Note: Descriptions are shown in the official language in which they were submitted.
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This is a division of co-pending Canadian Patent
app]ication Serial No. 335,868 which was filed on
September 18, 1979.
BAC~GROUND OF THE INVENTION
Field of the Invention:
The present invention relates to portable chain
saw equipment and in particular relates to an improved
chain saw brake control and actuating mechanism for main-
taining the brake in disengaed condition during normal
operation and for automatically engaging the brake to
protect the operator from the cutting chain in the event
of contact between the operator and the safety lever which
may occur as a result of "kickback".
Description of the Prior Art:
A manually operated, portable chain saw commonly
includes an engine carrying housing, a guide bar projecting
forwardly from the housing and an engine driven cutter
chain mounted on the guide bar for continuous movement.
Proper operation of the chain saw requires that an operator
grasp the machine with both hands, one hand holding a
gripping handle mounted on the housing, and the other hand
engaging a housing control handle for actuating a trigger
throttle mechanism.
A well known safety problem in the use of a
manually operated portable chain saw of this type is the
occurrence of "kickback". Kickback is characterized by a
violent movement of the saw which may occur when the nose
of the guide bar and cutting chain contacts a solid object.
The cutting chain of the saw tends to bite into the solid
object with a force proportional to the speed of the chain.
At the same time, there is a corresponding reaction force
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exerted on the saw by the object. If the momentum of the
chain and other moving parts of the saw carries the chain
into the object, then the energy of the chain is expended in
the cutting action and the reaction force on the saw is
greatly reduced. However, at lower chain speeds, the
momentum may not be sufficient to sustain the cutting
action, and the chain may be come seized within the object.
If the chain is not carried on through the cut, the saw is
suddenly subjected to a full reactive force. When this
force is exerted at the middle or on the upper quadrant of
the nose of the guide bar and cutting chain, the nose moves
suddenly upward in rotation generally about the rear of the
saw.
Because of the way that a chain saw is held, the
kickback motion is extremely difficult for an operator to
control; thus there is considerable risk that he will be hit
by the moving chain. If the saw is being held horizontally
at the time of the kickback, then its motion will be some-
what opposed by the weight of the saw. This opposition
decreases substantially as the saw i5 held more nearly
vertically. For this reason, perhaps the most dangerous
kickback situation is when the saw is being used to cut
overhanging limbs or other such objects. There may be
additional lack of control in this situation if the
operator's arms are extended to reach the object above.
A number of safety brakes have been developed for
quickly stopping the chain when kickback occurs. Although
these safety brakes and their actuating mechanisms represent
significant advancements, room for further improvement in
the art remains. For example, there is a continuing interest
in reducing the reaction time of the actuating and braking
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mechanism, and in reducing the number and size of the
mechanical components required for carrying out the
actuating and braking mechanism in order to minimize the
weight and size of the manually portable chain saw.
Therefore, it is an important object of the
invention to provide a chain saw actuating and braking
apparatus which is capable of imposing sufficient braking
forces to stop the cutter chain in less time than it takes
a violent kickback reaction to occur.
It is another object of the invention to provide a
chain saw braking mechanism which operates reliably,
effectively and only in response to positive actuation of a
safety lever.
It is yet another object of the invention to
provide a chain saw brake actuating mechanism which involves
a minimal number of parts that are capable of compact
arrangement.
SUMMARY OF THE INVENTION
In accordance with an aspect of the invention there
is provided in a chain saw of the type including a housing,
a guide bar projecting from said housing, a cutting chain
mounted to run on said guide bar in a closed loop, motive
means carried by said housing coupled to said cutting chain
for propelling said cutting chain around said guide bar,
said housing including a portion forming a channel through
which said cutting chain travels as it is propelled around
said guide bar, and a chain guard member comprising a pin
mounted on said housing portion, said pin including a shank
portion projecting into said channel and disposed between
opposite ends of said loop and beneath the lower run of said
loop of said cutting chain and projecting transversely with
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respect to the plane of said loop through the probable
trajectory followed by said cutting chain when said chain
becomes disengaged from said guide bar during operation
whereby said chain guard member serves to catch or intercept
said cutting chain and retard its movement or at least fore-
shorten said cutting chain to prevent it from striking an
operator of said chain saw.
In one preferred embodiment, the spring member
comprises a lineally acting coil spring which is com-
pressively seated intermediate the housing and latchingmember. In a preferred arrangement of this embodiment, the
end of the brake band which is coupled to the safety lever
projects through and is enclosed by the lineally acting coil
spring. Also according to this arrangement, the end of the
brake band is bifurcated thereby defining a central passage
for receiving the portion of the latching member which
engages the safety lever.
In yet another preferred embodiment, the spring
member comprises a torsion spring coupled under a torsion
load intermediate the latching member and the housing. In
this arrangement, it is preferred that the torsion spring be
mounted in coaxial relation with the pivotal axis of the
safety lever.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention taken in conjunction with the
invention disclosed in copending Canadian Patent Application
Serial No. 335,868 which was filed on September 18, 1979,
will be described in detail hereinbelow with the aid of the
accompanying drawings, in which:
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Figure 1 is a side elevation view of a portion of a
chain saw constructed according to the present invention;
Figure 2 is a sectional view taken along the lines
II-II of Figure l;
Figure 3 is a sectional view taken along the lines
III-III of Figure l;
Figure 4 is a sectional view taken along the lines
IV-IV of Figure l;
Figure 5 is a front elevation view, partly in
section, of the chain saw shown in Figure 1;
Figure 6 is a fragmentary, sectional view of a
safety braking system forming a part of the chain saw of
Figure 1, in which the braking system is in the operating
(non-braking) position;
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,l FIC-URES 7 and 8 are fragmentary elevation views of the
actuating mechanism shown in FIGURE 1, showing the brake in the
operating and braking conditions, respectively;
I I FIGURE 9 is a fragmentary elevation view of an alternative
embodiment in which a torsion spring is utilized; and,
, I FIGURE 10 is a side elevation view of the apparatus shown in
FIGURE 9.
i DETAILED DESCRIPTION OF THE PREFERRED EMBODIM13NTS
l In the description which follows, like parts are marked
10 1 throughout the specification and drawing with the same reference
numerals, respectively.
Il Referring now to FIGURE 1 of the drawing, a manually operated,
¦¦ portabl0 chain saw 10 includes a frame or housing 12 having a forward
handle bar 14 and a rearward handle 16. Carried by the housing 12 is an I
internal combustion engine 18 and a guide bar 20. Power transmission
¦ means including a centrifugal clutch, a crank shaft and a chain sprocket
. ~ j (not shown) are coupled to the internal combustion engine 18. Trained
¦ around the chain sprocket and guided by the guide bar 20 is a cutting
: chain 22. Forming a part of the engine 18 is a carburetor (not shown)
20 . which includes a throttle (not shown) controlled by a linkage connected to
I a throttle controlling trigger 24 which is pivotally mounted on the rear
handle 16. A rewind starter assembly 26 is accessible on one side of the
- ll housing 12 (FIGURE 5), and a chain brake assembly 28, described in i
¦ further detail below, is located on the opposite side . The above
components are all well known in the art.
According to the invention, the chain brake assembly 28 includes
Il
a olutch drum 30 wbich is driven by the internel combu/~tion ene~ine a~ it
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drives the cutting chain 22. Typically, the clutch drum 30 is mechanically
coupled to a shaft 32 on which the sprocket wheel which drives the cutting
j, chain 22 rotates. In other constructions, the clutch drum 30 rotates with
an intermediate driven member of a clutch assembly which drives the
cutting chain 22. The braking action is obtained by the frictional
(1 engagement of a flexible brake band 34 with the clutch drum 30. As can
!I best be seen in FIGURES 1 and 6 the brake band 34 encircles the outer
jl periphery of the clutch drum 30. During normal operation, that is during
the usual cutting operation, the brake band 34 is loosely coupled about the
l' clutch drum 30 with a small gap 36 (FIGURE 6) separating the brake band
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from frictional contact with the clutch drum 30. One end 34A of the brake
band is looped and fastened about a pin 40 which is anchored to the
¦ housing 12. As the opposite end of the brake band i8 displaced forwardly
relatlve to the housing, the brake band 34 becomes tightened in frictional
engagement with the clutch drum 30 thereby causing the clutch drum to
cease rotating and thus indirectly stopping the motion of the cutting chain
22.
In operation, the chain saw 10 is held by an operator using one
hand to grasp the handle 14 and the other hand to engage the rear control
~; 1 20 ¦
handle 16. Cutting manipulation of the saw 10 is typically achieved by
utilizing the control handle 16 as a fulcrum and applying guiding pressure
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to the forward handle 14. It will be appreciated that a potential hazard is
presented by the phenomenon known as "kickback" which may occur when
the cutting chain 22 momentarily stops and is siezed by the work material.
The kinetic energy of the chain normally used to remove the material is
suddenly transferred to the guide bar 20 thereby imparting a force to the
guide bar that causes it to kick upward toward the operator. The
magnitude of the kickback force is related to the speed of the chain and,
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¦ i the nature of engagement of the chain with the work material . Since
kickback may occur in less than one-tenth of a second, serious injury can
result to the operator.
I According to prior art approaches, a manually operated hand
guard actuator is placed in a posiffon to be contacted by the back of the
- hand or wrist of the operator in the event of "kickback" and thereupon
actuate a chain brake device to apply the brake and stop the cutting
chain. However, it may sometimes occur that in applying a forward
pressure upon the forward frame handle that an operator's hand may slip
toward and into the rapidly moving cutting chain. Alternatively, the
kickback reaction may be so violent that the chain saw will pivot about its
center of gravity towards the operator. It will be readily appreciated that
a potentially injurious situation is presented by the occurrence of either of
l the foregolng mentioned operational incidents. The pre8ent invention is
; particularly designed to minimize the injuries associated with the
¦ "kickback" phenomenon and with inadvertent or accidental movements of an
; operator's hands and arms relative to the cutting chain during operation.
According to the invention, a hand guard actuator assembly 42
is coupled to the flexible brake band 34 for holding the brake band 34 in
2 0 disengaged relation with the clutch drum 30 during normal cutting
operation, and for maintaining the brake band 34 in frictional engagement
1~ with the clutch drum when it is desirable to stop the movement of the
cutting chain 22. The hand guard actuator assembly includes a safety
lever 44 which is pivotally mounted on a pivot pin 46 which projects from
I the housing 12. The safety lever 44 is initially placed in a position to be
contacted by the back of the hand or wrist of an operator in the event of
"kickback" and thereby actuate the chain brake assembly 28 to apply the
brake and stop the cutting chain. This initial position will be referred to
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hereinafter as the "operating position" of the safety lever 44 . The lever
is shown to be in the operating position in FIGURES 1, 6 and 7 of the
¦ drawing. This is a stable operating position which requires the application
of an external force acting on the safety lever 44 to cause it to rotate to
¦ the "braking" poæition as shown in FIGURE 8 of the drawing. In the
"braking" position, the flexible brake band 34 is drawn into frictional
engagement with the clutch drum 30 thereby stopping movement of the
cutting chain 22.
~Referring again to FIGURE 5 it will be seen that a shank portion
1146A of the pivot pin 46 projects into a channel 47 through which the
cutting chain 22 travels as it is propelled around the guide bar 20 . The
shank portion 46A is disposed beneath the lower loop of the cutting chain
i directly in the probable trajectory followed by the cutting chain should it
¦ become disengaged from the guide bar during operation . The pivot pin
shank portion 46A functions as a "chain catcher" or chain guard for
retarding the motion of the chain 22 in the event it should become
disengaged from the guide bar which might occur when the chain becomes
loose or is displaced because of kickback. Should the chain jump the
guide bar 20 the chain tends to whip back toward the operator's legs or
2 0 ¦ arms which can cause severe personal injury . The shank portion 46A
¦ serves to catch or intercept the chain and stop its movement or at least
foreshorten the chain to keep it from striking the operator.
The hand guard actuator assembly 42 is a bi-stable system in
which the safety lever 44 is maintained indefinitely in either the operating
position or in the braking position unless acted upon by an external
source. The safety lever 44 is held in either of the stable positions by
means of a spring member 48 and a latching member 50. In this
embodiment, the spring member 48 is preferably a lineally acting coil
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spring which is compressively seated between a platform surface projection
52 of the housing 12 and a lever arm portion 50A of the latching member
50. According to the invention, the latching member 50 is pivotally
mounted on the safety lever 44 for rotational movement relative to the
safety lever. The latching member 50 is mounted on a pivot pin 54 which
is anchored to the safety lever 44 and which projects orthogonally with
respect to the safety lever. According to this arrangement, the spring
member 48 exerts a yieldable force through the latching member 50 and
pivot pin 54 to the safety lever 44 which constantly biases the safety lever
for movement from the operating position to the working position. The
spring member 48 also simultaneously exerts a yieldable latching force on
the latching member 50 and cooperates with the safety lever for holding
the detented end portion 50B of the latching member in releasable latching
engagement with a portion of the housin~ thereby preventing inadvertent
frictional engagement of the brake band 34 with the brake drum 30 when
the safety lever 44 is in the operating position. The spring member 48
also cooperates with the safety lever 44 for permitting rotation and
disengagement of the latching member 50 from the housing portion as the
safety lever rotates from the operating position to the braking position in 1l
response to an actuating force acting on the safety lever. In a preferred i
embodiment, the detented end portion 50B of the latching member engages
a roller 56 which is concentrically mounted on a latch pin 58 which is
anchored to the housing 12 as can best be seen in FIGURE 2 of the
drawing.
The compression spring 48 is held in place by means of the
platform surface projection 52 and by means of a tang 60 which projects
orthogonally with respect to the lever arm portion 50A of the latching
member S0 ss csn bese be seen in EIGURE 6 of the drawing. Aocording to
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this arrangement, the lever arm portion 50A of the latching member 50 is
confined intermediate the compression spring 48 and the safety lever 44 so
that the single spring 48 serves the dual purpose of constantly biasing the
safety lever 44 towards the braking position while also holding the
detented end portion 50B of the latching member 50 in releasable
engagement with the roller 56. Thereby preventing inadvertent release of
the safety lever 44.
To permit the safety lever to be fully actuated to the braking
1 position, the detented end portion 50B of the latching member 50 is
10 ~! provided with an inclined surface or ramp surface 62 which can best be
I seen in FIGURE 6 of the drawing. In response to an external force, for
example, which may be applied by movement of the hand or arm against
the safety lever 44 during a violent kickback reaction, the safety lever 44
1 ¦ is rotated forwardly under the influence of the external applied force and
¦¦ under the influence of the force exerted by the spring member 48. As
can be seen in FIGURE 8, as the safety lever 44 rotates clockwise, the
spring member 48 compresses slightly as the latching member 50 rotates
counterclockwise because of the interference engagement between the
detent portion 50B of the latching member and the roller 56. However,
20 ¦ because of the ramp surface 62, and because of the differential rotation of
i the latching member relative to the safety lever, the detented portion 50B
slips out of latching engagement on the roller 56 until the interference
~ ~ relation is cleared, thereby permitting the spring member 48 to fully
¦ ! extend and drive the safety lever 44 fully forward . The end portion 50A
¦ clears the pin 64 in the released position with spring pressure being
applied to the safety lever 44 through the pivot pin 54. The magnitude of
the pressure is limited by the interaction of the roller 56 with a control
surface 65 of the detented end portion 50B.
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¦ I The forward end 34B of the flexible brake band 34 is looped
around and attached to a pin 64 which i8 anchored in the safety lever 44
I as can best be seen in FIGURE 3 of the drawing, thereby causing the
! brake band 34 to be pulled into frictional engagement with the clutch drum
30. Thus it will be ,seen that the actuating system is "bi-stable" and that
by reason of the interference engagement, differential rotation and the
¦ resiliency of the actuating structure, that the lever arm 44 is retained in
one or the other of its two positions, the operating position or the braking
position, until a force is applied to move it to the other position. The
safety lever 44 is "cocked" or returned to the operating position by
. manually pulling the lever 44 rearwardly toward the operator which permits
the ramp surface 62 of the detent portion 50B of the latching member to
ride over the roller 56 as the latching member 50 rotate8 about the pivot
pin 54 and the spring member 48 compresses 61ightly. Once the roller 56
engages the detented posiffon, the force of the spring member 48 acting
¦ through the lever arm portion 50A holds the detented portion of the
latching member in releasable latching engagement with the roller 56 and
~- ~ latch pin 58.
As can best be seen in FIGUl~ES 1, 4 and 6 of the drawing,
2 0 ! ¦ according to a preferred arrangement, the spring member 48 is a lineally
. ¦ acting compression coil spring which is fitted around and encloses an end
1l ~ portion of the brake band 34. This arrangement is very compact and
r ~i 11 effective. According to another feature, the end of the brake band 34 is
bifurcated as shown in FIGURE 3 of the drawing, defining a central
11 opening 66 for receiving the lever arm portion 50A of the latching member
;i I, 50. The central opening 66 is defined by the parallel bifurcated end
;,
portions 68 and 70 of the brake band 34. In this compact arrangement,
¦ the central opening is necessary to permit relative movement of the
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~! latching member 50 as it rotates relative to the safety lever 44. When the
¦~ latching mechanism becomes unlatched or is in the braking position, the
ramp surface 62 (FIGURE 6) rides on the latch roller 56 and engages the
~ ~ control surface 65 which stops latch 50 from further rotation . Therefore,
¦~1 the spring pressure applied transfers from spring 48 through latch 50,
l latch pivot pin 54, to actuating lever 44 causing it to pivot about pin 46
and tighten the brake band 34 around the drum 30. '
Il Referring now to FIGURES 9 and 10, an alternate embodiment of
¦~ the invention is illustrated in which a torsion spring 72 is employed. In;
10 ¦ this arrangement, the latching member 50 comprises a central body portion
pivotally mounted on the safety lever 44 having a detented arm portion 50B
and an end portion 50C defining a moment arm for transmitting the
yieldable force exerted by the torsion spring through the lever arm
portion of the latching member to the safety lever 44 and through the,
detent end portion 50B of the latching member to the roller 56. As can be
seen in FIGURE 9, the torsion spring includes a first end portion 74 which
¦ is anchored to the housing 12 and a second end portion 76 which is
coupled to the moment arm portion 50C of the latching member. It is
preferred that the second end portion 76 be coupled to the moment arm
20 ¦ portion 50C at a point above the longitudinal centerline 77 of the pivot pin
54 to maintain a bias force on the latch and hold it in the normally latched
position. The torsion spring 72 exerts a yieldable force on the latching
member 50 which is translated through the moment arm portion 50C and
pivot pin 54 to the safety lever 44. The same yieldable force operates to
hold the detent portion 50B in releasable latching engagement with the
I roller 56 as previously discussed.
¦ It will be seen that the chain brake system of the present
¦ invention represents an improvement over the prior art because of its
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I t simplicity, effectiveness and compactness . Although the chain brake
il system of the invention will not prevent kickback, it will drastically reduce
t I the personal injury hazards associated with kickback. When kickback
¦! occurs, the operator's wrist or hand will pivot about the forward handle
14 . The wrist or hand will strike the safety lever 44 thereby applying a
force on the latching member 50. The external force applied to the safety
lever 44 will be added to the yieldable force exerted by the spring member
¦ 48 to cause the safety lever 44 to rotate quickly forwardly, thereby
I engaging the brake band 34. Thus the spring member 48 is double acting
10 I in that it maintains the actuating mechanism in the latched or nonbraking
position, and when an external force is added to the spring by striking
the safety lever 44, the cam angle detent of the latching member i6
defeated and the spring directly applies the braking pressure. The two
combined $orces, that is the yieldable $orce o$ the spring member and the
external force, serve to remove the actuating mechanism from the t
equilibrium state as the yieldable force from the spring becomes dominant, I
thereby forcing the safety lever forward. As the safety lever moves t
forward, it brings the brake band 34 into frictional engagement with the
;~ clutch drum 30. This frictional force is great enough to bring the clutch i
to a halt which indirectly brings the cutting chain to a halt since the ¦
clutch drives the cutter chain.
Although preferred embodiments of the invention have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made therein without departing from
the spirit ~nd scope oi the invention a= deiined by the appended cl~ims.
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