FR2692832A1 - Tensioning device for a saw chain. - Google Patents

Abstract

A known device serving as a tensioner for a saw chain running on a guide bar (12) of a chain saw has a rotating disc (16) with a spiral guide groove in which a tenon ( 9) of a slide (8). By rotation of the disc (16) there is thus produced a longitudinal movement of the chain guide (12). You therefore need a tool to turn the disc (16) and another tool to tighten the guide bar. The required clamping force is very large because the forces acting on the guide bar (12) are transmitted to the disc (16) in such a way that the latter tends to rotate. According to the invention the guide groove extends in the disc (16) through a rotation angle of at least 270 degree, thus reducing the pitch of the guide groove and hence also the forces tending to rotate the disc. (16).

Description

Tensioning device for a saw chain

  The present invention relates to a device

  front of tensioner to a saw chain circulating on a guide

  chain of a chain saw and in which the guide

  chain is held tight at one of its ends between an envelope, receiving the drive motor, and a clamping member and, when the clamping member is loosened, the guide bar can be caused to slide in the longitudinal direction, a slide, provided with a tenon

  projecting transversely to the sliding direction

  ment, and a rotary disc having a curvilinear guide groove, in which engages said stud, being provided

for sliding.

  Patent CA-A 1106264 describes a chain motor saw equipped with a tensioning device which comprises

  basically a slide and a rotating disc, the

  slider being engaged with the guide bar The slider

  has a lug that projects into a guide groove

  curvilinear dage provided in the disc, so that in case of

  disc rotation the slide and, therefore, equal

  the guide bar slides longitudinally To make

  re turn the disc you need a screwdriver or similar tool

  which, when engaged in appropriate slots in the disc,

  puts to turn this last step by step Given

  that a cover plate with a window does not

  guarantee that a small angular interval of all the windows

  tes, the desired voltage adjustment operation of the

  chain is extremely laborious To subjugate the organ-

  nes of adjustment, the cover plate is then tightened by means of two nuts, which are screwed on bolts integral with the casing, against the disc, the guide bar

  and the envelope This also requires a tool,

see a wrench.

  Consequently, the present invention aims to create a tensioning device of the kind defined above.

  but by means of which one can, without any tool and ma-

  simple, adjust the guide bar and secure the

  adjustment nes securely. This object is achieved, for a device serving as a tensioner for a saw chain, circulating on a chain guide, of a chain motor saw and in which the chain guide is held tight at one of its ends between

  an envelope, receiving the drive motor, and an

  clamping gane and, when the clamping member is loose-

  re, the guide bar can be made to slide in the di-

  longitudinal rection, a slide, fitted with a weak tenon

  projecting transversely to the sliding direction

  ment, and a rotary disc having a curvilinear guide groove, in which the pin engages, being provided,

  according to the invention by the fact that the guide groove is

  tends to have an angle of rotation of at least 2,700.

  The essential advantages of the present invention are that, due to the reduced pitch of the guide groove, exact adjustment by hand is possible and all

  the forces acting in the longitudinal direction on the guide

  chain are absorbed by the disc without it exerting itself on

  the disk of forces acting in the direction of rotation.

  This last effect is obtained since the tangent to the groove

  guide at the point of support of the post is sensitive-

  lie a line perpendicular to the longitudinal direction of the chain guide, which is inside the cone of

  friction thus formed The forces produced are thus absorbed

optimally.

  A particularly preferred embodiment of the object of the invention consists in that the guide groove extends over an angle of rotation of between 360 and 4500 Thanks to such an important angle of rotation the pitch of the guide groove is extremely reduced, this solution being considered optimal for reasons

  constructive and with regard to handling The diffe-

  The difference between the minimum distance and the maximum distance of the guide groove from the center of rotation of the disc determines the maximum sliding path of the guide bar. This difference will preferably be approximately mm. In order to be handy and to be able to be easily turned in the loose state of the tensioning device, this disc

  has at its outer periphery recesses or recesses.

  For various reasons it can occur in the guide-

  chain of forces acting on the guide bar as

  that couple For this couple to be absorbed it is necessary to

  ference attached to the envelope a guide member which engages in a slot of the chain guide The guide member

can be oblong or round.

  An advantageous embodiment of the slide consists in that the latter is produced substantially in a U, the tenon cooperating with the guide groove located on the arc of the U, and near the end of each of the branches of the U being arranged a projection directed towards

  the other side and intended to engage in corresponding holes

  of the guide bar The slide can however also

  LEMENT be in the form of a flat plate which has on one side the pin for the guide groove and

  the other side a projection intended to engage in the guide-

  chain, the tenon and the projection being at least approxi-

  matively on the same straight line perpendicular to the plane of the slide.

  So that the tensioning device can be manipulated

  lé perfectly without tools it is proposed to provide as a tightening member a wing nut capable of being screwed on a bolt integral with the casing This wing nut is appropriately sized so that manual tightening is sufficient to easily apply the required clamping force As a clamping member can also

  a wheel or a ripple with marginal ripple must be provided

  nale capable of being screwed onto a bolt secured to the casing Between the clamping member and the disc, a support plate can be placed so as not to

not be able to turn.

  The present invention is explained in more detail

  tail below using the attached drawings in which:

  FIG. 1 is an exploded view of a pre-

  better embodiment of the tensioning device; Figure 2 is a horizontal section through a second embodiment of the tensioning device; Figure 3 shows a section along line III-III of Figure 2; and Figure 4 is a view along arrow IV of the

figure 2.

  In figure l is shown a detail of a

  veloppe 10 of a chain saw, namely the region where there is an opening il for the motor pinion, not shown in the figure, and the retainer for a chain guide 12 The retainer comprises a bolt 13 secured to the casing and a guide pin 14, the bolt 13 having a sufficient height so that it passes, in the region of a longitudinal opening 15, to

  through the guide bar 12, a rotating disc 16 and a plate

  that support 17 and that a hand wheel 18 can be screwed

  on the end thread The guide pin 14 is dimensioned

  sectioned so as to engage in the longitudinal opening of the chain guide, thus allowing longitudinal guidance

  exact guide bar 12 and the resorption of couples.

  Next to the longitudinal opening 15 of the guide-

  chain 12 are two openings 19 in the form of small

  your holes in which engage in an adjusted manner projections 21 disposed laterally at the ends of the branches 20 of a slide 8 in U The slide 8 in U has on its arc 22 a tenon 9 which projects on the slide on the side far from the guide bar 12 This tenon 9 engages in a curvilinear guide groove 5 formed in the rotary disc 16 The guide groove 5 extends over a rotation angle of approximately 3900 In this case, one end 6 of the guide groove 5 is at a minimum distance and the other end 7 at a maximum distance from the center of rotation D When the disc 16 is rotated, the rotational movement is transformed, due to the pin 9 engaging in the guide groove 5, in a longitudinal sliding of the slide 8, which determines

  in turn a sliding of the same importance of the guide-

  chain 12 The total sliding path possible is de-

  ended with the difference between the minimum distance and the

  maximum distance from the center of rotation.

  The rotating disc 16 has on its edge

  regularly distributed hollows 23 which ensure good handling

  Ability when adjusting the chain tension To be able to be mounted on the bolt 13 the disc 16 has a central hole 24 The support plate 17 and the hand wheel 18 are provided to allow the adjusted chain tension d 'be made fixed The support plate 17 has a hole, through which passes the bolt 13, and a projection 26 oriented towards the casing 10 and which engages in a corresponding opening 27 of the casing, preventing thus the support plate, namely the cover 17 of the wheel

  chain, to turn The support plate 17 is pressed against

  be the disc 16, by means of the hand wheel 18 capable

  to be screwed on the bolt 13, so as to exclude any

  inadvertent placement of the disc 16 due to vibrations, or the like Advantageously, the side of the disc 16 contiguous to the slide 8 as well as the side of the slide 8 contiguous to the

  disc 16 are provided with cross or ana-

  in order to increase the friction adjustment between the parts

  These are thus avoided, when tightening the handwheel 18, the disc 16 is not rotated so that a

  sufficient force can be exerted on the vehicle without tools

  hand lant 18 this is provided with a marginal corrugation 28. The tensioning device shown in Figures 2 to 4 is based on the same principle as that of Figure 1 It

  However, a slide of another form is used there.

  which the bearing force between the disc and the guide bar

  ne and / or the envelope and the guide bar is increased The fig-

  re 2 shows a detail of an envelope 1 which is for example made of plastic In the envelope 1 is fixed a bolt

  13 which passes through the longitudinal opening 15 of the guide

  chain 12, a slide 2 and a rotating disc 3 A gold-

  oblong guide rod 29 made in one piece with the envelope

  loppe 1 engages in the longitudinal opening 15 of the guide

  chain 12 The slider 2 has the shape of a flat plate on the plane of which is attached, on the side of the disc 3, a stud 9 which engages in a guide groove 4 of the disc 3 On the other side of the slider 2 there is a projection 30 which engages in the longitudinal opening 15 of the

  guide bar 12 and extends along the same perpendicular line

  cular to the plane of the slide 2 as the tenon 9.

  The shape of the slide 2 is shown on the

  figure 3 This is a roughly rec-

  tangular with a longitudinal slot 31 which is oriented

  exactly like the longitudinal opening 15 of the guide bar

  ne 12 The pin 9 enters the guide groove 4 which extends in a spiral around a central hole crossed by the bolt 13 The whole angle of rotation of the guide groove 4 is, in FIG. 3 , of approximately 4500 The same operation would be obtained, with a somewhat different pitch, if the angle of rotation was only 3600. By turning the disc 3 clockwise, the tenon moves, thanks to the layout of the guide groove 4, with the slider 2 to the right so that the projection 30 of the slider 2 pushes the guide bar also to the right so as to tension the

  saw chain not shown in the figure.

  A wing nut 32, which is screwed onto the plug

  lon 13 and has a pressure surface 33 for taking

  pressing a large area against the disc 3, serves to re-

  hold the disc 3 in the adjusted position A cover 34 made of plastic, which extends substantially in the plane of

  the wing nut, covers the upper part of the guide

  chain and the saw chain running on it as

  as shown in FIG. 4, the cover 34 made of pre-plastic

  feels an opening 35 so that the wing nut 32 is accessible without having to remove the material cover

plastic.

Claims (6)

  1 Device serving as a tensioner for a sawing chain circulating on a chain guide (12) of a chain motor saw and in which the chain guide (12) is retained at one of its ends by clamping between an envelope ( 1,   ), receiving the drive motor, and a   rage (18, 32) and, when the clamping member (18, 32) is loosened, the guide bar (12) can be made to slide in the longitudinal direction, a slide (2, 8), provided   a stud (9) projecting transversely to the direction   sliding, and a rotating disc (3, 16) with a curvilinear guide groove (4, 5), in which engages   the pin (9), being provided for sliding of the guide-   chain, characterized in that the guide groove (4, 5)   extends over a rotation angle of at least 2,700.   2 tensioning device according to claim 1, characterized in that the guide groove (4, 5) extends   on an angle of rotation between 360 and 4500.   3 tensioning device according to claim 1 or   2, characterized in that the difference between the mid distance   nimal and the maximum distance from the guide groove (4,) to the center of rotation (D) of the disc (3, 16) is approximately mm. 4 Tensioner device according to any one   of the preceding claims, characterized in that the   disc (16) has, at its outer periphery, recesses or hollow (23).   Tensioning device according to any one of   previous claims, characterized in that with the   veloppe (1) is made in one piece a guide member a (29) which engages in a longitudinal opening (15) of the chain guide (12).   6 Tensioning device according to any one of   previous claims, characterized in that the coulis-   bucket (8) is essentially U-shaped, the pin (9) cooperating with the guide groove (5) located on the arc (22) of the U, and near the end of each   branches (20) of the U being provided with a projection (21) ori-   entered on the other side and intended to engage in   corresponding holes (19) of the chain guide (12).   7 Tensioning device according to any one of   Claims 1 to 5, characterized in that the slide   (2) has the shape of a flat plate which has a   side of the pin (9) for the guide groove (4) and the   tre side a projection (30) intended to engage in the   guide bar (12), the lug (9) and the projection (30) extend   at least approximately along the same straight line pendulum to the plane of the slide.   8 Tensioning device according to any one of   previous claims, characterized in that it is pre-   seen as a clamping member a wing nut (32) which can be screwed onto a bolt (13) integral with the casing. 9 Tensioning device according to any one of   claims 1 to 7, characterized in that the serving member   rage is a hand wheel or hand wheel (18) fitted with a   marginal dulation (28), which can be screwed onto a bolt   (13) integral with the envelope.   Tensioning device according to claim 9, characterized in that between the clamping member (18) and the disc (16) is mounted a support plate, preferably the cover (17) of the chain wheel, which is prevented from turning.