CN107912053B - Direct torque path differential with carrier-less pinion - Google Patents

Abstract

A side pinion (44) for use with a differential (22) of a mobile machine (10) is disclosed. The side pinion may include a body having a flat bottom (74) and a flat top (76) at an end opposite the flat bottom. The side pinion may also have a plurality of gear teeth (78) formed adjacent the flat top portion, and an arcuate outer surface (80) connecting the plurality of gear teeth to the flat bottom portion.

Description

Direct torque path differential with carrier-less pinion

Technical Field

The present disclosure relates generally to differentials, and more particularly, to direct torque path differentials having carrier-less pinions.

Background

Machines such as wheel loaders and haul trucks typically include a drivetrain that powers traction devices of the machine. The drivetrain is made up of at least three different elements, including a power source (e.g., an engine), a transmission driven by the power source, and a differential that distributes power from the transmission between pairs of traction devices. The differential allows pairs of traction devices to be driven at different speeds to accommodate rotation of the machine.

The differential is usually composed of a main pinion, which is driven by the transmission to rotate a crown gear. The carrier housing is fixed for rotation with the crown gear and includes two or more (e.g., four) different carrier pinions located around the circumference of the carrier housing. The carrier pinion is oriented radially inward and is rotatably disposed on a carrier shaft (e.g., a cross having four shaft ends) with its ends connected to the carrier housing. Thus, when the carrier housing rotates about its own axis, the rack pinion also rotates about the same axis. In addition, each carrier pinion rotates about its own axis, which is generally perpendicular to and passes through the axis of the carrier housing. Side gears are mounted at each end of the carrier housing and intermesh with the carrier pinions. The side gears are rotatable about an axis of the carrier housing and are connected to axle shafts extending outwardly from the differential to respective ones of the pair of traction devices. With this arrangement, input rotation provided through the main pinion causes the traction devices to rotate apart at substantially equal torques. When the machine travels straight under good ground conditions, both traction devices are driven at the same speed. During a turn or poor ground conditions, one traction device (e.g., the outer traction device or the slip traction device during a turn) accelerates as the remaining traction devices decelerate.

While acceptable for some applications, conventional differentials may present problems in other applications. In particular, because of the typical carrier pinion configuration, a moment is generated when the teeth of the carrier pinion engage the corresponding teeth of the side gears. This moment tilts the carrier pinion about the carrier shaft end. Such tilting may restrict the flow of lubrication along the spider shaft (i.e., within the bore of the spider pinion) and even, in some cases, cause mechanical engagement between the bore wall of the spider pinion and the spider shaft. Limited lubrication and mechanical engagement can lead to premature wear of the differential.

An attempt to extend the useful life of the differential is disclosed in U.S. patent publication No. 2010/0151983 (' 983 publication) to Ziech et al, published 6, 17, 2010. Specifically, the' 983 publication discloses a differential having a case with a ring gear coupled to an outer surface of the case and intermeshed with a pinion gear. Four grooves are formed in the inner surface of the shell and are directed radially inward toward the cavity in the shell. The grooves are equally spaced around the circumference of the shell. A wear cup is positioned within each recess and a tab of the wear cup is received within a slot of the shell to prevent rotation of the wear cup. The wear cup has a flat base and a sidewall perpendicular to the base. A side pinion is located within each wear cup. Each pinion has a flat heel end that fits within a respective wear cup, a toe end, and a cylindrical wall extending from the heel end to the toe end. The heel end directly contacts the flat base of the cup and the side wall of the cup engages the cylindrical wall of the pinion to drive rotation of the pinion about the axis of the shell. Side gears are also located within the housing and are in meshing engagement with the side pinions. The side gears are hollow and include splines that mesh with corresponding splines of the axle shafts that project from the housing. This design eliminates the need for a support shaft.

Although the differential of the '983 publication may not be affected by the mechanical engagement between the side pinions and the carrier shafts (because the differential of the' 983 publication does not include carrier shafts), the differential may still not be optimal. In particular, the above-mentioned moment that may be generated by the engagement of the side pinions with the side gears may still be present. This moment may cause the heel end of the side pinion to tilt within the cup, thereby enabling mechanical engagement between the cylinder wall of the side pinion and the cup sidewall. In the same manner as described above, this engagement may limit lubrication of the toe end of the pinion and cause premature wear.

The disclosed differentials are directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.

Disclosure of Invention

In one aspect, the present disclosure relates to a side pinion for a differential. The side pinion may include a body having a flat bottom and a flat top at an end opposite the flat bottom. The side pinion may also include a plurality of gear teeth formed adjacent the flat top portion and an arcuate outer surface connecting the plurality of gear teeth to the flat bottom portion.

In another aspect, the present disclosure is directed to a differential. The differential may include an input gear and a carrier fixedly connected to the input gear. The carrier may be configured to rotate with the input gear about a main axis and may have an inner annular surface in which a plurality of cups are formed that are equally spaced about a circumference of the carrier. The differential may also include a first side gear disposed inside the carrier and configured to rotate about the primary axis, a second side gear disposed in the carrier at an end opposite the first side gear and also configured to rotate about the primary axis, and a side pinion disposed in each of the plurality of cups and intermeshed with the first and second side gears. The side pinion may have a plurality of gear teeth projecting radially inward toward the main axis from an associated one of the plurality of cups, and an arcuate outer surface connected to the plurality of gear teeth at an axial transition region. The arcuate outer surface may conform to the inner contour of a plurality of cups.

In another aspect, the present disclosure is directed to a drivetrain for a mobile machine having first and second traction devices on opposite sides. The powertrain may include a power source, a transmission driven by the power source, and a main pinion operatively connected to an output of the transmission. The drivetrain may also include a first half-shaft coupled to the first traction device, a second half-shaft coupled to the second traction device, and a differential driven by the primary pinion to rotate the first and second half-shafts with substantially equal torque. The differential may have an input gear intermeshed with the primary pinion and a carrier fixedly connected to the input gear and configured to rotate with the input gear about the primary shaft. The carrier may have an inner annular surface in which a plurality of cups are formed, equally spaced around the circumference of the carrier. The differential may also have a first side gear disposed within the carrier and having external teeth at an inner end and an outer end connected to the first axle shaft, a second side gear disposed within the carrier and having external teeth at an inner end and an outer end connected to the second axle shaft, and a side pinion gear disposed within each of the plurality of cups and intermeshed with the external teeth of the first and second side gears. The side pinion may have a plurality of gear teeth projecting radially inward toward the main axis from an associated one of the plurality of cups, and an arcuate outer surface connected to the plurality of gear teeth at an axial transition region and conforming to an inner profile of the plurality of cups. The arcuate outer surface of the side pinion may be formed by a polynomial curve rotated three times or more about the axis of the side pinion. When the first and second side gears engage the plurality of gear teeth on opposite sides of the side pinion, a reaction force may be generated, and the polynomial curve is selected such that a gradient of the arcuate outer surface at a point of application of the reaction force may be generally aligned with the reaction force.

Drawings

FIG. 1 is an isometric view of an exemplary disclosed machine;

FIG. 2 is an isometric illustration of an exemplary disclosed drivetrain that may be used with the machine of FIG. 1;

FIG. 3 is a cross-sectional view of an exemplary disclosed differential that may be used with the powertrain of FIG. 2;

FIGS. 4, 5, 6A and 6B are, respectively, plan, isometric, cross-sectional and enlarged views of an exemplary disclosed side pinion that may form a portion of the differential of FIG. 3;

FIGS. 7 and 8 are cross-sectional views through an exemplary lubrication flow path of the differential of FIG. 3;

FIGS. 9 and 10 are cross-sectional and end views, respectively, of another exemplary disclosed differential that may be used with the powertrain of FIG. 2;

FIGS. 11 and 12 are perspective and side cross-sectional views, respectively, of an exemplary disclosed nested carrier that may be used with the differential of FIGS. 8 and 9;

FIG. 13 is a cross-sectional view of another exemplary disclosed differential that may be used with the powertrain of FIG. 2;

FIG. 14 is a side perspective view of another exemplary disclosed nested carrier that may be used with the differential of FIG. 13; and

FIG. 15 is a cross-sectional view of another exemplary disclosed differential that may be used with the powertrain of FIG. 2.

Detailed Description

FIG. 1 illustrates an exemplary mobile machine 10. In the illustrated embodiment, machine 10 is a wheel loader. However, it is contemplated that machine 10 may embody another type of mobile machine such as, for example, an articulated hauler truck, an off-highway mining truck, a motor grader, or another machine known in the art. Machine 10 may include an operator station 12, one or more traction devices 14 located on opposite sides of machine 10 supporting operator station 12, and a transmission 16 operatively connected to propulsion traction devices 14 to respond to received inputs by operator station 12.

As shown in FIG. 2, drivetrain 16 may be an assembly of components that transmits power from a power source (e.g., an engine) 18 to traction devices 14. In the disclosed embodiment, these components include a transmission 20 operatively connected to and driven by power source 18, one or more differentials 22 operatively connected between pairs of opposing traction devices 14, and one or more output shafts 24 connecting transmission 20 to differentials 22. Transmission 20 may be configured to selectively vary the speed-to-torque ratio of the output from power source 18 that is delivered to differential 22. Each differential 22 may be configured to provide substantially equal torque to associated traction devices 14, allowing pairs of traction devices 14 to rotate at different speeds during rotation of machine 10.

FIG. 3 illustrates an exemplary embodiment of differential 22. As can be seen in this figure, differential 22 is configured to receive input from shaft 24 via a primary pinion gear 26 and direct output to traction devices 14 (referring to FIG. 2) via first and second axle shafts 28 and 30. In the disclosed embodiment, differential 22 may have a principal axis 32 along which first axle shaft 28 and second axle shaft 30 are aligned. In this embodiment, the main shaft 32 is oriented substantially perpendicular to the axis 34 of the main pinion 26. However, it is contemplated that in other embodiments, the major axis 32 may be substantially parallel to the axis 34, if desired.

The main pinion 26 may be any type of gear known in the art that may be connected to the end of the shaft 24. The primary pinion 26 is depicted in fig. 3 as a hypoid gear having a frustoconical shape and welded to the end of the shaft 24. The teeth formed in the outer surface of the primary pinion 26 have a helical trajectory, with the axis 34 of the primary pinion 26 not passing through the primary axis 32 of the differential 22. It is contemplated that the main pinion 26 may alternatively be embodied as a spiral bevel gear, a straight bevel gear, a single or double bevel gear, or a spur gear, if desired.

First axle shaft 28 and second axle shaft 30 may each have an inner end configured to connect with differential 22, and an outer end configured to connect, directly or indirectly, with an associated traction device 14. In some embodiments, the outer ends of first axle shaft 28 and second axle shaft 30 are directly connected to an intermediate speed reducer (e.g., final drive — not shown) and then to traction devices 14. Other configurations are also possible. The inner ends of the first axle shaft 28 and the second axle shaft 30 are shown as having external splines for facilitating connection to the differential 22. However, in other embodiments, the first axle shaft 28 and the second axle shaft 30 may additionally or alternatively have bolted flanges, keyways, and/or other connecting means.

Differential 22 may be an assembly of components that cooperate to distribute torque received from primary pinion 26 between first and second axle shafts 28, 30. The components may include, among other things, an input gear 36 configured to mesh with the main pinion 26; a carrier 38 fixedly connected for rotation with input gear 36 about main axis 32; first and second side gears 40 and 42 connected to the first and second axle shafts 28 and 30, respectively; and a plurality of side pinions 44 that rotate with carrier 38 about axis 32 while intermeshing with first side gear 40 and second side gear 42. Rotational power received from shaft 24 may enter carrier 38 through main pinion 26 via input gear 36. The carrier 38 may then transmit rotational power to the first and second axle shafts 28, 30 through the side pinions 44 and the first and second side gears 40, 42, respectively.

The input gear 36, such as the main pinion 26, may also be a hypoid gear having teeth that intermesh with the teeth of the main pinion 26. As shown in fig. 3, the teeth of the input gear 36 are located at an axial end adjacent the carrier 38. However, in other embodiments, the teeth of the input gear 36 may alternatively be located at the opposite axial end or the outer annular edge, if desired. A bore 46 may pass through the input gear 36 to receive the first axle half 28. It is contemplated that input gear 36 may alternatively be embodied as a spiral bevel gear, a straight bevel gear, a single or double bevel gear, or a spur gear.

The carrier 38 may be a hollow and cylindrical housing that also serves as a power transmission component. In particular, the carrier 38 may have a generally closed end 48 and an opposite end 50 that is open to an interior cavity 52. An integral mounting flange 54 may be located at the first end 48, and a plurality of fasteners 56 may be distributed around the outer periphery of the carrier 38 to connect the mounting flange 54 to the input gear 36. The first and second side gears 40, 42 and the side pinion gear 44 may be assembled into the cavity 52 via the second end 50. A cap 58 may be coupled to the second end 50 to enclose these components.

Each of the first end 48 of the carrier 38 and the cap 58 may have a bore 60 formed therein that is configured to receive the first axle shaft 28 and the second axle shaft 30. In some embodiments, seals (not shown) may be installed within the carrier 38 and/or the cover 58 about the first and second axle shafts 28, 30 to prevent debris from entering and lubrication from leaking.

A plurality of cups 62 may be formed within the interior annular wall of the carrier 38 (i.e., within the wall of the annular surrounding cavity 52). In the disclosed embodiment, the carrier 38 includes four cups 62, and each cup 62 is configured to receive a respective side pinion 44. It is contemplated that a greater or lesser number of cups 62 may be formed within the interior annular wall of the carrier 38, if desired. The cups 62 may be co-located at substantially the same axial position and evenly distributed around the inner periphery of the carrier 38. In embodiments having four cups 62, each cup 62 may be angularly spaced from each other by about 90 °. That is, each cup 62 may have a generally circular shape, and the axis 64 of each shape may be orthogonal to the axis 64 of an adjacent shape. In embodiments with a different number of cups 62, the spacing between the axes 64 may be less than or greater than 90 °. For example, when only two cups 62 are included in the carrier 38, the axes 64 of the cups 62 may be angularly spaced apart by about 180 °. In the cross-sectional view of FIG. 3, only three cups 62 are shown, with the respective side pinions 44 removed from the center cup 62 for clarity.

Each of the cups 62 may have a generally flat bottom surface and curved sidewalls intersecting the flat bottom surface. Generally, the shape of the curved sidewall may conform to the outer shape of the side pinions 44 such that forces passing diagonally from the side gears 40, 42 through the side pinions 44 may be transmitted along the normal direction of the curved sidewall. In this manner, torque may not be generated within the side pinions 44 by the force. A gap 66 having a substantially constant thickness of about one-thousandth may be located between the curved sidewall of the cup 62 and the side pinion 44 and filled with lubrication during operation. Apertures 68 may be formed in the flat bottom surface of each cup and, as explained in more detail below, serve as lubrication conduits. The inner diameter of the aperture 68 may be approximately equal to half the inner diameter of the flat bottom surface of the cup 62.

A plurality of additional apertures 70 may be formed in the closed end 48 of the carrier 38. In one embodiment, the number of additional apertures 70 may match the number of side pinions 44 installed in differential 22. In another embodiment, the number of additional apertures 70 may be a multiple (e.g., 2x) of the number of side pinions 44. The apertures 70 should generally be radially aligned with and/or extend to a grid location between each pinion gear 44 and the teeth of the first side gear 40 (e.g., at least aligned with an entry location where the gear teeth begin to mesh). The small holes 70 may facilitate lubrication of the differential 22, as will be explained in more detail below.

The first side gear 40 and the second side gear 42 may be substantially identical bevel gears oriented opposite one another. The external teeth of the two gears 40, 42 may be configured to intermesh with the teeth of all of the side pinions 44 simultaneously (e.g., on opposite sides of the pinions 44), such that when the side pinions 44 rotate with the carrier 38 about the axis 32, the side gears 40, 42 may also be driven to rotate about the same axis 32. The base end of the first side gear 40 may be supported in the bracket 38 in the respective steps, and the base end of the second side gear 42 may be supported in the cap 58 rotatably in the respective steps. Each of the first and second side gears 40, 42 may have a splined bore 72 formed therein that is configured to receive the respective inner ends of the first and second axle shafts 28, 30. With this configuration, rotation of the first and second side gears 40, 42 may result in rotation of the first and second axle shafts 28, 30.

The side pinions 44 may be substantially identical bevel gears. As shown in fig. 4, 5, 6A, and 6B, each side pinion 44 may have a generally flat bottom portion 74, a generally flat top portion 76 positioned opposite the bottom portion 74, a plurality of gear teeth 78 positioned adjacent the top portion 76, and an arcuate outer surface ("surface") 80 connecting the bottom portion 74 and the teeth 78. The surface 80 may be connected to the gear teeth 78 at a transition region 82. The outer diameter at the top portion 76 may be smaller than the outer diameter at the bottom portion 74, and the outer diameter at the transition region 82 may be larger than the outer diameter at the bottom portion 74.

The teeth 78 of the side pinions 44 may have a geometry at least partially defined by a plurality of angles. For example, the first angle α shown in FIG. 5_PMay represent the pressure angle of each tooth 78; second angle α shown in FIG. 6B_FMay represent the face of the tooth 78; the third angle α shown in FIGS. 5 and 6B_CMay represent the taper angle of the teeth 78; and a fourth angle α shown in fig. 6B_RThe root angle of the tooth 78 may be represented. Pressure angle alpha_PMay be defined as the angle between the primary pressure surface of the teeth 78 and the tangent of the pitch circle of the pinion gear 44. Each of the remaining angles may be defined by an arc extending between axis 64 and a corresponding line drawn through the pitch apex (shown in fig. 5 and 6A) of side pinion 44 located on axis 64.

As shown in FIGS. 4, 5, 6A, and 6B, when teeth 78 of pinion gear 44 engage the teeth of side gears 40, 42, a normal force F may be generated on the opposite side of pinion gear 44_N(angle α with pressure-_PPerpendicular forces on the faces of teeth 78). These normal forces FN may combine to produce a resultant force F_R. Resultant force F_RMay lie in a plane between opposite sides of the pinion gear 44 (see fig. 4) and may be inclined relative to the bottom 74 and top 76 (see fig. 6A and 6B). If the resultant force F_RAt an oblique angle relative to the surface gradient across surface 80, when pinion gear 44 is forced by a resultant force F_RPushing into the cup 62, a moment may be created that causes the pinion gear 44 to tilt.

The curvature of surface 80 may be designed such that the resultant force F_RThrough the arcuate outer surface 80 at an angle that is always perpendicular to the surface 80. That is, the arcuate outer surface 80 may be shaped such that the resultant force F_RAt resultant force F_RIs oriented at about 90 deg. to surface 80. In one embodiment, the surface 80 may be at least partially defined by a curve 81 that rotates about the axis 64 of the pinion gear 44. The curve 81 may be a polynomial curve of a higher order (e.g., 3 rd order or higher), for example, defined by the following equation:

wherein:

p represents curve 81;

n represents the order of the curve;

a is a coefficient; and

x is the distance along axis 64.

Resultant force F_RThe angular orientation in space may be defined by an angle β (as shown in FIG. 5) and by a pressure angle α_PAnd a cone angle alpha_CControlled according to the following formula:

tan β＝tan α_P·sin α_C Eq.2

wherein:

beta is the resultant force F_RAngular orientation in space;

α_Prepresenting a pressure angle; and

α_Cpitch or taper angle is indicated.

Using equations 1 and 2 above, curve 81 may be determined by requiring the resultant force F_RAt the point of application of (a), the gradient of the surface 80

With combined force F_RThe cross product between is equal to zero (i.e.,

) Thus obtaining the product.

It is contemplated that in some applications, surface 80 may be divided into a plurality of portions axially adjacent to one another. For example, the surface 80 may be divided into a first portion 80a (see fig. 6A) adjacent the teeth 78 and a second portion 80b located between the first portion 80a and the base 74. In this example, the portion 80b may be larger (e.g., 2-3 times larger) than the portion 80 a. It should be noted that surface 80 may be divided into more than two portions and/or the portions may have different relative dimensions, if desired. Each portion of surface 80 may have a unique curvature defined by a different polynomial (e.g., a polynomial of a different order) and be designed to perform differently under different circumstances. For example, portion 80a may have a lower order polynomial than portion 80b, as portion 80a may experience less loading than portion 80 b. In general, higher power/lower speed applications may utilize surfaces 80 that are generated using more portions and higher order polynomials (e.g., orders 5-6), while lower power/higher speed applications may use fewer portions (e.g., only one portion) and lower order polynomials (e.g., orders 3-4). For purposes of this application, a higher power/lower speed application may be considered an application that delivers about 600 horsepower or more at a speed of less than about 100 rpm.

In one particular exemplary embodiment of the pinion gear 44, the pressure angle α_PMay be about 14-25 °; face angle alpha_FMay be about 35-37 °; cone angle alpha_CMay be about 28-38 °; root angle alpha_RMay be about 23-25. It is expected that these angles may have different values for different applications. For purposes of this disclosure, the term "about" when used in reference to a dimensional value can be defined as within an acceptable range of manufacturing tolerances.

In the specific exemplary embodiments provided above, the radius r₁Can be used to at least partially define the curvature of surface 80 and can have its origin along resultant force F_RIs determined. E.g. radius r₁May be located at coordinates (dx, dy)₁) May be included in the resultant force F_RAnd is located in a vector of (1) and is located in a distance of from F_RIn the same plane. In the disclosed embodiment, r is measured from the axis 64 and the pitch apex of the pinion gear 44₁May be about 40-45mm, and (dx, dy)₁) May be approximately equal to (15-20mm, 90-95 mm). In this configuration, r₁May be located at a distance dy of about 20-25 mm from the bottom 74₂。

The axial ends of the arcuate outer surface 80 may be designed to inhibit stress concentration formation. For example, the lower edge connecting the flat bottom 74 with the arcuate outer surface 80 may be rounded and have a radius r2 of about 1-3 mm. Similarly, transition region 82 connecting surface 80 with tooth 78 may taper inwardly to have a relief angle α of about 2-4 °_B。

Fig. 7 and 8 illustrate the flow of lubricant through differential 22 under two different conditions. Specifically, fig. 7 illustrates the flow of lubrication oil during high speed travel of machine 10, while fig. 8 illustrates the flow of lubrication oil during low speed travel. During any operation of machine 10, differential 22 may be filled with approximately half of the lubricating oil. Specifically, the lubricating oil may fill the lower half of the axle housing (not shown) in which differential 22 is located, and the lubricating oil may reach approximately up to axis 32 of carrier 38.

As shown in fig. 7, during high speed travel, as carrier 38 is driven to rotate at high rpms, the outer surface of carrier 38 may continuously drag through the volume of lubricant in the axle housing. During this rotation, the small holes 68 may be filled with oil, and a layer of oil may adhere to the outer surface of the carrier 38. High speed rotation of carrier 38 may result in high speed rotation of side pinions 44 and corresponding high speed rotation of side gears 40, 42. When the teeth of these gears mesh with one another, they can act as a pump, drawing lubricant radially inward from the small holes 68 when the teeth are disengaged, and pushing lubricant axially outward when the teeth mesh. The lubricating oil can be discharged axially outward through the small hole 70. By this action, a lubricating film can be created between the side pinions 44 and the cups 62 (i.e., within the gaps 66) and between the teeth of the intermeshing gears.

When the travel of machine 10 shifts from high speed travel to low speed travel, the direction of the flow of lubricant through differential 22 may reverse. Specifically, when the carrier 38 is driven to rotate at a low rpms, the teeth of the input gear 36 may act as radially-oriented fluid screws (e.g., due to their pitch and helix angle). That is, the teeth of the input gear 36 may be filled when immersed in the volume of lubricant in the shaft housing, and the pitch angle of the teeth and the rotational motion of the input gear 36 may overcome any centrifugal forces acting on the lubricant and urge the lubricant radially inward toward the small holes 70. The lubricating oil may be pushed through the intermeshing engagement of the side pinions 44 with the side gears 40, 42 and then discharged radially outward through the small holes 68. In such a case, the centrifugal force of the oil discharging radially outward through the small holes 68 may be greater than the pumping force of the intermeshing teeth, which would otherwise pull the oil radially inward. For purposes of this disclosure, high speed travel may be considered travel at speeds in the upper two-thirds of the total speed range.

Fig. 9 and 10 illustrate an alternative differential embodiment, labeled element 84. Like differential 22 of fig. 1-8, differential 84 of fig. 9 may include input gear 36, first side gear 40, second side gear 42, and side pinions 44. However, unlike differential 22, differential 84 may not include carrier 38. Instead, nested carrier 86 may be used to transfer torque from input gear 36 to side pinion gear 44. In this embodiment, nested carrier 86 may be used primarily as a power transmitting component, and additional housing members 88, 90 may be used to enclose the other components of differential 84. The housing members 88, 90 may be substantially identical to one another (e.g., within manufacturing tolerances) and bolted to opposite sides of the input gear 36 via the fasteners 56. A plurality of orifices 92 may be formed in the housing members 88, 90 to serve as conduits for lubrication. Because the housing members 88, 90 may not be power transmitting components, the housing members 88, 90 may have thinner walls and lighter weight when compared to the carrier 38.

As shown in fig. 9, differential 84 may be relatively compact. In particular, because the carrier 86 may be radially nested inside the input gear 36 (i.e., not bolted at an axial end), the overall axial length of the differential 84 may be small. In this configuration, the first side gear 40 may be located at a first axial end of the input gear 36, and the second side gear 42 may be located at a second axial end of the input gear 36 opposite the first axial end. In other words, the first side gear 40 and the second side gear 42 may be located on opposite sides of the input gear 36, rather than on the same side. This may provide greater flexibility in packaging of the drivetrain 16 (see FIG. 2). One or more spacers 94 may be included to axially position nested carrier 86 within input gear 36. Each spacer 94 may be generally annular and positioned between a respective one of the housing members 88, 90 and an end of a respective one of the side gears 40, 42.

For clarity, the housing members 88 and 90, the spacer 94 and the side gears 40 and 42 have been removed from FIG. 10. As shown, the carrier 86 may be connected to the input gear 36 by a splined interface 96. This type of interface may allow the carrier 86 (and other components carried by the carrier 86) to float slightly axially within the input gear 36 during assembly and operation of the differential 84. This axial float capability may lead to manufacturing inconsistencies that may otherwise cause binding between the carrier 86 and the input gear 36.

Fig. 11 illustrates an outside view of nested carrier 86, while fig. 12 illustrates a side cross-sectional view of nested carrier 86 taken along a first axially-oriented plane of symmetry 98. As shown in these figures, nesting bracket 86 may be generally cylindrical and hollow, having two opposing open ends. In addition to being generally symmetrical with respect to plane 98, nested carrier 86 may also be generally symmetrical with respect to a second axially oriented plane 100 and with respect to a radially downward facing plane 102. Nested carrier 86 may have formed therein a plurality of cups 104 (e.g., four cups 104) identical to cups 62 associated with differential 22. Specifically, each cup 104 may include a flat bottom surface 106 and a curved sidewall 108 that intersects the bottom surface 106. In general, the shape of the curved sidewall 108 may conform to the outer shape of the side pinion gear 44 such that the reaction force F from the side gears 40, 42 diagonally across the side pinion gear 44_RMay be transferred to the curved sidewall 108 along the normal direction. An aperture 110 may be formed in the bottom surface 106 of each cup 104 and for lubrication purposes in a manner similar to that explained above with respect to fig. 7 and 8. The outer edges of nested carrier 86 may be rounded or beveled as desired to facilitate assembly into input gear 36.

FIG. 13 illustrates another alternative differential embodiment, labeled as element 112. As with the differentials of fig. 9 and 10, the differential 112 of fig. 13 may include a first side gear 40, a second side gear 42 (omitted from fig. 13 for clarity), and a side pinion gear 44. However, unlike differential 84, differential 112 may include a different input gear 114 and a different nested carrier 116 for transferring rotation from input gear 114 to side pinions 44. Unlike nested carrier 86, nested carrier 116 may not form a complete cylinder. Rather, nesting brackets 116 may be formed from two or more (e.g., four) substantially identical carrier members 116a, the carrier members 116a being annularly spaced from one another. Each carrier member 116a may be located within a pocket 118 formed within the interior of the input gear 114, and spacers 120 may project radially inward to annularly separate adjacent carrier members 116 a. In the disclosed embodiment, the spacer 120 may be integral with the input gear 114. However, in other embodiments, the spacer 120 may be a separate, stand-alone component.

As shown in fig. 14, each carrier member 116a can include external splines 122 configured to engage corresponding splines within pockets 118 (see fig. 13) of the input gear 114 and the single cup 104. Each carrier member 116a can float slightly axially relative to the input gear 114, but still connect to the input gear 114 via splines 122 to receive input torque. By forming nesting brackets 116 through a plurality of individual members 116a, the likelihood of causing misalignment or manufacturing inconsistencies of the bonding of nesting brackets 116 may be further reduced. It is contemplated that splines 122 may be omitted, if desired, and spacer 120 used instead for torque transmission.

FIG. 15 illustrates another alternative differential embodiment, labeled as element 124. Like differential 84 of fig. 9 and 10, differential 124 of fig. 15 may include input gear 36, first side gear 40, second side gear 42, side pinions 44, and housing member 90. However, unlike differential 84, differential 124 may include a different nested carrier 126 for transmitting rotation from input gear 36 to side pinions 44, a lock-up clutch 128 configured to selectively lock rotation of side gear 42 to side gear 40 via nested carrier 126, and a larger (e.g., axially longer) housing member 130 for enclosing nested carrier 126 and lock-up clutch 128.

Unlike nesting bracket 86, nesting bracket 126 may not be axisymmetrical. In particular, nested carrier 126 may extend axially a distance in one direction through pinion gear 44 toward the base end of side gear 42. One or more internal gear teeth (e.g., splines) 132 may be formed at an inner annular surface of the protruding portion of the nesting bracket 126. As will be explained in more detail below, the teeth 132 may be used to selectively connect the nested carrier 126 to the second side gear 42 via the lock-up clutch 128.

The lockup clutch 128 itself may be a subassembly of multiple components arranged to rotate about the axis 32. For example, the lockup clutch 128 may include a disc stack 136 and a hydraulic actuator (not shown) configured to selectively compress the disc stack 136. The disc stack 136 may include a plurality of friction discs, a plurality of separator discs interleaved with the friction discs, and in some cases a damper (not shown) located at one or both ends of the disc stack 136. The friction discs may be connected for rotation with one of the nested carrier 126 (e.g., via the teeth 132) and the second side gear 42 (e.g., via the corresponding external teeth 134), while the separator discs may be connected for rotation with the other of the nested carrier 126 and the second side gear 42. In this manner, when the hydraulic actuator is activated, the friction discs may be sandwiched between the separator discs, thereby creating friction that resists relative rotation between the nested carrier 126 and the second side gear 42. When rotation of the second side gear 42 is limited to rotation of the nested carrier 126, the second side gear 42 may rotate at the same speed as the first side gear 40 regardless of machine rotation or ground conditions. This may help to improve traction in rough ground conditions. Fluid pressure within the hydraulic actuator may be related to the amount of friction that resists relative rotation and is provided via one or more axial ports 138.

The hydraulic actuator may be implemented as a working piston to compress the disc stack 136 under different conditions. The working piston may be annular and form a control chamber with the housing member 130. When the control chamber is filled with pressurized oil through port 138, the hydraulic actuator may be pushed toward disc stack 136, thereby compressing disc stack 136.

In some embodiments, one or more springs (not shown) may be arranged in various configurations to bias the hydraulic actuator away from the disc stack 136. In these configurations, when pressurized fluid is not being supplied into the control chamber, the hydraulic actuator may be deactivated by the spring and moved away from the disc stack 136 to reduce friction generated between the discs and their plates.

Together, the housing member 130 and the housing member 90 may substantially enclose the other rotating components of the differential 124. As with the differential embodiment of fig. 9 and 10, the housing members 90, 130 associated with the differential 124 may be used primarily to house other components, rather than to transmit torque. Therefore, the case members 90, 130 can be relatively thin-walled and lightweight. Similar to the housing member 88, the housing member 130 may additionally serve to axially position the second side gear 42 via the spacer 94.

Industrial applicability

The disclosed differential and side pinions of the present disclosure have potential application in any machine that requires torque transfer to paired traction devices. The disclosed differential and side pinions may have increased life and efficiency. The extended life may be provided by reducing or even eliminating moments in the side pinions that tend to offset the side pinions from the desired positions. The moment can be eliminated by the unique outer curvature of the side pinions. The unique outer curvature of the side pinions may help ensure that the load forces are directed perpendicularly into the corresponding cups formed in the differential. By maintaining the side pinions in their desired positions, lubrication flow may be ensured toward the rotating components of the disclosed differentials, which may extend the life of these components and also reduce rotational friction. The reduced friction may improve the efficiency of the disclosed differential.

Further, because the disclosed side pinions may not require carrier shafts for supporting their rotation, the size, weight, and cost of the disclosed differentials may be low. Furthermore, without a carrier shaft, it may be easier to avoid moment generation and/or to distribute load forces over a larger area. This increased force distribution may reduce the likelihood of metal contact between components, which may further reduce wear of the disclosed differentials. Finally, because the disclosed side pinions may not have a central bore that would normally be required to accommodate a spider shaft, all of the lubrication oil directed into the disclosed differentials at the side pinions may be used to maintain an oil film between the side pinions and the associated cups. Such a load-bearing oil layer may further reduce the likelihood of metal-to-metal contact, which may extend the life of the disclosed differential.

Finally, the disclosed differential may have greater packaging flexibility. In particular, the axially compact design of some of the disclosed differentials may provide more space for other driveline components.

It will be apparent to those skilled in the art that various modifications and variations can be made to the differential and side pinions 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 differential and side pinions 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 (9)

1. A side pinion (44) for a differential (22), comprising:

a body having a flat bottom (74) and a flat top (76) at an end opposite the flat bottom;

a plurality of gear teeth (78) formed near the flat top; and

an arcuate outer surface (80) connecting the plurality of gear teeth to the flat bottom,

wherein the arcuate outer surface is formed by a third order or higher polynomial curve rotated about the side pinion axis (64).

2. The side pinion of claim 1, wherein:

the differential having side gears (40, 42) configured to engage the plurality of gear teeth at opposite sides of the side pinions;

generating a reaction force when the side gear engages the plurality of gear teeth on an opposite side of the side pinion; and

the polynomial curve is selected such that the gradient of the arcuate outer surface at the point of application of the reaction force is substantially aligned with the reaction force.

3. The side pinion of claim 2, wherein:

a pressure angle of the plurality of gear teeth is about 14-25 °;

a root angle of the plurality of gear teeth is about 23-25 °; and

the side pinions have a taper angle of about 28-38 deg..

4. The side pinion of claim 3, wherein the radius of the arcuate outer surface at the point of application of the reaction force is about 40-45 mm.

5. The side pinion of claim 4, wherein an edge radius at a transition of the arcuate outer surface and the flat bottom is about 1-3 mm.

6. The side pinion of claim 5, wherein:

the arcuate outer surface connects the plurality of gear teeth at a transition region (82); and

the transition region tapers inwardly away from the arcuate outer surface at a relief angle of about 2-4 deg..

7. The side pinion of claim 1, wherein the arcuate outer surface includes a plurality of portions (80a, 80b) axially adjacent to one another and each defined by a different polynomial curve.

8. The side pinion of claim 7, wherein a first portion (80a) of the arcuate outer surface adjacent the plurality of gear teeth is defined by a polynomial curve having a lower height than a second portion (80b) of the arcuate outer surface located between the first portion and the bottom.

9. A differential (22) comprising:

an input gear (36);

a carrier (38) fixedly connected to the input gear and configured to rotate with the input gear about a main axis (32), the carrier having an inner annular surface with a plurality of cups (62) formed therein equally spaced about a circumference of the carrier;

a first side gear (40) disposed within the carriage and configured to rotate about the primary axis;

a second side gear (42) disposed in the carrier at an end opposite the first side gear and further configured to rotate about the primary axis; and

side pinion (44) according to any one of claims 1 to 8.

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