Machine element or mechanism – Gearing – Directly cooperating gears
Reexamination Certificate
1999-06-08
2001-01-09
Wright, Dirk (Department: 3681)
Machine element or mechanism
Gearing
Directly cooperating gears
Reexamination Certificate
active
06170350
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to speed gear reducer drive assemblies and, more particularly, to a novel gear reducer assembly for use on the boom of aerial lift trucks. The novel assembly includes a primary worm gear set and a secondary spur gear set mounted within a common one-piece housing.
In aerial lift trucks, a top boom plate is rotatably mounted with respect to a lower truck plate by way of an intermediate turntable bearing. The top boom plate is connected to the inner race of the turntable bearing and the outer race is fixed to the truck plate. Currently, there are two drive configurations used in the market place for rotating the boom plate on aerial lift trucks. Each of those has distinct drawbacks. In one drive configuration, a gear reducer is externally mounted on the top boom plate and includes a drive spur pinion which extends downwardly through the boom plate and drivingly engages spur gear teeth formed on the external face of the large diameter outer race of the turntable bearing. This type of drive assembly encounters a number of problems. For example, the top surface of the boom plate must be machined to accommodate a mounting plate for the reducer. The overhung drive pinion often causes misalignment and uneven wear on both the pinion and the turntable bearing, and holding the reducer down to resist rotation requires the use of jack bolts.
Another drive configuration, known as a swing drive, includes a worm gear reducer mounted directly between the boom plate and the truck plate, the
Another drive configuration, known as a swing drive, includes a worm gear reducer mounted directly between the boom plate and the truck plate, the worm engaging against a helical gear formation on the external surface of the outer race of the turntable bearing. This configuration is substantially less expensive than the externally mounted reducer, but suffers from low torque rating, poor life due to point contact between the worm and turntable bearing, causing high wear on the turntable bearing due to high contact stresses. In addition, performance problems such as backlash and “slip sticking” occur when turning down a slope due to high friction and loads bearing on the conventional steel worm and steel helical gear.
The combined spur/worm swing drive assembly of the invention was developed to overcome those problems.
SUMMARY OF THE INVENTION
Accordingly, the primary object of this invention is to provide a novel spur/worm swing drive assembly particularly useful for rotating the boom on aerial lift trucks, the drive assembly being significantly cheaper to produce than the conventional externally mounted reducer while at the same time delivering much higher output than the conventional worm swing drive. The unique drive assembly provides an attractive choice for large swing drive applications experiencing performance problems and also for smaller reducer applications where cost is a concern.
The novel drive assembly of the invention accomplishes its objectives by providing a primary worm gear reduction set driving a secondary spur gear reduction set which includes a spur pinion rotating against spur teeth formed on the external surface of the large diameter outer race of the turntable bearing which is fixed to the truck plate. The primary worm gear set and the secondary spur gear set are assembled within a common, one-piece support and the entire assembly is readily positioned and supported in the space between the top boom plate and the lower truck plate. This assembly affords a number of advantages. For example, the amount of machining required on mounting surfaces is substantially reduced. The spur pinion does not overhang from the boom plate, but rather is mounted on a common shaft with the worm gear and the shaft is supported at its upper and lower ends within bearings. Thus, there is no misalignment or uneven wear between the spur pinion and the spur gear teeth formed on the outer race of the turntable bearing. The line contact between the spur pinion and the spur gear formed on the turntable bearing reduces wear between those mating parts. In the primary worm gear set, the worm is constructed from steel and the worm gear is bronze, thus eliminating slip stick.
The one-piece support member of the invention acts as a mounting surface on the turntable bearing and also as the housing for the worm gear, the worm, and the spur pinion. This eliminates any chance of lateral movement between the spur pinion and the gear teeth on the outer race of the turntable bearing during operation of the gear reducer. The worm of the primary set has one end connected to an hydraulic drive motor and has a hex extension at its opposite end to allow for manual operation of the worm gear set if necessary.
To facilitate assembly with the truck and boom plates, the combined worm/spur reducer unit and its hydraulic motor drive can be pre-assembled in the one-piece member and then fastened on the inner race of the turntable bearing, the outer race of which is already bolted to the truck plate or bed. The boom plate is then placed on the top surface of the housing of the unit and bolted down to the housing and the inner race.
Other objects and advantages of the invention will become apparent from reading the following detailed description of the invention wherein reference is made to the accompanying drawings.
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Worm box swing drive.
Worm swing drive.
Perfection Gear, Inc.
Tamburro David A.
Wright Dirk
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