Note: Descriptions are shown in the official language in which they were submitted.
111~t;8~3
The present invention is directed to a drilling
and chipping hammer with a percussion mechanism and an
internal combustion engine drive with the engine connected
to a crankshaft with a crank at one end which drives the
percussion mechanism in a reciprocating motion over a
connecting rod.
Drilling and chipping hammers of this type are
used primarily in heavy drilling and breaking operations.
With an internal combustion engine serving as the drive for
the hammer, a so-called two-cycle engine is usually employed.
On a comparitive output basis, such an engine has the
advantage of a simple assembly over a four-cycle engine and,
further, is of a lower weight. As a result, two-cycle
engines are standard with manually operated drilling and
chipping hammers for weight as well as cost reasons.
Following each power stroke, the combustion
chamber in two-cycle engine must be scavenged with a fuel-
air mixture so that any exhaust gases within the chamber
are displaced by the mixture and a new combustible charge is
provided. To maintain a flow of the fuel-air mixture into
the combustion chamber, a pump is required. With practi-
cally all small two-cycle engines, the engine crankcase is
used as a scavenger pump. Such an arrangement, however,
causes a considerable drawback. The crankshaft and
connecting rod bearings as well as the cylinder walls must
be kept sufficiently lubricated. Without taking any
countermeasures, the scavenging of the lubricating oil by
the fuel-air mixture would destroy the tool within a short
period of time. To avoid this problem in twb-cycle engines
the fuel~air mixture usually includes a mixture of gasoline
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and oil~ The gasoline functions as the energy source for
the internal combustion engine.
Since oil is present within the combustion
cham~er, it is only incompletely burned and ends up as a
bothersome blue exhaust smoke.
In most cases the efficiency of a conventional
two-cycle engine is lower than that of a comparable four-
cycle engine. The lower efficiency can be traced mostly to
scavenger losses occurring in the combustion chamber. With
large size, stationary or vehicular-mounted ~ngines, a
considerable input is used in scavenging the combustion
chamber. In such units, turboblowers, rotary disc blowers
or even reciprocating pumps are used. In portable units,
such as drilling and chipping hammers, such devices cannot
be used because of their weight.
The primary object of the present invention is to
provide a drilling and chipping hammer using an internal
combustion engine as its power source where an effective
scavenging action is afforded which develops a high
efficiency while maintaining an optimal unit weight for the
hammer.
In accordance with the present invention, the
hammer housing is divided into a percussion mechanism space
and an engine space with the two spaces separated from one
another. An inlet valve in the housing admits air or a
fuel air mixture into the percussion mechanism space and a
flow passageway conducts the air or fuel-air mixture into
the combustion chamber in the engine without passing
through the engine space.
With the percussion mechanism space separated
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from the rest of the hammer mechanism, it can be used as a
scavenyer pump Eor the internal combustion engine. Since
for any given two-cycle engine the percussion stroke volume
about matches that of the engine, the percussion mechanism
space is most suitable as an engine scavenger pump.
Genera~ly, the crankshaft bearing is located in the engine
space and the percussion piston is usually lubricated by
the percussion mechanism. The connecting rod bearings can
be equipped with sealed lubricated bearings. Consequently,
no lubrication of the percussion mechanism space is required.
Since the engine space is not contacted by the fuel-air
mixture (in the case of a gasoline engine) or with drawn-in
air (in the case of a fuel injection engine), the lubrication
of the crankshaft bearings, the connecting rod bearings and
the other working surfaces associated with the engine can be
accomplished in an effective manner using a splash or oil
mist lubrication method. Accordingly, the fuel-air mixture
does not have to provide any special lubricating function.
Therefore, it is possible to operate a drilling and chipping
hammer embodying the present invention without adding oil
into the two-cycle fuel-air mixture and such a factor has a
favorable effect on the operating costs and the waste gases.
Known two-cycle engines have another drawback.
During the scavenging operation, part of the fuel-air
mixture is released along with the scavenged losses from
the combustion chamber through the exhaust muffler into the
ambient atmosphere. With two-cycle engines this effect
usually cannot be avoided. Furthermore, a high fuel
consumption results because a certain amount of the fuel is
lost to the combustion process and a high percentage of
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unburned and mostly toxic gases escape with the exhaust.
In so~called injectlon engines, this problem is avoided by
using pure air for the scavenging action. During operation,
as soon as the engine piston covers the exhaust openings,
fuel is injected by means of a high-pressure nozzle. Such
operation results in three advantages: (1) because of the
delayed fuel injection a measurable boost is gained in the
engine performance, (2) fuel consumption is appreciably
reduced, and (3) the quality of the waste gases is
substantially improved. The scavenging action according to
the invention utilizing the percussion mechanism space is
suitable for both gasoline and injection engines.
An inlet valve is provided through which a fuel-
air mixture is drawn in through a known carburetor or pure
air is drawn in through an air filter. Though this system
is particularly suitable for a two-cycle engine, it can also
be used for a four-cycle engine to produce a so-called
charge for increasing performance.
The present i~vention provides a particularly
simple arrangement and, in comparison with known combustion
engine driven drilling and chipping hammers, it requires
only an inlet valve and piping to connect the outlet from
the percussion mechanism space with the inlet openings into
the combustion chamber. As a result, there is practically
no increase in weight of the drilling and chipping hammer.
To simplify the arrangement of the hammer, the
end face of the percussion piston joined to the connecting
rod acts as a movable wall and seals the percussion
mechanism space from other parts of the hammer. Therefore,
particularly with a pneumatic percussion mechanism, no
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additional sealing action is required because the percus-
sion piston reciprocating in a cylinder is sealed against
the air cushion located between the piston forming a
portion of the percussion mechanism space and the piston
effecting the actual percussion action. The compression of
the air or fuel-air mixture drawn into the percussion
mechanism space can be optimized by establishing, indepen-
dently from the engine drive, a crank stroke and dead space
within specified limits. In comparison with known units,
where the end of the crankshaft with its drive crank
extends into the percussion mechanism space, new possibi-
lities open up since this space can be separated from the
reminder of the hammer components. In a conventional two-
cycle engine, the fuel-air mixture is drawn into the engine
crankcase and is precompressed therein during the expansion
phase in the combustion chamber. Just before reaching the
bottom dead centre, the inlet openings are uncovered by the
piston and the precompressed mixture is free to flow into
the combustion chamber. As the crankshaft continues to
rotate, howev~r, the pressure within the engine crankcase
drops so that the flow into the combustion chamber is
reduced. Accordingly, only an incomplete scavenging of the
combustion chamber is possible. If, however, the scavenging
pressure is increased by a reduction in the space, there is
the danger that too much of the fuel-air mixture escapes
unburned through the exhaust openings as scavenging losses
with an increase in fuel consumption. Accordingly, for
adjusting the pressure to optimize the scavenging process,
it is advantageous if the connection from the crank to the
percussion mechanism is angularly offset relative to the
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connection from the engine to the crankshaft so that the
percussion piston lags behind the engine piston in an
angular range of 10 to 60. The effect of such an arrange-
ment is that as the engine piston moves from the dead
centre position a sufficient scavenging pressure is still
present until the engine piston again covers the inlet or
outlet openings from the combustion chamber. Because the
percussion mechanism is coupled with the crankshaft, -the
angular offset relationship remains constant.
From practical experience, the angular offset has
been established as 40. Accordingly, with given inlet and
exhaust opening positions, the effect of a sufficient
scavenging pressure lasts until the closure of such openings,
so that a back blow of the scavenging air is prevented and
an improved scavenging is afforded as compared with conven-
tional crankcase scavenging. On the other hand, the pres-
sure gradient between scavenging and combustion chamber
pressures effective upon the opening of the inlet openings
is so minimal that a flow can develop into the combustion
chamber with the fresh inflowing mixture displacing the
exhaust gases mostly through the exhaust openings.
The various features of novelty which characterize
the invention are pointed out with particularity in the
claims annexed to and forming a part of this disclosure.
For a better understanding of the invention, its operating
advantages and specific objects attained by its use,
reference should be had to the accompanying drawings and
descriptive matter in which there are illustrated and
described preferred embodiments of the invention.
IN THE DRAWING:
3689
Figure 1 is a side view, partly in section, of a
drilling and chipping hammer embodying the present inven-
tion;
Figure 2 is a cross-sectional view taken along
the line A-A in Figure 1 showing the upper dead-centre
position of the percussion piston in the percussion mechan-
ism as compared to the engine piston; and
Figure 3 is a view similar to ~'igure 2, however,
showing the percussion piston in the bottom dead-centre
position.
In Figure 1 a drilling and chipping hammer is
I illustrated having a housing 1. A handle 2 is attached to
¦ the right or rear end of the housing 1. At its front or
left-hand end, the housing 1 supports a tool holder 3. A
crankshaft 4 of an internal combustion engine is rotatably
supported within the housing 1. A connecting rod 5 is
rotatably mounted on a crank web 4a of the crankshaft 4.
The connecting rod at its end spaced from the crank web 4a
is secured to a piston 6 of the internal combustion engine.
The piston 6 is displaceably mounted within a cylinder lc
mounted on the housing. As viewed in Figure 1, a crank 7
is attached to the upper end of the crankshaft 4 by a
thread 4b. A connecting rod 8 is mounted at one end on a
crank pin 7a secured to the crank 7. Connecting rod 8
forms a part of the percussion mechanism a~d is connected
to a piston 9 such as is used in a pneumatic percussion
mechanism. Piston 9 is reciprocally mounted in a sleeve
10. Located in the housing 1, adjacent the crank 7, is an
inlet valve 11. Inlet valve 11 includes a ball lla biased
against a valve seat llc by a spring llb. If the piston 9
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moves toward the tool holder 3, either air or a fuel-air
mixtu-re can be drawn into a space la through the inlet
valve 11. Crank 7 and connecting rod 8 are located within
the space la. The interior of the housing is constructed
so that a seal 12 separates the space la from the remainder
of the interior of the housing. Space la has an outlet
opening ld. A pipeline 13 extends from the outlet opening
ld to an inlet opening le in the cylinder lc opening into
the combustion chamber lb in the engine. When piston 9
reverses direction and moves toward the handle 2, the end
face of the piston 9 forms a movable wall in the space la
and the volume within the space is reduced and the air or
fuel-air mixture drawn into it is ejected into the pipeline
13. When the piston 6 moves rearwardly toward the handle
and uncovers the inlet opening le into the combustion
chamber, then the air or fuel-air mixture in the pipeline
13 can flow into the combustion chamber lb. Therefore, the
waste gases resulting from ignition in the combustion
chamber lb are displaced through an exhaust opening lf.
Technically, this operation is known as scavenging. With
an internal combustion engine, a fuel-air mixture is used
in the scavenging operation. The drawback in such a
scavenging operation is that a part of the fuel-air mixture
can also escape through the exhaust opening lf causing a
reduction in the efficiency of the engine. Where so-called
fuel injection engines are used, however, the scavenging
action is effected with air alone. Fuel is injected into
the combustion chamber lb through a nozzle only after both
the inlet opening le and the exhaust opening lf are closed.
Such an arrangement has a positive effect on the engine
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efficiellcy. A flywileel 14 is positioned on the lower end
of the crankshaft 4 as viewed in Figure 1. Such a flywheel
14 is standard on internal combustion engines. The fly-
wheel 14 serves as a compensator between the internal
combustion engine power output and the engine power input
during the compression cycle and the percussion mechanism
operation. Further, the flywheel is used to generate
ignition voltage and also as a fan wheel for a cooling air
flow drawn in through a screen 15 in the housing 1 and
conveyed over the cylinder lc of the engine.
In Figure 2, the sectional view taken along the
line A-A in Figure 1, the drive and driven components of
the hammer are illustrated. The percussion mechanism
piston 9, shown in full line, is located in its upper dead-
centre position. The engine piston 6, however, shown in
dashed lines, hàs already passed its upper dead-centre
position. Accordingly, the crank pin 7a connected to the
percussion mechanism is offset relative to the internal
combustion engine crank web 4a by an angle 0~ so that the
percussion mechanism lags the internal combustion engine
by the angle OC. As the crank 7 continues to rotate, the
volume of space la is reduced as the end face of the piston
9 moves toward the right-hand end of the housing and the
air or fuel-air mixture previously drawn into the space is
forced through the outlet opening ld into the pipeline 13.
In comparison with conventional two-cycle engines in which
the engine crank housing serves as a scavenger pump, the
advantage of the lagging action of the percussion mechanism
relative to the engine is that, during the entire scavenging
process, the scavenging pressure exceeds combustion engine
111~3689
pressure so that back-flow is prevented.
In Figure 3, the same components are illustrated
as in Figure 2, however the percussion mechanism piston 9
is in its bottom dead-centre position. Accordingly, engine
piston 6 has already moved past its bottom dead-centre
position. In this arrangement, the fuel-air mixture which
has entered the combustion chamber lb through the pipeline
13 from space la is compressed. At this position, the
percussion mechanism output consumption is low so that the
stored energy of the flywheel can be used fully for
compressing the fuel-air mixture in the combustion chamber
lb. In this way, the phased or angular displacement
between the percussion mechanism and the engine affords an
equally positive effect.
As stated above the angle 0~ may be between 10
and 60, but in practice the preferred range is in the
region of 40.
Having described what is believed to be the best
mode by which the invention may be performed, it will be
seen that the invention may be particularly defined as
follows:
A drilling and chipping hammer comprising a
housing, a percussion mechanism located within said housing,
an internal combustion engine mounted on said housing and
including an engine piston, an engine crankshaft located in
said housing, a first connecting rod connected at one end
to said engine piston and at the opposite end to said
crankshaft, a crank connected to said crankshaft at a
position spaced from said first connecting rod, said
percussion mechanism including a reciprocal percussion
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piston, a second connecting rod located within said housing
and attached to said crank and to said percussion piston
for transmitting the reciprocating action to said percussion
piston from said crankshaft for effecting a percussion
application stroke and a return stroke, wherein the improve-
ment comprises means Eor dividing the interior of said housing
into a percussion mechanism space containing said crank and
said second connecting rod and an engine space containing
said first connecting rod with said percussion mechanism space
sealed from said engine space and said crankshaft extending
from said engine space into said percussion space, said engine
including a combustion chamber separated from said engine
space by said engine piston, an inlet valve mounted in said
housing for selectively supplying one of air and a fuel-air
mixture into said percussion mechanism space during the percus-
sion application stroke of said percussion piston, and means
forming a flow passageway for conveying the one of air and
fuel-air mixture from said percussion mechanism space to said
combustion chamber during the return stroke of said percussion
piston.
The invention further comprises such a drilling
and chipping hammer wherein said second connecting rod
being connected to said crank angularly offset relative to
the connection of said first connecting rod to said crank-
shaft so that said engine piston leads said percussion
piston by an angle in the range of 10 to 60 and preferably
in the region of about 40.
While specific embodiments of the invention have
been shown and described in detail to illustrate the appli-
cation of the inventive principles, it will be understood
that the invention may be embodied otherwise without
departing from s~ch principles.
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