TM 5-3805-294-23-1
0003
HYEX THEORY OF OPERATION - Continued
Engine Electronic Control System - Continued
The oil pressure sensor sends an oil pressure equivalent signal to the ECU. The ECU uses this signal to determine
if engine oil pressure is adequate for the current operating conditions. The ECU monitors oil pressure for engine
protection purposes.
Measuring Speed
The camshaft position sensor measures engine speed by detecting the rotating teeth of a timing wheel mounted on
the front of the camshaft drive gear. It can also measure the position of the rotation of the engine because it can
detect a gap in teeth of the timing wheel where two of the teeth have been removed. This gap corresponds to top-
dead-center (TDC) of piston #1.
The sensor uses a coil wound around a magnet to create a voltage signal. As the tooth in the timing wheel passes
directly under the sensor, the magnetic field is pulled towards the tooth. As the tooth passes the sensor, the magnetic
field moves back toward the sensor. This creates a voltage in the coil that is sent to the ECU. By monitoring the
frequency of these signals, the ECU calculates the component speed. When the gap in the teeth of the timing wheel
is detected, the ECU interprets this change in the voltage pattern to be TDC.
The ECU uses the inputs of both the crankshaft position and pump position sensors to precisely control the timing
and duration of fuel injection.
The crankshaft position sensor is an inductive-type pickup sensor that detects teeth on a special tone wheel that is
mounted to the crankshaft timing gear. The ECU uses the crankshaft position input to determine engine speed and
the angular position of the crankshaft in its 360 field of rotation. The crankshaft timing gear is composed of 45
evenly-spaced teeth. There is a 3-tooth section with no notches. The 3-tooth section helps the ECU determine when
cylinder #1 is at TDC.
The pump position sensor is an inductive-type pickup sensor that detects teeth on the upper idler gear. The upper
idler gear is composed of 12 evenly-spaced notches with one additional notch offset to tell the ECU that cylinder #1
is approaching TDC. The ECU uses the inputs of both the crankshaft position and pump position sensors to precisely
control the timing and duration of fuel injection. If there is a problem with the crankshaft position sensor, the ECU
will use the pump position sensor to determine engine timing. This may require prolonged engine cranking to start
the engine. The ECU provides engine protection for crankshaft position sensor problems.
Controller Area Network (CAN)
The engine speed dial sends a signal via the CAN to the ECU. The CAN bus is a high-speed open interconnect
network for electronic systems on the machine. It allows electronic systems to communicate with each other through
a standard architecture of electronic signals over shielded twisted-pair wires. Just about any type of information can
be communicated over the CAN bus. Information such as throttle position, safety systems, engine condition, and
fuel system information can be transferred between machines different controllers. The machine can communicate
with computers. Information on the network can be displayed to the operator on a display panel, or relayed to another
location via telemetry. Up to 30 ECUs or modules can be connected together through a single CAN segment.
Other Electronic Control Components
The suction control valve is located on the high-pressure fuel pump. The ECU sends an electronic signal to the
suction control valve through its solenoid to regulate the delivery of fuel to the high-pressure common rail. When the
suction control valve is energized, fuel is allowed into the pumping chamber of the high-pressure fuel pump. The
pressurized fuel is then sent to the high-pressure common rail. The ECU varies the ON-time of this signal to ensure
the proper amount of fuel is available.
The water in fuel (WIF) sensor is located on the bottom of the primary fuel filter in the water separator sediment bowl.
When water is detected in the fuel, a signal is sent to the ECU. The WIF sensor uses the resistance of fuel and water
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