Automatic chainsaw tensioning device

Abstract

An apparatus for automatically adjusting a chainsaw cutting element as the chainsaw cutting element lengthens during use due to thermal expansion includes an elongate flat bar circumscribed by the chainsaw cutting element, a motor for causing the chainsaw cutting element to rotate about the elongate flat bar, a motor housing for housing the motor and a cover housing secured to the motor housing for covering a proximal end of the elongate flat bar and a rotatably mounted sprocket gear that engages a proximal end of the chainsaw cutting element. The elongate flat bar has a first, fully retracted position, a second, fully extended position, and an infinite number of positions of adjustment therebetween. Bias members continuously urge the elongate flat bar to displace during saw operation in a proximal-to-distal direction from the first, fully retracted position to the second, fully extended position to maintain chain tension at all times.

Claims

1. An apparatus for automatically adjusting an elongate flat bar on a chainsaw circumscribed by a chainsaw cutting element as said chainsaw cutting element lengthens during use, wherein said chainsaw has a motor and said chainsaw cutting element is adapted to rotate about said elongate flat bar, said apparatus comprising: a motor housing adapted to house said motor; a cover housing secured to said motor housing for covering a proximal end of said elongate flat bar; said elongate flat bar having a first, fully retracted proximal position, a second, fully extended distal position, and an infinite number of positions of adjustment therebetween; a biasing member for urging said elongate flat bar to move in a proximal-to-distal direction as said biasing member displaces from said first, fully retracted position to said second, fully extended position, said proximal-to-distal displacement being movement away from said motor housing in a plane of said elongate flat bar; said biasing member including an elongate screw; said biasing member further including a proximal block fixedly secured to said cover housing and having an unthreaded bore formed therein; said biasing member further including a distal block fixedly secured to said cover housing in longitudinally spaced apart relation to said proximal block and having an unthreaded bore formed therein; said elongate screw having a proximal end that slideably extend through said unthreaded bore formed in said proximal block; said elongate screw having a distal end that slidably extends through said unthreaded bore formed in said distal block; said biasing member further including a flat base plate having an unthreaded bore formed therein to receive said elongate screw, said flat base plate being welded to said elongate screw; said flat base plate positioned between said proximal block and said distal block; said biasing member further including an elongate spring, said elongate spring having a distal end that abuts said distal block and having a proximal end that abuts said flat, internally threaded base plate; said flat, unthreaded base plate abutting said proximal block when said elongate spring is fully extended; and said flat base plate being spaced away from said proximal block when said elongate spring is compressed, said flat base plate being spaced a maximum distance from said proximal block when said elongate spring is fully compressed.

2. The apparatus of claim 1, further comprising: said base plate having a surface that abuts said cover housing and slides but does not rotate relative to said cover housing; a compression tool that rotatably engages the distal end of said elongate screw; said elongate spring being compressed as said base plate is drawn in a proximal-to-distal direction by rotation of said compression tool that engages said distal end of said screw when said compression tool abuts said distal block; said elongate screw and said base plate traveling in a distal-to-proximal direction without rotation as said elongate spring extends.

3. The apparatus of claim 2, further comprising: a pivotally mounted ratchet base plate having an unrotated position or repose when said elongate spring is fully compressed; said ratchet base plate having a fully rotated position when said elongate spring is fully extended; said ratchet base plate being positioned on a proximal side of said proximal block in longitudinal alignment with said elongate screw so that distal-to-proximal travel of said elongate screw effect pivotal rotation of said ratchet base plate away from said position of repose.

4. The apparatus of claim 3, further comprising: a ratchet main body plate is fixedly secured to and depends from said ratchet base plate; a plurality of teeth formed in a proximal edge of said ratchet main body plate; a pawl positioned adjacent said ratchet main body plate; said pawl sequentially engaging said teeth, beginning at a first end of said ratchet main body plate, as said ratchet base plate is pivotally displaced by said elongate screw as said elongate spring extends; and said plurality of teeth being sloped so that said pawl allows the pivoting of said ratchet main body plate in a first direction and such that said pawl does interfere with and prevent pivoting of said ratchet main body plate in a second direction opposite to said first direction.

5. The apparatus of claim 4, further comprising: said pawl being provided with handles that allow said pawl to be pulled out of engagement with said teeth by overcoming the bias of a spring that loads said pawl; said pawl being pulled out of engagement with said teeth when a new chain is being installed; said ratchet base plate being rotated from its fully rotated position to its initial, unrotated position of repose when said pawl is pulled out of engagement with said teeth.

6. The apparatus of claim 5, further comprising: an elongate control arm for interconnecting said ratchet main body plate and said elongate flat bar; a control slot formed in the proximal end of said elongate control arm; a distal edge of said ratchet main body plate being disposed within said control slot so that the teeth formed in the proximal edge of said ratchet main body plate are in open communication with said pawl; a displacement aperture formed in a proximal end of said elongate flat bar; said elongate control arm having a ninety degree (90) bend formed in a distal end of said elongate control arm; a displacement pin extending from said distal end so that said displacement pin can engage said displacement aperture; said ratchet main body plate being displaced by pivoting of said ratchet base plate in first direction, which pivoting is caused by expansion of said elongate spring as said ratchet base plate is pivotally displaced by the bias of said elongate spring; said displacement of aid ratchet base plate being simultaneously transmitted to said elongate flat bar by said elongate control bar and said displacement pin as said cutting element lengthens under thermal expansion, which allows expansion of said elongate spring, said spring expansion resulting in proximal-to-distal travel of said elongate control rod.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:

(2) FIG. 1 is a perspective view of a first embodiment in its starting configuration, showing springs that are fully loaded;

(3) FIG. 2 is a perspective view of the first embodiment in its ending configuration, showing springs that are fully unloaded;

(4) FIG. 3 is a perspective view of a second embodiment in its starting configuration, showing a spring that is fully loaded; and

(5) FIG. 4 is a perspective view of the second embodiment in its ending configuration, showing the spring fully unloaded.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(6) A first embodiment of the novel apparatus for automatically adjusting a chainsaw cutting element as said chainsaw cutting element lengthens during use due to thermal expansion is denoted as a whole in the Figures by the reference numeral 10.

(7) Elongate flat bar 12 is circumscribed by chainsaw cutting element 14. A motor, not depicted, causes cutting element 14 to rotate about elongate flat bar 12 in a well-known way.

(8) Motor housing 16 houses the motor and cover plate 18 is secured to motor housing 16;

(9) it covers a proximal end of elongate flat bar 12 and a rotatably mounted sprocket gear, not depicted, that engages a proximal end of cutting element 14.

(10) Elongate flat bar 12 has a first, fully retracted position, a second, fully extended position, and an infinite number of positions of adjustment therebetween. The fully retracted position is depicted in FIGS. 1 and 3 and the fully extended position is depicted in FIGS. 2 and 4.

(11) A biasing member, disclosed hereinafter, urges elongate flat bar 12 to move in a proximal-to-distal direction, denoted by directional arrow 13, as it displaces from its first, fully retracted position to its second, fully extended position. The proximal-to-distal displacement is movement away from motor housing 16 in the plane of elongate flat bar 12.

(12) Longitudinally-extending slot 20 (FIG. 2) is formed in a proximal end of elongate flat bar 12 and is hidden from view in FIG. 1.

(13) Adjustment plate 22 is secured to or integrally formed with cover plate 18 in closely spaced parallel relation to a proximal end of elongate flat bar 12 and has a fixed position. Step 18a is formed in cover plate 18 and interconnects cover plate 18 and adjustment plate 22. Step 18a is normal to cover plate 18 and adjustment plate 22 and extends into the plane of the paper. Flat spacer plate 24 is disposed between adjustment plate 22 and elongate flat bar 12. Flat spacer plate 24 is secured in a fixed position to adjustment plate 22.

(14) Spacer plate pin 26 is secured to flat spacer plate 24 in normal relation thereto and extends into longitudinally-extending slot 20. Pin 26 is disposed in a distal end of slot 20 when elongate flat bar 12 is in its fully retracted position as depicted in FIG. 1, i.e., when chainsaw cutting element 14 is new and has not undergone thermal expansion. Pin 26 is disposed in a proximal end of slot 20 when elongate flat bar 12 is in its fully extended position as depicted in FIG. 2, i.e., when cutting element 14 is fully thermally expanded due to extensive use.

(15) A control aperture is formed in a proximal end of elongate flat bar 12 and displacement pin 30 is disposed normal to the plane of elongate flat bar 12 and extends into said control aperture. Displacement pin 30 is biased by the biasing member to travel in a proximal-to-distal direction within elongate slot 33 formed in adjustment plate 22 so that as chainsaw cutting element 14 undergoes thermal expansion during use, displacement pin 30 travels in proximal-to-distal direction 13 and carries elongate flat bar 12 in said proximal-to-distal direction as said thermal expansion takes place.

(16) Flat mounting plate 32 is secured to cover plate 18 in overlying relation thereto.

(17) Upper block 34 is fixedly secured to an upper end of mounting plate 32. Lower block 36 is positioned below upper block 34 but is not connected to mounting plate 32.

(18) A pair of high tension springs, denoted 38, 40, is disposed between upper block 34 and lower block 36.

(19) Spring guide rod 42 is ensleeved by first spring 38 and compression rod 44 is ensleeved by second spring 40.

(20) Spring guide rod 42 has an upper end received within and secured to a first vertical bore formed in upper block 34 so that it cannot rotate about its longitudinal axis. A lower end of spring guide rod 42 is slideably received within a first vertical bore formed in lower block 36. The first vertical bores are in axial alignment with one another.

(21) Compression rod 44 has an externally threaded upper end extending through and slideably received within a second vertical bore formed in upper block 34. Compression rod 44 has a lower end received within and secured to a second vertical bore formed in lower block 36 so that it cannot rotate about its longitudinal axis. The second vertical bores are also in axial alignment with one another.

(22) Compression tool 46 engages the threaded upper end of compression rod 44 and causes lower block 36 to travel toward upper block 34 as compression tool 46 rotates. Compression rod 44 is unable to rotate about its longitudinal axis due to its lower end being fixedly secured to lower block 36. Compression rod 44 is therefore forced to travel longitudinally in response to rotation of compression tool 46 which rotation causes said compression tool to urge upper block 34 downwardly; said upper block cannot displace downwardly so the reaction caused by compression tool 46 is the upward travel of compression rod 44 along its longitudinal axis. The travel of lower block 36 toward upper block 34 causes compression of springs 38, 40.

(23) The leading end of compression tool 46 has a centered internally threaded bore with ACME square load bearing threads that are machined and matched with the ACME external threads formed in compression rod 44. The trailing end of compression tool 46 preferably has a non-circular bore that is releasably engaged by the mating non-circular drive of a socket/ratchet wrench 46a. Of course, the compression tool trailing end could have any tool-engageable surface that enables rotation of the compression tool about its longitudinal axis of symmetry so that the internal threads formed in the leading end can be advanced relative to the external threads of compression rod 44.

(24) Longitudinally-extending mounting plate slot 48 is formed in mounting plate 32 and in cover housing 18. Elongate control arm 50 has a control aperture formed in a proximal end thereof. Displacement pin housing 52, from which displacement pin 30 extends, is secured to a distal end of said elongate control arm. The proximal end of elongate control arm 50 is visible through mounting plate slot 48 in FIG. 1 but is not numbered in said slot to avoid cluttering the drawings.

(25) Displacement pin housing 52 is apertured so that it can slide relative to displacement housing guide rod 51 that is mounted between mounting plate 32 and adjustment plate 22 in parallel relation to said plates. Displacement pin housing 52 follows a path of travel defined by displacement housing guide rod 51 when said displacement pin housing is displaced in a proximal-to-distal direction by said biasing member.

(26) Cam 54 is pivotally mounted to mounting plate 32 so that a top edge of said cam abuts a bottom surface of lower block 36 as depicted. Accordingly, displacement of lower block 36 in the direction indicated by directional arrow 31 causes pivotal displacement of cam 54 about pivot point 56 in a clockwise direction as drawn in FIG. 1.

(27) Cam 54 has a fully retracted, unpivoted position as depicted in FIG. 1 when springs 38, 40 are fully compressed and has a fully extended, pivoted position as depicted in FIG. 2 when said springs are fully extended.

(28) Angle iron 58 has a first end pivotally mounted to mounting plate 32 as at 60. Angle iron slot 62 (hidden in FIG. 1, visible in FIG. 2) is formed in a second, lower end of angle iron 58 to prevent jamming when angle iron 58 is pivoted in a counterclockwise direction from its FIG. 1 position. In a direction from inside the plane of the paper to the plane of the paper, control pin 64 extends through control aperture 28 formed in the proximal end of elongate control arm 50, an undepicted slot formed in cover plate 18 in registration with mounting plate slot 48, mounting plate slot 48, angle iron slot 62, and through a central aperture formed in angle iron square sliding plate 29. Displacement of control pin 64 in the proximal-to-distal direction thus effects simultaneous and corresponding displacement of displacement pin 30 and elongate flat bar 12. The novel biasing member prevents movement of control pin 64, displacement pin 30 and elongate flat bar 12 in a distal-to-proximal direction at all times.

(29) Angle iron 58 has a fully retracted, unpivoted position when control pin 64 is positioned at a proximal end of mounting plate slot 48 when springs 38, 40 are fully compressed. Angle iron 58 has a fully extended, pivoted position when control pin 64 is positioned at a distal end of mounting plate slot 48 when springs 38, 40 are fully expanded.

(30) Cam 54 has lobe 66 that abuts angle iron 58 when springs 38, 40 are fully compressed, when said springs are fully unloaded, and at all spring compressions therebetween.

(31) Control pin 64, control arm 50, displacement pin housing 52, displacement pin 30 and elongate flat bar 12 have a fully retracted position when springs 38, 40 are fully compressed as depicted in FIG. 1 and have a fully extended position when said springs are fully expanded.

(32) Control pin 64 and displacement pin 30 are displaced in proximal-to-distal direction 13 by counterclockwise pivotal rotation of angle iron 58.

(33) The pivotal displacement of angle iron 58 is caused by pivoting of cam 54 as springs 38, 40 expand.

(34) Spring expansion is caused by thermal-related lengthening of cutting element/chain 14.

(35) Longitudinally-extending slot 20 is formed in elongate flat bar 12 as mentioned above. Longitudinally spaced apart adjustment screws extend through slot 20 and are respectively engaged by nuts 68, 70 so that when said nuts are tightly secured, elongate flat bar 12 is held against movement. The nuts are depicted but not numbered to avoid cluttering of the drawings.

(36) The nuts having a first fully tightened position that locks elongate flat bar 12 against movement. The nuts have a second position where they are backed off about half to three-quarters of a turn from said fully tightened position. Elongate flat bar 12 is free to longitudinally displace in the proximal-to-distal direction indicated by directional arrow 13 when said pair of nuts is in the second, slightly loosened position but distal-to-proximal displacement is prevented by the novel biasing member at all times.

(37) Nut 72 secures anti-rotation plate 71 against movement, said anti-rotation plate being disposed between nuts 68, 70 when said pair of nuts is in said second position so that said nuts cannot rotate from said second position.

(38) Spacer plate 26 is also apertured to receive adjustment screws 68, 70.

(39) An anti-rotation pin, not depicted, is formed integrally with spacer plate 26 and extends into elongate slot 20 formed in elongate flat bar 12 to prevent rotation of said elongate flat bar 12 in the plane of the paper as drawn.

(40) When a new cutting element/chain 14 is secured in encircling relation to elongate flat bar 12, the trailing or proximal end of flat bar 12 is positioned to the left as drawn in FIG. 1. As saw 10 is operated and cutting element/chain 14 expands in length due to thermal expansion, elongate flat bar 12 is displaced further and further to the right in order to take up slack in cutting element/chain 14. Longitudinally-extending slot 20 enables elongate flat bar 12 to slide in a proximal-to-distal direction, denoted by directional arrow 13 as aforesaid, as the cutting element/chain 14 loosens and is continually re-tightened with the saw in operation.

(41) Chain 14 reaches the end of its useful life, having been re-tensioned automatically during operation throughout its lifetime and never having been re-tensioned during a downtime.

(42) A second embodiment, denoted 80 as a whole, is depicted in FIGS. 3 and 4.

(43) Externally threaded elongate screw 82 extends through fixed position proximal block 84 and fixed position distal block 86. Said blocks 84 and 86 are secured to brackets 84a and 86a, respectively, that are secured to cover plate or housing 88 which is secured to motor housing 16, not depicted in FIGS. 3 and 4.

(44) Compression spring 90 is sandwiched between blocks 84 and 86 but its proximal end does not abut proximal block 84.

(45) The proximal end of screw 82 extends through but does not engage a bore formed in proximal block 84.

(46) The distal end of screw 82 extends through but does not engage a bore formed in distal block 86.

(47) The proximal end of spring 90 abuts flat base plate 92 which has an unthreaded bore formed therein to slidably receive elongate screw 82. Flat base plate 92 is welded or otherwise fixedly secured to elongate screw 82.

(48) Flat base plate 92 has a flat edge that slideably engages flat vertical surface 88a of cover housing 88 so that said flat base plate travels in a proximal-to-distal direction as indicated by directional arrow 94 when compression tool 46 engages the threaded distal end of elongate screw 82, said compression tool being rotated by ratchet/socket wrench 46a. This causes sliding displacement of flat base plate 92.

(49) Accordingly, spring 90 compresses as base plate 92 is drawn in said proximal-to-distal direction by rotation of compression tool 46 that engages the distal end of screw 82 and causes said flat base plate to travel in said direction. Screw 82 does not rotate about its longitudinal axis of symmetry.

(50) The proximal end of screw 82 abuts ratchet base plate 96 which is formed integrally with ratchet main body plate 98 having teeth 100 formed along a curved proximal edge of said ratchet main body plate.

(51) The position of ratchet base plate 96 depicted in FIG. 3 is its position of repose. As spring 90 unloads as cutting element 14 lengthens with use, elongate screw 82 and base plate 92 travel without rotation in a direction opposite to the direction indicated by directional arrow 94, i.e., in a distal-to-proximal direction. Ratchet base plate 96 therefore pivots about pivot point 102 in a counterclockwise direction as at 104.

(52) Pawl 106 sequentially engages teeth 100, beginning away from the top of ratchet main body plate 98 as depicted in FIG. 3 and teeth 100 are sloped so that pawl 106 does not interfere with the counterclockwise rotation of ratchet main body plate 98. However, clockwise pivoting of ratchet main body plate 98 is prevented by said teeth.

(53) Pawl 106 is spring-loaded as at 108. It is also provided with finger-grip handles 110 that enable a saw operator to pull pawl 106 out of engagement with teeth 100 by overcoming the bias of spring 108. Nylon lock nut 105 enables the position of handles 110 to be adjusted, thereby adjusting the bias of spring 108. Disengagement of pawl 106 from teeth 100 is needed only when a new chain is being installed at which time it is necessary to rotate ratchet base plate 96 from its fully rotated FIG. 4 position to its initial, unrotated position depicted in FIG. 3. The pawl assembly is welded to back plate 81 of the chainsaw housing. When the chainsaw operator pulls finger-grip handles 110, spring 108 is momentarily compressed and pawl 106 disengages from teeth 100. Release of handles 110 allows pawl 106 to re-engage teeth 100 under the bias of spring 108.

(54) Elongate control arm 112 interconnects ratchet main body plate 98 and elongate flat bar 12, not depicted in FIGS. 3 and 4. Control slot 114 is formed in the proximal end of elongate control arm 112 and ratchet main body plate 98 is disposed within said control slot.

(55) The distal end 116 of elongate control arm 112 has a ninety degree (90) bend formed therein and includes displacement pin 116a that engages the displacement aperture, not depicted, formed in elongate flat bar 12.

(56) Elongate control arm 112 slideably extends through hollow guide housing 113 which is mounted in fixed relation to cover housing 88.

(57) Displacement of ratchet main body plate 98, caused by pivoting of ratchet base plate 96 in a counterclockwise direction as drawn in FIG. 3, which in turn is caused by the expansion of spring 90 as base plate 92 and elongate screw 82 are displaced without rotation in a distal-to-proximal direction by the bias of spring 90, is thus simultaneously transmitted to elongate flat bar 12, i.e., as cutting element 14 lengthens under thermal expansion, compression spring 90 unloads, resulting in proximal-to-distal travel as at 118 of elongate control rod 112 and hence of elongate flat bar 12 just as in the first embodiment.

(58) Nuts 68, 70 respectively engage the same adjustment screws as in the first embodiment and they are tightened fully and then backed off in the same way as disclosed in connection with the first embodiment. Anti-rotation plate 71 is positioned between the nuts as in the first embodiment for the same reason. Plate 71 is mounted to the end of L-shaped plate 73, said plate 73 being secured to cover housing 88 by suitable fastening means 75.

(59) This second embodiment presents a more narrow profile than the profile of the first embodiment and has less weight than said first embodiment. It also uses one spring instead of two and eliminates the need for a cam and a pivotally mounted angle iron. It further eliminates the need for a longitudinally-extending slot formed in the mounting plate of the first embodiment into which a control pin is inserted.

(60) The advantages set forth above, and those made apparent from the foregoing description, are efficiently attained. Since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.