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Description  |
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FIELD OF THE INVENTION
The present invention relates to electronic engine control systems, and
more particularly to internal combustion engine control systems using mass
air sensors. Still more particularly, the present invention relates to
techniques for accurately adapting engine control parameters in response
to integrated mass air flow corresponding to engine cylinder events.
BACKGROUND AND SUMMARY OF THE INVENTION
Using mass air flow to provide a control input to an electronic engine
control system ("ECS") is well known, as is evidenced by the following
listing of exemplary prior issued commonly-assigned U.S. patents generally
relating to electronic engine control arrangements:
U.S. Pat. No. 4,421,089
U.S. Pat. No. 4,401,063
U.S. Pat. No. 4,387,602
U.S. Pat. No. 4,250,842
U.S. Pat. No. 4,246,639
U.S. Pat. No. 4,245,317
U.S. Pat. No. 4,228,777
U S. Pat. No. 4,214,307
U S. Pat. No. 4,212,065
U S. Pat. No. 4,193,380
U S. Pat. No. 4,186,602
U S. Pat. No. 4,096,833
U S. Pat. No. 4,096,831
U S. Pat. No. 4,091,773.
The following additional patents also relate to air flow sensing
arrangements within electronic engine control systems:
U.S. Pat. No. 4,860,222
U.S. Pat. No. 4,587,884
U.S. Pat. No. 4,448,070
U.S. Pat. No. 4,494,405
U.S. Pat. No. 4,445,369
U.S. Pat. No. 4,433,576
U.S. Pat. No. 4,125,093
U.S. Pat. No. 4,425,886
U.S. Pat. No. 4,403,506
U.S. Pat. No. 4,317,365
U.S. Pat. No. 4,237,830
U.S. Pat. No. 4,083,244
U.S. Pat. No. 3,433,069
U.S. Pat. No. 3,374,673
As is well known, mass air flow parameters are extremely useful in
controlling the operation of an internal combustion engine. Mass air flow
relates to the mass of the air actually flowing through (into) the engine,
and thus provides information useful in calculating and controlling
critical engine operating parameters such as air-fuel ratio. One of the
advantages of measuring mass air flow directly using, for example, a mass
air flow meter (as opposed to indirectly using an air volume flow meter)
is independence of the measurement on variables such as engine tolerances
(which may change as the engine wears). See, for example, Loesing et al,
"Mass Air Flow Meter--Design and Application", SAE Technical Paper Series
No. 890779 (International Congress and Exposition, Detroit, Mich., Feb.
27-Mar. 3 1989).
Typical conventional mass air flow meters found in many of today's
automotive systems operate on the hot wire anemometer principle. Briefly,
a hot film or wire is heated by an electrical current so as to maintain a
constant temperature differential between the heated element and another
non-heated (i.e., at ambient temperature) element. The air flowing past
the heated element removes heat from that element (with higher mass air
flow removing more heat)--requiring additional electrical heating current
to maintain the heated element at the constant temperature differential
above ambient. A voltage differential V.sub.out appearing across a
resistor coupled (typically in series) with the heating element is
measured or otherwise used to provide a direct measure of mass air flow.
As is well known, this hot wire anemometer type mass air flow sensor
provides mass air flow as a fourth order function of the voltage output
signal:
##EQU1##
where V.sub.out is the output voltage, k.sub.1 and k.sub.2 are constants,
and m.sub.L is the mass air flow. FIG. 1 shows a typical transfer function
for an exemplary hot wire anemometer type mass air flow sensor showing
this fourth-order relationship.
One problem arises as to how to efficiently obtain the mass air flow from
the sensor V.sub.out output without introducing errors or using costly
components.
In automotive fuel management systems, it is desirable to calculate or
estimate the mass of air taken into a corresponding individual combustion
chamber cylinder during the intake stroke (in a Otto cycle type
four-stroke internal combustion engine for example) in order to determine
the amount of fuel that must be injected into that cylinder so as to
provide a desired air/fuel ratio. Unfortunately, the air flow is anything
but constant over an engine cycle, but rather may be more accurately
thought of as surges or pulses of air flowing into the cylinder during the
time the intake valve is open.
One technique used in the past to determine the air mass flowing into a
cylinder during the intake stroke is to apply a wave form factor to the
sampled air flow value. However, this technique is generally successful
only if the wave shape is constant and the sample location on the wave
form is known. Neither of these conditions exist in modern engines
including variable valve timing. Variable valve timing control can add
large variations to the mass air flow during an engine cycle. The wave
shapes of these variations are not predictable, and wave shape factor
and/or synchronous sampling techniques are therefore not effective to
provide accurate mass air flow determinations based on more limited
measurement information. To obtain the air "charge" (trapped air mass) in
a cylinder combustion chamber under these circumstances, the air flow may
be integrated (e.g., with respect to time) for each cylinder "event"
(e.g., intake stroke) using a sufficiently large number of sufficiently
high resolution samples to yield an accurate air mass determination.
One attempt to filter (integrate) the flow signal using analog circuitry
introduced large errors attributable to the non-linear nature of the
V.sub.out signal. Difficulties with this method can be demonstrated by
providing a somewhat simplified but nevertheless illustrative example. The
following Table I provides the transform for a typical mass air flow
sensor:
TABLE I
______________________________________
Sensor Calibration
Mass Air Flow
kg/hr Sensor Voltage
X Y
______________________________________
13.0000 0.48500
15.00000 0.55500
20.00000 0.71700
25.00000 0.84200
30.00000 0.94000
35.00000 1.02400
40.00000 1.10400
45.00000 1.18200
50.00000 1.25600
60.00000 1.39400
70.00000 1.52000
80.00000 1.63500
90.00000 1.74100
100.00000 1.83900
110.00000 1.92900
130.00000 2.09400
150.00000 2.24000
160.00000 2.30800
170.00000 2.37200
180.00000 2.43500
190.00000 2.49400
200.00000 2.55300
210.00000 2.60900
230.00000 2.71500
250.00000 2.81200
270.00000 2.90900
300.00000 3.04400
350.00000 3.25200
400.00000 3.44200
450.00000 3.61500
500.00000 3.77600
550.00000 3.92900
600.00000 4.07300
650.00000 4.20900
700.00000 4.33600
750.00000 4.45800
850.00000 4.69200
______________________________________
The left-hand (X) column sets forth mass air flow in kg/hour, and the
right-hand (Y) column indicates the corresponding mass air flow sensor
output voltage V.sub.out (in volts) for an exemplary mass air flow sensor.
Assume for purposes of this example a simplified combustion cylinder air
intake waveform in which the flow is 600 kg/hr for 1/2 second and then
drops to 30 kg/hr for 1/2 second. The correct average (integrated) value
of mass air flow during the one second sample period would then be given
by:
(600 kg/hr * 0.5 seconds)+(30 kg/hr * 0.5 seconds) =315 kg/hr * sec.
If the corresponding voltages V.sub.out from Table I are referenced, it
will be seen that 600 kg/hr corresponds to an output voltage V.sub.out of
4.073 V, and 30 kg/hr corresponds to a sensor output voltage V.sub.out of
0.940 V.
Integrating these voltages V.sub.out over time yields the following result:
(4.073 V * 0.5 sec)+(0.940 V * 0.5 sec) =2.507 volts sec.
From Table I (using interpolation), 2.506 volts corresponds to only 193
kg/hr- This represents an error of 39% with respect to the actual value of
313 kg/hr. FIG. 2 shows these values superimposed on the exemplary sensor
transfer function curve shown in FIG. 1. The error arises because of the
non-linear nature of the V.sub.out signal. Accordingly, it is desirable to
linearize the signal so as to eliminate non-linearity.
It is generally known to linearize a non-linear analog signal by converting
the non-linear signal to a digital value and to then map or convert (e.g.,
using a look-up table stored in a read only memory device) the resulting
digital value into a linearized value. Unfortunately, when the V.sub.out
signal from a mass air flow sensor is converted to the digital domain for
subsequent digital processing, special attention to accuracy of the lower
end of the scale is required to obtain adequate resolution due to the
fourth-order characteristic of the sensor transfer function (see the
"crowding" of points on the portions of the FIG. 1 curves corresponding to
flows less than 250 kg/hour, for example). Thus, a high cost, higher
resolution digital-to-analog (D/A) converter is typically required to
obtain the resolution required (even though the higher resolution is
really only required on the lower end of the scale).
The present invention provides an improved electronic internal combustion
engine control system and technique which more effectively utilize
measured mass air flow.
In accordance with one feature of the invention, a lower cost non-linear
A/D converter (e.g., of the type commonly used in the communications
field) can be used to convert an analog output signal produced by a mass
air flow sensor into a digital signal. Such A/D converters offer higher
resolution at lower cost, but also introduce further non-linearities into
an already non-linear signal. In accordance with this feature of the
present invention, the digital output of the A/D converter is applied to a
look-up table (e.g., implemented by a ROM storing predetermined mapping
information) containing linearizing information at each memory location.
The linearizing information is defined by the combined functions of: (a)
conversion to linearize the output of the mass air flow sensor, and (b)
further conversion to eliminate the non-linearities introduced by the
non-linear A/D converter. Thus, the two functions required to obtain a
linear digital signal can be combined into a single look-up table--saving
resources (memory and time) in the processing of the digital signal.
An electronic circuit thus accepts a non-linear analog signal from a Mass
Air Flow (MAF) sensor and converts it to a digital signal by means of a
linear or non-linear analog to digital (A/D) converter. The digital signal
may then be processed by a two-dimensional look-up table which includes
corrections for the MAF sensor non-linearity and additional corrections
for non-linearity of the A/D converter. This linearized MAF signal is then
integrated or averaged to provide air mass per engine event or average
mass air flow during an event. This circuit is useful in obtaining better
accuracy in fuel management systems that use MAF sensors, particularly if
variable valve control is included as part of the control system. The
look-up table and integrator can be easily implemented in a digital signal
processor or microcontroller.
Digital linearized flow is thus integrated in the preferred embodiment of
the present invention by summing samples taken at regular fixed engine
positions, and by dividing by the number of samples to obtain average flow
over the cycle. Alternatively, the sample may be multiplied by the time
between samples and summed to obtain total air mass for the cycle. If
total mass per cycle is desired and the sampling rate is constant rate
(not fixed engine degrees), then the samples can be summed over the cycle
and the resulting sum may be multiplied by the fixed sampling time
(thereby saving a multiplication per sample).
The present invention also provides an improved technique for accurately
controlling various functions of an internal combustion engine using
electronically measured mass air flow into the engine. A microprocessor
based electronic control unit (ECU) may receive input signals from a mass
air flow sensor (MAFS) as well as other engine operating parameters (e.g.,
engine speed or period, coolant temperature, throttle position, etc.). An
engine load factor (representing the trapped mass of air in a given
combustion chamber) is calculated by multiplying the MAFS signal with the
engine period. This load factor better utilizes the MAFS output--giving a
result similar to the commonly used manifold pressure without the need for
such a special sensor. The load factor may then be used to program spark
timing, correct the fuel pulse width, program idle/deceleration air,
program acceleration enrichment/deceleration enleanment and deceleration
fuel cutoff, bias closed loop control, and/or other control functions
using conventional engine control algorithms.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features and advantages of the present invention may be
better and more completely understood by referring to the following
detailed description of a presently preferred exemplary embodiment in
conjunction with the sheets of FIGS. of which:
FIG. 1 is a graphical illustration of a typical transfer function of an
exemplary mass air flow sensor;
FIG. 2 is a graphical illustration of the results of one analog averaging
technique that might be used to process the signal provided by the FIG. 1
transfer function;
FIG. 3 is a schematic block diagram of an exemplary electronic engine
control system in accordance with the presently preferred exemplary
embodiment of the present invention;
FIG. 4 is a graphical illustration of interpolation along line segments
performed by the exemplary integrator shown in FIG. 3;
FIG. 5 is a graphical illustration of a further exemplary integration
process performed by a preferred embodiment integrator shown in FIG. 3;
FIG. 6 is a graphical illustration of an exemplary three-dimensional plot
of a fuel correction factor provided by the preferred embodiment shown in
FIG. 3.
FIGS. 7 and 8 are graphical illustrations of actual measured test results
provided by a preferred embodiment; and
FIG. 9 is a schematic flowchart of exemplary program control steps
performed by a microprocessor-based electronic engine control system in
the preferred embodiment so as to calculate engine "load factor" and use
such a calculated value to control an internal combustion engine.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 3 is a detailed schematic block diagram of a presently preferred
exemplary embodiment of an internal combustion engine system 10 in
accordance with the present invention. Engine system 10 includes a
conventional internal combustion engine 12 and associated support
components (the combination of the engine 12 and its support components is
referred to herein as "the engine system 10"). Engine 12 may include a
plurality of cylinders each having an associated piston. The pistons
reciprocate in response to rotation of the engine crankshaft, as is well
known. Intake and exhaust valves also coupled to the crankshaft (e.g., via
a camshaft) open and close at predetermined crankshaft rotation positions
as is well known.
A mass air flow meter or sensor (MAFS) 14 is conventionally disposed (e.g.,
within an intake manifold or passage, throttle body, or the like) to
measure the instantaneous mass of air flowing into engine 12. MAFS 14
produces an output signal V.sub.out indicative of the mass of air flowing
into the engine. MAFS 14 provides signal V.sub.out to an electronic engine
control unit (ECU) 16, which processes the signal and generates engine
control signals in response to the V.sub.out signal. Such engine control
signals may, for example, control the fuel injector system (not shown) of
engine 12 to deliver fuel to the engine cylinders in appropriate amounts
(e.g., for appropriate durations).
ECU 16 receives additional input signals relating to the operation of
engine 12 such as, for example, an engine position signal indicative of
the angular position of the engine crankshaft. This engine position signal
may for example be provided by a conventional shaft encoder or magnetic
sensor arrangement which produces a pulse each time the engine crankshaft
rotates through an additional preset angle (as those skilled in this art
well know). This engine position signal may be used in the preferred
embodiment to indicate the occurrence and durations of engine events such
as cylinder events, as will be explained shortly.
ECU 16 in the preferred embodiment includes an analog-to-digital (A/D)
converter 20, a "linear function" block 22, an integrator block 24, a real
time clock 26, and an "engine management unit" 28. In one preferred
embodiment, A/D converter 20, linear function block 22, and integrator 24
process the MAF signal provided by MAFS 14 and provide a digital value
representing "load factor" (e.g., the air "charge" or total mass of air
that has flowed into the engine corresponding to a particular engine event
such as, for example, the intake stroke of a given engine cylinder).
Engine management unit 28 in the preferred embodiment comprises a
conventional (e.g., microprocessor based) digital signal processor
appropriately preprogrammed to perform conventional engine
management/control algorithms and to generate and provide engine control
signals in accordance with those algorithms. One portion of the
conventional engine management/control algorithm preferably performed by
engine management unit 28 in the preferred embodiment involves
conventional control of the engine 12 fuel delivery (e.g., fuel injection)
system in response to the load factor signal provided by integrator 24.
However, as will be understood, the engine control signals provided by
engine management unit 28 may control many other engine operating
parameters in addition to engine fuel delivery system parameters (and some
of these additional engine operating parameters may also be responsive to
the "load factor" signal).
In the preferred embodiment, the engine management unit 28 is entirely
conventional and performs engine management and fuel delivery control
algorithms which are conventional and well known to those skilled in this
art. Such conventional engine management and fuel delivery control
algorithms may include, for example, control of ignition spark timing,
correction of fuel pulse width, control of idle/deceleration air intake,
control of acceleration enrichment/deceleration enleanment, providing
deceleration fuel cutoff, providing closed loop control bias, and the like
as is well known.
In the preferred embodiment, MAFS 14 comprises a conventional hot wire
anemometer type mass air flow sensor which provides a voltage output level
V.sub.out indicative of instantaneous mass air flow. For example, MAFS 14
may have a transfer function of the type shown in FIG. 1 and thereby
provide output voltage V.sub.out having the following relationship with
mass air flow X:
X=A(V.sub.out -B).sup.4 (1)
where V.sub.out is the sensor voltage, A is the sensor gain, and B is the
sensor offset voltage (typically nearly constant).
In the preferred embodiment, A/D converter 20 may have a desired sampling
rate (which sampling rate may if desired be synchronized with engine
rotation in response to the "position" signal provided by engine 12) and
resolution (e.g., 8 bits or the like).
To provide additional resolution, it may be desirable to connect two
different A/D converters essentially "in parallel" to provide a "low air"
digital value and a "high air" digital value. For example, suppose the
output voltage range of MAFS 14 is 0-6 volts. This voltage could be
multiplied by a factor of 5/6 (e.g., using a conventional precision
operational amplifier or similar active or inactive analog circuit having
a gain of 5/6) to obtain a 0-5 volt signal, and could also be further
multiplied by a factor of 2 to provide a signal 0 to 10 volts, which is
then limited to a maximum of 5.00 volts range. When this signal is fed to
a 0 to 5.00 A/D converter, the effective resolution of the lower half of
the original signal is essentially doubled. These two signals may then
each be converted to digital form independently using different
conventional A/D converters (one having an input voltage range of 0-5 V
and the other having an input voltage range of 0-0.5 V) to provide "low
air" and "high air" signals. The "low air" digital signal could be
linearized by block 22 for low mass air flow values (e.g., 0-250 cfm in
1023 steps), and the "high air" digital signal could be linearized by
block 22 for higher mass air flows (e.g., 0-250 cfm in 255 steps --that
is, -1000 cfm in 1023 steps). In this way, two different "ranges" may be
provided using off the shelf standard, inexpensive A/D converters
(somewhat like standard digital voltmeters provide different voltage
"ranges" and provide additional resolution for lower voltage ranges). If
desired, both signals may be linearized and presented to integrator block
24, which in turn may integrate both signals independently to provide two
different integrated values. The appropriate integrated value (low or
high) may then be selected and processed by engine management unit 28
depending upon the magnitude of the mass air flow.
The "linear function" block 22 accepts a digital coded voltage signal from
A/D converter 20 and generates a digital signal which represents the
linearized mass air flow. In one embodiment, the linear function block 22
comprises a microprocessor (or a time-shared portion of the same
microprocessor used to provide digital signal processing within engine
management unit 28) appropriately programmed to perform the calculation of
the sensor transfer function set forth above (X=A(V.sub.out -B).sup.4) and
solving for X based on predetermined programmed values for B and A (these
values are associated with the particular MAFS 14 used). One advantage of
using this calculation is that it requires only one subtraction (to
calculate V.sub.out -B) (see FIG. 9 block 104) and three multiplications
(to calculate (V.sub.out -B).sup.2, (V.sub.out -B).sup.3, and (V.sub.out
-B).sup.4) (see FIG. 9 block 106), which makes it a very fast calculation
to implement and perform using a standard conventional microprocessor, bit
slice processor or the like with mathematical calculation capabilities.
Implementation of this calculation using an off-the-shelf microprocessor
is straight-forward and well within the capabilities of one of ordinary
skill in this art.
In an alternate preferred embodiment of the present invention, A/D
converter 20 may comprise a conventional non-linear type (e.g.,
"companding") A/D converter of the type widely used in the communications
field and linear function block 22 may comprise a read only memory (ROM)
or similar microprocessor or digital signal processor based look-up
process. This type of companding A/D converter has good resolution at the
lower end of the scale, but introduces an additional (predictable and
well-defined) non-linearity into the digitized signal. Linear function
block 22 may comprise a read only memory device addressed by the parallel
output bits generated by A/D converter and storing predetermined
linearizing information specified with regard to both the fourth-order
transfer function of the MAFS 14 and the non-linear transfer function of
A/D converter 20. In one specific exemplary arrangement, a ROM device
would be programmed to store in each of its locations a digital word
determined experimentally, empirically and/or by calculation so as to
convert the digitized voltage output of A/D converter 20 into a linearized
digital value representing mass air flow. TABLE I above sets forth one
exemplary set of linearization information that might be combined with
additional linearization information corresponding to a particular
non-linear A/D converter 20 transfer function to provide the contents for
a look-up table referenced by linear function block 22.
In this embodiment, a linear mass air flow signal is, in effect, obtained
by storing and referencing the end points of straight line segments
approximating the MAFS 14 transfer function (as corrected for by any
additional non-linearities introduced by A/D converter 20). Only line
segment end points are stored in the look-up table and referenced, since
the A/D conversion process performed by A/D converter 20 inherently
discards input information between the end points and automatically
approximates to the closest end point. FIG. 4 shows how intermediate
points are effectively interpolated along line segments by the A/D
conversion and look-up process.
Integrator 24 receives the linearized digital air flow signal provided by
linear function block 22 and may derive from that signal a mass air flow
value integrated with respect to engine position, time, or both. In the
preferred embodiment, integrator 24 may be a microprocessor or other
digital processor (e.g., a PERI64); or it may be a time shared portion of
another processor, e.g., the processor within engine management unit 28.
Integrator 24 is appropriately programmed to perform a desired integration
function.
In one embodiment, integration is performed at fixed engine positions as
indicated by the "position" signal provided by engine 12. For example,
each time the engine crankshaft rotates by a predetermined angle such as
one degree of engine rotation, integrator 24 may sum linearized air mass.
Integrator 24 may thus perform the following calculation:
##EQU2##
where Y is the average mass air flow during a cylinder event, Y.sub.i is
the linear mass air flow sample, and n is the number of samples for each
cylinder event and is equal to the total number of samples for a complete
engine cycle divided by the number of cylinders the engine has.
Since n is a fixed number of a particular engine system 10 design, it can
be considered a scaling factor of the average mass air flow. For the
example of one (1) degree sample rate and four (4) engine cylinders, after
each 180 degrees of rotation the average mass air flow rate may be
presented to engine management unit 28 and a new average may then be
accumulated.
In another embodiment, integrator 24 may integrate the linearized mass air
flow signal with respect to time for one cylinder event to obtain the
cylinder air "charge" (i.e., the trapped mass of air within the combustion
chamber just after the intake valve closes). An exemplary equation for
simple rectangle integration is:
##EQU3##
where Y is the air mass, X.sub.i is the linearized mass air flow sample,
and t.sub.i is the sample time interval.
FIG. 5 shows an exemplary graphical interpretation for the equation set
forth above. In the preferred embodiment, the time period between samples
is preferably fixed as determined by real time clock 26 (although the
calculation could just as easily be implemented if desired to provide
different time intervals between samples such that t.sub.0.noteq.t.sub.1
.noteq.t.sub.2. . . ).
The calculated trapped air mass can be used as a "load factor" of the
engine to provide similar results as may be obtained by measuring and
using intake manifold pressure--this eliminating the need to measure
intake manifold pressure directly. This calculated load factor is
automatically compensated for the volumetric efficiency of the engine.
A special case of mass air flow integration with respect to time
particularly useful if engine 12 has fixed valve timing is where a
synchronous mass air flow sample is taken for each cylinder event and is
then multiplied by the period of the cylinder event. This engine load
factor can be very useful in engine control algorithms where the load
factor and engine speed are used to index a three dimensional look-up
table to determine an operating parameter such as fuel schedule or spark
advance. FIG. 6 shows a typical three-dimensional plot corresponding to
fuel correction factors developed by referencing such a look-up table. A
conventional approach uses similar three-dimensional look-up tables with
manifold pressure and engine speed as independent variables for the
look-up.
FIGS. 7 and 8 are graphical illustrations of actual experimental results
obtained with an exemplary test engine system 10 of the type shown in FIG.
3 wherein engine 12 was a 1.9 liter engine. FIG. 7 plots air (vacuum)
pressure in Torr versus numerical values for both linearized mass air flow
("flow") and integrated mass air flow ("PAIR") for two different engine
speeds: 2000 rpm and 5000 rpm. Mass air flow from MAFS 14 was converted
into an 8-bit digital value (FF hex=250 cfm) by A/D converter 20 and
linearized using a look-up table (wherein each entry of the table
comprised an 8-bit value with a weighting of 5.625 per bit+60 offset
corresponding to the particular MAFS 14 used). This value was then
integrated into the 8-bit values shown plotted and labelled "PAIR". Engine
speed was measured and converted to an 8-bit value using a conventional
speed sensing arrangement in which each bit is weighted to 25 rpm. FIG. 8
is a similar plot of experimentally measured pressure (Torr) versus
(linearized) mass air flow (Torr/second or other time period) for five
different engine speeds in rpm: 1500, 2000, 2500, 3500 and 4500.
FIG. 9 is a flowchart of exemplary program control steps performed by a
microcontroller or other digital signal processor in accordance with the
preferred embodiment of the present invention. A/D converter 20 may be
controlled to sample the output
V.sub.out of MAFS 14 upon each occurrence of a pulse from engine 12
representing 1 degree of engine crankshaft rotation (block 102). An
appropriately programmed digital signal processor may then linearize the
digital output of A/D converter 20 using the calculation mentioned above
(block 104,106)--as alternatively, the digital output may be linearized as
described using a look-up process. The linearized output may then be
summed (added) into a temporary storage location S (block 108).
It is then determined whether the engine event cycle of interest is over
(block 110). For example, it may be determined whether the engine 12
crankshaft has rotated 720 degrees (corresponding to one complete engine
cycle) or an appropriate angle corresponding to a cylinder event (e.g.,
180.degree. for a 4-cylinder engine. If the engine cycle of interest is
not yet completed, blocks 100-108 are repeated for each degree at
crankshaft rotation until the engine cycle is completed.
The summed value S may then be further processed to provide integrated mass
air flow for a desired engine event. In the example shown, S may be
acquired over 720 degrees of crankshaft rotation and then divided by the
number of cylinders of engine 12 to provide on average "load factor"--the
amount of air trapped within each cylinder at the end of the cylinder
intake stroke (block 112). Engine management unit 28 may then calculate a
fuel correction factor (and/or other engine control parameters) based on
this processed value S (block 114) using conventional three-dimensional
analysis (in conjunction with measured engine RPM) if desired. The
temporary storage location S is cleared in preparation for the next engine
cycle (block 116) and blocks 100-116 are repeated.
While the invention has been described in connection with what is presently
considered to be the most practical and preferred embodiment, it is to be
understood that the invention is not to be limited to the disclosed
embodiment, but on the contrary, is intended to cover various
modifications and equivalent arrangements included within the spirit and
scope of the appended claims.
* * * * *
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