Electricity: electrical systems and devices – Control circuits for electromagnetic devices – Systems for magnetizing – demagnetizing – or controlling the...
Reexamination Certificate
2000-01-14
2003-06-10
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
Systems for magnetizing, demagnetizing, or controlling the...
C361S160000
Reexamination Certificate
active
06577488
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronically controlled inductive load actuator, and more particularly an electronically controlled diesel fuel injector.
2. Discussion of Related Art
From the 1960's to the present there has been increasing awareness of the effect that vehicular emissions have on the environment. Accordingly, increasingly demanding emissions standards have been imposed on vehicles in a number of countries, including the United States.
One way that has been used in the past to control emissions in vehicles is to have an accurate knowledge and control of the start and stop of fuel injection as well as the amount of fuel delivery. One method of such control is to have a rapid rise/fall in current enabling the fuel injection valve to move from a closed to an open position in a very short predictable period of time. This allows for an accurate understanding of the start and stop of fuel injection. Also the faster the armature moves, the more accurate the prediction of fuel flow, especially with the demand for higher fuel rail pressures.
In the past, the rapid rise in current, if the vehicle battery could not provide it, was provided by a boost supply that comprised a capacitor that stored the energy required for the rapid rise in current. The power output of the boost supply and the choice in capacitance involved an understanding of the required current rise rate, load inductance and the minimum spacing between fuel injection events. The rapid fall in current was typically provided by turning off the injection driver abruptly by actively clamping the voltage across the load so as to rapidly dissipate the energy stored in the load. This energy was dissipated as a power loss in the circuit elements.
As shown in
FIG. 1
, a typical method of driving an inductive load is via a battery B. To drive the load L to a higher current level, both switches S
1
and S
2
are closed, and current flows from the battery B through S
1
, the load L, returning to ground via S
2
. To provide a slow current decay, S
1
is then opened causing current to flow through diode D
2
and S
2
. In the alternative, for a rapid decay in current, S
1
and S
2
are opened so that current flows from ground, through D
2
, the load L, and returns through diode D
1
to the battery B. Note that it is possible to eliminate the diode D
1
when the switch S
2
operates like an FET or similar type switch so that the current flows from ground, through diode D
2
, through the load L and returns to ground through the switch S
2
when the switch S
2
is operating in an unsaturated/linear manner.
In another known structure shown in
FIG. 2
, the inductive load L is driven by a battery B and an independent boost supply. The output filter is represented by the boost capacitor C. For an initial rapid rise in current, switches S
1
and S
2
are both closed so that current will flow out of the boost capacitor C and through S
1
, the load L, returning to the capacitor C via S
2
. The load L can then be driven to a higher current level via battery B by opening switch S
1
and closing switches S
2
and S
3
so that current flows from the battery B through S
3
, the load L, and returning to ground via S
2
. At this point, the current can either decay slowly or quickly. To provide a slow current decay, switch S
2
is closed and switches S
1
and S
3
are opened so that current flows through diode D
2
and S
2
. For a rapid decay in current, switches S
1
, S
2
and S
3
are all opened so that current flows from ground, through D
2
, the load L, and returns to ground through the switch S
2
when the switch S
2
operates like an FET or similar type switch and the switch S
2
is operating in an unsaturated/linear manner.
There has become an increased need for multiple injection events on the same fuel injector during a given engine cycle. These multiple injection requirements add a burden to inductive load driver systems that use a boost supply in that the boost supply is required to provide a given amount of energy to the load repeatedly in rapid succession. For an independent boost supply to provide this energy, the power output requirements and therefore its cost, size, and power losses become excessive.
In an attempt to accommodate these multiple injection events using the known methods described above with respect to the inductive load driver systems of
FIGS. 1 and 2
, the supply providing the initial current rise may require a substantial power output capability. This is not an issue if the supply is a battery as with the inductive load driver system of FIG.
1
. However, for the inductive load driver system of
FIG. 2
that uses a separate boost power supply, this could have substantial impact on the design, such as increasing component sizes and costs.
One known way to get around the shortcomings of the inductive load driver system of
FIG. 2
is to recovery energy from the load L. Two embodiments and methods for recovering energy from the load L are illustrated in
FIGS. 3 and 4
. In the embodiment of
FIG. 3
, when switch S
3
is open, switches S
1
and S
2
are closed to cause current to flow out of the boost capacitor C through S
1
so as to cause an initial rapid rise in current in the load L. The current is later returned to the capacitor C through ground via switch S
2
. To drive the load L to a higher current level through the battery B, switches S
2
and S
3
are closed while S
1
is open. In this case, the current flows from the battery B through S
3
, the load L and returning to ground through S
2
. To provide a slow current decay, S
2
is closed and S
1
and S
3
are open so that current flows through D
2
and S
2
. For energy recovery from the load charging the boost capacitor C (which also provides for a rapid decay in current), S
1
, S
2
and S
3
are open, current flows from ground, through D
2
, the load, and returns to the boost capacitor C through D
1
.
In the embodiment of
FIG. 4
, an initial rapid rise in current in the load L is caused by closing switches S
1
and S
2
so that current will flow out of the boost capacitor C through S
1
, the load L, and returning to the capacitor C via S
2
. To drive the load to a higher current level through the battery B, switch S
2
is closed while switch S
1
is open. In this case, current flows from the battery B through diode D
2
, the load L, returning to ground through S
2
. To provide a slow current decay, S
1
is closed with S
2
open causing current to flow through S
1
and D
1
. For energy recovery from the load L charging the boost capacitor C (which also provides for a rapid decay in current), S
1
and S
2
are open so that current flows from the battery B through D
2
, the load L, and returns to the boost capacitor C through D
1
.
Note that the embodiments of
FIGS. 3 and 4
are such that the separate boost supply is eliminated and all of the energy required for the initial current rise may be derived from the load(s), since the loads are inductive in nature, and, thus, may be used as the inductive element of a boost supply. Of course, when the load is used for charging the boost capacitor C it is desirable to drive the load with a current that does not actuate the load.
The four methods of operating the prior inductive load driver systems of
FIGS. 1-4
are summarized in the table below. In reading the table, the term S
2
BD
denotes the situation when the switch S
2
operates like an FET or similar type switch and the switch S
2
is operating in an unsaturated/linear manner, i.e., the voltage is clamped to a high voltage during turnoff. The term “Recirculate/Freewheel” regards the current slowly decaying from the load due to a slow energy discharge with no energy transfer from the load. The term “Rapid Current Fall/Recovery” regards a rapid current decay from the load caused by a rapid energy transfer from the load to an energy storage device like a capacitor C.
Summary of Prior Art
Battery Drive
Independent
Boost With Energy Recovery
Method
(FIG. 1)
Boost (FIG. 2)
FIG. 3
FIG. 4
Rap
Albanese Salvatore
Freeman James A.
Seifert Betty-Rose G.
Jackson Stephen W.
May Steven A.
Miller Thomas V.
Motorola Inc.
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