Project description Background Technology after reconstruction

Refurbishment and Revision of two MOB Gm 4/4
Pascal Tritten
Railtec Systems GmbH
Paul Baillif
MOB / Golden Pass Services
Project description
In the course of reconstructing the
two diesel-electric shunting
locomotives of type Gm 4/4 for MOB/
Golden Pass Services the vehicle
control systems were renewed. This
involved complete refurbishment of
the motor control system, generator
controller, relay control, drive and
braking control as well as the control
systems for the auxiliary hydraulic
plant. Railtec Systems GmbH
performed these tasks in cooperation
with the MOB workshop in Chernex.
Background
MOB Golden Pass Services own two
diesel-electric locomotives of type Gm
4/4. These locomotives,
manufactured in 1976 and 1982, were
each equipped with a V12 Poyaud
diesel engine rated at 485kW, which
in turn powered a 3 phase
synchronous generator supplied by
Leroy-Somer. Two rectifiers supplied
two direct current traction motors.
The accelerator lever had a direct
effect on the injection pump, altering
the injection quantity and therefore
indirectly the engine speed. A relay
switch controlled the generator via a
resistor switch, depending amongst
other things on the engine- and
vehicle speed.
Technology after
reconstruction
Observation of normal operation
showed that the locomotives are
generally operated at low speeds. For
this reason the decision was made to
supply the current using two smaller
The body of the Gm 4/4 2004 under construction, all electric components are still
missing, the engines (at the back) are already installed. (Photo: Railtec Systems)
'gensets' (one diesel engine with its
coupled generator each) with their
rectifiers in serial connection. This
means that at low speeds only one
diesel engine needs to be used, as
the current passing through the serial
coupling of the motors supplies
sufficient traction force. Only when
higher speeds or
maximum traction
force are required
both diesel engines
need to be used. The
engines selected for
use were new sixcylinder
straight
engines supplied by
Scania with an
electronically
controlled unit injector
system, each rated at
316kW and powering
a Leroy-Somer
synchronous
generator. Each of
the diesel engines
are connected to two
hydraulic pumps to
provide hydrostatic
fans, traction motor fan and the
vacuum pump for the vacuum brake.
In each case, one of the pumps is
used for the diesel engine's fan unit
and the other for the traction motor
fan and the vacuum pump for the
brake.
drive force for cooling
3D-drawing of the engine's installation (Graphics: MOB)

Front view: On the right diesel engine 1 with flange-mounted hydraulic pump (Photo:
MOB)
Mechanical features
It was decided to use the available
space to accommodate the new
drives without any significant
alterations of the vehicle's frame. This
was accomplished without raising
problems of noise and heat
generation. Owing to circumstances
the two gensets had to be installed
opposite to each other. Another
requirement to be met was to allow,
despite the cramped conditions, easy
access to all components needing
maintenance.
Through the use of hydrostatic force
for the operation of fans and vacuum
pump, components could be freely
positioned. This way, the driver's cab
could be significantly lengthened.
The entire drive chain – from the
electric motor over the bogie to the
transmission – could be used for the
currently rated maximum load without
Hydraulic contol, vehicle control,
underneath the extension modules
(Photo: MOB)
any modifications.
Control devices
The vehicle control system consists of
components selected from the
Selectron MAS-T product range. A
CPU 854 is used as master vehicle
controller. The speed acquisition is
performed by a module with RPM
inputs. An additional CPU 723 serves
as diesel engine coupler with two
CAN interfaces. Finally, a separate I/
O module with linked input and output
extension units provides the required
number of digital I/O. The hydraulic
control system consists of two control
devices supplied by Bosch-Rexroth.
They are part of a package of
hydraulic pumps and engines which
includes configurable standard
software for fan control.
Drive-, brake- and serial/parallel
contactors (Photo: MOB)
Instead of the instrument panel
supplied by the motor manufacturer, it
was decided to provide the relevant
motor information using a display. On
one hand the panels would have
taken up a considerable amount of
space, on the other hand the control
and monitoring of the individual diesel
engines via CAN bus would not have
been possible. Instead, the
generation of digital and analogue
signals would have become
necessary. The display solution is less
expensive than using two instrument
panels and also provides
considerably more flexibility in respect
of operation and provided information.
Also, data can be displayed which
has nothing to do with the engines
and which would otherwise have
made one or more extra display
devices or control lamps necessary.
Finally, the conversion costs could
also be reduced because the cabling
is less complicated and only one
installation recess for the display is
needed.
CAN Bus
The CAN bus was divided into three
sections, i.e. engine bus 1, engine
bus 2 (each J1939) and the vehicle
bus (CANopen). This division is
necessary because it is not possible
to modify the diesel engines' CAN bus
node-ID, which made parallel
operation of two engine control
devices on one and the same bus
impossible. The diesel engine coupler
serves only to transmit data from
diesel engine 2 to engine bus 2 and
vice versa. Also, the possibility of
connecting extension modules directly
to the engine coupler has been
implemented to interface digital input
and output signals. Engine bus 1 is
Motor power supply with rectifiers (Photo:
MOB)

connected directly to the second CAN
interface of the master vehicle
controller. The protocol used for the
two engine buses is the standard
protocol used for serial
communication within vehicle
networks, written in SAE J1939.
The hydraulic controls are also
connected to the engine bus. The
master vehicle controller, the
computer for speed acquisition, the
engine coupler, additional I/O nodes
and the display are connected to the
vehicle bus.
Control
In exceptional cases, e.g. when a
genset or a traction motor is defect,
the driver can manually select the
diesel engine to be used. Then only
one genset is in operation, supplying
power to one of the two traction
motors.
In automatic operation one or the
other of the engines is in operation
and the traction motors are coupled in
series.
The automatic diesel engine selection
is managed by the master vehicle
controller. When both engines are
cold, the engine with fewer operating
hours is selected. If one of the
Busaufteilung (Grafik: Railtec Systems)
engines has already warmed up, then
this one is used on every subsequent
start-up so as to reduce the number
of cold starts and therefore help
protect both the engines and the
environment.
In dual engine mode both gensets are
in operation and the rectifiers and
2 March 2008: Comissioning on the line Blonay-Chamby (Photo: Railtec Systems)
traction motors are switched in series.
This mode is required to attain
maximum speed.
In both operating modes the master
vehicle controller calculates the
engine activity according to the
position of the accelerator lever and
the diesel engine's rated RPM. The
necessary voltage (0..40V DC) for
excitation of the synchronous
generators is provided by an
excitation device supplied by Syko
Power. The excitation device is
powered through the vehicle's 24V
system. The desired value is set via
an analogue voltage signal 0..5V.
The diesel engine's speed is
optimised for fuel economy. The
master vehicle controller monitors and
limits motor voltages and currents as
well as cooling water, generator,
rectifier and traction motor
temperatures. If the limiting values
are exceeded the speed and
generator excitation are automatically
adjusted or the respective drive
component is switched off. The
master vehicle controller also controls
the slip and overspeed protection
systems (only for the electric brake).
All relays are switched by the master
vehicle controller (traction and braking
relay, direction of travel relay,
switching from parallel to series
operation, shunt relay). All relays are
equipped with auxiliary contacts
which allow the relay state to be
monitored. If the return signal does
not match the command given, then
either the activation is cancelled or
only an error message is issued.
The master vehicle controller also
controls the driver's safety device
(dead man's switch), the sand
dispenser, battery levels and other
functions.
The software for the two hydraulic
controls is an adapted version of the
automatic AFC20 fan control program
supplied by Bosch-Rexroth.
The option to provide for an
emergency power supply (using a
genset to generate 3x400V 50Hz, for
instance for electrical equipment in
the field) was not implemented due to
cost and absence of urgent necessity.

Test run on 15 March 2008 in Sonzier (Photo: Railtec Systems)
However, it can be implemented
subsequently without difficulty.
Error recognition and
diagnosis
All the relay states are registered and
compared with the commands issued
for their activation. If a discrepancy is
found, an error message is issued
and an appropriate action triggered.
Diesel engine malfunctions are
detected and stored by the respective
engine control devices. For the
purposes of reading these error
entries, part of the diagnostic protocol
UDS on CAN (as per ISO 15765) was
implemented. This protocol is
increasingly displacing the KWP2000
(Key Word Protocol 2000) protocol
widely used in road vehicles. This
means that the data from
neighbouring components can be
queried corresponding to the point in
time when the error has occurred.
Also, it is possible to delete individual
errors or the whole error memory. It is
no longer necessary to buy an
expensive proprietary test and
diagnostic device.
Display
The display is PC based and supplied
by Pixy AG from Aargau, Switzerland.
As operating system a Linux kernel is
installed. All texts and labels are
provided in German and French.
The items displayed are modelled as
conventional instruments. Process
values displayed in this fashion can
generally be more easily and quickly
interpreted than numeric displays,
and the interface can be configured
more clearly.
The display is also used for the
storage and display of vehicle-,
motor- or engine malfunctions.
Malfunctions are stored in non-volatile
memory together with the relevant
data from neighbouring components.
This information can be used for
subsequent localisation and
correction of faults.
Summary
The conversion has provided MOB
with diesel locomotives equipped with
most modern technology. During the
conversion, environmental aspects
such as fuel consumption, exhaust
and noise emissions were treated
with high priority. The two Gm 4/4 can
now continue to fulfil their tasks for
another 20 years.
16 March 2008: Gm 4/4 2004 in Les
Cases (Photo: Railtec Systems)