The present disclosure is directed to a drive assembly and, more particularly, to a drive assembly having a compound planetary arrangement.
Machines, including on and off-highway haul and vocational trucks, wheel loaders, skid-steers, motor graders, and other types of heavy equipment generally include a mechanical transmission drivingly coupled to opposing traction devices by way of a differential and two substantially identical final drives (e.g., one final drive located between the differential and each traction device). The differential receives a power input from the transmission and produces two power outputs directed through the final drives to the traction devices. The final drives function to reduce an output rotational speed of the differential to a level appropriate to drive the associated traction devices and thereby propel the machine.
Each final drive generally includes an input shaft driven by the differential, an output shaft connected to the associated traction device, and a planetary gear arrangement connected between the input and output shafts. The planetary gear arrangement generally includes a sun gear fixed to rotate with the input shaft, a planet gear arrangement having a plurality of planet gears that are driven by the sun gear and a corresponding planet carrier fixed to rotate with the output shaft, and a stationary ring gear that also engages the planet gears. In most conventional configurations, three or four planet gears are used inside each planetary gear arrangement to transfer torque from the sun gear to the planet carrier. Although the conventional configuration may be suitable for some applications, it may be inadequate for other applications. In particular, in high-reduction applications, it can be difficult to package a 3- or 4-planet arrangement inside an associated housing due to the large sizes required of each planet gear.
One attempt to provide a compact high-reduction final drive is disclosed in JP Patent No. 5696450B2 (the '450 patent) of Nissan Motor Company that issued on Apr. 8, 2015. In particular, the '450 patent discloses a final drive having a planetary gear arrangement. The planetary gear arrangement includes a sun gear; four stepped planet gears each having a smaller gear portion engaged with the sun gear, and a larger gear portion placed axially adjacent the smaller gear portion; a planet carrier having a plurality of shafts, each shaft being configured to rotatably support one of the planet gears; a stationary ring gear engaged with the larger gear portions of the planet gears; and a wheel hub driven by the planet carrier and configured to rotationally support the sun gear and the ring gear.
Although the four-planet gear configuration described in the '450 patent may provide a high-reduction arrangement that could be adequate for some situations, it may also be problematic. Specifically, the four planet gears are supported on the planet carrier shafts via needle bearings. Because of uneven torque loading common in stepped planet gears, the needle bearings may tend to bind at their opposing ends. In addition, the needles within the bearings may be size-limited due to their location and, accordingly, have limited bearing capacity.
The drive assembly of the present disclosure is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.
One aspect of the present disclosure is directed to a final drive. The final drive may include a sun gear, a ring gear, and a plurality of planet gears. Each of the plurality of planet gears may have a large diameter portion configured to engage external teeth of the sun gear, and a small diameter portion configured to engage internal teeth of the ring gear. The final drive may also include a planet carrier operatively connected to each of the plurality of planet gears, and a plurality of bearings. The plurality of bearings may be disposed within the planet carrier and configured to support opposing ends of the plurality of planet gears.
Another aspect of the present disclosure is directed to another final drive. This final drive may include a sun gear, a ring gear, and at least four planet gears. The at least four planet gears may each have a large diameter portion configured to engage external teeth of the sun gear, and a small diameter portion configured to engage internal teeth of the ring gear. The final drive may also include a planet carrier operatively connected to each of the at least four planet gears. The planet carrier may have a base, a hub, and at least one fastener configured to connect the hub to the base. The final drive may further include a plurality of bearings disposed within the base and the hub of the planet carrier and configured to support the at least four planet gears.
In yet another aspect, the present disclosure is directed to a drive assembly. The drive assembly may include a differential having an input member, a traction device, an output member operatively connected to the traction device, and a final drive connected between the differential and the output member. The final drive may have a sun gear with a shaft connected to the differential, a stationary ring gear, and at least four planet gears. The at least four planet gears may each have a large diameter portion configured to engage external teeth of the sun gear, and a small diameter portion configured to engage internal teeth of the stationary ring gear. The final drive may also include a planet carrier operatively connected to each of the at least four planet gears. The planet carrier may have a base, a hub operatively connected to the output member, and at least one fastener configured to connect the hub to the base. The final drive may further include a plurality of cylindrical bearings disposed within the base and the hub of the planet carrier and configured to support opposing ends of the at least four planet gears. The sun gear, the at least four planet gears, the ring gear, and the plurality of bearings may be located axially between the base and the hub of the planet carrier.
For the purposes of this disclosure, a planetary gear arrangement may have at least three elements, including a sun gear, a planet carrier having at least one set of connected planet gears, and a ring gear. The planet gears of the planet carrier mesh with the sun gear and the ring gear. The sun gear, planet carrier, and planet gears all rotate simultaneously (although not necessarily at the same speeds and/or in the same directions), while the ring gear is held stationary. Each planetary gear arrangement receives one input rotation via the sun gear, and generates one corresponding output rotation via the planet carrier. The change in rotational speed between the input and the output rotations depends on the number of teeth in the sun gear, the planet gears, and the ring gear.
In the exemplary embodiment of
As further illustrated in
Each of base 26a and hub 26b may include four bearing bores 50, which are each configured to receive a corresponding cylindrical bearing 52. Each bearing bore 50 (and bearing 52, after assembly) in base 26a may be axially aligned with a paired bearing bore 50 (and bearing 52, after assembly) in hub 26b. Each pair of aligned bearings 52 may be configured to receive a corresponding planet gear 28 therebetween. For example, a shaft 54 may extend from opposing axial ends of each planet gear 28 and be received by a corresponding pair of bearings 52, such that steps 28a and 28b of each planet gear 28 are sandwiched between and rotationally supported by bearings 52. Accordingly, planet gears 28 may be held inside of planet carrier 26 by way of shafts 54, bearings 52, and bearing bores 50.
Clearance openings 58 may be formed within base 26a of planet carrier 26 to accommodate sun gear 24 and planet gears 28. For example, a single centralized clearance opening 56 may be provided for sun gear 24, and four clearance openings 58 may be provided for the four planet gears 28 around clearance opening 56. Clearance opening 56 in base 26a may be stepped, having a larger diameter adjacent where sun gear 24 resides after assembly and a smaller diameter located axially closer to hub 26b. The smaller diameter of clearance opening 56 may be configured to internally receive a hollow cylindrical protrusion 60 of hub 26b, which functions as a splined-connector for output member 18 (referring to
Sun gear 24, planet carrier 26, planet gears 28, ring gear 30, and bearings 52 may all be sub-assembled prior to insertion within housing 32. The sub-assembly may be supported within housing 32 only by way of interface 34 between ring gear 30 and housing 32. During assembly, ring gear 30 may be axially located and/or retained in place relative to the remaining components by way of base 26a and hub 26b. That is, base 26a and hub 26b may form axial movement boundaries at opposing sides of ring gear 30. After connection to differential 12 and output member 18 (referring to
The drive assembly of the present disclosure may be applicable to any drivetrain having a planetary gear assembly where a high-reduction of speed is required within the confines of a small space. The high-reduction of speed may be provided within a small space by using four planet gears, each having a stepped profile. In the disclosed embodiment, the speed reduction is about 7:1.
The disclosed drive assembly may also provide increased durability. In particular, by supporting each of the disclosed planet gears at opposing ends (i.e., rather than using needle bearings that are located radially inward on a separate shaft), the support may experience reduced moments. In addition, the location of the bearings at axial ends of the planet gears may allow for large-diameter bearings. The reduced moments, combined with the large diameter bearings, may provide for the increased durability.
It will be apparent to those skilled in the art that various modifications and variations can be made to the drive assembly of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the drivetrain disclosed herein. For example, although ring gear 30 is shown and described as being stationary, it is contemplated that ring gear 30 could be free to rotate in particular applications, if desired. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.