Wheel drive unit

A wheel drive unit includes: a planetary gear mechanism including a planetary gear and an internally-toothed gear; a casing integrated with the internally-toothed gear, a wheel being attached to the casing, and the casing transmitting rotation of the internally-toothed gear to the wheel; a bearing nut configured to prevent axial movement of the casing; and an oil seal provided more toward an interior of a vehicle than the planetary gear mechanism and axially fixed with respect the casing. An inner diameter of the detachment prevention member is smaller than an outer diameter of the externally-toothed gear.

Priority is claimed to Japanese Patent Application No. 2012-250544, filed Nov. 14, 2012, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wheel drive unit to drive wheels of a utility vehicle.

2. Description of the Related Art

Wheel drive units for driving wheels of a utility vehicle such as a forklift in which a reducer mechanism is built are known. Some wheel drive units having such a structure are configured such that a wheel hub to which a tire is attached is arranged outside the reducer mechanism.FIG. 1is a cross sectional view of the wheel drive unit described in WO00/36317. As seen from theFIG. 1, a planetary gear mechanism C embodying a reducer and a disk brake6are accommodated in a housing9of the unit. A wheel (not shown) is tightened by bolts A to a hub12located toward the exterior of the vehicle. The hub12is joined to the unit via a spline formed on the inner circumference of an output carrier11and is axially fixed by a bolt B.

SUMMARY OF THE INVENTION

The wheel drive unit according to one embodiment of the present invention includes: a planetary gear mechanism including a planetary gear and an internally-toothed gear; a casing integrated with the internally-toothed gear, a wheel being attached to the casing, and the casing transmitting the rotation of the internally-toothed gear to the wheel; a movement restriction member configured to restrict axial movement of the casing; and a detachment prevention member provided more toward an interior of a vehicle than the planetary gear mechanism and axially fixed with respect the casing, wherein an inner diameter of the detachment prevention member is smaller than an outer diameter of the planetary gear.

According to the embodiment, a detachment prevention member having an inner diameter smaller than an outer diameter of the planetary gear is provided more toward an interior of a vehicle than the planetary gear mechanism. Therefore, even when the movement restriction member becomes loose and the function thereof to prevent movement is lost, detachment of the casing from the wheel drive unit is prevented due to contact of the detachment prevention member more toward the vehicle with the planetary gear.

The planetary gear mechanism may be of eccentric oscillation and meshing type or simple type. In the case of eccentric oscillation and meshing type, “a diameter of the planetary gear” means an outermost diameter (addendum circle) of the externally-toothed gear oscillating within a plane defined about a central axis normal to the plane. In the case of simple type, the phrase refers to an outer diameter of a circle connecting points located on two or more planet gears rotated around the sun gear that are farthest from the central axis of the sun gear (points located on the addendums of the planet gears that are farthest from the center of the sun gear).

Optional combinations of the aforementioned constituting elements, and implementations of the invention in the form of methods, apparatuses, and systems may also be practiced as additional modes of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

When a bolt connecting the hub and the rotating housing of the related-art wheel drive unit becomes loose, the hub might be detached from the wheel drive unit along with the wheel.

Embodiments of the present invention address a need to provide a structure of a wheel drive unit capable of preventing the casing from being detached from the wheel drive unit even when the member for preventing the axial movement of the casing to which the wheel is attached becomes loose.

FIG. 2is a cross sectional view that results when the wheel drive unit100according to an embodiment of the present invention is severed by a vertical plane that includes the central axis. The wheel drive unit100may be used in a utility vehicle such as a forklift.

The wheel drive unit100includes a reducer10, which is a kind of planetary gear mechanism of eccentric oscillation and meshing type, and a motor (not shown) connected to the reducer10in the left ofFIG. 2, i.e., toward the interior of the vehicle.

The output shaft of the motor is joined to an input shaft16of the reducer10via a spline (not shown). The input shaft16is located at the radial center of externally-toothed gears24and26described later. Two eccentric bodies18and20eccentric relative to the input shaft16are formed so as to be integrated with the input shaft16. The two eccentric bodies18and20are eccentric relative to each other by a phase difference of 180°. Channels18A and20A for supplying lubricant to roller bearings21and23are formed in the input shaft16. The eccentric bodies18and20may be configured as components independent of the input shaft16and fixed to the input shaft using a key, etc.

Two externally-toothed gears24and26are oscillatably fitted to the outer circumference of the eccentric bodies18and20, respectively, via roller bearings21and23. The externally-toothed gears24and26internally mesh with internally-toothed gear28.

The internally-toothed gear28primarily includes cylindrical internal gear pins (also referred to as external rollers)28A and28B forming internally-toothed gears and configured to promote sliding motion, an external pin (also referred to as a retention pin)28C extending through the internal gear pins28A and28B and rotatably retaining the internal gear pins28A and28B, and an internally-toothed gear body28D rotatably retaining the external pin28C and integrated with the inner circumferential surface of a casing30. The external pin may be supported by the casing30so as not to be rotatable.

The number of internal teeth of the internally-toothed gear28, i.e., the number of each of the internal gear pins28A and28B, is slightly (in this case, by one) larger than the number of external teeth of each of the externally-toothed gears24and26.

A first carrier body34fixed to a vehicle frame (not shown) is located at the axial end of the externally-toothed gears24and26toward the vehicle (toward the interior of the vehicle). At the axial end of the externally-toothed gears24and26away from the vehicle (toward the exterior of the vehicle) is located a second carrier body38integrated with the first carrier body34via carrier bolts36and carrier pins42. Internal pins40are formed to be integrated with the second carrier body38.

Twelve through holes having the equal radius are formed at positions in the externally-toothed gear24offset from the shaft center so as to be equidistant from each other (the externally-toothed gear26is configured similarly, although not shown). The carrier pins42are inserted through three of these through holes equidistant from each other by 120°, and internal pins40are inserted through the remaining nine holes. Therefore, the three holes will be referred to as carrier pin holes24B, and the nine holes will be referred to as internal pin holes24A. However, the carrier pin holes24B and the internal pin holes24A are not different in their shape and radial position. Gear teeth of waveform are formed on the outer circumference of the externally-toothed gear24. As the gear teeth move on the internal gear pins28A of the internally-toothed gear28, maintaining contact with the internal gear pins28A, the externally-toothed gear24is capable of oscillating within a plane defined about a central axis normal to the plane. The externally-toothed gear26is similarly structured (not shown) except that there is a phase difference of 180° to the externally-toothed gear24.

The internal pins40are inserted through the internal pin holes24A and26A formed through the externally-toothed gears24and26, creating a gap between the internal pins40and the internal pin holes24A and26A. The ends of the internal pins40are fitted in recesses34A of the first carrier body34. The internal pins40are in contact with parts of the internal pin holes24A and26A formed in the externally-toothed gears24and26via sliding motion promoting members44. The internal pins40prevent the rotation of the externally-toothed gears24and26and permit only the oscillation thereof.

The internal pins40are merely press-fitted in the recesses34A and are not bolted, etc. The internal pins can be said to be joint members contributing to transmission of power between the first and second carrier bodies34and38and the externally-toothed gears24and26.

The carrier pins42are inserted through the carrier pin holes24B and26B formed through the externally-toothed gears24and26, creating a gap between the carrier pins42and the carrier pin holes24B and26B. Contact portions42C of the carrier pins42with an enlarged diameter are in contact with the surface of the first carrier body34away the vehicle. The carrier pins42and the first carrier body34are tightened to each other by carrier bolts36. The first carrier body34is formed with through holes34C for guiding the carrier bolts36and spot facings34B. The axial end faces of the carrier pins42are formed with screw holes42E for receiving the carrier bolts36. Female screw holes38A are formed in the second carrier body38. The female screw holes38A are coupled to male screws at the ends of the carrier pins42away from the vehicle so that the carrier pins42and the second carrier body38are tightened to each other.

The carrier pins42are not in contact with the carrier pin holes24B and26B of the externally-toothed gears24and26and so do not contribute to prevention of the rotation of the externally-toothed gears24and26. The carrier pins42can be said to be joint members contributing only to joint between the first carrier body34and the second carrier body38.

The casing30of the reducer10is substantially cylindrically shaped. A first main bearing46is fitted in a recess30A formed on the inner circumference of the casing30toward the interior of the vehicle. The casing30is rotatably supported on the outer circumference of the first carrier body34via the first main bearing46. A flange extending radially inward is formed in the casing30more toward the exterior of the vehicle than the externally-toothed gears24and26. A second main bearing47is fitted in a recess30C formed on the inner circumference of the flange. The casing30is rotatably supported on the outer circumference of the second carrier body38via the second main bearing47. The first and second main bearings46and47may be press-fitted into the casing30. Alternatively, the first and second main bearings46and47may be fitted in the casing30, creating a gap, and then fixed to the casing30by a stopper ring (not shown). In other words, the first and second main bearings46and47need only be fixed in the axial direction with respect to the casing30.

A wheel48is joined via bolts49to the end surface of the casing30away from the vehicle. A tire50of a forklift (not shown) is mounted to the wheel48. The reducer10is accommodated within an axial range of the tire50(within the range denoted by a dashed two dotted line ofFIG. 2).

A bearing nut56is screwed into the threaded portion formed on the outer circumferential surface of the second carrier body38. An inner race47C of the second main bearing47is in contact with the left end face of the bearing nut56, and an outer race47B of the second main bearing47is in contact with the recess30C of the casing30. An outer race46B of the first main bearing46is in contact with the recess30A of the casing30, and an inner race46C of first main bearing46is in contact with a shoulder part34E formed in the first carrier body34. As a result, axial movement of the casing30in which the first and second main bearings46and47are fitted is prevented by the bearing nut56.

By modifying the amount by which the bearing nut56is pushed when the second carrier body38, the casing30, and the main bearings46and47are assembled, the preload given to the main bearings46and47can be controlled.

A cover60covering the bearing nut from outside is attached by bolts62to the end face of the casing30further away from the vehicle than the bearing nut56.

An oil seal70for sealing the gap between the inner circumference of the casing30and the outer circumferential surface of the first carrier body34is provided more toward the interior of the vehicle than the first main bearing46. The oil seal70is fitted (press-fitted) into a recess30B formed on the inner circumference of the casing30such that a rip of the oil seal is contact with the outer circumferential surface of the first carrier body34.

The input shaft16(input member) of the reducer10is rotatably supported by the first carrier body34and the second carrier body38via a pair of angular contact ball bearings52and54in face-to-face arrangement. The angular contact ball bearings52and54have rolling elements52A and54A, and outer races52B and54B, respectively. However, the angular contact ball bearings do not have inner races. Instead, rolling surfaces52C and54C are formed in the input shaft16and function as inner races of the angular contact ball bearings. The above-described configuration is non-limiting, and separate inner races may be provided.

Referring toFIG. 2, axial movement of the angular contact ball bearing52located to the left of the externally-toothed gear24is prevented by a recess34D formed in the first carrier body34and the rolling surface52C of the input shaft16. Axial movement of the angular contact ball bearing54away from the vehicle is prevented by a recess38B formed in the second carrier body38and the rolling surface54C of the input shaft16. Therefore, axial movement of the input shaft16is prevented in both directions by the first carrier body34and the second carrier body38and so is positioned in the axial direction without play.

A description will now be given of the action of the wheel drive unit100.

The rotation of the output shaft of the motor (not shown) is transmitted to the input shaft16of the reducer10via the spline. When the input shaft16is rotated, the outer circumferences of the eccentric bodies18and20move eccentrically, causing the externally-toothed gears24and26to oscillate via the roller bearings21and23. The oscillation causes the positions of meshing between the outer teeth of the externally-toothed gears24,26and the internal gear pins28A,28B of the internally-toothed gear28, respectively, to be shifted successively.

The difference in the number of teeth between the externally-toothed gears24,26and the internally-toothed gear28is defined to be “1”. Further, the rotation of the externally-toothed gears24and26is prevented by the internal pins40fixed to the first carrier body34, which is fixed to the vehicle frame. Therefore, each time the input shaft16is rotated 360°, the internally-toothed gear28is rotated relative to the externally-toothed gears24and26, the rotation of which is prevented, by an angle defined by the difference in the number of teeth. As a result, the rotation of the input shaft16causes the casing30integrated with the internally-toothed gear body28D to be rotated at a rotational speed reduced by 1/(the number of teeth of the internally-toothed gear). The rotation of the casing30causes the tire50of the forklift to be rotated via the wheel48fixed to the casing30by the bolts49.

As described above, axial movement of the casing30of the wheel drive unit100according to the embodiment is prevented by the bearing nut56. When the inner race47C of the second main bearing47in such a structure is fitted to the second carrier body38so as to create a gap, if the bearing nut56becomes loose for some reason, the casing30might be moved axially outward with respect to the second carrier body38so as to be detached from the wheel drive unit.

This is prevented in the embodiment by allowing the first main bearing46and the oil seal70located opposite to the bearing nut56across the reducer10to function as a detachment prevention member for preventing detachment of the casing30. More specifically, the inner diameter of the outer race46B of the main bearing46fitted to the inner circumference of the casing30is configured to be smaller than the outer diameter (addendum circle) of the externally-toothed gear24and/or configuring the inner diameter of the oil seal70fitted to the inner circumference of the casing30to be smaller than the outer diameter of the externally-toothed gear24.

If the bearing nut56becomes loose and the function of preventing axial movement of the casing30is lost in this structure, contact between the outer race46B of the first main bearing46or the oil seal70with the externally-toothed gear24prevents further movement of the casing30away from the vehicle. Accordingly, detachment of the casing30is prevented.

The first main bearing may be implemented by a roller bearing of a structure in which a rolling element46A is press-fitted into the rail of the outer race46B. In this case, axial movement of the rolling element46A with respect to the outer race46B is prevented. Therefore, detachment of the casing30is prevented if the inner diameter of the rolling element46A is smaller than the outer diameter of the externally-toothed gear24. The first main bearing46may be a roller bearing instead of a ball bearing.

Further, in place of the first main bearing40and the oil seal70, or in addition to the first main bearing40and the oil seal70, an annular member dedicated to prevention of detachment may be engaged with the inner circumference of the casing30toward the interior of the vehicle so as to be adjacent to the bearing or the oil seal.

It is preferable that a distance L2between the outer race46B of the first main bearing46and the surface of the externally-toothed gear24axially adjacent to the outer race46B is smaller than a distance L1between the bearing nut56and the surface of the cover60axially adjacent to the bearing nut56. Normally, the bearing outer race and the externally-toothed gear are formed of a material harder than that of the bearing nut or the cover. For this reason, contact between the outer race46B and the externally-toothed gear24occurs before contact between the bearing nut56and the cover60, when the bearing nut56becomes loose and the casing30is moved away from the vehicle accordingly. Therefore, abrasion due to contact is reduced.

As described above, the wheel drive unit according to the embodiment including a casing to which a wheel is tightened is configured such that a detachment prevention member axially fixed with respect to the casing is provided on the inner circumference of the casing opposite to the bearing nut for preventing axial movement of the casing and across the planetary gear mechanism embodying the reducer. For this reason, even when the bearing nut positioned toward the exterior of the vehicle becomes loose, detachment of the casing is prevented due to contact of the detachment prevention member toward the interior of the vehicle with the externally-toothed gear of the reducer.

The planetary gear reducer for a wheel drive unit of eccentric oscillation and meshing type in which the input shaft (eccentric body shaft)16is provided at the center of the internally-toothed gear28is described by way of example. However, the reducer may not be of this type. For example, invention may be applied to wheel drive units provided with any type of planetary gear reducer (e.g., a planetary gear reducer of eccentric oscillation type in which a plurality of eccentric body shafts are arranged at positions offset from the center of the internally-toothed gear, or a planetary gear reducer of simple planetary type).

Control of preload on the angular contact ball bearing fitted to the input shaft is described by way of example. However, the bearing fitted to the power transmission shaft may not be an angular contact ball bearing but may be a bearing capable of supporting radial load or axial load, i.e., a bearing that requires application of a preload. For example, a taper-rolling bearing may serve the purpose.

A forklift is described by way of example of a utility vehicle driven by the wheel drive unit. However, the invention is applicable to any utility vehicle. For example, the invention is applicable to utility vehicles capable of carrying machinery for construction, civil engineering, or transportation.