U.S. patent application number 15/520645 was filed with the patent office on 2017-10-26 for engine control strategy.
The applicant listed for this patent is WALBRO LLC. Invention is credited to Martin N. Andersson, Mark S. Swanson.
Application Number | 20170306863 15/520645 |
Document ID | / |
Family ID | 55909835 |
Filed Date | 2017-10-26 |
United States Patent
Application |
20170306863 |
Kind Code |
A1 |
Andersson; Martin N. ; et
al. |
October 26, 2017 |
ENGINE CONTROL STRATEGY
Abstract
In at least some implementations, a method of controlling engine
idle speed includes comparing engine speed to a speed threshold
where the speed threshold may include a range of speeds, if the
engine speed is outside of the speed threshold, adjusting the
timing of an ignition spark up to a threshold amount of ignition
timing adjustment, and if the engine speed is not within said speed
threshold after adjustment up to the threshold amount of ignition
timing adjustment then adjusting the air/fuel mixture provided to
the engine to bring the engine speed within said speed
threshold.
Inventors: |
Andersson; Martin N.; (Caro,
MI) ; Swanson; Mark S.; (Cass City, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WALBRO LLC |
Tucson |
AZ |
US |
|
|
Family ID: |
55909835 |
Appl. No.: |
15/520645 |
Filed: |
November 6, 2015 |
PCT Filed: |
November 6, 2015 |
PCT NO: |
PCT/US2015/059376 |
371 Date: |
April 20, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62075945 |
Nov 6, 2014 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02D 41/26 20130101;
F02D 31/008 20130101; F02D 37/02 20130101; Y02T 10/46 20130101;
F02D 2200/101 20130101; Y02T 10/40 20130101; F02P 5/1508 20130101;
F02D 31/002 20130101; F02D 31/007 20130101; F02D 41/1454 20130101;
F02P 5/045 20130101 |
International
Class: |
F02D 31/00 20060101
F02D031/00; F02D 37/02 20060101 F02D037/02; F02P 5/15 20060101
F02P005/15 |
Claims
1. A method of controlling engine idle speed, comprising: comparing
engine speed to a speed threshold where the speed threshold may
include a range of speeds; if the engine speed is outside of the
speed threshold, adjusting the timing of an ignition spark up to a
threshold amount of ignition timing adjustment; and if the engine
speed is not within said speed threshold after adjustment up to the
threshold amount of ignition timing adjustment then adjusting the
air/fuel mixture provided to the engine to bring the engine speed
within said speed threshold.
2. The method of claim 1 wherein the air/fuel mixture adjustment
may be provided in an amount sufficient to reduce the magnitude of
a previously made ignition timing adjustment.
3. The method of claim 2 wherein when the ignition timing
adjustment reaches the high side of the threshold amount of
ignition timing adjustment the fuel mixture is leaned out to
increase the engine speed.
4. The method of claim 2 wherein when the ignition timing
adjustment reaches the low side of the threshold amount of ignition
timing adjustment the fuel mixture is enriched to decrease the
engine speed.
5. The method of claim 3 wherein the high side of the threshold
amount of ignition timing adjustment is the maximum increase in
spark advance within the threshold for ignition timing
adjustment.
6. The method of claim 4 wherein the low side of the threshold
amount of ignition timing adjustment is the maximum decrease in
spark advance within the threshold for ignition timing
adjustment.
7. A method of detecting engine cycles, comprising: determining the
time for consecutive engine revolutions; comparing the time of a
revolution to a consecutive revolution; repeating the comparison
for a first threshold number of revolutions; and determining if
every other revolution is either faster or slower than the
intervening revolutions for a second threshold number of
revolutions.
8. The method of claim 7 wherein when the second threshold is
satisfied an ignition spark is skipped based upon the engine
revolution timing.
9. The method of claim 7 wherein if the second threshold is not
satisfied within the first threshold number of engine revolutions,
then an ignition spark is skipped every other engine revolution and
then the engine speed is determined.
10. The method of claim 9 wherein if the engine speed has decreased
below a threshold amount, the ignition event skipping is changed to
the opposite engine revolutions.
11. The method of claim 9 wherein if the engine speed has not
decreased below a threshold amount, the ignition event skipping is
continued.
12. The method of claim 10 wherein after the ignition event
skipping is changed, the fuel supply to the engine is adjusted to
correspond to the engine intake cycle.
13. The method of claim 11 wherein in addition to continuing the
ignition event skipping, the fuel supply to the engine is adjusted
to correspond to the engine intake cycle.
14. A method of controlling engine acceleration or deceleration,
comprising: determining occurrence of an engine acceleration or
deceleration; adjusting ignition timing within preselected
threshold limits during acceleration or deceleration of the engine;
and adjusting an air/fuel mixture delivered to the engine during
acceleration and deceleration of the engine.
15. The method of claim 14 wherein the ignition timing is adjusted
up to a threshold amount of adjustment either before or while the
air/fuel mixture adjustment occurs.
16. The method of claim 14 wherein when an engine acceleration is
determined the ignition timing is advanced and the air/fuel mixture
is enriched.
17. The method of claim 14 wherein when an engine deceleration is
determined the ignition timing is retarded and the air/fuel mixture
is enriched.
18. The method of claim 16 wherein the air/fuel mixture is
controlled by controlling a valve that reduces fuel flow to the
engine and the air/fuel mixture is enriched by reducing the period
of time that the valve reduces fuel flow to the engine.
19. The method of claim 17 wherein the air/fuel mixture is
controlled by controlling a valve that reduces fuel flow to the
engine and the air/fuel mixture is enriched by reducing the period
of time that the valve reduces fuel flow to the engine.
Description
REFERENCE TO CO-PENDING APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 62/075,945 filed Nov. 6, 2014, which is
incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0002] The present disclosure relates generally to an engine
control strategy.
BACKGROUND
[0003] Combustion engines are provided with a fuel mixture that
typically includes liquid fuel and air. The air/fuel ratio of the
fuel mixture may be calibrated for a particular engine, but
different operating characteristics such as type of fuel, altitude,
condition of filters or other engine components, and differences
among engines and other components in a production run may affect
engine operation.
SUMMARY
[0004] In at least some implementations, a method of controlling
engine idle speed includes:
[0005] comparing engine speed to a speed threshold where the speed
threshold may include a range of speeds;
[0006] if the engine speed is outside of the speed threshold,
adjusting the timing of an ignition spark up to a threshold amount
of ignition timing adjustment; and
[0007] if the engine speed is not within said speed threshold after
adjustment up to the threshold amount of ignition timing adjustment
then adjusting the air/fuel mixture provided to the engine to bring
the engine speed within said speed threshold.
[0008] In at least one example, the air/fuel mixture adjustment may
be provided in an amount sufficient to reduce the magnitude of a
previously made ignition timing adjustment. In at least one
example, when the ignition timing adjustment reaches the high side
of the threshold amount of ignition timing adjustment the fuel
mixture is leaned out to increase the engine speed. The high side
of the threshold amount of ignition timing adjustment may be the
maximum increase in spark advance within the threshold for ignition
timing adjustment. And in at least one example, when the ignition
timing adjustment reaches the low side of the threshold amount of
ignition timing adjustment the fuel mixture is enriched to decrease
the engine speed. The low side of the threshold amount of ignition
timing adjustment may be the maximum decrease in spark advance
within the threshold for ignition timing adjustment.
[0009] In at least some implementations, a method of detecting
engine cycles includes:
[0010] determining the time for consecutive engine revolutions;
[0011] comparing the time of a revolution to a consecutive
revolution;
[0012] repeating the comparison for a first threshold number of
revolutions; and
[0013] determining if every other revolution is either faster or
slower than the intervening revolutions for a second threshold
number of revolutions.
[0014] In at least one example, when the second threshold is
satisfied an ignition spark is skipped based upon the engine
revolution timing.
[0015] In at least one example, if the second threshold is not
satisfied within the first threshold number of engine revolutions,
then an ignition spark is skipped every other engine revolution and
then the engine speed is determined. If the determined engine speed
indicates that the engine speed has not decreased below a threshold
amount, the ignition event skipping may be continued. And in
addition to continuing the ignition event skipping, the fuel supply
to the engine may be adjusted to correspond to the engine intake
cycle. If the determined engine speed indicates that the engine
speed has decreased below a threshold amount, the ignition event
skipping may be changed to the opposite engine revolutions. After
the ignition event skipping is changed, the fuel supply to the
engine may be adjusted to correspond to the engine intake
cycle.
[0016] In at least some implementations, a method of controlling
engine acceleration or deceleration, includes:
[0017] determining occurrence of an engine acceleration or
deceleration;
[0018] adjusting ignition timing within preselected threshold
limits during acceleration or deceleration of the engine; and
[0019] adjusting an air-fuel mixture delivered to the engine during
acceleration and deceleration of the engine.
[0020] In at least one example, the ignition timing may be adjusted
up to a threshold amount of adjustment either before or while the
air-fuel mixture adjustment occurs. When an engine acceleration is
determined the ignition timing may be advanced and the air-fuel
mixture may be enriched. When an engine deceleration is determined
the ignition timing may be retarded and the air-fuel mixture may be
enriched. In at least some engine systems, the air-fuel mixture is
controlled by controlling a valve that reduces fuel flow to the
engine and the air-fuel mixture may be controlled by reducing the
period of time that the valve reduces fuel flow to the engine to
enrich the mixture or by increasing the time that the valve reduces
fuel flow to the engine to enlean the mixture.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The following detailed description of preferred
implementations and best mode will be set forth with regard to the
accompanying drawings, in which:
[0022] FIG. 1 is a schematic view of an engine and a carburetor
including a fuel mixture control device;
[0023] FIG. 2 is a fragmentary view of a flywheel and ignition
components of the engine;
[0024] FIG. 3 is a schematic diagram of an ignition circuit;
[0025] FIG. 4 is a flowchart for an engine control process;
[0026] FIG. 5 is a graph of a representative engine power
curve;
[0027] FIGS. 6-8 are graphs showing several variables that may be
tracked during an engine speed test;
[0028] FIG. 9 is a flow chart of an example of an engine idle
operation control process; and
[0029] FIG. 10 is a flow chart of an example of an engine ignition
and/or fuel control process.
DETAILED DESCRIPTION
[0030] Referring in more detail to the drawings, FIG. 1 illustrates
an engine 2 and a charge forming device 4 that delivers a fuel and
air mixture to the engine 2 to support engine operation. In at
least one implementation, the charge forming device 4 includes a
carburetor, and the carburetor may be of any suitable type
including, for example, diaphragm and float bowl carburetors. A
diaphragm-type carburetor 4 is shown in FIG. 1. The carburetor 4
takes in fuel from a fuel tank 6 and includes a mixture control
device 8 capable of altering the air/fuel ratio of the mixture
delivered from the carburetor. To determine a desired instantaneous
air/fuel ratio, a comparison is made of the engine speed before and
after the air/fuel ratio is altered. Based upon that comparison,
the mixture control device 8 or some other component may be used to
alter the fuel and air mixture to provide a desired air/fuel
ratio.
[0031] The engine speed may be determined in a number of ways, one
of which uses signals within an ignition system 10 such as may be
generated by a magnet on a rotating flywheel 12. FIGS. 2 and 3
illustrates an exemplary signal generation or ignition system 10
for use with an internal combustion engine 2, such as (but not
limited to) the type typically employed by hand-held and
ground-supported lawn and garden equipment. Such equipment includes
chainsaws, trimmers, lawn mowers, and the like. The ignition system
10 could be constructed according to one of numerous designs,
including magneto or capacitive discharge designs, such that it
interacts with an engine flywheel 12 and generally includes a
control system 14, and an ignition boot 16 for connection to a
spark plug (not shown).
[0032] The flywheel 12 rotates about an axis 20 under the power of
the engine 2 and includes magnets or magnetic sections 22. As the
flywheel 12 rotates, the magnetic sections 22 spin past and
electromagnetically interact with components of the control system
14 for sensing engine speed among other things.
[0033] The control system 14 includes a ferromagnetic stator core
or lamstack 30 having wound thereabout a charge winding 32, a
primary ignition winding 34, and a secondary ignition winding 36.
The primary and secondary windings 34, 36 basically define a
step-up transformer or ignition coil used to fire a spark plug. The
control system also includes a circuit 38 (shown in FIG. 3), and a
housing 40, wherein the circuit 38 may be located remotely from the
lamstack 30 and the various windings. As the magnetic sections 22
are rotated past the lamstack 30, a magnetic field is introduced
into the lamstack 30 that, in turn, induces a voltage in the
various windings. For example, the rotating magnetic sections 22
induce a voltage signal in the charge winding 32 that is indicative
of the number of revolutions of the engine 2 in the control system.
The signal can be used to determine the rotational speed of the
flywheel 12 and crankshaft 19 and, hence, the engine 2. Finally,
the voltage induced in the charge winding 32 is also used to power
the circuit 38 and charge an ignition discharge capacitor 62 in
known manner. Upon receipt of a trigger signal, the capacitor 62
discharges through the primary winding 34 of the ignition coil to
induce a stepped-up high voltage in the secondary winding 36 of the
ignition coil that is sufficient to cause a spark across a spark
gap of a spark plug 47 to ignite a fuel and air mixture within a
combustion chamber of the engine.
[0034] In normal engine operation, downward movement of an engine
piston during a power stroke drives a connecting rod (not shown)
that, in turn, rotates the crankshaft 19, which rotates the
flywheel 12. As the magnetic sections 22 rotate past the lamstack
30, a magnetic field is created which induces a voltage in the
nearby charge winding 32 which is used for several purposes. First,
the voltage may be used to provide power to the control system 14,
including components of the circuit 38. Second, the induced voltage
is used to charge the main discharge capacitor 62 that stores the
energy until it is instructed to discharge, at which time the
capacitor 62 discharges its stored energy across primary ignition
winding 34. Lastly, the voltage induced in the charge winding 32 is
used to produce an engine speed input signal, which is supplied to
a microcontroller 60 of the circuit 38. This engine speed input
signal can play a role in the operation of the ignition timing, as
well as controlling an air/fuel ratio of a fuel mixture delivered
to the engine, as set forth below.
[0035] Referring now primarily to FIG. 3, the control system 14
includes the circuit 38 as an example of the type of circuit that
may be used to implement the ignition timing control system 14.
However, many variations of this circuit 38 may alternatively be
used without departing from the scope of the invention. The circuit
38 interacts with the charge winding 32, primary ignition winding
34, and preferably a kill switch, and generally comprises the
microcontroller 60, an ignition discharge capacitor 62, and an
ignition thyristor 64.
[0036] The microcontroller 60 as shown in FIG. 3 may be an 8-pin
processor, which utilizes internal memory or can access other
memory to store code as well as for variables and/or system
operating instructions. Any other desired controllers,
microcontrollers, or microprocessors may be used, however. Pin 1 of
the microcontroller 60 is coupled to the charge winding 32 via a
resistor and diode, such that an induced voltage in the charge
winding 32 is rectified and supplies the microcontroller with
power. Also, when a voltage is induced in the charge winding 32, as
previously described, current passes through a diode 70 and charges
the ignition discharge capacitor 62, assuming the ignition
thyristor 64 is in a nonconductive state. The ignition discharge
capacitor 62 holds the charge until the microcontroller 60 changes
the state of the thyristor 64. Microcontroller pin 5 is coupled to
the charge winding 32 and receives an electronic signal
representative of the engine speed. The microcontroller uses this
engine speed signal to select a particular operating sequence, the
selection of which affects the desired spark timing Pin 7 is
coupled to the gate of the thyristor 64 via a resistor 72 and
transmits from the microcontroller 60 an ignition signal which
controls the state of the thyristor 64. When the ignition signal on
pin 7 is low, the thyristor 64 is nonconductive and the capacitor
62 is allowed to charge. When the ignition signal is high, the
thyristor 64 is conductive and the capacitor 62 discharges through
the primary winding 34, thus causing an ignition pulse to be
induced in the secondary winding 36 and sent on to the spark plug
47. Thus, the microcontroller 60 governs the discharge of the
capacitor 62 by controlling the conductive state of the thyristor
64. Lastly, pin 8 provides the microcontroller 60 with a ground
reference.
[0037] To summarize the operation of the circuit, the charge
winding 32 experiences an induced voltage that charges ignition
discharge capacitor 62, and provides the microcontroller 60 with
power and an engine speed signal. The microcontroller 60 outputs an
ignition signal on pin 7, according to the calculated ignition
timing, which turns on the thyristor 64. Once the thyristor 64 is
conductive, a current path through the thyristor 64 and the primary
winding 34 is formed for the charge stored in the capacitor 62. The
current discharged through the primary winding 34 induces a high
voltage ignition pulse in the secondary winding 36. This high
voltage pulse is then delivered to the spark plug 47 where it arcs
across the spark gap thereof, thus igniting an air/fuel charge in
the combustion chamber to initiate the combustion process.
[0038] As noted above, the microcontroller 60, or another
controller, may play a role in altering an air/fuel ratio of a fuel
mixture delivered by a carburetor 4 (for example) to the engine 2.
In the embodiment of FIG. 1, the carburetor 4 is a diaphragm type
carburetor with a diaphragm fuel pump assembly 74, a diaphragm fuel
metering assembly 76, and a purge/prime assembly 78, the general
construction and function of each of which is well-known. The
carburetor 4 includes a fuel and air mixing passage 80 that
receives air at an inlet end and fuel through a fuel circuit 82
supplied with fuel from the fuel metering assembly 76. The fuel
circuit 82 includes one or more passages, port and/or chambers
formed in a carburetor main body. One example of a carburetor of
this type is disclosed in U.S. Pat. No. 7,467,785, the disclosure
of which is incorporated herein by reference in its entirety. The
mixture control device 8 is operable to alter the flow of fuel in
at least part of the fuel circuit to alter the air/fuel ratio of a
fuel mixture delivered from the carburetor 4 to the engine to
support engine operation as commanded by a throttle.
[0039] For a given throttle position, the power output for an
engine will vary as a function of the air/fuel ratio. A
representative engine power curve 94 is shown in FIG. 5 as a
function of air/fuel ratio, where the air/fuel ratio becomes leaner
from left-to-right on the graph. This curve 94 shows that the slope
of the curve on the rich side is notably less than the slope of the
curve on the lean side. Hence, when a richer fuel mixture is
enleaned the engine speed will generally increase by a lesser
amount than when a leaner fuel mixture is enleaned by the same
amount. This is shown in FIG. 5, where the amount of enleanment
between points 96 and 98 is the same as between points 100 and 102,
yet the engine speed difference is greater between points 100 and
102 than it is between points 96 and 98. In this example, points 96
and 98 are richer than a fuel mixture that corresponds to engine
peak power output, while point 100 corresponds to a fuel mixture
that provides engine peak power output and point 102 is leaner than
all of the other points.
[0040] The characteristics of the engine power curve 94 may be used
in an engine control process 84 that determines a desired air/fuel
ratio for a fuel mixture delivered to the engine. One example of an
engine control process 84 is shown in FIG. 4 and includes an engine
speed test wherein engine speed is determined as a function of a
change in the air/fuel ratio of the fuel mixture, and an analysis
portion where data from the engine speed test is used to determine
or confirm a desired air/fuel ratio of the fuel mixture.
[0041] The engine control process 84 begins at 86 and includes one
or more engine speed tests. Each engine speed test may essentially
include three steps. The steps include measuring engine speed at
87, changing the air/fuel ratio of the fuel mixture provided to the
engine at 88, and then measuring the engine speed again at 92 after
at least a portion of the air/fuel ratio change has occurred.
[0042] The first step is to measure the current engine speed before
the fuel mixture is enleaned. Engine speed may be determined by the
microcontroller 60 as noted above, or in any other suitable way.
This is accomplished, in one implementation, by measuring three
engine speed parameters with the first being the cyclic engine
speed. This is the time difference for one revolution of the
engine. In most engines, there is a large amount of repeatable
cyclic engine speed variation along with a significant amount of
non-repeatable cyclic engine speed variation. This can be seen in
FIG. 6, where the cyclic engine speed is shown at 104. Because this
cyclic variability is difficult to use in further determinations, a
rolling average (called F1-XX) is created, where XX is the number
of revolutions being averaged, and generally F1 is a low averaging
value such as 4 or 6. This greatly eliminates the large repeatable
cyclic engine speed variation but does not dampen out too much the
non-repeatable cyclic engine speed variation. The third engine
speed value is F2-XX, and F2 is a greater averaging value, such as
80 revolutions. This amount of averaging greatly dampens out any
variations of speed change and the intent is to dampen out the
effect of the enleanment engine speed change. Now that there are
two usable rpm values, F1-6 and F2-80 in this example, the
difference of these values can be used to represent the engine
speed change caused by the enleanment of the fuel mixture during an
engine speed test.
[0043] In addition to measuring engine speed, the engine speed test
includes changing the air/fuel ratio of the fuel mixture delivered
to the engine. This may be accomplished with the mixture control
device, e.g. solenoid valve 8 may be actuated thereby changing an
air/fuel ratio of a mixture delivered to the engine 2 from the
carburetor 4. In at least some implementations, the solenoid valve
8 may be actuated to its closed position to reduce fuel flow to a
main fuel port or jet 90, thereby enleaning the fuel and air
mixture. The valve 8 may be closed for a specific time period, or a
duration dependent upon an operational parameter, such as engine
speed. In one form, the valve 8 is closed (or nearly closed) for a
certain number or range of engine revolutions, such as 1 to 150
revolutions. This defines an enleanment period wherein the leaner
fuel and air mixture is delivered to the engine 2. Near, at or just
after the end of the enleanment period, the engine speed is again
determined at 92 as noted above.
[0044] FIGS. 6-8 show engine speed (in rpm) versus number of engine
revolutions during one or more engine speed tests. F1-6 is shown by
line 106, F2-80 is shown by line 108, the solenoid actuation signal
is shown by line 110, and a fuel/air ratio (Lambda) is shown by
line 112.
[0045] FIG. 6 shows the initial air/fuel ratio to be rich at
Lambda=0.81. The amount of enleanment in the example test was 50
degrees for 20 revolutions. This means that the solenoid valve was
actuated 50 degrees earlier in the engine stroke than it would have
been for normal engine operation (e.g. operation other than during
the test). The increased duration of solenoid actuation leads to an
enleaned fuel mixture. From this enleanment, the average rpm
difference of F1-6 and F2-80 is 30 rpm. Because the enleanment is
so large, 50 degrees, a decrease of 30 rpm is observed even though
the initial air/fuel ratio is still 6% richer than a fuel mixture
ratio that would yield peak engine power.
[0046] FIG. 7 shows the same 50 degree enleanment test for 20
revolutions but the starting air/fuel ratio is at Lambda=0.876
which approximately corresponds to peak engine power. The average
engine speed difference between F1-6 and F2-80 in this example is
148 rpm, approximately five times greater than the speed difference
from a starting air/fuel ration of Lambda=0.81.
[0047] Because the process as described involves enleaning a fuel
mixture, the initial or calibrated air/fuel ratio should be richer
than desired. This ensures that at least some enleanment will lead
to a desired air/fuel ratio. In at least some implementations, the
initial air/fuel ratio may be up to about 30% richer than the fuel
mixture corresponding to peak engine power. Instead of or in
addition to enleaning, enriching the fuel mixture may be possible
in a given carburetor construction, and in that case the engine
speed test could include an enriching step if an unduly lean
air/fuel ratio where determined to exist. Enriching may be done,
for example, by causing additional fuel to be supplied to the
engine, or by reducing air flow. The process may be simpler by
starting with a richer fuel mixture and enleaning it, as noted
herein.
[0048] Referring again to the engine control process shown in FIG.
4, the two engine speed measurements obtained at 87 and 92 are
compared at 93. To improve the accuracy of the engine control
process, several engine speed tests may be performed, with a
counter incremented at 97 after each engine speed test, and the
counter compared to a threshold at 99 to determine if a desired
number of engine speed tests have been performed. If a desired
number of tests have been performed, the process 84 then analyzes
the data from the engine speed test(s).
[0049] To determine whether the fuel mixture delivered to the
engine before the engine speed tests were performed was within a
desired range of air/fuel ratios, the engine speed differences
determined at 93 are compared against one or more thresholds at 95.
Minimum and maximum threshold values may be used for the engine
speed difference that occurs as a result of enleaning the fuel
mixture provided to the engine. An engine speed difference that is
below the minimum threshold (which could be a certain number of
rpm's) likely indicates that the air/fuel ratio before that
enleanment was richer than a mixture corresponding to peak engine
power. Conversely, an engine speed difference that is above the
maximum threshold (which could be a certain number of rpm's)
indicates that the air/fuel ratio became too lean (indicating the
fuel mixture started leaner than a peak power fuel mixture, as
noted above). In at least some implementations, the minimum
threshold is 15 rpm, and the maximum threshold is 500 rpm or
higher. These values are intended to be illustrative and not
limiting--different engines and conditions may permit use of
different thresholds.
[0050] In the process 84 shown in FIG. 4, the engine speed test is
performed multiple times in a single iteration of the process 84.
In one iteration of the process 84, it is determined at 95 if the
engine speed difference of any one or more of the engine speed
tests is within the threshold values, and if so, the process may
end at 101. That is, if a threshold number (one or more) of the
determined engine speed differences from 93 are within the
thresholds, the process may end because the starting air/fuel ratio
(e.g. the air/fuel ratio of the mixture prior to the first engine
speed test of that process iteration) is at or within an acceptable
range of a desired air/fuel ratio. In one implementation, five
engine speed tests may be performed, and an engine speed difference
within the thresholds may be required from at least three of the
five engine speed tests. Of course, any number of engine speed
tests may be performed (including only one) and any number of
results within the thresholds may be required (including only one
and up to the number of engine speed tests performed).
[0051] If a threshold number of engine speed differences
(determined at 93) are not within the thresholds, the air/fuel
ratio of the mixture may be altered at 103 to a new air/fuel ratio
and the engine speed tests repeated using the new air/fuel ratio.
At 95, if an undesired number of engine speed differences were less
than the minimum threshold, the air/fuel ratio of the fuel mixture
may be enleaned at 103 before the engine speed tests are repeated.
This is because an engine speed difference less than the minimum
threshold indicates the fuel mixture at 87 was too rich. Hence, the
new air fuel ratio from 103 is leaner than when the prior engine
speed tests were performed. This can be repeated until a threshold
number of engine speed differences are within the thresholds, which
indicates that the fuel mixture provided to the engine before the
engine speed tests were conducted (e.g. at 87) is a desired
air/fuel ratio. Likewise, at 95, if an undesired number of engine
speed differences were greater than the maximum threshold, the
air/fuel ratio of the fuel mixture may be enleaned less, or even
enriched, at 103 before the engine speed tests are repeated. This
is because an engine speed difference greater than the maximum
threshold indicates the fuel mixture at 87 was too lean. Hence, the
new air fuel ratio from 103, in this instance, is richer than when
the prior engine speed tests were performed. This also can be
repeated until a threshold number of engine speed differences are
within the thresholds, with a different starting air/fuel ratio for
each iteration of the process.
[0052] When a desired number of satisfactory engine speed
differences (i.e. between the thresholds) occur at a given air/fuel
ratio, that air/fuel ratio may be maintained for further operation
of the engine. That is, the solenoid valve 8 may be actuated during
normal engine operation generally in the same manner it was for the
engine speed tests that provided the satisfactory results.
[0053] FIG. 8 shows a fuel mixture adjustment test series starting
from a rich air/fuel ratio of about Lambda=0.7, and ending with an
air/fuel ratio of about Lambda=0.855. In this series, the
enleanment step was repeated several times until a desired number
of engine speed differences within the thresholds occurred. That
resulted in a chosen air/fuel ratio of about Lambda=0.855, and the
engine may thereafter be operated with a fuel mixture at or nearly
at that value for improved engine performance by control of the
solenoid valve 8 or other mixture control device(s).
[0054] As noted above, instead of trying to find an engine speed
difference (after changing the air/fuel ratio) that is as small as
possible to indicate the engine peak power fuel mixture, the
process may look for a relatively large engine speed difference,
which may be greater than a minimum threshold. This may be
beneficial because it can sometimes be difficult to determine a
small engine speed difference during real world engine usage, when
the engine is under load and the load may vary during the air/fuel
ratio testing process. For example, the engine may be used with a
tool used to cut grass (e.g. weed trimmer) or wood (e.g. chainsaw).
Of course, the engine could be used in a wide range of
applications. By using a larger speed difference in the process,
the "noise" of the real world engine load conditions have less of
an impact on the results. In addition, as noted above, there can be
significant variances in cyclic speed during normal operation of at
least some small engines making determination of smaller engine
speed differences very difficult.
[0055] As noted above, the engine load may change as a tool or
device powered by the engine is in use. Such engine operating
changes may occur while the engine speed test is being conducted.
To facilitate determining if an engine operating condition (e.g.
load) has changed during the engine speed test, the engine speed
may be measured a third time, a sufficient period of time after the
air/fuel ratio is changed during an engine speed test to allow the
engine to recover after the air/fuel ratio change. If the first
engine speed (taken before the fuel mixture change) and the third
engine speed (taken after the fuel mixture change and after a
recovery period) are significantly different, this may indicate a
change in engine load occurred during the test cycle. In that
situation, the engine speed change may not have been solely due to
the fuel mixture change (enleanment) during the engine speed test.
That test data may either be ignored (i.e. not used in further
calculation) or a correction factor may be applied to account for
the changed engine condition and ensure a more accurate air/fuel
ratio determination.
[0056] In one form, and as noted above, the mixture control device
that is used to change the air/fuel ratio as noted above includes a
valve 8 that interrupts or inhibits a fluid flow within the
carburetor 4. In at least one implementation, the valve 8 affects a
liquid fuel flow to reduce the fuel flow rate from the carburetor 4
and thereby enlean the fuel and air mixture delivered from the
carburetor to the engine. The valve may be electrically controlled
and actuated. An example of such a valve is a solenoid valve. The
valve 8 may be reciprocated between open and closed positions when
the solenoid is actuated. In one form, the valve prevents or at
least inhibits fuel flow through a passage 120 (FIG. 1) when the
valve is closed, and permits fuel flow through the passage when the
valve is opened. As shown, the valve 8 is located to control flow
through a portion of the fuel circuit that is downstream of the
fuel metering assembly and upstream of a main fuel jet that leads
into the fuel and air mixing passage. Of course, the valve 8 may be
associated with a different portion of the fuel circuit, if
desired. By opening or closing the valve 8, the flow rate of fuel
to the main fuel jet is altered (i.e. reduced when the valve is
closed) as is the air/fuel ratio of a fuel mixture delivered from
the carburetor. A rotary throttle valve carburetor, while not
required, may be easily employed because all fuel may be provided
to the fuel and air mixing passage from a single fuel circuit,
although other carburetors may be used.
[0057] In some engine systems, an ignition circuit 38 may provide
the power necessary to actuate the solenoid valve 8. A controller
60 associated with or part of the ignition circuit 38 may also be
used to actuate the solenoid valve 8, although a separate
controller may be used. As shown in FIG. 3, the ignition circuit 38
may include a solenoid driver subcircuit 130 communicated with pin
3 of the controller 60 and with the solenoid at a node or connector
132. The controller may be a programmable device and may have
various tables, charts or other instructions accessible to it (e.g.
stored in memory accessible by the controller) upon which certain
functions of the controller are based.
[0058] The timing of the solenoid valve, when it is energized
during the portion of the time when fuel is flowing into the fuel
and air mixing passage, may be controlled as a calibrated state in
order to determine the normal air/fuel ratio curve. To reduce power
consumption by the solenoid, the fuel mixture control process may
be implemented (that is, the solenoid may be actuated) during the
later portion of the time when fuel flows to the fuel and air
mixing passage (and fuel generally flows to the fuel metering
chamber during the engine intake stroke). This reduces the duration
that the solenoid must be energized to achieve a desired
enleanment. Within a given window, energizing the solenoid earlier
within the fuel flow time results in greater enleanment and
energizing the solenoid later results in less enleanment. In one
example of an enleanment test, the solenoid may be energized during
a brief number of revolutions, such as 30. The resultant engine
speed would be measured around the end of this 30 revolution
enleanment period, and thereafter compared with the engine speed
before the enleanment period.
[0059] With a 4-stroke engine, the solenoid actuated enleanment may
occur every other engine revolution or only during the intake
stroke. This same concept of operating the solenoid every other
revolution could work on a 2-stroke engine with the main difference
being the solenoid energized time would increase slightly. At
slower engine speeds on a 2-stroke engine the solenoid control
could then switch to every revolution which may improve both engine
performance and system accuracy.
[0060] It is also believed possible to utilize the system to
provide a richer air/fuel mixture to support engine acceleration.
This may be accomplished by altering the ignition timing (e.g.
advancing ignition timing) and/or by reducing the duration that the
solenoid is energized so that less enleanment, and hence a richer
fuel mixture, is provided. When the initial carburetor calibration
is rich (e.g. approximately 20-25% rich), no solenoid actuation or
less solenoid actuation will result in a richer fuel mixture being
delivered to the engine. Further, if the amount of acceleration or
acceleration rate can be sensed or determined, a desired enrichment
amount could be mapped or determined based on the acceleration
rate. Combining both the ignition timing advance and the fuel
enrichment during transient conditions, both acceleration and
deceleration can be controlled for improved engine performance.
Ignition timing may be controlled, in at least some
implementations, as disclosed in U.S. Pat. No. 7,000,595, the
disclosure of which is incorporated by reference herein, in its
entirety.
[0061] Idle engine speed can be controlled using ignition spark
timing. While not wishing to be held to any particular theory, it
is currently believed that using a similar concept, fuel control
could be used to improve the idle engine speed control and
stability. This could be particularly useful during the end of
transient engine conditions such as come-down. The combination of
ignition and fuel control during idle could improve engine
performance.
[0062] Ignition timing control is considered a fast response
control method in that the engine speed or other engine parameter
may change quickly when the ignition timing is changed. However,
the controllable engine speed range is constrained by the maximum
and minimum amount of ignition timing advance the engine can
tolerate. Air/fuel mixture changes are considered a somewhat slower
response control method in that the engine operating changes may be
slower than with an ignition timing change. Combining the slower
response air fuel mixture control with the faster response ignition
control can greatly expand the engine speed control range, and this
may be particularly useful, in at least some engines and
applications, at engine idle or near idle operating speeds and
conditions. Of course, the innovations disclosed herein are not
limited to idle and near-idle engine operation.
[0063] As noted above, the range of engine speed control that may
be achieved by ignition timing control (e.g. advancing or retarding
ignition events) is confined to the combustible range of ignition
advance. Practical limitations could be even narrower in any given
engine application, around 20-30 degrees of ignition advance, to
ensure proper engine performance such as acceptable acceleration,
roll-out, come-down, etc. While most engines can experience
performance benefits from ignition timing based idle engine speed
control, it is possible to exceed the ignition control range which
can negatively affect engine performance in at least some
instances, such as when different fuel is used or the air density
changes from altitude and temperature changes. Some of these
changes or combinations of changes can effectively exceed the
ignition timing idle speed control range resulting in the idle
speed exceeding its specified set-point. To expand the effective
idle engine speed control window the addition of fuel and air
mixture control (i.e. changing the air/fuel ratio of the mixture
delivered to the engine) can be combined with ignition timing.
[0064] In a combined control system, a desired threshold of
ignition timing change may be established, and a desired engine
idle speed threshold, likely set as a range of speed, may also be
established. Idle engine speed outside of the engine idle speed
threshold may first result in a change of the engine ignition
timing. The ignition timing may be altered up to the ignition
timing change threshold, and if the engine speed ends up within the
engine idle speed threshold by only the change in ignition timing,
nothing more needs to be done. Subsequent engine speed changes may
be handled in the same manner. If, however, the ignition timing is
altered up to the threshold ignition timing change and the engine
speed is still outside of the engine speed threshold, then the fuel
and air mixture ratio may be altered until the engine speed is
within the threshold. This combination of ignition timing control
and air/fuel mixture control can greatly expand the ability to
control engine idle speed for all environmental conditions.
Further, utilizing the faster response ignition timing control as
the first measure to control engine idle speed enables more rapid
engine speed control in many instances, and only when that is
insufficient is the slower response fuel/air adjustment control
implemented. This enables more rapid and responsive engine speed
control.
[0065] Increases in spark advance (where the spark is the start of
an ignition event) generally result in increases in engine speed
and decreases in spark advance generally result in engine speed
decreasing. Likewise since most small engine carburetors are
initially set with a slightly rich air/fuel mixture (and slightly
open throttle valve setting), increasing the air/fuel mixture ratio
(which makes the air/fuel mixture leaner, for example from 9:1 to
11:1) will result in an engine idle speed increase and decreasing
the air/fuel mixture (which makes the air/fuel mixture richer, for
example from 13:1 to 10:1) will generally result in an engine speed
decrease.
[0066] In a representative system, the ignition timing control
threshold may be set at plus or minus four (4) degrees of the
normal ignition timing, where the degrees indicate the angular
engine position relative to TDC or some other reference position at
which the ignition spark is provided. Once the ignition control
threshold is exceeded on the high side (e.g. at +4.degree.) the
fuel mixture can then be leaned out to increase the engine speed
while maintaining the ignition timing within the threshold, or even
allowing a reduction in the magnitude of the ignition timing change
from the nominal/normal ignition timing. Likewise, if the ignition
timing advance is reduced below the low threshold (e.g. -4.degree.)
the air/fuel mixture can be richened to reduce the engine speed
while maintaining the ignition timing within the threshold, or even
allowing a reduction in the magnitude of the ignition timing change
from the normal ignition timing.
[0067] One representative control process 200 is generally shown in
FIG. 9. The process starts at 201, the engine speed is checked at
202 and a determination is made at 204 as to whether the engine is
idling or near enough to idle for the process. In this example, the
process is used only for engine idle and near idle operation and
other strategies may be used when the engine is not at or near
idle, if desired. If the engine operation does not satisfy the
first condition then the process may end at 205. If the engine
operation satisfies the first condition, then it is determined in
206 whether the engine speed is within a desired range for idle or
near idle operation. If the engine speed is within the threshold,
then the process may be started over, to again check engine idle
operation as desired. This check may be run at any desired periodic
timing.
[0068] If the engine speed is outside of the threshold, then it is
determined at 208 whether the maximum ignition timing adjustment
has already been made (i.e. if the ignition timing is within a
threshold range). If the ignition timing is within its threshold,
then the ignition timing may be adjusted at 210 up to its threshold
in one or more iterative steps or otherwise, as desired. If
additional ignition timing is not available within that threshold,
then the process continues to 212 where the air/fuel mixture may be
adjusted to provide a desired engine speed change. The process may
continue to check engine speed periodically (such as every
revolution or at longer intervals) or the process may end. The
process may be run again, as desired, to monitor and change as
needed the engine idle speed operation.
[0069] Additional control calibration techniques can be applied to
further refine the idle speed stability and accuracy. Things like
looking statistically at the number of revolutions or time the
ignition timing has exceeded the threshold or the standard
deviation of the ignition timing value exceeding the threshold
value can further refine the strategy. Among other things, the
normal ignition timing may be altered, and or the ignition timing
control threshold adjusted, depending upon actual engine operating
data.
[0070] By knowing which phase the engine is operating on the total
electrical power consumption used by the engine can be greatly
reduced when only consuming electrical power every other
revolution. This is particularly beneficial at low engine speeds
when the power generation capacity of the ignition module is often
less than the required power to control the engine every revolution
(ignition timing and secondary electrical loads such as an
electronic carburetor).
[0071] Four stroke engines have four distinct cycles; intake,
compression, power and exhaust. These four cycles take place over
two engine revolutions. Beginning at TDC the intake cycle begins
and at the subsequent BDC the intake cycle ends and the compression
stroke begins. At the next TDC the compression cycle is completed
and the power stroke begins. At the next BDC, the power cycle is
completed and the exhaust stroke begins. Hence, the intake and
compression cycles occur in one engine revolution and the power and
exhaust cycles occur in the next engine revolution. The time for
the engine revolution including the intake and compression cycles
is greater (slower engine speed) than the time for the engine
revolution power and exhaust cycles (faster engine speed). This is
largely due to losses from intake pumping and compression resulting
in the engine speed decreasing during the intake and compression
engine revolution. Conversely during the power or combustion cycle
the engine speeds up due to the increase in pressure developed
during a combustion event.
[0072] The difference in speed is detectable with the use of a
microprocessor clock such as is found in digital ignition modules.
Measuring the time for an engine revolution may be performed on
small engines that have a single magnet group mounted on/in the
flywheel. As the flywheel magnet rotates past the ignition module
an electrical signal is produced that can be used as a crankshaft
angle measurement. Every engine revolution produces one electrical
signal therefore the time between these signals represents the
average engine speed for a single revolution. Further refinement of
this concept can be done with multiple magnet groups thereby
allowing detection of the individual engine cycles rather than the
just the engine revolution that produces power. This also will
result in greater crankshaft angular resolution (ability to
determine crankshaft position) within a single engine
revolution.
[0073] Since there can be a large amount of cyclic variation from
revolution to revolution, it sometimes can be difficult to
guarantee the determination of the engine revolutions (e.g. the
revolution that corresponds to the intake and compression cycles,
or the revolution that corresponds to the power and exhaust
cycles).
[0074] To improve the accuracy of phase detection, a process that
determines engine speed for a number of engine revolutions may be
used. An example of such a process is described below. At engine
startup, an ignition spark is provided every engine revolution, as
is common, and a threshold number of engine revolution speeds or
time is recorded. In one example, the time for each of 20 engine
revolutions is recorded, and this data may be recorded in any
suitable manner on any suitable device, such as but not limited to
a First-In-First-Out (FIFO) buffer. In this way, the last or most
recent 20 engine revolution times/speeds are stored. Of course, the
data for more or fewer engine revolutions may be used and 20 is
just one example.
[0075] After a threshold number of engine revolutions, for example
chosen to permit the engine speed to stabilize, the recorded engine
revolution data is checked to see if an alternating pattern has
occurred, for example where every other revolution is longer than
the intervening revolutions. The second threshold may be any
desired number of engine revolutions, or it may simply be a time
from engine start or other engine event. In one example, the second
threshold is 12 revolutions although other numbers of revolutions
can be utilized as desired.
[0076] The process may look at any number of engine revolution
times/speeds to determine if a desired pattern has occurred. For
example, the process may look at all 20 recorded engine revolution
times to determine if the desired timing pattern has occurred. And
the process may continue until 20 consecutive engine revolutions
show a desired timing pattern, e.g. every other revolution being
shorter or longer than the intervening revolutions. This analysis
may be conducted for a given number of engine revolutions after
engine starting, or some other chosen engine event. For example, in
one form, this analysis of the last 20 revolutions occurs for only
the first 50 engine revolutions after engine starting. This
relatively short window may be chosen to reduce the likelihood that
the engine operation will change (for example, due to throttle
valve actuation) which would cause an engine speed change not due
to the various engine cycle effects.
[0077] A general description of the process 300 is shown in FIG.
10. At 306 it is determined if the desired number of consecutive
(or perhaps a threshold percentage of) engine cycles indicates a
desired pattern of engine speed changes within a desired window of
engine revolutions, then the process may continue to 308 wherein an
ignition event is skipped every other revolution. In one form, the
ignition event is provided only during the engine revolution
including the power cycle and an ignition spark is not provided
during the engine revolution including the intake and compression
cycles. This avoids wasting an ignition spark and the energy
associated therewith. Also, fuel may be provided from the
carburetor or other fuel supplying device only during the correct
engine revolution or cycle, e.g. the engine revolution including
the intake and compression cycles, which is noted at 310. In this
way, more efficient engine operation can be achieved to conserve
electrical energy, conserve fuel and reduce engine emissions.
[0078] When ignition events are skipped, a check of the engine
speed can be performed at 312 to ensure that the engine speed is
not adversely affected, which could mean that the incorrect spark
is being skipped. For example, if after a couple of skipped
ignition events the engine speed decreases beyond a threshold, this
could mean that the ignition spark needed for combustion was
skipped. If an engine speed decrease is detected, the ignition
spark may be provided every engine revolution at 314, or the
skipped spark may be changed to the other engine revolution and a
check of the engine speed performed to see if the ignition spark is
being provided during the correct engine revolution.
[0079] The engine speed check may occur as the revolutions are
recorded, or the check may look to previously recorded data for
engine revolutions. In the example below, the most recent engine
revolution recorded is rpm[0], the previous revolution is rpm[-1],
the revolution before that is rpm[-2], etc. For the engine
cycle/revolution detection to be considered successful, then the
recorded revolution data needs to satisfy: (rpm[0]>rpm[-1]) AND
(rpm[-1]<rpm[-2]). If satisfied, then the review continues to
(rpm[-2]>rpm[-3]) AND (rpm[-3]<rpm[-4]). And so on until a
threshold number of revolutions satisfy the pattern, where the
threshold number of revolutions needed can be any number up to and
including all of the revolutions stored on the buffer. When the
threshold number of revolutions satisfies the pattern, the system
moves to the next phase which is to skip ignition events and
provide fuel in accordance with the determined engine revolutions
and the engine cycles occurring during these revolutions.
[0080] If the desired number of consecutive engine revolutions does
not indicate a desired pattern of engine speed changes within a
desired window of engine revolutions (a "no" response at 306), then
the ignition event may be terminated or not provided every other
engine revolution for a determined number of engine revolutions.
While in FIG. 10 the "skip ignition" step is shown as 308 in either
determination from 306, where the threshold revolution criteria is
satisfied at 306, the "skip ignition" occurs based on this data,
and when the criteria is not satisfied, the skip ignition occurs
based on something else. When to skip the spark may be chosen based
upon an analysis of the recorded revolutions (e.g. if more
revolutions are slower than the others, on an every other
revolution basis, then this information may be used for the initial
spark skip even though the full threshold of revolutions did not
satisfy the set rule) or the next scheduled or any subsequent spark
may be skipped without regard to the recorded data. In one example,
an ignition event is skipped every other engine revolution for four
engine revolutions. If the engine speed does not decrease beyond a
threshold after the skipped ignition events (as determined at 312),
then the system considers that the ignition events were skipped
during the correct engine revolutions. Subsequent ignition events
may also be skipped during corresponding engine revolutions, and
the fuel supply may also be controlled based on this timing. If,
however, the engine speed does decrease beyond a threshold after
the skipped ignition events, then the ignition events were skipped
during the incorrect engine revolutions. Subsequent skipped
ignition events can then be set to the other engine revolutions and
the fuel supply to the engine may also be controlled based on this
timing. Subsequent checking of engine speed may also be used to
ensure the skipped ignition events are not adversely affecting
engine speed.
[0081] Additionally statistical analysis of the alternating pattern
can be performed to provide an accurate determination of engine
cycle/phase when there are larger amounts of cyclic variation or
small differences in cyclic engine speed. This type of analysis can
be done to effectively reduce the determination time required.
[0082] In general, most small engines idle run quality is best when
the ignition timing is slightly retarded and the air/fuel mixture
is near optimum. But during these conditions most small engines
will also experience performance problems during fast transient
accelerations and decelerations. To help alleviate this issue, both
rapidly advancing the ignition timing and enriching the fuel
mixture for several revolutions can improve engine performance. The
difficulty in doing so on small low cost engines stems from not
having sensors to indicate that a rapid load change is starting to
occur, such as a throttle position sensor or a manifold pressure
sensor.
[0083] This disclosure describes how using the raw ignition signal
along with controlling ignition timing and fuel mixture on a cyclic
basis can improve engine performance during these fast transient
conditions. Controlling ignition timing based on transient changes
in the ignition signal has been described in U.S. Pat. No.
7,198,028. Use of these detection methods can now be applied to
rapidly change the ignition timing and also rapidly change the fuel
mixture via an electronic fuel control actuator in the carburetor,
thereby improving the acceleration and deceleration qualities of
the engine.
[0084] One example of a fuel control actuator includes a solenoid
that blocks at least a portion of the fuel flow during the engine
intake cycle. As an example, if the blocking action normally occurs
at the end of the intake cycle, the fuel mixture can be leaned-out
by activating a normally open solenoid at an earlier crank angle
position, in other words by blocking at least some fuel flow for a
longer duration of the intake cycle. Many possible calibration
configurations exist but an example might be activating the
solenoid at 200.degree. ATDC results in a Lambda value of 0.78
(rich) and a solenoid activation angle of 145.degree. ATDC results
in a Lambda value of 0.87 (9% leaner). Therefore, changing the
solenoid activation angle to a richer Lambda setting (less fuel
flow blocking) during transient accelerations can improve the
engine response and performance. This enriching of the mixture
during acceleration can be tailored up to a full rich setting (no
solenoid activation, so no fuel flow blocking) and also controlled
for any number of engine revolutions after the detection of a
transient change has occurred. Additionally, the fuel flow control
can be optimized in any number of ways, for example, running full
rich (no fuel flow blocking) for a certain number of revolutions
and decreasing the richness of the fuel mixture (i.e. increasing
the fuel flow blocking) at a set rate for a certain number of
additional revolutions. In just one of nearly limitless examples,
no fuel flow blocking may be provided for 3 revolutions and the
richness may be decreased (i.e. increased fuel flow blocking) for
10 revolutions. Many additional options for the actual control
calibration exist. Likewise control of the deceleration performance
can be improved through similar control techniques, and in at least
some implementations, the richness of the fuel mixture can be
increased (i.e. decreasing the fuel blocking) during the
deceleration event. During acceleration, the ignition timing may
also be advanced up to its maximum advancement, which may be a
predetermined and/or calibrated value relative to a nominal or
normal ignition timing for a given engine operating condition.
During deceleration or come-down periods, the ignition timing may
be retarded for a desired time (such as, but not limited to, a
certain number of revolutions). When to alter/retard/advance the
ignition timing and by how much to alter the timing may be
predetermined or calibrated values. In this way, the ignition
timing and fuel control may be adjusted together or in series
during acceleration and deceleration of the engine.
[0085] While the forms of the invention herein disclosed constitute
presently preferred embodiments, many others are possible. It is
not intended herein to mention all the possible equivalent forms or
ramifications of the invention. It is understood that the terms
used herein are merely descriptive, rather than limiting, and that
various changes may be made without departing from the spirit or
scope of the invention.
* * * * *