Vehicle drive device

Abstract

To provide a vehicle drive device capable of preventing input of excessive torque into a power transmission path even when a brake mechanism is brought into an engagement state while suppressing complication of a structure.SOLUTION: The engine is connected to the first rotary element through a torque limiter that limits a torque transmitted between the first driveshaft and the engine, and the brake device is disposed in a power transmission path between the torque limiter and the engine. As a result, even if an excessive torque is input from the first drive shaft in the engaged state of the brake mechanism, it is possible to prevent an excessive input load from being applied to a rotating member such as a gear or a shaft in the power transmission path by one torque limiter. According to the embodiment of the present disclosure, therefore, an excessive torque may not be applied to the power transmission path even if the brake device is engaged.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a vehicle drive system that includes an engine, two electric motors, a planetary gear device, and a drive shaft that drives one of the front and rear wheels. [Background technology]

[0002] A well-known vehicle drive system includes an engine, a first electric motor, a second electric motor, a planetary gear set having three rotating elements, i.e., a first rotating element, a second rotating element, and a third rotating element, and a first drive shaft that drives one of the front and rear wheels. For example, Patent Document 1 discloses a vehicle power transmission system that includes such a system. Patent Document 1 discloses that the system further includes a brake mechanism that stops the engine and a first torque limiter that limits torque transmitted between the first drive shaft and the engine. Patent Document 1 also discloses that the system further includes a second torque limiter that limits torque transmitted between the first drive shaft and the brake mechanism, thereby preventing excessive torque from being input to gears, shafts, etc. in the power transmission path when the brake mechanism is engaged. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-35991 Summary of the Invention [Problem to be solved by the invention]

[0004] To realize various drive modes, a configuration is conceivable in which, for each rotating element of the planetary gear set, an engine and a first electric motor are coupled to a first rotating element, a second electric motor is coupled to a second rotating element, and a first drive shaft is coupled to a third rotating element. The drive mode is, for example, a Battery Electric Vehicle (BEV) mode in which the engine is stopped and torque is generated in the first and second electric motors. In this BEV mode, a brake mechanism that stops the rotation of the first rotating element is further provided to perform motor running, i.e., BEV running, in which the vehicle runs using the second electric motor as a power source without generating torque in the first electric motor. Even in a vehicle drive system configured in this manner, it is desirable to prevent excessive torque from being input to gears, shafts, etc. in the power transmission path when the brake mechanism is engaged. Therefore, even in a vehicle drive system configured in this manner, a second torque limiter that limits torque transmitted between the first drive shaft and the brake mechanism may be provided in addition to a first torque limiter that limits torque transmitted between the first drive shaft and the engine. However, in this case, two torque limiters are required, which causes a problem of complicated structure.

[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 can prevent excessive torque from being input into the power transmission path even when the brake mechanism is engaged, while suppressing structural complexity. [Means for solving the problem]

[0006] The gist of the first invention is (a) a vehicle drive device comprising an engine, a first electric motor, a second electric motor, a planetary gear device having three rotating elements, namely a first rotating element, a second rotating element, and a third rotating element, and a first drive shaft that drives one of the front wheels and rear wheels, (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) further comprising a brake mechanism that stops rotation of the first rotating element by being engaged, and a torque limiter that limits the torque transmitted between the first drive shaft and the engine, (d) the engine is connected to the first rotating element via the torque limiter, and (e) the brake mechanism is provided in a power transmission path between the torque limiter and the engine. [Effects of the Invention]

[0007] According to the first aspect of the present invention, the planetary gear device has an engine and a first electric motor connected to a first rotating element, a second electric motor connected to a second rotating element, and a first drive shaft connected to a third rotating element. The vehicle drive device further includes a brake mechanism that stops rotation of the first rotating element. This allows the vehicle drive device to realize a variety of drive modes, including a BEV mode in which the vehicle runs using the second electric motor as a power source while the engine is stopped. The engine is also connected to the first rotating element via a torque limiter that limits the torque transmitted between the first drive shaft and the engine, and the brake mechanism is provided in the power transmission path between the torque limiter and the engine. This allows the single torque limiter to prevent excessive input loads from being applied to rotating members, such as gears and shafts, in the power transmission path, even if excessive torque is input from the first drive shaft when the brake mechanism is engaged. The power transmission path here is the path from the first drive shaft to the brake mechanism, which is synonymous with the path from the first drive shaft to the engine. Therefore, even when the brake mechanism is engaged, excessive torque can be prevented from being input into the power transmission path while suppressing structural complexity. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a schematic configuration of a vehicle equipped with a vehicle drive device 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. 4 is a collinear diagram illustrating an example of a drive mode driven by an electric motor. [Figure 4] FIG. 3 is a collinear diagram illustrating an example of an engine-driven drive mode. [Figure 5] 10A and 10B are diagrams illustrating an example of the effect achieved when a brake mechanism is provided in a power transmission path between a torque limiter and an engine. [Figure 6] FIG. 1 is a diagram illustrating a schematic configuration of a vehicle equipped with a vehicle drive device of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Example]

[0010] FIG. 1 is a diagram illustrating a 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 system 10f that drives the front wheels 12f and a rear drive system 10r that drives the rear wheels 12r. The vehicle drive system 10 is equipped with a drive shaft 14 that drives the drive wheels 12 and a drive unit 16 that drives the drive shaft 14. The drive shaft 14 includes left and right front drive shafts 14f and left and right rear drive shafts 14r. The drive unit 16 includes a front drive unit 16f and a rear drive unit 16r. Note that the above "left and right" refer to left and right with respect to the forward direction of the vehicle 8.

[0011] The front drive system 10f includes an engine 18, a front drive shaft 14f, and a front drive unit 16f. The rear drive system 10r includes a rear drive shaft 14r and a rear drive unit 16r. The front drive shaft 14f is a first drive shaft that drives the front wheels 12f, which are one of the front wheels 12f and the rear wheels 12r. The rear drive shaft 14r is a second drive shaft that drives the rear wheels 12r, which are the other of the front wheels 12f and the rear wheels 12r. The front drive unit 16f is a first drive unit that drives the front drive shaft 14f. The rear drive unit 16r is a second drive unit that drives the rear drive shaft 14r.

[0012] The front drive unit 16f includes a first electric motor MG1, a second electric motor MG2, a front power transmission mechanism 20, an input shaft 22, and a differential mechanism 24. The rear drive unit 16r includes a third electric motor MG3 and a rear power transmission mechanism 50.

[0013] 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.

[0014] The engine 18 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 18. 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.

[0015] 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 a prime mover that generates mechanical power from electric power and as a generator that generates electric power from mechanical power. 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 an electronic control device 70 (described later) controlling the inverter 62. 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. The torque of the electric motors is power running torque when the electric motors function as prime movers, and is 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. The first electric motor MG1, the second electric motor MG2, and the third electric motor MG3 are controlled via the inverter 62 so that electric power is supplied and received 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 and simultaneously.

[0016] The front power transmission mechanism 20 is a first power transmission mechanism provided in a power transmission path between the differential mechanism 24 and the front drive shaft 14f, i.e., the front wheels 12f. The front power transmission mechanism 20 includes a counter gear pair 26, a counter driven shaft 28, a final gear pair 30, a front differential gear 32, etc.

[0017] The input shaft 22 is a rotating member that connects the engine 18 and the differential mechanism 24. The counter gear pair 26 is a first gear pair that has a counter drive gear 34 and a counter driven gear 36 that meshes with the counter drive gear 34. The final gear pair 30 is a second gear pair that has a final drive gear 38 and a final driven gear 32r that meshes with the final drive gear 38. The counter driven shaft 28 is a rotating shaft that is arranged parallel to the front drive shaft 14f. The counter driven gear 36 and the final drive gear 38 are provided on the counter driven shaft 28 so that they cannot rotate relative to each other. The counter driven gear 36 and the final drive gear 38 are arranged side by side on the counter driven shaft 28. The final drive gear 38 has a smaller diameter than the counter driven gear 36. The final driven gear 32r is a ring gear of the front differential gear 32 and functions as an input rotation member of the front differential gear 32. The front differential gear 32 is a differential gear to which the front drive shaft 14f is connected. The differential mechanism 24 and the front drive shaft 14f are connected via the front power transmission mechanism 20 and the like.

[0018] The differential mechanism 24 is a double-pinion planetary gear device having a sun gear S, pinions Pa and Pb, a carrier C that supports the pinions Pa and Pb so that they can rotate and revolve, and a ring gear R that meshes with the sun gear S via the pinions Pa and Pb. The pinions Pa and Pb are multiple pairs of pinions that mesh with each other. A second electric motor MG2 is connected to the sun gear S. An engine 18 and a first electric motor MG1 are connected to the carrier C. A front drive shaft 14f is connected to the ring gear R via a counter gear pair 26, a final gear pair 30, etc.

[0019] The engine 18, the second electric motor MG2, the differential mechanism 24, and the counter drive gear 34 are each disposed on a first axis CS1, which is the rotation axis of the differential mechanism 24. The first axis CS1 is a rotation axis parallel to the counter driven shaft 28. The first electric motor MG1 is disposed on a second axis CS2. The second axis CS2 is a rotation axis parallel to the first axis CS1. The counter driven gear 36 and the final drive gear 38 are each disposed on a third axis CS3, which is the rotation axis of the counter driven shaft 28. The front differential gear 32 and the front drive shaft 14f are each disposed on a fourth axis CS4, which is the rotation axis of the front drive shaft 14f. Disposing the first electric motor MG1 on the second axis CS2 reduces the size of the front drive device 10f in the direction of the first axis CS1, compared to when the first electric motor MG1 is disposed on the first axis CS1. In other words, the axial dimension of the front drive unit 16f is reduced.

[0020] The engine 18 is connected to the carrier C of the differential mechanism 24 via the input shaft 22. The first electric motor MG1 is disposed on a second axis CS2 that is different from the first axis CS1. For this reason, the front drive unit 16f further includes a power transmission member 40. The first electric motor MG1 is connected to the carrier C via the power transmission member 40. Part or all of the first electric motor MG1 is disposed in a position that overlaps with the range on the first axis CS1 from the position where the engine 18 is disposed to the position where the second electric motor MG2 is disposed, when viewed radially from the first axis CS1.

[0021] The power transmission member 40 includes, for example, a motor drive gear 40a, a motor driven gear 40b, an idler gear 40c, a motor drive shaft 40d, and an idler shaft 40e. The motor drive shaft 40d is a rotating shaft arranged on the second axis CS2 and is integrally connected to the rotor shaft MG1rs of the first electric motor MG1 by spline fitting so as not to rotate relative to it. The motor drive shaft 40d is a rotating shaft on which the motor drive gear 40a is arranged so as not to rotate relative to it. The idler shaft 40e is a rotating shaft arranged on the fifth axis CS5, which is a rotational axis parallel to the first axis CS1. The idler shaft 40e is a rotating shaft on which the idler gear 40c is arranged so as not to rotate relative to it. The motor drive gear 40a is a gear arranged on the second axis CS2 and connected to the first electric motor MG1. The motor driven gear 40b is a gear arranged on the first axis CS1 and connected to the carrier C. The idler gear 40c is a gear arranged on a fifth axis CS5 different from the first axis CS1 and the second axis CS2 and meshes with the motor drive gear 40a and the motor driven gear 40b. Both the motor drive gear 40a and the idler gear 40c have smaller diameters and fewer teeth than the motor driven gear 40b. The power transmission member 40 functions as, for example, a reduction mechanism.

[0022] The front drive unit 16f further includes a brake BR. The brake BR is an engagement device that is operated by an actuator, such as an electric or hydraulic actuator, to selectively connect members at both ends. The brake BR functions as a braking mechanism that selectively stops the rotation of the carrier C. The carrier C is selectively made rotatable or non-rotatable by the brake BR.

[0023] The rear power transmission mechanism 50 is a second power transmission mechanism provided in the power transmission path between the third electric motor MG3 and the rear drive shaft 14r, i.e., the rear wheels 12r. The rear power transmission mechanism 50 includes an output gear 52, a rear counter gear 54, a rear differential gear 56, and the like. 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 differential gear 56 is a differential gear to which the rear drive shaft 14r is connected. The third electric motor MG3 is connected to the rear drive shaft 14r via the rear power transmission mechanism 50 and the like. 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.

[0024] The rear drive unit 16r further includes a parking mechanism PLC, which is a known parking lock device that switches between a parking lock state in which the output gear 52 is mechanically fixed so as not to rotate, and a non-parking lock state in which the output gear 52 is rotatable.

[0025] The vehicle drive system 10 further includes an electronic control device 70 as a controller including control devices related to the control of the vehicle drive system 10 and the like. The electronic control device 70 includes, for example, a so-called microcomputer equipped with a CPU, RAM, ROM, an input / output interface, and the like. The CPU executes various controls of the vehicle 8 by, for example, performing signal processing according to programs stored in the ROM in advance. For example, the electronic control device 70 executes output control of the engine 18, the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3, and executes drive mode switching control, which will be described later.

[0026] Various signals based on detection signals from various sensors provided in the vehicle 8 are input to the electronic control device 70. The various signals include, for example, the engine speed Ne, the vehicle speed V, the first electric motor rotation speed Nmg1, the second electric motor rotation speed Nmg2, the third electric motor rotation speed Nmg3, the accelerator opening θacc, and the state of charge SOC. The state of charge SOC [%] is the remaining charge of the battery 64, calculated based on, for example, the battery charge / discharge current and the battery voltage.

[0027] The electronic control device 70 outputs various command signals to various devices (e.g., engine control device 60, inverter 62, brake BR, etc.) provided in the vehicle 8. The various command signals include, for example, an engine control command signal Se, a first electric motor control command signal Smg1, a second electric motor control command signal Smg2, a third electric motor control command signal Smg3, and a brake control command signal Sbr. The engine control command signal Se is a command signal for controlling the intake amount, ignition timing, fuel injection amount, etc., for controlling the engine 18. The first electric motor control command signal Smg1 is a command signal for controlling the first electric motor MG1, for example, a first electric motor current, etc. The second electric motor control command signal Smg2 is a command signal for controlling the second electric motor MG2, for example, a second electric motor current, etc. The third electric motor control command signal Smg3 is a command signal for controlling the third electric motor MG3, for example, a third electric motor current, etc. 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).

[0028] FIG. 2 is a nomographic diagram showing the configuration of the vehicle drive system 10. In FIG. 2, the rear drive system 10r is a main unit that is used for driving with priority over, for example, the front drive system 10f. In this case, the front drive system 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.

[0029] The differential mechanism 24 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 24. The nomographic diagram of FIG. 2 illustrates the three rotating elements of the differential mechanism 24 arranged in a straight line. Expressed using the nomographic diagram, the first rotating element RE1 is the carrier C. The engine 18 and the first electric motor MG1 are connected to the first rotating element RE1. The second rotating element RE2 is the sun gear S. The second electric motor MG2 is connected to the second rotating element RE2. The third rotating element RE3 is the ring gear R. The front drive shaft 14f, 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.

[0030] 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.

[0031] The electronic control device 70 controls the engine 18, the first electric motor MG1, the second electric motor MG2, and the third electric motor MG3, and is capable of switching the drive mode to one of a plurality of modes.

[0032] The multiple modes into which the drive mode of the vehicle 8 can be switched will be described with reference to FIGS. 3 and 4. FIGS. 3 and 4 each show the relative rotational speeds of the rotational elements RE1-RE3 of the differential mechanism 24 in the nomographic diagram of FIG. 2. In this nomographic diagram, 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 ring gear R, 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 carrier C, which is the first rotational element RE1 connected to the engine 18 (see "ENG" in the drawing) and the first electric motor MG1. Furthermore, this indicates that the third electric motor MG3, which is 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.

[0033] Fig. 3 is a nomographic diagram illustrating examples of drive modes (BEV mode, series mode) driven by electric motors. Fig. 3(a) is a nomographic diagram illustrating Mode 1, which enables BEV driving, i.e., the BEV mode in which torque is generated by the second electric motor MG2. Fig. 3(b) is a nomographic diagram illustrating Mode 2, which enables series driving, i.e., the series mode in which the engine 18 is rotationally driven and power is exchanged between the first electric motor MG1 and the third electric motor MG3.

[0034] 3(a), Mode 1 is a mode in which the engine 18 is stopped, and torque is generated in the second electric motor MG2 with the brake BR in an engaged state, thereby performing BEV running. In Mode 1, the brake BR is engaged and the rotational speed of the first rotating element RE1 is fixed to zero, so forward and backward BEV running is possible with the second electric motor MG2 using power from the battery 64, without generating torque in the first electric motor MG1. In Mode 1, the differential mechanism 24 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.

[0035] In Mode 1, instead of or in addition to the second electric motor MG2, it is also possible to generate torque in the third electric motor MG3 to generate a drive torque Tr. When BEV driving is performed by generating torque only in the third electric motor MG3, the brake BR does not need to be engaged. Alternatively, in Mode 1, the first electric motor MG1 and the second electric motor MG2 generate mutual torque so that the moment around the third rotating element RE3 becomes zero while exchanging power with the battery 64, thereby enabling BEV driving with the brake BR released. In this case, the first electric motor torque Tmg1 is controlled, for example, so as not to cause drag of the engine 18, that is, so that the rotational speed of the first rotating element RE1 becomes zero.

[0036] In FIG. 3B, Mode 2 is a mode enabling hybrid driving, or HEV driving, and is a series mode enabling series driving using the engine 18 as a power source. Mode 2 is a mode in which the engine 18 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 released, an electric continuously variable transmission function can be realized that performs series mode operation, with the input being the engine 18 and the output being the rear wheels 12r. In Mode 2, explosive vibration torque of the engine 18 is not transmitted to the front driveshaft 14f, 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 for use in low-speed, low-load ranges where quietness is required, for example.

[0037] Fig. 4 is a nomographic diagram illustrating examples of engine-driven drive modes (input split mode, output split mode). Fig. 4(a) is a nomographic diagram illustrating Mode 3 in which the engine 18 is operated and power is exchanged between the second electric motor MG2 and the third electric motor MG3. Fig. 4(b) is a nomographic diagram illustrating Mode 4 in which the engine 18 is operated and power is exchanged between the first electric motor MG1 and the second electric motor MG2.

[0038] In FIG. 4(a), Mode 3 is an input split mode that allows HEV driving and enables input split driving using the engine 18 as a power source. In Mode 3, the differential mechanism 24 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 that allows for an electrically variable speed function to be realized that performs input split mode operation with the engine 18 as the input and the front wheels 12f and rear wheels 12r as the output, with the brake BR in a released state. Expressed using a nomographic diagram, input split refers to a type in which two electric motors (MG2, MG3) and one engine are connected to the three rotating elements of the differential mechanism, and the electric motor (MG3) is arranged as the output element (RE3).

[0039] As shown in FIG. 4( a), Mode 3 includes at least a mode in which the engine 18 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. Mode 3 has high transmission efficiency in high load ranges, and is therefore useful for use in high load ranges, for example. Note that Mode 3 may also include a mode in which the engine 18 is operated while the second electric motor MG2 is operated as a prime mover by the electric power generated by the third electric motor MG3. In this case, 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. The electric power consumed by the second electric motor MG2 during power running is covered by the regenerative electric power of the third electric motor MG3, which is generated by the kinetic energy of the vehicle 8.

[0040] The two-dot chain line A in FIG. 4(a) indicates a state in which a mechanical point is formed in the differential mechanism 24 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 24, 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 24 is set by the reduction ratio. In FIG. 4(a), Mode 3 is the U / D input split mode.

[0041] In FIG. 4B, Mode 4 is an output split mode that enables HEV driving and enables output split driving using the engine 18 as a power source. In Mode 4, the differential mechanism 24 is in a differential state, and the second electric motor MG2 takes up the reaction force of the engine torque Te, mechanically transmitting torque to the third rotating element RE3. Mode 4 is a mode that realizes an electrically variable speed function that performs output split mode operation with the brake BR in a disengaged state, with the engine 18 as the input and the front wheels 12f as the output. 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. Because the mechanical point of the differential mechanism 24 is set by the reduction ratio, Mode 4 in FIG. 4B is U / D output split mode.

[0042] As shown in FIG. 4(b), Mode 4 includes at least a mode in which the engine 18 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, the second electric motor MG2 is rotated in the forward direction when torque is mechanically transmitted to the third rotating element RE3. Therefore, the electric power consumed by the power running of the second electric motor MG2 is supplied by the electric power generated by the first electric motor MG1 using the power of the engine 18. Mode 4 has high transmission efficiency at high vehicle speeds, and is therefore useful for use at high vehicle speeds, for example. Note that Mode 4 may also include a mode in which the engine 18 is operated to operate the first electric motor MG1 as a prime mover by the electric power generated by the second electric motor MG2. In this case, in Mode 4, the second electric motor MG2 is rotated in the reverse direction when torque is mechanically transmitted to the third rotating element RE3. 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.

[0043] Returning to FIG. 1, the vehicle drive system 10 further includes a damper mechanism DP and a damper torque limiter TLdp. The front drive unit 16f includes a damper mechanism DP in a power transmission path between the engine 18 and the input shaft 22. The damper mechanism DP is, for example, a known damper that absorbs torque fluctuations of the engine 18. The front drive unit 16f includes a damper torque limiter TLdp in a power transmission path between the engine 18 and the damper mechanism DP. The damper torque limiter TLdp is a torque limiter that limits the torque transmitted between the front drive shaft 14f (also synonymous with the front wheels 12f) and the input shaft 22 (also synonymous with the engine 18). The front drive unit 16f further includes an engine connecting shaft 19, which is a rotating member that connects the damper torque limiter TLdp and the engine 18.

[0044] The damper torque limiter TLdp is a torque limiting mechanism that prevents torque transmission exceeding a predetermined limit torque Tlim, i.e., limits the transmission of torque greater than the limit torque Tlim. For example, when torque exceeding the limit torque Tlim is input, the damper torque limiter TLdp causes slippage, preventing the transmission of torque exceeding the limit torque Tlim. For example, even if the front drive shaft input torque Tfds is deemed excessive and exceeds the limit torque Tlim, the input shaft input torque Tin is reduced to or below the limit torque Tlim by the damper torque limiter TLdp. The front drive shaft input torque Tfds is the input torque to the front drive shaft 14f. The input shaft input torque Tin is the input torque to the input shaft 22. The excessive front drive shaft input torque Tfds is, for example, torque input from the front wheels 12f that occurs when the front wheels 12f repeatedly slip and grip on an uneven road.

[0045] In the vehicle drive system 10, the engine 18 is connected to the first rotating element RE1 of the differential mechanism 24 via a damper torque limiter TLdp. The position of the brake BR that stops the rotation of the first rotating element RE1 will be described.

[0046] FIG. 6 is a diagram illustrating the schematic configuration of a vehicle 100 equipped with a vehicle drive system 110 (including a front drive system 110f and a rear drive system 110r) of a comparative example. In FIG. 6, the vehicle drive system 110 has a drive unit 116 (including a front drive unit 116f and a rear drive unit 116r) in which the connection relationships between the components are the same as those of the drive unit 16 of the vehicle drive system 10. In the front drive system 110f, the brake BR is disposed on the idler shaft 40e. One end of the brake BR is connected to the idler shaft 40e, 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 drive unit 116f and the like. However, when the brake BR is engaged, the first rotating element RE1, i.e., the input shaft 22, is fixed so as not to rotate, and therefore the torque limiter function of the damper portion torque limiter TLdp does not work. If the front drive shaft input torque Tfds becomes excessive when the brake BR is engaged, an excessive input load may be applied to the brake BR and to rotating components, such as gears and shafts, in the power transmission path between the input shaft 22 and the front wheels 12f. For this reason, the front drive unit 116f further includes a brake section torque limiter TLbr that limits the torque transmitted between the front drive shaft 14f and the brake BR. Similar to the damper section torque limiter TLdp, the brake section torque limiter TLbr functions to prevent torque transmission exceeding the limit torque Tlim. The brake section torque limiter TLbr is provided, for example, in the power transmission path between the idler gear 40c and the brake BR on the idler shaft 40e on which the brake BR is disposed. The front drive unit 110f requires two torque limiters, the damper section torque limiter TLdp and the brake section torque limiter TLbr, which results in a complex structure. The rear drive unit 110r is the same as the rear drive unit 10r, and therefore a description thereof will be omitted.

[0047] Returning to FIG. 1, in the front drive device 10f of this embodiment, the brake BR is provided in the power transmission path between the damper section torque limiter TLdp and the engine 18. The brake BR is disposed on, for example, the engine connecting shaft 19. One end of the brake BR is connected to the engine connecting shaft 19, 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 drive unit 16f and the like. By disposing the brake BR on the engine connecting shaft 19, the damper section torque limiter TLdp also has the function of the brake section torque limiter TLbr, that is, the function of limiting the torque transmitted between the front drive shaft 14f and the brake BR.

[0048] Fig. 5 is a diagram showing an example of the effect achieved when a brake BR is provided in the power transmission path between the damper torque limiter TLdp and the engine 18. In Fig. 5, even if the front drive shaft input torque Tfds becomes excessive torque exceeding the limit torque Tlim when the brake BR is engaged, the damper torque limiter TLdp functions to reduce the input shaft input torque Tin to equal to or less than the limit torque Tlim.

[0049] As described above, according to this embodiment, the differential mechanism 24 has the engine 18 and the first electric motor MG1 coupled to the first rotating element RE1, the second electric motor MG2 coupled to the second rotating element RE2, and the front drive shaft 14f coupled to the third rotating element RE3. The vehicle drive system 10 further includes a brake BR that stops the rotation of the first rotating elements. This allows the vehicle drive system 10 to realize a variety of drive modes, including a BEV driving mode in which the vehicle runs using the second electric motor MG2 as a power source while the engine 18 is stopped. The engine 18 is coupled to the first rotating element RE1 via a damper torque limiter TLdp, and the brake BR is provided in the power transmission path between the damper torque limiter TLdp and the engine 18. This allows the single torque limiter to prevent excessive input loads from being applied to rotating members, such as gears and shafts, in the power transmission path, even if excessive torque is input from the front drive shaft 14f when the brake BR is engaged. The power transmission path here refers to the power transmission path from the front drive shaft 14f to the brake BR, and is synonymous with the power transmission path from the front drive shaft 14f to the engine 18. Therefore, even when the brake BR is engaged, it is possible to prevent excessive torque from being input into the power transmission path while suppressing structural complexity.

[0050] Furthermore, according to this embodiment, the third electric motor MG3 is coupled to the rear drive shaft 14r. This allows the vehicle drive system 10 to realize a variety of drive modes, including a mode in which so-called series running can be performed. For example, when running the vehicle 8 with the engine 18 running, the first electric motor MG1 is operated as a generator using power from the engine 18, and the third electric motor MG3 is operated as a prime mover using the generated power to drive the rear drive shaft 14r, thereby enabling series running.

[0051] 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.

[0052] For example, the above-described embodiment does not necessarily require the rear drive unit 10r. Even in this case, the present invention can be applied by providing the brake BR in the power transmission path between the damper torque limiter TLdp and the engine 18. Furthermore, various drive modes can be realized, such as "Mode 1" and "Mode 4," excluding the mode in which torque is generated in the third electric motor MG3 to perform BEV driving.

[0053] In the differential mechanism 24 of the above-described embodiment, 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 18 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.

[0054] Furthermore, in the differential mechanism 24 of the above-described embodiment, the first rotating element RE1 may be the ring gear R, 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. In this case, the differential mechanism 24 has a mechanical point where the rotational speed of the third rotating element RE3, which is the output element, is on the speed-up side, i.e., the overdrive (O / D) side, relative to the engine rotational speed Ne. That is, the mechanical point of the differential mechanism 24 is set by the speed-up ratio. Therefore, Mode 3 is an O / D input split mode, and Mode 4 is an O / D output split mode. Alternatively, the differential mechanism 24 may be a single-pinion planetary gear device having a sun gear, pinion, carrier, and ring gear. Even if the differential mechanism 24 is a single-pinion planetary gear device, the mechanical point may be configured on either the U / D side or the O / D side. Even in this case, the same effect as in the above embodiment can be obtained.

[0055] Here, the second rotating element RE2 is a rotating element that is arranged at either end in a collinear diagram in which the three rotating elements of the differential mechanism 24 are arranged in a straight line.

[0056] In the above-described embodiment, the power transmission member 40 may be configured so that the motor drive gear 40a and the motor driven gear 40b are connected via a connecting member such as a belt, without including the idler gear 40c, or so that the motor drive gear 40a and the motor driven gear 40b are meshed with each other, without including the idler gear 40c.

[0057] In the above-described embodiment, the brake BR may be replaced with a one-way clutch.

[0058] In the above-described embodiment, one of the front wheels 12f and the rear wheels 12r to which the power of the engine 18 and 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 14r, and the second drive shaft may be the front drive shaft 14f.

[0059] Furthermore, in the above-described embodiment, in a PHEV, it is expected that BEV driving using the third electric motor MG3 will be used frequently, and therefore the drive unit equipped with the third electric motor MG3 is used as the main engine, but in an HEV, the drive unit equipped with the engine 18 or the second electric motor MG2 may be used as the main engine.

[0060] 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]

[0061] 10: Vehicle drive unit 12f: Front wheels 12r: Rear wheels 14f: Front drive shaft (first drive shaft) 14r: Rear drive shaft (second drive shaft) 18: Engine 24: Differential mechanism (planetary gear device) S: Sun gear (second rotating element) C: Carrier (first rotating element) R: Ring gear (third rotating element) BR: Brake (brake mechanism) MG1: First electric motor MG2: Second electric motor MG3: Third electric motor RE1: First rotating element RE2: Second rotating element RE3: Third rotating element TLdp: Damper torque limiter (torque limiter)

Claims

1. A vehicle drive device including an engine, a first electric motor, a second electric motor, a planetary gear device having three rotation elements, i.e., a first rotation element, a second rotation element, and a third rotation element, and a first drive shaft that drives one of front wheels and rear wheels, 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 transmission further includes a brake mechanism that stops rotation of the first rotating element by being brought into an engaged state, and a torque limiter that limits torque transmitted between the first drive shaft and the engine, the engine is connected to the first rotating element via the torque limiter, The vehicle drive device is characterized in that the brake mechanism is provided in a power transmission path between the torque limiter and the engine.

2. 2. The vehicle drive device according to claim 1, further comprising: a second drive shaft that drives the other of the front wheels and the rear wheels; and a third electric motor connected to the second drive shaft.

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