[0001] The present invention relates to an air-fuel ratio control device for injection carburetors
which is equipped with a slow fuel controller and a main fuel controller, and adjusts
fuel injection rate adequately on the basis of negative pressure produced dependently
on flow rate of air to be sucked.
[0002] This type of injection carburetors have already been proposed, for example, by European
Patent Application No. 89 109 196.9 submitted by the applicant. Fig. 1 is a sectional
view illustrating the fundamental structure of the air-fuel ratio control device of
the injection carburetor. In this drawing, the reference numeral 1 represents a suction
bore of a carburetor having a venturi 2, the reference numeral 3 designates a fuel
control unit arranged at a location neighboring the venturi 2 and the reference numeral
4 denotes an air section of regulator arranged at a location also neighboring the
venturi 2 but on the side opposite to the fuel control unit 3 with regard to the suction
bore 1. The air section of regulator 4 has an air chamber and a depression chamber
5 which is separated from each other by a negative pressure diaphragm 6, and formed
in the depression chamber 5 is an opening 5a for communication with the venturi 2.
Further, a fuel section of regulator 7 has a fuel injection chamber 8 and a fuel pressure
chamber 9 which are separated from each other by a fuel diaphragm 10, and formed in
the fuel injection chamber 8 is a fuel injection port 8a in opposite to the opening
5a of the depression chamber 5. The fuel injection chamber 8 is communicated with
the fuel pressure chamber 9 through a main jet 11. The reference numeral 12 represents
a connecting member inserted through the opening 5a of the depression chamber 5 and
the fuel injection port 8a of the fuel injection chamber 8, one end of the connecting
member 12 is fixed to the negative pressure diaphragm 10 and the other end of the
connecting member 12 is fixed to the fuel diaphragm 10. Formed on the connecting member
12 is a conical valve 12a capable of controlling opening degree of the fuel injection
port 8a by opening and closing said port. The reference numeral 13 represents a spring
which is arranged in the depression chamber 5 and functions to urge the negative pressure
diaphragm 6 upward, i.e., to move the valve 12a in the direction to close the fuel
injection port 8a. When a negative pressure corresponding to the flow rate of the
air flowing through the venturi 2 is introduced into the depression chamber 5 and
the negative pressure diaphragm 6 is displaced toward the depression chamber 5 in
the injection carburetor having the structure described above, also the fuel diaphragm
10 is displaced in the same direction (downward) to allow the valve 12a to open the
fuel injection port 8a, whereby fuel is ejected into the suction bore 1 and pressure
drops in the fuel injection chamber 8 accordingly. When pressure differential between
the negative pressure in the depression chamber 5 and atmospheric pressure is balanced
with the fuel pressure differential between both the sides of the main jet 11, the
pressure applied to the negative pressure diaphragm 6 is balanced with the pressure
applied to the fuel diaphragm 10 and air-fuel ratio is maintained constant in this
condition. When resilience of the spring 13 is so selected as to be equal to the total
weight of the assembly consisting of both the diaphragms 6 and 10 and the connecting
member 12 in order to obtain high responsibility of the injection carburetor of this
type, however, a negative pressure is not produced substantially at the starting time
of an engine as shown in Fig. 2A since air flows through the venturi at a low rate
at that time. Accordingly, variation of fuel flow rate is slower than variation of
air flow rate, thereby producing a deviation of x from a target value as illustrated
in Fig. 2B. Therefore, the injection carburetor of this type has a defect that a long
time is required until an air-fuel ratio of the mixture attains to a target value
corresponding to an opening degree of the throttle valve after it is opened widely
in the main zone as shown in Fig. 2C.
[0003] Fig. 3 illustrates a carburetor so adapted as to control air-fuel ratio of the mixture
in a broad range by combining two air-fuel ratio control devices having the fundamental
structure illustrated in Fig. 1 as a slow fuel control unit 14 mainly for controlling
the slow zone and a main fuel control unit 15 chiefly for controlling the main zone.
In Fig. 3, the members and parts of the slow fuel control unit 14 which are similar
to those illustrated in Fig. 1 are represented by the same numerals but with a prime,
and the members and parts of the main fuel control unit 15 similar to those shown
in Fig. 1 are designated with the same numerals but with double primes. The reference
numeral 16 represents an air valve arranged openably and closably downstream the venturi
2 in the suction bore 1, the reference numeral 17 designates a stopper for holding
the air valve 16 at the minimum opening degree thereof, the reference numeral 18 denotes
a negative pressure actuator which is connected to the air valve 16, and functions
to open and close the air valve 16 in conjunction with variation of the negative pressure
produced downstream the air valve 16, the reference numeral 19 represents a throttle
valve arranged downstream the air valve 16, the reference numeral 20 designates a
fuel tank and the reference numeral 21 denotes a fuel pump. The discharge side of
the fuel pump 21 is communicated with the fuel pressure chamber 9˝ of the main fuel
control unit 15 and the fuel injection chamber 8˝ thereof is communicated with the
fuel pressure chamber 9′ of the slow fuel control unit 14. The negative pressure chamber
of the slow fuel control unit 14 is communicated with the suction bore 1 at a location
downstream the air valve 16, whereas the negative pressure chamber of the main fuel
control unit 15 is communicated with the venturi 2. The fuel injection port 8a′ of
the slow fuel control unit 14 and the fuel injection port 8a˝ of the main fuel control
unit 15 are communicated with a fuel passage 22 which is open to the suction bore
1 at a location downstream the throttle valve 19.
[0004] The carburetor described above has already been proposed by the applicant and functions
as follows. In the slow zone of the engine where the throttle valve is opened at a
small degree, a low negative pressure is produced downstream the air valve 16 and
the negative pressure actuator does not operate. Accordingly, the air valve 16 is
held at the position shown in Fig. 3 and only the slow fuel control unit 14 is set
in the operating condition. The slow fuel control unit 14 functions in the same manner
as the fuel control unit described with reference to Fig. 1, and the fuel ejected
through the fuel injection port 8a′ is discharged into the suction bore 1 through
the fuel passage 22. When the throttle valve 19 is opened to a predetermined degree
from the condition described above, the negative pressure actuator operates to displace
the air valve 16 to the fully open position thereof. During this transient process,
the negative pressure acting on the depression chamber of the slow fuel control unit
14 is gradually reduced and the negative pressure acting on the depression chamber
of the main fuel control unit 15 is gradually increased, whereby the fuel injection
port 8a˝ of the main fuel control unit 15 begins to eject the fuel. The fuel ejected
from the fuel injection port 8a˝ is discharged into the suction bore 1 through the
fuel passage 22 and operating condition of the engine shifts to the main zone. However,
since both the slow fuel control unit 14 and the main fuel control unit 15 have the
defect described with reference to the carburetor illustrated in Fig. 1, the air-fuel
ratio controlled by both the fuel control units are disturbed as shown in Fig. 4 during
the transition from the slow zone to the main zone, or the transition from the slow
zone to the main zone is not performed smoothly.
[0005] In order to correct these defects, i.e., to match actual air-fuel ratios with target
values from the beginning of the main zone, there has been proposed a carburetor wherein
the negative pressure diaphragms 6 and 6˝ are so designed as to operate with higher
responsibility to air flow rate by selecting resilience of the spring 13 so as to
be smaller than the total weight of the diaphragm assembly 6, 10, 12 in Fig. 1 and
resilience of the spring 13˝ so as to be smaller than the total weight of the diaphragm
assembly 6˝, 10˝, 12˝ in Fig. 3, or arranging, in the air chamber of the air section
of regulator 4, a compensating spring 23 urging the negative pressure diaphragm 6
toward the depression chamber 5, and providing an adjusting screw permitting adjustment
of resilience of the adjusting spring 23 as illustrated in Fig. 5. This proposal makes
it possible to match fuel flow rates to be controlled nearly with target values from
the beginning of the main zone and to control air-fuel ratios of the mixture nearly
at target values from the beginning of the main zone as illustrated in Fig. 6B. When
the fuel control units are composed as described above, however, the forces for urging
the negative pressure diaphragms 6 and 6˝ toward the depression chambers 5 and 5˝
are too strong, and the fuel injection ports 8a and 8a˝ are kept in the open condition
thereof even while the engine is rested, thereby producing defects that the mixture
is made overrich by the fuel discharged from the main fuel control unit 15 even in
the slow zone and that the fuel is ejected through the fuel injection ports 8a and
8a˝ before the engine starts rotating at the restart time by the fuel pump 21 which
starts operating upon the ON operation by the engine key.
[0006] A primary object of the present invention is to provide an air-fuel ratio control
device for injection carburetors which is capable maintaining of air-fuel ratio of
the mixture at a constant level during transition from the slow zone to the main zone.
[0007] Another object of the present invention is to provide an air-fuel ratio control device
for injection carburetors which is capable of securely preventing unnecessary fuel
from being discharged into the suction bore at the rest time or restart time of an
engine.
[0008] A further object of the present invention is to provide an air-fuel ratio control
device for injection carburetors which has very excellent responsibility over the
entire operating range of an engine.
[0009] According to the present invention, the objects mentioned above are attained by equipping
with a slow negative pressure passage for introducing the negative pressure produced
downstream the air valve into the depression chamber of the slow fuel control unit,
a main negative pressure passage for introducing the negative pressure from the venturi
into the depression chamber of a main fuel control unit, a bypass passage for communicating
the main negative pressure passage with the slow negative pressure passage, and a
means which is provided in the bypass passage and capable of adjusting a ratio of
the negative pressure to be added into the main negative pressure passage through
the slow negative pressure passage.
[0010] The air-fuel ratio control device according to the present invention allows the negative
pressure produced downstream the air valve to be added at a predetermined ratio into
the main negative pressure passage through the bypass passage so that a total of the
negative pressure in the venturi and the added negative pressure if introduced into
the depression chamber of the main fuel control unit in the slow zone, and opens the
fuel injection valve to start discharging the fuel when the total negative pressure
exceeds a predetermined level, whereby the air-fuel control device is capable of
maintaining air-fuel ratio of the mixture at a constant level during the transition
from the slow zone to the main zone.
[0011] In a preferred formation of the present invention, provided in the main fuel control
unit is a resilient means which functions to generate a force acting to close the
fuel injection valve which is stronger than the force acting to open the fuel injection
valve until the negative pressure to be introduced into the depression chamber of
the main fuel control unit exceed the predetermined level. This means prevents the
fuel from being leaked while the engine is rested or at the initial stage of the slow
zone.
[0012] These and other objects as well as the features and the advantages of the present
invention will become apparent from the following detailed description of the preferred
embodiment when taken in conjunction with the accompanying drawings.
[0013] In the drawings:
Fig. 1 is a sectional view illustrating the fundamental structure of the conventional
air-fuel ratio control device for injection carburetors;
Fig. 2A, Fig. 2B and Fig. 2C are graphs illustrating various characteristics of the
air-fuel ratio control device shown in Fig. 1;
Fig. 3 is a sectional view illustrating overall structure of the injection carburetor;
Fig. 4 shows characteristic curves illustrating relationship between air flow rate
and air-fuel ratio during transition from the slow zone to the main zone in the carburetor
shown in Fig. 3;
Fig. 5 is a schematic sectional view illustrating another conventional example obtained
by improving the air-fuel ratio control device shown in Fig. 1;
Fig. 6A, Fig. 6B and Fig. 6C are graphs illustrating various characteristics of the
air-fuel ratio control device shown in Fig. 5;
Fig. 7 is a sectional view illustrating the main members of an embodiment of the air-fuel
ratio control device according to the present invention;
Fig. 8A and Fig. 8B are characteristic curves illustrating variations of air-fuel
ratio in the embodiment of the air-fuel ratio control device according to the present
invention; and
Fig. 9 is a curve visualizing variation characteristic of the negative pressure produced
downstream the air valve.
[0014] Now, the embodiment of the present invention will be described with reference to
Fig. 7. In this drawing wherein the slow fuel control unit is omitted, the members
and the parts which are substantially the same as those shown in Fig. 3 are represented
by the same reference numerals. The reference numeral 25 represents a main negative
pressure passage which is open to the venturi 2, has a jet 25a and serves for introducing
a negative pressure P₁ of the venturi into the depression chamber of the main fuel
control unit 15, the reference numeral 26 designates a slow negative pressure passage
which is open at a location downstream the air valve 16 and serves for introducing
a negative pressure P₂ produced downstream the air valve 16 into the depression chamber
of the slow fuel control unit 14, the reference numeral 27 denotes a bypass passage
communicated at one end thereof with the slow negative pressure passage 27 and at
the other end thereof with the main negative pressure passage 25 at a location dowstream
the jet 25a, the reference numeral 28 represents an adjusting screw which is adjustably
provided in the bypass passage 27 and capable of adjusting a ratio of the negative
pressure P₂ downstream the air valve 16 to be added into the main negative pressure
passage 25, and the reference numeral 29 designates a spring which is arranged in
the air chamber 5˝ of the main fuel control unit 15 and functions to urge the negative
pressure diaphragm 6˝ toward the depression chamber. Let us now assume that a reference
symbol w₁ represents weight of the diaphragm assembly of the main fuel control unit
15, a reference symbol w₂ designates resilience of the spring 13˝, a reference symbol
w₃ denotes resilience of the spring 29, and a reference symbol w₄ represents a force
which is generated by the total negative pressure P₃ of the negative pressures P₁
and P₂ produced in the slow zone during operation of the engine, and acts to raise
the diaphragm assembly. Resilience of the spring 13˝ and that of the spring 29 are
selected so as to satisfy the following relation (1) in the rest condition of the
engine and the following condition (2) when the force w₄ exceeds a predetermined value:
w₃ < w₁+ w₂ (1)
w₃ + w₄ > w₁+ w₂ (2)
In this embodiment, the air-fuel ratio control device illustrated in Fig. 3 is used
as the slow fuel control unit 14.
[0015] Now, functions of the air-fuel control device preferred as the embodiment will be
described below:
[0016] While the engine is rested, the negative pressures P₁ and P₂ are not produced, whereby
the fuel injection valves 12a′ and 12a˝ are held in the closed positions thereof to
prevent the fuel from being leaked into the fuel passage 22. While the engine is operating
in the slow zone after it is started, a very low negative pressure is produced in
the venturi 2, whereas the negative pressure P₂ at a certain level is produced downstream
the air valve 16. This negative pressure P₂ is introduced through the slow negative
pressure passage 26 into the depression chamber of the slow fuel control unit 14.
Accordingly, the fuel is ejected from the fuel injection port 8a′ in a quantity corresponding
to the level of the negative pressure P₂ in the slow fuel control unit 14 as already
described with reference to Fig. 3, whereby the mixture at the air-fuel ratio suited
for operation in the slow zone (target value) is fed to the engine as indicated by
the solid line in Fig. 8B. On the other hand, the negative pressure P₂ is added, at
the predetermined ratio set by the adjusting screw 28, through the bypass passage
27 into the main negative pressure passage 25, and a total negative pressure P₃ of
the added pressure and the very low pressure P₂ in the venturi 2 is introduced into
the depression chamber of the main fuel control unit 15. At the initial stage of the
slow zone, however the fuel injection port 8a˝ is closed by the valve 12a˝ since the
raising force w₄ generated by the total negative pressure P₃ is small and the force
w₁+ w2 acting to close the fuel injection valve 12a˝ is larger than the force w₃ acting
to open the fuel injection valve 12a˝. The negative pressure P₃ increases as air is
sucked at higher rates into the suction bore 1. (See Fig. 9) When the total negative
pressure P₃ exceeds a predetermined level in the depression chamber of the main fuel
control unit 15 to establish the above-mentioned relation (2), the negative pressure
diaphragm 6˝ is displaced toward the depression chamber against the force w₁ + w₂
acting to close the fuel injection valve 12 a˝and the valve 12a˝ is opened, whereby
the fuel is ejected through a fuel discharge passage 22 into the suction bore 1. Air-fuel
ratio of the mixture which is low at the beginning is gradually enhanced as indicated
by the curves a in Fig. 8A and Fig. 8B, and reaches a target valve. As opening degree
of the throttle valve 19 is increased, the slow zone is switched to the main zone
in a condition where the air-fuel ratio is maintained at the target value, and the
condition is kept also in the main zone. (See Fig. 8A and Fig. 8B ) Further, at restart
time after the engine is stopped, the above-mentioned relation (1) is satisfied and
the fuel injection valve 12a˝ is kept at the closed condition thereof before the engine
starts rotation even in the condition where the engine key is turned ON and the fuel
pump 21 is operating.
[0017] As is understood from the foregoing description, the embodiment of the present invention
prevents unnecessary fuel from being discharged at rest time of engine or initial
stage of the slow zone since the force w₁ + w₂ acting to close the fuel injection
valve 12a˝ is stronger than the force w₃ acting to close the valve 12a˝ at the engine
rest time or initial stage of the slow zone before the total negative pressure P₃
in the depression chamber of the main fuel control unit 15, exceeds a predetermined
level, assures stable operation of the fuel injection valve 12a˝ at opening start
time thereof, and is capable of maintaining air-fuel ratio of the mixture at a constant
level with the main fuel control unit 15 during transition from the slow zone to the
main zone as well as in the main zone by adding a predetermined ratio of the negative
pressure produced dependently on air flow rate into the depression chamber of the
main fuel control unit 15 at the stage of the slow zone. Further, the embodiment of
the present invention does not allow mechanical operation delay since opening and
closing of the fuel injection valve 12a˝ are controlled by variation of the negative
pressure.
[0018] Furthermore, it is possible, needless to say, to use the known piston valve as the
air valve 16 though the embodiment uses a leaf valve. In addition, though the embodiment
is so constructed as the strengthen the closing force for the fuel injection valve
12a˝ by the resilience of the spring 13˝, it is possible to select such a structure
as the strengthen the closing force for the fuel injection valve 12a˝ weakening the
resilience of the spring 28 with the spring 13˝ omitted.
1. An air-fuel ratio control device for injection carburetors comprising a slow fuel
control unit and a main fuel control unit each including a negative pressure diaphragm
forming a depression chamber for receiving negative pressures produced dependently
on flow rates of air to be sucked into a suction bore, and a fuel injection valve
for opening and closing a fuel injection port in accordance with displacement of said
negative pressure diaphragm, characterized in that said air-fuel ratio control device
comprises a negative pressure passage for introducing negative pressures from a venturi
in the seuction bore into the depression chamber of the main negative pressure control
unit, a slow negative pressure passage for introducing negative pressure produce downstream
an air valve arranged in the suction bore at a location downstream said venturi into
the depression chamber of the slow fuel control unit, a bypass passage connected between
said main negative pressure passage and said slow negative pressure passage, and an
adjusting means arranged in said bypass passage and capable of adjusting ratios of
the negative pressure to be introduced from said slow negative pressure passage into
said main negative pressure passage.
2. An air-fuel ratio control device according to Claim 1 wherein said adjusting means
is designed as an adjusting screw fitted in said bypass passage and capable of effective
across sectional area of said bypass passage.
3. An air-fuel ratio control device according to Claim 1 wherein said air valve is
designed as a leaf valve.
4. An air-fuel ratio control device according to Claim 1 wherein said air valve is
designed as a piston valve.
5. An air-fuel ratio control device according to any one of Claims 1 through 4 further
comprising a resilient means functioning in such a manner that a force acting to close
the fuel injection valve of the main fuel control unit is stronger than a force acting
to open said valve until the negative pressure to be introduced into the depression
chamber of said main fuel control unit exceeds a predetermined level while operating
condition of the engine is in the slow zone.