Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02852579 2014-05-20
CROSSBOW TRIGGER WITH IMPROVED SEAR SURFACE AND ADJUSTMENT WITH
ABILITY TO CONTROL TRIGGER PULL WEIGHT WITH VARIOUS INPUT DRAW
WEIGHTS
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Provisional Patent Application No.
61/855,605 filed May 20,
2013 by Derrick J. Middleton and titled "Crossbow trigger with improved sear
surface and
adjustment with ability to control trigger pull weight with various input draw
weights".
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to trigger mechanisms, and more
specifically, to a trigger
device for a crossbow.
2. Description of the Related Art
Crossbows have long been known in the archery field for use in hunting game.
Crossbows have
higher draw weights than conventional archery bows and fire arrows (or
"bolts") with greater
speeds. It is a function of a crossbow to have a lock or trigger mechanism
that is able to hold the
crossbow string in the ready to fire position once the string is drawn.
When crossbows are configured for firing, the force exerted by the retracted
bowstring can be in
the range of approximately 100 to 400 pounds. The trigger assembly of the
crossbow must be
capable of holding the bowstring in firing position, while allowing the
bowstring to be released as
the user pulls the trigger. This often results in an excessive pull force
which the user must exert
upon the trigger of the crossbow to fire the arrow, which in turn decreases
the accuracy of the shot.
Typical trigger mechanisms known in the art use a metal to metal sear
mechanism which, during
shooting, relies upon one flat metal surface sliding across another flat metal
surface, until their
engagement breaks off In view of the substantial pressure exerted between
these two flat engaged
surfaces, the mating parts need be made of hardened steel to prevent rapid
wear; in some cases,
wear remains a problem, causing inconsistent trigger pressure and possible
misfires. Furthermore,
many earlier devices lacked sufficient structure to provide positive, reliable
safety means when
handling the loaded crossbow.
A common configuration known in the art comprise trigger assemblies that use
upward-opening
claws (string retaining members) that hold the string once engaged, as seen
for example in U.S.
Patent No. 4,877,008 (to inventor Troubridge), in which two flat metal
engaging surfaces (sears)
slide off each other upon the activation or depression of a trigger arm,
releasing the upward-
opening claw and firing the arrow.
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One other commonly used trigger assembly utilizes a downward-opening claw
(string-retaining
member); as exemplified by U.S. Patent No. 4,192,281 (to inventor King). In
this system, the claw
folds down below the string (thus releasing the string) when the trigger is
activated; typically,
"metal sliding on metal" is the method by which the two flat metal engaging
surfaces (sears)
disengage.
In both of the above trigger actions (and, generally, in all trigger systems),
trigger pull weight is the
weight (or, more exactly the horizontal force, expressed in lbs. force)
required to physically depress
the trigger and get the string to release. It is a function of these prior art
crossbow actions that the
trigger pull weight is affected by the draw weight of the bow; for example, a
300 lbs. draw weight
bow may require 4lbs of trigger pull weight to get the string to release; with
a 150 lbs draw weight
bow, the same action would require less trigger pull weight (possibly 2lbs) to
get the bow to release
the same.
In the case of the two types of prior art trigger systems discussed above, the
manufacturers have
tried to improve (reduce) trigger draw weight by polishing the engaging
surfaces (or sear surfaces)
for smoother release. In some other cases, manufacturers reduced trigger draw
weight by reducing
the overlap of the sear surfaces, which in turn causes an unsafe situation,
because a heavier trigger
and a heavier draw weight is utilizing less engagement area on the sears to
achieve an acceptable
trigger pull. It should be understood that these sear surfaces are prone to
abrasive wear from the
fact they engage each other frictionally with significant weight.
One other trigger mechanism known in the art, as exemplified by U.S. Patent
No. 4,693,228 (to
inventors Simonds et al.) also uses a downward opening claw, but one of the
sear surfaces is
replaced with a rotating member (a wheel), which engages a slightly curved
second sear surface.
While one would expect that a wheel would afford reduced friction, thus
causing a reduced trigger
pull, the Simonds trigger mechanism still exhibits a heavier trigger pull when
paired with heavier
input draw weights.
When studying the Simonds trigger, it was realized that its design is less
efficient, despite the use
of rotating means (wheel) to overcome friction between the two sear surfaces.
Because of its
structural and functional design, the Simonds trigger has three points of
contact (engagement under
force) compared to two such points in the Troubridge and King patents
discussed above. The three
points of contact in the Simonds trigger assembly are: the trigger sear, the
latch wheel sear surface,
and the pin surface around which the wheel rotates. Friction, as we know, is
the force that resists
relative motion between two bodies in contact. Rolling friction occurs when
two objects move
relative to each other and one rolls on the other (like a car's wheel would
roll on the ground). This
is classified under static friction because the patch of tire in contact with
the ground, at any point
while the tire spins, is stationary relative to the ground.
There is a need in the market, and a sought-after feature by crossbow
manufacturers, to have a
trigger system that can be utilized on many products with different draw
weights, without the need
for reconfiguring of the internal levers, toggles and such, that would allow
the trigger pull weight to
be kept relatively constant, even when paired with crossbows with different
input string weights.
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The above is important because changing movement internally affects the
function and engagement
of various safety features that need certain clearances and would also need to
be altered based on
any changed geometry.
It would be a further desirable feature to have a trigger that retains a
relatively constant trigger pull
distance, while keeping the trigger pull weight to a comfortable level, while
also being easily to
maintain.
It would be a further desirable feature to have a trigger with an auto-safety
feature, whereby the
safety latch would be automatically placed in the safe position when the
trigger assembly is cocked,
blocking the possibility of trigger actuation without a further positive
action by the user to switch
the safety latch out of the safe position.
Lastly, there is a need in the market for a trigger assembly that uses a
rolling sear surface and two
immediate points of contact, to truly achieve a reduction in friction when two
sear surfaces are
engaged under force.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the shortcomings of the
prior art, as described
above. The present invention use a truly reduced friction sear engaging
system, a rolling sear
surface and two immediate points of contact, to achieve and maintain a well-
controlled and
relatively constant trigger pull weight with various input bow draw weights.
The improved
crossbow trigger of this invention also allows varying input weights (bow draw
weights) without
changing the geometric function of the trigger assembly components.
It is a further object of this invention to allow manufacturers (and possibly
users) a degree of
adjustability of the trigger pull or draw weight, by the use of an internal
spring adjustment
mechanism. Another object of this invention is a trigger that is able to
achieve mechanical
advantage of internal components without the use of excessively long lever
arms that often result in
undesirable long trigger pull distance, commonly referred to as "trigger
travel".
The present invention uses a metal to metal sear mechanism, in which one sear
is implemented as a
rolling sear surface, namely a dowel mounted on outward roller bearings, to
reduce friction and
maintain optimal sear engagement at all times.
It is a further object of this invention to implement an auto-safety feature,
whereby the safety latch
is automatically placed in the safe position when the trigger assembly is
cocked, blocking the
possibility of trigger actuation without a further positive action by the user
to switch the safety
latch out of the safe position.
BRIEF DESCRIPTION OF THE DRAWINGS
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Fig. 1 is a frontal view of a preferred embodiment of the present invention,
in its locked position,
ready for discharge, with half (front) of the housing removed to show the
internal components;
Fig. 2 is a frontal view of a preferred embodiment of the present invention,
in its after-fired
position, with half (front) of the housing removed to show the internal
components;
Fig_ 3a is a top view of the lower sear of a preferred embodiment the present
invention;
Fig. 3b is a frontal view of the lower sear of a preferred embodiment the
present invention;
Fig. 3b is a perspective view of the lower sear of a preferred embodiment the
present invention;
Fig. 4 is a top view of the two halves of the housing of a preferred
embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the invention in more detail, in Fig. 1 is a crossbow trigger
assembly of a
preferred embodiment. Fig.1 shows the trigger in its locked position which
would have a string in
the string retaining area I .d, ready for discharge. Fig.2 is the same
mechanism in the after-fired
position. In Fig. 1, components are housed in housing 1.i., which is machined
with cavity areas or
pockets to accept the internal components of the system. The claw 1.b pivots
around the claw pivot
point 1.a; the claw 1.b must pivot upwardly in order to fire. The housing 1.i
includes an opening
1.c. in which the string enters, while an area 1.d. is where the string is
retained on the back side of
the downwardly facing claw 1.b. The housing 1.i further includes an area 1.e.
for receiving a
spring which would bias the claw into an upward position, should it not have
the string to force it to
do the same. On the lower portion of the claw member 1.b is the upper sear
surface 1.f for the
primary engagement of the input claw weight to the rest of the system. Further
lower in housing 1.i
is the lower sear pivoting point 1.g, around which lower sear 1.h pivots. The
housing 1.i is
preferably machined from an aluminum block, to accept all components. An auto-
safety pin 1.j is
slidably mounted in a cylindrical channel machined between the safety 1.k and
the claw 1.b. When
the claw 1.b is cocked with a string, the auto-safety pin 1.j is forced
rearward, and, in turn, moves
the safety 1.k into contact with rear portion of lower sear 1.h, placing the
trigger in a safe position.
The safety 1.k pivots around the safety pivot point 1.t. A trigger 1.0 is
attached to the lower sear
1.h.
Fig. 3a, 3.b and 3.c are respectively a top view, a frontal view, and a
perspective view of the lower
sear of a preferred embodiment the present invention. In these figures, the
lower sear 1.h is fitted
with two wings ln.1 and 1n.2. Each of these two wings has two bearing pockets
1Ø1 and 1Ø2,
between which a dowel pin 1.p is rotatably fixed. A threaded orifice 1.q is
machined into 1.h to
affix the trigger arm 1.0 to lower sear 1.h.
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Fig. 4 depicts the top view of the two halves of the housing 1.i, shown in
exploded (apart)
configuration. A spring pocket 1.1 is machined into the bottom of housing I.i,
providing biasing
means (a spring) for lower sear 1.h to be pushed against, engage and hold
upper sear 1.b when
upper sear is moved to its loaded position. The spring pocket 1.1 is threaded
with a blind set screw
at the bottom portion; the screw has the ability to be moved in and out,
allowing tension adjustment
of spring 1.n, thus allowing the trigger pull to be adjusted based on an
incoming pressure of upper
sear 1.b that may be 1001bs. to 4001bs.
As shown in Fig.4, also machined into the bottom of housing Li is a set screw
1.m that allows the
further adjustment of lower sear 1.h (impinging on wing 1.n.2), to enable
proper angle of lower
sear 1.h relative to the bottom of housing 1.i; this angle is critical to
maintain lower sear 1.h at a
parallel position to the bottom of housing 1.i.
Also in Fig.4, part 1.a is the pivot point for the claw 1.b and 1.t. is the
pivot point for the safety 1.k.
The embodiment being described herein utilizes an upward opening claw or
string retaining means,
the lower portion of this has a sear surface which when pulled back forces the
keeper or holding
sear portion out of the way allowing the bow to be cocked. Sear engagement in
the present
embodiment is the amount the sear surfaces overlap at the 90-degree
intersection. The lower sear
portion is attached in this case to a trigger arm, which is pulled rearward to
activate the firing of the
crossbow it is spring tensioned to always be in an engaged state. The sear in
this case on the lower
engaging sear area is a 0.125" or 1/8" dowel pin; we know the circumference is
described as 0.125"
x 3.14 = 0.3925", if we divide this by 360 degrees we know that the round
dowel sear when
allowed to engage the preferred flat sear surface would do so on an area
described as 0.001" (one
thousandth of an inch). The rotation of such a sear is achieved through the
use of an outward roller
bearing on both the left and right hand side of the lower sear, this allows
the upper sear when
pushing back ward to move the dowel down and under it's spring biasing means
returning back to
its position to hold the sears in place ready for discharge. The rolling
action of the two bearings
have an extremely efficient friction coefficient, coupled with a reduced
contact area of 0.001" of an
inch on one sear surface allow for such a light trigger pull that effecting
the trigger pull to the
required 3lbs. or so can be adjusted through the use of a spring pocket that
has a threaded insert in
it allowing varying tension adjustment for the lower sear through the said
spring biasing means.
The spring tensioning allows the trigger geometry to stay the same maintaining
the integrity of the
internal components, while maintaining optimal sear engagement at all times
through a two contact
point rolling sear surface.
Operation of the preferred embodiment
The trigger described above would be installed in a crossbow; to load it, the
user would place the
crossbow on the ground supported by one foot, usually in a stirrup. The user
would then grab the
string with left and right hands and pull back on the crossbow string. The
string would be pulled
into opening 1.c and this rearward movement will cause claw I .b to move
rearward, forcing lower
sear 1.h to pivot about it pivot point 1.g; this movement will also cause pin
I .j to force safety 1.k to
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pivot about 1.t, placing the safety into a safe position because it interferes
with the rear portion of
lower sear 1.h. The upper sear surface 1.f will come and engage against dowel
pin 1.p, which is
preferably a 0.125" diameter dowel pin. The crossbow is now ready to load an
arrow for firing at a
later time.
To fire the user will move safety 1.k into the fire (or unsafe) position and
depress the trigger 1.0
which is rigidly attached to lower sear 1.h. This action will cause lower sear
I.h to pivot, allowing
claw 1.b to pivot upward, thus disengaging upper sear surface 1.f from dowel
pin 1.p, and fire the
arrow.
While the foregoing written description of the invention enables one of
ordinary skill to make and
use what is considered presently to be the best mode thereof, those of
ordinary skill will understand
and appreciate the existence of variations, combinations, and equivalents of
the specific
embodiment, method, and examples herein. The invention should therefore not be
limited by the
above described embodiment, method, and examples, but by all embodiments and
methods within
the scope and spirit of the invention. For example, embodiments of this
invention can be used for
any other devices that use a trigger, such as guns, rifles, pistols,
slingshots, etc. Similarly, adapting
a long rod or an arm to replace or to actuate the trigger 1.0 of the
embodiments herein, could enable
the positioning of a trigger far from the action, such as in a bull pup
configuration.
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