Why are romancecars articulated?

[utrainia]

Why are most Odakyu romacecars articulated with a shared bogie between carriages?

 

It is a fairly unusual design, so I assumed there must be a good reason for it. However JA wikipedia seems to suggest that it it all started because Risaburo Yamamoto held an interest in such designs, having seen Spanish Talgos. Further down the page it suggests that by sharing a bogie the weight can be reduced allowing a higher top speed, and by sharing the bogie with shorter carriages, a more comfortable ride quality is achieved on serpentine tracks. But these seem more like nice consequences of using an articulated design, rather than reasons to use one?

 

Curiously, another site (papercraft!) says that for the 20000 series romancecar, JR Tokai wouldn't allow them to use articulated cars and they had to adopt a standardised design.

[kvp]

Considering they are meant to be luxury limited expresses for resort service, ride quality and speed could be the main factor. This design was popular in germany too for some luxury trains around the same time. Flexibility and maintenance are broblems though, since these are not emus, but articulated railcars, like the settebello from italy and the flying hamburgers from germany.

 

The speed record they achived was easier to reach at that time with articulated cars. Nowdays technology has advaned enough that the standard two bogies design is good enough but much cheaper.

[utrainia]

Thanks. Sounds like the articulated design was the best choice at the time then. Interesting they have kept the design, guess it has become synonymous with the romance car design.

[Densha]

I read somewhere (but cannot confirm) that the main advantage of using jacobs bogies (in combination with shorter cars) is that narrower curves can be taken with less swaying which makes for better passenger comfort.

 

Many European trains use this kind of composition nowadays. From the TGV to commuter trains as the DB BR423, which for commuter trains results in a very open interior view because of the wide, or actually non-exist 'gangways'.

[trainsforever8]

I also saw in a french documentary about the TGV that having shared bogies make it that during a derailment, the cars wont completely disconnect and fly all over the place. But I really think that it's for comfort, the bogies aren't under the passenger seats which makes it better. However, it is indeed a unusual design for Japanese trains and Odakyu cannot adopt it for all of their trains because of different regulations, especially with the trough running with Tokyo Metro.

[miyakoji]

There are far fewer bogies, but then the connection between cars is more complex.  I wonder how it works out weight-wise.

[katoftw]

The whole point of them is to reduce weight, so it must be enough for them to care doing it.  The French still do it with their TGV and AGV.  So it must have some merit.

[kvp]

One reason they are still used on some european railcars, like most Stadler trains is that it's easier to make them low floor. When the bogies are not under the cars, but between them, you can lower the floor height to the common european low platform height and can make a nearly 100% low floor vehicle. On the aforementioned Stadler cars that are very popular in Hungary the trick is to put the traction equipment and the powered bogies under the two ends. This gives a simple 2 bogie propulsion system like on a normal locomotive hauled train but with the capacity of a 4 car train integrated into one. The short high floor end sections contain the raised driver's cab, the control equipment on top of the power bogies and the main trasformers right behind the bogies. This results in a very good crash safety, since anything coming from the front or rear will meet the bulk of the equipment before reaching any passenger sections, which are riding on jackobs bogies, so can't jackknife. The same design is used on the classic TGV-s, mainly two normal 2 axle locomotives on each end, each powering one 2 axle power bogie on the ends of the single articulated passenger car by cow-calf jumper cables, giving a total of 6 powered bogies on the two ends.

 

The japanese design was probably influenced by the older high speed emu designs. The benefits of using jackobs bogies:

-no end swing on corners between cars, so no passengers get swung out and then back in or back and forth on S curves (turnouts)

-reduced middle swing on corners in the middle of the cars, mainly due to using shorter cars

-larger body width is usable with the same loading gauge due to reduced car length (if platforms and tunnels allow it)

-easier to make full width gangeways and gangeways can have large round rotational plates instead of two small plates moving on top of each other

-less sideways forces on the track on curves, thanks to cars being connected at the bogies and not through couplers moving off from the centerline on curves, allowing high speeds and causing less damage to the track

-less sideways forces on the track on curves, thanks to less swing in the cars, so less weight and momentum acting against the wheels at higher speeds

 

So generally jackobs bogies are better on the tracks while allowing higher speeds and better passenger comfort on tracks with high amount of sharp curves. This is why they are still popular on legacy tracks and tram networks. The modern solution is to move the bogies as far out to the ends of the cars as possible, so conventional body mounted couplers are nearer to the bogie centers and very little part of the car swings outside on a curve. At the same time, use larger curves and more straight routes, so no snaking happens at high speeds and finally use heavier rails, that can resist the horizontal forces of heavy trains at high speeds. Using the conventional two bogies system is also better from an operational point, since instead of having single articulated railcars in a fixed configuration, separate cars can be disconnected and even rearranged as traffic needs or maintencance requires.

[Densha]

Very interesting read kvp! That makes me understand why the Siemens Velaro and Shinkansen have the bogies very close to the ends of the cars.