Buffer system for fastener driving devices

The present buffer system for a fastener driving device includes two cooperating buffer elements (16, 22) located at the bottom (17) of the driving cylinder (2). A first buffer element (16) of hard elastic material rests on the inwardly facing surface of the cylinder bottom (17) in such a manner that at least a portion of the surface (18) of the first buffer element (16) contacting the bottom (17) is movable relative to the bottom (17) of the driving cylinder (2). A second buffer element (22) made of an elastic material softer than the hard elastic material of the first buffer element, rests on the first buffer element.

CROSS-REFERENCE TO RELATED APPLICATION 
The present application is based on German Ser. No. P 3,047,662.1, filed in 
the Federal Republic of Germany on Dec. 18, 1980. The priority of the 
German filing date is claimed for the present application. 
BACKGROUND OF THE INVENTION 
The present invention relates to a buffer system for fastener driving 
devices. Such devices drive, for example, nails or the like by means of a 
driver piston which is guided in a cylinder and activated by pressurized 
air. 
German Pat. (DE-PS) No. 2,339,163 corresponding to U.S. Pat. No. 3,969,989 
discloses a driving device for driving nails or the like which is equipped 
with a buffer system including a relatively soft buffer element made of a 
material, the volume of which is compressible. 
The buffer system further comprises a hard buffer element cooperating with 
the soft buffer element. The hard buffer element is resting with its 
entire contact surface on the bottom of the lower end or foot of the 
cylinder. 
This prior art buffer system is capable to safely take up impacts having 
excess pressure as well as idle impacts while having a high useful life. 
However, due to the contact between the hard buffer element and the bottom 
of the cylinder foot, each impact generates an unpleasant body noise which 
is a nuisance to the operator. Under extreme conditions the buffer element 
may be subject to a substantial deformation, whereby the buffer elements 
may be damaged due to inner friction and heat up. 
OBJECTS OF THE INVENTION 
In view of the above it is the aim of the invention to achieve the 
following objects singly or in combination: 
to provide a buffer system of the type described which is capable to safely 
take up and dissipate the excess impact energy while keeping the body 
noise as small as possible and while simultaneously having a useful life 
as long as possible; 
to construct the buffer system in such a manner that a friction stage, so 
to speak, is operatively effective between a buffer element of soft 
material, and a buffer element of hard material; 
to assure an efficient heat dissipation in a buffer system of the 
invention; 
to arrange the buffer system in such a manner that a change in its 
operational noise provides an indication that it needs to be replaced; and 
to make sure that the noise is minimized, including the noise caused by the 
escaping pressurized air during the return stroke of the driving piston. 
SUMMARY OF THE INVENTION 
According to the invention there is provided a buffer system for fastener 
driving devices which comprises at least two buffer elements made of a 
hard elastic buffer material and a soft elastic buffer material. The two 
buffer elements are arranged in the impact facing end of the driving 
cylinder and cooperate with each other for taking up and dissipating 
excess impact energy of the driving piston. The arrangement is such, that 
the buffer element of hard elastic material is provided with a contact 
surface, at least a portion of which is in movable contact with the bottom 
of the cylinder formed by the inwardly facing surface of the cylinder 
foot. In the normal condition of the hard material buffer element, when it 
is not subject to an impact, a spacing is provided between a portion of 
the contact surface of the hard buffer element and the inwardly facing 
surface of the cylinder foot. 
The movable arrangement of the hard buffer element constitutes the 
interposition of a friction stage between the soft spring characteristic 
of the soft buffer element and the hard spring characteristic of the hard 
buffer element. During normal nailing operations when there is little 
excess pressure, only the soft portion of the combined spring 
characteristic is utilized. The hard portion of the spring characteristic 
becomes effective, for example, when idle strokes are performed. This type 
of structure has resulted in a noticeable reduction of the body noise 
during normal nailing operations. Reductions up to six dB have been 
measured which means that the noise generation has been reduced to about 
one half of the noise generated by a comparable prior art structure. 
According to an advantageous embodiment the hard buffer element is arranged 
in the cylinder with a biasing load so that the hard element is pressed 
with an even larger force against the inner surface of the cylinder ring 
surrounding the hard buffer element when the soft buffer element is 
compressed by an impact stroke. Thus, upon further compression the excess 
impact energy is dissipated by friction at the contact surfaces between 
the hard buffer element and the cylinder foot or between the hard buffer 
element and the inner surface of the cylinder or cylinder ring surrounding 
the hard buffer element. This cooperation between the contacting surfaces 
also provides for an efficient heat dissipation or heat removal. 
According to the invention the hard buffer element during its normal 
operation is thus not fully in contact with the inner surface of the 
cylinder foot. However, if the hard buffer element comes into contact with 
the inner surface of the cylinder foot then the hard buffer element 
operates as a hard, deformable buffer which is heated substantially due to 
inner friction. This inner friction may, however, also cause the 
destruction of the hard buffer element, as in the prior art. However, when 
in the apparatus according to the invention the hard buffer element rests 
entirely against the inwardly facing surface of the cylinder foot, the 
body noise is increased, whereby the operator receives a signal that the 
replacement of the hard buffer element is necessary. Thus, the invention 
has the advantage that a damage or destruction of parts of the driving 
device is avoided with certainty. 
If the present buffer system is used in a driving device equipped in a 
known manner with an air storage for storing the pressurized air required 
for the return stroke of the piston, the present buffer system has the 
further advantage that the pressurized air escapes only slowly during the 
return stroke of the driving piston, whereby such escape from the driving 
cylinder is less noisy. This is so because the soft buffer element rests 
on the hard buffer element and thus the soft buffer element substantially 
reduces the cross-sectional area of the venting opening for the escaping 
air.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE 
OF THE INVENTION 
FIG. 1 shows an axial, longitudinal sectional view through a fastener 
driver which is only partially shown. The driver for nails or the like 
comprises a housing 1 in which a driver cylinder 2 is arranged for guiding 
a driver piston 3 equipped with an impact rod 4 displaceably supported in 
the cylinder. Air under pressure is supplied to the driver apparatus 
through the handle 5 from a pressurized air source not shown. The 
pressurized air travels into the inner space of the cylinder 2 in response 
to the operation of a trigger lever 6 and in response to actuation of a 
tubular valve slide 7. The pressurized air in the cylinder 2 above the 
piston 3 accelerates the driving piston 3 in the direction toward the 
cylinder foot 9 when the cylinder is released by its elastic click 
mechanism 8. As a result of the acceleration of the piston 3 the impact 
rod 4 drives the nail 10 into a work piece not shown. Further nails are 
held ready by a magazine 11. 
The cylinder 2 is surrounded by an air storage space 12 which is filled 
with air under pressure through openings 13 and 14 in the cylinder 2 
during the driving stroke in a known manner. This pressurized air is 
effective on the underside or surface of the driving piston 3 when the 
trigger lever 6 is released, whereby the driving piston 3 is again moved 
into the starting position. 
When the driving piston 3 reaches the lower limit of its driving stroke it 
impacts on a buffer system 15 shown on an enlarged scale in FIG. 2. The 
buffer system 15 comprises a first buffer element 16 made of a hard 
elastic material which suitably may be cross-linked polyurethane. The 
contact surface 18 of the buffer element 16 facing the conical bottom 17 
of the cylinder foot 9 has also a frustum shape. However, the cone angle 
of the contact surface 18 is smaller than the cone angle of the upwardly 
facing inner surface 17 of the cylinder foot 9. Thus, when the buffer 
system is not subject to an impact an intermediate space 19 is formed 
between the surface 17 and the contact surface 18 as shown in the 
left-hand portion of FIG. 2. However, when the buffer system is subject to 
an impact as shown in the right-hand portion of FIG. 2, the surfaces 17 
and 18 contact each other, whereby the space 19 disappears. 
The buffer element 16 further comprises a cylindrical section 21, the outer 
diameter of which is somewhat larger than the inner diameter of the 
cylinder 2 and also larger than the inner diameter of the lower end ring 
2' of the cylinder 2. Thus, the buffer element 16 is held in the cylinder 
with a biasing which has the above mentioned advantage that additional 
buffering is accomplished by the friction between the outer surface of the 
cylinder portion 21 and the inner surface of the cylinder 2 and that the 
resulting frictional heat is efficiently dissipated. 
A second buffer element 22 rests on the first buffer element 16 and faces 
the driving piston 3. The second buffer element 22 is preferably made out 
of a cellular material such as polyurethane elastomer. Such cellular 
structure provides in a known manner a progressive spring characteristic 
for the buffer element 22. The upwardly facing surface 23 of the buffer 
element 22 is also slanting slightly radially outwardly relative to the 
longitudinal central axis. The downwardly facing surface of the driving 
piston 3 is provided with a cylindrical recess 24, the inner diameter of 
which is larger than the outer diameter of the buffer element 22. 
As mentioned, the left half of FIG. 2 shows the buffer system 15 when it is 
not subject to any loading. However, the impact or driving piston 3 is in 
a position just about contacting the second buffer element 22. At this 
point the intermediate space 19 between the bottom surface 17 and the 
contact surface 18 is still fully present. For dissipating any excess 
driving energy the buffer system 15 is compressed as illustrated in the 
right-hand portion of FIG. 2. During this compression the first buffer 
element 16 is spread out by the compaction of the second buffer element 
22, whereby the cylindrical section 21 of the first buffer element 16 is 
pressed radially outwardly against the cylinder 2, 2' said radial outward 
pressing exceeding the radially outward biasing of the ring portion 21 of 
the buffer element 16. As further braking action is applied to the driving 
or striking piston 3, the cylindrical section 22 is displaced relative to 
the inner cylinder surface of the cylinder 2, 2' and portions of the 
contact surface 18 of the buffer 16 are shifted against the inner bottom 
surface 20, whereby a substantial friction is generated. The resulting 
energy is dissipated in the form of heat. Since the components surrounding 
the buffer system are metal components such as the cylinder 2 and the 
cylinder foot 9, an efficient heat dissipation is accomplished. 
If the contact surface 18 rests completely against the bottom surface 17, 
then the first buffer element 16 acts in the same manner as a respective 
prior art element, namely, as a hard buffer which is able to take up still 
further excess driving energy as a result of its inner deformation. 
During the just described friction phase of the buffer system 15 very 
little body noise is generated while the buffer elements are substantially 
protected against destruction. When after a certain period of operation 
the buffer elements have been exposed, nevertheless, to a certain wear and 
tear, the resulting body noise is increased and the operator is thereby 
informed, that the buffer elements require replacement. 
Although the invention has been described with reference to specific 
example embodiments, it will be appreciated that it is intended to cover 
all modifications and equivalents within the scope of the appended claims.