Abstract:
A chain saw is provided in which the tension of a cutting chain extending along a periphery of the guide bar may be adjusted without use of a tool. A locking knob is provided which engages with a cover of the chain saw. Protrusions of the locking knob fit within corresponding notches of the cover. The shape of the protrusions and the notches allow rotation of the locking knob in a first direction but not a second direction. Upon disengaging the locking knob from the cover, the guide bar may move relative to the engine housing and clutch cover to tighten the cutting chain extending along a periphery of the guide bar.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a locking mechanism for the guide bar of a chain saw. 
       BACKGROUND 
       [0002]    Proper operation of a cutting chain of a chain saw requires that the links of the cutting chain be securely seated within a channel or groove extending along the periphery of a guide bar of the chain saw. Continual use of a cutting chain of a chain saw may cause the chain to loosen along the periphery of an elongated plate or guide bar. Such loosening of the chain causes slack in the chain. Removal of the slack may be achieved by moving the guide bar longitudinally with respect to the engine housing and cover such that the cutting chain is tightened about the periphery of the guide bar. 
         [0003]    Conventional chain saws may require an operator to use one or more tools to loosen the guide bar disposed between the engine housing and the cover so that the guide bar can move to cause tightening of the cutting chain along the guide bar. Additionally, such saws require tools to secure the guide bar in its new position. The use of one or more tools may increase downtime of the chain saw and require intensive labor. 
         [0004]    Conventional chain saws may also be prone to inadvertent slippage of the guide bar during operation of the chain saw if the guide bar fails to remain secured between the engine housing and the cover. It would be desirable to provide a chain saw in which the guide bar can be quickly and reliably moved in the longitudinal direction to tighten a cutting chain extending along the periphery of the guide bar and thereafter secured in its new position. 
       SUMMARY 
       [0005]    In a first aspect of the invention, a chain saw is provided. The chain saw comprises a housing supporting an engine, a cover selectively secured to the housing, a cutting chain, a locking mechanism, and an adjustment mechanism. The cover includes a plurality of notches. Each of the plurality of notches is defined by a first notch edge inclined in a first direction and a second notch edge opposite the first edge and substantially perpendicular to a flat surface of the cover. The cutting chain extends along a periphery of a guide bar located between the housing and the cover. The locking knob includes a plurality of protrusions adapted to fit within the notches. Each of the plurality of protrusions includes a first protrusion edge inclined in a direction opposite the first notch edge and a second protrusion edge substantially perpendicular to a flat surface of the knob. The second protrusion edge abuts against the second edge to define a locked position to secure the guide bar from movement with respect to the housing and the cover. The protrusions of the knob are configured to disengage from within the plurality of notches to allow the guide bar to move with respect to the housing and the cover. 
         [0006]    In a second aspect of the invention, a chain saw is provided. The chain saw includes a housing supporting an engine, a cover selectively secured to the housing and including a plurality of notches, a cutting chain extending along a periphery of a guide bar located between the housing and the cover, and a locking knob comprising a plurality of tooth-like protrusions configured to removably engage with the notches of the cover in a one-way ratcheted arrangement so as to secure the guide bar from relative movement with respect to the cover and housing. Each of the plurality of notches of the cover is defined by a first notch edge inclined in a first direction and a second notch edge opposite the first edge and substantially perpendicular to a flat surface of the cover. The plurality of tooth-like protrusions of the knob are configured to disengage from the plurality of notches of the cover to allow an intermeshed gear assembly to move the guide bar with respect to the housing and the cover without any tools. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Embodiments will now be described by way of example with reference to the accompanying drawings. 
           [0008]      FIG. 1  is a perspective view of a chain saw incorporating the features of the present invention. 
           [0009]      FIG. 2  is side perspective view of the locking knob. 
           [0010]      FIG. 3  is a perspective view of a portion of the cover shown with the other portions not shown to increase clarity. 
           [0011]      FIG. 4  is a rear view of an intermeshed gear assembly coupled to a bar adjustment pin for moving the guide bar. 
           [0012]      FIG. 5  is a rear perspective of the locking knob engaged with the cover. 
           [0013]      FIG. 6  is a perspective view of the engine housing. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The embodiments are described with reference to the drawings in which like elements are referred to by like numerals. The relationship and functioning of the various elements of the embodiments are better understood by the following detailed description. However, the embodiments as described below are by way of example only, and the invention is not limited to the embodiments illustrated in the drawings. It should also be understood that the drawings are not to scale and in certain instances details have been omitted, which are not necessary for an understanding of the embodiments, such as conventional details of fabrication and assembly. 
         [0015]      FIG. 1  shows a chain saw  100  incorporating the locking mechanism  111  of the present invention. The chain saw  100  includes an engine (not shown) at least partially located in a housing  600 . A cutting chain  105  extends along a periphery of a guide bar  115  located between the housing  600  ( FIG. 6 ) and the cover  125 . The guide bar  115  is an elongated plate with at least one groove around its periphery into which the cutting chain  105  rides. A rear portion of the guide bar  115  is disposed between the engine housing  600  and the cover  125 . 
         [0016]    The cover  125  includes a locking mechanism  111  that includes a locking knob  110  that is rotatable between a locked configuration and an unlocked configuration.  FIG. 1  shows the locking knob  110  in the locked configuration. Generally speaking, rotating the locking knob  110  from the locked to the unlocked configuration allows the guide bar  115  to move with respect to the housing  600  and the cover  125  so that the cutting chain  105  can be tightened around the guide bar  115 . 
         [0017]    Engagement of the locking knob  110  with the cover  125  secures the guide bar  115  in a fixed position between the engine housing  600  and the cover  125 . The cover  125  is operatively connected to the engine housing  600  by a knob insert  130 , as shown in  FIG. 2 . The knob insert  130  attaches to a bar stud of the guide bar  115  to secure the guide bar  115  to the chain saw  100 . Rotating the locking knob  110  from the unlocked to the locked configuration causes the knob insert  130  to move from a loosened position to a tightened position. When the knob insert  130  is in the tightened position, the cover  125  is pressed toward the guide bar  115  and the engine housing  600 , thereby securing the guide bar  115  between the engine housing  600  and the cover  125 . 
         [0018]    Disengagement of the locking knob  110  with the cover  125  allows the guide bar  115  to move relative to the engine housing  600  and the cover  125 . In particular, rotating the locking knob  110  from the locked to the unlocked configuration causes the knob insert  130  to move from a tightened to a loosened position. When the knob insert  130  is in the loosened position, the cover  100  is released away from the guide bar  115  to allow the guide bar  115  to move relative to the engine housing  600  and the cover  125 . 
         [0019]    In one embodiment, the locking knob  110  includes a one-way ratchet mechanism. Turning to  FIG. 2 , the locking knob  110  comprises a plurality of protrusions  120  extending along edges  140  and  150  of the knob  110 . It is also contemplated that the protrusions  120  may be provided on only one of the edges  140  and  150 . Each of the protrusions  120  has a first protrusion edge  121  inclined, as shown in  FIG. 2 . The first protrusion edge  121  may be inclined at any appropriate angle from the vertical (i.e., angled from a plane perpendicular to a flat surface  160  of the knob  110 ). Rather than being inclined, the first edge  121  may be convexly curved. Each protrusion  120  also has a second protrusion edge  122 . The second protrusion edge  122  is shown in  FIG. 2  to be substantially perpendicular to a flat surface  160  of the knob  110 . The distal end  123  of the edge  121  may be rounded to facilitate one-way tightening as will become clear from the description below. 
         [0020]    The first and second protrusion edges  121  and  122  of the locking knob  110  are adapted to fit within a plurality of notches  170  of the cover  125 , as best seen in  FIG. 5 .  FIG. 3  shows a portion of the rear of the cover  125 . A plurality of notches  170  extend circumferentially about the periphery of an opening provided in the cover  125 . Each of the plurality of notches  170  has a first notch edge  180  and a second notch edge  185 . The first notch edge  180  is inclined in a first direction at a predetermined angle. As with the first protrusion edge  121 , the first notch edge  180  may be inclined at any angle from the vertical (i.e., angled from a plane perpendicular to a peripheral edge  190  of the cover). In one embodiment, the inclination of the first protrusion edge  121  is about the same as the inclination of the first notch edge  180  so that one may slide over the other when in contact and the knob  110  is rotated with respect to the cover  125 . The second notch edge  185  is oriented opposite the first notch edge  180 . In this regard, when the first protrusion edge  121  is convexly curved, the first notch edge  180  will likewise be convexly curved. The second notch edge  185  is also shown oriented substantially perpendicular to a peripheral edge  190  ( FIG. 3 ) of the cover  125 . 
         [0021]    When the knob  110  is in the locked position, each of the protrusions  120  of the knob  110  mate with a corresponding notch  170  of the cover  125  ( FIG. 5 ). The second protrusion edge  122  abuts the second notch edge  185  to define a locked position. It will be understood that because each of the second protrusion edge  122  and second notch edge  185  are parallel to each other and because the edges  122  and  185  abut (desirably along a parallel line, i.e., they about along more than a point), the knob  110  will not rotate (or loosen) with respect to the cover  125 . Thus, the guide bar  115  will be securely held in a selected position even during use. 
         [0022]    Disengagement of the protrusions  120  from the notches  170  is achieved by pushing the knob  110  inwards towards the cover  125  and engine housing  600 . In one embodiment, the biasing structure of the knob  110  is a spring. It is to be appreciated that any biasing structure for the knob  110  is contemplated. Pushing on the knob  130  causes the spring to compress so that the knob  110  is pushed inwards and away from the user. The knob  110  is pushed inwards a sufficient amount to enable the protrusions  120  of the knob  110  to disengage from the notches  170  of the cover  125 . This disengagement allows the knob  110  to be rotated with respect to the cover  125 . When the protrusions  120  of the knob  110  are disengaged from the notches  170  of the cover  125 , the adjustment mechanism can be actuated to move the guide bar  115  with respect to the cover  125  and engine housing  600 . The adjustment mechanism includes the knob  110  which can be rotated in a loosening direction so that the cover  125  can be moved away from the engine housing  600  to allow the guide bar  115  to move with respect to the cover  125  and engine housing  600 . Rotation of the knob  110  in a loosening direction is continued until the guide bar  115  can be moved. 
         [0023]    After the guide bar  115  is moved to the selected desired position, the knob  110  can be rotated in an opposite, tightening position. It will be appreciated that the knob  110  can be rotated in a tightening direction to lock the guide bar  115  in the selected desired position because of the inclination of the edges  121  and  180 . As the knob  110  is rotated, the first protrusion edge  121  can rotatably slide upwardly pass the incline of first notch edge  180  of the cover  125 . Because the incline of the first protrusion edge  121  and the incline of the first notch edge  180  are opposite, selective rotation in one tightening direction. The orientation of the second protrusion edge  122  with the second notch edge  185  of the cover  125  enables one-way ratcheted movement in a first rotational tightening direction in which the first protrusion edge  121  rotatably slides pass the first notch edge  180  of successive notches  170 . As noted above, the second protrusion edge  122  is not able to slide pass successive second notch edges  185  of the cover  125  in a second rotational direction opposite to the first rotational direction because of the abutment (i.e., desirably along a line) between the second protrusion edge  122  and the second notch edge  185 , thereby avoiding inadvertent loosening of the knob  110 . Accordingly, the cover  125  is secured to the engine housing  600  and the guide bar  115  is locked in a selected position. 
         [0024]    It is to be further appreciated that the locking arrangement between the knob  110  and the cover  125  may be modified. For example, the notches  170  of the cover  125  need not extend completely circumferentially about the periphery of the cover  125 . Alternatively, the protrusions  120  may be disposed along the cover  125  and the notches  170  disposed along the knob  110 . 
         [0025]    Movement of the guide bar  115  when the knob  110  is in an unlocked configuration will now be discussed with reference to  FIG. 4 . When the knob  110  is unlocked, the guide bar  115  can be moved and the tension of the cutting chain  105  can be changed. The portion of the cover  125  adjacent the engine housing  600  is configured to locationally position various components of the adjustment mechanism. The adjustment mechanism comprises intermeshed gears  400  to cause movement of the guide bar  115  via movement of a bar adjust pin  410 . An opening is provided in the guide bar  115  and it receives a finger  411  extending from the bar adjust pin  410  such that the finger  411  is secured within the guide bar opening  115 . The bar adjust pin  410  is internally threaded to threadably mate with an externally threaded shaft  460 . 
         [0026]      FIGS. 1 and 4  show an adjustment dial  420 . In operation, rotation of the adjustment dial  420  causes the externally threaded elongate member  460  to rotate through the intermeshed gears  400  which causes the bar adjustment pin  410  to travel along the longitudinal length of the elongate member  460 . Because the finger  411  is engaged with the guide bar  115 , as the bar adjustment pin  410  moves, the guide bar  115  moves. 
         [0027]    The adjustment dial  420  has swirled meshed grooves  425  that receive spokes  430  of a wheel  435 . The wheel  435  is affixed to one end of a shaft  470 . The other end of the shaft  470  has a first intermeshed gear  440 . The first intermeshed gear  440  is engaged with a second intermeshed gear  450  which is fixed to one end of the elongate member  460 . The other end of the elongate member  460  is rotatably received within an opening of the cover  125  so that the elongate member  460  remains aligned. A collar  480  fitted within a slot in the cover  125  rotatably receives a portion of the elongate member  460  near gear  450  so that elongate member  460  will be axially fixed with respect to the cover  125 . In addition, the collar  480  helps to maintain the first and second gears  440  and  450  in a meshed engagement. Although an intermeshed gear mechanism  400  has been described, other means for urging the guide bar  115  are contemplated and would be appreciated by one of ordinary skill in the art. 
         [0028]    Once adjustment is accomplished, the locking knob  110  can be rotated in a tightening direction to secure the guide bar  115  in its new longitudinal position. Re-engagement is achieved by the user releasing the knob  110  so that the spring-like structure of the knob  110  returns to its uncompressed configuration towards the user. This causes the protrusions  170  of the locking knob  110  to mate within the notches  170  of the cover  125  to define a locked configuration. Thus, the guide bar  115  can be secured in its new position without the use of any tools. 
         [0029]    Operation of the chain saw  100  is advantageous as compared to conventional chain saws because a user may adjust the tension of the cutting chain  105  from the exterior of the chain saw  100 . There is no need to remove any parts when a user manually rotates the manual adjust dial  420  to loosen the guide bar  115  from the engine housing  600  and cover  125 . The manual adjust dial  420  is rotated by hand without the use of any tools. There is also no need to use any tools to secure the guide bar  115  in its new longitudinal position. 
         [0030]    The above figures and disclosure are intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in the art. All such variations and alternatives are intended to be encompassed within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the attached claims.