Drive system for hybrid vehicle

A drive system includes: a first planetary gear unit, in which a carrier is connected to an internal combustion engine, a sun gear is connected to a first MG, and a ring gear is connected, via a first drive gear and a first driven gear, to a counter shaft; and a second planetary gear unit, in which a brake is provided to a sun gear, a carrier is connected to the internal combustion engine, and a ring gear is connected, via a second drive gear and a second driven gear, to the counter shaft. A gear ratio of the first drive gear and the first driven gear is larger than a gear ratio of the second drive gear and the second driven gear.

CROSS-REFERENCE TO RELATED APPLICATION

This is a national phase application based on the PCT International Patent Application No. PCT/JP2013/063321 filed May 13, 2013, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a drive system for a hybrid vehicle that can transmit rotation of an internal combustion engine to drive wheels by changing a speed of the rotation in a differential mechanism and a motor generator.

BACKGROUND ART

A hybrid vehicle in which an internal combustion engine, a motor generator, and an output shaft are connected to different rotational elements to each other of a planetary gear unit so as to continuously change a ratio between a speed of the internal combustion engine and a rotational speed of the output shaft, that is, a transmission gear ratio in the planetary gear unit and the motor generator has been known. As a drive system of such a hybrid vehicle, a system that includes two planetary gear units and a brake to realize a continuously variable state in which the transmission gear ratio is continuously changed by these and a overdrive state in which the speed of the internal combustion engine is lower than the rotational speed of the output shaft has been known (see Patent Literature 1). In this system of Patent Literature 1, only one planetary gear unit of the two planetary gear units is used to transmit rotation in the case of the continuously variable state. Thus, mechanical loss is suppressed.

RELATED ART LITERATURE

Patent Literature

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

In the system of Patent Literature 1, both of the two planetary gear units are used in the case of the overdrive state to transmit the rotation of the internal combustion engine to the output shaft. Thus, there still remains room to further reduce the mechanical loss.

For this reason, the invention has an object of providing a drive system for a hybrid vehicle that can further reduce mechanical loss compared to conventional systems.

Means for Solving the Problem

A drive system of the invention includes: an internal combustion engine; a motor generator; an output member connected to a drive wheel so as to be able to transmit power; a first differential mechanism that has a first rotation element, a second rotation element, and a third rotation element capable of making differential rotation with each other and in which the third rotation element is arranged between the first rotation element and the second rotation element in a collinear diagram; a second differential mechanism that has a first rotation element, a second rotation element, and a third rotation element capable of making differential rotation with each other and in which the third rotation element is arranged between the first rotation element and the second rotation element in the collinear diagram; and locking mechanism capable of being switched between a locked state in which the first rotation element of the second differential mechanism is unrotatably locked and a released state in which rotation of the first rotation element of the second differential mechanism is allowed. An output shaft of the internal combustion engine, the third rotation element of the first differential mechanism, and the third rotation element of the second differential mechanism are coupled to rotate integrally, an output shaft of the motor generator and the first rotation element of the first differential mechanism are coupled to rotate integrally, the second rotation element of the first differential mechanism is connected to the output member via a first rotation transmission path so as to be able to transmit rotation, the second rotation element of the second differential mechanism is connected to the output member via a second rotation transmission path so as to be able to transmit rotation, the first rotation transmission path is formed such that the rotation is transmitted from the second rotation element of the first differential mechanism to the output member by changing a speed thereof at a first transmission gear ratio, and the second rotation transmission path is formed such that the rotation is transmitted from the second rotation element of the second differential mechanism to the output member by changing the speed thereof at a second transmission gear ratio that is smaller than the first transmission gear ratio.

In the drive system of the invention, the rotation of the internal combustion engine can be transmitted to the output member only via the first differential mechanism by switching the locking mechanism to the released state and generating a reaction force by the motor generator. In this case, a transmission gear ratio between a speed of the internal combustion engine and a rotational speed of the output member can continuously be changed by changing a rotational speed of the motor generator. That is, the drive system can be brought into a continuously variable state. Meanwhile, the rotation of the internal combustion engine can be transmitted to the output member only via the second differential mechanism by switching the locking mechanism to the locked state and bringing torque of the motor generator to zero. By switching the locking mechanism to the locked state, just as described, the speed of the internal combustion engine can be reduced to be lower than the rotational speed of the output member. Thus, the drive system can be brought into an overdrive state. Just as described, according to the drive system of the invention, the rotation of the internal combustion engine is transmitted via only one of the differential mechanisms in either state of the continuously variable state or the overdrive state. Therefore, mechanical loss can be reduced in comparison with a conventional drive system.

In one embodiment of the drive system of the invention, the internal combustion engine, the motor generator, the first differential mechanism, the second differential mechanism, and the locking mechanism may be coaxially arranged, the first differential mechanism and the second differential mechanism may be arranged between the internal combustion engine and the motor generator, and the locking mechanism may be arranged on an opposite side of the internal combustion engine with the motor generator, the first differential mechanism, and the second differential mechanism being interposed therebetween. According to this embodiment, since the locking mechanism is not arranged between the motor generator and the internal combustion engine, an outer diameter of the locking mechanism can be reduced. Thus, the locking mechanism can be downsized.

The one embodiment of the drive system of the invention may further include vehicle control unit for switching the locking mechanism to the locked state and bringing the torque of the motor generator to zero in the case where a speed of the vehicle is at least equal to a specified determination speed that is set in advance. By controlling the locking mechanism and the motor generator, just as described, the drive system can be brought into the overdrive state when the vehicle runs at a high speed. In this way, the speed of the internal combustion engine can be reduced. Therefore, fuel economy can be improved.

MODES FOR CARRYING OUT THE INVENTION

FIG. 1is a skeletal view of a drive system according to a first embodiment of the invention. This drive system10A is mounted in a hybrid vehicle1and includes an internal combustion engine (hereinafter may be referred to as an engine)11, a first motor generator (hereinafter may be abbreviated as a first MG)12, a second motor generator (hereinafter may be abbreviated as a second MG)13. The engine11is a well-known spark-ignition-type internal combustion engine mounted in the hybrid vehicle. Thus, a detailed description thereon will not be made. The first MG12and the second MG13are well-known motor generators, each of which functions as a motor and a generator. The first MG12includes: a rotor12bthat integrally rotates with a rotor shaft12a; and a stator12cthat is coaxially arranged on an outer circumference of the rotor12band is fixed to a case (not shown). Similarly, the second MG13includes: a rotor13bthat integrally rotates with a rotor shaft13a; and a stator13cthat is coaxially arranged on an outer circumference of the rotor13band is fixed to a case.

An output shaft11aof the engine11and the rotor shaft12aof the first MG12are connected to a power split mechanism20. An output section14for outputting power to drive wheels2of the vehicle1is also connected to the power split mechanism20. The output section14includes a counter shaft15as an output member and an output gear16that integrally rotates with the counter shaft15. The output gear16meshes with a ring gear17athat is provided in a case of a differential mechanism17. The differential mechanism17is a well-known mechanism that splits the power transmitted to the ring gear17ato the right and left drive wheels2.

The power split mechanism20includes a first planetary gear unit21and a second planetary gear unit22. These planetary gear units21,22are planetary gear units of a single pinion type. The first planetary gear unit21includes: a sun gear S1as an outer tooth gear; a ring gear R1as an inner tooth gear that is coaxially arranged with the sun gear S1; and a carrier C1for retaining a pinion gear P1that meshes with these gears S1, R1in a manner to allow rotation and revolution thereof around the sun gear S1. Hereinafter, there are cases where the sun gear S1of the first planetary gear unit21is referred to as the first sun gear S1, the ring gear R1thereof is referred to as the first ring gear R1, and the carrier C1thereof is referred to as the first carrier C1. Similarly, the second planetary gear unit22includes: a sun gear S2as the outer tooth gear; a ring gear R2as an inner tooth gear that is coaxially arranged with the sun gear S2; and a carrier C2for retaining a pinion gear P2that meshes with these gears S2, R2in a manner to allow rotation and revolution thereof around the sun gear S2. Hereinafter, there are cases where the sun gear S2of the second planetary gear unit22is referred to as the second sun gear S2, the ring gear R2thereof is referred to as the second ring gear R2, and the carrier C2thereof is referred to as the second carrier C2. Each of the first planetary gear unit21and the second planetary gear unit22is configured that transmission gear ratios among the sun gear, the carrier, and the ring gear are the same.

As shown in this drawing, the first carrier C1and the second carrier C2are coupled to rotate integrally with the output shaft11aof the engine11. The first sun gear S1is coupled to the rotor shaft12aof the first MG12. The second sun gear S2is coupled to a brake23. This brake23can be switched between a locked state in which the second sun gear S2is unrotatably locked and a released state in which rotation of the second sun gear S2is allowed. It should be noted that a well-known friction brake or the like may be used as the brake23. Thus, a detailed description on the brake23will not be made.

As shown in this drawing, the engine11, the first MG12, the first planetary gear unit21, the second planetary gear unit22, and the brake23are coaxially arranged. In addition, the first planetary gear unit21and the second planetary gear unit22are arranged between the engine11and the first MG12. The brake23is arranged on an opposite side of the engine11with the first MG12, the first planetary gear unit21, and the second planetary gear unit22being interposed therebetween. That is, the brake23is arranged not to be interposed between the engine11and the first MG12.

The first ring gear R1is coupled to rotate integrally with a first drive gear24. This first drive gear24meshes with a first driven gear25that is provided on the counter shaft15. In addition, the second ring gear R2is coupled to rotate integrally with a second drive gear26. The second drive gear26meshes with a second driven gear27that is provided on the counter shaft15. A value set for a gear ratio γ1 between the first drive gear24and the first driven gear25is larger than a value set for a gear ratio γ2 between the second drive gear26and the second driven gear27. That is, these gear ratios have a relationship of γ1>γ2.

A third drive gear28is provided on the rotor shaft13aof the second MG13. The third drive gear28meshes with a third driven gear29that is provided on the counter shaft15.

In this drive system10A, a continuously variable mode and an overdrive mode are realized by switching states of the brake23. In the continuously variable mode, the brake23is switched to the released state.FIG. 2shows one example of a collinear diagram of the drive system10A during the continuously variable mode. In this diagram, “ENG” indicates the engine11, “OUT” indicates the counter shaft15, and “MG1” indicates the first MG12. In addition, a solid line L1indicates a relationship of each rotation element of the first planetary gear unit21, and a broken line L2indicates a relationship of each rotation element of the second planetary gear unit22. “ρ” indicates a transmission gear ratio between the first carrier C1and the first ring gear R1. As shown in this diagram, when the transmission gear ratio between the first sun gear S1and the first carrier C1is “1”, a smaller value than 1 is set as the transmission gear ratio ρ. It should be noted that this drawing is the collinear diagram at a time that a rotational speed of the first MG12is 0.

As described above, since the brake23is switched to the released mode in the continuously variable mode, the second sun gear S2rotates idle. Accordingly, rotation of the engine11is transmitted to the counter shaft15only via the first planetary gear unit21. In addition, in this case, a ratio (the transmission gear ratio) between a speed of the engine11and a rotational speed of the counter shaft15can continuously be changed by appropriately adjusting the rotational speed of the first MG12. Meanwhile, since the second sun gear S2rotates idle, the second planetary gear unit22does not contribute to transmission of the rotation of the engine11.

The brake23is switched to the locked state in the overdrive mode. Then, torque of the first MG12is brought to zero. That is, the first MG12rotates idle.FIG. 3shows one example of a collinear diagram of the drive system10A during the overdrive mode. It should be noted that, in this diagram, common parts as those inFIG. 2are denoted by the same reference numerals and symbols and a description thereon will not be made. In this mode, since the brake23is switched to the locked state, the second sun gear S2is unrotatably locked. In addition, since the first MG12rotates idle, the rotation of the engine11is transmitted to the counter shaft15only via the second planetary gear unit22. As shown in this diagram, the rotational speed of the counter shaft15is higher than the speed of the engine11in the overdrive mode. Accordingly, the drive system10A is brought into an overdrive state. Meanwhile, since the first MG12rotates idle, the first planetary gear unit21does not contribute to transmission of the rotation of the engine11. It should be noted that, when the transmission gear ratio between the second sun gear S2and the second carrier C2is 1 as described above, the smaller value than 1 is set as the transmission gear ratio ρ between the second carrier C2and the second ring gear R2. Accordingly, in the case of switching to the overdrive mode, a difference between a rotational speed of the second sun gear S2and a rotational speed of the first sun gear S1can be reduced. Thus, the rotational speed of the first MG12can be reduced.

As described above, the torque is output from the first planetary gear unit21in the continuously variable mode. On the other hand, the torque is output from the second planetary gear unit22in the overdrive mode. However, in either one of the modes, the same counter shaft15receives the torque in the end. A rotational speed of the first planetary gear unit21and a rotational speed of the second planetary gear unit22are the same in either one of the modes. Thus, output of the counter shaft15does not change. However, the speed of the engine11is reduced in the overdrive mode. Accordingly, the three rotation elements of the second planetary gear unit22constitute the overdrive state.

The brake23is controlled by a vehicle control unit30. The vehicle control unit30is configured as a computer unit that includes a microprocessor and peripheral equipment like a RAM, a ROM, and the like that are required for an operation thereof. The vehicle control unit30retains various types of control programs for making the vehicle1run appropriately. The vehicle control unit30executes control of control targets, such as the engine11and each of the MGs12,13, by executing these programs. Various sensors for obtaining information on the vehicle1are connected to the vehicle control unit30. For example, a vehicle speed sensor31is connected to the vehicle control unit30. The vehicle speed sensor31outputs a signal that corresponds to a speed (a vehicle speed) of the vehicle1. In addition to the above, various sensors, switches, and the like are connected to the vehicle control unit30. However, those are not shown.

The vehicle control unit30switches the mode of the drive system10A on the basis of the vehicle speed. The vehicle control unit30switches the brake23to the locked state in the case where the vehicle speed is at least equal to a determination speed that is set in advance. In this way, the mode of the drive system10A is switched to the overdrive mode. It should be noted that the determination speed is set as a reference that is used to determine whether the vehicle1runs at a high speed. On the other hand, the vehicle control unit30switches the brake23to the released state in the case where the vehicle speed is lower than the determination speed. In this way, the mode of the drive system10A is switched to the continuously variable mode.

As it has been described so far, in this embodiment, as shown inFIG. 3, the overdrive mode can substantially be realized by the three rotation elements of the second planetary gear unit22. In addition, the continuously variable mode can also be realized by the three rotation elements of the first planetary gear unit21. Accordingly, in either mode of the continuously variable mode or the overdrive mode, the rotation of the engine11is transmitted to the counter shaft15via only one of the planetary gear units. Thus, mechanical loss can be reduced.

In addition, as shown inFIG. 1, the brake23is arranged not to be interposed between the engine11and the first MG12. In this case, an outer diameter of the brake23can be reduced. Thus, the brake23can be downsized.

In the case where the vehicle1runs at the high speed, the brake23is switched to the locked state, and the torque of the first MG12is brought to zero. Accordingly, the mode of the drive system10A is switched to the overdrive mode, and thus the speed of the engine11can be reduced. Therefore, fuel economy can be improved.

In this embodiment, the first MG12corresponds to the motor generator of the invention. The first planetary gear unit21corresponds to the first differential mechanism of the invention. The first sun gear S1corresponds to the first rotation element of the first differential mechanism of the invention. The first ring gear R1corresponds to the second rotation element of the first differential mechanism of the invention. The first carrier C1corresponds to the third rotation element of the first differential mechanism of the invention. The second planetary gear unit22corresponds to the second differential mechanism of the invention. The second sun gear S2corresponds to a first rotation element of the second differential mechanism of the invention. The second ring gear R2corresponds to the second rotation element of the second differential mechanism of the invention. The second carrier C2corresponds to the third rotation element of the second differential mechanism of the invention. The brake23corresponds to the locking mechanism of the invention. The vehicle control unit30corresponds to a vehicle control unit of the invention. In this embodiment, the first rotation transmission path of the invention is formed by the first drive gear24and the first driven gear25. In addition, the second rotation transmission path of the invention is formed by the second drive gear26and the second driven gear27.

Next, a description will be made on a drive system according to a second embodiment of the invention with reference toFIG. 4.FIG. 4is a skeletal view of a drive system10B according to this embodiment. It should be noted that, in this drawing, common parts as those inFIG. 1are denoted by the same reference numerals and symbols and a description thereon will not be made.

In this embodiment, an outer tooth T1is provided on an outer circumferential surface of the first ring gear R1. Hereinafter, this outer tooth T1may be referred to as a first outer tooth. In addition, an outer tooth T2is provided on an outer circumferential surface of the second ring gear R2. Hereinafter, this outer tooth T2may be referred to as a second outer tooth. Furthermore, the first ring gear R1is formed to have a smaller outer diameter than the second ring gear R2. Thus, the number of teeth of the first outer tooth T1is smaller than the number of teeth of the second outer tooth T2. It should be noted that an inner diameter of the first ring gear R1and an inner diameter of the second ring gear R2are the same, and the number of teeth of inner teeth of these ring gears R1, R2are the same.

As shown in this drawing, on a radially outer side of the first ring gear R1and the second ring gear R2, a transmission shaft40is provided in a manner to be parallel with axes of these ring gears R1, R2. A first intermediate gear41and a second intermediate gear42are provided on the transmission shaft40. The first intermediate gear41meshes with the first outer tooth T1. The second intermediate gear42meshes with the second outer tooth T2. In addition, a value set for a gear ratio γ11 between the first outer tooth T1and the first intermediate gear41is larger than a value set for a gear ratio γ12 between the second outer tooth T2and the second intermediate gear42. That is, these gear ratios have a relationship of γ11>γ12. Thus, a rotational speed of the first ring gear R1is lower than a rotational speed of the second ring gear R2.

Also in this drive system10B, the continuously variable mode and the overdrive mode are realized by switching the state of the brake23. The brake23is switched to the released state in the continuously variable mode. Thus, the second sun gear S2rotates idle. In this case, the rotation of the engine11is transmitted to the counter shaft15via the first planetary gear unit21, the transmission shaft40, the second ring gear R2, and the second drive gear26. At this time, the second ring gear R2only functions as a member for transmitting rotation of the second intermediate gear42to the second drive gear26. Thus, also in this continuously variable mode, the second planetary gear unit22does not contribute to the transmission of the rotation of the engine11.

The brake23is switched to the locked state in the overdrive mode. Then, the torque of the first MG12is brought to zero. In this case, the rotation of the engine11is transmitted to the counter shaft15via the second planetary gear unit22and the second drive gear26. Thus, the first planetary gear unit21does not contribute to the transmission of the rotation of the engine11.

It should be noted that, also in this embodiment, the brake23is controlled by the vehicle control unit30. The vehicle control unit30switches the brake23to the locked state in the case where the vehicle speed is at least equal to the determination speed. In this way, the mode of the drive system10B is switched to the overdrive mode. On the other hand, the vehicle control unit30switches the brake23to the released state in the case where the vehicle speed is lower than the determination speed. In this way, the mode of the drive system10B is switched to the continuously variable mode.

As it has been described so far, also in this embodiment, the rotation of the engine11is transmitted to the counter shaft15via only one of the planetary gear units in both modes of the continuously variable mode and the overdrive mode. Thus, the mechanical loss can be reduced. In addition, the brake23is arranged so as not to be interposed between the engine11and the first MG12. Thus, the brake23can be downsized. Furthermore, in the case where the vehicle1runs at the high speed, the mode of the drive system10B is switched to the overdrive mode. Therefore, the fuel economy can be improved.

In this embodiment, the first rotation transmission path of the invention is formed by the first intermediate gear41, the transmission shaft40, the second intermediate gear42, the second ring gear R2, the second drive gear26, and the second driven gear27.

The invention is not limited to the above-described embodiments, but can be implemented in various embodiments. For example, the planetary gear units provided in the drive system of the invention are not limited to the planetary gear units of the single pinion type. In the drive system of the invention, planetary gear units of a double pinion type may be used. However, in this case, connection destinations of the ring gear and the carrier are appropriately changed in each embodiment.