Patent ID: 12214518

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG.1illustrates a handheld chainsaw10comprising a drive unit12, a guide bar14, and a saw chain16configured as an endless loop, guided along the guide bar14between a drive sprocket arrangement (not illustrated) and a nose sprocket arrangement18. The drive unit12comprises battery20and an electric motor22, powered by the battery20. A handle24is provided with a trigger26for operating the electric motor22.

FIG.2illustrates the guide bar14, the saw chain16, and a drive sprocket arrangement28, some features of which are configured in accordance with design principles established in the art. The saw chain16comprises a plurality of drive links30interconnected by tie straps32. For ease of illustration, all tie straps32ofFIG.2are illustrated without a saw tooth, even though it will be appreciated that at least some of the tie straps32may typically be provided with a saw tooth. The portions of the saw chain16which are located within the sprocket arrangement28are illustrated by dashed lines. The electric motor22(FIG.1) is drivingly connected to a drive shaft34, which drivingly engages with the drive sprocket arrangement28to rotate the sprocket arrangement28about a rotation axis A, concentric with the drive shaft and perpendicular to the general plane of extension of the sprocket arrangement18. Some sprocket arrangements28have a drive shaft connection interface configured to fixedly attach to the drive shaft34, whereas other sprocket arrangements28have internal splines configured to allow the sprocket arrangement to float on the drive shaft34along the axial direction A. The sprocket arrangement28is of so-called rim type, i.e. it comprises a sprocket36axially aligned with the drive links30, and a pair of radial support plates38, which are positioned on opposite axial sides of the sprocket36and radially support the tie straps32of the saw chain16. The rotation axis A of the sprocket36defines a cylindrical coordinate system of the sprocket arrangement, with a radial direction R facing perpendicularly away from the rotation axis A, and a tangential direction T corresponding to the movement direction of any point rotating about the axis A. The radial support plates38are circular and concentric with the rotation axis A. Typically, the sprocket36and radial support plates38may be integrally formed. For clarity of illustration, the sprocket36is illustrated in solid lines even though it's located behind a radial support plate38. A prior art sprocket36typically comprises between six and twelve sprocket teeth40, which are configured to drivingly engage with the drive links30of the saw chain16; in the illustrated example, the sprocket36comprises six sprocket teeth40. For the purpose, each drive link30comprises a guide tooth42configured to extend into a space between the radial support plates38, and engage with and be driven by the sprocket teeth40in a tangential direction, with respect to said rotation axis A. The pitch of the sprocket36is carefully matched to the pitch of the saw chain16, such that all drive links30will, when passing the sprocket arrangement28, engage with and be driven by a respective sprocket tooth40of the drive sprocket36.

FIG.3Aillustrates a drive link30in greater detail. The drive link comprises a leading rivet bore44aand a trailing rivet bore44, each of which is connected to a pair of adjacent tie straps32(FIG.2) by rivets.

FIG.3Billustrates a detail of a cross-section of the guide bar14(FIG.1). A guide channel46extends along the periphery of the guide bar14, which guide channel46has a width W1. Referring back toFIG.3A, the guide tooth42has a width W2<W1, which width W2is adapted to allow the guide tooth42to be guided within the guide channel46(FIG.3B).

FIG.3Cillustrates an exemplary saw chain16in greater detail. Each drive link30is, at each longitudinal end as seen along the longitudinal direction L of the chain, connected to a pair of tie straps32, which are located on opposite sides of the plane of the drive link30such that in the view ofFIG.3C, only one tie strap32of each such pair is visible. Some of the tie straps32are provided with a respective saw tooth48to form a cutting link32a, whereas other tie straps32bare not provided with any saw tooth. For a typical forestry saw chain16for cutting wood, the saw tooth48has a sharp cutting edge97configured to shave off wood chips from the material being cut.

The pitch of the saw chain16is defined as half the distance D between the trailing rivet pivot axes P of two consecutive drive links30.

FIG.4illustrates the guide bar14, the saw chain16, and a drive sprocket arrangement128according to a first exemplary embodiment of the present invention. The drive sprocket arrangement128is identical to the drive sprocket arrangement28ofFIG.2except in a few details, which will be pointed out in the following. Again, the sprocket arrangement128is of rim type, comprising a sprocket136integrally formed with a pair of radial support plates38. The sprocket136differs from the sprocket36ofFIG.2in that the pitch of the sprocket136does not match the pitch of the saw chain16. Instead, compared to the sprocket36FIG.2, the number of sprocket teeth40of the sprocket136ofFIG.4has been divided in half by removing, compared again to the sprocket36ofFIG.2, every second sprocket tooth40, resulting in a three-toothed sprocket136. Thereby, the sprocket tooth spacing50between each pair of consecutive sprocket teeth40of the sprocket136relates to the drive link spacing D (FIG.3C) between consecutive drive links30of the saw chain16such that the guide teeth42of two consecutive drive links30may enter between a pair of consecutive sprocket teeth40. For a typical saw chain pitch of ¼″, 0.325″, ⅜″, or 0.404″, this translates to a sprocket pitch, i.e. a tangential distance T1between consecutive sprocket teeth along the pitch circle C, of between about 24 mm and about 44 mm. For a chainsaw sprocket arrangement28,128, the pitch circle C is defined as the circle followed by the centres of the chain pins, e.g. rivets, as the sprocket arrangement28,128revolves in mesh with the chain16. It is pointed out that although the three-toothed sprocket arrangement128ofFIG.4has only half the number of teeth compared to the six-toothed sprocket arrangement28ofFIG.2, the two sprocket arrangements28,128have the same pitch diameter, i.e. diameter of the pitch circle C. For a three-toothed sprocket arrangement128allowing two drive links30of a typical standard saw chain having a pitch of between 0.325″ and ⅜″, this would correspond to a pitch diameter of between about 33 mm and about 39 mm. Each sprocket tooth40extends radially, relative to the rotation axis A, from a sprocket base98, along a radial sprocket tooth height H, to a sprocket tip99. At a radial distance from the sprocket base98corresponding to half the radial sprocket tooth height H, each of said sprocket teeth40has a tangential tooth width W, and each gap50between respective pairs of consecutive sprocket teeth40has a tangential gap width G. In the illustrated embodiment, the tangential gap width G is several times greater than the tangential tooth width W.

FIGS.5-8illustrate a drive sprocket arrangement228according to a second exemplary embodiment. Similar to the sprocket arrangement128ofFIG.4, the sprocket arrangement228ofFIGS.5-8comprises a sprocket236provided with three sprocket teeth40configured to drivingly engage with the saw chain16(FIG.4), wherein the pitch of the sprocket is configured to allow the guide teeth42(FIG.4) of two consecutive drive links30to enter between a pair of consecutive sprocket teeth40. However, as is illustrated in the exploded view ofFIG.5, the sprocket arrangement228is not integrally formed in a single piece, but is instead composed of a plurality of distinct parts. Moreover, the sprocket arrangement228comprises a resilient radial support arrangement configured to radially support the saw chain16, which will be elucidated in the following.

Starting with the view ofFIG.5, which illustrates the sprocket arrangement28exploded along the rotation axis A, the sprocket arrangement228comprises a sprocket236sandwiched between a pair of radial support plates238, which radial support plates238are configured to support the tie straps32(FIG.4) in the radial direction. The sprocket236and radial support plates238are held together in the axial direction A by a first axial support plate252aand a second axial support plate252b, which are rigidly connected to each other and sandwich the sprocket236and radial support plates238between them. The first axial support plate252ais provided with outer splines254mating with inner splines256of the sprocket236, thereby rigidly engaging with the sprocket236in the radial direction as well as the tangential direction. Rivets258, integrally formed with the first axial support plate252a, mate with rivet holes260of the second axial support plate252b, such that when assembling the sprocket arrangement228, the components are brought together in the axial direction A until the rivets258penetrate the rivet holes260, and thereafter, the rivets are upset to firmly lock the axial support plates252a,252btogether. The first axial support plate252aalso comprises a drive shaft connection interface262, which is configured as a socket shaped to receive the drive shaft32(FIG.2). In an alternative configuration (not illustrated), the rivets258may be separate from the first axial support plate252a. In such a configuration, also the first axial support plate252amay instead be provided with rivet holes similar to the rivet holes260of the second axial support plate, for receiving said rivets.

The radial support plates238are held by the axial support plates252a,252bvia a resilient suspension arrangement264, which allows the radial support plates238to resiliently move somewhat in the plane defined by the radial and tangential directions. The resilient suspension arrangement264comprises a pair of rubber O-rings266, each of which is radially supported by a support shoulder268arranged on the axially inner face of a respective one of the axial support plates252a,252b.

FIG.7illustrates the sprocket arrangement as seen from the side of the second axial support plate252b, along the rotation axis A. The outer contour of the sprocket236, which is hidden behind axial and radial support plates252b,238, is illustrated in dashed lines. The resiliently suspended radial support plates238define the radially outermost periphery of the sprocket arrangement228, which is even further elucidated in the cross-section ofFIG.8. Referring toFIG.8, the radial support plates238each have a larger diameter than the axial support plates252a,252b. Similarly, the sprocket236has a diameter, defined as twice the distance between the rotation axis A and the radial end of the teeth40, which is smaller than the diameter of the radial support plates238.

FIG.9illustrates a drive sprocket arrangement328according to a third exemplary embodiment. The drive sprocket arrangement328is identical to the drive sprocket arrangement128ofFIG.4except in a few details, which will be pointed out in the following. Again, the sprocket arrangement328is of rim type, comprising a sprocket336integrally formed with a pair of radial support plates38. The sprocket336differs from the sprocket136ofFIG.4in that it is only provided with two sprocket teeth40configured to drivingly engage with the saw chain16. Thereby, at each given moment, at least one sprocket tooth40will be in driving engagement with the saw chain16. The pitch circle C of the sprocket336ofFIG.9has the same pitch diameter as the sprockets36and136ofFIGS.2and4, such that the guide teeth42of three consecutive drive links30are allowed to enter between a pair of consecutive sprocket teeth40.

FIG.10illustrates a fourth exemplary embodiment of the present invention. In the embodiment ofFIG.10, the sprocket arrangement28ofFIG.2, which has a pitch in accordance with design principles established in the art, is combined with a modified saw chain416. The saw chain416ofFIG.10is identical to the saw chain16ofFIG.2except in a few details, which will be pointed out in the following. Similar to the saw chain16ofFIG.2, the saw chain416comprises axially central, with respect to the rotation axis A, links430, which are axially aligned with the sprocket36. The axially central links430are interconnected by axially offset tie straps32, which ride on the radial support plates38. However, the saw chain416ofFIG.10differs from the saw chain16ofFIG.2in that only some of the central links430are provided with a respective guide tooth42to form a respective drive link430a, whereas other central links430bare not provided with a respective guide tooth configured to engage with the sprocket teeth40of the sprocket arrangement28, such that they do not operate as drive links. In the illustrated example, every second central link430of the saw chain416has a respective guide tooth42. Thereby, the saw chain has a pitch, again measured as half the distance between the trailing rivet pivot axes of two consecutive drive links430a, of twice the pitch of the saw chain16ofFIG.2. The spacing between consecutive teeth40of the sprocket36relates to the spacing between consecutive drive links430aof the saw chain416such that two sprocket teeth40may enter between the guide teeth42of a pair of consecutive drive links430a. Assembling the saw chain416using links for standard saw chains16(FIG.2) having anyone of the most common standard pitches of 0.325″, ⅜″, or 0.404″ would result in a saw chain pitch of the saw chain416of 0.650″, 6/8″, or 0.808″.

FIG.11illustrates a fifth exemplary embodiment of the present invention. In the embodiment ofFIG.11, a nose sprocket arrangement518of the guide bar14(FIG.1) comprises a sprocket536which has a sprocket tooth spacing between consecutive sprocket teeth, the sprocket tooth spacing relating to the drive link spacing between consecutive drive links of the saw chain16such that the guide teeth42(FIG.3C) of two drive links30may enter between a pair of consecutive sprocket teeth. Thereby, the noise of the nose sprocket arrangement518may be reduced. In the embodiment ofFIG.11, the periphery538of the guide bar14operates as a radial support arrangement, radially supporting the saw chain16.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.