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United States Patent |
6,205,988
|
Luttrelll
,   et al.
|
March 27, 2001
|
System and method for ignition spark energy optimization
Abstract
A method for controlling spark energy from a spark plug of a combustion
engine. The method includes determining a spark energy intensity based on
at least one engine operating condition, determining a period of time to
supply current to an ignition coil connected to the spark plug to achieve
the determined spark energy intensity from the spark plug as a function of
a voltage supplied from a power supply to the ignition coil, and
connecting the power supply to the ignition coil for the determined period
of time.
Inventors:
|
Luttrelll; Jabe R. (Burlington, CT);
Thibodeau; David (Coventry, CT);
Santoro; Stephen (Windsor Locks, CT)
|
Assignee:
|
Teledyne Technologies, Inc. (Los Angeles, CA)
|
Appl. No.:
|
268173 |
Filed:
|
March 15, 1999 |
Intern'l Class: |
F02P 9/0/0 |
Field of Search: |
123/609,625
|
References Cited
U.S. Patent Documents
4389994 | Jun., 1983 | Denz et al. | 123/478.
|
4625704 | Dec., 1986 | Wheelock.
| |
4773380 | Sep., 1988 | Narita et al.
| |
4788942 | Dec., 1988 | Pouring et al. | 123/430.
|
4829973 | May., 1989 | White | 123/609.
|
4915086 | Apr., 1990 | Ciliberto et al.
| |
5007397 | Apr., 1991 | Akasu | 123/609.
|
5043900 | Aug., 1991 | Allen et al. | 123/609.
|
5048487 | Sep., 1991 | Fujimoto | 123/609.
|
5054461 | Oct., 1991 | Deutsch et al. | 123/609.
|
5058021 | Oct., 1991 | Scott | 123/609.
|
5140970 | Aug., 1992 | Akaki et al.
| |
5143553 | Sep., 1992 | Mukaihira et al. | 123/609.
|
5334938 | Aug., 1994 | Kugler et al.
| |
5456241 | Oct., 1995 | Ward.
| |
5513620 | May., 1996 | Pyko et al.
| |
5758629 | Jun., 1998 | Bahr et al.
| |
5871002 | Feb., 1999 | Nada | 123/609.
|
Primary Examiner: Solis; Erick
Attorney, Agent or Firm: Kirkpatrick & Lockhart LLP
Claims
What is claimed is:
1. A computer-assisted method for controlling spark energy from a spark
plug of a combustion engine, comprising:
determining a spark energy intensity based on an exhaust temperature of the
engine;
determining a period of time to supply current to an ignition coil
connected to the spark plug to achieve the determined spark energy
intensity from the spark plug as a function of a voltage supplied from a
power supply to the ignition coil; and
connecting the power supply to the ignition coil for the determined period
of time.
2. The method of claim 1, wherein determining the spark energy intensity
includes determining the spark energy intensity based on a second engine
operating condition selected from the group consisting of cylinder head
temperature and engine speed.
3. The method of claim 1, further comprising:
determining a time during a cycle of the engine to ignite a spark from the
spark plug based on at least one sensed engine operating condition; and
disconnecting the power supply from the ignition coil at the determined
time during the engine cycle.
4. The method of claim 3, wherein determining the time during the cycle
includes determining the time during the cycle based on at least one
sensed engine operating condition selected from the group consisting of
engine manifold pressure and engine knock.
5. A computer-assisted method for controlling spark energy from a spark
plug of a combustion engine, comprising:
connecting the spark plug to a secondary winding;
inductively coupling the secondary winding to a primary winding;
determining a spark energy intensity based on an exhaust temperature of the
engine;
determining a period of time to supply current to the primary winding to
achieve the determined spark energy intensity from the spark plug as a
function of a voltage supplied from a power supply to the primary winding;
and
connecting the power supply to the primary winding for the determined
period of time.
6. The method of claim 5, further comprising:
determining a point during a cycle of the engine to ignite a spark from the
spark plug based on at least one sensed operating condition of the engine;
and
disconnecting the power supply from the primary winding at the determined
point during the engine cycle.
7. The method of claim 5, wherein determining the spark energy intensity
includes determining the spark energy intensity based on a second sensed
engine operating condition selected from the group consisting of cylinder
head temperature and engine speed.
8. The method of claim 6, wherein determining the point during the cycle to
ignite the spark includes determining a point during the cycle of the
engine to ignite the spark based on at least one sensed engine operating
condition selected from the group consisting of engine manifold pressure
and engine knock.
9. A system for controlling spark energy of a combustion engine,
comprising:
a spark plug;
a secondary winding connected to the spark plug;
a primary winding inductively coupled to the secondary winding;
a switch connected to the primary winding;
a power supply connected to the switch; and
a spark control module in communication with the switch, the spark control
module for controlling the switch based on sensed engine operating
conditions and a voltage supplied from the power supply, wherein the spark
control module includes:
a first circuit for determining a spark energy intensity based on an
exhaust temperature of the engine;
a second circuit in communication with the first circuit for determining a
period of time to supply current to the primary winding to achieve the
determined spark energy intensity from the spark plug as a function of the
voltage supplied from the power supply; and
a third circuit in communication with the second circuit for transmitting a
signal to the switch to connect the power supply to the primary winding
for the determined period of time.
10. (Amended) The system of claim 9, wherein the spark control module
further includes:
a fourth circuit for determining a time during a cycle of the engine to
ignite a spark from the spark plug based on at least one sensed engine
operating condition; and
a fifth circuit in communication with the fourth circuit for transmitting a
signal to the switch to disconnect the power supply from the primary
winding at the determined time during the engine cycle.
11. The system of claim 9, wherein the first circuit is for determining the
spark energy intensity based on a second sensed engine operating condition
selected from the group consisting of cylinder head temperature and engine
speed.
12. The system of claim 9, wherein the spark control module is in
communication with the switch via a logic circuit.
13. A computer-implemented method for controlling spark energy from a spark
plug of a combustion engine, comprising:
determining a desired spark energy intensity based on an exhaust
temperature of the engine;
determining a period of time to energize an ignition coil connected to the
spark plug to achieve the desired spark energy intensity as a function of
a voltage supplied to the ignition coil; and
transmitting a signal to energize the ignition coil for the determined
period of time.
14. The method of claim 13, further comprising:
determining a point during a cycle of the engine to ignite a spark from the
spark plug based on at least one sensed engine operating condition; and
transmitting a signal to de-energize the ignition coil at the determined
point during the engine cycle.
15. The method of claim 13, wherein determining a desired spark energy
intensity includes determining the desired spark energy intensity based on
a second sensed engine operating condition.
16. A computer-readable medium having stored thereon instructions which
when executed by a processor cause the processor to:
determine a desired spark energy intensity for a spark plug of a combustion
engine based on an exhaust temperature of the engine;
determine a period of time to energize an ignition coil connected to the
spark plug to achieve the desired spark energy intensity based on a
voltage supplied to the ignition coil.
17. The computer-readable medium of claim 16 further comprising
instructions which when executed by the processor cause the processor to
determine a time during a cycle of the engine to ignite a spark from the
spark plug based on at least one sensed engine operating condition.
18. The computer readable medium of claim 16, further comprising
instructions which when executed by the processor cause the processor to
determine the desired spark energy intensity based on a second sensed
engine operating condition.
19. An ignition spark energy module, comprising:
a first circuit for determining a desired spark energy intensity for a
spark plug of a combustion engine based on an exhaust temperature of the
engine; and
a circuit in communication with the first circuit for determining a period
of time to energize an ignition coil connected to the spark to achieve the
determined spark energy based a magnitude of a voltage supplied to the
ignition coil.
20. The module of claim 19, further comprising a third circuit in
communication with the first circuit for determining a time during a cycle
of the engine to de-energize the ignition coil based on at least one
sensed engine operating condition.
21. The module of claim 20, further comprising a fourth circuit in
communication with the second circuit for scheduling energizing and
de-energizing tasks during the engine cycle.
22. The ignition spark energy module of claim 19, wherein the first circuit
is further for determining a desired spark energy intensity based on a
second sensed engine operating condition.
23. An ignition spark control module, comprising:
means for determining a desired spark energy intensity for a spark plug of
a combustion engine based on an exhaust temperature of the engine; and
means for determining a period of time to energize an ignition coil
connected to the spark to achieve the determined spark energy based a
magnitude of a voltage supplied to the ignition coil.
24. The module of claim 23, further comprising means for determining a time
during a cycle of the engine to de-energize the ignition coil based on at
least one sensed engine operating condition.
25. The module of claim 24, further comprising means for scheduling
energizing and de-energizing tasks during the engine cycle.
26. The ignition spark energy module of claim 23, wherein the means for
determining a desired spark is further for determining a desired spark
based on a second sensed engine operating condition.
27. A system for controlling spark energy of a combustion engine,
comprising:
a spark plug;
a secondary winding connected to the spark plug;
a primary winding inductively coupled to the secondary winding;
a power supply;
means for determining a desired spark energy intensity based on an exhaust
temperature of the engine; and
means for connecting the power supply to the primary winding for a period
of time to achieve the desired spark energy intensity based on a voltage
supplied from the power supply to the primary winding.
28. The system of claim 27, further comprising:
means for determining a time during a cycle of the engine to ignite a spark
from the spark plug based on at least one sensed engine operating
condition; and
means for disconnecting the power supply from the primary winding at the
determined time during the cycle.
29. The system of claim 27, wherein the means for determining a desired
spark is further for determining a desired spark based on a second sensed
engine operating condition.
30. A system for controlling spark energy of a combustion engine,
comprising:
a plurality of spark plugs;
a plurality of secondary windings, each of the plurality of secondary
windings connected to one of the plurality of spark plugs;
a plurality of primary windings, each of the plurality of primary windings
inductively coupled to one of the secondary windings;
a plurality of switches, each of the plurality of switches connected to one
of the plurality of primary windings;
a plurality of power supplies, each of said plurality of power supplies
connected to one of the plurality of switches;
a plurality of spark control modules in communication with the plurality of
switches, each of the spark control modules for controlling one of the
plurality of switches to achieve a desired spark energy intensity based on
an exhaust temperature of the engine.
31. The system of claim 30, wherein each of the spark control modules
includes:
a first circuit for determining a desired spark energy intensity for one of
the plurality of spark plugs based on the exhaust temperature;
a second circuit in communication with the first circuit for determining a
period of time to supply current to one of the plurality of primary
windings from the power supply to achieve the desired spark energy
intensity as a function of a voltage supplied from the power supply; and
a third circuit in communication with the second circuit for transmitting a
signal to one of the plurality of switches to connect one of the plurality
of power supplies to the primary winding for the determined period of
time.
32. The system of claim 30, wherein each of the plurality of spark control
modules is in communication with two of the plurality of switches.
33. The system of claim 31, wherein the spark control module further
includes:
a fourth circuit for determining a time during the engine cycle to ignite a
spark from one of the plurality of spark plugs based on at least one
sensed engine operating condition; and
a fifth circuit in communication with the fourth circuit for transmitting a
signal to one of the plurality of switches to disconnect the power supply
from the primary winding at the determined time during the engine cycle.
34. The system of claim 31, wherein the first circuit is further for
determining the desired spark for one of the plurality of spark plugs
based on a second sensed engine operating condition.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
Not Applicable.
BACKGROUND OF INVENTION
1. Field of Invention
The present invention is directed generally to a system and method for
controlling ignition spark for a combustion engine and, more particularly,
to a system and method for optimizing ignition spark based on the engine
operating conditions.
2. Description of Background
Modern reciprocating engine control systems are designed to achieve precise
control of the fuel-to-air ratio of the charging mixture supplied to the
combustion chambers and to control the timing and magnitude of the spark
which initiates the combustion process and expansion of the mixture. If
the spark occurs too late during the engine cycle, i.e., the spark is too
"retarded," or with insufficient energy to achieve a combustion process
with the desired rate of flame front propagation, then the combustion and
gas expansion process may not be completed before the engine piston has
left the power producing portion of that cycle. This may result in less
power from the engine, increased fuel consumption, and undesirable levels
of exhaust emissions. Conversely, if the spark is too early in the
combustion cycle, i.e., the spark is too "advanced," or with too much
energy, early detonation of the fuel-air mixture may result, which
consequently may cause damaging engine "knock" or excessive cylinder head
temperatures, both of which may severely reduce the life of the engine.
Such control is of particular significance for aircraft engines, where it
is important for an engine to last a long time, despite the fact that an
aircraft engine typically runs "hot" most of its life. For example,
aircraft engines are typically designed to operate at relatively low
engine speeds to reduce wear and stress on the engine components. Thus, in
order to gain the necessary power for flight, the engine cylinders are
made relatively large, for example, 1.5 liters. To further enhance
durability, when the aircraft engine is cold, because it is relatively
difficult to spark the gap of the spark plug, increased spark energy is
required to ensure the starting of the aircraft. Conversely, when the
engine is hot, less energy is required to spark the gap, allowing engine
stress to be decreased by decreasing the spark energy.
Proper control of the ignition spark is made more difficult if the power
required to generate the spark is capable of varying over a broad range.
In power supplies for aircrafts, for example, the ignition spark typically
relies on a twenty-eight volt DC power supply which can typically
deteriorate to as low a twelve volts DC during aircraft operation. The
power supply is used by an ignition coil to generate a high voltage
required by the spark plug to ignite. Because of the vacillation in the
voltage supplied to the ignition coil, the ignition spark energy will
accordingly vary, resulting in deterioration in the precision of the
ignition process.
Modern reciprocating engine control systems utilize digital electronic
processors to calculate the desired timing for the ignition spark during
the engine cycle based on measured engine operating parameters. Typical
relevant art engine control systems do not attempt to vary the intensity
of the spark energy, although it may vary significantly over the starting
and operational power range of the engine. Further, in the case of an
aircraft engine, the spark energy may vary over a wide altitude and speed
envelope. In addition, the relevant art engine control sensors do not
compensate for variations in electrical power supplied to the ignition
coils, except for engines requiring a nominally constant spark energy.
Accordingly, there exists a need in the relevant art for a system and
method to optimize and control the spark energy intensity under
circumstances of varying electrical power.
SUMMARY OF INVENTION
The present invention is directed to a method for controlling spark energy
from a spark plug of a combustion engine including determining a spark
energy intensity based on at least one engine operating condition,
determining a period of time to supply current to an ignition coil
connected to the spark plug to achieve the determined spark energy
intensity from the spark plug as a function of a voltage supplied from a
power supply to the ignition coil, and connecting the power supply to the
ignition coil for the determined period of time.
The present invention represents an advance over prior systems and methods
for controlling ignition spark energy in that the present invention
compensates for broad variation in the electrical power supplied to the
ignition coils in optimizing the energy spark intensity. These and other
advantages and benefits of the present invention will become apparent from
the description hereinbelow.
BRIEF DESCRIPTION OF THE DRAWINGS
For the present invention to be clearly understood and readily practiced,
the present invention will be described in conjunction with the following
figures, wherein:
FIG. 1 is a diagram illustrating an aircraft propulsion and control system
in which the present invention may be used;
FIG. 2 is a diagram illustrating a process flow through the spark control
module of the system illustrated in FIG. 1;
FIG. 3 is a diagram illustrating a basic timing advance schedule which may
be used in the present invention; and
FIG. 4 is a diagram illustrating the control system according to another
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
It is to be understood that the figures and descriptions of the present
invention have been simplified to illustrate elements that are relevant
for a clear understanding of the present invention, while eliminating, for
purposes of clarity, other elements found in a typical aircraft propulsion
and control system. For example, specific operating system details and
modules contained in the electronic engine controller are not shown. Those
of ordinary skill in the art will recognize that other elements may be
desirable to produce an operational system incorporating the present
invention. However, because such elements are well known in the art, and
because they do not facilitate a better understanding of the present
invention, a discussion of such elements is not provided herein.
FIG. 1 is a diagram illustrating an aircraft propulsion and control system
10 in which the present invention may be used. The system 10 will be
described herein as implemented in an aircraft, although it may be
implemented in any combustion engine. The system 10 may be used in an
engine of any number of cylinders such as, for example, a four, six, or
eight cylinder engine. In addition, the system 10 may be implemented in a
naturally aspirated or super-charged aspirated, air-cooled, horizontally
opposed, reciprocating direct drive engine.
The system 10 includes an electronic engine controller 12 which accepts
various engine parameters as inputs and outputs various control signals to
control portions of the system 10. The controller 12 includes a spark
control module 14, which generates signals directing the charging and
discharging of a spark plug ignition coil 15 to control ignition timing
and energy level. A fuel control module 16 generates signals which control
the amount of fuel that is delivered by fuel injectors 18. It is desirable
to have one fuel injector per cylinder of an engine 20. The fuel injectors
18 can be, for example, electromagnetically operated valves with coils
that can be energized and de-energized to open and close the valves. A
knock accommodation module 22 generates signals which control engine
detonation, or knock, by controlling ignition timing and enriching the
fuel mixture at the fuel injectors 18. An engine speed control module 24
generates signals which determine how much current should be applied to a
coil (not shown) in a governor 30 to change the angle of a propeller 28.
A fuel pump control module 32 generates signals which control the delivery
of fuel by an electric fuel pump 34 from a fuel tank 36 to the fuel
injectors 18. An annunciator control module 38 generates signals which
determine which of annunciators 40, if any, are illuminated such as during
a component failure or when conditions such as low engine oil pressure or
high engine oil temperature are present. A fault detection module 42
detects faults in the controller 12 and, upon confirming the presence of a
fault, annunciates the fault via the annunciators 40.
An input/output module 44 receives input signals from the an input
interface 46 and outputs signals via an output interface 48. The input
interface 46 receives various input signals from sensors throughout the
system 10. The interface 46 receives a manifold pressure signal Pm from a
manifold pressure sensor (not shown) which can be located on, for example,
the body of a throttle 50 or on the induction plenum (not shown) or
induction splitter (not shown) of the engine 20. The throttle 50 controls
the amount of air that is introduced into the cylinders (not shown) of the
engine 20. The interface 46 receives a fuel pressure signal Pf from a fuel
pressure sensor (not shown) which can be mounted on, for example, the fuel
distribution block (not shown) of the engine 20. The manifold pressure and
fuel pressure sensors can be, for example, resistance strain gauges. The
interface 46 receives a manifold temperature signal Tm from a manifold
temperature sensor (not shown) which can be located on, for example, the
body of the throttle 50 or on the induction plenum (not shown) or
induction splitter (not shown) of the engine 20. The manifold temperature
sensor may be, for example, a thermistor. The interface 46 receives a
throttle position sensor signal TPS from a throttle position sensor (not
shown) located on the body of the throttle 50. The throttle position
sensor may be, for example, a potentiometer. The interface 46 receives a
turbine inlet temperature sensor signal Tt from a turbine inlet sensor of
the engine 20. The interface 46 receives a cylinder head temperature
signal Tc from a cylinder head temperature sensor located on, for example,
the thermowells of each cylinder (not shown) of the engine 20. The turbine
inlet temperature and cylinder head temperature sensor may be, for
example, thermistors. The interface 46 receives an exhaust gas temperature
signal Te from an exhaust gas temperature sensor 51 which are located in
each exhaust pipe 54 at, for example, a location approximately 2 inches
from the exhaust pipe to cylinder mating flange (not shown). The exhaust
gas temperature sensor may be, for example, a thermocouple. The interface
46 receives a crankshaft speed sensor signal Ne, which may, for example,
provide a pulse every 45.degree. of crankshaft rotation and may be used to
schedule all software events within the system 10. The interface 46
receives camshaft speed sensor signal Nc from a speed sensor assembly (not
shown) which is mounted on the engine 20. The crankshaft speed and
camshaft speed sensors may be, for example, Hall effect, magnetically
biased, magnetic pickups. The interface 46 receives a knock sensor signal
K from a knock sensor (not shown) which is located on, for example, the
cylinder heads of air cooled engines and the engine case for unitized
block liquid cooled engines. The knock sensor may be, for example, a
piezoelectric accelerometer.
The output interface 48 outputs a spark signal SP, which is generated by
the spark control module 14 and the knock accommodation module 22, to
control the spark coil current and timing of pulses to interrupt the spark
coil primary winding current and generate a spark at each spark plug 52
located in the engine 20. The interface 48 outputs a fuel injection signal
FI, which is generated by the fuel control module 16 and the knock
accommodation module 22, to control the opening and closing of the valves
(not shown) in the fuel injectors 18. The fuel control module 16 and the
fuel injectors 18 are detailed in a pair of patent applications entitled
"Automatic Aircraft Engine Fuel Mixture Optimization" and "Fuel Injector
Assembly" respectively, which were filed concurrently herewith by the
assignee of the instant application, and which are incorporated herein by
reference. The interface 48 outputs a speed control signal SC, which is
generated by the engine speed control module 24, to the governor 30. The
signal SC can be, for example, a pulse width modulated signal that causes
the governor 30 to change the pitch of the propeller 28 as appropriate.
The interface 48 outputs a fuel pump control signal FP, which is generated
by the fuel pump control module 32, to control the operation of the fuel
pump 34. The output interface 48 outputs an annunciator signal A, which is
generated by the annunciator control module 38, to the annunciators 40.
The system 10 includes a power supply 54, which may, for example, be a
device that produces a controlled DC output, such as an ORing diode, from
a variable input power source, such as an alternator or a battery. A
signal, Ord, indicative of the voltage outputted from the power supply 54
is input to the input interface 46.
The interfaces 46 and 48 can be implemented using, for example, one or a
plurality of RS-485 serial data buses.
The controller 12 can be implemented as, for example, a microprocessor such
as, for example, a N87C196KT microprocessor, sold by Intel Corp., of Santa
Clara, Calif., with or without internal memory, or an application specific
integrated circuit (ASIC). The modules 14, 16, 22, 24, 32, 38, 42 and 44
can be implemented using any type of computer instructions types such as,
for example, microcode, and can be stored in, for example, an electrically
erasable programmable read only memory (EEPROM) or can be configured into
the logic of the controller 12. The controller 12 can be mounted on, for
example, the mount frame (not shown) of the engine 20 or on either side of
the firewall (not shown) of the engine 20. The power supply 54 and the
ignition coil 15 may be housed with the controller 12. For such an
embodiment, the ignition coil 15 may be housed in a separately shielded
portion of the controller housing to protect the controller 12 from
electromagnetic fields generated from the ignition coil 15.
The system 10 includes an on-time logic circuit 56 receiving the signal SP
from the controller 12 via the output interface 48. The on-time logic
circuit 56 outputs the signal SP to a primary coil switch 58. The switch
58 may be, for example, a field-effect transistor (FET) or a bipolar
junction transistor (BJT). The switch 58 operates according to the signal
SP transmitted from the controller 12 via the on-time logic circuit 56.
The on-time logic circuit 56 may control the switch 58 with positive
logic. That is, when the output from the controller 12 is positive, the
switch 58 is closed. The ignition coil 15 is connected to the switch 58,
and includes a primary winding 60 inductively coupled to a secondary
winding 62 configured as a step-up transformer. The secondary winding 62
may have more turns than the primary winding 60 such as, for example, one
hundred times more turns. The controller 12 operates the switch 58 through
signal SP such that the primary winding 60 is connected to the power
supply 54 when the switch 58 is closed and disconnected when the switch 58
is open. The secondary winding 62 is coupled to a spark plug 52.
In operation, when the switch 58 is closed, the power supply 54 supplies
electrical current to the primary winding 60, inducing an electromagnetic
flux in the coil 15. When the switch 58 opens, the voltage supplied to the
primary winding 60 is removed, causing the flux field to collapse. The
collapse of the flux field induces a high voltage in the secondary winding
62 because of the turn ratio between the primary winding 60 and the
secondary winding 62. A voltage of 12,000-15,000 volts may be realized on
the secondary winding 62 due to the voltage supplied to the primary
winding 60 and the turn ratio. Such high voltages are sufficient to ionize
the spark plug gap of the spark plug 52, causing the spark plug 52 to
spark, igniting the fuel-air mixture in the combustion chamber of the
engine 20. The energy intensity of the spark from the spark plug 52 is a
function of the magnitude of the flux field induced by current in the
primary winding 60, and may be expressed as:
E.sub.spark =1/2(LI.sup.2) (1)
where L is the inductance of the primary winding 60 and I is the current in
the primary winding 60. The current magnitude of the flux field is
dependent on the amount of time that the primary winding 60 is connected
to the power supply 54 and the magnitude of the voltage supplied from the
power supply 54.
The amount of time that the switch 58 is closed is controlled by the
controller 12. Based on the various inputs indicative of engine operating
conditions, the controller 12 determines the optimal spark energy
intensity for the particular engine operating conditions. The amount of
time that the switch 58 must be closed in order to achieve the desired
spark energy intensity, called the dwell time, may be determined according
to the expression:
T.sub.dwell =(LI)/V (2)
where V is the voltage supplied from the power supply 54. Substituting an
expression for I derived from equation (1), an expression for the dwell
time can be obtained as a function of the desired spark energy intensity,
which may be represented as:
T.sub.dwell =(2EL).sup.1/2 /V (3)
Thus the amount of time that the switch 58 must be closed in order to
achieve a desired spark energy intensity, i.e., the dwell time, is a
function of the voltage supplied from the power supply 54. In many
engines, however, the voltage supplied from the power supply 54 to the
ignition coil 15 may vary significantly. Consequently, to achieve the
optimal spark energy intensity considering the operating conditions of the
engine, it is necessary to monitor the voltage supplied from the power
supply 54.
In addition to determining the optimal spark energy intensity, it is
desirous to ignite the spark at the proper time during the engine cycle.
Ignition of the spark at the proper time in the engine cycle typically
improves, among other things, fuel efficiency and engine service life. The
controller 12 may also determine the proper time during the engine cycle
to ignite the spark according to the particular engine operating
conditions as communicated to the controller 12 via the input interface
46.
FIG. 2 is a diagram illustrating a process flow through the spark control
module 14 illustrated in FIG. 1. The ignition module 14 determines the
proper spark energy and the proper spark timing, and schedules the events
for execution by the system 10 to optimize energy operating conditions.
FIG. 2 illustrates one embodiment of the process flow, and may be modified
for a particular engine and desired operating conditions.
The process flow begins at block 108, where all internal flag values are
reset. The flow proceeds to block 110.
Block 110 determines if the engine 20 is off. If the engine 20 is off, the
process proceeds to block 112, where no ignition timing signals are
generated, and thereafter back to block 110. The process cycles between
blocks 108 and 110 until the engine 20 is turned on. If the engine 20 is
on, the process proceeds to block 114 which determines whether the engine
20 is in start-up mode.
At block 114, if the engine 20 is not is start-up mode, the process
proceeds to block 116. If the engine 20 is in start-up mode, the engine 20
is starting and the process waits for an "Enable" signal, which is
indicative of a command to turn the controller 12 on, and the first
camshaft pulse (Nc) before generating ignition timing commands. Block 118
determines if the "Enable" signal is asserted and block 120 determines if
signal Nc, indicative of a camshaft pulse, has been received. If either of
those conditions are not satisfied, the process proceeds to block 112. If
both are satisfied, the process proceeds to block 116, which indicates
that the engine is in the running mode and, therefore, ignition signals
should be generated.
Block 122 determines if a timing flag has been set during a prior ignition
timing event for reasons described hereinbelow. If no timing flag has been
set, the process flow continues to block 124.
Block 124 determines whether the engine manifold pressure is increasing at
a rate greater than a predetermined rate. If the engine manifold pressure
is not increasing greater than the predetermined rate, the process
continues to block 126, and if the pressure is increasing at rate greater
than the predetermined value, the process proceeds to block 128. In the
illustrated embodiment, the predetermined rate is 3 psi/s. A high rate of
increase in manifold pressure is indicative of rapid engine acceleration,
for which special ignition timing commands may be beneficial. For example,
under rapid acceleration peak pressure in the combustion chamber may occur
prematurely unless ignition timing is retarded. The special timing
commands are discussed hereinbelow with respect to block 128.
Block 126 sets the spark timing to a predetermined basic advance schedule
particular to the engine and desired operating conditions. The
predetermined basic advance timing schedule indicates spark timing for a
given engine speed and mode. For example, for an aircraft engine, the
predetermined basic advance timing schedule may indicate the point during
the engine cycle to ignite a spark based on whether the aircraft is, for
example, starting, idling, cruising, and taking off.
One example of the basic advance timing schedule for an aircraft engine is
provided in FIG. 3. For the embodiment illustrated in FIG. 3, the timing
schedule is broken down into various engine modes, including starting,
idle, low power, low power (LP) cruise, high power (HP) cruise, maximum
continuous power (MCP), takeoff, and overspeed. Provided for each
applicable engine speed and mode combination is a base spark timing in
degrees BTDC. Where a range of base spark timings is provided for a
particular range of engine speeds, the spark timing is related linearly to
the engine speed range. Thus, for example, where the timing schedule shows
an engine speed of 300 to 900 rpm, the spark timing increases linearly
with the engine speed from 0 to 18 degrees BTDC. The timing schedule may
be stored in the memory of the controller 12. FIG. 3 illustrates one
example of a basic advance timing schedule, which may be modified for a
particular engine or desired operating conditions.
Returning to FIG. 2, block 128 determines whether the timing advance is
greater than a predetermined value. In the illustrated embodiment, the
value is 18.degree. BTDC. If the timing advance is greater than the
predetermined value, then spark timing is retarded to another
predetermined value until the rate of increase of the engine manifold
decreases. For the illustrated embodiment, the predetermined timing is set
at 18.degree. BTDC at block 130, and the timing flag is set at block 131.
If the timing is not greater than the predetermined value, then the
process proceeds to block 126.
The significance of the timing flag will be discussed by returning to block
122. If the timing flag is set, indicating that the timing flag has been
set at block 130, the process proceeds from block 122 to block 132. Block
132 determines if the engine manifold pressure is increasing less than a
predetermined value. For the illustrated embodiment, the predetermined
value is 2 psi/s. If engine manifold pressure is not increasing less than
the predetermined value, the flow proceeds to block 130, where the
ignition timing is retarded to the predetermined value, such as 18.degree.
BTDC as in the illustrated embodiment. Maintaining the ignition timing at
the retarded value until the rate of increase of the engine manifold
pressure decreases to the predetermined value provides hysteresis to
prevent cycling between timing controls in block 126 and timing controls
in block 130. Otherwise, such cycling may occur when the manifold pressure
increase rate is approximately the predetermined value (e.g. 3 psi/s),
resulting in less efficient operation of the engine. If the engine
manifold pressure is increasing less than the predetermined value, the
process proceeds to block 133 where the flag is reset, and then to block
126.
With the ignition timing determined according to either block 126 or 130,
the process flow advances to block 134 where the controller 12 modifies
the ignition timing to compensate for engine knock. Engine knock is the
detonation of the fuel-air mixture in the engine cylinder, and may cause
engine damage and excessive cylinder head temperatures, both of which may
severely reduce the life of the engine. To compensate for engine knock,
the ignition time may be retarded according to the severity of the knock.
For example, the signal K may supply a signal indicative of the severity
of engine knock to the controller 12. Based on the severity of the knock,
the knock accommodation module 22 generates signals which may be utilized
by the spark control module 14 to retard the ignition timing.
Alternatively, the knock accommodation module 22 may generate knock signal
to retard timing only when the engine manifold pressure is greater than 10
psia. The knock accommodation module 22 may generate signals according to
a predetermined compensation table. For example, the following table may
be utilized in determining the level of retardation of the spark to
compensate for knock:
KNOCK SIGNAL LEVEL COMPENSATION
No Knock -0.0.sup.0
Incipient Knock -0.5.sup.0
Light Knock -2.0.sup.0
Heavy Knock -8.0.sup.0
Severe Knock -16.0.sup.0
The above table illustrates but one example of a compensation schedule, and
may be modified according to the particular engine and the desired engine
operating conditions. In addition, the knock compensation may be applied
cumulatively to the base advance timing schedule up to a maximum
retardation of, for example, 0.degree. BTDC. That is, if the amount of
knock changes from one ignition event to the next, then the appropriate
timing compensation may be applied and accumulated even if it differed
from the compensation of the last ignition event. To allow the spark
timing to "creep" back to the schedule over a period of ignition events,
regardless of the compensation due to knock, the spark timing may be
advanced by a small increment such as, for example 0.01.degree., up to
limit for the base advance schedule for the current operating conditions,
thereby allowing the cylinder time to cool and avoid knocking.
The flow then continues to block 136, where the controller 12 computes the
spark advance timing with the reference point of Top Dead Center (TDC) of
the engine cycle to ignite the spark. The equivalent time is based on the
length of time of the engine cycle and the determined optimal spark timing
as a function of crankshaft angle. The length of time of the engine cycle
may be determined by the controller 12 according to signal Ne, which is
indicative of the crankshaft speed.
Having determined the desired spark timing, the process determines the
desired spark energy intensity based on the energy operating conditions.
To determine the desired spark energy, the flow proceeds to block 138.
Block 138 determines the exhaust temperature of the engine. If the exhaust
temperature is greater than a predetermined value, the engine may be
considered to be running "hot," and it may be desirous to provide a
relatively low spark energy intensity. For example, for the illustrated
embodiment, if the exhaust temperature is greater than 1500.degree. F.,
the spark energy is set at 64 millijoules (mJ) at block 140. In other
embodiments of the present invention, the critical exhaust temperature at
which to establish a lower spark energy may vary according to the
particular engine and the desired operating conditions. If the engine
exhaust temperature does not exceed the predetermined value, the flow
advances to block 142.
Block 142 determines if the engine is operating below a predetermined value
of revolutions per minute (rpm). For the illustrated embodiment, the
predetermined value is 1000 rpm. If the engine is operating below the
predetermined speed, it may be beneficial to provide a relatively high
spark energy. If the engine is operating at less than predetermined speed,
the flow proceeds to block 144 where the controller sets the spark energy
at 96 mJ. In other embodiments of the present invention, the predetermined
operating speed and spark energy may vary according to the particular
engine and the desired operating conditions. If the engine 20 is not
operating at a speed less than the predetermined speed, the flow continues
to block 146.
Block 146 determines whether the cylinder head temperature is less than a
predetermined value. For the illustrated embodiment, the predetermined
temperature is 200.degree. F. If the cylinder head temperature is below
the predetermined value, it may be desirous to provide a relatively high
spark energy, in which case flow continues to block 144 where the spark
energy is set at 96 mJ. In other embodiments of the present invention, the
critical cylinder head temperature at which to provide a relatively high
spark energy may vary according to the particular engine and the desired
operating conditions. In addition, in other embodiments of the present
invention, the spark energy provided when the cylinder head temperature is
less than the predetermined value is not the same as the spark energy
provided when the engine operating speed is less than the predetermined
rpm. If the cylinder head temperature is not less than the predetermined
value, the flow proceeds to block 148.
Block 148 determines if the exhaust temperature is less than a
predetermined value. For the illustrated embodiment, the value is
1000.degree. F. If the exhaust temperature is less than the predetermined
value, it may be beneficial to provide a relatively high spark energy
intensity, in which case the flow proceeds to block 144 where the spark
energy is set at 96 mJ. In other embodiments of the present invention, the
critical exhaust temperature at which to provide a relatively high spark
energy may vary according to the particular engine and the desired
operating conditions. In addition, in other embodiments of the present
invention, the provided spark energy may be different than the spark
energy provided under other engine operating circumstances in which a
relatively high spark energy is desired. If the exhaust temperature is
greater than the predetermined value, the flow advances to block 150.
Block 150 sets the spark energy to a predetermined value which may be
considered a "normal" level. For the illustrated embodiment, the
predetermined value is 80 mJ. For other embodiments of the present
invention, the normal spark energy may be set at alternative levels
according to the particular engine and the desired operating conditions.
Having determined the desired spark energy at either blocks 140, 144, or
150 depending on the engine operating conditions, the flow proceeds to
block 152. Block 152 computes the dwell time to realize the desired spark
energy intensity at block 152. As discussed hereinbefore, the dwell time
is the length of time necessary for the magnetic flux field induced by
electrical current in the primary winding 60 to reach the desired limit,
and corresponds to the length of time that switch 58 is closed and the
voltage supplied by the power supply 54. The dwell time necessary to
achieve a desired spark energy, as discussed hereinbefore, may expressed
according to the relationship:
T.sub.dwell =(2EL).sup.1/2 /V (4)
where E is the desired spark energy, L is the inductance of the primary
winding 60, and V is the voltage supplied from the power supply 54. As
discussed hereinbefore, particularly for aircraft engines, the voltage
supplied from the power supply 54 may vary significantly, which
consequently affects the necessary dwell time to achieve an optimal spark
energy. The flow then proceeds to block 154.
Block 154 determines the equivalent time earlier than TDC to energize the
coil 15, which corresponds to the time earlier than TDC to close the
switch 58. The point in time may be determined by adding the necessary
dwell time necessary to achieve the desired spark energy, as determined at
block 152, to the time earlier than TDC at which the switch 58 is to open
to achieve the proper spark timing, as determined at block 136.
Having determined the time to open and close the switch 58 to realize the
desired spark timing and energy, the process schedules the respective
tasks. Block 156 computes the time between crankshaft pulses (Nc) to
schedule the de-energizing control task. Block 158 computes the time
between crankshaft pulses (Nc) to schedule the energizing task control.
The flow then proceeds to block 160, which schedules the de-energizing and
energizing tasks to achieve optimal spark timing and spark energy.
FIG. 4 illustrates an alternative embodiment of the present invention
wherein the system 10 includes a controller 12 for each spark plug 52, and
where each controller 12 controls the timing and energy of two spark plugs
52. For simplicity, the input interface and output interface have been
omitted from FIG. 3. The controllers 12 may be the same as illustrated in
FIG. 1, and include a spark control module 14 as illustrated in FIG. 2.
The redundant control illustrated in FIG. 4 may be beneficial for certain
applications, such as for aircraft engines to allow continued operation of
the aircraft if one of the controllers 12 should happen to lose power
during flight. The system illustrated in FIG. 4 includes an engine 20
having a number of spark plugs 52, each connected to one ignition coil 15,
having a primary winding 60 and a secondary winding 62. Alternatively,
each ignition coil 15 may control two spark plugs 58, both of which may be
in one cylinder. Each ignition coil 52 is connected to a switch 58, which
may be, for example, a FET or a BJT. Each switch 58 is connected to a
power supply 54, and in communication with two controllers 12. The
switches 58 are connected to the controllers 12 via on-time logic circuits
56, and the controller 12 transmits signal SP to the switches 58 in order
to control their operation as described hereinbefore. In other embodiments
of the present invention, alternative redundant control configurations may
be employed.
The present invention is also directed to a method of controlling spark
energy of a spark plug of a combustion engine. The method includes
connecting the spark plug 52 to the secondary winding 62 of the ignition
coil 15. The secondary winding 62 is inductively coupled to the primary
winding 60. The method also includes determining a spark energy intensity
based on at least one engine operating condition, and determining a period
of time to supply current to the primary winding 60 to achieve the
determined spark energy intensity from the spark plug 52 as a function of
a voltage supplied from a power supply 54 to the primary winding 60. The
method further includes connecting the power supply 54 to the primary
winding 60 for the determined period of time. The method may further
include determining the proper time during the engine cycle to ignite a
spark from the spark plug 52, and disconnecting the power supply 54 from
the primary winding 60 at the determined time.
Those of ordinary skill in the art will recognize that many modifications
and variations of the present invention may be implemented. For example,
the flow through module 14 may be alternatively arranged to still realize
the benefit of the present invention. The foregoing description and the
following claims are intended to cover all such modifications and
variations. Furthermore, the materials and processes disclosed are
illustrative, but are not exhaustive. Other materials and processes may
also be used to make devices embodying the present invention. Moreover,
the present invention may be realized by performing the steps in processes
described herein in various sequences.
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