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Claims  |
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What is claimed is:
1. An electronic fuel injection control system of the type having a
plurality of fuel injection valves, each valve operated by an
electromagnetic solenoid, the control system comprising:
at least one driver circuit for supplying power to a selected solenoid;
at least one control circuit for providing controlled operation of the
selected solenoid;
a multiplexing means for selectively interconnecting the at least one
driver circuit and the at least one control circuit to the terminals of
the selected solenoid for selectively energizing the selected solenoid,
the means including:
a first switch array having at least two switches selectively
interconnecting at least one driver circuit to a first terminal of the
solenoids; and
a second switch array having at least two switches selectively
interconnecting at least one control circuit to a second terminal of the
solenoids;
the multiplexing means being interconnected among the at least one driver
circuit, the at least one control circuit, and the solenoids so that
closure of any single switch from each switch array uniquely selects and
energizes a single solenoid.
2. The control system according to claim 1, wherein the multiplexing means
is interconnected among the at least one driver circuit, the at least one
control circuit, and the solenoids, in such a way that the number of
control circuits is less than the number of solenoids.
3. The control system according to claim 1, wherein the multiplexing means
is interconnected among the at least one driver circuit, the at least one
control circuit, and the solenoids, in such a way that the number of
driver circuits is less than the number of solenoids.
4. The control system according to claim 1, wherein the product of the
number of driver circuits multiplied by the number of control circuits is
equal to the number of solenoids.
5. The control system according to claim 4, wherein the switches of the
driver and control circuits are transistor switches.
6. The control system according to claim 1, wherein the product of the
number of driver circuits multiplied by the number of control circuits is
equal to the product of the number of solenoids multiplied by the number
of solenoids that may be energized simultaneously.
7. The control system according to claim 1, further including blocking
diodes in series connection with the solenoids, the blocking diodes
prohibiting reverse current flow through the solenoids.
8. An electronic fuel injection control system of the type having a
plurality of fuel injection valves, each valve operated by an
electromagnetic solenoid, the control system comprising:
at least one driver circuit for supplying power to a drive terminal of the
solenoids, the driver circuit including a current limiting circuit for
safeguarding the system from excessive current surges;
at least one control circuit for controlling the current flow through a
selected solenoid;
a first array of switches electrically connected in series between the
power source and the first terminals of the solenoids; and
a second array of switches electrically connected in series between the
control circuits and a second terminal on the solenoids;
the first and second arrays of switches being interconnected among the
power source, the at least one control circuit, and the solenoids so that
closure of any single switch from each array of switches uniquely selects
and energizes a single solenoid.
9. The control system according to claim 8, wherein the arrays of switches
are interconnected among the power source, the at least one control
circuit, and the solenoids, in such a way that the number of control
circuits is less than the number of solenoids.
10. The control system according to claim 9, wherein the switches of the
first and second arrays of switches are transistor switches.
11. An electronic fuel injection control system of the type having a
plurality of fuel injection valves, each valve operated by an
electromagnetic solenoid, the control system comprising:
at least one driver circuit for supplying power to a drive terminal of the
solenoids, the driver circuit including means for providing continuous
current flow through a selected solenoid throughout the fuel injection
cycle;
at least one control circuit for controlling the current flow through the
selected solenoid, the control circuit being configured to operate by
pulse width modulating the voltage applied across the selected solenoid to
effect a predetermined current flow therethrough;
a first array of transistor switches electrically connected in series
between the at least one driver circuit and the drive terminals of the
solenoids;
a second array of switches electrically connected in series between the
control circuits and control terminals of the solenoids;
the first and second arrays of switches being interconnected among the at
least one driver circuit, the at least one control circuit, and the
solenoids so that closure of any single switch from each array of switches
uniquely selects and energizes a single solenoid; and
a central computer having output signals for selectively operating the
individual transistor switches of each array of switches.
12. An electronic fuel injection control system of the type having a
plurality of fuel injection valves, each valve operated by an
electromagnetic solenoid, the control system comprising:
at least one driver circuit for supplying power to the solenoid during a
fuel injection cycle, the driver circuit including means for collapsing
the magnetic field of a selected solenoid and, thus, rapidly dissipating
the energy stored therein at the end of the fuel injection cycle;
at least one control circuit for providing precision control of the current
flow through the selected solenoid during the fuel injection cycle;
a first array of switches electrically connected in series between the
power source and the first terminals of the solenoids; and
a second array of switches electrically connected in series between the
control circuits and a second terminal on the solenoids;
the first and second arrays of switches being interconnected among the
power source, the at least one control circuit, and the solenoids so that
closure of any single switch from each array of switches uniquely selects
and energizes a single solenoid.
13. The electronic fuel injection control system according to claim 12,
wherein the at least one driver circuit further includes a means for
maintaining continuous current flow through the selected solenoid
throughout the fuel injection cycle.
14. The electronic fuel injection control system according to claim 13,
wherein the means for maintaining continuous current flow includes a
flyback diode and a driver switch.
15. The electronic fuel injection control system according to claim 14,
wherein a closed current loop for maintaining current flow through the
selected solenoid is formed by the flyback diode, the solenoid, and the
driver switch, when the driver switch is in the closed position.
16. The electronic fuel injection control system according to claim 12,
wherein the means for collapsing the magnetic field includes a speedup
diode, a flyback diode, and a driver switch.
17. The electronic fuel injection control system according to claim 16,
wherein a closed current loop for dissipating the energy stored in the
selected solenoid is formed by the speedup diode, the solenoid, the
flyback diode, and a power supply, when the driver switch is in the open
position.
18. The electronic fuel injection control system according to claim 12,
further including blocking diodes in series connection with the solenoids,
the blocking diodes prohibiting reverse current flow through the
solenoids. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Art
The present invention relates to electronic fuel injection systems, and
more particularly, to an improved electronic fuel injection control system
for multi-cylinder fuel injection control in large combustion engines.
2. Discussion of the Related Art
As is well known, electronic fuel injection systems operate by controlling
a solenoid to open and close a fuel injection valve, where the fuel
injection valve is electromagnetically coupled to the solenoid. When the
valve is opened, fuel is injected into a cylinder bore. In its simplest
form, such a fuel injection valve may be opened by applying a constant
voltage across the terminals of the solenoid, thereby energizing the
solenoid and opening the valve. However, and as described in copending
U.S. patent application S/N 08/083,613 (the '613 application)--filed Jun.
28, 1993, now U.S. Pat. No. 5,398,724 issued Mar. 21, 1995, entitled High
Speed Electrically Actuated Gaseous Fuel Admission Valve, assigned to the
assignee of the present invention, and hereby incorporated by
reference--in very large internal combustion engines it is desired to
provide balanced operation of the solenoids for each cylinder. This
balanced operation is provided in part by circuitry adapted to control the
current flow through the solenoid, and in part through a central
controller which generates electronic control signals for operating the
control circuitry.
More specifically, the control circuitry includes separate driver and
control circuits disposed on opposite sides of the solenoids. The driver
circuit delivers a current-limited energizing voltage of approximately one
hundred volts to one terminal (hereinafter "drive terminal") of each
solenoid. The control circuit is electrically connected to the other
terminal (hereinafter "control terminal") of each solenoid, and operates
to complete the current path through the solenoid by controllably and
intermittently grounding the control terminal so as to effect a
predetermined current flow through the solenoid. Both the driver and
control circuits have an input signal generated by a central or master
controller, which serves to turn on and off the operation of the
respective driver and control circuits.
Typically, such prior art systems have a dedicated driver and control
circuit associated with each solenoid. The driver and control circuits
and, therefore, the solenoids are independently operated and controlled by
the central controller. Some prior art systems are known, however, to have
only a single driver circuit which has its output electrically connected
to the drive terminal of each solenoid. Independent control circuits,
however, remain dedicated to each solenoid in order to maintain
independent control over the individual solenoids.
Regardless of whether the system utilizes a single or multiple driver
circuit, the system operates as follows: Control signals generated by the
central controller are input to the appropriate driver and control
circuits to energize a given solenoid and, thus, open the corresponding
fuel injection valve. Precise and repeated operation of the fuel injection
valve is achieved by effecting tight control over the current through the
solenoid. In this regard, it is desired to open the valve quickly by
initially applying a relatively large magnitude current through the
solenoid. Then, the current is reduced to a lower magnitude holding
current, sufficient to retain the valve in its fully open position.
Finally, rapid closure of the fuel injection valve is achieved by breaking
the current path through the solenoid and quickly dissipating the energy
stored therein.
The precision control of the current through the solenoid and, thus, the
operation of the fuel injection valve described above is achieved by the
control circuit being configured to intermittently ground the control
terminal so as to pulse-width modulate the voltage applied across the
terminals of the solenoid. Since the control circuitry utilized to effect
this current control is duplicated for each solenoid, a more balanced
operation among the cylinders, and thus improved engine operation, is
achieved.
While such systems do provide effective control of large multi-cylinder
internal combustion engines, further improvements are desired. In this
regard, cost is always a significant factor in any system design. It is
observed that the cost associated with the prior art systems is inflated
in some measure due to the replication of the driver and control circuitry
for each cylinder. This replication in circuitry is particularly
noteworthy since, due to the sequential firing of the cylinders, typically
only one solenoid will be energized at any given time. Accordingly, only
one driver and one control circuit will be active at any given time.
Additional shortcomings of the prior art systems are reliability and power
consumption. As the number of system components is increased, the overall
system reliability is decreased, due to the normal lifetime and expected
failure of the individual components. Also, the excessive circuitry
increases the power demands of the system.
The problems highlighted above are further compounded as the number of
engine cylinders is increased. To be sure, many large stationary internal
combustion engines, have sixteen to twenty cylinders. In such systems, the
expense and other shortcomings of the prior art become particularly acute.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide an
electronic fuel injection control system having fewer electronic
components, such as those components comprising the driving and control
circuitry, than systems presently known in the prior art.
A related object of the present invention is to provide an electronic fuel
injection control system having a lower cost than prior systems.
Another object of the present invention is to provide an electronic fuel
injection control system having a reduced circuit board space.
It is still another object of the present invention to provide an
electronic fuel injection control system having a reduced package size,
thereby reducing the system's spatial demands.
Another object of the present invention is to provide an electronic fuel
injection control system having lower power requirements than prior art
systems.
Still another object of the present invention is to provide an electronic
fuel injection control system having an improved reliability over systems
in the prior art.
Yet another object of the present invention is to provide an electronic
fuel injection control system affording more balanced operation among the
fuel injection valves and, thus, yields improved engine performance.
Additional objects, advantages and other novel features of the invention
will be set forth in part in the description that follows and in part will
become apparent to those skilled in the art upon examination of the
following or may be learned with the practice of the invention. The
objects and advantages of the invention may be realized and obtained by
means of the instrumentalities and combinations particularly pointed out
in the appended claims.
To achieve the foregoing and other objects, the present invention is
generally directed to an electronic fuel injection control system of the
type having a plurality of fuel injection valves, wherein each valve is
operated by an electromagnetic solenoid. The control system includes at
least one driver circuit for supplying power to the solenoid, at least one
control circuit for controlling the current passing through the solenoid,
and a multiplexing means for selectively interconnecting the at least one
driver circuit and the at least one control circuit to the terminals of a
selected solenoid for selectively energizing the solenoid. The
multiplexing means includes two switch arrays. The first switch array has
at least one switch that selectively interconnects at least one driver
circuit to a first terminal of the solenoids. The second switch array has
at least one switch selectively interconnecting at least one control
circuit to a second terminal of the solenoids. The multiplexing means is
further characterized in that the two switch arrays are interconnected
among the at least one driver circuit, the at least one control circuit,
and the solenoids so that closure of any single switch from each switch
bank uniquely selects and energizes a single solenoid.
Having summarized the present invention above, the discussion will now be
directed to a presently preferred embodiment of that invention. In a
preferred embodiment, the at least one driver circuit serves to apply a
power source of approximately one hundred volts to the drive terminals of
the solenoids. The driver circuit, however, includes a current limiting
feature that provides circuit protection in the event that the solenoid is
inadvertently shorted to ground. The driver circuit also includes a means
for rapidly dissipating the energy stored in the solenoid so that the fuel
injection valve is quickly closed at the end of the fuel injection cycle.
The at least one control circuit employs a feedback term to actively
control the current passing through the solenoid. Indeed, each control
circuit includes a switch that serves to intermittently turn the solenoids
on and off by effectively grounding the control terminals thereof.
Specifically, when the driver circuit has applied the voltage of
approximately one hundred volts to the drive terminal of a solenoid, and
the control circuit grounds the control terminal of that solenoid, that
solenoid is turned on so as to pass current through it.
If the control circuit switch were permitted to remain on continuously, the
current passing through the solenoid would far exceed the desired level.
Accordingly, the control circuit utilizes a feedback term to monitor the
current passing through the solenoid and controllably open and close the
switch so as to control the current flow through the solenoid. In this
regard, a separate means is provided to ensure that there is a continuous
current path through the solenoid during the fuel admittance cycle.
Moreover, the inductance of the solenoid ensures that the change in
current flow through the solenoid (e.g., di/dt) is controlled.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings incorporated in and forming a part of the
specification, illustrate several aspects of the present invention, and
together with the description serves to explain the principals of the
invention. In the drawings:
FIG. 1 is a top-level block diagram of a preferred embodiment of the fuel
injection control system of the present invention, as adapted for use in
an eight cylinder engine;
FIG. 2 is a schematic diagram showing the primary circuit elements of both
the driver and control circuits, and the interconnection of these elements
with a selected solenoid;
FIG. 3 is a top-level diagram of a preferred embodiment of the fuel
injection control system of the present invention, as adapted for use in a
twenty cylinder engine, wherein only one cylinder fires at a time;
FIG. 4 is a top-level diagram of a preferred embodiment of the fuel
injection control system of the present invention, as adapted for use in a
twenty cylinder engine, wherein two adjacent cylinders may fire
simultaneously; and
FIG. 5 is a top-level diagram showing an alternative embodiment of the
present invention.
Reference will now be made in detail to various present preferred
embodiments of the invention, examples of which are illustrated in the
accompanying drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a block diagram of a preferred embodiment of the fuel
injection control system of the present invention, as adapted for use in
an eight cylinder engine. In this embodiment, there are two driver
circuits 100 and 102. Each driver circuit has a one hundred volt dc input
103 and 105, and a control input 106 and 107, generated by a central
computer 109 for commanding the driver circuit to apply the one hundred
volt input to a group of drive terminals (the drive terminals are
designated by reference numerals 110 through 117) which include the
selected solenoid.
Four control circuits, 120 through 123 are shown. The control circuits
serve to control the current flow through the operative solenoid. This
current control is achieved by controllably grounding a group of control
terminals (control terminals are designated as 130 through 137) which
include the operative solenoid, so as to pulse width modulate the one
hundred volts supplied from the driver circuit to the drive terminal of
the selected solenoid. That is, when the control terminal of the operative
solenoid is grounded, the one hundred volts applied to the driver terminal
by the driver circuit is then applied across, and thereby energizes, the
solenoid. When, however, the ground connection at the control terminal is
broken, the one hundred volts is no longer applied across the solenoid and
the magnetic field of the solenoid begins to collapse. As will be
described in reference to FIG. 2, means are provided in connection with
the driver circuit to provide a continued current path, so that the energy
stored in the solenoid may be dissipated. In this regard, the control
circuit may intermittently establish and break the ground connection with
the control terminal of the operative solenoid, but, during the operative
time of the fuel injection cycle as determined by the central computer
109, the system nevertheless maintains a continuous flow of current
through the solenoid sufficient to retain the fuel injection valve in its
fully open position.
Each control circuit has a control signal input 140 through 143. These
control signals 140-143 combine with the driver circuit control signals
106 and 107 to select the operable solenoid. More particularly, and as
shown in the figure, the output of driver circuit #1 100 is electrically
connected to the drive terminal of solenoids S1, S2, S3, and S4. The
output of driver circuit #2 102 is electrically connected to the drive
terminal of solenoids S5, S6, S7, and S8. In similar fashion, the outputs
of the control circuits are connected to the control terminals of the
solenoids as follows: control circuit #1 120 is connected to S1 and S5;
control circuit #2 121 is connected to S2 and S6; control circuit #3 122
is connected to S3 and S7; and control circuit #4 123 is connected to S4
and S7.
As previously mentioned, and as described in the '613 application, there is
a class of engines, such as large stationary power plant engines, where
significant advantages can be achieved from precise control of the fuel
injection cycle. In this regard, the word "precise" is used to distinguish
the general level of precision normally associated with, for example,
automotive applications. In this class of engines, precise control of the
fuel injection cycle is achieved by opening the fuel injection valve at a
given point in time by applying a relatively large magnitude current to
the solenoid, retaining the valve in the open position with a smaller
magnitude holding current, and rapidly closing the valve at the proper
time instant.
In this environment, separate control and driver circuits are particularly
desired. As previously described, the driver circuit provides a
current-limited supply voltage to the drive terminals of the solenoids,
and the control circuit operates to control the current flow therethrough.
Separate means are provided and associated with the driver circuit,
however, to: (1) maintain a continuous flow of current through the
solenoid during those times within the fuel injection cycle that the
control circuit breaks the ground connection with the solenoid so as to
decrease the current flow therethrough; and (2) rapidly dissipate the
energy stored in the solenoid at the end of the fuel injection cycle, so
that swift closure of the fuel injection valve is achieved. For these
reasons, it is preferred to have separate control and driver circuits
disposed on opposing sides of the solenoids.
In this environment, the invention resides in associating multiplexing
means with switches in the respective control and driver circuits.
Accordingly, a multiplexing means having first and second switch arrays
selectively interconnects the driver circuits 100 and 102 and the control
circuits 120-123 to the drive and control terminals, respectively, of the
solenoids. The first switch array includes switches SW1 and SW2, which are
controlled by the central computer 109 and form a part of the driver
circuits. Similarly, the second switch array includes switches SW3-SW6,
which are controlled by the central computer 109 and form a part of the
control circuits. In a preferred embodiment, the switches SW1-SW6 are
implemented as transistor switches.
The multiplexing means of the preferred embodiment also includes the
control logic and control signals associated with the central computer 109
that are responsible for actuating the appropriate driver and control
circuits at the proper time during the fuel injection cycle.
Current blocking diodes D1-D8 are electrically connected in series with
solenoids S1-S8 to insure unidirectional current flow through the
solenoids. As will be understood from the discussion that follows, the
blocking diodes D1-D8 help insure that additional solenoids are not
energized. The blocking diodes D1-D8 further serve to maintain the
integrity of the current control through the operative solenoid.
In order to energize solenoid S1, for example and in view of the
multiplexing means described above, the computer 109 sends the appropriate
control signals to driver circuit #1 100 and control circuit #1 120, which
close switches SW1 and SW3, thereby creating a direct current path through
S1. As another example, to create a direct current path through, and
thereby energize, solenoid S7, the computer 109 sends the appropriate
control signals to driver circuit #2 102 and control circuit #3 122, which
close switches SW2 and SW5.
It should be appreciated that without the blocking diodes D1-D8, when
switches SW1 and SW3 are closed to create a direct current path through
S1, additional current paths between driver circuit #1 and control circuit
#1 would be created. For example, one additional current path would be
created through S2 in the forward direction, S6 in the reverse direction,
and S5 in the forward direction. Another current path would be created
through S3 in the forward direction, S7 in the reverse direction, and S5
in the forward direction. A third additional current path would be created
through S4 in the forward direction, S8 in the reverse direction, and S5
in the forwards direction. Similar stray current paths would also be
created when other solenoids are selected.
Undesirably, the current passing through the additional paths may be
sufficient to energize other solenoids (i.e., S2-S8), particularly
solenoid S5 which passes current from all three additional paths.
Furthermore, the control circuits are unnecessarily complicated since they
must account for the accumulation of all current paths, rather than merely
the single direct current path. Inclusion of the blocking diodes D1-D8,
therefore, advantageously eliminates the additional current paths and thus
the potential to energize other solenoids. Moreover, the blocking diodes
simplify the control circuits.
In reference to the first example presented above, it is understood that
when the computer 109 sends the appropriate control signal to driver
circuit #1 100, the one hundred volt dc voltage is applied by the driver
circuit #1 100 to the drive terminal of solenoids S1, S2, S3, and S4.
Similarly, when the computer 109 sends the appropriate control signal to
control circuit #1 120, the output of that circuit intermittently grounds
the control terminals of S1 and S5. Since, however, the control terminals
of S2 through S4 are floating (i.e., not grounded), the voltage applied to
the drive terminals 111 through 113 is of no consequence. Similarly, when
the drive terminals of S5 through S8 are floating, the fact that the
control terminal 134 of solenoid S5 is grounded is of no consequence.
The following table illustrates the driver and control circuits which must
be activated in order to energize any given solenoid:
______________________________________
Solenoid Driver Circuit Control Circuit
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S1 # 1 (item 100) # 1 (item 120)
S2 # 1 (item 100) # 2 (item 121)
S3 # 1 (item 100) # 3 (item 122)
S4 # 1 (item 100) # 4 (item 123)
S5 # 2 (item 102) # 1 (item 120)
S6 # 2 (item 102) # 2 (item 121)
S7 # 2 (item 102) # 3 (item 122)
S8 # 2 (item 102) # 4 (item 123)
______________________________________
Multiplexing the output signals of the driver and control circuits in the
manner shown in the figure and described above allows the total number of
circuit components to be greatly reduced from the number required by prior
art systems, in which the sophisticated control circuitry was duplicated
for each solenoid.
Assume now that it is desired to energize solenoid S1, whereby driver
circuit #1 and control circuit #1 are activated. In this regard, reference
is made to FIG. 2 to discuss the detailed operation of the driver and
control circuitry of a preferred embodiment of the present invention. The
particular control and driver circuits 120 and 100 of a preferred
embodiment are shown in FIG. 2 as superimposed in broken lines.
The control circuit has a single control input 200, and the driver circuit
has a single control input 300. Input signal 200 has a leading edge 201, a
trailing edge 202, and a time duration between the leading and trailing
edges designated as "W". Similarly, input signal 300 has a leading edge
301, a trailing edge 302, and a time duration "X". The input signals 200
and 300 dictate the controlled energization of the solenoid 182 and, thus,
the open and close instances of the fuel injection valve 151.
The input pulse 300 occurs at the same time that the input pulse 200
occurs. The leading edge 201 of pulse 200 is coincident with the leading
edge 301 of pulse 300, and the trailing edge 202 of pulse 200 is
coincident with the trailing edge 302 of pulse 300. Indeed, the pulses 200
and 300 differ only in respect to their repetition frequency, in that
pulse 200 will be sent to control circuit 120 (see FIG. 1) when energizing
solenoids S1 and S5, whereas pulse 300 will be sent to driver circuit 100
(see FIG. 1) when energizing solenoids S1, S2, S3, and S4.
The pulses are produced by the central computer controller 109, but contain
insufficient energy for directly operating the fuel injection valve. In
addition, simple digital pulses would not be capable of realizing the
exacting current control through the solenoid that is required to achieve
the balanced fuel injection sought by the illustrated embodiment.
Consequently, driver circuitry is provided for driving the electromagnetic
circuitry of the solenoid 182 in response to the pulses 200 and 300.
The pulse 200 is initially passed through a timer 210. In the preferred
embodiment, the timer is a one millisecond timer, the output of which is
passed through biasing circuitry to the non-inverting input of a current
control amplifier 211. The purpose of the one millisecond timer 210 is to
divide the width "W" of the input pulse 200 into two intervals, a pull-in
phase (designated "P") of one millisecond, which provides the solenoid 182
with a high energy pull-in current to assure rapid valve opening, and a
hold-in phase (designated "H") which provides a hold-in current for
maintaining the fuel injection valve in the open position.
The one millisecond pulse 212 and the input pulse 200 are added together
through the summing resistors 223 and 224 and filtered by capacitor 222 to
create the current demand pulse 219. Thus, the composite pulse 219 is seen
to have two levels, a first or higher level 215 which, in the illustrated
embodiment of the invention, is representative of an output current of
fourteen amperes, and a second or lower level 214 which, in the same
illustrated embodiment, is representative of an output current of four
amperes.
The "P" pull-in phase in this preferred embodiment is set to be about one
millisecond, and has a leading edge 216 which is coincident with the
leading edge 201 of the input pulse. The trailing edge 218 of the one
millisecond pulse then occurs one millisecond after the leading edge 216,
providing an interval of one millisecond for a fourteen ampere drive to
the solenoid 182. That one millisecond, fourteen ampere interval "P" is
then followed by a hold-in phase "H" in which the drive current is
established at four amperes.
The current control amplifier 211 has an input coupled to the inverting
input of the amplifier which is produced by a current sensing resistor 220
which, as will be described below, senses the magnitude of the current
passing through the solenoid 182. That signal is passed through a input
resistor 221 and coupled to the inverting input 211, where it is matched
with the current demand pulse 219.
The amplifier 211 has an output that drives a pulse width modulator 226
which controllably closes a control switch 227 to effectively ground the
control terminal 130 of the solenoid 182 through resistor 220. In a
preferred embodiment, the valve of resistor 220 is 0.1 Ohm. Therefore,
during interval "P" when fourteen amperes of current are drawn through
solenoid 182 and resistor 220, there is a voltage drop of only 1.4 volts
across resistor 220. Thus, this 1.4 volts at the control terminal 130 is
effectively ground in reference to the approximately 100 volts applied to
the drive terminal 110.
The current drawn through the current sensing resistor 220 matches the
demand current 219 at the capacitor 222. Due to the two level nature of
the current demand pulse 219, the current sensed in the resistor 220 is
first at a high level (fourteen amperes in the illustrated embodiment) for
a period of one millisecond, then reverts to a lower level (four amperes
in the illustrated embodiment) for the duration of the width of the input
pulse 200. This two interval drive pulse 219 results in a high current
being passed through the solenoid 182 initially (on the order of fourteen
amperes) thereby insuring a rapid opening of the fuel injection valve.
Then, to avoid any damage to the circuit's components which might result
from a sustained current of this level and to enable the rapid collapse of
the magnetic field in the solenoid 182, the current is dropped in the
hold-in phase to a level (four amperes in the illustrated embodiment),
which is still sufficient to hold the fuel injection valve fully open.
Advantageously, this lower hold-in current also results in less heat
build-up in the driver circuitry than would occur with higher current
levels. Since power consumption is directly related to the square of the
current, such a current reduction provides a drastic reduction in power.
Thus, the two phase current control not only affords rapid opening and
closing of the fuel injection valve, but also achieves a substantial
savings in power consumption and improved thermal conditions.
In the illustrated embodiment, the pulse width modulator 226 is a circuit
which operates at a relatively high frequency to produce an output voltage
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