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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a carburetor and, more particularly, an
improvement of a carburetor for use with stratified-charged rotary piston
engine with regard to the overall air/fuel ratio performance thereof for
effecting a stabilized low speed and low load operation of the engine had
a better purification of exhaust gasses.
2. Description of the Prior Art
In the Wankel type rotary piston engine which comprises a casing composed
of a rotor housing having a trochoidal inner peripheral surface and side
housings which close the opposite ends of the rotor housing, an eccentric
shaft, and a polygonal rotor adapted to eccentrically rotate around said
eccentric shaft with apex portions thereof sliding over said trochoidal
inner peripheral surface, the flame in the combustion chamber initiated by
the ignition plug generally propagates very rapidly toward the leading
side of the combustion chamber as seen in the rotational direction of the
rotor due to a flow of fuel-air mixture generated by the rotation of the
rotor, whereas the flame is hard to propagate toward the opposite trailing
side of the combustion chamber. Because of this, the fuel-air mixture
existing in the trailing region of the combustion chamber is prone to
imperfect combustion thereby causing poor fuel comsumption, simultaneously
increasing the emission of harmful uncombusted components such as HC and
CO.
In order to solve these problems, there has been proposed a new type of
stratified-charged rotary piston engine having a first intake port formed
as a peripheral port which opens in the trochoidal inner peripheral
surface of the rotor housing and a second intake port preferably formed as
a side intake port which opens in the flat inside surface of the side
housing at a position advanced from said first intake port as seen in the
rotational direction of the rotor. The first intake port supplies a
relatively rich fuel-air mixture whereas said second port supplies only
air thereby ultimately providing a stratified charge in the combustion
chamber of the engine in a manner such that the leading side of the
combustion chamber is charged with a relatively rich fuel-air mixture
while the trailing side thereof is charged substantially with air. This
pattern of stratified charging facilities complete combustion of fuel in
the combustion chamber and provides an advantage that a higher overall
air/fuel ratio can be employed thereby improving the fuel consumption and
reducing the emission of harmful uncombusted components. In this
connection, there has been proposed a new type of carburetor for use with
a stratified-charged rotary piston engine of the aforementioned type, said
carburetor comprising a first supply system adapted to supply fuel-air
mixture and a second supply system adapted to supply only air, said two
supply systems having individual throttle valves operationally co-related
with each other to control the total supply of air to the engine. In this
case, it has also been proposed to incorporate a special timing mechanism
into the linkage co-relating the two throttle valves so that the opening
phase of the throttle valve in said second supply system is somewhat
delayed from that of the throttle valve in said first supply system,
thereby effecting a temporary supply of a richer fuel-air mixture during
acceleration of the engine to provide better accelerating performance.
Although a stratified-charge rotary piston engine of the aforementioned
type is capable of operating satisfactorily at a normal speed and load
operating condition, it still has the problem that operation at a low
speed and low load condition (performed by a very small supply of fuel) is
prone to become unstable. Furthermore, in a low speed and load operation
or idling operation, the exhaust gas temperature substantially lowers and
causes a problem that a reactor for purifying uncombusted components such
as HC and CO is not maintained in a hot condition required for performing
its purification process, thereby causing poor purification efficiency.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to deal with the
aforementioned problems and to provide an improved carburetor for use with
a stratified-charged rotary piston engine of the aforementioned particular
type.
In accordance with the present invention, the above-mentioned object is
accomplished by a carburetor for use with a stratified-charged rotary
piston engine, comprising a first supply system having an air-flow
passage, a throttle valve, main fuel supply system and a slow/idle fuel
supply system, and a second supply system having an air flow passage and a
throttle valve which is operationally co-related with said throttle valve
in said first supply system. The improvement comprises a second slow/idle
fuel supply system provided in one of said first and second supply
systems, said second slow/idle fuel supply system having a control valve
which selectively intercepts the flow of fuel through said second
slow/idle fuel supply system, a first sensing means for sensing the speed
condition of the engine, a second sensing means for sensing the
temperature condition of the exhaust gas of the engine, and a control
means for controlling said control valve depending upon the information
received from said first and second sensing means in a manner such that
the flow of fuel through said second slow/idle fuel supply system is
intercepted when the engine speed is above a predetermined slow level and
the exhaust gas temperature is above a predetermined value.
By employing a carburetor of the above-mentioned construction, the engine
is supplied with an additional amount of fuel through said second
slow/idle fuel supply system when it is in a slow or idle operating
condition or when the exhaust gas temperature is below a predetermined
value, whereby when either one of these two conditions is encountered, the
engine is operated with a temporary enrichment of fuel-air mixture thereby
ensuring a stable operation of the engine as well as a high purifying
efficiency of the reactor means.
BRIEF DESCRIPTION OF THE DRAWING
In the accompanying drawing,
FIG. 1 is a diagrammatical sectional view of a rotary piston engine of a
particular stratified-charged type for which the carburetor of the present
invention is used;
FIG. 2 is a diagrammatical sectional view of an embodiment of the
carburetor of the present invention; and
FIG. 3 is a view similar to FIG. 2 showing another embodiment of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the following the invention will be described in more detail with
respect to some preferred embodiments thereof with reference to the
accompanying drawings.
Referring first to FIG. 1 showing a particular stratified rotary piston
engine for which the carburetor of the present invention is used, the
engine comprises a rotor housing 2 having a trochoidal inner peripheral
surface 1, the opposite open ends thereof being closed by side housings 4
each having a flat inside surface 3, thus forming an engine casing in
which is mounted a triangular rotor 5 to eccentrically rotate around an
eccentric shaft 9 while apex seals 6 provided at apex portions of the
rotor slide over the trochoidal inner peripheral surface 1, side seals 7
provided in the side walls of the rotor sliding over the flat inside
surfaces 3 of the side housing and an internal gear 8 of the rotor meshing
with a fixed gear 10 provided in side housing 4. The three flanks 11 of
the rotor 5 are individually provided with recesses 12. In one short axis
portion 13 of the rotor housing are spark plugs 14, while in the other
short axis portion 15 are provided an exhaust port 16 formed as a
peripheral port and an intake port 17 also formed as a peripheral port.
Spaced from the peripheral intake port 17 in the rotating direction of the
rotor is another intake port 18 formed as a side port which opens in the
inside surface of the side housing 4. The peripheral intake port 17 and
the side intake port 18 are connected with a carburetor 21 by means of
intake tubes 19 and 20, respectively. In this type of stratified charge
rotary piston engine, a fuel-air mixture is supplied from the port 17 and
is first charged in the combustion chamber such as shown by A defined by
the trochoidal inner peripheral surface and one of the arcuately curved
flanks 11 having the recess 12 and, thereafter, when the side port 18 is
traversed by the side seal 7 and is opened, air is supplied from the side
port 18. In this case, the initially charged fuel-air mixture is dragged
forward in accordance with the rotation of the rotor to principally fill
the leading region of the combustion chamber while the air supplied from
the side port 18 principally fills the trailing region of the combustion
chamber, thereby accomplishing a particular leading-rich, trailing lean
stratified-charged condition. This stratified charge is then compressed
and is further ignited by the spark plug 14 to proceed to the combustion
stroke. As mentioned above, the leading-rich, trailing-lean stratified
charge is combusted in a very desirable manner when compared with a
uniform charge or a reverse leading-lean, trailing-rich charge due to the
particular flame propagation characteristic in the rotary piston engine of
this type.
FIG. 2 shows an embodiment of the carburetor 21 in which the present
invention is incorporated. The carburetor has first and second air flow
passages 22 and 23 arranged in parallel with each other, wherein, however,
the first air flow passage 22 is incorporated in a fuel-air supply system
and is adapted to discharge a fuel-air mixture toward the intake tube 19
connected thereto, whereas the second air flow passage 23 is incorporated
in an air supply system and discharges only air toward the intake tube
connected thereto. In FIG. 2, the two air flow passages 22 and 23 are
shown as substantially spaced from each other for the convenience of
illustration, but it is to be understood that these two air flow passages
are arranged close to each other in actual carburetors. The passages 22
and 23 have air intake ports 24 and 24' and venturi portions 25 and 25',
respectively, and are controlled by throttle valves 26 and 26',
respectively. The throttle valve 26 is connected with a cam 27 while the
throttle valve 26' is connected with a lever 28 which operates as a cam
follower engaged with the cam 27, thereby co-relating the operation of the
throttle valve 26' to that of the throttle valve 26. The first supply
system including the air flow passage 22 further comprises a float chamber
29 which supplies fuel to a main nozzle 30 opening in the throat of the
venturi 25 through a main fuel passage 33 including a main jet 31 and an
air bleed 32. The carburetor further comprises a conventional slow/idle
fuel supply system including a slow port 34 which opens to closely oppose
the throttle valve 26, a slow/idle fuel supply passage 38 including a slow
jet 35 an economizer jet 36 and two air bleeds 37, and an idle port 40
provided on the downstream side of the slow port 34 and having a fuel
adjusting screw 39.
In addition to the above-explained conventional slow/idle fuel supply
system, the carburetor of the present invention comprises a second
slow/idle fuel supply system having a second idle port 41 provided to open
near the first idle port 40 and a second slow port 42 provided to open
near the first slow port 34, these second ports being supplied with fuel
through a second slow/idle fuel supply passage 46. Here it is to be noted
that the illustration of the of the second slow/idle fuel supply system in
FIG. 2 is a development of a section which is different from that of the
first slow/idle fuel supply system for the convenience of illustration and
that in the actual structure the second slow and idle ports 42 and 41 are
located near the first slow and idle ports 34 and 40 as mentioned above.
Similarly, the passage 46 for supplying fuel to the second slow and idle
ports 42 and 41 may be provided close to the fuel passage 38 in the first
slow/idle fuel supply system. For the same reason, the right side float
chamber 29 which supplies fuel to the second slow/idle fuel supply system
in a manner such as explained hereinunder is the same chamber as the left
side chamber 29.
The fuel passage 46 includes the similar elements such as provided in the
fuel passage 38 of the first slow/idle supply system, such as a slow jet
51, two air bleeds 44, an economizer jet 45 and a fuel adjust screw 43.
However, the second slow/idle fuel supply passage 46 further includes a
control valve 47 adapted to selectively intercept the passage. The control
valve 47 may preferably be a solenoid valve electrically operated by an
electronic control means 48 which is powered by the automobile battery by
way of the ignition switch 49. The control means 48 receives first
information with regard to the speed condition of the engine from a first
sensing means 52. The first information may be the opening of the throttle
valve 26 when the sensing means 52 is a means adapted to detect the
rotational angle of the throttle valve. Alternatively, the first
information may be the intake vacuum when the sensing means 52 is a means
adapted to measure the intake vacuum. The control means 48 receives second
information with regard to the temperature condition of the exhaust gas of
the engine from a second sensing means 53 which may be a thermostat
adapted to detect whether the exhaust gas temperature of the engine is
above or below a predetermined value. Depending upon the information
received from the sensing means 52 and 53, the control means 48 controls
the operation of the control valve 47 in a manner such that the valve 47
is closed to intercept the flow of fuel through the passage 46 when the
engine speed is above a predetermined slow level and the exhaust gas
temperature is above a predetermined value. In other words, the valve 47
is opened to permit the flow of fuel therethrough when the engine is in a
predetermined slow to idling operation and/or the exhaust gas temperature
of the engine is below a predetermined value.
When the engine operates in a medium to high load condition after it has
been warmed up, the first supply system including the first air flow
passage 22, main nozzle 30, main fuel passage 33, etc. produces a fuel-air
mixture and supplies it to the peripheral intake port 17 through the
intake tube 19, whereas the second supply system including the second air
flow passage 23 supplies only air to the side intake port 18 through the
intake tube 20. In this operating condition, a small amount of fuel is
also drawn out through the conventional slow/idle fuel supply system
including the slow port 34, idle port 40, fuel passage 38, etc. By this
continuous operation of the conventional slow/idle fuel supply system, the
operation of the engine is smoothly transferred from a middle to high load
condition to a slow or idling condition. On the other hand, in this
operating condition, the second slow/idle fuel supply system including the
idle port 41, slow port 42, fuel passage 46, control valve 47, etc. is
shut down by the control valve 47 which intercepts the flow of fuel
through the passage 46. Therefore, it is avoided that an excessive amount
of fuel is supplied from the second slow/idle fuel supply system.
When the engine operates in a slow or idling condition, the operating
condition is detected by the sensing means 52 and the control means 48
actuates to open the control valve 47. In this condition, therefore, the
second slow/idle fuel supply system operates and an additional amount of
fuel is supplied from this system, thereby temporarily lowering the
overall air/fuel ratio so that a stable slow operation or idling operation
is ensured.
When the exhaust gas temperature is below a predetermined level, regardless
of the speed condition of the engine, though such a low temperature of the
exhaust gas generally occurs in a low speed or idling condition, except a
cold state of the engine, this is detected by the sensing means 53,
whereby the control means 48 opens the control valve 47. In this
condition, therefore, an additional amount of fuel is supplied from the
second slow/idle fuel supply system to temporarily lower the air/fuel
ratio so that the exhaust gas temperature of the engine is maintained
above a predetermined value required for ensuring a satisfactory purifying
performance of the thermal reactor, especially when a secondary air
injection is performed.
FIG. 3 is a view similar to FIG. 2 showing another embodiment of the
present invention. In FIG. 3, the portions corresponding to those shown in
FIG. 2 are designated by the same reference numerals. In this embodiment,
the second slow/idle fuel supply system is incorporated in the second
supply system which is originally constituted to provide only air. In this
case, therefore, both the second idle port 41 and the second slow port 42
open to the second air flow passage 23 so as to supply an additional
amount of fuel from the side port 18 when the engine is operating in a low
speed or idling condition and/or when the exhaust gas temperature of the
engine is below a predetermined value. It will also be apppreciated that a
supplement of fuel from the side port 18 in those operating conditions has
the same effect of temporarily lowering the overall air/fuel ratio and
ensures a stable operation of the engine and/or a satisfactory performance
of the reactor for purifying exhaust gasses.
Although the invention has been shown and described with some preferred
embodiments thereof, it should be understood by those skilled in the art
that various changes and omissions of the form and detail thereof may be
made therein without departing from the spirit of the invention.
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