WO2009032135A1

WO2009032135A1 - Drive assembly having failure containment feature

Info

Publication number: WO2009032135A1
Application number: PCT/US2008/010163
Authority: WO
Inventors: Richard J. Gibes; Josh Nolke; John D. Gates
Original assignee: Caterpillar Inc.
Priority date: 2007-08-31
Filing date: 2008-08-27
Publication date: 2009-03-12
Also published as: CN101790654B; RU2010112433A; CN101790654A; RU2467230C2

Abstract

A drive assembly (10) for use with a mobile vehicle is disclosed. The drive assembly comprises a housing (34) and a first drive component (46) located within the housing. The drive assembly has a fastener (50) located to constrain the first drive component, and a second drive component (66) configured to contain the fastener in the event of fastener failure.

Description

DRIVE ASSEMBLY HAVING FAILURE CONTAINMENT GEOMETRY

Technical Field

The present disclosure is directed to a drive assembly and, more particularly, to a drive assembly having failure containment geometry.

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 some configurations, one or more of the sun gear, planet carrier, and ring gear is held stationary or connected to a housing or shaft by a fastener such as a bolt, a snap ring, a dowel pin, or another fastener that extends from the housing or shaft through or near the respective gear. In this manner, the fastener can prevent relative axial and/or rotational movement of the gear. An example of this type of axle arrangement is described in US Patent No. 4,883,373 (the '373 patent) issued to Rieke on 28 November 1989. Specifically, the '373 patent describes a planet carrier being mounted to an axle shaft by a snap ring that engages a shallow circumferential groove defined on an end of the shaft. The planet carrier is thus trapped by the snap ring to constrain axial movement of the carrier.

Although the axle configuration described in the '373 patent may be adequate for some situations, it may also be problematic. Specifically, it may be possible for the snap ring to be assembled incorrectly, to disengage the circumferential groove during operation, and/or to break apart (i.e., fail) during operation. In any of these circumstances, the snap ring may be allowed to move throughout the axle housing and interfere with other rotating components. This interference could cause costly damage to the components and/or interruption of machine operation.

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 housing and a first drive component located within the housing. The drive assembly may also include a fastener located to constrain the first drive component, and a second drive component configured to contain the fastener in the event of fastener failure. Another aspect of the present disclosure is directed to another drive assembly. This drive assembly may include a housing, and a first drive component located within the housing. The drive assembly may also include a fastener located to constrain the first drive component, and a second drive component configured to provide a visual indication of improper fastener assembly. 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 -A-

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. 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.

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. Referring to both Figs. 2 and 3, drive assembly 10 may be equipped with an internal braking system 60 (i.e., braking system 60 may be at least partially enclosed by center housing 26 and leg housing 34) configured to resist the rotation of output shafts 20, 22. Braking system 60 may include an actuator 62, one or more brake disks 64, and a reaction plate 66. Brake disks 64 may be connected to rotate with output shafts 20, 22 such that, when actuator 62 is acted on by pressurized fluid, brake disks 64 may be sandwiched between actuator 62 and reaction plate 66 creating friction that resists the rotation of output shafts 20, 22. In this configuration, a pressure of the fluid acting on actuator 62 may relate to a magnitude of the force resisting motion of output shafts 20, 22. If multiple brake disks 64 are included within braking system 60, a separation plate 68 may be disposed between brake disks 64. A return spring 70 may be disposed to separate actuator 62 from reaction plate 66 and cause a release of brake disks 64. As illustrated in Fig. 3, reaction plate 66 may be assembled to engage and press against an end face of ring gear 46. Reaction plate 66 may be an annular member having a generally L-shaped cross section, with one protrusion of the L-shape engaging ring gear 46, and the other protrusion mating with, but not engaging, end face 35 of leg housing 34 (i.e., a space having an axial distance less than a width of snap ring 50 may be maintained between reaction plate 66 and end face 35) . In this arrangement, a substantially enclosed space 72 may be formed by reaction plate 66, leg housing 34, and ring gear 46.

During manufacture of drive assembly 10, the engagement of center housing 26 with leg housing 34 may provide a visual indication as to the successful placement of snap ring 50 into groove 52. That is, if snap ring 50 is not fully seated within groove 52, reaction plate 66 may bottom out on snap ring 50, instead of ring gear 46, thereby preventing center housing 26 from fully engaging leg housing 34. As a result of improper snap ring assembly, a space may be observed between end face 32 of center housing 26 and end face 35 of leg housing 34. This space may provide the visual indication that snap ring 50 has been improperly installed into leg housing 34 or has exited groove 52 after assembly. If this space is observed, an assembly technician may be trained to remove reaction plate 66 and inspect snap ring 50.

Space 72 may provide for failure containment. That is, it may be possible for snap ring 50 to fail (i.e., break apart and/or exit groove 52) during operation. If allowed to move through center housing 26 and/or leg housing 34, the fragments of snap ring 50 could interfere with other moving components of drive assembly 10, thereby causing additional malfunctions, failures, and/or power transfer interruptions. However, because of the mating of reaction plate 66 with leg housing 34 and engagement with ring gear 46, snap ring 50 may be contained within space 72. Within space 72, the fragments of snap ring 50 may cause only minimal damage, if any.

Industrial Applicability The drive assembly of the present disclosure may be applicable to any drivetrain having components constrained by fasteners that could fail during operation. The disclosed drive assembly may minimize subsequent damage caused by the failed fasteners by containing the failed fasteners within a space away from sensitive rotating components. In addition, the disclosed drive assembly may provide visual indications of the proper assembly thereof.

Because of the geometry of drive assembly 10 (i.e., reaction plate 66, ring gear 46, and leg housing 34), it may be ensured that ring gear 46 and snap ring 50 are properly installed. That is, a space observed between end face 32 of center housing 26 and end face 35 of leg housing 34 may provide a visual indication of proper assembly. If no space exists, it can be concluded that snap ring 50 is fully seated within groove 52. If a space does exist, the assembly of snap ring 50 must be inspected and corrected.

The relation between reaction plate 66, ring gear 46, and leg housing 34 may also provide failure containment benefits. Specifically, if snap ring 50 were to fail, enclosed space 72 may contain the fragments of snap ring 50 until service can be performed. By containing the fragments of snap ring 50, minimal damage to the remaining components of drive assembly 10 may be possible.

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.

Claims

1. A drive assembly (10), comprising: a housing (34); a first drive component (46) located within the housing; a fastener (50) located to constrain the first drive component; and a second drive component (66) configured to contain the fastener in the event of fastener failure.

2. The drive assembly of claim 1 , wherein the second drive component mates with the housing and engages the first drive component to create a substantially enclosed space (72).

3. The drive assembly of claim 1, wherein the second drive component is an annular ring having a generally L-shaped cross section.

4. The drive assembly of claim 1, wherein the second drive component is a braking reaction plate.

5. The drive assembly of claim 1, wherein the fastener is a snap ring.

6. The drive assembly of claim 1, wherein the first drive component is a ring gear.

7. The drive assembly of claim 1, wherein the second drive component is prevented from engaging the first drive component when the fastener is improperly installed.

8. The drive assembly of claim 1, wherein the fastener locks the first drive component to the housing.

9. A drivetrain (10, 12, 18, 24, 26, 28), comprising: a differential (12) having a center housing (26), a differential gear arrangement (28), and an input shaft (18) extending into the center housing to drivingly engage the differential gear arrangement; a traction device (24); and the drive assembly (10) as in any one of claims 1-8 connected between the differential and the traction device to drive the traction device.

10. The drivetrain of claim 9, wherein the first drive component is rotationally locked to the housing.