National Instruments NI EDIDS-2400 Series, User Manual, Page: 170 / 314

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All EPT functions have a common internal core that tracks angular position. The supporting internal logic around the
core interprets the incoming crank and cam position pulses according to an expected pattern. Each EPT function
has a Boolean crankshaft and camshaft input. These signals may be connected via any available NI 9411 digital
input source within the DI Driver System. The pattern input signals are named according to the most common
engine applications, such that there is a crankshaft trigger wheel and an optional 4-stroke camshaft trigger wheel.
However, it is also possible to operate with a single trigger wheel mounted to a camshaft of a 4-stroke engine. This
would require routing the physical camshaft trigger wheel sensor signal into the Crank_DigChanAsn of the DI Driver
System. Refer to the Digital Input Setup window description for assigning NI 9411 digital inputs to internal signals.
Digital Signal Filtering
It is often necessary to implement filtering of the crank and/or cam signals prior to entering the EPT function. The
DI Driver System software provides an integrating filter function which rejects positive and negative digital signal
pulses having a pulse width less than the filter time. Refer to the Digital Input Setup window description for further
information about filtering the NI 9411 digital inputs.
EPT Pattern Simulation
All EPT functions contain a built in pattern simulation tool specific to the pattern for which the EPT function was
configured. Pattern simulation is turned on simply by setting EngineSimEnable button of the EPT tab to TRUE and
setting the SimulatedSpeed to an appropriate value for the simulated speed. When simulation is turned on, the
Crank and Cam inputs to the EPT function are internally disconnected and replaced by the internally simulated
counterparts. The simulation feature allows the designer to bench test the DI Driver System functionality at any stage
of the development without the need for external simulation hardware.
Achieving Sync
In order for position tracking (sync) to start, a few conditions must be met. First, some pattern specific values must
be set correctly to the EPT function, such as NumberOfCrankTeeth , NumberOfMissingTeeth (if N-M), Stroke , and
StallSpeed . Next, the SyncEnable must be turned
ON
. Next, the EngineSpeed must exceed the StallSpeed . When
the stall speed (RPM) is exceeded, the CrankStalled indicator will be set to Spinning and the EPT function begins
counting a complete cycle of crank teeth. After a complete engine cycle of crank teeth is received, the EPT function
begins looking for the first occurrence of a unique feature of the crankshaft and camshaft pattern which identifies an
absolute position. For example, if an N-M pattern is being used, the function searches for the occurrence of the M-
tooth gap. This is the moment of achieving sync. When sync is achieved, the SyncStopped indicator is set to
Sync
and the angular position of the crankshaft will be tracked. As sync is maintained, CrankCount will show the latest
crankshaft tooth count with respect to absolute 0 position. Each EPT function will have different rules for achieving
and maintaining sync, as well as location for absolute position 0. This information is contained in the EPT Pattern-
Specific Information section below.
CrankCount
During sync, the EPT function provides the latest crank tooth count at the CrankCount indicator, referenced to tooth
0. Tooth 0 is determined according to the pattern that is being tracked and is discussed within the Pattern-Specific
Information section below. CrankCount is provided in terms of a complete engine cycle and is reported as if there
were no missing or extra teeth in the pattern. For example, if the pattern type is N-M, NumberOfCrankTeeth = 60 and
Stroke = TRUE, then CrankCount will range from 0 to 119. CrankCount is for monitoring purposes only.
Crank Position
During sync, the EPT function calculates the latest crankshaft position in terms of absolute Crank Angle Ticks (CAT)
over a complete engine cycle, referenced to position 0. It is internally converted to a crank angle position in terms of
Crank Angle Degrees (CAD), referenced to position 0, so that injection angles may be specified in CAD. Position 0
is determined according to the pattern that is being tracked and is discussed within the Pattern-Specific Information
section below. The CurrentPosition in CAD is calculated according to the following:
CurrentPosition(CAD) = [CurrentPosition(CAT) * Stroke * 360] / MAX_CAT
Where Stroke = 2 if 4-stroke, and Stroke = 1 if 2-stroke.