Shop Notes - Engine Protective Devices
Engine
Protective Devices on Q-Tron microprocessor controlled EMD locomotives /
Article by Claude Gaudet.
Background
Dash-2 and non-dash EMD locomotives are equipped with some standard engine
protection features. These devices protect the engine against all abnormal
conditions that can be harmful for the engine such as overspeed, low oil
pressure, low coolant pressure, low/high coolant temperature, high crankcase
pressure, hot lubricating oil, and overload.
EPDs
on Q-tron equipped locomotives
Q-tron is a state-of-the art locomotive computer system used on many new
and newly rebuilt diesel-electric locomotives distributed by the Wabtec
Group. Basically, all main systems are controlled by the Q-Tron including,
but not limited to, the engine, alternator excitation, locomotive adhesion,
dynamic braking, cooling system, air compressor controls, and various
safety features.
System components:
Fuel Rack Actuator
The Actuator Unit (AU) replaces the standard PG engine governor. The engine
controls, or “the brain functions”, are achieved by the Q-tron
Electronic Control Unit (ECU). The rack actuation, or “muscle”
function, is performed by an electric step motor, a gearbox mechanism,
and a torque arm within the AU connecting to the fuel rack as the standard
governor. An Actuator Control Unit between the ECU and the AU convert
the ECU digital signal to an electric current for the step motor control.
Two speed sensors (RPM1 and RPM2) in the AU read and transmit the engine
RPM signal to the ECU for engine speed control. The ECU reads the throttle
position and sends corresponding engine speed command to the ACU as the
MRPM. The ACU commands the AU to reduce or increase the fuel rack in order
to match the MRPM. The AU adjusts the rack as required and returns two
redundant speed feedback signals to the ECU commanding it to close the
control loop. In case of speed sensor failure the higher speed signal
is always taken as the reference signal to be compare with the MRPM. A
rack position feedback signal is also transmited to the ECU via the ACU
for load control. All sensors’ readings are monitor by a screen and
keypad display called the MMI (Man Machine Interface).
Overspeed
The ECU is programmed to display various alarms, limit the engine speed,
and/or unload or shut down the engine in case of malfunction. The ECU
overspeed is redundant to the standard overspeed trip mechanism.
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Low Oil Pressure
A governor manifold housed the EPD’s temperature and pressure sensors.
One of these sensors is used to monitor engine lubricating oil pressure.
The oil pressure is then converted to an electrical signal and transmitted
to the ECU. The following messages codes and alarms are displayed in case
of malfunction:
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Low Coolant Pressure
Three sensors monitor the engine coolant pressure. One at the pump inlet
and one at each pump discharge.
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Low/high Coolant Temperature
The engine is protected against operation when the coolant temperature
is too low or too high. Sensors are provided to protect the engine in
such cases.
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High Crankcase Pressure
A standard EMD type crankcase pressure detector is used to detect abnormal
crankcase pressure conditions. As for engine with PG type governors, the
detector is connected to the oil pressure sensing line. The crankcase
pressure shall be negative at all time. When a high crankcase pressure
condition takes place, the detector drains the oil pressure line to the
engine sump. The pressure drop is sensed by the oil pressure sensor in
the governor manifold, and the engine shuts down.
Hot Lubricating Oil
The standard mechanical hot oil detector is replaced by a temperature
sensor monitored by the ECU.
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Overload
As usual the engine is protected from overload conditions. The fuel limiting
device part of the previous PG governor is replaced by an air box pressure
sensor linked to the ECU and an additional sensor that reads the air box
temperature. These two sensors and all other parameters such as engine
speed, and water and oil temperatures and pressures are used for the calculation
of the maximum and safest available engine output.