Description

DRIVE ASSEMBLY

Technical Field

The present disclosure is directed to a drive assembly and, more particularly, to a drive assembly having an internal braking system.

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, a planetary gear arrangement connected between the input and the output shafts, and a brake assembly provided to slow the rotation of the output shaft. 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. The brake assembly includes one or more brake disks that interconnect with the sun gear of the planetary unit. An actuator piston is located on one side of the brake disks, and a reaction plate is located on an opposing side. The actuator piston and

reaction plate are typically annular disk-like structures having an outer diameter substantially equal to the outer diameter of the brake disks. Pressurized fluid directs the actuator piston against the first disk which in turn presses against the second disk, and subsequently, against the reaction plate. In this manner, the actuator piston may generate friction against both the first and second disks, thereby slowing rotation of the sun gear.

In configurations of the above type, activation of the brake generates a substantial amount of heat. During operation, it is possible for the disks to become overheated and to warp, with excessive heat shortening the life of the brake disks. Some heat is dissipated from the disks through the actuator piston, reaction plate, and separator plate components. However the size of these components may limit the amount of heat that can be absorbed and dissipated. In addition, as the brake disks wear, debris can be generated within the central housing. Without space for the debris to accumulate, the debris may remain in contact with the brake disks, thereby causing drag on rotation of the axle, debris contamination of the friction surfaces, and accelerated wear on the axle components.

In some configurations, design modifications are made to the brake disks and assembly to provide continuous cooling and clearance of accumulated debris. An example of a differential axle assembly using a system of cooling channels is described in U.S. Patent No. 6,345,712 Bl (the '712 patent) issued to Dewald et al. on 12 February 2002. In the '712 patent, grooves are formed in the friction disks to cause lubricating oil to be thrown outward through the plates and enter oil cooling channels. The lubricating oil absorbs heat as it flows over the brake, and the heat is dissipated to the differential housing as it flows through the channels. Additionally, the force of flow provides a washing action to eliminate the possibility of debris becoming entrapped in the brake piston bore and seal area.

Although the cooling channels described in the '712 patent may be adequate for some situations, they may not provide adequate cooling efficiency. The small space at the periphery of the brakes may not accommodate enough cooling oil, resulting in undercooled brake disks. Furthermore, the method disclosed by the '712 patent may lead to non-uniform heat transfer resulting in distortions in the brake disks, especially under extreme operating conditions.

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 with an internal braking system. The drive assembly may include a center housing, a drive component located within the center housing, and at least one brake disk having a predetermined diameter and secured to the drive component to rotate with the drive component. The drive assembly may also include an element with a diameter greater than the predetermined diameter, and configured to frictionally engage the at least one brake disk and absorb heat generated by the frictional engagement.

Another aspect of the present disclosure is directed to a method of enhancing cooling of components of a braking system of a drive assembly, the braking system including at least one brake disk, and an actuator piston and a reaction plate on opposite sides of the at least one brake disk, at least one of the actuator piston and reaction plate having a larger diameter and greater mass than the at least one brake disk. The method may include operating the drive assembly, and actuating the braking assembly by engaging the actuator piston against the at least one brake disk, thereby generating heat. The method may also include dissipating the generated heat from the at least one brake disk into the larger diameter and greater mass of the actuator piston or reaction plate.

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Brief Description of the Drawings

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

Figure 2 is a cross-sectional illustration of the drive assembly of Fig. 1 ; and

Figure 3 is an enlarged cross-sectional illustration of an exemplary internal braking system 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 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.

Referring to both Figs. 2 and 3, drive assembly 10 may be equipped with an internal braking system 48 (i.e., braking system 48 may be at least partially enclosed by center housing 26 and leg housing 34) configured to resist the rotation of sun gear 42. Braking system 48 may include an actuator piston 50, at least one brake disk 52, and a reaction plate 54. Brake disks 52 may be connected to rotate with sun gear 42 such that, when actuator piston 50 is acted on by pressurized fluid, the actuator piston 50 and reaction plate 54 may frictionally engage the at least one brake disk 52, thereby slowing the rotation of sun gear 42. In this configuration, a pressure of the fluid acting on actuator piston 50 may relate to a magnitude of the force resisting motion of sun gear 42. If multiple brake disks 52 are included within braking system 48, a separator plate 56 may be disposed between brake disks 52. A return spring 58 may be disposed to separate actuator piston 50 from reaction plate 54 and cause a release of brake disks 52.

As illustrated in Fig. 3, the actuator piston 50, separator plate 56, and/or reaction plate 54 may have annular disk-like structures with an increased outer diameter, as compared to the outer diameter of the brake disks 52. For an actuator piston 50 and/or reaction plate 54 the outer diameter may be as much as 28 mm larger than an outer diameter of the brake disk 52. When actuating the braking assembly, the associated material mass increase of the actuator piston 50, separator plate 56, and/or reaction plate 54 can act as a heat sink with an increased capacity to absorb heat from the brake disks 52.

As further illustrated in Fig. 3, by increasing the size of the actuator piston 50, separator plate 56, and/or reaction plate 54, a space 60 located radially outwardly of the at least one brake disks 52 and enclosed within the center housing 26 may be available. This enclosed space 60 may be configured to accept debris generated by braking.

Industrial Applicability

The drive assembly of the present disclosure may be applicable to any drivetrain having an internal braking system requiring cooling of the brake assembly. The disclosed drive assembly may enhance brake cooling capacity by increasing the material mass of the actuator piston, reaction plate, and/or separator plate components relative to the brake disk. Debris carrying capacity may be enhanced by increased space provided by the increased diameter of one or more of the actuator piston, reaction plate, or separator plate. The enhanced cooling and debris carrying capacity may improve operation efficiency. Referring to the exemplary embodiment illustrated in Fig. 3, when engaging the brake assembly 48, pressurized fluid may act upon the braking assembly by urging the actuator piston 50 against at least one brake disk 52. The first of the brake disks 52 may press against the separator plate 56, which may in turn press against the second brake disk 52, which may press against the reaction plate 54. In this manner, brake disks 52 may generate heat through frictional engagement. Heat may be dissipated from the brake disks 52 into the larger diameter and greater mass of the adjacent actuator piston 50, reaction plate 54, and separator plate 56 components. Furthermore, the larger outer diameter of the actuator piston 50, reaction plate 54, and separator plate 56 in relation to the brake disks 52, may create a space located radially outwardly of the brake disks 52. This space may be configured to accept debris generated by braking.

The relative size of the actuator piston 50, reaction plate 54, and separator plate 56 components, may enhance the capacity for the components to absorb heat from the adjacent brake disks 52. By increasing the material mass of

the actuator piston 50, reaction plate 54, and/or separator plate 56, the components may act as a heat sink allowing for uniform heat transfer from the smaller diameter brake disks 52.

Furthermore, by increasing the size of the actuator piston 50, reaction plate 54, and separator plate 56, an enclosed space 60 may be available on the periphery of the brakes. This enclosed space 60 may collect debris generated by the wear and tear of the brake components. In addition, this enclosed space 60 may accommodate a larger volume of coolant oil, thereby increasing the cooling capacity of the brake system 48. It will be understood that the number of brake disks and/or separator plates may vary, depending, for example, on the machine braking capacity. For example, brake system 48 may include a single brake disk 52 between actuator piston 50 and reaction plate 54. As another example, while two brake disks 52 and a single separator plate 56 are illustrated in the exemplary embodiment of Fig. 3, there may be three or more brake disks 52 and two or more separator plates 56. The volume of space 60 for accommodating debris accumulation may vary, depending, for example, on the number of brake disks and/or separator plates, and depending on the predetermined diameter of the brake disk(s) relative to actuator piston 50, reaction plate 54, and/or separator plate 56.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed drive assembly 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 embodiments 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.