Wheel drive transmission unit

Structural arrangements of wheel drive components facilitate the use of robust main roller bearings that are widely spaced apart from one another. This wide spacing minimizes the torque borne by the bearings for a given external load, because at least one bearing is placed closer to the expected load application point (e.g., the center of gravity of the wheel attached to the wheel hub of the drive unit). The present wheel drive bearings can support a heavy external load without expanding the overall size and configuration of a given wheel drive application.

BACKGROUND

1. Technical Field

The present disclosure relates to vehicle power transmission units, and, more particularly, to wheel-mounted gear reduction units.

2. Description of the Related Art

Wheel drives are used to provide gear reduction at or near the point of service, such as at the hub of a driven wheel. Wheel drives may be used for the large driven wheels commonly found on construction equipment and earth moving vehicles, for example, or for auger bits used in drilling post holes in the ground.

Referring toFIG. 1, a known wheel drive10includes a planetary gear system functionally interposed between spindle12and wheel hub14. Spindle12is designed to affix to a vehicle frame (not shown), while wheel hub14is designed to attach to a vehicle wheel via mounting bolts received in bolt holes16. When so configured, the planetary gear system operates to receive power from the vehicle motor via an input shaft, and to increase torque and decrease rotational speed of the driven wheel with respect to the input shaft.

The planetary system includes primary planetary stage70and secondary planetary stage80. Primary stage70includes sun gear20and ring gear38, with planet gears24interposed therebetween and carried on planet gear carrier26via respective planet gear axles28. Primary stage70receives power at input coupler18, which transfers input torque to sun gear20via disconnect shaft22. Secondary stage80receives its input from primary planet gear carrier26of primary stage70via secondary sun gear30, which is rotationally fixed to carrier26. Secondary stage80provides further gear reduction via secondary planet gears32carried on secondary planet gear carrier34via respective secondary planet gear axles36.

Ring gear38is driven by both primary and secondary planet gears24,32, such that the primary and secondary planetary gear stages70and80cooperate to substantially reduce the speed of ring gear38with respect to input coupler18and primary sun gear20. Ring gear38is, in turn, fixed to hub14by bolts40, so the reduced speed and concomitant increase in available torque resulting from the gear reduction is made available to the driven wheel.

Wheel drive10utilizes a pair of roller bearings42,44to facilitate the rotation of hub14over spindle12. As shown inFIG. 1, bearings42,44are both disposed between spindle12, and wheel hub14.

Roller bearings may be heavily loaded components when used in wheel drives such as wheel drive10. For example, when a wheel is mounted to the wheel hub and the drive unit is placed in service, the bearings must bear the weight of the vehicle and absorb the dynamic, chaotic forces associated with vehicle operation. These dynamic forces may be particularly acute in certain applications, such as in off-road vehicles, earth-moving equipment, construction and demolition vehicles, etc.

SUMMARY

The present disclosure provides structural arrangements of wheel drive components that facilitate the use of robust main roller bearings that are widely spaced apart from one another. This wide spacing minimizes the torque borne by the bearings for a given external load, because at least one bearing is placed closer to the expected load application point (e.g., the center of gravity of the wheel attached to the wheel hub of the drive unit). The present wheel drive bearings can support a heavy external load without expanding the overall size and configuration of a given wheel drive application.

In one form thereof, the present disclosure provides a wheel drive transmission unit comprising: a spindle defining a longitudinal spindle axis, the spindle configured to affix to a vehicle frame at an input side of the transmission unit; a hub defining a longitudinal hub axis, the hub rotatable with respect to the spindle about the longitudinal hub axis and configured to affix to a driven wheel at an output side of the transmission unit; a primary planetary stage functionally interposed between the spindle and the hub, the primary planetary stage comprising: a primary input component positioned and configured to receive power from a vehicle power source; a plurality of primary planet gears in splined engagement with the primary input component; a primary planet gear carrier rotatably attached to each of the plurality of primary planet gears; and a primary ring gear in splined engagement with each of the plurality of primary planet gears, one of the primary planet gear carrier and the primary ring gear comprising a primary output component operably coupled to the hub such that the hub rotates at a rotational speed slower than the primary input component when the primary input component receives power; an input-side bearing mounted to an outer wall of the spindle and occupying a first space between the outer wall of the spindle and an inner wall of the hub, such that the input-side bearing rotatably supports the hub; and an output-side bearing mounted to the outer wall of the spindle at a location spaced axially from the input-side bearing by a bearing spacing distance, the output-side bearing occupying a second space between the outer wall of the spindle and an inner wall of the primary ring gear, the second space larger than the first space whereby the output-side bearing has a larger overall cross-section as compared to the input-side bearing.

In another form thereof, the present disclosure provides a wheel drive transmission unit comprising: a spindle defining a longitudinal spindle axis, the spindle configured to affix to a vehicle frame at an input side of the transmission unit; a hub defining a longitudinal hub axis, the hub rotatable with respect to the spindle about the longitudinal hub axis and configured to affix to a driven wheel at an output side of the transmission unit; a primary planetary stage functionally interposed between the spindle and the hub, the primary planetary stage comprising: a primary input component positioned and configured to receive power from a vehicle power source; a plurality of primary planet gears in splined engagement with the primary input component; a primary planet gear carrier rotatably attached to each of the plurality of primary planet gears; and a primary ring gear monolithically formed as part of the spindle, the primary ring gear in splined engagement with each of the plurality of primary planet gears, such that the primary input component, the plurality of primary planet gears and the primary planet gear carrier are disposed radially inwardly of the primary ring gear formed in the spindle; a secondary planetary stage functionally interposed between the spindle and the hub, the secondary planetary stage comprising: a secondary input component positioned and configured to receive power from the primary planet gear carrier of the primary planetary stage; a plurality of secondary planet gears in splined engagement with the secondary input component; a secondary planet gear carrier rotatably attached to each of the plurality of secondary planet gears, the secondary planet gear carrier monolithically formed as part of the spindle; and a secondary ring gear in splined engagement with each of the plurality of secondary planet gears, the secondary ring gear comprises a secondary output component, the secondary ring gear operably affixed to the hub such that the hub rotates at a rotational speed slower than the primary input component and the secondary input component when power is transmitted through the primary and secondary planetary stages.

In yet another form thereof, the present disclosure provides a wheel drive transmission unit comprising: a spindle defining a longitudinal spindle axis, the spindle configured to affix to a vehicle frame at an input side of the transmission unit; a hub defining a longitudinal hub axis, the hub rotatable with respect to the spindle about the longitudinal hub axis and configured to affix to a driven wheel at an output side of the transmission unit; a primary planetary stage comprising: a primary input component positioned and configured to receive power from a vehicle power source; a plurality of primary planet gears in splined engagement with the primary input component; a primary planet gear carrier rotatably attached to each of the plurality of primary planet gears, the primary planet gear carrier including an output-side surface comprising a plurality of recesses formed therein; and a primary ring gear in splined engagement with each of the plurality of primary planet gears; a secondary planetary stage comprising: a secondary input component including a sun gear portion and a plurality of face splines protruding axially away from the sun gear portion, the secondary input component axially moveable to selectively engage or disengage the face splines with the recesses of the primary planet gear carrier, such that the secondary input component receives power from the primary planet gear carrier when the secondary input component is axially moved into its engaged position; a plurality of secondary planet gears in splined engagement with the secondary input component; a secondary planet gear carrier rotatably attached to each of the plurality of secondary planet gears; and a secondary ring gear in splined engagement with each of the plurality of secondary planet gears, the secondary ring gear operably affixed to the hub such that the hub rotates at a rotational speed slower than the primary input component and the secondary input component when the face splines of the secondary input component are engaged with the recesses of the primary planet gear carrier.

DETAILED DESCRIPTION

Turning now toFIG. 2, wheel drive110includes a spatial arrangement of internal components which allows roller bearings142,144to be spaced apart from one another such that output-side bearing144is disposed at an axially outward position and relatively close to the center of gravity of wheel W mounted to hub114(FIG. 10). As explained in detail below, this spacing of bearings142,144results in a lower application of torque and stress thereupon during service, thereby enabling bearings142,144to absorb heavier loads as bearings142,144support the driven wheel W mounted to hub114and driven by ring gear138.

In addition, the spatial arrangement of components of wheel drive110allows output-side bearing144to be disposed between hub114and ring gear138, rather than between hub114and spindle112. As a result, bearing144can utilize a larger cross-sectional area for support of driven wheel W (FIG. 10) attached to hub114and ring gear138, in turn facilitating the use of a stronger, more robust bearing at the output side of wheel drive110.

Various components of wheel drive110have a generally cylindrical shape, including spindle112, hub114, brake system121and its related components, input component117, primary gear carrier126, bearings142,144, primary/secondary coupler component129, ring gear138, seal146and outer cover148. These components define respective longitudinal axes that are coaxial with longitudinal axis A1when wheel drive110is assembled as shown inFIGS. 2 and 4.

1. Overview of Wheel Drive Components and Operation

As best seen inFIG. 3, wheel drive110includes spindle112, which affixes to a vehicle frame F (FIG. 10) via mounting holes113, and hub114, which affixes to a driven wheel W via mounting holes116and rotates with respect to spindle112about longitudinal axis A1of wheel drive110. Driven wheel W and wheel hub114are also affixed to ring gear138, as described further below, such that wheel W and wheel hub114are powered by rotation of ring gear138about axis A1.

Referring toFIG. 2, wheel hub114is rotatably mounted to spindle112via roller bearings142,144. Input-side bearing142is disposed between, and directly abuts the outer surface of spindle112and an inner surface of hub114. Output-side bearing144is also mounted upon and directly abuts the outer surface of spindle112as illustrated, but is abutted at its radial outward surface by ring gear138rather than hub114. Thus, input-side bearing142is both axially constrained (i.e., prevented from axial movement) and radially constrained (i.e., prevented from radially outward movement or expansion) by cooperation of adjacent surfaces of spindle112and hub114. However, output-side bearing144is only axially constrained by spindle112and hub114, while radial constraint is provided by ring gear138. As described in further detail below, bearings142,144define a wide nominal spacing SB(and an associated wide functional spacing SB′) with respect to one another as measured parallel to axis A1, which enhances the ability of drive110to absorb external loads during service.

Wheel drive110includes two planetary gear stages, namely primary planetary stage170and secondary planetary stage180, which each contribute to the overall gear reduction between input component117and ring gear138. Primary planetary stage170receives powered input from input component117and produces an intermediate output having reduced rotational speed and concomitantly higher torque as compared to input component117. As described in further detail below, this intermediate output selectively provides the powered input to secondary planetary stage180, by selectively rotationally fixing primary planet gear carrier126(which is the output component of primary stage170) to secondary sun gear130(which is the input component of secondary stage180). Secondary planet stage180in turn produces a final output having reduced rotational speed and increased torque with respect to the intermediate output of primary planetary stage170. The final output is transmitted to ring gear138, which is fixed to wheel hub114.

Thus, the final output of wheel drive110rotates driven wheel W (FIG. 10) at a rotational speed that has been reduced twice—once by each of the two planetary stages170,180. This double reduction arrangement establishes wheel drive110as a “two stage” system, though it is contemplated that systems with other reduction mechanisms may be used. For example, a single stage wheel drive having only one planetary stage may be used in designs requiring relatively smaller overall reduction ratios, while multiple-stage wheel drives having three or more stages may be used where larger overall reduction ratios are desired. Where a single-stage wheel drive is desired, a ring gear may form the output component (as is the case with secondary stage180described herein), or a planet gear carrier may form the output component (as is the case with primary stage170described herein). A three-stage wheel drive210is shown inFIG. 9and described further below.

Turning toFIGS. 2 and 4, the configuration of both primary planetary stage170and secondary planetary stage180is illustrated. First, primary planetary stage170receives power from input component117which includes input coupler118and sun gear120monolithically formed as a single part. An externally splined input shaft (not shown) transmits power from a vehicle power source to the internal splines of input coupler118to rotate sun gear120. External splines formed on sun gear120engage correspondingly formed external splines on a plurality of planet gears124, such as three planet gears124in the illustrated embodiment. Only two planet gears124are visible within the cross sectional views ofFIGS. 2, 4 and 6A, it being understood that a lower planet gear124is shown in section, an upper planet gear124is shown behind the cross sectional plane and partially obscured by sun gear120, and a second upper planet gear is not shown in the sectioned view. As best shown inFIG. 6, the external splines of planet gears124also engage ring gear127, which is integrally formed along the inner wall of spindle112as further described below. Planet gears124are held in their respective positions by planet gear carrier126, and are rotatable about the respective planet gear longitudinal axes via planet gear axles128. Bearings123may be interposed between planet gears124and axles128to facilitate rotation therebetween.

Rotation of sun gear120causes planet gears124to rotate about planet gear axles128, as well as to rotate about longitudinal axis A1within stationary ring gear127. Because spindle112is mounted to the vehicle frame F (FIG. 10) and ring gear127is monolithically formed as part of spindle112, ring gear127is a stationary component in the context of primary planetary stage170and wheel drive110. Accordingly, planet gears124are free to circumnavigate sun gear120while rotating about axis A1and, in doing so, cause primary gear carrier126to rotate about axis A1at the speed of such circumnavigation. Primary gear carrier126is selectively rotatably fixed to sun gear130, and therefore provides the input to drive rotation of secondary planetary stage180, as further detailed below.

Turning toFIGS. 5 and 6B, secondary planetary stage180is arranged similarly to primary planetary stage170. As described further below, however, secondary planetary stage180includes gear carrier134which is integrally and monolithically formed as a part of spindle112, and is therefore stationary in the context of wheel drive110. For secondary planetary stage180, ring gear138is the rotatable component which serves as the output of secondary stage180.

Similar to primary stage170described above, external splines of secondary sun gear130engage with external splines formed on each of three planet gears132which are in turn engaged with the internal splines formed in ring gear138. Like primary stage170, only two planet gears132are visible in the cross-sectional views ofFIGS. 2, 4 and 6B, with the upper planet gear132shown in section and the lower planet gear132partially obscured by adjacent components. Rotation of secondary sun gear130causes planet gears132to rotate about planetary gear axles136, but such rotation cannot cause circumnavigation of planet gears132about axis A1because planet gear carrier134is fixed as noted above. Instead, rotation of planet gears132drives rotation of ring gear138. Thus, unlike primary stage170with stationary ring gear127and gear carrier126as the output component, secondary stage180utilizes ring gear138as its output component while gear carrier134remains stationary. Bearings133may be interposed between planet gears132and axles136to facilitate rotation therebetween.

Spindle112therefore serves multiple roles in wheel drive110, including the role of a stationary component in each of the planetary stages170,180(i.e., ring gear127and planet gear carrier134respectively). For clarity,FIG. 5illustrates spindle112in cross-section without other components, whileFIGS. 6A and 6Bshow spindle112with only primary and secondary planetary stages170,180respectively.

As most clearly illustrated inFIGS. 5 and 6A, stationary ring gear127is integrally formed in spindle112for interaction with the other components of primary planetary stage170. Unlike spindle12of wheel drive10, spindle112of wheel drive110encircles primary planetary stage170.FIGS. 5 and 6Billustrate that gear carrier134as an integrally, monolithically formed part of spindle112, with gear carrier134receiving planetary gear axles136through axle apertures137(FIG. 5). In short, spindle112serves as both a housing and a support structure for both planetary stages170,180, with primary planetary stage170axially rotating within the cavity of spindle112and secondary planet gears132rotating about gear axles136received within apertures137formed in spindle112(FIG. 5). As described in further detail below, this arrangement of components moves primary planetary stage170into spindle112such that the space radially outside of spindle112normally occupied by primary stage170is made available, which in turn allows output-side bearing144to occupy the space normally occupied by primary stage170.

Wheel drive110may be used outside, and may therefore be exposed to the elements. Wheel drive110includes seal146, best shown inFIG. 2, disposed between hub114and spindle112. Referring toFIGS. 2 and 3, outer cover148is fitted on the axial outward end of ring gear138. Seal146and outer cover148cooperate to retain lubricant contained within wheel drive110, while also preventing dust, moisture, and other contaminants from infiltrating the interior of wheel drive110.

As best seen inFIG. 2, wheel drive110optionally includes brake system121operable to selectively arrest rotation of input component117. Clutch pack121A includes alternating clutch plates engaging inner splines121B (FIG. 5) formed on the inner surface of spindle112or outer splines formed on coupler portion118of input component117. Springs121C, which may be provided as Belleville-type springs, urge clutch release component121E into engagement with clutch pack121A, biasing the alternating clutch plates into abutting engagement with one another. This creates frictional resistance to rotation of input component117. Hydraulic line121D selectively provides pressurized fluid to move clutch release component121E axially toward the input side of wheel drive110, against the biasing force of springs121C. This allows the clutch plates of clutch pack121A to spread apart from one another, relieving the friction therebetween and allowing input component117to rotate.

As noted above and shown inFIG. 2, the arrangement of the components disclosed in the present wheel drive allows bearings142,144to be spaced from one another by a large spacing distance SB, which in turn results in a large load spacing SB′. Spacing distance SBis the axial extent of the space between bearings142,144, i.e., the shortest distance between the respective outer surfaces of bearings142,144. Load spacing SB′ is the axial extent between intersection points between longitudinal axis A1and bearing load lines142L,144L respectively. Load lines142L,144L extend perpendicularly to the longitudinal axes defined by bearing rollers143,145, respectively, and originate halfway along the axial extent of rollers143,145, respectively. Load lines142L,144L extend radially inwardly to the respective intersection points with axis A1. Thus, load spacing SB′ can be made larger by canting bearing rollers143,145, further out of parallel relationship with axis A1, and smaller by canting bearing rollers143,145toward a parallel orientation with respect to axis A1. Such canting affects the ability of bearings142,144to absorb forces and stresses without damage, with larger load spacing SB′ associated with increased ability to absorb bending moments but decreased ability to absorb radial forces. An increase in spacing distance SBresults in a corresponding increase in load spacing SB′ for any given arrangement of rollers143,145, while also preserving the full radial capabilities of the roller arrangement. This, in turn, facilitates greater ability for bearings142,144to absorb the chaotic forces and stresses which may be exerted when used on a vehicle.

Spacing distance SBalso cooperates with the respective sizes of bearings142,144to define functional bearing center line BC. Center line BC is axially positioned such that, when a radial force is applied to bearings142,144over time, bearings142,144can be expected to wear at an even rate. Thus, if bearings142,144shared equal load ratings (and usually, equal cross-sectional sizes), center line BC would be halfway between bearings142,144(i.e., oriented at one-half of distance SB).

However, as shown in the exemplary embodiment ofFIGS. 2 and 4, bearings142,144have differing load ratings. Output-side bearing144is disposed between the outer wall of spindle112and the inner wall of ring gear138, which is a relatively larger radial and axial space such that output-side bearing144has a larger overall cross-section compared to input-side bearing142, which is disposed in the relatively smaller space between the outer wall of spindle112and the inner wall of hub114. The larger cross-section of output-side bearing144enables utilization of a higher load rating with respect to input-side bearing142. Thus, center line BC is biased toward the bearing with a higher load rating as illustrated inFIG. 2. The amount of such biasing is proportional to the relative strengths of the bearings, i.e., if bearing144has a load rating twice that of bearing142, center line SB is twice as far from bearing142as it is from bearing144.

Output-side bearing144is axially spaced from mounting holes116of output hub114toward the output side of wheel drive110, such that output-side bearing144is positioned within the axial extent of wheel W (i.e., the distance along the axis of wheel rotation from the outboard-most point of wheel W to the inboard-most point thereof, as shown inFIG. 10). This positioning is enabled by the placement of primary planetary stage170within spindle112, which in turn allows output-side bearing144to be placed at a common axial position with primary stage170as illustrated inFIGS. 2 and 4. Moreover, this common axial position is such that the axial extent of bearing144is substantially subsumed by the axial extent of primary stage170.

In addition, the position and relative load ratings of bearings142,144dispose the functional bearing center line BC also within the axial extent of wheel W. Load spacing SB/SB′ and the positioning of bearings142,144cooperate to minimize stresses exerted on bearings142,144during operation of wheel drive110, as described in detail below.

In exemplary embodiments of wheel drives110used on vehicle hubs, spacing distance SBmay be as little as 0.419 inches, 0.75 inches or 1 inch, and as large as 1.5 inches, 1.75 inches, or 2.00 inches, or may be any distance within any range defined by any of the foregoing values. For exemplary bearings142,144, this results in load spacing distance SB′ that is as small as 2.5 inches, 3.0 inches or 3.5 inches, and as large as 4.5 inches, 5.0 inches, or 5.5 inches, or may be any distance within any range defined by any of the foregoing values.

Each bearing142,144defines bore diameter DBsized to fittingly encircle spindle112. Diameter DBof bearings142,144is slightly larger than the outer diameter of spindle112, such that bearings142,144slide easily over the outer surface of spindle112. In exemplary embodiments of wheel drives110used on vehicle hubs, diameter DBmay be as small as 2.0 inches, 3.0 inches or 4.0 inches, and as large as 6.0 inches, 7.0 inches, or 8.0 inches, or may have any bore size within any range defined by any of the foregoing values.

The present arrangement of components within wheel drive110facilitates the bearing spacing SBbetween bearings142,144, which in turn shortens the axial distance between the most axial outward point of the assembly (i.e., the approximate location of the wheel center of gravity of driven wheel Was shown inFIG. 10) and output-side bearing144/center line BC. In other words, output-side bearing144and center line BC are placed closer to the point of load application upon wheel W attached to hub114, which in turn reduces the bending torque and minimizes the stresses on bearings142,144.

Increasing the distance between the two bearings142,144and thus decreasing the distance between center line BC and the center of gravity of wheel W is an effective way to decrease the stresses on the bearings142,144while maintaining the other dimensions of wheel drive110according to industry standards and/or application demands. For some wheel drive designs, the overall size and configuration of wheel drive110are imposed as design constraints because wheel drive110must be compatible with existing vehicle frame mounting geometry and/or existing available vehicle wheels. For example, referring toFIG. 2, spindle112includes mounting holes113arranged annularly around a spindle bolt circle having diameter DS, while hub114and ring gear138similarly include mounting holes116arranged annularly around a hub bolt circle having diameter DH. For the exemplary embodiments noted above, diameters DHand DSare between 6.5 inches and 17.0 inches. In addition, wheel drive110defines overall axial length L, which in the exemplary embodiments noted above is between 7.5 inches and 15.0 inches.

The present wheel drive arrangement increases spacing SBwithout making any other changes to overall size and configuration of wheel drive110, including bolt circle diameters DHand DSand overall axial length L, such that wheel drive110provides greater strength and capacity for bearings142,144while maintaining the ability to fit wheel drive110into existing vehicle infrastructure.

Thus, wheel drives110can be provided in a wide range of overall sizes. Some very small sizes may be provided for passenger vehicle applications, such as pickup trucks and other off-road applications, while very large sizes may be provided for earth moving equipment, large construction vehicle, and the like. Generally speaking, the nominal spacing SBof bearings142,144increases as the other components increase in size. Accordingly, one way to express the present wide bearing spacing in the context of a wide range of wheel drive sizes is as a ratio of spacing SB′ and/or spacing SBto bearing bore diameter DB. A higher SB:DBratio or SB′:DBratio is indicative of a relatively greater relative spacing between bearings142,144, and is also indicative of the output-side bearing144and center line BC being closer to the center of gravity of driven wheel W (FIG. 10). Accordingly, a greater SB:DBratio or SB′:DBratio generally results in higher bearing support capability for a given wheel drive size. In an exemplary design, for example, the SB:DBratio may be between 0.11 and 0.50, which results in a stronger and more robust wheel drive110as compared to existing designs. In this exemplary arrangement, the SB′:DBratio may be between 0.690 and 1.090.

Another feature of wheel drive110indicative of wide spacing SBis the positioning of output side bearing144and center line BC relative to mounting holes116for driven wheel W at hub114and ring gear138. As best illustrated inFIG. 2, bearing144is disposed axially outward relative to mounting holes116, thereby placing bearing144and bearing load center line BC within the axial extent of driven wheel W when wheel W is mounted to wheel drive110(as shown inFIG. 10). More particularly, ring gear138and cover148are both contained within the generally cylindrical cavity C created by wheel W on a typical installation, such that ring gear138is directly radially inward of the contact patch P between tire T and the adjacent ground G. Stated another way, a line taken from the center of contact patch P and perpendicular to ground G intersects ring gear138. The placing of bearing144axially outward of mounting holes116disposes bearing144within the axial extent of wheel W, thereby minimizing or eliminating the axial spacing between the application of force to wheel W and center line BC. This, in turn, minimizes or eliminates the lever arm which would result in a torque being placed upon bearings142,144, such that bearings142,144need only handle the radial inward force applied by wheel W rather than such force together with a resultant torque.

FIGS. 7-8Cillustrate short-stroke disconnect mechanism that can be used to disengage sun gear130of secondary planetary stage180from planet gear carrier126of primary stage170, thereby allowing wheel hub114and wheel W to disengage from the influence of the vehicle power source. When so disengaged, the attached wheel W can spin freely with respect to spindle112, such as for towing the vehicle. Referring toFIG. 8, the present arrangement utilizes primary/secondary coupler component129which facilitates a short disengagement stroke by utilizing face splines131protruding axially away from sun gear portion130. Face splines131selectively engage corresponding recesses125formed in an axial end surface of primary planet gear carrier126to rotationally fix primary stage170to secondary stage180, as further detailed below.

In an exemplary embodiment, sun gear portion130and face splines131are monolithically formed as a single piece, namely, primary/secondary coupler component129. Similarly, recesses125are monolithically formed as a part of primary planet gear carrier126. This monolithic construction contributes to long life and high strength of the short-stroke disconnection mechanism, as well as minimizing rotational backlash through the system when short-stroke disconnection mechanism is subjected to forces and torques. Moreover, as illustrated inFIGS. 8A and 8B, a minimal amount of internal volume is consumed by structures dedicated to the disconnection functionality of the short-stroke disconnection mechanism, because the bulk of primary/secondary coupler component129and primary planet gear carrier126are already present serving other functions within wheel drive110as described in detail above.

FIGS. 8A-8Billustrate the transition from engagement to disengagement of the short-stroke disconnection mechanism. InFIG. 8A, the mechanism is shown in the actuated configuration, in which face splines131are received within recesses125. When so received, primary/secondary coupler component129is rotationally fixed to primary planet gear carrier126, such that torque output from primary planetary stage170is input into secondary planetary stage180as described above. Component129is maintained in this engaged position by spring135, which is compressed between an internal bore formed in sun gear portion130and spring plunger139, which is fixed to lever150as detailed below.

FIG. 8Bshows face splines131of sun gear130withdrawn from engagement with corresponding recesses125. As described below, this withdrawn engagement is effected by rotating lever150to axially displace primary/secondary coupler component129against the biasing force of spring135such that face splines131move axially toward the output side of wheel drive110, thereby withdrawing splines131axially out of recesses125. When so withdrawn, any torque imparted to gear carrier126from input component117will no longer input into the secondary planetary stage180, such that ring gear138is effectively decoupled from the vehicle power source and will not be driven by input from input component117.

The present short-stroke withdrawal mechanism allows wheel drive110to be reconfigured between the engaged position ofFIG. 8A, in which hub114and ring gear138are driven by input component117, and the disengaged position ofFIG. 8B, in which the input component117is functionally decoupled from hub114and ring gear138(such that the vehicle using wheel drive110can be towed or pushed without interference from the braking system121, vehicle engine or transmission as noted above). In addition, decoupling ring gear138from the power source avoids rotation of the components of primary planetary stage170during rotation of wheel W (FIG. 10), thereby preventing wear of such components when wheel W is rotating and wheel drive110is not being powered by input component117.

As noted above, the short-stroke disconnect mechanism is toggled between the engaged and disengaged configurations by rotating lever150. Referring toFIG. 8C, such rotation results in axial displacement of lever150which in turn axially displaces primary/secondary coupler component129with respect to primary planet gear carrier126(FIGS. 8A and 8B). More particularly,FIG. 8Cillustrates the center portion of wheel drive cover148, which includes cam surfaces152and lands154within recess156. When lever150is rotated from the engaged position (shown in solid lines ofFIG. 8C) and the disengage position (shown in dashed lines), lever150engages cam surfaces152which urges lever150axially outwardly. As this axial outward travel occurs, spring plunger139(which is axially fixed to lever150) is drawn outwardly, carrying primary/secondary coupler component129with it. This compresses spring135, and simultaneously withdraws face splines131out of engagement with the corresponding recesses125formed in primary planet gear carrier126. Resting lever150upon lands154maintains the disconnect mechanism in the disengaged state, and rotating lever150back down cam surfaces152allow spring135to bias lever150, spring plunger139and primary/secondary coupler component129back in to the engaged state.

Wheel drive110utilizes primary and secondary planetary stages170,180to achieve a final reduced speed and increased torque of ring gear138with respect to input component117, as described above. However, it is also contemplated that other arrangements having fewer or more planetary stages can be used, such as three-stage wheel drive210shown inFIG. 9. This arrangement includes primary stage270contained within spindle212, secondary planetary stage280disposed at the axial outward end of wheel drive210and operably connected to primary stage270via secondary sun gear230, and tertiary stage290operably connected to secondary stage280via tertiary sun gear260. Secondary and tertiary stages280and290cooperate to drive ring gear238.

Except as otherwise noted herein, reference numbers used to refer to components of wheel drive110are correspondingly used in reference to wheel drive210, except with 100 added thereto.

Primary planetary stage270is functionally identical to primary planetary stage170, except that sun gear220is larger than sun gear120and planet gears224are concomitantly smaller than planet gears124. It is, of course, contemplated that primary planetary stage170of wheel drive110could be identical to primary planetary stage270. Moreover, any arrangement of planetary components may be used to provide a desired gear reduction as required or desired for a particular design.

Secondary planetary stage280is arranged as the output-side planetary stage, i.e., closest to the outboard side of the wheel (FIG. 10), and is disposed axially outside of spindle212. Secondary stage280receives power from primary planet gear carrier226, via primary/secondary coupler component229in similar fashion to wheel drive110described above, except that secondary sun gear230is a separate component rotatably fixed to coupler component229rather than being integrally formed therewith.

Secondary sun gear230includes outer splines with engage correspondingly formed outer splines of three planet gears232, causing planet gears232to rotate about planet gear axles236within ring gear238. Similar toFIG. 2illustrating wheel drive110,FIG. 9shows only two planet gears232in the cross-sectional view, with the lower gear232shown in section and the upper gear232partially obscured by adjacent components. However, unlike the primary stage having stationary ring gear227formed along the inner wall of spindle212, ring gear238of secondary stage280rotates as a result of the rotation of internal planet gears232. Further, gear carrier234of secondary planetary stage280rotates as a result of the rotation of internal planet gears232in addition to ring gear238. Thus, secondary planetary stage280has both a rotating ring gear238and a rotating gear carrier234. Gear carrier234is rotatably fixed to sun gear260of tertiary planetary stage290and rotates sun gear260.

Splines formed on the outer surface of tertiary sun gear260engage correspondingly formed external splines on the three planet gears252, which are in turn supported by and rotate about gear axles256in gear carrier254. Tertiary gear carrier254is integrally formed as part of spindle212, and is therefore stationary in the context of wheel drive210. Tertiary planet gears252rotate about gear axles256while engaging the internal splines of ring gear238to aid in rotation of ring gear238. Accordingly, planet gears232and252of both secondary and tertiary planetary stages270,280cooperate to drive ring gear238, with secondary planet gears232allowed to circumnavigate secondary sun gear230while tertiary planet gears252do not circumnavigate.

As with wheel drive110, rotation of ring gear238forms the final output of wheel drive210, and rotates wheel W at a rotational speed that has been reduced three times once by each of the three planetary stages270,280, and290.