There is no doubt that the Alstom Citadis Spirit was not a ‘tried and true’ vehicle. It was a rather hastily cobbled together vehicle to satisfy some unrealistic requirements that Ottawa imposed. There were some compromises from the city (e.g., the required top speed was dropped from 120 KPH to 100 KPH), but most of the requirements remained, limiting what components could be used. Alstom also had a very limited knowledge of the working environment that the vehicle would be enduring. For example, the electrical insulators on the pantograph were fine for the French environment that it was taken from, but insufficient when doused with salt-water from the ice clearing done on the roads in Ottawa.
As issues with the new Spirit vehicle arose, they were cleared up. Door sensors were adjusted, new electrical insulators were designed and installed, and problems with maintenance procedures were corrected (e.g., the Jack Screws were removed from new wheels before the wheels were installed and torqued down).
However, all of those corrections, although needed, have not made the vehicles reliable enough. Of all of the improvements, there is one main problem that has persisted – the IPONAM bogie.
The design of the IPONAM was the direct result of the requirements that Ottawa put forth for its Light Rail Vehicles. No existing bogie could satisfy those demands so Alstom set about creating one. But with the short lead time to delivery, Alstom relied on modifying existing designs.
Some of the design requirements, and the resulting changes Alstom had to make to create the IPONAM:
100% Low Floor:
- Brake disks and drive motors moved to outside the bogie frame;
- Smaller wheel diameter.
Smooth ride with minimum running noise:
120 KPH top speed:
- Higher gearing between the motor and the wheel. Smaller wheels rotate faster for a given speed – which means an even higher gear ratio was needed.
High acceleration rate:
- The higher gear ratio meant that a much larger, more powerful, motor is required. (Think of a 10-speed bike. It is easy to start and quickly accelerate in 1st gear, but your top speed will be low. Starting in 10th takes a lot more effort, but you eventually get up to a much higher top speed. Now imagine if you had to accelerate as fast as you do in 1st, but reach the same top speed you do in 10th – but you have to do it without changing the gear ratio. This is in effect, what the city wanted from Alstom.)
Handle tight curves:
- The carriage would be supported on a central pivot on the bogie, allowing the bogies to turn to better follow the tracks.
Additional climate insulation, which increased the carriage weight:
- Increased load on the bogie required increased strength.
Ultimately, the top speed requirement was dropped to 100 KPH so that the gearing could be relaxed a bit, so the motors didn’t have to be so large that they stuck out too far, limiting how close the vehicle could get to the platform. Already, the SPIRIT vehicle requires ‘fender flares’ to cover the larger motors.
In the end, this bogie was a completely new design for Alstom’s entry into the North American market. But that, as I mentioned above, led to ‘teething pains’. Since the resilient wheels were a custom size, Alstom found a new supplier for them. However, that manufacturer put the Jack Screws in the wheels for shipping – which had not been done by previous wheel manufacturers. Issues like the Jack Screws are annoying when they are discovered, but fairly easily fixed. What is not so easy to fix is the IPONAM design.
The latest manifestation of the IPONAM problem is that it is eating wheel bearings much too fast. In fact, bearing destruction has been so severe that, in one case, the heat generated was intense enough to melt through the axle, resulting in the separation of the wheel from the axle. In this incident, a loosened pre-load locking ring was blamed. Since then, the locking rings have been pinned to prevent loosening.
However, that is a Band-Aid for the problem. It doesn’t determine WHY the lock nuts were loosening. Just as replacing every Bearing Cartridge Assembly (CBA) that runs more than 100,000 km is covering the symptom, not finding the root problem. (These CBAs were, apparently, designed for a 1.2-million km life.) Their next ‘solution’, is to add a sensor to detect when a bearing goes bad. While, finding a failed bearing is a great thing, it does nothing to increase the service life of the CBAs up to the theoretical design specification.
For years, there has been investigation into finding ways to get around the symptoms of the problem – but no real work on fixing the fundamental problem. There are, I believe, under-designed components in the IPONAM bogie.
My guess as to what is needed:
Based on absolutely no expertise at all, I can logically base a conclusion on what I have read about the problems with the IPONAM.
- Spalling, and its more severe version, Shelling, are classic signs of overloading of a bearing. I believe that the increased weight of the carriage, the increased torque of the more powerful motor, and to an extent, the higher rotational speed due to smaller diameter wheels, overloads the bearings. They need to be 'beefed up’.
- The loosening off of the pre-load lock nut should only occur if there is ‘interference’; i.e., drag on that part. This resistance can be from rubbing on a housing, or by being influenced by bearings that are not moving at the correct speed. Excessive flex in the axle shaft might have the ability of overcoming any clearance, causing drag. Any slight deflection of the axle shaft might also cause localized overloading of the bearings – which could show up as spalling. I would suggest that the axle shaft be stiffened to reduce any deflection.
Luckily, those two things can probably be done and analyzed in software before any new casting needs to be made. This is the type of work that needs to be done. Slapping on Band-Aids is not a good way for Alstom to build any confidence in its products.
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