Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF Tt~E INVENTION
_ ld of the Invention
This inven-tion relates to fuel injection
systems for spark ignited internal cornbustion engines
employiny at least one injector fed by a constant
pressure fuel supply, and more particularly to l,leans to
prevent fuel injection to the system during startiny
when the fuel delivery rate provided by the injector
would be insufficient to prevent emissions of hiyh
leveLs of unburned hydrocarbons.
Prior Art
Canadian Patent 1,075,9~7 discloses a form of ~ !
fuel injection system for a spark iyllition internal
colnbustion engine employing electrically eneryized fuel
injectors disposed at each engine cylinder and connected
lS to a common fuel line. Duriny the engine operation the
pressure in the fuel line and at the injectors is
maintained at a regulated, relatively hiyh value such as
100 psiy by a camshaft driven fuel pressure booster.
The latter is fed from a low pressure fuel su~ply pump.
The regulated, high pressure fuel line insures that the
quantity oE fuel provided to a cylinder by an injector
will always be at a predetermined value. rrhe injectors
are each eneryized into open condition by individual
variable width pulse yenerators controlled by sensors
which measure engine operating parameters such as
manifold vacuum and the like.
~ ecause the pressurized fuel delivery line
is located in proximity to the enyine, and the
injectors are positioned in iml~lediate proxi1nity to
the cylinders, -the fuel within the line becomes ~leated
during normal engine operation and expands. During
normal engine opera-tion the pressure booster retains
regulated fuel pressure independent of the variable fuel
density.
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After the engine stops, the booster is no longer operative, with
the result that the cooling fuel will contract in volume and cause
a drop in pressure in the fuel line. Pressure wave converters
employing flexible diaphragms connected to the line on one side
and a reference pressure on the opposite side ac~ to adjust auto-
matically the high pressure fuel line volume as the pressure
decays.
When the engine is restarted the initial fuel pressure
may be substantially lower than the normal operating pressure.
Such low fuel pressure will result in a diminution of the fuel
charges provided to the cylinders by the injectors during starting.
Since the variable width pulse generators that control the injec-
tors as a function of measured engine operating parameters are
programmed on the basis of an assumed constant pressure in the
fuel line the lowered pressure will result in a decreased fuel
flow rate through the injectors during actuation thereof.
If the engine has been allowed to cool to an appreciable
degree below its normal operating temperature before restarting is
attempted, the diminished fuel charge provided to the cylinders as
a result of the drop in fuel line pressure may not inhibit start-
ing. The variable width pulse generators are programmed to provide
an excessive fuel charge during cold start. ~oreover, at cooler
engine starting temperatures the fuel charge tends to accumulate~
providing an air-fuel mixture that may be sufficient for ignition.
In the event that restarting is attempted while the
engine is still fully close to operating temperature, however, the
reduced fuel charge provided to the engine because of the lowered
fuel line pressure may be insufficient tG produce an ignitable
air-fuel mixture ~uickly. The unburned hydrocarbons pumped into
the exhaust system prior to ignition may substantially raise
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pollutants sufficiently to exceed limits imposed by ~vernment
regulations.
After a period of cranking without combustion, the
fuel booster or fuel pump will raise the fuel pressure, increas-
ing the quantities of injected fuel to a level sufficient for
starting of the engine. Further, the time period required for
the pressure booster to raise fuel pressure to a level suffl-
cient for clean combustion is increased by injection of dimin-
ished fuel charge during the starting mode.
SU~ARY OF THE INVENTION
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The present invention provides a fuel injection system
that eliminates the problems arising from the injection of fuel
into the cylinders of an engine in insufficient quantities to
sustain ignition during starting of the engine. The improved
system incorporates means for sensing the fuel pressure in the
lines feeding the injector and means for inhibiting the energi~
zation of the injectors during starting until the fuel pressure
exceeds a preselected value.
In accordance with one aspect of this invention there
is provided in a fuel injection system for a spark ignition
engine having a supply of pressuri~ed fuel, an injector valve
connected to the supply, sensors for measuring engine operating
conditions and an electric circuit for energizing the injector
in timed relation to the engine operation for periods controlled
by the output of said sensors, the improvement comprising:
means actuated in response to the pressure of the fuel in said
supply for inhibiting energization of the injector during start-
ing of said engine until the fuel pressure exceeds a preselected
minimum pressure.
In accordance with another aspect of this invention
there is provided a fuel injection system for a spark ignited
internal combustion engine, comprising: a Euel source; a fuel
supply line; means powered by the engine for feeding fuel from
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the source to the supply line to maintain a predetermined,
operating fuel pressure in the supply line; an injector con-
nected to the supply line; sensors connec-ted to the engine
to measure Pngine operating parame~erSi an electric circuit
connected to the outputs of the sensors and to the engine op-
erative to energize the injector at periods occurring in timed
relation to the operation of the engine and having durations
dependent upon the outputs of said sensors; and means actuated
in response to the pressure of the fuel in said supply line
for inhibiting energization of the injector during starting
of said engine, independent of the output of said electric
circuit, unti]. the pressure of said fuel in said supply line
exceeds a preselected minimum pressure.
In one embodiment of the invention, described here-
in-aEter in more detail, a pressure switch is connected to
the fuel line and is set to switch at a pressure which is some
substantial portion of the normal fuel pressure; for example,
with a system having a normal fuel pressure of 100 psig, the
pressure switch may be set to change outputs at 70 psig. A
thermistor supported in proximity to the engine provides the
variable width pulse generators with an electrical signal pro-
portional to engine temperature. This siynal is also compared
to a reference value to derive a signal indicative o~ whether
the engine temperature is above a predetermined level, below
normal hot engine temperature. The system includes logic which
receives the output of -the pressure switch and the temperature
signal and acts to prevent $he genera-
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tion of actuating pulses for the injectors when the pressure is
below the level at which the switch actuates and the engine temp-
erature is above the comparator level.
In another embodiment of the invention circuitry could be
provided for comparing continuous functions of pressure and tem-
perature so that the injectors would be inhibited at relatively
low engine temperatures if the fuel pressure was very low and at
higher temperatures if the fuel pressure was somewhat higher but
still below full pressure.
The system prevents the injectors from operating while
the engine is being cranked during a hot start until the booster
or fuel pump raises the pressure in the fuel line above the
required fuel pressure. This will typically only require a few
turns of the cranking motor. On continued cranking, the injectors
are energized and the fuel flow through the injectors should be
sufficient to create a fuel-ai-r mi~ture which will sustain com-
bustion, preventing the unburned fuel from being pumped into the
engine exhaust.
Other objectives, advantages and applications of the
present invention will be made apparent by the following detailed
description of a preferred embodiment oE the invention. The
description makes reference to the accompanying drawings in which:
FIGURE 1 is a partially schematic, partially block dia
gram of a fuel ignition system for an internal combustion engine,
forming the prefered embodiment of the invention;
FIGURE 2 is a more detailed schematic diagram of the
circuitry of the present invention which measures engine tempera~
ture and fuel line pressure to inhibit fuel injection during high
temperature, low pressure starting conditions.
Referring to the dra~ings, FIGURE 1 schematically illus-
trates a system for providing fuel under a high~ relatively con-
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stant pressure to eight fuel injectors or transducers 10 arranged
to provide controlled bursts of fuel to the intake valve areas of
an eight cylinder internal combustion engine, as well as relevant
portions of the ignition system. The injectors 10 may be of any
well-known type such as those disclosed in my U.S. Patent 3,~12,718.
Electric signals applied to the injectors 10 through wires 12 open
the injectors for controlled periods of time based on measured
engine operating conditions, such as manifold vacuum pressurer
engine temperature, atmospheric pressure and the like. The
quantity of fuel provided by the injector during this signal
period is a function of the pressure at the injector.
Fuel is provided to the injectors by a pair of conduits
14 termed fuel rails~ Fuel for feeding the rails is derived from a
fuel tank 16. A pump 18 receives fuel from the tank 16 through a
one-way valve 17 and operates to feed fuel from the tank through
a one-way valve 20. The pump 18 may be electrically powered or
driven by the engine in the manner of a conventional automotive
fuel pump. It must be capable of pumping fuel at a volumetric
rate in excess of the engine requirements at the maximum throttle
opening. For a relatively large 8-cyclinder engine this may be
in excess of 25 gallons per hour. The outlet pressure of the pump
18 may be substantially lower than the 25-50 pounds per square
inch provided by fuel pumps for typical injection fuel systems of
the prior art. In a preferred embodiment of the system a 5-10
pound per square inch outlet pressure will suffice. This pressure
need not be well regulated and may vary with engine speed. Accord-
ingly, the pump 18 should be substantially simpler and lower in
cost than fuel pumps used with previous injection systems.
A fuel pressure booster and regulator generally indicated
at 22 receives fuel passed through the one-way valve 20 from pump
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18. The booster and regulator is schematically illustrated as
comprising a piston 24 movable within a cylinder 26 and biased
by a spring 28. The spring biases the piston in a direction as
to move the piston 24 to contract the volume of the cylinder 26
in communication with the fuel line 30. This increases the fluid
pressure in the fuel line 30. The one~way valve 20 prevents this
increase in pressure from forcing a reverse flow to the pump 18. ::
A reset mechanism 32 is schematically illustrated as
being connected to the piston 24 to periodically move the piston
against the bias of the spring 28 to enlarge the volume of the
cylinder 26 in communication with the fuel line 30. The reset
mechanism is cocked once each engine cycle by the engine cam
shaft 33. This lowers the pressure in the fuel line 30 and allows
momentary flow from the pump 18 through the one-way valve 20.
A second one-way valve 34 is connected downstream of
the booster and regulator 22. When the piston 24 moves under the
bias of the spring 28 to contract the volume of the cylinder 26,
the valve allows the resulting high or elevated pressure to
communicate with a fuel line 36 that connects to the fuel rails
20 14, thus imposing this higher pressure on the rails. When the ~.
reset mechanism 32 withdraws the piston against the force of the
spring 28, allowing the pump 18 to force fuel into the low-pres-
sure fuel line 30, the one-way valve 34 prevents backflow in the ~:
high pressure fuel line 36 toward the pressure booster 22 and ~hus
maintains the high fluid pressure in the rails 14. In alternative
embodiments of the invention a conventional high pressure regu-
lated fuel pump could replace the booster and regulator 32.
Optionally, the far ends of the rails are connected
together by a fuel line 38 to form a closed circuit. A constant
bleed one-way valve 40 connects the fuel. line 38 back to the fuel
tank 16.
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A fluid wave regulator or converter 42 is connected to
the fluid line immediately upstream of the valve 20. The conver-
ter is essentially of -the same type disclosed in my U.S. Patent
3,507,263. Schematically, it comprises an enclosed volume 44
separated from the fluid line by an elastic diaphragm 46. The
diaphragm 46 assumes a position wherein the forces on its opposite
sides are equal, thus when the line pressure increases, the dia-
phragm moves to contract the volume of the chamber 44 and thus
pressurize the fluid sealed within that volume. Conversely, when
the line pressure Ealls the diaphragm moves to expand the sealed
volume. When the diaphragm 46 moves outwardly in response to a
lowering in the fluid pressure in the line it effectively pumps
a volume of fluid into the line, tending to raise the line pres-
sure. Conversely, when the diaphragm contracts in response to an
increase in line pressure it increases the flow volume connected
to the line and thus tends to decrease the pressure. The conver-
ter 42 thus acts as a flow regulator.
When the piston 24 is retracted against the bias of the
spring 28 by the unit 32 so that the pressure in the line 30 falls
below the outlet pressure of the pump 18, and the flow valve 20
opens, the decrease in pressure at the inlet to the converter 42
causes the diaphragm 46 to expand and supply a volume of fuel
which replenishes the chamber 26. In the absence of this device
the sharp low pressure wave generated by expansion of the cylinder
26 might vaporize the fuel in the line between the pump and the
booster.
A similar regulator or converter 48 is connected to the
fuel line immediately downstream of the uni-directional valve 34.
This converter provides a pressurized fuel source to the line
during the short interval when the piston 24 is resetting and
accordingly the valve 34 is isolating the line 30 from the line
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36. The converter 18 also acts as a cushion to minimize the
travel of expansion and compression waves through the line 36.
In the preEerred embodiment of the invention a pair of
pressure converters 52 and 54 are connected adjacent to the input
ends of the fuel rails 14. A second pair of converters 56 and 58
are connected adjacent to the outlet ends of the Euel rails, where
they connect to the common fuel line 38. These converters all
similarly act to regulate the pressure in the rails by cancelling
pressure waves created in the system by injection of fluid from
the booster 22 or ejection of fluid through the injectors 10.
FIGURE 1 also illustrates the circuitry for providing
electrical power to the coils of the injector valves 10 over lines
12. One of the injectors 10 is illustrated as having a coil 60.
Considering the circuitry that derives the energization pulses for
this coil, the ignition system includes a distributor generally
indicated at 62 having an arm 64 rotated in timed relation to the
engine operation to sequentially move into position with contacts
that are connected to the engine spark plugs 66, only one of which
is illustrated. The arm 64 is connected to the secondary of an
ignition coil, generally indicated at 68, having its primary
connected to the vehicle battery 70 through a pair of engine
actuated breaker points 72. The breaker points are shunted by a
capacitor 74. -
The breaker points are also connected to a counter 76
forming part of the injector circuitry~ The counter is advanced
by one count each time the breaker points 72 close. The counter
76 has a plurality of output lines 78 which connect to a number
of variable width pulse genera-tors 80, only one of which is illus-
trated. The various lines 78 are sequentially energi~ed as the
counter advances so tha-t each line is energized once each engine
cycle.
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The variable width pulse generators each receive outputs
from a group of engine sensors 82 which measure such operating
variables as manifold pressure and the like. Each variable width
pulse generator also receives an electrical output from a thermis-
tor 82 supported relative to the engine to experience the engine
temperature. The thermistor 84 is illustrated separately from the
other engine sensors 82 because of its roll in the low pressure,
high engine temperature inhibit circuitry.
The output of the variable width pulse generators 80
are provided to gates 86 and the outputs of the gates constitute
the lines 12 which energize the injectors 10.
The gates 86 are controlled by an injection inhibit
circuit 8~. Only a single injection inhibit circuit services the
gates 86 associated with each of the variable width pulse genera-
tors 80. The injection inhibit circuit 88 has inputs from the
thermistor 84 and from a pressure switch 90 connected to the fuel
line 14. The switch 90 preferably closes when the pressure in the
line 14 is above a predetermined Lraction of normal oepratiny line
pressure. In the case of the preferred embodiment, the normal
20 operating line pressure may be 100 psi and the switch 90 may close
when the pressure exceeds 65 psi. The injection inhibit circuit
88 can, alternatively, be provided with an input from the pressure
switch 90 solely, making it operative in response to pressure of
; the fuel in line 14 to inhibit energization of the injector during
starting of the engine until the fuel pressure exceeds a preselec-
ted minimum pressure in the order of about 65 psi.
The injection inhibit circuit 88 processes the output
of the switch 90 and of the thermistor 84 to control the gate 86u
The control is such that the gate 86 passes output pulses from the
generator 80 to the injector coil 60 as long as the pressure switch
is closed. When the pressure switch is open, indicating a pres-
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sure in the line 14 of less than 65 psi, the gate 86 still passesinjector signals if the output of the thermistor 84 is such as to
indicate that the temperature of the engine is below a predeter-
mined value. In the preferred embodiment of the invention this
value may be approximately 150F as compared to a normal engine
operating temperature of about 200F.
When the pressure in the line 14 is less than 65 psi
and the engine temperature is above 150F the gate 86 is energized
by the circuit 88 to prevent the application of firing pulses from
the generator 80 to the coil 60. This condition occurs when the
engine is being restarted a relatively short period of time after
it stopped while at or near operating temperature; i.e., within
5-20 minutes or thereabouts, depending upon the ambient temperature.
Were the injectors not to be inhibited during this time the reduced
~uel quantity that they would provide to the cylinders as a result
of the lowered pressure in the line 14 would likely not result in
a rich enough fuel/air ratio to achieve ignition and the unburned
hydrocarbon vapors would be pumped out of the engine exhaust.
FIGURE 2 illustrates the circuitry of the injection
inhibit device 88 and its associated components in greater detail.
The thermistor 84 is connected in series with a resis-
tance 100 between a positive voltage provided by a power supply
and ground so that the two act as a voltage divider. The mid-
p~int of this voltage divider, which experiences a voltage depen-
dent upon the resistance of the thermistor 84, is applied to one
terminal of an operational amplifier 102 connected to a comparator
mode. The reference input to the comparator 102 is provided by a
voltage divider consisting of the series combination of two resis-
tances 104 and 106. One end of resistance 104 is connected to
-~ 30 ground and one end of resistance 106 is connected to a positive
reference voltage. Resistance 104 is shunted by the pressure
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switch 90 which is closed when the pressure in line 12 exceeds the
predetermined pressure such as 65 psig. When the pressure is in
: excess of that value the switch 90 is closed and the comparator
ln2 cannot provide a high output, independent of the resistance
of the thermistor 84~ However, when the pressure is above 65 psi,
so that the switch 90 is open, and the engine temperature and thus
the thermistor temperature are above a predetermined value, such
as 150F, the voltage at the connection between the thermistor 84
: and the resistance 100 will exceed the reference voltage and will
provide an output from the comparator 102. This voltage is applied
to the gates 86, one for each engine cylinder, through a plurality
of isolating diodes 106. When the gates are activated by outputs
from the comparator 102 the output pulses from the variable width
pulse generators 80 are applied to the coils 60 of the i.njector
10. When the fuel line pressure is below the predetermined value
and the engine temperature is above the comparator value, the
output of the comparator 102 ~ill be such ~ha~ the gates 86 will
block pulses from the variable width generators from being applied
to the injectors.
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