechanically transmitted to the third rotating element RE3. Therefore, the electric power generated by the second electric motor MG2 is supplied to the first electric motor MG1, causing the first electric motor MG1 to generate torque. In Mode 4 in FIG. 9(b), power conversion is performed between the engine 20 and the second electric motor MG2, and power conversion is performed between the second electric motor MG2 and the first electric motor MG1.

[0055] The vehicle drive device 10 is controlled to perform Mode 4 shown in (a) of Fig. 9 during normal driving where the drive mode is switched with emphasis on energy efficiency, for example. On the other hand, when the drive mode is switched with emphasis on power performance, for example, and Mode 4 shown in (a) of Fig. 9 is not executed, the vehicle drive device 10 is controlled to perform Mode 4 shown in (b) of Fig. 9.

[0056] The electronic control unit 70 is configured to switch the drive mode based on the vehicle speed V and the road load. The road load is, for example, the accelerator opening θacc. Alternatively, the road load is, for example, the required value of the driving force Fr based on the accelerator opening θacc and the vehicle speed V, or the actual value of the driving force Fr. For example, in the low vehicle speed / low load range, the first HEV mode, or Mode 2, is set as the drive mode (see Mode 2 shown in FIG. 7). In the low vehicle speed / high load range, the second HEV mode, or Mode 3, is set as the drive mode (see Mode 3 shown in FIG. 8). In the high vehicle speed range, the third HEV mode, or Mode 4, is set as the drive mode (see Mode 4 shown in FIG. 9).

[0057] Figures 10, 11, 12, and 13 each show an example of a drive mode switching map used for drive mode switching control. Each of these drive mode switching maps is a predetermined relationship on a two-dimensional coordinate system with vehicle speed V on the horizontal axis and road load on the vertical axis, with boundaries defining an area corresponding to one of a plurality of modes. In other words, each of these drive mode switching maps is a predetermined relationship for determining which drive mode to set.

[0058] Figures 10 and 11 show the case where the road load is set to driving force Fr, and Figures 12 and 13 show the case where the road load is set to accelerator pedal position θacc. Figure 12 shows the case where the driving force Fr in Figure 10 is replaced with accelerator pedal position θacc, and Figure 13 shows the case where the driving force Fr in Figure 11 is replaced with accelerator pedal position θacc. Figures 10 and 12 are drive mode switching maps used in CD (Charge Depleting) driving, in which the vehicle drives while consuming the state of charge SOC. Figures 11 and 13 are drive mode switching maps used in CS (Charge Sustain) driving, in which the vehicle drives to maintain the state of charge SOC.

[0059] 10 and 12 are used, for example, in a PHEV or the like equipped with a battery 64 of a relatively large capacity, when a CD mode is set for CD running, i.e., running while consuming the charged amount. In an HEV or the like equipped with a battery 64 of a smaller capacity than a PHEV, FIGS. 10 and 12 may not be used. FIGS. 11 and 13 are used, for example, in a PHEV or the like, when a CS mode is set for CS running, i.e., running while maintaining the charged amount. Alternatively, FIGS. 11 and 13 are used, for example, in an HEV or the like.

[0060] When the CD mode is set and the SOC is sufficient, FIG. 10 or FIG. 12 is selected, and Mode 1 is set across the entire range. When the CD mode is set but the SOC is low, or when the CS mode is set, FIG. 11 or FIG. 13 is selected. In FIG. 11 or FIG. 13, Mode 2 is set in the low-speed, low-load range where muffled noise is likely to be a problem. Mode 3 is set in the high-load range because it has high transmission efficiency in the high-load range. Mode 4 is set in the high-speed range because it has good transmission efficiency at the overdrive gear ratio, which is frequently used at high vehicle speeds. Even when the SOC is low and the usable range of the SOC is narrow, Mode 1 may be set in the range where the output of power from the battery 64 is small if consumption of the SOC is acceptable. Alternatively, Mode 1 may be set when the operating efficiency of the engine 20 is poor. In FIG. 11 or FIG. 13, Mode 1 is set in the low-speed, low-load range depending on the SOC.

[0061] 11 or 13, it can be seen that in the low vehicle speed / high load range, Mode 3 is set as the drive mode, and in the high vehicle speed range, Mode 4 is set as the drive mode. Or, looking at it from another perspective, it can be seen that in the high load range, Mode 3 is set as the drive mode, and in the high vehicle speed / low load range, Mode 4 is set as the drive mode.

[0062] FIG. 14 is a flowchart explaining the main parts of the control operation of the electronic control device 70, which is a flowchart explaining the control operation for realizing various modes as drive modes when the vehicle 8 is driven with the engine 20 running, and is executed, for example, repeatedly.

[0063] In Figure 14, each step in the flowchart corresponds to a function of the hybrid control ECU 72. In step S10 (hereinafter, "step" is omitted), a determination is made as to whether the accelerator pedal position θacc is smaller than a predetermined accelerator pedal position threshold θaccth for determining a high load, in order to confirm the road load. If the determination in S10 is negative, in S20, Mode 3 for a high load is selected as the drive mode. If the determination in S10 is positive, in S30, a determination is made as to whether the vehicle speed V is smaller than a predetermined vehicle speed threshold Vth for determining a high vehicle speed. If the determination in S30 is negative, in S40, Mode 4 for a high vehicle speed is selected as the drive mode. If the determination in S30 is positive, in S50, Mode 2 for a low vehicle speed and low load is selected as the drive mode. Note that instead of setting the drive mode using the flowchart of Figure 14, the drive mode may be set by applying the vehicle speed V and the road load to the drive mode switching maps shown in Figures 10 to 13.

[0064] FIG. 15 is a diagram showing an example of a time chart when the control operation shown in the flowchart of FIG. 14 is executed. In FIG. 15, time t1 indicates the time when the accelerator is depressed while the vehicle is stopped. After the accelerator is depressed, acceleration is initially performed at a low accelerator opening θacc (see time t1 and thereafter). If the state of charge SOC exceeds a predetermined threshold for permitting BEV driving, BEV driving is performed in Mode 1 (see time t1-t2). As the vehicle speed V increases, the vehicle enters the Mode 2 region, so the drive mode is switched to Mode 2 (see time t2). After that, the accelerator pedal is depressed further, increasing the accelerator opening θacc, and the vehicle enters the Mode 3 region, so the drive mode is switched to Mode 3 (see time t3). After that, as the vehicle speed V increases, the accelerator opening θacc is reduced, and the vehicle enters the Mode 4 region, so the drive mode is switched to Mode 4 (see time t4).

[0065] Here, the relationship between the rotation speed and the maximum possible torque that can be output in each of the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3 will be explained, taking the second electric motor MG2 as a representative example.

[0066] 16 is a diagram illustrating an example of the relationship between the second electric motor rotation speed Nmg2 and the maximum possible torque of the second electric motor torque Tmg2. The maximum possible torque of the second electric motor torque Tmg2 has a stable output characteristic that allows continuous output, and a short-term output characteristic that allows temporary output.

[0067] First, the stable output characteristic will be described. The second motor current Img2 when the maximum possible torque of the second motor torque Tmg2 is output in the stable output characteristic will be referred to as the maximum drive current Img2_max1.

[0068] When the second motor rotation speed Nmg2 is zero, the rotation speed of the rotating magnetic field generated by the stator is zero. That is, in the second motor MG2, when a multi-phase AC current is passed as the second motor current Img2 through a stator coil provided in the stator, a large driving current flows continuously and unevenly through a specific phase among the multiple phases. To protect the elements of the inverter 62 that pass the driving current through this specific phase, when the second motor rotation speed Nmg2 is zero, the maximum driving current Img2_max1 is reduced. That is, when the second motor rotation speed Nmg2 is zero, the maximum possible torque of the second electric motor torque Tmg2 is reduced. Note that even if the maximum driving current Img2_max1 is continuously passed through the stator, the durability of the elements of the inverter 62 is not deteriorated.

[0069] When the second motor rotation speed Nmg2 becomes non-zero and the second motor MG2 starts rotating at a relatively low rotation speed on the forward or reverse rotation side, the rotation speed of the rotating magnetic field generated by the stator becomes non-zero. That is, when a multi-phase AC current is passed through the stator of the second motor MG2 as the second motor current Img2, the bias of the drive current to a specific phase is eliminated, and the drive current flowing through the multiple phases becomes equal. This allows the maximum drive current Img2_max1 to be increased, and the maximum possible torque of the second motor torque Tmg2 under the stable output characteristic also increases. The rotation speed range of the second motor rotation speed Nmg2, where the current is limited due to the second motor current Img2 being biased to a specific phase among the multiple phases under the stable output characteristic, causing a large current to flow continuously, is referred to as the "predetermined current limit range" (see FIG. 16).

[0070] As the absolute value of the second motor rotation speed Nmg2 gradually increases and the motor rotates at a relatively high rotation speed, the maximum drive current Img2_max1 gradually decreases as the frequency of the rotating magnetic field generated by the stator increases. As a result, the maximum possible torque of the second motor torque Tmg2 in the stable output characteristic gradually decreases on both the positive rotation side and the negative rotation side. The rotation speed range of the second motor rotation speed Nmg2 in which the maximum possible torque in the stable output characteristic is maximized is referred to as the "predetermined maximum torque range" (see FIG. 16).

[0071] In this way, the maximum possible torque of the second electric motor torque Tmg2 is determined by the maximum drive current Img2_max1. That is, the second electric motor torque Tmg2 is limited by the current limit based on the maximum drive current Img2_max1. The current limit based on the maximum drive current Img2_max1 and the limit on the second electric motor torque Tmg2 are the same.

[0072] Next, the short-term output characteristic will be described. The second motor current Img2 when the maximum possible torque of the second motor torque Tmg2 in the short-term output characteristic is output will be referred to as the maximum drive current Img2_max2.

[0073] 16, the shorter the short-term output characteristic Tsht, the larger the maximum drive current Img2_max2, i.e., the larger the maximum possible torque of the second motor torque Tmg2. Although the maximum drive current Img2_max2 is larger than the maximum drive current Img1_max1, the period during which the second motor current Img2 flows is shorter. Therefore, even if the maximum drive current Img2_max2 flows through the stator, the durability of the elements of the inverter 62 will not deteriorate.

[0074] Thus, in both the stable output characteristic and the short-term output characteristic, when the absolute value of the second electric motor rotation speed Nmg2 is zero or near zero, both the maximum drive current Img2_max1 and the maximum drive current Img2_max2 are smaller than when the absolute value of the second electric motor rotation speed Nmg2 is slightly greater than near zero. In other words, when the absolute value of the second electric motor rotation speed Nmg2 is zero or near zero, the maximum possible torque of the second electric motor torque Tmg2 is smaller than when the absolute value is slightly greater than near zero.

[0075] As with the second motor MG2, the first motor current Img1 when the maximum possible torque of the first motor torque Tmg1 in the stable output characteristic is output will be referred to as the maximum drive current Img1_max1, and the first motor current Img1 when the maximum possible torque of the first motor torque Tmg1 in the short-term output characteristic is output will be referred to as the maximum drive current Img1_max2. As with the second motor MG2, the third motor current Img3 when the maximum possible torque of the third motor torque Tmg3 in the stable output characteristic is output will be referred to as the maximum drive current Img3_max1, and the third motor current Img3 when the maximum possible torque of the third motor torque Tmg3 in the short-term output characteristic is output will be referred to as the maximum drive current Img3_max2.

[0076] Next, the control operation of the electronic control unit 70 when starting on a rocky road or the like at a low vehicle speed and a high load range, that is, when traveling at an extremely low vehicle speed and a high load range, will be described.

[0077] The electronic control unit 70 determines whether the crawl-on signal CRon is in the ON state. The electronic control unit 70 determines whether the kick-down-on signal KDon is in the ON state.

[0078] When the electronic control device 70 determines that the crawl-on signal CRon is in the OFF state, it selects one of Mode1, Mode2, Mode3, and Mode4 as the drive mode and starts the vehicle 8.

[0079] When the electronic control unit 70 determines that the crawl-on signal CRon is in an ON state and that the kick-down-on signal KDon is in an OFF state, the electronic control unit 70 selects the fourth HEV mode, i.e., Mode 5, which is substantially the same as Mode 3, as the drive mode. In Mode 5, the electronic control unit 70 causes the first electric motor MG1 to generate positive torque so as to transmit positive torque to the front drive shaft 38, causes the second electric motor MG2 to generate positive torque as a reaction torque, and causes the third electric motor MG3 to generate positive torque so as to transmit positive torque to the rear drive shaft 58. "Positive torque" refers to torque acting in the same direction as engine torque Te when the engine 20 is running, and also to torque acting in a direction that moves the vehicle 8 forward. "Negative torque" refers to torque acting in the opposite direction to positive torque. The reaction torque of the second electric motor MG2 refers to torque acting in a direction that causes the second electric motor rotation speed Nmg2 to become zero. In this embodiment, the second electric motor torque Tmg2, which is a positive torque when the second electric motor MG2 rotates in the forward direction, is a powering torque, and the second electric motor torque Tmg2, which is a positive torque when the second electric motor MG2 rotates in the reverse direction, is a regenerative torque. The second electric motor torque Tmg2 is a reaction torque of the second electric motor MG2, and corresponds to the "reaction torque" in this invention.

[0080] Mode 5 is substantially the same as Mode 3, except that the engine 20 may be in either an operating or stopped state. Mode 5 also differs in that the first electric motor MG1 is operated as a prime mover and that the power balance does not need to be balanced by supplying the generated power of the second electric motor MG2 to the third electric motor MG3, as in Mode 3. For example, in Mode 5, the first electric motor torque Tmg1, the second electric motor torque Tmg2, and the third electric motor torque Tmg3 are each maximized, so that if the power balance deviates positively or negatively, compensation is made by charging the battery 64 or supplying power from the battery 64. In Mode 5, as described below, the differential mechanism 32 is in a differential state. For example, the first electric motor torque Tmg1, the second electric motor torque Tmg2, and the third electric motor torque Tmg3 are each maximized to the maximum possible torque that is maximized in the stable output characteristics. A vehicle state in which the crawl-on signal CRon is in an ON state corresponds to a "predetermined driving state" in the present invention. The "predetermined driving state" is a predetermined state in which the driving load is in a high load range and the vehicle speed can be extremely low when starting or driving. The "predetermined driving state" is not limited to the case where the driving load is in a high load range and the vehicle speed is extremely low, but also includes the case where the crawl-on signal CRon is in an ON state, assuming a situation in which the vehicle will be driving on a rocky road or the like at an extremely low speed and a high load.

[0081] When the electronic control unit 70 determines that the crawl-on signal CRon is in the ON state and that the kick-down-on signal KDon is in the ON state, it selects Mode 5 as the drive mode. The electronic control unit 70 executes torque increase control, which causes the first electric motor MG1 to generate positive torque, the second electric motor MG2 to generate positive torque as a reaction torque, and the third electric motor MG3 to generate positive torque, and increases the reaction torque of the second electric motor MG2 in a stepped manner. The electronic control unit 70 executes torque increase control in response to the driver's depression of the accelerator pedal 22, which causes the kick-down-on signal KDon to turn ON. Preferably, the second electric motor rotation speed Nmg2 is controlled to be outside a predetermined current limit range (see FIG. 16). More preferably, the second electric motor rotation speed Nmg2 is controlled to be within a predetermined maximum torque range (see FIG. 16). For example, when Mode 5 is selected, the reaction torque of the second motor torque Tmg2 is increased by the torque increase control so that the current limit imposed by the maximum drive current Img2_max1 in the stable output characteristic is exceeded and the current limit imposed by the maximum drive current Img2_max2 in the short-term output characteristic is met only within a predetermined period Tpred. The predetermined period Tpred is a period during which the second motor current Img2 exceeds the maximum drive current Img2_max1 in the stable output characteristic but does not exceed the maximum drive current Img2_max2 in the short-term output characteristic, and is a period determined in advance through experimentation or design. For example, the second motor torque Tmg2 during the torque increase control is set to the maximum possible torque in the short-term output characteristic when the short-term output characteristic Tsht described with reference to FIG. 16 is equal to the predetermined period Tpred.

[0082] FIG. 17 is a nomographic diagram illustrating the fourth HEV mode, or Mode 5, in which the engine 20 is driven to rotate, causing the first electric motor MG1 and the third electric motor MG3 to generate positive torque, and the second electric motor MG2 to generate reaction torque. The arrows in FIG. 17 indicate the magnitude and direction of torque converted onto the axes of the rotating elements RE1-RE3. In Mode 5, when the rotational speed of the third rotating element RE3 connected to the front wheels 12f via the front drive shaft 38 is zero or near zero, the first electric motor MG1 generates positive torque, and the second electric motor MG2 generates positive torque, which is a reaction torque. This places the differential mechanism 32 in a differential state in which the engine 20 and the first electric motor MG1 rotate in the forward direction and the second electric motor MG2 rotates in the reverse direction. Because the first electric motor rotation speed Nmg1 is set to the rotation speed on the positive rotation side and the second electric motor rotation speed Nmg2 is set to the rotation speed on the negative rotation side, the rotation speed of the rotating magnetic field generated by the stator of each of the first electric motor MG1 and the second electric motor MG2 is not zero. That is, when multi-phase AC currents are passed through the stators of the first electric motor MG1 and the second electric motor MG2 as the first electric motor current Img1 and the second electric motor current Img2, the bias of the drive currents to specific phases is eliminated and the drive currents flowing through the multiple phases are equally divided. In Mode 5, the second electric motor MG2 takes up the reaction force of the combined torque Tsum (= Te + Tmg1) of the engine torque Te and the first electric motor torque Tmg1, and torque is mechanically transmitted to the third rotating element RE3.

[0083] 17, when it is determined that the crawl-on signal CRon is in the ON state and the kick-down-on signal KDon is in the OFF state, the engine torque Te, the first electric motor torque Tmg1, the second electric motor torque Tmg2, and the third electric motor torque Tmg3 are each indicated by a thick solid line, and the torque transmitted to the front drive shaft 38 is indicated by a thick dashed line. During torque increase control when it is determined that the crawl-on signal CRon is in the ON state and the kick-down-on signal KDon is in the ON state, the engine torque Te, the first electric motor torque Tmg1, and the third electric motor torque Tmg3 are each indicated by a thick solid line, the second electric motor torque Tmg2 is indicated by a thick dashed line, and the torque transmitted to the front drive shaft 38 is indicated by a thick dashed double-dot line.

[0084] A case where it is determined that the crawl-on signal CRon is in the ON state and the kick-down-on signal KDon is in the OFF state is assumed to be a case where the driver operates the crawl switch 91 to travel on a rocky road or the like at an extremely low vehicle speed and in a high-load range, but the driver has not yet reached the maximum depression of the accelerator pedal 22. In this case, in order to start the vehicle 8, torque mechanically transmitted to the third rotating element RE3 shown by the thick dashed line in Figure 17 is transmitted to the front wheels 12f, and third electric motor torque Tmg3 is transmitted to the rear wheels 12r.

[0085] The case where the crawl-on signal CRon is determined to be in the ON state and the kick-down-on signal KDon is determined to be in the ON state refers to a situation in which the driver operates the crawl switch 91 to travel on a rocky road or the like at an extremely low vehicle speed and in a high-load range, and the driver's depression of the accelerator pedal 22 is at its maximum. In this case, torque increase control is executed to increase the second electric motor torque Tmg2 in a stepped manner by a predetermined amount ΔTmg2 only within a predetermined period Tpred. For example, the second electric motor torque Tmg2 is increased by the predetermined amount ΔTmg2 from the maximum possible torque that is maximum in the stable output characteristic to the maximum possible torque in the short-term output characteristic. Immediately before the start of the torque increase control, the engine torque Te and the first electric motor torque Tmg1 are output for a period longer than the predetermined period Tpred. Therefore, the resultant torque Tsum (= Te + Tmg1) is equivalent to the inertia torque, which is the product of the sum (= Ie + I1) of the inertia moments Ie and I1 and the engine angular acceleration dωe / dt. The inertia moment Ie is the inertia moment of the engine 20, and the inertia moment I1 is the inertia moment of the first electric motor MG1. The engine angular acceleration dωe / dt is the time derivative of the angular velocity ωe of the engine 20 corresponding to the engine rotation speed Ne, and is equal to the angular acceleration of the rotor shaft MG1rs of the first electric motor MG1. Because the torque increase control is executed only within the predetermined period Tpred, the torque applied to the first rotating element RE1 due to inertia is substantially the same as the resultant torque Tsum (= Te + Tmg1) immediately before the start of the torque increase control. Therefore, when the second electric motor torque Tmg2 is increased by a predetermined amount ΔTmg2, the torque mechanically transmitted to the third rotating element RE3 is temporarily increased accordingly from the thick dashed line to the thick two-dot chain line. During at least the start period of the predetermined period Tpred, the torque mechanically transmitted to the third rotating element RE3 is increased by the torque increase control. When the torque increase control is executed to start the vehicle 8, the torque mechanically transmitted to the third rotating element RE3, indicated by the thick two-dot chain line in FIG. 17, is transmitted to the front wheels 12f, and the third electric motor torque Tmg3, indicated by the thick solid line, is transmitted to the rear wheels 12r.

[0086] Fig. 18 is a flowchart illustrating the main control operations of the electronic control unit 70 when the vehicle 8 is in a predetermined driving state. The flowchart of Fig. 18 is repeatedly executed, for example, when starting off.

[0087] First, in step S110, it is determined whether the crawl-on signal CRon is in the ON state. If the determination in S110 is positive, then in step S120, it is determined whether the kick-down-on signal KDon is in the ON state. If the determination in S120 is positive, then in step S130, Mode 5 is selected as the drive mode, the first electric motor torque Tmg1 is set to positive torque, the second electric motor torque Tmg2 is set to positive torque as a reaction torque, and the third electric motor torque Tmg3 is set to positive torque. Furthermore, torque increase control is executed to increase the positive torque as a reaction torque of the second electric motor MG2 in a stepped manner. If the determination in S120 is negative, then in step S140, Mode 5 is selected as the drive mode, the first electric motor torque Tmg1 is set to positive torque, the second electric motor torque Tmg2 is set to positive torque as a reaction torque, and the third electric motor torque Tmg3 is set to positive torque. Note that torque increase control is not executed in S140. If the determination in S110 is negative, in S150, one of Mode 1, Mode 2, Mode 3, and Mode 4 is selected as the drive mode and the vehicle 8 is started. After execution of S130, S140, and S150, the process returns.

[0088] FIG. 19 is a diagram showing an example of a time chart when the control operation shown in the flowchart of FIG. 18 is executed. In FIG. 19, from time t11 to time t12, the crawl-on signal CRon is in an ON state, but the kick-down-on signal KDon is in an OFF state. Furthermore, from time t11 to time t12, Mode 5 is selected as the drive mode, and the first electric motor torque Tmg1, the second electric motor torque Tmg2, and the third electric motor torque Tmg3 (not shown) are each set to positive torque, but the vehicle 8 cannot start, and the front wheel rotation speed Nwf is zero. Note that the front wheel rotation speed Nwf is the average of the rotation speeds of the left and right front wheels 12f. The rear wheel rotation speed Nwr is the average of the rotation speeds of the left and right rear wheels 12r. For example, the vehicle 8 is stopped by a step on the road, such as a rocky road, and the vehicle 8 is therefore unable to start. Time t12 indicates the time when the driver strongly depresses the accelerator pedal 22 and the kick-down on signal KDon switches from the off state to the on state.

[0089] Torque increase control is executed from time t12 to time t13. The period between time t12 and time t13 is a predetermined period Tpred. Execution of the torque increase control temporarily increases the torque transmitted to the front wheels 12f. This enables the vehicle 8 to overcome bumps on the road, such as a rocky road, and the front wheel rotation speed Nwf increases from zero, causing the vehicle 8 to start moving.

[0090] According to this embodiment, the differential mechanism 32 has three rotating elements: a first rotating element RE1, a second rotating element RE2, and a third rotating element RE3. The first rotating element RE1 is connected to the engine 20 and the first electric motor MG1. The second rotating element RE2 is connected to the second electric motor MG2. The third rotating element RE3 is connected to the front drive shaft 38. The third electric motor MG3 is connected to the rear drive shaft 58. This allows so-called series running to be performed when the vehicle 8 is running with the engine 20. The first electric motor MG1, which is connected to the same rotating element as the engine 20, is operated as a generator, and the third electric motor MG3 is operated as a prime mover using the generated electric power to drive the rear drive shaft 58. In series running, torque vibration of the engine 20 is prevented from being transmitted to the front drive shaft 38, thereby reducing the likelihood of vibration of the vehicle body when the vehicle 8 is running with the engine 20. Furthermore, when the vehicle 8 is in a predetermined traveling state, the electronic control device 70 is configured to control the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3 to generate a positive torque in the first electric motor MG1, a reaction torque in the second electric motor MG2, and a positive torque in the third electric motor MG3. When the vehicle 8 is in a predetermined traveling state, the first electric motor MG1 generates a positive torque and the second electric motor MG2 generates a reaction torque, thereby bringing the differential mechanism 32 into a differential state and causing the first electric motor MG1 and the second electric motor MG2 to rotate on the positive rotation side or the negative rotation side, respectively. In other words, the rotational speed of the rotating magnetic field generated by the stator of each of the first electric motor MG1 and the second electric motor MG2 is no longer zero, and bias of the drive current of each of the first electric motor MG1 and the second electric motor MG2 to a specific phase is eliminated. For example, even when the vehicle 8 is in a predetermined driving state, the first electric motor MG1 and the second electric motor MG2 can transmit positive torque to the front drive shaft 38 while preventing a large current from flowing continuously and unevenly through a specific phase of the inverter 62. In addition, the third electric motor MG3 can transmit positive torque to the rear drive shaft 58, thereby improving the power performance when the vehicle 8 is in a predetermined driving state.

[0091] According to this embodiment, the electronic control device 70 is configured to generate a reaction torque in the second electric motor MG2 and to increase the reaction torque of the second electric motor MG2 in a stepwise manner. By increasing the reaction torque of the second electric motor MG2 in a stepwise manner, the inertia torque of the first rotating element RE1 is maintained, and the torque transmitted to the front drive shaft 38 can be temporarily increased. For example, even when the engine 20 and the first electric motor MG1 are fully outputting torque, the driving force Fr can be temporarily increased.

[0092] According to this embodiment, the electronic control device 70 is configured to increase the reaction torque of the second electric motor MG2 in a stepwise manner in response to the driver's depression of the accelerator pedal 22, which causes the kick down on signal KDon to turn on. This allows the driving force Fr to be increased in response to the driver's intention, thereby improving drivability in situations where the driving force Fr is required.

[0093] Next, another embodiment of the present invention will be described. In the following description, parts common to the embodiments will be given the same reference numerals and the description thereof will be omitted. [Example]

[0094] 20 is a diagram illustrating a schematic configuration of a vehicle 300 equipped with a vehicle drive system 310 (including a front drive unit 310f and a rear drive unit 310r) to which the present invention is applied. In FIG. 20, a front power transmission device 330 of the front drive unit 310f includes a differential mechanism 332. The differential mechanism 332 and a front differential gear 36 are connected via a front counter gear 34, similar to the front power transmission device 30 of the first embodiment described above.

[0095] The differential mechanism 332 is a single-pinion planetary gear device having a sun gear S, a pinion P, a carrier C, and a ring gear R. A second electric motor MG2 is connected to the sun gear S. The engine 20 and a first electric motor MG1 are connected to the carrier C. The first electric motor MG1 is connected to the carrier C via a power transmission member 40. The ring gear R is in mesh with a front counter gear 34. A front drive shaft 38 is connected to the ring gear R. One end of a brake BR is connected to the output shaft of the engine 20 or the carrier C, and the other end is connected to a non-rotating member (not shown) such as a case.

[0096] FIG. 21 is a nomographic diagram illustrating the configuration of the vehicle drive device 310. In FIG. 21, the differential mechanism 332 of the front drive unit 310f has three rotating elements: a first rotating element RE1, a second rotating element RE2, and a third rotating element RE3. Each of the rotating elements RE1-RE3 of the differential mechanism 332 is coupled to an actuator. Expressed using the nomographic diagram, the first rotating element RE1 is the carrier C. The engine 20 and the first electric motor MG1 are coupled to the first rotating element RE1. The second rotating element RE2 is the sun gear S. The second rotating element RE2 is coupled to the second electric motor MG2. The third rotating element RE3 is the ring gear R. The front drive shaft 38, i.e., the front wheels 12f, are coupled to the third rotating element RE3. The brake BR is a brake mechanism that stops rotation of the first rotating element RE1 when engaged. The rear drive unit 310r is the same as the rear drive unit 10r in the first embodiment described above, and therefore a description thereof will be omitted.

[0097] Similar to the vehicle driving device 10 of the first embodiment, the vehicle driving device 310 is capable of switching between a plurality of driving modes by controlling the engine 20, the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3 by the electronic control device 70. Furthermore, when switching between driving modes, the vehicle driving device 310 is controlled by the electronic control device 70 to engage the brake BR as necessary.

[0098] In the differential mechanism 332, the rotational speed of the third rotating element RE3, which is the output element, is set to the speed-increasing side, or overdrive (O / D) side, relative to the engine rotational speed Ne at the mechanical point. That is, in the differential mechanism 332, the mechanical point is set by the speed-increasing ratio. Therefore, in the vehicle drive device 310, Mode 3 is the O / D input split mode, and Mode 4 is the O / D output split mode.

[0099] Next, the control operation of the electronic control unit 70 when traveling in an extremely low vehicle speed, high load range will be described. The control operation of the electronic control unit 70 is substantially the same as that of the first embodiment described above, but the content of Mode 5 is different. Therefore, only the parts that are different from the first embodiment will be described, and the description of the parts that are essentially the same will be omitted as appropriate.

[0100] In Mode 5, the electronic control unit 70 causes the first electric motor MG1 to generate positive torque so as to transmit positive torque to the front drive shaft 38, causes the second electric motor MG2 to generate negative torque as reaction torque, and causes the third electric motor MG3 to generate positive torque so as to transmit positive torque to the rear drive shaft 58. In Mode 5, the differential mechanism 332 is placed in a differential state. In torque increase control, which increases the reaction torque of the second electric motor MG2 in a stepped manner, the negative torque as reaction torque of the second electric motor MG2 is increased. In this embodiment, when the second electric motor MG2 is rotating in the forward direction, the second electric motor torque Tmg2, which is positive torque, is powering torque, and the second electric motor torque Tmg2, which is negative torque, is regenerative torque. Although not described further, the predetermined current limit range and the predetermined maximum torque range in this embodiment are both within the range in which the second electric motor MG2 is rotating in the forward direction.

[0101] FIG. 22 is a nomographic diagram illustrating the fourth HEV mode, or Mode 5, in which the engine 20 is rotationally driven to generate positive torque in the first electric motor MG1 and the third electric motor MG3 and generate reaction torque in the second electric motor MG2. The arrows in FIG. 22 indicate the magnitude and direction of torque converted onto the axis of each of the rotating elements RE1-RE3. In Mode 5, when the rotation speed of the third rotating element RE3 connected to the front wheels 12f via the front drive shaft 38 is zero or close to zero, the first electric motor MG1 generates positive torque and the second electric motor MG2 generates negative torque, which is reaction torque. This places the differential mechanism 332 in a differential state in which the engine 20 and the first electric motor MG1 rotate in the forward direction and the second electric motor MG2 rotates in the forward direction. Because the first electric motor rotation speed Nmg1 is set to the rotation speed on the forward rotation side and the second electric motor rotation speed Nmg2 is set to the rotation speed on the forward rotation side, the rotation speed of the rotating magnetic field generated by the stator of each of the first electric motor MG1 and the second electric motor MG2 is not zero. That is, when multi-phase AC currents are passed through the stators of the first electric motor MG1 and the second electric motor MG2 as the first electric motor current Img1 and the second electric motor current Img2, the bias of the drive currents to specific phases is eliminated and the drive currents flowing through the multiple phases are equally divided. In Mode 5, the second electric motor MG2 takes up the reaction force of the combined torque Tsum (= Te + Tmg1) of the engine torque Te and the first electric motor torque Tmg1, and torque is mechanically transmitted to the third rotating element RE3.

[0102] 22, when it is determined that the crawl-on signal CRon is in the ON state and the kick-down-on signal KDon is in the OFF state, the engine torque Te, the first electric motor torque Tmg1, the second electric motor torque Tmg2, and the third electric motor torque Tmg3 are each indicated by a thick solid line, and the torque transmitted to the front drive shaft 38 is indicated by a thick dashed line. During torque increase control when it is determined that the crawl-on signal CRon is in the ON state and the kick-down-on signal KDon is in the ON state, the engine torque Te, the first electric motor torque Tmg1, and the third electric motor torque Tmg3 are each indicated by a thick solid line, the second electric motor torque Tmg2 is indicated by a thick dashed line, and the torque transmitted to the front drive shaft 38 is indicated by a thick dashed double-dot line. When torque increase control is executed to start the vehicle 300, the torque mechanically transmitted to the third rotating element RE3 shown by the thick dotted line in Figure 22 is transmitted to the front wheels 12f, and the third electric motor torque Tmg3 shown by the thick solid line is transmitted to the rear wheels 12r.

[0103] Figure 23 is a flowchart illustrating the main control operations of the electronic control unit 70 when the vehicle 300 is in a predetermined driving state. The flowchart in Figure 23 is repeatedly executed, for example, when starting. The flowchart in Figure 23 is substantially the same as the flowchart in Figure 18 in the first embodiment, except that S230 and S240 are used instead of S130 and S140. Therefore, only the different parts will be described, and the same reference numerals will be used to denote substantially common parts, and descriptions thereof will be omitted as appropriate.

[0104] In S230, Mode 5 is selected as the drive mode, the first electric motor torque Tmg1 is set to positive torque, the second electric motor torque Tmg2 is set to negative torque as reaction torque, and the third electric motor torque Tmg3 is set to positive torque. Furthermore, torque increase control is executed to increase the negative torque as reaction torque of the second electric motor MG2 in a stepped manner. In S240, Mode 5 is selected as the drive mode, the first electric motor torque Tmg1 is set to positive torque, the second electric motor torque Tmg2 is set to negative torque as reaction torque, and the third electric motor torque Tmg3 is set to positive torque. Note that torque increase control is not executed in S240.

[0105] Fig. 24 is a diagram showing an example of a time chart when the control operation shown in the flowchart of Fig. 23 is executed. In Fig. 24, from time t21 to time t22, the crawl-on signal CRon is in the ON state, but the kick-down-on signal KDon is in the OFF state. Furthermore, from time t21 to time t22, Mode 5 is selected as the drive mode, the first electric motor torque Tmg1 and the third electric motor torque Tmg3 (not shown) are each set to positive torque, and the second electric motor torque Tmg2 is set to negative torque, but the vehicle 300 cannot start moving, and the front wheel rotation speed Nwf is zero. Time t22 indicates the time when the kick-down-on signal KDon switches from the OFF state to the ON state.

[0106] The torque increase control is executed from time t22 to time t23. The period between time t22 and time t23 is a predetermined period Tpred. By executing the torque increase control, the torque transmitted to the front wheels 12f is temporarily increased.

[0107] As described above, according to this embodiment, the same effects as those of the first embodiment can be obtained. [Example]

[0108] 25 is a diagram illustrating a schematic configuration of a vehicle 400 equipped with a vehicle drive system 410 (including a front drive unit 410f and a rear drive unit 410r) to which the present invention is applied. In FIG. 25, a front power transmission device 430 of the front drive unit 410f includes a differential mechanism 432. The differential mechanism 432 and the front differential gear 36 are connected via the front counter gear 34, similar to the front power transmission device 30 of the first embodiment described above.

[0109] The differential mechanism 432 is a double-pinion planetary gear device having a sun gear S, pinions Pa and Pb, a carrier C, and a ring gear R. The pinions Pa and Pb are pairs of pinions that mesh with each other. A second electric motor MG2 is connected to the sun gear S. The engine 20 and a first electric motor MG1 are connected to the carrier C. The first electric motor MG1 is connected to the carrier C via a power transmission member 40. The ring gear R meshes with the front counter gear 34. A front drive shaft 38 is connected to the ring gear R. One end of the brake BR is connected to the output shaft of the engine 20 or the carrier C, and the other end is connected to a non-rotating member (not shown) such as a case.

[0110] FIG. 26 is a nomographic diagram illustrating the configuration of the vehicle drive device 410. In FIG. 26, the differential mechanism 432 of the front drive unit 410f has three rotating elements: a first rotating element RE1, a second rotating element RE2, and a third rotating element RE3. Each of the rotating elements RE1-RE3 of the differential mechanism 432 is coupled to an actuator. Expressed using the nomographic diagram, the first rotating element RE1 is the carrier C. The engine 20 and the first electric motor MG1 are coupled to the first rotating element RE1. The second rotating element RE2 is the sun gear S. The second rotating element RE2 is coupled to the second electric motor MG2. The third rotating element RE3 is the ring gear R. The front drive shaft 38, i.e., the front wheel 12f, is coupled to the third rotating element RE3. The brake BR is a brake mechanism that stops rotation of the first rotating element RE1 when engaged. The rear drive unit 410r is the same as the rear drive unit 10r in the first embodiment described above, and therefore a description thereof will be omitted.

[0111] Similar to the vehicle driving device 10 of the first embodiment, the vehicle driving device 410 is capable of switching between a plurality of driving modes by controlling the engine 20, the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3 by the electronic control device 70. Furthermore, when switching between driving modes, the vehicle driving device 410 is controlled by the electronic control device 70 to engage the brake BR as necessary.

[0112] In the differential mechanism 432, the rotational speed of the third rotating element RE3, which is the output element, is on the deceleration side, i.e., the underdrive (U / D) side, relative to the engine rotational speed Ne at the mechanical point. That is, in the differential mechanism 432, the mechanical point is set by the reduction ratio. Therefore, in the vehicle drive device 410, Mode 3 is the U / D input split mode, and Mode 4 is the U / D output split mode. In Mode 5 of this embodiment, the alignment chart is substantially the same as the alignment chart of FIG. 17 described in the first embodiment, and is as shown in the alignment chart of FIG. 27.

[0113] As described above, according to this embodiment, the same effects as those of the first embodiment can be obtained. [Example]

[0114] 28 is a diagram illustrating a schematic configuration of a vehicle 500 equipped with a vehicle drive device 510 (including a front drive unit 510f and a rear drive unit 510r) to which the present invention is applied. In FIG. 28, a front power transmission device 530 of the front drive unit 510f includes a differential mechanism 532. The differential mechanism 532 and the front differential gear 36 are connected via the front counter gear 34, similar to the front power transmission device 30 of the first embodiment described above.

[0115] The differential mechanism 532 is a double-pinion planetary gear device having a sun gear S, pinions Pa and Pb, a carrier C, and a ring gear R. A second electric motor MG2 is connected to the sun gear S. An engine 20 and a first electric motor MG1 are connected to the ring gear R. The first electric motor MG1 is connected to the ring gear R via a power transmission member 40. The carrier C is in mesh with the front counter gear 34. A front drive shaft 38 is connected to the carrier C. One end of the brake BR is connected to the ring gear R, and the other end is connected to a non-rotating member (not shown) such as a case.

[0116] FIG. 29 is a diagram illustrating the configuration of a vehicle drive device 510 using a collinear diagram. In FIG. 29, a differential mechanism 532 of a front drive unit 510f has three rotating elements: a first rotating element RE1, a second rotating element RE2, and a third rotating element RE3. Each of the rotating elements RE1-RE3 of the differential mechanism 532 is coupled to an actuator. Expressed using the collinear diagram, the first rotating element RE1 is a ring gear R. The engine 20 and a first electric motor MG1 are coupled to the first rotating element RE1. The second rotating element RE2 is a sun gear S. The second rotating element RE2 is coupled to a second electric motor MG2. The third rotating element RE3 is a carrier C. The front drive shaft 38, i.e., the front wheel 12f, is coupled to the third rotating element RE3. The brake BR is a brake mechanism that stops rotation of the first rotating element RE1 when engaged. The rear drive unit 510r is the same as the rear drive unit 10r in the first embodiment described above, and therefore a description thereof will be omitted.

[0117] Similar to the vehicle driving device 10 of the first embodiment, the vehicle driving device 510 is capable of switching between a plurality of driving modes by controlling the engine 20, the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3 by the electronic control device 70. Furthermore, when switching between driving modes, the vehicle driving device 510 is controlled by the electronic control device 70 to engage the brake BR as necessary.

[0118] In differential mechanism 532, the rotational speed of third rotating element RE3, which is the output element, is set to the speed-increasing side, or overdrive (O / D) side, relative to engine rotational speed Ne at a mechanical point. That is, in differential mechanism 532, the mechanical point is set by a speed-increasing ratio. Therefore, in vehicle drive device 510, Mode 3 is an O / D input split mode, and Mode 4 is an O / D output split mode. In Mode 5 of this embodiment, the alignment chart is substantially the same as the alignment chart of FIG. 22 described in the second embodiment, and is as shown in the alignment chart of FIG. 30.

[0119] As described above, according to this embodiment, the same effects as those of the first embodiment can be obtained.

[0120] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the present invention can also be applied to other embodiments.

[0121] In the above-described Examples 1-4, the first electric motor MG1 and the second electric motor MG2 both have stable output characteristics and short-term output characteristics in which the maximum drive current is smaller when the absolute values ​​of their rotational speeds are near zero compared to when the absolute values ​​of their rotational speeds are slightly greater than near zero. However, the present invention is not limited to this. For example, the present invention may be applied to any case in which at least one of the first electric motor MG1 and the second electric motor MG2 has such characteristics. When the first electric motor MG1 has such characteristics, a continuous large current is prevented from flowing unevenly through a specific phase of the inverter 62 that controls the first electric motor MG1. When the second electric motor MG2 has such characteristics, a continuous large current is prevented from flowing unevenly through a specific phase of the inverter 62 that controls the second electric motor MG2.

[0122] In the above-described first to fourth embodiments, the torque increase control increases the second electric motor torque Tmg2 by a predetermined amount ΔTmg2 from the maximum possible torque in the stable output characteristic to the maximum possible torque in the short-term output characteristic. However, the present invention is not limited to this. For example, the second electric motor torque Tmg2 before the torque increase control may be lower than the maximum possible torque in the stable output characteristic, or the second electric motor torque Tmg2 after the torque increase control may be lower than the maximum possible torque in the short-term output characteristic. Preferably, the torque increase control causes the second electric motor torque Tmg2 to exceed the maximum possible torque in the stable output characteristic. In other words, the torque increase control causes the second electric motor torque Tmg2 to exceed the current limit imposed by the maximum drive current Img2_max1 in the stable output characteristic. Even in such an embodiment, a certain effect can be achieved, such as temporarily increasing the driving force Fr, even when, for example, the engine 20 or the first electric motor MG1 is fully generating torque.

[0123] In the above-described first to fourth embodiments, the torque increase control is performed while the engine 20 is running, but the present invention is not limited to this. For example, the torque increase control may be performed while the engine 20 is stopped.

[0124] In the above-described first to fourth embodiments, the kick-down on signal KDon is turned on when the kick-down switch 24 is turned on. However, the present invention is not limited to this. For example, the kick-down on signal KDon may be turned on when the accelerator pedal opening θacc is greater than a predetermined value θacc_jdg and the increase rate α, which is the time derivative of the accelerator pedal opening θacc, is greater than a predetermined value α_jdg. The predetermined values ​​θacc_jdg and α_jdg are each predetermined values ​​determined experimentally or by design in order to determine whether the magnitude of the driver's depression of the accelerator pedal 22 is near its maximum value. In this embodiment, the driver's depression of the accelerator pedal 22, which turns the kick-down on signal KDon on, corresponds to the "operation by the driver to increase the driving force" in the present invention.

[0125] In the above-described first to fourth embodiments, the "predetermined driving state" may be determined based on the accelerator opening θacc and the vehicle speed V. For example, a required value of driving force Fr may be calculated based on the accelerator opening θacc and the vehicle speed V, and the "predetermined driving state" may be determined when the required value of driving force Fr is higher than a predetermined value Fr_jdg and the vehicle speed V is lower than the predetermined value V_jdg. The predetermined values ​​Fr_jdg and V_jdg are predetermined values ​​that are determined experimentally or by design in order to determine whether the vehicle is in the predetermined driving state.

[0126] For example, in the differential mechanism 32 of the first embodiment described above, the first rotating element RE1 may be one of the ring gear R and the sun gear S, and the second rotating element RE2 may be the other of the ring gear R and the sun gear S. When the first rotating element RE1 is the sun gear S and the second rotating element RE2 is the ring gear R, the engine 20 and the first electric motor MG1 are connected to the sun gear S, and the second electric motor MG2 is connected to the ring gear R.

[0127] In the differential mechanism 332 of the second embodiment described above, the second rotating element RE2 may be one of the sun gear S and the ring gear R, and the third rotating element RE3 may be the other of the sun gear S and the ring gear R. When the second rotating element RE2 is the ring gear R and the third rotating element RE3 is the sun gear S, the second electric motor MG2 is connected to the ring gear R, and the front drive shaft 38 is connected to the sun gear S.

[0128] In the differential mechanism 432 of the third embodiment described above, the first rotating element RE1 may be one of the carrier C and the sun gear S, and the second rotating element RE2 may be the other of the carrier C and the sun gear S. When the first rotating element RE1 is the sun gear S and the second rotating element RE2 is the carrier C, the engine 20 and the first electric motor MG1 are connected to the sun gear S, and the second electric motor MG2 is connected to the carrier C.

[0129] In the differential mechanism 532 of the fourth embodiment described above, the second rotating element RE2 may be one of the sun gear S and the carrier C, and the third rotating element RE3 may be the other of the sun gear S and the carrier C. When the second rotating element RE2 is the carrier C and the third rotating element RE3 is the sun gear S, the second electric motor MG2 is connected to the carrier C, and the front drive shaft 38 is connected to the sun gear S.

[0130] Here, as shown in the above-mentioned Examples 1-4, the second rotating element RE2 is a rotating element that is arranged at either end of a nomographic diagram in which the three rotating elements of the differential mechanism are arranged in a straight line.

[0131] In the above-described Examples 1-4, the power transmission member 40 may be, for example, a chain and sprocket, or a gear pair. For example, when the power transmission member 40 is a gear pair, the intermediate gear 40a and the first rotating element RE1 are connected via a counter gear that meshes with both of them.

[0132] In addition, in the above-described Examples 1 to 4, the first electric motor MG1 may be arranged on the same rotational axis as the engine 20 and the second electric motor MG2. In other words, the first electric motor MG1 may be arranged on the first axis CS1, which is the rotational axis of the differential mechanism 32. Even in this case, a certain effect can be obtained in that a variety of drive modes can be realized when traveling with the engine 20 running.

[0133] In addition, in the above-described embodiments 1-4, a one-way clutch may be used as the brake mechanism for stopping the rotation of the first rotating element RE1 instead of the brake BR.

[0134] In addition, in the above-described Examples 1 to 4, the brake BR does not necessarily have to be provided. In this case, Mode1_MG2_BRon in Mode 1 is not executed. As described above, in Mode1_MG3, BEV driving is possible even if the brake BR is not engaged, so Mode1_MG3 can be executed even if the brake BR is not provided.

[0135] In addition, in the above-described Examples 1 to 4, one of the front wheels 12f and the rear wheels 12r to which the power of the engine 20 or the second electric motor MG2 is transmitted may be the rear wheels 12r, and the other of the front wheels 12f and the rear wheels 12r to which the power of the third electric motor MG3 is transmitted may be the front wheels 12f. In other words, the first drive shaft may be the rear drive shaft 58, and the second drive shaft may be the front drive shaft 38.

[0136] Furthermore, in the above-mentioned Examples 1-4, since it is expected that BEV driving using Mode1_MG3 will be frequently used in a PHEV, a drive unit equipped with the third electric motor MG3 is used as the main engine, but in an HEV, a drive unit equipped with the engine 20 or the second electric motor MG2 may be used as the main engine.

[0137] It should be noted that the above is merely one embodiment, and the present invention can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art. [Explanation of symbols]

[0138] 8: Vehicle 10: Vehicle drive unit 12f: Front wheels 12r: Rear wheels 20: Engine 32: Differential mechanism S: Sun gear (second rotating element) C: Carrier (third rotating element) R: Ring gear (first rotating element) 38: Front drive shaft (first drive shaft) 58: Rear drive shaft (second drive shaft) 70: Electronic control unit (control unit) 300: Vehicle 310: Vehicle drive unit 332: Differential mechanism S: Sun gear (second rotating element) C: Carrier (first rotating element) R: Ring gear (third rotating element) 400: Vehicle 410: Vehicle drive unit 432: Differential mechanism S: Sun gear (second rotating element) C: Carrier (first rotating element) R: Ring gear (third rotating element) 500: Vehicle 510: Vehicle drive unit 532: Differential mechanism S: Sun gear (second rotating element) C: Carrier (third rotating element) R: Ring gear (first rotating element) Fr: Driving force MG1: First electric motor MG2: Second electric motor MG3: Third electric motor RE1: First rotating element RE2: Second rotating element RE3: Third rotating element Tmg2: Second electric motor torque (reaction torque)

Claims

1. A vehicle drive device including an engine, a first electric motor, a second electric motor, a third electric motor, a differential mechanism, a first drive shaft that drives one of front wheels and rear wheels, a second drive shaft that drives the other of the front wheels and the rear wheels, and a control device, the differential mechanism has three rotation elements: a first rotation element, a second rotation element, and a third rotation element; the engine and the first electric motor are connected to the first rotating element, the second electric motor is connected to the second rotating element, and the first drive shaft is connected to the third rotating element, The third electric motor is connected to the second drive shaft, The control device is configured to control the first electric motor, the second electric motor, and the third electric motor when the vehicle is in a predetermined running state, to cause the first electric motor to generate a positive torque, the second electric motor to generate a reaction torque, and the third electric motor to generate a positive torque. A vehicle drive device characterized by:

2. The control device is configured to generate a reaction torque in the second electric motor and to increase the reaction torque of the second electric motor in a stepwise manner.

2. The vehicle drive system according to claim 1.

3. The control device is configured to increase the reaction torque of the second electric motor in a stepwise manner using an operation by a driver to increase the driving force as a trigger.

3. The vehicle drive system according to claim 2.

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