Elongated-member-driving apparatus – Explosive-type driving means – With plunger
Reexamination Certificate
2003-06-03
2004-02-24
Smith, Scott A. (Department: 3721)
Elongated-member-driving apparatus
Explosive-type driving means
With plunger
C227S130000, C123S0460SC
Reexamination Certificate
active
06695195
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a combustion-powered nail gun that generates drive force by igniting a gas/air mixture to drive a nail into a work piece.
2. Description of Related Art
U.S. Pat. No. 5,197,646 discloses a conventional combustion-powered tool assembly.
FIG. 1
schematically shows configuration of a conventional combustion-powered nail gun
1
similar to that disclosed in U.S. Pat. No. 5,197,646. The nail gun
1
includes a housing
14
, a handle
11
, a tail cover
17
, a push lever
21
, and a magazine
13
.
The housing
14
accommodates therein a head cover
23
, a combustion chamber wall
15
, a cylinder
4
, and a piston
10
. The combustion chamber wall
15
, the head cover
23
, and the piston
10
together define a combustion chamber
5
. The head cover
23
and the cylinder
4
are fixed with respect to the housing
14
. The combustion chamber wall
15
is vertically movable within the housing
14
as guided by the housing
14
and the cylinder
4
. Although not shown in the drawings, a connection rod linkingly connects the combustion chamber wall
15
with the push lever
21
so that the combustion chamber wall
15
and the push lever
21
move together in a ganged manner. Further, a spring (not shown) is provided for urging the push lever
21
downward. Therefore, the push lever
21
and the combustion chamber wall
15
are in their lower most position shown in
FIG. 1
while no force operates against the urging force of the spring. At this time, because the head cover
23
and the cylinder
4
are fixed, an inlet
26
is opened between the head cover
23
and the combustion chamber wall
15
and an outlet
25
is opened between the cylinder
4
and the combustion chamber wall
15
. Although not shown in the drawings, seals for forming a tight seal at the inlet
26
and the outlet
25
are provided at the lower end of the head cover
23
and the upper end of the cylinder
4
. An intake vent
30
is provided in the upper end of the housing
14
and a discharge vent
32
is provided in the lower end of the housing
14
.
The housing
14
further accommodates a motor
8
, a spark plug
9
, and a gas canister connection
7
in a space above the head cover
23
. The gas canister connection
7
is connected to a gas canister (not shown) that hold combustible gas. An injection port
22
connects the gas canister connection
7
with the inside of the combustion chamber
5
and supplies combustible gas from the gas canister connection
7
into the combustion chamber
5
. A fan
6
is disposed in the combustion chamber
5
. The fan is attached to and rotated by the drive shaft of the motor
8
. Electrodes of the spark plug
9
are exposed in the combustion chamber
5
. Ribs
24
are provided on the inner surface of the combustion chamber wall
15
so as to protrude into the combustion chamber
5
.
The piston
10
is supported by a slide seal member (not shown) so as to be vertically movable in the cylinder
4
. A bumper
2
is provided below the piston
10
for absorbing excessive energy of the piston
10
after a nail driving operation. Also, an exhaust hole
3
is formed in the cylinder
4
. A check valve (not shown) of well-known construction is provided on the exhaust hole
3
and the outer side of the exhaust hole
3
.
The handle
11
is attached to a middle section of the housing
14
. A trigger
12
is provided on the handle
11
. Each time the trigger
12
is pulled (turned on), the spark plug
9
generates a spark.
The magazine
13
and the tail cover
17
are attached to the lower end of the housing
14
. The magazine
13
is filled with nails (not shown). The magazine
13
feeds the nails one at a time to the tail cover
17
. The tail cover
17
sets the nails fed from the magazine
13
in a position below the piston
10
and guides movement of the nails when the nails are driven downward by the piston
10
.
FIG. 1
shows the nail gun
1
before a nail driving operation is performed. At this time, the push lever
21
is urged downward by the spring (not shown) to protrude below the lower end of the tail cover
17
. The combustion chamber wall
15
is also in its lowermost position so that the inlet
26
is open between the combustion chamber wall
15
and the head cover
23
and the outlet
25
is open between the combustion chamber wall
15
and the cylinder
4
. Also, the piston
10
is in its top dead position before a nail driving operation starts.
Next, a nail driving operation by the nail gun
1
will be described with reference to
FIGS. 1
to
4
.
FIGS. 1
to
4
show changes in the nail gun
1
in chronological order when a nail driving operation is performed.
To prepare to drive a nail into a work piece
27
, the user grips the handle
11
and presses the push lever
21
against the work piece
27
as shown in FIG.
2
. As a result the push lever
21
rises upward against the urging force of the spring and the combustion chamber wall
15
, being connected to the push lever
21
, moves upward also into the position shown in FIG.
2
. When the combustion chamber wall
15
moves upward in this manner, the inlet
26
and the outlet
25
, which are above and below the combustion chamber wall
15
respectively, close up to seal close the combustion chamber
5
with the seals (not shown). In a linked operation, the gas canister connection
7
is pressed and so supplies combustible gas from the gas canister (not shown) to the injection port
22
, which injects the combustible gas into the combustion chamber
5
. Further, the motor
8
is turned on to rotate the fan
6
. The injected combustible gas and air in the combustion chamber
5
are agitated and mixed together by rotation of the fan
6
in the sealed off combustion chamber
5
and influence of the ribs
24
that protrude into the combustion chamber
5
.
Next, the user pulls the trigger
12
on the handle
11
to generate a spark at the spark plug
9
. The spark ignites and explodes the air/gas mix in the combustion chamber
5
. The gas expands as a result. The expanding gas drives the piston
10
downward as shown in
FIG. 3
to drive the nail that is set in the tail cover
17
into the work piece
27
.
Directly after combustion, the combusted gas that remains in the cylinder
4
and the combustion chamber
5
is extremely hot and in a high pressure state from having expanded. Because, as shown in
FIG. 3
, the piston
10
is in contact with the bumper
2
at a position below the exhaust hole
3
, the combusted gas from the combustion chamber
5
flows through the exhaust hole
3
to outside of the cylinder
4
until the pressure in the cylinder
4
and the combustion chamber
5
reaches atmospheric pressure, whereupon the check valve in the exhaust hole
3
closes shut. During this time, the inner surface of the cylinder
4
and the inner surface of the combustion chamber wall
15
absorb the heat of the combusted gas so that the combusted gas rapidly cools and contracts. Therefore, after the check valve (not shown) closes, pressure in the thus sealed combustion chamber
5
above the piston
10
decreases to below atmospheric pressure. This is referred to as a thermal vacuum. This thermal vacuum pulls the piston
10
back to the upper dead position of before the nail driving operation.
After the nail is driven into the work piece
27
, the user releases the trigger
12
and lifts the nail gun
1
upward away from the work piece
27
. When the push lever
21
separates from the work piece
27
, the spring (not shown) urges the push lever
21
and the combustion chamber wall
15
back into the positions shown in FIG.
4
. Even after the trigger
12
is released and turned off, a control unit (not shown) continues rotation of the fan
6
for a fixed period of time to scavenge the combusted gas in the combustion chamber
5
. That is, in the condition shown in
FIG. 4
, the inlet
26
and the outlet
25
are opened up above and below the combustion chamber wall
15
respectively. The combusted gas in the combustion chamber
5
is scavenged b
Nishikawa Tomomasa
Ohtsu Shinki
Hitachi Koki Co,. Ltd.
Smith Scott A.
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