
_____________________________________________________
Tec3r Manual Version 1.11
- Page 61 -
©2017 Electromotive, Inc.
D.4. Fuel Injector Pulse Width Derivation
D.4.a. Introduction
Duty Cycle
The fuel injectors are controlled by the
Tec3-r
in several different modes. The most common mode
would be phase-sequential injection. During this mode of operation, injectors are fired once per revolution
(TDC compression & TDC exhaust). As the engine speed increases, the time between TDC events
decreases. However, the fuel injector needs to fire for roughly the same amount of time each revolution,
regardless of engine speed (assuming an engine with a fairly flat torque curve). As a result, the percentage of
time that the injector is turned on increases. We refer to the percentage of time on vs. time available as the
Duty Cycle
. We refer to the time (in milliseconds) that the injector is turned on as the
pulse width.
Duty Cycle
= Time On
(Time On + Time Off) = Time On
Time Available
Phase-Sequential:
Time Available = Time for 1 engine revolution
Full-Sequential:
Time Available = Time for 2 engine revolutions
UAP, POT, and the Raw Fuel Curve
The TEC³r software establishes a
raw fuel curve
for the engine with two numbers: User
Adjustable Pulse Width (UAP) and Pulse Width Offset Time (POT). The UAP sets the slope of the fuel
curve (related to MAP load), while the POT offsets the curve up or down. These two numbers work in much
the same way as the main jet and metering rod on a carburetor. That is, the UAP has a large effect on the
high-load injector pulsewidths, while the POT has a large effect on the light-load injector pulsewidths. UAP
dynamically manipulates the raw fuel curve as a function of load, while POT adds or subtracts a fixed pulse
width to the raw fuel curve for all load points. See
Figures D.4 1-5
for graphical representations of the UAP
and POT correlation. The following equation is used to determine the injector pulse width as a function of
MAP Voltage, UAP, and POT:
Pulse Width = [(MAP Voltage
5)
UAP] + POT
Load Percentage
In the above equation, the variable “MAP Voltage
5” is the
load percentage
at which the MAP
sensor is operating. Since all MAP sensors output a maximum of +5 Volts at full load, the TEC³r uses
this number to determine the percentage of full load at which the engine is operating. For a MAP reading of
4.5 Volts, the load percentage would be 4.5
5 = 0.9, or 90%. Since the TEC does NOT know whether the
MAP voltage is from a 1-, 2-, or 3-Bar MAP sensor (that is, it only knows the voltage), it is necessary to
enter the MAP sensor that is being used into the software. See
Table D.4 1
for a numerical breakdown of
the MAP sensor voltage and corresponding load percentage.
Table D.4 1:
MAP sensor load percentage,
voltage, and kPa relationship.
Linear Thermodynamics
There is no RPM-dependency for the raw fuel curve derivation. The governing principle behind this
is that the pulse width requirements for an engine with a smooth (flat) torque curve will not have a very large
MAP volts % Load 1 bar kPa 2 bar kPa 3 bar kPa
5
100
104.8
208
316
4
80
86
168
252
3
60
67
128
190
2
40
48
88
127
1
20
29
48
64
0
0
10.3
8
1.1
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