| JP3948125 | CHAIN TENSION ADJUSTMENT DEVICE |
| JP2003251602 | SAW CHAIN TENSION ADJUSTING DEVICE |
| WO/2005/007360 | VEGETATION PRUNING DEVICE |
PERSSON, Joakim (N Trädgårdsgatan 20, Skillingaryd, S-568 31, SE)
MARTINSSON, Pär (Orrvägen 4, Jönköping, SE-556 26, SE)
PERSSON, Joakim (N Trädgårdsgatan 20, Skillingaryd, S-568 31, SE)
| CLAIMS 1. Method (200) for tensioning a chain in a chain saw (100), said chain saw (100) comprising a housing (102) and a guide bar arrangement (112) comprising a guide bar (114), a transmitting means (304) and said chain, the method comprising the steps of: tensioning (202) the chain with a predetermined force such that an excessive tension in the chain is provided, and moving (204) a part of the guide bar arrangement (112) a predetermined distance relative to the housing (102) such that the chain is slackened a predetermined amount to an optimal tension. 2. Method according to claim 1 , wherein the step of moving (204) a part of the guide bar arrangement (112) comprises the step of moving the guide bar (114) or a part of the guide bar (114) relative to the housing (102). 3. Method according to claim 1 or 2, wherein the guide bar (114) is adapted for longitudinal movement relative to the housing (102), and the step of moving (204) a part of the guide bar arrangement (112) comprises the step of moving the guide bar (114) a predetermined distance longitudinally relative to the housing (102), such that the tension in the chain is decreased to an optimal chain tension. 4. Method according to claim 3, wherein the guide bar arrangement (112) further comprises a tensioning device, wherein the step of tensioning the chain comprises the step of moving the tensioning device relative to the housing (102) such that the guide bar (114) is moved relative to the housing (102) in a longitudinal direction such that the chain is tensioned with a predetermined force. 5. Method according to claim 4, wherein the tensioning device transfers a transversal movement of a part of the tensioning device into a longitudinal movement of the guide bar (114) during the step (204) of moving a part of the guide bar arrangement (112) the predetermined distance. 6. Method according to claim 4 or 5, wherein the tensioning device comprises a tensioning pin (410) and a slackening wedge (416), wherein the guide bar (114) is provided with a hole (412) adapted to receive the tensioning pin (410) , and wherein the step (204) of moving a part of the guide bar (114) a predetermined distance comprises the step of moving the slackening wedge (416) such that it protrudes said hole (412) in the guide bar (114) next to the tensioning pin (410), providing a longitudinal movement of the guide bar (114) relative to the housing (102) and relative to the tensioning device such that the chain is slackened a predetermined amount to an optimal tension. 7. Method according to claim 4 or 5, wherein the tensioning device comprises: an inner tensioning plate (802) attached to the guide bar (114), and an outer tensioning plate (804) placed next to the inner tensioning plate (802), such that the inner tensioning plate (802) is placed between the outer tensioning plate (804) and the guide bar (114), and the outer tensioning plate (804) and the inner tensioning plate (802) are coupled to each other via a joint (816), said joint (816) being adapted for rotational movement relative to each of the inner (802) and outer (804) tensioning plates, wherein the step of moving a part of the guide bar (114) a predetermined distance comprises the step of moving the outer tensioning plate (804) towards the inner tensioning plate (802) such that a transversal movement of the outer tensioning plate (804) via the joint (816) is transferred to a longitudinal movement of the inner tensioning plate (802) and the guide bar (114) moves relative to the outer tensioning plate (804) such that the chain is slackened to an optimal tension. 8. Method according to claim 4, wherein the tensioning device transfers a rotational movement of a part of the tensioning device into a longitudinal movement of the guide bar (114) during the step of moving a part of the guide bar (114) a predetermined distance. 9. Method according to claim 4 or 8, wherein the tensioning device (622) comprises a first knee joint part (624), a second knee joint part (626) and a tensioning pin (628), the first knee joint part (624) is rotatably attached to the second knee joint part (626), and the second knee joint part (626) is connected to the tensioning pin (628), wherein the guide bar (114) is provided with a hole (412) adapted to receive the tensioning pin (628), and wherein the step of moving a part of the guide bar (114) a predetermined distance comprises the step of turning the first knee joint part (624) in a first rotational direction providing a rotational movement of the second knee joint part (626) in a rotational direction opposite the first direction, the rotational movement of the second knee joint part (626) providing a longitudinal movement of the tensioning pin (628), pushing the guide bar (114) in a longitudinal direction relative to the housing (102) such that the chain is slackened a predetermined amount to an optimal tension. 10. Method according to claim 1 or 2, wherein the guide bar (114) comprises a nose sprocket (302) in the end of the guide bar (114) facing away from the housing (102), the nose sprocket (302) is moveable relative to the guide bar (114), and wherein the step of moving a part of the guide bar arrangement (112) comprises the step of moving the nose sprocket (302) a predetermined distance in a longitudinal direction along the guide bar (114) towards the housing (102), such that the tension in the chain is decreased to an optimal chain tension. 1 1 . Method according to claim 1 or 2, wherein the step of tensioning the chain comprises the steps of; turning the guide bar (114) from a first position to a second position providing an angle (a) between the guide bar's second position and the guide bar's first position, and tensioning the chain with a predetermined force such that an excessive tension in the chain is provided, and wherein the step of moving a part of the guide bar arrangement (112) comprises the step of turning the guide bar (114) back to the first position, such that the tension in the chain is decreased to an optimal tension. 12. Method according to claim 1, wherein the transmitting means (304) is a drive sprocket (304) and the step of moving a part of the guide bar arrangement (112) comprises the step of moving the drive sprocket (304) a predetermined distance towards the guide bar (114), such that the tension in the chain (306) is decreased to an optimal chain tension. 13. Method according to claim 1, wherein the step of tensioning the chain comprises the steps of; lifting the chain (306) relative to the guide bar (114) by means of a lifting device (308), and tensioning the chain (306) with a predetermined force such that an excessive tension in the chain (306) is provided, and wherein the step of moving a part of the guide bar arrangement (112) comprises the step of lowering the chain (306) by moving the lifting device (308), such that the tension in the chain (306) is decreased to an optimal chain tension. |
TECHNICAL FIELD
The present invention relates to a chain saw. In particular, the present invention relates to a method and system for tensioning a chain in the chain saw.
BACKGROUND
Typically, a chain saw includes a housing and a guide bar arrangement having a guide bar. The housing accommodates a prime mover such as, but not limited to, an electric motor or an internal combustion engine, drivably connected to a drive sprocket which is provided on an output shaft of said prime mover. Further, the guide bar is provided with a continuous peripheral guiding slot to support a chain and the guide bar is longitudinally mounted relative to the sprocket. The chain is guided along the sprocket onto the peripheral guiding slot of the guide bar and during operation, the chain moves along the peripheral guiding slot and the sprocket to perform cutting. Because of the various forces acting on the chain during the cutting operation, the chain is required to optimally tighten around the guide bar and the sprocket to avoid any jump off the guide bar and/or the sprocket.
As well known in prior art, to avoid jump off, or undesired slackening in the chain, the chain is required to be manually adjusted by moving the guide bar in a longitudinal direction relative to the sprocket and/or the housing, and maintain the chain at an optimum tension. The chain tension may vary depending on the knowledge and skill of an operator who may or may not able to achieve the required optimum tension. This may also involve use of various tools and equipments to move the guide bar and to lock in a new position. Further, during operation due to the frictional forces, the chain links may wear out and elongate, hence the guide bar is repeatedly required to be adjusted.
In other known methods, automatic chain tensioners are used to generate tension in the chain. But by using the automatic chain tensioners, the chain tension may reach a high value due to the tolerances of friction between the chain links and the guide bar. A high tension in the chain may lead to an increase in frictional losses and may reduce the efficiency of the chain saw. A very high chain tension may also lead to an increased wear of the chain links and shorten the life of the guide bar.
In light of the foregoing, there is a need for an improved method and system to generate an optimum tension in the chain.
SUMMARY
In view of the above, it is an objective of the present invention to solve or at least reduce the problems discussed above. In particular, the objective is to provide an improved method for tensioning a chain in a chain saw.
The objective is at least partially achieved with a novel method according to claim
1. The method is provided for tensioning a chain in a chain saw, wherein said chain saw includes a housing and a guide bar arrangement comprising a guide bar, a transmitting means and said chain, the method includes a step of tensioning the chain with a predetermined force and such that an excessive tension in the chain is provided. Further, the method includes a step of moving a part of the guide bar arrangement a predetermined distance relative to the housing such that the chain is slackened a predetermined amount. By slackening the chain, the chain may achieve an optimal tension. At the optimal tension, the chain may have a lower tendency to jump off and there is also reduced wear and tear of the chain links. The chain may thereby be tensioned harder in order to guarantee that friction forces due to for instance sticking oil between the chain and the guide bar is overcome, without the chain being over tensioned.
According to claim 2, the step of moving a part of the guide bar arrangement may include a step of moving the guide bar and/or a part of the guide bar relative to a housing of the chain saw. Further, according to claim 3, the guide bar may be adapted for longitudinal movement relative to the housing, and the step of moving the guide bar and/or a part of the guide bar may include the step of moving the guide bar a predetermined distance along a longitudinal direction relative to the housing. The tension of the chain may thereby be decreased to an optimal tension. The longitudinal movement of the guide bar may be described as a movement along a longitudinal axis of the chain saw. According to claim 4, the guide bar arrangement may include a tensioning device. The tensioning device may move relative to the housing to cause the guide bar to move in the longitudinal direction relative to the housing.
According to claim 5, the tensioning device may transfer a transversal movement of a part of the tensioning device into a longitudinal movement of the guide bar during the step of moving a part of the guide bar a predetermined distance. The transversal movement may be described as a movement along a transversal axis, wherein the transversal axis may be an axis perpendicular to the longitudinal axis of the chain saw. Further, during operation wherein a part of the tensioning device may be pushed or pulled in the transversal direction in order to move the guide bar in the longitudinal direction.
According to claim 6, the tensioning device may include a tensioning pin and a slackening wedge. Further, the guide bar may be provided with a hole to receive the tensioning pin. Further, the slackening wedge may be configured to move into and protrude through the hole of the guide bar adjacent to the tensioning pin. By moving the slackening wedge into the hole a longitudinal movement of the guide bar relative to the housing is achieved.
According to claim 7, the tensioning device may include an inner tensioning plate attached to the guide bar and an outer tensioning plate placed next to the inner tensioning plate such that the inner tensioning plate is placed between the outer tensioning plate and the guide bar. Further, the outer tensioning plate and the inner tensioning plate may be coupled to each other via a joint, said joint may be adapted for rotational movement relative to each of the inner and outer tensioning plates. In this arrangement, the step of moving a part of the guide bar a predetermined distance may include the step of moving the outer tensioning plate towards the inner tensioning plate such that a transversal movement of the outer tensioning plate via the joint may be transferred to a longitudinal movement of the inner tensioning plate. Moreover, the guide bar may move relative to the outer tensioning plate such that the chain is slackened to an optimal tension.
According to claim 8, the tensioning device may transfer a rotational movement of a part of the tensioning device into a longitudinal movement of the guide bar during the step of moving a part of the guide bar a predetermined distance. The rotational movement may be described as a rotational movement relative to other parts of the tensioning device or relative to the guide bar.
Alternatively, according to claim 9, the tensioning device may include a first knee joint part, a second knee joint part and a tensioning pin. Further, the tensioning pin may be configured to be received in a hole of the guide bar. The first knee joint part may be rotatably attached with the second knee joint part and the second knee joint part may be connected to the tensioning pin via a bracket. The first knee joint part may be configured to rotate in a first rotational direction, such that, due to the rotation of the first knee joint part the second knee joint part may rotate in an opposite direction. As the second knee joint part may be connected with the tensioning pin, the rotation of the second knee joint part may cause a movement of the guide bar in the longitudinal direction.
According to claim 10, the step of moving a part of the guide bar arrangement may include the step of moving a nose sprocket by a predetermined distance along the guide bar towards the housing. By moving the nose sprocket the chain may be slackened to the optimal tension.
According to claim 1 1 , the step of tensioning the chain may include turning the guide bar to a second position such that, at the second position, the guide bar may be at an angle relative to the longitudinal direction of the chain saw. Further, the chain may be tensioned with a predetermined force and then the guide bar may be turned back to a first position such that, at the first position the guide bar may be substantially parallel to the longitudinal direction.
According to claim 12, the step of moving a part of the guide bar arrangement may include moving a drive sprocket a predetermined distance towards the guide bar, which drive sprocket is the transmitting means. By moving the drive sprocket the chain may be slackened to the optimal tension. According to claim 13, the step of tensioning the chain may include lifting the chain relative to the guide bar by means of a lifting device and tensioning the chain with a predetermined force. Subsequently, the chain is lowered by moving the lifting device to achieve the optimal chain tension. BRIEF DESCRIPTION OF THE DRAWINGS
The invention will in the following be described in more detail with reference to the enclosed drawings, wherein:
FIG. 1 illustrates a perspective view of a chain saw, according to an embodiment of the present invention;
FIG. 2 A illustrates a flow chart for an exemplary method of tensioning a chain of a chain saw, according to an embodiment of the present invention;
FIG. 2B illustrates a flow chart for an exemplary method of tensioning a chain of a chain saw, according to another embodiment of the present invention;
FIG. 3 A illustrates a plane view of the guide bar arrangement, according to an embodiment of the present invention;
FIG. 3B illustrates a plane view of the guide bar arrangement, according to another embodiment of the present invention;
FIG. 3C illustrates a plane view of the guide bar arrangement, according to yet another embodiment of the present invention;
FIG. 3D illustrates a plane view of the guide bar arrangement, according to yet another embodiment of the present invention;
FIG. 4 illustrates an exploded view of a guide bar arrangement, according to an embodiment of the present invention;
FIG. 5A illustrates a partial perspective view of the guide bar arrangement, according to an embodiment of the present invention;
FIG. 5B illustrates another partial perspective view of the guide bar arrangement, according to an embodiment of the present invention;
FIG. 6 illustrates an exploded view of a guide bar arrangement, according to another embodiment of the present invention;
FIG. 7A illustrates a partial side view of the guide bar arrangement, according to another embodiment of the present invention;
FIG. 7B illustrates another partial side view of the guide bar arrangement, according to another embodiment of the present invention;
FIG. 8 illustrates an exploded view of the guide bar arrangement, according to yet another embodiment of the present invention; FIG. 9A illustrates a partial side view of the guide bar arrangement, according to yet another embodiment of the present invention; and
FIG. 9B illustrates another partial side view of the guide bar arrangement, according to yet another embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which example embodiments of the invention incorporating one or more aspects of the present invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. For example, one or more aspects of the present invention can be utilized in other embodiments and even other types of devices. In the drawings, like numbers refer to like elements.
FIG. 1 illustrates a chain saw 100, according to an example embodiment of the present invention. The chain saw 100 includes a housing 102 which may enclose a prime mover (not shown). In various other embodiments of the invention, the prime mover may include an electric motor or an internal combustion engine, and a transmission assembly, for example, but not limited to, one or more gears, belt drive, friction drive, or any combination of these. In an embodiment of the present invention, the electric motor may be an electrically powered motor, such as, but not limited to, AC motor, DC motor, or the like. In an embodiment of the present invention, the electric motor is selectively supplied with electrical energy by a battery (not shown) also enclosed within the housing 102. The activation or deactivation of the electric motor is controlled by an on/off switch 104. Further, the housing 102 may include a rear handle 106 and a front handle 108. The rear handle 106 may include a grip portion to aid in manual grasping of the chain saw 100. Further, a guard 110 may be present to safeguard a user during a cutting operation.
As illustrated in FIG. 1, in an embodiment of the present invention, the chain saw 100 includes a guide bar arrangement 112. The guide bar arrangement 112 includes a guide bar 114, and a transmitting means 304 (not shown in FIG. 1 ) for transmitting rotational movement of an output shaft to a chain 306. The transmitting means 304 is preferably a drive sprocket 304, but other configurations may be possible. The guide bar 114 is attached to the housing 102 and extends in a longitudinal direction. The longitudinal direction, without further specificity, may be substantially parallel to the longitudinal axis A. The guide bar arrangement 112 may also include the output shaft. Further, the guide bar arrangement 112 may include the chain 306 (not shown in FIG. 1), which is supported on a continuous peripheral guiding slot 116 along a nose sprocket 302 (not shown in FIG. 1) and extends to the other side of the guide bar 114. The nose sprocket 302 is provided at a distal end of the guide bar 114 with respect to the housing 102. Further, the chain 306 is mounted on the drive sprocket 304 (not shown in FIG. 1) provided at a proximal end of the guide bar 114 with respect to the housing 102. The drive sprocket 304 may be substantially enclosed within the housing 102 and is drivably connected to the output shaft. A cross-section of the output shaft is illustrated by a circle in FIGs 3 A and 3B in a centre portion of the cross-section of the drive sprocket 304. If the prime mover is a combustion engine, the output shaft is preferably a crankshaft, driven by the reciprocating movement of at least one piston. In the case of an electric motor the output shaft is preferably a motor shaft driven by the electric motor. As is also illustrated in FIGs 3A and 3B, the longitudinal axis A may at least substantially intersect with an axis of rotation of the output shaft and the drive sprocket 304. During operation, the transmission assembly may be used to transfer the movement of the prime mover to the output shaft and drive the chain.
FIG. 2A illustrates a flow chart of a method 200 of tensioning the chain in the chain saw 100, according to an embodiment of the present invention. In step 202 of method 200, a predetermined force may apply a tension on the chain such that an excessive tension may be provided in the chain. In some case, the chain may be tensioned with the predetermined force while mounting the chain on the guide bar 114. Further, the predetermined force is a specified tensioning force for the chain saw 100 or may depend on the knowledge and the skill of an operator.
Following step 202, at step 204, a part of the guide bar arrangement 112 may move a predetermined distance relative to the housing 102. At step 204, the chain may slack by a predetermined amount to an optimal tension. At the optimal tension, the frictional losses and an over-tensioning of the chain may be reduced. Consequently, the wear and tear of the chain and the guide bar 114 may reduce and overall efficiency and life of the guide bar 114 increases.
According to various embodiments of the present invention, at step 204, a part of the guide bar 114 and/or the guide bar 114 may move relative to the housing 102. In an embodiment of the present invention, at step 204, the guide bar 114 may move by a predetermined distance along the longitudinal axis A, such that the tension in the chain decreases to the optimal tension.
FIG. 2B illustrates a flow chart of method 200 of tensioning the chain in the chain saw 100, in accordance with another embodiment of the present invention. As illustrated in FIG. 2B, before step 202 method may also include a step 201, such that at step 201 a clamping force around the guide bar 114 is released to ease the tensioning of the chain over the guide bar 114 with the predetermined force, in the following step 202. Further, at step 205, following step 204, the clamping force around the guide bar 114 is again applied. In various embodiments of the present invention, step 201 and step 205 may include moving a part of the guide bar arrangement 112 in relation to the housing 102 of the chain saw 100.
FIG. 3A illustrates a plane view of the guide bar arrangement 112, according to an embodiment of the present invention. As illustrated in FIG. 3A, the guide bar arrangement 112 may include a nose sprocket 302 and the drive sprocket 304. In an embodiment of the present invention, at step 204, the nose sprocket 302 may move towards the housing 102 by the predetermined distance along the longitudinal axis A. Thereby, the guide bar 114 remains fixed relative to the housing 102 during step 204. Only the nose sprocket 302, located at the distal end of the guide bar 114 facing away from the housing 102 is moved towards the housing 102 relative to the guide bar 114. Further, during step 202 of tensioning the chain, the nose sprocket 302 is moved together with the guide bar 114 in the longitudinal direction away from the housing 102.
FIG. 3B illustrates a plane view of the guide bar arrangement 112, according to another embodiment of the present invention. As illustrated in FIG. 3B, at step 204 the drive sprocket 304 may move towards the distal end of the guide bar 114 by a predetermined distance along the longitudinal axis A. The chain is placed around the drive sprocket 304 and the guide bar 114, running in the continuous peripheral guiding slot 116. While slackening the chain, at step 204, the drive sprocket 304 is moved towards the guide bar 114, moving relative to the housing 102 and the guide bar 114. Thereby, a path of the chain along the peripheral guiding slot 116 is shortened and the chain is slackened to an optimal tension. Preferably, the drive sprocket 304 is mounted on the output shaft, which means that the drive sprocket 304 moves with the output shaft along the axis A. In another embodiment the transmitting means 304 may be moved independently relative to the output shaft along the axis A.
FIG. 3C illustrates a plane view of the guide bar arrangement 112, according to yet another embodiment of the present invention. As illustrated in FIG. 3C, step 202 of method 200 may include rotating the guide bar 114 about an axis substantially orthogonal to the longitudinal axis A from a first position to a second position. Further, at the second position a predetermined force may apply a tension on the chain. Following step 202, at step 204 the guide bar 114 may rotate back to the first position, such that tension in the chain decreases to the optimal tension. In an embodiment of the present invention, at the first position the guide bar 114 is substantially aligned along the longitudinal axis A and at the second position the guide bar 114 is inclined at an angle a with respect to the longitudinal axis A and the first position.
FIG. 3D illustrates a plane view of the guide bar arrangement 112, according to yet another embodiment of the present invention. As illustrated in FIG. 3D, step 202 of method 200 may include lifting a chain 306 relative to the guide bar 114 by means of a lining device and then apply a predetermined force to tension the chain. The tensioning may be provided by moving the guide bar 114 relative to the housing 102. In an embodiment of the present invention, the lifting device may include an insert 308 provided between the chain and the peripheral guiding slot 116 of the guide bar 114. Following step 202, at step 204, the guide bar 114 may include lowering the chain by removing the insert 306, such that the tension in the chain decreases to the optimal tension.
FIG. 4 illustrates an exploded view of the guide bar arrangement 112, according to an embodiment of the present invention. As illustrated in FIG. 4, during assembling, a tensioning bracket 402 and a bar mount portion 404 may be secured with the guide bar 114 by being pressed between a chainsaw cover and the housing 102. Two or more extending members 406 are secured to the bar mount portion 404, such that, during assembly, the extending members 406 may extend through a slot 408 provided in the guide bar 114. In case of the prime mover being a combustion engine the bar mount portion 404 is preferably a portion of a crankcase, and in the case of an electric motor, the bar mount portion 404 is preferably a portion of the housing 102.
Moreover, according to an embodiment of the present invention, the tensioning bracket 402 includes a tensioning pin 410, such that, during assembly, either of holes 412 provided on the guide bar 114 may receive the tensioning pin 410. In an embodiment of the present invention, the guide bar arrangement 112 further includes a spring member 414 and a slackening wedge 416. The slackening wedge 416 is provided with a projection 418 such that, during assembly, either of the holes 412 may also receive the spring member 414 and the projection 418 along with the tensioning pin 410. The spring member 414, the slackening wedge 416 and the tensioning pin 410 together may act as a tensioning device for the guide bar arrangement 112.
In an embodiment of the present invention, during assembly, the chain is tensioned with the predetermined force such that the predetermined force exceeds frictional forces and sticking lubricating oil between the chain and the peripheral guiding slot 116. It may be known to a person ordinary skilled in the art that a clutch assembly 420 and an outer handle 422 are provided to control the predetermined force. In an embodiment of the present invention, the clutch assembly 420 may include an inner tension wheel 424, an outer tension wheel 426, a wrap spring 428 and a clutch cover 430. The outer handle 422 may rotate to push the tensioning bracket 402, the slackening wedge 416 and the spring member 414 in a transverse axis B. In an embodiment of the present invention, during assembly, a gap is provided between the spring member 414 and the tensioning pin 410, such that the gap defines a predetermined distance the guide bar 114 may move in the longitudinal axis A.
In an embodiment of the present invention, the guide bar arrangement 112 may also include, two helical spring members 432 separating the slackening wedge 416 from the tensioning bracket 402 and a push rod 434. Further, an axle 436 and a lever 438 are provided to engage with the push rod 434 to facilitate a movement of the push rod 434 along the transverse axis B. In an embodiment of the present invention, the lever 438 may slide in the outer handle 422 to push the axle 436 along the transverse axis B. The transverse movement of the push rod 434 may further push the slackening wedge 416 along the transverse axis B and move the guide bar 114 backwards along the longitudinal axis A and exceed the force applied by the spring member 414.
FIG 5A and 5B illustrate two partial perspective views of the guide bar arrangement 112, as illustrated in FIG. 4. As illustrated in FIG. 5A, the spring member 414 and tensioning pin 410 are completely received in the hole 412 of the guide bar 114 and the projection 418 is only halfway inserted in the hole 412. Further, as shown in FIG. 5B, after sliding the lever 438 the projection 418 may be pushed completely in the hole 412. The projection 418 moves next to the tensioning pin 410 and facilitate a longitudinal movement of the guide bar 114 along the longitudinal direction. Due to a wedge shape of the projection 418, as it the further moved into the hole 412, causes a further longitudinal movement of the guide bar 114. The spring member 414 may bend and stop against the tensioning pin 410 due to the force applied by the projection 418 of the slackening wedge 416. Thus, the spring member 414 may prevent any further movement of the guide bar 114 in the longitudinal axis A.
FIG. 6 illustrates an exploded view of the guide bar arrangement 112, in accordance with another embodiment of the present invention. As illustrated in FIG. 6, a clutch assembly 602 is provided to tension the chain on the guide bar 114. In an embodiment of the present invention, the clutch assembly 602 may include an inner tension wheel 604, an outer tension wheel 606, a wrap spring 608, an axle 610, an inner clutch cover 612 and an outer clutch cover 614. The clutch assembly 602 and a bar mount portion 616 may be secured with the guide bar 114 by being pressed between a chainsaw cover (not shown) and the housing 102. Further, the guide bar arrangement 112 may include a bracket 618, a guide piece 620, and a tensioning device assembly 622. The bracket 618, the guide piece 620 and the tensioning device assembly 622 may also be secured to the guide bar 114 by being pressed between the housing 102 and the chainsaw cover. In case of the prime mover being a combustion engine the bar mount portion 616 is preferably a portion of a crankcase, and in the case of an electric motor, the bar mount portion 616 is preferably a portion of the housing 102.
In an embodiment of the present invention, the tensioning device assembly 622 includes a first knee joint part 624, a second knee joint part 626 and a tensioning pin 628. The tensioning pin 628 may be received in either of the holes 412 provided in the guide bar 114. During assembly, by turning the outer tension wheel 606, the guide piece 620, the first knee joint part 624, the second knee joint part 626 and the tensioning pin 628 may move forward along the longitudinal axis A and tension the chain by a predetermined force. Further, a spring 630 may be provided adjacent to the tensioning pin 628, such that it compensate for tolerance differences in various parts of the guide bar arrangement 112.
In an embodiment of the present invention, the guide bar arrangement 112 also includes a first plate spring 632, a rocker lever 634 and a second plate spring 636. The first plate spring 632 is provided between the inner tension wheel 604 and the outer tension wheel 606. After applying the predetermined force to tension the chain, a relative motion between the inner tension wheel 604 and the outer tension wheel 606 may activate the first plate spring 632. Thus, the first plate spring 632 presses the rocker lever 634 and rotate the first knee joint part 624 about the transverse axis B. The second plate spring 636 may bias the rocker lever 634 such that the inner tension wheel 604 may not continue to rotate after the chain has been slackened. As the first knee joint part 624 is rotatably attached with the second knee joint part 626, the rotational movement of the first knee joint part 624 causes a rotation of the second knee joint part 626 in an opposite direction. Further, the second knee joint part 626 connected with the tensioning pin 628 moves the guide bar 114 to move backwards along the longitudinal axis A.
FIG 7A and 7B illustrate side views of the guide bar arrangement 112, as illustrated in FIG. 6. As illustrated in FIG. 7A, under the predetermined force, the rocker lever 634 is in a first position and the first knee joint part 624 is also in a corresponding first position. As illustrated in FIG. 7B, due to the activation of the first plate spring 632, the rocker lever 634 may move the first knee joint part 624 to a second position. The second knee joint part 626 also moves to a second position and shifts the guide bar 114 along the longitudinal direction. Also as shown in FIG 7B, the rocker lever 634 prevents any further rotation of the inner tension wheel 604. The outer tension wheel 606 may still rotate relative to the inner tension wheel 604.
FIG. 8 illustrates an exploded view of the guide bar arrangement 112, according to yet another embodiment of the present invention. The guide bar arrangement 112 may include an inner tensioning plate 802 and an outer tensioning plate 804. Further, the guide bar arrangement 112 includes a handle 806, a wrap spring 808, an axel 810 and a tension wheel 812, which are used to tension the chain with the predetermined force. It will be apparent to a person ordinary skilled in art, that all the parts of the guide bar arrangement 112 may be secured to the guide bar 114 by being pressed between the housing 102 and the chain saw cover.
In an embodiment of the present invention, during assembly, the inner tensioning plate 802 is attached to the guide bar 114, and the outer tensioning plate 804 is placed next to the inner tensioning plate 802. Further, the outer tensioning plate 804 and the inner tensioning plate 802 are coupled to each other via a joint 816. The joint 816 is rotatably attached to the outer tensioning plate 804 and the inner tensioning plate 802, such that the inner tensioning plate 802 is movable in along a plane transverse to the axis B. Further, the joint 816 may impart a transversal movement of the outer tensioning plate 804, such that it is transferred to a longitudinal movement of the inner tensioning plate 802 and the guide bar relative to the outer tensioning plate such that the chain is slackened to an optimal tension.
In an embodiment of the present invention, a cup spring 818 is provided between the outer tensioning plate 804 and the inner tensioning plate 802 to allow the transversal movement of the outer tensioning plate 804 against the inner tensioning plate 802. The cup spring 818 may be made of stainless steel or any other suitable material. According to an embodiment of the present invention, the cup spring 818 may be in a biased position to retain the joint 816 in a pressed position. Further, a locking ring 820 is provided between the inner tensioning plate 802 and the guide bar 114 and a screw 822 to fasten the inner tensioning plate 802 with the guide bar 114. The locking ring 820 may prevent the inner tensioning plate 802 and the guide bar 114 from becoming loose during a relative motion between the both. FIG 9A and 9B illustrate side views of the guide bar arrangement 112, as illustrated in FIG. 8. As illustrated in FIG. 9A, the joint 816 is in a first position with respect to the guide bar 114 such that, the inner tensioning plate 802 and the outer tensioning plate 804 are arranged with a space between. Further, the space between the inner tensioning plate 802 and the outer tensioning plate 804 may hold cup spring 818 in a biased state. However, as illustrated in FIG. 9B, the joint 816 is moved to a second position with respect to the guide bar 114 such that, the space between the inner tensioning plate 802 and the outer tensioning plate 804 may decrease and the cup spring 818 is compressed. To accommodate a transverse movement of the outer tensioning plate 804, the inner tensioning plate 802 may move along the longitudinal direction and shifts the guide bar 114 along the longitudinal direction.
In the drawings and specification, there have been disclosed preferred embodiments and examples of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation, the scope of the invention being set forth in the following claims.