Two-cycle internal combustion engine with reduced unburned hydrocarbons in the exhaust gas

A two-cycle internal combustion engine configuration and control strategy in which the unburned hydrocarbon emissions in the exhaust gas are measured by a sensor in the exhaust manifold. The information from the sensor is used to control the outflow of air from a blower mixed with the fuel to vary the total volume of fuel and air to thus reduce unburned hydrocarbons in the exhaust gas.

FIELD OF THE INVENTION 
This invention is in the field of two-cycle internal combustion engines, 
particularly including the types used for power boats and power tools and 
where poor fuel efficiency and where high unburned hydrocarbons in the 
exhaust gas have been common characteristics. 
BACKGROUND 
The two-stroke engine, also referred to as the two-cycle engine, has long 
been the power plant of choice for applications where power to weight 
ratio and mechanical simplicity are critical parameters for the operator. 
This is evident by their wide spread use as outboard motors, motorcross 
motorcycle racing engines and as the power plants for small, hand held 
tools such as chain saws and weed cutters. Although the large power to 
weight ratio of these engines is a desirable characteristic for automobile 
power plants, their high unburned hydrocarbon emissions (from short 
circuited air fuel mixture during the scavenging process) and the 
attendant fuel economy penalty has precluded their widespread acceptance 
into these markets. 
Typical in these engines is a simple exhaust gas scavenging system 
established mainly by ports in the cylinder head that are covered and 
uncovered by movement of the piston. Thus, numerous complicated and 
expensive seals, valves and related components required in four cycle 
engines are omitted and not required. 
As the CAFE standards for the automobile fleets have increased, the 
industry has placed even more of a premium on the power to weight ratio of 
the engine. A small engine of the same power as a larger one lowers the 
weight of the vehicle and enables designs of smaller frontal area (less 
wind resistance). Both of these design factors have beneficial effects on 
fuel economy. 
Interest in two-stroke engines is very high in the automotive industry yet 
the problems of unburned hydrocarbon emissions remains unsolved. Also, 
legislation on exhaust emission for off-highway vehicles, lawn and garden 
equipment and marine craft has brought the emission problems of the 
two-stroke engine to the forefront of those industries. The industries, 
both recreational and automotive, are anxious for an economical way to 
control the emissions, in particular the unburned hydrocarbon emissions, 
and improve the fuel efficiency from two-stroke engines. 
Numerous U.S. patents and other publications discuss the operation and 
characteristics of these engines, examples including U.S. Pat. Nos. 
4,995,354; 4,960,097; 4,936,277; 4,903,648; 4,556,030; 4,576,126; 
4,399,778; and a description on pages 9-78 through 9-114 from Marks' 
Standard Handbook for Mechanical Engineers, Eighth Edition published by 
McGraw-Hill Book Company, 1978; and pages 299 through 356 of Chapter 7 of 
The Basic Design of Two-Stroke Engines by Gordon P. Blair, published by 
The Society of Automotive Engineers, Inc., 1990, all of these references 
including the complete text of the latter reference being incorporated by 
reference into this specification. In Marks', for example, on page 9-111 
it is stated "in carbureted engines where intake pressure exceeds exhaust 
(as in two-cycle engines) raw-mixture loss to the exhaust during the 
valve-overlap period creates very high hydrocarbon emissions. Emissions 
from two-cycle carbureted engines may be 10 times higher than four-cycle 
engine emissions." 
The massive quantity of unburned hydrocarbons discharged by the exhaust 
contribute greatly to inefficiency, waste of fuel, and to pollution of the 
atmosphere, all of these problems being matters of great concern at all 
levels of society including individual, manufacturer, governmental and 
international. To some extent these problems have been ignored by 
continuing the old technology or by choosing alternative power sources 
with their own inherent disadvantages such as higher cost, higher 
complexity and lower power-to-weight ratio. 
In addressing the above-mentioned problems and operational characteristics 
in two-cycle engines engineers and mechanics have dealt with a variety of 
structural components, seeking improvements and solutions. Typical 
carburetor and throttle devices vary the air/fuel ratio or the rate or 
directional path of air/fuel flow, or timing, ignition, fuel composition, 
etc. 
A principal focus herein is the high degree of unburned hydrocarbons in the 
exhaust gas of two-cycle engines due to short circuiting of fuel in the 
scavenging process. Typically, the carburetor is adjusted to a selected 
air/fuel ratio, and then the flow of this mixture is throttled by an 
appropriate valve. In an outboard two-cycle engine the up-stroke of the 
piston creates a suction which draws in the mixture the flow of which 
being throttled by partial blockage of flow into the crankcase. 
One alternative control technique used in an engine under the commercial 
name Orbital, is to use fuel injection directly into the cylinder. Inlet 
air is pumped into the cylinder to scavenge or clean out exhaust gas. 
Later, as the piston rises and closes the inlet air port, fuel injection 
follows. In theory this should substantially eliminate unburned fuel from 
short circuiting since the scavenging air passing through the cylinder 
head is not carrying the new charge of fuel with it. On the negative side 
is the added work input of high pressure fuel injection directly into a 
closed cylinder head, as compared to the Roots blower low pressure air 
flow (1 to 11/2 atmospheres) which carries the fuel into the cylinder via 
a typical simple and inexpensive carburetor. The air/fuel mixture is 
varied by varying the high pressure fuel injection within the cylinder 
after the port is closed. To control such adjustments over a wide range is 
difficult, costly, and has not been proven satisfactory. 
SUMMARY OF THE INVENTION 
The present invention refers to a new two-stroke engine system 
configuration and operation sequence in which a closed loop sensing system 
monitors unburned fuel in the exhaust manifold during the scavenging 
process and implements a fuel and air control sequence to reduce or 
terminate the intake air flow (and included fuel) if and when unburned 
fuel is detected. By implementing this closed loop system a major weakness 
of the two-stroke engine, namely large unburned hydrocarbon emissions from 
short circuiting, can be controlled without having to implement more 
costly in-cylinder fuel injection. 
The new two-cycle internal combustion engine has an air blower providing a 
low pressure air flow into the cylinder. Preferably this blower is 
hydraulically driven for fast response independent of piston or 
crank-shaft speed or operation. The engine includes fuel introduction 
whereby the air/fuel mixture is established outside the cylinder. More 
specifically, fuel or a fuel-oil mixture is introduced either upstream of 
the blower and then carried in the air flow in an amount proportionate to 
the blower's air flow this air/fuel mixture being the blower's outflow, or 
the fuel or fuel-oil mixture is introduced downstream of the blower with 
the fuel flow directed to be correctly proportional to said blower's air 
flow. The preferred blower is a typical, simple, inexpensive and reliable 
Roots type blower. 
In this new invention power control is by varying the blower's air flow 
with an attendant proportional change in fuel flow, and with air/fuel 
ratio being generally maintained unless intentionally varied separately 
from the above-described variation in air flow. 
A sensor monitors the exhaust gas and/or its components and determines the 
presence of excessive unburned hydrocarbons. The above-mentioned The Basic 
Design of Two-Stroke Engines, on pages 40, 305-316 and elsewhere, 
describes monitoring the exhaust gas and its components including 
hydrocarbon oxygen, carbon monoxide and nitrogen oxides emissions. SAE 
Article No. 910720, mentioned below, further describes exhaust gas 
emissions and sensors for monitoring and evaluating same. An appropriate 
signal from the sensor through a control system directs the blower to send 
more or less air and proportionate amount of fuel into the cylinder's 
inlet. 
Control and adjustment in this new engine is dynamic in that monitoring of 
the exhaust gas is essentially continuous and nearly instantaneous with a 
very high speed sensor. Feedback is to the air blower, which is preferably 
hydraulically controlled and thus has a high speed response. Throttling of 
the air flow cuts air and fuel at generally the same percent and thus 
generally maintains a fixed air/fuel ratio, unless and until it is 
intentionally altered. 
In one embodiment of this invention the blower would run essentially 
continuously with variation in its speed and resultant air flow and 
associated fuel flow. In an alternate embodiment the blower would be 
intermittently stopped when the sensor determined excessive unburned 
hydrocarbons. In either case the sensor's high speed response time would 
be followed by a relatively fast response in the blower operation due to 
its hydraulic motor. 
As a further optional variation the blower could essentially charge a 
pressure holding chamber. Such chamber being operable via valves could 
provide any required air flow in combination with fuel introduction as 
described earlier. Such air flow and attendant fuel flow could supply a 
single combustion cylinder or via a manifold could supply a plurality of 
combustion cylinders. 
The invention described herein is a new technique for monitoring the 
unburned hydrocarbon emissions from the two-stroke engine and using a 
feedback control scheme to alter the air and fuel flow into the intake 
system and thus minimize the unburned hydrocarbon emissions from short 
circuiting. In the operation of such engine the unburned hydrocarbon 
sensor located in the exhaust is known to exist, for example the Nissan 
Air Fuel Ratio Sensor (see "The Application of an Air-to-Fuel Ratio Sensor 
to the Investigation of a Two-Stroke Engine" by D. Watry, R. Sawyer, R. 
Green and B. Cousyn published in SAE Article No. 910720, pp. 1-8). If 
during the scavenging process the air fuel sensor detects unburned 
hydrocarbons in the exhaust manifold, the output voltage of the sensor 
rapidly changes (response times of approximately 50 msec.) which then 
triggers the control circuitry for the hydraulic drive system and the fuel 
and oil flow. This will rapidly reduce or terminate air flow and reduce or 
terminate short circuiting of the unburned hydrocarbons into the exhaust 
and out into the atmosphere. In this way the engine dynamically controls 
the air and fuel flow into the engine. 
This design yields an engine of high delivery ratio and good scavenging 
efficiency, retains the advantages of the high power to weight ratio of 
the two-stroke engine, and reduces the unburned hydrocarbon emission of a 
typical two-stroke engine without having to use in-cylinder fuel 
injection. It is anticipated that this control device and strategy will be 
most effective under conditions of high loading, the conditions under 
which the unburned hydrocarbons are the worst. As this system reduces 
unburned hydrocarbon emissions, engine power may be altered for a variety 
of reasons, however a principal benefit is removal of a quantity of fuel 
from the inlet air which fuel was not going to be burned anyway. 
In addition to the features described above there is optional installation 
of the ground electrode into the piston crown instead of being integral to 
the spark plug. This will attempt to dynamically move, both compress and 
expand the spark plasma and discharge current to enhance the early flame 
development. 
It is evident from the prior art patents and publications cited in the 
specification, that vast efforts have been made and vast sums spent trying 
to solve the hydrocarbon emissions problems in two-cycle engines. As these 
efforts continue they appear to become more sophisticated, more 
complicated more expensive and still without the satisfaction of success. 
The present invention represents an approach that is totally different 
from the past, remarkably simple and inexpensive, and one that has promise 
to be successful despite its most unlikeness in view of the vast prior 
efforts.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In describing these two figures elements common to both will use the same 
reference numbers as a matter of convenience. 
In FIG. 1 the new engine 10 is shown in highly simplified schematic form 
with control system 11, cylinder 12, cylinder head 14, piston 16, piston 
rod 18, inlet port 20 and exhaust port 22. Downstream of the exhaust port 
22 is a sensor 24 for monitoring unburned hydrocarbons in the exhaust gas. 
Communicating with inlet port 20 is a Roots type air blower 26 driven by 
hydraulic motor or pump 28 which in turn is powered from the engine drive 
shaft or other power output. Speed is controlled by the engine's operating 
logic control system 11, which can achieve rapid slowing of the blower as 
required. 
The sensor 24 which determines excessive unburned hydrocarbons in the 
exhaust may be, for example, the Nissan Air Fuel ratio sensor as described 
above. The sensor used was derived from the one developed by Nissan, with 
a response time between 25 ms and 100 ms and accuracy within 3% in the 
range of 10-25 A/F using gasoline as the fuel. This article and further 
references recited on page 7 of this article are incorporated herein by 
reference. 
The Roots blower 26 has inlet 26a and outlet 26b as shown, the outlet 
directed to cylinder head inlet 20. Fuel for this engine is introduced via 
a fuel/oil injector or carburetor 40 upstream of blower 26 and into the 
air stream of the blower. In contrast to prior art engines which vary 
fuel, air/fuel ratio, flow of fuel or air/fuel and other parameters, this 
engine primarily varies air flow driven into the cylinder, with the 
variation dynamically controlled as a reaction to the exhaust gas sensor. 
FIG. 2 shows the new engine 10 in simplified schematic form generally 
similar to FIG. 1 but with additions and variations. This engine 10 
includes a control system 11, cylinder 12, cylinder head 14, piston 16, 
piston rod 18, inlet port 20 and exhaust port 22. Downstream of the 
exhaust port 22 is a sensor 24 for monitoring unburned hydrocarbons in the 
exhaust gas. Communicating with inlet port 20 is a Roots type air blower 
26 driven by hydraulic motor 28 associated with inlet and outlet fluid 
flow ducts 30 and 32 respectively. Speed is controlled by hydraulic motor 
controller 37 and associated dump valve 36 of larger diameter than the 
inflow duct 30 and situated so that fluid tends to flow in a straight line 
when dumped. Additionally, there is spring loaded valve 38 associated with 
the oil outflow line set to achieve a quick stop when oil pressure 
decreases. This will aid a rapid slowing of the blower when directly 
connected to the hydraulic motor. 
The sensor 24 which determines excessive unburned hydrocarbons in the 
exhaust may be, for example, the Nissan Air Fuel ratio sensor as described 
above. 
The Roots blower 26 has inlet 26a and outlet 26b as shown, the outlet 
directed to cylinder head inlet 20. Fuel for this engine is injected into 
the air box 40a upstream of blower 26 and into the air stream of the 
blower. As an alternate addition there may be an air dump valve 27 
provided for quick relief or termination of inlet flow. Where this air 
flow contains fuel it would be redirected in an appropriately safe manner. 
In contrast to prior art engines which vary fuel, air/fuel ratio, flow of 
fuel or air/fuel and other parameters, this engine primarily varies air 
flow driven into the cylinder, with the variation dynamically controlled 
as a reaction to the exhaust gas sensor. To enhance efficiency the air 
flow from blower 26 passes angled deflectors 42 which serve both to flush 
the mixture in the proper direction into the cylinder and to aid as a 
flame arrestor. 
As a further refinement a combined plug-coil 44 fires onto electrode insert 
46 in the piston head seeking to provide a longer, hotter spark. The 
piston may also be shaped to improve dispersion of the air/fuel mixture. 
The firing timing would be controlled by contacts 48 on timing gear 50 
making contact with points 52 which vary position around the circumference 
of the timing gear similar to that of a conventional distributor. To allow 
for more rapid changes of speed such as with passing, a hook-up from 
throttle to valve assembly would be provided, similar to the "passing 
gear" arrangement currently utilized. 
While the preferred embodiments herein of the present invention have been 
shown and described, it is to be understood that the disclosure is for the 
purpose of illustration and that various changes and modifications may be 
made without departing from the scope of the invention as set forth in the 
appended claims.