Note: Descriptions are shown in the official language in which they were submitted.
lOS90~1
BACKGROUND OF THE INVENTION
This invention relates to handling and safety improve-
ments in a hand portable chain saw. In particular, it provides
an improved mechanism for braking the saw chain in the event
of untoward movement of the saw, including in particular the
hazardous kickback to which chain saws are subject. The inven-
tion also provides improvements in both the carrying handle of
the saw and in the safety bar which is located forward of the
handle and initiates the braking operation.
It is known that hand portable chain saws are subject to
a hazardous kickback motion during operation, and that a chain
brake can be provided to reduce the risk of operator injury in
the event of a kickback or other untoward saw movement. See
for example U.S. Patents Nos. 3,776,331 of Gustafsson; 3,934,345
of Hirschkoff; and 3,937,306 of Naslund et al; and see also the
February 1976 issue of Chain Saw Age for a state-of-the-art view
of these aspects of chain saws.
However, some prior safety brake mechanisms do not pro-
vide protection for all operating positions of the saw. Others
are relatively complex in construction and/or operation, such as
employing multiple-step release and braking action. Prior saws
also have not provided all-position handle structures with
equally-accessible chain brake actuation.
Accordingly, it is an object of this invention to pro
vide improved handle and chain braking structures for hand port-
able chain saws.
A more specific object is to provide a chain saw having
both a carrying handle and a safety bar which are readily access-
ible during operation of the saw in multiple orientations.
Another object of the invention is to provide a single-
action chain brake which operates with a rotatable safety bar
and which is located spaced from the rotation axis of the bar.
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It is also an object of the invention to provide a
chain brake employing a lineally-acting resilient element, such
as a coil spring, which both holds the brake in disengagement,
and alternatively applies braking force upon brake actuation.
Other objects of the invention will in part be obvious
and will in part appear hereinafter.
GENERAL DESCRIPTION OF THE INVENTION
A hand portable chain saw embodying features of the
invention has a carry handle, with which the operator supports
most if not all the saw weight during use, which extends fully
in wrap-around fashion about the top and the two sides of the
saw housing. This handle is in addition to the control handle
conventionally located at the rear of the saw opposite the chain-
carrying arm, and which is fitted with the throttle and on-off
controls. The wrap-around configuration of the carry handle
provides ready access to the operator from both above and at
least one side of the saw for any upright or sideways orientation
of the saw, i.e. without regard to whether the saw is oriented
for cutting vertically or horizontally to the right or to the
left.
Located forward of the wrap-around housing-encircling
drive handle, and in the path of the operator's hand, wrist, or
arm in the event of kickback or other untoward movement of the
saw, is a safety bar which has a similar housing-encircling wrap-
around configuration. The safety bar is mounted to the housing,
by means of rotatable connection at the ends of the bar, for a
swinging movement about an axis located adjacent the lower face
of the housing. This remote location of the rotation axis endows
the safety bar with maximal sensitivity for deflection to actuate
the brake mechanism.
The wrap-around handle configuration facilitates orient-
ating the saw as appropriate for the desired cut. Hence it
10590~1
dimishes restrictions on the orientations with which the
operator can use the saw, and correspondingly minimizes the
likelihood that the operator will use the saw with an awkward,
off-balance or otherwise insecure posture. The wrap-around
safety bar with its extremely-located axis of rotation provides
automatic chain braking for any such orientation of the saw.
The combination of wrap-axound handle and safety bar structures
thus enhances both the efficiency and the safety of the saw.
A further characterization of the invention is a brake
control and actuating mechanism having a lineally-acting spring
which both biases the safety bar to apply the braking force
and applies a brake latching detent to the safety bar. The
brake employs the known arrangement in which a braking member
is linked to the safety bar for brake engagement and, alterna-
tively, disengagement. These known brakes also have a mechan-
ism for holding the safety bar in the operating, i.e. brake-
disengaging, position. However, a characteristic of a saw
embodying the present invention is a coil spring or equivalent
resilient element having substantially lineal action. When
the safety bar is in the brake-disengaging position, the spring
presses a detent against the safety bar. This action holds
the safety bar cocked in an operating condition where the brake
is released from the cutting chain. When the safety bar is
disengaged from the detent, the same spring assumes the oppo-
site role and thrusts the safety bar into the brake-engaging
position.
This control and actuating mechanism of the invention
is advantageously used with the wrap-around safety bar which
the invention provides. This is because the remote location
of the pivotal mounting of the wrap-around safety bar to the
housing results in essentially lineal motion of the safety bar
at the point where the brake-controlling mechanism advantage-
lOS9011
ously is applied. Further, the spacings between the severalrotation axes and operating points of the safety bar and the
control mechanism provide positive mechanical operation.
Hence, a saw combining the features of the invention provides
a rapid, essentially snap-like, single-action braking which
the operator automatically initiates when using the saw in
essentially any orientation. The force of the hand against
the safety bar plus the force of the spring causes a faster
application of the brake and since the force of the hand is
additive to the force of the spring, the stopping time of the
chain is greatly shortened.
STATEMENT OF T~E INVENTION
The invention as claimed herein is a hand portable chain
saw having a housing, a sawing chain mounted on an arm
extending forward from the housing, motive means coupled for
driving the sawing chain, a safety bar rotatable relative
to the housing between a braking position and an operating
position, and brake means coupled with the safety bar for
brakingly engaging the motive means for stopping the sawing
chain and alternatively for release from the motive means,
and characterized by the improvement comprising detent-
engaging means mounted for movement with the safety bar along
a first direction between the brakiny and the operating
positions thereof, first arm means extending longitudinal to
the first direction and rotatably mounted for rotation re-
lative to the housing about an axis different from the rota-
tion axis of the safety bar, and having detent means for
releasable latching engagement with the engaging means when
the safety bar is in the operating position, and lineally-
acting spring means engaged with the first arm means and withthe safety bar for applying a resilient force for urging the
arm means rotatably into the latching engagement with the
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engaging means, and for urging the safety bar from the
operating position into the braking position.
The chain saw may have the further improvement wherein
the safety bar comprises a U-shaped barrier, the side portions
and bottom portion of which extend respectively about the sides
and top of the housing, and which is rotatably mounted at the
end of each side portion to the housing adjacent a lowermost
location on the housing.
The chain saw may have the further improvement comprising
a detent bracket rotatably mounted to the housing and forming
the first arm means and further providing a second arm extend-
ing transversely to the first direction, and wherein the spring
means is engaged between the second arm and the safety bar.
The~chain saw may have the further improvement wherein the
spring means is located spaced from the rotatable mounting of
the safety bar in the direction toward the top of the housing,
and the detent bracket is rotatably mounted to the housing
at a location intermediate the rotatable mounting of the safety
bar and the location of the spring means.
The chain saw may have the further improvement comprising
first shaft means mounting the safety bar to the housing for
rotation about a first axis, and second shaft means mounting
the detent member for rotation about a second axis parallel
to the first axis. A further improvement may be wherein the
first shaft means locates the first axis adjacent a lowermost
location on the housing, and the second shaft means locates
the second axis spaced, along a second direction transverse to
the first direction, by a first distance toward the top of the
housing from the first axis. The spring means may be engaged
between the safety bar and the first arm means at a location
spaced along the second direction by a distanGe greater than
the first distance. The safety bar means may have a wrap-
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around configuration extending about the top and sides of
the housing and may extend continuously along the wrap-around
configuration between a pair of end portions, and the first
shaft means may engage the end portions for rotatably mounting
the safety bar means.
The chain saw may have the further improvement wherein the
spring means is engaged between the safety bar and the first
arm means to constantly bias the safety bar forward to the
braking position, and to impose yieldable latching force on
the first arm means to resist forward movement of the safety
bar and thereby prevent inadvertent brake engagement.
The chain saw may have the further improvement wherein the
detent means is movable with the first arm means between a
holding position for restraining movement of the safety bar
means along the first direction and a release position allowing
forward movement of the safety bar means, the lineally-acting
spring means is arranged to bias the detent means into the
holding position for imposing a yieldable latching force on the
safety bar to resist forward movement of the safety bar and
thereby to prevent inadvertent brake activation, and the detent
means is movable to the release position against the bias of
the spring means in response to forward movement o~ the safety
bar. The spring means and the detent means may be arranged for
increasing the bias of the spring means on the safety bar upon
movement of the detent means from the holding position to the
release position.
The chain saw may have a housing with top, bottom and sides
and a carrying handle; a safety bar mounted on the housing for
swinging movement between the operating position and the braking
position; and a chain brake coupled with the safety bar for
brakingly engaging the motive means to stop the chain and
alternatively for release from the motive means; characterized
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by the further improvement wherein the carrying handle
comprises a housing-encircling wrap-around hahdle extending
about the top and sides of the housing, and the safety bar
comprises a housing-encircling wrap-around barrier disposed
forward of the carrying handle and extending at least sub-
stantially coextensively with the handle about the top and
sides of the housing. The chain saw may also include shaft
means mounting the safety bar to the housing adjacent the
bottom thereof, and spring-mounting means on the safety bar
and on the housing and disposing the spring means for applying
the resilient force to the safety bar at a distance from the
mounting thereof such that the span of the safety bar along
such distance provides a moment arm for the force of the spring.
The invention accordingly comprises the features of
çonstruction, combinations of elements, and arrangements of
parts exemplified in the embodiment hereinafter set forth, and
the scQpe of the invention is indicated in the claims.
BRIEF DESCRIPTION OF DRAWINGS
.
For a further understanding of the nature and objects
of the invention, reference should be had to the following
detailed description and the accompanying drawings, in which:
FIGURE 1 shows a hand portable chain saw embodying the
invention;
FIGURE 2 is a side elevation view of the saw of FIGURE
1 showing both the operating and the braking positions of the
safety bar;
FIGURE 3 is a front elevation view of the saw of FIGURE
l;
FIGURE 4 is a partial sectional view of the saw as shown
in FIGURE 3 and detailing the brake mechanism; and
FIGURE 5 and 6 are fragmentary elevation views, of the
side opposite to that shown in FIGURE 2 and partly bro~en
a~7ay, showing the brake in the operating and the braking condi-
tions,respectmvely.
1059011
DESCRIPTION OF ILLUSTRATED EMBODIMENTS
A hand portable chain saw 10 embodying the invention
as shown in FIGURES 1, 2 and 3 has a housing 12 and a sawing
chain 14 trained over a forwardly projecting support arm 16.
The housing contains the saw drive mechanism, conventionally
an internal combustion engine coupled by way of a power trans-
mission and clutch to the sawing chain. A rewind starter 18
is accessible on one side of the housing 12 and a chain brake
20, described in further detail below, is located on the other
side of the housing. At the rear of the housing is a control
handle 22 fitted with a throttle trigger 24 and an on-off
switch 26.
A carry handle 28 encircles the housing top 12a and two
sides 12b and 12c roughly midway along the housing length so
that the saw weight is approximately balanced at the handle.
The operator supports the weight of the saw from the handle 28,
and hence this weight balance is important for operator conven-
ience and safety. The operator uses the control handle 22 to
stabilize the saw, and to control the chain operation and speed
by means of the throttle trigger 24 and the switch 26.
The carry handle 28 is rigidly fixed to the housing 12.
In the illustrated embodiment the handle ends are secured with-
in a tubular mount 30 which projects on the housing below the
bottom panel 12d; this tubular projection provides a raised
base on which to rest the saw. The carry handle 28 has a con-
tinuous, housing-encircling wrap-around configuration between
the angled end portions 28a, by which it is mounted. It thus
has an overall U-shape between these end portions and formed
with side portions 28c and 28d that form legs of the U and a
top portion 28e that forms the base of the U-shape. A support
stud 32 extends from the handle 28 adjacent the juncture of the
top portion 28e with the side portion 28d, and is fastened at
1059(1 11
its other end to the housing, illustratively at the corner
where the top and side meet. Thus in the preferred embodiment
illustrated, the carry handle 28 has three points of attachment
to the saw housing for secure rigidity throughout the entire
wrap-around extent of the handle. Further, there are no free
ends or other protrusions that could snag clothing or other-
wise be hazardous.
FIGURES 1 and 3 show that this handle construction
fully encircles the housing top and sides. The drive handle
accordingly is accessible from both above and at least one side
of the saw for the many orientations in which the saw is likely
to be used. Further, except for the attachments to the housing,
the entire span of the drive handle is spaced outwardly from
the housing openly to receive the operator's hand between the
handle and the housing for secure gripping of the handle.
With further reference to FIGURES 1, 2 and 3, the saw
10 has a safety bar 34 that actuates the chain brake 20 when
displaced from an operating position 36a, FIGURE 2, to a braking
position 36b. The safety bar follows the full wrap-around con-
tour of the carry handle 28 to be interposed between the opera-
tor's hand on the carry handle and forward portions of the saw
for all cutting orientations. The safety bar 34 thus has a
continuous structure which encircles the top and both sides of
the saw housing 12, and has an overall U-shape with leg portions
34a and 34b and a base portion 34c.
The safety bar is located on the housing 12 spaced
forward of the drive handle and aligned generally parallel to
it when in the operating position 36a. The bar is mounted for
swinging rotation relative to the housing about an axis 38 by
means of shafts 37 and 39 fixed on the ends of the bar and
rotatably seated to the housing at locations lowermost on the
housing sides.
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This structure interposes the safety bar in the path of
the operator's hand, wrist or arm in the event the saw kicks
back or in case of other potentially hazardous untoward move-
ment of the saw. The operator's body accordingly will engage
the safety bar and thereby displace it from the operating posi-
tion 36a. As will now be described, this displacement of the
safety bar actuates the chain brake to stop the chain essent-
ially instantaneously.
With reference to FIGURES 4, 5 and 6, the chain brake
20 (FIGURE 2) applies braking force to a brake drum 40 that
the saw drive mechanism rotates upon driving the saw chain.
Typically, within the housing, the chain is trained on a sproc-
ket wheel which is mechanically coupled to the shaft 42 on
which the brake drum rotates. In one construction, the brake
drum 40 rotates with a driven member of the clutch that drives
the chain.
The brake employs a flexible brake band 44 which has
one end 44a secured to the housing, illustratively by seating
a loop at that end of the band within a cavity 46 recessing the
housing. The other end 44b of the brake band is secured to the
safety bar 34, for example, by seating a loop at that end on a
pin 48 extending from the safety bar. The brake band extends
from the pin 48 along a path extending length-wise of the saw
and then around the periphery of the brake drum 40. Adjacent
the fixed end 44a, the brake band passes over a guide surface
provided by a housing pin 50 and thence to the housing anchor-
age in cavity 46. The brake band thus encircles nearly the full
periphery of the brake drum 40.
The pin 48 is located on the safety bar spaced from
the rotation axis 38 by a sufficient distance such that it moves
along an essentially straight path directed along the saw length
when the safety bar moves between the two positions shown in
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FIGURE 2.
This movement of the pin 48 operates the brake, as
FIGURES 5 and 6 illustrate. In particular, when the safety
bar 34 is in the non-braking, operating position of FIGURE 5,
the brake band 44 loosely circles the drum 40 and hence applies
no brake force to it. The brake accordingly does not interfere
with free rotation of the drum 40 and correspondingly with the
drive motion applied to the chain. However, upon movement of
the safety bar to the braking position, FIGURE 6, the pin 48
moves forward with the safety bar and pulls the brake band taut
around the brake drum. Frictional engagement between the drum
and the brake band, either of which can carry brake linings
according to conventional practice, arrests the rotation of the
brake drum 40 and thereby stops the sawing chain.
A detent and thrust mechanism, formed by a detent
bracket 52 and a lineally-acting spring 54, latches the safety
bar in the operating position but yet drives it into the braking
position when the safety bar is unlatched. As FIGURE 4 shows,
the bracket and the spring are nested between the safety bar
and one side of the housing. The bracket 52 forms two substan-
tially orthogonal arms, one a detent arm 56 which extends along
the length of the saw and the other an upstanding lever arm 58.
The arm 56 has an upwardly-facing detent step 56a dimension to
latchingly receive and retain the pin 48, as FIGURE 5 shows,
when the safety bar is retracted to the operating position.
The bracket 52 is mounted -- between the two arms which it
forms -- to the housing on a stem 60 for rotation about an axis
parallel to the axis 38 of safety bar rotation. The two rota-
tion axes are spaced apart along the safety bar, i.e. in the
direction transverse to the saw length. The spring 54, prefer-
ably a coil spring as shown, is compressively seated between
the arm 58 and a rearwardly facing platform surface 34d on the
~OSS~011
safety bar. Each element 58 and 34 illustratively includes a
stud which fits within the open center of the spring to retain
it from accidental dislodgement. Further, the studs are ar-
ranged to abut one another in the event the safety bar is ro-
tated too far counterclockwise; they thus prevent over-compres-
sion of the spring 54. Clockwise rotation of the safety bar is
limited by the length of the brake band 44, as FIGURE 6 shows.
(Directions of rotation are termed clockwise and counterclock-
wise with reference to FIGURES 2, 5 and 6.)
With the foregoing mounting by way of the detent brack-
et 52, the spring 54 is oriented along the saw length and is
compressed more when the safety bar is in the operating position
(FIGURE 5) than when in the braking position (FIGURE 6). This
additional compression stores kinetic energy in the spring.
Hence, when in the operating position, the spring increasingly
pushes the bracket 52 counterclockwise about the stem 60, and
thereby resiliently presses the detent shoulder 56a in front of
the pin 48, to latch the safety bar in the operating position.
However, when the safety bar is struck or otherwise
pressed in the forward direction, it rotates clockwise about the
axis 38. This motion carries the pin 48 forward. The pin
accordingly cams past the detent shoulder 56a, thereby rotating
the bracket 52 and hence the arm 58, clockwise. This in turn
maintains initial compression in the spring 54. The force of
the compressed spring pushes against the safety bar and thereby
thrusts it and the pin 48 forward to engage the brake band
against the drum 40.
The brake thereafter is released simply by swinging
the safety bar backwards, i.e. counterclockwise. This motion
latchingly re-engages the pin 48 in the detent of arm 56 and
again compresses the spring 54 so that it biases the detent
bracket 52 to hold the brake cocked in the operating condition.
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~059011
The foregoing construction of the control and actuating
mechanism provides a moment arm in the length of the safety
bar between the axis 38 and the spring 54, i.e. and the spring-
engaging shoulder 34d. As illustrated, this moment arm pre-
ferably is longer than the second moment arm provided by the
length of safety bar between the axis 38 and the pin 48. It is
the former moment arm through which the spring acts to rotate
the safety arm, and the latter moment arm moves the pin 48 to
apply the brake.
NON-OBVIOUSNESS AND SCOPE OF INVENTION
AND SUMMARY OF ADVANTAGES
The present invention is characterized by means,
operation and results which are wholly different from those of
the prior art. These differences, coupled with the failure of
the prior art to suggest the present invention as well as that
of the aforesaid parent application Serial No. 515,047, evidence
the non-obviousness of the invention of the present application
and applicant's parent case.
For example, structures disclosed and claimed in prior
patents such as Gustafsson 3,776,331 (1973) and Naslund et al
3,937,306 (1976) are predicated on the use of separate springs
for operating brake band biasing means and latching means. They
do not contemplate either the unique linear or torsional embodi-
ments of the detent-biasing arrangements of this application
and its parent case.
Moreover, prior art devices as featured in the
Gustafsson patent involve the use of a rigid locking mechanism
with an associated trigger releasP device which entail two-step
operation and require a recocking of lock components before
relatching can be effected. In the first Gustafsson step, the
locking mechanism is released. In the second Gustafsson step,
which is sequentially independent of the release step, setting
~059011
of the brake band is commenced.
The different structure of the present invention and of
the aforesaid parent case, in relation to prior proposals such
as Gustafsson and Naslund et al, entails the use of a unique
single spring arrangement -- as opposed to multiple springs --
for performing both brake band and safety bar biasing and safe-
ty bar detenting in a novel and advantageous manner. Moreover,
in contrast with Gustafsson, this different structure enables
movement of the safety bar serving, in one-step, concurrently
to release the detent and initiate the setting of the brake
band. The rigid locking mechanism of Gustafsson is displaced
entirely in favor of a yieldable detent approach for yieldably
securing the safety bar.
A different mode of operation of the present invention,
as well as the aforesaid parent case, in relation to prior art
such as Gustafsson, entails the concurrence of safety bar re-
lease and brake setting action in contrast with the sequential
and independent unlocking and brake band setting actions of
Gustafsson. In addition, instead of moving a pawl out of en-
gagement with a brake as contemplated by Gustafsson, the inven-
tions of this application and its parent case entail the use
of a detent which remains engaged so as to avoid the need for
a recocking of trigger elements.
A different result achieved by the present invention,
in contrast with Gustafsson, entails the initiation of brake
setting action concurrent with the initiation of the safety bar
movement, in lieu of the unlocking action of Gustafsson which
intervenes before setting of the brake band can commence.
And, as noted, the yieldable detent approach of the
present invention and that of its parent case wholly avoids the
recocking concept of Gustafsson which is necessary to reposition
the elements of a trigger-type locking mechanism before relatch-
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~OS90~1
ing of the safety bar can occur.
As to the wrap-around handle aspect of the present in-
vention and that of the parent case, there simply is no sug-
gestion to be found in prior art such as Gustafsson and Naslund
et al.
The handle and brake of the invention will now be
understood to provide improvements in operation, control and
safety for a hand portable chain saw. The wrap-around carry
handle mounts to the housing at a lowermost location and other-
wise encircles the housing for ready gripping by the operatorfrom essentially any direction. The saw safety bar encircles
the housing in a like manner so that any untoward movement will
automatically cause the operator to strike the bar and thereby
trip the chain brake.
A single bracket and single spring element coupled
between the safety bar and the saw housing latch the safety bar
in a normal standby position where the saw operates free of the
brake. However, dislodgement of the safety bar from this posi-
tion causes the bracket-spring combination to drive the safety
bar -- aided by whatever force the operator's thrust applies --
to the braking position. A single movement of the spring-
biased bracket produces both the release and the brake-applying
thrust.
It will thus be seen that the objects set forth above,
among those made apparent from the preceding description, are
efficiently attained. Since certain changes may be made in the
above constructions without departing from the scope of the
invention, it is intended that all matter contained in the above
description or shown in the accompanying drawings shall be
interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims
are intended to cover all of the generic and specific features
- 15 -
10590~1
of the invention herein described, and all statements of the
scope of the invention which, as a matter of language, might
be said to fall therebetween.
16 ~
