Fast response two coil solenoid driver

A system for energizing a fuel injector, of a fuel injected engine having a metering chamber and a two coil solenoid operatively situated thereto for permitting a controlled quantity of fuel to flow therein. The system includes a pulse generator for generating a plurality of timing and fuel metering pulse width signals in synchronism with the combustion process within a cylinder of the engine, a voltage boost circuit responsive to timing and metering pulses and means for transferring, in seriatim energy from the boost circuit to a first low inductance pull-in coil and for energizing a second high inductance hold coil.

BRIEF DESCRIPTION OF THE PRIOR ART AND SUMMARY OF THE INVENTION 
The invention relates to a driver circuit and method of controlling the 
modes of operation of a solenoid having two coils. More particularly, the 
invention relates to a fuel injection control system for controlling the 
operation of an electromagnetic fuel injector for internal combustion 
diesel engines. 
Many techniques have been developed for controlling the operation of 
electromagnetic solenoids. These techniques often result in solenoid 
operation having a sluggish response time. When the speed of operation of 
the solenoid is an important feature the solenoid is often overdriven 
which results in excessive heating. Heat dissipation is also a problem 
with solenoids that have long duty cycles. Fast opening solenoids that are 
characterized by low power dissipation and low current requirements are 
significant considerations when incorporated within the mobile environment 
of an automotive fuel injection system to prevent excessive current drain 
from the battery. A reduced current drain is especially important during 
cold starts because of the lowered capacity of the battery. 
It is desirable to control injector operation to provide repeatable 
intervals of fuel injection throughout the dynamic range of engine 
operating conditions. Errors in the amount of fuel that is injected into 
each of the combustion chambers of an engine, due to a lack of 
repeatability, will produce degraded performance, poor acceleration, smoke 
and noxious exhaust fumes. 
It is an object of the present invention to rapidly open a solenoid having 
a pull-in and a hold coil. It is a further object of the present invention 
to provide a driving circuit for a two coil electromagnetic fuel injector. 
Another object of the invention is to accurately meter fuel to an 
injector, having a metering chamber therein. A further object of the 
present invention is to operate a plurality of fuel injectors at reduced 
levels of heat and current drain. A feature of the present invention is 
the use of a two coil solenoid in cooperation with a driver circuit. The 
two coil solenoid allows the freedom of using a first low inductance 
pull-in coil for fast pull-in and a many turn, high inductance hold coil 
for low current draw during the period of fuel metering during which time 
the solenoid is held open. 
According to the specific circuitry described in detail below, the 
invention is a system including a driver circuit that is used to activate 
a solenoid of a diesel fuel injector. The solenoid being of the type 
comprising at least two coils, including a pull-in coil and a hold coil 
that are magnetically coupled one to the other. The solenoid further 
having a plunger that is movable in response to the magnetic fields 
generated by each coil. The fuel injector is of the type having a metering 
chamber and a solenoid that is operatively connected thereto to permit 
fuel to flow into the metering chamber prior to injection of fuel into the 
engine in response to solenoid control or activation signals. The driver 
circuit includes a signal generator including an electronic control 
circuit responsive to at least one engine operating parameter for 
generating a plurality of periodic signals that are synchronized to the 
combustion process within each cylinder of the engine. A boost circuit, 
responsive to a first or boost signal and connected to the engine battery 
is used to develop a voltage that is substantially larger than the battery 
voltage. A first switch responsive to a second or pull-in signal and 
connected to the boost circuit and to the pull-in coil is utilized for 
transferring the electrical energy within the boost circuit to the pull-in 
coil to initially move the solenoid plunger to permit fuel to flow into 
the metering chamber; and a second switch, responsive to a variable 
duration third or metering signal to activate the hold coil and to 
maintain or hold the plunger in its activated position at a reduced 
current drain level. 
Many other objects, features and purposes of the invention will be clear 
from the detailed description of the drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
Reference is made to FIG. 1 which illustrates a fuel injection system 20 
comprising an electronic control unit or ECU 22 of a known variety 
connected with a plurality of sensors such as sensors 24, 26 and 28 which 
translate operational parameters of the engine such as crankshaft 
position, temperature and pressure respectively, into input signals for 
the electronic control unit 22. The electronic control unit 22 produces a 
plurality of output signals which are synchronized to an engine event, 
such as the combustion process within each of the combustion chambers or 
cylinders of the engine. The electronic control unit 22 produces a 
plurality of timing and metering signals which transforms the operational 
parameters of the engine into variable metering intervals during which 
time specific quantities of fuel are metered to a metering chambers 52 
within each fuel injector 50 prior to being injected into the 
corresponding cylinders of the internal combustion engine in accordance 
with engine demand. These timing and metering signals are transferred to a 
driver circuit 40 via a plurality of lines such as lines 30, 32 and 34. 
Injector 50 is of the type having a metering chamber 52 and a solenoid 54. 
One such injector containing a metering chamber is disclosed in the 
commonly assigned U.S. Pat. No. 4,281,792 entitled "Single Solenoid Unit 
Injector", by Sisson et al, which is herein incorporated by reference. The 
solenoid comprises a core, a movable plunger 56 operatively situated 
relative to the metering chamber 52 to control fuel flow therein and a 
pull-in coil 62 and a hold coil 64 that are magnetically coupled onto the 
other. The driver circuit 40 is connected to the injector 50 and 
selectively energizes each coil in response to the timing and metering 
pulses. Upon energizing the coils 62 and 64 the plunger 56 is displaced 
for a determinable period thus enabling a determinable quantity of fuel to 
enter the metering chamber 52. Subsequently the fuel in the metering 
chamber 52 is mechanically injected into the engine. The mechanism for 
injecting the fuel is not shown in FIG. 1, however, typical mechanisms are 
illustrated by Sisson et al. 
Reference is made to FIG. 2 which illustrates a more detailed schematic 
diagram of the present invention and more specifically illustrates a 
driver circuit 40 for controlling the operation of an injector 50 having a 
solenoid comprising a first or pull-in coil 62 and a second or hold coil 
64. The driver circuit 40 includes a boost circuit 100 connected to a 
source of potential energy such as battery 102. The boost circuit 100 is 
further adapted to receive at an input terminal a timing signal or boost 
pulse, e.sub.B, transmitted from the electronic control unit 22 via line 
30. This timing signal is a relatively short pulse width signal and serves 
to activate the boost circuit 100 in order to develop a control voltage 
having a magnitude significantly higher than that of the battery voltage 
and to supply this boosted voltage to increase the response time of the 
pull-in coil 62. The output of the boost circuit 100 is connected to one 
terminal 120 of the pull-in coil 62. The other terminal of the pull-in 
coil 62 is connected to ground via a switching means 124 such as through 
the collector emitter path of transistor 126 and a current limiting 
resistor 128. The switching means 124 is adapted to receive, via line 32, 
another pulse such as a turn-on pulse e.sub.p, from the electronic control 
unit 22. One terminal of the hold coil 64 is connected to the pull-in coil 
62 via an isolation diode 130. The other terminal of the hold coil 64 is 
connected to a second switching means 140 which is adapted to receive the 
metering signal, e.sub.H, from the electronic control unit 22 via line 34. 
As illustrated in FIG. 2, the switching means 140 may include a transistor 
142 having its base connected to line 34, its collector connected to the 
hold coil 64 and its emitter connected to ground via a current limiting 
resistor 128. In addition, other coils may be connected to the boost 
circuit 100 and the electronic control unit 22 in a similar manner. 
Heat generation is reduced and boost voltage distribution is simplified by 
winding the pull-in coil 62 and the hold coil 64 about the same magnetic 
core. This arrangement permits a rapid transfer of magnetic and electrical 
energy from the pull-in coil 62 to the hold coil 64. It is desirable to 
fabricate the pull-in coil 62 to be a low inductance coil and the hold 
coil 64 to be a large inductance coil. The utilization of a two coil 
solenoid allows freedom in designing a low inductance pull-in coil 62 for 
fast pull-in response and for designing a many turn, high inductance, low 
resistance hold coil 64 for low power dissipation during the time that 
injector 50 is in a fuel metering mode of operation. 
In general, the operation of the circuit illustrated in FIG. 2 is as 
follows. At some point in time, prior to the injection of fuel from the 
metering chamber (not shown) of the injector 50, the electronic control 
unit 22 will issue, on line 30, a boost pulse signal, e.sub.B, to the 
boost circuit 100. This signal causes the boost circuit 100 to transfer 
energy from the battery 102 to generate a voltage that is significantly 
higher than the battery voltage. The application of this increased voltage 
to the pull-in coil 62 will tend to reduce the time required for the 
build-up of current flow through the pull-in coil 62. As an example, an 
automotive battery voltage will typically produce an output voltage of 
approximately 12 volts, while the output of the boost circuit 100 may be 
in the vicinity of 80 to 150 volts. After the generation of the boost 
pulse, the electronic control unit 22 then generates a short second signal 
of turn-on pulse, e.sub.p, which causes the boosted voltage to be 
transferred to the pull-in coil 62. The turn-on pulse e.sub.p, is 
preferrably phased such that it begins approximately at the time the boost 
pulse e.sub.B terminates. The electronic control unit 22 then generates a 
third signal such as the metering pulse e.sub.H, on line 34 having a 
larger and variable duration. The metering pulse activates the second 
switching means 140 which transfers the electrical energy from the battery 
102 and the pull-in coil 62 to the hold coil 64. The hold coil 64 is 
maintained in an energized state during the entire metering interval 
during which time fuel enters the metering chamber of the injector 50. As 
will be discussed below, the turn-on pulse and the metering pulse may be 
generated simultaneously or time shifted, one relative to the other. 
Reference is briefly made to FIG. 3 which illustrates an alternate two coil 
driver circuit 160. This circuit 160 eliminates the need for the boost 
circuit 100. Circuit 160 includes a pulse width controller 162 which 
functions to modify the duration of the turn-on pulse as a function of 
engine parameters including battery voltage. The pulse width controller 
162 may be implemented as a look up table within the electronic control 
unit 22 or incorporated in the driver circuit 160. The driver circuit 160 
may further include current regulators 164 and 166 to maintain the level 
of pull-in current and of the hold current at regulated values during 
solenoid operation. 
FIG. 4 is a more detailed embodiment of the schematic diagram of FIG. 2. 
More specifically, FIG. 4 illustrates a driver circuit 200 for controlling 
a plurality of injection circuits 250a.-.f, wherein each injection circuit 
250 contains like components having similar reference numerals. The 
structure and method of operation of the driver circuit 200 will be 
explained for one injection circuit 250 is as much as each injection 
circuit is the same. It should be noted that while FIG. 4 illustrates a 
driver circuit communicating with six (6) injection circuits 250, the 
present invention is not so limited. The driver circuit 200 comprising a 
pulsed high voltage generator circuit 202 comprising an inductor or boost 
coil 210, a switching transistor 212 and the blocking diodes 216 and 218. 
The positive terminal of the battery 204 is connected to a first terminal 
of the inductor 210. The other terminal of the inductor 210 is connected 
to the collector of the transistor 212. The emitter of the transistor 212 
is connected to ground through the current limiting resistor 220. The base 
terminal of the transistor 212 is adapted to receive the boost voltage 
pulse (e.sub. B). The cathode terminal of each of the diodes 216 and 218 
are connected together at a junction or node 222. The anode terminal of 
the diode 216 is connected to the junction between the inductor 210 and 
the switching transistor 212. The anode terminal of the diode 218 is 
connected to the first terminal of the inductor 210 and to the positive 
terminal of the battery 204. One terminal of the pull-in coil 230a is 
connected to the collector of the transistor 240a. The base terminal of 
the transistor 240a is adapted to receive the pull-in pulse, e.sub.p, from 
the ECU 22. The emitter of the transistor 240a is connected to one 
terminal of the current limiting resistor 220. In addition, the other 
terminal of the pull-in coil 230a is connected through the isolation diode 
242a to one terminal of the hold coil 244a. The other terminal of the hold 
coil 244a is connected through the collector-emitter path of the switching 
transistor 246a to a current limiting resistor 248a. The base of the 
switching transistor 246a is adapted to receive the variable duration 
metering pulse e.sub.H. If the pull-in pulse (e.sub.p) and boost voltage 
pulse (e.sub.B) are not properly synchronized it may be necessary to 
utilize an additional blocking diode 219 (shown in phantom lines) inserted 
between the first terminal of the inductor or boost coil 210 and the 
cathode of the diode 218 to protect the battery 204 from voltage surges. 
A feature of the present invention is that by utilizing a solenoid having 
two coils such as coils 230a and 244a that are wound about a common core, 
heat generation can be minimized and the design of the solenoid boost 
voltage generator 202 is greatly simplified. The operation of the circuit 
shown in FIG. 4 is similar to that of FIG. 2 and is described in 
conjunction with the timing diagram of FIG. 5. 
FIG. 5 illustrates one complete cycle of operation which corresponds to two 
rotations (720 degrees) of the engine crankshaft. The e.sub.B pulse (line 
1, FIG. 5) is a periodically recurring boost voltage timing signal for 
each cylinder that is generated in synchronism with the combustion process 
for that cylinder. At the beginning of each pulse interval transistor 212 
is made conductive therein creating a current charging path from battery 
204 to ground through inductor or boost coil 210 and the current limiting 
resistor 220. After a predetermined interval, as determined by the pulse 
width of the e.sub.B pulse, the transistor 212 is turned off thereby 
generating the boosted value of voltage and transistors 240 and 246 are 
simultaneously turned on by the pull-in and metering pulses (lines 2 and 
3, FIG. 5). By virtue of turning off the transistor 212 and turning on the 
transistors 230a and 244a, the current flowing through the boost coil 210 
and current from the battery 204 is given an alternative current flow 
path. The boost current now flows to ground through the pull-in coil 230a, 
the transistor 240a and through the resistor 220. Because the pull-in coil 
230 has been chosen to be a low inductance high current coil, a high 
valued, fast rising electromagnetic force is created to move the armature 
of the solenoid thereby permitting fuel to begin to flow into the metering 
chamber. It is not necessary to stagger the application of the pull-in and 
metering pulses since current will not initially flow through the hold 
coil 244a because of its high inductance. A magnetic flux having a 
magnitude in excess of that necessary to hold the armature in an activated 
position will be established in the solenoid core by virtue of the current 
flowing through the pull-in coil 230 at the end of the pull-in pulse. The 
duration of each metering pulse (line 3, FIG. 5) is dictated by the 
instantaneous performance requirements of the engine and by the flow 
capacity of the fuel system components. As an example, the duration of the 
metering pulse may be as short as the duration between successive boost 
pulses or span a number of such pulses. The physical injection of fuel 
into each cylinder occurs after the termination of, and before the next 
metering pulse for a particular cylinder. The precise timing of the 
initiation of fuel injection varies with engine demand and engine control 
philosophy. Lines 4-13 of FIG. 5 illustrate the pull-in and metering 
pulse, for the other cylinders of a six cylinder engine. 
Many changes and modifications in the above described embodiment of the 
invention can of course be carried out without departing from the scope 
thereof. Accordingly, that scope is intended to be limited only by the 
scope of the appended claims.