U.S. patent application number 09/795389 was filed with the patent office on 2001-09-06 for internal combustion engine having a choke flap arranged in an air filter housing.
Invention is credited to Bergmann, Lars, Raffenberg, Michael, Rosskamp, Heiko.
Application Number | 20010018898 09/795389 |
Document ID | / |
Family ID | 7632987 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010018898 |
Kind Code |
A1 |
Raffenberg, Michael ; et
al. |
September 6, 2001 |
Internal combustion engine having a choke flap arranged in an air
filter housing
Abstract
The invention relates to a two-stroke engine in a portable
handheld work apparatus. A combustion chamber (3) is formed in a
cylinder (2) and the chamber is delimited by a piston (5). At least
one transfer channel (14) is provided which connects the crankcase
(4) to the combustion chamber (3). An air channel (22) opens into
the transfer channel (14) and this channel supplies essentially
fuel-free gas, preferably air. The intake channel (28) of a
carburetor (8) is connected to an intake opening (45) in the
housing base (41) of the air filter housing (43) upstream of a
carburetor throttle flap. The intake channel (28) connects
downstream of the carburetor throttle flap to an intake channel (9)
to the crankcase (4). To provide an ignition-ready mixture in order
to start and run up the engine, it is provided that the air channel
(22) is connected to a bypass opening (25) in the housing base (41)
of the air filter (42) and a common pivotable choke element (24) is
assigned to the intake opening (45) as well as the bypass opening
(25). The choke element (24) clears the openings (25, 45) in the
operating position and closes the passthrough cross section of the
bypass opening (25) in the start position whereas the passthrough
cross section of the intake opening (45) is reduced to a start
cross section.
Inventors: |
Raffenberg, Michael;
(Fellbach, DE) ; Bergmann, Lars; (Welzheim,
DE) ; Rosskamp, Heiko; (Adelberg, DE) |
Correspondence
Address: |
Walter Ottesen
Patent Attorney
P.O. Box 4026
Gaithersburg
MD
20885-4026
US
|
Family ID: |
7632987 |
Appl. No.: |
09/795389 |
Filed: |
March 1, 2001 |
Current U.S.
Class: |
123/73A |
Current CPC
Class: |
F02B 33/04 20130101;
F02M 35/1019 20130101; F02M 35/1017 20130101; F02B 63/02 20130101;
Y02T 10/12 20130101; F02M 35/04 20130101; Y02T 10/14 20130101; F02M
1/02 20130101; F02B 2075/025 20130101; F02M 35/10019 20130101; F02M
35/10196 20130101; F02B 25/22 20130101 |
Class at
Publication: |
123/73.00A |
International
Class: |
F02B 033/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 1, 2000 |
DE |
100 09 796.0 |
Claims
What is claimed is:
1. An internal combustion engine including an engine in a portable
handheld work apparatus, the internal combustion engine comprising:
a cylinder having a cylinder wall; a piston mounted in said
cylinder to undergo a reciprocating movement along a stroke path
between top dead center and bottom dead center during operation of
said engine; said cylinder and said piston conjointly delimiting a
combustion chamber; a crankcase connected to said cylinder; a
crankshaft rotatably mounted in said crankcase; a connecting rod
connecting said piston to said crankshaft to permit said piston to
drive said crankshaft as said piston reciprocates in said cylinder;
at least one transfer channel connecting said crankcase to said
combustion chamber; said transfer channel having a first end
defining an entry window opening into said combustion chamber and a
second end opening into said crankcase; an air channel connected to
said transfer channel for supplying essentially fuel-free gas flow
thereto; a carburetor for supplying an air/fuel mixture; said
carburetor having an intake channel and a carburetor throttle flap;
an inlet channel downstream of said carburetor flap for conducting
said air/fuel mixture into said crankcase; an air filter having an
air filter housing; said air filter housing having a base wall and
said base wall having an intake opening formed therein; said intake
channel being connected to said intake opening upstream of said
carburetor throttle flap; said base wall also having a bypass
opening formed therein and said air channel being connected to said
bypass opening; a common choke element provided for said intake
opening and said bypass opening; and, said choke element being
displaceable between an operating position wherein said intake
opening and said bypass opening are clear and a start position
wherein the cross section of said intake opening is reduced to a
start cross section and said bypass opening is essentially
closed.
2. The engine of claim 1, wherein said choke element is
displaceable to an intermediate position between said operating
position and said start position wherein said intake opening is
essentially open and said bypass opening is essentially closed.
3. The engine of claim 1, said air filter housing defining a clean
air space and said choke element being mounted in said clean air
space.
4. The engine of claim 3, wherein said choke element is configured
as a flat slider and lies approximately parallel to said base wall
of said air filter housing.
5. The engine of claim 4, wherein said choke element is pivotable
about a rotational axis.
6. The engine of claim 1, wherein said choke element includes and
actuating lever extending out of said air filter housing to
facilitate manual movement of said choke element between said
operating position and said start position.
7. The engine of claim 1, wherein said choke element is made of
plastic.
8. The engine of claim 7, wherein said choke element is a plastic
injection molded part.
9. The engine of claim 3, wherein said air filter housing having
stops formed therein to define said operating position and said
start position.
10. The engine of claim 1, wherein said start cross section of said
intake channel is defined by an opening in said choke element.
11. The engine of claim 1, wherein said start cross section is
defined by a notch or slot in said base wall of said air filter
housing.
12. The engine of claim 1, further comprising a cover part formed
on said base wall of said air filter housing; said choke element
including a closure part; and, said cover part and said closure
part conjointly forming a slot defining a start cross section when
said choke element is in said start position.
13. The engine of claim 12, wherein said cover part includes: a
part-ring baffle plate held by said part-ring segment at an axial
spacing in front of said intake opening; and, said closure part
being a part-ring segment which forms a full ring with said
part-ring segment formed on said base wall when said choke element
is in said start position with said part-ring segment of said choke
element and said baffle plate conjointly defining said start cross
section.
14. The engine of claim 1, further comprising a throttle device
having an adjustable air throttle element; said air channel being
connected to said base wall of said air filter housing via said
throttle device; and, said throttle device including a throttle
housing attached to said air filter housing and said air throttle
element being mounted in said throttle housing.
15. The engine of claim 14, further comprising a lever transmission
for position-dependently coupling said air throttle element and
said carburetor throttle flap to each other.
Description
FIELD OF THE INVENTION
[0001] The invention relates to an internal combustion engine such
as the drive motor of a portable handheld work apparatus including
a motor-driven chain saw, a brushcutter, a cutoff machine or the
like.
BACKGROUND OF THE INVENTION
[0002] In known two-stroke engines, a choke flap is mounted in the
carburetor upstream of the throttle flap. The choke flap is closed
except for a start cross section in the case of starting for
enriching the mixture. In the start case, it should be
simultaneously ensured that the throttle element mounted in the air
channel closes completely so that no air can flow into the transfer
channels via the air channels in the start case. This would lead to
a leaning of the mixture and this makes the start of the engine
more difficult and hinders a problem-free runup of the engine. For
this reason, the throttle in the air channel must therefore be set
to a start position with a position-dependent coupling to the choke
flap.
SUMMARY OF THE INVENTION
[0003] It is an object of the invention to improve an internal
combustion engine of the kind referred to above so that well
defined operating conditions are provided without leaning the
mixture for part-air positions especially when starting the
engine.
[0004] The internal combustion engine of the invention includes an
engine in a portable handheld work apparatus. The internal
combustion engine includes: a cylinder having a cylinder wall; a
piston mounted in the cylinder to undergo a reciprocating movement
along a stroke path between top dead center and bottom dead center
during operation of the engine; the cylinder and the piston
conjointly delimiting a combustion chamber; a crankcase connected
to the cylinder; a crankshaft rotatably mounted in the crankcase; a
connecting rod connecting the piston to the crankshaft to permit
the piston to drive the crankshaft as the piston reciprocates in
the cylinder; at least one transfer channel connecting the
crankcase to the combustion chamber; the transfer channel having a
first end defining an entry window opening into the combustion
chamber and a second end opening into the crankcase; an air channel
connected to the transfer channel for supplying essentially
fuel-free gas flow thereto; a carburetor for supplying an air/fuel
mixture; the carburetor having an intake channel and a carburetor
throttle flap; an inlet channel downstream of the carburetor flap
for conducting the air/fuel mixture into the crankcase; an air
filter having an air filter housing; the air filter housing having
a base wall and the base wall having an intake opening formed
therein; the intake channel being connected to the intake opening
upstream of the carburetor throttle flap; the base wall also having
a bypass opening formed therein and the air channel being connected
to the bypass opening; a common choke element provided for the
intake opening and the bypass opening; and, the choke element being
displaceable between an operating position wherein the intake
opening and the bypass opening are clear and a start position
wherein the cross section of the intake opening is reduced to a
start cross section and the bypass opening is essentially
closed.
[0005] The arrangement of a common choke element for the intake
opening of the carburetor as well as for the bypass opening of the
air channel makes possible a simple switchover from the start
position into the operating position. The bypass opening can be
closed separately from the carburetor intake opening. If the choke
flap is pivoted back into the operating position after starting,
the intake opening and the bypass opening are preferably enabled
sequentially so that a switchover of the engine from the start
state into the operating state is provided without the problem of
the engine stalling. According to the invention, the choke element
is assigned to the bypass opening or intake opening and need not
lie in the channel connected to the opening so that a closing of
the bypass opening or intake opening is possible in a simple manner
by overlapping. Accordingly, there is no need to maintain tight
tolerances. The choke element can be pushed transversely to the
channel as a blocking slider.
[0006] The choke element is advantageously arranged as an external
component in the clean air space of the air filter and is there
provided as an approximately flat slider approximately parallel to
the base of the housing. A slider can be moved in a simple manner
without complex mechanics and is especially pivotable about a
rotational axis so that the constructive complexity for the
configuration of the choke element and its actuation is minor.
[0007] The choke element can be made of plastic in a simple manner
and especially be configured as a plastic injection-molded part and
so becomes a series part which can be manufactured in mass
production. This part nonetheless prevents the penetration of
unwanted air into the bypass opening or intake opening. With an
advantageous configuration as a flat slider parallel to the housing
base of the air filter, an underpressure, which builds up in the
intake channel of the carburetor or in the throttle channel of the
air channel, pulls the slider onto the intake opening to thereby
close this opening tightly. This is especially significant for the
throttle channel of the bypass air. With the first ignitions, the
engine runs up to idle rpm and a corresponding underpressure is
built up in the air channel which could facilitate the inflow of
unwanted air and therefore cause a leaning of the mixture. Because
of the configuration of the choke element of the invention as a
flat slider, the underpressure which builds up leads to the
situation that the plate of the slider, which closes the bypass
opening, is drawn by suction and lays seal-tight on the edge of the
bypass opening. In this way, a penetration of unwanted air into the
air channel is reliably prevented just at the time point of the
runup of the engine so that a leaning of the mixture during runup
of the two-stroke engine is avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The invention will now be described with reference to the
drawings wherein:
[0009] FIG. 1 is a schematic section through a two-stroke engine
having transfer channels lying on opposite sides of a symmetrical
plane of the cylinder;
[0010] FIG. 2 is a schematic cross section through a cylinder of a
two-stroke engine with an air filter mounted thereon;
[0011] FIG. 3 is a section view taken through the air filter
housing along line III--III of FIG. 2;
[0012] FIG. 4 is a detailed section view of an air filter housing
of another embodiment with the view corresponding to that of FIG.
3;
[0013] FIG. 5 is a plan view of a throttle flap for use in an air
filter housing of FIG. 4; and,
[0014] FIG. 6 is a schematic section through a carburetor with a
one-piece formed-on bypass and throttle.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
[0015] The internal combustion engine shown in FIG. 1 is a
two-stroke engine 1 and includes essentially a cylinder 2 and a
piston 5 movable up and down in the cylinder. The piston 5 imparts
rotational movement to a crankshaft 7 via a connecting rod 6. The
crankshaft 7 is arranged in a crankcase 4. The piston 5 is held at
the end of the connecting rod 6 by means of a piston bolt 5a to
facilitate pivotal movement of the connecting rod.
[0016] A combustion chamber 3 is formed in the cylinder 2 and this
chamber is delimited by the base 13 of the piston 5. The combustion
chamber 3 includes an outlet 10 through which the combustion gases
are directed away after a work stroke. The air/fuel mixture, which
is needed to operate the engine 1, is supplied to the crankcase 4
from the carburetor 8 via an inlet 11 and an intake channel 9
connected thereto. The carburetor 8 is preferably a membrane
carburetor.
[0017] In the embodiment shown, the inlet 11 is slot-controlled by
the wall surface 30 of the piston 5. In the stroke position of the
piston 5 shown in FIG. 1, the inlet 11 is completely closed by the
piston wall surface 30. An alternative configuration of the inlet
11 as a membrane inlet can be practical.
[0018] The air/fuel mixture, which is already inducted into the
crankcase 4, is compressed with a further movement of the piston 5
in the direction toward bottom dead center as indicated by arrow 50
and flows via the transfer channels 14 into the combustion chamber
3. As shown in FIG. 2, two transfer channels 14 are arranged on
each side of a symmetry plane 49 of the cylinder 2. The symmetry
plane 49 contains the cylinder axis 17 and partitions the outlet
10, that is, its outlet window, approximately symmetrically. The
number of transfer channels 14 is only exemplary. n channels
(n.gtoreq.2) are possible.
[0019] The first ends 20 of the transfer channels 14 face toward
the cylinder head 18. The ends 20 open into the combustion chamber
3, on the one hand, away or remote from the outlet 10 via an entry
window 12 and, on the other hand, close to the outlet 10 via an
entry window 15 in the cylinder wall 16; whereas, the second end 19
of each overflow channel 14 faces toward the crankcase and is open
toward the crankcase 4. The transfer channels 14 are configured so
as to be closed toward the piston 5 and run essentially parallel to
the cylinder axis 17 in the cylinder wall 16. The transfer channel
14 can, however, also be curved in the flow direction or can even
run in the manner of a screw thread which is a departure from the
embodiment shown.
[0020] As shown in FIG. 2, external air channels 22 preferably open
into the transfer channels 14. A check valve 21 is provided and
closes the flow connection between the air channel 22 and the
transfer channel 14 in each case. The check valve 21 opens into the
transfer channel 14. In the embodiment shown, the check valve 21 is
configured as a membrane valve. The membrane 23 clears an outlet
slot in the open position and this outlet slot faces toward the
roof (not shown) of the transfer channel 14. In the open position,
the membrane 23 is held by a sheet metal support 26 which, together
with a connecting piece 27 of the air channel 22, is fixed on the
outer cylinder wall 29. In lieu of a membrane valve 21, the supply
of fuel-free air or air having a low fuel content is also possible
via a slot-controlled window in the cylinder wall 16 and, if
required, via a peripheral slot in the skirt 30 of the piston.
[0021] The air channels 22 supply fluid, preferably air, which is
free of fuel or has only slight amounts thereof. The air channels
22 are connected at the base of a throttle housing 35 which, in
this embodiment, is fixed on the housing base wall 41 of an air
filter housing 43 which is arranged upstream of the carburetor 8.
The intake channel 28 of the carburetor 8 communicates with an
intake opening 45 in the housing base 41 of the air filter 42 and
draws combustion air from the clean space of the air filter 42.
[0022] The air channels 22 connect via the throttle channel 36 of
the throttle housing 35 and a bypass opening 25 in the base 41 of
the air filter housing 43 to the clean space of the air filter 42
so that dirt-free air is likewise supplied to the transfer channels
14 via the air channels 22.
[0023] A common pivotable choke element 24 is assigned to the
bypass opening 25 and the intake opening 45. The choke element 24
is configured essentially as a flat slider 31 and lies
approximately parallel to the housing base 41. The choke element is
adjustable about a pivot axis 41 in the direction of arrow 47 as
shown in FIG. 3. The choke element 24 is shown in its first end
position, the operating position, in FIG. 3 in phantom outline. In
this position, the choke element clears the bypass opening 25 as
well as the intake opening 45. The volumes of air, which flow
through the intake channel 28 or the throttle channel 36, are
adjusted by the throttle flaps which are adjustable in a manner
known per se via throttle flap levers 39 and 46. In the embodiment,
the throttle flap levers 39 and 46 are coupled position-dependent
to each other via a connecting rod 44. A corresponding position of
the air throttle flap in the throttle channel 36 is assigned to
each position of the carburetor throttle flap.
[0024] In a second end position, the start position, the flat choke
element lies across the element openings 25 and 45. In this way,
the bypass opening 25 is completely and substantially closed
air-tight whereas the transverse cross section of the intake
opening 45 is reduced to a start cross section which is determined
by an opening 70 in the choke element 24. In FIG. 3, the start
position is shown by the solid line and the opening 33 lies
approximately centrically to the intake opening 45. Other positions
can be practical.
[0025] The choke element 24 is assigned to the carburetor 8 and the
throttle 32 of the air channels 22. In the embodiment shown, the
choke element 24 is arranged in the air filter housing 43 and
preferably in the clean space 40 of the air filter 42. The
actuation of the choke element 24 takes place via an actuation
lever 33 which is lead to the outside through a slot 34 in the
lateral housing wall of the air filter housing 43. The slider 31
can be manually displaced about the rotational axis 48 from the one
end position (shown in phantom outline) into the other end position
(shown by solid lines). The choke element 24 is advantageously
manufactured of plastic as one piece with the actuating lever 33
and is especially configured as a plastic injection-molded
part.
[0026] The end positions of the choke element 24 can be determined
by housing stops. A first housing stop is determined for the
operating position by the housing side wall 37 of the air filter
housing 43 and the other housing stop is defined by the boundary
edge 38 of the slot 34.
[0027] The choke element 24 shown in FIG. 3 is shown in FIG. 2 in
cross section. The choke element 24 comprises essentially two
cup-shaped cover plates 60 and 61 which are positioned in the start
position (solid line) shown in FIG. 3 in front of the openings 25
and 45. The diameters of the cup-shaped cover plates are configured
to be greater than the diameters of the openings 25 and 45 so that
the plate edge 62 lies approximately seal-tight against the housing
base 41 of the air filter housing 43. The base body of the slider
31 lies at a spacing (a) to the housing base 41 whereby a pivot
movement in the direction of arrow 47 is possible without an
application of much force.
[0028] The cup-shaped cover plate ensures the desired seal-tight
covering of the intake openings 25 and 45 even under unfavorable
operating conditions. In the operation of the two-stroke engine 1,
an underpressure builds up in the throttle channel 36 of the
throttle 32 as well as in the intake channel 28 of the carburetor 8
and, because of the action of the underpressure, the cup-shaped
cover plates 60 and 61 are drawn so that their edges 62 lie
seal-tight against the housing base 41. In this way, the start
cross section, which is pregiven constructively by the opening 70,
is effective without unwanted air entering which could have lead to
a leaning of the start mixture and therefore to start difficulties.
As an alternative to opening 70, the start cross section can also
be provided by a slot 72 in the housing base 41. The slot 72 is
only partially covered in the closed position of the choke element
24 and defines a flow path into the covered bypass opening 45.
[0029] In an alternate embodiment of FIGS. 4 and 5, the choke
element 24 is formed from a cup-shaped cover plate 60 for the
air-tight closure of the bypass opening 25 and a half-ring-shaped
closure element 63 which, together with a part ring section 64
defines a complete ring when the choke element 24 is in the start
position shown in FIG. 4. The part ring section 64 is formed on the
edge of the intake opening 45. The part ring section 64 holds a
baffle plate 65 at an axial spacing forward of the intake opening
45 on the air filter housing base 41. In the end position shown in
FIG. 4, that is, the start position, the half-ring-shaped closure
element 63 of the choke element 24 and the baffle plate 65
conjointly delimit an intake slot 66. The intake slot 66 defines
the start cross section of the intake opening 45. The part ring
section 64 is formed on the housing base 41 to hold the baffle
plate 65 and serves simultaneously as the end stop for the start
position of the choke element 24.
[0030] In the embodiment of FIG. 6, the carburetor 8 and the bypass
throttle 32 are provided in a common housing 63. The intake channel
28 and the bypass channel 22 lie approximately parallel to each
other and open separately to the clean space 40 of the air filter
42. It is practical to provide the common choke element configured
especially as a cylinder 61 which is adjusted by an actuating lever
62.
[0031] It is understood that the foregoing description is that of
the preferred embodiments of the invention and that various changes
and modifications may be made thereto without departing from the
spirit and scope of the invention as defined in the appended
claims.
* * * * *