 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.
| LOW RPM |
displayed if speed is 100 RPM under
the MRPM (call) |
| ENGINE RPM
EXCESSIVE |
engine speed exceeds 975 RPM (normal
speed is 954 RPM) |
| ENGINE RPM
LOW |
displayed if speed is 100 RPM above
the MRPM (call) in power mode. |
| ENGINE RPM
very LOW |
displayed if speed is 175 RPM under
the MRPM (call). (Fuel starvation) |
| ENGINE SHUTDOWN
by RPM |
engine speed exceeds 1075 RPM for 1
second. |
| INJECTOR RACK
DROPOUT |
abnormal rack control. (A seized injector
symptom) |
| LIMP HOME
MODE THR 6 |
throttle limit to notch 6 if a sensor
problem occurs. |
|
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:
| LOW OIL PESS
THR 3 LMT |
Throttle is limited to notch 3 if oil
pressure is lower than 9 psi @ 150°F and linearly 3 psi
@ 250°F. Engine shuts down if throttle is moved beyond notch
3. |
| LOW OIL PSI
ENG SHUTDOWN |
Engine is in LOW OIL PESS THR 3 LMT
condition for 1 minute. |
|
Low Coolant Pressure
Three sensors monitor the engine coolant pressure. One at the pump inlet
and one at each pump discharge.
| LOW WATER
PRESS THR 3 LMT |
Throttle is limited to notch 3 if water
pressure is lower than 2.5 psi @ 300 RPM and 30 psi @ 900 RPM,
typically. Engine shuts down if this condition persists for
one minute or throttle is moved beyond notch 3. |
| WATER LEFT
PUMP FAILED |
engine shut down. |
| WATER RIGHT
PUMP FAILED |
message is displayed if the malfunction
signal is coming from the right side pump. |
|
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.
| COLD ENG THR
4 LMT |
coolant temperature is below 100°F.
Throttle is limited to notch 4. |
| HIGH IDLE
LOW WATER TEMP |
coolant temperature falls below 122°F.
Engine speed is maintained to notch 4 speed. |
| HOT ENG RETURN
TO IDLE |
engine will shutdown if coolant reaches
217°F for one minute and after 10 seconds if temperature
reaches 223°F. |
| HOT ENGINE
THR 6 LMT |
coolant temperature exceeds 215°F
for 2 seconds and hasn’t dropped below 205°F. |
| POWER REDUCTION
HOT ENGINE |
water temperature is over 208°F
and under 216°F. Power is linearly de-rated to notch 6 @
215°F. |
|
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.
| HOT OIL TEMP
THR 3 LMT |
Oil temperature went over 265°F
for 2 seconds and throttle is limited to notch 3 until temperature
is reduced below 255°F. |
| HOT OIL TEMP
ENG SHUTDOWN |
if HOT OIL TEMP THR 3 LMT condition
persists for one minute. |
|
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.
|
