Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF INVENTION
Field of Invention
This invention relates in general to fuel management systems for
internal combustion engines and, in particular, to control systems
responding to the fuel mixture for controlling the amount of fuel`supplied
to the system.
Prior Art
Most fuel management systems can be classified as either an open
loop control or a closed- 1DOP control system. In the open loop control
system, the fuel mixture is preprogrammed and the fuel management system
responds only to certain engine operation parameters for selecting the
desired fuel mixture. In the closed loop control system, the fuel mixture
is also preprogrammed with the fuel management system responding to certain
engine operation parameters for selecting the proper fuel mixture; however,
lS with the use of an output sensor, the fuel mana~ement system is continuously
updated to account for fuel management system tolerances, ambient conditions
` and for particular engine operating conditions so that the actual air/fuelratio is substantially equal to the desired proper air/fuel ratio.
Typically most output sensors which respond to the characteristics
of the fuel mixture are positioned in the exhaust system of the engine ;
substantially downstream from the point where all the exhaust gases are
gathered. This position is generally necessary because most of the sensors
I ; are operated at elevated temperatures and the exhaust gases provide the
1, heat source necessary to heat the sensor to its operating temperature.
However, this position is a lon9 "time" distance away from the source of the
fuel mixture and therefore the response time of the system is slow.
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Additionally, the system response time is further altered
according to the mode of operation of the engine.
By positioning the fuel mixture sensor close to the
source of the ~uel mixture, the response time i5 greatly
speeded up and in the operation of the fuel management sys-
tem the actual air/fuel ratio more closely reflects the
desired proper air/fuel ratio.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention overcomes
t~e problems of the prior art by pr~viding, a fuel manage-
ment system for an internal combustion engine wherein the
fuel and air are mixed in a mixture control means and dis-
tributed through intake manifold means to the cylinders of ;
the engine, a system for controlling the air/fuel ratio in
the fuel mixture comprising: variable fuel delivery means
for controlling the amount of fuel discharged into the mix-
ture control means; sensor means positioned in the intake
manifold means for directly sensing the oxygen partial .
pressure in the fuel mixture flowing thereby, the~. sensor
having an electrical characteristic which varies in response
to changes in the oxygen partial pressure and control means
responsive to the. sensor for controlling thé variable fuel
delivery means and controlling the quantity of fuel discharged
into the mixture control means in accordance with a function
of the electrical characteristic.
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DESCRIPTION OF THE DRAWINGS
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In the drawings:
Fig. 1 is a block diagram schematic of the system of the present
invention.
Fig. 2 is an illustration of the position of the sensor in the
manifold at the e~it of the throttle body.
Fig. 3 is one embodiment of the mi~ture control unit.
DETAILED DESCRIPTION
Referring to the Figures by the characters of reference there is
illustrated in Fig. 1 a block diagram of the system of the present invention.
The system is used to afford a precise control of the air~fuel mixture for
an internal combustion engine where the air and the fuel are mixed at a
single point such as a carburetor, as opposed to fuel injection systems
wherein the fuel is mixed with the air either within the cylinder or adjacent
to the intake valve thereof. In the embodiment of Fig. 1 the air/fuel
~ mixture ratio is measured immediately after the air and the fuel are mixed
i and therefore closed loop control of the mixture can immediately take place.
This present system avoids errors in the fuel mixture due to the problem
defined as transport lag within a system.
zo Referring to Fig. 1 there is illustrated in block diagram a gas
sensor 10 positioned in the intake manifold 12 and responsive to the fuel
; ~ mi~ture flowing thereby. The output of the sensor 10 is supplied to a
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summer 14 wherein it is subtracted from a reference voltage 16 to generate
an error signal 18. The error signal 18 is then electrically supplied to a
'~ 25 comparator 20 for generating a step voltage output. The output of the
¦~ ~ comparator 20 is supplied to a controller 22 generating a command sipnal
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for a servo unit 24. The servo unit 24 meters and measures the flow of
fuel 26 into the mixture control unit 28 through a variable fuel delivery
means 30. The flow of air 32 into the mixture control unit 28 i5
control1ed by a throttle valve 34 actuated by the operator of the engine.
In the mixture control unit 28 the air 32 and fuel 26 are mixed and
discharged into the intake manifold 12. From the intake manifold 12 the
air and fuel mixture is supplied to the cylinders 36 for combustion and
the exhaust gases are discharged into the exhaust system.
The mixture control unit 28 in Fig. 1 may take the form of any
of the well-known fuel mixture units used on internal combustion engines.
Such units may be the conventional carburetor or any form of throttle :
body wherein the air 32 and fuel 26 are mixed for combustion by the engine.
The throttle valve 34 is illustrated in the dra~ings and represents any ~;
similar device which is used to control the flow of air and the flow of the
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resulting fuel mixture into the intake manifold 12.
~ As illustrated in Fig. 2 the sensor 10 is positioned so as to
; respond to the fuel mixture leaving the mixture control unit 28. The gas
sensor 10 comprises a sensor hody 38 in the form of a tube having a heater
- winding 40 encircling the outside or the inside of the tube. The sensor
body 38 is contained within a flame arrester means 42 having a plurality
,~ of apertures 44 in the wall of the arrester means 42 allowing the fuel
mixture to flow to the sensor body 38. Aligned with either end of the
sensor body 38 and the arrester body 42 are an inlet 46 and outlet 48
tube ~espectively admitting the reference gas which is ambient air into
the inside of the sénsor body 38 and exhausting it therefrom. The output
of the outlet tube 48 is directed so that the reference air is mixed with
the fuel mixture and is sensed by the sensor 10.
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The inlet tube 46 to the sensor ;n the preferred embodiment ;s
connected to the air cleaner 50 and due to the vacuum in the intake
manifold 12 the air is drawn through the in1et tube 46 through the
sensor 10 and through the outlet tube 48. A restrictor 52 is placed in
the inlet tube 46 in order to equalize ~he pressure on the reference side
or inside of the sensor 10 to that of the pressure on the outs;de or the
manifold side of the sensor 10. This is necessary because the sensor 10
detects the ratio of the partial pressures of oxygen in the ~ases on the
outside and inside of the sensor.
By discharging the reference gas into the intake man;fold 12
the fuel mixture leaving the mixture control unit 28 is made leaner; however,
as will hereinafter become apparent by the response of the sensor 10 this
added air is compensated for by the addition of more fuel.
In the preferred embodiment the sensor 10 is an oxygen gas sensor
wherein the material of the sensor body or cell 38 generates a voltage
I proportional to the amount of oxygen on either side of the cell. If the
;I cell 38 is fabricated from zirconia, by the use of different stabilizers
added to the material different physical and electrical properties can be
achieved. Regardless of the stabilizers used, the oxygen sensor cell 38
must be heated to an elevated temperature in order to overcome the output
impedance of the cell to therefore generate useable electrical signals.
The electrical output of the sensor cell 38 is connected to a
control means 54 comprising the above-indicated summer 14, comparator 20, and
controller 22. The output of the control means 54 is coupled to a servo
unit 24 for controlling the fuel 26 flow into the mixture control unit 28.
Fig. 3 illustrates one embodiment of the mixture control unit 28
as may be used in the system of Fig. 1. In particular, Fig. 3 is an
illustration of a carburetor wherein the fuel 26 flows from the bowl 56
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of the carburetor through an orifice 58 comprising the main metering jet
to the main discharge tube 60 in the venturi 62 of the carburetor. As
is well known the fuel is discharged into the carburetor in response to
the air 32 flowing through the venturi 62. Of particular interest in
the present application is the control of the main metering jet 58. As
illustrated in Fig. 3 the main metering jet is controlled by a two-stage
contour needle 64 operating in an orifice 58. As the needle 64 is moved
axially through the orifice 58 the size of the orif;ce changes therefore
the amount of fuel 26 flowing from thè bowl 56 of the carburetor is
1~ controlled, In ~ig. 3 the contoured needle 64 is moved axially in and
out of the orifice 58 by a servo unit 24 or torque motor electrically
responding to the controller 22.
Also illustrated in Fig. 3 are the several idle function elements
of the carburetor which operate to supply fuel into the enaine during idle.
Such elements are the idle port 66, the off-;dle port 68, the idle mixture
screw 70, idle fuel cross-over port 72, and the ;dle tube 74. The idle
control system also receives fuel 26 from the main metering jet 58 under
the control of the needle valve 64 and the torque motor 24.
The sensor used in the embodiment of Fig. 1 is an oxygen gas
sensor lO which is fabricated from a zirconia stabilized material. The
outer surface 76 of the sensor body 38 is plated with a catalytic material
such as platinu~ functioning to give the sensor a step voltage output and
the inner surface 78 is also plated with electrically conductive material
although the inner plating need not be catalytic. The voltage output of
the sensor 10 switches from one voltage level to the second voltage level
j at a predefined air/fuel mixture ~Jhich in the present embodiment of the
ùrygen senson is at or very near to stoichiometric air/fuel r~t;o. ~t ;s
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apparent that other types of sensors other than an oxygen gas sensor may
be used wherein the sensors respond to a predetermined air/fuel ratio
and generate an electrical signal indicating whenever the fuel mixture
is equal to less than or greater than that predetermined air/fuel ratio.
If the sensor 10 is an oxygen gas sensor ~ it is necessary
that the temperature of the sensor body 38 be elevated above the temperatures
normally found in the intake manifold 12 system. A typical minimum operation
temperature of the sensor 10 is approximately 700 F. In order to achieve
this temperature, a heating hinding 40 is wound around the zirconium tube 38
and receives power from an appropriate electrical source in the vehicle
(not shown). This heating winding 40 will locally raise the temperature
of the sensor 10 to the proper operating temperature allowing the sensor
to function. Since this added heat may cause the gas around the sensor to
burn, a flame arrestor 42 is provided to contain and prevent any propagation
of flame throughout the intake manifold 12.
The reference gas for the sensor 10 is supplied from the ambient
air surrounding the engine which has been passed through the air cleaner 50
and piped by means of the inlet tube 46 into the manifold 12 and to the
sensor 10. Since the response of the sensor 10 is a function of the change
in the oxygen partial pressure across the sensor, it is desirable that the
total pressures be equalized or nearly equalized. This is accomplished by
providing the restrictor 52 in the inlet tube 46.
The effectiveness of the restrictor 52 depends on the rate of air
flow through the restrictor and the size of the restrictor. The rate of
idle air flow at id1e for small engines (140 cu.in. displacemeht) is
approximately 30 lbs/hr. The pressure downstream of the restrictor is
approximately 7 psia and the pressure upstream of restrictor is ambient or
approximately 15 psia; therefore the ratio of the downstream to the upstream
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pressure is 7/15 or 0.46. This gives a restrictor diameter size under
sonic air flow conditions of approximately .04 in. which, a1though small,
is not too dirt sensitive. Therefore, with such a restrictor 52 in the
inlet tube 46, the pressure of the reference gas and the pressure of the
fuel mixture in the intake manifold are approximately equal.
The electrica1 signal generated by the sensor 10 is e1ectrically
conducted by a pair of wires one of which is connected to the inside
surface and the other is connected to the outside surface of the sensor
and ;s supplied to the control means 54 as indicated in Fig. 2. However,
one side of the sensor may be grounded to the same ground as the control
means 54 and therefore only one wire would be required. As previously
indicated the control means 54 comprises a summer 14 which is responsive
to the signal from the sensor 10 and to a signal 16 generated by a voltage
threshold device and generates an output therefrom which has both magnitude
and direction. The output signal is ~ypically called error signal 18 and
in the preferred embodiment if the error signal 18 is posit;ve the mixture
is rich and if the error signal is negative the mixture is lean. The
error signal 18 is supplied to a comparator 20 means having either one of
two outputs of fixed magnitude. The output of the comparator 20 is dependent
upon the sign of the error signal 18 being supplied to it. The output of
the comparator 20 is electrically connected to a controller or an integrator
means 22 the output of which is an electrical signal having either a positive
going or a negative going slope thereto. This electrical signal from the
integrator means 22 is supplied to a servo unit 24 such as a torque motor
of Fig. 3 which controls the amount of fuel 26 flowing into the mixture
control unit 28.
With this sensor 10 being positioned substantially at the output
of the mixture control unit 28 and in the intake manifold 12, the problems
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due to transport lag have been greatly minim;zed and immediately after the
air and fuel are brought together for mixing the makeup of the mixture is
sensed and the flow of fuel is metered accordingly. It is apparent that
by any of the we11-known techniques responding to a mixture sensor, the
air/fuel ratio of the mixture supplied to an internal combustion eng;ne
may be controlled to any desired air/fuel ratio. Biasing signals may be
supplied indicating engine operations such as idle, wide-open throttle, and
altitude changes so as to continuously monitor the fuel being supplied to
the engine for best operation requirements of the engine.
As illustrated in Figs. 2 and 3, the fuel delivery means is
represented as being a variable fuel delivery means. In particular in
; Fig. 3 is illustrated a two-stage contour needle 64 moving through an
orifice valve 58. Fig. 2 represents the fuel del;very means 30 as comprising
a variable valve and a pump 80 and the servo unit 24 controll;ng either the
output action of the pump 80 or the opening of the variable valve.
There has thus been shown and described a system for maintaining
a desired air/fuel mixture in an intake manifold by measuring the mixture
, by means of the alr/fuel sensor immediately after the mixture is formed
and, using the electrical intelligence generated by said measurement to
control or meter'the fuel being supplied to the mixture unit.
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