Power-driven screwdriver with torque-dependent release clutch

Tool driving or impacting – Automatic control of power operated means – Drive means responsive to torque or speed condition

Reexamination Certificate

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Details

C173S048000, C192S150000

Reexamination Certificate

active

06173792

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a power-driven screwdriver comprising:
a housing;
an axially displaceable tool drive shaft, mounted rotatably in the housing, that is mounted at a first end in the housing and at its second end has a receptacle for a tool;
a motor-driven drive gear, mounted rotatably on the tool drive shaft, that on the housing side is secured against axial displacement;
a cam ring that is axially immobilized on the tool drive shaft and is secured against axial displacements outward;
a spring element in order to preload the tool drive shaft outward toward the receptacle;
first clutch elements on the drive gear;
second clutch elements on the cam ring that coact with the first clutch elements in order to constitute a torque-dependent release clutch; and
an adjusting device for axial adjustment of the tool drive shaft.
Screwdrivers of this kind, having an adjustable, torque-dependent shutoff clutch that generally has mutually coacting cam elements with oblique flanks, have been common for years.
An example of one such screwdriver is represented by the screwdriver marketed under the designation “ASse639” (cf. general catalog of the Applicant, “Fein Hochleistungs-Elektrowerkzeuge” 1995/96, pages 78, 79, 224).
In many situations it is desirable in this context to make the torque-dependent shutoff clutch nonfunctional, for example if the screwdriver is to be used for drilling. For this purpose, it is known to clamp the two clutch elements, which have cams with oblique entraining flanks, to one another so that torque-dependent release is prevented. This situation is referred to as “rigid through drive.”
The disadvantage of a configuration of this kind is that because of the oblique cams, very large axial forces occur and must be absorbed by the bearings.
Although a variety of solutions are known in the existing art for rigidly coupling a drive shaft and an output shaft to one another (cf. U.S. Pat. Nos. 5,016,501, 3,243,023, and EP-A-0 792 723), coupling mechanisms of this kind are of complex construction and are poorly suited for use in a simple screwdriver with a torque-dependent release clutch (single-claw clutch).
SUMMARY OF THE INVENTION
It is therefore a first object of the invention to disclose an improved screwdriver comprising a clutch that releases in torque-dependent fashion and which can be selectively made nonfunctional so that rigid through drive is achieved.
It is a second object of the invention to disclose an improved power-driven screwdriver having a torque-dependent release clutch and being of simple design and of reliable construction.
According to the present invention these and other objects are achieved, in the case of a screwdriver of the kind cited initially, in that first entrainment elements, which coact with second entrainment elements on the cam gear for positive power transfer, are provided on the drive gear; and that the adjusting device allows an axial adjustment of the tool drive shaft in such a way that in a first position the first and second entrainment elements are in positive engagement with one another, and in a second position the entrainment elements are out of engagement, while the clutch elements are in engagement with one another.
These objects of the invention are completely achieved in this fashion.
The use of additional entrainment elements on the drive gear and on the cam ring brings about, in simple fashion, a positive power transfer from the drive gear to the cam ring and thus to the tool drive shaft; for switchover, the adjusting device that is present in any case is used for axial adjustment of the tool drive shaft, so that in a first position the entrainment elements on the drive gear and on the cam ring are in positive engagement with one another, and in a second, axially displaced position of the tool drive shaft, only the clutch elements are in engagement with one another, so that the release clutch can release in torque-dependent fashion.
The result is to achieve, with simple means, a particularly reliable capability for switching between torque-dependent shutoff and rigid through drive, the disadvantages of the existing art, such as high axial forces, being avoided.
According to a further embodiment of the invention, the clutch elements and the entrainment elements are arranged on the respectively facing sides of the drive gear.
This results in a particular simple configuration.
According to an advantageous development of the invention, the clutch elements are out of engagement in the first position.
This feature ensures that when the screwdriver is set to the first position (rigid through drive), the clutch elements are out of engagement and thus also cannot exert any further axial forces. This simplifies the construction and relieves loads on the bearings.
In an additional development of the invention, the clutch elements are configured as cam elements with oblique flanks.
This results in a particularly simple construction of the mutually coacting clutch elements. Alternatively, however, it would also be conceivable to provide, for example, curved entrainment flanks on one clutch half that coact with suitable entrainment elements, e.g. a straight pin, on the other clutch half.
In an additional development of the invention, the entrainment elements are configured as claw elements with straight flanks axially parallel to the rotation axis.
This ensures a particularly simple construction of the entrainment elements.
According to a further embodiment of the invention, at least two, preferably three, first clutch elements are arranged on the drive gear at uniform angular distances from one another; and at least two, preferably three, first entrainment elements are arranged on the drive gear at uniform angular distances from one another, and associated therewith are respective correspondingly arranged and shaped second clutch elements and entrainment elements on the cam ring, the first and second entrainment elements each extending over an angle at center that is greater than the angle at center over which the clutch elements extend.
This guarantees, with simple means, that in the first position (rigid through drive), the clutch elements are nonfunctional and thus cannot exert any axial forces. At the same time, the result is that the first and second entrainment elements are nonfunctional in the second position (torque-dependent shutoff).
With this embodiment, the first and second clutch elements are preferably constructed so that when viewed in the axial direction, they have a height greater than the height of the first and second entrainment elements.
In an additional development of this embodiment, the clutch elements are arranged on a circle that is offset concentrically outward with respect to the entrainment elements, each clutch element preferably being associated with an entrainment element in a radially outwardly offset position.
These features make possible a particularly stable construction of the clutch elements and entrainment elements, and allow the clutch elements to be designed generously, since the latter can transfer greater forces because of the radially outwardly offset position. Another result achieved is that minimal wear phenomena occur, even in continuous operation.
According to a further feature of the invention, the adjusting device comprises an adjusting sleeve that is guided on the housing adjustably in the axial direction by way of threads; a snap ring that is rotatable with respect to the housing and can be immobilized in snap-lock fashion in various angular positions is immobilized on the adjusting sleeve in axially displaceable fashion and nonrotatably with respect to the latter.
It is thereby possible to achieve easy adjustment of the release torque of the release clutch that is to release in torque-dependent fashion, and to combine that with a corresponding adjustment in order to ensure rigid through drive.
In an additional development of the invention, an axial bearing that is supported on the housing via a resilient element, preferably via an O-ring,

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