Chain saw

A chain saw includes a guide bar for a saw chain, a housing, a sprocket wheel cover, and a stud fixed on the housing for threadably fastening the sprocket wheel cover and the guide bar. The free thread end of the stud has a maximum usable screw-in depth (tmax) for a nut. A stop for the sprocket wheel cover having a stop surface as well as a support surface for contact engaging the stop surface are provided. In the mounted state of the guide bar, a distance (a) remains between the stop surface and the support surface. The support surface contact engages the stop surface when the guide bar is removed and the nut is tightened and screwed onto the studs to a stop screw-in depth. The stop is configured in such a manner that the maximum usable screw-in depth (tmax) is greater than the stop screw-in depth.

CROSS REFERENCE TO RELATED APPLICATION

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.

BACKGROUND OF THE INVENTION

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.

SUMMARY OF THE INVENTION

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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1shows a handheld, motor-driven chain saw. The chain saw includes a housing3in which a drive motor, not shown, is arranged. In the shown embodiment, the drive motor is a two-stroke combustion engine but can also be a four-stroke engine. An electric motor can also be provided in place of the combustion engine. A guide bar1protruding forwards from the housing3, in relation to the usual operating position, is arranged laterally of the housing3. A saw chain2driven by the drive motor is circulatingly guided about the outer edge of the guide bar1. A front handle17is arranged toward the center above the housing3. A back handle18is provided on the rear end of the housing3which is opposite to the guide bar1. The chain saw is carried and guided by hand via the handles (17,18) during operation.

The drive motor drives a sprocket wheel, not shown, whose external teeth engage between the links of the saw chain2and thus set the saw chain2in motion. The sprocket wheel and a section of the guide bar1adjacent to the sprocket wheel are covered by the sprocket wheel cover4. At least one stud, here two studs5, are fixed to the housing3. Respective nuts6threadably engage the studs5on the exterior side19of the sprocket wheel cover4. The nuts6press the sprocket wheel cover4against the housing3, with the guide bar1being clamped and fixed between the sprocket wheel cover4and the housing3.

FIG. 2shows an exploded view of the arrangement ofFIG. 1in the region of the sprocket wheel cover4.FIG. 3shows a longitudinal section of the arrangement ofFIG. 2in the assembled state.FIGS. 2 and 3viewed in combination show that the housing.3has a bearing opening25through which a drive shaft, not shown, together with a sprocket wheel, not shown either, is passed through in the assembled state. Two studs5are fixed to the housing3towards the front in the direction of the guide bar1, as viewed from the bearing opening25. The two studs5are guided through openings8in the side wall of the sprocket wheel cover4to the exterior side19thereof, and each have free thread ends7on their ends facing the exterior side19of the sprocket wheel cover4on which the nuts6are screwed onto. According toFIG. 4, the nuts6are captive, rotatable, and designed as collar nuts having a collar24, which nuts are held with play in the opening8of the sprocket wheel cover4. The collar24is beaded radially outwardly at its end facing the housing3, so that the nuts6cannot fall out of the opening8.

A portion of the housing3is a side plate15made of steel plate which can be fixed on a plastic base body of the housing3via a screw13. An adjusting screw20for a chain tensioner, not shown in detail, is arranged between the two studs5. The studs5and the adjusting screw20are guided through corresponding openings of the side plate15. In the assembled state, the guide bar1is clampingly pressed against the side plate15of the housing3by the sprocket wheel cover4.FIG. 3shows that the sprocket wheel cover4has a back cover edge26, which is opposite the two studs5in the longitudinal direction, and a front cover edge27adjacent to the two front studs5. When the nuts6are tightened, the sprocket wheel cover4is pressed against the housing3with its back cover edge26and is pressed against the guide bar1with its front cover edge27. Thus, the guide bar1is pressed against the housing3and is clampingly held thereby.

On its end facing the bearing opening25, the guide bar has a slot-shaped opening16extending in the direction of the longitudinal axis of the guide bar1. In the assembled state, the two studs5pass through the slot-shaped opening16and allow for a longitudinal displaceability of the guide bar1in the direction of its longitudinal axis when the nuts are loosened.

The studs5have an annularly peripheral thickened part23, whose diameter is larger than the diameter of the free thread ends7, adjacent to the side plate15. The diameter of the thickened parts23corresponds to the diameter inside of the slot-shaped opening16, so that when the guide bar is mounted, the thickened parts23come to rest at least approximately free of play in the slot-shaped opening16. Hereby, the guide bar1is fixed in a precise position relative to the housing3. Only a single degree of freedom of movement remains for the guide bar1relative to the housing3, namely in the longitudinal direction of the guide bar1for setting the chain tension.

The guide bar1is provided with a bore21above the slot-shaped opening16and a bore21below the slot-shaped opening16. In the assembled state, a pin (not shown) of the chain tensioner (not shown either) engages in the lower bore21. By actuating the chain tensioner via the adjusting screw20, the guide bar1can be displaced in the direction of its longitudinal axis and thereby be adjusted to such an extent that the desired tension in the saw chain2(FIG. 1) is set when the sprocket wheel cover4is at least partially loosened or the nut6is at least partially loosened. After completely loosening the nut6, the sprocket wheel cover4can be removed from the housing3, which enables a disassembly and/or changing of the guide bar1or a changing of the saw chain2(FIG. 1).

FIG. 4shows an enlarged view of the arrangement ofFIG. 3in the region of the studs5. According to the invention, a stop9is provided for the sprocket wheel cover4. The stop9is arranged and fixed to the housing3in the embodiment ofFIG. 4. For this, different appropriate configurations can be considered, for example, a one-piece nose or the like integrally formed on the housing3. In the shown embodiment, the stop9is formed by the head14of a screw. For this, a separate screw screwed into the housing3can be provided. According toFIG. 4, the head14of that screw13, via which the side plate15is screwed on the base body of the housing3, is provided as the stop9. When the guide bar1is mounted, the head14projects into the slot-shaped opening16of the guide bar1without protruding beyond the guide bar1on the side of the sprocket wheel cover4. Moreover, the height of the head14is less than the thickness of the guide bar1, so that a distance (a) remains between the head14and the sprocket wheel cover4when the guide bar1is mounted. When the guide bar1and the sprocket wheel cover4are mounted there is no interaction between the stop9and the sprocket wheel cover4.

Nevertheless, the head14of the screw13, that is, its free abutting face forms a stop surface10while a support surface11is formed opposite thereto on the sprocket wheel cover4. The stop surface10of the stop9and the corresponding support surface11of the sprocket wheel cover4are arranged perpendicularly to the longitudinal axes12of the studs5and are positioned relative to one another at the aforementioned distance (a). Their function and effect will be described below in relation toFIG. 6.

FromFIG. 4it can be seen that a thread-free section28is optionally provided between the free thread end7and the thickened part23of the individual studs5. The diameter of the thread-free section28is smaller than the outer diameter of the free thread end7to at least such an extent that the nut6can be screwed onto the thickened part23beyond the free thread end7. Of course, it is also possible that the free thread end7continuously extends from the outermost end of the stud5to the thickened part23. The lengths of the free thread end7and the optional thread-free section28predetermine a maximum usable screw-in depth tmaxfor the nut6, starting from the outer end of the stud5up to the thickened part23.

The two nuts6are screwed onto the thread ends7of the two studs with an operating screw-in depth t1to such an extent that the front cover edge27rests against the outer side surface of the guide bar1and thereby presses the guide bar1against the housing3, that is, against its side plate15. The operating screw-in depth t1is measured from the outermost end of the studs5up to the housing-side end of the two nuts6, here up to the housing-side edge of the corresponding collar24. The maximum usable screw-in depth tmaxis 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 nut6, that is, its collar24, and the thickened part23of the corresponding stud5. Furthermore, when the guide bar1and the sprocket wheel cover4are mounted, the distance (a) between the stop surface10and the support surface11is advantageously at least 0.2 mm and expediently at most 2.0 mm.

FIG. 5shows a variant of the arrangement ofFIG. 4with the guide bar1(FIG. 3) removed but with the sprocket wheel cover4applied and screwed-on in a configuration according to the state of the art with no stop9(FIG. 4). If, in accordance withFIG. 5, the guide bar1shown inFIG. 3is not mounted, the nuts6can be screwed onto the studs5to such an extent that the front cover edge27comes to rest on the housing3, that is, on the side plate15. Hereby, the sprocket wheel cover4performs a pivot-motion about its back cover edge26(FIG. 3), which also rests on the housing3, and the sprocket wheel cover4is thus tilted and tensioned relative to its operating position according toFIG. 3. This also applies to the nut6, shown in tilted position, which leads to damage done to the sprocket wheel cover4and its screw connection.

In the embodiment according toFIG. 5, the two nuts6are screwed onto the corresponding studs5by an impermissible screw-in depth t3to such an extent that the front cover edge27rests against the housing3, that is, the side plate15. The impermissible screw-in depth t3is larger than the maximum usable and thus permissible screw-in depth tmax. As a result, the nuts6with their portions facing the housing3, here with their corresponding collars24, shown in broken lines, collide with each of the corresponding thickened parts23of the two studs5. The impermissible screw-in depth t3is measured from the outermost end of the corresponding stud5up to the housing-side end of the nut6, here up to the housing-side edge of the collar24. The nuts6and the studs5, that is, their inner and outer threads, can be damaged because of the collision with the thickened part23. Furthermore, the studs5can be loosened in their mounting on the housing3or even be ripped out.

FIG. 6shows an embodiment of the invention according toFIG. 4, with the guide bar1being removed, the sprocket wheel cover4screwed onto the housing3and the nuts6tightened. Departing from the state of the art according toFIG. 5, the front cover edge27lies at a distance to the housing3, that is, to its side plate15. In fact, the sprocket wheel cover4is pressed against the stop surface10of the stop9with its support surface11due to the effect of the tightened nuts6. Relative to their operating screw-in depth t1, the two nuts6are further screwed onto the studs5by distance (a) (FIG. 4) so that a stop screw-in depth t2results. The stop9is configured such that the maximum usable or permissible screw-in depth tmaxis larger than the stop screw-in depth t2. This results in particular from the borders to distance (a), described above in relation toFIG. 4, and to the difference between the maximum usable screw-in depth tmaxand the operating screw-in depth t1. It is ensured that the nuts6, that is their collars24, have a sufficient axial distance from the corresponding thickened part23of the studs5, so that no damage can be done to the nuts6and the studs5including their inner or outer threads and including the collar24or the thickened part23. Because of the large free distance between the front cover edge27of the sprocket wheel cover4and the housing3, the sprocket wheel cover4is only minimally tilted in its operating position according toFIG. 3as compared to the state of the art according toFIG. 5so that no technically relevant tilting or tensioning will result on the sprocket wheel cover4, the housing3, the studs5or the nuts6.

FIG. 7shows a variant of the arrangement ofFIG. 4. In deviation from the embodiment according toFIGS. 1 to 4and6, the stop9is not arranged or fixed on the housing3but on the sprocket wheel cover4. Vice versa, the support surface11, which is provided to rest on the stop surface10of the stop9, is not arranged on the sprocket wheel cover4but on the opposite lying housing3.

In the shown embodiment, the stop9with its stop surface10is formed by a screw screwed into the sprocket wheel cover4. Of course, other configurations can also be considered in which a differently configured stop9, for example, in the form of an integrally formed part of the sprocket wheel cover4or the like, for example, in the form of a nose, a pin, or the like is provided. As an example, here the support surface11is formed by the surface of the side plate15which is arranged on the housing; however, it can also be provided by another surface associated with the housing3.

Just like in the embodiment ofFIG. 4, the support surface11lies at a distance (a) to the stop surface10of the stop9when the guide bar1is mounted, the sprocket wheel cover4is mounted and the nuts6are tightened. If analogously toFIG. 6the guide bar1is removed and the sprocket wheel cover4is screwed on, the support surface11and the stop surface10will contact one another, that is, rest against one another, thus resulting in the same conditions as described in relation toFIG. 6. The other features and reference characters in the embodiment ofFIG. 7are the same as those in the embodiments according toFIGS. 1 to 4and6.