Internal-combustion engines – Two-cycle – Rear compression
Reexamination Certificate
2003-11-20
2004-11-16
Dolinar, Andrew M. (Department: 3747)
Internal-combustion engines
Two-cycle
Rear compression
C123S0730FA
Reexamination Certificate
active
06817323
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to internal combustion engines and, in particular, to crankcase scavenging two stroke internal combustion engines.
Whilst the invention will be described in relation to gasoline engines operating on a liquid fuel comprising a mixture of gasoline and oil, the invention is equally applicable to diesel engines operating on diesel fuel (liquid) or engines which operate on natural gas or other gaseous fuels.
The term “fluid”, as used herein is intended to embrace both liquids and gases and atomized liquids.
The term “gaseous fuel mixture” refers to liquid fuel that has been atomised and mixed with air into a gaseous state, or to a mixture of gaseous fuel (eg natural gas) and air.
The term “fuel free air” refers to air which has been introduced into the engine without atomising of liquid fuel. The air is therefore substantially fuel free when residual in the transfer passage and when transferred into the cylinder.
The term “combustion chamber” is the zone within the cylinder where the initial combustion of the combustion gases occurs.
The term “cylinder” includes the combustion chamber within the cylinder.
The term “swept volume of the cylinder” is the volume which is calculated by the piston travel distance, from top dead centre to bottom dead centre, multiplied by the effective internal diameter of the cylinder.
BACKGROUND ART
Two stroke engines have been known for many years and have many advantages including their simplicity and ability to be made in small sizes and light weights. In particular two stroke engines find application in many appliances such as outboard motors, mopeds, motor scooters, brush cutters, chain saws, lawn mowers and the like and numbers in use worldwide are in the many tens of millions. A particular disadvantage of prior art two stroke engines is that the scavenging of the cylinder so as to remove the combustion products is accomplished by means of the incoming gaseous fuel mixture. Thus, some of the incoming gaseous fuel mixture passes directly through the cylinder and into the exhaust without having been burnt in the cylinder. As a consequence, there is an inherent loss of efficiency in that a proportion of the fuel consumed is wasted. There is also an undesirable contribution to pollution in that unburnt fuel is allowed to escape into the exhaust system.
In the past there have been various attempts to overcome this higher fuel consumption and in recent times also the high exhaust emission problems. However these various attempts have been operationally complicated, expensive to manufacture, and generally not commercially successful.
Another disadvantage of the conventional two-stroke engine is the relatively high amount of oil that is required to be mixed with the gasoline in order for the engine to be lubricated. This leads to not only higher exhaust emission problems but also higher economic cost in terms of oil consumed.
The following prior art specifications disclosed by novelty searches conducted after the due date, are representation of the prior art.
Japanese Patent 11-82081 (Hirano) discloses an engine of complicated construction. One version has 3 rotary valve mechanisms to control exhaust, air and gaseous fuel mixture respectively. The other versions have a single rotary valve mechanism. These rotary valve mechanisms complicate the construction and cost of such an engine.
U.S. Pat. No. 4,026,254 Ehrlich, U.S. Pat. No. 4,051,820 Boyesen and U.S. Pat. No. 4,067,302 Ehrlich all show inlet valves into the transfer passage without flow control for engine speed. In addition in U.S. Pat. No. 4,067,302 Ehrlich states “the air employed to scavenge the cylinder 215 can also be used to ignite unburned combustibles in the exhaust system and thereby to produce an engine with cleaner emission”. This clearly demonstrates that gaseous fuel mixture is also used in the cylinder scavenging process.
U.S. Pat. No. 4,481,911 (Sheaffer et al.) discloses a two stroke engine which has the detriment of having gaseous fuel residual in the transfer passage
11
from the previous cycle. Even with air inducted into the central transfer passage
11
as shown at
25
, residual gaseous fuel remains at the transfer port end of the transfer passage
11
. Consequently, this engine does not have air scavenging of the transfer passage
11
and transfer port
12
. Instead gaseous fuel mixture is residual in the transfer passage for the initial scavenging of the cylinder, this gaseous fuel mixture then passing through the exhaust port
16
and into the exhaust passage.
Japanese Patent 02125966-A (Komatsu Zenoah) discloses in
FIGS. 1 and 2
an engine which has the problem of residual gaseous fuel mixture in scavenging passage
9
from the previous cycle which is not scavenged at the transfer port end of the scavenging passage
9
by the incoming air. This has the result of gaseous fuel mixture initially scavenging the cylinder and flowing through the exhaust port and into the exhaust passage
13
thus producing additional exhaust emissions. Similarly, the arrangement of
FIG. 3
has the problem of residual gaseous fuel mixture in the scavenging passage
9
, and in the transfer port
9
a
and in the air supply passage
10
and
10
a
. When the piston
4
compresses the gaseous fuel mixture in the crankcase
5
, it also compresses the air in the scavenging passage
9
and in the air passage
10
. At the same time the crankcase pressure reverses the air flow, thereby causing backwards flow through the venturi of the carburettor
12
. This reverse air flow draws extra fuel into the air stream as a gaseous fuel mixture and up into a portion of air supply tube
10
. Because of the compression of the gaseous fuel mixture, the residual air in the scavenging passage
9
is forced into air passage
10
by gaseous fuel mixture from the crankcase
5
. Thus the scavenging passage
9
is filled with a considerable quantity of gaseous fuel mixture. Hence when the piston
4
moves further towards bottom dead centre and the cylinder scavenging transfer port
9
a
is opened, the residual gaseous fuel mixture in the scavenge port
9
initially scavenges the cylinder and also flows into the exhaust port
13
, thus producing additional exhaust emissions.
U.S. Pat. No. 4,075,985 (Iwai) discloses arrangements in
FIGS. 1
,
2
,
3
and
8
that have the problem of residual gaseous fuel mixture, from the previous cycle, remaining in the corners at the combustion chamber end of the scavenging passages
16
and
25
and of the scavenging (transfer) ports
15
and
24
which are not scavenged by the air. Thus the initial cylinder scavenging is with residual gaseous fuel mixture. The arrangement of
FIGS. 1 & 8
also suffer from insufficient volume of the scavenging passages. Iwai's
FIG. 6
shows the scavenging passages
16
connected to air branch passages
17
A with reed valves
18
at the start of the air passages. The air branch passage
17
A together with scavenging passages
16
form a larger volume but this larger volume in this configuration is detrimental as just prior to the opening of the transfer port
15
with the piston's downward thrust, the residual air in both the scavenging passage
16
and the air passage
17
A is compressed back into the air passage leaving little or no air in the scavenging passage
16
for initial cylinder scavenging.
U.S. Pat. No. 4,253,433 (Blair) shows an extended transfer duct K into which the carburettor fuel is inducted through admission port F and check valve C.
Either fuel free air, or oiled air, is inducted into the crankcase through aperture G and check valve D. If the crankcase air is oiled, then this oiled air, and some fuelled air (as per line 33 & 34 of column 2) is used for initial cylinder scavenging which then proceeds unburnt into the exhaust muffler to add to the exhaust emissions. If the crankcase air is not oiled, then the engine will not function, as the piston and cylinder walls not being lubricated with sufficient gaseous fuel mixture will cause the engine to seize.
U.S. Pat. No. 4,70
Notaras Angelo Lambrinos
Notaras John Arthur
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