Auto chain tensioner

Abstract

The invention relates to an auto tensioner of a chain saw. A spiral guide groove ( 16 ) of the disk ( 15 ) engages with a protrusion 10 a of a slider piece ( 10 ) and the slider piece ( 10 ) is slidably stored in a guide portion ( 9 ) formed in a chain cover ( 2 ) via a spring ( 14 ). A tensioner ( 11 ) comprising a protrusion ( 11 ) engaged with a guide bar is slidably stored in the slider piece 10 via a coin spring ( 12 ). The protrusion ( 10 a ) contacts an outer circumference face of the spiral guide groove 16 on a diameter passing through a rotating center of the disk, and an unshown nut for engaging with a stud bold 6 provided on an engine cover side is attached on the rotating center of the disk ( 15 ). A rotation of the disk enables to fix the chain cover ( 2 ) and move the guide bar.

1 . An auto chain tensioner for providing a tension to a saw chain running along a guide bar by moving the guide bar, characterized by the chain tensioner comprising 
 chain cover fixing means for pressing and holding the guide bar between an engine case and a chain cover and for fixing the chain cover to the engine case,    a slider piece which is disposed at one of places between the chain cover and the guide bar and between an engine cover and the guide bar, and slides linearly in a back and forth moving direction of the guide bar for providing the tension or a relaxation to the saw chain, and    a tensioner which is connected to the slider piece via a spring and is slidable in a sliding direction of the slider piece,    wherein the chain cover fixing means further includes a sliding mechanism for allowing one of the slider piece and the tensioner to slide in the back and forth moving direction of the guide bar, and    wherein the other one of the tensioner and the slider piece is engaged with the guide bar.    
   
   
       2 . The auto chain tensioner according to  claim 1 , characterized in that the chain cover fixing means has a rotatable disk screwed together with a stud bolt for guiding the guide bar fixed to an engine case side, and the sliding mechanism forms a spiral guide groove on the disk, the spiral guide groove extending over a prescribed rotation angle, being engaged with a protrusion provided in one of the slider piece and tensioner, and centers on a rotation center of the disk.  
   
   
       3 . The auto chain tensioner according to  claim 2 , characterized in that one of an outermost circumference and an innermost circumference of the spiral guide groove is formed in an annular groove.  
   
   
       4 . The auto chain tensioner according to any one of claims  2  and  3 , characterized in that the chain cover comprises an annular concave portion open to an outer surface side of the chain cover, an internal tooth formed along an edge portion of an opening portion of the concave portion and having a smaller diameter than an inner diameter of the concave portion, and a through hole passing through the stud bolt at a center of a bottom face of the concave portion, 
 the disk has a lever which can rise and fall freely and rotates the disk,    an external tooth is formed at a part of an outer circumference face of the lever, and    the disk passes through the opening portion by a prescribed suppress strength and is rotatably fitted into the concave portion with a play, and the external tooth of the lever and the internal tooth of the opening are engaged with each other when the lever falls on a disk surface side.    
   
   
       5 . The auto chain tensioner according to any one of  claims 2  to  4 , characterized in that a detent mechanism is provided between the disk and the lever, the detent mechanism able to fix rising and falling angles of the lever at plural angular positions.  
   
   
       6 . The auto chain tensioner according to any one of claims  2  to  5 , characterized in that a support axis supporting the lever so as to allow the lever to raise and fall freely is disposed at a part away from a rotation centerline of the disk without intersecting with the rotation centerline of the disk.  
   
   
       7 . The auto chain tensioner according to  claim 1 , characterized in that 
 the chain cover fixing means has a link mechanism, and    the link mechanism comprises: a fixing link mechanism which presses and holds the guide bar between the engine case and the chain cover by an engagement with a fixing member fixed to an engine case side, and fixes the chain cover to the engine case; and a sliding link mechanism which slides one of the slider piece and the tensioner in the back and forth moving direction of the guide bar.    
   
   
       8 . The auto chain tensioner according to any one of  claims 1  to  7 , characterized in that a spring connecting the slider piece and the tensioner is a coil spring, one end of the coil spring is fixed to the tensioner, and the other end of the coil spring is screwed together with a screw portion disposed at the slider piece directly or via a screw portion attached to an end of the coil spring.  
   
   
       9 . The auto chain tensioner according to  claim 8 , characterized in that the slider piece and the tensioner are guided into the chain cover irrotationally but slidably, and the screw portion disposed at the slider piece is supported to the slider piece rotatably and disposed such that rotating operation is possible from an outside.  
   
   
       10 . The auto chain tensioner according to any one of claims  8  and  9 , characterized in that at least one of screw heads, i.e., a screw head at a screwing portion of the screw portion disposed at the slider piece and the coil spring, a screw head at a screwing portion of the screw portion disposed at the slider piece and the screw portion attached to the end of the coil spring, and a screw head at a screwing portion of the coil spring and the screw portion attached to the end of the coil spring, is formed into such a shape that the other member screwed together with the screw head by a spring force added to the coil spring more than a prescribed strength overleaps the screw head.  
   
   
       11 . The auto chain tensioner according to  claim 1 , characterized in that one of the slider piece and the tensioner comprises a engagement protrusion for engaged with the guide bar, a pawl in a ratchet mechanism is formed at a front end portion of the engagement protrusion, a pawl receiving member for engaged with the pawl in the ratchet mechanism is disposed in the engine case, and the pawl receiving member is urged to a side of the engagement protrusion.  
   
   
       12 . The auto chain tensioner according to  claim 1 , characterized in that a contact face of the engine case which contacts with the guide bar and/or a contact face of the chain cover is formed such that a friction coefficient at the contact face is increasing.  
   
   
       13 . The auto chain tensioner according to  claim 1 , characterized in that at a contact face of the guide bar which contacts with the engine case and/or contact face which contacts with the chain cover, a wedge face is formed.  
   
   
       14 . The auto chain tensioner according to  claim 1 , characterized by further comprising one or more fixing portion of the chain cover for enabling to fix the chain cover at plural portions in conjunction with operation of the chain cover fixing means in the chain cover.  
   
   
       15 . The auto chain tensioner according to  claim 1 , characterized by comprising temporary fixing means for temporarily fixing the guide bar to the engine cover so that a fixing face of the guide bar is in parallel with a fixing face of the engine cover.