This application claims priority of German patent application no. 10 2010 012 748.5, filed Mar. 25, 2010, the entire content of which is incorporated herein by reference.
Handheld chain saws include a saw chain which revolves around the periphery of a guide bar. To drive the saw chain, a sprocket wheel having an externally toothed gear, which is driven by a drive motor, is provided. The external teeth of the sprocket wheel engage between the members of the saw chain and drive them.
The drive shaft of the sprocket wheel is mounted in a housing of the chain saw. A sprocket wheel cover which covers the area of the sprocket wheel is threadably engaged with the housing. At least one stud, which in its mounted state is guided through an opening of the sprocket wheel cover, is fixed to the housing for the threaded fastening. A nut is screwed onto a free thread end of the stud and presses the sprocket wheel cover against the housing.
The guide bar of the saw chain is strung onto the stud, of which there is at least one, and is held clamped between the housing and the sprocket wheel cover. The sprocket wheel cover also has a holding function for the guide bar aside from its protective function.
The sprocket wheel cover is removed for maintenance work on the guide bar or the saw chain or for changing the same components, and also for the space-saving storing of the chain saw; the guide bar including the saw chain can be removed or exchanged. For assembly, first the guide bar is strung onto the at least one stud and then the sprocket wheel cover is attached in such a manner that the at least one stud projects through the opening in the sprocket wheel cover. For completion of assembly, the nut is threaded onto the free thread portion of the stud and tightened. The free thread end of the stud has a maximum usable screw-in depth for the nut. The tightened nut is threadably engaged with an operating screw-in depth that is smaller than the maximum screw-in depth, so that a sufficient tolerance in the tightening direction of the nut remains for the effective tightening without damaging the arrangement.
If the guide bar is removed for extended periods of time, for example for transport or maintenance work, the sprocket wheel cover is re-applied and screwed on even without the guide bar. Thus, it is ensured that the sprocket wheel cover remains on the chain saw. Thus, the sprocket wheel cover will be handy during any later assembly and cannot get lost. In practice, however, it turns out that the at least one nut for fixing the sprocket wheel cover is often pulled too tight when the guide bar is removed. As a result, the sprocket wheel cover and the nut may tilt and become damaged. Depending on the configuration of the arrangement, the actual screw-in depth can exceed the permissible maximum screw-in depth, so that the result can be damage done to the threads on the studs and on the nuts. It is even possible that the studs are ripped out of their anchoring in the housing.
It is an object of the invention to provide a chain saw of the type described above wherein the sprocket wheel cover can also be applied and screwed down without any danger of overstressing the arrangement when the guide bar has been removed.
The chain saw of the invention includes: a guide bar for a saw chain; a housing; a sprocket wheel cover; at least one stud fixed to the housing configured for threadably fastening the sprocket wheel cover to the housing with the guide bar clamped between the sprocket wheel cover and the housing; the stud having a free threaded end; a nut configured to threadably engage the free threaded end of the stud; the free threaded end having a maximum usable screw-in depth (tmax) for the nut; a stop for the sprocket wheel cover; the stop having a stop surface; a support surface for contact engaging the stop surface; the stop surface being at a distance (a) to the support surface when the guide bar and the sprocket wheel cover are mounted and the nut is tightened; the support surface contact engaging the stop surface of the stop when the guide bar is removed and the nut is tightened and threadably engaging the stud to a stop screw-in depth (t2); and, the stop being so configured that the maximum usable screw-in depth (tmax) is greater than the stop screw-in depth (t2).
It is suggested to provide a stop for the sprocket wheel cover having a stop surface as well as a support surface for contact engaging the stop surface. In the assembled state of the guide bar and the sprocket wheel cover, a distance remains between the stop surface and the support surface when the nut is tightened. The support surface contacts the stop surface of the stop when the guide bar is missing and the nut is tightened, and thus the nut is screwed onto the stud with a stop screw-in depth. The stop is configured such that the maximum usable screw-in depth is larger than the screw-in depth of the stop.
The distance between the stop and the support surface ensures that the stop has no effect when the guide bar is mounted and the at least one nut can be screwed onto the stud and tightened to such an extent that the guide bar is reliably held clamped between the sprocket wheel cover and the housing. When the guide bar is missing, the nut screwed on tightens the sprocket wheel cover to such an extent that the support surface contacts the stop surface of the stop. The stop is configured in such a manner that the sprocket wheel cover does not tilt and sustain damage here. The nut does not tilt either. The stop further prevents the nut from being screwed down beyond the maximum permissible screw-in depth or the maximum usable screw-in depth. In fact, the maximum usable screw-in depth is larger than the stop screw-in depth, so that the studs and the nut including their outer and inner threads remain undamaged.
In a preferred embodiment of the invention, the stop has a stop surface and the sprocket wheel cover has a support surface corresponding to the stop surface. The stop surface and the support surface are at least approximately perpendicular to a longitudinal axis of the stud. The perpendicular alignment leads to contact forces acting exclusively in parallel to the longitudinal axis of the stud without any directional components transversely thereto. The sprocket wheel cover and the arrangement collectively remain free from transverse forces, so that the sprocket wheel cover does not slide sideways and remains tilt-free upon tightening of the sprocket wheel cover.
The stop is preferably formed by a screw head. It can be expedient to arrange the stop on the sprocket wheel cover or on another component of the chain saw. In an advantageous alternate embodiment, the stop is arranged on the housing and in particular is formed by the head of that screw via which a side plate is fixed as a support for the guide bar. The construction is simple and effective in structure. By using the fixing screw of the side plate also as a stop, the former has a double function, so that additional components can be avoided along with any additional costs associated therewith.
In an advantageous embodiment, the guide bar has an opening which the stop projects into in the mounted state of the guide bar. Thus, it is ensured that the guide bar does not collide with the stop when in the mounted state. Any incorrect Mounting of the guide bar is avoided. At the same time, it is ensured that the stop remains without effect in the desired way when the guide bar is mounted and has the desired effect only when the guide bar is missing.
It has been shown to be practical that the distance between the stop surface and the support surface in the mounted state of the guide bar is at least 0.2 mm and advantageously is 2.0 mm at maximum. The minimum distance ensures that even when dirt is accumulated during operation and when the guide bar is mounted there is no interaction between the stop and the sprocket wheel cover, so that a reliable clamping is ensured. Limiting the maximum distance means the sprocket wheel cover cannot be stressed or overly stressed when the guide bar is missing.
In a preferred embodiment, the tightened nut is threadably engaged with an operating screw-in depth when the guide bar and sprocket wheel cover are in the mounted state. The maximum usable screw-in depth is at least 1.5 mm larger than the operating screw-in depth. Thus, a sufficient tolerance remains in the screw-in direction by means of which the guide bar can be reliably clamped without damaging the inner or outer threads of the screw connection.
The nut is expediently a collar nut that is captive, rotatable, and held with play in an opening of the sprocket wheel cover. When placing the sprocket wheel cover, the nut is on-the-spot and cannot get lost. When the guide bar is mounted or missing, the nut is brought directly to the location of the screw connection upon placement of the sprocket wheel cover and can be screwed on without being damaged or stressed.
The invention will now be described with reference to the drawings wherein:
The drive motor drives a sprocket wheel, not shown, whose external teeth engage between the links of the saw chain 2 and thus set the saw chain 2 in motion. The sprocket wheel and a section of the guide bar 1 adjacent to the sprocket wheel are covered by the sprocket wheel cover 4. At least one stud, here two studs 5, are fixed to the housing 3. Respective nuts 6 threadably engage the studs 5 on the exterior side 19 of the sprocket wheel cover 4. The nuts 6 press the sprocket wheel cover 4 against the housing 3, with the guide bar 1 being clamped and fixed between the sprocket wheel cover 4 and the housing 3.
A portion of the housing 3 is a side plate 15 made of steel plate which can be fixed on a plastic base body of the housing 3 via a screw 13. An adjusting screw 20 for a chain tensioner, not shown in detail, is arranged between the two studs 5. The studs 5 and the adjusting screw 20 are guided through corresponding openings of the side plate 15. In the assembled state, the guide bar 1 is clampingly pressed against the side plate 15 of the housing 3 by the sprocket wheel cover 4.
On its end facing the bearing opening 25, the guide bar has a slot-shaped opening 16 extending in the direction of the longitudinal axis of the guide bar 1. In the assembled state, the two studs 5 pass through the slot-shaped opening 16 and allow for a longitudinal displaceability of the guide bar 1 in the direction of its longitudinal axis when the nuts are loosened.
The studs 5 have an annularly peripheral thickened part 23, whose diameter is larger than the diameter of the free thread ends 7, adjacent to the side plate 15. The diameter of the thickened parts 23 corresponds to the diameter inside of the slot-shaped opening 16, so that when the guide bar is mounted, the thickened parts 23 come to rest at least approximately free of play in the slot-shaped opening 16. Hereby, the guide bar 1 is fixed in a precise position relative to the housing 3. Only a single degree of freedom of movement remains for the guide bar 1 relative to the housing 3, namely in the longitudinal direction of the guide bar 1 for setting the chain tension.
The guide bar 1 is provided with a bore 21 above the slot-shaped opening 16 and a bore 21 below the slot-shaped opening 16. In the assembled state, a pin (not shown) of the chain tensioner (not shown either) engages in the lower bore 21. By actuating the chain tensioner via the adjusting screw 20, the guide bar 1 can be displaced in the direction of its longitudinal axis and thereby be adjusted to such an extent that the desired tension in the saw chain 2 (
Nevertheless, the head 14 of the screw 13, that is, its free abutting face forms a stop surface 10 while a support surface 11 is formed opposite thereto on the sprocket wheel cover 4. The stop surface 10 of the stop 9 and the corresponding support surface 11 of the sprocket wheel cover 4 are arranged perpendicularly to the longitudinal axes 12 of the studs 5 and are positioned relative to one another at the aforementioned distance (a). Their function and effect will be described below in relation to
From
The two nuts 6 are screwed onto the thread ends 7 of the two studs with an operating screw-in depth t1 to such an extent that the front cover edge 27 rests against the outer side surface of the guide bar 1 and thereby presses the guide bar 1 against the housing 3, that is, against its side plate 15. The operating screw-in depth t1 is measured from the outermost end of the studs 5 up to the housing-side end of the two nuts 6, here up to the housing-side edge of the corresponding collar 24. The maximum usable screw-in depth tmax is larger than the operating screw-in depth t1, preferably being at least 1.5 mm larger than the operating screw-in depth t1. This ensures that there is no collision between the nut 6, that is, its collar 24, and the thickened part 23 of the corresponding stud 5. Furthermore, when the guide bar 1 and the sprocket wheel cover 4 are mounted, the distance (a) between the stop surface 10 and the support surface 11 is advantageously at least 0.2 mm and expediently at most 2.0 mm.
In the embodiment according to
In the shown embodiment, the stop 9 with its stop surface 10 is formed by a screw screwed into the sprocket wheel cover 4. Of course, other configurations can also be considered in which a differently configured stop 9, for example, in the form of an integrally formed part of the sprocket wheel cover 4 or the like, for example, in the form of a nose, a pin, or the like is provided. As an example, here the support surface 11 is formed by the surface of the side plate 15 which is arranged on the housing; however, it can also be provided by another surface associated with the housing 3.
Just like in the embodiment of
It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
Number | Date | Country | Kind |
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10 2010 012 748 | Mar 2010 | DE | national |
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Number | Date | Country | |
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20110232110 A1 | Sep 2011 | US |