Note: Descriptions are shown in the official language in which they were submitted.
113~7416
The present invention is d:Lrected to a hand tool
and in particular to a drilling and chipping hammer which
is driven by an internal combustion engine and has a fly-
wheel connected to the engine crankshaft.
~ land tools of the general type to which the
invention is directed, are used for heavy duty work and at
remote construction sites where no electrical current
supply is available. An advantage of these tools over
electrically operated ones is their great mobility. As
compared to electrically operated tools, known internal
combustion engine operated units weigh considerably more,
operate at significantly higher noise levels and develop
greater vibrations.
Working with presently known internal combustion
engine operated units over long periods of time can be
very tiring. To compensate, on the one hand, for engine
drive irregularities and, on the other hand, for the timed
shift between internal combustion engine power output and
hammer power consumption, known drilling and chipping
~0 hammers have been equipped with a flywheel connected to the
engine crankshaft. The flywheel stored energy must be
sufficiently high to cover the percussion work required by
the hammer mechanism and the internal combustion engine
compression work without any increased rpm output. To
prevent increased engine rpm and, accordingly, undesirable
noise levels when the tool is lifted free from the surface
being worked, known tools have been provided with
throttling devices which cause the engine to idle. These
throttling devices can be manually or automatically
actuated. To prevent the engine from "dying" at minimal
~ '
1~L37~1~
idling during operational pauses and primarily on
operational restarts, the flywheel must have a specific
flywheel moment. Such a characteristic is possible with a
flywheel of sufficiently large size, however, difficulties
are presented where the size of the flywheel is limited by
weight and positional factors.
With presently known internal combustion engine
operated hand tools, so-called high-speed engines are
utilized where the required output is achieved only at
relatively high nominal speed. Such operation, however,
produces extremely high noise levels and strong vibrations
and, accordingly, such units are a health menace and are
not adapted for continuous operation. In the case of slow
moving engines, however, large and heavy flywheels are
required which render the tool unsuitable for use as a
portable unit.
The primary object of the present invention is to
provide a light weight hand tool capable of operation at
low engine rpm.
In accordance with the present invention a
transmission gearing system is provided between the crank-
shaft and the flywheel which raises the flywheel rpm over
the crankshaft rpm. Since the energy content of a flywheel
quadruples with rpm, the effect is a saving in total unit
weight and a reduction in engine rpm even with the added
transmission gearing system.
With small sized hand tools, the flywheel
normally assumes other functions. Usually, the flywheel
is employed as a fan providing a flow of engine cooling
air. With increased flywheel rpm, a considerably higher
1137~16
air throughput is achieved so that even with continuous
tool operation, despite a reduced flywheel diameter,
adequate engine cooling is accomplished. secause the fly-
wheel in most cases also serves as an ignition spark
generatOr, the ignition voltage can be maintained at a
somewhat constant rate even at low engine drive rpm.
Another advantageous feature of the transmission gearing
system of the present invention which increases the fly-
wheel rpm over that of the crankshaft, is the positional
stabilization of the overall unit by the flywheel gyro-
scope effect. As a result, any undesirable tilting motion
during operation caused by eccentrically acting forces can,
to a large degree, be prevented. Further, the unit also
operates at a substantially lower vibration rate.
Both for positional and weight related reasons,
it is advantageous to provide a transmission gearing system
of a very compact design. Accordingly, it is advantageous
to provide the transmission gearing system as a planetary ~ -
gear system. Furthermore, a planetary gear system can be
arranged coaxially with the crankshaft so that the external
shape of the hand tool i5 not adversely affected to any
practical extent.
For affording an optimum transmission of force
and also for dimensional reasons, it is advantageous to
provide a planetary gear system including a crankshaft
driven planetary gear crosspiece, a gear ring fixed to
the housing, and a sun wheel coupled to the flywheel. Two
or more planet wheels can be mounted on the crosspiece in
meshed engagement with the gear ring and the sun wheel so
that a uniform power distribution is achieved.
-- 3 --
1~L37~
For practical reasons, the transmission ratio
between the crankshaft and the flywheel is limited. The
added transmission gearing system cancels a part of the
potential saving in the weight of the flywheel. Accordingly,
the rpm of the flywheel is considerably raised over that of
the crankshaft. However, the nominal engine driven fly-
wheel rpm must not be set too high, because the gyroscope
effect of the flywheel becomes so strong that handling the
tool is almost impossible. To achieve an optimal mean
value, it is desirable to set the transmission ration at
1:3. The transmission ratio must be a whole number multiple
because the flywheel picks up the magneto for an ignition
coil induction effect.
The various features of novelty which charac--
terize 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:
Figure 1 is a side view, partly in section, of a
drilling and chipping hammer embodying the present invention;
and
Figure 2 is a sectional view taken along the line
II-II in Figure 1 and illustrated on an enlarged scale.
In Figure 1 a drilling and chipping hammer is
illustrated enclosed within a housing 1. As viewed in
Figure 1, the right-hand end of the housing 1 contains a
1~37gl6
handle 2. At the left-hand or front end of the housing 1 a
tool holder 3 is positioned. Within the housiny 1, an
engine drive crankshaft 4 is rotatably supported. A piston
rod 5 is connected to a crank arm 4a of the crankshaft. At
its opposite end from the crankshaft, the piston rod 5 is
connected to an engine drive piston 6. As seen in Figure 1,
a crank 7 is positioned at the upper end of crankshaft 4
and is connected to the crankshaft by a threaded section
4b. A crank stud 7a projects from one side of the crank 7
and a hammer mechanism piston rod 8 is rotatably attached
to the crank stud. The opposite end of the piston rod from
the crank 7 is connected to a drive piston 9 which is
located within a liner 10.
At its lower end, that is the opposite end from
the crank 7, the crankshaft 4 is encircled by a planetary
gear system. The planetary gear system includes a cross-
piece 11 fixed to the crankshaft. As can be seen in Figure
2, pins 12 are secured to and extend outwardly from the
crosspiece 11. A planet gear wheel 1~ is mounted on each
of the pins 12, there being three planet gear wheels in all,
equiangularly spaced apart. Each planet wheel 13 is in
meshed engagement with an annulus or gear ring 14 located
outwardly from the crosspiece and encircling the crankshaft.
The gear ring is fixed to the housing 1. Rotatably mounted
on the crankshaft and located inwardly of the planet wheels
13, is a sun gear wheel 15a. The sun wheel l5a is formed
as a part of a flywheel 15. A bearing bush 16 rotatably
supports the integral flywheel 15 and sun wheel 15a on the
crankshaft 4. The rpm of the flywheel is raised over the
rpm of the crankshaft 4 by the planetary gear system made
-- 5 --
., .. .. =.. .. .
113~6
up of the crosspiece 11, the planet wh~els 13, the gear
ring 14 and the sun wheel 15a.
In Fiyure 2 it can be seen that the planetary
gear system includes three pins 12 space~ angularly apart
on the crosspiece 11. Each pin 12 supports one of the
planet wheels 13. Radially inwardly, each planet wheel 13
is in meshed engagement with the centrally arranged sun
wheel 15a and radially outwardly each planet wheel is in
meshed engagement with the gear ring 14. While three
` 10 planet wheels are illustrated, it is to be understood that
this is only shown for purposes of example. Instead of
three planet wheels a single planet wheel could be used or
more than three planet wheels could be employed.
As explained above, the ignition system for the
internal combustion engine, indicated generally by the
piston 6 and connecting rod 5, is provided by a magneto-
type system, indicated generally by reference 17, located
to one side of the flywheel 15.
This is of course the simplest ignition system
for this type of internal combustion engine, although the
invention is not absolutely dependent thereon, and where
any other suitable form of ignition system may be substi-
tuted for such a magneto 17, then it is to be deemed to be
included within the scope of the invention in its broader
concepts.
As shown in this embodiment of the invention
however wherersuch.a mag~eto system is used, and where its
operation is related to the flywheel 15, then it is of
course apparent to those skilled in the art that the fly-
wheel 15 will have to rotate at a pre-determined whole
. ...
" 1137~16
number of rpm's relative to the rpm of the crankshaft 4,
since ~he timing in the ignition spark is, of course,
dependent upon the rotation of the flywheel 15 in this
particular case.
As mentioned, however, where the ignition spark
is procured by, or is timed by some other mechanism, that
is not directly related to the rpm's of the flywheel 15,
then of course such a whole number relationship is not a
prerequisite.
The operation of the invention as shown is
self-evident.
Rotation of the crankshaft 4 will, through the
planetary gear system, procure a rotation of the flywheel
; 15 at a predetermined whole number rpm greater than that ofthe crankshaft 4. As mentioned, in the particular case
indicated, the ratio is 1:3, this particular ratio having
been found to produce an optimum result in practice, for
the reasons described above.
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 hand tool, such as a drilling and chipping
hammer, comprising a housing, an internal combustion
engine including an engine crankshaft located within said
housing, a flywheel mounted on said engine crankshaft and
located within said housing, wherein the improvement comprises
balanced transmission means located within said housing and
positioned between said crankshaft and said flywheel for
transmitting the rotational movement of said crankshaft to
1~3~16
said flywheel and for raising the revolutions per minute of
said flywheel over the revolutions per minute of said crank-
shaft.
The invention further comprises a hand tool
having the foregoing features and wherein said transmission
means comprises a planetary gear system.
The invention further comprises a hand tool
having the foregoing features and wherein the internal
combustion engine incorporates an ignition system, and
wherein the ignition system is operated in timed relation
to the rotation of the flywheel, and wherein the trans-
mission means operates the flywheel at a ratio of rpm's
which is a whole number in relation to the rpm's of the
crankshaft.
The invention further comprises a hand tool
having the forego~ng features and wherein the transmission
ratio of said planetary gear system between said crankshaft
and said flywheel is 1:3.
While specific embodiments of the invention have
been shown and described in detail to illustrate the
application of the inventive principles, it will be under-
stood that the invention may be embodied otherwise without
departing from such principles.
