Chain saw tensioning mechanism

A mechanism for tensioning the chain of a chain saw. The apparatus includes a cutting bar around which the chain extends. The cutting bar has a base portion mounted to an operating housing of the chain saw, and a distal portion carried by the base portion at an end thereof remote from the housing. The distal portion of the cutting bar is disposed for sliding extension relative to the base portion of the cutting bar. The distal portion of the cutting bar mounts a sprocket, around which the chain passes, at an outer end thereof. The sprocket is disposed for rotation about an axis. Structure is included to effect extension of the distal portion of the cutting bar relative to the base portion thereof. Tensioning of the chain saw is, thereby, accomplished.

TECHNICAL FIELD 
The present invention deals broadly with the field of cutting implements. 
More narrowly, however, the present invention is related to cutting 
implements known as chain saws. The focus of the invention is structure 
employed to maintain a proper tension on the cutting chain of a chain saw. 
BACKGROUND OF THE INVENTION 
Various types of cutting implements are known in the prior art. The 
particular implement that would be selected by a person would, of course, 
depend upon the function to be achieved. 
One particular application for a cutting instrument is one wherein heavy 
wooden items are to be sawed. An example of this type of use is the 
logging industry wherein trees are cut down, cut into segments, etc. An 
implement known as a chain saw is used to effect this function. 
On a smaller scale, homeowners purchase and use chain saws, for example, to 
prune trees in their yards. That is not to say that chain saws, in a 
residential environment, do not have other applications. The chain saw is, 
in fact, a very versatile appliance. 
Use of chain saws dictates certain features be incorporated into the 
device. The features are functions of a desire to maximize efficiency and 
minimize dangers in use. A feature which derives from both of these 
considerations is one wherein the chain is maintained in a taut 
configuration both at start-up and during use. Certainly, the more taut 
the chain is, the more efficiently the appliance will cut. If the chain is 
slack, the cutting process will be slower, and the cut-line will be less 
clean. 
Probably of more significance is the safety aspect. It is essential that 
all precautions be taken when utilizing any implement having a cutting 
element which is moving at a very high rate of speed. This dictate is 
particularly necessary to be observed in the case of chain saws. 
In furtherance of maximization of safety, it is extremely important that 
unnecessary slack be eliminated from the run of the chain saw chain. If 
too much slack is present, it might even be possible for the chain to jump 
off the sprockets over which it runs. As will be clear to the casual 
observer, if this occurred, the results could be disastrous. 
If the chain is not maintained in a taut configuration, the chain could, 
possible, snap. A tension might become applied while the equipment were 
running and slack might be eliminated in a microsecond. This application 
of a high measure of tension in a very short period of time can result in 
the breaking of the chain. Again, one can envision the hazard to life and 
limb that would result. 
It is optimum, therefore, that the chain of a chain saw be maintained 
uniformly at an appropriate level of tension. By doing so, both efficiency 
and safety are maximized. 
It is to these problems and dictates of the prior art that the present 
invention is directed. It is an improved tensioning mechanism for use in a 
chain saw application. 
SUMMARY OF THE INVENTION 
The present invention is a structure which functions to tension the chain 
of the chain saw in order to achieve an appropriate level of uniform 
tensioning of the chain. It includes a cutting bar around which the chain 
is made to extend. The cutting bar is bifurcated to include a base portion 
and a distal portion. The base portion is mounted to an operating housing 
of the chain saw, and the distal portion is carried by the base portion at 
an end thereof remote from the operating housing. The distal portion is 
disposed for sliding extension relative to the base portion. The distal 
portion carries a sprocket at its outer end. The run of the chain passes 
over the sprocket, and the sprocket is disposed for rotation about an axis 
in order to facilitate operation of the implement. Means are included for 
extending the distal portion of the cutting bar relative to the base 
portion thereof in order to apply the desired measure of tension to the 
chain. 
A first embodiment of the invention, while it is intended to be hydraulic 
in operation, can also function pneumatically. In this embodiment, the 
base portion of the cutting bar is provided with a channel therewithin. 
The channel, it is intended, would run generally parallel to inner and 
outer runs of the continuous chain. An access port is provided to 
communicate with the channel, and this port is formed through a wall 
defined by the base portion of the cutting bar. Typically, the access port 
would be proximate an inner end of the channel. 
The distal portion of the cutting bar, in this embodiment, is provided with 
an inwardly extending piston. The piston is received within the channel 
for telescoping movement relative thereto. An inner edge of the piston 
closes the channel to define a plenum inwardly from the piston. Fluid can 
be injected into this plenum through the access port. As fluid, such as 
grease, is injected into the plenum, the fluid acts upon the piston to 
urge it outwardly. As a result, extension of the distal portion of the 
cutting bar, relative to the base portion, is effectuated. 
In order to maintain the tension applied, the access port is normally 
closed and affords one-way passage of fluid into the plenum. This can be 
accomplished by the means of a ball valve, a ball of which is biased 
outwardly within the plenum to be normally seated against the port. With a 
structure so configured, grease can be inserted into the port, and the 
insertion of the grease will overcome the bias of the check valve. After 
the injection device is withdrawn, however, the valve will close to 
preclude leakage of the fluid outwardly through the access port. 
Similarly, means can be provided for precluding leakage of the fluid 
outwardly through the channel. This can be accomplished by means of 
sealing the piston relative to the inner wall defining the channel. A 
block seal can be utilized for this purpose. Other appropriate sealing 
means could also be employed. 
A second embodiment of the invention is mechanical in operation. That is, 
it employs mechanical actuation means urging the piston outwardly, rather 
than hydraulic or pneumatic means. 
One mechanical actuation means embodiment employs a cam received within a 
generally circular aperture within the base portion of the cutting bar. An 
outermost edge of the cam, typically, would be in close proximity to a 
circumferential edge of the generally circular aperture within the base 
portion of the cutting bar, and an outer surface of the cam would be in 
engagement with an inner edge of the piston which extends into the 
generally circular aperture. The cam is disposed for rotation about an 
axis generally transverse to an intended direction of extension of the 
distal portion of the cutting bar. As a result, as the cam is rotated 
about the axis in a first direction, the piston will be urged outwardly. 
In this embodiment, the outermost edge of the cam can be provided with an 
outwardly biased pawl. The pawl can be provided with teeth, and the 
circumferential edge of the generally circular aperture within the base 
portion of the cutting bar can be toothed in a manner so that it 
cooperates with the teeth of the pawl. As a result, as the cam is made to 
rotate in a first direction, the pawl/toothed circumferential edge 
assembly will preclude rotation of the cam in a second direction which 
would permit retraction of the distal portion of the cutting bar relative 
to the base portion. 
A third embodiment of the invention is intended to be substantially 
automatic in operation. That is, it is intended that, in this embodiment, 
the tension be automatically adjusted. 
In this embodiment also, a reciprocally disposed piston is provided. The 
inner end of the piston is tapered on both sides to define ramped 
surfaces. The piston is normally biased outwardly by means of a strong 
spring which engages the base of a channel within the base portion of the 
cutting bar, at one end, and an inner edge of the piston, at the other. 
It will be understood that, possibly, such outward biasing of the piston 
might be overcome during operation of the chain saw. As a result, in this 
embodiment, a pair of ramped members can be provided within the channel 
within which the piston reciprocates. The ramp members are in positions 
engageable with the ramped surfaces of the piston. The ramp members are 
also outwardly biased so that, when the chain of the saw is not subject to 
external forces and the strong spring biasing of the piston in an outward 
direction occurs, the ramp members will be biased into positions to wedge 
the piston against subsequent withdrawal. 
If desired, the ramp members are provided with pins which ride along tracks 
in the cutting bar. Such cooperation enables appropriate positioning of 
the ramp members. 
The present invention is thus an improved apparatus for tensioning the 
chain of a chain saw implement. More specific features and advantages 
obtained in view of those features will become apparent with reference to 
the DETAILED DESCRIPTION OF THE INVENTION, appended claims, and 
accompanying drawing figures.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings wherein like reference numerals denote like 
elements throughout the several views. FIG. 1 illustrates a first 
embodiment of a structure in accordance with the present invention. That 
figure shows the end of a chain saw cutting bar 10 which is remote from 
the operating housing (not shown) of a chain saw implement. A chain (not 
shown) having cutting teeth mounted thereto, extends around the cutting 
bar 10 and runs at a high speed to effect cutting. 
FIG. 1 (and FIGS. 2 and 3 also) illustrate a cutting bar 10 which is 
bifurcated. That is, the cutting bar is comprised of two portions. A base 
portion 12 of the bar 10 is mounted to the operating housing, and a distal 
portion 14 of the bar 10 is carried by the base portion 12 at an end 
thereof which is remote from the housing. 
The distal portion 14 of the cutting bar 10 is disposed for reciprocating 
movement relative to the base portion 12. As will be seen hereinafter, as 
the distal portion 14 is made to move outwardly relative to the base 
portion 12, the chain extending over the cutting bar 10 will be tensioned 
in view of the fact that an outer end of the distal portion 14 mounts a 
sprocket 16 over which the chain passes. 
All three embodiments illustrated in FIG. 1-3 function to accomplish 
tensioning of the chain by urging the distal portion 14 of the cutting bar 
10 outwardly from the base portion 12. The embodiment illustrated in FIG. 
1, however, functions hydraulically or pneumatically. FIG. 4b illustrates 
the end of the base portion 12 of the cutting bar 10 remote from the 
operating housing. As seen in that figure, the base portion 12 can be 
laminar in configuration. Lateral closure plates 18 sandwich therebetween 
upper and lower track members 20, 22. A window 24 is defined within the 
end of the base portion 12 remote from the operating housing, and the size 
and shape of the window 24 is such that the distal portion 14 of the 
cutting bar 10 can be received within the window 24 for longitudinal 
movement therealong. 
As in seen in FIG. 4A, the distal portion 14 of the cutting bar 10 is also 
laminar in construction. A pair of lateral plates 26 sandwich a piston 28 
therebetween. The piston 28 is provided with a vertical dimension 
substantially the same as the distance 30 between upper and lower tracks 
defined by corresponding upper and lower track members 20, 22 sandwiched 
between the lateral plates 18 of the base portion 12 of the cutting bar 
10. The piston 28 extends inwardly from inner edges 32 of the plates 26 
sandwiching the piston 28 therebetween. 
Referring again to FIG. 4B, it can be seen that the upper and lower track 
defining members 20, 22 are such that they are spaced vertically from one 
another. As will be able to be seen then, a longitudinally-extending 
channel 34 is formed within the base portion 12 of the cutting bar 10. The 
distal portion 14 and base portion 12 of the cutting bar 10 cooperate so 
that the piston 28 extending inwardly with respect to the inner edges 32 
of the plates 26 of the distal portion 14 of the cutting bar 10 extends 
into the channel 34 as upper and lower grooves 36, 38 formed in the distal 
portion 14 ride along the upper and lower track members 20, 22 provided in 
the base portion 12. 
As best seen in FIG. 5, an access port 40 is provided in order to afford 
fluid communication from outside the base portion 12 of the cutting bar 10 
to a plenum 42 defined within the channel 34 by the upper and lower track 
forming members 20, 22, the lateral plates 18 sandwiching those members 
20, 22 therebetween, an inner wall 44 defining the base of the channel 34, 
and the piston 28, when the piston 28 is received within the channel 34. 
FIG. 5 also shows a ball check valve 46 as being seated internally within 
the plenum 42 against the access port 40. The ball check valve 46 is 
biased to a closure position by means of a coil spring 48. It will be 
understood, however, that any appropriate biasing means could be employed. 
As will be able to be seen in view of this disclosure, increasing of fluid 
pressure within the plenum 42 will serve to urge the piston 28 outwardly 
and concurrently drive the distal portion 14 of the cutting bar 10 
relatively outward with respect to the base portion 12. By increasing 
fluid pressure within the plenum 42, therefore, the chain can be 
tensioned. 
It is frequently necessary to grease or oil an implement such as a chain 
saw. It is envisioned that, while performing such a function, grease, for 
example, could be injected into the plenum 42 through the access port 40. 
Increased pressure in a grease gun would overcome the biasing of the ball 
check valve 46, and grease would enter into the plenum 42 to drive the 
piston 28 outwardly. As the grease gun would be withdrawn, however, the 
spring 48 would bias the ball check valve 46 to a closure position to 
preclude egress of the injected fluid. As a result, the piston 28 would be 
maintained in its extended disposition. The chain would, thereby, be 
maintained in a tensioned configuration. 
FIGS. 1, 4A, and 5 illustrate a seal 50 which, if used, would be received 
within the channel 34 against the inner face 52 of the piston 28. The size 
and shape of the seal 50 would be selected in view of the dimensions of 
the channel 34. The figures illustrate a "block" seal member 50 which has 
dimensions so as to preclude leakage of fluid around the piston 28. 
It will be understood that, while grease has been described as a fluid that 
could function to effect extension of the piston 28, such a fluid is not 
exclusive. Other fluids, such as air, could be employed in certain 
embodiments to effect extension. 
FIG. 6 illustrates a cross-section of the cutting bar 10 at a location 
intersecting both the distal portion 14 and the base portion 12 thereof. 
As is able to be seen in that figure, rivets 54 or other appropriate 
securing means can be employed to effect a tight sandwiching of the 
various laminar structures. It will be understood, however, that any 
appropriate securing means could be employed. 
FIG. 2 illustrates a second embodiment of the invention. This embodiment 
employs mechanical means, rather than hydraulic or pneumatic means, to 
effect extension of the piston 28 and outward relative movement of the 
distal portion 14 of the cutting bar 10 relative to the base portion 12. 
The construction of the distal portion 14 and base portion 12 of the 
cutting bar 10 are substantially identical to the construction of those 
components in the embodiment of FIG. 1. In FIG. 2, however, an 
axially-extending channel 34 in the base portion 12 communicates with a 
circular aperture 56 sandwiched between the lateral laminar plates 18. The 
piston 28, thereby, extends into this circular aperture 56. A cam 58 is 
mounted within this aperture 56 and journalled between the lateral plates 
18. It is disposed for rotation about an axis which is oriented generally 
transverse to an intended direction of extension of the distal portion 14 
of the cutting bar 10 and the piston 28 carried thereby. 
The cam 58 is mounted for rotation so that an outermost edge 60 thereof 
passes closely proximate a toothed, circumferential edge 62 defining the 
circular aperture 56. The outermost edge 60 of the cam 58 can, in one 
embodiment, carry a pawl structure 64. The pawl 64 would be outwardly 
biased so that a toothed surface 66 thereof would cooperate with the 
toothed circumferential edge 62 of the generally circular aperture 56 in 
the base portion 12 of the cutting bar 10 to preclude rotation of the cam 
58 in a second direction (counter-clockwise as viewed in FIG. 2). 
As seen in FIG. 2, the cam 58 is provided with a coaxial, faceted aperture 
68 which is accessible externally with respect to the cutting bar base 
portion sandwiching plates 18. In the embodiment illustrated, this 
aperture 68 is square. It will be understood, however, that any faceted 
geometric figure would be appropriate. The aperture 68 receives the 
insertion of a correspondingly sized and shaped tool (not shown) so that 
the cam 58 can be volitionally rotated in a first direction (a clockwise 
direction as viewed in FIG. 2). 
When tensioning of the chain is necessary, the tool is inserted into the 
faceted aperture 68, and the cam 58 is rotated in the first direction. The 
directions of cant of the teeth of the circumferential edge 62 defining 
the circular aperture 56 and of the teeth of the toothed surface 66 of the 
pawl 64 are such that the rotation of the cam 58 in the first direction 
will not be precluded. Intermeshing of the teeth, however, will preclude 
rotation in the second direction. When the tool is inserted into the 
faceted aperture 68 and the cam 58 is rotated in the first direction, 
therefore, an increasingly larger radiused section of the cam 58 will be 
made to engage the inner face 52 of the piston 28, and the piston 28 will, 
concurrently, be urged outwardly. Rotation of the cam 58 in the first 
direction will thereby effect "cinching up" of the piston 28 in an 
outwardly direction. As will be able to be seen in view of this 
disclosure, therefore, the chain will be tensioned as a result. 
FIG. 3 illustrates a third embodiment of the invention. The embodiment of 
FIG. 3 again employs mechanical means. In the case of this embodiment, 
however, tensioning is effected automatically. Again, construction of the 
distal portion 14 of the cutting bar 10 is substantially the same as in 
the case of the embodiments of FIGS. 1 and 2. That is, a piston 28 extends 
inwardly within a channel 34 defined within the base portion 12 of the 
cutting bar 10. 
In the embodiment of FIG. 3, however, a strong spring member 70 is disposed 
generally centrally within the channel 34. One end of the spring member 70 
engages a base 44 of the channel 34, and the other end engages the piston 
28 through an intermediate transmission member portion 72 of the piston 28 
which is disposed between the spring 70 and a main portion of the piston 
28. It will be understood that, while FIG. 3 shows transmission member 
portion 72 as being separate from the main portion of the piston 28, 
transmission member portion 72 could, in fact, be formed integrally with 
the main portion of the piston 28. 
FIG. 3 shows this transmission member portion 72 as being generally 
trapezoidal in shape, upper and lower sloped surfaces 74, 76 thereof 
converging toward the center of the channel 34 as they approach the base 
44 of the channel 34. That figure also illustrates the transmission member 
portion 72 as carrying a pin 78 which is positioned to ride along a 
longitudinally extending slot 80 in one or both of the lateral sandwiching 
plates 18 of the base portion 12 of the cutting bar 10. More positive 
control of movement of the transmission member portion 72 is, thereby, 
afforded. 
As previously indicated, the transmission member portion 72 is intermediate 
the urging spring 70 and the inner face 52 of the piston 28, and the 
member portion 72 engages the inner face 52 of the piston 28 at its end 
opposite that engaged by the spring 70. Consequently, force exerted upon 
the transmission member portion 72 by the spring 70, is, in turn, 
transmitted to the distal portion 14 of the cutting bar 10 to urge the 
sprocket 16 outwardly in order to effect tensioning of the chain. 
FIG. 3 also illustrates means which function to inhibit withdrawal of the 
piston 28 within the channel 34 during operation of the chain saw. As will 
be understood, the outward urging of the distal portion 14 of the cutting 
bar 10 by the spring 70 occurs when the chain saw implement is in a 
non-operational mode. If such means to inhibit withdrawal were not 
provided, during operation of the chain saw, the sprocket 16 might be 
driven inwardly against the bias of the spring 70 urging the piston 28 
outwardly. 
FIG. 3 illustrates one embodiment of such means. Shown are a pair of ramp 
members 82 received within the channel 34, each member 82 engaging an 
upper or lower edge of the channel 34, on a first side, and having sloped 
second sides 84 in engagement with corresponding sloped edges 74, 76 of 
the transmission member 72. The ramp members 82 operatively cooperate with 
the transmission member portion 72 since the angles of the ramp members 82 
are complementary with those of the transmission member portion 72. As a 
result, the transmission member portion 72 is rotationally posited within 
the channel 34. 
As seen in FIG. 3 also, each ramp member 82 is biased outwardly within the 
channel 34. A pair of second springs 86 are illustrated as being provided 
for this purpose. The pair of second springs 86, while being strong enough 
to urge the ramp members 82 outwardly within the channel 34, are less 
strong than the first spring 70 which engages the transmission member 
portion 72. Consequently, the primary urging of the distal portion 14 of 
the cutting bar 10 outwardly is effected by the first spring 70 acting 
against the transmission member portion 72. As the piston 28 and its 
transmission member portion 72 are moved outwardly, however, the second 
springs 86 urge the ramp members 82 outwardly so as to preclude withdrawal 
of the piston 28 back into the channel 34 during an operational mode of 
the chain saw implement. 
FIG. 7 illustrates one sloped surface 76 of the transmission member portion 
72 as having a plurality of recesses 88 formed therein. Each recess 88 is 
provided with a roller bearing 90 which is biased to the lower end of the 
recess 88 by, for example, a small coil spring 92. As shown in FIG. 7, the 
lower end of the recess 88 has a smaller dimension perpendicular to sloped 
surface 76 than does the upper end of the recess 88. As a result, when a 
roller bearing 90 is at the lower end of the recess 88 in which it is 
received, bearing 90 will more significantly protrude from recess 88. In 
view of the location to which the roller bearing 90 is urged by coil 
spring 92 within its corresponding recess 88, therefore, and the 
commensurate greater protrusion of bearing 90 from recess 88 and resultant 
increased wedging effect withdrawal of the piston 28 and transmission 
member portion 72 back within the channel 34 will be more effectively 
inhibited. Extension of the piston 28 and distal portion 14 of the cutting 
bar 10 with which the piston 28 operates will not, however, be retarded, 
since ramp members 82 do not work against extension. 
FIG. 3 illustrates a corresponding plurality of recesses 88 formed in an 
upper sloped surface 74 of the piston transmission member portion 72. It 
will be understood, however, that such a recess or recesses 88 are not 
essential to the invention, and embodiments wherein no recesses are 
provided or more or less than two recesses are provided in each sloped 
surface 74, 76 are within the scope of the invention. 
Numerous characteristics and advantages of the invention covered by this 
document have been set forth in the foregoing description. It will be 
understood, however, that this disclosure is, in many respects, only 
illustrative. Changes may be made in details, particularly in matters of 
shape, size, and arrangement of parts without exceeding the scope of the 
invention. The invention's scope is, of course, defined in the language in 
which the appended claims are expressed.