INTRO: Computer diagnostics and the ability to replace electronic assemblies translates directly into higher asset utilisation, bringing major financial benefits
BYLINE: Vic Sergeant
Senior Systems Engineer,
General Electric Transportation Systems
GENERAL ELECTRIC introduced the first ever microprocessor controlled diesel locomotive in production quantities in 1985. With the 4 000 hp C39-8, the concept of ’replaceable units’ (RUs) was introduced for elecronic modules in the GE product line. By December 31 1996, GE had supplied 4739 locos with microprocessor control that are maintained on the RU principle.
Even the largest and heaviest power electronics unit on GE’s new AC6000 loco rated at 6250hp gross with asynchronous traction motors - the inverter phase module for one motor - can be completely changed in two hours by one person. The control microprocessor identifies any defective unit, and in the case of an inverter phase module, for example, will automatically reconfigure the other five traction motors and inverters so that the loco continues in service until the defective inverter can be replaced.
Prior to 1985, electronic units were repaired as necessary by changing plug-in cards. To assist troubleshooting, later cards were fitted with LED indicators, but it was still time consuming to hold the loco out of service until the defect had been identified and repaired.
Multi-function microprocessors
With the introduction of the microprocessor, a number of things happened simultaneously. Fortunately, at the same time as the electronic module became more complex, it also became more reliable. Along with processing power came the ability to monitor many locomotive functions (Fig 1), and to diagnose any abnormality, sometimes before it became a failure. This enables a defect to be corrected much more quickly, allowing the locomotive to return to traffic sooner.
The ability to monitor a locomotive’s condition by radio is now becoming available, allowing a control centre to predict the maintenance or repair requirements before the loco arrives at the servicing point.
Before microprocessors arrived, electro-mechanical logic in the form of relays performed the power control functions. Power electronics were initially used for regulating excitation current both for traction and auxiliary power generation, and for adhesion management.
From 1985 until the AC6000 appeared in prototype form in 1995, followed by pre-production units in 1996, three computers were used in GE locomotives (Fig 2). The first managed total loco control functions, and monitored the response and performance of overall systems. The second controlled traction alternator excitation and the power transmitted to the motors.
A third computer monitored the auxiliaries, constantly evaluating the ancillary power needs and adjusting them to optimise performance. This allows unneeded auxiliary power to be used for traction, providing higher speeds on grades, more rapid acceleration, and fuel economy.
Sensors throughout the locomotive equipment forward information regarding operating conditions to the microprocessors, which analyse the information and make adjustments automatically.
Memory capability is provided both with the volatile RAM, the EPROM, and battery backed RAM. The computer program records mileage operated, total hours elapsed, total hours of engine running, and hours in each controller notch position including braking. Total kWh of traction power expended and regenerated braking power absorbed is recorded. These figures have been found to be invaluable to the builder, owner and operator.
Any identified faults and corrective actions are recorded in memory, which can later be interrogated and the data transferred to a shore based or portable computer for manipulation, printout, and investigation by maintenance personnel. Such interrogation can be made by radio link on a routine or specific time basis to provide advance information for scheduled or unscheduled maintenance.
With the introduction of the AC6000, which is scheduled for series production early in 1998, the increasing power of microprocessors has allowed a new control system to be introduced, needing only two processors instead of three. The general principles remain the same, but the functions controlled include each inverter output voltage and frequency.
Every operator of GE locos is offered free computer storage of the locomotive microcomputer memory. This is first downloaded into a compatible portable computer, and then uploaded to the GE mainframe computer in Erie for permanent retention. The owner has continuous access to this data, and can manipulate it to obtain analysis in many different ways. No other railway has access to the data for a particular customer. The facility is known as Dash-H (pronounced ’dash star’).
Microprocessors permit self-test features to be incorporated for all major items of equipment or sub-units. This can prevent a locomotive being sent into service with a previously undetected (or unreported) defect, increasing the likelihood of successful conclusion of the turn of duty.
Mechanical components of the locomotive have not been neglected. Each model of locomotive provides good access to aid maintenance or replacement and reduce downtime, while the need to maintain has been periodically reduced by design changes. The primary maintenance inspection interval is now 92 days. This may be varied by agreement dependent on duty, and some railways are already at 112 days, with more stretch being considered.
The human interface
Drivers and maintenance personnel communicate with the on-board microprocessors using an interface unit with a two-line text display screen and five function keys.
Recent locomotives also carry an in-cab display which provides the driver with all the information he needs to operate the train. Another display is available for a second crew member riding in the cab.
These displays are generated by a further microprocessor known as the Integrated Functions Computer. The IFC communicates with the other microprocessors which already hold all the data required to generate the in-cab displays, thus avoiding the need for additional sensors. Separate instruments displaying train speed, for example, can be eliminated.
The driver sees two interactive colour graphics screens complying with AAR standards displaying all the locomotive and train information that he requires, including diagnostics, set-up, and control of IFC functions. A third screen for the second crew member is optional. Each screen is of the LCD type with a 150 mm by 200mm viewing area. Yellow is used to alert the driver to active alarms and out-of-limit conditions.
Menu-driven soft keys at the bottom of each screen allow the operator to select the information to be viewed and to control various locomotive functions including slow-speed control, air brake set-up, end-of-train set-up, and integrated diagnostics. The displays are defined as:
