Driven wheel unit including an axially compact two-speed planetary gear drive assembly

A driven wheel unit includes an electric motor coupled to a two-speed, three stage planetary drive assembly and has a width dimensioned for traveling between rows of crop. A wheel hub is supported on an outer surface of a fixed housing by large diameter wheel bearings surrounding both a motor-containing cavity and an adjacent cavity containing first and second planetary stages. Nested radially and surrounding the two planetary stages are two SAHR disc clutches including pistons engaging inner and outer surfaces of a compact piston guide member. The third stage planet carrier defines a cap and is fixed to an axially outer end of the wheel hub. A third stage ring gear has an outside diameter approximately equal to that of the wheel bearings and has an inside diameter fixed to the housing by a planar, annular wheel bearing retainer plate that is fixed to an end of the housing.

FIELD OF THE DISCLOSURE

The present disclosure relates to a driven wheel unit including a two-speed planetary gear drive assembly, and more specifically relates to such a driven wheel unit that includes multiple speed reduction planetary stages and is particularly suited for use on a row-crop tractor or sprayer intended to be easily driven between rows of crop having a spacing of about 20 inches (508 mm) without running over the crop.

BACKGROUND

A planetary drive arrangement is often used in a vehicle driven wheel unit for providing high and low operating speeds as well as stepped speed reductions effected by routing power delivered by drive unit motors (hydrostatic or electric, for example) through multiple planetary gear stages. While those familiar with powered wheel units have long appreciated the severe limitations that such designs place upon available space in which to locate the drive motor and constituent components of the planetary gear arrangements of such wheel units, they will agree that these space constraints are even more severe when the wheel units are being used to drive wheels of a row-crop tractor intended for being driven between rows of crop planted as close as 20 inches (508 mm) apart and when the wheel units are powered by an electric motor. In this particular usage of a drive unit, it is important for the drive unit to be axially compact, while maintaining desired torque output and reliability in view of the ever increasing size of implements being drawn or carried by the tractor. Therefore, what is needed is a driven wheel unit especially designed for use with a row-crop tractor to be driven between rows of crop spaced apart as narrow as 20 inches (508 mm).

SUMMARY

According to a first aspect of the present disclosure, there is provided a driven wheel unit of a row crop tractor, with the driven wheel unit comprising a two-speed planetary drive assembly including at least two planetary stages located within a fixed housing, with the fixed housing having a cylindrical outer surface on which is mounted a main support bearing assembly supporting a wheel hub for rotation, with the drive assembly including radially outer and inner friction clutches located radially within a diameter of the main support bearing assembly and being arranged in a compact, radially nested fashion so as to occupy a minimum of axial width.

According to a second aspect of the disclosure, the aforementioned inner and outer disc clutches are each spring applied hydraulically released (SAHR) friction clutches which each include an annular piston, and a compact annular piston support and guide member fixed to the fixed housing and having radially outer surfaces engaged by the outer SAHR friction clutch and having radially inner surfaces engaged by the inner SAHR friction clutch.

According to a third aspect of the disclosure, the annular friction clutches are each L-shaped in cross section, with the legs of the radially outer SAHR friction clutch cooperating with the annular piston guide and support member to define a first annular working fluid cavity adapted for selectively receiving pressurized fluid for disengaging the radially outer SAHR friction clutch, and with the legs of the radially inner SAHR friction clutch cooperating with the annular piston guide and support member to define a second annular working fluid cavity adapted for selectively receiving pressurized fluid for disengaging the radially inner SAHR friction clutch.

According to a fourth aspect of the disclosure, the inner and outer SAHR friction clutches are in an annular arrangement surrounding the entire first planetary stage and surrounding the second stage sun and planet carrier and with an outer clutch disc pack being coupled between an outer annular surface of the second stage ring gear and the fixed housing, and with an inner clutch disc pack being coupled between an inner annular surface of the second stage ring gear and an outer annular surface of the second stage planet carrier.

According to a fifth aspect of the disclosure, a planar annular retainer plate is releasably fixed to an annular, axially outward facing end surface of the fixed housing and engages and retains a first bearing of the main support bearing assembly in place on the housing, the retainer plate having a toothed outer diameter engaged with, and directly fixing, a third stage ring gear to the fixed housing.

According to a sixth aspect of the present disclosure, a floating face seal assembly is located on the outer cylindrical surface of the fixed housing at an opposite side of the main support bearing assembly from the retainer plate and, in addition to acting to seal a clearance gap existing at an interface between the hub and the fixed housing, the face seal assembly is in biasing engagement with a second bearing of the main support wheel bearing arrangement and acts to retain the second bearing in place on the housing.

According to a seventh aspect of the disclosure, the planetary gear arrangement includes three stages with first, second and third stage sun gears being located serially in end-to-end relationship to each other along an axis of rotation of the wheel unit and with each sun gear being mounted for rotation relative to each other sun gear.

These and other aspects of the disclosure will become apparent from a reading of the ensuing description together with the appended drawings.

DETAILED DESCRIPTION

Referring now toFIGS. 1 and 2, there is shown an exemplary embodiment of a drive wheel unit10including a fixed housing12, with an axially outer end section of the housing having a radially outer cylindrical surface14disposed concentrically relative to an axis of rotation X. An annular wheel hub16is supported on the cylindrical surface14for rotating about the axis of rotation X by a main wheel support bearing assembly including a pair of axially spaced roller thrust bearings18. Located in an annular cavity defined by, and extending between, an inner annular wall of the rim16and an outer annular wall14of the fixed housing12is an annular metal face seal assembly20that, as viewed inFIG. 2, is located immediately leftward of the left roller thrust bearing18. The face seal assembly20is positioned against a left surface of the left thrust bearing18and keeps an outer race of the latter positioned against a shoulder defined by the inner surface of the wheel hub16.

A wheel rim22includes an annular, radially inward extending mounting plate24joined at a right angle to an interior surface of the wheel rim20and respectively secured to a plurality of radially outward projecting spokes26of the hub16by a plurality of fasteners (not shown). A tire28is mounted on the rim20and has a width W of approximately 16.75 inches (425 mm) which is suitable for traveling between rows of agricultural plants, spaced as narrow as 20 inches (508 mm) from each other, without running over the plants.

The drive wheel unit10includes a powered drive assembly30located centrally within, and coupled for driving, the hub16. The drive assembly30includes an electric motor32and a two-speed, multi-stage, planetary gear arrangement34. Importantly, the drive assembly30has a width approximately equal to the width W of the tire26so as to not disturb plants grown in rows as the tire26travels between the rows of plants

Referring also toFIG. 3, it can be seen that the electric motor32includes a substantially cylindrical housing36having left and right circular end walls38and40, respectively. An axially outer end region of the motor housing36is snugly received in an axially inwardly opening, cylindrical cavity42formed in the fixed housing12in concentric relationship to the rotation axis X and including an annular right end wall44, with the right end wall40of the motor housing36abutting the cavity end wall44. The motor32has an output shaft46disposed along the axis X and rotatably supported within, and projecting to a location rightward of, the motor housing end wall40.

Three planetary gear stages comprise the multi-stages of the planetary gear arrangement34and are spaced axially rightward along the axis X beginning at the motor housing end wall40. A first stage sun gear48is formed as an integral part of the motor output shaft46and is meshed with three first stage planetary gears50(most clearly visible inFIGS. 4 and 5) that are, in turn, meshed with a first stage ring gear52having an annular vertical flange54, with the ring gear52being secured against rotation by a circular pattern of fasteners (not shown) extending through the flange54and into mating threaded holes provided in the right end wall40of the motor housing36. A first stage planet carrier56includes three spindles58on which the three first stage planetary gears50are respectively mounted for rotation.

An intermediate short shaft60has a left end received on a reduced diameter right end of the motor output shaft46and can rotate relative to the shaft46. The shaft60is externally splined and a left end region of these splines is engaged with a radially inner splined surface of the first stage carrier56so that rotation of the carrier56is transferred to the shaft60. Also having a splined connection with the intermediate shaft60is a second stage sun gear62, which, as can best be seen inFIG. 6, rotates with the planet carrier56and is meshed with four second stage planetary gears64, which, in turn, are meshed with a second stage ring gear66. The second stage ring gear66is mounted for rotation relative to the fixed housing12, but is adapted for being selectively coupled or fixed to the housing, in a manner described below, to change the drive speed of the planetary gear arrangement34.

Referring also toFIG. 4, it can be seen that axially outward movement of the ring gear66is constrained by a flat, annular retainer plate68bolted to an annular axially outward facing, outermost end surface70of the fixed housing12by a plurality of mounting bolts72, the retainer plate68having a radially outer region engaged with an outer surface of the axially outer main bearing18and having a stepped, radially inner portion trapping a guide ring74between the retainer plate68and a shoulder defined by a step formed on an outer circumference of the second stage ring gear66at an axially outer region of the ring gear. Inward axial movement of the ring gear66is constrained by an annular guide disc or shim76loosely sandwiched between an axially inward facing surface of the second stage ring gear66and an axially outward facing surface of an annular clutch piston guide member78. The piston guide member78includes an axially inward projecting, annular mounting rib80having an axially inward facing annular surface engaged with an axially outward facing annular surface of an axially outward projecting mounting rib82of the fixed housing12, with the guide member78being fixed to the spindle housing12by a circular pattern of mounting bolts83projecting through holes provided in the guide member mounting rib80and screwed into aligned threaded holes provided in the housing mounting rib82.

A second stage planet carrier84is provided with spindles86on which the planetary gears64are respectively mounted for rotation. Further, the carrier84has an interiorly toothed, axially outer portion meshed with an axially inner region of teeth of a third stage sun gear88formed as an integral part of a short output shaft having axially inner and outer ends respectively supported for rotation in the right end of the intermediate shaft60and in a circular end wall or plate defined by a third stage planet carrier90and being secured, by a circular arrangement of bolts (not shown) to an axially outward facing annular surface92of the wheel mounting hub16located radially outward of the main bearings18. The third stage sun gear88is meshed with three, third stage planetary gears94, which are respectively mounted for rotation about three spindles96of the planet carrier90. The planetary gears94are meshed with a third stage ring gear98, with an axially inner region100of each of the teeth of the ring gear98being modified and respectively engaged with teeth102(seeFIG. 4) formed on a radially outer circumference of the retainer plate68so as to prevent relative rotation between the ring gear98and the fixed housing12.

Mounted in the housing12in surrounding relationship to the entire first planetary stage and in a location for cooperating with the second stage ring gear66and carrier84are nested, radially inner and outer spring applied hydraulically released (SAHR) disc clutches104and106, respectively.

The outer clutch104includes an annular disc pack108located in a large diameter section of an annular, stepped diameter cylindrical cavity110(seeFIG. 6) provided in the spindle housing12immediately axially inward of, or just to the left of, the retainer plate68. The disc pack108is located radially outward of the second stage ring gear66and includes first and second sets of interleaved friction plates. The first set of friction plates is fixed against rotation and for this purpose have an outer perimeter including radially projecting, semi-circular tabs spaced equally from each other and mounted for shifting axially in complimentary shaped, axially extending slots109provided in a larger diameter section of a stepped diameter cavity110of the fixed housing12. The second set of friction plates are mounted for rotation with the second stage ring gear66and for this purpose each have a toothed, radially inner annular surface engaged for sliding along mating teeth67formed axially along an outer diameter of the second stage ring gear66.

As can best be seen inFIG. 6, the outer clutch104further includes an annular outer clutch piston112that is L-shaped in cross section with a long leg of the L extending axially and having cylindrical outer and inner surfaces114and116, respectively, with the outer surface114being mounted for sliding axially within a smaller diameter section of the stepped diameter cavity110, and with the inner surface116being mounted for sliding axially along an outer cylindrical surface118of the clutch piston guide member78. A short leg of the L extends radially inward from the long leg of the L and defines a relatively narrow inner cylindrical surface120mounted for sliding axially along a radially outer cylindrical surface122of the mounting rib80of the guide member78. The piston guide member78and the piston112cooperate to define an annular work fluid cavity124that expands and contracts respectively with leftward and rightward movement of the piston112, as viewed inFIG. 2. A first sealing ring126is mounted in an annular groove provided in the outer cylindrical surface116of the piston guide member84and a second sealing ring128is provided in the inner cylindrical surface118of the short leg of the L of the piston112. The first and second sealing rings126and128thus act to prevent pressure fluid from leaking from the work fluid cavity124along the respective interfaces between the piston inner surface116and guide member outer surface118and between the piston inner surface120and guide member outer surface122.

The outer disc clutch104, as shown inFIG. 2, is in a disengaged condition wherein fluid pressure in the cavity124acts against the radially extending leg of the outer clutch piston112so as to hold the piston leftward against the biasing force of a circular array of coil compression springs130located in an annular spring cavity132formed in the spindle housing12adjacent a left end of the annular outer clutch piston112. In this condition, the interleaved first and second sets of friction plates of the disc pack108are not pressed against each other. Thus, the second stage ring gear72is free to rotate any time that second stage sun gear68is driven. Upon the supply of pressure fluid being disconnected from the work fluid cavity124, the loaded compression springs130will extend axially and act to shift the piston112axially outward so as to press the first and second sets of friction plates of the outer annular disc pack108together, thereby resulting in the second stage ring gear66being fixed to, and prevented from rotating relative to, the spindle housing12.

The inner disc clutch106is constructed in a manner similar to the outer disc clutch104and includes an annular disc pack134located between an inner diameter of the second stage ring gear66and an outer annular surface136of the second stage planet carrier84. The disc pack134includes a first set of friction plates interleaved with a second set of friction plates. The first set of friction plates is mounted for rotation with the second stage ring gear66and for this purpose each of these plates includes a toothed outer diameter received for sliding axially along mating teeth provided at the inner diameter of the second stage ring gear66. The second set of friction plates are mounted for rotating with the second stage planet carrier84and for this purpose each of these plates has a toothed outer diameter received for sliding axially along a toothed outer annular surface136of the second stage planet carrier84.

As can best be seen inFIG. 5, an annular thrust bearing137having a flat ring construction has an axially inner portion located in an annular step provided in a radially inner location of the piston guide member78, the bearing137having an axially outer face located beside an axially inner friction plate of the inner clutch disc pack134.

Referring once again toFIGS. 2, 5 and 6, it can be seen that the inner disc clutch106further includes an annular clutch piston138that is L-shaped in cross section with a long leg of the L extending axially and having cylindrical outer and inner surfaces140and142, respectively, with the outer surface140being mounted for sliding axially along an inside diameter of the piston guide member78and with the inner surface142being mounted for sliding axially along an outer cylindrical surface of the first stage ring gear52. A short leg of the L extends radially outward from the long leg of the L and defines a relatively narrow outer cylindrical surface146mounted for sliding axially along a radially inner cylindrical surface of the mounting rib80of the piston guide member78. The piston guide member78and the piston138cooperate to define an annular work fluid cavity148(FIG. 5) that expands and contracts respectively with leftward and rightward movement of the piston138, as viewed inFIGS. 1 and 5. A first sealing ring150is mounted in an annular groove provided in an inner cylindrical surface of the piston guide member78and a second sealing ring152is provided in the outer cylindrical surface146of the short leg of the L of the piston138to prevent pressure fluid from leaking from the work fluid cavity148along the interfaces respectively between the piston inner surface142and guide member inner surface142and between the piston outer surface146and inner surface of the mounting rib80of the guide member78.

The inner disc clutch106is shown in a disengaged condition inFIG. 2wherein the clutch piston138is held leftward away from the thrust bearing137and against the biasing force of a circular array of coil compression springs154located in an annular spring cavity156formed in part by an annular portion of the spindle housing wall44located radially inward of the mounting rib82and in part by the annular flange54of the first stage ring gear52. In this condition, the interleaved first and second sets of friction plates of the disc pack134are not pressed into engagement with each other to establish a driving connection between the second stage planet carrier84and the second stage ring gear66. Thus, the second stage ring gear66is free to be rotated by the second stage planetary gears64any time that the second stage sun gear62is driven. Upon the supply of pressure fluid being disconnected from the work fluid cavity124, the loaded compression springs130will extend axially and act to press the inner clutch piston138axially outward so as to cause the thrust bearing137to press the first and second sets of friction plates of the inner annular disc pack134together so as to establish a driving connection between the second stage planet carrier84and the second stage ring gear66.

Due to the clutches104and106acting to selectively couple the second stage ring gear66to the fixed housing12with all of the ring gears of the three stages thus being coupled to the fixed housing, the planetary gear arrangement34will operate without recirculating power losses as is the case when a ring gear free wheels. A related operational benefit of significance is the fact that due to the inner and outer clutches104and106functioning to turn on and off the second stage of the three stage planetary arrangement, as opposed to turning on and off the first planetary stage, for example, high clutch and sun speeds will occur in the low range, thus taking advantage of the maximum speed of the electric motor32.

Also of significance is the fact that the inner and outer clutches104and106are nested radially and that the piston guide member78comprises a sealing part which is common to both clutches to allow complex machining operations to be performed on this smaller, robust part rather than on two parts or on a large housing.

Having described one or more example embodiments, it will become apparent that various modifications can be made without departing from the scope of the accompanying claims.