Heavy Bogies

[AndrewE]

Back to bogies: it seems ther have been recent accidents from cracking:
a report "
Report 09-101 (incorporating 08-105): express freight train derailments owing to the failure of
bogie side frames, various locations on the North Island Main Trunk, between 21 June 2008 and 7 May 2009" (sorry, can't see where I found it) says

Summary
1.2. Between 21 June 2008 and 7 May 2009, 3 express freight trains derailed at various locations on the North Island Main Trunk (NIMT) line. All 3 derailments were caused by the failure and collapse of bogie side frames on wagons. The side frame failures were all similar in that they started with a fatigue crack that propagated over a period of days rather than weeks, through the box section of the side frame, until the remaining material failed in overload during normal train operations.
1.3. The side frame failures were also similar to previous side frame failures investigated and reported on by the Commission.
1.4. The cracks started in an area that would have been difficult to detect during normal operational and maintenance wagon checks. The side frames sometimes lacked identifying marks and historically there had been no records kept of their age and maintenance history, so the operator had started a programme of magnetic particle inspections (MPIs) to detect the presence of fatigue cracking in the side frames when the bogies were brought in for overhaul.
1.5. The inspection programme found over 4 years an average 60% of side frames with cracks that required repair. At the current inspection rate, all side frames will not be inspected before 2020. Until all side frames are tested for cracks and repaired, the potential for main-line derailments attributed to bogie side frame failures remains. Given the risk that main-line derailments pose to people and infrastructure, the Commission has made a recommendation to the Chief Executive of the NZ Transport Agency to conduct a risk assessment and if necessary require the inspection rate of side frames to be accelerated.

 

[O L Leigh]

Frankly, I've never been able to feel any ride quality difference.

Heavy bogies do not necessarily equate to a rougher ride.

What a few people in this thread are overlooking is that not all of the mass of the bogie is unsprung, as the primary suspension sits between the axleboxes and the bogie frame. This means that the difference in unsprung mass between, say, Cl220 and Cl221 is probably not that great. What has also been overlooked is that ride quality is affected not only by the characteristics of the suspension system, but also by the ratio of sprung to unsprung mass. I would estimate that the sprung weight of a Cl221 car would be slightly higher than that of an equivalent Cl220 vehicle, bringing the ratio of sprung to unsprung mass closer thereby cancelling out any overall weigh penalty (well, from a ride quality perspective anyway).

 

[GC class B1]

Heavy bogies do not necessarily equate to a rougher ride.

What a few people in this thread are overlooking is that not all of the mass of the bogie is unsprung, as the primary suspension sits between the axleboxes and the bogie frame. This means that the difference in unsprung mass between, say, Cl220 and Cl221 is probably not that great. What has also been overlooked is that ride quality is affected not only by the characteristics of the suspension system, but also by the ratio of sprung to unsprung mass. I would estimate that the sprung weight of a Cl221 car would be slightly higher than that of an equivalent Cl220 vehicle, bringing the ratio of sprung to unsprung mass closer thereby cancelling out any overall weigh penalty (well, from a ride quality perspective anyway).

I have been assessing the ride of passenger vehicles, both professionally and personally for nearly 50 years. You are correct that it is not only the weight of the bogie that determines the ride quality. In practice the bogie weight is probably a very small factor in vehicle ride. Wheel profile, vehicle suspension characteristics, vehicle body dynamics, natural frequency of key components and track quality are much greater factors.
However I expect that a heavier bogie will be somewhat more stable and have a lower natural frequency than a lighter bogie so if all other factors are similar I would expect a vehicle with a heavier bogie will ride a bit better at high speed than a similar vehicle with a lighter bogie. I have not checked this out but it will be interesting to compare the ride of class 800 vehicle in the same set with both inside (lighter) and outside (heavier) framed bogies.

 

[MarkyT]

Heavy bogies do not necessarily equate to a rougher ride.

What a few people in this thread are overlooking is that not all of the mass of the bogie is unsprung, as the primary suspension sits between the axleboxes and the bogie frame. This means that the difference in unsprung mass between, say, Cl220 and Cl221 is probably not that great. What has also been overlooked is that ride quality is affected not only by the characteristics of the suspension system, but also by the ratio of sprung to unsprung mass. I would estimate that the sprung weight of a Cl221 car would be slightly higher than that of an equivalent Cl220 vehicle, bringing the ratio of sprung to unsprung mass closer thereby cancelling out any overall weigh penalty (well, from a ride quality perspective anyway).

I think some above have been arguing the heavier bogies give a better ride. As I say, in the Voyager case I haven't been able to tell the difference, but maybe my buttocks aren't so professionally calibrated as theirs! I remember when the notoriously heavy-bogied 444s and 450s were introduced on the SW, their ride quality seemed broadly excellent on plain track, much better than the Mk 1s they replaced. Initially, however, those I travelled on often lost their composure completely when passing through high speed junctions, bucking and swaying all over the place. That improved markedly however as engineers tuned the suspension of the new trains.

 

[dosxuk]

I think some above have been arguing the heavier bogies give a better ride. As I say, in the Voyager case I haven't been able to tell the difference, but maybe my buttocks aren't so professionally calibrated as theirs!

I don't think it's possible to get any sort of consensus - for many years there have been arguments about which of the 222's and Mk3's had the best ride on the MML, one man's smoothly gliding over pointwork is another man's wallowey and swayey. Some people like that you don't feel even the slightest jolt, but others dislike the bouncing all over the place effect you get in exchange.

 

[Wyrleybart]

I don't think it's possible to get any sort of consensus - for many years there have been arguments about which of the 222's and Mk3's had the best ride on the MML, one man's smoothly gliding over pointwork is another man's wallowey and swayey. Some people like that you don't feel even the slightest jolt, but others dislike the bouncing all over the place effect you get in exchange.

You are right on that.
My favourite ride is a well maintained Mk3 and I was treated to a great display a couple of years ago. I was heading west in the TF on XC's 1V44 HST. It wasn't a bad run at all but then we ran down Filton bank on the new track (then recently four tracked) towards Temple Meads and it was as smooth as satin. That was the proof that a good design, in good condition, on brand new track gave an absolutely fantastic ride.

But like you say, one person's gentle glide is preferable to someone else's motor racing track hugging stance.

In this thread I wonder if anyone has tried to compare the non tilt fitted XC 221s to the tilting AWC 22s ? The XC vehicles are thought to be a tonne lighter per vehicle, but that is obviously only 250kg on each wheelset.

 

[Pigeon]

This means that the difference in unsprung mass between, say, Cl220 and Cl221 is probably not that great.

Yes, I would expect that you could group axles into classes - unpowered as one, and a few different powered ones depending on how the power gets to the axle - and find that within each class the unsprung mass has a reasonably close and identifiable distribution of its own. Reason being that there's not a lot to vary - you're just down to the inevitable stuff of the wheelset itself and the axleboxes, with the wheel size being limited by the need to fit them under the body, and for powered axles some proportion of the mass of whatever couples the power to the axle, which comes in a small number of types that are similar amongst themselves. I would guess that wheel diameter and solid vs hollow axles are the main variations.

Between the wheelset and the body you have two filter sections in cascade - the primary suspension to the bogie frame, and then the secondary suspension to the body. If you have a heavy bogie frame you have more ability to select the filter constants of the two sections to give a faster rate of roll-off and greater attenuation at frequencies relative to comfort. So all else being equal I would expect heavier-framed bogies to generally give a better ride. But in a real situation all else isn't equal because there are other considerations, especially the control of the dynamics of the interaction between the wheels and the track. So I would expect to see any correlation between bogie frame mass and ride quality become much less noticeable after the time when research into wheel/track dynamics really got going, and when computers made it practical to juggle all the calculations involved in choosing which bogie characteristics you are trying to optimise and how much you optimise them, which would make it roughly from the end of the 60s onwards.