Adjustable gearhead for a hedge trimmer attachment

Details Adjustable gearhead for a hedge trimmer attachment Adjustable gearhead for a hedge trimmer attachment

1998-12-02

2001-02-27

Bucci, David A. (Department: 3682)

Machine element or mechanism

Gearing

Adjustable

C074S025000, C074S423000, C056S233000, C030S199000, C030S208000

Reexamination Certificate

active

06192769

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a gearhead assembly of a drive shaft and a output shaft, especially of a hedge trimmer attachment for a trimmer, in which the output shaft is arranged in a second housing part and is positioned laterally displaced to the drive shaft positioned in a first housing part. A central gear is positioned between the drive shaft and the output shaft and is secured on a bearing shaft extending perpendicularly to the drive shaft and the output shaft. The bearing shaft is positioned with one end in the first housing part and with the other end in the second housing part. The second housing part together with the output shaft is pivotable in a plane parallel to the drive shaft relative to the first housing part about the bearing shaft.
Such a gear head assembly is known from German Patent Application 41 16 885. The drive shaft is supported in a first housing part which is connectable to the free end of the guide tube of a trimmer. At the first housing part a second housing part is rotatably secured which houses the output shaft. A central gear wheel is provided in the housing between the drive shaft and the output shaft which is secured on a transversely extending bearing shaft secured with one end in the first housing part and with the other end in the second housing part. The bearing shaft intercepts at a right angle the imaginary axes of rotation of the drive shaft and the output shaft whereby the second housing part with the output shaft is pivotable relative to the first housing part about the bearing shaft in a plane which extends parallel to the drive shaft. For securing respective pivot positions, a catch device is provided between the first housing part and the second housing part. The catch device is embodied as a toothed catch curve which cooperates with a matching multi-tooth catch lever. One problem of such a catch device is that play usually results between the catch lever and the catch curve which may result in shaking and knocking of the tool resulting from the drive moments acting on the gearhead. Especially in the case of an adjustable gearhead (in connection with a hedge trimmer attachment) arranged at the lower end of a long guide tube of a trimmer such shaking movements resulting from the drive moments are very disruptive and prevent a fatigue-free, precise guiding of the tool.
It is therefore an object of the present invention to embody a gearhead assembly of the aforementioned kind such that without great constructive expenditure a substantially play-free locking of the adjustable housing parts to one another is possible.
SUMMARY OF THE INVENTION
According to the present invention, the bearing shaft is embodied as a hub and the hub is penetrated by the clamping shaft of a clamping device, whereby the clamping shaft with its ends engages the two housing parts.
The arrangement of a clamping device coaxially to the pivot axis allows for a force-locking connection of the adjustable housing parts. This ensures that drive moments are securely supported, and vibrations, knocking, etc. of the tool are prevented. The clamping device may be adjustable such that for adjusting the clamping force can be significantly reduced or even canceled. When a predetermined clamping force is fixedly adjusted, it is selected such that it can be overcome upon movement of one housing part by the required adjusting force with acceptable force expenditure.
In order to ensure, manufacturing tolerances, a safe engagement of the drive shaft and the output shaft connected by the central gear, it is suggested that the central gear is comprised of two bevel gears that are connected to one another such that they rotate with one another whereby one bevel gear has an elongate hub extension which engages the other bevel gear so as to rotate therewith. One of the bevel gears is axially moveable relative to the other so that possible axis spacing tolerances can be easily compensated. Expediently, between the bevel gears a spring, especially a coil spring, is arranged with which in any pivot position, independent of possibly present manufacturing tolerances, a complete engagement of the central gear at the drive shaft and the output shaft is ensured.
In order to prevent an axial movement of the gearhead assembly for great force expenditure on the tool, in addition to the force-locking clamping by a clamping device which penetrates the bearing shaft of the central gear, a mechanical form-locking (positive-locking) catch device is provided between the housing parts. The catch device can be comprised of a catch curve having catch openings and of a catch pin that is radially moveable relative to the catch curve.


REFERENCES:
patent: 511966 (1894-01-01), Olsen
patent: 558973 (1896-01-01), Milliken
patent: 1839009 (1931-12-01), Bankson
patent: 1857342 (1932-05-01), Albrecht
patent: 1937586 (1933-12-01), Ortt
patent: 5079841 (1992-01-01), Ohkanda et al.
patent: 5165720 (1992-11-01), Hoblingre
patent: 4116885 (1991-12-01), None

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