Description

DRIVE ASSEMBLY HAVING RECESSED RING GEAR

Technical Field

The present disclosure is directed to a drive assembly and, more particularly, to a drive assembly having a ring gear recessed within a housing.

Background

Machines, including on and off-highway haul and vocational trucks, wheel loaders, 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 drive assemblies (one 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 drive assemblies to the traction devices. The final drive assemblies function to reduce a rotational speed of the differential output to a level appropriate to drive the associated traction devices and thereby propel the machine.

Each final drive assembly 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 the 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 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 configurations, the ring gear is held stationary by fasteners that extend from a center housing through the ring gear and into a leg housing that encloses the output shaft, the ring gear forming a portion of the axle enclosure. In this manner, the fasteners not only prevent rotation of the ring gear, but also connect

and help to fluidly seal the center housing to the leg housing. An example of this type of axle arrangement is described in US Patent No. 6,866,605 (the '605 patent) issued to Fabry on 15 March 2005.

Although the axle configuration described in the '605 patent may be adequate for some situations, it may also be problematic. Specifically, the tolerance stack up between the center housing, ring gear, and leg housing may make alignment between the ring gear and planet gears difficult to achieve. As a result, the components must be manufactured to tight tolerances that increase component cost. And, the configuration of the '605 patent may introduce an additional leak path for lubricant to exit the assembly (i.e., oil may exit the axle enclosure between the leg housing and the ring gear, as well as between the ring gear and the center housing).

The drive assembly of the present disclosure solves one or more of the problems set forth above.

Summary

One aspect of the present disclosure is directed to a drive assembly. The drive assembly may include a center housing and a leg housing configured to mate and seal against the center housing. The leg housing may include a recess and a groove located within a wall of the recess. The drive assembly may also include a gear member disposed within the recess of the leg housing, and a ring member located within the groove of the leg housing to retain the gear member within the recess.

Another aspect of the present disclosure is directed to a method of assembling a drivetrain. The method may include pressing a ring gear into a first housing, and axially blocking the ring gear from exiting the housing. The method may also include connecting a second housing to the first housing to completely enclose the ring gear.

Brief Description of the Drawings

Fig. 1 is a pictorial illustration of an exemplary disclosed drive assembly;

Fig. 2 is a cross-sectional illustration of the drive assembly of Fig. l; and

Fig. 3 is an enlarged cross-sectional illustration of an exemplary ring gear connection in the drive assembly of Fig. 1.

Detailed Description

Fig. 1 illustrates an exemplary disclosed drive assembly 10. Drive assembly 10 may be associated with a mobile vehicle (not shown) so as to propel the vehicle. As such, drive assembly 10 may include a differential assembly 12 and first and second final drive assemblies 14, 16. An input member such as a driveshaft 18 may drivingly connect a power source (i.e., an engine and transmission, both of which are not shown) of the vehicle to differential assembly 12. Two output members such as a first output shaft 20 and a second output shaft 22 may drivingly connect final drive assemblies 14, 16 to traction devices 24 located on opposing sides of the vehicle. In one embodiment, traction devices 24 may embody wheels. Final drive assemblies 14, 16, may be drivingly coupled to differential assembly 12 such that a rotation of driveshaft 18 results in a corresponding rotation of output shafts 20, 22 and traction devices 24.

As illustrated in Fig. 2, differential assembly 12 may include a center housing 26 and a differential gear arrangement 28 supported within center housing 26. Center housing 26 may be a generally cylindrical housing having an axial direction substantially aligned with output shafts 20, 22. One or more bearings 30 may be located within center housing 26 to support the rotation of output shafts 20, 22. Driveshaft 18 may extend through a side of center housing 26 to engage and rotationally drive differential gear arrangement 28. In turn, differential gear arrangement 28 may operatively engage and transfer the input

rotation of driveshaft 18 to output shafts 20, 22. At each opposing end of center housing 26, an end face 32 may be located to engage and seal against a leg housing 34 of final drive assemblies 14, 16. Specifically, end face 32 of center housing 26 may mate against an end face 35 of each leg housing 34. Leg housing 34 of each final drive assembly 14, 16 may enclose and support a planetary gear arrangement 36 and an associated one of output shafts 20, 22. One or more bearings 38 may be located to support the rotation of output shafts 20, 22 within leg housing 34. Output shafts 20, 22 may be driven by differential gear arrangement 28 and speed reduced by planetary gear arrangement 36. Leg housing 34 may be connected to center housing 26 by way of, for example, threaded fasteners 40 located around an outer periphery thereof. 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 may mesh with the sun gear and the ring gear, and with intermediate planet gears of the same planet carrier if intermediate planet gears are included in the planetary gear arrangement. The sun gear, planet carrier, planet gears, and ring gear may all rotate together simultaneously. Alternatively, one or more of the sun gear, planet carrier, and ring gear may be held stationary to alter a reduction ratio of the arrangement. Each planetary gear arrangement may receive one or more input rotations and generate one or more corresponding output rotations. The change in rotational speed between the inputs and the outputs may depend upon the number of teeth in the sun gear and the ring gear. The change in rotational speed may also depend upon the gear(s) that is used to receive the input rotation, the gear(s) that is selected to provide the output rotation, and which gear, if any, is held stationary.

In the exemplary embodiment of Fig. 2, planetary gear arrangement 36 may include a sun gear 42, a planet carrier 44, and a ring gear 46. Each sun gear 42 may be drivingly connected to rotate with differential gear

arrangement 28. Each ring gear 46 may be fixed stationary within leg housing 34. A plurality of planet gears 44a may be connected to rotate with planet carrier 44 and to mesh with sun gear 42 and ring gear 46. Each planet carrier 44 may be connected to rotate one of output shafts 20, 22. Thus, the motion and power of driveshaft 18 may be transmitted through differential gear arrangement 28 to output shafts 20, 22 via sun gear 42, planet gears 44a, and planet carrier 44, with fixed ring gear 46 only affecting the reduction ratio of the motion.

As illustrated in Fig. 3, ring gear 46 may be located within a recess 48 of leg housing 34. In one embodiment, ring gear 46 may be press fitted into recess 48 until a shoulder 48a of recess 48 is engaged by an end face of ring gear 46. A snap ring 50 may then be inserted into a groove 52 located in an internal wall of recess 48 to axially constrain ring gear 46 within recess 48. That is, ring gear 46 may be free to move axially between shoulder 48a and snap ring 50. A fastener such as, for example, a dowel pin 54 may be located within a partial slot 56 of ring gear 46 and a partial slot 58 of recess 48, thereby rotationally locking ring gear 46 to leg housing 34.

Industrial Applicability

The drive assembly of the present disclosure may be applicable to any drivetrain having a planetary gear assembly where a component of the assembly must be axially constrained. The disclosed drive assembly may minimize machining tolerance requirements and the likelihood of leakage, while providing an improved method of assembly. Machine tolerances may be relaxed and the likelihood of leakage minimized by recessing a ring gear within an associated housing, and axially blocking the ring gear from exiting the housing. Construction of the drive assembly will now be explained.

During manufacture of drive assembly 10, ring gear 46 may be inserted (e.g. press fitted) into recess 48. After ring gear 46 is fully seated against shoulder 48a (or at least moved axially past groove 52), snap ring 50 may be inserted into groove 52, thereby limiting the axial motion of ring gear 46 out of

recess 48. Leg housing 34 may then be joined to center housing 26, thereby fully enclosing ring gear 46. A sealing element such as, for example, a gasket (not shown) may be inserted between end faces 32 and 35 of center and leg housings 26, 34, if desired, to improve fluid sealing at that interface. Because ring gear 46 may be fully retained within leg housing 34 by geometry of leg housing 34 (shoulder 48a and groove 52 of recess 48), the manufacturing tolerances of drive assembly 10 may be reduced. That is, only leg housing 34, and more specifically, the geometry of recess 48 must be tightly controlled to ensure proper positioning of ring gear 46. By including the tightly controlled tolerances within a single component, the likelihood of improper positioning may be minimized and the cost of the assembly may be reduced. In addition, by recessing ring gear 46 within leg housing 34, fewer leak points may be available.

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. 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.