Hybrid electric vehicle and powertrain

A hybrid electric vehicle and powertrain includes an engine and an electric machine connected to each other in a power-split arrangement. The electric machine is operable as a motor or a generator, and is offset from the engine, thereby reducing the overall length of the powertrain. A power transfer arrangement includes a planetary gear set in which the carrier is directly connected to an output shaft of the engine. The electric machine is connected to the planetary gear set through an intermediate gear, thereby facilitating the offset of the electric machine and the engine and facilitating an easy change of gear ratio for the motor/generator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hybrid electric vehicle and a powertrain for such a vehicle.

2. Background Art

With the ever increasing need to produce vehicles that are more fuel efficient, hybrid electric vehicles (HEV's) have provided an improvement in fuel economy over many conventional vehicles that utilize only an internal combustion engine to drive the vehicle. One of the primary advantages of an HEV is that it allows the vehicle to be powered by one or more electric motors under certain operating conditions. For example, if the speed of the vehicle is relatively moderate, and the battery or other electrical power source is sufficiently charged, the engine may be shut off, and the vehicle powered exclusively by the electric motors. As operating conditions change, the engine may be started to provide additional power, and if needed, operate a generator to charge the battery.

Various arrangements of internal combustion engines and electric machines—i.e., generators and motors—have been utilized in HEV's. For example, series arrangements, parallel arrangements, and power-split arrangements provide different ways for the engine and electric machines to interact to output torque to drive the vehicle. In one example of a power-split arrangement, an engine and an electric machine are both operatively connected to a planetary gear set, the output of which provides torque to vehicle drive wheels. One or more additional electric machines can be used to provide additional torque to the drive wheels, charge an energy storage device, such as a battery, provide electrical energy directly to another electric machine, or some combination thereof. In the power-split arrangement, power output from the engine flows through the planetary gear set, where a portion of the power is applied to the electric machine connected to the planetary gear set, and another portion of the engine power is transferred to the vehicle drive wheels.

In many examples of power-split arrangements, an engine output shaft is connected to one of the members of a planetary gear set, and an output shaft from an electric machine is connected to another of the members of the planetary gear set. These two torque-producing devices are often in-line with each other, such that their respective output shafts lie along the same axis. In some vehicle platforms, it may be desirable to reduce overall powertrain length by having torque-producing devices that are not in-line with each other.

In addition, it may be desirable to have a power-split configuration for an HEV powertrain that includes an electric machine having an output shaft that is not directly connected to a member of the planetary gear set. This would add flexibility to the configuration by providing a way to adjust gear ratios without changing the basic members of the transmission—e.g., the members of the planetary gear set.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a hybrid electric vehicle and powertrain having a power-split configuration where the engine output shaft and the electric machine output shaft are offset from each other, thereby providing a shorter length to accommodate smaller packaging requirements.

The invention also provides a hybrid electric vehicle and powertrain that include one or more electric machines having outputs that are connected to intermediate and/or idler gears, such that the gear ratios for the electric machines can be changed without changing the primary members of the planetary gear set.

The invention also provides a hybrid electric vehicle having a plurality of wheels, and including an engine and a first electric machine, each of which is operable to output mechanical power. The first electric machine is also operable as a generator, and is configured to receive mechanical power from the engine and to output electrical power. The engine includes an output shaft defining a first axis, and the first electric machine includes an output shaft defining a second axis. The first and second axes are not coincident with each other, thereby providing an offset between the first electric machine and the engine. A power transfer arrangement cooperates with the engine and the first electric machine to provide power flow paths between the engine and at least one of the vehicle wheels, and between the first electric machine and the at least one vehicle wheel. The power transfer arrangement includes a planetary gear set having a plurality of members, including a sun gear, a plurality of planet gears, a carrier connecting the planet gears to each other, and a ring gear connected to the planet gears. One of the members of the planetary gear set provides an output member for the planetary gear set. The engine output shaft is directly connected to one of the members of the planetary gear set such that the mechanical power output from the engine is split between the first electric machine and the output member of the planetary gear set.

The invention further provides a hybrid electric vehicle as described above, and further includes a second electric machine defining a motor axis, and having an output connected to one of the members of the planetary gear set, such that the motor axis is coincident with the first axis. In such embodiments, the ring gear may provide the output member for the planetary gear set, and a planetary gear reduction arrangement can be connected to the output of the second electric machine and the ring gear. This increases the torque transferred from the second electric machine to the ring gear. In some embodiments, the planetary gear reduction arrangement includes a plurality of pinion gears that are connected to each other by a carrier. The carrier can be grounded to allow the pinions to rotate about their own axes without orbiting around the second electric machine.

The invention also provides a powertrain for a hybrid electric vehicle that includes an engine and a first electric machine, each of which is operable to output mechanical power to drive the vehicle. Embodiments of this powertrain can include a second electric machine that is also operable to provide torque to drive the vehicle. The first and second electric machines can each be connected to the powertrain through one or more intermediate or idler gears, and one or more intermediate or idler gears can be used on the output side of the powertrain such that the gear ratios of the electric machines can be changed without changing the members of the planetary gear set.

In one embodiment of the present invention, a hybrid electric vehicle powertrain includes an engine and two electric machines connected through a planetary gear set. Specifically, the engine is connected to the carrier of the planetary gear set, while the first electric machine is connected to the sun gear. An output shaft from the engine is directly connected to the carrier, while an output shaft of the first electric machine is connected to the sun gear through a first mounted gear attached to its output shaft, and a second gear mounted on a shaft directly connected to the sun gear. In this way, the engine and first electric machine are offset from each other, thereby reducing the overall length of the powertrain.

The ring gear provides the output for the planetary gear set, which provides power flow paths from the first electric machine and the engine to vehicle drive wheels. The vehicle drive wheels are connected to a differential, which itself is connected to the ring gear through a mounted gear on a differential shaft, and an idler gear intermeshing with the differential mounted gear and the ring gear of the planetary gear set. The second electric machine is also connected to the powertrain through a mounted gear on its output shaft, and an idler gear intermeshing with its mounted gear and the ring gear from the planetary gear set. The differential shaft and the shaft of the second electric machine are also offset from each other, thereby further helping to ensure a shorter powertrain.

In some embodiments, the second electric machine can be a relatively small unit, and in such a case can be connected to the planetary gear set such that it is in-line with the engine. This can be accomplished by connecting the first electric machine to the planetary gear set as described above, and providing a central opening through the second electric machine so that the sun gear shaft passes through it. The output from the second electric machine can be provided to a planetary gear reduction arrangement to increase the torque provided to the ring gear of the planetary gear set. This may be advantageous, since, as described above, the second electric machine may be a relatively small unit. As with other embodiments, the output from the planetary gear set can be through the ring gear, which is connected to an idler gear intermeshing with a mounted gear on the differential shaft. Thus, embodiments of the present invention provide a combination of flexibility with regard to changing gear ratios and compact size to accommodate the smaller packaging requirements of many HEV platforms.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a vehicle10in accordance with one embodiment of the present invention. The vehicle10includes a powertrain12having three torque producing devices: an engine14and two electric machines16,18. In the embodiment shown inFIG. 1, the first electric machine16is labeled “Generator” and the second electric machine18is labeled “Motor”; however, it is understood that each of the electric machines16,18can act as either a motor to produce mechanical power, or as a generator to produce electric power upon receiving a mechanical power input. The engine14and the electric machines16,18are each connected to a power transfer arrangement19that provides power flow paths from these torque-producing devices to an output of the powertrain12to drive the vehicle10.

The engine14includes an output shaft20that is connected to a carrier22of a planetary gear set24, which is part of the power transfer arrangement19. The carrier22connects a plurality of planet gears25to each other. The planetary gear set24also includes a ring gear26, and a sun gear28. The sun gear28is connected to a first input shaft30, which has a first intermediate gear32attached thereto. The generator16has an output shaft34, which has attached to it a first mounted gear36. The mounted gear36cooperates with the intermediate gear32to provide a power flow path between the generator16and the planetary gear set24. As shown inFIG. 1, the output shaft20of the engine14defines a first axis38, while the output shaft34of the generator16defines a second axis40. The two axes38,40are not coincident with each other, which can help to reduce the overall length of the powertrain12.

As shown inFIG. 1, the vehicle10includes a pair of drive wheels42,44. The drive wheels42,44receive power through a differential46in the powertrain12. The differential46includes an input shaft48that is attached to a second mounted gear50. The mounted gear50intermeshes with a first idler gear52, which, in turn, intermeshes with a second intermediate gear54mounted to the ring gear26. The ring gear26is the output member for the planetary gear set24. Thus, the power transfer arrangement19provides power flow paths from each of the generator16and the engine14through the planetary gear set24, through the idler gear52and the mounted gear50, and through the differential46to the vehicle drive wheels42,44.

The power transfer arrangement19also provides a power flow path from the motor18to the vehicle drive wheels42,44through the following elements. The motor18includes an output shaft56attached to a third mounted gear58. The third mounted gear intermeshes with a second idler gear60, which itself intermeshes with the gear54attached to the ring gear26of the planetary gear set24.

The vehicle10and its powertrain12provide advantages over conventional power-split arrangements, in that the gear ratios for any of the torque-producing members can be modified by changing one or more of the mounted gears36,50,58; one or more of the intermediate gears30,54; one or more of the idler gears52,60; or some combination of the above. None of these gear changes, however, requires a change of the primary elements of the planetary gear set24. This provides a relatively easy and cost effective way to effect gear ratio changes, for example, when a power-split configuration is adapted to a new vehicle platform.

As discussed above, the engine axis38and the generator axis40are offset from each other to reduce the overall length of the powertrain12. Similarly, the motor output shaft56defines a third axis62, and the differential shaft48defines a fourth axis64, which are also not coincident with each other. This allows the motor18and the differential46to be offset from each other, and again, may help to reduce the overall length of the powertrain12.

FIG. 2shows a vehicle10′ having a powertrain12′ in accordance with another embodiment of the present invention. Throughout the description of the vehicle10′, and the powertrain12′, elements having counterparts in the vehicle10shown inFIG. 1, are marked with the prime (′) symbol. Similar to powertrain12, the powertrain12′ includes an engine14′ having an output shaft20′ directly connected to a carrier22′ of a planetary gear set24′. The generator16′ includes an output shaft34′ defining an axis40′. The axis40′ is not coincident with axis38′ defined by the engine output shaft20′. Thus, like the embodiment shown inFIG. 1, the vehicle10′ provides the advantage of a reduced overall length for the powertrain12′ by offsetting the generator16′ from the engine14′. Unlike the powertrain12shown inFIG. 1, the powertrain12′ includes a second motor18′ that is directly in-line with the engine14′. The vehicle10′ provides an example of using a small second motor18′ to reduce the size and weight of the vehicle10′. Because the motor18′ is relatively small, it can be placed in-line with the engine14′ without undesirably increasing the length of the powertrain12′.

As shown inFIG. 2, the shaft30′, which provides an input to the sun gear28′, traverses an opening65in the motor18′ to allow the generator16′ to be connected to the sun gear28′ with the motor18′ disposed therebetween. Because it is contemplated that the motor18′ will be a smaller electric machine, it may be desirable to increase the torque output from the motor18′ to the vehicle wheels42′,44′. In the embodiment shown inFIG. 2, this is accomplished through the use of a planetary gear reduction arrangement66.

The planetary gear reduction arrangement66includes a plurality of pinions68that are connected to each other by a carrier70. The carrier70is grounded, which allows the pinions68to rotate about their own axes without orbiting around the motor18′. This arrangement provides for an increase in torque from the motor18′ to the ring gear26′, and ultimately, to the vehicle drive wheels42′,44′. Also shown inFIG. 2, the generator axis40′ and the differential axis48′ are coincident with each other, but can easily be made offset from each other to further help reduce the overall length of the powertrain12′. Similar to the embodiment shown inFIG. 1, the gear ratios for the torque producing elements—i.e., the engine14′, the generator16′, and the motor18′—can all be changed without changing the primary elements of the planetary gear set24′.